S-scheme g-C3N4/BiOBr heterojunction with enhanced interfacial charge separation for highly efficient photocatalytic hydrogen evolution

In this study, a series of g-C 3 N 4 /BiOBr S-scheme heterojunction photocatalysts with varying BiOBr contents were synthesized via an in-situ hydrothermal strategy. The optimized composite, CB-15 (15 wt% BiOBr), exhibited a remarkable hydrogen evolution rate of 1925.9 μmol g −1  h −1 under visible light, significantly surpassing those of pristine g-C 3 N 4 and BiOBr. Comprehensive characterizations revealed enhanced light absorption, expanded surface area, improved surface wettability, interfacial coupling, and electrochemical active surface area (ECSA) as confirmed by water contact angle, in situ XPS, and CV measurements. Photophysical analyses and femtosecond transient absorption spectroscopy provided further insights into the charge transfer mechanism, supporting the conclusion that g-C 3 N 4 and BiOBr form a direct S-type heterojunction structure. Density Functional Theory calculations validated this mechanism, revealing enhanced interfacial charge redistribution and a reduced Gibbs free energy barrier for hydrogen evolution. Electron Paramagnetic Resonance analysis showed the co-generation of •O 2 − and •OH radicals, aligning with the proposed S-scheme pathway. This work provides a comprehensive strategy for the rational design of high-performance photocatalysts for solar-driven hydrogen production.