Synergistic hydrazine-driven regulation and Mo/S co-doping to endow BiOBr with heterovalent molybdenum states and abundant oxygen vacancy defects for photocatalytic hydrogen evolution

Herein, we demonstrate a Mo/S co-doped BiOBr-based bimetal bismuth sulfur-oxybromide (Mo/S-BiOBr) catalyst with heterovalent molybdenum states and abundant oxygen vacancy defects for photocatalytic hydrogen evolution (PHER) via a facile method. Mo/S co-doping adjusts the energy band structure of BiOBr and expands the visible light absorption. The hydrazine regulates the molybdenum with heterovalent states while endows Mo/S-BiOBr with oxygen vacancy defects to balance the valence-charge deviations from electrical neutrality induced by Mo6+→Mo4+. These oxygen-vacancy defects act as active sites for capturing water molecules and activating the H-O-H bond to produce protons for hydrogen generation. The heterovalent Mo6+/Mo4+ states act as photogenerated electron hosts to hop fast between Mo6+ and Mo4+, facilitating efficient electron transfer for PHER. The hybridization between S3p and O2p orbital improves the stability of continuous PHER. The hydrazine-regulated Mo/S-BiOBr-3 with an optimal n(Mo4+)/n(Mo4+ + Mo6+) ratio and abundant oxygen vacancy defects exhibits excellent PHER activity of 710.5 µmol·h−1 at the catalyst weight of 50 mg and an apparent quantum efficiency (AQE) of 13.9% at 420 nm. After six recycles, the H2 yield of Mo/S-BiOBr-3 decreased by only about 3.5%, indicating good stability and durability. This work provides a practical approach to using bismuth-based oxyhalides in PHER.