The electrical double layer of carbon and graphite electrodes. Part II. Fast and slow charging processes

Scanning differential voltammograms of a graphite cloth electrode revealed the existence of slow and fast double-layer charging processes spread over the entire potential range studied (-600 to +600 mV vs. 0.1 M NaCl calomel electrode). At high potential sweep rates, the slow processes do not contribute to the double-layer capacitance. Within the potential range studied, the shape of the differential voltammograms, from which the capacity-potential curves are calculated, is independent of solution concentration, composition and pH. Tris implies that the slow processes do not originate from solution IR drops or from changing oxidation or ionization states of surface groups. The possibility that micropores are responsible for the slow charging processes was ruled out by utilizing bulky ions instead of small ones. The slow charging processes had not changed. A second mechanism for the slow charging process could be localized surface electrons which are due to surface structural or chemical defects other than pH-sensitive groups.