On the Characterization of Small Iridium Oxide Nanoparticles Public Deposited

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  • March 19, 2019
  • Gambardella, Alessa An
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • Chapter One provides a general introduction of the research on iridium oxide bulk and nanoparticles, highlighting their function as water oxidation electrocatalysts. Emphasis is given to the importance of nanoparticle characterization to support the utility of nanoparticles with unique function. The accomplished work in the area of gold nanoparticles is summarized, providing a strong foundation for the methods employed throughout this dissertation. Furthermore, the challenges of developing methodology to investigate a mostly uncharacterized small metal oxide nanoparticle, namely an iridium oxide nanoparticle (IrOX NPs) ~2 nm in diameter, are addressed. Chapter Two describes the pH dependence of the redox couples of freely-diffusing IrOX NPs as compared to electrofloccuated films using cyclic voltammetry, among other electroanalytical methods. Despite being produced from the same nanoparticles, the dependence of the redox couples of diffusing IrOX NPs, while holding similarities, has dramatic differences from that of IrOX NP films. Such variation is attributed to changes in surface pKa, as discussed in detail. Chapter Three observes the electron transfer kinetics of IrOX NPs attached to self-assembled monolayers (SAMs) on planar gold electrodes. Varied lengths of carboxylic acid terminated SAMs, which provide a means for IrOX NP association, demonstrate that the electron transfer properties of the iridium IV/III couple and water oxidation (as catalyzed by IrOX NPs) depend on chain length. Modified Butler-Volmer theory is used to determine apparent rates constants. Chapter Four details carboxylic acid association at the IrOX NP surface, which renders organic solubility, as driven by solvent extraction conditions. The results show strong dependence on pH and indicate that the surface of the IrOX NP plays a significant role in determining association. While UV-Vis spectrophotometry is the predominant method for analysis, 1H-NMR spectroscopy is also employed providing unique insight into the poorly understood surface properties of IrOX NPs. Chapter Five investigates size and dispersity of IrOX NPs, both aqueous and organic soluble, using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Comparison is made with transmission electron microscopy (TEM) analysis. The difficulties in accurately characterizing the size of small, polydisperse nanoparticles using these two methods are addressed while also noting the lack of further sufficient techniques for such measurement. Chapter Six studies the optical, catalytic, and electron transfer properties of IrOX NPs coupled to a ruthenium chromophore using spectroelectrochemistry, photolysis, and transient absorption spectroscopy. This chromophore-catalyst assembly is prepared in a layer-by-layer fashion that allows for the individual components to be easily analyzed for direct comparison.
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  • Murray, Royce W.
  • Doctor of Philosophy
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  • 2013

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