SPATIALLY-RESOLVED RAMAN-SPECTROSCOPY OF CARBON ELECTRODE SURFACES - OBSERVATIONS OF STRUCTURAL AND CHEMICAL HETEROGENEITY

Raman spectroscopy and Raman imaging were used to examine several type s of carbon electrode materials, including glassy carbon (GC) and high ly ordered pyrolytic graphite (HOPG). Variations in the intensity rati o of the D and E-2g Raman bands across the carbon surface indicated va rying carbon microstructure, The D/E-2g ratio for polished GC and pyro lytic graphite edge (PG) was relatively constant, while that of basal HOPG and PG varied significantly due to defects. The spatial heterogen eity of Rhodamine 6G Raman intensity following physisorption to carbon surfaces indicated that adsorption occurs at disordered regions, part icularly defects on HOPG. This observation provides visual confirmatio n of previously reported correlations of defect area and physisorption ., Chemisorption of dinitrophenylhydrazine was observed only at edge p lane regions, confirming the localization of surface carbonyl groups o n graphitic edge plane, Finally, chemisorption of nitroazobenzene radi cal formed from a diazonium precursor occurred at both basal and edge regions, but more rapidly at edge sites, The higher concentrations obs erved at edges are attributable either to more rapid reduction of the diazonium precursor or to more rapid attack of the radical, compared t o basal plane. The results represent the first spatially resolved Rama n examination of physi- and chemisorption at the monolayer level on ca rbon surfaces.