Aqueous anthraquinone redox flow batteries (AARFBs) offer a safe and potentially inexpensive solution to the problem of storing massive amounts of electricity produced from intermittent renewables and are especially well-suited for large-scale stationary deployment. However, mass production cost of anthraquinone-based electrolytes and molecular instability are the two major challenges preventing them from being commercialized. We report continuous-flow electrochemical (re)synthetic approaches to both these problems: anthraquinone electrosynthesis from lower-cost anthracene feedstock, and the electrochemically-induced reversal of decomposition. We demonstrate the electrochemical oxidation of an anthracene derivative to a redox-active anthraquinone at room temperature in a continuous flow cell without the use of hazardous oxidants or noble metal catalysts. The anthraquinone, generated in situ, was used as the active species in a flow battery electrolyte without further modification or purification. Utilizing 2,6-dihydroxy-anthraquinone (DHAQ) without further structural modification, we demonstrate that the recomposition of the original redox-active molecule from the redox-inactive decomposition species represents a viable route to achieve low-cost, long-lifetime AARFBs. We used in situ (online) NMR and EPR and complementary electrochemical analyses to show that the decomposition compounds 2,6-dihydroxy-anthrone (DHA) and its tautomer, 2,6-dihydroxy-anthranol (DHAL), can be recomposed to DHAQ electrochemically through two steps: oxidation of DHA(L)2− to the dimer (DHA)24− by one-electron transfer followed by oxidation of (DHA)24− to DHAQ2− by three-electron transfer per DHAQ molecule. This in situ electrochemical regeneration process also rejuvenates the positive electrolyte – rebalancing the states of charge of both electrolytes without introducing extra ions.

In situ electro-synthesis and resynthesis of redox actives in aqueous organic redox flow batteries

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.