Preparation of Mesoporous Carbon with Silica Template and Application of the Carbon in Electrochemical Capacitors

• Main Authors: Hsin-Yu Liu, 劉信佑
• Other Authors: Hsisheng Teng
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/4gmxda

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 92 === 　　Mesoporous carbon was prepared from resol-type phenol-formaldehyde resin using mesoporous silica as template. By filling the resin into the pores of the template, followed by resin carbonization and template dissolution, mesoporous carbon can be obtained in a unsophisticated way. Small-angle X-ray diffraction reflected the long-range ordering of the pores in the carbon. TEM and N2-adsorption analysis showed that the carbon contained mesopores of different sizes and a high proportion of micropores. 　　Electrochemical cyclic voltammetry was conducted in H2SO4 to examine the surface accessibility of the carbon. In comparison with microporous activated carbon prepared, also from the resol resin, the double-layer capacitances per unit area for both carbons are similar (with a value of ca. 10 mF/cm2) at low potential sweep rates. However, the capacitance decline with the sweep rate was less significant for the mesoporous carbon, an indication that the mesoporous carbon has a smaller resistance for electrolyte migration. Upon gasification of the carbons to increase their surface area, the capacitance per unit area of the mesoporous carbon was significantly enhanced (to a value of ca. 13 mF/cm2) while that of the activated carbon was unchanged. It is suggested that the presence of mesopores has facilitated the electrolyte migration into carbon interior. Symmetric two-electrode capacitors fabricated using both carbons were tested with cyclic voltammetry. The mesoporous-carbon capacitor was shown to have a small resistance and still exhibited a capacitive behavior at relatively high potential sweep rates. 　　The AC impedance analysis was also used to estimate the electrochemical behavior and the data were fitted with an equivalent circuit. The responses of mesoporous and microporous carbon electrodes at high frequencies correspond to electrolyte resistance in series with the parallel RC circuit of the electrode. At low frequencies, the impedance spectra exhibit nonideal capacitive behaviors due to the presence of pore resistance. The pore resistance of the mesporous carbon was estimated to be 2.0Ω, while 4.4Ωwas found for the microporous carbon.