Improvement of active carbon fiber electrode for electric double layer capacitor by electrochemical redox pretreatment

Electric double layer capacitance of phenolic-resin based active carbon fiber(ACF) electrode was enhanced by an electrochemical oxidation. However, the enhanced capacitance was effectively used as a capacitor only after an electrochemical reduction treatment. The effect of reduction treatment after oxidation of ACF electrode was evaluated by galvanic polarization, ac impedance analysis and constant current charge-discharge in 0.5 mol dm^-3 H₂SO₂ aqueous solution. The reduction treatment made the neutral electrode potential of oxidized ACF cathodic, thus during the charging, the ACF of positive electrode worked without the side reaction of gas evolution. AC impedance analysis proved that the capacitance and resistance of oxidized ACF were effectively increased and decreased, respectively, by the reduction treatment. The XPS results of ACF suggested that the surface oxide was removed by the reduction treatment, and the capacitor performance was enhanced by the surface change.