Because of its mild redox potential, viologen compounds have gained popularity for aqueous redox-flow batteries (RFBs) applications. However, cost-effective RFBs require a high concentration of viologen electrolyte that exceeds their maximum solubility. Redox-targeting flow batteries (RTFBs) have emerged as a promising solution to this limitation of RFBs. RTFBs store energy in a bulk solid and utilizes a homogenous electrolyte to shuttle electrons from the electrochemical cell to the solid. Recently, an all-organic, non-aqueous viologen RTFB was reported that achieved high volumetric capacities by simple additions of the bulk solid. This work details the bottom-up design of an aqueous, viologen RTFB. The synthesis of aqueous soluble shuttles was required to address the low solubility of the non-aqueous variants. Furthermore, co-polymerization was used to improve the hydrophilicity of the polymer to allow for diffusion of the aqueous-soluble shuttles. Using this design strategy, an aqueous, viologen RTFB was demonstrated that can achieve high volumetric capacities compared to previously reported aqueous RFBs.

Design of a high-capacity, aqueous, viologen redox-targeting flow battery

ACS Spring 2022

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