Surface Halogen Compensation on CsPbBr₃ Nanocrystals with SOBr₂ for Photocatalytic CO₂ Reduction

Metal halide perovskite nanocrystals (MHP NCs) have attracted great interest for photocatalytic CO₂ reduction. However, monodispersed MHP NCs generally possess a halogen-deficient surface and are capped by labile long-chain organic ligands, exhibiting low charge transfer rates to nearby cocatalysts in photocatalytic systems. Conventional methods of removing the surface ligands easily bring new surface defects, leading to serious charge recombination and low photocatalytic performance. Herein, we demonstrate a facile halogen compensation method to obtain high-quality CsPbBr₃ NCs with a Br-filled surface toward photocatalytic CO₂ reduction. The use of reactive thionyl bromide (SOBr₂) not only promotes the stripping of native ligands but also repairs Br vacancies (V_Br) on CsPbBr₃ NCs. Such a halogen compensation method facilitates the charge transfer from CsPbBr₃ NCs to nearby cocatalysts (e.g., g-C₃N₄), resulting in a high CO/CH₄ production rate of 190 μmol g^–1 h^–1 in photocatalytic CO₂ reduction. This work provides a new strategy to simultaneously enhance the surface properties of photocatalysts and build a favorable interface for their charge transfer, showing great potential in the design and application of perovskites NCs for photocatalytic applications.