The electrical double layer of carbon and graphite electrodes. Part III. Charge and dimensional changes at wide potential range

By monitoring the changes in length of high-surface carbon and graphite electrodes, it was possible to distinguish between slow charging processes of the electrode interface as manifested by the dimensional changes, and Faradaic processes. Both processes take place at potentials remote from the electrocapillary maximum. Ohmic drops were eliminated by using high electrolyte concentration; thus, it could be deduced that the rate determining step of the slow interfacial processes originates from the interface itself. The irreversible current increments always observed at the edges of wide potential range cyclic voltammograms of carbon and graphite electrodes could obviously be considered as a result of Faradaic or charge transfer processes. However, in the present work, by monitoring the dimensional changes at wide potential range, it is shown that prior or in parallel to the Faradaic process, slow charging of the interface occurs. In this sense carbon and the graphite electrode behave very similarly, providing a hint that the slow sites are located at basal plane surfaces, which are common to graphite and carbon.