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Sample records for acid proton exchange

  1. Proton exchange in acid-base complexes induced by reaction coordinates with heavy atom motions

    NASA Astrophysics Data System (ADS)

    Alavi, Saman; Taghikhani, Mahdi

    2012-06-01

    We extend previous work on nitric acid-ammonia and nitric acid-alkylamine complexes to illustrate that proton exchange reaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strong acid-strong base complexes. The complexes studied involve the biologically and atmospherically relevant glycine, formic, acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of the imaginary frequencies associated with the proton exchange transition states are <400 cm-1. This contrasts with widely studied proton exchange reactions between symmetric carboxylic acid dimers or asymmetric DNA base pair and their analogs where the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for the transition states are >1100 cm-1. Calculations on complexes of these acids with water are performed for comparison. Variations of normal vibration modes along the reaction coordinate in the complexes are described.

  2. Polybenzimidazole film containing phosphoric acid as proton exchange membrane (PEM)

    NASA Astrophysics Data System (ADS)

    Ameri, Roya

    Polybenzimidazole is a linear polymer with a very high glass transition temperature. It has exceptional properties at elevated temperature such as stability, retention of stiffness, and toughness. PBI containing phosphoric acid has high proton conductivity and low water vapor permeability. A new way of direct film casting of PBI containing phosphoric acid, has been found. The use of trifluoroacetic acid as a solvent resulted in a new and quick way to prepare PBI film containing phosphoric acid which showed about four times more conductivity at a given doping level than PBI doped with phosphoric acid from DMAc solution. Mechanical property studies of different molecular weight PBI films etasb{inh} = 0.91 to 142 dl/g) have shown that increasing molecular weight linearly improved mechanical properties of PBI films with pronounced effect on toughness. As PBI film was doped with sulfuric acid, mechanical properties decreased with very sharp drop in toughness. More reduction in mechanical properties was observed as the concentration of sulfuric acid in the film increased. Doping PBI film with low concentrations of phosphoric acid improved modulus and strength at break while lowering the toughness. Increasing the concentration of acid in these films lowered the strength and modulus of PBI film. However, toughness first increased up to concentration of 200-300M% phosphoric acid and then decreased. Comparison of phosphoric acid doped PBI film and PBI film cast from PBI/TFA/Hsb3POsb4 solution reveals that phosphoric acid doped PBI film has at least three times better mechanical properties: toughness, modulus, and strength. X-ray photographs of PBI film cast from PBI/TFA/Hsb3POsb4 solution shows a crystalline pattern with a monoclinic unit cell of dimensions: a = 15.8 A, b = 13.23 A, c = 16.83 A, and gamma = 79.1sp0. On the other hand, phosphoric acid doped PBI film has relatively low crystallinity. PBI can cocrystallize with some complexing agent like trifluoroacetic acid

  3. Acid-induced exchange of the imino proton in G.C pairs.

    PubMed Central

    Nonin, S; Leroy, J L; Gueron, M

    1996-01-01

    Acid-induced catalysis of imino proton exchange in G.C pairs of DNA duplexes is surprisingly fast, being nearly as fast as for the isolated nucleoside, despite base-pair dissociation constants in the range of 10(-5) at neutral or basic pH. It is also observed in terminal G.C pairs of duplexes and in base pairs of drug-DNA complexes. We have measured imino proton exchange in deoxyguanosine and in the duplex (ATATAGATCTATAT) as a function of pH. We show that acid-induced exchange can be assigned to proton transfer from N7-protonated guanosine to cytidine in the open state of the pair. This is faster than transfer from neutral guanosine (the process of intrinsic catalysis previously characterized at neutral ph) due to the lower imino proton pK of the protonated form, 7.2 instead of 9.4. Other interpretations are excluded by a study of exchange catalysis by formiate and cytidine as exchange catalysts. The cross-over pH between the regimes of pH-independent and acid-induced exchange rates is more basic in the case of base pairs than in the mononucleoside, suggestive of an increase by one to two decades in the dissociation constant of the base pair upon N7 protonation of G. Acid-induced catalysis is much weaker in A.T base pairs, as expected in view of the low pK for protonation of thymidine. PMID:8604298

  4. Insight into proton transfer in phosphotungstic acid functionalized mesoporous silica-based proton exchange membrane fuel cells.

    PubMed

    Zhou, Yuhua; Yang, Jing; Su, Haibin; Zeng, Jie; Jiang, San Ping; Goddard, William A

    2014-04-01

    We have developed for fuel cells a novel proton exchange membrane (PEM) using inorganic phosphotungstic acid (HPW) as proton carrier and mesoporous silica as matrix (HPW-meso-silica) . The proton conductivity measured by electrochemical impedance spectroscopy is 0.11 S cm(-1) at 90 °C and 100% relative humidity (RH) with a low activation energy of ∼14 kJ mol(-1). In order to determine the energetics associated with proton migration within the HPW-meso-silica PEM and to determine the mechanism of proton hopping, we report density functional theory (DFT) calculations using the generalized gradient approximation (GGA). These DFT calculations revealed that the proton transfer process involves both intramolecular and intermolecular proton transfer pathways. When the adjacent HPWs are close (less than 17.0 Å apart), the calculated activation energy for intramolecular proton transfer within a HPW molecule is higher (29.1-18.8 kJ/mol) than the barrier for intermolecular proton transfer along the hydrogen bond. We find that the overall barrier for proton movement within the HPW-meso-silica membranes is determined by the intramolecular proton transfer pathway, which explains why the proton conductivity remains unchanged when the weight percentage of HPW on meso-silica is above 67 wt %. In contrast, the activation energy of proton transfer on a clean SiO2 (111) surface is computed to be as high as ∼40 kJ mol(-1), confirming the very low proton conductivity on clean silica surfaces observed experimentally. PMID:24628538

  5. Anhydrous phosphoric Acid functionalized sintered mesoporous silica nanocomposite proton exchange membranes for fuel cells.

    PubMed

    Zeng, Jie; He, Beibei; Lamb, Krystina; De Marco, Roland; Shen, Pei Kang; Jiang, San Ping

    2013-11-13

    A novel inorganic proton exchange membrane based on phosphoric acid (PA)-functionalized sintered mesoporous silica, PA-meso-silica, has been developed and investigated. After sintering at 650 °C, the meso-silica powder forms a dense membrane with a robust and ordered mesoporous structure, which is critical for retention of PA and water within the porous material. The PA-meso-silica membrane achieved a high proton conductivity of 5 × 10(-3) to 5 × 10(-2) S cm(-1) in a temperature range of 80-220 °C, which is between 1 and 2 orders of magnitudes higher than a typical membrane Nafion 117 or polybenzimidazole (PBI)/PA in the absence of external humidification. Furthermore, the PA-meso-silica membranes exhibited good chemical stability along with high performance at elevated temperatures, producing a peak power density of 632 mW cm(-2) using a H2 fuel at 190 °C in the absence of external humidification. The high membrane proton conductivity and excellent fuel cell performance demonstrate the utility of PA-meso-silica as a new class of inorganic proton exchange membranes for use in the high-temperature proton exchange membrane fuel cells (PEMFCs). PMID:24125494

  6. Copoly(arlene ether)s containing pendant sulfonic acid groups as proton exchange membrane

    SciTech Connect

    Kim, Yu Seung; Kim, Dae Sik; Robertson, Gilles; Guiver, Michael

    2008-01-01

    A copoly(arylene ether) (PAE) with high fluorine content and a copoly(arylene ether nitrile) (PAEN) with high nitrile content, each containing pendant phenyl sulfonic acids were synthesized. The P AE and PAEN were prepared from decafluorobiphenyl (DFBP) and difluorobenzonitrile (DFBN) respectively, by polycondensation with 2-phenylhydroquinone (PHQ) by conventional aromatic nucleophilic substitution reactions. The sulfonic acid groups were introduced by mild post-sulfonation exclusively on the para-position of the pendant phenyl ring in PHQ. The membrane properties of the resulting sulfonated copolymers sP AE and sP AEN were compared for fuel cell applications. The copolymers sPAE and sPAEN, each having a degree of sulfonation (DS) of 1.0 had high ion exchange capacities (IEC{sub v}(wet) (volume-based, wet state)) of 1.77 and 2.55 meq./cm{sup 3}, high proton conductivities of 135.4 and 140.1 mS/cm at 80 C, and acceptable volume-based water uptake of 44.5-51.9 vol% at 80 C, respectively, compared to Nafion. The data points of these copolymer membranes are located in the area of outstanding properties in the trade-off plot of alternative hydrocarbon polyelectrolyte membranes (PEM) for the relationship between proton conductivity versus water uptake (weight based or volume based). Furthermore, the relative selectivity derived from proton conductivity and methanol permeability is higher than that of Nafion.

  7. Copoly(arylene ether)s containing pendant sulfonic acid groups as proton exchange membranes

    SciTech Connect

    Dae Sik, Kim; Yu Seung, Kim; Gilles, Robertson; Guiver, Michael D

    2009-01-01

    A copoly(arylene ether) (PAE) with high fluorine content and a copoly(arylene ether nitrile) (PAEN) with high nitrile content, each containing pendant phenyl sulfonic acids were synthesized. The PAE and P AEN were prepared from decafluorobiphenyl (DFBP) and difluorobenzonitrile (DFBN) respectively, by polycondensation with 2phenylhydroquinone (PHQ) by conventional aromatic nucleophilic substitution reactions. sulfonic acid groups were introduced by mild post-sulfonation exclusively on the para-position of the pendant phenyl ring in PHQ. The membrane properties of the resulting sulfonated copolymers sPAE and sPAEN were compared for fuel cell applications. The copolymers sPAE and sPAEN, each having a degree of sulfonation (OS) of 1.0 had high ion exchange capacities (IEC{sub v})(wet) (volume-based, wet state) of 1.77 and 2.55 meq./cm3, high proton conductivities of 135.4 and 140.1 mS/cm at 80 C, and acceptable volume-based water uptake of 44.5 -51.9 vol% at 80 C, respectively, compared to Nafion. The data points of these copolymer membranes are located in the upper left-hand corner in the trade-off plot of alternative hydrocarbon polyelectrolyte membranes (PEM) for the relationship between proton conductivity versus water uptake (weight based or volume based), i.e., high proton conductivity and low water uptake. Furthermore, the relative selectivity derived from proton conductivity and methanol permeability is higher than that of Nafion.

  8. Organic-inorganic hybrid proton exchange membranes based on silicon-containing polyacrylate nanoparticles with phosphotungstic acid

    NASA Astrophysics Data System (ADS)

    Cui, Xuejun; Zhong, Shuangling; Wang, Hongyan

    A series of silicon-containing polyacrylate nanoparticles (SiPANPs) were successfully synthesized by simple emulsifier-free emulsion polymerization technique. The resulting latex particles were characterized by Fourier transform infrared (FTIR) spectrometry, dynamic light scattering (DLS) analysis, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The SiPANP membranes and SiPANP/phosphotungstic acid (SiPANP/PWA) hybrid membranes were also prepared and characterized to evaluate their potential as proton exchange membranes in proton exchange membrane fuel cell (PEMFC). Compared with the pure SiPANP membrane, the hybrid membranes displayed lower thermal stability. However, the degradation temperatures were still above 190 °C, satisfying the requirement of thermal stability for PEMFC operation. In addition, the hybrid membranes showed lower water uptake but higher proton conductivity than the SiPANP precursor. The proton conductivity of the hybrid membranes was in the range of 10 -3 to 10 -2 S cm -1 and increased gradually with PWA content and temperature. The excellent hydrolytic stability was also observed in the hybrid membranes because of the existence of crosslinked silica network. The good thermal stability, reasonable water uptake, excellent hydrolytic stability, suitable proton conductivity and cost effectiveness make these hybrids quite attractive as proton exchange membranes for PEMFC applications.

  9. Conductivity Measurements of Synthesized Heteropoly Acid Membranes for Proton Exchange Membrane Fuel Cells

    SciTech Connect

    Record, K.A.; Haley, B.T.; Turner, J.

    2006-01-01

    Fuel cell technology is receiving attention due to its potential to be a pollution free method of electricity production when using renewably produced hydrogen as fuel. In a Proton Exchange Membrane (PEM) fuel cell H2 and O2 react at separate electrodes, producing electricity, thermal energy, and water. A key component of the PEM fuel cell is the membrane that separates the electrodes. DuPont’s Nafion® is the most commonly used membrane in PEM fuel cells; however, fuel cell dehydration at temperatures near 100°C, resulting in poor conductivity, is a major hindrance to fuel cell performance. Recent studies incorporating heteropoly acids (HPAs) into membranes have shown an increase in conductivity and thus improvement in performance. HPAs are inorganic materials with known high proton conductivities. The primary objective of this work is to measure the conductivity of Nafion, X-Ionomer membranes, and National Renewable Energy Laboratory (NREL) Developed Membranes that are doped with different HPAs at different concentrations. Four-point conductivity measurements using a third generation BekkTech conductivity test cell are used to determine membrane conductivity. The effect of multiple temperature and humidification levels is also examined. While the classic commercial membrane, Nafion, has a conductivity of approximately 0.10 S/cm, measurements for membranes in this study range from 0.0030 – 0.58 S/cm, depending on membrane type, structure of the HPA, and the relative humidity. In general, the X-ionomer with H6P2W21O71 HPA gave the highest conductivity and the Nafion with the 12-phosphotungstic (PW12) HPA gave the lowest. The NREL composite membranes had conductivities on the order of 0.0013 – 0.025 S/cm.

  10. Acid/base equilibria in clusters and their role in proton exchange membranes: Computational insight

    SciTech Connect

    Glezakou, Vanda A; Dupuis, Michel; Mundy, Christopher J

    2007-10-24

    We describe molecular orbital theory and ab initio molecular dynamics studies of acid/base equilibria of clusters AH:(H2O)n↔A-:H+(H2O)n in low hydration regime (n = 1-4), where AH is a model of perfluorinated sulfonic acids, RSO3H (R = CF3CF2), encountered in polymeric electrolyte membranes of fuel cells. Free energy calculations on the neutral and ion pair structures for n = 3 indicate that the two configurations are close in energy and are accessible in the fluctuation dynamics of proton transport. For n = 1,2 the only relevant configuration is the neutral form. This was verified through ab initio metadynamics simulations. These findings suggest that bases are directly involved in the proton transport at low hydration levels. In addition, the gas phase proton affinity of the model sulfonic acid RSO3H was found to be comparable to the proton affinity of water. Thus, protonated acids can also play a role in proton transport under low hydration conditions and under high concentration of protons. This work was supported by the Division of Chemical Science, Office of Basic Energy Sciences, US Department of Energy (DOE under Contract DE-AC05-76RL)1830. Computations were performed on computers of the Molecular Interactions and Transformations (MI&T) group and MSCF facility of EMSL, sponsored by US DOE and OBER located at PNNL. This work was benefited from resource of the National Energy Research Scientific Computing Centre, supported by the Office of Science of the US DOE, under Contract No. DE-AC03-76SF00098.

  11. Acid loaded porous silicon as a proton exchange membrane for micro-fuel cells

    NASA Astrophysics Data System (ADS)

    Gold, Scott; Chu, Kuan-Lun; Lu, Chang; Shannon, Mark A.; Masel, Richard I.

    Silicon-based fuel cells are under active development to supply chip-scale electrical power supply. In this paper, we demonstrate the use of sulfuric acid loaded nanoporous silicon as a proton electrolytic membrane (PEM) material for micro-fuel cell applications. Sulfuric acid loaded nanoporous silicon membranes with thickness of 40-70 μm have proton conductivities (0.0068-0.33 S/cm) comparable to, and in some cases better than, Nafion ® (0.05 S/cm), which is the most commonly used commercial PEM material. Additionally, the permeability of formic acid at room temperature through nanoporous silicon membranes was found to be similar to that of Nafion ® membranes, which increases with increasing anodization current density (4.3 × 10 -8 to 3.9 × 10 -7 mol/(s cm 2) for nanoporous silicon as compared to 1.23 × 10 -7 mol/(s cm 2) for Nafion ® 117). These results represent the discovery of a new class of protonic conductor that can be integrated into standard silicon microfabrication processes.

  12. Free volume of poly(perfluorosulfonic acid)/SiO 2 composite proton exchange membranes by 129Xe NMR

    NASA Astrophysics Data System (ADS)

    Utiu, Lavinia; Filipoi, Carmen; Demco, Dan E.; Zhu, Xiaomin; Vinokur, Rostislav; Conradi, Oliver; Graichen, Andreas; Blümich, Bernhard; Möller, Martin

    2011-04-01

    Poly(perfluorosulfonic acid)/silica (PFSA/SiO2) composites were investigated by 129Xe NMR spectroscopy and relaxometry. 129Xe chemical shift extrapolated to zero pressure was used for calculation of average free volume hole size. This quantity reaches a maximum at 2 wt.% SiO2 that could be correlated to the performance of composites proton exchange membrane. 129Xe longitudinal magnetization relaxation revealed a bimodal distribution of the free volume that was explained by the presence of xenon atoms in the backbone and pendant-chain domains. Thus, the free volume is heterogeneous and depends on the content of SiO2. Implications of the free volume changes for the hydrogen crossover through PFSA/SiO2 membranes are also discussed.

  13. Proton channels and exchangers in cancer.

    PubMed

    Spugnini, Enrico Pierluigi; Sonveaux, Pierre; Stock, Christian; Perez-Sayans, Mario; De Milito, Angelo; Avnet, Sofia; Garcìa, Abel Garcìa; Harguindey, Salvador; Fais, Stefano

    2015-10-01

    Although cancer is characterized by an intratumoral genetic heterogeneity, a totally deranged pH control is a common feature of most cancer histotypes. Major determinants of aberrant pH gradient in cancer are proton exchangers and transporters, including V-ATPase, Na+/H+ exchanger (NHE), monocarboxylate transporters (MCTs) and carbonic anhydrases (CAs). Thanks to the activity of these proton transporters and exchangers, cancer becomes isolated and/or protected not only from the body reaction against the growing tumor, but also from the vast majority of drugs that when protonated into the acidic tumor microenvironment do not enter into cancer cells. Proton transporters and exchangers represent a key feature tumor cells use to survive in the very hostile microenvironmental conditions that they create and maintain. Detoxifying mechanisms may thus represent both a key survival option and a selection outcome for cells that behave as unicellular microorganisms rather than belonging to an organ, compartment or body. It is, in fact, typical of malignant tumors that, after a clinically measurable yet transient initial response to a therapy, resistant tumor clones emerge and proliferate, thus bursting a more malignant behavior and rapid tumor progression. This review critically presents the background of a novel and efficient approach that aims to fight cancer through blocking or inhibiting well characterized proton exchangers and transporters active in human cancer cells. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers. PMID:25449995

  14. Sulfonic acid-functionalized hybrid organic-inorganic proton exchange membranes synthesized by sol-gel using 3-mercaptopropyl trimethoxysilane (MPTMS)

    NASA Astrophysics Data System (ADS)

    Mosa, J.; Durán, A.; Aparicio, M.

    2015-11-01

    Organic/inorganic hybrid membranes based on (3-glycidoxypropyl) trimethoxysilane (GPTMS) and 3-mercaptopropyl trimethoxysilane (MPTMS) have been prepared by sol-gel method and organic polymerisation, as candidate materials for proton exchange membranes in direct alcohol fuel cell (DMFC) applications. The -SH groups of MPTMS are oxidized to sulfonic acid groups, which are attributed to enhance the proton conductivity of hybrid membranes. FTIR, XPS and contact angle were used to characterize and confirm the hybrid structure and oxidation reaction progress. Membranes characterization also includes ion exchange capacity, water uptake, methanol permeability and proton conductivity to confirm their applicability in fuel cells. All the membranes were homogeneous and thermally and chemically resistant. In particular, the hybrid membranes demonstrated proton conductivities as high as 0.16 S cm-1 at high temperature, while exhibiting a low methanol permeability as compared to Nafion®. These results are associated with proton conducting paths through the silica pseudo-PEO network in which sulfonic acid groups work as proton donor.

  15. Modification and improvement of proton-exchange membrane fuel cells via treatment using peracetic acid

    NASA Astrophysics Data System (ADS)

    Xu, Zhiqiang; Qi, Zhigang; Kaufman, Arthur

    Electrodes and catalyst-coated membranes (CCMs) were treated using peracetic acid. After such a treatment, the properties and performance of these electrodes and CCMs were changed in several aspects. First, their catalytic activity was increased compared to the untreated counterparts. Second, their ability to hold water within the catalyst layers was increased so that the cathode did not need to be humidified. Third, if the cathode was humidified together with the anode, some of the electrodes were more readily to be flooded than the untreated counterparts.

  16. A boron phosphate-phosphoric acid composite membrane for medium temperature proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Mamlouk, M.; Scott, K.

    2015-07-01

    A composite membrane based on a non-stoichiometric composition of BPO4 with excess of PO4 (BPOx) was synthesised and characterised for medium temperature fuel cell use (120-180 °C). The electrolyte was characterised by FTIR, SS-NMR, TGA and XRD and showed that the B-O is tetrahedral, in agreement with reports in the literature that boron phosphorus oxide compounds at B:P < 1 are exclusively built of borate and phosphate tetrahedra. Platinum micro electrodes were used to study the electrolyte compatibility and stability towards oxygen reduction at 150 °C and to obtain kinetic and mass transport parameters. The conductivities of the pure BPOx membrane electrolyte and a Polybenzimidazole (PBI)-4BPOx composite membrane were 7.9 × 10-2 S cm-1 and 4.5 × 10-2 S cm-1 respectively at 150 °C, 5%RH. Fuel cell tests showed a significant enhancement in performance of BPOx over that of typical 5.6H3PO4-PBI membrane electrolyte. The enhancement is due to the improved ionic conductivity (3×), a higher exchange current density of the oxygen reduction (30×) and a lower membrane gas permeability (10×). Fuel cell current densities at 0.6 V were 706 and 425 mA cm-2 for BPOx and 5.6H3PO4-PBI, respectively, at 150 °C with O2 (atm).

  17. A novel phosphoric acid doped poly(ethersulphone)-poly(vinyl pyrrolidone) blend membrane for high-temperature proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Xu, Xin; Wang, Haining; Lu, Shanfu; Guo, Zhibin; Rao, Siyuan; Xiu, Ruijie; Xiang, Yan

    2015-07-01

    A high-temperature proton exchange membrane, poly(ethersulphone)-poly(vinyl pyrrolidone) (PES-PVP) blend membrane is successfully prepared by scalable polymer blending method. The physical properties of blend membrane are characterized by DSC, TG and tensile strength test. The DSC and TG results indicate PES-PVP blend membranes possess excellent thermal stability. After phosphoric acid (PA) doping treatment, the blend membrane shows enhanced proton conductivity. PA doping level and volume swelling ratio of the blend membrane are found to be positively related to the PVP content. A high proton conductivity of 0.21 S/cm is achieved at 180 °C for PA doped PES-PVP 80% with a PA doping level of 9.1. PEM fuel cell based on PA doped PES-PVP 80% membrane shows a high power density of 850 mW/cm2 and outstanding stability at 180 °C without extra humidification.

  18. Synthesis and characterization of novel sulfonated poly(arylene ether ketone) copolymers with pendant carboxylic acid groups for proton exchange membranes

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Cui, Zhiming; Zhao, Chengji; Shao, Ke; Li, Hongtao; Fu, Tiezhu; Na, Hui; Xing, Wei

    A series of novel side-chain-type sulfonated poly(arylene ether ketone)s with pendant carboxylic acid groups copolymers (C-SPAEKs) were synthesized by direct copolymerization of sodium 5,5‧-carbonyl-bis(2-fluorobenzenesulfonate), 4,4‧-difluorobenzophenone and 4,4‧-bis(4-hydroxyphenyl) valeric acid (DPA). The expected structure of the sulfonated copolymers was confirmed by FT-IR and 1H NMR. Membranes with good thermal and mechanical stability could be obtained by solvent cast process. It should be noted that the proton conductivity of these copolymers with high sulfonatation degree (DS > 0.6) was higher than 0.03 S cm -1 and increased with increasing temperature. At 80 °C, the conductivity of C-SPAEK-3 (DS = 0.6) and C-SPAEK-4 (DS = 0.8) reached up to 0.12 and 0.16 S cm -1, respectively, which were higher than that of Nafion 117 (0.10 S cm -1). Moreover, their methanol permeability was much lower than that of Nafion 117. These results showed that the synthesized materials might have potential applications as the proton exchange membranes for DMFCs.

  19. Proton Exchange Membranes for Fuel Cells

    SciTech Connect

    Devanathan, Ramaswami

    2010-11-01

    Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero-emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start-stop cycling under sub-freezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)-based membranes, such as Nafion®, have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design and reduce the cost of fuel cells. Hydrocarbon-based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation

  20. A new class of polyelectrolytes, poly(phenylene sulfonic acids) and its copolymers as proton exchange membranes for PEMFC's

    NASA Astrophysics Data System (ADS)

    Granados-Focil, Sergio

    A novel rigid rod liquid crystalline poly(biphenylene disulfonic acid), PBPDSA, was synthesized for the first time using the Ullman coupling reaction. The resulting water soluble, polymer showed a complex aggregation behavior in solution, which complicated the estimation of its molecular weight. The proton conductivity of PBPDSA was higher than that of Nafion over the whole tested range of relative humidities and temperatures. The unparalleled properties of this material were attributed to its liquid crystalline lamellar solid state structure. In order to obtain water insoluble membranes, PBPDSA was modified by grafting bulky or crosslinkable hydrophobic groups. The resulting grafted copolymers showed a solid state structure similar to that of PBPDSA, as well as an analogous anisotropy in some of its properties. The in plane proton conductivity of these materials, measured as a function of relative humidity and temperature, was higher or comparable to that of Nafion. The membranes performance at low relative humidities and high temperatures is remarkable, showing conductivity values up to 2 orders of magnitude larger than those found for Nafion. TGA and FTIR studies indicate that the polymers are stable up to 175°C. The most important discovery was that this class of materials forms almost perfect MeOH vapor barriers. A 20mu film was more than 1000 times less permeable than Nafion 117. The effect of the bulky and crosslinkable groups on the conductivity, mechanical properties and dimensional stability of the copolymer membranes was evaluated. However, an unequivocal correlation between polymer structure and its properties was complicated by the presence of structural defects generated during the grafting process. Experimental conditions allowing the control but not the elimination of such defects were found and used to prepare grafted copolymers in a controlled and reproducible manner. The initial results of an effort to produce random copolymers using new

  1. Ring current proton decay by charge exchange

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Hoffman, R. A.; Fritz, T.

    1975-01-01

    Explorer 45 measurements during the recovery phase of a moderate magnetic storm have confirmed that the charge exchange decay mechanism can account for the decay of the storm-time proton ring current. Data from the moderate magnetic storm of 24 February 1972 was selected for study since a symmetrical ring current had developed and effects due to asymmetric ring current losses could be eliminated. It was found that after the initial rapid decay of the proton flux, the equatorially mirroring protons in the energy range 5 to 30 keV decayed throughout the L-value range of 3.5 to 5.0 at the charge exchange decay rate calculated by Liemohn. After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange can entirely account for the storm-time proton ring current decay, and that this mechanism must be considered in all studies involving the loss of proton ring current particles.

  2. Protein-like proton exchange in a synthetic host cavity

    PubMed Central

    Hart-Cooper, William M.; Sgarlata, Carmelo; Perrin, Charles L.; Toste, F. Dean; Bergman, Robert G.; Raymond, Kenneth N.

    2015-01-01

    The mechanism of proton exchange in a metal–ligand enzyme active site mimic (compound 1) is described through amide hydrogen–deuterium exchange kinetics. The type and ratio of cationic guest to host in solution affect the rate of isotope exchange, suggesting that the rate of exchange is driven by a host whose cavity is occupied by water. Rate constants for acid-, base-, and water-mediated proton exchange vary by orders of magnitude depending on the guest, and differ by up to 200 million-fold relative to an alanine polypeptide. These results suggest that the unusual microenvironment of the cavity of 1 can dramatically alter the reactivity of associated water by magnitudes comparable to that of enzymes. PMID:26621709

  3. Protein-like proton exchange in a synthetic host cavity.

    PubMed

    Hart-Cooper, William M; Sgarlata, Carmelo; Perrin, Charles L; Toste, F Dean; Bergman, Robert G; Raymond, Kenneth N

    2015-12-15

    The mechanism of proton exchange in a metal-ligand enzyme active site mimic (compound 1) is described through amide hydrogen-deuterium exchange kinetics. The type and ratio of cationic guest to host in solution affect the rate of isotope exchange, suggesting that the rate of exchange is driven by a host whose cavity is occupied by water. Rate constants for acid-, base-, and water-mediated proton exchange vary by orders of magnitude depending on the guest, and differ by up to 200 million-fold relative to an alanine polypeptide. These results suggest that the unusual microenvironment of the cavity of 1 can dramatically alter the reactivity of associated water by magnitudes comparable to that of enzymes. PMID:26621709

  4. Mechanism of Proton Transport in Proton Exchange Membranes: Insights from Computer Simulation

    SciTech Connect

    Gregory A. Voth

    2010-11-30

    The solvation and transport of hydrated protons in proton exchange membranes (PEMs) such as NafionTM will be described using a novel multi-state reactive molecular dynamics (MD) approach, combined with large scale MD simulation to help probe various PEM morphological models. The multi-state MD methodology allows for the treatment of explicit (Grotthuss) proton shuttling and charge defect delocalization which, in turn, can strongly influence the properties of the hydrated protons in various aqueous and complex environments. A significant extension of the methodology to treat highly acidic (low pH) environments such as the hydrophilic domains of a PEM will be presented. Recent results for proton solvation and transport in NafionTM will be described which reveal the significant role of Grotthuss shuttling and charge defect delocalization on the excess proton solvation structures and transport properties. The role of PEM hydration level and morphology on these properties will also be described.

  5. Cross-linked poly (vinyl alcohol)/sulfosuccinic acid polymer as an electrolyte/electrode material for H2-O2 proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ebenezer, D.; Deshpande, Abhijit P.; Haridoss, Prathap

    2016-02-01

    Proton exchange membrane fuel cell (PEMFC) performance with a cross-linked poly (vinyl alcohol)/sulfosuccinic acid (PVA/SSA) polymer is compared with Nafion® N-115 polymer. In this study, PVA/SSA (≈5 wt. % SSA) polymer membranes are synthesized by a solution casting technique. These cross-linked PVA/SSA polymers and Nafion are used as electrolytes and ionomers in catalyst layers, to fabricate different membrane electrode assemblies (MEAs) for PEMFCs. Properties of each MEA are evaluated using scanning electron microscopy, contact angle measurements, impedance spectroscopy and hydrogen pumping technique. I-V characteristics of each cell are evaluated in a H2-O2 fuel cell testing fixture under different operating conditions. PVA/SSA ionomer causes only an additional ≈4% loss in the anode performance compared to Nafion ionomer. The maximum power density obtained from PVA/SSA based cells range from 99 to 117.4 mW cm-2 with current density range of 247 to 293.4 mA cm-2. Ionic conductivity of PVA/SSA based cells is more sensitive to state of hydration of MEA, while maximum power density obtained is less sensitive to state of hydration of MEA. Maximum power density of cross-linked PVA/SSA membrane based cell is about 35% that of Nafion® N-115 based cell. From these results, cross-linked PVA/SSA polymer is identified as potential candidate for PEMFCs.

  6. Proton dynamics in sulfonated ionic salt composites: Alternative membrane materials for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    De Almeida, N. E.; Goward, G. R.

    2014-12-01

    Hydrated Nafion, the most prevalent proton exchange membrane utilizes a vehicular mechanism for proton conduction. However, there is an increasing need for such membranes to perform under anhydrous conditions, at high temperatures, which would employ a structural transport mechanism for proton conductivity. Here, several solid-acids are characterized, both as pristine salts, and as polymer composites. Materials of interest include benzimidazolium methanesulfonate (BMSA), imidazolium methanesulfonate (IMSA), and imidazolium trifluoromethanesulfate (IFMS). The proton dynamics of these solid acids are characterized as pure salts, and as composites, embedded into porous Teflon, by solid state NMR. It was determined that spin lattice (T1) relaxation of the composites are systematically lower than that of the pure salt, indicating that local dynamics are enhanced in the composites. Spin-spin relaxation (T2∗) was measured as a function of temperature to determine the activation energy for local mobility for each salt and composite. The activation energy for local proton mobility in each salt decreased after being inserted into porous Teflon. Finally, the long-range ion transport was characterized using impedance spectroscopy. The IFMS-Teflon composite possessed the lowest activation energy for local proton mobility, the highest thermal stability, and the most favorable proton conductivity, among the investigated materials.

  7. Phosphonic acid based exchange resins

    DOEpatents

    Horwitz, E. Philip; Alexandratos, Spiro D.; Gatrone, Ralph C.; Chiarizia, Ronato

    1995-01-01

    An ion exchange resin for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene.

  8. Phosphonic acid based exchange resins

    DOEpatents

    Horwitz, E.P.; Alexandratos, S.D.; Gatrone, R.C.; Chiarizia, R.

    1995-09-12

    An ion exchange resin is described for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene. 10 figs.

  9. Ion-exchange properties of strontium hydroxyapatite under acidic conditions

    SciTech Connect

    Sugiyama, Shigeru; Nishioka, Hitoshi; Moriga, Toshihiro; Hayashi, Hiromu; Moffat, J.B.

    1998-09-01

    The ion exchange of strontium hydroxyapatite (SrHAp) with Pb{sup 2+} has been investigated under acidic conditions at 293 K. The addition of various acids to the exchanging solution enhanced the exchange capacity in the order HCl > HBr > HF > HNO{sub 3} > no acid, corresponding to the formation of halogen apatites with the former three acids or hydrogen phosphate with HNO{sub 3}. Since the ion-exchange capacity of SrHAp under nonacidic conditions is higher than that of chlorapatite, the aforementioned observations can be attributed to the participation of the protons introduced by the acids.z

  10. High temperature polymers for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Einsla, Brian Russel

    Novel proton exchange membranes (PEMs) were investigated that show potential for operating at higher temperatures in both direct methanol (DMFC) and H 2/air PEM fuel cells. The need for thermally stable polymers immediately suggests the possibility of heterocyclic polymers bearing appropriate ion conducting sites. Accordingly, monomers and random disulfonated poly(arylene ether) copolymers containing either naphthalimide, benzoxazole or benzimidazole moieties were synthesized via direct copolymerization. The ion exchange capacity (IEC) was varied by simply changing the ratio of disulfonated monomer to nonsulfonated monomer in the copolymerization step. Water uptake and proton conductivity of cast membranes increased with IEC. The water uptake of these heterocyclic copolymers was lower than that of comparable disulfonated poly(arylene ether) systems, which is a desirable improvement for PEMs. Membrane electrode assemblies were prepared and the initial fuel cell performance of the disulfonated polyimide and polybenzoxazole (PBO) copolymers was very promising at 80°C compared to the state-of-the-art PEM (NafionRTM); nevertheless these membranes became brittle under operating conditions. Several series of poly(arylene ether)s based on disodium-3,3'-disulfonate-4,4 '-dichlorodiphenylsulfone (S-DCDPS) and a benzimidazole-containing bisphenol were synthesized and afforded copolymers with enhanced stability. Selected properties of these membranes were compared to separately prepared miscible blends of disulfonated poly(arylene ether sulfone) copolymers and polybenzimidazole (PBI). Complexation of the sulfonic acid groups with the PBI structure reduced water swelling and proton conductivity. The enhanced proton conductivity of NafionRTM membranes has been proposed to be due to the aggregation of the highly acidic side-chain sulfonic acid sites to form ion channels. A series of side-chain sulfonated poly(arylene ether sulfone) copolymers based on methoxyhydroquinone was

  11. Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca(2+) exchangers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tonoplast-localised proton-coupled Ca(2+) transporters encoded by cation/H(+) exchanger (CAX) genes play a critical role in sequestering Ca(2+) into the vacuole. These transporters may function in coordination with Ca(2+) release channels, to shape stimulus-induced cytosolic Ca(2+) elevations. Recen...

  12. Acid, protons and Helicobacter pylori.

    PubMed Central

    Sachs, G.; Meyer-Rosberg, K.; Scott, D. R.; Melchers, K.

    1996-01-01

    The anti-ulcer drugs that act as covalent inhibitors of the gastric acid pump are targeted to the gastric H+/K+ ATPase by virtue of accumulation in acid and conversion to the active sulfenamide. This results in extremely effective inhibition of acid secretion. Appropriate dosage is able to optimize acid control therapy for reflux and peptic ulcer disease as compared to H2 receptor antagonists. However, clinical data on recurrence show that Helicobacter pylori eradication should accompany treatment of the lesion. These drugs have been found to synergize with many antibiotics for eradication. The survival of aerobes depends on their ability to maintain a driving force for protons across their inner membrane, the sum of a pH and potential difference gradient, the protonmotive force (pmf). The transmembrane flux of protons across the F1F0 ATPase, driven by the pmf, is coupled to the synthesis of ATP. The internal pH of H. pylori was measured using the fluorescent dye probe, BCECF, and the membrane potential defined by the uptake of the carbocyanine dye, DiSC3 [5] at different pHs to mimic the gastric environment. The protonmotive force at pH 7.0 was composed of a delta pH of 1.4 (-84mV) and a delta potential difference of -131mV, to give a pmf of -215 mV. The effect of variations in external pH on survival of the bacteria in the absence of urea correlated with the effect of external pH on the ability of the bacteria to maintain a pmf. The effect of the addition of 5 mM urea on the pmf was measured at different medium pH values. Urea restored the pmf at pH 3.0 or 3.5, but abolished the pmf at pH 7.0 or higher, due the production of the alkalinizing cation, NH3. Hence H. pylori is an acid-tolerant neutrophile due to urease activity, but urease activity also limits its survival to an acidic environment. These data help explain the occupation of the stomach by the organism and its distribution between fundus and antrum. This distribution and its alteration by proton pump

  13. Ionic Liquids and New Proton Exchange Membranes for Fuel Cells

    NASA Technical Reports Server (NTRS)

    Belieres, Jean-Philippe

    2004-01-01

    There is currently a great surge of activity in fuel cell research as laboratories across the world seek to take advantage of the high energy capacity provided by &el cells relative to those of other portable electrochemical power systems. Much of this activity is aimed at high temperature fie1 cells, and a vital component of such &el cells must be the availability of a high temperature stable proton-permeable membrane. NASA Glenn Research Center is greatly involved in developing this technology. Other approaches to the high temperature fuel cell involve the use of single- component or almost-single-component electrolytes that provide a path for protons through the cell. A heavily researched case is the phosphoric acid fuel cell, in which the electrolyte is almost pure phosphoric acid and the cathode reaction produces water directly. The phosphoric acid fie1 cell delivers an open circuit voltage of 0.9 V falling to about 0.7 V under operating conditions at 170 C. The proton transport mechanism is mainly vehicular in character according to the viscosity/conductance relation. Here we describe some Proton Transfer Ionic Liquids (PTILs) with low vapor pressure and high temperature stability that have conductivities of unprecedented magnitude for non-aqueous systems. The first requirement of an ionic liquid is that, contrary to experience with most liquids consisting of ions, it must have a melting point that is not much above room temperature. The limit commonly suggested is 100 C. PTILs constitute an interesting class of non-corrosive proton-exchange electrolyte, which can serve well in high temperature (T = 100 - 250 C) fuel cell applications. We will present cell performance data showing that the open circuit voltage output, and the performance of a simple H2(g)Pt/PTIL/Pt/O2(g) fuel cell may be superior to those of the equivalent phosphoric acid electrolyte fuel cell both at ambient temperature and temperatures up to and above 200 C. My work at NASA Glenn Research

  14. Water hydrogen bonding in proton exchange and neutral polymer membranes

    NASA Astrophysics Data System (ADS)

    Smedley, Sarah Black

    Understanding the dynamics of water sorbed into polymer films is critical to reveal structure-property relationships in membranes for energy and water treatment applications, where membranes must interact with water to facilitate or inhibit the transport of ions. The chemical structure of the polymer has drastic effects on the transport properties of the membrane due to the morphological structure of the polymer and how water is interacting with the functional groups on the polymer backbone. Therefore studying the dynamics of water adsorbed into a membrane will give insight into how water-polymer interactions influence transport properties of the film. With a better understanding of how to design materials to have specific properties, we can accelerate development of smarter materials for both energy and water treatment applications to increase efficiency and create high-flux materials and processes. The goal of this dissertation is to investigate the water-polymer interactions in proton exchange and uncharged membranes and make correlations to their charge densities and transport properties. A linear Fourier Transform Infrared (FTIR) spectroscopic method for measuring the hydrogen bonding distribution of water sorbed in proton exchange membranes is described in this thesis. The information on the distribution of the microenvironments of water in an ionic polymer is critical to understanding the effects of different acidic groups on the proton conductivity of proton exchange membranes at low relative humidity. The OD stretch of dilute HOD in H2O is a single, well-defined vibrational band. When HOD in dilute H2O is sorbed into a proton exchange membrane, the OD stretch peak shifts based on the microenvironment that water encounters within the nanophase separated structure of the material. This peak shift is a signature of different hydrogen bonding populations within the membrane, which can be deconvoluted rigorously for dilute HOD in H 2O compared to only

  15. Proton-exchange membrane regenerative fuel cells

    NASA Astrophysics Data System (ADS)

    Swette, Larry L.; LaConti, Anthony B.; McCatty, Stephen A.

    This paper will update the progress in developing electrocatalyst systems and electrode structures primarily for the positive electrode of single-unit solid polymer proton-exchange membrane (PEM) regenerative fuel cells. The work was done with DuPont Nafion 117 in complete fuel cells (40 cm 2 electrodes). The cells were operated alternately in fuel cell mode and electrolysis mode at 80°C. In fuel cell mode, humidified hydrogen and oxygen were supplied at 207 kPa (30 psi); in electrolysis mode, water was pumped over the positive electrode and the gases were evolved at ambient pressure. Cycling data will be presented for Pt-Ir catalysts and limited bifunctional data will be presented for Pt. Ir, Ru. Rh and Na xPt 3O 4 catalysts as well as for electrode structure variations.

  16. Epoxy-crosslinked sulfonated poly (phenylene) copolymer proton exchange membranes

    DOEpatents

    Hibbs, Michael; Fujimoto, Cy H.; Norman, Kirsten; Hickner, Michael A.

    2010-10-19

    An epoxy-crosslinked sulfonated poly(phenylene) copolymer composition used as proton exchange membranes, methods of making the same, and their use as proton exchange membranes (PEM) in hydrogen fuel cells, direct methanol fuel cell, in electrode casting solutions and electrodes, and in sulfur dioxide electrolyzers. These improved membranes are tougher, have higher temperature capability, and lower SO.sub.2 crossover rates.

  17. Composite proton exchange membrane based on sulfonated organic nanoparticles

    NASA Astrophysics Data System (ADS)

    Pitia, Emmanuel Sokiri

    As the world sets its sight into the future, energy remains a great challenge. Proton exchange membrane (PEM) fuel cell is part of the solution to the energy challenge because of its high efficiency and diverse application. The purpose of the PEM is to provide a path for proton transport and to prevent direct mixing of hydrogen and oxygen at the anode and the cathode, respectively. Hence, PEMs must have good proton conductivity, excellent chemical stability, and mechanical durability. The current state-of-the-art PEM is a perfluorosulfonate ionomer, Nafion®. Although Nafion® has many desirable properties, it has high methanol crossover and it is expensive. The objective of this research was to develop a cost effective two-phase, composite PEM wherein a dispersed conductive organic phase preferentially aligned in the transport direction controls proton transport, and a continuous hydrophobic phase provides mechanical durability to the PEM. The hypothesis that was driving this research was that one might expect better dispersion, higher surface to volume ratio and improved proton conductivity of a composite membrane if the dispersed particles were nanometer in size and had high ion exchange capacity (IEC, = [mmol sulfonic acid]/gram of polymer). In view of this, considerable efforts were employed in the synthesis of high IEC organic nanoparticles and fabrication of a composite membrane with controlled microstructure. High IEC, ~ 4.5 meq/g (in acid form, theoretical limit is 5.4 meq/g) nanoparticles were achieved by emulsion copolymerization of a quaternary alkyl ammonium (QAA) neutralized-sulfonated styrene (QAA-SS), styrene, and divinylbenzene (DVB). The effects of varying the counterion of the sulfonated styrene (SS) monomer (alkali metal and QAA cations), SS concentration, and the addition of a crosslinking agent (DVB) on the ability to stabilize the nanoparticles to higher IECs were assessed. The nanoparticles were ion exchanged to acid form. The extent of ion

  18. Advanced proton-exchange materials for energy efficient fuel cells.

    SciTech Connect

    Fujimoto, Cy H.; Grest, Gary Stephen; Hickner, Michael A.; Cornelius, Christopher James; Staiger, Chad Lynn; Hibbs, Michael R.

    2005-12-01

    The ''Advanced Proton-Exchange Materials for Energy Efficient Fuel Cells'' Laboratory Directed Research and Development (LDRD) project began in October 2002 and ended in September 2005. This LDRD was funded by the Energy Efficiency and Renewable Energy strategic business unit. The purpose of this LDRD was to initiate the fundamental research necessary for the development of a novel proton-exchange membranes (PEM) to overcome the material and performance limitations of the ''state of the art'' Nafion that is used in both hydrogen and methanol fuel cells. An atomistic modeling effort was added to this LDRD in order to establish a frame work between predicted morphology and observed PEM morphology in order to relate it to fuel cell performance. Significant progress was made in the area of PEM material design, development, and demonstration during this LDRD. A fundamental understanding involving the role of the structure of the PEM material as a function of sulfonic acid content, polymer topology, chemical composition, molecular weight, and electrode electrolyte ink development was demonstrated during this LDRD. PEM materials based upon random and block polyimides, polybenzimidazoles, and polyphenylenes were created and evaluated for improvements in proton conductivity, reduced swelling, reduced O{sub 2} and H{sub 2} permeability, and increased thermal stability. Results from this work reveal that the family of polyphenylenes potentially solves several technical challenges associated with obtaining a high temperature PEM membrane. Fuel cell relevant properties such as high proton conductivity (>120 mS/cm), good thermal stability, and mechanical robustness were demonstrated during this LDRD. This report summarizes the technical accomplishments and results of this LDRD.

  19. Proton conduction in exchange membranes across multiple length scales.

    PubMed

    Jorn, Ryan; Savage, John; Voth, Gregory A

    2012-11-20

    Concerns over global climate change associated with fossil-fuel consumption continue to drive the development of electrochemical alternatives for energy technology. Proton exchange fuel cells are a particularly promising technology for stationary power generation, mobile electronics, and hybrid engines in automobiles. For these devices to work efficiently, direct electrical contacts between the anode and cathode must be avoided; hence, the separator material must be electronically insulating but highly proton conductive. As a result, researchers have examined a variety of polymer electrolyte materials for use as membranes in these systems. In the optimization of the membrane, researchers are seeking high proton conductivity, low electronic conduction, and mechanical stability with the inclusion of water in the polymer matrix. A considerable number of potential polymer backbone and side chain combinations have been synthesized to meet these requirements, and computational studies can assist in the challenge of designing the next generation of technologically relevant membranes. Such studies can also be integrated in a feedback loop with experiment to improve fuel cell performance. However, to accurately simulate the currently favored class of membranes, perfluorosulfonic acid containing moieties, several difficulties must be addressed including a proper treatment of the proton-hopping mechanism through the membrane and the formation of nanophase-separated water networks. We discuss our recent efforts to address these difficulties using methods that push the limits of computer simulation and expand on previous theoretical developments. We describe recent advances in the multistate empirical valence bond (MS-EVB) method that can probe proton diffusion at the nanometer-length scale and accurately model the so-called Grotthuss shuttling mechanism for proton diffusion in water. Using both classical molecular dynamics and coarse-grained descriptions that replace atomistic

  20. The Strongest Acid: Protonation of Carbon Dioxide.

    PubMed

    Cummings, Steven; Hratchian, Hrant P; Reed, Christopher A

    2016-01-22

    The strongest carborane acid, H(CHB11F11), protonates CO2 while traditional mixed Lewis/Brønsted superacids do not. The product is deduced from IR spectroscopy and calculation to be the proton disolvate, H(CO2)2(+). The carborane acid H(CHB11F11) is therefore the strongest known acid. The failure of traditional mixed superacids to protonate weak bases such as CO2 can be traced to a competition between the proton and the Lewis acid for the added base. The high protic acidity promised by large absolute values of the Hammett acidity function (H0) is not realized in practice because the basicity of an added base is suppressed by Lewis acid/base adduct formation. PMID:26663640

  1. Two-photon exchange and elastic electron-proton scattering

    SciTech Connect

    Peter Blunden; Wally Melnitchouk; John Tjon

    2003-06-01

    Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small, but with a strong angular dependence at fixed Q{sup 2}. This is significant for the Rosenbluth technique for determining the ratio of electric and magnetic form factors of the proton, and partly reconciles the apparent discrepancy with the results of the polarization transfer technique.

  2. Water hydrogen bonding in proton exchange and neutral polymer membranes

    NASA Astrophysics Data System (ADS)

    Smedley, Sarah Black

    Understanding the dynamics of water sorbed into polymer films is critical to reveal structure-property relationships in membranes for energy and water treatment applications, where membranes must interact with water to facilitate or inhibit the transport of ions. The chemical structure of the polymer has drastic effects on the transport properties of the membrane due to the morphological structure of the polymer and how water is interacting with the functional groups on the polymer backbone. Therefore studying the dynamics of water adsorbed into a membrane will give insight into how water-polymer interactions influence transport properties of the film. With a better understanding of how to design materials to have specific properties, we can accelerate development of smarter materials for both energy and water treatment applications to increase efficiency and create high-flux materials and processes. The goal of this dissertation is to investigate the water-polymer interactions in proton exchange and uncharged membranes and make correlations to their charge densities and transport properties. A linear Fourier Transform Infrared (FTIR) spectroscopic method for measuring the hydrogen bonding distribution of water sorbed in proton exchange membranes is described in this thesis. The information on the distribution of the microenvironments of water in an ionic polymer is critical to understanding the effects of different acidic groups on the proton conductivity of proton exchange membranes at low relative humidity. The OD stretch of dilute HOD in H2O is a single, well-defined vibrational band. When HOD in dilute H2O is sorbed into a proton exchange membrane, the OD stretch peak shifts based on the microenvironment that water encounters within the nanophase separated structure of the material. This peak shift is a signature of different hydrogen bonding populations within the membrane, which can be deconvoluted rigorously for dilute HOD in H 2O compared to only

  3. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, Helena L.; Sopher, David W.

    1984-01-01

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100.degree. C. and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  4. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, H.L.; Sopher, D.W.

    1983-05-09

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100/sup 0/C and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  5. Proton conducting membrane using a solid acid

    NASA Technical Reports Server (NTRS)

    Haile, Sossina M. (Inventor); Chisholm, Calum (Inventor); Boysen, Dane A. (Inventor); Narayanan, Sekharipuram R. (Inventor)

    2006-01-01

    A solid acid material is used as a proton conducting membrane in an electrochemical device. The solid acid material can be one of a plurality of different kinds of materials. A binder can be added, and that binder can be either a nonconducting or a conducting binder. Nonconducting binders can be, for example, a polymer or a glass. A conducting binder enables the device to be both proton conducting and electron conducting.

  6. Biological Effectiveness of Accelerated Protons for Chromosome Exchanges

    PubMed Central

    George, Kerry A.; Hada, Megumi; Cucinotta, Francis A.

    2015-01-01

    We have investigated chromosome exchanges induced in human cells by seven different energies of protons (5–2500 MeV) with LET values ranging from 0.2 to 8 keV/μm. Human lymphocytes were irradiated in vitro and chromosome damage was assessed using three-color fluorescence in situ hybridization chromosome painting in chemically condensed chromosomes collected during the first cell division post irradiation. The relative biological effectiveness (RBE) was calculated from the initial slope of the dose–response curve for chromosome exchanges with respect to low dose and low dose-rate γ-rays (denoted as RBEmax), and relative to acute doses of γ-rays (denoted as RBEγAcute). The linear dose–response term was similar for all energies of protons, suggesting that the decrease in LET with increasing proton energy was balanced by the increase in dose from the production of nuclear secondaries. Secondary particles increase slowly above energies of a few hundred megaelectronvolts. Additional studies of 50 g/cm2 aluminum shielded high-energy proton beams showed minor differences compared to the unshielded protons and lower RBE values found for shielded in comparison to unshielded beams of 2 or 2.5 GeV. All energies of protons produced a much higher percentage of complex-type chromosome exchanges when compared to acute doses of γ-rays. The implications of these results for space radiation protection and proton therapy are discussed. PMID:26539409

  7. Proton conducting membrane using a solid acid

    NASA Technical Reports Server (NTRS)

    Chisholm, Calum (Inventor); Narayanan, Sekharipuram R. (Inventor); Boysen, Dane (Inventor); Haile, Sossina M. (Inventor)

    2002-01-01

    A solid acid material is used as a proton conducting membrane in an electrochemical device. The solid acid material can be one of a plurality of different kinds of materials. A binder can be added, and that binder can be either a nonconducting or a conducting binder. Nonconducting binders can be, for example, a polymer or a glass. A conducting binder enables the device to be both proton conducting and electron conducting. The solid acid material has the general form M.sub.a H.sub.b (XO.sub.t).sub.c.

  8. Design and Characterization of Styrene-Based Proton Exchange Membranes

    NASA Astrophysics Data System (ADS)

    Ebrasu, D.; Petreanu, I.; Patularu, L.; Stefanescu, I.; Valeanu, M.

    This paper deals with preparation of PEM, based on commercial block copolymer of the styrene-butadiene. The copolymer was structurally changed by sulfonation followed by cross linking, in order to design a Proton Exchange Membrane for Fuel Cells. The membranes were structural tested by FTIR Spectroscopy and Scanning Electron Microscopy. Ionic Exchange Capacity (IEC) and thermal behavior by Differential Scanning Calorimetry (DSC) were measured too.

  9. Cryo-SEM of hydrated high temperature proton exchange membranes

    SciTech Connect

    Perry, Kelly A; More, Karren Leslie; Walker, Larry R; Benicewicz, Brian

    2009-01-01

    Alternative energy technologies, such as high temperature fuel cells and hydrogen pumps, rely on proton exchange membranes (PEM). A chemically and thermally stable PEM with rapid proton transport is sol-gel phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes. It is believed that the key to the high ionic conductivity of PA-doped PBI membranes is related to the gel morphology. However, the gel structure and general morphology of this PA-doped PBI membrane has not been widely investigated. In an effort to understand the gel morphology, two SEM sample preparation methodologies have been developed for PA-doped PBI membranes. Due to the high vacuum environment of conventional SEM, the beam-sensitivity of these membranes was reduced with a mild 120 C heat treatment to remove excess water without structural rearrangement (as verified from wide angle X-ray scattering). Cryo-SEM has also been implemented for both initial and heated membranes. Cryo-SEM is known to prevent dehydration of the specimen and reduce beam-sensitivity. The SEM cross-section image (Fig. 1A) of the heated samples exhibit 3{micro}m spheroidal features that are elongated in the direction of the casting blade. These features are distorted to 2{micro}m under conventional SEM conditions (Fig. 1B). The fine-scale gel morphology image (Fig. 2) is composed of 65nm diameter domains and 30nm walls, which resembles a cellular structure. In the future, the PA-doped PBI membranes will be cryo-microtomed and cryotransferred for elemental analysis in a TEM.

  10. Phosphonic acid based ion exchange resins

    DOEpatents

    Horwitz, E. Philip; Alexandratos, Spiro D.; Gatrone, Ralph C.; Chiarizia, Ronato

    1996-01-01

    An ion exchange resin for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene.

  11. Phosphonic acid based ion exchange resins

    DOEpatents

    Horwitz, E. Philip; Alexandratos, Spiro D.; Gatrone, Ralph C.; Chiarizia, Ronato

    1994-01-01

    An ion exchange resin for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene disphosphonic acid with styrene, acrylonitrile and divinylbenzene.

  12. Phosphonic acid based ion exchange resins

    DOEpatents

    Horwitz, E.P.; Alexandratos, S.D.; Gatrone, R.C.; Chiarizia, R.

    1994-01-25

    An ion exchange resin is described for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene. 9 figures.

  13. Phosphonic acid based ion exchange resins

    DOEpatents

    Horwitz, E.P.; Alexandratos, S.D.; Gatrone, R.C.; Chiarizia, R.

    1996-07-23

    An ion exchange resin is described for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene. 10 figs.

  14. CAPSTONE SENIOR DESIGN - SUPRAMOLECULAR PROTON EXCHANGE MEMBRANES FOR FUEL CELLS

    EPA Science Inventory

    In order to assume a leading role in the burgeoning hydrogen economy, new infrastructure will be required for fuel cell manufacturing and R&D capabilities. The objective of this proposal is the development of a new generation of advanced proton exchange membrane (PEM) technol...

  15. Activity inhibition and its mitigation in high temperature proton exchange membrane fuel cells: The role of phosphoric acid, ammonium trifluoromethanesulfonate, and polyvinylidene difluoride

    NASA Astrophysics Data System (ADS)

    Holst-Olesen, Kaspar; Nesselberger, Markus; Perchthaler, Markus; Hacker, Viktor; Arenz, Matthias

    2014-12-01

    In the presented work we systematically study the influence of phosphoric acid, ammonium trifluoromethanesulfonate (ATFMS), and polyvinylidene difluoride (PVDF) on the oxygen reduction reaction (ORR) activity of carbon supported, Pt based catalysts. The influence of phosphoric acid is investigated in a mixed solution of perchloric acid with small amounts of phosphoric acid added. Thin-film rotating disk electrode (TF-RDE) measurements show that such a mixed electrolyte is advantageous as the oxygen reduction reaction (ORR) is inhibited without influencing the oxygen solubility in the electrolyte. In contrast to previous reports it is seen when investigating additives that ATFMS acts as a catalyst poison; whereas the results provide evidence of a better performance in case of the PVDF incorporated catalysts as compared to reference samples without PVDF. The technological relevance of the PVDF improvements and its stability over prolonged time was validated by membrane electrode assembly (MEA) tests.

  16. Proton Translocation in Cytochrome c Oxidase: Insights from Proton Exchange Kinetics and Vibrational Spectroscopy

    PubMed Central

    Ishigami, Izumi; Hikita, Masahide; Egawa, Tsuyoshi; Yeh, Syun-Ru; Rousseau, Denis L.

    2014-01-01

    Cytochrome c oxidase is the terminal enzyme in the electron transfer chain. It reduces oxygen to water and harnesses the released energy to translocate protons across the inner mitochondrial membrane. The mechanism by which the oxygen chemistry is coupled to proton translocation is not yet resolved owing to the difficulty of monitoring dynamic proton transfer events. Here we summarize several postulated mechanisms for proton translocation, which have been supported by a variety of vibrational spectroscopic studies. We recently proposed a proton translocation model involving proton accessibility to the regions near the propionate groups of the heme a and heme a3 redox centers of the enzyme based by hydrogen/deuterium (H/D) exchange Raman scattering studies (Egawa et al., PLOS ONE 2013). To advance our understanding of this model and to refine the proton accessibility to the hemes, the H/D exchange dependence of the heme propionate group vibrational modes on temperature and pH was measured. The H/D exchange detected at the propionate groups of heme a3 takes place within a few seconds under all conditions. In contrast, that detected at the heme a propionates occurs in the oxidized but not the reduced enzyme and the H/D exchange is pH-dependent with a pKa of ~8.0 (faster at high pH). Analysis of the thermodynamic parameters revealed that, as the pH is varied, entropy/enthalpy compensation held the free energy of activation in a narrow range. The redox dependence of the possible proton pathways to the heme groups is discussed. PMID:25268561

  17. High power density proton exchange membrane fuel cells

    NASA Technical Reports Server (NTRS)

    Murphy, Oliver J.; Hitchens, G. Duncan; Manko, David J.

    1993-01-01

    Proton exchange membrane (PEM) fuel cells use a perfluorosulfonic acid solid polymer film as an electrolyte which simplifies water and electrolyte management. Their thin electrolyte layers give efficient systems of low weight, and their materials of construction show extremely long laboratory lifetimes. Their high reliability and their suitability for use in a microgravity environment makes them particularly attractive as a substitute for batteries in satellites utilizing high-power, high energy-density electrochemical energy storage systems. In this investigation, the Dow experimental PEM (XUS-13204.10) and unsupported high platinum loading electrodes yielded very high power densities, of the order of 2.5 W cm(exp -2). A platinum black loading of 5 mg per cm(exp 2) was found to be optimum. On extending the three-dimensional reaction zone of fuel cell electrodes by impregnating solid polymer electrolyte into the electrode structures, Nafion was found to give better performance than the Dow experimental PEM. The depth of penetration of the solid polymer electrolyte into electrode structures was 50-70 percent of the thickness of the platinum-catalyzed active layer. However, the degree of platinum utilization was only 16.6 percent and the roughness factor of a typical electrode was 274.

  18. Preparations of an inorganic-framework proton exchange nanochannel membrane

    NASA Astrophysics Data System (ADS)

    Yan, X. H.; Jiang, H. R.; Zhao, G.; Zeng, L.; Zhao, T. S.

    2016-09-01

    In this work, a proton exchange membrane composed of straight and aligned proton conducting nanochannels is developed. Preparation of the membrane involves the surface sol-gel method assisted with a through-hole anodic aluminum oxide (AAO) template to form the framework of the PEM nanochannels. A monomolecular layer (SO3Hsbnd (CH2)3sbnd Sisbnd (OCH3)3) is subsequently added onto the inner surfaces of the nanochannels to shape a proton-conducting pathway. Straight nanochannels exhibit long range order morphology, contributing to a substantial improvement in the proton mobility and subsequently proton conductivity. In addition, the nanochannel size can be altered by changing the surface sol-gel condition, allowing control of the active species/charge carrier selectivity via pore size exclusion. The proton conductivity of the nanochannel membrane is reported as high as 11.3 mS cm-1 at 70 °C with a low activation energy of 0.21 eV (20.4 kJ mol-1). First-principle calculations reveal that the activation energy for proton transfer is impressively low (0.06 eV and 0.07 eV) with the assistance of water molecules.

  19. Random and Block Sulfonated Polyaramides as Advanced Proton Exchange Membranes

    SciTech Connect

    Kinsinger, Corey L.; Liu, Yuan; Liu, Feilong; Yang, Yuan; Seifert, Soenke; Knauss, Daniel M.; Herring, Andrew M; Maupin, C. Mark

    2015-11-05

    Presented here is the experimental and computational characterization of two novel copolyaramide proton exchange membranes (PEMs) with higher conductivity than Nafion at relatively high temperatures, good mechanical properties, high thermal stability, and the capability to operate in low humidity conditions. The random and block copolyaramide PEMs are found to possess different ion exchange capacities (IEC) in addition to subtle structural and morphological differences, which impact the stability and conductivity of the membranes. SAXS patterns indicate the ionomer peak for the dry block copolymer resides at q = 0.1 Å–1, which increases in amplitude when initially hydrated to 25% relative humidity, but then decrease in amplitude with additional hydration. This pattern is hypothesized to signal the transport of water into the polymer matrix resulting in a reduced degree of phase separation. Coupled to these morphological changes, the enhanced proton transport characteristics and structural/mechanical stability for the block copolymer are hypothesized to be primarily due to the ordered structure of ionic clusters that create connected proton transport pathways while reducing swelling upon hydration. Interestingly, the random copolymer did not possess an ionomer peak at any of the hydration levels investigated, indicating a lack of any significant ionomer structure. The random copolymer also demonstrated higher proton conductivity than the block copolymer, which is opposite to the trend normally seen in polymer membranes. However, it has reduced structural/mechanical stability as compared to the block copolymer. This reduction in stability is due to the random morphology formed by entanglements of polymer chains and the adverse swelling characteristics upon hydration. Therefore, the block copolymer with its enhanced proton conductivity characteristics, as compared to Nafion, and favorable structural/mechanical stability, as compared to the random copolymer

  20. Plasma-induced Styrene Grafting onto the Surface of Polytetrafluoroethylene Powder for Proton Exchange Membrane Application

    NASA Astrophysics Data System (ADS)

    Lan, Yan; Cheng, Cheng; Zhang, Suzhen; Ni, Guohua; Chen, Longwei; Yang, Guangjie; Nagatsu, M.; Meng, Yuedong

    2011-10-01

    Low-temperature plasma treatment was adopted to graft styrene onto polytetrafluoroethylene (PTFE) powder, which is widely used in the fabrication of proton exchange membrane (PEM). The grafted PTFE powder was sulfonated in chlorosulfonic acid and fabricated into a membrane, which was used as inexpensive PEM material for a proton exchange membrane fuel cell (PEMFC). Fourier transform infrared spectroscopy attenuated total reflection spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) analysis were used to characterize the structure of the sulfonated PTFE powder. The results showed that all the PTFE powders were successfully grafted by nitrogen plasma and then sulfonated under such experimental conditions. A scanning electron microscopy (SEM) image indicated that the fabricated membrane exhibits flat morphology and homogenous structure. The ion exchange capacity (IEC) of this kind of PEM was also investigated.

  1. Proton/calcium ion exchange behavior of calcite.

    PubMed

    Villegas-Jiménez, Adrián; Mucci, Alfonso; Paquette, Jeanne

    2009-10-21

    The characterization of the proton sorptive properties of calcite in aqueous solutions at 25 +/- 1 degrees C over a relatively wide range of chemical conditions (7.16 proton uptake, coupled with a significant release of Ca(2+) ions is consistently observed, greatly exceeding the theoretical number of reactive surface sites. These observations are interpreted as a fast proton/calcium exchange equilibrium between the solution and "exchangeable cation sites" (e.g., lattice positions) at and/or beneath the calcite surface (species identified by "(exc)"), , that leads to a transient, "apparent" incongruent dissolution regime and the formation of a stable calcium-deficient, proton-enriched layer within the calcite lattice under circum-neutral and alkaline regimes at standard conditions. The 2H(+)/Ca(2+) ion exchange is quantitatively described by the Langmuir-power exchange function under the Vanselow convention: where n = 1 and log(10)K(ex) = 13.0 +/- 0.3. This calcite behavior, never reported before, masks surface equilibria and directly impacts the aqueous speciation of carbonate-rock systems with poor CO(2)(g) ventilation (e.g., aquifers, pore and deep sea waters, industrial reactors) via the buffering of pH and calcite dissolution. In contrast, at fixed pCO(2) conditions, aqueous speciation remains unaffected upon CO(2)(g) sequestration resulting from ion exchange-induced calcite precipitation: ([triple bond]CaCO3)2(exc) + CO2(g) + H2O <==> [triple bond]Ca(HCO3)2(exc) + CaCO3(s). Accordingly, reliable predictions of aqueous speciation in natural or engineered calcite-containing systems at variable pCO(2) conditions must consider this exchange reaction and the associated K(ex). The postulated proton/calcium exchange may have far

  2. Proton transfer and water exchange in the green fluorescent protein

    NASA Astrophysics Data System (ADS)

    Agmon, Noam

    2014-03-01

    The green fluorescent protein (GFP) is the only naturally occurring protein in which excited-state proton-transfer has been identified. Upon excitation, a proton is ejected from its chromophore, travelling through the ``privileged water molecule'' (PWM) and Ser205 to Glu222, on a 10 ps timescale or faster. However, time-resolved fluorescence from the chromophore exhibits a t-α power-law decay extending into the ns regime. With increasing temperature, α switches from 1/2 (below 230 K) to 3/2 (above it). This has been interpreted as pseudo one-dimensional proton hopping along an internal ``proton wire,'' with an activated process that opens a ``doorway'' for proton escape to solution at the higher temperatures. To identify such putative pathways, we have developed a computer code mapping all ``proton wires'' within a protein structure. Applying it to a X-ray GFP structure of 0.9 Angstrom resolution, a proton wire indeed continues from Glu222 along the axis of the GFP ``barrel,'' connecting to a negatively charged surface patch (a ``proton collecting antenna''?). This might explain the t- 1 / 2 behavior. However, a direct escape pathway opening from the chromophore to solution is not readily identified in the X-ray structure. Here we report molecular dynamics results showing that the PWM escapes to solution on the 100 ps timescale. This occurs by fluctuations of the beta-sheet, creating an opening through which water molecules can leave and enter the protein. The exact pathway of the PWM on its way in and out has been identified, as well as the water-exchange kinetics that follows a stretched-exponential time behavior. This research was supported by the ISRAEL SCIENCE FOUNDATION grant No. 766/12.

  3. Lobster hepatopancreatic epithelial single cell suspensions as models for electrogenic sodium-proton exchange.

    PubMed

    Mandal, Prabir K

    2004-03-01

    Sodium-proton antiporters, also called Na+/H+ exchangers (NHE), are vital transmembrane proteins involved in multiple cellular functions including transepithelial ion transport and Na+ homeostasis of cells throughout the biological kingdom. Na+/H+ exchange is accelerated by cytosolic acidification and also by osmotically induced cell shrinking, thereby promoting recovery of the physiological pHi and volume. Eight isoforms of Na+/H+ exchangers have been cloned and characterized to date and share the same overall structure, but exhibit differences with respect to cellular localization, kinetic variables and plasma membrane targeting, in polarized epithelial cells. The electrogenic Na+ absorption across tight epithelia from invertebrates follow significantly different principles from the electroneutral Na+/H+ antiporter found in vertebrates. In all invertebrate cells examined, the antiporter displayed a 2Na+/1H+ transport stoichiometry and this transport was markedly inhibited by exogenous calcium and zinc. Na+/H+ exchangers (NHE) are present in crustacean hepatopancreatic cell type suspensions and are believed to function in acid-base regulation by driving the extrusion of protons across the hepatopancreatic epithelium in exchange for Na+ in the sea water. A brief review of current knowledge about Na+/H+ exchangers has been presented. In addition, understanding of hepatopancreatic Na+/H+ exchange is described as obtained after isolation of purified E-, R-, F- and B-cell suspensions from the whole organ by centrifugal elutriation. PMID:15123186

  4. Optomechanical characterization of proton-exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Jalani, Nikhil H.; Mizar, Shivananda P.; Choi, Pyoungho; Furlong, Cosme; Datta, Ravindra

    2004-08-01

    Nafion is widely used as the polymer electrolyte in proton exchange membrane (PEM) fuel cells. The properties that make the Nafion membrane indispensable are the combination of good water uptake, ion-exchange capacity, proton conductivity, gas permeability, and excellent electrochemical stability. The amount of water sorbed in the Nafion membrane is critical as the proton conductivity depends directly on the water content of the membrane which determines the fuel cell performance. The factors which affect the extent of the solvent uptake by Nafion are temperature, ion-exchange capacity, pretreatment of membrane, and the physical state of absorbing water, whether it is in liquid or vapor phase. The water sorption in the membrane is explained in terms of thermodynamic equilibrium of water in the vapor and absorption phases. As the membrane imbibes more water, the membrane matrix expands and exerts a pressure on the pore liquid which affects its chemical potential and limits extent of swelling. The extent of matrix expansion of the membranes depends on the elastic modulus, E, of the membrane, which directly affects the sorption. Hence, it is important to understand the variation of E for Nafion membrane with relative humidity (RH) and temperature. Optoelectronic holography (OEH) techniques are applied to perform quantitative, noninvasive, full field of view investigations to determine temperature and water activity dependence of E. The results obtained confirm that with the increase in temperature, E decreases and the membranes imbibes more water. Such results will allow optimization and realization of fuel cells with improved efficiency and performance.

  5. Stereochemistry-Dependent Proton Conduction in Proton Exchange Membrane Fuel Cells.

    PubMed

    Thimmappa, Ravikumar; Devendrachari, Mruthyunjayachari Chattanahalli; Kottaichamy, Alagar Raja; Tiwari, Omshanker; Gaikwad, Pramod; Paswan, Bhuneshwar; Thotiyl, Musthafa Ottakam

    2016-01-12

    Graphene oxide (GO) is impermeable to H2 and O2 fuels while permitting H(+) shuttling, making it a potential candidate for proton exchange membrane fuel cells (PEMFC), albeit with a large anisotropy in their proton transport having a dominant in plane (σIP) contribution over the through plane (σTP). If GO-based membranes are ever to succeed in PEMFC, it inevitably should have a dominant through-plane proton shuttling capability (σTP), as it is the direction in which proton gets transported in a real fuel-cell configuration. Here we show that anisotropy in proton conduction in GO-based fuel cell membranes can be brought down by selectively tuning the geometric arrangement of functional groups around the dopant molecules. The results show that cis isomer causes a selective amplification of through-plane proton transport, σTP, pointing to a very strong geometry angle in ionic conduction. Intercalation of cis isomer causes significant expansion of GO (001) planes involved in σTP transport due to their mutual H-bonding interaction and efficient bridging of individual GO planes, bringing down the activation energy required for σTP, suggesting the dominance of a Grotthuss-type mechanism. This isomer-governed amplification of through-plane proton shuttling resulted in the overall boosting of fuel-cell performance, and it underlines that geometrical factors should be given prime consideration while selecting dopant molecules for bringing down the anisotropy in proton conduction and enhancing the fuel-cell performance in GO-based PEMFC. PMID:26652316

  6. Novel polymer and inorganic/organic hybrid composite materials for proton exchange membrane applications

    NASA Astrophysics Data System (ADS)

    Yang, Zhiwei

    In this study, various novel proton exchange membranes (PEM) have been synthesized and investigated for high temperature PEM applications. Sulfonic acid functionalized polysilsesquioxane hybrid membranes with the empirical formula of R-Si-(O)1.5 consist of a highly cross-linked Si-O backbone and pendant organic side chain R, which is terminated in a proton conducting functional group (i.e., sulfonic acid). The membranes exhibited excellent proton conductivities (sigma) of >10-2 S/cm under low humidity conditions and a wide range of temperatures. The fuel cell (FC) performance of the membranes under low humidity conditions has been evaluated. Acid-doped linear meta-polyaniline membranes have been prepared through solution casting of m-PANI. The obtained membrane shows good proton conductivities at temperatures above 100°C, achieving 10-2.7 S/cm under 120°C and practically no humidity conditions. The effects of doping acids, doping levels and humidity on the conductivity are discussed. Polyethylenimine (PEI)/SiO2 nanocomposites membranes have been synthesized through sol-gel processes. The introduction of SiO2 clusters into high molecule weight, linear PEI greatly improved its thermal stability at high temperatures and O2 atmosphere. During the sol-gel processes, trifluoromethanesulfonimide (HTFSI) was added to dope the amine groups of PEI and form immobilized proton-conducting ionic liquids, which provide the hybrid membranes with proton-conducting behavior. The resultant membranes show good proton conductivities at high temperatures and low to zero humidity conditions. The effects of temperature, humidity and mobility of active groups on the conductivity are discussed. Various organic amine/HTFSI ionic group functionalized polysilsesquioxane hybrid membranes have been prepared. The Si-O backbone provides excellent thermal/chemical/mechanical properties and the HTFSI-doped amine end groups provide the proton conducting properties. The membranes exhibited proton

  7. Recovery of boric acid from ion exchangers

    DOEpatents

    Pollock, Charles W.

    1976-01-01

    The recovery of boric acid from an anion exchange resin is improved by eluting the boric acid with an aqueous solution of ammonium bicarbonate. The boric acid can be readily purified and concentrated by distilling off the water and ammonium bicarbonate. This process is especially useful for the recovery of boric acid containing a high percentage of .sup.10 B which may be found in some nuclear reactor coolant solutions.

  8. HYDROGEN ISOTOPE RECOVERY USING PROTON EXCHANGE MEMBRANE ELECTROLYSIS OF WATER

    SciTech Connect

    Fox, E; Scott Greenway, S; Amy Ekechukwu, A

    2007-08-27

    A critical component of tritium glovebox operations is the recovery of high value tritium from the water vapor in the glove box atmosphere. One proposed method to improve existing tritium recovery systems is to replace the disposable hot magnesium beds used to separate the hydrogen and oxygen in water with continuous use Proton Exchange Membrane Electrolyzers (PEMEs). This study examines radiation exposure to the membrane of a PEME and examines the sizing difference that would be needed if the electrolyzer were operated with a cathode water vapor feed instead of an anode liquid water feed.

  9. pH Replica-Exchange Method based on discrete protonation states

    PubMed Central

    Itoh, Satoru G.; Damjanović, Ana; Brooks, Bernard R.

    2012-01-01

    We propose a new algorithm for obtaining proton titration curves of ionizable residues. The algorithm is a pH replica-exchange method (PHREM) which is based on the constant pH algorithm of Mongan et al. [1]. In the original replica-exchange method, simulations of different replicas are performed at different temperature, and the temperatures are exchanged between the replicas. In our pH replica-exchange method, simulations of different replicas are performed at different pH values, and the pHs are exchanged between the replicas. The PHREM was applied to a blocked amino acid and to two protein systems (Snake Cardiotoxin and Turkey Ovomucoid Third Domain), in conjunction with a generalized Born implicit solvent. The performance and accuracy of this algorithm and the original constant pH method (PHMD) were compared. For a single set of simulations at different pHs, the use of PHREM yields more accurate Hill coefficients of titratable residues. By performing multiple sets of constant pH simulations started with different initial states the accuracy of predicted pKa values and Hill coefficients obtained with PHREM and PHMD methods becomes comparable. However, the PHREM algorithm exhibits better samplings of the protonation states of titratable residues and less scatter of the titration points and thus better precision of measured pKa values and Hill coefficients. In addition, PHREM exhibits faster convergence of individual simulations than the original constant pH algorithm. PMID:22002801

  10. Durability of symmetrically and asymmetrically porous polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Jheng, Li-Cheng; Chang, Wesley Jen-Yang; Hsu, Steve Lien-Chung; Cheng, Po-Yang

    2016-08-01

    Two types of porous polybenzimidazole (PBI) membranes with symmetric and asymmetric morphologies were fabricated by the template-leaching method and characterized by scanning electron microscope (SEM). Their physicochemical properties were compared in terms of acid-doping level, proton conductivity, mechanical strength, and oxidative stability. The durability of fuel cell operation is one of the most challenging for the PBI based membrane electrode assembly (MEA) used in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In the present work, we carried out a long-term steady-state fuel cell test to compare the effect of membrane structure on the cell voltage degradation. It has also been demonstrated that the asymmetrically porous PBI could bring some notable improvements on the durability of fuel cell operation, the fuel crossover problem, and the phosphoric acid leakage.

  11. The Exchangeability of Amino Acids in Proteins

    PubMed Central

    Yampolsky, Lev Y.; Stoltzfus, Arlin

    2005-01-01

    The comparative analysis of protein sequences depends crucially on measures of amino acid similarity or distance. Many such measures exist, yet it is not known how well these measures reflect the operational exchangeability of amino acids in proteins, since most are derived by methods that confound a variety of effects, including effects of mutation. In pursuit of a pure measure of exchangeability, we present (1) a compilation of data on the effects of 9671 amino acid exchanges engineered and assayed in a set of 12 proteins; (2) a statistical procedure to combine results from diverse assays of exchange effects; (3) a matrix of “experimental exchangeability” values EXij derived from applying this procedure to the compiled data; and (4) a set of three tests designed to evaluate the power of an exchangeability measure to (i) predict the effects of amino acid exchanges in the laboratory, (ii) account for the disease-causing potential of missense mutations in the human population, and (iii) model the probability of fixation of missense mutations in evolution. EX not only captures useful information on exchangeability while remaining free of other effects, but also outperforms all measures tested except for the best-performing alignment scoring matrix, which is comparable in performance. PMID:15944362

  12. Control of lateral domain spreading in congruent lithium niobate by selective proton exchange

    NASA Astrophysics Data System (ADS)

    Grilli, S.; Canalias, C.; Laurell, F.; Ferraro, P.; De Natale, P.

    2006-07-01

    Proton exchange was observed to increase the poling voltage for congruent lithium niobate. Patterned proton exchange was then used to control domain nucleation and inhibit broadening of reversed domains. Periodically proton exchanged samples were used to form domain gratings by electric field poling just using planar electrodes and without need for poling current control. The reversed domain gratings had a duty cycle faithfully reproducing that of the proton exchanged pattern with straight domain walls parallel to the x face, thus demonstrating that high-fidelity reversed domain patterning is possible to obtain by a relatively simple process.

  13. Ion exchange properties of humus acids

    NASA Astrophysics Data System (ADS)

    Shoba, V. N.; Chudnenko, K. V.

    2014-08-01

    Ion exchange equilibriums in a complex of brown humic acids (HAs) and related fulvic acids (FAs) with cations (H+, K+, Na+, Ca2+, Mg2+, Zn2+, Mn2+, Cu2+, Fe3+, and Al3+) have been studied, and the activity coefficients of the acid monoionic forms have been determined. The composition of the stoichiometric cell in the system of black and brown HAs and related FAs in a leached chernozem of the Ob' region has been calculated with consideration for the earlier studies of the ion exchange properties of black HAs and related FAs. It has been shown that hydrogen, calcium, magnesium, aluminum, and iron are the major components in the exchange complex of humus acids in the leached chernozem with the other cations being of subordinate importance. In spite of some differences between the analytical and calculated compositions of the humus acids, the results of the calculations can be considered satisfactory. They indicate that calculations are feasible for such complex objects as soils, and their accuracy will improve with the expansion of the experimental studies. The physicochemical simulation of the transformation of the humus acid composition under different acid-base conditions shows that the contents of most cations decrease under alkalization, and hydroxides or carbonates become the most stable forms of these cations. Under the acidification of solutions, the binding of alkaline and alkaline-earth elements by humus acids decreases and the adsorption of iron and aluminum by humus acids increases.

  14. Influence of water and membrane microstructure on the transport properties of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Siu, Ana Rosa

    Proton transport in proton exchange membranes (PEMs) depends on interaction between water and acid groups covalently bound to the polymer. Although the presence of water is important in maintaining the PEM's functions, a thorough understanding of this topic is still lacking. The objective of this work is to provide a better understanding of how the nature water, confined to ionic domains of the polymer, influences the membrane's ability to transport protons, methanol and water. Understanding this topic will facilitate development of new materials with favorable transport properties for fuel cells use. Five classes of polymer membranes were used in this work: polyacrylonitrile-graft-poly(styrenesulfonic) acid (PAN-g-macPSSA); poly(vinylidene difluoride) irradiation-graft-poly(styrenesulfonic) acid (PVDF-g-PSSA); poly(ethylenetetrafluoroethylene) irradiation-graft-poly(styrenesulfonic) acid (ETFE-gPSSA); PVDF-g-PSSA with hydroxyethylmethacrylate (HEMA); and perfluorosulfonic acid membrane (Nafion). The nature of water within the polymers (freezable versus non-freezable states) was measured by systematically freezing samples, and observing the temperature at which water freezes and the amount of heat released in the process. Freezing water-swollen membranes resulted in a 4-fold decrease in the proton conductivity of the PEM. Activation energies of proton transport before and after freezing were ˜ 0.15 eV and 0.5 eV, consistent with proton transport through liquid water and bound water, respectively. Reducing the content of water in membrane samples decreased the amount of freezable and non-freezable water. Calorimetric measurements of membranes in various degrees of hydration showed that water molecules became non-freezable when lambda, (water molecules per sulfonic acid group) was less than ˜14. Proton conduction through membranes containing only non-freezable water was demonstrated to be feasible. Diffusion experiments showed that the permeability of methanol

  15. Proton form factors and two-photon exchange in elastic electron-proton scattering

    SciTech Connect

    Nikolenko, D. M.; Arrington, J.; Barkov, L. M.; Vries, H. de; Gauzshtein, V. V.; Golovin, R. A.; Gramolin, A. V.; Dmitriev, V. F.; Zhilich, V. N.; Zevakov, S. A.; Kaminsky, V. V.; Lazarenko, B. A.; Mishnev, S. I.; Muchnoi, N. Yu.; Neufeld, V. V.; Rachek, I. A.; Sadykov, R. Sh.; Stibunov, V. N.; Toporkov, D. K.; Holt, R. J.; and others

    2015-05-15

    Proton electromagnetic form factors are among the most important sources of information about the internal structure of the proton. Two different methods for measuring these form factors, the method proposed by Rosenbluth and the polarization-transfer method, yield contradictory results. It is assumed that this contradiction can be removed upon taking into account the hard part of the contribution of two-photon exchange to the cross section for elastic electron-proton scattering. This contribution can measured experimentally via a precision comparison of the cross sections for the elastic scattering of positrons and electrons on protons. Such a measurement, performed at the VEPP-3 storage ring in Novosibirsk at the beam energies of 1.6 and 1.0 GeV for positron (electron) scattering angles in the ranges of θ{sub e} = 15°–25° and 55°–75° in the first case and in the range of θ{sub e} = 65°–105° in the second case is described in the present article. Preliminary results of this experiment and their comparison with theoretical predictions are described.

  16. Amide proton exchange rates of a bound pepsin inhibitor determined by isotope-edited proton NMR experiments

    SciTech Connect

    Fesik, S.W.; Luly, J.R.; Stein, H.H.; BaMaung, N.

    1987-09-30

    From a series of isotope-edited proton NMR spectra, amide proton exchange rates were measured at 20 C, 30 C, and 40/sup 0/C for a tightly bound /sup 15/N-labeled tripeptide inhibitor of porcine pepsin (IC50 = 1.7 X 10(-) M). Markedly different NH exchange rates were observed for the three amide protons of the bound inhibitor. The P1 NH exchanged much more slowly than the P2 NH and P3 NH. These results are discussed in terms of the relative solvent accessibility in the active site and the role of the NH protons of the inhibitor for hydrogen bonding to the enzyme. In this study a useful approach is demonstrated for obtaining NH exchange rates on ligands bound to biomacromolecules, the knowledge of which could be of potential utility in the design of therapeutically useful nonpeptide enzyme inhibitors from peptide leads.

  17. On the Importance of Exchangeable NH Protons in Creatine for the Magnetic Coupling of Creatine Methyl Protons in Skeletal Muscle

    NASA Astrophysics Data System (ADS)

    Kruiskamp, M. J.; Nicolay, K.

    2001-03-01

    The methyl protons of creatine in skeletal muscle exhibit a strong off-resonance magnetization transfer effect. The mechanism of this process is unknown. We previously hypothesized that the exchangeable amide/amino protons of creatine might be involved. To test this the characteristics of the creatine magnetization transfer effect were investigated in excised rat hindleg skeletal muscle that was equilibrated in either H2O or D2O solutions containing creatine. The efficiency of off-resonance magnetization transfer to the protons of mobile creatine in excised muscle was similar to that previously reported in intact muscle in vivo. Equilibrating the isolated muscle in D2O solution had no effect on the magnetic coupling to the immobile protons. It is concluded that exchangeable protons play a negligible role in the magnetic coupling of creatine methyl protons in muscle.

  18. Study and development of sulfated zirconia based proton exchange fuel cell membranes

    NASA Astrophysics Data System (ADS)

    Kemp, Brittany Wilson

    With the increasing consumption of energy, fuel cells are among the most promising alternatives to fossil fuels, provided some technical challenges are overcome. Proton exchange membrane fuel cells (PEMFCs) have been investigated and improvements have been made, but the problem with NafionRTM, the main membrane for PEMFCs, has not been solved. NafionRTM restricts the membranes from operating at higher temperatures, thus preventing them from working in small electronics. The problem is to develop a novel fuel cell membrane that performs comparably to NafionRTM in PEMFCs. The membranes were fabricated by applying sulfated zirconia, via template wetting, to porous alumina membranes. The fabricated membranes showed a proton conductivity of 0.016 S/cm in comparison to the proton conductivity of Nafion RTM (0.05 S/cm). Both formic acid and methanol had a lower crossover flux through the sulfated zirconia membranes (formic acid- 2.89x10 -7 mols/cm2s and methanol-1.78x10-9 mols/cm2s) than through NafionRTM (formic acid-2.03x10 -8 mols/cm2s methanol-2.42x10-6 mols/cm 2s), indicating that a sulfated zirconia PEMFC may serve as a replacement for NafionRTM.

  19. Preparation of biodiesel from rice bran fatty acids catalyzed by heterogeneous cesium-exchanged 12-tungstophosphoric acids.

    PubMed

    Srilatha, K; Sree, Rekha; Prabhavathi Devi, B L A; Sai Prasad, P S; Prasad, R B N; Lingaiah, N

    2012-07-01

    Biodiesel synthesis from rice bran fatty acids (RBFA) was carried out using cesium exchanged 12-tungstophosphoric acid (TPA) catalysts. The physico-chemical properties of the catalysts were derived from X-ray diffraction (XRD), Fourier transform infrared (FTIR), temperature programmed desorption (TPD) of NH(3) and scanning electron microscopy (SEM). The characterization techniques revealed that the Keggin structure of TPA remained intact as Cs replaced protons. The partial exchange of Cs for protons resulted in an increase in acidity and the catalysts with one Cs(+) (Cs(1)H(2)PW(12)O(40)) showed highest acidity. Under optimized conditions about 92% conversion of RBFA was obtained. The catalyst was reused for five times and retained of its original activity. Pseudo-first order model was applied to correlate the experimental kinetic data. Modified tungstophosphoric acids are efficient solid acid catalysts for the synthesis of biodiesel from the oils containing high FFA. PMID:22609655

  20. Hydrocarbon-based polymer electrolyte cerium composite membranes for improved proton exchange membrane fuel cell durability

    NASA Astrophysics Data System (ADS)

    Lee, Hyejin; Han, Myungseong; Choi, Young-Woo; Bae, Byungchan

    2015-11-01

    Hydrocarbon-based cerium composite membranes were prepared for proton exchange membrane fuel cell applications to increase oxidative stability. Different amounts of cerium ions were impregnated in sulfonated poly(arylene ether sulfone) (SPES) membranes and their physicochemical properties were investigated according to the cerium content. Field-emission scanning electron microscopy and inductively coupled plasma analyses confirmed the presence of cerium ions in the composite membranes and 1H NMR indicated the successful coordination of sulfonic acid groups with the metal ions. Increasing amounts of cerium ions resulted in decreases in the proton conductivity and water uptake, but enhanced oxidative stability. The oxidative stability of the composite membranes was proven via a hydrogen peroxide exposure experiment which mimicked fuel cell operating conditions. In addition, more than 2200 h was achieved with the composite membrane under in situ accelerated open circuit voltage (OCV) durability testing (DOE protocol), whereas the corresponding pristine SPES membrane attained only 670 h.

  1. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Technical Reports Server (NTRS)

    Eisman, G. A.

    1989-01-01

    Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities can lead to higher system efficiencies while, at the same time, not sacrificing other critical properties pertinent to membrane fuel cell operation. A series of tests to determine response times indicated that on-off cycles are on the order of 80 milliseconds to reach 90 percent of full power. The IR free voltage at 100 amps/sq ft was determined and the results indicating a membrane/electrode package resistance to be .15 ohm-sq cm at 100 amps/sq ft.

  2. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Eisman, G. A.

    1989-12-01

    Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities can lead to higher system efficiencies while, at the same time, not sacrificing other critical properties pertinent to membrane fuel cell operation. A series of tests to determine response times indicated that on-off cycles are on the order of 80 milliseconds to reach 90 percent of full power. The IR free voltage at 100 amps/sq ft was determined and the results indicating a membrane/electrode package resistance to be .15 ohm-sq cm at 100 amps/sq ft.

  3. Percolation in a Proton Exchange Membrane Fuel Cell Catalyst Layer

    SciTech Connect

    Stacy, Stephen; Allen, Jeffrey

    2012-07-01

    Water management in the catalyst layers of proton exchange membrane fuel cells (PEMFC) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. At the present time, the data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited. A method and apparatus for measuring the percolation pressure in the catalyst layer has been developed based upon an experimental apparatus used to test water percolation in porous transport layers (PTL). The experimental setup uses a pseudo Hele-Shaw type testing where samples are compressed and a fluid is injected into the sample. Testing the samples gives percolation pressure plots which show trends in increasing percolation pressure with an increase in flow rate. A decrease in pressure was seen as percolation occurred in one sample, however the pressure only had a rising effect in the other sample.

  4. Towards developing a backing layer for proton exchange membrane electrolyzers

    NASA Astrophysics Data System (ADS)

    Lettenmeier, P.; Kolb, S.; Burggraf, F.; Gago, A. S.; Friedrich, K. A.

    2016-04-01

    Current energy policies require the urgent replacement of fossil energy carriers by carbon neutral ones, such as hydrogen. The backing or micro-porous layer plays an important role in the performance of hydrogen proton exchange membrane (PEM) fuel cells, reducing contact resistance and improving reactant/product management. Such carbon-based coating cannot be used in PEM electrolysis since it oxidizes to CO2 at high voltages. A functional titanium macro-porous layer (MPL) on the current collectors of a PEM electrolyzer is developed by thermal spraying. It improves the contact with the catalyst layers by ca. 20 mΩ cm2, increasing significantly the efficiency of the device when operating at high current densities.

  5. Two-photon exchange in proton elastic scattering

    NASA Astrophysics Data System (ADS)

    Bernauer, Jan C.

    2015-10-01

    Recent interest in the proton electromagnetic form factors is partly motivated by the discrepancy found in the determination of the electric-to-magnetic form factor ratio using different techniques. Results from scattering experiments using the Rosenbluth technique indicate that the form factor ratio is constant as a function of Q2 while experiments employing polarization show a clear, roughly linear, decline of the ratio. A possible explanation is the typically unaccounted for contribution of hard two-photon exchange to the scattering process. Theoretical calculations show large variations, many indicating an effect of the right sign and magnitude. Direct verification was sought by experiments at VEPP-3, Jefferson Lab and by the OLYMPUS collaboration at DESY. In the talk, I will discuss the OLYMPUS experiment and the current state of experimental and theoretical results.

  6. Synthesis of proton conducting mesoporous materials and composite membranes for high temperature proton exchange membrane (PEM) fuel cells

    NASA Astrophysics Data System (ADS)

    Feng, Fangxia

    ), and bis(trifluoromethanesulfonyl)imide (HTFSI). The effect of TMOS/template content and the acid on the conductivity as well as H2/O2 performance were investigated. The results indicated that the incorporation of TMOs/surfactant/acid could increase the proton conductivity and the fuel cell performance. Sulfonated silica/heteropolyacid (HPA) composite membranes were investigated for high temperature proton exchange membrane (PEM) fuel cells. HPAs included tungstosilicic acid (WSA) and tungstophosphoric acid (WPA). The influence of the HPA type, and HPA content on the proton conductivity and fuel cell performance was investigated. (Abstract shortened by UMI.)

  7. A Novel Unitized Regenerative Proton Exchange Membrane Fuel Cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1996-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel single cell unitized regenerative fuel cell and results obtained on testing it are presented.

  8. A novel unitized regenerative proton exchange membrane fuel cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1995-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

  9. A novel unitized regenerative proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1995-04-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

  10. TWO-PHOTON EXCHANGE IN ELECTRON-PROTON ELASTIC SCATTERING: THEORY UPDATE

    SciTech Connect

    Andrei Afanasev

    2007-05-21

    Recent theoretical developments in the studies of two-photon exchange effects in elastic electron-proton scattering are reviewed. Two-photon exchange mechanism is considered a likely source of discrepancy between polarized and unpolarized experimental measurements of the proton electric form factor at momentum transfers of several GeV$^2$. This mechanism predicts measurable effects that are currently studied experimentally.

  11. Fabrication BaZrO3/PBI-based nanocomposite as a new proton conducting membrane for high temperature proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Hooshyari, Khadijeh; Javanbakht, Mehran; Shabanikia, Akbar; Enhessari, Morteza

    2015-02-01

    Novel PBI (polybenzimidazole)-BaZrO3 (PBZ) nanocomposite membranes have been prepared for the high temperature proton exchange membrane (HT-PEM) fuel cells. The results showed that the water uptake, acid doping level and proton conductivity of the PBZ nanocomposite membranes were higher than that of virgin PBI membrane due to the presence of perovskite structure BaZrO3 nanoparticles, which as protonic conductor can perform as a special pathway for hydrogen transport. The proton conductivity of the PBZ nanocomposite membranes with 13 mol phosphoric acid per PBI repeat unit was obtained 125 mS/cm at 180 °C and 5% relative humidity. It was found that the performance of the fuel cells increases by increasing temperature; this was explained by faster reaction kinetic and higher proton conductivity. The power density and current density at 0.5 V 180 °C with 5% relative humidity were observed 0.56 W/cm2 and 1.12 A/cm2, respectively for PBZ nanocomposite membranes containing 4 wt% of the nanofillers. The results suggested that PBZ nanocomposite membranes are promising electrolytes for HT-PEM fuel cells with improved proton conductivity.

  12. Proton exchange membranes prepared by grafting of styrene/divinylbenzene into crosslinked PTFE membranes

    NASA Astrophysics Data System (ADS)

    Li, Jingye; Ichizuri, Shogo; Asano, Saneto; Mutou, Fumihiro; Ikeda, Shigetoshi; Iida, Minoru; Miura, Takaharu; Oshima, Akihiro; Tabata, Yoneho; Washio, Masakazu

    2005-07-01

    Thin PTFE membranes were prepared by coating the PTFE dispersion onto the aluminum films. Thus the thin crosslinked PTFE (RX-PTFE) membranes were obtained by means of electron beam irradiation above the melting temperature of PTFE under oxygen-free atmosphere. The RX-PTFE membranes were pre-irradiated and grafted by styrene with or without divinylbenzene (DVB) in liquid phase. The existence of DVB accelerated the initial grafting rate. The styrene grafted RX-PTFE membranes are white colored, on the other hand, the styrene/DVB grafted RX-PTFE membranes are colorless. The proton exchange membranes (PEMs) were obtained by sulfonating the grafted membranes using chlorosulfonic acid. The ion exchange capacity (IEC) values of the PEMs ranging from 1.5 to 2.8 meq/g were obtained. The PEMs made from the styrene/DVB grafted membranes showed higher chemical stability than those of the styrene grafted membranes under oxidative circumstance.

  13. Rapid amide proton exchange rates in peptides and proteins measured by solvent quenching and two-dimensional NMR.

    PubMed Central

    Zhang, Y. Z.; Paterson, Y.; Roder, H.

    1995-01-01

    In an effort to develop a more versatile quenched hydrogen exchange method for studies of peptide conformation and protein-ligand interactions, the mechanism of amide proton exchange for model peptides in DMSO-D2O mixtures was investigated by NMR methods. As in water, H-D exchange rates in the presence of 90% or 95% DMSO exhibit characteristic acid- and base-catalyzed processes and negligible water catalysis. However, the base-catalyzed rate is suppressed by as much as four orders of magnitude in 95% DMSO. As a result, the pH at which the exchange rate goes through a minimum is shifted up by about two pH units and the minimum exchange rate is approximately 100-fold reduced relative to that in D2O. The solvent-dependent decrease in base-catalyzed exchange rates can be attributed primarily to a large increase in pKa values for the NH group, whereas solvent effects on pKW seem less important. Addition of toluene and cyclohexane resulted in improved proton NMR chemical shift dispersion. The dramatic reduction in exchange rates observed in the solvent mixture at optimal pH makes it possible to apply 2D NMR for NH exchange measurements on peptides under conditions where rates are too rapid for direct NMR analysis. To test this solvent-quenching method, melittin was exchanged in D2O (pH 3.2, 12 degrees C), aliquots were quenched by rapid freezing, lyophilized, and dissolved in quenching buffer (70% DMSO, 25% toluene, 4% D2O, 1% cyclohexane, 75 mM dichloroacetic acid) for NMR analysis. Exchange rates for 21 amide protons were measured by recording 2D NMR spectra on a series of samples quenched at different times. The results are consistent with a monomeric unfolded conformation of melittin at acidic pH. The ability to trap labile protons by solvent quenching makes it possible to extend amide protection studies to peptide ligands or labile protons on the surface of a protein involved in macromolecular interactions. PMID:7613478

  14. Protonated hydrochlorous acid (HOClH + ): Molecular structure, vibrational frequencies, and proton affinity

    NASA Astrophysics Data System (ADS)

    Francisco, J. S.; Sander, S. P.

    1995-06-01

    Protonated hydrochlorous acid (HOClH+) has been examined theoretically. Equilibrium geometries have been optimized and harmonic vibrational frequencies obtained for each of the parent and protonated structures at various levels of theory employing second-order Møller-Plesset perturbation interaction theory (MP2), singles and doubles excitation configuration interaction theory (CISD), and coupled-cluster theory (CCSD). Our study has found that protonation of the oxygen of HOCl is favored over protonation at the chlorine site. Protonation of the oxygen leads to a pyramidal structure of Cs symmetry. There is a planar Cs structure which is the inversion transition state. The inversion barrier is 3.2 kcal mol-1. The proton affinity of hypochlorous acid, HOCl, is found to be 153.1 kcal mol-1 at 0 K.

  15. Proton affinity of several basic non-standard amino acids

    NASA Astrophysics Data System (ADS)

    Rožman, Marko

    2012-08-01

    The structures and absolute proton affinities of several arginine (2-amino-3-guanidinopropionic acid, 2-amino-4-guanidinobutyric acid, homoarginine, citrulline and canavanine), histidine (1-methylhistidine and 3-methylhistidine) and lysine (2,3-diaminopropanoic acid, 2,4-diaminobutanoic acid, ornithine, 5-hydroxylysine, canaline and thialysine) homologues and analogues have been estimated using composite G3MP2B3 computational protocol. For a majority of here studied non-standard amino acids the gas-phase proton affinities were established for the first time, while for the others obtained values are used to improve the accuracy of the computational and experimental proton affinities reported previously. In addition, structures and proton affinities are discussed in order to rationalize their biological activity.

  16. A New Hybrid Proton-Exchange-Membrane Fuel Cells-Battery Power System with Efficiencies Considered

    NASA Astrophysics Data System (ADS)

    Chao, Chung-Hsing; Shieh, Jenn-Jong

    Hybrid systems, based on lead-acid or lithium-ion batteries and proton-exchange-membrane fuel cells (PEMFCs), give the possibility of combining the benefit of both technologies. The merits of high energy density and power density for different applications are discussed in this paper in recognition of the practical realization of such hybrid power systems. Furthermore, experimental data for such a hybrid system is described and the results are shown and discussed. The results show that the combination of lead-acid batteries or lithium-ion batteries and PEMFCs shows advantages in cases of applications with high peak power requirements, such as electric scooters and applications where the fuel cell (FC) is used as an auxiliary power-supply to recharge the battery. The high efficiency of FCs operating with a partial load results in a good fuel economy for the purpose of recharging batteries within a FC system.

  17. The Influenza M2 Cytoplasmic Tail Changes the Proton-Exchange Equilibria and the Backbone Conformation of the Transmembrane Histidine Residue to Facilitate Proton Conduction

    PubMed Central

    Liao, Shu Y.; Yang, Yu; Tietze, Daniel; Hong, Mei

    2015-01-01

    The influenza M2 protein forms an acid-activated tetrameric proton channel important for the virus lifecycle. Residue His37 in the transmembrane domain is responsible for channel activation and proton selectivity. While the structure and dynamics of His37 have been well studied in TM peptide constructs, it has not been investigated in the presence of the full cytoplasmic domain, which increases the proton conductivity by 2-fold compared to the TM peptide. We report here 13C and 15N chemical shifts of His37 in the cytoplasmic-containing M2(21-97), and show that cationic histidines are already present at neutral pH, in contrast to the TM peptide, indicating that the cytoplasmic domain shifts the protonation equilibria. Quantification of the imidazole 15N intensities yielded two resolved proton dissociation constants (pKa’s) of 7.1 and 5.4, which differ from the TM result but resemble the M2(18–60) result, suggesting cooperative proton binding. The average His37 pKa is higher for M2(21–97) than for the shorter constructs. We attribute this higher pKa to direct and indirect effects of the cytoplasmic domain, which is rich in acidic residues. 2D 13C-13C correlation spectra reveal seven His37 Cα-Cβ cross peaks at different pH, some of which are unique to the cytoplasmic-containing M2 and correspond to more ideal α-helical conformations. Based on the pH at which these chemical shifts appear and their sidechain structures, we assign these conformations to His37 in differently charged tetramers. Thus, the cytoplasmic domain facilitates proton conduction through the transmembrane pore by modifying the His37-water proton-exchange equilibria and the His37 backbone conformational distribution. PMID:25892574

  18. New High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells

    NASA Technical Reports Server (NTRS)

    Kinder, James D.

    2004-01-01

    Fuel cells are receiving a considerable amount of attention for potential use in a variety of areas, including the automotive industry, commercial power generation, and personal electronics. Research at the NASA Glenn Research Center has focused on the development of fuel cells for use in aerospace power systems for aircraft, unmanned air vehicles, and space transportation systems. These applications require fuel cells with higher power densities and better durability than what is required for nonaerospace uses. In addition, membrane cost is a concern for any fuel cell application. The most widely used membrane materials for proton exchange membrane (PEM) fuel cells are based on sulfonated perfluorinated polyethers, typically Nafion 117, Flemion, or Aciplex. However, these polymers are costly and do not function well at temperatures above 80 C. At higher temperatures, conventional membrane materials dry out and lose their ability to conduct protons, essential for the operation of the fuel cell. Increasing the operating temperature of PEM fuel cells from 80 to 120 C would significantly increase their power densities and enhance their durability by reducing the susceptibility of the electrode catalysts to carbon monoxide poisoning. Glenn's Polymers Branch has focused on developing new, low-cost membranes that can operate at these higher temperatures. A new series of organically modified siloxane (ORMOSIL) polymers were synthesized for use as membrane materials in a high-temperature PEM fuel cell. These polymers have an organic portion that can allow protons to transport through the polymer film and a cross-linked silica network that gives the polymers dimensional stability. These flexible xerogel polymer films are thermally stable, with decomposition onset as high as 380 C. Two types of proton-conducting ORMOSIL films have been produced: (1) NASA-A, which can coordinate many highly acid inorganic salts that facilitate proton conduction and (2) NASA-B, which has been

  19. DEVELOPMENT OF NOVEL ELECTROCATALYSTS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

    SciTech Connect

    Shamsuddin Ilias

    2002-06-11

    The Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising power sources for stand-alone utility and electric vehicle applications. Platinum (Pt) Catalyst is used for both fuel and air electrodes in PEMFCs. However, carbon monoxide (CO) contamination of H{sub 2} greatly affects electro catalysts used at the anode of PEMFCs and decreases cell performance. The irreversible poisoning of the anode can occur even in CO concentrations as low as few parts per million (ppm). In this work, we have synthesized several novel elctrocatalysts (Pt/C, Pt/Ru/C, Pt/Mo/C, Pt/Ir and Pt/Ru/Mo) for PEMFCs. These catalysts have been tested for CO tolerance in the H{sub 2}/air fuel cell, using CO concentrations in the H{sub 2} fuel that varies from 10 to 100 ppm. The performance of the electrodes was evaluated by determining the cell potential against current density. The effects of catalyst composition and electrode film preparation method on the performance of PEM fuel cell were also studied. It was found that at 70 C and 3.5 atm pressure at the cathode, Pt-alloy catalyst (10 wt% Pt/Ru/C, 20 wt% Pt/Mo/C) were more CO tolerant than the 20 wt% Pt/C catalyst alone. It was also observed that spraying method was better than the brushing technique for the preparation of electrode film.

  20. Tandem cathode for proton exchange membrane fuel cells.

    PubMed

    Siahrostami, Samira; Björketun, Mårten E; Strasser, Peter; Greeley, Jeff; Rossmeisl, Jan

    2013-06-21

    The efficiency of proton exchange membrane fuel cells is limited mainly by the oxygen reduction reaction at the cathode. The large cathodic overpotential is caused by correlations between binding energies of reaction intermediates in the reduction of oxygen to water. This work introduces a novel tandem cathode design where the full oxygen reduction, involving four electron-transfer steps, is divided into formation (equilibrium potential 0.70 V) followed by reduction (equilibrium potential 1.76 V) of hydrogen peroxide. The two part reactions contain only two electron-transfer steps and one reaction intermediate each, and they occur on different catalyst surfaces. As a result they can be optimized independently and the fundamental problem associated with the four-electron catalysis is avoided. A combination of density functional theory calculations and published experimental data is used to identify potentially active and selective materials for both catalysts. Co-porphyrin is recommended for the first step, formation of hydrogen peroxide, and three different metal oxides - SrTiO3(100), CaTiO3(100) and WO3(100) - are suggested for the subsequent reduction step. PMID:23661187

  1. Carbon monoxide poisoning of proton-exchange membrane fuel cells

    SciTech Connect

    Rodrigues, A.; Amphlett, J.C.; Mann, R.F.; Peppley, B.A.; Roberge, P.R.

    1997-12-31

    The platinum-alloy catalyst used in proton-exchange membrane (PEM) fuel cell anodes is highly susceptible to carbon monoxide (CO) poisoning. CO reduces the catalyst activity by blocking active catalyst sites normally available for hydrogen chemisorption and dissociation. The reaction kinetics at the anode catalyst surface can be used to estimate the decrease in cell voltage due to various levels of CO contamination in the inlet fuel streams on PEM fuel cell performance have been reviewed and analyzed in an attempt to further understand the electrochemical properties of the CO adsorption process. A fuel cell performance model of bipolar, Nafion 117 PEM fuel cell stack has been developed which predicts equilibrium cell output voltage as a function of current density and partial pressure of CO. The model contains both empirical and mechanistic parameters and evolved from a steady-state electrochemical model for a PEM fuel cell fed with a CO-free anode gas. Reaction kinetics and equilibrium surface coverage have been incorporated into the electrochemical model to predict the decrease in fuel cell performance at equilibrium. The effects of CO were studied at various concentrations of CO in hydrogen as the anode feed gas. Literature data were used to develop the model parameters and the resulting model is used to compare the model-predicted voltages, with and without CO, to data found in the literature.

  2. Gold Nanoparticles-Enhanced Proton Exchange Membrane (PEM) Fuel Cell

    NASA Astrophysics Data System (ADS)

    Li, Hongfei; Pan, Cheng; Liu, Ping; Zhu, Yimei; Adzic, Radoslav; Rafailovich, Miriam

    Proton exchange membrane fuel cells have drawn great attention and been taken as a promising alternated energy source. One of the reasons hamper the wider application of PEM fuel cell is the catalytic poison effect from the impurity of the gas flow. Haruta has predicted that gold nanoparticles that are platelet shaped and have direct contact with the metal oxide substrate to be the perfect catalysts of the CO oxidization, yet the synthesis method is difficult to apply in the Fuel Cell. In our approach, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. We deposit these Au particles with stepped surface directly onto the Nafion membrane in the PEM fuel cell by Langmuir-Blodgett method, resulting in over 50% enhancement of the efficiency of the fuel cell. DFT calculations were conducted to understand the theory of this kind of enhancement. The results indicated that only when the particles were in direct surface contact with the membrane, where AuNPs attached at the end of the Nafion side chains, it could reduce the energy barrier for the CO oxidation that could happen at T<300K.

  3. A flexible portable proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Hsu, Fu-Kuang; Lee, Ming-San; Lin, Chi-Chang; Lin, Yu-Kuo; Hsu, Wei-Ting

    2012-12-01

    A flexible portable proton exchange membrane fuel cell (PEMFC) is developed with non-directional flexibility acquired through new carbon-fibre-made current collectors and a new cell structure. The performance of a pilot cell suffers no significant loss when bent to curvatures with various radii in multiple directions. It also compares well with a nonflexible cylindrical portable PEMFC composed of similar components. The new cell is made with a single cup-like flexible main body with the membrane glued to the inside rim. The current collector is composed of several bunches of carbon fibre, each with metal wires embedded in them. The soft and flexible fibres not only allow for close and evenly-distributed contact with the bent electrode, but also change the character of the contact so that a large compressional force is no longer required to acquire low contact resistance which is, above all, the key to the success of this flexible cell design. The metal wire provides the needed flexibility to cover large curved electrode areas. A wire spring is used to pressure the collector against the electrode while the main body bends.

  4. Fault tolerance control for proton exchange membrane fuel cell systems

    NASA Astrophysics Data System (ADS)

    Wu, Xiaojuan; Zhou, Boyang

    2016-08-01

    Fault diagnosis and controller design are two important aspects to improve proton exchange membrane fuel cell (PEMFC) system durability. However, the two tasks are often separately performed. For example, many pressure and voltage controllers have been successfully built. However, these controllers are designed based on the normal operation of PEMFC. When PEMFC faces problems such as flooding or membrane drying, a controller with a specific design must be used. This paper proposes a unique scheme that simultaneously performs fault diagnosis and tolerance control for the PEMFC system. The proposed control strategy consists of a fault diagnosis, a reconfiguration mechanism and adjustable controllers. Using a back-propagation neural network, a model-based fault detection method is employed to detect the PEMFC current fault type (flooding, membrane drying or normal). According to the diagnosis results, the reconfiguration mechanism determines which backup controllers to be selected. Three nonlinear controllers based on feedback linearization approaches are respectively built to adjust the voltage and pressure difference in the case of normal, membrane drying and flooding conditions. The simulation results illustrate that the proposed fault tolerance control strategy can track the voltage and keep the pressure difference at desired levels in faulty conditions.

  5. Interfacial Water-Transport Effects in Proton-Exchange Membranes

    SciTech Connect

    Kienitz, Brian; Yamada, Haruhiko; Nonoyama, Nobuaki; Weber, Adam

    2009-11-19

    It is well known that the proton-exchange membrane is perhaps the most critical component of a polymer-electrolyte fuel cell. Typical membranes, such as Nafion(R), require hydration to conduct efficiently and are instrumental in cell water management. Recently, evidence has been shown that these membranes might have different interfacial morphology and transport properties than in the bulk. In this paper, experimental data combined with theoretical simulations will be presented that explore the existence and impact of interfacial resistance on water transport for Nafion(R) 21x membranes. A mass-transfer coefficient for the interfacial resistance is calculated from experimental data using different permeation cells. This coefficient is shown to depend exponentially on relative humidity or water activity. The interfacial resistance does not seem to exist for liquid/membrane or membrane/membrane interfaces. The effect of the interfacial resistance is to flatten the water-content profiles within the membrane during operation. Under typical operating conditions, the resistance is on par with the water-transport resistance of the bulk membrane. Thus, the interfacial resistance can be dominant especially in thin, dry membranes and can affect overall fuel-cell performance.

  6. Proton exchange membrane fuel cell technology for transportation applications

    SciTech Connect

    Swathirajan, S.

    1996-04-01

    Proton Exchange Membrane (PEM) fuel cells are extremely promising as future power plants in the transportation sector to achieve an increase in energy efficiency and eliminate environmental pollution due to vehicles. GM is currently involved in a multiphase program with the US Department of Energy for developing a proof-of-concept hybrid vehicle based on a PEM fuel cell power plant and a methanol fuel processor. Other participants in the program are Los Alamos National Labs, Dow Chemical Co., Ballard Power Systems and DuPont Co., In the just completed phase 1 of the program, a 10 kW PEM fuel cell power plant was built and tested to demonstrate the feasibility of integrating a methanol fuel processor with a PEM fuel cell stack. However, the fuel cell power plant must overcome stiff technical and economic challenges before it can be commercialized for light duty vehicle applications. Progress achieved in phase I on the use of monolithic catalyst reactors in the fuel processor, managing CO impurity in the fuel cell stack, low-cost electrode-membrane assembles, and on the integration of the fuel processor with a Ballard PEM fuel cell stack will be presented.

  7. Protonation of diethylaminoethyl methacrylate by acids in various solvents

    SciTech Connect

    Zhuravleva, I.L.; Bune, E.V.; Bogachev, Yu.S.; Sheinker, A.P.; Teleshov, E.N.

    1988-04-10

    It was established by /sup 1/H and /sup 13/C NMR that diethylaminoethyl methacrylate exists in the unprotonated form in solvents which are not acids. In the presence of an equimolar amount of hydrochloric or trifluoroacetic acids the amino ester is fully protonated, irrespective of the solvent. The diethylaminoethyl methacrylate-acetic acid system exists in the form of a molecular complex with a hydrogen bond and in the protonated form; the proportions of the protonated form were estimated in various solvents. The change in the reactivity of diethylaminoethyl methacrylate and its salts in polymerization was explained by a change in the electronic state of CH/sub 2/ = group of the monomer as a result of its protonation and of the formation of a hydrogen bond between the C = O group of the monomer and the solvent.

  8. Computational modeling and optimization of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Secanell Gallart, Marc

    Improvements in performance, reliability and durability as well as reductions in production costs, remain critical prerequisites for the commercialization of proton exchange membrane fuel cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on a two-dimensional through-the-channel isothermal, isobaric and single phase membrane electrode assembly (MEA) model. The model input parameters are the manufacturing parameters used to build the MEA: platinum loading, platinum to carbon ratio, electrolyte content and gas diffusion layer porosity. The governing equations of the fuel cell model are solved using Netwon's algorithm and an adaptive finite element method in order to achieve quadratic convergence and a mesh independent solution respectively. The analysis module is used to solve two optimization problems: (i) maximize performance; and, (ii) maximize performance while minimizing the production cost of the MEA. To solve these problems a gradient-based optimization algorithm is used in conjunction with analytical sensitivities. The presented computational framework is the first attempt in the literature to combine highly efficient analysis and optimization methods to perform optimization in order to tackle large-scale problems. The framework presented is capable of solving a complete MEA optimization problem with state-of-the-art electrode models in approximately 30 minutes. The optimization results show that it is possible to achieve Pt-specific power density for the optimized MEAs of 0.422 gPt/kW. This value is extremely close to the target of 0.4 gPt/kW for large-scale implementation and demonstrate the potential of using numerical optimization for fuel cell design.

  9. Preparation of a Proton-Exchange Me mbrane with -SO3H Group Based on Polyethylene and Poly(vinylidene fluoride) Film by Radiation-Induced Graft Polymerization for Proton-Exchange Fuel Cell.

    PubMed

    Kim, Sang-Kyum; Lee, Yong-Sang; Koo, Kee-Kahb; Kim, Sang-Ho; Choi, Seong-Ho

    2015-09-01

    This paper reports the preparation of a proton-exchange membrane (PEM) with sulfonic acid (-SO3H) groups based on polyethylene (PE) films and poly(vinylidene fluoride) (PVdF) films by the radiation-induced graft polymerization (RIGP) of sodium styrene sulfonate (NaSS) in the presence of the polymerizable access agents, such as acrylic acid and pyrollidone in a methanol solution. A PEM with -SO3H based on PE and PVdF films were confirmed by ATR, XPS and contact angle measurements. The water uptake (%), graft yield (%), ion-exchange content (mmol/g), and proton conductivity (S/cm), as well as the current density (mA/cm2), and power density (mW/cm) for PEM with -SO3H groups prepared by RIGP were evaluated. The PEM prepared with the -SO3H groups based on PE and PVdF films can be used as a proton-exchange fuel cell membrane. PMID:26716266

  10. Two-Photon-Exchange and {gamma}Z-Exchange Corrections to Parity-Violating Elastic Electron-Proton Scattering

    SciTech Connect

    Zhou Haiqing; Kao Chungwen; Yang Shinnan

    2007-12-31

    Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and {gamma}Z-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of {gamma}Z exchange is in general larger than that of TPE, especially at low momentum transfer Q{sup 2}{<=}1 GeV{sup 2}. Their combined effects on the values of G{sub E}{sup s}+G{sub M}{sup s} extracted in recent experiments can be as large as -40% in certain kinematics.

  11. Multi-block sulfonated poly(phenylene) copolymer proton exchange membranes

    DOEpatents

    Fujimoto, Cy H.; Hibbs, Michael; Ambrosini, Andrea

    2012-02-07

    Improved multi-block sulfonated poly(phenylene) copolymer compositions, methods of making the same, and their use as proton exchange membranes (PEM) in hydrogen fuel cells, direct methanol fuel cells, in electrode casting solutions and electrodes. The multi-block architecture has defined, controllable hydrophobic and hydrophilic segments. These improved membranes have better ion transport (proton conductivity) and water swelling properties.

  12. Excited States of Nucleic Acids Probed by Proton Relaxation Dispersion NMR Spectroscopy.

    PubMed

    Juen, Michael Andreas; Wunderlich, Christoph Hermann; Nußbaumer, Felix; Tollinger, Martin; Kontaxis, Georg; Konrat, Robert; Hansen, D Flemming; Kreutz, Christoph

    2016-09-19

    In this work an improved stable isotope labeling protocol for nucleic acids is introduced. The novel building blocks eliminate/minimize homonuclear (13) C and (1) H scalar couplings thus allowing proton relaxation dispersion (RD) experiments to report accurately on the chemical exchange of nucleic acids. Using site-specific (2) H and (13) C labeling, spin topologies are introduced into DNA and RNA that make (1) H relaxation dispersion experiments applicable in a straightforward manner. The novel RNA/DNA building blocks were successfully incorporated into two nucleic acids. The A-site RNA was previously shown to undergo a two site exchange process in the micro- to millisecond time regime. Using proton relaxation dispersion experiments the exchange parameters determined earlier could be recapitulated, thus validating the proposed approach. We further investigated the dynamics of the cTAR DNA, a DNA transcript that is involved in the viral replication cycle of HIV-1. Again, an exchange process could be characterized and quantified. This shows the general applicablility of the novel labeling scheme for (1) H RD experiments of nucleic acids. PMID:27533469

  13. Controlling the conductivity and stability of azoles: Proton and hydroxide exchange functionalities

    NASA Astrophysics Data System (ADS)

    Chaloux, Brian Leonard

    For low temperature hydrogen fuel cells to achieve widespread adoption in transport applications, it is necessary to both decrease their cost and improve the range of environmental conditions under which they effectively operate. These problems can be addressed, respectively, by either switching the catalyst from platinum to a less expensive metal, or by reducing the polymer exchange membrane's reliance upon water for proton conduction. This work focuses on understanding the chemistry and physics that limit cation stability in alkaline environments and that enable high proton conductivity in anhydrous polymer exchange membranes. Polystyrenic 1H-azoles (including 1H-tetrazole, 1H-1,2,3-triazole, and 1H-imidazoline) were synthesized to investigate whether pKa and pKb of an amophoteric, proton-conductive group have a systematic effect on anhydrous proton conductivity. It was discovered that the 1H-tetrazole (PS-Tet) exhibited distinct phase separation not seen in its carboxylic acid analog (PSHA) or reported for other 1 H-azole--containing homopolymers in literature. The resulting microstructured polymer, hypothesized to be the result of regions of high and low clustering of azoles, analogous to the multiplet-cluster model of ionomer microstructure, resulted in proton conductivity coupled with simultaneous rubbery behavior of the polymer well above its glass transition (Tg). Phase separation was similarly observed in PS-Tri and PS-ImH2 (the triazole- and imidazoline-containing polymers); soft phases with similar Tgs and hard phases with varying Tgs lend support to this hypothesis of aggregation-driven phase separation. Electrode polarization exhibited in the impedance spectra of PS-Tet and PS-HA was modeled to determine the extent of proton dissociation in undoped 1H-tetrazoles and carboxylic acids. Dry polymers (0% relative humidity) retained ~1% by weight residual water, which was observed to act as the proton acceptor in both cases. Despite doping by residual water

  14. Nanocomposite membranes based on polybenzimidazole and ZrO2 for high-temperature proton exchange membrane fuel cells.

    PubMed

    Nawn, Graeme; Pace, Giuseppe; Lavina, Sandra; Vezzù, Keti; Negro, Enrico; Bertasi, Federico; Polizzi, Stefano; Di Noto, Vito

    2015-04-24

    Owing to the numerous benefits obtained when operating proton exchange membrane fuel cells at elevated temperature (>100 °C), the development of thermally stable proton exchange membranes that demonstrate conductivity under anhydrous conditions remains a significant goal for fuel cell technology. This paper presents composite membranes consisting of poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI4N) impregnated with a ZrO2 nanofiller of varying content (ranging from 0 to 22 wt %). The structure-property relationships of the acid-doped and undoped composite membranes have been studied using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray scattering, infrared spectroscopy, and broadband electrical spectroscopy. Results indicate that the level of nanofiller has a significant effect on the membrane properties. From 0 to 8 wt %, the acid uptake as well as the thermal and mechanical properties of the membrane increase. As the nanofiller level is increased from 8 to 22 wt % the opposite effect is observed. At 185 °C, the ionic conductivity of [PBI4N(ZrO2 )0.231 ](H3 PO4 )13 is found to be 1.04×10(-1)  S cm(-1) . This renders membranes of this type promising candidates for use in high-temperature proton exchange membrane fuel cells. PMID:25801848

  15. Structural description of acid-denatured cytochrome c by hydrogen exchange and 2D NMR

    SciTech Connect

    Jeng, Meifen; Englander, S.W.; Elove, G.A.; Wand, A.J.; Roder, H. )

    1990-11-01

    Hydrogen exchange and two-dimensional nuclear magnetic resonance (2D NMR) techniques were used to characterize the structure of oxidized horse cytochrome c at acid pH and high ionic strength. Under these conditions, cytochrome c is known to assume a globular conformation (A state) with properties resembling those of the molten globule state described for other proteins. In order to measure the rate of hydrogen-deuterium exchange for individual backbone amide protons in the A state, samples of oxidized cytochrome c were incubated at 20 {degree}C in D{sub 2}O buffer for time periods ranging from 2 min to 500 h. The exchange reaction was then quenched by transferring the protein to native conditions. The extent of exchange for 44 amide protons trapped in the refolded protein was measured by 2D NMR spectroscopy. The results show that this approach can provide detailed information on H-bonded secondary and tertiary structure in partially folded equilibrium forms of a protein. All of the slowly exchanging amide protons in the three major helices of native cytochrome c are strongly protected from exchange at acid pH, indicating that the A state contains native-like elements of helical secondary structure. By contrast, a number of amide protons involved in irregular tertiary H-bonds of the native structure are only marginally protected in the A state, indicating that these H-bonds are unstable or absent. The H-exchange results suggest that the major helices of cytochrome c and their common hydrophobic domain are largely preserved in the globular acidic form while the loop region of the native structure is flexible and partly disordered.

  16. Transport properties of proton-exchange membranes: Effect of supercritical-fluid processing and chemical functionality

    NASA Astrophysics Data System (ADS)

    Pulido Ayazo

    NafionRTM membranes commonly used in direct methanol fuel cells (DMFC), are tipically limited by high methanol permeability (also known as the cross-over limitation). These membranes have phase segregated sulfonated ionic domains in a perfluorinated backbone, which makes processing challenging and limited by phase equilibria considerations. This study used supercritical fluids (SCFs) as a processing alternative, since the gas-like mass transport properties of SCFs allow a better penetration into the membranes and the use of polar co-solvents influenced their morphology, fine-tuning the physical and transport properties in the membrane. Measurements of methanol permeability and proton conductivity were performed to the NafionRTM membranes processed with SCFs at 40ºC and 200 bar and the co-solvents as: acetone, tetrahydrofuran (THF), isopropyl alcohol, HPLC-grade water, acetic acid, cyclohexanone. The results obtained for the permeability data were of the order of 10 -8-10-9 cm2/s, two orders of magnitude lower than unprocessed Nafion. Proton conductivity results obtained using AC impedance electrochemical spectroscopy was between 0.02 and 0.09 S/cm, very similar to the unprocessed Nafion. SCF processing with ethanol as co-solvent reduced the methanol permeability by two orders of magnitude, while the proton conductivity was only reduced by 4%. XRD analysis made to the treated samples exhibited a decreasing pattern in the crystallinity, which affects the transport properties of the membrane. Also, SAXS profiles of the Nafion membranes processed were obtained with the goal of determining changes produced by the SCF processing in the hydrophilic domains of the polymer. With the goal of searching for new alternatives in proton exchange membranes (PEMs) triblock copolymer of poly(styrene-isobutylene-styrene) (SIBS) and poly(styrene-isobutylene-styrene) SEBS were studied. These sulfonated tri-block copolymers had lower methanol permeabilities, but also lower proton

  17. Synthesis and characterization of nanostructured sulfonated polyimides for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Zou, Lijun

    Sulfonated polyimides (SPI) are considered to be good candidates for proton exchange membranes (PEMs) since they exhibit high strength, good film-forming ability, chemical resistance, thermal stability, and, in their hydrated state, relatively high proton conductivity. Despite intense research in the area of SPIs, fundamental investigations of hydrophilic/hydrophobic phase segregation and studies of humidity dependent morphologies are scarce. In an effort to influence the order and distribution of ionic groups in rigid-rod SPIs and to understand the interrelationships between morphology, hydration and proton conductivity, two novel model systems of SPI polymers containing hydrophobic polysiloxane (SPI-PSX) and hydrophilic silica nanoparticles (SPI-Si) were developed. The first model system of sulfonated polyimide containing hydrophobic polysiloxane segmented copolymers was prepared by a one-pot synthesis. SPI-PSX materials were evaluated using 1H NMR, size-exclusion chromatography. The presence of ion-containing diamines in the reaction mixture was found to inhibit stoichiometric incorporation of hydrophobic siloxane segments. Siloxane segments were found to lower the thermal stability of the polyimide host. Equilibrium water sorption studies of free standing films of copolymers with and without siloxane segments show that the presence of siloxane segments does not interfere with water swelling, which suggests a microphase-segregated morphology may exist. TEM and SAXS analyses show evidence of phase-segregation in sulfonated polyimides and reveal that siloxane segments strongly affect ionic clustering. However, proton conductivity only changes slightly when polysiloxane segments are incorporated. Sulfonated polyimides containing hydrophilic silica nanoparticles is our second model system developed for stabilizing the dispersed morphologies to promote proton conductivity. SPI-Si nanocomposites were prepared by a pre-polymer of anhydride-terminated sulfonated

  18. Proton affinity of methyl nitrate - Less than proton affinity of nitric acid

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Rice, Julia E.

    1992-01-01

    Several state-of-the-art ab initio quantum mechanical methods were used to investigate the equilibrium structure, dipole moments, harmonic vibrational frequencies, and IR intensities of methyl nitrate, methanol, and several structures of protonated methyl nitrate, using the same theoretical methods as in an earlier study (Lee and Rice, 1992) of nitric acid. The ab initio results for methyl nitrate and methanol were found to be in good agreement with available experimental data. The proton affinity (PA) of methyl nitrate was calculated to be 176.9 +/-5 kcal/mol, in excellent agreement with the experimental value 176 kcal/mol obtained by Attina et al. (1987) and less than the PA value of nitric acid. An explanation of the discrepancy of the present results with those of an earlier study on protonated nitric acid is proposed.

  19. Carboxylic-Acid-passivated metal oxide nanocrystals: ligand exchange characteristics of a new binding motif.

    PubMed

    De Roo, Jonathan; Justo, Yolanda; De Keukeleere, Katrien; Van den Broeck, Freya; Martins, José C; Van Driessche, Isabel; Hens, Zeger

    2015-05-26

    Ligand exchange is central in the processing of inorganic nanocrystals (NCs) and requires understanding of surface chemistry. Studying sterically stabilized HfO2 and ZrO2 NCs using (1) H solution NMR and IR spectroscopy as well as elemental analysis, this paper demonstrates the reversible exchange of initial oleic acid ligands for octylamine and self-adsorption of oleic acid at NC surfaces. Both processes are incompatible with an X-type binding motif of carboxylic acids as reported for sulfide and selenide NCs. We argue that this behavior stems from the dissociative adsorption of carboxylic acids at the oxide surface. Both proton and carboxylate moieties must be regarded as X-type ligands yielding a combined X2 binding motif that allows for self-adsorption and exchange for L-type ligands. PMID:25866095

  20. Resonance charge exchange between excited states in slow proton-hydrogen collisions

    SciTech Connect

    Tolstikhina, Inga Yu.; Kato, Daiji

    2010-09-15

    The theory of resonance charge exchange in slow collisions of a proton with a hydrogen atom in the excited state is developed. It extends the Firsov-Demkov theory of resonance charge exchange to the case of degenerate initial and final states. The theory is illustrated by semiclassical and quantum calculations of charge exchange cross sections between states with n=2 in parabolic and spherical coordinates. The results are compared with existing close-coupling calculations.

  1. Acid tolerance, proton permeabilities, and membrane ATPases of oral streptococci.

    PubMed Central

    Bender, G R; Sutton, S V; Marquis, R E

    1986-01-01

    Differences in acid tolerance among representative oral streptococci were found to be related more closely to the dynamic permeabilities of the bacteria to protons than to differences in the sensitivities of cell membranes to gross damage caused by environmental acidification. For Streptococcus mutans GS-5, Streptococcus sanguis NCTC 10904, and Streptococcus salivarius ATCC 13419, gross membrane damage, indicated by the release of magnesium from whole cells, occurred at pH values below about 4 and was rapid and extensive at pH values of about 3 or less. A more aciduric, lactic acid bacterium, Lactobacillus casei ATCC 4646, was more resistant to environmental acidification, and gross membrane damage was evident only at pH values below 3. Assessments of the movements of protons into S. mutans cells after an acid pulse at various pH values indicated that permeability to protons was minimal at a pH value of about 5, at which the average half time for pH equilibration across the cell membrane was about 12 min. The corresponding values for the less aciduric organism S. sanguis were pH 7 and 8.2 min, and the values for the intermediate organism S. salivarius were pH 6 and 6.6 min. The ATPase inhibitor dicyclohexylcarbodiimide acted to increase markedly the permeability of each organism to protons, and this action indicated that permeability involved not only the passive inflow of protons but also active outflow through the proton-translocating membrane ATPase. Membranes were isolated from each of the bacteria, and pH profiles for ATPase activities indicated pH optima of about 7.5, 7.0, 6.0, and 5.0 for S. sanguis, S. salivarius, S. mutans, and L. casei, respectively. Thus, the pH profiles for the enzymes reflected the acid tolerances of the bacteria and the permeabilities of whole cells to protons. PMID:3015800

  2. Determination of proton affinities and acidity constants of sugars.

    PubMed

    Feng, Shuting; Bagia, Christina; Mpourmpakis, Giannis

    2013-06-20

    Proton transfer reactions play a key role in the conversion of biomass derived sugars to chemicals. In this study, we employ high level ab initio theoretical methods, in tandem with solvation effects to calculate the proton affinities (PA) and acidity constants (pKa) of various d-glucose and d-fructose tautomers (protonation-deprotonation processes). In addition, we compare the theoretically derived pH values of sugar solutions against experimentally measured pH values in our lab. Our results demonstrate that the protonation of any of the O atoms of the sugars is thermodynamically preferred without any significant variation in the PA values. Intramolecular hydrogen transfers, dehydration reactions, and ring-opening processes were observed, resulting from the protonation of specific hydroxyl groups on the sugars. Regarding the deprotonation processes (pKa), we found that the sugars' anomeric hydroxyls exhibit the highest acidity. The theoretically calculated pH values of sugar solutions are in excellent agreement with experimental pH measurements at low sugar concentrations. At higher sugar concentrations the calculations predict less acidic solutions than the experiments. In this case, we expect the sugars to act as solvents increasing the proton solvation energy and the acidity of the solutions. We demonstrated through linear relationships that the pKa values are correlated with the relative stability of the conjugate bases. The latter is related to hydrogen bonding and polarization of the C-O(-) bond. A plausible explanation for the good performance of the direct method in calculating the pKa values of sugars can be the presence of intramolecular hydrogen bonds on the conjugate base. Both theory and experiments manifest that fructose is a stronger acid than glucose, which is of significant importance in self-catalyzed biomass-relevant dehydration reactions. PMID:23706015

  3. IRMPD signature of protonated pantothenic acid, an ubiquitous nutrient

    NASA Astrophysics Data System (ADS)

    Corinti, Davide; Mannina, Luisa; Chiavarino, Barbara; Steinmetz, Vincent; Fornarini, Simonetta; Crestoni, Maria Elisa

    2016-02-01

    Intrinsic properties of pantothenic acid, an essential nutraceutical, are examined. The effect of protonation on the energetic and geometric features of pantothenic acid, generated as gaseous protonated species, are investigated by infrared multiple photon dissociation (IRMPD) spectroscopy over an extended frequency range (800-2000 cm-1 and 2800-3700 cm-1). DFT calculations are exploited to identify the possible structures and predict the absorption spectra at the B3LYP/6-311++G(d,p) level. Two amide-protonated structures, characterized by the most stable binding motifs, account well for the experimental spectrum, thus revealing structurally diagnostic features of potential benefit for the development of highly sensitive and selective nutrient screening.

  4. Preparation of Proton Exchange Membranes and Lithium Batteries from Melamine-containing Ormosils

    NASA Technical Reports Server (NTRS)

    Tigelaar, Dean M.; Kinder, James D.; Meador, Mary Ann; Waldecker, James; Bennett, William R.

    2004-01-01

    Our laboratory has recently reported a series of rodcoil polymers for lithium batteries that display dimensionally stable films with good ionic conductivity. The rod segments consist of rigid linear and branched polyimides and the coil segments are polyethylene oxides (PEO). It has been proposed that good mechanical and transport properties are due to phase separation between the rod and coil segments. It was also observed that increased branching and molecular weight lead to increased conductivity. The following study was undertaken to assess the effects of phase separation in polyalkylene oxides connected by melamine linkages. Melamine was chosen as the linking unit because it provides a branching site, cation binding sites to help ionic transport between polymer chains, and the opportunity for self assembly through hydrogen bonding. Polymers were made by the reaction of cyanuric chloride with a series of amine-terminated alkylene oxides. A linear polymer was first made, followed by reaction of the third site on cyanuric chloride with varying ratios of monofunctional Jeffamine and (3-aminopropyl)triethoxysilane. The lithium trifluoromethane sulfonamide-doped polymers are then crosslinked through a sol-gel process to form free-standing films. Initial results have shown mechanically strong films with lithium conductivities on the order of 2 x 10(exp -5) S/cm at ambient temperature. In a separate study, organically modified silanes (Ormosils) that contain sulfonic acid derivatized melamines have been incorporated into proton exchange membranes. The membranes are made by reaction of the primary amine groups of various ratios of melamine derivative and difunctional Jeffamine (MW = 2000) with the epoxide group of (3-Glycidyloxypropyl)trimethoxysilane. The films were then cross-linked through a sol-gel process. Resulting sulfuric acid doped films are strong, flexible, and have proton conductivities on the order of 2 x l0(exp -2) S/cm (120 C, 25% relative humidity). Our

  5. Proton-exchange membrane materials based on blends of poly(ether ketone ketone) and poly(ether imide)

    NASA Astrophysics Data System (ADS)

    Swier, S.; Gasa, J.; Shaw, M. T.; Weiss, R. A.

    2004-03-01

    The development of materials for proton-exchange membranes (PEM) involves finding a compromise between high proton conductivities and sufficient mechanical and chemical stability to withstand the conditions in the fuel cell. The currently used perfluorinated polymer electrolyte membranes tend to be expensive and have problems in case of extensive application. New polymer electrolytes based on hydrocarbon polymers are therefore the focus of a considerable research effort. Blends of sulfonated poly(ether ketone ketone) (SPEKK) and poly(ether imide) (PEI) were evaluated as PEMs. Sulfonation of PEKK was achieved by using a mixture of concentrated sulfuric acid and fuming sulfuric acid, and blend membranes were prepared by casting a solution of the two polymers in N-methyl-2- pyrrolidone. The hydration level of the membrane decreased with increasing PEI concentration, but a proton conductivity comparable to NafionTM was obtained for blends containing less than 20 wt% PEI. The fuel cell performance of the membranes was affected by the sulfonation level of the PEKK, the blend composition and the casting procedure employed. The state of water in the membrane was evaluated from the depression of the glass transition and from the melting endotherms associated with water. Proton conductivity depended strongly on the hydration number (water molecules per sulfonate group), which depended on the sulfonation level of the PEKK and the blend morphology. Sorption data from gravimetric techniques provided important transport information like the solubility and diffusivity of water and methanol.

  6. Kinetic isotope effects for fast deuterium and proton exchange rates

    PubMed Central

    Mammoli, Daniele; Kadeřávek, Pavel; Pelupessy, Philippe; Bodenhausen, Geoffrey

    2016-01-01

    By monitoring the effect of deuterium decoupling on the decay of transverse 15N magnetization in D–15N spin pairs during multiple-refocusing echo sequences, we have determined fast D–D exchange rates k D and compared them with fast H–H exchange rates k H in tryptophan to determine the kinetic isotope effect as a function of pH and temperature. PMID:27009684

  7. Single-spin asymmetries from two-photon exchange in elastic electron proton scattering

    SciTech Connect

    A.V. Afanasev; N.P. Merenkov

    2005-02-01

    The parity-conserving single-spin beam asymmetry of elastic electron-proton scattering is induced by an absorptive part of the two-photon exchange amplitude. We demonstrate that this asymmetry has logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasi-real photons. An optical theorem is used to evaluate the asymmetry in terms of the total photoproduction cross section on the proton.

  8. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Eisman, G. A.

    1990-02-01

    Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes, useful as the proton transport medium and separator. The following work will outline some of the performance characteristics which are typical for such membranes.

  9. Tuning surface hydrophilicity/hydrophobicity of hydrocarbon proton exchange membranes (PEMs).

    PubMed

    He, Chenfeng; Mighri, Frej; Guiver, Michael D; Kaliaguine, Serge

    2016-03-15

    The effect of annealing on the surface hydrophilicity of various representative classes of hydrocarbon-based proton exchange membranes (PEMs) is investigated. In all cases, a more hydrophilic membrane surface develops after annealing at elevated temperatures. The annealing time also had some influence, but in different ways depending on the class of PEM. Longer annealing times resulted in more hydrophilic membrane surfaces for copolymerized sulfonated poly(ether ether ketone) (SPEEK-HQ), while the opposite behavior occurred in sulfonated poly(aryl ether ether ketone) (Ph-SPEEK), sulfonated poly(aryl ether ether ketone ketone) (Ph-m-SPEEKK) and sulfonated poly (aryl ether ether nitrile) (SPAEEN-B). Increased surface hydrophilicity upon annealing results from ionic cluster decomposition, according to the "Eisenberg-Hird-Moore model" (EHM). The increased surface hydrophilicity is supported by contact angle (CA) measurements, and the cluster decomposition is auxiliarily supported by probing the level of atomic sulfur (sulfonic acid) within different surface depths using angle-dependent XPS as well as ATR-FTIR. Membrane acidification leads to more hydrophilic surfaces by elimination of the hydrogen bonding that occurs between strongly-bound residual solvent (dimethylacetamide, DMAc) and PEM sulfonic acid groups. The study of physicochemical tuning of surface hydrophilicity/hydrophobicity of PEMs by annealing and acidification provides insights for improving membrane electrode assembly (MEA) fabrication in fuel cell (FC). PMID:26722798

  10. Synthesis and characterization of sulfonated poly (arylene ether sulfone) copolymers via direct copolymerization: Candidates for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Harrison, William Lamont

    A designed series of directly copolymerized homo- and disulfonated copolymers containing controlled degrees of pendant sulfonic acid groups have been synthesized via nucleophilic step polymerization. Novel sulfonated poly (arylene ether sulfone) copolymers using 4,4'-bisphenol A, 4,4'-biphenol, hexafluorinated (6F) bisphenol AF, and hydroquinone, respectively, with dichlorodiphenyl sulfone (DCDPS) and 3,3'-disodiumsulfonyl-4,4'-dichlorodiphenylsulfone (SDCDPS) were investigated. Molar ratios of DCDPS and SDCDPS were systematically varied to produce copolymers of controlled compositions, which contained up to 70 mol% of disulfonic acid moiety. The goal is to identify thermally, hydrolytically, and oxidatively stable high molecular weight, film-forming, ductile ion conducting copolymers, which had properties desirable for proton exchange membranes (PEM) in fuel cells. Commercially available bisphenols were selected to produce cost effective alternative PEMs. Partially aliphatic bisphenol A and hexafluorinated (6F) bisphenol AF produced amorphous copolymers with different thermal oxidative and surface properties. Biphenol and hydroquinone was utilized to produce wholly aromatic copolymers. The sulfonated copolymers were prepared in the sodium-salt form and converted to the acid moiety via two different methodologies and subsequently investigated as proton exchange membranes for fuel cells. Hydrophilicity increased with the level of disulfonation, as expected. Moreover, water sorption increased with increasing mole percent incorporation of SDCDPS. The copolymers' water uptake was a function of both bisphenol structure and degree of disulfonation. Furthermore, the acidification procedures were shown to influence the Tg values, water uptake, and conductivity of the copolymers. Atomic force microscopy (AFM) in the tapping mode confirmed that the morphology of the copolymers could be designed to display nanophase separation in the hydrophobic and hydrophilic (sulfonated

  11. Global analysis of proton elastic form factor data with two-photon exchange corrections

    SciTech Connect

    J. Arrington; W. Melnitchouk; J. A. Tjon

    2007-09-01

    We use the world's data on elastic electron-proton scattering and calculations of two-photon exchange effects to extract corrected values of the proton's electric and magnetic form factors over the full Q^2 range of the existing data. Our analysis combines the corrected Rosenbluth cross section and polarization transfer data, and is the first extraction of G_Ep and G_Mp including explicit two-photon exchange corrections and their associated uncertainties. In addition, we examine the angular dependence of the corrected cross sections, and discuss the possible nonlinearities of the cross section as a function of epsilon.

  12. Two-photon exchange correction in elastic unpolarized electron-proton scattering at small momentum transfer

    NASA Astrophysics Data System (ADS)

    Tomalak, O.; Vanderhaeghen, M.

    2016-01-01

    We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer Q2 . We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the Q2 expansion of the TPE correction and goes beyond this approximation by keeping the full Q2 dependence of the proton structure functions. In the range of small momentum transfer, our result is in good agreement with the empirical TPE fit to existing data.

  13. MnO2 nanotube-Pt/graphene mixture as an ORR catalyst for proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Divya, P.; Ramaprabhu, S.

    2013-02-01

    In the present study, MnO2 nanotubes are synthesized by hydrothermal method and Pt/graphene by co reduction of hexachloroplatinic acid and graphite oxide. The formation of MnO2 nanotubes and Pt/graphene are confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy. MnO2 nanotubes are mixed with Pt/graphene is applied as the ORR catalyst in proton exchange membrane fuel cell. The single cell measurement is carried out after fabricating the membrane electrode assembly and polarization curves are recorded at different temperatures and the results are discussed.

  14. Proton exchange rates in transfer RNA as a function of spermidine and magnesium.

    PubMed Central

    Tropp, J S; Redfield, A G

    1983-01-01

    Solvent exchange rates of selected protons were measured by NMR saturation recovery for E. coli tRNAVal, E. colifMet and yeast tRNAPhe, at temperatures from 20 to 40 degrees C, in the presence of 0.12M Na+ and various levels of added spermidine. tRNAVal was also studied with added Mg++. The exchange rates in zero spermidine and Mg++ indicate early melting of the U8 A14 interaction, in accord with thermodynamic melting studies. Exchange rates for secondary protons suggest early melting of the T stem in tRNAfMet and the acceptor stem in tRNAPhe, in contradiction with melting transition assignments from thermodynamic work. Addition of 10 spermidines per tRNA stabilizes the secondary and tertiary interactions more effectively than added Na+, but less so than Mg++. Added spermidine has the curious effect of increasing the exchange rate of the psi 55 N1 proton, while protecting the psi 55 N3 proton from exchange in all three tRNA's. Added Mg++ has the same effect on tRNAVal. PMID:6340067

  15. Lamellar crystals as proton conductors to enhance the performance of proton exchange membrane for direct methanol fuel cell

    NASA Astrophysics Data System (ADS)

    Zhao, Yuning; Jiang, Zhongyi; Xiao, Lulu; Xu, Tao; Wu, Hong

    2011-08-01

    Zirconium glyphosate (ZrG) is a solid proton conductor with layered crystal structure. The inorganic veneer sheets of ZrG are covalently intercalated by glyphosate molecules with carboxylic acid end groups (-COOH). The existence of abundant -COOH groups both inside and on the surface of ZrG provides additional proton-conducting channels facilitating the proton conduction through and around the inorganic crystals. ZrG is incorporated into the sulfonated polyether ether ketone (SPEEK) matrices to prepare proton-conducting hybrid membranes. The conductivity of the hybrid membranes is higher than the pristine SPEEK membrane, and increases with increasing ZrG content. Furthermore, the enhancement of the proton conductivity is more obvious at elevated temperatures. At 25 °C, the proton conductivity of the hybrid membrane with 16 wt% ZrG is 1.4 times higher than that of the pristine membrane. When the temperature increases to 55 °C, the conductivity of the hybrid membrane with 8 wt% ZrG is more than twice that of the pristine SPEEK membrane. The prolonged and tortuous pathways originated from the incorporation of inorganic crystals lead to reduced methanol permeability. The selectivity of the hybrid membrane is increased by as much as 72% compared to the pristine SPEEK membrane.

  16. Tuning a High Transmission Ion Guide to Prevent Gas-Phase Proton Exchange During H/D Exchange MS Analysis.

    PubMed

    Guttman, Miklos; Wales, Thomas E; Whittington, Dale; Engen, John R; Brown, Jeffery M; Lee, Kelly K

    2016-04-01

    Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for protein structural analysis has been adopted for many purposes, including biopharmaceutical development. One of the benefits of examining amide proton exchange by mass spectrometry is that it can readily resolve different exchange regimes, as evidenced by either binomial or bimodal isotope patterns. By careful analysis of the isotope pattern during exchange, more insight can be obtained on protein behavior in solution. However, one must be sure that any observed bimodal isotope patterns are not artifacts of analysis and are reflective of the true behavior in solution. Sample carryover and certain stationary phases are known as potential sources of bimodal artifacts. Here, we describe an additional undocumented source of deuterium loss resulting in artificial bimodal patterns for certain highly charged peptides. We demonstrate that this phenomenon is predominantly due to gas-phase proton exchange between peptides and bulk solvent within the initial stages of high-transmission conjoined ion guides. Minor adjustments of the ion guide settings, as reported here, eliminate the phenomenon without sacrificing signal intensity. Such gas-phase deuterium loss should be appreciated for all HDX-MS studies using such ion optics, even for routine studies not focused on interpreting bimodal spectra. Graphical Abstract ᅟ. PMID:26810432

  17. Tuning a High Transmission Ion Guide to Prevent Gas-Phase Proton Exchange During H/D Exchange MS Analysis

    NASA Astrophysics Data System (ADS)

    Guttman, Miklos; Wales, Thomas E.; Whittington, Dale; Engen, John R.; Brown, Jeffery M.; Lee, Kelly K.

    2016-04-01

    Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for protein structural analysis has been adopted for many purposes, including biopharmaceutical development. One of the benefits of examining amide proton exchange by mass spectrometry is that it can readily resolve different exchange regimes, as evidenced by either binomial or bimodal isotope patterns. By careful analysis of the isotope pattern during exchange, more insight can be obtained on protein behavior in solution. However, one must be sure that any observed bimodal isotope patterns are not artifacts of analysis and are reflective of the true behavior in solution. Sample carryover and certain stationary phases are known as potential sources of bimodal artifacts. Here, we describe an additional undocumented source of deuterium loss resulting in artificial bimodal patterns for certain highly charged peptides. We demonstrate that this phenomenon is predominantly due to gas-phase proton exchange between peptides and bulk solvent within the initial stages of high-transmission conjoined ion guides. Minor adjustments of the ion guide settings, as reported here, eliminate the phenomenon without sacrificing signal intensity. Such gas-phase deuterium loss should be appreciated for all HDX-MS studies using such ion optics, even for routine studies not focused on interpreting bimodal spectra.

  18. Two-Photon Exchange in Elastic Electron-Proton Scattering: A QCD Factorization Approach

    SciTech Connect

    Kivel, Nikolai; Vanderhaeghen, Marc

    2009-08-28

    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer Q{sup 2}. It is shown that the leading two-photon exchange amplitude behaves as 1/Q{sup 4}, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.

  19. Sulfonated poly(ether ether ketone)/clay-SO 3H hybrid proton exchange membranes for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Fu, Tiezhu; Cui, Zhiming; Zhong, Shuangling; Shi, Yuhua; Zhao, Chengji; Zhang, Gang; Shao, Ke; Na, Hui; Xing, Wei

    A new type of sulfonated clay (clay-SO 3H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO 3H was 51.8 mequiv. (100 g) -1, which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO 3H hybrid membranes which composed of SPEEK and different weight contents of clay-SO 3H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method. The performances of hybrid membranes for direct methanol fuel cells (DMFCs) in terms of mechanical and thermal properties, water uptake, water retention, methanol permeability and proton conductivity were investigated. The mechanical and thermal properties of the SPEEK membranes had been improved by introduction of clay and clay-SO 3H, obviously. The water desorption coefficients of the SPEEK and hybrid membranes were studied at 80 °C. The results showed that the addition of the inorganic part into SPEEK membrane enhanced the water retention of the membrane. Both methanol permeability and proton conductivity of the hybrid membranes decreased in comparison to the pristine SPEEK membrane. However, it was worth noting that higher selectivity defined as ratio of proton conductivity to methanol permeability of the SPEEK/clay-SO 3H-1 hybrid membrane with 1 wt.% clay-SO 3H was obtained than that of the pristine SPEEK membrane. These results showed that the SPEEK/clay-SO 3H hybrid membrane with 1 wt.% clay-SO 3H had potential usage of a proton exchange membrane (PEM) for DMFCs.

  20. Two-photon exchange corrections in elastic lepton-proton scattering at small momentum transfer

    NASA Astrophysics Data System (ADS)

    Tomalak, Oleksandr; Vanderhaeghen, Marc

    2016-03-01

    In recent years, elastic electron-proton scattering experiments, with and without polarized protons, gave strikingly different results for the electric over magnetic proton form factor ratio. A mysterious discrepancy (``the proton radius puzzle'') has been observed in the measurement of the proton charge radius in muon spectroscopy experiments versus electron spectroscopy and electron scattering. Two-photon exchange (TPE) contributions are the largest source of the hadronic uncertainty in these experiments. We compare the existing models of the elastic contribution to TPE correction in lepton-proton scattering. A subtracted dispersion relation formalism for the TPE in electron-proton scattering has been developed and tested. Its relative effect on cross section is in the 1 - 2 % range for a low value of the momentum transfer. An alternative dispersive evaluation of the TPE correction to the hydrogen hyperfine splitting was found and applied. For the inelastic TPE contribution, the low momentum transfer expansion was studied. In addition with the elastic TPE it describes the experimental TPE fit to electron data quite well. For a forthcoming muon-proton scattering experiment (MUSE) the resulting TPE was found to be in the 0 . 5 - 1 % range, which is the planned accuracy goal.

  1. Investigation of the structural stability of the human acidic fibroblast growth factor by hydrogen-deuterium exchange.

    PubMed

    Chi, Ya-Hui; Kumar, Thallampuranam Krishnaswamy S; Kathir, Karuppanan Muthusamy; Lin, Dong-Hai; Zhu, Guang; Chiu, Ing-Ming; Yu, Chin

    2002-12-24

    The conformational stability of the human acidic fibroblast growth factor (hFGF-1) is investigated using amide proton exchange and temperature-dependent chemical shifts, monitored by two-dimensional NMR spectroscopy. The change in free energy of unfolding (DeltaG(u)) of hFGF-1 is estimated to be 5.00 +/- 0.09 kcal.mol(-)(1). Amide proton-exchange rates of 74 residues (in hFGF-1) have been unambiguously measured, and the exchange process occurs predominately according to the conditions of the EX2 limit. The exchange rates of the fast-exchanging amide protons exposed to the solvent have been measured using the clean SEA-HSQC technique. The amide proton protection factor and temperature coefficient estimates show reasonably good correlation. Residues in beta-strands II and VI appear to constitute the stability core of the protein. Among the 12 beta-strands constituting the beta-barrel architecture of hFGF-1, beta-strand XI, located in the heparin binding domain, exhibits the lowest average protection factor value. Amide protons involved in the putative folding nucleation site in hFGF-1, identified by quench-flow NMR studies, do not represent the slow-exchanging core. Residues in portions of hFGF-1 experiencing high conformational flexibility mostly correspond to those involved in receptor recognition and binding. PMID:12484774

  2. Ordinary and extraordinary waveguides realized by reverse proton exchange on LiTaO 3

    NASA Astrophysics Data System (ADS)

    El Hadi, K.; Baldi, P.; De Micheli, M. P.; Ostrowsky, D. B.; Korkishko, Yu. N.; Fedorov, V. A.; Kondrat'ev, A. V.

    1997-02-01

    In this paper, we report a study of the reverse proton exchange process in lithium tantalate based on the observation of the buried extraordinary index waveguide and the surface ordinary index waveguide. This allows us to determine approximately all the parameters of these waveguides and in particular the ordinary index variation for all H xLi 1- xTaO 3 phases.

  3. PEM (Proton exchange membrane) fuel cell stack heat and mass measurement

    SciTech Connect

    Vanderborgh, N.E.; Kimble, M.C.; Huff, J.R.; Hedstrom, J.C.

    1992-08-01

    PEM stacks are under evaluation as candidates for future space power technology. Results of long-term operation on a set of contemporary stacks fitted with different proton exchange membrane materials are given. Data on water balances show effects of membrane materials on stack performance. 15 refs.

  4. PEM (Proton exchange membrane) fuel cell stack heat and mass measurement

    SciTech Connect

    Vanderborgh, N.E.; Kimble, M.C.; Huff, J.R.; Hedstrom, J.C.

    1992-01-01

    PEM stacks are under evaluation as candidates for future space power technology. Results of long-term operation on a set of contemporary stacks fitted with different proton exchange membrane materials are given. Data on water balances show effects of membrane materials on stack performance. 15 refs.

  5. DEVELOPMENT OF DESIGN TOOLS TO FACILITATE/PROMOTE SUSTAINABLE DESIGN OF PROTON EXCHANGE MEMBRANE FUEL CELLS

    EPA Science Inventory

    Objective is to develop and demonstrate 2 sets of of design tools that are applicable to the manufacture of proton exchange membrane fuel cell systems. First set will offer guidance to fuel cell designers for end of life options suited to subassembly. Second set will give fuel ...

  6. Nickel-Catalyzed Proton-Deuterium Exchange (HDX) Procedures for Glycosidic Linkage Analysis of Complex Carbohydrates.

    PubMed

    Price, Neil P J; Hartman, Trina M; Vermillion, Karl E

    2015-07-21

    The structural analysis of complex carbohydrates typically requires the assignment of three parameters: monosaccharide composition, the position of glycosidic linkages between monosaccharides, and the position and nature of noncarbohydrate substituents. The glycosidic linkage positions are often determined by permethylation analysis, but this can be complicated by high viscosity or poor solubility, resulting in under-methylation. This is a drawback because an under-methylated position may be misinterpreted as the erroneous site of a linkage or substituent. Here, we describe an alternative approach to linkage analysis that makes use of a nonreversible deuterium exchange of C-H protons on the carbohydrate backbone. The exchange reaction is conducted in deuterated water catalyzed by Raney nickel, and results in the selective exchange of C-H protons adjacent to free hydroxyl groups. Hence, the position of the residual C-H protons is indicative of the position of glycosidic linkages or other substituents and can be readily assigned by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) or, following suitable derivatization, by gas chromatography-mass spectroscopy (GC/MS) analysis. Moreover, because the only changes to the parent sugar are proton/deuterium exchanges, the composition and linkage analysis can be determined in a single step. PMID:26075577

  7. Analysing powers and spin correlations in deuteron-proton charge exchange at 726 MeV

    NASA Astrophysics Data System (ADS)

    Dymov, S.; Azaryan, T.; Bagdasarian, Z.; Barsov, S.; Carbonell, J.; Chiladze, D.; Engels, R.; Gebel, R.; Grigoryev, K.; Hartmann, M.; Kacharava, A.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Kurbatov, V.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Mchedlishvili, D.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Shmakova, V.; Ströher, H.; Tabidze, M.; Trusov, S.; Tsirkov, D.; Uzikov, Yu.; Valdau, Yu.; Weidemann, C.; Wilkin, C.

    2015-05-01

    The charge exchange of vector polarised deuterons on a polarised hydrogen target has been studied in a high statistics experiment at the COSY-ANKE facility at a deuteron beam energy of Td = 726 MeV. By selecting two fast protons at low relative energy Epp, the measured analysing powers and spin correlations are sensitive to interference terms between specific neutron-proton charge-exchange amplitudes at a neutron kinetic energy of Tn ≈1/2Td = 363 MeV. An impulse approximation calculation, which takes into account corrections due to the angular distribution in the diproton, describes reasonably the dependence of the data on both Epp and the momentum transfer. This lends broad support to the current neutron-proton partial wave solution that was used in the estimation.

  8. {Delta} resonance contribution to two-photon exchange in electron-proton scattering

    SciTech Connect

    S. Kondratyuk; P. G. Blunden; W. Melnitchouk; J. A. Tjon

    2005-06-01

    We calculate the effects on the elastic electron-proton scattering cross section of the two-photon exchange contribution with an intermediate {Delta} resonance. The {Delta} two-photon exchange contribution is found to be smaller in magnitude than the previously evaluated nucleon contribution, with an opposite sign at backward scattering angles. The sum of the nucleon and {Delta} two-photon exchange corrections has the angular dependence compatible with both the polarization transfer and the Rosenbluth methods of measuring the nucleon electromagnetic form factors.

  9. Surface modification of a proton exchange membrane and hydrogen storage in a metal hydride for fuel cells

    NASA Astrophysics Data System (ADS)

    Andrews, Lisa

    Interest in fuel cell technology is rising as a result of the need for more affordable and available fuel sources. Proton exchange membrane fuel cells involve the catalysis of a fuel to release protons and electrons. It requires the use of a polymer electrolyte membrane to transfer protons through the cell, while the electrons pass through an external circuit, producing electricity. The surface modification of the polymer, NafionRTM, commonly researched as a proton exchange membrane, may improve efficiency of a fuel cell. Surface modification can change the chemistry of the surface of a polymer while maintaining bulk properties. Plasma modification techniques such as microwave discharge of an argon and oxygen gas mixture as well as vacuum-ultraviolet (VUV) photolysis may cause favorable chemical and physical changes on the surface of Nafion for improved fuel cell function. A possible increase in hydrophilicity as a result of microwave discharge experiments may increase proton conductivity. Grafting of acrylic acid from the surface of modified Nafion may decrease the permeation of methanol in a direct methanol fuel cell, a process which can decrease efficiency. Modification of the surface of Nafion samples were carried out using: 1) An indirect Ar/O2 gas mixture plasma investigating the reaction of oxygen radicals with the surface, 2) A direct Ar/O2 gas mixture plasma investigating the reaction of oxygen radicals and VUV radiation with the surface and, 3) VUV photolysis investigating exclusively the interaction of VUV radiation with the surface and any possible oxidation upon exposure to air. Acrylic acid was grafted from the VUV photolysed Nafion samples. All treated surfaces were analyzed using X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) was used to analyze the grafted Nafion samples. Scanning electron microscopy (SEM) and contact angle measurements were used to analyze experiments 2 and 3. Using hydrogen as fuel is a

  10. Measuring the 2{gamma} Exchange Effect in Electron-Proton Scattering at CLAS

    SciTech Connect

    Bennett, Robert Paul

    2011-10-24

    Recent results from experiments at Jefferson Laboratory, Newport News VA, which measure the ratio of the electric to magnetic form factors of the proton, G{sub E}/G{sub M}, have forced us to reexamine the single photon exchange approximation in lepton-proton elastic scattering. Discrepancies between the ratio obtained via the time-tested Rosenbluth separation method and new polarization transfer measurements, which differ by as much as a factor of three, may be resolved by considering the effect of two photon exchange (TPE). Theoretical corrections for the TPE effect are difficult due to the large number of excited nucleon states that can contribute to the process. The TPE effect can, however, be determined directly by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = {sigma}(e{sup +})/{sigma}(e{sup -}), since the TPE effect changes sign with the charge of the incident particle. The CLAS TPE experiment at Jefferson Laboratory, will determine the effect of two-photon exchange in elastic lepton-proton scattering by precisely measuring the ratio of positron-proton to electron-proton elastic cross sections over a large kinematic range (0.1<{epsilon}<0.96, 0.02{<=}Q{sup 2}{<=}2.0). We will accomplish this by directing the 5.5 GeV primary electron beam, provided by the Continuous Electron Beam Accelerator Facility (CEBAF), onto a set of radiators and converters to produce simultaneous and identical beams of electron and positrons. Acceptance and efficiency concerns are minimized by only considering the ratios of the elastic cross sections and switching polarity of magnets in the beam line and the spectrometer. Guided by the results of a short 2006 test run and extensive GEANT based modeling, new shielding and beam line components were designed to maximize luminosity. The unique experimental design and challenges of the TPE experiment and the projected luminosities will be presented.

  11. Nanostructure and Properties of Sulfonated Polyarylenethioethersulfone Copolymers as Proton Exchange Fuel Cell Membranes

    SciTech Connect

    Yoonessi,M.; Bai, Z.; Dang, T.

    2007-01-01

    A systematic investigation of properties and nanostructure of sulfonated polyarylenethioethersulfone (SPTES) copolymer proton exchange membranes for fuel cell applications has been presented. SPTES copolymers are high temperature resistant (250 C), and form tough films with excellent proton conductivity up to 170 {+-} 5 mS/cm (SPTES 70 @ 85 C, 85%RH). Small angle X-ray scattering of hydrated SPTES 70 revealed the presence of local water domains (diameter {approx}5 nm) within the copolymer. The high proton conductivity of the membranes is attributed to the formation of these ionic aggregates containing water molecules, which facilitate proton transfer. AFM studies of SPTES 70 as a function of humidity (25-65%RH) showed an increase in hydrophilic domains with increasing humidity at 22 C.

  12. Two-photon exchange correction to muon-proton elastic scattering at low momentum transfer

    NASA Astrophysics Data System (ADS)

    Tomalak, Oleksandr; Vanderhaeghen, Marc

    2016-03-01

    We evaluate the two-photon exchange (TPE) correction to the muon-proton elastic scattering at small momentum transfer. Besides the elastic (nucleon) intermediate state contribution, which is calculated exactly, we account for the inelastic intermediate states by expressing the TPE process approximately through the forward doubly virtual Compton scattering. The input in our evaluation is given by the unpolarized proton structure functions and by one subtraction function. For the latter, we provide an explicit evaluation based on a Regge fit of high-energy proton structure function data. It is found that, for the kinematics of the forthcoming muon-proton elastic scattering data of the MUSE experiment, the elastic TPE contribution dominates, and the size of the inelastic TPE contributions is within the anticipated error of the forthcoming data.

  13. Anticorrosion properties of tin oxide coatings for carbonaceous bipolar plates of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kinumoto, Taro; Nagano, Keita; Yamamoto, Yuji; Tsumura, Tomoki; Toyoda, Masahiro

    2014-03-01

    An anticorrosive surface treatment of a carbonaceous bipolar plate used in proton exchange membrane fuel cells (PEMFCs) was demonstrated by addition of a tin oxide surface coating by liquid phase deposition (LPD), and its effectiveness toward corrosion prevention was determined. The tin oxide coating was deposited by immersion in tin fluoride and boric acid solutions, without any observable decrease in the bipolar plate electrical conductivity. Anticorrosion properties of a flat carbonaceous bipolar plate were investigated in an aqueous HClO4 electrolyte solution (10 μmol dm-3) at 80 °C. CO2 release due to corrosion was significant for the bare specimen above 1.3 V, whereas no CO2 release was noted for the tin-oxide-coated specimen, even approaching 1.5 V. Moreover, minimal changes in contact angle against a water droplet before and after treatment indicated suppressed corrosion of the surface-coated specimen. Anticorrosion properties were also confirmed for a model bipolar plate having four gas flow channels. The tin oxide layer remained on the channel surfaces (inner walls, corners and intersections) after durability tests. Based on these results, tin-oxide-based surface coatings fabricated by LPD show promise as an anticorrosion technique for carbonaceous bipolar plates for PEMFCs.

  14. Current short circuit implementation for performance improvement and lifetime extension of proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Zhan, Yuedong; Guo, Youguang; Zhu, Jianguo; Li, Li

    2014-12-01

    To improve its performance, extend its lifetime, and overcome the problem of the slow dynamic during the start-up and the operation process of a proton exchange membrane fuel cell (PEMFC), this paper presents current short circuit and smart energy management approaches for a main PEMFC with auxiliary PEMFC, battery and supercapacitor as hybrid power source in parallel with an intelligent uninterrupted power supply (UPS) system. The hybrid UPS system consists of two low-cost 63-cell 300 W PEMFC stacks, 3-cell lead-acid battery, and 20-cell series-connected supercapacitors. Based on the designed intelligent hybrid UPS system, experimental tests and theoretical studies are conducted. Firstly, the modeling of PEMFC is obtained and evaluated. Then the performance improvement mechanism of the current short circuit is proposed and analyzed based on the Faradaic process and non-Faradaic process of electrochemical theory. Finally, the performances of the main PEMFC with the auxiliary PEMFC/battery/supercapacitor hybrid power source and intelligent energy management are experimentally measured and analyzed. The proposed current short circuit method can significantly extend the lifetime, improve the performance of PEMFC and decrease the size of the main FC for stationary, backup power sources and vehicular applications.

  15. Polypyrrole layered SPEES/TPA proton exchange membrane for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Neelakandan, S.; Kanagaraj, P.; Sabarathinam, R. M.; Nagendran, A.

    2015-12-01

    Hybrid membranes based on sulfonated poly(1,4-phenylene ether ether sulfone) (SPEES)/tungstophosphoric acid (TPA) were prepared. SPEES/TPA membrane surfaces were modified with polypyrrole (Ppy) by in situ polymerization method to reduce the TPA leaching. The morphology and electrochemical property of the surface coated membranes were studied by SEM, AFM, water uptake, ion exchange capacity, proton conductivity, methanol permeability and tensile strength. The water uptake and the swelling ratio of the surface coated membranes decreased with increasing the Ppy layer. The surface roughness of the hybrid membrane was decreased with an increase in Ppy layer on the membrane surface. The methanol permeability of SPEES/TPA-Ppy4 hybrid membrane was significantly suppressed and found to be 2.1 × 10-7 cm2 s-1, which is 1.9 times lower than pristine SPEES membrane. The SPEES/TPA-Ppy4 membrane exhibits highest relative selectivity (2.86 × 104 S cm-3 s) than the other membrane with low TPA leaching. The tensile strength of hybrid membranes was improved with the introduction of Ppy layer. Combining their lower swelling ratio, high thermal stability and selectivity, SPEES/TPA-Ppy4 membranes could be a promising material as PEM for DMFC applications.

  16. Electronically conducting proton exchange polymers as catalyst supports for proton exchange membrane fuel cells. Electrocatalysis of oxygen reduction, hydrogen oxidation, and methanol oxidation

    SciTech Connect

    Lefebvre, M.C.; Qi, Z.; Pickup, P.G.

    1999-06-01

    A variety of supported catalysts were prepared by the chemical deposition of Pt and Pt-Ru particles on chemically prepared poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate) (PEDOT/PSS) and PEDOT/polyvinylsulfate (PVS) composites. The polymer particles were designed to provide a porous, proton-conducting and electron-conducting catalyst support for use in fuel cells. These polymer-supported catalysts were characterized by electron microscopy, impedance spectroscopy, cyclic voltammetry, and conductivity measurements. Their catalytic activities toward hydrogen and methanol oxidation and oxygen reduction were evaluated in proton exchange membrane fuel-cell-type gas diffusion electrodes. Activities for oxygen reduction comparable to that obtained with a commercial carbon-supported catalyst were observed, whereas those for hydrogen and methanol oxidation were significantly inferior, although still high for prototype catalysts.

  17. Structural and Electrical Characterization of Protonic Acid Doped Polyaniline

    NASA Astrophysics Data System (ADS)

    Shaktawat, Vinodini; Saxena, Narendra S.; Sharma, Kananbala; Sharma, Thaneshwar P.

    2008-04-01

    Polyaniline doped with different protonic acids were chemically synthesized using ammonium persulfate (APS) as an oxidant. These samples were characterized through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, which confirms the amorphous nature and acid doping, respectively. Electrical conduction in these samples has been studied through the measurement of I-V characteristics at room temperature as well as in the temperature range from 313 K to 413 K. So obtained characteristic curves were found to be nonlinear. The conductivity of phosphoric acid doped polyaniline sample is higher as compared to HCl doped polyaniline and pure polyaniline. Temperature dependence of conductivity suggests a semiconducting nature with increase in temperature. Activation energies have been found to be 50.86, 25.74 and 21.05 meV for pure polyaniline (base), polyaniline doped with hydrochloric, phosphoric acid, respectively.

  18. The neutron-proton charge-exchange amplitudes measured in the dp → ppn reaction

    NASA Astrophysics Data System (ADS)

    Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H. J.; Steffens, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Uzikov, Yu.; Valdau, Yu.; Wilkin, C.

    2013-04-01

    The unpolarised differential cross section and the two deuteron tensor analysing powers A xx and A yy of the ěc dp to \\{ pp\\} _s n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27GeV, data were obtained for small momentum transfers to a { pp} s system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C x,x and C y,y that were carried out in the ěc děc p to \\{ pp\\} _s n reaction at 1.2 and 2.27GeV. The values obtained for the proton analysing power A {/y p } also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

  19. Cationic Covalent Organic Frameworks: A Simple Platform of Anionic Exchange for Porosity Tuning and Proton Conduction.

    PubMed

    Ma, Heping; Liu, Bailing; Li, Bin; Zhang, Liming; Li, Yang-Guang; Tan, Hua-Qiao; Zang, Hong-Ying; Zhu, Guangshan

    2016-05-11

    Mimicking proton conduction mechanism of Nafion to construct novel proton-conducting materials with low cost and high proton conductivity is of wide interest. Herein, we have designed and synthesized a cationic covalent organic framework with high thermal and chemical stability by combining a cationic monomer, ethidium bromide (EB) (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide), with 1,3,5-triformylphloroglucinol (TFP) in Schiff base reactions. This is the first time that the stable cationic crystalline frameworks allowed for the fabrication of a series of charged COFs (EB-COF:X, X = F, Cl, Br, I) through ion exchange processes. Exchange of the extra framework ions can finely modulate the COFs' porosity and pore sizes at nanoscale. More importantly, by introducing PW12O40(3-) into this porous cationic framework, we can greatly enhance the proton conductivity of ionic COF-based material. To the best of our knowledge, EB-COF:PW12 shows the best proton conductivity at room temperature among ever reported porous organic materials. PMID:27094048

  20. Purification Or Organic Acids Using Anion Exchange Chromatography.

    DOEpatents

    Ponnampalam; Elankovan

    2001-09-04

    Disclosed is a cost-effective method for purifying and acidifying carboxylic acids, including organic acids and amino acids. The method involves removing impurities by allowing the anionic form of the carboxylic acid to bind to an anion exchange column and washing the column. The carboxylic anion is displaced as carboxylic acid by washing the resin with a strong inorganic anion. This method is effective in removing organic carboxylic acids and amino acids from a variety of industrial sources, including fermentation broths, hydrolysates, and waste streams.

  1. Neopentane and solid acids: direct hydron exchange before cracking.

    PubMed

    Walspurger, Stéphane; Sun, Yinyong; Souna Sido, Abdelkarim Sani; Sommer, Jean

    2006-09-21

    The hydrogen/deuterium exchange reaction of 2,2-dimethylpropane (neopentane) over D(2)O-exchanged zeolites (MOR, FAU, BEA, MFI) using a batch recirculation reactor was studied by means of gas chromatography coupled with mass spectrometer. In the temperature range 473-573 K, H/D exchange proceeds without side reaction such as cracking at short contact times. Indeed the C-H bond has appeared favorably involved in the activation of neopentane compared to the less accessible C-C bond. The transition state allowing hydron exchange is most likely a carbonium species (pentacoordinated carbon) as in the case of the H/D exchange between methane and solid acid. The activation energies of the H/D exchange between neopentane and zeolites are the same for all zeolites indicating a common carbonium ion type transition state. On the basis of previous results in the case of the exchange between methane and liquid superacids, the deuterium exchange rates in neopentane were tentatively related to the acidity of the solids. However the order of activity MOR > MFI > BEA > FAU seems to be related to the size of the pores, which may suggest the involvement of a confinement effect in the zeolites cavities. Moreover we found that H/D exchange takes also place between neopentane and deuterated sulfated zirconia (SZ) emphasizing its strong acidity. PMID:16970460

  2. Studies on PVA based nanocomposite Proton Exchange Membrane for Direct methanol fuel cell (DMFC) applications

    NASA Astrophysics Data System (ADS)

    Bahavan Palani, P.; Kannan, R.; Rajashabala, S.; Rajendran, S.; Velraj, G.

    2015-02-01

    Different concentrations of Poly (vinyl alcohol)/Montmorillonite (PVA/MMT) based proton exchange membranes (PEMs) have been prepared by solution casting method. The structural and electrical properties of these composite membranes have been characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopic (FTIR) and AC impedance spectroscopic methods. The conductivity of the PEMs has been estimated for the different concentration of MMT. Water/Methanol uptake measurement were also analyzed for the prepared PEMs and presented. The proton conductivity studies were carried out at room temperature with 100% of humidity.

  3. Nonlinear diffusion model for annealed proton-exchanged waveguides in zirconium-doped lithium niobate.

    PubMed

    Langrock, Carsten; Roussev, Rostislav V; Nava, Giovanni; Minzioni, Paolo; Argiolas, Nicola; Sada, Cinzia; Fejer, Martin M

    2016-08-20

    Photorefractive-damage- (PRD) resistant zirconium-oxide-doped lithium niobate is investigated as a substrate for the realization of annealed proton-exchanged (APE) waveguides. Its advantages are a favorable distribution coefficient, PRD resistance comparable to magnesium-oxide-doped lithium niobate, and a proton-diffusion behavior resembling congruent lithium niobate. A 1D model for APE waveguides was developed based on a previous model for congruently melting lithium niobate. Evidence for a nonlinear index dependence on concentration was found. PMID:27556972

  4. Correlation of the antimicrobial activity of salicylaldehydes with broadening of the NMR signal of the hydroxyl proton. Possible involvement of proton exchange processes in the antimicrobial activity.

    PubMed

    Elo, Hannu; Kuure, Matti; Pelttari, Eila

    2015-03-01

    Certain substituted salicylaldehydes are potent antibacterial and antifungal agents and some of them merit consideration as potential chemotherapeutic agents against Candida infections, but their mechanism of action has remained obscure. We report here a distinct correlation between broadening of the NMR signal of the hydroxyl proton of salicylaldehydes and their activity against several types of bacteria and fungi. When proton NMR spectra of the compounds were determined using hexadeuterodimethylsulfoxide as solvent and the height of the OH proton signal was measured, using the signal of the aldehyde proton as an internal standard, it was discovered that a prerequisite of potent antimicrobial activity is that the proton signal is either unobservable or relatively very low, i.e. that it is extremely broadened. Thus, none of the congeners whose OH proton signal was high were potent antimicrobial agents. Some congeners that gave a very low OH signal were, however, essentially inactive against the microbes, indicating that although drastic broadening of the OH signal appears to be a prerequisite, also other (so far unknown) factors are needed for high antimicrobial activity. Because broadening of the hydroxyl proton signal is related to the speed of the proton exchange process(es) involving that proton, proton exchange may be involved in the mechanism of action of the compounds. Further studies are needed to analyze the relative importance of different factors (such as electronic effects, strength of the internal hydrogen bond, co-planarity of the ring and the formyl group) that determine the rates of those processes. PMID:25621992

  5. Phase composition and stress in LiTaO3 proton-exchanged optical waveguides

    NASA Astrophysics Data System (ADS)

    Kuneva, M.; Christova, K.; Tonchev, S.

    2013-09-01

    The phase composition of the top layer of Li1-xHxTaO3 waveguide layers produced at different modifications of the proton exchange (PE) technology has been analyzed based on their IR reflection spectra. These spectra contain new bands within the range 850\\text{--}1050\\ \\text{cm}^{-1} , each phase having its own reflection spectrum. Since the top layer is actually the strongest proton-exchanged one of all sublayers building the waveguide layer, the recognition of the top sublayer's phase in many cases could be used to make conclusions about the phases building the rest of the entire PE layer. The intrinsic stress caused by crystal lattice deformation due to the PE was calculated by an optical integral method. An attempt to explain the level of stress is made based on the phase composition of the studied samples.

  6. Cr3+ ions in hydrogenated and proton exchanged lithium niobate crystals

    NASA Astrophysics Data System (ADS)

    Kamiska, A.; Arizmendi, L.; Barcz, A.; Usakowska, E.; Suchocki, A.

    2004-01-01

    We studied influence of annealing in water vapour and proton exchange on high-pressure low-temperature luminescence spectra of near stoichiometric LN:Cr, MgO crystals, containing both CrLi and CrNb centers by using diamond-anvil cell technique. The observed changes of the spectra of Cr3+ ions are associated with the larger inhomogeneous broadening and increase of the splitting of the 2E level of the so called CrNb center. This shows that neither increase of hydrogen concentration in LN by almost two orders of magnitude (from 1018 to almost 1020 cm-3) nor proton-exchange procedure do not create any new optically active Cr3+ centers in those crystals. This does not support the hypothesis about the close compensation of Cr3+Nb sites in LiNbO3 crystals by hydrogen ions.

  7. Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals

    SciTech Connect

    Balobaid, Laila; Craig Carville, N.; Collins, Liam; Rodriguez, Brian J.; Manzo, Michele; Gallo, Katia

    2013-10-28

    Local reactivity on periodically proton exchanged lithium niobate (PPE:LN) surfaces is a promising route for the fabrication of regularly spaced nanostructures. Here, using MgO-doped PPE:LN templates, we investigate the influence of the doping on the nanostructure formation as a function of the proton exchange (PE) depth. The deposition is found to occur preferentially along the boundary between MgO-doped LN and the PE region when the PE depth is at least 1.73 μm, however, for shallower depths, deposition occurs across the entire PE region. The results are found to be consistent with an increased photoconductivity of the MgO-doped LN.

  8. Chitin nanowhisker-supported sulfonated poly(ether sulfone) proton exchange for fuel cell applications.

    PubMed

    Zhang, Chan; Zhuang, Xupin; Li, Xiaojie; Wang, Wei; Cheng, Bowen; Kang, Weimin; Cai, Zhanjun; Li, Mengqin

    2016-04-20

    To balance the relationship among proton conductivity and mechanic strength of sulfonated poly(ether sulfone) (SPES) membrane, chitin nanowhisker-supported nanocomposite membranes were prepared by incorporating whiskers into SPES. The as-prepared chitin whiskers were prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated oxidation of α-chitin from crab shells. The structure and properties of the composite membranes were examined as proton exchange membrane (PEM). Results showed that chitin nanowhiskers were dispersed incompactly in the SPES matrix. Thermal stability, mechanical properties, water uptake and proton conductivity of the nanocomposite films were improved from those of the pure SPES film with increasing whisker content, which ascribed to strong interactions between whiskers and between SPES molecules and chitin whiskers via hydrogen bonding. These indicated that composition of filler and matrix got good properties and whisker-supported membranes are promising materials for PEM. PMID:26876844

  9. Collinear Photon Exchange in the Beam Normal Polarization Asymmetry of Elastic Electron-Proton Scattering

    SciTech Connect

    Andrei Afanasev; N.P. Merenkov

    2004-07-01

    The parity-conserving single-spin beam asymmetry of elastic electron-proton scattering is induced by an absorptive part of the two-photon exchange amplitude. We demonstrate that this asymmetry has logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasi-real photons. An optical theorem is used to evaluate the asymmetry in terms of the total photoproduction cross section on the proton, predicting its magnitude at 20-30 parts per million for high electron beam energies and small scattering angles. At fixed 4-momentum transfers, the asymmetry is rising logarithmically with increasing electron beam energy, following the high-energy diffractive behavior of total photoproduction cross section on the proton.

  10. Chitosan/silica coated carbon nanotubes composite proton exchange membranes for fuel cell applications.

    PubMed

    Liu, Hai; Gong, Chunli; Wang, Jie; Liu, Xiaoyan; Liu, Huanli; Cheng, Fan; Wang, Guangjin; Zheng, Genwen; Qin, Caiqin; Wen, Sheng

    2016-01-20

    Silica-coated carbon nanotubes (SCNTs), which were obtained by a simple sol-gel method, were utilized in preparation of chitosan/SCNTs (CS/SCNTs) composite membranes. The thermal and oxidative stability, morphology, mechanical properties, water uptake and proton conductivity of CS/SCNTs composite membranes were investigated. The insulated and hydrophilic silica layer coated on CNTs eliminates the risk of electronic short-circuiting and enhances the interaction between SCNTs and chitosan to ensure the homogenous dispersion of SCNTs, although the water uptake of CS/SCNTs membranes is reduced owing to the decrease of the effective number of the amino functional groups of chitosan. The CS/SCNTs composite membranes are superior to the pure CS membrane in thermal and oxidative stability, mechanical properties and proton conductivity. The results of this study suggest that CS/SCNTs composite membranes exhibit promising potential for practical application in proton exchange membranes. PMID:26572483

  11. Constant pH Replica Exchange Molecular Dynamics in Explicit Solvent Using Discrete Protonation States: Implementation, Testing, and Validation

    PubMed Central

    2015-01-01

    By utilizing Graphics Processing Units, we show that constant pH molecular dynamics simulations (CpHMD) run in Generalized Born (GB) implicit solvent for long time scales can yield poor pKa predictions as a result of sampling unrealistic conformations. To address this shortcoming, we present a method for performing constant pH molecular dynamics simulations (CpHMD) in explicit solvent using a discrete protonation state model. The method involves standard molecular dynamics (MD) being propagated in explicit solvent followed by protonation state changes being attempted in GB implicit solvent at fixed intervals. Replica exchange along the pH-dimension (pH-REMD) helps to obtain acceptable titration behavior with the proposed method. We analyzed the effects of various parameters and settings on the titration behavior of CpHMD and pH-REMD in explicit solvent, including the size of the simulation unit cell and the length of the relaxation dynamics following protonation state changes. We tested the method with the amino acid model compounds, a small pentapeptide with two titratable sites, and hen egg white lysozyme (HEWL). The proposed method yields superior predicted pKa values for HEWL over hundreds of nanoseconds of simulation relative to corresponding predicted values from simulations run in implicit solvent. PMID:24803862

  12. Organic-inorganic hybrid proton exchange membrane based on polyhedral oligomeric silsesquioxanes and sulfonated polyimides containing benzimidazole

    NASA Astrophysics Data System (ADS)

    Pan, Haiyan; Zhang, Yuanyuan; Pu, Hongting; Chang, Zhihong

    2014-10-01

    A new series of organic-inorganic hybrid proton exchange membranes (PEMs) were prepared using sulfonated polyimides containing benzimidazole (SPIBIs) and glycidyl ether of polyhedral oligomeric silsesquioxanes (G-POSS). SPIBIs were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 5-amino-2-(4-aminophenyl) benzimidazole (APBIA) and 4,4‧-diaminodiphenyl ether-2,2‧-disulfonic acid (ODADS). The organic-inorganic cross-linked membranes can be prepared by SPIBIs with G-POSS by a thermal treatment process. The cross-linking density of the membranes was evaluated by gel fractions. The water uptake, swelling ratio, mechanical property, thermal behavior, proton conductivity, oxidative and hydrolytic stability of the cross-linked organic-inorganic membranes were intensively investigated. All the cross-linked membranes exhibit high cross-linking density for the gel fraction higher than 70%. Compared to pristine membranes (SPIBIs) and membranes without benzimidazole groups (SPI), the anti-free-radical oxidative and hydrolytic stabilities of cross-linked membranes are significantly higher. The anti-free-oxidative stability of SPIBI-100-P (cross-linked SPIBI membrane with 100% degree of sulfonation) is nearly four-fold higher than that of SPIBI-100. The proton conductivity of the cross-linked membranes ranges from 10-3 S cm-1 to 10-2 S cm-1 depending both on the degree of sulfonation (DS) of the SPIBI and temperature.

  13. Potential heat exchange fluids for use in sulfuric acid vaporizers

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Petersen, G. R.

    1979-01-01

    A series of perhalocarbons are proposed as candidate heat exchange fluids for service in thermochemical cycles for hydrogen production that involve direct contact of the fluid with sulfuric acid and vaporization of the acid. The required chemical and physical criteria of the liquids are described and the results of some preliminary high temperature test data are presented.

  14. Electrolyte incorporation into composite electrodes for proton-exchange membrane fuel cells and lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Oh, Jung Min

    2011-12-01

    This dissertation describes research on the preparation and characterization of composite electrodes for use in proton-exchange membrane (PEM) fuel cells and lithium ion batteries. The general focus of the research was on high-surface-area carbon supports for platinum catalysts in fuel cells, and integration of electrolytes, particularly fluoropolymer electrolytes, into composite electrodes both batteries and fuel cells. Results are described for work in the following three specific topical areas. (1) Carbon nanofibers for use as platinum (Pt) catalyst supports in fuel cells were prepared by carbonization of electrospun acrylic fibers. The resulting carbon nanofibers were found to contain mainly micropores. Following grinding to a powder form, the carbon nanofibers were used as supports for Pt nanoparticles. The pulverized carbon nanofibers were found to be not suitable as supports for Pt catalysts because the microporosity of the individual carbon nanofibers cannot provide continuous porous channels in the electrode. As a result, the Pt utilization was found to be low. (2) Mesoporous carbon composites containing nanoscale embedded zirconia particles (ZCS) were prepared and found to be highly porous and electrically conductive. Surface modification of the composites with organic compounds having phenylphosphonic acid groups (e.g., phenylphosphonic acid, m-sulfophenylphosphonic acid, or sulfonated fluoropolymer ionomer having terminal phosphonic acid groups) was accomplished by simple exposure of the carbon composite to organophosphonate solutions. Nanoscale ZrO2 surfaces present in the composite skeleton acted as reactive sites for anchoring of phosphonates through formation of robust Zr--O--P bonding. Proton-exchange sites were introduced onto the nanocomposite surface by grafting m-sulfophenylphosphonic acid or a sulfonated fluoropolymer ionomer. Modification with the ionomer provided an increase in proton-exchange capacity relative to that found following

  15. Nafion-Initiated ATRP of 1-Vinylimidazole for Preparation of Proton Exchange Membranes.

    PubMed

    Feng, Kai; Liu, Lei; Tang, Beibei; Li, Nanwen; Wu, Peiyi

    2016-05-11

    Nafion is one of the most widely investigated materials applied in proton exchange membranes. Interestingly, it was found that Nafion could serve as a macroinitiator to induce atom transfer radical polymerization (ATRP) on its C-F sites. In this study, poly(1-vinylimidazole) was selectively bonded on the side chains of Nafion via the Nafion-initiated ATRP process, which was confirmed by the measurements of (1)H/(19)F nuclear magnetic resonance spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and matrix-assisted laser desorption ionization-time-of-flight/time-of-flight mass spectrometry. The as-prepared Nafion-co-poly(1-vinylimidazole) (Nafion-PVIm) membranes, with tunable loading amount of imidazole rings, presented greatly enhanced proton conductivity and methanol resistivity due to their well-controlled chemical structures. Especially, chemically bonding PVIm with Nafion chains endowed the Nafion-PVIm membranes with high stability in proton conductivity. For the first time, we revealed the great potentials of the Nafion-initiated ATRP process in developing high-performance proton exchange membranes. PMID:27077232

  16. Wavelength-tunable polarization converter utilizing the strain induced by proton exchange in lithium niobate

    NASA Astrophysics Data System (ADS)

    Wang, T.-J.; Chung, J.-S.

    2005-02-01

    A new wavelength-tunable polarization converter utilizing the strain induced by proton exchange is demonstrated in x-cut LiNbO3. The light polarization is converted by the strain-optic effect through the phase-matched coupling of two orthogonal polarizations. The stress-applying structure is designed to be composed of several proton-exchanged strip regions for maximization of the stress distribution. The principle of birefringent chain filters is utilized to design the device structure in order to avoid the requirement of large stress, which results in serious cracks on the substrate surface. The overlap integral between the optical field distribution and the stress distribution can be enhanced simply by prolonging the proton-exchange time. Besides, the stress distribution and its strength in the stress-applying structure can be fine tuned without affecting the waveguide characteristics such that the principle of the birefringent chain filters is completely satisfied. Therefore, the polarization-conversion efficiency can be optimized when utilizing this exclusive stress-tuning ability. By the thermal-optic effect, the wavelength of maximum conversion can be tuned at a rate of -0.115 nm/°C with a maximum conversion efficiency of 92.41%. The proposed polarization converter has the advantages of adequate stress distribution and strength, high parameter-tuning feasibility, low propagation loss, easy fabrication, and low fabrication cost.

  17. Theoretical and computational studies of renewable energy materials: Room temperature ionic liquids and proton exchange membranes

    NASA Astrophysics Data System (ADS)

    Feng, Shulu

    2011-12-01

    Two kinds of renewable energy materials, room temperature ionic liquids (RTILs) and proton exchange membranes (PEMs), especially Nafion, are studied by computational and theoretical approaches. The ultimate purpose of the present research is to design novel materials to meet the future energy demands. To elucidate the effect of alkyl side chain length and anion on the structure and dynamics of the mixtures, molecular dynamics (MD) simulations of three RTILs/water mixtures at various water mole fractions: 1-butyl-3-methylimidazolium (BMIM+)/BF4-, 1-octyl-3-methylimidazolium (OMIM+)/BF4-, and OMIM +/Cl- are performed. Replacing the BMIM + cation with OMIM+ results in stronger aggregation of the cations as well as a slower diffusion of the anions, and replacing the BF4- anion with Cl- alters the water distribution at low water mole fractions and slows diffusion of the mixtures. Potential experimental manifestations of these behaviors in both cases are provided. Proton solvation properties and transport mechanisms are studied in hydrated Nafion, by using the self-consistent multistate empirical valence bond (SCI-MS-EVB) method. It is found that by stabilizing a more Zundel-like (H5O 2+) structure in the first solvation shells, the solvation of excess protons, as well as the proton hydration structure are both influenced by the sulfonate groups. Hydrate proton-related hydrogen bond networks are observed to be more stable than those with water alone. In order to characterize the nature of the proton transport (PT), diffusive motion, Arrhenius activation energies, and transport pathways are calculated and analyzed. Analysis of diffusive motion suggests that (1) a proton-hopping mechanism dominates the proton transport for the studied water loading levels and (2) there is an obvious degree of anti-correlation between the proton hopping and the vehicular transport. The activation energy drops rapidly with an increasing water content when the water loading level is smaller

  18. Evaluation of the annealing effect of proton-exchanged LiTaO3 optical waveguides by the line-focus-beam ultrasonic material characterization system

    NASA Astrophysics Data System (ADS)

    Miyashita, Masahito; Kushibiki, Jun-ichi

    2002-09-01

    We established an experimental procedure and collected basic data to evaluate the annealing process and effects for proton-exchanged LiTaO3 optical waveguides using the line-focus-beam ultrasonic material characterization (LFB-UMC) system in a frequency range of 100 to 300 MHz. Twelve Z-cut LiTaO3 substrates were proton-exchanged at 260 degC for 14 min in a pyrophosphoric acid solution and annealed at 420 degC for various periods from 10 sec to 24 h. The leaky surface acoustic wave (LSAW) velocities were decreased by the proton exchange, and were then increased and recovered by annealing in all propagation directions as the annealing time increased. The Y-axis propagation is most useful for an evaluation. The LSAW velocities decrease with an increase of the product fH, obtained from the frequency dependences and proton-diffused layer depths analyzed by secondary-ion mass spectrometry. Gradients of the fH dependences of the LSAW velocities become gentler with increases in the annealing time, corresponding to the concentrations and distributions of hydrogen and lithium ions in the proton-diffused layers. The relationships among the LSAW velocities, proton-diffused layer depths, relative concentrations of hydrogen ions at the specimen surfaces, and the annealing times were experimentally obtained. The measurement resolutions of the LFB-UMC system at 225 MHz to the proton-diffused layer depth, the relative concentration of hydrogen ions, and the typical annealing time for 1 min were estimated to be 4 nm, 0.2%, and 0.6 sec.

  19. Quantitative evaluation of fabrication processes of proton-exchanged layers in LiTaO3 optoelectronic devices by the line-focus-beam ultrasonic material characterization system

    NASA Astrophysics Data System (ADS)

    Kushibiki, J.; Miyashita, M.

    2001-02-01

    Experimental investigations are conducted in order to collect basic data for evaluating proton-exchanged LiTaO3 optical waveguides and their fabrication processes and systems using the line-focus-beam ultrasonic material characterization system, in the frequency range 100-300 MHz. Seven Z-cut LiTaO3 substrates are proton exchanged at several process temperatures (220-280 °C) and times (5-30 min) in a pyrophosphoric acid solution. Leaky surface acoustic wave (LSAW) velocities, measured for all specimens, decrease for all propagation directions. The decrease rate is at maximum in the Y-axis propagation direction, in which the measurement sensitivity to the process conditions is highest. The fH dependences of LSAW velocities, obtained from frequency dependences of LSAW velocities and proton-exchanged layer depths analyzed by secondary-ion mass spectrometry, have almost constant gradients of -0.78 (m/s)/(Hz m). Normalized depth distributions of the elastic properties of proton-exchanged layers are nearly equal; only the depths differ. Also, the relationships among LSAW velocities, layer depths, process times, process temperatures, and diffusion coefficients are experimentally obtained. Homogeneity evaluation of a proton-exchanged, 2-in., Z-cut LiTaO3 wafer processed at 260 °C for 14 min is demonstrated, resulting in a maximum LSAW velocity variation of 1.3 m/s. This corresponds to a depth variation of 7.4 nm and a temperature variation of 0.8 °C for the whole surface.

  20. Measuring the 2-gamma Exchange Effect in Electron-Proton Scattering at CLAS

    SciTech Connect

    Bennett, Robert

    2011-10-01

    Recent results from experiments at Jefferson Laboratory, Newport News VA, which measure the ratio of the electric to magnetic form factors of the proton, G{sub E}/G{sub M}, have forced us to reexamine the single photon exchange approximation in lepton-proton elastic scattering. Discrepancies between the ratio obtained via the time-tested Rosenbluth separation method and new polarization transfer measurements, which differ by as much as a factor of three, may be resolved by considering the effect of two photon exchange (TPE). Theoretical corrections for the TPE effect are difficult due to the large number of excited nucleon states that can contribute to the process. The TPE effect can, however, be determined directly by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = {sigma}(e{sup +})/{sigma}(e{sup -}), since the TPE effect changes sign with the charge of the incident particle. The CLAS TPE experiment at Jefferson Laboratory, will determine the effect of two-photon exchange in elastic lepton-proton scattering by precisely measuring the ratio of positron-proton to electron-proton elastic cross sections over a large kinematic range (0.1 < {var_epsilon} < 0.96, 0.02 {le} Q{sup 2} {le} 2.0). We will accomplish this by directing the 5.5 GeV primary electron beam, provided by the Continuous Electron Beam Accelerator Facility (CEBAF), onto a set of radiators and converters to produce simultaneous and identical beams of electron and positrons. Acceptance and efficiency concerns are minimized by only considering the ratios of the elastic cross sections and switching polarity of magnets in the beam line and the spectrometer. Guided by the results of a short 2006 test run and extensive GEANT based modeling, new shielding and beam line components were designed to maximize luminosity. The unique experimental design and challenges of the TPE experiment and the projected luminosities will be presented.

  1. Second-order optical non-linearity of proton exchanged lithium tantalate waveguides

    NASA Astrophysics Data System (ADS)

    Korkishko, Y. N.; Fedorov, V. A.; Alkaev, A. N.; Laurell, F.

    2001-10-01

    A detailed correlation between the fabrication conditions, crystallographic phase state of HxLi1-xTaO3 waveguides and second-order optical non-linearity has been investigated by using reflected SHG measurements from the polished waveguide end face. The non-linearity, strongly reduced after the initial proton exchange, is found to be restored and even increased after annealing. However, this apparent increase in the non-linearity is accompanied by a strong degradation of the quality of the SHG reflected beam in the region of the initial as-exchanged waveguide due to beam scattering. The high temperature proton exchange technique has been shown to produce high-quality α-phase waveguides with essentially undegraded non-linear optical properties. There is no phase transition when the α-phase waveguides are fabricated by direct exchange. This phase presents the same crystalline structure as that of LiTaO3 and maintains the excellent non-linear properties of the bulk material. The results obtained are important for the design, fabrication and optimization of guided-wave non-linear optical devices in LiTaO3.

  2. H2O and D2 mixtures under pressure: Spectroscopy and proton exchange kinetics

    NASA Astrophysics Data System (ADS)

    Borstad, Gustav M.; Yoo, Choong-Shik

    2011-11-01

    We have investigated the pressure-induced spectral changes and the proton exchange reactions of D2-H2O mixtures to 64 GPa using micro-Raman spectroscopy. The results show the profound difference in the rotational and vibrational Raman spectra of hydrogen isotopes from those of the pure samples, showing the vibrational modes at higher frequencies and continuing to increase with pressure without apparent turnover. This indicates the repulsive nature of D2-H2O interaction without hydrogen bonds between the two and, thus, interstitial fillings of D2 molecules into the bcc-like ice lattice. The spectral analysis using the Morse potential yields a hydrogen bond distance of 0.734 Å at 6 GPa—slightly shorter than that in pure—attributed to the repulsive interaction. The pressure-dependent spectral changes suggest that the proton-ordering transition in the ice lattice occurs over a large pressure range between 28 and 50 GPa, which is substantially lower than that of pure ice (40-80 GPa). This again indicates the presence of high internal pressure arising from the repulsive interaction. The Raman spectra show evidences that the proton exchange occurs in various phases including in solid D2 and H2O mixtures. Based on the time-dependent spectral changes, we obtained the proton exchange rates of k ˜ 0.085 h-1 at 0.2 GPa in fluid D2 and water mixtures, k ˜ 0.03 h-1 and 0.003 h-1 at 2 GPa and 4 GPa, respectively, in fluid D2-ice mixtures, and k ˜ 10-3 h-1 at 8 GPa in solid D2 and ice mixtures.

  3. pH-replica exchange molecular dynamics in proteins using a discrete protonation method.

    PubMed

    Sabri Dashti, Danial; Meng, Yilin; Roitberg, Adrian E

    2012-08-01

    Protonation equilibria in biological molecules modulates structure, dynamics, and function. A pH-replica exchange molecular dynamics (pH-REMD) method is described here to improve the coupling between conformational and protonation sampling. Under a Hamiltonian replica exchange setup, conformations are swapped between two neighboring replicas, which themselves are at different pHs. The method has been validated on a series of biological systems. We applied pH-REMD to a series of model compounds, to an terminally charged ADFDA pentapeptide, and to a heptapeptide derived from the ovomucoid third domain (OMTKY3). In all of those systems, the predicted pK(a) by pH-REMD is very close to the experimental value and almost identical to the ones obtained by constant pH molecular dynamics (CpH MD). The method presented here, pH-REMD, has the advantage of faster convergence properties due to enhanced sampling of both conformation and protonation spaces. PMID:22694266

  4. Highly efficient sulfonated polybenzimidazole as a proton exchange membrane for microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Singha, Shuvra; Jana, Tushar; Modestra, J. Annie; Naresh Kumar, A.; Mohan, S. Venkata

    2016-06-01

    Although microbial fuel cells (MFCs) represent a promising bio-energy technology with a dual advantage (i.e., electricity production and waste-water treatment), their low power densities and high installation costs are major impediments. To address these bottlenecks and replace highly expensive Nafion, which is a proton exchange membrane (PEM), the current study focuses for the first time on membranes made from an easily synthesizable and more economical oxy-polybenzimidazole (OPBI) and its sulfonated analogue (S-OPBI) as alternate PEMs in single-chambered MFCs. The S-OPBI membrane exhibits better properties, with high water uptake, ion exchange capacity (IEC) and proton conductivity and a comparatively smaller degree of swelling compared to Nafion. The membrane morphology is characterized by atomic force microscopy, and the bright and dark regions of the S-OPBI membrane reveals the formation of ionic domains in the matrix, forming continuous water nanochannels when doped with water. These water-filled nanochannels are responsible for faster proton conduction in S-OPBI than in Nafion; therefore, the power output in the MFC with S-OPBI as the PEM is higher than in other MFCs. The open circuit voltage (460 mV), current generation (2.27 mA) and power density profile (110 mW/m2) as a function of time, as well as the polarization curves, exhibits higher current and power density (87.8 mW/m2) with S-OPBI compared to Nafion as the PEM.

  5. Microelectrode investigation of oxygen permeation in perfluorinated proton exchange membranes with different equivalent weights

    SciTech Connect

    Buechi, F.N.; Wakizoe, Masanobu; Srinivasan, S.

    1996-03-01

    Oxygen concentrations (C{sub b}) and diffusion coefficients (D) in various proton exchange membranes were measured using chronoamperometry at microelectrodes. These measurements were made under conditions similar to those prevailing in proton-exchange-membrane fuel cells. Knowledge of the D and C{sub b} parameters is essential for the determination of oxygen permeation in the catalytic layers of gas diffusion electrodes, which could be rate limiting in these low-temperature fuel cells. Furthermore, the D and C{sub b} values also provide the permeation rates of oxygen through the bulk of the proton conducting membrane. it was found that the concentration of oxygen increased and the diffusion coefficient decreased with increasing equivalent weight of the membranes. These results were interpreted using a model based on the microstructure of the swollen membranes separated into two phases, one hydrophobic and the other hydrophilic, with distinctly different O{sub 2}-permeation properties. According to this model the relative amounts of the two phases in the membranes, caused by the different water contents, determine the O{sub 2} solubility and diffusion coefficient in the different membrane materials.

  6. Amide proton exchange rates of oxidized and reduced Saccharomyces cerevisiae iso-1-cytochrome c.

    PubMed Central

    Marmorino, J. L.; Auld, D. S.; Betz, S. F.; Doyle, D. F.; Young, G. B.; Pielak, G. J.

    1993-01-01

    Proton NMR spectroscopy was used to determine the rate constant, kobs, for exchange of labile protons in both oxidized (Fe(III)) and reduced (Fe(II)) iso-1-cytochrome c. We find that slowly exchanging backbone amide protons tend to lack solvent-accessible surface area, possess backbone hydrogen bonds, and are present in regions of regular secondary structure as well as in omega-loops. Furthermore, there is no correlation between kobs and the distance from a backbone amide nitrogen to the nearest solvent-accessible atom. These observations are consistent with the local unfolding model. Comparisons of the free energy change for denaturation, delta Gd, at 298 K to the free energy change for local unfolding, delta Gop, at 298 K for the oxidized protein suggest that certain conformations possessing higher free energy than the denatured state are detected at equilibrium. Reduction of the protein results in a general increase in delta Gop. Comparisons of delta Gd to delta Gop for the reduced protein show that the most open states of the reduced protein possess more structure than its chemically denatured form. This persistent structure in high-energy conformations of the reduced form appears to involve the axially coordinated heme. PMID:8268806

  7. Conductivity and water uptake of aromatic-based proton exchange membrane electrolytes

    SciTech Connect

    Kopitzke, R.W.; Linkous, C.A.; Anderson, H.R.; Nelson, G.L.

    2000-05-01

    Water uptake and proton conductivity as a function of temperature were determined for three aromatic-based, sulfonic acid-bearing polymers, plus the perfluoroalkyl sulfonic acid Nafion{reg_sign} 117. Water uptake of submerged, equilibrated samples ranged from less than five water molecules per acid group for a high equivalent weight, sulfonated polyethersulfone to almost fifty waters per acid for a low equivalent weight, sulfonated polyetheretherketone. The most conductive aromatic-based polymer, sulfonated polyphenylquinoxaline (S-PPQ), had a room temperature conductivity of 9.8 x 10{sup {minus}3} S/cm, about an order of magnitude less than that of a perfluoroalkyl sulfonic acid under identical conditions. The slope of the S-PPQ Arrhenius conductivity plot was sufficiently steep that at 180 C, the proton conductivity, 1.3 x 10{sup {minus}1} S/cm, was only a factor of two lower than that of Nafion under similar conditions. The lower conductivity of the aromatic-based sulfonic acid polymers can be attributed to chain rigidity, lack of ion channels, and lower acidity.

  8. Improving the proton conductivity and water uptake of polybenzimidazole-based proton exchange nanocomposite membranes with TiO2 and SiO2 nanoparticles chemically modified surfaces

    NASA Astrophysics Data System (ADS)

    Namazi, Hassan; Ahmadi, Hossein

    2011-03-01

    Poly [2,2‧-(m-pyrazolidene)-5,5‧-bibenzimidazole] (PPBI) was synthesized from pyrazole-3,5-dicarboxylic acid and 3,3‧,4,4‧-tetraaminobiphenyle (TAB) through polycondensation reaction in polyphosphoric acid (PPA) as reaction solvent. And polymer-grafted SiO2 and TiO2 nanoparticles were prepared through radical polymerization of 1-vinylimidazole and sulfonated vinylbenzene on the surface-vinylated nanoparticles. The polymer-grafted SiO2 and TiO2 nanoparticles were utilized as a functional additive to prepare PPBI/polymer-grafted SiO2 and TiO2 nanocomposite membranes. Imidazole and sulfonated vinylbenzene groups on the surface of modified nanoparticles forming linkages with PPBI chains, improved the compatibility between PPBI and nanoparticles, and enhanced the mechanical strength of the prepared nanocomposite membranes. The prepared nanocomposite membranes showed higher water uptake and acid doping levels comparing to PPBI. Also, after acid doping with phosphoric acid, nanocomposite membranes exhibited enhanced proton conductivity in comparison to the pristine PPBI and PPBI/un-modified SiO2 and TiO2 nanocomposite membranes. The enhancement in proton conductivity of nanocomposite membranes resulted from modified SiO2 nanoparticles showed higher conductivity than modified TiO2 nanoparticles. The above results indicated that the PPBI/modified SiO2 and TiO2 nanocomposite membranes could be utilized as proton exchange membranes for medium temperature fuel cells.

  9. Receptor for protons: First observations on Acid Sensing Ion Channels.

    PubMed

    Krishtal, Oleg

    2015-07-01

    The history of ASICs began in 1980 with unexpected observation. The concept of highly selective Na(+) current gated by specific receptors for protons was not easily accepted. It took 16 years to get these receptor/channels cloned and start a new stage in their investigation. "The receptor for protons" became ASIC comprising under this name a family of receptor/channels ubiquitous for mammalian nervous system, both peripheral and central. The role of ASICs as putative nociceptors was suggested almost immediately after their discovery. This role subsequently was proven in many forms of pain-related phenomena. Many other functions of ASICs have been also found or primed for speculations both in physiology and in disease. Despite the width of field and strength of efforts, numerous basic questions are to be answered before we understand how the local changes in pH in the nervous tissue transform into electric and messenger signaling via ASICs as transducers. This article is part of the Special Issue entitled 'Acid-Sensing Ion Channels in the Nervous System'. PMID:25582296

  10. Correlating Humidity-Dependent Ionically Conductive Surface Area with Transport Phenomena in Proton-Exchange Membranes

    SciTech Connect

    He, Qinggang; Kusoglu, Ahmet; Lucas, Ivan T.; Clark, Kyle; Weber, Adam Z.; Kostecki, Robert

    2011-08-01

    The objective of this effort was to correlate the local surface ionic conductance of a Nafion? 212 proton-exchange membrane with its bulk and interfacial transport properties as a function of water content. Both macroscopic and microscopic proton conductivities were investigated at different relative humidity levels, using electrochemical impedance spectroscopy and current-sensing atomic force microscopy (CSAFM). We were able to identify small ion-conducting domains that grew with humidity at the surface of the membrane. Numerical analysis of the surface ionic conductance images recorded at various relative humidity levels helped determine the fractional area of ion-conducting active sites. A simple square-root relationship between the fractional conducting area and observed interfacial mass-transport resistance was established. Furthermore, the relationship between the bulk ionic conductivity and surface ionic conductance pattern of the Nafion? membrane was examined.

  11. The first proton sponge-based amino acids: synthesis, acid-base properties and some reactivity.

    PubMed

    Ozeryanskii, Valery A; Gorbacheva, Anastasia Yu; Pozharskii, Alexander F; Vlasenko, Marina P; Tereznikov, Alexander Yu; Chernov'yants, Margarita S

    2015-08-21

    The first hybrid base constructed from 1,8-bis(dimethylamino)naphthalene (proton sponge or DMAN) and glycine, N-methyl-N-(8-dimethylamino-1-naphthyl)aminoacetic acid, was synthesised in high yield and its hydrobromide was structurally characterised and used to determine the acid-base properties via potentiometric titration. It was found that the basic strength of the DMAN-glycine base (pKa = 11.57, H2O) is on the level of amidine amino acids like arginine and creatine and its structure, zwitterionic vs. neutral, based on the spectroscopic (IR, NMR, mass) and theoretical (DFT) approaches has a strong preference to the zwitterionic form. Unlike glycine, the DMAN-glycine zwitterion is N-chiral and is hydrolytically cleaved with the loss of glycolic acid on heating in DMSO. This reaction together with the mild decarboxylative conversion of proton sponge-based amino acids into 2,3-dihydroperimidinium salts under air-oxygen was monitored with the help of the DMAN-alanine amino acid. The newly devised amino acids are unique as they combine fluorescence, strongly basic and redox-active properties. PMID:26159785

  12. Quantitative chemical exchange saturation transfer (qCEST) MRI--RF spillover effect-corrected omega plot for simultaneous determination of labile proton fraction ratio and exchange rate.

    PubMed

    Sun, Phillip Zhe; Wang, Yu; Dai, ZhuoZhi; Xiao, Gang; Wu, Renhua

    2014-01-01

    Chemical exchange saturation transfer (CEST) MRI is sensitive to dilute proteins and peptides as well as microenvironmental properties. However, the complexity of the CEST MRI effect, which varies with the labile proton content, exchange rate and experimental conditions, underscores the need for developing quantitative CEST (qCEST) analysis. Towards this goal, it has been shown that omega plot is capable of quantifying paramagnetic CEST MRI. However, the use of the omega plot is somewhat limited for diamagnetic CEST (DIACEST) MRI because it is more susceptible to direct radio frequency (RF) saturation (spillover) owing to the relatively small chemical shift. Recently, it has been found that, for dilute DIACEST agents that undergo slow to intermediate chemical exchange, the spillover effect varies little with the labile proton ratio and exchange rate. Therefore, we postulated that the omega plot analysis can be improved if RF spillover effect could be estimated and taken into account. Specifically, simulation showed that both labile proton ratio and exchange rate derived using the spillover effect-corrected omega plot were in good agreement with simulated values. In addition, the modified omega plot was confirmed experimentally, and we showed that the derived labile proton ratio increased linearly with creatine concentration (p < 0.01), with little difference in their exchange rate (p = 0.32). In summary, our study extends the conventional omega plot for quantitative analysis of DIACEST MRI. PMID:24706610

  13. Activation of acid-sensing ion channels by localized proton transient reveals their role in proton signaling

    PubMed Central

    Zeng, Wei-Zheng; Liu, Di-Shi; Liu, Lu; She, Liang; Wu, Long-Jun; Xu, Tian-Le

    2015-01-01

    Extracellular transients of pH alterations likely mediate signal transduction in the nervous system. Neuronal acid-sensing ion channels (ASICs) act as sensors for extracellular protons, but the mechanism underlying ASIC activation remains largely unknown. Here, we show that, following activation of a light-activated proton pump, Archaerhodopsin-3 (Arch), proton transients induced ASIC currents in both neurons and HEK293T cells co-expressing ASIC1a channels. Using chimera proteins that bridge Arch and ASIC1a by a glycine/serine linker, we found that successful coupling occurred within 15 nm distance. Furthermore, two-cell sniffer patch recording revealed that regulated release of protons through either Arch or voltage-gated proton channel Hv1 activated neighbouring cells expressing ASIC1a channels. Finally, computational modelling predicted the peak proton concentration at the intercellular interface to be at pH 6.7, which is acidic enough to activate ASICs in vivo. Our results highlight the pathophysiological role of proton signalling in the nervous system. PMID:26370138

  14. Amide Proton Solvent Protection in Amylin Fibrils Probed by Quenched Hydrogen Exchange NMR

    PubMed Central

    Alexandrescu, Andrei T.

    2013-01-01

    Amylin is an endocrine hormone that accumulates in amyloid plaques in patients with advanced type 2 diabetes. The amyloid plaques have been implicated in the destruction of pancreatic β-cells, which synthesize amylin and insulin. To better characterize the secondary structure of amylin in amyloid fibrils we assigned the NMR spectrum of the unfolded state in 95% DMSO and used a quenched hydrogen-deuterium exchange technique to look at amide proton solvent protection in the fibrils. In this technique, partially exchanged fibrils are dissolved in 95% DMSO and information about amide proton occupancy in the fibrils is determined from DMSO-denatured monomers. Hydrogen exchange lifetimes at pH 7.6 and 37°C vary between ∼5 h for the unstructured N-terminus to 600 h for amide protons in the two β-strands that form inter-molecular hydrogen bonds between amylin monomers along the length of the fibril. Based on the protection data we conclude that residues A8-H18 and I26-Y37 comprise the two β-strands in amylin fibrils. There is variation in protection within the β-strands, particularly for strand β1 where only residues F15-H18 are strongly protected. Differences in protection appear to be due to restrictions on backbone dynamics imposed by the packing of two-layers of C2-symmetry-related β-hairpins in the protofilament structure, with strand β1 positioned on the surface and β2 in the interior. PMID:23457571

  15. Potential heat exchange fluids for use in sulfuric acid vaporizers

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Petersen, G. R.

    1981-01-01

    A series of liquids have been screened as candidate heat exchange fluids for service in thermochemical cycles that involve the vaporization of sulfuric acid. The required chemical and physical criteria of the liquids is described with the results of some preliminary high temperature test data presented.

  16. Heat-Exchange Fluids for Sulfuric Acid Vaporizers

    NASA Technical Reports Server (NTRS)

    Lawson, D. D.; Petersen, G. R.

    1982-01-01

    Some fluorine-substituted organic materials meet criteria for heat-exchange fluids in contact with sulfuric acid. Most promising of these are perfluoropropylene oxide polymers with degree of polymerization (DP) between 10 and 50. It is desirable to have DP in high range because vapor pressure of material decreases as DP increases, and high-DP liquids have lower loss due to vaporization.

  17. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Technical Reports Server (NTRS)

    Eisman, G. A.

    1989-01-01

    Dow Chemical's research activities in fuel cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the effects of equivalent weight, thickness, water of hydration, pretreatment procedures, as well as the degree of water management required for a given membrane separator in the cell. The presentation will include details of certain aspects of the above as well as some of the requirements for high and low power generation.

  18. Mathematical Modeling of Cation Contamination in a Proton-exchange Membrane

    SciTech Connect

    Weber, Adam; Delacourt, Charles

    2008-09-11

    Transport phenomena in an ion-exchange membrane containing both H+ and K+ are described using multicomponent diffusion equations (Stefan-Maxwell). A model is developed for transport through a Nafion 112 membrane in a hydrogen-pump setup. The model results are analyzed to quantify the impact of cation contamination on cell potential. It is shown that limiting current densities can result due to a decrease in proton concentration caused by the build-up of contaminant ions. An average cation concentration of 30 to 40 percent is required for appreciable effects to be noticed under typical steady-state operating conditions.

  19. Improved Electrodes for High Temperature Proton Exchange Membrane Fuel Cells using Carbon Nanospheres.

    PubMed

    Zamora, Héctor; Plaza, Jorge; Cañizares, Pablo; Lobato, Justo; Rodrigo, Manuel A

    2016-05-23

    This work evaluates the use of carbon nanospheres (CNS) in microporous layers (MPL) of high temperature proton exchange membrane fuel cell (HT-PEMFC) electrodes and compares the characteristics and performance with those obtained using conventional MPL based on carbon black. XRD, hydrophobicity, Brunauer-Emmett-Teller theory, and gas permeability of MPL prepared with CNS were the parameters evaluated. In addition, a short life test in a fuel cell was carried out to evaluate performance under accelerated stress conditions. The results demonstrate that CNS is a promising alternative to traditional carbonaceous materials because of its high electrochemical stability and good electrical conductivity, suitable to be used in this technology. PMID:27076055

  20. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Eisman, G. A.

    1989-12-01

    Dow Chemical's research activities in fuel cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the effects of equivalent weight, thickness, water of hydration, pretreatment procedures, as well as the degree of water management required for a given membrane separator in the cell. The presentation will include details of certain aspects of the above as well as some of the requirements for high and low power generation.

  1. Uptake of metal ions by a new chelating ion exchange resin. Part 3: Protonation constants via potentiometric titration and solid state [sup 31]P NMR spectroscopy

    SciTech Connect

    Nash, K.L.; Rickert, P.G.; Muntean, J.V.; Alexandratos, S.D.

    1994-01-01

    A new chelating ion exchange resin which incorporates methylenediphosphonate, carboxylate, and sulfonate functional groups in a polystyrene-divinylbenzene matrix has been prepared. This resin exhibits exceptionally high affinity for polyvalent cations even from moderately acidic aqueous media. Metal ion coordination occurs primarily at the diphosphonate group with the secondary binding sites contributing to charge neutralization when necessary and possible, and to increasing hydrophilicity of the resin pores. In the present investigation, the protonation equilibria of the phosphonate groups in the resin are investigated via potentiometric titration and solid-state [sup 31]P NMR spectroscopy of the resin. Intrinsic equilibrium constants for the first two diphosphonate protonation reactions are pK[sub 4] = 10.47 and pK[sub 3] = 7.24. The last two protons added to the diphosphonate group are acidic having pK[sub a] values less than 2.5. These protonation constants are consistent with those reported previously for monomer analog 1,1-diphosphonic acids. This result implies that thermodynamic data available in the literature can be used to predict the relative affinity of the resin for polyvalent cations. 17 refs., 2 figs., 3 tabs.

  2. Presolvated Electron Reaction with Methylacetoacetate: Electron Localization, Proton-Deuteron Exchange, and H-atom Abstraction

    PubMed Central

    Petrovici, Alex; Adhikary, Amitava; Kumar, Anil; Sevilla, Michael D.

    2015-01-01

    Radiation-produced electrons initiate various reaction processes that are important to radiation damage to biomolecules. In this work, the site of attachment of the prehydrated electrons with methylacetoacetate (MAA, CH3-CO-CH2-CO-OCH3) at 77 K and subsequent reactions of the anion radical (CH3-CO•−-CH2-CO-OCH3) in the temperature range (77 to ca. 170 K) have been investigated in homogeneous H2O and D2O aqueous glasses by electron spin resonance (ESR) spectroscopy. At 77 K, the prehydrated electron attaches to MAA forming the anion radical in which the electron is delocalized over the two carbonyl groups. This species readily protonates to produce the protonated electron adduct radical CH3-C(•)OH-CH2-CO-OCH3. The ESR spectrum of CH3-C(•)OH-CH2-CO-OCH3 in H2O shows line components due to proton hyperfine couplings of the methyl and methylene groups. Whereas, the ESR spectrum of CH3-C(•)OH-CH2-CO-OCH3 in D2O glass shows only the line components due to proton hyperfine couplings of CH3 group. This is expected since the methylen protons in MAA are readily exchangeable in D2O. On stepwise annealing to higher temperatures (ca. 150 to 170 K), CH3-C(•)OH-CH2-CO-OCH3 undergoes bimolecular H-atom abstraction from MAA to form the more stable radical, CH3-CO-CH•-CO-OCH3. Theoretical calculations using density functional theory (DFT) support the radical assignments. PMID:25255751

  3. RADIATION STABILITY OF NAFION MEMBRANES USED FOR ISOTOPE SEPARATION BY PROTON EXCHANGE MEMBRANE ELECTROLYSIS

    SciTech Connect

    Fox, E

    2009-05-15

    Proton Exchange Membrane Electrolyzers have potential interest for use for hydrogen isotope separation from water. In order for PEME to be fully utilized, more information is needed on the stability of Nafion when exposed to radiation. This work examines Nafion 117 under varying exposure conditions, including dose rate, total dosage and atmospheric condition. Analytical tools, such as FT-IR, ion exchange capacity, DMA and TIC-TOC were used to characterize the exposed membranes. Analysis of the water from saturated membranes can provide important data on the stability of the membranes during radiation exposure. It was found that the dose rate of exposure plays an important role in membrane degradation. Potential mechanisms for membrane degradation include peroxide formation by free radicals.

  4. Development of sulfonated FEP Nafion hybrid proton exchange membranes for PEFC

    NASA Astrophysics Data System (ADS)

    Sato, Y.; Fujii, K.; Mitani, N.; Matsuura, A.; Kakigi, T.; Muto, F.; Li, J.; Oshima, A.; Washio, M.

    2007-12-01

    The performance of polymer electrolyte fuel cell (PEFC) is affected by an interfacial property between a proton exchange membrane (PEM) and electrodes. Thus, to develop a well-laminated membrane electrode assembly (MEA), a hybrid PEM (FN) was fabricated by mixing a radiation grafted membrane (sulfonated FEP) with ionomer (Nafion ® dispersion) which is applied to coat the interface of the PEM and electrodes. The obtained FN, sulfonated FEP and Nafion ®112 were characterized in terms of water uptake, ion exchange capacity (IEC), polarization performance and electrochemical impedance. FN showed high IEC and water uptake, which would induce the highest ionic conductivity (IC) among tested PEMs. In terms of FN, the interface between the PEM and electrodes should have been improved because FN showed the lowest charge transfer resistance than other tested PEMs. The high IC and improved interface between the PEM and electrodes resulted in the best cell performance of FN in tested PEMs.

  5. Polymeric nanocomposite proton exchange membranes prepared by radiation-induced polymerization for direct methanol fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Young-Seok; Seo, Kwang-Seok; Choi, Seong-Ho

    2016-01-01

    The vinyl group-modified montmorillonite clay (F-MMT), vinyl group-modified graphene oxide (F-GO), and vinyl group-modified multi-walled carbon nanotube (F-MWNT) were first prepared by ion exchange reaction of 1-[(4-ethylphenyl)methyl]-3-butyl-imidazolium chloride in order to use the materials for protection against methanol cross-over in direct methanol fuel cell (DMFC) membrane. Then polymeric nanocomposite membranes with F-MMT, F-GO, and F-MWNT were prepared by the solvent casting method after radiation-induced polymerization of vinyl monomers in water-methanol mixture solvents. The proton conductivity, water uptake, ion-exchange capacity, methanol permeability, and DMFC performance of the polymeric nanocomposite membranes with F-MMT, F-GO, and F-MWNT were evaluated.

  6. Proton-binding study of standard and reference fulvic acids, humic acids, and natural organic matter

    NASA Astrophysics Data System (ADS)

    Ritchie, Jason D.; Perdue, E. Michael

    2003-01-01

    The acid-base properties of 14 standard and reference materials from the International Humic Substances Society (IHSS) were investigated by potentiometric titration. Titrations were conducted in 0.1 M NaCl under a nitrogen atmosphere, averaging 30 min from start to finish. Concentrations of carboxyl groups and phenolic groups were estimated directly from titration curves. Titration data were also fit to a modified Henderson-Hasselbalch model for two classes of proton-binding sites to obtain "best fit" parameters that describe proton-binding curves for the samples. The model was chosen for its simplicity, its ease of implementation in computer spreadsheets, and its excellent ability to describe the shapes of the titration curves. The carboxyl contents of the IHSS samples are in the general order: terrestrial fulvic acids > aquatic fulvic acids > Suwannee River natural organic matter (NOM) > aquatic humic acids > terrestrial humic acids. Overall, fulvic acids and humic acids have similar phenolic contents; however, all of the aquatically derived samples have higher phenolic contents than the terrestrially derived samples. The acid-base properties of reference Suwannee River NOM are surprisingly similar to those of standard Suwannee River humic acid. Results from titrations in this study were compared with other published results from both direct and indirect titrations. Typically, carboxyl contents for the IHSS samples were in agreement with the results from both methods of titration. Phenolic contents for the IHSS samples were comparable to those determined by direct titrations, but were significantly less than estimates of phenolic content that were based on indirect titrations with Ba(OH) 2 and Ca(OAc) 2. The average phenolic-to-carboxylic ratio of the IHSS samples is approximately 1:4. Models that assume a 1:2 ratio of phenolic-to-carboxylic groups may overestimate the relative contribution of phenolic groups to the acid-base chemistry of humic substances.

  7. Direct-hydrogen-fueled proton-exchange-membrane fuel cell system for transportation applications

    SciTech Connect

    Oei, D.; Adams, J.A.; Kinnelly, A.A.

    1997-07-01

    In partial fulfillment of the U.S. Department of Energy Contract No. DE-ACO2-94CE50389, {open_quotes}Direct Hydrogen-Fueled Proton-Exchange-Membrane (PEM) Fuel Cell System for Transportation Applications{close_quotes}, this conceptual vehicle design report addresses the design and packaging of battery augmented fuel cell powertrain vehicles. This report supplements the {open_quotes}Conceptual Vehicle Design Report - Pure Fuel Cell Powertrain Vehicle{close_quotes} and includes a cost study of the fuel cell power system. The three classes of vehicles considered in this design and packaging exercise are the same vehicle classes that were studied in the previous report: the Aspire, representing the small vehicle class; the AIV (Aluminum Intensive Vehicle) Sable, representing the mid-size vehicle; and the E-150 Econoline, representing the van-size class. A preliminary PEM fuel cell power system manufacturing cost study is also presented. As in the case of the previous report concerning the {open_quotes}Pure Fuel Cell Powertrain Vehicle{close_quotes}, the same assumptions are made for the fuel cell power system. These assumptions are fuel cell system power densities of 0.33 kW/ka and 0.33 kW/l, platinum catalyst loading of less than or equal to 0.25 mg/cm{sup 2} total, and hydrogen tanks containing compressed gaseous hydrogen under 340 atm (5000 psia) pressure. The batteries considered for power augmentation of the fuel cell vehicle are based on the Ford Hybrid Electric Vehicle (HEV) program. These are state-of-the-art high power lead acid batteries with power densities ranging from 0.8 kW/kg to 2 kW/kg. The results reported here show that battery augmentation provides the fuel cell vehicle with a power source to meet instant high power demand for acceleration and start-up. Based on the assumptions made in this report, the packaging of the battery augmented fuel cell vehicle appears to be as feasible as the packaging of the pure fuel cell powered vehicle.

  8. In situ measurements of water transfer due to different mechanisms in a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Husar, Attila; Higier, Andrew; Liu, Hongtan

    Water management is of critical importance in a proton exchange membrane (PEM) fuel cell, in particular, those based on a sulfonic acid polymer, which requires water to conduct protons. Yet there are limited in situ studies of water transfer through the membrane and no data are available for water transfer due to individual mechanisms through the membrane in an operational fuel cell. Thus it is the objective of this study to measure water transfer through the membrane due to each individual mechanism in an operational PEM fuel cell. The three different mechanisms of water transfer, i.e., electro-osmotic drag, diffusion and hydraulic permeation are isolated by specially imposed boundary conditions. Therefore water transfer through the membrane due to each mechanism is measured separately. In this study, all the data is collected in an actual assembled operational fuel cell. The experimental results show that water transfer due to hydraulic permeation, i.e. the pressure difference between the anode and cathode is at least an order of magnitude lower than those due to the other two mechanisms. The data for water transfer due to diffusion through the membrane are in good agreement with some of the ex situ data in the literature. The data for electro-osmosis show that the number of water molecules dragged per proton increases not only with temperature but also with current density, which is different from existing data in the literature. The methodology used in this study is simple and can be easily adopted for in situ water transfer measurement due to different mechanisms in other PEM fuel cells without any cell modifications.

  9. ¹H and (15)N NMR Analyses on Heparin, Heparan Sulfates and Related Monosaccharides Concerning the Chemical Exchange Regime of the N-Sulfo-Glucosamine Sulfamate Proton.

    PubMed

    Pomin, Vitor H

    2016-01-01

    Heparin and heparan sulfate are structurally related glycosaminoglycans (GAGs). Both GAGs present, although in different concentrations, N-sulfo-glucosamine (GlcNS) as one of their various composing units. The conditional fast exchange property of the GlcNS sulfamate proton in these GAGs has been pointed as the main barrier to its signal detection via NMR experiments, especially ¹H-(15)N HSQC. Here, a series of NMR spectra is collected on heparin, heparan sulfate and related monosaccharides. The N-acetyl glucosamine-linked uronic acid types of these GAGs were properly assigned in the ¹H-(15)N HSQC spectra. Dynamic nuclear polarization (DNP) was employed in order to facilitate 1D spectral acquisition of the sulfamate (15)N signal of free GlcNS. Analyses on the multiplet pattern of scalar couplings of GlcNS (15)N has helped to understand the chemical properties of the sulfamate proton in solution. The singlet peak observed for GlcNS happens due to fast chemical exchange of the GlcNS sulfamate proton in solution. Analyses on kinetics of alpha-beta anomeric mutarotation via ¹H NMR spectra have been performed in GlcNS as well as other glucose-based monosaccharides. 1D ¹H and 2D ¹H-(15)N HSQC spectra recorded at low temperature for free GlcNS dissolved in a proton-rich solution showed signals from all exchangeable protons, including those belonging to the sulfamate group. This work suits well to the current grand celebration of one-century-anniversary of the discovery of heparin. PMID:27618066

  10. Leaky-Surface-Acoustic-Wave Properties on Reverse-Proton-Exchanged LiNbO3

    NASA Astrophysics Data System (ADS)

    Kakio, Shoji; Shimizu, Hidenori; Nakagawa, Yasuhiko

    2009-07-01

    A proton-exchanged (PE) layer with an elastically soft property can be buried into a substrate by a reverse proton exchange (RPE) process. It is expected that an RPE layer with a property similar to that of bulk LiNbO3 will prevent the degradation of coupling factor, and that the buried PE layer will change the anisotropy of the substrate effectively and reduce the leaky surface acoustic wave (LSAW) attenuation as compared with bulk LN. In this study, first, a layered structure of air/bulk LN/softened LN was assumed for rotated Y-X LN and LSAW attenuation was calculated. By controlling the elastic constant of the softened LN, the rotation angle from the Y-axis giving zero attenuation shifted from 64 to 5° for a metallized surface, and the rotation angle at which the attenuation decreases as compared with bulk LN was drastically changed for a free surface. Next, the LSAW propagation loss PL was measured on 41° Y-X LN. The PL for the metallized surface was decreased by carrying out the RPE process from 0.036 dB/λ of a virgin sample to 0.015 dB/λ. The decrease in PL for the free surface was also observed.

  11. Ionosphere-exosphere coupling through charge exchange and momentum transfer in hydrogen-proton collisions

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Breig, E. L.

    1991-01-01

    The implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer are examined. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H - H(+) collision process, differential and cumulative cross sections were calculated for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere-exosphere coupling through H - H(+) collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamic approach, leads to unacceptable abundances of coronal atoms in long-term, highly elliptic trajectories.

  12. Hydrogen-oxygen proton-exchange membrane fuel cells and electrolyzers

    NASA Technical Reports Server (NTRS)

    Baldwin, R.; Pham, M.; Leonida, A.; Mcelroy, J.; Nalette, T.

    1989-01-01

    Hydrogen-oxygen solid polymer electrolyte (SPE) fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. These solid electrolyte devices have been under continuous development for over 30 years. This experience has resulted in a demonstrated ten-year SPE cell life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluoride loss rates and average expected ultimate cell life. This relationship is shown. Several features have been introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability has been demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density.

  13. NMR resonance splitting of urea in stretched hydrogels: proton exchange and (1)H/(2)H isotopologues.

    PubMed

    Kuchel, Philip W; Naumann, Christoph; Chapman, Bogdan E; Shishmarev, Dmitry; Håkansson, Pär; Bacskay, George; Hush, Noel S

    2014-10-01

    Urea at ∼12 M in concentrated gelatin gel, that was stretched, gave (1)H and (2)H NMR spectral splitting patterns that varied in a predictable way with changes in the relative proportions of (1)H2O and (2)H2O in the medium. This required consideration of the combinatorics of the two amide groups in urea that have a total of four protonation/deuteration sites giving rise to 16 different isotopologues, if all the atoms were separately identifiable. The rate constant that characterized the exchange of the protons with water was estimated by back-transformation analysis of 2D-EXSY spectra. There was no (1)H NMR spectral evidence that the chiral gelatin medium had caused in-equivalence in the protons bonded to each amide nitrogen atom. The spectral splitting patterns in (1)H and (2)H NMR spectra were accounted for by intra-molecular scalar and dipolar interactions, and quadrupolar interactions with the electric field gradients of the gelatin matrix, respectively. PMID:25241007

  14. HOGEN{trademark} proton exchange membrane hydrogen generators: Commercialization of PEM electrolyzers

    SciTech Connect

    Smith, W.F.; Molter, T.M.

    1997-12-31

    PROTON Energy Systems` new HOGEN series hydrogen generators are Proton Exchange Membrane (PEM) based water electrolyzers designed to generate 300 to 1000 Standard Cubic Feet Per Hour (SCFH) of high purity hydrogen at pressures up to 400 psi without the use of mechanical compressors. This paper will describe technology evolution leading to the HOGEN, identify system design performance parameters and describe the physical packaging and interfaces of HOGEN systems. PEM electrolyzers have served US and UK Navy and NASA needs for many years in a variety of diverse programs including oxygen generators for life support applications. In the late 1970`s these systems were advocated for bulk hydrogen generation through a series of DOE sponsored program activities. During the military buildup of the 1980`s commercial deployment of PEM hydrogen generators was de-emphasized as priority was given to new Navy and NASA PEM electrolysis systems. PROTON Energy Systems was founded in 1996 with the primary corporate mission of commercializing PEM hydrogen generators. These systems are specifically designed and priced to meet the needs of commercial markets and produced through manufacturing processes tailored to these applications. The HOGEN series generators are the first step along the path to full commercial deployment of PEM electrolyzer products for both industrial and consumer uses. The 300/1000 series are sized to meet the needs of the industrial gases market today and provide a design base that can transition to serve the needs of a decentralized hydrogen infrastructure tomorrow.

  15. Reduction and Reoxidation of Humic Acid: Influence on Spectroscopic Properties and Proton Binding

    SciTech Connect

    Maurer, F.; Christl, I; Kretzschmar, R

    2010-01-01

    Previous studies on proton and metal binding to humic substances have not considered a potential influence of reduction and oxidation of functional groups. Therefore, we investigated how proton binding of a purified soil humic acid was affected by reduction. Reduction of the humic acid was carried out using an electrochemical cell that allowed us to measure the amounts of electrons and protons involved in reduction reactions. We further applied spectroscopic methods (UV-vis, fluorescence, FT-IR, C-1s NEXAFS) to detect possible chemical changes in the humic acid induced by reduction and reoxidation. The effect of reduction on proton binding was determined with acid-base titrations in the pH range 4-10 under controlled redox conditions. During reduction, 0.54 mol kg{sup -1} protons and 0.55 mol kg{sup -1} electrons were transferred to humic acid. NICA-Donnan modeling revealed an equivalent increase in proton-reactive sites (0.52 mol kg{sup -1}) in the alkaline pH-range. Our results indicate that reduction of humic acid increased the amount of proton-reactive sites by 15% compared to the untreated state. Spectroscopic differences between the untreated and reduced humic acid were minor, apart from a lower UV-vis absorption of the reduced humic acid between 400 and 700 nm.

  16. Comparative assessment of the methods for exchangeable acidity measuring

    NASA Astrophysics Data System (ADS)

    Vanchikova, E. V.; Shamrikova, E. V.; Bespyatykh, N. V.; Zaboeva, G. A.; Bobrova, Yu. I.; Kyz"yurova, E. V.; Grishchenko, N. V.

    2016-05-01

    A comparative assessment of the results of measuring the exchangeable acidity and its components by different methods was performed for the main mineral genetic horizons of texturally-differentiated gleyed and nongleyed soddy-podzolic and gley-podzolic soils of the Komi Republic. It was shown that the contents of all the components of exchangeable soil acidity determined by the Russian method (with potassium chloride solution as extractant, c(KCl) = 1 mol/dm3) were significantly higher than those obtained by the international method (with barium chloride solution as extractant, c(BaCl2) = 0.1 mol/dm3). The error of the estimate of the concentration of H+ ions extracted with barium chloride solution equaled 100%, and this allowed only qualitative description of this component of the soil acidity. In the case of the extraction with potassium chloride, the error of measurements was 50%. It was also shown that the use of potentiometric titration suggested by the Russian method overestimates the results of soil acidity measurement caused by the exchangeable metal ions (Al(III), Fe(III), and Mn(II)) in comparison with the atomic emission method.

  17. Microwave Spectroscopy and Proton Transfer Dynamics in the Formic Acid-Acetic Acid Dimer

    NASA Astrophysics Data System (ADS)

    Howard, B. J.; Steer, E.; Page, F.; Tayler, M.; Ouyang, B.; Leung, H. O.; Marshall, M. D.; Muenter, J. S.

    2012-06-01

    The rotational spectrum of the doubly hydrogen-bonded {hetero} dimer formed between formic acid and acetic acid has been recorded between 4 and 18 GHz using a pulsed-nozzle Fourier transform microwave spectrometer. Each rigid-molecule rotational transition is split into four as a result of two concurrent tunnelling motions, one being proton transfer between the two acid molecules, and the other the torsion/rotation of the methyl group within the acetic acid. We present a full assignment of the spectrum for {J} = 1 to {J} = 7 for these four torsion/tunnelling states. Spectra have been observed for the main isotopic species, with deuterium substitution at the C of the formic acid and all 13C species in natural abundance, The observed transitions are fitted to within a few kilohertz using a molecule-fixed effective rotational Hamiltonian for the separate {A} and {E} vibrational species of the G12 permutation-inversion group which is applicable to this complex. To reduce the effects of internal angular momentum, a non-principal axis system is used throughout. Interpretation of the internal motion uses an internal-vibration and overall rotation scheme, and full sets of rotational and centrifugal distortion constants are determined. The proton tunnelling rates and the internal angular momentum of the methyl group in the {E} states is interpreted in terms of a dynamical model which involves coupled proton transfer and internal rotation. The resulting potential energy surface not only describes these internal motions, but can also explain the observed shifts in rotational constants between {A} and {E} species, and the deviations of the tunnelling frequencies from the expected 2:1 ratio. It also permits the determination of spectral constants free from the contamination effects of the internal dynamics. M.C.D. Tayler, B. Ouyang and B.J. Howard, J. Chem. Phys., {134}, 054316 (2011).

  18. Pulse radiolytic study of the acid dissociation of OH protons in radicals related to salicylic acid

    SciTech Connect

    Sun, Q.; Schuler, R.H.

    1987-08-13

    The deprotonation of carboxylated benzosemiquinone radicals prepared by pulse radiolytic oxidation of dihydroxybenzoic acids has been examined by time-resolved absorption spectrophotometry. The pK/sub a/ for dissociation of the OH proton in 3-carboxyl-1,4-benzosemiquinone is found to be 6.47 or 2.4 units higher than that in the unsubstituted radical. This pK/sub a/ is, however, well below that of the OH proton in salicyclic acid (13.6) so that hydrogen bonding is appreciably decreased by the delocalization of the unpaired spin in this radical. Protonation of the basic form of the radical occurs at the diffusion-controlled rate. The rate constant for deprotonation by OH/sup -/ is relatively low, 4.7 X 10/sup 7/ M/sup -1/ s/sup -1/, so that reaction with base becomes important only above pH 10. As a result this radical provides an excellent system for studying acid-base equilibration processes in near neutral solutions. Azide ion is shown to be an efficient catalyst which allows the acid-base equilibrium to be examined on the 10-..mu..s time scale. Deprotonation is also catalyzed by the dihydroxybenzoic acid used as the radical source. Analogous studies on 4-carboxy-1,3-benzosemiquinone give the pK/sub a/ as 7.9. In spite of this high pK/sub a/, which indicates the rate constant for spontaneous dissociation of this radical to be > 10/sup 3/ s/sup -1/, the rate constant for deprotonation by OH/sup -/, 4.9 X 10/sup 8/ M/sup -1/ s/sup -1/, is considerably higher than in the case of 3-carboxy-1,4-benzosemiquinone.

  19. Double-peak elution profile of a monoclonal antibody in cation exchange chromatography is caused by histidine-protonation-based charge variants.

    PubMed

    Luo, Haibin; Cao, Mingyan; Newell, Kelcy; Afdahl, Christopher; Wang, Jihong; Wang, William K; Li, Yuling

    2015-12-11

    We have systemically investigated unusual elution behaviors of an IgG4 (mAb A) in cation exchange chromatography (CEX). This mAb A exhibited two elution peaks under certain conditions when being purified by several strong CEX columns. When either of the two peaks was isolated and re-injected on the same column, the similar pattern was observed again during elution. The protein distribution between the two peaks could be altered by NaCl concentration in the feed, or NaCl concentration in wash buffer, or elution pH, suggesting two pH-associated strong-and-weak binding configurations. The protein distributions under different pH values showed good correlation with protonated/un-protonated fractions of a histidine residue. These results suggest that the double-peak elution profile associates with histidine-protonation-based charge variants. By conducting pepsin digestion, amino-acid specific chemical modifications, peptide mapping, and measuring the effects of elution residence time, a histidine in the variable fragment (Fab) was identified to be the root cause. Besides double-peak pattern, mAb A can also exhibit peak-shouldering or single elution peak on different CEX resins, reflecting different resins' resolving capability on protonated/un-protonated forms. This work characterizes a novel cause for unusual elution behaviors in CEX and also provides alternative avenues of purification development for mAbs with similar behaviors. PMID:26596869

  20. Time resolved confocal luminescence investigations on Reverse Proton Exchange Nd:LiNbO(3) channel waveguides.

    PubMed

    Rodríguez, E M; Jaque, D; Cantelar, E; Cussó, F; Lifante, G; Busacca, A C; Cino, A; Sanseverino, S R

    2007-07-01

    In this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO(3) channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the comparison between diffusion simulations and the spatial dependence of the (4)F(3/2) fluorescence decay rate we have concluded that the observed fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO(3) lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the (4)F(3/2)?(4)I(9/2) fluorescence band. PMID:19547216

  1. Time resolved confocal luminescence investigations on Reverse Proton Exchange Nd:LiNbO3 channel waveguides

    NASA Astrophysics Data System (ADS)

    Rodríguez, E. M.; Jaque, D.; Cantelar, E.; Cussó, F.; Lifante, G.; Busacca, A. C.; Cino, A.; Sanseverino, S. R.

    2007-07-01

    In this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO3 channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the comparison between diffusion simulations and the spatial dependence of the 4F3/2 fluorescence decay rate we have concluded that the observed fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO3 lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the 4F3/2→4I9/2 fluorescence band.

  2. Isotopic exchange of hydrogen in aromatic amino acids

    SciTech Connect

    Pshenichnikova, A.B.; Karnaukhova, E.N.; Mitsner, B.I.

    1993-10-20

    The kinetics of the isotopic replacement of hydrogen in the aromatic amino acids L-tryptophan, L-tyrosine, and L-phenylalanine in solutions of deuterochloric and deuterosulfuric acids in deuterium oxide were investigated by PMR spectroscopy. The reactions were shown to be of first orders with respect both to the concentration of the substrate and to the activity of the deuterium ion. The isotopic effects of hydrogen and the values of the activation energy of H-D exchange in different positions of the aromatic ring in tryptophan and tyrosine were determined. The effect of properties of the medium on the rate of the isotopic exchange of hydrogen is discussed. 17 refs., 2 figs., 2 tabs.

  3. Highly durable silica-coated Pt/carbon nanotubes for proton-exchange membrane fuel cells application

    NASA Astrophysics Data System (ADS)

    Yaowarat, Wattanachai; Li, Oi Lun Helena; Saito, Nagahiro

    2016-01-01

    Platinum nanoparticles supported on carbon nanotubes (Pt/CNTs) have been used as an electrocatalyst in proton-exchange membrane fuel cells (PEMFCs). These catalysts show higher activity in oxygen reduction reaction in PEMFCs than conventional carbon-black-supported Pt nanoparticles. However, their durability is lower than that of other metal-alloy-based or nonmetal-based catalysts. In this study, Pt/CNTs were synthesized by solution plasma followed by coating with silica layer by the sol-gel method using a cationic surfactant [cetyltrimethylammonium bromide (CTAB)]. This material can be used as a cathode in PEMFCs. The silica layer was coated on the surface of Pt/CNTs to prevent agglomeration and detachment of Pt nanoparticles from carbon nanotubes during operation. The formation of silica layers significantly improved the durability of the Pt/CNT catalysts under acidic conditions. After 300 cycles of the cyclic voltammetry test in 0.5#M sulfuric acid (H2SO4), silica-coated Pt/CNTs increased the durability by 43.0 and 24.0% compared with those of noncoated commercial Pt/C and Pt/CNTs, respectively.

  4. A conductive and hydrophilic bipolar plate coating for enhanced proton exchange membrane fuel cell performance and water management

    NASA Astrophysics Data System (ADS)

    Nowak, Andrew P.; Salguero, Tina T.; Kirby, Kevin W.; Zhong, Feng; Blunk, Richard H. J.

    2012-07-01

    Electrically conductive and hydrophilic coatings for proton exchange membrane fuel cell (PEMFC) stainless steel bipolar plates have been developed in order to minimize voltage losses at the plate and gas diffusion layer (GDL) interface and facilitate liquid water transport in plate channels for efficient stack operation. The coatings are based on a multifunctional silane, 1,2-bis(triethoxysilyl)ethane (BTSE), mixed with conductive, hydrophilic carbon black. Vulcan® XC72 carbon black was modified with either polar phenylsulfonic acid (PSA) or carboxylic acid (COOH) groups to increase hydrophilic character and wetting behavior. Wetting and electrical contact resistance performance was compared with coatings based on nano-particle titania and silica. These conductive silane and carbon composite coating precursors are conveniently formulated in alcohol solution for scalable application via spray coating. Cured films exhibit negligible contact resistance increase (<2 mΩ cm2) at 1.4 MPa when deposited on both physical vapor deposited (PVD) carbon and electroplated gold coated stainless steel. The coatings were tested for hydrophilicity retention under wet and dry fuel cell conditions where the BTSE-COOH coating remained hydrophilic on stamped stainless steel bipolar plate prototypes after greater than 1200 h of simulated fuel cell testing with only moderate loss of hydrophilicity.

  5. A self-sustained, complete and miniaturized methanol fuel processor for proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Yang, Mei; Jiao, Fengjun; Li, Shulian; Li, Hengqiang; Chen, Guangwen

    2015-08-01

    A self-sustained, complete and miniaturized methanol fuel processor has been developed based on modular integration and microreactor technology. The fuel processor is comprised of one methanol oxidative reformer, one methanol combustor and one two-stage CO preferential oxidation unit. Microchannel heat exchanger is employed to recover heat from hot stream, miniaturize system size and thus achieve high energy utilization efficiency. By optimized thermal management and proper operation parameter control, the fuel processor can start up in 10 min at room temperature without external heating. A self-sustained state is achieved with H2 production rate of 0.99 Nm3 h-1 and extremely low CO content below 25 ppm. This amount of H2 is sufficient to supply a 1 kWe proton exchange membrane fuel cell. The corresponding thermal efficiency of whole processor is higher than 86%. The size and weight of the assembled reactors integrated with microchannel heat exchangers are 1.4 L and 5.3 kg, respectively, demonstrating a very compact construction of the fuel processor.

  6. Kinetic and thermodynamic acidity of hydrido transition-metal complexes. 4. Kinetic acidities toward aniline and their use in identifying proton-transfer mechanisms

    SciTech Connect

    Edidin, R.T.; Sullivan, J.M.; Norton, J.R.

    1987-06-24

    The kinetic deuterium isotope effects for CpM(CO)3H/CpM(CO)3 (M = Cr, Mo, W) self-exchange reactions in acetonitrile are consistent with a proton-transfer mechanism. The small counterion effect on the rate of self-exchange between H2Fe(CO)4 and HFe(CO)4 is consistent with the absence of IR-observable contact ion pair formation by (HFe(CO)4) . Broensted plots (log of the rate constant vs. log of the equilibrium constant) are linear for proton transfers in acetonitrile from transition-metal hydrides to a series of para-substituted anilines. For CpW(CO)3H the Broensted slope, , is 0.65; for HMn(CO)5 it is 0.54, for H2Fe(CO)4 it is 0.55, and for HCo(CO)4 it is 0.48. The rates of proton transfer to aniline cover a range of 9 orders of magnitude for the transition-metal hydrides studied: from 1.0 x 10 T M s for HRe(CO)5 to 1.7 x 10W M s for HCo(CO)4. These rates define a kinetic acidity series which for the most part parallels the thermodynamic acidities of these hydrides. This kinetic acidity series has been used to demonstrate that the reaction of Cp2Zr(CH3)2 with CpM(CO)3H M = Cr, Mo, W) occurs by a proton-transfer mechanism.

  7. A Comparative Ab Initio Study of the Primary Hydration and Proton Dissociation of Various Imide and Sulfonic Acid Ionomers

    SciTech Connect

    Clark II, Jeffrey K.; Paddison, Stephen J.; Eikerling, Michael; Dupuis, Michel; Zawodzinski, Jr., Thomas A.

    2012-03-29

    We compare the role of neighboring group substitutions on proton dissociation of hydrated acidic moieties suitable for proton exchange membranes through electronic structure calculations. Three pairs of ionomers containing similar electron withdrawing groups within the pair were chosen for the study: two fully fluorinated sulfonyl imides (CF3SO2NHSO2CF3 and CF3CF2SO2NHSO2CF3), two partially fluorinated sulfonyl imides (CH3SO2NHSO2CF3 and C6H5SO2NHSO2CF2CF3), and two aromatic sulfonic acid based material s (CH3C6H4SO3H and CH3 OC6 - H3OCH3C6H4SO3H). Fully optimized counterpoise (CP) corrected geometries were obtained for each ionomer fragment with the inclusion of water molecules at the B3LYP/6-311G** level of density functional theory. Spontaneous proton dissociation was observed upon addition of three water molecules in each system, and the transition to a solvent-separated ion pair occurred when four water molecules were introduced. No considerable quantitative or qualitative differences in proton dissociation, hydrogen bond networks formed, or water binding energies were found between systems containing similar electron withdrawing groups. Each of the sulfonyl imide ionomers exhibited qualitatively similar results regarding proton dissociation and separation. The fully fluorinated sulfonyl imides, however, showed a greater propensity to exist in dissociated and ion-pair separated states at low degrees of hydration than the partially fluorinated sulfonyl imides. This effect is due to the additional electron withdrawing groups providing charge stabilization as the dissociated proton migrates away from the imide anion.

  8. Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence

    SciTech Connect

    Craig Carville, N.; Denning, Denise; Rodriguez, Brian J.; Manzo, Michele; Gallo, Katia

    2013-05-14

    Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO{sub 3} solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 {+-} 0.02 {mu}m and a height of 1.61 {+-} 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 {+-} 0.06 {mu}m, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO{sub 3} (10{sup -2} M), the amount of silver deposition for 5 min UV illumination is greater (2.88 {+-} 0.58 nm) compared to that at low (10{sup -4} M) concentrations (0.78 {+-} 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10{sup -4} M had greater overall deposition, 6.90 {+-} 1.52 nm, compared to 4.50 {+-} 0.76 nm at 10{sup -2} M. For longer exposure times (30 min) at 10{sup -2} M, the nanostructure height is 4.72 {+-} 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10{sup -2} and 10{sup -4} M

  9. Proton-Binding Sites of Acid-Sensing Ion Channel 1

    PubMed Central

    Ishikita, Hiroshi

    2011-01-01

    Acid-sensing ion channels (ASICs) are proton-gated cation channels that exist throughout the mammalian central and peripheral nervous systems. ASIC1 is the most abundant of all the ASICs and is likely to modulate synaptic transmission. Identifying the proton-binding sites of ASCI1 is required to elucidate its pH-sensing mechanism. By using the crystal structure of ASIC1, the protonation states of each titratable site of ASIC1 were calculated by solving the Poisson-Boltzmann equation under conditions wherein the protonation states of all these sites are simultaneously in equilibrium. Four acidic-acidic residue pairs—Asp238-Asp350, Glu220-Asp408, Glu239-Asp346, and Glu80-Glu417—were found to be highly protonated. In particular, the Glu80-Glu417 pair in the inner pore was completely protonated and possessed 2 H+, implying its possible importance as a proton-binding site. The pKa of Glu239, which forms a pair with a possible pH-sensing site Asp346, differs among each homo-trimer subunit due to the different H-bond pattern of Thr237 in the different protein conformations of the subunits. His74 possessed a pKa of ≈6–7. Conservation of His74 in the proton-sensitive ASIC3 that lacks a residue corresponding to Asp346 may suggest its possible pH-sensing role in proton-sensitive ASICs. PMID:21340031

  10. Proton transport pathways in an acid-base complex consisting of a phosphonic acid group and a 1,2,3-triazolyl group.

    PubMed

    Yue, Baohua; Yan, Liuming; Han, Shuaiyuan; Xie, Liqing

    2013-07-01

    The proton transport pathways in an acid-base complex consisting of a phosphonic acid group and a 1,2,3-triazolyl group were studied using density functional theory (DFT) calculations in terms of stable configurations and transition states of the molecular or ionic dimers and trimers and verified by proof-of-concept experiments including experimental measurements of overall conductivity and (1)H NMR and FTIR spectroscopy of the methylphosphonic acid (MPA) and 1,2,3-triazole (Tri) complex as well as overall proton conductivity of polymeric blend of poly(vinylphosphonic acid) (PVPA) and poly(4-vinyl-1H-1,2,3-triazole) (PVTri). From the DFT calculations of dimers and trimers composed of ethylphosphonic acid (EPA), Tri, and their deprotonated counterparts, it was concluded that the intermolecular hydrogen bonds of the transition states corresponding to proton transport are much shorter than those of stable configurations, but the O-H and N-H bonds are much longer than those of stable configurations. The tautomerization activation energy decreases from 0.927-1.176 eV in Tri-Tri dimers to 0.336-0.444 eV in the EPA-Tri dimers. From the proof-of-concept experiments, about a 50 fold increase in overall conductivity was observed in the MPA-Tri complex consisting of 10% (molar ratio) MPA compared to pure Tri, and the calculated activation energy is consistent with the experimental activation energy evaluated from temperature dependence of proton conductivity of pure Tri and the MPA-Tri complex. In addition, the fast proton exchange between MPA and Tri, consistent with the DFT calculations, was verified by (1)H NMR and FTIR spectroscopy. Finally, a polymeric blend of PVPA and PVTri was prepared, and its proton conductivity at about 2.1 mS·cm(-1) in anhydrous state at 100 °C was observed to be significantly higher than that of PVPA or of poly(VPA-co-1-vinyl-1,2,4-triazole). The proton conductivity of the polymeric PVPA and PVTri blend in humidity state is in the same range as

  11. Inductive phenomena at low frequencies in impedance spectra of proton exchange membrane fuel cells - A review

    NASA Astrophysics Data System (ADS)

    Pivac, Ivan; Barbir, Frano

    2016-09-01

    The results of electrochemical impedance spectroscopy of proton exchange membrane (PEM) fuel cells may exhibit inductive phenomena at low frequencies. The occurrence of inductive features at high frequencies is explained by the cables and wires of the test system. However, explanation of inductive loop at low frequencies requires a more detailed study. This review paper discusses several possible causes of such inductive behavior in PEM fuel cells, such as side reactions with intermediate species, carbon monoxide poisoning, and water transport, also as their equivalent circuit representations. It may be concluded that interpretation of impedance spectra at low frequencies is still ambiguous, and that better equivalent circuit models are needed with clearly defined physical meaning of each of the circuit elements.

  12. Proton exchange membrane fuel cells for electrical power generation on-board commercial airplanes.

    SciTech Connect

    Curgus, Dita Brigitte; Munoz-Ramos, Karina; Pratt, Joseph William; Akhil, Abbas Ali; Klebanoff, Leonard E.; Schenkman, Benjamin L.

    2011-05-01

    Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole. Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today's technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured.

  13. Proton Exchange Membrane Fuel Cells for Electrical Power Generation On-Board Commercial Airplanes

    SciTech Connect

    Pratt, Joesph W.; Klebanoff, Leonard E.; Munoz-Ramos, Karina; Akhil, Abbas A.; Curgus, Dita B.; Schenkman, Benjamin L.

    2011-05-01

    Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole. Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today’s technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured.

  14. Emerging roles of alkali cation/proton exchangers in organellar homeostasis

    PubMed Central

    Orlowski, John; Grinstein, Sergio

    2016-01-01

    The regulated movement of monovalent cations such as H+, Li+, Na+ and K+ across biological membranes influences a myriad of cellular processes and is fundamental to all living organisms. This is accomplished by a multiplicity of ion channels, pumps and transporters. Our insight into their molecular, cellular and physiological diversity has increased greatly in the past few years with the advent of genome sequencing, genetic manipulation and sophisticated imaging techniques. One of the revelations from these studies is the emergence of novel alkali cation/protons exchangers that are present in endomembranes, where they function to regulate not only intraorganellar pH but also vesicular biogenesis, trafficking and other aspects of cellular homeostasis. PMID:17646094

  15. Uncovering the Stabilization Mechanism in Bimetallic Ruthenium-Iridium Anodes for Proton Exchange Membrane Electrolyzers.

    PubMed

    Saveleva, Viktoriia A; Wang, Li; Luo, Wen; Zafeiratos, Spyridon; Ulhaq-Bouillet, Corinne; Gago, Aldo S; Friedrich, K Andreas; Savinova, Elena R

    2016-08-18

    Proton exchange membrane (PEM) electrolyzers are attracting an increasing attention as a promising technology for the renewable electricity storage. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied for in situ monitoring of the surface state of membrane electrode assemblies with RuO2 and bimetallic Ir0.7Ru0.3O2 anodes during water splitting. We demonstrate that Ir protects Ru from the formation of an unstable hydrous Ru(IV) oxide thereby rendering bimetallic Ru-Ir oxide electrodes with higher corrosion resistance. We further show that the water splitting occurs through a surface Ru(VIII) intermediate, and, contrary to common opinion, the presence of Ir does not hinder its formation. PMID:27477824

  16. Development of a proton-exchange membrane electrochemical reclaimed water post-treatment system

    NASA Technical Reports Server (NTRS)

    Kaba, Lamine; Verostko, Charles E.; Hitchens, G. D.; Murphy, Oliver J.

    1991-01-01

    A single-cell electrochemical reactor that utilizes a proton exchange membrane (PEM) as a solid electrolyte is being investigated for posttreatment of reclaimed waste waters with low or negligible electrolyte content. Posttreatment is a final 'polishing' of reclaimed waste waters prior to reuse, and involves removing organic impurities at levels as high as 100 ppm to below 500 ppb total organic carbon (TOC) content to provide disinfection. The system does not utilize or produce either expendable hardware components or chemicals and has no moving parts. Test data and kinetic analysis are presented. The feasibility and application for water reclamation processes in controlled ecological environments (e.g., lunar/Mars habitats) are also presented. Test results show that the electrochemical single cell reactor provides effective posttreatment.

  17. Resonance assignments of non-exchangeable protons in B type DNA oligomers, an overview.

    PubMed Central

    van de Ven, F J; Hilbers, C W

    1988-01-01

    The chemical shifts of 1H resonances of non exchangeable protons (except H5', H5" and adenine H2) of over six hundred nucleotides have been collected. The influence which the base of the nucleotide itself as well as the bases on its 5' and 3' side exert on the chemical shifts of the various resonances has been investigated. Most of the resonances appear to be predominantly influenced by only one base. For H2', H2", H3', H4' and H6/H8 this is the base of the central nucleotide, for H5(C) and CH3(T) it is the one on the 5' side and for H1' it is the one on the 3' side. Chemical shift distribution profiles are presented which allow an estimation of the probability of finding a particular resonance at a particular position in the spectrum. PMID:2840632

  18. Effect of anode electrocatalyst for direct hydrazine fuel cell using proton exchange membrane

    NASA Astrophysics Data System (ADS)

    Yamada, Koji; Yasuda, Kazuaki; Tanaka, Hirohisa; Miyazaki, Yoshinori; Kobayashi, Tetsuhiko

    Hydrazine was examined as a fuel in a direct-liquid-fueled fuel cell that uses proton exchange membrane (PEM) such as Nafion ®. Different kinds of noble metals were examined as anode electrocatalysts for direct hydrazine fuel cells (DHFCs). In DHFC using platinum or palladium as the anode electrocatalyst, more than 1 V of cell voltage was obtained in the low-current density region. The I- V characteristics changed drastically depending on the kind of anode electrocatalyst used. Compositions of the exhaust materials from each electrode were analyzed to investigate the reaction occurring at the electrodes. The analysis revealed that the catalytic decomposition reaction of hydrazine proceeded further than the electro-oxidation reaction on the anode side using rhodium or ruthenium.

  19. High surface area graphite as alternative support for proton exchange membrane fuel cell catalysts

    NASA Astrophysics Data System (ADS)

    Ferreira-Aparicio, P.; Folgado, M. A.; Daza, L.

    The suitability of a high surface area graphite (HSAG) as proton exchange membrane fuel cell (PEMFC) catalyst support has been evaluated and compared with that of the most popular carbon black: the Vulcan XC72. It has been observed that Pt is arranged on the graphite surface resulting in different structures which depend on the catalysts synthesis conditions. The influence that the metal particle size and the metal-support interaction exert on the catalysts degradation rate is analyzed. Temperature programmed oxidation (TPO) under oxygen containing streams has been shown to be a useful method to assess the resistance of PEMFC catalysts to carbon corrosion. The synthesized Pt/HSAG catalysts have been evaluated in single cell tests in the cathode catalytic layer. The obtained results show that HSAG can be a promising alternative to the traditionally used Vulcan XC72 carbon black when suitable catalysts synthesis conditions are used.

  20. Diffusion-driven proton exchange membrane fuel cell for converting fermenting biomass to electricity.

    PubMed

    Malati, P; Mehrotra, P; Minoofar, P; Mackie, D M; Sumner, J J; Ganguli, R

    2015-10-01

    A membrane-integrated proton exchange membrane fuel cell that enables in situ fermentation of sugar to ethanol, diffusion-driven separation of ethanol, and its catalytic oxidation in a single continuous process is reported. The fuel cell consists of a fermentation chamber coupled to a direct ethanol fuel cell. The anode and fermentation chambers are separated by a reverse osmosis (RO) membrane. Ethanol generated from fermented biomass in the fermentation chamber diffuses through the RO membrane into a glucose solution contained in the DEFC anode chamber. The glucose solution is osmotically neutral to the biomass solution in the fermentation chamber preventing the anode chamber from drying out. The fuel cell sustains >1.3 mW cm(-2) at 47°C with high discharge capacity. No separate purification or dilution is necessary, resulting in an efficient and portable system for direct conversion of fermenting biomass to electricity. PMID:26208756

  1. Oxygen diffusion coefficient and solubility in a new proton exchange membrane

    SciTech Connect

    Haug, A.T.; White, R.E.

    2000-03-01

    The electrochemical monitoring technique is used to measure the solubility and the diffusion coefficient of oxygen in a new proton exchange membrane that is being developed by Cape Cod Research, Inc., Using the method of least squares, the data were fit to an analytical solution of Fick's second law to determine D and c{sub 0}. Values of 0.40 x 10{sup {minus}6}cm{sup 2}/s and 4.98 x 10{sup {minus}6} mol/cm{sup 3} were obtained for the diffusion coefficient and solubility, respectively, of the Cape Cod membrane. These values are significantly less than those of Nafion 117 tested under identical conditions.

  2. Proton exchange membrane fuel cell system diagnosis based on the signed directed graph method

    NASA Astrophysics Data System (ADS)

    Hua, Jianfeng; Lu, Languang; Ouyang, Minggao; Li, Jianqiu; Xu, Liangfei

    The fuel-cell powered bus is becoming the favored choice for electric vehicles because of its extended driving range, zero emissions, and high energy conversion efficiency when compared with battery-operated electric vehicles. In China, a demonstration program for the fuel cell bus fleet operated at the Beijing Olympics in 2008 and the Shanghai Expo in 2010. It is necessary to develop comprehensive proton exchange membrane fuel cell (PEMFC) diagnostic tools to increase the reliability of these systems. It is especially critical for fuel-cell city buses serving large numbers of passengers using public transportation. This paper presents a diagnostic analysis and implementation study based on the signed directed graph (SDG) method for the fuel-cell system. This diagnostic system was successfully implemented in the fuel-cell bus fleet at the Shanghai Expo in 2010.

  3. A review on the performance and modelling of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Boucetta, A.; Ghodbane, H.; Ayad, M. Y.; Bahri, M.

    2016-07-01

    Proton Exchange Membrane Fuel Cells (PEMFC), are energy efficient and environmentally friendly alternative to conventional energy conversion for various applications in stationary power plants, portable power device and transportation. PEM fuel cells provide low operating temperature and high-energy efficiency with near zero emission. A PEM fuel cell is a multiple distinct parts device and a series of mass, energy, transport through gas channels, electric current transport through membrane electrode assembly and electrochemical reactions at the triple-phase boundaries. These processes play a decisive role in determining the performance of the Fuel cell, so that studies on the phenomena of gas flows and the performance modelling are made deeply. This paper gives a comprehensive overview of the state of the art on the Study of the phenomena of gas flow and performance modelling of PEMFC.

  4. Passive hydrogen recovery schemes using a vacuum ejector in a proton exchange membrane fuel cell system

    NASA Astrophysics Data System (ADS)

    Hwang, Jenn-Jiang

    2014-02-01

    The present work describes the development of a passive hydrogen-recirculating scheme for the anode of a proton exchange membrane (PEM) fuel cell system. A vacuum ejector is fluidly connected to the stack anode outlet to entrain the unused hydrogen into the main hydrogen supply. A combination of a continuous-flow mode and a pulse-flow mode is employed to cover a wide range of power consumption. The former deals with the normal and high stack power conditions, while the latter is active only at low stack power. Transient results showed that the hydrogen anode stoichiometry has been successfully stabilized in the range of 1.4-1.6 with an entrainment ratio of 40-50% under the constant system load of 1.45 kW. In addition, the reliable operation of the PEM fuel cell system without any failure during the approximate 1-h test indicates the stability and reliability of the present hydrogen recovery scheme.

  5. Periodic domain patterning by electron beam of proton exchanged waveguides in lithium niobate

    NASA Astrophysics Data System (ADS)

    Chezganov, D. S.; Vlasov, E. O.; Neradovskiy, M. M.; Gimadeeva, L. V.; Neradovskaya, E. A.; Chuvakova, M. A.; Tronche, H.; Doutre, F.; Baldi, P.; De Micheli, M. P.; Shur, V. Ya.

    2016-05-01

    Formation of domain structure by electron beam irradiation in congruent lithium niobate covered by surface dielectric layer with planar and channel waveguides produced by Soft Proton Exchange (SPE) process has been studied. Formation of domains with arbitrary shapes as a result of discrete switching has been revealed. The fact was attributed to ineffective screening of depolarization field in the crystals with a surface layer modified by SPE process. The dependences of the domain sizes on the dose and the distance between irradiated areas have been revealed. Finally, we have demonstrated that electron beam irradiation of lithium niobate crystals with surface resist layer can produce high quality periodical domain patterns after channel waveguide fabrication. Second harmonic generation with normalized nonlinear conversion efficiency up to 48%/(W cm2) has been achieved in such waveguides.

  6. In-situ monitoring of internal local temperature and voltage of proton exchange membrane fuel cells.

    PubMed

    Lee, Chi-Yuan; Fan, Wei-Yuan; Hsieh, Wei-Jung

    2010-01-01

    The distribution of temperature and voltage of a fuel cell are key factors that influence performance. Conventional sensors are normally large, and are also useful only for making external measurements of fuel cells. Centimeter-scale sensors for making invasive measurements are frequently unable to accurately measure the interior changes of a fuel cell. This work focuses mainly on fabricating flexible multi-functional microsensors (for temperature and voltage) to measure variations in the local temperature and voltage of proton exchange membrane fuel cells (PEMFC) that are based on micro-electro-mechanical systems (MEMS). The power density at 0.5 V without a sensor is 450 mW/cm(2), and that with a sensor is 426 mW/cm(2). Since the reaction area of a fuel cell with a sensor is approximately 12% smaller than that without a sensor, but the performance of the former is only 5% worse. PMID:22163556

  7. Hydrogen-oxygen proton-exchange membrane fuel cells and electrolyzers

    NASA Technical Reports Server (NTRS)

    Baldwin, R.; Pham, M.; Leonida, A.; Mcelroy, J.; Nalette, T.

    1989-01-01

    Hydrogen-oxygen SPE fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. The SPE cells have demonstrated a ten year life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton-exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluroride loss rates and average expected ultimate cell life. Several features were introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability were demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density. The SPE electrolyzers have demonstrated the same at 1000 ASF. Many future extraterrestrial applications for fuel cells require that they be self recharged. To translate the proven SPE cell life and stability into a highly reliable extraterrestrial electrical energy storage system, a simplification of supporting equipment is required. Static phase separation, static fluid transport and static thermal control will be most useful in producting required system reliability. Although some 200,000 SPE fuel cell hours were recorded in earth orbit with static fluid phase separation, no SPE electrolyzer has, as yet, operated in space.

  8. Two-Photon Exchange Effects in Elastic Electron-Proton Scattering

    SciTech Connect

    Johnson, Myriam James

    2013-08-01

    Two methods, Rosenbluth separation and polarization transfer, can be used to extract the proton form factor ratio μp GEp/GMp, but they do not yield the same results. It is thought that the disagreement is due to two photon exchange corrections to the differential cross sections. High precision proton Rosenbluth extractions were carried out at 102 kinematics points spanning 16 values of momentum transfer Q2, from 0.40 to 5.76 GeV2. Reduced cross sections were found to 1.1% or better for Q2 less than 3 GeV2 increasing to 4% at 5.76 GeV2 The form factor ratios were determined to 1:5-3% for Q2 < 1.5 GeV2, increasing to 9% by 3 GeV2 and rapidly above. Our data agrees with prior Rosenbluth, improving upon it the 1.0 - 2.0 GeV2 range to conclusively show a separation from polarization transfer where it had not been certain before. In addition, reduced cross sections at each Q2 were tested for nonlinearity in the angular variable. Such a departure from linearity would be a signature of two photon exchange effects, and prior data had not been sufficiently precise to show nonzero curvature. Our data begins to hint at negative curvature but does not yet show a significant departure from zero.

  9. An extended stochastic reconstruction method for catalyst layers in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kang, Jinfen; Moriyama, Koji; Kim, Seung Hyun

    2016-09-01

    This paper presents an extended, stochastic reconstruction method for catalyst layers (CLs) of Proton Exchange Membrane Fuel Cells (PEMFCs). The focus is placed on the reconstruction of customized, low platinum (Pt) loading CLs where the microstructure of CLs can substantially influence the performance. The sphere-based simulated annealing (SSA) method is extended to generate the CL microstructures with specified and controllable structural properties for agglomerates, ionomer, and Pt catalysts. In the present method, the agglomerate structures are controlled by employing a trial two-point correlation function used in the simulated annealing process. An off-set method is proposed to generate more realistic ionomer structures. The variations of ionomer structures at different humidity conditions are considered to mimic the swelling effects. A method to control Pt loading, distribution, and utilization is presented. The extension of the method to consider heterogeneity in structural properties, which can be found in manufactured CL samples, is presented. Various reconstructed CLs are generated to demonstrate the capability of the proposed method. Proton transport properties of the reconstructed CLs are calculated and validated with experimental data.

  10. Nonhumidified High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells

    NASA Technical Reports Server (NTRS)

    Kinder, James D.

    2005-01-01

    Fuel cells are being considered for a wide variety of aerospace applications. One of the most versatile types of fuel cells is the proton-exchange-membrane (PEM) fuel cell. PEM fuel cells can be easily scaled to meet the power and space requirements of a specific application. For example, small 100-W PEM fuel cells are being considered for personal power for extravehicular activity suit applications, whereas larger PEM fuel cells are being designed for primary power in airplanes and in uninhabited air vehicles. Typically, PEM fuel cells operate at temperatures up to 80 C. To increase the efficiency and power density of the fuel cell system, researchers are pursuing methods to extend the operating temperature of the PEM fuel cell to 180 C. The most widely used membranes in PEM fuel cells are Nafion 112 and Nafion 117--sulfonated perfluorinated polyethers that were developed by DuPont. In addition to their relatively high cost, the properties of these membranes limit their use in a PEM fuel cell to around 80 C. The proton conductivity of Nafion membranes significantly decreases above 80 C because the membrane dehydrates. The useful operating range of Nafion-based PEM fuel cells can be extended to over 100 C if ancillary equipment, such as compressors and humidifiers, is added to maintain moisture levels within the membrane. However, the addition of these components reduces the power density and increases the complexity of the fuel cell system.

  11. Proton exchange membrane materials for the advancement of direct methanol fuel-cell technology

    DOEpatents

    Cornelius, Christopher J.

    2006-04-04

    A new class of hybrid organic-inorganic materials, and methods of synthesis, that can be used as a proton exchange membrane in a direct methanol fuel cell. In contrast with Nafion.RTM. PEM materials, which have random sulfonation, the new class of materials have ordered sulfonation achieved through self-assembly of alternating polyimide segments of different molecular weights comprising, for example, highly sulfonated hydrophilic PDA-DASA polyimide segment alternating with an unsulfonated hydrophobic 6FDA-DAS polyimide segment. An inorganic phase, e.g., 0.5 5 wt % TEOS, can be incorporated in the sulfonated polyimide copolymer to further improve its properties. The new materials exhibit reduced swelling when exposed to water, increased thermal stability, and decreased O.sub.2 and H.sub.2 gas permeability, while retaining proton conductivities similar to Nafion.RTM.. These improved properties may allow direct methanol fuel cells to operate at higher temperatures and with higher efficiencies due to reduced methanol crossover.

  12. Pressure pyrolysed non-precious oxygen reduction catalysts for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Nallathambi, Vijayadurga

    2011-12-01

    and increased the porosity, particularly micro and mesopores of the catalysts that led to increased active site density and reduced oxygen transport hindrances respectively. Collaborative efforts with the University of New Mexico facilitated XPS characterization of MNC catalysts. XPS analyses indicated that pyridinic nitrogen sites, present in the edge plane of the catalysts and pyridinic nitrogen coordinated to transition metals correlated to oxygen reduction activity. Further insight into the role of transition metal and the structure of active site was gained through EXAFS measurements, carried out in collaboration with Northeastern University. Electrochemical studies performed in the presence of poisoning anions such as cyanide in alkaline environment indicated a 25% decrease in oxygen reduction activity, suggesting that the metal is part of the active sites and participates in oxygen reduction. In-situ EXAFS analysis of the catalysts indicated the active reaction site for oxygen reduction to be Fe metal coordinated to 4 nitrogen atoms. These low cost MNC catalysts find direct application in Proton Exchange Membrane Fuel cells for transportation applications, where there is a huge drive to improve the economy of the fuel cell by reducing the costs associated with state-of the art platinum-based catalysts.

  13. How Acid-Catalyzed Decarboxylation of 2,4-Dimethoxybenzoic Acid Avoids Formation of Protonated CO2.

    PubMed

    Howe, Graeme W; Vandersteen, Adelle A; Kluger, Ronald

    2016-06-22

    The decarboxylation of 2,4-dimethoxybenzoic acid (1) is accelerated in acidic solutions. The rate of reaction depends upon solution acidity in a manner that is consistent with the formation of the conjugate acid of 1 (RCO2H2(+)), with its higher energy ring-protonated tautomer allowing the requisite C-C bond cleavage. However, this would produce the conjugate acid of CO2, a species that would be too energetic to form. Considerations of mechanisms that fit the observed rate law were supplemented with DFT calculations. Those results indicate that the lowest energy pathway from the ring-protonated reactive intermediate involves early proton transfer from the carboxyl group to water along with C-C bond cleavage, producing 1,3-dimethoxybenzene and CO2 directly. PMID:27241436

  14. Phosphorylation of the vacuolar anion exchanger AtCLCa is required for the stomatal response to abscisic acid.

    PubMed

    Wege, Stefanie; De Angeli, Alexis; Droillard, Marie-Jo; Kroniewicz, Laetitia; Merlot, Sylvain; Cornu, David; Gambale, Franco; Martinoia, Enrico; Barbier-Brygoo, Hélène; Thomine, Sébastien; Leonhardt, Nathalie; Filleur, Sophie

    2014-01-01

    Eukaryotic anion/proton exchangers of the CLC (chloride channel) family mediate anion fluxes across intracellular membranes. The Arabidopsis thaliana anion/proton exchanger AtCLCa is involved in vacuolar accumulation of nitrate. We investigated the role of AtCLCa in leaf guard cells, a specialized plant epidermal cell that controls gas exchange and water loss through pores called stomata. We showed that AtCLCa not only fulfilled the expected role of accumulating anions in the vacuole during stomatal opening but also mediated anion release during stomatal closure in response to the stress hormone abscisic acid (ABA). We found that this dual role resulted from a phosphorylation-dependent change in the activity of AtCLCa. The protein kinase OST1 (also known as SnRK2.6) is a key signaling player and central regulator in guard cells in response to ABA. Phosphorylation of Thr(38) in the amino-terminal cytoplasmic domain of AtCLCa by OST1 increased the outward anion fluxes across the vacuolar membrane, which are essential for stomatal closure. We provide evidence that bidirectional activities of an intracellular CLC exchanger are physiologically relevant and that phosphorylation regulates the transport mode of this exchanger. PMID:25005229

  15. Using the water signal to detect invisible exchanging protons in the catalytic triad of a serine protease

    PubMed Central

    Lauzon, Carolyn B.; van Zijl, Peter; Stivers, James T.

    2011-01-01

    Chemical Exchange Saturation Transfer (CEST) is an MRI approach that can indirectly detect exchange broadened protons that are invisible in traditional NMR spectra. We modified the CEST pulse sequence for use on high-resolution spectrometers and developed a quantitative approach for measuring exchange rates based upon CEST spectra. This new methodology was applied to the rapidly exchanging Hδ1 and Hε2 protons of His57 in the catalytic triad of bovine chymotrypsinogen-A (bCT-A). CEST enabled observation of Hε2 at neutral pH values, and also allowed measurement of solvent exchange rates for His57-Hδ1 and His57-Hε2 across a wide pH range (3–10). Hδ1 exchange was only dependent upon the charge state of the His57 (kex,Im+ = 470 s−1, kex,Im = 50 s−1), while Hε2 exchange was found to be catalyzed by hydroxide ion and phosphate base (kOH− = 1.7 × 1010 M−1s−1, kHPO42−=1.7×106M−1s−1), reflecting its greater exposure to solute catalysts. Concomitant with the disappearance of the Hε2 signal as the pH was increased above its pKa, was the appearance of a novel signal (δ = 12 ppm), which we assigned to Hγ of the nearby Ser195 nucleophile, that is hydrogen bonded to Nε2 of neutral His57. The chemical shift of Hγ is about 7 ppm downfield from a typical hydroxyl proton, suggesting a highly polarized O-Hγ bond. The significant alkoxide character of Oγ indicates that Ser195 is preactivated for nucleophilic attack before substrate binding. CEST should be generally useful for mechanistic investigations of many enzymes with labile protons involved in active site chemistry. PMID:21809183

  16. Characterization of commercial proton exchange membrane materials after exposure to beta and gamma radiation

    SciTech Connect

    Thomson, S.N.; Carson, R.; Muirhead, C.; Li, H.; Castillo, I.; Boniface, H.; Suppiah, S.; Ratnayake, A.; Robinson, J.

    2015-03-15

    Proton Exchange Membrane (PEM) type electrolysis cells have a potential use for tritium removal and heavy water upgrading. AECL is currently exposing various commercial PEM materials to both gamma (Cobalt-60 source) and beta (tritiated water) radiation to study the effects of radiation on these materials. This paper summarizes the testing methods and results that have been collected to date. The PEM materials that are or have been exposed to radiation are: Nafion 112, 212, 117 and 1110. Membrane characterization pre- and post- exposure consists of non-destructive inspection (FTIR, SEM/XPS), mechanical (tensile strength, percentage elongation, and modulus), electrical (resistance), or chemical (ion-exchange capacity - IEC). It has appeared that the best characterization techniques to compare exposed versus unexposed membranes were IEC, ultimate tensile strength and percent elongation. These testing techniques are easy and cheap to perform. The non-destructive tests, such as SEM and FTIR did not provide particularly useful information on radiation-induced degradation. Where changes in material properties were measured after radiation exposure, they would be expected to result in poorer cell performance. However, for modest γ-radiation exposure, all membranes showed a slight decrease in cell voltage (better performance). In contrast, the one β-radiation exposed membrane did show the expected increase in cell voltage. The counterintuitive trend for γ-radiation exposed membranes is not yet understood. Based on these preliminary results, it appears that γ- and β-radiation exposures have different effects.

  17. Investigations on degradation of the long-term proton exchange membrane water electrolysis stack

    NASA Astrophysics Data System (ADS)

    Sun, Shucheng; Shao, Zhigang; Yu, Hongmei; Li, Guangfu; Yi, Baolian

    2014-12-01

    A 9-cell proton exchange membrane (PEM) water electrolysis stack is developed and tested for 7800 h. The average degradation rate of 35.5 μV h-1 per cell is measured. The 4th MEA of the stack is offline investigated and characterized. The electrochemical impedance spectroscopy (EIS) shows that the charge transfer resistance and ionic resistance of the cell both increase. The linear sweep scan (LSV) shows the hydrogen crossover rate of the membrane has slight increase. The electron probe X-ray microanalyze (EPMA) illustrates further that Ca, Cu and Fe elements distribute in the membrane and catalyst layers of the catalyst-coated membranes (CCMs). The cations occupy the ion exchange sites of the Nafion polymer electrolyte in the catalyst layers and membrane, which results in the increase in the anode and the cathode overpotentials. The metallic impurities originate mainly from the feed water and the components of the electrolysis unit. Fortunately, the degradation was reversible and can be almost recovered to the initial performance by using 0.5 M H2SO4. This indicates the performance degradation of the stack running 7800 h is mainly caused by a recoverable contamination.

  18. Proton Form Factor Puzzle and the CEBAF Large Acceptance Spectrometer (CLAS) two-photon exchange experiment

    NASA Astrophysics Data System (ADS)

    Rimal, Dipak

    The electromagnetic form factors are the most fundamental observables that encode information about the internal structure of the nucleon. The electric (GE) and the magnetic ( GM) form factors contain information about the spatial distribution of the charge and magnetization inside the nucleon. A significant discrepancy exists between the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors of the proton. One possible explanation for the discrepancy is the contributions of two-photon exchange (TPE) effects. Theoretical calculations estimating the magnitude of the TPE effect are highly model dependent, and limited experimental evidence for such effects exists. Experimentally, the TPE effect can be measured by comparing the ratio of positron-proton elastic scattering cross section to that of the electron-proton [R = sigma(e +p)/sigma(e+p)]. The ratio R was measured over a wide range of kinematics, utilizing a 5.6 GeV primary electron beam produced by the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This dissertation explored dependence of R on kinematic variables such as squared four-momentum transfer (Q2) and the virtual photon polarization parameter (epsilon). A mixed electron-positron beam was produced from the primary electron beam in experimental Hall B. The mixed beam was scattered from a liquid hydrogen (LH2) target. Both the scattered lepton and the recoil proton were detected by the CEBAF Large Acceptance Spectrometer (CLAS). The elastic events were then identified by using elastic scattering kinematics. This work extracted the Q2 dependence of R at high epsilon(epsilon > 0.8) and the $epsilon dependence of R at approx 0.85 GeV2. In these kinematics, our data confirm the validity of the hadronic calculations of the TPE effect by Blunden, Melnitchouk, and Tjon. This hadronic TPE effect, with additional corrections contributed by higher excitations of the intermediate state nucleon, largely

  19. Enhancing proton conduction via doping of supramolecular liquid crystals (4-alkoxybenzoic acids) with imidazole

    NASA Astrophysics Data System (ADS)

    Liang, Ting; Wu, Yong; Tan, Shuai; Yang, Xiaohui; Wei, Bingzhuo

    2015-09-01

    Enhancing proton conduction via doping was first achieved in hydrogen-bonded liquid crystals consisting of benzoic acids. Supramolecular liquid crystals formed by pure 4-alkoxybenzoic acids (nAOBA, n = 8, 10, 12) exhibited the maximum proton conductivity of 5.0 × 10-8 S cm-1. Doping of nAOBA with 25 mol% imidazole (Im0.25) had little impact on mesomorphism but increased proton conductivities by at least 3 orders of magnitude. The liquid crystals formed by nAOBA-Im0.25 exhibited the maximum proton conductivity of 1.9 × 10-4 S cm-1. It was proposed that structure diffusion of imidazole bridged interdimer proton transfer to form continuous conducting pathways in mesomorphic nAOBA-Im0.25.

  20. Novel solid state proton-conductors based on polymeric non-oxy acids. Final report

    SciTech Connect

    Appleby, A.J.; Srinivasan, S.; Parthasarathy, A.; Gonzalez, E.R.; DesMarteau, D.; Gillette, M.S.; Ghosh, J.K.; Jalan, V.; Desai, M.

    1992-01-01

    Objectives of this project were to prepare and characterize novel solid state proton-conductors and to evaluate these compounds as fuel cell electrolytes. The thrust was on the synthesis of new proton-conducting ``model`` and ``polymeric`` compounds, based on acid functions of the type (R{sub f}SO{sub 2}){sub 2}NH and (R{sub f}SO{sub 2}){sub 2}CH{sub 2} in appropriate fluorinated carbon structures, their physics-chemical characterization (Infra-red, Nuclear Magnetic Resonance, Differential Scanning Calorimetry, and X-ray Diffraction), and is pro. evaluation as candidate fuel cell electrolytes for use at elevated temperatures. This project consisted of four tasks (i) Synthesis of Proton-Conducting Polymer Electrolytes; (ii) Physical and Chemical Characterization of Proton-Conducting Polymer Electrolytes; (iii) Electrochemical Characterization of Proton-Conducting Polymer Electrolytes; and (iv) Evaluation of Proton-Conducting Polymer Electrolytes for Fuel Cells.

  1. The Protonation Site of para-Dimethylaminobenzoic Acid Using Atmospheric Pressure Ionization Methods

    NASA Astrophysics Data System (ADS)

    Chai, Yunfeng; Weng, Guofeng; Shen, Shanshan; Sun, Cuirong; Pan, Yuanjiang

    2015-04-01

    The protonation site of para-dimethylaminobenzoic acid ( p-DMABA) was investigated using atmospheric pressure ionization methods (ESI and APCI) coupled with collision-induced dissociation (CID), nuclear magnetic resonance (NMR), and computational chemistry. Theoretical calculations and NMR experiments indicate that the dimethyl amino group is the preferred site of protonation both in the gas phase and aqueous solution. Protonation of p-DMABA occurs at the nitrogen atom by ESI independent of the solvents and other operation conditions under typical thermodynamic control. However, APCI produces a mixture of the nitrogen- and carbonyl oxygen-protonated p-DMABA when aprotic organic solvents (acetonitrile, acetone, and tetrahydrofuran) are used, exhibiting evident kinetic characteristics of protonation. But using protic organic solvents (methanol, ethanol, and isopropanol) in APCI still leads to the formation of thermodynamically stable N-protonated p-DMABA. These structural assignments were based on the different CID behavior of the N- and O-protonated p-DMABA. The losses of methyl radical and water are the diagnostic fragmentations of the N- and O-protonated p-DMABA, respectively. In addition, the N-protonated p-DMABA is more stable than the O-protonated p-DMABA in CID revealed by energy resolved experiments and theoretical calculations.

  2. Measuring the proton conductivity of ion-exchange membranes using electrochemical impedance spectroscopy and through-plane cell.

    PubMed

    Müller, Franciélli; Ferreira, Carlos A; Azambuja, Denise S; Alemán, Carlos; Armelin, Elaine

    2014-01-30

    The role of the incorporation of conducting polymer (CP), doped with different sulfonic acid organic molecules, in polystyrene (PS) and high-impact polystyrene (HIPS) with poly(styrene-ethylene-butylene) (SEBS) triblock copolymer has been investigated. Two factors associated with this model membrane system are addressed: (i) the influence of the presence of a low concentration of doped conducting polymer and (ii) the influence of the membrane preparation method. Membrane characterization and bulk conductivity measurements allowed the conclusion that proton conductivity has been promoted by the addition of CP; the best results were achieved for PAni-CSA, in either PS/SEBS or HIPS/SEBS blends. Additionally, the water uptake only decreased with the addition of PAni-doped molecules compared to the pure copolymer, without loss of ion-exchange capacity (IEC). Electrodialysis efficiency for HIPS/SEBS (before annealing) is higher than that for HIPS/SEBS (after annealing), indicating that membrane preparation method is crucial. Finally, through-plane cell arrangement proved to be an effective, quick, and time-saving tool for studying the main resistance parameters of isolating polymers, which is useful for application in industry and research laboratories working with membranes for electrodialysis or fuel cells. PMID:24428522

  3. Low platinum loading for high temperature proton exchange membrane fuel cell developed by ultrasonic spray coating technique

    NASA Astrophysics Data System (ADS)

    Su, Huaneng; Jao, Ting-Chu; Barron, Olivia; Pollet, Bruno G.; Pasupathi, Sivakumar

    2014-12-01

    This paper reports use of an ultrasonic-spray for producing low Pt loadings membrane electrode assemblies (MEAs) with the catalyst coated substrate (CCS) fabrication technique. The main MEA sub-components (catalyst, membrane and gas diffusion layer (GDL)) are supplied from commercial manufacturers. In this study, high temperature (HT) MEAs with phosphoric acid (PA)-doped poly(2,5-benzimidazole) (AB-PBI) membrane are fabricated and tested under 160 °C, hydrogen and air feed 100 and 250 cc min-1 and ambient pressure conditions. Four different Pt loadings (from 0.138 to 1.208 mg cm-2) are investigated in this study. The experiment data are determined by in-situ electrochemical methods such as polarization curve, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The high Pt loading MEA exhibits higher performance at high voltage operating conditions but lower performances at peak power due to the poor mass transfer. The Pt loading 0.350 mg cm-2 GDE performs the peak power density and peak cathode mass power to 0.339 W cm-2 and 0.967 W mgPt-1, respectively. This work presents impressive cathode mass power and high fuel cell performance for high temperature proton exchange membrane fuel cells (HT-PEMFCs) with low Pt loadings.

  4. Proton transfer reactions between nitric acid and acetone, hydroxyacetone, acetaldehyde and benzaldehyde in the solid phase.

    PubMed

    Lasne, Jérôme; Laffon, Carine; Parent, Philippe

    2012-12-01

    The heterogeneous and homogeneous reactions of acetone, hydroxyacetone, acetaldehyde and benzaldehyde with solid nitric acid (HNO(3)) films have been studied with Reflection-Absorption Infrared Spectroscopy (RAIRS) under Ultra-High Vacuum (UHV) conditions in the 90-170 K temperature range. In the bulk or at the surface of the films, nitric acid transfers its proton to the carbonyl function of the organic molecules, producing protonated acetone-H(+), hydroxyacetone-H(+), acetaldehyde-H(+) and benzaldehyde-H(+), and nitrate anions NO(3)(-), a reaction not observed when nitric acid is previously hydrated [J. Lasne, C. Laffon and Ph. Parent, Phys. Chem. Chem. Phys., 2012, 14, 697]. This provides a molecular-scale description of the carbonyl protonation reaction in an acid medium, the first step of the acid-catalyzed condensation of carbonyl compounds, fuelling the growth of secondary organic aerosols (SOA) in the atmosphere. PMID:23090634

  5. Final Project Report for project titled "Fluoroalkylphosphonic-acid-based proton conductors"

    SciTech Connect

    Stephen Creager

    2011-12-08

    The overall objective of this research was to create new proton-conducting polymer electrolytes for use in energy conversion devices including hydrogen fuel cells that could operate at high temperatures (95-130 C) and under low relative humidity (< 50% RH) conditions. The new polymers were based on the fluoroalkylphosphonic and phosphinic acid (FPA) groups (see illustration below) which offer prospects for rapid proton transport by a proton-hopping mechanism similar to that which operates in phosphoric acid, a well-known proton-transporting electrolyte that is used in a class of hydrogen fuel cells that work well under the conditions noted above and are already commercially successful. The two specific project objectives were as follows: (1) synthesize and characterize new proton-conducting electrolytes based on the fluoroalkylphosphonic and phosphinic acid (FPA) functional groups; and (2) create and apply new computer models to study protonic conduction in FPA-based electrolytes. The project was successful in creating the desired polymer electrolytes and also a series of molecular model compounds which were used to study proton transport in FPA electrolytes in general. Computer models were created to study both structure and proton-transport dynamics in the electrolytes, particularly the molecular model compounds. Rapid proton transport by a hopping mechanism was found in many of the model compounds and correlations with transport rates with molecular structure were identified. Several polymeric analogs of FPA model compounds were prepared and studied, however FPA-based polymeric materials having very high protonic conductivities under either wet or dry conditions were not obtained. Several possible reasons for the failure of polymeric materials to exhibit the expected high protonic conductivities were identified, including a failure of the polymers to adopt the phase-separated secondary structure/morphology necessary for high proton conductivity, and an

  6. Investigation of high temperature operation of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Adjemian, Kevork Tro

    Proton exchange membrane fuel cells (PEMFCs) have garnered much attention in the media over the past years as they can provide a clean, environmentally friendly alternative to internal combustion engines. PEMFCs also have the flexibility to operate on many different types of fuels, thereby diminishing our reliance on foreign oil. PEMFCs, however, suffer from many drawbacks which need to be overcome before mass production becomes viable. One drawback is the expense of the fuel cell system, costing several times more than existing technologies. Another problem is that if the fuel cell is running on reformed fuels, trace amounts of carbon monoxide (10 ppm) in the hydrogen gas stream will completely poison the anode electrocatalyst, killing the PEMFC. Also, as a lot of waste heat is generated, a very elaborate cooling system needs to be used, making the overall system more expensive and complex. A possible solution to both the carbon monoxide poisoning and thermal management of a PEMFC is to elevate its operating temperature above 100°C. Unfortunately, current state-of-the-art electrolytes used in PEMFCs, i.e. Nafion 115, rely on water for the conduction of protons and by elevating the temperature, water loss occurs due to evaporation resulting in inadequate PEMFC performance. This thesis delves into the modification of Nafion and similar electrolytes to permit PEMFC operation above 100°C. This was accomplished by impregnating the pores of the Nafion with hydrophilic inorganic materials-silicon oxide via sol-gel processing and various inorganic particles. By performing these modifications to the various electrolytes, several composite membranes performed exceptionally well at an operating temperature of 130°C and demonstrated carbon monoxide tolerance of up to 500 ppm. In addition, a theory on how these materials help improve the water management characteristics of Nafion was developed, laying the foundation for the development of a completely novel membrane to

  7. Characterization of Polyethylene-Graft-Sulfonated Polyarylsulfone Proton Exchange Membranes for Direct Methanol Fuel Cell Applications

    PubMed Central

    Kim, Hyung Kyu; Zhang, Gang; Nam, Changwoo; Chung, T.C. Mike

    2015-01-01

    This paper examines polymer film morphology and several important properties of polyethylene-graft-sulfonated polyarylene ether sulfone (PE-g-s-PAES) proton exchange membranes (PEMs) for direct methanol fuel cell applications. Due to the extreme surface energy differences between a semi-crystalline and hydrophobic PE backbone and several amorphous and hydrophilic s-PAES side chains, the PE-g-s-PAES membrane self-assembles into a unique morphology, with many proton conductive s-PAES channels embedded in the stable and tough PE matrix and a thin hydrophobic PE layer spontaneously formed on the membrane surfaces. In the bulk, these membranes show good mechanical properties (tensile strength >30 MPa, Young’s modulus >1400 MPa) and low water swelling (λ < 15) even with high IEC >3 mmol/g in the s-PAES domains. On the surface, the thin hydrophobic and semi-crystalline PE layer shows some unusual barrier (protective) properties. In addition to exhibiting higher through-plane conductivity (up to 160 mS/cm) than in-plane conductivity, the PE surface layer minimizes methanol cross-over from anode to cathode with reduced fuel loss, and stops the HO• and HO2• radicals, originally formed at the anode, entering into PEM matrix. Evidently, the thin PE surface layer provides a highly desirable protecting layer for PEMs to reduce fuel loss and increase chemical stability. Overall, the newly developed PE-g-s-PAES membranes offer a desirable set of PEM properties, including conductivity, selectivity, mechanical strength, stability, and cost-effectiveness for direct methanol fuel cell applications. PMID:26690232

  8. A Durable Alternative for Proton-Exchange Membranes: Sulfonated Poly(Benzoxazole Thioether Sulfone)s

    SciTech Connect

    Zhao, Dan; Li, Jin Hui; Song, Min Kyu; Yi, Baolian; Zhang, Huamin; Liu, Meilin

    2011-02-24

    To develop a durable proton-exchange membrane (PEM) for fuel-cell applications, a series of sulfonated poly(benzoxazole thioether sulfone)s ( SPTESBOs) are designed and synthesized, with anticipated good dimensional stability (via acid–base cross linking), improved oxidative stability against free radicals (via incorporation of thioether groups), and enhanced inherent stability (via elimination of unstable end groups) of the backbone. The structures and the degree of sulfonation of the copolymers are characterized using Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy ({sup 1}H NMR and {sup 19}F NMR). The electrochemical stabilities of the monomers are examined using cyclic voltammetry in a typical three-electrode cell configuration. The physicochemical properties of the membranes vital to fuel-cell performance are also carefully evaluated under conditions relevant to fuel-cell operation, including chemical and thermal stability, proton conductivity, solubility in different solvents, water uptake, and swelling ratio. The new membranes exhibit low dimensional change at 25°C to 90°C and excellent thermal stability up to 250°C. Upon elimination of unstable end groups, the co-polymers display enhanced chemical resistance and oxidative stability in Fenton's test. Further, the SPTESBO-HFB-60 (HFB-60=hexafluorobenzene, 60 mol% sulfone) membrane displays comparable fuel-cell performance to that of an NRE 212 membrane at 80°C under fully humidified condition, suggesting that the new membranes have the potential to be more durable but less expensive for fuel-cell applications.

  9. Comparison of platinum/MWCNTs Nanocatalysts Synthesis Processes for Proton Exchange Membrane Fuel Cells

    NASA Astrophysics Data System (ADS)

    Liu, Xuan

    Due to the growing concerns on the depletion of petroleum based energy resources and climate change; fuel cell technologies have received much attention in recent years. Proton exchange membrane fuel cell (PEMFCs) features high energy conversion efficiency and nearly zero greenhouse gas emissions, because of its combination of the hydrogen oxidation reaction (HOR) at anode side and oxygen reduction reaction (ORR) at cathode side. Synthesis of Pt nanoparticles supported on multi walled carbon nanotubes (MWCNTs) possess a highly durable electrochemical surface area (ESA) and show good power output on proton exchange membrane (PEM) fuel cell performance. Platinum on multi-walled carbon nanotubes (MWCNTs) support were synthesized by two different processes to transfer PtCl62- from aqueous to organic phase. While the first method of Pt/MWCNTs synthesis involved dodecane thiol (DDT) and octadecane thiol (ODT) as anchoring agent, the second method used ammonium lauryl sulfate (ALS) as the dispersion/anchoring agent. The particle size and distribution of platinum were examined by high-resolution transmission electron microscope (HRTEM). The TEM images showed homogenous distribution and uniform particle size of platinum deposited on the surface of MWCNTs. The single cell fuel cell performance of the Pt/MWCNTs synthesized thiols and ALS based electrode containing 0.2 (anode) and 0.4 mg (cathode) Pt.cm-2 were evaluated using Nafion-212 electrolyte with H2 and O2 gases at 80 °C and ambient pressure. The catalyst synthesis with ALS is relatively simple compared to that with thiols and also showed higher performance (power density reaches about 1070 mW.cm -2). The Electrodes with Pt/MWCNTs nanocatalysts synthesized using ALS were characterized by cyclic voltammetry (CV) for durability evaluation using humidified H2 and N2 gases at room temperature (21 °C) along with commercial Pt/C for comparison. The ESA measured by cyclic voltammetry between 0.15 and 1.2 V showed significant

  10. Design, integration and control of proton exchange membrane electrolyzer for wind based renewable energy applications

    NASA Astrophysics Data System (ADS)

    Harrison, Kevin W.

    This research endeavor began with the design and construction of a new hydrogen test facility at the National Renewable Energy Laboratory (NREL). To improve the electrical link of wind-based electrolysis the characterization of a proton exchange membrane (PEM) electrolyzer under varying input power was performed at NRELs new test facility. The commercially available electrolyzer from Proton Energy Systems (PES) was characterized using constant direct current (DC), sinusoidally varying DC, photovoltaics and variable magnitude and frequency energy from a 10 kW wind turbine. At rated stack current and ˜ 40°C the system efficiency of the commercial electrolyzer was measured to be 55%. At lower stack current it was shown that commercial electrolyzer system efficiency falls because of the continuous hydrogen purge (˜0.1 Nm3 hr-1) used to maintain the hydrogen desiccant drying system. A novel thermoelectric-based dew point controller is designed and modeled to reduce the penalty to renewable sources because they do not always operate at 100% of rated stack current. It is predicted that the thermoelectric design when operated 100% of the time at full current to the thermoelectric modules would consume 3.1 kWh kg -1 of hydrogen. Using the higher heating value of hydrogen and a stack efficiency of 60% to produce the hydrogen that is continuously vented, the desiccant system consumes about 5.7 kWh kg-1. Design of the UND electrolyzer sub-systems responsible for all aspects of water, power to the stack, and hydrogen conditioning enables more flexible and precise experimental data to be obtained than from an off-the-shelf system. Current-voltage (IV) characteristic curves were obtained on the UND system at temperatures between 7--70°C. The anode and cathode exchange current densities are fitted to 2.0 E-06 e0.043T and 0.12 e 0.026T A cm-2 respectively. Stack conductivity was fitted to 0.001T + 0.03 S cm-1. The three coefficients represent physical stack parameters and are

  11. Electrical characterization of proton conducting polymer electrolyte based on bio polymer with acid dopant

    NASA Astrophysics Data System (ADS)

    Kalaiselvimary, J.; Pradeepa, P.; Sowmya, G.; Edwinraj, S.; Prabhu, M. Ramesh

    2016-05-01

    This study describes the biodegradable acid doped films composed of chitosan and Perchloric acid with different ratios (2.5 wt %, 5 wt %, 7.5 wt %, 10 wt %) was prepared by the solution casting technique. The temperature dependence of the proton conductivity of complex electrolytes obeys the Arrhenius relationship. Proton conductivity of the prepared polymer electrolyte of the bio polymer with acid doped was measured to be approximately 5.90 × 10-4 Scm-1. The dielectric data were analyzed using Complex impedance Z*, Dielectric loss ɛ', Tangent loss for prepared polymer electrolyte membrane with the highest conductivity samples at various temperature.

  12. Ca2+/H+ exchange in acidic vacuoles of Trypanosoma brucei.

    PubMed Central

    Vercesi, A E; Moreno, S N; Docampo, R

    1994-01-01

    The use of digitonin to permeabilize the plasma membrane of Trypanosoma brucei procyclic and bloodstream trypomastigotes allowed the identification of a non-mitochondrial nigericin-sensitive Ca2+ compartment. The proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) was able to cause Ca2+ release from this compartment, which was also sensitive to sodium orthovanadate. Preincubation of the cells with the vacuolar H(+)-ATPase inhibitor bafilomycin A1 greatly reduced the nigericin-sensitive Ca2+ compartment. Bafilomycin A1 inhibited the initial rate of ATP-dependent non-mitochondrial Ca2+ uptake and stimulated the initial rate of nigericin-induced Ca2+ release by permeabilized procyclic trypomastigotes. ATP-dependent and bafilomycin A1- and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl)-sensitive Acridine Orange uptake was demonstrated in permeabilized cells. Under these conditions Acridine Orange was concentrated in abundant cytoplasmic round vacuoles by a process inhibited by bafilomycin A1, NBD-Cl, nigericin, and Ca2+. Vanadate or EGTA significantly increased Acridine Orange uptake, while Ca2+ released Acridine Orange from these preparations, thus suggesting that the dye and Ca2+ were being accumulated in the same acidic vacuole. Acridine Orange uptake was reversed by nigericin, bafilomycin A1 and NH4Cl. The results are consistent with the presence of a Ca2+/H(+)-ATPase system pumping Ca2+ into an acidic vacuole, that we tentatively named the acidocalcisome. Images Figure 5 PMID:7998937

  13. Low proton conductance of plant cuticles and its relevance to the acid-growth theory

    SciTech Connect

    Dreyer, S.A.; Seymour, V.; Cleland, R.E.

    1981-09-01

    Evidence obtained on the relation between the pH of the medium and the growth of intact stem sections is compatible with the acid-growth theory only if the proton conductance of the cuticle is an effective barrier to the entry or exit of protons from the tissue. By measuring the rate at which protons cross frozen-thawed epidermal strips of sunflower (Helianthus annus L.) and soybean hypocotyls (Glycine max Morr.) and enzymically isolated cuticles of Berberis aquifolium Persh. and tomato (Lycopersicum esculentum Mill.) fruit, we have now demonstrated the low proton conductance of the cuticular layer. Unless the conductance is enhanced by abrasion of the cuticle or by removal of the cuticular waxes, proton movement into and out of a tissue across the cuticle will be significant only over long time periods.

  14. Characterization and Modification of Electrospun Fiber Mats for Use in Composite Proton Exchange Membranes

    NASA Astrophysics Data System (ADS)

    Mannarino, Matthew Marchand

    . Post-spin thermal annealing was used to modify the fiber morphology, inter-fiber welding, and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient, and wear rate were characterized as functions of the annealing temperature. The Young's moduli, yield stresses and toughnesses of the PA 6(3)T nonwoven mats improved by two- to ten-fold when annealed slightly above the glass transition temperature, but at the expense of mat porosity. The mechanical and tribological properties of the thermally annealed P A 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous P A 6(3)T electrospun mats annealed near the glass transition temperature. The wear rates for both polymer systems correlate with the yield properties of the mat, in accordance with a modified Ratner-Lancaster model. The variation in mechanical and tribological properties of the mats with increasing annealing temperature is consistent with the formation of fiber-to-fiber junctions and a mechanism of abrasive wear that involves the breakage of these junctions between fibers. A mechanically robust proton exchange membrane with high ionic conductivity and selectivity is an important component in many electrochemical energy devices such as fuel cells, batteries, and photovoltaics. The ability to control and improve independently the mechanical response, ionic conductivity, and selectivity properties of a membrane is highly desirable in the development of next generation electrochemical devices. In this thesis, the use of layer-by-layer (LbL) assembly of polyelectrolytes is used to generate three different polymer film morphologies on highly porous electrospun fiber mats: webbed, conformal coating, and pore-bridging films. Specifically, depending on whether a vacuum is applied to the backside of the mat or not, the spray-LbL assembly either fills the voids of the mat with the proton

  15. Evaluation of nitrided titanium separator plates for proton exchange membrane electrolyzer cells

    NASA Astrophysics Data System (ADS)

    Toops, Todd J.; Brady, Michael P.; Zhang, Feng-Yuan; Meyer, Harry M.; Ayers, Katherine; Roemer, Andrew; Dalton, Luke

    2014-12-01

    Proton exchanges membrane (PEM) regenerative fuel cell electrolysis of water is of great recent interest as a hydrogen generation technology. Anode side titanium current collectors and separator plates used in these applications typically employ coatings of platinum group metals to achieve durability and performance requirements in the high voltage, oxidizing environment. The present work assessed the potential for lower cost surface modified titanium by both thermal (gas) nitridation and plasma nitridation approaches. The nitrided Ti was found to result in far less hydrogen uptake in coupon testing than did Pt-plated Ti. Short-term (48 h) single-cell performance at 25 °C was approximately 13% better (lower voltage) at 1.2 A cm-2 for thermal and plasma nitrided plates vs. untreated Ti. However, at 50 °C and 1.5 A cm-2, the thermally nitrided plate exhibited only on the order of 3% better behavior (lower voltage) compared to the untreated Ti and plasma nitrided Ti. Durability testing for 500 h resulted in only a minor degradation in cell performance, on the order of 1-2% voltage increase, with the best behavior exhibited by the thermally nitrided Ti plate. Despite their relatively stable cell performance, extensive local oxidation of the thermally nitrided and plasma nitrided flow field regions was observed.

  16. Fatigue and creep to leak tests of proton exchange membranes using pressure-loaded blisters

    NASA Astrophysics Data System (ADS)

    Li, Yongqiang; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Gittleman, Craig S.; Miller, Daniel P.

    In this study, three commercially available proton exchange membranes (PEMs) are biaxially tested using pressure-loaded blisters to characterize their resistance to gas leakage under either static (creep) or cyclic fatigue loading. The pressurizing medium, air, is directly used for leak detection. These tests are believed to be more relevant to fuel cell applications than quasi-static uniaxial tensile-to-rupture tests because of the use of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test, in which a bare PEM or catalyst coated membrane is clamped with gas diffusion media and flow field plates and subjected to cyclic changes in relative humidity, because of the flexibility in allowing controlled mechanical loading and accelerated testing. Nafion ® NRE-211 membranes are tested at three different temperatures and the time-temperature superposition principle is used to construct stress-lifetime master curve. Tested at 90 °C, 2%RH extruded Ion Power ® N111-IP membranes have a longer lifetime than Gore™-Select ® 57 and Nafion ® NRE-211 membranes.

  17. Method to improve catalyst layer model for modelling proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxian; Gao, Yuan; Ostadi, Hossein; Jiang, Kyle; Chen, Rui

    2015-09-01

    Correctly describing oxygen reduction within the cathode catalyst layer (CL) in modelling proton exchange membrane fuel cell is an important issue remaining unresolved. In this paper we show how to derive an agglomerate model for calculating oxygen reactions by describing dissolved oxygen in the agglomerates using two independent random processes. The first one is the probability that an oxygen molecule, which dissolves in the ionomer film on the agglomerate surface, moves into and then remains in the agglomerates; the second one is the probability of the molecule being consumed in reactions. The first probability depends on CL structure and can be directly calculated; the second one is derived by assuming that the oxygen reduction is first-order kinetic. It is found that the distribution functions of the first process can be fitted to a generalised gamma distribution function, which enables us to derive an analytical agglomerate model. We also expend the model to include oxygen dissolution in the ionomer film, and apply it to simulate cathode electrodes. The results reveal that the resistance to oxygen diffusion in ionomer film and agglomerate in modern CL is minor, and that the main potential loss is due to oxygen dissolution in the ionomer film.

  18. Chlorobenzene Poisoning and Recovery of Platinum-Based Cathodes in Proton Exchange Membrane Fuel Cells

    PubMed Central

    Zhai, Yunfeng; Baturina, Olga; Ramaker, David; Farquhar, Erik; St-Pierre, Jean; Swider-Lyons, Karen

    2015-01-01

    The platinum electrocatalysts found in proton exchange membrane fuel cells are poisoned both reversibly and irreversibly by air pollutants and residual manufacturing contaminants. In this work, the poisoning of a Pt/C PEMFC cathode was probed by a trace of chlorobenzene in the air feed. Chlorobenzene inhibits the oxygen reduction reaction and causes significant cell performance loss. The performance loss is largely restored by neat air operation and potential cycling between 0.08 V and 1.2 V under H2/N2 (anode/cathode). The analysis of emissions, in situ X-ray absorption spectroscopy and electrochemical impedance spectra show the chlorobenzene adsorption/reaction and molecular orientation on Pt surface depend on the electrode potential. At low potentials, chlorobenzene deposits either on top of adsorbed H atoms or on the Pt surface via the benzene ring and is converted to benzene (ca. 0.1 V) or cyclohexane (ca. 0 V) upon Cl removal. At potentials higher than 0.2 V, chlorobenzene binds to Pt via the Cl atom and can be converted to benzene (less than 0.3 V) or desorbed. Cl− is created and remains in the membrane electrode assembly. Cl− binds to the Pt surface much stronger than chlorobenzene, but can slowly be flushed out by liquid water. PMID:26388963

  19. Improvement in high temperature proton exchange membrane fuel cells cathode performance with ammonium carbonate

    NASA Astrophysics Data System (ADS)

    Song, Ying; Wei, Yu; Xu, Hui; Williams, Minkmas; Liu, Yuxiu; Bonville, Leonard J.; Russell Kunz, H.; Fenton, James M.

    Proton exchange membrane (PEM) fuel cells with optimized cathode structures can provide high performance at higher temperature (120 °C). A "pore-forming" material, ammonium carbonate, applied in the unsupported Pt cathode catalyst layer of a high temperature membrane electrode assembly enhanced the catalyst activity and minimized the mass-transport limitations. The ammonium carbonate amount and Nafion ® loading in the cathode were optimized for performance at two conditions: 80 °C cell temperature with 100% anode/75% cathode R.H. and 120 °C cell temperature with 35% anode/35% cathode R.H., both under ambient pressure. A cell with 20 wt.% ammonium carbonate and 20 wt.% Nafion ® operating at 80 °C and 120 °C presented the maximum cell performance. Hydrogen/air cell voltages at a current density of 400 mA cm -2 using the Ionomem/UConn membrane as the electrolyte with a cathode platinum loading of 0.5 mg cm -2 were 0.70 V and 0.57 V at the two conditions, respectively. This was a 19% cell voltage increase over a cathode without the "pore-forming" ammonium carbonate at the 120 °C operating condition.

  20. Impact of heat and water management on proton exchange membrane fuel cells degradation in automotive application

    NASA Astrophysics Data System (ADS)

    Nandjou, F.; Poirot-Crouvezier, J.-P.; Chandesris, M.; Blachot, J.-F.; Bonnaud, C.; Bultel, Y.

    2016-09-01

    In Proton Exchange Membrane Fuel Cells, local temperature is a driving force for many degradation mechanisms such as hygrothermal deformation and creep of the membrane, platinum dissolution and bipolar plates corrosion. In order to investigate and quantify those effects in automotive application, durability testing is conducted in this work. During the ageing tests, the local performance and temperature are investigated using in situ measurements of a printed circuit board. At the end of life, post-mortem analyses of the aged components are conducted. The experimental results are compared with the simulated temperature and humidity in the cell obtained from a pseudo-3D multiphysics model in order to correlate the observed degradations to the local conditions inside the stack. The primary cause of failure in automotive cycling is pinhole/crack formation in the membrane, induced by high variations of its water content over time. It is also observed that water condensation largely increases the probability of the bipolar plates corrosion while evaporation phenomena induce local deposits in the cell.

  1. Degradation of proton exchange membrane fuel cells due to CO and CO 2 poisoning

    NASA Astrophysics Data System (ADS)

    Yan, Wei-Mon; Chu, Hsin-Sen; Lu, Meng-Xi; Weng, Fang-Bor; Jung, Guo-Bin; Lee, Chi-Yuan

    The CO and CO 2 poisoning effects on the degradation of cell performance of proton exchange membrane fuel cell (PEMFC) under transient stage were investigated. The mechanism of CO poisoning lies in the preferential adsorbing of CO to the platinum surface and the blocking of active sites of hydrogen. These phenomena were described with adsorption, desorption, and electro-oxidation processes of CO and hydrogen in the present work. In addition, it is well known that the reverse water gas shift reaction (RWGS) is the main effect of the CO 2 poisoning, through which a large part of the catalytic surface area becomes inactive due to the hydrogen dissociation. The predicted results showed that, by contaminating the fuel with 10 ppm CO at the condition of P H = 0.8 atm and PCO2 = 0.2 atm , the current density of the PEM fuel cell was lowered 28% with rate constant of RWGS k rs from zero to 0.02. With 50 ppm CO, the performance drop was only 18%. For the reformed gas, CO 2 poisoning became much more significantly when the CO content in the reactant gas was small.

  2. Femtoelectron-Based Terahertz Imaging of Hydration State in a Proton Exchange Membrane Fuel Cell

    NASA Astrophysics Data System (ADS)

    Buaphad, P.; Thamboon, P.; Kangrang, N.; Rhodes, M. W.; Thongbai, C.

    2015-08-01

    Imbalanced water management in a proton exchange membrane (PEM) fuel cell significantly reduces the cell performance and durability. Visualization of water distribution and transport can provide greater comprehension toward optimization of the PEM fuel cell. In this work, we are interested in water flooding issues that occurred in flow channels on cathode side of the PEM fuel cell. The sample cell was fabricated with addition of a transparent acrylic window allowing light access and observed the process of flooding formation (in situ) via a CCD camera. We then explore potential use of terahertz (THz) imaging, consisting of femtoelectron-based THz source and off-angle reflective-mode imaging, to identify water presence in the sample cell. We present simulations of two hydration states (water and nonwater area), which are in agreement with the THz image results. A line-scan plot is utilized for quantitative analysis and for defining spatial resolution of the image. Implementing metal mesh filtering can improve spatial resolution of our THz imaging system.

  3. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    SciTech Connect

    WANG,Z.H.; WANG,C.Y.; CHEN,KEN S.

    2000-03-20

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Four regimes of water distribution and transport are classified by defining three threshold current densities and a maximum current density. They correspond to first appearance of liquid water at the membrane/cathode interface, extension of the gas-liquid two-phase zone to the cathode/channel interface, saturated moist air exiting the gas channel, and complete consumption of oxygen by the electrochemical reaction. When the cell operates above the first threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multi-component mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A/cm{sup 2}.

  4. Prognostics of Proton Exchange Membrane Fuel Cells stack using an ensemble of constraints based connectionist networks

    NASA Astrophysics Data System (ADS)

    Javed, Kamran; Gouriveau, Rafael; Zerhouni, Noureddine; Hissel, Daniel

    2016-08-01

    Proton Exchange Membrane Fuel Cell (PEMFC) is considered the most versatile among available fuel cell technologies, which qualify for diverse applications. However, the large-scale industrial deployment of PEMFCs is limited due to their short life span and high exploitation costs. Therefore, ensuring fuel cell service for a long duration is of vital importance, which has led to Prognostics and Health Management of fuel cells. More precisely, prognostics of PEMFC is major area of focus nowadays, which aims at identifying degradation of PEMFC stack at early stages and estimating its Remaining Useful Life (RUL) for life cycle management. This paper presents a data-driven approach for prognostics of PEMFC stack using an ensemble of constraint based Summation Wavelet- Extreme Learning Machine (SW-ELM) models. This development aim at improving the robustness and applicability of prognostics of PEMFC for an online application, with limited learning data. The proposed approach is applied to real data from two different PEMFC stacks and compared with ensembles of well known connectionist algorithms. The results comparison on long-term prognostics of both PEMFC stacks validates our proposition.

  5. Comparing shut-down strategies for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Oyarce, Alejandro; Zakrisson, Erik; Ivity, Matthew; Lagergren, Carina; Ofstad, Axel Baumann; Bodén, Andreas; Lindbergh, Göran

    2014-05-01

    Application of system strategies for mitigating carbon corrosion of the catalyst support in proton exchange fuel cells (PEMFCs) is a requirement for PEMFC systems, especially in the case of systems for transport application undergoing thousands of start-ups and shut-downs (SU/SD) during its lifetime. This study compares several of the most common shut-down strategies for 1100 cycles SU/SD cycles at 70 °C and 80% RH using commercially available fuel cell components. Each cycle simulates a prolonged shut-down, i.e. finishing each cycle with air filled anode and cathode. Furthermore, all start-ups are unprotected, i.e. introducing the H2 rich gas into an air filled anode. Finally, each cycle also includes normal fuel cell operation at 0.5 A cm-2 using synthetic reformate/air. H2 purge of the cathode and O2 consumption using a load were found to be the most effective strategies. The degradation rate using the H2 purge strategy was 23 μV cycle-1 at 0.86 A cm-2 using H2 and air at the anode and cathode, respectively. This degradation rate may be regarded as a generally low value, especially considering that this value also includes the degradation rate caused by unprotected start-ups.

  6. Binary and ternary nano-catalysts as cathode materials in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Trimm, Bryan Dunning

    The need for alternative energy, in order to reduce dependence on petroleum based fuels, has increased in recent years. Public demand is at an all-time high for low emitting or none polluting energy sources, driving the research for cleaner technology. Lithium batteries and fuel cells have the ability to produce this alternative energy with much cleaner standards, while allowing for portability and high energy densities. This work focuses on the performance of nanocatalysts in Proton Exchange Membrane Fuel Cell or PEMFC. A key technical challenge is the sluggish rate for oxygen reduction reaction at the cathode of PEMFC, which requires highly-active and stable catalysts. Our investigation is directed at increasing stability and durability as well as reducing high loading of noble metals in these catalyst materials. Binary and ternary structured nanomaterials, e.g., Pt51V1Co48/C and Pd xCu1-x/C, have been synthesized and tested in a PEMFC, in order to gain a better understanding of their durability and efficiency. In addition to electrochemical characterization, synchrotron x-ray techniques at the Advance Photon Source in Argonne National Lab have also been used for the structural characterization.

  7. Recovery mechanisms in proton exchange membrane fuel cells after accelerated stress tests

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Guo, Liejin; Liu, Hongtan

    2015-11-01

    The mechanisms of performance recovery after accelerated stress test (AST) in proton exchange membrane fuel cells (PEMFCs) are systematically studied. Experiments are carried out by incorporating a well-designed performance recovery procedure right after the AST protocol. The experiment results show that the cell performance recovers significantly from the degraded state after the AST procedure. The results from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements further show that the performance recovery can be divided into kinetic and mass transport recoveries. It is further determined that the kinetic recovery, i.e. the recovery of electrochemical active area (ECA), is due to two distinct mechanisms: the reduction of platinum oxide and the re-attachment of detached platinum nanoparticles onto the carbon surface. The mass transport resistance is probably due to reduction of hydrophilic oxide groups on the carbon surface and the microstructure change that alleviates flooding. Performance comparisons show that the recovery procedure is highly effective, indicating the results of AST significantly over-estimate the true degradation in a PEM fuel cell. Therefore, a recovery procedure is highly recommended when an AST protocol is used to evaluate cell degradations to avoid over-estimating true performance degradations in PEMFCs.

  8. Proton Exchange Membrane Fuel Cell Engineering Model Powerplant. Test Report: Benchmark Tests in Three Spatial Orientations

    NASA Technical Reports Server (NTRS)

    Loyselle, Patricia; Prokopius, Kevin

    2011-01-01

    Proton exchange membrane (PEM) fuel cell technology is the leading candidate to replace the aging alkaline fuel cell technology, currently used on the Shuttle, for future space missions. This test effort marks the final phase of a 5-yr development program that began under the Second Generation Reusable Launch Vehicle (RLV) Program, transitioned into the Next Generation Launch Technologies (NGLT) Program, and continued under Constellation Systems in the Exploration Technology Development Program. Initially, the engineering model (EM) powerplant was evaluated with respect to its performance as compared to acceptance tests carried out at the manufacturer. This was to determine the sensitivity of the powerplant performance to changes in test environment. In addition, a series of tests were performed with the powerplant in the original standard orientation. This report details the continuing EM benchmark test results in three spatial orientations as well as extended duration testing in the mission profile test. The results from these tests verify the applicability of PEM fuel cells for future NASA missions. The specifics of these different tests are described in the following sections.

  9. Performance of differently cross-linked, partially fluorinated proton exchange membranes in polymer electrolyte fuel cells

    SciTech Connect

    Buechi, F.N.; Gupta, B.; Haas, O.; Scherer, G.G.

    1995-09-01

    A series of differently cross-linked FEP-g-polystyrene proton exchange membranes has been synthesized by the preirradiation grafting method [FEP: poly(tetrafluoroethylene-co-hexafluoropropylene)]. Divinylbenzene (DVB) and/or triallyl cyanurate (TAC) were used as cross-linkers in the membranes. It was found that the physical properties of the membranes, such as water-uptake and specific resistance, are strongly influenced by the nature of the cross-linker. Generally it can be stated that DVB decreases water-uptake and increases specific resistance; on the other hand TAC increases swelling and decreases specific resistance to values as low as 5.0 {Omega} cm at 60 C. The membranes were tested in H{sub 2}/O{sub 2} fuel cells for stability and performance. It was found that thick (170 {micro}m) DVB cross-linked membranes showed stable operation for 1,400 h at temperatures up to 80 C. The highest power density in the fuel cell was found for the DVB and TAC double-cross-linked membrane; it exceeded the value of a cell with a Nafion{reg_sign} 117 membrane by more than 60%.

  10. High energy density proton exchange membrane fuel cell with dry reactant gases

    SciTech Connect

    Srinivasan, S.; Gamburzev, S.; Velev, O.A.

    1996-12-31

    Proton exchange membrane fuel cells (PEMFC) require careful control of humidity levels in the cell stack to achieve a high and stable level of performance. External humidification of the reactant gases, as in the state-of-the-art PEMFCs, increases the complexity, the weight, and the volume of the fuel cell power plant. A method for the operation of PEMFCs without external humidification (i.e., self-humidified PEMFCs) was first developed and tested by Dhar at BCS Technology. A project is underway in our Center to develop a PEMFC cell stack, which can work without external humidification and attain a performance level of a current density of 0.7 A/cm{sup 2} at a cell potential of 0.7 V, with hydrogen/air as reactants at 1 atm pressure. In this paper, the results of our efforts to design and develop a PEMFC stack requiring no external humidification will be presented. This paper focuses on determining the effects of type of electrodes, the methods of their preparation, as well as that of the membrane and electrode assembly (MEA), platinum loading and types of electrocatalyst on the performance of the PEMFC will be illustrated.

  11. Carbon composite bipolar plate for high-temperature proton exchange membrane fuel cells (HT-PEMFCs)

    NASA Astrophysics Data System (ADS)

    Lee, Dongyoung; Lee, Dai Gil

    2016-09-01

    A carbon/epoxy composite bipolar plate is an ideal substitute for the brittle graphite bipolar plate for lightweight proton exchange membrane fuel cells (PEMFCs) because of its high specific strength and stiffness. However, conventional carbon/epoxy composite bipolar plates are not applicable for high-temperature PEMFCs (HT-PEMFCs) because these systems are operated at higher temperatures than the glass transition temperatures of conventional epoxies. Therefore, in this study, a cyanate ester-modified epoxy is adopted for the development of a carbon composite bipolar plate for HT-PEMFCs. The composite bipolar plate with exposed surface carbon fibers is produced without any surface treatments or coatings to increase the productivity and is integrated with a silicone gasket to reduce the assembly cost. The developed carbon composite bipolar plate exhibits not only superior electrical properties but also high thermo-mechanical properties. In addition, a unit cell test is performed, and the results are compared with those of the conventional graphite bipolar plate.

  12. An analytical model and parametric study of electrical contact resistance in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Wu, Zhiliang; Wang, Shuxin; Zhang, Lianhong; Hu, S. Jack

    This paper presents an analytical model of the electrical contact resistance between the carbon paper gas diffusion layers (GDLs) and the graphite bipolar plates (BPPs) in a proton exchange membrane (PEM) fuel cell. The model is developed based on the classical statistical contact theory for a PEM fuel cell, using the same probability distributions of the GDL structure and BPP surface profile as previously described in Wu et al. [Z. Wu, Y. Zhou, G. Lin, S. Wang, S.J. Hu, J. Power Sources 182 (2008) 265-269] and Zhou et al. [Y. Zhou, G. Lin, A.J. Shih, S.J. Hu, J. Power Sources 163 (2007) 777-783]. Results show that estimates of the contact resistance compare favorably with experimental data by Zhou et al. [Y. Zhou, G. Lin, A.J. Shih, S.J. Hu, J. Power Sources 163 (2007) 777-783]. Factors affecting the contact behavior are systematically studied using the analytical model, including the material properties of the two contact bodies and factors arising from the manufacturing processes. The transverse Young's modulus of chopped carbon fibers in the GDL and the surface profile of the BPP are found to be significant to the contact resistance. The factor study also sheds light on the manufacturing requirements of carbon fiber GDLs for a better contact performance in PEM fuel cells.

  13. Proton exchange membranes based on the short-side-chain perfluorinated ionomer

    NASA Astrophysics Data System (ADS)

    Ghielmi, A.; Vaccarono, P.; Troglia, C.; Arcella, V.

    Due to the renovated availability of the base monomer for the synthesis of the short-side-chain (SSC) perfluorinated ionomer, fuel cell membrane development is being pursued using this well known ionomer structure, which was originally developed by Dow in the 1980s. The new membranes under development have the trade name Hyflon Ion. After briefly reviewing the literature on the Dow ionomer, new characterization data are reported on extruded Hyflon Ion membranes. The data are compared to those available in the literature on the Dow SSC ionomer and membranes. Comparison is made also with data obtained in this work or available in the literature on the long-side-chain (LSC) perfluorinated ionomer (Nafion). Thermal, visco-elastic, water absorption and mechanical properties of Hyflon Ion are studied. While the general behavior is similar to that shown in the past by the Dow membranes, slight differences are evident in the hydration behavior at equivalent weight (EW) < 900, probably due to different EW distributions. Measurements on dry membranes confirm that Hyflon Ion has a higher glass transition temperature compared to Nafion, which makes it a more promising material for high temperature proton exchange membrane (PEM) fuel cell operation ( T > 100 °C). Beginning of life fuel cell performance has also been confirmed to be higher than that given by a Nafion membrane of equal thickness.

  14. Protective nitride formation on stainless steel alloys for proton exchange membrane fuel cell bipolar plates

    NASA Astrophysics Data System (ADS)

    Yang, B.; Brady, M. P.; Wang, H.; Turner, J. A.; More, K. L.; Young, D. J.; Tortorelli, P. F.; Payzant, E. A.; Walker, L. R.

    Gas nitridation has shown excellent promise to form dense, electrically conductive and corrosion-resistant Cr-nitride surface layers on Ni-Cr base alloys for use as proton exchange membrane fuel cell (PEMFC) bipolar plates. Due to the high cost of nickel, Fe-base bipolar plate alloys are needed to meet the cost targets for many PEMFC applications. Unfortunately, nitridation of Fe-base stainless steel alloys typically leads to internal Cr-nitride precipitation rather than the desired protective surface nitride layer formation, due to the high permeability of nitrogen in these alloys. This paper reports the finding that it is possible to form a continuous, protective Cr-nitride (CrN and Cr 2N) surface layer through nitridation of Fe-base stainless steel alloys. The key to form a protective Cr-nitride surface layer was found to be the initial formation of oxide during nitridation, which prevented the internal nitridation typically observed for these alloys, and resulted in external Cr-nitride layer formation. The addition of V to the alloy, which resulted in the initial formation of V 2O 3-Cr 2O 3, was found to enhance this effect, by making the initially formed oxide more amenable to subsequent nitridation. The Cr-nitride surface layer formed on model V-modified Fe-27Cr alloys exhibited excellent corrosion resistance and low interfacial contact resistance under simulated PEMFC bipolar plate conditions.

  15. Numerical simulation of proton exchange membrane fuel cells at high operating temperature

    NASA Astrophysics Data System (ADS)

    Peng, Jie; Lee, Seung Jae

    A three-dimensional, single-phase, non-isothermal numerical model for proton exchange membrane (PEM) fuel cell at high operating temperature (T ≥ 393 K) was developed and implemented into a computational fluid dynamic (CFD) code. The model accounts for convective and diffusive transport and allows predicting the concentration of species. The heat generated from electrochemical reactions, entropic heat and ohmic heat arising from the electrolyte ionic resistance were considered. The heat transport model was coupled with the electrochemical and mass transport models. The product water was assumed to be vaporous and treated as ideal gas. Water transportation across the membrane was ignored because of its low water electro-osmosis drag force in the polymer polybenzimidazole (PBI) membrane. The results show that the thermal effects strongly affect the fuel cell performance. The current density increases with the increasing of operating temperature. In addition, numerical prediction reveals that the width and distribution of gas channel and current collector land area are key optimization parameters for the cell performance improvement.

  16. A water and heat management model for proton-exchange-membrane fuel cells

    SciTech Connect

    Nguyen, T.V.; White, R.E. . Dept. of Chemical Engineering)

    1993-08-01

    Proper water and heat management are essential for obtaining high-power-density performance at high energy efficiency for proton-exchange-membrane fuel cells. A water and heat management model was developed and used to investigate the effectiveness of various humidification designs. The model accounts for water transport across the membrane by electro-osmosis and diffusion, heat transfer from the solid phase to the gas phase and latent heat associated with water evaporation and condensation in the flow channels. Results from the model showed that at high current (> 1A/cm[sup 2]) ohmic loss in the membrane accounts for a large fraction of the voltage loss in the cell and back diffusion of water from the cathode side of the membrane is insufficient to keep the membrane hydrated (i.e., conductive). Consequently, to minimize this ohmic loss the anode stream must be humidified, and when air is used instead of pure oxygen the cathode stream must also be humidified.

  17. Proton exchange membrane micro fuel cells on 3D porous silicon gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Kouassi, S.; Gautier, G.; Thery, J.; Desplobain, S.; Borella, M.; Ventura, L.; Laurent, J.-Y.

    2012-10-01

    Since the 90's, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm-2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices.

  18. Chloride contamination effects on proton exchange membrane fuel cell performance and durability

    NASA Astrophysics Data System (ADS)

    Li, Hui; Wang, Haijiang; Qian, Weimin; Zhang, Shengsheng; Wessel, Silvia; Cheng, Tommy T. H.; Shen, Jun; Wu, Shaohong

    2011-08-01

    Chlorine is a major fuel contaminant when by-product hydrogen from the chlor-alkali industry is used as the fuel for proton exchange membrane (PEM) fuel cells. Understanding the effects of chlorine contamination on fuel cell performance and durability is essential to address fuel cell applications for the automotive and stationary markets. This paper reports our findings of chloride contamination effects on PEM fuel cell performance and durability, as our first step in understanding the effects of chlorine contamination. Fuel cell contamination tests were conducted by injecting ppm levels of contaminant into the fuel cell from either the fuel stream or the air stream. In situ and ex situ diagnosis were performed to investigate the contamination mechanisms. The results show that cell voltage during chloride contamination is characterized by an initial sudden drop followed by a plateau, regardless of which side the contaminant is introduced into the fuel cell. The drop in cell performance is predominantly due to increased cathode charge transfer resistance as a result of electrochemical catalyst surface area (ECSA) loss attributable to the blocking of active sites by Cl- and enhanced Pt dissolution.

  19. Electrochemical investigation of stainless steel corrosion in a proton exchange membrane electrolyzer cell

    DOE PAGESBeta

    Mo, Jingke; Steen, Stuart M.; Zhang, Feng-Yuan; Toops, Todd J.; Brady, Michael P.; Green, Johney B.

    2015-08-05

    The lack of a fundamental understanding of the corrosion mechanisms in the electrochemical environments of proton exchange membrane (PEM) electrolyzer and/or fuel cells (ECs/FCs) has seriously hindered the improvement of performance and efficiency of PEM ECs/FCs. In this study, a stainless steel mesh was purposely used as an anode gas diffusion layer that was intentionally operated with high positive potentials under harsh oxidative environments in a PEMEC to study the corrosion mechanism of metal migration. A significant amount of iron and nickel cations were determined to transport through the anode catalyst layer, the PEM and the cathode catalyst layer duringmore » the PEMEC operation. The formation/deposition of iron oxide and nickel oxide on the carbon paper gas diffusion layer at the cathode side is first revealed by both scanning electron microscope and X-ray diffraction. The results indicate the corrosion elements of iron and nickel are transported from anode to cathode through the catalyst-coated membrane, and deposited on carbon fibers as oxides. This phenomenon could also open a new corrosion-based processing approach to potentially fabricate multifunctional oxide structures on carbon fiber devices. This study has demonstrated a new accelerated test method for investigating the corrosion and durability of metallic materials as well.« less

  20. Electrochemical investigation of stainless steel corrosion in a proton exchange membrane electrolyzer cell

    SciTech Connect

    Mo, Jingke; Steen, Stuart M.; Zhang, Feng-Yuan; Toops, Todd J.; Brady, Michael P.; Green, Johney B.

    2015-08-05

    The lack of a fundamental understanding of the corrosion mechanisms in the electrochemical environments of proton exchange membrane (PEM) electrolyzer and/or fuel cells (ECs/FCs) has seriously hindered the improvement of performance and efficiency of PEM ECs/FCs. In this study, a stainless steel mesh was purposely used as an anode gas diffusion layer that was intentionally operated with high positive potentials under harsh oxidative environments in a PEMEC to study the corrosion mechanism of metal migration. A significant amount of iron and nickel cations were determined to transport through the anode catalyst layer, the PEM and the cathode catalyst layer during the PEMEC operation. The formation/deposition of iron oxide and nickel oxide on the carbon paper gas diffusion layer at the cathode side is first revealed by both scanning electron microscope and X-ray diffraction. The results indicate the corrosion elements of iron and nickel are transported from anode to cathode through the catalyst-coated membrane, and deposited on carbon fibers as oxides. This phenomenon could also open a new corrosion-based processing approach to potentially fabricate multifunctional oxide structures on carbon fiber devices. This study has demonstrated a new accelerated test method for investigating the corrosion and durability of metallic materials as well.

  1. Protective coatings on stainless steel bipolar plates for proton exchange membrane (PEM) electrolysers

    NASA Astrophysics Data System (ADS)

    Gago, A. S.; Ansar, S. A.; Saruhan, B.; Schulz, U.; Lettenmeier, P.; Cañas, N. A.; Gazdzicki, P.; Morawietz, T.; Hiesgen, R.; Arnold, J.; Friedrich, K. A.

    2016-03-01

    Proton exchange membrane (PEM) electrolysis is a promising technology for large H2 production from surplus electricity from renewable sources. However, the electrolyser stack is costly due to the manufacture of bipolar plates (BPP). Stainless steel can be used as an alternative, but it must be coated. Herein, dense titanium coatings are produced on stainless steel substrates by vacuum plasma spraying (VPS). Further surface modification of the Ti coating with Pt (8 wt% Pt/Ti) deposited by physical vapour deposition (PVD) magnetron sputtering reduces the interfacial contact resistance (ICR). The Ti and Pt/Ti coatings are characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). Subsequently, the coatings are evaluated in simulated and real PEM electrolyser environments, and they managed to fully protect the stainless steel substrate. In contrast, the absence of the thermally sprayed Ti layer between Pt and stainless steel leads to pitting corrosion. The Pt/Ti coating is tested in a PEM electrolyser cell for almost 200 h, exhibiting an average degradation rate of 26.5 μV h-1. The results reported here demonstrate the possibility of using stainless steel as a base material for the stack of a PEM electrolyser.

  2. Design and simulation of novel flow field plate geometry for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ruan, Hanxia; Wu, Chaoqun; Liu, Shuliang; Chen, Tao

    2015-12-01

    Bipolar plate is one of the many important components of proton exchange membrane fuel cell (PEMFC) stacks as it supplies fuel and oxidant to the membrane-electrode assembly (MEA), removes water, collects produced current and provides mechanical support for the single cells in the stack. The flow field design of a bipolar plate greatly affects the performance of a PEMFC. It must uniformly distribute the reactant gases over the MEA and prevent product water flooding. This paper aims at improving the fuel cell performance by optimizing flow field designs and flow channel configurations. To achieve this, a novel biomimetic flow channel for flow field designs is proposed based on Murray's Law. Computational fluid dynamics based simulations were performed to compare three different designs (parallel, serpentine and biomimetic channel, respectively) in terms of current density distribution, power density distribution, pressure distribution, temperature distribution, and hydrogen mass fraction distribution. It was found that flow field designs with biomimetic flow channel perform better than that with convectional flow channel under the same operating conditions.

  3. Development of novel proton exchange membrane fuel cells using stamped metallic bipolar plates

    NASA Astrophysics Data System (ADS)

    Jung, Shiauh-Ping; Lee, Chun-I.; Chen, Chi-Chang; Chang, Wen-Sheng; Yang, Chang-Chung

    2015-06-01

    This study presents the development of novel proton exchange membrane fuel cells using stamped metallic bipolar plates. To achieve uniformly distributed and low pressure-drop flow fields within fuel cells, a novel bipolar plate with straight channels is designed and verification of a fuel-cell short stack using this bipolar plate is performed. In the experiments, low-temperature and low-humidity operations and high-temperature and high-humidity operations are adopted to evaluate effects of stack temperature and inlet relative humidity on performance at various outlet pressures. Experimental results show that under low-temperature and low-humidity operations, increasing the outlet pressure enhances stack performance and reduces performance differences between various stack temperatures. Under high-temperature and high-humidity operations, stack performance increases with increasing outlet pressures, while the extent of their increase becomes smaller. Compared to low-temperature and low-humidity operations, high-temperature and high-humidity operations have better electrochemical reactions and membrane hydration and, thus, better stack performance. In this study, the operation with a stack temperature of 80 °C and outlet pressure of 4 atm produces the best performance of 1100 mA cm-2 at 0.646 V.

  4. Distribution of proton dissociation constants for model humic and fulvic acid molecules.

    PubMed

    Atalay, Yasemin B; Carbonaro, Richard F; Di Toro, Dominic M

    2009-05-15

    The intrinsic proton binding constants of 10 model humic acid and six model fulvic acid molecules are calculated using SPARC Performs Automated Reasoning in Chemistry (SPARC). The accuracy of the SPARC calculations is examined using estimated microscopic binding constants of various small organic acids. An equimolar mixture of the appropriate hypothetical molecules is used as a representation of soil and aqueous humic acid and fulvic acid. The probability distributions of the mixture microscopic proton binding constants and the intrinsic proton binding constants in the metal speciation models WHAM V and WHAM VI (Windermere humic aqueous models) are compared. The idea is to assess the predictive value of the molecular mixture models as representations of heterogeneous natural organic matter. For aqueous humic and fulvic acids, the results are comparable to the WHAM distribution. For soil humic acid, the WHAM probability distribution is less acidic for the carboxylic sites but similar to that of the phenolic sites. Computations made using the WHAM molecular distributions and WHAM VI are comparable to titration data for Suwannee River fulvic acid. These results suggest that mixture molecular models can be used to investigate and predict the binding of metal cations to humic and fulvic acids. PMID:19544864

  5. Effect of Temperature on the Protonation of the TALSPEAK Ligands: Lactic and Diethylenetrinitropentaacetic Acids

    SciTech Connect

    Tian, Guoxin; Rao, Linfeng

    2009-10-20

    The protonation reactions of two ligands that play important roles in the TALSPEAK process for the separation of trivalent actinides from lanthanides, lactic acid and diethylenetrinitropentaacetic acid (DTPA), have been studied at variable temperatures. The protonation constants at 10-70 C were determined by titration potentiometry and the protonation enthalpies were determined at 25 C by titration microcalorimetry. The protonation constants remain essentially unchanged (25-70 C) within the experimental uncertainties, indicating that the effect of temperature on the protonation of lactate is insignificant. In contrast, the protonation constants of DTPA (log {beta}H's) generally decrease as the temperature is increased. Results from this study indicate that the effect of temperature on the protonation of DTPA could alter the speciation of metal ions (actinides and lanthanides) in the TALSPEAK system, since lower values of log{beta}H at higher temperatures suggest that the hydrogen ions would compete less strongly with the metal ions for the complexation of DTPA at higher temperatures.

  6. Challenges in preparing, preserving and detecting para-water in bulk: overcoming proton exchange and other hurdles.

    PubMed

    Mammoli, Daniele; Salvi, Nicola; Milani, Jonas; Buratto, Roberto; Bornet, Aurélien; Sehgal, Akansha Ashvani; Canet, Estel; Pelupessy, Philippe; Carnevale, Diego; Jannin, Sami; Bodenhausen, Geoffrey

    2015-10-28

    Para-water is an analogue of para-hydrogen, where the two proton spins are in a quantum state that is antisymmetric under permutation, also known as singlet state. The populations of the nuclear spin states in para-water are believed to have long lifetimes just like other Long-Lived States (LLSs). This hypothesis can be verified by measuring the relaxation of an excess or a deficiency of para-water, also known as a "Triplet-Singlet Imbalance" (TSI), i.e., a difference between the average population of the three triplet states T (that are symmetric under permutation) and the population of the singlet state S. In analogy with our recent findings on ethanol and fumarate, we propose to adapt the procedure for Dissolution Dynamic Nuclear Polarization (D-DNP) to prepare such a TSI in frozen water at very low temperatures in the vicinity of 1.2 K. After rapid heating and dissolution using an aprotic solvent, the TSI should be largely preserved. To assess this hypothesis, we studied the lifetime of water as a molecular entity when diluted in various solvents. In neat liquid H2O, proton exchange rates have been characterized by spin-echo experiments on oxygen-17 in natural abundance, with and without proton decoupling. One-dimensional exchange spectroscopy (EXSY) has been used to study proton exchange rates in H2O, HDO and D2O mixtures diluted in various aprotic solvents. In the case of 50 mM H2O in dioxane-d8, the proton exchange lifetime is about 20 s. After dissolving, one can observe this TSI by monitoring intensities in oxygen-17 spectra of H2O (if necessary using isotopically enriched samples) where the AX2 system comprising a "spy" oxygen A and two protons X2 gives rise to binomial multiplets only if the TSI vanishes. Alternatively, fast chemical addition to a suitable substrate (such as an activated aldehyde or ketone) can provide AX2 systems where a carbon-13 acts as a spy nucleus. Proton signals that relax to equilibrium with two distinct time constants can be

  7. Pt nanoparticle-dispersed graphene-wrapped MWNT composites as oxygen reduction reaction electrocatalyst in proton exchange membrane fuel cell.

    PubMed

    Aravind, S S Jyothirmayee; Ramaprabhu, Sundara

    2012-08-01

    Chemical and electrical synergies between graphite oxide and multiwalled carbon nanotube (MWNT) for processing graphene wrapped-MWNT hybrids has been realized by chemical vapor deposition without any chemical functionalization. Potential of the hybrid composites have been demonstrated by employing them as electrocatalyst supports in proton exchange membrane fuel cells. The defects present in the polyelectrolyte, which have been wrapped over highly dispersed MWNT, act as anchoring sites for the homogeneous deposition of platinum nanoparticles. Single-cell proton exchange membrane fuel cells show that the power density of the hybrid composite-based fuel cells is higher compared to the pure catalyst-support-based fuel cells, because of enhanced electrochemical reactivity and good surface area of the nanocomposites. PMID:22850438

  8. Spectroscopy and dynamics of double proton transfer in formic acid dimer.

    PubMed

    Mackeprang, Kasper; Xu, Zhen-Hao; Maroun, Zeina; Meuwly, Markus; Kjaergaard, Henrik G

    2016-09-21

    We present the isolated gas phase infrared spectra of formic acid dimer, (HCOOH)2, and its deuterated counterpart formic-d acid, (DCOOH)2, at room temperature. The formic acid dimer spectrum was obtained by spectral subtraction of a spectrum of formic acid vapor recorded at low pressure from that recorded at a higher pressure. The spectra of formic acid vapor contain features from both formic acid monomer and formic acid dimer, but at low and high pressures of formic acid, the equilibrium is pushed towards the monomer and dimer, respectively. A similar approach was used for the formic-d acid dimer. Building on the previous development of the Molecular Mechanics with Proton Transfer (MMPT) force field for simulating proton transfer reactions, molecular dynamics (MD) simulations were carried out to interpret the experimental spectra in the OH-stretching region. Within the framework of MMPT, a combination of symmetric single and double minimum potential energy surfaces (PESs) provides a good description of the double proton transfer PES. In a next step, potential morphing together with electronic structure calculations at the B3LYP and MP2 level of theory was used to align the computed and experimentally observed spectral features in the OH-stretching region. From this analysis, a barrier for double proton transfer between 5 and 7 kcal mol(-1) was derived, which compares with a CCSD(T)/aug-cc-pVTZ calculated barrier of 7.9 kcal mol(-1). Such a combination of experimental and computational techniques for estimating barriers for proton transfer in gas phase systems is generic and holds promise for further improved PESs and energetics of these important systems. Additional MD simulations at the semi-empirical DFTB level of theory agree quite well for the center band position but underestimate the width of the OH-stretching band. PMID:27545453

  9. Proton transport in triflic acid pentahydrate studied via ab initio path integral molecular dynamics.

    PubMed

    Hayes, Robin L; Paddison, Stephen J; Tuckerman, Mark E

    2011-06-16

    Trifluoromethanesulfonic acid hydrates provide a well-defined system to study proton dissociation and transport in perfluorosulfonic acid membranes, typically used as the electrolyte in hydrogen fuel cells, in the limit of minimal water. The triflic acid pentahydrate crystal (CF(3)SO(3)H·5H(2)O) is sufficiently aqueous that it contains an extended three-dimensional water network. Despite it being extended, however, long-range proton transport along the network is structurally unfavorable and would require considerable rearrangement. Nevertheless, the triflic acid pentahydrate crystal system can provide a clear picture of the preferred locations of local protonic defects in the water network, which provides insights about related structures in the disordered, low-hydration environment of perfluorosulfonic acid membranes. Ab initio molecular dynamics simulations reveal that the proton defect is most likely to transfer to the closest water that has the expected presolvation and only contains water in its first solvation shell. Unlike the tetrahydrate of triflic acid (CF(3)SO(3)H·4H(2)O), there is no evidence of the proton preferentially transferring to a water molecule bridging two of the sulfonate groups. However, this could be an artifact of the crystal structure since the only such water molecule is separated from the proton by long O-O distances. Hydrogen bonding criteria, using the two-dimensional potential of mean force, are extracted. Radial distribution functions, free energy profiles, radii of gyration, and the root-mean-square displacement computed from ab initio path integral molecular dynamics simulations reveal that quantum effects do significantly extend the size of the protonic defect and increase the frequency of proton transfer events by nearly 15%. The calculated IR spectra confirm that the dominant protonic defect mostly exists as an Eigen cation but contains some Zundel ion characteristics. Chain lengths and ring sizes determined from the

  10. Correlation of infrared spectra and phase transitions in annealed proton-exchanged MgO doped LiNbO{sub 3}

    SciTech Connect

    Sun, Jian; Xu, Chang-qing

    2015-01-28

    Infrared spectra of OH{sup −} groups in annealed proton-exchanged (APE) 5 mol. % MgO-doped LiNbO{sub 3} (MgO:LiNbO{sub 3}) crystals were studied using the Fourier transform infrared spectroscopy technique. Samples were prepared by benzoic acid proton-exchange followed with thermal annealing in oxygen. Evolutions of absorption peaks in APE MgO:LiNbO{sub 3} crystals were recorded and analyzed. Comparing with none-doped APE LiNbO{sub 3} crystals, a different phase transition behavior was found during thermal annealing. A periodically poled MgO:LiNbO{sub 3} slab waveguide was prepared using identical procedures, and the second harmonic generation (SHG) signals were measured. Comparing the obtained SHG results with the infrared spectra, relationships between the phase transitions and the recovery of second-order nonlinear coefficients during thermal annealing were investigated. Finally, a method for optimizing the performance of MgO:LiNbO{sub 3} waveguides was proposed.

  11. Correlation of infrared spectra and phase transitions in annealed proton-exchanged MgO doped LiNbO3

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Xu, Chang-qing

    2015-01-01

    Infrared spectra of OH- groups in annealed proton-exchanged (APE) 5 mol. % MgO-doped LiNbO3 (MgO:LiNbO3) crystals were studied using the Fourier transform infrared spectroscopy technique. Samples were prepared by benzoic acid proton-exchange followed with thermal annealing in oxygen. Evolutions of absorption peaks in APE MgO:LiNbO3 crystals were recorded and analyzed. Comparing with none-doped APE LiNbO3 crystals, a different phase transition behavior was found during thermal annealing. A periodically poled MgO:LiNbO3 slab waveguide was prepared using identical procedures, and the second harmonic generation (SHG) signals were measured. Comparing the obtained SHG results with the infrared spectra, relationships between the phase transitions and the recovery of second-order nonlinear coefficients during thermal annealing were investigated. Finally, a method for optimizing the performance of MgO:LiNbO3 waveguides was proposed.

  12. Isotopic exchange plus substrate and inhibition kinetics of D-xylose isomerase do not support a proton-transfer mechanism.

    PubMed

    Allen, K N; Lavie, A; Farber, G K; Glasfeld, A; Petsko, G A; Ringe, D

    1994-02-15

    The D-xylose isomerase of Streptomyces olivochromogenes is a Mg2+- or Mn(2+)-dependent enzyme that catalyzes the aldose-ketose isomerization of xylose to xylulose or of glucose to fructose. Proton exchange into water during enzyme-catalyzed isomerization of C-2 tritiated glucose at 15, 25 and 55 degrees C shows < 0.6% exchange (the loss of one proton in every billion turnovers). High concentrations of guanidine hydrochloride and extremes of pH had no effect on the amount of exchange detected. Such a low percentage of exchange is inconsistent with a proton-transfer mechanism as the main kinetic pathway for isomerization. 19F NMR experiments showed no release of fluoride after incubation of the enzyme for 4 weeks with 800 mM 3-deoxy-3-fluoroglucose or 3-deoxy-3-fluoroallose (both are competitive inhibitors with Ki values of 600 mM). This result is also inconsistent with a proton-transfer mechanism. A hydride-shift mechanism following ring opening has been proposed for the isomerization. Enzyme-catalyzed ring opening was directly measured by demonstrating H2S release upon reaction of xylose isomerase with 1-thioglucose. D-Xylose isomerase-catalyzed interconversion of glucose to fructose exhibited linear Arrhenius behavior with an activation energy of 14 kcal/mol from 0 to 50 degrees C. No change in rate-determining step occurs over this temperature range. 13C NMR experiments with glucose show that enzyme-bound magnesium or manganese does not interact specifically with any one site on the sugar. These results are consistent with nonproductive binding modes for the substrate glucose in addition to productive binding. PMID:8312268

  13. Dissecting Proton Delocalization in an Enzyme's Hydrogen Bond Network with Unnatural Amino Acids.

    PubMed

    Wu, Yufan; Fried, Stephen D; Boxer, Steven G

    2015-12-01

    Extended hydrogen bond networks are a common structural motif of enzymes. A recent analysis proposed quantum delocalization of protons as a feature present in the hydrogen bond network spanning a triad of tyrosines (Y(16), Y(32), and Y(57)) in the active site of ketosteroid isomerase (KSI), contributing to its unusual acidity and large isotope shift. In this study, we utilized amber suppression to substitute each tyrosine residue with 3-chlorotyrosine to test the delocalization model and the proton affinity balance in the triad. X-ray crystal structures of each variant demonstrated that the structure, notably the O-O distances within the triad, was unaffected by 3-chlorotyrosine substitutions. The changes in the cluster's acidity and the acidity's isotope dependence in these variants were assessed via UV-vis spectroscopy and the proton sharing pattern among individual residues with (13)C nuclear magnetic resonance. Our data show pKa detuning at each triad residue alters the proton delocalization behavior in the H-bond network. The extra stabilization energy necessary for the unusual acidity mainly comes from the strong interactions between Y(57) and Y(16). This is further enabled by Y(32), which maintains the right geometry and matched proton affinity in the triad. This study provides a rich picture of the energetics of the hydrogen bond network in enzymes for further model refinement. PMID:26571340

  14. Nonlinear optical properties of different types of proton-exchanged LiNbO3 and LiTaO3 waveguides

    NASA Astrophysics Data System (ADS)

    Korkishko, Yuri N.; Fedorov, Vyacheslav A.; Kostritskii, Sergey M.; Alkaev, Alexander N.; Maslennikov, Evgeny I.; Laurell, Fredrik

    2003-04-01

    Reflection second-harmonic generation (SHG) from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of different types of PE LiNbO3 and LiTaO3 waveguides in different HxLi1-xNbO3 and HxLi1-xTaO3 phases: as-exchanged and annealed proton-exchanged (APE) waveguides, high-temperature proton-exchanged (HTPE) waveguides, as well as reverse proton exchanged (RPE) waveguides. A detailed correlation is done between the nonlinear properties, the processing conditions, crystal structure parameters, the refractive index changes and the optical losses of the waveguides. The intensity of reflected SH signal, strongly reduced after the initial proton exchange in both LiNbO3 and LiTaO3, is found to be restored and even increased after annealing. However, this apparent increase of the nonlinearity is accompanied by high scattering and a strong degradation of the quality of the SHG reflected beam in the region of initial step-like PE waveguides. The recently proposed HTPE technique has been shown to produce high-quality alpha-phase PE LiNbO3 or PE LiTaO3 waveguides with essentially undegraded nonlinear optical properties. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO3 and LiTaO3 waveguides can be effectively recovered by the reverse proton exchange technique.

  15. Proton transport in triflic acid hydrates studied via path integral car-parrinello molecular dynamics.

    PubMed

    Hayes, Robin L; Paddison, Stephen J; Tuckerman, Mark E

    2009-12-31

    The mono-, di-, and tetrahydrates of trifluoromethanesulfonic acid, which contain characteristic H(3)O(+), H(5)O(2)(+), and H(9)O(4)(+) structures, provide model systems for understanding proton transport in materials with high perfluorosulfonic acid density such as perfluorosulfonic acid membranes commonly employed in hydrogen fuel cells. Ab initio molecular dynamics simulations indicate that protons in these solids are predisposed to transfer to the water most strongly bound to sulfonate groups via a Grotthuss-type mechanism, but quickly return to the most solvated defect structure either due to the lack of a nearby species to stabilize the new defect or a preference for the proton to be maximally hydrated. Path integral molecular dynamics of the mono- and dihydrate reveal significant quantum effects that facilitate proton transfer to the "presolvated" water or SO(3)(-) in the first solvation shell and increase the Zundel character of all the defects. These trends are quantified in free energy profiles for each bonding environment. Hydrogen bonding criteria for HOH-OH(2) and HOH-O(3)S are extracted from the two-dimensional potential of mean force. The quantum radial distribution function, radius of gyration, and root-mean-square displacement position correlation function show that the protonic charge is distributed over two or more water molecules. Metastable structural defects with one excess proton shared between two sulfonate groups and another Zundel or Eigen type cation defect are found for the mono- and dihydrate but not for the tetrahydrate crystal. Results for the tetrahydrate native crystal exhibit minor differences at 210 and 250 K. IR spectra are calculated for all native and stable defect structures. Graph theory techniques are used to characterize the chain lengths and ring sizes in the hydrogen bond network. Low conductivities when limited water is present may be attributable to trapping of protons between SO(3)(-) groups and the increased

  16. Carbonic anhydrase II binds to and increases the activity of the epithelial sodium-proton exchanger, NHE3.

    PubMed

    Krishnan, Devishree; Liu, Lei; Wiebe, Shane A; Casey, Joseph R; Cordat, Emmanuelle; Alexander, R Todd

    2015-08-15

    Two-thirds of sodium filtered by the renal glomerulus is reabsorbed from the proximal tubule via a sodium/proton exchanger isoform 3 (NHE3)-dependent mechanism. Since sodium and bicarbonate reabsorption are coupled, we postulated that the molecules involved in their reabsorption [NHE3 and carbonic anhydrase II (CAII)] might physically and functionally interact. Consistent with this, CAII and NHE3 were closely associated in a renal proximal tubular cell culture model as revealed by a proximity ligation assay. Direct physical interaction was confirmed in solid-phase binding assays with immobilized CAII and C-terminal NHE3 glutathione-S-transferase fusion constructs. To assess the effect of CAII on NHE3 function, we expressed NHE3 in a proximal tubule cell line and measured NHE3 activity as the rate of intracellular pH recovery, following an acid load. NHE3-expressing cells had a significantly greater rate of intracellular pH recovery than controls. Inhibition of endogenous CAII activity with acetazolamide significantly decreased NHE3 activity, indicating that CAII activates NHE3. To ascertain whether CAII binding per se activates NHE3, we expressed NHE3 with wild-type CAII, a catalytically inactive CAII mutant (CAII-V143Y), or a mutant unable to bind other transporters (CAII-HEX). NHE3 activity increased upon wild-type CAII coexpression, but not in the presence of the CAII V143Y or HEX mutant. Together these studies support an association between CAII and NHE3 that alters the transporter's activity. PMID:26041446

  17. Nanosized IrxRu1-xO2 electrocatalysts for oxygen evolution reaction in proton exchange membrane water electrolyzer

    NASA Astrophysics Data System (ADS)

    Hanh Pham, Hong; Nguyen, Ngoc Phong; Linh Do, Chi; Thang Le, Ba

    2015-01-01

    Normally in proton exchange membrane water electrolysis (PEMWE), the anode has the largest overpotential at typical operating current densities. By development of the electrocatalytic material used for the oxygen evolving electrode, great improvements in efficiency can be performed. In electrochemistry, rare metallic oxides RuO2 and IrO2 exhibit the best catalytic properties for the oxygen evolution reaction (OER) in acid electrolytes compared to other noble metals. RuO2 is the most active catalyst and IrO2 is the most stable catalyst. An oxide containing both elements is therefore expected to be a good catalyst for the OER. In this study IrxRu1-xO2 nanosized powder electrocatalysts for oxygen evolution reaction is synthesized by hydrolysis method. Cyclic voltammetry, anodic polarization and galvanostatic measurements were conducted in solution of 0.5 M H2SO4 to investigate electrocatalytic behavior and stability of the electrocatalyst. The mechanisms of the thermal decomposition process of RuCl3.nH2O and IrCl3.mH2O precursors to form oxide powders were studied by means of thermal gravity analysis (TGA). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used analysis for determination of the crystallographic structure, morphology and catalysts particle size. Based on the given results, the IrxRu1-xO2 (x = 0.5 0.7) compounds were found to be more active than pure IrO2 and more stable than pure RuO2.

  18. Carbonic anhydrase II binds to and increases the activity of the epithelial sodium-proton exchanger, NHE3

    PubMed Central

    Krishnan, Devishree; Liu, Lei; Wiebe, Shane A.; Casey, Joseph R.; Cordat, Emmanuelle; Alexander, R. Todd

    2016-01-01

    Two-thirds of sodium filtered by the renal glomerulus is reabsorbed from the proximal tubule via a sodium/proton exchanger isoform 3 (NHE3)-dependent mechanism. Since sodium and bicarbonate reabsorption are coupled, we postulated that the molecules involved in their reabsorption [NHE3 and carbonic anhydrase II (CAII)] might physically and functionally interact. Consistent with this, CAII and NHE3 were closely associated in a renal proximal tubular cell culture model as revealed by a proximity ligation assay. Direct physical interaction was confirmed in solid-phase binding assays with immobilized CAII and C-terminal NHE3 glutathione-S-transferase fusion constructs. To assess the effect of CAII on NHE3 function, we expressed NHE3 in a proximal tubule cell line and measured NHE3 activity as the rate of intracellular pH recovery, following an acid load. NHE3-expressing cells had a significantly greater rate of intracellular pH recovery than controls. Inhibition of endogenous CAII activity with acetazolamide significantly decreased NHE3 activity, indicating that CAII activates NHE3. To ascertain whether CAII binding per se activates NHE3, we expressed NHE3 with wild-type CAII, a catalytically inactive CAII mutant (CAII-V143Y), or a mutant unable to bind other transporters (CAII-HEX). NHE3 activity increased upon wild-type CAII coexpression, but not in the presence of the CAII V143Y or HEX mutant. Together these studies support an association between CAII and NHE3 that alters the transporter’s activity. PMID:26041446

  19. Monitoring lactic acid production during milk fermentation by in situ quantitative proton nuclear magnetic resonance spectroscopy.

    PubMed

    Bouteille, R; Gaudet, M; Lecanu, B; This, H

    2013-04-01

    When fermenting milk, lactic bacteria convert part of α- and β-lactoses into d- and l- lactic acids, causing a pH decrease responsible for casein coagulation. Lactic acid monitoring during fermentation is essential for the control of dairy gel textural and organoleptic properties, and is a way to evaluate strain efficiency. Currently, titrations are used to follow the quantity of acids formed during jellification of milk but they are not specific to lactic acid. An analytical method without the use of any reagent was investigated to quantify lactic acid during milk fermentation: in situ quantitative proton nuclear magnetic resonance spectroscopy. Two methods using in situ quantitative proton nuclear magnetic resonance spectroscopy were compared: (1) d- and l-lactic acids content determination, using the resonance of their methyl protons, showing an increase from 2.06 ± 0.02 to 8.16 ± 0.74 g/L during 240 min of fermentation; and (2) the determination of the α- and β-lactoses content, decreasing from 42.68 ± 0.02 to 30.76 ± 1.75 g/L for the same fermentation duration. The ratio between the molar concentrations of produced lactic acids and consumed lactoses enabled cross-validation, as the value (2.02 ± 0.18) is consistent with lactic acid bacteria metabolism. PMID:23403188

  20. Conceptual design report for a Direct Hydrogen Proton Exchange Membrane Fuel Cell for transportation application

    SciTech Connect

    1995-09-05

    This report presents the conceptual design for a Direct-Hydrogen-Fueled Proton Exchange Membrane (PEM) Fuel Cell System for transportation applications. The design is based on the initial selection of the Chrysler LH sedan as the target vehicle with a 50 kW (gross) PEM Fuel Cell Stack (FCS) as the primary power source, a battery-powered Load Leveling Unit (LLU) for surge power requirements, an on-board hydrogen storage subsystem containing high pressure gaseous storage, a Gas Management Subsystem (GMS) to manage the hydrogen and air supplies for the FCS, and electronic controllers to control the electrical system. The design process has been dedicated to the use of Design-to-Cost (DTC) principles. The Direct Hydrogen-Powered PEM Fuel Cell Stack Hybrid Vehicle (DPHV) system is designed to operate on the Federal Urban Driving Schedule (FUDS) and Hiway Cycles. These cycles have been used to evaluate the vehicle performance with regard to range and hydrogen usage. The major constraints for the DPHV vehicle are vehicle and battery weight, transparency of the power system and drive train to the user, equivalence of fuel and life cycle costs to conventional vehicles, and vehicle range. The energy and power requirements are derived by the capability of the DPHV system to achieve an acceleration from 0 to 60 MPH within 12 seconds, and the capability to achieve and maintain a speed of 55 MPH on a grade of seven percent. The conceptual design for the DPHV vehicle is shown in a figure. A detailed description of the Hydrogen Storage Subsystem is given in section 4. A detailed description of the FCS Subsystem and GMS is given in section 3. A detailed description of the LLU, selection of the LLU energy source, and the power controller designs is given in section 5.

  1. Hygrothermal characterization of the viscoelastic properties of Gore-Select® 57 proton exchange membrane

    NASA Astrophysics Data System (ADS)

    Patankar, Kshitish A.; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Budinski, Michael K.; Gittleman, Craig S.

    2008-09-01

    When a proton exchange membrane (PEM) based fuel cell is placed in service, hygrothermal stresses develop within the membrane and vary widely with internal operating environment. These hygrothermal stresses associated with hygral contraction and expansion at the operating conditions are believed to be critical in membrane mechanical integrity and durability. Understanding and accurately modeling the viscoelastic constitutive properties of a PEM is important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. The tensile stress relaxation moduli of a commercially available PEM, Gore-Select® 57, were obtained over a range of humidities and temperatures. These tests were performed using TA Instruments 2980 and Q800 dynamic mechanical analyzers (DMA), which are capable of applying specified tensile loading conditions on small membrane samples at a given temperature. A special humidity chamber was built in the form of a cup that encloses tension clamps of the DMA. The chamber was inserted in the heating furnace of the DMA and connected to a gas humidification unit by means of plastic tubing through a slot in the chamber. Stress relaxation data over a temperature range of 40 90°C and relative humidity range of 30 90% were obtained. Thermal and hygral master curves were constructed using thermal and hygral shift factors and were used to form a hygrothermal master curve using the time temperature moisture superposition principle. The master curve was also constructed independently using just one shift factor. The hygrothermal master curve was fitted with a 10-term Prony series for use in finite element software. The hygrothermal master curve was then validated using longer term tests. The relaxation modulus from longer term data matches well with the hygrothermal master curve. The long term test showed a plateau at longer times, suggesting an equilibrium modulus.

  2. Interface modulated currents in periodically proton exchanged Mg doped lithium niobate

    NASA Astrophysics Data System (ADS)

    Neumayer, Sabine M.; Manzo, Michele; Kholkin, Andrei L.; Gallo, Katia; Rodriguez, Brian J.

    2016-03-01

    Conductivity in Mg doped lithium niobate (Mg:LN) plays a key role in the reduction of photorefraction and is therefore widely exploited in optical devices. However, charge transport through Mg:LN and across interfaces such as electrodes also yields potential electronic applications in devices with switchable conductivity states. Furthermore, the introduction of proton exchanged (PE) phases in Mg:LN enhances ionic conductivity, thus providing tailorability of conduction mechanisms and functionality dependent on sample composition. To facilitate the construction and design of such multifunctional electronic devices based on periodically PE Mg:LN or similar ferroelectric semiconductors, fundamental understanding of charge transport in these materials, as well as the impact of internal and external interfaces, is essential. In order to gain insight into polarization and interface dependent conductivity due to band bending, UV illumination, and chemical reactivity, wedge shaped samples consisting of polar oriented Mg:LN and PE phases were investigated using conductive atomic force microscopy. In Mg:LN, three conductivity states (on/off/transient) were observed under UV illumination, controllable by the polarity of the sample and the externally applied electric field. Measurements of currents originating from electrochemical reactions at the metal electrode-PE phase interfaces demonstrate a memresistive and rectifying capability of the PE phase. Furthermore, internal interfaces such as domain walls and Mg:LN-PE phase boundaries were found to play a major role in the accumulation of charge carriers due to polarization gradients, which can lead to increased currents. The insight gained from these findings yield the potential for multifunctional applications such as switchable UV sensitive micro- and nanoelectronic devices and bistable memristors.

  3. Novel proton exchange membrane fuel cell electrodes to improve performance of reversible fuel cell systems

    NASA Astrophysics Data System (ADS)

    Brown, Tim Matthew

    Proton exchange membrane (PEM) fuel cells react fuel and oxidant to directly and efficiently produce electrical power, without the need for combustion, heat engines, or motor-generators. Additionally, PEM fuel cell systems emit zero to virtually zero criteria pollutants and have the ability to reduce CO2 emissions due to their efficient operation, including the production or processing of fuel. A reversible fuel cell (RFC) is one particular application for a PEM fuel cell. In this application the fuel cell is coupled with an electrolyzer and a hydrogen storage tank to complete a system that can store and release electrical energy. These devices can be highly tailored to specific energy storage applications, potentially surpassing the performance of current and future secondary battery technology. Like all PEM applications, RFCs currently suffer from performance and cost limitations. One approach to address these limitations is to improve the cathode performance by engineering more optimal catalyst layer geometry as compared to the microscopically random structure traditionally used. Ideal configurations are examined and computer modeling shows promising performance improvements are possible. Several novel manufacturing methods are used to build and test small PEM fuel cells with novel electrodes. Additionally, a complete, dynamic model of an RFC system is constructed and the performance is simulated using both traditional and novel cathode structures. This work concludes that PEM fuel cell microstructures can be tailored to optimize performance based on design operating conditions. Computer modeling results indicate that novel electrode microstructures can improve fuel cell performance, while experimental results show similar performance gains that bolster the theoretical predictions. A dynamic system model predicts that novel PEM fuel cell electrode structures may enable RFC systems to be more competitive with traditional energy storage technology options.

  4. Waveguides in single-crystal lithium niobate thin film by proton exchange.

    PubMed

    Cai, Lutong; Han, Shuang Li Huangpu; Hu, Hui

    2015-01-26

    The proton exchanged (PE) planar and channel waveguides in a 500 nm thick single-crystal lithium niobate thin film (lithium niobate on insulator, LNOI) were studied. The mature PE technique and strong confinement of light in the LN single-crystal thin film were used. The single mode and cut-off conditions of the channel waveguides were obtained by finite difference simulation. The results showed that the single mode channel waveguide would form if the width of the PE region was between 0.75 μm and 2.1 μm in the β(4) phase. The channel waveguide in LNOI had a much smaller mode size than that in the bulk material due to the high-refractive-index contrast. The mode size reached as small as 0.6 μm(2). in simulation. In the experiment, the refractive index and phase transition after PE in LNOI were analyzed using the prism coupling method and X-ray diffraction. Three different width waveguides (5 μm, 7 μm and 11 μm) were optically characterized. Near-field intensity distribution showed that their mode sizes were 3.3 μm(2).,5 μm(2). and 7 μm(2). The propagation losses were evaluated to be about 16 dB/cm, 12 dB/cm and 11 dB/cm, respectively. The results indicate that PE is a promising method for building more complicated photonic integrated circuits in single-crystal LN thin film. PMID:25835882

  5. Hydrocarbon and partially fluorinated sulfonated copolymer blends as functional membranes for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Arnett, Natalie Y.; Harrison, William L.; Badami, Anand S.; Roy, Abhishek; Lane, Ozma; Cromer, Frank; Dong, Limin; McGrath, James E.

    Polymer blending is recognized as a valuable technique used to modify and improve the mechanical, thermal, and surface properties of two different polymers or copolymers. This paper investigated the solution properties and membrane properties of a biphenol-based disulfonated poly (arylene ether sulfone) random copolymer (BPS-35) with hexafluoroisopropylidene bisphenol based sulfonated poly (arylene ether sulfone) copolymers (6FSH) and an unsulfonated biphenol-based poly (arylene ether sulfone)s. The development of blended membranes with desirable surface characteristics, reduced water swelling and similar proton conductivity is presented. Polymer blends were prepared both in the sodium salt and acid forms from dimethylacetamide (DMAc). Water uptake, specific conductivity, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and contact angles were used to characterize the blended films. Surface enrichment of the fluorinated component is illustrated by an significant increase in the water-surface contact angle was observed when 10 wt.% 6FBPA-00 (106°) was added to BPS 35 (80°). Water weight gain was reduced by a factor of 2.

  6. Novel composite proton-exchange membrane based on proton-conductive glass powders and sulfonated poly (ether ether ketone)

    NASA Astrophysics Data System (ADS)

    Di, Zhigang; Xie, Qiang; Li, Haibin; Mao, Dali; Li, Ming; Zhou, Daowu; Li, Lu

    2015-01-01

    The SiO2-Nafion/sulfonated poly (ether ether ketone) (SPEEK) composite membranes are fabricated by using the simple mechanical ball-milling process to combine SiO2 glass powders with small portion of Nafion, in which SiO2 glass powders are prepared by modified sol-gel progress and Nafion is embedded in situ into a highly porous silica network. The morphology, thermal and mechanical properties, pore structure, proton conductivity and fuel cell performance of the SiO2-Nafion/SPEEK composite membranes are investigated. The poor miscibility of Nafion and sulfonated aromatic polymer is solved by fixing Nafion into SiO2 glass powders. The composite membranes perform well even if the proportion of inorganic component in membranes is as high as 40 wt.%. A maximum of proton conductivity, 0.018 S cm-1, is obtained from the membrane of 4(8Si-2N)/6SPEEK at 80 °C and 90% relative humidity, which is owing to its enhanced hygroscopicity and highly dispersed Nafion clusters. In addition, a single fuel cell equipped with the composite membrane shows a peak power density of 589.2 mW cm-2 at 70 °C.

  7. Calcineurin homologous proteins regulate the membrane localization and activity of sodium/proton exchangers in C. elegans.

    PubMed

    Allman, Erik; Wang, Qian; Walker, Rachel L; Austen, Molly; Peters, Maureen A; Nehrke, Keith

    2016-02-01

    Calcineurin B homologous proteins (CHP) are N-myristoylated, EF-hand Ca(2+)-binding proteins that bind to and regulate Na(+)/H(+) exchangers, which occurs through a variety of mechanisms whose relative significance is incompletely understood. Like mammals, Caenorhabditis elegans has three CHP paralogs, but unlike mammals, worms can survive CHP loss-of-function. However, mutants for the CHP ortholog PBO-1 are unfit, and PBO-1 has been shown to be required for proton signaling by the basolateral Na(+)/H(+) exchanger NHX-7 and for proton-coupled intestinal nutrient uptake by the apical Na(+)/H(+) exchanger NHX-2. Here, we have used this genetic model organism to interrogate PBO-1's mechanism of action. Using fluorescent tags to monitor Na(+)/H(+) exchanger trafficking and localization, we found that loss of either PBO-1 binding or activity caused NHX-7 to accumulate in late endosomes/lysosomes. In contrast, NHX-2 was stabilized at the apical membrane by a nonfunctional PBO-1 protein and was only internalized following its complete loss. Additionally, two pbo-1 paralogs were identified, and their expression patterns were analyzed. One of these contributed to the function of the excretory cell, which acts like a kidney in worms, establishing an alternative model for testing the role of this protein in membrane transporter trafficking and regulation. These results lead us to conclude that the role of CHP in Na(+)/H(+) exchanger regulation differs between apical and basolateral transporters. This further emphasizes the importance of proper targeting of Na(+)/H(+) exchangers and the critical role of CHP family proteins in this process. PMID:26561640

  8. Closed cycle ion exchange method for regenerating acids, bases and salts

    DOEpatents

    Dreyfuss, Robert M.

    1976-01-01

    A method for conducting a chemical reaction in acidic, basic, or neutral solution as required and then regenerating the acid, base, or salt by means of ion exchange in a closed cycle reaction sequence which comprises contacting the spent acid, base, or salt with an ion exchanger, preferably a synthetic organic ion-exchange resin, so selected that the counter ions thereof are ions also produced as a by-product in the closed reaction cycle, and then regenerating the spent ion exchanger by contact with the by-product counter ions. The method is particularly applicable to closed cycle processes for the thermochemical production of hydrogen.

  9. Ion exhange and molecular sorption of oxalic acid with a highly basic anion exchanger

    NASA Astrophysics Data System (ADS)

    Krisilova, E. V.; Oros, G. Yu.; Krisilov, A. V.; Selemenev, V. F.

    2014-04-01

    Ab initio modeling of a matrix fragment of resin and geometry optimization of the molecular structure of oxalic acid were performed. The isotherm of oxalic acid sorption with AV-17-8 anion exchange resin was obtained by the variable concentrations technique. The ion-exchange and molecular components of sorbate fixation with the ion exchanger were determined. The hydration of the highly basic anion exchanger that absorbed different quantities of dicarboxylic acid was evaluated by the centrifuging method. The dependence of the amount of water and sorbate concentration in the resin was linear antibatic.

  10. Membrane electrode assembly with enhanced platinum utilization for high temperature proton exchange membrane fuel cell prepared by catalyst coating membrane method

    NASA Astrophysics Data System (ADS)

    Liang, Huagen; Su, Huaneng; Pollet, Bruno G.; Linkov, Vladimir; Pasupathi, Sivakumar

    2014-11-01

    In this work, membrane electrode assemblies (MEAs) prepared by catalyst coating membrane (CCM) method are investigated for reduced platinum (Pt) loading and improved Pt utilization of high temperature proton exchange membrane fuel cell (PEMFC) based on phosphoric acid (PA)-doped poly(2,5-benzimidazole) (AB-PBI) membrane. The results show that CCM method exhibits significantly higher cell performance and Pt-specific power density than that of MEAs prepared with conventional gas diffusion electrode (GDE) under a low Pt loading level. In-suit cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show that the MEAs prepared by the CCM method have a higher electrochemical surface area (ECSA), low cell ohmic resistance and low charge transfer resistance as compared to those prepared with GDEs at the same Pt loading.

  11. Proton induced tautomeric switching in N-rich aromatics with tunable acid-base character

    NASA Astrophysics Data System (ADS)

    Centore, Roberto; Manfredi, Carla; Fusco, Sandra; Maglione, Cira; Carella, Antonio; Capobianco, Amedeo; Peluso, Andrea; Colonna, Daniele; Di Carlo, Aldo

    2015-08-01

    The acid-base properties of selected derivatives of the [1,2,4]triazolo[3,2-c][1,2,4]triazole fused aromatic system have been investigated by UV-vis spectroscopy. Neutral heterobicycles (HL) exhibit amphoteric behavior (they can deliver the N-H proton forming the conjugated base L- and can accept up to two protons, forming the species H2L+ and H3L++) and show an unprecedented tautomeric switching upon protonation, as revealed by single crystal X-ray analysis and confirmed by theoretical calculations. By varying the groups attached at the heterocycle, a remarkable shift of pKai values, up to 5-6 units, is observed. In particular, with strong electron attractor groups at position 7 (e.g. p-nitrophenyl or pentafluorophenyl) the neutral compounds are stronger acids than phenol or p-nitrophenol.

  12. Isotope fractionation of Si in protonation/deprotonation reaction of silicic acid: A new pH proxy

    NASA Astrophysics Data System (ADS)

    Fujii, Toshiyuki; Pringle, Emily A.; Chaussidon, Marc; Moynier, Frédéric

    2015-11-01

    Isotopic fractionation of Si in protonation/deprotonation reactions of monomeric silicic acids was theoretically and experimentally studied. The reduced partition function ratio for Si (as 1000 ln β) complexes was theoretically estimated by ab initio methods. Three permil of isotope fractionation was estimated to be possible for the 28Si-30Si isotope pair. This prediction was experimentally demonstrated by multi-collector inductively coupled plasma mass spectrometer measurements of Si-bearing aqueous solutions, for which equilibrated Si(OH)4 and SiO(OH)3- were separated using an anionic exchange column. The results create a new possibility for the application of Si isotopes as proxies for paleo-pH in the 9 < pH < 12 range.

  13. A concise guide to sustainable PEMFCs: recent advances in improving both oxygen reduction catalysts and proton exchange membranes.

    PubMed

    Scofield, Megan E; Liu, Haiqing; Wong, Stanislaus S

    2015-08-21

    The rising interest in fuel cell vehicle technology (FCV) has engendered a growing need and realization to develop rational chemical strategies to create highly efficient, durable, and cost-effective fuel cells. Specifically, technical limitations associated with the major constituent components of the basic proton exchange membrane fuel cell (PEMFC), namely the cathode catalyst and the proton exchange membrane (PEM), have proven to be particularly demanding to overcome. Therefore, research trends within the community in recent years have focused on (i) accelerating the sluggish kinetics of the catalyst at the cathode and (ii) minimizing overall Pt content, while simultaneously (a) maximizing activity and durability as well as (b) increasing membrane proton conductivity without causing any concomitant loss in either stability or as a result of damage due to flooding. In this light, as an example, high temperature PEMFCs offer a promising avenue to improve the overall efficiency and marketability of fuel cell technology. In this Critical Review, recent advances in optimizing both cathode materials and PEMs as well as the future and peculiar challenges associated with each of these systems will be discussed. PMID:26119055

  14. Transport properties of fast proton conducting mesoporous silica xerogels

    NASA Astrophysics Data System (ADS)

    Colomer, M. T.; Rubio, F.; Jurado, J. R.

    Mesoporous acid-free silica xerogels exhibiting a proton conductivity of 2.0 × 10 -2 S cm -1 at 80 °C and 81% RH is reported for the first time. The proton conductivity values, lower cost and higher hydrophilicity of mesoporous silica xerogels make them potential substitutes for Nafion membranes in proton exchange membranes fuel cells (PEMFCs).

  15. Improved measurement of labile proton concentration-weighted chemical exchange rate (kws) with experimental factor-compensated and T1-normalized quantitative chemical exchange saturation transfer (CEST) MRI

    PubMed Central

    Wu, Renhua; Liu, Charng-Ming; Liu, Philip K; Sun, Phillip Zhe

    2012-01-01

    Chemical exchange saturation transfer (CEST) MRI enables measurement of dilute CEST agents and microenvironment properties such as pH and temperature, holding great promise for in vivo applications. However, because of confounding concomitant RF irradiation and relaxation effects, the CEST-weighted MRI contrast may not fully characterize the underlying CEST phenomenon. We postulated that the accuracy of quantitative CEST MRI could be improved if the experimental factors (labeling efficiency and RF spillover effect) were estimated and taken into account. Specifically, the experimental factor was evaluated as a function of exchange rate and CEST agent concentration ratio, which remained relatively constant for intermediate RF irradiation power levels. Hence, the experimental factors can be calculated based on the reasonably estimated exchange rate and labile proton concentration ratio, which significantly improved quantification. The simulation was confirmed with Creatine phantoms of serially varied concentration titrated to the same pH, whose reverse exchange rate (kws) was found to be linearly correlated with the concentration. In summary, the proposed solution provides simplified yet reasonably accurate quantification of the underlying CEST system, which may help guide the ongoing development of quantitative CEST MRI. PMID:22649044

  16. Proton-dependent glutamine uptake by aphid bacteriocyte amino acid transporter ApGLNT1.

    PubMed

    Price, Daniel R G; Wilson, Alex C C; Luetje, Charles W

    2015-10-01

    Aphids house large populations of the gammaproteobacterial symbiont Buchnera aphidicola in specialized bacteriocyte cells. The combined biosynthetic capability of the holobiont (Acyrthosiphon pisum and Buchnera) is sufficient for biosynthesis of all twenty protein coding amino acids, including amino acids that animals alone cannot synthesize; and that are present at low concentrations in A. pisum's plant phloem sap diet. Collaborative holobiont amino acid biosynthesis depends on glutamine import into bacteriocytes, which serves as a nitrogen-rich amino donor for biosynthesis of other amino acids. Recently, we characterized A. pisum glutamine transporter 1 (ApGLNT1), a member of the amino acid/auxin permease family, as the dominant bacteriocyte plasma membrane glutamine transporter. Here we show ApGLNT1 to be structurally and functionally related to mammalian proton-dependent amino acid transporters (PATs 1-4). Using functional expression in Xenopus laevis oocytes, combined with two-electrode voltage clamp electrophysiology we demonstrate that ApGLNT1 is electrogenic and that glutamine induces large inward currents. ApGLNT1 glutamine induced currents are dependent on external glutamine concentration, proton (H+) gradient across the membrane, and membrane potential. Based on these transport properties, ApGLNT1-mediated glutamine uptake into A. pisum bacteriocytes can be regulated by changes in either proton gradients across the plasma membrane or membrane potential. PMID:26028424

  17. Analysis and Test of a Proton Exchange Membrane Fuel Cell Power System for Space Power Applications

    NASA Technical Reports Server (NTRS)

    Vasquez, Arturo; Varanauski, Donald; Clark, Robert, Jr.

    2000-01-01

    An effort is underway to develop a prototype Proton Exchange Membrane (PEM) Fuel Cell breadboard system for fuhlre space applications. This prototype will be used to develop a comprehensive design basis for a space-rated PEM fuel cell powerplant. The prototype system includes reactant pressure regulators, ejector-based reactant pumps, a 4-kW fuel cell stack and cooling system, and a passive, membranebased oxygen / water separator. A computer model is being developed concurrently to analytically predict fluid flow in the oxidant reactant system. Fuel cells have historically played an important role in human-rated spacecraft. The Gemini and Apollo spacecraft used fuel cells for vehicle electrical power. The Space Shuttle currently uses three Alkaline Fuel Cell Powerplants (AFCP) to generate all of the vehicle's 15-20kW electrical power. Engineers at the Johnson Space Center have leveraged off the development effort ongoing in the commercial arena to develop PEM fuel cel ls for terrestrial uses. The prototype design originated from efforts to develop a PEM fuel cell replacement for the current Space Shuttle AFCP' s. In order to improve on the life and an already excellent hi storical record of reliability and safety, three subsystems were focused on. These were the fuel cell stack itself, the reactant circulation devices, and reactant / product water separator. PEM fuel cell stack performance is already demonstrating the potential for greater than four times the useful life of the current Shuttle's AFCP. Reactant pumping for product water removal has historically been accomplished with mechanical pumps. Ejectors offer an effective means of reactant pumping as well as the potential for weight reduction, control simplification, and long life. Centrifugal water separation is used on the current AFCP. A passive, membrane-based water separator offers compatibility with the micro-gravity environment of space, and the potential for control simplification, elimination of

  18. Proton-Exchange-Membrane Fuel Cell Powerplants Developed and Tested for Exploration Missions

    NASA Astrophysics Data System (ADS)

    Hoberecht, Mark A.; Pham, Nang T.

    2005-06-01

    Proton-exchange-membrane fuel cell (PEMFC) technology has received major attention for terrestrial applications, such as the automotive and residential markets, for the past 20 years. This attention has significantly advanced the maturity of the technology, resulting in ever more compact, efficient, reliable, and inexpensive PEMFC designs. In comparison to the terrestrial operating environment, the space operating environment is much more demanding. Microgravity to high-gravity loads and the need to use pure oxygen (rather than air) as the fuel cell oxidizer place more stringent demands on PEMFC technology. NASA and its partners from industry are leveraging terrestrial PEMFC advancements by conducting parallel space technology development for future exploration missions. A team from the NASA Glenn Research Center, NASA Johnson Space Center, and NASA Kennedy Space Center recently completed the first phase of a PEMFC powerplant development effort for exploration missions. The industry partners for this phase of the development effort were ElectroChem, Inc., and Teledyne Energy Systems, Inc. Under contract to Glenn, both of these industry partners successfully designed, fabricated, and tested a breadboard PEMFC powerplant in the 1- to 5-kW power range. These powerplants were based on existing company-proprietary fuel cell stack designs, combined with off-the-shelf components, which formed the balance of the powerplant design. Subsequent to the contractor development efforts, both powerplants were independently tested at Johnson to verify operational and performance characteristics, and to determine suitability for further technology development in the second phase of the NASA-led effort. Following the independent NASA testing, Teledyne Energy Systems, Inc., was selected to develop an engineering model PEMFC powerplant. This effort was initiated by the 2nd Generation Reusable Launch Vehicle (RLV) Program Office in 2001; it transitioned to the Next Generation Launch

  19. Mass transport in gas diffusion layers of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Martinez, Michael J.

    This dissertation describes fundamental properties of gas diffusion media (GDM) and their relationship to the mass transport in proton exchange membrane fuel cells (PEMFCs). First, the accuracy of solving the multi-component equations for PEMFC by using a computational fluid dynamics (CFD) technique is examined. This technique uses an approximated multi-component (AMC) model with a correction term that guarantees the overall mass balance. Accuracy is assessed by comparing the species concentrations computed with the Maxwell-Stefan and the AMC model. This comparison is important because the structure of some CFD programs does not permit the direct use of the Maxwell-Stefan equations. Here, it is shown that the maximum error between the two models is less than 5%. Second, the ratio of tortuosity to porosity, known as the MacMullin number, is reported for different carbon cloth and carbon paper GDM. This analysis show that only carbon cloths GDM follow the commonly accepted Bruggeman equation and that carbon paper GDM have a different relationship between the tortuosity and the porosity. These differences are discussed in terms of path length created by the orientation of fibers of each GDM. Third, data for the hydrophilic and hydrophobic pore size distributions (PSD) are presented for two types of GDM used in PEMFCs. The data were obtained by using two common measurement methods, intrusion porosimetry (IP) and the method of standard porosimetry (MSP). The use of multiple working fluids to access hydrophilic and hydrophobic pores is discussed as well as the limitations associated with structural changes of the GDM during the tests. The differences in interpretations of the data between the two methods for both GDM have significant implications relative to the distribution of hydrophilic and hydrophobic pores that control liquid water transport. Finally, a two-phase mass-transport-only model (MTOM) that incorporates the tortuosity and the PSD data described above is

  20. Sorption of Water/Methanol on Teflon and Hydrocarbon Proton Exchange Membranes.

    PubMed

    He, Chenfeng; Mighri, Frej; Guiver, Michael D; Kaliaguine, Serge

    2016-05-18

    The sorption of water and methanol droplets on Teflon films, as well as on various representative classes of hydrocarbon-based proton exchange membranes (PEMs) was investigated using contact angle measurement (drop shape method) during wetting under ambient open-air conditions. Teflon films exhibited constant hydrophobic surfaces when contacted with water, but a significant sorption of methanol. The PEMs showed slow sorption of water, and a significant sorption of methanol. The differences in sorption of water and methanol on Teflon and PEMs arose from the match/compatibility in the surface free energies as well as polarities between a liquid and a membrane. The significant discrepancies in surface free energies and polarities between water (72.0 mJ m(-2) and 70.1%, respectively) and Teflon film (14.0 mJ m(-2) and 4.9%, respectively) lead to a highly hydrophobic surface and no discernible sorption of water on Teflon films, while the relative similarity or minor discrepancy in surface free energies and polarities between methanol (22.5 mJ m(-2) and 17.0%, respectively) and Teflon film (14.0 mJ m(-2) and 4.9%, respectively) results in a significant sorption of methanol on Teflon. The surface free energies of PEMs were calculated using the harmonic-mean approach, based on contact angle measurements using both water and diiodomethane as probes. The results show that PEMs have initial surface free energies ranging from 44.1 to 54.0 mJ m(-2) along with polarities in the range of 20.8 to 29.1%, for a selection of typical sulfonated polymers. The surface free energies of ionomers were principally contributed to by the nonpolar component, but the presence of polar groups in the polymer increased the polar component, leading to an increase in surface free energy. Of the PEMs investigated, sulfonated poly(aryl ether ether nitrile) has a higher surface energy than those of other ionomers with similar sulfonate contents. The compatibility between water/methanol and PEMs was

  1. Non-precious metal catalysis for proton-exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Leonard, Nathaniel Dean

    Non-precious metal catalysts (NPMC) for proton exchange membrane fuel cells (PEMFC) are explored. Research into NPMCs is motivated by the growing need for cleaner, more efficient energy options. NPMCs are one option to make fuel cells more commercially viable. To this end, the present work studies and simulates the morphology and function of metal-nitrogen-carbon (MNC) oxygen reduction catalysts. A porosity study finds that mesoporosity is critical to high performance of autogenic pressure metal-nitrogen-carbon (APMNC) oxygen reduction catalysts. Various carbon materials are used as precursors to synthesis APMNC catalysts. The catalysts and the associated porous carbon materials are characterized morphologically, chemically, and electrochemically. The results indicated that substrates adsorbing the most nitrogen and iron show the highest activity. Furthermore, a relationship is found between mesoporosity and nitrogen content indicating the importance of transport to active site creation. A correlation is found between surface alkalinity and catalytic activity for APMNC catalysts. The basic site strength and quantity were calculated by two different methods, and it was shown that increased Bronsted- Lowry basicity correlates to more active catalysts. The relationship between alkalinity and catalytic activity could be the result of the impact of alkalinity on the electron density of the metal centers or basic sites could encourage active site formation. It is found that the oxygen reduction reaction (ORR) proceeds both via a direct four-electron pathway to water at high potentials and an indirect peroxide pathway at low potentials on an APMNC catalyst. At higher potential, site availability inhibits peroxide generation causing the direct four-electron reduction pathway to dominate. Oxygen reduction begins to shift to the indirect peroxide pathway due to fast kinetics and higher site availability around 0.6 V vs RHE. The net peroxide generation remains relatively low

  2. Oxidation-resistant catalyst supports for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Chhina, Harmeet

    In automotive applications, when proton exchange membrane fuel cells (PEMFCs) are subjected to frequent startup-shutdown cycles, a significant drop in performance is observed. One reason for this drop in performance is oxidation of the carbon in the catalyst layer when cathode potential excursions as high as 1.5V are observed. In this work, non-carbon based catalyst support materials were studied. The materials investigated include: tungsten carbide (WC), tungsten oxide (WOx), and niobium (Nb) or tungsten (W) doped titania. Platinum was dispersed on commercial samples of WC and WO x. Stability tests were performed by stepping the materials between 0.6 to 1.8V. Higher stability of both WC and WOx was observed compared to carbon based commercial catalyst (HiSpec 4000). The performance of Pt supported on WC or WOx was found to be lower than that of Pt/C due to poor dispersion of Pt on these low surface area commercial powders. High surface area Nb and W doped titania materials synthesized using sol-gel techniques were subjected to several heat treatments and atmospheres, and their resulting physical properties characterized. The materials' phase changes and their impact on electrical conductivity were evaluated. W doped titania was found to be resistive, and for Nb doped titania, the rutile phase was found to be more conductive than the anatase phase. Conventionally, 10-50 wt% Pt is supported on carbon, but as the non-carbon catalyst support materials have different densities, similar mass ratios of catalyst to support will not result in directly comparable performances. It is recommended that the ratio of Pt surface area to the support surface area should be similar when comparing Pt supported on carbon to Pt supported on a non-carbon support. A normalization approach was investigated in this work, and the ORR performance of 40wt.%Pt/C was found to be similar to that of 10wt.%Pt/Nb-TiO2. Fuel cell performance tests showed significantly higher stability of Pt on Nb

  3. Proton-Exchange-Membrane Fuel Cell Powerplants Developed and Tested for Exploration Missions

    NASA Technical Reports Server (NTRS)

    Hoberecht, Mark A.; Pham, Nang T.

    2005-01-01

    Proton-exchange-membrane fuel cell (PEMFC) technology has received major attention for terrestrial applications, such as the automotive and residential markets, for the past 20 years. This attention has significantly advanced the maturity of the technology, resulting in ever more compact, efficient, reliable, and inexpensive PEMFC designs. In comparison to the terrestrial operating environment, the space operating environment is much more demanding. Microgravity to high-gravity loads and the need to use pure oxygen (rather than air) as the fuel cell oxidizer place more stringent demands on PEMFC technology. NASA and its partners from industry are leveraging terrestrial PEMFC advancements by conducting parallel space technology development for future exploration missions. A team from the NASA Glenn Research Center, NASA Johnson Space Center, and NASA Kennedy Space Center recently completed the first phase of a PEMFC powerplant development effort for exploration missions. The industry partners for this phase of the development effort were ElectroChem, Inc., and Teledyne Energy Systems, Inc. Under contract to Glenn, both of these industry partners successfully designed, fabricated, and tested a breadboard PEMFC powerplant in the 1- to 5-kW power range. These powerplants were based on existing company-proprietary fuel cell stack designs, combined with off-the-shelf components, which formed the balance of the powerplant design. Subsequent to the contractor development efforts, both powerplants were independently tested at Johnson to verify operational and performance characteristics, and to determine suitability for further technology development in the second phase of the NASA-led effort. Following the independent NASA testing, Teledyne Energy Systems, Inc., was selected to develop an engineering model PEMFC powerplant. This effort was initiated by the 2nd Generation Reusable Launch Vehicle (RLV) Program Office in 2001; it transitioned to the Next Generation Launch

  4. Measurement of proton chemical shifts in invisible states of slowly exchanging protein systems by chemical exchange saturation transfer.

    PubMed

    Bouvignies, Guillaume; Kay, Lewis E

    2012-12-13

    Chemical exchange saturation transfer (CEST) NMR spectroscopy has emerged as a powerful technique for studies of transiently formed, sparsely populated (excited) conformational states of protein molecules in slow exchange with a dominant structure. The most popular form of the experiment, and the version originally developed, uses a weak (1)H radio frequency field to perturb longitudinal magnetization of one state with the effect transferred to magnetization in the second conformation via chemical exchange. A significant limitation of the method for protein applications emerges from (1)H magnetization transfer via dipolar relaxation (NOE effect) that can severely complicate analysis of the resulting CEST profile. This is particularly an issue since the (1)H chemical shifts of the excited state, critical for structural studies of these elusive conformers, become difficult to extract. Here we present a method for measurement of these shifts via CEST experiments in which the NOE effect is not an issue. The methodology is illustrated through applications to a pair of exchanging systems where the results are cross-validated. PMID:23194058

  5. Conversion of CO2 and C2H6 to propanoic acid over a Au-exchanged MCM-22 zeolite.

    PubMed

    Sangthong, Winyoo; Probst, Michael; Limtrakul, Jumras

    2014-02-24

    Finding novel catalysts for the direct conversion of CO2 to fuels and chemicals is a primary goal in energy and environmental research. In this work, density functional theory (DFT) is used to study possible reaction mechanisms for the conversion of CO2 and C2H6 to propanoic acid over a gold-exchanged MCM-22 zeolite catalyst. The reaction begins with the activation of ethane to produce a gold ethyl hydride intermediate. Hydrogen transfers to the framework oxygen leads then to gold ethyl adsorbed on the Brønsted-acid site. The energy barriers for these steps of ethane activation are 9.3 and 16.3 kcal mol(-1), respectively. Two mechanisms of propanoic acid formation are investigated. In the first one, the insertion of CO2 into the Au-H bond of the first intermediate yields gold carboxyl ethyl as subsequent intermediate. This is then converted to propanoic acid by forming the relevant C-C bond. The activation energy of the rate-determining step of this pathway is 48.2 kcal mol(-1). In the second mechanism, CO2 interacts with gold ethyl adsorbed on the Brønsted-acid site. Propanoic acid is formed via protonation of CO2 by the Brønsted acid and the simultaneous formation of a bond between CO2 and the ethyl group. The activation energy there is 44.2 kcal mol(-1), favoring this second pathway at least at low temperatures. Gold-exchanged MCM-22 zeolite can therefore, at least in principle, be used as the catalyst for producing propanoic acid from CO2 and ethane. PMID:24375933

  6. Electrocatalytic reduction of acetone in a proton-exchange-membrane reactor: a model reaction for the electrocatalytic reduction of biomass.

    PubMed

    Green, Sara K; Tompsett, Geoffrey A; Kim, Hyung Ju; Bae Kim, Won; Huber, George W

    2012-12-01

    Acetone was electrocatalytically reduced to isopropanol in a proton-exchange-membrane (PEM) reactor on an unsupported platinum cathode. Protons needed for the reduction were produced on the unsupported Pt-Ru anode from either hydrogen gas or electrolysis of water. The current efficiency (the ratio of current contributing to the desired chemical reaction to the overall current) and reaction rate for acetone conversion increased with increasing temperature or applied voltage for the electrocatalytic acetone/water system. The reaction rate and current efficiency went through a maximum with respect to acetone concentration. The reaction rate for acetone conversion increased with increasing temperature for the electrocatalytic acetone/hydrogen system. Increasing the applied voltage for the electrocatalytic acetone/hydrogen system decreased the current efficiency due to production of hydrogen gas. Results from this study demonstrate the commercial feasibility of using PEM reactors to electrocatalytically reduce biomass-derived oxygenates into renewable fuels and chemicals. PMID:22961747

  7. Desulfonation of amino sulfonic acids of the benzene series in proton-donor media

    SciTech Connect

    Khelevin, R.N.

    1986-11-10

    In this work the desulfonation of amino sulfonic acids was studied by the determination of the kinetics of homogeneous isotopic exchange in radioactive sulfuric acid labeled with the isotope /sup 35/S, either containing HB(HSO/sub 4/)/sub 4/, or not containing it. The radioactive sulfuric acid was taken in an amount of 20 moles per mole of the amino sulfonic acid. Preliminary experiments showed that under these conditions neither the formation of disulfonic acids, nor the accumulation of desulfonated products occurs.

  8. UV-visible spectroscopy method for screening the chemical stability of potential antioxidants for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Banham, Dustin; Ye, Siyu; Knights, Shanna; Stewart, S. Michael; Wilson, Mahlon; Garzon, Fernando

    2015-05-01

    A novel method based on UV-visible spectroscopy is reported for screening the chemical stability of potential antioxidant additives for proton exchange membrane fuel cells, and the chemical stabilities of three CeOx samples of varying crystallite sizes (6, 13, or 25 nm) are examined. The chemical stabilities predicted by this new screening method are compared to in-situ membrane electrode assembly (MEA) accelerated stress testing, with the results confirming that this rapid and inexpensive method can be used to accurately predict performance impacts of antioxidants.

  9. Photoregenerative I−/I3− couple as a liquid cathode for proton exchange membrane fuel cell

    PubMed Central

    Liu, Zhen; Wang, Yadong; Ai, Xinping; Tu, Wenmao; Pan, Mu

    2014-01-01

    A photoassisted oxygen reduction reaction (ORR) through I−/I3− redox couple was investigated for proton exchange membrane (PEM) fuel cell cathode reaction. The I−/I3−-based liquid cathode was used to replace conventional oxygen cathode, and its discharge product I− was regenerated to I3− by photocatalytic oxidation with the participation of oxygen. This new and innovative approach may provide a strategy to eliminate the usage of challenging ORR electrocatalysts, resulting in an avenue for developing low-cost and high-efficiency PEM fuel cells. PMID:25348812

  10. The Investigation and Development of Low Cost Hardware Components for Proton-Exchange Membrane Fuel Cells - Final Report

    SciTech Connect

    George A. Marchetti

    1999-12-15

    Proton exchange membrane (PEM) fuel cell components, which would have a low-cost structure in mass production, were fabricated and tested. A fuel cell electrode structure, comprising a thin layer of graphite (50 microns) and a front-loaded platinum catalyst layer (600 angstroms), was shown to produce significant power densities. In addition, a PEM bipolar plate, comprising flexible graphite, carbon cloth flow-fields and an integrated polymer gasket, was fabricated. Power densities of a two-cell unit using this inexpensive bipolar plate architecture were shown to be comparable to state-of-the-art bipolar plates.

  11. Association between pH-weighted endogenous amide proton chemical exchange saturation transfer MRI and tissue lactic acidosis during acute ischemic stroke.

    PubMed

    Sun, Phillip Zhe; Cheung, Jerry S; Wang, Enfeng; Lo, Eng H

    2011-08-01

    The ischemic tissue becomes acidic after initiation of anaerobic respiration, which may result in impaired tissue metabolism and, ultimately, in severe tissue damage. Although changes in the major cerebral metabolites can be studied using magnetic resonance (MR) spectroscopy (MRS)-based techniques, their spatiotemporal resolution is often not sufficient for routine examination of fast-evolving and heterogeneous acute stroke lesions. Recently, pH-weighted MR imaging (MRI) has been proposed as a means to assess tissue acidosis by probing the pH-dependent chemical exchange of amide protons from endogenous proteins and peptides. In this study, we characterized acute ischemic tissue damage using localized proton MRS and multiparametric imaging techniques that included perfusion, diffusion, pH, and relaxation MRI. Our study showed that pH-weighted MRI can detect ischemic lesions and strongly correlates with tissue lactate content measured by (1)H MRS, indicating lactic acidosis. Our results also confirmed the correlation between apparent diffusion coefficient and lactate; however, no significant relationship was found for perfusion, T(1), and T(2). In summary, our study showed that optimized endogenous pH-weighted MRI, by sensitizing to local tissue pH, remains a promising tool for providing a surrogate imaging marker of lactic acidosis and altered tissue metabolism, and augments conventional techniques for stroke diagnosis. PMID:21386856

  12. Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids--part I: Eu3+ and Am3+ complexes in weakly acidic conditions.

    PubMed

    Wenming, Dong; Hongxia, Zhang; Meide, Huang; Zuyi, Tao

    2002-06-01

    The conditional stability constants for tracer concentrations of Eu(III) and Am(III) with a red earth humic acid (REHA), a red earth fulvic acid (REFA) and a fulvic acid from weathered coal (WFA) were determined at pH 5.2-6.4 (such values are similar to those in non-calcareous soils) in the presence of HAc/NaAc or NaNO3 by using the cation exchange method. It was found that 1:1 complexes were predominately formed in weakly acidic conditions. The total exchangeable proton capacities and the degrees of dissociation of these humic substances were determined by using a potentiometric titration method. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in weakly acidic conditions by using the cation exchange method were discussed. The conditional stability constants of 1:1 complexes obtained in this paper were compared with the literature data of Am(III) determined by using the ion exchange method and the solvent extraction method and with the stability constants of 1:1 complexes of UO2(2+) and Th4+ with the same soil humic substances. These results indicate the great stability of bivalent UO2(2+), trivalent Eu3+, Am3+ and tetravalent Th4+ complexes with humic and fulvic acids in weakly acidic conditions. PMID:12102358

  13. Meson exchange effects in elastic ep scattering at loop level and the electromagnetic form factors of the proton

    NASA Astrophysics Data System (ADS)

    Chen, Hong-Yu; Zhou, Hai-Qing

    2014-10-01

    A new form of two-photon exchange (TPE) effect is studied to explain the discrepancy between unpolarized and polarized experimental data in elastic ep scattering. The mechanism is based on a simple idea that apart from the usual TPE effects from box and crossed-box diagrams, the mesons may also be exchanged in elastic ep scattering by two-photon coupling at loop level. The detailed study shows such contributions to reduced unpolarized cross section (σun) and polarized observables (Pt,Pl) at fixed Q2 are only dependent on proton's electromagnetic form factors GE ,M and a new unknown universal parameter g. After combining this contribution with the usual TPE contributions from box and crossed-box diagrams, the ratio μpGE/GM extracted from the recent precise unpolarized and polarized experimental data can be described consistently.

  14. Electrochemical synthesis of poly(3-aminophenylboronic acid) in ethylene glycol without exogenous protons.

    PubMed

    Wang, Feifan; Zou, Feixue; Yu, Xinxin; Feng, Zhenyu; Du, Na; Zhong, Yaohua; Huang, Xirong

    2016-04-21

    A non-aqueous solution of tetra-n-butylammonium fluoride (TBAF) in ethylene glycol has been tried for the first time as a supporting electrolyte for the electropolymerization of 3-aminophenylboronic acid (APBA). Unlike the traditional acidic aqueous solution, the present medium needs no exogenous protons; moreover, the presence of CF3COOH is found to be unfavorable for the polymerization. The protons are in situ generated by the reaction between the boronic acid group on APBA and 1,2-dihydroxyl on ethylene glycol. So, ethylene glycol serves as not only the solvent but also the proton source. As a part of the supporting electrolyte, F(-) is found to be involved in the electrochemical synthesis of poly(3-aminophenylboronic acid) (PAPBA), but it is not indispensable. Studies on the electropolymerization process indicate that the size of the ions in the electrolyte affects the rate of the doping/dedoping process. The smaller the cation, the easier the doping/dedoping process, and the better the stability of the grown film. As demonstrated by Fourier transform infrared spectra, UV-vis spectra, and scanning electron microscopy, the obtained PAPBA is a cross-linked nanoporous polymer membrane that has a good adherence to the glassy carbon electrode. PMID:27004602

  15. Dual role for the tyrosine decarboxylation pathway in Enterococcus faecium E17: response to an acid challenge and generation of a proton motive force.

    PubMed

    Pereira, C I; Matos, D; San Romão, M V; Crespo, M T Barreto

    2009-01-01

    In this work we investigated the role of the tyrosine decarboxylation pathway in the response of Enterococcus faecium E17 cells to an acid challenge. It was found that 91% of the cells were able to remain viable in the presence of tyrosine when they were incubated for 3 h in a complex medium at pH 2.5. This effect was shown to be related to the tyrosine decarboxylation pathway. Therefore, the role of tyrosine decarboxylation in pH homeostasis was studied. The membrane potential and pH gradient, the parameters that compose the proton motive force (PMF), were measured at different pHs (pH 4.5 to 7). We obtained evidence showing that the tyrosine decarboxylation pathway generates a PMF composed of a pH gradient formed due to proton consumption in the decarboxylation reaction and by a membrane potential which results from electrogenic transport of tyrosine in exchange for the corresponding biogenic amine tyramine. The properties of the tyrosine transporter were also studied in this work by using whole cells and right-side-out vesicles. The results showed that the transporter catalyzes homologous tyrosine/tyrosine antiport, as well as electrogenic heterologous tyrosine-tyramine exchange. The tyrosine transporter had properties of a typical precursor-product exchanger operating in a proton motive decarboxylation pathway. Therefore, the tyrosine decarboxylation pathway contributes to an acid response mechanism in E. faecium E17. This decarboxylation pathway gives the strain a competitive advantage in nutrient-depleted conditions, as well as in harsh acidic environments, and a better chance of survival, which contributes to higher cell counts in food fermentation products. PMID:19011061

  16. Sterically Demanding Multidentate Ligand Tris[(2-(6-methylpyridyl))methyl]amine Slows Exchange and Enhances Solution State Ligand Proton NMR Coupling to 199Hg(II)

    PubMed Central

    Bebout, Deborah C.; Bush, James F.; Crahan, Kathleen K.; Bowers, Edith V.; Butcher, Raymond J.

    2006-01-01

    The solution state coordination chemistry of Hg(ClO4)2 with tris[(2-(6-methylpyridyl))methyl]amine (TLA) was investigated in acetonitrile-d3 by proton NMR. Although Hg(II) is a d10 metal ion commonly associated with notoriously rapid exchange between coordination environments, as many as six ligand environments were observed to be in slow exchange on the chemical shift time scale at select metal-to-ligand ratios. One of these ligand environments was associated with extensive heteronuclear coupling between protons and 199Hg and was assigned to the complex [Hg(TLA)]2+. The 5J(1H199Hg) = 8 Hz associated with this complex is the first example of five-bond coupling in a nitrogen coordination compound of Hg(II). The spectral complexity of related studies conducted in acetone-d6 precluded analysis of coordination equilibria. Crystallographic characterization of the T-shaped complex [Hg(TLAH)(CH2COCH3)](ClO4)2 (1) in which two pyridyl rings are pendant suggested that the acidity of acetone combined with the poor coordinating abilities of the neutral solvent adds additional complexity to solution equilibria. The complex crystallizes in the triclinic space group P1¯ with a = 9.352(2) Å, b = 12.956(2) Å, c = 14.199(2) Å, α = 115.458(10)°, β = 90.286(11)°, γ = 108.445(11)°, and Z = 2. The HgNamine, Hg-Npyridyl, and Hg-C bond lengths in the complex are 2.614(4), 2.159(4), and 2.080(6) Å, respectively. Relevance to development of 199Hg NMR as a metallobioprobe is discussed. PMID:11978122

  17. Performance evaluation and characterization of metallic bipolar plates in a proton exchange membrane (PEM) fuel cell

    NASA Astrophysics Data System (ADS)

    Hung, Yue

    Bipolar plate and membrane electrode assembly (MEA) are the two most repeated components of a proton exchange membrane (PEM) fuel cell stack. Bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack. The bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cell, and constitute the backbone of a power stack. In addition, bipolar plates must have excellent corrosion resistance to withstand the highly corrosive environment inside the fuel cell, and they must maintain low interfacial contact resistance throughout the operation to achieve optimum power density output. Currently, commercial bipolar plates are made of graphite composites because of their relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite's manufacturability, permeability, and durability for shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. Since bipolar plates must possess the combined advantages of both metals and graphite composites in the fuel cell technology, various methods and techniques are being developed to combat metallic corrosion and eliminate the passive layer formed on the metal surface that causes unacceptable power reduction and possible fouling of the catalyst and the electrolyte. The main objective of this study was to explore the possibility of producing efficient, cost-effective and durable metallic bipolar plates that were capable of functioning in the highly corrosive fuel cell environment. Bulk materials such as Poco graphite, graphite composite, SS310, SS316, incoloy 800, titanium carbide and zirconium carbide were investigated as potential bipolar plate materials. In this work, different alloys and compositions of chromium carbide coatings on aluminum and SS316

  18. Nanostructured TiOx as a catalyst support material for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Phillips, Richard S.

    Recent interest in the development of new catalyst support materials for proton exchange membrane fuel cells (PEMFCs) has stimulated research into the viability of TiO2-based support structures. Specifically, substoichiometric TiO2 (TiOx) has been reported to exhibit a combination of high conductivity, stability, and corrosion resistance. These properties make TiOx-based support materials a promising prospect when considering the inferior corrosion resistance of traditional carbon-based supports. This document presents an investigation into the formation of conductive and stable TiOx thin films employing atomic layer deposition (ALD) and a post deposition oxygen reducing anneal (PDORA). Techniques for manufacturing TiOx-based catalyst support nanostructures by means of ALD in conjunction with carbon black (CB), anodic aluminum oxide (AAO) and silicon nanowires (SiNWs) will also be presented. The composition and thickness of resulting TiOx thin films was determined with the aid of Auger electron spectroscopy (AES), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Film crystal structure was determined with X-ray diffraction (XRD) analysis. Film conductivity was calculated using four-point probe (4-PP) and film thickness measurement data. Resulting thin films show a significant decrease of oxygen in ALD TiOx films corresponding with a great increase in conductivity following the PDORA. The effectiveness of the PDORA was also found to be highly dependent on ALD process parameters. TiOx-based nanostructures were coated with platinum using one of three Pt deposition techniques. First, liquid phase deposition (LPD), which was performed at room temperature, provided equal access to catalyst support material surfaces which were suspended in solution. Second, plasma enhanced atomic layer deposition (PEALD), which was performed at 450°C, provided good Pt

  19. Intracellular pH regulation in rainbow trout (Oncorhynchus mykiss) hepatocytes: the activity of sodium/proton exchange is oxygen-dependent.

    PubMed

    Tuominen, A; Rissanen, E; Bogdanova, A; Nikinmaa, M

    2003-06-01

    We studied pH regulation in freshly isolated rainbow trout hepatocytes using microspectrofluorometry with the fluorescent dye BCECF. In accordance with earlier data on rainbow trout hepatocytes, ion substitution (N-methyl D-glucamine for sodium and gluconate for chloride) and transport inhibitor [10 microM M methyl isobutyl amiloride (MIA) to inhibit sodium/proton exchange and 100 microM DIDS to inhibit bicarbonate transport] studies in either Hepes-buffered or bicarbonate/carbon dioxide-buffered media (extracellular pH 7.6) indicated a role for sodium/proton exchange, sodium-dependent bicarbonate transport, and sodium-independent anion exchange in the regulation of hepatocyte pH. In Hepes-buffered medium, the activity of the sodium/proton exchanger (i.e. proton extrusion inhibited by MIA) was greater at 1% than at 21% oxygen. The oxygen dependency of the sodium/proton exchange is not caused by hydroxyl radicals, which appear to mediate the oxygen sensitivity of potassium-chloride cotransport in erythrocytes. PMID:12820008

  20. Proton transfer aiding phase transitions in oxalic acid dihydrate under pressure.

    PubMed

    Bhatt, Himal; Mishra, A K; Murli, Chitra; Verma, Ashok K; Garg, Nandini; Deo, M N; Sharma, Surinder M

    2016-03-21

    Oxalic acid dihydrate, an important molecular solid in crystal chemistry, ecology and physiology, has been studied for nearly 100 years now. The most debated issues regarding its proton dynamics have arisen due to an unusually short hydrogen bond between the acid and water molecules. Using combined in situ spectroscopic studies and first-principles simulations at high pressures, we show that the structural modification associated with this hydrogen bond is much more significant than ever assumed. Initially, under pressure, proton migration takes place along this strong hydrogen bond at a very low pressure of 2 GPa. This results in the protonation of water with systematic formation of dianionic oxalate and hydronium ion motifs, thus reversing the hydrogen bond hierarchy in the high pressure phase II. The resulting hydrogen bond between a hydronium ion and a carboxylic group shows remarkable strengthening under pressure, even in the pure ionic phase III. The loss of cooperativity of hydrogen bonds leads to another phase transition at ∼ 9 GPa through reorientation of other hydrogen bonds. The high pressure phase IV is stabilized by a strong hydrogen bond between the dominant CO2 and H2O groups of oxalate and hydronium ions, respectively. These findings suggest that oxalate systems may provide useful insights into proton transfer reactions and assembly of simple molecules under extreme conditions. PMID:26924455

  1. Proton dynamics in the hydrogen bonds of 4-amino-3,5-dihalogenobenzoic acid

    NASA Astrophysics Data System (ADS)

    Asaji, Tetsuo; Ueda, Kouhei; Oguni, Masaharu

    2015-08-01

    On the polycrystalline sample of 4-amino-3,5-dihalogenobenzoic acid, 4-NH2-3,5-X2C6H2COOH, which has a symmetric dimer structure in the crystal, the proton tunneling in the hydrogen bonds has been investigated by NQR and NMR spin-lattice relaxation times T1 measurements. Two 35Cl NQR lines of the X = Cl derivative show the existence of two crystallographically inequivalent chlorine atoms in the high-temperature phase, in consistency with the reported crystal structure. Below 138 K, each splits into a doublet indicating the symmetry breaking of the benzoic acid dimer. The proton dynamics was analyzed by a coherent and incoherent tunneling models, for the high- and low-temperature phases, respectively. The temperature dependence of the correlation time of proton translation was estimated. As for the X = I derivative, the proton dynamics was discussed similarly by 1H NMR T1 data by assuming occurrence of a phase transition at low-temperature.

  2. Proton-mediated Conformational Changes in an Acid-sensing Ion Channel*

    PubMed Central

    Ramaswamy, Swarna S.; MacLean, David M.; Gorfe, Alemayehu A.; Jayaraman, Vasanthi

    2013-01-01

    Acid-sensing ion channels are cation channels activated by external protons and play roles in nociception, synaptic transmission, and the physiopathology of ischemic stroke. Using luminescence resonance energy transfer (LRET), we show that upon proton binding, there is a conformational change that increases LRET efficiency between the probes at the thumb and finger subdomains in the extracellular domain of acid-sensing ion channels. Additionally, we show that this conformational change is lost upon mutating Asp-238, Glu-239, and Asp-260, which line the finger domains, to alanines. Electrophysiological studies showed that the single mutant D260A shifted the EC50 by 0.2 pH units, the double mutant D238A/E239A shifted the EC50 by 2.5 pH units, and the triple mutant D238A/E239A/D260A exhibited no response to protons despite surface expression. The LRET experiments on D238A/E239A/D260A showed no changes in LRET efficiency upon reduction in pH from 8 to 6. The LRET and electrophysiological studies thus suggest that the three carboxylates, two of which are involved in carboxyl/carboxylate interactions, are essential for proton-induced conformational changes in the extracellular domain, which in turn are necessary for receptor activation. PMID:24196950

  3. Development of multiblock copolymers with novel hydroquinone-based hydrophilic blocks for proton exchange membrane (PEM) applications

    NASA Astrophysics Data System (ADS)

    Lee, Hae-Seung; Lane, Ozma; McGrath, James E.

    Hydrophilic-hydrophobic sequenced multiblock copolymers were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers were prepared by a coupling reaction between fully disulfonated hydroquinone-based hydrophilic oligomers (HQS100) and unsulfonated poly(arylene ether sulfone) hydrophobic oligomers (BPS0). The hydroquinone-based hydrophilic oligomers possess several advantages over previously utilized biphenol-based hydrophilic oligomers (BPS100), including higher hydrophilicity, enhanced nano-phase separation with hydrophobic segments, and lower cost. To maintain the hydrophilic-hydrophobic sequences in the system, the coupling reactions were conducted at low temperature (e.g., 105 °C) to avoid ether-ether exchange reactions. The coupling reaction was solvent sensitive due to a low reactivity of the hydroquinone-phenoxide end-group on the HQS100. All copolymers produced tough ductile films when cast from an NMP or DMF solution. Fundamental membrane parameters including water uptake, proton conductivity, and swelling ratio were investigated along with morphology characterizations by atomic force microscopy (AFM).

  4. Synthesis and characterization of partially fluorinated hydrophobic-hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane

    NASA Astrophysics Data System (ADS)

    Li, Yanxiang; Roy, Abhishek; Badami, Anand S.; Hill, Melinda; Yang, Juan; Dunn, Stuart; McGrath, James E.

    A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. 19F and 1H NMR spectra were used to characterize the oligomers' molecular weights and multiblock copolymer's structure. The comparison of the multiblock copolymer 13C NMR spectrum with that of the random copolymer showed that the transetherification side reaction was minimized in this synthesis. The morphologies of membranes were investigated by tapping mode atomic force microscopy (AFM), which showed that the multiblock membrane acidified by the high temperature method has sharp phase separation. Membrane properties like protonic conductivity, water uptake, and self-diffusion coefficient of water as a function of temperature and relative humidity (RH) were characterized for the multiblock copolymer and compared with ketone type random copolymers at similar ion exchange capacity value and Nafion ® controls. The multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity.

  5. Soil surface acidity plays a determining role in the atmospheric-terrestrial exchange of nitrous acid

    PubMed Central

    Donaldson, Melissa A.; Bish, David L.; Raff, Jonathan D.

    2014-01-01

    Nitrous acid (HONO) is an important hydroxyl (OH) radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Recent studies report the release of HONO from nonacidic soils, although it is unclear how soil that is more basic than the pKa of HONO (∼3) is capable of protonating soil nitrite to serve as an atmospheric HONO source. Here, we used a coated-wall flow tube and chemical ionization mass spectrometry (CIMS) to study the pH dependence of HONO uptake onto agricultural soil and model substrates under atmospherically relevant conditions (1 atm and 30% relative humidity). Experiments measuring the evolution of HONO from pH-adjusted surfaces treated with nitrite and potentiometric titrations of the substrates show, to our knowledge for the first time, that surface acidity rather than bulk aqueous pH determines HONO uptake and desorption efficiency on soil, in a process controlled by amphoteric aluminum and iron (hydr)oxides present. The results have important implications for predicting when soil nitrite, whether microbially derived or atmospherically deposited, will act as a net source or sink of atmospheric HONO. This process represents an unrecognized mechanism of HONO release from soil that will contribute to HONO emissions throughout the day. PMID:25512517

  6. Soil surface acidity plays a determining role in the atmospheric-terrestrial exchange of nitrous acid.

    PubMed

    Donaldson, Melissa A; Bish, David L; Raff, Jonathan D

    2014-12-30

    Nitrous acid (HONO) is an important hydroxyl (OH) radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Recent studies report the release of HONO from nonacidic soils, although it is unclear how soil that is more basic than the pKa of HONO (∼ 3) is capable of protonating soil nitrite to serve as an atmospheric HONO source. Here, we used a coated-wall flow tube and chemical ionization mass spectrometry (CIMS) to study the pH dependence of HONO uptake onto agricultural soil and model substrates under atmospherically relevant conditions (1 atm and 30% relative humidity). Experiments measuring the evolution of HONO from pH-adjusted surfaces treated with nitrite and potentiometric titrations of the substrates show, to our knowledge for the first time, that surface acidity rather than bulk aqueous pH determines HONO uptake and desorption efficiency on soil, in a process controlled by amphoteric aluminum and iron (hydr)oxides present. The results have important implications for predicting when soil nitrite, whether microbially derived or atmospherically deposited, will act as a net source or sink of atmospheric HONO. This process represents an unrecognized mechanism of HONO release from soil that will contribute to HONO emissions throughout the day. PMID:25512517

  7. Proton exchange membrane fuel cells for space and electric vehicle applications: From basic research to technology development

    NASA Technical Reports Server (NTRS)

    Srinivasan, Supramaniam; Mukerjee, Sanjeev; Parthasarathy, A.; CesarFerreira, A.; Wakizoe, Masanobu; Rho, Yong Woo; Kim, Junbom; Mosdale, Renaut A.; Paetzold, Ronald F.; Lee, James

    1994-01-01

    The proton exchange membrane fuel cell (PEMFC) is one of the most promising electrochemical power sources for space and electric vehicle applications. The wide spectrum of R&D activities on PEMFC's, carried out in our Center from 1988 to date, is as follows (1) Electrode Kinetic and Electrocatalysis of Oxygen Reduction; (2) Optimization of Structures of Electrodes and of Membrane and Electrode Assemblies; (3) Selection and Evaluation of Advanced Proton Conducting Membranes and of Operating Conditions to Attain High Energy Efficiency; (4) Modeling Analysis of Fuel Cell Performance and of Thermal and Water Management; and (5) Engineering Design and Development of Multicell Stacks. The accomplishments on these tasks may be summarized as follows: (1) A microelectrode technique was developed to determine the electrode kinetic parameters for the fuel cell reactions and mass transport parameters for the H2 and O2 reactants in the proton conducting membrane. (2) High energy efficiencies and high power densities were demonstrated in PEMFCs with low platinum loading electrodes (0.4 mg/cm(exp 2) or less), advanced membranes and optimized structures of membrane and electrode assemblies, as well as operating conditions. (3) The modeling analyses revealed methods to minimize mass transport limitations, particularly with air as the cathodic reactant; and for efficient thermal and water management. (4) Work is in progress to develop multi-kilowatt stacks with the electrodes containing low platinum loadings.

  8. Asparagine promotes cancer cell proliferation through use as an amino acid exchange factor

    PubMed Central

    Krall, Abigail S.; Xu, Shili; Graeber, Thomas G.; Braas, Daniel; Christofk, Heather R.

    2016-01-01

    Cellular amino acid uptake is critical for mTOR complex 1 (mTORC1) activation and cell proliferation. However, the regulation of amino acid uptake is not well-understood. Here we describe a role for asparagine as an amino acid exchange factor: intracellular asparagine exchanges with extracellular amino acids. Through asparagine synthetase knockdown and altering of media asparagine concentrations, we show that intracellular asparagine levels regulate uptake of amino acids, especially serine, arginine and histidine. Through its exchange factor role, asparagine regulates mTORC1 activity and protein synthesis. In addition, we show that asparagine regulation of serine uptake influences serine metabolism and nucleotide synthesis, suggesting that asparagine is involved in coordinating protein and nucleotide synthesis. Finally, we show that maintenance of intracellular asparagine levels is critical for cancer cell growth. Collectively, our results indicate that asparagine is an important regulator of cancer cell amino acid homeostasis, anabolic metabolism and proliferation. PMID:27126896

  9. Elusive Sulfurous Acid: Gas-Phase Basicity and IR Signature of the Protonated Species.

    PubMed

    Sinha, Rajeev K; Scuderi, Debora; Maitre, Philippe; Chiavarino, Barbara; Crestoni, Maria Elisa; Fornarini, Simonetta

    2015-05-01

    The ion corresponding to protonated sulfurous acid, H3SO3(+), has been successfully delivered into the gas phase by electrospray ionization of the solution of a suitable precursor and an in-source fragmentation process. The neutral acid is a highly elusive molecule. However, its gas-phase basicity has been ascertained by means of a kinetic study of proton-transfer reactivity. The structure of the H3SO3(+) sampled ion has been probed by IRMPD spectroscopy in two complementary IR frequency ranges in conjunction with density functional theory calculations and found to conform to a trihydroxosulfonium ion. The characteristic IR signatures may aid in deciphering the presence of this species in extraterrestrial atmospheres. PMID:26263321

  10. Sulphur Kβ emission spectra reveal protonation states of aqueous sulfuric acid

    NASA Astrophysics Data System (ADS)

    Niskanen, Johannes; Sahle, Christoph J.; Ruotsalainen, Kari O.; Müller, Harald; Kavčič, Matjaž; Žitnik, Matjaž; Bučar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-02-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range.

  11. Sulphur Kβ emission spectra reveal protonation states of aqueous sulfuric acid.

    PubMed

    Niskanen, Johannes; Sahle, Christoph J; Ruotsalainen, Kari O; Müller, Harald; Kavčič, Matjaž; Žitnik, Matjaž; Bučar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-01-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range. PMID:26888159

  12. Sulphur Kβ emission spectra reveal protonation states of aqueous sulfuric acid

    PubMed Central

    Niskanen, Johannes; Sahle, Christoph J.; Ruotsalainen, Kari O.; Müller, Harald; Kavčič, Matjaž; Žitnik, Matjaž; Bučar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-01-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range. PMID:26888159

  13. Quantum chemical ab initio prediction of proton exchange barriers between CH4 and different H-zeolites.

    PubMed

    Tuma, Christian; Sauer, Joachim

    2015-09-14

    A hybrid MP2:DFT (second-order Møller-Plesset perturbation theory-density functional theory) method that combines MP2 calculations for cluster models with DFT calculations for the full periodic structure is used to localize minima and transition structures for proton jumps at different Brønsted sites in different frameworks (chabazite, faujasite, ferrierite, and ZSM-5) and at different crystallographic positions of a given framework. The MP2 limit for the periodic structures is obtained by extrapolating the results of a series of cluster models of increasing size. A coupled-cluster (CCSD(T)) correction to MP2 energies is calculated for cluster models consisting of three tetrahedra. For the adsorption energies, this difference is small, between 0.1 and 0.9 kJ/mol, but for the intrinsic proton exchange barriers, this difference makes a significant (10.85 ± 0.25 kJ/mol) and almost constant contribution across different systems. The total values of the adsorption energies vary between 22 and 34 kJ/mol, whereas the total proton exchange energy barriers fall in the narrow range of 152-156 kJ/mol. After adding nuclear motion contributions (harmonic approximation, 298 K), intrinsic enthalpy barriers between 134 and 141 kJ/mol and apparent energy barriers between 105 and 118 kJ/mol are predicted for the different sites examined for the different frameworks. These predictions are consistent with experimental results available for faujasite, ferrierite, and ZSM-5. PMID:26374003

  14. Quantum chemical ab initio prediction of proton exchange barriers between CH{sub 4} and different H-zeolites

    SciTech Connect

    Tuma, Christian; Sauer, Joachim

    2015-09-14

    A hybrid MP2:DFT (second-order Møller–Plesset perturbation theory–density functional theory) method that combines MP2 calculations for cluster models with DFT calculations for the full periodic structure is used to localize minima and transition structures for proton jumps at different Brønsted sites in different frameworks (chabazite, faujasite, ferrierite, and ZSM-5) and at different crystallographic positions of a given framework. The MP2 limit for the periodic structures is obtained by extrapolating the results of a series of cluster models of increasing size. A coupled-cluster (CCSD(T)) correction to MP2 energies is calculated for cluster models consisting of three tetrahedra. For the adsorption energies, this difference is small, between 0.1 and 0.9 kJ/mol, but for the intrinsic proton exchange barriers, this difference makes a significant (10.85 ± 0.25 kJ/mol) and almost constant contribution across different systems. The total values of the adsorption energies vary between 22 and 34 kJ/mol, whereas the total proton exchange energy barriers fall in the narrow range of 152–156 kJ/mol. After adding nuclear motion contributions (harmonic approximation, 298 K), intrinsic enthalpy barriers between 134 and 141 kJ/mol and apparent energy barriers between 105 and 118 kJ/mol are predicted for the different sites examined for the different frameworks. These predictions are consistent with experimental results available for faujasite, ferrierite, and ZSM-5.

  15. Computing in mammalian cells with nucleic acid strand exchange

    NASA Astrophysics Data System (ADS)

    Groves, Benjamin; Chen, Yuan-Jyue; Zurla, Chiara; Pochekailov, Sergii; Kirschman, Jonathan L.; Santangelo, Philip J.; Seelig, Georg

    2016-03-01

    DNA strand displacement has been widely used for the design of molecular circuits, motors, and sensors in cell-free settings. Recently, it has been shown that this technology can also operate in biological environments, but capabilities remain limited. Here, we look to adapt strand displacement and exchange reactions to mammalian cells and report DNA circuitry that can directly interact with a native mRNA. We began by optimizing the cellular performance of fluorescent reporters based on four-way strand exchange reactions and identified robust design principles by systematically varying the molecular structure, chemistry and delivery method. Next, we developed and tested AND and OR logic gates based on four-way strand exchange, demonstrating the feasibility of multi-input logic. Finally, we established that functional siRNA could be activated through strand exchange, and used native mRNA as programmable scaffolds for co-localizing gates and visualizing their operation with subcellular resolution.

  16. Computing in mammalian cells with nucleic acid strand exchange

    PubMed Central

    Pochekailov, Sergii; Kirschman, Jonathan L.; Santangelo, Philip J.; Seelig, Georg

    2015-01-01

    DNA strand displacement has been widely used for the design of molecular circuits, motors, and sensors in cell-free settings. Recently, it has been shown that this technology can also operate in biological environments, but capabilities remain limited. Here, we look to adapt strand displacement and exchange reactions to mammalian cells and report DNA circuitry that can directly interact with a native mRNA. We began by optimizing the cellular performance of fluorescent reporters based on four-way strand exchange reactions and identified robust design principles by systematically varying the molecular structure, chemistry and delivery method. Next, we developed and tested AND and OR logic gates based on four-way strand exchange, demonstrating the feasibility of multi-input logic. Finally, we established that functional siRNA could be activated through strand exchange, and used native mRNA as programmable scaffolds for co-localizing gates and visualizing their operation with subcellular resolution. PMID:26689378

  17. Computing in mammalian cells with nucleic acid strand exchange.

    PubMed

    Groves, Benjamin; Chen, Yuan-Jyue; Zurla, Chiara; Pochekailov, Sergii; Kirschman, Jonathan L; Santangelo, Philip J; Seelig, Georg

    2016-03-01

    DNA strand displacement has been widely used for the design of molecular circuits, motors, and sensors in cell-free settings. Recently, it has been shown that this technology can also operate in biological environments, but capabilities remain limited. Here, we look to adapt strand displacement and exchange reactions to mammalian cells and report DNA circuitry that can directly interact with a native mRNA. We began by optimizing the cellular performance of fluorescent reporters based on four-way strand exchange reactions and identified robust design principles by systematically varying the molecular structure, chemistry and delivery method. Next, we developed and tested AND and OR logic gates based on four-way strand exchange, demonstrating the feasibility of multi-input logic. Finally, we established that functional siRNA could be activated through strand exchange, and used native mRNA as programmable scaffolds for co-localizing gates and visualizing their operation with subcellular resolution. PMID:26689378

  18. Simultaneous experimental determination of labile proton fraction ratio and exchange rate with irradiation radio frequency power-dependent quantitative CEST MRI analysis.

    PubMed

    Sun, Phillip Zhe; Wang, Yu; Xiao, Gang; Wu, Renhua

    2013-01-01

    Chemical exchange saturation transfer (CEST) imaging is sensitive to dilute proteins/peptides and microenvironmental properties, and has been increasingly evaluated for molecular imaging and in vivo applications. However, the experimentally measured CEST effect depends on the CEST agent concentration, exchange rate and relaxation time. In addition, there may be non-negligible direct radio-frequency (RF) saturation effects, particularly severe for diamagnetic CEST (DIACEST) agents owing to their relatively small chemical shift difference from that of the bulk water resonance. As such, the commonly used asymmetry analysis only provides CEST-weighted information. Recently, it has been shown with numerical simulation that both labile proton concentration and exchange rate can be determined by evaluating the RF power dependence of DIACEST effect. To validate the simulation results, we prepared and imaged two CEST phantoms: a pH phantom of serially titrated pH at a fixed creatine concentration and a concentration phantom of serially varied creatine concentration titrated to the same pH, and solved the labile proton fraction ratio and exchange rate per-pixel. For the concentration phantom, we showed that the labile proton fraction ratio is proportional to the CEST agent concentration with negligible change in the exchange rate. Additionally, we found the exchange rate of the pH phantom is dominantly base-catalyzed with little difference in the labile proton fraction ratio. In summary, our study demonstrated quantitative DIACEST MRI, which remains promising to augment the conventional CEST-weighted MRI analysis. PMID:23606428

  19. Simultaneous determination of labile proton fraction ratio and exchange rate with irradiation radio frequency (RF) power dependent quantitative CEST MRI analysis

    PubMed Central

    Sun, Phillip Zhe; Wang, Yu; Xiao, Gang; Wu, Renhua

    2014-01-01

    Chemical exchange saturation transfer (CEST) imaging is sensitive to dilute proteins/peptides and microenvironmental properties, and has been increasingly evaluated for molecular imaging and in vivo applications. However, the experimentally measured CEST effect depends on the CEST agent concentration, exchange rate and relaxation time. In addition, there may be non-negligible direct radio-frequency (RF) saturation effects, particularly severe for diamagnetic CEST (DIACEST) agents due to their relatively small chemical shift difference from that of the bulk water resonance. As such, the commonly used asymmetry analysis only provides CEST-weighted information. Recently, it has been shown with numerical simulation that both labile proton concentration and exchange rate can be determined by evaluating the RF power dependence of DIACEST effect. To validate the simulation results, we prepared and imaged two CEST phantoms: a pH phantom of serially titrated pH at a fixed creatine concentration and a concentration phantom of serially varied creatine concentration titrated to the same pH, and solved the labile proton fraction ratio and exchange rate per-pixel. For the concentration phantom, we showed that the labile proton fraction ratio is proportional to the CEST agent concentration with negligible change in the exchange rate. Additionally, we found the exchange rate of the pH phantom is dominantly base-catalyzed with little difference in the labile proton fraction ratio. In summary, our study demonstrated quantitative DIACEST MRI, which remains promising to augment the conventional CEST-weighted MRI analysis. PMID:23606428

  20. Selective exchange of divalent transition metal ions in cryptomelane-type manganic acid with tunnel structure

    SciTech Connect

    Tsuji, M. ); Komarneni, S. )

    1993-03-01

    The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients ([ital K][sub [ital d

  1. Direct measurements of two photon exchange on lepton-proton elastic scattering using simultaneous electron-positron beams in CLAS

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni Kalhari

    The electric (GE) and magnetic ( GM) form factors of the proton are fundamental observables which characterize its charge and magnetization distributions. There are two methods to measure the proton form factors: the Rosenbluth separation method and the polarization transfer technique. However, the ratio of the electric and magnetic form factors measured by those methods significantly disagree at momentum transfer Q2 > 1 GeV2. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section which significantly changes the extraction of GE from the Rosenbluth separation measurement. The Jefferson Lab CLAS TPE experiment determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections. The primary electron beam was used to create an intense bremsstrahlung photon beam. Some of the photons were then converted to a mixed e+/ e- beam which then interacted with a liquid hydrogen target. The e+p and e-p events were detected by the CLAS (CEBAF Large Acceptance Spectrometer). The elastic cross section ratios ((sigma( e+p)/(sigma(e -p)) were measured over a wide range of virtual photon polarization epsilon and Q2. The cross section ratios displayed a strong epsilon dependence at Q2 = 1.45 GeV2. There is no significant Q2 dependence observed at epsilon = 0.45. The results are consistent with a recent measurement at the VEPP-3 lepton storage ring in Novosibirsk and with the hadronic calculation by Blunders, Melnitchouk and Tjon. The hadronic calculation resolves the disagreement between the Rosenbluth separation and polarization transfer extractions of GE/GM at Q2 up to 2 -- 3 GeV2. Applying the GLAS TPE correction to the Rosenbluth cross section measurements significantly decreases the extracted value of GE and brings it into good agreement with the polarization transfer measurement at Q2˜1.75 GeV2. Thus, these

  2. The proton exchange chemistry of layered Ni(OH){sub 2} for two types of high-capacity cathode materials in rechargeable batteries

    SciTech Connect

    Sun Yanzhi; Pan Junqing Wan Pingyu; Liu Xiaoguang

    2009-01-08

    Based on the studies of the first proton exchange/remove of layered Ni(OH){sub 2}, super nickel oxide has been prepared with strongly alkaline concentrated sodium hypochlorite solution. The primary alkaline super nickel battery equipped with the prepared NiOOH cathode provides an energy capacity 2 times as large as that of the existing alkaline manganese batteries under high drain. In addition, according to the second proton exchange of Ni(OH){sub 2}, the layered NiOOLi has also been synthesized by means of the proton/Li-ion exchange of super nickel oxide in LiOH solution, and then in molten lithium hydroxide. It provides higher discharge voltage and capacity than that of the widely adopted LiCoO{sub 2} and LiMn{sub 2}O{sub 4}.

  3. Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD3OD

    NASA Astrophysics Data System (ADS)

    Herrmann, Kristin A.; Kuppannan, Krishna; Wysocki, Vicki H.

    2006-03-01

    Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD3OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD3OD pressure of 4 × 10-7 Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D0, D1, D2, D5, D6, D7, D8, D9, D10, and D11) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D0-D2 ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D5-D11) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b1/y8 and b2/y7 ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y1/a8 pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD3OD at a pressure of 1 × 10-7 Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D0-D7 ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI

  4. Functional role of polar amino acid residues in Na+/H+ exchangers.

    PubMed Central

    Wiebe, C A; Dibattista, E R; Fliegel, L

    2001-01-01

    Na(+)/H(+) exchangers are a family of ubiquitous membrane proteins. In higher eukaryotes they regulate cytosolic pH by removing an intracellular H(+) in exchange for an extracellular Na(+). In yeast and Escherichia coli, Na(+)/H(+) exchangers function in the opposite direction to remove intracellular Na(+) in exchange for extracellular H(+). Na(+)/H(+) exchangers display an internal pH-sensitivity that varies with the different antiporter types. Only recently have investigations examined the amino acids involved in pH-sensitivity and in cation binding and transport. Histidine residues are good candidates for H(+)-sensing amino acids, since they can ionize within the physiological pH range. Histidine residues have been shown to be important in the function of the E. coli Na(+)/H(+) exchanger NhaA and in the yeast Na(+)/H(+) exchanger sod2. In E. coli, His(225) of NhaA may function to interact with, or regulate, the pH-sensory region of NhaA. In sod2, His(367) is also critical to transport and may be a functional analogue of His(225) of NhaA. Histidine residues are not critical for the function of the mammalian Na(+)/H(+) exchanger, although an unusual histidine-rich sequence of the C-terminal tail has some influence on activity. Other amino acids involved in cation binding and transport by Na(+)/H(+) exchangers are only beginning to be studied. Amino acids with polar side chains such as aspartate and glutamate have been implicated in transport activity of NhaA and sod2, but have not been studied in the mammalian Na(+)/H(+) exchanger. Further studies are needed to elucidate the mechanisms involved in pH-sensitivity and cation binding and transport by Na(+)/H(+) exchangers. PMID:11415429

  5. A mutation affecting the sodium/proton exchanger, SLC9A6, causes mental retardation with tau deposition

    PubMed Central

    Neumann, Manuela; Trojanowski, John Q.; Lee, Virginia M.-Y.; Feldman, Gerald; Norris, Joy W.; Friez, Michael J.; Schwartz, Charles E.; Stevenson, Roger; Sima, Anders A. F.

    2010-01-01

    We have studied a family with severe mental retardation characterized by the virtual absence of speech, autism spectrum disorder, epilepsy, late-onset ataxia, weakness and dystonia. Post-mortem examination of two males revealed widespread neuronal loss, with the most striking finding being neuronal and glial tau deposition in a pattern reminiscent of corticobasal degeneration. Electron microscopic examination of isolated tau filaments demonstrated paired helical filaments and ribbon-like structures. Biochemical studies of tau demonstrated a preponderance of 4R tau isoforms. The phenotype was linked to Xq26.3, and further analysis identified an in-frame 9 base pair deletion in the solute carrier family 9, isoform A6 (SLC9A6 gene), which encodes sodium/hydrogen exchanger-6 localized to endosomal vesicles. Sodium/hydrogen exchanger-6 is thought to participate in the targeting of intracellular vesicles and may be involved in recycling synaptic vesicles. The striking tau deposition in our subjects reveals a probable interaction between sodium/proton exchangers and cytoskeletal elements involved in vesicular transport, and raises the possibility that abnormalities of vesicular targeting may play an important role in more common disorders such as Alzheimer’s disease and autism spectrum disorders. PMID:20395263

  6. Contribution of two-boson exchange with {delta}(1232) excitation to parity-violating elastic electron-proton scattering

    SciTech Connect

    Nagata, Keitaro; Kao, C. W.; Zhou Haiqing; Yang Shinnan

    2009-06-15

    We study the leading electroweak corrections in the precision measurement of the strange form factors. Specifically, we calculate the two-boson exchange (TBE), two-photon exchange (TPE) plus {gamma}Z exchange ({gamma}ZE), and corrections with {delta}(1232) excitation to the parity-violating asymmetry of the elastic electron-proton scattering. The interplay between nucleon and {delta} contributions is found to depend strongly on the kinematics, as {delta}{sub {delta}} begins as negligible at backward angles but becomes very large and negative and dominant at forward angles, while {delta}{sub N} always stays positive and decreases monotonically with increasing {epsilon}. The total TBE corrections to the extracted values of G{sub E}{sup s}+{beta}G{sub M}{sup s} in recent experiments of HAPPEX and G0 are, depending on kinematics, found to be large and range between 13% and -75%, but are found to be small in the case of A4 experiments.

  7. Investigation of the gas-phase hydrogen/deuterium exchange behavior of aromatic dicarboxylic acids in a quadrupole ion trap

    NASA Astrophysics Data System (ADS)

    Chipuk, Joseph E.; Brodbelt, Jennifer S.

    2007-11-01

    Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid and 2,6-naphthalic acid) with D2O were performed in a quadrupole ion trap mass spectrometer. Experimental results showed significant differences in the rate and extent of exchange when the relative position of the carboxylic acid groups varied. Spontaneous and near complete exchange of one aromatic hydrogen atom occurred when the carboxylic acid groups were in the meta-position, whereas no additional exchange was observed for either the ortho- or para-isomers or for the structurally similar naphthalic acid. Computational investigations support the participation of several possible exchange mechanisms with the contribution of each relying heavily on the relative orientation of the acid moieties. A relay mechanism that bridges the deprotonation site and the labile hydrogen site appears to be responsible for the H/D exchange of not only the labile hydrogen atom of isophthalic acid, but also for the formation of a stable carbanion and corresponding subsequent exchange of one aromatic hydrogen atom. The impact of hydrogen bonding on the relay mechanism is demonstrated by the reaction of phthalic acid as the extent and rate of reaction are greatly retarded by the favorable interaction of the two carboxylic acid groups. Finally, a flip-flop mechanism is likely responsible for the exchange of both terephthalic acid and 2,6-naphthalic acid where the reactive sites are too remote for exchange via relay.

  8. Performance evaluation and characterization of metallic bipolar plates in a proton exchange membrane (PEM) fuel cell

    NASA Astrophysics Data System (ADS)

    Hung, Yue

    Bipolar plate and membrane electrode assembly (MEA) are the two most repeated components of a proton exchange membrane (PEM) fuel cell stack. Bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack. The bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cell, and constitute the backbone of a power stack. In addition, bipolar plates must have excellent corrosion resistance to withstand the highly corrosive environment inside the fuel cell, and they must maintain low interfacial contact resistance throughout the operation to achieve optimum power density output. Currently, commercial bipolar plates are made of graphite composites because of their relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite's manufacturability, permeability, and durability for shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. Since bipolar plates must possess the combined advantages of both metals and graphite composites in the fuel cell technology, various methods and techniques are being developed to combat metallic corrosion and eliminate the passive layer formed on the metal surface that causes unacceptable power reduction and possible fouling of the catalyst and the electrolyte. The main objective of this study was to explore the possibility of producing efficient, cost-effective and durable metallic bipolar plates that were capable of functioning in the highly corrosive fuel cell environment. Bulk materials such as Poco graphite, graphite composite, SS310, SS316, incoloy 800, titanium carbide and zirconium carbide were investigated as potential bipolar plate materials. In this work, different alloys and compositions of chromium carbide coatings on aluminum and SS316

  9. Deuterium exchange during acid-demineralisation. [of Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Kerridge, John F.; Chang, Sherwood; Shipp, Ruth

    1988-01-01

    Isotopic analyses of residues prepared by demineralization of the Murchison meteorite using D-labelled reagents provide evidence for measurable exchange of H-isotopes between residue and reagents. Precise quantification of this effect is precluded by substantial inhomogeneity of the meteoritic organic matter. A conservative estimate of the degree of exchange is 3-5 percent of the H pyrolyzable as H2O. This could affect the shape of the curve defining D release as a function of temperature, but does not change conclusions previously drawn concerning the nature of the bulk D enrichment of insoluble organic matter in meteorites.

  10. Molecular structure, tautomeric stability, protonation and deprotonation effects, vibrational, NMR and NBO analyses of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA) by quantum chemical calculations.

    PubMed

    Sridevi, C; Velraj, G

    2014-01-01

    This study represents the conformation, tautomeric stability, protonation and deprotonation effects, vibrational, electronic, NBO and NMR aspects of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA). Theoretical calculations were performed by ab initio HF and density functional theory (DFT)/B3LYP method using 6-311++G(d,p) basis sets. Tautomerism and the effect of solvent on the tautomeric equilibria in the gas phase and in different solvents were studied. The protonation and deprotonation effects on the reactivity and conformations of DOIAA were investigated. Electronic transitions were also studied and the most prominent transition corresponds to π→π*. Natural bond orbital (NBO) analysis was also carried out to find the intramolecular interactions and their stabilization energy. In DOIAA, the interaction between the lone pair donor orbital (n(LP1N5)) and the acceptor antibonding orbital π*(C6O7) reveals the strong stabilization energy of 224.9 kJ mol(-1). Molecular electrostatic potential (MEP) was calculated to predict the reactive sites of the title compound. The NMR results indicated that the observed chemical shifts for NH, COOH protons of DOIAA not only depend on the structure of the molecule being studied but also on the nature of the solvent, concentration of the sample and the presence of the other exchangeable protons. PMID:24291430

  11. Sulfation of metal-organic framework: Opportunities for acid catalysis and proton conductivity

    SciTech Connect

    Goesten, M.G.; Stavitski, E.; Juan-Alcaniz, J.; Ramos-Fernandez, E.V.; Sai Sankar Gupta, K.B.; van Bekkum, H.; Gascon, J. and Kapteijn, F.

    2011-05-24

    A new post-functionalization method for metal-organic frameworks (MOFs) has been developed to introduce acidity for catalysis. Upon treatment with a mixture of triflic anhydride and sulfuric acid, chemically stable MOF structures MIL-101(Cr) and MIL-53(Al) can be sulfated, resulting in a Broensted sulfoxy acid group attached to up to 50% of the aromatic terephthalate linkers of the structure. The sulfated samples have been extensively characterized by solid-state NMR, XANES, and FTIR spectroscopy. The functionalized acidic frameworks show catalytic activity similar to that of acidic polymers like Nafion{reg_sign} display in the esterification of n-butanol with acetic acid (TOF {approx} 1 min{sup -1} {at} 343 K). Water adsorbs strongly up to 4 molecules per sulfoxy acid group, and an additional 2 molecules are taken up at lower temperatures in the 1-D pore channels of S-MIL-53(Al). The high water content and Broensted acidity provide the structure S-MIL-53(Al) a high proton conductivity up to moderate temperatures.

  12. A united physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid

    USGS Publications Warehouse

    Ephraim, J.; Alegret, S.; Mathuthu, A.; Bicking, M.; Malcolm, R.L.; Marinsky, J.A.

    1986-01-01

    Potentiometric studies of the neutralization of several fulvic acid sources with standard base in aqueous and nonaqueous media have been conducted. Analysis of the results with a recently developed unified physicochemical model has shown that the protonation behavior of these fulvic acid sources is a reflection of (1) their polyelectrolyte nature and (2) their heterogeneity. It has been possible to ascribe the polyelectrolyte properties observed to a rather inflexible fulvic acid molecule whose variably charged surface is impermeable to simple electrolyte. ?? 1986 American Chemical Society.

  13. Two-photon exchange contribution to proton form factors in the time-like region

    SciTech Connect

    Chen, D. Y.; Dong, Y. B.; Zhou, H. Q.

    2008-10-15

    We estimate the two-photon exchange contribution to the process e{sup +}+e{sup -}{yields}p+p . The two-photon exchange corrections to double spin polarization observables and form factors in the time-like region are calculated. The corrections are found to be small in magnitude but with a strong angular dependence at fixed momentum transfer. These two features are the same as those in the space-like region. In future experiments, the double spin polarization observable P{sub z} deserves to be considered.

  14. Studies related to primitive chemistry. A proton and nitrogen-14 nuclear magnetic resonance amino acid and nucleic acid constituents and a and their possible relation to prebiotic

    NASA Technical Reports Server (NTRS)

    Manatt, S. L.; Cohen, E. A.; Shiller, A. M.; Chan, S. I.

    1973-01-01

    Preliminary proton nuclear magnetic resonance (NMR) studies were made to determine the applicability of this technique for the study of interactions between monomeric and polymeric amino acids with monomeric nucleic acid bases and nucleotides. Proton NMR results for aqueous solutions (D2O) demonstrated interactions between the bases cytosine and adenine and acidic and aromatic amino acids. Solutions of 5'-AMP admixed with amino acids exhibited more complex behavior but stacking between aromatic rings and destacking at high amino acids concentration was evident. The multisite nature of 5'-AMP was pointed out. Chemical shift changes for adenine and 5'-AMP with three water soluble polypeptides demonstrated that significant interactions exist. It was found that the linewidth-pH profile of each amino acid is unique. It is concluded that NMR techniques can give significant and quantitative data on the association of amino acid and nucleic acid constituents.

  15. Composition of exchangeable bases and acidity in soils of the Crimean Mountains

    NASA Astrophysics Data System (ADS)

    Kostenko, I. V.

    2015-08-01

    Acid forest and mountainous meadow soils of the Crimean Mountains were studied. The amount of hydrogen and aluminum ions extracted from these soils depended on the pH of extracting agents. The maximum values of the soil acidity were obtained upon the extraction with a strongly alkaline solution of sodium acetate in 0.05 N NaOH. The application of this extractant made it possible to determine the total exchange acidity, the total amount of extractable aluminum, and the total cation exchange capacity of the soils after the extraction of all the acidic components from them. The values of these characteristics were significantly higher than the values of the potential acidity and cation exchange capacity obtained by the routine analytical methods. Hydrogen predominated among the acidic components of the exchange acidity in the humus horizons, whereas aluminum predominated among them in the underlying mineral horizons. Hydrothermic conditions and the character of vegetation and parent materials were the major factors affecting the relationships between bases and acidic components in the soil adsorption complex.

  16. Separation of the rare earths by anion-exchange in the presence of lactic acid

    NASA Technical Reports Server (NTRS)

    Faris, J. P.

    1969-01-01

    Investigation of adsorption of rare earths and a few other elements to an anion-exchange resin from mixed solvents containing lactic acid shows that the lanthanides are absorbed more strongly than from the alpha-hydroxyisobutryric acid system, but with less separation between adjacent members of the series.

  17. Temperature distribution on anodic surface of membrane electrode assembly in proton exchange membrane fuel cell with interdigitated flow bed

    NASA Astrophysics Data System (ADS)

    Guo, Hang; Wang, Mao Hai; Liu, Jia Xing; Nie, Zhi Hua; Ye, Fang; Ma, Chong Fang

    2015-01-01

    Temperature distribution on the surface of a membrane electrode assembly (MEA) significantly influences the performance, lifetime, and reliability of proton exchange membrane fuel cells (PEMFCs). Entire temperature fields on the surface of an MEA anode side under an interdigitated flow field are experimentally measured at non-humidification conditions with a self-designed PEMFC and infrared imaging technology. The highest temperature on the surface of the MEA anode side appears in the bottom bordered two side channels, and the lowest temperature exists in the area closed to the inlet of the middle channel. The hot region on the surface of the MEA anode side is easy to locate in the infrared temperature image. The reason for the temperature distribution under the interdigitated flow field is analyzed. The temperature of the MEA, the non-uniformity of temperature distribution on the surface of the MEA anode side, and the fuel cell temperature increase with the loaded current density.

  18. Electro-optic 1x2 switch based on proton-exchanged channel waveguides in LiNbO3

    NASA Astrophysics Data System (ADS)

    Kostritskii, S. M.; Korkishko, Yu. N.; Fedorov, V. A.

    2015-05-01

    Integrated-optic 1×2 switch utilizing electro-optically controllable Y-fed directional coupler has been fabricated in LiNbO3 substrates with proton exchange technology. Such an integrated-optic switch has the newly designed Y-branching power divider allowing for high switching contrast at the both optical output ports and low driving voltage. To obtain an acceptable value of the interaction-length-to-coupling-length ratio, the novel trimming procedure is proposed. A rather high switching contrast ≥ 23 dB (power extinction ratio) at any output port and 2.5 dB insertion losses were obtained for a device with the 9 mm electrodes length.

  19. Effect of through-plane polytetrafluoroethylene distribution in gas diffusion layers on performance of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Iwamura, Takuya; Someya, Satoshi; Munakata, Tetsuo; Nakano, Akihiro; Heo, Yun; Ishida, Masayoshi; Nakajima, Hironori; Kitahara, Tatsumi

    2016-02-01

    This experimental study identifies the effect of through-plane polytetrafluoroethylene (PTFE) distribution in gas diffusion backing (GDB) on the performance of proton exchange membrane fuel cells (PEMFC). PTFE-drying under vacuum pressure created a relatively uniform PTFE distribution in GDB compared to drying under atmospheric pressure. Carbon paper samples with different PTFE distributions due to the difference in drying conditions were prepared and used for the cathode gas diffusion layer (GDL) of PEMFCs. Also investigated is the effect of MPL application on the performance for those samples. The current density (i) - voltage (V) characteristics of these PEMFCs measured under high relative humidity conditions clearly showed that, with or without MPL, the cell using the GDL with PTFE dried under vacuum condition showed better performance than that dried under atmospheric condition. It is suggested that this improved performance is caused by the efficient transport of liquid water through the GDB due to the uniform distribution of PTFE.

  20. Electro-optic MZI modulators, utilizing different phases in proton-exchanged LiTaO3 waveguides

    NASA Astrophysics Data System (ADS)

    Kostritskii, S. M.; Korkishko, Yu. N.; Fedorov, V. A.; Tavlykaev, R. F.; Ramaswamy, R. V.

    2005-09-01

    Electro-optic Mach-Zehnder interferometric (MZI) modulators have been fabricated by proton exchange in LiTaO3. Electro-optic efficiency of these modulators has been found to be depending on phase composition of HxLi1-xTaO3 waveguide in full accordance with the data of Raman scattering spectroscopy on microscopic contributions in electro-optic effect for the different HxLi1-xTaO3 phases. These spectroscopy data were used to found an appropriate phase composition and, thus, optimize MZI modulators. The experimental samples of MZI modulator fabricated at the optimal technological conditions exhibit the improved electro-optical efficiency with far superior photorefractive resistance compared to the LiNbO3 waveguides and modulators.

  1. The Structure and Properties of Pulsed dc Sputtered Nanocrystalline NbN Coatings for Proton Exchange Membrane Fuel Cell.

    PubMed

    Chun, Sung-Yong

    2016-02-01

    Niobium nitride coatings for the surface modified proton exchange membrane fuel cells with various pulse parameters have been prepared using dc (direct current) and asymmetric-bipolar pulsed dc magnetron sputtering. The pulse frequency and the duty cycle were varied from 5 to 50 kHz and 50 to 95%, respectively. The deposition rate, grain size and resistivity of pulsed dc sputtered films were decreased when the pulse frequency increased, while the nano hardness of niobium nitride films increased. We present in detail coatings (e.g., deposition rate, grain size, prefer-orientation, resistivity and hardness). Our studies show that niobium nitride coatings with superior properties can be prepared using asymmetric-bipolar pulsed dc sputtering. PMID:27433732

  2. Investigating the effects of proton exchange membrane fuel cell conditions on carbon supported platinum electrocatalyst composition and performance

    SciTech Connect

    A. Patel; K. Artyushkova; P. Atanassov; V. Colbow; M. Dutta; D. Harvey; S. Wessel

    2012-04-30

    Changes that carbon-supported platinum electrocatalysts undergo in a proton exchange membrane fuel cell environment were simulated by ex situ heat treatment of catalyst powder samples at 150 C and 100% relative humidity. In order to study modifications that are introduced to chemistry, morphology, and performance of electrocatalysts, XPS, HREELS and three-electrode rotating disk electrode experiments were performed. Before heat treatment, graphitic content varied by 20% among samples with different types of carbon supports, with distinct differences between bulk and surface compositions within each sample. Following the aging protocol, the bulk and surface chemistry of the samples were similar, with graphite content increasing or remaining constant and Pt-carbide decreasing for all samples. From the correlation of changes in chemical composition and losses in performance of the electrocatalysts, we conclude that relative distribution of Pt particles on graphitic and amorphous carbon is as important for electrocatalytic activity as the absolute amount of graphitic carbon present

  3. Investigating the effects of proton exchange membrane fuel cell conditions on carbon supported platinum electrocatalyst composition and performance

    SciTech Connect

    Patel, Anant; Artyushkova, Kateryna; Atanassov, Plamen; Colbow, Vesna; Dutta, Monica; Harvey, Davie; Wessel, Silvia

    2012-04-01

    Changes that carbon-supported platinum electrocatalysts undergo in a proton exchange membrane fuel cell environment were simulated by ex situ heat treatment of catalyst powder samples at 150 #2;C and 100% relative humidity. In order to study modifications that are introduced to chemistry, morphology, and performance of electrocatalysts, XPS, HREELS and three-electrode rotating disk electrode experiments were performed. Before heat treatment, graphitic content varied by 20% among samples with different types of carbon supports, with distinct differences between bulk and surface compositions within each sample. Following the aging protocol, the bulk and surface chemistry of the samples were similar, with graphite content increasing or remaining constant and Pt-carbide decreasing for all samples. From the correlation of changes in chemical composition and losses in performance of the electrocatalysts, we conclude that relative distribution of Pt particles on graphitic and amorphous carbon is as important for electrocatalytic activity as the absolute amount of graphitic carbon present

  4. Carbon nano-chain and carbon nano-fibers based gas diffusion layers for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kannan, Arunachala M.; Munukutla, Lakshmi

    Gas diffusion layers (GDL) for proton exchange membrane fuel cell have been developed using a partially ordered graphitized nano-carbon chain (Pureblack ® carbon) and carbon nano-fibers. The GDL samples' characteristics such as, surface morphology, surface energy, bubble-point pressure and pore size distribution were characterized using electron microscope, inverse gas chromatograph, gas permeability and mercury porosimetry, respectively. Fuel cell performance of the GDLs was evaluated using single cell with hydrogen/air at ambient pressure, 70 °C and 100% RH. The GDLs with combination of vapor grown carbon nano-fibers with Pureblack carbon showed significant improvement in mechanical robustness as well as fuel cell performance. The micro-porous layer of the GDLs as seen under scanning electron microscope showed excellent surface morphology showing the reinforcement with nano-fibers and the surface homogeneity without any cracks.

  5. Sulfamate proton solvent exchange in heparin oligosaccharides: evidence for a persistent hydrogen bond in the antithrombin-binding pentasaccharide Arixtra.

    PubMed

    Langeslay, Derek J; Young, Robert P; Beni, Szabolcs; Beecher, Consuelo N; Mueller, Leonard J; Larive, Cynthia K

    2012-09-01

    Sulfamate groups (NHSO(3)(-)) are important structural elements in the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS). In this work, proton nuclear magnetic resonance (NMR) line-shape analysis is used to explore the solvent exchange properties of the sulfamate NH groups within heparin-related mono-, di-, tetra- and pentasaccharides as a function of pH and temperature. The results of these experiments identified a persistent hydrogen bond within the Arixtra (fondaparinux sodium) pentasaccharide between the internal glucosamine sulfamate NH and the adjacent 3-O-sulfo group. This discovery provides new insights into the solution structure of the Arixtra pentasaccharide and suggests that 3-O-sulfation of the heparin N-sulfoglucosamine (GlcNS) residues pre-organize the secondary structure in a way that facilitates binding to antithrombin-III. NMR studies of the GlcNS NH groups can provide important information about heparin structure complementary to that available from NMR spectral analysis of the carbon-bound protons. PMID:22593556

  6. High energy efficiency and high power density proton exchange membrane fuel cells: Electrode kinetics and mass transport

    NASA Technical Reports Server (NTRS)

    Srinivasan, Supramaniam; Velev, Omourtag A.; Parthasathy, Arvind; Manko, David J.; Appleby, A. John

    1991-01-01

    The development of proton exchange membrane (PEM) fuel cell power plants with high energy efficiencies and high power densities is gaining momentum because of the vital need of such high levels of performance for extraterrestrial (space, underwater) and terrestrial (power source for electric vehicles) applications. Since 1987, considerable progress has been made in achieving energy efficiencies of about 60 percent at a current density of 200 mA/sq cm and high power densities (greater than 1 W/sq cm) in PEM fuel cells with high (4 mg/sq cm) or low (0.4 mg/sq cm) platinum loadings in electrodes. The following areas are discussed: (1) methods to obtain these high levels of performance with low Pt loading electrodes - by proton conductor impregnation into electrodes, localization of Pt near front surface; (2) a novel microelectrode technique which yields electrode kinetic parameters for oxygen reduction and mass transport parameters; (3) demonstration of lack of water transport from anode to cathode; (4) modeling analysis of PEM fuel cell for comparison with experimental results and predicting further improvements in performance; and (5) recommendations of needed research and development for achieving the above goals.

  7. The Role of Lactic Acid Adsorption by Ion Exchange Chromatography

    PubMed Central

    Zhang, Tongcun; Zhang, Jian; Jia, Shiru; Yu, Changyan; Jiang, Kunyu; Gao, Nianfa

    2010-01-01

    Background The polyacrylic resin Amberlite IRA-67 is a promising adsorbent for lactic acid extraction from aqueous solution, but little systematic research has been devoted to the separation efficiency of lactic acid under different operating conditions. Methodology/Principal Findings In this paper, we investigated the effects of temperature, resin dose and lactic acid loading concentration on the adsorption of lactic acid by Amberlite IRA-67 in batch kinetic experiments. The obtained kinetic data followed the pseudo-second order model well and both the equilibrium and ultimate adsorption slightly decreased with the increase of the temperature at 293–323K and 42.5 g/liter lactic acid loading concentration. The adsorption was a chemically heterogeneous process with a mean free energy value of 12.18 kJ/mol. According to the Boyd_plot, the lactic acid uptake process was primarily found to be an intraparticle diffusion at a lower concentration (<50 g/liter) but a film diffusion at a higher concentration (>70 g/liter). The values of effective diffusion coefficient Di increased with temperature. By using our Equation (21), the negative values of ΔG° and ΔH° revealed that the adsorption process was spontaneous and exothermic. Moreover, the negative value of ΔS° reflected the decrease of solid-liquid interface randomness at the solid-liquid interface when adsorbing lactic acid on IRA-67. Conclusions/Significance With the weakly basic resin IRA-67, in situ product removal of lactic acid can be accomplished especially from an open and thermophilic fermentation system without sterilization. PMID:21085600

  8. Demonstration of Synaptic Behaviors and Resistive Switching Characterizations by Proton Exchange Reactions in Silicon Oxide

    PubMed Central

    Chang, Yao-Feng; Fowler, Burt; Chen, Ying-Chen; Zhou, Fei; Pan, Chih-Hung; Chang, Ting-Chang; Lee, Jack C.

    2016-01-01

    We realize a device with biological synaptic behaviors by integrating silicon oxide (SiOx) resistive switching memory with Si diodes. Minimal synaptic power consumption due to sneak-path current is achieved and the capability for spike-induced synaptic behaviors is demonstrated, representing critical milestones for the use of SiO2–based materials in future neuromorphic computing applications. Biological synaptic behaviors such as long-term potentiation (LTP), long-term depression (LTD) and spike-timing dependent plasticity (STDP) are demonstrated systematically using a comprehensive analysis of spike-induced waveforms, and represent interesting potential applications for SiOx-based resistive switching materials. The resistive switching SET transition is modeled as hydrogen (proton) release from (SiH)2 to generate the hydrogen bridge defect, and the RESET transition is modeled as an electrochemical reaction (proton capture) that re-forms (SiH)2. The experimental results suggest a simple, robust approach to realize programmable neuromorphic chips compatible with large-scale CMOS manufacturing technology. PMID:26880381

  9. Demonstration of Synaptic Behaviors and Resistive Switching Characterizations by Proton Exchange Reactions in Silicon Oxide

    NASA Astrophysics Data System (ADS)

    Chang, Yao-Feng; Fowler, Burt; Chen, Ying-Chen; Zhou, Fei; Pan, Chih-Hung; Chang, Ting-Chang; Lee, Jack C.

    2016-02-01

    We realize a device with biological synaptic behaviors by integrating silicon oxide (SiOx) resistive switching memory with Si diodes. Minimal synaptic power consumption due to sneak-path current is achieved and the capability for spike-induced synaptic behaviors is demonstrated, representing critical milestones for the use of SiO2-based materials in future neuromorphic computing applications. Biological synaptic behaviors such as long-term potentiation (LTP), long-term depression (LTD) and spike-timing dependent plasticity (STDP) are demonstrated systematically using a comprehensive analysis of spike-induced waveforms, and represent interesting potential applications for SiOx-based resistive switching materials. The resistive switching SET transition is modeled as hydrogen (proton) release from (SiH)2 to generate the hydrogen bridge defect, and the RESET transition is modeled as an electrochemical reaction (proton capture) that re-forms (SiH)2. The experimental results suggest a simple, robust approach to realize programmable neuromorphic chips compatible with large-scale CMOS manufacturing technology.

  10. Demonstration of Synaptic Behaviors and Resistive Switching Characterizations by Proton Exchange Reactions in Silicon Oxide.

    PubMed

    Chang, Yao-Feng; Fowler, Burt; Chen, Ying-Chen; Zhou, Fei; Pan, Chih-Hung; Chang, Ting-Chang; Lee, Jack C

    2016-01-01

    We realize a device with biological synaptic behaviors by integrating silicon oxide (SiO(x)) resistive switching memory with Si diodes. Minimal synaptic power consumption due to sneak-path current is achieved and the capability for spike-induced synaptic behaviors is demonstrated, representing critical milestones for the use of SiO2-based materials in future neuromorphic computing applications. Biological synaptic behaviors such as long-term potentiation (LTP), long-term depression (LTD) and spike-timing dependent plasticity (STDP) are demonstrated systematically using a comprehensive analysis of spike-induced waveforms, and represent interesting potential applications for SiO(x)-based resistive switching materials. The resistive switching SET transition is modeled as hydrogen (proton) release from (SiH)2 to generate the hydrogen bridge defect, and the RESET transition is modeled as an electrochemical reaction (proton capture) that re-forms (SiH)2. The experimental results suggest a simple, robust approach to realize programmable neuromorphic chips compatible with large-scale CMOS manufacturing technology. PMID:26880381

  11. Control of proton exchange for LiTaO3 waveguides and the crystal structure of HxLi1 - xTaO3

    NASA Astrophysics Data System (ADS)

    El Hadi, K.; Baldi, P.; Nouh, S.; de Micheli, M. P.; Leycuras, A.; Fedorov, V. A.; Korkishko, Yu. N.

    1995-08-01

    We show how the phase diagram of the HxLi 1-xTaO 3 waveguiding layer on top of a crystal of a given orientation allows one to understand, and thus to control, the proton-exchange process in lithium tantalate. Different ways of producing high-quality waveguides are identified.

  12. Teledyne Energy Systems, Inc., Proton Exchange Member (PEM) Fuel Cell Engineering Model Powerplant. Test Report: Initial Benchmark Tests in the Original Orientation

    NASA Technical Reports Server (NTRS)

    Loyselle, Patricia; Prokopius, Kevin

    2011-01-01

    Proton Exchange Membrane (PEM) fuel cell technology is the leading candidate to replace the alkaline fuel cell technology, currently used on the Shuttle, for future space missions. During a 5-yr development program, a PEM fuel cell powerplant was developed. This report details the initial performance evaluation test results of the powerplant.

  13. Gas-phase acidity and dynamics of the protonation processes of carbidopa and levodopa. A QM/QD study.

    PubMed

    Sukker, Ghader M; Elroby, Shaaban A; Hilal, Rifaat

    2016-10-01

    The present work details, our efforts to investigate and compare the acid-base properties of levodopa (LD) and carbidopa (CD), a drug combination being used in the treatment of Parkinson's disease. Protonation and deprotonation were examined for all possible sites in the two drugs. Proton affinity and proton detachment enthalpies were computed at the B3LYP/6-311++G** level of theory. Results of the present work reveal that CD is more basic and can abstract protons in solution much more efficiently than LD. Furthermore, at all deportation sites considered, CD is more acidic than LD. DFT-based ADMP, dynamic simulations have been performed to explore the dynamics of the protonation processes in LD and CD. Thus, while the dynamics of the protonation process of LD is very straightforward leading to the formation of the corresponding cation, the protonation process in CD is very complex involving a major geometry change and rearrangement. Results of the present work reveal that the active species in acid medium is not CD in its normal geometry but a carbonyl hydrazine form instead. The presence of the carbonyl group β to the hydrazine group may very well underlie its enhanced activity which allows it to bind to the active site of the DDC enzyme. The relative stabilities of various water-water-CD complexes have been computed and compared. PMID:26511889

  14. Modeling the Hydrogen-Proton Charge-Exchange Process in Global Heliospheric Simulations

    NASA Astrophysics Data System (ADS)

    DeStefano, A.; Heerikhuisen, J.

    2015-12-01

    The environment surrounding our Solar System has a vast and dynamic structure. As the Sun rounds the Milky Way galaxy, interstellar dust and gas interact with the Sun's outflow of solar wind. A bubble of hot plasma forms around the Sun due to this interaction, called the heliosphere. In order to understand the structure of the heliosphere, observations and simulations must work in tandem. Within the past decade or so, 3D models of the heliosphere have been developed exhibiting non- symmmetric as well as predicting structures such as the hydrogen wall and the IBEX ribbon. In this poster we explore new ways to compute charge-exchange source terms. The charge-exchange process is the coupling mechanism between the MHD and kinetic theories. The understanding of this process is crucial in order to make valuable predictions. Energy dependant cross section terms will aid in settling non-linear affects coupling the intestellar and solar particles. Through these new ways of computing source terms, resolving fine structures in the plasma in the heliopause may be possible. In addition, other non-trivial situations, such as charge-exchange mediated shocks, may be addressed.

  15. How pulse modes affect proton-barriers and anion-exchange membrane mineral fouling during consecutive electrodialysis treatments.

    PubMed

    Cifuentes-Araya, Nicolás; Pourcelly, Gérald; Bazinet, Laurent

    2013-02-15

    Mineral fouling of cation-exchange membrane (CEM) was recently reduced by pulsed electric fields (PEFs) during the electrodialysis (ED) of solutions containing high Mg(2+)/Ca(2+) ratios. However, a fouling layer appeared on the diluate side of anion-exchange membrane (AEM) once the pause lapse surpassed certain duration. Recent studies presented a multilayer mineral growth on CEM, but the case of AEM needs yet to be cleared. The current study reveals the mechanisms involved in AEM fouling growth when applying pulse modes of current in comparison with dc current. The results showed that dc current generated steady proton barriers given by water splitting at AEM interfaces that impeded fouling on both membrane sides. The higher frequency of PEF ratio 1 (Ton/Toff=10s/10s) acted removing completely an initial mineral deposit on the concentrate side of AEM, keeping it clean after two and three consecutive runs. Particularly, an undesirable brucite layer was formed on the AEM-diluate side for longer pause lapses as for a PEF ratio 0.3 (Ton/Toff=10s/33.3s) current regime. This structure caused violent water splitting resulting in amorphous magnesium hydroxide formation and consequently in fouling precipitation on the concentrate side during a third run through current exaltation. PMID:23141696

  16. Voltage-dependent processes in the electroneutral amino acid exchanger ASCT2

    PubMed Central

    Zander, Catherine B.; Albers, Thomas

    2013-01-01

    Neutral amino acid exchange by the alanine serine cysteine transporter (ASCT)2 was reported to be electroneutral and coupled to the cotransport of one Na+ ion. The cotransported sodium ion carries positive charge. Therefore, it is possible that amino acid exchange is voltage dependent. However, little information is available on the electrical properties of the ASCT2 amino acid transport process. Here, we have used a combination of experimental and computational approaches to determine the details of the amino acid exchange mechanism of ASCT2. The [Na+] dependence of ASCT2-associated currents indicates that the Na+/amino acid stoichiometry is at least 2:1, with at least one sodium ion binding to the amino acid–free apo form of the transporter. When the substrate and two Na+ ions are bound, the valence of the transport domain is +0.81. Consistently, voltage steps applied to ASCT2 in the fully loaded configuration elicit transient currents that decay on a millisecond time scale. Alanine concentration jumps at the extracellular side of the membrane are followed by inwardly directed transient currents, indicative of translocation of net positive charge during exchange. Molecular dynamics simulations are consistent with these results and point to a sequential binding process in which one or two modulatory Na+ ions bind with high affinity to the empty transporter, followed by binding of the amino acid substrate and the subsequent binding of a final Na+ ion. Overall, our results are consistent with voltage-dependent amino acid exchange occurring on a millisecond time scale, the kinetics of which we predict with simulations. Despite some differences, transport mechanism and interaction with Na+ appear to be highly conserved between ASCT2 and the other members of the solute carrier 1 family, which transport acidic amino acids. PMID:23669717

  17. Design and Development of Highly Sulfonated Polymers as Proton Exchange Membranes for High Temperature Fuel Cell Applications

    NASA Astrophysics Data System (ADS)

    Dang, Thuy D.; Bai, Zongwu; Yoonessi, Mitra

    A series of high molecular weight, highly sulfonated poly(arylenethioethersulfone) (SPTES) polymers were synthesized by polycondensation, which allowed controlled sulfonation of up to 100 mol %. The SPTES polymers were prepared via step growth polymerization of sulfonated aromatic difluorosulfone, aromatic difluorosulfone, and 4,4 '-thiobisbenzenthiol in sulfolane solvent at the temperature up to 180 °C. The composition and incorporation of the sulfonated repeat unit into the polymers were confirmed by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Solubility tests on the SPTES polymers confirmed that no cross-linking and probably no branching occurred during the polymerizations. The end-capping groups were introduced in the SPTES polymers to control the molecular weight distribution and reduce the water solubility of the polymers. Tough, ductile membranes formed via solvent-casting exhibited increased water absorption with increasing degrees of sulfonation. The polymerizations conducted with the introduction of end-capping groups resulted in a wide variation in polymer proton conductivity, which spanned a range of 100 -300 mS cm-1, measured at 65 °C and 85 % relative humidity. The measured proton conductivities at elevated temperatures and high relative humidities are up to three times higher than that of the state-of-the-art Nafion-H proton exchange membrane under nearly comparable conditions. The thermal and mechanical properties of the SPTES polymers were investigated by TGA, DMA, and tensile measurements. The SPTES polymers show high glass transition temperatures (Tg), ˜220 °C, depending on the degree of sulfonation in polymerization. SPTES-50 polymer shows a Tg of 223 °C, with high tensile modulus, high tensile strengths at break and at yield as well as elongation at break. Wide angle X-ray scattering of the polymers shows two broad scattering features centered at 4.5 Å and 3.3 Å, the latter peak being

  18. Understanding selenocysteine through conformational analysis, proton affinities, acidities and bond dissociation energies

    NASA Astrophysics Data System (ADS)

    Kaur, Damanjit; Sharma, Punita; Bharatam, Prasad V.; Kaur, Mondeep

    Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6-31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6-311++G*//B3LYP/6-31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine.0

  19. Synthesis and Proton NMR Spectroscopy of Intra-Vesicular Gamma-Aminobutyric Acid (GABA)*

    PubMed Central

    Wang, Luke Y.-J.; Tong, Rong; Kohane, Daniel S.

    2014-01-01

    We report the synthesis of vesicles containing gamma-aminobutyric acid (GABA), and their proton nuclear magnetic resonance (1H NMR) spectra. These vesicles were constructed to more closely mimic the intracellular environment wherein GABA exists. For this study, these GABA-containing vesicles were examined under 1H NMR as a potential platform for future studies on the differences between aqueous phantoms, ex vivo brain extracts, and in vivo magnetic resonance spectroscopy results. We found that intra-vesicular GABA faithfully yielded the chemical shifts and J-coupling constants of free aqueous GABA, alongside the chemical shift signals of the vesicle wall. PMID:24109882

  20. Single charge exchange in collision of fast protons with hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Sattarpour, Seyedeh Hedyeh

    2015-11-01

    Single charge transfer process in collision of energetic protons with molecular hydrogens is theoretically studied using a first-order two-effective-center Born approximation. The correct boundary conditions are incorporated in the formalism and the Hartree-Fock molecular wave function for molecular targets and the residual ions are used to calculate the transition amplitude. The interference patterns in the capture differential cross-sections (DCSs) for a given fixed orientation of the molecule, due to the scattering from the two-atomic centers in the molecular targets, are examined. The dependence of the DCSs upon the angle between the molecular axis and the direction of the incident velocity is theoretically investigated. Both average differential and integral cross-sections are calculated. The obtained results are compared with the available experimental data.

  1. Modeling the dynamic behavior of proton-exchange membrane fuel cell

    SciTech Connect

    Llapade, Peter O; Mukundan, Rangachary; Davey, John R; Borup, Rodney L; Meyers, Jeremy P

    2010-01-01

    A two-phase transient model that incorporates the permanent hysteresis observed in the experimentally measured capillary pressure of GDL has been developed. The model provides explanation for the difference in time constant between membrane hydration and dehydration observed in the HFR experiment conducted at LANL. When there is liquid water at the cathode catalyst layer, time constant of the water content in the membrane is closely tied to that of liquid water saturation in the CCL, as the vapor is already saturated. The water content in the membrane will not reach steady state as long as the liquid water flow in the CCL is not at steady state. Also, Increased resistance to proton transport in the membrane is observed when the cell voltage is stepped down to a very low value.

  2. Hydration effect on proton transfer in melamine-cyanuric acid complex.

    PubMed

    Yan, Shihai; Kang, Baotao; Lee, Jin Yong; Sun, Lixiang

    2016-07-01

    Self-assembly of melamine-cyanuric acid (MC) leads to urinary tract calculi and renal failure. The hydration effects on molecular geometry, the IR spectra, the frontier molecular orbital, the energy barrier of proton transfer (PT), as well as the stability of MC were explored by density functional theory (DFT) calculations. The intramolecular PT breaks the big π-conjugated ring of melamine or converts the p-π conjugation (:N-C'=O) to π-π conjugation (O=C-N=C') of cyanuric acid. The intermolecular PT varies the coupling between melamine and cyanuric acid from pure hydrogen bonds (Na…HNd and NH…O) to the cooperation of cation…anion electrostatic interaction (NaH(+)…Nd (-)) and two NH…O hydrogen bonds. Distinct IR spectra shifts occur for Na…HNd stretching mode upon PT, i.e., blue-shift upon intramolecular PT and red-shift upon intermolecular PT. It is expected that the PT would inhibit the generation of rosette-like structure or one-dimensional tape conformer for the MC complexes. Hydration obviously effects the local geometric structure around the water binding site, as well as the IR spectra of NH…O and N…HN hydrogen bonds. Hydration decreases the intramolecular PT barrier from ~45 kcal mol(-1) in anhydrous complex to ~11.5 kcal mol(-1) in trihydrated clusters. While, the hydration effects on intermolecular PT barrier is slight. The relative stability of MC varies slightly by hydration due to the strong hydrogen bond interaction between melamine and cyanuric acid fragments. Graphical Abstract Hydration effect on proton transfer in melamine-cyanuric acid complex. PMID:27351422

  3. The rules of variation: Amino acid exchange according to the rotating circular genetic code

    PubMed Central

    Castro-Chavez, Fernando

    2011-01-01

    General guidelines for the molecular basis of functional variation are presented while focused on the rotating circular genetic code and allowable exchanges that make it resistant to genetic diseases under normal conditions. The rules of variation, bioinformatics aids for preventive medicine, are: (1) same position in the four quadrants for hydrophobic codons, (2) same or contiguous position in two quadrants for synonymous or related codons, and (3) same quadrant for equivalent codons. To preserve protein function, amino acid exchange according to the first rule takes into account the positional homology of essential hydrophobic amino acids with every codon with a central uracil in the four quadrants, the second rule includes codons for identical, acidic, or their amidic amino acids present in two quadrants, and the third rule, the smaller, aromatic, stop codons, and basic amino acids, each in proximity within a 90 degree angle. I also define codifying genes and palindromati, CTCGTGCCGAATTCGGCACGAG. PMID:20371250

  4. Relativistic proton-nucleus scattering and one-boson-exchange models

    NASA Technical Reports Server (NTRS)

    Maung, Khin Maung; Gross, Franz; Tjon, J. A.; Townsend, L. W.; Wallace, S. J.

    1993-01-01

    Relativistic p-(Ca-40) elastic scattering observables are calculated using four sets of relativistic NN amplitudes obtained from different one-boson-exchange (OBE) models. The first two sets are based upon a relativistic equation in which one particle is on mass shell and the other two sets are obtained from a quasipotential reduction of the Bethe-Salpeter equation. Results at 200, 300, and 500 MeV are presented for these amplitudes. Differences between the predictions of these models provide a study of the uncertainty in constructing Dirac optical potentials from OBE-based NN amplitudes.

  5. Electrodeposited conductive polypyrrole/polyaniline composite film for the corrosion protection of copper bipolar plates in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Pan, T. J.; Zuo, X. W.; Wang, T.; Hu, J.; Chen, Z. D.; Ren, Y. J.

    2016-01-01

    A conductive composite coating consisting of an inner polypyrrole (PPY) layer and an outer polyaniline (PANI) layer is prepared on a copper substrate by an electrochemical synthesis. Potential application of these composite coatings in a proton exchange membrane fuel cell (PEMFC) is evaluated. The corrosion performance of the copper substrate without and with the polymer coatings in the acidic solutions containing H2SO4 (0.2 M), HCl (0.1 M) and HF (3 ppm) is investigated by electrochemical impedance spectroscopy, polarization and open-circuit potential measurements. The results indicate that both the bilayered PPY/PANI and the single PPY coating can increase the corrosion potential of copper substrate by more than 250 mV (SCE), and effectively decrease the corrosion current density by an order of magnitude in comparison with the uncoated copper substrate. Long-term test further confirms that the bilayered PPY/PANI coating with acceptable contact resistance provides better protection for the substrate than the single PPY coating. The bilayered structure with different ion-permselective nature may serve as an effective physical barrier to the inward penetration of corrosive species.

  6. SPEEK/PVDF/PES Composite as Alternative Proton Exchange Membrane for Vanadium Redox Flow Batteries

    NASA Astrophysics Data System (ADS)

    Fu, Zhimin; Liu, Jinying; Liu, Qifeng

    2016-01-01

    A membrane consisting of a blend of sulfonated poly(ether ether ketone) (SPEEK), poly(vinylidene fluoride) (PVDF), and poly(ether sulfone) (PES) has been fabricated and used as an ion exchange membrane for application in vanadium redox flow batteries (VRBs). The vanadium ion permeability of the SPEEK/PVDF/PES membrane was one order of magnitude lower than that of Nafion 117 membrane. The low-cost composite membrane exhibited better performance than Nafion 117 membrane at the same operating condition. A VRB single cell with SPEEK/PVDF/PES membrane showed significantly lower capacity loss, higher coulombic efficiency (>95%), and higher energy efficiency (>82%) compared with Nafion 117 membrane. In the self-discharge test, the duration of the cell with the SPEEK/PVDF/PES membrane was nearly two times longer than that with Nafion 117 membrane. Considering these good properties and its low cost, SPEEK/PVDF/PES membrane is expected to have excellent commercial prospects as an ion exchange membrane for VRB systems.

  7. Silylium ion-catalyzed challenging Diels-Alder reactions: the danger of hidden proton catalysis with strong Lewis acids.

    PubMed

    Schmidt, Ruth K; Müther, Kristine; Mück-Lichtenfeld, Christian; Grimme, Stefan; Oestreich, Martin

    2012-03-01

    The pronounced Lewis acidity of tricoordinate silicon cations brings about unusual reactivity in Lewis acid catalysis. The downside of catalysis with strong Lewis acids is, though, that these do have the potential to mediate the formation of protons by various mechanisms, and the thus released Brønsted acid might even outcompete the Lewis acid as the true catalyst. That is an often ignored point. One way of eliminating a hidden proton-catalyzed pathway is to add a proton scavenger. The low-temperature Diels-Alder reactions catalyzed by our ferrocene-stabilized silicon cation are such a case where the possibility of proton catalysis must be meticulously examined. Addition of the common hindered base 2,6-di-tert-butylpyridine resulted, however, in slow decomposition along with formation of the corresponding pyridinium ion. Quantitative deprotonation of the silicon cation was observed with more basic (Mes)(3)P to yield the phosphonium ion. A deuterium-labeling experiment verified that the proton is abstracted from the ferrocene backbone. A reasonable mechanism of the proton formation is proposed on the basis of quantum-chemical calculations. This is, admittedly, a particular case but suggests that the use of proton scavengers must be carefully scrutinized, as proton formation might be provoked rather than prevented. Proton-catalyzed Diels-Alder reactions are not well-documented in the literature, and a representative survey employing TfOH is included here. The outcome of these catalyses is compared with our silylium ion-catalyzed Diels-Alder reactions, thereby clearly corroborating that hidden Brønsted acid catalysis is not operating with our Lewis acid. Several simple-looking but challenging Diels-Alder reactions with exceptionally rare dienophile/enophile combinations are reported. Another indication is obtained from the chemoselectivity of the catalyses. The silylium ion-catalyzed Diels-Alder reaction is general with regard to the oxidation level of the

  8. Molecular recognition of isomeric protonated amino acid esters monitored by ESI-mass spectrometry.

    PubMed

    Liesenfeld, Andrea; Lützen, Arne

    2014-01-01

    Two new 9,9'-spirobifluorene-derived crown ethers were prepared and used to recognise constitutionally isomeric amino acid derivatives. The performance of the receptors was evaluated by ESI-mass spectrometry using the isomer labelled guest method (ILGM). This method revealed the preferred binding of L-norleucine and L-leucine compared to L-isoleucine for both receptors. Furthermore, non-covalent isotope effects demonstrate the relevance of dispersive interactions for the overall binding event. These effects also provide hints for the relative spatial orientation of the guest molecules within the host-guest complex, and thereby prove the importance of the spirobifluorene moiety for the observed binding of the protonated amino acid esters. PMID:24778737

  9. Beyond gastric acid reduction: Proton pump inhibitors induce heme oxygenase-1 in gastric and endothelial cells

    SciTech Connect

    Becker, Jan C. . E-mail: beckeja@uni-muenster.de; Grosser, Nina; Waltke, Christian; Schulz, Stephanie; Erdmann, Kati; Domschke, Wolfram; Schroeder, Henning; Pohle, Thorsten

    2006-07-07

    Proton pump inhibitors (PPIs) have been demonstrated to prevent gastric mucosal injury by mechanisms independent of acid inhibition. Here we demonstrate that both omeprazole and lansoprazole protect human gastric epithelial and endothelial cells against oxidative stress. This effect was abrogated in the presence of the heme oxygenase-1 (HO-1) inhibitor ZnBG. Exposure to either PPI resulted in a strong induction of HO-1 expression on mRNA and protein level, and led to an increased activity of this enzyme. Expression of cyclooxygenase isoforms 1 and 2 remained unaffected, and COX-inhibitors did not antagonize HO-1 induction by PPIs. Our results suggest that the antioxidant defense protein HO-1 is a target of PPIs in both endothelial and gastric epithelial cells. HO-1 induction might account for the gastroprotective effects of PPIs independently of acid inhibition, especially in NSAID gastropathy. Moreover, our findings provide additional perspectives for a possible but yet unexplored use of PPIs in vasoprotection.

  10. Ion exchange selectivity for cross-linked polyacrylic acid

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.

    1983-01-01

    The ion separation factors for 21 common metal ions with cross-linked polyacrylic acid were determined as a function of pH and the percent of the cross-linked polyacrylic acid neutralized. The calcium ion was used as a reference. At a pH of 5 the decreasing order of affinity of the ions for the cross-linked polyacrylic acid was found to be: Hg++, Fe+++, Pb++, Cr+++, Cu++, Cd++, Al+++, Ag+, Zn++, Ni++, Mn++, Co++, Ca++, Sr++, Ba++, Mg++, K+, Rb+, Cs+, Na+, and Li+. Members of a chemical family exhibited similar selectivities. The Hg++ ion appeared to be about a million times more strongly bound than the alkali metal ions. The relative binding of most of the metal ions varied with pH; the very tightly and very weakly bound ions showed the largest variations with pH. The calcium ion-hydrogen ion equilibrium was perturbed very little by the presence of the other ions. The separation factors and selectivity coefficients are discussed in terms of equilibrium and thermodynamic significance.

  11. Carbon quantum dots with photo-generated proton property as efficient visible light controlled acid catalyst

    NASA Astrophysics Data System (ADS)

    Li, Haitao; Liu, Ruihua; Kong, Weiqian; Liu, Juan; Liu, Yang; Zhou, Lei; Zhang, Xing; Lee, Shuit-Tong; Kang, Zhenhui

    2013-12-01

    Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34

  12. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  13. Mode of action and resistance studies unveil new roles for tropodithietic acid as an anticancer agent and the γ-glutamyl cycle as a proton sink

    PubMed Central

    Wilson, Maxwell Z.; Wang, Rurun; Gitai, Zemer; Seyedsayamdost, Mohammad R.

    2016-01-01

    While we have come to appreciate the architectural complexity of microbially synthesized secondary metabolites, far less attention has been paid to linking their structural features with possible modes of action. This is certainly the case with tropodithietic acid (TDA), a broad-spectrum antibiotic generated by marine bacteria that engage in dynamic symbioses with microscopic algae. TDA promotes algal health by killing unwanted marine pathogens; however, its mode of action (MoA) and significance for the survival of an algal–bacterial miniecosystem remains unknown. Using cytological profiling, we herein determine the MoA of TDA and surprisingly find that it acts by a mechanism similar to polyether antibiotics, which are structurally highly divergent. We show that like polyether drugs, TDA collapses the proton motive force by a proton antiport mechanism, in which extracellular protons are exchanged for cytoplasmic cations. The α-carboxy-tropone substructure is ideal for this purpose as the proton can be carried on the carboxyl group, whereas the basicity of the tropylium ion facilitates cation export. Based on similarities to polyether anticancer agents we have further examined TDA’s cytotoxicity and find it to exhibit potent, broad-spectrum anticancer activities. These results highlight the power of MoA-profiling technologies in repurposing old drugs for new targets. In addition, we identify an operon that confers TDA resistance to the producing marine bacteria. Bioinformatic and biochemical analyses of these genes lead to a previously unknown metabolic link between TDA/acid resistance and the γ-glutamyl cycle. The implications of this resistance mechanism in the context of the algal-bacterial symbiosis are discussed. PMID:26802120

  14. Mode of action and resistance studies unveil new roles for tropodithietic acid as an anticancer agent and the γ-glutamyl cycle as a proton sink.

    PubMed

    Wilson, Maxwell Z; Wang, Rurun; Gitai, Zemer; Seyedsayamdost, Mohammad R

    2016-02-01

    While we have come to appreciate the architectural complexity of microbially synthesized secondary metabolites, far less attention has been paid to linking their structural features with possible modes of action. This is certainly the case with tropodithietic acid (TDA), a broad-spectrum antibiotic generated by marine bacteria that engage in dynamic symbioses with microscopic algae. TDA promotes algal health by killing unwanted marine pathogens; however, its mode of action (MoA) and significance for the survival of an algal-bacterial miniecosystem remains unknown. Using cytological profiling, we herein determine the MoA of TDA and surprisingly find that it acts by a mechanism similar to polyether antibiotics, which are structurally highly divergent. We show that like polyether drugs, TDA collapses the proton motive force by a proton antiport mechanism, in which extracellular protons are exchanged for cytoplasmic cations. The α-carboxy-tropone substructure is ideal for this purpose as the proton can be carried on the carboxyl group, whereas the basicity of the tropylium ion facilitates cation export. Based on similarities to polyether anticancer agents we have further examined TDA's cytotoxicity and find it to exhibit potent, broad-spectrum anticancer activities. These results highlight the power of MoA-profiling technologies in repurposing old drugs for new targets. In addition, we identify an operon that confers TDA resistance to the producing marine bacteria. Bioinformatic and biochemical analyses of these genes lead to a previously unknown metabolic link between TDA/acid resistance and the γ-glutamyl cycle. The implications of this resistance mechanism in the context of the algal-bacterial symbiosis are discussed. PMID:26802120

  15. Cysteine pK[subscript a] Depression by a Protonated Glutamic Acid in Human DJ-1

    SciTech Connect

    Witt, Anna C.; Lakshminarasimhan, Mahadevan; Remington, Benjamin C.; Hasim, Sahar; Pozharski, Edwin; Wilson, Mark A.

    2008-07-09

    Human DJ-1, a disease-associated protein that protects cells from oxidative stress, contains an oxidation-sensitive cysteine (C106) that is essential for its cytoprotective activity. The origin of C106 reactivity is obscure, due in part to the absence of an experimentally determined pK{sub a} value for this residue. We have used atomic-resolution X-ray crystallography and UV spectroscopy to show that C106 has a depressed pK{sub a} of 5.4 {+-} 0.1 and that the C106 thiolate accepts a hydrogen bond from a protonated glutamic acid side chain (E18). X-ray crystal structures and cysteine pK{sub a} analysis of several site-directed substitutions at residue 18 demonstrate that the protonated carboxylic acid side chain of E18 is required for the maximal stabilization of the C106 thiolate. A nearby arginine residue (R48) participates in a guanidinium stacking interaction with R28 from the other monomer in the DJ-1 dimer and elevates the pK{sub a} of C106 by binding an anion that electrostatically suppresses thiol ionization. Our results show that the ionizable residues (E18, R48, and R28) surrounding C106 affect its pK{sub a} in a way that is contrary to expectations based on the typical ionization behavior of glutamic acid and arginine. Lastly, a search of the Protein Data Bank (PDB) produces several candidate hydrogen-bonded aspartic/glutamic acid-cysteine interactions, which we propose are particularly common in the DJ-1 superfamily.

  16. Electrochemical analysis of proton and electron transfer equilibria of the reducible moieties in humic acids.

    PubMed

    Aeschbacher, Michael; Vergari, Daniele; Schwarzenbach, René P; Sander, Michael

    2011-10-01

    Humic substances play a key role in biogeochemical and pollutant redox reactions. The objective of this work was to characterize the proton and electron transfer equilibria of the reducible moieties in different humic acids (HA). Cyclic voltammetry experiments demonstrated that diquat and ethylviologen mediated electron transfer between carbon working electrodes and HA. These compounds were used also to facilitate attainment of redox equilibria between redox electrodes and HA in potentiometric E(h) measurements. Bulk electrolysis of HA combined with pH-stat acid titration demonstrated that electron transfer to the reducible moieties in HA also resulted in proton uptake, suggesting decreasing reduction potentials E(h) of HA with increasing pH. This was confirmed by potentiometric E(h)-pH titrations of HA at different redox states. E(h) measurements of HA samples prereduced to different redox states by bulk electrolysis revealed reducible moieties in HA that cover a wide range of apparent standard reduction potentials at pH 7 from E(h)(0)* = +0.15 to -0.3 V. Modeling revealed an overall increase in the relative abundance of reducible moieties with decreasing E(h). The wide range of HA is consistent with its involvement in numerous environmental electron transfer reactions under various redox conditions. PMID:21823669

  17. The Uranian corona as a charge exchange cascade of plasma sheet protons

    NASA Astrophysics Data System (ADS)

    Herbert, F.

    1993-03-01

    The paper uses models of magnetic convection and interparticle interactions to examine the collisional interactions between atmospheric neutral hydrogen and magnetospheric charged particles observed by Voyager to be convecting through the Uranian magnetosphere. The e(-)-H collisional ionization process, continually reenergized by compressional heating of the electrons as they drift toward Uranus, produces a cascade of new plasma. This process has been suggested elsewhere as the source of the warm (10 eV at L = 5) plasma and is found in the present study to continue in a cascade to even cooler and more abundant plasma. This newly created plasma consists almost entirely of electrons and protons because He and H2 are nearly absent from the uppermost layers of the atmosphere. If this plasma crosses the dayside magnetopause and mixes with magnetopause boundary layers such as the plasma mantle, there to be swept back along the magnetotail, reincorporated into the magnetotail by the same processes postulated for solar wind plasma entry, and reenergized in the magnetotail current sheet, it would constitute an important source for the hot plasma observed by Voyager.

  18. The Peculiarities of the NMR Spin-Lattice Relaxation in Proton Exchanged LINBO_{3}

    NASA Astrophysics Data System (ADS)

    Vertegel, Igor; Chesnokov, Eugeny; Ovcharenko, Alexander; Vertegel, Ivan

    2013-06-01

    The temperature dependence of the spin-lattice relaxation time T_{1} of Li^{7} nuclei in the temperature range (170-430 K) was investigated in LiNbO_{3} polycrystalline samples: the clean and annealed ones in a hydrogen environment at temperature around 1000° C. The anomaly in the temperature dependence of T_{1} was found in range 300-340 K for both pure and annealed crystals. The reduction of the time T_{1} in the annealed lithium niobate crystal is caused by the creation of point defects (F^{+} or F-centers), with the dominant F-centers contribution. An increase in the activation energy in the annealed crystal can be explained by the following. It is known for the pure lithium niobate that an oscillation of lithium occurs in a symmetrical potential consisting of three wells. Formation of the oxygen vacancies in the annealed crystals is accompanied with extrinsic protons occupation of the vacancies. It leads to the symmetry violation and causes an i ncrease of the activation barrier.

  19. Vertically aligned carbon nanotube electrodes for high current density operating proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Murata, Shigeaki; Imanishi, Masahiro; Hasegawa, Shigeki; Namba, Ryoichi

    2014-05-01

    We successfully developed cathode electrodes for polymer electrolyte membrane fuel cells (PEMFC) that enable operation at high current densities by incorporating vertically aligned carbon nanotubes (CNTs) as the catalyst support; additionally, we prepared 236 cm2 membrane electrodes assemblies (MEAs) for vehicular use. The electrode structure improved the mass transport of reactants, i.e. oxygen, proton, electron and water, in systems performing at a 2.6 A cm-2 current density and 0.6 V with extremely low platinum (Pt) loading at the cathode (0.1 mg cm-2). The improved mass transport caused the 70 mV dec-1 Tafel slope to continue up to 1.0 A cm-2. The mass transport was improved because the pores were continuous, the catalyst support materials did not agglomerate and the catalyst layer made good electrical contact with the microporous layer. Utilizing wavy coil-shaped CNTs was also crucial. These CNTs displayed anti-agglomerative characteristics during the wet manufacturing process and maintained a continuous pore structure framing the layered catalyst structure. Because the CNTs had elastic characteristics, they might fill the space between catalyst and microporous layers to prevent flooding. However, the compressed CNTs in the cells were no longer vertically aligned. Therefore, vertically aligning the nanotubes was important during the MEA manufacturing process but was irrelevant for cell performance.

  20. The HP-1 maquette: From an apoprotein structure to a structured hemoprotein designed to promote redox-coupled proton exchange

    PubMed Central

    Huang, Steve S.; Koder, Ronald L.; Lewis, Mitchell; Wand, A. Joshua; Dutton, P. Leslie

    2004-01-01

    Synthetic heme-binding four-α-helix bundles show promise as working model systems, maquettes, for understanding heme cofactor–protein assembly and function in oxidoreductases. Despite successful inclusion of several key functional elements of natural proteins into a family of heme protein maquettes, the lack of 3D structures, due principally to conformational heterogeneity, has prevented them from achieving their full potential. We report here the design and synthesis of HP-1, a disulfide-bridged two-α-helix peptide that self-assembles to form an antiparallel twofold symmetric diheme four-α-helix bundle protein with a stable conformation on the NMR time-scale. The HP-1 design strategy began with the x-ray crystal structure of the apomaquette L31M, an apomaquette derived from the structurally heterogeneous tetraheme-binding H10H24 prototype. L31M was functionally redesigned to accommodate two hemes ligated to histidines and to retain the strong coupling of heme oxidation-reduction to glutamate acid–base transitions and proton exchange that was characterized in molten globule predecessors. Heme insertion was modeled with angular constraints statistically derived from natural proteins, and the pattern of hydrophobic and hydrophilic residues on each helix was then altered to account for this large structural reorganization. The transition to structured holomaquette involved the alteration of 6 of 31 residues in each of the four identical helices and, unlike our earlier efforts, required no design intermediates. Oxidation-reduction of both hemes displays an unusually low midpoint potential (–248 mV vs. normal hydrogen electrode at pH 9.0), which is strongly coupled to proton binding, as designed. PMID:15056758

  1. Acid-sensing ion channel 1a is a postsynaptic proton receptor that affects the density of dendritic spines

    PubMed Central

    Zha, Xiang-ming; Wemmie, John A.; Green, Steven H.; Welsh, Michael J.

    2006-01-01

    Extracellular proton concentrations in the brain may be an important signal for neuron function. Proton concentrations change both acutely when synaptic vesicles release their acidic contents into the synaptic cleft and chronically during ischemia and seizures. However, the brain receptors that detect protons and their physiologic importance remain uncertain. Using organotypic hippocampal slices and biolistic transfection, we found the acid-sensing ion channel 1a (ASIC1a), localized in dendritic spines where it functioned as a proton receptor. ASIC1a also affected the density of spines, the postsynaptic site of most excitatory synapses. Decreasing ASIC1a reduced the number of spines, whereas overexpressing ASIC1a had the opposite effect. Ca2+-mediated Ca2+/calmodulin-dependent protein kinase II (CaMKII) signaling was probably responsible, because acid evoked an ASIC1a-dependent elevation of spine intracellular Ca2+ concentration, and reducing or increasing ASIC1a levels caused parallel changes in CaMKII phosphorylation in vivo. Moreover, inhibiting CaMKII prevented ASIC1a from increasing spine density. These data indicate that ASIC1a functions as a postsynaptic proton receptor that influences intracellular Ca2+ concentration and CaMKII phosphorylation and thereby the density of dendritic spines. The results provide insight into how protons influence brain function and how they may contribute to pathophysiology. PMID:17060608

  2. Surface modification of Fe2TiO5 nanoparticles by silane coupling agent: Synthesis and application in proton exchange composite membranes.

    PubMed

    Salarizadeh, Parisa; Javanbakht, Mehran; Pourmahdian, Saeed; Bagheri, Ahmad; Beydaghi, Hossein; Enhessari, Morteza

    2016-06-15

    Modifying surfaces of nanoparticles with silane coupling agent provides a simple method to alter their surface properties and improve their dispersibility in organic solvents and polymer matrix. Fe2TiO5 nanoparticles (IT) were modified with 3-aminopropyltriethoxysilane (APTES) as novel reinforcing filler for proton exchange membranes. The main operating parameters such as reaction time (R.T), APTES/IT and triethylamine (TEA)/IT ratios have been optimized for maximum grafting efficiency. The optimum conditions for R.T, APTES/IT and TEA/IT ratios were 6h, 4 and 0.3 respectively. It was observed that the APTES/IT and TEA/IT ratios were the most significant parameters affecting the grafting percentage. Modified nanoparticles were characterized using FT-IR, TGA, SEM, TEM and XRD techniques. Effects of modified nanoparticles in proton exchange membrane fuel cells (PEMFC) were evaluated. The resulting nanocomposite membranes exhibited higher proton conductivity in comparison with pristine SPPEK and SPPEK/IT membranes. This increase is attributed to connectivity of the water channels which creates more direct pathways for proton transport. Composite membrane with 3% AIT (6.46% grafting amount) showed 0.024Scm(-1) proton conductivity at 25°C and 149mWcm(-2) power density (at 0.5V) at 80°C which were about 243% and 51%, respectively higher than that of pure SPPEK. PMID:27023633

  3. Proton-sensitive cation channels and ion exchangers in ischemic brain injury: new therapeutic targets for stroke?

    PubMed Central

    Leng, Tiandong; Shi, Yejie; Xiong, Zhi-Gang; Sun, Dandan

    2014-01-01

    Ischemic brain injury results from complicated cellular mechanisms. The present therapy for acute ischemic stroke is limited to thrombolysis with the recombinant tissue plasminogen activator (rtPA) and mechanical recanalization. Therefore, a better understanding of ischemic brain injury is needed for the development of more effective therapies. Disruption of ionic homeostasis plays an important role in cell death following cerebral ischemia. Glutamate receptor-mediated ionic imbalance and neurotoxicity have been well established in cerebral ischemia after stroke. However, non-NMDA receptor-dependent mechanisms, involving acid-sensing ion channel 1a (ASIC1a), transient receptor potential melastatin 7 (TRPM7), and Na+/H+ exchanger isoform 1 (NHE1), have recently emerged as important players in the dysregulation of ionic homeostasis in the CNS under ischemic conditions. These H+-sensitive channels and/or exchangers are expressed in the majority of cell types of the neurovascular unit. Sustained activation of these proteins causes excessive influx of cations, such as Ca2+, Na+, and Zn2+, and leads to ischemic reperfusion brain injury. In this review, we summarize recent pre-clinical experimental research findings on how these channels/exchangers are regulated in both in vitro and in vivo models of cerebral ischemia. The blockade or transgenic knockdown of these proteins was shown to be neuroprotective in these ischemia models. Taken together, these non-NMDA receptor-dependent mechanisms may serve as novel therapeutic targets for stroke intervention. PMID:24467911

  4. The role of phosphatidylcholine in fatty acid exchange and desaturation in Brassica napus L. leaves.

    PubMed Central

    Williams, J P; Imperial, V; Khan, M U; Hodson, J N

    2000-01-01

    The role of phosphatidylcholine (PC) in fatty acid exchange and desaturation was examined and compared with that of monogalactosyldiacylglycerol (MGDG) in Brassica napus leaves using (14)C-labelling in vivo. Data are presented which indicate that in the chloroplast newly formed saturated (palmitic acid, 16:0) and monounsaturated (oleic acid, 18:1) fatty acid is incorporated into MGDG and desaturated in situ. In the non-plastidic compartments, however, newly formed fatty acid is exchanged with polyunsaturated fatty acid in PC, the probable major site of subsequent desaturation. The unsaturated fatty acid is released to the acyl-CoA pool, which is then used to synthesize diacylglycerol (DAG) containing a high level of unsaturated fatty acid. This highly unsaturated DAG may be the source for the biosynthesis of other cellular glycerolipids. The generally accepted pathway in which PC is synthesized from molecular species of DAG containing 16:0 and 18:1 followed by desaturation of the 18:1 to linoleic (18:2) and linolenic (18:3) acids is questioned. PMID:10861220

  5. Molecular mechanism of proton transport in CLC Cl-/H+ exchange transporters

    PubMed Central

    Feng, Liang; Campbell, Ernest B.; MacKinnon, Roderick

    2012-01-01

    CLC proteins underlie muscle, kidney, bone, and other organ system function by catalyzing the transport of Cl- ions across cell and organellar membranes. Some CLC proteins are ion channels while others are pumps that exchange Cl- for H+. The pathway through which Cl- ions cross the membrane has been characterized, but the transport of H+ and the principle by which their movement is coupled to Cl- movement is not well understood. Here we show that H+ transport depends not only on the presence of a specific glutamate residue but also the presence of Cl- ions. H+ transport, however, can be isolated and analyzed in the absence of Cl- by mutating the glutamate to alanine and adding carboxylate-containing molecules to solution, consistent with the notion that H+ transfer is mediated through the entry of a carboxylate group into the anion pathway. Cl- ions and carboxylate interact with each other strongly. These data support a mechanism in which the glutamate carboxylate functions as a surrogate Cl- ion, but it can accept a H+ and transfer it between the external solution and the central Cl- binding site, coupled to the movement of 2 Cl- ions. PMID:22753511

  6. Sulfated Titania-Silica Reinforced Nafion Nanocomposite Membranes for Proton Exchange Membrane Fuel Cells.

    PubMed

    Abu Sayeed, M D; Kim, Hee Jin; Gopalan, A I; Kim, Young Ho; Lee, Kwang-Pill; Choi, Sang-June

    2015-09-01

    Sulfated titania-silica (SO4(2-)-/TiO2-SiO2) composites were prepared by a sol-gel method with sulfate reaction and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The nanometric diameter and geometry of the sulfated titania-silica (STS) was investigated by transmission electron microscopy (TEM). A small amount of the STS composite in the range of 0.5-3 wt% was then added as reinforcing into the Nafion membrane by water-assisted solution casting method to prepare STS reinforced Nafion nanocomposite membranes (STS-Nafion nanocomposite membranes). The additional functional groups, sulfate groups, of the nanocomposite membrane having more surface oxygenated groups enhanced the fuel cell membrane properties. The STS-Nafion nanocomposite membranes exhibited improved water uptake compared to that of neat Nafion membranes, whereas methanol uptake values were decreased dramatically improved thermal property of the prepared nanocomposite membranes were measured by thermogravimetric analysis (TGA). Furthermore, increased ion exchange capacity values were obtained by thermoacidic pretreatment of the nanocomposite membranes. PMID:26716283

  7. Lithium polymer batteries and proton exchange membrane fuel cells as energy sources in hydrogen electric vehicles

    NASA Astrophysics Data System (ADS)

    Corbo, P.; Migliardini, F.; Veneri, O.

    This paper deals with the application of lithium ion polymer batteries as electric energy storage systems for hydrogen fuel cell power trains. The experimental study was firstly effected in steady state conditions, to evidence the basic features of these systems in view of their application in the automotive field, in particular charge-discharge experiments were carried at different rates (varying the current between 8 and 100 A). A comparison with conventional lead acid batteries evidenced the superior features of lithium systems in terms of both higher discharge rate capability and minor resistance in charge mode. Dynamic experiments were carried out on the overall power train equipped with PEM fuel cell stack (2 kW) and lithium batteries (47.5 V, 40 Ah) on the European R47 driving cycle. The usage of lithium ion polymer batteries permitted to follow the high dynamic requirement of this cycle in hard hybrid configuration, with a hydrogen consumption reduction of about 6% with respect to the same power train equipped with lead acid batteries.

  8. Separation of phenolic acids from natural plant extracts using molecularly imprinted anion-exchange polymer confined ionic liquids.

    PubMed

    Bi, Wentao; Tian, Minglei; Row, Kyung Ho

    2012-04-01

    Polymer-confined ionic liquids were used for the separation of phenolic acids from natural plant extract by utilizing an anion-exchange mechanism. They were synthesized using molecular imprinting technique to reduce non-directional ion-ion interactions during anion-exchange and other interactions with interference substances that could decrease selectivity. A suitable sorbent for phenolic acid separation could be identified based on the adsorption behaviors of phenolic acids on different polymer-confined ionic liquids. Thus, the developed ionic liquid-based molecularly imprinted anion-exchange polymer (IMAP) achieved high recovery rates by solid-phase extraction of phenolic acids from Salicornia herbacea L. extract: 90.1% for protocatechuic acid, 95.5% for ferulic acid and 96.6% for caffeic acid. Moreover, the phenolic acids were separable from each other by repeated solid phase extraction cycles. The proposed method could be used to separate other phenolic acids or organic acids from complex samples. PMID:21903215

  9. Hydrogen-Deuterium Exchange of Meteoritic Dicarboxylic Acids During Aqueous Extraction

    NASA Technical Reports Server (NTRS)

    Fuller, M.; Huang, Y.

    2002-01-01

    This study examines the extent of hydrogen-deuterium exchange on dicarboxylic acids during aqueous extraction. Deuterium enrichment was observed to be a function of diacid structure as well as delta-D. Additional information is contained in the original extended abstract.

  10. ALUMINUM SOLUBILITY, CALCIUM-ALUMINUM EXCHANGE, AND PH IN ACID FOREST SOILS

    EPA Science Inventory

    Important components in several models designed to describe the effects of acid deposition on soils and surface waters are the pH-A1 and Ca-A1 exchange relationships. f A1 solubility is controlled by A1 trihydroxide minerals, the theoretical pH-A1 relationship can be described by...

  11. Transport of amino acids in Lactobacillus casei by proton-motive-force-dependent and non-proton-motive-force-dependent mechanisms.

    PubMed

    Strobel, H J; Russell, J B; Driessen, A J; Konings, W N

    1989-01-01

    Lactobacillus casei 393 cells which were energized with glucose (pH 6.0) took up glutamine, asparagine, glutamate, aspartate, leucine, and phenylalanine. Little or no uptake of several essential amino acids (valine, isoleucine, arginine, cysteine, tyrosine, and tryptophan) was observed. Inhibition studies indicated that there were at least five amino acid carriers, for glutamine, asparagine, glutamate/aspartate, phenylalanine, or branched-chain amino acids. Transport activities had pH optima between 5.5 and 6.0, but all amino acid carriers showed significant activity even at pH 4.0. Leucine and phenylalanine transport decreased markedly when the pH was increased to 7.5. Inhibitors which decreased proton motive force (delta p) nearly eliminated leucine and phenylalanine uptake, and studies with de-energized cells and membrane vesicles showed that an artificial electrical potential (delta psi) of at least -100 mV was needed for rapid uptake. An artificial delta p was unable to drive glutamine, asparagine, or glutamate uptake, and transport of these amino acids was sensitive to a decline in intracellular pH. When intracellular pH was greater than 7.7, glutamine, asparagine, or glutamate was transported rapidly even though the proton motive force had been abolished by inhibitors. PMID:2492498

  12. Calibration and intercomparison of acetic acid measurements using proton transfer reaction mass spectrometry (PTR-MS)

    USGS Publications Warehouse

    Haase, K.B.; Keene, W.C.; Pszenny, A.A.P.; Mayne, H.R.; Talbot, R.W.; Sive, B.C.

    2012-01-01

    Acetic acid is one of the most abundant organic acids in the ambient atmosphere, with maximum mixing ratios reaching into the tens of parts per billion by volume (ppbv) range. The identities and associated magnitudes of the major sources and sinks for acetic acid are poorly characterized, due in part to the limitation in available measurement techniques. This paper demonstrates that Proton Transfer Reaction Mass Spectrometry (PTR-MS) can reliably quantify acetic acid vapor in ambient air. Three different PTR-MS configurations were calibrated at low ppbv mixing ratios using permeation tubes, which yielded calibration factors between 7.0 and 10.9 normalized counts per second per ppbv (ncps ppbv−1) at a drift tube field strength of 132 townsend (Td). Detection limits ranged from 0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factors showed negligible humidity dependence. Using the experimentally determined calibration factors, PTR-MS measurements of acetic acid during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign were validated against results obtained using Mist Chambers coupled with Ion Chromatography (MC/IC). An orthogonal least squares linear regression of paired data yielded a slope of 1.14 ± 0.06 (2σ), an intercept of 0.049 ± 20 (2σ) ppbv, and an R2 of 0.78. The median mixing ratio of acetic acid on Appledore Island, ME during the ICARTT campaign was 0.530 ± 0.025 ppbv with a minimum of 0.075 ± 0.004 ppbv, and a maximum of 3.555 ± 0.171 ppbv.

  13. Acidity field of soils as ion-exchange systems and the diagnostics of genetic soil horizons

    NASA Astrophysics Data System (ADS)

    Kokotov, Yu. A.; Sukhacheva, E. Yu.; Aparin, B. F.

    2014-12-01

    For the comprehensive description of the acidity of a two-phase ion-exchange system, we should analyze two curves of the ionite titration by a strong base in water and salt solutions and find the quantitative relationships between the corresponding pH characteristics. An idea of the three-dimensional field of acidity of ion-exchange systems (the phase space of the soil acidity characteristics) and its three two-dimensional projections is suggested. For soils, three interrelated characteristics—the pH values of the salt and water extracts and the degree of base saturation—can serve as spatial coordinates for the acidity field. Representation of factual data in this field makes it possible to compare and analyze the acidity characteristics of different soils and soil horizons and to determine their specific features. Differentiation of the field into separate volumes allows one to present the data in a discrete form. We have studied the distribution patterns of the groups of soil horizons from Leningrad oblast and other regions of northwestern Russia in the acidity field. The studied samples are grouped in different partially overlapping areas of the projections of the acidity field. The results of this grouping attest to the correctness of the modern classification of Russian soils. A notion of the characteristic soil area in the acidity field is suggested; it can be applied to all the soils with a leaching soil water regime.

  14. Reduced sodium/proton exchanger NHE3 activity causes congenital sodium diarrhea.

    PubMed

    Janecke, Andreas R; Heinz-Erian, Peter; Yin, Jianyi; Petersen, Britt-Sabina; Franke, Andre; Lechner, Silvia; Fuchs, Irene; Melancon, Serge; Uhlig, Holm H; Travis, Simon; Marinier, Evelyne; Perisic, Vojislav; Ristic, Nina; Gerner, Patrick; Booth, Ian W; Wedenoja, Satu; Baumgartner, Nadja; Vodopiutz, Julia; Frechette-Duval, Marie-Christine; De Lafollie, Jan; Persad, Rabindranath; Warner, Neil; Tse, C Ming; Sud, Karan; Zachos, Nicholas C; Sarker, Rafiquel; Zhu, Xinjun; Muise, Aleixo M; Zimmer, Klaus-Peter; Witt, Heiko; Zoller, Heinz; Donowitz, Mark; Müller, Thomas

    2015-12-01

    Congenital sodium diarrhea (CSD) refers to an intractable diarrhea of intrauterine onset with high fecal sodium loss. CSD is clinically and genetically heterogeneous. Syndromic CSD is caused by SPINT2 mutations. While we recently described four cases of the non-syndromic form of CSD that were caused by dominant activating mutations in intestinal receptor guanylate cyclase C (GC-C), the genetic cause for the majority of CSD is still unknown. Therefore, we aimed to determine the genetic cause for non-GC-C non-syndromic CSD in 18 patients from 16 unrelated families applying whole-exome sequencing and/or chromosomal microarray analyses and/or direct Sanger sequencing. SLC9A3 missense, splicing and truncation mutations, including an instance of uniparental disomy, and whole-gene deletion were identified in nine patients from eight families with CSD. Two of these nine patients developed inflammatory bowel disease (IBD) at 4 and 16 years of age. SLC9A3 encodes Na(+)/H(+) antiporter 3 (NHE3), which is the major intestinal brush-border Na(+)/H(+) exchanger. All mutations were in the NHE3 N-terminal transport domain, and all missense mutations were in the putative membrane-spanning domains. Identified SLC9A3 missense mutations were functionally characterized in plasma membrane NHE null fibroblasts. SLC9A3 missense mutations compromised NHE3 activity by reducing basal surface expression and/or loss of basal transport function of NHE3 molecules, whereas acute regulation was normal. This study identifies recessive mutations in NHE3, a downstream target of GC-C, as a cause of CSD and implies primary basal NHE3 malfunction as a predisposition for IBD in a subset of patients. PMID:26358773

  15. Current density and ohmic resistance distribution in the land-channel direction of a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Shrivastava, Udit N.; Tajiri, Kazuya; Chase, Michael

    2015-12-01

    A highly instrumented segmented cell is designed to measure current density and ohmic resistance distribution in the land-channel direction of a proton exchange membrane fuel cell at resolution of 350 μm. A customized catalyst coated membrane with an active area of 9 mm2 is prepared, and a printed-circuit board technique is introduced to ease fabrication of segmented anode and to adapt design to any flow arrangement. Design of segmented cell is validated by electrochemical pumping of hydrogen from anode to cathode. Current density and ohmic resistance distribution are measured in two wet conditions (at 40 °C and 60 °C) and a dry condition at 60 °C. In all cases a strong correlation between current generation and ohmic resistance distribution is observed. Outcomes from these experiments revealed that the water distribution has a strong effect on the local current generation and ohmic resistance. In wet condition ohmic resistance is uniform but current generation found to be non-uniform because of the non-uniform liquid water distribution. In dry condition, on the other hand, non-uniform water generation resulted in both uneven current generation and ohmic resistance.

  16. Real-Time Remote Monitoring of Temperature and Humidity Within a Proton Exchange Membrane Fuel Cell Using Flexible Sensors

    PubMed Central

    Kuo, Long-Sheng; Huang, Hao-Hsiu; Yang, Cheng-Hao; Chen, Ping-Hei

    2011-01-01

    This study developed portable, non-invasive flexible humidity and temperature microsensors and an in situ wireless sensing system for a proton exchange membrane fuel cell (PEMFC). The system integrated three parts: a flexible capacitive humidity microsensor, a flexible resistive temperature microsensor, and a radio frequency (RF) module for signal transmission. The results show that the capacitive humidity microsensor has a high sensitivity of 0.83 pF%RH−1 and the resistive temperature microsensor also exhibits a high sensitivity of 2.94 × 10−3 °C−1. The established RF module transmits the signals from the two microsensors. The transmission distance can reach 4 m and the response time is less than 0.25 s. The performance measurements demonstrate that the maximum power density of the fuel cell with and without these microsensors are 14.76 mW·cm−2 and 15.90 mW·cm−2, with only 7.17% power loss. PMID:22164099

  17. Numerical investigation of interfacial transport resistance due to water droplets in proton exchange membrane fuel cell air channels

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa; Kandlikar, Satish G.

    2013-12-01

    Oxygen transport resistance at the air flow channel and gas diffusion layer (GDL) interface is needed in modelling the performance of a proton exchange membrane fuel cell (PEMFC). This resistance is expressed through the non-dimensional Sherwood number (Sh). The effect of the presence of a droplet on Sh is studied numerically in an isolated air flow channel using a commercially available package, COMSOL Multiphysics®. A droplet is represented as a solid obstruction placed on the GDL-channel interface and centred along the channel width. The effect of a single droplet is first studied for a range of superficial mean air velocities and droplet sizes. Secondly, the effect of droplet spacing on Sh is studied through simulations of two consecutive droplets. Lastly, multiple droplets in a row are studied as a more representative case of a PEMFC air flow channel. The results show that the droplets significantly increase Sh above the fully developed value in the wake region. This enhancement increases with the number of droplets, droplet size, and superficial mean air velocity. Moreover, the analogy between mass and heat transfer is investigated by comparing Sh to the equivalent Nusselt number.

  18. Coupled modeling of water transport and air-droplet interaction in the electrode of a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Esposito, Angelo; Pianese, Cesare; Guezennec, Yann G.

    In this work, an accurate and computationally fast model for liquid water transport within a proton exchange membrane fuel cell (PEMFC) electrode is developed by lumping the space-dependence of the relevant variables. Capillarity is considered as the main transport mechanism within the gas diffusion layer (GDL). The novelty of the model lies in the coupled simulation of the water transport at the interface between gas diffusion layer and gas flow channel (GFC). This is achieved with a phenomenological description of the process that allows its simulation with relative simplicity. Moreover, a detailed two-dimensional visualization of such interface is achieved via geometric simulation of water droplets formation, growth, coalescence and detachment on the surface of the GDL. The model is useful for optimization analysis oriented to both PEMFC design and balance of plant. Furthermore, the accomplishment of reduced computational time and good accuracy makes the model suitable for control strategy implementation to ensure PEM fuel cells operation within optimal electrode water content.

  19. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells.

    PubMed

    Kongkanand, Anusorn; Mathias, Mark F

    2016-04-01

    Substantial progress has been made in reducing proton-exchange membrane fuel cell (PEMFC) cathode platinum loadings from 0.4-0.8 mgPt/cm(2) to about 0.1 mgPt/cm(2). However, at this level of cathode Pt loading, large performance loss is observed at high-current density (>1 A/cm(2)), preventing a reduction in the overall stack cost. This next developmental step is being limited by the presence of a resistance term exhibited at these lower Pt loadings and apparently due to a phenomenon at or near the catalyst surface. This issue can be addressed through the design of catalysts with high and stable Pt dispersion as well as through development and implementation of ionomers designed to interact with Pt in a way that does not constrain oxygen reduction reaction rates. Extrapolating from progress made in past decades, we are optimistic that the concerted efforts of materials and electrode designers can resolve this issue, thus enabling a large step toward fuel cell vehicles that are affordable for the mass market. PMID:26961326

  20. Surface composition of magnetron sputtered Pt-Co thin film catalyst for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Vorokhta, Mykhailo; Khalakhan, Ivan; Václavů, Michal; Kovács, Gábor; Kozlov, Sergey M.; Kúš, Peter; Skála, Tomáš; Tsud, Natalia; Lavková, Jaroslava; Potin, Valerie; Matolínová, Iva; Neyman, Konstantin M.; Matolín, Vladimír

    2016-03-01

    Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

  1. Modeling the performance of hydrogen-oxygen unitized regenerative proton exchange membrane fuel cells for energy storage

    NASA Astrophysics Data System (ADS)

    Guarnieri, Massimo; Alotto, Piergiorgio; Moro, Federico

    2015-11-01

    Thanks to the independent sizing of power and energy, hydrogen-based energy storage is one of the very few technologies capable of providing long operational times in addition to the other advantages offered by electrochemical energy storage, for example scalability, site versatility, and mobile service. The typical design consists of an electrolyzer in charge mode and a separate fuel cell in discharge mode. Instead, a unitized regenerative fuel cell (URFC) is a single device performing both energy conversions, achieving a higher compactness and power-to-weight ratio. This paper presents a performance model of a URFC based on a proton exchange membrane (PEM) electrolyte and working on hydrogen and oxygen, which can provide high energy and power densities (>0.7 W cm-2). It provides voltage, power, and efficiency at varying load conditions as functions of the controlling physical quantities: temperature, pressure, concentration, and humidification. The model constitutes a tool for designing the interface and control sub-system as well as for exploring optimized cell/stack designs and operational conditions. To date, only a few of such analyses have been carried out and more research is needed in order to explore the true potential of URFCs.

  2. Real-time remote monitoring of temperature and humidity within a proton exchange membrane fuel cell using flexible sensors.

    PubMed

    Kuo, Long-Sheng; Huang, Hao-Hsiu; Yang, Cheng-Hao; Chen, Ping-Hei

    2011-01-01

    This study developed portable, non-invasive flexible humidity and temperature microsensors and an in situ wireless sensing system for a proton exchange membrane fuel cell (PEMFC). The system integrated three parts: a flexible capacitive humidity microsensor, a flexible resistive temperature microsensor, and a radio frequency (RF) module for signal transmission. The results show that the capacitive humidity microsensor has a high sensitivity of 0.83 pF%RH(-1) and the resistive temperature microsensor also exhibits a high sensitivity of 2.94 × 10(-3) °C(-1). The established RF module transmits the signals from the two microsensors. The transmission distance can reach 4 m and the response time is less than 0.25 s. The performance measurements demonstrate that the maximum power density of the fuel cell with and without these microsensors are 14.76 mW·cm(-2) and 15.90 mW·cm(-2), with only 7.17% power loss. PMID:22164099

  3. Study of acetylene poisoning of Pt cathode on proton exchange membrane fuel cell spatial performance using a segmented cell system

    NASA Astrophysics Data System (ADS)

    Reshetenko, Tatyana V.; St-Pierre, Jean

    2015-08-01

    Acetylene is a welding fuel and precursor for organic synthesis, which requires considering it to be a possible air pollutant. In this work, the spatial performance of a proton exchange membrane fuel cell exposed to 300 ppm C2H2 and different operating currents was studied with a segmented cell system. The injection of C2H2 resulted in a cell performance decrease and redistribution of segments' currents depending on the operating conditions. Performance loss was 20-50 mV at 0.1-0.2 A cm-2 and was accompanied by a rapid redistribution of localized currents. Acetylene exposure at 0.4-1.0 A cm-2 led to a sharp voltage decrease to 0.07-0.13 V and significant changes in current distribution during a transition period, when the cell reached a voltage of 0.55-0.6 V. A recovery of the cell voltage was observed after stopping the C2H2 injection. Spatial electrochemical impedance spectroscopy (EIS) data showed different segments' behavior at low and high currents. It was assumed that acetylene oxidation occurs at high cell voltage, while it reduces at low cell potential. A detailed analysis of the current density distribution, its correlation with EIS data and possible C2H2 oxidation/reduction mechanisms are presented and discussed.

  4. Dynamic analysis and linear control strategies for proton exchange membrane fuel cell using a distributed parameter model

    NASA Astrophysics Data System (ADS)

    Methekar, R. N.; Prasad, V.; Gudi, R. D.

    To satisfy high power density demand in proton exchange membrane fuel cells (PEMFCs), a robust control strategy is essential. A linear ratio control strategy is examined in this work. The manipulated variables are selected using steady-state relative gain array (RGA) analysis to be the inlet molar flow rates of hydrogen and coolant, and the controlled variables are average power density and average solid temperature, respectively. By selecting proper manipulated variables, the PEMFC does not exhibit sign change in gain and hence can be controlled by using a linear controller. Transfer function models obtained from step tests on the distributed parameter PEMFC model are used to design controllers for the multiple input-multiple output (MIMO) system. In addition, a ratio control strategy is proposed and evaluated, where the inlet molar flow rate of oxygen is used as a dependent manipulated variable and changed in a constant ratio with respect to the inlet molar flow rate of hydrogen. Simulation results show that the ratio control strategy provides a faster response than a MIMO control strategy. This ratio control strategy is able to circumvent the problem of oxygen starvation, and the increase in average solid temperature is small as compared to the MIMO control strategy.

  5. Analytical Investigation and Improvement of Performance of a Proton Exchange Membrane (Pem) Fuel Cell in Mobile Applications

    NASA Astrophysics Data System (ADS)

    Khazaee, I.

    2015-05-01

    In this study, the performance of a proton exchange membrane fuel cell in mobile applications is investigated analytically. At present the main use and advantages of fuel cells impact particularly strongly on mobile applications such as vehicles, mobile computers and mobile telephones. Some external parameters such as the cell temperature (Tcell ) , operating pressure of gases (P) and air stoichiometry (λair ) affect the performance and voltage losses in the PEM fuel cell. Because of the existence of many theoretical, empirical and semi-empirical models of the PEM fuel cell, it is necessary to compare the accuracy of these models. But theoretical models that are obtained from thermodynamic and electrochemical approach, are very exact but complex, so it would be easier to use the empirical and smi-empirical models in order to forecast the fuel cell system performance in many applications such as mobile applications. The main purpose of this study is to obtain the semi-empirical relation of a PEM fuel cell with the least voltage losses. Also, the results are compared with the existing experimental results in the literature and a good agreement is seen.

  6. Performance and degradation of Proton Exchange Membrane Fuel Cells: State of the art in modeling from atomistic to system scale

    NASA Astrophysics Data System (ADS)

    Jahnke, T.; Futter, G.; Latz, A.; Malkow, T.; Papakonstantinou, G.; Tsotridis, G.; Schott, P.; Gérard, M.; Quinaud, M.; Quiroga, M.; Franco, A. A.; Malek, K.; Calle-Vallejo, F.; Ferreira de Morais, R.; Kerber, T.; Sautet, P.; Loffreda, D.; Strahl, S.; Serra, M.; Polverino, P.; Pianese, C.; Mayur, M.; Bessler, W. G.; Kompis, C.

    2016-02-01

    Proton Exchange Membrane Fuel Cells (PEMFC) are energy efficient and environmentally friendly alternatives to conventional energy conversion systems in many yet emerging applications. In order to enable prediction of their performance and durability, it is crucial to gain a deeper understanding of the relevant operation phenomena, e.g., electrochemistry, transport phenomena, thermodynamics as well as the mechanisms leading to the degradation of cell components. Achieving the goal of providing predictive tools to model PEMFC performance, durability and degradation is a challenging task requiring the development of detailed and realistic models reaching from the atomic/molecular scale over the meso scale of structures and materials up to components, stack and system level. In addition an appropriate way of coupling the different scales is required. This review provides a comprehensive overview of the state of the art in modeling of PEMFC, covering all relevant scales from atomistic up to system level as well as the coupling between these scales. Furthermore, it focuses on the modeling of PEMFC degradation mechanisms and on the coupling between performance and degradation models.

  7. Influence of the cathode architecture in the frequency response of self-breathing proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ferreira-Aparicio, P.; Chaparro, A. M.

    2014-12-01

    Self-breathing proton exchange membrane fuel cells are apparently simple devices, but efficient water management is critical for their performance. The cathode configuration should guarantee balanced rates between O2 accessibility from the circumventing air and H2O removal, and a good electric contact between catalyst layers and current collectors at the same time. By applying progressive modifications to the initial concept of a conventional PEMFC, the effect of the cathode architecture on cell performance has been analyzed. Frequency response analyses of the cell during steady-state potentiostatic stepping have yielded relevant information regarding limitations originated by the cathode impedance under high current load conditions. The primitive cell design has been optimized for self-breathing operation by means of this diagnostic tool. The thickness of the perforated plate in the cathode has been found to be one of the main factors contributing to limit oxygen accessibility when a high current load is demanded. Adequate cathode architecture is critical for reducing mass transport limitations in the catalytic layer and enhancing performance under self-breathing conditions.

  8. Dry gas operation of proton exchange membrane fuel cells with parallel channels: Non-porous versus porous plates

    NASA Astrophysics Data System (ADS)

    Litster, Shawn; Santiago, Juan G.

    We present a study of proton exchange membrane (PEM) fuel cells with parallel channel flow fields for the cathode, dry inlet gases, and ambient pressure at the outlets. The study compares the performance of two designs: a standard, non-porous graphite cathode plate design and a porous hydrophilic carbon plate version. The experimental study of the non-porous plate is a control case and highlights the significant challenges of operation with dry gases and non-porous, parallel channel cathodes. These challenges include significant transients in power density and severe performance loss due to flooding and electrolyte dry-out. Our experimental study shows that the porous plate yields significant improvements in performance and robustness of operation. We hypothesize that the porous plate distributes water throughout the cell area by capillary action; including pumping water upstream to normally dry inlet regions. The porous plate reduces membrane resistance and air pressure drop. Further, IR-free polarization curves confirm operation free of flooding. With an air stoichiometric ratio of 1.3, we obtain a maximum power density of 0.40 W cm -2, which is 3.5 times greater than that achieved with the non-porous plate at the same operating condition.

  9. Membrane patterned by pulsed laser micromachining for proton exchange membrane fuel cell with sputtered ultra-low catalyst loadings

    NASA Astrophysics Data System (ADS)

    Cuynet, S.; Caillard, A.; Kaya-Boussougou, S.; Lecas, T.; Semmar, N.; Bigarré, J.; Buvat, P.; Brault, P.

    2015-12-01

    Proton exchange membranes were nano- and micro-patterned on their cathode side by pressing them against stainless steel molds previously irradiated by a Ti:Sapphire femtosecond laser. The membranes were associated to ultra-low loaded thin catalytic layers (25 μgPt cm-2) prepared by plasma magnetron sputtering. The Pt catalyst was sputtered either on the membrane or on the porous electrode. The fuel cell performance in dry conditions were found to be highly dependent on the morphology of the membrane surface. When nanometric ripples covered by a Pt catalyst were introduced on the surface of the membrane, the fuel cell outperformed the conventional one with a flat membrane. By combining nano- and micro-patterns (nanometric ripples and 11-24 μm deep craters), the performance of the cells was clearly enhanced. The maximum power density achieved by the fuel cell was multiplied by a factor of 3.6 (at 50 °C and 3 bar): 438 mW cm-2 vs 122 mW cm-2. This improvement is due to high catalyst utilization with a high membrane conductivity. When Pt is sputtered on the porous electrode (and not on the membrane), the contribution of the patterned membrane to the fuel cell efficiency was less significant, except in the presence of nanometric ripples. This result suggests that the patterning of the membrane must be consistent with the way the catalyst is synthesized, on the membrane or on the porous electrode.

  10. Proton exchange membrane fuel cells cold startup global strategy for fuel cell plug-in hybrid electric vehicle

    NASA Astrophysics Data System (ADS)

    Henao, Nilson; Kelouwani, Sousso; Agbossou, Kodjo; Dubé, Yves

    2012-12-01

    This paper investigates the Proton Exchange Membrane Fuel Cell (PEMFC) Cold Startup problem within the specific context of the Plugin Hybrid Electric Vehicles (PHEV). A global strategy which aims at providing an efficient method to minimize the energy consumption during the startup of a PEMFC is proposed. The overall control system is based on a supervisory architecture in which the Energy Management System (EMS) plays the role of the power flow supervisor. The EMS estimates in advance, the time to start the fuel cell (FC) based upon the battery energy usage during the trip. Given this estimation and the amount of additional energy required, the fuel cell temperature management strategy computes the most appropriate time to start heating the stack in order to reduce heat loss through the natural convection. As the cell temperature rises, the PEMFC is started and the reaction heat is used as a self-heating power source to further increase the stack temperature. A time optimal self-heating approach based on the Pontryagin minimum principle is proposed and tested. The experimental results have shown that the proposed approach is efficient and can be implemented in real-time on FC-PHEVs.

  11. Application of proton exchange membrane fuel cells for the monitoring and direct usage of biohydrogen produced by Chlamydomonas reinhardtii

    NASA Astrophysics Data System (ADS)

    Oncel, S.; Vardar-Sukan, F.

    Photo-biologically produced hydrogen by Chlamydomonas reinhardtii is integrated with a proton exchange (PEM) fuel cell for online electricity generation. To investigate the fuel cell efficiency, the effect of hydrogen production on the open circuit fuel cell voltage is monitored during 27 days of batch culture. Values of volumetric hydrogen production, monitored by the help of the calibrated water columns, are related with the open circuit voltage changes of the fuel cell. From the analysis of this relation a dead end configuration is selected to use the fuel cell in its best potential. After the open circuit experiments external loads are tested for their effects on the fuel cell voltage and current generation. According to the results two external loads are selected for the direct usage of the fuel cell incorporating with the photobioreactors (PBR). Experiments with the PEM fuel cell generate a current density of 1.81 mA cm -2 for about 50 h with 10 Ω load and 0.23 mA cm -2 for about 80 h with 100 Ω load.

  12. Proton exchange membrane fuel cell model for aging predictions: Simulated equivalent active surface area loss and comparisons with durability tests

    NASA Astrophysics Data System (ADS)

    Robin, C.; Gérard, M.; Quinaud, M.; d'Arbigny, J.; Bultel, Y.

    2016-09-01

    The prediction of Proton Exchange Membrane Fuel Cell (PEMFC) lifetime is one of the major challenges to optimize both material properties and dynamic control of the fuel cell system. In this study, by a multiscale modeling approach, a mechanistic catalyst dissolution model is coupled to a dynamic PEMFC cell model to predict the performance loss of the PEMFC. Results are compared to two 2000-h experimental aging tests. More precisely, an original approach is introduced to estimate the loss of an equivalent active surface area during an aging test. Indeed, when the computed Electrochemical Catalyst Surface Area profile is fitted on the experimental measures from Cyclic Voltammetry, the computed performance loss of the PEMFC is underestimated. To be able to predict the performance loss measured by polarization curves during the aging test, an equivalent active surface area is obtained by a model inversion. This methodology enables to successfully find back the experimental cell voltage decay during time. The model parameters are fitted from the polarization curves so that they include the global degradation. Moreover, the model captures the aging heterogeneities along the surface of the cell observed experimentally. Finally, a second 2000-h durability test in dynamic operating conditions validates the approach.

  13. Isothermal Ice Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell

    SciTech Connect

    Dursch, Thomas J.; Ciontea, Monica A.; Radke, Clayton J.; Weber, Adam Z.

    2011-12-01

    Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are studied using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. Finally, a validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.

  14. Accurate measurement of the through-plane water content of proton-exchange membranes using neutron radiography

    NASA Astrophysics Data System (ADS)

    Hussey, D. S.; Spernjak, D.; Weber, A. Z.; Mukundan, R.; Fairweather, J.; Brosha, E. L.; Davey, J.; Spendelow, J. S.; Jacobson, D. L.; Borup, R. L.

    2012-11-01

    The water sorption of proton-exchange membranes (PEMs) was measured in situ using high-resolution neutron imaging in small-scale fuel cell test sections. A detailed characterization of the measurement uncertainties and corrections associated with the technique is presented. An image-processing procedure resolved a previously reported discrepancy between the measured and predicted membrane water content. With high-resolution neutron-imaging detectors, the water distributions across N1140 and N117 Nafion membranes are resolved in vapor-sorption experiments and during fuel cell and hydrogen-pump operation. The measured in situ water content of a restricted membrane at 80 °C is shown to agree with ex situ gravimetric measurements of free-swelling membranes over a water activity range of 0.5 to 1.0 including at liquid equilibration. Schroeder's paradox was verified by in situ water-content measurements which go from a high value at supersaturated or liquid conditions to a lower one with fully saturated vapor. At open circuit and during fuel cell operation, the measured water content indicates that the membrane is operating between the vapor- and liquid-equilibrated states.

  15. Spatial proton exchange membrane fuel cell performance under carbon monoxide poisoning at a low concentration using a segmented cell system

    NASA Astrophysics Data System (ADS)

    Reshetenko, Tatyana V.; Bethune, Keith; Rocheleau, Richard

    2012-11-01

    The impact of the fuel contaminant CO, which was intentionally injected in to the hydrogen stream at a concentration of 2 ppm, on proton exchange membrane fuel cell (PEMFC) performance distribution was studied using a segmented cell system and spatial electrochemical impedance spectroscopy (EIS). The cell was operated under a galvanostatic control of the overall cell current at 0.8 A cm-2, and tests were carried out under H2/O2, H2/air, and H2/H2 gas configurations. Upon CO injection the voltage decreased by 0.080, 0.300, and 0.320 V for O2, air, and H2 cathode gases, respectively. The voltage drop was accompanied by changes in the current density distributions. Inlet segments 1-4 showed a decrease in current due to CO adsorption on Pt, while, downstream segments 7-10 exhibited an increase in current. The performance completely recovered within 1-2 h after CO injection was stopped. The conversion of CO proceeds through a combination of catalytic and electrochemical oxidation reactions; however, the catalytic oxidation of CO is likely the dominant process. It was found that an increased membrane gas permeability can mitigate the impact of CO, mainly due to the catalytic oxidation of adsorbed CO on the Pt anode by the permeated O2.

  16. Numerical study of a novel micro-diaphragm flow channel with piezoelectric device for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ma, H. K.; Huang, S. H.; Chen, B. R.; Cheng, L. W.

    Previous studies have shown that the amplitude of the vibration of a piezoelectric (PZT) device produces an oscillating flow that changes the chamber volume along with a curvature variation of the diaphragm. In this study, an actuating micro-diaphragm with piezoelectric effects is utilized as an air-flow channel in proton exchange membrane fuel cell (PEMFC) systems, called PZT-PEMFC. This newly designed gas pump, with a piezoelectric actuation structure, can feed air into the system of an air-breathing PEMFC. When the actuator moves outward to increase the cathode channel volume, the air is sucked into the chamber; moving inward decreases the channel's volume and thereby compresses air into the catalyst layer and enhancing the chemical reaction. The air-standard PZT-PEMFC cycle is proposed to describe an air-breathing PZT-PEMFC. A novel design for PZT-PEMFCs has been proposed and a three-dimensional, transitional model has been successfully built to account for its major phenomena and performance. Moreover, at high frequencies, PZT actuation leads to a more stable current output, more drained water, higher sucked air, higher hydrogen consumption, and also overcomes concentration losses.

  17. Improvement the equation of polarization curve of a proton exchange membrane fuel cell at different channel geometry

    NASA Astrophysics Data System (ADS)

    Khazaee, I.

    2015-12-01

    The polarization curve of a proton exchange membrane fuel cell is an important parameter which is expressed by the change of voltage and current of it that indicates the performance of the cell. The voltage of the cell is a function of temperature that is expressed by the Nernst equation and the equation of voltage losses such as activation loss, ohmic loss and concentration loss. In this study a new correlation for polarization curve is obtained that it in addition to temperature, a new parameter is involved in it that shows the effect of the geometry of cross-section area of channels. For this purpose three PEM fuel cells with different channels geometry of rectangular, elliptical and triangular have constructed. The active area of each cell is 25 cm2 that its weight is 1300 g. The material of the gas diffusion layer is carbon clothes, the membrane is nafion 117 and the catalyst layer is a plane with 0.004 g/cm2 platinum. Also a test bench designed and constructed for testing the cell and a series of experiments are carried out to investigate the influence of the geometry of the cell on performance of the cell. The results show that when the geometry of channel is rectangular the performance of the cell is better than the triangular and elliptical channel.

  18. An application of indirect model reference adaptive control to a low-power proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Yang, Yee-Pien; Liu, Zhao-Wei; Wang, Fu-Cheng

    2008-05-01

    Nonlinearity and the time-varying dynamics of fuel cell systems make it complex to design a controller for improving output performance. This paper introduces an application of a model reference adaptive control to a low-power proton exchange membrane (PEM) fuel cell system, which consists of three main components: a fuel cell stack, an air pump to supply air, and a solenoid valve to adjust hydrogen flow. From the system perspective, the dynamic model of the PEM fuel cell stack can be expressed as a multivariable configuration of two inputs, hydrogen and air-flow rates, and two outputs, cell voltage and current. The corresponding transfer functions can be identified off-line to describe the linearized dynamics with a finite order at a certain operating point, and are written in a discrete-time auto-regressive moving-average model for on-line estimation of parameters. This provides a strategy of regulating the voltage and current of the fuel cell by adaptively adjusting the flow rates of air and hydrogen. Experiments show that the proposed adaptive controller is robust to the variation of fuel cell system dynamics and power request. Additionally, it helps decrease fuel consumption and relieves the DC/DC converter in regulating the fluctuating cell voltage.

  19. A review of composite and metallic bipolar plates in proton exchange membrane fuel cell: Materials, fabrication, and material selection

    NASA Astrophysics Data System (ADS)

    Taherian, Reza

    2014-11-01

    Proton exchange membrane (PEM) fuel cells offer exceptional potential for a clean, efficient, and reliable power source. The bipolar plate (BP) is a key component in this device, as it connects each cell electrically, supplies reactant gases to both anode and cathode, and removes reaction products from the cell. BPs have primarily been fabricated from high-density graphite, but in recent years, much attention has been paid to develop the cost-effective and feasible alternative materials. Recently, two different classes of materials have been attracted attention: metals and composite materials. This paper offers a comprehensive review of the current researches being carried out on the metallic and composite BPs, covering materials and fabrication methods. In this research, the phenomenon of ionic contamination due to the release of the corrosion products of metallic BP and relative impact on the durability as well as performance of PEM fuel cells is extensively investigated. Furthermore, in this paper, upon several effective parameters on commercialization of PEM fuel cells, such as stack cost, weight, volume, durability, strength, ohmic resistance, and ionic contamination, a material selection is performed among the most common BPs currently being used. This material selection is conducted by using Simple Additive Weighting Method (SAWM).

  20. Synthesis of transport layers with controlled anisotropy and application thereof to study proton exchange membrane fuel cell performance

    NASA Astrophysics Data System (ADS)

    Todd, Devin; Mérida, Walter

    2016-04-01

    We report on a novel method for the synthesis of fibre-based proton exchange membrane (PEM) fuel cell porous transport layers (PTLs) with controllable fibre alignment. We also report the first application of such layers as diagnostics tools to probe the effect of within-plane PTL anisotropy upon PEM fuel cell performance. These structures are realized via adaptation of electrospinning technology. Electrospun layers with progressive anisotropy magnitude are produced and evaluated. This novel approach is distinguished from the state-of-the-art because an equivalent study using commercially available materials is impossible due to lack of structurally similar substrates with different anisotropies. The anisotropy is visualized via scanning electron microscopy, and quantified using electrical resistivity. The capacity is demonstrated to achieve fibre alignment, and the associated impact on transport properties. A framework is presented for assessing the in-situ performance, whereby transport layer orientation versus bipolar plate flow-field geometry is manipulated. While an effect upon the commercial baseline cannot be discerned, electrospun transport layers with greater anisotropy magnitude suggest greater sensitivity to orientation; where greater performance is obtained with fibres cross-aligned to flow-field channels. Our approach of electrospun transport enables deterministic structures by which fuel cell performance can be explained and optimized.

  1. Bifunctional phenyl monophosphonic/sulfonic acid ion exchange resin and process for using the same

    DOEpatents

    Alexandratos, Spiro; Shelley, Christopher A.; Horwitz, E. Philip; Chiarizia, Renato; Gula, Michael J.; Xue, Sui; Harvey, James T.

    2002-01-01

    A cross-linked water-insoluble ion exchange resin comprised of polymerized monomers having a phenyl ring is disclosed. A contemplated resin contains (i) polymerized phenyl ring-containing monomers having a phosphonic acid ligand linked to the phenyl ring, (ii) about 2 to about 5 millimoles per gram (mmol/g) of phosphorus as phosphonic acid ligands, and (iii) a sufficient amount of a sulfonic acid ligand such that the ratio of mmol/g of phosphonic acid to mmol/g sulfonic acid is up to 3:1. A process for removing polyvalent metal cations from aqueous solution, and a process for removing iron(III) cations from acidic copper(II) cation-containing solutions that utilize the contemplated resin or other resins are disclosed.

  2. Bifunctional phenyl monophosphonic/sulfonic acid ion exchange resin and process for using the same

    DOEpatents

    Alexandratos, Spiro; Shelley, Christopher A.; Horwitz, E. Philip; Chiarizia, Renato

    2001-01-01

    A cross-linked water-insoluble ion exchange resin comprised of polymerized monomers having a phenyl ring is disclosed. A contemplated resin contains (i) polymerized phenyl ring-containing monomers having a phosphonic acid ligand linked to the phenyl ring, (ii) about 2 to about 5 millimoles per gram (mmol/g) of phosphorus as phosphonic acid ligands, and (iii) a sufficient amount of a sulfonic acid ligand such that the ratio of mmol/g of phosphonic acid to mmol/g sulfonic acid is up to 3:1. A process for removing polyvalent metal cations from aqueous solution, and a process for removing iron(III) cations from acidic copper(II) cation-containing solutions that utilize the contemplated resin or other resins are disclosed.

  3. Improving Evolutionary Models for Mitochondrial Protein Data with Site-Class Specific Amino Acid Exchangeability Matrices

    PubMed Central

    Dunn, Katherine A.; Jiang, Wenyi; Field, Christopher; Bielawski, Joseph P.

    2013-01-01

    Adequate modeling of mitochondrial sequence evolution is an essential component of mitochondrial phylogenomics (comparative mitogenomics). There is wide recognition within the field that lineage-specific aspects of mitochondrial evolution should be accommodated through lineage-specific amino-acid exchangeability matrices (e.g., mtMam for mammalian data). However, such a matrix must be applied to all sites and this implies that all sites are subject to the same, or largely similar, evolutionary constraints. This assumption is unjustified. Indeed, substantial differences are expected to arise from three-dimensional structures that impose different physiochemical environments on individual amino acid residues. The objectives of this paper are (1) to investigate the extent to which amino acid evolution varies among sites of mitochondrial proteins, and (2) to assess the potential benefits of explicitly modeling such variability. To achieve this, we developed a novel method for partitioning sites based on amino acid physiochemical properties. We apply this method to two datasets derived from complete mitochondrial genomes of mammals and fish, and use maximum likelihood to estimate amino acid exchangeabilities for the different groups of sites. Using this approach we identified large groups of sites evolving under unique physiochemical constraints. Estimates of amino acid exchangeabilities differed significantly among such groups. Moreover, we found that joint estimates of amino acid exchangeabilities do not adequately represent the natural variability in evolutionary processes among sites of mitochondrial proteins. Significant improvements in likelihood are obtained when the new matrices are employed. We also find that maximum likelihood estimates of branch lengths can be strongly impacted. We provide sets of matrices suitable for groups of sites subject to similar physiochemical constraints, and discuss how they might be used to analyze real data. We also discuss how

  4. Low Mass MS/MS Fragments of Protonated Amino Acids Used for Distinction of Their 13C- Isotopomers in Metabolic Studies

    NASA Astrophysics Data System (ADS)

    Ma, Xin; Dagan, Shai; Somogyi, Árpád; Wysocki, Vicki H.; Scaraffia, Patricia Y.

    2013-04-01

    Glu, Gln, Pro, and Ala are the main amino acids involved in ammonia detoxification in mosquitoes. In order to develop a tandem mass spectrometry method (MS2) to monitor each carbon of the above isotopically-labeled 13C-amino acids for metabolic studies, the compositions and origins of atoms in fragments of the protonated amino acid should be first elucidated. Thus, various electrospray (ESI)-based MS2 tools were employed to study the fragmentation of these unlabeled and isotopically-labeled amino acids and better understand their dissociation pathways. A broad range of fragments, including previously-undescribed low m/z fragments was revealed. The formulae of the fragments (from m/z 130 down to m/z 27) were confirmed by their accurate masses. The structures and conformations of the larger fragments of Glu were also explored by ion mobility mass spectrometry (IM-MS) and gas-phase hydrogen/deuterium exchange (HDX) experiments. It was found that some low m/z fragments ( m/z 27-30) are common to Glu, Gln, Pro, and Ala. The origins of carbons in these small fragments are discussed and additional collision induced dissociation (CID) MS2 fragmentation pathways are proposed for them. It was also found that small fragments (≤ m/z 84) of protonated, methylated Glu, and methylated Gln are the same as those of the underivatized Glu and Gln. Taken together, the new approach of utilizing low m/z fragments can be applied to distinguish, identify, and quantify 13C-amino acids labeled at various positions, either in the backbone or side chain.

  5. Absolute quantification for benzoic acid in processed foods using quantitative proton nuclear magnetic resonance spectroscopy.

    PubMed

    Ohtsuki, Takashi; Sato, Kyoko; Sugimoto, Naoki; Akiyama, Hiroshi; Kawamura, Yoko

    2012-09-15

    The absolute quantification method of benzoic acid (BA) in processed foods using solvent extraction and quantitative proton nuclear magnetic resonance spectroscopy was developed and validated. BA levels were determined using proton signals (δ(H) 7.53 and 7.98) referenced to 2-dimethyl-2-silapentane-5-sulfonate-d(6) sodium salt (DSS-d(6)) after simple solvent extraction from processed foods. All recoveries from several kinds of processed foods, spiked at their specified maximum Japanese usage levels (0.6-2.5 g kg(-1)) and at 0.13 g kg(-1) and 0.063 g kg(-1), were greater than 80%. The limit of quantification was confirmed as 0.063 g kg(-1) in processed foods, which was sufficiently low for the purposes of monitoring BA. The accuracy of the proposed method is equivalent to the conventional method using steam-distillation extraction and high-performance liquid chromatography. The proposed method was both rapid and simple. Moreover, it provided International System of Units traceability without the need for authentic analyte standards. Therefore, the proposed method is a useful and practical tool for determining BA levels in processed foods. PMID:22967562

  6. High temperature proton exchange membranes with enhanced proton conductivities at low humidity and high temperature based on polymer blends and block copolymers of poly(1,3-cyclohexadiene) and poly(ethylene glycol)

    SciTech Connect

    Deng, Shawn; Hassan, Mohammad K.; Nalawade, Amol; Perry, Kelly A.; More, Karren L.; Mauritz, Kenneth A.; McDonnell, Marshall T.; Keffer, David J.; Mays, Jimmy W.

    2015-09-16

    Hot (at 120 °C) and dry (20% relative humidity) operating conditions benefit fuel cell designs based on proton exchange membranes (PEMs) and hydrogen due to simplified system design and increasing tolerance to fuel impurities. In this paper, presented are preparation, partial characterization, and multi-scale modeling of such PEMs based on cross-linked, sulfonated poly(1,3-cyclohexadiene) (xsPCHD) blends and block copolymers with poly(ethylene glycol) (PEG). These low cost materials have proton conductivities 18 times that of current industry standard Nafion at hot, dry operating conditions. Among the membranes studied, the blend xsPCHD-PEG PEM displayed the highest proton conductivity, which exhibits a morphology with higher connectivity of the hydrophilic domain throughout the membrane. Simulation and modeling provide a molecular level understanding of distribution of PEG within this hydrophilic domain and its relation to proton conductivities. Finally, this study demonstrates enhancement of proton conductivity at high temperature and low relative humidity by incorporation of PEG and optimized sulfonation conditions.

  7. High temperature proton exchange membranes with enhanced proton conductivities at low humidity and high temperature based on polymer blends and block copolymers of poly(1,3-cyclohexadiene) and poly(ethylene glycol)

    DOE PAGESBeta

    Deng, Shawn; Hassan, Mohammad K.; Nalawade, Amol; Perry, Kelly A.; More, Karren L.; Mauritz, Kenneth A.; McDonnell, Marshall T.; Keffer, David J.; Mays, Jimmy W.

    2015-09-16

    Hot (at 120 °C) and dry (20% relative humidity) operating conditions benefit fuel cell designs based on proton exchange membranes (PEMs) and hydrogen due to simplified system design and increasing tolerance to fuel impurities. In this paper, presented are preparation, partial characterization, and multi-scale modeling of such PEMs based on cross-linked, sulfonated poly(1,3-cyclohexadiene) (xsPCHD) blends and block copolymers with poly(ethylene glycol) (PEG). These low cost materials have proton conductivities 18 times that of current industry standard Nafion at hot, dry operating conditions. Among the membranes studied, the blend xsPCHD-PEG PEM displayed the highest proton conductivity, which exhibits a morphology withmore » higher connectivity of the hydrophilic domain throughout the membrane. Simulation and modeling provide a molecular level understanding of distribution of PEG within this hydrophilic domain and its relation to proton conductivities. Finally, this study demonstrates enhancement of proton conductivity at high temperature and low relative humidity by incorporation of PEG and optimized sulfonation conditions.« less

  8. Sorption of REE and TPE from HNO{sub 3} solutions on strong-acid sulfonated cation exchanger KU-2

    SciTech Connect

    Chuveleva, E.A.; Kharitonov, O.V.; Firsova, L.A.

    1995-05-01

    Sorption of rare earths (REE) on the strong-acid sulfonated cation exchanger KU-2 is studied as a function of the solution acidity (0.1-2.0 M HNO{sub 3}) and REE concentration. In concentrated nitrate solutions where M(NO{sub 3}){sub 2}{sup +} and M(NO{sub 3}){sub 2}{sup +} can form and be sorbed by the cation exchanger, the capacity of the exchanger seems to increase by 20%.

  9. Electrodialysis of Sulfuric Acid with Cation-Exchange Membranes Prepared by Electron-Beam-Induced Graft Polymerization

    NASA Astrophysics Data System (ADS)

    Asari, Yuki; Shoji, Nobuyoshi; Miyoshi, Kazuyoshi; Umeno, Daisuke; Saito, Kyoichi

    Strongly acidic cation-exchange membranes were prepared by the electron-beam-induced graft polymerization of glycidyl methacrylate onto a high-density polyethylene film with a thickness of 35 μm and the subsequent conversion of the resulting epoxy group into a sulfonic acid group. The resulting cation-exchange membranes with various ion-exchange capacities or sulfonic acid group densities ranging from 1.9 to 2.7 mmol/g were applied to the enrichment of 0.50 mol/L sulfuric acid by electrodialysis. Concentrated sulfuric acids at concentrations of 1.4 to 2.9 mol/L were obtained in the concentrate chamber during the electrodialysis operated at 30 mA/cm2 and 298 K, using a pair of this cation-exchange membrane and a commercially available anion-exchange membrane.

  10. Fabrication parameter optimization of a low-threshold high-efficiency proton-exchanged waveguide laser in Nd:LiTaO3

    NASA Astrophysics Data System (ADS)

    Nouh, S.; Baldi, P.; El Hadi, K.; de Micheli, M.; Monnom, G.; Ostrowsky, D. B.; Lallier, E.; Papuchon, M.

    1995-07-01

    Knowing the correlation between the Nd3+ excited-state lifetime in proton-exchanged waveguides and the phase diagram of the Hx Li1-xTaO 3 compound permits optimized waveguide fabrication parameters to be found. These have been used to with a threshold of 2.9mW and a slope efficiency of 33%, in good agreement with the best predicted values. Nevertheless this component suffers from instabilities because of the photorefractive effect.

  11. Russian studies of the safety of anion exchange in nitric acid

    SciTech Connect

    Hyder, M.L.; Bartenev, S.A.; Lazarev, L.N.

    1997-07-01

    Synthetic ion exchange resins came into use in the Soviet Union in the 1950`s, and domestic anion exchange resins based on quaternary amine groups have long been used in the Russian nuclear industry. These resins are similar to resins used in the West, and include pyridine-based resins, as well as the more conventional aryl polymers with substituted methyl amines. (Slide 1) The sensitivity of these amines to reaction with nitric acid and other oxidants has been a concern in Russia as in the West, and numerous laboratory studies have been conducted on the reactions involved. Several incidents involving pressure or temperature excursions have provided incentives for such studies. (Slide 2) This report briefly summarizes this work. A report by the Russian authors of this paper providing greater detail is to be issued as a U.S. Dept. of Energy document. Additionally, a second report by these authors, describing new studies on anion exchange resin safety, will also be issued as a DOE report. The separation of plutonium, neptunium, etc. from other materials by ion exchange requires rather strong nitric acid (6-8 M). In some systems, such as the processing of {sup 238}Pu, intense ionizing radiation may also be present during ion exchange separation. As a result, it is necessary to consider not only thermal hydrolysis and oxidation and their effects on the resin, but also radiolysis. All of these were investigated in the Russian studies.

  12. Some investigations on the radiation stability of a strongly acidic cation exchange resin

    NASA Astrophysics Data System (ADS)

    Dessouki, A. M.; Zahran, A. H.; Rabie, A. M.; Amer, S. I.

    The radiation-chemical stability of Merck Cation Exchanger I, a strongly acidic sulphonated cation exchanger of the polymerization type based on styrene-divinylbenze (DVB) copolymers was investigated. The radiation stability of the resin was assessed from the change in exchange capacity, loss in weight, change in swelling behaviour and formation of new exchange groups. The loss in capacity was 44 and 32% for resin specimens in the H +-form irradiated to 1000 Mrad in air and in vacuum, respectively. The Na +-form of the exchanger showed high resistance to radiation and the loss in capacity did not exceed 7% at a dose of 1000 Mrad. The loss in capacity was accompanied by a loss in weight and a decrease in the degree of swelling of the irradiated resin. The formation of new functional groups of the carboxylic and phenolic types was confirmed. The amount of these group increases with the increase in the integral dose. The amount of sulphuric acid formed as a result of irradiating the resin in the dry and moist states was determined. An increase in the moisture content of the resin resulted in a marked decrease in its radiation stability.

  13. Analysis of Ca2+ Signaling Motifs That Regulate Proton Signaling through the Na+/H+ Exchanger NHX-7 during a Rhythmic Behavior in Caenorhabditis elegans*

    PubMed Central

    Allman, Erik; Waters, Korrie; Ackroyd, Sarah; Nehrke, Keith

    2013-01-01

    Membrane proton transporters contribute to pH homeostasis but have also been shown to transmit information between cells in close proximity through regulated proton secretion. For example, the nematode intestinal Na+/H+ exchanger NHX-7 causes adjacent muscle cells to contract by transiently acidifying the extracellular space between the intestine and muscle. NHX-7 operates during a Ca2+-dependent rhythmic behavior and contains several conserved motifs for regulation by Ca2+ input, including motifs for calmodulin and phosphatidylinositol 4,5-bisphosphate binding, protein kinase C- and calmodulin-dependent protein kinase type II phosphorylation, and a binding site for calcineurin homologous protein. Here, we tested the idea that Ca2+ input differentiates proton signaling from pH housekeeping activity. Each of these motifs was mutated, and their contribution to NHX-7 function was assessed. These functions included pH recovery from acidification in cells in culture expressing recombinant NHX-7, extracellular acidification measured during behavior in live moving worms, and muscle contraction strength as a result of this acidification. Our data suggest that multiple levels of Ca2+ input regulate NHX-7, whose transport capacity normally exceeds the minimum necessary to cause muscle contraction. Furthermore, extracellular acidification limits NHX-7 proton transport through feedback inhibition, likely to prevent metabolic acidosis from occurring. Our findings are consistent with an integrated network whereby both Ca2+ and pH contribute to proton signaling. Finally, our results obtained by expressing rat NHE1 in Caenorhabditis elegans suggest that a conserved mechanism of regulation may contribute to cell-cell communication or proton signaling by Na+/H+ exchangers in mammals. PMID:23319594

  14. Analysis of Ca2+ signaling motifs that regulate proton signaling through the Na+/H+ exchanger NHX-7 during a rhythmic behavior in Caenorhabditis elegans.

    PubMed

    Allman, Erik; Waters, Korrie; Ackroyd, Sarah; Nehrke, Keith

    2013-02-22

    Membrane proton transporters contribute to pH homeostasis but have also been shown to transmit information between cells in close proximity through regulated proton secretion. For example, the nematode intestinal Na(+)/H(+) exchanger NHX-7 causes adjacent muscle cells to contract by transiently acidifying the extracellular space between the intestine and muscle. NHX-7 operates during a Ca(2+)-dependent rhythmic behavior and contains several conserved motifs for regulation by Ca(2+) input, including motifs for calmodulin and phosphatidylinositol 4,5-bisphosphate binding, protein kinase C- and calmodulin-dependent protein kinase type II phosphorylation, and a binding site for calcineurin homologous protein. Here, we tested the idea that Ca(2+) input differentiates proton signaling from pH housekeeping activity. Each of these motifs was mutated, and their contribution to NHX-7 function was assessed. These functions included pH recovery from acidification in cells in culture expressing recombinant NHX-7, extracellular acidification measured during behavior in live moving worms, and muscle contraction strength as a result of this acidification. Our data suggest that multiple levels of Ca(2+) input regulate NHX-7, whose transport capacity normally exceeds the minimum necessary to cause muscle contraction. Furthermore, extracellular acidification limits NHX-7 proton transport through feedback inhibition, likely to prevent metabolic acidosis from occurring. Our findings are consistent with an integrated network whereby both Ca(2+) and pH contribute to proton signaling. Finally, our results obtained by expressing rat NHE1 in Caenorhabditis elegans suggest that a conserved mechanism of regulation may contribute to cell-cell communication or proton signaling by Na(+)/H(+) exchangers in mammals. PMID:23319594

  15. Protons and Psalmotoxin-1 reveal nonproton ligand stimulatory sites in chicken acid-sensing ion channel

    PubMed Central

    Smith, Rachel N; Gonzales, Eric B

    2014-01-01

    Acid-sensing ion channels (ASICs) are proton-sensitive, sodium-selective channels expressed in the nervous system that sense changes in extracellular pH. These ion channels are sensitive to an increasing number of nonproton ligands that include natural venom peptides and guanidine compounds. In the case of chicken ASIC1, the spider toxin Psalmotoxin-1 (PcTx1) activates the channel, resulting in an inward current. Furthermore, a growing class of ligands containing a guanidine group has been identified that stimulate peripheral ASICs (ASIC3), but exert subtle influence on other ASIC subtypes. The effects of the guanidine compounds on cASIC1 have not been the focus of previous study. Here, we investigated the interaction of the guanidine compound 2-guanidine-4-methylquinazoline (GMQ) on cASIC1 proton activation and PcTx1 stimulation. Exposure of expressed cASIC1 to PcTx1 resulted in biphasic currents consisting of a transient peak followed by an irreversible cASIC1 PcTx1 persistent current. This cASIC1 PcTx1 persistent current may be the result of locking the cASIC1 protein into a desensitized transition state. The guanidine compound GMQ increased the apparent affinity of protons on cASIC1 and decreased the half-maximal constant of the cASIC1 steady-state desensitization profile. Furthermore, GMQ stimulated the cASIC1 PcTx1 persistent current in a concentration-dependent manner, which resulted in a non-desensitizing inward current. Our data suggests that GMQ may have multiple sites within cASIC1 and may act as a “molecular wedge” that forces the PcTx1-desensitized ASIC into an open state. Our findings indicate that guanidine compounds, such as GMQ, may alter acid-sensing ion channel activity in combination with other stimuli, and that additional ASIC subtypes (along with ASIC3) may serve to sense and mediate signals from multiple stimuli. PMID:24262969

  16. The production of sulfonated chitosan-sodium alginate found in brown algae (Sargassum sp.) composite membrane as proton exchange membrane fuel cell (PEMFC)

    NASA Astrophysics Data System (ADS)

    Wafiroh, Siti; Pudjiastuti, Pratiwi; Sari, Ilma Indana

    2016-03-01

    The majority of energy was used in this period is from fossil fuel, which getting decreased in the future. The objective of this research is production and characterization of sulfonated chitosan-sodium alginate found in brown algae (Sargassum sp.) composite membrane as Proton Exchange Membrane Fuel Cell (PEMFC) for alternative energy. PEMFC was produced with 4 variations (w/w) ratio between chitosan and sodium alginate, 8 : 0, 8 : 1, 8 : 2, 8 : 4 (w/w). The production of membrane was mixed sodium alginate solution into chitosan solution and sulfonated with H2SO4 0.72 N. The characterization of the PEM was uses Modulus Young analysis, water swelling, ion exchange capacity, FTIR, SEM, DTA, methanol permeability and proton conductivity. The result of the research, showed that the optimum membrane was with ratio 8 : 2 (w/w) that the Modulus Young 8564 kN/m2, water swelling 31.86%, ion exchange capacity 1.020 meq/g, proton conductivity 8,8 × 10-6 S/cm, methanol permeability 1.90 × 10-8 g/cm2s and glass transition temperature (Tg) 100.9 °C, crystalline temperature (Tc) 227.6 °C, and the melting temperature (Tm) 267.9 °C.

  17. Membrane Potential and Proton Cotransport of Alanine and Phosphate as Affected by Permeant Weak Acids in Lemna gibba1

    PubMed Central

    Basso, Barbara; Ullrich-Eberius, Cornelia I.

    1987-01-01

    The treatment of Lemna gibba plants with the weak acids (trimethylacetic acid and butyric acid), used as tools to decrease intracellular pH, induced a hyperpolarization of membrane potential, dependent on the concentration of the undissociated permeant form of the weak acid and on the value of the resting potential. Measurements were carried out both with `high potential' and `low potential' plants and the maximum values af acid induced hyperpolarizations were about 35 and 71 millivolts, respectively. Weak acids influenced also the transient light-dark membrane potential changes, typical for photosynthesizing material, suggesting a dependence of these changes on an acidification of cytoplasm. In the presence of the weak acids, the membrane depolarization induced by the cotransport of alanine and phosphate with protons was reduced; the maximum reduction (about 90%) was obtained with alanine during 2 millimolar trimethylacetic acid perfusion at pH 5. A strong inhibition of the uptake rates (up to 48% for [14C]alanine and 68% for 32P-phosphate) was obtained in the presence of the weak acids, both by decreasing the pH of the medium and by increasing the concentration of the acid. In these experimental conditions, the ATP level and O2 uptake rates did not change significantly. These results constitute good evidence that H+/solute cotransport in Lemna, already known to be dependent on the electrochemical potential difference for protons, is also strongly regulated by the cytoplasmic pH value. PMID:16665758

  18. Production of sodium-22 from proton irradiated aluminum

    DOEpatents

    Taylor, Wayne A.; Heaton, Richard C.; Jamriska, David J.

    1996-01-01

    A process for selective separation of sodium-22 from a proton irradiated minum target including dissolving a proton irradiated aluminum target in hydrochloric acid to form a first solution including aluminum ions and sodium ions, separating a portion of the aluminum ions from the first solution by crystallization of an aluminum salt, contacting the remaining first solution with an anion exchange resin whereby ions selected from the group consisting of iron and copper are selectively absorbed by the anion exchange resin while aluminum ions and sodium ions remain in solution, contacting the solution with an cation exchange resin whereby aluminum ions and sodium ions are adsorbed by the cation exchange resin, and, contacting the cation exchange resin with an acid solution capable of selectively separating the adsorbed sodium ions from the cation exchange resin while aluminum ions remain adsorbed on the cation exchange resin is disclosed.

  19. Collision Cross Sections for 20 Protonated Amino Acids: Fourier Transform Ion Cyclotron Resonance and Ion Mobility Results

    NASA Astrophysics Data System (ADS)

    Anupriya; Jones, Chad A.; Dearden, David V.

    2016-08-01

    We report relative dephasing cross sections for the 20 biogenic protonated amino acids measured using the cross sectional areas by Fourier transform ion cyclotron resonance (CRAFTI) technique at 1.9 keV in the laboratory reference frame, as well as momentum transfer cross sections for the same ions computed from Boltzmann-weighted structures determined using molecular mechanics. Cross sections generally increase with increasing molecular weight. Cross sections for aliphatic and aromatic protonated amino acids are larger than the average trend, suggesting these side chains do not fold efficiently. Sulfur-containing protonated amino acids have smaller than average cross sections, reflecting the mass of the S atom. Protonated amino acids that can internally hydrogen-bond have smaller than average cross sections, reflecting more extensive folding. The CRAFTI measurements correlate well with results from drift ion mobility (IMS) and traveling wave ion mobility (TWIMS) spectrometric measurements; CRAFTI results correlate with IMS values approximately as well as IMS and TWIMS values from independent measurements correlate with each other. Both CRAFTI and IMS results correlate well with the computed momentum transfer cross sections, suggesting both techniques provide accurate molecular structural information. Absolute values obtained using the various methods differ significantly; in the case of CRAFTI, this may be due to errors in measurements of collision gas pressure, measurement of excitation voltage, and/or dependence of cross sections on kinetic energy.

  20. Collision Cross Sections for 20 Protonated Amino Acids: Fourier Transform Ion Cyclotron Resonance and Ion Mobility Results.

    PubMed

    Anupriya; Jones, Chad A; Dearden, David V

    2016-08-01

    We report relative dephasing cross sections for the 20 biogenic protonated amino acids measured using the cross sectional areas by Fourier transform ion cyclotron resonance (CRAFTI) technique at 1.9 keV in the laboratory reference frame, as well as momentum transfer cross sections for the same ions computed from Boltzmann-weighted structures determined using molecular mechanics. Cross sections generally increase with increasing molecular weight. Cross sections for aliphatic and aromatic protonated amino acids are larger than the average trend, suggesting these side chains do not fold efficiently. Sulfur-containing protonated amino acids have smaller than average cross sections, reflecting the mass of the S atom. Protonated amino acids that can internally hydrogen-bond have smaller than average cross sections, reflecting more extensive folding. The CRAFTI measurements correlate well with results from drift ion mobility (IMS) and traveling wave ion mobility (TWIMS) spectrometric measurements; CRAFTI results correlate with IMS values approximately as well as IMS and TWIMS values from independent measurements correlate with each other. Both CRAFTI and IMS results correlate well with the computed momentum transfer cross sections, suggesting both techniques provide accurate molecular structural information. Absolute values obtained using the various methods differ significantly; in the case of CRAFTI, this may be due to errors in measurements of collision gas pressure, measurement of excitation voltage, and/or dependence of cross sections on kinetic energy. Graphical Abstract ᅟ. PMID:27220844