MORPHOLOGY AND ELECTROCHEMICAL EFFECTS OF DEFECTS ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE

Highly oriented pyrolytic graphite (HOPG) has been studied by several groups as an electrode material, due mainly to its well-defined surface structure compared to more commonly used materials such as glassy carbon. The basal plane of HOPG is also a common standard for scanning tunneling microscopy because it is atomically flat over regions up to at least 10(4) A2 and is generally free of gross microstructural defects. Thus, HOPG serves well as a nearly perfect single-crystal surface for studies of the chemical properties of basal plane sp2 carbon. In previous reports on laser activation of HOPG, it was demonstrated that electrode capacitance, electron transfer kinetics, and Raman spectrum depend on laser-induced disorder, particularly edge plane defects. The present work was undertaken to describe surface defects on HOPG at the STM level for two grades of HOPG and the laser-activated surface. Capacitance, k-degrees for Fe(CN)6(-3/-4), and anthraquinone disulfonate adsorption all correlate with the presence of STM observable defects. In addition, STM of the laser-activated surface is consistent with a damage mechanism driven by thermal expansion. The results confirm the importance of edge plane defects to the electrochemical behavior of carbon electrodes.