Analysis of Capacitance Characteristics of C60, C70, and La@C82

Fullerenes and their derivatives are promising materials for supercapacitor devices due to their unique nanostructure that combines the reversible redox charge storage with the high surface area. In this article, the reversible redox charge storage of C60, C70, and La@C82 in liquid ammonia solution is reported. An electrochemical analysis of these species using cyclic voltammetry is presented in conjunction with the theoretical interpretation. The relative magnitudes of transfer coefficients, which represent a measure of the symmetry of the energy barrier for oxidation and reduction of the monoanionic species of these fullerenes, suggest that the availability of the surface area permitting delocalization of π electrons is a determining factor of their first reduction potential. The relationship between these transfer coefficients and fullerene geometry also support previous conclusions that the La atom is located within the fullerene cage of La@C82. The electrochemical measurements analyzed were made using a modified three-compartment cell. Advantages associated with this modified cell for analysis of capacitance characteristics of C60, C70, and La@C82 are discussed.