Design, Synthesis, and Characterization of Quinone Electrode Materials for Sustainable Energy Storage

The energy crisis and environmental issues have instigated the integration of renewable energy sources into the electric grid. A robust, safe, and long-life energy storage system is therefore strongly desired to maximize the benefits of intermittent renewable resources. Organic electrode materials, such as quinones, have recently attracted significant attention due to their high capacity, environmental friendliness, and ability to be derived from biomass. The objective of this dissertation is to design, synthesize, and characterize multiple quinone-based electrode materials in aqueous and non-aqueous electrolytes towards building next-generation energy storage technologies. My aim is to better understand the complex interactions amongst redox molecules/oligomers, ions, electrons, and electrolytes, and find ways to design better materials with improved performance. In this dissertation, I report the design, synthesis, and characterization of quinone-based oligomers and corresponding electrochemical properties in aqueous and non-aqueous electrolytes. I first report the synthesis of two cross-conjugated quinone oligomers and the effects of cross-conjugation and molecular conformations on the electrochemical properties. I further investigate the oligomers in aqueous electrolytes and discover the maximum capacity can be realized when the pH of electrolyte is above the pKa2 of the reduced quinones. Third, I discover that a sufficient swelling of the polyquinone film may be imperative to release full capacity. The combination of electrochemical quartz crystal microbalance and constant current chargedischarge techniques reveal that hydrated cations serve as charge carriers in aqueous electrolytes, and that the hydration numbers dynamically vary with the state of charge and current density. Finally, an oligomer based on pyrene-4,5,9,10-tetraone core capable of 4-electron reduction was synthesized and characterized in various electrolytes (H+, Li+, Na+, and Mg2+ over a pH range of 0-13). A Pourbaix diagram was then derived to understand the competition between H+ and metal-ion coordination. The work described in this dissertation strives to provide an in-depth understanding of the working mechanisms of quinone-based electrodes and guidelines for future organic battery development.