▎ 摘　　要

As a new member of the MXene group, 2D Mo2C has attracted considerable interest due to its potential application as electrodes for energy storage and catalysis. The large-area synthesis of Mo2C film is needed for such applications. Here, the one-step direct synthesis of 2D Mo2C-on-graphene film by molten copper-catalyzed chemical vapor deposition (CVD) is reported. High-quality and uniform Mo2C film in the centimeter range can be grown on graphene using a Mo-Cu alloy catalyst. Within the vertical heterostructure, graphene acts as a diffusion barrier to the phase-segregated Mo and allows nanometer-thin Mo2C to be grown. Graphene-templated growth of Mo2C produces well-faceted, large-sized single crystals with low defect density, as confirmed by scanning transmission electron microscopy (STEM) measurements. Due to its more efficient graphene-mediated charge-transfer kinetics, the as-grown Mo2C-on-graphene heterostructure shows a much lower onset voltage for hydrogen evolution reactions as compared to Mo2C-only electrodes.