A-site Ca Substitution Optimizing SrCoO 3-δ Phase Structure and B-site Environment for Efficient Oxygen Evolution

Abstract

SrCoO3-δ has been regarded as a promising electrocatalyst for the oxygen evolution reaction (OER) owing to its superior structural tunability and elemental flexibility. However, the regulation of the B-site local environment and phase structure by A-site ions remains underexplored. Herein, a series of Sr1-xCaxCoO3-δ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) (SCxCO) catalysts have been synthesized via a sol-gel method. The introduction of Ca2+ induces the transformation from the hexagonal (x = 0) to the orthorhombic (x = 0.3-0.5) crystal structure while optimizing the electronic structure of B-site Co ions. Among them, the orthorhombic Sr0.5Ca0.5CoO3-δ exhibits the best OER performance with an overpotential of 336 mV at 10 mA cm-2 (1 M KOH), which further decreases by 41 mV after 1000 CV cycles. Ca doping suppresses surface Sr enrichment to expose B-site Co ions, while simultaneously optimizing the Co3+/Co4+ ratio by lowering the average oxidation state from +3.45 to +3.30. The resulting orthorhombic structure facilitates the generation of oxygen vacancies and highly oxidative oxygen species (O22-/O-), as well as the formation of surface CoOOH to significantly boost OER kinetics. This work reveals the critical role of A-site Ca doping in modulating the crystal structure and B-site environment in perovskite oxides, providing new insights for the rational design of efficient OER catalysts.