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 beltshaped 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.