Adsorption at metal electrodes is usually a very fast process and it plays a most important role in many areas of industry. The thermodynamics of the process are well known for many systems. However, there is currently no good method that allows a determination of very fast kinetics of adsorption to be made. Previously, many attempts at evaluation of kinetic parameters of adsorption were made, but in moat cases, due to the inadequacy of the experimental methods used, the parameters obtained were much lower than expected. This thesis aims at providing the means for determining the kinetics of adsorption at metal electrodes. The methods herein described are based on two different experimental techniques. These techniques are: (i) fast cyclic voltammetry (FCV, potential sweep rate up to 100000 V/s) and (ii) high frequency AC and FFT SW (Fast Fourier Transform Square-wave) voltammetry (frequency up to 50 MHz) at ultramicroelectrodes (5 or 6.25 ìm in radius). A theoretical description of the adsorption process for both kinds of experiments is presented. A simulation program was written to provide a better understanding of the process and to elucidate the development of methods for determining the kinetics of adsorption. Thermodynamic and kinetic descriptions of the process are based on the Frumkin adsorption isotherm. Both the equilibrium constant and the adsorption rate constant are treated as functions of potential and the electrode coverage. Comparison of results for different systems is presented as an analysis of the dependence of the adsorption rate constant on the equilibrium constant. FCV proved to be useful in the evaluation of kinetics of chemisorption (standard rate constant in the range of 10<sup>6</sup> s$\sp{-1})$ but the results for adsorption of aliphatic alcohols were unreliable. High frequency AC methods allowed the determination of kinetics of physical adsorption. It was found that the activation energy of the adsorption process can be expressed as a linear combination of the electrical component of the standard free energy of adsorption (a major contribution) and the energy of lateral interactions (a minor contribution). At the zero charge potential the rate constant reaches the maximum value of $\rm(4.6\pm0.3)10\sp9\ s\sp{-1}.$
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-10212004-000613 |
| Date | 01 January 1996 |
| Creators | Moyana, Agata |
| Contributors | Baranski, Andrzej S. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-10212004-000613 |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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