INSITU RAMAN MONITORING OF ELECTROCHEMICAL GRAPHITE-INTERCALATION AND LATTICE DAMAGE IN MILD AQUEOUS ACIDS

Slmultaneous Raman spectroscopy and electrochemical oxidation of highly ordered pyrolytic graphite (HOPG) permitted monitoring of lattice damage and staging. Intercalation of bisulfate in concentrated H2SO4 results in well-known Raman spectral changes in the E2g mode at ca. 1600 cm-1. In addition, damage to the sp2 lattice is revealed by the "D" band at 1360 cm-1, which occurs when graphitic edges are formed. During oxidation of HOPG in 96% H2SO4 or 1 M NaClO4/CH3CN, intercalation was observed but accompanying lattice damage did not occur at the potentials examined. For 1 M H3PO4, neither intercalation nor lattice damage was observed at Potentials up to 2.0 V vs SSCE. For 1 M H2SO4, 1 M HClO4, or 1 M HNO3, however, intercalation always preceded or accompanied lattice damage. The results are consistent with a mechanism where oxidation results in a graphite intercalation compound (GIC) which oxidizes either water or the graphite itself to produce carbon oxides. The formation of oxides depends on both the thermodynamic stability of the GIC and the kinetics of intercalation, which In turn correlate with the size of the intercalating ion.