Inducing Bifunctionality by Mechanical Blending of OER- and ORR-Active 3D Perovskite Electrocatalysts for Zinc-Air Batteries.

Bifunctional electrocatalysts for oxygen electrocatalysis are typically developed by combining separate OER and ORR electrocatalysts to form composites, often requiring complex synthesis methods. In this study, we present a simplified approach by mechanical blending of BaSr2CoTiSbO9 (BSCTS), an OER catalyst, with BaSr2MnTiSbO9 (BSMTS), an ORR catalyst, to construct a composite bifunctional electrocatalyst. The DFT 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/cm2 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 zinc-air batteries.