Bifunctional electrocatalysts for rechargeable Zn-air batteries

Zn-air batteries have attracted extensive attention for their unique features including high energy density, safety, low cost and environmental friendliness. However, due to their poor chargeability and low efficiency, the practical application remains a challenge. The main obstacles are the intrinsic slow reaction kinetics on air cathodes, including oxygen reduction reaction during the discharging process and oxygen evolution reaction during the recharging process. Searching for efficient bifunctional oxygen electrocatalysts is key to solve these problems. In this review, the configuration and fundamental oxygen electrochemical reactions on air cathodes are briefly introduced for Zn-air batteries first. Then, the latest bifunctional oxygen electrocatalysts are summarized in detail. Finally, the perspectives are provided for the future investigations on bifunctional oxygen electrocatalysts.