Decoupling of Carrier Pathways in Au/Cu‐Zn ₃ In ₂ S ₆ Through Bulk Hole Trapping and Surface Hot Electron Accumulation Enhances Photocatalytic Hydrogen Peroxide Production

Abstract Artificial photosynthesis offers a sustainable route to H ₂ O ₂ production but is hindered by charge recombination and non‐selective reactive species generation, resulting in parasitic reactions that reduce selectivity and yield. Here, Au‐Cu co‐modified Zn ₃ In ₂ S ₆ (Au/Cu‐d/ZIS) is presented, a catalyst that spatially decouples charge carriers across bulk and surface sites, suppressing recombination and stabilizing intermediates for photocatalytic oxygen reduction. Cu doping introduces trap states that localize holes in the bulk and improve the separation and transportation of bulk photogenerated carriers. Plasmonic Au nanoparticles drive surface hot electron accumulation and further contribute to the oxygen reduction reaction. The optimized catalyst achieves an H ₂ O ₂ evolution rate of 94.2 µmol g ⁻¹ min ⁻¹ using pure water without any sacrificial agents, outperforming pristine Zn ₃ In ₂ S ₆ by nearly threefold. DRIFTS identifies stabilized oxygenated species on the catalyst surface, and DFT calculations demonstrate that Cu trap states lower energy barriers for •O ₂ ⁻ formation, while Au NPs enhance the charge transfer and ORR reaction between ZIS and O ₂ . The catalyst maintains stability and reusability, producing 2300 µmol g ⁻¹ of H ₂ O ₂ under natural sunlight over 4 h with consistent performance across multiple cycles. Furthermore, it is successfully applied for bacterial sterilization and pharmaceutical pollutant degradation, demonstrating its potential for environmental remediation.