Screening Spinel Oxide Supports for RuO₂ to Boost Bifunctional Electrocatalysts for Advanced Zn–Air Batteries

The compositing strategy offers great potential in designing bifunctional oxygen electrocatalysts for Zn–air batteries. Recent reports reveal that the couple of RuO₂, serving as a benchmark oxygen evolution reaction (OER) catalyst, with other oxygen reduction reaction (ORR) catalysts is a wise choice to build highly efficient bifunctional electrocatalysts. However, the design criteria for ORR and OER activities of RuO₂-based composite catalysts are still unclear. Herein, a series of transition metal (Fe, Co, Mn, and Ni)-doped spinel oxides are designed to support RuO₂ nanorods for exploring the reaction mechanism. Through advanced technology, it is considered that increasing the content and binding energy of Co³⁺ and enhancing the oxidation state of Ru⁴⁺ is an efficient strategy to promote ORR and OER activities for RuO₂/Co-based spinel oxide composite catalysts. It is found that coupling Mn-doping Co₃O₄ (CMO) supports with RuO₂ can induce the highest catalytic activities in ORR/OER and excellent performance in rechargeable Zn–air batteries. Operando electrochemical impedance spectroscopy and theoretical calculation further prove the synergistic effect between RuO₂ and CMO supports originated from the oxygen overflow to overcome the large barrier for oxygen desorption on RuO₂ during OER and oxygen adsorption on CMO supports during ORR.