Enhanced Photocatalytic Hydrogen Production Assisted by Seawater Ions

ABSTRACT Photocatalytic hydrogen production from water, particularly seawater, offers a promising route for converting solar energy into storable chemical fuels. However, despite considerable efforts in photocatalyst design, the influence of seawater ions on photocatalytic processes remains poorly understood. In this study, covalent organic frameworks (COFs) are adopted as a structurally well‐defined platform to investigate how representative inorganic ions present in seawater influence photocatalytic hydrogen production. Among the ionic species commonly present in seawater, sodium bromide (NaBr) is identified as the most effective promoter. Mechanistic studies reveal that Br − regulates the catalytic process through multiple pathways. During Pt photodeposition, Br − modulates the electronic structure of Pt nanoparticulate cocatalyst, promoting interfacial charge separation. During the photocatalytic reaction, Br − interacts with photogenerated holes and stabilizes the excited‐state charge, thereby prolonging the lifetime of charge carriers. At high concentrations, Br − reduces the number of accessible active sites on the Pt surface, leading to catalyst poisoning. Significantly, the mechanistic insights gained from COF systems can be extended to common semiconductor photocatalysts, offering valuable guidance for ion‐regulated photocatalysis under seawater‐relevant conditions.