Abstract: Light driven hydrogen generation technologies, such as photocatalysis (PC) or photoelectrocatalysis (PEC), although still relatively underexplored, offer significant environmental benefits, particularly when seawater is used as feedstock. However, seawater introduces stability challenges, which motivate this study on the performance and durability of the photoelectrocatalytic seawater splitting for hydrogen generation. CdS-based materials, known for their favorable photocatalytic properties, were selected due to their simplicity, cost-effectiveness, and availability. Accordingly, this work reports the experimental validation of PEC hydrogen generation under long-term operation in a semi-continuous system using natural seawater and an immobilized catalyst. The results demonstrate that this CdS-based system enables stable and scalable hydrogen production, representing a significant advancement in the field. The operational conditions investigated included catalyst type (CdS and CdS/TiO2 heterojunction), light wavelength (UV and VIS), sacrificial agent concentration (0.01-1 M Na2S and Na2SO3), and system stability. The superior performance of CdS/TiO2 composites compared to CdS was attributed to enhanced charge transfer mechanisms, as supported by electrochemical characterization. Long-term stability tests over 400 h for CdS/TiO2 and 650 h for CdS demonstrated excellent durability and highlighted the crucial role of the sacrificial agent, achieving a maximum hydrogen production rate of 27,940 µmol h-¹ gcat-¹ with CdS and negligible Cd leaching

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