Origin of the Enhanced Hydrogen Evolution Reaction Activity of Grain Boundaries in MoS2 Monolayers

As one of the most attractive catalysts for the electrochemical hydrogen evolution reaction (HER), MoS2 has gained great attention. With respect to the MoS2 monolayer, nevertheless, the active sites are confined to edges. To activate the inert basal plane of MoS2 of large area, the HER activity of experimentally frequently observed grain boundaries (GBs) is examined by first-principles calculations. It is interesting to find the charge gathering in one dimension, and thus, GBs in MoS2 behave as metallic quantum wires with high conductivity. In comparison to the basal plane, GBs indicate enhanced HER activity with a significantly lower ΔG*H due to the unique local geometry and electronic properties. In this work, an effective and uniform descriptor Δεp→d is proposed, which can unambiguously unravel the origin of the enhanced HER activity of GBs, providing a theoretical guide for improving the electrochemical HER activity of other catalysts in general.