Using a Hands-On Hydrogen Peroxide Decomposition Activity to Teach Catalysis Concepts to K-12 Students

ERIC Educational Resources Information Center

Cybulskis, Viktor J.; Ribeiro, Fabio H.; Gounder, Rajamani

2016-01-01

A versatile and transportable laboratory apparatus was developed for middle and high school (6th-12th grade) students as part of a hands-on outreach activity to estimate catalytic rates of hydrogen peroxide decomposition from oxygen evolution rates measured by using a volumetric displacement method. The apparatus was constructed with inherent…

Nanocomposites of AgInZnS and graphene nanosheets as efficient photocatalysts for hydrogen evolution

NASA Astrophysics Data System (ADS)

Tang, Xiaosheng; Chen, Weiwei; Zu, Zhiqiang; Zang, Zhigang; Deng, Ming; Zhu, Tao; Sun, Kuan; Sun, Lidong; Xue, Junmin

2015-11-01

In this study, AgInZnS-reduced graphene (AIZS-rGO) nanocomposites with tunable band gap absorption and large specific surface area were synthesized by a simple hydrothermal route, which showed highly efficient photocatalytic hydrogen evolution under visible-light irradiation. The relationships between their crystal structures, morphology, surface chemical states and photocatalytic activity have been explored in detail. Importantly, the AIZS-rGO nanocomposites with 0.02 wt% of graphene exhibited the highest hydrogen production rate of 1.871 mmol h-1 g-1, which was nearly 2 times the hydrogen production rate when using pure AIZS nanoparticles as the photocatalyst. This high photocatalytic H2-production activity was attributed predominantly to the incorporation of graphene sheets, which demonstrated an obvious influence on the structure and optical properties of the AIZS nanoparticles. In the AIZS-rGO nanocomposites, graphene could not only serve as an effective supporting layer but also is a recombination center for conduction band electrons and valence band holes. It is believed that this kind of graphene-based material would attract much attention as a promising photocatalyst with a high efficiency and a low cost for photocatalytic H2 evolution and facilitates their application in the environmental protection field.In this study, AgInZnS-reduced graphene (AIZS-rGO) nanocomposites with tunable band gap absorption and large specific surface area were synthesized by a simple hydrothermal route, which showed highly efficient photocatalytic hydrogen evolution under visible-light irradiation. The relationships between their crystal structures, morphology, surface chemical states and photocatalytic activity have been explored in detail. Importantly, the AIZS-rGO nanocomposites with 0.02 wt% of graphene exhibited the highest hydrogen production rate of 1.871 mmol h-1 g-1, which was nearly 2 times the hydrogen production rate when using pure AIZS nanoparticles as the photocatalyst. This high photocatalytic H2-production activity was attributed predominantly to the incorporation of graphene sheets, which demonstrated an obvious influence on the structure and optical properties of the AIZS nanoparticles. In the AIZS-rGO nanocomposites, graphene could not only serve as an effective supporting layer but also is a recombination center for conduction band electrons and valence band holes. It is believed that this kind of graphene-based material would attract much attention as a promising photocatalyst with a high efficiency and a low cost for photocatalytic H2 evolution and facilitates their application in the environmental protection field. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05145b

The ionization parameter of star-forming galaxies evolves with the specific star formation rate

NASA Astrophysics Data System (ADS)

Kaasinen, Melanie; Kewley, Lisa; Bian, Fuyan; Groves, Brent; Kashino, Daichi; Silverman, John; Kartaltepe, Jeyhan

2018-07-01

We investigate the evolution of the ionization parameter of star-forming galaxies using a high-redshift (z˜ 1.5) sample from the FMOS-COSMOS (Fibre Multi-Object Spectrograph-COSMic evOlution Survey) and matched low-redshift samples from the Sloan Digital Sky Survey. By constructing samples of low-redshift galaxies for which the stellar mass (M*), star formation rate (SFR), and specific star formation rate (sSFR) are matched to the high-redshift sample, we remove the effects of an evolution in these properties. We also account for the effect of metallicity by jointly constraining the metallicity and ionization parameter of each sample. We find an evolution in the ionization parameter for main-sequence, star-forming galaxies and show that this evolution is driven by the evolution of sSFR. By analysing the matched samples as well as a larger sample of z< 0.3, star-forming galaxies we show that high ionization parameters are directly linked to high sSFRs and are not simply the by-product of an evolution in metallicity. Our results are physically consistent with the definition of the ionization parameter, a measure of the hydrogen ionizing photon flux relative to the number density of hydrogen atoms.

Comparative amperometric study of uptake hydrogenase and hydrogen photoproduction activities between heterocystous cyanobacterium Anabaena cylindrica B629 and nonheterocystous cyanobacterium Oscillatoria sp. strain Miami BG7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumazawa, S.; Mitsui, A.

Heterocystous filamentous cyanobacterium Anabaena cylindrica B629 and nonheterocystous filamentous cyanobacterium Oscillatoria sp. strain Miami BG7 were cultured in media with N/sub 2/ as the sole nitrogen source; and activities of oxygen-dependent hydrogen uptake, photohydrogen production photooxygen evolution, and respiration were compared amperometrically under the same or similar experimental conditions for both strains. Distinct differences in these activities were observed in both strains. The rates of hydrogen photoproduction and hydrogen accumulation were significantly higher in Oscillatoria sp. strain BG7 than in A. cylindrica B629 at every light intensity tested. The major reason for the difference was attributable to the fact thatmore » the heterocystous cyanobacterium had a high rate of oxygen-dependent hydrogen consumption activity and the nonheterocystous cyanobacterium did not. The activity of oxygen photoevolution and respiration also contributed to the difference. Oscillatoria sp. strain BG7 had lower O/sub 2/ evolution and higher respiration than did A. cylindrica B629. Thus, the effect of O/sub 2/ on hydrogen photoproduction was minimized in Oscillatoria sp. strain BG7. 32 references, 5 figures.« less

Volcano plots in hydrogen electrocatalysis - uses and abuses.

PubMed

Quaino, Paola; Juarez, Fernanda; Santos, Elizabeth; Schmickler, Wolfgang

2014-01-01

Sabatier's principle suggests, that for hydrogen evolution a plot of the rate constant versus the hydrogen adsorption energy should result in a volcano, and several such plots have been presented in the literature. A thorough examination of the data shows, that there is no volcano once the oxide-covered metals are left out. We examine the factors that govern the reaction rate in the light of our own theory and conclude, that Sabatier's principle is only one of several factors that determine the rate. With the exception of nickel and cobalt, the reaction rate does not decrease for highly exothermic hydrogen adsorption as predicted, because the reaction passes through more suitable intermediate states. The case of nickel is given special attention; since it is a 3d metal, its orbitals are compact and the overlap with hydrogen is too low to make it a good catalyst.

Volcano plots in hydrogen electrocatalysis – uses and abuses

PubMed Central

Quaino, Paola; Juarez, Fernanda; Santos, Elizabeth

2014-01-01

Summary Sabatier’s principle suggests, that for hydrogen evolution a plot of the rate constant versus the hydrogen adsorption energy should result in a volcano, and several such plots have been presented in the literature. A thorough examination of the data shows, that there is no volcano once the oxide-covered metals are left out. We examine the factors that govern the reaction rate in the light of our own theory and conclude, that Sabatier’s principle is only one of several factors that determine the rate. With the exception of nickel and cobalt, the reaction rate does not decrease for highly exothermic hydrogen adsorption as predicted, because the reaction passes through more suitable intermediate states. The case of nickel is given special attention; since it is a 3d metal, its orbitals are compact and the overlap with hydrogen is too low to make it a good catalyst. PMID:24991521

Bacteria-directed construction of hollow TiO2 micro/nanostructures with enhanced photocatalytic hydrogen evolution activity.

PubMed

Zhou, Han; Fan, Tongxiang; Ding, Jian; Zhang, Di; Guo, Qixin

2012-03-12

A general method has been developed for the synthesis of various hollow TiO2 micro/nanostructures with bacteria as templates to further study the structural effect on photocatalytic hydrogen evolution properties. TiO2 hollow spheres and hollow tubes, served as prototypes, are obtained via a surface sol-gel process using cocci and bacillus as biotemplates, respectively. The formation mechanisms are based on absorption of metal-alkoxide molecules from solution onto functional cell wall surfaces and subsequent hydrolysis to give nanometer-thick oxide layers. The UV-Vis absorption spectrum shows that the porous TiO2 hollow spheres have enhanced light harvesting property compared with the corresponding solid counterpart. This could be attributed to their unique hollow porous micro/nanostructures with microsized hollow cavities and nanovoids which could bring about multiple scattering and rayleigh scattering of light, respectively. The hollow TiO2 structures exhibit superior photocatalytic hydrogen evolution activities under UV and visible light irradiation in the presence of sacrificial reagents. The hydrogen evolution rate of hollow structures is about 3.6 times higher than the solid counterpart and 1.5 times higher than P25-TiO2. This work demonstrates the structural effect on enhancing the photocatalytic hydrogen evolution performance which would pave a new pathway to tailor and improve catalytic properties over a broad range.

Preparation of Cu-loaded SrTiO3 nanoparticles and their photocatalytic activity for hydrogen evolution from methanol aqueous solution

NASA Astrophysics Data System (ADS)

Bui, Duc-Nguyen; Mu, Jin; Wang, Lei; Kang, Shi-Zhao; Li, Xiangqing

2013-06-01

Cu-loaded SrTiO3 nanoparticles (Cu-SrTiO3) were prepared using a simple in situ photo-deposition method and their photocatalytic activity for hydrogen evolution from methanol aqueous solution was evaluated. The results characterized with XRD, TEM, XPS and EDX indicated that the as-synthesized sample was composed of metallic Cu and cubic SrTiO3, and the metallic Cu was homogeneously loaded on the surface of SrTiO3 nanoparticles. Under UV light irradiation, Cu-SrTiO3 displayed much higher photocatalytic activity for hydrogen evolution and excellent stability in comparison with pure SrTiO3 nanoparticles. The results further confirmed that the efficient separation of photogenerated electron/hole pairs was critical for the enhanced photocatalytic activity of Cu-SrTiO3. Moreover, the rate of hydrogen evolution of 0.5 wt.% Cu-SrTiO3 is comparable with that of 0.5 wt.% Pt-SrTiO3 photocatalyst under optimum conditions, implying that the metallic Cu is an efficient alternative to Pt as a co-catalyst on SrTiO3. The high photocatalytic activity, low cost and chemical stability mean that the Cu-loaded SrTiO3 is a potential catalyst for the photocatalytic hydrogen evolution from methanol aqueous solution.

A new prescription for the mass-loss rates of hydrogen-free WR stars

NASA Astrophysics Data System (ADS)

Tramper, Frank; Sana, Hugues; de Koter, Alex

2017-11-01

We present a new empirical prescription for the mass-loss rates of hydrogen-free Wolf-Rayet stars based on results of detailed spectral analyses of WC and WO stars. Compared to the prescription of Nugis & Lamers (2000), M⊙ is less sensitive to the surface helium abundance, implying a stronger mass loss at the late stages of Wolf-Rayet evolution. The winds of hydrogen-free WN stars have a strong metallicity dependence, while those of WC and WO stars have a very weak metallicity dependence.

Highly Efficient Photocatalytic H2 Evolution from Water using Visible Light and Structure-Controlled Graphitic Carbon Nitride**

PubMed Central

Martin, David James; Qiu, Kaipei; Shevlin, Stephen Andrew; Handoko, Albertus Denny; Chen, Xiaowei; Guo, Zhengxiao; Tang, Junwang

2014-01-01

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported. The g-C3N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced. PMID:25045013

Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheng, WC; Zhuang, ZB; Gao, MR

2015-01-08

The hydrogen oxidation/evolution reactions are two of the most fundamental reactions in distributed renewable electrochemical energy conversion and storage systems. The identification of the reaction descriptor is therefore of critical importance for the rational catalyst design and development. Here we report the correlation between hydrogen oxidation/evolution activity and experimentally measured hydrogen binding energy for polycrystalline platinum examined in several buffer solutions in a wide range of electrolyte pH from 0 to 13. The hydrogen oxidation/evolution activity obtained using the rotating disk electrode method is found to decrease with the pH, while the hydrogen binding energy, obtained from cyclic voltammograms, linearlymore » increases with the pH. Correlating the hydrogen oxidation/evolution activity to the hydrogen binding energy renders a monotonic decreasing hydrogen oxidation/evolution activity with the hydrogen binding energy, strongly supporting the hypothesis that hydrogen binding energy is the sole reaction descriptor for the hydrogen oxidation/evolution activity on monometallic platinum.« less

Composition and evolution of the atmosphere of Venus

NASA Technical Reports Server (NTRS)

Donahue, Thomas (Principal Investigator)

1996-01-01

The contract year started by analyzing Jovian atmospheric data acquired by the Galileo Probe Mass Spectrometer (GPMS). Two Venus hydrogen projects got underway as well. The first study strives to understand how to reconcile the standard treatment of the evolution of the H2O and HDO resevoirs on Venus over 4.5 Gyr in the presence of H and D escape and injection by comets. The second study is calculating the charge exchange contribution to hydrogen loss rates, using realistic models for exospheric H, H(+), D, D(+), and ion temperature from PV data. This report includes the following papers as attachments and supporting data: 'The Galileo Probe Mass Spectrometer: Composition of Jupiter's Atmosphere'; 'Chemical Composition Measurements of the Atmosphere of Jupiter with the Galileo Probe Mass Spectrometer'; 'Ion/Neutral Escape of Hydrogen and Deuterium: Evolution of Water'; 'Hydrogen and Deuterium in the Thermosphere of Venus: Solar Cycle Variations and Escape'; and 'Solar Cycle Variations in H(+) and D(+) Densities in the Venus Ionosphere: Implications for Escape'.

Core thermal response and hydrogen generation of the N Reactor hydrogen mitigation design basis accident

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, M.D.; Lombardo, N.J.; Heard, F.J.

1988-04-01

Calculations were performed to determine core heatup, core damage, and subsequent hydrogen production of a hypothetical loss-of-cooling accident at the Department of Energy's N Reactor. The thermal transient response of the reactor core was solved using the TRUMP-BD computer program. Estimates of whole-core thermal damage and hydrogen production were made by weighting the results of multiple half-length pressure tube simulations at various power levels. The Baker-Just and Wilson parabolic rate equations for the metal-water chemical reactions modeled the key phenomena of chemical energy and hydrogen evolution. Unlimited steam was assumed available for continuous oxidation of exposed Zircaloy-2 surfaces and formore » uranium metal with fuel cladding beyond the failure temperature (1038 C). Intact fuel geometry was modeled. Maximum fuel temperatures (1181 C) in the cooled central regions of the core were predicted to occur one-half hour into the accident scenario. Maximum fuel temperatures of 1447 C occurred in the core GSCS-regions at the end of the 10-h transient. After 10-h 26% of the fuel inventory was predicted to have failed. Peak hydrogen evolution equaled 42 g/s, while 10-h integrated hydrogen evolution equaled 167 kg. 12 refs., 12 figs., 2 tabs.« less

CoMoS2/rGO/C3N4 ternary heterojunctions catalysts with high photocatalytic activity and stability for hydrogen evolution under visible light irradiation

NASA Astrophysics Data System (ADS)

Xu, Xuejun; Si, Zhichun; Liu, Liping; Wang, Zehao; Chen, Ze; Ran, Rui; He, Yonghong; Weng, Duan

2018-03-01

Noble metal free MoS2/g-C3N4 catalyst has attracted intense attentions for visible light photocatalytic hydrogen evolution as a result of its earth abundance, low cost and unique heterojunctions stacked with two dimensional sheets. However, the low charge separation efficiency resulted from the poor conductivity of g-C3N4 and MoS2, and lack of abundant active sites from coordinative unsaturated atoms in MoS2, restricts the photocatalytic hydrogen evolution activity and stability enhancement of MoS2/C3N4 composite catalysts. Herein, CoMoS2/rGO/g-C3N4 catalysts with ternary heterojunctions are prepared by facile solvothermal method, which exhibit high visible light photocatalytic activity and stability for hydrogen evolution. The optimal hydrogen evolution rate of CoMoS2/rGO/g-C3N4 catalysts is 684 μmol g-1 h-1 when the content of CoMoS2 is 2% and the content of rGO is 0.5%. The stability of CoMoS2/rGO/C3N4 catalysts just decrease about 3% after 4 cycling runs for 16 h. The good catalytic performances of catalysts are attributed to the synergistic effect among the g-C3N4 nanosheets, rGO nanosheets and CoMoS2 nanosheets. The high conductivity of rGO nanosheets enhances the electron-hole separation and charge transfer, and Co doping increases the active sites for hydrogen evolution due to the increase of unsaturated atoms in CoMoS2 nanosheets.

HELIUM ATMOSPHERES ON WARM NEPTUNE- AND SUB-NEPTUNE-SIZED EXOPLANETS AND APPLICATIONS TO GJ 436b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Renyu; Yung, Yuk L.; Seager, Sara, E-mail: renyu.hu@jpl.nasa.gov

2015-07-01

Warm Neptune- and sub-Neptune-sized exoplanets in orbits smaller than Mercury’s are thought to have experienced extensive atmospheric evolution. Here we propose that a potential outcome of this atmospheric evolution is the formation of helium-dominated atmospheres. The hydrodynamic escape rates of Neptune- and sub-Neptune-sized exoplanets are comparable to the diffusion-limited escape rate of hydrogen, and therefore the escape is heavily affected by diffusive separation between hydrogen and helium. A helium atmosphere can thus be formed—from a primordial hydrogen–helium atmosphere—via atmospheric hydrodynamic escape from the planet. The helium atmosphere has very different abundances of major carbon and oxygen species from those ofmore » a hydrogen atmosphere, leading to distinctive transmission and thermal emission spectral features. In particular, the hypothesis of a helium-dominated atmosphere can explain the thermal emission spectrum of GJ 436b, a warm Neptune-sized exoplanet, while also being consistent with the transmission spectrum. This model atmosphere contains trace amounts of hydrogen, carbon, and oxygen, with the predominance of CO over CH{sub 4} as the main form of carbon. With our atmospheric evolution model, we find that if the mass of the initial atmosphere envelope is 10{sup −3} planetary mass, hydrodynamic escape can reduce the hydrogen abundance in the atmosphere by several orders of magnitude in ∼10 billion years. Observations of exoplanet transits may thus detect signatures of helium atmospheres and probe the evolutionary history of small exoplanets.« less

High Performance Electrocatalytic Reaction of Hydrogen and Oxygen on Ruthenium Nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Ruquan; Liu, Yuanyue; Peng, Zhiwei

2017-01-18

The development of catalytic materials for the hydrogen oxidation, hydrogen evolution, oxygen reduction or oxygen evolution reactions with high reaction rates and low overpotentials are key goals for the development of renewable energy. We report here Ru(0) nanoclusters supported on nitrogen-doped graphene as high-performance multifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), showing activities similar to that of commercial Pt/C in alkaline solution. For HER performance in alkaline media, sample Ru/NG-750 reaches 10 mA cm-2 at an overpotential of 8 mV with a Tafel slope of 30 mV dec-1. The high HER performance in alkalinemore » solution is advantageous because most catalysts for ORR and oxygen evolution reaction (OER) also prefer alkaline solution environment whereas degrade in acidic electrolytes. For ORR performance, Ru/NG effectively catalyzes the conversion of O2 into OH- via a 4e process at a current density comparable to that of Pt/C. The unusual catalytic activities of Ru(0) nanoclusters reported here are important discoveries for the advancement of renewable energy conversion reactions.« less

PtNi Alloy Cocatalyst Modification of Eosin Y-Sensitized g-C3N4/GO Hybrid for Efficient Visible-Light Photocatalytic Hydrogen Evolution

NASA Astrophysics Data System (ADS)

Wang, Peng; Zong, Lanlan; Guan, Zhongjie; Li, Qiuye; Yang, Jianjun

2018-02-01

An economic and effective Pt-based alloy cocatalyst has attracted considerable attention due to their excellent catalytic activity and reducing Pt usage. In this study, PtNi alloy cocatalyst was successfully decorated on the g-C3N4/GO hybrid photocatalyst via a facile chemical reduction method. The Eosin Y-sensitized g-C3N4/PtNi/GO-0.5% composite photocatalyst yields about 1.54 and 1178 times higher hydrogen evolution rate than the Eosin Y-sensitized g-C3N4/Pt/GO-0.5% and g-C3N4/Ni/GO-0.5% samples, respectively. Mechanism of enhanced performance for the g-C3N4/PtNi/GO composite was also investigated by different characterization, such as photoluminescence, transient photocurrent response, and TEM. These results indicated that enhanced charge separation efficiency and more reactive sites are responsible for the improved hydrogen evolution performance due to the positive synergetic effect between Pt and Ni. This study suggests that PtNi alloy can be used as an economic and effective cocatalyst for hydrogen evolution reaction. [Figure not available: see fulltext.

Noble-metal-free g-C3N4/Ni(dmgH)2 composite for efficient photocatalytic hydrogen evolution under visible light irradiation

NASA Astrophysics Data System (ADS)

Cao, Shao-Wen; Yuan, Yu-Peng; Barber, James; Loo, Say Chye Joachim; Xue, Can

2014-11-01

We report an economic photocatalytic H2 generation system consisting of earth-abundant elements only by coupling graphitic carbon nitride (g-C3N4) with Ni(dmgH)2 sub-microwires that serve as effective co-catalysts for H2 evolution. This composite photocatalyst exhibits efficient hydrogen evolution under visible-light irradiation in the presence of triethanolamine as electron donor. The optimal coupling of 3.5 wt% Ni(dmgH)2 to g-C3N4 (5 mg composite) allows for a steady H2 generation rate of 1.18 μmol/h with excellent stability. This study demonstrates that the combination of polymeric g-C3N4 semiconductor and small proportion of transition-metal-based co-catalyst could serve as a stable, earth-abundant and low-cost system for solar-to-hydrogen conversion.

Metal phosphonate coordination networks and frameworks as precursors of electrocatalysts for the hydrogen and oxygen evolution reactions

NASA Astrophysics Data System (ADS)

Zhang, Rui; El-Refaei, Sayed M.; Russo, Patrícia A.; Pinna, Nicola

2018-05-01

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) play key roles in the conversion of energy derived from renewable energy sources into chemical energy. Efficient, robust, and inexpensive electrocatalysts are necessary for driving these reactions at high rates at low overpotentials and minimize energetic losses. Recently, electrocatalysts derived from hybrid metal phosphonate compounds have shown high activity for the HER or OER. We review here the utilization of metal phosphonate coordination networks and metal-organic frameworks as precursors/templates for transition-metal phosphides, phosphates, or oxyhydroxides generated in situ in alkaline solutions, and their electrocatalytic performance in HER or OER.

Biodegradability engineering of biodegradable Mg alloys: Tailoring the electrochemical properties and microstructure of constituent phases

PubMed Central

Cha, Pil-Ryung; Han, Hyung-Seop; Yang, Gui-Fu; Kim, Yu-Chan; Hong, Ki-Ha; Lee, Seung-Cheol; Jung, Jae-Young; Ahn, Jae-Pyeong; Kim, Young-Yul; Cho, Sung-Youn; Byun, Ji Young; Lee, Kang-Sik; Yang, Seok-Jo; Seok, Hyun-Kwang

2013-01-01

Crystalline Mg-based alloys with a distinct reduction in hydrogen evolution were prepared through both electrochemical and microstructural engineering of the constituent phases. The addition of Zn to Mg-Ca alloy modified the corrosion potentials of two constituent phases (Mg + Mg2Ca), which prevented the formation of a galvanic circuit and achieved a comparable corrosion rate to high purity Mg. Furthermore, effective grain refinement induced by the extrusion allowed the achievement of much lower corrosion rate than high purity Mg. Animal studies confirmed the large reduction in hydrogen evolution and revealed good tissue compatibility with increased bone deposition around the newly developed Mg alloy implants. Thus, high strength Mg-Ca-Zn alloys with medically acceptable corrosion rate were developed and showed great potential for use in a new generation of biodegradable implants. PMID:23917705

Rational construction of multiple interfaces in ternary heterostructure for efficient spatial separation and transfer of photogenerated carriers in the application of photocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Shi, Jian-Wen; Ma, Dandan; Zou, Yajun; Fan, Zhaoyang; Shi, Jinwen; Cheng, Linhao; Ji, Xin; Niu, Chunming

2018-03-01

The design of efficient and stable photocatalyst plays a critical role in the photocatalytic hydrogen evolution from water splitting. Herein, we develop a novel ZnS/CdS/ZnO ternary heterostructure by the in-situ sulfuration of CdS/ZnO, which includes four contact interfaces: CdS-ZnS interface, ZnS-ZnO interface, CdS-ZnO interface and ZnS-CdS-ZnO ternary interface, forming three charge carrier-transfer modes (type-I, type-II and direct Z-scheme) through five carrier-transfer pathways. As a result, the separation and transfer of photoexcited electron-hole pairs are promoted significantly, resulting in a high hydrogen evolution rate of 44.70 mmol h-1 g-1, which is 2, 3.7 and 8 times higher than those of binary heterostructures, CdS/ZnO, CdS/ZnS and ZnS/ZnO, respectively, and 26.5, 280 and 298 times higher than those of single CdS, ZnO and ZnS, respectively. As a counterpart ternary heterostructure, CdS/ZnS/ZnO contains only two interfaces: CdS-ZnS interface and ZnS-ZnO interface, which form two charge carrier-transfer modes (type-I and type-II) through two carrier-transfer pathways, leading to its much lower hydrogen evolution rate (27.25 mmol h-1 g-1) than ZnS/CdS/ZnO ternary heterostructure. This work is relevant for understanding the charge-transfer pathways between multi-interfaces in multicomponent heterojunctions.

Influence of phosphoric acid on the electrochemistry of lead electrodes in sulfuric acid electrolyte containing antimony

NASA Astrophysics Data System (ADS)

Venugopalan, S.

The influence of phosphoric acid (0 to 40 g 1 -1) on the Pb/PbSO 4 reaction and the kinetics of hydrogen evolution on pure, smooth lead and lead alloy electrodes is studied via galvanostatic polarization in the linear and Tafel domains with and without antimony (0 to 10 mg 1 -1) addition to the H 2SO 4 (3 to 10 M) electrolyte. Phosphoric acid is found to offset significantly the adverse effect of antimony. H 3PO 4 is also found to increase the hydrogen overpotential without affecting the Pb/PbSO 4 reaction. This implies that the open-circuit corrosion of lead and the consequent hydrogen evolution rate on lead are reduced in the presence of H 3PO 4. The beneficial effects of H 3PO 4 additive are found to be optimum at around 20 g 1 -1. Suppression of hydrogen evolution on the negative electrode, a crucial criterion for sealed cell operation, can be achieved using a H 3PO 4 additive.

Molecular dynamics investigation of dynamical properties of phosphatidylethanolamine lipid bilayers

NASA Astrophysics Data System (ADS)

Pitman, Michael C.; Suits, Frank; Gawrisch, Klaus; Feller, Scott E.

2005-06-01

We describe the dynamic behavior of a 1-stearoyl-2-oleoyl-phosphatidylethanolamine (SOPE) bilayer from a 20ns molecular dynamics simulation. The dynamics of individual molecules are characterized in terms of H2 spin-lattice relaxation rates, nuclear overhauser enhancement spectroscopy (NOESY) cross-relaxation rates, and lateral diffusion coefficients. Additionally, we describe the dynamics of hydrogen bonding through an analysis of hydrogen bond lifetimes and the time evolution of clusters of hydrogen bonded lipids. The simulated trajectory is shown to be consistent with experimental measures of internal, intermolecular, and diffusive motion. Consistent with our analysis of SOPE structure in the companion paper, we see hydrogen bonding dominating the dynamics of the interface region. Comparison of H2 T1 relaxation rates for chain methylene segments in phosphatidylcholine and phosphatidylethanolamine bilayers indicates that slower motion resulting from hydrogen bonding extends at least three carbons into the hydrophobic core. NOESY cross-relaxation rates compare well with experimental values, indicating the observed hydrogen bonding dynamics are realistic. Calculated lateral diffusion rates (4±1×10-8cm2/s) are comparable, though somewhat lower than, those determined by pulsed field gradient NMR methods.

Experimental Proof of the Bifunctional Mechanism for the Hydrogen Oxidation in Alkaline Media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jingkun; Ghoshal, Shraboni; Bates, Michael K.

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data,more » which provide convincing evidence for the presence of hydroxy groups on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.« less

Experimental Proof of the Bifunctional Mechanism for the Hydrogen Oxidation in Alkaline Media

DOE PAGES

Li, Jingkun; Ghoshal, Shraboni; Bates, Michael K.; ...

2017-10-16

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data,more » which provide convincing evidence for the presence of hydroxy groups on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.« less

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy

PubMed Central

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-01-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER. PMID:27034988

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy.

PubMed

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-03-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

Hydrogen evolution using palladium sulfide (PdS) nanocorals as photoanodes in aqueous solution.

PubMed

Barawi, M; Ferrer, I J; Ares, J R; Sánchez, C

2014-11-26

Palladium sulfide (PdS) nanostructures are proposed to be used as photoanodes in photoelectrochemical cells (PECs) for hydrogen evolution due to their adequate transport and optical properties shown in previous works. Here, a complete morphological and electrochemical characterization of PdS films has been performed by different techniques. PdS flatband potential (Vfb=-0.65±0.05 V vs NHE) was determined by electrochemical impedance spectroscopy measurements in aqueous Na2SO3 electrolyte, providing a description of the energy levels scheme at the electrolyte-semiconductor interface. This energy levels scheme confirms PdS as a compound able to photogenerate hydrogen in a PEC. At last, photogenerated hydrogen rates are measured continuously by mass spectrometry as a function of the external bias potential under illumination, reaching values up to 4.4 μmolH2/h at 0.3 V vs Ag/AgCl.

High Electrocatalytic Hydrogen Evolution Activity of an Anomalous Ruthenium Catalyst.

PubMed

Zheng, Yao; Jiao, Yan; Zhu, Yihan; Li, Lu Hua; Han, Yu; Chen, Ying; Jaroniec, Mietek; Qiao, Shi-Zhang

2016-12-14

Hydrogen evolution reaction (HER) is a critical process due to its fundamental role in electrocatalysis. Practically, the development of high-performance electrocatalysts for HER in alkaline media is of great importance for the conversion of renewable energy to hydrogen fuel via photoelectrochemical water splitting. However, both mechanistic exploration and materials development for HER under alkaline conditions are very limited. Precious Pt metal, which still serves as the state-of-the-art catalyst for HER, is unable to guarantee a sustainable hydrogen supply. Here we report an anomalously structured Ru catalyst that shows 2.5 times higher hydrogen generation rate than Pt and is among the most active HER electrocatalysts yet reported in alkaline solutions. The identification of new face-centered cubic crystallographic structure of Ru nanoparticles was investigated by high-resolution transmission electron microscopy imaging, and its formation mechanism was revealed by spectroscopic characterization and theoretical analysis. For the first time, it is found that the Ru nanocatalyst showed a pronounced effect of the crystal structure on the electrocatalytic activity tested under different conditions. The combination of electrochemical reaction rate measurements and density functional theory computation shows that the high activity of anomalous Ru catalyst in alkaline solution originates from its suitable adsorption energies to some key reaction intermediates and reaction kinetics in the HER process.

Bi2O3 cocatalyst improving photocatalytic hydrogen evolution performance of TiO2

NASA Astrophysics Data System (ADS)

Xu, Difa; Hai, Yang; Zhang, Xiangchao; Zhang, Shiying; He, Rongan

2017-04-01

Photocatalytic hydrogen production using water splitting is of potential importance from the viewpoint of renewable energy development. Herein, Bi2O3-TiO2 composite photocatalysts presented as Bi-Bi2O3-anatase-rutile TiO2 multijunction were first fabricated by a simple impregnation-calcination method using Bi2O3 as H2-production cocatalysts. The obtained multijunction samples exhibit an obvious enhancement in photocatalytic H2 evolution activity in the presence of glycerol. The effect of Bi2O3 amount on H2-evolution activity of TiO2 was investigated and the optimal Bi2O3 content was found to be 0.89 mol%, achieving a H2-production rate of 920 μmol h-1, exceeding that of pure TiO2 by more than 73 times. The enhanced mechanism of photocatalytic H2-evolution activity is proposed. This study will provide new insight into the design and fabrication of TiO2-based hydrogen-production photocatalysts using low-cost Bi2O3 as cocatalyst.

Hydrogen production using hydrogenase-containing oxygenic photosynthetic organisms

DOEpatents

Melis, Anastasios; Zhang, Liping; Benemann, John R.; Forestier, Marc; Ghirardi, Maria; Seibert, Michael

2006-01-24

A reversible physiological process provides for the temporal separation of oxygen evolution and hydrogen production in a microorganism, which includes the steps of growing a culture of the microorganism in medium under illuminated conditions to accumulate an endogenous substrate, depleting from the medium a nutrient selected from the group consisting of sulfur, iron, and/or manganese, sealing the culture from atmospheric oxygen, incubating the culture in light whereby a rate of light-induced oxygen production is equal to or less than a rate of respiration, and collecting an evolved gas. The process is particularly useful to accomplish a sustained photobiological hydrogen gas production in cultures of microorganisms, such as Chlamydomonas reinhardtii.

Hydrogen Production Using Hydrogenase-Containing Oxygenic Photosynthetic Organisms

DOEpatents

Melis, A.; Zhang, L.; Benemann, J. R.; Forestier, M.; Ghirardi, M.; Seibert, M.

2006-01-24

A reversible physiological process provides for the temporal separation of oxygen evolution and hydrogen production in a microorganism, which includes the steps of growing a culture of the microorganism in medium under illuminated conditions to accumulate an endogenous substrate, depleting from the medium a nutrient selected from the group consisting of sulfur, iron, and/or manganese, sealing the culture from atmospheric oxygen, incubating the culture in light whereby a rate of light-induced oxygen production is equal to or less than a rate of respiration, and collecting an evolved gas. The process is particularly useful to accomplish a sustained photobiological hydrogen gas production in cultures of microorganisms, such as Chlamydomonas reinhardtii.

Self-assembled inorganic clusters of semiconducting quantum dots for effective solar hydrogen evolution.

PubMed

Gao, Yu-Ji; Yang, Yichen; Li, Xu-Bing; Wu, Hao-Lin; Meng, Shu-Lin; Wang, Yang; Guo, Qing; Huang, Mao-Yong; Tung, Chen-Ho; Wu, Li-Zhu

2018-05-08

Owing to promoted electron-hole separation, the catalytic activity of semiconducting quantum dots (QDs) towards solar hydrogen (H2) production has been significantly enhanced by forming self-assembled clusters with ZnSe QDs made ex situ. Taking advantage of the favored interparticle hole transfer to ZnSe QDs, the rate of solar H2 evolution of CdSe QDs can be increased to ∼30 000 μmol h-1 g-1 with ascorbic acid as the sacrificial reagent, ∼150-fold higher than that of bare CdSe QDs clusters under the same conditions.

A Study of the Mechanism of the Hydrogen Evolution Reaction on Nickel by Surface Interrogation Scanning Electrochemical Microscopy.

PubMed

Liang, Zhenxing; Ahn, Hyun S; Bard, Allen J

2017-04-05

The hydrogen evolution reaction (HER) on Ni in alkaline media was investigated by scanning electrochemical microscopy under two operating modes. First, the substrate generation/tip collection mode was employed to extract the "true" cathodic current associated with the HER from the total current in the polarization curve. Compared to metallic Ni, the electrocatalytic activity of the HER is improved in the presence of the low-valence-state oxide of Ni. This result is in agreement with a previous claim that the dissociative adsorption of water can be enhanced at the Ni/Ni oxide interface. Second, the surface-interrogation scanning electrochemical microscopy (SI-SECM) mode was used to directly measure the coverage of the adsorbed hydrogen on Ni at given potentials. Simulation indicates that the hydrogen coverage follows a Frumkin isotherm with respect to the applied potential. On the basis of the combined analysis of the Tafel slope and surface hydrogen coverage, the rate-determining step is suggested to be the adsorption of hydrogen (Volmer step) in the investigated potential window.

Low-cost industrially available molybdenum boride and carbide as "platinum-like" catalysts for the hydrogen evolution reaction in biphasic liquid systems.

PubMed

Scanlon, Micheál D; Bian, Xiaojun; Vrubel, Heron; Amstutz, Véronique; Schenk, Kurt; Hu, Xile; Liu, BaoHong; Girault, Hubert H

2013-02-28

Rarely reported low-cost molybdenum boride and carbide microparticles, both of which are available in abundant quantities due to their widespread use in industry, adsorb at aqueous acid-1,2-dichloroethane interfaces and efficiently catalyse the hydrogen evolution reaction in the presence of the organic electron donor - decamethylferrocene. Kinetic studies monitoring biphasic reactions by UV/vis spectroscopy, and further evidence provided by gas chromatography, highlight (a) their superior rates of catalysis relative to other industrially significant transition metal carbides and silicides, as well as a main group refractory compound, and (b) their highly comparable rates of catalysis to Pt microparticles of similar dimensions. Insight into the catalytic processes occurring for each adsorbed microparticle was obtained by voltammetry at the liquid-liquid interface.

Interface Engineering of Colloidal CdSe Quantum Dot Thin Films as Acid-Stable Photocathodes for Solar-Driven Hydrogen Evolution.

PubMed

Li, Hui; Wen, Peng; Hoxie, Adam; Dun, Chaochao; Adhikari, Shiba; Li, Qi; Lu, Chang; Itanze, Dominique S; Jiang, Lin; Carroll, David; Lachgar, Abdou; Qiu, Yejun; Geyer, Scott M

2018-05-23

Colloidal semiconductor quantum dot (CQD)-based photocathodes for solar-driven hydrogen evolution have attracted significant attention because of their tunable size, nanostructured morphology, crystalline orientation, and band gap. Here, we report a thin film heterojunction photocathode composed of organic PEDOT:PSS as a hole transport layer, CdSe CQDs as a semiconductor light absorber, and conformal Pt layer deposited by atomic layer deposition (ALD) serving as both a passivation layer and cocatalyst for hydrogen evolution. In neutral aqueous solution, a PEDOT:PSS/CdSe/Pt heterogeneous photocathode with 200 cycles of ALD Pt produces a photocurrent density of -1.08 mA/cm 2 (AM-1.5G, 100 mW/cm 2 ) at a potential of 0 V versus reversible hydrogen electrode (RHE) ( j 0 ) in neutral aqueous solution, which is nearly 12 times that of the pristine CdSe photocathode. This composite photocathode shows an onset potential for water reduction at +0.46 V versus RHE and long-term stability with negligible degradation. In the acidic electrolyte (pH = 1), where the hydrogen evolution reaction is more favorable but stability is limited because of photocorrosion, a thicker Pt film (300 cycles) is shown to greatly improve the device stability and a j 0 of -2.14 mA/cm 2 is obtained with only 8.3% activity degradation after 6 h, compared with 80% degradation under the same conditions when the less conformal electrodeposition method is used to deposit the Pt layer. Electrochemical impedance spectroscopy and time-resolved photoluminescence results indicate that these enhancements stem from a lower bulk charge recombination rate, higher interfacial charge-transfer rate, and faster reaction kinetics. We believe that these interface engineering strategies can be extended to other colloidal semiconductors to construct more efficient and stable heterogeneous photoelectrodes for solar fuel production.

Efficient Electron Transfer across a ZnO-MoS2 -Reduced Graphene Oxide Heterojunction for Enhanced Sunlight-Driven Photocatalytic Hydrogen Evolution.

PubMed

Kumar, Suneel; Reddy, Nagappagari Lakshmana; Kushwaha, Himmat Singh; Kumar, Ashish; Shankar, Muthukonda Venkatakrishnan; Bhattacharyya, Kaustava; Halder, Aditi; Krishnan, Venkata

2017-09-22

The development of noble metal-free catalysts for hydrogen evolution is required for energy applications. In this regard, ternary heterojunction nanocomposites consisting of ZnO nanoparticles anchored on MoS 2 -RGO (RGO=reduced graphene oxide) nanosheets as heterogeneous catalysts show highly efficient photocatalytic H 2 evolution. In the photocatalytic process, the catalyst dispersed in an electrolytic solution (S 2- and SO 3 2- ions) exhibits an enhanced rate of H 2 evolution, and optimization experiments reveal that ZnO with 4.0 wt % of MoS 2 -RGO nanosheets gives the highest photocatalytic H 2 production of 28.616 mmol h -1  g cat -1 under sunlight irradiation; approximately 56 times higher than that on bare ZnO and several times higher than those of other ternary photocatalysts. The superior catalytic activity can be attributed to the in situ generation of ZnS, which leads to improved interfacial charge transfer to the MoS 2 cocatalyst and RGO, which has plenty of active sites available for photocatalytic reactions. Recycling experiments also proved the stability of the optimized photocatalyst. In addition, the ternary nanocomposite displayed multifunctional properties for hydrogen evolution activity under electrocatalytic and photoelectrocatalytic conditions owing to the high electrode-electrolyte contact area. Thus, the present work provides very useful insights for the development of inexpensive, multifunctional catalysts without noble metal loading to achieve a high rate of H 2 generation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cellular Automaton Study of Hydrogen Porosity Evolution Coupled with Dendrite Growth During Solidification in the Molten Pool of Al-Cu Alloys

NASA Astrophysics Data System (ADS)

Gu, Cheng; Wei, Yanhong; Yu, Fengyi; Liu, Xiangbo; She, Lvbo

2017-09-01

Welding porosity defects significantly reduce the mechanical properties of welded joints. In this paper, the hydrogen porosity evolution coupled with dendrite growth during solidification in the molten pool of Al-4.0 wt pct Cu alloy was modeled and simulated. Three phases, including a liquid phase, a solid phase, and a gas phase, were considered in this model. The growth of dendrites and hydrogen gas pores was reproduced using a cellular automaton (CA) approach. The diffusion of solute and hydrogen was calculated using the finite difference method (FDM). Columnar and equiaxed dendrite growth with porosity evolution were simulated. Competitive growth between different dendrites and porosities was observed. Dendrite morphology was influenced by porosity formation near dendrites. After solidification, when the porosities were surrounded by dendrites, they could not escape from the liquid, and they made pores that existed in the welded joints. With the increase in the cooling rate, the average diameter of porosities decreased, and the average number of porosities increased. The average diameter of porosities and the number of porosities in the simulation results had the same trend as the experimental results.

One-pot Synthesis of CdS Irregular Nanospheres Hybridized with Oxygen-Incorporated Defect-Rich MoS2 Ultrathin Nanosheets for Efficient Photocatalytic Hydrogen Evolution.

PubMed

Zhang, Shouwei; Yang, Hongcen; Gao, Huihui; Cao, Ruya; Huang, Jinzhao; Xu, Xijin

2017-07-19

Robust and highly active photocatalysts, CdS@MoS 2 , for hydrogen evolution were successfully fabricated by one-step growth of oxygen-incorporated defect-rich MoS 2 ultrathin nanosheets on the surfaces of CdS with irregular fissures. Under optimized experimental conditions, the CdS@MoS 2 displayed a quantum yield of ∼24.2% at 420 nm and the maximum H 2 generation rate of ∼17203.7 umol/g/h using Na 2 S-Na 2 SO 3 as sacrificial agents (λ ≥ 420 nm), which is ∼47.3 and 14.7 times higher than CdS (∼363.8 μmol/g/h) and 3 wt % Pt/CdS (∼1173.2 μmol/g/h), respectively, and far exceeds all previous hydrogen evolution reaction photocatalysts with MoS 2 as co-catalysts using Na 2 S-Na 2 SO 3 as sacrificial agents. Large volumes of hydrogen bubbles were generated within only 2 s as the photocatalysis started, as demonstrated by the photocatalytic video. The high hydrogen evolution activity is attributed to several merits: (1) the intimate heterojunctions formed between the MoS 2 and CdS can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs; and (2) the defects in the MoS 2 provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H 2 evolution and increases the electric conductivity of the MoS 2 . Considering its low cost and high efficiency, this highly efficient hybrid photocatalysts would have great potential in energy-generation and environment-restoration fields.

Nickel sulfide/graphitic carbon nitride/strontium titanate (NiS/g-C3N4/SrTiO3) composites with significantly enhanced photocatalytic hydrogen production activity.

PubMed

Luo, Xiu-Li; He, Gang-Ling; Fang, Yue-Ping; Xu, Yue-Hua

2018-05-15

NiS/g-C 3 N 4 /SrTiO 3 (NS/CN/STO) composites were prepared using a facile hydrothermal method. The synergistic effect of g-C 3 N 4 /SrTiO 3 (CN/STO) heterojunction and NiS cocatalyst enhanced the photocatalytic hydrogen evolution activity of NS/CN/STO. A hydrogen production rate of 1722.7 μmol h -1  g -1 was obtained when the 2%NiS/20%g-C 3 N 4 /SrTiO 3 (2NS/20CN/STO) was used for the photocatalytic hydrogen evolution in the presence of methanol used as a sacrificial agent under UV-vis light irradiation; the photocatalytic hydrogen production rate of 2NS/20CN/STO is 32.8, 8.9 and 4.2 times the value of that obtained with pure g-C 3 N 4 , SrTiO 3 and 20%g-C 3 N 4 /SrTiO 3 (20CN/STO), respectively. Moreover, in photoelectrochemical investigations when compared with 20CN/STO, SrTiO 3 and g-C 3 N 4 , 2NS/20CN/STO exhibited significant photocurrent enhancement. The heterojunction and cocatalyst in NS/CN/STO improved the charge separation efficiency and the lifetime of the charge carriers, leading to the enhanced generation of electrons for photocatalytic hydrogen production. Copyright © 2018 Elsevier Inc. All rights reserved.

Promotion effect of nickel loaded on CdS for photocatalytic H2 production in lactic acid solution

NASA Astrophysics Data System (ADS)

Chen, Shu; Chen, Xiaoping; Jiang, Qizhong; Yuan, Jian; Lin, Caifang; Shangguan, Wenfeng

2014-10-01

Low-cost Ni modified CdS was prepared via a hydrothermal reduction method. The hydrogen production activity of CdS loaded with 5 wt% Ni under visible light was even higher than that of the one loaded with 0.5 wt% Pt. The highest H2 evolution rate (3004.8 μmol h-1) occurred when the concentration of sacrificial agent (lactic acid) was 50 vol%. The nickel can quickly transfer excited electrons and enhance the photocatalytic H2 production activity. It was also found that the hydrogen evolution in this system was generated steadily from both water and lactic acid.

Active hydrogen evolution through lattice distortion in metallic MoTe2

NASA Astrophysics Data System (ADS)

Seok, Jinbong; Lee, Jun-Ho; Cho, Suyeon; Ji, Byungdo; Kim, Hyo Won; Kwon, Min; Kim, Dohyun; Kim, Young-Min; Oh, Sang Ho; Wng Kim, Sung; Lee, Young Hee; Son, Young-Woo; Yang, Heejun

2017-06-01

Engineering surface atoms of transition metal dichalcogenides (TMDs) is a promising way to design catalysts for efficient electrochemical reactions including the hydrogen evolution reaction (HER). However, materials processing based on TMDs, such as vacancy creation or edge exposure, for active HER, has resulted in insufficient atomic-precision lattice homogeneity and a lack of clear understanding of HER over 2D materials. Here, we report a durable and effective HER at atomically defined reaction sites in 2D layered semimetallic MoTe2 with intrinsic turnover frequency (TOF) of 0.14 s-1 at 0 mV overpotential, which cannot be explained by the traditional volcano plot analysis. Unlike former electrochemical catalysts, the rate-determining step of the HER on the semimetallic MoTe2, hydrogen adsorption, drives Peierls-type lattice distortion that, together with a surface charge density wave, unexpectedly enhances the HER. The active HER using unique 2D features of layered TMDs enables an optimal design of electrochemical catalysts and paves the way for a hydrogen economy.

Lyman-alpha observations of Comet West /1975n/

NASA Technical Reports Server (NTRS)

Opal, C. B.; Carruthers, G. R.

1977-01-01

The rate of hydrogen production of Comet West is studied through rocket observation of solar Lyman-alpha radiation resonantly scattered by the escaping hydrogen atoms. Two sets of Lyman-alpha exposure sequences are used to obtain computer-smoothed brightness contour (isophote) maps covering a density range of 100:1. A simple radial outflow model is applied to the contour maps to determine the rate of hydrogen production (3.2 by 10 to the 30th power atoms/sec.) Discrepancies between the observed shape of the outer isophotes and predicted models may be explained by optical depth effects, or by the presence of small pieces of the comet's nucleus distributed along the orbit. Hydrogen, carbon, and oxygen production for Comet West and Comet Kohoutek are compared; differences may be accounted for by variations in the composition or evolution of the two comets.

Investigation of hydrogen evolution activity for the nickel, nickel-molybdenum nickel-graphite composite and nickel-reduced graphene oxide composite coatings

NASA Astrophysics Data System (ADS)

Jinlong, Lv; Tongxiang, Liang; Chen, Wang

2016-03-01

The nickel, nickel-molybdenum alloy, nickel-graphite and nickel-reduced graphene oxide composite coatings were obtained by the electrodeposition technique from a nickel sulfate bath. Nanocrystalline molybdenum, graphite and reduced graphene oxide in nickel coatings promoted hydrogen evolution reaction in 0.5 M H2SO4 solution at room temperature. However, the nickel-reduced graphene oxide composite coating exhibited the highest electrocatalytic activity for the hydrogen evolution reaction in 0.5 M H2SO4 solution at room temperature. A large number of gaps between 'cauliflower' like grains could decrease effective area for hydrogen evolution reaction in slight amorphous nickel-molybdenum alloy. The synergistic effect between nickel and reduced graphene oxide promoted hydrogen evolution, moreover, refined grain in nickel-reduced graphene oxide composite coating and large specific surface of reduced graphene oxide also facilitated hydrogen evolution reaction.

Impact of fermentation rate changes on potential hydrogen sulfide concentrations in wine.

PubMed

Butzke, Christian E; Park, Seung Kook

2011-05-01

The correlation between alcoholic fermentation rate, measured as carbon dioxide (CO2) evolution, and the rate of hydrogen sulfide (H2S) formation during wine production was investigated. Both rates and the resulting concentration peaks in fermentor headspace H2S were directly impacted by yeast assimilable nitrogenous compounds in the grape juice. A series of model fermentations was conducted in temperature-controlled and stirred fermentors using a complex model juice with defined concentrations of ammonium ions and/or amino acids. The fermentation rate was measured indirectly by noting the weight loss of the fermentor; H2S was quantitatively trapped in realtime using a pre-calibrated H2S detection tube which was inserted into a fermentor gas relief port. Evolution rates for CO2 and H2S as well as the relative ratios between them were calculated. These fermentations confirmed that total sulfide formation was strongly yeast strain-dependent, and high concentrations of yeast assimilable nitrogen did not necessarily protect against elevated H2S formation. High initial concentrations of ammonium ions via addition of diammonium phosphate (DAP) caused a higher evolution of H2S when compared with a non-supplemented but nondeficient juice. It was observed that the excess availability of a certain yeast assimilable amino acid, arginine, could result in a more sustained CO2 production rate throughout the wine fermentation. The contribution of yeast assimilable amino acids from conventional commercial yeast foods to lowering of the H2S formation was marginal.

Nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tashlykova-Bushkevich, Iya I.

2015-12-31

The present work summarizes recent progress in the investigation of nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys foils produced at exceptionally high cooling rates. We focus here on the potential of modification of hydrogen desorption kinetics in respect to weak and strong trapping sites that could serve as hydrogen sinks in Al materials. It is shown that it is important to elucidate the surface microstructure of the Al alloy foils at the submicrometer scale because rapidly solidified microstructural features affect hydrogen trapping at nanostructured defects. We discuss the profound influence of solute atoms on hydrogen−lattice defectmore » interactions in the alloys. with emphasis on role of vacancies in hydrogen evolution; both rapidly solidified pure Al and conventionally processed aluminum samples are considered.« less

Co-axial heterostructures integrating palladium/titanium dioxide with carbon nanotubes for efficient electrocatalytic hydrogen evolution.

PubMed

Valenti, Giovanni; Boni, Alessandro; Melchionna, Michele; Cargnello, Matteo; Nasi, Lucia; Bertoni, Giovanni; Gorte, Raymond J; Marcaccio, Massimo; Rapino, Stefania; Bonchio, Marcella; Fornasiero, Paolo; Prato, Maurizio; Paolucci, Francesco

2016-12-12

Considering the depletion of fossil-fuel reserves and their negative environmental impact, new energy schemes must point towards alternative ecological processes. Efficient hydrogen evolution from water is one promising route towards a renewable energy economy and sustainable development. Here we show a tridimensional electrocatalytic interface, featuring a hierarchical, co-axial arrangement of a palladium/titanium dioxide layer on functionalized multi-walled carbon nanotubes. The resulting morphology leads to a merging of the conductive nanocarbon core with the active inorganic phase. A mechanistic synergy is envisioned by a cascade of catalytic events promoting water dissociation, hydride formation and hydrogen evolution. The nanohybrid exhibits a performance exceeding that of state-of-the-art electrocatalysts (turnover frequency of 15000 H 2 per hour at 50 mV overpotential). The Tafel slope of ∼130 mV per decade points to a rate-determining step comprised of water dissociation and formation of hydride. Comparative activities of the isolated components or their physical mixtures demonstrate that the good performance evolves from the synergistic hierarchical structure.

Co-axial heterostructures integrating palladium/titanium dioxide with carbon nanotubes for efficient electrocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Valenti, Giovanni; Boni, Alessandro; Melchionna, Michele; Cargnello, Matteo; Nasi, Lucia; Bertoni, Giovanni; Gorte, Raymond J.; Marcaccio, Massimo; Rapino, Stefania; Bonchio, Marcella; Fornasiero, Paolo; Prato, Maurizio; Paolucci, Francesco

2016-12-01

Considering the depletion of fossil-fuel reserves and their negative environmental impact, new energy schemes must point towards alternative ecological processes. Efficient hydrogen evolution from water is one promising route towards a renewable energy economy and sustainable development. Here we show a tridimensional electrocatalytic interface, featuring a hierarchical, co-axial arrangement of a palladium/titanium dioxide layer on functionalized multi-walled carbon nanotubes. The resulting morphology leads to a merging of the conductive nanocarbon core with the active inorganic phase. A mechanistic synergy is envisioned by a cascade of catalytic events promoting water dissociation, hydride formation and hydrogen evolution. The nanohybrid exhibits a performance exceeding that of state-of-the-art electrocatalysts (turnover frequency of 15000 H2 per hour at 50 mV overpotential). The Tafel slope of ~130 mV per decade points to a rate-determining step comprised of water dissociation and formation of hydride. Comparative activities of the isolated components or their physical mixtures demonstrate that the good performance evolves from the synergistic hierarchical structure.

Co-axial heterostructures integrating palladium/titanium dioxide with carbon nanotubes for efficient electrocatalytic hydrogen evolution

PubMed Central

Valenti, Giovanni; Boni, Alessandro; Melchionna, Michele; Cargnello, Matteo; Nasi, Lucia; Bertoni, Giovanni; Gorte, Raymond J.; Marcaccio, Massimo; Rapino, Stefania; Bonchio, Marcella; Fornasiero, Paolo; Prato, Maurizio; Paolucci, Francesco

2016-01-01

Considering the depletion of fossil-fuel reserves and their negative environmental impact, new energy schemes must point towards alternative ecological processes. Efficient hydrogen evolution from water is one promising route towards a renewable energy economy and sustainable development. Here we show a tridimensional electrocatalytic interface, featuring a hierarchical, co-axial arrangement of a palladium/titanium dioxide layer on functionalized multi-walled carbon nanotubes. The resulting morphology leads to a merging of the conductive nanocarbon core with the active inorganic phase. A mechanistic synergy is envisioned by a cascade of catalytic events promoting water dissociation, hydride formation and hydrogen evolution. The nanohybrid exhibits a performance exceeding that of state-of-the-art electrocatalysts (turnover frequency of 15000 H2 per hour at 50 mV overpotential). The Tafel slope of ∼130 mV per decade points to a rate-determining step comprised of water dissociation and formation of hydride. Comparative activities of the isolated components or their physical mixtures demonstrate that the good performance evolves from the synergistic hierarchical structure. PMID:27941752

Rationally designed n-n heterojunction with highly efficient solar hydrogen evolution.

PubMed

Xu, Miao; Ye, Tiannan; Dai, Fang; Yang, Jindi; Shen, Jingmei; He, Qingquan; Chen, Wenlong; Liang, Na; Zai, Jiantao; Qian, Xuefeng

2015-04-13

In most of the reported n-n heterojunction photocatalysts, both the conduction and valence bands of one semiconductor are more negative than those of the other semiconductor. In this work, we designed and synthesized a novel n-n heterojunction photocatalyst, namely CdS-ZnWO4 heterojunctions, in which ZnWO4 has more negative conduction band and more positive valence band than those of CdS. The hydrogen evolution rate of CdS-30 mol %-ZnWO4 reaches 31.46 mmol h(-1)  g(-1) under visible light, which is approximately 8 and 755 times higher than that of pure CdS and ZnWO4 under similar conditions, respectively. The location of the surface active sites is researched and a plausible mechanism of performance enhancement by the tuning of the structure is proposed based on the photoelectrochemical characterization. The results illustrate that this kind of nonconventional n-n heterojunctions is also suitable and highly efficient for solar hydrogen evolution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Clean hydrogen generation through the electrocatalytic oxidation of ethanol in a Proton Exchange Membrane Electrolysis Cell (PEMEC): Effect of the nature and structure of the catalytic anode

NASA Astrophysics Data System (ADS)

Lamy, Claude; Jaubert, Thomas; Baranton, Stève; Coutanceau, Christophe

2014-01-01

The electrocatalytic oxidation of ethanol was investigated in a Proton Exchange Membrane Electrolysis Cell (PEMEC) working at low temperature (20°C) on several Pt-based catalysts (Pt/C, PtSn/C, PtSnRu/C) in order to produce very clean hydrogen by electrolysis of a biomass compound. The electrocatalytic activity was determined by cyclic voltammetry and the rate of hydrogen evolution was measured for each catalyst at different current densities. The cell voltages UEtOH were recorded as a function of time for each current density. At 100 mA cm-2, i.e. 0.5 A with the 5 cm2 surface area PEMEC used, the cell voltage did not exceed 0.9 V for an evolution rate of about 220 cm3 of hydrogen per hour and the electrical energy consumed was less than 2.3 kWh (Nm3)-1, i.e. less than one half of the energy needed for water electrolysis (4.7 kWh (Nm3)-1 at UH2O = 2 V). This result is valid for the decomposition of any organic compound, particularly those originated from biomass resource, provided that their electro-oxidation rate is sufficient (>100 mA cm-2) at a relatively low cell voltage (Ucell < 1 V) which necessitates the development of efficient electrocatalysts for the electrochemical decomposition of this compound.

Evaluation of AA5052 alloy anode in alkaline electrolyte with organic rare-earth complex additives for aluminium-air batteries

NASA Astrophysics Data System (ADS)

Wang, Dapeng; Li, Heshun; Liu, Jie; Zhang, Daquan; Gao, Lixin; Tong, Lin

2015-10-01

Behaviours of the AA5052 aluminium alloy anode of the alkaline aluminium-air battery are studied by the hydrogen evolution test, the electrochemical measurements and the surface analysis method. The combination of amino-acid and rare earth as electrolyte additives effectively retards the self-corrosion of AA5052 aluminium alloy in 4 M NaOH solution. It shows that the combination of L-cysteine and cerium nitrate has a synergistic effect owing to the formation of a complex film on AA5052 alloy surface. The organic rare-earth complex can decrease the anodic polarisation, suppress the hydrogen evolution and increase the anodic utilization rate.

Effect of annealing ambience on the formation of surface/bulk oxygen vacancies in TiO2 for photocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Hou, Lili; Zhang, Min; Guan, Zhongjie; Li, Qiuye; Yang, Jianjun

2018-01-01

The surface and bulk oxygen vacancy have a prominent effect on the photocatalytic performance of TiO2. In this study, TiO2 possessing different types and concentration of oxygen vacancies were prepared by annealing nanotube titanic acid (NTA) at various temperatures in air or vacuum atmosphere. TiO2 with the unitary bulk single-electron-trapped oxygen vacancies (SETOVs) formed when NTA were calcined in air. Whereas, TiO2 with both bulk and surface oxygen vacancies were obtained when NTA were annealed in vacuum. The series of TiO2 with different oxygen vacancies were systematically characterized by TEM, XRD, PL, XPS, ESR, and TGA. The PL and ESR analysis verified that surface oxygen vacancies and more bulk oxygen vacancies could form in vacuum atmosphere. Surface oxygen vacancies can trap electron and hinder the recombination of photo-generated charges, while bulk SETOVs act as the recombination center. The surface or bulk oxygen vacancies attributed different roles on the photo-absorbance and activity, leading that the sample of NTA-A400 displayed higher hydrogen evolution rate under UV light, whereas NTA-V400 displayed higher hydrogen evolution rate under visible light because bulk SETOVs can improve visible light absorption because sub-band formed by bulk SETOVs prompted the secondary transition of electron excited.

Pt deposited TiO2 catalyst fabricated by thermal decomposition of titanium complex for solar hydrogen production

NASA Astrophysics Data System (ADS)

Truong, Quang Duc; Le, Thanh Son; Ling, Yong-Chien

2014-12-01

C, N codoped TiO2 catalyst has been synthesized by thermal decomposition of a novel water-soluble titanium complex. The structure, morphology, and optical properties of the synthesized TiO2 catalyst were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Pt deposited TiO2 catalysts synthesized at different temperatures was evaluated by means of hydrogen evolution reaction under both UV-vis and visible light irradiation. The investigation results reveal that the photocatalytic H2 evolution rate strongly depended on the crystalline grain size as well as specific surface area of the synthesized catalyst. Our studies successfully demonstrate a simple method for the synthesis of visible-light responsive Pt deposited TiO2 catalyst for solar hydrogen production.

Enhanced catalytic activity of the nanostructured Co-W-B film catalysts for hydrogen evolution from the hydrolysis of ammonia borane.

PubMed

Li, Chao; Wang, Dan; Wang, Yan; Li, Guode; Hu, Guijuan; Wu, Shiwei; Cao, Zhongqiu; Zhang, Ke

2018-08-15

In this work, nanostructured Co-W-B films are successfully synthesized on the foam sponge by electroless plating method and employed as the catalysts with enhanced catalytic activity towards hydrogen evolution from the hydrolysis of ammonia borane (NH 3 BH 3 , AB) at room temperature. The particle size of the as-prepared Co-W-B film catalysts is varied by adjusting the depositional pH value to identify the most suitable particle size for hydrogen evolution of AB hydrolysis. The Co-W-B film catalyst with the particle size of about 67.3 nm shows the highest catalytic activity and can reach a hydrogen generation rate of 3327.7 mL min -1 g cat -1 at 298 K. The activation energy of the hydrolysis reaction of AB is determined to be 32.2 kJ mol -1 . Remarkably, the as-obtained Co-W-B film is also a reusable catalyst preserving 78.4% of their initial catalytic activity even after 5 cycles in hydrolysis of AB at room temperature. Thus, the enhanced catalytic activity illustrates that the Co-W-B film is a promising catalyst for AB hydrolytic dehydrogenation in fuel cells and the related fields. Copyright © 2018 Elsevier Inc. All rights reserved.

Hydrogen evolution reaction catalyst

DOEpatents

Subbaraman, Ram; Stamenkovic, Vojislav; Markovic, Nenad; Tripkovic, Dusan

2016-02-09

Systems and methods for a hydrogen evolution reaction catalyst are provided. Electrode material includes a plurality of clusters. The electrode exhibits bifunctionality with respect to the hydrogen evolution reaction. The electrode with clusters exhibits improved performance with respect to the intrinsic material of the electrode absent the clusters.

Fabrication of Carbon-Platinum Interdigitated Array Electrodes and Their Application for Investigating Homogeneous Hydrogen Evolution Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fei; Divan, Ralu; Parkinson, Bruce A.

2015-06-29

Carbon interdigitated array (IDA) electrodes have been applied to study the homogeneous hydrogen evolution electrocatalyst [Ni(PPh2NBn2)2]2+ (where PPh2NBn2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane). The existence of reaction intermediates in the catalytic cycle is inferred from the electrochemical behavior of a glassy carbon disk electrodes and carbon IDA electrodes. The currents on IDA electrodes for an EC’ (electron transfer reaction followed by a catalytic reaction) mechanism are derived from the number of redox cycles and the contribution of non-catalytic currents. The catalytic reaction rate constant was then extracted from the IDA current equations. Applying the IDA current and kinetic equations to the electrochemical responsemore » of the [Ni(PPh2NBn2)2]2+ catalyst yielded a rate constant of 0.10 s-1 for the hydrogen evolution reaction that agrees with the literature value. The quantitative analysis of IDA cyclic voltammetry can be used as a simple and straightforward method for determining rate constants in other catalytic systems. This work was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for DOE. Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.« less

An efficient molybdenum disulfide/cobalt diselenide hybrid catalyst for electrochemical hydrogen generation

PubMed Central

Gao, Min-Rui; Liang, Jin-Xia; Zheng, Ya-Rong; Xu, Yun-Fei; Jiang, Jun; Gao, Qiang; Li, Jun; Yu, Shu-Hong

2015-01-01

The electroreduction of water for sustainable hydrogen production is a critical component of several developing clean-energy technologies, such as water splitting and fuel cells. However, finding a cheap and efficient alternative catalyst to replace currently used platinum-based catalysts is still a prerequisite for the commercialization of these technologies. Here we report a robust and highly active catalyst for hydrogen evolution reaction that is constructed by in situ growth of molybdenum disulfide on the surface of cobalt diselenide. In acidic media, the molybdenum disulfide/cobalt diselenide catalyst exhibits fast hydrogen evolution kinetics with onset potential of −11 mV and Tafel slope of 36 mV per decade, which is the best among the non-noble metal hydrogen evolution catalysts and even approaches to the commercial platinum/carbon catalyst. The high hydrogen evolution activity of molybdenum disulfide/cobalt diselenide hybrid is likely due to the electrocatalytic synergistic effects between hydrogen evolution-active molybdenum disulfide and cobalt diselenide materials and the much increased catalytic sites. PMID:25585911

Carbon and hydrogen metabolism of green algae in light and dark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-01-01

After adaptation to a hydrogen metabolism, Chlamydomonas reinhardtii can photoanaerobically metabolize acetate with the evolution of H{sub 2} and CO{sub 2}. An enzyme profile of the chloroplastic, cytoplasmic, and mitochondrial fractions were obtained with a cellular fractionation procedure that incorporated cell wall removal by autolysine, digestion of the plasmalemma with digitonin and fractionation by differential centrifugation on a Percoll step gradient. The sequence of events leading to the photo-evolution of H{sub 2} from acetate includes the conversion of acetate into succinate via the extraplastidic glyoxylate cycle, the oxidation of succinate to fumarate by chloroplastic succinic dehydrogenase and the oxidation ofmore » malate to oxaloacetate in the chloroplast by NAD dependent malate dehydrogenase. The level of potential activity of the enzymes was sufficient to accommodate the observed rate of gas evolution. The isolated darkened chloroplast evolves aerobically CO{sub 2} from glucose indicating a chloroplastic respiratory pathway. Evolution of CO{sub 2} is blocked by mitochondrial inhibitors.« less

Reaping Environmental Benefits of a Global Hydrogen Economy: How Large, Fow Soon, and at What Risks?

NASA Astrophysics Data System (ADS)

Dubey, M. K.; Horowitz, L. W.; Rahn, T. A.; Kinnison, D. E.

2004-12-01

The Western world has taken an aggressive posture to transition to a global hydrogen economy. While numerous technical challenges need to be addressed to achieve this it is timely to examine the environmental benefits and risks of this transition. Hydrogen provides an efficient energy carrier that promises to enhance urban and regional air quality that will benefit human health. It could also reduce risks of climate change if large-scale hydrogen production by renewable or nuclear energy sources becomes viable. While it is well known that the byproduct of energy produced from hydrogen is water vapor, it is not well known that the storage and transfer of hydrogen is inevitably accompanied by measurable leakage of hydrogen. Unintended consequences of hydrogen leakage include reduction in global oxidative capacity, changes in tropospheric ozone, and increase in stratospheric water that would exacerbate halogen induced ozone losses as well as impact the earth's radiation budget and climate. We construct plausible global hydrogen energy use and leak scenarios and assess their impacts using global 3-D simulations by the Model for Ozone And Related Trace species (MOZART). The hydrogen fluxes and photochemistry in our model successfully reproduce the contemporary hydrogen cycle as observed by a network of remote global stations. Our intent is to determine environmentally tolerable leak rates and also facilitate a gradual phasing in of a hydrogen economy over the next several decades as the elimination of the use of halocarbons gradually reduces halogen induced stratospheric ozone loss rates. We stress that the leak rates in global hydrogen infrastructure and the future evolution of microbial soil sink of hydrogen that determines its current lifetime (about 2 years) are principal sources of uncertainty in our assessment.

Interface engineering of colloidal CdSe quantum dots thin films as acid-stable photocathodes for solar-driven hydrogen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hui; Wen, Peng; Hoxie, Adam

Colloidal semiconductor quantum dots-based (CQD) photocathodes for solar-driven hydrogen evolution have attracted significant attention due to their tunable size, nanostructured morphology, crystalline orientation, and band-gap. Here, we report a thin film heterojunction photocathode composed of organic PEDOT:PSS as a hole transport layer, CdSe CQDs as a semiconductor light absorber, and conformal Pt layer deposited by atomic layer deposition (ALD) serving as both a passivation layer and cocatalyst for hydrogen evolution. In neutral aqueous solution, a PEDOT:PSS/CdSe/Pt heterogeneous photocathode with 200 cycles of ALD Pt produces a photocurrent density of -1.08 mA/cm 2 (AM1.5G, 100 mW/cm 2) at a potential ofmore » 0 V vs. RHE (j 0) in neutral aqueous solution, which is nearly 12 times that of the pristine CdSe photocathode. This composite photocathode shows an onset potential for water reduction at +0.46 V vs. RHE and long-term stability with negligible degradation. In acidic electrolyte (pH = 1), where the hydrogen evolution reaction is more favorable but stability is limited due to photocorrosion, a thicker Pt film (300 cycles) is shown to greatly improve the device stability and a j 0 of -2.14 mA/cm 2 is obtained with only 8.3% activity degradation after 6 h, compared to 80% degradation under the same conditions when the less conformal electrodeposition method is used to deposit the Pt layer. Electrochemical impedance spectroscopy and time-resolved photoluminescence results indicate that these enhancements stem from a lower bulk charge recombination rate, higher interfacial charge transfer rate, and faster reaction kinetics. In conclusion, we believe that these interface engineering strategies can be extended to other colloidal semiconductors to construct more efficient and stable heterogeneous photoelectrodes for solar fuel production.« less

Interface engineering of colloidal CdSe quantum dots thin films as acid-stable photocathodes for solar-driven hydrogen evolution

DOE PAGES

Li, Hui; Wen, Peng; Hoxie, Adam; ...

2018-04-30

Colloidal semiconductor quantum dots-based (CQD) photocathodes for solar-driven hydrogen evolution have attracted significant attention due to their tunable size, nanostructured morphology, crystalline orientation, and band-gap. Here, we report a thin film heterojunction photocathode composed of organic PEDOT:PSS as a hole transport layer, CdSe CQDs as a semiconductor light absorber, and conformal Pt layer deposited by atomic layer deposition (ALD) serving as both a passivation layer and cocatalyst for hydrogen evolution. In neutral aqueous solution, a PEDOT:PSS/CdSe/Pt heterogeneous photocathode with 200 cycles of ALD Pt produces a photocurrent density of -1.08 mA/cm 2 (AM1.5G, 100 mW/cm 2) at a potential ofmore » 0 V vs. RHE (j 0) in neutral aqueous solution, which is nearly 12 times that of the pristine CdSe photocathode. This composite photocathode shows an onset potential for water reduction at +0.46 V vs. RHE and long-term stability with negligible degradation. In acidic electrolyte (pH = 1), where the hydrogen evolution reaction is more favorable but stability is limited due to photocorrosion, a thicker Pt film (300 cycles) is shown to greatly improve the device stability and a j 0 of -2.14 mA/cm 2 is obtained with only 8.3% activity degradation after 6 h, compared to 80% degradation under the same conditions when the less conformal electrodeposition method is used to deposit the Pt layer. Electrochemical impedance spectroscopy and time-resolved photoluminescence results indicate that these enhancements stem from a lower bulk charge recombination rate, higher interfacial charge transfer rate, and faster reaction kinetics. In conclusion, we believe that these interface engineering strategies can be extended to other colloidal semiconductors to construct more efficient and stable heterogeneous photoelectrodes for solar fuel production.« less

Ultrafast visualization of the structural evolution of dense hydrogen towards warm dense matter

NASA Astrophysics Data System (ADS)

Fletcher, Luke

2016-10-01

Hot dense hydrogen far from equilibrium is ubiquitous in nature occurring during some of the most violent and least understood events in our universe such as during star formation, supernova explosions, and the creation of cosmic rays. It is also a state of matter important for applications in inertial confinement fusion research and in laser particle acceleration. Rapid progress occurred in recent years characterizing the high-pressure structural properties of dense hydrogen under static or dynamic compression. Here, we show that spectrally and angularly resolved x-ray scattering measure the thermodynamic properties of dense hydrogen and resolve the ultrafast evolution and relaxation towards thermodynamic equilibrium. These studies apply ultra-bright x-ray pulses from the Linac Coherent Light (LCLS) source. The interaction of rapidly heated cryogenic hydrogen with a high-peak power optical laser is visualized with intense LCLS x-ray pulses in a high-repetition rate pump-probe setting. We demonstrate that electron-ion coupling is affected by the small number of particles in the Debye screening cloud resulting in much slower ion temperature equilibration than predicted by standard theory. This work was supported by the DOE Office of Science, Fusion Energy Science under FWP 100182.

Bio-inspired co-catalysts bonded to a silicon photocathode for solar hydrogen evolution

NASA Astrophysics Data System (ADS)

Hou, Yidong; Abrams, Billie L.; Vesborg, Peter C. K.; Bjørketun, Mårten E.; Herbst, Konrad; Bech, Lone; Seger, Brian; Pedersen, Thomas; Hansen, Ole; Rossmeisl, Jan; Dahl, Søren; Nørskov, Jens K.; Chorkendorff, Ib

2011-10-01

The production of fuels directly or indirectly from sunlight represents one of the major challenges to the development of a sustainable energy system. Hydrogen is the simplest fuel to produce and while platinum and other noble metals are efficient catalysts for photoelectrochemical hydrogen evolution, earth-abundant alternatives are needed for largescale use. We show that bio-inspired molecular clusters based on molybdenum sulfides and tungsten sulfides mimic nature's enzymes for hydrogen evolution, molybdenum sulfides evolve hydrogen at a slightly higher overpotential than platinum when deposited on various supports. It will be demonstrated how this overpotential can be eliminated by depositing the same type of hydrogen evolution catalyst on p-type Si which can harvest the red part of the solar spectrum. Such a system could constitute the cathode part of a tandem dream device where the red part of the spectrum is utilized for hydrogen evolution while the blue part is reserved for the more difficult oxygen evolution. The samples have been illuminated with a simulated red part of the solar spectrum i.e. long wavelength (" > 620 nm) part of simulated AM 1.5G radiation. The current densities at the reversible potential match the requirement of a photoelectrochemical hydrogen production system with a solar-to-hydrogen efficiency in excess of 10%. The experimental observations are supported by DFT calculations of the Mo3S4 cluster adsorbed on the hydrogen-terminated silicon surface providing insights into the nature of the active site.

An in situ mediator-free route to fabricate Cu2O/g-C3N4 type-II heterojunctions for enhanced visible-light photocatalytic H2 generation

NASA Astrophysics Data System (ADS)

Ji, Cong; Yin, Su-Na; Sun, Shasha; Yang, Shengyang

2018-03-01

Cu2O nanoparticles doped g-C3N4 are synthesized via an in situ method and investigated in detail by IR techniques, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet visible diffuse reflection spectroscopy, and photoluminescence spectroscopy. The as-prepared Cu2O/g-C3N4 hybrids demonstrate enhanced photocatalytic activity toward hydrogen generation compared to pure bulk g-C3N4, the effect of Cu2O content on the rate of visible light photocatalytic hydrogen evolution reveals the optimal hydrogen evolution rate can reach 33.2 μmol h-1 g-1, which is about 4 times higher that of pure g-C3N4. The enhanced photocatalytic activity can be attributed to the improved separation and transfer of photogenerated electron-hole pairs at the intimate interface between g-C3N4 and Cu2O. A possible photocatalytic mechanism of the Cu2O/g-C3N4 composite is also discussed. This mediator-free in situ chemical doping strategy developed in this work will contribute to the achievement of other multicomponent photocatalysts.

In situ photodeposition of cobalt on CdS nanorod for promoting photocatalytic hydrogen production under visible light irradiation

NASA Astrophysics Data System (ADS)

Chen, Wei; Wang, Yanhong; Liu, Mei; Gao, Li; Mao, Liqun; Fan, Zeyun; Shangguan, Wenfeng

2018-06-01

Non-noble metal Co were loaded on CdS for enhancing photocatalytic activity of water splitting by a simple and efficient in situ photodeposition method. The Co particles with diameter ca. 5 nm were photoreduced and then loaded on the surface of CdS. The loading of Co can not only effectively promote the separation of electrons and holes photoexcited by CdS, but reduce the overpotential of hydrogen evolution as well, thus enhancing photocatalytic activity of water splitting. The highest photocatalytic H2 evolution rate of Co/CdS reaches up to 1299 μmol h-1 under visible light irradiation(λ > 420 nm) when the amount of loading is 1.0 wt%, which is 17 times of that of pure CdS and achieves 80% of that of 0.5 wt%Pt/CdS. This work not only exhibits a pathway to obtain photocatalysts with high photocatalytic activity for hydrogen production, but provides a possibility for the utilization of low cost Co as a substitute for noble metals in photocatalytic hydrogen production.

Coupled molybdenum carbide and reduced graphene oxide electrocatalysts for efficient hydrogen evolution.

PubMed

Li, Ji-Sen; Wang, Yu; Liu, Chun-Hui; Li, Shun-Li; Wang, Yu-Guang; Dong, Long-Zhang; Dai, Zhi-Hui; Li, Ya-Fei; Lan, Ya-Qian

2016-04-01

Electrochemical water splitting is one of the most economical and sustainable methods for large-scale hydrogen production. However, the development of low-cost and earth-abundant non-noble-metal catalysts for the hydrogen evolution reaction remains a challenge. Here we report a two-dimensional coupled hybrid of molybdenum carbide and reduced graphene oxide with a ternary polyoxometalate-polypyrrole/reduced graphene oxide nanocomposite as a precursor. The hybrid exhibits outstanding electrocatalytic activity for the hydrogen evolution reaction and excellent stability in acidic media, which is, to the best of our knowledge, the best among these reported non-noble-metal catalysts. Theoretical calculations on the basis of density functional theory reveal that the active sites for hydrogen evolution stem from the pyridinic nitrogens, as well as the carbon atoms, in the graphene. In a proof-of-concept trial, an electrocatalyst for hydrogen evolution is fabricated, which may open new avenues for the design of nanomaterials utilizing POMs/conducting polymer/reduced-graphene oxide nanocomposites.

Coupled molybdenum carbide and reduced graphene oxide electrocatalysts for efficient hydrogen evolution

NASA Astrophysics Data System (ADS)

Li, Ji-Sen; Wang, Yu; Liu, Chun-Hui; Li, Shun-Li; Wang, Yu-Guang; Dong, Long-Zhang; Dai, Zhi-Hui; Li, Ya-Fei; Lan, Ya-Qian

2016-04-01

Electrochemical water splitting is one of the most economical and sustainable methods for large-scale hydrogen production. However, the development of low-cost and earth-abundant non-noble-metal catalysts for the hydrogen evolution reaction remains a challenge. Here we report a two-dimensional coupled hybrid of molybdenum carbide and reduced graphene oxide with a ternary polyoxometalate-polypyrrole/reduced graphene oxide nanocomposite as a precursor. The hybrid exhibits outstanding electrocatalytic activity for the hydrogen evolution reaction and excellent stability in acidic media, which is, to the best of our knowledge, the best among these reported non-noble-metal catalysts. Theoretical calculations on the basis of density functional theory reveal that the active sites for hydrogen evolution stem from the pyridinic nitrogens, as well as the carbon atoms, in the graphene. In a proof-of-concept trial, an electrocatalyst for hydrogen evolution is fabricated, which may open new avenues for the design of nanomaterials utilizing POMs/conducting polymer/reduced-graphene oxide nanocomposites.

The effect of urea on microstructures of Ni{sub 3}S{sub 2} on nickel foam and its hydrogen evolution reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jinlong, Lv, E-mail: ljltsinghua@126.com; State Key Lab of New Ceramic and Fine Processing, Tsinghua University, Beijing 100084; Tongxiang, Liang, E-mail: txliang@mail.tsinghua.edu.cn

The effects of urea concentration on microstructures of Ni{sub 3}S{sub 2}formed on nickel foam and its hydrogen evolution reaction were investigated. The Ni{sub 3}S{sub 2} nanosheets with porous structure were formed on nickel foam during hydrothermal process due to low urea concentration. While high urea concentration facilitated the forming of Ni{sub 3}S{sub 2} nanotube arrays. The resulting Ni{sub 3}S{sub 2} nanotube arrays exhibited higher catalytic activity than Ni3S2nanosheets for hydrogen evolution reaction. This was mainly attributed to a fact that Ni{sub 3}S{sub 2} nanotube arrays facilitated diffusion of electrolyte for hydrogen evolution reaction. - Graphical abstract: The resulting Ni{sub 3}S{submore » 2} nanotube arrays exhibited higher catalytic activity than Ni{sub 3}S{sub 2} nanosheets for hydrogen evolution reaction. This was mainly attributed to a fact that Ni{sub 3}S{sub 2} nanotube arrays facilitated diffusion of electrolyte for hydrogen evolution reaction and hydrogen evolution. - Highlights: • Urea promoted to forming more Ni{sub 3}S{sub 2} nanotube arrays on nickel foam. • Ni{sub 3}S{sub 2} nanotube arrays showed higher catalytic activity in alkaline solution. • Ni{sub 3}S{sub 2} nanotube arrays promoted electron transport and reaction during the HER.« less

Hydrogen storage and evolution catalysed by metal hydride complexes.

PubMed

Fukuzumi, Shunichi; Suenobu, Tomoyoshi

2013-01-07

The storage and evolution of hydrogen are catalysed by appropriate metal hydride complexes. Hydrogenation of carbon dioxide by hydrogen is catalysed by a [C,N] cyclometalated organoiridium complex, [Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))benzoic acid-κC(3))(OH(2))](2)SO(4) [Ir-OH(2)](2)SO(4), under atmospheric pressure of H(2) and CO(2) in weakly basic water (pH 7.5) at room temperature. The reverse reaction, i.e., hydrogen evolution from formate, is also catalysed by [Ir-OH(2)](+) in acidic water (pH 2.8) at room temperature. Thus, interconversion between hydrogen and formic acid in water at ambient temperature and pressure has been achieved by using [Ir-OH(2)](+) as an efficient catalyst in both directions depending on pH. The Ir complex [Ir-OH(2)](+) also catalyses regioselective hydrogenation of the oxidised form of β-nicotinamide adenine dinucleotide (NAD(+)) to produce the 1,4-reduced form (NADH) under atmospheric pressure of H(2) at room temperature in weakly basic water. In weakly acidic water, the complex [Ir-OH(2)](+) also catalyses the reverse reaction, i.e., hydrogen evolution from NADH to produce NAD(+) at room temperature. Thus, interconversion between NADH (and H(+)) and NAD(+) (and H(2)) has also been achieved by using [Ir-OH(2)](+) as an efficient catalyst and by changing pH. The iridium hydride complex formed by the reduction of [Ir-OH(2)](+) by H(2) and NADH is responsible for the hydrogen evolution. Photoirradiation (λ > 330 nm) of an aqueous solution of the Ir-hydride complex produced by the reduction of [Ir-OH(2)](+) with alcohols resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir-hydride complex, which can catalyse hydrogen evolution from alcohols in a basic aqueous solution (pH 11.9). The catalytic mechanisms of the hydrogen storage and evolution are discussed by focusing on the reactivity of Ir-hydride complexes.

Corrosion rate estimations of microscale zerovalent iron particles via direct hydrogen production measurements.

PubMed

Velimirovic, Milica; Carniato, Luca; Simons, Queenie; Schoups, Gerrit; Seuntjens, Piet; Bastiaens, Leen

2014-04-15

In this study, the aging behavior of microscale zerovalent iron (mZVI) particles was investigated by quantifying the hydrogen gas generated by anaerobic mZVI corrosion in batch degradation experiments. Granular iron and nanoscale zerovalent iron (nZVI) particles were included in this study as controls. Firstly, experiments in liquid medium (without aquifer material) were performed and revealed that mZVI particles have approximately a 10-30 times lower corrosion rate than nZVI particles. A good correlation was found between surface area normalized corrosion rate (RSA) and reaction rate constants (kSA) of PCE, TCE, cDCE and 1,1,1-TCA. Generally, particles with higher degradation rates also have faster corrosion rates, but exceptions do exists. In a second phase, the hydrogen evolution was also monitored during batch tests in the presence of aquifer material and real groundwater. A 4-9 times higher corrosion rate of mZVI particles was observed under the natural environment in comparison with the aquifer free artificial condition, which can be attributed to the low pH of the aquifer and its buffer capacity. A corrosion model was calibrated on the batch experiments to take into account the inhibitory effects of the corrosion products (dissolved iron, hydrogen and OH(-)) on the iron corrosion rate. Copyright © 2014 Elsevier B.V. All rights reserved.

Amorphous MoS{sub x} on CdS nanorods for highly efficient photocatalytic hydrogen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaofang; Tang, Chaowan; Zheng, Qun

Loading cocatalyst on semiconductors was crucially necessary for improving the photocatalytic hydrogen evolution. Amorphous MoS{sub x} as a novel and noble metal-free cocatalyst was loaded on CdS nanorods by a simple photodeposition method. Efficient hydrogen evolution with amount of 15 mmol h{sup −1} g{sup −1} was observed over the MoS{sub x} modified CdS nanorods, which was about 6 times higher than that by using Pt as cocatalyst. Meanwhile, with MoS{sub x} cocatalyst, the efficiency of CdS nanorods was superior to that of CdS nanoparticles and bulk CdS. No deactivation could be observed in the efficiency of MoS{sub x} modified CdSmore » nanorods under irradiation for successive 10 h. Further experimental results indicated that the efficient electrons transfer, low overpotential of hydrogen evolution and active S atoms over the MoS{sub x} modified CdS nanorods were responsible for the higher efficiency. Our results provided guidance for synthesizing noble metal-free materials as cocatalyst for photocatalytic hydrogen evolution. - Graphical abstract: Photodeposition of amorphous MoS{sub x} on CdS nanorods for highly efficient photocatalytic hydrogen evolution. - Highlights: • Amorphous MoSx cocatalyst was loaded on CdS NRs by a simple photodeposition. • MoS{sub x}/CdS NRs exhibited 6 times higher hydrogen evolution efficiency than Pt/CdS NRs. • The hydrogen evolution of MoS{sub x}/CdS NRs linearly increased with prolonging time. • Lower overpotential and efficient electron transfer were observed over MoS{sub x}/CdS NRs.« less

Nickel centred H+ reduction catalysis in a model of [NiFe] Hydrogenase

PubMed Central

Brazzolotto, Deborah; Gennari, Marcello; Queyriaux, Nicolas; Simmons, Trevor R.; Pécaut, Jacques; Demeshko, Serhiy; Meyer, Franc; Orio, Maylis; Artero, Vincent; Duboc, Carole

2017-01-01

Hydrogen production through water splitting is one of the most promising solutions for the storage of renewable energy. [NiFe] hydrogenases are organometallic enzymes containing nickel and iron centers that catalyze hydrogen evolution with performances that rival those of platinum. These enzymes provide inspiration for the design of new molecular catalysts that do not require precious metals. However, all heterodinuclear NiFe models reported so far do not reproduce the Ni-centered reactivity found at the active site of [NiFe] hydrogenases. Here we report a structural and functional NiFe mimic that displays reactivity at the Ni site. This is shown by the detection of two catalytic intermediates that reproduce structural and electronic features of the Ni-L and Ni-R states of the enzyme during catalytic turnover. Under electrocatalytic conditions, this mimic displays high rates for H2 evolution (second order rate constant of 2.5 104 M-1s-1; turnover frequency of 225 s-1 at 10 mM H+ concentration) from mildly acidic solutions. PMID:27768098

Probing the Surface of Platinum during the Hydrogen Evolution Reaction in Alkaline Electrolyte

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoerzinger, Kelsey A.; Favaro, Marco; Ross, Philip N.

Understanding the surface chemistry of electrocatalysts in operando can bring insight into the reaction mechanism, and ultimately the design of more efficient materials for sustainable energy storage and conversion. Recent progress in synchrotron based X-ray spectroscopies for in operando characterization allows us to probe the solid/liquid interface directly while applying an external potential, applied here to the model system of Pt in alkaline electrolyte for the hydrogen evolution reaction (HER). We employ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to identify the oxidation and reduction of Pt-oxides and hydroxides on the surface as a function of applied potential, and further assessmore » the potential for hydrogen adsorption and absorption (hydride formation) during and after the HER. This new window into the surface chemistry of Pt in alkaline brings insight into the nature of the rate limiting step, the extent of H ad/absorption and it’s persistence at more anodic potentials.« less

Hierarchical Heterostructure of ZnO@TiO2 Hollow Spheres for Highly Efficient Photocatalytic Hydrogen Evolution

NASA Astrophysics Data System (ADS)

Li, Yue; Wang, Longlu; Liang, Jian; Gao, Fengxian; Yin, Kai; Dai, Pei

2017-09-01

The rational design and preparation of hierarchical nanoarchitectures are critical for enhanced photocatalytic hydrogen evolution reaction (HER). Herein, well-integrated hollow ZnO@TiO2 heterojunctions were obtained by a simple hydrothermal method. This unique hierarchical heterostructure not only caused multiple reflections which enhances the light absorption but also improved the lifetime and transfer of photogenerated charge carriers due to the potential difference generated on the ZnO-TiO2 interface. As a result, compared to bare ZnO and TiO2, the ZnO@TiO2 composite photocatalyst exhibited higher hydrogen production rated up to 0.152 mmol h-1 g-1 under simulated solar light. In addition, highly repeated photostability was also observed on the ZnO@TiO2 composite photocatalyst even after a continuous test for 30 h. It is expected that this low-cost, nontoxic, and readily available ZnO@TiO2 catalyst could exhibit promising potential in photocatalytic H2 to meet the future fuel needs.

Revisited reaction-diffusion model of thermal desorption spectroscopy experiments on hydrogen retention in material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guterl, Jerome, E-mail: jguterl@ucsd.edu; Smirnov, R. D.; Krasheninnikov, S. I.

Desorption phase of thermal desorption spectroscopy (TDS) experiments performed on tungsten samples exposed to flux of hydrogen isotopes in fusion relevant conditions is analyzed using a reaction-diffusion model describing hydrogen retention in material bulk. Two regimes of hydrogen desorption are identified depending on whether hydrogen trapping rate is faster than hydrogen diffusion rate in material during TDS experiments. In both regimes, a majority of hydrogen released from material defects is immediately outgassed instead of diffusing deeply in material bulk when the evolution of hydrogen concentration in material is quasi-static, which is the case during TDS experiments performed with tungsten samplesmore » exposed to flux of hydrogen isotopes in fusion related conditions. In this context, analytical expressions of the hydrogen outgassing flux as a function of the material temperature are obtained with sufficient accuracy to describe main features of thermal desorption spectra (TDSP). These expressions are then used to highlight how characteristic temperatures of TDSP depend on hydrogen retention parameters, such as trap concentration or activation energy of detrapping processes. The use of Arrhenius plots to characterize retention processes is then revisited when hydrogen trapping takes place during TDS experiments. Retention processes are also characterized using the shape of desorption peaks in TDSP, and it is shown that diffusion of hydrogen in material during TDS experiment can induce long desorption tails visible aside desorption peaks at high temperature in TDSP. These desorption tails can be used to estimate activation energy of diffusion of hydrogen in material.« less

Porphyrin-Sensitized Evolution of Hydrogen using Dawson and Keplerate Polyoxometalate Photocatalysts.

PubMed

Panagiotopoulos, Athanassios; Douvas, Antonios M; Argitis, Panagiotis; Coutsolelos, Athanassios G

2016-11-23

Hydrogen evolution using photocatalytic systems based on artificial photosynthesis is a major approach toward solar energy conversion and storage. In the polyoxometalate-based photocatalytic systems proposed in the past, middle/near UV light irradiation and noble-metal catalysts were mainly used. Although recently polyoxometalates were sensitized in visible light, photosensitizers or catalysts based on noble metals, and/or poor activity of polyoxometalates were generally obtained. Here we show the highly efficient [turnover number (TON)=215] hydrogen evolution induced by the zinc(II) mesotetrakis(N-methyl-pyridinium-4-yl)porphyrin (ZnTMPyP 4+ ) sensitization of a series of polyoxometalate catalysts (two Dawson type, P 2 Mo 18 O 62 6- and P 2 W 18 O 62 6- anions, and one Keplerate {Mo 132 } cluster) in a visible-light-driven, noble-metal-free, and fully water-soluble system. We attributed the high efficiency for hydrogen evolution to the multi-electron reduction of polyoxometalates and found that: (a) both Dawson polyoxometalates exhibit higher hydrogen evolution efficiency upon ZnTMPyP 4+ sensitization in relation to the direct photoreduction of those compounds; (b) the P 2 Mo 18 O 62 6- anion is more efficient (TON=65 vs. 38, respectively) for hydrogen evolution than the P 2 W 18 O 62 6- anion; and (c) the high nuclearity Keplerate {Mo 132 } cluster exhibits the highest efficiency (TON=215) for hydrogen evolution compared with the polyoxometalates studied. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of Light/Dark Regimens on Hydrogen Production by Tetraselmis subcordiformis Coupled with an Alkaline Fuel Cell System.

PubMed

Guo, Zhen; Li, Ying; Guo, Haiyan

2017-12-01

To improve the photoproduction of hydrogen (H 2 ) by a green algae-based system, the effect of light/dark regimens on H 2 photoproduction regulated by carbonyl cyanide m-chlorophenylhydrazone (CCCP) was investigated. A fuel cell was integrated into a photobioreactor to allow online monitoring of the H 2 evolution rate and decrease potential H 2 feedback inhibition by consuming the generated H 2 in situ. During the first 15 h of H 2 evolution, the system was subjected to dark treatment after initial light illumination (L/D = 6/9 h, 9/6 h, and 12/3 h). After the dark period, all systems were again exposed to light illumination until H 2 evolution stopped. Two peaks were observed in the H 2 evolution rate under all three light/dark regimens. Additionally, a high H 2 yield of 126 ± 10 mL L -1 was achieved using a light/dark regimen of L 9 h/D 6 h/L until H 2 production ceased, which was 1.6 times higher than that obtained under continuous illumination. H 2 production was accompanied by some physiological and morphological changes in the cells. The results indicated that light/dark regimens improved the duration and yield of H 2 photoproduction by the CCCP-regulated process of Tetraselmis subcordiformis.

Characterization and evaluation of cadmium indate photocatalysts for solar hydrogen conversion

NASA Astrophysics Data System (ADS)

Thornton, Jason M.

Alternative energy sources are needed to respond to the continued increase in the global energy needs and a potential decrease in the future supplies of fossil fuels. Solar hydrogen conversion in which sunlight is harnessed to split water into H2 fuel and O2 is a promising source of energy because it is renewable and produces no CO2. A number of semiconducting oxide materials have shown promise for overall water splitting for the generation of hydrogen over the years. In this work we focus on the synthesis and analysis of undoped and C-doped cadmium indate (CdIn2O 4) thin films and nanoparticle powders, and their evaluation for hydrogen evolution via water splitting. The catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis, scanning electron microscopy (SEM), and BET surface adsorption measurements. Spray and sol-gel pyrolysis methods were used for the synthesis of the materials. Doping C into CdIn 2O4 leads to enhancement in light absorption and the band gap was determined to be 2.3 eV in the nanoparticle powders. Carbon doping improves the photocurrent density by 33% and the H2 evolution rate by a factor of two. The performance of C-doped CdIn2O4 were optimized with respect to several synthetic parameters, including the In:Cd molar ratio and glucose concentration, calcination temperature, and the film thickness while the nanoparticles were additionally optimized to F127 concentration and platinum cocatalyst loading. Hydrogen generation activity was evaluated under UV-visible irradiation without the use of a sacrificial reagent and using bandpass filters the quantum efficiency was determined. Compared to platinized TiO2 in methanol C-CdIn2O4 showed a 4-fold increase in hydrogen production. The material was capable of hydrogen generation using visible light only and with good efficiency even at 510 nm. Using natural sunlight illumination, the material evolved hydrogen at a rate of 17 micromol h-1. These studies show carbon-doped cadmium indate to be a promising catalyst for solar hydrogen conversion.

Dynamic evolution of the spectrum of long-period fiber Bragg gratings fabricated from hydrogen-loaded optical fiber by ultraviolet laser irradiation.

PubMed

Fujita, Keio; Masuda, Yuji; Nakayama, Keisuke; Ando, Maki; Sakamoto, Kenji; Mohri, Jun-pei; Yamauchi, Makoto; Kimura, Masanori; Mizutani, Yasuo; Kimura, Susumu; Yokouchi, Takashi; Suzaki, Yoshifumi; Ejima, Seiki

2005-11-20

Long-period fiber Bragg gratings fabricated by exposure of hydrogen-loaded fiber to UV laser light exhibit large-scale dynamic evolution for approximately two weeks at room temperature. During this time two distinct features show up in their spectrum: a large upswing in wavelength and a substantial deepening of the transmission minimum. The dynamic evolution of the transmission spectrum is explained quantitatively by use of Malo's theory of UV-induced quenching [Electron. Lett. 30, 442 (1994)] followed by refilling of hydrogen in the fiber core and the theory of hydrogen diffusion in the fiber material. The amount of hydrogen quenched by the UV irradiation is 6% of the loaded hydrogen.

Synthesis of hydrogen-carbon clathrate material and hydrogen evolution therefrom at moderate temperatures and pressures

DOEpatents

Lueking, Angela [State College, PA; Narayanan, Deepa [Redmond, WA

2011-03-08

A process for making a hydrogenated carbon material is provided which includes forming a mixture of a carbon source, particularly a carbonaceous material, and a hydrogen source. The mixture is reacted under reaction conditions such that hydrogen is generated and/or released from the hydrogen source, an amorphous diamond-like carbon is formed, and at least a portion of the generated and/or released hydrogen associates with the amorphous diamond-like carbon, thereby forming a hydrogenated carbon material. A hydrogenated carbon material including a hydrogen carbon clathrate is characterized by evolution of molecular hydrogen at room temperature at atmospheric pressure in particular embodiments of methods and compositions according to the present invention.

An advanced Ni-Cd battery cell design

NASA Technical Reports Server (NTRS)

Miller, L.

1986-01-01

The evolution of an advanced Ni-Cd space battery cell design continues to prove very promising. High oxygen/hydrogen gas recombination rates (currently up to a C/5 charge rate) and increased electrolyte activation level tolerance (currently up to 5.6 grams Ah of positive capacity) were demonstrated by test. A superior performance, extended life battery cell offering advantages should soon be available for mission applications

Carbon nanotubes-modified graphitic carbon nitride photocatalysts with synergistic effect of nickel(II) sulfide and molybdenum(II) disulfide co-catalysts for more efficient H2 evolution.

PubMed

Zhang, Yun-Xiao; Li, Kui; Yu, Yu-Xiang; Zhang, Wei-De

2018-09-15

This work reports effective photocatalysts which are composed of carbon nitride (CN), carbon nanotubes (CNTs), MoS 2 and NiS, for hydrogen evolution aiming at energy crises and environmental pollutions. The morphologies and optical properties of the photocatalysts were carefully characterized and their photocatalytic performance towards water reduction was studied afterwards. MoS 2 and NiS exhibit a significant synergistic effect working as co-catalysts. Compared to MoS 2 /CN nanohybrid, carbon nanotubes and NiS improved the absorption of visible light and the separation of charge carriers effectively. NiS-MoS 2 /CNTs/CN catalyst exhibits high performance for H 2 evolution and the optimized rate is 309.9 μmol·h -1 ·g -1 with no noble metals under visible light irradiation. The study demonstrates a non-noble metal photocatalyst system for effective generation of hydrogen with low cost. Copyright © 2018 Elsevier Inc. All rights reserved.

Hydrogen Peroxide - Material Compatibility Studied by Microcalorimetry

NASA Technical Reports Server (NTRS)

Homung, Steven D.; Davis, Dennis D.; Baker, David; Popp, Christopher G.

2003-01-01

Environmental and toxicity concerns with current hypergolic propellants have led to a renewed interest in propellant grade hydrogen peroxide (HP) for propellant applications. Storability and stability has always been an issue with HP. Contamination or contact of HP with metallic surfaces may cause decomposition, which can result in the evolution of heat and gas leading to increased pressure or thermal hazards. The NASA Johnson Space Center White Sands Test Facility has developed a technique to monitor the decompositions of hydrogen peroxide at temperatures ranging from 25 to 60 C. Using isothermal microcalorimetry we have measured decomposition rates at the picomole/s/g level showing the catalytic effects of materials of construction. In this paper we will present the results of testing with Class 1 and 2 materials in 90 percent hydrogen peroxide.

Galacti chemical evolution: Hygrogen through zinc

NASA Technical Reports Server (NTRS)

Timmes, F. X.; Woosley, S. E.; Weaver, Thomas A.

1995-01-01

Using the output from a grid of 60 Type II supernova models (Woosley & Weaver 1995) of varying mass (11 approx. less than (M/solar mass) approx. less than 40) and metallicity (0, 10(exp -4), 0.01, and 1 solar metallicity), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 Gyr e-folding timescale onto a exponential dsk and 1/r(exp 2) bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 approx. less than (Fe/H) approx. less than 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernova rates, an intrinsically Galactic quality, are also discussed.

The effect of grain size on aluminum anodes for Al-air batteries in alkaline electrolytes

NASA Astrophysics Data System (ADS)

Fan, Liang; Lu, Huimin

2015-06-01

Aluminum is an ideal material for metallic fuel cells. In this research, different grain sizes of aluminum anodes are prepared by equal channel angular pressing (ECAP) at room temperature. Microstructure of the anodes is examined by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Hydrogen corrosion rates of the Al anodes in 4 mol L-1 NaOH are determined by hydrogen collection method. The electrochemical properties of the aluminum anodes are investigated in the same electrolyte using electrochemical impedance spectroscopy (EIS) and polarization curves. Battery performance is also tested by constant current discharge at different current densities. Results confirm that the electrochemical properties of the aluminum anodes are related to grain size. Finer grain size anode restrains hydrogen evolution, improves electrochemical activity and increases anodic utilization rate. The proposed method is shown to effectively improve the performance of Al-air batteries.

Capture of liquid hydrogen boiloff with metal hydride absorbers

NASA Technical Reports Server (NTRS)

Rosso, M. J.; Golben, P. M.

1984-01-01

A procedure which uses metal hydrides to capture some of this low pressure (,1 psig) hydrogen for subsequent reliquefaction is described. Of the five normally occurring sources of boil-off vapor the stream associated with the off-loading of liquid tankers during dewar refill was identified as the most cost effective and readily recoverable. The design, fabrication and testing of a proof-of-concept capture device, operating at a rate that is commensurate with the evolution of vapor by the target stream, is described. Liberation of the captured hydrogen gas at pressure .15 psig at normal temperatures (typical liquefier compressor suction pressure) are also demonstrated. A payback time of less than three years is projected.

Ni-C-N Nanosheets as Catalyst for Hydrogen Evolution Reaction.

PubMed

Yin, Jie; Fan, Qiaohui; Li, Yuxuan; Cheng, Fangyi; Zhou, Panpan; Xi, Pinxian; Sun, Shouheng

2016-11-09

We report a facile nitrogenation/exfoliation process to prepare hybrid Ni-C-N nanosheets. These nanosheets are <2 nm thin, chemically stable, and metallically conductive. They serve as a robust catalyst for the hydrogen evolution reaction in 0.5 M H 2 SO 4 , or 1.0 M KOH or 1.0 M PBS (pH = 7). For example, they catalyze the hydrogen evolution reaction in 0.5 M H 2 SO 4 at an onset potential of 34.7 mV, an overpotential of 60.9 mV (at j = 10 mA cm -2 ) and with remarkable long-term stability (∼10% current drop after 70 h testing period). They are promising as a non-Pt catalyst for practical hydrogen evolution reaction.

Chemical looping of metal nitride catalysts: low-pressure ammonia synthesis for energy storage† †Electronic supplementary information (ESI) available: Experimental and computational details, free energy plots for the NH3 evolution and N2 reduction with Co3N/Co, Fe4N/Fe, Mn5N2/Mn4N, Mo2N/Mo, CrN/Cr2N, TaN/Ta2N, NbN/Nb2N, Li3N/LiH, Ba3N2/BaH2, Sr3N2/SrH2, and Ca3N2/CaH2, surface oxidation energetics, ΔGvac[NH*x, yH*] based on gas phase H2 as hydrogen source, NH3 evolution with Fe-doped Mn4N, NH3 evolution with Mn6N2.58, Ca3N2 and Sr2N after correcting for partial nitride hydrolysis, NH3 yield from Ca3N2vs. time and H2 gas flow rate. See DOI: 10.1039/c5sc00789e

PubMed Central

Avram, A. M.; Peterson, B. A.; Pfromm, P. H.; Peterson, A. A.

2015-01-01

The activity of many heterogeneous catalysts is limited by strong correlations between activation energies and adsorption energies of reaction intermediates. Although the reaction is thermodynamically favourable at ambient temperature and pressure, the catalytic synthesis of ammonia (NH3), a fertilizer and chemical fuel, from N2 and H2 requires some of the most extreme conditions of the chemical industry. We demonstrate how ammonia can be produced at ambient pressure from air, water, and concentrated sunlight as renewable source of process heat via nitrogen reduction with a looped metal nitride, followed by separate hydrogenation of the lattice nitrogen into ammonia. Separating ammonia synthesis into two reaction steps introduces an additional degree of freedom when designing catalysts with desirable activation and adsorption energies. We discuss the hydrogenation of alkali and alkaline earth metal nitrides and the reduction of transition metal nitrides to outline a promoting role of lattice hydrogen in ammonia evolution. This is rationalized via electronic structure calculations with the activity of nitrogen vacancies controlling the redox-intercalation of hydrogen and the formation and hydrogenation of adsorbed nitrogen species. The predicted trends are confirmed experimentally with evolution of 56.3, 80.7, and 128 μmol NH3 per mol metal per min at 1 bar and above 550 °C via reduction of Mn6N2.58 to Mn4N and hydrogenation of Ca3N2 and Sr2N to Ca2NH and SrH2, respectively. PMID:29218166

Dual organism design cycle reveals small subunit substitutions that improve [NiFe] hydrogenase hydrogen evolution.

PubMed

Yonemoto, Isaac T; Matteri, Christopher W; Nguyen, Thao Amy; Smith, Hamilton O; Weyman, Philip D

2013-07-02

Photosynthetic microorganisms that directly channel solar energy to the production of molecular hydrogen are a potential future biofuel system. Building such a system requires installation of a hydrogenase in the photosynthetic organism that is both tolerant to oxygen and capable of hydrogen production. Toward this end, we have identified the [NiFe] hydrogenase from the marine bacterium Alteromonas macleodii "Deep ecotype" that is able to be heterologously expressed in cyanobacteria and has tolerance to partial oxygen. The A. macleodii enzyme shares sequence similarity with the uptake hydrogenases that favor hydrogen uptake activity over hydrogen evolution. To improve hydrogen evolution from the A. macleodii hydrogenase, we examined the three Fe-S clusters found in the small subunit of many [NiFe] uptake hydrogenases that presumably act as a molecular wire to guide electrons to or from the active site of the enzyme. Studies by others altering the medial cluster of a Desulfovibrio fructosovorans hydrogenase from 3Fe-4S to 4Fe-4S resulted in two-fold improved hydrogen evolution activity. We adopted a strategy of screening for improved hydrogenase constructs using an Escherichia coli expression system before testing in slower growing cyanobacteria. From the A. macleodii enzyme, we created a mutation in the gene encoding the hydrogenase small subunit that in other systems is known to convert the 3Fe-4S medial cluster to 4Fe-4S. The medial cluster substitution did not improve the hydrogen evolution activity of our hydrogenase. However, modifying both the medial cluster and the ligation of the distal Fe-S cluster improved in vitro hydrogen evolution activity relative to the wild type hydrogenase by three- to four-fold. Other properties of the enzyme including thermostability and tolerance to partial oxygen did not appear to be affected by the substitutions. Our results show that substitution of amino acids altering the ligation of Fe-S clusters in the A. macleodii [NiFe] uptake hydrogenase resulted in increased hydrogen evolution activity. This activity can be recapitulated in multiple host systems and with purified protein. These results validate the approach of using an E. coli-cyanobacteria shuttle system for enzyme expression and improvement.

Prereduction of Metal Oxides via Carbon Plasma Treatment for Efficient and Stable Electrocatalytic Hydrogen Evolution.

PubMed

Zhang, Yongqi; Ouyang, Bo; Xu, Kun; Xia, Xinhui; Zhang, Zheng; Rawat, Rajdeep Singh; Fan, Hong Jin

2018-04-01

Prereduction of transition metal oxides is a feasible and efficient strategy to enhance their catalytic activity for hydrogen evolution. Unfortunately, the prereduction via the common H 2 annealing method is unstable for nanomaterials during the hydrogen evolution process. Here, using NiMoO 4 nanowire arrays as the example, it is demonstrated that carbon plasma (C-plasma) treatment can greatly enhance both the catalytic activity and the long-term stability of transition metal oxides for hydrogen evolution. The C-plasma treatment has two functions at the same time: it induces partial surface reduction of the NiMoO 4 nanowire to form Ni 4 Mo nanoclusters, and simultaneously deposits a thin graphitic carbon shell. As a result, the C-plasma treated NiMoO 4 can maintain its array morphology, chemical composition, and catalytic activity during long-term intermittent hydrogen evolution process. This work may pave a new way for simultaneous activation and stabilization of transition metal oxide-based electrocatalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fragmentation during primordial star formation

NASA Astrophysics Data System (ADS)

Dutta, Jayanta

Understanding the physics of the very first stars in the universe, the so-called Population III (or Pop III) stars, is crucial in determining how the universe evolved into what we observe today. In the standard model of Pop III star formation, the baryonic matter, mainly atomic hydrogen, collapses gravitationally into small Dark Matter (DM) minihalos. However, so far there is little understanding on how the thermal, dynamical and chemical evolution of the primordial gas depend on the initial configuration of the minihalos (for example, rotation of the unstable clumps inside minihalos, turbulence, formation of molecular hydrogen and cosmic variance of the minihalos). We use the modified version of the Gadget-2 code, a three-dimensional smoothed particle hydrodynamics (SPH) simulations, to follow the evolution of the collapsing gas in both idealized as well as more realistic minihalos. Unlike some earlier cosmological calculations, the implementation of sink particles allows us to follow the evolution of the accretion disk that builds up in the centre of each minihalo and fragments. We find that the fragmentation behavior depends on the adopted choice of three-body H2 formation rate coefficient. The increasing cooling rate during rapid conversion of the atomic to molecular hydrogen is offset by the heating due to gas contraction. We propose that the H2 cooling, the heating due to H2 formation and compressional heating together set a density and temperature structure in the disk that favors fragmentation. We also find that the cloud's initial degree of rotation has a significant effect on the thermal and dynamical evolution of the collapsing gas. Clouds with higher rotation exhibit spiral-arm-like structures that become gravitationally unstable to fragmentation on several scales. These type of clouds tend to fragment more and have lower accretion rates compared to their slowly rotating counterparts. In addition, we find that the distribution of specific angular momentum (L) of the gas follows a power-law relation with the enclosed gas mass (M), L ∝ M1.125, which is controlled by the gravitational and pressure torque, and does not depend on the cloud's initial degree of rotation and turbulence.

Nickel-silver alloy electrocatalysts for hydrogen evolution and oxidation in an alkaline electrolyte.

PubMed

Tang, Maureen H; Hahn, Christopher; Klobuchar, Aidan J; Ng, Jia Wei Desmond; Wellendorff, Jess; Bligaard, Thomas; Jaramillo, Thomas F

2014-09-28

The development of improved catalysts for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in basic electrolytes remains a major technical obstacle to improved fuel cells, water electrolyzers, and other devices for electrochemical energy storage and conversion. Based on the free energy of adsorbed hydrogen intermediates, theory predicts that alloys of nickel and silver are active for these reactions. In this work, we synthesize binary nickel-silver bulk alloys across a range of compositions and show that nickel-silver alloys are indeed more active than pure nickel for hydrogen evolution and, possibly, hydrogen oxidation. To overcome the mutual insolubility of silver and nickel, we employ electron-beam physical vapor codeposition, a low-temperature synthetic route to metastable alloys. This method also produces flat and uniform films that facilitate the measurement of intrinsic catalytic activity with minimal variations in the surface area, ohmic contact, and pore transport. Rotating-disk-electrode measurements demonstrate that the hydrogen evolution activity per geometric area of the most active catalyst in this study, Ni0.75Ag0.25, is approximately twice that of pure nickel and has comparable stability and hydrogen oxidation activity. Our experimental results are supported by density functional theory calculations, which show that bulk alloying of Ni and Ag creates a variety of adsorption sites, some of which have near-optimal hydrogen binding energy.

3D ordered porous MoxC (x = 1 or 2) for advanced hydrogen evolution and Li storage.

PubMed

Yu, Hong; Fan, Haosen; Wang, Jiong; Zheng, Yun; Dai, Zhengfei; Lu, Yizhong; Kong, Junhua; Wang, Xin; Kim, Young Jin; Yan, Qingyu; Lee, Jong-Min

2017-06-01

3D ordered porous structures of Mo x C are prepared with different Mo to C ratios and tested for two possible promising applications: hydrogen evolution reaction (HER) through water splitting and lithium ion batteries (LIBs). Mo 2 C and MoC with 3D periodic ordered structures are prepared with a similar process but different precursors. The 3D ordered porous MoC exhibits excellent cycling stability and rate performance as an anode material for LIBs. A discharge capacity of 450.9 mA h g -1 is maintained up to 3000 cycles at 10.0 A g -1 . The Mo 2 C with a similar ordered porous structure shows impressive electrocatalytic activity for the HER in neutral, alkaline and acidic pH solutions. In particular, Mo 2 C shows an onset potential of only 33 mV versus a reversible hydrogen electrode (RHE) and a Tafel slope of 42.5 mV dec -1 in a neutral aqueous solution (1.0 M phosphate buffer solution), which is approaching that of the commercial Pt/C catalyst.

Exploring Hydrogen Evolution and the Overpotential

ERIC Educational Resources Information Center

Lyon, Yana A.; Roberts, Adrienne A.; McMillin, David R.

2015-01-01

The laboratory experiment described provides insight into the energetics of hydrogen evolution at an electrode as well as the intrinsic barrier that typically impedes reaction. In the course of the exercise, students find that Sn(s) is thermodynamically capable of combining with protons to form hydrogen, but that the direct reaction occurs at a…

Nickel-centred proton reduction catalysis in a model of [NiFe] hydrogenase

NASA Astrophysics Data System (ADS)

Brazzolotto, Deborah; Gennari, Marcello; Queyriaux, Nicolas; Simmons, Trevor R.; Pécaut, Jacques; Demeshko, Serhiy; Meyer, Franc; Orio, Maylis; Artero, Vincent; Duboc, Carole

2016-11-01

Hydrogen production through water splitting is one of the most promising solutions for the storage of renewable energy. [NiFe] hydrogenases are organometallic enzymes containing nickel and iron centres that catalyse hydrogen evolution with performances that rival those of platinum. These enzymes provide inspiration for the design of new molecular catalysts that do not require precious metals. However, all heterodinuclear NiFe models reported so far do not reproduce the Ni-centred reactivity found at the active site of [NiFe] hydrogenases. Here, we report a structural and functional NiFe mimic that displays reactivity at the Ni site. This is shown by the detection of two catalytic intermediates that reproduce structural and electronic features of the Ni-L and Ni-R states of the enzyme during catalytic turnover. Under electrocatalytic conditions, this mimic displays high rates for H2 evolution (second-order rate constant of 2.5 × 104 M-1 s-1 turnover frequency of 250 s-1 at 10 mM H+ concentration) from mildly acidic solutions.

Bubble Transport through Micropillar Arrays

NASA Astrophysics Data System (ADS)

Lee, Kenneth; Savas, Omer

2012-11-01

In current energy research, artificial photosynthetic devices are being designed to split water and harvest hydrogen gas using energy from the sun. In one such design, hydrogen gas bubbles evolve on the catalytic surfaces of arrayed micropillars. If these bubbles are not promptly removed from the surface, they can adversely affect gas evolution rates, water flow rates, sunlight capture, and heat management of the system. Therefore, an efficient method of collecting the evolved gas bubbles is crucial. Preliminary flow visualization has been conducted of bubbles advecting through dense arrays of pillars. Bubbles moving through square and hexagonal arrays are tracked, and the results are qualitatively described. Initial attempts to correlate bubble motion with relevant lengthscales and forces are also presented. These observations suggest how bubble transport within such pillar arrays can be managed, as well as guide subsequent experiments that investigate bubble evolution and collection. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

Fabrication of efficient TiO2-RGO heterojunction composites for hydrogen generation via water-splitting: Comparison between RGO, Au and Pt reduction sites

NASA Astrophysics Data System (ADS)

El-Bery, Haitham M.; Matsushita, Yoshihisa; Abdel-moneim, Ahmed

2017-11-01

A facile one-step synthesis approach of M/TiO2/RGO (M = Au or Pt) ternary composite by hydrothermal treatment for hydrogen generation via water-splitting was investigated. Photocurrent response measurements revealed that TiO2 (P25) nanoparticles anchored on the reduced graphene oxide (RGO) surface exhibited a p-n heterojunction interface by changing the photocurrent direction with the applied bias from reverse to forward potential. H2 evolution rate of TiO2/RGO (5 wt.%) composite was substantially enhanced by 12-fold in comparison to bare TiO2 under simulated solar light irradiation. Cyclic volatmmetry measurements manifested, that the optimized 0.3 wt.% of platinum metal loaded on TiO2/RGO composite was the most active catalytic reduction sites for hydrogen generation reaction with an initial hydrogen rate of 670 μmol h-1. This study sheds the light on the tunable semiconductor type of TiO2/RGO composite fabricated by solution mixing pathway and its merits to improve the photocatalytic activity.

High-Capacity and Long-Cycle Life Aqueous Rechargeable Lithium-Ion Battery with the FePO4 Anode.

PubMed

Wang, Yuesheng; Yang, Shi-Ze; You, Ya; Feng, Zimin; Zhu, Wen; Gariépy, Vincent; Xia, Jiexiang; Commarieu, Basile; Darwiche, Ali; Guerfi, Abdelbast; Zaghib, Karim

2018-02-28

Aqueous lithium-ion batteries are emerging as strong candidates for a great variety of energy storage applications because of their low cost, high-rate capability, and high safety. Exciting progress has been made in the search for anode materials with high capacity, low toxicity, and high conductivity; yet, most of the anode materials, because of their low equilibrium voltages, facilitate hydrogen evolution. Here, we show the application of olivine FePO 4 and amorphous FePO 4 ·2H 2 O as anode materials for aqueous lithium-ion batteries. Their capacities reached 163 and 82 mA h/g at a current rate of 0.2 C, respectively. The full cell with an amorphous FePO 4 ·2H 2 O anode maintained 92% capacity after 500 cycles at a current rate of 0.2 C. The acidic aqueous electrolyte in the full cells prevented cathodic oxygen evolution, while the higher equilibrium voltage of FePO 4 avoided hydrogen evolution as well, making them highly stable. A combination of in situ X-ray diffraction analyses and computational studies revealed that olivine FePO 4 still has the biphase reaction in the aqueous electrolyte and that the intercalation pathways in FePO 4 ·2H 2 O form a 2-D mesh. The low cost, high safety, and outstanding electrochemical performance make the full cells with olivine or amorphous hydrated FePO 4 anodes commercially viable configurations for aqueous lithium-ion batteries.

A hydrogen-ferric ion rebalance cell operating at low hydrogen concentrations for capacity restoration of iron-chromium redox flow batteries

NASA Astrophysics Data System (ADS)

Zeng, Y. K.; Zhao, T. S.; Zhou, X. L.; Zou, J.; Ren, Y. X.

2017-06-01

To eliminate the adverse impacts of hydrogen evolution on the capacity of iron-chromium redox flow batteries (ICRFBs) during the long-term operation and ensure the safe operation of the battery, a rebalance cell that reduces the excessive Fe(III) ions at the positive electrolyte by using the hydrogen evolved from the negative electrolyte is designed, fabricated and tested. The effects of the flow field, hydrogen concentration and H2/N2 mixture gas flow rate on the performance of the hydrogen-ferric ion rebalance cell have been investigated. Results show that: i) an interdigitated flow field based rebalance cell delivers higher limiting current densities than serpentine flow field based one does; ii) the hydrogen utilization can approach 100% at low hydrogen concentrations (≤5%); iii) the apparent exchange current density of hydrogen oxidation reaction in the rebalance cell is proportional to the square root of the hydrogen concentration at the hydrogen concentration from 1.3% to 50%; iv) a continuous rebalance process is demonstrated at the current density of 60 mA cm-2 and hydrogen concentration of 2.5%. Moreover, the cost analysis shows that the rebalance cell is just approximately 1% of an ICRFB system cost.

Redox Chemistry of Molybdenum Trioxide for Ultrafast Hydrogen-Ion Storage.

PubMed

Wang, Xianfu; Xie, Yiming; Tang, Kai; Wang, Chao; Yan, Chenglin

2018-05-11

Hydrogen ions are ideal charge carriers for rechargeable batteries due to their small ionic radius and wide availability. However, little attention has been paid to hydrogen-ion storage devices because they generally deliver relatively low Coulombic efficiency as a result of the hydrogen evolution reaction that occurs in an aqueous electrolyte. Herein, we successfully demonstrate that hydrogen ions can be electrochemically stored in an inorganic molybdenum trioxide (MoO 3 ) electrode with high Coulombic efficiency and stability. The as-obtained electrode exhibits ultrafast hydrogen-ion storage properties with a specific capacity of 88 mA hg -1 at an ultrahigh rate of 100 C. The redox reaction mechanism of the MoO 3 electrode in the hydrogen-ion cell was investigated in detail. The results reveal a conversion reaction of the MoO 3 electrode into H 0.88 MoO 3 during the first hydrogen-ion insertion process and reversible intercalation/deintercalation of hydrogen ions between H 0.88 MoO 3 and H 0.12 MoO 3 during the following cycles. This study reveals new opportunities for the development of high-power energy storage devices with lightweight elements. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-pot synthesis of K-doped g-C3N4 nanosheets with enhanced photocatalytic hydrogen production under visible-light irradiation

NASA Astrophysics Data System (ADS)

Wang, Yanyun; Zhao, Shuo; Zhang, Yiwei; Fang, Jiasheng; Zhou, Yuming; Yuan, Shenhao; Zhang, Chao; Chen, Wenxia

2018-05-01

Graphite carbon nitride (g-C3N4), as a promising low cost, visible light driven conjugated polymer semiconductor photocatalyst, has attracted wide attentions from researchers. However, low light absorption efficiency and inadequate charge separation limit the potential applications of g-C3N4. This paper exhibits K-doped g-C3N4 prepared by a facile thermal polymerization with KBr as the K source. The experiments of photocatalytic hydrogen evolution demonstrate that KBr content strongly affects the activity of the catalyst. XRD, FT-IR, XPS, SEM, TEM, UV-vis diffuse reflectance spectra, photoluminescence (PL) characterization methods are used to study the effects of potassium on the catalyst performance. The results find that K-modified g-C3N4 has a narrower band gap and enhanced light harvesting properties. Moreover, the photocatalytic hydrogen evolution rate (HER) of the optimized K-doped g-C3N4 nanosheets (10 wt % KBr) reaches 1337.2 μmol g-1h-1, which is about 5.6 times in comparison with that of pure g-C3N4 (239.8 μmol g-1h-1). The doping of the potassium may increase the π-conjugated systems and accelerate the electron transport rate, then improve the photocatalytic properties. Based on the results of the analysis, a possible mechanism is proposed.

Efficient hydrogen evolution by ternary molybdenum sulfoselenide particles on self-standing porous nickel diselenide foam

DOE PAGES

Zhou, Haiqing; Yu, Fang; Huang, Yufeng; ...

2016-09-16

With the massive consumption of fossil fuels and its detrimental impact on the environment, methods of generating clean power are urgent. Hydrogen is an ideal carrier for renewable energy; however, hydrogen generation is inefficient because of the lack of robust catalysts that are substantially cheaper than platinum. Therefore, robust and durable earth-abundant and cost-effective catalysts are desirable for hydrogen generation from water splitting via hydrogen evolution reaction. In this paper, we report an active and durable earth-abundant transition metal dichalcogenide-based hybrid catalyst that exhibits high hydrogen evolution activity approaching the state-of-the-art platinum catalysts, and superior to those of most transitionmore » metal dichalcogenides (molybdenum sulfide, cobalt diselenide and so on). Our material is fabricated by growing ternary molybdenum sulfoselenide particles on self-standing porous nickel diselenide foam. This advance provides a different pathway to design cheap, efficient and sizable hydrogen-evolving electrode by simultaneously tuning the number of catalytic edge sites, porosity, heteroatom doping and electrical conductivity.« less

Efficient hydrogen evolution by ternary molybdenum sulfoselenide particles on self-standing porous nickel diselenide foam

NASA Astrophysics Data System (ADS)

Zhou, Haiqing; Yu, Fang; Huang, Yufeng; Sun, Jingying; Zhu, Zhuan; Nielsen, Robert J.; He, Ran; Bao, Jiming; Goddard, William A., III; Chen, Shuo; Ren, Zhifeng

2016-09-01

With the massive consumption of fossil fuels and its detrimental impact on the environment, methods of generating clean power are urgent. Hydrogen is an ideal carrier for renewable energy; however, hydrogen generation is inefficient because of the lack of robust catalysts that are substantially cheaper than platinum. Therefore, robust and durable earth-abundant and cost-effective catalysts are desirable for hydrogen generation from water splitting via hydrogen evolution reaction. Here we report an active and durable earth-abundant transition metal dichalcogenide-based hybrid catalyst that exhibits high hydrogen evolution activity approaching the state-of-the-art platinum catalysts, and superior to those of most transition metal dichalcogenides (molybdenum sulfide, cobalt diselenide and so on). Our material is fabricated by growing ternary molybdenum sulfoselenide particles on self-standing porous nickel diselenide foam. This advance provides a different pathway to design cheap, efficient and sizable hydrogen-evolving electrode by simultaneously tuning the number of catalytic edge sites, porosity, heteroatom doping and electrical conductivity.

Electron density modulation of NiCo2S4 nanowires by nitrogen incorporation for highly efficient hydrogen evolution catalysis.

PubMed

Wu, Yishang; Liu, Xiaojing; Han, Dongdong; Song, Xianyin; Shi, Lei; Song, Yao; Niu, Shuwen; Xie, Yufang; Cai, Jinyan; Wu, Shaoyang; Kang, Jian; Zhou, Jianbin; Chen, Zhiyan; Zheng, Xusheng; Xiao, Xiangheng; Wang, Gongming

2018-04-12

Metal sulfides for hydrogen evolution catalysis typically suffer from unfavorable hydrogen desorption properties due to the strong interaction between the adsorbed H and the intensely electronegative sulfur. Here, we demonstrate a general strategy to improve the hydrogen evolution catalysis of metal sulfides by modulating the surface electron densities. The N modulated NiCo 2 S 4 nanowire arrays exhibit an overpotential of 41 mV at 10 mA cm -2 and a Tafel slope of 37 mV dec -1 , which are very close to the performance of the benchmark Pt/C in alkaline condition. X-ray photoelectron spectroscopy, synchrotron-based X-ray absorption spectroscopy, and density functional theory studies consistently confirm the surface electron densities of NiCo 2 S 4 have been effectively manipulated by N doping. The capability to modulate the electron densities of the catalytic sites could provide valuable insights for the rational design of highly efficient catalysts for hydrogen evolution and beyond.

Iodine oxidation by hydrogen peroxide and Bray-Liebhafsky oscillating reaction: effect of the temperature.

PubMed

Schmitz, Guy

2011-04-21

This work presents a new experimental kinetic study at 39° and 50° of the iodine oxidation by hydrogen peroxide. The results allow us to obtain the temperature effect on the rate constants previously proposed at 25° for our model of the Bray-Liebhafsky oscillating reaction (G. Schmitz, Phys. Chem. Chem. Phys. 2010, 12, 6605.). The values calculated with the model are in good agreement with many experimental results obtained under very different experimental conditions. Numerical simulations of the oscillations observed formerly by different authors are presented, including the evolutions of the iodine, hydrogen peroxide, iodide ions and oxygen concentrations. Special attention is paid to the perturbing effects of oxygen and of the iodine loss to the gas phase.

Characterization of electrochemically deposited films from aqueous and ionic liquid cobalt precursors toward hydrogen evolution reactions

NASA Astrophysics Data System (ADS)

Dushatinski, Thomas; Huff, Clay; Abdel-Fattah, Tarek M.

2016-11-01

Electrodepositions of cobalt films were achieved using an aqueous or an ethylene glycol based non-aqueous solution containing choline chloride (vitamin B4) with cobalt chloride hexahydrate precursor toward hydrogen evolution reactions from sodium borohydride (NaBH4) as solid hydrogen feedstock (SHF). The resulting cobalt films had reflectivity at 550 nm of 2.2% for aqueously deposited films (ACoF) and 1.3% for non-aqueously deposited films (NCoF). Surface morphology studied by scanning electron microscopy showed a positive correlation between particle size and thickness. The film thicknesses were tunable between >100 μm and <300 μm for each film. The roughness (Ra) value measurements by Dektak surface profiling showed that the NCoF (Ra = 165 nm) was smoother than the ACoF (Ra = 418 nm). The NCoFs and ACoFs contained only α phase (FCC) crystallites. The NCoFs were crystalline while the ACoFs were largely amorphous from X-ray diffraction analysis. The NCoF had an average Vickers hardness value of 84 MPa as compared to 176 MPa for ACoF. The aqueous precursor has a single absorption maximum at 510 nm and the non-aqueous precursor had three absorption maxima at 630, 670, and 695 nm. The hydrogen evolution reactions over a 1 cm2 catalytic surface with aqueous NaBH4 solutions generated rate constants (K) = equal to 4.9 × 10-3 min-1, 4.6 × 10-3 min-1, and 3.3 × 10-3 min-1 for ACoF, NCoF, and copper substrate respectively.

Fermentative hydrogen production from liquid swine manure with glucose supplement using an anaerobic sequencing batch reactor

NASA Astrophysics Data System (ADS)

Wu, Xiao

2009-12-01

The idea of coupling renewable energy production and agricultural waste management inspired this thesis. The production of an important future fuel---hydrogen gas---from high strength waste stream-liquid swine manure---using anaerobic treatment processes makes the most sustainable sense for both wastewater utilization and energy generation. The objectives of this thesis were to develop a fermentation process for converting liquid swine manure to hydrogen and to maximize hydrogen productivity. Anaerobic sequencing batch reactor (ASBR) systems were constructed to carry out this fermentation process, and seed sludge obtained from a dairy manure anaerobic digester and pretreated by nutrient acclimation, heat and pH treatment was used as inoculum. High system stability was indicated by a short startup period of 12 days followed by stable hydrogen production, and successful sludge granulation occurred within 23 days of startup at a hydraulic retention time (HRT) of 24 hours. Operation at a progressively decreasing HRT from 24 to 8h gave rise to an increasing biogas production rate from 15.2-34.4L/d, while good linear relationships were observed between both total biogas and hydrogen production rates correlated to HRT, with R2 values of 0.993 and 0.997, respectively. The maximum hydrogen yield of 1.63 mol-H 2/mol-hexose-feed occurred at HRT of 16h, while the HRT of 12h was highly suggested to achieve both high production rate and efficient yield. Hexose utilization efficiencies over 98%, considerable hydrogen production rate up to 14.3 L/d and hydrogen percentage of off-gas up to 43% (i.e., a CO 2/H2 ratio of 1.2) with the absence of CH4 production throughout the whole course of experiment at a pH of 5.0 strongly validated the feasibility of the fermentative H2 production from liquid swine manure using an ASBR system. Ethanol as well as acetic, butyric and valeric acids were produced in the system accompanying the hydrogen production, with acetic acid being the dominant one, which contributed to 56-58% of the total soluble metabolite production, indicative of an acetic acid fermentation system, and acetate-to-butyrate ratio was found to be closely related to hydrogen yield. pH level influenced every aspect of the ASBR performance for hydrogen production. ASBR operation at five pHs ranging from 4.4 to 5.6 (4.4, 4.7, 5.0, 5.3, 5.6) showed distinct dynamic profiles of both biogas production and the changes of H2 and CH4 percentage in the biogas during a running period of 22 days. The H2 content in biogas, H 2 production rate and H2 yield were all pH-dependent, in the range of 5.1-36.9 %, 0.71-8.97 L/d and 0.12-1.50 mol-H2/mol-glucose, respectively, and maximum values for all three responses were simultaneously achieved at pH 5.0. Methanogens appeared to be significantly activated at pH of 5.3 or higher since significant CH4 evolution and concurrent reduction in H2 production was observed at pH 5.3 and 5.6. Acetate, propionate, butyrate, valerate, and ethanol were main aqueous products in all pH tests and their distribution was influenced by pH. Analysis of kinetic models developed from modified Gompertz equations for batch experiments showed that pH had a profound effect on all kinetic parameters for hydrogen production including hydrogen potential, maximum hydrogen production rate and the length of the lag phase, as well as the maximum substrate utilization rate. The low pH of 4.4 gave the highest hydrogen production potential but with the lowest hydrogen production rate. A contrast experiment was conducted with an initial pH of 5.3 but not controlled, came up with a rapid pH decline, leading to a low hexose degradation efficiency of 33.2% and a significantly suppressed H2 production, indicating the importance of pH control and the effect of pH on H2 production and substrate consumption. pH 5.0 was verified as the optimal for the proposed fermentation system by kinetic models. An extremely linear relationship (R2= 0.993) between the maximum H2 production rate and the maximum hexose degradation rate suggested that the pH inhibition on H2 production was a result of the suppression on the bacterial activity for substrate utilization due to an unfavorable pH level. System optimization was realized through experiments conducted according to a response surface methodology, with a central composite design and empirical quadratic response equations obtained for three responses including the hydrogen content in the biogas, hydrogen evolution rate and hydrogen yield, against three independent variables, pH (4.4-5.6), HRT (8-24h) and substrate glucose concentrations (Cg, 0-20 g/L). Contour plots revealed that all three responses were significantly impacted by the variable and squared pH. Furthermore, pH and Cg had a significant interaction effect on H2 production rate, while HRT and glucose concentration were interdependent, or they had a mildly significant interaction effect on H2 production rate. The hydrogen content decreased when pH was greater than 5.0 or less than 4.6 and a largest value of 42.7% could be obtained at pH 4.8, HRT 8 h, and Cg of 18.7 g/L. The highest hydrogen production rate of 26.1 L/d happened under a pH of 4.6, HRT of 8h, and Cg of 20 g/L; Lower HRT and higher Cg was found to benefit the H2 production rate because they provide elevated organic loading and food to microorganism ratio for the system. HRT shorter than 17h resulted in declined hydrogen yield, while the glucose concentration up to 20 g/L did not cause suppression on hydrogen yield. The revised optimal condition of pH 4.8, HRT 11h, and Cg of 20 g/L, which could achieve 85% of the maximum values of all three hydrogen productivity responses, was determined by surface response methodology. Highly reproducible results from confirming experiments at the optimal condition indicated that the results modeled in this study possessed a high reliability, while the results of H2 content, H2 production rate and yield were obtained as 40.3%, 23.16 L/d, and 1.36mol H2/mol hexose, respectively. Results obtained in this study indicated that ASBR system using swine manure based substrate had significant potential of fermentative hydrogen production. Key words: biohydrogen production, hydrogen fermentation, liquid swine manure, anaerobic sequencing batch reactor (ASBR), hydrogen content, hydrogen production rate, hydrogen yield

Hydrogen loss and its improved retention in hydrogen plasma treated a-SiNx:H films: ERDA study with 100 MeV Ag7+ ions

NASA Astrophysics Data System (ADS)

Bommali, R. K.; Ghosh, S.; Khan, S. A.; Srivastava, P.

2018-05-01

Hydrogen loss from a-SiNx:H films under irradiation with 100 MeV Ag7+ ions using elastic recoil detection analysis (ERDA) experiment is reported. The results are explained under the basic assumptions of the molecular recombination model. The ERDA hydrogen concentration profiles are composed of two distinct hydrogen desorption processes, limited by rapid molecular diffusion in the initial stages of irradiation, and as the fluence progresses a slow process limited by diffusion of atomic hydrogen takes over. Which of the aforesaid processes dominates, is determined by the continuously evolving Hydrogen concentration within the films. The first process dominates when the H content is high, and as the H concentration falls below a certain threshold (Hcritical) the irradiation generated H radicals have to diffuse through larger distances before recombining to form H2, thereby significantly bringing down the hydrogen evolution rate. The ERDA measurements were also carried out for films treated with low temperature (300 °C) hydrogen plasma annealing (HPA). The HPA treated films show a clear increase in Hcritical value, thus indicating an improved diffusion of atomic hydrogen, resulting from healing of weak bonds and passivation of dangling bonds. Further, upon HPA films show a significantly higher H concentration relative to the as-deposited films, at advanced fluences. These results indicate the potential of HPA towards improved H retention in a-SiNx:H films. The study distinguishes clearly the presence of two diffusion processes in a-SiNx:H whose diffusion rates differ by an order of magnitude, with atomic hydrogen not being able to diffuse further beyond ∼ 1 nm from the point of its creation.

Environmental and Health Benefits and Risks of a Global Hydrogen Economy

NASA Astrophysics Data System (ADS)

Dubey, M.; Horowitz, L. W.; Rahn, T. A.; Kinnison, D. E.

2003-12-01

Rapid development in hydrogen fuel-cell technologies will create a strong impetus for a massive hydrogen supply and distribution infrastructure in the coming decades. Hydrogen provides an efficient energy carrier that promises to enhance urban and regional air quality that will benefit human health. It could also reduce risks of climate change if large-scale hydrogen production by renewable or nuclear energy sources becomes viable. While it is well known that the byproduct of energy produced from hydrogen is water vapor, it is not well known that the storage and transfer of hydrogen is inevitably accompanied by measurable leakage of hydrogen. Unintended consequences of hydrogen leakage include reduction in global oxidative capacity, changes in tropospheric ozone, and increase in stratospheric water that would exacerbate halogen induced ozone losses as well as impact the earth's radiation budget and climate. Stratospheric ozone depletion would increase exposure to harmful ultraviolet radiation and increased risk to melanoma. We construct plausible global hydrogen energy use and leak scenarios and assess their impacts using global 3-D simulations by the Model for Ozone And Related Trace species (MOZART). The hydrogen fluxes and photochemistry in our model successfully reproduce the contemporary hydrogen cycle as observed by a network of remote global stations. Our intent is to determine environmentally tolerable leak rates and also facilitate a gradual phasing in of a hydrogen economy over the next several decades as the elimination of the use of halocarbons gradually reduces halogen induced stratospheric ozone loss rates. We stress that the future evolution of microbial soil sink of hydrogen that determines its current lifetime (about 2 years) is the principal source of uncertainty in our assessment. We propose global monitoring of hydrogen and its deuterium content to define a baseline and track its budget to responsibly prepare for a global hydrogen economy.

Dual organism design cycle reveals small subunit substitutions that improve [NiFe] hydrogenase hydrogen evolution

PubMed Central

2013-01-01

Background Photosynthetic microorganisms that directly channel solar energy to the production of molecular hydrogen are a potential future biofuel system. Building such a system requires installation of a hydrogenase in the photosynthetic organism that is both tolerant to oxygen and capable of hydrogen production. Toward this end, we have identified the [NiFe] hydrogenase from the marine bacterium Alteromonas macleodii “Deep ecotype” that is able to be heterologously expressed in cyanobacteria and has tolerance to partial oxygen. The A. macleodii enzyme shares sequence similarity with the uptake hydrogenases that favor hydrogen uptake activity over hydrogen evolution. To improve hydrogen evolution from the A. macleodii hydrogenase, we examined the three Fe-S clusters found in the small subunit of many [NiFe] uptake hydrogenases that presumably act as a molecular wire to guide electrons to or from the active site of the enzyme. Studies by others altering the medial cluster of a Desulfovibrio fructosovorans hydrogenase from 3Fe-4S to 4Fe-4S resulted in two-fold improved hydrogen evolution activity. Results We adopted a strategy of screening for improved hydrogenase constructs using an Escherichia coli expression system before testing in slower growing cyanobacteria. From the A. macleodii enzyme, we created a mutation in the gene encoding the hydrogenase small subunit that in other systems is known to convert the 3Fe-4S medial cluster to 4Fe-4S. The medial cluster substitution did not improve the hydrogen evolution activity of our hydrogenase. However, modifying both the medial cluster and the ligation of the distal Fe-S cluster improved in vitro hydrogen evolution activity relative to the wild type hydrogenase by three- to four-fold. Other properties of the enzyme including thermostability and tolerance to partial oxygen did not appear to be affected by the substitutions. Conclusions Our results show that substitution of amino acids altering the ligation of Fe-S clusters in the A. macleodii [NiFe] uptake hydrogenase resulted in increased hydrogen evolution activity. This activity can be recapitulated in multiple host systems and with purified protein. These results validate the approach of using an E. coli-cyanobacteria shuttle system for enzyme expression and improvement. PMID:23819621

Interface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfide

PubMed Central

Chen, Zhongxin; Leng, Kai; Zhao, Xiaoxu; Malkhandi, Souradip; Tang, Wei; Tian, Bingbing; Dong, Lei; Zheng, Lirong; Lin, Ming; Yeo, Boon Siang; Loh, Kian Ping

2017-01-01

Interface confined reactions, which can modulate the bonding of reactants with catalytic centres and influence the rate of the mass transport from bulk solution, have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T′-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral molecules. This points a way forward for using bulk intercalated compounds for energy related applications. PMID:28230105

Atomically Thin Mesoporous Nanomesh of Graphitic C₃N₄ for High-Efficiency Photocatalytic Hydrogen Evolution.

PubMed

Han, Qing; Wang, Bing; Gao, Jian; Cheng, Zhihua; Zhao, Yang; Zhang, Zhipan; Qu, Liangti

2016-02-23

Delamination of layer materials into two-dimensional single-atom sheets has induced exceptional physical properties, including large surface area, ultrahigh intrinsic carrier mobility, pronounced changes in the energy band structure, and other properties. Here, atomically thin mesoporous nanomesh of graphitic carbon nitride (g-C3N4) is fabricated by solvothermal exfoliation of mesoporous g-C3N4 bulk made from thermal polymerization of freeze-drying assembled Dicyandiamide nanostructure precursor. With the unique structural advantages for aligned energy levels, electron transfer, light harvesting, and the richly available reaction sites, the as-prepared monolayer of mesoporous g-C3N4 nanomesh exhibits a superior photocatalytic hydrogen evolution rate of 8510 μmol h(-1) g(-1) under λ > 420 nm and an apparent quantum efficiency of 5.1% at 420 nm, the highest of all the metal-free g-C3N4 nanosheets photocatalysts.

Chemistry and evolution of Titan's atmosphere

NASA Technical Reports Server (NTRS)

Strobel, D. F.

1982-01-01

The chemistry and evolution of Titan's atmosphere are reviewed, in light of the scientific findings from the Voyager mission. It is argued that the present N2 atmosphere may be Titan's initial atmosphere, rather than one photochemically derived from an original NH3 atmosphere. The escape rate of hydrogen from Titan is controlled by photochemical production from hydrocarbons. CH4 is irreversibly converted to less hydrogen-rich hydrocarbons, which over geologic time accumulate on the surface to a layer thickness of about 0.5 km. Magnetospheric electrons interacting with Titan's exosphere may dissociate enough N2 into hot, escaping N atoms to remove about 0.2 of Titan's present atmosphere over geologic time. The energy dissipation of magnetospheric electrons exceeds solar EUV energy deposition in Titan's atmosphere by an order of magnitude, and is the principal driver of nitrogen photochemistry. The environmental conditions in Titan's upper atmosphere are favorable to building up complex molecules, particularly in the north polar cap region.

Ionic liquid as an electrolyte additive for high performance lead-acid batteries

NASA Astrophysics Data System (ADS)

Deyab, M. A.

2018-06-01

The performance of lead-acid battery is improved in this work by inhibiting the corrosion of negative battery electrode (lead) and hydrogen gas evolution using ionic liquid (1-ethyl-3-methylimidazolium diethyl phosphate). The results display that the addition of ionic liquid to battery electrolyte (5.0 M H2SO4 solution) suppresses the hydrogen gas evolution to very low rate 0.049 ml min-1 cm-2 at 80 ppm. Electrochemical studies show that the adsorption of ionic liquid molecules on the lead electrode surface leads to the increase in the charge transfer resistance and the decrease in the double layer capacitance. I also notice a noteworthy improvement of battery capacity from 45 mAh g-1 to 83 mAh g-1 in the presence of ionic liquid compound. Scanning electron microscopy and energy dispersive X-ray analysis confirm the adsorption of ionic liquid molecules on the battery electrode surface.

Tension-Enhanced Hydrogen Evolution Reaction on Vanadium Disulfide Monolayer

NASA Astrophysics Data System (ADS)

Pan, Hui

2016-02-01

Water electrolysis is an efficient way for hydrogen production. Finding efficient, cheap, and eco-friendly electrocatalysts is essential to the development of this technology. In the work, we present a first-principles study on the effects of tension on the hydrogen evolution reaction of a novel electrocatalyst, vanadium disulfide (VS2) monolayer. Two electrocatalytic processes, individual and collective processes, are investigated. We show that the catalytic ability of VS2 monolayer at higher hydrogen coverage can be efficiently improved by escalating tension. We find that the individual process is easier to occur in a wide range of hydrogen coverage and the collective process is possible at a certain hydrogen coverage under the same tension. The best hydrogen evolution reaction with near-zero Gibbs free energy can be achieved by tuning tension. We further show that the change of catalytic activity with tension and hydrogen coverage is induced by the change of free carrier density around the Fermi level, that is, higher carrier density, better catalytic performance. It is expected that tension can be a simple way to improve the catalytic activity, leading to the design of novel electrocatalysts for efficient hydrogen production from water electrolysis.

Local potential evolutions during proton exchange membrane fuel cell operation with dead-ended anode - Part II: Aging mitigation strategies based on water management and nitrogen crossover

NASA Astrophysics Data System (ADS)

Abbou, S.; Dillet, J.; Maranzana, G.; Didierjean, S.; Lottin, O.

2017-02-01

Proton exchange membrane (PEM) fuel cells operate with dead-ended anode in order to reduce system cost and complexity when compared with hydrogen re-circulation systems. In the first part of this work, we showed that localized fuel starvation events may occur, because of water and nitrogen accumulation in the anode side, which could be particularly damaging to the cell performance. To prevent these degradations, the anode compartment must be purged which may lead to an overall system efficiency decrease because of significant hydrogen waste. In the second part, we present several purge strategies in order to minimize both hydrogen waste and membrane-electrode assembly degradations during dead-ended anode operation. A linear segmented cell with reference electrodes was used to monitor simultaneously the current density distribution along the gas channel and the time evolution of local anode and cathode potentials. To asses MEA damages, Platinum ElectroChemical Surface Area (ECSA) and cell performance were periodically measured. The results showed that dead-end mode operation with an anode plate maintained at a temperature 5 °C hotter than the cathode plate limits water accumulation in the anode side, reducing significantly purge frequency (and thus hydrogen losses) as well as MEA damages. As nitrogen contribution to hydrogen starvation is predominant in this thermal configuration, we also tested a microleakage solution to discharge continuously most the nitrogen accumulating in the anode side while ensuring low hydrogen losses and minimum ECSA losses provided the right microleakage flow rate is chosen.

In situ photodeposition of amorphous CoSx on the TiO2 towards hydrogen evolution

NASA Astrophysics Data System (ADS)

Chen, Feng; Luo, Wei; Mo, Yanping; Yu, Huogen; Cheng, Bei

2018-02-01

Cocatalyst modification of photocatalysts is an important strategy to enhance the photocatalytic performance by promoting effective separation of photoinduced electron-hole pairs and providing abundant active sites. In this study, a facile in situ photodeposition method was developed to prepare amorphous CoSx-modified TiO2 photocatalysts. It was found that amorphous CoSx nanoparticles were solidly loaded on the TiO2 surface, resulting in a greatly improved photocatalytic H2-evolution performance. When the amount of amorphous CoSx was 10 wt%, the hydrogen evolution rate of the CoSx/TiO2 reached 119.7 μmol h-1, which was almost 16.7 times that of the pure TiO2. According to the above experimental results, a reasonable mechanism of improved photocatalytic performance is proposed for the CoSx/TiO2 photocatalysts, namely, the photogenerated electrons of TiO2 can rapidly transfer to amorphous CoSx nanoparticles due to the solid contact between them, and then amorphous CoSx can provide plenty of sulfur active sites to rapidly adsorb protons from solution to produce hydrogen by the photogenerated electrons. Considering the facile synthesis method, the present cheap and highly efficient amorphous CoSx-modified TiO2 photocatalysts would have great potential for practical use in photocatalytic H2 production.

Method and System for Hydrogen Evolution and Storage

DOEpatents

Thorn, David L.; Tumas, William; Hay, P. Jeffrey; Schwarz, Daniel E.; Cameron, Thomas M.

2008-10-21

A method and system for storing and evolving hydrogen employ chemical compounds that can be hydrogenated to store hydrogen and dehydrogenated to evolve hydrogen. A catalyst lowers the energy required for storing and evolving hydrogen. The method and system can provide hydrogen for devices that consume hydrogen as fuel.

Facile Synthesis of Single Crystal Vanadium Disulfide Nanosheets by Chemical Vapor Deposition for Efficient Hydrogen Evolution Reaction.

PubMed

Yuan, Jiangtan; Wu, Jingjie; Hardy, Will J; Loya, Philip; Lou, Minhan; Yang, Yingchao; Najmaei, Sina; Jiang, Menglei; Qin, Fan; Keyshar, Kunttal; Ji, Heng; Gao, Weilu; Bao, Jiming; Kono, Junichiro; Natelson, Douglas; Ajayan, Pulickel M; Lou, Jun

2015-10-07

A facile chemical vapor deposition method to prepare single-crystalline VS2 nanosheets for the hydrogen evolution reaction is reported. The electrocatalytic hydrogen evolution reaction (HER) activities of VS2 show an extremely low overpotential of -68 mV at 10 mA cm(-2), small Tafel slopes of ≈34 mV decade(-1), as well as high stability, demonstrating its potential as a candidate non-noble-metal catalyst for the HER. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metastable Metal Hydrides for Hydrogen Storage

DOE PAGES

Graetz, Jason

2012-01-01

The possibility of using hydrogen as a reliable energy carrier for both stationary and mobile applications has gained renewed interest in recent years due to improvements in high temperature fuel cells and a reduction in hydrogen production costs. However, a number of challenges remain and new media are needed that are capable of safely storing hydrogen with high gravimetric and volumetric densities. Metal hydrides and complex metal hydrides offer some hope of overcoming these challenges; however, many of the high capacity “reversible” hydrides exhibit a large endothermic decomposition enthalpy making it difficult to release the hydrogen at low temperatures. Onmore » the other hand, the metastable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favorable under ambient conditions. The rapid, low temperature hydrogen evolution rates that can be achieved with these materials offer much promise for mobile PEM fuel cell applications. However, a critical challenge exists to develop new methods to regenerate these hydrides directly from the reactants and hydrogen gas. This spotlight paper presents an overview of some of the metastable metal hydrides for hydrogen storage and a few new approaches being investigated to address the key challenges associated with these materials.« less

Bioinspired Tungsten Dithiolene Catalysts for Hydrogen Evolution: A Combined Electrochemical, Photochemical, and Computational Study.

PubMed

Gomez-Mingot, Maria; Porcher, Jean-Philippe; Todorova, Tanya K; Fogeron, Thibault; Mellot-Draznieks, Caroline; Li, Yun; Fontecave, Marc

2015-10-29

Bis(dithiolene)tungsten complexes, W(VI)O2 (L = dithiolene)2 and W(IV)O (L = dithiolene)2, which mimic the active site of formate dehydrogenases, have been characterized by cyclic voltammetry and controlled potential electrolysis in acetonitrile. They are shown to be able to catalyze the electroreduction of protons into hydrogen in acidic organic media, with good Faradaic yields (75-95%) and good activity (rate constants of 100 s(-1)), with relatively high overpotentials (700 mV). They also catalyze proton reduction into hydrogen upon visible light irradiation, in combination with [Ru(bipyridine)3](2+) as a photosensitizer and ascorbic acid as a sacrificial electron donor. On the basis of detailed DFT calculations, a reaction mechanism is proposed in which the starting W(VI)O2 (L = dithiolene)2 complex acts as a precatalyst and hydrogen is further formed from a key reduced W-hydroxo-hydride intermediate.

Thermal desorption of hydrogen from Mg2Ni hydrogen storage materials.

PubMed

Hur, Tae Hong; Han, Jeong Seb; Kim, Jin Ho; Kim, Byung Kwan

2011-07-01

In order to investigate the influence of HCS on the hydrogen occupation site of Mg2Ni alloy, the thermal desorption technique has been applied to Mg2Ni hydride made by hydriding combustion synthesis (HCS). Mg2Ni was made under low temperature in a short time by the HCS compared to conventional melting process. At various initial hydride wt% from 0.91 to 3.52, the sample was heated to 623 K at a rate of 1.0 K/min. The starting temperature of the evolution of hydrogen goes higher as the initial hydride wt% increases. Only one peak is shown in the case of the small initial hydride wt%. But two peaks appeared with increasing initial hydride wt%. The activation energies obtained by the first and second peaks are 113.0 and 99.5 kJ/mol respectively. The two site occupation model by Darriet et al. was proved. The influence of HCS on the hydrogen occupation site of Mg2Ni alloy is nonexistent.

Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier.

PubMed

Zhou, Xiaorun; Lu, Taiping; Zhu, Yadan; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Yang, Yongzhen; Chen, Yongkang; Xu, Bingshe

2017-12-01

Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H 2 ) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H 2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H 2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H 2 proportion further increases, stress relaxation and H 2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.

Correlation between Gas Bubble Formation and Hydrogen Evolution Reaction Kinetics at Nanoelectrodes.

PubMed

Chen, Qianjin; Luo, Long

2018-04-17

We report the correlation between H 2 gas bubble formation potential and hydrogen evolution reaction (HER) activity for Au and Pt nanodisk electrodes (NEs). Microkinetic models were formulated to obtain the HER kinetic information for individual Au and Pt NEs. We found that the rate-determining steps for the HER at Au and Pt NEs were the Volmer step and the Heyrovsky step, respectively. More interestingly, the standard rate constant ( k 0 ) of the rate-determining step was found to vary over 2 orders of magnitude for the same type of NEs. The observed variations indicate the HER activity heterogeneity at the nanoscale. Furthermore, we discovered a linear relationship between bubble formation potential ( E bubble ) and log( k 0 ) with a slope of 125 mV/decade for both Au and Pt NEs. As log ( k 0 ) increases, E bubble shifts linearly to more positive potentials, meaning NEs with higher HER activities form H 2 bubbles at less negative potentials. Our theoretical model suggests that such linear relationship is caused by the similar critical bubble formation condition for Au and Pt NEs with varied sizes. Our results have potential implications for using gas bubble formation to evaluate the HER activity distribution of nanoparticles in an ensemble.

Oxygen Mass Flow Rate Generated for Monitoring Hydrogen Peroxide Stability

NASA Technical Reports Server (NTRS)

Ross, H. Richard

2002-01-01

Recent interest in propellants with non-toxic reaction products has led to a resurgence of interest in hydrogen peroxide for various propellant applications. Because peroxide is sensitive to contaminants, material interactions, stability and storage issues, monitoring decomposition rates is important. Stennis Space Center (SSC) uses thermocouples to monitor bulk fluid temperature (heat evolution) to determine reaction rates. Unfortunately, large temperature rises are required to offset the heat lost into the surrounding fluid. Also, tank penetration to accomodate a thermocouple can entail modification of a tank or line and act as a source of contamination. The paper evaluates a method for monitoring oxygen evolution as a means to determine peroxide stability. Oxygen generation is not only directly related to peroxide decomposition, but occurs immediately. Measuring peroxide temperature to monitor peroxide stability has significant limitations. The bulk decomposition of 1% / week in a large volume tank can produce in excess of 30 cc / min. This oxygen flow rate corresponds to an equivalent temperature rise of approximately 14 millidegrees C, which is difficult to measure reliably. Thus, if heat transfer were included, there would be no temperature rise. Temperature changes from the surrounding environment and heat lost to the peroxide will also mask potential problems. The use of oxygen flow measurements provides an ultra sensitive technique for monitoring reaction events and will provide an earlier indication of an abnormal decomposition when compared to measuring temperature rise.

Enhanced hydrogen production in microbial electrolysis cell with 3D self-assembly nickel foam-graphene cathode.

PubMed

Cai, Weiwei; Liu, Wenzong; Han, Jinglong; Wang, Aijie

2016-06-15

In comparison to precious metal catalyst especially Platinum (Pt), nickel foam (NF) owned cheap cost and unique three-dimensional (3D) structure, however, it was scarcely applied as cathode material in microbial electrolysis cell (MEC) as the intrinsic laggard electrochemical activity for hydrogen recovery. In this study, a self-assembly 3D nickel foam-graphene (NF-G) cathode was fabricated by facile hydrothermal approach for hydrogen evolution in MECs. Electrochemical analysis (linear scan voltammetry and electrochemical impedance spectroscopy) revealed the improved electrochemical activity and effective mass diffusion after coating with graphene. NF-G as cathode in MEC showed a significant enhancement in hydrogen production rate compared with nickel foam at a variety of biases. Noticeably, NF-G showed a comparable averaged hydrogen production rate (1.31 ± 0.07 mL H2 mL(-1) reactor d(-1)) to Platinum/carbon (Pt/C) (1.32 ± 0.07 mL H2 mL(-1) reactor d(-1)) at 0.8 V. Profitable energy recovery could be achieved by NF-G cathode at higher applied voltage, which performed the best hydrogen yield of 3.27 ± 0.16 mol H2 mol(-1) acetate at 0.8 V and highest energy efficiency of 185.92 ± 6.48% at 0.6 V. Copyright © 2016 Elsevier B.V. All rights reserved.

Nucleation, growth and evolution of calcium phosphate films on calcite.

PubMed

Naidu, Sonia; Scherer, George W

2014-12-01

Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence. Copyright © 2014 Elsevier Inc. All rights reserved.

Effect of high repetition laser shock peening on biocompatibility and corrosion resistance of magnesium

NASA Astrophysics Data System (ADS)

Caralapatti, Vinodh Krishna; Narayanswamy, Sivakumar

2017-02-01

Magnesium, as a biomaterial has the potential to replace conventional implant materials owing to its numerous advantages. However, high corrosion rate is a major obstacle that has to be addressed for its implementation as implants. This study aims to evaluate the feasibility and effects of High Repetition Laser Shock Peening (HRLSP) on biocompatibility and corrosion resistance of Mg samples and as well as to analyze the effect of operational parameters such as peening with overlap on corrosion rate. From the results obtained using hydrogen evolution and mass loss methods, it was found that corrosion rates of both 0% overlap and 66% overlap peened samples reduced by more than 50% compared to that of unpeened sample and sample peened with 66% overlap exhibited least corrosion. The biocompatibility of peened Mg samples was also enhanced as there was neither rapid pH variation nor large hydrogen bubble formation around samples.

Method and system for hydrogen evolution and storage

DOEpatents

Thorn, David L.; Tumas, William; Hay, P. Jeffrey; Schwarz, Daniel E.; Cameron, Thomas M.

2012-12-11

A method and system for storing and evolving hydrogen (H.sub.2) employ chemical compounds that can be hydrogenated to store hydrogen and dehydrogenated to evolve hydrogen. A catalyst lowers the energy required for storing and evolving hydrogen. The method and system can provide hydrogen for devices that consume hydrogen as fuel.

Selective electrochemical generation of hydrogen peroxide from water oxidation

DOE PAGES

Viswanathan, Venkatasubramanian; Hansen, Heine A.; Norskov, Jens K.

2015-10-08

Water is a life-giving source, fundamental to human existence, yet over a billion people lack access to clean drinking water. The present techniques for water treatment such as piped, treated water rely on time and resource intensive centralized solutions. In this work, we propose a decentralized device concept that can utilize sunlight to split water into hydrogen and hydrogen peroxide. The hydrogen peroxide can oxidize organics while the hydrogen bubbles out. In enabling this device, we require an electrocatalyst that can oxidize water while suppressing the thermodynamically favored oxygen evolution and form hydrogen peroxide. Using density functional theory calculations, wemore » show that the free energy of adsorbed OH* can be used to determine selectivity trends between the 2e– water oxidation to H 2O 2 and the 4e– oxidation to O 2. We show that materials which bind oxygen intermediates sufficiently weakly, such as SnO 2, can activate hydrogen peroxide evolution. Furthermore, we present a rational design principle for the selectivity in electrochemical water oxidation and identify new material candidates that could perform H 2O 2 evolution selectively.« less

Synthesis of Ultra-Small Palladium Nanoparticles Deposited on CdS Nanorods by Pulsed Laser Ablation in Liquid: Role of Metal Nanocrystal Size in the Photocatalytic Hydrogen Production.

PubMed

Park, Hanbit; Reddy, D Amaranatha; Kim, Yujin; Lee, Seunghee; Ma, Rory; Kim, Tae Kyu

2017-09-21

It is imperative to suppress the rate of recombination of photogenerated carriers to improve the semiconductor-catalyzed solar-driven production of hydrogen. To this end, photocatalysts comprising active sunlight-harvesting photo-absorbers and stable metal co-catalysts have attracted significant attention. However, the size, clean surface, and highly dispersed nature of the metal co-catalysts are crucial factors affecting catalyst performance and reaction rate. Nevertheless, most of the available metal nanocrystals have been synthesized by complex procedures using harmful organic templates and stabilizers, affording high-purity compounds with difficulty and high cost. To overcome these problems, in this study, the pulsed laser ablation in liquid approach was utilized to generate palladium and bimetallic palladium-platinum nanoparticles with an average size and distribution by adjusting the laser wavelength and fluence. A high rate of evolution of hydrogen of 130.33 mmol g -1  h -1 was obtained by using the optimized CdS-PdPt catalyst under simulated sunlight irradiation. This value is 51.31 times greater than that observed for bare CdS nanostructures. Furthermore, the amount of hydrogen evolved was significantly better than that obtained by using several other noble-metal co-catalysts deposited on CdS. This proposed strategy is thought to open new avenues for the design of advanced photocatalytic materials for efficient solar-driven production of hydrogen. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Active Cocatalysts for Photocatalytic Hydrogen Evolution Derived from Nickel or Cobalt Amine Complexes.

PubMed

Huang, Yi; Zhang, Bin

2017-11-20

A cost-effective and robust strategy for the anchoring of molecular hydrogen evolution cocatalysts onto semiconductors has recently been reported. The composite materials were highly efficient and stable towards photocatalytic H 2 evolution. This study provides guidance for the design and construction of highly active heterogeneous photocatalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Helium stars: Towards an understanding of Wolf-Rayet evolution

NASA Astrophysics Data System (ADS)

McClelland, Liam A. S.; Eldridge, J. J.

2017-11-01

Recent observational modelling of the atmospheres of hydrogen-free Wolf-Rayet stars have indicated that their stellar surfaces are cooler than those predicted by the latest stellar evolution models. We have created a large grid of pure helium star models to investigate the dependence of the surface temperatures on factors such as the rate of mass loss and the amount of clumping in the outer convection zone. Upon comparing our results with Galactic and LMC WR observations, we find that the outer convection zones should be clumped and that the mass-loss rates need to be slightly reduced. We discuss the implications of these findings in terms of the detectability of Type Ibc supernovae progenitors, and in terms of refining the Conti scenario.

Hydrodynamic escape from planetary atmospheres

NASA Astrophysics Data System (ADS)

Tian, Feng

Hydrodynamic escape is an important process in the formation and evolution of planetary atmospheres. Due to the existence of a singularity point near the transonic point, it is difficult to find transonic steady state solutions by solving the time-independent hydrodynamic equations. In addition to that, most previous works assume that all energy driving the escape flow is deposited in one narrow layer. This assumption not only results in less accurate solutions to the hydrodynamic escape problem, but also makes it difficult to include other chemical and physical processes in the hydrodynamic escape models. In this work, a numerical model describing the transonic hydrodynamic escape from planetary atmospheres is developed. A robust solution technique is used to solve the time dependent hydrodynamic equations. The method has been validated in an isothermal atmosphere where an analytical solution is available. The hydrodynamic model is applied to 3 cases: hydrogen escape from small orbit extrasolar planets, hydrogen escape from a hydrogen rich early Earth's atmosphere, and nitrogen/methane escape from Pluto's atmosphere. Results of simulations on extrasolar planets are in good agreement with the observations of the transiting extrasolar planet HD209458b. Hydrodynamic escape of hydrogen from other hypothetical close-in extrasolar planets are simulated and the influence of hydrogen escape on the long-term evolution of these extrasolar planets are discussed. Simulations on early Earth suggest that hydrodynamic escape of hydrogen from a hydrogen rich early Earth's atmosphere is about two orders magnitude slower than the diffusion limited escape rate. A hydrogen rich early Earth's atmosphere could have been maintained by the balance between the hydrogen escape and the supply of hydrogen into the atmosphere by volcanic outgassing. Origin of life may have occurred in the organic soup ocean created by the efficient formation of prebiotic molecules in the hydrogen rich early Earth's atmosphere. Simulations show that hydrodynamic escape of nitrogen from Pluto is able to remove a ~3 km layer of ice over the age of the solar system. The escape flux of neutral nitrogen may interact with the solar wind at Pluto's orbit and may be detected by the New Horizon mission.

Photoproduction of hydrogen by marine blue-green algae. Progress report 15 August 80-14 February 81

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitsui, A.

The growth of Miami BG 7 (Oscillatoria sp.) in seawater was studied using 2.8 liters of Fernbach batch cultures, 14 liters of Carboy batch cultures, and 7 liters of a controlled environment system. In the batch culture tests, both 'instant ocean' and natural seawater from the local environment were used. The effects of adding supplemental nitrate and ammonia to the seawater bases were also examined. The 7-liter controlled environment culture system provides for the control and monitoring of physical and chemical parameters, and can be used for continuous culture experiments. Work on the comparative study of Anabaena cylindrica and Miamimore » BG 7 indicates that their hydrogen metabolism is quite different having a direct bearing on their applied potential. In particular, this study has shown that there is a strong uptake hydrogenase activity in Anabaena cylindrica in a closed system. This differs sharply with the high rates of production achieved by Anabaena cylindrica in 'flow through systems,' where hydrogen gas is continuously eliminated from the experimental chamber. In contrast, Miami BG 7 exhibits no uptake hydrogenase activity. Consequently, a high rate of hydrogen evolution is maintained.« less

Glutathione-capped gold nanoclusters as photosensitizers. Visible light-induced hydrogen generation in neutral water.

PubMed

Chen, Yong-Siou; Kamat, Prashant V

2014-04-23

Glutathione-capped metal nanoclusters (Aux-GSH NCs) which exhibit molecular-like properties are employed as a photosensitizer for hydrogen generation in a photoelectrochemical cell (PEC) and a photocatalytic slurry reactor. The reversible reduction (E(0) = -0.63 V vs RHE) and oxidation (E(0) = 0.97 and 1.51 V vs RHE) potentials of these metal nanoclusters make them suitable for driving the water-splitting reaction. When a mesoscopic TiO2 film sensitized by Aux-GSH NCs is used as the photoanode with a Pt counter electrode in aqueous buffer solution (pH = 7), we observe significant photocurrent activity under visible light (400-500 nm) excitation. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs in an aqueous slurry system and irradiating with visible light produce H2 at a rate of 0.3 mmol of hydrogen/h/g of Aux-GSH NCs. The rate of H2 evolution is significantly enhanced (∼5 times) when a sacrificial donor, such as EDTA, is introduced into the system. Using metal nanoclusters as a photosensitizer for hydrogen generation lays the foundation for the future exploration of other metal nanoclusters with well-controlled numbers of metal atoms and capping ligands.

Survey of selected seaweeds for simultaneous photoproduction of hydrogen and oxygen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenbaum, E.; Ramus, J.

1983-03-01

Then seaweed species were surveyed for simultaneous photoevolution of hydrogen and oxygen. In an attempt to induce hydrogenase activity (as measured by hydrogen photoproduction) the seaweeds were maintained under anaerobiosis in CO/sub 2/-free seawater for varying lengths of time. Although oxygen evolution was observed in every alga studied, hydrogen evolution was not observed. One conclusion of this research is that, in contrast to the microscopic algae, there is not a single example of a macroscopic alga for which the photoevolution of hydrogen has been observed, in spite of the fact that there are now at least nine macroscopic algal speciesmore » known for which hydrogenase activity has been reported (either by dark hydrogen evolution or light-activated hydrogen uptake). These results are in conflict with the conventional view that algal hydrogenase can catalyze a multiplicity of reactions, one of which is the photoproduction of molecular hydrogen. Two possible explanations for the lack of hydrogen photoproduction in macroscopic algae are presented. It is postulated that electron acceptors other than carbon dioxide can take up reducing equivalents from Photosystem I to the measurable exclusion of hydrogen photoproduction. Alternatively, the hydrogenase system in macroscopic algae may be primarily a hydrogen-uptake system with respect to light-activated reactions. A simple kinetic argument based on recent measurements of the photosynthetic turnover times of simultaneous light-activated hydrogen and oxygen production is presented that supports the second explanation. 25 references, 3 figures, 1 table.« less

A Facile Method for the Preparation of Colored Bi4Ti3O12−x Nanosheets with Enhanced Visible-Light Photocatalytic Hydrogen Evolution Activity

PubMed Central

Zhang, Yizeng; Chen, Zhiwu; Lu, Zhenya

2018-01-01

Bi4Ti3O12−x nanosheet photocatalysts with abundant oxygen vacancies are fabricated by a facile solid-state chemical reduction method for the first time. This method is simple in operation, has short reaction time, and can be conducted at mild temperatures (300~400 °C). The electron paramagnetic resonance, thermogravimetric analysis, X-ray photoelectron spectrometer, and positron annihilation lifetime spectra results indicate that oxygen vacancies are produced in Bi4Ti3O12−x, and they can be adjusted by tuning the reduction reaction conditions. Control experiments show that the reduction time and temperature have great influences on the photocatalytic activities of Bi4Ti3O12−x. The optimal Bi4Ti3O12−x is the sample undergoing the reduction treatment at 350 °C for 60 min and it affords a hydrogen evolution rate of 129 μmol·g−1·h−1 under visible-light irradiation, which is about 3.4 times that of the pristine Bi4Ti3O12. The Bi4Ti3O12−x photocatalysts have good reusability and storage stability and can be used to decompose formaldehyde and formic acid for hydrogen production. The surface oxygen vacancies states result in the broadening of the valence band and the narrowing of the band gap. Such energy level structure variation helps promote the separation of photo-generated electron-hole pairs thus leading to enhancement in the visible-light photocatalytic hydrogen evolution. Meanwhile, the narrowing of the band gap leads to a broader visible light absorption of Bi4Ti3O12−x. PMID:29690518

Sea water magnesium fuel cell power supply

NASA Astrophysics Data System (ADS)

Hahn, Robert; Mainert, Jan; Glaw, Fabian; Lang, K.-D.

2015-08-01

An environmentally friendly magnesium fuel cell system using seawater electrolyte and atmospheric oxygen was tested under practical considerations for use as maritime power supply. The hydrogen rate and therefore the power density of the system were increased by a factor of two by using hydrogen evolution cathodes with a gas separation membrane instead of submerged cathodes without gas separation. Commercial magnesium AZ31 rolled sheet anodes can be dissolved in seawater for hydrogen production, down to a thickness below 100 μm thickness, resulting in hydrogen generation efficiency of the anode of over 80%. A practical specific energy/energy density of the alloy of more than 1200 Wh/kg/3000 Wh/l was achieved when coupled to a fuel cell with atmospheric air breathing cathode. The performance of several AZ31 alloy anodes was tested as well as the influence of temperature, electrolyte concentration and anode - cathode separation. The excess hydrogen produced by the magnesium hydrogen evolving cell, due to the negative difference effect, is proportional to the cell current in case of the AZ31 alloys, which simplifies system control considerably. Stable long-term operation of the system was demonstrated at low pressures which can be maintained in an open-seawater-submerged hydrogen generator.

The effect of zinc on the aluminum anode of the aluminum-air battery

NASA Astrophysics Data System (ADS)

Tang, Yougen; Lu, Lingbin; Roesky, Herbert W.; Wang, Laiwen; Huang, Baiyun

Aluminum is an ideal material for batteries, due to its excellent electrochemical performance. Herein, the effect of zinc on the aluminum anode of the aluminum-air battery, as an additive for aluminum alloy and electrolytes, has been studied. The results show that zinc can decrease the anodic polarization, restrain the hydrogen evolution and increase the anodic utilization rate.

Protoplanetary Nebulae

NASA Astrophysics Data System (ADS)

Kwok, S.; Murdin, P.

2000-11-01

Protoplanetary nebulae (or pre-planetary nebulae, PPNs) are defined as objects that are in transition between the asymptotic giant branch (AGB) and planetary nebula phases of STELLAR EVOLUTION. Stars on the AGB lose mass at a high rate ((10-7-10-4)M⊙ yr-1) in the form of a stellar wind. Such mass loss eventually depletes the hydrogen envelope of the star and exposes the electron-degenerate carbon...

Pulse-reverse electrodeposition for mesoporous metal films: combination of hydrogen evolution assisted deposition and electrochemical dealloying.

PubMed

Cherevko, Serhiy; Kulyk, Nadiia; Chung, Chan-Hwa

2012-01-21

Hydrogen evolution assisted electrodeposition is a new bottom-up technique allowing the fast and simple synthesis of nanometals. Electrochemical dealloying is a top-down approach with the same purpose. In this work, we show that a combination of these two methods in sequence by pulse-reverse electrodeposition can be used to prepare high-surface-area nanostructured metals. Highly porous adherent platinum is obtained by the deposition of CuPt alloy during the cathodic cycles and the selective dissolution of copper during the anodic cycles. The convection created by the movement of the hydrogen bubbles increases the deposition rate and removes the dissolved copper ions from the diffusion layer, which ensures the deposition of a film with the same stoichiometry throughout the whole process. Due to the relatively high ratio of copper atoms on the surface in the as-deposited layer, it is proposed that the dealloying kinetics is significantly higher than that usually observed during the dealloying process in a model system. The proposed approach has several advantages over other methods, such as a very high growth rate and needlessness of any post-treatment processes. A detailed analysis of the effect of pulse-reverse waveform parameters on the properties of the films is presented. Mesoporous platinum with pores and ligaments having characteristic sizes of less than 10 nm, an equivalent surface area of up to ca. 220 m(2) cm(-3), and a roughness factor of more than 1000 is fabricated.

Electron Irradiation of Kuiper Belt Surface Ices: Ternary N2-CH4-CO Mixtures as a Case Study

NASA Astrophysics Data System (ADS)

Kim, Y. S.; Kaiser, R. I.

2012-10-01

The space weathering of icy Kuiper Belt Objects was investigated in this case study by exposing methane (CH4) and carbon monoxide (CO) doped nitrogen (N2) ices at 10 K to ionizing radiation in the form of energetic electrons. Online and in situ Fourier transform infrared spectroscopy was utilized to monitor the radiation-induced chemical processing of these ices. Along with isocyanic acid (HNCO), the products could be mainly derived from those formed in irradiated binary ices of the N2-CH4 and CO-CH4 systems: nitrogen-bearing products were found in the form of hydrogen cyanide (HCN), hydrogen isocyanide (HNC), diazomethane (CH2N2), and its radical fragment (HCN2); oxygen-bearing products were of acetaldehyde (CH3CHO), formyl radical (HCO), and formaldehyde (H2CO). As in the pure ices, the methyl radical (CH3) and ethane (C2H6) were also detected, as were carbon dioxide (CO2) and the azide radical (N3). Based on the temporal evolution of the newly formed products, kinetic reaction schemes were then developed to fit the temporal profiles of the newly formed species, resulting in numerical sets of rate constants. The current study highlights important constraints on the preferential formation of isocyanic acid (HNCO) over hydrogen cyanide (HCN) and hydrogen isocyanide (HNC), thus guiding the astrobiological and chemical evolution of those distant bodies.

Microbial detection method based on sensing molecular hydrogen

NASA Technical Reports Server (NTRS)

Wilkins, J. R.; Stoner, G. E.; Boykin, E. H.

1974-01-01

An approach involving the measurement of hydrogen evolution by test organisms was used to detect and enumerate various members of the Enterobacteriaceae group. The experimental setup for measuring hydrogen evolution consisted of a test tube containing two electrodes plus broth and organisms. The test tube was kept in a water bath at a temperature of 35 C. It is pointed out that the hydrogen-sensing method, coupled with the pressure transducer technique reported by Wilkins (1974) could be used in various experiments in which gas production by microorganisms is being measured.

Enhancement in hydrogen evolution using Au-TiO2 hollow spheres with microbial devices modified with conjugated oligoelectrolytes

PubMed Central

Ngaw, Chee Keong; Wang, Victor Bochuan; Liu, Zhengyi; Zhou, Yi; Kjelleberg, Staffan; Zhang, Qichun; Tan, Timothy Thatt Yang; Loo, Say Chye Joachim

2015-01-01

Objective: Although photoelectrochemical (PEC) water splitting heralds the emergence of the hydrogen economy, the need for external bias and low efficiency stymies the widespread application of this technology. By coupling water splitting (in a PEC cell) to a microbial fuel cell (MFC) using Escherichia coli as the biocatalyst, this work aims to successfully demonstrate a sustainable hybrid PEC–MFC platform functioning solely by biocatalysis and solar energy, at zero bias. Through further chemical modification of the photo-anode (in the PEC cell) and biofilm (in the MFC), the performance of the hybrid system is expected to improve in terms of the photocurrent generated and hydrogen evolved. Methods: The hybrid system constitutes the interconnected PEC cell with the MFC. Both PEC cell and MFC are typical two-chambered systems housing the anode and cathode. Au-TiO2 hollow spheres and conjugated oligoelectrolytes were synthesised chemically and introduced to the PEC cell and MFC, respectively. Hydrogen evolution measurements were performed in triplicates. Results: The hybrid PEC–MFC platform generated a photocurrent density of 0.35 mA/cm2 (~70× enhancement) as compared with the stand-alone P25 standard PEC cell (0.005 mA/cm2) under one-sun illumination (100 mW/cm2) at zero bias (0 V vs. Pt). This increase in photocurrent density was accompanied by continuous H2 production. No H2 was observed in the P25 standard PEC cell whereas H2 evolution rate was ~3.4 μmol/h in the hybrid system. The remarkable performance is attributed to the chemical modification of E. coli through the incorporation of novel conjugated oligoelectrolytes in the MFC as well as the lower recombination rate and higher photoabsorption capabilities in the Au-TiO2 hollow spheres electrode. Conclusions: The combined strategy of photo-anode modification in PEC cells and chemically modified MFCs shows great promise for future exploitation of such synergistic effects between MFCs and semiconductor-based PEC water splitting. PMID:28721235

Testing the 'free radical theory of aging' hypothesis: physiological differences in long-lived and short-lived colubrid snakes.

PubMed

Robert, Kylie A; Brunet-Rossinni, Anja; Bronikowski, Anne M

2007-06-01

We test the 'free radical theory of aging' using six species of colubrid snakes (numerous, widely distributed, non-venomous snakes of the family Colubridae) that exhibit long (> 15 years) or short (< 10 years) lifespans. Because the 'rate of living theory' predicts metabolic rates to be correlated with rates of aging and oxidative damage results from normal metabolic processes we sought to answer whether physiological parameters and locomotor performance (which is a good predictor of survival in juvenile snakes) mirrored the evolution of lifespans in these colubrid snakes. We measured whole animal metabolic rate (oxygen consumption Vo2), locomotor performance, cellular metabolic rate (mitochondrial oxygen consumption), and oxidative stress potential (hydrogen peroxide production by mitochondria). Longer-lived colubrid snakes have greater locomotor performance and reduced hydrogen peroxide production than short-lived species, while whole animal metabolic rates and mitochondrial efficiency did not differ with lifespan. We present the first measures testing the 'free radical theory of aging' using reptilian species as model organisms. Using reptiles with different lifespans as model organisms should provide greater insight into mechanisms of aging.

Effect of Soret diffusion on lean hydrogen/air flames at normal and elevated pressure and temperature

NASA Astrophysics Data System (ADS)

Zhou, Zhen; Hernández-Pérez, Francisco E.; Shoshin, Yuriy; van Oijen, Jeroen A.; de Goey, Laurentius P. H.

2017-09-01

The influence of Soret diffusion on lean premixed flames propagating in hydrogen/air mixtures is numerically investigated with a detailed chemical and transport models at normal and elevated pressure and temperature. The Soret diffusion influence on the one-dimensional (1D) flame mass burning rate and two-dimensional (2D) flame propagating characteristics is analysed, revealing a strong dependency on flame stretch rate, pressure and temperature. For 1D flames, at normal pressure and temperature, with an increase of Karlovitz number from 0 to 0.4, the mass burning rate is first reduced and then enhanced by Soret diffusion of H2 while it is reduced by Soret diffusion of H. The influence of Soret diffusion of H2 is enhanced by pressure and reduced by temperature. On the contrary, the influence of Soret diffusion of H is reduced by pressure and enhanced by temperature. For 2D flames, at normal pressure and temperature, during the early phase of flame evolution, flames with Soret diffusion display more curved flame cells. Pressure enhances this effect, while temperature reduces it. The influence of Soret diffusion of H2 on the global consumption speed is enhanced at elevated pressure. The influence of Soret diffusion of H on the global consumption speed is enhanced at elevated temperature. The flame evolution is more affected by Soret diffusion in the early phase of propagation than in the long run due to the local enrichment of H2 caused by flame curvature effects. The present study provides new insights into the Soret diffusion effect on the characteristics of lean hydrogen/air flames at conditions that are relevant to practical applications, e.g. gas engines and turbines.

Multiphysics phase field modeling of hydrogen diffusion and delta-hydride precipitation in alpha-zirconium

NASA Astrophysics Data System (ADS)

Jokisaari, Andrea M.

Hydride precipitation in zirconium is a significant factor limiting the lifetime of nuclear fuel cladding, because hydride microstructures play a key role in the degradation of fuel cladding. However, the behavior of hydrogen in zirconium has typically been modeled using mean field approaches, which do not consider microstructural evolution. This thesis describes a quantitative microstructural evolution model for the alpha-zirconium/delta-hydride system and the associated numerical methods and algorithms that were developed. The multiphysics, phase field-based model incorporates CALPHAD free energy descriptions, linear elastic solid mechanics, and classical nucleation theory. A flexible simulation software implementing the model, Hyrax, is built on the Multiphysics Object Oriented Simulation Environment (MOOSE) finite element framework. Hyrax is open-source and freely available; moreover, the numerical methods and algorithms that have been developed are generalizable to other systems. The algorithms are described in detail, and verification studies for each are discussed. In addition, analyses of the sensitivity of the simulation results to the choice of numerical parameters are presented. For example, threshold values for the CALPHAD free energy algorithm and the use of mesh and time adaptivity when employing the nucleation algorithm are studied. Furthermore, preliminary insights into the nucleation behavior of delta-hydrides are described. These include a) the sensitivities of the nucleation rate to temperature, interfacial energy, composition and elastic energy, b) the spatial variation of the nucleation rate around a single precipitate, and c) the effect of interfacial energy and nucleation rate on the precipitate microstructure. Finally, several avenues for future work are discussed. Topics encompass the terminal solid solubility hysteresis of hydrogen in zirconium and the effects of the alpha/delta interfacial energy, as well as thermodiffusion, plasticity, and irradiation, which are not yet accounted for in the model.

Cell-Free Synthetic Biology Chassis for Nanocatalytic Photon-to-Hydrogen Conversion

DOE PAGES

Wang, Peng; Chang, Angela Y.; Novosad, Valentyn; ...

2017-06-11

We report on entirely man-made nanobio hybrid fabricated through assembly of cell-free expressed transmembrane proton pump and semiconductor nanoparticles as an efficient nanocatalysis for photocatalytic H 2 evolution. The system produces H 2 at a turnover rate of 239 (μmole protein) -1 h -1 under green and 17742 (μmole protein) -1 h -1 under white light at ambient conditions, in water at neutral pH with methanol as a sacrificial electron donor. Robustness and flexibility of this approach allows for systemic manipulation at nanoparticle-bio interface toward directed evolution of energy transformation materials and artificial systems.

Cell-Free Synthetic Biology Chassis for Nanocatalytic Photon-to-Hydrogen Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Peng; Chang, Angela Y.; Novosad, Valentyn

We report on entirely man-made nanobio hybrid fabricated through assembly of cell-free expressed transmembrane proton pump and semiconductor nanoparticles as an efficient nanocatalysis for photocatalytic H 2 evolution. The system produces H 2 at a turnover rate of 239 (μmole protein) -1 h -1 under green and 17742 (μmole protein) -1 h -1 under white light at ambient conditions, in water at neutral pH with methanol as a sacrificial electron donor. Robustness and flexibility of this approach allows for systemic manipulation at nanoparticle-bio interface toward directed evolution of energy transformation materials and artificial systems.

Highly efficient hydrogen storage system based on ammonium bicarbonate/formate redox equilibrium over palladium nanocatalysts.

PubMed

Su, Ji; Yang, Lisha; Lu, Mi; Lin, Hongfei

2015-03-01

A highly efficient, reversible hydrogen storage-evolution process has been developed based on the ammonium bicarbonate/formate redox equilibrium over the same carbon-supported palladium nanocatalyst. This heterogeneously catalyzed hydrogen storage system is comparable to the counterpart homogeneous systems and has shown fast reaction kinetics of both the hydrogenation of ammonium bicarbonate and the dehydrogenation of ammonium formate under mild operating conditions. By adjusting temperature and pressure, the extent of hydrogen storage and evolution can be well controlled in the same catalytic system. Moreover, the hydrogen storage system based on aqueous-phase ammonium formate is advantageous owing to its high volumetric energy density. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced electrocatalytic activity of MoS(x) on TCNQ-treated electrode for hydrogen evolution reaction.

PubMed

Chang, Yung-Huang; Nikam, Revannath D; Lin, Cheng-Te; Huang, Jing-Kai; Tseng, Chien-Chih; Hsu, Chang-Lung; Cheng, Chia-Chin; Su, Ching-Yuan; Li, Lain-Jong; Chua, Daniel H C

2014-10-22

Molybdenum sulfide has recently attracted much attention because of its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 °C. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo(5+) and S2(2-) species in the MoSx, especially with S2(2-) serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mL g(-1) cm(-2) h(-1) (286 mmol g(-1) cm(-2) h(-1)) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy.

Towards a better understanding of the evolution of Wolf-Rayet stars and Type Ib/Ic supernova progenitors

NASA Astrophysics Data System (ADS)

Yoon, Sung-Chul

2017-10-01

Hydrogen-deficient Wolf-Rayet (WR) stars are potential candidates of Type Ib/Ic supernova (SN Ib/Ic) progenitors and their evolution is governed by mass-loss. Stellar evolution models with the most popular prescription for WR mass-loss rates given by Nugis & Lamers have difficulties in explaining the luminosity distribution of WR stars of WC and WO types and the SN Ic progenitor properties. Here, we suggest some improvements in the WR mass-loss rate prescription and discuss its implications for the evolution of WR stars and SN Ib/Ic progenitors. Recent studies on Galactic WR stars clearly indicate that the mass-loss rates of WC stars are systematically higher than those of WNE stars for a given luminosity. The luminosity and initial metallicity dependences of WNE mass-loss rates are also significantly different from those of WC stars. These factors have not been adequately considered together in previous stellar evolution models. We also find that an overall increase of WR mass-loss rates by about 60 per cent compared to the empirical values obtained with a clumping factor of 10 is needed to explain the most faint WC/WO stars. This moderate increase with our new WR mass-loss rate prescription results in SN Ib/Ic progenitor models more consistent with observations than those given by the Nugis & Lamers prescription. In particular, our new models predict that the properties of SN Ib and SN Ic progenitors are distinctively different, rather than they form a continuous sequence.

Design of catalysts by different substituent groups to the ;cut g-C3N4; single layer

NASA Astrophysics Data System (ADS)

Xu, Weiwei; Tang, Chao; Chen, Chongyang; Li, Youyong; Xu, Lai

2017-09-01

Graphitic carbon nitride has been wildly studied as a kind of promising photocatalysts for hydrogen evolution. However, it has a low intrinsic activity. Herein, we designed new periodic structures "cut g-C3N4", and adding the new substituent groups. We employed density functional theory to calculate the charge distribution and catalytic properties of hydrogen evolution on the structures. We got a theoretical view that introducing conjugate substituents can enhance the catalytic performance for hydrogen evolution. Furthermore, it provided a theoretical guidance for the reasonable design of two dimensional non-metallic photocatalysts, with lower activation barrier of the catalytic reaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Viswanathan, Venkatasubramanian; Hansen, Heine A.; Norskov, Jens K.

Water is a life-giving source, fundamental to human existence, yet over a billion people lack access to clean drinking water. The present techniques for water treatment such as piped, treated water rely on time and resource intensive centralized solutions. In this work, we propose a decentralized device concept that can utilize sunlight to split water into hydrogen and hydrogen peroxide. The hydrogen peroxide can oxidize organics while the hydrogen bubbles out. In enabling this device, we require an electrocatalyst that can oxidize water while suppressing the thermodynamically favored oxygen evolution and form hydrogen peroxide. Using density functional theory calculations, wemore » show that the free energy of adsorbed OH* can be used to determine selectivity trends between the 2e– water oxidation to H 2O 2 and the 4e– oxidation to O 2. We show that materials which bind oxygen intermediates sufficiently weakly, such as SnO 2, can activate hydrogen peroxide evolution. Furthermore, we present a rational design principle for the selectivity in electrochemical water oxidation and identify new material candidates that could perform H 2O 2 evolution selectively.« less

In situ grown Ni9S8 nanorod/O-MoS2 nanosheet nanocomposite on carbon cloth as a free binder supercapacitor electrode and hydrogen evolution catalyst

NASA Astrophysics Data System (ADS)

Li, Songzhan; Chen, Tian; Wen, Jian; Gui, Pengbin; Fang, Guojia

2017-11-01

Transition metal sulfide nanostructure composites have received significant attention as energy conversion and storage devices. In this work, we report a three-dimension (3D) nanostructure with the Ni9S8 nanorods embedded in oxygen-incorporated MoS2 (O-MoS2) nanosheets for supercapacitors and hydrogen evolution catalysts. The in situ grown Ni9S8/O-MoS2 nanocomposite on carbon cloth can be used as a free binder supercapacitor electrode and hydrogen evolution catalyst. The Ni9S8/O-MoS2 nanocomposite exhibits electrochemical behaviors with a specific capacitance of 907 F g-1 (at 2 A g-1) and good cycle stability after 1200 cycles due to its unique mutual embedding 3D nanostructure. Furthermore, the Ni9S8/O-MoS2 nanocomposite also shows highly electrocatalytic features for hydrogen production with an onset overpotential of ˜150 mV and a low Tafel slope of ˜81 mV dec-1. The oxygen incorporation of MoS2 provides more active sites to participate in the catalytic process for the hydrogen evolution reaction.

Programming temporal shapeshifting

NASA Astrophysics Data System (ADS)

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad; Daniel, William F. M.; Li, Qiaoxi; Zhushma, Aleksandr P.; Dobrynin, Andrey V.; Sheiko, Sergei S.

2016-09-01

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds, this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. This generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.

Biomass transition metal hydrogen-evolution electrocatalysts and electrodes

DOEpatents

Chen, Wei-Fu; Iyer, Shweta; Iyer, Shilpa; Sasaki, Kotaro; Muckerman, James T.; Fujita, Etsuko

2017-02-28

A catalytic composition from earth-abundant transition metal salts and biomass is disclosed. A calcined catalytic composition formed from soybean powder and ammonium molybdate is specifically exemplified herein. Methods for making the catalytic composition are disclosed as are electrodes for hydrogen evolution reactions comprising the catalytic composition.

Photosynthetic water splitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenbaum, E.

1981-01-01

The photosynthetic unit of hydrogen evolution, the turnover time of photosynthetic hydrogen production, and hydrogenic photosynthesis are discussed in the section on previous work. Recent results are given on simultaneous photoproduction of hydrogen and oxygen, kinetic studies, microscopic marine algae-seaweeds, and oxygen profiles.

Graphene quantum dots to enhance the photocatalytic hydrogen evolution efficiency of anatase TiO2 with exposed {001} facet.

PubMed

Yu, Shan; Zhong, Yun-Qian; Yu, Bao-Quan; Cai, Shi-Yi; Wu, Li-Zhu; Zhou, Ying

2016-07-27

Hydrogen evolution through photocatalysis is promising with respect to the environmental problems and challenges of energy shortage that we encounter today. In this paper, we have combined graphene quantum dots (GQDs) and {001} faceted anatase TiO2 (with an exposed percentage of 65-75%) together for effective photocatalytic hydrogen evolution. A series of characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and UV-visible absorption spectroscopy have been carried out to study the structure of the as-prepared GQDs/{001}TiO2 composite. It turns out that GQDs could be effectively decorated on {001}TiO2 sheet without changing its intrinsic structure. With an optimum loading amount of GQDs (0.5 wt% to {001}TiO2), GQDs/{001}TiO2 exhibits a hydrogen evolution efficiency 8 times higher than that of bare {001}TiO2, which is a significantly more obvious improvement than many other photocatalytic systems relevant to GQDs and TiO2 hybrids. In addition, GQDs/{001}TiO2 could stand long-term photocatalytic experiments. Photocurrent tests show that such an improvement of the photocatalytic efficiency over GQDs/{001}TiO2 may originate from a higher charge separation efficiency. The present study could offer reference for the construction of photocatalytic hydrogen evolution systems with low cost and long term stability.

In situ study of LaY2Ni9 compound as Ni MH negative-electrode material

NASA Astrophysics Data System (ADS)

Latroche, M.; Isnard, O.

2008-03-01

The behavior of a Ni-MH (metal hydride) negative composite electrode made of LaY2Ni9 active material has been studied dynamically using in situ neutron diffraction during a complete charge-discharge electrochemical cycle. From the analysis of the collected diffraction patterns, the phase identity, phase amount variations and cell volume evolutions have been determined as a function of the electrochemical state of (dis)charge. The active material shows a typical two-phase behavior with equilibrium between a hydrogen-poor α phase and a hydrogen-rich β one. The lower electrochemical reversible capacity as compared to solid-gas properties has been interpreted in terms of hydrogen gas evolving during charge and kinetic limitation due to slow β to α transformation during discharge, which hinders high discharge rates.

Mace-like hierarchical MoS2/NiCo2S4 composites supported by carbon fiber paper: An efficient electrocatalyst for the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Sun, Lan; Wang, Tao; Zhang, Long; Sun, Yunjin; Xu, Kewei; Dai, Zhengfei; Ma, Fei

2018-02-01

The rational design and preparation of earth-abundant, stable and efficient electrocatalysts for hydrogen production is currently the subject in extensive scientific and technological researches toward the future of a clean-energy society. Herein, a mace-like MoS2/NiCo2S4 hierarchical structure is designed and synthesized on carbon fiber paper via a facile hydrothermal method, and evaluated as electrocatalyst for hydrogen evolution reaction. In the MoS2/NiCo2S4/carbon fiber paper hierarchical structures, MoS2 nanosheets are dispersively distributed on the surface of NiCo2S4 nanowires, which provides an enlarged surface area, abundant interfaces and catalytic active sites. As for hydrogen evolution reaction, such MoS2/NiCo2S4/carbon fiber paper heterostructures give rise to a hydrogen evolution reaction catalytic current density of 10 mA cm-2 with a lower overpotential of 139 mV and a smaller Tafel slope of 37 mV·dec-1 than those of MoS2/carbon fiber paper and NiCo2S4/carbon fiber paper counterparts, exhibiting a prominent electrocatalytic performance. Moreover, the electrocatalytic properties change little after 5000 CV cycles and continual electrolysis for 12 h without obvious decay, respectively, demonstrating high durability and stability. The excellent hydrogen evolution reaction performances endow the hierarchical configuration MoS2/NiCo2S4/carbon fiber paper with promising alternative in HER and other related renewable energy fields.

Zinc electrodeposition from flowing alkaline zincate solutions: Role of hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Dundálek, Jan; Šnajdr, Ivo; Libánský, Ondřej; Vrána, Jiří; Pocedič, Jaromír; Mazúr, Petr; Kosek, Juraj

2017-12-01

The hydrogen evolution reaction is known as a parasitic reaction during the zinc electrodeposition from alkaline zincate solutions and is thus responsible for current efficiency losses during the electrolysis. Besides that, the rising hydrogen bubbles may cause an extra convection within a diffusion layer, which leads to an enhanced mass transport of zincate ions to an electrode surface. In this work, the mentioned phenomena were studied experimentally in a flow through electrolyzer and the obtained data were subsequently evaluated by mathematical models. The results prove the indisputable influence of the rising hydrogen bubbles on the additional mixing of the diffusion layer, which partially compensates the drop of the current efficiency of the zinc deposition at higher current flows. Moreover, the results show that the current density ratio (i.e., the ratio of an overall current density to a zinc limiting current density) is not suitable for the description of the zinc deposition, because the hydrogen evolution current density is always involved in the overall current density.

Enzyme electrokinetics: hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase.

PubMed

Léger, Christophe; Jones, Anne K; Roseboom, Winfried; Albracht, Simon P J; Armstrong, Fraser A

2002-12-31

The mechanism of catalytic hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase has been studied by protein film voltammetry (PFV) with the enzyme adsorbed at a pyrolytic graphite edge electrode. By analyzing the entire shapes of catalytic voltammograms, the energetics of the catalytic cycles (reduction potentials and acidity constants of the active states), including the detailed profiles of activity against pH and the sequences of proton and electron transfers, have been determined, and these are discussed with respect to the mechanism. PFV, which probes rates as a continuous function of the electrochemical potential (i.e., in the "potential domain"), is proven to be an invaluable tool for determining the redox properties of an active site in the presence of its substrate, at room temperature, and during turnover. This is especially relevant in the case of the active states of hydrogenase, since one of its substrates (the proton) is always present at significant levels in the titration medium at physiological pH values.

Enhanced lithium-ion storage and hydrogen evolution reaction catalysis of MoS2/graphene nanoribbons hybrids with loose interlaced three-dimension structure

NASA Astrophysics Data System (ADS)

Wu, Xuan; Fan, Zihan; Ling, Xiaolun; Wu, Shuting; Chen, Xin; Hu, Xiaolin; Zhuang, Naifeng; Chen, Jianzhong

2018-06-01

Molybdenum disulfide hybridized with graphene nanoribbon (MoS2/GNR) was prepared by mild method. MoS2/GNR hybrids interlace loosely into a three-dimension structure. GNR hybridization can improve the dispersity of MoS2, reduce the grain size of MoS2 to 3-6 nm, increase the specific surface area, and broaden the interlamellar spacing of MoS2 (002) plane to 0.67-0.73 nm, which facilitates the transportation of Li+ ions for lithium-ion battery. MoS2/GNR hybrids have better cyclic durability, higher specific discharge capacity, and superior rate performance than MoS2. The electrocatalytic activity in hydrogen evolution reaction shows that MoS2/GNR hybrids have the lower overpotential and the larger current density with a negligible current loss after 2000 cycles. Hybridizing with GNRs enhances both the lithium-ion electrochemical storage and the electrocatalytic activity of MoS2. [Figure not available: see fulltext.

Unique Fe2P Nanoparticles Enveloped in Sandwichlike Graphited Carbon Sheets as Excellent Hydrogen Evolution Reaction Catalyst and Lithium-Ion Battery Anode.

PubMed

Zhang, Yan; Zhang, Huijuan; Feng, Yangyang; Liu, Li; Wang, Yu

2015-12-09

The novel Fe2P nanoparticles encapsulated in sandwichlike graphited carbon envelope nanocomposite (Fe2P/GCS) that can be first applied in hydrogen evolution reaction (HER) as well as lithium-ion batteries (LIBs) has been designed and fabricated. The unique sandwiched Fe2P/GCS is characterized with several prominent merits, including large specific surface area, nanoporous structure, excellent electronic conductivity, enhanced structural integrity and so on. All of these endow the Fe2P/GCS with brilliant electrochemical performance. When used as a HER electrocatalyst in acidic media, the harvested Fe2P/GCS demonstrates low onset overpotential and Tafel slope as well as particularly outstanding durability. Moreover, as an anode material for LIBs, the sandwiched Fe2P/GCS presents high specific capacity and excellent cyclability and rate capability. As a consequence, the acquired Fe2P/GCS is a promising material for energy applications, especially HER and LIBs.

White dwarf models for type 1 supernovae and quiet supernovae, and presupernova evolution

NASA Technical Reports Server (NTRS)

Nomoto, K.

1980-01-01

Supernova mechanisms in accreting white dwarfs are considered with emphasis on deflagration as a plausible mechanism for producing Type I supernovae and electron captures to form quiet supernovae leaving neutron stars. These outcomes depend on accretion rate of helium, initial mass and composition of the white dwarf. The various types of hydrogen shell burning in the presupernova stage are also discussed.

The Rise of Oxygen and the Hydrogen Hourglass

NASA Technical Reports Server (NTRS)

Zahnle, Kevin; Catling, David C.; Claire, Mark W.

2013-01-01

Oxygenic photosynthesis appears to be necessary for an oxygen-rich atmosphere like Earth's. But available geological and geochemical evidence suggest that at least 200 Myr, and possibly more than 700 Myr, elapsed between the advent of oxygenic photosynthesis and the establishment of an oxygen atmosphere. The interregnum implies that at least one other necessary condition for O2 needed to be met. Here we argue that the second condition was the oxidation of the surface and crust to the point where O2 became more stable than competing reduced gases such as CH4. The cause of Earth's surface oxidation would be the same cause as it is for other planets with oxidized surfaces: hydrogen escape to space. The duration of the interregnum would have been determined by the rate of hydrogen escape and by the size of the reduced reservoir that needed to be oxidized before O2 became favored. We suggest that continental growth has been influenced by hydrogen escape, and we speculate that, if there must be an external bias to biological evolution, hydrogen escape can be that bias.

On the mobility of carbon-supported platinum nanoparticles towards unveiling cathode degradation in water electrolysis

NASA Astrophysics Data System (ADS)

Paciok, Paul; Schalenbach, Maximilian; Carmo, Marcelo; Stolten, Detlef

2017-10-01

This study investigates the influence of the hydrogen evolution reaction (HER) overpotential on the mobility of carbon-supported platinum particles. The migration of the platinum over the carbon support was analyzed by means of identical location transmission electron microscopy (IL-TEM). While at potentials of 0.1 and 0 V vs. reversible hydrogen electrode (RHE), no changes to the Pt/C material were observed. With a decrease of the overpotential to -0.1 V vs. RHE, an increase in the quantity of migrating platinum particles took place. At -0.2 V vs. RHE, a further rise in the particle migration was observed. The effect of the overpotential on the migration was explained by a higher hydrogen generation rate, the formation of a hydrogen monolayer on the platinum and the resulting changes of the platinum support distance. The mechanisms revealed in this study could describe a relevant source of degradation of PEM water electrolyzers.

Seasonal variability of the hydrogen exosphere of Mars

NASA Astrophysics Data System (ADS)

Halekas, J. S.

2017-05-01

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures both the upstream solar wind and collisional products from energetic neutral hydrogen atoms that precipitate into the upper atmosphere after their initial formation by charge exchange with exospheric hydrogen. By computing the ratio between the densities of these populations, we derive a robust measurement of the column density of exospheric hydrogen upstream of the Martian bow shock. By comparing with Chamberlain-type model exospheres, we place new constraints on the structure and escape rates of exospheric hydrogen, derived from observations sensitive to a different and potentially complementary column from most scattered sunlight observations. Our observations provide quantitative estimates of the hydrogen exosphere with nearly complete temporal coverage, revealing order of magnitude seasonal changes in column density and a peak slightly after perihelion, approximately at southern summer solstice. The timing of this peak suggests either a lag in the response of the Martian atmosphere to solar inputs or a seasonal effect driven by lower atmosphere dynamics. The high degree of seasonal variability implied by our observations suggests that the Martian atmosphere and the thermal escape of light elements depend sensitively on solar inputs.

Ambient ammonia synthesis via palladium-catalyzed electrohydrogenation of dinitrogen at low overpotential.

PubMed

Wang, Jun; Yu, Liang; Hu, Lin; Chen, Gang; Xin, Hongliang; Feng, Xiaofeng

2018-05-15

Electrochemical reduction of N 2 to NH 3 provides an alternative to the Haber-Bosch process for sustainable, distributed production of NH 3 when powered by renewable electricity. However, the development of such process has been impeded by the lack of efficient electrocatalysts for N 2 reduction. Here we report efficient electroreduction of N 2 to NH 3 on palladium nanoparticles in phosphate buffer solution under ambient conditions, which exhibits high activity and selectivity with an NH 3 yield rate of ~4.5 μg mg -1 Pd h -1 and a Faradaic efficiency of 8.2% at 0.1 V vs. the reversible hydrogen electrode (corresponding to a low overpotential of 56 mV), outperforming other catalysts including gold and platinum. Density functional theory calculations suggest that the unique activity of palladium originates from its balanced hydrogen evolution activity and the Grotthuss-like hydride transfer mechanism on α-palladium hydride that lowers the free energy barrier of N 2 hydrogenation to *N 2 H, the rate-limiting step for NH 3 electrosynthesis.

A high performance neutron spectrometer for planetary hydrogen measurement

NASA Astrophysics Data System (ADS)

Naito, Masayuki; Hasebe, Nobuyuki; Nagaoka, Hiroshi; Ishii, Junya; Aoki, Daisuke; Shibamura, Eido; Kim, Kyeong J.; Matias-Lopes, José A.; Martínez-Frías, Jesús

2017-08-01

The elemental composition and its distribution on planetary surface provide important constraints on the origin and evolution of the planetary body. The nuclear spectrometer consisting of a neutron spectrometer and a gamma-ray spectrometer obtains elemental compositions by remote sensing. Especially, the neutron spectrometer is able to determine the hydrogen concentration, a piece of information that plays an important role in thermal history of the planets. In this work, numerical and experimental studies on the neutron spectrometer for micro-satellite application were conducted. It is found that background count rate of neutron produced from micro-satellite is very small, which enables to obtain successful results in short time observation. The neutron spectrometer combining a lithium-6 glass scintillator with a boron loaded plastic scintillator was used to be able to detect neutrons in different energy ranges. It was experimentally confirmed that the neutron signals from these scintillators were successfully discriminated by the difference of scintillation decay time between two detectors. The measurement of neutron count rates of two scintillators is found to determine hydrogen concentration on the planetary surfaces in the future missions.

Hydrogen-Treated Rutile TiO2 Shell in Graphite-Core Structure as a Negative Electrode for High-Performance Vanadium Redox Flow Batteries.

PubMed

Vázquez-Galván, Javier; Flox, Cristina; Fàbrega, Cristian; Ventosa, Edgar; Parra, Andres; Andreu, Teresa; Morante, Joan Ramón

2017-05-09

Hydrogen-treated TiO 2 as an electrocatalyst has shown to boost the capacity of high-performance all-vanadium redox flow batteries (VRFBs) as a simple and eco-friendly strategy. The graphite felt-based GF@TiO 2 :H electrode is able to inhibit the hydrogen evolution reaction (HER), which is a critical barrier for operating at high rate for long-term cycling in VRFBs. Significant improvements in charge/discharge and electron-transfer processes for the V 3+ /V 2+ reaction on the surface of reduced TiO 2 were achieved as a consequence of the formation of oxygen functional groups and oxygen vacancies in the lattice structure. Key performance indicators of VRFB have been improved, such as high capability rates and electrolyte-utilization ratios (82 % at 200 mA cm -2 ). Additionally, high coulombic efficiencies (ca. 100 % up to the 96th cycle, afterwards >97 %) were obtained, demonstrating the feasibility of achieving long-term stability. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Is light-induced degradation of a-Si:H/c-Si interfaces reversible?

DOE Office of Scientific and Technical Information (OSTI.GOV)

El Mhamdi, El Mahdi; Holovsky, Jakub; Demaurex, Bénédicte

2014-06-23

Thin hydrogenated amorphous silicon (a-Si:H) films deposited on crystalline silicon (c-Si) surfaces are sensitive probes for the bulk electronic properties of a-Si:H. Here, we use such samples during repeated low-temperature annealing and visible-light soaking to investigate the long-term stability of a-Si:H films. We observe that during annealing the electronic improvement of the interfaces follows stretched exponentials as long as hydrogen evolution in the films can be detected. Once such evolution is no longer observed, the electronic improvement occurs much faster. Based on these findings, we discuss how the reversibility of light-induced defects depends on (the lack of observable) hydrogen evolution.

Photocatalytic hydrogen evolution over β-iron silicide under infrared-light irradiation.

PubMed

Yoshimizu, Masaharu; Kobayashi, Ryoya; Saegusa, Makoto; Takashima, Toshihiro; Funakubo, Hiroshi; Akiyama, Kensuke; Matsumoto, Yoshihisa; Irie, Hiroshi

2015-02-18

We investigated the ability of β-iron silicide (β-FeSi2) to serve as a hydrogen (H2)-evolution photocatalyst due to the potential of its conduction band bottom, which may allow thermodynamically favorable H2 evolution in spite of its small band-gap of 0.80 eV. β-FeSi2 had an apparent quantum efficiency for H2 evolution of ∼24% up to 950 nm (near infrared light), in the presence of the dithionic acid ion (S2O6(2-)) as a sacrificial agent. It was also sensitive to infrared light (>1300 nm) for H2 evolution.

Shortest recurrence periods of novae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kato, Mariko; Saio, Hideyuki; Hachisu, Izumi

Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M {sub ☉} WD with a mass accretion rate of 3.6 × 10{sup –7} M {sub ☉} yr{sup –1}. A 1 yr recurrence period is realized for very massivemore » (≳ 1.3 M {sub ☉}) WDs with very high accretion rates (≳ 1.5 × 10{sup –7} M {sub ☉} yr{sup –1}). We revised our stability limit of hydrogen shell burning, which will be useful for binary evolution calculations toward Type Ia supernovae.« less

Electrochemical Hydrogen Evolution: Sabatier's Principle and the Volcano Plot

ERIC Educational Resources Information Center

Laursen, Anders B.; Varela, Ana Sofia; Dionigi, Fabio; Fanchiu, Hank; Miller, Chandler; Trinhammer, Ole L.; Rossmeisl, Jan; Dahl, Soren

2012-01-01

The electrochemical hydrogen evolution reaction (HER) is growing in significance as society begins to rely more on renewable energy sources such as wind and solar power. Thus, research on designing new, inexpensive, and abundant HER catalysts is important. Here, we describe how a simple experiment combined with results from density functional…

Polyallylamine-Rh nanosheet nanoassemblies-carbon nanotubes organic-inorganic nanohybrids: A electrocatalyst superior to Pt for the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Bai, Juan; Xing, Shi-Hui; Zhu, Ying-Ying; Jiang, Jia-Xing; Zeng, Jing-Hui; Chen, Yu

2018-05-01

Rationally tailoring the surface/interface structures of noble metal nanostructures emerges as a highly efficient method for improving their electrocatalytic activity, selectivity, and long-term stability. Recently, hydrogen evolution reaction is attracting more and more attention due to the energy crisis and environment pollution. Herein, we successfully synthesize polyallylamine-functionalized rhodium nanosheet nanoassemblies-carbon nanotube nanohybrids via a facile one-pot hydrothermal method. Three-dimensionally branched rhodium nanosheet nanoassemblies are consisted of two dimensionally atomically thick ultrathin rhodium nanosheets. The as-prepared polyallylamine-functionalized rhodium nanosheet nanoassemblies-carbon nanotube nanohybrids show the excellent electrocatalytic activity for the hydrogen evolution reaction in acidic media, with a low onset reduction potential of -1 mV, a small overpotential of 5 mV at 10 mA cm-2, which is much superior to commercial platinum nanocrystals. Two dimensionally ultrathin morphology of rhodium nanosheet, particular rhodium-polyallylamine interface, and three-dimensionally networks induced by carbon nanotube are the key factors for the excellent hydrogen evolution reaction activity in acidic media.

MoS2 @HKUST-1 Flower-Like Nanohybrids for Efficient Hydrogen Evolution Reactions.

PubMed

Wang, Chengli; Su, Yingchun; Zhao, Xiaole; Tong, Shanshan; Han, Xiaojun

2018-01-24

A novel MoS 2 -based flower-like nanohybrid for hydrogen evolution was fabricated through coating the Cu-containing metal-organic framework (HKUST-1) onto MoS 2 nanosheets. It is the first time that MoS 2 @HKUST-1 nanohybrids have been reported for the enhanced electrochemical performance of HER. The morphologies and components of the MoS 2 @HKUST-1 flower-like nanohybrids were characterized by scanning electron microscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. Compared with pure MoS 2 , the MoS 2 @HKUST-1 hybrids exhibit enhanced performance on hydrogen evolution reaction with an onset potential of -99 mV, a smaller Tafel slope of 69 mV dec -1 , and a Faradaic efficiency of nearly 100 %. The MoS 2 @HKUST-1 flower-like nanohybrids exhibit excellent stability in acidic media. This design opens new possibilities to effectively synthesize non-noble metal catalysts with high performance for the hydrogen evolution reaction (HER). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-Pressurization of a Flightweight, Liquid Hydrogen Tank: Simulation and Comparison with Experiments

NASA Technical Reports Server (NTRS)

Stewart, Mark E. M.; Moder, Jeffrey P.

2016-01-01

This paper presents ANSYS Fluent simulation results and analysis for self-pressurization of a flightweight, cryogenic, liquid hydrogen tank in 1-g. These results are compared with experimental data, in particular, pressure evolution and temperature measurements at a set of sensors. The simulations can be analyzed to identify and quantify heat flows in the tank. Heat flows change over time and influence the self-pressurization process. The initial rate of self-pressurization is sensitive to the initial temperature profile near the interface. Uncertainty in saturation pressure data and the accuracy of experimental measurements complicate simulation of self-pressurization. Numerical issues encountered, and their resolution, are also explained.

Efficient Photocatalytic Hydrogen Evolution via Band Alignment Tailoring: Controllable Transition from Type-I to Type-II.

PubMed

Cheng, Zhongzhou; Wang, Fengmei; Shifa, Tofik Ahmed; Jiang, Chao; Liu, Quanlin; He, Jun

2017-11-01

Considering the sizable band gap and wide spectrum response of tin disulfide (SnS 2 ), ultrathin SnS 2 nanosheets are utilized as solar-driven photocatalyst for water splitting. Designing a heterostructure based on SnS 2 is believed to boost their catalytic performance. Unfortunately, it has been quite challenging to explore a material with suitable band alignment using SnS 2 nanomaterials for photocatalytic hydrogen generation. Herein, a new strategy is used to systematically tailor the band alignment in SnS 2 based heterostructure to realize efficient H 2 production under sunlight. A Type-I to Type-II band alignment transition is demonstrated via introducing an interlayer of Ce 2 S 3 , a potential photocatalyst for H 2 evolution, between SnS 2 and CeO 2 . Subsequently, this heterostructure demonstrates tunability in light absorption, charge transfer kinetics, and material stability. The optimized heterostructure (SnS 2 -Ce 2 S 3 -CeO 2 ) exhibits an incredibly strong light absorption ranging from deep UV to infrared light. Significantly, it also shows superior hydrogen generation with the rate of 240 µmol g -1 h -1 under the illumination of simulated sunlight with a very good stability. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A novel versatile microbiosensor for local hydrogen detection by means of scanning photoelectrochemical microscopy.

PubMed

Zhao, Fangyuan; Conzuelo, Felipe; Hartmann, Volker; Li, Huaiguang; Stapf, Stefanie; Nowaczyk, Marc M; Rögner, Matthias; Plumeré, Nicolas; Lubitz, Wolfgang; Schuhmann, Wolfgang

2017-08-15

The development of a versatile microbiosensor for hydrogen detection is reported. Carbon-based microelectrodes were modified with a [NiFe]-hydrogenase embedded in a viologen-modified redox hydrogel for the fabrication of a sensitive hydrogen biosensor By integrating the microbiosensor in a scanning photoelectrochemical microscope, it was capable of serving simultaneously as local light source to initiate photo(bio)electrochemical reactions while acting as sensitive biosensor for the detection of hydrogen. A hydrogen evolution biocatalyst based on photosystem 1-platinum nanoparticle biocomplexes embedded into a specifically designed redox polymer was used as a model for proving the capability of the developed hydrogen biosensor for the detection of hydrogen upon localized illumination. The versatility and sensitivity of the proposed microbiosensor as probe tip allows simplification of the set-up used for the evaluation of complex electrochemical processes and the rapid investigation of local photoelectrocatalytic activity of biocatalysts towards light-induced hydrogen evolution. Copyright © 2017 Elsevier B.V. All rights reserved.

Water Splitting via Decoupled Photocatalytic Water Oxidation and Electrochemical Proton Reduction Mediated by Electron-Coupled-Proton Buffer.

PubMed

Li, Fei; Yu, Fengshou; Du, Jian; Wang, Yong; Zhu, Yong; Li, Xiaona; Sun, Licheng

2017-10-18

Water splitting mediated by electron-coupled-proton buffer (ECPB) provides an efficient way to avoid gas mixing by separating oxygen evolution from hydrogen evolution in space and time. Though electrochemical and photoelectrochemcial water oxidation have been incorporated in such a two-step water splitting system, alternative ways to reduce the cost and energy input for decoupling two half-reactions are desired. Herein, we show the feasibility of photocatalytic oxygen evolution in a powder system with BiVO 4 as a photocatalyst and polyoxometalate H 3 PMo 12 O 40 as an electron and proton acceptor. The resulting reaction mixture was allowed to be directly used for the subsequent hydrogen evolution with the reduced H 3 PMo 12 O 40 as electron and proton donors. Our system exhibits excellent stability in repeated oxygen and hydrogen evolution, which brings considerable convenience to decoupled water splitting. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The anodic surface film and hydrogen evolution on Mg

DOE PAGES

Song, Guang -Ling; Unocic, Kinga A.

2015-06-04

This paper clarifies that the inner and outer layers of the anodic film consist of a nano/micro-porous MgO+Mg(OH) 2 mixture. The film becomes thicker and more porous with increasing potential. It can rupture when potential is too positive in a non-corrosive Mg(OH) 2 solution. Hydrogen evolution becomes more intensive as polarization potential increases, particularly when the potential at the film-covered Mg surface is close to or more positive than the hydrogen equilibrium potential, suggesting that an “anodic hydrogen evolution” (AHE) reaction occurs on the substrate Mg in film pores, and the significantly intensified AHE causes film rupture at high potential.

Time-resolved X-Ray Absorption Spectroscopy of a Cobalt-Based Hydrogen Evolution System for Artificial Photosynthesis

NASA Astrophysics Data System (ADS)

Moonshiram, Dooshaye; Gimbert, Carolina; Lehmann, Carl; Southworth, Stephen; Llobet, Antoni; Argonne National Laboratory Team; Institut Català d'Investigació Química Collaboration

2015-03-01

Production of cost-effective hydrogen gas through solar power is an important challenge of the Department of Energy among other global industry initiatives. In natural photosynthesis, the oxygen evolving complex(OEC) can carry out four-electron water splitting to hydrogen with an efficiency of around 60%. Although, much progress has been carried out in determining mechanistic pathways of the OEC, biomimetic approaches have not duplicated Nature's efficiency in function. Over the past years, we have witnessed progress in developments of light harvesting modules, so called chromophore/catalytic assemblies. In spite of reportedly high catalytic activity of these systems, quantum yields of hydrogen production are below 40 % when using monochromatic light. Proper understanding of kinetics and bond making/breaking steps has to be achieved to improve efficiency of hydrogen evolution systems. This project shows the timing implementation of ultrafast X-ray absorption spectroscopy to visualize in ``real time'' the photo-induced kinetics accompanying a sequence of redox reactions in a cobalt-based molecular photocatalytic system. Formation of a Co(I) species followed by a Co(III) hydride species all the way towards hydrogen evolution is shown through time-resolved XANES.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds,more » this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. In conclusion, this generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.« less

Programming temporal shapeshifting

DOE PAGES

Hu, Xiaobo; Zhou, Jing; Vatankhah-Varnosfaderani, Mohammad; ...

2016-09-27

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds,more » this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. In conclusion, this generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.« less

H2 Production Under Visible Light Irradiation from Aqueous Methanol Solution on CaTiO3:Cu Prepared by Spray Pyrolysis

NASA Astrophysics Data System (ADS)

Lim, Sung Nam; Song, Shin Ae; Jeong, Yong-Cheol; Kang, Hyun Woo; Park, Seung Bin; Kim, Ki Young

2017-10-01

Perovskite-type photocatalysts of CaCu x Ti1- x O3 (0 ≤ x ≤ 0.02) powder were prepared by spray pyrolysis of aqueous solution or aqueous solution with polymeric additive. The effects of the amount of copper ions doped in the photocatalyst and the precursor type on the photocatalytic activity under visible-light irradiation were investigated. The crystal structure, oxidation state, and light adsorption properties of the prepared photocatalysts were analyzed using x-ray diffraction, x-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy, respectively. The doping of copper ions in CaTiO3 allowed visible-light absorption owing to a narrowing of the band gap energy of the host material through the formation of a new donor level for copper ions. Among the doped samples prepared from the aqueous precursor, CaTiO3 doped with 1 mol.% copper ions had the highest hydrogen evolution rate (140.7 μmol g-1 h-1). Notably, the hydrogen evolution rate of the photocatalyst doped with 1 mol.% copper ions prepared from the aqueous precursor with polymeric additive (295.0 μmol g-1 h-1) was two times greater than that prepared from the aqueous precursor, due to the morphology effect.

In vitro degradation behavior and cytocompatibility of Mg–Zn–Zr alloys

PubMed Central

Huan, Z. G.; Leeflang, M. A.; Fratila-Apachitei, L. E.; Duszczyk, J.

2010-01-01

Zinc and zirconium were selected as the alloying elements in biodegradable magnesium alloys, considering their strengthening effect and good biocompatibility. The degradation rate, hydrogen evolution, ion release, surface layer and in vitro cytotoxicity of two Mg–Zn–Zr alloys, i.e. ZK30 and ZK60, and a WE-type alloy (Mg–Y–RE–Zr) were investigated by means of long-term static immersion testing in Hank’s solution, non-static immersion testing in Hank’s solution and cell-material interaction analysis. It was found that, among these three magnesium alloys, ZK30 had the lowest degradation rate and the least hydrogen evolution. A magnesium calcium phosphate layer was formed on the surface of ZK30 sample during non-static immersion and its degradation caused minute changes in the ion concentrations and pH value of Hank’s solution. In addition, the ZK30 alloy showed insignificant cytotoxicity against bone marrow stromal cells as compared with biocompatible hydroxyapatite (HA) and the WE-type alloy. After prolonged incubation for 7 days, a stimulatory effect on cell proliferation was observed. The results of the present study suggested that ZK30 could be a promising material for biodegradable orthopedic implants and worth further investigation to evaluate its in vitro and in vivo degradation behavior. PMID:20532960

Corrosion resistance and cytocompatibility of biodegradable surgical magnesium alloy coated with hydrogenated amorphous silicon.

PubMed

Xin, Yunchang; Jiang, Jiang; Huo, Kaifu; Tang, Guoyi; Tian, Xiubo; Chu, Paul K

2009-06-01

The fast degradation rates in the physiological environment constitute the main limitation for the applications of surgical magnesium alloys as biodegradable hard-tissue implants. In this work, a stable and dense hydrogenated amorphous silicon coating (a-Si:H) with desirable bioactivity is deposited on AZ91 magnesium alloy using magnetron sputtering deposition. Raman spectroscopy and Fourier transform infrared spectroscopy reveal that the coating is mainly composed of hydrogenated amorphous silicon. The hardness of the coated alloy is enhanced significantly and the coating is quite hydrophilic as well. Potentiodynamic polarization results show that the corrosion resistance of the coated alloy is enhanced dramatically. In addition, the deterioration process of the coating in simulated body fluids is systematically investigated by open circuit potential evolution and electrochemical impedance spectroscopy. The cytocompatibility of the coated Mg is evaluated for the first time using hFOB1.19 cells and favorable biocompatibility is observed. 2008 Wiley Periodicals, Inc.

Compatibility Studies of Hydrogen Peroxide and a New Hypergolic Fuel Blend

NASA Technical Reports Server (NTRS)

Baldridge, Jennifer; Villegas, Yvonne

2002-01-01

Several preliminary materials compatibility studies have been conducted to determine the practicality of a new hypergolic fuel system. Hypergolic fuel ignites spontaneously as the oxidizer decomposes and releases energy in the presence of the fuel. The bipropellant system tested consists of high-test hydrogen peroxide (HTP) and a liquid fuel blend consisting of a hydrocarbon fuel, an ignition enhancer and a transition metal catalyst. In order for further testing of the new fuel blend to take place, some basic materials compatibility and HTP decomposition studies must be accomplished. The thermal decomposition rate of HTP was tested using gas evolution and isothermal microcalorimetry (IMC). Materials were analyzed for compatibility with hydrogen peroxide including a study of the affect welding has on stainless steel elemental composition and its relation to HTP decomposition. Compatibility studies of valve materials in the fuel blend were performed to determine the corrosion resistance of the materials.

Influence of degree of ambient medium rarefaction on deformation of copper and aluminum

NASA Technical Reports Server (NTRS)

Lyubarskiy, I. M.; Guslyakov, A. A.; Ashukin, A. V.; Kuleba, V. I.

1974-01-01

The influence of high vacuum 1 x 10 to the minus 9th power torr on the plastic deformation of copper and aluminum was studied. When stretching polycrystalline aluminum and copper specimens in vacuum, it was found that the deformation at failure increases and the ultimate strength decreases. Deformation in vacuum is accompanied by the evolution of hydrogen. For copper, gas evolution is observed only at failure, while for aluminum hydrogen evolution takes place in the initial stage and the gas evolution peaks correspond to small steps on the deformation curve.

Photon underproduction crisis and the redshift evolution of escape fraction of hydrogen ionizing photons from galaxies

NASA Astrophysics Data System (ADS)

Khaire, Vikram; Srianand, Raghunathan

2016-01-01

In the standard picture, the only sources of cosmic UV background are the quasars and the star forming galaxies. The hydrogen ionizing emissivity from galaxies depends on a parameter known as escape fraction (fesc). It is the ratio of the escaping hydrogen ionizing photons from galaxies to the total produced by their stellar population. Using available multi-wavelength and multi-epoch galaxy luminosity function measurements, we update the galaxy emissivity by estimating a self-consistent combination of the star formation rate density and dust attenuation. Using the recent quasar luminosity function measurements, we present an updated hydrogen ionizing emissivity from quasars which shows a factor of ~2 increase as compared to the previous estimates at z<2. We use these in a cosmological radiative transfer code developed by us to generate the UV background and show that the recently inferred high values of hydrogen photoionization rates at low redshifts can be easily obtained with reasonable values of fesc. This resolves the problem of 'photon underproduction crisis' and shows that there is no need to invoke non-standard sources of the UV background such as decaying dark matter particles. We will present the implications of this updated quasar and galaxy emissivity on the values of fesc at high redshifts and on the cosmic reionization. We will also present the effect of the updated UV background on the inferred properties of the intergalactic medium, especially on the Lyman alpha forest and the metal line absorption systems.

Effect of Doping on Hydrogen Evolution Reaction of Vanadium Disulfide Monolayer.

PubMed

Qu, Yuanju; Pan, Hui; Kwok, Chi Tat; Wang, Zisheng

2015-12-01

As cheap and abundant materials, transitional metal dichalcogenide monolayers have attracted increasing interests for their application as catalysts in hydrogen production. In this work, the hydrogen evolution reduction of doped vanadium disulfide monolayers is investigated based on first-principles calculations. We find that the doping elements and concentration affect strongly the catalytic ability of the monolayer. We show that Ti-doping can efficiently reduce the Gibbs free energy of hydrogen adsorption in a wide range of hydrogen coverage. The catalytic ability of the monolayer at high hydrogen coverage can be improved by low Ti-density doping, while that at low hydrogen coverage is enhanced by moderate Ti-density doping. We further show that it is much easier to substitute the Ti atom to the V atom in the vanadium disulfide (VS2) monolayer than other transitional metal atoms considered here due to its lowest and negative formation energy. It is expected that the Ti-doped VS2 monolayer may be applicable in water electrolysis with improved efficiency.

Modeling of hydrogen evolution reaction on the surface of GaInP2

NASA Astrophysics Data System (ADS)

Choi, Woon Ih; Wood, Brandon; Schwegler, Eric; Ogitsu, Tadashi

2012-02-01

GaInP2 is promising candidate material for hydrogen production using sunlight. It reduces solvated proton into hydrogen molecule using light-induced excited electrons in the photoelectrochemical cell. However, it is challenging to model hydrogen evolution reaction (HER) using first-principles molecular dynamics. Instead, we use Anderson-Newns model and generalized solvent coordinate in Marcus-Hush theory to describe adiabatic free energy surface of HER. Model parameters are fitted from the DFT calculations. We model Volmer-Heyrovsky reaction path on the surfaces of CuPt phase of GaInP2. We also discuss effects of surface oxide and catalyst atoms that exist on top of bare surfaces in experimental circumstances.

A theoretical study on the mechanism of hydrogen evolution on non-precious partially oxidized nickel-based heterostructures for fuel cells.

PubMed

Pan, Xinju; Zhou, Gang

2018-03-28

It is desirable, yet challenging, to utilize non-precious metals instead of noble-metals as efficient catalysts in the renewable energy manufacturing industry. Using first principles calculations, we study the structural characteristics of partially oxidized nickel-based nanoheterostructures (NiO/Ni NHSs), and the interfacial effects on hydrogen evolution. The origin of the enhanced hydrogen evolution performance is discussed at the microscopic level. This study identifies two types of active sites of the exposed Ni surface available for the hydrogen evolution reaction (HER). One is the hcp-hollow sites near the perimeter boundary that exhibit a more excellent HER performance than platinum (Pt), and the other the second nearest neighbor fcc-hollow sites away from the boundary that exhibit a similar performance to Pt. The interfacial effects result from the competitive charge transfer between NiO and Ni surfaces in NHSs, and enhance the reactivity of NiO/Ni NHSs by shifting the d-states of surface atoms down in energy. The illumination of the mechanism would be helpful for the design of more efficient and cheap transition metal-based catalysts.

Efficient whole cell biocatalyst for formate-based hydrogen production.

PubMed

Kottenhahn, Patrick; Schuchmann, Kai; Müller, Volker

2018-01-01

Molecular hydrogen (H 2 ) is an attractive future energy carrier to replace fossil fuels. Biologically and sustainably produced H 2 could contribute significantly to the future energy mix. However, biological H 2 production methods are faced with multiple barriers including substrate cost, low production rates, and low yields. The C1 compound formate is a promising substrate for biological H 2 production, as it can be produced itself from various sources including electrochemical reduction of CO 2 or from synthesis gas. Many microbes that can produce H 2 from formate have been isolated; however, in most cases H 2 production rates cannot compete with other H 2 production methods. We established a formate-based H 2 production method utilizing the acetogenic bacterium Acetobacterium woodii . This organism can use formate as sole energy and carbon source and possesses a novel enzyme complex, the hydrogen-dependent CO 2 reductase that catalyzes oxidation of formate to H 2 and CO 2 . Cell suspensions reached specific formate-dependent H 2 production rates of 71 mmol g protein -1 h -1 (30.5 mmol g CDW -1 h -1 ) and maximum volumetric H 2 evolution rates of 79 mmol L -1 h -1 . Using growing cells in a two-step closed batch fermentation, specific H 2 production rates reached 66 mmol g CDW -1 h -1 with a volumetric H 2 evolution rate of 7.9 mmol L -1  h -1 . Acetate was the major side product that decreased the H 2 yield. We demonstrate that inhibition of the energy metabolism by addition of a sodium ionophore is suitable to completely abolish acetate formation. Under these conditions, yields up to 1 mol H 2 per mol formate were achieved. The same ionophore can be used in cultures utilizing formate as specific switch from a growing phase to a H 2 production phase. Acetobacterium woodii reached one of the highest formate-dependent specific H 2 productivity rates at ambient temperatures reported so far for an organism without genetic modification and converted the substrate exclusively to H 2 . This makes this organism a very promising candidate for sustainable H 2 production and, because of the reversibility of the A. woodii enzyme, also a candidate for reversible H 2 storage.

A highly-active and stable hydrogen evolution catalyst based on pyrite-structured cobalt phosphosulfide

DOE PAGES

Liu, Wen; Hu, Enyuan; Jiang, Hong; ...

2016-02-19

Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superiormore » activity for hydrogen evolution, achieving current densities of 10 mA cm –2 and 100 mA cm –2 at overpotentials of 48 mV and 109 mV, respectively. Lastly, phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation.« less

Pt-like Hydrogen Evolution Electrocatalysis on PANI/CoP Hybrid Nanowires by Weakening the Shackles of Hydrogen Ions on the Surfaces of Catalysts.

PubMed

Feng, Jin-Xian; Tong, Si-Yao; Tong, Ye-Xiang; Li, Gao-Ren

2018-04-18

The search for high active, stable, and cost-efficient hydrogen evolution reaction (HER) electrocatalysts for water electrolysis has attracted great interest. The coordinated water molecules in the hydronium ions will obviously reduce the positive charge density of H + and hamper the ability of H + to receive electrons from the cathode, leading to large overpotential of HER on nonprecious metal catalysts. Here we realize Pt-like hydrogen evolution electrocatalysis on polyaniline (PANI) nanodots (NDs)-decorated CoP hybrid nanowires (HNWs) supported on carbon fibers (CFs) (PANI/CoP HNWs-CFs) as PANI can effectively capture H + from hydronium ions to form protonated amine groups that have higher positive charge density than those of hydronium ions and can be electro-reduced easily. The PANI/CoP HNWs-CFs as low-cost electrocatalysts show excellent catalytic performance toward HER in acidic solution, such as super high catalytic activity, small Tafel slope, and superior stability.

Data on the synthesis processes optimization of novel β-NiS film modified CdS nanoflowers heterostructure nanocomposite for photocatalytic hydrogen evolution.

PubMed

Zhang, Yu; Peng, Zhijian; Guan, Shundong; Fu, Xiuli

2018-02-01

The data presented in this article are related to a research article entitled 'Novel β-NiS film modified CdS nanoflowers heterostructure nanocomposite: extraordinarily highly efficient photocatalysts for hydrogen evolution' (Zhang et al., 2018) [1]. In this article, we report original data on the synthesis processes optimization of the proposed nanocomposite on the basis of their optimum photocatalytic performance together with the comparison on the results of literatures and comparative experiments. The composition, microstructure, morphology, photocatalytic hydrogen evolution and photocatalytic stability of the corresponding samples are included in this report. The data are presented in this format in order to facilitate comparison with data from other researchers in the field and understanding the mechanism of similar catalysts.

Ultrathin platinum nanowires grown on single-layered nickel hydroxide with high hydrogen evolution activity.

PubMed

Yin, Huajie; Zhao, Shenlong; Zhao, Kun; Muqsit, Abdul; Tang, Hongjie; Chang, Lin; Zhao, Huijun; Gao, Yan; Tang, Zhiyong

2015-03-02

Design and synthesis of effective electrocatalysts for hydrogen evolution reaction in alkaline environments is critical to reduce energy losses in alkaline water electrolysis. Here we report a hybrid nanomaterial comprising of one-dimensional ultrathin platinum nanowires grown on two-dimensional single-layered nickel hydroxide. Judicious surface chemistry to generate the fully exfoliated nickel hydroxide single layers is explored to be the key for controllable growth of ultrathin platinum nanowires with diameters of about 1.8 nm. Impressively, this hybrid nanomaterial exhibits superior electrocatalytic activity for hydrogen evolution reaction in alkaline solution, which outperforms currently reported catalysts, and the obviously improved catalytic stability. We believe that this work may lead towards the development of single-layered metal hydroxide-based hybrid materials for applications in catalysis and energy conversion.

Bioinspired Mesoporous Chiral Nematic Graphitic Carbon Nitride Photocatalysts modulated by Polarized Light.

PubMed

Lin, Wensheng; Hong, Wei; Sun, Lu; Yu, Di; Yu, Dingshan; Chen, Xudong

2018-01-10

Endowing materials with chirality and exploring the responses of the material under circularly polarized light (CPL) can enable further insight into the physical and chemical properties of the semiconductors to be gained, thus expanding on optoelectronic applications. Herein a bioinspired mesoporous chiral nematic graphitic carbon nitride (g-C 3 N 4 ) for efficient hydrogen evolution with polarized light modulation based on chiral nematic cellulose nanocrystal films prepared through silica templating is described. The mesoporous nematic chiral g-C 3 N 4 exhibits an ultrahigh hydrogen evolution rate of 219.9 μmol h -1 (for 20 mg catalyst), corresponding to a high enhancement factor of 55 when compared to the bulk g-C 3 N 4 under λ>420 nm irradiation. Furthermore, the chiral g-C 3 N 4 material exhibits unique photocatalytic activity modulated by CPL within the absorption region. This CPL-assisted photocatalytic regulation strategy holds great promise for a wide range of applications including optical devices, asymmetric photocatalysis, and chiral recognition/separation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Photocarrier Separation in Hierarchical Graphitic-C3N4-Supported CuInS2 for Noble-Metal-Free Z-Scheme Photocatalytic Water Splitting.

PubMed

Li, Xiaoxue; Xie, Keyu; Song, Long; Zhao, Mengjia; Zhang, Zhipan

2017-07-26

The effective separation of photogenerated electrons and holes in photocatalysts is a prerequisite for efficient photocatalytic water splitting. CuInS 2 (CIS) is a widely used light absorber that works properly in photovoltaics but only shows limited performance in solar-driven hydrogen evolution due to its intrinsically severe charge recombination. Here, we prepare hierarchical graphitic C 3 N 4 -supported CuInS 2 (denoted as GsC) by an in situ growth of CIS directly on exfoliated thin graphitic C 3 N 4 nanosheets (g-C 3 N 4 NS) and demonstrate efficient separation of photoinduced charge carriers in the GsC by forming the Z-scheme system for the first time in CIS-catalyzed water splitting. Under visible light illumination, the GsC features an enhanced hydrogen evolution rate up to 1290 μmol g -1 h -1 , which is 3.3 and 6.1 times higher than that of g-C 3 N 4 NS and bare-CIS, respectively, thus setting a new performance benchmark for CIS-based water-splitting photocatalysts.

Phase Transformation Synthesis of Strontium Tantalum Oxynitride-based Heterojunction for Improved Visible Light-Driven Hydrogen Evolution.

PubMed

Zeng, Weixuan; Bian, Yuan; Cao, Sheng; Ma, Yongjin; Liu, Yi; Zhu, Anquan; Tan, Pengfei; Pan, Jun

2018-06-07

Tantalum oxynitride-based materials, which possess narrow bandgaps and sufficient band energy potentials, have been of immense interest for water splitting. However, the efficiency of photocatalytic reactions is still low due to the fast electron-hole recombination. Here, a Sr2Ta2O7-xNx/SrTaO2N heterostructured photocatalyst with well-matched band structure was in situ constructed by nitridation of hydrothermal-prepared Sr2Ta2O7 nanosheets. Compared to Sr2Ta2O7-xNx and pure SrTaO2N, the Sr2Ta2O7-xNx/SrTaO2N heterostructured photocatalyst exhibited highest rate of hydrogen evolution, which is ca. 2.0 and 76.4 times of Sr2Ta2O7-xNx and pure SrTaO2N under the similar reaction condition, respectively. The enhanced performance arises from the formation of suitable band matched heterojunction accelerated charge separation. This work provides a promising strategy for the construction of tantalum oxynitride-based heterojunction photocatalysts.

Onset of hydrogen bonded collective network of water in 1,4-dioxane.

PubMed

Luong, Trung Quan; Verma, Pramod Kumar; Mitra, Rajib Kumar; Havenith, Martina

2011-12-22

We have studied the evolution of water hydrogen bonded collective network dynamics in mixtures of 1,4-dioxane (Dx) as the mole fraction of water (X(w)) increases from 0.005 to 0.54. The inter- and intramolecular vibrations of water have been observed using terahertz time domain spectroscopy (THz-TDS) in the frequency range 0.4-1.4 THz (13-47 cm(-1)) and Fourier transform infrared (FTIR) spectroscopy in the far-infrared (30-650 cm(-1)) and mid-infrared (3000-3700 cm(-1)) regions. These results have been correlated with the reactivity of water in these mixtures as determined by kinetic studies of the solvolysis reaction of benzoyl chloride (BzCl). Our studies show an onset of intermolecular hydrogen bonded water network dynamics beyond X(w) ≥ 0.1. At the same concentration, we observe a rapid increase of the rate constant of solvolysis of BzCl in water-Dx mixtures. Our results establish a correlation between the onset of collective hydrogen bonded network with the solvation dynamics and the activity of clustered water.

Hydrogen Production and Storage on a Formic Acid/Bicarbonate Platform using Water-Soluble N-Heterocyclic Carbene Complexes of Late Transition Metals.

PubMed

Jantke, Dominik; Pardatscher, Lorenz; Drees, Markus; Cokoja, Mirza; Herrmann, Wolfgang A; Kühn, Fritz E

2016-10-06

The synthesis and characterization of two water-soluble bis-N-heterocyclic carbene (NHC) complexes of rhodium and iridium is presented. Both compounds are active in H 2 generation from formic acid and in hydrogenation of bicarbonate to formate. The rhodium derivative is most active in both reactions, reaching a TOF of 39 000 h -1 and a TON of 449 000 for H 2 production. The catalytic hydrogenation reactions were carried out in an autoclave system and analyzed using the integrated peak areas in the 1 H NMR spectra. Decomposition of formic acid was investigated using a Fisher-Porter bottle equipped with a pressure transducer. Long-term stability for hydrogen evolution was tested by surveillance of the gas flow rate. The procedure does not require any additives like amines or inert gas conditions. Density functional theory calculations in agreement with experimental results suggest a bicarbonate reduction mechanism involving a second catalyst molecule, which provides an external hydride acting as reducing agent. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of the Propensity of Niobium to Absorb Hydrogen During Fabrication of Superconducting Radio Frequency Cavities for Particle Accelerators

PubMed Central

Ricker, R. E.; Myneni, G. R.

2010-01-01

During the fabrication of niobium superconducting radio frequency (SRF) particle accelerator cavities procedures are used that chemically or mechanically remove the passivating surface film of niobium pentoxide (Nb2O5). Removal of this film will expose the underlying niobium metal and allow it to react with the processing environment. If these reactions produce hydrogen at sufficient concentrations and rates, then hydrogen will be absorbed and diffuse into the metal. High hydrogen activities could result in supersaturation and the nucleation of hydride phases. If the metal repassivates at the conclusion of the processing step and the passive film blocks hydrogen egress, then the absorbed hydrogen or hydrides could be retained and alter the performance of the metal during subsequent processing steps or in-service. This report examines the feasibility of this hypothesis by first identifying the postulated events, conditions, and reactions and then determining if each is consistent with accepted scientific principles, literature, and data. Established precedent for similar events in other systems was found in the scientific literature and thermodynamic analysis found that the postulated reactions were not only energetically favorable, but produced large driving forces. The hydrogen activity or fugacity required for the reactions to be at equilibrium was determined to indicate the propensity for hydrogen evolution, absorption, and hydride nucleation. The influence of processing conditions and kinetics on the proximity of hydrogen surface coverage to these theoretical values is discussed. This examination found that the hypothesis of hydrogen absorption during SRF processing is consistent with published scientific literature and thermodynamic principles. PMID:27134791

Is Current CMBR Temperature: The Scale Independent Quantum Gravitational Result of Black Hole Cosmology?

NASA Astrophysics Data System (ADS)

Seshavatharam, U. V. S.; Lakshminarayana, S.

If one is willing to consider the current cosmic microwave back ground temperature as a quantum gravitational effect of the evolving primordial cosmic black hole (universe that constitutes dynamic space-time and exhibits quantum behavior) automatically general theory of relativity and quantum mechanics can be combined into a `scale independent' true unified model of quantum gravity. By considering the `Planck mass' as the initial mass of the baby Hubble volume, past and current physical and thermal parameters of the cosmic black hole can be understood. Current rate of cosmic black hole expansion is being stopped by the microscopic quantum mechanical lengths. In this new direction authors observed 5 important quantum mechanical methods for understanding the current cosmic deceleration. To understand the ground reality of current cosmic rate of expansion, sensitivity and accuracy of current methods of estimating the magnitudes of current CMBR temperature and current Hubble constant must be improved and alternative methods must be developed. If it is true that galaxy constitutes so many stars, each star constitutes so many hydrogen atoms and light is coming from the excited electron of galactic hydrogen atom, then considering redshift as an index of `whole galaxy' receding may not be reasonable. During cosmic evolution, at any time in the past, in hydrogen atom emitted photon energy was always inversely proportional to the CMBR temperature. Thus past light emitted from older galaxy's excited hydrogen atom will show redshift with reference to the current laboratory data. As cosmic time passes, in future, the absolute rate of cosmic expansion can be understood by observing the rate of increase in the magnitude of photon energy emitted from laboratory hydrogen atom. Aged super novae dimming may be due to the effect of high cosmic back ground temperature. Need of new mathematical methods & techniques, computer simulations, advanced engineering skills seem to be essential in this direction.

Development of Inorganic Nanomaterials as Photocatalysts for the Water Splitting Reaction

NASA Astrophysics Data System (ADS)

Frame, Fredrick Andrew

The photochemical water splitting reaction is of great interest for converting solar energy into usable fuels. This dissertation focuses on the development of inorganic nanoparticle catalysts for solar energy driven conversion of water into hydrogen and oxygen. The results from these selected studies have allowed greater insight into nanoparticle chemistry and the role of nanoparticles in photochemical conversion of water in to hydrogen and oxygen. Chapter 2 shows that CdSe nanoribbons have photocatalytic activity for hydrogen production from water in the presence of Na2S/Na2SO 3 as sacrificial electron donors in both UV and visible light. Quantum confinement of this material leads to an extended bandgap of 2.7 eV and enables the photocatalytic activity of this material. We report on the photocatalytic H2 evolution, and its dependence on platinum co-catalysts, the concentration of the electron donor, and the wavelength of incident radiation. Transient absorption measurements reveal decay of the excited state on multiple timescales, and an increase of lifetimes of trapped electrons due to the sacrificial electron donors. In chapter 3, we explore the catalytic activity of citrate-capped CdSe quantum dots. We show that the process is indeed catalytic for these dots in aqueous 0.1 M Na2S:Na2SO3, but not in pure water. Furthermore, optical spectroscopy was used to report electronic transitions in the dots and electron microscopy was used to obtain morphology of the catalyst. Interestingly, an increasing catalytic rate is noted for undialyzed catalyst. Dynamic light scattering experiments show an increased hydrodynamic radius in the case of undialyzed CdSe dots in donor solution. In chapter 4 we show that CdSe:MoS2 nanoparticle composites with improved catalytic activity can be assembled from CdSe and MoS2 nanoparticle building units. We report on the photocatalytic H 2 evolution, quantum efficiency using LED irriadiation, and its dependence on the co-catalyst loading. Furthermore, optical spectroscopy, cyclic voltammetry, and electron microscopy were used to obtain morphology, optical properties, and electronic structure of the catalysts. In chapter 5, illumination with visible light (lambda > 400 nm) photoconverts a red V2O5 gel in aqueous methanol solution into a green VO2 gel. The presence of V(4+) in the green VO2 gel is supported by Electron Energy Loss Spectra. High-resolution electron micrographs, powder X-ray diffraction, and selective area electron diffraction (SAED) data show that the crystalline structure of the V2O5 gel is retained upon reduction. After attachment of colloidal Pt nanoparticles, H2 evolution proceeds catalytically on the VO2 gel. The Pt nanoparticles reduce the H2 evolution overpotential. However, the activity of the new photocatalyst remains limited by the VO2 conduction band edge just below the proton reduction potential. Chapter 6 studies the ability of IrO2 to evolve oxygen from aqueous solutions under UV irradiation. We show that visible illumination (lambda > 400 nm) of iridium dioxide (IrO2) nanocrystals capped in succinic acid in aqueous sodium persulfate solution leads to catalytic oxygen evolution. While the majority of catalytic hydrogen evolution comes from UV light, the process can still be driven with visible light. Morphology, optical properties, surface photovoltage measurements, and oxygen evolution rates are discussed.

Relative Importance of Various Sources of Defect-Producing Hydrogen Introduced into Steel During Application of Vitreous Coatings

NASA Technical Reports Server (NTRS)

Moore, Dwight G; Mason, Mary A; Harrison, William N

1953-01-01

When porcelain enamels or vitreous-type ceramic coatings are applied to ferrous metals, there is believed to be an evolution of hydrogen gas both during and after the firing operation. At elevated temperatures rapid evolution may result in blistering while if hydrogen becomes trapped in the steel during the rapid cooling following the firing operation gas pressures may be generated at the coating-metal interface and flakes of the coating literally blown off the metal. To determine experimentally the relative importance of the principal sources of the hydrogen causing the defects, a procedure was devised in which heavy hydrogen (deuterium) was substituted in turn for regular hydrogen in each of five possible hydrogen-producing operations in the coating process. The findings of the study were as follows: (1) the principal source of the defect-producing hydrogen was the dissolved water present in the enamel frit that was incorporated into the coating. (2) the acid pickling, the milling water, the chemically combined water in the clay, and the quenching water were all minor sources of defect-producing hydrogen under the test conditions used. Confirming experiments showed that fishscaling could be eliminated by using a water-free coating.

Oxidation driven ZnS Core-ZnO shell photocatalysts under controlled oxygen atmosphere for improved photocatalytic solar water splitting

NASA Astrophysics Data System (ADS)

Bak, Daegil; Kim, Jung Hyeun

2018-06-01

Zinc type photocatalysts attract great attentions in solar hydrogen production due to their easy availability and benign environmental characteristics. Spherical ZnS particles are synthesized with a facile hydrothermal method, and they are further used as core materials to introduce ZnO shell layer surrounding the core part by partial oxidation under controlled oxygen contents. The resulting ZnS core-ZnO shell photocatalysts represent the heterostructural type II band alignment. The existence of oxide layer also influences on proton adsorption power with an aid of strong base cites derived from highly electronegative oxygen atoms in ZnO shell layer. Photocatalytic water splitting reaction is performed to evaluate catalyst efficiency under standard one sun condition, and the highest hydrogen evolution rate (1665 μmolg-1h-1) is achieved from the sample oxidized at 16.2 kPa oxygen pressure. This highest hydrogen production rate is achieved in cooperation with increased light absorption and promoted charge separations. Photoluminescence analysis reveals that the improved visible light response is obtained after thermal oxidation process due to the oxygen vacancy states in the ZnO shell layer. Therefore, overall photocatalytic efficiency in solar hydrogen production is enhanced by improved charge separations, crystallinity, and visible light responses from the ZnS core-ZnO shell structures induced by thermal oxidation.

Regenerable Nickel-Functionalized Activated Carbon Cathodes Enhanced by Metal Adsorption to Improve Hydrogen Production in Microbial Electrolysis Cells.

PubMed

Kim, Kyoung-Yeol; Yang, Wulin; Logan, Bruce E

2018-06-07

While nickel is a good alternative to platinum as a catalyst for the hydrogen evolution reaction, it is desirable to reduce the amount of nickel needed for cathodes in microbial electrolysis cells (MECs). Activated carbon (AC) was investigated as a cathode base structure for Ni as it is inexpensive and an excellent adsorbent for Ni, and it has a high specific surface area. AC nickel-functionalized electrodes (AC-Ni) were prepared by incorporating Ni salts into AC by adsorption, followed by cathode fabrication using a phase inversion process using a poly(vinylidene fluoride) (PVDF) binder. The AC-Ni cathodes had significantly higher (∼50%) hydrogen production rates than controls (plain AC) in smaller MECs (static flow conditions) over 30 days of operation, with no performance decrease over time. In larger MECs with catholyte recirculation, the AC-Ni cathode produced a slightly higher hydrogen production rate (1.1 ± 0.1 L-H 2 /L reactor /day) than MECs with Ni foam (1.0 ± 0.1 L-H 2 /L reactor /day). Ni dissolution tests showed that negligible amounts of Ni were lost into the electrolyte at pHs of 7 or 12, and the catalytic activity was restored by simple readsorption using a Ni salt solution when Ni was partially removed by an acid wash.

Thermally induced evolution of hydrogenated amorphous carbon

NASA Astrophysics Data System (ADS)

Mangolini, Filippo; Rose, Franck; Hilbert, James; Carpick, Robert W.

2013-10-01

The thermally induced structural evolution of hydrogenated amorphous carbon (a-C:H) films was investigated in situ by X-ray photoelectron spectroscopy for annealing temperatures up to 500 °C. A model for the conversion of sp3- to sp2-hybridized carbon in a-C:H vs. temperature and time was developed and applied to determine the ranges of activation energies for the thermally activated processes occurring. The energies are consistent with ordering and clustering of sp2 carbon, scission of sp3 carbon-hydrogen bonds and formation of sp2 carbon, and direct transformation of sp3- to sp2-hybridized carbon.

Ionic liquid-assisted synthesis of Br-modified g-C3N4 semiconductors with high surface area and highly porous structure for photoredox water splitting

NASA Astrophysics Data System (ADS)

Zhao, Shuo; Zhang, Yiwei; Wang, Yanyun; Zhou, Yuming; Qiu, Kaibo; Zhang, Chao; Fang, Jiasheng; Sheng, Xiaoli

2017-12-01

Coping with the gradually increasing worldwide energy and environmental issues, it is urgent to develop efficient, cheap and visible-light-driven photocatalysts for hydrogen production. Here, we present a facile way to synthesize bromine doped graphitic carbon nitride (CN-BrX) with highly porous structure by using ionic liquid (1-butyl-3-vinylimidazolium bromide) as the Br source and soft-template for the first time, which applied in hydrogen evolution under visible light irradiation. A systematic study is conducted on the optimization in the doping amount. The results find that the as-fabricated CN-BrX photocatalysts possess a uniform porous network with thin walls due to the release of volatile domains and decomposition of ionic liquids. The highly porous structure with the large surface area (≤150 m2/g) benefits the exposure of active sites. Moreover, the bromine modification and porous structure can narrow the band gap, enhance the transportation capability of photogenerated electrons, improve the optical and conductive properties of CN, thus contribute to an outstanding H2 evolution rate under visible light irradiation (120 μmol h-1), which is about 3.6 times higher than pure CN. This work provides a new insight for designing the novel g-C3N4 based photocatalysts for hydrogen production, CO2 conversion and environmental remediation.

Enhanced photocatalytic activity for H2 evolution under irradiation of UV-vis light by Au-modified nitrogen-doped TiO2.

PubMed

Zhao, Weirong; Ai, Zhuyu; Dai, Jiusong; Zhang, Meng

2014-01-01

Photocatalytic water splitting for hydrogen evolution is a potential way to solve many energy and environmental issues. Developing visible-light-active photocatalysts to efficiently utilize sunlight and finding proper ways to improve photocatalytic activity for H2 evolution have always been hot topics for research. This study attempts to expand the use of sunlight and to enhance the photocatalytic activity of TiO2 by N doping and Au loading. Au/N-doped TiO2 photocatalysts were synthesized and successfully used for photocatalytic water splitting for H2 evolution under irradiation of UV and UV-vis light, respectively. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and photoelectrochemical characterizations. DRS displayed an extension of light absorption into the visible region by doping of N and depositing with Au, respectively. PL analysis indicated electron-hole recombination due to N doping and an efficient inhibition of electron-hole recombination due to the loaded Au particles. Under the irradiation of UV light, the photocatalytic hydrogen production rate of the as-synthesized samples followed the order Au/TiO2 > Au/N-doped TiO2 > TiO2 > N-doped TiO2. While under irradiation of UV-vis light, the N-TiO2 and Au/N-TiO2 samples show higher H2 evolution than their corresponding nitrogen-free samples (TiO2 and Au/TiO2). This inconsistent result could be attributed to the doping of N and the surface plasmonic resonance (SPR) effect of Au particles extending the visible light absorption. The photoelectrochemical characterizations further indicated the enhancement of the visible light response of Au/N-doped TiO2. Comparative studies have shown that a combination of nitrogen doping and Au loading enhanced the visible light response of TiO2 and increased the utilization of solar energy, greatly boosting the photocatalytic activity for hydrogen production under UV-vis light.

NASA’s MAVEN Mission Observes Ups and Downs of Water Escape from Mars

NASA Image and Video Library

2017-12-08

After investigating the upper atmosphere of the Red Planet for a full Martian year, NASA’s MAVEN mission has determined that the escaping water does not always go gently into space. Sophisticated measurements made by a suite of instruments on the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft revealed the ups and downs of hydrogen escape – and therefore water loss. The escape rate peaked when Mars was at its closest point to the sun and dropped off when the planet was farthest from the sun. The rate of loss varied dramatically overall, with 10 times more hydrogen escaping at the maximum. “MAVEN is giving us unprecedented detail about hydrogen escape from the upper atmosphere of Mars, and this is crucial for helping us figure out the total amount of water lost over billions of years,” said Ali Rahmati, a MAVEN team member at the University of California at Berkeley who analyzed data from two of the spacecraft’s instruments. Hydrogen in Mars’ upper atmosphere comes from water vapor in the lower atmosphere. An atmospheric water molecule can be broken apart by sunlight, releasing the two hydrogen atoms from the oxygen atom that they had been bound to. Several processes at work in Mars’ upper atmosphere may then act on the hydrogen, leading to its escape. Read more: go.nasa.gov/2dAgAV4 NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: atmospheric expansion and thermal escape.

PubMed

Erkaev, Nikolai V; Lammer, Helmut; Odert, Petra; Kulikov, Yuri N; Kislyakova, Kristina G; Khodachenko, Maxim L; Güdel, Manuel; Hanslmeier, Arnold; Biernat, Helfried

2013-11-01

The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H₂O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R(Earth) and a mass of 10 M(Earth). We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general.

Wrinkle-free atomically thin CdS nanosheets for photocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Pan, Ziwei; Li, Junnan; Zhou, Kebin

2018-05-01

Two-dimensional (2D) nanosheets of atomic thickness have attracted extensive research interest recently. In this work, atomically thin (0.7 nm) flat CdS (F-CdS) nanosheets of several tens of micrometers in lateral size were synthesized by a solvent-thermal method. The as-synthesized F-CdS could maintain flat morphology well in solution, while irreversible wrinkles could be generated after drying, forming wrinkled CdS (W-CdS) samples. It was revealed that the formation of wrinkles could reduce light absorbance, narrow the band gap, move down the conduction band position and accelerate electron–hole recombination. As photocatalysts, the F-CdS achieved a photocatalytic H2 evolution rate of 138.7 mmol g‑1 h‑1 without any co-catalyst under visible light, which was much higher than that of the W-CdS sample (with an H2 evolution rate of only 52.8 mmol g‑1 h‑1). This work demonstrates that great attention should be paid to the wrinkles in 2D materials as photocatalysts.

In Situ Formation of AgCo Stabilized on Graphitic Carbon Nitride and Concomitant Hydrolysis of Ammonia Borane to Hydrogen.

PubMed

Wang, Qi; Xu, Caili; Ming, Mei; Yang, Yingchun; Xu, Bin; Wang, Yi; Zhang, Yun; Wu, Jie; Fan, Guangyin

2018-04-26

The development of highly-efficient heterogeneous supported catalysts for catalytic hydrolysis of ammonia borane to yield hydrogen is of significant importance considering the versatile usages of hydrogen. Herein, we reported the in situ synthesis of AgCo bimetallic nanoparticles supported on g-C₃N₄ and concomitant hydrolysis of ammonia borane for hydrogen evolution at room temperature. The as-synthesized Ag 0.1 Co 0.9 /g-C₃N₄ catalysts displayed the highest turnover frequency (TOF) value of 249.02 mol H₂·(mol Ag ·min) −1 for hydrogen evolution from the hydrolysis of ammonia borane, which was higher than many other reported values. Furthermore, the Ag 0.1 Co 0.9 /g-C₃N₄ catalyst could be recycled during five consecutive runs. The study proves that Ag 0.1 Co 0.9 /g-C₃N₄ is a potential catalytic material toward the hydrolysis of ammonia borane for hydrogen production.

Cuboid Ni2 P as a Bifunctional Catalyst for Efficient Hydrogen Generation from Hydrolysis of Ammonia Borane and Electrocatalytic Hydrogen Evolution.

PubMed

Du, Yeshuang; Liu, Chao; Cheng, Gongzhen; Luo, Wei

2017-11-16

The design of high-performance catalysts for hydrogen generation is highly desirable for the upcoming hydrogen economy. Herein, we report the colloidal synthesis of nanocuboid Ni 2 P by the thermal decomposition of nickel chloride hexahydrate (NiCl 2 ⋅6 H 2 O) and trioctylphosphine. The obtained nanocuboid Ni 2 P was characterized by using powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission spectroscopy. For the first time, the as-synthesized nanocuboid Ni 2 P is used as a bifunctional catalyst for hydrogen generation from the hydrolysis of ammonia borane and electrocatalytic hydrogen evolution. Owing to the strong synergistic electronic effect between Ni and P, the as-synthesized Ni 2 P exhibits catalytic performance that is superior to its counterpart without P doping. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen pickup mechanism of zirconium alloys

NASA Astrophysics Data System (ADS)

Couet, Adrien

Although the optimization of zirconium based alloys has led to significant improvements in hydrogen pickup and corrosion resistance, the mechanisms by which such alloy improvements occur are still not well understood. In an effort to understand such mechanisms, a systematic study of the alloy effect on hydrogen pickup is conducted, using advanced characterization techniques to rationalize precise measurements of hydrogen pickup. The hydrogen pick-up fraction is accurately measured for a specially designed set of commercial and model alloys to investigate the effects of alloying elements, microstructure and corrosion kinetics on hydrogen uptake. Two different techniques to measure hydrogen concentrations were used: a destructive technique, Vacuum Hot Extraction, and a non-destructive one, Cold Neutron Prompt Gamma Activation Analysis. The results indicate that hydrogen pickup varies not only from alloy to alloy but also during the corrosion process for a given alloy. For instance Zircaloy type alloys show high hydrogen pickup fraction and sub-parabolic oxidation kinetics whereas ZrNb alloys show lower hydrogen pickup fraction and close to parabolic oxidation kinetics. Hypothesis is made that hydrogen pickup result from the need to balance charge during the corrosion reaction, such that the pickup of hydrogen is directly related to (and indivisible of) the corrosion mechanism and decreases when the rate of electron transport or oxide electronic conductivity sigmao xe through the protective oxide increases. According to this hypothesis, alloying elements (either in solid solution or in precipitates) embedded in the oxide as well as space charge variations in the oxide would impact the hydrogen pick-up fraction by modifying sigmaox e, which drives oxidation and hydriding kinetics. Dedicated experiments and modelling were performed to assess and validate these hypotheses. In-situ electrochemical impedance spectroscopy (EIS) experiments were performed on Zircaloy-4 tubes to directly measure the evolution of sigma oxe as function of exposure time. The results show that sigmao xe decreases as function of exposure time and that its variations are directly correlated to the instantaneous hydrogen pickup fraction variations. The electron transport through the oxide layer is thus altered as the oxide grows, reasons for which are yet to be exactly determined. Preliminary results also show that sigma oxe of ZrNb alloys would be much higher compared with Zircaloy-4. Thus, it is confirmed that sigmaox e is a key parameter in the hydrogen and oxidation mechanism. Because the mechanism whereby alloying elements are incorporated into the oxide layer is critical to changing sigmao xe, the evolution of the oxidation state of two common alloying elements, Fe and Nb, when incorporated into the growing oxide layers is investigated using X-Ray Absorption Near-Edge Spectroscopy (XANES) using micro-beam synchrotron radiation on cross sectional oxide samples. The results show that the oxidation of both Fe and Nb is delayed in the oxide layer compared to that of Zr, and that this oxidation delay is related to the variations of the instantaneous hydrogen pick-up fraction with exposure time. The evolution of Nb oxidation as function of oxide depth is also compatible with space charge compensation in the oxide and with an increase in sigmaox e of ZrNb alloys compared to Zircaloys. Finally, various successively complex models from the well-known Wagner oxidation theory to the more complex effect of space charge on oxidation kinetics have been developed. The general purpose of the modeling effort is to provide a rationale for the sub-parabolic oxidation kinetics and demonstrate the correlation with hydrogen pickup fraction. It is directly demonstrated that parabolic oxidation kinetics is associated with high sigmao xe and low space charges in the oxide whereas sub-parabolic oxidation kinetics is associated with lower sigmaox e and higher space charge in the oxide. All these observations helped us to propose a general corrosion mechanism of zirconium alloys involving both oxidation and hydrogen pickup mechanism to better understand and predict the effect of alloying additions on the behavior of zirconium alloys.

Tunneling Rate Constants for H2CO+H on Amorphous Solid Water Surfaces

NASA Astrophysics Data System (ADS)

Song, Lei; Kästner, Johannes

2017-12-01

Formaldehyde (H2CO) is one of the most abundant molecules observed in the icy mantle covering interstellar grains. Studying its evolution can contribute to our understanding of the formation of complex organic molecules in various interstellar environments. In this work, we investigated the hydrogenation reactions of H2CO yielding CH3O, CH2OH, and the hydrogen abstraction resulting in H2+HCO on an amorphous solid water (ASW) surface using a quantum mechanics/molecular mechanics (QM/MM) model. The binding energies of H2CO on the ASW surface vary broadly, from 1000 to 9370 K. No correlation was found between binding energies and activation energies of hydrogenation reactions. Combining instanton theory with QM/MM modeling, we calculated rate constants for the Langmuir-Hinshelwood and the Eley-Rideal mechanisms for the three product channels of H+H2CO surface reactions down to 59 K. We found that the channel producing CH2OH can be ignored, owing to its high activation barrier leading to significantly lower rates than the other two channels. The ASW surface influences the reactivity in favor of formation of CH3O (branching ratio ˜80%) and hinders the H2CO dissociation into H2+HCO. In addition, kinetic isotope effects are strong in all reaction channels and vary strongly between the channels. Finally, we provide fits of the rate constants to be used in astrochemical models.

Design of Copper and Titanium Dioxide Nanoparticles Doped with Reduced Graphene Oxide for Hydrogen Evolution by Water Splitting

NASA Astrophysics Data System (ADS)

Yang, Yuhao; Huang, Wenhuan

2018-05-01

TiO2-graphene (P25-GR, PG) nanocomposite was fabricated from P25 titania and graphite oxide by hydrothermal method, and then Cu nanoparticles (Cu NPs) were assembled in P25-GR composite (Cu- P25-GR, CPG) under microwave-assisted chemical reduction. The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-Vis absorption (UV-Vis) and Raman spectroscopies. Cu NPs were well dispersed on the surface of PG and are in metallic state. The ternary Cu-P25-GR (CPG) nanocomposites show an extended light absorption range and more efficient charge separation properties compared to binary P25-GR (PG) composite. Methylene blue photodegradation experiment proved that surface plasmon resonance (SPR) phenomenon had an effect on photoreaction efficiency. The corresponding hydrogen evolution rate for CPG prepared using 0.002 M Cu(NO3)2 solution was 10 times higher than with pure P25, and 2.3 times higher than with PG in the same test conditions. The improved photocatalytic performance can be attributed to the presence of GR in the prepared composite and to the SPR effect, leading to the longer lifetime of photogenerated electronhole pairs and faster interfacial charge transfer rate. We expect that our work would be useful for the further exploration of GR-based nanocomposites.

Photocatalysts Based on Cobalt-Chelating Conjugated Polymers for Hydrogen Evolution from Water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Lianwei; Hadt, Ryan G.; Yao, Shiyu

Developing photocatalytic systems for water splitting to generate oxygen and hydrogen is one of the biggest chemical challenges in solar energy utilization. In this work, we report the first example of heterogeneous photocatalysts for hydrogen evolution based on in-chain cobalt-chelating conjugated polymers. Four conjugated polymers chelated with earth abundant cobalt ions were synthesized and found to evolve hydrogen photocatalytically from water. These polymers are designed to combine functions of the conjugated backbone as light-harvesting antenna and electron transfer conduit with the in-chain bipyridyl chelated transition metal centers as catalytic active sites. In addition, these polymers are soluble in organic solvents,more » enabling effective interactions with the substrates as well as detailed characterization. We also found a polymer-dependent optimal cobalt chelating concentration at which the highest photocatalytic hydrogen production (PHP) activity can be achieved.« less

Microbial detection method based on sensing molecular hydrogen

NASA Technical Reports Server (NTRS)

Wilkins, J. R.; Stoner, G. E.; Boykin, E. H.

1974-01-01

A simple method for detecting bacteria, based on the time of hydrogen evolution, was developed and tested against various members of the Enterobacteriaceae group. The test system consisted of (1) two electrodes, platinum and a reference electrode, (2) a buffer amplifier, and (3) a strip-chart recorder. Hydrogen evolution was measured by an increase in voltage in the negative (cathodic) direction. A linear relationship was established between inoculum size and the time hydrogen was detected (lag period). Lag times ranged from 1 h for 1 million cells/ml to 7 h for 1 cell/ml. For each 10-fold decrease in inoculum, length of the lag period increased 60 to 70 min. Based on the linear relationship between inoculum and lag period, these results indicate the potential application of the hydrogen-sensing method for rapidly detecting coliforms and other gas-producing microorganisms in a variety of clinical, food, and other samples.

Efficient hydrogen evolution catalysis using ternary pyrite-type cobalt phosphosulphide

NASA Astrophysics Data System (ADS)

Cabán-Acevedo, Miguel; Stone, Michael L.; Schmidt, J. R.; Thomas, Joseph G.; Ding, Qi; Chang, Hung-Chih; Tsai, Meng-Lin; He-Hau, Jr.; Jin, Song

2015-12-01

The scalable and sustainable production of hydrogen fuel through water splitting demands efficient and robust Earth-abundant catalysts for the hydrogen evolution reaction (HER). Building on promising metal compounds with high HER catalytic activity, such as pyrite structure cobalt disulphide (CoS2), and substituting non-metal elements to tune the hydrogen adsorption free energy could lead to further improvements in catalytic activity. Here we present a combined theoretical and experimental study to establish ternary pyrite-type cobalt phosphosulphide (CoPS) as a high-performance Earth-abundant catalyst for electrochemical and photoelectrochemical hydrogen production. Nanostructured CoPS electrodes achieved a geometrical catalytic current density of 10 mA cm-2 at overpotentials as low as 48 mV, with outstanding long-term operational stability. Integrated photocathodes of CoPS on n+-p-p+ silicon micropyramids achieved photocurrents up to 35 mA cm-2 at 0 V versus the reversible hydrogen electrode (RHE), onset photovoltages as high as 450 mV versus RHE, and the most efficient solar-driven hydrogen generation from Earth-abundant systems.

Hydrodynamic and chemical effects of hydrogen dilution on soot evolution in turbulent nonpremixed bluff body ethylene flames

NASA Astrophysics Data System (ADS)

Deng, Sili; Mueller, Michael E.; Chan, Qing N.; Qamar, Nader H.; Dally, Bassam B.; Alwahabi, Zeyad T.; Nathan, Graham J.

2015-11-01

A turbulent nonpremixed bluff body ethylene/hydrogen (volume ratio 2:1) flame is studied and compared with the ethylene counterpart [Mueller et al., Combust. Flame, 160, 2013]. Similar to the ethylene buff body flame, a low-strain recirculation zone, a high-strain neck region, and a downstream jet-like region are observed. However, the maximum soot volume fraction in the recirculation zone of the hydrogen diluted case is significantly lower than the ethylene case. Large Eddy Simulation is used to further investigate soot evolution in the recirculation zone and to elucidate the role of hydrogen dilution. Since the central jet Reynolds numbers in both cases are the same (approximately 30,900), the jet velocity of the hydrogen diluted case is higher, resulting in a shorter and leaner recirculation zone. In addition, hydrogen dilution chemically suppresses soot formation due to the reduction of C/H ratio. Consequently, the reduction of the soot volume fraction for the hydrogen diluted ethylene flame is attributed to two major effects: hydrodynamic and chemical effects.

Analysis of Pressure Variations in a Low-Pressure Nickel-Hydrogen Battery – Part 1

PubMed Central

Purushothaman, B. K.; Wainright, J. S.

2012-01-01

A low pressure nickel-hydrogen battery using either a metal hydride or gaseous hydrogen for H2 storage has been developed for use in implantable neuroprosthetic devices. In this paper, pressure variations inside the cell for the gaseous hydrogen version are analyzed and correlated with oxygen evolution side reaction at the end of charging, the recombination of oxygen with hydrogen during charging and a subsequent rest period, and the self-discharge of the nickel electrode. About 70% of the recombination occurred simultaneously with oxygen evolution during charging and the remaining oxygen recombined with hydrogen during the 1st hour after charging. Self-discharge of the cell varies linearly with hydrogen pressure at a given state of charge and increased with increasing battery charge levels. The coulometric efficiency calculated based on analysis of the pressure-time data agreed well with the efficiency calculated based on the current-time data. Pressure variations in the battery are simulated accurately to predict coulometric efficiency and the state of charge of the cell, factors of extreme importance for a battery intended for implantation within the human body. PMID:22423175

Analysis of Pressure Variations in a Low-Pressure Nickel-Hydrogen Battery - Part 1.

PubMed

Purushothaman, B K; Wainright, J S

2012-05-15

A low pressure nickel-hydrogen battery using either a metal hydride or gaseous hydrogen for H(2) storage has been developed for use in implantable neuroprosthetic devices. In this paper, pressure variations inside the cell for the gaseous hydrogen version are analyzed and correlated with oxygen evolution side reaction at the end of charging, the recombination of oxygen with hydrogen during charging and a subsequent rest period, and the self-discharge of the nickel electrode. About 70% of the recombination occurred simultaneously with oxygen evolution during charging and the remaining oxygen recombined with hydrogen during the 1(st) hour after charging. Self-discharge of the cell varies linearly with hydrogen pressure at a given state of charge and increased with increasing battery charge levels. The coulometric efficiency calculated based on analysis of the pressure-time data agreed well with the efficiency calculated based on the current-time data. Pressure variations in the battery are simulated accurately to predict coulometric efficiency and the state of charge of the cell, factors of extreme importance for a battery intended for implantation within the human body.

Vibrational spectroscopy reveals the initial steps of biological hydrogen evolution.

PubMed

Katz, S; Noth, J; Horch, M; Shafaat, H S; Happe, T; Hildebrandt, P; Zebger, I

2016-11-01

[FeFe] hydrogenases are biocatalytic model systems for the exploitation and investigation of catalytic hydrogen evolution. Here, we used vibrational spectroscopic techniques to characterize, in detail, redox transformations of the [FeFe] and [4Fe4S] sub-sites of the catalytic centre (H-cluster) in a monomeric [FeFe] hydrogenase. Through the application of low-temperature resonance Raman spectroscopy, we discovered a novel metastable intermediate that is characterized by an oxidized [Fe I Fe II ] centre and a reduced [4Fe4S] 1+ cluster. Based on this unusual configuration, this species is assigned to the first, deprotonated H-cluster intermediate of the [FeFe] hydrogenase catalytic cycle. Providing insights into the sequence of initial reaction steps, the identification of this species represents a key finding towards the mechanistic understanding of biological hydrogen evolution.

Two-dimensional boron: Lightest catalyst for hydrogen and oxygen evolution reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mir, Showkat H.; Chakraborty, Sudip, E-mail: sudiphys@gmail.com, E-mail: prakash.jha@cug.ac.in; Wärnå, John

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) have been envisaged on a two-dimensional (2D) boron sheet through electronic structure calculations based on a density functional theory framework. To date, boron sheets are the lightest 2D material and, therefore, exploring the catalytic activity of such a monolayer system would be quite intuitive both from fundamental and application perspectives. We have functionalized the boron sheet (BS) with different elemental dopants like carbon, nitrogen, phosphorous, sulphur, and lithium and determined the adsorption energy for each case while hydrogen and oxygen are on top of the doping site of themore » boron sheet. The free energy calculated from the individual adsorption energy for each functionalized BS subsequently guides us to predict which case of functionalization serves better for the HER or the OER.« less

Hydrogenation of benzaldehyde via electrocatalysis and thermal catalysis on carbon-supported metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Yang; Sanyal, Udishnu; Pangotra, Dhananjai

Abstract Selective reduction of benzaldehyde to benzyl alcohol on C-supported Pt, Rh, Pd, and Ni in aqueous phase was conducted using either directly H2 (thermal catalytic hydrogenation, TCH) or in situ electrocatalytically generated hydrogen (electrocatalytic hydrogenation, ECH). In TCH, the intrinsic activity of the metals at room temperature and 1 bar H2 increased in the sequence Rh/C < Pt/C < Pd/C, while Ni/C is inactive at these conditions due to surface oxidation in the absence of cathodic potential. The reaction follows a Langmuir-Hinshelwood mechanism with the second hydrogen addition to the adsorbed hydrocarbon being the rate-determining step. All tested metalsmore » were active in ECH of benzaldehyde, although hydrogenation competes with the hydrogen evolution reaction (HER). The minimum cathodic potentials to obtain appreciable ECH rates were identical to the onset potentials of HER. Above this onset, the relative rates of H reacting to H2 and H addition to the hydrocarbon determines the selectivity to ECH and TCH. Accordingly, the selectivity of the metals towards ECH increases in the order Ni/C < Pt/C < Rh/C < Pd/C. Pd/C shows exceptionally high ECH selectivity due to its surprisingly low HER reactivity under the reaction conditions. Acknowledgements The authors would like to thank the groups of Hubert A. Gasteiger at the Technische Universität München of Jorge Gascon at the Delft University of Technology for advice and valuable discussions. The authors are grateful to Nirala Singh, Erika Ember, Gary Haller, and Philipp Rheinländer for fruitful discussions. We are also grateful to Marianne Hanzlik for TEM measurements and to Xaver Hecht and Martin Neukamm for technical support. Y.S. would like to thank the Chinese Scholarship Council for the financial support. The research described in this paper is part of the Chemical Transformation Initiative at Pacific Northwest National Laboratory (PNNL), conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.« less

Improved stress corrosion cracking resistance of a novel biodegradable EW62 magnesium alloy by rapid solidification, in simulated electrolytes.

PubMed

Hakimi, O; Aghion, E; Goldman, J

2015-06-01

The high corrosion rate of magnesium (Mg) and Mg-alloys precludes their widespread acceptance as implantable biomaterials. Here, we investigated the potential for rapid solidification (RS) to increase the stress corrosion cracking (SCC) resistance of a novel Mg alloy, Mg-6%Nd-2%Y-0.5%Zr (EW62), in comparison to its conventionally cast (CC) counterpart. RS ribbons were extrusion consolidated in order to generate bioimplant-relevant geometries for testing and practical use. Microstructural characteristics were examined by SEM. Corrosion rates were calculated based upon hydrogen evolution during immersion testing. The surface layer of the tested alloys was analyzed by X-ray photoelectron spectroscopy (XPS). Stress corrosion resistance was assessed by slow strain rate testing and fractography. The results indicate that the corrosion resistance of the RS alloy is significantly improved relative to the CC alloy due to a supersaturated Nd enrichment that increases the Nd2O3 content in the external oxide layer, as well as a more homogeneous structure and reduced grain size. These improvements contributed to the reduced formation of hydrogen gas and hydrogen embrittlement, which reduced the SCC sensitivity relative to the CC alloy. Therefore, EW62 in the form of a rapidly solidified extruded structure may serve as a biodegradable implant for biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Type IA Supernovae

NASA Technical Reports Server (NTRS)

Wheeler, J. Craig

1992-01-01

Spectral calculations show that a model based on the thermonuclear explosion of a degenerate carbon/oxygen white dwarf provides excellent agreement with observations of Type Ia supernovae. Identification of suitable evolutionary progenitors remains a severe problem. General problems with estimation of supernova rates are outlined and the origin of Type Ia supernovae from double degenerate systems are discussed in the context of new rates of explosion per H band luminosity, the lack of observed candidates, and the likely presence of H in the vicinity of some SN Ia events. Re-examination of the problems of triggering Type Ia by accretion of hydrogen from a companion shows that there may be an avenue involving cataclysmic variables, especially if extreme hibernation occurs. Novae may channel accreting white dwarfs to a unique locus in accretion rate/mass space. Systems that undergo secular evolution to higher mass transfer rates could lead to just the conditions necessary for a Type Ia explosion. Tests involving fluorescence or absorption in a surrounding circumstellar medium and the detection of hydrogen stripped from a companion, which should appear at low velocity inside the white dwarf ejecta, are suggested. Possible observational confirmation of the former is described.

THE FORMATION AND EVOLUTION OF YOUNG LOW-MASS STARS WITHIN HALOS WITH HIGH CONCENTRATION OF DARK MATTER PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casanellas, Jordi; Lopes, IlIDio, E-mail: jordicasanellas@ist.utl.p, E-mail: ilidio.lopes@ist.utl.p

2009-11-01

The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M {sub sun}. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, thesemore » stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|DELTAT{sub eff}|>10{sup 3} K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M{sub sun} will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density rho{sub c}hi = 10{sup 9} GeV cm{sup -3}. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.« less

Hydrogen as a fuel for today and tomorrow: expectations for advanced hydrogen storage materials/systems research.

PubMed

Hirose, Katsuhiko

2011-01-01

History shows that the evolution of vehicles is promoted by several environmental restraints very similar to the evolution of life. The latest environmental strain is sustainability. Transport vehicles are now facing again the need to advance to use sustainable fuels such as hydrogen. Hydrogen fuel cell vehicles are being prepared for commercialization in 2015. Despite intensive research by the world's scientists and engineers and recent advances in our understanding of hydrogen behavior in materials, the only engineering phase technology which will be available for 2015 is high pressure storage. Thus industry has decided to implement the high pressure tank storage system. However the necessity of smart hydrogen storage is not decreasing but rather increasing because high market penetration of hydrogen fuel cell vehicles is expected from around 2025 onward. In order to bring more vehicles onto the market, cheaper and more compact hydrogen storage is inevitable. The year 2025 seems a long way away but considering the field tests and large scale preparation required, there is little time available for research. Finding smart materials within the next 5 years is very important to the success of fuel cells towards a low carbon sustainable world.

Atomistic simulations of the effect of embedded hydrogen and helium on the tensile properties of monocrystalline and nanocrystalline tungsten

NASA Astrophysics Data System (ADS)

Chen, Zhe; Kecskes, Laszlo J.; Zhu, Kaigui; Wei, Qiuming

2016-12-01

Uniaxial tensile properties of monocrystalline tungsten (MC-W) and nanocrystalline tungsten (NC-W) with embedded hydrogen and helium atoms have been investigated using molecular dynamics (MD) simulations in the context of radiation damage evolution. Different strain rates have been imposed to investigate the strain rate sensitivity (SRS) of the samples. Results show that the plastic deformation processes of MC-W and NC-W are dominated by different mechanisms, namely dislocation-based for MC-W and grain boundary-based activities for NC-W, respectively. For MC-W, the SRS increases and a transition appears in the deformation mechanism with increasing embedded atom concentration. However, no obvious embedded atom concentration dependence of the SRS has been observed for NC-W. Instead, in the latter case, the embedded atoms facilitate GB sliding and intergranular fracture. Additionally, a strong strain enhanced He cluster growth has been observed. The corresponding underlying mechanisms are discussed.

Comparative experimental study of gas evolution and gas consumption reactions in sealed Ni-Cd and Ni-MH cells

NASA Astrophysics Data System (ADS)

Cha, Chuansin; Yu, Jingxian; Zhang, Jixiao

The behavior of the sealed Ni-Cd and Ni-MH systems are compared experimentally with regard to their ability to consume gaseous products generated during the overcharge stage of these systems. It was found that the Ni-Cd system could only consume oxygen, while the Ni-MH system possesses the additional ability to adsorb hydrogen and to catalyze the recombination reaction of hydrogen and oxygen. The internal pressure within both sealed Ni-Cd cells and sealed Ni-MH cells can be kept well under control during the charge/overcharge processes if the rate of overcharge is not too high and if there is sufficient surplus of charging capacity at the negative electrodes. However, the internal pressure can rise to dangerously high levels if the rate of overcharge is too high or there is a deficiency of the charging capacity at the negative electrodes. The various factors that may affect the surplus of charging capacity of the negative electrodes are also discussed.

Photocatalytic hydrogen evolution of palladium nanoparticles decorated black TiO2 calcined in argon atmosphere

NASA Astrophysics Data System (ADS)

Wu, Ming-Chung; Hsiao, Kai-Chi; Chang, Yin-Hsuan; Chan, Shun-Hsiang

2018-02-01

Black TiO2 nanoparticles (BTN) was prepared by sol-gel derived precursor calcined in an argon atmosphere. The synthesized BTN with trivalent titanium ion, structural defect, and oxygen vacancy shows a remarkably high absorbance in the visible light spectrum. BTN thus behaves a higher visible-active nanoreactor than white TiO2 nanoparticles (WTN) in the aqueous solution for organic pollutant degradation. Moreover, palladium decoration on the BTN surface (Pd-BTN) demonstrates a fascinating clean energy application. The obtained Pd-BTN fulfills a satisfied green material demand in the photocatalytic hydrogen production application. Pd-BTN calcined at 400 °C (Pd-BTN-400) shows the high photocatalytic hydrogen generation rate of 5200 μmol/g h under UV-A irradiation and 9300 μmol/g h under UV-B irradiation, respectively. The well-developed material, Pd-BTN-400, could be one of the best solutions in the concern of clean energy and water-purification with regard to the continuous environmental issue.

A theoretical study of the effect of a non-aqueous proton donor on electrochemical ammonia synthesis

DOE PAGES

Zhang, Linan; Mallikarjun Sharada, Shaama; Singh, Aayush R.; ...

2018-01-17

We report that ammonia synthesis is one of the most studied reactions in heterogeneous catalysis. To date, however, electrochemical N 2 reduction in aqueous systems has proven to be extremely difficult, mainly due to the competing hydrogen evolution reaction (HER). Recently, it has been shown that transition metal complexes based on molybdenum can reduce N 2 to ammonia at room temperature and ambient pressure in a non-aqueous system, with a relatively small amount of hydrogen output. We demonstrate that the non-aqueous proton donor they have chosen, 2,6-lutidinium (LutH +), is a viable substitute for hydronium in the electrochemical process atmore » a solid surface, since this donor can suppress the HER rate. Finally, we also show that the presence of LutH + can selectively stabilize the *NNH intermediate relative to *NH or *NH 2via the formation of hydrogen bonds, indicating that the use of non-aqueous solvents can break the scaling relationship between limiting potential and binding energies.« less

A theoretical study of the effect of a non-aqueous proton donor on electrochemical ammonia synthesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Linan; Mallikarjun Sharada, Shaama; Singh, Aayush R.

We report that ammonia synthesis is one of the most studied reactions in heterogeneous catalysis. To date, however, electrochemical N 2 reduction in aqueous systems has proven to be extremely difficult, mainly due to the competing hydrogen evolution reaction (HER). Recently, it has been shown that transition metal complexes based on molybdenum can reduce N 2 to ammonia at room temperature and ambient pressure in a non-aqueous system, with a relatively small amount of hydrogen output. We demonstrate that the non-aqueous proton donor they have chosen, 2,6-lutidinium (LutH +), is a viable substitute for hydronium in the electrochemical process atmore » a solid surface, since this donor can suppress the HER rate. Finally, we also show that the presence of LutH + can selectively stabilize the *NNH intermediate relative to *NH or *NH 2via the formation of hydrogen bonds, indicating that the use of non-aqueous solvents can break the scaling relationship between limiting potential and binding energies.« less

Carbon-Encapsulated WOx Hybrids as Efficient Catalysts for Hydrogen Evolution.

PubMed

Jing, Shengyu; Lu, Jiajia; Yu, Guangtao; Yin, Shibin; Luo, Lin; Zhang, Zengsong; Ma, Yanfeng; Chen, Wei; Shen, Pei Kang

2018-05-29

Developing non-noble metal catalysts as Pt substitutes, with good activity and stability, remains a great challenge for cost-effective electrochemical evolution of hydrogen. Herein, carbon-encapsulated WO x anchored on a carbon support (WO x @C/C) that has remarkable Pt-like catalytic behavior for the hydrogen evolution reaction (HER) is reported. Theoretical calculations reveal that carbon encapsulation improves the conductivity, acting as an electron acceptor/donor, and also modifies the Gibbs free energy of H* values for different adsorption sites (carbon atoms over the W atom, O atom, WO bond, and hollow sites). Experimental results confirm that WO x @C/C obtained at 900 °C with 40 wt% metal loading has excellent HER activity regarding its Tafel slope and overpotential at 10 and 60 mA cm -2 , and also has outstanding stability at -50 mV for 18 h. Overall, the results and facile synthesis method offer an exciting avenue for the design of cost-effective catalysts for scalable hydrogen generation. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal organic framework-derived CoPS/N-doped carbon for efficient electrocatalytic hydrogen evolution.

PubMed

Li, Yuzhi; Niu, Siqi; Rakov, Dmitrii; Wang, Ying; Cabán-Acevedo, Miguel; Zheng, Shijian; Song, Bo; Xu, Ping

2018-04-19

Electrocatalytic hydrogen evolution has attracted a great deal of attention due to the urgent need for clean energy. Herein, we demonstrate the synthesis of ternary pyrite-type cobalt phosphosulphide (CoPS) nanoparticles supported on a nitrogen-doped carbon matrix, CoPS/N-C, through carbonization and subsequent phosphosulfurization of Co-based zeolitic imidazolate frameworks (ZIF-67), as promising hydrogen evolution reaction (HER) electrocatalysts in both acidic and alkaline solutions. The polyhedral structure of ZIF-67 can be well maintained in the as-prepared CoPS/N-C nanocomposites. In particular, CoPS/N-C provides a geometric catalytic current density of -10 mA cm-2 at overpotentials of -80 and -148 mV vs. a reversible hydrogen electrode (RHE) and a Tafel slope of 68 and 78 mV dec-1 in 0.5 M H2SO4 and 1 M KOH, respectively, which is superior to most of the transition metal phosphosulfide materials. This MOF-derived synthesis of a transition metal phosphosulfide supported heteroatom-doped carbon matrix provides a promising opportunity for the development of highly efficient electrocatalysts for renewable energy devices.

Photoelectrochemistry by Design: Tailoring the Nanoscale Structure of Pt/NiO Composites Leads to Enhanced Photoelectrochemical Hydrogen Evolution Performance

PubMed Central

2017-01-01

Photoelectrochemical hydrogen evolution is a promising avenue to store the energy of sunlight in the form of chemical bonds. The recent rapid development of new synthetic approaches enables the nanoscale engineering of semiconductor photoelectrodes, thus tailoring their physicochemical properties toward efficient H2 formation. In this work, we carried out the parallel optimization of the morphological features of the semiconductor light absorber (NiO) and the cocatalyst (Pt). While nanoporous NiO films were obtained by electrochemical anodization, the monodisperse Pt nanoparticles were synthesized using wet chemical methods. The Pt/NiO nanocomposites were characterized by XRD, XPS, SEM, ED, TEM, cyclic voltammetry, photovoltammetry, EIS, etc. The relative enhancement of the photocurrent was demonstrated as a function of the nanoparticle size and loading. For mass-specific surface activity the smallest nanoparticles (2.0 and 4.8 nm) showed the best performance. After deconvoluting the trivial geometrical effects (stemming from the variation of Pt particle size and thus the electroactive surface area), however, the intermediate particle sizes (4.8 and 7.2 nm) were found to be optimal. Under optimized conditions, a 20-fold increase in the photocurrent (and thus the H2 evolution rates) was observed for the nanostructured Pt/NiO composite, compared to the benchmark nanoparticulate NiO film. PMID:28620447

Surface composition changes in massive star evolution with mass loss

NASA Technical Reports Server (NTRS)

Noels, A.; Gabriel, M.; Vreux, J.-M.; Conti, P. S.

1980-01-01

A series of evolutionary models of 40-100 solar mass objects undergoing mass loss are constructed with the explicit inclusion of the surface composition of H, He, C, N, O elements. Mass loss rates similar to those observed in Of stars, 4 to 7 x 10 to the -6th solar masses/yr, result in an appearance at the surface of equilibrium CNO products, i.e. enhanced nitrogen and diminished carbon, while that star is still burning hydrogen in the core. This result obtains because the initial convection core is a relatively large fraction of the total mass and rather modest loss exposes levels of anomalous composition. It is suggested that these objects might reasonably be identified as those luminous late type WN stars still containing surface hydrogen.

Hydrogen Assisted Cracking in Pearlitic Steel Rods: The Role of Residual Stresses Generated by Fatigue Precracking

PubMed Central

Toribio, Jesús; Aguado, Leticia; Lorenzo, Miguel; Kharin, Viktor

2017-01-01

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress. PMID:28772845

Pre-main Sequence Evolution and the Hydrogen-Burning Minimum Mass

NASA Astrophysics Data System (ADS)

Nakano, Takenori

There is a lower limit to the mass of the main-sequence stars (the hydrogen-burning minimum mass) below which the stars cannot replenish the energy lost from their surfaces with the energy released by the hydrogen burning in their cores. This is caused by the electron degeneracy in the stars which suppresses the increase of the central temperature with contraction. To find out the lower limit we need the accurate knowledge of the pre-main sequence evolution of very low-mass stars in which the effect of electron degeneracy is important. We review how Hayashi and Nakano (1963) carried out the first determination of this limit.

Solar hydrogen production using epitaxial SrTiO 3 on a GaAs photovoltaic

DOE PAGES

Kornblum, L.; Fenning, D. P.; Faucher, J.; ...

2016-12-22

We demonstrate an oxide-stabilized III–V photoelectrode architecture for solar fuel production from water in neutral pH. For this tunable architecture we demonstrate 100% Faradaic efficiency for hydrogen evolution, and incident photon-to-current efficiencies (IPCE) exceeding 50%. High IPCE for hydrogen evolution is a consequence of the low-loss interface achieved via epitaxial growth of a thin oxide on a GaAs solar cell. Developing optimal energetic alignment across the interfaces of the photoelectrode using well-established III–V technology is key to obtaining high performance. This advance constitutes a critical milestone towards efficient, unassisted fuel production from solar energy.

Hydrogen addition reactions of aliphatic hydrocarbons in comets

NASA Astrophysics Data System (ADS)

Kobayashi, Hitomi; Watanabe, N.; Watanabe, Y.; Fukushima, T.; Kawakita, H.

2013-10-01

Comets are thought as remnants of early solar nebula. Their chemical compositions are precious clue to chemical and physical evolution of the proto-planetary disk. Some hydrocarbons such as C2H6, C2H2 and CH4 in comets have been observed by using near-infrared spectroscopy. Although the compositions of C2H6 were about 1% relative to the water in normal comets, there are few reports on the detection of C2H6 in ISM. Some formation mechanisms of C2H6 in ISM have been proposed, and there are two leading hypotheses; one is the dimerizations of CH3 and another is the hydrogen addition reactions of C2H2 on cold icy grains. To evaluate these formation mechanisms for cometary C2H6 quantitatively, it is important to search the C2H4 in comets, which is the intermediate product of the hydrogen addition reactions toward C2H6. However, it is very difficult to detect the C2H4 in comets in NIR (3 microns) regions because of observing circumstances. The hydrogen addition reactions of C2H2 at low temperature conditions are not well characterized both theoretically and experimentally. For example, there are no reports on the reaction rate coefficients of those reaction system. To determine the production rates of those hydrogen addition reactions, we performed the laboratory experiments of the hydrogenation of C2H2 and C2H4. We used four types of the initial composition of the ices: pure C2H4, pure C2H2, C2H2 on amorphous solid water (ASW) and C2H4 on ASW at three different temperatures of 10, 20, and 30K. We found 1) reactions are more efficient when there are ASW in the initial compositions of the ice; 2) hydrogenation of C2H4 occur more rapid than that of C2H2.

XUV-Exposed, Non-Hydrostatic Hydrogen-Rich Upper Atmospheres of Terrestrial Planets. Part II: Hydrogen Coronae and Ion Escape

PubMed Central

Lammer, Helmut; Holmström, Mats; Panchenko, Mykhaylo; Odert, Petra; Erkaev, Nikolai V.; Leitzinger, Martin; Khodachenko, Maxim L.; Kulikov, Yuri N.; Güdel, Manuel; Hanslmeier, Arnold

2013-01-01

Abstract We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a “super-Earth” with a radius of 2 REarth and a mass of 10 MEarth, located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×1025 s−1 to ∼5.3×1030 s−1, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EOH) to <3 EOH and usually is several times smaller in comparison to the thermal atmospheric escape rates. Key Words: Stellar activity—Low-mass stars—Early atmospheres—Earth-like exoplanets—Energetic neutral atoms—Ion escape—Habitability. Astrobiology 13, 1030–1048. PMID:24283926

XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part II: hydrogen coronae and ion escape.

PubMed

Kislyakova, Kristina G; Lammer, Helmut; Holmström, Mats; Panchenko, Mykhaylo; Odert, Petra; Erkaev, Nikolai V; Leitzinger, Martin; Khodachenko, Maxim L; Kulikov, Yuri N; Güdel, Manuel; Hanslmeier, Arnold

2013-11-01

We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a "super-Earth" with a radius of 2 R(Earth) and a mass of 10 M(Earth), located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×10²⁵ s⁻¹ to ∼5.3×10³⁰ s⁻¹, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EO(H)) to <3 EO(H) and usually is several times smaller in comparison to the thermal atmospheric escape rates.

Self-supported three-dimensional Cu/Cu2O-CuO/rGO nanowire array electrodes for an efficient hydrogen evolution reaction.

PubMed

Ye, Lin; Wen, Zhenhai

2018-06-14

We report the fabrication of self-supported Cu/Cu2O-CuO/rGO nanowire arrays on commercial porous copper foam, which exhibit excellent activity and durability for electrochemical hydrogen evolution, presenting a small onset potential of 84 mV and a low overpotential of 105 mV at a current density of 10 mA cm-2.

Photocatalytic Hydrogen-Evolution Cross-Couplings: Benzene C-H Amination and Hydroxylation.

PubMed

Zheng, Yi-Wen; Chen, Bin; Ye, Pan; Feng, Ke; Wang, Wenguang; Meng, Qing-Yuan; Wu, Li-Zhu; Tung, Chen-Ho

2016-08-17

We present a blueprint for aromatic C-H functionalization via a combination of photocatalysis and cobalt catalysis and describe the utility of this strategy for benzene amination and hydroxylation. Without any sacrificial oxidant, we could use the dual catalyst system to produce aniline directly from benzene and ammonia, and phenol from benzene and water, both with evolution of hydrogen gas under unusually mild conditions in excellent yields and selectivities.

Improving the intrinsic electrocatalytic hydrogen evolution activity of few-layer NiPS3 by cobalt doping.

PubMed

Li, Kai; Rakov, Dmitrii; Zhang, Wei; Xu, Ping

2017-07-18

Here we demonstrate the improvement of the intrinsic electrocatalytic hydrogen evolution activity of NiPS 3 by proper cobalt doping. The optimized Ni 0.95 Co 0.05 PS 3 nanosheets display a geometric catalytic current density of -10 mA cm -2 at an overpotential of 71 mV vs. RHE and a Tafel slope of 77 mV dec -1 in 1.0 M KOH.

Precise tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis

PubMed Central

Wang, Pengtang; Zhang, Xu; Zhang, Jin; Wan, Sheng; Guo, Shaojun; Lu, Gang; Yao, Jianlin; Huang, Xiaoqing

2017-01-01

Comprising abundant interfaces, multicomponent heterostructures can integrate distinct building blocks into single entities and yield exceptional functionalities enabled by the synergistic components. Here we report an efficient approach to construct one-dimensional metal/sulfide heterostructures by directly sulfuring highly composition-segregated platinum-nickel nanowires. The heterostructures possess a high density of interfaces between platinum-nickel and nickel sulfide components, which cooperate synergistically towards alkaline hydrogen evolution reaction. The platinum-nickel/nickel sulfide heterostructures can deliver a current density of 37.2 mA cm−2 at an overpotential of 70 mV, which is 9.7 times higher than that of commercial Pt/C. The heterostructures also offer enhanced stability revealed by long-term chronopotentiometry measurements. The present work highlights a potentially powerful interface-engineering strategy for designing multicomponent heterostructures with advanced performance in hydrogen evolution reaction and beyond. PMID:28239145

Ultrafast Spectroscopy Reveals Electron-Transfer Cascade That Improves Hydrogen Evolution with Carbon Nitride Photocatalysts.

PubMed

Corp, Kathryn L; Schlenker, Cody W

2017-06-14

Solar hydrogen generation from water represents a compelling component of a future sustainable energy portfolio. Recently, chemically robust heptazine-based polymers known as graphitic carbon nitrides (g-C 3 N 4 ) have emerged as promising photocatalysts for hydrogen evolution using visible light while withstanding harsh chemical environments. However, since g-C 3 N 4 electron-transfer dynamics are poorly understood, rational design rules for improving activity remain unclear. Here, we use visible and near-infrared femtosecond transient absorption (TA) spectroscopy to reveal an electron-transfer cascade that correlates with a near-doubling in photocatalytic activity from 2050 to 3810 μmol h -1 g -1 when we infuse a suspension of bulk g-C 3 N 4 with 10% mass loading of chemically exfoliated carbon nitride. TA spectroscopy indicates that exfoliated carbon nitride quenches photogenerated electrons on g-C 3 N 4 at rates approaching the molecular diffusion limit. The TA signal for photogenerated electrons on g-C 3 N 4 decays with a time constant of 1/k e ' = 660 ps in the mixture versus 1/k e = 4.1 ns in g-C 3 N 4 alone. Our TA measurements suggest that the charge generation efficiency in g-C 3 N 4 is greater than 65%. Exfoliated carbon nitride, which liberates only trace hydrogen levels when photoexcited directly, does not appear to independently sustain appreciable long-lived charge generation. Thus, the activity enhancement in the two-component infusion evidently results from a cooperative effect in which charge is generated on g-C 3 N 4 , followed by electron transfer to exfoliated carbon nitride containing photocatalytic chain terminations. This correlation between electron transfer and photocatalytic activity provides new insight into structural modifications for controlling charge separation dynamics and activity of carbon-based photocatalysts.

Tidal dissipation and evolution of white dwarfs around massive black holes: an eccentric path to tidal disruption

NASA Astrophysics Data System (ADS)

Vick, Michelle; Lai, Dong; Fuller, Jim

2017-06-01

A white dwarf (WD) captured into a high-eccentricity orbit around a massive black hole (MBH) may undergo many pericentre passages before tidal disruption. During these passages, the tidal potential of the MBH excites internal oscillations or waves in the WD, and the dissipation of these oscillations can significantly influence the physical properties of the WD prior to its disruption. We calculate the amplitude of the tidally excited gravity (buoyancy) waves in the WD as a function of the pericentre distance and eccentricity for realistic WD models, under the assumption that these outgoing gravity waves are efficiently dissipated in the outer layers of the WD by non-linear effects or radiative damping. We obtain fitting formulae for the tidal energy and angular momentum transfer rates as well as the tidal heating rate. We find that these dynamical tides are much weaker than gravitational radiation in driving the orbital decay of the WD-MBH binary, and they are also inefficient in changing the WD spin during the orbital evolution. Incorporating our computed tidal dissipation rate into a mesa-based WD evolution code, we find that tidal heating can lead to appreciable brightening of the WD and may induce runaway fusion in the hydrogen envelope well before the WD undergoes tidal disruption.

Highly efficient photocatalytic hydrogen evolution from nickel quinolinethiolate complexes under visible light irradiation

NASA Astrophysics Data System (ADS)

Rao, Heng; Yu, Wen-Qian; Zheng, Hui-Qin; Bonin, Julien; Fan, Yao-Ting; Hou, Hong-Wei

2016-08-01

Earth-abundant metal complexes have emerged as promising surrogates of platinum for catalyzing the hydrogen evolution reaction (HER). In this study, we report the design and synthesis of two novel nickel quinolinethiolate complexes, namely [Ni(Hqt)2(4, 4‧-Z-2, 2‧-bpy)] (Hqt = 8-quinolinethiol, Z = sbnd H [1] or sbnd CH3 [2], bpy = bipyridine). An efficient three-component photocatalytic homogeneous system for hydrogen generation working under visible light irradiation was constructed by using the target complexes as catalysts, triethylamine (TEA) as sacrificial electron donor and xanthene dyes as photosensitizer. We obtain turnover numbers (TON, vs. catalyst) for H2 evolution of 5923/7634 under the optimal conditions with 5.0 × 10-6 M complex 1/2 respectively, 1.0 × 10-3 M fluorescein and 5% (v/v) TEA at pH 12.3 in EtOH/H2O (1:1, v/v) mixture after 8 h irradiation (λ > 420 nm). We discuss the mechanism of H2 evolution in the homogeneous photocatalytic system based on fluorescence spectrum and cyclic voltammetry data.

Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces

DOE PAGES

Coridan, Robert H.; Schichtl, Zebulon G.; Sun, Tao; ...

2016-08-30

Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubblemore » evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.« less

Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coridan, Robert H.; Schichtl, Zebulon G.; Sun, Tao

Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubblemore » evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.« less

Water electrolysis with a conducting carbon cloth: subthreshold hydrogen generation and superthreshold carbon quantum dot formation.

PubMed

Biswal, Mandakini; Deshpande, Aparna; Kelkar, Sarika; Ogale, Satishchandra

2014-03-01

A conducting carbon cloth, which has an interesting turbostratic microstructure and functional groups that are distinctly different from other ordered forms of carbon, such as graphite, graphene, and carbon nanotubes, was synthesized by a simple one-step pyrolysis of cellulose fabric. This turbostratic disorder and surface chemical functionalities had interesting consequences for water splitting and hydrogen generation when such a cloth was used as an electrode in the alkaline electrolysis process. Importantly, this work also gives a new twist to carbon-assisted electrolysis. During electrolysis, the active sites in the carbon cloth allow slow oxidation of its surface to transform the surface groups from COH to COOH and so forth at a voltage as low as 0.2 V in a two-electrode system, along with platinum as the cathode, instead of 1.23 V (plus overpotential), which is required for platinum, steel, or even graphite anodes. The quantity of subthreshold hydrogen evolved was 24 mL cm(-2)  h(-1) at 1 V. Interestingly, at a superthreshold potential (>1.23 V+overpotential), another remarkable phenomenon was found. At such voltages, along with the high rate and quantity of hydrogen evolution, rapid exfoliation of the tiny nanoscale (5-7 nm) units of carbon quantum dots (CQDs) are found in copious amounts due to an enhanced oxidation rate. These CQDs show bright-blue fluorescence under UV light. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic investigation of the formation of H2 from HCOOH with a dinuclear Ru model complex for formate hydrogen lyase.

PubMed

Tokunaga, Taisuke; Yatabe, Takeshi; Matsumoto, Takahiro; Ando, Tatsuya; Yoon, Ki-Seok; Ogo, Seiji

2017-01-01

We report the mechanistic investigation of catalytic H 2 evolution from formic acid in water using a formate-bridged dinuclear Ru complex as a formate hydrogen lyase model. The mechanistic study is based on isotope-labeling experiments involving hydrogen isotope exchange reaction.

Iron vs. cobalt clathrochelate electrocatalysts of HER: the first example on a cage iron complex.

PubMed

Dolganov, Alexander V; Belov, Alexander S; Novikov, Valentin V; Vologzhanina, Anna V; Mokhir, Andriy; Bubnov, Yurii N; Voloshin, Yan Z

2013-04-07

New macrobicyclic 2-thiopheneboron-capped iron and cobalt(II) tris-dioximates showed high electrocatalytic activity for hydrogen production from H(+) ions. This is the first example of the hydrogen evolution reaction electrocatalyzed by a clathrochelate iron complex, which catalyzes the hydrogen production at low overpotential.

The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

PubMed Central

Mueller, Wolf-Dieter; Hornberger, Helga

2014-01-01

Mg and Mg alloys are becoming more and more of interest for several applications. In the case of biomaterial applications, a special interest exists due to the fact that a predictable degradation should be given. Various investigations were made to characterize and predict the corrosion behavior in vitro and in vivo. Mostly, the simple oxidation of Mg to Mg2+ ions connected with adequate hydrogen development is assumed, and the negative difference effect (NDE) is attributed to various mechanisms and electrochemical results. The aim of this paper is to compare the different views on the corrosion pathway of Mg or Mg alloys and to present a neglected pathway based on thermodynamic data as a guideline for possible reactions combined with experimental observations of a delay of visible hydrogen evolution during cyclic voltammetry. Various reaction pathways are considered and discussed to explain these results, like the stability of the Mg+ intermediate state, the stability of MgH2 and the role of hydrogen overpotential. Finally, the impact of MgH2 formation is shown as an appropriate base for the prediction of the degradation behavior and calculation of the corrosion rate of Mg and Mg alloys. PMID:24972140

Neutral hydrogen in the post-reionization universe

NASA Astrophysics Data System (ADS)

Padmanabhan, Hamsa

2018-05-01

The evolution of neutral hydrogen (HI) across redshifts is a powerful probe of cosmology, large scale structure in the universe and the intergalactic medium. Using a data-driven halo model to describe the distribution of HI in the post-reionization universe (z ~ 5 to 0), we obtain the best-fitting parameters from a rich sample of observational data: low redshift 21-cm emission line studies, intermediate redshift intensity mapping experiments, and higher redshift Damped Lyman Alpha (DLA) observations. Our model describes the abundance and clustering of neutral hydrogen across redshifts 0 - 5, and is useful for investigating different aspects of galaxy evolution and for comparison with hydrodynamical simulations. The framework can be applied for forecasting future observations with neutral hydrogen, and extended to the case of intensity mapping with molecular and other line transitions at intermediate redshifts.

Using directed evolution to improve hydrogen production in chimeric hydrogenases from Clostridia species.

PubMed

Plummer, Scott M; Plummer, Mark A; Merkel, Patricia A; Hagen, Moira; Biddle, Jennifer F; Waidner, Lisa A

2016-11-01

Hydrogenases are enzymes that play a key role in controlling excess reducing equivalents in both photosynthetic and anaerobic organisms. This enzyme is viewed as potentially important for the industrial generation of hydrogen gas; however, insufficient hydrogen production has impeded its use in a commercial process. Here, we explore the potential to circumvent this problem by directly evolving the Fe-Fe hydrogenase genes from two species of Clostridia bacteria. In addition, a computational model based on these mutant sequences was developed and used as a predictive aid for the isolation of enzymes with even greater efficiency in hydrogen production. Two of the improved mutants have a logarithmic increase in hydrogen production in our in vitro assay. Furthermore, the model predicts hydrogenase sequences with hydrogen productions as high as 540-fold over the positive control. Taken together, these results demonstrate the potential of directed evolution to improve the native bacterial hydrogenases as a first step for improvement of hydrogenase activity, further in silico prediction, and finally, construction and demonstration of an improved algal hydrogenase in an in vivo assay of C. reinhardtii hydrogen production. Copyright © 2016 Elsevier Inc. All rights reserved.

Role of the Edge Properties in the Hydrogen Evolution Reaction on MoS2.

PubMed

Lazar, Petr; Otyepka, Michal

2017-04-06

Molybdenum disulfide, in particular its edges, has attracted considerable attention as possible substitute for platinum catalysts in the hydrogen evolution reaction (HER). The complex nature of the reaction complicates its detailed experimental investigations, which are mostly indirect and sample dependent. Therefore, density functional theory calculations were employed to study how the properties of the MoS 2 Mo-edge influence the thermodynamics of hydrogen adsorption onto the edge. The effect of the computational model (one-dimensional nanostripe), border symmetry imposed by its length, sulfur saturation of the edge, and dimensionality of the material are discussed. Hydrogen adsorption was found to depend critically on the coverage of extra sulfur at the Mo edge. The bare Mo-edge and fully sulfur-covered Mo-edge are catalytically inactive. The most favorable hydrogen binding towards HER was found for the Mo-edge covered by sulfur monomers. This edge provides hydrogen adsorption free energies positioned around -0.25 eV at up to 50 % hydrogen coverage, close to the experimental values of overpotential needed for the HER reaction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A manganese-hydrogen battery with potential for grid-scale energy storage

NASA Astrophysics Data System (ADS)

Chen, Wei; Li, Guodong; Pei, Allen; Li, Yuzhang; Liao, Lei; Wang, Hongxia; Wan, Jiayu; Liang, Zheng; Chen, Guangxu; Zhang, Hao; Wang, Jiangyan; Cui, Yi

2018-05-01

Batteries including lithium-ion, lead-acid, redox-flow and liquid-metal batteries show promise for grid-scale storage, but they are still far from meeting the grid's storage needs such as low cost, long cycle life, reliable safety and reasonable energy density for cost and footprint reduction. Here, we report a rechargeable manganese-hydrogen battery, where the cathode is cycled between soluble Mn2+ and solid MnO2 with a two-electron reaction, and the anode is cycled between H2 gas and H2O through well-known catalytic reactions of hydrogen evolution and oxidation. This battery chemistry exhibits a discharge voltage of 1.3 V, a rate capability of 100 mA cm-2 (36 s of discharge) and a lifetime of more than 10,000 cycles without decay. We achieve a gravimetric energy density of 139 Wh kg-1 (volumetric energy density of 210 Wh l-1), with the theoretical gravimetric energy density of 174 Wh kg-1 (volumetric energy density of 263 Wh l-1) in a 4 M MnSO4 electrolyte. The manganese-hydrogen battery involves low-cost abundant materials and has the potential to be scaled up for large-scale energy storage.

XUV-Exposed, Non-Hydrostatic Hydrogen-Rich Upper Atmospheres of Terrestrial Planets. Part I: Atmospheric Expansion and Thermal Escape

PubMed Central

Lammer, Helmut; Odert, Petra; Kulikov, Yuri N.; Kislyakova, Kristina G.; Khodachenko, Maxim L.; Güdel, Manuel; Hanslmeier, Arnold; Biernat, Helfried

2013-01-01

Abstract The recently discovered low-density “super-Earths” Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H2O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 REarth and a mass of 10 MEarth. We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general. Key Words: Stellar activity—Low-mass stars—Early atmospheres—Earth-like exoplanets—Energetic neutral atoms—Ion escape—Habitability. Astrobiology 13, 1011–1029. PMID:24251443

Towards identifying the active sites on RuO 2 (110) in catalyzing oxygen evolution

DOE PAGES

Rao, Reshma R.; Kolb, Manuel J.; Halck, Niels Bendtsen; ...

2017-11-17

While the surface atomic structure of RuO 2 has been well studied in ultra high vacuum, much less is known about the interaction between water and RuO 2 in aqueous solution. In this work, in situ surface X-ray scattering measurements combined with density functional theory (DFT) were used to determine the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions associated with the successive deprotonation of –H 2O on the coordinatively unsaturated Ru sites (CUS)more » and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an –OO species on the Ru CUS sites was detected, which was stabilized by a neighboring –OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the –OH group used to stabilize –OO was found to be rate-limiting.« less

Towards identifying the active sites on RuO 2 (110) in catalyzing oxygen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao, Reshma R.; Kolb, Manuel J.; Halck, Niels Bendtsen

While the surface atomic structure of RuO 2 has been well studied in ultra high vacuum, much less is known about the interaction between water and RuO 2 in aqueous solution. In this work, in situ surface X-ray scattering measurements combined with density functional theory (DFT) were used to determine the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions associated with the successive deprotonation of –H 2O on the coordinatively unsaturated Ru sites (CUS)more » and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an –OO species on the Ru CUS sites was detected, which was stabilized by a neighboring –OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the –OH group used to stabilize –OO was found to be rate-limiting.« less

Nanoplasmonically Engineered Interfaces on Amorphous TiO2 for Highly Efficient Photocatalysis in Hydrogen Evolution.

PubMed

Liang, Huijun; Meng, Qiuxia; Wang, Xiaobing; Zhang, Hucheng; Wang, Jianji

2018-04-25

The nanoplasmonic metal-driven photocatalytic activity depends heavily on the spacing between metal nanoparticles (NPs) and semiconductors, and this work shows that ethylene glycol (EG) is an ideal candidate for interface spacer. Controlling the synthetic systems at pH 3, the composite of Ag NPs with EG-stabilized amorphous TiO 2 (Ag/TiO 2 -3) was synthesized by the facile light-induced reduction. It is verified that EG spacers can set up suitable geometric arrangement in the composite: the twin hydroxyls act as stabilizers to bind Ag NPs and TiO 2 together and the nonconductive alkyl chains consisting only of two CH 2 are able to separate the two building blocks completely and also provide the shortest channels for an efficient transfer of radiation energies to reach TiO 2 . Employed as photocatalysts in hydrogen evolution under visible light, amorphous TiO 2 hardly exhibits the catalytic activity due to high defect density, whereas Ag/TiO 2 -3 represents a remarkably high catalytic efficiency. The enhancement mechanism of the reaction rate is proposed by the analysis of the compositional, structural, and optical properties from a series of Ag/TiO 2 composites.

Hydrogen production by recombinant Escherichia coli strains

PubMed Central

Maeda, Toshinari; Sanchez‐Torres, Viviana; Wood, Thomas K.

2012-01-01

Summary The production of hydrogen via microbial biotechnology is an active field of research. Given its ease of manipulation, the best‐studied bacterium Escherichia coli has become a workhorse for enhanced hydrogen production through metabolic engineering, heterologous gene expression, adaptive evolution, and protein engineering. Herein, the utility of E. coli strains to produce hydrogen, via native hydrogenases or heterologous ones, is reviewed. In addition, potential strategies for increasing hydrogen production are outlined and whole‐cell systems and cell‐free systems are compared. PMID:21895995

Large-scale atomistic simulations of helium-3 bubble growth in complex palladium alloys

DOE PAGES

Hale, Lucas M.; Zimmerman, Jonathan A.; Wong, Bryan M.

2016-05-18

Palladium is an attractive material for hydrogen and hydrogen-isotope storage applications due to its properties of large storage density and high diffusion of lattice hydrogen. When considering tritium storage, the material’s structural and mechanical integrity is threatened by both the embrittlement effect of hydrogen and the creation and evolution of additional crystal defects (e.g., dislocations, stacking faults) caused by the formation and growth of helium-3 bubbles. Using recently developed inter-atomic potentials for the palladium-silver-hydrogen system, we perform large-scale atomistic simulations to examine the defect-mediated mechanisms that govern helium bubble growth. Our simulations show the evolution of a distribution of materialmore » defects, and we compare the material behavior displayed with expectations from experiment and theory. In conclusion, we also present density functional theory calculations to characterize ideal tensile and shear strengths for these materials, which enable the understanding of how and why our developed potentials either meet or confound these expectations.« less

A preliminary study on isotopic evolution of ice by a melting experiment

NASA Astrophysics Data System (ADS)

Ham, J. Y.; Lee, J.; Lee, W. S.; Han, Y.; Hur, S. D.

2016-12-01

Evidences of melted snow at surface were found on some ice cores. Melted layers may generate a significant error when paleo-temperature was retrieved from ice cores using stable water isotopes. To resolve this problem, it is necessary to understand the isotopic changes of ice and its meltwater that is made during the ice and snow melting. Isotopic fractionations between liquid water and snow have been discussed by Taylor et al. (2002) and Lee et al. (2009). The goal of this work is to understand isotopic evolution of ice and its meltwater. Melting experiments in a cold room were designed and conducted with heat source (infrared lamp) to mimic solar radiation. Melting rates were calculated in terms of specific discharge (g/min). To control melting rates, distances between ice surface and heat source were adjusted in various conditions (1 cm, 10 cm and 20 cm). The experiments were conducted by three different melting rates, 1.6 g/min, 3.5 g/min and 5.8 g/min. We used cubic ice that has 3 cm in width, length and height in dimension with 1.5 kg or 2 kg of ice used totally. The total time spent melting the whole ice was 592, 783, and 1180 minutes, respectively. Cold room temperature was range of -1 to 1°C, which removes an effect of air temperature. Meltwater samples were collected and isotopic compositions of oxygen and hydrogen were determined by a cavity ring down spectrometer (Picarro L-1120) installed at the Korea Polar Research Institute. We also analyzed bulk water and bulk ice to make the ice used in the experiments (-8.20 ‰ and -58.73 ‰ for oxygen and hydrogen isotopes, respectively). The isotopic compositions of meltwater increased linearly or to a second degree polynomial. The isotopic variations were larger in the lower melting rates, compared to the higher melting rates (0.65 of lower melting rates vs. 0.35 higher melting rates for oxygen isotope). The slope of linear regression between oxygen and hydrogen ranged 6.2, 7.3 and 6.2, which is less than that of the Global Meteoric Water Line (8) and the sublimation (7.7) suggested by Earman et al. (2006). We believe that isotopic exchange between liquid water and ice plays a crucial role in the variations of isotopes for the ice and its meltwater. We will modify a physically based 1-D model used in the previous studies to better understand the isotopic compositions of ice and its meltwater.

The Interior Angular Momentum of Core Hydrogen Burning Stars from Gravity-mode Oscillations

NASA Astrophysics Data System (ADS)

Aerts, C.; Van Reeth, T.; Tkachenko, A.

2017-09-01

A major uncertainty in the theory of stellar evolution is the angular momentum distribution inside stars and its change during stellar life. We compose a sample of 67 stars in the core hydrogen burning phase with a {log} g value from high-resolution spectroscopy, as well as an asteroseismic estimate of the near-core rotation rate derived from gravity-mode oscillations detected in space photometry. This assembly includes 8 B-type stars and 59 AF-type stars, covering a mass range from 1.4 to 5 M ⊙, I.e., it concerns intermediate-mass stars born with a well-developed convective core. The sample covers projected surface rotation velocities v\\sin I\\in [9,242] km s-1 and core rotation rates up to 26 μHz, which corresponds to 50% of the critical rotation frequency. We find deviations from rigid rotation to be moderate in the single stars of this sample. We place the near-core rotation rates in an evolutionary context and find that the core rotation must drop drastically before or during the short phase between the end of the core hydrogen burning and the onset of core helium burning. We compute the spin parameter, which is the ratio of twice the rotation rate to the mode frequency (also known as the inverse Rossby number), for 1682 gravity modes and find the majority (95%) to occur in the sub-inertial regime. The 10 stars with Rossby modes have spin parameters between 14 and 30, while the gravito-inertial modes cover the range from 1 to 15.

The Role of Hydrogen Sulfide in Evolution and the Evolution of Hydrogen Sulfide in Metabolism and Signaling.

PubMed

Olson, Kenneth R; Straub, Karl D

2016-01-01

The chemical versatility of sulfur and its abundance in the prebiotic Earth as reduced sulfide (H2S) implicate this molecule in the origin of life 3.8 billion years ago and also as a major source of energy in the first seven-eighths of evolution. The tremendous increase in ambient oxygen ∼ 600 million years ago brought an end to H2S as an energy source, and H2S-dependent animals either became extinct, retreated to isolated sulfide niches, or adapted. The first 3 billion years of molecular tinkering were not lost, however, and much of this biochemical armamentarium easily adapted to an oxic environment where it contributes to metabolism and signaling even in humans. This review examines the role of H2S in evolution and the evolution of H2S metabolism and signaling. ©2016 Int. Union Physiol. Sci./Am. Physiol. Soc.

The effect of non-equilibrium metal cooling on the interstellar medium

NASA Astrophysics Data System (ADS)

Capelo, Pedro R.; Bovino, Stefano; Lupi, Alessandro; Schleicher, Dominik R. G.; Grassi, Tommaso

2018-04-01

By using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of 10 simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium; optically thin versus thick approximation), the initial gas metallicity (from 10 to 100 per cent solar), and how molecular hydrogen forms on dust. This is the first work in which metal injection from supernovae, turbulent metal diffusion, and a metal network with non-equilibrium metal cooling are self-consistently included in a galaxy simulation. We find that properly modelling the chemical evolution of several metal species and the corresponding non-equilibrium metal cooling has important effects on the thermodynamics of the gas, the chemical abundances, and the appearance of the galaxy: the gas is typically warmer, has a larger molecular-gas mass fraction, and has a smoother disc. We also conclude that, at relatively high metallicity, the choice of molecular-hydrogen formation rates on dust is not crucial. Moreover, we confirm that a higher initial metallicity produces a colder gas and a larger fraction of molecular gas, with the low-metallicity simulation best matching the observed molecular Kennicutt-Schmidt relation. Finally, our simulations agree quite well with observations that link star formation rate to metal emission lines.

Defects Engineered Monolayer MoS 2 for Improved Hydrogen Evolution Reaction

DOE PAGES

Ye, Gonglan; Gong, Yongji; Lin, Junhao; ...

2016-01-13

MoS 2 is a promising, low-cost material for electrochemical hydrogen production due to its high activity and stability during the reaction. Our work represents an easy method to increase the hydrogen production in electrochemical reaction of MoS 2 via defect engineering, and helps to understand the catalytic properties of MoS 2.

Photosynthesis in Hydrogen-Dominated Atmospheres

PubMed Central

Bains, William; Seager, Sara; Zsom, Andras

2014-01-01

The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life. PMID:25411926

Photosynthesis in hydrogen-dominated atmospheres.

PubMed

Bains, William; Seager, Sara; Zsom, Andras

2014-11-18

The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life.

Hydrogen Isotopes Record the History of the Martian Hydrosphere and Atmosphere

NASA Technical Reports Server (NTRS)

Usui, T.; Simon, J. I.; Jones, J. H.; Kurokawa, H.; Sato, M.; Alexander, C. M. O'D; Wang, J.

2015-01-01

The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. This study presents insights from hydrogen isotopes for the origin and evolution of Martian water reservoirs.

The evolution of rotating very massive stars with LMC composition

NASA Astrophysics Data System (ADS)

Köhler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Gräfener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2015-01-01

Context. With growing evidence for the existence of very massive stars at subsolar metallicity, there is an increased need for corresponding stellar evolution models. Aims: We present a dense model grid with a tailored input chemical composition appropriate for the Large Magellanic Cloud (LMC). Methods: We use a one-dimensional hydrodynamic stellar evolution code, which accounts for rotation, transport of angular momentum by magnetic fields, and stellar wind mass loss to compute our detailed models. We calculate stellar evolution models with initial masses from 70 to 500 M⊙ and with initial surface rotational velocities from 0 to 550 km s-1, covering the core-hydrogen burning phase of evolution. Results: We find our rapid rotators to be strongly influenced by rotationally induced mixing of helium, with quasi-chemically homogeneous evolution occurring for the fastest rotating models. Above 160 M⊙, homogeneous evolution is also established through mass loss, producing pure helium stars at core hydrogen exhaustion independent of the initial rotation rate. Surface nitrogen enrichment is also found for slower rotators, even for stars that lose only a small fraction of their initial mass. For models above ~150 M⊙ at zero age, and for models in the whole considered mass range later on, we find a considerable envelope inflation due to the proximity of these models to their Eddington limit. This leads to a maximum ZAMS surface temperature of ~56 000 K, at ~180 M⊙, and to an evolution of stars in the mass range 50 M⊙...100 M⊙ to the regime of luminous blue variables in the Hertzsprung-Russell diagram with high internal Eddington factors. Inflation also leads to decreasing surface temperatures during the chemically homogeneous evolution of stars above ~180 M⊙. Conclusions: The cool surface temperatures due to the envelope inflation in our models lead to an enhanced mass loss, which prevents stars at LMC metallicity from evolving into pair-instability supernovae. The corresponding spin-down will also prevent very massive LMC stars to produce long-duration gamma-ray bursts, which might, however, originate from lower masses. The dataset of the presented stellar evolution models is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A71Appendices are available in electronic form at http://www.aanda.org

Estimation of the tritium retention in ITER tungsten divertor target using macroscopic rate equations simulations

NASA Astrophysics Data System (ADS)

Hodille, E. A.; Bernard, E.; Markelj, S.; Mougenot, J.; Becquart, C. S.; Bisson, R.; Grisolia, C.

2017-12-01

Based on macroscopic rate equation simulations of tritium migration in an actively cooled tungsten (W) plasma facing component (PFC) using the code MHIMS (migration of hydrogen isotopes in metals), an estimation has been made of the tritium retention in ITER W divertor target during a non-uniform exponential distribution of particle fluxes. Two grades of materials are considered to be exposed to tritium ions: an undamaged W and a damaged W exposed to fast fusion neutrons. Due to strong temperature gradient in the PFC, Soret effect’s impacts on tritium retention is also evaluated for both cases. Thanks to the simulation, the evolutions of the tritium retention and the tritium migration depth are obtained as a function of the implanted flux and the number of cycles. From these evolutions, extrapolation laws are built to estimate the number of cycles needed for tritium to permeate from the implantation zone to the cooled surface and to quantify the corresponding retention of tritium throughout the W PFC.

Macroporous Inverse Opal-like MoxC with Incorporated Mo Vacancies for Significantly Enhanced Hydrogen Evolution.

PubMed

Li, Feng; Zhao, Xianglong; Mahmood, Javeed; Okyay, Mahmut Sait; Jung, Sun-Min; Ahmad, Ishfaq; Kim, Seok-Jin; Han, Gao-Feng; Park, Noejung; Baek, Jong-Beom

2017-07-25

The hydrogen evolution reaction (HER) is one of the most important pathways for producing pure and clean hydrogen. Although platinum (Pt) is the most efficient HER electrocatalyst, its practical application is significantly hindered by high-cost and scarcity. In this work, an Mo x C with incorporated Mo vacancies and macroporous inverse opal-like (IOL) structure (Mo x C-IOL) was synthesized and studied as a low-cost efficient HER electrocatalyst. The macroporous IOL structure was controllably fabricated using a facile-hard template strategy. As a result of the combined benefits of the Mo vacancies and structural advantages, including appropriate hydrogen binding energy, large exposed surface, robust IOL structure and fast mass/charge transport, the synthesized Mo x C-IOL exhibited significantly enhanced HER electrocatalytic performance with good stability, with performance comparable or superior to Pt wire in both acidic and alkaline solutions.

An amorphous FeMoS4 nanorod array toward efficient hydrogen evolution electrocatalysis under neutral conditions.

PubMed

Ren, Xiang; Wang, Weiyi; Ge, Ruixiang; Hao, Shuai; Qu, Fengli; Du, Gu; Asiri, Abdullah M; Wei, Qin; Chen, Liang; Sun, Xuping

2017-08-08

It is highly attractive to develop efficient hydrogen-evolving electrocatalysts under neutral conditions. In this communication, we report an amorphous FeMoS 4 nanorod array on carbon cloth (FeMoS 4 NRA/CC) prepared by hydrothermal treatment of an FeOOH nanorod array on carbon cloth (FeOOH NRA/CC) in (NH 4 ) 2 MoS 4 solution. As a 3D electrode for hydrogen evolution electrocatalysis, this FeMoS 4 NRA/CC demonstrates superior catalytic activity and strong long-term electrochemical durability in 1.0 M phosphate buffered saline (pH: 7). It needs an overpotential of 204 mV to drive a geometrical current density of 10 mA cm -2 , which is 450 mV less than that for FeOOH NRA/CC. Density functional theory calculations suggest that FeMoS 4 has a more favourable hydrogen adsorption free energy than FeOOH.

Evolution behavior of nanohardness after thermal-aging and hydrogen-charging on austenite and strain-induced martensite in pre-strained austenitic stainless steel

NASA Astrophysics Data System (ADS)

Zheng, Yuanyuan; Zhou, Chengshuang; Hong, Yuanjian; Zheng, Jinyang; Zhang, Lin

2018-05-01

Nanoindentation has been used to study the effects of thermal-aging and hydrogen on the mechanical property of the metastable austenitic stainless steel. Thermal-aging at 473 K decreases the nanohardness of austenite, while it increases the nanohardness of strain-induced ɑ‧ martensite. Hydrogen-charging at 473 K increases the nanohardness of austenite, while it decreases the nanohardness of strain-induced ɑ‧ martensite. The opposite effect on austenite and ɑ‧ martensite is first found in the same pre-strained sample. This abnormal evolution behavior of hardness can be attributed to the interaction between dislocation and solute atoms (carbon and hydrogen). Carbon atoms are difficult to move and redistribute in austenite compared with ɑ‧ martensite. Therefore, the difference in the diffusivity of solute atoms between austenite and ɑ‧ martensite may result in the change of hardness.

On Helium-Dominated Stellar Evolution: The Mysterious Role of the O(He)-Type Stars

NASA Technical Reports Server (NTRS)

Reindl, N.; Rauch, T.; Werner, K.; Kruk, J. W.; Todt, H.

2014-01-01

Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

Nanoplasmonic hydrogen sensing

NASA Astrophysics Data System (ADS)

Wadell, Carl; Syrenova, Svetlana; Langhammer, Christoph

2014-09-01

In this review we discuss the evolution of surface plasmon resonance and localized surface plasmon resonance based hydrogen sensors. We put particular focus on how they are used to study metal-hydrogen interactions at the nanoscale, both at the ensemble and the single nanoparticle level. Such efforts are motivated by a fundamental interest in understanding the role of nanosizing on metal hydride formation processes. However, nanoplasmonic hydrogen sensors are not only of academic interest but may also find more practical use as all-optical gas detectors in industrial and medical applications, as well in a future hydrogen economy, where hydrogen is used as a carbon free energy carrier.

Rubisco mutants of Chlamydomonas reinhardtii enhance photosynthetic hydrogen production.

PubMed

Pinto, T S; Malcata, F X; Arrabaça, J D; Silva, J M; Spreitzer, R J; Esquível, M G

2013-06-01

Molecular hydrogen (H2) is an ideal fuel characterized by high enthalpy change and lack of greenhouse effects. This biofuel can be released by microalgae via reduction of protons to molecular hydrogen catalyzed by hydrogenases. The main competitor for the reducing power required by the hydrogenases is the Calvin cycle, and rubisco plays a key role therein. Engineered Chlamydomonas with reduced rubisco levels, activity and stability was used as the basis of this research effort aimed at increasing hydrogen production. Biochemical monitoring in such metabolically engineered mutant cells proceeded in Tris/acetate/phosphate culture medium with S-depletion or repletion, both under hypoxia. Photosynthetic activity, maximum photochemical efficiency, chlorophyll and protein levels were all measured. In addition, expression of rubisco, hydrogenase, D1 and Lhcb were investigated, and H2 was quantified. At the beginning of the experiments, rubisco increased followed by intense degradation. Lhcb proteins exhibited monomeric isoforms during the first 24 to 48 h, and D1 displayed sensitivity under S-depletion. Rubisco mutants exhibited a significant decrease in O2 evolution compared with the control. Although the S-depleted medium was much more suitable than its complete counterpart for H2 production, hydrogen release was observed also in sealed S-repleted cultures of rubisco mutated cells under low-moderate light conditions. In particular, the rubisco mutant Y67A accounted for 10-15-fold higher hydrogen production than the wild type under the same conditions and also displayed divergent metabolic parameters. These results indicate that rubisco is a promising target for improving hydrogen production rates in engineered microalgae.

Enhanced photocatalytic hydrogen evolution from in situ formation of few-layered MoS2/CdS nanosheet-based van der Waals heterostructures.

PubMed

Iqbal, Shahid; Pan, Ziwei; Zhou, Kebin

2017-05-25

Here we report for the first time that the H 2 bubbles generated by photocatalytic water splitting are effective in the layer-by-layer exfoliation of MoS 2 nanocrystals (NCs) into few layers. The as-obtained few layers can be in situ assembled with CdS nanosheets (NSs) into van der Waals heterostructures (vdWHs) of few-layered MoS 2 /CdS NSs which, in turn, are effective in charge separation and transfer, leading to enhanced photocatalytic H 2 production activity. The few-layered MoS 2 /CdS vdWHs exhibited a H 2 evolution rate of 140 mmol g (CdS) -1 h -1 and achieved an apparent quantum yield of 66% at 420 nm.

Fundamental studies of hydrogen attack in carbon-0.5molybdenum steel and weldments applied in petroelum and petrochemical industries

NASA Astrophysics Data System (ADS)

Liu, Peng

High temperature hydrogen attack (HTHA) is a form of surface decarburization, internal decarburization, and/or intergranular cracking in steels exposed to high temperature (>400°F) and high hydrogen pressure. Hydrogen attack is an irreversible process which can cause permanent damage resulting in degradation of mechanical properties and failures such as leakage, bursting, fire, and/or explosion. The continuous progression of hydrogen attack in C-0.5Mo steel and weldments below the C-0.5Mo Nelson Curve has caused a significant concern for the integrity and serviceability of C-0.5Mo steel utilized for pressure vessels and piping in the petroleum refinery and petrochemical industries. A state-of-the-art literature review was implemented to provide a comprehensive overview of the published research efforts on hydrogen attack studies. The evolution of "Nelson Curves" for carbon steel, C-0.5Mo, and Cr-Mo steels was historically reviewed in regard to design applications and limitations. Testing techniques for hydrogen attack assessment were summarized under the categories of hydrogen exposure testing, mechanical evaluation, and dilatometric swelling testing. In accord with the demands of these industries, fundamental studies of hydrogen attack in C-0.5Mo steel and weldments were accomplished in terms of quantitative methodologies for hydrogen damage evaluation; hydrogen damage assessment of service exposed weldments and autoclave exposed materials; effects of carbon and alloying elements, heat treatments, hot and cold working, welding processes and postweld heat treatment (PWHT) on hydrogen attack susceptibility; development of continuous cooling transformation (CCT) diagrams for C-0.5Mo base metals and the coarse grained heat-affected zone (CGHAZ); carbide evaluation for the C-0.5Mo steel after service exposure and heat treatment; methane evolution by the reaction of hydrogen and carbides; hydrogen diffusion and methane pressure through the wall thickness of one-sided hydrogen exposure assembly; hydrogen attack mechanism and hydrogen attack limit modeling.

Winds of change: reionization by starburst galaxies

NASA Astrophysics Data System (ADS)

Sharma, Mahavir; Theuns, Tom; Frenk, Carlos; Bower, Richard G.; Crain, Robert A.; Schaller, Matthieu; Schaye, Joop

2017-06-01

We investigate the properties of the galaxies that reionized the Universe and the history of cosmic reionization using the 'Evolution and Assembly of Galaxies and their Environments' (eagle) cosmological hydrodynamical simulations. We obtain the evolution of the escape fraction of ionizing photons in galaxies assuming that galactic winds create channels through which 20 per cent of photons escape when the local surface density of star formation is greater than 0.1 M⊙ yr-1 kpc-2. Such threshold behaviour for the generation of winds is observed, and the rare local objects that have such high star formation surface densities exhibit high escape fractions of ˜10 per cent. In our model, the luminosity-weighted mean escape fraction increases with redshift as \\bar{f}_esc=0.045 ((1+z)/4)^{1.1} at z > 3, and the galaxy number weighted mean as = 2.2 × 10-3 ((1 + z)/4)4, and becomes constant ≈0.2 at redshift z > 10. The escape fraction evolves as an increasingly large fraction of stars forms above the critical surface density of star formation at earlier times. This evolution of the escape fraction, combined with that of the star formation rate density from eagle, reproduces the inferred evolution of the filling factor of ionized regions during the reionization epoch (6 < z < 8), the evolution of the post-reionization (0 ≤ z < 6) hydrogen photoionization rate and the optical depth due to Thomson scattering of the cosmic microwave background photons measured by the Planck satellite.

Facile Modification of TiO2 with Nickel Sulfide and Sulfate Species for Photoreformation of Cellulose into H2.

PubMed

Hao, Hongchang; Zhang, Ling; Wang, Wenzhong; Zeng, Shuwen

2018-06-19

Photocatalytic cellulose reformation is regarded as a potential and affordable route for sustainable H2 evolution. However, the direct photoreformation still suffers from challenges such as the limited solubility of cellulose and dependence on catalytic activity of noble-metals. Herein, we reported a novel photoreformation of cellulose into H2 over TiO2 which is synchronously modified with nickel sulfide (NixSy) and chemisorbed sulfate species (SO42-) by a one-pot approach. A significant elevation in photocatalytic hydrogen evolution rate is achieved, with the maximal value of 3.02 mmol/g/h during the first three hours, almost 76-fold higher than that of P25 and comparable to Pt-P25. Aided by systematic investigation, it is proposed that nickel sulfide and sulfate modification synergistically contribute to the remarkably raised efficiency of biomass transformation. Specifically, NixSy serves as co-catalyst for photocatalytic H2 production, while SO42- ions are inferred to promote cellulose hydrolyzation and consequent accessibility of biomass to catalysts. Further, the accumulated formate intermediates are found to have a poison effect on catalysts, desorption of which can be controlled by tuning aqueous alkalinity. Overall, our strategy for modifying TiO2 with SO42- and NixSy provides a novel perspective of concurrently accelerating cellulose hydrolyzation process and supplementing hydrogen evolution sites, for efficient photocatalytic reformation of cellulose into H2. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic modeling of sulfur-deprived photosynthesis and hydrogen production in suspensions of Chlamydomonas reinhardtii

PubMed Central

Williams, C R; Bees, MA

2014-01-01

The ability of unicellular green algal species such as Chlamydomonas reinhardtii to produce hydrogen gas via iron-hydrogenase is well known. However, the oxygen-sensitive hydrogenase is closely linked to the photosynthetic chain in such a way that hydrogen and oxygen production need to be separated temporally for sustained photo-production. Under illumination, sulfur-deprivation has been shown to accommodate the production of hydrogen gas by partially-deactivating O2 evolution activity, leading to anaerobiosis in a sealed culture. As these facets are coupled, and the system complex, mathematical approaches potentially are of significant value since they may reveal improved or even optimal schemes for maximizing hydrogen production. Here, a mechanistic model of the system is constructed from consideration of the essential pathways and processes. The role of sulfur in photosynthesis (via PSII) and the storage and catabolism of endogenous substrate, and thus growth and decay of culture density, are explicitly modeled in order to describe and explore the complex interactions that lead to H2 production during sulfur-deprivation. As far as possible, functional forms and parameter values are determined or estimated from experimental data. The model is compared with published experimental studies and, encouragingly, qualitative agreement for trends in hydrogen yield and initiation time are found. It is then employed to probe optimal external sulfur and illumination conditions for hydrogen production, which are found to differ depending on whether a maximum yield of gas or initial production rate is required. The model constitutes a powerful theoretical tool for investigating novel sulfur cycling regimes that may ultimately be used to improve the commercial viability of hydrogen gas production from microorganisms. Biotechnol. Bioeng. 2014;111: 320–335. © 2013 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc. PMID:24026984

Mechanistic modeling of sulfur-deprived photosynthesis and hydrogen production in suspensions of Chlamydomonas reinhardtii.

PubMed

Williams, C R; Bees, M A

2014-02-01

The ability of unicellular green algal species such as Chlamydomonas reinhardtii to produce hydrogen gas via iron-hydrogenase is well known. However, the oxygen-sensitive hydrogenase is closely linked to the photosynthetic chain in such a way that hydrogen and oxygen production need to be separated temporally for sustained photo-production. Under illumination, sulfur-deprivation has been shown to accommodate the production of hydrogen gas by partially-deactivating O2 evolution activity, leading to anaerobiosis in a sealed culture. As these facets are coupled, and the system complex, mathematical approaches potentially are of significant value since they may reveal improved or even optimal schemes for maximizing hydrogen production. Here, a mechanistic model of the system is constructed from consideration of the essential pathways and processes. The role of sulfur in photosynthesis (via PSII) and the storage and catabolism of endogenous substrate, and thus growth and decay of culture density, are explicitly modeled in order to describe and explore the complex interactions that lead to H2 production during sulfur-deprivation. As far as possible, functional forms and parameter values are determined or estimated from experimental data. The model is compared with published experimental studies and, encouragingly, qualitative agreement for trends in hydrogen yield and initiation time are found. It is then employed to probe optimal external sulfur and illumination conditions for hydrogen production, which are found to differ depending on whether a maximum yield of gas or initial production rate is required. The model constitutes a powerful theoretical tool for investigating novel sulfur cycling regimes that may ultimately be used to improve the commercial viability of hydrogen gas production from microorganisms. © 2013 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction

PubMed Central

Wang, Haotian; Lu, Zhiyi; Xu, Shicheng; Kong, Desheng; Cha, Judy J.; Zheng, Guangyuan; Hsu, Po-Chun; Yan, Kai; Bradshaw, David; Prinz, Fritz B.; Cui, Yi

2013-01-01

The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li+ ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity. PMID:24248362

Single cell performance studies on the FE/CR Redox Energy Storage System using mixed reactant solutions at elevated temperature

NASA Technical Reports Server (NTRS)

Gahn, R. F.; Hagedorn, N. H.; Ling, J. S.

1983-01-01

Experimental studies in a 14.5 sq cm single cell system using mixed reactant solutions at 65 C are described. Systems were tested under isothermal conditions, i.e., reactants and the cell were at the same temperature. Charging and discharging performance were evaluated by measuring watt-hour and coulombic efficiencies, voltage-current relationships, hydrogen evolution and membrane resistivity. Watt-hour efficiencies ranged from 86 percent at 43 ma/sq cm to 75 percent at 129 ma/sq cm with corresponding coulombic efficiencies of 92 percent and 97 percent, respectively. Hydrogen evolution was less than 1 percent of the charge coulumbic capacity during charge-discharge cycling. Bismuth amd bismuth-lead catalyzed chromium electrodes maintained reversible performance and low hydrogen evolution under normal and adverse cycling conditions. Reblending of the anode and cathode solutions was successfully demonstrated to compensate for osmotic volume changes. Improved performance was obtained with mixed reactant systems in comparison to the unmixed reactant systems. Previously announced in STAR as N83-25042

Platinum single-atom and cluster catalysis of the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Cheng, Niancai; Stambula, Samantha; Wang, Da; Banis, Mohammad Norouzi; Liu, Jian; Riese, Adam; Xiao, Biwei; Li, Ruying; Sham, Tsun-Kong; Liu, Li-Min; Botton, Gianluigi A.; Sun, Xueliang

2016-11-01

Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance.

Single cell performance studies on the Fe/Cr Redox Energy Storage System using mixed reactant solutions at elevated temperature

NASA Technical Reports Server (NTRS)

Gahn, R. F.; Hagedorn, N. H.; Ling, J. S.

1983-01-01

Experimental studies in a 14.5 sq cm single cell system using mixed reactant solutions at 65 C are described. Systems were tested under isothermal conditions i.e., reactants and the cell were at the same temperature. Charging and discharging performance were evaluted by measuring watt-hour and coulombic efficiencies, voltage-current relationships, hydrogen evolution and membrane resistivity. Watt-hour efficiencies ranged from 86% at 43 ma/sq cm to 75% at 129 ma/sq cm with corresponding coulombic efficiencies of 92% and 97%, respectively. Hydrogen evolution was less than 1% of the charge coulombic capacity during charge-discharge cycling. Bismuth and bismuth-lead catalyzed chromium electrodes maintained reversible performance and low hydrogen evolution under normal and adverse cycling conditions. Reblending of the anode and cathode solutions was successfully demonstrated to compensate for osmotic volume changes. Improved performance was obtained with mixed reactant systems in comparison to the unmixed reactant systems.

Platinum single-atom and cluster catalysis of the hydrogen evolution reaction

PubMed Central

Cheng, Niancai; Stambula, Samantha; Wang, Da; Banis, Mohammad Norouzi; Liu, Jian; Riese, Adam; Xiao, Biwei; Li, Ruying; Sham, Tsun-Kong; Liu, Li-Min; Botton, Gianluigi A.; Sun, Xueliang

2016-01-01

Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance. PMID:27901129

Molecular metal-Nx centres in porous carbon for electrocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Liang, Hai-Wei; Brüller, Sebastian; Dong, Renhao; Zhang, Jian; Feng, Xinliang; Müllen, Klaus

2015-08-01

Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt-nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt-N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s-1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols.

Hydrogen embrittlement in nickel-hydrogen cells

NASA Technical Reports Server (NTRS)

Gross, Sidney

1989-01-01

It was long known that many strong metals can become weakened and brittle as the result of the accumulation of hydrogen within the metal. When the metal is stretched, it does not show normal ductile properties, but fractures prematurely. This problem can occur as the result of a hydrogen evolution reaction such as corrosion or electroplating, or due to hydrogen in the environment at the metal surface. High strength alloys such as steels are especially susceptible to hydrogen embrittlement. Nickel-hydrogen cells commonly use Inconel 718 alloy for the pressure container, and this also is susceptible to hydrogen embrittlement. Metals differ in their susceptibility to embrittlement. Hydrogen embrittlement in nickel-hydrogen cells is analyzed and the reasons why it may or may not occur are discussed. Although Inconel 718 can display hydrogen embrittlement, experience has not identified any problem with nickel-hydrogen cells. No hydrogen embrittlement problem is expected with the 718 alloy pressure container used in nickel-hydrogen cells.

Ternary Pt/SnO(x)/TiO2 photocatalysts for hydrogen production: consequence of Pt sites for synergy of dual co-catalysts.

PubMed

Gu, Quan; Long, Jinlin; Zhuang, Huaqiang; Zhang, Chaoqiang; Zhou, Yangen; Wang, Xuxu

2014-06-28

A variety of ternary nanoheterostructures composed of Pt nanoparticles (NPs), SnOx species, and anatase TiO2 are designed elaborately to explore the effect of interfacial electron transfer on photocatalytic H2 evolution from a biofuel-water solution. Among numerous factors controlling the H2 evolution, the significance of Pt sites for the H2 evolution is highlighted by tuning the loading procedure of Pt NPs and SnOx species over TiO2. A synergistic enhancement of H2 evolution can be achieved over the Pt/SnOx/TiO2 heterostructures formed by anchoring Pt NPs at atomically-isolated Sn-oxo sites, whereas the Pt/TiO2/SnOx counterparts prepared by grafting single-site Sn-oxo species on Pt/TiO2 show a marked decrease in the rate of H2 evolution. The characterization results clearly reveal that the synergy of Pt NPs and SnOx species originates from the vectorial electron transfer of TiO2 → SnOx → Pt occurring on the former, while the latter results from the competitive electron transfer from TiO2 to SnOx and to Pt NPs.

Optimizing the deposition of hydrogen evolution sites on suspended semiconductor particles using on-line photocatalytic reforming of aqueous methanol solutions.

PubMed

Busser, G Wilma; Mei, Bastian; Muhler, Martin

2012-11-01

The deposition of hydrogen evolution sites on photocatalysts is a crucial step in the multistep process of synthesizing a catalyst that is active for overall photocatalytic water splitting. An alternative approach to conventional photodeposition was developed, applying the photocatalytic reforming of aqueous methanol solutions to deposit metal particles on semiconductor materials such as Ga₂O₃ and (Ga₀.₆ Zn₀.₄)(N₀.₆O₀.₄). The method allows optimizing the loading of the co-catalysts based on the stepwise addition of their precursors and the continuous online monitoring of the evolved hydrogen. Moreover, a synergetic effect between different co-catalysts can be directly established. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoelectron emission yield experiments on evolution of sub-gap states in amorphous In-Ga-Zn-O thin films with post deposition hydrogen treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, Kazushi, E-mail: hayashi.kazushi@kobelco.com; Hino, Aya; Tao, Hiroaki

Total photoyield emission spectroscopy (TPYS) was applied to study the evolution of sub-gap states in hydrogen-treated amorphous In-Ga-Zn-O (a-IGZO) thin films. The a-IGZO thin films were subjected to hydrogen radicals and subsequently annealed in ultra-high vacuum (UHV) conditions. A clear onset of the electron emission was observed at around 4.3 eV from the hydrogen-treated a-IGZO thin films. After successive UHV annealing at 300 °C, the onset in the TPYS spectra was shifted to 4.15 eV, and the photoelectron emission from the sub-gap states was decreased as the annealing temperature was increased. In conjunction with the results of thermal desorption spectrometer, it was deducedmore » that the hydrogen atoms incorporated in the a-IGZO thin films induced metastable sub-gap states at around 4.3 eV from vacuum level just after the hydrogenation. It was also suggested that the defect configuration was changed due to the higher temperature UHV annealing, and that the hydrogen atoms desorbed with the involvement of Zn atoms. These experiments produced direct evidence to show the formation of sub-gap states as a result of hydrogen incorporation into the a-IGZO thin films.« less

In situ/Operando studies of electrocatalysts using hard X-ray spectroscopy

DOE PAGES

Lassalle-Kaiser, Benedikt; Gul, Sheraz; Kern, Jan; ...

2017-05-02

This review focuses on the use of X-ray absorption and emission spectroscopy techniques using hard X-rays to study electrocatalysts under in situ/operando conditions. The importance and the versatility of methods in the study of electrodes in contact with the electrolytes are described, when they are being cycled through the catalytic potentials during the progress of the oxygen-evolution, oxygen reduction and hydrogen evolution reactions. The catalytic oxygen evolution reaction is illustrated with examples using three oxides, Co, Ni and Mn, and two sulfides, Mo and Co. These are used as examples for the hydrogen evolution reaction. A bimetallic, bifunctional oxygen evolvingmore » and oxygen reducing Ni/Mn oxide is also presented. The various advantages and constraints in the use of these techniques and the future outlook are discussed.« less

Towards Forming a Primordial Protostar in a Cosmological AMR Simulation

NASA Astrophysics Data System (ADS)

Turk, Matthew J.; Abel, Tom; O'Shea, Brian W.

2008-03-01

Modeling the formation of the first stars in the universe is a well-posed problem and ideally suited for computational investigation.We have conducted high-resolution numerical studies of the formation of primordial stars. Beginning with primordial initial conditions appropriate for a ΛCDM model, we used the Eulerian adaptive mesh refinement code (Enzo) to achieve unprecedented numerical resolution, resolving cosmological scales as well as sub-stellar scales simultaneously. Building on the work of Abel, Bryan and Norman (2002), we followed the evolution of the first collapsing cloud until molecular hydrogen is optically thick to cooling radiation. In addition, the calculations account for the process of collision-induced emission (CIE) and add approximations to the optical depth in both molecular hydrogen roto-vibrational cooling and CIE. Also considered are the effects of chemical heating/cooling from the formation/destruction of molecular hydrogen. We present the results of these simulations, showing the formation of a 10 Jupiter-mass protostellar core bounded by a strongly aspherical accretion shock. Accretion rates are found to be as high as one solar mass per year.

Decrease in hydrogen sulfide content during the final stage of beer fermentation due to involvement of yeast and not carbon dioxide gas purging.

PubMed

Oka, Kaneo; Hayashi, Teruhiko; Matsumoto, Nobuya; Yanase, Hideshi

2008-09-01

We observed a rapid decrease in hydrogen sulfide content in the final stage of beer fermentation that was attributed to yeast and not to the purging of carbon dioxide (CO(2)) gas. The well known immature off-flavor in beer due to hydrogen sulfide (H(2)S) behavior during beer fermentation was closely investigated. The H(2)S decrease occurred during the final stage of fermentation when the CO(2)-evolution rate was extremely small and there was a decrease in the availability of fermentable sugars, suggesting that the exhaustion of fermentable sugars triggered the decrease in H(2)S. An H(2)S-balance analysis suggested that the H(2)S decrease might have been caused due to sulfide uptake by yeast. Further investigation showed that the time necessary for H(2)S to decrease below the sensory threshold was related to the number of suspended yeast cells. This supported the hypothesis that yeast cells contributed to the rapid decrease in H(2)S during the final stage of beer fermentation.

Facile synthesis of polypyrrole functionalized nickel foam with catalytic activity comparable to Pt for the poly-generation of hydrogen and electricity

NASA Astrophysics Data System (ADS)

Tang, Tiantian; Li, Kan; Shen, Zhemin; Sun, Tonghua; Wang, Yalin; Jia, Jinping

2016-01-01

Polypyrrole functionalized nickel foam is facilely prepared through the potentiostatic electrodeposition. The PPy-functionalized Ni foam functions as a hydrogen-evolution cathode in a rotating disk photocatalytic fuel cell, in which hydrogen energy and electric power are generated by consuming organic wastes. The PPy-functionalized Ni foam cathode exhibits stable catalytic activities after thirteen continuous runs. Compared with net or plate structure, the Ni foam with a unique three-dimensional reticulate structure is conducive to the electrodeposition of PPy. Compared with Pt-group electrode, PPy-coated Ni foam shows a satisfactory catalytic performance for the H2 evolution. The combination of PPy and Ni forms a synergistic effect for the rapid trapping and removal of proton from solution and the catalytic reduction of proton to hydrogen. The PPy-functionalized Ni foam could be applied in photocatalytic and photoelectrochemical generation of H2. In all, we report a low cost, high efficient and earth abundant PPy-functionalized Ni foam with a satisfactory catalytic activities comparable to Pt for the practical application of poly-generation of hydrogen and electricity.

Evolution of dislocation loops in austenitic stainless steels implanted with high concentration of hydrogen

NASA Astrophysics Data System (ADS)

Zheng, Zhongcheng; Gao, Ning; Tang, Rui; Yu, Yanxia; Zhang, Weiping; Shen, Zhenyu; Long, Yunxiang; Wei, Yaxia; Guo, Liping

2017-10-01

It has been found that under certain conditions, hydrogen retention would be strongly enhanced in irradiated austenitic stainless steels. To investigate the effect of the retained hydrogen on the defect microstructure, AL-6XN stainless steel specimens were irradiated with low energy (100 keV) H2+ so that high concentration of hydrogen was injected into the specimens while considerable displacement damage dose (up to 7 dpa) was also achieved. Irradiation induced dislocation loops and voids were characterised by transmission electron microscopy. For specimens irradiated to 7 dpa at 290 °C, dislocation loops with high number density were found and the void swelling was observed. At 380 °C, most of dislocation loops were unfaulted and tangled at 7 dpa, and the void swellings were observed at 5 dpa and above. Combining the data from low dose in previous work to high dose, four stages of dislocation loops evolution with hydrogen retention were suggested. Finally, molecular dynamics simulation was made to elucidate the division of large dislocation loops under irradiation.

An electrochemical study of the corrosion behavior of primer coated 2219-T87 aluminum

NASA Technical Reports Server (NTRS)

Danford, M. D.; Higgins, R. H.

1985-01-01

The corrosion behavior for 2219-T87 aluminum coated with various primers, including those used for the external tank and solid rocket boosters of the Space Shuttle Transportation System, were investigated using electrochemical techniques. Corrosion potential time, polarization resistance time, electrical resistance time, and corrosion rate time measurements were all investigated. It was found that electrical resistance time and corrosion rate time measurement were most useful for studying the corrosion behavior of painted aluminum. Electrical resistance time determination give useful information concerning the porosity of paint films, while corrosion rate time curves give important information concerning overall corrosion rates and corrosion mechanisms. In general, the corrosion rate time curves all exhibited at least one peak during the 30 day test period, which was attributed, according to the proposed mechanisms, to the onset of the hydrogen evolution reaction and the beginning of destruction of the protective properties of the paint film.

Massive star evolution and SN 1987A

NASA Technical Reports Server (NTRS)

Arnett, David

1991-01-01

The evolution of massive stars through hydrogen and helium burning is addressed. A set of stellar evolutionary sequences for mass/solar mass of 15, 20, and 25, and metallicity of 0.002, 0.005, 0.007, 0.010, and 0.20 are presented; semiconvection is restricted to operating slower than the local thermal time scale. Using these sequences, simple models of the massive star content of the LMC are found to agree moderately well with the new observational data of Fitzpatrick and Garmany (1990). LMC supergiants were detected only in their postmain-sequence phases, so that 5-10 times more massive stars are there but not identified as such. It is argued that SN 1987A exhibits the normal evolution of a single star of about 20 solar mases having LMC abundances. Despite the variety of envelope behavior, the structure of the core at collapse is rather similar for the stars of a given mass. Variations due to different rates of mass loss are likely to be larger than those due to composition.

Oxygen and hydrogen evolution reaction on oriented single crystals of ruthenium dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, L I; Pollak, F H; Canivez, Y

1979-01-01

A novel design for water electrolysis using a solid polymer electrolyte is being developed by General Electric. Ruthenium is one of the best electrocatalysts for the oxygen evolution reaction. There are problems connected with the significant loss in electrocatalytic activity with time. This performance degradation is presumably due to the gradual formation of an RuO/sub 2/ film. We have performed electrochemical measurements on (100), (110) and (111) oriented single crystals of RuO/sub 2/ in order to elucidate the mechanism of the electrocatalytic process. Large single crystals were grown by the vapor transport method. Our investigation has revealed several interesting differencesmore » for the various orientations. This study indicates that RuO/sub 3/ may be an important intermediate species prior to oxygen evolution and that the formation of the RuO/sub 3/ is the rate limiting process. Similar results were previously obtained for IrO/sub 2/.« less

Elevated atmospheric escape of atomic hydrogen from Mars induced by high-altitude water

NASA Astrophysics Data System (ADS)

Chaffin, M. S.; Deighan, J.; Schneider, N. M.; Stewart, A. I. F.

2017-01-01

Atmospheric loss has controlled the history of Martian habitability, removing most of the planet’s initial water through atomic hydrogen and oxygen escape from the upper atmosphere to space. In standard models, H and O escape in a stoichiometric 2:1 ratio because H reaches the upper atmosphere via long-lived molecular hydrogen, whose abundance is regulated by a photochemical feedback sensitive to atmospheric oxygen content. The relatively constant escape rates these models predict are inconsistent with known H escape variations of more than an order of magnitude on seasonal timescales, variation that requires escaping H to have a source other than H2. The best candidate source is high-altitude water, detected by the Mars Express spacecraft in seasonally variable concentrations. Here we use a one-dimensional time-dependent photochemical model to show that the introduction of high-altitude water can produce a large increase in the H escape rate on a timescale of weeks, quantitatively linking these observations. This H escape pathway produces prompt H loss that is not immediately balanced by O escape, influencing the oxidation state of the atmosphere for millions of years. Martian atmospheric water loss may be dominated by escape via this pathway, which may therefore potentially control the planet’s atmospheric chemistry. Our findings highlight the influence that seasonal atmospheric variability can have on planetary evolution.

One-carbon substrate-based biohydrogen production: microbes, mechanism, and productivity.

PubMed

Rittmann, Simon K-M R; Lee, Hyun Sook; Lim, Jae Kyu; Kim, Tae Wan; Lee, Jung-Hyun; Kang, Sung Gyun

2015-01-01

Among four basic mechanisms for biological hydrogen (H2) production, dark fermentation has been considered to show the highest hydrogen evolution rate (HER). H2 production from one-carbon (C1) compounds such as formate and carbon monoxide (CO) is promising because formate is an efficient H2 carrier, and the utilization of CO-containing syngas or industrial waste gas may render the industrial biohydrogen production process cost-effective. A variety of microbes with the formate hydrogen lyase (FHL) system have been identified from phylogenetically diverse groups of archaea and bacteria, and numerous efforts have been undertaken to improve the HER for formate through strain optimization and bioprocess development. CO-dependent H2 production has been investigated to enhance the H2 productivity of various carboxydotrophs via an increase in CO gas-liquid mass transfer rates and the construction of genetically modified strains. Hydrogenogenic CO-conversion has been applied to syngas and by-product gas of the steel-mill process, and this low-cost feedstock has shown to be promising in the production of biomass and H2. Here, we focus on recent advances in the isolation of novel phylogenetic groups utilizing formate or CO, the remarkable genetic engineering that enhances H2 productivity, and the practical implementation of H2 production from C1 substrates. Copyright © 2014 Elsevier Inc. All rights reserved.

A pyruvate formate lyase-deficient Chlamydomonas reinhardtii strain provides evidence for a link between fermentation and hydrogen production in green algae.

PubMed

Philipps, Gabriele; Krawietz, Danuta; Hemschemeier, Anja; Happe, Thomas

2011-04-01

The green alga Chlamydomonas reinhardtii has a complex anaerobic metabolism characterized by a plastidic hydrogenase (HYD1) coupled to photosynthesis and a bacterial-type fermentation system in which pyruvate formate lyase (PFL1) is the central fermentative enzyme. To identify mutant strains with altered hydrogen metabolism, a C. reinhardtii nuclear transformant library was screened. Mutant strain 48F5 showed lower light-dependent hydrogen (H₂) evolution rates and reduced in vitro hydrogenase activity, and fermentative H₂ production in the dark was enhanced. The transformant has a single integration of the paromomycin resistance cassette within the PFL1 gene, and is unable to synthesize PFL1 protein. 48F5 secretes no formate, but produces more ethanol, D-lactate and CO₂ than the wild type. Moreover, HYD1 transcript and HYD1 protein levels were lower in the pfl1 mutant strain. Complementation of strain 48F5 with an intact copy of the PFL1 gene restored formate excretion and hydrogenase activity to the wild type level. This analysis shows that the PFL1 pathway has a significant impact on hydrogen metabolism in C. reinhardtii. © 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd.

Two-temperature equilibration in warm dense hydrogen measured with x-ray scattering from the LCLS

NASA Astrophysics Data System (ADS)

Fletcher, Luke; High Energy Density Sciences Collaboration

2017-10-01

Understanding the properties of warm dense hydrogen plasmas is critical for modeling stellar and planetary interiors, as well as for inertial confinement fusion (ICF) experiments. Of central importance are the electron-ion collision and equilibration times that determine the microscopic properties in a high energy density state. Spectrally and angularly resolved x-ray scattering measurements from fs-laser heated hydrogen have resolved the picosecond evolution and energy relaxation from a two-temperature plasma towards thermodynamic equilibrium in the warm dense matter regime. The interaction of rapidly heated cryogenic hydrogen irradiated by a 400 nm, 5x1017 W/cm2 , 70 fs-laser is visualized with ultra-bright 5.5 kev x-ray pulses from the Linac Coherent Light (LCLS) source in 1 Hz repetition rate pump-probe setting. We demonstrate that the energy relaxation is faster than many classical binary collision theories that use ad hoc cutoff parameters used in the Landau-Spitzer determination of the Coulomb logarithm. This work was supported by the DOE Office of Science, Fusion Energy Science under contract No. SF00515 and supported under FWP 100182 and DOE Office of Basic Energy Sciences, Materials Sciences and Engineering Division, contract DE-AC02-76SF00515.

Atomic hydrogen and diatomic titanium-monoxide molecular spectroscopy in laser-induced plasma

NASA Astrophysics Data System (ADS)

Parigger, Christian G.; Woods, Alexander C.

2017-03-01

This article gives a brief review of experimental studies of hydrogen Balmer series emission spectra. Ongoing research aims to evaluate early plasma evolution following optical breakdown in laboratory air. Of interest is as well laser ablation of metallic titanium and characterization of plasma evolution. Emission of titanium monoxide is discussed together with modeling of diatomic spectra to infer temperature. The behavior of titanium particles in plasma draws research interests ranging from the modeling of stellar atmospheres to the enhancement of thin film production via pulsed laser deposition.

Improving the photocatalytic hydrogen production of Ag/g-C3N4 nanocomposites by dye-sensitization under visible light irradiation

NASA Astrophysics Data System (ADS)

Qin, Jiayi; Huo, Jingpei; Zhang, Piyong; Zeng, Jian; Wang, Tingting; Zeng, Heping

2016-01-01

Ag nanoparticles were deposited on the surface of g-C3N4 by a chemical reduction method to increase visible-light absorption via the localized surface plasmon resonance effect, resulting in the reduced recombination of photo-generated electron-holes and enhanced photocatalytic activity. The Ag/g-C3N4 composite with a Ag loading of 3 wt% has the optimum photoactivity that is almost 3.6 and 3.4 times higher than pure g-C3N4 and the same photocatalysis system which has been reported, respectively. Fluorescein was introduced as a photosensitizer and H2 evolution soared to 2014.20 μmol g-1 h-1 and the rate is even about 4.8 times higher than that of the 3 wt% Ag/g-C3N4 composite. The chemical structure, composites, morphologies and optical properties of the obtained products are well-characterized by XRD, FTIR, TEM, EDS, XPS and UV-Vis DRS. Meanwhile, the photocatalyst exhibits high stability and reusability.Ag nanoparticles were deposited on the surface of g-C3N4 by a chemical reduction method to increase visible-light absorption via the localized surface plasmon resonance effect, resulting in the reduced recombination of photo-generated electron-holes and enhanced photocatalytic activity. The Ag/g-C3N4 composite with a Ag loading of 3 wt% has the optimum photoactivity that is almost 3.6 and 3.4 times higher than pure g-C3N4 and the same photocatalysis system which has been reported, respectively. Fluorescein was introduced as a photosensitizer and H2 evolution soared to 2014.20 μmol g-1 h-1 and the rate is even about 4.8 times higher than that of the 3 wt% Ag/g-C3N4 composite. The chemical structure, composites, morphologies and optical properties of the obtained products are well-characterized by XRD, FTIR, TEM, EDS, XPS and UV-Vis DRS. Meanwhile, the photocatalyst exhibits high stability and reusability. Electronic supplementary information (ESI) available: TEM images, TGA curves, PXRD and FTIR spectra, the recycling experiment of 3% Ag/g-C3N4, the specific process for H2 production, the diagram for the rate of hydrogen generation vs. the amount of fluorescein, the figure for the photocatalytic hydrogen production testing system, tables of contrast experiments for photocatalytic hydrogen generation and elemental composition of the CN in all the samples. See DOI: 10.1039/c5nr06346a

THE EFFECT OF THE {sup 14}N(p, {gamma}){sup 15}O REACTION ON THE BLUE LOOPS IN INTERMEDIATE-MASS STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halabi, Ghina M.; El Eid, Mounib F.; Champagne, Arthur

2012-12-10

We present stellar evolutionary sequences of stars in the mass range 5-12 M{sub Sun }, having solar-like initial composition. The stellar models are obtained using updated input physics, including recent rates of thermonuclear reactions. We investigate the effects of a modification of the {sup 14}N(p, {gamma}){sup 15}O reaction rate, as suggested by recent evaluations, on the formation and extension of the blue loops encountered during the evolution of the stars in the above mass range. We find that a reduced {sup 14}N(p, {gamma}){sup 15}O rate, as described in the text, has a striking impact on the physical conditions of burningmore » and mixing during shell hydrogen burning when the blue loops are formed. In particular, we find that the efficiency of shell hydrogen burning is crucial for the formation of an extended blue loop. We show that a significantly reduced {sup 14}N(p, {gamma}){sup 15}O rate affects severely the extension of the blue loops and the time spent by the star in the blue part of the Hertzsprung-Russell diagram in the mass range 5-7 M{sub Sun} if the treatment of convection is based on the Schwarzschild criterion only. In this case, envelope overshooting helps to restore well-extended blue loops as supported by the observations of the Cepheid stars. If core overshooting is included during the core hydrogen and core helium burning phases, the loop formation and its properties depend on how this overshooting is treated for a given stellar mass range, as well as on its efficiency.« less

Study on optical emission analysis of AC air water discharges under He, Ar and N2 environments

NASA Astrophysics Data System (ADS)

Park, J. Y.; Kostyuk, P. V.; Han, S. B.; Kim, J. S.; Vu, C. N.; Lee, H. W.

2006-09-01

In this paper, hybrid air-water discharges were used to develop an optimal condition for providing a high level of water decomposition for hydrogen evolution. Electrical and optical phenomena accompanying the discharges were investigated along with feeding gases, flow rates and point-to-plane electrode gap distance. The experiments were primarily focused on the optical emission of the near UV range, providing a sufficient energy threshold for water dissociation and excitation. The OH(A 2Σ+ → X 2Π, Δν = 0) band optical emission intensity indicated the presence of plasma chemical reactions involving hydrogen formation. Despite the fact that energy input was high, the OH(A-X) optical emission was found to be negligible at the zero gap distance between the tip of the metal rod and water surface. In the gas atmosphere saturated with water vapour the OH(A-X) intensity was relatively high compared with the liquid and transient phases although the optical emission strongly depended on the flow rate and type of feeding gas. The gas phase was found to be more favourable because of less energy consumption in the cases of He and Ar carrier gases, and quenching mechanisms of oxygen in the N2 carrier gas atmosphere, preventing hydrogen from recombining with oxygen. In the gas phase the discharge was at a steady state, in contrast to the other phases, in which bubbles interrupted propagation of the plasma channel. Optical emission intensity of OH(A-X) band increased according to the flow rate or residence time of the He feeding gas. Nevertheless, a reciprocal tendency was acquired for N2 and Ar carrier gases. The peak value of OH(A-X) band optical emission intensity was observed near the water surface; however in the cases of Ar and N2 with a 0.5 SLM flow rate, it was shifted below the water surface. Rotational temperature was estimated to be in the range of 900-3600 K, according to the carrier gas and flow rate, which is sufficient for hydrogen production.

Spectral Quasi-Equilibrium Manifold for Chemical Kinetics.

PubMed

Kooshkbaghi, Mahdi; Frouzakis, Christos E; Boulouchos, Konstantinos; Karlin, Iliya V

2016-05-26

The Spectral Quasi-Equilibrium Manifold (SQEM) method is a model reduction technique for chemical kinetics based on entropy maximization under constraints built by the slowest eigenvectors at equilibrium. The method is revisited here and discussed and validated through the Michaelis-Menten kinetic scheme, and the quality of the reduction is related to the temporal evolution and the gap between eigenvalues. SQEM is then applied to detailed reaction mechanisms for the homogeneous combustion of hydrogen, syngas, and methane mixtures with air in adiabatic constant pressure reactors. The system states computed using SQEM are compared with those obtained by direct integration of the detailed mechanism, and good agreement between the reduced and the detailed descriptions is demonstrated. The SQEM reduced model of hydrogen/air combustion is also compared with another similar technique, the Rate-Controlled Constrained-Equilibrium (RCCE). For the same number of representative variables, SQEM is found to provide a more accurate description.

Feasibility of hydrogen density estimation from tomographic sensing of Lyman alpha emission

NASA Astrophysics Data System (ADS)

Waldrop, L.; Kamalabadi, F.; Ren, D.

2015-12-01

In this work, we describe the scientific motivation, basic principles, and feasibility of a new approach to the estimation of neutral hydrogen (H) density in the terrestrial exosphere based on the 3-D tomographic sensing of optically thin H emission at 121.6 nm (Lyman alpha). In contrast to existing techniques, Lyman alpha tomography allows for model-independent reconstruction of the underlying H distribution in support of investigations regarding the origin and time-dependent evolution of exospheric structure. We quantitatively describe the trade-off space between the measurement sampling rate, viewing geometry, and the spatial and temporal resolution of the reconstruction that is supported by the data. We demonstrate that this approach is feasible from either earth-orbiting satellites such as the stereoscopic NASA TWINS mission or from a CubeSat platform along a trans-exosphere trajectory such as that enabled by the upcoming Exploration Mission 1 launch.

Solar Luminosity on the Main Sequence, Standard Model and Variations

NASA Astrophysics Data System (ADS)

Ayukov, S. V.; Baturin, V. A.; Gorshkov, A. B.; Oreshina, A. V.

2017-05-01

Our Sun became Main Sequence star 4.6 Gyr ago according Standard Solar Model. At that time solar luminosity was 30% lower than current value. This conclusion is based on assumption that Sun is fueled by thermonuclear reactions. If Earth's albedo and emissivity in infrared are unchanged during Earth history, 2.3 Gyr ago oceans had to be frozen. This contradicts to geological data: there was liquid water 3.6-3.8 Gyr ago on Earth. This problem is known as Faint Young Sun Paradox. We analyze luminosity change in standard solar evolution theory. Increase of mean molecular weight in the central part of the Sun due to conversion of hydrogen to helium leads to gradual increase of luminosity with time on the Main Sequence. We also consider several exotic models: fully mixed Sun; drastic change of pp reaction rate; Sun consisting of hydrogen and helium only. Solar neutrino observations however exclude most non-standard solar models.

Enhanced activity of CaFeMg layered double hydroxides-supported gold nanodendrites for the electrochemical evolution of oxygen and hydrogen in alkaline media

NASA Astrophysics Data System (ADS)

Havakeshian, Elaheh; Salavati, Hossein; Taei, Masoumeh; Hasheminasab, Fatemeh; Seddighi, Mohadeseh

2018-02-01

In this study, Au was electrodeposited on a support of CaFeMg layered double hydroxide and then, its catalytic activity was investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Field emission scanning electron microscopy images showed that a uniform porous film of aggregated nano-particles of the LDH has been decorated with Au nanodendrite-like structures (AuNDs@LDH). The results obtained from polarization curves, Tafel plots and electrochemical impedance spectroscopy showed that the AuNDs@LDH exhibits lower overpotential, higher current density, faster kinetics and enhanced stability for both of the OER and HER, in comparison with the single AuNPs and LDH catalysts.

An Historical Summary and Prospects for the Future of Spacecraft Batteries

NASA Technical Reports Server (NTRS)

Halpert, Gerald; Surampudi, S.

1998-01-01

Subjects covered in this report include a historical evolution of batteries in space, evolution and status of nickel-cadmium batteries and nickel-hydrogen batteries, present applications, future applications and advanced batteries for future missions.

Evaluating Hydrogen Evolution and Oxidation in Alkaline Media to Establish Baselines

DOE PAGES

Alia, Shaun M.; Pivovar, Bryan S.

2018-04-28

This paper fills a significant gap in the literature for alkaline hydrogen evolution (HER) and oxidation (HOR) baseline performance, while reviewing the different variables that influence observed properties. Although high-performing HER-HOR catalysts in acidic electrolytes are too active to measure kinetic in rotating disk electrode (RDE) half-cells, under alkaline conditions RDE kinetics evaluations are relevant and half-cell performances are comparable to hydrogen pump data. This paper focuses on best practices to ensure that half-cell tests don't unnecessarily lower platinum group metal (PGM) performance or improve non-PGM performance. Specific aspects examined include experiments on PGMs minimizing the impact of impurities (electrolyte,more » cell material) and experiments on non-PGMs minimizing the impact from test protocols (counter electrode).« less

Probing Transition-Metal Silicides as PGM-Free Catalysts for Hydrogen Oxidation and Evolution in Acidic Medium

PubMed Central

Mittermeier, Thomas; Madkikar, Pankaj; Wang, Xiaodong; Gasteiger, Hubert A.; Piana, Michele

2017-01-01

In this experimental study, we investigate various transition-metal silicides as platinum-group-metal-(PGM)-free electrocatalysts for the hydrogen oxidation reaction (HOR), and for the hydrogen evolution reaction (HER) in acidic environment for the first time. Using cyclic voltammetry in 0.1 M HClO4, we first demonstrate that the tested materials exhibit sufficient stability against dissolution in the relevant potential window. Further, we determine the HOR and HER activities for Mo, W, Ta, Ni and Mo-Ni silicides in rotating disk electrode experiments. In conclusion, for the HOR only Ni2Si shows limited activity, and the HER activity of the investigated silicides is considerably lower compared to other PGM-free HER catalysts reported in the literature. PMID:28773022

Enhanced hydrogen evolution reaction on hybrids of cobalt phosphide and molybdenum phosphide

NASA Astrophysics Data System (ADS)

Fang, Si-Ling; Chou, Tsu-Chin; Samireddi, Satyanarayana; Chen, Kuei-Hsien; Chen, Li-Chyong; Chen, Wei-Fu

2017-03-01

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention owing to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer-Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP2 crystal phase is formed which enhances the electrochemical activity.

Silicon oxidation in fluoride solutions

NASA Technical Reports Server (NTRS)

Sancier, K. M.; Kapur, V.

1980-01-01

Silicon is produced in a NaF, Na2SiF6, and Na matrix when SiF4 is reduced by metallic sodium. Hydrogen is evolved during acid leaching to separate the silicon from the accompanying reaction products, NaF and Na2SiF6. The hydrogen evolution reaction was studied under conditions simulating leaching conditions by making suspensions of the dry silicon powder in aqueous fluoride solutions. The mechanism for the hydrogen evolution is discussed in terms of spontaneous oxidation of silicon resulting from the cooperative effects of (1) elemental sodium in the silicon that reacts with water to remove a protective silica layer, leaving clean reactive silicon, and (2) fluoride in solution that complexes with the oxidized silicon in solution and retards formation of a protective hydrous oxide gel.

Evaluating Hydrogen Evolution and Oxidation in Alkaline Media to Establish Baselines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alia, Shaun M.; Pivovar, Bryan S.

This paper fills a significant gap in the literature for alkaline hydrogen evolution (HER) and oxidation (HOR) baseline performance, while reviewing the different variables that influence observed properties. Although high-performing HER-HOR catalysts in acidic electrolytes are too active to measure kinetic in rotating disk electrode (RDE) half-cells, under alkaline conditions RDE kinetics evaluations are relevant and half-cell performances are comparable to hydrogen pump data. This paper focuses on best practices to ensure that half-cell tests don't unnecessarily lower platinum group metal (PGM) performance or improve non-PGM performance. Specific aspects examined include experiments on PGMs minimizing the impact of impurities (electrolyte,more » cell material) and experiments on non-PGMs minimizing the impact from test protocols (counter electrode).« less

Polydopamine mediated assembly of hydroxyapatite nanoparticles and bone morphogenetic protein-2 on magnesium alloys for enhanced corrosion resistance and bone regeneration.

PubMed

Jiang, Yanan; Wang, Bi; Jia, Zhanrong; Lu, Xiong; Fang, Liming; Wang, Kefeng; Ren, Fuzeng

2017-10-01

Magnesium alloys have the great potential to be used as orthopedic implants due to their biodegradability and mechanical resemblance to human cortical bone. However, the rapid degradation in physiological environment with the evolution of hydrogen gas release hinders their clinical applications. In this study, we developed a novel functional and biocompatible coating strategy through polydopamine mediated assembly of hydroxyapatite nanoparticles and growth factor, bone morphogenetic protein-2 (BMP-2), onto the surface of AZ31 Mg alloys. Such functional coating has strong bonding with the substrate and can increase surface hydrophilicity of magnesium alloys. In vitro electrochemical corrosion and hydrogen evolution tests demonstrate that the coating can significantly enhance the corrosion resistance and therefore slow down the degradation of AZ31 Mg alloys. In vitro cell culture reveals that immobilization of HA nanoparticles and BMP-2 can obviously promote cell adhesion and proliferation. Furthermore, in vivo implantation tests indicate that with the synergistic effects of HA nanoparticles and BMP-2, the coating does not cause obvious inflammatory response and can significantly reduce the biodegradation rate of the magnesium alloys and induce the new bone formation adjacent to the implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2750-2761, 2017. © 2017 Wiley Periodicals, Inc.

Enhanced performance of Zn(II)-doped lead-acid batteries with electrochemical active carbon in negative mass

NASA Astrophysics Data System (ADS)

Xiang, Jiayuan; Hu, Chen; Chen, Liying; Zhang, Dong; Ding, Ping; Chen, Dong; Liu, Hao; Chen, Jian; Wu, Xianzhang; Lai, Xiaokang

2016-10-01

The effect and mechanism of Zn(II) on improving the performances of lead-acid cell with electrochemical active carbon (EAC) in negative mass is investigated. The hydrogen evolution of the cell is significantly reduced due to the deposition of Zn on carbon surface and the increased porosity of negative mass. Zn(II) additives can also improve the low-temperature and high-rate capacities of the cell with EAC in negative mass, which ascribes to the formation of Zn on lead and carbon surface that constructs a conductive bridge among the active mass. Under the co-contribution of EAC and Zn(II), the partial-state-of-charge cycle life is greatly prolonged. EAC optimizes the NAM structure and porosity to enhance the charge acceptance and retard the lead sulfate accumulation. Zn(II) additive reduces the hydrogen evolution during charge process and improves the electric conductivity of the negative electrode. The cell with 0.6 wt% EAC and 0.006 wt% ZnO in negative mass exhibits 90% reversible capacity of the initial capacity after 2100 cycles. In contrast, the cell with 0.6 wt% EAC exhibits 84% reversible capacity after 2100 cycles and the control cell with no EAC and Zn(II) exhibits less than 80% reversible capacity after 1350 cycles.

Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering

NASA Astrophysics Data System (ADS)

Li, Jie; Zhan, Guangming; Yu, Ying; Zhang, Lizhi

2016-05-01

Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi-S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h-1 g-1. Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE.

Loading Cd0.5Zn0.5S Quantum Dots onto Onion-Like Carbon Nanoparticles to Boost Photocatalytic Hydrogen Generation.

PubMed

Zhou, Xiaolong; Wang, Xina; Feng, Xi; Zhang, Kun; Peng, Xiaoniu; Wang, Hanbin; Liu, Chunlei; Han, Yibo; Wang, Hao; Li, Quan

2017-07-12

Carbon dots (C dots, size < 10 nm) have been conventionally decorated onto semiconductor matrixes for photocatalytic H 2 evolution, but the efficiency is largely limited by the low loading ratio of the C dots on the photocatalyst. Here, we propose an inverse structure of Cd 0.5 Zn 0.5 S quantum dots (QDs) loaded onto the onionlike carbon (OLC) matrix for noble metal-free photocatalytic H 2 evolution. Cd 0.5 Zn 0.5 S QDs (6.9 nm) were uniformly distributed on an OLC (30 nm) matrix with both upconverted and downconverted photoluminescence property. Such an inverse structure allows the full optimization of the QD/OLC interfaces for effective energy transfer and charge separation, both of which contribute to efficient H 2 generation. An optimized H 2 generation rate of 2018 μmol/h/g (under the irradiation of visible light) and 58.6 μmol/h/g (under the irradiation of 550-900 nm light) was achieved in the Cd 0.5 Zn 0.5 S/OLC composite samples. The present work shows that using the OLC matrix in such a reverse construction is a promising strategy for noble metal-free solar hydrogen production.

Excellent photocatalytic hydrogen production over CdS nanorods via using noble metal-free copper molybdenum sulfide (Cu2MoS4) nanosheets as co-catalysts

NASA Astrophysics Data System (ADS)

Hong, Sangyeob; Kumar, D. Praveen; Reddy, D. Amaranatha; Choi, Jiha; Kim, Tae Kyu

2017-02-01

Charge carrier recombination and durability issues are major problems in photocatalytic hydrogen (H2) evolution processes. Thus, there is a very important necessitate to extend an efficient photocatalyst to control charge-carrier dynamics in the photocatalytic system. We have developed copper molybdenum sulfide (Cu2MoS4) nanosheets as co-catalysts with CdS nanorods for controlling charge carriers without recombination for use in photocatalytic H2 evolution under simulated solar light irradiation. Effective control and utilization of charge carriers are possible by loading Cu2MoS4 nanosheets onto the CdS nanorods. The loading compensates for the restrictions of CdS, and stimulated synergistic effects, such as efficient photoexcited charge separation, lead to an improvement in photostability because of the layered structure of the Cu2MoS4nanosheets. These layered Cu2MoS4 nanosheets have emerged as novel and active replacements for precious noble metal co-catalysts in photocatalytic H2 production by water splitting. We have obtained superior H2 production rates by using Cu2MoS4 loaded CdS nanorods. The physicochemical properties of the composites are analyzed by diverse characterization techniques.

Constructing 2D layered MoS2 nanosheets-modified Z-scheme TiO2/WO3 nanofibers ternary nanojunction with enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

Zhao, Jiangtao; Zhang, Peng; Fan, Jiajie; Hu, Junhua; Shao, Guosheng

2018-02-01

Advanced materials for photoelectrochemical H2 production are important to the field of renewable energy. Despite great efforts have been made, the present challenge in materials science is to explore highly active photocatalysts for splitting of water at low cost. In this work, we report a new composite material consisting of 2D layered MoS2 nanosheets grown on the presence of TiO2/WO3 nanofibers (TW) as a high-performance photocatalyst for H2 evolution. This composite material was prepared by a two-step simple process of electrospinning and hydrothermal. We found that the as-prepared TiO2/WO3@MoS2 (TWM) hybrid exhibited superior photocatalytic activity in the hydrogen evolution reaction (HER) even without the noble metal-cocatalyst. Importantly, the TiO2/WO3@MoS2 heterostructure with 60 wt% of MoS2 exhibits the highest hydrogen production rate. This great improvement is attributed to the positive synergetic effect between the WO3 and MoS2 components in this hybrid cocatalyst, which serve as hole collector and electron collector, respectively. Moreover, the effective charge separation was directly proved by ultraviolet photoelectron spectroscopy, electrochemical impedance spectroscopy, and photocurrent analysis.

Autoignition of hydrogen in shear flows

NASA Astrophysics Data System (ADS)

Kalbhor, Abhijit; Chaudhuri, Swetaprovo; Chitilappilly, Lazar

2018-05-01

In this paper, we compare the autoignition characteristics of laminar, nitrogen-diluted hydrogen jets in two different oxidizer flow configurations: (a) co-flowing heated air and (b) wake of heated air, using two-dimensional numerical simulations coupled with detailed chemical kinetics. In both cases, autoignition is observed to initiate at locations with low scalar dissipation rates and high HO2 depletion rates. It is found that the induction stage prior to autoignition is primarily dominated by chemical kinetics and diffusion while the improved scalar mixing imparted by the large-scale flow structures controls the ignition progress in later stages. We further investigate the ignition transience and its connection with mixing by varying the initial wake conditions and fuel jet to oxidizer velocity ratios. These studies reveal that the autoignition delay times are independent of initial wake flow conditions. However, with increased jet velocity ratios, the later stages of ignition are accelerated, mainly due to enhanced mixing facilitated by the higher scalar dissipation rates. Furthermore, the sensitivity studies for the jet in wake configuration show a significant reduction in ignition delay even for about 0.14% (by volume) hydrogen dilution in the oxidizer. In addition, the detailed autoignition chemistry and the relative roles of certain radical species in the initiation of the autoignition process in these non-premixed jets are investigated by tracking the evolution of important chain reactions using a Lagrangian particle tracking approach. The reaction H2 + O2 ↔ HO2 + H is recognized to be the dominant chain initiation reaction that provides H radicals essential for the progress of subsequent elementary reactions during the pre-ignition stage.

Evolution of a steam atmosphere during earth's accretion

NASA Astrophysics Data System (ADS)

Zahnle, K. J.; Kasting, J. F.; Pollack, J. B.

1988-04-01

The evolution of an impact-generated steam atmosphere around an accreting earth is presently modeled under the assumption of Safronov (1978) accretion, in a scheme that encompasses the degassing of planetesimals on impact, thermal blanketing by the steam atmosphere, surface-to-interior water exchange, the shock heating and convective cooling of the earth's interior, and hydrogen escape due both to solar EUV-powered planetary wind and impact erosion. The model yields four distinct classes of impact-generated atmospheres: the first, on which emphasis is placed, has as its salient feature a molten surface that is maintained by the opacity of a massive water vapor atmosphere; the second occurs when the EUV-limited escape exceeds the impact degassing rate, while the third is dominated by impact erosion and the fourth is characterized by an atmosphere more massive than any thus far encountered.

Evolution of a steam atmosphere during earth's accretion

NASA Technical Reports Server (NTRS)

Zahnle, Kevin J.; Kasting, James F.; Pollack, James B.

1988-01-01

The evolution of an impact-generated steam atmosphere around an accreting earth is presently modeled under the assumption of Safronov (1978) accretion, in a scheme that encompasses the degassing of planetesimals on impact, thermal blanketing by the steam atmosphere, surface-to-interior water exchange, the shock heating and convective cooling of the earth's interior, and hydrogen escape due both to solar EUV-powered planetary wind and impact erosion. The model yields four distinct classes of impact-generated atmospheres: the first, on which emphasis is placed, has as its salient feature a molten surface that is maintained by the opacity of a massive water vapor atmosphere; the second occurs when the EUV-limited escape exceeds the impact degassing rate, while the third is dominated by impact erosion and the fourth is characterized by an atmosphere more massive than any thus far encountered.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Narayan, Sri R. (Inventor); Hays, Charles C. (Inventor)

2015-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Hays, Charles C. (Inventor); Narayan, Sri R. (Inventor)

2013-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

The Star Formation Rate Efficiency of Neutral Atomic-Dominated Hydrogen Gas in the Ooutskirts of Star-Forming Galaxies From z approx. 1 to z approx. 3

NASA Technical Reports Server (NTRS)

Rafelski, Marc; Gardner, Jonathan P.; Fumagalli, Michele; Neeleman, Marcel; Teplitz, Harry I.; Grogin, Norman; Koekemoer, Anton M.; Scarlata, Claudia

2016-01-01

Current observational evidence suggests that the star formation rate (SFR)efficiency of neutral atomic hydrogen gas measured in damped Ly(alpha) systems (DLAs) at z approx. 3 is more than 10 times lower than predicted by the Kennicutt-Schmidt (KS)relation. To understand the origin of this deficit, and to investigate possible evolution with redshift and galaxy properties, we measure the SFR efficiency of atomic gas at z approx. 1, z approx. 2, and z approx. 3 around star-forming galaxies. We use new robust photometric redshifts in the Hubble Ultra Deep Field to create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies' outskirts. We find that the SFR efficiency of H I gas at z > 1 is approx. 1%-3% of that predicted by the KS relation. Contrary to simulations and models that predict a reduced SFR efficiency with decreasing metallicity and thus with increasing redshift, we find no significant evolution in the SFR efficiency with redshift. Our analysis instead suggests that the reduced SFR efficiency is driven by the low molecular content of this atomic-dominated phase, with metallicity playing a secondary effect in regulating the conversion between atomic and molecular gas. This interpretation is supported by the similarity between the observed SFR efficiency and that observed in local atomic-dominated gas, such as in the outskirts of local spiral galaxies and local dwarf galaxies.

Evidence From Hydrogen Isotopes in Meteorites for a Martian Permafrost

NASA Technical Reports Server (NTRS)

Usui, T.; Alexander, C. M. O'D.; Wang, J.; Simon, J. I.; Jones, J. H.

2014-01-01

Fluvial landforms on Mars suggest that it was once warm enough to maintain persistent liquid water on its surface. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. We have investigated the evolution of surface water/ ice and its interaction with the atmosphere by measurements of hydrogen isotope ratios (D/H: deuterium/ hydrogen) of martian meteorites. Hydrogen is a major component of water (H2O) and its isotopes fractionate significantly during hydrological cycling between the atmosphere, surface waters, ground ice, and polar cap ice. Based on in situ ion microprobe analyses of three geochemically different shergottites, we reported that there is a water/ice reservoir with an intermediate D/H ratio (delta D = 1,000?2500 %) on Mars. Here we present the possibility that this water/ice reservoir represents a ground-ice/permafrost that has existed relatively intact over geologic time.

Accreting white dwarf models for type 1 supernovae. 1: Presupernova evolution and triggering mechanisms

NASA Technical Reports Server (NTRS)

Nomoto, K.

1981-01-01

As a plausible explosion model for a Type I supernova, the evolution of carbon-oxygen white dwarfs accreting helium in binary systems was investigated from the onset of accretion up to the point at which a thermonuclear explosion occurs. The relationship between the conditions in the binary system and the triggering mechanism for the supernova explosion is discussed, especially for the cases with relatively slow accretion rate. It is found that the growth of a helium zone on the carbon-oxygen core leads to a supernova explosion which is triggered either by the off-center helium detonation for slow and intermediate accretion rates or by the carbon deflagration for slow and rapid accretion rates. Both helium detonation and carbon deflagration are possible for the case of slow accretion, since in this case the initial mass of the white dwarf is an important parameter for determining the mode of ignition. Finally, various modes of building up the helium zone on the white dwarf, namely, direct transfer of helium from the companion star and the various types and strength of the hydrogen shell flashes are discussed in some detail.

A Self-consistent Model for a Full Cycle of Recurrent Novae—Wind Mass-loss Rate and X-Ray Luminosity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kato, Mariko; Saio, Hideyuki; Hachisu, Izumi, E-mail: mariko.kato@hc.st.keio.ac.jp

2017-04-01

An unexpectedly slow evolution in the pre-optical-maximum phase was suggested in the very short recurrence period of nova M31N 2008-12a. To obtain reasonable nova light curves we have improved our calculation method by consistently combining optically thick wind solutions of hydrogen-rich envelopes with white dwarf (WD) structures calculated by a Henyey-type evolution code. The wind mass-loss rate is properly determined with high accuracy. We have calculated light curve models for 1.2 M {sub ⊙} and 1.38 M {sub ⊙} WDs with mass accretion rates corresponding to recurrence periods of 10 yr and 1 yr, respectively. The outburst lasts 590/29 days,more » in which the pre-optical-maximum phase is 82/16 days, for 1.2/1.38 M {sub ⊙}, respectively. Optically thick winds start at the end of the X-ray flash and cease at the beginning of the supersoft X-ray phase. We also present supersoft X-ray light curves including a prompt X-ray flash and later supersoft X-ray phase.« less

Self-assembled monolayers of n-alkanethiols suppress hydrogen evolution and increase the efficiency of rechargeable iron battery electrodes.

PubMed

Malkhandi, Souradip; Yang, Bo; Manohar, Aswin K; Prakash, G K Surya; Narayanan, S R

2013-01-09

Iron-based rechargeable batteries, because of their low cost, eco-friendliness, and durability, are extremely attractive for large-scale energy storage. A principal challenge in the deployment of these batteries is their relatively low electrical efficiency. The low efficiency is due to parasitic hydrogen evolution that occurs on the iron electrode during charging and idle stand. In this study, we demonstrate for the first time that linear alkanethiols are very effective in suppressing hydrogen evolution on alkaline iron battery electrodes. The alkanethiols form self-assembled monolayers on the iron electrodes. The degree of suppression of hydrogen evolution by the alkanethiols was found to be greater than 90%, and the effectiveness of the alkanethiol increased with the chain length. Through steady-state potentiostatic polarization studies and impedance measurements on high-purity iron disk electrodes, we show that the self-assembly of alkanethiols suppressed the parasitic reaction by reducing the interfacial area available for the electrochemical reaction. We have modeled the effect of chain length of the alkanethiol on the surface coverage, charge-transfer resistance, and double-layer capacitance of the interface using a simple model that also yields a value for the interchain interaction energy. We have verified the improvement in charging efficiency resulting from the use of the alkanethiols in practical rechargeable iron battery electrodes. The results of battery tests indicate that alkanethiols yield among the highest faradaic efficiencies reported for the rechargeable iron electrodes, enabling the prospect of a large-scale energy storage solution based on low-cost iron-based rechargeable batteries.

Protein hydrogen exchange: Testing current models

PubMed Central

Skinner, John J; Lim, Woon K; Bédard, Sabrina; Black, Ben E; Englander, S Walter

2012-01-01

To investigate the determinants of protein hydrogen exchange (HX), HX rates of most of the backbone amide hydrogens of Staphylococcal nuclease were measured by NMR methods. A modified analysis was used to improve accuracy for the faster hydrogens. HX rates of both near surface and well buried hydrogens are spread over more than 7 orders of magnitude. These results were compared with previous hypotheses for HX rate determination. Contrary to a common assumption, proximity to the surface of the native protein does not usually produce fast exchange. The slow HX rates for unprotected surface hydrogens are not well explained by local electrostatic field. The ability of buried hydrogens to exchange is not explained by a solvent penetration mechanism. The exchange rates of structurally protected hydrogens are not well predicted by algorithms that depend only on local interactions or only on transient unfolding reactions. These observations identify some of the present difficulties of HX rate prediction and suggest the need for returning to a detailed hydrogen by hydrogen analysis to examine the bases of structure-rate relationships, as described in the companion paper (Skinner et al., Protein Sci 2012;21:996–1005). PMID:22544567

Analysis conditions of an industrial Al-Mg-Si alloy by conventional and 3D atom probes.

PubMed

Danoix, F; Miller, M K; Bigot, A

2001-10-01

Industrial 6016 Al-Mg-Si(Cu) alloys are presently regarded as attractive candidates for heat treatable sheet materials. Their mechanical properties can be adjusted for a given application by age hardening of the alloys. The resulting microstructural evolution takes place at the nanometer scale, making the atom probe a well suited instrument to study it. Accuracy of atom probe analysis of these aluminium alloys is a key point for the understanding of the fine scale microstructural evolution. It is known to be strongly dependent on the analysis conditions (such as specimen temperature and pulse fraction) which have been widely studied for ID atom probes. The development of the 3D instruments, as well as the increase of the evaporation pulse repetition rate have led to different analysis conditions, in particular evaporation and detection rates. The influence of various experimental parameters on the accuracy of atom probe data, in particular with regard to hydride formation sensitivity, has been reinvestigated. It is shown that hydrogen contamination is strongly dependent on the electric field at the specimen surface, and that high evaporation rates are beneficial. Conversely, detection rate must be limited to smaller than 0.02 atoms/pulse in order to prevent drastic pile-up effect.

Does the Chemothermal Instability Have Any Role in the Fragmentation of Primordial Gas

NASA Astrophysics Data System (ADS)

Dutta, Jayanta

2015-10-01

The collapse of the primordial gas in the density regime ˜108-1010 cm-3 is controlled by the three-body H2 formation process, in which the gas can cool faster than free-fall time—a condition proposed as the chemothermal instability. We investigate how the heating and cooling rates are affected during the rapid transformation of atomic to molecular hydrogen. With a detailed study of the heating and cooling balance in a 3D simulation of Pop III collapse, we follow the chemical and thermal evolution of the primordial gas in two dark matter minihalos. The inclusion of sink particles in modified Gadget-2 smoothed particle hydrodynamics code allows us to investigate the long-term evolution of the disk that fragments into several clumps. We find that the sum of all the cooling rates is less than the total heating rate after including the contribution from the compressional heating (pdV). The increasing cooling rate during the rapid increase of the molecular fraction is offset by the unavoidable heating due to gas contraction. We conclude that fragmentation occurs because H2 cooling, the heating due to H2 formation and compressional heating together set a density and temperature structure in the disk that favors fragmentation, not the chemothermal instability.

The effects of temperature and aeration on the corrosion of A508III low alloy steel in boric acid solutions at 25-95 °C

NASA Astrophysics Data System (ADS)

Xiao, Qian; Lu, Zhanpeng; Chen, Junjie; Yao, Meiyi; Chen, Zhen; Ejaz, Ahsan

2016-11-01

The effects of temperature, solution composition and dissolved oxygen on the corrosion rate and electrochemical behavior of an A508III low alloy steel in boric acid solution with lithium hydroxide at 25-95 °C are investigated. In aerated solutions, increasing the boric acid concentration increases the corrosion rate and the anodic current density. The corrosion rate in deaerated solutions increases with increasing temperature. A corrosion rate peak value is found at approximately 75 °C in aerated solutions. Increasing temperature increases the oxygen diffusion coefficient, decreases the dissolved oxygen concentration, accelerates the hydrogen evolution reaction, and accelerates both the active dissolution and the film forming reactions. Increasing dissolved oxygen concentration does not significantly affect the corrosion rate at 50 and 60 °C, increases the corrosion rate at 70 and 80 °C, and decreases the corrosion rate at 87.5 and 95 °C in a high concentration boric acid solution with lithium hydroxide.

Amorphous nickel-cobalt complexes hybridized with 1T-phase molybdenum disulfide via hydrazine-induced phase transformation for water splitting

NASA Astrophysics Data System (ADS)

Li, Haoyi; Chen, Shuangming; Jia, Xiaofan; Xu, Biao; Lin, Haifeng; Yang, Haozhou; Song, Li; Wang, Xun

2017-05-01

Highly active and robust eletcrocatalysts based on earth-abundant elements are desirable to generate hydrogen and oxygen as fuels from water sustainably to replace noble metal materials. Here we report an approach to synthesize porous hybrid nanostructures combining amorphous nickel-cobalt complexes with 1T phase molybdenum disulfide (MoS2) via hydrazine-induced phase transformation for water splitting. The hybrid nanostructures exhibit overpotentials of 70 mV for hydrogen evolution and 235 mV for oxygen evolution at 10 mA cm-2 with long-term stability, which have superior kinetics for hydrogen- and oxygen-evolution with Tafel slope values of 38.1 and 45.7 mV dec-1. Moreover, we achieve 10 mA cm-2 at a low voltage of 1.44 V for 48 h in basic media for overall water splitting. We propose that such performance is likely due to the complete transformation of MoS2 to metallic 1T phase, high porosity and stabilization effect of nickel-cobalt complexes on 1T phase MoS2.

Molecular metal–Nx centres in porous carbon for electrocatalytic hydrogen evolution

PubMed Central

Liang, Hai-Wei; Brüller, Sebastian; Dong, Renhao; Zhang, Jian; Feng, Xinliang; Müllen, Klaus

2015-01-01

Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt–nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s−1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols. PMID:26250525

Nuclear fusion and carbon flashes on neutron stars

NASA Technical Reports Server (NTRS)

Taam, R. E.; Picklum, R. E.

1978-01-01

This paper reports on detailed calculations of the thermal evolution of the carbon-burning shells in the envelopes of accreting neutron stars for mass-accretion rates of 1 hundred-billionth to 2 billionths of a solar mass per yr and neutron-star masses of 0.56 and 1.41 solar masses. The work of Hansen and Van Horn (1975) is extended to higher densities, and a more detailed treatment of nuclear processing in the hydrogen- and helium-burning regions is included. Results of steady-state calculations are presented, and results of time-dependent computations are examined for accretion rates of 3 ten-billionths and 1 billionth of solar mass per yr. It is found that two evolutionary sequences lead to carbon flashes and that the carbon abundance at the base of the helium shell is a strong function of accretion rate. Upper limits are placed on the accretion rates at which carbon flashes will be important.

Ir4+-Doped NiFe LDH to expedite hydrogen evolution kinetics as a Pt-like electrocatalyst for water splitting.

PubMed

Chen, Qian-Qian; Hou, Chun-Chao; Wang, Chuan-Jun; Yang, Xiao; Shi, Rui; Chen, Yong

2018-06-06

NiFe-layered double hydroxide (NiFe LDH) is a state-of-the-art oxygen evolution reaction (OER) electrocatalyst, yet it suffers from rather poor catalytic activity for the hydrogen evolution reaction (HER) due to its extremely sluggish water dissociation kinetics, severely restricting its application in overall water splitting. Herein, we report a novel strategy to expedite the HER kinetics of NiFe LDH by an Ir4+-doping strategy to accelerate the water dissociation process (Volmer step), and thus this catalyst exhibits superior and robust catalytic activity for finally oriented overall water splitting in 1 M KOH requiring only a low initial voltage of 1.41 V delivering at 20 mA cm-2 for more than 50 h.

Atomic Scale Analysis of the Enhanced Electro- and Photo-Catalytic Activity in High-Index Faceted Porous NiO Nanowires

NASA Astrophysics Data System (ADS)

Shen, Meng; Han, Ali; Wang, Xijun; Ro, Yun Goo; Kargar, Alireza; Lin, Yue; Guo, Hua; Du, Pingwu; Jiang, Jun; Zhang, Jingyu; Dayeh, Shadi A.; Xiang, Bin

2015-02-01

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.

Structural evolution and electronic properties of n-type doped hydrogenated amorphous silicon thin films

NASA Astrophysics Data System (ADS)

He, Jian; Li, Wei; Xu, Rui; Qi, Kang-Cheng; Jiang, Ya-Dong

2011-12-01

The relationship between structure and electronic properties of n-type doped hydrogenated amorphous silicon (a-Si:H) thin films was investigated. Samples with different features were prepared by plasma enhanced chemical vapor deposition (PECVD) at various substrate temperatures. Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to evaluate the structural evolution, meanwhile, electronic-spin resonance (ESR) and optical measurement were applied to explore the electronic properties of P-doped a-Si:H thin films. Results reveal that the changes in materials structure affect directly the electronic properties and the doping efficiency of dopant.

Chemical and phase evolution of amorphous molybdenum sulfide catalysts for electrochemical hydrogen production [Chemical and phase evolution of amorphous molybdenum sulfide catalysts for electrochemical hydrogen production directly observed using environmental transmission electron microscopy

DOE PAGES

Lee, Sang Chul; Benck, Jesse D.; Tsai, Charlie; ...

2015-12-01

Amorphous MoS x is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS 3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS 2 in composition and chemical state. However, structural changes in the Mo Sx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoS x catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmentalmore » TEM. For the first time, we directly observe the formation of crystalline domains in the MoS x catalyst after both activation procedures as well as spatially localized changes in the chemical state detected via electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoS x catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS 2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. Finally, these results have important implications for the application of this highly active electrocatalyst for sustainable H 2 generation.« less

Self-Supported Ni(P, O)x·MoOx Nanowire Array on Nickel Foam as an Efficient and Durable Electrocatalyst for Alkaline Hydrogen Evolution.

PubMed

Hua, Wei; Liu, Huanyan; Wang, Jian-Gan; Wei, Bingqing

2017-12-06

Earth-abundant and low-cost catalysts with excellent electrocatalytic hydrogen evolution reaction (HER) activity in alkaline solution play an important role in the sustainable production of hydrogen energy. In this work, a catalyst of Ni(P, O) x ·MoO x nanowire array on nickel foam has been prepared via a facile route for efficient alkaline HER. Benefiting from the collaborative advantages of Ni(P, O) x and amorphous MoO x , as well as three-dimensional porous conductive nickel scaffold, the hybrid electrocatalyst shows high catalytic activity in 1 M KOH aqueous solution, including a small overpotential of 59 mV at 10 mA cm -2 , a low Tafel slope of 54 mV dec -1 , and excellent cycling stability.

Self-Supported Ni(P, O)x·MoOx Nanowire Array on Nickel Foam as an Efficient and Durable Electrocatalyst for Alkaline Hydrogen Evolution

PubMed Central

Hua, Wei; Liu, Huanyan

2017-01-01

Earth-abundant and low-cost catalysts with excellent electrocatalytic hydrogen evolution reaction (HER) activity in alkaline solution play an important role in the sustainable production of hydrogen energy. In this work, a catalyst of Ni(P, O)x·MoOx nanowire array on nickel foam has been prepared via a facile route for efficient alkaline HER. Benefiting from the collaborative advantages of Ni(P, O)x and amorphous MoOx, as well as three-dimensional porous conductive nickel scaffold, the hybrid electrocatalyst shows high catalytic activity in 1 M KOH aqueous solution, including a small overpotential of 59 mV at 10 mA cm−2, a low Tafel slope of 54 mV dec-1, and excellent cycling stability. PMID:29210991

Investigating Catalyst–Support Interactions To Improve the Hydrogen Evolution Reaction Activity of Thiomolybdate [Mo 3 S 13 ] 2– Nanoclusters

DOE PAGES

Hellstern, Thomas R.; Kibsgaard, Jakob; Tsai, Charlie; ...

2017-09-22

Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonpreciousmetal catalysts. The thiomolybdate [Mo 3S 13] 2- nanocluster catalyst contains a structural motif that resembles the active site of MoS 2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo 3S 13] 2- catalysts through catalyst-support interactions. We synthesize [Mo 3S 13] 2- on gold, silver, glassy carbon, and copper supports to demonstrate the ability tomore » tune the hydrogen binding energy of [Mo 3S 13] 2- using catalyst-support electronic interactions and optimize HER activity.« less

Investigating Catalyst–Support Interactions To Improve the Hydrogen Evolution Reaction Activity of Thiomolybdate [Mo 3 S 13 ] 2– Nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hellstern, Thomas R.; Kibsgaard, Jakob; Tsai, Charlie

Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonpreciousmetal catalysts. The thiomolybdate [Mo 3S 13] 2- nanocluster catalyst contains a structural motif that resembles the active site of MoS 2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo 3S 13] 2- catalysts through catalyst-support interactions. We synthesize [Mo 3S 13] 2- on gold, silver, glassy carbon, and copper supports to demonstrate the ability tomore » tune the hydrogen binding energy of [Mo 3S 13] 2- using catalyst-support electronic interactions and optimize HER activity.« less

Structure-Activity Relationships for Pt-Free Metal Phosphide Hydrogen Evolution Electrocatalysts.

PubMed

Owens-Baird, Bryan; Kolen'ko, Yury V; Kovnir, Kirill

2018-05-23

In the field of renewable energy, the splitting of water into hydrogen and oxygen fuel gases using water electrolysis is a prominent topic. Traditionally, these catalytic processes have been performed by platinum-group metal catalysts, which are effective at promoting water electrolysis but expensive and rare. The search for an inexpensive and Earth-abundant catalyst has led to the development of 3d-transition-metal phosphides for the hydrogen evolution reaction. These catalysts have shown excellent activity and stability. In this review, we discuss the electronic and crystal structures of bulk and surface of selected Fe, Co, and Ni phosphides, and their relationships to the experimental catalytic activity. The various synthetic protocols towards the state-of-the-art transition metal phosphide electrocatalysts are also discussed. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-discharge performance of Ni-MH battery by using electrodes with hydrophilic/hydrophobic surface

NASA Astrophysics Data System (ADS)

Li, Xiaofeng; Wang, Xiaojie; Dong, Huichao; Xia, Tongchi; Wang, Lizhen; Song, Yanhua

2013-12-01

The polytetrafluoroethylene (PTFE) and carboxymethyl cellulose (CMC) film is separately coated on the surface of the metal hydride (MH) and Ni(OH)2 electrodes to obtain the electrodes with hydrophobic or hydrophilic surface. The effects of the surface treatment on the oxygen and hydrogen evolution from the electrodes are studied by using cyclic voltammetry tests. Although the positive and negative active materials of the Ni-MH batteries show a lower self-decomposition rate after the CMC treatment, the self-discharge rate of the batteries show little change. On the contrary, the self-discharge rate of the batteries decreases from 35.9% to 27.1% by using the PTFE-treated Ni(OH)2 electrodes, which might be related to the suppression of the reaction between NiOOH and H2 by the hydrophobic film.

Ceria-supported ruthenium nanoparticles as highly active and long-lived catalysts in hydrogen generation from the hydrolysis of ammonia borane.

PubMed

Akbayrak, Serdar; Tonbul, Yalçın; Özkar, Saim

2016-07-05

Ruthenium(0) nanoparticles supported on ceria (Ru(0)/CeO2) were in situ generated from the reduction of ruthenium(iii) ions impregnated on ceria during the hydrolysis of ammonia borane. Ru(0)/CeO2 was isolated from the reaction solution by centrifugation and characterized by ICP-OES, BET, XRD, TEM, SEM-EDS and XPS techniques. All the results reveal that ruthenium(0) nanoparticles were successfully supported on ceria and the resulting Ru(0)/CeO2 is a highly active, reusable and long-lived catalyst for hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value of 361 min(-1). The reusability tests reveal that Ru(0)/CeO2 is still active in the subsequent runs of hydrolysis of ammonia borane preserving 60% of the initial catalytic activity even after the fifth run. Ru(0)/CeO2 provides a superior catalytic lifetime (TTO = 135 100) in hydrogen generation from the hydrolysis of ammonia borane at 25.0 ± 0.1 °C before deactivation. The work reported here includes the formation kinetics of ruthenium(0) nanoparticles. The rate constants for the slow nucleation and autocatalytic surface growth of ruthenium(0) nanoparticles were obtained using hydrogen evolution as a reporter reaction. An evaluation of rate constants at various temperatures enabled the estimation of activation energies for both the reactions, Ea = 60 ± 7 kJ mol(-1) for the nucleation and Ea = 47 ± 2 kJ mol(-1) for the autocatalytic surface growth of ruthenium(0) nanoparticles, as well as the activation energy of Ea = 51 ± 2 kJ mol(-1) for the catalytic hydrolysis of ammonia borane.

Hydrothermal growth of two dimensional hierarchical MoS2 nanospheres on one dimensional CdS nanorods for high performance and stable visible photocatalytic H2 evolution

NASA Astrophysics Data System (ADS)

Chava, Rama Krishna; Do, Jeong Yeon; Kang, Misook

2018-03-01

The visible photocatalytic H2 production from water splitting considered as a clean and renewable energy source could solve the problem of greenhouse gas emission from fossil fuels. Despite tremendous efforts, the development of cost effective, highly efficient and more stable visible photocatalysts for splitting of water remains a great challenge. Here, we report the heteronanostructures consisting of hierarchical MoS2 nanospheres grown on 1D CdS nanorods referred to as CdS-MoS2 HNSs as a high performance visible photocatalyst for H2 evolution. The as-synthesized CdS-MoS2 HNSs exhibited ∼11 fold increment of H2 evolution rate when compared to pure CdS nanorods. This remarkable enhanced hydrogen evolution performance can be assigned to the positive synergetic effect from heteronanostructures formed between the CdS and MoS2 components which assist as an electron sink and source for abundant active edge sites and in turn increases the charge separation. This study presents a low-cost visible photocatalyst for solar energy conversion to achieve efficient H2.

OGLE-2014-SN-073 as a fallback accretion powered supernova

NASA Astrophysics Data System (ADS)

Moriya, Takashi J.; Terreran, Giacomo; Blinnikov, Sergei I.

2018-03-01

We investigate the possibility that the energetic Type II supernova OGLE-2014-SN-073 is powered by a fallback accretion following the failed explosion of a massive star. Taking massive hydrogen-rich supernova progenitor models, we estimate the fallback accretion rate and calculate the light-curve evolution of supernovae powered by the fallback accretion. We find that such fallback accretion powered models can reproduce the overall observational properties of OGLE-2014-SN-073. It may imply that some failed explosions could be observed as energetic supernovae like OGLE-2014-SN-073 instead of faint supernovae as previously proposed.

Facile Synthesis of Vanadium-Doped Ni3S2 Nanowire Arrays as Active Electrocatalyst for Hydrogen Evolution Reaction.

PubMed

Qu, Yuanju; Yang, Mingyang; Chai, Jianwei; Tang, Zhe; Shao, Mengmeng; Kwok, Chi Tat; Yang, Ming; Wang, Zhenyu; Chua, Daniel; Wang, Shijie; Lu, Zhouguang; Pan, Hui

2017-02-22

Ni 3 S 2 nanowire arrays doped with vanadium(V) are directly grown on nickel foam by a facile one-step hydrothermal method. It is found that the doping can promote the formation of Ni 3 S 2 nanowires at a low temperature. The doped nanowires show excellent electrocatalytic performance toward hydrogen evolution reaction (HER), and outperform pure Ni 3 S 2 and other Ni 3 S 2 -based compounds. The stability test shows that the performance of V-doped Ni 3 S 2 nanowires is improved and stabilized after thousands of linear sweep voltammetry test. The onset potential of V-doped Ni 3 S 2 nanowire can be as low as 39 mV, which is comparable to platinum. The nanowire has an overpotential of 68 mV at 10 mA cm -2 , a relatively low Tafel slope of 112 mV dec -1 , good stability and high Faradaic efficiency. First-principles calculations show that the V-doping in Ni 3 S 2 extremely enhances the free carrier density near the Fermi level, resulting in much improved catalytic activities. We expect that the doping can be an effective way to enhance the catalytic performance of metal disulfides in hydrogen evolution reaction and V-doped Ni 3 S 2 nanowire is one of the most promising electrocatalysts for hydrogen production.

Using Proton Radiation from the Moon to Probe Regolith Hydrogenation in the Upper 1-10 cm

NASA Astrophysics Data System (ADS)

Schwadron, N.; Wilson, J. K.; Jordan, A.; Looper, M. D.; Zeitlin, C. J.; Townsend, L.; Spence, H. E.; Farrell, W. M.; Petro, N. E.; Stubbs, T. J.; Pieters, C. M.

2017-12-01

Detection of proton radiation from the Moon offers a new observational method for mapping compositional variations over the lunar surface. Recently, it was discovered that the yield of high energy "albedo" proton radiation coming from the lunar regolith due to bombardment by galactic cosmic rays (GCRs) depends on latitude: the yield increases toward higher latitudes. This dependence was attributed to a surface layer of hydrogenated regolith near the poles. Here, an improved technique is developed to use the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter to detect proton radiation from the lunar horizon and from lunar nadir and to use this to investigate diurnal variation in near-surface hydrogenation. Based on measurements taken in 2015, CRaTER observes an average proton albedo rate with a higher yield of protons from the lunar horizon than from the nadir. Both the average proton radiation albedo rate and the excess of proton radiation from the lunar horizon agree well with simulations. The measurements provide further evidence for the existence of the lunar hydrogenation layer. Lastly, CRaTER finds a yield (defined by the proton albedo divided by the GCR input) that is higher on the morning terminator compared to the evening terminator. Based on the observational statistics, there is a significant likelihood that the AM terminator produces a higher yield in the proton radiation albedo than the PM terminator during the period studied. While this presents some possible evidence of an AM enhancement, the excess could also potentially be explained by variation in GCR heavy species (He and heavier species). While initial results of an improved technique for measuring the proton radiation albedo are promising, the observational dataset utilized by CRaTER must be expanded significantly to reduce uncertainties in the search for temporal evolution and the excess of proton radiation from the lunar horizon as we probe hydrogenation excess in the upper 1 - 10 cm lunar regolith.

Bioengineering of the Enterobacter aerogenes strain for biohydrogen production.

PubMed

Zhang, Chong; Lv, Feng-Xiang; Xing, Xin-Hui

2011-09-01

Enterobacter aerogenes is one of the most widely-studied model strains for fermentative hydrogen production. To improve the hydrogen yield of E. aerogenes, the bioengineering on a biomolecular level and metabolic network level is of importance. In this review, the fermentative technology of E. aerogenes for hydrogen production will be first briefly summarized. And then the bioengineering of E. aerogenes for the improvement of hydrogen yield will be thoroughly reviewed, including the anaerobic metabolic networks for hydrogen evolution in E. aerogenes, metabolic engineering for improving hydrogen production in E. aerogenes and mixed culture of E. aerogenes with other hydrogen-producing bacteria to enhance the overall yield in anaerobic cultivation. Finally, a perspective on E. aerogenes as a hydrogen producer including systems bioengineering approach for improving the hydrogen yield and application of the engineered E. aerogenes in mixed culture will be presented. Copyright © 2011 Elsevier Ltd. All rights reserved.

A mini-type hydrogen generator from aluminum for proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Wang, Er-Dong; Shi, Peng-Fei; Du, Chun-Yu; Wang, Xiao-Rui

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min -1 of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s -1 dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.

Hydrogen content and mechanical stress in glow discharge amorphous silicon

NASA Astrophysics Data System (ADS)

Paduschek, P.; Eichinger, P.; Kristen, G.; Mitlehner, H.

1982-08-01

The hydrogen content of plasma deposited amorphous silicon thin films on silicon has been determined as a function of annealing parameters (200-700°C, 12 h) using the proton-proton scattering method. It is shown that hydrogen is released with an activation energy of 1.3 eV. Different deposition temperatures are compared with respect to the hydrogen evolution. The mechanical stress of the layers on silicon substrates has been measured by interferometric techniques for each annealing step. As the hydrogen content decreases monotonically with rising annealing temperature the mechanical stress converts from compressive to tensile. While only a weak correlation exists between the total hydrogen content and the mechanical stress, the bound hydrogen as determined by IR absorption displays a linear relation with the measured mechanical stress.

In situ probing of doping- and stress-mediated phase transitions in a single-crystalline VO2 nanobeam by spatially resolved Raman spectroscopy

NASA Astrophysics Data System (ADS)

Chang, Sung-Jin; Park, Jong Bae; Lee, Gaehang; Kim, Hae Jin; Lee, Jin-Bae; Bae, Tae-Sung; Han, Young-Kyu; Park, Tae Jung; Huh, Yun Suk; Hong, Woong-Ki

2014-06-01

We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO2 nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO2 nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO2 nanostructures through doping and stress.We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO2 nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO2 nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO2 nanostructures through doping and stress. Electronic supplementary information (ESI) available: Illustration, photograph, Raman data, and EDX spectra. See DOI: 10.1039/c4nr01118j

An Optical Study of Processes in Hydrogen Flame in a Tube

DTIC Science & Technology

2002-07-01

growth of the hydrogen- flame length with the hydrogen flow rate was observed, whereas for a turbulent hydrogen jet (Reynolds number Re > 104 [5]), the... flame length remained almost constant and varied only weakly with the flow rate of hydrogen. For a subsonic jet flow, flame images display an...There are some data in the literature which show how the diffusive- flame length varies with the rate of hydrogen flow [4, 7]. The length of a

Evaluation of advanced propulsion options for the next manned transportation system: Propulsion evolution study

NASA Technical Reports Server (NTRS)

Spears, L. T.; Kramer, R. D.

1990-01-01

The objectives were to examine launch vehicle applications and propulsion requirements for potential future manned space transportation systems and to support planning toward the evolution of Space Shuttle Main Engine (SSME) and Space Transportation Main Engine (STME) engines beyond their current or initial launch vehicle applications. As a basis for examinations of potential future manned launch vehicle applications, we used three classes of manned space transportation concepts currently under study: Space Transportation System Evolution, Personal Launch System (PLS), and Advanced Manned Launch System (AMLS). Tasks included studies of launch vehicle applications and requirements for hydrogen-oxygen rocket engines; the development of suggestions for STME engine evolution beyond the mid-1990's; the development of suggestions for STME evolution beyond the Advanced Launch System (ALS) application; the study of booster propulsion options, including LOX-Hydrocarbon options; the analysis of the prospects and requirements for utilization of a single engine configuration over the full range of vehicle applications, including manned vehicles plus ALS and Shuttle C; and a brief review of on-going and planned LOX-Hydrogen propulsion technology activities.

Black TiO2 synthesized via magnesiothermic reduction for enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

Wang, Xiangdong; Fu, Rong; Yin, Qianqian; Wu, Han; Guo, Xiaoling; Xu, Ruohan; Zhong, Qianyun

2018-04-01

Utilizing solar energy for hydrogen evolution is a great challenge for its insufficient visible-light power conversion. In this paper, we report a facile magnesiothermic reduction of commercial TiO2 nanoparticles under Ar atmosphere and at 550 °C followed by acid treatment to synthesize reduced black TiO2 powders, which possesses a unique crystalline core-amorphous shell structure composed of disordered surface and oxygen vacancies and shows significantly improved optical absorption in the visible region. The unique core-shell structure and high absorption enable the reduced black TiO2 powders to exhibit enhanced photocatalytic activity, including splitting of water in the presence of Pt as a cocatalyst and degradation of methyl blue (MB) under visible light irradiation. Photocatalytic evaluations indicate that the oxygen vacancies play key roles in the catalytic process. The maximum hydrogen production rates are 16.1 and 163 μmol h-1 g-1 under the full solar wavelength range of light and visible light, respectively. This facile and versatile method could be potentially used for large scale production of colored TiO2 with remarkable enhancement in the visible light absorption and solar-driven hydrogen production.

Multicomponent hollow tubules formed using phytosterol and gamma-oryzanol-based compounds: an understanding of their molecular embrace.

PubMed

Rogers, Michael A; Bot, Arjen; Lam, Ricky Sze Ho; Pedersen, Tor; May, Tim

2010-08-19

The formation kinetics of self-assembling tubules composed of phytosterol:gamma-oryzanol mixtures were investigated at the Canadian Light Source on the mid-IR beamline using synchrotron radiation and Fourier transform infrared spectroscopy (FT-IR). The Avrami model was fitted to the changing hydrogen bonding density occurring at 3450 cm(-1). The nucleation process was found to be highly dependent on the molecular structure of the phytosterol. The nucleation event for cholesterol:gamma-oryzanol was determined to be sporadic whereas 5alpha-cholestan-3beta-ol:gamma-oryzanol and beta-sitosterol:gamma-oryzanol underwent instantaneous nucleation. One-dimensional growth occurred for each phytosterol:gamma-oryzanol mixture and involved the evolution of highly specific intermolecular hydrogen bonds. More detailed studies on the cholesterol:gamma-oryzanol system indicated that the nucleation activation energy, determined from multiple rate constants, obtained using the Avrami model, was at a minimum when the two compounds were at a 1:1 weight ratio. This resulted in drastic differences to the microscopic structures and affected the macroscopic properties such as turbidity. The formation of the phytosterol:gamma-oryzanol complex was due to intermolecular hydrogen bonding, which was in agreement with the infrared spectroscopic evidence.

Elucidating hydrogen oxidation/evolution kinetics in base and acid by enhanced activities at the optimized Pt shell thickness on the Ru core

DOE PAGES

Elbert, Katherine; Hu, Jue; Ma, Zhong; ...

2015-10-05

Hydrogen oxidation and evolution on Pt in acid are facile processes, while in alkaline electrolytes, they are 2 orders of magnitude slower. Thus, developing catalysts that are more active than Pt for these two reactions is important for advancing the performance of anion exchange membrane fuel cells and water electrolyzers. Herein, we detail a 4-fold enhancement of Pt mass activity that we achieved using single-crystalline Ru@Pt core–shell nanoparticles with two-monolayer-thick Pt shells, which doubles the activity on Pt–Ru alloy nanocatalysts. For Pt specific activity, the two- and one-monolayer-thick Pt shells exhibited enhancement factors of 3.1 and 2.3, respectively, compared tomore » the Pt nanocatalysts in base, differing considerably from the values of 1 and 0.4, respectively, in acid. To explain such behavior and the orders of magnitude difference in activity on going from acid to base, we performed kinetic analyses of polarization curves over a wide range of potential from –250 to 250 mV using the dual-pathway kinetic equation. From acid to base, the activation free energies increase the most for the Volmer reaction, resulting in a switch of the rate-determining step from the Tafel to the Volmer reaction, and a shift to a weaker optimal hydrogen binding energy. Furthermore, the much higher activation barrier for the Volmer reaction in base than in acid is ascribed to one or both of the two catalyst-insensitive factors: slower transport of OH – than H + in water and a stronger O–H bond in water molecules (HO–H) than in hydrated protons (H 2O–H +).« less

Electrodeposition of Nickel Nanoparticles for the Alkaline Hydrogen Evolution Reaction: Correlating Electrocatalytic Behavior and Chemical Composition.

PubMed

Tao, Shasha; Yang, Florent; Schuch, Jona; Jaegermann, Wolfram; Kaiser, Bernhard

2018-03-09

Ni nanoparticles (NPs) consisting of Ni, NiO, and Ni(OH) 2 were formed on Ti substrates by electrodeposition as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution. Additionally, the deposition parameters including the potential range and the scan rate were varied, and the resulting NPs were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. The chemical composition of the NPs changed upon using different conditions, and it was found that the catalytic activity increased with an increase in the amount of NiO. From these data, optimized NPs were synthesized; the best sample showed an onset potential of approximately 0 V and an overpotential of 197 mV at a cathodic current density of 10 mA cm -2 as well as a small Tafel slope of 88 mV dec -1 in 1 m KOH, values that are comparable to those of Pt foil. These NPs consist of approximately 25 % Ni and Ni(OH) 2 each, as well as approximately 50 % NiO. This implies that to obtain a successful HER electrocatalyst, active sites with differing compositions have to be close to each other to promote the different reaction steps. Long-time measurements (30 h) showed almost complete transformation of the highly active catalyst compound consisting of Ni 0 , NiO, and Ni(OH) 2 into the less active Ni(OH) 2 phase. Nevertheless, the here-employed electrodeposition of nonprecious metal/metal-oxide combination compounds represents a promising alternative to Pt-based electrocatalysts for water reduction to hydrogen. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal-Rich Transition Metal Diborides as Electrocatalysts for Hydrogen Evolution Reactions in a Wide Range of pH

DOE PAGES

Sitler, Steven J.; Raja, Krishnan S.; Charit, Indrajit

2016-09-23

Solid solutions of HfB 2-ZrB 2 mixtures were prepared by high-energy ball milling of diboride and additive powders followed by spark plasma sintering (SPS). A mixture of stoichiometric 1:1 HfB 2-ZrB 2 borides was the base composition to which Hf, Zr, Ta, LaB 6 or Gd 2O 3 was added. Hf, Zr and Ta were added in order to bring the boron-to-metal ratio down to 1.86, rendering the boride as MeB 1.86. In the case of LaB 6 and Gd 2O 3, 1.8 mol% was added. Electroanalytical behavior of hydrogen evolution reactions was evaluated in 1 M H 2SO 4more » and 1 M NaOH solutions. The LaB 6 additive material showed Tafel slopes of 125 and 90 mV/decade in acidic and alkaline solutions respectively. The Hf and Zr rich samples showed Tafel slopes of about 120 mV/decade in both electrolytes. The over potentials of hydrogen evolution reactions (at 10 mA/cm 2) in the alkaline solution were about 100 mV lower than those in acidic solution. The metal-rich diborides and addition of LaB 6 showed better hydrogen evolution reaction (HER) activities than the base 1:1 HfB 2-ZrB 2 stoichiometric diboride solid solution. Furthermore, the higher activity of metal-rich borides could be attributed to the increased electron population at the d-orbitals of the metal shown by band structure modeling calculations using the Density Functional Theory approach.« less

Hydrogen Production and Delivery | Hydrogen and Fuel Cells | Hydrogen and

Science.gov Websites

degrees Celsius. Ultra-high temperatures are required for thermochemical reaction cycles to produce for the environmentally benign production of hydrogen. Very high reaction rates at these elevated temperatures give rise to very fast reaction rates, which significantly enhance production rates and more than

Stable and Efficient CuO Based Photocathode through Oxygen-Rich Composition and Au-Pd Nanostructure Incorporation for Solar-Hydrogen Production.

PubMed

Masudy-Panah, Saeid; Siavash Moakhar, Roozbeh; Chua, Chin Sheng; Kushwaha, Ajay; Dalapati, Goutam Kumar

2017-08-23

Enhancing stability against photocorrosion and improving photocurrent response are the main challenges toward the development of cupric oxide (CuO) based photocathodes for solar-driven hydrogen production. In this paper, stable and efficient CuO-photocathodes have been developed using in situ materials engineering and through gold-palladium (Au-Pd) nanoparticles deposition on the CuO surface. The CuO photocathode exhibits a photocurrent generation of ∼3 mA/cm 2 at 0 V v/s RHE. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis and X-ray spectroscopy (XPS) confirm the formation of oxygen-rich (O-rich) CuO film which demonstrates a highly stable photocathode with retained photocurrent of ∼90% for 20 min. The influence of chemical composition on the photocathode performance and stability has been discussed in detail. In addition, O-rich CuO photocathodes deposited with Au-Pd nanostructures have shown enhanced photoelectrochemical performance. Linear scan voltammetry characteristic shows ∼25% enhancement in photocurrent after Au-Pd deposition and reaches ∼4 mA/cm 2 at "0" V v/s RHE. Hydrogen evolution rate significantly depends on the elemental composition of CuO and metal nanostructure. The present work has demonstrated a stable photocathode with high photocurrent for visible-light-driven water splitting and hydrogen production.

Hydrogen escape from Mars enhanced by deep convection in dust storms

NASA Astrophysics Data System (ADS)

Heavens, Nicholas G.; Kleinböhl, Armin; Chaffin, Michael S.; Halekas, Jasper S.; Kass, David M.; Hayne, Paul O.; McCleese, Daniel J.; Piqueux, Sylvain; Shirley, James H.; Schofield, John T.

2018-02-01

Present-day water loss from Mars provides insight into Mars's past habitability1-3. Its main mechanism is thought to be Jeans escape of a steady hydrogen reservoir sourced from odd-oxygen reactions with near-surface water vapour2, 4,5. The observed escape rate, however, is strongly variable and correlates poorly with solar extreme-ultraviolet radiation flux6-8, which was predicted to modulate escape9. This variability has recently been attributed to hydrogen sourced from photolysed middle atmospheric water vapour10, whose vertical and seasonal distribution is only partly characterized and understood11-13. Here, we report multi-annual observational estimates of water content and dust and water transport to the middle atmosphere from Mars Climate Sounder data. We provide strong evidence that the transport of water vapour and ice to the middle atmosphere by deep convection in Martian dust storms can enhance hydrogen escape. Planet-encircling dust storms can raise the effective hygropause (where water content rapidly decreases to effectively zero) from 50 to 80 km above the areoid (the reference equipotential surface). Smaller dust storms contribute to an annual mode in water content at 40-50 km that may explain seasonal variability in escape. Our results imply that Martian atmospheric chemistry and evolution can be strongly affected by the meteorology of the lower and middle atmosphere of Mars.

Characterization of Pulse Reverses Electroforming on Hard Gold Coating.

PubMed

Byoun, Young-Min; Noh, Young-Tai; Kim, Young-Geun; Ma, Seung-Hwan; Kim, Gwan-Hoon

2018-03-01

Effect of pulse reverse current (PRC) method on brass coatings electroplated from gold solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. The reversed current results in a significant change in the morphology of electrodeposits, improvement of the overall current efficiency and reduction of deposit porosity. With longer pulses, hemispherical surface features are generated, while larger grains result from shorter pulse widths. The porosity of the plated samples is found to decrease compared with results at the same time-average plating rate obtained from DC or Pulse plating. A major impediment to reducing gold later thickness is the corrosion of the underlying substrate, which is affected by the porosity of the gold layer. Both the morphology and the hydrogen evolution reaction have significant impact on porosity. PRC plating affect hydrogen gold and may oxidize hydrogen produced during the cathodic portion of the waveform. Whether the dissolution of gold and oxidation of hydrogen occur depends on the type of plating bath and the plating conditions adapted. In reversed pulse plating, the amount of excess near-surface cyanide is changed after the cathodic current is applied, and the oxidation of gold under these conditions has not been fully addressed. The effects of the current density, pulse-reverse ratio and brightener concentration of the electroplating process were investigated and optimized for suitable performance.

"A bridge over troubled gaps": up-conversion driven photocatalysis for hydrogen generation and pollutant degradation by near-infrared excitation.

PubMed

Acosta-Mora, P; Domen, K; Hisatomi, T; Lyu, H; Méndez-Ramos, J; Ruiz-Morales, J C; Khaidukov, N M

2018-02-15

Spectral up-conversion (UC) has been attracting growing interest for the effective harvesting of the near-infrared (NIR) part of sunlight for photocatalytic hydrogen production and environmental purification. We present evidence of NIR-to-UV-VIS photon conversion for degradation of organic dyes and hydrogen and oxygen evolution via water-splitting by TiO 2 and Rh-Cr oxide-loaded SrTiO 3 :Al photocatalysts, respectively.

Variable photosynthetic units, energy transfer and light-induced evolution of hydrogen in algae and bacteria.

NASA Technical Reports Server (NTRS)

Gaffron, H.

1971-01-01

The present state of knowledge regarding the truly photochemical reactions in photosynthesis is considered. Nine-tenths of the available knowledge is of a biochemical nature. Questions regarding the activities of the chlorophyll system are examined. The simplest photochemical response observed in living hydrogen-adapted algal cells is the release of molecular hydrogen, which continues even after all other known natural reactions have been eliminated either by heating or the action of poisons.

Hydrogen Isotopic Constraints on the Evolution of Surface and Subsurface Water on Mars

NASA Technical Reports Server (NTRS)

Usui, T.; Kurokawa, H.; Wang, J.; Alexander, C. M. O’D.; Simon, J. I.; Jones, J. H.

2017-01-01

The geology and geomorphology of Mars provide clear evidence for the presence of liquid water on its surface during the Noachian and Hesperien eras (i.e., >3 Ga). In contrast to the ancient watery environment, today the surface of Mars is relatively dry. The current desert-like surface conditions, however, do not necessarily indicate a lack of surface or near-surface water/ice. In fact, massive deposits of ground ice and/or icy sediments have been proposed based on subsurface radar sounder observations. Hence, accurate knowledge of both the evolution of the distribution of water and of the global water inventory is crucial to our understanding of the evolution of the climate and near-surface environments and the potential habitability of Mars. This study presents insights from hydrogen isotopes for the interactive evolution of Martian water reservoirs. In particular, based on our new measurement of the D/H ratio of 4 Ga-old Noachian water, we constrain the atmospheric loss and possible exchange of surface and subsurface water through time.

A [NiFe]hydrogenase model that catalyses the release of hydrogen from formic acid.

PubMed

Nguyen, Nga T; Mori, Yuki; Matsumoto, Takahiro; Yatabe, Takeshi; Kabe, Ryota; Nakai, Hidetaka; Yoon, Ki-Seok; Ogo, Seiji

2014-11-11

We report the decomposition of formic acid to hydrogen and carbon dioxide, catalysed by a NiRu complex originally developed as a [NiFe]hydrogenase model. This is the first example of H2 evolution, catalysed by a [NiFe]hydrogenase model, which does not require additional energy.

Hydrophilic cobalt sulfide nanosheets as a bifunctional catalyst for oxygen and hydrogen evolution in electrolysis of alkaline aqueous solution.

PubMed

Zhu, Mingchao; Zhang, Zhongyi; Zhang, Hu; Zhang, Hui; Zhang, Xiaodong; Zhang, Lixue; Wang, Shicai

2018-01-01

Hydrophilic medium and precursors were used to synthesize a hydrophilic electro-catalyst for overall water splitting. The cobalt sulfide (Co 3 S 4 ) catalyst exhibits a layered nanosheet structure with a hydrophilic surface, which can facilitate the diffusion of aqueous substrates into the electrode pores and towards the active sites. The Co 3 S 4 catalyst shows excellent bifunctional catalytic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline solution. The assembled water electrolyzer based on Co 3 S 4 exhibits better performance and stability than that of Pt/C-RuO 2 catalyst. Thereforce the hydrophilic Co 3 S 4 is a highly promising bifunctional catalyst for the overall water splitting reaction. Copyright © 2017 Elsevier Inc. All rights reserved.

Evolutionary sequences of very hot, low-mass, accreting white dwarfs with application to symbiotic variables and ultrasoft/supersoft low-luminosity x-ray sources

NASA Technical Reports Server (NTRS)

Sion, Edward M.; Starrfield, Sumner G.

1994-01-01

We present the first detailed model results of quasi-static evolutionary sequences of very hot low-mass white dwarfs accreting hydrogen-rich material at rates between 1 x 10(exp -7) and 1 x 10(exp -9) solar mass/yr. Most of the sequences were generated from starting models whose core thermal structures were not thermally relaxed in the thermal pulse cycle-averaged sense of an asymptotic giant branch stellar core. Hence, the evolution at constant accretion rate was not invariably characterized by series of identical shell flashes. Sequences exhibiting stable steady state nuclear burning at the accretion supply rate as well as sequences exhibiting recurrent thermonuclear shell flashes are presented and discussed. In some cases, the white dwarf accretors remain small (less than 10(exp 11) cm) and very hot even during the shell flash episode. They then experience continued but reduced hydrogen shell burning during the longer quiescent intervals while their surface temperatures increase both because of compressional heating and envelope structure readjustment in response to accretion over thousands of years. Both accretion and continued hydrogen burning power these models with luminosities of a few times 10(exp 37) ergs/s. We suggest that the physical properties of these model sequences are of considerable relevance to the observed outburst and quiescent behavior of those symbiotic variables and symbiotic novae containing low-mass white dwarfs. We also suggest that our models are relevant to the observational characteristics of the growing class of low-luminosity, supersoft/ultrasoft X-ray sources in globular clusters, and the Magellanic Clouds.

Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics

NASA Astrophysics Data System (ADS)

Zhang, Jian; Wang, Tao; Liu, Pan; Liao, Zhongquan; Liu, Shaohua; Zhuang, Xiaodong; Chen, Mingwei; Zschech, Ehrenfried; Feng, Xinliang

2017-05-01

Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi4 electrocatalyst supported by MoO2 cuboids on nickel foam (MoNi4/MoO2@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO4 cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi4 electrocatalyst. As a result, the MoNi4 electrocatalyst exhibits zero onset overpotential, an overpotential of 15 mV at 10 mA cm-2 and a low Tafel slope of 30 mV per decade in 1 M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi4 electrocatalyst is promising for practical water-alkali electrolysers.

Activating and optimizing MoS 2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies

DOE PAGES

Li, Hong; Tsai, Charlie; Koh, Ai Leen; ...

2015-11-09

As a promising non-precious catalyst for the hydrogen evolution reaction, molybdenum disulphide (MoS 2) is known to contain active edge sites and an inert basal plane. Activating the MoS 2 basal plane could further enhance its HER activity but is not often a strategy for doing so. Herein, we report the first activation and optimization of the basal plane of monolayer 2H-MoS 2 for HER by introducing sulphur (S) vacancies and strain. Our theoretical and experimental results show that the S-vacancies are new catalytic sites in the basal plane, where gap states around the Fermi level allow hydrogen to bindmore » directly to exposed Mo atoms. The hydrogen adsorption free energy (ΔG H) can be further manipulated by straining the surface with S-vacancies, which fine-tunes the catalytic activity. Furthermore, proper combinations of S-vacancy and strain yield the optimal ΔG H = 0 eV, which allows us to achieve the highest intrinsic HER activity among molybdenum-sulphide-based catalysts.« less

Platinum Group Metal-free Catalysts for Hydrogen Evolution Reaction in Microbial Electrolysis Cells.

PubMed

Yuan, Heyang; He, Zhen

2017-07-01

Hydrogen gas is a green energy carrier with great environmental benefits. Microbial electrolysis cells (MECs) can convert low-grade organic matter to hydrogen gas with low energy consumption and have gained a growing interest in the past decade. Cathode catalysts for the hydrogen evolution reaction (HER) present a major challenge for the development and future applications of MECs. An ideal cathode catalyst should be catalytically active, simple to synthesize, durable in a complex environment, and cost-effective. A variety of noble-metal free catalysts have been developed and investigated for HER in MECs, including Nickel and its alloys, MoS 2 , carbon-based catalysts and biocatalysts. MECs in turn can serve as a research platform to study the durability of the HER catalysts. This personal account has reviewed, analyzed, and discussed those catalysts with an emphasis on synthesis and modification, system performance and potential for practical applications. It is expected to provide insights into the development of HER catalysts towards MEC applications. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photocatalyzed Hydrogen Evolution from Water by a Composite Catalyst of NH2 -MIL-125(Ti) and Surface Nickel(II) Species.

PubMed

Meyer, Kim; Bashir, Shahid; Llorca, Jordi; Idriss, Hicham; Ranocchiari, Marco; van Bokhoven, Jeroen A

2016-09-19

A composite of the metal-organic framework (MOF) NH 2 -MIL-125(Ti) and molecular and ionic nickel(II) species, catalyzed hydrogen evolution from water under UV light. In 95 v/v % aqueous conditions the composite produced hydrogen in quantities two orders of magnitude higher than that of the virgin framework and an order of magnitude greater than that of the molecular catalyst. In a 2 v/v % water and acetonitrile mixture, the composite demonstrated a TOF of 28 mol H 2  g(Ni) -1  h -1 and remained active for up to 50 h, sustaining catalysis for three times longer and yielding 20-fold the amount of hydrogen. Appraisal of physical mixtures of the MOF and each of the nickel species under identical photocatalytic conditions suggest that similar surface localized light sensitization and proton reduction processes operate in the composite catalyst. Both nickel species contribute to catalytic conversion, although different activation behaviors are observed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modelling of hydrogen conditioning, retention and release in Tore Supra

NASA Astrophysics Data System (ADS)

Grisolia, C.; Horton, L. D.; Ehrenberg, J. K.

1995-04-01

A model based on a local mixing model has been previously developed at JET to explain the recovery of tritium after the first PTE experiment. This model is extended by a 0D plasma particle balance model and is applied to data from Tore Supra wall saturation experiments. With only two free parameters, representing the diffusion of hydrogen atoms and the volume recombination process between hydrogen atoms into molecules, the model can reproduce experimental data. The time evolution of the after-shot outgassing and the integral amount of particles recovered after the shot (assuming 13 m 2 of interacting surfaces between plasma and walls) are in good agreement with the experimental observations. The same set of parameters allows the model to simulate after-shot outgassing of five consecutive discharges. However, the model fails to predict the observed saturation of the walls by the plasma. Results from helium glow discharge (HeGD) can only be partially described. Good agreement with the experimental hydrogen release and its time evolution during HeGD is observed, but the model fails to describe the stability of a saturated graphite wall.

Understanding catalysis in a multiphasic two-dimensional transition metal dichalcogenide.

DOE PAGES

Chou, Stanley Shihyao; Sai, Na; Lu, Ping; ...

2015-10-07

Establishing processing–structure–property relationships for monolayer materials is crucial for a range of applications spanning optics, catalysis, electronics and energy. Presently, for molybdenum disulfide, a promising catalyst for artificial photosynthesis, considerable debate surrounds the structure/property relationships of its various allotropes. Here we unambiguously solve the structure of molybdenum disulfide monolayers using high-resolution transmission electron microscopy supported by density functional theory and show lithium intercalation to direct a preferential transformation of the basal plane from 2H (trigonal prismatic) to 1T' (clustered Mo). These changes alter the energetics of molybdenum disulfide interactions with hydrogen (ΔG H), and, with respect to catalysis, the 1T'more » transformation renders the normally inert basal plane amenable towards hydrogen adsorption and hydrogen evolution. Furthermore, we show basal plane activation of 1T' molybdenum disulfide and a lowering of ΔG H from +1.6 eV for 2H to +0.18 eV for 1T', comparable to 2H molybdenum disulfide edges on Au(111), one of the most active hydrogen evolution catalysts known.« less

Investigation of the Alkaline Electrochemical Interface and Development of Composite Metal/Metal-Oxides for Hydrogen and Oxygen Electrodes

NASA Astrophysics Data System (ADS)

Bates, Michael

Understanding the fundamentals of electrochemical interfaces will undoubtedly reveal a path forward towards a society based on clean and renewable energy. In particular, it has been proposed that hydrogen can play a major role as an energy carrier of the future. To fully utilize the clean energy potential of a hydrogen economy, it is vital to produce hydrogen via water electrolysis, thus avoiding co-production of CO2 inherent to reformate hydrogen. While significant research efforts elsewhere are focused on photo-chemical hydrogen production from water, the inherent low efficiency of this method would require a massive land-use footprint to achieve sufficient hydrogen production rates to integrate hydrogen into energy markets. Thus, this research has primarily focused on the water splitting reactions on base-metal catalysts in the alkaline environment. Development of high-performance base-metal catalysts will help move alkaline water electrolysis to the forefront of hydrogen production methods, and when paired with solar and wind energy production, represents a clean and renewable energy economy. In addition to the water electrolysis reactions, research was conducted to understand the de-activation of reversible hydrogen electrodes in the corrosive environment of the hydrogen-bromine redox flow battery. Redox flow batteries represent a promising energy storage option to overcome the intermittency challenge of wind and solar energy production methods. Optimization of modular and scalable energy storage technology will allow higher penetration of renewable wind and solar energy into the grid. In Chapter 1, an overview of renewable energy production methods and energy storage options is presented. In addition, the fundamentals of electrochemical analysis and physical characterization of the catalysts are discussed. Chapter 2 reports the development of a Ni-Cr/C electrocatalyst with unprecedented mass-activity for the hydrogen evolution reaction (HER) in alkaline electrolyte. The HER kinetics of numerous binary & ternary Ni-alloys and composite Ni/metal-oxide/C samples were evaluated in aqueous 0.1 M KOH electrolyte. Furthermore a model of the double layer interface is proposed, which helps explain the observed ensemble effect in the presence of AEI. In Chapter 3, Ni-Fe and Ni-Fe-Co mixed-metal-oxide (MMO) films were investigated for oxygen evolution reaction (OER) activity in 0.1M KOH on high surface area Raney-Nickel supports. During investigations of MMO activity, aniline was identified as a useful "capping agent" for synthesis of high-surface area MMO-polyaniline (PANI) composite materials. A Ni-Fe-Co/PANI-Raney-Ni catalyst was developed which exhibits enhanced mass-activity compared to state-of-the-art Ni-Fe OER electrocatalysts reported to date. The morphology of the MMO catalyst film on PANI/Raney-Ni support provides excellent dispersion of active-sites and should maintain high active-site utilization for catalyst loading on gas-diffusion electrodes. In Chapter 4, the de-activation of reversible-hydrogen electrode catalysts was investigated and the development of a Pt-Ir-Nx/C catalyst is reported, which exhibits significantly increased stability in the HBr/Br 2 electrolyte. In contrast a Pt-Ir/C catalyst exhibited increased tolerance to high-voltage cycling and in particular showed recovery of electrocatalytic activity after reversible de-activation (presumably from bromide adsorption and subsequent oxidative bromide stripping). Under the harshest testing conditions of high-voltage cycling or exposure to Br2 the Pt-based catalyst showed a trend in stability: Pt < Pt-Ir < Pt-Ir-Nx. (Abstract shortened by UMI.).

Mechanistic Studies at the Interface Between Organometallic Chemistry and Homogeneous Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casey, Charles P

Mechanistic Studies at the Interface Between Organometallic Chemistry and Homogeneous Catalysis Charles P. Casey, Principal Investigator Department of Chemistry, University of Wisconsin - Madison, Madison, Wisconsin 53706 Phone 608-262-0584 FAX: 608-262-7144 Email: casey@chem.wisc.edu http://www.chem.wisc.edu/main/people/faculty/casey.html Executive Summary. Our goal was to learn the intimate mechanistic details of reactions involved in homogeneous catalysis and to use the insight we gain to develop new and improved catalysts. Our work centered on the hydrogenation of polar functional groups such as aldehydes and ketones and on hydroformylation. Specifically, we concentrated on catalysts capable of simultaneously transferring hydride from a metal center and a proton frommore » an acidic oxygen or nitrogen center to an aldehyde or ketone. An economical iron based catalyst was developed and patented. Better understanding of fundamental organometallic reactions and catalytic processes enabled design of energy and material efficient chemical processes. Our work contributed to the development of catalysts for the selective and mild hydrogenation of ketones and aldehydes; this will provide a modern green alternative to reductions by LiAlH4 and NaBH4, which require extensive work-up procedures and produce waste streams. (C5R4OH)Ru(CO)2H Hydrogenation Catalysts. Youval Shvo described a remarkable catalytic system in which the key intermediate (C5R4OH)Ru(CO)2H (1) has an electronically coupled acidic OH unit and a hydridic RuH unit. Our efforts centered on understanding and improving upon this important catalyst for reduction of aldehydes and ketones. Our mechanistic studies established that the reduction of aldehydes by 1 to produce alcohols and a diruthenium bridging hydride species occurs much more rapidly than regeneration of the ruthenium hydride from the diruthenium bridging hydride species. Our mechanistic studies require simultaneous transfer of hydride from ruthenium to the aldehyde carbon and of a proton from the CpOH unit to the aldehyde oxygen and support reduction of the aldehyde without its prior coordination to ruthenium. Another important step in the catalysis is the regeneration of 1 from reaction of H2 with the stable diruthenium bridging hydride complex 2. Studies of the microscopic reverse of this process (hydrogen evolution from 1 which occurs at 80°C) in the presence of alcohol (the product of aldehyde hydrogenation) have shown that a dihydrogen complex is formed reversibly at a rate much faster than hydrogen evolution. Kinetic and theoretical studies in collaboration with Professor Qiang Cui of Wisconsin indicated an important role for alcohol in mediating transfer of hydrogen to ruthenium. One key to developing more active catalysts was to destabilize the bridging hydride intermediate 2 to prevent its formation or to speed its conversion to a reactive monohydride 1 by reaction with H2. We found several successful ways to destabilize the bridging hydride and to obtain more active catalysts. Most recently, we discovered related iron catalysts for hydrogenation that do not form dimers; the cost advantage of iron catalysts is spectacular. Iron Catalysts. In an exciting development, we found that a related iron complex is also a very active ketone hydrogenation catalyst. This hydrogenation catalyst shows high chemoselectivity for aldehydes, ketones, and imines and isolated C=C, CºC, C-X, -NO2, epoxides, and ester functions are unaffected by the hydrogenation conditions. Mechanistic studies have established a reversible hydrogen transfer step followed by rapid dihydrogen activation. The same iron complex also catalyzes transfer hydrogenation of ketones.« less

Hollow core-shell structured Ni-Sn@C nanoparticles: a novel electrocatalyst for the hydrogen evolution reaction.

PubMed

Lang, Leiming; Shi, Yi; Wang, Jiong; Wang, Feng-Bin; Xia, Xing-Hua

2015-05-06

Pt-free electrocatalysts with high activity and low cost are highly pursued for hydrogen production by electrochemically splitting water. Ni-based alloy catalysts are potential candidates for the hydrogen evolution reaction (HER) and have been studied extensively. Here, we synthesized novel hollow core-shell structure Ni-Sn@C nanoparticles (NPs) by sol-gel, chemical vapor deposition, and etching processes. The prepared electrocatalysts with porous hollow carbon layers have a high conductivity and large active area, which exhibit good electrocatalytic activity toward HER. The Tafel slope of ∼35 millivolts per decade measured in acidic solution for Ni-Sn@C NPs is the smallest one to date for the Ni-Sn alloy catalysts, and exceeds those of the most non-noble metal catalysts, indicating a possible Volmer-Heyrovsky reaction mechanism. The synthetic method can be extended to prepare other hollow core-shell structure electrocatalysts for low-temperature fuel cells.

Cathodic electrochemical activation of Co3O4 nanoarrays: a smart strategy to significantly boost the hydrogen evolution activity.

PubMed

Yang, Li; Zhou, Huang; Qin, Xin; Guo, Xiaodong; Cui, Guanwei; Asiri, Abdullah M; Sun, Xuping

2018-02-22

Co(hydro)oxides show unsatisfactory catalytic activity for the hydrogen evolution reaction (HER) in alkaline media, and it is thus highly desirable but still remains a challenge to design and develop Co(hydro)oxide derived materials as superb hydrogen-evolving catalysts using a facile, rapid and less energy-intensive method. Here, we propose a cathodic electrochemical activation strategy toward greatly boosted HER activity of a Co 3 O 4 nanoarray via room-temperature cathodic polarization in sodium hypophosphite solution. After activation, the overpotential significantly decreases from 260 to 73 mV to drive a geometrical catalytic current density of 10 mA cm -2 in 1.0 M KOH. Notably, this activated electrode also shows strong long-term electrochemical durability with the retention of its catalytic activity at 100 mA cm -2 for at least 40 h.

Summary of FY17 ParaChoice Accomplishments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levinson, Rebecca Sobel; West, Todd H.

As part of analysis support for FCTO, Sandia assesses the factors that influence the future of FCEVs and Hydrogen in the US vehicle fleet. Using ParaChoice, we model competition between FCEVs, conventional vehicles, and other alternative vehicle technologies in order to understand the drivers and sensitivities of adoption of FCEVs. ParaChoice leverages existing tools such as Autonomie (Moawad et al., 2016), AEO (U.S. Energy Information Administration, 2016), and the Macro System Model (Ruth et al., 2009) in order to synthesize a complete picture of the co-evolution of vehicle technology development, energy price evolution, and hydrogen production and pricing, with consumermore » demand for vehicles and fuel. We then assess impacts of FCEV market penetration and hydrogen use on green- house gas (GHG) emissions and petroleum consumption, providing context for the role of policy, technology development, infrastructure, and consumer behavior on the vehicle and fuel mix through parametric and sensitivity analyses.« less

Cobalt-embedded nitrogen-rich carbon nanotubes efficiently catalyze hydrogen evolution reaction at all pH values.

PubMed

Zou, Xiaoxin; Huang, Xiaoxi; Goswami, Anandarup; Silva, Rafael; Sathe, Bhaskar R; Mikmeková, Eliška; Asefa, Tewodros

2014-04-22

Despite being technically possible, splitting water to generate hydrogen is still practically unfeasible due mainly to the lack of sustainable and efficient catalysts for the half reactions involved. Herein we report the synthesis of cobalt-embedded nitrogen-rich carbon nanotubes (NRCNTs) that 1) can efficiently electrocatalyze the hydrogen evolution reaction (HER) with activities close to that of Pt and 2) function well under acidic, neutral or basic media alike, allowing them to be coupled with the best available oxygen-evolving catalysts-which also play crucial roles in the overall water-splitting reaction. The materials are synthesized by a simple, easily scalable synthetic route involving thermal treatment of Co(2+) -embedded graphitic carbon nitride derived from inexpensive starting materials (dicyandiamide and CoCl2 ). The materials' efficient catalytic activity is mainly attributed to their nitrogen dopants and concomitant structural defects. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Versatile Titanium Silicide Monolayers with Prominent Ferromagnetic, Catalytic, and Superconducting Properties: Theoretical Prediction.

PubMed

Wu, Qisheng; Zhang, Jun-Jie; Hao, Peipei; Ji, Zhongyang; Dong, Shuai; Ling, Chongyi; Chen, Qian; Wang, Jinlan

2016-10-06

On the basis of global structure search and density functional theory calculations, we predict a new class of two-dimensional (2D) materials, titanium silicide (Ti 2 Si, TiSi 2 , and TiSi 4 ) monolayers. They are proved to be energetically, dynamically, and thermally stable and own excellent mechanical properties. Among them, Ti 2 Si is a ferromagnetic metal with a magnetic moment of 1.37 μ B /cell, while TiSi 2 is an ideal catalyst for the hydrogen evolution reaction with a nearly zero free energy of hydrogen adsorption. More importantly, electron-phonon coupling calculations suggest that TiSi 4 is a robust 2D phonon-mediated superconductor with a transition temperature of 5.8 K, and the transition temperature can be enhanced up to 11.7 K under a suitable external strain. The versatility makes titanium silicide monolayers promising candidates for spintronic materials, hydrogen evolution catalysts, and 2D superconductors.

Dimeric [Mo₂S₁₂]²⁻ Cluster: A Molecular Analogue of MoS₂ Edges for Superior Hydrogen-Evolution Electrocatalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zhongjie; Luo, Wenjia; Ma, Lu

2015-12-07

Proton reduction is one of the most fundamental and important reactions in nature. MoS2 edges have been identified as the active sites for hydrogen evolution reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge sites is an attractive strategy to understand the underlying catalytic mechanism of different edge sites and improve their activities. Herein we report a dimeric molecular analogue [Mo₂S₁₂]²⁻, as the smallest unit possessing both the terminal and bridging disulfide ligands. Our electrochemical tests show that [Mo₂S₁₂]²⁻ is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo₂S₁₂]²⁻ exhibits a hydrogenmore » adsorption free energy near zero (-0.05eV). This work helps shed light on the rational design of HER catalysts and biomimetics of hydrogen-evolving enzymes.« less

A tunable azine covalent organic framework platform for visible light-induced hydrogen generation

PubMed Central

Vyas, Vijay S.; Haase, Frederik; Stegbauer, Linus; Savasci, Gökcen; Podjaski, Filip; Ochsenfeld, Christian; Lotsch, Bettina V.

2015-01-01

Hydrogen evolution from photocatalytic reduction of water holds promise as a sustainable source of carbon-free energy. Covalent organic frameworks (COFs) present an interesting new class of photoactive materials, which combine three key features relevant to the photocatalytic process, namely crystallinity, porosity and tunability. Here we synthesize a series of water- and photostable 2D azine-linked COFs from hydrazine and triphenylarene aldehydes with varying number of nitrogen atoms. The electronic and steric variations in the precursors are transferred to the resulting frameworks, thus leading to a progressively enhanced light-induced hydrogen evolution with increasing nitrogen content in the frameworks. Our results demonstrate that by the rational design of COFs on a molecular level, it is possible to precisely adjust their structural and optoelectronic properties, thus resulting in enhanced photocatalytic activities. This is expected to spur further interest in these photofunctional frameworks where rational supramolecular engineering may lead to new material applications. PMID:26419805

Modeling of hydrogen/deuterium dynamics and heat generation on palladium nanoparticles for hydrogen storage and solid-state nuclear fusion.

PubMed

Tanabe, Katsuaki

2016-01-01

We modeled the dynamics of hydrogen and deuterium adsorbed on palladium nanoparticles including the heat generation induced by the chemical adsorption and desorption, as well as palladium-catalyzed reactions. Our calculations based on the proposed model reproduce the experimental time-evolution of pressure and temperature with a single set of fitting parameters for hydrogen and deuterium injection. The model we generated with a highly generalized set of formulations can be applied for any combination of a gas species and a catalytic adsorbent/absorbent. Our model can be used as a basis for future research into hydrogen storage and solid-state nuclear fusion technologies.

Modification of molybdenum disulfide in methanol solvent for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Niyitanga, Theophile; Jeong, Hae Kyung

2018-05-01

Molybdenum disulfide is a promising catalyst to replace the expensive platinum as an electrocatalyst but needs to be modified to present excellent electrocatalytic properties. Herein, we successfully modify molybdenum disulfide in methanol solvent for hydrogen evolution reaction by using a simple hydrothermal method. Overpotential reduced to -0.6 V from -1.5 V, and energy band gap decreased from 1.73 eV to 1.58 eV after the modification. The modified molybdenum disulfide also demonstrated lower resistance (42 Ω) at high frequency (1000 kHz) compared with that (240 Ω) of the precursor, showing that conductivity of the modified molybdenum disulfide has improved.

One- or two-electron water oxidation, hydroxyl radical, or H 2O 2 evolution

DOE PAGES

Siahrostami, Samira; Li, Guo -Ling; Viswanathan, Venkatasubramanian; ...

2017-02-23

Electrochemical or photoelectrochemcial oxidation of water to form hydrogen peroxide (H 2O 2) or hydroxyl radicals (•OH) offers a very attractive route to water disinfection, and the first process could be the basis for a clean way to produce hydrogen peroxide. A major obstacle in the development of effective catalysts for these reactions is that the electrocatalyst must suppress the thermodynamically favored four-electron pathway leading to O 2 evolution. Here, we develop a thermochemical picture of the catalyst properties that determine selectivity toward the one, two, and four electron processes leading to •OH, H 2O 2, and O 2.

Pyrite-Induced Hydrogen Peroxide Formation as a Driving Force in the Evolution of Photosynthetic Organisms on an Early Earth

NASA Astrophysics Data System (ADS)

Borda, Michael J.; Elsetinow, Alicia R.; Schoonen, Martin A.; Strongin, Daniel R.

2001-09-01

The remarkable discovery of pyrite-induced hydrogen peroxide (H2O2) provides a key step in the evolution of oxygenic photosynthesis. Here we show that H2O2 can be generated rapidly via a reaction between pyrite and H2O in the absence of dissolved oxygen. The reaction proceeds in the dark, and H2O2 levels increase upon illumination with visible light. Since pyrite was stable in most photic environments prior to the rise of O2 levels, this finding represents an important mechanism for the formation of H2O2 on early Earth.

Amorphous nickel-cobalt complexes hybridized with 1T-phase molybdenum disulfide via hydrazine-induced phase transformation for water splitting

PubMed Central

Li, Haoyi; Chen, Shuangming; Jia, Xiaofan; Xu, Biao; Lin, Haifeng; Yang, Haozhou; Song, Li; Wang, Xun

2017-01-01

Highly active and robust eletcrocatalysts based on earth-abundant elements are desirable to generate hydrogen and oxygen as fuels from water sustainably to replace noble metal materials. Here we report an approach to synthesize porous hybrid nanostructures combining amorphous nickel-cobalt complexes with 1T phase molybdenum disulfide (MoS2) via hydrazine-induced phase transformation for water splitting. The hybrid nanostructures exhibit overpotentials of 70 mV for hydrogen evolution and 235 mV for oxygen evolution at 10 mA cm−2 with long-term stability, which have superior kinetics for hydrogen- and oxygen-evolution with Tafel slope values of 38.1 and 45.7 mV dec−1. Moreover, we achieve 10 mA cm−2 at a low voltage of 1.44 V for 48 h in basic media for overall water splitting. We propose that such performance is likely due to the complete transformation of MoS2 to metallic 1T phase, high porosity and stabilization effect of nickel-cobalt complexes on 1T phase MoS2. PMID:28485395

Preparation of NiCoP Hollow Quasi-Polyhedra and Their Electrocatalytic Properties for Hydrogen Evolution in Alkaline Solution.

PubMed

Li, Yapeng; Liu, Jindou; Chen, Chen; Zhang, Xiaohua; Chen, Jinhua

2017-02-22

Double metal phosphide (NiCoP) with hollow quasi-polyhedron structure was prepared by acidic etching and precipitation of ZIF-67 polyhedra and further phosphorization treatment with NaH 2 PO 2 . The morphology and microstructure of NiCoP quasi-polyhedron and its precursors were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a micropore and chemisorption analyzer. Electrocatalytic properties were examined by typical electrochemical methods, such as linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 1.0 M KOH aqueous solution. Results reveal that, compared with CoP hollow polyhedra, NiCoP hollow quasi-polyhedra exhibit better electrochemical properties for hydrogen evolution with a low onset overpotential of 74 mV and a small Tafel slope of 42 mV dec -1 . When the current density is 10 mA cm -2 , the corresponding overpotential is merely 124 mV, and 93% of its electrocatalytic activity can be maintained for 12 h. This indicates that NiCoP with hollow quasi-polyhedron structure, bimetallic merit, and low cost may be a good candidate as electrocatalyst in the practical application of hydrogen evolution.

Misfit-layered Bi1.85 Sr2 Co1.85 O7.7-δ for the hydrogen evolution reaction: beyond van der Waals heterostructures.

PubMed

Chua, Chun Kiang; Sofer, Zdeněk; Jankovský, Ondřej; Pumera, Martin

2015-03-16

Recent research on stable 2D nanomaterials has led to the discovery of new materials for energy-conversion and energy-storage applications. A class of layered heterostructures known as misfit-layered chalcogenides consists of well-defined atomic layers and has previously been applied as thermoelectric materials for use as high-temperature thermoelectric batteries. The performance of such misfit-layered chalcogenides in electrochemical applications, specifically the hydrogen evolution reaction, is currently unexplored. Herein, a misfit-layered chalcogenide consisting of CoO2 layers interleaved with an SrO-BiO-BiO-SrO rock-salt block and having the formula Bi1.85 Sr2 Co1.85 O7.7-δ is synthesized and examined for its structural and electrochemical properties. The hydrogen-evolution performance of misfit-layered Bi1.85 Sr2 Co1.85 O7.7-δ , which has an overpotential of 589 mV and a Tafel slope of 51 mV per decade, demonstrates the promising potential of misfit-layered chalcogenides as electrocatalysts instead of classical carbon. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cu2O/CuO Bilayered Composite as a High-Efficiency Photocathode for Photoelectrochemical Hydrogen Evolution Reaction

NASA Astrophysics Data System (ADS)

Yang, Yang; Xu, Di; Wu, Qingyong; Diao, Peng

2016-10-01

Solar powered hydrogen evolution reaction (HER) is one of the key reactions in solar-to-chemical energy conversion. It is desirable to develop photocathodic materials that exhibit high activity toward photoelectrochemical (PEC) HER at more positive potentials because a higher potential means a lower overpotential for HER. In this work, the Cu2O/CuO bilayered composites were prepared by a facile method that involved an electrodeposition and a subsequent thermal oxidation. The resulting Cu2O/CuO bilayered composites exhibited a surprisingly high activity and good stability toward PEC HER, expecially at high potentials in alkaline solution. The photocurrent density for HER was 3.15 mA·cm-2 at the potential of 0.40 V vs. RHE, which was one of the two highest reported at the same potential on copper-oxide-based photocathode. The high photoactivity of the bilayered composite was ascribed to the following three advantages of the Cu2O/CuO heterojunction: (1) the broadened light absorption band that made more efficient use of solar energy, (2) the large space-charge-region potential that enabled a high efficiency for electron-hole separation, and (3) the high majority carrier density that ensured a faster charge transportation rate. This work reveals the potential of the Cu2O/CuO bilayered composite as a promising photocathodic material for solar water splitting.

MoS 2/TiO 2 heterostructures as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, L.; Yang, Z.; Marcus, K.

In this study, we report a nonmetal plasmonic MoS2@TiO2 heterostructure for highly efficient photocatalytic H2 generation. Large area laminated Z-scheme MoS2 in conjunction with TiO2 nanocavity arrays are achieved via carefully controlled anodization, physical vapor deposition, and chemical vapor deposition processes. Broad spectral response ranging from ultraviolet (UV)-visible (vis) to near-infrared (NIR) wavelengths and finite element frequency-domain simulation suggest that this MoS2@TiO2 heterostructured photocatalyst possesses an enhanced activity for H+ reduction. A high H2 yield rate of 580 mmol h-1 g-1 is achieved using a low catalyst loading mass of 10.2 μg. The spatially uniform heterostructure, correlated to plasmon-resonance throughmore » conformal coating MoS2 that effectively regulated charge transfer pathways, is proven to be vitally important for the unique solar energy harvesting and photocatalytic H2 production. As an innovative exploration, our study demonstrates that the photocatalytic activities of nonmetal, earth-abundant materials can be enhanced with plasmonic effects, which may serve as an excellent catalytic agent for solar energy conversion to chemical fuel. Periodically patterned MoS 2/TiO 2heterostructures were rationally designed as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution.« less

Water in Earth's mantle: Hydrogen analysis of mantle olivine, pyroxenes and garnet using the SIMS

NASA Technical Reports Server (NTRS)

Kurosawa, Masanori; Yurimoto, Hisayoshi; Sueno, Shigeho

1993-01-01

Hydrogen (or water) in the Earth's interior plays a key role in the evolution and dynamics of the planet. However, the abundance and the existence form of the hydrogen have scarcely been clear in practice. Hydrogen in the mantle was incorporated in the interior during the formation of the Earth. The incorporated hydrogen was hardly possible to concentrate locally inside the Earth considering its high mobility and high reactivity. The hydrogen, preferably, could be distributed homogeneously over the mantle and the core by the subsequent physical and chemical processes. Therefore, hydrogen in the mantle could be present in the form of trace hydrogen in nominally anhydrous mantle minerals. The hydrogen and the other trace elements in mantle olivines, orthopyroxenes, clinopyroxenes, and garnets were determined using secondary ion mass spectrometry (SIMS) for elucidating (1) the exact hydrogen contents, (2) the correlation between the hydrogen and the other trace elements, (3) the dependence of the hydrogen contents on the depth, and (4) the dependence of the whole rock water contents on the depth.

Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2 Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation.

PubMed

Du, Hong; Guo, Hong-Li; Liu, Ya-Nan; Xie, Xiao; Liang, Kuang; Zhou, Xiao; Wang, Xin; Xu, An-Wu

2016-02-17

In the present work, metallic 1T-LixMoS2 is utilized as a novel cocatalyst for Cd0.5Zn0.5S photocatalyst. The obtained LixMoS2/Cd0.5Zn0.5S hybrids show excellent photocatalytic performance for H2 generation from aqueous solution containing Na2S and Na2SO3 under splitting visible light illumination (λ ≥ 420 nm) without precious metal cocatalysts. It turns out that a certain amount of intercalating Li(+) ions ultimately drives the transition of MoS2 crystal from semiconductor triagonal phase (2H phase) to metallic phase (1T phase). The distinct properties of 1T-LixMoS2 promote the efficient separation of photoexcited electrons and holes when used as cocatalyst for Cd0.5Zn0.5S photocatalyst. As compared to 2H-MoS2 nanosheets only having edge active sites, photoinduced electrons not only transfer to the edge sites of 1T-LixMoS2, but also to the plane active sites of 1T-LixMoS2 nanosheets. The content of LixMoS2 in hybrid photocatalysts influences the photocatalytic activity. The optimal 1T-LixMoS2 (1.0 wt %)/Cd0.5Zn0.5S nanojunctions display the best activity for hydrogen production, achieving a hydrogen evolution rate of 769.9 μmol h(-1), with no use of noble metal loading, which is about 3.5 times higher than that of sole Cd0.5Zn0.5S, and 2 times higher than that of 2H-MoS2 (1.0 wt %)/Cd0.5Zn0.5S samples. Our results demonstrate that Li(+)-intercalated MoS2 nanosheets with high conductivity, high densities of active sites, low cost, and environmental friendliness are a prominent H2 evolution cocatalyst that might substitute for noble metal for potential hydrogen energy applications.

Overshoot Convective Mixing in Nova Outbursts

NASA Astrophysics Data System (ADS)

Glasner, A. S.; Livne, E.; Truran, J. W.

2014-12-01

We present a 2D study of the overshoot convective mechanism in nova outbursts for a wide range of possible compositions of the layer underlying the accreted envelope. Previous surveys studied this mechanism only for solar composition matter accreted on top of carbon oxygen (CO) white dwarfs. Since, during the runaway, mixing with carbon enhances the hydrogen burning rates dramatically, one should question whether significant enrichment of the ejecta is possible also for other underlying compositions (He, O, Ne, Mg) predicted by stellar evolution models. When needed we upgraded our reaction network and simulated several non-carbon cases. Despite large differences in rates, time scales and energetics, our results show that the convective dredge up mechanism predicts significant enrichment in all cases, including that of helium enrichment in recurrent novae.

Core-shell rhodium sulfide catalyst for hydrogen evolution reaction / hydrogen oxidation reaction in hydrogen-bromine reversible fuel cell

NASA Astrophysics Data System (ADS)

Li, Yuanchao; Nguyen, Trung Van

2018-04-01

Synthesis and characterization of high electrochemical active surface area (ECSA) core-shell RhxSy catalysts for hydrogen evolution oxidation (HER)/hydrogen oxidation reaction (HOR) in H2-Br2 fuel cell are discussed. Catalysts with RhxSy as shell and different percentages (5%, 10%, and 20%) of platinum on carbon as core materials are synthesized. Cyclic voltammetry is used to evaluate the Pt-equivalent mass specific ECSA and durability of these catalysts. Transmission electron microscopy (TEM), X-ray Photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDX) techniques are utilized to characterize the bulk and surface compositions and to confirm the core-shell structure of the catalysts, respectively. Cycling test and polarization curve measurements in the H2-Br2 fuel cell are used to assess the catalyst stability and performance in a fuel cell. The results show that the catalysts with core-shell structure have higher mass specific ECSA (50 m2 gm-Rh-1) compared to a commercial catalyst (RhxSy/C catalyst from BASF, 6.9 m2 gm-Rh-1). It also shows better HOR/HER performance in the fuel cell. Compared to the platinum catalyst, the core-shell catalysts show more stable performance in the fuel cell cycling test.

Design principles for hydrogen evolution reaction catalyst materials

DOE PAGES

Strmcnik, Dusan; Lopes, Pietro Papa; Genorio, Bostjan; ...

2016-04-19

Design and synthesis of active, stable and cost-effective materials for efficient hydrogen production (hydrogen evolution reaction, HER) is of paramount importance for the successful deployment of hydrogen -based alternative energy technologies. The HER, seemingly one of the simplest electrochemical reactions, has served for decades to bridge the gap between fundamental electrocatalysis and practical catalyst design. However, there are still many open questions that need to be answered before it would be possible to claim that design principles of catalyst materials are fully developed for the efficient hydrogen production. Here in this review, by summarizing key results for the HER onmore » well-characterized electrochemical interfaces in acidic and alkaline media, we have broadened our understanding of the HER in the whole range of pH by considering three main parameters: the nature of the proton donor (H 3O + in acid and H 2O in alkaline), the energy of adsorption of H ad and OH ad, and the presence of spectator species. Simply by considering these three parameters we show that great deal has already been learned and new trends are beginning to emerge, giving some predictive ability with respect to the nature of electrochemical interface and electrocatalytic activity of the HER.« less

Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water

NASA Astrophysics Data System (ADS)

Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

2015-11-01

Splitting water for hydrogen production using light, or electrical energy, is the most developed ‘green technique’. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production.

Water oxidation catalysts and methods of use thereof

DOEpatents

Hill, Craig L.; Gueletii, Yurii V.; Musaev, Djamaladdin G.; Yin, Qiushi; Botar, Bogdan

2017-12-05

Homogeneous water oxidation catalysts (WOCs) for the oxidation of water to produce hydrogen ions and oxygen, and methods of making and using thereof are described herein. In a preferred embodiment, the WOC is a polyoxometalate WOC which is hydrolytically stable, oxidatively stable, and thermally stable. The WOC oxidized waters in the presence of an oxidant. The oxidant can be generated photochemically, using light, such as sunlight, or electrochemically using a positively biased electrode. The hydrogen ions are subsequently reduced to form hydrogen gas, for example, using a hydrogen evolution catalyst (HEC). The hydrogen gas can be used as a fuel in combustion reactions and/or in hydrogen fuel cells. The catalysts described herein exhibit higher turn over numbers, faster turn over frequencies, and/or higher oxygen yields than prior art catalysts.

Polyoxometalate water oxidation catalysts and methods of use thereof

DOEpatents

Hill, Craig L.; Gueletii, Yurii V.; Musaev, Djamaladdin G.; Yin, Qiushi; Botar, Bogdan

2014-09-02

Homogeneous water oxidation catalysts (WOCs) for the oxidation of water to produce hydrogen ions and oxygen, and methods of making and using thereof are described herein. In a preferred embodiment, the WOC is a polyoxometalate WOC which is hydrolytically stable, oxidatively stable, and thermally stable. The WOC oxidized waters in the presence of an oxidant. The oxidant can be generated photochemically, using light, such as sunlight, or electrochemically using a positively biased electrode. The hydrogen ions are subsequently reduced to form hydrogen gas, for example, using a hydrogen evolution catalyst (HEC). The hydrogen gas can be used as a fuel in combustion reactions and/or in hydrogen fuel cells. The catalysts described herein exhibit higher turn over numbers, faster turn over frequencies, and/or higher oxygen yields than prior art catalysts.

Trapping hydrogen atoms from a neon-gas matrix: a theoretical simulation.

PubMed

Bovino, S; Zhang, P; Kharchenko, V; Dalgarno, A

2009-08-07

Hydrogen is of critical importance in atomic and molecular physics and the development of a simple and efficient technique for trapping cold and ultracold hydrogen atoms would be a significant advance. In this study we simulate a recently proposed trap-loading mechanism for trapping hydrogen atoms released from a neon matrix. Accurate ab initio quantum calculations are reported of the neon-hydrogen interaction potential and the energy- and angular-dependent elastic scattering cross sections that control the energy transfer of initially cold atoms are obtained. They are then used to construct the Boltzmann kinetic equation, describing the energy relaxation process. Numerical solutions of the Boltzmann equation predict the time evolution of the hydrogen energy distribution function. Based on the simulations we discuss the prospects of the technique.

Comparison of hydrogen production and electrical power generation for energy capture in closed-loop ammonium bicarbonate reverse electrodialysis systems.

PubMed

Hatzell, Marta C; Ivanov, Ivan; Cusick, Roland D; Zhu, Xiuping; Logan, Bruce E

2014-01-28

Currently, there is an enormous amount of energy available from salinity gradients, which could be used for clean hydrogen production. Through the use of a favorable oxygen reduction reaction (ORR) cathode, the projected electrical energy generated by a single pass ammonium bicarbonate reverse electrodialysis (RED) system approached 78 W h m(-3). However, if RED is operated with the less favorable (higher overpotential) hydrogen evolution electrode and hydrogen gas is harvested, the energy recovered increases by as much ~1.5× to 118 W h m(-3). Indirect hydrogen production through coupling an RED stack with an external electrolysis system was only projected to achieve 35 W h m(-3) or ~1/3 of that produced through direct hydrogen generation.

A NEW TIMESCALE FOR PERIOD CHANGE IN THE PULSATING DA WHITE DWARF WD 0111+0018

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Montgomery, M. H.; Winget, D. E.

2013-03-20

We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10{sup -12} s s{sup -1}, exceeds by more than two orders of magnitude the expected rate from cooling alone for this class of slow and simply evolving pulsating WDs. This result indicates the presence of an additional timescale for period evolution in these pulsating objects. We also measure the rates of period change of nonlinear combination frequencies and show that they share the evolutionarymore » characteristics of their parent modes, confirming that these combination frequencies are not independent modes but rather artifacts of some nonlinear distortion in the outer layers of the star.« less

Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution

NASA Astrophysics Data System (ADS)

Schootemeijer, A.; Langer, N.

2018-03-01

Context. The majority of the Wolf-Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. Wind stripping in single stars is expected to be inefficient in producing WR stars in metal-poor environments such as the Small Magellanic Cloud (SMC). While binary interaction can also produce WR stars at low metallicity, it is puzzling that the fraction of WR binaries appears to be about 40%, independent of the metallicity. Aim. We aim to use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with stellar models. Methods: We used the MESA stellar evolution code to construct two grids of stellar models with SMC metallicity. One of these consists of models of rapidly rotating single stars, which evolve in part or completely chemically homogeneously. In a second grid, we analyzed core helium burning stellar models assuming constant hydrogen and helium gradients in their envelopes. Results: We find that chemically homogeneous evolution is not able to account for the majority of the WR stars in the SMC. However, in particular the apparently single WR star SMC AB12, and the double WR system SMC AB5 (HD 5980) appear consistent with this channel. We further find a dichotomy in the envelope hydrogen gradients required to explain the observed temperatures of the SMC WR stars. Shallow gradients are found for the WR stars with O star companions, while much steeper hydrogen gradients are required to understand the group of hot apparently single WR stars. Conclusions: The derived shallow hydrogen gradients in the WR component of the WR+O star binaries are consistent with predictions from binary models where mass transfer occurs early, in agreement with their binary properties. Since the hydrogen profiles in evolutionary models of massive stars become steeper with time after the main sequence, we conclude that most of the hot (Teff > 60 kK ) apparently single WR stars lost their envelope after a phase of strong expansion, e.g., as the result of common envelope evolution with a lower mass companion. The so far undetected companions, either main sequence stars or compact objects, are then expected to still be present. A corresponding search might identify the first immediate double black hole binary progenitor with masses as high as those detected in GW150914.

Harnessing genetic diversity in Saccharomyces cerevisiae for fermentation of xylose in hydrolysates of alkaline hydrogen peroxide-pretreated biomass.

PubMed

Sato, Trey K; Liu, Tongjun; Parreiras, Lucas S; Williams, Daniel L; Wohlbach, Dana J; Bice, Benjamin D; Ong, Irene M; Breuer, Rebecca J; Qin, Li; Busalacchi, Donald; Deshpande, Shweta; Daum, Chris; Gasch, Audrey P; Hodge, David B

2014-01-01

The fermentation of lignocellulose-derived sugars, particularly xylose, into ethanol by the yeast Saccharomyces cerevisiae is known to be inhibited by compounds produced during feedstock pretreatment. We devised a strategy that combined chemical profiling of pretreated feedstocks, high-throughput phenotyping of genetically diverse S. cerevisiae strains isolated from a range of ecological niches, and directed engineering and evolution against identified inhibitors to produce strains with improved fermentation properties. We identified and quantified for the first time the major inhibitory compounds in alkaline hydrogen peroxide (AHP)-pretreated lignocellulosic hydrolysates, including Na(+), acetate, and p-coumaric (pCA) and ferulic (FA) acids. By phenotyping these yeast strains for their abilities to grow in the presence of these AHP inhibitors, one heterozygous diploid strain tolerant to all four inhibitors was selected, engineered for xylose metabolism, and then allowed to evolve on xylose with increasing amounts of pCA and FA. After only 149 generations, one evolved isolate, GLBRCY87, exhibited faster xylose uptake rates in both laboratory media and AHP switchgrass hydrolysate than its ancestral GLBRCY73 strain and completely converted 115 g/liter of total sugars in undetoxified AHP hydrolysate into more than 40 g/liter ethanol. Strikingly, genome sequencing revealed that during the evolution from GLBRCY73, the GLBRCY87 strain acquired the conversion of heterozygous to homozygous alleles in chromosome VII and amplification of chromosome XIV. Our approach highlights that simultaneous selection on xylose and pCA or FA with a wild S. cerevisiae strain containing inherent tolerance to AHP pretreatment inhibitors has potential for rapid evolution of robust properties in lignocellulosic biofuel production.

Convergent evolution of reduced energy demands in extremophile fish

PubMed Central

Arias-Rodriguez, Lenin; Tobler, Michael

2017-01-01

Convergent evolution in organismal function can arise from nonconvergent changes in traits that contribute to that function. Theory predicts that low resource availability and high maintenance costs in extreme environments select for reductions in organismal energy demands, which could be attained through modifications of body size or metabolic rate. We tested for convergence in energy demands and underlying traits by investigating livebearing fish (genus Poecilia) that have repeatedly colonized toxic, hydrogen sulphide-rich springs. We quantified variation in body size and routine metabolism across replicated sulphidic and non-sulphidic populations in nature, modelled total organismal energy demands, and conducted a common-garden experiment to test whether population differences had a genetic basis. Sulphidic populations generally exhibited smaller body sizes and lower routine metabolic rates compared to non-sulphidic populations, which together caused significant reductions in total organismal energy demands in extremophile populations. Although both mechanisms contributed to variation in organismal energy demands, variance partitioning indicated reductions of body size overall had a greater effect than reductions of routine metabolism. Finally, population differences in routine metabolism documented in natural populations were maintained in common-garden reared individuals, indicating evolved differences. In combination with other studies, these results suggest that reductions in energy demands may represent a common theme in adaptation to physiochemical stressors. Selection for reduced energy demand may particularly affect body size, which has implications for life history evolution in extreme environments. PMID:29077740

High pressure Raman spectroscopy of H2O-CH3OH mixtures.

PubMed

Hsieh, Wen-Pin; Chien, Yu-Hsiang

2015-02-23

Complex intra-molecular interactions and the hydrogen-bonding network in H2O-volatile mixtures play critical roles in many dynamics processes in physical chemistry, biology, and Earth and planetary sciences. We used high pressure Raman spectroscopy to study the pressure evolution of vibrational frequencies and bonding behavior in H2O-CH3OH mixtures. We found that the presence of low CH3OH content in H2O increases the transition pressure where water crystallizes to ice VI, but does not significantly change the pressure where ice VI transforms to ice VII. Furthermore, the stiffening rates of C-H stretching frequencies dω/dP in CH3OH significantly decrease upon the crystallization of water, and the softening rates of the O-H stretching frequencies of ice VII are suppressed over a narrow pressure range, after which the frequencies of these modes shift with pressure in ways similar to pure CH3OH and ice VII, respectively. Such complex pressure evolution of Raman frequencies along with pronounced variations in Raman intensities of CH3OH within the sample, and the hysteresis of the water-ice VI phase transition suggest pressure-induced segregation of low content CH3OH from ice VII. These findings indicate the significant influence of volatiles on the crystallization of sub-surface ocean and thermal evolution within large icy planets and satellites.

Infrared spectroscopy of solid normal hydrogen doped with CH3F and O2 at 4.2 K: CH3F:O2 complex and CH3F migration

NASA Astrophysics Data System (ADS)

Abouaf-Marguin, L.; Vasserot, A.-M.

2011-04-01

Double doping of solid normal hydrogen with CH3F and O2 at about 4.2 K gives evidence of (ortho-H2)n:CH3F clusters and of O2:CH3F complex formation. FTIR analysis of the time evolution of the spectra in the region of the v3 C-F stretching mode indicates that these clusters behave very differently from (ortho-H2)n:H2O clusters. The main point is the observed migration of CH3F molecules in solid para-H2 at 4.2 K which differs from that of H2O under identical experimental conditions. This is confirmed by an increase over time of the integrated intensity of the CH3F:O2 complex with a rate constant K = 2.7(2) . 10-4 s-1.

Recent Observations of AG Pegasi's Latest Outburst Phase by Harvard Observing Project

NASA Astrophysics Data System (ADS)

Espinel, Jose Luis; Lewis, John; Budreviciute, Rimute; Bieryla, Allyson; Denham Alexander, Kate; Blanchard, Peter; Carmichael, Theron; Garrison, Lehman H.; Huang, Jane; Mayo, Andrew; McIntosh, Missy; Vanderburg, Andrew; Alam, Munazza; Cordova, Rodrigo; Gomez, Sebastian; Weaver, Ian; Yuan, Sihan; Price, Evander

2017-01-01

AG Pegasi (AG Peg) is a symbiotic binary star composed of a red supergiant and a white dwarf. Between 1860 and 1870, AG Peg brightened from magnitude 9 to 6, before gradually dimming. In 2015, the star began another brightening phase. The outbursts are thought to be caused by accretion of material onto the white dwarf. Once there is enough hydrogen accreted, hydrogen shell-burning starts leading to the the star’s evolution into a A-supergiant with a high mass-loss rate (Kenyon et al. 1993). The Harvard Observing Project (HOP) collected photometric data in BVRI filters using Harvard’s 16-inch Clay Telescope in the Fall term of 2015 and again in the Fall term of 2016. HOP is designed to get undergraduate students interested in astronomy and observing, and to allow graduate students opportunities to interact with undergraduates and get more observing/teaching experience. This study monitors the luminosity of AG Peg to constrain the amplitude and duration of the latest outburst.

Polyvinylpyrrolidone stabilized-Ru nanoclusters loaded onto reduced graphene oxide as high active catalyst for hydrogen evolution

NASA Astrophysics Data System (ADS)

Zhang, Jiao; Hao, Jinghao; Ma, Qianli; Li, Chuanqi; Liu, Yushan; Li, Baojun; Liu, Zhongyi

2017-06-01

Ruthenium/reduced graphene oxide nanocomposites (Ru/rGO NCs) were synthesized via an electrostatic self-assembly approach. Polyvinylpyrrolidone (PVP) stabilized and positively charged metallic ruthenium nanoclusters about 1.2 nm were synthesized and uniformly loaded onto negatively charged graphene oxide (GO) sheets via strong electrostatic interactions. The as-prepared Ru/rGO NCs exhibited superior performance in catalytic hydrolysis of sodium borohydride (NaBH4) to generate H2. The hydrogen generation rate was up to 14.87 L H2 min-1 gcat -1 at 318 K with relatively low activation energy of 38.12 kJ mol-1. Kinetics study confirmed that the hydrolysis of NaBH4 was first order with respect to concentration of catalysts. Besides, the conversion of NaBH4 remained at 97% and catalytic activity retained more than 70% after 5 reaction cycles at room temperature. These results suggested that the Ru/rGO NCs have a promising prospect in the field of clean energy.

Carbon Quantum Dot Implanted Graphite Carbon Nitride Nanotubes: Excellent Charge Separation and Enhanced Photocatalytic Hydrogen Evolution.

PubMed

Wang, Yang; Liu, Xueqin; Liu, Jia; Han, Bo; Hu, Xiaoqin; Yang, Fan; Xu, Zuwei; Li, Yinchang; Jia, Songru; Li, Zhen; Zhao, Yanli

2018-05-14

Graphite carbon nitride (g-C 3 N 4 ) is a promising candidate for photocatalytic hydrogen production, but only shows moderate activity owing to sluggish photocarrier transfer and insufficient light absorption. Herein, carbon quantum dots (CQDs) implanted in the surface plane of g-C 3 N 4 nanotubes were synthesized by thermal polymerization of freeze-dried urea and CQDs precursor. The CQD-implanted g-C 3 N 4 nanotubes (CCTs) could simultaneously facilitate photoelectron transport and suppress charge recombination through their specially coupled heterogeneous interface. The electronic structure and morphology were optimized in the CCTs, contributing to greater visible light absorption and a weakened barrier of the photocarrier transfer. As a result, the CCTs exhibited efficient photocatalytic performance under light irradiation with a high H 2 production rate of 3538.3 μmol g -1  h -1 and a notable quantum yield of 10.94 % at 420 nm. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hierarchical CoP/Ni 5 P 4 /CoP microsheet arrays as a robust pH-universal electrocatalyst for efficient hydrogen generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, Ishwar Kumar; Zhou, Haiqing; Sun, Jingying

Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni 5 P 4 /CoP microsheet arrays for pH-universal hydrogen evolution through simply wrapping Ni 5 P 4 nanosheet arrays in CoP nanoparticles.

Hierarchical CoP/Ni 5 P 4 /CoP microsheet arrays as a robust pH-universal electrocatalyst for efficient hydrogen generation

DOE PAGES

Mishra, Ishwar Kumar; Zhou, Haiqing; Sun, Jingying; ...

2018-01-01

Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni 5 P 4 /CoP microsheet arrays for pH-universal hydrogen evolution through simply wrapping Ni 5 P 4 nanosheet arrays in CoP nanoparticles.

Detecting and measuring metabolic byproducts by electrochemical sensing

NASA Technical Reports Server (NTRS)

Wilkins, J. R.; Stoner, G. E.

1974-01-01

Method of detecting certain groups of bacteria is based on sensing buildup in molecular hydrogen. Apparatus is easy to assemble and use, and it has added advantage that hydrogen evolution by test micro-organisms can be measured automatically and accurately. System has been used to detect and enumerate variety of gram-negative bacteria of enterobacteriaceae group.

Boron-Based Hydrogen Storage: Ternary Borides and Beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vajo, John J.

DOE continues to seek reversible solid-state hydrogen materials with hydrogen densities of ≥11 wt% and ≥80 g/L that can deliver hydrogen and be recharged at moderate temperatures (≤100 °C) and pressures (≤100 bar) enabling incorporation into hydrogen storage systems suitable for transportation applications. Boron-based hydrogen storage materials have the potential to meet the density requirements given boron’s low atomic weight, high chemical valance, and versatile chemistry. However, the rates of hydrogen exchange in boron-based compounds are thus far much too slow for practical applications. Although contributing to the high hydrogen densities, the high valance of boron also leads to slowmore » rates of hydrogen exchange due to extensive boron-boron atom rearrangements during hydrogen cycling. This rearrangement often leads to multiple solid phases occurring over hydrogen release and recharge cycles. These phases must nucleate and react with each other across solid-solid phase boundaries leading to energy barriers that slow the rates of hydrogen exchange. This project sought to overcome the slow rates of hydrogen exchange in boron-based hydrogen storage materials by minimizing the number of solid phases and the boron atom rearrangement over a hydrogen release and recharge cycle. Two novel approaches were explored: 1) developing matched pairs of ternary borides and mixed-metal borohydrides that could exchange hydrogen with only one hydrogenated phase (the mixed-metal borohydride) and only one dehydrogenated phase (the ternary boride); and 2) developing boranes that could release hydrogen by being lithiated using lithium hydride with no boron-boron atom rearrangement.« less

H NMR studies of substrate hydrogen exchange reactions catalyzed by L-methionine gamma-lyase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esaki, N.; Nakayama, T.; Sawada, S.

Hydrogen exchange reactions of various L-amino acids catalyzed by L-methionine gamma-lyase (EC 4.4.1.11) have been studied. The enzyme catalyzes the rapid exchange of the alpha- and beta-hydrogens of L-methionine and S-methyl-L-cysteine with deuterium from the solvent. The rate of alpha-hydrogen exchange was about 40 times faster than that of the enzymatic elimination reaction of the sulfur-containing amino acids. The enzyme also catalyzes the exchange reaction of alpha- and beta-hydrogens of the straight-chain L-amino acids which are not susceptible to elimination. The exchange rates of the alpha-hydrogen and the total beta-hydrogens of L-alanine and L-alpha-aminobutyrate with deuterium followed first-order kinetics. Formore » L-norvaline, L-norleucine, S-methyl-L-cysteine, and L-methionine, the rate of alpha-hydrogen exchange followed first-order kinetics, but the rate of total beta-hydrogen exchange decreased due to a primary isotope effect at the alpha-position. L-Phenylalanine and L-tryptophan slowly underwent alpha-hydrogen exchange. The pro-R hydrogen of glycine was deuterated stereospecifically.« less

Dicationic ionic liquid mediated fabrication of Au@Pt nanoparticles supported on reduced graphene oxide with highly catalytic activity for oxygen reduction and hydrogen evolution

NASA Astrophysics Data System (ADS)

Shi, Ya-Cheng; Chen, Sai-Sai; Feng, Jiu-Ju; Lin, Xiao-Xiao; Wang, Weiping; Wang, Ai-Jun

2018-05-01

Ionic liquids as templates or directing agents have attracted great attention for shaping-modulated synthesis of advanced nanomaterials. In this work, reduced graphene oxide supported uniform core-shell Au@Pt nanoparticles (Au@Pt NPs/rGO) were fabricated by a simple one-pot aqueous approach, using N-methylimidazolium-based dicationic ionic liquid (1,1-bis(3-methylimadazoilum-1-yl)butylene bromide, [C4(Mim)2]2Br) as the shape-directing agent. The morphology evolution, structural information and formation mechanism of Au@Pt NPs anchored on rGO were investigated by a series of characterization techniques. The obtained nanocomposites displayed superior electrocatalytic features toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) compared with commercial Pt/C catalyst. This approach provides a novel route for facile synthesis of nanocatalysts in fuel cells.

Conversion rate of para-hydrogen to ortho-hydrogen by oxygen: implications for PHIP gas storage and utilization.

PubMed

Wagner, Shawn

2014-06-01

To determine the storability of para-hydrogen before reestablishment of the room temperature thermal equilibrium mixture. Para-hydrogen was produced at near 100% purity and mixed with different oxygen quantities to determine the rate of conversion to the thermal equilibrium mixture of 75: 25% (ortho: para) by detecting the ortho-hydrogen (1)H nuclear magnetic resonance using a 9.4 T imager. The para-hydrogen to ortho-hydrogen velocity constant, k, near room temperature (292 K) was determined to be 8.27 ± 1.30 L/mol · min(-1). This value was calculated utilizing four different oxygen fractions. Para-hydrogen conversion to ortho-hydrogen by oxygen can be minimized for long term storage with judicious removal of oxygen contamination. Prior calculated velocity rates were confirmed demonstrating a dependence on only the oxygen concentration.

Bootstrapping a Sustainable North American PEM Fuel Cell Industry: Could a Federal Acquisition Program Make a Difference?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greene, David L; Duleep, Dr. K. G.

2008-10-01

The North American Proton Exchange Membrane (PEM) fuel cell industry may be at a critical juncture. A large-scale market for automotive fuel cells appears to be several years away and in any case will require a long-term, coordinated commitment by government and industry to insure the co-evolution of hydrogen infrastructure and fuel cell vehicles (Greene et al., 2008). The market for non-automotive PEM fuel cells, on the other hand, may be much closer to commercial viability (Stone, 2006). Cost targets are less demanding and manufacturers appear to be close, perhaps within a factor of two, of meeting them. Hydrogen supplymore » is a significant obstacle to market acceptance but may not be as great a barrier as it is for hydrogen-powered vehicles due to the smaller quantities of hydrogen required. PEM fuel cells appear to be potentially competitive in two markets: (1) Backup power (BuP) supply, and (2) electrically-powered MHE (Mahadevan et al., 2007a, 2007b). There are several Original Equipment Manufacturers (OEMs) of PEM fuel cell systems for these applications but production levels have been quite low (on the order of 100-200 per year) and cumulative production experience is also limited (on the order of 1,000 units to date). As a consequence, costs remain above target levels and PEM fuel cell OEMs are not yet competitive in these markets. If cost targets can be reached and acceptable solutions to hydrogen supply found, a sustainable North American PEM fuel cell industry could be established. If not, the industry and its North American supply chain could disappear within a year or two. The Hydrogen Fuel Cell and Infrastructure Technologies (HFCIT) program of the U.S. Department of Energy (DOE) requested a rapid assessment of the potential for a government acquisition program to bootstrap the market for non-automotive PEM fuel cells by driving down costs via economies of scale and learning-by-doing. The six week study included in-depth interviews of three manufacturers, visits to two production facilities, review of the literature on potential markets in North America and potential federal government procurements, development of a cost model reflecting economies of scale and learning-by-doing, and estimation of the impact of federal PEM fuel cell procurements on fuel cell system costs and the evolution of private market demand. This report presents the findings of that study. Section 2 outlines the status of the industry and describes potential markets based on interviews of manufacturers and the existing literature. Section 3 describes the modeling methodology including key premises and assumptions, and presents estimates of market evolution under four scenarios: (1) Base Case with no federal government procurement program, (2) Scenario 1, an aggressive program beginning with less than 200 units procured in 2008 ramping up to more than 2,000 units in 2012, (3) Scenario 2 which is identical to Scenario 1 except that the private market is assumed to be twice as sensitive to price, and (4) Scenario 3, a delayed, smaller federal procurement program beginning in 2011 increasing to a maximum of just over 1,000 units per year in 2012. The analysis suggests that the aggressive program of Scenario 1 would likely stimulate a sustainable, competitive North American non-automotive PEM fuel cell industry. Given plausible assumptions about learning rates and scale economies, the procurements assumed in Scenario 1 appear to be sufficient to drive down costs to target levels. These findings are conditional on the evolution of acceptable hydrogen supply strategies, which were not explicitly analyzed in this study. Success is less certain under Scenarios 2 and 3, and there appears to be a strong probability that existing OEMs would not survive until 2011. In the Base Case, no program, a viable North American industry does not emerge before 2020.« less

Variations on a theme - the evolution of hydrocarbon solids. I. Compositional and spectral modelling - the eRCN and DG models

NASA Astrophysics Data System (ADS)

Jones, A. P.

2012-04-01

Context. The compositional properties of hydrogenated amorphous carbons are known to evolve in response to the local conditions. Aims: We present a model for low-temperature, amorphous hydrocarbon solids, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, that can be used to study and predict the evolution of their properties in the interstellar medium. Methods: We adopt an adaptable and prescriptive approach to model these materials, which is based on a random covalent network (RCN) model, extended here to a full compositional derivation (the eRCN model), and a defective graphite (DG) model for the hydrogen poorer materials where the eRCN model is no longer valid. Results: We provide simple expressions that enable the determination of the structural, infrared and spectral properties of amorphous hydrocarbon grains as a function of the hydrogen atomic fraction, XH. Structural annealing, resulting from hydrogen atom loss, results in a transition from H-rich, aliphatic-rich to H-poor, aromatic-rich materials. Conclusions: The model predicts changes in the optical properties of hydrogenated amorphous carbon dust in response to the likely UV photon-driven and/or thermal annealing processes resulting, principally, from the radiation field in the environment. We show how this dust component will evolve, compositionally and structurally in the interstellar medium in response to the local conditions. Appendices A and B are available in electronic form at http://www.aanda.org

Bioinspired design of redox-active ligands for multielectron catalysis: effects of positioning pyrazine reservoirs on cobalt for electro- and photocatalytic generation of hydrogen from water† †Electronic supplementary information (ESI) available: Non-aqueous cyclic voltammetry; Levich plots and scan rate dependence of aqueous voltammetry; pH dependence of photocatalysis; computational details; and supporting figures. CCDC 1060291–1060296. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01414j Click here for additional data file. Click here for additional data file.

PubMed Central

Jurss, Jonah W.; Khnayzer, Rony S.; Panetier, Julien A.; El Roz, Karim A.; Nichols, Eva M.

2015-01-01

Mononuclear metalloenzymes in nature can function in cooperation with precisely positioned redox-active organic cofactors in order to carry out multielectron catalysis. Inspired by the finely tuned redox management of these bioinorganic systems, we present the design, synthesis, and experimental and theoretical characterization of a homologous series of cobalt complexes bearing redox-active pyrazines. These donor moieties are locked into key positions within a pentadentate ligand scaffold in order to evaluate the effects of positioning redox non-innocent ligands on hydrogen evolution catalysis. Both metal- and ligand-centered redox features are observed in organic as well as aqueous solutions over a range of pH values, and comparison with analogs bearing redox-inactive zinc(ii) allows for assignments of ligand-based redox events. Varying the geometric placement of redox non-innocent pyrazine donors on isostructural pentadentate ligand platforms results in marked effects on observed cobalt-catalyzed proton reduction activity. Electrocatalytic hydrogen evolution from weak acids in acetonitrile solution, under diffusion-limited conditions, reveals that the pyrazine donor of axial isomer 1-Co behaves as an unproductive electron sink, resulting in high overpotentials for proton reduction, whereas the equatorial pyrazine isomer complex 2-Co is significantly more active for hydrogen generation at lower voltages. Addition of a second equatorial pyrazine in complex 3-Co further minimizes overpotentials required for catalysis. The equatorial derivative 2-Co is also superior to its axial 1-Co congener for electrocatalytic and visible-light photocatalytic hydrogen generation in biologically relevant, neutral pH aqueous media. Density functional theory calculations (B3LYP-D2) indicate that the first reduction of catalyst isomers 1-Co, 2-Co, and 3-Co is largely metal-centered while the second reduction occurs at pyrazine. Taken together, the data establish that proper positioning of non-innocent pyrazine ligands on a single cobalt center is indeed critical for promoting efficient hydrogen catalysis in aqueous media, akin to optimally positioned redox-active cofactors in metalloenzymes. In a broader sense, these findings highlight the significance of electronic structure considerations in the design of effective electron–hole reservoirs for multielectron transformations. PMID:29142725

Effects of Exhaust Gas Recirculation on Performance and Emission Characteristic of SI Engine using Hydrogen and CNG Blends

NASA Astrophysics Data System (ADS)

Nitnaware, Pravin Tukaram; Suryawanshi, Jiwak G.

2018-01-01

This paper shows exhaust gas recirculation (EGR) effects on multi-cylinder bi-fuel SI engine using blends of 0, 5, 10 and 15% hydrogen by energy with CNG. All trials are performed at a speed of 3000, 3500 and 4000 rpm with EGR rate of 0, 5, 10 and 15%, with equal spark timing and injection pressure of 2.6 bar. At specific hydrogen percentage with increase in EGR rate NOx emission reduces drastically and increases with increase in hydrogen addition. Hydrocarbon (HC) and carbon monoxide (CO) emission decreases with increase in speed and hydrogen addition. There is considerable improvement in brake thermal efficiency (BTE) and brake specific energy consumption (BSEC) at 15% EGR rate. At 3000 rpm, 5% EGR rate with 5% hydrogen had shown maximum cylinder pressure. Brake specific fuel consumption (b.s.f.c) increased with increase in EGR rate and decreased with increase in hydrogen addition for all speeds.

Liquid-phase hydrogenation of citral over Pt/SiO{sub 2} catalysts. 2. Hydrogenation of reaction intermediate compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, U.K.; Sysak, M.N.; Vannice, M.A.

2000-04-01

Liquid-phase hydrogenation of the four principal reaction intermediates formed during citral hydrogenation, i.e., nerol, geraniol, citronellal, and citronellol, was studied at 298 and 373 K under 20 atm H{sub 2} at concentrations of 0.5 to 1.0 M in hexane. A decrease in the initial reaction rate as temperature increased from 298 to 373 K was exhibited during the hydrogenation of all four compounds, just as reported earlier for citral; however, the decrease in rate at 373 K was only one-half for citronellal whereas it was orders of magnitude greater for nerol and geraniol. Furthermore, simultaneous hydrogenation of citronellal and geraniolmore » at 298 K resulted in a continuous decrease in the rate of citronellal disappearance in contrast to the nearly constant rate of disappearance observed during hydrogenation of citronellal alone. Competitive hydrogenation of citral with either geraniol or citronellal showed that geraniol hydrogenation to citronellol is kinetically insignificant during citral hydrogenation at 373 K. The initial activity for hydrogenation of the intermediates at 298 K follows the following trend: geraniol > nerol < citronellol < E-citral, citronellal > Z-citral. Based on the relative hydrogenation rates of the intermediate alone versus its hydrogenation in the presence of other reactants, the relative size of the adsorption equilibrium constants for the various organic compounds appears to be as follows: citral > citronellal > geraniol, nerol > citronellol > 3,7-dimethyloctanol. This study indicates that activation of the C{double_bond}O bond should be performed at higher reaction temperatures to maximize selectivity to the unsaturated alcohols.« less

The cosmological density of baryons from observations of 3He+ in the Milky Way.

PubMed

Bania, T M; Rood, Robert T; Balser, Dana S

2002-01-03

Primordial nucleosynthesis after the Big Bang can be constrained by the abundances of the light elements and isotopes 2H, 3He, 4He and 7Li (ref. 1). The standard theory of stellar evolution predicts that 3He is also produced by solar-type stars, so its abundance is of interest not only for cosmology, but also for understanding stellar evolution and the chemical evolution of the Galaxy. The 3He abundance in star-forming (H II) regions agrees with the present value for the local interstellar medium, but seems to be incompatible with the stellar production rates inferred from observations of planetary nebulae, which provide a direct test of stellar evolution theory. Here we develop our earlier observations, which, when combined with recent theoretical developments in our understanding of light-element synthesis and destruction in stars, allow us to determine an upper limit for the primordial abundance of 3He relative to hydrogen: 3He/H = (1.1 +/- 0.2) x 10(-5). The primordial density of all baryons determined from the 3He data is in excellent agreement with the densities calculated from other cosmological probes. The previous conflict is resolved because most solar-mass stars do not produce enough 3He to enrich the interstellar medium significantly.

Microstructural Aspects of Localized Corrosion Behavior of Mg Alloys

NASA Astrophysics Data System (ADS)

Chu, Peng-Wei

Combining high specific strength and unique electrochemical properties, magnesium (Mg) alloys are promising lightweight materials for various applications from automotive, consumer electronics, biomedical body implant, to battery electrodes. Engineering solutions such as coatings have enabled the use of Mg alloys, despite their intrinsic low corrosion resistance. Consequently, the fundamental mechanisms responsible for the unique localized corrosion behavior of bare Mg alloys, the associated abnormal hydrogen evolution response, and the relationships between corrosion behavior and alloy microstructure are still unsolved. This thesis aims to uncover the specificities of Mg corrosion and the roles of alloy chemistry and microstructure. To this end, multiscale site-specific microstructure characterization techniques, including in situ optical microscopy, scanning electron microscopy with focused ion beam milling, and transmission electron microscopy, combined with electrochemical analysis and hydrogen evolution rate monitoring, were performed on pure Mg and selected Mg alloys under free corrosion and anodic polarization, revealing key new information on the propagation mode of localized corrosion and the role of alloy microstructures, thereby confirming or disproving the validity of previously proposed corrosion models. Uniform surface corrosion film on Mg alloys immersed in NaCl solution consisted a bi-layered structure, with a porous Mg(OH)2 outer layer on top of a MgO inner layer. Presence of fine scale precipitates in Mg alloys interacted with the corrosion reaction front, reducing the corrosion rate and surface corrosion film thickness. Protruding hemispherical dome-like corrosion products, accompanied by growing hydrogen bubbles, formed on top of the impurity particles in Mg alloys by deposition of Mg(OH)2 via a microgalvanic effect. Localized corrosion on Mg alloys under both free immersion and anodic polarization was found to be governed by a common mechanism, with the corrosion front propagating laterally a few mum inside the alloy and underneath the surface corrosion film, with finger-like features aligned with (0001) Mg basal planes at the localized corrosion/alloy interface. Rising streams of hydrogen bubbles were found to follow the anodic dissolution of Mg and formation of Mg(OH)2 corrosion products at the propagating localized corrosion fronts. Alloying elements segregation to the grain boundaries showed the ability to stop localized corrosion propagation momentarily. By revealing the microstructure of corrosion features on Mg alloys, a descriptive model was proposed. Relationships between the corrosion behavior and alloy microstructures were also identified. This microscopic information can serve as a guideline for future development of Mg alloys by tailoring the microstructure to achieve proper corrosion responses for applications under different environments.

An ultrafine platinum-cobalt alloy decorated cobalt nanowire array with superb activity toward alkaline hydrogen evolution.

PubMed

Wang, Ziqiang; Ren, Xiang; Luo, Yonglan; Wang, Liang; Cui, Guanwei; Xie, Fengyu; Wang, Hongjing; Xie, Ying; Sun, Xuping

2018-06-22

It is highly desired to design and develop highly efficient electrocatalysts for alkaline hydrogen evolution reactions. Herein, we report the development of ultrafine PtCo alloy nanoparticle decorated one-dimensional Co nanowires grown on Ti mesh (PtCo-Co/TiM). Owing to its favorable composition and structure, the PtCo-Co/TiM can deliver an ultrahigh current density of 46.5 mA cm-2 at an overpotential of 70 mV in 1.0 M KOH, superior to recently reported Pt-based electrocatalysts. This catalyst also provides excellent long-term electrochemical durability with its catalytic activity being maintained for at least 50 h.

Negative impact of surface Ti3+ defects on the photocatalytic hydrogen evolution activity of SrTiO3

NASA Astrophysics Data System (ADS)

Chen, Haidong; Zhang, Feng; Zhang, Weifeng; Du, Yingge; Li, Guoqiang

2018-01-01

Defects play an important and in many cases dominant role in the physical and chemical properties of many oxide materials. In this work, we show that the surface Ti3+ defects in SrTiO3 (STO), characterized by electron paramagnetic resonance and X-ray photoelectron spectroscopy, directly impact the photocatalytic activity of STO. O2 species are found to absorb preferentially on Ti3+ defect sites. Hydrogen evolution under ambient air diminishes with the increase in the concentration of surface Ti3+. This is explained by the over-accumulation of Pt cocatalysts on the site of surface Ti3+ defects after the removal of adsorbed O2.

Graphite oxide and molybdenum disulfide composite for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Niyitanga, Theophile; Jeong, Hae Kyung

2017-10-01

Graphite oxide and molybdenum disulfide (GO-MoS2) composite is prepared through a wet process by using hydrolysis of ammonium tetrathiomolybdate, and it exhibits excellent catalytic activity of the hydrogen evolution reaction (HER) with a low overpotential of -0.47 V, which is almost two and three times lower than those of precursor MoS2 and GO. The high performance of HER of the composite attributes to the reduced GO supporting MoS2, providing a conducting network for fast electron transport from MoS2 to electrodes. The composite also shows high stability after 500 cycles, demonstrating a synergistic effect of MoS2 and GO for efficient HER.

Multifunctional nanostructured electrocatalysts for energy conversion and storage: current status and perspectives.

PubMed

Ghosh, Srabanti; Basu, Rajendra N

2018-06-21

Electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) have attracted widespread attention because of their important role in the application of various energy storage and conversion devices, such as fuel cells, metal-air batteries and water splitting devices. However, the sluggish kinetics of the HER/OER/ORR and their dependency on expensive noble metal catalysts (e.g., Pt) obstruct their large-scale application. Hence, the development of efficient and robust bifunctional or trifunctional electrocatalysts in nanodimension for both oxygen reduction/evolution and hydrogen evolution reactions is highly desired and challenging for their commercialization in renewable energy technologies. This review describes some recent developments in the discovery of bifunctional or trifunctional nanostructured catalysts with improved performances for application in rechargeable metal-air batteries and fuel cells. The role of the electronic structure and surface redox chemistry of nanocatalysts in the improvement of their performance for the ORR/OER/HER under an alkaline medium is highlighted and the associated reaction mechanisms developed in the recent literature are also summarized.

MOF-Derived Ultrathin Cobalt Phosphide Nanosheets as Efficient Bifunctional Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

PubMed Central

Li, Hong; Ke, Fei; Zhu, Junfa

2018-01-01

The development of a highly efficient and stable bifunctional electrocatalyst for water splitting is still a challenging issue in obtaining clean and sustainable chemical fuels. Herein, a novel bifunctional catalyst consisting of 2D transition-metal phosphide nanosheets with abundant reactive sites templated by Co-centered metal−organic framework nanosheets, denoted as CoP-NS/C, has been developed through a facile one-step low-temperature phosphidation process. The as-prepared CoP-NS/C has large specific surface area and ultrathin nanosheets morphology providing rich catalytic active sites. It shows excellent electrocatalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic and alkaline media, with the Tafel slopes of 59 and 64 mV/dec and a current density of 10 mA/cm2 at the overpotentials of 140 and 292 mV, respectively, which are remarkably superior to those of CoP/C, CoP particles, and comparable to those of commercial noble-metal catalysts. In addition, the CoP-NS/C also shows good durability after a long-term test. PMID:29414838

Co-fermentation of sewage sludge with ryegrass for enhancing hydrogen production: Performance evaluation and kinetic analysis.

PubMed

Yang, Guang; Wang, Jianlong

2017-11-01

The low C/N ratio and low carbohydrate content of sewage sludge limit its application for fermentative hydrogen production. In this study, perennial ryegrass was added as the co-substrate into sludge hydrogen fermentation with different mixing ratios for enhancing hydrogen production. The results showed that the highest hydrogen yield of 60mL/g-volatile solids (VS) added was achieved when sludge/perennial ryegrass ratio was 30:70, which was 5 times higher than that from sole sludge. The highest VS removal of 21.8% was also achieved when sludge/perennial ryegrass ratio was 30:70, whereas VS removal from sole sludge was only 0.7%. Meanwhile, the co-fermentation system simultaneously improved hydrogen production efficiency and organics utilization of ryegrass. Kinetic analysis showed that the Cone model fitted hydrogen evolution better than the modified Gompertz model. Furthermore, hydrogen yield and VS removal increased with the increase of dehydrogenase activity. Copyright © 2017 Elsevier Ltd. All rights reserved.

Separating hydrogen and oxygen evolution in alkaline water electrolysis using nickel hydroxide

PubMed Central

Chen, Long; Dong, Xiaoli; Wang, Yonggang; Xia, Yongyao

2016-01-01

Low-cost alkaline water electrolysis has been considered a sustainable approach to producing hydrogen using renewable energy inputs, but preventing hydrogen/oxygen mixing and efficiently using the instable renewable energy are challenging. Here, using nickel hydroxide as a redox mediator, we decouple the hydrogen and oxygen production in alkaline water electrolysis, which overcomes the gas-mixing issue and may increase the use of renewable energy. In this architecture, the hydrogen production occurs at the cathode by water reduction, and the anodic Ni(OH)2 is simultaneously oxidized into NiOOH. The subsequent oxygen production involves a cathodic NiOOH reduction (NiOOH→Ni(OH)2) and an anodic OH− oxidization. Alternatively, the NiOOH formed during hydrogen production can be coupled with a zinc anode to form a NiOOH-Zn battery, and its discharge product (that is, Ni(OH)2) can be used to produce hydrogen again. This architecture brings a potential solution to facilitate renewables-to-hydrogen conversion. PMID:27199009

Hydrogen in tungsten as plasma-facing material

NASA Astrophysics Data System (ADS)

Roth, Joachim; Schmid, Klaus

2011-12-01

Materials facing plasmas in fusion experiments and future reactors are loaded with high fluxes (1020-1024 m-2 s-1) of H, D and T fuel particles at energies ranging from a few eV to keV. In this respect, the evolution of the radioactive T inventory in the first wall, the permeation of T through the armour into the coolant and the thermo-mechanical stability after long-term exposure are key parameters determining the applicability of a first wall material. Tungsten exhibits fast hydrogen diffusion, but an extremely low solubility limit. Due to the fast diffusion of hydrogen and the short ion range, most of the incident ions will quickly reach the surface and recycle into the plasma chamber. For steady-state operation the solute hydrogen for the typical fusion reactor geometry and wall conditions can reach an inventory of about 1 kg. However, in short-pulse operation typical of ITER, solute hydrogen will diffuse out after each pulse and the remaining inventory will consist of hydrogen trapped in lattice defects, such as dislocations, grain boundaries and irradiation-induced traps. In high-flux areas the hydrogen energies are too low to create displacement damage. However, under these conditions the solubility limit will be exceeded within the ion range and the formation of gas bubbles and stress-induced damage occurs. In addition, simultaneous neutron fluxes from the nuclear fusion reaction D(T,n)α will lead to damage in the materials and produce trapping sites for diffusing hydrogen atoms throughout the bulk. The formation and diffusive filling of these different traps will determine the evolution of the retained T inventory. This paper will concentrate on experimental evidence for the influence different trapping sites have on the hydrogen inventory in W as studied in ion beam experiments and low-temperature plasmas. Based on the extensive experimental data, models are validated and applied to estimate the contribution of different traps to the tritium inventory in future fusion reactors.

Early evolution without a tree of life.

PubMed

Martin, William F

2011-06-30

Life is a chemical reaction. Three major transitions in early evolution are considered without recourse to a tree of life. The origin of prokaryotes required a steady supply of energy and electrons, probably in the form of molecular hydrogen stemming from serpentinization. Microbial genome evolution is not a treelike process because of lateral gene transfer and the endosymbiotic origins of organelles. The lack of true intermediates in the prokaryote-to-eukaryote transition has a bioenergetic cause.

Polyethyleneimine functionalized platinum superstructures: enhancing hydrogen evolution performance by morphological and interfacial control† †Electronic supplementary information (ESI) available: Experimental details and additional physical characterization. See DOI: 10.1039/c7sc04109h

PubMed Central

Xu, Guang-Rui; Bai, Juan; Jiang, Jia-Xing

2017-01-01

The electrocatalytic hydrogen evolution reaction (HER) is a highly promising green method for sustainable and efficient hydrogen production. So far, Pt nanocrystals are still the most active electrocatalysts for the HER in acidic media, although a tremendous search for alternatives has been done in the past decade. In this work, we synthesize polyethyleneimine (PEI) functionalized Pt superstructures (Pt-SSs@PEI) with tetragonal, hierarchical, and branched morphologies with a facile wet chemical reduction method. A series of physical characterizations are conducted to investigate the morphology, electronic structure, surface composition, and formation mechanism of Pt-SSs@PEI. Impressively, the as-prepared Pt-SSs@PEI show an unprecedented onset reduction potential (+64.6 mV vs. reversible hydrogen electrode) for the HER in strong acidic media due to the protonation of –NH2 groups in the PEI adlayers on the Pt surface, and they outperform all currently reported HER electrocatalysts. The work highlights a highly effective interface-engineering strategy for improving the electrocatalytic performance of Pt nanocrystals for the HER. PMID:29619188

Mn-doped NiP2 nanosheets as an efficient electrocatalyst for enhanced hydrogen evolution reaction at all pH values

NASA Astrophysics Data System (ADS)

Wang, Xiaodeng; Zhou, Hongpeng; Zhang, Dingke; Pi, Mingyu; Feng, Jiajia; Chen, Shijian

2018-05-01

Developing stable and high-efficiency hydrogen generation electrocatalysts, particularly for the cathode hydrogen evolution reaction (HER), is an urgent challenge in energy conversion technologies. In this work, we have successfully synthesized Mn-doped NiP2 nanosheets on carbon cloth (Mn-NiP2 NSs/CC), which behaves as a higher efficient three dimensional HER electrocatalyst with better stability at all pH values than pure NiP2. Electrochemical tests demonstrate that the catalytic activity of NiP2 is enhanced by Mn doping. In 0.5 M H2SO4, this Mn-NiP2 NSs/CC catalyst drives 10 mA cm-2 at an overpotential of 69 mV, which is 20 mV smaller than pure NiP2. To achieve the same current density, it demands overpotentials of 97 and 107 mV in 1.0 M KOH and phosphate-buffered saline (PBS), respectively. Compared with pure NiP2, higher HER electrocatalytic performance for Mn-NiP2 NSs/CC can be attributed to its lower thermo-neutral hydrogen adsorption free energy, which is supported by density functional theory calculations.

Design of active and stable Co-Mo-S x chalcogels as pH-universal catalyst for the hydrogen evolution reaction

DOE PAGES

Staszak-Jirkovský, Jakub; Malliakas, Christos D.; Lopes, Pietro P.; ...

2015-11-30

Three of the fundamental catalytic limitations that have plagued the electrochemical production of hydrogen for decades still remain: low efficiency, short lifetime of catalysts and a lack of low-cost materials. Here, we address these three challenges by establishing and exploring an intimate functional link between the reactivity and stability of crystalline (CoS 2 and MoS 2) and amorphous (CoS x and MoS x) hydrogen evolution catalysts. We propose that Co 2+ and Mo 4+ centers promote the initial discharge of water (alkaline solutions) or hydronium ions (acid solutions). We establish that although CoS x materials are more active than MoSmore » x they are also less stable, suggesting that the active sites are defects formed after dissolution of Co and Mo cations. Finally, by combining the higher activity of CoS x building blocks with the higher stability of MoS x units into a compact and robust CoMoS x structure, we are able to design a low-cost alternative to noble metal catalysts for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.« less

Hydrogen evolution in [NiFe] hydrogenases and related biomimetic systems: similarities and differences.

PubMed

Das, Ranjita; Neese, Frank; van Gastel, Maurice

2016-09-21

In this work, a detailed quantum chemical study of the mechanism of [Ni(bdt)(dppf)] (Ni(II)L) catalyzed hydrogen formation [A. Gan, T. L. Groy, P. Tarakeshwar, S. K. S. Mazinani, J. Shearer, V. Mujica and A. K. Jones, J. Am. Chem. Soc., 2015, 137, 1109-1115] following an electro-chemical-electro-chemical (ECEC) pathway is reported. The complex exclusively catalyzes the reduction of protons to molecular hydrogen. The calculations suggest that the first one-electron reduction of the [Ni(II)L] catalyst is the rate limiting step of the catalytic cycle and hence, the buildup of detectable reaction intermediates is not expected. The catalytic activity of the [Ni(II)L] complex is facilitated by the flexibility of the ligand system, which allows the ligand framework to adapt to changes in the Ni oxidation state over the course of the reaction. Additionally, a comparison is made with the catalytic activity of [NiFe] hydrogenase. It is argued that the directionality of the reversible hydrogen formation reaction is controlled by the ligand field of the nickel ion and the possibility for side-on (η(2)) binding of H2: if the ligand framework does not allow for η(2) binding of H2, as is the case for [Ni(II)L], the catalyst irreversibly reduces protons. If the ligand field allows η(2) binding of H2, the catalyst can in principle work reversibly. The conditions for η(2) binding are discussed.

Was Ferrocyanide a Prebiotic Reagent?

NASA Technical Reports Server (NTRS)

Keefe, Anthony D.; Miller, Stanley L.

1996-01-01

Hydrogen cyanide is the starting material for a diverse array of prebiotic syntheses, including those of amino acids and purines. Hydrogen cyanide also reacts with ferrous ions to give ferrocyanide, and so it is possible that ferrocyanide was common in the early ocean. This can only be true if the hydrogen cyanide concentration was high enough and the rate of reaction of cyanide with ferrous ions was fast enough. We show experimentally that the rate of formation of ferrocyanide is rapid even at low concentrations of hydrogen cyanide in the pH range 6-8, and therefore an equilibrium calculation is valid. The equilibrium concentrations of ferrocyanide are calculated as a function of hydrogen cyanide concentration, pH and temperature. The steady state concentration of hydrogen cyanide depends on the rate of synthesis by electric discharges and ultraviolet light and the rate of hydrolysis, which depends on pH and temperature. Our conclusions show that ferrocyanide was a major species in the prebiotic ocean only at the highest production rates of hydrogen cyanide in a strongly reducing atmosphere and at temperatures of 0 C or less, although small amounts would have been present at lower hydrogen cyanide production rates. The prebiotic application of ferrocyanide as a source of hydrated electrons, as a photochemical replication process, and in semi-permeable membranes is discussed.

Characterization and reactivity of organic monolayers on gold and platinum surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Chien-Ching

1995-12-06

Purpose is to understand how the mobilization, dielectric, orientation, composition, coverage, and structure of self-assembled organic monolayers on metal surfaces affects the surface reactivities and properties of these films in order to facilitate the construction of desired films. Two model systems were used: tiols at Au and aromatic acids at Pt. Surface analysis methods, including contact angle, electrochemistry, ellipsometry, infrared reflection absorption spectroscopy (IRRAS), and x-ray photospectroscopy, were used to study the self-assembled organic monolayers on Au and Pt. IRRAS, contact angle, and electrochemistry were used to determine the surface pK a of phenylcarboxylic acids and pyridylcarboxylic acids monolayers onmore » Pt. These techniques were also used to determine the orientation of polymethylene chain axis and the carboxylic follow the structural evolution of the chains and end group of the thiolate monolayers during formation. IRRAS was also used to assess the carboxylic acid group in terms of its possible existence as the non-hydrogen-bonded species, the hydrogen-bonded dimeric group, and the hydrogen-bonded polymeric group. These different forms of the end group were also followed vs coverage, as well as the reactivity vs solution pH. IRRAS and contact angle were used to calculate the rate constant of the esterification of carboxylic acid-terminated monolayers on Au.« less

An iron-iron hydrogenase mimic with appended electron reservoir for efficient proton reduction in aqueous media

PubMed Central

Becker, René; Amirjalayer, Saeed; Li, Ping; Woutersen, Sander; Reek, Joost N. H.

2016-01-01

The transition from a fossil-based economy to a hydrogen-based economy requires cheap and abundant, yet stable and efficient, hydrogen production catalysts. Nature shows the potential of iron-based catalysts such as the iron-iron hydrogenase (H2ase) enzyme, which catalyzes hydrogen evolution at rates similar to platinum with low overpotential. However, existing synthetic H2ase mimics generally suffer from low efficiency and oxygen sensitivity and generally operate in organic solvents. We report on a synthetic H2ase mimic that contains a redox-active phosphole ligand as an electron reservoir, a feature that is also crucial for the working of the natural enzyme. Using a combination of (spectro)electrochemistry and time-resolved infrared spectroscopy, we elucidate the unique redox behavior of the catalyst. We find that the electron reservoir actively partakes in the reduction of protons and that its electron-rich redox states are stabilized through ligand protonation. In dilute sulfuric acid, the catalyst has a turnover frequency of 7.0 × 104 s−1 at an overpotential of 0.66 V. This catalyst is tolerant to the presence of oxygen, thereby paving the way for a new generation of synthetic H2ase mimics that combine the benefits of the enzyme with synthetic versatility and improved stability. PMID:26844297

Enhanced Hydrogen Evolution Reactions on Nanostructured Cu2ZnSnS4 (CZTS) Electrocatalyst

NASA Astrophysics Data System (ADS)

Digraskar, Renuka V.; Mulik, Balaji B.; Walke, Pravin S.; Ghule, Anil V.; Sathe, Bhaskar R.

2017-08-01

A novel and facile one-step sonochemical method is used to synthesize Cu2ZnSnS4 (CZTS) nanoparticles (2.6 ± 0.4 nm) as cathode electrocatalyst for hydrogen evolution reactions. The detailed morphology, crystal and surface structure, and composition of the CZTS nanostructures were characterized by high resolution transmission electron microscopy (HR-TEM), Selected area electron diffraction (SAED), X-ray diffraction, Raman spectroscopy, FTIR analysis, Brunauer-Emmett-Teller (BET) surface area measurements, Electron dispersive analysis, X-ray photoelectron spectroscopy respectively. Electrocatalytic abilities of the nanoparticles toward Hydrogen Evolution Reactions (HER) were verified through cyclic voltammograms (CV) and Linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements. It reveals enhanced activity at lower onset potential 300 mV v/s RHE, achieved at exceptionally high current density -130 mA/cm2, which is higher than the existing non-nobel metal based cathodes. Further result exhibits Tafel slope of 85 mV/dec, exchange current density of 882 mA/cm2, excellent stability (> 500 cycles) and lower charge transfer resistance. This sonochemically fabricated CZTSs nanoparticles are leading to significantly reduce cell cost and simplification of preparation process over existing high efficiency Pt and other nobel metal-free cathode electrocatalyst.

White dwarf stars with carbon atmospheres.

PubMed

Dufour, P; Liebert, J; Fontaine, G; Behara, N

2007-11-22

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.

Impact of the hydrogen partial pressure on lactate degradation in a coculture of Desulfovibrio sp. G11 and Methanobrevibacter arboriphilus DH1.

PubMed

Junicke, H; Feldman, H; van Loosdrecht, M C M; Kleerebezem, R

2015-04-01

In this study, the impact of the hydrogen partial pressure on lactate degradation was investigated in a coculture of Desulfovibrio sp. G11 and Methanobrevibacter arboriphilus DH1. To impose a change of the hydrogen partial pressure, formate was added to the reactor. Hydrogen results from the bioconversion of formate besides lactate in the liquid phase. In the presence of a hydrogen-consuming methanogen, this approach allows for a better estimation of low dissolved hydrogen concentrations than under conditions where hydrogen is supplied externally from the gas phase, resulting in a more accurate determination of kinetic parameters. A change of the hydrogen partial pressure from 1,200 to 250 ppm resulted in a threefold increase of the biomass-specific lactate consumption rate. The 50 % inhibition constant of hydrogen on lactate degradation was determined as 0.692 ± 0.064 μM dissolved hydrogen (831 ± 77 ppm hydrogen in the gas phase). Moreover, for the first time, the maximum biomass-specific lactate consumption rate of Desulfovibrio sp. G11 (0.083 ± 0.006 mol-Lac/mol-XG11/h) and the affinity constant for hydrogen uptake of Methanobrevibacter arboriphilus DH1 (0.601 ± 0.022 μM dissolved hydrogen) were determined. Contrary to the widely established view that the biomass-specific growth rate of a methanogenic coculture is determined by the hydrogen-utilizing partner; here, it was found that the hydrogen-producing bacterium determined the biomass-specific growth rate of the coculture grown on lactate and formate.

Subnanometer Molybdenum Sulfide on Carbon Nanotubes as a Highly Active and Stable Electrocatalyst for Hydrogen Evolution Reaction.

PubMed

Li, Ping; Yang, Zhi; Shen, Juanxia; Nie, Huagui; Cai, Qiran; Li, Luhua; Ge, Mengzhan; Gu, Cancan; Chen, Xi'an; Yang, Keqin; Zhang, Lijie; Chen, Ying; Huang, Shaoming

2016-02-10

Electrochemically splitting water for hydrogen evolution reaction (HER) has been viewed as a promising approach to produce renewable and clean hydrogen energy. However, searching for cheap and efficient HER electrocatalysts to replace the currently used Pt-based catalysts remains an urgent task. Herein, we develop a one-step carbon nanotube (CNT) assisted synthesis strategy with CNTs' strong adsorbability to mediate the growth of subnanometer-sized MoS(x) on CNTs. The subnanometer MoS(x)-CNT hybrids achieve a low overpotential of 106 mV at 10 mA cm(-2), a small Tafel slope of 37 mV per decade, and an unprecedentedly high turnover frequency value of 18.84 s(-1) at η = 200 mV among all reported non-Pt catalysts in acidic conditions. The superior performance of the hybrid catalysts benefits from the presence of a higher number of active sites and the abundant exposure of unsaturated S atoms rooted in the subnanometer structure, demonstrating a new class of subnanometer-scale catalysts.

Vibrational spectroscopy reveals the initial steps of biological hydrogen evolution† †Electronic supplementary information (ESI) available: Complementary resonance Raman and infrared spectroscopic data. See DOI: 10.1039/c6sc01098a Click here for additional data file.

PubMed Central

Katz, S.; Noth, J.; Shafaat, H. S.; Happe, T.; Hildebrandt, P.

2016-01-01

[FeFe] hydrogenases are biocatalytic model systems for the exploitation and investigation of catalytic hydrogen evolution. Here, we used vibrational spectroscopic techniques to characterize, in detail, redox transformations of the [FeFe] and [4Fe4S] sub-sites of the catalytic centre (H-cluster) in a monomeric [FeFe] hydrogenase. Through the application of low-temperature resonance Raman spectroscopy, we discovered a novel metastable intermediate that is characterized by an oxidized [FeIFeII] centre and a reduced [4Fe4S]1+ cluster. Based on this unusual configuration, this species is assigned to the first, deprotonated H-cluster intermediate of the [FeFe] hydrogenase catalytic cycle. Providing insights into the sequence of initial reaction steps, the identification of this species represents a key finding towards the mechanistic understanding of biological hydrogen evolution. PMID:28451119

Ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles for enhanced electrocatalytic hydrogen evolution.

PubMed

Xu, You; Li, Yinghao; Yin, Shuli; Yu, Hongjie; Xue, Hairong; Li, Xiaonian; Wang, Hongjing; Wang, Liang

2018-06-01

Design of highly active and cost-effective electrocatalysts is very important for the generation of hydrogen by electrochemical water-splitting. Herein, we report the fabrication of ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles (CoRu@NCs) and demonstrate their promising feasibility for efficiently catalyzing the hydrogen evolution reaction (HER) over a wide pH range. The resultant CoRu@NC nanohybrids possess an alloy-carbon core-shell structure with encapsulated low-ruthenium-content CoRu bimetallic alloy nanoparticles (10-30 nm) as the core and ultrathin nitrogen-doped graphitized carbon layers (2-6 layers) as the shell. Remarkably, the optimized catalyst (CoRu@NC-2 sample) with a Ru content as low as 2.04 wt% shows superior catalytic activity and excellent durability for HER in acidic, neutral, and alkaline conditions. This work offers a new method for the design and synthesis of non-platium-based electrocatalysts for HER in all-pH.

A porous proton-relaying metal-organic framework material that accelerates electrochemical hydrogen evolution

DOE PAGES

Hod, Idan; Deria, Pravas; Bury, Wojciech; ...

2015-09-14

The availability of efficient hydrogen evolution reaction (HER) catalysts is of high importance for solar fuel technologies aimed at reducing future carbon emissions. Even though Pt electrodes are excellent HER electrocatalysts, commercialization of large-scale hydrogen production technology requires finding an equally efficient, low-cost, earth-abundant alternative. Here, high porosity, metal-organic framework (MOF) films have been used as scaffolds for the deposition of a Ni-S electrocatalyst. Compared with an MOF-free Ni-S, the resulting hybrid materials exhibit significantly enhanced performance for HER from aqueous acid, decreasing the kinetic overpotential by more than 200 mV at a benchmark current density of 10 mA cm −2. In conclusion,more » although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst.« less

2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions.

PubMed

Lu, Qipeng; Yu, Yifu; Ma, Qinglang; Chen, Bo; Zhang, Hua

2016-03-09

Hydrogen (H2) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H2. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble-metal-based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot-injection method, the heating-up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles for enhanced electrocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Xu, You; Li, Yinghao; Yin, Shuli; Yu, Hongjie; Xue, Hairong; Li, Xiaonian; Wang, Hongjing; Wang, Liang

2018-06-01

Design of highly active and cost-effective electrocatalysts is very important for the generation of hydrogen by electrochemical water-splitting. Herein, we report the fabrication of ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles (CoRu@NCs) and demonstrate their promising feasibility for efficiently catalyzing the hydrogen evolution reaction (HER) over a wide pH range. The resultant CoRu@NC nanohybrids possess an alloy–carbon core–shell structure with encapsulated low-ruthenium-content CoRu bimetallic alloy nanoparticles (10–30 nm) as the core and ultrathin nitrogen-doped graphitized carbon layers (2–6 layers) as the shell. Remarkably, the optimized catalyst (CoRu@NC-2 sample) with a Ru content as low as 2.04 wt% shows superior catalytic activity and excellent durability for HER in acidic, neutral, and alkaline conditions. This work offers a new method for the design and synthesis of non-platium-based electrocatalysts for HER in all-pH.

Rationally Designed Hierarchically Structured Tungsten Nitride and Nitrogen-Rich Graphene-Like Carbon Nanocomposite as Efficient Hydrogen Evolution Electrocatalyst.

PubMed

Zhu, Yanping; Chen, Gao; Zhong, Yijun; Zhou, Wei; Shao, Zongping

2018-02-01

Practical application of hydrogen production from water splitting relies strongly on the development of low-cost and high-performance electrocatalysts for hydrogen evolution reaction (HER). The previous researches mainly focused on transition metal nitrides as HER catalysts due to their electrical conductivity and corrosion stability under acidic electrolyte, while tungsten nitrides have reported poorer activity for HER. Here the activity of tungsten nitride is optimized through rational design of a tungsten nitride-carbon composite. More specifically, tungsten nitride (WN x ) coupled with nitrogen-rich porous graphene-like carbon is prepared through a low-cost ion-exchange/molten-salt strategy. Benefiting from the nanostructured WN x , the highly porous structure and rich nitrogen dopant (9.5 at%) of the carbon phase with high percentage of pyridinic-N (54.3%), and more importantly, their synergistic effect, the composite catalyst displays remarkably high catalytic activity while maintaining good stability. This work highlights a powerful way to design more efficient metal-carbon composites catalysts for HER.

Self-assembly synthesis of precious-metal-free 3D ZnO nano/micro spheres with excellent photocatalytic hydrogen production from solar water splitting

NASA Astrophysics Data System (ADS)

Guo, Si-yao; Zhao, Tie-jun; Jin, Zu-quan; Wan, Xiao-mei; Wang, Peng-gang; Shang, Jun; Han, Song

2015-10-01

A simple and straightforward solution growth routine is developed to prepare microporous 3D nano/micro ZnO microsphere with a large BET surface area of 288 m2 g-1 at room temperature. The formation mechanism of the hierarchical 3D nano/micro ZnO microsphere and its corresponding hydrogen evolution performance has been deeply discussed. In particular, this novel hierarchical 3D ZnO microspheres performs undiminished hydrogen evolution for at least 24 h under simulated solar light illumination, even under the condition of no precious metal as cocatalyst. Since the complex production process of photocatalysts and high cost of precious metal cocatalyst remains a major constraint that hinders the application of solar water splitting, this 3D nano/micro ZnO microspheres could be expected to be applicable in the precious-metal-free solar water splitting system due to its merits of low cost, simple procedure and high catalytic activity.

A porous proton-relaying metal-organic framework material that accelerates electrochemical hydrogen evolution

PubMed Central

Hod, Idan; Deria, Pravas; Bury, Wojciech; Mondloch, Joseph E.; Kung, Chung-Wei; So, Monica; Sampson, Matthew D.; Peters, Aaron W.; Kubiak, Cliff P.; Farha, Omar K.; Hupp, Joseph T.

2015-01-01

The availability of efficient hydrogen evolution reaction (HER) catalysts is of high importance for solar fuel technologies aimed at reducing future carbon emissions. Even though Pt electrodes are excellent HER electrocatalysts, commercialization of large-scale hydrogen production technology requires finding an equally efficient, low-cost, earth-abundant alternative. Here, high porosity, metal-organic framework (MOF) films have been used as scaffolds for the deposition of a Ni-S electrocatalyst. Compared with an MOF-free Ni-S, the resulting hybrid materials exhibit significantly enhanced performance for HER from aqueous acid, decreasing the kinetic overpotential by more than 200 mV at a benchmark current density of 10 mA cm−2. Although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst. PMID:26365764

On the Role of Dissolved Gases in the Atmosphere Retention of Low-mass Low-density Planets

NASA Astrophysics Data System (ADS)

Chachan, Yayaati; Stevenson, David J.

2018-02-01

Low-mass low-density planets discovered by Kepler in the super-Earth mass regime typically have large radii for their inferred masses, implying the presence of H2–He atmospheres. These planets are vulnerable to atmospheric mass loss due to heating by the parent star’s XUV flux. Models coupling atmospheric mass loss with thermal evolution predicted a bimodal distribution of planetary radii, which has gained observational support. However, a key component that has been ignored in previous studies is the dissolution of these gases into the molten core of rock and iron that constitute most of their mass. Such planets have high temperatures (>2000 K) and pressures (∼kbars) at the core-envelope boundary, ensuring a molten surface and a subsurface reservoir of hydrogen that can be 5–10 times larger than the atmosphere. This study bridges this gap by coupling the thermal evolution of the planet and the mass loss of the atmosphere with the thermodynamic equilibrium between the dissolved H2 and the atmospheric H2 (Henry’s law). Dissolution in the interior allows a planet to build a larger hydrogen repository during the planet formation stage. We show that the dissolved hydrogen outgasses to buffer atmospheric mass loss. The slow cooling of the planet also leads to outgassing because solubility decreases with decreasing temperature. Dissolution of hydrogen in the interior therefore increases the atmosphere retention ability of super-Earths. The study highlights the importance of including the temperature- and pressure-dependent solubility of gases in magma oceans and coupling outgassing to planetary evolution models.

Thermochemical hydrogen production via a cycle using barium and sulfur - Reaction between barium sulfide and water

NASA Technical Reports Server (NTRS)

Ota, K.; Conger, W. L.

1977-01-01

The reaction between barium sulfide and water, a reaction found in several sulfur based thermochemical cycles, was investigated kinetically at 653-866 C. Gaseous products were hydrogen and hydrogen sulfide. The rate determining step for hydrogen formation was a surface reaction between barium sulfide and water. An expression was derived for the rate of hydrogen formation.

The Evolution of Remnant Ice at the Lunar South Pole from Diviner Surface Temperature Results

NASA Technical Reports Server (NTRS)

Elphic, Richard C.; Siegler, Mathew; Paige, David; Teodoro, Luis Filipe; Vasavada, Ashwin R.

2010-01-01

The Diviner lunar radiometer instrument aboard the Lunar Reconnaissance Orbiter mission has revealed large areas of lunar polar terrain with surface temperatures well below 100K. At these temperatures, the sublimation rate of water ice is well below 1 mm per billion years. In contrast, the loss rate at 120K is more than 1 meter of ice in that time consequently volatiles delivered to the coldest locations can be trapped for over 1 Ga, but will be quickly lost from warmer locales. Here we investigate the loss or retention of a layer of ice-bearing regolith at the lunar south poe, assuming contemporary surface temperature conditions and no other loss processes. We use an analytic solution for the one-dimensional diffusion equation of water ice, assuming an isothermal regolith with pore space comparable to mean grain size, 75 micrometers. Only the top meter of soil is assumed to be ice-bearing. We can then calculate the history of ice content with time based on local temperature, and predict what the epithermal neutron output would be in the presence of such a concentration of hydrogen. We compare the present, observed distribution of hydrogen with what one would expect from the temperature-dependent loss or retention of ice for various times since emplacement.