Computer simulation studies on kinetics of electrode surface reactions.
Creators: name: Klinger, Jiri G.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1977
Subjects: subject: Chemistry, Analytical.

description: In the work described in the present thesis, which deals with simulation of the kinetic behaviour of various reaction mechanisms, conditions which give rise to particular and characteristic current-potential profiles under different "experimental" conditions for the reaction process in question have been sought. Attention has been focussed on parameters such as the reduced sweep-rate s/k and the ratio of the rate constants governing the individual processes in a given complex reaction mechanism, which in turn give rise to particular shapes of i-V profiles. It is shown that relative values of electrochemical and chemical rate constants, k, interaction parameters, g, and standard electrode potentials, E°, can be derived using the characteristic kinetic features which are shown to be generated by a given reaction mechanism. Such features are the half-width potentials, DeltaV1/2, the peak currents, ip, the coverage of the chemisorbed species up to the current peak, theta p, etc. Where appropriate, comparisons of the simulated kinetic behaviour derived in the present work have been made with experimental results for various systems recorded in the literature. First, the kinetic behaviour of a single step, 1-e surface reaction is treated theoretically as a simple reference case, especially with regard to: (a) characteristic aspects of its behaviour when significant attractive or repulsive interactions arise between the atoms in the electrodeposited monolayer film and (b) formulation of characteristic features of its kinetic and equilibrium behaviour which provide a reference case for distinguishing the behaviour of other, more complex reactions. The analytical derivations of characteristic parameters, derived previously by some other workers only for Langmuir behaviour, are made more general by extension to cases where two-dimensional interactions are significant. For surface processes involving parallel steps in which two chemisorbed species are involved, it is shown how a "kinetic relaxation method" can be developed and used for resolution of the behaviour of the two species when the electrochemical reactions in which they are deposited or desorbed occur over the same potential range. This method can be applied when one of the two chemisorbed species behaves more "irreversibly" than the other. It is shown how experimental results for acetonitrile at Pt electrode obtained by other workers in this laboratory can be treated by this technique. The potentiodynamic linear sweep method has often been applied to sequential reactions involving at least one chemisorbed intermediate species. The simulation calculations were extended to cases of this kind. The mechanisms which were analyzed involve a first-order chemical surface step coupled with a simple 1-e electro-chemical process, thus giving rise to either an "ec" or a "ce" type of overall mechanism. Characteristic features of the kinetic behaviour derived from the computed current-potential profiles were compared with those for the simple 1-e surface reaction case. Holding of the potential, especially at the end of the sweep, proves to be of great importance as it affects the i-V curves obtained on the subsequent reverse sweep in characteristic ways for these types of processes. (Abstract shortened by UMI.)