Density Functional Theory Study of Janus In2S2X Photocatalytic Reduction of CO2 under "Double Carbon" Target

Photocatalytic reduction of CO2 into usable chemical products can effectively alleviate the two major problems of greenhouse effect and resource shortage, and help to achieve the great goals of "carbon peak" and "carbon neutrality". However, due to the influence of quantum efficiency and low product selectivity, it is still not possible to apply it to large-scale industrial production. Among them, the photocatalyst plays a key role. Metal sulfides are considered to be a class of promising photocatalysts due to their good light absorption ability and reduction potential. Based on the research of two-dimensional (2D) In2S3, a 2D In2S2X (X=Se, Te) Janus structure is designed using density functional theory (DFT). In2S2X not only possesses suitable band edge positions and moderate bandgap for photocatalytic CO2 reduction, but also has excellent visible light absorption. Moreover, the valence band maximum (VBM) and conduction band minimum (CBM) of In2S2X are contributed by the bottom and top atoms, respectively, so that the reduction and oxidation reactions are spatially separated and the photocatalytic efficiency is improved. In particular, due to the intrinsic polarization, the direction of the built-in electric field generated by In2S2X is just opposite to the direction of electronic transition, which can improve the carrier mobility. On this basis, different concentrations of vacancy defects are introduced on the surface, and its stable configuration, electronic structure and absorption spectrum are analyzed. Calculation of the CO2 reduction pathways reveal that the vacancy concentration can effectively regulate the selectivity of reduction products, and the catalysts with single-vacancy and double-vacancy surfaces reduced CO2 to HCOOH and HCHO, respectively. The mechanism of the effect of vacancy concentration on the catalytic performance is further revealed. Vs-In2S2Se and Vd-In2S2Te show more excellent photocatalytic performance in the process of reducing CO2 to HCOOH and HCHO, respectively. This work provides some theoretical guidance for experimental design and preparation of highly efficient photocatalysts.