In-situ synthesis of NiS2 nanoparticles/MoS2 nanosheets hierarchical sphere anchored on reduced graphene oxide for enhanced electrocatalytic hydrogen evolution reaction

As an important energy storage and transportation carrier, hydrogen has the advantages of high combustion heat, non-toxic, and pollution-free energy conversion process. Bimetallic sulfide composites are one of the emerging catalysts for hydrogen evolution reactions (HER) during water splitting. Herein, a hydrothermal method has been employed for the in-situ synthesis of NiS2 nanoparticles/MoS2 nanosheets (NiS2/MoS2) hierarchical sphere anchored on reduced graphene oxide (RGO) for enhanced electrocatalytic HER activity. The NiS2/MoS2/RGO composite displays improved HER activity compared to MoS2/RGO and NiS2/RGO. The optimized NiS2/MoS2/RGO-9 requires only an overpotential of 136 mV at a current density of 10 mA cm-2, a small Tafel slope of 53.4 mV dec-1, and good stability in acid solution. The synergetic effect between NiS2 nanoparticles and MoS2 nanosheets is responsible for enhanced HER performance. Moreover, RGO provides the substrate for NiS2/MoS2 species and maintains the overall conductivity of NiS2/MoS2/RGO composites. Finally, density functional theory (DFT) calculations justify and approve the efficient HER activity of NiS2/MoS2/RGO in terms of lower Gibbs free energy (0.07 eV) and lower work function (3.98 eV) that subsequently enhance the dissociation of H2O.