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

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 BaFe 0.8 Ce 0.1 Y 0.1 O 3-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 BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (BZCY) electrolyte after the calcining treatment at 1000 °C. XPS analysis indicates the existence of Ce 3+/4+ and Fe 3+/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 (BaCe 0.8 Fe 0.1 Y 0.1 O 3-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 cm 2 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. • BFCY shows stable cubic perovskite structure in investigated temperature range. • A peak power density of 750 mW cm −2 is reached at 700 °C. • BFCY-BCFY cathode shows a low area specific resistance of 0.05 Ω cm 2 at 700 °C.