The identified intrinsic active sites for efficient and stable bi-functional catalyst N-MoS2·Ni3S2/NiS: the Mo–N structure and Ni–S structure on the heterogeneous interface synergistically enhance water splitting

Effective analysis and identification of intrinsic active catalytic sites in composite catalysts will favor the regulation of catalyst structures, which could effectually improve their intrinsic catalytic activity and further enhance their water splitting ability. Therefore, a bi-functional composite catalyst of N-MoS2·Ni3S2/NiS with specific Mo–N structure and heterogeneous interface was rationally prepared through the self-catalysis strategy. The ultra-thin hierarchical morphology of N-MoS2·Ni3S2/NiS facilitates the exposure of active catalytic sites and the acceleration of electron transmission at the reaction interface. Furthermore, both theoretical calculations and experiments testify that the Mo–N structure and Ni–S sites on the heterogeneous interface between Ni3S2 and NiS are, respectively, specific intrinsic active catalytic sites for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), and the NiOOH formed by in situ oxidation at the interface is a synergistic catalytic site for the OER, and the doping of heteroatom N and the heterogeneous interface jointly regulate the electronic structure of N-MoS2·Ni3S2/NiS, boosting overall water splitting. The optimized catalyst, N-MoS2·Ni3S2/NiS, exhibits excellent performance; the overpotential is only 70 mV and 231 mV, respectively, for the HER and OER at 10 mA cm−2.