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Full text release has been delayed at the author's request until August 07, 2027

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Design Principles for All-Organic, Redox-Targeting Flow Batteries

Wong, Curt M
http://rave.ohiolink.edu/etdc/view?acc_num=osu165400424162916

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Chemistry.
Increasing concerns about carbon emissions has led to the global adoption of renewable energy initiatives. Direct integration of renewable energy sources, however, is difficult because of the intermittency of such sources. Furthermore, direct integration would overload the grid and lead to blackouts. Thus, grid-scale electrical energy storage is required to store and provide energy on-demand. Redox flow batteries have attracted attention as a scalable, inexpensive storage technology. Flow batteries store energy in solvated, redox-active electrolytes, as opposed to conductive, solid materials. These solutions are stored in separated reservoirs and are flowed to the electrochemical cell to cycle the redox-active compound. Energy stored in this fashion decouples energy and power, which allow for increased operational control. While many electrolytes exist, few electrolyte examples have achieved commercialization because of low solubility and low cell voltage. Redox-targeting flow batteries have emerged as an improvement to classic flow technology. Rather than storing energy in solution, redox -targeting flow batteries store energy in an insoluble solid while a solubilized electrolyte serves to shuttle electrons from the electrochemical cell to the solid. This strategy serves to combine the high energy density of solid-state batteries and scalability of flow batteries. Current redox targeting technology is mainly limited to the use of inorganic solid materials. These materials are cycle by an intercalation mechanism, which requires low current densities that lead to long cycle times. Furthermore, pairing shuttles with these materials are difficult because of distinct redox potentials and electron transfer rates of these solids. Our efforts focused on the development of an all-organic redox targeting flow battery. Organic materials generally do not operate based on intercalation mechanisms and the synthetic flexibility of organic compounds allow for the fine tuning of the shuttle-solid redox targeting reaction. To take advantage of these properties, we wanted to develop a strategy for an inherently paired shuttle and solid for an efficient redox targeting reaction. We hypothesized that utilizing the same redox-active core for both the solid and shuttle would allow for a paired system. Our efforts targeted viologen compounds because of their well-studied redox characteristics. Initial polymers containing viologen monomers were found to be soluble in battery solvents. We found that crosslinking presented a viable strategy to the development of insoluble organic polymers. To determine the proper shuttle system, we developed an analytical technique that utilized cyclic voltammetry to monitor the redox targeting reaction. Utilizing this technique, we were able to quickly analyze various shuttles and identify two viologen shuttles to independently charge and discharge the polymer. Furthermore, this technique led to the observation that kinetic parameters, such as mass transfer and shuttle diffusion, are equally important as the thermodynamic considerations of the redox targeting reaction. In some cases, the diffusion of the shuttle limited cycling performance even if the redox targeting was thermodynamically favored. Using these analyses, we demonstrated a battery that achieved a capacity equivalent to a 100 mM redox flow battery with only 20 mM of dissolved shuttles. Also, the shuttle optimization process led to high voltaic efficiencies with a two-shuttle system. Our initial studies on organic redox-targeting flow batteries led us to develop a strategy for insoluble polymers and easily pair shuttles to the solid. Although our initial viologen redox-targeting system was demonstrated with nonaqueous solvents, the mild redox potential of viologen derivatives make them better suited for aqueous applications. We next wanted to translate the nonaqueous, viologen redox targeting system to an aqueous application. Direct translation of the system proved to be difficult as the shuttles precipitated during cycling. We also found that the initial polymer was too hydrophobic to allow for the diffusion of water-soluble shuttles to achieve efficient cycling. We derivatized the shuttles with hydrophilic functional groups to improve their aqueous solubility. In a similar fashion, we employed a co-polymerization approach to incorporate hydrophilic monomers into the insoluble polymer. By pairing the new viologen system with an iodide catholyte, we were able to demonstrate an aqueous redox-targeting flow battery that was enabled by molecular derivatization. We finally leveraged our knowledge of flow systems to develop a triphenylphosphine oxide reduction. Flow chemistry was utilized to increase current density without sacrificing yield or selectivity for the desired product. Furthermore, the high current density allowed for gram-scale reactions to be run with an overall low reaction time. Our work towards the development of all-organic, redox-targeting flow batteries have focused on a general approach to developing paired solid-shuttle pairs. We have developed a universal approach that will allow for the use of new organic, redox-active cores in redox-targeting flow batteries. We also have demonstrated the power of synthetic derivatization to enable the development of both aqueous and nonaqueous batteries. Finally, flow strategies from energy storage research were used in the development of an electroreduction of triphenylphosphine oxide to triphenylphosphine.
Christo Sevov (Advisor)
Yiying Wu (Committee Member)
Jovica Badjic (Committee Member)
220 p.
Chemistry; Energy
energy storage; renewable energy; grid-scale energy storage; batteries; redox flow batteries; redox-targeting flow batteries; electrochemistry; organic chemistry

Recommended Citations

Citations

  • Wong, C. M. (2022). Design Principles for All-Organic, Redox-Targeting Flow Batteries [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu165400424162916

    APA Style (7th edition)

  • Wong, Curt. Design Principles for All-Organic, Redox-Targeting Flow Batteries. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu165400424162916.

    MLA Style (8th edition)

  • Wong, Curt. "Design Principles for All-Organic, Redox-Targeting Flow Batteries." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu165400424162916

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.
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