NiS nanoparticle-MoS₂ nanosheet core-shell spheres: PVP-assisted synthesis and efficient electrocatalyst for hydrogen evolution reaction

The synthesis of an effective, robust, and cost-efficient electrocatalyst for H₂ through water electrolysis is crucial for developing clean and sustainable energy technology. Herein, we report polyvinylpyrrolidone (PVP)-assisted synthesis of NiS nanoparticle-MoS₂ nanosheets core-shell (NiS@MoS₂) spheres as an efficient electrocatalyst for the hydrogen evolution reaction (HER) using the hydrothermal method. The PVP controls the size and morphology of the NiS@MoS₂ sphere, and it converts into N-doped carbon (NC) as a conductive material during the calcination process to form NiS@MoS₂/NC spheres. The change in MoS₂ concentration (NiS@MoS₂/NC_x) of different catalysts significantly influences the material, size, and electrocatalytic performance. NiS@MoS₂/NC₅₀ exhibits excellent HER performance, showing a small Tafel slope of 56.7 mV dec^-1, and exhibiting good stability with an overpotential of 189 mV at a current density of 10 mA cm^-2. HER performance is believed to be enhanced by the synergistic interaction between NiS nanoparticles and MoS₂ nanosheets at the heterointerface. Furthermore, N-doped carbon enhances the conductivity of the NiS@MoS₂/NC_x composites to enhance HER performance. Density Functional Theory (DFT) simulations indicate that the best catalytic site of NiS@MoS₂ is Mo, where optimal electron transfer occurs between MoS₂ nanosheets and NiS nanoparticles. This electron transfer promotes H+ adsorption, reducing Gibbs free energy (ΔGH* ≈ 0.04 eV) and requiring a work function of 4.81 eV, thereby boosting HER performance. This work will open a low-cost approach for synthesis of non-precious core-shell electrocatalyst with high activity and stability for HER.