Study on Ce and Y co-doped BaFeO3-δ cubic perovskite as free-cobalt cathode for proton-conducting solid oxide fuel cells

Abstract The use of triple-conducting (electron, proton, oxide ion) cathodes is an effective strategy for significantly decreasing cathode polarization of proton-conducting SOFCs. In this study, a new triple-conducting BaFe0.8Ce0.1Y0.1O3-δ (BFCY) perovskite cathode is prepared by Pechini sol-gel process and its properties are evaluated comprehensively. High-temperature XRD measurement demonstrates that the codoping of Ce and Y can stabilize the cubic perovskite of BFCY in investigated temperature range from room temperature to 900 °C. BFCY material exhibits a moderate average thermal expansion coefficient of 22.08 × 10−6 K−1 smaller than cobalt-based cathode and good chemical compatibility with BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte after the calcining treatment at 1000 °C. XPS analysis indicates the existence of Ce3+/4+ and Fe3+/4+ ions and abundant oxygen vacancies in BFCY powder surface. Thermal gravimetric analysis reveals that a larger number of oxygen deficiencies -are generated at elevated temperatures, which favors the catalytic activity on oxygen reduction. The maximum value of BFCY electrical conductivity remains at 1.55 S cm−1 at 600 °C in humidified air. BCFY (BaCe0.8Fe0.1Y0.1O3-δ) material is introduced in order to construct BFCY-BCFY composite cathode with the good cathode/electrolyte interface adhesion. For the single cell with BFCY-BCFY composite cathode, the polarization resistance as low as 0.05 Ω cm2 and peak power density as high as 750 mW cm−2 are reached at 700 °C, respectively, demonstrating the great potential of BFCY oxides as proton-conducting SOFC cathode.