Ga‐on‐In Substitution with Zn Vacancies in Zn ₃ In ₂ S ₆ Induces Electron–Hole Asymmetry and In─O Bond Weakening for Coupled Two‐Electron Oxygen Reduction and H ₂ O ₂ Stabilization

ABSTRACT Artificial photosynthesis of H 2 O 2 offers a sustainable route to decentralized chemical production, yet remains limited by sluggish oxygen reduction kinetics, rapid charge recombination, and undesired decomposition of H 2 O 2 on catalyst active sites. Herein, we report a Zn 3 In 2 S 6 catalyst (Ga‐ZvIS) featuring Ga‐on‐In substitution and Zn vacancies that together establish electron–hole asymmetry and weaken In ─ O bonding. Ga substitution on In sites lowers the In‐5p‐band center level and reduces H 2 O 2 adsorption strength, thereby suppressing surface decomposition, while Zn vacancies serve as hole‐localized domains that accelerate isopropanol oxidation and furnish the protons required for the two‐electron oxygen reduction reaction (2e − ORR). This site‐specific dopant–defect interplay produces energetically differentiated electron‐ and hole‐dominated regions, promotes directional charge migration, and sustains the 2e − ORR pathway. The optimized catalyst exhibits a H 2 O 2 production rate of 187.8 µmol g − 1 min − 1 in O 2 ‐saturated aqueous isopropanol, outperforming most reported photocatalysts. Kelvin probe force microscopy and femtosecond transient absorption spectroscopy confirm efficient carrier separation consistent with the built‐in electrostatic potential arising from electron–hole asymmetry, while DFT calculations reveal favorable O 2 adsorption and weakened H 2 O 2 binding on Ga–In sites. A proof‐of‐concept continuous‐flow photoreactor further demonstrates in situ Fenton‐assisted oxidation of organic contaminants, validating the practical utilization of the photosynthesized H 2 O 2 .