Interfacial engineering of two-dimensional NiS2/VS heterostructure nanosheets as bifunctional electrocatalysts for urea-assisted energy-saving water electrolysis

Heterostructure electrocatalysts based on transition metal sulfides (TMS) have been extensively applied in renewable energy research because the rich interfaces afford high intrinsic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we have fabricated two-dimensional (2D) nickel sulfide and vanadium sulfide heterojunction nanosheets (NiS2/VS-3:1) arranged on carbon cloth as efficient bifunctional catalysts for electrocatalytic water splitting. The strong electronic interaction between NiS2 and VS in the NiS2/VS-3:1 heterostructure nanosheets was beneficial to tune the electronic structures and induce the formation of dual-functional reactive sites (Ni3+ for OER and V2+ for HER) in one heterojunction electrocatalyst, contributing to the promising catalytic activities toward electrocatalytic water splitting. The NiS2/VS-3:1 electrocatalyst has exhibited prominent catalytic activities toward HER and OER, which required low overpotentials of 74 and 235 mV to yield the current density of 10 mA cm−2 in 1 M KOH. Compared with pure NiS2 or VS, the NiS2/VS-3:1 electrocatalyst delivered faster reaction kinetics, improved electron-transfer ability, and enlarged electrochemical active surface area, which were mainly attributed to the fascinating heterostructure in the nanosheets. Some more easily oxidized substances have been added into electrolyte as adjuvants to realize energy-saving hydrogen production, pollutant degradation, and biomass upgrading.