Novel activated carbons as electrode materials for electrochemical capacitors from a series of starch

A series of activated carbons (ACs) was fabricated with the same preparation method, using cationic starch, cassava starch, corn starch and graft copolymer starch as precursors. The pore size of these ACs was mainly distributed at the range of 1–3 nm and 5–6 nm, and the specific surface area was between 1330 and 1510 m2/g. The Cyclic Voltammetric (CV) curves of the starch ACs displayed approximate rectangular shape even at high voltage sweep rate (100 mV/s), except for cassava starch ACs whose CV plot only presented rectangular shape at low voltage sweep rates. The specific capacitance for all the starch ACs was between 170 and 200 F/g in the electrolyte of 30 wt.% KOH aqueous solution. And cationic starch ACs, corn starch ACs, graft copolymer starch ACs and cassava starch ACs retained as high as 93.81%, 87.64%, 87.43% and 77.65% of their initial specific capacitance, respectively, when the specific current increases from 370 mA/g to 7.4 A/g. The impedance spectra of the ACs exhibited the behavior for typical porous carbon electrodes of electrochemical capacitor.