The application of disc-ring electrodes to the kinetics of reactions in solution

• Main Author: Hitchman, Michael L.
• Published: University of Oxford 1968
• Subjects: 543
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635164

The ring-disc electrode consists of a central disc electrode which has an insulating annulus around it, forming the gap, and this in turn is surrounded by a ring electrode. The usefulness of this system lies in the fact that a reactant can be generated on the disc, and then it can be monitored at the ring as it is transported outwards by radial convection and diffusion. The first chapter of this thesis discusses the importance of the ring-disc electrode and reviews its development and application to the study of electrode processes, to solution kinetics, and to analytical problems. Most of the work prior to 1966 was of a qualitative or semi-quantitative nature owing to the lack of exact solutions to the problem of the transport of a species from the disc to the ring. This was largely resolved by the publication of a series of papers by Albery and Bruckenstein (1), who presented a new approach to the theory and in particular obtained solutions for cases where the intermediate is consumed by first- or by second-order kinetics. The work described in this thesis has been directed towards testing and applying these theories. Experiments with the ring-disc electrode usually involve the simultaneous and independent measurement of the ring electrode and disc electrode currents, while maintaining the potential of one electrode constant with respect to a reference potential. This is most readily achieved by the use of operational amplifiers, and Chapter 2 of this thesis describes the design, construction and use of a multi-purpose, operational amplifier, electrochemical control unit; experiments on the amplifiers used in the unit were carried out to test their suitability for use in D.C. electrochemical control circuits and this is dealt with in an Appendix to the thesis. The other apparatus used throughout this work together with other essential experimental details are dealt with in the third chapter. A fundamental parameter for the ring-disc electrode is the collection efficiency, N. This is a function only of electrode geometry and the theoretical value is obtained by calculating the limiting ring current for a given disc current; a resumandeacute; of this theory is contained in Chapter 4. The final chapter of the thesis discusses the range of first- and second-order rate constants measurable with the ring- disc electrode, the various advantages and disadvantages of the technique and possible future applications to homogeneous kinetic studies.