Inducing Bifunctionality by Mechanical Blending of Oxygen Evolution Reaction– and Oxygen Reduction Reaction–Active 3D Perovskite Electrocatalysts for Zinc–Air Batteries

Bifunctional electrocatalysts for oxygen electrocatalysis are typically developed by combining separate oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts to form composites, often requiring complex synthesis methods. In this study, a simplified approach is presented by mechanical blending of BaSr₂CoTiSbO₉ (BSCTS), an OER catalyst, with BaSr₂MnTiSbO₉ (BSMTS), an ORR catalyst, to construct a composite bifunctional electrocatalyst. The density-functional theory calculation supports superior ORR activity of BSMTS due to an uplifted Mn d-band center than the Co d band and its proximity to the Fermi level, whereas the greater OER activity of BSCTS is due to the uplifted O 2p band center. While microstructural similarity of BSCTS and BSMTS facilitates efficient mixing for composite formation, the mechanical blending avoids intervention of complex synthesis procedures. The resulting bifunctional composite electrocatalyst demonstrates excellent performance with a bifunctional index of 0.72 V and a peak power density of 125 mW cm^-2 when used as an air-cathode electrocatalyst in Zn-air battery (ZAB). This approach underscores the importance of mechanical blending of microstructurally compatible OER and ORR catalysts in designing practical bifunctional electrocatalysts for ZABs.