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

MoC/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 MoC while the high electrical conductivity of graphene facilitates charge transfer. In the as-grown direct vertical order, graphene is placed above the MoC 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 MoC and the electrode, enhancing charge transfer between them, which results in an overpotential of 440 mV at 10 mA cm and corresponds to ∼65 mV overpotential reduction as compared to the direct heterostructure. At the same time, when a direct Cu/MoC/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 with a correspondent ∼230 mV reduction. All above performances are accompanied with excellent endurance.