Size-Dependent Intercalation of Ions into Highly Oriented Pyrolytic Graphite in Ionic Liquids: An Electrochemical Atomic Force Microscopy Study

Morphological changes of the highly oriented pyrolytic graphite (HOPG) surface during electrochemical intercalation–deintercalation process in pure ionic liquids (ILs) have been studied using electrochemical atomic force microscopy (EC-AFM). The results show that electrochemical intercalation of ions into HOPG is strongly dependent on anionic size of the ILs used. Up to 0.8 V versus the Ag quasi reference, drastic reversible morphological changes of HOPG surface during anion intercalation–deintercalation were observed in [BMIM][HSO4], whereas these changes were absent in [BMIM][N(Tf)2]. However, at and above 1.2 V, the HOPG surface degrades in both the ILs to form carbon nanoparticles.