| The development of high performance electrode materials for electrochemical capacitors has been an active area of research over the past ten years due to the demand for high power portable energy storage devices. One class of material which has shown promising capacitive characteristics in aqueous electrolytes is carbon aerogels. These unique materials exhibit low resistivity, high surface area, and a controllable open microstructure. In this work, the interrelationships between the electrochemical characteristics of the carbon aerogel materials in sulfuric acid electrolytes and the chemical and physical nature of the aerogels have been identified. Specifically, this study examines the influence of surface chemistry and microstructure on the voltammetric response of the carbon aerogel electrodes.; Carbon aerogels exhibit a specific capacitance greater than 80 F/g in 1.0 M {dollar}rm Hsb2SOsb4.{dollar} This value is is dependent upon the specific surface area of each sample but is relatively independent of the bulk density of the aerogel. The density of the material does, however, influence the charging time of the electrode due to distributed capacitance effects. The surface of the carbon aerogels can be electrochemically activated to supplement the double-layer charging of the surface with a pseudocapacitive charge storage mechanism at redox-active surface functionalities.; A second aspect of this work addresses improving the capacitance of the carbon aerogel materials by chemically modifying the surface of the aerogels. Hydrous ruthenium dioxide, which has shown exceptional pseudocapacitance {dollar}rm ({lcub}>{rcub} 750 F/g)sp3,{dollar} was deposited onto the surface of the carbon aerogel materials by two approaches: chemical vapor impregnation and electrodeposition. Ruthenium metal loadings of greater than 50 wt.% could be achieved using chemical vapor impregnation. Transmission electron microscopy revealed 20A metal particles uniformly distributed on the large interior surface of the aerogels. These modified carbon aerogels exhibit capacitances as high as 250 F/g in sulfuric acid. The electrodeposition and oxidation of hydrous ruthenium dioxide onto non-porous polycrystalline graphite demonstrates the feasibility of this modification technique for increasing the capacitance of the carbon/electrolyte interface. When applied to carbon aerogels, however, the tortuous nature of the aerogel structure limits the practicality of this approach. |
