Oxygen-vacancy-engineered TiO2-supported Ag-Ag2S heterojunction co-catalyst for enhanced photocatalytic hydrogen evolution

Abstract

Engineering semiconductor defects in conjunction with heterojunction co-catalysts is an effective strategy to enhance photocatalytic hydrogen evolution. Herein, an oxygen-vacancy-rich TiO2-supported Ag-Ag2S heterojunction (TiO2(ov)-Ag-Ag2S) was constructed. Under simulated solar irradiation (AM 1.5G) using methanol as a sacrificial agent, the catalyst achieves a hydrogen evolution rate of 1738.37μmol h-1g−1, which is 7.0, 1.6, and 1.2 times higher than TiO2(ov), TiO2(ov)-Ag, and TiO2-Ag-Ag2S, respectively, and retains 91% of its initial activity after 12 h of cycling. Spectroscopic and electro(photo)chemical analyses reveal enhanced visible-light absorption, suppressed charge recombination, and accelerated interfacial charge transfer resulting from the dual-modification strategy. Density functional theory calculations demonstrate that oxygen vacancies reduce the work function of TiO2, thereby enhancing its electron-donating capability, while the Ag-Ag2S heterojunction induces directional electron redistribution and generates a built-in electric field that facilitates charge separation. Furthermore, projected density of states analysis indicates an upshift of the d-band center of interfacial Ag relative to bulk-like Ag, and the Ag-Ag2S interfacial sites exhibit a reduced hydrogen adsorption free energy (ΔGH∗ = 0.52 eV), leading to improved hydrogen evolution kinetics. This work highlights a synergistic defect/heterojunction design strategy for simultaneously optimizing charge separation and interfacial catalytic activity in metal oxide-based photocatalysts.