Mo₂C/graphene heterostructures: low temperature chemical vapor deposition on liquid bimetallic Sn–Cu and hydrogen evolution reaction electrocatalytic properties

Abstract

Thin 2D Mo₂C/graphene vertical heterostructures have attracted significant attention due to their potential application as electrodes in the hydrogen evolution reaction (HER) and energy storage. A common drawback in the chemical vapor deposition synthesis of these structures is the demand for high temperature growth, which should be higher than the melting temperature of the metal catalyst. The most common metallic catalyst is Cu, which has a melting temperature of 1084 °C. Here, we report the growth of thin, ∼200 nm in thickness, semitransparent micrometer-sized Mo₂C domains and Mo₂C/graphene heterostructures at lower temperatures using liquid Sn-Cu alloys. No Sn-associated defects are observed, making the alloy an appealing growth substrate. Raman spectroscopy reveals the vertical interaction between graphene and Mo₂C, as shown by the variation in the strain of the graphene film. The results demonstrate the capability to grow continuous nanometer-thin Mo₂C films at temperatures as low as 880 °C, without sacrificing the growth rate. Mo₂C films are proven to be efficient electrocatalysts for the HER. Moreover, we demonstrate the beneficial role of graphene overgrown on Mo₂C in reducing the HER overpotential values, which is attributed to more efficient charge transfer kinetics, compared to pure Mo₂C films.