Realizing Unassisted Photo‐Charging of Zinc–Air Batteries by Anisotropic Charge Separation in Photoelectrodes

Abstract Solar rechargeable zinc–air battery is a promising approach for capturing and storing intermittent solar energy through photoelectrochemical reactions. However, unassisted photo‐charging of zinc–air batteries is challenging due to suboptimal carrier accumulation on photoelectrodes, resulting in sluggish reaction kinetics. Here, unassisted photo‐charging of zinc–air battery is achieved by investigating anisotropic photogenerated charge separation on a series of representative semiconductors (ZnIn₂S₄, TiO₂, and In₂O₃), among which the exceptional anisotropic charge separation on a ZnIn₂S₄ photoelectrode is revealed based on anisotropic charge diffusion capabilities. The charge separation is facet‐dependent, which is observed using Kelvin probe force microscopy, verifying a cause‐and‐effect relationship between the photo‐charge accumulation on photoelectrodes and their photo‐charging performance in zinc–air batteries. This work achieves an unassisted photo‐charging current density of 1.9 mA cm⁻² with a light‐to‐chemical energy conversion efficiency of 1.45%, highlighting the importance of anisotropic semiconductors for unassisted photo‐charging of zinc–air batteries via efficient photogenerated charge separation.