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    Development of an alkaline redox flow battery : from fundamentals to benchtop prototype

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    ARROYOCURRAS-DISSERTATION-2015.pdf (43.25Mb)
    Date
    2015-05
    Author
    Arroyo Currás, Netzahualcóyotl
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    Abstract
    This work presents the first alkaline redox flow battery (a-RFB) based on the coordination chemistry of cobalt(III/II) and iron(III/II) with amino-alcohol ligands in concentrated NaOH([subscript aq]). The a-RFB was developed by carrying out systematic structural and electrochemical characterizations of various redox-active coordination compounds to find the most suitable candidates for electrochemical energy storage. In the characterization studies, particular attention was given to the redox couple Fe(III/II)- TEA, where TEA = triethanolamine, because of its importance in the fields of supramolecular chemistry, magnetic memory films, and electrochemical energy storage. The structures of Fe(III)-TEA in the solid state and in alkaline solution are reported for the first time. Moreover, experimental evidence is presented for the existence of an EC reaction in the heterogeneous reduction of Fe(III/II)-TEA in concentrated base. Furthermore, experiments were carried out to study the reactivity of Fe(II)-TEA with O2. This is important because O2 reacts spontaneously with Fe(II)-TEA to produce hydrogen peroxide, decreasing the charging-discharging capacity of the a-RFB. The reduction of oxygen by Fe(II)-TEA in concentrated base was studied by UV-Vis spectroscopy and coulometric titrations. Additionally, a new method for the quick identification of redox couples with slow EC reactions, k[subscript f] < 0.1 s-1, is presented. The new method is based on scanning electrochemical microscopy (SECM) and consists of creating a thin-layer cell between the tip and substrate electrode. During analysis of a redox couple, the tip reports a current transient proportional to the decaying concentration of the product of the E reaction, from which an apparent forward rate constant for the C reaction can be determined. This method was designed for the field of RFB research, where the identification of redox couples with no EC reactions is necessary to ensure that a battery can run for thousands of cycles. Lastly, surface oxidation of polycrystalline Ir ultramicroelectrodes was studied by the surface interrogation mode of SECM (SI-SECM), using Fe(II)-TEA as the titrant. This was done to demonstrate the existence of hydrous oxides of Ir(IV) and Ir(V) prior to the onset of oxygen evolution in concentrated base. Numerical simulations were carried out using commercial software and were used to validate the experimental results reported in this work.
    Department
    Chemistry
    Description
    text
    Subject
    Flow battery
    Alkaline
    Triethanolamine
    Sodium hydroxide
    Iron
    Cobalt
    Reversible
    URI
    http://hdl.handle.net/2152/30510
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    • facebook
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    © The University of Texas at Austin