Macroporous Carbon Monoliths with Large Surface Area for Electric Double-Layer Capacitor
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Macroporous Carbon Monoliths with Large Surface Area for Electric Double-Layer Capacitor. George Hasegawa,1 Mami Aoki,2 Kazuyoshi Kanamori,1 Kazuki Nakanishi,1 Teiichi Hanada,1 and Kiyoharu Tadanaga2 1 Department of Chemistry, Graduate School of Science, Kyoto University Kitashirakawa, Sakyo-ku, Kyoto, 606-8502, Japan 2 Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University Sakai, Osaka, 599-8531, Japan ABSTRACT Macro/meso/microporous carbon monoliths doped with sulfur have been prepared from sulfonated polydivinylbenzene networks followed by the activation with CO2 resulted in the activated carbon monoliths with high surface area of 2400 m2 g−1. The monolithic electrode of the activated carbon shows remarkably high specific capacitance (175 F g−1 at 5 mV s−1 and 206 F g−1 at 0.5 A g−1). INTRODUCTION Increasing demands for the electrochemical devices, such as batteries [1], fuel cells [2], and electric double-layer capacitors (EDLCs) [3,4], has triggered the development of porous carbon materials. The physical properties of carbon materials, including surface area, pore volume and pore size, must be controlled to be suitable for each application, because they are closely related to the electrochemical performance. A practical polarized electrode material for EDLCs is activated carbon with a high specific surface area [5,6] because EDLCs are based on electrostatic interactions, i.e., the electric charge is accumulated on an electric double-layer of the polarizable electrode, and the electrodes with the higher specific surface area can store more energy. However, the conventional electrodes consisting of microporous carbon particles or powders are not effective enough because the narrow and disordered pores in-between particles or powders are not suitable for the effective transport of ions to the micropore surfaces. In other words, a certain portion of micropores are inaccessible for ions and remain unused. For the better capacitive characteristics, therefore, it is indispensable for porous carbons to have the well-defined larger pores (mesopores and macropores) in addition to the micropores. The mesopores and macropores facilitate the diffusion of the electrolyte ions in the materials while the micropores can provide abundant adsorbing sites for ions [5,7,8]. Thus, great efforts are focused on the preparation of macro/microporous, meso/microporous, and macro/meso/microporous hierarchically porous carbons for EDLCs [9-14]. Monolithic porous carbons are more advantageous for EDLCs rather than the traditional composite pellet electrodes, because the pellet electrodes are fabricated using a mixture of activated carbon powders and binders, such as polytetrafluoroethylene (PTFE), which lower the electric conductivity, and the electrodes are possibly broken into fragments during the charge-discharge cycles. In addition, there is a possibility that binders unfavorably fill the pores of the activated carbons. Meanwhile, monolithic carbons with continuous skeletons can reduce the internal
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