Ga-on-In Substitution with Zn Vacancies in Zn₃In₂S₆ Induces Electron-Hole Asymmetry and In─O Bond Weakening for Coupled Two-Electron Oxygen Reduction and H₂O₂ Stabilization.

Abstract

Artificial photosynthesis of H₂O₂ offers a sustainable route to decentralized chemical production, yet remains limited by sluggish oxygen reduction kinetics, rapid charge recombination, and undesired decomposition of H₂O₂ on catalyst active sites. Herein, we report a Zn₃In₂S₆ 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 H₂O₂ 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 H₂O₂ production rate of 187.8 µmol g^- ¹ min^- ¹ in O₂-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 O₂ adsorption and weakened H₂O₂ 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 H₂O₂.