The effect of cyclic voltammetry speed on anion intercalation in HOPG

It is generally accepted that anion intercalation occurs when HOPG is kept at high electrochemical potentials in oxidant electrolytes, such as perchloric and sulfuric acids. The graphite surface undergoes a detriment, made also evident by the swelling of the uppermost layers (blisters formation) caused by gas evolution in standard electrochemical conditions (namely, by cycling the HOPG voltage at speeds up to 25 mV/s). Surface swelling is therefore considered as being indicative of anion intercalation. Recently, suppression of blister formation when the potential is swept at larger speeds (such as 600 mV/s) has been observed, raising the question as to whether this phenomenon might be able to suppress anion intercalation. In this work, by combining atomic force microscopy and X-ray photoemission spectroscopy, we unequivocally show that the HOPG electrode undergoes similar chemical modifications, regardless of the chosen electrochemical conditions and consequently of the morphological evolution at the surface.