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

Abstract

Phase instabilities of the RBaCo2O5+δ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3-z at 800 oC in air were investigated. This will restrict their high temperature applications such as cathodes in solid oxide fuel cell (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 by decreasing oxygen vacancies at R-O layer, decreasing R-O bonding length, and consequent improvement of 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.