Step-scheme CsPbBr₃/BiOBr photocatalyst with oxygen vacancies for efficient CO₂ photoreduction

Metal halide perovskites with suitable energy band structures and excellent visible-light responses have emerged as promising photocatalysts for CO₂ reduction to valuable chemicals and fuels. However, the efficiency of CO₂ photocatalytic reduction often suffers from inefficient separation and sluggish transfer. Herein, a step-scheme (S-scheme) CsPbBr₃/BiOBr photocatalyst with oxygen vacancies possessing intimate interfacial contact was fabricated by anchoring CsPbBr₃ QDs on BiOBr-Ov nanosheets using a mild anti-precipitation method. The results showed that CsPbBr₃/BiOBr-Ov-2 with an internal electric field (IEF) heterojunction exhibited a boosted evolution rate of 27.4 μmol g^-1 h^-1 (CO: 23.8 μmol g^-1 h^-1 and CH₄: 3.6 μmol g^-1 h^-1) with an electron consumption rate (R_electron) of 76.4 μmol g^-1 h^-1, which was 5.9 and 3.2 times that of single CsPbBr₃ and BiOBr-Ov, respectively. Density functional theory (DFT) calculations revealed that BiOBr with oxygen vacancies can effectively enhance the adsorption and activation of CO₂ molecules. More importantly, in situ infrared Fourier transform spectroscopy (DRIFTS) spectra show the transformation process of the surface species, while the femtosecond transient absorption spectrum (fs-TA) reveals the charge transfer kinetics of the CsPbBr₃/BiOBr-Ov. Overall, this work provides some guidance for the rational design of S-scheme heterojunctions and vacancy-engineered photocatalysts, which are expected to have potential applications in the fields of photocatalysis and solar energy conversion.