Oxygen vacancy mediation of BiOX (X=Cl, Br) towards enhanced photocatalytic CO2 reduction activity

Surface defects in semiconductors play a significant role in modulating the performance of photocatalytic reactions. However, there is still insufficient exploration regarding the influence of defects on the photocatalytic CO2 reduction performance. In this study, we achieved controllable construction of oxygen vacancies (OVs) in BiOX (X=Cl, Br) samples through one-step solvothermal treatment in polyols by adjusting the reaction time. The introduction of OVs significantly enhanced the photocatalytic activity of BiOX (X=Cl, Br) for converting CO2 to CO. Among all the tested BiOX (X=Cl, Br) samples with OVs, BiOCl-OV-2 and BiOBr-OV-2 samples with a moderate amount of OVs exhibited the highest CO yield of 28.51 and 15.22 μmol gcat−1 after 4 hours of irradiation, respectively. Photo-/electrochemical measurements results revealed that engineering OVs into BiOX (X=Cl, Br) effectively adjusted their electronic structure, charge density and separation; however, excessive OVs may slightly degrade their photoelectrochemical properties and thus lead to reduced photocatalytic activity. Furthermore, an appropriate amount of OV was found to enhance both CO2 adsorption capacity and photo-generated electron reduction ability, thereby further promoting the overall efficiency of photocatalytic CO2 conversion. Through in situ FTIR spectra analysis, we uncovered the process of photocatalytic conversion from CO2 to CO.