Modulation of oxygen and sulfur dual-vacancies in Ag₃PO₄/CdIn₂S₄ S-scheme heterojunction for superior hydrogen...

Rationally regulating the insufficient interfacial driving forces and sluggish reaction kinetics remains a significant challenge toward the construction of high-performance heterojunction photocatalysts. To overcome this bottleneck, a dual-vacancy-engineered Ag₃PO₄/CdIn₂S₄ S-scheme heterojunction was prepared through an easy ultrasonic chemical route, in which sulfur and oxygen vacancies synergistically reconfigure charge transfer dynamics and reaction barriers through dual microenvironment modulation. Comprehensive experimental analyses and theoretical calculations revealed that tailoring oxygen vacancies in Ag₃PO₄ results in an enhanced built-in electric field near the heterointerface, which provides a strong driving force for directed electron transport from Ag₃PO₄ to CdIn₂S₄, thereby significantly promoting charge separation within the S-scheme heterojunction. Concurrently, modifying the surface microenvironment with sulfur vacancies in CdIn₂S₄ facilitates electron transfer by creating defect energy levels and optimizes the hydrogen evolution reaction kinetics by lowering the hydrogen adsorption/activation barrier. Consequently, the optimized dual-vacancy-modulated Ag₃PO₄/CdIn₂S₄ S-scheme heterojunction demonstrated outstanding photocatalytic hydrogen production activity of 1327.9 μmol g^-1 h^-1 under simulated sunlight, achieving a 113.5-fold enhancement relative to pristine CdIn₂S₄. The findings offer critical insights for the development of heterojunction catalysts for highly efficient solar-to-chemical energy conversion through targeted dual-vacancy-mediated heterointerface engineering.