Nanotubes and other nanostructures of VS2, WS2, and MoS2: Structural effects on the hydrogen evolution reaction

Vanadium sulfide (VS2) is a layered transition metal dichalcogenide (TMD), comparable in crystal structure to the well-known MoS2 and WS2. Theoretical predictions attribute much potential to VS2, since it is metallic-like and has an active basal plane, essential for catalytic performance. However, it is much less studied than other members of the TMD family due to the difficulties in synthesizing specific structures with controlled properties. Here we present unique structures of VS2 nanotubes and conduct a comparative study with other well-known inorganic nanotubes and nanostructures of MoS2 and WS2. We evaluate the effect of the curvature and strain, the abundance of surface defects, and the availability of surface sites in various structures by electrochemical methods. We show that MoS2 has the best intrinsic activity, which is enhanced by an extensive electrochemical surface area. The woven-like structure of the MoS2 nanotube walls provides a combined effect of strain, crystallinity, and defects. For WS2 structures, the strained surface of the nanotubes results in sites with higher intrinsic activity than the edge sites, but structures such as the nano-triangles, which provide a higher number of edge sites, exhibit competing activity. As for the VS2 structures, although theoretical calculations predict optimal active sites for the hydrogen evolution reaction (HER), they are extremely sensitive to stoichiometry variations that hamper their catalytic activity. Our findings contribute insights to the improvement and design of VS2-based nanocatalysts for the HER and shed light on the general factors that govern the activity in the unique TMD nanotubes family.