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

Abstract

New N-doped graphene-coated molybdenum carbide nanoparticles are prepared, which exhibit superior electrocatalytic activity and long-term durability for the hydrogen evolution reaction.

Abstract

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[PMo ₁₂O ₄₀] ₂·2H ₂O ( 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 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 MoC _x-based HER electrocatalysts in acidic media. Such performance is also better than that of uncoated MoCx-2 nanoparticles prepared by carburizing another PECP [Bu ₄N][Zn ₃(bimb) ₄Cl(MoO ₄)][PMo ^VMo ^VI ₁₁O ₄₀]·4H ₂O ( 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.