Abstract
Abstract Phase instabilities of the RBaCo2O5+δ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3−z at 800 °C in air were investigated. The phase instability will restrict their high temperature applications such as cathodes in solid oxide fuel cells (SOFC). However, appropriate amount of Sr substitution (≥ 60% for R = Y and ≥ 70% for R = Ho) for Ba successfully stabilized the R(Ba1−xSrx)Co2O5+δ phase at elevated temperatures. This can be explained to be due to the decrease in oxygen vacancies in the R–O layer, decrease in R O bond length, and consequent improvement in structural integrity. In addition, the Sr substitution (x = 0.6–1.0) for Ba provided added benefit with respect to the chemical stability against Ce0.8Gd0.2O1.9 (GDC) electrolyte, which is a critical requirement for the cathodes in SOFC. Among the various compositions investigated, the Y(Ba0.3Sr0.7)Co2O5+δ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase, demonstrating the potential as a cathode in SOFC.
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