To produce pure activated carbon (AC) with low potassium ions (K+) content for supercapacitor, coconut-shell AC activated by KOH was treated with a novel oxidation-ultrasound process on the basis of hydrochloric acid (HCl) washing. The electrochemical performances of the ACs as supercapacitor electrodes were characterized by cyclic voltammetry (CV), galvanostatic charge-discharge (GC), and electrochemical impedance spectroscopy (EIS). Results showed that the obtained AC, which was washed with 1.0 wt% HCl solution for 120 min and subsequently treated with 0.6 wt% H2O2 solution at 60°C in an ultrasonic oscillator for 8 h, possessed a K+ content of 46 mg/kg, much lower than that of 417 mg/kg of the AC without oxidation-ultrasound treatment. Furthermore, a large specific surface area and pore volume of 3460 m2/g and 1.869 cm3/g, respectively, were obtained for AC after oxidation-ultrasound treatment. A high specific capacitance of 306 F/g at the current density of 1 A/g in 1 M H2SO4 electrolyte was observed for the prepared AC, indicating it has good electrochemical performances, and remained at 294 F/g with a capacitance retention of 96% after 3000 cycles, indicating excellent stability and capacitive behavior of the AC electrode for supercapacitor.
Part of the book: Supercapacitor Design and Applications