Electrochemical intercalation of perchlorate ions in HOPG: an SFM/LFM and XPS study

Highly oriented pyrolitic graphite (HOPG) in perchloric acid was adopted as a model system in order to elucidate the electrochemical anion intercalation process in graphite. The effects of the intercalation process were studied in terms of the changes in surface friction and on the electronic structure of the HOPG. Lateral force microscopy (LFM) combined with cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) indicated that the speci®c adsorption of perchlorate ions is responsible for changes in friction occurring in proximity of the steps on the HOPG surface. The friction changes reversibly within a narrow potential window preceding intercalation. After an intercalation and deintercalation cycle the change of the friction at a step is irreversible. No change in the friction could be observed on the basal plane. The binding energies in the C 1s, O 1s and Cl 2p XPS spectra of the intercalated compound are shifted relative to those of the nonintercalated host and adsorbed perchlorate ions, which is attributed to a shifted Fermi level.# 2001 Elsevier Science B.V. All rights reserved.