N-doped molybdenum carbides embedded in porous carbon for efficient hydrogen evolution

Abstract

Transition metal carbides (TMCs) are regarded as cost-efficient and stable electrocatalysts for hydrogen evolution reaction (HER). Nitrogen doping into nanosized TMCs in a control manner (e.g. doping amount and site) is one of the most effective routes to intrinsically enhance the activity and durability owing to the ameliorated Mo–H strength and amplified active sites. Herein, an approach based on reticular chemistry is developed to synthesize nanosized N-doped Mo2C embedded in porous carbon (N–Mo2C/PC), via pyrolyzing a hybrid precursor consisting of highly-dispersed molybdates within melamine-benzenetricarboxylic acid supermolecule networks. With optimal N-doping, the N–Mo2C/PC electrocatalyst exhibits an excellent HER stability and activity with overpotential of 109 mV at 10 mA cm−2 in 0.5 M H2SO4, as well as 100 mV at 10 mA cm−2 in 1.0 M KOH. Density functional theory calculations confirm that the appropriate N doping on the surface of Mo2C nanoparticles would accelerate the HER process via weakening the Mo–H bond strength and lowering the H–H coupling barrier. Furthermore, Mo2C nanoparticles loaded on carbon cloth with high HER activity can also be successfully achieved by this strategy. This work paves a universal way to design active sites-enriched TMCs with high performance in energy conversion and storages.