Pomegranate-like N,P-Doped Mo₂C@C Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution

Well-defined pomegranate-like N,P-doped Mo₂C@C nanospheres were prepared by simply using phosphomolybdic acid (PMo₁₂) to initiate the polymerization of polypyrrole (PPy) and as a single source for Mo and P to produce N,P-doped Mo₂C nanocrystals. The existence of PMo₁₂ at the molecular scale in the polymer network allows the formation of pomegranate-like Mo₂C@C nanospheres with a porous carbon shell as peel and Mo₂C nanocrystals well-dispersed in the N-doped carbon matrix as seeds. This nanostructure provides several favorable features for hydrogen evolution application: (1) the conductive carbon shell and matrix effectively prevent the aggregation of Mo₂C nanocrystals and facilitate electron transportation; (2) the uniform N,P-doping in the carbon shell/matrix and plenty of Mo₂C nanocrystals provide abundant catalytically highly active sites; and (3) nanoporous structure allows the effective exposure of active sites and mass transfer. Moreover, the uniform distribution of P and Mo from the single source of PMo₁₂ and N from PPy in the polymeric PPy-PMo₁₂ precursor guarantees the uniform N- and P-co-doping in both the graphitic carbon matrix and Mo₂C nanocrystals, which contributes to the enhancement of electrocatalytic performance. As a result, the pomegranate-like Mo₂C@C nanospheres exhibit extraordinary electrocatalytic activity for the hydrogen evolution reaction (HER) in terms of an extremely low overpotential of 47 mV at 10 mA cm^-2 in 1 M KOH, which is one of the best Mo-based HER catalysts. The strategy for preparing such nanostructures may open up opportunities for exploring low-cost high-performance electrocatalysts for various applications.