Intercalation of ClO_4~- into HOPG Investigated by EC-STM

The electrochemical intercalation and surface morphology of highly oriented pyrolytic graphite(HOPG) electrode in2 mol·L~(-1) HClO_4 were studied by in situ scanning tunneling microscopy(STM) and cyclic voltammetry(CV). Based on the step-height changes observed before and after the intercalation, the effects of different step sites on intercalation are compared. The feasibility,reversibility and speed of intercalation are discussed. The intercalation of ClO_4~- into HOPG can be divided into three types depending on the number of graphite layers at the step site: When the layers of graphite are more than three, the intercalation becomes feasible; when the layers of graphite are four to eight, the intercalation can take place reversibly; however, when the graphite layers are one or two only, the intercalation cannot be observed because of the required high potential at which drastic oxidation reaction occurs concurrently. Exfoliation and etching of HOPG are the main morphological changes in this situation.