Sulfur-vacancy rich nonstoichiometric TiS2−x/NiS heterostructures for superior universal hydrogen evolution

Water electrolysis has been recognized as one of the most promising approaches to produce green hydrogen and eventually target carbon neutrality. Various cost-effective and light transition metal sulfides have been developed as the electrocatalysts to promote hydrogen evolution reaction (HER), one half-reaction of water electrolysis. Unfortunately, full use of their intrinsic electrocatalytic traits and exposed active sites is still challenging. Here, a nonstoichiometric titanium sulfide/nickel sulfide (TiS2−x/NiS) hetero-catalyst is designed and constructed to induce a high-density of sulfur vacancies. As a HER electrocatalyst, it features the overpotentials of only 63 and 134 mV at a current density of 10 mA cm−2 in 1.0 M KOH and 0.5 M H2SO4, respectively, which is equipped with glorious durability even at high current densities (e.g., 100 mA cm−2 and 500 mA cm−2). Such outstanding performance partially stems from the sulfur vacancies induced by a nonstoichiometric effect, namely the intensified interfacial charge transfer nearby the TiS2−x/NiS heterointerface. The existence of sulfur vacancies partially regulates the d-electronic structure of Ti and Ni active sites, ultimately bringing in reduced energy barrier of water dissociation as well as optimized adsorption free energy for H* intermediates. The strategy of employing both a nonstoichiometric effect and interface engineering of a metal sulfide catalyst paves a new way to design high-performance and cost-effective HER electrocatalyst in universal media.