Effect of removing potassium ions from activated carbon on its electrochemical performance for supercapacitors

Abstract

To produce pure activated carbon (AC) with a low potassium ion (K⁺) content for supercapacitors, coconut shell-derived AC activated by KOH was treated using a novel oxidation-ultrasound process based on hydrochloric acid (HCl) washing. The effects of different treatment conditions on the K⁺ content of AC were investigated, and the physical properties of the as-prepared samples were characterized by scanning electron microscopy (SEM) and N₂ adsorption–desorption isotherms. The electrochemical performance of AC as a supercapacitor electrode was characterized by cyclic voltammetry (CV), galvanostatic charge–discharge (GC) and electrochemical impedance spectroscopy (EIS). The results showed that the AC that 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⁻¹, which was much lower than the value of 417 mg kg⁻¹ found for the AC that did not undergo oxidation-ultrasound treatment. Moreover, the AC subjected to oxidation-ultrasound treatment possessed a large specific surface area and pore volume of 3460 m² g⁻¹ and 1.869 cm³ g⁻¹, respectively. In terms of the electrochemical performance, this exhibited a high specific capacitance of 306 F g⁻¹ at a current density of 1 A g⁻¹ in 1 M H₂SO₄ electrolyte and remained at 294 F g⁻¹ with a capacitance retention of 96% after 3000 cycles, indicating excellent stability and capacitive behavior of the AC electrode with respect to its use as a supercapacitor.