Cu vapor-assisted formation of nanostructured Mo2C electrocatalysts via direct chemical conversion of Mo surface for efficient hydrogen evolution reaction applications

Abstract In order to fulfill the demands for sustainable hydrogen production, novel, more efficient and inexpensive (precious metal-free) catalysts are thoroughly investigated. In the present study, a nanostructured Mo carbide film is prepared, using a chemical vapor deposition (CVD) process in Cu vapor, which promotes CH4 decomposition and the rapid carbonization of a commercial Mo foil. Structural X-ray diffraction (XRD) analysis reveals the orthorhombic crystal structure of the film. The Mo carbide film is tested as an electrocatalyst for the hydrogen evolution reaction (HER) in acidic media. The interconnection between the carbide and the underlying Mo foil leads to an enhanced electrocatalytic activity (Tafel slope - 65 mV/dev, overpotential at 10 mA/cm2 - 330 mV), followed by excellent durability after 1000 cycles. Ultraviolet photoemission spectroscopy (UPS) provides clear evidences verifying the enhanced activity on the carbonized Mo surface. Furthermore, an increase in the carbon precursor flow favors the simultaneous growth of graphene/Mo2C heterostrustructure that forms a vertical stack and exhibits even greater electrocatalytic properties. Thus, the heterostructure possesses Tafel slope and overpotential of 56 mV/dec, at n=212-218mV, and 270 mV, respectively, which approach values of commercially available Pt catalysts.