Effects of microstructure on heterogeneous electron transfer at carbon electrodes

Raman spectroscopy is applied to the study of carbon electrode materials. For the first time, spectroscopic correlations with electrode microstructure and heterogeneous electron transfer rates are observed for the hexacyanoferrate (II/III) system.; The effect of changing microstructure on electrode performance after laser and electrochemical electrode pre-treatments is demonstrated for the first time at highly oriented pyrolytic graphite (HOPG). The advantages of using HOPG as a model substrate for these studies are its clean surface and well-defined structure.; Raman spectroscopy has previously been shown to be sensitive to changes in the size of the carbon lattice. In work presented here, increasing amounts of edge plane regions are observed after laser and electrochemical pre-treatments at basal plane HOPG by monitoring the intensity of the 1360 cm{dollar}sp{lcub}-1{rcub}{dollar} band using Raman spectroscopy. After electrode pre-treatments, increases in heterogeneous electron transfer kinetics by up to five orders of magnitude are observed for the hexacyanoferrate (II/III) system.; Hexacyanoferrate (II/III) is used as a bench-mark redox system to probe electrode performance because it has been studied extensively and believed to be a simple, one-electron redox system free of the effects of adsorption.; In addition, electrogenerated chemiluminescence (ECL) of luminol is used as an in-situ probe of electrode heterogeneity. By monitoring the intensity of the chemiluminescence of luminol during potential sweep experiments, the difference in heterogeneous kinetics at edge versus basal plane regions of HOPG can be monitored directly and in one experiment. For the luminol system studied here, kinetic enhancement at edge plane regions is observed to be greater than the basal plane regions by a factor of approximately 100.; The Raman spectroscopic correlations and results of the ECL experiments presented here indicate a mechanism of electrode activation at basal plane HOPG based on the presence of edge plane carbon regions.; Finally, the feasibility of near-infrared Raman spectroscopy using a diode laser (783 nm) and a charge-coupled device detector is demonstrated. Advantages of using diode laser excitation are discussed and compared to conventional and Fourier Transform Raman techniques.