Small-Size Atom-Driven Distortion Realizes High-Entropy Oxides with Simultaneous Chemical Stability and Activity Enhancement Enabling a Practical Cathode for Solid Oxide Fuel Cells

Both high activity for oxygen reduction reaction and excellent chemical stability against contaminants in the surrounding atmosphere under operating conditions are required for a viable cathode of solid oxide fuel cells. However, traditional Ba 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ (BSCF) crystal structures suffer from instability under both high-temperature, high-reduction conditions and low-temperature, high-oxidation environments, making them prone to poisoning and significantly compromising their long-term operational stability. In this study, we engineered lattice distortion in BSCF by incorporating small-sized atoms at the A-site, resulting in a novel Ba 0.2 Sr 0.2 La 0.2 Pr 0.2 Sm 0.2 Co 0.2 Fe 0.8 O 3-δ (H-BSCF) high-entropy perovskite oxide, which shows significantly improved resistance to CO 2 and Cr vapor poisoning without impairing catalytic activity. Both experimental and results show the high-entropy strategy introduces lattice distortion, enhancing structural stability to prevent phase transitions and segregation. This distortion induces a spin state transition in Co 3+ ions that increases the density of unpaired electrons and significantly enhances Co 3d-O 2p orbital hybridization, which also prevent structural collapse, thereby markedly improving chemical stability without sacrificing catalytic activity. Density functional theory calculations demonstrate that H-BSCF possesses favorable oxygen migration energy and high segregation energy. The combined superior catalytic activity and stability make H-BSCF promising for industrial application.