Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-131).

The work described in this thesis employs 'dual activation' methodologies and in particular sonovoltammetry to study a variety of electrochemical systems. First, the effect of 20 kHz power ultrasound on the electrochemistry of simple redox systems in both water and acetonitrile is explored and characterised for different cell geometries. A simple Nernst diffusion layer model is validated. Second, the use of insonation for efficient pre-concentration of target species in anodic stripping voltammetry (ASV) is reported. 'Sonotrodes', where the electrodes are incorporated into the ultrasonic horn tips are shown to offer particularly high rates of mass transport and additionally cause ablation of mercury from plated platinum electrodes. The key benefits of sonication are shown to be electrode depassivation and extraction plus rapidity and ease of determination, coupled with the lack of any sample pre-treatment for the detection of lead in both wine and petrol by ASV. Lead levels determined by this method and calibrated by use of standard microaddition are in excellent agreement with those obtained 'blind' by atomic absorption spectroscopy performed at independent laboratories. Third, the novel use of ultrasonically formed emulsions is examined for both analytical and synthetic purposes. The possibility of extracting species both out of an organic phase for analysis and into an organic phase for the synthesis of water-insoluble redox products is realised. Fourth, the sonovoltammetric determination of ascorbic acid in both aqueous solution and the fruit drink Ribena®, is compared with results obtained by laser activated electroanalysis, where low level laser illumination of an electrode is employed to maintain a fresh electrode surface. Small amounts of laser-induced thermal convection at the electrode result in steady-state voltammetry. The level of agreement is excellent between the two methods and also agrees very well with independent chemical analysis. Fifth, laser activated voltammetry (LAV) is further explored and a simple mass transport model verified. Damage caused by high power laser ablation is evidenced by atomic force microscopy (AFM). Applications of the technique for depassivation are illustrated by the reduction of toluidine blue dye and oxidation of ferrocyanide in the presence of blood proteins. The technique is further employed under channel flow conditions to elucidate an unambiguous mechanism for aqueous iodide oxidation at platinum electrodes in the absence of the usual build up of bulk iodine (as evidenced by AFM). Finally, the reduction of methylene green dye at platinum electrodes is used to compare and contrast sonovoltammetry and LAV with thermal and microwave dual activation techniques. The build-up of the passivating reduced form of the dye on the electrode surface, again seen by AFM, is removed by sono-emulsion and laser activation but not by microwave heating. However, greater conductivity is observed at higher temperatures and an electron-hopping mechanism is postulated.

In this thesis, mathematical modelling is used to theoretically investigate the electrochemical behaviour of surfaces which can be broadly classified as being ‘electrochemically heterogeneous’. Simulated voltammetry is used in the exploration of a number of specific systems as listed below. The cyclic voltammetry of electrodes composed of two different electroactive materials that differ in terms of their electrochemical rate constants towards any given redox couple. The effect of the distribution of the two materials was investigated and the occurrence of split peak cyclic voltammetry where two peaks are observed in the forward sweep, was studied. The technique was specifically applied to the modelling of highly-ordered pyrolytic graphite (HOPG). The steady-state voltammetry of a conducting spherical particle resting on an insulating supporting surface. An algebraic expression that completely describes the voltammetric waveform in the limit of irreversible kinetics was developed. The cyclic voltammetry of the EC′ (catalytic) mechanism at a regularly distributed array of hemispherical particles on an insulating supporting surface. Particular attention was paid to the ‘split-wave’ phenomenon, where two peaks are observed in the forward scan of a cyclic voltammogram and the conditions under which these peaks are resolvable were elucidated. The linear sweep voltammetry of micro- and nano-particle modified electrodes and other electrodes of partially covered and non-planar geometry. It was demonstrated that the apparent electrochemical rate constant of the reaction and thus the peak position of the voltammetry is dependent only on the relative electroactive surface area of the particles on the surface and not upon their shape or distribution. This has wide reaching implications as it can be used to explain some instances of a purported nano-catalytic effect without appeal to altered properties at the nanoscale. The linear sweep voltammetry of the interior of a partially electroactive cylindrical pore. Four limiting cases were observed and fully characterised. The linear sweep voltammetry of porous surfaces. It was established that if the pores are less than a certain threshold depth, then a porous surface will also display an apparent catalytic effect that is dependent on the relative electroactive surface area (including the area in the interior of the pores).

This thesis presents the development and redesign of a commercial electrochemical quartz crystal microbalance with dissipation (E–QCM–D). This was used to study factors affecting the efficiency of the four electron reduction catalysed by the fuel cell enzyme bilirubin oxidase from Myrothecium verrucaria immobilised on thiol modified gold surfaces. Within this thesis, the E–QCM–D was used to show that application of a constant potential to bilirubin oxidase adsorbed to thiol-modified gold surfaces causes activity loss that can be attributed to a change in structural arrangement. Varying the load by potential cycling distorts the enzyme by inducing rapid mass loss and denaturation. Attaching the enzyme covalently reduces the mass loss caused by potential cycling but does not mitigate activity loss. Covalent attachment also changes the orientation of the surface bound enzyme as verified by the position of the catalytic wave (related to the overpotential for catalysis) and reactive labelling followed by mass spectrometry analysis. The E–QCM–D was used to show how electrostatic interactions affect enzyme conformation where high pH causes a reduction in both mass loading at the electrode and a reduction in activity. At pH lower than the enzyme isoelectric point, there is a build up of multilayers in a clustered adsorption. When enzyme adsorbs to hydrophobic surfaces there is a rapid denaturation which completely inactivates the enzyme. Changing the surface chemistry from carboxyl groups to hydroxyl and acetamido groups shows that catalysis is shifted to more negative potentials as a result of an enzyme misorientation. Further to this, increasing the chain length of the thiol modifier indicates that an increased distance between surface and enzyme reduces activity, enzyme loading and results in a conformational rearrangement that permits electron transfer over longer distances.