The capacitances of the negative and positive electrodes of supercapacitors, using nitrogen-doped mesoporous carbons as the active materials, in different electrolytes

Nitrogen-doped mesoporous carbons (NMCs) with controllable nitrogen contents and similar pore structures were prepared by a sol-gel process coupled with hard templating method, using melamine, phenol and formaldehyde as precursors, and colloidal silica as hard templating. The effects of nitrogen doping content on the asymmetric capacitance of the mesoporous carbon in H₂SO₄, KOH and Et₄NBF₄/PC electrolyte were systematically investigated. The nitrogen-doping has significantly improved the capacitance performance, and both positive and negative electrodes deliver the highest specific capacitance at a nitrogen-doping content of around 8%. In the KOH electrolyte, the negative pseudo-capacitances is significantly higher than that of the positive ones, and the capacity difference is up to 57.9 F/g. In H₂SO₄ electrolyte, the nearly same capacitances for each electrode are found for all samples. And in the organic Et₄NBF₄/PC system, the increased capacitance is mainly attributed to the negative. The study on asymmetrical capacitance response of nitrogen-doped mesoporous carbon paves the way for optimizing the ratio of positive and negative electrode active materials, leading a higher energy density.