Thermodynamic and kinetic considerations on degradations in solid oxide fuel cell cathodes

Abstract

Analyses have been made to understand the chemical behaviors of the perovskite cathode/rare earth doped ceria interlayer/YSZ (yttria stabilized zirconia) electrolyte multilayer structure and their relation to the electrochemical performance. Particular focus was given to the thermodynamic activities of SrO in the cathodes and their relation to the reaction with rare earth doped ceria or YSZ. The possibility of Sr diffusion from the cathode through the rare earth doped ceria to the YSZ electrolyte to form SrZrO 3 was analyzed in terms of the SrO activity. It has been found that the SrO activity at the cathode/ceria interfaces is important for the steepening of the chemical potential gradient of SrO inside the doped ceria and for the enhancement of the solubility of SrO in doped ceria. Two possible effects influencing the SrO activities have been examined; these are chemical reactions between perovskite cathodes and doped ceria and kinetic decomposition under the oxygen potential gradient. Effects of cathodic polarization have been also examined in terms of changes in chemical equilibria and change in oxygen potential gradients.