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NShaheen PhD Dissertation.pdf (7.9 MB)

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Investigation of mechanisms governing charge transfer in redox-active organic molecules

Shaheen, Nora Adel
http://orcid.org/0000-0001-7260-6034
http://rave.ohiolink.edu/etdc/view?acc_num=case1662464354134756

Abstract Details

, Doctor of Philosophy, Case Western Reserve University, Chemical Engineering.
Organic compounds containing nitroxide radicals such as 4–hydroxy–2,2,6,6–tetramethylpiperidine–1–oxyl (4–hydroxy–TEMPO) are redox–active and are of interest for potential applications in redox flow batteries. The mechanisms governing charge–transfer reactions of such compounds are not well understood. Specifically, the anodic charge transfer coefficient (α_a) corresponding to the electro–oxidation of 4–hydroxy–TEMPO in an aqueous and non–aqueous electrolyte is ~0.9, i.e., α_a deviates considerably from the expected value (0.5) for a symmetric single–step one–electron transfer redox reaction. To explain this observation, a two–step oxidation mechanism is proposed wherein the nitroxide–containing species undergo fast charge transfer at an electrode surface followed by slow rate–limiting desorption of the adsorbed oxidized species. Numerical simulations are reported to characterize how the proposed two–step mechanism manifests in transient cyclic voltammetry behavior of the 4–hydroxy–TEMPO oxidation reaction, and good agreement with experiments is noted. In the present contribution, supporting evidence is provided for the aforementioned mechanism. In situ surface–enhanced Raman spectroscopy is employed to confirm the presence of surface–adsorbed species at a Au electrode during electro–oxidation of 4–hydroxy–TEMPO. Furthermore, chronopotentiometry is used to track the gradual re–equilibration of the electrode–electrolyte interface following the electro–oxidation of 4–hydroxy–TEMPO. Analysis of the chronopotentiometry data further suggests the presence of adsorbed species. Electrochemical cycling and spectroscopic evidence are presented to investigate the passivating effect of surface films that form following the electro–oxidation of 4–hydroxy–TEMPO.
Rohan Akolkar (Committee Chair)
Lydia Kisley (Committee Member)
Burcu Gurkan (Committee Member)
Robert Savinell (Committee Member)
128 p.
Chemical Engineering
nitroxide radicals, tempo, redox-active organic, non-aqueous electrolyte, reversible, cyclic voltammetry, electrochemistry

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Citations

  • Shaheen, N. A. (n.d.). Investigation of mechanisms governing charge transfer in redox-active organic molecules [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1662464354134756

    APA Style (7th edition)

  • Shaheen, Nora. Investigation of mechanisms governing charge transfer in redox-active organic molecules. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1662464354134756.

    MLA Style (8th edition)

  • Shaheen, Nora. "Investigation of mechanisms governing charge transfer in redox-active organic molecules." Doctoral dissertation, Case Western Reserve University. Accessed NOVEMBER 24, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=case1662464354134756

    Chicago Manual of Style (17th edition)

case1662464354134756
120
© , some rights reserved.Creative Commons License Investigation of mechanisms governing charge transfer in redox-active organic molecules by Nora Adel Shaheen is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.