Ultralow charge-discharge voltage gap of 0.05 V in sunlight-responsive neutral aqueous Zn-air battery

Rechargeable neutral aqueous zinc-air batteries (ZABs) are a promising type of energy storage device with longer operating life and less corrosiveness compared with conventional alkaline ZABs. However, the neutral ZABs normally possess poor oxygen evolution reactions (OERs) and oxygen reduction reactions performance, resulting in a large charge-discharge voltage gap and low round-trip efficiency. Herein, we demonstrate a sunlight-assisted strategy for achieving an ultralow voltage gap of 0.05 V in neutral ZABs by using the FeOOH-decorated BiVO4 (Fe-BiVO4) as an oxygen catalyst. Under sunlight, the electrons move from the valence band (VB) of Fe-BiVO4 to the conduction band producing holes in VB to promote the OER process and hence reduce the overpotential. Meanwhile, the photopotential generated by the Fe-BiVO4 compensates a part of the charging potential of neutral ZABs. Accordingly, the energy loss of the battery could be compensated via solar energy, leading to a record-low gap of 0.05 V between the charge and discharge voltage with a high round-trip efficiency of 94%. This work offers a simple but efficient pathway for solar-energy utilization in storage devices, further guiding the design of high energy efficiency of neutral aqueous ZABs. The neutral aqueous zinc-air batteries with Fe-BiVO4 photocatalyst as cathode could be photoactivated, exhibiting ultralow charge-discharge voltage gap of 0.05 V with increased energy efficiency under illumination, due to overpotential reduction and photovoltaic compensation. image