In‐Depth Understanding of the Effect of Halogen‐Induced Stable 2D Bismuth‐Based Perovskites for Photocatalytic Hydrogen Evolution Activity

Abstract Halide perovskites are excellent catalysts for photocatalytic hydrogen (H 2 ) evolution; however, their instability in aqueous systems limits their applications. In this study, an alternative system is presented to avoid the ionization of halide perovskites based on ethanol splitting and three Bi‐based halide perovskite nanosheets (Cs 3 Bi 2 X 9 PNs; X = I, Br, Cl) are prepared for H 2 evolution. Small amounts of these halide perovskites possess good stability in ethanol, where the optimal Cs 3 Bi 2 I 9 PNs exhibit the highest H 2 evolution rate of 2157.8 µmol h −1 g −1 . In particular, the effects of halogen regulation on the H 2 evolution activity are investigated in depth from various perspectives for Cs 3 Bi 2 X 9 . The increased number of halogen atoms reduces the Bi···Bi distance in the octahedral configuration and eliminates the strong localization of electron–hole pairs, which are conducive to photogenerated charge separation and transfer. In addition, the dominant contribution of halogens to the conduction band is enhanced with an increase in the halogen atomic number. This study establishes a novel strategy for studying Bi‐based perovskites for optimizing their photocatalytic properties. Furthermore, it provides a new perspective for developing highly efficient and stable H 2 evolution systems for halide perovskites.