APPLICATIONS OF EXFOLIATED CARBON FIBER FOR ELECTROCHEMICAL CAPACITOR ELECTRODE

Electric double layer capacitor (EDLC) using carbon electrodes have been anticipated as an energy storage device for electric vehicle, distributed energy system applications and so on. High surface area carbons were employed for the electrode materials of EDLC to store energy in the electric double layer, and the control of pore size distribution of its carbons was recognized to be very important [1-3]. On the other hand, when the electrode material shows faradic reactions at the electrode surface in wide range of potential window under the capacitor-like working conditions, the energy stored by the charge transfer can be accounted as pseudo-capacitance. This type of energy storage is found in transition metal oxides, conducting polymers and intercalation reaction with carbons, and called as the electrochemical capacitor [4]. In our previous papers [5, 6], carbon fibers were exfoliated by rapid heating of their intercalation compounds prepared in either nitric acid or formic acid, single fiber splitting into a number of thin filaments. These exfoliated carbon fibers (ExCFs) were found to give huge capacitance in concentrated sulfuric acid [7]. In the present work, the electrochemical capacitor behavior of ExCFs was studied in different concentration of sulfuric acid electrolyte and the mechanism to give large capacitance was discussed.