Rechargeable sunlight-promoted Zn-air battery constructed by bifunctional oxygen photoelectrodes: Energy-band switching between ZnO/Cu2O and ZnO/CuO in charge-discharge cycles

Effective utilization of solar energy in battery systems has become an active attractive and active research in the field of green energy. Herein, highly efficient and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) photoelectrodes are constructed for rechargeable Zn-air batteries. This work introduces a simple and efficient method for designing bifunctional ZnO/CuO composite materials with impressive photocatalytic activity, superhydrophilicity and excellent stability. Through the strategy of sunlight promotion, the ZnO/CuO photoelectrodes are used in the charging and discharging processes of Zn-air batteries, achieving low charge potential and high discharge potential of around 1.50 V and 1.28 V by galvanostatic charge and discharge, respectively. Under illumination, the short-circuit current and open-circuit voltage can reach up to 49 mA cm-2 and 0.9 V, respectively. We revealed that this bifunctionality is originated from the valence change mechanism of Cu, meaning that ZnO/Cu2O and ZnO/CuO play the photoelectric catalytic roles in charge and discharge processes, respectively. This work paves the way to introduce a facile and efficient method for the development of integrated single-cell photo-assisted Zn-air batteries.