▎ 摘　　要

Two-dimensional (2D) ultrathin transition metal nitrides (TMNs) have attracted increasing research interests as a family of rising functional materials for various applications especially energy storage and catalysis. In addition, graphene-based van der Waals (vdW) heterostructures could remarkably promote the catalysis performance compared to the intrinsic TMNs due to the interfacial synergy effect and more efficient charge-transfer kinetics. Here we first report a facile two-step method for synthesis of high-quality molybdenum nitride/graphene (MoN/G) vdW vertical heterostructure through liquid copper-assisted chemical vapor deposition followed by a nitri-dation process. Graphene not only acts as a Mo diffusion barrier for growth of 2D thin MoN crystals, but also facilitates the charge transport within the heterostructure. Therefore, the as-grown MoN/G heterostructure shows a relatively low overpotential of 155 mV and 259 mV in H2SO4 and KOH solutions, respectively, which indeed exhibits outstanding pH-universal (pH = 0-14) hydrogen evolution reaction (HER) catalytic performance. These results provide a general method for the controllable synthesis of MoN/G heterostructure and promote the further research of TMNs-related catalysts in HER catalysis area.