The application of microelectrode and low-temperature voltammetry to the measurement of reaction kinetics
Abstract
The work presented in this thesis is an investigation of the capabilities of microelectrodes for making voltammetric measurements of the rates of electron transfer processes. The distorting effects of solution resistance, R$\sb{\rm s},$ and double-layer capacitance, C$\sb{\rm dl},$ upon the voltammetric wave-shape observed using a microdisk electrode is examined by use of a simulational procedure. These distortions are shown to be potentially significant even in solvents of moderate resistivity. The results of this simulation are compared to the experimentally observed voltammograms of several simple redox couples. Moreover, the simulated voltammetric wave-shape is shown to agree with experiment over the entire diffusional range of the microdisk. The use of microdisk electrodes for measuring values of k$\rm \sbsp{s}{o}$ in low temperature solutions is examined. The ability to measure k$\rm \sbsp{s}{o}$ is predicted to and observed to increase as the temperature is reduced. Thus, at sufficiently low temperatures even redox couples that exhibit immeasurably fast electron transfer at room temperature should become measurable. Correlations between simulated voltammograms and experimental results are also made. Fast-scan and low temperature voltammetry is used to examine the electron transfer reactions of $\eta\sp6$-(hexamethylbenzene)-$\eta\sp 5$-(penta-methyl-cyclo-penta-dienyl)-rhodium(III)$\sp{2+}.$ This compound undergoes an $\eta\sp6$ to $\eta\sp4$ conformational change in conjunction with reduction to the Rh(I) neutral species. The effects which the conformational change exerts upon the energetics of the electron transfer is observed in the value of the cathodic transfer coefficient, $\alpha.$ The results of this study suggest that the conformational change occurs concurrently with electron transfer. Several appendices are provided that deal with various aspects of simulation methods for electrochemical situations. Additionally, FORTRAN source code for two sample simulations are provided.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Analytical chemistry
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