Stabilizing Unsaturated S at Interface for the Enhanced Photothermal Evolution of CH₄ From CO₂

Abstract Highly selective photocatalytic CO₂ reduction (PCR) to methane is restricted severely due to the multiple consecutive proton‐coupled electron transfer steps and the stabilization of crucial intermediates. Herein, an In₂O₃/CuInS₂ composite with multifunction is meticulously fabricated via heterojunction engineering and achieves a remarkable selectivity of CH₄ (95.73%) and a yield of 54.9 umol·g⁻¹·h⁻¹. The electrons are enriched around S atoms to form unsaturated S sites, thereby improving the efficiency of photocatalytic reduction reactions involving multiple electrons. The interfacial effect induces electron/photogenerated electron transfer from In₂O₃ to the unsaturated S sites, suppressing excessive oxidation states and reducing local positive charge accumulation, thereby stabilizing the unsaturated S sites. Unsaturated S sites acts as electron‐rich centers for CO₂ adsorption and activation function, enhancing the coverage of ^*CO species on the surface of photocatalyst and lowering the energy barrier of ^*CHO intermediate, thereby inducing the generation of CH₄. The photothermal effect improves the sluggish kinetics of the PCR efficiency, which is ascribed to the transferred electrons that are excited into hot electrons on CuInS₂ via the LSPR effect, accelerating the activation of adsorbed CO₂ molecules.