Effect of vacancy concentration on the production selectivity of Janus In2S2X (X=Se, Te) monolayer heterojunction photocatalytic reduction of CO2

Photocatalytic reduction of CO2 to renewable energy is considered as one of the important strategies to simul-taneously solve the problems of environmental pollution and energy shortage. However, high carrier recombi-nation probability and low product selectivity seriously affect the further development of this technique. Here, we propose a novel 2D In2S2X (X = Se, Te) Janus structure catalyst. It exhibits excellent photocatalytic per-formance: (a) The valence band maximum and the conduction band minimum are contributed by the bottom and top atoms, respectively, so the photogenerated electrons have a bottom-up transition direction. The intrinsic polarization makes In2S2X have a built-in electric field opposite to the electron transition direction, so it extremely promotes the separation of carriers and inhibits electrons-holes recombination. (b) More importantly, the vacancy concentration on the catalyst surface can control the selectivity of the reduction products, and CO2 molecules are reduced to HCOOH and HCHO on the surfaces of single and double vacancies, respectively. The calculated free energies reveal that In2S2Te exhibits excellent catalytic performance for photoreduction of CO2 on both single-and double-vacancy surfaces, indicating the great potential of In2S2Te in the field of photocatalysis. This work sheds some light on the design of novel materials and provides some insights into the regulation of desired functions through defect engineering.