Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS2

Abstract Here, the hydrogen evolution reaction (HER) activities at the edge and basal‐plane sites of monolayer molybdenum disulfide (MoS 2 ) synthesized by chemical vapor deposition (CVD) are studied using a local probe method enabled by selected‐area lithography. Reaction windows are opened by e‐beam lithography at sites of interest on poly(methyl methacrylate) (PMMA)‐covered monolayer MoS 2 triangles. The HER properties of MoS 2 edge sites are obtained by subtraction of the activity of the basal‐plane sites from results containing both basal‐plane and edge sites. The catalytic performances in terms of turnover frequencies (TOFs) are calculated based on the estimated number of active sites on the selected areas. The TOFs follow a descending order of 3.8 ± 1.6, 1.6 ± 1.2, 0.008 ± 0.002, and 1.9 ± 0.8 × 10 −4 s −1 , found for 1T′‐, 2H‐MoS 2 edges, and 1T′‐, 2H‐MoS 2 basal planes, respectively. Edge sites of both 2H‐ and 1T′‐MoS 2 are proved to have comparable activities to platinum (≈1–10 s −1 ). When fitted into the HER volcano plot, the MoS 2 active sites follow a trend distinct from conventional metals, implying a possible difference in the reaction mechanism between transition‐metal dichalcogenides (TMDs) and metal catalysts.