Browsing by Author "Fang, Xiaoting"

Now showing 1 - 4 of 4
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    A cooperative degradation pathway for organic phenoxazine catholytes in aqueous redox flow batteries
    (Elsevier, 2023-03) Fang, Xiaoting; Zeng, Lifan; Li, Zhiguang; Robertson, Lily A.; Shkrob, Ilya A.; Zhang , Lu; Wei, Xioaliang; Mechanical Engineering, School of Engineering and Technology
    Redox-active organic molecules that store positive charge in aqueous redox flow cells (catholyte redoxmers) frequently exhibit poor chemical stability for reasons that are not entirely understood. While for some catholyte molecules, deprotonation in their charged state is resposible for shortening the lifetime, for well designed molecules that avoid this common fate, it is seldom known what causes their eventual decomposition as it appears to be energetically prohibitive. Here, a highly soluble (1.6 M) phenoxazine molecule with a redox potential of 0.48 V vs. Ag/AgCl has been examined in flow cells. While this molecule has highly reversible redox chemistry, during cycling the capacity fades in a matter of hours. Our analyses suggest a cooperative decomposition pathway involving disproportionation of two charged molecules followed by anion substitution and deprotonation. This example suggests that cooperative reactions can be responsible for unexpectedly low chemical instability in the catholyte redoxmers and that researchers need to be keenly aware of such reactions and methods for their mitigation.
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    Multielectron Organic Redoxmers for Energy-Dense Redox Flow Batteries
    (ACS, 2022-01) Fang, Xiaoting; Li, Zhiguang; Zhao, Yuyue; Yue, Diqing; Zhang, Lu; Wei, Xiaoliang; Mechanical Engineering, School of Engineering and Technology
    Redox flow battery is a highly promising stationary energy storage method, but the limited energy density and high chemical cost are among the main barriers for commercialization. Multielectron organic redoxmers represent a family of structurally tailorable candidates that can achieve multiplied energy density with decreased materials consumption, potentially resulting in a viable solution to address these challenges. Here, the recent development of organic molecules with reversible multiredox activities in both aqueous and nonaqueous electrolytes is reviewed. The major focus is on the fundamental correlation between the chemical structures and the functional properties of reported multielectron organic molecules. Valuable insights are offered on rational structural design strategies for improving the relevant physicochemical and electrochemical properties. Finally, the current challenges are discussed to suggest future research needs along the avenue of using the multielectron approach to achieve energy-dense, stable, cost-effective redox flow batteries.
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    Six-electron organic redoxmers for aqueous redox flow batteries
    (Royal Society of Chemistry, 2022-12) Fang, Xiaoting; Cavazos, Andres T.; Li, Zhiguang; Li, Chenzhao; Xie, Jian; Wassall, Stephen R.; Zhang, Lu; Wei, Xiaoliang; Physics, School of Science
    We have developed a novel molecular design that enables six-electron redox activity in fused phenazine-based organic scaffolds. Combined electrochemical and spectroscopic tests successfully confirm the two-step 6e− redox mechanism. This work offers an opportunity for achieving energy-dense redox flow batteries, on condition that the solubility and stability issues are addressed.
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    Techno-economic analysis of non-aqueous hybrid redox flow batteries
    (Elsevier, 2022-07-15) Li, Zhiguang; Fang, Xiaoting; Cheng, Lei; Wei, Xiaoliang; Zhang, Lu; Mechanical Engineering, School of Engineering and Technology
    Renewable energy has become indispensable to improving human life, but its growth is hampered by a lack of cost-effective energy storage systems to solve the intermittency problem. Non-aqueous hybrid redox flow batteries (NAqHRFBs), based on lithium metal anode and organic redox molecules (redoxmers), have been investigated as an attractive energy storage option because of their high cell voltages and energy densities compared to other redox flow battery candidates. However, little is known about the economic potential of NAqHRFBs, as well as the operational and materials impacts. This work establishes a techno-economic model to analyze the capital costs of NAqHRFBs with selected organic redoxmers, including 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Sensitivity analyses for current density, area-specific resistance, cell voltage, electrolyte composition, redoxmer price, and equivalent molecular weight indicate the key factors in controlling NAqHRFB capital cost. To make the current NAqHRFB cost-effective, the first priority is to increase the operation current density over 10 times of those used in lab-scale tests, followed by adjusting redoxmer-related characteristics to afford more cost reduction space such as decreasing the unit price by ∼20 fold. The results have shed light on potential material development and system engineering directions to make NAqHRFBs viable for renewable energy storage.