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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Choosing Compositions Of Electrocatalysts

Simple theory predicts compositions of alloys that exhibit maximum catalytic activities in presence of certain reactants. Method used to select best catalysts for electrochemical batteries and fuel cells. Oxygen-electrode overvoltage plotted against solubility parameter of lead/platinum electrode in acidic and basic solutions. Electrode formed by plating mixtures of lead and platinum, corresponding to various solubility parameters. Method based on one used to analyze activities of nonelectrical catalysts in reactions involving hydrogen or oxygen. Rate of such reaction increases when solubility parameter of catalyst matches reactant.

Lawson, Daniel D.↗
NASA NTRS1983

Electrode kinetics of oxygen reduction - A theoretical and experimental analysis of the rotating ring-disc electrode method

In order to calculate most of the rate constants for the intermediate formation of H2O2 in the electroreduction of O2 to H2O, the theoretical treatments of the rotating ring-disc electrode method by Damjanovic et al. (1966, 1967), Bagotskii et al. (1968, 1969), and Wroblowa et al. (1976) are modified. Rotating ring-disc electrode experimental data obtained for O2 reduction in Pt in 0.55 M H2SO4 are used to illustrate the calculations of rate constants according to the above theoretical treatments. A simple reaction model as proposed by the first author is consistent with the experimental data. The results indicate that O2 (97 percent) reduces to H2O in a direct four-electron transfer reaction. The adsorption of O2 is probably the rate-determining step in the potential region more negative than 0.5 V vs. reversible hydrogen electrode.

Hsueh, K.-L.↗
NASA NTRS1993

Advances in direct oxidation methanol fuel cells

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt/Ru and Pt catalyzed fuel and air/O2 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 C. The cell voltage is near 0.5 V at 300 mA/cm(exp 2) current density and an operating temperature of 90 C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate.

Surampudi, S.↗
NASA NTRS1972

The gas exchange of hydrogen-adapted algae as followed by mass spectrometry.

The combination of a mass spectrometer inlet and an oxygen electrode in the same vessel permitted continuous recording of the gas exchange of hydrogenase-containing anaerobically adapted algae. In contrast to conventional manometry, the present method made it possible to discern the simultaneous course of reactions involving O2, CO2, and H2. The experiments strongly support the idea of a balance between the photoproduction and photoutilization of H2.

Stuart, T. S.↗
NASA NTRS1976

Oxygen electrocatalysts for life support systems

The irreversibility of the oxygen electrode increases by 30 to 60 percent the energy required for water electrolysis over the thermodynamic value in life support systems involving conventional water electrolysis cells. To minimize this voltage loss, high area electrocatalysts, such as platinum metal, are often used for the O2 anode, but even so, the losses are still very substantial. In an attempt to find more effective electrocatalysts for this application, a number of defect metal oxides have been examined.

Ogrady, W. E.↗
NASA NTRS1989

A survey of advanced battery systems for space applications

The results of a survey on advanced secondary battery systems for space applications are presented. The objectives were: to identify advanced battery systems capable of meeting the requirements of various types of space missions, with significant advantages over currently available batteries, to obtain an accurate estimate of the anticipated improvements of these advanced systems, and to obtain a consensus for the selection of systems most likely to yield the desired improvements. Few advanced systems are likely to exceed a specific energy of 150 Wh/kg and meet the additional requirements of safety and reliability within the next 15 years. The few that have this potential are: (1) regenerative fuel cells, both alkaline and solid polymer electrolyte (SPE) types for large power systems; (2) lithium-intercalatable cathodes, particularly the metal ozides intercalatable cathodes (MnO2 or CoO2), with applications limited to small spacecrafts requiring limited cycle life and low power levels; (3) lithium molten salt systems (e.g., LiAl-FeS2); and (4) Na/beta Alumina/Sulfur or metal chlorides cells. Likely technological advances that would enhance the performance of all the above systems are also identified, in particular: improved bifunctional oxygen electrodes; improved manufacturing technology for thin film lithium electrodes in combination with polymeric electrolytes; improved seals for the lithium molten salt cells; and improved ceramics for sodium/solid electrolyte cells.

Attia, Alan I.↗
NASA NTRS2000

BOREAS TE-10 Photosynthetic Response Data

The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-10 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the gas exchange, reflectance, transmittance, chlorophyll content, carbon content, hydrogen content, nitrogen content, and photosynthetic response of boreal vegetation. This data set contains measurements of quantitative parameters and leaf photosynthetic response to increases in light conducted in the SSA during the growing seasons of 1994 and 1996 using an oxygen electrode system. Leaf photosynthetic responses were not collected in 1996. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗
NASA NTRS1992

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

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.

Parthasarathy, Arvind↗
NASA NTRS1993

A High Performance H2-Cl2 Fuel Cell for Space Power Applications

NASA has numerous airborne/spaceborne applications for which high power and energy density power sources are needed. The proton exchange membrane fuel cell (PEMFC) is an attractive candidate for such a power source. PEMFC's offer many advantages for airborne/spaceborne applications. They have high power and energy densities, convert fuel to electrical power with high efficiency at both part and full load, and can rapidly startup and shutdown. In addition, PEMFC's are lightweight and operate silently. A significant impediment to the attainment of very high power and energy densities by PEMFC's is their current exclusive reliance on oxygen as the oxidant. Conventional PEMFC's oxidize hydrogen at the anode and reduce oxygen at the cathode. The electrode kinetics of oxygen reduction are known to be highly irreversible, incurring large overpotential losses. In addition, the modest open circuit potential of 1.2V for the H2-O2 fuel cell is unattainable due to mixed potential effects at the oxygen electrode. Because of the high overpotential losses, cells using H2 and O2 are capable of achieving high current densities only at very low cell voltages, greatly curtailing their power output. Based on experimental work on chlorine reduction in a gas diffusion electrode, we believe significant increases in both the energy and power densities of PEMFC systems can be achieved by employing chlorine as an alternative oxidant.

Anderson, Everett B.↗
NASA NTRS1990

Space Electrochemical Research and Technology Conference, 2nd, Cleveland, OH, Apr. 11-13, 1989, Proceedings

Attention is given to topics of advanced concepts, hydrogen-oxygen fuel cells and electrolyzers, nickel electrodes, and advanced rechargeable batteries. Papers are presented on human exploration mission studies, advanced rechargeable sodium batteries with novel cathodes, advanced double-layer capacitors, recent advances in solid-polymer electrolyte fuel cell technology with low platinum loading electrodes, electrocatalysts for oxygen electrodes in fuel cells and water electrolyzers for space applications, and the corrosion testing of candidates for the alkaline fuel cell cathode. Other papers are on a structural comparison of nickel electodes and precursor phases, the application of electrochemical impedance spectroscopy for characterizing the degradation of Ni(OH)2/NiOOH electrodes, advances in lightweight nickel electrode technology, multimission nickel-hydrogen battery cell for the 1990s, a sodium-sulfur battery flight experiment definition study, and advances in ambient-temperature secondary lithium cells.

O'Donnell, Patricia M.↗