Surface properties of MoS₂ probed by inverse gas chromatography and their impact on electrocatalytic properties

Layered transition metal dichalcogenides (TMDs) are at the forefront of materials research. One of the most important applications of these materials is their electrocatalytic activity towards hydrogen evolution, and these materials are suggested to replace scarce platinum. Whilst there are significant efforts towards this goal, there are various reports of electrocatalysis of MoS₂ (which is the most commonly tested TMD) with large variations of the reported electrocatalytic effect of the material, with overpotential varying by several hundreds of millivolts. Here, we analyzed surface properties of various bulk as well as single layer MoS₂ samples using inverse gas chromatography. All samples displayed significant variations in surface energies and their heterogeneities. The surface energy ranged from 50 to 120 mJ m^-2 depending on the sample and surface coverage. We correlated the surface properties and previously reported structural features of MoS₂ with their electrochemical activities. We concluded that the observed differences in electrochemistry are caused by the surface properties. This is an important finding with an enormous impact on the whole field of electrocatalysis of layered materials.