KOH activation of a HyperCoal to develop activated carbons for electric double-layer capacitors

• The HyperCoal based ACs for EDLCs were prepared by single step direct KOH-activation.
• The capacitance of ACs not only depends on surface area, but also on pore size distribution.
• AC-500 shows the capacitance of 46.0 F g−1 and BET surface area of 2540 m2 g−1.
• HyperCoal is an excellent and low-cost candidate for manufacturing ACs for EDLC.

A series of activated carbons (ACs) was prepared from HyperCoal by conventional and direct KOH activation methods, and was used as electrodes in electric double-layer capacitors (EDLCs) using 0.5 M TEABF4/PC as the electrolytic solution. The effects of carbonization temperature (CT), activation temperature (AT) and KOH/sample ratio on BET surface area, average pore size and capacitance of ACs were investigated in this study. Nitrogen adsorption isotherms of all ACs indicated that the pores in ACs were mainly micropores. The BET surface area and capacitance decreased with raising CT from 500 to 900 °C, while the highest BET surface area of 2540 m2 g−1 and maximum capacitance of 46.0 F g−1 were achieved at CT of 500 °C and AT of 800 °C in conventional activation. On the contrary, in the direct activation, the BET surface area and the capacitance increased with the increase of AT and KOH/sample ratio, getting the maximum value of 2440 m2 g−1 and 44.4 F g−1, which is comparable with that of conventional method, at AT of 800 °C and KOH/sample ratio of 4.0. Such a procedure provides a cost-effective approach to preparation of high performance activated carbons from HyperCoal for EDLC.