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.