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+xS₂ cathode that can generate current densities of 1,000 mA cm^-2. Our theoretical results reveal that 2H Nb_1+xS₂ with Nb-terminated surface has free energy for hydrogen adsorption that is close to thermoneutral, facilitating HER. Therefore, 2H Nb_1+xS₂ could be a viable catalyst for practical electrolysers.