Activating Basal Planes of NiPS₃ for Hydrogen Evolution by Nonmetal Heteroatom Doping

NiPS₃, one of the most promising catalysts among transition metal trichalcogenidophosphates (MTPs) in hydrogen evolution reaction (HER) electrocatalysis, is still inhibited by its unsatisfactory activity originating from its semiconducting nature and inert basal plane. Here, it is proposed, for the first time, to engineer the basal surface activity of NiPS₃ by nonmetal heteroatom doping, and predict that the degree to which the valance band of NiPS₃ is filled dominates not only the electrical conductivity of the catalyst, but also the strength of hydrogen adsorption at its surface. Direct experimental evidence is offered that in all the single nonmetal doping samples, C-doped NiPS₃ exhibits the optimum activity owing to its moderate filled state of valance band and that C, N codoping even shows Pt-like activity with an ultralow overpotential of 53.2 mV to afford 10 mA cm⁻² current density and a high exchange current density of 0.7 mA cm⁻² in 1 m KOH. The findings that less valance electrons of dopants than substitutional atoms are of pivotal importance for improving HER activity of NiPS₃ catalyst pave the way for readily designing novel MTPs of ever high performance to replace the incumbent Pt-based catalysts.