Photocatalytic water splitting for H2 evolution represents a viable approach to address energy and environmental challenges, but it still remains a significant challenge by inefficient light absorption, insufficient charge separation, and weak redox potentials. To tackle these problems, a defect-engineered S-scheme photocatalyst is designed and constructed by in-situ growing Zn0.5Cd0.5S nanoparticles on flower-like TiO2 microspheres with oxygen vacancies (TiO2-Ov) via a hydrothermal method, thus forming defect-engineered TiO2-Ov/Zn0.5Cd0.5S S-scheme heterojunction. Remarkably, the optimal heterojunction achieves a superior H2 evolution rate of 15.31 mmol g-1 h-1, surpassing those of TiO2, TiO2-Ov, Zn0.5Cd0.5S, and defect-free TiO2/Zn0.5Cd0.5S by factors of 306.2, 56.7, 4.7, and 1.9, respectively. Notably, the presence of oxygen vacancies in TiO2-Ov enables a broadened light absorption and introduces an intermediate energy level to provide an additional photo-induced charge transfer channel within the S-scheme heterojunction. Combining with defect engineering and S-scheme mechanism, the photocatalytic system significantly exhibits enhanced light-harvesting ability, accelerated the spatial separation and transfer of photo-induced charge, and preserved strong redox power. Simultaneously, the S-scheme charge transfer pathway in the TiO2-Ov/Zn0.5Cd0.5S heterojunction is systematically validated through a combination of in-situ irradiated X-ray photoelectron spectroscopy, kelvin probe force microscopy, femtosecond transient absorption spectra, electron paramagnetic resonance, and density functional theory calculation. This work highlights the synergistic effect of defect engineering and S-scheme heterojunction in boosting photocatalytic H2 evolution, offering insights for designing high-performance photocatalyst.
