Differential capacitance study on the edge orientation of pyrolytic graphite and glassy carbon electrodes

Abstract

Summary The differential electrode capacitance of the edge orientation (plane perpendicular to the basal one) of stress-annealed pyrolytic graphite and glassy carbon have been studied in concentrated aqueous solutions using an a.c. impedance bridge. The salient features are as follows: o (1) The apparent differential capacity for the edge orientation of stress-annealed pyrolytic graphite is much higher than on the basal plane because of higher surface roughness and capacitive contribution of the surface groups. The capacity strongly depends on the electrolyte, pH and potential scan range and exhibits a complex potential dependence, probably as a result of the specific chemical groups on the surface. A model is proposed to explain the behavior of the edge orientation. (2) The capacity minimum for the glassy carbon is sufficiently low so as to suggest a space charge contribution from within the electrode phase. (3) The similarities between the potential dependence of the capacity for the edge orientation of pyrolytic graphite and glassy carbon indicate similarity in the surface groups although the particular groups cannot be specifically identified from the electrochemical measurements.