Coupling Ni-Induced Spin-State Modulation and Schottky Junction Engineering in CdS−NiCoS x for Photocatalytic H ₂ Evolution in Natural Seawater

Efficient photocatalytic H 2 evolution in natural seawater is challenged by sluggish interfacial electron extraction, severe carrier recombination, and deteriorated surface reaction kinetics in saline media. Here, we construct a CdS−NiCoS x Schottky heterojunction by integrating snowflake-like CdS with an amorphous hollow NiCoS x cocatalyst, where Ni incorporation simultaneously modulates the spin-related electronic structure of the cocatalyst and the interfacial Schottky energetics. Under visible-light irradiation (λ > 420 nm) in the presence of sacrificial reagents, the optimized photocatalyst delivers an H 2 evolution rate of 19.89 mmol g −1 h −1 in natural seawater and 29.44 mmol g −1 h −1 in pure water, outperforming pristine CdS by 8.23-fold and an optimized CdS−Pt benchmark by 2.51-fold under identical conditions while retaining 92% of its initial activity after 16 h in natural seawater. Spectroscopic, photoelectrochemical, magnetic, and theoretical analyses collectively indicate that Ni incorporation increases the work function of the cocatalyst, strengthens band bending at the CdS−cocatalyst interface, and enhances the spin asymmetry of electronic states near the Fermi level. These changes facilitate interfacial electron extraction and suppress charge recombination. In parallel, Ni incorporation improves H 2 O adsorption and moderates H* binding at Co-centered sites, thereby accelerating the intrinsic kinetics of hydrogen evolution. This work identifies Ni incorporation as an effective means of coupling spin-state modulation with Schottky junction engineering in sulfide cocatalysts and provides a more rigorous framework for designing photocatalysts for sacrificial H 2 evolution in natural seawater.