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.