Monodispersed N-doped carbon nanospheres for supercapacitor application.

Highly monodispersed nitrogen-doped carbon nanospheres are prepared by the pyrolytic carbonization of emulsion-polymerized polystyrene-based colloidal spheres in the presence of a nitrogen-enriched molecule, melamine (1,3,5-triazine-2,4,6-triamine). The nitrogen-doped carbon spheres are successfully tested for use as electrode materials in supercapacitors. The nitrogen content incorporated into the carbon sphere is controlled by changing the weight ratio of melamine to the polymer spheres. The nitrogen doping concentration is proportional to the mixing weight ratio. The nitrogen doping produces relatively abundant pyridinic and pyrrolic configurations, and these configurations are observed to be more abundant for carbon spheres with high nitrogen doping. The nitrogen doping enhances the pseudocapacitance and the electrical conductivity of carbon, thereby enhancing the specific capacitance. We obtain a specific capacitance of up to 191.9 F g(-1) with 20% nitrogen doped carbon nanospheres, which is 14 times higher than that of the undoped carbon nanospheres. Moreover, the capacitance retention remains up to 10,000 cycles, which clearly displays a good cycling stability the nitrogen-doped carbon nanospheres as the supercapacitve electrode materials.