Direct versus reverse vertical two-dimensional Mo₂C/graphene heterostructures for enhanced hydrogen evolution reaction electrocatalysis

Mo₂C/graphene heterostructures prepared by chemical vapor deposition have demonstrated excellent electrocatalytic activity in a hydrogen evolution reaction (HER). This is attributed to the high catalytic activity of Mo₂C while the high electrical conductivity of graphene facilitates charge transfer. In the as-grown direct vertical order, graphene is placed above the Mo₂C film. This reduces the catalytic activity of the heterostructure, since graphene in chemically inert. Here, a simple transfer method is proposed that results in the reverse order deposition of the heterostructure on the electrode. This method places graphene at the interface between Mo₂C and the electrode, enhancing charge transfer between them, which results in an overpotential of 440 mV at 10 mA cm⁻² and corresponds to ∼65 mV overpotential reduction as compared to the direct heterostructure. At the same time, when a direct Cu/Mo₂C/graphene junction with a Cu catalyst substrate is used as a working electrode, the improvement of the heterostructure HER activity is observed which is manifested in an overpotential of 275 mV at 10 mA cm⁻² with a correspondent ∼230 mV reduction. All above performances are accompanied with excellent endurance. (paper)