Designing Champion Nanostructures of Tungsten Dichalcogenides for Electrocatalytic Hydrogen Evolution.

Fine-tuning strain and vacancies in 2H-phase transition-metal dichalcogenides, although extremely challenging, is crucial for activating the inert basal plane for boosting the hydrogen evolution reaction (HER). Here, atomically curved 2H-WS2 nanosheets with precisely tunable strain and sulfur vacancies (S-vacancies) along with rich edge sites are synthesized via a one-step approach by harnessing geometric constraints. The approach is based on the confined epitaxy growth of WS2 in ordered mesoporous graphene derived from nanocrystal superlattices. The spherical curvature imposed by the graphitic mesopores enables the generation of uniform strain and S-vacancies in the as-grown WS2 nanosheets, and simultaneous manipulation of these two key parameters can be realized by simply adjusting the pore size. In addition, the formation of unique mesoporous WS2 @graphene van der Waals heterostructures ensures the ready access of active sites. Fine-tuning the WS2 layer number, strain, and S-vacancies enables arguably the best-performing HER 2H-WS2 electrocatalysts ever reported. Density functional theory calculations indicate that compared with strain, S-vacancies play a more critical role in enhancing the HER activity.