This study proposes breaking the symmetric electronic structure of NiS via Co doping to construct homogeneous NiCoS cocatalysts with asymmetric electron distribution. This strategy successfully optimizes the electronic configuration of S sites and effectively modulates the strength of S-Hₐd bonds, offering a new approach for designing non-noble metal cocatalysts. In this work, homogeneous amorphous NiCoS nanoparticles were first modified on TiO₂ surfaces via a one-step photodeposition method. Theoretical calculations and XPS results reveal that Co introduction induces charge density redistribution in the NiS structure, forming an asymmetric electron distribution state. Electrons transfer from Co to S atoms, generating electron-rich S^(2+δ)-active sites. When electron-rich S^(2+δ)-active sites interact with hydrogen evolution intermediate Hₐd, increased antibonding orbital occupancy effectively weakens S-Hₐd bonds, bringing the Gibbs free energy of hydrogen adsorption (ΔG_H*) closer to zero. This endows NiCoS cocatalysts with higher interfacial catalytic hydrogen evolution efficiency. When the Co-to-Ni atomic ratio is 2:1, the photocatalytic hydrogen production rate of the NiCoS/TiO₂(1:2) sample is 2.1 times that of the NiS/TiO₂ sample. Meanwhile, the NiCoS/TiO₂(1:2) photocatalyst exhibits excellent photocatalytic cycling stability.

Figure 1. Mechanism of Co-induced asymmetric charge distribution enhancing the photocatalytic hydrogen production efficiency of NiCoS cocatalysts