INVESTIGATION OF THE OXIDATION OF GLASSY-CARBON BY THE METHOD OF ELECTROREFLECTANCE - RELEVANCE TO ACTIVATION PROCESSES

The oxidation of the surface of glassy carbon (GC) in 0.5 M KOH was st udied by the method of electroreflectance (ER). For a freshly-prepared mechanically polished GC surface, the ER spectra have relatively low intensity and exhibit inversion of sign at the electrode potential -0. 4 V. The ER spectra of the GC electrode change substantially after the electrochemical oxidation at E = + 0.6 V. Oxidation considerably incr eases the intensity of ER, and the band located at quantum energies fr om 1.8 to 2.4 eV (Band A) becomes much broader. The maximum of the ban d shifts towards higher energies. The ER spectra depend strongly on th e electrode modulation frequency. It is concluded that anodic oxidatio n leads to the generation of surface states whose impact on the ER spe ctra of GC is especially important at potentials close to the pzc. Str ucturally, the surface states seem to be related to the generation of edge-type carbon atoms caused by oxidation. Broadening and the shift o f Band A in the ER spectra of an oxidized surface are hypothesized to be a manifestation of optical transitions from the Fermi level to the surface states. The frequency dispersion shows that there are several surface states with distinct kinetic differences. These observations s upport the hypothesis that activation of the surface of carbon materia ls is accompanied by the generation of surface states. (C) 1998 Elsevi er Science S.A. All rights reserved.