Correlation of Phase, Microstructure and Surface Chemistry Evolution to the Long-Term Performance Stability of (La, Ca)CoO3 SOFC Electrodes

Abstract

Long-term electrochemical performance of polymeric precursor-derived films of LaCoO3 doped with Ca2+ (LCC), instead of the larger Sr2+ which segregates at the electrode surface forming oxides/hydroxides, was investigated in the present study. It was determined that pre-calcination at 800 °C (LCC02-800) resulted in a higher electrochemical performance but a poorer long-term stability than those pre-calcined at 700 °C (LCC02-700) or 900 °C (LCC02-900). Increasing Ca2+ content (LCC04-800) enhanced the initial electrochemical performance slightly, while causing a much poorer long-term stability. Microstructural evolution analyses revealed that, although it had some impact on the initial and long-term performance of LCC electrodes, it was not the strongest influence. It was determined via XPS analyses that formation of CaO and CaO + La2O3 layers at the LCC02-800 and LCC04-800 surfaces, respectively, accompanied by a decrease in the relative amounts of adsorbed oxygen species (corresponding to surface oxygen vacancies) caused a faster performance degradation in these samples than those pre-calcined at 700 or 900 °C. Eventually, only the surface cation ratio of LCC02-700 became close to the theoretical one after long-term operation.