Controlled synthesis of 2D Mo2C/graphene heterostructure on liquid Au substrates as enhanced electrocatalytic electrodes.

2D Mo2C has drawn considerable interest recently for its excellent properties in 2D superconductivity and enhanced hydrogen evolution reaction (HER). Liquid metals have been demonstrated to be an ideal substrate for large-area 2D Mo2C growth. However, the growth mechanism of 2D Mo2C on liquid metals has rarely been explored. Here we report the synthesis of high-quality 2D Mo2C crystals and Mo2C/graphene heterostructures on liquid Au by chemical vapor deposition method. A sunk growth mode of 2D Mo2C on liquid Au substrates has revealed, by atomic force microscope characterizations, that some Mo2C crystals grow below the level of Au terraces around tens of nanometers. Furthermore, graphene/Mo2C heterostructure is controllably synthesized by tuning the hydrogen/carbon ratio, which is proven to be an enhanced electrocatalyst for HER against pure Mo2C crystal grown on liquid Au substrates.