A Comparative Study of Oxygen Reduction Reaction on Bi- and La-Doped SrFeO3-delta Perovskite Cathodes

In this work the oxygen reduction reaction on Bi0.5Sr0.5FeO3-delta (BSF) and La0.5Sr0.5FeO3-delta (LSF) as cathodes for intermediate temperature solid oxide fuel cells (600-750 degrees C) is compared in detail. Partial substitution of Sr in SrFeO3-delta with 50 mole % of Bi or La results in the distinct structural features which strongly impact its electrochemical characteristics due to the presence of a lone electron pair in Bi3+, which is not available in La3+. Cubic structure for BSF favours higher ionic conductivity and enhanced formation of oxygen vacancies relative to rhombohedral structure for LSF. Large oxygen nonstoichiometry for BSF, nevertheless, leads to the dominance of Fe3+ and subsequent low electronic conductivity relative to LSF. It was found that upon cathodic polarization, the oxygen vacancies are created on LSF which helps reducing its interfacial resistance afterward, which is not the case for BSF. Overall, BSF demonstrates good electrochemical performance which can be further optimized by enhancing its electronic conductivity. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3521316] All rights reserved.