Incipient Anion Intercalation of Highly Oriented Pyrolytic Graphite Close to the Oxygen Evolution Potential: A Combined X-ray Photoemission and Raman Spectroscopy Study

In the present work, we used two different electrochemical (EC) techniques, namely, cyclic voltammetry and normal pulsed voltammetry, applied to a highly oriented pyrolytic graphite (HOPG) electrode for anion intercalation in two different aqueous electrolytes (i.e., perchloric and sulphuric acid). We performed comparative X-ray photoemission (XPS) and Raman spectroscopy studies at various EC potentials. The chemical analysis obtained by XPS and Raman spectroscopy, the latter applied in situ and in real time during the EC processes, indicates that at oxygen evolution potential (i.e., before reaching the well-known intercalation stage potentials), the HOPG intercalation process is already active. These results suggest that the intercalated compound is efficiently obtained before reaching higher potentials, which usually cause a detriment of the graphite crystal.