Low-Potential Pyridinium Anolyte for Aqueous Redox Flow Batteries

Aqueous redox flow batteries (RFBs) can serve as inexpensive grid-scale energy storage devices. A key challenge for developing these systems is identifying storage materials that undergo reversible redox events at potentials near the voltaic limits of aqueous media. This work details the development of a benzoylpyridinium-based anolyte for this application. A combination of electrochemical and spectroscopic studies guided the selection of a supporting electrolyte to mitigate anolyte-catalyzed proton reduction at the low potentials. These insights were used to achieve stable one-electron cycling with KOH as the support in both a H cell and in a laboratory-scale flow cell. In the latter experiment, cycling versus iron ferrocyanide afforded an aqueous RFB with an open-circuit voltage exceeding 1 V.