Redox-Targeting Reactions of Viologen-Based Shuttles and Polymers Translated From Nonaqueous to Aqueous Electrolyte

Redox-targeting flow batteries (RTFBs) present an attractive strategy for enhancing the energy density of conventional redox flow batteries (RFBs) by integrating heterogeneous energy storage materials as capacity boosters. However, nearly all RTFB systems have been developed with nonaqueous redox chemistries, while capacity boosters in aqueous storage systems are limited to anthraquinone chemistries. In this work, we expand the chemistry of aqueous RTFBs to viologen-based compounds by translating a nonaqueous RTFB into an aqueous platform. All redox chemistries of the prior nonaqueous RTFB-redox shuttles and solids-required a synthetic redesign to address challenges associated with promoting fast redox targeting reactions of organic solids and shuttles in aqueous media. The effects of molecular structure, ion pairing, and supporting electrolytes on RTFB performance are detailed in this report to provide a case study for developing future aqueous organic RTFBs. The redesigned RTFBs achieve 50% utilization of the aqueous capacity booster for charge storage.