Ultrahigh-current-density niobium disulfide catalysts for hydrogen evolution

Metallic transition metal dichalcogenides (TMDs)^1–8 are good catalysts for the hydrogen evolution reaction (HER). The overpotential and Tafel slope values of metallic phases and edges⁹ of two-dimensional (2D) TMDs approach those of Pt. However, the overall current density of 2D TMD catalysts remains orders of magnitude lower (~10–100 mA cm⁻²) than industrial Pt and Ir electrolysers (>1,000 mA cm⁻²)^10,11. Here, we report the synthesis of the metallic 2H phase of niobium disulfide with additional niobium (2H Nb_1+xS₂, where x is ~0.35)¹² as a HER catalyst with current densities of >5,000 mA cm⁻² at ~420 mV versus a reversible hydrogen electrode. We find the exchange current density at 0 V for 2H Nb_1.35S₂ to be ~0.8 mA cm⁻², corresponding to a turnover frequency of ~0.2 s⁻¹. We demonstrate an electrolyser based on a 2H Nb_{1+ x}S₂ cathode that can generate current densities of 1,000 mA cm⁻². Our theoretical results reveal that 2H Nb_{1+ x}S₂ with Nb-terminated surface has free energy for hydrogen adsorption that is close to thermoneutral, facilitating HER. Therefore, 2H Nb_{1+ x}S₂ could be a viable catalyst for practical electrolysers.