Large capacitive enhancement of N-doped nanoporous carbon by the addition of novel redox additive of diphenylcarbazide

• N-doped carbon materials are derived from diphenylcarbazide.
• Diphenylcarbazide can also serve as novel redox additive.
• Incorporating redox additive into electrode is simple but highly effective.
• The specific capacitance has been largely improved up to 497.8 F g−1.

Nitrogen-doped nanoporous carbon materials have been prepared by a template carbonization method, in which diphenylcarbazide serves as carbon/nitrogen source and Mg(NO3)2·6H2O powder as hard template, respectively. The mass ratio of diphenylcarbazide and Mg(NO3)2·6H2O powder plays a crucial role in determining the pore structures and electrochemical performances. The resulting carbon-2:1 sample displays large BET surface area of 1366 m2 g−1, and high pore volume of 2.18 cm3 g−1. It also exhibits good cycling stability and superior electrochemical behaviors, including high specific capacitance of 323.5 F g−1 at 1 mA cm−2 in a three-electrode system using 6 mol L−1 KOH as electrolyte. More importantly, to further improve the electrochemical performance, different amounts (8, 16 and 24 mg) diphenylcarbazide herein serving as novel redox additive is introduced into the carbon-2:1 system to form the carbon-2:1-8/16/24 electrodes. As a result, the specific capacitances of the carbon-2:1-8/16/24 electrodes at 2 mA cm−2 have been improved up to be 232.7, 344.4 and 497.8 F g−1, respectively, which are 1.02, 1.51, and 2.18 times than that of the pristine system (∼228.8 F g−1). Furthermore, the carbon-2:1-24 also retains high cycling stability as 77.5% after 5000 cycles. The present method of incorporating diphenylcarbazide (redox additive) into carbon system is simple but efficient for large improvement of supercapacitor performances.