Molten-droplet-driven growth of MoS flakes with controllable morphology transition for hydrogen evolution reactions.

The controllable fabrication of two-dimensional transition-metal dichalcogenides (2D TMDs) and a deep understanding of the corresponding process mechanisms are of fundamental importance for their further applications. In this study, the molten-droplet-driven (MDD) growth of MoS based on a Na-Mo-O molten-salt chemical vapor deposition (CVD) method is demonstrated temperature-dependent dispersion and spreading of droplets on a surface, yielding MoS flakes with morphology transition from compact triangles to fractal dendrites with the increase in temperature. By building up the dependence between the formed morphologies of grown MoS flakes and the corresponding kinetics during successive growth processes, it was found that the wetting-driven force, which is governed by interface free energies (surface tension) of molten droplets, would largely determine the driven movement of the droplet, and then the formation of different morphologies. Finally, based on these MoS flakes, a systematic improvement of the hydrogen evolution reaction (HER) was demonstrated in accordance with the evolution of morphologies from compact to fractal. This study presents an important advance in understanding the growth mechanisms related to the molten-salt-assisted CVD fabrication of 2D TMDs and provides a facile method for tailoring the growth and application of 2D TMDs with controllably trimmed morphologies.