Constructing an Active Sulfur‐Vacancy‐Rich Surface for Selective *CH₃‐CH₃ Coupling in CO₂‐to‐C₂H₆ Conversion With 92% Selectivity

Abstract To achieve high selectivity in photocatalytic CO₂ reduction to C₂₊ products, increasing the number of CO₂ adsorption sites and lowering the energy barriers for key intermediates are critical. A ZnIn₂S₄ (ZIS)/MoO_3‐x (Z‐M) photocatalyst is presented, in which plasmonic MoO_3‐x generates hot electrons, creating a multielectron environment in ZIS that facilitates efficient C─C coupling reactions. Density functional theory (DFT) calculations reveal that MoO_3‐x reduces the formation energy of sulfur vacancies (S_V) in ZIS, thereby enhancing CO₂ adsorption and activation. The S_V‐rich surface lowers the energy barrier for forming HCOO^* to −0.33 eV whereas the energy barrier for forming ^*COOH is 0.77 eV. Successive hydrogenation of HCOO^* leads to ^*CH₂, which converts to ^*CH₃ with an energy barrier of −0.63 eV. The energy barrier for ^*CH₃‐CH₃ coupling is 0.54 eV, which is lower than the 0.73 eV for ^*CH₂‐CH₂ coupling to form ^*C₂H₄. Thus, Z‐M preferentially produces C₂H₆ over C₂H₄. Under visible light, Z‐M achieves a CO₂‐to‐C₂H₆ conversion rate of 467.3 µmol g⁻¹ h⁻¹ with 92.0% selectivity. This work highlights the dual role of plasmonic photocatalysts in enhancing CO₂ adsorption and improving C₂₊ production in CO₂ reduction.