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.