Bismuth Vacancy-Tuned Bismuth Oxybromide Ultrathin Nanosheets toward Photocatalytic CO₂ Reduction

Surface defects in semiconductors have a significant role to tune the photocatalytic reactions. However, the dominant studied defect type is oxygen vacancy, and metal cation vacancies are seldom explored. Herein, bismuth vacancies are engineered into BiOBr through ultrathin structure control and employed to tune photocatalytic CO₂ reduction. V_Bi-BiOBr ultrathin nanosheets deliver a high selective CO generation rate of 20.1 μmol g^-1 h^-1 in pure water, without any cocatalyst, photosensitizer, and sacrificing reagent, roughly 3.8 times higher than that of BiOBr nanosheets. The increased CO₂ reduction activity is ascribed to the tuned electronic structure, optimized CO₂ adsorption, activation, and CO desorption process over V_Bi-BiOBr ultrathin nanosheets. This work offers new opportunities for designing surface metal vacancies to optimize the CO₂ photoreduction performances.