Electrode kinetics of fuel oxidation on nickel and cobalt electrodes is discussed for three selected molten carbonate mixtures. The measurements were made using a potential step technique. The highest exchange current values were found on nickel anodes in all melts, and the highest of these values were found in the melt comprised of 43.5 mole percent Li2COa-31.5 mole percent Na2CO3-25 mole percent K2CO3. In this ternary melt the exchange current density on nickel varied from 78 mA/cm 2 for intermediate-BTU fuel to 22 mA/cm 2 for low-BTU fuel at 650~ The exchange current density was found to have an electrochemical reaction order parameter at constant overpotential of around 0.25 for hydrogen, carbon dioxide, and water. Electrochemical performance of the two anode materials in the three melts is discussed, and a tentative reaction mechanism is suggested for the oxidation reaction.The molten carbonate fuel cell (MCFC) operates at 650~ and consists of a porous nickel anode together with a porous nickel cathode, both of which are pressed against what is called the electrolyte tile. This tile contains both an inert matrix into which can be supported a variety of alkali carbonate mixtures which, at the fuel cell operating temperature, are molten.The empirical electrode reactions taking place in this cell are Anode: H2 + CO82---> CO2 + H20 + 2e- CO + CO~ 2--> 2CO2 + 2e-Cathode: 2e--5 CO2 + I/2 02--> CO32-The CO present at the fuel cell anode may react electrochemically as indicated above, but at the cell operating temperature of 650~ the water-gas shift equilibrium CO + H20 ~ CO2 + H2 will be attained more rapidly, Hence the major contribution of CO to the fuel cell anode performance may be in hydrogen produced via the water-gas shift reaction. Several factors must be considered in the selection of a molten carbonate mixture supported on the lithiumaluminate (LiA1Of) matrix of the tile. These factors are (i) ionic conductivity, (ii) solubility of reactants and reaction products, (iii) the diffusion coefficients of reactants and products, (iv) the rate of the anodic and cathodic reactions, (v) electrolyte vapor pressure, and
The photoelectrochemical (PEC) performance of p-TnP single crystal, surface modified by the sequentialdeposition of cobalt and platinum, has been investigated in 6N KOH. Efficiencies of 14.2% were realized from the photocathode for the electrical power savings obtained compared to a platinum cathode, operating at the same current density. A variety of definitions of efficiency for the conversion of light to hydrogen are discussed.
RESULTS AND DISCUSSIONSeveral approaches have been discussed previously for improving the performance of photoelectrodes by surface modification procedures. These have been discussed in several PEC review articles (1-4). The role of platinum for improving the performance of ironoxide photoanodes was discussed by us some time ago to assist the photoelectrochemical oxygen-evolution reaction (15). Improving the performance of p~InP in both acid (6,7,8) and alkaline electrolyte (9) for specific photoelectrochemical reactions has also been observed. We wish to report on the enhanced performance of p-lnP photocathodes realized by the sequential deposition of Co and Pt on its surface.The p-lnP single crystals (Zn-doped, carrier density 1016/cm 3,
The sulfur tolerance of candidate anode and anode current collector materials for the molten carbonate fuel cell were evaluated in an electrochemical half‐cell using both steady‐state and transient potentiostatic techniques. Hydrogen sulfide was introduced into the fuel at concentrations of 50 and 1000 ppm. At the higher sulfur concentration using low BTU fuel, both nickel and cobalt were observed to undergo a negative shift in their open‐circuit potentials, and high anodic and cathodic currents were observed compared with clean fuels. Exchange currents measured using the transient potentiostatic technique were not greatly affected by 50 ppm H2S introduced into the fuel. However, at higher sulfur concentrations, higher apparent exchange currents were observed, indicating a probable sulfidation reaction. Of the new anode materials evaluated, Mg0.05La0.95CrO3 and normalTiC showed good stability in the anodic region. With the former material, exchange current densities in low BTU fuel were calculated to be ≃8 mA/cm2 at 650°C, lower values than found for either nickel or cobalt anodes under similar conditions. Of the anode current collector materials evaluated, high stabilities were found for 410 and 310 stainless steels. The implications and relevance of these results on fuel cell performance are discussed.
Articles you may be interested inReflection anisotropy spectroscopy, surface photovoltage spectroscopy, and contactless electroreflectance investigation of the InP/In0.53Ga0.47As(001) heterojunction system J.
Photoelectrochemical cells having the capability of energy storage are covered. Photoanodes used for these cells were selected from MoSe,, GaAs and CdSe. Redox electrolyte species present at the semiconductor-electrolyte interface included Br-/Brz (MoSez), S'-/Sf-(CdSe) and Se2-/Se$-(GaAs). Electroactive materials at the counter-electrode of the storage systems were 1-12, Se2-/Se$and Cd.The performance of these photoelectrochemical storage cells for charge upon photoanode illumination and their subsequent electrochemical discharge is discussed.
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