Composite electrode composed of bimodal porous carbon and polypyrrole for electrochemical capacitors

Three-dimensionally ordered macroporous (3DOM) carbons having walls composed of mesosized spherical pores were prepared by a colloidal crystal templating method. A composite electrode consisting of bimodal porous carbon and polypyrrole (PPy) was prepared by electropolymerization of pyrrole within the macropores of the bimodal porous carbon. The porous structure of the composite electrode was analyzed using a scanning electron microscope and by nitrogen adsorption–desorption measurement. It was found that the deposition of PPy decreased the porosity and specific surface area of the electrode. The electrochemical properties of the composite electrode were characterized in a mixed solution of ethylene carbonate and diethyl carbonate containing 1 mol dm−3 LiPF6. The discharge capacity of the carbon–PPy composite electrode was 78 mAh gcarbon–PPy−1 in the potential range of 2.0–4.0 V vs. Li/Li+, which corresponded to a volumetric discharge capacity of 53 mAh cm−3. Both the double-layer capacity (31 mAh g−1) and the redox capacity of PPy (47 mAh g−1) contributed to the discharge capacity of the composite electrode. This indicates that the incorporation of PPy into the macropores of bimodal porous carbon is effective in increasing the volumetric discharge capacity of the composite electrode. The composite of carbon and PPy showed good rate capability, and its discharge capacity at a high current density of 4.0 A g−1 was as high as 49 mAh g−1.