In situ studies of adsorption of organic compounds on platinum electrodes /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | Studies of adsorption of organic species on polycrystalline platinum electrodes were carried out in 0.01 N HCl solution under potential controlled conditions. In situ techniques, i.e., radiotracer, Fourier Transform Infrared Spectroscopy (FTIR) and ellipsometry, as well as the potential sweep method were applied in the measurements. Good agreement in results was obtained among these techniques. The electrosorption process was found to be rather slow but a bell-shaped coverage (θ) versus potential (V) curve was generally obtained in the double layer region with a submonolayer adsorption. The difference between the pzc and the maximum potential of adsorption is about [plus or minus]0.1 V. A water displacement adsorption model, based on the statistical mechanics approach, was proposed. Both lateral interactions between adsorbed species and the effect of heterogeneity of the electrode surface were taken into account. The standard state coverage for the adsorption was found by equating f(θ) to unity. A Temkin-type isotherm was obtained in all cases indicating a strong effect of heterogeneity of the surface. The interaction factor (f) is about 10-14 and the free energy of adsorption at the standard state coverage is around 7-12 kcal/mol. Also, an Elovich-type kinetics was found with an adsorption activation energy around 6-10 kcal/mol. The transfer coefficients (α) were calculated to be 0.4-0.8. The bonding strength between the adsorbate and the electrode surface is around 20-40 kcal/mol which is comparable to that measured in the gas phase. The heat of adsorption is around -4-4 kcal/mol and the entropy of adsorption is about 10-60 cal/mol°K. Conditions of the adsorbed states for both organic species and water molecule were proposed. The adsorbed species generally adopt a flat orientation. Electropolymerization for some phenyl species may occur at a potential more positive than 0.9 V(NHE). A vertical orientation for these compounds seems to occur at high concentrations (>10^-3 M) on a smooth surface. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xvi, 320 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |