Multi-hydrogen adsorption of amorphous ReSx cocatalysts for boosting photocatalytic hydrogen evolution†

An ideal H₂-evolution cocatalyst must achieve near-balanced hydrogen adsorption/desorption energetics at active sites to promote H₂-evolution kinetics, yet existing cocatalysts typically exhibit imbalanced H adsorption (either too strong or too weak) that severely compromises their hydrogen-evolution performance. Moving beyond conventional electronic structure modulation approaches involving doping or heterojunctions, we demonstrate a synergistic hydrogen-evolution mechanism of multi-hydrogen adsorption, namely multi-hydrogen adsorption on cocatalyst surfaces can effectively balance H* adsorption/desorption, dramatically enhancing photocatalytic hydrogen production. For this purpose, the ReS_x/TiO₂ photocatalyst is prepared by loading sulfur-rich amorphous ReS_x with multiple S active sites onto TiO₂. The optimized ReS_x/TiO₂(1 : 10) achieves an exceptional photocatalytic hydrogen-evolution rate of 9.9 mmol g⁻¹ h⁻¹, which is 2.1 times higher than the crystalline c-ReS₂/TiO₂. Combined experimental and theoretical investigations reveal the multi-hydrogen adsorption mechanism: (1) the multi-hydrogen adsorption effectively lowers the p-band center of active S sites in the ReS_x cocatalyst, increasing antibonding state occupancy, thereby greatly weakening S–H_ads bond strength; (2) in situ XPS and KPFM verify efficient photogenerated electron transfer from TiO₂ to ReS_x for a rapid H₂ evolution reaction. These findings fundamentally advance the understanding of multi-site adsorption effects in photocatalysis and establish new design principles for high-performance photocatalytic systems.