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Bifunctional CdS@Co9S8/Ni3S2 for efficient electrocatalytic and photo-assisted electrocatalytic overall water splitting with 86.5% electrical-to-hydrogen (ηETH) and 5.72% solar-to-hydrogen (ηSTH) conversion efficiencies.

The rational design and construction of cost‐effective nickel‐based phosphide or sulfide (photo)electrocatalysts for hydrogen production from water splitting has sparked a huge investigation surge in recent years. Whereas, nickel phosphides (NixPy) possess more than ten stoichiometric compositions with different crystalline. Constructing NixPy with well crystalline and revealing their intrinsic catalytic mechanism at atomic/molecular levels remains a great challenge. Herein, an easy‐to‐follow phase‐controllable phosphating strategy is first proposed to prepare well crystalline NixPy (Ni3P and Ni12P5) modified CdS@Ni3S2 heterojunction electrocatalysts. It is found that Ni3P modified CdS@Ni3S2 (CdS@Ni3S2/Ni3P) exhibits remarkable stability and bifunctional electrocatalytic activities in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory results suggest that P–Ni sites and P sites in CdS@Ni3S2/Ni3P, respectively, serve as OER and HER active sites during electrocatalytic water splitting processes. Moreover, benefiting from the advantageous photocatalyst@electrocatalyst core@shell structure, CdS@Ni3S2/Ni3P delivers an advantaged photoassisted electrocatalytic water splitting property. The champion electrical to hydrogen and solar to hydrogen energy conversion efficiencies of CdS@Ni3S2/Ni3P, respectively, reach 93.35% and 4.65%. This work will provide a general guidance for synergistically using solar energy and electric energy for large‐scale H2 production from water splitting.

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