Dual-Vacancy-Mediated Charge Separation in Cd_0.5Zn_0.5S/NaNbO₃ S-Scheme Heterojunction for Enhanced Photocatalytic Hydrogen Evolution

Sodium niobate (NaNbO3) is recognized as a promising photocatalyst for solar energy conversion. However, its practical application in photocatalytic hydrogen evolution (PHE) is severely limited by inherent drawbacks, including low quantum efficiency, insufficient visible-light absorption, and poor charge separation efficiency. To address these issues, we propose a strategy integrating dual-vacancy regulation and S-scheme heterojunction construction. A dual-vacancy S-scheme Sv-Cd0.5Zn0.5S/Ov-NaNbO3 heterojunction photocatalyst was synthesized via a simple hydrothermal method, with the relative concentrations of sulfur vacancies (Sv) and oxygen vacancies (Ov) precisely controlled by tuning the mass ratio of Sv-Cd0.5Zn0.5S to Ov-NaNbO3. The synergistic interaction between the dual vacancies and the S-scheme heterojunction significantly broadens the photocatalyst’s light absorption range, enhances the built-in electric field, improves the spatial separation efficiency of photogenerated charge carriers, and optimizes the hydrogen evolution reaction kinetics by exposing more active sites. The dual vacancies not only improved the PHE activity but also further enhanced the stability of the catalyst. The optimized Sv-Cd0.5Zn0.5S/Ov-NaNbO3-0.2 catalyst exhibits a remarkable enhancement in PHE performance, achieving a hydrogen evolution rate of 1593.0 μmol·g–1·h–1 under simulated sunlight and 375.6 μmol·g–1·h–1 under visible-light irradiation. Furthermore, its AQE at 350 nm reaches 1.8%, which is approximately 3.5 and 6.0 times higher than those of Ov-NaNbO3 and Sv-Cd0.5Zn0.5S, respectively. This study provides an important theoretical foundation for the design of efficient and stable multivacancy S-scheme heterojunction photocatalysts based on ABO3, with visible-light responsiveness.