Graphite Intercalation in H2SO4–CH3COOH Electrolytes

Abstract

The anodic oxidation of highly oriented pyrolytic graphite in H2SO4–CH3COOH electrolytes in a galvanostatic mode (I = 1.5 mA) is studied as a function of electrolyte composition. The concentration ranges for the formation of stage I–V graphite intercalation compounds (GICs) are determined. The concentration threshold for intercalation is ∼1 wt % H2SO4 . There are three distinct concentration ranges differing in the shape of the charging curve E(Q), which depends primarily on the content of H2SO4 (active intercalant). The potentials of formation of stage I–III GICs in H2SO4–CH3COOH electrolytes are found to be higher than those for graphite bisulfate, which points to an increase in the potential barrier for intercalation and is obviously associated with the intercalation of acetic acid into the graphite host. The specifics of the charging curves obtained in 60–80% H2SO4 , together with gravimetry and chemical analysis data, indicate the formation of ternary GICs with sulfuric and acetic acids. In this composition range, stage I* and II* cointercalation compounds are obtained, with an intercalate layer thickness di = 7.94 A. The composition of the ternary GICs is shown to depend on the relative amounts of the acids in the electrolyte. A mechanism of the formation of graphite cointercalation compounds is proposed. In solutions containing less than 40 wt % H2SO4 , only graphite bisulfate is formed.