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. MoC x @C-1 ) is prepared from an entangled polyoxometalate-encapsulated coordination polymer (PECP), [Zn(bimbp) 2 ] 3 [PMo 12 O 40 ] 2 ·2H 2 O ( PECP-1 ) (bimbp = 4,4′-bis(imidazolyl)biphenyl) via the annealing and etching processes. The synergistic effects between highly dispersive MoC x particles, graphene coatings and N dopants in MoC x @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, MoC x @C-1 exhibiting an overpotential of 79 mV at a current density of 10 mA cm −2 represents one of the currently best reported MoC x -based HER electrocatalysts in acidic media. Such performance is also better than that of uncoated MoC x -2 nanoparticles prepared by carburizing another PECP [Bu 4 N][Zn 3 (bimb) 4 Cl(MoO 4 )][PMo V Mo VI 11 O 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. New N-doped graphene-coated molybdenum carbide nanoparticles are prepared, which exhibit superior electrocatalytic activity and long-term durability for the hydrogen evolution reaction.