A thermal-expansion offset to cobalt-based cathode materials for solid oxide fuel cells

The mismatch in thermal expansion coefficients (TECs) between cobalt-containing perovskite cathodes and commonly used electrolytes is a significant challenge to the development of durable solid oxide fuel cells (SOFCs). In this investigation, we propose to introduce low thermal expansion (LTE) cathode (Y_0.5Ca_0.5)_0.8In_0.2BaCo₃ZnO_7 + δ (YCIBCZ) to high thermal expansion (HTE) cathode LaBa_0.5Sr_0.5Co₂O_5 + δ (LBSC) to prepare YCIBCZ–LBSC composite cathodes. The addition of YCIBCZ oxide to LBSC oxide results in good thermal matching between the cathode and electrolyte, effectively improving the electrochemical performance of SOFCs. The TEC is significantly reduced from 27.2 × 10⁻⁶ K⁻¹ for LBSC to 12.9 × 10⁻⁶ K⁻¹ for YCIBCZ70–LBSC30. For all the cathode compositions studied, YCIBCZ50–LBSC50 exhibits a relatively low area-specific resistance value (0.011 Ω cm² at 800 °C) and a high power density (571 mW cm⁻² at 800 °C). These results should be associated with the balance of the TEC values of cathode/electrolyte interfaces, the magnitude of the total conductivity, and the electrocatalaytic activity of composite cathodes. In all, it provides a novel idea to develop fully thermal expansion compatible and highly active cobalt-based cathodes for SOFCs.