| This thesis is concerned with the application of the Electrochemical Quartz Crystal Microbalance (EQCM) technique, which measures mass changes at electrode surfaces with exceptional sensitivity (submonolayer amounts), to the study of adsorption processes in electrocatalysis. Systems examined included electro-oxidations of small organic molecules (methanol, formic acid and glucose) at platinum, underpotential deposition (UPD) of metals, and the effect of UPD metal layers on such oxidations.; In the first section of this thesis, the underpotential deposition of lead and bismuth has been investigated at Pt electrodes in perchloric acid. It is shown that the mass changes obtained with the EQCM provide additional, unique information about the UPD process which cannot be obtained from the voltammogram because of the partial overlap of the currents associated with removal and development of UPD deposits with those resulting from the oxidation and reduction of the electrode surface respectively.; The oxidation of glucose in both acidic and alkaline media as well as the effect of UPD Pb on this oxidation in acid has also been investigated. In acid, the presence of adsorbates derived from glucose was observed in the hydrogen UPD potential region through the removal of features associated with the presence of adsorbed anions in the background electrolyte. A decrease in mass is seen in this potential region as the electrode becomes covered with poisoning species.; In the presence of UPD Pb at Pt in acid, a multiple peak structure in the double layer region of potential was observed in the voltammogram at low glucose concentrations and low UPD coverages because the poison formation cannot be suppressed sufficiently. But it is changed to the more familiar single peak as UPD coverage increases. On the other hand, the presence of glucose is seen, from mass measurements, to have a large effect on changes in UPD Pb coverage in acid media.; Finally, the investigation was extended to the oxidation of some simple organic molecules namely methanol and formic acid at Pt in acidic media. It is found that accumulation of strongly adsorbed species at the electrode surface during the oxidation of both organic molecules gives rise to a mass decrease, relative to that of the background electrolyte. The oxidative removal of these adsorbates causes a stepped mass increase. Mass responses also reveal that increasing amounts of methanol or formic acid in the electrolyte cause a shifting of the oxidative removal of strongly adsorbed species to more positive potentials, and a significant suppression of the irreversible oxidation of the electrode surface. (Abstract shortened by UMI.)... |
