Full-faradaic-active nitrogen species doping enables high-energy-density carbon-based supercapacitor

Nitrogen doping is usually adopted in carbon based supercapacitor to enhance its relatively low energy density by providing extra pseudocapacity. However, the improvement of energy density is normally limited because the content of the introduced nitrogen species is not high and meanwhile only part of them is electrochemically active. Herein, we designed and fabricated a class of hierarchical nitrogen-rich porous carbons (HNPCs) possessing not only very high nitrogen content (up to 21.7 atom%) but also fully electrochemically active nitrogen species (i.e., pyridinic N, pyrrolic N and oxidized N). Especially, in the synthesis of HNPCs, graphitic carbon nitride (g-C3N4) was used in situ not only as a nitrogen source but also as a catalyst to facilitate the polymerization of phenol and formaldehyde (as carbon precursor) and as a template to create the hierarchical porous structure. As electrodes for aqueous symmetric supercapacitor, the HNPCs with full faradaic-active nitrogen functionalities exhibit excellent supercapacitor performance: high energy density of 36.8 Wh/kg at 2.0 kW/kg (maintaining 25.7 Wh/kg at 38 kW/kg), superior rate capability with 78% capacitance retention from 1.0 to 20 A/g and excellent cycling stability with over 95% capacitance retention after 10 000 cycles, indicating their promising application potential in electrochemical energy storage. This novel carbon material with high-content and full electrochemically active nitrogen species may find extensive potential applications in the energy storage/conversion, catalysis, adsorption, and so on.