Copper Vacancy-Tuned CuIn ₅ S ₈ Atomic Layers with Enhanced CO ₂ Photoreduction to Formic Acid

Photocatalytic CO2 reduction reaction (CO2RR) can utilize solar energy to convert CO2 into higher-value-added fuels and industrial raw materials. However, existing catalysts generally have problems such as high carrier recombination rate and slow reaction kinetics. Defect engineering is expected to enhance catalytic performance by regulating the electronic structure of materials, among which copper vacancies have significant potential in optimizing sulfide catalytic pathways. To enhance the efficiency of photocatalytic CO2RR, in this study, CuIn5S8 atomic layers rich in copper vacancies (VCu-CuIn5S8) and CuIn5S8 atomic layers with poor copper vacancies were synthesized by a hydrothermal method. The characterization results show that VCu-CuIn5S8 has a definite copper vacancy defect and a stronger near-infrared light absorption capability. In the photocatalytic CO2RR test, the VCu-CuIn5S8 catalyst exhibited a formic acid formation rate of 16.7 μmol·g–1 in first hour, which was 1.7 times higher than that of the CuIn5S8 atomic layers with limited vacancies (9.8 μmol·g–1). Moreover, the catalyst demonstrated excellent stability, maintaining consistent performance over a continuous 12 h reaction period. Mechanism studies demonstrated that copper vacancies can optimize the energy band structure, serve as polarization center to enhance the separation efficiency of photogenerated carriers, and improve the hydrophilicity and surface reductivity of the material, thereby significantly promoting the conversion of CO2 to formic acid.