Development of Electrode for Super Capacitor by Using Carbon Gels with Hieratically Controlled Porous Structure

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Interesting porous carbon materials, called carbon cryogels, have been synthesized via sol-gel polymerization of resorcinol with formaldehyde, freeze drying, and pyrolysis. The cryogel consists of nanoparticles of carbon, and mesopores are formed among the particles. Carbon cryogels are unique materials with high surface areas and large mesopore volumes, being expected to be used as catalysts, adsorbents, electric double layer capacitors, lithium ion battery, and materials for chromatographic separation.Monolithic carbon cryogels can be synthesized by molding the hydrogels prior to drying. In the present work, carbon cryogel electrodes in the form of tablet were prepared without using a binder for electric double layer capacitor systems. A three-electrode cell with an Ag/AgCl reference electrode whereby 40 M KOH was served as an electrolyte was performed to measure the capacitance. It was found that capacitance per carbon electrode weight could be increased based on precise controlling of porous structure and CO_2 activation at 1000℃. However, the capacitance per electrode volume could not be improved by these methodologies.The apparent density of carbon cryogel electrode was tried to be increased by repolymerizing resorcinol and formaldehyde in the large mesopores and macropores of organic cryogels, precursors of carbon cryogels. As the results, the density of electrode could be doubled. Cyclic characteristics of tablet-type carbon cryogel electrode synthesized were experimentally studied. The capacitance of carbon electrode could be doubled by the repolymerization in organic cryogels. The decrease of capacitance was within 3 %, even if the charging/discharging were repeated 10000 times. It was found that charging/discharging using the carbon electrode prepared were reversible by cyclic voltammetry.