Rich Sulfur\nVacancies and Reduced Schottky Barrier\nHeight Synergistically Enable Au/ZnIn₂S₄ with\nEnhanced Photocatalytic CO₂ Reduction into CO

Abstract

Constructing the plasmonic metal/semiconductor heterostructure\nwith a suitable Schottky barrier height (SBH) and the sufficiently\nreliable active sites is of importance to achieve highly efficient\nand selective photocatalytic CO₂ reduction into hydrocarbon\nfuels. Herein, we report Au/sulfur vacancy-rich ZnIn₂S₄ (Au/V_SR-ZIS) hierarchical photocatalysts, fabricated\nvia in situ photodepositing Au nanoparticles (NPs) onto the nanosheet\nself-assembled ZnIn₂S₄ (ZIS) micrometer flowers\n(MFs) with rich sulfur vacancies (V_S). Density functional\ntheory (DFT) calculations confirm that for the Au/V_SR-ZIS\nsystem, the Au NPs serve as the reaction sites for H₂O\noxidation, and the V_SR-ZIS MFs serve as those for CO₂ reduction. The rich V_S in the Au/V_SR-ZIS hybrid can reduce its SBH so as to boost more hot electrons\nin the Au NPs across its Schottky barrier and then inject into the\nconduction band (CB) of the V_SR-ZIS MFs. In addition, V_S can also act as the electron sink to trap the photogenerated\nelectrons, retarding the recombination of photogenerated carriers.\nThe two merits effectively enhance the photogenerated electron density\nin the surface of V_SR-ZIS MFs, availing CO₂ photoreduction.\nIn addition, the introduction of rich V_S in the Au/V_SR-ZIS hybrid can offer more active sites, benefiting the CO₂ adsorption and accelerating the desorption of CO* from the\nsurface of the photocatalyst. Therefore, under visible light illumination\nwith no sacrificial reagent, the optimum photocatalyst (Au/V_SR-ZIS-0.4) presents the enhanced and selective CO₂ photoreduction\ninto CO (8.15 μmol g^–1h^–1 and near 100%), which are superior to those of most of ZIS-based\nand plasmon-based photocatalysts. The photocatalytic activity is about\n40.0-fold as high as that of the Vs-poor-ZIS (V_SP-ZIS)\nMFs. This work contributes a viable strategy for designing highly\nefficient plasmonic photocatalysts by using the synergism of the anion\nvacancies and the optimized SBH induced by them.