Characterization And Application In EDLC Of Carbons Prepared By Using Porous Minerals As Templates

For the decrease of the cost of carbons prepared by template method, inthe present paper, characterization and electrochemical behaviors of carbonsprepared by template method ( templated carbons ) using diatomite,halloysite, zeolite minerals as templates, and furfuryl alcohol, sucrose ascarbon sources were investigated, respectively.X-ray Diffraction (XRD) analysis indicated that structures of diatomiteand zeolite minerals were stable, but halloysite's changed from crystals toamorphous at high-temperature. The results showed that no new peaksappeared in the XRD patterns of carbon/template compounds, and indicatedthat there were no chemical reactions between templates and carbon sourcesduring carbonization. For templated carbons, there were some impurities suchas KMgAlF₆ or Ca(MgAlF₆)₂. Scan Electron Micoscope (SEM) observationshowed that the morphologies between tempalted carbons and correspondingtemplates were similar. N₂ adsorption analysis indicated that the specificsurface areas and pore volumes of the templated carbons, were 10 more timeshigher than the corresponding templates, which were the minerals with lowspecific surface areas and high meso-porisities.As the electrodes of EDLC in organic system, the specific capacitancesof templated carbons were larger than the commercial activated carbons(CACs) at similar specific surface areas. It could be reasoned that the largepore size of templated carbons could easily form the electric double layer, butthe CACs could not, due to their small pore size and the large ion diameter ofthe electrolyte. The charge/discharge efficiencies of templated carbons werelower than CACs, due to the effect of impurities.In inorganic system (1M H₂SO₄), the specific capacitances of templatedcarbons were smaller at low scan ratio, but the decrease of specificcapacitances as the increment of scan ratio was lower comparing withcommercial activated carbons. We reasoned that when the size of ions in theelectrolyte was small enough, the micro-pores were the preponderant factor tospecific capacitance due to their high specific surface area, and when the ionssize was large, the meso-pores and macro-pores were dominant because of thesupply of good accesses for larger ions to form the electric double layers.Therefore, at slow scan ratio, the specific capacitances of commercialactivated carbons with high specific surface area and rich micro-pores werelarger, but the templated carbons with large pore volume and pore size,became larger at the fast scaning ratio.