Electrochemical Kinetic Properties and Stability of A-Site Cation-Deficient Perovskite Ba1–xCo0.6Fe0.2Zr0.1Y0.1O3−δ (x = 0, 0.05) as Cathode Materials for Low-Temperature SOFCs

A family of Co-based perovskites BaCo_1–xFe_xO₃ exhibits exceptional electrochemical activity as cathode materials for low-temperature solid-oxide fuel cells. Due to the size mismatch between Ba in the A-site and Co/Fe in the B-site, BaCo_1–xFe_xO₃ usually experiences phase transition from cubic symmetry at high temperatures to hexagonal structure at low temperatures and surface Ba-cation segregation. The phase transition would deteriorate bulk diffusivity and cause structural reliability issues, while the surface cation segregation could worsen surface-exchange property and long-term stability. Herein, A-site cation deficiency in combination with a B-site doping strategy is employed to tune the crystal structure and associated defects of Ba_1–xCo_0.6Fe_0.2Zr_0.1Y_0.1O_3−δ, achieving both excellent oxygen reduction reaction activity and stability. The materials are synthesized and systematically characterized. Compared to BaCo_0.6Fe_0.2Zr_0.1Y_0.1O_3−δ, the A-site deficient perovskite Ba_0.95Co_0.6Fe_0.2Zr_0.1Y_0.1O_3−δ obtains better electrochemical kinetics properties and stability as well as tolerance to CO₂. The fundamental mechanisms associated with these properties are discussed from the perspective of crystal structure, defects, charge-carrier transport route, average bonding energy, and surface cation segregation.