The effects of fullerene (C60) crystal structure on its electrochemical capacitance

The electrochemical properties of different types of fullerene crystals (x-C-60), having hollow-long cylindrical (C-C-60), hollow-long square (S-C-60), and thick solid-short hexagonal (H-C-60) shapes were investigated. The prepared x-C-60 samples had specific dimensions with respect to aspect ratio (12.0, 6.7, and 1.5) and lattice spacing distance (1.12, 1.04, and 1.00 nm). Interestingly, it was possible to control the aspect ratio and lattice spacing distance by adjusting the molecular ratio of C-60 to the aromatic solvent (m-xylene) used in the preparation. In addition, the number of m-xylene molecule in the x-C-60 crystal structure increased with decreasing ratio of x-C-60 to m-xylene in the solution, corresponding to ca. C-60.0.83m-xylene (for C-C-60), C-60.0.39m-xylene (for s-C-60), and C-60.0.36m-xylene (for H-C-60). A more ordered arrangement of m-xylene molecules resulted in an improved electrochemical capacitance of x-C-60. Importantly, in the case of the regular structure (C-, S-, H-C-60), when m-xylene was assembled in the x-C-60 structure, the large lattice spacing distance increased. This explains why the C-C-60 sample had the largest electrochemical capacitance, compared to the S- and H-C-60 samples. Such a configuration would allow for a high charge accumulation and the formation of a donor-acceptor complex, which would permit an easier charge transfer. (C) 2010 Published by Elsevier Ltd.