Hydrogen Oxidation Mechanisms on Perovskite Solid Oxide Fuel Cell Anodes

Solid oxide fuel cells with (La,Sr)(Ga,Mg)O-3 electrolytes and Sr(Ti0.3Fe0.7)O-3 anodes and cathodes yield a power density of 0.6 W/cm(2) at 0.7 V at 800 degrees C in air and humidified hydrogen. The polarization resistance values are 0.085 Omega . cm(2) for the cathodes and 0.13 Omega . cm(2) for the anodes. The cell current-voltage characteristics and the anode resistance dependence on hydrogen partial pressure (pH(2)) both indicate that adsorption limits the hydrogen oxidation process. A model is developed where dissociative hydrogen adsorption becomes an increasingly important rate-limiting step, relative to charge transfer, as temperature and pH(2) decrease. The model fits the data well for cell voltages >0.5 V, deviations at lower voltages are tentatively explained by an increase in anode oxygen content. The model also fits the electrochemical characteristics of cells with (La,Sr)(Cr,Fe)O-3 anodes and previously-reported data on other oxide anodes. (C) 2016 The Electrochemical Society. All rights reserved.