Abstracts Category : Other

Nonlinear Instabilities in Chemical and Electrochemical Systems

by Jeffrey Gordon Bell

This dissertation focuses on designing and manipulating nonlinear chemical and electrochemical reactions, with the aim of discovering new behaviors as well as gaining insights into their underlying mechanisms. In Chapter 2 the nonlinear behavior of the 4-aminophenol bromate photoreaction was investigated from two directions. First, a second autocatalytic cycle was introduced through the incorporation of the metal catalyst cerium (IV). It was found that once the autocatalytic cycles were effectively balanced, complexity in the form of mixed mode oscillations was observed in a closed reactor. This dynamic behavior was successfully simulated using a modified model, which qualitatively reproduced the experimental results. It was also found that the precipitate which forms at the onset of the reaction of 4-aminophenol with bromate, N-bromo-1,4-benzoquinone-4-imine, could form a new bromate-based photochemical oscillator. In Chapter 3, the autocatalytic oxidation of 2-methyl-1,4-hydroquinone by acidic bromate lead to the discovery of a new photochemical oscillator. The system was found to be very sensitive to the intensity of illumination supplied, and complexity in the form of sequential oscillations was discovered using either ferroin or cerium (IV) as catalysts. Interestingly, cerium (IV) had a much more profound effect on the dynamical behavior, substantially lengthening the oscillatory period as well as being capable of inducing mixed-mode oscillations. Chapter 4 reports findings on the photosensitive 4-nitrophenol - bromate reaction. Extreme photo-inhibition was found to occur when illumination was supplied to the system whether in a stirred reactor or when being studied in a spatially extended system. Reaction diffusion experiments showed that under certain conditions long lasting complexity in the form of propagation failures took place. In Chapter 5, oscillations in both current density and potential were observed during the electro-oxidation of bromide ions. Interestingly, mechanistic findings suggest that the oscillations occurring during the oxidation of bromide ions on a platinum electrode belong to the type of oscillator referred to as Capacitance Mediated Positive Differential Resistance oscillator, and is the first solution based system to fit this class. In Chapter 6, the electro-oxidation of two sulfur compounds was seen to display nonlinear behavior. First, the oxidation of hydroxymethanesulfinate leads to oscillations in both current and potential on platinum or gold electrodes. The formation of an inhibiting layer was seen to have a substantial influence on the systems ability to support sustained oscillatory behavior. Electrochemical Impedance Spectroscopy showed that the oxidation of hydroxymethanesulfinate fits the class of an HN-NDR type oscillator. The oxidation of methionine only displayed nonlinear behavior on a gold surface, and only when operated under potentiostatic conditions. The oscillations were accompanied by gold dissolution and it was found that the electro-oxidation of methionineAdvisors/Committee Members: Wang, Jichang.