Semimetallic molybdenum disulfide ultrathin nanosheets as an efficient electrocatalyst for hydrogen evolution.

Molybdenum disulfide (MoS₂) ultrathin nanosheets, as a well-known inorganic two dimensional (2D) material with a graphene-like structure, has attracted tremendous attention due to its unique microscopic and macroscopic properties brought by the confinement of charge and heat transfer upon the basal plane. However, as the prototype Mott-insulator, its relatively low conductivity and carrier concentration still greatly hamper its wide applications. Here, we developed a novel intralayer vanadium-doping strategy to produce semimetallic vanadium-doped MoS₂ (VMS) ultrathin nanosheets with less than five S-(V, Mo)-S atomic layers, as a new inorganic 2D material. By incorporation of intralayer vanadium atoms, fine regulation of intrinsic electrical properties within the pristine MoS₂ structure has been successfully realized, achieving semimetallic MoS₂-based 2D materials with tunable conductivity and higher carrier concentration for the first time. Benefiting from the enhanced in-plane conductivity, the improved carrier concentration as well as the shortened electron transfer paths, the semimetal-like VMS nanosheet have enhanced catalytic activity with an overpotential of 0.13 V and a smaller Tafel slope, exhibiting enhanced catalytic performance compared with that of a pure MoS₂ system. The intralayer doping in the 2D structure opens a new avenue in building highly efficient catalysts through the regulation of their intrinsic electrical properties, and also gives a new perspective for enlarging the design space of 2D materials.