  Chemical activation of the intrinsically inert basal planes of transition
metal dichalcogenides (TMDs) is crucial for developing high-efficiency
electrocatalysts for energy technology applications. Here we report the
discovery of an efficient TMD-based topological catalyst for hydrogen evolution
reaction (HER), containing high-density single-atom reactive centers on a
few-layer (7x7)-PtTe2-x superstructure with a Te-vacancy density of x. Compared
with pristine Pt(111), PtTe2, and (2x2)-PtTe2-x, (7x7)-PtTe2-x exhibits
superior HER performance owing to its substantially increased density of
undercoordinated Pt sites, and displays exceptional catalytic stability when
operating at high current densities. Our first-principles calculations confirm
that multiple types of undercoordinated Pt sites on (7x7)-PtTe2-x exhibit
favorable hydrogen adsorption Gibbs free energies, and that the reactive sites
can further increase their population upon increasing hydrogen coverage. Both
the (2x2)- and (7x7)-PtTe2-x are also shown to possess nontrivial band topology
with robust edge states that may further facilitate HER.
