Abstract: The electrochemical characteristics and pseudocapacitive effects of Fe3+/Fe2+ ion pair were investigated in an electrochemical capacitor (EC) system using porous carbon as electrode material and with H2SO4 solution containing Fe3+/Fe2+ ion pair as electrolyte. The cyclic voltammetric results indicated that highly reversible electrochemical redox reactions of Fe3+/Fe2+ ion pair occurred within the nano-pore structures of the porous carbon electrodes. Symmetrical charge/discharge cycles were achieved due to the existence of Fe3+/Fe2+ ion pair, which effectively improved the capacity of the electrochemical capacitor system. Apart from its excellent cyclic stability, the specific capacitance of the single electrode system reached 174 mAh•g−1, which is 109 mAh•g−1 higher than that obtained for H2SO4 as the electrolyte. The charge/discharge mechanism of Fe3+/Fe2+ ion pair in the EC systems was discussed and a new type of redox electrolyte electrochemical capacitor was suggested.

Key words: Electrochemical capacitor, Faradic pseudocapacitance, Porous carbon, Fe3+/Fe2+ ion pair, Electrosorption