EFFECTS OF HIGH-INTENSITY ULTRASOUND ON GLASSY-CARBON ELECTRODES

Glassy carbon electrodes which have been irradiated with 20-kHz ultrasound from a 475-W generator in dioxane are shown to exhibit enhanced heterogeneous electron-transfer rates for a variety of aqueous redox probes. When sonications are performed in water, however, no significant enhancement effects are observed. Several electroanalytical techniques with different time scales are employed along with scanning electron microscopy to characterize surfaces before and after ultrasonic modification in different solvents. Results indicate that surface roughness does not change appreciably after brief sonication in dioxane, although a small amount of surface pitting occurs. These electrodes are demonstrated to remain active for up to 5 days and to be more prone to adsorb aromatic redox probes in aqueous media than polished electrodes. After sonication in water, carbon surfaces are highly pitted and show evidence of an increase in the density of electro active surface oxides. Thus, the improvement in kinetics observed after sonication in dioxane is probably not associated with either increased microscopic electrode area or mediated electron transfer between surface oxides and solution analytes, but instead is likely to involve surface cleaning.