Regulating Charge Transfer in a Heterojunction Photoanode for Efficient Photo‐Charging of Zn‐Air/Sulfion Hybrid Batteries

Abstract Integrating sulfion‐rich wastewater purification with photo‐charging Zn‐Air batteries enables dual benefits for solar energy storage and environmental protection. However, photo‐charging efficiency is hindered by charge transfer issues. Here, the study synthesizes a CdS@CdIn₂S₄ core–shell photoelectrode and uses Kelvin Probe Force Microscopy (KPFM) to probe surface potential changes and photo‐charge transfer under illumination. The outer shell (CdIn₂S₄) exhibits upward band bending and a Conduction Band (CB) more negative than bulk CdS, leading to the accumulation of photoelectrons on the surface, which is detrimental to sulfion oxidation. Vacancy engineering aligns the Fermi energy of two materials, creating an optimal type‐II configuration that accumulates holes on the surface, thereby boosting the photo‐charging current density in Zn‐Air/Sulfion hybrid batteries by 18‐fold. A benchmark photo‐charging current density of 1.26 mA cm⁻² is therefore achieved for Zn‐Air/Sulfion hybrid batteries. This work demonstrates the effectiveness of regulating charge transfer pathways in photo‐charging Zn‐Air/Sulfion hybrid batteries, showing potential applications in various photo‐assisted batteries.