High-performance piezocatalytic hydrogen evolution over bismuth oxyhalides with halogen-dependent piezoelectricity and surface activity

The piezocatalytic characteristic of bismuth oxyhalides (BiOX, X = Cl, Br, and I) has been increasingly capturing interest for its potential in hydrogen evolution reaction (HER) through water splitting process. The performance regarding these piezocatalysts is closely related to the halogen element present in BiOX; yet, the specific influence mechanisms remain unclear. In this study, we prepared BiOX catalysts via a hydrothermal process and explored their piezocatalytic HER activities. Owing to the layered bismuth structure, the resulting sheet-like piezocatalysts can efficiently capture the mechanic stimulus and allow the robust piezoelectric field, contributing to the piezocatalytic operation. It demonstrates that the BiOBr achieves a remarkable piezocatalytic HER efficiency of 813 µmol g⁻¹ h⁻¹, outperforming BiOCl and BiOI. The density functional theory (DFT) calculation results reveal that the BiOBr with moderate halogen atom size and lattice layer spacing possesses the strongest piezoelectricity, which enhances the separation and transfer of electron–hole pairs. Meanwhile, the exposed Br atom layer facilitates a large Bader charge and a low surface Gibbs free energy (ΔG_H), enhancing charge transfer for hydrogen reduction at the solid–liquid surface, thereby increasing the HER efficiency. This research sheds light on the halogen-dependent piezocatalytic activity of BiOX catalysts, offering valuable insights for the development of high-performance piezocatalysts.