Oxygen and Sulfur Dual-Vacancy-Mediated Electronic-Structure Modulation in a CeO2-CdS-Ni Z-Scheme Heterostructure for Photocatalytic Hydrogen Evolution

Harnessing abundant solar energy to generate hydrogen via photocatalytic water splitting offers a promising route toward sustainable carbon-neutral energy systems. Efficient photocatalysts must be developed to achieve high hydrogen evolution rates. Heterojunction formation and vacancy-mediated enhancement of photophysical properties can broaden the absorption range, increase charge-carrier mobility, and reduce recombination. Therefore, a dual-vacancy-rich CeO2-CdS-Ni heterostructure with a high concentration of both sulfur (Sv) and oxygen (Ov) vacancies was engineered from a UiO-66 (Ce) metal–organic framework. CeO2-CdS-Ni composites with varying degrees of Ov and Sv were prepared by in situ growth of CdS-Ni on CeO2. The introduction of Ov created charge-induced electron-rich centers. Furthermore, the Ov on meso-engineered CeO2 significantly improved the adsorption and oxidation of sacrificial agents during PHE. More importantly, integrating Sv-rich CdS-Ni on the Ov-rich meso-engineered CeO2 further increased light absorption, internal electric field generation, and charge-carrier migration. Thus, this study provides fundamental insights into the synergistic effect of vacancy–vacancy (Ov and Sv) interactions to tune electronic structures through multivariate defect engineering. Notably, the dual-vacancy photocatalyst having optimum Ov and CdS-Ni loading (CeO2-CdS-Ni-45) achieved a PHE rate of 379 μmol g–1 h–1 under sunlight irradiation. We also showed large-scale applicability for PHE of the catalyst by thin-film deposition on glass slides. Further, efficient recyclability of the catalyst up to four cycles was observed.