Influence of nitric acid acitivation on structure and capacitive performances of ordered mesoporous carbon

Ordered mesoporous carbon CMK-3 was successfully prepared by a hard template nanocasting method followed by carbonization at temperatures from 700 to 900 °C. The values of specific surface area, pore diameter and pore volume were found to increase with the rise of carbonization temperatures. After chemical activation by 6 M HNO3, the specific surface areas decreased significantly, but the specific capacitances increased remarkably in both alkaline (3 M KOH) and neutral (0.5 M Na2SO4) electrolytes. Analysis of the surface structure and composition showed that the chemical activation introduced oxygen-containing functional groups on carbon surface, which are responsible for the enhancement of supercapacitive performances revealed by electrochemical tests. The best achieved specific capacitance is 182.1 F/g in 0.5 M Na2SO4, and 223.5 F/g in 3 M KOH, both at the current density of 0.5 A/g. The specific capacitance retentions after 500 cycles are 95.6% and 86.3% in 0.5 M Na2SO4 and 3 M KOH, respectively. The higher specific capacitance in KOH electrolyte is due to the lower faradic charge transfer resistance and better electrochemical surface area utilization than in Na2SO4 electrolyte.