Various carbon aerogels (CAs) were prepared from polymerization of resorcinol and formaldehyde and applied as the electrode materials of an electric double layer capacitor (EDLC) with the aim of controlling the textural and electrochemical properties of CAs by the type of base catalyst and the ratio of resorcinol to catalyst (R/C). The CAs from NaHCO3 and KHCO3 with H+ ions had higher specific surface areas but exhibited lower electrochemical properties than those from K2CO3 and Na2CO3, which had more uniform pore size distributions. The electrochemical properties of Na2CO3 were superior to those of K2CO3 probably because the polarizing power of Na+ ions was higher than K+ ions. With an increasing R/C ratio, the pore sizes of CA showed a tendency to increase but the uniformity of the pore size distribution got worse. For the four base catalysts, the highest electrochemical property was obtained at the R/C ratio of 500.

Activated carbons (ACs) have been used as EDLC (electric double-layer capacitor) electrode materials due to their high specific area, stability, and ecological advantages. In order to prepare ACs with high density and crystallinity, coal tar pitch (CTP) was activated by K2CO3 and the textural and electrochemical properties of the obtained ACs were investigated. Although the CTP ACs formed by K2CO3 activation had much smaller specific surface area and pore volume than did the CTP ACs formed by KOH activation, their volumetric specific capacitance (F/cc) levels as electrode materials for EDLC were comparable due to their higher density and micro-crystallinity. Structural characterization and EDLC-electrode performance were studied with different activation conditions of CTP/K2CO3 ratio, activation temperature, and activation period.

Commercial activated-carbon used as the electrode material of an electric double-layer capacitor (EDLC) was posttreated with various acids and alkalis to increase its capacitance. The carbon samples prepared were then heat-treated in order to control the amount of acidic functional groups formed by the acid treatments. Coin-type EDLC cells with two symmetric carbon electrodes were assembled using the prepared carbon materials and an organic electrolyte. The electrochemical performance of the EDLC was measured by galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the various activated carbons, the carbon electrodes (CSsb800) prepared by the treatments of coconutshell-based carbon activated with NaOH and H3BO5, and then heat treated at 800˚C under a flow of nitrogen gas, showed relatively good electrochemical performance. Although the specific-surface-area of the carbon-electrode material (1,096m2/g) was less than that of pristine activated-carbon (1,122m2/g), the meso-pore volume increased after the combined chemical and heat treatments. The specific capacitance of the EDLC increased from 59.6 to 74.8 F/g (26%) after those post treatments. The equivalent series resistance of EDLC using CSsb800 as electrode was much lower than that of EDLC using pristine activated carbon. Therefore, CSsb800 exhibited superior electrochemical performance at high scan rates due to its low internal resistance.

Coconut shell 계 상용 활성탄을 후처리하여 EDLC 전극재로 적용하였다. Coconut shell계 활성탄을 별도의 처리없이 EDLC 전극재로 사용하였을 때, 초기 무게용량 및 부피용량은 66 F/g 및 39 F/cc이었고, 100 사이클 충 방전을 반복한 후, 각각 54 F/g 및 32 F/cc로 감소하여 82%의 충 방전효율을 나타내었다. 충 방전 반복에 따른 용량의 감소폭이 크며, CV 특성에서 부반응에 의한 분극현상이 발생하여 전극재로 적합하지 않았다. 상업용 활성탄에 포함된 불순물을 효율적으로 제거하기 위하여 알칼리 및 산 처리를 하였고, 그 후 세공 분포와 표면의 산성 관능기 함량을 제어하기 위하여 질소 분위기에서 열처리하였다. 알칼리 및 질산처리 한 후 800℃에서 열처리한 전극재의 경우, 초기부피용량 44 F/cc, 100사이클 후 42 F/cc로서 실용화 가능한 수준의 높은 부피용량 및 95% 이상의 높은 충 방전 효율을 나타내었다.

The commercial activated carbons are typically prepared by activation from coconut shell char or coal char containing lots of inorganic impurities. They also have pore structure and pore size distribution depending on nanostructure of precursor materials. In this study, two types of commercial activated carbons were applied for EDLC electrode by removing impurities with acid treatments, and controlling pore size distribution and contents of functional group with heat treatment. The effect of the surface functional groups on electrochemical performance of the activated carbon electrodes was investigated. The initial gravimetric and volumetric capacitance of coconut based activated carbon electrode which was acid treated by HNO3 and then heat treated at 800℃ were 90 F/g and 42 F/cc respectively showing 94% of charge-discharge efficiency. Such a good electrochemical performance can be possibly applied to the medium capacitance of EDLC.