Browsing by Subject "Flow battery"
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Item Development of an alkaline redox flow battery : from fundamentals to benchtop prototype(2015-05) Arroyo Currás, Netzahualcóyotl; Bard, Allen J.; Crooks, Richard M; Mullins, Charles B; Rose, Michael; Yu, GuihuaThis 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.Item A dynamic model-based estimate of the potential value of a vanadium redox flow battery for energy arbitrage and frequency regulation in Texas(2012-08) Fares, Robert Leo; Webber, Michael E., 1971-; Meyers, Jeremy P.Large-scale electrochemical energy storage is a technology that is uniquely suited to integrate intermittent renewable energy sources with the electric grid on a large scale. Grid-based energy storage also has the potential to reduce costs associated with periods of peak electric demand. For these reasons, this work describes the potential applications for grid-based energy storage, and then reviews large-scale energy storage technology innovations since the development of the lead-acid battery. The potential value of grid-based battery energy storage is discussed in the context of restructured electricity markets; then, a dynamic model-based economic optimization routine is developed to gauge the potential value of a vanadium redox flow battery (VRFB) operating for wholesale energy arbitrage and frequency regulation in Texas. Based on this analysis, the relative value of a VRFB in various regions of Texas for energy arbitrage and frequency regulation is examined. It is shown that frequency regulation is an appealing application for a grid-based VRFB, with a VRFB utilized for frequency regulation service in Texas potentially worth approximately $1500/kW. Finally, the effect of a VRFB’s characteristics on its value for frequency regulation and energy arbitrage are compared, and the operational insight developed in this work is used to glean how policies to integrate a large-scale energy storage with the electricity market might be crafted.Item Modeling, estimation, and control of proton exchange membrane-based electrochemical systems(2015-12) Yu, Victor Kin-Wah; Chen, Dongmei, Ph. D.; Longoria, Raul G; Deshpande, Ashish D; Fahrenthold, Eric P; Edgar, Thomas FTo reduce emissions and meet the rapidly growing global energy demand, affordable and efficient methods of electrical energy storage and generation are needed to exploit renewable energy sources more effectively. Proton exchange membrane (PEM) based electrochemical systems, such as vanadium redox flow batteries (VRFB) and PEM fuel cells, are playing an increasingly important role because they have a fast response rate, high efficiency, and small environmental impact. However, widespread commercial viability of these technologies in the future heavily depends on further improvements in their performance and reliability. Accordingly, this dissertation focuses on developing new methodologies to predict and control the behavior of these PEM-based electrochemical systems. In the first part of this work, a control-oriented physics-based model of a VRFB system is developed. This model can predict the transient response of the cell voltage under different operating conditions and inputs such as current, flow rate, and temperature. The significance of this study is having the ability to predict the short and long term effects of membrane crossover on the system performance. One major challenge of operating VRFB systems is that monitoring the state-of-charge (SOC) in real-time using traditional measurement techniques is expensive and impractical. To address this problem, an SOC estimator is developed based on a constrained extended Kalman filter that can be used for real-time optimization and control because it requires only simple voltage measurements and a low-order model. Simulation results demonstrate the ability to predict the vanadium concentrations of a VRFB system without knowledge of the crossover dynamics. A major obstacle preventing the widespread commercialization of VRFBs is excessive capital costs. This issue is addressed by developing a methodology to optimally size a VRFB system using the minimum amount of materials required for the intended power range. For PEM fuel cells, proper water and thermal management is critical to optimizing performance and longevity. However, this can be a challenging task due to strong system interactions between multiple input and output variables. In the final part of this work, these system interactions are studied in detail and a suitable controller is designed to regulate the stack voltage, stack temperature, and relative humidity during load transients.