Thermochemical Properties of the Lattice Oxygen in W,Mn-Containing Mixed Oxide Catalysts for the Oxidative Coupling of Methane

NASA Astrophysics Data System (ADS)

Lomonosov, V. I.; Gordienko, Yu. A.; Sinev, M. Yu.; Rogov, V. A.; Sadykov, V. A.

2018-03-01

Mixed NaWMn/SiO2 oxide, samples containing individual components (Na, W, Mn) and their double combinations (Na-W, Na-Mn, W-Mn) supported on silica were studied by temperature programmed reduction (TPR) and desorption (TPD), and heat flow calorimetry during their reoxidation with molecular oxygen in pulse mode. The NaWMn/SiO2 mixed oxide was shown to contain two different types of reactive lattice oxygen. The weakly-bonded oxygen can be reversibly released from the oxide in a flow of inert gas in the temperature range of 575‒900°C, while the strongly-bonded oxygen can be removed during the reduction of the sample with hydrogen at 700-900°C. The measured thermal effect of oxygen consumption for these two oxygen forms are 185 and 350 kJ/mol, respectively. The amount of oxygen removed at reduction ( 443 μmol/g) considerably exceeded the amount desorbed in an inert gas flow ( 56 μmol/g). The obtained results suggest that the reversible oxygen desorption is due to the redox process in which manganese ions are involved, while during the temperature programmed reduction, mainly oxygen bonded with tungsten is removed.

Ordered WO3-x nanorods: facile synthesis and their electrochemical properties for aluminum-ion batteries.

PubMed

Tu, Jiguo; Lei, Haiping; Yu, Zhijing; Jiao, Shuqiang

2018-02-01

In this work, we have synthesized ordered WO 3 nanorods via a facile hydrothermal process. And the series WO 3-x nanorods with oxygen vacancies are obtained via a subsequent thermal reduction process. The formation mechanisms of WO 3-x nanorods with different oxygen vacancies are proposed. And the electrochemical results reveal that the WO 3-x nanorods exhibit the improved specific capacity due to the oxygen vacancies caused by the thermal reduction. More importantly, the reaction mechanism of the WO 3-x nanorods as cathodes for aluminum-ion batteries has been proved.

Oxygen Extraction from Minerals

NASA Technical Reports Server (NTRS)

Muscatello, Tony

2017-01-01

Oxygen, whether used as part of rocket bipropellant or for astronaut life support, is a key consumable for space exploration and commercialization. In Situ Resource Utilization (ISRU) has been proposed many times as a method for making space exploration more cost effective and sustainable. On planetary and asteroid surfaces the presence of minerals in the regolith that contain oxygen is very common, making them a potential oxygen resource. The majority of research and development for oxygen extraction from minerals has been for lunar regolith although this work would generally be applicable to regolith at other locations in space. This presentation will briefly survey the major methods investigated for oxygen extraction from regolith with a focus on the current status of those methods and possible future development pathways. The major oxygen production methods are (1) extraction from lunar ilmenite (FeTiO3) with either hydrogen or carbon monoxide, (2) carbothermal reduction of iron oxides and silicates with methane, and (3) molten regolith electrolysis (MRE) of silicates. Methods (1) and (2) have also been investigated in a two-step process using CO reduction and carbon deposition followed by carbothermal reduction. All three processes have byproducts that could also be used as resources. Hydrogen or carbon monoxide reduction produce iron metal in small amounts that could potentially be used as construction material. Carbothermal reduction also makes iron metal along with silicon metal and a glass with possible applications. MRE produces iron, silicon, aluminum, titanium, and glass, with higher silicon yields than carbothermal reduction. On Mars and possibly on some moons and asteroids, water is present in the form of mineral hydrates, hydroxyl (-OH) groups on minerals, andor water adsorbed on mineral surfaces. Heating of the minerals can liberate the water which can be electrolyzed to provide a source of oxygen as well. The chemistry of these processes, some key development and demonstration projects, the challenges remaining to be overcome, and possible future directions will be discussed with a goal of increased understanding of these important ISRU technologies and their potential applications to space exploration and settlement.

The mechanisms of oxygen reduction and evolution reactions in nonaqueous lithium-oxygen batteries.

PubMed

Cao, Ruiguo; Walter, Eric D; Xu, Wu; Nasybulin, Eduard N; Bhattacharya, Priyanka; Bowden, Mark E; Engelhard, Mark H; Zhang, Ji-Guang

2014-09-01

A fundamental understanding of the mechanisms of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in nonaqueous lithium-oxygen (Li-O2) batteries is essential for the further development of these batteries. In this work, we systematically investigate the mechanisms of the ORR/OER reactions in nonaqueous Li-O2 batteries by using electron paramagnetic resonance (EPR) spectroscopy, using 5,5-dimethyl-pyrroline N-oxide as a spin trap. The study provides direct verification of the formation of the superoxide radical anion (O2(˙-)) as an intermediate in the ORR during the discharge process, while no O2(˙-) was detected in the OER during the charge process. These findings provide insight into, and an understanding of, the fundamental reaction mechanisms involving oxygen and guide the further development of this field. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of the electrocatalytic oxygen reduction and evolution reactions in lithium–oxygen batteries

DOE PAGES

Zheng, Dong; Zhang, Xuran; Qu, Deyu; ...

2015-04-21

Oxygen reduction and oxygen evolution reactions were examined on graphite electrodes with different crystal orientations. The kinetics for the redox couple O 2/O 2 •- are very fast, therefore no catalyst seems necessary to assist the charge transfer process. Apparently, the main source of the overpotential for the O 2 reduction reaction is from mass diffusion. Li 2O 2 becomes soluble in non-aqueous electrolytes in the presence of the tetraethylammonium tetrafluoroborate additive. The soluble B-O 2 2- ions can be oxidized electro-catalytically. The edge orientation of graphite demonstrates superior catalytic activity for the oxidation over basal orientation. The findings revealmore » an opportunity for recharging Li-air batteries efficiently and a new strategy of developing the catalyst for oxygen evolution reaction.« less

NASA Space Engineering Research Center for Utilization of Local Planetary Resources

NASA Technical Reports Server (NTRS)

Ramohalli, Kumar; Lewis, John S.

1991-01-01

In the processing of propellants, volatiles, and metals subject area, the following topics are discussed: reduction of lunar regolith; reduction of carbon dioxide; and reduction of carbonaceous materials. Other areas addressed include: (1) production of structural and refractory materials; (2) resource discovery and characterization; (3) system automation and optimization; and (4) database development. The majority of these topics are discussed with respect to the development of lunar and mars bases. Some main topics of interest include: asteroid resources, lunar resources, mars resources, materials processing, construction materials, propellant production, oxygen production, and space-based oxygen production plants.

Oxygen production processes on the Moon: An overview

NASA Technical Reports Server (NTRS)

Taylor, Lawrence A.; Carrier, W. David, III

1991-01-01

The production of oxygen on the Moon utilizing indigenous material is paramount to a successful lunar colonization. Several processes were put forth to accomplish this. The lunar liquid oxygen (LLOX) generation schemes which have received the most study to date are those involving: (1) the reduction of ilmenite (FeTiO3) by H2, C, CO, CH4, CO-Cl2 plasma; (2) magma electrolysis, both unadulterated and fluoride-fluxed, and (3) several others, including carbo-chlorination, HF acid leaching, fluorine extraction, magma oxidation, and vapor pyrolysis. The H2 reduction of ilmenite and magma electrolysis processes have received the most study to date. At this stage of development, they both appear feasible schemes with various pros and cons. However, all processes should be addressed at least at the onset of the considerations. It is ultimatley the energy requirements of the entire process, including the acquisition of feedstock, which will determine the mode of oxygen productions. There is an obvious need for considerably more experimentation and study. Some of these requisite studies are in progress, and several of the most studied and feasible processes for winning oxygen from lunar materials are reviewed.

The Development of Models for Carbon Dioxide Reduction Technologies for Spacecraft Air Revitalization

NASA Technical Reports Server (NTRS)

Swickrath, Michael J.; Anderson, Molly

2012-01-01

Through the respiration process, humans consume oxygen (O2) while producing carbon dioxide (CO2) and water (H2O) as byproducts. For long term space exploration, CO2 concentration in the atmosphere must be managed to prevent hypercapnia. Moreover, CO2 can be used as a source of oxygen through chemical reduction serving to minimize the amount of oxygen required at launch. Reduction can be achieved through a number of techniques. NASA is currently exploring the Sabatier reaction, the Bosch reaction, and co- electrolysis of CO2 and H2O for this process. Proof-of-concept experiments and prototype units for all three processes have proven capable of returning useful commodities for space exploration. All three techniques have demonstrated the capacity to reduce CO2 in the laboratory, yet there is interest in understanding how all three techniques would perform at a system level within a spacecraft. Consequently, there is an impetus to develop predictive models for these processes that can be readily rescaled and integrated into larger system models. Such analysis tools provide the ability to evaluate each technique on a comparable basis with respect to processing rates. This manuscript describes the current models for the carbon dioxide reduction processes under parallel developmental efforts. Comparison to experimental data is provided were available for verification purposes.

Oxidation-reduction processes in ground water at Naval Weapons Industrial Reserve Plant, Dallas, Texas

USGS Publications Warehouse

Jones, S.A.; Braun, Christopher L.; Lee, Roger W.

2003-01-01

Concentrations of trichloroethene in ground water at the Naval Weapons Industrial Reserve Plant in Dallas, Texas, indicate three source areas of chlorinated solvents?building 1, building 6, and an off-site source west of the facility. The presence of daughter products of reductive dechlorination of trichloroethene, which were not used at the facility, south and southwest of the source areas are evidence that reductive dechlorination is occurring. In places south of the source areas, dissolved oxygen concentrations indicated that reduction of oxygen could be the dominant process, particularly south of building 6; but elevated dissolved oxygen concentrations south of building 6 might be caused by a leaking water or sewer pipe. The nitrite data indicate that denitrification is occurring in places; however, dissolved hydrogen concentrations indicate that iron reduction is the dominant process south of building 6. The distributions of ferrous iron indicate that iron reduction is occurring in places south-southwest of buildings 6 and 1; dissolved hydrogen concentrations generally support the interpretation that iron reduction is the dominant process in those places. The generally low concentrations of sulfide indicate that sulfate reduction is not a key process in most sampled areas, an interpretation that is supported by dissolved hydrogen concentrations. Ferrous iron and dissolved hydrogen concentrations indicate that ferric iron reduction is the primary oxidation-reduction process. Application of mean first-order decay rates in iron-reducing conditions for trichloroethene, dichloroethene, and vinyl chloride yielded half-lives for those solvents of 231, 347, and 2.67 days, respectively. Decay rates, and thus half-lives, at the facility are expected to be similar to those computed. A weighted scoring method to indicate sites where reductive dechlorination might be likely to occur indicated strong evidence for anaerobic biodegradation of chlorinated solvents at six sites. In general, scores were highest for samples collected on the northeast side of the facility.

Production of oxygen from lunar ilmenite

NASA Technical Reports Server (NTRS)

Zhao, Y.; Shadman, F.

1990-01-01

The following subjects are addressed: (1) the mechanism and kinetics of carbothermal reduction of simulated lunar ilmenite using carbon and, particularly, CO as reducing agents; (2) the determination of the rate-limiting steps; (3) the investigation of the effect of impurities, particularly magnesium; (4) the search for catalysts suitable for enhancement of the rate-limiting step; (5) the comparison of the kinetics of carbothermal reduction with those of hydrogen reduction; (6) the study of the combined use of CO and hydrogen as products of gasification of carbonaceous solids; (7) the development of reduction methods based on the use of waste carbonaceous compounds for the process; (8) the development of a carbothermal reaction path that utilizes gasification of carbonaceous solids to reducing gaseous species (hydrocarbons and carbon monoxide) to facilitate the reduction reaction kinetics and make the process more flexible in using various forms of carbonaceous feeds; (9) the development of advanced gas separation techniques, including the use of high-temperature ceramic membranes; (10) the development of an optimum process flow sheet for carbothermal reduction, and comparison of this process with the hydrogen reduction scheme, as well as a general comparison with other leading oxygen production schemes; and (11) the use of new and advanced material processing and separation techniques.

Effects of dissolved oxygen on performance and microbial community structure in a micro-aerobic hydrolysis sludge in situ reduction process.

PubMed

Niu, Tianhao; Zhou, Zhen; Shen, Xuelian; Qiao, Weimin; Jiang, Lu-Man; Pan, Wei; Zhou, Jijun

2016-03-01

A sludge process reduction activated sludge (SPRAS), with a sludge process reduction module composed of a micro-aerobic tank and a settler positioned before conventional activated sludge process, showed good performance of pollutant removal and sludge reduction. Two SPRAS systems were operated to investigate effects of micro-aeration on sludge reduction performance and microbial community structure. When dissolved oxygen (DO) concentration in the micro-aerobic tank decreased from 2.5 (SPH) to 0.5 (SPL) mg/L, the sludge reduction efficiency increased from 42.9% to 68.3%. Compared to SPH, activated sludge in SPL showed higher contents of extracellular polymeric substances and dissolved organic matter. Destabilization of floc structure in the settler, and cell lysis in the sludge process reduction module were two major reasons for sludge reduction. Illumina-MiSeq sequencing showed that microbial diversity decreased under high DO concentration. Proteobacteria, Bacteroidetes and Chloroflexi were the most abundant phyla in the SPRAS. Specific comparisons down to the class and genus level showed that fermentative, predatory and slow-growing bacteria in SPL community were more abundant than in SPH. The results revealed that micro-aeration in the SPRAS improved hydrolysis efficiency and enriched fermentative and predatory bacteria responsible for sludge reduction. Copyright © 2016 Elsevier Ltd. All rights reserved.

Bioinspired Electrocatalysis of Oxygen Reduction Reaction in Fuel Cells Using Molecular Catalysts.

PubMed

Zion, Noam; Friedman, Ariel; Levy, Naomi; Elbaz, Lior

2018-04-23

One of the most important chemical reactions for renewable energy technologies such as fuel cells and metal-air batteries today is oxygen reduction. Due to the relatively sluggish reaction kinetics, catalysts are necessary to generate high power output. The most common catalyst for this reaction is platinum, but its scarcity and derived high price have raised the search for abundant nonprecious metal catalysts. Inspired from enzymatic processes which are known to catalyze oxygen reduction reaction efficiently, employing transition metal complexes as their catalytic centers, many are working on the development of bioinspired and biomimetic catalysts of this class. This research news article gives a glimpse of the recent progress on the development of bioinspired molecular catalyst for oxygen reduction, highlighting the importance of the molecular structure of the catalysts, from advancements in porphyrins and phthalocyanines to the most recent work on corroles, and 3D networks such as metal-organic frameworks and polymeric networks, all with nonpyrolyzed, well-defined molecular catalysts for oxygen reduction reaction. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon supported MnO2-CoFe2O4 with enhanced electrocatalytic activity for oxygen reduction and oxygen evolution

NASA Astrophysics Data System (ADS)

Wang, Ying; Liu, Qing; Hu, Tianjun; Zhang, Limin; Deng, Youquan

2017-05-01

The catalyst MnO2-CoFe2O4/C was firstly synthesized via a two-step process and applied as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media. The composite exhibits better bifunctional activity than CoFe2O4/C and MnO2/C. Moreover, superior durability and high methanol tolerance in alkaline media outperforms the commercial Pt/C electrocatalyst, which signifying its excellent potential for applications in metal-air batteries and alkaline fuel cells.

In-Situ Formation of Cobalt-Phosphate Oxygen-Evolving Complex-Anchored Reduced Graphene Oxide Nanosheets for Oxygen Reduction Reaction

PubMed Central

Zhao, Zhi-Gang; Zhang, Jing; Yuan, Yinyin; Lv, Hong; Tian, Yuyu; Wu, Dan; Li, Qing-Wen

2013-01-01

Oxygen conversion process between O2 and H2O by means of electrochemistry or photochemistry has lately received a great deal of attention. Cobalt-phosphate (Co-Pi) catalyst is a new type of cost-effective artificial oxygen-evolving complex (OEC) with amorphous features during photosynthesis. However, can such Co-Pi OEC also act as oxygen reduction reaction (ORR) catalyst in electrochemical processes? The question remains unanswered. Here for the first time we demonstrate that Co-Pi OEC does be rather active for the ORR. Particularly, Co-Pi OEC anchoring on reduced graphite oxide (rGO) nanosheet is shown to possess dramatically improved electrocatalytic activities. Differing from the generally accepted role of rGO as an “electron reservoir”, we suggest that rGO serves as “peroxide cleaner” in enhancing the electrocatalytic behaviors. The present study may bridge the gap between photochemistry and electrochemistry towards oxygen conversion. PMID:23877331

Surface Modification of Boron-Doped Diamond with Microcrystalline Copper Phthalocyanine: Oxygen Reduction Catalysis.

PubMed

Gan, Patrick; Foord, John S; Compton, Richard G

2015-10-01

Surface modification of boron-doped diamond (BDD) with copper phthalocyanine was achieved using a simple and convenient dropcast deposition, giving rise to a microcrystalline structure. Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution. A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD. Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide. The lack of a further conversion of the peroxide was attributed to its rapid diffusion away from the triple phase boundary at which the reaction is expected to exclusively occur.

Preventing Corrosion by Controlling Cathodic Reaction Kinetics

DTIC Science & Technology

2016-03-25

electrochemical reaction rates of processes that drive corrosion, e.g. the oxygen reduction reaction (ORR). To this end, we have used reactive...elements on the kinetics of oxygen reduction reaction catalyzed on titanium oxide in order to develop new approaches for controlling galvanic corrosion... consumption of anions in reactions with metal cations can deplete the electrolyte. However, in the atmospheric electrolyte, the electrolyte

The Development of Models for Carbon Dioxide Reduction Technologies for Spacecraft Air Revitalization

NASA Technical Reports Server (NTRS)

Swickrath, Michael J.; Anderson, Molly

2011-01-01

Through the respiration process, humans consume oxygen (O2) while producing carbon dioxide (CO2) and water (H2O) as byproducts. For long term space exploration, CO2 concentration in the atmosphere must be managed to prevent hypercapnia. Moreover, CO2 can be used as a source of oxygen through chemical reduction serving to minimize the amount of oxygen required at launch. Reduction can be achieved through a number of techniques. The National Aeronautics and Space Administration (NASA) is currently exploring the Sabatier reaction, the Bosch reaction, and co-electrolysis of CO2 and H2O for this process. Proof-of-concept experiments and prototype units for all three processes have proven capable of returning useful commodities for space exploration. While all three techniques have demonstrated the capacity to reduce CO2 in the laboratory, there is interest in understanding how all three techniques would perform at a system-level within a spacecraft. Consequently, there is an impetus to develop predictive models for these processes that can be readily re-scaled and integrated into larger system models. Such analysis tools provide the ability to evaluate each technique on a comparable basis with respect to processing rates. This manuscript describes the current models for the carbon dioxide reduction processes under parallel developmental e orts. Comparison to experimental data is provided were available for veri cation purposes.

Operando Raman Micro Spectroscopy of Polymer Electrolyte Fuel Cells

DTIC Science & Technology

2016-01-16

understanding of the processes such as oxygen reduc- tion reaction (ORR), carbon corrosion, and catalysis process of ORR in PEMFCs catalyzed by Pt or...Journal of Membrane Science, 392, 88 (2012). 46. F. Jaouen, F. Charreteur, and J. P. Dodelet, “Fe-based catalysts for oxygen reduction in PEMFCs

A Critical Look at the Combined Use of Sulfur and Oxygen Isotopes to Study Microbial Metabolisms in Methane-Rich Environments

PubMed Central

Antler, Gilad; Pellerin, André

2018-01-01

Separating the contributions of anaerobic oxidation of methane and organoclastic sulfate reduction in the overall sedimentary sulfur cycle of marine sediments has benefited from advances in isotope biogeochemistry. Particularly, the coupling of sulfur and oxygen isotopes measured in the residual sulfate pool (δ18OSO4 vs. δ34SSO4). Yet, some important questions remain. Recent works have observed patterns that are inconsistent with previous interpretations. We differentiate the contributions of oxygen and sulfur isotopes to separating the anaerobic oxidation of methane and organoclastic sulfate reduction into three phases; first evidence from conventional high methane vs. low methane sites suggests a clear relationship between oxygen and sulfur isotopes in porewater and the metabolic process taking place. Second, evidence from pure cultures and organic matter rich sites with low levels of methane suggest the signatures of both processes overlap and cannot be differentiated. Third, we take a critical look at the use of oxygen and sulfur isotopes to differentiate metabolic processes (anaerobic oxidation of methane vs. organoclastic sulfate reduction). We identify that it is essential to develop a better understanding of the oxygen kinetic isotope effect, the degree of isotope exchange with sulfur intermediates as well as establishing their relationships with the cell-specific metabolic rates if we are to develop this proxy into a reliable tool to study the sulfur cycle in marine sediments and the geological record. PMID:29681890

Reaction engineering for materials processing in space: Reduction of ilmenite by hydrogen and carbon monoxide

NASA Technical Reports Server (NTRS)

Zhao, Y.; Shadman, F.

1991-01-01

Oxygen is a consumable material which needs to be produced continuously in most space missions. Its use for propulsion as well as life support makes oxygen one of the largest volume chemicals to be produced in space. Production of oxygen from lunar materials is of particular interest and is very attractive possibility. The kinetics and mechanism of reduction of ilmenite by carbon monoxide and hydrogen at 800 to 1100 C were investigated. The temporal profiles of conversion for carbon monoxide have a sigmoidal shape and indicate the presence of three different stages (induction, acceleration, and deceleration) during the reduction reaction. The apparent activation energy decreases from 18 kcal/mole at 10 percent conversion to 10 kcal/mole at 50 percent conversion. The reaction is first order with respect to carbon monoxide under the experimental conditions studied. Both SEM and EDX analysis show that the diffusion of Fe product away from the reaction front and through the TiO2 phase, followed by the nucleation and growth of a separate Fe phase are important steps affecting the process kinetics. The results from hydrogen reduction show that the mechanism of ilmenite reduction by hydrogen is similar to that by carbon monoxide. However, the titanium dioxide can be further reduced by hydrogen at 800 to 1000 C. The detailed comparison and theoretical modeling of both reduction processes is presented.

Study of Oxygen Diffusion in Reduced LiNbO3 Crystals

NASA Astrophysics Data System (ADS)

Yatsenko, A. V.; Pritulenko, A. S.; Yagupov, S. V.; Sugak, D. Yu.; Sol'skii, I. M.

2018-03-01

Using the method of impedance spectroscopy and optical density measurements, the diffusion of oxygen in single crystals of lithium niobate of the congruent composition after the reductive thermochemical processing is studied. The parameters describing the diffusion of oxygen in the temperature range 493-693 K are established.

Evaluation of a Stirling Solar Dynamic System for Lunar Oxygen Production

NASA Technical Reports Server (NTRS)

Colozza, Anthony J.; Wong, Wayne A.

2006-01-01

An evaluation of a solar concentrator-based system for producing oxygen from the lunar regolith was performed. The system utilizes a solar concentrator mirror to provide thermal energy for the oxygen production process as well as thermal energy to power a Stirling heat engine for the production of electricity. The electricity produced is utilized to operate the equipment needed in the oxygen production process. The oxygen production method utilized in the analysis was the hydrogen reduction of ilmenite. Utilizing this method of oxygen production a baseline system design was produced. This baseline system had an oxygen production rate of 0.6 kg/hr with a concentrator mirror size of 5 m. Variations were performed on the baseline design to show how changes in the system size and process rate effected the oxygen production rate.

The impact of oxygen on the final alcohol content of wine fermented by a mixed starter culture.

PubMed

Morales, Pilar; Rojas, Virginia; Quirós, Manuel; Gonzalez, Ramon

2015-05-01

We have developed a wine fermentation procedure that takes advantage of the metabolic features of a previously characterized Metschnikowia pulcherrima strain in order to reduce ethanol production. It involves the use of M. pulcherrima/Saccharomyces cerevisiae mixed cultures, controlled oxygenation conditions during the first 48 h of fermentation, and anaerobic conditions thereafter. The influence of different oxygenation regimes and initial inoculum composition on yeast physiology and final ethanol content was studied. The impact of oxygenation on yeast physiology goes beyond the first aerated step and influences yields and survival rates during the anaerobic stage. The activity of M. pulcherrima in mixed oxygenated cultures resulted in a clear reduction in ethanol yield, as compared to S. cerevisiae. Despite relatively low initial cell numbers, S. cerevisiae always predominated in mixed cultures by the end of the fermentation process. Strain replacement was faster under low oxygenation levels. M. pulcherrima confers an additional advantage in terms of dissolved oxygen, which drops to zero after a few hours of culture, even under highly aerated conditions, and this holds true for mixed cultures. Alcohol reduction values about 3.7 % (v/v) were obtained for mixed cultures under high aeration, but they were associated to unacceptable volatile acidity levels. In contrast, under optimized conditions, only 0.35 g/L acetic acid was produced, for an alcohol reduction of 2.2 % (v/v), and almost null dissolved oxygen during the process.

Enhancement of activity of RuSex electrocatalyst by modification with nanostructured iridium towards more efficient reduction of oxygen

NASA Astrophysics Data System (ADS)

Dembinska, Beata; Kiliszek, Malgorzata; Elzanowska, Hanna; Pisarek, Marcin; Kulesza, Pawel J.

2013-12-01

Electrocatalytic activity of carbon (Vulcan XC-72) supported selenium-modified ruthenium, RuSex/C, nanoparticles for reduction of oxygen was enhanced through intentional decoration with iridium nanostructures (dimensions, 2-3 nm). The catalytic materials were characterized in oxygenated 0.5 mol dm-3 H2SO4 using cyclic and rotating ring disk voltammetric techniques as well as using transmission electron microscopy and scanning electron microscopy equipped with X-ray dispersive analyzer. Experiments utilizing gas diffusion electrode aimed at mimicking conditions existing in the low-temperature fuel cell. Upon application of our composite catalytic system, the reduction of oxygen proceeded at more positive potentials, and higher current densities were observed when compared to the behavior of the simple iridium-free system (RuSex/C) investigated under the analogous conditions. The enhancement effect was more pronounced than that one would expect from simple superposition of voltammetric responses for the oxygen reduction at RuSex/C and iridium nanostructures studied separately. Nanostructured iridium acted here as an example of a powerful catalyst for the reduction of H2O2 (rather than O2) and, when combined with such a moderate catalyst as ruthenium-selenium (for O2 reduction), it produced an integrated system of increased electrocatalytic activity in the oxygen reduction process. The proposed system retained its activity in the presence of methanol that could appear in a cathode compartment of alcohol fuel cell.

Method for oxygen reduction in a uranium-recovery process. [US DOE patent application

DOEpatents

Hurst, F.J.; Brown, G.M.; Posey, F.A.

1981-11-04

An improvement in effecting uranium recovery from phosphoric acid solutions is provided by sparging dissolved oxygen contained in solutions and solvents used in a reductive stripping stage with an effective volume of a nonoxidizing gas before the introduction of the solutions and solvents into the stage. Effective volumes of nonoxidizing gases, selected from the group consisting of argon, carbon dioxide, carbon monoxide, helium, hydrogen, nitrogen, sulfur dioxide, and mixtures thereof, displace oxygen from the solutions and solvents thereby reduce deleterious effects of oxygen such as excessive consumption of elemental or ferrous iron and accumulation of complex iron phosphates or cruds.

Controlled temperature expansion in oxygen production by molten alkali metal salts

DOEpatents

Erickson, Donald C.

1985-06-04

A continuous process is set forth for the production of oxygen from an oxygen containing gas stream, such as air, by contacting a feed gas stream with a molten solution of an oxygen acceptor to oxidize the acceptor and cyclically regenerating the oxidized acceptor by releasing oxygen from the acceptor wherein the oxygen-depleted gas stream from the contact zone is treated sequentially to temperature reduction by heat exchange against the feed stream so as to condense out entrained oxygen acceptor for recycle to the process, combustion of the gas stream with fuel to elevate its temperature and expansion of the combusted high temperature gas stream in a turbine to recover power.

Controlled temperature expansion in oxygen production by molten alkali metal salts

DOEpatents

Erickson, D.C.

1985-06-04

A continuous process is set forth for the production of oxygen from an oxygen containing gas stream, such as air, by contacting a feed gas stream with a molten solution of an oxygen acceptor to oxidize the acceptor and cyclically regenerating the oxidized acceptor by releasing oxygen from the acceptor wherein the oxygen-depleted gas stream from the contact zone is treated sequentially to temperature reduction by heat exchange against the feed stream so as to condense out entrained oxygen acceptor for recycle to the process, combustion of the gas stream with fuel to elevate its temperature and expansion of the combusted high temperature gas stream in a turbine to recover power. 1 fig.

ISRU System Model Tool: From Excavation to Oxygen Production

NASA Technical Reports Server (NTRS)

Santiago-Maldonado, Edgardo; Linne, Diane L.

2007-01-01

In the late 80's, conceptual designs for an in situ oxygen production plant were documented in a study by Eagle Engineering [1]. In the "Summary of Findings" of this study, it is clearly pointed out that: "reported process mass and power estimates lack a consistent basis to allow comparison." The study goes on to say: "A study to produce a set of process mass, power, and volume requirements on a consistent basis is recommended." Today, approximately twenty years later, as humans plan to return to the moon and venture beyond, the need for flexible up-to-date models of the oxygen extraction production process has become even more clear. Multiple processes for the production of oxygen from lunar regolith are being investigated by NASA, academia, and industry. Three processes that have shown technical merit are molten regolith electrolysis, hydrogen reduction, and carbothermal reduction. These processes have been selected by NASA as the basis for the development of the ISRU System Model Tool (ISMT). In working to develop up-to-date system models for these processes NASA hopes to accomplish the following: (1) help in the evaluation process to select the most cost-effective and efficient process for further prototype development, (2) identify key parameters, (3) optimize the excavation and oxygen production processes, and (4) provide estimates on energy and power requirements, mass and volume of the system, oxygen production rate, mass of regolith required, mass of consumables, and other important parameters. Also, as confidence and high fidelity is achieved with each component's model, new techniques and processes can be introduced and analyzed at a fraction of the cost of traditional hardware development and test approaches. A first generation ISRU System Model Tool has been used to provide inputs to the Lunar Architecture Team studies.

Surface Modification of Boron-Doped Diamond with Microcrystalline Copper Phthalocyanine: Oxygen Reduction Catalysis

PubMed Central

Gan, Patrick; Foord, John S; Compton, Richard G

2015-01-01

Surface modification of boron-doped diamond (BDD) with copper phthalocyanine was achieved using a simple and convenient dropcast deposition, giving rise to a microcrystalline structure. Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution. A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD. Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide. The lack of a further conversion of the peroxide was attributed to its rapid diffusion away from the triple phase boundary at which the reaction is expected to exclusively occur. PMID:26491640

Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction.

PubMed

He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

2016-08-09

The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon.

Oxygen production System Models for Lunar ISRU

NASA Technical Reports Server (NTRS)

Santiago-Maldonado, Edgardo

2007-01-01

In-Situ Resource Utilization (ISRU) seeks to make human space exploration feasible; by using available resources from a planet or the moon to produce consumables, parts, and structures that otherwise would be brought from Earth. Producing these in situ reduces the mass of such that must be launched and doing so allows more payload mass' for each mission. The production of oxygen from lunar regolith, for life support and propellant, is one of the tasks being studied under ISRU. NASA is currently funding three processes that have shown technical merit for the production of oxygen from regolith: Molten Salt Electrolysis, Hydrogen Reduction of Ilmenite, and Carbothermal Reduction. The ISRU program is currently developing system models of, the , abovementioned processes to: (1) help NASA in the evaluation process to select the most cost-effective and efficient process for further prototype development, (2) identify key parameters, (3) optimize the oxygen production process, (4) provide estimates on energy and power requirements, mass and volume.of the system, oxygen production rate, mass of regolith required, mass of consumables, and other important parameters, and (5) integrate into the overall end-to-end ISRU system model, which could be integrated with mission architecture models. The oxygen production system model is divided into modules that represent unit operations (e.g., reactor, water electrolyzer, heat exchanger). Each module is modeled theoretically using Excel and Visual Basic for Applications (VBA), and will be validated using experimental data from on-going laboratory work. This modularity (plug-n-play) feature of each unit operation allows the use of the same model on different oxygen production systems simulations resulting in comparable results. In this presentation, preliminary results for mass, power, volume will be presented along with brief description of the oxygen production system model.

Cryptic oxygen cycling in anoxic marine zones.

PubMed

Garcia-Robledo, Emilio; Padilla, Cory C; Aldunate, Montserrat; Stewart, Frank J; Ulloa, Osvaldo; Paulmier, Aurélien; Gregori, Gerald; Revsbech, Niels Peter

2017-08-01

Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30-50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O 2 to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteria Prochlorococcus spp. Free O 2 levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O 2 production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O 2 production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling.

Microbial Manganese and Sulfate Reduction in Black Sea Shelf Sediments

PubMed Central

Thamdrup, Bo; Rosselló-Mora, Ramón; Amann, Rudolf

2000-01-01

The microbial ecology of anaerobic carbon oxidation processes was investigated in Black Sea shelf sediments from mid-shelf with well-oxygenated bottom water to the oxic-anoxic chemocline at the shelf-break. At all stations, organic carbon (Corg) oxidation rates were rapidly attenuated with depth in anoxically incubated sediment. Dissimilatory Mn reduction was the most important terminal electron-accepting process in the active surface layer to a depth of ∼1 cm, while SO42− reduction accounted for the entire Corg oxidation below. Manganese reduction was supported by moderately high Mn oxide concentrations. A contribution from microbial Fe reduction could not be discerned, and the process was not stimulated by addition of ferrihydrite. Manganese reduction resulted in carbonate precipitation, which complicated the quantification of Corg oxidation rates. The relative contribution of Mn reduction to Corg oxidation in the anaerobic incubations was 25 to 73% at the stations with oxic bottom water. In situ, where Mn reduction must compete with oxygen respiration, the contribution of the process will vary in response to fluctuations in bottom water oxygen concentrations. Total bacterial numbers as well as the detection frequency of bacteria with fluorescent in situ hybridization scaled to the mineralization rates. Most-probable-number enumerations yielded up to 105 cells of acetate-oxidizing Mn-reducing bacteria (MnRB) cm−3, while counts of Fe reducers were <102 cm−3. At two stations, organisms affiliated with Arcobacter were the only types identified from 16S rRNA clone libraries from the highest positive MPN dilutions for MnRB. At the third station, a clone type affiliated with Pelobacter was also observed. Our results delineate a niche for dissimilatory Mn-reducing bacteria in sediments with Mn oxide concentrations greater than ∼10 μmol cm−3 and indicate that bacteria that are specialized in Mn reduction, rather than known Mn and Fe reducers, are important in this niche. PMID:10877783

Extraction processes for the production of aluminum, titanium, iron, magnesium, and oxygen and nonterrestrial sources

NASA Technical Reports Server (NTRS)

Rao, D. B.; Choudary, U. V.; Erstfeld, T. E.; Williams, R. J.; Chang, Y. A.

1979-01-01

The suitability of existing terrestrial extractive metallurgical processes for the production of Al, Ti, Fe, Mg, and O2 from nonterrestrial resources is examined from both thermodynamic and kinetic points of view. Carbochlorination of lunar anorthite concentrate in conjunction with Alcoa electrolysis process for Al; carbochlorination of lunar ilmenite concentrate followed by Ca reduction of TiO2; and subsequent reduction of Fe2O3 by H2 for Ti and Fe, respectively, are suggested. Silicothermic reduction of olivine concentrate was found to be attractive for the extraction of Mg becaue of the technological knowhow of the process. Aluminothermic reduction of olivine is the other possible alternative for the production of magnesium. The large quantities of carbon monoxide generated in the metal extraction processes can be used to recover carbon and oxygen by a combination of the following methods: (1) simple disproportionation of CO,(2) methanation of CO and electrolysis of H2O, and (3) solid-state electrolysis of gas mixtures containing CO, CO2, and H2O. The research needed for the adoption of earth-based extraction processes for lunar and asteroidal minerals is outlined.

Oxygen Reduction Reaction on Graphene in an Electro-Fenton System: In Situ Generation of H2 O2 for the Oxidation of Organic Compounds.

PubMed

Chen, Chen-Yu; Tang, Cheng; Wang, Hao-Fan; Chen, Cheng-Meng; Zhang, Xiaoyuan; Huang, Xia; Zhang, Qiang

2016-05-23

Fenton oxidation using an aqueous mixture of Fe(2+) and H2 O2 is a promising environmental remediation strategy. However, the difficulty of storage and shipment of concentrated H2 O2 and the generation of iron sludge limit its broad application. Therefore, highly efficient and cost-effective electrocatalysts are in great need. Herein, a graphene catalyst is proposed for the electro-Fenton process, in which H2 O2 is generated in situ by the two-electron reduction of the dissolved O2 on the cathode and then decomposes to generate (.) OH in acidic solution with Fe(2+) . The π bond of the oxygen is broken whereas the σ bond is generally preserved on the metal-free reduced graphene oxide owing to the high free energy change. Consequently, the oxygen is reduced to H2 O2 through a two-electron pathway. The thermally reduced graphene with a high specific surface area (308.8 m(2)  g(-1) ) and a large oxygen content (10.3 at %) exhibits excellent reactivity for the two-electron oxygen reduction reaction to H2 O2 . A highly efficient peroxide yield (64.2 %) and a remarkable decolorization of methylene blue (12 mg L(-1) ) of over 97 % in 160 min are obtained. The degradation of methylene blue with hydroxyl radicals generated in situ is described by a pseudo first-order kinetics model. This provides a proof-of-concept of an environmentally friendly electro-Fenton process using graphene for the oxygen reduction reaction in an acidic solution to generate H2 O2 . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Methane Post-Processing for Oxygen Loop Closure

NASA Technical Reports Server (NTRS)

Greenwood, Zachary W.; Abney, Morgan B.; Miller, Lee

2016-01-01

State-of-the-art United States Atmospheric Revitalization carbon dioxide (CO2) reduction is based on the Sabatier reaction process, which recovers approximately 50% of the oxygen (O2) from crew metabolic CO2. Oxygen recovery from carbon dioxide is constrained by the limited availability of reactant hydrogen. Post-processing of methane to recover hydrogen with the Umpqua Research Company Plasma Pyrolysis Assembly (PPA) has the potential to further close the Atmospheric Revitalization oxygen loop. The PPA decomposes methane into hydrogen and hydrocarbons, predominantly acetylene, and a small amount of solid carbon. The hydrogen must then be purified before it can be recycled for additional oxygen recovery. Long duration testing and evaluation of a four crew-member sized PPA and a discussion of hydrogen recycling system architectures are presented.

Thermodynamics of lunar ilmenite reduction

NASA Technical Reports Server (NTRS)

Altenberg, B. H.; Franklin, H. A.; Jones, C. H.

1993-01-01

With the prospect of returning to the moon, the development of a lunar occupation would fulfill one of the goals of the Space Exploration Initiative (SEI) of the late 1980's. Processing lunar resources into useful products, such as liquid oxygen for fuel and life support, would be one of many aspects of an active lunar base. ilmenite (FeTiO3) is found on the lunar surface and can be used as a feed stock to produce oxygen. Understanding the various ilmenite-reduction reactions elucidates many processing options. Defining the thermodynamic chemical behavior at equilibrium under various conditions of temperature and pressures can be helpful in specifying optimal operating conditions. Differences between a previous theoretical analysis and experimentally determined results has sparked interest in trying to understand the effect of operating pressure on the hydrogen-reduction-of-ilmenite reaction. Various aspects of this reduction reaction are discussed.

Sulfur and oxygen isotope fractionation during benzene, toluene, ethyl benzene, and xylene degradation by sulfate-reducing bacteria.

PubMed

Knöller, Kay; Vogt, Carsten; Richnow, Hans-Herrmann; Weise, Stephan M

2006-06-15

We examined the oxygen and sulfur isotope fractionation of sulfate during anaerobic degradation of toluene by sulfate-reducing bacteria in culture experiments with Desulfobacula toluolica as a type strain and with an enrichment culture Zz5-7 obtained from a benzene, toluene, ethylbenzene, and xylene (BTEX)-contaminated aquifer. Sulfur isotope fractionation can show considerable variation upon sulfate reduction and may react extremely sensitively to changes in environmental conditions. In contrast, oxygen isotope fractionation seems to be less sensitive to environmental changes. Our results clearly indicate that oxygen isotope fractionation is dominated by isotope exchange with ambient water. To verify our experimental results and to test the applicability of oxygen and sulfur isotope investigations under realistic field conditions, we evaluated isotope data from two BTEX-contaminated aquifers presented in the recent literature. On a field scale, bacterial sulfate reduction may be superimposed by processes such as dispersion, adsorption, reoxidation, or mixing. The dual isotope approach enables the identification of such sulfur transformation processes. This identification is vital for a general qualitative evaluation of the natural attenuation potential of the contaminated aquifer.

[Participation of oxygen in the reduction of methylviologen, photosensitized by chlorophyll, in an aqueous solution of detergent].

PubMed

Luganskaia, A N; Krasnovskiĭ, A A

1975-01-01

Dependence of chlorophyll "a" photosensitized reduction of methylviologene with tiourea on the temperature of reaction mixture was studied in aerobic conditions in triton X-100 aqueous solution. It was found that the reaction consisted of two stages: the light and dark ones. Photosensitized oxidation of tiourea with air oxygen proceeds at the temperatures up to -70 degrees C. Reduction of methylviologen is a dark stage for which diffusion processes are necessary. The role of hydrogen peroxide in the reaction studied has been investigated. It has been shown that hydrogen peroxide is not the "initiator" of the reaction which results in the reduction of methylviologen. Reduced glutation and the mixture of reduced and oxidized glutations were used as electron donors in photosensitized reaction in the presence of air oxygen. An increase of the depth and rate of the reduction of methylviologen under aerobic conditions as compared to anaerobic ones points to the formation of more active reducers than the initial electron donor.

Combined 34S, 33S and 18O isotope fractionations record different intracellular steps of microbial sulfate reduction

NASA Astrophysics Data System (ADS)

Antler, Gilad; Turchyn, Alexandra V.; Ono, Shuhei; Sivan, Orit; Bosak, Tanja

2017-04-01

Several enzymatic steps in microbial sulfate reduction (MSR) fractionate the isotope ratios of 33S/32S, 34S/32S and 18O/16O in extracellular sulfate, but the effects of different intracellular processes on the isotopic composition of residual sulfate are still not well quantified. We measured combined multiple sulfur (33S/32S, 34S/32S) and oxygen (18O/16O) isotope ratios of sulfate in pure cultures of a marine sulfate reducing bacterium Desulfovibrio sp. DMSS-1 grown on different organic substrates. These measurements are consistent with the previously reported correlations of oxygen and sulfur isotope fractionations with the cell-specific rate of MSR: faster reduction rates produced smaller isotopic fractionations for all isotopes. Combined isotope fractionation of oxygen and multiple sulfur isotopes are also consistent with the relationship between the rate limiting step during microbial sulfate reduction and the availability of the DsrC subunit. These experiments help reconstruct and interpret processes that operate in natural pore waters characterized by high 18O/16O and moderate 34S/32S ratios and suggest that some multiple isotope signals in the environment cannot be explained by microbial sulfate reduction alone. Instead, these signals support the presence of active, but slow sulfate reduction as well as the reoxidation of sulfide.

Carbon Dioxide Reduction Post-Processing Sub-System Development

NASA Technical Reports Server (NTRS)

Abney, Morgan B.; Miller, Lee A.; Greenwood, Zachary; Barton, Katherine

2012-01-01

The state-of-the-art Carbon Dioxide (CO2) Reduction Assembly (CRA) on the International Space Station (ISS) facilitates the recovery of oxygen from metabolic CO2. The CRA utilizes the Sabatier process to produce water with methane as a byproduct. The methane is currently vented overboard as a waste product. Because the CRA relies on hydrogen for oxygen recovery, the loss of methane ultimately results in a loss of oxygen. For missions beyond low earth orbit, it will prove essential to maximize oxygen recovery. For this purpose, NASA is exploring an integrated post-processor system to recover hydrogen from CRA methane. The post-processor, called a Plasma Pyrolysis Assembly (PPA) partially pyrolyzes methane to recover hydrogen with acetylene as a byproduct. In-flight operation of post-processor will require a Methane Purification Assembly (MePA) and an Acetylene Separation Assembly (ASepA). Recent efforts have focused on the design, fabrication, and testing of these components. The results and conclusions of these efforts will be discussed as well as future plans.

Nano-Structured Bio-Inorganic Hybrid Material for High Performing Oxygen Reduction Catalyst.

PubMed

Jiang, Rongzhong; Tran, Dat T; McClure, Joshua P; Chu, Deryn

2015-08-26

In this study, we demonstrate a non-Pt nanostructured bioinorganic hybrid (BIH) catalyst for catalytic oxygen reduction in alkaline media. This catalyst was synthesized through biomaterial hemin, nanostructured Ag-Co alloy, and graphene nano platelets (GNP) by heat-treatment and ultrasonically processing. This hybrid catalyst has the advantages of the combined features of these bio and inorganic materials. A 10-fold improvement in catalytic activity (at 0.8 V vs RHE) is achieved in comparison of pure Ag nanoparticles (20-40 nm). The hybrid catalyst reaches 80% activity (at 0.8 V vs RHE) of the state-of-the-art catalyst (containing 40% Pt and 60% active carbon). Comparable catalytic stability for the hybrid catalyst with the Pt catalyst is observed by chronoamperometric experiment. The hybrid catalyst catalyzes 4-electron oxygen reduction to produce water with fast kinetic rate. The rate constant obtained from the hybrid catalyst (at 0.6 V vs RHE) is 4 times higher than that of pure Ag/GNP catalyst. A catalytic model is proposed to explain the oxygen reduction reaction at the BIH catalyst.

Cryptic oxygen cycling in anoxic marine zones

PubMed Central

Padilla, Cory C.; Stewart, Frank J.; Ulloa, Osvaldo; Paulmier, Aurélien; Gregori, Gerald; Revsbech, Niels Peter

2017-01-01

Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30–50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O2 to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteria Prochlorococcus spp. Free O2 levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O2 production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O2 production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling. PMID:28716941

Beneficiation and extraction of nonterrestrial materials, part 2

NASA Technical Reports Server (NTRS)

Agosto, William N.

1992-01-01

A review of options for processing extraterrestrial materials was dominated by industrial materials scientist who tried to identify which processes utilizing space materials could be implemented in the near term. The most practical process seem to us to be the extraction of lunar oxygen and the extraction of metals and ceramics from the residues of the reduction process. The growth of space activity will be accompanied by increased demand for liquid oxygen for each round trip to the Moon. The oxygen and the intermediary product water will be needed for the life support at the base. The reduced metals and ceramics may be considered byproducts or may develop into primary products. Some of the same processes would be directly applicable to recovery of products from asteroids. We also discussed other processes for directly utilizing asteroid metals. Some of the topics covered include beneficiation and oxygen extraction methods, metallurgy, and extraterrestrial cement.

Beneficiation and extraction of nonterrestrial materials, part 2

NASA Astrophysics Data System (ADS)

Agosto, William N.

A review of options for processing extraterrestrial materials was dominated by industrial materials scientist who tried to identify which processes utilizing space materials could be implemented in the near term. The most practical process seem to us to be the extraction of lunar oxygen and the extraction of metals and ceramics from the residues of the reduction process. The growth of space activity will be accompanied by increased demand for liquid oxygen for each round trip to the Moon. The oxygen and the intermediary product water will be needed for the life support at the base. The reduced metals and ceramics may be considered byproducts or may develop into primary products. Some of the same processes would be directly applicable to recovery of products from asteroids. We also discussed other processes for directly utilizing asteroid metals. Some of the topics covered include beneficiation and oxygen extraction methods, metallurgy, and extraterrestrial cement.

Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study

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

Zhang, Libo; Zhou, Gang, E-mail: gzhou@mail.buct.edu.cn

2016-04-14

The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO{sub 2} is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximatemore » to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs.« less

North American International Society for Microbial Electrochemical Technologies Meeting (Abstracts)

DTIC Science & Technology

2016-04-18

systems. Unlike the well-studied case of dissolved oxygen (D.O.) effects on the facultative metabolic shift between aerobic respiration and nitrate...The Pt catalyst can effectively catalyze oxygen reduction and ensure a healthy operation of bioelectrochemical systems but its high cost limits the... effect of COEs on other species in bioelectrochemical systems. Effects of additional electron acceptors in bio-anodic processes: oxygen and sulfate

Reductive dehalogenase structure suggests a mechanism for B12-dependent dehalogenation.

PubMed

Payne, Karl Ap; Quezada, Carolina P; Fisher, Karl; Dunstan, Mark S; Collins, Fraser A; Sjuts, Hanno; Levy, Colin; Hay, Sam; Rigby, Stephen Ej; Leys, David

2015-01-22

Organohalide chemistry underpins many industrial and agricultural processes, and a large proportion of environmental pollutants are organohalides. Nevertheless, organohalide chemistry is not exclusively of anthropogenic origin, with natural abiotic and biological processes contributing to the global halide cycle. Reductive dehalogenases are responsible for biological dehalogenation in organohalide respiring bacteria, with substrates including polychlorinated biphenyls or dioxins. Reductive dehalogenases form a distinct subfamily of cobalamin (B12)-dependent enzymes that are usually membrane associated and oxygen sensitive, hindering detailed studies. Here we report the characterization of a soluble, oxygen-tolerant reductive dehalogenase and, by combining structure determination with EPR (electron paramagnetic resonance) spectroscopy and simulation, show that a direct interaction between the cobalamin cobalt and the substrate halogen underpins catalysis. In contrast to the carbon-cobalt bond chemistry catalysed by the other cobalamin-dependent subfamilies, we propose that reductive dehalogenases achieve reduction of the organohalide substrate via halogen-cobalt bond formation. This presents a new model in both organohalide and cobalamin (bio)chemistry that will guide future exploitation of these enzymes in bioremediation or biocatalysis.

Bio-inspired nanocatalysts for the oxygen reduction reaction.

PubMed

Grumelli, Doris; Wurster, Benjamin; Stepanow, Sebastian; Kern, Klaus

2013-01-01

Electrochemical conversions at fuel cell electrodes are complex processes. In particular, the oxygen reduction reaction has substantial overpotential limiting the electrical power output efficiency. Effective and inexpensive catalytic interfaces are therefore essential for increased performance. Taking inspiration from enzymes, earth-abundant metal centres embedded in organic environments present remarkable catalytic active sites. Here we show that these enzyme-inspired centres can be effectively mimicked in two-dimensional metal-organic coordination networks self-assembled on electrode surfaces. Networks consisting of trimesic acid and bis-pyridyl-bispyrimidine coordinating to single iron and manganese atoms on Au(111) effectively catalyse the oxygen reduction and reveal distinctive catalytic activity in alkaline media. These results demonstrate the potential of surface-engineered metal-organic networks for electrocatalytic conversions. Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis.

Identifying biogeochemical processes beneath stormwater infiltration ponds in support of a new best management practice for groundwater protection

USGS Publications Warehouse

O'Reilly, Andrew M.; Chang, Ni-Bin; Wanielista, Martin P.; Xuan, Zhemin; Schirmer, Mario; Hoehn, Eduard; Vogt, Tobias

2011-01-01

 When applying a stormwater infiltration pond best management practice (BMP) for protecting the quality of underlying groundwater, a common constituent of concern is nitrate. Two stormwater infiltration ponds, the SO and HT ponds, in central Florida, USA, were monitored. A temporal succession of biogeochemical processes was identified beneath the SO pond, including oxygen reduction, denitrification, manganese and iron reduction, and methanogenesis. In contrast, aerobic conditions persisted beneath the HT pond, resulting in nitrate leaching into groundwater. Biogeochemical differences likely are related to soil textural and hydraulic properties that control surface/subsurface oxygen exchange. A new infiltration BMP was developed and a full-scale application was implemented for the HT pond. Preliminary results indicate reductions in nitrate concentration exceeding 50% in soil water and shallow groundwater beneath the HT pond.

Contaminant Removal from Oxygen Production Systems for In Situ Resource Utilization

NASA Technical Reports Server (NTRS)

Anthony, Stephen M.; Santiago-Maldonado, Edgardo; Captain, James G.; Pawate, Ashtamurthy S.; Kenis, Paul J. A.

2012-01-01

The In Situ Resource Utilization (ISRU) project has been developing technologies to produce oxygen from lunar regolith to provide consumables to a lunar outpost. The processes developed reduce metal oxides in the regolith to produce water, which is then electrolyzed to produce oxygen. Hydrochloic and hydrofluoric acids are byproducts of the reduction processes, as halide minerals are also reduced at oxide reduction conditions. Because of the stringent water quality requirements for electrolysis, there is a need for a contaminant removal process. The Contaminant Removal from Oxygen Production Systems (CROPS) team has been developing a separation process to remove these contaminants in the gas and liquid phase that eliminates the need for consumables. CROPS has been using Nafion, a highly water selective polymeric proton exchange membrane, to recover pure water from the contaminated solution. Membrane thickness, product stream flow rate, and acid solution temperature and concentration were varied with the goal of maximizing water permeation and acid rejection. The results show that water permeation increases with increasing solution temperature and product stream flow rate, while acid rejection increases with decreasing solution temperature and concentration. Thinner membranes allowed for higher water flux and acid rejection than thicker ones. These results were used in the development of the hardware built for the most recent Mars ISRU demonstration project.

Soil Oxidation-Reduction in Wetlands and Its Impact on Plant Functioning

PubMed Central

Pezeshki, S. R.; DeLaune, R. D.

2012-01-01

Soil flooding in wetlands is accompanied by changes in soil physical and chemical characteristics. These changes include the lowering of soil redox potential (Eh) leading to increasing demand for oxygen within the soil profile as well as production of soil phytotoxins that are by-products of soil reduction and thus, imposing potentially severe stress on plant roots. Various methods are utilized for quantifying plant responses to reducing soil conditions that include measurement of radial oxygen transport, plant enzymatic responses, and assessment of anatomical/morphological changes. However, the chemical properties and reducing nature of soil environment in which plant roots are grown, including oxygen demand, and other associated processes that occur in wetland soils, pose a challenge to evaluation and comparison of plant responses that are reported in the literature. This review emphasizes soil-plant interactions in wetlands, drawing attention to the importance of quantifying the intensity and capacity of soil reduction for proper evaluation of wetland plant responses, particularly at the process and whole-plant levels. Furthermore, while root oxygen-deficiency may partially account for plant stress responses, the importance of soil phytotoxins, produced as by-products of low soil Eh conditions, is discussed and the need for development of methods to allow differentiation of plant responses to reduced or anaerobic soil conditions vs. soil phytotoxins is emphasized. PMID:24832223

[Respiratory oxidases: the enzymes which use most of the oxygen which living things breathe].

PubMed

Toledo-Cuevas, E M

1997-01-01

The respiratory oxidases are the last enzymes of the aerobic respiratory chain. They catalize the reduction of molecular oxygen to water, with generation of an electrochemical gradient useful for the energy demanding cellular processes. Most of the oxidases belong to the heme-copper superfamily. They possess a heme-copper center, constituted of a high spin heme and a CuB center, where the reduction of oxygen takes place and probably where the link to proton pumping is located. The superfamily is divided in two classes: the quinol- and the cytochrome c-oxidases. The latter are divided in the aa3 and the cbb3-type cytochrome c oxidases. The main difference between quinol- and the aa3-type cytochrome c-oxidases is the CuA center, which is absent in the quinol oxidases. The cbb3-type cytochrome oxidases have the binuclear center, but lack the CuA center. They also does not have the classical subunits II and III. These differences seem not to affect the oxygen reduction or the proton pumping. Probably the oxidases have evolved from some denitrification enzymes and prior the photosynthetic process. Also is possible that the cbb3-type cytochrome oxidases or others very similar have been the first oxidases to appear.

Effects of soil oxidation-reduction conditions on internal oxygen transport, root aeration, and growth of wetland plants

Treesearch

S.R. Pezeshki; R.D. DeLaune

2000-01-01

Characterization of hydric soils and the relationship between soil oxidation-reduction processes and wetland plant distribution are critical to the identification and delineation of wetlands and to our understanding of soil processes and plant functioning in wetland ecosystems. However, the information on the relationship between flood response of wetland plants and...

Lunar Regolith Simulant Feed System for a Hydrogen Reduction Reactor System

NASA Technical Reports Server (NTRS)

Mueller, R. P.; Townsend, Ivan I., III

2009-01-01

One of the goals of In-Situ Resource Utilization (ISRU) on the moon is to produce oxygen from the lunar regolith which is present in the form of Ilmenite (FeTi03) and other compounds. A reliable and attainable method of extracting some of the oxygen from the lunar regolith is to use the hydrogen reduction process in a hot reactor to create water vapor which is then condensed and electrolyzed to obtain oxygen for use as a consumable. One challenge for a production system is to reliably acquire the regolith with an excavator hauler mobility platform and then introduce it into the reactor inlet tube which is raised from the surface and above the reactor itself. After the reaction, the hot regolith (-1000 C) must be expelled from the reactor for disposal by the excavator hauler mobility system. In addition, the reactor regolith inlet and outlet tubes must be sealed by valves during the reaction in order to allow collection of the water vapor by the chemical processing sub-system. These valves must be able to handle abrasive regolith passing through them as well as the heat conduction from the hot reactor. In 2008, NASA has designed and field tested a hydrogen reduction system called ROxygen in order to demonstrate the feasibility of extracting oxygen from lunar regolith. The field test was performed with volcanic ash known as Tephra on Mauna Kea volcano on the Big Island of Hawai'i. The tephra has similar properties to lunar regolith, so that it is regarded as a good simulant for the hydrogen reduction process. This paper will discuss the design, fabrication, operation, test results and lessons learned with the ROxygen regolith feed system as tested on Mauna Kea in November 2008.

Strategies for dephenolization of raw olive mill wastewater by means of Pleurotus ostreatus.

PubMed

Olivieri, Giuseppe; Russo, Maria Elena; Giardina, Paola; Marzocchella, Antonio; Sannia, Giovanni; Salatino, Piero

2012-05-01

The reduction of polyphenols content in olive mill wastewater (OMW) is a major issue in olive oil manufacturing. Although researchers have pointed out the potential of white-rot fungus in dephenolizing OMW, the results available in the literature mainly concern pretreated (sterilized) OMW. This paper deals with the reduction of polyphenols content in untreated OMW by means of a white-rot fungus, Pleurotus ostreatus. Dephenolization was performed both in an airlift bioreactor and in aerated flasks. The process was carried out under controlled non-sterile conditions, with different operating configurations (batch, continuous, biomass recycling) representative of potential industrial operations. Total organic carbon, polyphenols concentration, phenol oxidase activity, dissolved oxygen concentration, oxygen consumption rate, and pH were measured during every run. Tests were carried out with or without added nutrients (potato starch and potato dextrose) and laccases inducers (i.e., CuSO₄). OMW endogenous microorganisms were competing with P. ostreatus for oxygen during simultaneous fermentation. Dephenolization of raw OMW by P. ostreatus under single batch was as large as 70%. Dephenolization was still extensive even when biomass was recycled up to six times. OMW pre-aeration had to be provided under continuous operation to avoid oxygen consumption by endogenous microorganisms that might spoil the process. The role of laccases in the dephenolization process has been discussed. Dephenolization under batch conditions with biomass recycling and added nutrients proved to be the most effective configuration for OMW polyphenols reduction in industrial plants (42-68% for five cycles).

Reduction of oxygen concentration by heater design during Czochralski Si growth

NASA Astrophysics Data System (ADS)

Zhou, Bing; Chen, Wenliang; Li, Zhihui; Yue, Ruicun; Liu, Guowei; Huang, Xinming

2018-02-01

Oxygen is one of the highest-concentration impurities in single crystals grown by the Czochralski (CZ) process, and seriously impairs the quality of the Si wafer. In this study, computer simulations were applied to design a new CZ system. A more appropriate thermal field was acquired by optimization of the heater structure. The simulation results showed that, compared with the conventional system, the oxygen concentration in the newly designed CZ system was reduced significantly throughout the entire CZ process because of the lower crucible wall temperature and optimized convection. To verify the simulation results, experiments were conducted on an industrial single-crystal furnace. The experimental results showed that the oxygen concentration was reduced significantly, especially at the top of the CZ-Si ingot. Specifically, the oxygen concentration was 6.19 × 1017 atom/cm3 at the top of the CZ-Si ingot with the newly designed CZ system, compared with 9.22 × 1017 atom/cm3 with the conventional system. Corresponding light-induced degradation of solar cells based on the top of crystals from the newly designed CZ system was 1.62%, a reduction of 0.64% compared with crystals from the conventional system (2.26%).

Functionalized Cobalt Triarylcorrole Covalently Bonded with Graphene Oxide: A Selective Catalyst for the Two- or Four-Electron Reduction of Oxygen.

PubMed

Tang, Jijun; Ou, Zhongping; Guo, Rui; Fang, Yuanyuan; Huang, Dong; Zhang, Jing; Zhang, Jiaoxia; Guo, Song; McFarland, Frederick M; Kadish, Karl M

2017-08-07

A cobalt triphenylcorrole (CorCo) was covalently bonded to graphene oxide (GO), and the resulting product, represented as GO-CorCo, was characterized by UV-vis, FT-IR, and micro-Raman spectroscopy as well as by HRTEM, TGA, XRD, XPS, and AFM. The electrocatalytic activity of GO-CorCo toward the oxygen reduction reaction (ORR) was then examined in air-saturated 0.1 M KOH and 0.5 M H 2 SO 4 solutions by cyclic voltammetry and linear sweep voltammetry using a rotating disk electrode and/or a rotating ring-disk electrode. An overall 4-electron reduction of O 2 is obtained in alkaline media while under acidic conditions a 2-electron process is seen. The ORR results thus indicate that covalently bonded GO-CoCor can be used as a selective catalyst for either the 2- or 4-electron reduction of oxygen, the prevailing reaction depending upon the acidity of the solution.

System Modeling of Lunar Oxygen Production: Mass and Power Requirements

NASA Technical Reports Server (NTRS)

Steffen, Christopher J.; Freeh, Joshua E.; Linne, Diane L.; Faykus, Eric W.; Gallo, Christopher A.; Green, Robert D.

2007-01-01

A systems analysis tool for estimating the mass and power requirements for a lunar oxygen production facility is introduced. The individual modeling components involve the chemical processing and cryogenic storage subsystems needed to process a beneficiated regolith stream into liquid oxygen via ilmenite reduction. The power can be supplied from one of six different fission reactor-converter systems. A baseline system analysis, capable of producing 15 metric tons of oxygen per annum, is presented. The influence of reactor-converter choice was seen to have a small but measurable impact on the system configuration and performance. Finally, the mission concept of operations can have a substantial impact upon individual component size and power requirements.

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance.

PubMed

Alia, Shaun M; Pivovar, Bryan S

2018-04-27

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 °C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 °C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

Nano-structured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell fed with a synthetic wastewater.

PubMed

Liu, Xian-Wei; Sun, Xue-Fei; Huang, Yu-Xi; Sheng, Guo-Ping; Zhou, Kang; Zeng, Raymond J; Dong, Fang; Wang, Shu-Guang; Xu, An-Wu; Tong, Zhong-Hua; Yu, Han-Qing

2010-10-01

Microbial fuel cells (MFCs) provide new opportunities for the simultaneous wastewater treatment and electricity generation. Enhanced oxygen reduction capacity of cost-effective metal-based catalysts in an air cathode is essential for the scale-up and commercialization of MFCs in the field of wastewater treatment. We demonstrated that a nano-structured MnO(x) material, prepared by an electrochemically deposition method, could be an effective catalyst for oxygen reduction in an MFC to generate electricity with the maximum power density of 772.8 mW/m(3) and remove organics when the MFC was fed with an acetate-laden synthetic wastewater. The nano-structured MnO(x) with the controllable size and morphology could be readily obtained with the electrochemical deposition method. Both morphology and manganese oxidation state of the nano-scale catalyst were largely dependent on the electrochemical preparation process, and they governed its catalytic activity and the cathodic oxygen reduction performance of the MFC accordingly. Furthermore, cyclic voltammetry (CV) performed on each nano-structured material suggests that the MnO(x) nanorods had an electrochemical activity towards oxygen reduction reaction via a four-electron pathway in a neutral pH solution. This work provides useful information on the facile preparation of cost-effective cathodic catalysts in a controllable way for the single-chamber air-cathode MFC for wastewater treatment. Copyright © 2010 Elsevier Ltd. All rights reserved.

Advanced air revitalization system modeling and testing

NASA Technical Reports Server (NTRS)

Dall-Baumann, Liese; Jeng, Frank; Christian, Steve; Edeer, Marybeth; Lin, Chin

1990-01-01

To support manned lunar and Martian exploration, an extensive evaluation of air revitalization subsystems (ARS) is being conducted. The major operations under study include carbon dioxide removal and reduction; oxygen and nitrogen production, storage, and distribution; humidity and temperature control; and trace contaminant control. A comprehensive analysis program based on a generalized block flow model was developed to facilitate the evaluation of various processes and their interaction. ASPEN PLUS was used in modelling carbon dioxide removal and reduction. Several life support test stands were developed to test new and existing technologies for their potential applicability in space. The goal was to identify processes which use compact, lightweight equipment and maximize the recovery of oxygen and water. The carbon dioxide removal test stands include solid amine/vacuum desorption (SAVD), regenerative silver oxide chemisorption, and electrochemical carbon dioxide concentration (EDC). Membrane-based carbon dioxide removal and humidity control, catalytic reduction of carbon dioxide, and catalytic oxidation of trace contaminants were also investigated.

Use of ion conductors in the pyrochemical reduction of oxides

DOEpatents

Miller, William E.; Tomczuk, Zygmunt

1994-01-01

An electrochemical process and electrochemical cell for reducing a metal oxide are provided. First the oxide is separated as oxygen gas using, for example, a ZrO.sub.2 oxygen ion conductor anode and the metal ions from the reduction salt are reduced and deposited on an ion conductor cathode, for example, sodium ion reduced on a .beta.-alumina sodium ion conductor cathode. The generation of and separation of oxygen gas avoids the problem with chemical back reaction of oxygen with active metals in the cell. The method also is characterized by a sequence of two steps where an inert cathode electrode is inserted into the electrochemical cell in the second step and the metallic component in the ion conductor is then used as the anode to cause electrochemical reduction of the metal ions formed in the first step from the metal oxide where oxygen gas formed at the anode. The use of ion conductors serves to isolate the active components from chemically reacting with certain chemicals in the cell. While applicable to a variety of metal oxides, the invention has special importance for reducing CaO to Ca.degree. used for reducing UO.sub.2 and PuO.sub.2 to U and Pu.

Layer-separated MoS2 bearing reduced graphene oxide formed by an in situ intercalation-cum-anchoring route mediated by Co(OH)2 as a Pt-free electrocatalyst for oxygen reduction.

PubMed

Illathvalappil, Rajith; Unni, Sreekuttan M; Kurungot, Sreekumar

2015-10-28

A significant improvement in the electrochemical oxygen reduction reaction (ORR) activity of molybdenum sulphide (MoS2) could be accomplished by its layer separated dispersion on graphene mediated by cobalt hydroxide (Co(OH)2) through a hydrothermal process (Co(OH)2-MoS2/rGO). The activity makeover in this case is found to be originated from a controlled interplay of the favourable modulations achieved in terms of electrical conductivity, more exposure of the edge planes of MoS2 and a promotional role played by the coexistence of Co(OH)2 in the proximity of MoS2. Co(OH)2-MoS2/rGO displays an oxygen reduction onset potential of 0.855 V and a half wave potential (E1/2) of 0.731 V vs. RHE in 0.1 M KOH solution, which are much higher than those of the corresponding values (0.708 and 0.349 V, respectively) displayed by the as synthesized pristine MoS2 (P-MoS2) under identical experimental conditions. The Tafel slope corresponding to oxygen reduction for Co(OH)2-MoS2/rGO is estimated to be 63 mV dec(-1) compared to 68 mV dec(-1) displayed by the state-of-the-art Pt/C catalyst. The estimated number of electrons transferred during oxygen reduction for Co(OH)2-MoS2/rGO is in the range of 3.2-3.6 in the potential range of 0.77 V to 0.07 V, which again stands out as valid evidence on the much favourable mode of oxygen reduction accomplished by the system compared to its pristine counterpart. Overall, the present study, thus, demonstrates a viable strategy of tackling the inherent limitations, such as low electrical conductivity and limited access to the active sites, faced by the layered structures like MoS2 to position them among the group of potential Pt-free electrocatalysts for oxygen reduction.

Review of Membrane Oxygen Enrichment for Efficient Combustion

NASA Astrophysics Data System (ADS)

Ariono, Danu; Kusuma Wardani, Anita

2017-07-01

Oxygen enrichment from air is a simple way of increasing the efficiency of combustion process, as in oxy-combustion. Oxy-combustion has become one of the most attracting combustion technologies because of its potential to address both pollutant reduction and CO2 capture. In oxy-combustion, the fuel and recycled flue gas are combusted with oxygen enriched air (OEA). By using OEA, many benefits can be obtained, such as increasing available heat, improving ignition characteristics, flue gas reduction, increasing productivity, energy efficiency, turndown ratio, and flame stability. Membrane-based gas separation for OEA production becomes an attractive technology over the conventional technology due to the some advantages, including low capital cost, low energy consumption, compact size, and modularity. A single pass through membrane usually can enrich O2 concentration in the air up to 35% and a 50% concentration can be achieved with a double pass of membrane. The use of OEA in the combustion process eliminates the presence of nitrogen in the flue gas. Hence, the flue gas is mainly composed of CO2 and condensable water that can be easily separated. This paper gives an overview of oxy-combustion with membrane technology for oxygen enrichment process. Special attention is given to OEA production and the effect of OEA to the efficiency of combustion.

Oxygen production by pyrolysis of lunar regolith

NASA Technical Reports Server (NTRS)

Senior, Constance L.

1991-01-01

Oxygen was identified as the most important product of initial lunar materials processing efforts. A source of oxygen on the Moon provides an alternative to the costly transport of propellant to the Moon or to low earth orbit. Pyrolysis, or vapor-phase reduction, involves heating a feedstock to temperatures sufficient to decompose the constituent metal oxides and release oxygen. The process relies on the vaporization of metal oxides in the form of reduced suboxides or atomic species. The reduced species must then be condensed without re-oxidizing, yielding oxygen in the gas phase. The feasibility of obtaining oxygen from common lunar minerals was demonstrated using solar furnace experiments. These results are discussed together with chemical equilibrium models which were extended to include the multicomponent oxides used in experiments. For the first time, both experiments and theoretical models dealt with the complex oxides that make up potential lunar feedstocks. Two major conclusions are drawn from this preliminary work. First, unbeneficiated regolith is a suitable feedstock for pyrolysis. Second, the process can operate at moderate temperatures, circa 2000 K, which could be supplied by direct solar or electrical energy. In addition to these advantages in choice of feedstock and energy source, the pyrolysis process requires no chemicals or reagents, making it an attractive process for lunar oxygen production.

Mechanisms of ilmenite reduction and their impact on the design of effective reactor systems

NASA Technical Reports Server (NTRS)

Briggs, R. A.; Sacco, A.

1991-01-01

One of the first activities at a lunar base could be oxygen recovery from ilmenite (FeTiO3). Oxygen produced from lunar soils could be used to fuel transportation vehicles operating in near-earth space. The first step in developing a suitable reactor system for lunar operation is to determine the mechanisms and rates of oxygen removal from ilmenite. In-situ gravimetric measurements and microscopic examinations were used to determine the hydrogen reduction mechanisms of synthetic ilmenite discs between 823 to 1353 K. A shrinking core reaction model, modified to account for the growth of an iron film on the surface of discs, was capable of predicting experimentally observed conversion-time relationships. The observed reduction mechanism, kinetic rates, and associated activation energy established a base line from which comparisons could be made to improve oxygen yield and removal rates. One proposed technique to improve the rate and extent of oxygen removal was to preoxidize ilmenite. Preoxidation is commonly used during the reduction of ilmenite ores in the iron industry and has been employed for many years to lower operating temperatures and increase reduction rates. This technology could prove beneficial for oxygen production facilities on the Moon as less massive reactor vessels and/or less energy could be associated with a process including preoxidation. X ray diffraction and energy dispersive spectroscopy were utilized to follow the progression of ilmenite oxidation at 1123 and 1140 K and the reduction of pseudobrookite (Fe2TiO5) at 873 and 973 K. Structures formed during the progress of oxidation were related to the system's phase diagrams. Results indicated that after initially producing ilmenite-hematite solutions and rutile (TiO2), pseudobrookite was the end product of oxidation at all temperatures examined (1049 to 1273 K). Initial results from the reduction of pseudobrookite indicate a series of phases are produced including ferropseudobrookite (FeTi2O5), ulvospinel (Fe2TiO4), and ilmenite. Rates of pseudobrookite reduction were typically 50 to 200 times that of ilmenite.

Binuclear Phthalocyanines as Model Electrocatalysts for the Reduction of Oxygen.

DTIC Science & Technology

1985-05-01

solution, in which case the final product is Co(II)Pc. Aqueous acid addition (under nitrogen) to Co(I)Pc (in DCB/OH-) yields Co(II)Pc and presumably hydrogen ...little doubt, given the tendency for Co(I) to reduce aqueous acid to hydrogen [101, that hydrogen is produced in this reaction, though it was not proven...reduction occurs in water by a 2-electron process to hydrogen peroxide or a 4-electron process to water. This latter process must be catalysed on a

Unifying theoretical framework for deciphering the oxygen reduction reaction on platinum.

PubMed

Huang, Jun; Zhang, Jianbo; Eikerling, Michael

2018-05-07

Rapid conversion of oxygen into water is crucial to the operation of polymer electrolyte fuel cells and other emerging electrochemical energy technologies. Chemisorbed oxygen species play double-edged roles in this reaction, acting as vital intermediates on one hand and site-blockers on the other. Any attempt to decipher the oxygen reduction reaction (ORR) must first relate the formation of oxygen intermediates to basic electronic and electrostatic properties of the catalytic surface, and then link it to parameters of catalyst activity. An approach that accomplishes this feat will be of great utility for catalyst materials development and predictive model formulation of electrode operation. Here, we present a theoretical framework for the multiple interrelated surface phenomena and processes involved, particularly, by incorporating the double-layer effects. It sheds light on the roles of oxygen intermediates and gives out the Tafel slope and exchange current density as continuous functions of electrode potential. Moreover, it develops the concept of a rate determining term, which should replace the concept of a rate determining step for multielectron reactions, and offers a new perspective on the volcano relation of the ORR.

Chemical oxygen demand reduction in coffee wastewater through chemical flocculation and advanced oxidation processes.

PubMed

Zayas Pérez, Teresa; Geissler, Gunther; Hernandez, Fernando

2007-01-01

The removal of the natural organic matter present in coffee processing wastewater through chemical coagulation-flocculation and advanced oxidation processes (AOP) had been studied. The effectiveness of the removal of natural organic matter using commercial flocculants and UV/H2O2, UV/O3 and UV/H2O2/O3 processes was determined under acidic conditions. For each of these processes, different operational conditions were explored to optimize the treatment efficiency of the coffee wastewater. Coffee wastewater is characterized by a high chemical oxygen demand (COD) and low total suspended solids. The outcomes of coffee wastewater treatment using coagulation-flocculation and photodegradation processes were assessed in terms of reduction of COD, color, and turbidity. It was found that a reduction in COD of 67% could be realized when the coffee wastewater was treated by chemical coagulation-flocculation with lime and coagulant T-1. When coffee wastewater was treated by coagulation-flocculation in combination with UV/H2O2, a COD reduction of 86% was achieved, although only after prolonged UV irradiation. Of the three advanced oxidation processes considered, UV/H2O2, UV/O3 and UV/H2O2/O3, we found that the treatment with UV/H2O2/O3 was the most effective, with an efficiency of color, turbidity and further COD removal of 87%, when applied to the flocculated coffee wastewater.

Polymer Electrolyte Fuel Cells Employing Heteropolyacids as Redox Mediators for Oxygen Reduction Reactions: Pt-Free Cathode Systems.

PubMed

Matsui, Toshiaki; Morikawa, Eri; Nakada, Shintaro; Okanishi, Takeou; Muroyama, Hiroki; Hirao, Yoshifumi; Takahashi, Tsuyoshi; Eguchi, Koichi

2016-07-20

In this study, the heteropolyacids of H3+xPVxMO12-xO40 (x = 0, 2, and 3) were applied as redox mediators for the oxygen reduction reaction in polymer electrolyte fuel cells, of which the cathode is free from the usage of noble metals such as Pt/C. In this system, the electrochemical reduction of heteropolyacid over the carbon cathode and the subsequent reoxidation of the partially reduced heteropolyacid by exposure to the dissolved oxygen in the regenerator are important processes for continuous power generation. Thus, the redox properties of catholytes containing these heteropolyacids were investigated in detail. The substitution quantity of V in the heteropolyacid affected the onset reduction potential as well as the reduction current density, resulting in a difference in cell performance. The chemical composition of heteropolyacid also had a significant impact on the reoxidation property. Among the three compounds, H6PV3Mo9O40 was the most suitable redox mediator. Furthermore, the pH of the catholyte was found to be the crucial factor in determining the reoxidation rate of partially reduced heteropolyacid as well as cell performance.

Synthesis of an efficient heteroatom-doped carbon electro-catalyst for oxygen reduction reaction by pyrolysis of protein-rich pulse flour cooked with SiO2 nanoparticles.

PubMed

Gokhale, Rohan; Unni, Sreekuttan M; Puthusseri, Dhanya; Kurungot, Sreekumar; Ogale, Satishchandra

2014-03-07

Development of a highly durable, fuel-tolerant, metal-free electro-catalyst for oxygen reduction reaction (ORR) is essential for robust and cost-effective Anion Exchange Membrane Fuel Cells (AEMFCs). Herein, we report the development of a nitrogen-doped (N-doped) hierarchically porous carbon-based efficient ORR electrocatalyst from protein-rich pulses. The process involves 3D silica nanoparticle templating of the pulse flour(s) followed by their double pyrolysis. The detailed experiments are performed on gram flour (derived from chickpeas) without any in situ/ex situ addition of dopants. The N-doped porous carbon thus generated shows remarkable electrocatalytic activity towards ORR in the alkaline medium. The oxygen reduction on this material follows the desired 4-electron transfer mechanism involving the direct reduction pathway. Additionally, the synthesized carbon catalyst also exhibits good electrochemical stability and fuel tolerance. The results are also obtained and compared with the case of soybean flour having higher nitrogen content to highlight the significance of different parameters in the ORR catalyst performance.

Impacts of chemical gradients on microbial community structure

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

Chen, Jianwei; Hanke, Anna; Tegetmeyer, Halina E.

Succession of redox processes is sometimes assumed to define a basic microbial community structure for ecosystems with oxygen gradients. In this paradigm, aerobic respiration, denitrification, fermentation and sulfate reduction proceed in a thermodynamically determined order, known as the ‘redox tower’. Here, we investigated whether redox sorting of microbial processes explains microbial community structure at low-oxygen concentrations. We subjected a diverse microbial community sampled from a coastal marine sediment to 100 days of tidal cycling in a laboratory chemostat. Oxygen gradients (both in space and time) led to the assembly of a microbial community dominated by populations that each performed aerobicmore » and anaerobic metabolism in parallel. This was shown by metagenomics, transcriptomics, proteomics and stable isotope incubations. Effective oxygen consumption combined with the formation of microaggregates sustained the activity of oxygen-sensitive anaerobic enzymes, leading to braiding of unsorted redox processes, within and between populations. Analyses of available metagenomic data sets indicated that the same ecological strategies might also be successful in some natural ecosystems.« less

Impacts of chemical gradients on microbial community structure

DOE PAGES

Chen, Jianwei; Hanke, Anna; Tegetmeyer, Halina E.; ...

2017-01-17

Succession of redox processes is sometimes assumed to define a basic microbial community structure for ecosystems with oxygen gradients. In this paradigm, aerobic respiration, denitrification, fermentation and sulfate reduction proceed in a thermodynamically determined order, known as the ‘redox tower’. Here, we investigated whether redox sorting of microbial processes explains microbial community structure at low-oxygen concentrations. We subjected a diverse microbial community sampled from a coastal marine sediment to 100 days of tidal cycling in a laboratory chemostat. Oxygen gradients (both in space and time) led to the assembly of a microbial community dominated by populations that each performed aerobicmore » and anaerobic metabolism in parallel. This was shown by metagenomics, transcriptomics, proteomics and stable isotope incubations. Effective oxygen consumption combined with the formation of microaggregates sustained the activity of oxygen-sensitive anaerobic enzymes, leading to braiding of unsorted redox processes, within and between populations. Analyses of available metagenomic data sets indicated that the same ecological strategies might also be successful in some natural ecosystems.« less

Impacts of chemical gradients on microbial community structure

PubMed Central

Chen, Jianwei; Hanke, Anna; Tegetmeyer, Halina E; Kattelmann, Ines; Sharma, Ritin; Hamann, Emmo; Hargesheimer, Theresa; Kraft, Beate; Lenk, Sabine; Geelhoed, Jeanine S; Hettich, Robert L; Strous, Marc

2017-01-01

Succession of redox processes is sometimes assumed to define a basic microbial community structure for ecosystems with oxygen gradients. In this paradigm, aerobic respiration, denitrification, fermentation and sulfate reduction proceed in a thermodynamically determined order, known as the ‘redox tower'. Here, we investigated whether redox sorting of microbial processes explains microbial community structure at low-oxygen concentrations. We subjected a diverse microbial community sampled from a coastal marine sediment to 100 days of tidal cycling in a laboratory chemostat. Oxygen gradients (both in space and time) led to the assembly of a microbial community dominated by populations that each performed aerobic and anaerobic metabolism in parallel. This was shown by metagenomics, transcriptomics, proteomics and stable isotope incubations. Effective oxygen consumption combined with the formation of microaggregates sustained the activity of oxygen-sensitive anaerobic enzymes, leading to braiding of unsorted redox processes, within and between populations. Analyses of available metagenomic data sets indicated that the same ecological strategies might also be successful in some natural ecosystems. PMID:28094795

Impacts of chemical gradients on microbial community structure.

PubMed

Chen, Jianwei; Hanke, Anna; Tegetmeyer, Halina E; Kattelmann, Ines; Sharma, Ritin; Hamann, Emmo; Hargesheimer, Theresa; Kraft, Beate; Lenk, Sabine; Geelhoed, Jeanine S; Hettich, Robert L; Strous, Marc

2017-04-01

Succession of redox processes is sometimes assumed to define a basic microbial community structure for ecosystems with oxygen gradients. In this paradigm, aerobic respiration, denitrification, fermentation and sulfate reduction proceed in a thermodynamically determined order, known as the 'redox tower'. Here, we investigated whether redox sorting of microbial processes explains microbial community structure at low-oxygen concentrations. We subjected a diverse microbial community sampled from a coastal marine sediment to 100 days of tidal cycling in a laboratory chemostat. Oxygen gradients (both in space and time) led to the assembly of a microbial community dominated by populations that each performed aerobic and anaerobic metabolism in parallel. This was shown by metagenomics, transcriptomics, proteomics and stable isotope incubations. Effective oxygen consumption combined with the formation of microaggregates sustained the activity of oxygen-sensitive anaerobic enzymes, leading to braiding of unsorted redox processes, within and between populations. Analyses of available metagenomic data sets indicated that the same ecological strategies might also be successful in some natural ecosystems.

Some reflections on the understanding of the oxygen reduction reaction at Pt(111)

PubMed Central

Gómez-Marín, Ana M; Rizo, Ruben

2013-01-01

Summary The oxygen reduction reaction (ORR) is a pivotal process in electrochemistry. Unfortunately, after decades of intensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global and critical view on the most important experimental and theoretical results regarding the ORR on Pt(111) and its vicinal surfaces, in both acidic and alkaline media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a reduction current at high potentials are discussed in the light of the surface oxidation and disordering processes and the possible relevance of the hydrogen peroxide reduction and oxidation reactions in the ORR mechanism. The necessity to build precise and realistic reaction models, which are deducted from reliable experimental results that need to be carefully taken under strict working conditions is shown. Therefore, progress in the understanding of this important reaction on a molecular level, and the choice of the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperative approach between theory and experiments. PMID:24455454

Some reflections on the understanding of the oxygen reduction reaction at Pt(111).

PubMed

Gómez-Marín, Ana M; Rizo, Ruben; Feliu, Juan M

2013-12-27

The oxygen reduction reaction (ORR) is a pivotal process in electrochemistry. Unfortunately, after decades of intensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global and critical view on the most important experimental and theoretical results regarding the ORR on Pt(111) and its vicinal surfaces, in both acidic and alkaline media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a reduction current at high potentials are discussed in the light of the surface oxidation and disordering processes and the possible relevance of the hydrogen peroxide reduction and oxidation reactions in the ORR mechanism. The necessity to build precise and realistic reaction models, which are deducted from reliable experimental results that need to be carefully taken under strict working conditions is shown. Therefore, progress in the understanding of this important reaction on a molecular level, and the choice of the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperative approach between theory and experiments.

Reductive dehalogenase structure suggests a mechanism for B12-dependent dehalogenation

PubMed Central

Fisher, Karl; Dunstan, Mark S; Collins, Fraser A; Sjuts, Hanno; Levy, Colin; Hay, Sam; Rigby, Stephen EJ; Leys, David

2015-01-01

Organohalide chemistry underpins many industrial and agricultural processes, and a large proportion of environmental pollutants are organohalides1. Nevertheless, organohalide chemistry is not exclusively of anthropogenic origin, with natural abiotic and biological processes contributing to the global halide cycle2–3. Reductive dehalogenases are responsible for biological dehalogenation in organohalide respiring bacteria4–5, with substrates including the notorious polychlorinated biphenyls (PCBs) or dioxins6–7. These proteins form a distinct subfamily of cobalamin (B12) dependent enzymes that are usually membrane-associated and oxygen-sensitive, hindering detailed studies8–12. We report the characterisation of a soluble, oxygen-tolerant reductive dehalogenase and, by combining structure determination with EPR spectroscopy and simulation, show that a direct interaction between the cobalamin cobalt and the substrate halogen underpins catalysis. In contrast to the carbon-Co bond chemistry catalyzed by the other cobalamin-dependent subfamilies13 we propose that reductive dehalogenases achieve reduction of the organohalide substrate via halogen-Co bond formation. This presents a new paradigm in both organohalide and cobalamin (bio)chemistry that will guide future exploitation of these enzymes in bioremediation or biocatalysis. PMID:25327251

Sediment-Overlying Water Relationships Affecting Wintertime Dissolved Oxygen Conditions in the Big Eau Pleine Reservoir, Wisconsin.

DTIC Science & Technology

1992-07-01

22202-4302. and to the Office of Managel ent and Bidget . P worki Reduction Pfo4ect(07T4-016 Wahington. DC 20S03. -1. AGENCY USE ONLY (Leave blank) 2...higher pool elevation can not be maintained, it is likely that additional aerators must be installed for incremental use to meet periodic heavy oxygen...install additional aerators throughout the reservoir for incremental use as needed to enhance oxygen diffusion processes. The difficulty with this

Techniques for the conversion to carbon dioxide of oxygen from dissolved sulfate in thermal waters

USGS Publications Warehouse

Nehring, N.L.; Bowen, P.A.; Truesdell, A.H.

1977-01-01

The fractionation of oxygen isotopes between dissolved sulfate ions and water provides a useful geothermometer for geothermal waters. The oxygen isotope composition of dissolved sulfate may also be used to indicate the source of the sulfate and processes of formation. The methods described here for separation, purification and reduction of sulfate to prepare carbon dioxide for mass spectrometric analysis are modifications of methods by Rafter (1967), Mizutani (1971), Sakai and Krouse (1971), and Mizutani and Rafter (1969). ?? 1976.

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

DOE PAGES

Alia, Shaun M.; Pivovar, Bryan S.

2018-01-01

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing tomore » 250 degrees C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 degrees C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. Furthermore, these techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.« less

Oxygen Annealing in the Synthesis of the Electron-Doped Cuprates

NASA Astrophysics Data System (ADS)

Higgins, J. S.; Bach, P. L.; Yu, W.; Weaver, B. D.; Greene, R. L.

2015-03-01

Post-synthesis oxygen reduction (annealing) in the electron-doped, high-temperature superconducting cuprates is necessary for the establishment of superconductivity. It is not established what effect this reduction has microscopically on the lattice structure. Several mechanisms have been put forth as explanations; they range from disorder minimization1, antiferromagnetic suppression2, and copper migration3. Here we present an electronic transport study on electron-doped cuprate Pr2-xCexCuO4+/-δ (PCCO) thin films in an attempt to better understand the need for this post-synthesis process. Several different cerium doping concentrations of PCCO were grown. Within each doping, a series of films were grown with varying levels of oxygen concentration. As a measure of disorder on the properties of PCCO, several films were irradiated with various doses of 2 MeV protons. Analysis within each series, and among the different dopings, favors disorder minimization through the removal of apical oxygen as the explanation for the necessary post-synthesis annealing process. 1P. K. Mang, et al., Physical Review Letters, 93(2):027002, 2004. 2P. Richard, et al., Physical Review B, 70 (6), 064513, 2004. 3Hye Jung Kang, et al., Nature Materials, 2007. Supported by NSF DMR 1104256.

CO2 decomposition using electrochemical process in molten salts

NASA Astrophysics Data System (ADS)

Otake, Koya; Kinoshita, Hiroshi; Kikuchi, Tatsuya; Suzuki, Ryosuke O.

2012-08-01

The electrochemical decomposition of CO2 gas to carbon and oxygen gas in LiCl-Li2O and CaCl2-CaO molten salts was studied. This process consists of electrochemical reduction of Li2O and CaO, as well as the thermal reduction of CO2 gas by the respective metallic Li and Ca. Two kinds of ZrO2 solid electrolytes were tested as an oxygen ion conductor, and the electrolytes removed oxygen ions from the molten salts to the outside of the reactor. After electrolysis in both salts, the aggregations of nanometer-scale amorphous carbon and rod-like graphite crystals were observed by transmission electron microscopy. When 9.7 %CO2-Ar mixed gas was blown into LiCl-Li2O and CaCl2-CaO molten salts, the current efficiency was evaluated to be 89.7 % and 78.5 %, respectively, by the exhaust gas analysis and the supplied charge. When a solid electrolyte with higher ionic conductivity was used, the current and carbon production became larger. It was found that the rate determining step is the diffusion of oxygen ions into the ZrO2 solid electrolyte.

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

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

Alia, Shaun M.; Pivovar, Bryan S.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing tomore » 250 degrees C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 degrees C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. Furthermore, these techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.« less

Oxidation of trichloroethylene by the hydroxyl radicals produced from oxygenation of reduced nontronite.

PubMed

Liu, Xixiang; Yuan, Songhu; Tong, Man; Liu, Deng

2017-04-15

Reduction by Fe(II)-bearing silicate minerals has been proposed as an important mechanism for the attenuation of chlorinated hydrocarbons (CHCs) in anoxic subsurfaces. The redox condition of subsurface often changes from anoxic to oxic due to natural processes and human activities, but little is known about the transformation of CHCs induced by Fe(II)-bearing silicate minerals under oxic conditions. This study reveals that trichloroethylene (TCE) can be efficiently oxidized during the oxygenation of reduced nontronite at pH 7.5, whereas the reduction was negligible under anoxic conditions. The maximum oxidation of TCE (initially 1 mg/L) attained 89.6% for 3 h oxygenation of 2 g/L nontronite with 50% reduction extent. TCE oxidation is attributed to the strongly oxidizing hydroxyl radicals (OH) produced by the oxygenation of Fe(II) in nontronite. Fe(II) on the edges is preferentially oxygenated for OH production, and the interior Fe(II) serves as an electron pool to regenerate the Fe(II) on the edges. Oxidation of TCE could be sustainable through chemically or biologically reducing the oxidized silicate minerals. Our findings present a new mechanism for the transformation of CHCs and other redox-active substances in the redox-fluctuation environments. Copyright © 2017 Elsevier Ltd. All rights reserved.

In-situ diagnostic tools for hydrogen transfer leak characterization in PEM fuel cell stacks part II: Operational applications

NASA Astrophysics Data System (ADS)

Niroumand, Amir M.; Homayouni, Hooman; DeVaal, Jake; Golnaraghi, Farid; Kjeang, Erik

2016-08-01

This paper describes a diagnostic tool for in-situ characterization of the rate and distribution of hydrogen transfer leaks in Polymer Electrolyte Membrane (PEM) fuel cell stacks. The method is based on reducing the air flow rate from a high to low value at a fixed current, while maintaining an anode overpressure. At high air flow rates, the reduction in air flow results in lower oxygen concentration in the cathode and therefore reduction in cell voltages. Once the air flow rate in each cell reaches a low value at which the cell oxygen-starves, the voltage of the corresponding cell drops to zero. However, oxygen starvation results from two processes: 1) the electrochemical oxygen reduction reaction which produces current; and 2) the chemical reaction between oxygen and the crossed over hydrogen. In this work, a diagnostic technique has been developed that accounts for the effect of the electrochemical reaction on cell voltage to identify the hydrogen leak rate and number of leaky cells in a fuel cell stack. This technique is suitable for leak characterization during fuel cell operation, as it only requires stack air flow and voltage measurements, which are readily available in an operational fuel cell system.

Use of ion conductors in the pyrochemical reduction of oxides

DOEpatents

Miller, W.E.; Tomczuk, Z.

1994-02-01

An electrochemical process and electrochemical cell for reducing a metal oxide are provided. First the oxide is separated as oxygen gas using, for example, a ZrO[sub 2] oxygen ion conductor anode and the metal ions from the reduction salt are reduced and deposited on an ion conductor cathode, for example, sodium ion reduced on a [beta]-alumina sodium ion conductor cathode. The generation of and separation of oxygen gas avoids the problem with chemical back reaction of oxygen with active metals in the cell. The method also is characterized by a sequence of two steps where an inert cathode electrode is inserted into the electrochemical cell in the second step and the metallic component in the ion conductor is then used as the anode to cause electrochemical reduction of the metal ions formed in the first step from the metal oxide where oxygen gas formed at the anode. The use of ion conductors serves to isolate the active components from chemically reacting with certain chemicals in the cell. While applicable to a variety of metal oxides, the invention has special importance for reducing CaO to Ca[sup o] used for reducing UO[sub 2] and PuO[sub 2] to U and Pu. 2 figures.

Nitrogen-doped carbon-supported cobalt-iron oxygen reduction catalyst

DOEpatents

Zelenay, Piotr; Wu, Gang

2014-04-29

A Fe--Co hybrid catalyst for oxygen reaction reduction was prepared by a two part process. The first part involves reacting an ethyleneamine with a cobalt-containing precursor to form a cobalt-containing complex, combining the cobalt-containing complex with an electroconductive carbon supporting material, heating the cobalt-containing complex and carbon supporting material under conditions suitable to convert the cobalt-containing complex and carbon supporting material into a cobalt-containing catalyst support. The second part of the process involves polymerizing an aniline in the presence of said cobalt-containing catalyst support and an iron-containing compound under conditions suitable to form a supported, cobalt-containing, iron-bound polyaniline species, and subjecting said supported, cobalt-containing, iron bound polyaniline species to conditions suitable for producing a Fe--Co hybrid catalyst.

Direct reduction processes for titanium oxide in molten salt

NASA Astrophysics Data System (ADS)

Suzuki, Ryosuke O.

2007-02-01

Molten salt electrolysis using CaCl2 is employed to produce pure titanium and its alloys directly from TiO2 and a mixture of elemental oxides, respectively, as an alternate to the Kroll process. This is because CaO, which is a reduction by-product, is highly soluble in CaCl2. Good-quality titanium containing only a small amount of residual oxygen has been successfully produced and scaled to industrial levels. Thermochemical and electrochemical bases are reviewed to optimize the process conditions. Several processes using molten salt are being examined for future progress in titanium processing.

Removing oxygen from a solvent extractant in an uranium recovery process

DOEpatents

Hurst, Fred J.; Brown, Gilbert M.; Posey, Franz A.

1984-01-01

An improvement in effecting uranium recovery from phosphoric acid solutions is provided by sparging dissolved oxygen contained in solutions and solvents used in a reductive stripping stage with an effective volume of a nonoxidizing gas before the introduction of the solutions and solvents into the stage. Effective volumes of nonoxidizing gases, selected from the group consisting of argon, carbon dioxide, carbon monoxide, helium, hydrogen, nitrogen, sulfur dioxide, and mixtures thereof, displace oxygen from the solutions and solvents thereby reduce deleterious effects of oxygen such as excessive consumption of elemental or ferrous and accumulation of complex iron phosphates or cruds.

HIGH EFFICIENCY SYNGAS GENERATION

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

Robert J. Copeland; Yevgenia Gershanovich; Brian Windecker

2005-02-01

This project investigated an efficient and low cost method of auto-thermally reforming natural gas to hydrogen and carbon monoxide. Reforming is the highest cost step in producing products such as methanol and Fisher Tropsch liquids (i.e., gas to liquids); and reducing the cost of reforming is the key to reducing the cost of these products. Steam reforming is expensive because of the high cost of the high nickel alloy reforming tubes (i.e., indirectly fired reforming tubes). Conventional auto-thermal or Partial Oxidation (POX) reforming minimizes the size and cost of the reformers and provides a near optimum mixture of CO andmore » hydrogen. However POX requires pure oxygen, which consumes power and significantly increases the cost to reforming. Our high efficiency process extracts oxygen from low-pressure air with novel oxygen sorbent and transfers the oxygen to a nickel-catalyzed reformer. The syngas is generated at process pressure (typically 20 to 40 bar) without nitrogen dilution and has a 1CO to 2H{sub 2} ratio that is near optimum for the subsequent production of Fisher-Tropsch liquid to liquids and other chemicals (i.e., Gas to Liquids, GTL). Our high process efficiency comes from the way we transfer the oxygen into the reformer. All of the components of the process, except for the oxygen sorbent, are commonly used in commercial practice. A process based on a longlived, regenerable, oxygen transfer sorbent could substantially reduce the cost of natural gas reforming to syngas. Lower cost syngas (CO + 2H{sub 2}) that is the feedstock for GTL would reduce the cost of GTL and for other commercial applications (e.g., methanol, other organic chemicals). The vast gas resources of Alaska's North Slope (ANS) offer more than 22 Tcf of gas and GTL production in this application alone, and could account for as much as 300,000 to 700,000 bpd for 20 to 30+ years. We developed a new sorbent, which is an essential part of the High Efficiency Oxygen Process (HOP). We tested the sorbent and observed that it has both a good oxygen capacity and operates as a highly effective reforming catalyst. We conducted a long duration tests of the sorbent (1,500 hours of continuous operation in the HOP cycle). Although the sorbent lost some oxygen capacity with cycling, the sorbent oxygen capacity stabilized after 1,000 hours and remained constant to the end of the test, 1,500 hour. The activity of the catalyst to reform methane to a hydrogen and carbon monoxide mixture was unchanged through the oxidation/reduction cycling. Our cost and performance analyses indicated a significant reduction in the cost of GTL production when using the HOP process integrated into a GTL plant.« less

Reductive dechlorination of chlorinated ethenes under oxidation-reduction conditions and potentiometric surfaces in two trichloroethene-contaminated zones at the Double Eagle and Fourth Street Superfund sites in Oklahoma City, Oklahoma

USGS Publications Warehouse

Braun, Christopher L.

2004-01-01

The Double Eagle Refining Superfund site and the Fourth Street Abandoned Refinery Superfund site are in northeast Oklahoma City, Oklahoma, adjacent to one another. The Double Eagle facility became a Superfund site on the basis of contamination from lead and volatile organic compounds; the Fourth Street facility on the basis of volatile organic compounds, pesticides, and acid-base neutral compounds. The study documented in this report was done to investigate whether reductive dechlorination of chlorinated ethenes under oxidation-reduction conditions is occurring in two zones of the Garber-Wellington aquifer (shallow zone 30–60 to 75 feet below land surface, deep zone 75 to 160 feet below land surface) at the sites; and to construct potentiometric surfaces of the two water-yielding zones to determine the directions of groundwater flow at the sites. The presence in some wells of intermediate products of reductive dechlorination, dichloroethene and vinyl chloride, is an indication that reductive dechlorination of trichloroethene is occurring. Dissolved oxygen concentrations (less than 0.5 milligram per liter) indicate that consumption of dissolved oxygen likely had occurred in the oxygen-reducing microbial process associated with reductive dechlorination. Concentrations of nitrate and nitrite nitrogen (generally less than 2.0 and 0.06 milligrams per liter, respectively) indicate that nitrate reduction probably is not a key process in either aquifer zone. Concentrations of ferrous iron greater than 1.00 milligram per liter in the majority of wells sampled indicate that iron reduction is probable. Concentrations of sulfide less than 0.05 milligram per liter in all wells indicate that sulfate reduction probably is not a key process in either zone. The presence of methane in ground water is an indication of strongly reducing conditions that facilitate reductive dechlorination. Methane was detected in all but one well. In the shallow zone in the eastern part of the study area, ground water flowing from the northwest and south coalesces in a potentiometric trough, then moves westward and ultimately northwestward. In the western part of the study area, ground water in the shallow zone flows northwest. In the deep zone in the eastern part of the study area, ground water generally flows northwestward; and in the western part of the study area, ground water in the deep zone generally flows northward.

Comparison of Eh and H2 measurements for delineating redox processes in a contaminated aquifer

USGS Publications Warehouse

Chapelle, Francis H.; Haack, Sheridan K.; Adriaens, Peter; Henry, Mark A.; Bradley, Paul M.

1996-01-01

Measurements of oxidation-reduction potential (Eh) and concentrations of dissolved hydrogen (H2) were made in a shallow groundwater system contaminated with solvents and jet fuel to delineate the zonation of redox processes. Eh measurements ranged from +69 to -158 mV in a cross section of the contaminated plume and accurately delineated oxic from anoxic groundwater. Plotting measured Eh and pH values on an equilibrium stability diagram indicated that Fe(III) reduction was the predominant redox process in the anoxic zone and did not indicate the presence of methanogenesis and sulfate reduction. In contrast, measurements of H2concentrations indicated that methanogenesis predominated in heavily contaminated sediments near the water table surface (H2 ∼ 7.0 nM) and that the methanogenic zone was surrounded by distinct sulfate-reducing (H2 ∼ 1-4 nM) and Fe(III)-reducing (H2 ∼ 0.1-0.8 nM) zones. The presence of methanogenesis, sulfate reduction, and Fe(III) reduction was confirmed by the distribution of dissolved oxygen, sulfate, Fe(II), and methane in groundwater. These results show that H2 concentrations were more useful for identifying anoxic redox processes than Ehmeasurements in this groundwater system. However, H2-based redox zone delineations are more reliable when H2 concentrations are interpreted in the context of electron-acceptor (oxygen, nitrate, sulfate) availability and the presence of final products [Fe(II), sulfide, methane] of microbial metabolism.

Overview of Research for Lunar Oxygen Processing at Carbotek Development Laboratories

NASA Astrophysics Data System (ADS)

Ortego, J. D., Jr.; Sorge, L. L.; Guo-Murray, M.; Gibson, M. A.; Knudsen, C. W.

1997-01-01

Oxygen production from indigenous lunar material is considered an enabling technology for future solar system exploration. Lunar derived oxygen provides many lunar base program enhancements. A great mass benefit can be derived when Earth return propellant oxidizer is not manifested for transit vehicles traveling to the moon. This results in substantial cost savings to the overall space transportation infrastructure. In addition, lunar produced oxygen can be used to supplement life support systems. Finally, many of the lunar oxygen processes under development produce by-products which are excellent construction materials, rich in iron and titanium, for shielding habitats and lunar surface equipment from cosmic radiation and more lethal solar flares. As a result of the apparent benefits of lunar derived oxygen, NASA has funded research for the development of promising techniques since the mid- 1980's in order for the technology to be available for lunar return missions. Carbotek, with funding and technical assistance f om NASA Johnson Space Center and the Shimizu Corporation, Space Systems Division, has been developing oxygen producing technology since 1984. This paper describes past and future work by Carbotek on two processes, hydrogen reduction of ilmenite and magma electrolysis.

Pinpoint and bulk electrochemical reduction of insulating silicon dioxide to silicon.

PubMed

Nohira, Toshiyuki; Yasuda, Kouji; Ito, Yasuhiko

2003-06-01

Silicon dioxide (SiO(2)) is conventionally reduced to silicon by carbothermal reduction, in which the oxygen is removed by a heterogeneous-homogeneous reaction sequence at approximately 1,700 degrees C. Here we report pinpoint and bulk electrochemical methods for removing oxygen from solid SiO(2) in a molten CaCl(2) electrolyte at 850 degrees C. This approach involves a 'contacting electrode', in which a metal wire supplies electrons to a selected region of the insulating SiO(2). Bulk reduction of SiO(2) is possible by increasing the number of contacting points. The same method was also demonstrated with molten LiCl-KCl-CaCl(2) at 500 degrees C. The novelty and relative simplicity of this method might lead to new processes in silicon semiconductor technology, as well as in high-purity silicon production. The methodology may be applicable to electrochemical processing of a wide variety of insulating materials, provided that the electrolyte dissolves the appropriate constituent ion(s) of the material.

A New Pyrometallurgical Process for Producing Antimony White from By-Product of Lead Smelting

NASA Astrophysics Data System (ADS)

Liu, Weifeng; Yang, Tianzu; Zhang, Duchao; Chen, Lin; Liu, Yunfeng

2014-09-01

Antimonial dust is a by-product of lead smelting and an important material for extracting antimony. A new pyrometallurgical process for producing antimony white from the antimonial dust is reported. The process mainly consists of three steps, which are reduction smelting, alkaline refining, and blowing oxidation. First, the reduction smelting of antimonial dust is carried out in an oxygen-rich bottom blow furnace to enrich antimony and lead in the crude alloy. The antimony and lead contents in the slag can thus be reduced to 2.8 wt.% and 0.1 wt.%, respectively. Second, the conventional method of alkaline refining is adopted to remove arsenic from the crude alloy, and arsenic content in the low-arsenic alloy could be decreased to 0.009 wt.%. Finally, the low-arsenic alloy is oxidized in a special oxidizing pan at 650°C by blowing compressed air or oxygen-rich air on the surface, during which qualified antimony white can be produced and collected in a bag house. The oxygen concentration and antimony content in the bottom alloy have a significant impact on production efficiency and product quality during blowing oxidation.

Electrochemical oxygen reduction behavior of selectively deposited platinum atoms on gold nanoparticles.

PubMed

Sarkar, A; Kerr, J B; Cairns, E J

2013-07-22

Carbon-supported Pt@Au "core-shell" nanoparticles with varying surface concentration of platinum atoms have been synthesized using a novel redox-mediated synthesis approach. The synthesis technique allows for a selective deposition of platinum atoms on the surface of prefabricated gold nanoparticles. Energy dispersive spectroscopic analyses in a scanning electron microscope reveal that the platinum to gold atomic ratios are close to the nominal values, validating the synthesis scheme. X-ray diffraction data indicate an un-alloyed structure. The platinum to gold surface atomic ratio determined from cyclic voltammetry and copper under-potential deposition experiments reveal good agreement with the calculated values at low platinum concentration. However, there is an increase in non-uniformity in the deposition process upon increasing the platinum concentration. Koutecky-Levich analysis of the samples indicates a transition of the total number of electrons transferred (n) in the electrochemical oxygen reduction reaction from two to four electrons upon increasing the surface concentration of platinum atoms. Furthermore, the data indicate that isolated platinum atoms can reduce molecular oxygen but via a two-electron route. Moreover, successful four-electron reduction of molecular oxygen requires clusters of platinum atoms. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficiency of autothermal thermophilic aerobic digestion under two different oxygen flow rates.

PubMed

Aynur, Sebnem Koyunluoglu; Riffat, Rumana; Murthy, Sudhir

2014-01-01

The objective of this research was to understand the influence of oxygenation at two different oxygen flow rates (0.105 and 0.210 L/L/h) on autothermal thermophilic aerobic digestion (ATAD), and on the overall performance of Dual Digestion (DD). Profile experiments on an ATAD reactor showed that a significant portion of volatile fatty acids and ammonia were produced in the first 12 h period, and both followed first order kinetics. Ammonia concentrations of ATAD effluent were 1015 mg/L and 1450 mg/L, respectively, at the two oxygenation rates. Ammonia production was not complete in the ATAD reactor at the lower oxygenation rate. However, it was sufficient to maximize volatile solids reduction in the DD process. The biological heat of oxidations were 14,300 J/g Volatile Solids (VS) removed and 15,900 J/g VS removed for the two oxygen flow rates, respectively. The ATAD step provided enhanced digestion for the DD process with higher volatile solids removal and methane yield when compared to conventional digestion.

Development and Validation of a Model for Hydrogen Reduction of JSC-1A

NASA Technical Reports Server (NTRS)

Hegde, U.; Balasubramaniam, R.; Gokoglu, S.

2009-01-01

Hydrogen reduction of lunar regolith has been proposed as a viable technology for oxygen production on the moon. Hydrogen reduces FeO present in the lunar regolith to form metallic iron and water. The water may be electrolyzed to recycle the hydrogen and produce oxygen. Depending upon the regolith composition, FeO may be bound to TiO2 as ilmenite or it may be dispersed in glassy substrates. Some testing of hydrogen reduction has been conducted with Apollo-returned lunar regolith samples. However, due to the restricted amount of lunar material available for testing, detailed understanding and modeling of the reduction process in regolith have not yet been developed. As a step in this direction, hydrogen reduction studies have been carried out in more detail with lunar regolith simulants such as JSC-1A by NASA and other organizations. While JSC-1A has some similarities with lunar regolith, it does not duplicate the wide variety of regolith types on the moon, for example, it contains almost no ilmenite. Nonetheless, it is a good starting point for developing an understanding of the hydrogen reduction process with regolith-like material. In this paper, a model utilizing a shrinking core formulation coupled with the reactor flow is described and validated against experimental data on hydrogen reduction of JSC-1A.

Evolution of Structural and Electrical Properties of Oxygen-Deficient VO2 under Low Temperature Heating Process.

PubMed

Zhang, Jiasong; Zhao, Zhengjing; Li, Jingbo; Jin, Haibo; Rehman, Fida; Chen, Pengwan; Jiang, Yijie; Chen, Chunxu; Cao, Maosheng; Zhao, Yongjie

2017-08-16

Structural stability and functional performances of vanadium dioxide (VO 2 ) are strongly influenced by oxygen vacancies. However, the mechanism of metal-insulator transition (MIT) influenced by defects is still under debate. Here, we study the evolution of structure and electrical property of oxygen-deficient VO 2 by a low temperature annealing process (LTP) based on a truss-structured VO 2 nanonet. The oxygenation process of the oxygen-deficient VO 2 is greatly prolonged, which enables us to probe the gradual change of properties of the oxygen-deficient VO 2 . A continuous lattice reduction is observed during LTP. No recrystallization and structural collapse of the VO 2 nanonet can be found after LTP. The valence-band X-ray photoelectron spectroscopy (XPS) measurements indicate that the oxygen deficiency strongly affects the energy level of the valence band edge. Correspondingly, the resistance changes of the VO 2 films from 1 to 4.5 orders of magnitude are achieved by LTP. The effect of oxygen vacancy on the electric field driven MIT is investigated. The threshold value of voltage triggering the MIT decreases with increasing the oxygen vacancy concentration. This work demonstrates a novel and effective way to control the content of oxygen vacancies in VO 2 and the obvious impact of oxygen vacancy on MIT, facilitating further research on the role of oxygen vacancy in structure and MIT of VO 2 , which is important for the deep understanding of MIT and exploiting innovative functional application of VO 2 .

Process of activation of a palladium catalyst system

DOEpatents

Sobolevskiy, Anatoly [Orlando, FL; Rossin, Joseph A [Columbus, OH; Knapke, Michael J [Columbus, OH

2011-08-02

Improved processes for activating a catalyst system used for the reduction of nitrogen oxides are provided. In one embodiment, the catalyst system is activated by passing an activation gas stream having an amount of each of oxygen, water vapor, nitrogen oxides, and hydrogen over the catalyst system and increasing a temperature of the catalyst system to a temperature of at least 180.degree. C. at a heating rate of from 1-20.degree./min. Use of activation processes described herein leads to a catalyst system with superior NOx reduction capabilities.

Investigation of catalytic activity towards oxygen reduction reaction of Pt dispersed on boron doped graphene in acid medium.

PubMed

Pullamsetty, Ashok; Sundara, Ramaprabhu

2016-10-01

Boron doped graphene was prepared by a facile method and platinum (Pt) decoration over boron doped graphene was done in various chemical reduction methods such as sodium borohydride (NaBH4), polyol and modified polyol. X-ray diffraction analysis indicates that the synthesized catalyst particles are present in a nanocrystalline structure and transmission and scanning electron microscopy were employed to investigate the morphology and particle distribution. The electrochemical properties were investigated with the help of the rotating disk electrode (RDE) technique and cyclic voltammetry. The results show that the oxygen reduction reaction (ORR) takes place by a four-electron process. The kinetics of the ORR was evaluated using K-L and Tafel plots. The electrocatalyst obtained in modified polyol reduction method has shown the better catalytic activity compared to other two electrocatalysts. Copyright © 2016 Elsevier Inc. All rights reserved.

Nitrogen and Fluorine-Codoped Carbon Nanowire Aerogels as Metal-Free Electrocatalysts for Oxygen Reduction Reaction

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

Fu, Shaofang; Zhu, Chengzhou; Song, Junhua

2017-07-11

The development of active, durable, and low-cost catalysts to replace noble metal-based materials is highly desirable to promote the sluggish oxygen reduction reaction in fuel cells. Herein, nitrogen and fluorine-codoped three-dimensional carbon nanowire aerogels, composed of interconnected carbon nanowires, were synthesized for the first time by a hydrothermal carbonization process. Owing to their porous nanostructures and heteroatom-doping, the as-prepared carbon nanowire aerogels, with optimized composition, present excellent electrocatalytic activity that is comparable to commercial Pt/C. Remarkably, the aerogels also exhibit superior stability and methanol tolerance. This synthesis procedure paves a new way to design novel heteroatomdoped catalysts.

Carbothermal Processing of Lunar Regolith Using Methane

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Hegde, U.; Gokoglu, S.

2009-01-01

The processing of lunar regolith for the production of oxygen is a key component of the In-Situ Resource Utilization plans currently being developed by NASA. Among various candidate processes, the modeling of oxygen production by hydrogen reduction, molten salt electrolysis, and carbothermal processing are presently being pursued. In the carbothermal process, a portion of the surface of the regolith in a container is heated by exposure to a heat source such as a laser beam or a concentrated solar heat flux, so that a small zone of molten regolith is established. The molten zone is surrounded by solid regolith particles that are poor conductors of heat. A continuous flow of methane is maintained over the molten regolith zone. Our model is based on a mechanism where methane pyrolyzes when it comes in contact with the surface of the hot molten regolith to form solid carbon and hydrogen gas. Carbon is deposited on the surface of the melt, and hydrogen is released into the gas stream above the melt surface. We assume that the deposited carbon mixes in the molten regolith and reacts with metal oxides in a reduction reaction by which gaseous carbon monoxide is liberated. Carbon monoxide bubbles through the melt and is released into the gas stream. Oxygen is produced subsequently by (catalytically) processing the carbon monoxide downstream. In this paper, we discuss the development of a chemical conversion model of the carbothermal process to predict the rate of production of carbon monoxide.

Carbothermal Processing of Lunar Regolith Using Methane

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Hegde, U.; Gokoglu, S.

2008-01-01

The processing of lunar regolith for the production of oxygen is a key component of the In-Situ Resource Utilization plans currently being developed by NASA. Among various candidate processes, the modeling of oxygen production by hydrogen reduction, molten salt electrolysis, and carbothermal processing are presently being pursued. In the carbothermal process, a portion of the surface of the regolith in a container is heated by exposure to a heat source such as a laser beam or a concentrated solar heat flux, so that a small zone of molten regolith is established. The molten zone is surrounded by solid regolith particles that are poor conductors of heat. A continuous flow of methane is maintained over the molten regolith zone. Our model is based on a mechanism where methane pyrolyzes when it comes in contact with the surface of the hot molten regolith to form solid carbon and hydrogen gas. Carbon is deposited on the surface of the melt, and hydrogen is released into the gas stream above the melt surface. We assume that the deposited carbon mixes in the molten regolith and reacts with metal oxides in a reduction reaction by which gaseous carbon monoxide is liberated. Carbon monoxide bubbles through the melt and is released into the gas stream. Oxygen is produced subsequently by (catalytically) processing the carbon monoxide downstream. In this paper, we discuss the development of a chemical conversion model of the carbothermal process to predict the rate of production of carbon monoxide.

Reduction of surface leakage current by surface passivation of CdZn Te and other materials using hyperthermal oxygen atoms

DOEpatents

Hoffbauer, Mark A.; Prettyman, Thomas H.

2001-01-01

Reduction of surface leakage current by surface passivation of Cd.sub.1-x Zn.sub.x Te and other materials using hyperthermal oxygen atoms. Surface effects are important in the performance of CdZnTe room-temperature radiation detectors used as spectrometers since the dark current is often dominated by surface leakage. A process using high-kinetic-energy, neutral oxygen atoms (.about.3 eV) to treat the surface of CdZnTe detectors at or near ambient temperatures is described. Improvements in detector performance include significantly reduced leakage current which results in lower detector noise and greater energy resolution for radiation measurements of gamma- and X-rays, thereby increasing the accuracy and sensitivity of measurements of radionuclides having complex gamma-ray spectra, including special nuclear materials.

A combined electrocoagulation-sorption process applied to mixed industrial wastewater.

PubMed

Linares-Hernández, Ivonne; Barrera-Díaz, Carlos; Roa-Morales, Gabriela; Bilyeu, Bryan; Ureña-Núñez, Fernando

2007-06-01

The removal of organic pollutants from a highly complex industrial wastewater by a aluminium electrocoagulation process coupled with biosorption was evaluated. Under optimal conditions of pH 8 and 45.45 Am(-2) current density, the electrochemical method yields a very effective reduction of all organic pollutants, this reduction was enhanced when the biosorption treatment was applied as a polishing step. Treatment reduced chemical oxygen demand (COD) by 84%, biochemical oxygen demand (BOD(5)) by 78%, color by 97%, turbidity by 98% and fecal coliforms by 99%. The chemical species formed in aqueous solution were determined. The initial and final pollutant levels in the wastewater were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and elemental composition of the biosorbent was characterized with scanning electron microscopy (SEM) and energy dispersion spectra (EDS).

Heterojunction-Assisted Co3 S4 @Co3 O4 Core-Shell Octahedrons for Supercapacitors and Both Oxygen and Carbon Dioxide Reduction Reactions.

PubMed

Yan, Yibo; Li, Kaixin; Chen, Xiaoping; Yang, Yanhui; Lee, Jong-Min

2017-12-01

Expedition of electron transfer efficiency and optimization of surface reactant adsorption products desorption processes are two main challenges for developing non-noble catalysts in the oxygen reduction reaction (ORR) and CO 2 reduction reaction (CRR). A heterojunction prototype on Co 3 S 4 @Co 3 O 4 core-shell octahedron structure is established via hydrothermal lattice anion exchange protocol to implement the electroreduction of oxygen and carbon dioxide with high performance. The synergistic bifunctional catalyst consists of p-type Co 3 O 4 core and n-type Co 3 S 4 shell, which afford high surface electron density along with high capacitance without sacrificing mechanical robustness. A four electron ORR process, identical to the Pt catalyzed ORR, is validated using the core-shell octahedron catalyst. The synergistic interaction between cobalt sulfide and cobalt oxide bicatalyst reduces the activation energy to convert CO 2 into adsorbed intermediates and hereby enables CRR to run at a low overpotential, with formate as the highly selective main product at a high faraday efficiency of 85.3%. The remarkable performance can be ascribed to the synergistic coupling effect of the structured co-catalysts; heterojunction structure expedites the electron transfer efficiency and optimizes surface reactant adsorption product desorption processes, which also provide theoretical and pragmatic guideline for catalyst development and mechanism explorations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of oxygen content of Nd-Fe-B sintered magnet on grain boundary diffusion process of DyH2 dip-coating

NASA Astrophysics Data System (ADS)

Bae, Kyoung-Hoon; Lee, Seong-Rae; Kim, Hyo-Jun; Lee, Min-Woo; Jang, Tae-Suk

2015-11-01

We investigated the effect of oxygen content on the microstructural and magnetic properties of a DyH2 dip-coated Nd-Fe-B sintered magnet. When the magnet had a low oxygen content (1500 ppm), the volume and size of the rare-earth-rich oxide (Nd-Dy-O) phase was reduced, and a uniform and continuous thin Nd-rich grain boundary phase (GBP) was well developed. The grain boundary diffusion depth of Dy increased from 200 to 350 μm with decreasing oxygen content from ˜3000 to 1500 ppm. The coercivity of the low-oxygen magnet increased from 19.98 to 23.59 kOe after grain boundary diffusion process (GBDP) while the remanence reduction was minimized. The formation of an fcc-NdOx Nd-rich phase in the high-oxygen magnet hindered the formation of a Nd-rich triple-junction phase and GBP. In contrast, a metallic dhcp-Nd phase, which was closely related to coercivity enhancement after GBDP, was formed in the low-oxygen magnet.

Pressure dependence of the oxygen reduction reaction at the platinum microelectrode/nafion interface - Electrode kinetics and mass transport

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Srinivasan, Supramaniam; Appleby, A. J.; Martin, Charles R.

1992-01-01

The investigation of oxygen reduction kinetics at the platinum/Nafion interface is of great importance in the advancement of proton-exchange-membrane (PEM) fuel-cell technology. This study focuses on the dependence of the oxygen reduction kinetics on oxygen pressure. Conventional Tafel analysis of the data shows that the reaction order with respect to oxygen is unity at both high and low current densities. Chronoamperometric measurements of the transport parameters for oxygen in Nafion show that oxygen dissolution follows Henry's isotherm. The diffusion coefficient of oxygen is invariant with pressure; however, the diffusion coefficient for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration. These results are of value in understanding the influence of O2 partial pressure on the performance of PEM fuel cells and also in elucidating the mechanism of oxygen reduction at the platinum/Nafion interface.

Vanadium proton exchange membrane water electrolyser

NASA Astrophysics Data System (ADS)

Noack, Jens; Roznyatovskaya, Nataliya; Pinkwart, Karsten; Tübke, Jens

2017-05-01

In order to reverse the reactions of vanadium oxygen fuel cells and to regenerate vanadium redox flow battery electrolytes that have been oxidised by atmospheric oxygen, a vanadium proton exchange membrane water electrolyser was set up and investigated. Using an existing cell with a commercial and iridium-based catalyst coated membrane, it was possible to fully reduce V3.5+ and V3+ solutions to V2+ with the formation of oxygen and with coulomb efficiencies of over 96%. The cell achieved a maximum current density of 75 mA/cm2 during this process and was limited by the proximity of the V(III) reduction to the hydrogen evolution reaction. Due to the specific reaction mechanisms of V(IV) and V(III) ions, V(III) solutions were reduced with an energy efficiency of 61%, making this process nearly twice as energy efficient as the reduction of V(IV) to V(III). Polarisation curves and electrochemical impedance spectroscopy were used to further investigate the losses of half-cell reactions and to find ways of further increasing efficiency and performance levels.

Sulfur cycling in plays an important role in the development of Ocean Anoxic Events

NASA Astrophysics Data System (ADS)

Gomes, M. L.; Raven, M. R.; Fike, D. A.; Gill, B. C.; Johnston, D. T.

2017-12-01

Ocean Anoxic Events (OAEs) are major carbon cycle perturbations marked by enhanced organic carbon deposition in the marine realm and carbon isotope excursions in organic and inorganic carbon. Although not as severe as the "big five" mass extinctions, OAEs had dire consequences for marine ecosystems and thus influenced Mesozoic evolutionary patterns. Sulfur cycle reconstructions provide insight into the biogeochemical processes that played a role in the development of OAEs because the sulfur cycle is linked with the carbon and oxygen cycles. We present sulfur and oxygen isotope records from carbonate-associated sulfate from the Toarcian OAE that documents a positive sulfate-oxygen isotope excursion of +6‰, which is similar to the magnitude of the positive sulfur isotope excursion documented at the same site and other globally distributed sites. This high-resolution record allows us to explore temporal variability in the onset of the isotopic excursions: the onset of the positive sulfate-oxygen isotope excursion occurs at the same stratigraphic interval as the onset of the positive carbon isotope excursion and both precede the onset of the positive sulfate-sulfur isotope excursion. Because oxygen is rapidly recycled during oxidative sulfur cycling, changes in oxidative sulfur cycling affect oxygen isotope values of sulfate without impacting sulfur isotope values. Thus, the early onset of the sulfate-oxygen isotope excursion implies a change in oxidative sulfur cycling, which is likely due to a shoaling of the zone of sulfate reduction. We explore the consequences of sulfate reduction zone shoaling for organic carbon preservation. Specifically, the sulfurization of organic matter, which makes organic matter less susceptible to degradation, occurs more rapidly when the top of the zone of sulfate reduction is near or above the sediment water interface. Therefore, we suggest that the shoaling of the sulfate reduction zone locally changed pathways of oxidative sulfur cycling and enhanced organic carbon preservation. Given synchronous changes in similar, globally-distributed depositional environments, this impacted the global biogeochemical cycles of oxygen, carbon, and nutrients in ways that sustained decreased oxygen availability and influenced extinction patterns of marine organisms.

Effect of temperature on reduction of CaSO{sub 4} oxygen carrier in chemical-looping combustion of simulated coal gas in a fluidized bed reactor

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

Song, Q.L.; Xiao, R.; Deng, Z.Y.

2008-12-15

Chemical-looping combustion (CLC) is a promising combustion technology for gaseous and solid fuel with efficient use of energy and inherent separation of CO{sub 2}. The concept of a coal-fueled CLC system using, calcium sulfate (CaSO{sub 4}) as oxygen carrier is proposed in this study. Reduction tests of CaSO{sub 4} oxygen carrier with simulated coal gas were performed in a laboratory-scale fluidized bed reactor in the temperature range of 890-950{degree}C. A high concentration of CO{sub 2} was obtained at the initial reduction period. CaSO{sub 4} oxygen carrier exhibited high reactivity initially and decreased gradually at the late period of reduction. Themore » sulfur release during the reduction of CaSO{sub 4} as oxygen carrier was also observed and analyzed. H{sub 2} and CO{sub 2} conversions were greatly influenced by reduction temperature. The oxygen carrier conversion and mass-based reaction rates during the reduction at typical temperatures were compared. Higher temperatures would enhance reaction rates and result in high conversion of oxygen carrier. An XRD patterns study indicated that CaS was the dominant product of reduction and the variation of relative intensity with temperature is in agreement with the solid conversion. ESEM analysis indicated that the surface structure of oxygen carrier particles changed significantly from impervious to porous after reduction. EDS analysis also demonstrated the transfer of oxygen from the oxygen carrier to the fuel gas and a certain amount of sulfur loss and CaO formation on the surface at higher temperatures. The reduction kinetics of CaSO{sub 4} oxygen carrier was explored with the shrinking unreacted-core model. The apparent kinetic parameters were obtained, and the kinetic equation well predicted the experimental data. Finally, some basic considerations on the use of CaSO{sub 4} oxygen carrier in a CLC system for solid fuels were discussed.« less

A dual-plate ITO-ITO generator-collector microtrench sensor: surface activation, spatial separation and suppression of irreversible oxygen and ascorbate interference.

PubMed

Hasnat, Mohammad A; Gross, Andrew J; Dale, Sara E C; Barnes, Edward O; Compton, Richard G; Marken, Frank

2014-02-07

Generator-collector electrode systems are based on two independent working electrodes with overlapping diffusion fields where chemically reversible redox processes (oxidation and reduction) are coupled to give amplified current signals. A generator-collector trench electrode system prepared from two tin-doped indium oxide (ITO) electrodes placed vis-à-vis with a 22 μm inter-electrode gap is employed here as a sensor in aqueous media. The reversible 2-electron anthraquinone-2-sulfonate redox system is demonstrated to give well-defined collector responses even in the presence of oxygen due to the irreversible nature of the oxygen reduction. For the oxidation of dopamine on ITO, novel "Piranha-activation" effects are observed and chemically reversible generator-collector feedback conditions are achieved at pH 7, by selecting a more negative collector potential, again eliminating possible oxygen interference. Finally, dopamine oxidation in the presence of ascorbate is demonstrated with the irreversible oxidation of ascorbate at the "mouth" of the trench electrode and chemically reversible oxidation of dopamine in the trench "interior". This spatial separation of chemically reversible and irreversible processes within and outside the trench is discussed as a potential in situ microscale sensing and separation tool.

Living with a large reduction in permited loading by using a hydrograph-controlled release scheme

USGS Publications Warehouse

Conrads, P.A.; Martello, W.P.; Sullins, N.R.

2003-01-01

The Total Maximum Daily Load (TMDL) for ammonia and biochemical oxygen demand for the Pee Dee, Waccamaw, and Atlantic Intracoastal Waterway system near Myrtle Beach, South Carolina, mandated a 60-percent reduction in point-source loading. For waters with a naturally low background dissolved-oxygen concentrations, South Carolina anti-degradation rules in the water-quality regulations allows a permitted discharger a reduction of dissolved oxygen of 0.1 milligrams per liter (mg/L). This is known as the "0.1 rule." Permitted dischargers within this region of the State operate under the "0.1 rule" and cannot cause a cumulative impact greater than 0.1 mg/L on dissolved-oxygen concentrations. For municipal water-reclamation facilities to serve the rapidly growing resort and retirement community near Myrtle Beach, a variable loading scheme was developed to allow dischargers to utilize increased assimilative capacity during higher streamflow conditions while still meeting the requirements of a recently established TMDL. As part of the TMDL development, an extensive real-time data-collection network was established in the lower Waccamaw and Pee Dee River watershed where continuous measurements of streamflow, water level, dissolved oxygen, temperature, and specific conductance are collected. In addition, the dynamic BRANCH/BLTM models were calibrated and validated to simulate the water quality and tidal dynamics of the system. The assimilative capacities for various streamflows were also analyzed. The variable-loading scheme established total loadings for three streamflow levels. Model simulations show the results from the additional loading to be less than a 0.1 mg/L reduction in dissolved oxygen. As part of the loading scheme, the real-time network was redesigned to monitor streamflow entering the study area and water-quality conditions in the location of dissolved-oxygen "sags." The study reveals how one group of permit holders used a variable-loading scheme to implement restrictive permit limits without experiencing prohibitive capital expenditures or initiating a lengthy appeals process.

Effects of oxidation reduction potential in the bypass micro-aerobic sludge zone on sludge reduction for a modified oxic-settling-anaerobic process.

PubMed

Li, Kexun; Wang, Yi; Zhang, Zhongpin; Liu, Dongfang

2014-01-01

Batch experiments were conducted to determine the effect of oxidation reduction potential (ORP) on sludge reduction in a bypass micro-aerobic sludge reduction system. The system was composed of a modified oxic-settling-anaerobic process with a sludge holding tank in the sludge recycle loop. The ORPs in the micro-aerobic tanks were set at approximately +350, -90, -150, -200 and -250 mV, by varying the length of aeration time for the tanks. The results show that lower ORP result in greater sludge volume reduction, and the sludge production was reduced by 60% at the lowest ORP. In addition, low ORP caused extracellular polymer substances dissociation and slightly reduced sludge activity. Comparing the sludge backflow characteristics of the micro-aerobic tank's ORP controlled at -250 mV with that of +350 mV, the average soluble chemical oxygen (SCOD), TN and TP increased by 7, 0.4 and 2 times, median particle diameter decreased by 8.5 μm and the specific oxygen uptake rate (SOUR) decreased by 0.0043 milligram O2 per gram suspended solids per minute. For the effluent, SCOD and TN and TP fluctuated around 30, 8.7 and 0.66 mg/L, respectively. Therefore, the effective assignment of ORP in the micro-aerobic tank can remarkably reduce sludge volume and does not affect final effluent quality.

Control of occupational exposure to hexavalent chromium and ozone in tubular wire arc-welding processes by replacement of potassium by lithium or by addition of zinc.

PubMed

Dennis, John H; French, Michael J; Hewitt, Peter J; Mortazavi, Seyed B; Redding, Christopher A J

2002-01-01

Hexavalent chromium [Cr(VI)] and ozone are produced in many arc-welding processes. Cr(VI) is formed when welding with chromium-containing alloys and is a suspected carcinogen. Ozone is formed by the action of ultraviolet light from the arc on oxygen and can cause severe irritation to the eyes and mucous membranes. Previous work has demonstrated that reduction of sodium and potassium in manual metal arc-welding electrodes leads to substantial reductions in Cr(VI) concentrations in the fume as well as a reduction in the fume formation rate. In this paper replacement of potassium by lithium in a tubular wire welding electrode (self-shielding flux-cored) is shown to give reductions in Cr(VI) concentrations and fume formation rates. Previous work has also demonstrated that use of a tubular wire (metal cored) containing 1% zinc can, under certain conditions, result in a reduction in Cr(VI) formation rate and in ozone concentration near the arc but with a rise in the total fume formation rate. The effects of different shield gases and different levels of zinc are examined. An experimental chromium-containing tubular wire with 1% zinc was used with the following shield gases: argon, Argoshield 5, Argoshield 20, Helishield 101, Ar + 2% CO2, Ar + 5% CO2, Ar + 1% O2 and Ar + 2% O2. The wire gave > 98% reduction in Cr(VI) formation rate compared to the control wire provided the shield gas contained no oxygen. When the shield gas did contain oxygen, 1% zinc enhanced Cr(VI) formation rate, resulting in more than double the rates measured when welding with the control wire. Experiments with zinc concentrations, from 0.018 to 0.9% using Helishield 101, gave results indicating that there is an optimum zinc concentration from the point of view of Cr(VI) reduction. Implications of the use of lithium or zinc on the overall exposure risk are discussed.

Impact of microbial activity on the hydraulic properties of fractured chalk.

PubMed

Arnon, Shai; Adar, Eilon; Ronen, Zeev; Yakirevich, Alexander; Nativ, Ronit

2005-02-01

The impact of microbial activity on fractured chalk transmissivity was investigated on a laboratory scale. Long-term experiments were conducted on six fractured chalk cores (20 cm diameter, 23-44 cm long) containing a single natural fracture embedded in a porous matrix. Biodegradation experiments were conducted under various conditions, including several substrate and oxygen concentrations and flow rates. 2,4,6-Tribromophenol (TBP) was used as a model contaminant (substrate). TBP biodegradation efficiency depended mainly on the amount of oxygen. However, under constant oxygen concentration at the core inlet, elevating the flow rates increased the removal rate of TBP. Transmissivity reduction was clearly related to TBP removal rate, following an initial slow decline and a further sharp decrease with time. The fracture's transmissivity was reduced by as much as 97% relative to the initial value, with no leveling off of the clogging process. For the most extreme cases, reductions of 262 and 157 microm in the equivalent hydraulic apertures were recorded for fractures with initial apertures of 495 and 207 microm, respectively. The reductions in fracture transmissivity occurred primarily because of clogging by bacterial cells and extracellular polymeric substances (EPS) produced by the bacteria. Most of the biodegradation activity was concentrated near the fracture inlet, where the most suitable biodegradation conditions (nutrients and oxygen) prevailed, suggesting that the clogging had occurred in that vicinity. The clogging must have changed the structure of the fracture void, thereby reducing the active volume participating in flow and transport processes. This phenomenon caused accelerated transport of non-reactive tracers and doubled the fracture's dispersivity under constant flow rates.

Onion-derived N, S self-doped carbon materials as highly efficient metal-free electrocatalysts for the oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Yang, Shuting; Mao, Xinxin; Cao, Zhaoxia; Yin, Yanhong; Wang, Zhichao; Shi, Mengjiao; Dong, Hongyu

2018-01-01

Onion-derived nitrogen, sulfur self-doped nanoporous carbon spheres (NSC) as efficient metal-free electrocatalyst were synthesized via a facile hydrothermal and subsequent pyrolysis process. The typical NSC with a high BET specific surface area of 1558 m2 g-1, contains 6.23 at.% N and 0.36 at.% S, and possesses high concentration of pyridinic and graphitic nitrogen species. Experimentally, the best performance was the NSC-A2 which showed excellent catalytic activity to oxygen reduction reaction via a 4 electron mechanism with an onset potential of 0.88 V (vs. RHE), and a superior stability comparable to commercial Pt/C catalyst. The high electrocatalytic activity is attributed to not only the synergistic effect of N and S dual doping in carbon and the sufficient active sites, but also its high BET specific surface area and suitable microporous structure. The results demonstrate that it is a simple and scalable approach for preparing efficient and low-cost carbon-based electrocatalysts for oxygen reduction reaction.

Impedimetric investigation of dual electrical properties of reduced graphene-oxide-based biosensors in the detection of dopamine.

PubMed

Shu-Ping Lin; Jhong-Yi Ciou; Tung-Yen Lai; Tsung-Wu Lin

2017-07-01

Because of the properties of high charge mobility, large detection area and chemical stability of graphene, it has been applied in many biomedical applications. Graphene oxide (GO) with abundant oxygenated functional groups is easily to form an aqueous suspension by sonication. Here, the exposed areas on the patterned-circuit silicon-based chips were first modified by (3-aminopropyl) trimethoxysilane (APTMS) for later chemically immobilized GO. After that, solution-based reduction process using hydrazine was used to gain reduced GO (RGO)-based biosensors. ESCA survey spectra showed oxygen-containing functional groups of GO decreased from 47% to 5.7%, 4.1%, 3.8%, and 3.6% under varied reduction times of 30 min, 40 min, 50 min, and 60 min, respectively. D/G intensity ratio (I D /I G ) in Raman spectra showed 1.03 after 60-min reduction process. The 60-min reduction process was further used in the electrical sensing experiments. Since different deposited layers of graphene were obtained in our experimental processes, 60-min-RGO-based biosensors have been found that those immobilized RGO possessed semiconductive property as the layers are less than 11. By contrary, when the layers were above 11, the immobilized RGO would resemble metallic material. In addition, the impedimetric analyses indicated obvious signal responses above 86 kHz and showed a concentration-dependent trend in dopamine sensing in physiological phosphate buffered saline (PBS) using 60-min-RGO-based biosensors which were feature of semiconductor.

Methane Post-Processor Development to Increase Oxygen Recovery beyond State-of-the-Art Carbon Dioxide Reduction Technology

NASA Technical Reports Server (NTRS)

Abney, Morgan; Miller, Lee; Greenwood, Zach; Iannantuono, Michelle; Jones, Kenny

2013-01-01

State-of-the-art life support carbon dioxide (CO2) reduction technology, based on the Sabatier reaction, is theoretically capable of 50% recovery of oxygen from metabolic CO2. This recovery is constrained by the limited availability of reactant hydrogen. Post-processing of the methane byproduct from the Sabatier reactor results in hydrogen recycle and a subsequent increase in oxygen recovery. For this purpose, a Methane Post-Processor Assembly containing three sub-systems has been developed and tested. The assembly includes a Methane Purification Assembly (MePA) to remove residual CO2 and water vapor from the Sabatier product stream, a Plasma Pyrolysis Assembly (PPA) to partially pyrolyze methane into hydrogen and acetylene, and an Acetylene Separation Assembly (ASepA) to purify the hydrogen product for recycle. The results of partially integrated testing of the sub-systems are reported.

Methane Post-Processor Development to Increase Oxygen Recovery beyond State-of-the-Art Carbon Dioxide Reduction Technology

NASA Technical Reports Server (NTRS)

Abney, Morgan B.; Greenwood, Zachary; Miller, Lee A.; Alvarez, Giraldo; Iannantuono, Michelle; Jones, Kenny

2013-01-01

State-of-the-art life support carbon dioxide (CO2) reduction technology, based on the Sabatier reaction, is theoretically capable of 50% recovery of oxygen from metabolic CO2. This recovery is constrained by the limited availability of reactant hydrogen. Post-processing of the methane byproduct from the Sabatier reactor results in hydrogen recycle and a subsequent increase in oxygen recovery. For this purpose, a Methane Post-Processor Assembly containing three sub-systems has been developed and tested. The assembly includes a Methane Purification Assembly (MePA) to remove residual CO2 and water vapor from the Sabatier product stream, a Plasma Pyrolysis Assembly (PPA) to partially pyrolyze methane into hydrogen and acetylene, and an Acetylene Separation Assembly (ASepA) to purify the hydrogen product for recycle. The results of partially integrated testing of the sub-systems are reported

The production of oxygen and metal from lunar regolith

NASA Astrophysics Data System (ADS)

Schwandt, Carsten; Hamilton, James A.; Fray, Derek J.; Crawford, Ian A.

2012-12-01

The present article summarises the various methods that have been, and still are, explored for the production of oxygen from lunar materials. These include the classical concepts based on chemical reduction with hydrogen or methane, vapour phase pyrolysis, sulphuric acid treatment, and molten oxide electrolysis. Our main focus in this paper is on a novel approach developed at the University of Cambridge that employs molten salt electrochemistry to achieve the combined winning of oxygen and metal from solid lunar materials of varying composition. This makes the Cambridge process attractive because it will work equally well in mare as in highland regions. We also discuss the implications of the recent apparent discovery of water ice at the poles of the Moon and conclude that, even if this discovery is confirmed, it will nevertheless be desirable to provide oxygen at non-polar localities, and the Cambridge process is a strong candidate for achieving this.

Heavily Graphitic-Nitrogen Self-doped High-porosity Carbon for the Electrocatalysis of Oxygen Reduction Reaction

NASA Astrophysics Data System (ADS)

Feng, Tong; Liao, Wenli; Li, Zhongbin; Sun, Lingtao; Shi, Dongping; Guo, Chaozhong; Huang, Yu; Wang, Yi; Cheng, Jing; Li, Yanrong; Diao, Qizhi

2017-11-01

Large-scale production of active and stable porous carbon catalysts for oxygen reduction reaction (ORR) from protein-rich biomass became a hot topic in fuel cell technology. Here, we report a facile strategy for synthesis of nitrogen-doped porous nanocarbons by means of a simple two-step pyrolysis process combined with the activation of zinc chloride and acid-treatment process, in which kidney bean via low-temperature carbonization was preferentially adopted as the only carbon-nitrogen sources. The results show that this carbon material exhibits excellent ORR electrocatalytic activity, and higher durability and methanol-tolerant property compared to the state-of-the-art Pt/C catalyst for the ORR, which can be mainly attributed to high graphitic-nitrogen content, high specific surface area, and porous characteristics. Our results can encourage the synthesis of high-performance carbon-based ORR electrocatalysts derived from widely-existed natural biomass.

Oxygen and Temperature Effects on Vertically Migrating Animals in Oxygen Minimum Zones

NASA Astrophysics Data System (ADS)

Seibel, B.

2016-02-01

Large populations of oceanic nekton and zooplankton undergo daily migrations from shallow water at night to depths greater than 200 m during the daytime. In some regions, these migrations cross extreme gradients of temperature, oxygen and carbon dioxide. Oxygen minimum zones (OMZs) are extensive and characterized by deep-water (100-800 m) oxygen partial pressures that would be lethal to most marine organisms, yet are tolerated by vertical migrators. Climate change is predicted to further deplete oxygen, and measurable reductions in oxygen have already been documented in some regions. Increases in shallow water temperature and carbon dioxide are occurring simultaneously. Oxygen levels and temperature are important drivers of biodiversity and distribution, and documented changes in community structure and function are reportedly associated with OMZ expansion and warming. Here I answer fundamental questions concerning zooplankton distributions, adaptations, and functions in oxygen minimum zones. In particular I report that metabolic suppression is a common strategy that facilitates diel occupancy of extreme hypoxia in many oceanic taxa. Anaerobic metabolic pathways play a minimal role in compensating for reduced aerobic ATP production. Numerous epigenetic mechanisms lead to reductions in energetically costly cellular processes, such as transcription and translation. Total metabolism is reduced by 50% or more during exposure to levels of hypoxia that characterize the daytime habitat for most vertically-migrating zooplankton. I further show that many migrators approach their upper thermal maximum in shallow water at night. Thus expanding OMZs and global warming may together compress the habitable depth range for many species.

In situ measurements of microbially-catalyzed nitrification and nitrate reduction rates in an ephemeral drainage channel receiving water from coalbed natural gas discharge, Powder River Basin, Wyoming, USA

USGS Publications Warehouse

Harris, S.H.; Smith, R.L.

2009-01-01

Nitrification and nitrate reduction were examined in an ephemeral drainage channel receiving discharge from coalbed natural gas (CBNG) production wells in the Powder River Basin, Wyoming. CBNG co-produced water typically contains dissolved inorganic nitrogen (DIN), primarily as ammonium. In this study, a substantial portion of discharged ammonium was oxidized within 50??m of downstream transport, but speciation was markedly influenced by diel fluctuations in dissolved oxygen (> 300????M). After 300??m of transport, 60% of the initial DIN load had been removed. The effect of benthic nitrogen-cycling processes on stream water chemistry was assessed at 2 locations within the stream channel using acrylic chambers to conduct short-term (2-6??h), in-stream incubations. The highest ambient DIN removal rates (2103????mol N m- 2 h- 1) were found at a location where ammonium concentrations > 350????M. This occurred during light incubations when oxygen concentrations were highest. Nitrification was occurring at the site, however, net accumulation of nitrate and nitrite accounted for < 12% of the ammonium consumed, indicating that other ammonium-consuming processes were also occurring. In dark incubations, nitrite and nitrate consumption were dominant processes, while ammonium was produced rather than consumed. At a downstream location nitrification was not a factor and changes in DIN removal rates were controlled by nitrate reduction, diel fluctuations in oxygen concentration, and availability of electron donor. This study indicates that short-term adaptation of stream channel processes can be effective for removing CBNG DIN loads given sufficient travel distances, but the long-term potential for nitrogen remobilization and nitrogen saturation remain to be determined.

Unique phase identification of trimetallic copper iron manganese oxygen carrier using simultaneous differential scanning calorimetry/thermogravimetric analysis during chemical looping combustion reactions with methane

DOE PAGES

Benincosa, William; Siriwardane, Ranjani; Tian, Hanjing; ...

2017-07-05

Chemical looping combustion (CLC) is a promising combustion technology that generates heat and sequestration-ready carbon dioxide that is undiluted by nitrogen from the combustion of carbonaceous fuels with an oxygen carrier, or metal oxide. This process is highly dependent on the reactivity and stability of the oxygen carrier. The development of oxygen carriers remains one of the major barriers for commercialization of CLC. Synthetic oxygen carriers, consisting of multiple metal components, have demonstrated enhanced performance and improved CLC operation compared to single metal oxides. However, identification of the complex mixed metal oxide phases that form after calcination or during CLCmore » reactions has been challenging. Without an understanding of the dominant metal oxide phase, it is difficult to determine reaction parameters and the oxygen carrier reduction pathway, which are necessary for CLC reactor design. This is particularly challenging for complex multi-component oxygen carriers such as copper iron manganese oxide (CuFeMnO 4). This study aims to differentiate the unique phase formation of a highly reactive, complex trimetallic oxygen carrier, CuFeMnO 4, from its single and bimetallic counterparts using thermochemical and reaction data obtained from simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) during temperature programmed reductions (TPR) with methane. DSC/TGA experiments during TPR with methane provides heat flow data and corresponding reaction rate data that can be used to determine reaction routes and mechanisms during methane reduction. Furthermore, non-isothermal TPR data provides the advantage of distinguishing reactions that may not be observable in isothermal analysis. The detailed thermochemical and reaction data, obtained during TPR with methane, distinguished a unique reduction pathway for CuFeMnO 4 that differed from its single and bimetallic counterparts. This is remarkable since X-ray diffraction (XRD) data alone could not be used to distinguish the reactive trimetallic oxide phase due to overlapping peaks from various single and mixed metal oxides. The unique reduction pathway of CuFeMnO 4 was further characterized in this study using in-situ XRD TPR with methane to determine changes in the dominant trimetallic phase that influenced the thermochemical and reaction rate data.« less

Unique phase identification of trimetallic copper iron manganese oxygen carrier using simultaneous differential scanning calorimetry/thermogravimetric analysis during chemical looping combustion reactions with methane

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

Benincosa, William; Siriwardane, Ranjani; Tian, Hanjing

Chemical looping combustion (CLC) is a promising combustion technology that generates heat and sequestration-ready carbon dioxide that is undiluted by nitrogen from the combustion of carbonaceous fuels with an oxygen carrier, or metal oxide. This process is highly dependent on the reactivity and stability of the oxygen carrier. The development of oxygen carriers remains one of the major barriers for commercialization of CLC. Synthetic oxygen carriers, consisting of multiple metal components, have demonstrated enhanced performance and improved CLC operation compared to single metal oxides. However, identification of the complex mixed metal oxide phases that form after calcination or during CLCmore » reactions has been challenging. Without an understanding of the dominant metal oxide phase, it is difficult to determine reaction parameters and the oxygen carrier reduction pathway, which are necessary for CLC reactor design. This is particularly challenging for complex multi-component oxygen carriers such as copper iron manganese oxide (CuFeMnO 4). This study aims to differentiate the unique phase formation of a highly reactive, complex trimetallic oxygen carrier, CuFeMnO 4, from its single and bimetallic counterparts using thermochemical and reaction data obtained from simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) during temperature programmed reductions (TPR) with methane. DSC/TGA experiments during TPR with methane provides heat flow data and corresponding reaction rate data that can be used to determine reaction routes and mechanisms during methane reduction. Furthermore, non-isothermal TPR data provides the advantage of distinguishing reactions that may not be observable in isothermal analysis. The detailed thermochemical and reaction data, obtained during TPR with methane, distinguished a unique reduction pathway for CuFeMnO 4 that differed from its single and bimetallic counterparts. This is remarkable since X-ray diffraction (XRD) data alone could not be used to distinguish the reactive trimetallic oxide phase due to overlapping peaks from various single and mixed metal oxides. The unique reduction pathway of CuFeMnO 4 was further characterized in this study using in-situ XRD TPR with methane to determine changes in the dominant trimetallic phase that influenced the thermochemical and reaction rate data.« less

Chemical activation of commercial CNTs with simultaneous surface deposition of manganese oxide nano flakes for the creation of CNTs-graphene supported oxygen reduction ternary composite catalysts applied in air fuel cell

NASA Astrophysics Data System (ADS)

Sun, Ling; Liu, Danxian

2018-07-01

To elevate power performance is crucial for commercally potential metal air fuel cells. Non-precious metal oxide-based oxygen reduction catalytic electrode is much desirable. Rational combination with low-dimension nanomaterials are greatly expected as the supports. Herein, carbon nanotubes (CNTs)-graphene supported manganese oxides composite catalysts (CMnCs) were obtained through activating commercial CNTs, namely, immersing them in acidic KMnO4 solution at room condition. It avoided conventional hydrothermal process and template surfactants. CMnCs-based air cathodes were made via pilot manufacture technology and equipped in fuel cells. Through characterizations, CNTs was found structurally defective and their outer walls suffered cracking into graphene nano pieces during processing, which further enhanced oxygen reduction reaction (ORR). Nano sized manganese oxide flakes were simulataneously grown on the CNTs-graphene surfaces, identified as the manganite. The areal distribution was found closely related to the additive amount of KMnO4 with regard to CNTs, somewhat influencing catalytic performance. The ORR activities of these CMnCs exceeded raw CNTs and referred manganese catalysts under identical conditions, and also the CMnCs air fuel cells were capable of outputting ∼15% more power at 100 mA/cm2. This reseach provided an inspiring pilot evidence for updating air fuel cell power from economical carbon as well as industrialization.

Biogeochemical cycles of carbon, sulfur, and free oxygen in a microbial mat

NASA Technical Reports Server (NTRS)

Canfield, Donald E.; Des Marais, David J.

1993-01-01

Complete budgets for carbon and oxygen have been constructed for cyanobacterial mats dominated by Microcoleus chthonoplastes from the evaporating ponds of a salt works. We infer from the data the various sinks for O2 as well as the sources of carbon for primary production. Although seasonal variability exists, a major percentage of the O2 produced during the day did not diffuse out of the mat but was used within the mat to oxidize both organic carbon and the sulfide produced by sulfate reduction. At night, most of the O2 that diffused into the mat was used to oxidize sulfide, with O2 respiration of minor importance. During the day, the internal mat processes of sulfate reduction and O2 respiration generated as much or more inorganic carbon (DIC) for primary production as diffusion into the mat. Oxygenic photosynthesis was the most important process of carbon fixation. At night, the DIC lost from the mat was mostly from sulfate reduction. Elemental fluxes across the mat/brine interface indicated that carbon with an oxidation state of greater than zero was taken up by the mat during the day and liberated from the mat at night. Overall, carbon with an average oxidation state of near zero accumulated in the mat. Both carbon fixation and carbon oxidation rates varied with temperature by a similar amount.

Sensing hypoxia by mitochondria: a unifying hypothesis involving S-nitrosation.

PubMed

Ullrich, Volker; Schildknecht, Stefan

2014-01-10

Sudden hypoxia requires a rapid response in tissues with high energy demand. Mitochondria are rapid sensors for a lack of oxygen, but no consistent mechanism for the sensing process and the subsequent counter-regulation has been described. In the present hypothesis review, we suggest an oxygen-sensing mechanism by mitochondria that is initiated at low oxygen tension by electrons from the respiratory chain, leading to the reduction of intracellular nitrite to nitric oxide ((•)NO) that would subsequently compete with oxygen for binding to cytochrome c oxidase. This allows superoxide ((•)O2(-)) formation in hypoxic areas, leading to S-nitrosation and the inhibition of mitochondrial Krebs cycle enzymes. With more formation of (•)O2(-), peroxynitrite is generated and known to damage the connection between the mitochondrial matrix and the outer membrane. A fundamental question on a regulatory mechanism is its reversibility. Readmission of oxygen and opening of the mitochondrial KATP-channel would allow electrons from glycerol-3-phosphate to selectively reduce the ubiquinone pool to generate (•)O2(-) at both sides of the inner mitochondrial membrane. On the cytosolic side, superoxide is dismutated and will support H2O2/Fe(2+)-dependent transcription processes and on the mitochondrial matrix side, it could lead to the one-electron reduction and reactivation of S-nitrosated proteins. It remains to be elucidated up to which stage the herein proposed silencing of mitochondria remains reversible and when irreversible changes that ultimately lead to classical reperfusion injury are initiated.

The platinum microelectrode/Nafion interface - An electrochemical impedance spectroscopic analysis of oxygen reduction kinetics and Nafion characteristics

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Dave, Bhasker; Srinivasan, Supramaniam; Appleby, John A.; Martin, Charles R.

1992-01-01

The objectives of this study were to use electrochemical impedance spectroscopy (EIS) to study the oxygen-reduction reaction under lower humidification conditions than previously studied. The EIS technique permits the discrimination of electrode kinetics of oxygen reduction, mass transport of O2 in the membrane, and the electrical characteristics of the membrane. Electrode-kinetic parameters for the oxygen-reduction reaction, corrosion current densities for Pt, and double-layer capacitances were calculated. The production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and the electrode kinetics at the Pt/Nafion interface. From the finite-length Warburg behavior, a measure of the diffusion coefficient of oxygen in Nafion and diffusion-layer thickness was obtained. An analysis of the EIS data in the high-frequency domain yielded membrane and interfacial characteristics such as ionic conductivity of the membrane, membrane grain-boundary capacitance and resistance, and uncompensated resistance.

A regenerable carbon dioxide removal and oxygen recovery system for the Japanese Experiment Module.

PubMed

Otsuji, K; Hirao, M; Satoh, S

1987-01-01

The Japanese Space Station Program is now under Phase B study by the National Space Development Agency of Japan in participation with the U.S. Space Station Program. A Japanese Space Station participation will be a dedicated pressurized module to be attached to the U.S. Space Station, and is called Japanese Experiment Module (JEM). Astronaut scientists will conduct various experimental operations there. Thus an environment control and life support system is required. Regenerable carbon dioxide removal and collection technique as well as oxygen recovery technique has been studied and investigated for several years. A regenerable carbon dioxide removal subsystem using steam desorbed solid amine and an oxygen recovery subsystem using Sabatier methane cracking have a good possibility for the application to the Japanese Experiment Module. Basic performance characteristics of the carbon dioxide removal and oxygen recovery subsystem are presented according to the results of a fundamental performance test program. The trace contaminant removal process is also investigated and discussed. The solvent recovery plant for the regeneration of various industrial solvents, such as hydrocarbons, alcohols and so on, utilizes the multi-bed solvent adsorption and steam desorption process, which is very similar to the carbon dioxide removal subsystem. Therefore, to develop essential components including adsorption tank (bed), condenser. process controller and energy saving system, the technology obtained from the experience to construct solvent recovery plant can be easily and effectively applicable to the carbon dioxide removal subsystem. The energy saving efficiency is evaluated for blower power reduction, steam reduction and waste heat utilization technique. According to the above background, the entire environment control and life support system for the Japanese Experiment Module including the carbon dioxide removal and oxygen recovery subsystem is evaluated and proposed.

Highly Selective TiN-Supported Highly Dispersed Pt Catalyst: Ultra Active toward Hydrogen Oxidation and Inactive toward Oxygen Reduction.

PubMed

Luo, Junming; Tang, Haibo; Tian, Xinlong; Hou, Sanying; Li, Xiuhua; Du, Li; Liao, Shijun

2018-01-31

The severe dissolution of the cathode catalyst, caused by an undesired oxygen reduction reaction at the anode during startup and shutdown, is a fatal challenge to practical applications of polymer electrolyte membrane fuel cells. To address this important issue, according to the distinct structure-sensitivity between the σ-type bond in H 2 and the π-type bond in O 2 , we design a HD-Pt/TiN material by highly dispersing Pt on the TiN surface to inhibit the unwanted oxygen reduction reaction. The highly dispersed Pt/TiN catalyst exhibits excellent selectivity toward hydrogen oxidation and oxygen reduction reactions. With a Pt loading of 0.88 wt %, our catalyst shows excellent hydrogen oxidation reaction activity, close to that of commercial 20 wt % Pt/C catalyst, and much lower oxygen reduction reaction activity than the commercial 20 wt % Pt/C catalyst. The lack of well-ordered Pt facets is responsible for the excellent selectivity of the HD-Pt/TiN materials toward hydrogen oxidation and oxygen reduction reactions. Our work provides a new and cost-effective solution to design selective catalysts toward hydrogen oxidation and oxygen reduction reactions, making the strategy of using oxygen-tolerant anode catalyst to improve the stability of polymer electrolyte membrane fuel cells during startup and shutdown more affordable and practical.

Temperature Dependence of the Oxygen Reduction Mechanism in Nonaqueous Li–O 2 Batteries

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

Liu, Bin; Xu, Wu; Zheng, Jianming

The temperature dependence of the oxygen reduction mechanism in Li-O 2 batteries was investigated using carbon nanotube-based air electrodes and 1,2-dimethoxyethane-based electrolyte within a temperature range of 20C to 40C. It is found that the discharge capacity of the Li-O 2 batteries decreases from 7,492 mAh g -1 at 40C to 2,930 mAh g -1 at 0C. However, a sharp increase in capacity was found when the temperature was further decreased and a very high capacity of 17,716 mAh g -1 was observed at 20C at a current density of 0.1 mA cm-2. When the temperature increases from 20C tomore » 40C, the morphologies of the Li 2O 2 formed varied from ultra-small spherical particles to small flakes and then to large flake-stacked toroids. The lifetime of superoxide and the solution pathway play a dominate role on the battery capacity in the temperature range of -20C to 0C, but the electrochemical kinetics of oxygen reduction and the surface pathway dominate the discharge behavior in the temperature range of 0C to 40C. These findings provide fundamental understanding on the temperature dependence of oxygen reduction process in a Li-O 2 battery and will enable a more rational design of Li-O 2 batteries.« less

Manganese Oxide Nanoarray-Based Monolithic Catalysts: Tunable Morphology and High Efficiency for CO Oxidation

DOE PAGES

Chen, Sheng-Yu; Song, Wenqiao; Lin, Hui-Jan; ...

2016-03-08

In this work, a generic one-pot hydrothermal synthesis route has been successfully designed and utilized to in situ grow uniform manganese oxide nanorods and nanowires onto the cordierite honeycomb monolithic substrates, forming a series of nanoarray-based monolithic catalysts. During the synthesis process, three types of potassium salt oxidants have been used with different reduction potentials, i.e., K 2Cr 2O 7, KClO 3, and K 2S 2O 8, denoted as HM-DCM, HM-PCR, and HM-PSF, respectively. The different reduction potentials of the manganese source (Mn 2+) and oxidants induced the formation of manganese oxide nanoarrays with different morphology, surface area, and reactivitymore » of carbon monoxide (CO) oxidation. K 2Cr 2O 7 and KClO 3 can induce sharp and long nanowires with slow growth rates due to their low reduction potentials. In comparison, the nanoarrays of HM-PSF presented shorter nanorods but displayed an efficient 90% CO oxidation conversion at 200 °C (T90) without noble-metal loading. Reducibility tests for the three monolithic catalysts by hydrogen temperature-programmed reduction revealed an activation energy order of HM-PSF > HM-DCM > HM-PCR for CO oxidation. The characterizations of oxygen temperature-programmed desorption and X-ray photoelectron spectroscopy indicated the abundant surface-adsorbed oxygen and lattice oxygen contributing to the superior reactivity of HM-PSF. Finally, the straightforward synthetic process showed a scalable, low-cost, and template-free method to fabricate manganese oxide nanoarray monolithic catalysts for exhaust treatment.« less

Oxygen Sensitivity of Anammox and Coupled N-Cycle Processes in Oxygen Minimum Zones

PubMed Central

Kalvelage, Tim; Jensen, Marlene M.; Contreras, Sergio; Revsbech, Niels Peter; Lam, Phyllis; Günter, Marcel; LaRoche, Julie; Lavik, Gaute; Kuypers, Marcel M. M.

2011-01-01

Nutrient measurements indicate that 30–50% of the total nitrogen (N) loss in the ocean occurs in oxygen minimum zones (OMZs). This pelagic N-removal takes place within only ∼0.1% of the ocean volume, hence moderate variations in the extent of OMZs due to global warming may have a large impact on the global N-cycle. We examined the effect of oxygen (O2) on anammox, NH3 oxidation and NO3 − reduction in 15N-labeling experiments with varying O2 concentrations (0–25 µmol L−1) in the Namibian and Peruvian OMZs. Our results show that O2 is a major controlling factor for anammox activity in OMZ waters. Based on our O2 assays we estimate the upper limit for anammox to be ∼20 µmol L−1. In contrast, NH3 oxidation to NO2 − and NO3 − reduction to NO2 − as the main NH4 + and NO2 − sources for anammox were only moderately affected by changing O2 concentrations. Intriguingly, aerobic NH3 oxidation was active at non-detectable concentrations of O2, while anaerobic NO3 − reduction was fully active up to at least 25 µmol L−1 O2. Hence, aerobic and anaerobic N-cycle pathways in OMZs can co-occur over a larger range of O2 concentrations than previously assumed. The zone where N-loss can occur is primarily controlled by the O2-sensitivity of anammox itself, and not by any effects of O2 on the tightly coupled pathways of aerobic NH3 oxidation and NO3 − reduction. With anammox bacteria in the marine environment being active at O2 levels ∼20 times higher than those known to inhibit their cultured counterparts, the oceanic volume potentially acting as a N-sink increases tenfold. The predicted expansion of OMZs may enlarge this volume even further. Our study provides the first robust estimates of O2 sensitivities for processes directly and indirectly connected with N-loss. These are essential to assess the effects of ocean de-oxygenation on oceanic N-cycling. PMID:22216239

Kinetics of oxygen reduction in perovskite cathodes for solid oxide fuel cells: A combined modeling and experimental approach

NASA Astrophysics Data System (ADS)

Miara, Lincoln James

Solid oxide fuel cells (SOFCs) have the potential to replace conventional stationary power generation technologies; however, there are major obstacles to commercialization, the most problematic of which is poor cathode performance. Commercialization of SOFCs will follow when the mechanisms occurring at the cathode are more thoroughly understood and adapted for market use. The catalytic reduction of oxygen occurring in SOFC cathodes consists of many elementary steps such as gas phase diffusion, chemical and/or electrochemical reactions which lead to the adsorption and dissociation of molecular oxygen onto the cathode surface, mass transport of oxygen species along the surface and/or through the bulk of the cathode, and full reduction and incorporation of the oxygen at the cathode/electrolyte two or three phase boundary. Electrochemical impedance spectroscopy (EIS) is the main technique used to identify the occurrence of these different processes, but when this technique is used without an explicit model describing the kinetics it is difficult to unravel the interdependence of each of these processes. The purpose of this dissertation is to identify the heterogeneous reactions occurring at the cathode of an SOFC by combining experimental EIS results with mathematical models describing the time dependent behavior of the system. This analysis is performed on two different systems. In the first case, experimental EIS results from patterned half cells composed of Ca-doped lanthanum manganite (LCM)| yttria-doped ZrO2 (YSZ) are modeled to investigate the temperature and partial pressure of oxygen, pO2, dependence of oxygen adsorption/dissociation onto the LCM surface, surface diffusion of atomic oxygen, and electrochemical reduction and incorporation of the oxygen into the electrolyte in the vicinity of the triple phase boundary (TPB). This model determines the time-independent state-space equations from which the Faradaic admittance transfer function is obtained. The unknown rate constants (kad, k des, k1, k1¯ ), and parameters (Ds, Q°, n) arising from the governing equations are estimated from a combination of experiments, mathematical analysis, and numerical data analysis. In the second system, dense patterned films of cathode with composition: La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF-6428) were fabricated on Ga-doped CeO2 coated YSZ substrates. These samples were analyzed by EIS over a temperature and pO 2 range of 600--800 °C and 10-3--1.00 atm, respectively. To understand the EIS results, a 2-dimensional model was developed which accounted for surface oxygen exchange, and both surface and bulk transport of oxygen to the electrolyte interface. The results were obtained by numerically solving a stationary partial differential equation describing the oxygen vacancy distribution in the cathode. From these results, the model impedance was derived and then fitted to the experimental EIS results. From the fitting results the contributions to the impedance from each of the processes were estimated. Also, the surface exchange rate was estimated over the experimental operating conditions. Finally, the results suggest that the surface diffusion occurred by an interstitial type mechanism in this material. The cathode surface is intimately involved in most of the oxygen reduction processes; however, the surface structure and chemistry is typically treated as an extension of the bulk without consideration of the actual surface properties. Recent evidence suggests that significant changes occur to the surface during operation which in turn leads to changes in electrochemical performance. To investigate these phenomena, well-oriented thin films (250 nm in thickness) of Sr-doped lanthanum manginite (LSM) films were grown on single crystals of YSZ (111). Films which were cathodically biased with a -1 V applied dc potential were compared to control samples. The cathodic bias results in both an enhancement in electrochemical performance and a change in surface chemistry. The changes in electrochemical performance were monitored by ES, while the surface changes were tracked with a combination of soft x-ray techniques such as x-ray photoemission spectroscopy and x-ray absorption spectroscopy. The soft x-ray results indicated that the removal of surface passivating phases (i.e., SrO and MnO) are correlated with improved performance. This work demonstrates the success of estimating fundamental parameters, such as diffusivity and surface coverage, from experimental EIS results using a physically realistic model without, as is commonly done, assuming a specific rate limiting step or using an ambiguous equivalent circuit. This allows researchers to fabricate designer cathodes by selecting materials with optimal kinetic properties such as rapid oxygen dissociation and rapid oxygen transport in (or on) the cathode, independent of geometry.

A Survey of Alternative Oxygen Production Technologies

NASA Technical Reports Server (NTRS)

Lueck, Dale E.; Parrish, Clyde F.; Buttner, William J.; Surma, Jan M.; Delgado, H. (Technical Monitor)

2000-01-01

Utilization of the Martian atmosphere for the production of fuel and oxygen has been extensively studied. The baseline fuel production process is a Sabatier reactor, which produces methane and water from carbon dioxide and hydrogen. The oxygen produced from the electrolysis of the water is only half of that needed for methane-based rocket propellant, and additional oxygen is needed for breathing air, fuel cells and other energy sources. Zirconia electrolysis cells for the direct reduction of CO2 are being developed as an alternative means of producing oxygen, but present many challenges for a large-scale oxygen production system. The very high operating temperatures and fragile nature of the cells coupled with fairly high operating voltages leave room for improvement. This paper will survey alternative oxygen production technologies, present data on operating characteristics, materials of construction, and some preliminary laboratory results on attempts to implement each.

Soil Oxidation-Reduction Potential and Plant Photosynthetic Capacity in the Northern Pantanal of Mato Grosso, Brazil

NASA Astrophysics Data System (ADS)

Lathuilliere, M. J.; Johnson, M. S.; Dalmagro, H. J.; Pinto Junior, O. B.; Couto, E. G.

2013-12-01

Plant communities of the Pantanal wetland are able to survive long periods of climatic and physiological stress in the dry and wet seasons. During inundation, soil oxygen demand increases dramatically as reducing soil conditions create stress in the root system with possible impacts on photosynthetic capacity of plants. We look at inundation cycles of a tree island (locally known as a cordilheira) in the Northern Pantanal near Poconé, Mato Grosso, and relate soil oxidation-reduction potential and soil oxygen depletion to the photosynthetic capacity of two plant communities of flooded scrub forest (Vochysia divergens and Curatela americana). Results show a drop in soil oxidation-reduction potential of over 400 mV, to levels below the absolute value of -200 mV, following inundation around the tree island. Both plant species showed increased carbon assimilation at highest soil oxygen demand despite a change in stomatal conductance, suggesting adaptation to the inundated environment. Absolute values of soil oxidation-reduction potential also allow for the determination of specific soil chemical reactions characteristic of the tree island environment, namely the reduction of iron(III), or carbon dioxide which in turn produces methane. Our combined analysis of soil chemistry with plant ecophysiology allows for a better understanding of soil-plant interactions in the Pantanal, specifically the drivers of biogeochemical processes between inundation periods.

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

Low Temperature ABC-Type Ru Atomic Layer Deposition through Consecutive Dissociative Chemisorption, Combustion, and Reduction Steps

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

Lu, Junling; Elam, Jeffrey W.

Thermal atomic layer deposition (ALD) of noble metals is frequently performed using molecular oxygen as the nonmetal precursor to effect a combustion-type chemistry at relatively high temperatures of 300 °C. Bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) is one of the common used metal precursors for Ru ALD. Using Ru(EtCp)2 and oxygen as reactants, Ru ALD was acheived at near 300 °C. Here, we demonstrate that Ru ALD can proceed at as low as 150 °C by using successive exposures to oxygen and hydrogen as the co-reactants. In situ quartz crystal microbalance (QCM) and quadrupole mass spectroscopy (QMS) measurements both suggest that this ABC-type ALDmore » occurs through dissociative chemisorption, combustion, and reduction for the Ru(EtCp)2, oxygen and hydrogen steps, respectively, in a similar manner to processes using ozone and hydrogen as co-reactants reported previously. Moreover, we believe this molecular O2 and H2 based ABC-type ALD could be exploited for the ALD of other noble metals to decrease the deposition temperature and reduce oxygen impurities.« less

Electrochemical Hydrogen Peroxide Generator

NASA Technical Reports Server (NTRS)

Tennakoon, Charles L. K.; Singh, Waheguru; Anderson, Kelvin C.

2010-01-01

Two-electron reduction of oxygen to produce hydrogen peroxide is a much researched topic. Most of the work has been done in the production of hydrogen peroxide in basic media, in order to address the needs of the pulp and paper industry. However, peroxides under alkaline conditions show poor stabilities and are not useful in disinfection applications. There is a need to design electrocatalysts that are stable and provide good current and energy efficiencies to produce hydrogen peroxide under acidic conditions. The innovation focuses on the in situ generation of hydrogen peroxide using an electrochemical cell having a gas diffusion electrode as the cathode (electrode connected to the negative pole of the power supply) and a platinized titanium anode. The cathode and anode compartments are separated by a readily available cation-exchange membrane (Nafion 117). The anode compartment is fed with deionized water. Generation of oxygen is the anode reaction. Protons from the anode compartment are transferred across the cation-exchange membrane to the cathode compartment by electrostatic attraction towards the negatively charged electrode. The cathode compartment is fed with oxygen. Here, hydrogen peroxide is generated by the reduction of oxygen. Water may also be generated in the cathode. A small amount of water is also transported across the membrane along with hydrated protons transported across the membrane. Generally, each proton is hydrated with 3-5 molecules. The process is unique because hydrogen peroxide is formed as a high-purity aqueous solution. Since there are no hazardous chemicals or liquids used in the process, the disinfection product can be applied directly to water, before entering a water filtration unit to disinfect the incoming water and to prevent the build up of heterotrophic bacteria, for example, in carbon based filters. The competitive advantages of this process are: 1. No consumable chemicals are needed in the process. The only raw materials needed are water and oxygen or air. 2. The product is pure and can therefore be used in disinfection applications directly or after proper dilution with water. 3. Oxygen generated in the anode compartment is used in the electrochemical reduction process; in addition, external oxygen is used to establish a high flow rate in the cathode compartment to remove the desired product efficiently. Exiting oxygen can be recycled after separation of liquid hydrogen peroxide product, if so desired. 4. The process can be designed for peroxide generation under microgravity conditions. 5. High concentrations of the order of 6-7 wt% can be generated by this method. This method at the time of this reporting is superior to what other researchers have reported. 6. The cell design allows for stacking of cells to increase the hydrogen peroxide production. 7. The catalyst mix containing a diquaternary ammonium compound enabled not only higher concentration of hydrogen peroxide but also higher current efficiency, improved energy efficiency, and catalyst stability. 8. The activity of the catalyst is maintained even after repeated periods of system shutdown. 9. The catalyst system can be extended for fuel-cell cathodes with suitable modifications.

High-pressure oxygen annealing of Al2O3 passivation layer for performance enhancement of graphene field-effect transistors

NASA Astrophysics Data System (ADS)

Kim, Yun Ji; Kim, Seung Mo; Heo, Sunwoo; Lee, Hyeji; In Lee, Ho; Chang, Kyoung Eun; Lee, Byoung Hun

2018-02-01

High-pressure annealing in oxygen ambient at low temperatures (∼300 °C) was effective in improving the performance of graphene field-effect transistors. The field-effect mobility was improved by 45% and 83% for holes and electrons, respectively. The improvement in the quality of Al2O3 and the reduction in oxygen-related charge generation at the Al2O3-graphene interface, are suggested as the reasons for this improvement. This process can be useful for the commercial implementation of graphene-based electronic devices.

RESOLVE OVEN Field Demonstration Unit for Lunar Resource Extraction

NASA Technical Reports Server (NTRS)

Paz, Aaron; Oryshchyn, Lara; Jensen, Scott; Sanders, Gerald B.; Lee, Kris; Reddington, Mike

2013-01-01

The Oxygen and Volatile Extraction Node (OVEN) is a subsystem within the Regolith & Environment Science and Oxygen & Lunar Volatile Extraction (RESOLVE) project. The purpose of the OVEN subsystem is to release volatiles from lunar regolith and extract oxygen by means of a hydrogen reduction reaction. The complete process includes receiving, weighing, sealing, heating, and disposing of core sample segments while transferring all gaseous contents to the Lunar Advanced Volatile Analysis (LAVA) subsystem. This document will discuss the design and performance of the OVEN Field Demonstration Unit (FDU), which participated in the 2012 RESOLVE field demonstration.

Reduction of Dissolved Oxygen at a Copper Rotating Disc Electrode

ERIC Educational Resources Information Center

Kear, Gareth; Albarran, Carlos Ponce-de-Leon; Walsh, Frank C.

2005-01-01

Undergraduates from chemical engineering, applied chemistry, and environmental science courses, together with first-year postgraduate research students in electrochemical technology, are provided with an experiment that demonstrates the reduction of dissolved oxygen in aerated seawater at 25°C. Oxygen reduction is examined using linear sweep…

Equivalent air depth: fact or fiction.

PubMed

Berghage, T E; McCraken, T M

1979-12-01

In mixed-gas diving theory, the equivalent air depth (EAD) concept suggests that oxygen does not contribute to the total tissue gas tension and can therefore be disregarded in calculations of the decompression process. The validity of this assumption has been experimentally tested by exposing 365 rats to various partial pressures of oxygen for various lengths of time. If the EAD assumption is correct, under a constant exposure pressure each incremental change in the oxygen partial pressure would produce a corresponding incremental change in pressure reduction tolerance. Results of this study suggest that the EAD concept does not adequately describe the decompression advantages obtained from breathing elevated oxygen partial pressures. The authors suggest that the effects of breathing oxygen vary in a nonlinear fashion across the range from anoxia to oxygen toxicity, and that a simple inert gas replacement concept is no longer tenable.

Cyanobacterial mats: Microanalysis of community metabolism

NASA Technical Reports Server (NTRS)

Cohen, Y.; Bermudes, D.; Fischer, U.; Haddad, R.; Prufert, L.; Scheulderman-Suylen, T.; Shaw, T.

1985-01-01

The microbial communities in two sites were studied using several approaches: (1) light microscopy; (2) the measurement of microprofiles of oxygen and sulfide at the surface of the microbial mat; (3) the study of diurnal variation of oxygen and sulfides; (4) in situ measurement of photosynthesis and sulfate reduction and study of the coupling of these two processes; (5) measurement of glutathione in the upper layers of the microbial mat as a possible oxygen quencher; (6) measurement of reduced iron as a possible intermediate electron donor along the established redoxcline in the mats; (7) measurement of dissolved phosphate as an indicator of processes of break down of organic matter in these systems; and (8) measurement of carbon dioxide in the interstitial water and its delta C-13 in an attempt to understand the flow of CO2 through the systems. Microbial processes of primary production and initial degradation at the most active zone of the microbial mat were analyzed.

Visualisation of gas-liquid mass transfer around a rising bubble in a quiescent liquid using an oxygen sensitive dye

NASA Astrophysics Data System (ADS)

Dietrich, Nicolas; Hebrard, Gilles

2018-02-01

An approach for visualizing and measuring the mass transfer around a single bubble rising in a quiescent liquid is reported. A colorimetric technique, developed by (Dietrich et al. Chem Eng Sci 100:172-182, 2013) using an oxygen sensitive redox dye was implemented. It was based on the reduction of the colorimetric indicator in presence of oxygen, this reduction being catalysed by sodium hydroxide and glucose. In this study, resazurin was selected because it offered various reduced forms with colours ranging from transparent (without oxygen) to pink (in presence of oxygen). These advantages made it possible to visualize the spatio-temporal oxygen mass transfer around rising bubbles. Images were recorded by a CCD camera and, after post-processing, the shape, size, and velocity of the bubbles were measured and the colours around the bubbles mapped. A calibration, linking the level of colour with the dissolved oxygen concentration, enabled colour maps to be converted into oxygen concentration fields. A rheoscopic fluid was used to visualize the wake of the bubbles. A calculation method was also developed to determine the transferred oxygen fluxes around bubbles of two sizes (d = 0.82 mm and d = 2.12 mm) and the associated liquid-side mass transfer coefficients. The results compared satisfactorily with classical global measurements made by oxygen micro-sensors or from the classical models. This study thus constitutes a striking example of how this new colorimetric method could become a remarkable tool for exploring gas-liquid mass transfer in fluids.

Visualisation of gas-liquid mass transfer around a rising bubble in a quiescent liquid using an oxygen sensitive dye

NASA Astrophysics Data System (ADS)

Dietrich, Nicolas; Hebrard, Gilles

2018-07-01

An approach for visualizing and measuring the mass transfer around a single bubble rising in a quiescent liquid is reported. A colorimetric technique, developed by (Dietrich et al. Chem Eng Sci 100:172-182, 2013) using an oxygen sensitive redox dye was implemented. It was based on the reduction of the colorimetric indicator in presence of oxygen, this reduction being catalysed by sodium hydroxide and glucose. In this study, resazurin was selected because it offered various reduced forms with colours ranging from transparent (without oxygen) to pink (in presence of oxygen). These advantages made it possible to visualize the spatio-temporal oxygen mass transfer around rising bubbles. Images were recorded by a CCD camera and, after post-processing, the shape, size, and velocity of the bubbles were measured and the colours around the bubbles mapped. A calibration, linking the level of colour with the dissolved oxygen concentration, enabled colour maps to be converted into oxygen concentration fields. A rheoscopic fluid was used to visualize the wake of the bubbles. A calculation method was also developed to determine the transferred oxygen fluxes around bubbles of two sizes (d = 0.82 mm and d = 2.12 mm) and the associated liquid-side mass transfer coefficients. The results compared satisfactorily with classical global measurements made by oxygen micro-sensors or from the classical models. This study thus constitutes a striking example of how this new colorimetric method could become a remarkable tool for exploring gas-liquid mass transfer in fluids.

The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.

PubMed

Chuang, C-H; Wang, Y-F; Shao, Y-C; Yeh, Y-C; Wang, D-Y; Chen, C-W; Chiou, J W; Ray, Sekhar C; Pong, W F; Zhang, L; Zhu, J F; Guo, J H

2014-04-10

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp(2) bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

Respiratory and digestive responses of postprandial Dungeness crabs, Cancer magister, and blue crabs, Callinectes sapidus, during hyposaline exposure.

PubMed

Curtis, Daniel L; McGaw, Iain J

2010-02-01

Respiratory responses and gastric processing were examined during hyposaline exposure in two crab species of differing osmoregulatory ability. The efficient osmoregulator, Callinectes sapidus, displayed an immediate increase in oxygen uptake when exposed to low salinity in isolation. In contrast, the weak osmoregulator, Cancer magister, showed no change in oxygen uptake upon acute exposure (<6 h), but slight increases in oxygen uptake tended to occur over longer time scales (12-24 h). These changes were likely attributable to an increase in avoidance activity after 6 h hyposaline exposure. Following feeding in 100% SW, oxygen uptake doubled for both species and remained elevated for 15 h. When postprandial crabs were exposed to low salinities, C. sapidus were able to sum the demands of osmoregulation and digestion. Thus, gastric processes continued unabated in low salinity. Conversely, postprandial C. magister prioritized responses to low salinity over those of digestion, resulting in a decrease in oxygen uptake when exposed to low salinity. This decrease in oxygen uptake corresponded to a reduction in the rate of contraction of the pyloric stomach and a subsequent doubling of gastric evacuation time. The current study is one of the few to illustrate how summation or prioritization of competing physiological systems is manifested in digestive processes.

The Reduction of Lunar Regolith by Carbothermal Processing Using Methane

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Hegde, U.; Gokoglu, S.

2010-01-01

The processing of lunar regolith for the production of oxygen is a key component of the In-Situ Resource Utilization plans Currently being developed by NASA. In the carbothermal process, a portion of the surface of the regolith in a container is heated by exposure to a heat source so that a small zone of molten regolith is established. A continuous flow of methane is maintained over the molten regolith zone. In this paper, we discuss the development of a chemical conversion model of the carbothermal process to predict the rate of production of carbon monoxide. Our model is based on a mechanism where methane pyrolyzes when it comes in contact with the surface of the hot molten regolith to form solid carbon and hydrogen gas. Carbon is deposited on the surface of the melt, and hydrogen is released into the gas stream above the melt surface. We assume that the deposited carbon mixes in the molten regolith and reacts with metal oxides in a reduction reaction by which gaseous carbon monoxide is liberated. Carbon monoxide bubbles through the melt and is released into the gas stream. It is further processed downstream to ultimately produce oxygen.

The Reduction of Lunar Regolith by Carbothermal Processing Using Methane

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Gokoglu, S. A.; Hegde, U.

2010-01-01

The processing of lunar regolith for the production of oxygen is a key component of the In-Situ Resource Utilization plans currently being developed by NASA. In the carbothermal process, a portion of the surface of the regolith in a container is heated by exposure to a heat source so that a small zone of molten regolith is established. A continuous flow of methane is maintained over the molten regolith zone. In this paper, we discuss the development of a chemical conversion model of the carbothermal process to predict the rate of production of carbon monoxide. Our model is based on a mechanism where methane pyrolyzes when it comes in contact with the surface of the hot molten regolith to form solid carbon and hydrogen gas. Carbon is deposited on the surface of the melt, and hydrogen is released into the gas stream above the melt surface. We assume that the deposited carbon mixes in the molten regolith and reacts with metal oxides in a reduction reaction by which gaseous carbon monoxide is liberated. Carbon monoxide bubbles through the melt and is released into the gas stream. It is further processed downstream to ultimately produce oxygen.

Evaluation of the participation of ferredoxin in oxygen reduction in the photosynthetic electron transport chain of isolated pea thylakoids.

PubMed

Kozuleva, Marina A; Ivanov, Boris N

2010-07-01

The contribution to reduction of oxygen by ferredoxin (Fd) to the overall reduction of oxygen in isolated pea thylakoids was studied in the presence of Fd versus Fd + NADP(+). The overall rate of electron transport was measured using a determination of Photosystem II quantum yield from chlorophyll fluorescence parameters, and the rate of oxidation of Fd was measured from the light-induced redox changes of Fd. At low light intensity, increasing Fd concentration from 5 to 30 microM in the absence of NADP(+) increased the proportion of oxygen reduction by Fd from 25-35 to 40-60% in different experiments. This proportion decreased with increasing light intensity. When NADP(+) was added in the presence of 15 microM Fd, which was optimal for the NADP(+) reduction rate, the participation of Fd in the reduction of oxygen was low, no more than 10%, and it also decreased with increasing light intensity. At high light intensity, the overall oxygen reduction rates in the presence of Fd + NADP(+) and in the presence of Fd alone were comparable. The significance of reduction of dioxygen either by water-soluble Fd or by the membrane-bound carriers of the photosynthetic electron transport chain for redox signaling under different light intensities is discussed.

Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates

PubMed Central

Klawonn, Isabell; Bonaglia, Stefano; Brüchert, Volker; Ploug, Helle

2015-01-01

Colonies of N2-fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. 15N-isotope labelling experiments and nutrient analyses revealed that N2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N2 were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (⩾1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ⩾0.1 mm) may only arise in low-oxygenated waters (⩽25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO3−-depleted, fully oxygenated (surface) waters. In NO3−-enriched (>1.5 μM), O2-depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes. PMID:25575306

Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates.

PubMed

Klawonn, Isabell; Bonaglia, Stefano; Brüchert, Volker; Ploug, Helle

2015-06-01

Colonies of N(2)-fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. (15)N-isotope labelling experiments and nutrient analyses revealed that N(2) fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N(2) were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (⩾1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ⩾0.1 mm) may only arise in low-oxygenated waters (⩽25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO(3)(-)-depleted, fully oxygenated (surface) waters. In NO(3)(-)-enriched (>1.5 μM), O(2)-depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes.

Alkaline electrochemical advanced oxidation process for chromium oxidation at graphitized multi-walled carbon nanotubes.

PubMed

Xue, Yudong; Zheng, Shili; Sun, Zhi; Zhang, Yi; Jin, Wei

2017-09-01

Alkaline electrochemical advanced oxidation processes for chromium oxidation and Cr-contaminated waste disposal were reported in this study. The highly graphitized multi-walled carbon nanotubes g-MWCNTs modified electrode was prepared for the in-situ electrochemical generation of HO 2 - . RRDE test results illustrated that g-MWCNTs exhibited much higher two-electron oxygen reduction activity than other nanocarbon materials with peak current density of 1.24 mA cm -2 , %HO 2 - of 77.0% and onset potential of -0.15 V (vs. Hg/HgO). It was originated from the highly graphitized structure and good electrical conductivity as illustrated from the Raman, XRD and EIS characterizations, respectively. Large amount of reactive oxygen species (HO 2 - and ·OH) were in-situ electro-generated from the two-electron oxygen reduction and chromium-induced alkaline electro-Fenton-like reaction. The oxidation of Cr(III) was efficiently achieved within 90 min and the conversion ratio maintained more than 95% of the original value after stability test, offering an efficient and green approach for the utilization of Cr-containing wastes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Critical soil conditions for oxygen stress to plant roots: Substituting the Feddes-function by a process-based model

NASA Astrophysics Data System (ADS)

Bartholomeus, Ruud P.; Witte, Jan-Philip M.; van Bodegom, Peter M.; van Dam, Jos C.; Aerts, Rien

2008-10-01

SummaryEffects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. On theoretical grounds it is expected that oxygen stress depends on various abiotic and biotic factors. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil ( ϕgas_min) at which oxygen stress occurs. First, we calculated the minimum oxygen concentration in the gas phase of the soil needed to sustain the roots through (micro-scale) diffusion with just enough oxygen to respire. Subsequently, ϕgas_min that corresponds to this minimum oxygen concentration was calculated from diffusion from the atmosphere through the soil (macro-scale). We analyzed the validity of constant critical values to represent oxygen stress in terms of ϕgas_min, based on model simulations in which we distinguished different soil types and in which we varied temperature, organic matter content, soil depth and plant characteristics. Furthermore, in order to compare our model results with the Feddes-function, we linked root oxygen stress to root water uptake (through the sink term variable F, which is the ratio of actual and potential uptake). The simulations showed that ϕgas_min is especially sensitive to soil temperature, plant characteristics (root dry weight and maintenance respiration coefficient) and soil depth but hardly to soil organic matter content. Moreover, ϕgas_min varied considerably between soil types and was larger in sandy soils than in clayey soils. We demonstrated that F of the Feddes-function indeed decreases approximately linearly, but that actual oxygen stress already starts at drier conditions than according to the Feddes-function. How much drier is depended on the factors indicated above. Thus, the Feddes-function might cause large errors in the prediction of transpiration reduction and growth reduction through oxygen stress. We made our method easily accessible to others by implementing it in SWAP, a user-friendly soil water model that is coupled to plant growth. Since constant values for ϕgas_min in plant and hydrological modeling appeared to be inappropriate, an integrated approach, including both physiological and physical processes, should be used instead. Therefore, we advocate using our method in all situations where oxygen stress could occur.

Application of integrated ozone and granular activated carbon for decolorization and chemical oxygen demand reduction of vinasse from alcohol distilleries.

PubMed

Hadavifar, Mojtaba; Younesi, Habibollah; Zinatizadeh, Ali Akbar; Mahdad, Faezeh; Li, Qin; Ghasemi, Zahra

2016-04-01

This study investigates the treatment of the distilleries vinasse using a hybrid process integrating ozone oxidation and granular activated carbons (GAC) in both batch and continuous operation mode. The batch-process studies have been carried out to optimize initial influent pH, GAC doses, the effect of the ozone (O3) and hydrogen peroxide (H2O2) concentrations on chemical oxygen demand (COD) and color removal of the distilleries vinasse. The continuous process was carried out on GAC and ozone treatment alone as well as the hybrid process comb both methods to investigate the synergism effectiveness of the two methods for distilleries vinasse COD reduction and color removal. In a continuous process, the Yan model described the experimental data better than the Thomas model. The efficiency of ozonation of the distilleries vinasse was more effective for color removal (74.4%) than COD removal (25%). O3/H2O2 process was not considerably more effective on COD and color removal. Moreover, O3/GAC process affected negatively on the removal efficiency by reducing COD and color from distilleries vinasse. The negative effect decreased by increasing pH value of the influent. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of Extrinsic and Intrinsic Proton Activity on The Mechanism of Oxygen Reduction in Ionic Liquids

NASA Astrophysics Data System (ADS)

Zeller, Robert August

Mechanisms for oxygen reduction are proposed for three distinct cases covering two ionic liquids of fundamentally different archetypes and almost thirty orders of magnitude of proton activity. Proton activity is treated both extrinsically by varying the concentration and intrinsically by selecting proton donors with a wide range of aqueous pKa values. The mechanism of oxygen reduction in ionic liquids is introduced by way of the protic ionic liquid (pIL) triethylammonium triflate (TEATf) which shares some similarities with aqueous acid solutions. Oxygen reduction in TEATf begins as the one electron rate limited step to form superoxide, O2 *-, which is then rapidly protonated by the pIL cation forming the perhydroxyl radical, HO2*. The perhydroxyl radical is further reduced to peroxidate (HO2-) and hydrogen peroxide in proportions in accordance with their pKa. The reaction does not proceed beyond this point due to the adsorption of the conjugate base triethylammine interfering with the disproportionation of hydrogen peroxide. This work demonstrates that this mechanism is consistent across Pt, Au, Pd, and Ag electrodes. Two related sets of experiments were performed in the inherently aprotic ionic liquid 1-butyl-2,3-dimethylimidazolium triflate (C4dMImTf). The first involved the titration of acidic species of varying aqueous pKa into the IL while monitoring the extent of oxygen reduction as a function of pKa and potential on Pt and glassy carbon (GC) electrodes. These experiments confirmed the greater propensity of Pt to reduce oxygen by its immediate and abrupt transition from one electron reduction to four electron reduction, while oxygen reduction on GC gradually approaches four electron reduction as the potentials were driven more cathodic. The potential at which oxygen reduction initiates shows general agreement with the Nernst equation and the acid's tabulated aqueous pKa value, however at the extremely acidic end, a small deviation is observed. The second set of experiments in C4dMImTf solicited water as the proton donor for oxygen reduction in an approximation of the aqueous alkaline case. The water content was varied between extremely dry (<0.1 mol% H2O) and saturated (approximately 15.8 mol% H2O). As the water content increased so too did the extent of oxygen reduction eventually approach two electrons on both Pt and GC. However, additional water led to a linear increase in the Tafel slope under enhanced mass transport conditions up to the point of 10 mol% water. This inhibition of oxygen adsorption is the result of the interaction between superoxide and water and more specifically is proposed to be associated with decomposition of theC4dMIm + cation by hydroxide at the elevated temperatures required for the experiment. Oxygen reduction on both Pt and GC follows Nernstian behavior as the water content is increased. Separate mechanisms for oxygen reduction on Pt and GC are proposed based on the nature of the Nernstian response in these systems.

A mature Bosch CO2 reduction technology. [for long-duration space missions

NASA Technical Reports Server (NTRS)

King, C. D.; Holmes, R. F.

1976-01-01

The reduction of CO2 is one of the steps in closing the oxygen loop for long-duration manned space missions. Several units utilizing the Bosch process, which catalytically reduces CO2 with hydrogen, have been built and operated during the past decade. Each contributed substantial information affecting subsequent designs. Early challenges were primarily concerned with carbon control, materials durability, and reliability of reaction initiation. These were followed by concern about power consumption, expendable weight, volume, and process rate control. Suitable materials and techniques for carbon containment and process reliability have been demonstrated. Power requirements have been reduced by almost an order of magnitude. Methods for significant reductions in expendable weight and volume have been developed. The technology is at a state of maturity directly applicable to designs for space missions.

Dissolution of Pt during Oxygen Reduction Reaction Produces Pt Nanoparticles

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

Bae, Je Hyun; Brocenschi, Ricardo F.; Kisslinger, Kim

The loss of Pt during the oxygen reduction reaction (ORR) affects the performance and economic viability of fuel cells and sensors. Our group previously observed the dissolution of Pt nanoelectrodes at moderately negative potentials during the ORR. Here we report a more detailed study of this process and identify its product. The nanoporous Pt surface formed during the ORR was visualized by AFM and high-resolution SEM, which also showed ~5 nm sized Pt particles on the glass surface surrounding the electrode. Furthermore, the release of these nanoparticles into the solution was confirmed by monitoring their catalytically amplified collisions with amore » Hg-coated microelectrode used as the tip in the scanning electrochemical microscope (SECM).« less

Dissolution of Pt during Oxygen Reduction Reaction Produces Pt Nanoparticles

DOE PAGES

Bae, Je Hyun; Brocenschi, Ricardo F.; Kisslinger, Kim; ...

2017-11-15

The loss of Pt during the oxygen reduction reaction (ORR) affects the performance and economic viability of fuel cells and sensors. Our group previously observed the dissolution of Pt nanoelectrodes at moderately negative potentials during the ORR. Here we report a more detailed study of this process and identify its product. The nanoporous Pt surface formed during the ORR was visualized by AFM and high-resolution SEM, which also showed ~5 nm sized Pt particles on the glass surface surrounding the electrode. Furthermore, the release of these nanoparticles into the solution was confirmed by monitoring their catalytically amplified collisions with amore » Hg-coated microelectrode used as the tip in the scanning electrochemical microscope (SECM).« less

Optical conductivity of partially oxidized graphene from first principles

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

Nasehnia, F., E-mail: f.nasehnia@gmail.com; Seifi, M., E-mail: Seifi@guilan.ac.ir

2015-07-07

We investigate the geometry, electronic structure, and optical properties of partially oxidized graphene using density functional theory. Our calculations show that oxygen atoms are chemisorbed on graphene plane and distort carbon atoms vertically, with almost no change in the in-plane structure. The ground state configurations for different oxygen coverages ranging from 2% to 50% (O/C ratio) are calculated and show the strong tendency of oxygen adatoms to aggregate and form discrete islands on graphene plane. It is found that the opened band gap due to oxygen functionalization depends on the oxygen density and the adsorption configuration. The gap is notmore » significant for oxygen densities lower than 8%. The optical conductivities are calculated in the infrared, visible, and ultraviolet regions and show different characteristic features depending on the degree of oxidation. These results imply that optical measurement techniques can be employed to monitor oxidation (or reduction) process as contact-free methods.« less

Cyclic interconversion of methionine containing peptide between oxidized and reduced phases monitored by reversed-phase HPLC and ESI-MS/MS.

PubMed

Jin, Yulong; Huang, Yanyan; Xie, Yunfeng; Hu, Wenbing; Wang, Fuyi; Liu, Guoquan; Zhao, Rui

2012-01-30

The cyclic oxidation and reduction of methionine (Met) containing peptides and proteins play important roles in biological system. This work was contributed to analysis the cyclic oxidation and reduction processes of a methionine containing peptide which is very likely to relate in the cell signal transduction pathways. To mimic the biological oxidation condition, hydrogen peroxide was used as the reactive oxygen species to oxidize the peptide. Reversed-phase high-performance liquid chromatography and mass spectrometry were employed to monitor the reactions and characterize the structural changes of the products. A rapid reduction procedure was developed by simply using KI as the reductant, which is green and highly efficient. By investigation of the cyclic oxidation and reduction process, our work provides a new perspective to study the function and mechanism of Met containing peptides and proteins during cell signaling processes as well as diseases. Copyright © 2011 Elsevier B.V. All rights reserved.

Phytoremediation of trichloroethene (TCE) using cottonwood trees

USGS Publications Warehouse

Jones, S.A.; Lee, R.W.; Kuniansky, E.L.; Leeson, Andrea; Alleman, Bruce C.

1999-01-01

Phytoremediation uses the natural ability of plants to degrade contaminants in ground water. A field demonstration designed to remediate aerobic shallow ground water that contains trichloroethene began in April 1996 with the planting of cottonwood trees over an approximately 0.2-hectare area at the Naval Air Station, Fort Worth, Tx. Ground water was sampled in July 1997, November 1997, February 1998, and June 1998. Analyses from samples indicate that tree roots have the potential to create anaerobic conditions in the ground water that will facilitate degradation of trichloroethene by microbially mediated reductive dichlorination. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about-20 years old) 60 meters southwest of the cottonwood plantings. Reduction of dissolved oxygen is the primary microbially mediated reaction occurring in the ground water beneath the planted trees, whereas near the mature cottonwood tree, data indicate that methanogenesis is the most probable reaction occurring. Reductive dichlorination either is not occurring or is not a primary process away from the mature tree. On the basis of isotopic analyses of carbon-13 at locations away from the mature tree, trichloroethene concentration is controlled by volatilization.Phytoremediation uses the natural ability of plants to degrade contaminants in ground water. A field demonstration designed to remediate aerobic shallow ground water that contains trichloroethene began in April 1996 with the planting of cottonwood trees over an approximately 0.2-hectare area at the Naval Air Station, Fort Worth, Tx. Ground water was sampled in July 1997, November 1997, February 1998, and June 1998. Analyses from samples indicate that tree roots have the potential to create anaerobic conditions in the ground water that will facilitate degradation of trichloroethene by microbially mediated reductive dichlorination. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about-20 years old) 60 meters southwest of the cottonwood plantings. Reduction of dissolved oxygen is the primary microbially mediated reaction occurring in the ground water beneath the planted trees, whereas near the mature cottonwood tree, data indicate that methanogenesis is the most probable reaction occurring. Reductive dichlorination either is not occurring or is not a primary process away from the mature tree. On the basis of isotopic analyses of carbon-13 at locations away from the mature tree, trichloroethene concentration is controlled by volatilization.

Oxygen and the light-dark cycle of nitrogenase activity in two unicellular cyanobacteria.

PubMed

Compaoré, Justine; Stal, Lucas J

2010-01-01

Cyanobacteria capable of fixing dinitrogen exhibit various strategies to protect nitrogenase from inactivation by oxygen. The marine Crocosphaera watsonii WH8501 and the terrestrial Gloeothece sp. PCC6909 are unicellular diazotrophic cyanobacteria that are capable of aerobic nitrogen fixation. These cyanobacteria separate the incompatible processes of oxygenic photosynthesis and nitrogen fixation temporally, confining the latter to the dark. Although these cyanobacteria thrive in fully aerobic environments and can be cultivated diazotrophically under aerobic conditions, the effect of oxygen is not precisely known due to methodological limitations. Here we report the characteristics of nitrogenase activity with respect to well-defined levels of oxygen to which the organisms are exposed, using an online and near real-time acetylene reduction assay combined with sensitive laser-based photoacoustic ethylene detection. The cultures were grown under an alternating 12-12 h light-dark cycle and acetylene reduction was recorded continuously. Acetylene reduction was assayed at 20%, 15%, 10%, 7.5%, 5% and 0% oxygen and at photon flux densities of 30 and 76 mumol m(-2) s(-1) provided at the same light-dark cycle as during cultivation. Nitrogenase activity was predominantly but not exclusively confined to the dark. At 0% oxygen nitrogenase activity in Gloeothece sp. was not detected during the dark and was shifted completely to the light period, while C. watsonii did not exhibit nitrogenase activity at all. Oxygen concentrations of 15% and higher did not support nitrogenase activity in either of the two cyanobacteria. The highest nitrogenase activities were at 5-7.5% oxygen. The highest nitrogenase activities in C. watsonii and Gloeothece sp. were observed at 29 degrees C. At 31 degrees C and above, nitrogenase activity was not detected in C. watsonii while the same was the case at 41 degrees C and above in Gloeothece sp. The differences in the behaviour of nitrogenase activity in these cyanobacteria are discussed with respect to their presumed physiological strategies to protect nitrogenase from oxygen inactivation and to the environment in which they thrive.

Polymer membrane based electrolytic cell and process for the direct generation of hydrogen peroxide in liquid streams

NASA Technical Reports Server (NTRS)

White, James H. (Inventor); Schwartz, Michael (Inventor); Sammells, Anthony F. (Inventor)

1997-01-01

An electrolytic cell for generating hydrogen peroxide is provided including a cathode containing a catalyst for the reduction of oxygen, and an anode containing a catalyst for the oxidation of water. A polymer membrane, semipermeable to either protons or hydroxide ions is also included and has a first face interfacing to the cathode and a second face interfacing to the anode so that when a stream of water containing dissolved oxygen or oxygen bubbles is passed over the cathode and a stream of water is passed over the anode, and an electric current is passed between the anode and the cathode, hydrogen peroxide is generated at the cathode and oxygen is generated at the anode.

Hydrothermal Synthesis of Platinum-Group-Metal-Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis

DOE PAGES

Gokhale, Rohan; Tsui, Lok-Kun; Roach, Kristin; ...

2017-12-07

In this paper, a hydrothermal approach to generate a platinum-group-metal-free (PGM-free) Fe-N-C catalyst for the oxygen reduction reaction (ORR) is introduced. The process involves partial carbonization by hydrothermal means followed by thermal treatment to obtain the final catalysts. Detailed X-ray scattering analysis of the glucose-imidazole catalysts (termed as GLU-IMID-C catalysts), obtained for the first time with the use of CarbonXS GUI program, reveals the presence of face-centered cubic (FCC) iron nanoparticles embedded in partially graphitic carbon in all catalyst variations. We also report the physical characterization of these catalysts by using X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area analysis, and transmissionmore » electron microscopy. The electrocatalytic behavior of the catalysts towards oxygen reduction is studied separately in acidic and alkaline electrolytes by rotating ring disk electrode measurements. The catalysts exhibit high ORR activity in acidic (0.5 M H 2SO 4) and alkaline (0.1 M KOH) electrolytes. Lastly, a precursor structure-performance relationship of these catalysts and their performance trends in both electrolytes has been discussed in this work.« less

Hydrothermal Synthesis of Platinum-Group-Metal-Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis

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

Gokhale, Rohan; Tsui, Lok-Kun; Roach, Kristin

In this paper, a hydrothermal approach to generate a platinum-group-metal-free (PGM-free) Fe-N-C catalyst for the oxygen reduction reaction (ORR) is introduced. The process involves partial carbonization by hydrothermal means followed by thermal treatment to obtain the final catalysts. Detailed X-ray scattering analysis of the glucose-imidazole catalysts (termed as GLU-IMID-C catalysts), obtained for the first time with the use of CarbonXS GUI program, reveals the presence of face-centered cubic (FCC) iron nanoparticles embedded in partially graphitic carbon in all catalyst variations. We also report the physical characterization of these catalysts by using X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area analysis, and transmissionmore » electron microscopy. The electrocatalytic behavior of the catalysts towards oxygen reduction is studied separately in acidic and alkaline electrolytes by rotating ring disk electrode measurements. The catalysts exhibit high ORR activity in acidic (0.5 M H 2SO 4) and alkaline (0.1 M KOH) electrolytes. Lastly, a precursor structure-performance relationship of these catalysts and their performance trends in both electrolytes has been discussed in this work.« less

Porous yolk-shell microspheres as N-doped carbon matrix for motivating the oxygen reduction activity of oxygen evolution oriented materials.

PubMed

Zhou, Jinqiu; Wang, Mengfan; Qian, Tao; Liu, Sisi; Cao, Xuecheng; Yang, Tingzhou; Yang, Ruizhi; Yan, Chenglin

2017-09-08

It is highly challenging to explore high-performance bi-functional oxygen electrode catalysts for their practical application in next-generation energy storage and conversion devices. In this work, we synthesize hierarchical N-doped carbon microspheres with porous yolk-shell structure (NCYS) as a metal-free electrocatalyst toward efficient oxygen reduction through a template-free route. The enhanced oxygen reduction performances in both alkaline and acid media profit well from the porous yolk-shell structure as well as abundant nitrogen functional groups. Furthermore, such yolk-shell microspheres can be used as precursor materials to motivate the oxygen reduction activity of oxygen evolution oriented materials to obtain a desirable bi-functional electrocatalyst. To verify its practical utility, Zn-air battery tests are conducted and exhibit satisfactory performance, indicating that this constructed concept for preparation of bi-functional catalyst will afford a promising strategy for exploring novel metal-air battery electrocatalysts.

Porous yolk-shell microspheres as N-doped carbon matrix for motivating the oxygen reduction activity of oxygen evolution oriented materials

NASA Astrophysics Data System (ADS)

Zhou, Jinqiu; Wang, Mengfan; Qian, Tao; Liu, Sisi; Cao, Xuecheng; Yang, Tingzhou; Yang, Ruizhi; Yan, Chenglin

2017-09-01

It is highly challenging to explore high-performance bi-functional oxygen electrode catalysts for their practical application in next-generation energy storage and conversion devices. In this work, we synthesize hierarchical N-doped carbon microspheres with porous yolk-shell structure (NCYS) as a metal-free electrocatalyst toward efficient oxygen reduction through a template-free route. The enhanced oxygen reduction performances in both alkaline and acid media profit well from the porous yolk-shell structure as well as abundant nitrogen functional groups. Furthermore, such yolk-shell microspheres can be used as precursor materials to motivate the oxygen reduction activity of oxygen evolution oriented materials to obtain a desirable bi-functional electrocatalyst. To verify its practical utility, Zn-air battery tests are conducted and exhibit satisfactory performance, indicating that this constructed concept for preparation of bi-functional catalyst will afford a promising strategy for exploring novel metal-air battery electrocatalysts.

Advanced Water Purification System for In Situ Resource Utilization

NASA Technical Reports Server (NTRS)

Anthony, Stephen M.; Jolley, Scott T.; Captain, James G.

2013-01-01

A main goal in the field of In Situ Resource Utilization is to develop technologies that produce oxygen from regolith to provide consumables to an extraterrestrial outpost. The processes developed reduce metal oxides in the regolith to produce water, which is then electrolyzed to produce oxygen. Hydrochloric and hydrofluoric acids are byproducts of the reduction processes, which must be removed to meet electrolysis purity standards. We previously characterized Nation, a highly water selective polymeric proton-exchange membrane, as a filtration material to recover pure water from the contaminated solution. While the membranes successfully removed both acid contaminants, the removal efficiency of and water flow rate through the membranes were not sufficient to produce large volumes of electrolysis-grade water. In the present study, we investigated electrodialysis as a potential acid removal technique. Our studies have shown a rapid and significant reduction in chloride and fluoride concentrations in the feed solution, while generating a relatively small volume of concentrated waste water. Electrodialysis has shown significant promise as the primary separation technique in ISRU water purification processes.

Advanced Water Purification System for In Situ Resource Utilization Project

NASA Technical Reports Server (NTRS)

Anthony, Stephen M.

2014-01-01

A main goal in the field of In Situ Resource Utilization is to develop technologies that produce oxygen from regolith to provide consumables to an extratrrestrial outpost. The processes developed reduce metal oxides in the regolith to produce water, which is then electrolyzed to produce oxygen. Hydrochloric and hydrofluoric acids are byproducts of the reduction processes, which must be removed to meet electrolysis purity standards. We previously characterized Nation, a highly water selective polymeric proton-exchange membrane, as a filtrtion material to recover pure water from the contaminated solution. While the membranes successfully removed both acid contaminants, the removal efficiency of and water flow rate through the membranes were not sufficient to produce large volumes of electrolysis-grade water. In the present study, we investigated electrodialysis as a potential acid removable technique. Our studies have show a rapid and significant reduction in chloride and fluoride concentrations in the feed solution, while generating a relatively small volume of concentrated waste water. Electrodialysis has shown significant promise as the primary separation technique in ISRU water purification processes.

Highly active non-PGM catalysts prepared from metal organic frameworks

DOE PAGES

Barkholtz, Heather M.; Chong, Lina; Kaiser, Zachary B.; ...

2015-06-11

Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/N x/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/N x/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity mustmore » be demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system.« less

Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode

NASA Astrophysics Data System (ADS)

Casalongue, Hernan Sanchez; Kaya, Sarp; Viswanathan, Venkatasubramanian; Miller, Daniel J.; Friebel, Daniel; Hansen, Heine A.; Nørskov, Jens K.; Nilsson, Anders; Ogasawara, Hirohito

2013-12-01

The performance of polymer electrolyte membrane fuel cells is limited by the reduction at the cathode of various oxygenated intermediates in the four-electron pathway of the oxygen reduction reaction. Here we use ambient pressure X-ray photoelectron spectroscopy, and directly probe the correlation between the adsorbed species on the surface and the electrochemical potential. We demonstrate that, during the oxygen reduction reaction, hydroxyl intermediates on the cathode surface occur in several configurations with significantly different structures and reactivities. In particular, we find that near the open-circuit potential, non-hydrated hydroxyl is the dominant surface species. On the basis of density functional theory calculations, we show that the removal of hydration enhances the reactivity of oxygen species. Tuning the hydration of hydroxyl near the triple phase boundary will be crucial for designing more active fuel cell cathodes.

Evaluation of an Atmosphere Revitalization Subsystem for Deep Space Exploration Missions

NASA Technical Reports Server (NTRS)

Perry, Jay L.; Abney, Morgan B.; Conrad, Ruth E.; Frederick, Kenneth R.; Greenwood, Zachary W.; Kayatin, Matthew J.; Knox, James C.; Newton, Robert L.; Parrish, Keith J.; Takada, Kevin C.;

Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

DOE PAGES

Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; ...

2017-07-31

Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering bymore » largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2–), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.« less

Innovative non-thermal plasma disinfection process inside sealed bags: Assessment of bactericidal and sporicidal effectiveness in regard to current sterilization norms

PubMed Central

Charpentier, Emilie; Le-Bras, Florian; Maho, Thomas; Robert, Eric; Pouvesle, Jean-Michel; Polidor, Franck; Gangloff, Sophie C.; Boudifa, Mohamed

2017-01-01

In this work, we developed a device capable to generate a non-thermal plasma discharge inside a sealed bag. The aim of this study was to assess the effectiveness of the oxygen, nitrogen and argon plasma sterilization on Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis spores according to the NF EN 556 Norm. Moreover the bag integrity which is a critical key to maintain the sterile state of items after the end of the process was verified by Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectrometry (XPS) analyses. After plasma treatments, the bacterial counting showed a 6 log reduction of P. aeruginosa and S. aureus in 45 min and 120 min respectively whatever the gas used and a 4 log reduction of B. subtilis spores in 120 min with only oxygen plasma. These results were confirmed by Scanning Electron Microscopy (SEM) observations showing altered bacteria or spores and numerous debris. Taking into account the studied microorganisms, the oxygen plasma treatment showed the highest efficiency. FTIR and XPS analyses showed that this treatment induced no significant modification of the bags. To conclude this non-thermal plasma sterilization technique could be an opportunity to sterilize heat and chemical-sensitive medical devices and to preserve their sterile state after the end of the process. PMID:28662202

Research on the use of space resources

NASA Technical Reports Server (NTRS)

Carroll, W. F. (Editor)

1983-01-01

The second year of a multiyear research program on the processing and use of extraterrestrial resources is covered. The research tasks included: (1) silicate processing, (2) magma electrolysis, (3) vapor phase reduction, and (4) metals separation. Concomitant studies included: (1) energy systems, (2) transportation systems, (3) utilization analysis, and (4) resource exploration missions. Emphasis in fiscal year 1982 was placed on the magma electrolysis and vapor phase reduction processes (both analytical and experimental) for separation of oxygen and metals from lunar regolith. The early experimental work on magma electrolysis resulted in gram quantities of iron (mixed metals) and the identification of significant anode, cathode, and container problems. In the vapor phase reduction tasks a detailed analysis of various process concepts led to the selection of two specific processes designated as ""Vapor Separation'' and ""Selective Ionization.'' Experimental work was deferred to fiscal year 1983. In the Silicate Processing task a thermophysical model of the casting process was developed and used to study the effect of variations in material properties on the cooling behavior of lunar basalt.

Oxygen chemical diffusion in hypo-stoichiometric MOX

NASA Astrophysics Data System (ADS)

Kato, Masato; Morimoto, Kyoichi; Tamura, Tetsuya; Sunaoshi, Takeo; Konashi, Kenji; Aono, Shigenori; Kashimura, Motoaki

2009-06-01

Kinetics of the oxygen-to-metal ratio change in (U 0.8Pu 0.2)O 2-x and (U 0.7Pu 0.3)O 2-x was evaluated in the temperature range of 1523-1623 K using a thermo-gravimetric technique. The oxygen chemical diffusion coefficients were decided as a function of temperature from the kinetics of the reduction process under a hypo-stoichiometric composition. The diffusion coefficient of (U 0.7Pu 0.3)O 2-x was smaller than that of (U 0.8Pu 0.2)O 2-x. No strong dependence was observed for the diffusion coefficient on the O/M variation of samples.

Reductive tetrachloroethene dehalogenation in the presence of oxygen by Sulfurospirillum multivorans: physiological studies and proteome analysis.

PubMed

Gadkari, Jennifer; Goris, Tobias; Schiffmann, Christian L; Rubick, Raffael; Adrian, Lorenz; Schubert, Torsten; Diekert, Gabriele

2018-01-01

Reductive dehalogenation of organohalides is carried out by organohalide-respiring bacteria (OHRB) in anoxic environments. The tetrachloroethene (PCE)-respiring Epsilonproteobacterium Sulfurospirillum multivorans is one of few OHRB able to respire oxygen. Therefore, we investigated the organism's capacity to dehalogenate PCE in the presence of oxygen, which would broaden the applicability to use S. multivorans, unlike other commonly oxygen-sensitive OHRB, for bioremediation, e.g. at oxic/anoxic interphases. Additionally, this has an impact on our understanding of the global halogen cycle. Sulfurospirillum multivorans performs dehalogenation of PCE to cis-1,2-dichloroethene at oxygen concentrations below 0.19 mg/L. The redox potential of the medium electrochemically adjusted up to +400 mV had no influence on reductive dehalogenation by S. multivorans in our experiments, suggesting that higher levels of oxygen impair PCE dechlorination by inhibiting or inactivating involved enzymes. The PCE reductive dehalogenase remained active in cell extracts of S. multivorans exposed to 0.37 mg/L oxygen for more than 96 h. Analysis of the proteome revealed that superoxide reductase and cytochrome peroxidase amounts increased with 5% oxygen in the gas phase, while the response to atmospheric oxygen concentrations involved catalase and hydrogen peroxide reductase. Taken together, our results demonstrate that reductive dehalogenation by OHRB is not limited to anoxic conditions. © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Reductive dissolution and reactive solute transport in a sewage-contaminated glacial outwash aquifer

USGS Publications Warehouse

Lee, R.W.; Bennett, P.C.

1998-01-01

Contamination of shallow ground water by sewage effluent typically contains reduced chemical species that consume dissolved oxygen, developing either a low oxygen geochemical environment or an anaerobic geochemical environment. Based on the load of reduced chemical species discharged to shallow ground water and the amounts of reactants in the aquifer matrix, it should be possible to determine chemical processes in the aquifer and compare observed results to predicted ones. At the Otis Air Base research site (Cape Cod, Massachusetts) where sewage effluent has infiltrated the shallow aquifer since 1936, bacterially mediated processes such as nitrification, denitrification, manganese reduction, and iron reduction have been observed in the contaminant plume. In specific areas of the plume, dissolved manganese and iron have increased significantly where local geochemical conditions are favorable for reduction and transport of these constituents from the aquifer matrix. Dissolved manganese and iron concentrations ranged from 0.02 to 7.3 mg/L, and 0.001 to 13.0 mg/L, respectively, for 21 samples collected from 1988 to 1989. Reduction of manganese and iron is linked to microbial oxidation of sewage carbon, producing bicarbonate and the dissolved metal ions as by-products. Calculated production and flux of CO2 through the unsaturated zone from manganese reduction in the aquifer was 0.035 g/m2/d (12% of measured CO2 flux during winter). Manganese is limited in the aquifer, however. A one-dimensional, reaction-coupled transport model developed for the mildly reducing conditions in the sewage plume nearest the source beds showed that reduction, transport, and removal of manganese from the aquifer sediments should result in iron reduction where manganese has been depleted.

Biodegradation of pulp and paper mill effluent using anaerobic followed by aerobic digestion.

PubMed

Bishnoi, Narsi R; Khumukcham, R K; Kumar, Rajender

2006-05-01

An experimental study was carried to find out the degradability of black liquor of pulp and paper mill wastewater for biomethanogenesis in continuous stirred tank reactor (CSTR) and followed by activated sludge process (ASP). Continuous stirred tank reactor was used in present study for anaerobic digestion of black liquor, while completely mixed activated sludge system was used for aerobic digestion. A maximum methane production was found up to 430 ml/day, chemical oxygen demand was reduced up to 64% and total volatile fatty acid increased up to 1500 mg/l from 975 mg/l at 7.3 pH, 37 degrees C temperature and 8 days hydraulic retention time during anaerobic digestion. In activated sludge process (aerobic digestion) chemical oxygen demand and biological oxygen demand reduction were 81% and 86% respectively at 72 hr hydraulic retention time.

High-Potential Electrocatalytic O2 Reduction with Nitroxyl/NOx Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis

PubMed Central

2015-01-01

Efficient reduction of O2 to water is a central challenge in energy conversion and many aerobic oxidation reactions. Here, we show that the electrochemical oxygen reduction reaction (ORR) can be achieved at high potentials by using soluble organic nitroxyl and nitrogen oxide (NOx) mediators. When used alone, neither organic nitroxyls, such as 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl (TEMPO), nor NOx species, such as sodium nitrite, are effective ORR mediators. The combination of nitroxyl/NOx species, however, mediates sustained O2 reduction with overpotentials as low as 300 mV in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The overpotentials accessible with this ORR system are significantly lower than widely studied molecular metal-macrocycle ORR catalysts and benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NOx species, together with kinetically efficient reduction of oxidized NOx species by TEMPO and other organic nitroxyls. PMID:27162977

FLAME DENITRATION AND REDUCTION OF URANIUM NITRATE TO URANIUM DIOXIDE

DOEpatents

Hedley, W.H.; Roehrs, R.J.; Henderson, C.M.

1962-06-26

A process is given for converting uranyl nitrate solution to uranium dioxide. The process comprises spraying fine droplets of aqueous uranyl nitrate solution into a hightemperature hydrocarbon flame, said flame being deficient in oxygen approximately 30%, retaining the feed in the flame for a sufficient length of time to reduce the nitrate to the dioxide, and recovering uranium dioxide. (AEC)

Solar heating of common lunar minerals for the production of oxygen

NASA Technical Reports Server (NTRS)

Senior, C. L.

1991-01-01

The purpose of this work was to demonstrate the feasibility of vapor-phase reduction (pyrolysis) of lunar materials to produce oxygen. Solar furnace experiments were conducted on two common lunar minerals, ilmenite and anorthite. Thermodynamic equilibrium calculations predicted that ilmenite should show a larger pressure increase than anorthite under conditions of the experiments and this was confirmed by the experiments. The measured mass loss of the ilmenite sample was consistent with loss of oxygen by reduction of iron in the liquid phase; this result was also predicted from equilibrium calculations. Based on preliminary experiments and equilibrium calculations, the temperatures needed for pyrolysis are expected to be in the range of 2000 to 2500 K, giving total gas pressures of 0.01 to 1 torr. Bulk regolith can be used as a feedstock without extensive beneficiation. Further, selective condensation of metal-containing species from the gas phase may yield metallic iron and silicon as byproducts from the process.

Systematic Sensitivity Analysis of Metabolic Controllers During Reductions in Skeletal Muscle Blood Flow

NASA Technical Reports Server (NTRS)

Radhakrishnan, Krishnan; Cabrera, Marco

2000-01-01

An acute reduction in oxygen delivery to skeletal muscle is generally associated with profound derangements in substrate metabolism. Given the complexity of the human bioenergetic system and its components, it is difficult to quantify the interaction of cellular metabolic processes to maintain ATP homeostasis during stress (e.g., hypoxia, ischemia, and exercise). Of special interest is the determination of mechanisms relating tissue oxygenation to observed metabolic responses at the tissue, organ, and whole body levels and the quantification of how changes in oxygen availability affect the pathways of ATP synthesis and their regulation. In this study, we apply a previously developed mathematical model of human bioenergetics to study effects of ischemia during periods of increased ATP turnover (e.g., exercise). By using systematic sensitivity analysis the oxidative phosphorylation rate was found to be the most important rate parameter affecting lactate production during ischemia under resting conditions. Here we examine whether mild exercise under ischemic conditions alters the relative importance of pathways and parameters previously obtained.

Reinterpreting the importance of oxygen-based biodegradation in chloroethene-contaminated groundwater

USGS Publications Warehouse

Bradley, Paul M.

2011-01-01

Chlororespiration is common in shallow aquifer systems under conditions nominally identified as anoxic. Consequently, chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products is interpreted as evidence that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, nonconservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms and is consistent with contaminant degradation to nondiagnostic mineralization products like CO2. While anoxic mineralization of chloroethene compounds has been proposed previously, recent results suggest that oxygen-based mineralization of chloroethenes also can be significant at dissolved oxygen concentrations below the currently accepted field standard for nominally anoxic conditions. Thus, reassessment of the role and potential importance of low concentrations of oxygen in chloroethene biodegradation are needed, because mischaracterization of operant biodegradation processes can lead to expensive and ineffective remedial actions. A modified interpretive framework is provided for assessing the potential for chloroethene biodegradation under different redox conditions and the probable role of oxygen in chloroethene biodegradation.

Isotopic evidence for oxygenated Mesoarchaean shallow oceans

NASA Astrophysics Data System (ADS)

Eickmann, Benjamin; Hofmann, Axel; Wille, Martin; Bui, Thi Hao; Wing, Boswell A.; Schoenberg, Ronny

2018-02-01

Mass-independent fractionation of sulfur isotopes (MIF-S) in Archaean sediments results from photochemical processing of atmospheric sulfur species in an oxygen-depleted atmosphere. Geological preservation of MIF-S provides evidence for microbial sulfate reduction (MSR) in low-sulfate Paleoarchaean (3.8-3.2 billion years ago (Ga)) and Neoarchaean (2.8-2.5 Ga) oceans, but the significance of MSR in Mesoarchaean (3.2-2.8 Ga) oceans is less clear. Here we present multiple sulfur and iron isotope data of early diagenetic pyrites from 2.97-Gyr-old stromatolitic dolomites deposited in a tidal flat environment of the Nsuze Group, Pongola Supergroup, South Africa. We identified consistently negative Δ33S values in pyrite, which indicates photochemical reactions under anoxic atmospheric conditions, but large mass-dependent sulfur isotope fractionations of 30‰ in δ34S, identifying active MSR. Negative pyrite δ56Fe values (-1.31 to -0.88‰) record Fe oxidation in oxygen-bearing shallow oceans coupled with biogenic Fe reduction during diagenesis, consistent with the onset of local Fe cycling in oxygen oases 3.0 Ga. We therefore suggest the presence of oxygenated near-shore shallow-marine environments with ≥5 μM sulfate at this time, in spite of the clear presence of an overall reduced Mesoarchaean atmosphere.

Transcriptional responses in Lactococcus lactis subsp. cremoris to the changes in oxygen and redox potential during milk acidification.

PubMed

Larsen, N; Brøsted Werner, B; Jespersen, L

2016-08-01

Milk acidification and metabolic activity of the starter cultures are affected by oxygen; however, molecular factors related to the redox changes are poorly defined. The objective of the study was to investigate transcriptional responses in Lactococcus lactis subsp. cremoris CHCCO2 grown in milk to the shifts of oxygen and redox potential (Eh7 ). Transcriptomic studies were performed with the use of Illumina HiSeq 2000 mRNA sequencing and validated by the real-time quantitative PCR. In total 105 differentially expressed genes were assigned functional gene names. Most of the differentially expressed genes were detected during aerobic reduction phase. Upregulated genes were implicated in lactose utilization, glycogen biosynthesis, amino sugar metabolism, oxidation-reduction, pyrimidine biosynthesis and DNA integration processes. Genes of purine nucleotide biosynthesis and genes encoding amino acid, multidrug resistance and ion ABC transporters were mostly downregulated, while oligopeptide transporter genes were reduced during oxygen depletion and induced at minimum Eh7 . Understanding of gene responses in starter cultures to the changes of oxidation-reduction state is important for the better control and reproducibility of dairy fermentations. We applied mRNA sequencing by Illumina HiSeq 2000 to investigate gene expression profile in a dairy strain of Lactococcus lactis subsp. cremoris during milk acidification. Novelty of this study lies in linking transcriptional responses to oxygen depletion and the changes of redox potential with the fermentation kinetics and clarification of molecular factors specifically expressed in milk which might be essential for bacterial performance and the final quality of cheeses. © 2016 The Society for Applied Microbiology.

Fungal oxygen exchange between denitrification intermediates and water.

PubMed

Rohe, Lena; Anderson, Traute-Heidi; Braker, Gesche; Flessa, Heinz; Giesemann, Anette; Wrage-Mönnig, Nicole; Well, Reinhard

2014-02-28

Fungi can contribute greatly to N2O production from denitrification. Therefore, it is important to quantify the isotopic signature of fungal N2O. The isotopic composition of N2O can be used to identify and analyze the processes of N2O production and N2O reduction. In contrast to bacteria, information about the oxygen exchange between denitrification intermediates and water during fungal denitrification is lacking, impeding the explanatory power of stable isotope methods. Six fungal species were anaerobically incubated with the electron acceptors nitrate or nitrite and (18)O-labeled water to determine the oxygen exchange between denitrification intermediates and water. After seven days of incubation, gas samples were analyzed for N2O isotopologues by isotope ratio mass spectrometry. All the fungal species produced N2O. N2O production was greater when nitrite was the sole electron acceptor (129 to 6558 nmol N2O g dw(-1)  h(-1)) than when nitrate was the electron acceptor (6 to 47 nmol N2O g dw(-1)  h(-1)). Oxygen exchange was complete with nitrate as electron acceptor in one of five fungi and with nitrite in two of six fungi. Oxygen exchange of the other fungi varied (41 to 89% with nitrite and 11 to 61% with nitrate). This is the first report on oxygen exchange with water during fungal denitrification. The exchange appears to be within the range previously reported for bacterial denitrification. This adds to the difficulty of differentiating N2O producing processes based on the origin of N2O-O. However, the large oxygen exchange repeatedly observed for bacteria and now also fungi could lead to less variability in the δ(18)O values of N2O from soils, which could facilitate the assessment of the extent of N2O reduction. Copyright © 2013 John Wiley & Sons, Ltd.

Modeling of the oxygen reduction reaction for dense LSM thin films

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

Yang, Tao; Liu, Jian; Yu, Yang

In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

Modeling of the oxygen reduction reaction for dense LSM thin films

DOE PAGES

Yang, Tao; Liu, Jian; Yu, Yang; ...

2017-10-17

In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

Evolution of Metallicity in Vanadium Dioxide by Creation of Oxygen Vacancies

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Zuo, Fan; Wan, Chenghao; Dutta, Aveek; Kim, Jongbum; Rensberg, Jura; Nawrodt, Ronny; Park, Helen Hejin; Larrabee, Thomas J.; Guan, Xiaofei; Zhou, You; Prokes, S. M.; Ronning, Carsten; Shalaev, Vladimir M.; Boltasseva, Alexandra; Kats, Mikhail A.; Ramanathan, Shriram

2017-03-01

Tuning of the electronic state of correlated materials is key to their eventual use in advanced electronics and photonics. The prototypical correlated oxide (VO2 ) is insulating at room temperature and transforms to a metallic state when heated to 67 °C (340 K). We report the emergence of a metallic state that is preserved down to 1.8 K by annealing thin films of VO2 at an ultralow oxygen partial pressure (PO2˜10-24 atm ). The films can be reverted back to their original state by annealing in oxygen, and this process can be iterated multiple times. The metallic phase created by oxygen deficiency has a tetragonal rutile structure and contains a large number of oxygen vacancies far beyond the solubility at equilibrium (greater than approximately 50 times). The oxygen starvation reduces the oxidation state of vanadium from V4 + to V3 + and leads to the metallization. The extent of resistance reduction (concurrent with tuning of optical properties) can be controlled by the time-temperature envelope of the annealing conditions since the process is diffusionally driven. This experimental platform, which can extensively tune oxygen vacancies in correlated oxides, provides an approach to study emergent phases and defect-mediated adaptive electronic and structural phase boundary crossovers.

Chem I Supplement: Chemistry of Steel Making.

ERIC Educational Resources Information Center

Sellers, Neal

1980-01-01

Provides information about the chemistry of steel making applicable to teaching secondary school science. Generalized chemical reactions describe the manufacture of steel from iron ore. Also discussed are raw materials, processing choices, and how various furnaces (blast, direct reduction, open hearth, basic oxygen, electric) work. (CS)

Electrochemical characterisation of air electrodes based on La 0.6Sr 0.4CoO 3 and carbon nanotubes

NASA Astrophysics Data System (ADS)

Thiele, Doreen; Züttel, Andreas

The efficiency of fuel cells suffers from the high activation polarisation at the cathode, where the oxygen reduction reaction takes place. In order to improve the performance, air electrodes composed of carbon nanotubes (CNTs) and the perovskite La 0.6Sr 0.4CoO 3 are produced by two different methods and investigated. In the first method CNTs are directly grown on the perovskite and in the second method CNTs and perovskite are combined by ultrasonic mixing. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. Best performance shows the electrode composed of 25 wt% CNTs, 55 wt% La 0.6Sr 0.4CoO 3 and 20 wt% PTFE as binder, produced by ultrasonic mixing. The Nyquist plot of this electrode displays two potential-dependent semi-circles, accounting for processes on the catalyst surface and for processes depending on the morphology of the electrode.

Oxygen Reduction Reaction for Generating H2 O2 through a Piezo-Catalytic Process over Bismuth Oxychloride.

PubMed

Shao, Dengkui; Zhang, Ling; Sun, Songmei; Wang, Wenzhong

2018-02-09

Oxygen reduction reaction (ORR) for generating H 2 O 2 through green pathways have gained much attention in recent years. Herein, we introduce a piezo-catalytic approach to obtain H 2 O 2 over bismuth oxychloride (BiOCl) through an ORR pathway. The piezoelectric response of BiOCl was directly characterized by piezoresponse force microscopy (PFM). The BiOCl exhibits efficient catalytic performance for generating H 2 O 2 (28 μmol h -1 ) only from O 2 and H 2 O, which is above the average level of H 2 O 2 produced by solar-to-chemical processes. A piezo-catalytic mechanism was proposed: with ultrasonic waves, an alternating electric field will be generated over BiOCl, which can drive charge carriers (electrons) to interact with O 2 and H 2 O, then to form H 2 O 2 . © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multimillennium changes in dissolved oxygen under global warming: results from an AOGCM and offline ocean biogeochemical model

NASA Astrophysics Data System (ADS)

Yamamoto, A.; Abe-Ouchi, A.; Shigemitsu, M.; Oka, A.; Takahashi, K.; Ohgaito, R.; Yamanaka, Y.

2016-12-01

Long-term oceanic oxygen change due to global warming is still unclear; most future projections (such as CMIP5) are only performed until 2100. Indeed, few previous studies using conceptual models project oxygen change in the next thousands of years, showing persistent global oxygen reduction by about 30% in the next 2000 years, even after atmospheric carbon dioxide stops rising. Yet, these models cannot sufficiently represent the ocean circulation change: the key driver of oxygen change. Moreover, considering serious effect oxygen reduction has on marine life and biogeochemical cycling, long-term oxygen change should be projected for higher validity. Therefore, we used a coupled atmosphere-ocean general circulation model (AOGCM) and an offline ocean biogeochemical model, investigating realistic long-term changes in oceanic oxygen concentration and ocean circulation. We integrated these models for 2000 years under atmospheric CO2 doubling and quadrupling. After global oxygen reduction in the first 500 years, oxygen concentration in deep ocean globally recovers and overshoots, despite surface oxygen decrease and weaker Atlantic Meridional Overturning Circulation. Deep ocean convection in the Weddell Sea recovers and overshoots, after initial cessation. Thus, enhanced deep convection and associated Antarctic Bottom Water supply oxygen-rich surface waters to deep ocean, resulting global deep ocean oxygenation. We conclude that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in the deep ocean; contrary to past reported long-term oxygen reduction and general expectation. In presentation, we will discuss the mechanism of response of deep ocean convection in the Weddell Sea and show the volume changes of hypoxic waters.

Organic radicals for the enhancement of oxygen reduction reaction in Li-O2 batteries.

PubMed

Tesio, A Y; Blasi, D; Olivares-Marín, M; Ratera, I; Tonti, D; Veciana, J

2015-12-25

We examine for the first time the ability of inert carbon free-radicals as soluble redox mediators to catalyze and enhance the oxygen reduction reaction in a (TEGDME)-based electrolyte. We demonstrate that the tris(2,4,6-trichlorophenyl)methyl (TTM) radical is capable of chemically favoring the oxygen reduction reaction improving significantly the Li-O2 battery performance.

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides

PubMed Central

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-01-01

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG. PMID:24717290

Sulfur transformations at the hydrogen sulfide/oxygen interface in stratified waters and in cyanobacterial mats

NASA Technical Reports Server (NTRS)

Cohen, Y.

1985-01-01

Stratified water bodies allow the development of several microbial plates along the water column. The microbial plates develop in relation to nutrient availability, light penetration, and the distribution of oxygen and sulfide. Sulfide is initially produced in the sediment by sulfate-reducing bacteria. It diffuses along the water column creating a zone of hydrogen sulfide/oxygen interface. In the chemocline of Solar Lake oxygen and sulfide coexist in a 0 to 10 cm layer that moves up and down during a diurnal cycle. The microbial plate at the chemocline is exposed to oxygen and hydrogen sulfide, alternating on a diurnal basis. The cyanobacteria occupying the interface switch from anoxygenic photosynthesis in the morning to oxygenic photosynthesis during the rest of the day which results in a temporal build up of elemental sulfur during the day and disappears at night due to both oxidation to thiosulfate and sulfate by thiobacilli, and reduction to hydrogen sulfide by Desulfuromonas sp. and anaerobically respiring cyanobacteria. Sulfate reduction was enhanced in the light at the surface of the cyanobacterial mats. Microsulfate reduction measurements showed enhanced activity of sulfate reduction even under high oxygen concentrations of 300 to 800 micrometer. Apparent aerobic SO sub 4 reduction activity is explained by the co-occurrence of H sub 2. The physiology of this apparent sulfate reduction activity is studied.

A bio-inspired N-doped porous carbon electrocatalyst with hierarchical superstructure for efficient oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Miao, Yue-E.; Yan, Jiajie; Ouyang, Yue; Lu, Hengyi; Lai, Feili; Wu, Yue; Liu, Tianxi

2018-06-01

The bio-inspired hierarchical "grape cluster" superstructure provides an effective integration of one-dimensional carbon nanofibers (CNF) with isolated carbonaceous nanoparticles into three-dimensional (3D) conductive frameworks for efficient electron and mass transfer. Herein, a 3D N-doped porous carbon electrocatalyst consisting of carbon nanofibers with grape-like N-doped hollow carbon particles (CNF@NC) has been prepared through a simple electrospinning strategy combined with in-situ growth and carbonization processes. Such a bio-inspired hierarchically organized conductive network largely facilitates both the mass diffusion and electron transfer during the oxygen reduction reactions (ORR). Therefore, the metal-free CNF@NC catalyst demonstrates superior catalytic activity with an absolute four-electron transfer mechanism, strong methanol tolerance and good long-term stability towards ORR in alkaline media.

Ni-O4 species anchored on N-doped graphene-based materials as molecular entities and electrocatalytic performances for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Jang, Dawoon; Lee, Seungjun; Shin, Yunseok; Ohn, Saerom; Park, Sunghee; Lim, Donggyu; Park, Gilsoo; Park, Sungjin

2017-12-01

The generation of molecular active species on the surface of nano-materials has become promising routes to produce efficient electrocatalysts. Development of cost-effective catalysts with high performances for oxygen reduction reaction (ORR) is an important challenge for fuel cell and metal-air battery applications. In this work, we report a novel hybrid produced by room-temperature solution processes using Ni-based organometallic molecules and N-doped graphene-based materials. Chemical and structural characterizations reveal that Ni-containing species are well-dispersed on the surface of graphene network as molecular entity. The hybrid shows excellent electrocatalytic performances for ORR in basic medium with an onset potential of 0.87 V (vs. RHE), superior durability and good methanol tolerance.

Numerical model on the material circulation for coastal sediment in Ago Bay, Japan

NASA Astrophysics Data System (ADS)

Anggara Kasih, G. A.; Chiba, Satoshi; Yamagata, Youichi; Shimizu, Yasuhiro; Haraguchi, Koichi

2009-04-01

In this paper, we study the sediment in Ago Bay from the aspects of the biogeochemical cycle and the mass transport by means of a numerical model. We developed the model by adopting the basic idea of Berg et al. (Berg, P., Rysgaard, S., Thamdrup, B., 2003. Dynamic modeling of early diagenesis and nutrient cycling: A case study in Artic marine sediment. Am. J. Sci. 303, 905-955.), Fossing et al. [Fossing, H., Berg, P., Thamdrup, B., Rysgaard, S., Sorensen, H.M., Nielsen, K.A., 2004. Model set-up for an oxygen and nutrient flux for Aarhus Bay (Denmark). National Environmental Research Institute (NERI) Technical Report No. 483. Ministry of the Environment, Denmark, 65 pp.] and Sayama [Sayama, M., 2000. Analytical technique for the nitrogen circulation in the boundary layer of the coastal sediment. Isao Koike edited, Japan Environmental Management Association for Industry, Tokyo, pp. 51-103. (in Japanese)]. In the model, the biogeochemical processes involve five primary reactions and sixteen secondary reactions. The primary reactions describe the degradation of organic matters, and the secondary reactions describe the miscellaneous reactions such as re-oxidation of reduced species formed as a product from primary reactions, and the crystallizing process of oxidized particles. The transports process includes molecular diffusion, advection, bioturbation and bioirrigation. The model performance is verified by comparing the model predicted data to the observed data. The comparison involves data of vertical distribution of material concentrations and the material fluxes at the sediment-water interface. The comparison shows that the model can reproduce the observed vertical profile and the observed material fluxes at the sediment-water interface. The material circulation result shows that about 42% of dissolved organic matter (DOM) is mineralized by sulfate reduction, around 41% by oxygen respiration, and the remaining is mineralized by denitrification, manganese and iron reduction. As a result, about 47% of the O 2 taken by the sediment is directly used through bacterial oxygen respiration and 34% is used through sulfate reduction. The sensitivity study on the impact of flux change of particulate organic matter shows that 30% reduction of deposition OM flux to the sediment suppresses the oxygen consumption in the sediment from 7.3 mmol O 2/m 2 day to 5.1 mmol O 2/m 2 day.

Multi-omic dynamics associate oxygenic photosynthesis with nitrogenase-mediated H 2 production in Cyanothece sp. ATCC 51142

DOE PAGES

Bernstein, Hans C.; Charania, Moiz A.; McClure, Ryan S.; ...

2015-11-03

This study combines transcriptomic and proteomic profiling to provide new insights on the metabolic relationship between oxygenic photosynthesis and nitrogenase-mediated H 2 production in the model cyanobacterium, Cyanothece sp. ATCC 51142. To date, the proposed mechanisms used to describe the energy metabolism processes that support H 2 production in Cyanothece 51142 have assumed that ATP and reductant requirements are derived solely from glycogen oxidation and/or cyclic-electron flow around photosystem I. The results from this study present and test an alternative hypothesis by showing that net-positive rates of oxygenic photosynthesis and increased expression of photosystem II reaction centers correspond and aremore » synchronized with nitrogenase expression and H 2 production. These findings provide a new and more complete view on the metabolic processes contributing to the energy budget of photosynthetic H 2 production and highlight the likely role of photocatalytic H 2O oxidation as a major participating process.« less

Particulate Formation from a Copper Oxide-Based Oxygen ...

EPA Pesticide Factsheets

Attrition behavior and particle loss of a copper oxide-based oxygen carrier from a methane chemical looping combustion (CLC) process was investigated in a fluidized bed reactor. The aerodynamic diameters of most elutriated particulates, after passing through a horizontal settling duct, range between 2 and 5 μm. A notable number of submicron particulates are also identified. Oxygen carrier attrition was observed to lead to increased CuO loss resulting from the chemical looping reactions, i.e., Cu is enriched in small particles generated primarily from fragmentation in the size range of 10-75 μm. Cyclic reduction and oxidation reactions in CLC have been determined to weaken the oxygen carrier particles, resulting in increased particulate emission rates when compared to oxygen carriers without redox reactions. The generation rate for particulates < 10 μm was found to decrease with progressive cycles over as-prepared oxygen carrier particles and then reach a steady state. The surface of the oxygen carrier is also found to be coarsened due to a Kirkendall effect, which also explains the enrichment of Cu on particle surfaces and in small particles. As a result, it is important to collect and reprocess small particles generated from chemical looping processes to reduce oxygen carrier loss. The redox reactions associated with chemical looping combustion play an important role in particle attrition in the fluidized bed. Reaction-induced local stresses, due to the r

Low-temperature solvothermal approach to the synthesis of La4Ni3O8 by topotactic oxygen deintercalation.

PubMed

Blakely, Colin K; Bruno, Shaun R; Poltavets, Viktor V

2011-07-18

A chimie douce solvothermal reduction method is proposed for topotactic oxygen deintercalation of complex metal oxides. Four different reduction techniques were employed to qualitatively identify the relative reduction activity of each including reduction with H(2) and NaH, solution-based reduction using metal hydrides at ambient pressure, and reduction under solvothermal conditions. The reduction of the Ruddlesden-Popper nickelate La(4)Ni(3)O(10) was used as a test case to prove the validity of the method. The completely reduced phase La(4)Ni(3)O(8) was produced via the solvothermal technique at 150 °C--a lower temperature than by other more conventional solid state oxygen deintercalation methods.

PhzA/B catalyzes the formation of the tricycle in phenazine biosynthesis.

USDA-ARS?s Scientific Manuscript database

Phenazines are redox-active bacterial secondary metabolites that participate in important biological processes such as the generation of toxic reactive oxygen species and the reduction of environmental iron. Their biosynthesis from chorismic acid depends on enzymes encoded by the phz operon, but man...

Kinetics of nitrate and sulfate removal using a mixed microbial culture with or without limited-oxygen fed.

PubMed

Xu, Xi-Jun; Chen, Chuan; Wang, Ai-Jie; Guo, Hong-Liang; Yuan, Ye; Lee, Duu-Jong; Ren, Nan-Qi

2014-07-01

The biological degradation of nitrate and sulfate was investigated using a mixed microbial culture and lactate as the carbon source, with or without limited-oxygen fed. It was found that sulfate reduction was slightly inhibited by nitrate, since after nitrate depletion the sulfate reduction rate increased from 0.37 mg SO4 (2-)/mg VSS d to 0.71 mg SO4 (2-)/mg VSS d, and the maximum rate of sulfate reduction in the presence of nitrate corresponded to 56 % of the non-inhibited sulfate reduction rate determined after nitrate depleted. However, simultaneous but not sequential reduction of both oxy-anions was observed in this study, unlike some literature reports in which sulfate reduction starts only after depletion of nitrate, and this case might be due to the fact that lactate was always kept above the limiting conditions. At limited oxygen, the inhibited effect on sulfate reduction by nitrate was relieved, and the sulfate reduction rate seemed relatively higher than that obtained without limited-oxygen fed, whereas kept almost constant (0.86-0.89 mg SO4 (2-)/mg VSS d) cross the six ROS states. In contrast, nitrate reduction rates decreased substantially with the increase in the initial limited-oxygen fed, showing an inhibited effect on nitrate reduction by oxygen. Kinetic parameters determined for the mixed microbial culture showed that the maximum specific sulfate utilization rate obtained (0.098 ± 0.022 mg SO4 (2-)/(mg VSS h)) was similar to the reported typical value (0.1 mg SO4 (2-)/(mg VSS h)), also indicating a moderate inhibited effect by nitrate.

Metal availability and the expanding network of microbial metabolisms in the Archaean eon

NASA Astrophysics Data System (ADS)

Moore, Eli K.; Jelen, Benjamin I.; Giovannelli, Donato; Raanan, Hagai; Falkowski, Paul G.

2017-09-01

Life is based on energy gained by electron-transfer processes; these processes rely on oxidoreductase enzymes, which often contain transition metals in their structures. The availability of different metals and substrates has changed over the course of Earth's history as a result of secular changes in redox conditions, particularly global oxygenation. New metabolic pathways using different transition metals co-evolved alongside changing redox conditions. Sulfur reduction, sulfate reduction, methanogenesis and anoxygenic photosynthesis appeared between about 3.8 and 3.4 billion years ago. The oxidoreductases responsible for these metabolisms incorporated metals that were readily available in Archaean oceans, chiefly iron and iron-sulfur clusters. Oxygenic photosynthesis appeared between 3.2 and 2.5 billion years ago, as did methane oxidation, nitrogen fixation, nitrification and denitrification. These metabolisms rely on an expanded range of transition metals presumably made available by the build-up of molecular oxygen in soil crusts and marine microbial mats. The appropriation of copper in enzymes before the Great Oxidation Event is particularly important, as copper is key to nitrogen and methane cycling and was later incorporated into numerous aerobic metabolisms. We find that the diversity of metals used in oxidoreductases has increased through time, suggesting that surface redox potential and metal incorporation influenced the evolution of metabolism, biological electron transfer and microbial ecology.

Multiscale Transient and Steady-State Study of the Influence of Microstructure Degradation and Chromium Oxide Poisoning on Solid Oxide Fuel Cell Cathode Performance

NASA Astrophysics Data System (ADS)

Li, Guanchen; von Spakovsky, Michael R.; Shen, Fengyu; Lu, Kathy

2018-01-01

Oxygen reduction in a solid oxide fuel cell cathode involves a nonequilibrium process of coupled mass and heat diffusion and electrochemical and chemical reactions. These phenomena occur at multiple temporal and spatial scales, making the modeling, especially in the transient regime, very difficult. Nonetheless, multiscale models are needed to improve the understanding of oxygen reduction and guide cathode design. Of particular importance for long-term operation are microstructure degradation and chromium oxide poisoning both of which degrade cathode performance. Existing methods are phenomenological or empirical in nature and their application limited to the continuum realm with quantum effects not captured. In contrast, steepest-entropy-ascent quantum thermodynamics can be used to model nonequilibrium processes (even those far-from equilibrium) at all scales. The nonequilibrium relaxation is characterized by entropy generation, which can unify coupled phenomena into one framework to model transient and steady behavior. The results reveal the effects on performance of the different timescales of the varied phenomena involved and their coupling. Results are included here for the effects of chromium oxide concentrations on cathode output as is a parametric study of the effects of interconnect-three-phase-boundary length, oxygen mean free path, and adsorption site effectiveness. A qualitative comparison with experimental results is made.

Effects of Synthesis Method on Electrical Properties of Graphene

NASA Astrophysics Data System (ADS)

Fuad, M. F. I. Ahmad; Jarni, H. H.; Shariffudin, W. N.; Othman, N. H.; Rahim, A. N. Che Abdul

2018-05-01

The aim of this study is to achieve the highest reduction capability and complete reductions of oxygen from graphene oxide (GO) by using different type of chemical methods. The modification of Hummer’s method has been proposed to produce GO, and hydrazine hydrate has been utilized in the GO’s reduction process into graphene. There are two types of chemical method are used to synthesize graphene; 1) Sina’s method and 2) Sasha’s method. Both GO and graphene were then characterized using X-Ray Powder Diffraction (XRD) and Fourier Transform Infrared Spectrometry (FT-IR). The graph patterns obtained from XRD showed that the values of graphene and GO are within their reliable ranges, FT-IR identified the comparison functional group between GO and graphene. Graphene was verified to experience the reduction process due to absent of functional group consist of oxygen has detected. Electrochemical impedance spectrometry (EIS) was then conducted to test the ability of conducting electricity of two batches (each weighted 1.6g) of graphene synthesized using different methods (Sina’s method and Sasha’s method). Sasha’s method was proven to have lower conductivity value compare to Sina’s method, with value of 6.2E+02 S/m and 8.1E+02 S/m respectively. These values show that both methods produced good graphene; however, by using Sina’s method, the graphene produced has better electrical properties.

A highly efficient electrocatalyst for oxygen reduction reaction: phosphorus and nitrogen co-doped hierarchically ordered porous carbon derived from an iron-functionalized polymer

NASA Astrophysics Data System (ADS)

Deng, Chengwei; Zhong, Hexiang; Li, Xianfeng; Yao, Lan; Zhang, Huamin

2016-01-01

Heteroatom-doped carbon materials have shown respectable activity for the oxygen reduction reaction (ORR) in alkaline media. However, the performances of these materials are not satisfactory for energy conversion devices, such as fuel cells. Here, we demonstrate a new type of phosphorus and nitrogen co-doped hierarchically ordered porous carbon (PNHOPC) derived from an iron-functionalized mesoporous polymer through an evaporation-induced self-assembly process that simultaneously combines the carbonization and nitrogen doping processes. The soft template and the nitrogen doping process facilitate the formation of the hierarchically ordered structure for the PNHOPC. The catalyst possesses a large surface area (1118 cm2 g-1) and a pore volume of 1.14 cm3 g-1. Notably, it exhibits excellent ORR catalytic performance, superior stability and methanol tolerance in acidic electrolytes, thus making the catalyst promising for fuel cells. The correlations between the unique pore structure and the nitrogen and phosphorus configuration of the catalysts with high catalytic activity are thoroughly investigated.Heteroatom-doped carbon materials have shown respectable activity for the oxygen reduction reaction (ORR) in alkaline media. However, the performances of these materials are not satisfactory for energy conversion devices, such as fuel cells. Here, we demonstrate a new type of phosphorus and nitrogen co-doped hierarchically ordered porous carbon (PNHOPC) derived from an iron-functionalized mesoporous polymer through an evaporation-induced self-assembly process that simultaneously combines the carbonization and nitrogen doping processes. The soft template and the nitrogen doping process facilitate the formation of the hierarchically ordered structure for the PNHOPC. The catalyst possesses a large surface area (1118 cm2 g-1) and a pore volume of 1.14 cm3 g-1. Notably, it exhibits excellent ORR catalytic performance, superior stability and methanol tolerance in acidic electrolytes, thus making the catalyst promising for fuel cells. The correlations between the unique pore structure and the nitrogen and phosphorus configuration of the catalysts with high catalytic activity are thoroughly investigated. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06749a

Multi-Omic Dynamics Associate Oxygenic Photosynthesis with Nitrogenase-Mediated H2 Production in Cyanothece sp. ATCC 51142.

PubMed

Bernstein, Hans C; Charania, Moiz A; McClure, Ryan S; Sadler, Natalie C; Melnicki, Matthew R; Hill, Eric A; Markillie, Lye Meng; Nicora, Carrie D; Wright, Aaron T; Romine, Margaret F; Beliaev, Alexander S

2015-11-03

To date, the proposed mechanisms of nitrogenase-driven photosynthetic H2 production by the diazotrophic unicellular cyanobacterium Cyanothece sp. ATCC 51142 have assumed that reductant and ATP requirements are derived solely from glycogen oxidation and cyclic-electron flow around photosystem I. Through genome-scale transcript and protein profiling, this study presents and tests a new hypothesis on the metabolic relationship between oxygenic photosynthesis and nitrogenase-mediated H2 production in Cyanothece 51142. Our results show that net-positive rates of oxygenic photosynthesis and increased expression of photosystem II reaction centers correspond and are synchronized with nitrogenase expression and H2 production. These findings provide a new and more complete view on the metabolic processes contributing to the energy budget of photosynthetic H2 production and highlight the role of concurrent photocatalytic H2O oxidation as a participating process.

A solution-processed quaternary oxide system obtained at low-temperature using a vertical diffusion technique

PubMed Central

Yoon, Seokhyun; Kim, Si Joon; Tak, Young Jun; Kim, Hyun Jae

2017-01-01

We report a method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) at low annealing temperatures using a vertical diffusion technique (VDT). The VDT is a deposition process for spin-coating binary and ternary oxide layers consecutively and annealing at once. With the VDT, uniform and dense quaternary oxide layers were fabricated at lower temperatures (280 °C). Compared to conventional IGZO and ternary In-Zn-O (IZO) thin films, VDT IGZO thin film had higher density of the metal-oxide bonds and lower density of the oxygen vacancies. The field-effect mobility of VDT IGZO TFT increased three times with an improved stability under positive bias stress than IZO TFT due to the reduction in oxygen vacancies. Therefore, the VDT process is a simple method that reduces the processing temperature without any additional treatment for quaternary oxide semiconductors with uniform layers. PMID:28230088

A solution-processed quaternary oxide system obtained at low-temperature using a vertical diffusion technique

NASA Astrophysics Data System (ADS)

Yoon, Seokhyun; Kim, Si Joon; Tak, Young Jun; Kim, Hyun Jae

2017-02-01

We report a method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) at low annealing temperatures using a vertical diffusion technique (VDT). The VDT is a deposition process for spin-coating binary and ternary oxide layers consecutively and annealing at once. With the VDT, uniform and dense quaternary oxide layers were fabricated at lower temperatures (280 °C). Compared to conventional IGZO and ternary In-Zn-O (IZO) thin films, VDT IGZO thin film had higher density of the metal-oxide bonds and lower density of the oxygen vacancies. The field-effect mobility of VDT IGZO TFT increased three times with an improved stability under positive bias stress than IZO TFT due to the reduction in oxygen vacancies. Therefore, the VDT process is a simple method that reduces the processing temperature without any additional treatment for quaternary oxide semiconductors with uniform layers.

Element Distribution in the Oxygen-Rich Side-Blow Bath Smelting of a Low-Grade Bismuth-Lead Concentrate

NASA Astrophysics Data System (ADS)

Yang, Tianzu; Xiao, Hui; Chen, Lin; Chen, Wei; Liu, Weifeng; Zhang, Duchao

2018-03-01

Oxygen-rich side-blow bath smelting (OSBS) technology offers an efficient method for processing complex bismuth-lead concentrates; however, the element distributions in the process remain unclear. This work determined the distributions of elements, i.e., bismuth, lead, silver, copper, arsenic and antimony, in an industrial-scale OSBS process. The feed, oxidized slag and final products were collected from the respective sampling points and analyzed. For the oxidative smelting process, 65% of bismuth and 76% of silver in the concentrate report to the metal alloy, whereas less lead reports to the metal ( 31%) than the oxidized slag ( 44%). Approximately 50% of copper enters the matte, while more than 63% of arsenic and antimony report to the slag. For the reductive smelting process, less than 4.5% of bismuth, lead, silver and copper in the oxidized slag enter the reduced slag, indicating high recoveries of these metal values.

A solution-processed quaternary oxide system obtained at low-temperature using a vertical diffusion technique.

PubMed

Yoon, Seokhyun; Kim, Si Joon; Tak, Young Jun; Kim, Hyun Jae

2017-02-23

We report a method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) at low annealing temperatures using a vertical diffusion technique (VDT). The VDT is a deposition process for spin-coating binary and ternary oxide layers consecutively and annealing at once. With the VDT, uniform and dense quaternary oxide layers were fabricated at lower temperatures (280 °C). Compared to conventional IGZO and ternary In-Zn-O (IZO) thin films, VDT IGZO thin film had higher density of the metal-oxide bonds and lower density of the oxygen vacancies. The field-effect mobility of VDT IGZO TFT increased three times with an improved stability under positive bias stress than IZO TFT due to the reduction in oxygen vacancies. Therefore, the VDT process is a simple method that reduces the processing temperature without any additional treatment for quaternary oxide semiconductors with uniform layers.

Element Distribution in the Oxygen-Rich Side-Blow Bath Smelting of a Low-Grade Bismuth-Lead Concentrate

NASA Astrophysics Data System (ADS)

Yang, Tianzu; Xiao, Hui; Chen, Lin; Chen, Wei; Liu, Weifeng; Zhang, Duchao

2018-06-01

Oxygen-rich side-blow bath smelting (OSBS) technology offers an efficient method for processing complex bismuth-lead concentrates; however, the element distributions in the process remain unclear. This work determined the distributions of elements, i.e., bismuth, lead, silver, copper, arsenic and antimony, in an industrial-scale OSBS process. The feed, oxidized slag and final products were collected from the respective sampling points and analyzed. For the oxidative smelting process, 65% of bismuth and 76% of silver in the concentrate report to the metal alloy, whereas less lead reports to the metal ( 31%) than the oxidized slag ( 44%). Approximately 50% of copper enters the matte, while more than 63% of arsenic and antimony report to the slag. For the reductive smelting process, less than 4.5% of bismuth, lead, silver and copper in the oxidized slag enter the reduced slag, indicating high recoveries of these metal values.

Reduction of ferredoxin or oxygen by flavin-based electron bifurcation in Megasphaera elsdenii.

PubMed

Chowdhury, Nilanjan P; Kahnt, Jörg; Buckel, Wolfgang

2015-08-01

Over 50 years ago, it was reported that, in the anaerobic rumen bacterium Megasphaera elsdenii, the reduction of crotonyl-CoA to butyryl-CoA by NADH involved an electron transferring flavoprotein (Etf) as mediator [Baldwin RL, Milligan LP (1964) Biochim Biophys Acta 92, 421-432]. Purification and spectroscopic characterization revealed that this Etf contained 2 FAD, whereas, in the Etfs from aerobic and facultative bacteria, one FAD is replaced by AMP. Recently we detected a similar system in the related anaerobe Acidaminococcus fermentans that differed in the requirement of additional ferredoxin as electron acceptor. The whole process was established as flavin-based electron bifurcation in which the exergonic reduction of crotonyl-CoA by NADH mediated by Etf + butyryl-CoA dehydrogenase (Bcd) was coupled to the endergonic reduction of ferredoxin also by NADH. In the present study, we demonstrate that, under anaerobic conditions, Etf + Bcd from M. elsdenii bifurcate as efficiently as Etf + Bcd from A. fermentans. Under the aerobic conditions used in the study by Baldwin and Milligan and in the presence of catalytic amounts of crotonyl-CoA or butyryl-CoA, however, Etf + Bcd act as NADH oxidase producing superoxide and H2 O2 , whereas ferredoxin is not required. We hypothesize that, during bifurcation, oxygen replaces ferredoxin to yield superoxide. In addition, the formed butyryl-CoA is re-oxidized by a second oxygen molecule to crotonyl-CoA, resulting in a stoichiometry of 2 NADH consumed and 2 H2 O2 formed. As a result of the production of reactive oxygen species, electron bifurcation can be regarded as an Achilles' heel of anaerobes when exposed to air. © 2015 FEBS.

Effect of elicitation on growth, respiration, and nutrient uptake of root and cell suspension cultures of Hyoscyamus muticus.

PubMed

Carvalho, Edgard B; Curtis, Wayne R

2002-01-01

The elicitation of Hyoscyamus muticus root and cell suspension cultures by fungal elicitor from Rhizoctonia solani causes dramatic changes in respiration, nutrient yields, and growth. Cells and mature root tissues have similar specific oxygen uptake rates (SOUR) before and after the onset of the elicitation process. Cell suspension SOUR were 11 and 18 micromol O2/g FW x h for non-elicited control and elicited cultures, respectively. Mature root SOUR were 11 and 24 micromol O2/g FW x h for control and elicited tissue, respectively. Tissue growth is significantly reduced upon the addition of elicitor to these cultures. Inorganic yield remains fairly constant, whereas yield on sugar is reduced from 0.532 to 0.352 g dry biomass per g sugar for roots and 0.614 to 0.440 g dry biomass per g sugar for cells. This reduction in yield results from increased energy requirements for the defense response. Growth reduction is reflected in a reduction in root meristem (tip) SOUR, which decreased from 189 to 70 micromol O2/g FW x h upon elicitation. Therefore, despite the increase in total respiration, the maximum local oxygen fluxes are reduced as a result of the reduction in metabolic activity at the meristem. This distribution of oxygen uptake throughout the mature tissue could reduce mass transfer requirements during elicited production. However, this was not found to be the case for sesquiterpene elicitation, where production of lubimin and solavetivone were found to increase linearly up to oxygen partial pressures of 40% O2 in air. SOUR is shown to similarly increase in both bubble column and tubular reactors despite severe mass transfer limitations, suggesting the possibility of metabolically induced increases in tissue convective transport during elicitation.

Cost analysis of oxygen recovery systems

NASA Technical Reports Server (NTRS)

Yakut, M. M.

1973-01-01

Report is made of the cost analysis of four leading oxygen recovery subsystems which include two carbon dioxide reduction subsystems and two water electrolysis subsystems, namely, the solid polymer electrolyte and the circulating KOH electrolyte. The four oxygen recovery systems were quantitatively evaluated. System characteristics, including process flows, performance, and physical characteristics were also analyzed. Additionally, the status of development of each of the systems considered and the required advance technology efforts required to bring conceptual and/or pre-prototype hardware to an operational prototype status were defined. Intimate knowledge of the operations, development status, and capabilities of the systems to meet space mission requirements were found to be essential in establishing the cost estimating relationships for advanced life support systems.

Salinity Responses of Benthic Microbial Communities in a Solar Saltern (Eilat, Israel)

PubMed Central

Sørensen, Ketil Bernt; Canfield, Donald E.; Oren, Aharon

2004-01-01

The salinity responses of cyanobacteria, anoxygenic phototrophs, sulfate reducers, and methanogens from the laminated endoevaporitic community in the solar salterns of Eilat, Israel, were studied in situ with oxygen microelectrodes and in the laboratory in slurries. The optimum salinity for the sulfate reduction rate in sediment slurries was between 100 and 120‰, and sulfate reduction was strongly inhibited at an in situ salinity of 215‰. Nevertheless, sulfate reduction was an important respiratory process in the crust, and reoxidation of formed sulfide accounted for a major part of the oxygen budget. Methanogens were well adapted to the in situ salinity but contributed little to the anaerobic mineralization in the crust. In slurries with a salinity of 180‰ or less, methanogens were inhibited by increased activity of sulfate-reducing bacteria. Unicellular and filamentous cyanobacteria metabolized at near-optimum rates at the in situ salinity, whereas the optimum salinity for anoxygenic phototrophs was between 100 and 120‰. PMID:15006785

Microbial Fuel Cell Performance with a Pressurized Cathode Chamber

USDA-ARS?s Scientific Manuscript database

Microbial fuel cell (MFC) power densities are often constrained by the oxygen reduction reaction rate on the cathode electrode. One important factor for this is the normally low solubility of oxygen in the aqueous cathode solution creating mass transport limitations, which hinder oxygen reduction a...

Influence of Oxygen Deficiency on the Rectifying Behavior of Transparent-Semiconducting-Oxide-Metal Interfaces

NASA Astrophysics Data System (ADS)

Schultz, Thorsten; Vogt, Sofie; Schlupp, Peter; von Wenckstern, Holger; Koch, Norbert; Grundmann, Marius

2018-06-01

Transparent semiconducting oxides (TSO) are promising candidates for the fabrication of flexible and low-cost electronic devices, as they contain only abundant materials, are nontoxic, and exhibit high carrier mobilities. The formation of rectifying Schottky-barrier contacts is a prerequisite for devices, such as rectifiers, photodetectors, and metal-semiconductor field-effect transistors, and it was found that the presence of oxygen plays an essential role during the formation of the Schottky contacts. With electrical measurements on Pt/zinc-tin-oxide (ZTO) and PtOx/ZTO Schottky-barrier contacts and depth-resolved x-ray photoelectron spectroscopy measurements we demonstrate the important role of oxygen at the interface between TSOs and the metal contact for the rectifying behavior of diodes. In the vicinity of the interface, PtOx is reduced to Pt in a two-step process. Pt (OH) 4 is reduced within one day, whereas the reduction of PtO takes place over a time period of several weeks. The reduction results in improved rectification compared to Pt /ZTO , due to a filling of oxygen vacancies, which leads to a reduction of the free-carrier concentration in the vicinity of the PtOx/ZTO interface. This increases the depletion layer width and subsequently reduces the tunneling current, resulting in a higher rectification ratio. The time scale of the permanent performance improvement can be shortened significantly by applying a reverse bias to the diode. The described mechanism is most likely also present at other transparent-semiconducting-oxide-metal interfaces.

Development and optimization of dark Fenton oxidation for the treatment of textile wastewaters with high organic load.

PubMed

Papadopoulos, A E; Fatta, D; Loizidou, M

2007-07-31

The examination of the effectiveness of the chemical oxidation using Fenton's reagent (H(2)O(2)/Fe(2+)) for the reduction of the organic content of wastewater generated from a textile industry has been studied. The experimental results indicate that the oxidation process leads to a reduction in the chemical oxygen demand (COD) concentration up to 45%. Moreover, the reduction is reasonably fast at the first stages of the process, since the COD concentration is decreased up to 45% within four hours and further treatment time does not add up to the overall decrease in the COD concentration (48% reduction within six hours). The maximum color removal achieved was 71.5%. In addition, the alterations observed in the organic matter during the development of the process, as indicated by the ratios of COD/TOC and BOD/COD and the oxidation state, show that a great part of the organic substances, which are not completely mineralized, are subjected to structural changes to intermediate organic by-products.

Cryogenic reactant storage for lunar base regenerative fuel cells

NASA Technical Reports Server (NTRS)

Kohout, Lisa L.

1989-01-01

There are major advantages to be gained by integrating a cryogenic reactant storage system with a hydrogen-oxygen regenerative fuel cell (RFC) to provide on-site electrical power during the lunar night. Although applicable to any power system using hydrogen-oxygen RFC's for energy storage, cryogenic reactant storage offers a significant benefit whenever the sun/shade cycle and energy storage period approach hundreds of hours. For solar power installations on the moon, cryogenic reactant storage reduces overall specific mass and meteoroid vulnerability of the system. In addition, it offers synergistic benefits to on-site users, such as availability of primary fuel cell reactants for surface rover vehicles and cryogenic propellants for OTV's. The integration involves processing and storing the RFC reactant streams as cryogenic liquids rather than pressurized gases, so that reactant containment (tankage per unit mass of reactants) can be greatly reduced. Hydrogen-oxygen alkaline RFC's, GaAs photovoltaic (PV) arrays, and space cryogenic processing/refrigeration technologies are assumed to be available for the conceptual system design. Advantages are demonstrated by comparing the characteristics of two power system concepts: a conventional lunar surface PV/RFC power system using pressurized gas storage in SOA filament wound pressure vessels and, that same system with gas liquefaction and storage replacing the pressurized storage. Comparisons are made at 20 and 250 kWe. Although cryogenic storage adds a processing plant (drying and liquefaction) to the system plus 30 percent more solar array to provide processing power, the approximate order of magnitude reduction in tankage mass, confirmed by this analysis, results in a reduction in overall total system mass of approximately 50 percent.

Molten salt applications in materials processing

NASA Astrophysics Data System (ADS)

Mishra, Brajendra; Olson, David L.

2005-02-01

The science of molten salt electrochemistry for electrowinning of reactive metals, such as calcium, and its in situ application in pyro-reduction has been described. Calcium electrowinning has been performed in a 5 10 wt% calcium oxide calcium chloride molten salt by the electrolytic dissociation of calcium oxide. This electrolysis requires the use of a porous ceramic sheath around the anode to keep the cathodically deposited calcium and the anodic gases separate. Stainless steel cathode and graphite anode have been used in the temperature range of 850 950 °C. This salt mixture is produced as a result of the direct oxide reduction (DOR) of reactive metal oxides by calcium in a calcium chloride bath. The primary purpose of this process is to recover the expensive calcium reductant and to recycle calcium chloride. Experimental data have been included to justify the suitability as well as limitations of the electrowinning process. Transport of oxygen ions through the sheath is found to be the rate controlling step. Under the constraints of the reactor design, a calcium recovery rate of approx. 150 g/h was achieved. Feasibility of a process to produce metals by pyrometallurgical reduction, using the calcium reductant produced electrolytically within the same reactor, has been shown in a hybrid process. Several processes are currently under investigation to use this electrowon calcium for in situ reduction of metal oxides.

Electrocatalysis of fuel cell reactions: Investigation of alternate electrolytes

NASA Technical Reports Server (NTRS)

Chin, D. T.; Hsueh, K. L.; Chang, H. H.

1983-01-01

Oxygen reduction and transport properties of the electrolyte in the phosphoric acid fuel cell are studied. A theoretical expression for the rotating ring-disk electrode technique; the intermediate reaction rate constants for oxygen reduction on platinum in phosphoric acid electrolyte; oxygen reduction mechanism in trifluoromethanesulfonic acid (TFMSA), considered as an alternate electrolyte for the acid fuel cells; and transport properties of the phosphoric acid electrolyte at high concentrations and temperatures are covered.

Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier

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

Xiao, Rui; Song, Min; Zhang, Shuai

2010-06-15

Chemical-looping combustion (CLC) is a new combustion technology with inherent separation of CO{sub 2}. Most of the previous investigations on CLC of solid fuels were conducted under atmospheric pressure. A pressurized CLC combined cycle (PCLC-CC) system is proposed as a promising coal combustion technology with potential higher system efficiency, higher fuel conversion, and lower cost for CO{sub 2} sequestration. In this study pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor. CVRD iron ore particles were exposed alternately to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasifiedmore » with 87.2% steam/N{sub 2} mixture and oxidation with 5% O{sub 2} in N{sub 2} at 970 C. The operating pressure was varied between 0.1 MPa and 0.6 MPa. First, control experiments of steam coal gasification over quartz sand were performed. H{sub 2} and CO{sub 2} are the major components of the gasification products, and the operating pressure influences the gas composition. Higher concentrations of CO{sub 2} and lower fractions of CO, CH{sub 4}, and H{sub 2} during the reduction process with CVRD iron ore was achieved under higher pressures. The effects of pressure on the coal gasification rate in the presence of the oxygen carrier were different for pyrolysis and char gasification. The pressurized condition suppresses the initial coal pyrolysis process while it also enhances coal char gasification and reduction with iron ore in steam, and thus improves the overall reaction rate of CLC. The oxidation rates and variation of oxygen carrier conversion are higher at elevated pressures reflecting higher reduction level in the previous reduction period. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analyses show that particles become porous after experiments but maintain structure and size after several cycles. Agglomeration was not observed in this study. An EDX analysis demonstrates that there is very little coal ash deposited on the oxygen carrier particles but no appreciable crystalline phases change as verified by X-ray diffraction (XRD) analysis. Overall, the limited pressurized CLC experiments carried out in the present work suggest that PCLC of coal is promising and further investigations are necessary. (author)« less

Greater heritability of photosynthesis in maize grown under elevated ozone

USDA-ARS?s Scientific Manuscript database

Tropospheric ozone (O3) pollution is estimated to reduce maize yields up to 10% in the US. O3 causes damage to cellular processes by forming reactive oxygen species that lead to reductions in photosynthetic capacity, accelerated leaf senescence, and ultimately a decrease in reproductive and economic...

Synthesis of Hierarchical Nanoporous Microstructures via the Kirkendall Effect in Chemical Reduction Process

NASA Astrophysics Data System (ADS)

Gao, Ling; Pang, Chao; He, Dafang; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

2015-11-01

A series of novel hierarchical nanoporous microstructures have been synthesized through one-step chemical reduction of micron size Cu2O and Co3O4 particles. By controlling the reduction time, non-porous Cu2O microcubes sequentially transform to nanoporous Cu/Cu2O/Cu dented cubic composites and hollow eightling-like Cu microparticles. The mechanism involved in the complex structural evolution is explained based on oxygen diffusion and Kirkendall effect. The nanoporous Cu/Cu2O/Cu dented cubic composites exhibit superior electrochemical performance as compared to solid Cu2O microcubes. The reduction of nonporous Co3O4 also exhibits a uniform sequential reduction process from nonporous Co3O4 to porous Co3O4/CoO composites, porous CoO, porous CoO/Co composites, and porous foam-like Co particles. Nanoscale channels originate from the particle surface and eventually develop inside the entire product, resulting in porous foam-like Co microparticles. The Kirkendall effect is believed to facilitate the formation of porous structures in both processes.

Trace detection of oxygen--ionic liquids in gas sensor design.

PubMed

Baltes, N; Beyle, F; Freiner, S; Geier, F; Joos, M; Pinkwart, K; Rabenecker, P

2013-11-15

This paper presents a novel electrochemical membrane sensor on basis of ionic liquids for trace analysis of oxygen in gaseous atmospheres. The faradaic response currents for the reduction of oxygen which were obtained by multiple-potential-step-chronoamperometry could be used for real time detection of oxygen down to concentrations of 30 ppm. The theoretical limit of detection was 5 ppm. The simple, non-expensive sensors varied in electrolyte composition and demonstrated a high sensitivity, a rapid response time and an excellent reproducibility at room temperature. Some of them were continuously used for at least one week and first results promise good long term stability. Voltammetric, impedance and oxygen detection studies at temperatures up to 200 °C (in the presence and absence of humidity and CO2) revealed also the limitations of certain ionic liquids for some electrochemical high temperature applications. Application areas of the developed sensors are control and analysis processes of non oxidative and oxygen free atmospheres. Copyright © 2013 Elsevier B.V. All rights reserved.

Reduction of the Powerful Greenhouse Gas N2O in the South-Eastern Indian Ocean.

PubMed

Raes, Eric J; Bodrossy, Levente; Van de Kamp, Jodie; Holmes, Bronwyn; Hardman-Mountford, Nick; Thompson, Peter A; McInnes, Allison S; Waite, Anya M

2016-01-01

Nitrous oxide (N2O) is a powerful greenhouse gas and a key catalyst of stratospheric ozone depletion. Yet, little data exist about the sink and source terms of the production and reduction of N2O outside the well-known oxygen minimum zones (OMZ). Here we show the presence of functional marker genes for the reduction of N2O in the last step of the denitrification process (nitrous oxide reductase genes; nosZ) in oxygenated surface waters (180-250 O2 μmol.kg(-1)) in the south-eastern Indian Ocean. Overall copy numbers indicated that nosZ genes represented a significant proportion of the microbial community, which is unexpected in these oxygenated waters. Our data show strong temperature sensitivity for nosZ genes and reaction rates along a vast latitudinal gradient (32°S-12°S). These data suggest a large N2O sink in the warmer Tropical waters of the south-eastern Indian Ocean. Clone sequencing from PCR products revealed that most denitrification genes belonged to Rhodobacteraceae. Our work highlights the need to investigate the feedback and tight linkages between nitrification and denitrification (both sources of N2O, but the latter also a source of bioavailable N losses) in the understudied yet strategic Indian Ocean and other oligotrophic systems.

Hydrogen Peroxide as a Sustainable Energy Carrier: Electrocatalytic Production of Hydrogen Peroxide and the Fuel Cell.

PubMed

Fukuzumi, Shunichi; Yamada, Yusuke; Karlin, Kenneth D

2012-11-01

This review describes homogeneous and heterogeneous catalytic reduction of dioxygen with metal complexes focusing on the catalytic two-electron reduction of dioxygen to produce hydrogen peroxide. Whether two-electron reduction of dioxygen to produce hydrogen peroxide or four-electron O 2 -reduction to produce water occurs depends on the types of metals and ligands that are utilized. Those factors controlling the two processes are discussed in terms of metal-oxygen intermediates involved in the catalysis. Metal complexes acting as catalysts for selective two-electron reduction of oxygen can be utilized as metal complex-modified electrodes in the electrocatalytic reduction to produce hydrogen peroxide. Hydrogen peroxide thus produced can be used as a fuel in a hydrogen peroxide fuel cell. A hydrogen peroxide fuel cell can be operated with a one-compartment structure without a membrane, which is certainly more promising for the development of low-cost fuel cells as compared with two compartment hydrogen fuel cells that require membranes. Hydrogen peroxide is regarded as an environmentally benign energy carrier because it can be produced by the electrocatalytic two-electron reduction of O 2 , which is abundant in air, using solar cells; the hydrogen peroxide thus produced could then be readily stored and then used as needed to generate electricity through the use of hydrogen peroxide fuel cells.

Electronic states of carbon alloy catalysts and nitrogen substituent effects on catalytic activity

NASA Astrophysics Data System (ADS)

Hata, Tomoyuki; Ushiyama, Hiroshi; Yamashita, Koichi

2013-03-01

In recent years, Carbon Alloy Catalysts (CACs) are attracting attention as a candidate for non-platinum-based cathode catalysts in fuel cells. Oxygen reduction reactions at the cathode are divided into two elementary processes, electron transfer and oxygen adsorption. The electron transfer reaction is the rate-determining, and by comparison of energy levels, catalytic activity can be evaluated quantitatively. On the other hand, to begin with, adsorption mechanism is obscure. The purpose of this study is to understand the effect of nitrogen substitution and oxygen adsorption mechanism, by first-principle electronic structure calculations for nitrogen substituted models. To reproduce the elementary processes of oxygen adsorption, we assumed that the initial structures are formed based on the Pauling model, a CACs model and nitrogen substituted CACs models in which various points are replaced with nitrogen. When we try to focus only on the DOS peaks of oxygen, in some substituted model that has high adsorption activity, a characteristic partial occupancy state was found. We conclude that this state will affect the adsorption activity, and discuss on why partially occupied states appear with simplification by using an orbital correlation diagram.

A novel approach to the assess biotic oxygen consumption in marine sediment communities

NASA Astrophysics Data System (ADS)

Baranov, Victor; Queiros, Ana; Widdicombe, Stephen; Stephens, Nick; Lessin, Gennadi; Krause, Stefan; Lewandowski, Joerg

2016-04-01

Bioturbation , the mixing of the sediment matrix by burrowing animals impacts sediment metabolism, including respiration through redistribution of particulate organics, changes in bacterial biota diversity and acitivity, as well as via burrowing fauna's own metabolism. Bioturbation, reflecting faunal activity, is also a proxy for the general sedimentary ecosystem health, and can be impacted by many of emerging marine environmental issues such as ocean acidification, warming and the occurrence of heat waves. Sedimentary oxygen consumption is often taken as a proxy for the activity of bioturbating fauna, but determining baselines can be difficult because of the confounding effects of other fauna and microbes present in sediments, as well as irnorganic processes that consume oxygen. Limitations therefore exist in current methodologies, and numerous confounding factors are hampering progress in this area. Here, we present novel method for the assessment of sediment respiration which is expected to be affected only by the biogenic oxygen consumption (namely aerobic respiration). As long as tracer reduction "immune" to inorganic oxygen consumption, so that measurements using this method can be used, alongside traditional methods, to decouple biological respiration from inorganic oxygen consumption reactions. The tracer is easily detectable, non-toxic and can be applied in systems with constant oxygen supply. The latter allow for incubation without the need to to work with unsealed experimental units, bringing procedural advantage over traditional methods. Consequently assessed bioturbating fauna is not exposed to hypoxia and additional stress. Here, we had applied system for the first time to investigate impacts of a common North-Atlantic bioturbator, the brittle star Amphiura filiformis, - on respiration of marine sediments. Two series of experiments were conducted with animals and sediment collected from Cawsand Bay, Plymouth, UK Preliminary results show that tracer reduction was about 30% higher in bioturbated sediment than in defaunated controls, and the correlation between tracer reduction and oxygen consumption was high (r=0.92). This study allowed us to calculate the actual amount of oxygen consumed by organisms in the tanks excluding inorganic oxygen consumption, and access the effects of bioturbation on respiration of the marine muds. We believe that this tracer system can be successfully used for respiration assessment in the marine environment and to improve the assessment of respiration in burrowing infauna.

Benthic metabolism and nitrogen dynamics in an urbanised tidal creek: Domination of DNRA over denitrification as a nitrate reduction pathway

NASA Astrophysics Data System (ADS)

Dunn, Ryan J. K.; Robertson, David; Teasdale, Peter R.; Waltham, Nathan J.; Welsh, David T.

2013-10-01

Benthic oxygen and nutrient fluxes and nitrate reduction rates were determined seasonally under light and dark conditions at three sites in a micro-tidal creek within an urbanised catchment (Saltwater Creek, Australia). It was hypothesized that stormwater inputs of organic matter and inorganic nitrogen would stimulate rates of benthic metabolism and nutrient recycling and preferentially stimulate dissimilatory nitrate reduction to ammonium (DNRA) over denitrification as a pathway for nitrate reduction. Stormwaters greatly influenced water column dissolved inorganic nitrogen (DIN) and suspended solids concentrations with values following a large rainfall event being 5-20-fold greater than during the preceding dry period. Seasonally, maximum and minimum water column total dissolved nitrogen (TDN) and DIN concentrations occurred in the summer (wet) and winter (dry) seasons. Creek sediments were highly heterotrophic throughout the year, and strong sinks for oxygen, and large sources of dissolved organic and inorganic nitrogen during both light and dark incubations, although micro-phytobenthos (MPB) significantly decreased oxygen consumption and N-effluxes during light incubations due to photosynthetic oxygen production and photoassimilation of nutrients. Benthic denitrification rates ranged from 3.5 to 17.7 μmol N m2 h-1, denitrification efficiencies were low (<1-15%) and denitrification was a minor process compared to DNRA, which accounted for ˜75% of total nitrate reduction. Overall, due to the low denitrification efficiencies and high rates of N-regeneration, Saltwater Creek sediments would tend to increase rather than reduce dissolved nutrient loads to the downstream Gold Coast Broadwater and Moreton Bay systems. This may be especially true during wet periods when increased inputs of particulate organic nitrogen (PON) and suspended solids could respectively enhance rates of N-regeneration and decrease light availability to MPB, reducing their capacity to ameliorate N-effluxes through photoassimilation.

Effective utilization of ozone in plasma-based advanced oxidation process

NASA Astrophysics Data System (ADS)

Takeuchi, Nozomi; Ishibashi, Naoto; Sugiyama, Tsuyoshi; Kim, Hyun-Ha

2018-05-01

Decomposition of acetic acid in water was conducted using multiple plasmas generated within oxygen bubbles. Ballast capacitors were used to control the plasma input power, allowing hydrogen peroxide and ozone to be produced at different rates in each plasma by adjusting the capacitance. By using an ozone absorber connected to the plasma reactor, OH radicals, both generated by the plasmas directly and reproduced from hydrogen peroxide through reactions with ozone, could be effectively utilized for the reduction of total organic carbon (TOC). Under the condition with the highest ozone production rate, higher processing speed and energy efficiency for the TOC reduction were achieved compared with other plasma methods.

Reverse electron transport effects on NADH formation and metmyoglobin reduction.

PubMed

Belskie, K M; Van Buiten, C B; Ramanathan, R; Mancini, R A

2015-07-01

The objective was to determine if NADH generated via reverse electron flow in beef mitochondria can be used for electron transport-mediated reduction and metmyoglobin reductase pathways. Beef mitochondria were isolated from bovine hearts (n=5) and reacted with combinations of succinate, NAD, and mitochondrial inhibitors to measure oxygen consumption and NADH formation. Mitochondria and metmyoglobin were reacted with succinate, NAD, and mitochondrial inhibitors to measure electron transport-mediated metmyoglobin reduction and metmyoglobin reductase activity. Addition of succinate and NAD increased oxygen consumption, NADH formation, electron transport-mediated metmyoglobin reduction, and reductase activity (p<0.05). Addition of antimycin A prevented electron flow beyond complex III, therefore, decreasing oxygen consumption and electron transport-mediated metmyoglobin reduction. Addition of rotenone prevented reverse electron flow, increased oxygen consumption, increased electron transport-mediated metmyoglobin reduction, and decreased NADH formation. Succinate and NAD can generate NADH in bovine tissue postmortem via reverse electron flow and this NADH can be used by both electron transport-mediated and metmyoglobin reductase pathways. Copyright © 2015 Elsevier Ltd. All rights reserved.

Bacterial transformations of inorganic nitrogen in the oxygen-deficient waters of the Eastern Tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Lipschultz, F.; Wofsy, S. C.; Ward, B. B.; Codispoti, L. A.; Friedrich, G.; Elkins, J. W.

1990-10-01

Rates of transformations of inorganic nitrogen were measured in the low oxygen, subsurface waters (50-450 m) of the Eastern Tropical South Pacific during February 1985, using 15N tracer techniques. Oxygen concentrations over the entire region were in a range (O 2 < 2.5 μM) that allowed both oxidation and reduction of nitrogen to occur. A wide range of rates was observed for the lowest oxygen levels, indicating that observed oxygen concentration was not a primary factor regulating nitrogen metabolism. High values for subsurface metabolic rates correspond with high levels for surface primary production, both apparently associated with mesoscale features observed in satellite imagery and with mesoscale features of the current field. Measured rates of nitrate reduction and estimated rates of denitrification were sufficient to respire nearly all of the surface primary production that might be transported into the oxygen deficient zone. These results imply that the supply of labile organic material, especially from the surface, was more important than oxygen concentration in modulating the rates of nitrogen transformations within the low oxygen water mass of the Eastern Tropical South Pacific. The pattern of nitrite oxidation and nitrite reduction activities in the oxygen minimum zone supports the hypothesis ( ANDERSONet al., 1982, Deep-Sea Research, 29, 1113-1140) that nitrite, produced from nitrate reduction, can be recycled by oxidation at the interface between low and high oxygen waters. Rates for denitrification, estimated from nitrate reduction rates, were in harmony with previous estimates based on electron transport system (ETS) measurements and analysis of the nitrate deficit and water residence times. Assimilation rates of NH 4+ were substantial, providing evidence for heterotrophic bacterial growth in low oxygen waters. Ambient concentrations of ammonium were maintained at low values primarily by assimilation; ammonium oxidation was an important mechanism at the surface boundary of the low oxygen zone.

Physical principle of airway design in human lungs

NASA Astrophysics Data System (ADS)

Park, Keunhwan; Son, Taeho; Kim, Wonjung; Kim, Ho-Young

2014-11-01

From an engineering perspective, lungs are natural microfluidic devices that extract oxygen from air. In the bronchial tree, airways branch by dichotomy with a systematic reduction of their diameters. It is generally accepted that in conducting airways, which air passes on the way to the acinar airways from the atmosphere, the reduction ratio of diameter is closely related to the minimization of viscous dissipation. Such a principle is formulated as the Hess-Murray law. However, in acinar airways, where oxygen transfer to alveolae occurs, the diameter reduction with progressive generations is more moderate than in conducting airways. Noting that the dominant transfer mechanism in acinar airways is diffusion rather than advection, unlike conducting airways, we construct a mathematical model for oxygen transfer through a series of acinar airways. Our model allows us to predict the optimal airway reduction ratio that maximizes the oxygen transfer in a finite airway volume, thereby rationalizing the observed airway reduction ratio in acinar airways.

Two component-three dimensional catalysis

DOEpatents

Schwartz, Michael; White, James H.; Sammells, Anthony F.

2002-01-01

This invention relates to catalytic reactor membranes having a gas-impermeable membrane for transport of oxygen anions. The membrane has an oxidation surface and a reduction surface. The membrane is coated on its oxidation surface with an adherent catalyst layer and is optionally coated on its reduction surface with a catalyst that promotes reduction of an oxygen-containing species (e.g., O.sub.2, NO.sub.2, SO.sub.2, etc.) to generate oxygen anions on the membrane. The reactor has an oxidation zone and a reduction zone separated by the membrane. A component of an oxygen containing gas in the reduction zone is reduced at the membrane and a reduced species in a reactant gas in the oxidation zone of the reactor is oxidized. The reactor optionally contains a three-dimensional catalyst in the oxidation zone. The adherent catalyst layer and the three-dimensional catalyst are selected to promote a desired oxidation reaction, particularly a partial oxidation of a hydrocarbon.

Low Oxygen and Ocean Acidification on the Vancouver Island Shelf

NASA Astrophysics Data System (ADS)

Bianucci, L.; Denman, K.

2008-12-01

In the recent years hypoxic events have been observed along the west coast of North America (off Oregon and California). Although a common cause of coastal hypoxia is usually anthropogenic eutrophication, in these upwelling regions the advection of oxygen-depleted waters from offshore is a key mechanism. Moreover, the high productivity typical of these margins generates a large flux of sinking particular organic matter. The remineralization of this matter below the euphotic zone produces an elevated consumption of oxygen. When concentrations become lower than certain threshold, hypoxia leads to a major change in the ecosystem and the affected areas are called 'dead zones'. Furthermore, the two processes that drive oxygen levels down (physical upwelling and biological demand) also increase dissolved inorganic carbon in the shelf, which leads to a pH reduction. Ocean acidification and hypoxia can severely affect ecosystems, and the links between these phenomena have not been explored. This presentation will discuss a model study of the carbon and oxygen coupling on the Vancouver Island shelf, with focus on the connection between acidification and hypoxia. Moreover, the role of biology versus physics will be investigated. This region comprises the northern end of the wind-driven upwelling margin off western North America, where low oxygen events have not been extensively studied. However, the proximity to an Oxygen Minimum Zone offshore and the observed decline of oxygen in the Northeast Pacific turns this shelf into a potential candidate to suffer from low-oxygen events. The model used is the Regional Ocean Modeling System (ROMS) in a quasi-2D configuration of the shelf (across-shore section with uniform properties alongshore). The biogeochemical model has carbon, oxygen, and nitrogen as state variables, and includes cycling of dissolved organic matter. Carbon and oxygen cycles are coupled through ecosystem processes such as photosynthesis and remineralization, while they are decoupled by other processes (e.g., nitrification and denitrification).

Transient heat and mass transfer analysis in a porous ceria structure of a novel solar redox reactor

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

Chandran, RB; Bader, R; Lipinski, W

2015-06-01

Thermal transport processes are numerically analyzed for a porous ceria structure undergoing reduction in a novel redox reactor for solar thermochemical fuel production. The cylindrical reactor cavity is formed by an array of annular reactive elements comprising the porous ceria monolith integrated with gas inlet and outlet channels. Two configurations are considered, with the reactor cavity consisting of 10 and 20 reactive elements, respectively. Temperature dependent boundary heat fluxes are obtained on the irradiated cavity wall by solving for the surface radiative exchange using the net radiation method coupled to the heat and mass transfer model of the reactive element.more » Predicted oxygen production rates are in the range 40-60 mu mol s(-1) for the geometries considered. After an initial rise, the average temperature of the reactive element levels off at 1660 and 1680 K for the two geometries, respectively. For the chosen reduction reaction rate model, oxygen release continues after the temperature has leveled off which indicates that the oxygen release reaction is limited by chemical kinetics and/or mass transfer rather than by the heating rate. For a fixed total mass of ceria, the peak oxygen release rate is doubled for the cavity with 20 reactive elements due to lower local oxygen partial pressure. (C) 2015 Elsevier Masson SAS. All rights reserved.« less

Taurus Littrow Pyroclastic Deposit-An Optimum Feedstock for Lunar Oxygen

NASA Technical Reports Server (NTRS)

Allen, Carlton C.

2014-01-01

Future human habitation of the Moon will likely require the use of locally derived materials because of the high cost of transportation from Earth. Oxygen, extracted from oxides and silicates, is a potentially abundant lunar resource vital for life support and spacecraft propulsion. The anticipated costs of supplying all oxygen needs for a lunar base from Earth are high enough to warrant serious study of oxygen production from local resources. Over 20 different processes have been proposed for oxygen production on the Moon. Among the simplest and best studied of these processes is the reduction of oxides in lunar minerals and glass using hydrogen gas. Oxygen can be extracted from lunar soils and pyroclastic glass beads by exposing the samples to flowing hydrogen at subsolidus temperatures (approx. 1050 C). Total oxygen yield is directly correlated to the sample's abundance of FeO, but is not correlated to the abundance of any other oxide. Oxygen is extracted predominantly from FeO, with lesser contributions from TiO2 and SiO2. Oxygen yield is independent of soil maturity. All major FeO-bearing phases contribute oxygen, with extraction from ilmenite and glass significantly more efficient than from olivine and pyroxene. This study demonstrates that the optimum location for a lunar resources demonstration mission can be identified, and that the oxygen yield can be predicted, using a combination of high-resolution imaging and thermal-infrared data. A mission to Taurus Littrow will encounter a deposit at least 10 m in depth with few landing hazards, a uniform composition, and a predicted oxygen yield of approximately 3 wt. %, among the highest values on the Moon.

Electrochemical oxygen reduction catalysed by Ni3(hexaiminotriphenylene)2.

PubMed

Miner, Elise M; Fukushima, Tomohiro; Sheberla, Dennis; Sun, Lei; Surendranath, Yogesh; Dincă, Mircea

2016-03-08

Control over the architectural and electronic properties of heterogeneous catalysts poses a major obstacle in the targeted design of active and stable non-platinum group metal electrocatalysts for the oxygen reduction reaction. Here we introduce Ni3(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene) as an intrinsically conductive metal-organic framework which functions as a well-defined, tunable oxygen reduction electrocatalyst in alkaline solution. Ni3(HITP)2 exhibits oxygen reduction activity competitive with the most active non-platinum group metal electrocatalysts and stability during extended polarization. The square planar Ni-N4 sites are structurally reminiscent of the highly active and widely studied non-platinum group metal electrocatalysts containing M-N4 units. Ni3(HITP)2 and analogues thereof combine the high crystallinity of metal-organic frameworks, the physical durability and electrical conductivity of graphitic materials, and the diverse yet well-controlled synthetic accessibility of molecular species. Such properties may enable the targeted synthesis and systematic optimization of oxygen reduction electrocatalysts as components of fuel cells and electrolysers for renewable energy applications.

Electrochemical oxygen reduction catalysed by Ni3(hexaiminotriphenylene)2

PubMed Central

Miner, Elise M.; Fukushima, Tomohiro; Sheberla, Dennis; Sun, Lei; Surendranath, Yogesh; Dincă, Mircea

2016-01-01

Control over the architectural and electronic properties of heterogeneous catalysts poses a major obstacle in the targeted design of active and stable non-platinum group metal electrocatalysts for the oxygen reduction reaction. Here we introduce Ni3(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene) as an intrinsically conductive metal-organic framework which functions as a well-defined, tunable oxygen reduction electrocatalyst in alkaline solution. Ni3(HITP)2 exhibits oxygen reduction activity competitive with the most active non-platinum group metal electrocatalysts and stability during extended polarization. The square planar Ni-N4 sites are structurally reminiscent of the highly active and widely studied non-platinum group metal electrocatalysts containing M-N4 units. Ni3(HITP)2 and analogues thereof combine the high crystallinity of metal-organic frameworks, the physical durability and electrical conductivity of graphitic materials, and the diverse yet well-controlled synthetic accessibility of molecular species. Such properties may enable the targeted synthesis and systematic optimization of oxygen reduction electrocatalysts as components of fuel cells and electrolysers for renewable energy applications. PMID:26952523

Electrochemical oxygen reduction catalysed by Ni 3(hexaiminotriphenylene) 2

DOE PAGES

Miner, Elise M.; Fukushima, Tomohiro; Sheberla, Dennis; ...

2016-03-08

Control over the architectural and electronic properties of heterogeneous catalysts poses a major obstacle in the targeted design of active and stable non-platinum group metal electrocatalysts for the oxygen reduction reaction. Here we introduce Ni 3(HITP) 2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene) as an intrinsically conductive metal-organic framework which functions as a well-defined, tunable oxygen reduction electrocatalyst in alkaline solution. Ni 3(HITP) 2 exhibits oxygen reduction activity competitive with the most active non-platinum group metal electrocatalysts and stability during extended polarization. The square planar Ni-N 4 sites are structurally reminiscent of the highly active and widely studied non-platinum groupmore » metal electrocatalysts containing M-N 4 units. Ni 3(HITP) 2 and analogues thereof combine the high crystallinity of metal-organic frameworks, the physical durability and electrical conductivity of graphitic materials, and the diverse yet well-controlled synthetic accessibility of molecular species. As a result, such properties may enable the targeted synthesis and systematic optimization of oxygen reduction electrocatalysts as components of fuel cells and electrolysers for renewable energy applications.« less

Highly regenerable carbon-Fe3O4 core-satellite nanospheres as oxygen reduction electrocatalyst and magnetic adsorbent

NASA Astrophysics Data System (ADS)

Zhou, Wenqiang; Liu, Minmin; Cai, Chao; Zhou, Haijun; Liu, Rui

2017-02-01

We present the synthesis and multifunctional utilization of core-satellite carbon-Fe3O4 nanoparticles to serve as the enabling platform for a range of applications including oxygen reduction reaction (ORR) and magnetic adsorbent. Starting from polydopamine (PDA) nanoparticles and Fe(NO3)3, carbon-Fe3O4 core-satellite nanospheres are synthesized through successive steps of impregnation, ammoniation and carbonization. The synergistic combination of Fe3O4 and N-doped carbon endows the nanocomposite with high electrochemical activity in ORR and mainly four electrons transferred in reaction process. Furthermore, carbon-Fe3O4 nanoparticles used as magnetic adsorbent exhibit the efficient removal of Rhodamine B from an aqueous solution. The recovery and reuse of the adsorbent is demonstrated 5 times without any detectible loss in activity.

Integration of the electrochemical depolorized CO2 concentrator with the Bosch CO2 reduction subsystem

NASA Technical Reports Server (NTRS)

Schubert, F. H.; Wynveen, R. A.; Hallick, T. M.

1976-01-01

Regenerative processes for the revitalization of spacecraft atmospheres require an Oxygen Reclamation System (ORS) for the collection of carbon dioxide and water vapor and the recovery of oxygen from these metabolic products. Three life support subsystems uniquely qualified to form such an ORS are an Electrochemical CO2 Depolarized Concentrator (EDC), a CO2 Reduction Subsystem (BRS) and a Water Electrolysis Subsystem (WES). A program to develop and test the interface hardware and control concepts necessary for integrated operation of a four man capacity EDC with a four man capacity BRS was successfully completed. The control concept implemented proved successful in operating the EDC with the BRS for both constant CO2 loading as well as variable CO2 loading, based on a repetitive mission profile of the Space Station Prototype (SSP).

Cobalt-doped carbon xerogel with different initial pH values toward oxygen reduction

NASA Astrophysics Data System (ADS)

Fitri, Azim; Loh, Kee Shyuan; Puspasari, Ifa; Mohamad, Abu Bakar

2017-12-01

In this study, cobalt-doped carbon xerogel (Co-CX) was synthesized via sol-gel polymerization resorcinol-formaldehyde, catalyzed with cobalt nitrate, followed by drying and carbonization process under nitrogen gas flow. The effect of initial pH value (5.5, 6.5 and 7.5) and the type of carbon precursors on the morphology of Co-CX have been investigated with Field Emission-Transmission Electron Microscopy (FESEM). The catalytic activity of Co-CX for the oxygen reduction reaction (ORR) in 0.1 M KOH has been studied by using a rotating ring-disk electrode (RRDE) technique. FESEM revealed that Co doping promotes the formation of more pores. While the conditions allow obtaining xerogel with higher porosity at pH 7.5. The RRDE result display that Co-CX exhibited good catalytic activity tends to favor two electrons pathway.

A polyacrylonitrile copolymer-silica template for three-dimensional hierarchical porous carbon as a Pt catalyst support for the oxygen reduction reaction.

PubMed

Liu, Minmin; Li, Jian; Cai, Chao; Zhou, Ziwei; Ling, Yun; Liu, Rui

2017-08-01

Herein, we report a novel route to construct a hierarchical three-dimensional porous carbon (3DC) through a copolymer-silica assembly. In the synthesis, silica acts as a hard template and leads to the formation of an interconnected 3D macropore, whereas styrene-co-acrylonitrile polymer has been used as both a carbon source and a soft template for micro- and meso-pores. The obtained 3DC materials possess a large surface area (∼550.5 m 2 g -1 ), which facilitates high dispersion of Pt nanoparticles on the carbon support. The 3DC-supported Pt electrocatalyst shows excellent performance in the oxygen reduction reaction (ORR). The easy processing ability along with the characteristics of hierarchical porosity offers a new strategy for the preparation of carbon nanomaterials for energy application.

Recovery Act: Novel Oxygen Carriers for Coal-fueled Chemical Looping

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

Pan, Wei-Ping; Cao, Yan

2012-11-30

Chemical Looping Combustion (CLC) could totally negate the necessity of pure oxygen by using oxygen carriers for purification of CO{sub 2} stream during combustion. It splits the single fuel combustion reaction into two linked reactions using oxygen carriers. The two linked reactions are the oxidation of oxygen carriers in the air reactor using air, and the reduction of oxygen carriers in the fuel reactor using fuels (i.e. coal). Generally metal/metal oxides are used as oxygen carriers and operated in a cyclic mode. Chemical looping combustion significantly improves the energy conversion efficiency, in terms of the electricity generation, because it improvesmore » the reversibility of the fuel combustion process through two linked parallel processes, compared to the conventional combustion process, which is operated far away from its thermo-equilibrium. Under the current carbon-constraint environment, it has been a promising carbon capture technology in terms of fuel combustion for power generation. Its disadvantage is that it is less mature in terms of technological commercialization. In this DOE-funded project, accomplishment is made by developing a series of advanced copper-based oxygen carriers, with properties of the higher oxygen-transfer capability, a favorable thermodynamics to generate high purity of CO{sub 2}, the higher reactivity, the attrition-resistance, the thermal stability in red-ox cycles and the achievement of the auto-thermal heat balance. This will be achieved into three phases in three consecutive years. The selected oxygen carriers with final-determined formula were tested in a scaled-up 10kW coal-fueled chemical looping combustion facility. This scaled-up evaluation tests (2-day, 8-hour per day) indicated that, there was no tendency of agglomeration of copper-based oxygen carriers. Only trace-amount of coke or carbon deposits on the copper-based oxygen carriers in the fuel reactor. There was also no evidence to show the sulphidization of oxygen carriers in the system by using the high-sulfur-laden asphalt fuels. In all, the scaled-up test in 10 kW CLC facility demonstrated that the preparation method of copper-based oxygen carrier not only help to maintain its good reactivity, also largely minimize its agglomeration tendency.« less

The demonstration of a novel sulfur cycle-based wastewater treatment process: sulfate reduction, autotrophic denitrification, and nitrification integrated (SANI®) biological nitrogen removal process.

PubMed

Lu, Hui; Wu, Di; Jiang, Feng; Ekama, George A; van Loosdrecht, Mark C M; Chen, Guang-Hao

2012-11-01

Saline water supply has been successfully practiced for toilet flushing in Hong Kong since 1950s, which saves 22% of freshwater in Hong Kong. In order to extend the benefits of saline water supply into saline sewage management, we have recently developed a novel biological organics and nitrogen removal process: the Sulfate reduction, Autotrophic denitrification, and Nitrification Integrated (SANI®) process. The key features of this novel process include elimination of oxygen demand in organic matter removal and production of minimal sludge. Following the success of a 500-day lab-scale trial, this study reports a pilot scale evaluation of this novel process treating 10 m(3) /day of 6-mm screened saline sewage in Hong Kong. The SANI® pilot plant consisted of a sulfate reduction up-flow sludge bed (SRUSB) reactor, an anoxic bioreactor for autotrophic denitrification and an aerobic bioreactor for nitrification. The plant was operated at a steady state for 225 days, during which the average removal efficiencies of both chemical oxygen demand (COD) and total suspended solids (TSS) at 87% and no excess sludge was purposefully withdrawn. Furthermore, a tracer test revealed 5% short circuit flow and a 34.6% dead zone in the SRUSB, indicating a good possibility to further optimize the treatment capacity of the process for full-scale application. Compared with conventional biological nitrogen removal processes, the SANI® process reduces 90% of waste sludge, which saves 35% of the energy and reduces 36% of fossil CO(2) emission. The SANI® process not only eliminates the major odor sources originating from primary treatment and subsequent sludge treatment and disposal during secondary saline sewage treatment, but also promotes saline water supply as an economic and sustainable solution for water scarcity and sewage treatment in water-scarce coastal areas. Copyright © 2012 Wiley Periodicals, Inc.

Oxygen, pH, and mitochondrial oxidative phosphorylation.

PubMed

Wilson, David F; Harrison, David K; Vinogradov, Sergei A

2012-12-15

The oxygen dependence of mitochondrial oxidative phosphorylation was measured in suspensions of isolated rat liver mitochondria using recently developed methods for measuring oxygen and cytochrome c reduction. Cytochrome-c oxidase (energy conservation site 3) activity of the mitochondrial respiratory chain was measured using an artificial electron donor (N,N,N',N'-tetramethyl-p-phenylenediamine) and ascorbate to directly reduce the cytochrome c, bypassing sites 1 and 2. For mitochondrial suspensions with added ATP, metabolic conditions approximating those in intact cells and decreasing oxygen pressure both increased reduction of cytochrome c and decreased respiratory rate. The kinetic parameters [K(M) and maximal rate (V(M))] for oxygen were determined from the respiratory rates calculated for 100% reduction of cytochrome c. At 22°C, the K(M) for oxygen is near 3 Torr (5 μM), 12 Torr (22 μM), and 18 Torr (32 μM) at pH 6.9, 7.4, and 7.9, respectively, and V(M) corresponds to a turnover number for cytochrome c at 100% reduction of near 80/s and is independent of pH. Uncoupling oxidative phosphorylation increased the respiratory rate at saturating oxygen pressures by twofold and decreased the K(M) for oxygen to <2 Torr at all tested pH values. Mitochondrial oxidative phosphorylation is an important oxygen sensor for regulation of metabolism, nutrient delivery to tissues, and cardiopulmonary function. The decrease in K(M) for oxygen with acidification of the cellular environment impacts many tissue functions and may give transformed cells a significant survival advantage over normal cells at low-pH, oxygen-limited environment in growing tumors.

Electro-biocatalytic production of formate from carbon dioxide using an oxygen-stable whole cell biocatalyst.

PubMed

Hwang, Hyojin; Yeon, Young Joo; Lee, Sumi; Choe, Hyunjun; Jang, Min Gee; Cho, Dae Haeng; Park, Sehkyu; Kim, Yong Hwan

2015-06-01

The use of biocatalysts to convert CO2 into useful chemicals is a promising alternative to chemical conversion. In this study, the electro-biocatalytic conversion of CO2 to formate was attempted with a whole cell biocatalyst. Eight species of Methylobacteria were tested for CO2 reduction, and one of them, Methylobacterium extorquens AM1, exhibited an exceptionally higher capability to synthesize formate from CO2 by supplying electrons with electrodes, which produced formate concentrations of up to 60mM. The oxygen stability of the biocatalyst was investigated, and the results indicated that the whole cell catalyst still exhibited CO2 reduction activity even after being exposed to oxygen gas. From the results, we could demonstrate the electro-biocatalytic conversion of CO2 to formate using an obligate aerobe, M. extorquens AM1, as a whole cell biocatalyst without providing extra cofactors or hydrogen gas. This electro-biocatalytic process suggests a promising approach toward feasible way of CO2 conversion to formate. Copyright © 2015 Elsevier Ltd. All rights reserved.

Hydrogen and Fuel Cells | Chemistry and Nanoscience Research | NREL

Science.gov Websites

Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion,"" , "Benchmarking the Oxygen Reduction Reaction Activity of Pt-Based Catalysts Using Standardized , B.S. Pivovar, S.S. Kocha. ""Suppression of Oxygen Reduction Reaction Activity on Pt-Based

Thermodynamic evaluation of oxygen behavior in Ti powder deoxidized by Ca reductant

NASA Astrophysics Data System (ADS)

Kim, Sun-Joong; Oh, Jung-Min; Lim, Jae-Won

2016-07-01

To produce low oxygen Ti powder of less than 1000 mass ppm, commercial Ti powder was deoxidized by two types of Ca reductants: a solid Ca and a Ca vapor. Compared with the iso-oxygen partial pressure in the Ti-O binary phase diagram, the PO2 in the raw Ti powder increased with temperature compared to the reduction reaction of Ca. Therefore, the O2 content in the Ti powder decreased as the deoxidation temperature increased from 873 K, showing a local minima at 1273 K. The oxygen concentration at 1373 K was greater than that at 1273 K because the oxygen solubility of the Ti powder was increased by the equilibrium relation between Ca and CaO. On the basis of the thermodynamic assessment, the deoxidation of Ti powder can be improved by increasing the temperature and lowering the oxygen solubility with the saturation of CaO.

Enhanced Sulfate Reduction and Carbon Sequestration in Sediments Underlying the Core of the Arabian Sea Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Fernandes, S. Q.; Mazumdar, A.; Peketi, A.; Bhattacharya, S.; Carvalho, M.; Da Silva, R.; Roy, R.; Mapder, T.; Roy, C.; Banik, S. K.; Ghosh, W.

2017-12-01

The oxygen minimum zone (OMZ) of the Arabian Sea in the northern Indian Ocean is one of the three major global sites of open ocean denitrification. The functionally anoxic water column between 150 to 1200 mbsl plays host to unique biogeochemical processes and organism interactions. Little is known, however, about the consequence of the low dissolved oxygen on the underlying sedimentary biogeochemical processes. Here we present, for the first time, a comprehensive investigation of sediment biogeochemistry of the Arabian Sea OMZ by coupling pore fluid analyses with microbial diversity data in eight sediment cores collected across a transect off the west coast of India in the Eastern Arabian Sea. We observed that in sediments underlying the core of the OMZ, high organic carbon sequestration coincides with a high diversity of all bacteria (the majority of which are complex organic matter hydrolyzers) and sulfate reducing bacteria (simple organic compound utilizers). Depth-integrated sulfate reduction rate also intensifies in this territory. These biogeochemical features, together with the detected shallowing of the sulfate-methane interface and buildup of pore-water sulfide, are all reflective of heightened carbon-sulfur cycling in the sediments underlying the OMZ core. Our data suggests that the sediment biogeochemistry of the OMZ is sensitive to minute changes in bottom water dissolved oxygen, and is dictated by the potential abundance and bioavailability of complex to simple carbon compounds which can stimulate a cascade of geomicrobial activities pertaining to the carbon-sulfur cycle. Our findings hold implications in benthic ecology and sediment diagenesis.

Venous saturation and blood flow behavior during laser-induced photodissociation of oxyhemoglobin

NASA Astrophysics Data System (ADS)

Mamilov, S. A.; Yesman, S. S.; Asimov, M. M.; Gisbrecht, A. I.

2013-03-01

The value of relative oxyhemoglobin concentration (saturation) in arterial (SаO2) and venous blood (SvO2) plays a significant role in the oxygen exchange in tissue and is used as criterion of delivery of oxygen adequate to the needs of tissue cells. Reduction of the volume of blood flows as well as reduction of oxygen concentration in arterial blood causes hypoxia - deficit of oxygen in tissue. One of the main mechanisms of elimination of hypoxia is based on compensation of the oxygen deficit by increasing the oxygen extraction from arterial blood, which leads to reduction of oxygen in the venous blood 1. In this report two optical techniques for measurement of venous blood saturation are presented. The first one is based on the pulseoximetry with artificial mechanical modulation of the tissue volume and the second one on the spectrophotometry of human respiratory rhythm. Good correlation between the results obtained with both techniques is observed.

Co@Co3O4 Encapsulated in Carbon Nanotube-Grafted Nitrogen-Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode.

PubMed

Aijaz, Arshad; Masa, Justus; Rösler, Christoph; Xia, Wei; Weide, Philipp; Botz, Alexander J R; Fischer, Roland A; Schuhmann, Wolfgang; Muhler, Martin

2016-03-14

Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal-air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core-shell Co@Co3O4 nanoparticles embedded in CNT-grafted N-doped carbon-polyhedra obtained by the pyrolysis of cobalt metal-organic framework (ZIF-67) in a reductive H2 atmosphere and subsequent controlled oxidative calcination. The catalysts afford 0.85 V reversible overvoltage in 0.1 m KOH, surpassing Pt/C, IrO2 , and RuO2 and thus ranking them among one of the best non-precious-metal electrocatalysts for reversible oxygen electrodes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced degradation of paracetamol by UV-C supported photo-Fenton process over Fenton oxidation.

PubMed

Manu, B; Mahamood, S

2011-01-01

For the treatment of paracetamol in water, the UV-C Fenton oxidation process and classic Fenton oxidation have been found to be the most effective. Paracetamol reduction and chemical oxygen demand (COD) removal are measured as the objective functions to be maximized. The experimental conditions of the degradation of paracetamol are optimized by the Fenton process. Influent pH 3, initial H(2)O(2) dosage 60 mg/L, [H(2)O(2)]/[Fe(2+)] ratio 60 : 1 are the optimum conditions observed for 20 mg/L initial paracetamol concentration. At the optimum conditions, for 20 mg/L of initial paracetamol concentration, 82% paracetamol reduction and 68% COD removal by Fenton oxidation, and 91% paracetamol reduction and 82% COD removal by UV-C Fenton process are observed in a 120 min reaction time. By HPLC analysis, 100% removal of paracetamol is observed at the above optimum conditions for the Fenton process in 240 min and for the UV-C photo-Fenton process in 120 min. The methods are effective and they may be used in the paracetamol industry.

Investigations of oxygen reduction reactions in non-aqueous electrolytes and the lithium-air battery

NASA Astrophysics Data System (ADS)

O'Laoire, Cormac Micheal

Unlocking the true energy capabilities of the lithium metal negative electrode in a lithium battery has until now been limited by the low capacity intercalation and conversion reactions at the positive electrodes. This is overcome by removing these electrodes and allowing lithium to react directly with oxygen in the atmosphere forming the Li-air battery. Chapter 2 discusses the intimate role of electrolyte, in particular the role of ion conducting salts on the mechanism and kinetics of oxygen reduction in non-aqueous electrolytes designed for such applications and in determining the reversibility of the electrode reactions. Such fundamental understanding of this high energy density battery is crucial to harnessing its full energy potential. The kinetics and mechanisms of O2 reduction in solutions of hexafluorophosphate salts of the general formula X+ PF6-, where, X = tetra butyl ammonium (TBA), K, Na and Li, in acetonitrile have been studied on glassy carbon electrodes using cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. Our results show that cation choice strongly influences the reduction mechanism of O2. Electrochemical data supports the view that alkali metal oxides formed via electrochemical and chemical reactions passivate the electrode surface inhibiting the kinetics and reversibility of the processes. The O2 reduction mechanisms in the presence of the different cations have been supplemented by kinetic parameters determined from detailed analyses of the CV and RDE data. The organic solvent present in the Li+-conducting electrolyte has a major role on the reversibility of each of the O2 reduction products as found from the work discussed in the next chapter. A fundamental study of the influence of solvents on the oxygen reduction reaction (ORR) in a variety of non-aqueous electrolytes was conducted in chapter 4. In this work special attention was paid to elucidate the mechanism of the oxygen electrode processes in the rechargeable Li-air battery. Towards this end, using either tetrabutylammonium hexafluorophosphate (TBAPF6) or lithium hexafluorophosphate (LiPF6) electrolyte solutions in four different solvents, namely, dimethyl sulfoxide (DMSO), acetonitrile (MeCN), dimethoxyethane (DME), and tetraethylene glycol dimethyl ether (TEGDME), possessing a range of properties, we have determined that the solvent and the supporting electrolyte cations in the solution act in concert to influence the nature of reduction products and their rechargeability. In solutions containing TBA +, O2 reduction is a highly reversible one-electron process involving the O2/O2- couple in all of the electrolytes examined with little effect on the nature of the solvent. On the other hand, in Li+-containing electrolytes relevant to the Li-air battery, O2 reduction proceeds in a stepwise fashion to form O2-, O22- and O2- as products. These reactions in presence of Li+ are irreversible or quasi-reversible electrochemical processes and the solvents have significant influence on the kinetics, and reversibility or lack thereof, of the different reduction products. Reversible reduction of O2 to long-lived superoxide in a Li+-conducting electrolyte in DMSO has been shown for the first time here. Chapter 5 is the culmination of the thesis where the practical application of the work is demonstrated. We designed electrolytes that facilitate Li-Air rechargeability, by applying the knowledge gained from chapters 2-4. A rechargeable Li-air cell utilizing an electrolyte composed of a solution of LiPF6 in tetraethylene glycol dimethyl ether, CH3O(CH2CH 2O)4CH3 was designed, built and its performance studied. It was shown that the cell yields high capacity and can be recharged in spite the absence of catalyst in the carbon cathode. The application of X-ray diffraction to identify these products formed in a porous carbon electrode is shown here for the first time. The rechargeability of the cell was investigated by repeated charge/discharge cycling of the cell, and the factors limiting the cycle life of the cell were studied using AC impedance spectra of the cells as a function of cycle number. In conclusion, the work carried out in this research has shown that the O2 electrochemistry in organic electrolytes is substantially different from that in aqueous electrolytes. Our work has uncovered the key roles the ion conducting salts and the organic solvents play in determining the nature of the reduction products and their reversibility. The results presented here for the first time provide a rational approach to the design and selection of organic electrolyte solutions for use in the rechargeable Li-air battery. (Abstract shortened by UMI.)

[Effects of hyperbaric oxygenation on oxidative phosphorylation in post-nephrotomy tissues sutured with different surgical threads (an experimental study)].

PubMed

Kostenko, V A

1998-01-01

The activity of mitochondrial respiration and oxidative phosphorylation (OP) was studied in white rats subjected to nephrotomy. The suture was made with absorbable surgical threads such as catgut plain, biofil (from dura mater spinalis of the cattle), dexon II (polyglycolic acid). The use of catgut plain inhibits biosynthetic processes 7 and 14 days after operation. Hyperbaric oxygenation enhances oxidative phosphorylation in postoperative renal tissue sutured with different biological and synthetic absorbable surgical threads (catgut, biofil, dexon II) and prevents sharp depression of the above processes in the course of catgut biodegradation. This fact is of great importance for reduction of normal functional and metabolic activity of the operated kidney.

The Nernst equation applied to oxidation-reduction reactions in myoglobin and hemoglobin. Evaluation of the parameters.

PubMed

Saroff, Harry A

Analyses of the binding of oxygen to monomers such as myoglobin employ the Mass Action equation. The Mass Action equation, as such, is not directly applicable for the analysis of the binding of oxygen to oligomers such as hemoglobin. When the binding of oxygen to hemoglobin is analyzed, models incorporating extensions of mass action are employed. Oxidation-reduction reactions of the heme group in myoglobin and hemoglobin involve the binding and dissociation of electrons. This reaction is described with the Nernst equation. The Nernst equation is applicable only to a monomeric species even if the number of electrons involved is greater than unity. To analyze the oxidation-reduction reaction in a molecule such as hemoglobin a model is required which incorporates extensions of the Nernst equation. This communication develops models employing the Nernst equation for oxidation-reduction reactions analogous to those employed for hemoglobin in the analysis of the oxygenation (binding of oxygen) reaction.

Oxygen reduction on a Pt(111) catalyst in HT-PEM fuel cells by density functional theory

NASA Astrophysics Data System (ADS)

Sun, Hong; Li, Jie; Almheiri, Saif; Xiao, Jianyu

2017-08-01

The oxygen reduction reaction plays an important role in the performance of high-temperature proton exchange membrane (HT-PEM) fuel cells. In this study, a molecular dynamics model, which is based on the density functional theory and couples the system's energy, the exchange-correlation energy functional, the charge density distribution function, and the simplified Kohn-Sham equation, was developed to simulate the oxygen reduction reaction on a Pt(111) surface. Additionally, an electrochemical reaction system on the basis of a four-electron reaction mechanism was also developed for this simulation. The reaction path of the oxygen reduction reaction, the product structure of each reaction step and the system's energy were simulated. It is found that the first step reaction of the first hydrogen ion with the oxygen molecule is the controlling step of the overall reaction. Increasing the operating temperature speeds up the first step reaction rate and slightly decreases its reaction energy barrier. Our results provide insight into the working principles of HT-PEM fuel cells.

Fungal Spoilage in Food Processing.

PubMed

Snyder, Abigail B; Worobo, Randy W

2018-06-01

Food processing, packaging, and formulation strategies are often specifically designed to inhibit or control microbial growth to prevent spoilage. Some of the most restrictive strategies rely solely or on combinations of pH reduction, preservatives, water activity limitation, control of oxygen tension, thermal processing, and hermetic packaging. In concert, these strategies are used to inactivate potential spoilage microorganisms or inhibit their growth. However, for select microbes that can overcome these controls, the lack of competition from additional background microbiota helps facilitate their propagation.

Improved photocatalytic degradation of Orange G using hybrid nanofibers

NASA Astrophysics Data System (ADS)

Ledwaba, Mpho; Masilela, Nkosiphile; Nyokong, Tebello; Antunes, Edith

2017-05-01

Functionalised electrospun polyamide-6 (PA-6) nanofibres incorporating gadolinium oxide nanoparticles conjugated to zinc tetracarboxyphenoxy phthalocyanine (ZnTCPPc) as the sensitizer were prepared for the photocatalytic degradation of Orange G. Fibres incorporating the phthalocyanine alone or a mixture of the nanoparticles and phthalocyanine were also generated. The singlet oxygen-generating ability of the sensitizer was shown to be maintained within the fibre mat, with the singlet oxygen quantum yields increasing upon incorporation of the magnetic nanoparticles. Consequently, the rate of the photodegradation of Orange G was observed to increase with an increase in singlet oxygen quantum yield. A reduction in the half-lives for the functionalised nanofibres was recorded in the presence of the magnetic nanoparticles, indicating an improvement in the efficiency of the degradation process.

Cold plasma processing of local planetary ores for oxygen and metallurgically important metals

NASA Technical Reports Server (NTRS)

Lynch, D. C.; Bullard, D.; Ortega, R.

1990-01-01

The utilization of a cold plasma in chlorination processing is described. Essential equipment and instruments were received, the experimental apparatus assembled and tested, and preliminary experiments conducted. The results of the latter lend support to the original hypothesis: a cold plasma can both significantly enhance and bias chemical reactions. In two separate experiments, a cold plasma was used to reduce TiCl4 vapor and chlorinate ilmenite. The latter, reacted in an argon-chlorine plasma, yielded oxygen. The former experiment reveals that chlorine can be recovered as HCl vapor from metal chlorides in a hydrogen plasma. Furthermore, the success of the hydrogen experiments has lead to an analysis of the feasibility of direct hydrogen reduction of metal oxides in a cold plasma. That process would produce water vapor and numerous metal by-products.

Biogeochemical cycles of carbon, sulfur, and free oxygen in a microbial mat

NASA Astrophysics Data System (ADS)

Canfield, Donald E.; Des Marais, David J.

1993-08-01

Complete budgets for carbon and oxygen have been constructed for cyanobacterial mats dominated by Microcoleus chthonoplastes from the evaporating ponds of a salt works located in Guerrero Negro, Baja California Sur, Mexico. Included in the budget are measured rates of O 2 production, sulfate reduction, and elemental exchange across the mat/brine interface, day and night, at various temperatures and times of the year. We infer from this data the various sinks for O 2, as well as the sources of carbon for primary production. To summarize, although seasonal variability exists, a major percentage of the O 2 produced during the day did not diffuse out of the mat but was used within the mat to oxidize both organic carbon and the sulfide produced by sulfate reduction. At night, most of the O 2 that diffused into the mat was used to oxidize sulfide, with O 2 respiration of minor importance. During the day, the internal mat processes of sulfate reduction and O 2 respiration generated as much or more inorganic carbon (DIC) for primary production as diffusion into the mat. Also, oxygenic photosynthesis was the most important process of carbon fixation, although anoxygenic photosynthesis may have been important at low light levels during some times of the year. At night, the DIC lost from the mat was mostly from sulfate reduction. Elemental fluxes across the mat/brine interface indicated that carbon with an oxidation state of greater than zero was taken up by the mat during the day and liberated from the mat at night. Overall, carbon with an average oxidation state of near zero accumulated in the mat. Both carbon fixation and carbon oxidation rates varied with temperature by a similar amount. These mats are thus closely coupled systems where rapid rates of photosynthesis both require and fuel rapid rates of heterotrophic carbon oxidation.

Sodium metasilicate based fiber opening for greener leather processing.

PubMed

Saravanabhavan, Subramani; Thanikaivelan, Palanisamy; Rao, Jonnalagadda Raghava; Nair, Balachandran Unni; Ramasamit, Thirumalachari

2008-03-01

Growing environmental regulations propound the need for a transformation in the current practice of leather making. The conventional dehairing and fiber opening process results in high negative impact on the environment because of its uncleanliness. This process accounts for most of the biochemical oxygen demand and chemical oxygen demand in tannery wastewater and generation of H2S gas. Hence, this study explores the use of a biological material and a nontoxic chemical for performing the above process more cleanly. In this study, the dehairing and fiber opening processes has been designed using enzyme and sodium metasilicate. The amount of sodium metasilicate required for fiber opening is standardized through the removal of proteoglycan, increase in weight, and bulk properties of leathers. It has been found that the extent of opening up of fiber bundles is comparable to that of conventionally processed leathers using a 2% sodium metasilicate solution. This has been substantiated through scanning electron microscopic analysis and softness measurements. The presence of silica in the crust leather enhances the bulk properties of the leather. This has been confirmed from the energy dispersive X-ray analysis. Performance of the leathers is shown to be on par with conventionally processed leathers through physical and hand evaluation. The process also exhibits significant reduction in chemical oxygen demand and total solid loads by 55 and 24%, respectively. Further, this newly developed process seems to be economically beneficial.

Free Electrons to Molecular Bonds and Back: Closing the Energetic Oxygen Reduction (ORR)-Oxygen Evolution (OER) Cycle Using Core-Shell Nanoelectrocatalysts.

PubMed

Strasser, Peter

2016-11-15

Nanomaterial science and electrocatalytic science have entered a successful "nanoelectrochemical" symbiosis, in which novel nanomaterials offer new frontiers for studies on electrocatalytic charge transfer, while electrocatalytic processes give meaning and often practical importance to novel nanomaterial concepts. Examples of this fruitful symbiosis are dealloyed core-shell nanoparticle electrocatalysts, which often exhibit enhanced kinetic charge transfer rates at greatly improved atom-efficiency. As such, they represent ideal electrocatalyst architectures for the acidic oxygen reduction reaction to water (ORR) and the acidic oxygen evolution reaction from water (OER) that require scarce Pt- and Ir-based catalysts. Together, these two reactions constitute the "O-cycle", a key elemental process loop in the field of electrochemical energy interconversion between electricity (free electrons) and molecular bonds (H 2 O/O 2 ), realized in the combination of water electrolyzers and hydrogen/oxygen fuel cells. In this Account, we describe our recent efforts to design, synthesize, understand, and test noble metal-poor dealloyed Pt and Ir core-shell nanoparticles for deployment in acidic polymer electrolyte membrane (PEM) electrolyzers and PEM fuel cells. Spherical dealloyed Pt core-shell particles, derived from PtNi 3 precursor alloys, showed favorable ORR activity. More detailed size-activity correlation studies further revealed that the 6-8 nm diameter range is a most desirable initial particle size range in order to maximize the particle Ni content after ORR testing and to preserve performance stability. Similarly, dealloyed and oxidized IrO x core-shell particles derived from Ni-rich Ir-Ni precursor particles proved highly efficient oxygen evolution reaction (OER) catalysts in acidic conditions. In addition to the noble metal savings in the particle cores, the Pt core-shell particles are believed to benefit in terms of their mass-based electrochemical kinetics from surface lattice strain effects that tune the adsorption energies and barriers of elementary steps. The molecular mechanism of the kinetic benefit of the dealloyed IrO x particle needs more attention, but there is mounting evidence for ligand hole effects in defect-rich IrO x shells that generate preactive oxygen centers.

Surface energy modification for biomedical material by corona streamer plasma processing to mitigate bacterial adhesion

NASA Astrophysics Data System (ADS)

Alhamarneh, Ibrahim; Pedrow, Patrick

2011-10-01

Bacterial adhesion initiates biofouling of biomedical material but the processes can be reduced by adjusting the material's surface energy. The surface of surgical-grade 316L stainless steel (316L SS) had its hydrophilic property enhanced by processing in a corona streamer plasma reactor using atmospheric pressure Ar mixed with O2. Reactor excitation was 60 Hz ac high-voltage (<= 10 kV RMS) applied to a multi-needle-to-grounded-torus electrode configuration. Applied voltage and streamer current pulses were monitored with a broadband sensor system. When Ar/O2 plasma was used, the surface energy was enhanced more than with Ar plasma alone. Composition of the surface before and after plasma treatment was characterized by XPS. As the hydrophilicity of the treated surface increased so did percent of oxygen on the surface thus we concluded that reduction in contact angle was mainly due to new oxygen-containing functionalities. FTIR was used to identify oxygen containing groups on the surface. The aging effect that accompanies surface free energy adjustments was also observed.

The kinetics of ulvoespinel reduction - Synthetic study and applications to lunar rocks.

NASA Technical Reports Server (NTRS)

Mccallister, R. H.; Taylor, L. A.

1973-01-01

The kinetics of Fe2TiO4 reduction to FeTiO3 + Fe were studied using CO-CO2 gas mixtures with fO2 measured by a solid ceramic (calcia-zirconia) oxygen electrolyte cell. Isothermal rate studies at 900 C suggest that the mechanism of Fe2TiO4 reduction is one of nucleation and growth, where the growth stage may be controlled by the diffusion of the reactant through the product layer or volume diffusion. The activation energy for the growth stage of the process was determined to be 46 plus or minus 4 kcal/mole.

Identification of an iron permease, cFTR1, in cyanobacteria involved in the iron reduction/re-oxidation uptake pathway.

PubMed

Xu, Ning; Qiu, Guo-Wei; Lou, Wen-Jing; Li, Zheng-Ke; Jiang, Hai-Bo; Price, Neil M; Qiu, Bao-Sheng

2016-12-01

Cyanobacteria are globally important primary producers and abundant in many iron-limited aquatic environments. The ways in which they take up iron are largely unknown, but reduction of Fe 3+ is an important step in the process. Here we report a special iron permease in Synechocystis, cFTR1, that is required for Fe 3+ uptake following Fe 2+ re-oxidation. The expression of cFTR1 is induced by iron starvation, and a mutant lacking the gene is abnormally sensitive to iron starvation. The cFTR1 protein localizes to the plasma membrane and contains the iron-binding motif "REXXE". Point-directed mutagenesis of the REXXE motif results in a sensitivity to Fe-deficiency. Measurements of iron ( 55 Fe) uptake rate show that cFTR1 takes up Fe 3+ rather than Fe 2+ . The function of cFTR1 in Synechocystis could be genetically complemented by the iron permease, Ftr1p, of Saccharomyces cerevisiae, that is known to transport Fe 3+ produced by the oxidation of Fe 2+ via a multicopper oxidase. Unlike yeast Ftr1p, cyanobacterial cFTR1 probably obtains Fe 3+ primarily from the oxidation of Fe 2+ by oxygen. Growth assays show that the cFTR1 is required during oxygenic, photoautotrophic growth but not when oxygen production is inhibited during photoheterotrophic growth. In cyanobacteria, iron reduction/re-oxidation uptake pathway may represent their adaptation to oxygenated environments. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Sensitivity of hypoxia predictions for the northern Gulf of Mexico to sediment oxygen consumption and model nesting

NASA Astrophysics Data System (ADS)

Fennel, Katja; Hu, Jiatang; Laurent, Arnaud; Marta-Almeida, Martinho; Hetland, Robert

2013-02-01

Every summer, a large area (15,000 km2 on average) over the Texas-Louisiana shelf in the northern Gulf of Mexico turns hypoxic due to decay of organic matter that is primarily derived from nutrient inputs from the Mississippi/Atchafalaya River System. Interannual variability in the size of the hypoxic zone is large. The 2008 Action Plan put forth by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, an alliance of multiple state and federal agencies and tribes, calls for a reduction of the size of the hypoxic zone through nutrient management in the watershed. Comprehensive models help build mechanistic understanding of the processes underlying hypoxia formation and variability and are thus indispensable tools for devising efficient nutrient reduction strategies and for building reasonable expectations as to what responses can be expected for a given nutrient reduction. Here we present such a model, evaluate its hypoxia simulations against monitoring observations, and assess the sensitivity of the hypoxia simulations to model resolution, variations in sediment oxygen consumption, and choice of physical horizontal boundary conditions. We find that hypoxia simulations on the shelf are very sensitive to the parameterization of sediment oxygen consumption, a result of the fact that hypoxic conditions are restricted to a relatively thin layer above the bottom over most of the shelf. We show that the strength of vertical stratification is an important predictor of dissolved oxygen concentration in bottom waters and that modification of physical horizontal boundary conditions can have a large effect on hypoxia simulations because it can affect stratification strength.

Optical in situ monitoring of plasma-enhanced atomic layer deposition process

NASA Astrophysics Data System (ADS)

Zeeshan Arshad, Muhammad; Jo, Kyung Jae; Kim, Hyun Gi; Jeen Hong, Sang

2018-06-01

An optical in situ process monitoring method for the early detection of anomalies in plasma process equipment is presented. Cyclic process steps of precursor treatment and plasma reaction for the deposition of an angstrom-scale film increase their complexity to ensure the process quality. However, a small deviation in process parameters, for instance, gas flow rate, process temperature, or RF power, may jeopardize the deposited film quality. As a test vehicle for the process monitoring, we have investigated the aluminum-oxide (Al2O3) encapsulation process in plasma-enhanced atomic layer deposition (PEALD) to form a moisture and oxygen diffusion barrier in organic-light emitting diodes (OLEDs). By optical in situ monitoring, we successfully identified the reduction in oxygen flow rates in the reaction steps, which resulted in a 2.67 times increase in the water vapor transmission ratio (WVTR) of the deposited Al2O3 films. Therefore, we are convinced that the suggested in situ monitoring method is useful for the detection of process shifts or drifts that adversely affect PEALD film quality.

Influence of mechanical disintegration on the microbial growth of aerobic sludge biomass: A comparative study of ultrasonic and shear gap homogenizers by oxygen uptake measurements.

PubMed

Divyalakshmi, P; Murugan, D; Sivarajan, M; Saravanan, P; Lajapathi Rai, C

2015-11-01

Wastewater treatment plant incorporates physical, chemical and biological processes to treat and remove the contaminants. The main drawback of conventional activated sludge process is the huge production of excess sludge, which is an unavoidable byproduct. The treatment and disposal of excess sludge costs about 60% of the total operating cost. The ideal way to reduce excess sludge production during wastewater treatment is by preventing biomass formation within the aerobic treatment train rather than post treatment of the generated sludge. In the present investigation two different mechanical devices namely, Ultrasonic and Shear Gap homogenizers have been employed to disintegrate the aerobic biomass. This study is intended to restrict the multiplication of microbial biomass and at the same time degrade the organics present in wastewater by increasing the oxidative capacity of microorganisms. The disintegrability on biomass was determined by biochemical methods. Degree of inactivation provides the information on inability of microorganisms to consume oxygen upon disruption. The soluble COD quantifies the extent of release of intra cellular compounds. The participation of disintegrated microorganism in wastewater treatment process was carried out in two identical respirometeric reactors. The results show that Ultrasonic homogenizer is very effective in the disruption of microorganisms leading to a maximum microbial growth reduction of 27%. On the other hand, Shear gap homogenizer does not favor the sludge growth reduction rather it facilitates the growth. This study also shows that for better microbial growth reduction, floc size reduction alone is not sufficient but also microbial disruption is essential. Copyright © 2015 Elsevier Inc. All rights reserved.

Influence of oxygen doping on resistive-switching characteristic of a-Si/c-Si device

NASA Astrophysics Data System (ADS)

Zhang, Jiahua; Chen, Da; Huang, Shihua

2017-12-01

The influence of oxygen doping on resistive-switching characteristics of Ag/a-Si/p+-c-Si device was investigated. By oxygen doping in the growth process of amorphous silicon, the device resistive-switching performances, such as the ON/OFF resistance ratios, yield and stability were improved, which may be ascribed to the significant reduction of defect density because of oxygen incorporation. The device I-V characteristics are strongly dependent on the oxygen doping concentration. As the oxygen doping concentration increases, the Si-rich device gradually transforms to an oxygen-rich device, and the device yield, switching characteristics, and stability may be improved for silver/oxygen-doped a-Si/p+-c-Si device. Finally, the device resistive-switching mechanism was analyzed. Project supported by the Zhejiang Provincial Natural Science Foundation of China (No. LY17F040001), the Open Project Program of Surface Physics Laboratory (National Key Laboratory) of Fudan University (No. KF2015_02), the Open Project Program of National Laboratory for Infrared Physics, Chinese Academy of Sciences (No. M201503), the Zhejiang Provincial Science and Technology Key Innovation Team (No. 2011R50012), and the Zhejiang Provincial Key Laboratory (No. 2013E10022).

A full understanding of oxygen reduction reaction mechanism on Au(1 1 1) surface

NASA Astrophysics Data System (ADS)

Yang, Yang; Dai, Changqing; Fisher, Adrian; Shen, Yanchun; Cheng, Daojian

2017-09-01

Oxygen reduction and hydrogen peroxide reduction are technologically important reactions in energy-conversion devices. In this work, a full understanding of oxygen reduction reaction (ORR) mechanism on Au(1 1 1) surface is investigated by density functional theory (DFT) calculations, including the reaction mechanisms of O2 dissociation, OOH dissociation, and H2O2 dissociation. Among these ORR mechanisms on Au(1 1 1), the activation energy of \\text{O}2* hydrogenation reaction is much lower than that of \\text{O}2* dissociation, indicating that \\text{O}2* hydrogenation reaction is more appropriate at the first step than \\text{O}2* dissociation. In the following, H2O2 can be formed with the lower activation energy compared with the OOH dissociation reaction, and finally H2O2 could be generated as a detectable product due to the high activation energy of H2O2 dissociation reaction. Furthermore, the potential dependent free energy study suggests that the H2O2 formation is thermodynamically favorable up to 0.4 V on Au(1 1 1), reducing the overpotential for 2e - ORR process. And the elementary step of first H2O formation becomes non-spontaneous at 0.4 V, indicating the difficulty of 4e - reduction pathway. Our DFT calculations show that H2O2 can be generated on Au(1 1 1) and the first electron transfer is the rate determining step. Our results show that gold surface could be used as a good catalyst for small-scale manufacture and on-site production of H2O2.

Uranium Sequestration During Biostimulated Reduction and In Response to the Return of Oxic Conditions In Shallow Aquifers

USGS Publications Warehouse

Fuller, Christopher C.; Johnson, Kelly J.; Akstin, Katherine; Singer, David M.; Yabusaki, Steven B.; Fang, Yilin; Fuhrmann, M.

2015-01-01

A proposed approach for groundwater remediation of uranium contamination is to generate reducing conditions by stimulating the growth of microbial populations through injection of electron donor compounds into the subsurface. Sufficiently reducing conditions will result in reduction of soluble hexavalent uranium, U(VI), and precipitation of the less soluble +4 oxidation state uranium, U(IV). This process is termed biostimulated reduction. A key issue in the remediation of uranium (U) contamination in aquifers by biostimulated reduction is the long term stability of the sequestered uranium. Three flow-through column experiments using aquifer sediment were used to evaluate the remobilization of bioreduced U sequestered under conditions in which biostimulation extended well into sulfate reduction to enhance precipitation of reduced sulfur phases such as iron sulfides. One column received added ferrous iron, Fe(II), increasing production of iron sulfides, to test their effect on remobilization of the sequestered uranium, either by serving as a redox buffer by competing for dissolved oxygen, or by armoring the reduced uranium. During biostimulation of the ambient microbial population with acetate, dissolved uranium was lowered by a factor of 2.5 or more with continued removal for over 110 days of biostimulation, well after the onset of sulfate reduction at ~30 days. Sequestered uranium was essentially all U(IV) resulting from the formation of nano-particulate uraninite that coated sediment grains to a thickness of a few 10’s of microns, sometimes in association with S and Fe. A multicomponent biogeochemical reactive transport model simulation of column effluents during biostimulation was generally able to describe the acetate oxidation, iron, sulfate, and uranium reduction for all three columns using parameters derived from simulations of field scale biostimulation experiments. Columns were eluted with artificial groundwater at equilibrium with atmospheric oxygen to simulate the upper limit of dissolved oxygen in recharge water. Overall about 9% of total uranium removed from solution during biostimulation was remobilized. Release of U during oxic elution was a continuous process over 140 days with dissolved uranium concentrations about 0.2 and 0.8 aM for columns with and without ferrous iron addition, respectively. Uranium remaining on the sediment was in the reduced form. The prolonged period of biostimulation and concomitant sulfate reduction appears to limit the rate of U(IV) oxidative remobilization in contrast to a large release observed for columns in previous studies that did not undergo sulfate reduction. Although continued sulfate reduction may cause decreased permeability from precipitation of iron sulfide, the greater apparent stability of the sequestered U(IV) provided by the sustained biostimulation should be considered in design of field scale remediation efforts. Remobilization of uranium following biostimulated reduction should be tested further at the field scale.

Column studies to assess the effects of climate variables on redox processes during riverbank filtration.

PubMed

Rudolf von Rohr, Matthias; Hering, Janet G; Kohler, Hans-Peter E; von Gunten, Urs

2014-09-15

Riverbank filtration is an established technique used world-wide to produce clean drinking water in a reliable and cost-efficient way. This practice is, however, facing new challenges posed by climate change, as already observed during past heat waves with the local occurrence of anoxic conditions. In this study we investigated the effect of direct (temperature) and indirect (dissolved organic matter (DOM) concentration and composition, flow rate) climate change variables on redox processes (aerobic respiration, denitrification and Mn(III/IV)/Fe(III) reduction) by means of column experiments. Natural river water, modified river water and river water mixed with treated wastewater effluent were used as feed waters for the columns filled with natural sand from a river-infiltration system in Switzerland. Biodegradable dissolved organic matter was mainly removed immediately at the column inlet and particulate organic matter (POM) associated with the natural sand was the main electron donor for aerobic respiration throughout the column. Low infiltration rates (≤0.01 m/h) enhanced the oxygen consumption leading to anoxic conditions. DOM consumption did not seem to be sensitive to temperature, although oxygen consumption (i.e., associated with POM degradation) showed a strong temperature dependence with an activation energy of ∼70 kJmol(-1). Anoxic conditions developed at 30 °C with partial denitrification and formation of nitrite and ammonium. In absence of oxygen and nitrate, Mn(II) was mobilized at 20 °C, highlighting the importance of nitrate acting as a redox buffer under anoxic conditions preventing the reductive dissolution of Mn(III/IV)(hydr)oxides. Reductive dissolution of Fe(III)(hydr)oxides was not observed under these conditions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Novel mesoporous MnCo2O4 nanorods as oxygen reduction catalyst at neutral pH in microbial fuel cells.

PubMed

Kumar, Ravinder; Singh, Lakhveer; Wahid, Zularisam Ab; Mahapatra, Durga Madhab; Liu, Hong

2018-04-01

The aim of this work was to evaluate the comparative performance of hybrid metal oxide nanorods i.e. MnCo 2 O 4 nanorods (MCON) and single metal oxide nanorods i.e. Co 3 O 4 nanorods (CON) as oxygen reduction catalyst in microbial fuel cells (MFC). Compared to the single metal oxide, the hybrid MCON exhibited a higher BET surface area and provided additional positively charged ions, i.e., Co 2+ /Co 3+ and Mn 3+ /Mn 4+ on its surfaces, which increased the electro-conductivity of the cathode and improved the oxygen reduction kinetics significantly, achieved an i o of 6.01 A/m 2 that was 12.4% higher than CON. Moreover, the porous architecture of MCON facilitated the diffusion of electrolyte, reactants and electrons during the oxygen reduction, suggested by lower diffusion (R d ), activation (R act ) and ohmic resistance (R ohm ) values. This enhanced oxygen reduction by MCON boosted the power generation in MFC, achieving a maximum power density of 587 mW/m 2 that was ∼29% higher than CON. Published by Elsevier Ltd.

Nitrogen-doped graphdiyne as a metal-free catalyst for high-performance oxygen reduction reactions

NASA Astrophysics Data System (ADS)

Liu, Rongji; Liu, Huibiao; Li, Yuliang; Yi, Yuanping; Shang, Xinke; Zhang, Shuangshuang; Yu, Xuelian; Zhang, Suojiang; Cao, Hongbin; Zhang, Guangjin

2014-09-01

Fuel cells and metal-air batteries will only become widely available in everyday life when the expensive platinum-based electrocatalysts used for the oxygen reduction reactions are replaced by other efficient, low-cost and stable catalysts. We report here the use of nitrogen-doped graphdiyne as a metal-free electrode with a comparable electrocatalytic activity to commercial Pt/C catalysts for the oxygen reduction reaction in alkaline fuel cells. Nitrogen-doped graphdiyne has a better stability and increased tolerance to the cross-over effect than conventional Pt/C catalysts.Fuel cells and metal-air batteries will only become widely available in everyday life when the expensive platinum-based electrocatalysts used for the oxygen reduction reactions are replaced by other efficient, low-cost and stable catalysts. We report here the use of nitrogen-doped graphdiyne as a metal-free electrode with a comparable electrocatalytic activity to commercial Pt/C catalysts for the oxygen reduction reaction in alkaline fuel cells. Nitrogen-doped graphdiyne has a better stability and increased tolerance to the cross-over effect than conventional Pt/C catalysts. Electronic supplementary information (ESI) available: Detailed RDE and RRDE experiments, additional tables and figures. See DOI: 10.1039/c4nr03185g

A novel differential electrochemical mass spectrometry method to determine the product distribution from parasitic Methanol oxidation reaction on oxygen reduction reaction catalysts

NASA Astrophysics Data System (ADS)

Jurzinsky, Tilman; Kurzhals, Philipp; Cremers, Carsten

2018-06-01

The oxygen reduction reaction is in research focus since several decades due to its importance for the overall fuel cell performance. In direct methanol fuel cells, the crossover of methanol and its subsequent parasitic oxidation are main issues when it comes to preventing fuel cell performance losses. In this work, we present a novel differential electrochemical mass spectrometry method to evaluate oxygen reduction reaction catalysts on their tolerance to methanol being present at the cathode. Besides this, the setup allows to measure under more realistic fuel cell conditions than typical rotating disc electrode measurements, because the oxygen reduction reaction is evaluated in gaseous phase and a gas diffusion electrode is used as working electrode. Due to the new method, it was possible to investigate the oxygen reduction reaction on two commonly used catalysts (Pt/C and Pt3Co/C) in absence and presence of methanol. It was found, that Pt3Co/C is less prone to parasitic current losses due to methanol oxidation reaction. By connecting a mass spectrometer to the electrochemical cell, the new method allows to determine the products formed on the catalysts due to parasitic methanol electrooxidation.

F-centers mechanism of long-term relaxation in lead zirconate-titanate based piezoelectric ceramics. 2. After-field relaxation

NASA Astrophysics Data System (ADS)

Ishchuk, V. M.; Kuzenko, D. V.

2016-08-01

The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O3 based solid solutions (PZT) after action of external DC electric field. The said process is a long-term one and is described by the logarithmic function of time. Reversible and nonreversible relaxation process takes place depending on the field intensity. The relaxation rate depends on the field strength also, and the said dependence has nonlinear and nonmonotonic form, if external field leads to domain disordering. The oxygen vacancies-based model for description of the long-term relaxation processes is suggested. The model takes into account the oxygen vacancies on the sample's surface ends, their conversion into F+- and F0-centers under external effects and subsequent relaxation of these centers into the simple oxygen vacancies after the action termination. F-centers formation leads to the violation of the original sample's electroneutrality, and generate intrinsic DC electric field into the sample. Relaxation of F-centers is accompanied by the reduction of the electric field, induced by them, and relaxation of the dielectric constant, as consequent effect.

Flexible nitrogen-doped graphene/carbon nanotube/Co3O4 paper and its oxygen reduction activity

NASA Astrophysics Data System (ADS)

Li, Shan-Shan; Cong, Huai-Ping; Wang, Ping; Yu, Shu-Hong

2014-06-01

Due to the demand of an efficient, inexpensive and scalable synthesis of oxygen reduction reaction (ORR) catalyst for practical application in fuel cell, we demonstrate a facile strategy to fabricate the flexible nitrogen-doped graphene/carbon nanotube/Co3O4 (NG/CNT/Co3O4) paper catalyst. In the hydrothermal process, the in situ formation of Co3O4 nanoparticles, reduction of GO and doping of nitrogen species occur simultaneously in the assembled paper in ammonia solution. Because of the synergistic effects of three active components and the spacing effect of CNTs and Co3O4 nanoparticles on avoiding the re-aggregation of assembled graphene nanosheets, the free-standing NG/CNT/Co3O4 paper exhibits an enhanced ORR catalytic performance with stable durability and strong methanol-tolerant capability, indicating promising potential as ORR electrocatalyst in practical applications.Due to the demand of an efficient, inexpensive and scalable synthesis of oxygen reduction reaction (ORR) catalyst for practical application in fuel cell, we demonstrate a facile strategy to fabricate the flexible nitrogen-doped graphene/carbon nanotube/Co3O4 (NG/CNT/Co3O4) paper catalyst. In the hydrothermal process, the in situ formation of Co3O4 nanoparticles, reduction of GO and doping of nitrogen species occur simultaneously in the assembled paper in ammonia solution. Because of the synergistic effects of three active components and the spacing effect of CNTs and Co3O4 nanoparticles on avoiding the re-aggregation of assembled graphene nanosheets, the free-standing NG/CNT/Co3O4 paper exhibits an enhanced ORR catalytic performance with stable durability and strong methanol-tolerant capability, indicating promising potential as ORR electrocatalyst in practical applications. Electronic supplementary information (ESI) available: XRD patterns, elemental mapping images, DSC-TGA curves and XPS spectrum of NG/CNT/Co3O4 paper; SEM images and XPS spectra of NG/Co3O4 paper; RDE curves and corresponding K-L plots of different catalysts. See DOI: 10.1039/c4nr02101k

X-ray diffraction and TGA kinetic analyses for chemical looping combustion applications.

PubMed

Tijani, Mansour Mohammedramadan; Aqsha, Aqsha; Mahinpey, Nader

2018-04-01

Synthesis and characterization of supported metal-based oxygen carriers were carried out to provide information related to the use of oxygen carriers for chemical looping combustion processes. The Cu, Co, Fe, Ni metals supported with Al 2 O 3 , CeO 2 , TiO 2 , ZrO 2 were prepared using the wetness impregnation technique. Then, the X-ray Diffraction (XRD) characterization of oxidized and reduced samples was obtained and presented. The kinetic analysis using Thermogravimetric analyzer (TGA) of the synthesized samples was conducted. The kinetics of reduction reaction of all samples were estimated and explained.

Tracking photosynthetic sulfide oxidation in a meromictic lake using sulfate δ34S and δ18O

NASA Astrophysics Data System (ADS)

Gilhooly, W. P.; Reinhard, C.; Lyons, T. W.; Glass, J. B.

2012-12-01

Phototrophic sulfur bacteria oxidize sulfide and fix carbon dioxide in the presence of sunlight without producing oxygen. Environmental conditions in the Paleo- and Mesoproterozoic, when atmospheric oxygen concentrations were at low levels and portions of the oceans were anoxic and sulfidic (euxinic), were conducive to widespread carbon fixation by anoxygenic photosynthesis. This pathway may have helped sustain euxinic conditions in the Proterozoic water column. With limited organic biomarker and geochemical evidence for widespread production of anoxygenic phototrophs, however, additional proxies are needed to fingerprint paleoecological and biogeochemical signals associated with photic zone euxinia. Paired δ34S and δ18O from ancient sulfates (gypsum, barite, or CAS) may offer an added constraint on the history and ecological dominance of photosynthetic S-oxidation. Sulfate-oxygen can fractionate during sulfate reduction, but the extent of isotopic enrichment is controlled either by kinetic isotope effects imparted during intracellular enzymatic steps or equilibrium oxygen exchange with ambient water. An improved understanding of these processes can be gained from modern natural environments. Mahoney Lake is a density-stratified lake located within the White Lake Basin of British Columbia. The euxinic water column supports a dense plate of purple sulfur bacteria (Amoebobacter purpureus) that thrives where free sulfide intercepts the photic zone at ~7 m water depth. We analyzed the isotopic composition of sulfate (δ34SSO4 and δ18OSO4), sulfide (δ34SH2S), and water (δ18OH2O) to track the potentially coupled processes of dissimilatory sulfate reduction and phototrophic sulfide oxidation within this meromictic lake. Large isotopic offsets observed between sulfate and sulfide within the monimolimnion (δ34SSO4-H2S = 51‰) and within pore waters along the oxic margin (δ34SSO4-H2S >50‰) are consistent with sulfate reduction in both the sediments and the anoxic water column. Given the high sulfide concentrations of the lake ([H2S] = 30 mM), sulfur disproportionation is likely inoperable, and so the large instantaneous fractionations are best explained by single-step sulfate reduction. The offset between sulfate and sulfide decreases at the chemocline (δ34SSO4-H2S = 37‰), a trend possibly explained by sulfide oxidation or decreasing sulfate reduction rates. Sulfate exhibits a curvilinear response in δ18OSO4/δ34SSO4 that approaches δ18OSO4 values (~24-33‰) in equilibrium with ambient water (δ18OH2O = -2.2‰). Although an inverse relationship between δ18OSO4/δ18OH2O is inconsistent with chemical sulfide oxidation (typically a positive relationship), fine-scale variations in δ34SSO4 and δ18OSO4 at the chemocline imply sulfate reduction coupled with near quantitative reoxidation by A. purpureus. Although observed within the microbial plate, this photosynthetic S-bacteria biosignature is restricted to the oxic/anoxic transition zone and is apparently swamped by the more prevalent process of sulfate reduction operative throughout the anoxic water column and sediment pore waters.

Increased Oxygen Recovery from Sabatier Systems Using Plasma Pyrolysis Technology and Metal Hydride Separation

NASA Technical Reports Server (NTRS)

Greenwood, Zachary W.; Abney, Morgan B.; Perry, Jay L.; Miller, Lee A.; Dahl, Roger W.; Hadley, Neal M.; Wambolt, Spencer R.; Wheeler, Richard R.

2015-01-01

State-of-the-art life support carbon dioxide (CO2) reduction technology is based on the Sabatier reaction where less than 50% of the oxygen required for the crew is recovered from metabolic CO2. The reaction produces water as the primary product and methane as a byproduct. Oxygen recovery is constrained by the limited availability of reactant hydrogen. This is further exacerbated when Sabatier methane (CH4) is vented as a waste product resulting in a continuous loss of reactant hydrogen. Post-processing methane with the Plasma Pyrolysis Assembly (PPA) to recover hydrogen has the potential to dramatically increase oxygen recovery and thus drastically reduce the logistical challenges associated with oxygen resupply. The PPA decomposes methane into predominantly hydrogen and acetylene. Due to the highly unstable nature of acetylene, a separation system is necessary to purify hydrogen before it is recycled back to the Sabatier reactor. Testing and evaluation of a full-scale Third Generation PPA is reported and investigations into metal hydride hydrogen separation technology is discussed.

Aquaporins-2 and -4 regulate glycogen metabolism and survival during hyposmotic-anoxic stress in Caenorhabditis elegans

PubMed Central

LaMacchia, John C.

2015-01-01

Periods of oxygen deprivation can lead to ion and water imbalances in affected tissues that manifest as swelling (edema). Although oxygen deprivation-induced edema is a major contributor to injury in clinical ischemic diseases such as heart attack and stroke, the pathophysiology of this process is incompletely understood. In the present study we investigate the impact of aquaporin-mediated water transport on survival in a Caenorhabditis elegans model of edema formation during complete oxygen deprivation (anoxia). We find that nematodes lacking aquaporin water channels in tissues that interface with the surrounding environment display decreased edema formation and improved survival rates in anoxia. We also find that these animals have significantly reduced demand for glycogen as an energetic substrate during anoxia. Together, our data suggest that reductions in membrane water permeability may be sufficient to induce a hypometabolic state during oxygen deprivation that reduces injury and extends survival limits. PMID:26017147

Lunar oxygen production by pyrolysis of regolith

NASA Technical Reports Server (NTRS)

Senior, Constance L.

1991-01-01

Oxygen represents one of the most desirable products of lunar mining and manufacturing. Among the many processes which have been proposed for oxygen production, pyrolysis stands out as one which is uncomplicated and easy to bootstrap. Pyrolysis or vapor-phase reduction involves heating regolith to temperatures sufficient to allow partial decomposition and vaporization. Some metal oxides give up oxygen upon heating, either in the gas phase to form reduced gaseous species or in the condensed phase to form a metallic phase. Based on preliminary experiments and equilibrium calculations, the temperatures needed for pyrolysis are expected to be in the range of 2000 to 2200 K, giving total gas pressures of 0.001 to 0.1 torr. Bulk regolith can be used as a feedstock without beneficiation with concentrated solar radiation supplying most of energy needed. Further, selective condensation of metal-containing species from the gas phase may yield metallic iron and silicon as byproducts.

Investigation of surface potentials in reduced graphene oxide flake by Kelvin probe force microscopy

NASA Astrophysics Data System (ADS)

Negishi, Ryota; Takashima, Kai; Kobayashi, Yoshihiro

2018-06-01

The surface potential (SP) of reduced graphene oxide (rGO) flakes prepared by thermal treatments of GO under several conditions was analyzed by Kelvin probe force microscopy. The low-crystalline rGO flakes in which a significant amount of oxygen functional groups and structural defects remain have a much lower SP than mechanically exfoliated graphene free from oxygen and defects. On the other hand, the highly crystalline rGO flake after a thermal treatment for the efficient removal of oxygen functional groups and healing of structural defects except for domain boundary shows SP equivalent to that of the mechanically exfoliated graphene. These results indicate that the work function of rGO is sensitively modulated by oxygen functional groups and structural defects remaining after the thermal reduction process, but is not affected significantly by the domain boundary remaining after the healing of structural defects through the thermal treatment at high temperature.

Proton enhanced dynamic battery chemistry for aprotic lithium-oxygen batteries.

PubMed

Zhu, Yun Guang; Liu, Qi; Rong, Yangchun; Chen, Haomin; Yang, Jing; Jia, Chuankun; Yu, Li-Juan; Karton, Amir; Ren, Yang; Xu, Xiaoxiong; Adams, Stefan; Wang, Qing

2017-02-06

Water contamination is generally considered to be detrimental to the performance of aprotic lithium-air batteries, whereas this view is challenged by recent contrasting observations. This has provoked a range of discussions on the role of water and its impact on batteries. In this work, a distinct battery chemistry that prevails in water-contaminated aprotic lithium-oxygen batteries is revealed. Both lithium ions and protons are found to be involved in the oxygen reduction and evolution reactions, and lithium hydroperoxide and lithium hydroxide are identified as predominant discharge products. The crystallographic and spectroscopic characteristics of lithium hydroperoxide monohydrate are scrutinized both experimentally and theoretically. Intriguingly, the reaction of lithium hydroperoxide with triiodide exhibits a faster kinetics, which enables a considerably lower overpotential during the charging process. The battery chemistry unveiled in this mechanistic study could provide important insights into the understanding of nominally aprotic lithium-oxygen batteries and help to tackle the critical issues confronted.

Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials

DOE PAGES

Lee, Jinhyuk; Papp, Joseph K.; Clément, Raphaële J.; ...

2017-10-17

Recent progress in the understanding of percolation theory points to cation-disordered lithium-excess transition metal oxides as high-capacity lithium-ion cathode materials. Nevertheless, the oxygen redox processes required for these materials to deliver high capacity can trigger oxygen loss, which leads to the formation of resistive surface layers on the cathode particles. Here, we demonstrate here that, somewhat surprisingly, fluorine can be incorporated into the bulk of disordered lithium nickel titanium molybdenum oxides using a standard solid-state method to increase the nickel content, and that this compositional modification is very effective in reducing oxygen loss, improving energy density, average voltage, and ratemore » performance. We argue that the valence reduction on the anion site, offered by fluorine incorporation, opens up significant opportunities for the design of high-capacity cation-disordered cathode materials.« less

Self-Calibrating Pressure Transducer

NASA Technical Reports Server (NTRS)

Lueck, Dale E. (Inventor)

2006-01-01

A self-calibrating pressure transducer is disclosed. The device uses an embedded zirconia membrane which pumps a determined quantity of oxygen into the device. The associated pressure can be determined, and thus, the transducer pressure readings can be calibrated. The zirconia membrane obtains oxygen .from the surrounding environment when possible. Otherwise, an oxygen reservoir or other source is utilized. In another embodiment, a reversible fuel cell assembly is used to pump oxygen and hydrogen into the system. Since a known amount of gas is pumped across the cell, the pressure produced can be determined, and thus, the device can be calibrated. An isolation valve system is used to allow the device to be calibrated in situ. Calibration is optionally automated so that calibration can be continuously monitored. The device is preferably a fully integrated MEMS device. Since the device can be calibrated without removing it from the process, reductions in costs and down time are realized.

Restorative effect of oxygen annealing on device performance in HfIZO thin-film transistors

NASA Astrophysics Data System (ADS)

Ha, Tae-Jun

2015-03-01

Metal-oxide based thin-film transistors (oxide-TFTs) are very promising for use in next generation electronics such as transparent displays requiring high switching and driving performance. In this study, we demonstrate an optimized process to secure excellent device performance with a favorable shift of the threshold voltage toward 0V in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs by using post-treatment with oxygen annealing. This enhancement results from the improved interfacial characteristics between gate dielectric and semiconductor layers due to the reduction in the density of interfacial states related to oxygen vacancies afforded by oxygen annealing. The device statistics confirm the improvement in the device-to-device and run-to-run uniformity. We also report on the photo-induced stability in such oxide-TFTs against long-term UV irradiation, which is significant for transparent displays.

One-Dimensional RuO2/Mn2O3 Hollow Architectures as Efficient Bifunctional Catalysts for Lithium-Oxygen Batteries.

PubMed

Yoon, Ki Ro; Lee, Gil Yong; Jung, Ji-Won; Kim, Nam-Hoon; Kim, Sang Ouk; Kim, Il-Doo

2016-03-09

Rational design and massive production of bifunctional catalysts with fast oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics are critical to the realization of highly efficient lithium-oxygen (Li-O2) batteries. Here, we first exploit two types of double-walled RuO2 and Mn2O3 composite fibers, i.e., (i) phase separated RuO2/Mn2O3 fiber-in-tube (RM-FIT) and (ii) multicomposite RuO2/Mn2O3 tube-in-tube (RM-TIT), by controlling ramping rate during electrospinning process. Both RM-FIT and RM-TIT exhibited excellent bifunctional electrocatalytic activities in alkaline media. The air electrodes using RM-FIT and RM-TIT showed enhanced overpotential characteristics and stable cyclability over 100 cycles in the Li-O2 cells, demonstrating high potential as efficient OER and ORR catalysts.

Proton enhanced dynamic battery chemistry for aprotic lithium–oxygen batteries

PubMed Central

Zhu, Yun Guang; Liu, Qi; Rong, Yangchun; Chen, Haomin; Yang, Jing; Jia, Chuankun; Yu, Li-Juan; Karton, Amir; Ren, Yang; Xu, Xiaoxiong; Adams, Stefan; Wang, Qing

2017-01-01

Water contamination is generally considered to be detrimental to the performance of aprotic lithium–air batteries, whereas this view is challenged by recent contrasting observations. This has provoked a range of discussions on the role of water and its impact on batteries. In this work, a distinct battery chemistry that prevails in water-contaminated aprotic lithium–oxygen batteries is revealed. Both lithium ions and protons are found to be involved in the oxygen reduction and evolution reactions, and lithium hydroperoxide and lithium hydroxide are identified as predominant discharge products. The crystallographic and spectroscopic characteristics of lithium hydroperoxide monohydrate are scrutinized both experimentally and theoretically. Intriguingly, the reaction of lithium hydroperoxide with triiodide exhibits a faster kinetics, which enables a considerably lower overpotential during the charging process. The battery chemistry unveiled in this mechanistic study could provide important insights into the understanding of nominally aprotic lithium–oxygen batteries and help to tackle the critical issues confronted. PMID:28165008

Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials

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

Lee, Jinhyuk; Papp, Joseph K.; Clément, Raphaële J.

Recent progress in the understanding of percolation theory points to cation-disordered lithium-excess transition metal oxides as high-capacity lithium-ion cathode materials. Nevertheless, the oxygen redox processes required for these materials to deliver high capacity can trigger oxygen loss, which leads to the formation of resistive surface layers on the cathode particles. Here, we demonstrate here that, somewhat surprisingly, fluorine can be incorporated into the bulk of disordered lithium nickel titanium molybdenum oxides using a standard solid-state method to increase the nickel content, and that this compositional modification is very effective in reducing oxygen loss, improving energy density, average voltage, and ratemore » performance. We argue that the valence reduction on the anion site, offered by fluorine incorporation, opens up significant opportunities for the design of high-capacity cation-disordered cathode materials.« less

Effect of diluted and preheated oxidizer on the emission of methane flameless combustion

NASA Astrophysics Data System (ADS)

Hosseini, Seyed Ehsan; Salehirad, Saber; Wahid, M. A.; Sies, Mohsin Mohd; Saat, Aminuddin

2012-06-01

In combustion process, reduction of emissions often accompanies with output efficiency reduction. It means, by using current combustion technique it is difficult to obtainlow pollution and high level of efficiency in the same time. In new combustion system, low NOxengines and burners are studied particularly. Recently flameless or Moderate and Intensive Low oxygen Dilution (MILD) combustion has received special attention in terms of low harmful emissions and low energy consumption. Behavior of combustion with highly preheated air was analyzed to study the change of combustion regime and the reason for the compatibility of high performance and low NOx production. Sustainability of combustion under low oxygen concentration was examined when; the combustion air temperature was above the self-ignition temperature of the fuel. This paper purposes to analyze the NOx emission quantity in conventional combustion and flameless combustion by Chemical Equilibrium with Applications (CEA) software.

Uric acid-derived Fe3C-containing mesoporous Fe/N/C composite with high activity for oxygen reduction reaction in alkaline medium

NASA Astrophysics Data System (ADS)

Ma, Jun; Xiao, Dejian; Chen, Chang Li; Luo, Qiaomei; Yu, Yue; Zhou, Junhao; Guo, Changding; Li, Kai; Ma, Jie; Zheng, Lirong; Zuo, Xia

2018-02-01

In this work, a category of Fe3C-containing Fe/N/C mesoporous material has been fabricated by carbonizing the mixture of uric acid, Iron (Ⅲ) chloride anhydrous and carbon support (XC-72) under different pyrolysis temperature. Of all these samples, pyrolysis temperature (800 °C) becomes the most crucial factor in forming Fe3C active sites which synergizes with high content of graphitic N to catalyze oxygen reduction reaction (ORR). X-ray absorption fine structure spectroscopy (XAFS) is used to exhibit that the space structure around Fe atoms in the catalyst. This kind of catalyst possesses comparable ORR properties with commercial 20% Pt/C (onset potential is 0 V vs. Ag/AgCl in 0.1 M KOH), the average transfer electron number is 3.84 reflecting the 4-electron process. Moreover, superior stability and methanol tolerance deserve to be mentioned.

Passive Biobarrier for Treating Co-mingled Perchlorate and RDX in Groundwater at an Active Range

DTIC Science & Technology

2016-05-12

and Groundwater Temperature ............................. 102 6.1.2 Dissolved Oxygen (DO) and Oxidation Reduction Potential (ORP...22 or equivalent). Parameters, including temperature , conductivity, dissolved oxygen , oxidation-reduction potential (ORP), turbidity, and pH were...3% for temperature and specific conductivity, and ᝺% for dissolved oxygen , ORP, and turbidity. When parameters were stable according to the above

Electrocatalysis of fuel cell reactions: Investigation of alternate electrolytes

NASA Technical Reports Server (NTRS)

Chin, D. T.; Hsueh, K. L.; Chang, H. H.

1984-01-01

Oxygen reduction and transport properties of the electrolyte in the phosphoric acid fuel cell are studied. The areas covered were: (1) development of a theoretical expression for the rotating ring disk electrode technique; (2) determination of the intermediate reaction rate constants for oxygen reduction on platinum in phosphoric acid electrolyte; (3) determination of oxygen reduction mechanism in trifluoreomethanesulfonic acid (TFMSA) which was considered as an alternate electrolyte for the acid fuel cells; and (4) the measurement of transport properties of the phosphoric acid electrolyte at high concentrations and temperatures.

Boron and oxygen-codoped porous carbon as efficient oxygen reduction catalysts

NASA Astrophysics Data System (ADS)

Lei, Zhidan; Chen, Hongbiao; Yang, Mei; Yang, Duanguang; Li, Huaming

2017-12-01

A low-cost boron- and oxygen-codoped porous carbon electrocatalyst towards oxygen reduction reaction (ORR) has been fabricated by a facile one-step pyrolysis approach, while a boron- and oxygen-rich polymer network was used as precursor. The boron- and oxygen-codoped carbon catalyst with high ORR electrocatalytic activity is comparable to that of Pt/C and is superior to that of catalysts doped solely with boron atoms or with oxygen atoms. Furthermore, the optimized boron- and oxygen-codoped carbon catalyst possesses excellent methanol tolerance and long-term durability in alkaline media. The high electrocatalytic activity of the dual-doped carbon catalysts can be attributed to the synergistic effects of high surface area, predominant mesostructure, abundant active oxygen-containing groups, and effective boron doping. The present results show that this boron- and oxygen-codoping strategy could be as a promising way for the preparation of highly efficient ORR catalysts.

Oxygen extraction from lunar soil by fluorination

NASA Technical Reports Server (NTRS)

Seboldt, W.; Lingner, S.; Hoernes, S.; Grimmeisen, W.

1991-01-01

Mining and processing of lunar material could possibly lead to more cost-efficient scenarios for permanent presence of man in space and on the Moon. Production of oxygen for use as propellant seems especially important. Different candidate processes for oxygen-extraction from lunar soil were proposed, of which the reduction of ilmenite by hydrogen was studied most. This process, however, needs the concentration of ilmenite from lunar regolith to a large extent and releases oxygen only with low efficiency. Another possibility - the fluorination method - which works with lunar bulk material as feedstock is discussed. Liberation of oxygen from silicate or oxide materials by fluorination methods has been applied in geoscience since the early sixties. The fact that even at moderate temperatures 98 to 100 percent yields can be attained, suggests that fluorination of lunar regolith could be an effective way of propellant production. Lunar soil contains about 50 percent oxygen by weight which is gained nearly completely through this process as O2 gas. The second-most element Si is liberated as gaseous SiF4. It could be used for production of Si-metal and fluorine-recycling. All other main elements of lunar soil will be converted into solid fluorides which also can be used for metal-production and fluorine-recycling. Preliminary results of small scale experiments with different materials are discussed, giving information on specific oxygen-yields and amounts of by-products as functions of temperature. These experiments were performed with an already existing fluorine extraction and collection device at the University of Bonn, normally used for determination of oxygen-isotopic abundances. Optimum conditions, especially concerning energy consumption, are investigated. Extrapolation of the experimental results to large industrial-type plants on the Moon is tried and seems to be promising at first sight. The recycling of the fluorine is, however, crucial for the process. It might be achieved by means of electrolysis. This needs further investigation. The technical problem of transport and handling of the toxic and corrosive fluorine seems to be solvable and could be done by inert storage vessels.

Electrochemical Reduction of Oxygen in Aprotic Ionic Liquids Containing Metal Cations: A Case Study on the Na-O2 system.

PubMed

Azaceta, Eneko; Lutz, Lukas; Grimaud, Alexis; Vicent-Luna, Jose Manuel; Hamad, Said; Yate, Luis; Cabañero, German; Grande, Hans-Jurgen; Anta, Juan A; Tarascon, Jean-Marie; Tena-Zaera, Ramon

2017-04-10

Metal-air batteries are intensively studied because of their high theoretical energy-storage capability. However, the fundamental science of electrodes, electrolytes, and reaction products still needs to be better understood. In this work, the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was chosen to study the influence of a wide range of metal cations (M n+ ) on the electrochemical behavior of oxygen. The relevance of the theory of Lewis hard and soft acids and bases to predict satisfactorily the reduction potential of oxygen in electrolytes containing metal cations is demonstrated. Systems with soft and intermediate M n+ acidity are shown to facilitate oxygen reduction and metal oxide formation, whereas oxygen reduction is hampered by hard acid cations such as sodium and lithium. Furthermore, DFT calculations on the energy of formation of the resulting metal oxides rationalize the effect of M n+ on oxygen reduction. A case study on the Na-O 2 system is described in detail. Among other things, the Na + concentration of the electrolyte is shown to control the electrochemical pathway (solution precipitation vs. surface deposition) by which the discharge product grows. All in all, fundamental insights for the design of advanced electrolytes for metal-air batteries, and Na-air batteries in particular, are provided. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Green Synthesis of Three-Dimensional Hybrid N-Doped ORR Electro-Catalysts Derived from Apricot Sap

PubMed Central

Karunagaran, Ramesh; Coghlan, Campbell; Gulati, Karan; Tung, Tran Thanh; Doonan, Christian

2018-01-01

Rapid depletion of fossil fuel and increased energy demand has initiated a need for an alternative energy source to cater for the growing energy demand. Fuel cells are an enabling technology for the conversion of sustainable energy carriers (e.g., renewable hydrogen or bio-gas) into electrical power and heat. However, the hazardous raw materials and complicated experimental procedures used to produce electro-catalysts for the oxygen reduction reaction (ORR) in fuel cells has been a concern for the effective implementation of these catalysts. Therefore, environmentally friendly and low-cost oxygen reduction electro-catalysts synthesised from natural products are considered as an attractive alternative to currently used synthetic materials involving hazardous chemicals and waste. Herein, we describe a unique integrated oxygen reduction three-dimensional composite catalyst containing both nitrogen-doped carbon fibers (N-CF) and carbon microspheres (N-CMS) synthesised from apricot sap from an apricot tree. The synthesis was carried out via three-step process, including apricot sap resin preparation, hydrothermal treatment, and pyrolysis with a nitrogen precursor. The nitrogen-doped electro-catalysts synthesised were characterised by SEM, TEM, XRD, Raman, and BET techniques followed by electro-chemical testing for ORR catalysis activity. The obtained catalyst material shows high catalytic activity for ORR in the basic medium by facilitating the reaction via a four-electron transfer mechanism. PMID:29382103

Green Synthesis of Three-Dimensional Hybrid N-Doped ORR Electro-Catalysts Derived from Apricot Sap.

PubMed

Karunagaran, Ramesh; Coghlan, Campbell; Shearer, Cameron; Tran, Diana; Gulati, Karan; Tung, Tran Thanh; Doonan, Christian; Losic, Dusan

2018-01-28

Rapid depletion of fossil fuel and increased energy demand has initiated a need for an alternative energy source to cater for the growing energy demand. Fuel cells are an enabling technology for the conversion of sustainable energy carriers (e.g., renewable hydrogen or bio-gas) into electrical power and heat. However, the hazardous raw materials and complicated experimental procedures used to produce electro-catalysts for the oxygen reduction reaction (ORR) in fuel cells has been a concern for the effective implementation of these catalysts. Therefore, environmentally friendly and low-cost oxygen reduction electro-catalysts synthesised from natural products are considered as an attractive alternative to currently used synthetic materials involving hazardous chemicals and waste. Herein, we describe a unique integrated oxygen reduction three-dimensional composite catalyst containing both nitrogen-doped carbon fibers (N-CF) and carbon microspheres (N-CMS) synthesised from apricot sap from an apricot tree. The synthesis was carried out via three-step process, including apricot sap resin preparation, hydrothermal treatment, and pyrolysis with a nitrogen precursor. The nitrogen-doped electro-catalysts synthesised were characterised by SEM, TEM, XRD, Raman, and BET techniques followed by electro-chemical testing for ORR catalysis activity. The obtained catalyst material shows high catalytic activity for ORR in the basic medium by facilitating the reaction via a four-electron transfer mechanism.

Enhanced performance of microbial fuel cell with in situ preparing dual graphene modified bioelectrode.

PubMed

Chen, Junfeng; Hu, Yongyou; Tan, Xiaojun; Zhang, Lihua; Huang, Wantang; Sun, Jian

2017-10-01

This study proposed a three-step method to prepare dual graphene modified bioelectrode (D-GM-BE) by in situ microbial-induced reduction of GO and polarity reversion in microbial fuel cell (MFC). Both graphene modified bioanode (GM-BA) and biocathode (GM-BC) were of 3D graphene/biofilm architectures; the viability and thickness of microbial biofilm decreased compared with control bioelectrode (C-BE). The coulombic efficiency (CE) of GM-BA was 2.1 times of the control bioanode (C-BA), which demonstrated higher rate of substrates oxidation; the relationship between peak current and scan rates data meant that GM-BC was of higher efficiency of catalyzing oxygen reduction than the control biocathode (C-BC). The maximum power density obtained in D-GM-BE MFC was 122.4±6.9mWm -2 , the interfacial charge transfer resistance of GM-BA and GM-BC were decreased by 79% and 75.7%. The excellent electrochemical performance of D-GM-BE MFC was attributed to the enhanced extracellular electron transfer (EET) process and catalyzing oxygen reduction. Copyright © 2017 Elsevier Ltd. All rights reserved.

The role of oxidative stress in the metabolic syndrome.

PubMed

Whaley-Connell, Adam; McCullough, Peter A; Sowers, James R

2011-01-01

Loss of reduction-oxidation (redox) homeostasis and generation of excess free oxygen radicals play an important role in the pathogenesis of diabetes, hypertension, and consequent cardiovascular disease. Reactive oxygen species are integral in routine in physiologic mechanisms. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways that promote impairments in insulin metabolic signaling, reduced endothelial-mediated vasorelaxation, and associated cardiovascular and renal structural and functional abnormalities. Redox control of metabolic function is a dynamic process with reversible pro- and anti-free radical processes. Labile iron is necessary for the catalysis of superoxide anion, hydrogen peroxide, and the generation of the damaging hydroxyl radical. Acute hypoxia and cellular damage in cardiovascular tissue liberate larger amounts of cytosolic and extracellular iron that is poorly liganded; thus, large increases in the generation of oxygen free radicals are possible, causing tissue damage. The understanding of iron and the imbalance of redox homeostasis within the vasculature is integral in hypertension and progression of metabolic dysregulation that contributes to insulin resistance, endothelial dysfunction, and cardiovascular and kidney disease.

Method of controlled reduction of nitroaromatics by enzymatic reaction with oxygen sensitive nitroreductase enzymes

DOEpatents

Shah, Manish M.; Campbell, James A.

1998-01-01

A method for the controlled reduction of nitroaromatic compounds such as nitrobenzene and 2,4,6-trinitrotoluene by enzymatic reaction with oxygen sensitive nitroreductase enzymes, such as ferredoxin NADP oxidoreductase.

Design of N-Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction.

PubMed

Wang, Jing; Huang, Zhengqing; Liu, Wei; Chang, Chunran; Tang, Haolin; Li, Zhijun; Chen, Wenxing; Jia, Chunjiang; Yao, Tao; Wei, Shiqiang; Wu, Yuen; Li, Yadong

2017-12-06

We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (E onset , 1.06 vs 1.03 V) and half-wave potential (E 1/2 , 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H 2 /O 2 and H 2 /air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50 000 cycles for electrode measurement and 100 h for H 2 /air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction.

Electrochemistry suggests proton access from the exit site to the binuclear center in Paracoccus denitrificans cytochrome c oxidase pathway variants.

PubMed

Meyer, Thomas; Melin, Frédéric; Richter, Oliver-M H; Ludwig, Bernd; Kannt, Aimo; Müller, Hanne; Michel, Hartmut; Hellwig, Petra

2015-02-27

Two different pathways through which protons access cytochrome c oxidase operate during oxygen reduction from the mitochondrial matrix, or the bacterial cytoplasm. Here, we use electrocatalytic current measurements to follow oxygen reduction coupled to proton uptake in cytochrome c oxidase isolated from Paracoccus denitrificans. Wild type enzyme and site-specific variants with defects in both proton uptake pathways (K354M, D124N and K354M/D124N) were immobilized on gold nanoparticles, and oxygen reduction was probed electrochemically in the presence of varying concentrations of Zn(2+) ions, which are known to inhibit both the entry and the exit proton pathways in the enzyme. Our data suggest that under these conditions substrate protons gain access to the oxygen reduction site via the exit pathway. Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Oxide nucleation on thin films of copper during in situ oxidation in an electron microscope

NASA Technical Reports Server (NTRS)

Heinemann, K.; Rao, D. B.; Douglass, D. L.

1975-01-01

Single-crystal copper thin films were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of 0.005 torr. Specimens were prepared by epitaxial vapor deposition onto polished faces of rocksalt and were mounted in a hot stage inside the ultrahigh-vacuum chamber of a high-resolution electron microscope. An induction period of roughly 30 min was established which was independent of the film thickness but depended strongly on the oxygen partial pressure and to exposure to oxygen prior to oxidation. Neither stacking faults nor dislocations were found to be associated with the Cu2O nucleation sites. The experimental data, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving the formation of a surface charge layer, oxygen saturation of the metal with formation of a supersaturated zone near the surface, and nucleation followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

In Situ Resource Utilization (ISRU) on the Moon: Moessbauer Spectroscopy as a Process Monitor for Oxygen Production. Results from a Field Test on Mauna Kea Volcano, Hawaii

NASA Technical Reports Server (NTRS)

Morris, R.V.; Schroder, C.; Graff, T.G.; Sanders, G.B.; Lee, K.A.; Simon, T.M.; Larson, W.E.; Quinn, J.W.; Clark, L.D.; Caruso, J.J.

2009-01-01

Essential consumables like oxygen must to be produced from materials on the lunar surface to enable a sustained, long-term presence of humans on the Moon. The Outpost Precursor for ISRU and Modular Architecture (OPTIMA) field test on Mauna Kea, Hawaii, facilitated by the Pacific International Space Center for Exploration Systems (PISCES) of the University of Hawaii at Hilo, was designed to test the implementation of three hardware concepts to extract oxygen from the lunar regolith: Precursor ISRU Lunar Oxygen Testbed (PILOT) developed by Lockheed Martin in Littleton, CO; Regolith & Environmental Science and Oxygen & Lunar Volatiles Extraction (RESOLVE) developed at the NASA Kennedy Space Center in Cape Canaveral, FL; and ROxygen developed at the NASA Johnson Space Center in Houston, TX. The three concepts differ in design, but all rely on the same general principle: hydrogen reduction of metal cations (primarily Fe2+) bonded to oxygen to metal (e.g., Fe0) with the production of water. The hydrogen source is residual hydrogen in the fuel tanks of lunar landers. Electrolysis of the water produces oxygen and hydrogen (which is recycled). We used the miniaturized M ssbauer spectrometer MIMOS II to quantify the yield of this process on the basis of the quantity of Fe0 produced. Iron M ssbauer spectroscopy identifies iron-bearing phases, determines iron oxidation states, and quantifies the distribution of iron between mineral phases and oxidation states. The oxygen yield can be calculated by quantitative measurements of the distribution of Fe among oxidation states in the regolith before and after hydrogen reduction. A M ssbauer spectrometer can also be used as a prospecting tool to select the optimum feedstock for the oxygen production plants (e.g., high total Fe content and easily reduced phases). As a demonstration, a MIMOS II backscatter spectrometer (SPESI, Germany) was mounted on the Cratos rover (NASA Glenn Research Center in Cleveland, OH), which is one of several rover concepts designed to excavate and transfer regolith to the stationary hydrogen reduction plants. Spaceflight versions of the MIMOS II are part of the instrument payloads of NASA s Mars Exploration Rovers and still operating five years after landing on the surface of the planet. MIMOS II was also selected for Phobos-Grunt, a Russian sample return mission to the martian moon Phobos scheduled to launch in 2009, and ESA s ExoMars rover, an exobiology mission scheduled to launch in 2013. An advanced version of the instrument is currently under development. A new detector system with a higher energy resolution will not only reduce the necessary measurement time considerably, but also allow the simultaneous acquisition of an X-ray fluorescence spectrum to determine the elemental composition of samples.

Influence of ultrasound on the heterogeneous Fenton-like oxidation of acetic acid.

PubMed

Cihanoğlu, Aydın; Gündüz, Gönül; Dükkancı, Meral

2017-11-01

The main objective of this study is to investigate the effect of ultrasound on the heterogeneous Fenton-like oxidation of acetic acid, which is one of the most resistant carboxylic acids to oxidation. For this purpose, firstly, the degradation of acetic acid was examined by using ultrasound alone and the effects of different parameters such as: type of sonication system, ultrasonic power, and addition of H 2 O 2 were investigated on the degradation of acetic acid. There was no chemical oxygen demand (COD) reduction in the presence of sonication alone. In the presence of the heterogeneous Fenton-like oxidation process alone, at 303 K, COD reduction reached only 7.1% after 2 h of reaction. However, the combination of the heterogeneous Fenton-like oxidation process with ultrasound increased the COD reduction from 7.1% to 25.5% after 2 h of reaction in an ultrasonic bath operated at 40 kHz, while the COD reduction only increased from 7.1% to 8.9% in the ultrasonic reactor operated at 850 kHz. This result indicates that the hybrid process of ultrasound and heterogeneous Fenton-like oxidation is a promising process to degrade acetic acid.

Solar Concentrator Demonstrator for Lunar Regolith Processing

NASA Technical Reports Server (NTRS)

Fikes, John C.; Howell, Joe T.; Gerrish, Harold P.; Patrick, Stephen L.

2008-01-01

NASA at the Marshall Space Flight Center (MSFC) is building a portable inflatable solar concentrator ground demonstrator for use in testing in-situ resource utilization (ISRU) lunar regolith processing methods. Of primary interest is the production of oxygen as a propellant oxidizer and for life support. There are various processes being proposed for the in-situ reduction of the lunar regolith, the leading processes are hydrogen reduction, carbothermal reduction and vapor phase pyrolysis. The concentrator system being built at MSFC could support demonstrations of all of these processes. The system consists of a light inflatable concentrator that will capture sunlight and focus it onto a receiver inside a vacuum chamber. Inflatable concentrators are good for space based applications due to their low weight and dense packaging at launch. The hexapod design allows the spot size to be increased to reduce the power density if needed for the process being demonstrated. In addition to the hardware development, a comprehensive simulation model is being developed and will be verified and validated using the system hardware. The model will allow for the evaluation of different lunar locations and operational scenarios for the lunar regolith processing with a high confidence in the predicted results.

Oxygenates from Electrochemical Reduction of CO2.

PubMed

Feng, Guanghui; Chen, Wei; Wang, Baiyin; Song, Yanfang; Li, Guihua; Fang, Jianhui; Wei, Wei; Sun, Yuhan

2018-05-29

Electrochemical reduction of carbon dioxide (CO2) driven by renewable electricity to chemicals and fuels is considered as an ideal approach that can alleviate both carbon emission and energy tension stresses. High-value chemicals such as oxygenates can be effectively produced from CO2 electroreduction, which is highly attractive for the great promotion of the economy and applicability of CO2 utilization. This review focuses the recent advancements on the CO2 electrochemical reduction to formic acid, methanol, ethanol, acetic acid, and other oxygenates. The related principles, influence factors, and typical catalysts are summarized. On the basis of the aforementioned discussions, we present the future prospects for further development of CO2 electroreduction to oxygenates. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Treatment of high-strength sulfate wastewater using an autotrophic biocathode in view of elemental sulfur recovery.

PubMed

Blázquez, Enric; Gabriel, David; Baeza, Juan Antonio; Guisasola, Albert

2016-11-15

Treatment of high-strength sulfate wastewaters is becoming a research issue not only for its optimal management but also for the possibility of recovering elemental sulfur. Moreover, sulfate-rich wastewater production is expected to grow due to the increased SO 2 emission contained in flue gases which are treated by chemical absorption in water. Bioelectrochemical systems (BESs) are a promising alternative for sulfate reduction with a lack of electron donor, since hydrogen can be generated in situ from electricity. However, complete sulfate reduction leads to hydrogen sulfide as final sulfur compound. This work is the first to demonstrate that, in addition to an efficient sulfate-rich wastewater treatment, elemental sulfur could be recovered in a biocathode of a BES under oxygen limiting conditions. The key of the process is the biological oxidation of sulfide to elemental sulfur simultaneously to the sulfate reduction in the cathode using the oxygen produced in the anode that diffuses through the membrane. High sulfate reduction rates (up to 388 mg S-SO 4 2-  L -1  d -1 ) were observed linked to a low production of sulfide. Accumulation of elemental sulfur over graphite fibers of the biocathode was demonstrated by energy dispersive spectrometry, discarding the presence of metal sulfides. Microbial community analysis of the cathode biofilm demonstrated the presence of sulfate-reducing bacteria (mainly Desulfovibrio sp.) and sulfide-oxidizing bacteria (mainly Sulfuricurvum sp.). Hence, this biocathode allows simultaneous biological sulfate reduction and biological sulfide oxidation to elemental sulfur, opening up a novel process for recovering sulfur from sulfate-rich wastewaters. Copyright © 2016 Elsevier Ltd. All rights reserved.

Augmented Oxygen-Dependent Killing of Leishmania.

DTIC Science & Technology

1992-06-30

reduction-oxidation cycling drugs: amphotericin B, menadione , and phenazine methosulfate. Promastigotes were exposed to the above drugs under...P02 = 2]..1 kPa) or hyperoxic conditions(P02 - 91.7 kPa). High oxygen tensions did not alter the lethal effects of either menadione or phenazine...effects of high oxygen tensions on the lethal effects of three reduction-oxidation cycling drugs: amphotericin B, menadione , and phenazine

Pneumatic Regolith Transfer Systems for In-Situ Resource Utilization

NASA Technical Reports Server (NTRS)

Mueller, Robert P.; Townsend, Ivan I., III; Mantovani, James G.

2010-01-01

One aspect of In-Situ Resource Utilization (lSRU) in a lunar environment is to extract oxygen and other elements from the minerals that make up the lunar regolith. Typical ISRU oxygen production processes include but are not limited to hydrogen reduction, carbothermal and molten oxide electrolysis. All of these processes require the transfer of regolith from a supply hopper into a reactor for chemical reaction processing, and the subsequent extraction of the reacted regolith from the reactor. This paper will discuss recent activities in the NASA ISRU project involved with developing pneumatic conveying methods to achieve lunar regolith simulant transfer under I-g and 1/6-g gravitational environments. Examples will be given of hardware that has been developed and tested by NASA on reduced gravity flights. Lessons learned and details of pneumatic regolith transfer systems will be examined as well as the relative performance in a 1/6th G environment

δ34S and δ18O of dissolved sulfate as biotic tracer of biogeochemical influences on arsenic mobilization in groundwater in the Hetao Plain, Inner Mongolia, China.

PubMed

Li, M D; Wang, Y X; Li, P; Deng, Y M; Xie, X J

2014-12-01

Environmental isotopology of sulfur and oxygen of dissolved sulfate in groundwater was conducted in the Hetao Plain, northwestern China, aiming to better understand the processes controlling arsenic mobilization in arsenic-rich aqueous systems. A total of 22 groundwater samples were collected from domestic wells in the Hetao Plain. Arsenic concentrations ranged from 11.0 to 388 μg/L. The δ(34)S-SO4 and δ(18)O-SO4 values of dissolved sulfate covered a range from +1.48 to +22.4‰ and +8.17‰ to +14.8‰ in groundwater, respectively. The wide range of δ(34)S-SO4 values reflected either an input of different sources of sulfate, such as gypsum dissolution and fertilizer application, or a modification from biogeochemical process of bacterial sulfate reduction. The positive correlation between δ(34)S-SO4 and arsenic concentrations suggested that bacteria mediated processes played an important role in the mobilization of arsenic. The δ(18)O-SO4 values correlated non-linearly with δ(34)S-SO4, but within a relatively narrow range (+8.17 to +14.8‰), implying that complexities inherent in the sulfate-oxygen (O-SO4(2-)) origins, for instance, water-derived oxygen (O-H2O), molecular oxygen (O-O2) and isotope exchanging with dissolved oxides, are accounted for oxygen isotope composition of dissolved sulfate in groundwater in the Hetao Plain.

Geochemical evidence for cryptic sulfur cycling in salt marsh sediments

NASA Astrophysics Data System (ADS)

Mills, Jennifer V.; Antler, Gilad; Turchyn, Alexandra V.

2016-11-01

Cryptic sulfur cycling is an enigmatic process in which sulfate is reduced to some lower-valence state sulfur species and subsequently quantitatively reoxidized; the rate and microbial energetics of this process and how prevalent it may be in the environment remain controversial. Here we investigate sulfur cycling in salt marsh sediments from Norfolk, England where we observe high ferrous iron concentrations with no depletion of sulfate or change in the sulfur isotope ratio of that sulfate, but a 5‰ increase in the oxygen isotope ratio in sulfate, indicating that sulfate has been through a reductive cycle replacing its oxygen atoms. This cryptic sulfur cycle was replicated in laboratory incubations using 18O-enriched water, demonstrating that the field results do not solely result from mixing processes in the natural environment. Numerical modeling of the laboratory incubations scaled to represent the salt marsh sediments suggests that the uptake rate of sulfate during this cryptic sulfur cycling is similar to the uptake rate of sulfate during the fastest microbial sulfate reduction that has been measured in the natural environment. The difference is that during cryptic sulfur cycling, all of the sulfur is subsequently reoxidized to sulfate. We discuss mechanisms for this pathway of sulfur cycling including the possible link to the subsurface iron cycle.

Decomposition of poly(amide-imide) film enameled on solid copper wire using atmospheric pressure non-equilibrium plasma.

PubMed

Sugiyama, Kazuo; Suzuki, Katsunori; Kuwasima, Shusuke; Aoki, Yosuke; Yajima, Tatsuhiko

2009-01-01

The decomposition of a poly(amide-imide) thin film coated on a solid copper wire was attempted using atmospheric pressure non-equilibrium plasma. The plasma was produced by applying microwave power to an electrically conductive material in a gas mixture of argon, oxygen, and hydrogen. The poly(amide-imide) thin film was easily decomposed by argon-oxygen mixed gas plasma and an oxidized copper surface was obtained. The reduction of the oxidized surface with argon-hydrogen mixed gas plasma rapidly yielded a metallic copper surface. A continuous plasma heat-treatment process using a combination of both the argon-oxygen plasma and argon-hydrogen plasma was found to be suitable for the decomposition of the poly(amide-imide) thin film coated on the solid copper wire.

Temperature dependence of the electrode kinetics of oxygen reduction at the platinum/Nafion interface - A microelectrode investigation

NASA Technical Reports Server (NTRS)

Parthasarathy, Arvind; Srinivasan, Supramanian; Appleby, A. J.; Martin, Charles R.

1992-01-01

Results of a study of the temperature dependence of the oxygen reduction kinetics at the Pt/Nafion interface are presented. This study was carried out in the temperature range of 30-80 C and at 5 atm of oxygen pressure. The results showed a linear increase of the Tafel slope with temperature in the low current density region, but the Tafel slope was found to be independent of temperature in the high current density region. The values of the activation energy for oxygen reduction at the platinum/Nafion interface are nearly the same as those obtained at the platinum/trifluoromethane sulfonic acid interface but less than values obtained at the Pt/H3PO4 and Pt/HClO4 interfaces. The diffusion coefficient of oxygen in Nafion increases with temperature while its solubility decreases with temperature. These temperatures also depend on the water content of the membrane.

Toxicity and genotoxicity of hospital laundry wastewaters treated with photocatalytic ozonation.

PubMed

Kern, Deivid I; Schwaickhardt, Rômulo de O; Mohr, Geane; Lobo, Eduardo A; Kist, Lourdes T; Machado, Ênio L

2013-01-15

The aim of the present study was to assess the efficiency of advanced oxidative processes based on photocatalytic ozonation (O(3), UV, UV/O(3), UV/O(3)/Fe(2+) 50 mg L(-1) and 150 mg L(-1)) in the treatment of hospital laundry wastewaters. The analysis of the investigated wastewater revealed high chemical oxygen demand (COD - 3343.8 mg L(-1)), biochemical oxygen demand (BOD(5) - 1906.4 mg L(-1)), total Kjeldahl nitrogen (TKN - 79.8 mg L(-1)) and Daphnia magna toxicity (EC50=1.73). Genotoxic effects were also detected for Allium cepa. Reductions of some parameters occurred after photocatalytic ozonation. The UV/O(3)/Fe(2+) 150 mg L(-1) method was more efficient in reducing COD (59.1%), BOD(5) (50.3%) and TKN (86.8%). There was significant reduction (p<0.05) in D. magna toxicity, O(3) (EC50=47.3%), UV (EC50=50.6%) and UV/O(3)/Fe(2+) 150 mg L(-1) (EC50=45.4%) processes. Normalization of the mitotic index and reduction of micronucleated cells were observed in A. cepa after the treatments. Results demonstrate that these methods were efficient in the degradation of hospital laundry wastewaters, representing a thriving alternative for the removal of pollutants that cause toxicity and genotoxicity. Copyright © 2012 Elsevier B.V. All rights reserved.

Highly exposed Fe-N4 active sites in porous poly-iron-phthalocyanine based oxygen reduction electrocatalyst with ultrahigh performance for air cathode.

PubMed

Anandhababu, Ganesan; Abbas, Syed Comail; Lv, Jiangquan; Ding, Kui; Liu, Qin; Babu, Dickson D; Huang, Yiyin; Xie, Jiafang; Wu, Maoxiang; Wang, Yaobing

2017-02-14

Progress in the development of efficient electrocatalysts for oxygen reduction reactions is imperative for various energy systems such as metal-air batteries and fuel cells. In this paper, an innovative porous two-dimensional (2D) poly-iron-phthalocyanine (PFe-Pc) based oxygen reduction electrocatalyst created with a simple solid-state chemical reaction without pyrolysis is reported. In this strategy, silicon dioxide nanoparticles play a pivotal role in preserving the Fe-N 4 structure during the polymerization process and thereby assist in the development of a porous structure. The new polymerized phthalocyanine electrocatalyst with tuned porous structure, improved specific surface area and more exposed catalytic active sites via the 2D structure shows an excellent performance towards an oxygen reduction reaction in alkaline media. The onset potential (E = 1.033 V) and limiting current density (I = 5.58 mA cm -2 ) are much better than those obtained with the commercial 20% platinum/carbon electrocatalyst (1.046 V and 4.89 mA cm -2 ) and also show better stability and tolerance to methanol crossover. For practical applications, a zinc-air (Zn-air) battery and methanol fuel cell equipped with the PFe-Pc electrocatalyst as an air cathode reveal a high open circuit voltage and maximum power output (1.0 V and 23.6 mW cm -2 for a methanol fuel cell, and 1.6 V and 192 mW cm -2 for the liquid Zn-air battery). In addition, using the PFe-Pc electrocatalyst as an air cathode in a flexible cable-type Zn-air battery exhibits excellent performance with an open-circuit voltage of 1.409 V. This novel porous 2D PFe-Pc has been designed logically using a new, simple strategy with ultrahigh electrochemical performances in Zn-air batteries and methanol fuel cell applications.

Model Studies on the Effectiveness of MBBR Reactors for the Restoration of Small Water Reservoirs

NASA Astrophysics Data System (ADS)

Nowak, Agata; Mazur, Robert; Panek, Ewa; Chmist, Joanna

2018-02-01

The authors present the Moving Bed Biofilm Reactor (MBBR) model with a quasi-continuous flow for small water reservoir restoration, characterized by high concentrations of organic pollutants. To determine the efficiency of wastewater treatment the laboratory analysis of physic-chemical parameters were conducted for the model on a semi-technical scale of 1:3. Wastewater treatment process was carried out in 24 h for 1 m3 for raw sewage. The startup period was 2 weeks for all biofilters (biological beds). Approximately 50% reduction in COD and BOD5 was obtained on average for the studied bioreactors. Significant improvements were achieved in theclarity of the treated wastewater, with the reduction of suspension by 60%. The oxygen profile has improved significantly in 7 to 9 hours of the process, and a diametric reduction in the oxidative reduction potential was recorded. A preliminary model of biological treatment effectiveness was determined based on the conducted studies. In final stages, the operation mode was set in real conditions of polluted water reservoirs.

Method of controlled reduction of nitroaromatics by enzymatic reaction with oxygen sensitive nitroreductase enzymes

DOEpatents

Shah, M.M.; Campbell, J.A.

1998-07-07

A method is described for the controlled reduction of nitroaromatic compounds such as nitrobenzene and 2,4,6-trinitrotoluene by enzymatic reaction with oxygen sensitive nitroreductase enzymes, such as ferredoxin NADP oxidoreductase. 6 figs.

Potential for Microbial Degradation of cis-Dichloroethene and Vinyl Chloride in Streambed Sediment at the U.S. Department of Energy, Kansas City Plant, Missouri, 2008

USGS Publications Warehouse

Bradley, Paul M.

2009-01-01

A series of carbon-14 (14C) radiotracer-based microcosm experiments was conducted to assess the mechanisms and products of degradation of cis-dichloroethene (cis-DCE) and vinyl chloride (VC) in streambed sediments at the U.S. Department of Energy, Kansas City Plant in Kansas City, Missouri. The focus of the investigation was the potential for biotic and abiotic cis-DCE and VC degradation in surficial and underlying hyporheic sediment from the Blue River and its tributaries, Indian Creek and Boone Creek. Substantial degradation of [1,2-14C] cis-DCE and [1,2-14C] VC to 14C-carbon dioxide (14CO2) was observed in all viable surficial sediment microcosms prepared under oxic conditions. No significant accumulation of reductive dechlorination products was observed under these oxic incubation conditions. The results indicate that microbial mineralization processes involving direct oxidation or co-metabolic oxidation are the primary mechanisms of cis-DCE and VC biodegradation in oxic stream sediment at the Kansas City Plant. Substantial mineralization of [1,2-14C] VC also was observed in all viable surficial sediment microcosms incubated in the absence of detectable oxygen (dissolved oxygen concentrations less than 25 micrograms per liter). In general, the accumulation of mineralization products (14CO2 and 14C-methane [14CH4]) predominated with only trace-level detection of the reductive dechlorination product, 14C-ethene. In contrast, microbial degradation of [1,2-14C] cis-DCE by reductive dechlorination or mineralization was not significant in the absence of detectable oxygen. The potential for [1,2-14C] VC biodegradation also was significant in sediments from the deeper hyporheic zones under oxic conditions and in the absence of detectable oxygen. In this study, microbial degradation of [1,2-14C] cis-DCE was not significant in hyporheic sediment treatments under either oxygen condition. Taken together, the results indicate that microbial mineralization processes in streambed sediments at the Kansas City Plant can be an important component of cis-DCE and VC degradation under oxic conditions and of VC degradation even in the absence of detectable oxygen. These results demonstrate that an evaluation of the efficiency of in situ cis-DCE and VC biodegradation in streambed sediments, based solely on observed accumulations of reduced daughter products, may underestimate substantially the total extent of contaminant biodegradation and, thus, the potential importance of the hyporheic zone and streambed sediments as barriers to the discharge of contaminated groundwater.

Unifying the 2e(-) and 4e(-) Reduction of Oxygen on Metal Surfaces.

PubMed

Viswanathan, Venkatasubramanian; Hansen, Heine Anton; Rossmeisl, Jan; Nørskov, Jens K

2012-10-18

Understanding trends in selectivity is of paramount importance for multi-electron electrochemical reactions. The goal of this work is to address the issue of 2e(-) versus 4e(-) reduction of oxygen on metal surfaces. Using a detailed thermodynamic analysis based on density functional theory calculations, we show that to a first approximation an activity descriptor, ΔGOH*, the free energy of adsorbed OH*, can be used to describe trends for the 2e(-) and 4e(-) reduction of oxygen. While the weak binding of OOH* on Au(111) makes it an unsuitable catalyst for the 4e(-) reduction, this weak binding is optimal for the 2e(-) reduction to H2O2. We find quite a remarkable agreement between the predictions of the model and experimental results spanning nearly 30 years.

Pulsed Plasma Processing of Diesel Engine Exhaust Final Report CRADA No. TC-0336-92-1-C

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

Merritt, Bernard T.; Broering, Louis

The goal was to develop an exhaust-gas treatment process for the reduction of NO x and hydrocarbon from diesel engines. The project began believing that direct chemical reduction on NO x was possible through the use of non-thermal plasmas. The original CRADA began in 1993 and was scheduled to finish in 1996. It had as its goals three metrics: 1) remove two grams/brake-horse-power-hour of NOx, 2) have no more than five percent energy penalty, and 3) cost no more than ten percent of the engine cost. These goals were all aimed at heavy-duty diesel trucks. This CRADA had its Defensemore » Program funding eliminated by DOE prior to completion in 1995. Prior to loss of funding from DOE, LLNL discovered that due to the large oxygen content in diesel exhaust, direct chemical reduction was not possible. In understanding why, a breakthrough was achieved that combined the use of a non-thermal plasma and a catalyst. This process was named Plasma Assisted Catalytic Reduction (P ACR). Because of this breakthrough, the CRADA became a funds-in only CRADA, once DOE DP funding ended. As a result, the funding decreased from about 1M dollars per year to about $400k per year. Subsequently, progress slowed as well. The CRADA was amended several times to reflect the funds-in nature. At each amendment, the deliverables were modified; the goals remained the same but the focus changed from heavy-duty to lightduty to SUVs. The diesel-engine NO x problem is similar to the furnace and boiler NO x emission problem with the added constraint that ammonia-like additives are impractical for a mobile source. Lean-burning gasoline engines are an additional area of application because the standard three-way catalyst is rendered ineffective by the presence of oxygen. In the P ACR process an electrical discharge is used to create a non-thermal plasma that contains oxidative radicals O and OH. These oxidative radicals convert NO to NO 2. Selective catalytic reduction using a readily available catalyst then converts the NO 2 to harmless gases, N 2 and 0 2.« less

Low content of Pt supported on Ni-MoCx/carbon black as a highly durable and active electrocatalyst for methanol oxidation, oxygen reduction and hydrogen evolution reactions in acidic condition

NASA Astrophysics Data System (ADS)

Zhang, Yan; Zang, Jianbing; Jia, Shaopei; Tian, Pengfei; Han, Chan; Wang, Yanhui

2017-08-01

Nickel and molybdenum carbide modified carbon black (Ni-MoCx/C) was synthesized by a two-step microwave-assisted deposition/carbonthermal reduction method and characterized by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The as-prepared Ni-MoCx/C supported Pt (10 wt%) electrocatalyst (10Pt/Ni-MoCx/C) was synthesized through a microwave-assisted reduction method and 10Pt/Ni-MoCx/C exhibited high electrocatalytic activity for methanol oxidation, oxygen reduction and hydrogen evolution reactions. Results showed that 10Pt/Ni-MoCx/C electrocatalyst had better electrocatalytic activity and stability performance than 20 wt% Pt/C (20Pt/C) electrocatalyst. Among them, the electrochemical surface area of 10Pt/Ni-MoCx/C reached 68.4 m2 g-1, which was higher than that of 20Pt/C (63.2 m2 g-1). The enhanced stability and activity of 10Pt/Ni-MoCx/C electrocatalyst were attributed to: (1) an anchoring effect of Ni and MoCx formed during carbonthermal reduction process; (2) a synergistic effect among Pt, Ni, MoOx and MoCx. These findings indicated that 10Pt/Ni-MoCx/C was a promising electrocatalyst for direct methanol fuel cells.

[Competition between redox mediator and oxygen in the microbial fuel cell].

PubMed

Alferov, S V; Vozchikova, S V; Arlyapov, V A; Alferov, V A; Reshetilov, A N

2017-01-01

The maximal rates and effective constants of 2,6-dichlorphenolindophenol and oxygen reduction by bacterim Gluconobacter oxydans in bacterial fuel cells under different conditions were evaluated. In an open-circuit mode, the rate of 2,6-dichlorphenolindophenol reduction coupled with ethanol oxidation under oxygen and nirogen atmospheres were 1.0 and 1.1 μM s–1 g–1, respectively. In closed-circuit mode, these values were 0.4 and 0.44 μM s–1 g–1, respectively. The initial rate of mediator reduction with the use of membrane fractions of bacteria in oxygen and nitrogen atmospheres in open-circuit mode were 6.3 and 6.9 μM s–1 g–1, whereas these values in closed-circuit mode comprised 2.2 and 2.4 μM s–1 g–1, respectively. The oxygen reduction rates in the presence and absence of 2,6-dichlorphenolindophenol were 0.31 and 0.32 μM s–1 g–1, respectively. The data obtained in this work demonstrated independent electron transfer from bacterial redox centers to the mediator and the absence of competition between the redox mediator and oxygen. The results can make it possible to reduce costs of microbial fuel cells based on activity of acetic acid bacteria G. oxydans.

Pretreatment of palm oil mill effluent (POME) using Moringa oleifera seeds as natural coagulant.

PubMed

Bhatia, Subhash; Othman, Zalina; Ahmad, Abdul Latif

2007-06-25

Moringa oleifera seeds, an environmental friendly and natural coagulant are reported for the pretreatment of palm oil mill effluent (POME). In coagulation-flocculation process, the M. oleifera seeds after oil extraction (MOAE) are an effective coagulant with the removal of 95% suspended solids and 52.2% reduction in the chemical oxygen demand (COD). The combination of MOAE with flocculant (NALCO 7751), the suspended solids removal increased to 99.3% and COD reduction was 52.5%. The coagulation-flocculation process at the temperature of 30 degrees C resulted in better suspended solids removal and COD reduction compared to the temperature of 40, 55 and 70 degrees C. The MOAE combined with flocculant (NALCO 7751) reduced the sludge volume index (SVI) to 210mL/g with higher recovery of dry mass of sludge (87.25%) and water (50.3%).

Mass and charge transport relevant to the formation of toroidal lithium peroxide nanoparticles in an aprotic lithium-oxygen battery: An experimental and theoretical modeling study

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

Luo, Xiangyi; Amine, Rachid; Lau, Kah Chun

2017-05-26

The discharge and charge mechanisms of rechargeable Li-O-2 batteries have been the subject of extensive investigation recently. However, they are not fully understood yet. Here we report a systematic study of the morphological transition of Li2O2 from a single crystalline structure to a toroid like particle during the discharge-charge cycle, with the help of a theoretical model to explain the evolution of the Li2O2 at different stages of this process. The model suggests that the transition starts in the first monolayer of Li2O2, and is subsequently followed by a transition from particle growth to film growth if the applied currentmore » exceeds the exchange current for the oxygen reduction reaction in a Li-O-2 cell. Furthermore, a sustainable mass transport of the diffusive active species (e.g., O-2 and Li+) and evolution of the underlying interfaces are critical to dictate desirable oxygen reduction (discharge) and evolution (charge) reactions in the porous carbon electrode of a Li-O-2 cell.« less

Effects of processing and dopant on radiation damage removal in silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Brandhorst, H. W., Jr.; Swartz, C. K.; Mehta, S.

1982-01-01

Gallium and boron doped silicon solar cells, processed by ion-implantation followed by either laser or furnace anneal were irradiated by 1 MeV electrons and their post-irradiation recovery by thermal annealing determined. During the post-irradiation anneal, gallium-doped cells prepared by both processes recovered more rapidly and exhibited none of the severe reverse annealing observed for similarly processed 2 ohm-cm boron doped cells. Ion-implanted furnace annealed 0.1 ohm-cm boron doped cells exhibited the lowest post-irradiation annealing temperatures (200 C) after irradiation to 5 x 10 to the 13th e(-)/sq cm. The drastically lowered recovery temperature is attributed to the reduced oxygen and carbon content of the 0.1 ohm-cm cells. Analysis based on defect properties and annealing kinetics indicates that further reduction in annealing temperature should be attainable with further reduction in the silicon's carbon and/or divacancy content after irradiation.

Spherical α-MnO₂ Supported on N-KB as Efficient Electrocatalyst for Oxygen Reduction in Al-Air Battery.

PubMed

Chen, Kui; Wang, Mei; Li, Guangli; He, Quanguo; Liu, Jun; Li, Fuzhi

2018-04-13

Traditional noble metal platinum (Pt) is regarded as a bifunctional oxygen catalyst due to its highly catalytic efficiency, but its commercial availability and application is often restricted by high cost. Herein, a cheap and effective catalyst mixed with α-MnO₂ and nitrogen-doped Ketjenblack (N-KB) (denoted as MnO₂-SM150-0.5) is examined as a potential electrocatalyst in oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). This α-MnO₂ is prepared by redox reaction between K₂S₂O₈ and MnSO₄ in acid conditions with a facile hydrothermal process (named the SM method). As a result, MnO₂-SM150-0.5 exhibits a good catalytic performance for ORR in alkaline solution, and this result is comparable to a Pt/C catalyst. Moreover, this catalyst also shows superior durability and methanol tolerance compared with a Pt/C catalyst. It also displays a discharge voltage (~1.28 V) at a discharge density of 50 mA cm -2 in homemade Al-air batteries that is higher than commercial 20% Pt/C (~1.19 V). The superior electrocatalytic performance of MnO₂-SM150-0.5 could be attributed to its higher Mn 3+ /Mn 4+ ratio and the synergistic effect between MnO₂ and the nitrogen-doped KB. This study provides a novel strategy for the preparation of an MnO₂-based composite electrocatalyst.

Microbial mineralization of cis-dichloroethene and vinyl chloride as a component of natural attenuation of chloroethene contaminants under conditions identified in the field as anoxic

USGS Publications Warehouse

Bradley, Paul M.

2012-01-01

Chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products may suggest that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, non-conservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms, and is consistent with contaminant degradation to non-diagnostic mineralization products. An ongoing technical debate over the potential for mineralization of dichloroethene (DCE) and vinyl chloride (VC) to CO2 in the complete absence of diatomic oxygen has largely obscured the importance of microbial DCE/VC mineralization at dissolved oxygen (DO) concentrations below the current field standard (DO < 0.1-0.5 milligrams per liter) for nominally anoxic conditions. This study demonstrates that oxygen-based microbial mineralization of DCE and VC can be substantial under field conditions that are frequently characterized as "anoxic." Because mischaracterization of operant contaminant biodegradation processes can lead to expensive and ineffective remedial actions, a modified framework for assessing the potential importance of oxygen during chloroethene biodegradation was developed.

Topical oxygen therapy promotes the healing of chronic diabetic foot ulcers: a pilot study.

PubMed

Hayes, P D; Alzuhir, N; Curran, G; Loftus, I M

2017-11-02

Interventions that can heal or reduce diabetic foot ulcer (DFU) size may reduce the incidence of infection and amputation, and reduce associated social and economic costs. Many chronic wounds exhibit a degree of hypoxia and this leads to a reduction in healing processes including cell division and differentiation, angiogenesis, infection prevention, and collagen production. The aim of this pilot study was to assess the effects of a device supplying continuous oxygen ambulatory therapy on healing in chronic DFUs. Patients with chronic DFUs from two tertiary referral hospitals in the UK received treatment with the device. Data were prospectively obtained on wound size using standardised digital images measured by a clinician blinded to the study. Data on device satisfaction and pain were also obtained. We recruited 10 patients, with a mean ulcer duration of 43 weeks (median: 43 weeks) before treatment. By week eight, mean ulcer size had decreased by 51% (median: 53%). Seven of the 10 ulcers were in a healing trajectory, one ulcer present for 56 weeks healed completely, a two-year old ulcer was reduced by more than 50%, and a third, present for 88 weeks, was down to 10% of its original size by the end of the eight-week study. There was also a non-significant trend towards reduction in pain and the device was extremely well tolerated. The ambulatory topical oxygen delivery device showed a significant beneficial effect on wound size. This poses practical advantages over currently existing oxygen-based wound therapies such as hyperbaric oxygen therapy due to its continuous oxygen delivery, ease of use, safety and lower cost. The results of this study warrant further review of the device in comparison to standard wound therapies.

Metal-Organic-Framework-Derived Hybrid Carbon Nanocages as a Bifunctional Electrocatalyst for Oxygen Reduction and Evolution.

PubMed

Liu, Shaohong; Wang, Zhiyu; Zhou, Si; Yu, Fengjiao; Yu, Mengzhou; Chiang, Chang-Yang; Zhou, Wuzong; Zhao, Jijun; Qiu, Jieshan

2017-08-01

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are cornerstone reactions for many renewable energy technologies. Developing cheap yet durable substitutes of precious-metal catalysts, especially the bifunctional electrocatalysts with high activity for both ORR and OER reactions and their streamlined coupling process, are highly desirable to reduce the processing cost and complexity of renewable energy systems. Here, a facile strategy is reported for synthesizing double-shelled hybrid nanocages with outer shells of Co-N-doped graphitic carbon (Co-NGC) and inner shells of N-doped microporous carbon (NC) by templating against core-shell metal-organic frameworks. The double-shelled NC@Co-NGC nanocages well integrate the high activity of Co-NGC shells into the robust NC hollow framework with enhanced diffusion kinetics, exhibiting superior electrocatalytic properties to Pt and RuO 2 as a bifunctional electrocatalyst for ORR and OER, and hold a promise as efficient air electrode catalysts in Zn-air batteries. First-principles calculations reveal that the high catalytic activities of Co-NGC shells are due to the synergistic electron transfer and redistribution between the Co nanoparticles, the graphitic carbon, and the doped N species. Strong yet favorable adsorption of an OOH* intermediate on the high density of uncoordinated hollow-site C atoms with respect to the Co lattice in the Co-NGC structure is a vital rate-determining step to achieve excellent bifunctional electrocatalytic activity. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanism and energetics by which glutamic acid 242 prevents leaks in cytochrome c oxidase.

PubMed

Kaila, Ville R I; Verkhovsky, Michael I; Hummer, Gerhard; Wikström, Mårten

2009-10-01

Cytochrome c oxidase (CcO) is the terminal enzyme of aerobic respiration. The energy released from the reduction of molecular oxygen to water is used to pump protons across the mitochondrial or bacterial membrane. The pump function introduces a mechanistic requirement of a valve that prevents protons from flowing backwards during the process. It was recently found that Glu-242, a key amino acid in transferring protons to be pumped across the membrane and to the site of oxygen reduction, fulfils the function of such a valve by preventing simultaneous contact to the pump site and to the proton-conducting D-channel (Kaila V.R.I. et al. Proc. Natl. Acad. Sci. USA 105, 2008). Here we have incorporated the valve model into the framework of the reaction mechanism. The function of the Glu valve is studied by exploring how the redox state of the surrounding metal centers, dielectric effects, and membrane potential, affects the energetics and leaks of this valve. Parallels are drawn between the dynamics of Glu-242 and the long-standing obscure difference between the metastable O(H) and stable O states of the binuclear center. Our model provides a suggestion for why reduction of the former state is coupled to proton translocation while reduction of the latter is not.

Respiratory processes in non-photosynthetic plastids

PubMed Central

Renato, Marta; Boronat, Albert; Azcón-Bieto, Joaquín

2015-01-01

Chlororespiration is a respiratory process located in chloroplast thylakoids which consists in an electron transport chain from NAD(P)H to oxygen. This respiratory chain involves the NAD(P)H dehydrogenase complex, the plastoquinone pool and the plastid terminal oxidase (PTOX), and it probably acts as a safety valve to prevent the over-reduction of the photosynthetic machinery in stress conditions. The existence of a similar respiratory activity in non-photosynthetic plastids has been less studied. Recently, it has been reported that tomato fruit chromoplasts present an oxygen consumption activity linked to ATP synthesis. Etioplasts and amyloplasts contain several electron carriers and some subunits of the ATP synthase, so they could harbor a similar respiratory process. This review provides an update on the study about respiratory processes in chromoplasts, identifying the major gaps that need to be addressed in future research. It also reviews the proteomic data of etioplasts and amyloplasts, which suggest the presence of a respiratory electron transport chain in these plastids. PMID:26236317

Following the electroreduction of uranium dioxide to uranium in LiCl-KCl eutectic in situ using synchrotron radiation

NASA Astrophysics Data System (ADS)

Brown, L. D.; Abdulaziz, R.; Jervis, R.; Bharath, V. J.; Atwood, R. C.; Reinhard, C.; Connor, L. D.; Simons, S. J. R.; Inman, D.; Brett, D. J. L.; Shearing, P. R.

2015-09-01

The electrochemical reduction of uranium dioxide to metallic uranium has been investigated in lithium chloride-potassium chloride eutectic molten salt. Laboratory based electrochemical studies have been coupled with in situ energy dispersive X-ray diffraction, for the first time, to deduce the reduction pathway. No intermediate phases were identified using the X-ray diffraction before, during or after electroreduction to form α-uranium. This suggests that the electrochemical reduction occurs via a single, 4-electron-step, process. The rate of formation of α-uranium is seen to decrease during electrolysis and could be a result of a build-up of oxygen anions in the molten salt. Slow transport of O2- ions away from the UO2 working electrode could impede the electrochemical reduction.

Nafion induced surface confinement of oxygen in carbon-supported oxygen reduction catalysts

DOE PAGES

Chlistunoff, Jerzy; Sansinena, Jose -Maria

2016-11-17

We studied the surface confinement of oxygen inside layers of Nafion self-assembled on carbon-supported oxygen reduction reaction (ORR) catalysts. It is demonstrated that oxygen accumulates in the hydrophobic component of the polymer remaining in contact with the carbon surface. Furthermore, the amount of surface confined oxygen increases with the degree of carbon surface graphitization, which promotes the self-assembly of the polymer. Planar macrocyclic ORR catalysts possessing a delocalized system of π electrons such as Co and Fe porphyrins and phthalocyanines have virtually no effect on the surface confinement of oxygen, in accordance with their structural similarity to graphitic carbon surfacesmore » where they adsorb. Platinum particles in carbon-supported ORR catalysts with high metal contents (20%) disrupt the self-assembly of Nafion and virtually eliminate the oxygen confinement, but the phenomenon is still observed for low Pt loading (4.8%) catalysts.« less

Nafion induced surface confinement of oxygen in carbon-supported oxygen reduction catalysts

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

Chlistunoff, Jerzy; Sansinena, Jose -Maria

We studied the surface confinement of oxygen inside layers of Nafion self-assembled on carbon-supported oxygen reduction reaction (ORR) catalysts. It is demonstrated that oxygen accumulates in the hydrophobic component of the polymer remaining in contact with the carbon surface. Furthermore, the amount of surface confined oxygen increases with the degree of carbon surface graphitization, which promotes the self-assembly of the polymer. Planar macrocyclic ORR catalysts possessing a delocalized system of π electrons such as Co and Fe porphyrins and phthalocyanines have virtually no effect on the surface confinement of oxygen, in accordance with their structural similarity to graphitic carbon surfacesmore » where they adsorb. Platinum particles in carbon-supported ORR catalysts with high metal contents (20%) disrupt the self-assembly of Nafion and virtually eliminate the oxygen confinement, but the phenomenon is still observed for low Pt loading (4.8%) catalysts.« less

Oxygen Generation from Carbon Dioxide for Advanced Life Support

NASA Technical Reports Server (NTRS)

Bishop, Sean; Duncan, Keith; Hagelin-Weaver, Helena; Neal, Luke; Sanchez, Jose; Paul, Heather L.; Wachsman, Eric

2007-01-01

The partial electrochemical reduction of carbon dioxide (CO2) using ceramic oxygen generators (COGs) is well known and widely studied. However, complete reduction of metabolically produced CO2 (into carbon and oxygen) has the potential of reducing oxygen storage weight for life support if the oxygen can be recovered. Recently, the University of Florida devel- oped novel ceramic oxygen generators employing a bilayer elec- trolyte of gadolinia-doped ceria and erbia-stabilized bismuth ox- ide (ESB) for NASA's future exploration of Mars. The results showed that oxygen could be reliably produced from CO2 at temperatures as low as 400 C. The strategy discussed here for advanced life support systems employs a catalytic layer com- bined with a COG cell so that CO2 is reduced all the way to solid carbon and oxygen without carbon buildup on the COG cell and subsequent deactivation.

Heating-Rate-Coupled Model for Hydrogen Reduction of JSC-1A

NASA Technical Reports Server (NTRS)

Hegde, U.; Balasubramaniam, R.; Gokoglu, S. A.

2010-01-01

A previously developed and validated model for hydrogen reduction of JSC-1A for a constant reaction-bed temperature is extended to account for reaction during the bed heat-up period. A quasisteady approximation is used wherein an expression is derived for a single average temperature of reaction during the heat-up process by employing an Arrhenius expression for regolith conversion. Subsequently, the regolith conversion during the heat-up period is obtained by using this representative temperature. Accounting for the reaction during heat-up provides a better estimate of the reaction time needed at the desired regolith-bed operating temperature. Implications for the efficiency of the process, as measured by the energy required per unit mass of oxygen produced, are also indicated.

Loading Rates and Impacts of Substrate Delivery for Enhanced Anaerobic Bioremediation

DTIC Science & Technology

2010-01-01

Naval Facilities Engineering Command/Engineering Services Center NDMA N-nitrosodimethylamine ORP oxidation reduction potential PCE...nitrosodimethylamine ( NDMA ) is used with propellants and is a carcinogen and emerging groundwater contaminant at a number of DoD and DOE facilities. NDMA may...demonstrating an alternative degradation process for NDMA using injection (biosparging) of propane gas and oxygen to stimulate degradation by 23

Series Bosch System Development

NASA Technical Reports Server (NTRS)

Abney, Morgan B.; Evans, Christopher; Mansell, Matt; Swickrath, Michael

2012-01-01

State-of-the-art (SOA) carbon dioxide (CO2) reduction technology for the International Space Station produces methane as a byproduct. This methane is subsequently vented overboard. The associated loss of hydrogen ultimately reduces the mass of oxygen that can be recovered from CO2 in a closed-loop life support system. As an alternative to SOA CO2 reduction technology, NASA is exploring a Series-Bosch system capable of reducing CO2 with hydrogen to form water and solid carbon. This results in 100% theoretical recovery of oxygen from metabolic CO2. In the past, Bosch-based technology did not trade favorably against SOA technology due to a high power demand, low reaction efficiencies, concerns with carbon containment, and large resupply requirements necessary to replace expended catalyst cartridges. An alternative approach to Bosch technology, labeled "Series-Bosch," employs a new system design with optimized multi-stage reactors and a membrane-based separation and recycle capability. Multi-physics modeling of the first stage reactor, along with chemical process modeling of the integrated system, has resulted in a design with potential to trade significantly better than previous Bosch technology. The modeling process and resulting system architecture selection are discussed.

High-performance thin-film transistors with solution-processed ScInO channel layer based on environmental friendly precursor

NASA Astrophysics Data System (ADS)

Song, Wei; Lan, Linfeng; Li, Meiling; Wang, Lei; Lin, Zhenguo; Sun, Sheng; Li, Yuzhi; Song, Erlong; Gao, Peixiong; Li, Yan; Peng, Junbiao

2017-09-01

Thin-film transistors (TFTs) with solution-processed scandium (Sc) substituted indium oxide (Sc x In1-x O3, ScInO) thin films based on environmental friendly water-induced precursor were fabricated. As the Sc concentration increases from 0% to 10%, the mobility decreases from 23.7 cm2 V-1 s-1 to 6.4 cm2 V-1 s-1, which is attributed to the non-overlapping of the Sc3+ electron orbit. However, the off current decreases and the turn-ON voltage (V ON) shifts towards the positive direction as the Sc content increases, which indicates lower carrier density after incorporation of Sc into In2O3. More interestingly, the incorporation of Sc into In2O3 can effectively improve the electrical stability of the TFT devices under gate bias stress, which is attributed to the reduction of the number of oxygen vacancies due to the relatively low standard electrode potential (-2.36) of Sc and strong bonding strength of Sc-O (680 kJ mol-1). The reduction of oxygen vacancies is confirmed by the x-ray photoelectron spectroscopy (XPS) experiments.

Evaluation of Alkylamine Modified Pt Nanoparticles as Oxygen Reduction Reaction Electrocatalyst for Fuel Cells via Electrochemical Impedance Spectroscopy.

PubMed

Joshi, Prerna; Okada, Toshihiko; Miyabayashi, Keiko; Miyake, Mikio

2018-05-15

Organically (octyl amine, OA) surface modified electrocatalyst (OA-Pt/CB) was studied for its oxygen reduction reaction (ORR) activity via dc methods and its charge and mass transfer properties were studied via electrochemical impedance spectroscopy (EIS). Comparison with a commercial catalyst (TEC10V30E) with similar Pt content was also carried out. In EIS, both the catalysts showed a single time-constant with an emerging high-frequency semicircle of very small diameter which was fitted using suitable equivalent circuits. The organically modified catalyst showed lower charge-transfer resistance and hence, low polarization resistance in high potential region as compared to the commercial catalyst. The dominance of kinetic processes was observed at 0.925-1.000 V, whereas domination of diffusion based processes was observed at lower potential region for the organic catalyst. No effect due to the presence of carbon was observed in the EIS spectra. Using the hydrodynamic method, higher current penetration depth was obtained for the organically modified catalyst at 1600 rpm. Exchange current density and Tafel slopes for both the electrocatalysts were calculated from the polarization resistance obtained from EIS which was in correlation with the results obtained from dc methods.

Study on emission characteristics and reduction strategy of nitrous oxide during wastewater treatment by different processes.

PubMed

Sun, Shichang; Bao, Zhiyuan; Sun, Dezhi

2015-03-01

Given the inexorable increase in global wastewater treatment, increasing amounts of nitrous oxide are expected to be emitted from wastewater treatment plants and released to the atmosphere. It has become imperative to study the emission and control of nitrous oxide in the various wastewater treatment processes currently in use. In the present investigation, the emission characteristics and the factors affecting the release of nitrous oxide were studied via full- and pilot-scale experiments in anoxic-oxic, sequencing batch reactor and oxidation ditch processes. We propose an optimal treatment process and relative strategy for nitrous oxide reduction. Our results show that both the bio-nitrifying and bio-denitrifying treatment units in wastewater treatment plants are the predominant sites for nitrous oxide production in each process, while the aerated treatment units are the critical sources for nitrous oxide emission. Compared with the emission of nitrous oxide from the anoxic-oxic (1.37% of N-influent) and sequencing batch reactor (2.69% of N-influent) processes, much less nitrous oxide (0.25% of N-influent) is emitted from the oxidation ditch process, which we determined as the optimal wastewater treatment process for nitrous oxide reduction, given the current technologies. Nitrous oxide emissions differed with various operating parameters. Controlling the dissolved oxygen concentration at a proper level during nitrification and denitrification and enhancing the utilization rate of organic carbon in the influent for denitrification are the two critical methods for nitrous oxide reduction in the various processes considered.

Chemical Looping Combustion Reactions and Systems

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

Sarofim, Adel; Lighty, JoAnn; Smith, Philip

2014-03-01

Chemical Looping Combustion (CLC) is one promising fuel-combustion technology, which can facilitate economic CO{sub 2} capture in coal-fired power plants. It employs the oxidation/reduction characteristics of a metal, or oxygen carrier, and its oxide, the oxidizing gas (typically air) and the fuel source may be kept separate. This topical report discusses the results of four complementary efforts: (5.1) the development of process and economic models to optimize important design considerations, such as oxygen carrier circulation rate, temperature, residence time; (5.2) the development of high-performance simulation capabilities for fluidized beds and the collection, parameter identification, and preliminary verification/uncertainty quantification; (5.3) themore » exploration of operating characteristics in the laboratoryscale bubbling bed reactor, with a focus on the oxygen carrier performance, including reactivity, oxygen carrying capacity, attrition resistance, resistance to deactivation, cost and availability; and (5.4) the identification of kinetic data for copper-based oxygen carriers as well as the development and analysis of supported copper oxygen carrier material. Subtask 5.1 focused on the development of kinetic expressions for the Chemical Looping with Oxygen Uncoupling (CLOU) process and validating them with reported literature data. The kinetic expressions were incorporated into a process model for determination of reactor size and oxygen carrier circulation for the CLOU process using ASPEN PLUS. An ASPEN PLUS process model was also developed using literature data for the CLC process employing an iron-based oxygen carrier, and the results of the process model have been utilized to perform a relative economic comparison. In Subtask 5.2, the investigators studied the trade-off between modeling approaches and available simulations tools. They quantified uncertainty in the high-performance computing (HPC) simulation tools for CLC bed applications. Furthermore, they performed a sensitivity analysis for velocity, height and polydispersity and compared results against literature data for experimental studies of CLC beds with no reaction. Finally, they present an optimization space using simple non-reactive configurations. In Subtask 5.3, through a series of experimental studies, behavior of a variety of oxygen carriers with different loadings and manufacturing techniques was evaluated under both oxidizing and reducing conditions. The influences of temperature, degree of carrier conversion and thermodynamic driving force resulting from the difference between equilibrium and system O{sub 2} partial pressures were evaluated through several experimental campaigns, and generalized models accounting for these influences were developed to describe oxidation and oxygen release. Conversion of three solid fuels with widely ranging reactivities was studied in a small fluidized bed system, and all but the least reactive fuel (petcoke) were rapidly converted by oxygen liberated from the CLOU carrier. Attrition propensity of a variety of carriers was also studied, and the carriers produced by freeze granulation or impregnation of preformed substrates displayed the lowest rates of attrition. Subtask 5.4 focused on gathering kinetic data for a copper-based oxygen carrier to assist with modeling of a functioning chemical looping reactor. The kinetics team was also responsible for the development and analysis of supported copper oxygen carrier material.« less

Bioreactor performance and functional gene analysis of microbial community in a limited-oxygen fed bioreactor for co-reduction of sulfate and nitrate with high organic input.

PubMed

Xu, Xi-jun; Chen, Chuan; Wang, Ai-jie; Yu, Hao; Zhou, Xu; Guo, Hong-liang; Yuan, Ye; Lee, Duu-jong; Zhou, Jizhong; Ren, Nan-qi

2014-08-15

Limited-oxygen mediated synergistic relationships between sulfate-reducing bacteria (SRB), nitrate-reducing bacteria (NRB) and sulfide-oxidizing bacteria (SOB, including nitrate-reducing, sulfide-oxidizing bacteria NR-SOB) were predicted to simultaneously remove contaminants of nitrate, sulfate and high COD, and eliminate sulfide generation. A lab-scale experiment was conducted to examine the impact of limited oxygen on these oxy-anions degradation, sulfide oxidation and associated microbial functional responses. In all scenarios tested, the reduction of both nitrate and sulfate was almost complete. When limited-oxygen was fed into bioreactors, S(0) formation was significantly improved up to ∼ 70%. GeoChip 4.0, a functional gene microarray, was used to determine the microbial gene diversity and functional potential for nitrate and sulfate reduction, and sulfide oxidation. The diversity of the microbial community in bioreactors was increased with the feeding of limited oxygen. Whereas the intensities of the functional genes involved in sulfate reduction did not show a significant difference, the abundance of the detected denitrification genes decreased in limited oxygen samples. More importantly, sulfide-oxidizing bacteria may alter their populations/genes in response to limited oxygen potentially to function more effectively in sulfide oxidation, especially to elemental sulfur. The genes fccA/fccB from nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB), such as Paracoccus denitrificans, Thiobacillus denitrificans, Beggiatoa sp., Thiomicrospira sp., and Thioalkalivibrio sp., were more abundant under limited-oxygen condition. Copyright © 2014 Elsevier B.V. All rights reserved.

Noninvasive monitoring of cerebral oxygenation in preterm infants: preliminary observations.

PubMed

Brazy, J E; Lewis, D V; Mitnick, M H; Jöbsis vander Vliet, F F

1985-02-01

A noninvasive optical method for bedside monitoring of cerebral oxygenation in small preterm infants was evaluated. Through differential absorbance of near infrared light, changes in the oxidation-reduction level of cytochrome aa3, in the oxygenation state of hemoglobin and in tissue blood volume were assessed in the transilluminated anterior cerebral field. Overall, cerebral oxygenated hemoglobin correlated significantly with transcutaneous oxygen, r = .44 p less than .0001; however, correlation was best in the absence of cardiorespiratory disease. Hypoxia with or without bradycardia led to hemoglobin deoxygenation and a shift in cytochrome aa3 to a more reduced state. When hypoxic episodes came in series or were prolonged, aa3 reduction occurred simultaneous with hemoglobin deoxygenation but its recovery to base-line values sometimes lagged behind the return of hemoglobin oxygenation. In one infant with a large patent ductus arteriosus, even brief episodes of mild bradycardia caused precipitous reduction of cytochrome aa3 before any shift to greater hemoglobin deoxygenation. This response disappeared after ductal ligation. In general, the antecedent state of cerebral oxygenation, the severity and duration of deoxygenation, and the presence or absence of circulatory abnormalities all influenced the aa3 response to hypoxia. Continuous noninvasive near infrared monitoring of cerebral oxygenation can be performed on sick preterm infants at the bedside.

Near-Infrared Spectroscopy to Reduce Prophylactic Fasciotomies for and Missed Cases of Acute Compartment Syndrome in Soldiers Injured in OEF/OIF

DTIC Science & Technology

2014-10-01

validate the accuracy and reliability of a specific NIRS sensor (Equanox, Nonin , Inc, Plymouth, MN) in diagnosing acute compartment syndrome in...clinical studies (the Nonin EquanoxTM 7600 oximeter) is for monitoring regional tissue oxygenation. This device has been validated and is currently...between Nonin , Inc and J+M Shuler – Completed in Year 2 4b: Begin reduction to practice process – Completed in Period 4. The process of reducing to

Impact of oxygen plasma postoxidation process on Al2O3/n-In0.53Ga0.47As metal-oxide-semiconductor capacitors

NASA Astrophysics Data System (ADS)

Lechaux, Y.; Fadjie-Djomkam, A. B.; Bollaert, S.; Wichmann, N.

2016-09-01

Capacitance-voltage (C-V) measurements and x-ray photoelectron spectroscopy (XPS) analysis were performed in order to investigate the effect of a oxygen (O2) plasma after oxide deposition on the Al2O3/n-In0.53Ga0.47As metal-oxide-semiconductor structure passivated with ammonia NH4OH solution. From C-V measurements, an improvement of charge control is observed using the O2 plasma postoxidation process on In0.53Ga0.47As, while the minimum of interface trap density remains at a good value lower than 1 × 1012 cm-2 eV-1. From XPS measurements, we found that NH4OH passivation removes drastically the Ga and As native oxides on the In0.53Ga0.47As surface and the O2 plasma postoxidation process enables the reduction of interface re-oxidation after post deposition annealing (PDA) of the oxide. The advanced hypothesis is the formation of interfacial barrier between Al2O3 and In0.53Ga0.47As which prevents the diffusion of oxygen species into the semiconductor surface during PDA.

High performance platinum single atom electrocatalyst for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Liu, Jing; Jiao, Menggai; Lu, Lanlu; Barkholtz, Heather M.; Li, Yuping; Wang, Ying; Jiang, Luhua; Wu, Zhijian; Liu, Di-Jia; Zhuang, Lin; Ma, Chao; Zeng, Jie; Zhang, Bingsen; Su, Dangsheng; Song, Ping; Xing, Wei; Xu, Weilin; Wang, Ying; Jiang, Zheng; Sun, Gongquan

2017-07-01

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm-2 at 80 °C with a low platinum loading of 0.09 mgPt cm-2, corresponding to a platinum utilization of 0.13 gPt kW-1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.

Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity

PubMed Central

Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.

2013-01-01

Nanosize platinum clusters with small diameters of 2–4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

High performance platinum single atom electrocatalyst for oxygen reduction reaction

PubMed Central

Liu, Jing; Jiao, Menggai; Lu, Lanlu; Barkholtz, Heather M.; Li, Yuping; Wang, Ying; Jiang, Luhua; Wu, Zhijian; Liu, Di-jia; Zhuang, Lin; Ma, Chao; Zeng, Jie; Zhang, Bingsen; Su, Dangsheng; Song, Ping; Xing, Wei; Xu, Weilin; Wang, Ying; Jiang, Zheng; Sun, Gongquan

2017-01-01

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm−2 at 80 °C with a low platinum loading of 0.09 mgPt cm−2, corresponding to a platinum utilization of 0.13 gPt kW−1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction. PMID:28737170

Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction

NASA Astrophysics Data System (ADS)

Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

2014-09-01

Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm-2) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst.

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

PubMed Central

Varnell, Jason A.; Tse, Edmund C. M.; Schulz, Charles E.; Fister, Tim T.; Haasch, Richard T.; Timoshenko, Janis; Frenkel, Anatoly I.; Gewirth, Andrew A.

2016-01-01

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites. PMID:27538720

Coproduction of volatiles and metals from extraterrestrial materials

NASA Technical Reports Server (NTRS)

Lewis, John S.

1991-01-01

Two main efforts in support of the general goals of SERC/culpr are presented. Investigations of processes for the coproduction of metals from extra-terrestrial materials in conjunction with plausible schemes for oxygen extraction continue. The principal emphasis was on the extraction and purification of iron from the ilmenite reduction process for oxygen, from the cathode metal deposits made in the magma electrolysis process for oxygen, and from native ferrous metal alloys on the moon and asteroids. All work on the separation and purification of ferrous metals was focussed upon the gaseous carbonyl process, a scheme that involves only temperatures attainable by passive thermal control. The exploration of a variety of schemes was initiated, involving the use of several different propulsion options and both propulsive and aerobraking capture at earth, for return of extraterrestrial resources to earth orbits. In addition, the search for new opportunities in space resource utilization continues. Examples include the continuation of work underway on: (1) the feasibility of locating solar power satellites in highly eccentric earth orbit; (2) the energetics of extracting the potential clean fusion fuel He-3 from the atmosphere for return to earth; and (3) the utility of a nuclear steam rocket (using non-terrestrial water as the working fluid) for transportation in the inner solar system.

Experimental manipulations of tissue oxygen supply do not affect warming tolerance of European perch.

PubMed

Brijs, Jeroen; Jutfelt, Fredrik; Clark, Timothy D; Gräns, Albin; Ekström, Andreas; Sandblom, Erik

2015-08-01

A progressive inability of the cardiorespiratory system to maintain systemic oxygen supply at elevated temperatures has been suggested to reduce aerobic scope and the upper thermal limit of aquatic ectotherms. However, few studies have directly investigated the dependence of thermal limits on oxygen transport capacity. By manipulating oxygen availability (via environmental hyperoxia) and blood oxygen carrying capacity (via experimentally induced anaemia) in European perch (Perca fluviatilis Linneaus), we investigated the effects of oxygen transport capacity on aerobic scope and the critical thermal maximum (CT(max)). Hyperoxia resulted in a twofold increase in aerobic scope at the control temperature of 23°C, but this did not translate to an elevated CT(max) in comparison with control fish (34.6±0.1 versus 34.0±0.5°C, respectively). Anaemia (∼43% reduction in haemoglobin concentration) did not cause a reduction in aerobic scope or CT(max) (33.8±0.3°C) compared with control fish. Additionally, oxygen consumption rates of anaemic perch during thermal ramping increased in a similar exponential manner to that in control fish, highlighting that perch have an impressive capacity to compensate for a substantial reduction in blood oxygen carrying capacity. Taken together, these results indicate that oxygen limitation is not a universal mechanism determining the CT(max) of fishes. © 2015. Published by The Company of Biologists Ltd.

A metal-free electrocatalyst for carbon dioxide reduction to multi-carbon hydrocarbons and oxygenates

NASA Astrophysics Data System (ADS)

Wu, Jingjie; Ma, Sichao; Sun, Jing; Gold, Jake I.; Tiwary, Chandrasekhar; Kim, Byoungsu; Zhu, Lingyang; Chopra, Nitin; Odeh, Ihab N.; Vajtai, Robert; Yu, Aaron Z.; Luo, Raymond; Lou, Jun; Ding, Guqiao; Kenis, Paul J. A.; Ajayan, Pulickel M.

2016-12-01

Electroreduction of carbon dioxide into higher-energy liquid fuels and chemicals is a promising but challenging renewable energy conversion technology. Among the electrocatalysts screened so far for carbon dioxide reduction, which includes metals, alloys, organometallics, layered materials and carbon nanostructures, only copper exhibits selectivity towards formation of hydrocarbons and multi-carbon oxygenates at fairly high efficiencies, whereas most others favour production of carbon monoxide or formate. Here we report that nanometre-size N-doped graphene quantum dots (NGQDs) catalyse the electrochemical reduction of carbon dioxide into multi-carbon hydrocarbons and oxygenates at high Faradaic efficiencies, high current densities and low overpotentials. The NGQDs show a high total Faradaic efficiency of carbon dioxide reduction of up to 90%, with selectivity for ethylene and ethanol conversions reaching 45%. The C2 and C3 product distribution and production rate for NGQD-catalysed carbon dioxide reduction is comparable to those obtained with copper nanoparticle-based electrocatalysts.

The Role of Subsurface Oxygen on Cu Surfaces for CO 2 Electrochemical Reduction

DOE PAGES

Fields, Meredith; Hong, Xin; Norskov, Jens K.; ...

2018-06-12

Under ambient conditions, copper with oxygen near the surface displays strengthened CO 2 and CO adsorption energies. This finding is often used to rationalize differences seen in product distributions between Cu-oxide and pure Cu electrodes during electrochemical CO 2 reduction. However, little evidence exists to confirm the presence of oxygen within first few layers of the Cu matrix under relevant experimental reducing conditions. As a result, using density functional theory calculations, we discuss the stability of subsurface oxygen from thermodynamic and kinetic perspectives, and show that under reducing potentials, subsurface oxygen alone should have negligible effects on the activity ofmore » crystalline Cu.« less

The Role of Subsurface Oxygen on Cu Surfaces for CO 2 Electrochemical Reduction

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

Fields, Meredith; Hong, Xin; Norskov, Jens K.

Under ambient conditions, copper with oxygen near the surface displays strengthened CO 2 and CO adsorption energies. This finding is often used to rationalize differences seen in product distributions between Cu-oxide and pure Cu electrodes during electrochemical CO 2 reduction. However, little evidence exists to confirm the presence of oxygen within first few layers of the Cu matrix under relevant experimental reducing conditions. As a result, using density functional theory calculations, we discuss the stability of subsurface oxygen from thermodynamic and kinetic perspectives, and show that under reducing potentials, subsurface oxygen alone should have negligible effects on the activity ofmore » crystalline Cu.« less

MO-Co@N-Doped Carbon (M = Zn or Co): Vital Roles of Inactive Zn and Highly Efficient Activity toward Oxygen Reduction/Evolution Reactions for Rechargeable Zn-Air Battery

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

Chen, Biaohua; He, Xiaobo; Yin, Fengxiang

A highly efficient bifunctional oxygen catalyst is required for practical applications of fuel cells and metal-air batteries, as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are their core electrode reactions. Here, the MO-Co@ N-doped carbon (NC, M = Zn or Co) is developed as a highly active ORR/OER bifunctional catalyst via pyrolysis of a bimetal metal-organic framework containing Zn and Co, i.e., precursor (CoZn). The vital roles of inactive Zn in developing highly active bifunctional oxygen catalysts are unraveled. When the precursors include Zn, the surface contents of pyridinic N for ORR and the surface contents of Co-N-xmore » and Co3+/Co2+ ratios for OER are enhanced, while the high specific surface areas, high porosity, and high electrochemical active surface areas are also achieved. Furthermore, the synergistic effects between Zn-based and Co-based species can promote the well growth of multiwalled carbon nanotubes (MWCNTs) at high pyrolysis temperatures (>= 700 degrees C), which is favorable for charge transfer. The optimized CoZn-NC-700 shows the highly bifunctional ORR/OER activity and the excellent durability during the ORR/OER processes, even better than 20 wt% Pt/C (for ORR) and IrO2 (for OER). CoZn-NC-700 also exhibits the prominent Zn-air battery performance and even outperforms the mixture of 20 wt% Pt/C and IrO2.« less

Synthesis of Pd 9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes

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

Sun, Yu; Hsieh, Yu -Chi; Chang, Li -Chung

2014-11-22

Nanoparticles of PdRu, Pd₃Ru, and Pd₉Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, Pd xRu/C (x=1/3/9), suggest succesful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of Pd xRu/C. Among these samples, the Pd₉Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in anmore » oxygen-saturated 0.1 M aqueous HClO₄ solution. Subsequently, the Pd₉Ru/C undegoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd₉Ru surface (Pd₉Ru@Pt). The Pd₉Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA μg⁻¹ Pt, as compared to that of commercially available Pt nanoparticles (0.107 mA μg⁻¹ Pt). Thus, the mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd₉Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost.« less

Synthesis of Pd9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes

NASA Astrophysics Data System (ADS)

Sun, Yu; Hsieh, Yu-Chi; Chang, Li-Chung; Wu, Pu-Wei; Lee, Jyh-Fu

2015-03-01

Nanoparticles of PdRu, Pd3Ru, and Pd9Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, PdxRu/C (x = 1/3/9), suggest successful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of PdxRu/C. Among these samples, the Pd9Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in an oxygen-saturated 0.1 M aqueous HClO4 solution. Subsequently, the Pd9Ru/C undergoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The Pd9Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA μg-1Pt, as compared to that of commercially available Pt nanoparticles (0.107 mA μg-1Pt). The mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd9Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost.

Fuel Cells | Hydrogen and Fuel Cells | NREL

Science.gov Websites

Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion, Electrochimica Acta (2016) Suppression of Oxygen Reduction Reaction Activity on Pt-Based Electrocatalysts from Ionomer Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction, Journal of the Electrochemical Society

Issues on the production and electrochemical separation of oxygen from carbon dioxide

NASA Technical Reports Server (NTRS)

Kaloupis, P.; Sridhar, K. R.

1991-01-01

There is considerable interest in in-situ propellant manufacturing on the moon and Mars. One of the concepts of oxygen production that is being actively pursued is the processing of atmospheric carbon dioxide on Mars to produce oxygen by means of thermal decomposition and electrochemical separation. The key component of such a production facility is the electrochemical separation cell that filters out the oxygen from the gas mixture of carbon dioxide, carbon monoxide, and oxygen. Efficient design of the separation cell and the selection of electrolyte and electrode materials of superior performance for the cell would translate to significant reduction in the power requirement and the mass of the production facility. The objective is to develop the technology required to produce the cells in-house and test various electrolyte and electrode materials systematically until the optimal combination is found. An effective technique was developed for the fabrication of disk shaped cells. Zirconia and Ceria cells were made in-house. Complete modules of the electrochemical cell and housings were designed, fabricated, and tested.

Removal of endocrine-disrupting chemicals and conventional pollutants in a continuous-operating activated sludge process integrated with ozonation for excess sludge reduction.

PubMed

Nie, Yafeng; Qiang, Zhimin; Ben, Weiwei; Liu, Junxin

2014-06-01

Sludge ozonation is considered as a promising technology to achieve a complete reduction of excess sludge, but as yet its effects on the removal of endocrine-disrupting chemicals (EDCs) and conventional pollutants (i.e., COD, N and P) in the activated sludge process are still unclear. In this study, two lab-scale continuous-operating activated sludge treatment systems were established: one was operated in conjunction with ozonation for excess sludge reduction, and the other was operated under normal conditions as control. The results indicate that an ozone dose of 100 mg O₃ g(-1)SS led to a zero yield of excess sludge in the sludge-reduction system during a continuous-operating period of 45d. Although ozonation gave a relatively lower specific oxygen uptake rate of activated sludge, it had little effect on the system's removal performance of COD and nitrogen substances. As a plus, sludge ozonation contributed a little more removal of target EDCs (estrone, 17β-estrodiol, estriol, 17α-ethinylestradiol, bisphenol A, and 4-nonylphenol). However, the total phosphorus removal declined notably due to its accumulation in the sludge-reduction system, which necessitates phosphorus recovery for the activated sludge process. Copyright © 2014 Elsevier Ltd. All rights reserved.

Standard reduction potentials for oxygen and carbon dioxide couples in acetonitrile and N, N -dimethylformamide

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

Pegis, Michael L.; Roberts, John A. S.; Wasylenko, Derek J.

A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O 2 + 4e – + 4H + ⇌ 2H 2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc +/0) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the freemore » energy for transferring water from aqueous solution to organic solvent, –0.43 kcal mol –1 for MeCN and –1.47 kcal mol –1 for DMF, and the potential of the H +/H 2 couple, – 0.028 V in MeCN and –0.662 V in DMF. The H +/H 2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O 2/H 2O couple has been extended to the CO 2/CO and CO 2/CH 4 couples to give values of –0.12 and +0.15 V in MeCN and –0.73 and –0.48 V in DMF, respectively. Here, extensions to other reduction potentials are discussed. Additionally, the free energy for transfer of protons from water to organic solvent is estimated as +14 kcal mol –1 for acetonitrile and +0.6 kcal mol –1 for DMF.« less

Standard reduction potentials for oxygen and carbon dioxide couples in acetonitrile and N, N -dimethylformamide

DOE PAGES

Pegis, Michael L.; Roberts, John A. S.; Wasylenko, Derek J.; ...

2015-12-07

A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O 2 + 4e – + 4H + ⇌ 2H 2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc +/0) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the freemore » energy for transferring water from aqueous solution to organic solvent, –0.43 kcal mol –1 for MeCN and –1.47 kcal mol –1 for DMF, and the potential of the H +/H 2 couple, – 0.028 V in MeCN and –0.662 V in DMF. The H +/H 2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O 2/H 2O couple has been extended to the CO 2/CO and CO 2/CH 4 couples to give values of –0.12 and +0.15 V in MeCN and –0.73 and –0.48 V in DMF, respectively. Here, extensions to other reduction potentials are discussed. Additionally, the free energy for transfer of protons from water to organic solvent is estimated as +14 kcal mol –1 for acetonitrile and +0.6 kcal mol –1 for DMF.« less

A novel additive for the reduction of acid gases and NO(x) in municipal waste incinerator flue gas.

PubMed

Hall, William J; Williams, Paul T

2006-08-01

The reduction of SO2, HCl, and NO(x) concentrations using calcium magnesium acetate (CMA) as a novel sorbent in a simulated municipal waste incinerator flue gas was investigated. The reduction of individual SO2, HCl, and NO(x) concentrations was tested at 850 degrees C and it was found that CMA could reduce the SO2 concentration by 74%, HCl concentration by 64%, or NO(x) concentration by 94%. It was observed that individual SO2 or HCl capture increased with increasing initial oxygen concentration in the reacting gas or increasing sorbent input. NO(x) reduction decreased with increasing initial oxygen concentration in the reacting gas. The simultaneous reduction of SO2, HCl, and NO(x) concentrations by CMA was also investigated. It was found that CMA could simultaneously capture 60% SO2 and 61% HCl and reduce NO(x) concentrations by 26%, when the initial oxygen concentration in the reacting gas was 4%. During the simultaneous reduction of SO2, HCl, and NO(x), it was noted that as the initial oxygen concentration in the reacting gas increased, the efficiency of SO2 capture increased too, but the efficiency of HCl capture and the efficiency of NO(x) destruction decreased.

Toxin detection using a tyrosinase-coupled oxygen electrode.

PubMed

Smit, M H; Rechnitz, G A

1993-02-15

An enzyme-based "electrochemical canary" is described for the detection of cyanide. The sensing system imitates cyanide's site of toxicity in the mitochondria. The terminal sequence of electron transfer in aerobic respiration is mimicked by mediator coupling of tyrosinase catalysis to an electro-chemical system. An enzyme-coupled oxygen electrode is created which is sensitive to selective poisoning. Biocatalytic reduction of oxygen is promoted by electrochemically supplying tyrosinase with electrons. Thus, ferrocyanide is generated at a cathode and mediates the enzymatic reduction of oxygen to water. An enzyme-dependent reductive current can be monitored which is inhibited by cyanide in a concentration-dependent manner. Oxygen depletion in the reaction layer can be minimized by addressing enzyme activity using a potential pulsing routine. Enzyme activity is electrochemically initiated and terminated and the sensor becomes capable of continuous monitoring. Cyanide poisoning of the biological component is reversible, and it can be reused after rinsing. The resulting sensor detects cyanide based on its biological activity rather than its physical or chemical properties.

Active and stable Ir@Pt core–shell catalysts for electrochemical oxygen reduction

DOE PAGES

Strickler, Alaina L.; Jackson, Ariel; Jaramillo, Thomas F.

2016-12-28

Electrochemical oxygen reduction is an important reaction for many sustainable energy technologies, such as fuel cells and metal–air batteries. Kinetic limitations of this reaction, expensive electrocatalysts, and catalyst instability, however, limit the commercial viability of such devices. Herein, we report an active Ir@Pt core–shell catalyst that combines platinum overlayers with nanostructure effects to tune the oxygen binding to the Pt surface, thereby achieving enhanced activity and stability for the oxygen reduction reaction. Ir@Pt nanoparticles with several shell thicknesses were synthesized in a scalable, inexpensive, one-pot polyol method. Electrochemical analysis demonstrates the activity and stability of the Ir@Pt catalyst, with specificmore » and mass activities increasing to 2.6 and 1.8 times that of commercial Pt/C (TKK), respectively, after 10 000 stability cycles. Furthermore, activity enhancement of the Ir@Pt catalyst is attributed to weakening of the oxygen binding to the Pt surface induced by the Ir core.« less

Effect of polymer additives on hydrodynamics and oxygen transfer in a bubble column bioreactor.

PubMed

Kawase, Y

1993-01-01

The influence of polymer additives (polyethylene oxide and polyacrylamide) on the hydrodynamics and oxygen transfer in a bubble column bioreactor was examined. The addition of small amounts of these polymers has been known to cause significant drag reduction in turbulent flow circumstances. The gas hold-up was slightly decreased and the liquid-phase mixing was somewhat enhanced due to the addition of the polymers. The addition of polymer additives brought about a reduction of the volumetric oxygen transfer coefficient by about 40%. In dilute polymer solutions, large bubbles formed by bubble coalescence moved with high rise velocities in the presence of many small bubbles and the bubble size distributions were less uniform compared with those in water. The complicated changes in bubble hydrodynamic characteristics were examined to give possible explanations for oxygen transfer reduction.

Crystal Structure and Transport Properties of Oxygen-Deficient Perovskite Sr 0.9Y 0.1CoO 3-δ

DOE PAGES

Yang, Tianrang; Mattick, Victoria F.; Chen, Yan; ...

2018-01-29

The present work reports a systematic study on temperature-dependent local crystal structure, oxygen stoichiometry, and electrical/electrochemical properties of an oxygen-deficient Sr 0.9Y 0.1CoO 3-δ (SYC10) perovskite using variable-temperature neutron diffraction (VTND), thermal gravimetric analysis, and electrical/electrochemical methods, respectively. The VTND reveals that the crystal symmetry of SYC10 remains P4/mmm tetragonal up to 900 °C. The tetragonal symmetry reflects the net effects of temperature and oxygen stoichiometry on crystal symmetry. The observed p-type electronic conductivity behavior originates from the charge-ordering between the two distinctive Co-sites. The partial oxide-ion conductivity and diffusivity obtained from oxygen permeation measurements are 2.3 × 10 –2more » S cm –1 and 7.98 × 10–8 cm 2/s at 800 °C in air, respectively. The electrochemical oxygen reduction reaction kinetics of the SYC10 cathode is primarily limited by the charge-transfer process at low temperatures (600–650 °C) and oxide-ion migration from the cathode into the electrolyte at high temperatures (700–800 °C).« less

Crystal Structure and Transport Properties of Oxygen-Deficient Perovskite Sr 0.9Y 0.1CoO 3-δ

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

Yang, Tianrang; Mattick, Victoria F.; Chen, Yan

The present work reports a systematic study on temperature-dependent local crystal structure, oxygen stoichiometry, and electrical/electrochemical properties of an oxygen-deficient Sr 0.9Y 0.1CoO 3-δ (SYC10) perovskite using variable-temperature neutron diffraction (VTND), thermal gravimetric analysis, and electrical/electrochemical methods, respectively. The VTND reveals that the crystal symmetry of SYC10 remains P4/mmm tetragonal up to 900 °C. The tetragonal symmetry reflects the net effects of temperature and oxygen stoichiometry on crystal symmetry. The observed p-type electronic conductivity behavior originates from the charge-ordering between the two distinctive Co-sites. The partial oxide-ion conductivity and diffusivity obtained from oxygen permeation measurements are 2.3 × 10 –2more » S cm –1 and 7.98 × 10–8 cm 2/s at 800 °C in air, respectively. The electrochemical oxygen reduction reaction kinetics of the SYC10 cathode is primarily limited by the charge-transfer process at low temperatures (600–650 °C) and oxide-ion migration from the cathode into the electrolyte at high temperatures (700–800 °C).« less

Phylogenetic analyses and nitrate-reducing activity of fungal cultures isolated from the permanent, oceanic oxygen minimum zone of the Arabian Sea.

PubMed

Manohar, Cathrine Sumathi; Menezes, Larissa Danielle; Ramasamy, Kesava Priyan; Meena, Ram M

2015-03-01

Reports on the active role of fungi as denitrifiers in terrestrial ecosystems have stimulated an interest in the study of the role of fungi in oxygen-deficient marine systems. In this study, the culturable diversity of fungi was investigated from 4 stations within the permanent, oceanic, oxygen minimum zone of the Arabian Sea. The isolated cultures grouped within the 2 major fungal phyla Ascomycota and Basidiomycota; diversity estimates in the stations sampled indicated that the diversity of the oxygen-depleted environments is less than that of mangrove regions and deep-sea habitats. Phylogenetic analyses of 18S rRNA sequences revealed a few divergent isolates that clustered with environmental sequences previously obtained by others. This is significant, as these isolates represent phylotypes that so far were known only from metagenomic studies and are of phylogenetic importance. Nitrate reduction activity, the first step in the denitrification process, was recorded for isolates under simulated anoxic, deep-sea conditions showing ecological significance of fungi in the oxygen-depleted habitats. This report increases our understanding of fungal diversity in unique, poorly studied habitats and underlines the importance of fungi in the oxygen-depleted environments.

A Quantitative Study of Oxygen as a Metabolic Regulator

NASA Technical Reports Server (NTRS)

Radhakrishnan, Krishnan; LaManna, Joseph C.; Cabera, Marco E.

2000-01-01

An acute reduction in oxygen delivery to a tissue is associated with metabolic changes aimed at maintaining ATP homeostasis. However, given the complexity of the human bio-energetic system, it is difficult to determine quantitatively how cellular metabolic processes interact to maintain ATP homeostasis during stress (e.g., hypoxia, ischemia, and exercise). In particular, we are interested in determining mechanisms relating cellular oxygen concentration to observed metabolic responses at the cellular, tissue, organ, and whole body levels and in quantifying how changes in tissue oxygen availability affect the pathways of ATP synthesis and the metabolites that control these pathways. In this study; we extend a previously developed mathematical model of human bioenergetics, to provide a physicochemical framework that permits quantitative understanding of oxygen as a metabolic regulator. Specifically, the enhancement - sensitivity analysis - permits studying the effects of variations in tissue oxygenation and parameters controlling cellular respiration on glycolysis, lactate production, and pyruvate oxidation. The analysis can distinguish between parameters that must be determined accurately and those that require less precision, based on their effects on model predictions. This capability may prove to be important in optimizing experimental design, thus reducing use of animals.

Graphene Synthesis & Graphene/Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

Liao, Ken-Hsuan

We successfully developed a novel, fast, hydrazine-free, high-yield method for producing single-layered graphene. Graphene sheets were formed from graphite oxide by reduction with de-ionized water at 130 ºC. Over 65% of the sheets are single graphene layers. A dehydration reaction of exfoliated graphene oxide was utilized to reduce oxygen and transform C-C bonds from sp3 to sp2. The reduction appears to occur in large uniform interconnected oxygen-free patches so that despite the presence of residual oxygen the sp2 carbon bonds formed on the sheets are sufficient to provide electronic properties comparable to reduced graphene sheets obtained using other methods. Cytotoxicity of aqueous graphene was investigated with Dr. Yu-Shen Lin by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methyl-thiazolyl-diphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. An appropriate alternate assessment, using the water soluble tetrazolium salt (WST-8) assay, reveals that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e. whether or not aggregation occurs) and mode of interaction with cells (i.e. suspension versus adherent cell types). Ultralow percolation concentration of 0.15 wt% graphene, as determined by surface resistance and modulus, was observed from in situ polymerized thermally reduced graphene (TRG)/ poly-urethane-acrylate (PUA) nanocomposite. A homogeneous dispersion of TRG in PUA was revealed by TEM images. The aspect ratio of dispersed TRG, calculated from percolation concentration and modulus, was found to be equivalent to the reported aspect ratio of single-layered free standing TRG. This indicates TRG is mono-layer-dispersed in the matrix polymer. How graphene/polymer nanocomposite glass transition temperatures ( Tg) vary was investigated in this study. We measured Tg in PMMA. We used isotactic PMMA (i-PMMA) and syndiotactic-rich atactic PMMA (a-PMMA) to make TRG/PMMA nanocomposites using solvent blending and in situ polymerization in order to investigate the stereo-regularity and processing effects on the Tg. A T g increase was found in i-PMMA and in situ PMMA but not in a-PMMA. The results can be explained by the thin film confinement effect of polymer. We attribute the Tg increase to both a higher interaction density and a stronger hydrogen bonding at the interfaces. We have studied the elastic modulus of graphene oxide with various oxygen content. We used in situ AFM nano-indentation to measure the influence of oxygen on the elastic modulus of graphene oxide with various carbon/oxygen (C/O) ratios. The results show that chemical reduction (lower oxygen contents) decreases the elastic modulus of graphene oxide. We speculate that chemical reduction of oxygen atoms of epoxy groups on graphene oxide surface removes the bridging effect between carbon atoms, which leads to more flexible sheets. (Abstract shortened by UMI.).

One Dimensional Graphitic Carbon Nitrides as Effective Metal-Free Oxygen Reduction Catalysts

PubMed Central

Tahir, Muhammad; Mahmood, Nasir; Zhu, Jinghan; Mahmood, Asif; Butt, Faheem K.; Rizwan, Syed; Aslam, Imran; Tanveer, M.; Idrees, Faryal; Shakir, Imran; Cao, Chuanbao; Hou, Yanglong

2015-01-01

To explore the effect of morphology on catalytic properties of graphitic carbon nitride (GCN), we have studied oxygen reduction reaction (ORR) performance of two different morphologies of GCN in alkaline media. Among both, tubular GCN react with dissolved oxygen in the ORR with an onset potential close to commercial Pt/C. Furthermore, the higher stability and excellent methanol tolerance of tubular GCN compared to Pt/C emphasizes its suitability for fuel cells. PMID:26201998

Effects of H2 Atmospheres on Sintering of Low Alloy Steels Containing Oxygen-Sensitive Masteralloys

NASA Astrophysics Data System (ADS)

de Oro Calderon, Raquel; Jaliliziyaeian, Maryam; Gierl-Mayer, Christian; Danninger, Herbert

2017-04-01

Processing of novel sintered steels with compositions including oxygen-sensitive elements requires deep understanding of the chemistry of sintering. The use of H2 atmospheres alleviates the oxygen transference from the base powder to the oxygen-sensitive particles. However, in H2, methane formation at 700-1200°C causes dramatic homogeneous decarburization of the part that affects both mechanical behavior and dimensional stability. The intensity and the critical temperatures of this effect depend strongly on the alloying elements, being significantly enhanced in presence of Si. When combining the alloying elements as Fe-Mn-Si masteralloys, methane formation is enhanced around 760°C due to the high Mn content (40 wt.%) in the masteralloys. Nevertheless, the benefits of H2 towards oxide reduction can still be advantageously used if diluting it in the form of N2-H2 atmospheres, or if limiting the use of H2 to temperatures below 500°C. Thus, decarburization due to methane formation can be successfully controlled.

Nitrous oxide production by nitrification and denitrification in the Eastern Tropical South Pacific oxygen minimum zone

NASA Astrophysics Data System (ADS)

Ji, Qixing; Babbin, Andrew R.; Jayakumar, Amal; Oleynik, Sergey; Ward, Bess B.

2015-12-01

The Eastern Tropical South Pacific oxygen minimum zone (ETSP-OMZ) is a site of intense nitrous oxide (N2O) flux to the atmosphere. This flux results from production of N2O by nitrification and denitrification, but the contribution of the two processes is unknown. The rates of these pathways and their distributions were measured directly using 15N tracers. The highest N2O production rates occurred at the depth of peak N2O concentrations at the oxic-anoxic interface above the oxygen deficient zone (ODZ) because slightly oxygenated waters allowed (1) N2O production from both nitrification and denitrification and (2) higher nitrous oxide production yields from nitrification. Within the ODZ proper (i.e., anoxia), the only source of N2O was denitrification (i.e., nitrite and nitrate reduction), the rates of which were reflected in the abundance of nirS genes (encoding nitrite reductase). Overall, denitrification was the dominant pathway contributing the N2O production in the ETSP-OMZ.

Oxygen reduction reaction: A framework for success

DOE PAGES

Allendorf, Mark D.

2016-05-06

Oxygen reduction at the cathode of fuel cells typically requires a platinum-based material to catalyse the reaction, but lower-cost, more stable catalysts are sought. Here, an intrinsically conductive metal–organic framework based on cheaper elements is shown to be a durable, structurally well-defined catalyst for this reaction.

Extremely high sulfate reduction, sediment oxygen demand and benthic nutrient flux associated with a large-scale artificial dyke and its implication to benthic-pelagic coupling in the Yeongsan River estuary, Yellow Sea.

PubMed

Kim, Sung-Han; Lee, Jae Seong; Hyun, Jung-Ho

2017-07-15

We investigated environmental impact of large-scale dyke on the sediment geochemistry, sulfate reduction rates (SRRs), sediment oxygen demand (SOD) and potential contribution of benthic nutrient flux (BNF) to primary production in the Yeongsan River estuary, Yellow Sea. The sediment near the dyke (YE1) with high organic carbon (C org ) content (>4%, dry wt.) was characterized by extremely high SOD (327mmolm -2 d -1 ) and SRRs (91-140mmolm -2 d -1 ). The sulfate reduction accounted for 73% of C org oxidation, and was responsible for strikingly high concentrations of NH 4 + (7.7mM), PO 4 3- (67μM) and HS - (487μM) in pore water. The BNF at YE1 accounted for approximately 200% of N and P required for primary production in the water column. The results present one of the most extreme cases that the construction of an artificial dyke may have profound impacts on the biogeochemical and ecological processes in coastal ecosystems. Copyright © 2017 Elsevier Ltd. All rights reserved.

Co- and defect-rich carbon nanofiber films as a highly efficient electrocatalyst for oxygen reduction

NASA Astrophysics Data System (ADS)

Kim, Il To; Song, Myeong Jun; Shin, Seoyoon; Shin, Moo Whan

2018-03-01

Many efforts are continuously devoted to developing high-efficiency, low-cost, and highly scalable oxygen reduction reaction (ORR) electrocatalysts to replace precious metal catalysts. Herein, we successfully synthesize Co- and defect-rich carbon nanofibers (CNFs) using an efficient heat treatment approach involving the pyrolysis of electrospun fibers at 370 °C under air. The heat treatment process produces Co-decorated CNFs with a high Co mass ratio, enriched pyridinic N, Co-pyridinic Nx clusters, and defect-rich carbon structures. The synergistic effects from composition and structural changes in the designed material increase the number of catalytically active sites for the ORR in an alkaline solution. The prepared Co- and defect-rich CNFs exhibit excellent ORR activities with a high ORR onset potential (0.954 V vs. RHE), a large reduction current density (4.426 mA cm-2 at 0.40 V), and a nearly four-electron pathway. The catalyst also exhibits a better long-term durability than commercial Pt/C catalysts. This study provides a novel hybrid material as an efficient ORR catalyst and important insight into the design strategy for CNF-based hybrid materials as electrochemical electrodes.

Nasal high-flow therapy reduces work of breathing compared with oxygen during sleep in COPD and smoking controls: a prospective observational study

PubMed Central

Kirkness, Jason P.; Grote, Ludger; Fricke, Kathrin; Schwartz, Alan R.; Smith, Philip; Schneider, Hartmut

2017-01-01

Patients with chronic obstructive pulmonary disease (COPD) endure excessive resistive and elastic loads leading to chronic respiratory failure. Oxygen supplementation corrects hypoxemia but is not expected to reduce mechanical loads. Nasal high-flow (NHF) therapy supports breathing by reducing dead space, but it is unclear how it affects mechanical loads of patients with COPD. The objective of this study was to compare the effects of low-flow oxygen and NHF therapy on ventilation and work of breathing (WOB) in patients with COPD and controls during sleep. Patients with COPD (n = 12) and controls (n = 6) were recruited and submitted to polysomnography to measure sleep parameters and ventilation in response to administration of oxygen and NHF. A subset of six patients also had an esophageal catheter inserted for the purpose of measuring WOB. Patients with COPD had similar minute ventilation (V̇e) but lower tidal volumes than matched controls. With oxygen, SaO2was increased and V̇e was reduced in both controls and patients with COPD, but there was an increase in transcutaneous CO2 levels. NHF produced a greater reduction in V̇e and was associated with a reduction in CO2 levels. Although NHF halved WOB, oxygen produced only a minor reduction in this parameter. We conclude that oxygen produced little change in WOB, which was associated with CO2 elevations. On the other hand, NHF produced a large reduction in V̇e and WOB with a concomitant decrease in CO2 levels. Our data indicate that NHF improves alveolar ventilation during sleep compared with oxygen and room air in patients with COPD and therefore can decrease their cost of breathing. NEW & NOTEWORTHY Nasal high-flow (NHF) therapy can support ventilation in patients with chronic obstructive pulmonary disease during sleep by decreasing the work of breathing and improving CO2 levels. On the other hand, oxygen supplementation corrects hypoxemia, but it produces only a minimal reduction in work of breathing and is associated with increased CO2 levels. Therefore, NHF can be a useful method to assist ventilation in patients with increased respiratory mechanical loads. PMID:27815367

Refurbishment of one-person regenerative air revitalization system

NASA Technical Reports Server (NTRS)

Powell, Ferolyn T.

1989-01-01

Regenerative processes for the revitalization of spacecraft atmospheres and reclamation of waste waters are essential for making long-term manned space missions a reality. Processes studied include: static feed water electrolysis for oxygen generation, Bosch carbon dioxide reduction, electrochemical carbon dioxide concentration, vapor compression distillation water recovery, and iodine monitoring. The objectives were to: provide engineering support to Marshall Space Flight Center personnel throughout all phases of the test program, e.g., planning through data analysis; fabricate, test, and deliver to Marshall Space Flight Center an electrochemical carbon dioxide module and test stand; fabricate and deliver an iodine monitor; evaluate the electrochemical carbon dioxide concentrator subsystem configuration and its ability to ensure safe utilization of hydrogen gas; evaluate techniques for recovering oxygen from a product oxygen and carbon dioxide stream; and evaluate the performance of an electrochemical carbon dioxide concentrator module to operate without hydrogen as a method of safe haven operation. Each of the tasks were related in that all focused on providing a better understanding of the function, operation, and performance of developmental pieces of environmental control and life support system hardware.

The Concept and Experimental Investigation of CO2 and Steam Co-electrolysis for Resource Utilization in Space Exploration

NASA Technical Reports Server (NTRS)

Stoots, Carl; Mulloth, Lila M.; Luna, Bernadette; Varghese, Mini M.

2009-01-01

CO2 acquisition and utilization technologies will have a vital role in determining sustained and affordable life support and in-situ fuel production architectures for human and robotic exploration of Moon and Mars. For long-term human exploration to be practical, reliable technologies have to be implemented to capture and chemically reduce the metabolic CO2 from the cabin air to restitute oxygen consumption. Technologies that facilitate the in-situ capture and conversion of atmospheric CO2 to fuel are essential for a viable human mission to Mars and their demonstration on the moon is critical as well. This paper describes the concept and experimental investigation of a CO2 capture and reduction system that comprises an adsorption compressor and a CO2 and steam co-electrolysis unit. The process products include oxygen for life support and Syngas (CO and H2) for synthetic fuel production. Electrochemical performance in terms of CO2 conversion, oxygen production, and power consumption of a system with a capacity to process 1kg CO2 per day (1-person equivalent) will be discussed.

Static Thermochemical Model of COREX Melter Gasifier

NASA Astrophysics Data System (ADS)

Srishilan, C.; Shukla, Ajay Kumar

2018-02-01

COREX is one of the commercial smelting reduction processes. It uses the finer size ore and semi-soft coal instead of metallurgical coke to produce hot metal from iron ore. The use of top gas with high calorific value as a by-product export gas makes the process economical and green. The predictive thermochemical model of the COREX process presented here enables rapid computation of process parameters such as (1) required amount of ore, coal, and flux; (2) amount of slag and gas generated; and (3) gas compositions (based on the raw material and desired hot metal quality). The model helps in predicting the variations in process parameters with respect to the (1) degree of metallization and (2) post-combustion ratio for given raw material conditions. In general reduction in coal, flux, and oxygen, the requirement is concomitant with an increase in the degree of metallization and post-combustion ratio. The model reported here has been benchmarked using industrial data obtained from the JSW Steel Plant, India.

Electrochemically Controlled Reconstitution of Immobilized Ferritins for Bioelectronic Applications

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo; Choi, Sang H.; Lillehei, Peter T.; Chu, Sang-Hong; King, Glen C.; Watt, Gerald D.

2007-01-01

Site-specific reconstituted nanoparticles were fabricated via electrochemically-controlled biomineralization through the immobilization of biomolecules. The work reported herein includes the immobilization of ferritin with various surface modifications, the electrochemical biomineralization of ferritins with different inorganic cores, and the electrocatalytic reduction of oxygen on the reconstituted Pt-cored ferritins. Protein immobilization on the substrate is achieved by anchoring ferritins with dithiobis-N-succinimidyl propionate (DTSP). A reconstitution process of site-specific electrochemical biomineralization with a protein cage loads ferritins with different core materials. The ferritin acts as a nano-scale template, a biocompatible cage, and a separator between the nanoparticles. This first demonstration of electrochemically controlled site-specific reconstitution of biomolecules provides a new tool for biomineralization and opens the way to produce the bio-templated nanoparticles by electrochemical control. The nanosized platinum-cored ferritins on gold displayed good catalytic activity for the electrochemical reduction of oxygen, which is applicable to biofuel cell applications. This results in a smaller catalyst loading on the electrodes for fuel cells or other bioelectronic devices.

Electrosynthesis of hydrogen peroxide via the reduction of oxygen assisted by power ultrasound.

PubMed

González-García, José; Banks, Craig E; Sljukić, Biljana; Compton, Richard G

2007-04-01

The electrosynthesis of hydrogen peroxide using the oxygen reduction reaction has been studied in the absence and presence of power ultrasound in a non-optimized sono-electrochemical flow reactor (20 cm cathodic compartment length with 6.5 cm inner diameter) with reticulated vitreous glassy carbon electrode (30 x 40 x 10 mm, 10 ppi, 7 cm(2)cm(-3)) as the cathode. The effect of several electrochemical operational variables (pH, volumetric flow, potential) and of the sono-electrochemical parameters (ultrasound amplitude and horn-to-electrode distance) on the cumulative concentration of hydrogen peroxide and current efficiency of the electrosynthesis process have been explored. The application of power ultrasound was found to increase both the cumulative concentration of hydrogen peroxide and the current efficiency. The application of ultrasound is therefore a promising approach to the increased efficiency of production of hydrogen peroxide by electrosynthesis, even in the solutions of lower pH (<12). The results demonstrate the feasibility of at-site-of-use green synthesis of hydrogen peroxide.

A one-pot hydrothermal synthesis of 3D nitrogen-doped graphene aerogels-supported NiS2 nanoparticles as efficient electrocatalysts for the oxygen-reduction reaction

NASA Astrophysics Data System (ADS)

Yuan, Wen-Jing; Li, Ju-Chuan; Chen, Ping; Shen, Yu-Hua; Xie, An-Jian

2014-03-01

Nitrogen-doped graphene aerogels-supported NiS2 nanoparticles (NiS2/NG) were synthesized by a one-pot hydrothermal method. In the process, l-cysteine was used not only as the nitrogen source to form the nitrogen-doped graphene aerogels, but also the sulfur source to form NiS2. The nitrogen-doped graphene (NG) hybrids show an interconnected reticulation of NG sheets with uniform deposition of NiS2 NPs, and the NiS2 NPs are deposited on the NG layers. In studying the effects of the NG and NiS2/NG for the ORR, we found that NiS2/NG shows a more positive onset potential, higher current density, and higher electron transfer number (˜4) for the oxygen-reduction reaction (ORR) in alkaline media than NG. Furthermore, NiS2/NG shows better durability and methanol tolerance than the commercial Pt/C catalyst.

Induced polarized state in intentionally grown oxygen deficient KTaO{sub 3} thin films

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

Mota, D. A.; Romaguera-Barcelay, Y.; Tkach, A.

2013-07-21

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO{sub 2}/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K{sub 2}O rich KTaO{sub 3} targets and specific deposition conditions, KTaO{sub 3-{delta}} oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO{sub 3-{delta}} thin films are under a compressive strain of 2.3% relative to KTaO{sub 3} crystals. Leakage current results reveal themore » presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below T{sub pol} {approx} 367 Degree-Sign C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above T{sub pol}, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.« less

Impact of oxygen chemistry on the emission and fluorescence spectroscopy of laser ablation plumes

NASA Astrophysics Data System (ADS)

Hartig, K. C.; Brumfield, B. E.; Phillips, M. C.; Harilal, S. S.

2017-09-01

Oxygen present in the ambient gas medium may affect both laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) emission through a reduction of emission intensity and persistence. In this study, an evaluation is made on the role of oxygen in the ambient environment under atmospheric pressure conditions in LIBS and laser ablation (LA)-LIF emission. To generate plasmas, 1064 nm, 10 ns pulses were focused on an aluminum alloy sample. LIF was performed by frequency scanning a CW laser over the 396.15 nm (3s24s 2S1/2 → 3s23p 2P°3/2) Al I transition. Time-resolved emission and fluorescence signals were recorded to evaluate the variation in emission intensity caused by the presence of oxygen. The oxygen partial pressure (po) in the atmospheric pressure environment using N2 as the makeup gas was varied from 0 to 400 Torr O2. 2D-fluorescence spectroscopy images were obtained for various oxygen concentrations for simultaneous evaluation of the emission and excitation spectral features. Results showed that the presence of oxygen in the ambient environment reduces the persistence of the LIBS and LIF emission through an oxidation process that depletes the density of atomic species within the resulting laser-produced plasma (LPP) plume.

Preparation of supported electrocatalyst comprising multiwalled carbon nanotubes

DOEpatents

Wu, Gang; Zelenay, Piotr

2013-08-27

A process for preparing a durable non-precious metal oxygen reduction electrocatalyst involves heat treatment of a ball-milled mixture of polyaniline and multiwalled carbon nanotubes in the presence of a Fe species. The catalyst is more durable than catalysts that use carbon black supports. Performance degradation was minimal or absent after 500 hours of operation at constant cell voltage of 0.40 V.

Respiration, respiratory metabolism and energy consumption under weightless conditions

NASA Technical Reports Server (NTRS)

Kasyan, I. I.; Makarov, G. F.

1975-01-01

Changes in the physiological indices of respiration, respiratory metabolism and energy consumption in spacecrews under weightlessness conditions manifest themselves in increased metabolic rates, higher pulmonary ventilation volume, oxygen consumption and carbon dioxide elimination, energy consumption levels in proportion to reduction in neuroemotional and psychic stress, adaptation to weightlessness and work-rest cycles, and finally in a relative stabilization of metabolic processes due to hemodynamic shifts.

Feasibility tests of nickel as a containment material of molten Li2O-LiCl salt containing Li metal at 650 °C during electrolytic reduction

NASA Astrophysics Data System (ADS)

Choi, Eun-Young; Lee, Jeong

2017-11-01

In this study, we investigated the feasibility of nickel (Ni) as a material to contain molten Li2O-LiCl salt containing lithium (Li) metal at 650 °C as an electrolyte during the electrolytic reduction process of pyroprocessing (also known as oxide reduction, OR). First, the behaviors of Ni in four different LiCl salts (0.1 wt% Li-LiCl, 1 and 8 wt% Li2O-LiCl, and 8 wt% Li2O-0.1 wt% Li-LiCl) in an argon atmosphere were examined through immersion tests. Then, Ni was used as a vessel material for five consecutive OR runs of simulated oxide fuel using 1.0 wt% Li2O-LiCl salt. The tested Ni was analyzed by microbalance, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Concentrations of Ni in the salt were measured using inductively coupled plasma atomic emission spectroscopy. No corrosion product of Ni, except Cr2Ni3, was observed on the Ni used for both the salt-immersion tests and the OR runs because the Ni was not exposed to oxygen gas. However, leaching of Ni in the OR salt containing excessive Li metal was observed. Therefore, Ni can be used as the salt containment material in the OR process when excessive Li metal and oxygen gas in the salt are maintained at low levels.

A novel aerobic sulfate reduction process in landfill mineralized refuse.

PubMed

Liu, Weijia; Long, Yuyang; Fang, Yuan; Ying, Luyao; Shen, Dongsheng

2018-05-08

It is thought that mineralized refuse could be excavated from almost-full landfill sites to provide space for the increasing burden of municipal solid waste. When excavating, however, the H 2 S emissions from the mineralized waste need to be considered carefully. In an attempt to understand how H 2 S emissions might change during this excavation process, we carried out a series of tests, including exposing anaerobic mineralized refuse to oxygen, isolating and determining possible functional bacteria, and characterizing the electron donors and/or acceptors. The results showed that H 2 S would be released when landfill mineralized refuse was exposed to oxygen (O 2 ), and could reach concentrations of 6 mg m -3 , which was 3 times the concentrations of H 2 S released from anaerobic mineralized refuse. Sulfur-metabolized microorganisms accounted for only 0.5% of the microbial functional bacteria (MFB) derived from the mineralized refuse when exposed to O 2 for 60 days, and SRB were not present. The MFB maintained H 2 S production by aerobic sulfate reduction using SO 4 2- and S 2 O 3 2- as electron acceptors, and sulfate-reducing rates of 16% and 55%, respectively, were achieved. Lactate and S 2 O 3 2- were the preferred electron donor and acceptor, respectively. By enhancing the carbon source and electron transfer, MFB may undergo strong aerobic sulfate reduction even at low abundances of sulfur-metabolized microorganisms. Copyright © 2018 Elsevier B.V. All rights reserved.

Microwave enhanced chemical reduction process for nitrite-containing wastewater treatment using sulfaminic acid.

PubMed

Li, Nan; Wang, Peng; Liu, Qingsong; Cao, Hailei

2010-01-01

High-concentration nitrite-containing wastewater that presents extreme toxicity to human health and organisms is difficult to be treated using traditional biological process. In this study, a novel microwave-enhanced chemical reduction process (MECRP) using sulfaminic acid (SA) was proposed as a new manner to treat such type of wastewater. Based on lab-scale experiments, it was shown that 75%-80% nitrite (NO2-) could be removed within time as short as 4 min under 50 W microwave irradiation in pH range 5-10 when molar ratio of SA to nitrite (SA/NO2-) was 0.8. Pilot-scale investigations demonstrated that MECRP was able to achieve nitrite and chemical oxygen demand (COD) removal with efficiency up to 80% and 20%, respectively under operating conditions of SA concentration 80 kg/m3, SA/NO2- ratio 0.8, microwave power 3.4 kW, and stirring time 3 min. Five-day biological oxygen demand (BOD5)/COD value of treated effluent after MECRP was increased from 0.05 to 0.36 (by 620%), which clearly suggested a considerable improvement of biodegradability for subsequent biological treatment. This study provided a demonstration of using microwave irradiation to enhance reaction between SA and nitrite in a short time, in which nitrite in wastewater was completely converted into nitrogen gas without leaving any sludge and secondary pollutants.

Slat templated formation of efficient oxygen reduction electrocatalyst with a fluidic precursor

NASA Astrophysics Data System (ADS)

Tan, Yao

2018-05-01

Development of cost-effective and efficient oxygen reduction catalyst is critical for the commercialization of proton exchange membrane fuel cell. Metal and nitrogen co-doped carbon is recognized as a promising alternative to traditional platinum-based oxygen reduction catalyst. Herein, we report a novel metal and nitrogen co-doped carbon catalyst with an ionic liquid precursor. Salt template, which can be easily removed with mild treatment after the synthesis, is used to generate abundant mesopores in the resulting catalyst. We show that the novel catalyst shows a superior activity comparable to commercial Pt/C catalyst. Furthermore, the important role of the mesopore for the activity of the catalyst is demonstrated.

Hydrogen Reduction of Lunar Regolith Simulants for Oxygen Production

NASA Technical Reports Server (NTRS)

Hegde, U.; Balasubramaniam, R.; Gokoglu, S. A.; Rogers, K.; Reddington, M.; Oryshchyn, L.

2011-01-01

Hydrogen reduction of the lunar regolith simulants JSC-1A and LHT-2M is investigated in this paper. Experiments conducted at NASA Johnson Space Center are described and are analyzed utilizing a previously validated model developed by the authors at NASA Glenn Research Center. The effects of regolith sintering and clumping, likely in actual production operations, on the oxygen production rate are studied. Interpretations of the obtained results on the basis of the validated model are provided and linked to increase in the effective particle size and reduction in the intra-particle species diffusion rates. Initial results on the pressure dependence of the oxygen production rate are also presented and discussed

Core-Shell Co/CoO Integrated on 3D Nitrogen Doped Reduced Graphene Oxide Aerogel as an Enhanced Electrocatalyst for the Oxygen Reduction Reaction

PubMed Central

Wang, Meng; Hou, Yuyang; Slade, Robert C. T.; Wang, Jiazhao; Shi, Dongqi; Wexler, David; Liu, Huakun; Chen, Jun

2016-01-01

Here, we demonstrate that Cobalt/cobalt oxide core-shell nanoparticles integrated on nitrogen-doped (N-doped) three-dimensional reduced graphene oxide aerogel-based architecture (Co/CoO-NGA) were synthesized through a facile hydrothermal method followed by annealing treatment. The unique endurable porous structure could provide sufficient mass transfer channels and ample active sites on Co/CoO-NGA to facilitate the catalytic reaction. The synthesized Co/CoO-NGA was explored as an electrocatalyst for the oxygen reduction reaction, showing comparable oxygen reduction performance with excellent methanol resistance and better durability compared with Pt/C. PMID:27597939

Reductions in greenhouse gas (GHG) generation and energy consumption in wastewater treatment plants.

PubMed

Yerushalmi, L; Ashrafi, O; Haghighat, F

2013-01-01

Greenhouse gas (GHG) emission and energy consumption by on-site and off-site sources were estimated in two different wastewater treatment plants that used physical-chemical or biological processes for the removal of contaminants, and an anaerobic digester for sludge treatment. Physical-chemical treatment processes were used in the treatment plant of a locomotive repair factory that processed wastewater at 842 kg chemical oxygen demand per day. Approximately 80% of the total GHG emission was related to fossil fuel consumption for energy production. The emission of GHG was reduced by 14.5% with the recovery of biogas that was generated in the anaerobic digester and its further use as an energy source, replacing fossil fuels. The examined biological treatment system used three alternative process designs for the treatment of effluents from pulp and paper mills that processed wastewater at 2,000 kg biochemical oxygen demand per day. The three designs used aerobic, anaerobic, or hybrid aerobic/anaerobic biological processes for the removal of carbonaceous contaminants, and nitrification/denitrification processes for nitrogen removal. Without the recovery and use of biogas, the aerobic, anaerobic, and hybrid treatment systems generated 3,346, 6,554 and 7,056 kg CO(2)-equivalent/day, respectively, while the generated GHG was reduced to 3,152, 6,051, and 6,541 kg CO(2)-equivalent/day with biogas recovery. The recovery and use of biogas was shown to satisfy and exceed the energy needs of the three examined treatment plants. The reduction of operating temperature of the anaerobic digester and anaerobic reactor by 10°C reduced energy demands of the treatment plants by 35.1, 70.6 and 62.9% in the three examined treatment systems, respectively.

Determination of pharmaceutical compounds in hospital wastewater and their elimination by advanced oxidation processes.

PubMed

Souza, Fernanda S; Da Silva, Vanessa V; Rosin, Catiusa K; Hainzenreder, Luana; Arenzon, Alexandre; Pizzolato, Tania; Jank, Louise; Féris, Liliana A

2018-02-23

This study investigates the mineralization efficiency, i.e. removal of total organic carbon (TOC) in hospital wastewater by direct ozonation, ozonation with UV radiation (O 3 /UV), homogeneous catalytic ozonation (O 3 /Fe 2+ ) and homogeneous photocatalytic ozonation (O 3 /Fe 2+ /UV). The influence of pH and reaction time was evaluated. For the best process, toxicity and degradation efficiency of the selected pharmaceutical compounds (PhCs) were determined. The results showed that the PhCs detected in the hospital wastewater were completely degraded when the mineralization efficiency reached 54.7% for O 3 /UV with 120 minutes of reaction time using a rate of 1.57 g O 3 h -1 . This process also achieved a higher chemical oxygen demand removal efficiency (64.05%), an increased aromaticity reduction efficiency (81%) and a toxicity reduction.

Winery wastewater treatment by a combined process: long term aerated storage and Fenton's reagent.

PubMed

Lucas, Marco S; Mouta, Maria; Pirra, António; Peres, José A

2009-01-01

The degradation of the organic pollutants present in winery wastewater was carried out by the combination of two successive steps: an aerobic biological process followed by a chemical oxidation process using Fenton's reagent. The main goal of this study was to evaluate the temporal characteristics of solids and chemical oxygen demand (COD) present in winery wastewater in a long term aerated storage bioreactor. The performance of different air dosage daily supplied to the biologic reactor, in laboratory and pilot scale, were examined. The long term hydraulic retention time, 11 weeks, contributed remarkably to the reduction of COD (about 90%) and the combination with the Fenton's reagent led to a high overall COD reduction that reached 99.5% when the mass ratio (R = H(2)O(2)/COD) used was equal to 2.5, maintaining constant the molar ratio H(2)O(2)/Fe(2+)=15.

Oxygen reduction reaction (orr) on bimetallic AuPt and AuPd(1 0 0)-electrodes: Effects of the heteroatomic junction on the reaction paths

NASA Astrophysics Data System (ADS)

Schulte, E.; Belletti, G.; Arce, M.; Quaino, P.

2018-05-01

The seek for materials to enhance the oxygen reduction reaction (orr) rate is a highly relevant topic due to its implication in fuel cell devices. Herein, the orr on bimetallic electrocatalysts based on Au-M (M = Pt, Pd) has been studied computationally, by performing density functional theory calculations. Bimetallic (1 0 0) electrode surfaces with two different Au:M ratios were proposed, and two possible pathways, associative and dissociative, were considered for the orr. Changes in the electronic properties of these materials with respect to the pure metals were acknowledged to gain understanding in the overall reactivity trend. The effect of the bimetallic junction on the stability of the intermediates O2 and OOH was also evaluated by means of geometrical and energetic parameters; being the intermediates preferably adsorbed on Pt/Pd atoms, but presenting in some cases higher adsorption energies compared with bare metals. Finally, the kinetics of the Osbnd O bond breaking in O2∗ and OOH∗ adsorbed intermediates in the bimetallic materials and the influence of the Au-M junction were studied by means of the nudge elastic-band method. A barrierless process for the scission of O2∗ was found in Au-M for the higher M ratios. Surprisingly, for Au-M with lower M ratios, the barriers were much lower than for pure Au surfaces, suggesting a highly reactive surface towards the orr. The Osbnd O scission of the OOH∗ was found to be a barrierless process in Ausbnd Pt systems and nearly barrierless in all Ausbnd Pd systems, implying that the reduction ofO2 in these systems proceeds via the full reduction of O2 to H2O , avoiding H2O2 formation.

[Anaerobic reduction of humus/Fe (III) and electron transport mechanism of Fontibacter sp. SgZ-2].

PubMed

Ma, Chen; Yang, Gui-qin; Lu, Qin; Zhou, Shun-gui

2014-09-01

Humus and Fe(III) respiration are important extracellular respiration metabolism. Electron transport pathway is the key issue of extracellular respiration. To understand the electron transport properties and the environmental behavior of a novel Fe(III)- reducing bacterium, Fontibacter sp. SgZ-2, capacities of anaerobic humus/Fe(III) reduction and electron transport mechanisms with four electron acceptors were investigated in this study. The results of anaerobic batch experiments indicated that strain SgZ-2 had the ability to reduce humus analog [ 9,10-anthraquinone-2,6-disulfonic acid (AQDS) and 9,10-anthraquinone-2-sulfonic acid (AQS)], humic acids (HA), soluble Fe(III) (Fe-EDTA and Fe-citrate) and Fe(III) oxides [hydrous ferric oxide (HFO)]. Fermentative sugars (glucose and sucrose) were the most effective electron donors in the humus/Fe(III) reduction by strain SgZ-2. Additionally, differences of electron carrier participating in the process of electron transport with different electron acceptors (i. e. , oxygen, AQS, Fe-EDTA and HFO) were investigated using respiratory inhibitors. The results suggested that similar respiratory chain components were involved in the reducing process of oxygen and Fe-EDTA, including dehydrogenase, quinones and cytochromes b-c. In comparison, only dehydrogenase was found to participate in the reduction of AQS and HFO. In conclusion, different electron transport pathways may be employed by strain SgZ-2 between insoluble and soluble electron acceptors or among soluble electron acceptors. Preliminary models of electron transport pathway with four electron acceptors were proposed for strain SgZ-2, and the study of electron transport mechanism was explored to the genus Fontibacter. All the results from this study are expected to help understand the electron transport properties and the environmental behavior of the genus Fontibacter.

Thioredoxins in evolutionarily primitive organisms

NASA Technical Reports Server (NTRS)

Buchanan, B. B.

1986-01-01

Thioredoxins are low molecular weight redox proteins, alternating between the S-S (oxidized) and SH (reduced) states, that function in a number of biochemical processes, including DNA synthesis, DNA replication, and enzyme regulation. Until recently, reduced ferredoxin was known to serve as the source of reducing power for the reduction of thioredoxins only in oxygenic photosynthetic cells. In all other organisms, the source of hydrogen (electrons) for thioredoxin reduction was considered to be NADPH. It was found that Clostridium pasteurianum, an anaerobic organism normally living in the soil unexposed to light, resembles photosynthetic cells in using ferredoxin for the reduction of thioredoxin. The results reveal the existence of a pathway in which ferredoxin, provides the reducing power for the reduction of thioredoxin via the flavoprotein enzyme, ferredoxinthioredoxin reductase. In related studies, it was found that Chromatium vinosum, an anaerobic photosynthetic purple sulfur bacterium, resembles evolutionarily more advanced micro-organisms in having an NADP-thioredoxin system composed of a single thioredoxin which is reduced by NADPH via NADP-thioredoxin reductase. The adoption of the NADP-thioredoxin system by Chromatium seems appropriate in view of evidence tha the organi sm utilizes ATP-driven reverse electron transport. Finally, results of research directed towards the identification of target enzymes of the ferredoxin/thioredoxin system in a cyanobacterium (Nostoc muscorum), show that thioredoxin-linked photosynthetic enzymes of cyanobateria are similar to those of chloroplasts. It now seems that the ferredoxin/thioredoxin system functions in regulating CO2 assimilation via the reductive pentose phosphate cycle in oxygenic but not anoxygenic photosynthetic cells.

Theoretical Study of the Structure, Stability and Oxygen Reduction Activity of Ultrathin Platinum Nanowires

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

Matanovic, Ivana; Kent, Paul; Garzon, Fernando

2012-10-10

We use density functional theory to study the difference in the structure, stability and catalytic reactivity between ultrathin, 0.5- 1.0 nm diameter, platinum nanotubes and nanowires. Model nanowires were formed by inserting an inner chain of platinum atoms in small diameter nanotubes. In this way more stable, nonhollow structures were formed. The difference in the electronic structure of platinum nanotubes and nanowires was examined by inspecting the density of surface states and band structure. Furthermore, reactivity towards the oxygen reduction reaction of platinum nanowires was addressed by studying the change in the chemisorption energies of oxygen and hydroxyl groups, inducedmore » by inserting the inner chain of platinum atoms into the hollow nanotubes. Both ultrathin platinum nanotubes and nanowires show distinct properties compared to bulk platinum. Nanotubes with diameters larger than 1 nm show promise for use as oxygen reduction catalysts.« less

Density Functional Study of the Structure, Stability and Oxygen Reduction Activity of Ultrathin Platinum Nanowires

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

Matanovic, Ivana; Kent, Paul; Garzon, Fernando

2013-03-14

We used density functional theory to study the difference in the structure, stability and catalytic reactivity between ultrathin, 0.5–1.0 nm diameter, platinum nanotubes and nanowires. Model nanowires were formed by inserting an inner chain of platinum atoms in small diameter nanotubes. In this way more stable, non-hollow structures were formed. The difference in the electronic structure of platinum nanotubes and nanowires was examined by inspecting the density of surface states and band structure. Furthermore, reactivity toward the oxygen reduction reaction of platinum nanowires was assessed by studying the change in the chemisorption energies of oxygen, hydroxyl, and hydroperoxyl groups, inducedmore » by converting the nanotube models to nanowires. Both ultrathin platinum nanotubes and nanowires show distinct properties compared to bulk platinum. Single-wall nanotubes and platinum nanowires with diameters larger than 1 nm show promise for use as oxygen reduction catalysts.« less

Development and testing of a wet oxidation waste processing system. [for waste treatment aboard manned spacecraft

NASA Technical Reports Server (NTRS)

Weitzmann, A. L.

1977-01-01

The wet oxidation process is considered as a potential treatment method for wastes aboard manned spacecraft for these reasons: (1) Fecal and urine wastes are processed to sterile water and CO2 gas. However, the water requires post-treatment to remove salts and odor; (2) the residual ash is negligible in quantity, sterile and easily collected; and (3) the product CO2 gas can be processed through a reduction step to aid in material balance if needed. Reaction of waste materials with oxygen at elevated temperature and pressure also produces some nitrous oxide, as well as trace amounts of a few other gases.

Influence of norepinephrine and phenylephrine on frontal lobe oxygenation during cardiopulmonary bypass in patients with diabetes.

PubMed

Brassard, Patrice; Pelletier, Claudine; Martin, Mickaël; Gagné, Nathalie; Poirier, Paul; Ainslie, Philip N; Caouette, Manon; Bussières, Jean S

2014-06-01

Although utilization of vasopressors recently has been associated with reduced cerebral oxygenation, the influence of vasopressors on cerebral oxygenation during cardiopulmonary bypass in patients with diabetes is unknown. The aim of this study was to document the impact of norepinephrine and phenylephrine utilization on cerebral oxygenation in patients with and without diabetes during cardiopulmonary bypass. Prospective, clinical study. Academic medical center. Fourteen patients with diabetes and 17 patients without diabetes undergoing cardiac surgery. During cardiopulmonary bypass, norepinephrine (diabetics n = 6; non-diabetics n = 8) or phenylephrine (diabetics n = 8; non-diabetics n = 9) was administered intravenously to maintain mean arterial pressure above 60 mmHg. Mean arterial pressure, venous temperature, arterial oxygenation, and frontal lobe oxygenation (monitored by near-infrared spectroscopy) were recorded before anesthesia induction (baseline) and continuously during cardiopulmonary bypass. Frontal lobe oxygenation was lowered to a greater extent in diabetics versus non-diabetics with administration of norepinephrine (-14±13 v 3±12%; p<0.05). There was also a trend towards a greater reduction in cerebral oxygenation in diabetics versus non-diabetics with administration of phenylephrine (-12±8 v -6±7%; p = 0.1) during cardiopulmonary bypass. Administration of norepinephrine to restore mean arterial pressure during cardiopulmonary bypass is associated with a reduction in frontal lobe oxygenation in diabetics but not in patients without diabetes. Administration of phenylephrine also were associated with a trend towards a greater reduction in frontal lobe oxygenation in diabetics. The clinical implications of these findings deserve future consideration. © 2013 Elsevier Inc. All rights reserved.

Anaemia only causes a small reduction in the upper critical temperature of sea bass: is oxygen delivery the limiting factor for tolerance of acute warming in fishes?

PubMed

Wang, Tobias; Lefevre, Sjannie; Iversen, Nina K; Findorf, Inge; Buchanan, Rasmus; McKenzie, David J

2014-12-15

To address how the capacity for oxygen transport influences tolerance of acute warming in fishes, we investigated whether a reduction in haematocrit, by means of intra-peritoneal injection of the haemolytic agent phenylhydrazine, lowered the upper critical temperature of sea bass. A reduction in haematocrit from 42±2% to 20±3% (mean ± s.e.m.) caused a significant but minor reduction in upper critical temperature, from 35.8±0.1 to 35.1±0.2°C, with no correlation between individual values for haematocrit and upper thermal limit. Anaemia did not influence the rise in oxygen uptake between 25 and 33°C, because the anaemic fish were able to compensate for reduced blood oxygen carrying capacity with a significant increase in cardiac output. Therefore, in sea bass the upper critical temperature, at which they lost equilibrium, was not determined by an inability of the cardio-respiratory system to meet the thermal acceleration of metabolic demands. © 2014. Published by The Company of Biologists Ltd.

High performance platinum single atom electrocatalyst for oxygen reduction reaction

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

Liu, Jing; Jiao, Menggai; Lu, Lanlu

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm –2 at 80 °C with a low platinum loading of 0.09 mgPt cm –2, corresponding to a platinum utilization of 0.13 gPt kWmore » –1 in the fuel cell. Good fuel cell durability is also observed. As a result, theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.« less

High performance platinum single atom electrocatalyst for oxygen reduction reaction

DOE PAGES

Liu, Jing; Jiao, Menggai; Lu, Lanlu; ...

2017-07-24

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm –2 at 80 °C with a low platinum loading of 0.09 mgPt cm –2, corresponding to a platinum utilization of 0.13 gPt kWmore » –1 in the fuel cell. Good fuel cell durability is also observed. As a result, theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.« less

Investigating the performance of three modified activated sludge processes treating municipal wastewater in organic pollutants removal and toxicity reduction.

PubMed

Han, Xue; Zuo, Yu-Ting; Hu, Yu; Zhang, Jie; Zhou, Meng-Xuan; Chen, Mo; Tang, Fei; Lu, Wen-Qing; Liu, Ai-Lin

2018-02-01

This study investigated the treatment performance of three types of modified activated sludge processes, i.e., anoxic/oxic (A/O), anaerobic/anoxic/oxic (A2/O) and oxidation ditch process, in treating municipal wastewater by measuring physicochemical and spectroscopic parameters, and the toxicity of the influents and effluents collected from 8 full-scale municipal wastewater treatment plants (MWTPs). The relationships between spectroscopic and physicochemical parameters of the wastewater samples and the applicability of the nematode Caenorhabditis elegans (C. elegans) bioassays for the assessment of the toxic properties of municipal wastewater were also evaluated. The results indicated that the investigated MWTPs employing any of A/O, A2/O and oxidation ditch processes could effectively control the discharge of major wastewater pollutants including biochemical oxygen demand (BOD), chemical oxygen demand, nitrogen and phosphorus. The oxidation ditch process appeared to have the advantage of removing tyrosine-like substances and presented slightly better removal efficiency of tryptophan-like fluorescent (peak T) substances than the A/O and A2/O processes. Both ultraviolet absorbance at 254nm and peak T may be used to characterize the organic load of municipal wastewater, and peak T can be adopted as a gauge of the BOD removal efficacy of municipal wastewater treatment. Using C. elegans-based oxygen consumption rate assay for monitoring municipal wastewater toxicity deserves further investigations. Copyright © 2017 Elsevier Inc. All rights reserved.

Integrated lunar materials manufacturing process

NASA Technical Reports Server (NTRS)

Gibson, Michael A. (Inventor); Knudsen, Christian W. (Inventor)

1990-01-01

A manufacturing plant and process for production of oxygen on the moon uses lunar minerals as feed and a minimum of earth-imported, process materials. Lunar feed stocks are hydrogen-reducible minerals, ilmenite and lunar agglutinates occurring in numerous, explored locations mixed with other minerals in the pulverized surface layer of lunar soil known as regolith. Ilmenite (FeTiO.sub.3) and agglutinates contain ferrous (Fe.sup.+2) iron reducible by hydrogen to yield H.sub.2 O and metallic Fe at about 700.degree.-1,200.degree. C. The H.sub.2 O is electrolyzed in gas phase to yield H.sub.2 for recycle and O.sub.2 for storage and use. Hydrogen losses to lunar vacuum are minimized, with no net hydrogen (or any other earth-derived reagent) consumption except for small leaks. Feed minerals are surface-mined by front shovels and transported in trucks to the processing area. The machines are manned or robotic. Ilmenite and agglutinates occur mixed with silicate minerals which are not hydrogen-reducible at 700.degree.-1,200.degree. C. and consequently are separated and concentrated before feeding to the oxygen generation process. Solids rejected from the separation step and reduced solids from the oxygen process are returned to the mine area. The plant is powered by nuclear or solar power generators. Vapor-phase water electrolysis, a staged, countercurrent, fluidized bed reduction reactor and a radio-frequency-driven ceramic gas heater are used to improve thermal efficiency.

Chemical, electrochemical and photochemical molecular water oxidation catalysts.

PubMed

Bofill, Roger; García-Antón, Jordi; Escriche, Lluís; Sala, Xavier

2015-11-01

Hydrogen release from the splitting of water by simply using sunlight as the only energy source is an old human dream that could finally become a reality. This process involves both the reduction and oxidation of water into hydrogen and oxygen, respectively. While the first process has been fairly overcome, the conversion of water into oxygen has been traditionally the bottleneck process hampering the development of a sustainable hydrogen production based on water splitting. Fortunately, a revolution in this field has occurred during the past decade, since many research groups have been conducting an intense research in this area. Thus, while molecular, well-characterized catalysts able to oxidize water were scarce just five years ago, now a wide range of transition metal based compounds has been reported as active catalysts for this transformation. This review reports the most prominent key advances in the field, covering either examples where the catalysis is triggered chemically, electrochemically or photochemically. Copyright © 2014 Elsevier B.V. All rights reserved.

Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range

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

Rouahi, A.; Kahouli, A.; Laboratoire Materiaux, Organisation et Proprietes

2012-11-01

Two relaxation processes have been identified in amorphous TiTaO thin films deposited by reactive magnetron sputtering. The parallel angle resolved x-ray photoelectron spectroscopy and field emission scanning electron microscopy analyses have shown that this material is composed of an agglomerates mixture of TiO{sub 2}, Ta{sub 2}O{sub 5}, and Ti-Ta bonds. The first relaxation process appears at low temperature with activation energy of about 0.26 eV and is related to the first ionisation of oxygen vacancies and/or the reduction of Ti{sup 4+} to Ti{sup 3+}. The second relaxation process occurs at high temperature with activation energy of 0.95 eV. This lastmore » peak is associated to the diffusion of the doubly ionized oxygen vacancies V{sub O}e. The dispersion phenomena observed at high temperature can be attributed to the development of complex defect such as (V{sub O}e - 2Ti{sup 3+}).« less

Process for light-driven hydrocarbon oxidation at ambient temperatures

DOEpatents

Shelnutt, John A.

1990-01-01

A photochemical reaction for the oxidation of hydrocarbons uses molecular oxygen as the oxidant. A reductive photoredox cycle that uses a tin(IV)- or antimony(V)-porphyrin photosensitizer generates the reducing equivalents required to activate oxygen. This artificial photosynthesis system drives a catalytic cycle, which mimics the cytochrome P.sub.450 reaction, to oxidize hydrocarbons. An iron(III)- or manganese(III)-porphyrin is used as the hydrocarbon-oxidation catalyst. Methylviologen can be used as a redox relay molecule to provide for electron-transfer from the reduced photosensitizer to the Fe or Mn porphyrin. The system is long-lived and may be used in photo-initiated spectroscopic studies of the reaction to determine reaction rates and intermediates.

Oxygen sensitive paper

NASA Technical Reports Server (NTRS)

Whidby, J. F.

1973-01-01

Paper is impregnated with mixture of methylene blue and ethylenediaminetetraacetic acid. Methylene blue is photo-reduced to leuco-form. Paper is kept isolated from oxygen until ready for use. Paper can be reused by photo-reduction after oxygen exposure.

A modified procedure for measuring oxygen-18 content of nitrate

NASA Astrophysics Data System (ADS)

Ahmed, M. A.; Aly, A. I. M.; Abdel Monem, N.; Hanafy, M.; Gomaa, H. E.

2012-11-01

SummaryMass spectrometric analysis of O-isotopic composition of nitrate has many potential applications in studies of environmental processes. Through this work, rapid, reliable, precise, broadly applicable, catalyst-free, low-priced and less labor intensive procedure for measuring δ18O of nitrate using Isotope Ratio Mass Spectrometer has been developed and implemented. The conditions necessary to effect complete nitrate recovery and complete removal of other oxygen containing anions and dissolved organic carbon (DOC) without scarifying the isotopic signature of nitrate were investigated. The developed procedure consists of two main parts: (1) wet chemistry train for extraction and purification of nitrate from the liquid matrix; (2) off-line pyrolysis of extracted nitrate salt with activated graphite at 550 °C for 30 min. The conditions necessary to effect complete nitrate recovery and complete removal of other oxygen containing compounds were investigated. Dramatic reduction in processing times needed for analysis of δ18O of nitrate at natural abundance level was achieved. Preservation experiments revealed that chloroform (99.8%) is an effective preservative. Isotopic contents of some selected nitrate salts were measured using the modified procedure and some other well established methods at two laboratories in Egypt and Germany. Performance assessment of the whole developed analytical train was made using internationally distributed nitrate isotopes reference materials and real world sample of initial zero-nitrate content. The uncertainty budget was evaluated using the graphical nested hierarchal approach. The obtained results proved the suitability for handling samples of complicated matrices. Reduction of consumables cost by about 80% was achieved.

Transition metal substituted SrTiO3 perovskite oxides as promising functional materials for oxygen sensor

NASA Astrophysics Data System (ADS)

Misra, Sunasira

2012-07-01

Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal substituted SrTiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt substituted SrTiO3.

Impedance spectroscopy of reduced monoclinic zirconia.

PubMed

Eder, Dominik; Kramer, Reinhard

2006-10-14

Zirconia doped with low-valent cations (e.g. Y3+ or Ca2+) exhibits an exceptionally high ionic conductivity, making them ideal candidates for various electrochemical applications including solid oxide fuel cells (SOFC) and oxygen sensors. It is nevertheless important to study the undoped, monoclinic ZrO2 as a model system to construct a comprehensive picture of the electrical behaviour. In pure zirconia a residual number of anion vacancies remains because of contaminants in the material as well as the thermodynamic disorder equilibrium, but electronic conduction may also contribute to the observed conductivity. Reduction of zirconia in hydrogen leads to the adsorption of hydrogen and to the formation of oxygen vacancies, with their concentration affected by various parameters (e.g. reduction temperature and time, surface area, and water vapour pressure). However, there is still little known about the reactivities of defect species and their effect on the ionic and electronic conduction. Thus, we applied electrochemical impedance spectroscopy to investigate the electric performance of pure monoclinic zirconia with different surface areas in both oxidizing and reducing atmospheres. A novel equivalent circuit model including parallel ionic and electronic conduction has previously been developed for titania and is used herein to decouple the conduction processes. The concentration of defects and their formation energies were measured using volumetric oxygen titration and temperature programmed oxidation/desorption.

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

2015-03-01

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm-2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm-2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Emerging climate change signals in the interior ocean oxygen content

NASA Astrophysics Data System (ADS)

Tjiputra, Jerry; Goris, Nadine; Schwinger, Jörg; Lauvset, Siv

2017-04-01

Earth System Models (ESMs) indicate that human-induced climate change will introduce spatially heterogeneous modifications of dissolved oxygen in the North Atlantic. In the upper ocean, an increase (decrease) is predicted at low (high) latitude. Oxygen increase is driven by a reduction of the oxygen consumption for biological remineralization while warming-induced reduction in air-sea fluxes and increase in remineralization due to weaker overturning circulation lead to the projected decrease. In the interior ocean, modifications in the apparent oxygen utilization (AOU) dominate the overall oxygen changes. Moreover, for the southern subpolar gyre, both observations and model hindcast indicate a close relationship between interior ocean oxygen and the subpolar gyre index. Over the 21st century, all ESMs consistently project a steady weakening of this index and consequently the oxygen. Our finding shows that climate change-induced oxygen depletion in the interior has likely occurred and can already be detected. Nevertheless, considering the observational uncertainties, we show that in the proximity of southern subpolar gyre the projected interior trend is sufficiently large enough for early detection.

A metal-free electrocatalyst for carbon dioxide reduction to multi-carbon hydrocarbons and oxygenates

PubMed Central

Wu, Jingjie; Ma, Sichao; Sun, Jing; Gold, Jake I.; Tiwary, ChandraSekhar; Kim, Byoungsu; Zhu, Lingyang; Chopra, Nitin; Odeh, Ihab N.; Vajtai, Robert; Yu, Aaron Z.; Luo, Raymond; Lou, Jun; Ding, Guqiao; Kenis, Paul J. A.; Ajayan, Pulickel M.

2016-01-01

Electroreduction of carbon dioxide into higher-energy liquid fuels and chemicals is a promising but challenging renewable energy conversion technology. Among the electrocatalysts screened so far for carbon dioxide reduction, which includes metals, alloys, organometallics, layered materials and carbon nanostructures, only copper exhibits selectivity towards formation of hydrocarbons and multi-carbon oxygenates at fairly high efficiencies, whereas most others favour production of carbon monoxide or formate. Here we report that nanometre-size N-doped graphene quantum dots (NGQDs) catalyse the electrochemical reduction of carbon dioxide into multi-carbon hydrocarbons and oxygenates at high Faradaic efficiencies, high current densities and low overpotentials. The NGQDs show a high total Faradaic efficiency of carbon dioxide reduction of up to 90%, with selectivity for ethylene and ethanol conversions reaching 45%. The C2 and C3 product distribution and production rate for NGQD-catalysed carbon dioxide reduction is comparable to those obtained with copper nanoparticle-based electrocatalysts. PMID:27958290

Chemical Reactions in the Processing of Mosi2 + Carbon Compacts

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Lee, Kang N.; Maloy, Stuart A.; Heuer, Arthur H.

1993-01-01

Hot-pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt pct oxygen MoSi2 powder and a 0.59 wt pct oxygen MoSi2 powder, both with additions of 2 wt pct carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) ratios interpreted in terms of the SiO(g) and CO(g) isobars on the Si-C-O predominance diagram. The MoSi2 + carbon mixtures were then heated at the hot-pressing temperature of 2100 K. Large weight losses were observed and could be correlated with the formation of a low-melting eutectic and the formation and vaporization of SiC.

Production of aluminum-silicon alloy and ferrosilicon and commercial purity aluminum by the direct reduction process. Second interim technical report, Phase B, December 1, 1978-February 28, 1979

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

Bruno, M.J.

1979-03-01

Experimental runs were made to determine the effect of a cooler product reservoir on metal alloy yield and recovery. The reservoir temperature had no significant effect. Difficulties were experienced with operation of an oxygen injected bench scale reactor. Many tests were terminated by burden bridging or flooding of the oxygen tuyeres with metal and slag. Runs were made in which refluxing vapors were condensed in a liquid slag. The addition of CaO decreased the tendency for formation of thick, strong burden bridges but did not completely eliminate bridging. Reduction of flame temperatures did not affect the volatilization rate in themore » bench reactor. Operation of VSR-1 pilot reactor with O injection was achieved after resolving reactor shell leakage problems, by replacing the permeable ceramic shell with impermeable fused silica. Various combustion parameters were investigated, including coke size, burden height and oxygen flow rate. Steady state operation of the oxygen-coke system was attained with smooth burden movement and a 2000/sup 0/C bed temperature in the raceway vicinity. To further reduce heat losses from the raceway area. VSR-1 was redesigned to facilitate locating an induction coil below the oxygen inlets. Further evaluation of effects of impurities on alloy purification in the bench scale unit indicated a 50% decrease in product yield for starting charges containing Fe greater than 5%. Site installation for the entire alloy purification complex was completed. Operations were continued in the bench scale units to obtain design information for the pilot commercial grade Al purification unit. Procurement of construction material was established.« less

Problems with the thermogravimetric determination of oxygen stoichiometries in pure and rare-earth substituted La2RuO5

NASA Astrophysics Data System (ADS)

Riegg, S.; Müller, T.; Ebbinghaus, S. G.

2013-06-01

The oxygen stoichiometries of pure and rare-earth substituted La2RuO5 have been investigated by thermogravimetry (TG) in reducing atmosphere. Assuming that the observed total weight loss is caused by the reduction of Ru4+ to Ru-metal, remarkable oxygen deficiencies were calculated. These would correspond to ruthenium oxidation states significantly lower than the ones experimentally observed by XANES. To explain this discrepancy we investigated the reduction products by X-ray absorption spectroscopy (XAS). EXAFS measurements at the Ru-K edge revealed the presence of an X-ray amorphous ruthenium oxide, indicating an incomplete reduction. The apparent oxygen deficiencies obtained for pure and rare-earth substituted samples correlate with the amount of remaining ruthenium oxide. The presence of a ruthenium oxide species was furthermore verified by Ru-LIII XANES investigations. Our results show that the determination of oxygen contents by thermogravimetry might fail even for the easily reducable nobel metal oxides and therefore has to be applied with caution if the reaction products cannot be identified unambiguously.

Protons accumulation during anodic phase turned to advantage for oxygen reduction during cathodic phase in reversible bioelectrodes.

PubMed

Blanchet, Elise; Pécastaings, Sophie; Erable, Benjamin; Roques, Christine; Bergel, Alain

2014-12-01

Reversible bioelectrodes were designed by alternating acetate and oxygen supply. It was demonstrated that the protons produced and accumulated inside the biofilm during the anodic phase greatly favored the oxygen reduction reaction when the electrode was switched to become the biocathode. Protons accumulation, which hindered the bioanode operation, thus became an advantage for the biocathode. The bioanodes, formed from garden compost leachate under constant polarization at -0.2 V vs. SCE, were able to support long exposure to forced aeration, with only a slight alteration of their anodic efficiency. They produced a current density of 16±1.7 A/m2 for acetate oxidation and up to -0.4 A/m2 for oxygen reduction. Analysis of the microbial communities by 16S rRNA pyrosequencing revealed strong selection of Chloroflexi (49±1%), which was not observed for conventional bioanodes not exposed to oxygen. Chloroflexi were found as the dominant phylum of electroactive biofilms for the first time. Copyright © 2014 Elsevier Ltd. All rights reserved.

Process for making ultra-fine ceramic particles

DOEpatents

Stangle, Gregory C.; Venkatachari, Koththavasal R.; Ostrander, Steven P.; Schulze, Walter A.

1995-01-01

A process for producing ultra-fine ceramic particles in which droplets are formed from a ceramic precursor mixture containing a metal cation, a nitrogen-containing fuel, a solvent, and an anion capable of participating in an anionic oxidation-reduction reaction with the nitrogen containing fuel. The nitrogen-containing fuel contains at least three nitrogen atoms, at least one oxygen atom, and at least one carbon atom. The ceramic precursor mixture is dried to remove at least 85 weight percent of the solvent, and the dried mixture is then ignited to form a combusted powder.

Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy.

PubMed

Opitz, Alexander K; Nenning, Andreas; Rameshan, Christoph; Kubicek, Markus; Götsch, Thomas; Blume, Raoul; Hävecker, Michael; Knop-Gericke, Axel; Rupprechter, Günther; Klötzer, Bernhard; Fleig, Jürgen

2017-10-18

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO 2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H 2 ) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO 3-δ and (La,Sr)CrO 3-δ based perovskite-type electrodes was studied during electrochemical CO 2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO 2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO 2 reduction. In contrast to water splitting, the CO 2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.

Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy

PubMed Central

2017-01-01

Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3−δ and (La,Sr)CrO3−δ based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view. PMID:28933825

[Long-term oxygen therapy (LTOT)--what should physicians, homecare-providers and health insurance companies know?].

PubMed

Koehler, U; Hildebrandt, O; Jerrentrup, L; Koehler, K-I; Kianinejad, P; Sohrabi, K; Schäfer, H; Kenn, K

2014-03-01

Long-term oxygen treatment (LTOT) has been demonstrated to improve prognosis in patients with chronic respiratory insufficiency. In terms of pathogenesis, improved oxygenation, reduction of pulmonary artery pressure as well as reduction of respiratory work are important. Since there are considerable differences between the LTOT systems, individually tailored therapy is needed. In particular, the mobility aspects of the patients must be taken into consideration. It is important to distinguish between stationary/mobile devices with a liquid oxygen system and stationary/mobile devices with oxygen concentrator. Oxygen titration should be performed in relation to rest and activity phases (e. g. 6 minute walk test) as well as in relation to the sleep phase. Employing devices with demand-controlled valves should be critically examined. This can be undertaken only under physician orders and requires continuous monitoring. © Georg Thieme Verlag KG Stuttgart · New York.

Convenient synthesis of Mn-doped Zn (O,S) nanoparticle photocatalyst for 4-nitrophenol reduction

NASA Astrophysics Data System (ADS)

Susanto Gultom, Noto; Abdullah, Hairus; Kuo, Dong-Hau

2018-04-01

The conversion of 4-nitrophenol as a toxic and waste pollutant to 4-aminophenol as a non-toxic and useful compound by photocatalytic reduction is highly important. In this work, the solid-solution concept by doping was involved to synthesis earth-abundant and green material of Mn-doped Zn(O,S). Zn(O,S) with different Mn doping contents was easily synthesized at low temperature 90°C for 4-NP reduction without using the reducing agent of NaBH4. The Mn-doped Zn(O,S) catalyst exhibited the enhancements in optical and electrochemical properties compared to un-doped Zn(O,S).It was found that 10% Mn-doped Zn(O,S) had the best properties and it could totally reduce 4-NP after 2h photoreactions under low UV illumination. The hydrogen ion was proposed to involve the 4-NP reduction to 4-AP, which is hydrogen ion and electron replaced the oxygen in amino (NO2) group of 4-NP to form the nitro (NH2) group. We alsoproposed the incorporation of Mn in Zn site in the Zn(O,S) host lattice could make the oxygen surface bonding weak for easily forming the oxygen vacancy. The more oxygen vacancy for more hydrogen ion would be generated to consume for 4-NP reduction.

Biodegradation of chlorinated ethenes at a karst site in middle Tennessee

USGS Publications Warehouse

Byl, Thomas Duane; Williams, Shannon D.

2000-01-01

This report presents results of field and laboratory investigations examining the biodegradation of chlorinated ethenes in a karst aquifer contaminated with trichloroethylene (TCE). The study site, located in Middle Tennessee, was selected because of the presence of TCE degradation byproducts in the karst aquifer and available site hydrologic and chlorinated-ethene information. Additional chemical, biological, and hydrologic data were gathered to evaluate whether the occurrence of TCE degradation byproducts in the karst aquifer was the result of biodegradation within the aquifer or simply transport into the aquifer. Geochemical analysis established that sulfate-reducing conditions, essential for reductive dechlorination of chlorinated solvents, existed in parts of the contaminated karst aquifer. Other areas of the aquifer fluctuated between anaerobic and aerobic conditions and contained compounds associated with cometabolism, such as ethane, methane, ammonia, and dissolved oxygen. A large, diverse bacteria population inhabits the contaminated aquifer. Bacteria known to biodegrade TCE and other chlorinated solvents, such as sulfate-reducers, methanotrophs, and ammonia-oxidizers, were identified from karst-aquifer water using the RNA-hybridization technique. Results from microcosms using raw karst-aquifer water found that aerobic cometabolism and anaerobic reductive-dechlorination degradation processes were possible when appropriate conditions were established in the microcosms. These chemical and biological results provide circumstantial evidence that several biodegradation processes are active in the aquifer. Additional site hydrologic information was developed to determine if appropriate conditions persist long enough in the karst aquifer for these biodegradation processes to be significant. Continuous monitoring devices placed in four wells during the spring of 1998 indicated that pH, specific conductance, dissolved oxygen, and oxidation-reduction potentials changed very little in areas isolated from active ground-water flow paths. These stable areas in the karst aquifer had geochemical conditions and bacteria conducive to reductive dechlorination of chlorinated ethenes. Other areas of the karst aquifer were associated with active ground-water flow paths and fluctuated between anaerobic and aerobic conditions in response to rain events. Associated with this dynamic environment were bacteria and geochemical conditions conducive to cometabolism. In summary, multiple lines of evidence developed from chemical, biological, and hydrologic data demonstrate that a variety of biodegradation processes are active in this karst aquifer.

Isothermal Oxidation of Magnetite to Hematite in Air and Cyclic Reduction/Oxidation Under Carbon Looping Combustion Conditions

NASA Astrophysics Data System (ADS)

Simmonds, Tegan; Hayes, Peter C.

2017-12-01

In the carbon looping combustion process the oxygen carrier is regenerated through oxidation in air; this process has been simulated by the oxidation of dense synthetic magnetite for selected temperatures and times. The oxidation of magnetite in air is shown to occur through the formation of dense hematite layers on the particle surface. This dense hematite forms through lath type shear transformations or solid-state diffusion through the product layer. Cyclic reduction in CO-CO2/oxidation in air of hematite single crystals has been carried out under controlled laboratory conditions at 1173 K (900 °C). It has been shown that the initial reduction step is critical to determining the product microstructure, which consists of gas pore dendrites in the magnetite matrix with blocky hematite formed on the pore surfaces. The progressive growth of the magnetite layer with the application of subsequent cycles appears to continue until no original hematite remains, after which physical disintegration of the particles takes place.

Dose of Biocoagulant-Mixing Rate Combinations for Optimum Reduction of COD in Wastewater

NASA Astrophysics Data System (ADS)

Patricia, Maria Faustina; Purwono; Budihardjo, Mochamad Arief

2018-02-01

Chemical oxygen demand (COD) in domestic wastewater can be treated using flocculation-coagulation process with addition of Oyster mushroom (Pleurotus ostreatus) in powder form as biocoagulant. The fungal cell wall of Oyster mushroom comprises of chitin that is high polyelectrolyte and can be function as an absorbent of heavy metals in wastewater. The effectiveness of flocculation-coagulation process in treating wastewater depends on dose of coagulant and mixing rate. Therefore, this study aims to determine the best combination of three variation of dose of biocoagulant which are 600 mg/l, 1000 mg/l, and 2000 mg/l and mixing rate which are 100 rpm, 125 rpm, and 150 rpm that give the most reduction of COD in the wastewater. The result indicates that the combination of 1000 mg/l of biocoagulant and 100 rpm of mixing rate were found to be the most optimum combination to treat COD in the wastewater with COD reduction of 47.7%.

Ionic Conductivity and its Role in Oxidation Reactions

NASA Astrophysics Data System (ADS)

Tamimi, Mazin Abdulla

In the field of solid oxide fuel cells (SOFCs), a substantial portion of research is focused on the ability of some oxide materials to conduct oxygen anions through their structure. For electrolytes, the benefits of improving bulk transport of ions are obvious: decrease the resistive losses of the electrolyte, and device efficiency goes up and higher power densities are possible. Even for cathode materials, better bulk ion transport leads to an increase in the oxygen exchange rate at the cathode surface, and the oxygen reduction reaction at the cathode surface is the rate limiting step for SOFC operation at intermediate temperatures (500-700ºC). As operation in this regime is a key step towards lowering the manufacturing cost and increasing the lifetime of devices, much effort is spent searching for new, more conductive materials, and analyzing existing materials to discover the structure-activity relationships that influence ionic conductivity. In the first part of this work, an overview is given of the neutron powder diffraction (NPD) techniques that are used to probe the structure of the materials in later parts. In the second part, NPD was used to analyze the structures of perovskite-type cathode materials, and show that increases in bulk conductivity led to increases in the surface oxygen exchange rate of these materials. In the final part, the methods used for SOFC cathode design were applied towards the design of oxide catalysts used for certain hydrocarbon partial oxidation reactions. The reactions studied follow the Mars van Krevelen mechanism, where oxygen atoms in the catalyst are consumed as part of the reaction and are subsequently replenished by oxygen in the gas phase. Similar to SOFC cathode operation, these processes include an oxygen reduction step, so it was hypothesized that increasing the ionic conductivity of the catalysts would improve their performance, just as it does for SOFC cathode materials. While the results are preliminary, the combination of a reference catalyst for the oxidative coupling of methane with a support with very high oxygen conductivity demonstrated a small increase in performance at low temperatures.

Energy-Efficient and Environmentally Friendly Solid Oxide Membrane Electrolysis Process for Magnesium Oxide Reduction: Experiment and Modeling

NASA Astrophysics Data System (ADS)

Guan, Xiaofei; Pal, Uday B.; Powell, Adam C.

2014-06-01

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM(La0.8Sr0.2MnO3-δ)-Inconel inert anode current collector for production of magnesium and oxygen directly from magnesium oxide at 1423 K (1150 °C). The electrochemical performance of the SOM cell was evaluated by means of various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan, and electrolysis. Electronic transference numbers of the flux were measured to assess the magnesium dissolution in the flux during SOM electrolysis. The effects of magnesium solubility in the flux on the current efficiency and the SOM stability during electrolysis are discussed. An inverse correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed. Based on the experimental results, a new equivalent circuit of the SOM electrolysis process is presented. A general electrochemical polarization model of SOM process for magnesium and oxygen gas production is developed, and the maximum allowable applied potential to avoid zirconia dissociation is calculated as well. The modeling results suggest that a high electronic resistance of the flux and a relatively low electronic resistance of SOM are required to achieve membrane stability, high current efficiency, and high production rates of magnesium and oxygen.

Potential Alternatives for Advanced Energy Material Processing in High Performance Li-ion Batteries (LIBs) via Atmospheric Pressure Plasma Treatment

NASA Astrophysics Data System (ADS)

Duh, Jenq-Gong; Chuang, Shang-I.; Lan, Chun-Kai; Yang, Hao; Chen, Hsien-Wei

2015-09-01

A new processing technique by atmospheric pressure plasma (APP) jet treatment of LIBs was introduced. Ar/N2 plasma enhanced the high-rate anode performance of Li4Ti5O12. Oxygen vacancies were discovered and nitrogen doping were achieved by the surface reaction between pristine Li4Ti5O12 and plasma reactive species (N* and N2+). Electrochemical impedance spectra confirm that plasma modification increases Li ions diffusivity and reduces internal charge-transfer resistance, leading to a superior capacity (132 mAh/g) and excellent stability with negligible capacity decay over 100 cycles under 10C rate. Besides 2D material surface treatment, a specially designed APP generator that are feasible to modify 3D TiO2 powders is proposed. The rate capacity of 20 min plasma treated TiO2 exhibited 20% increment. Plasma diagnosis revealed that excited Ar and N2 was contributed to TiO2 surface reduction as companied by formation of oxygen vacancy. A higher amount of oxygen vacancy increased the chance for excited nitrogen doped onto surface of TiO2 particle. These findings promote the understanding of APP on processing anode materials in high performance LIBs.

Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process

NASA Astrophysics Data System (ADS)

Shi, Junjun; Guan, Jianyu; Guo, Dawei; Zhang, Jiushun; France, Liam John; Wang, Lefu; Li, Xuehui

2016-06-01

Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration.

ELECTROLYTIC REDUCTION OF NITRIC ACID SOLUTIONS

DOEpatents

Alter, H.W.; Barney, D.L.

1958-09-30

A process is presented for the treatment of radioactivc waste nitric acid solutions. The nitric acid solution is neutralized with an alkali metal hydroxide in an amount sufficient to precipitate insoluble hydroxides, and after separation of the precipitate the solution is electrolyzed to convert the alkali nitrate formed, to alkali hydroxide, gaseous ammonla and oxygen. The solution is then reusable after reducing the volume by evaporating the water and dissolved ammonia.

Solar photolysis of water

NASA Technical Reports Server (NTRS)

Ryason, P. R. (Inventor)

1978-01-01

A cyclic process is described for the solar photolysis of water, including a first stage in which water is reduced in the presence of a Eu(+2) photooxidizable reagent producing hydrogen and spent oxidized Eu(+3) reagent. The spent reagent Eu(+3) is reduced by means of a transition metal ligand complex reductant, RuL(+3) in a photoexcited state, such as a ruthenium pyridyl complex. Due to competing reactions between the photolysis and regeneration products, the photooxidation reaction must be separated from the regeneration in space and time by supporting the reagent and/or the reductant on solid supports and utilizing pH, wavelength and flow control to maximize hydrogen and oxygen production.

Manganese oxide/poly(3,4-ethylenedioxythiophene) hybrid electrocatalysts for the oxygen reduction reaction in alkaline fuel cells

DOE PAGES

Lambert, Timothy N.; Vigil, Julian A.

2016-08-22

Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO x/PEDOT provided improvements over MnO x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO x/PEDOTmore » also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO x with PEDOT and due to the increase in Mn 3+ content at the surface of the oxide.« less

Manganese oxide/poly(3,4-ethylenedioxythiophene) hybrid electrocatalysts for the oxygen reduction reaction in alkaline fuel cells

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

Lambert, Timothy N.; Vigil, Julian A.

Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO x/PEDOT provided improvements over MnO x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO x/PEDOTmore » also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO x with PEDOT and due to the increase in Mn 3+ content at the surface of the oxide.« less

Oxygen reduction reaction catalyzed by nickel complexes based on thiophosphorylated calix[4]resorcinols and immobilized in the membrane electrode assembly of fuel cells.

PubMed

Kadirov, M K; Knyazeva, I R; Nizameev, I R; Safiullin, R A; Matveeva, V I; Kholin, K V; Khrizanforova, V V; Ismaev, T I; Burilov, A R; Budnikova, Yu H; Sinyashin, O G

2016-10-18

The catalytic activity of the nickel complexes of thiophosphorylated calix[4]resorcinols for oxygen reduction in a polymer electrolyte membrane fuel cell (PEMFC) has been studied. The conformation of the macrocyclic ligand determines the morphology and catalytic properties of the resulting organometallic species.

Trend in the Catalytic Activity of Transition Metals for the Oxygen Reduction Reaction by Lithium

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

Dathar, Gopi Krishna Phani; Shelton Jr, William Allison; Xu, Ye

2012-01-01

Periodic density functional theory (DFT) calculations indicate that the intrinsic activity of Au, Ag, Pt, Pd, Ir, and Ru for the oxygen reduction reaction by Li (Li-ORR) forms a volcano-like trend with respect to the adsorption energy of oxygen, with Pt and Pd being the most active. The trend is based on two mechanisms: the reduction of molecular O{sub 2} on Au and Ag and of atomic O on the remaining metals. Step edges are found to be more active for catalyzing the Li-ORR than close-packed surfaces. Our findings identify important considerations in the design of catalyst-promoted air cathodes formore » nonaqueous Li-air batteries.« less

Investigation on electrochemical behavior and its catalytic effect on oxygen reduction reaction of 3-Ferrocenyl dihydropyrazole derivative as electron relay

NASA Astrophysics Data System (ADS)

Zeng, Han; Huo, Wen-Shan; Zhao, Shu-Xian; Zhang, Yu-He

2017-11-01

Amino group surface tailored multi-wall carbon nano-tubes were covalently tethered to the gold disk electrode and Laccase molecules were covalently coupled to nano-tubes to prepare Lac-based electrode. Derivative of 3-ferrocenyl dihydropyrazole (FDPFFP) was proposed to be electron mediator for mediated oxygen reduction reaction. Investigation in electro-chemical behavior and catalytic performance to enzymatic reaction of FDPFFP indicated that it displayed quasi-reversible characteristics of electro-chemical reaction with rapid dynamics of electron shuttle and had apparent catalytic effect in oxygen reduction (onset potential for catalysis at 450 mV vs NHE). This enzymatic catalysis was restrained by the step in diffusion of substrate.

The roles of cerebral blood flow, capillary transit time heterogeneity, and oxygen tension in brain oxygenation and metabolism

PubMed Central

Jespersen, Sune N; Østergaard, Leif

2012-01-01

Normal brain function depends critically on moment-to-moment regulation of oxygen supply by the bloodstream to meet changing metabolic needs. Neurovascular coupling, a range of mechanisms that converge on arterioles to adjust local cerebral blood flow (CBF), represents our current framework for understanding this regulation. We modeled the combined effects of CBF and capillary transit time heterogeneity (CTTH) on the maximum oxygen extraction fraction (OEFmax) and metabolic rate of oxygen that can biophysically be supported, for a given tissue oxygen tension. Red blood cell velocity recordings in rat brain support close hemodynamic–metabolic coupling by means of CBF and CTTH across a range of physiological conditions. The CTTH reduction improves tissue oxygenation by counteracting inherent reductions in OEFmax as CBF increases, and seemingly secures sufficient oxygenation during episodes of hyperemia resulting from cortical activation or hypoxemia. In hypoperfusion and states of blocked CBF, both lower oxygen tension and CTTH may secure tissue oxygenation. Our model predicts that disturbed capillary flows may cause a condition of malignant CTTH, in which states of higher CBF display lower oxygen availability. We propose that conditions with altered capillary morphology, such as amyloid, diabetic or hypertensive microangiopathy, and ischemia–reperfusion, may disturb CTTH and thereby flow-metabolism coupling and cerebral oxygen metabolism. PMID:22044867

A comparison of antibacterial and antibiofilm efficacy of phenothiazinium dyes between Gram positive and Gram negative bacterial biofilm.

PubMed

Misba, Lama; Zaidi, Sahar; Khan, Asad U

2017-06-01

Antimicrobial photodynamic therapy (APDT) is a process that generates reactive oxygen species (ROS) in presence of photosensitizer, visible light and oxygen which destroys the bacterial cells. We investigated the photoinactivation efficiency of phenothiazinium dyes and the effect of ROS generation on Gram positive and Gram negative bacterial cell as well as on biofilm. Enterococcus faecalis and Klebsiella pneumonia were incubated with all the three phenothiazinium dyes and exposed to 630nm of light. After PDT, colony forming unit (CFU) were performed to estimate the cell survival fraction. Intracellular reactive oxygen species (ROS) was detected by DCFH-DA. Crystal violet (CV) assay and extracellular polysaccharides (EPS) reduction assay were performed to analyze antibiofilm effect. Confocal laser electron microscope (CLSM) scanning electron microscope (SEM) was performed to assess the disruption of biofilm. 8log 10 reduction in bacterial count was observed in Enterococcus faecalis while 3log 10 in Klebsiella pneumoniae. CV and EPS reduction assay revealed that photodynamic inhibition was more pronounced in Enterococcus faecalis. In addition to this CLSM and SEM study showed an increase in cell permeability of propidium iodide and leakage of cellular constituents in treated preformed biofilm which reflects the antibiofilm action of photodynamic therapy. We conclude that Gram-positive bacteria (Enterococcus faecalis) are more susceptible to APDT due to increased level of ROS generation inside the cell, higher photosensitizer binding efficiency and DNA degradation. Phenothiazinium dyes are proved to be highly efficient against both planktonic and biofilm state of cells. Copyright © 2017 Elsevier B.V. All rights reserved.

Evidence of alloy formation during reduction of platinized tin oxide surfaces

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

1989-01-01

Ion scattering spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis have been used to examine a platinized tin oxide catalyst surface before, during, and after reduction by annealing under vacuum at 250 to 450 C. These techniques were then used to examine the reduced surface after a room-temperature, low-pressure oxygen exposure. The spectral results and the behavior of the reduced surface toward oxygen exposure both indicate that a Pt/Sn alloy is produced during reduction.

Distribution of dissolved manganese in the Peruvian Upwelling and Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Vedamati, Jagruti; Chan, Catherine; Moffett, James W.

2015-05-01

The geochemistry of manganese (Mn) in seawater is dominated by its redox chemistry, as Mn(II) is soluble and Mn(IV) forms insoluble oxides, and redox transformations are mediated by a variety of processes in the oceans. Dissolved Mn (DMn) accumulates under reducing conditions and is depleted under oxidizing conditions. Thus the Peruvian upwelling region, characterized by highly reducing conditions over a broad continental shelf and a major oxygen minimum zone extending far offshore, is potentially a large source of Mn to the eastern Tropical South Pacific. In this study, DMn was determined on cruises in October 2005 and February 2010 in the Peruvian Upwelling and Oxygen Minimum Zone, to evaluate the relationship between Mn, oxygen and nitrogen cycle processes. DMn concentrations were determined using simple dilution and matrix-matched external standardization inductively coupled mass spectrometry. Surprisingly, DMn was depleted under the most reducing conditions along the Peruvian shelf. Concentrations of dissolved Mn in surface waters increased offshore, indicating that advection of Mn offshore from the Peruvian shelf is a minor source. Subsurface Mn maxima were observed within the oxycline rather than within the oxygen minimum zone (OMZ), indicating they arise from remineralization of organic matter rather than reduction of Mn oxides. The distribution of DMn appears to be dominated by non-redox processes and inputs from the atmosphere and from other regions associated with specific water masses. Lower than expected DMn concentrations on the shelf probably reflect limited fluvial inputs from the continent and efficient offshore transport. This behavior is in stark contrast to Fe, reported in a companion study which is very high on the shelf and undergoes dynamic redox cycling.

Effect of process variables on the sulfate reduction process in bioreactors treating metal-containing wastewaters: factorial design and response surface analyses.

PubMed

Villa-Gomez, D K; Pakshirajan, K; Maestro, R; Mushi, S; Lens, P N L

2015-07-01

The individual and combined effect of the pH, chemical oxygen demand (COD) and SO4 (2-) concentration, metal to sulfide (M/S(2-)) ratio and hydraulic retention time (HRT) on the biological sulfate reduction (SR) process was evaluated in an inverse fluidized bed reactor by factorial design analysis (FDA) and response surface analysis (RSA). The regression-based model of the FDA described the experimental results well and revealed that the most significant variable affecting the process was the pH. The combined effect of the pH and HRT was barely observable, while the pH and COD concentration positive effect (up to 7 and 3 gCOD/L, respectively) enhanced the SR process. Contrary, the individual COD concentration effect only enhanced the COD removal efficiency, suggesting changes in the microbial pathway. The RSA showed that the M/S(2-) ratio determined whether the inhibition mechanism to the SR process was due to the presence of free metals or precipitated metal sulfides.

Noninvasive investigation of skin local hypothermia influence upon local oxygenation and hemoglobin concentration

NASA Astrophysics Data System (ADS)

Douplik, Alexandre Y.; Kessler, Manfred D.; Kakihana, Yasuyuki; Krug, Alfons

1997-08-01

Functional evaluation of local hemoglobin concentration and hemoglobin oxygenation based on back scattering spectra from human skin in vivo have been obtained in visible range (502 - 628 nm) by a rapid microlightguide spectrometer (EMPHO II) with step 250 micrometer. Analysis of received results has shown that during local cooling there is two nearly simultaneous reactions: reduction of hemoglobin concentration and increase of hemoglobin oxygenation level. In a case when one has used previous heating of planning place for cooling, reduction of hemoglobin concentration is expressed higher by 22 - 33%.

Computational study: Reduction of iron corrosion in lead coolant of fast nuclear reactor

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

Arkundato, Artoto; Su'ud, Zaki; Abdullah, Mikrajuddin

2012-06-20

In this paper we report molecular dynamics simulation results of iron (cladding) corrosion in interaction with lead coolant of fast nuclear reactor. The goal of this work is to study effect of oxygen injection to the coolant to reduce iron corrosion. By evaluating diffusion coefficients, radial distribution functions, mean-square displacement curves and observation of crystal structure of iron before and after oxygen injection, we concluded that a significant reduction of corrosion can be achieved by issuing about 2% of oxygen atoms into lead coolant.

Compositional engineering of perovskite oxides for highly efficient oxygen reduction reactions.

PubMed

Chen, Dengjie; Chen, Chi; Zhang, Zhenbao; Baiyee, Zarah Medina; Ciucci, Francesco; Shao, Zongping

2015-04-29

Mixed conducting perovskite oxides are promising catalysts for high-temperature oxygen reduction reaction. Pristine SrCoO(3-δ) is a widely used parent oxide for the development of highly active mixed conductors. Doping a small amount of redox-inactive cation into the B site (Co site) of SrCoO(3-δ) has been applied as an effective way to improve physicochemical properties and electrochemical performance. Most findings however are obtained only from experimental observations, and no universal guidelines have been proposed. In this article, combined experimental and theoretical studies are conducted to obtain fundamental understanding of the effect of B-site doping concentration with redox-inactive cation (Sc) on the properties and performance of the perovskite oxides. The phase structure, electronic conductivity, defect chemistry, oxygen reduction kinetics, oxygen ion transport, and electrochemical reactivity are experimentally characterized. In-depth analysis of doping level effect is also undertaken by first-principles calculations. Among the compositions, SrCo0.95Sc0.05O(3-δ) shows the best oxygen kinetics and corresponds to the minimum fraction of Sc for stabilization of the oxygen-vacancy-disordered structure. The results strongly support that B-site doping of SrCoO(3-δ) with a small amount of redox-inactive cation is an effective strategy toward the development of highly active mixed conducting perovskites for efficient solid oxide fuel cells and oxygen transport membranes.

Prospective evaluation of haemoglobin oxygen saturation at rest and after exercise in paediatric sickle cell disease patients

PubMed Central

Campbell, Andrew; Minniti, Caterina P.; Nouraie, Mehdi; Arteta, Manuel; Rana, Sohail; Onyekwere, Onyinye; Sable, Craig; Ensing, Gregory; Dham, Niti; Luchtman-Jones, Lori; Kato, Gregory J.; Gladwin, Mark T.; Castro, Oswaldo L.; Gordeuk, Victor R.

2009-01-01

Summary Low steady state haemoglobin oxygen saturation in patients with sickle cell anaemia has been associated with the degree of anaemia and haemolysis. How much pulmonary dysfunction contributes to low saturation is not clear. In a prospective study of children and adolescents with sickle cell disease aged 3–20 years at steady state and matched controls, 52% of 391 patients versus 24% of 63 controls had steady state oxygen saturation <99% (P < 0·0001), 9% of patients versus no controls had saturation <95% (P = 0·008) and 8% of patients versus no controls had exercise-induced reduction in saturation ≥3%. Decreasing haemoglobin concentration (P ≤ 0·001) and increasing haemolysis (P ≤ 0·003) but not pulmonary function tests were independent predictors of both lower steady-state saturation and exercise-induced reduction in saturation. Neither history of stroke nor history of acute chest syndrome was significantly associated with lower steady-state oxygen saturation or exercise-induced reduction in saturation. Tricuspid regurgitation velocity was higher in patients with lower steady state haemoglobin oxygen saturation (P = 0·003) and with greater decline in oxygen saturation during the six-minute walk (P = 0·022). In conclusion, lower haemoglobin oxygen saturation is independently associated with increasing degrees of anaemia and haemolysis but not pulmonary function abnormalities among children and adolescents with sickle cell disease. PMID:19694721

Respiration of Nitrate and Nitrite.

PubMed

Cole, Jeffrey A; Richardson, David J

2008-09-01

Nitrate reduction to ammonia via nitrite occurs widely as an anabolic process through which bacteria, archaea, and plants can assimilate nitrate into cellular biomass. Escherichia coli and related enteric bacteria can couple the eight-electron reduction of nitrate to ammonium to growth by coupling the nitrate and nitrite reductases involved to energy-conserving respiratory electron transport systems. In global terms, the respiratory reduction of nitrate to ammonium dominates nitrate and nitrite reduction in many electron-rich environments such as anoxic marine sediments and sulfide-rich thermal vents, the human gastrointestinal tract, and the bodies of warm-blooded animals. This review reviews the regulation and enzymology of this process in E. coli and, where relevant detail is available, also in Salmonella and draws comparisons with and implications for the process in other bacteria where it is pertinent to do so. Fatty acids may be present in high levels in many of the natural environments of E. coli and Salmonella in which oxygen is limited but nitrate is available to support respiration. In E. coli, nitrate reduction in the periplasm involves the products of two seven-gene operons, napFDAGHBC, encoding the periplasmic nitrate reductase, and nrfABCDEFG, encoding the periplasmic nitrite reductase. No bacterium has yet been shown to couple a periplasmic nitrate reductase solely to the cytoplasmic nitrite reductase NirB. The cytoplasmic pathway for nitrate reduction to ammonia is restricted almost exclusively to a few groups of facultative anaerobic bacteria that encounter high concentrations of environmental nitrate.

Reversal of Increasing Tropical Ocean Hypoxia Trends With Sustained Climate Warming

NASA Astrophysics Data System (ADS)

Fu, Weiwei; Primeau, Francois; Keith Moore, J.; Lindsay, Keith; Randerson, James T.

2018-04-01

Dissolved oxygen (O2) is essential for the survival of marine animals. Climate change impacts on future oxygen distributions could modify species biogeography, trophic interactions, biodiversity, and biogeochemistry. The Coupled Model Intercomparison Project Phase 5 models predict a decreasing trend in marine O2 over the 21st century. Here we show that this increasing hypoxia trend reverses in the tropics after 2100 in the Community Earth System Model forced by atmospheric CO2 from the Representative Concentration Pathway 8.5 and Extended Concentration Pathway 8.5. In tropical intermediate waters between 200 and 1,000 m, the model predicts a steady decline of O2 and an expansion of oxygen minimum zones (OMZs) during the 21st century. By 2150, however, the trend reverses with oxygen concentration increasing and OMZ volume shrinking through 2300. A novel five-box model approach in conjunction with output from the full Earth system model is used to separate the contributions of biological and physical processes to the trends in tropical oxygen. The tropical O2 recovery is caused mainly by reductions in tropical biological export, coupled with a modest increase in ventilation after 2200. The time-evolving oxygen distribution impacts marine nitrogen cycling, with potentially important climate feedbacks.

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy

PubMed Central

Shearing, Paul R.; Brightman, Edward; Brett, Dan J. L.; Brandon, Nigel P.; Cohen, Lesley F.

2016-01-01

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single‐step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance. PMID:27595058

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy.

PubMed

Maher, Robert C; Shearing, Paul R; Brightman, Edward; Brett, Dan J L; Brandon, Nigel P; Cohen, Lesley F

2016-01-01

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single-step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance.

Methane–oxygen electrochemical coupling in an ionic liquid: a robust sensor for simultaneous quantification†

PubMed Central

Wang, Zhe; Guo, Min; Baker, Gary A.; Stetter, Joseph R.; Lin, Lu; Mason, Andrew J.

2017-01-01

Current sensor devices for the detection of methane or natural gas emission are either expensive and have high power requirements or fail to provide a rapid response. This report describes an electrochemical methane sensor utilizing a non-volatile and conductive pyrrolidinium-based ionic liquid (IL) electrolyte and an innovative internal standard method for methane and oxygen dual-gas detection with high sensitivity, selectivity, and stability. At a platinum electrode in bis(trifluoromethylsulfonyl)imide (NTf2)-based ILs, methane is electro-oxidized to produce CO2 and water when an oxygen reduction process is included. The in situ generated CO2 arising from methane oxidation was shown to provide an excellent internal standard for quantification of the electrochemical oxygen sensor signal. The simultaneous quantification of both methane and oxygen in real time strengthens the reliability of the measurements by cross-validation of two ambient gases occurring within a single sample matrix and allows for the elimination of several types of random and systematic errors in the detection. We have also validated this IL-based methane sensor employing both conventional solid macroelectrodes and flexible microfabricated electrodes using single- and double-potential step chronoamperometry. PMID:25093213

Multiscale modeling and experimental interpretation of perovskite oxide materials in thermochemical energy storage and conversion for application in concentrating solar power

NASA Astrophysics Data System (ADS)

Albrecht, Kevin J.

Decarbonization of the electric grid is fundamentally limited by the intermittency of renewable resources such as wind and solar. Therefore, energy storage will play a significant role in the future of grid-scale energy generation to overcome the intermittency issues. For this reason, concentrating solar power (CSP) plants have been a renewable energy generation technology of interest due to their ability to participate in cost effective and efficient thermal energy storage. However, the ability to dynamically dispatch a CSP plant to meet energy demands is currently limited by the large quantities of sensible thermal energy storage material needed in a molten salt plant. Perovskite oxides have been suggested as a thermochemical energy storage material to enhance the energy storage capabilities of particle-based CSP plants, which combine sensible and chemical modes of energy storage. In this dissertation, computational models are used to establish the thermochemical energy storage potential of select perovskite compositions, identify system configurations that promote high values of energy storage and solar-to-electric efficiency, assess the kinetic and transport limitation of the chemical mode of energy storage, and create receiver and reoxidation reactor models capable of aiding in component design. A methodology for determining perovskite thermochemical energy storage potential is developed based on point defect models to represent perovskite non-stoichiometry as a function of temperature and gas phase oxygen partial pressure. The thermodynamic parameters necessary for the model are extracted from non-stoichiometry measurements by fitting the model using an optimization routine. The procedure is demonstrated for Ca0.9Sr0.1MnO 3-d which displayed combined energy storage values of 705.7 kJ/kg -1 by cycling between 773 K and 0.21 bar oxygen to 1173 K and 10 -4 bar oxygen. Thermodynamic system-level models capable of exploiting perovskite redox chemistry for energy storage in CSP plants are presented. Comparisons of sweep gas and vacuum pumping reduction as well as hot storage conditions indicate that solar-to-electric efficiencies are higher for sweep gas reduction system at equivalent values of energy storage if the energy parasitics of commercially available devices are considered. However, if vacuum pump efficiency between 15% and 30% can be achieved, the reduction methods will be approximately equal. Reducing condition oxygen partial pressures below 10-3 bar for sweep gas reduction and 10-2 bar for vacuum pumping reduction result in large electrical parasitics, which significantly reduce solar-to-electric efficiency. A model based interpretation of experimental measurements made for perovskite redox cycling using sweep gas in a packed bed is presented. The model indicates that long reduction times for equilibrating perovskites with low oxygen partial pressure sweep gas, compared to reoxidation, are primarily due to the oxygen carrying capacity of high purity sweep gas and not surface kinetic limitations. Therefore, achieving rapid reduction in the limited receiver residence time will be controlled by the quantity of sweep gas introduced. Effective kinetic parameters considering surface reaction and radial particle diffusion are fit to the experimental data. Variable order rate expressions without significant particle radial diffusion limitations are shown to be capable of representing the reduction and oxidation data. Modeling of a particle reduction receiver using continuous flow of perovskite solid and sweep gas in counter-flow configuration has identified issues with managing the oxygen evolved by the solid as well as sweep gas flow rates. Introducing sweep gas quantities necessary for equilibrating the solid with oxygen partial pressures below 10-2 are shown to result in gas phase velocities above the entrainment velocity of 500 um particles. Receiver designs with considerations for gas management are investigated and the results indicate that degrees of reduction corresponding to only oxygen partial pressures of 10-2 bar are attained. Numerical investigation into perovskite thermochemical energy storage indicates that achieving high levels of reduction through sweep gas or vacuum pumping to lower gas phase oxygen partial pressure below 10-2 bar display issues with parasitic energy consumption and gas phase management. Therefore, focus on material development should place a premium on thermal reduction and reduction by shifting oxygen partial pressure between ambient and 10-2 bar. Such a material would enable the development of a system with high solar-to-electric efficiencies and degrees of reduction which are attainable in realistic component geometries.

Rooting Responses of Three Oak Species to Low Oxygen Stress

Treesearch

Karel A. Jacobs; James D. MacDonald; Alison M. Berry; Laurence R. Costello

1997-01-01

Rooting characteristics were compared in blue (Q. douglasii), valley (Q. lobata), and cork oak (Q. suber) seedlings under hypoxic (low oxygen) conditions. A 50 percent reduction in root growth occurred in all species at an oxygen level of 4 percent, or an oxygen diffusion rate of 0.3 mg cm-2...

Low oxygen level increases proliferation and metabolic changes in bovine granulosa cells.

PubMed

Shiratsuki, Shogo; Hara, Tomotaka; Munakata, Yasuhisa; Shirasuna, Koumei; Kuwayama, Takehito; Iwata, Hisataka

2016-12-05

The present study addresses molecular backgrounds underlying low oxygen induced metabolic changes and 1.2-fold change in bovine granulosa cell (GCs) proliferation. RNA-seq revealed that low oxygen (5%) upregulated genes associated with HIF-1 and glycolysis and downregulated genes associated with mitochondrial respiration than that in high oxygen level (21%). Low oxygen level induced high glycolytic activity and low mitochondrial function and biogenesis. Low oxygen level enhanced GC proliferation with high expression levels of HIF-1, VEGF, AKT, mTOR, and S6RP, whereas addition of anti-VEGF antibody decreased cellular proliferation with low phosphorylated AKT and mTOR expression levels. Low oxygen level reduced SIRT1, whereas activation of SIRT1 by resveratrol increased mitochondrial replication and decreased cellular proliferation with reduction of phosphorylated mTOR. These results suggest that low oxygen level stimulates the HIF1-VEGF-AKT-mTOR pathway and up-regulates glycolysis, which contributes to GC proliferation, and downregulation of SIRT1 contributes to hypoxia-associated reduction of mitochondria and cellular proliferation. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Mechanisms and detectability of oxygen depletion in the North Atlantic

NASA Astrophysics Data System (ADS)

Tjiputra, J. F.; Goris, N.; Lauvset, S. K.; Schwinger, J.

2016-12-01

Dissolved oxygen is a key tracer in models used to represent the tight interaction between ocean biogeochemical cycle and circulation. Future ocean warming and stratification are projected, leading to a reduced oxygen concentration. Reduction in export production, in contrast, is projected to increase subsurface concentration by lowering the oxygen consumption during organic matter remineralization. In this exercise, we use a suite of CMIP5 models to study the oxygen evolution under the RCP8.5 scenario focusing on the North Atlantic, a region of rapid and steady circulation change. Most models agree with a large reduction in the deep North Atlantic (north of 40N), whereas an increase is projected in the upper subtropical ocean region. We attribute the former to weakening of the net primary production due to stronger stratification and the latter to less air-sea oxygen flux owing to less ventilation. The models also show that interior oxygen could provide earlier indicator of climate change than surface tracers. Sustained observation of oxygen is therefore crucial to reaffirm the ongoing circulation change due to global warming.

Use of pulse oximeter placed on a gastroschisis silo to monitor intestinal oxygen saturation.

PubMed

Kim, Sunghoon; Betts, James; Yedlin, Steve; Rowe, Richard; Idowu, Olajire

2006-09-01

The use of a silo for temporary coverage of exposed viscera for newborns with gastroschisis has allowed gradual reduction of the externalized intestine into the abdominal cavity. However, there has not been an easy way to monitor blood perfusion to the intestine within the silo other than with visual examination. In addition, visual examination of bowel through the silo is sometimes difficult for medical staff due to serositis and peel over the bowel. We have adopted an approach to monitor oxygen saturation of silo-contained intestine by placing a pulse oximeter sensor on the surface of the transparent silo to detect intestinal ischemia. Pulse oximeter sensors were applied on both a patient's distal extremity and the silo on five consecutive patients who were born with gastroschisis. The sensor was left on the silo during the entire period of gradual reduction. Perfusion index, pulse and oxygen saturation were observed and checked against the sensor placed on a peripheral extremity. The silo-placed pulse oximeter and peripheral pulse oximeter sensors showed a similar pulse and oxygen saturation throughout the reduction period in all five patients. In general, perfusion index was higher from the silo pulse oximeter compared to the peripheral pulse oximeter reading. A pulse oximeter can be used to monitor intestinal oxygen saturation contained within a silo and help modulate the rate of manual reduction of intestine.