This research was performed to study the anode reaction in a molten carbonate fuel cell. Chronoamperometry experiments and impedance measurements were carried out at gold and nickel flag-type electrodes in a 62 mole percent (m/o) Li2COJ38 m/o K2CO3 eutectic carbonate mixture at 923 K as a function of gas composition (H2/CO2/H20), and as a function of temperature between 823 and 1073 K. The i -~ extrapolation technique, generally applied to evaluate chronoamperometry results, is shown to yield systematic errors for the hydrogen oxidation studies in molten carbonates. A direct fit of the Gerischer-Vielstich relation yields more reliable results for gold. The current responses on Ni cannot be described by the Gerischer-Vielstich relation. The high reaction orders for hydrogen (0.7 to 1.0), medium for carbon dioxide (order 0.5), and the low or even negative reaction order for water (0 to -0.25), indicate the hydrogen oxidation follows a Volmer-Heyrovsky-type mechanism on gold flag electrodes. The reaction rate at nickel electrodes was found to be too high to be studied accurately using impedance measurements and chronoamperometry on flag electrodes. In spite of the poor accuracy, reaction orders indicate that a final chemical react.ion is the rate-determining step in the reaction mechanism on nickel. The activation energy for the exchange current density was found to be in the order of 80 kJ/mol with a tendency to be higher for the gases richer in hydrogen. The activation energy for the Warburg coefficient (diffusion) was found to be about -15 kJ/mol. IntroductionThe molten carbonate fuel cell (MCFC) is a promising energy conversion system capable of producing electricity from hydrogen containing fuel gases with high efficiency. At the anode of an MCFC hydrogen oxidation takes place. The anode is made of porous Ni alloyed with Cr or A1.In this paper, the results of chronoamperometry and impedance measurements at gold and nickel electrodes are presented. The objective of these experiments was to study the reaction mechanism and kinetics of the hydrogen oxidation in molten carbonate. Gold was chosen as the electrode material to start with, because it has been reported that the kinetics of hydrogen oxidation on gold is relatively slow allowing a more accurate determination of the exchange current densities and hence the reaction orders. 1-5 Then experiments on Ni, being the actual anode material, were performed.

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Contact angles of various electrolyte compositions were determined on some candidate molten carbonate fuel cell anode materials in a typical anode gas atmosphere using the sessile drop method. The contact angles showed to increase with the nobility of the substrate composition in the order: Cr—Ni/Al—Ni/Cr—Ni/Cu—Cu—Ni and to decrease with carbonate composition in the order: Li/Na—Li K—Li/K/Ba.

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