Basal-Plane Pores Activate Monolayer MoS₂ for the Hydrogen Evolution Reaction

Identification of catalytically relevant sites in solid-state materials and our ability to manipulate such sites is critical to designing improved electrocatalysts. In this work, we prepare a series of monolayer MoS2 using chemical vapor deposition and install varied concentrations of defects through swift heavy ion irradiation. Electron micrographs indicate that the ion irradiation procedure generates pores within MoS2 flakes, and Raman microscopic maps show that the defects exert a strongly localized influence. The localization is strong enough that spectra acquired across individual particles can be classified in a binary fashion: regions are either affected by the irradiation-induced pore or appear as pristine MoS2. Besides providing insight into the nature of the defects within the monolayers, this feature enables spatial resolution of regions with significant densities of such pores. This capability is used to quantify the defect density across the sample series and show that the pores located within the MoS2 flakes are particularly active sites for electrocatalytic hydrogen evolution.