Hybrid capacitor capable of large increasing capacitance

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Activated carbon has high power density, but has limited specific capacity, if it is used as the electrode materials for double layer capacity. To increase the capacity of activated carbon, ruthenium oxide was loaded into coal-based activated carbon with surface area of 3000 m^2/g in an aqueous RuCl_3 solution followed by neutralization. Although the BET surface area of the activated carbon decreased upon ruthenium oxide loading compared to that of the starting material, its capacitance increased. The maximum capacity obtained in this study was 324 F/g for activated carbon loaded with 3.2 wt% ruthenium, an increase of about 25 %.This unexpected large increase is considered to be due to an introduction of pseudocapacitance of ruthenium oxide and new mesopore formation by oxidation of activated carbon through catalytic action of RuO_2 during the heating process of the composite in air to improve the pore utility for double layer capacitance.In order to increase the double layer capacitance of activated carbon, further study was carried out. Two sorts of conducting material such as Ketjen black(KB) and boron-doped hydrophobic acetylene black(WWAB) are added to activated carbon to construct the electro-conductive network in the electrode and to increase the effective efficiency of activated carbon. The best results are 329 F/g for KB,359 F/g for WWAB, about 27 % for KB, and 39 % for WWAB increase compared to un-added activated carbon respectively. The optimum content is 4 wt% for KB and 9 wt% for WWAB.