Ni Single Atoms and Ni Phosphate Clusters Synergistically Triggered Surface-Functionalized MoS₂ Nanosheets for High-performance Freshwater and Seawater Electrolysis

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.