An investigation of the capacitance dispersion on the fractal carbon electrode with edge and basal orientations

Abstract

Capacitance dispersion on the fractal carbon electrode with edge and basal orientations was investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and a.c.-impedance spectroscopy. For this purpose, four types of as-received pyrolytic graphite electrode, as-received, mechanically polished, and as-activated glassy carbon electrodes were prepared with different surface irregularities and amounts of edge orientations. The apparent self-similar fractal dimensions of the carbon electrodes were determined from the analyses of AFM images based upon triangulation method. The amounts of edge orientations on the surface of the carbon electrodes were qualitatively estimated from the XPS analysis of surface acidic functional groups that were preferably formed on the edge planes by the heat treatment of the carbon electrodes. The values of the constant phase element exponent α determined from the apparent self-similar fractal dimensions did not accord with those α determined from the measured impedance spectra. Instead, they were closely related to the amounts of the edge orientations. From the results, it is indicated that the contribution of surface inhomogeneity is much higher than the contribution of the surface irregularity to the capacitance dispersion on the carbon electrode.