Improvement of high-temperature oxygen reduction catalytic performance of medium-entropy perovskite by modulating the distribution of localized electrons

High-entropy oxides (HEOs) derive their exceptional properties from the atomic-level homogenization of multiple constituent elements within the crystal lattice, which induces a sophisticated local environment that fundamentally reconfigures electron density distributions and coordination environment at active sites. However, the mechanisms by which multi-component systems in HEOs precisely regulate high-activity catalytic sites remain poorly understood. This work addresses this gap by designing medium-entropy perovskite oxides through the strategic incorporation of transition metals with distinct electronegativities and ionic radii, aiming to unravel how local environmental modifications impact the energy band location, coordination states, and adsorption behavior of the Co site. A family of A2BO4-type medium-entropy oxides PrSr(Fe0.2Co0.2Ni0.2Cu0.2M0.2)O4 (M = Sc, Cr, Mn) was successfully synthesized. Divergent atomic properties among Sc, Cr, and Mn (electronegativity, ionic size, and metal–oxygen bond strength) triggered pronounced electron redistribution, effectively tuning the d-band center of Co. Remarkably, Cr substitution significantly enhanced O2 adsorption at Co-active sites, as indicated by an elongated O–O bond length (1.234 Å → 1.279 Å). Concurrently, Cr doping destabilized the M’–O–Cr bonds (M’ = Fe, Co, Ni, Cu) and lowered the thermodynamic barrier for oxygen vacancy formation. Electrochemical tests revealed that PrSr(Fe0.2Co0.2Ni0.2Cu0.2Cr0.2)O4 (PSMO-Cr) exhibited the highest electrical conductivity and fastest oxygen surface exchange kinetics. At 700 °C, the area-specific resistance (ASR) of the PSMO-Cr cathode was 0.07 Ω cm2. Corresponding fuel cells achieved a maximum power density of 0.76 W cm−2. In electrolysis mode, the maximum current density reached 0.56 A cm−2 under 1.3 V at 700 °C using PSMO-Cr as the anode. These results demonstrate that PSMO-Cr is a promising bi-functional catalyst for energy conversion applications.