Kinetic studies on the reaction at the La0.6Ca0.4MnO3/YSZ interface, as an SOFC air electrode
To determine the rate equation for the reaction at the SOFC (Solid Oxide Fuel Cell) air electrode of the type O2(g)/porous La0.6Ca0.4MnO3/YSZ, measurements were made on the impedance due to the electrode reaction and the steady-state polarization in the oxygen partial pressures, PO2, between 1 and 10−4 atm at temperatures, T, between 700 and 1000°C. At T > 900°C and in PO2<10−3 atm, the electrode conductivity (reciprocal of the electrode impedance) was proportional to PO2. The rate of reaction for this condition was found to be controlled by the oxygen gas diffusion in the electrode pores. At higher PO2 or at the lower temperatures, the steady-state current, i, was found to obey the rate equation, i=k[aO−PO2a−1O], where k is the rate constant and aO is the oxygen activity in YSZ at the La0.6Ca0.4MnO/YSZ interface. Here, aO is related to the electrode potential, E , by 2FE = RT 1n aO. The electrode conductivity for this condition was proportional to P12O2.