Electric-driven water dissociation is considered to be a sustainable approach for the generation of H2. Ni nanoparticles show poor freshwater/seawater electrolysis activity owing to the severe aggregation of Ni, which blocks the active sites to catalyze water splitting. Here, we present Ni nanoparticles/N-doped carbon sheets by the thermal treatment of Ni-based triazole-benzoic acid complexes. The electronic state and coordination environment of Ni are modulated by the formation of the confined space with the N-doped carbon layer. Ni/N-doped carbon sheets promote acidic/alkaline hydrogen evolution activity with 143/81 mV@10 mA/cm2. Upon being used as the catalysts for water oxidation reaction, it expedited alkaline oxygen evolution 218/312 mV@10/50 mA/cm2 for Ni/N-doped carbon, which is even superior to commercial RuO2 with 309/364 mV. Tests for alkaline freshwater/seawater splitting find that Ni/N-doped carbon sheets possess remarkable activity with 1.56/1.62 V@10 mA/cm2 as well as outstanding stability. Our work offers an efficient strategy to rationally regulate the coordination structure of metal nanoparticles for promoting water electrolysis activity. © 2024 Elsevier Ltd