Lateral modification and the organization of mixed adlattices on polycrystalline and single crystal platinum electrodes
Zurawski, Deborah Joy
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https://hdl.handle.net/2142/23605
Description
Title
Lateral modification and the organization of mixed adlattices on polycrystalline and single crystal platinum electrodes
Author(s)
Zurawski, Deborah Joy
Issue Date
1990
Doctoral Committee Chair(s)
Wieckowski, Andrzej
Department of Study
Chemistry, Analytical
Discipline
Chemistry, Analytical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Language
eng
Abstract
The modification of the electroactivity of carbon monoxide electrosorbed on platinum by the coadsorption of a variety of inorganic and organic compounds (surface lateral modifiers) was probed using linear scan voltammetry. The shift in the peak potential for the CO electrooxidation reaction induced by the presence of the modifiers was measured as the ratio of modifier to CO in the mixed adlattice was varied. All compounds coadsorbed with CO inhibited the reaction. The extent of the positive shift in the peak potential and its dependence on coverage was a function of the type of modifier and its mode of attachment to the platinum surface.
Two forces have been identified as factors in the poisoning of the CO electrooxidation reaction by coadsorbates. The structural component involves an alteration of the organization of the CO adlattice and was seen to be the major factor influencing the modification of the CO electrooxidation reaction by iodine. Low energy electron diffraction (LEED) results indicate that iodine compresses the CO adlattice electrosorbed on the single crystal Pt(111) surface. It has been postulated that these compressed structures are more difficult to nucleate towards oxidation than their unmodified counterparts, therefore a higher energy is needed to activate the adlattice and a more positive peak potential is observed. An electronic component was identified by analogy with gas phase, surface science research. The coadsorbates donate electronic charge to the surface which in turn causes an increase in the backdonation of electrons to the CO molecule. This shift in electronic charge strengthens the platinum-CO bond making it more difficult to remove CO from the surface. It has also been proposed that the modifier's electrons are polarized in the interfacial electric field present at the electrode surface. The electronic charge shifted towards the metal may screen the CO from the electric field which initiates the electrooxidation reaction.
Additional topics covered are the organization of CO electrosorbed on Pt(111) compared to gas phase dosed CO and a new method for the preparation of single crystals for electrochemical applications.
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