S-Scheme CdS/CuWO₄ Heterojunction Optimizes Reaction Kinetics for Enhanced Photocatalytic H₂ Evolution

In the field of photocatalytic water splitting for hydrogen (H₂) production, heterojunction engineering is regarded as one of the effective strategies to enhance the separation efficiency of photogenerated charge carriers and the redox capability. In this work, a simple electrostatic self-assembly method was employed to intimately couple CuWO₄ nanoparticles with CdS nanorods, thereby constructing a CdS/CuWO₄ heterojunction for photocatalytic H₂ evolution from water. In situ XPS and surface photovoltage measurements confirm the presence of a strong built-in electric field (IEF) and an S-scheme charge transfer pathway at the CdS/CuWO₄ heterojunction interface. Meanwhile, the IEF strength in the CdS/CuWO₄ heterojunction is 2.16 and 5.23 times that of CdS and CuWO₄, respectively. Furthermore, DFT calculations reveal that the H* adsorption energy on the CdS/CuWO₄ heterojunction is -0.19 eV, compared with -0.57 eV on CdS, indicating that constructing an S-scheme heterojunction can optimally tune the reaction kinetics of photocatalytic H₂ evolution and thereby enhance the H₂ production activity. Using lactic acid as a sacrificial agent, the optimized CdS/CuWO₄ S-scheme heterojunction exhibits a higher H₂ evolution rate of 54.53 mmol·g^-1·h^-1, which is approximately 3.86 times that of CdS nanorods (14.1 mmol·g^-1·h^-1). Continuous photocatalytic H₂ evolution tests demonstrate that the CdS/CuWO₄ heterojunction maintains excellent photostability after 12 h of uninterrupted illumination. This study provides insights into the design and development of efficient S-scheme heterojunctions to further improve the activity and stability of photocatalytic H₂ production.