Sulfur Vacancy-Driven Polarization Electric Field in CdIn₂S₄ Enhances CO₂ Photocatalytic Reduction by Facilitating *COOH Formation

Photoreduction of CO2 technology has attracted a great deal of interest from many scientists for the conversion of solar energy into value-added fuels. However, the activity of photoreduction of CO2 is unsatisfactory due to the very stable CO2 and low charge separation efficiency. In this work, ultrathin CdIn2S4 nanosheets (CIS) with sulfur vacancies (Sv) were prepared by a calcination technique to achieve efficient photocatalytic CO2 reduction. Scanning transmission electron microscopy with a spherical aberration corrector, electron paramagnetic resonance (EPR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) demonstrated the presence of a significant amount of Sv on the surface of CIS-300. Mechanistic studies show that Sv disrupt the crystal configuration of CIS to build a local electron polarization field, which facilitates CO2 activation and lowers the energy barrier for the generation of *COOH intermediates. Furthermore, density functional theory (DFT) calculations show that Sv improve the density of states at the conduction band edges and introduce defect energy levels that favor electron migration. This optimization resulted in a significant enhancement of the activity of the photocatalytic reduction of CO2 reaction, with a CO yield of 41.1 μmol·g–1·h–1, 5.1 times higher than that of pristine CIS (8.1 μmol·g–1·h–1). This work paves the way for facilitating CO2 activation and carrier separation for efficient CO2 photoreduction.