Creating Fluorine-Doped MoS 2 Edge Electrodes with Enhanced Hydrogen Evolution Activity.

The edge sites of MoS 2 are catalytically active for hydrogen evolution reactions (HER). However, pristine edge sites usually contain only intrinsic atoms or defects, limiting the tuning of on-site hydrogen species adsorption and desorption, the critical steps for HER. In addition, the number of atoms on pristine edges is small compared to that of electrochemically inert atoms in bulk. Thus, it is desirable to develop a scalable technique of creating a large number of highly HER-active edge sites. Here, a plasma etching strategy is developed for creating MoS 2 edge electrodes with a controllable number of active sites that enable the quantitative characterization of their HER activity using a local probe method. Fluorine atoms with large electronegativity are doped on the MoS 2 edge sites that lead to a fivefold activity enhancement compared to that from pristine edges and is attributed to the more moderate binding energy for hydrogen species. The scalability of such a method is further demonstrated by activating MoS 2 catalyst in macroscopic quantities with enhanced HER performance and stability. The work provides two-dimensional materials as a platform for understanding the doping effect on the edge sites at atomic-level, and offers a novel route for the design of efficient catalysts.