N-Doped graphene-coated molybdenum carbide nanoparticles as highly efficient electrocatalysts for the hydrogen evolution reaction

In our efforts to explore promising substitutes for Pt-based electrocatalysts for the hydrogen evolution reaction (HER), a new type of molybdenum carbide nanoparticle coated with graphene shells with nitrogen dopants (abbr. MoCx@ C-1) is prepared from an entangled polyoxometalate-encapsulated coordination polymer (PECP), [Zn(bimbp)(2)](3)[PMo12O40](2).2H(2)O (PECP-1) (bimbp = 4,4'-bis(imidazolyl) biphenyl) via the annealing and etching processes. The synergistic effects between highly dispersive MoCx particles, graphene coatings and N dopants in MoCx@ C-1 lead to remarkable HER performance in acidic media with a very positive onset potential close to that of commercial 20% Pt/C catalysts, a low Tafel slope of 56 mV dec (1), a high exchange current density of 0.27 mA cm (2), and superior long-term cycle stability. In particular, MoCx@ C-1 exhibiting an overpotential of 79 mV at a current density of 10 mA cm(-2) represents one of the currently best reported MoCx-based HER electrocatalysts in acidic media. Such performance is also better than that of uncoated MoCx-2 nanoparticles prepared by carburizing another PECP [Bu4N][Zn-3(bimb)(4)Cl(MoO4)][(PMoMoVI)-Mo-V O-11(40)].4H(2)O (PECP-2) (bimb - 1,4-bis(1-imidazolyl) benzene). This work provides a new feasible route to prepare nanostructured hybrids composed of transition metal carbides, graphene and N dopants with higher HER activity and stability.