Engineering sulfur vacancy defects in self-supporting Mo-doped NiS ultrathin nanosheets grown <i>in situ</i> on nickel foam for enhanced water splitting

Transition metal sulfide nanoparticles have emerged as awesome candidates to replace conventional noble metal catalysts for electrocatalytic water-splitting due to their unique structure and low cost. The creation of vacancies, an increase in active surface area and optimization of the electronic structure will enhance the electrocatalytic performance. In this study, with sulfur vacancy (S_V) defect engineering, we have grown Mo-doped NiS ultrathin nanosheets built from self-assembled nanoparticles <i>in situ</i> on nickel foam (Mo-NiS/NF) using a simple one-pot hydrothermal approach. Nickel ions originating from NF underwent a sulfation reaction with L-cysteine, while the heteroatom Mo was introduced into the NiS lattice to form S_V. Compared to pure NiS grown on NF (NiS/NF) and Mo-doped NiS powders (Mo-NiS/P), Mo-NiS/NF showed outstanding catalytic performance, achieving a current density of 10 mA cm^-2 (1.0 M KOH) at a low potential of 1.56 V. Simultaneously, density functional theory calculations confirmed that the heteroatom Mo and S_V substantially reduced the hydrolytic Gibbs free energy barrier of NiS. This strategy is expected to provide a simple route for the preparation of other metal sulfide nanoparticles for practical applications in water splitting.