Synthesis of Novel Mesoporous Carbons and Their Applications to Electrochemical Double-Layer Capacitors
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Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society
most commercially available activated carbons contains many micropores of < I nmn, which reduces their applicability. The micropores are not so easily wetted by electrolyte solution that much of the surface area in activated carbons is not utilized for charge storage. Furthermore, slower motions of charge balancing ions in wetted micropores have a harmful effect on the charge/discharge current characteristics. It is now generally accepted that the pore size control in mesoporous carbons is more demanding task than the expansion of surface area. In this sense, the template synthesis is projected as a promising route for pore size control of carbon materials for EDLCs. Here we report the synthesis of mesoporous carbons with regular three-dimensional pore networks. We also present results on the EDLC performance of mesoporous carbons. In our approach, mesoporous aluminosilicates with three-dimensional channel structure has been utilized as template for the synthesis of mesoporous carbon. EXPERIMENT Mesoporous silica MCM-48 was prepared by the reported method [1]. HMS was prepared by the reported method using the starting reaction mixture with a molar ratio of TEOS: hexadecylamine: EtOH: H20 = 1: 0.25: 10: 30 [9]. Surfactant was removed by extraction with refluxing ethanol. Aluminum was implanted onto MCM-48 and HMS silicas to generate strong acid catalytic sites for the polymerization of phenol and formaldehyde. Phenol and formaldehyde are incorporated into the pores of aluminum-implanted mesoporous MCM-48 (Al-MCM-48) and HMS silicas (Al-HMS) by heating for 12 hours at 90 'C under reduced pressure. The polymerization of phenol and formaldehyde to get phenol resin inside AIMCM-48 was carried out by heating the mixture under nitrogen atmosphere at 125 0C for 5 hours [10. 11]. The resulting phenol resin-AIMCM-48 composite was heated under N 2 flow at a heating rate of 5 'C /min to 700 'C and held there for 7 hours to carbonize phenol resin inside MCM-48 channels. The dissolution of mesoporous silica frameworks using 48% aqueous hydrofluoric acid (HF) generated mesoporous carbons, designated SNU-1 and SNU-2 (Seoul National University). RESULTS Synthesis of a Mesoporous SNU-1 Carbon using Al-MCM-48 as a Template The ordered mesoporous structures of SNU-1 were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and gas adsorption measurement. XRD patterns were obtained at various times during the course of the synthesis. Figure 1, trace A, shows the characteristic pattern of the AIMCM-48 template with a d spacing value of 3.37 nm. A carbonAIMCM-48 composite showed similar XRD pattern with lower intensity, confirming that the
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aluminosilicate framework of AIMCM-48 is retained after high-temperature carbonization step. To our surprise, intense peaks at 2 0 =1.6' and 2.70 from the long-range ordering of mesopores is clearly shown in the XRD pattern of SNU-I carbon (Figure 1, trace B). This result revealed that the carbon n
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