Preparation of three dimensionally ordered macroporous carbon with mesoporous walls for electric double-layer capacitors

Abstract

Three dimensionally ordered macroporous (3DOM) carbons with mesoporous walls were prepared by a colloidal crystal templating method. A three dimensionally ordered composite consisting of monodisperse polystyrene (PS) latex (100–450 nm) and colloidal silica (5–50 nm) was prepared by an evaporation process of suspensions containing PS latex and colloidal silica in water. In the course of the heat treatment of this composite membrane at 573 K under an inert atmosphere, the PS was melted and penetrated into the spaces between the colloidal silica. The penetrated PS was carbonized during further heat treatment to provide a very thin carbon layer on the colloidal silica, and the macropore corresponding to the PS particle size was formed simultaneously. After this procedure, the 3DOM carbon with mesoporous walls was obtained by removing the silica particles. From the results of scanning electron microscope observations and nitrogen adsorption-desorption measurements, it was confirmed that the prepared carbon had a bimodal porous structure, and the sizes of macropores and mesopores of prepared carbon were in good agreement with the sizes of the PS and silica particles used as templates, respectively. The bimodal porous carbon, which had a specific surface area of 1500 m² g⁻¹ and 5 nm mesopores, showed highest capacitance of 120 F g⁻¹ in propylene carbonate solution containing 1 mol dm⁻³ (C₂H₅)₄NBF₄. The mesopore size rather than macropore size gave significant effects on the rate capability of carbon electrode during charge and discharge. The bimodal porous carbon having 5 nm mesopores showed an excellent rate capability and its capacitance at a high current density of 4 A g⁻¹ was 109 F g⁻¹.