Transport Properties of Ions and Electroactive Solutes in Poly (Phenylene Oxide) Based Membranes 11 views

Grid scale energy storage is becoming increasingly important with increasing demand and growing implementation of renewable energy technologies. Redox flow batteries (RFBs) are a promising technology to meet a growing demand for grid-scale energy storage, but current technologies are based on aqueous electrolytes which limit the operating voltage of the RFB, and therefore, energy density. Non-aqueous electrolytes have been suggested because they offer wider potential windows and may promote high solubility of redox active material resulting in high energy density relative to their aqueous counterparts. Membrane separators, designed specifically for high lithium-ion conductivity in organic solvents, are necessary to advance these non-aqueous RFBs. The goal of this dissertation is to continue to evaluate how changes to the membrane structure influence the lithium-ion conductivity and redox molecule permeability in non-aqueous electrolytes. The structure-property relationships established in this dissertation may inform design strategies for non-aqueous RFB membranes and RFB systems more broadly. First, an uncharged poly(phenylene oxide) (PPO) based membrane was developed to evaluate the potential for poly (ethylene glycol) (PEG) to enhance the conductivity of the membrane in non-aqueous electrolytes. A series of PEG-PPO membranes were synthesized to investigate the influence of PEG side chain length and degree of PEGylation on membrane transport properties. Next, the influence of the degree of functionalization on the transport properties of previously developed sulfonated PPO-based membranes was systematically evaluated. To connect transport properties to flow cell performance, a set of membranes was evaluated in symmetric non-aqueous electrochemical flow cell testing. Finally, using the same POATS-PPO membrane chemistry evaluated in the flow cell, the relationship between redox molecule structure and permeability through the sulfonated PPO-based membrane was evaluated. The relationships highlighted in this work demonstrate improvements in membrane performance and key interactions which can focus research on CEMs for non-aqueous RFBs going forward. These interactions can also be leveraged to design specific RFB systems which capitalize on favorable redox molecule – membrane interactions.

PHD (Doctor of Philosophy)

Membrane; Redox Flow Battery; Energy Storage; Selectivity

English

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2025-12-10