The Double Layer and Surface Functionalities at Carbon

Abstract

A substantial fraction of the whole body of electrochemical capacitor development has depended, and continues to do so, on an understanding of the properties of carbon, especially in its more dispersed and conducting forms, including materials having fibrous or foamlike morphologies. It has been known for many years that there are two or really three natural allotropic forms of carbon: diamond, graphite, and the fullerenes, as noted in an earlier chapter. The graphite modification is crystalline and a moderately conducting, anisotropic, electronic conductor. Diamond is a highly ordered and insulating material. In addition, amorphous forms of carbon are well known, and transitions between amorphous and graphitic structures are possible at elevated temperatures, but are possible for diamond only at extremes of conditions. In more recent years, other modifications of carbon have been prepared or become known, namely, the fullerenes (which may exist in interstellar space), glassy carbon, and exotic species such as C2, which was also detected in interstellar space. Carbon “blacks” such as Shawinigan black or acetylene blacks (soots) are well known and have relatively high specific surface areas in the range of 30’1000 m2 per gram. However, they are not usually suitable for fabrication of capacitor electrodes.