Direct Synthesis of Large-Area 2D Mo₂ C on In Situ Grown Graphene

As a new member of the MXene group, 2D Mo₂ C has attracted considerable interest due to its potential application as electrodes for energy storage and catalysis. The large-area synthesis of Mo₂ C film is needed for such applications. Here, the one-step direct synthesis of 2D Mo₂ C-on-graphene film by molten copper-catalyzed chemical vapor deposition (CVD) is reported. High-quality and uniform Mo₂ C 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 Mo₂ C to be grown. Graphene-templated growth of Mo₂ C 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 Mo₂ C-on-graphene heterostructure shows a much lower onset voltage for hydrogen evolution reactions as compared to Mo₂ C-only electrodes.