Preparation of HyperCoal-based activated carbons for electric double layer capacitor

Coal-based activated carbons (ACs) were prepared from HyperCoal using KOH and CaCO₃ as activating agent, and were used as electrode materials for electric double layer capacitor (EDLC) using 0.5 mol/L TEABF4/PC as the electrolytic solution. The porosity of the ACs was characterized using N₂ adsorption at 77 K. The effects of carbonization temperature, activation temperature, activation time and activating agent on the capacitance characteristic of ACs were investigated. The results show that the specific surface area and the specific capacitance decreased with the increase of carbonization temperature. A high activation temperature and a long activation time is not beneficial for the specific capacitance of EDLC. CaCO₃ significantly inhibited the porosity development during KOH activation and gave ACs with quite low specific surface area and specific capacitance. The ACs prepared at carbonization temperature of 500 ℃, activation temperature of 800 ℃, KOH/char ratio of 4 and activation time of 2 h reached a specific surface area of 2 540 m²/g and a total pore volume of 1.65 cm³/g and achieved the maximum specific capacitance of 46.0 F/g.