3 years ago

Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS2

Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS2
Ulises Martinez, Jingjie Wu, Pulickel M. Ajayan, Jing Zhang, Weibing Chen, Jun Lou, Gautam Gupta, Jiangtan Yuan, Aditya Mohite, Hua Guo
Here, the hydrogen evolution reaction (HER) activities at the edge and basal-plane sites of monolayer molybdenum disulfide (MoS2) 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 MoS2 triangles. The HER properties of MoS2 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-MoS2 edges, and 1T′-, 2H-MoS2 basal planes, respectively. Edge sites of both 2H- and 1T′-MoS2 are proved to have comparable activities to platinum (≈1–10 s−1). When fitted into the HER volcano plot, the MoS2 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. Utilizing an on-chip electrochemical device, which is capable of measuring the hydrogen-evolution performance on the designated location of monolayer MoS2, the catalytic activities of the basal-plane and edge sites of both 2H and 1T′-MoS2 are identified. The activities of the MoS2 active sites follow a unique trend in the volcano plot.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201701955

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