Sc and Ta-doped SrCoO3-δ perovskite as a high-performance cathode for solid oxide fuel cells

Abstract

Sealing and stability is the challenge for solid oxide fuel cells (SOFCs) at high temperature. It is crucial to operate SOFCs at a low temperature to avoid these issues. Thus, it is necessary to improve the sluggish oxygen reduction reaction (ORR) activity of cathode. The SrCoO3-δ perovskite with a cubic phase is identified as a potential cathode material for SOFCs due to its high oxygen permeability and reasonable electrical conductivity. However, it readily decomposes into the orthorhombic structured brownmillerite Sr2Co2O5 or hexagonal Sr6Co5O15 during high-temperature sintering resulting in the loss of a significant amount of lattice oxygen. Herein, we partially replace Co with Sc and Ta at SrCoO3-δ to stabilize its cubic perovskite structure and restrain the lattice oxygen loss, thus improving the oxygen-ionic conductivity, and the structural and chemical stability. The synthesized SrSc0.175Ta0.025Co0.8O3-δ (SSTC) cathode achieves a remarkably high ORR performance and an area-specific resistance obtained in this study reaches as low as 0.233, 0.033, and 0.004 Ω cm2 at 500, 600, and 700 °C, respectively. The new Sc and Ta-doped SrCoO3-δ perovskite cathode even present a better ORR activity than the previously reported Sc and Nb-doped SrCoO3-δ cathode. The reason for the improved performance by Ta doping is possible that Ta–O bond is stronger than Nb–O bond and the electronegativity of Ta5+ is lower than that of Nb5+, resulting in a lower valence state of cobalt and a higher oxygen vacancies concentration.