AC IMPEDANCE AND TRANSIENT PHOTOELECTROCHEMICAL MEASUREMENTS ON PHTHALOCYANINE-MODIFIED ELECTRODES (ELECTROCHEMISTRY).

Abstract

This dissertation describes photocoulometric and AC impedance studies of dye-modified electrodes. The photocoulometric technique allowed photoelectrochemical phenomena to be observed without mass transport effects. These measurements confirmed the photoconductive properties of monomeric silicon phthalocyanine dye. They also showed that the photo-assisted oxidation of hydroquinone to benzoquinone at n-tin oxide electrodes modified with this dye involved a cation dye intermediate with a lifetime of between 0.05 and 350 ns, with the rate limiting step being charge transport through the dye film or charge transfer across the interface between the dye and the substrate. AC impedance studies included Mott-Schottky measurements and faradaic impedance experiments on tin oxide and gold metallized plastic optically transparent electrodes. They also examined the substrates modified with monomeric silicon phthalocyanine and chloro-gallium phthalocyanine. The Mott-Schottky measurement procedure was free of systematic errors that affected other published work, and the results of these measurements were consistent with those found by independent methods. The faradaic impedance technique was applied to dye-modified electrodes for the first time. These studies found evidence for an adsorption or electrodeposition process in the oxidation of hydroquinone at these electrodes, and gave exchange current densities that were consistent with the values that were found by other methods.