Overcoming phase instability of RBaCo2O5+δ (R=Y and Ho) by Sr substitution for application as cathodes in solid oxide fuel cells

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 RO 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.