Morphology-Controlled Electrocatalytic Performance of Two-Dimensional VSe2 Nanoflakes for Hydrogen Evolution Reactions.

VSe₂ is a typical two-dimensional (2D) transition-metal dichalcogenide material with various physical properties, such as ultrahigh electrical conductivity, controversial magnetism, and active catalytic properties. However, controllable preparation of VSe₂ 2D structures poses many challenges, and their application has not yet been developed. Here, we controllably synthesize VSe₂ 2D flakes on highly oriented pyrolytic graphite (HOPG) using molecular beam epitaxy. By controlling the growth temperature and the evaporation rate of the source, we obtained various morphologies of VSe₂ flakes, including single- and multilayers with triangular and belt shapes. Compared with the triangular structures of the flakes, the one-dimensional nanobelt structures have a larger edge density and can provide more catalytic active sites. Hydrogen evolution reaction results indicate that the belt-shaped VSe₂ flakes exhibit superior catalytic performance. Due to the presence of plenty of edges, the overpotential of the belt-shaped VSe₂ is 543 mV at a current density of 1 mA/cm², which is much lower than that in the triangular flakes. The VSe₂ flakes with a larger edge density are more conductive than the regular triangular flakes after loading metal atoms due to the efficient dispersion of the metal atoms. As a result, the multistructure of Co particle-decorated VSe₂ flakes achieves a high catalytic performance with 352 mV overpotential at a current density of 10 mA/cm², demonstrating their potential applications in the catalyst field. [ABSTRACT FROM AUTHOR]