Abstract

An overview of the literature in relation to the thermodynamics and kinetics of electron transfer across electrode/monolayer interfaces, microelectrodes, modified electrodes - in particular self-assembled monolayers of transition metal complexes and anthraquinones on various electrodes, and the background theory into the various electrochemical techniques used, is presented in Chapter 1. Various metal com plexes have been designed to form monolayers suitable for investigations into heterogeneous electron transfer across electrode/monolayer interfaces. These com plexes include [Os(bpy)2Cl2], [Os(bpy)2(p3p)2]2+, and QCat2'R u -l,2 w here bpy is dipyridyl, p3p is trimethylenedipyridine, and QCat is alizarin (l,2-dihydroxy-9,10- anthraquinone). Characterization o f these com plexes using HPLC, CV, U V -vis, NM R and CHN is described in Chapter 2. Fabrication o f platinum, gold, and carbon fibre microelectrodes and their characterization is illustrated in Chapter 3. The adsorption characteristics and general electrochemistry o f Anthraquinone-2,7- disulphonate adsorbed onto mercury electrodes is described in Chapter 4. The electrochemical response o f these monolayers is examined as a function of solution pH. The dependence of the surface coverage of 2,7-AQDS on its bulk concentration is studied and an adsorption isotherm fitted. By measuring the potential dependence of Cdl as the bulk concentration of 2,7-A QDS is system atically varied, an insight into the potential dependence of the free energy of adsorption, AGads*, has been obtained. Chapter 5 describes monolayers containing the Os2+/O s3+ redox couple adsorbed onto Pt and Au microelectrodes. Adsorption and desorption w as examined as were the heterogeneous electron transfer rate constants. Reaction entropies and enthalpies were also determined. Results indicate that adsorption/desorption characteristics differ with substrate, that heterogeneous electron transfer can be described using Marcus theory, and that the rate of electron transfer is pH dependent. The final experimental chapter describes the electrochemistry of solution phase and surface confined QCat2'R u-l,2. Diffusion coefficients, transfer coefficients and rate constants were determined for the solution phase species at Pt and Hg electrodes. Monolayers of the com plex were adsorbed onto carbon fibre microelectrodes and the reaction entropy, enthalpy, and rate constants probed.