In-situ formed NiS/Ni coupled interface for efficient oxygen evolution and hydrogen evolution

•NiS nanocrystals were in situ prepared on the surface of Ni nanoparticles via fast and controllable sulfurizing.•The strongly coupled NiS/Ni interface strengthens the electron transfer between Ni and NiS.•Electro-enriched S sites boost the catalytic activity of HER.•NiS/Ni interface facilitates the formation of Ni oxyhydroxide for OER.