Lead-Free Perovskite Cs₃Bi₂Br₉/Porous BiOCl S-Scheme Heterostructure with Greatly Enhanced Performance for CO₂ Reduction

BiOCl has emerged as a promising photocatalyst for CO₂ reduction for its non-toxicity and robust stability. However, the wide bandgap and fast recombination of photogenerated electron-hole pairs have hindered its practical application. Herein, a series of photocatalysts based on the heterojunction of porous BiOCl with a bandgap of 2.65 eV and lead-free perovskite Cs₃Bi₂Br₉ are designed and fabricated via a simple method combining hydrothermal and dipping processes. The optimized sample exhibits a greatly improved CO₂-CO conversion rate of 25.5 μmol g^-1 h^-1 with high selectivity and electron consumption value of 64.6 μmol g^-1 h^-1 under simulated sunlight, which are 9.1 (11.1) and 4.0 (6.0) times higher than those of pristine BiOCl (Cs₃Bi₂Br₉), respectively. In-depth analysis based on experimental results and first-principles calculations reveals that the improved photocatalytic activity is caused by the enhanced charge separation and transfer in the heterojunction via a S-scheme mechanism and the decreased reaction barrier for the CO₂ reduction by the heterojunction surface. This work gives insights into the S-scheme photocatalyst based on porous BiOCl and lead-free perovskite and is useful for design and application of environmentally friendly high-performance photocatalysts.