The edge of the 2H-MoS2 phase has good electrocatalytic behavior for hydrogen evolution reaction (HER). However, the shape of monolayer MoS2 synthesized under thermodynamic equilibrium conditions is triangular, which limits the density of catalytic sites at the edge of a crystal domain. The morphology of the edge of monolayer MoS2 grown under non-thermodynamic equilibrium conditions will show a large number of dendrite nanostructures. The abundant dendrite edge nanostructures make it have more catalytic site densities than monolayer MoS2 synthesized under thermodynamic equilibrium conditions. The relationship between MoO3 source supply and MoS2 fractal dimension was established through the simulation of fractal dimension. HER performance showed that the Tafel slope (59 mV/Dec) of dendrite monolayer MoS2 was much lower than that of the triangular sample (97 mV/Dec), which confirmed that the dendrite MoS2 monolayer was more conducive to the application of hydrogen evolution reaction.

The density and spatial distribution of substituted dopants affect the transition metal dichalcogenides (TMDCs) materials properties. Previous studies have demonstrated that the density of dopants in TMDCs increases with the amount of doping, and the phenomenon of doping concentration difference between the nucleation center and the edge is observed, but the spatial distribution law of doping atoms has not been carefully studied. Here, it is demonstrated that the spatial distribution of dopants changes at high doping concentrations. The spontaneous formation of an interface with a steep doping concentration change is named concentration phase separation (CPS). The difference in the spatial distribution of dopants on both sides of the interface can be identified by an optical microscope. This is consistent with the results of spectral analysis and microstructure characterization of scanning transmission electron microscope. According to the calculation results of density functional theory, the chemical potential has two relatively stable energies as the doping concentration increases, which leads to the spontaneous formation of CPS. Understanding the abnormal phenomena is important for the design of TMDCs devices. This work has great significance in the establishment and improvement of the doping theory and the design of the doping process for 2D materials.