A heterostructured electrocatalyst of small NiSe₂ nanoparticles confined NiMoN nanorods (NiSe₂–NPs/NiMoN–NRs) is prepared to accelerate both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a same alkaline medium. The synergistic effects caused by the combination of merits derived from NiSe₂ and NiMoN phases trigger an optimum electronic structure with high density of state at near Fermi level and enhance adsorption free energy, thereby resulting in excellent catalytic activities and strengthened working stability. The catalyst requires a low overpotential of 58 mV for HER and 241 mV for OER to reach 10 mA cm⁻² in 1.0 M KOH electrolyte. A two-electrode electrolyzer based on the developed catalyst shows outstanding cell voltage of 1.51 and 1.46 V to reach 10 mA cm⁻² in 1.0 M and 30 wt% KOH solution at 25 ℃ for overall water splitting, respectively. In addition, the solar-driven water splitting process delivers a high solar-to-H₂ conversion efficiency of ~18.4%, impressively unveiling that the developed bifunctional catalyst is highly potential for overall water splitting to produce green hydrogen fuel.

Two-dimensional metal dichalcogenides have been evidenced as potential electrocatalysts for hydrogen evolution reaction (HER); however, their application is limited by a poor oxygen evolution reaction (OER) activity due to insufficient number/types of multi-integrated active sites. In this study, we report a novel bifunctional catalyst developed by simultaneous engineering of single nickel atoms (Ni_SA) and nickel phosphate clusters (Ni_Pi) to synergistically trigger surface-functionalized MoS₂ nanosheets (NSs) resulting in high reactivities for both HER and OER. The Ni_SA-Ni_Pi/MoS₂ NSs material exhibits a fairly Pt-like HER behavior with an overpotential of 94.0 mV and a small OER overpotential of 314.0 mV to reach 10 mA cm⁻² in freshwater containing 1.0 M KOH. Experimental results of the catalyst are well supported by theoretical study, which reveals the significant modulation of electronic structure and enrichment of electroactive site number/types with their reasonably adjusted free adsorption energy. For evaluating practicability, the Ni_SA-Ni_Pi/MoS₂ NSs-based electrolyzer delivers effective operation voltage of 1.62, 1.52, and 1.66 V at 10 mA cm⁻² and superior long-term stability as compared to Pt/C//RuO₂ system in freshwater, mimic seawater, and natural seawater, respectively. The present study indicates that the catalyst is a promising candidate for the practical production of green hydrogen via water electrolysis.