Monosubstituted Low Molecular Weight Anthraquinone for Energy-Dense and Long-Life Redox Flow Batteries

Redox flow batteries (RFBs) are large-scale energy storage technologies that are attractive due to their safety, flexible design, and long life. Among different types of RFBs, aqueous organic systems have gained a lot of attention due to the possibility of tailoring the redox properties by modifying the organic chemical structure. We introduce 2-2-propionate ether anthraquinone (abbreviated 2-2PEAQ), which is a singly substituted anthraquinone that is synthesized via a facile synthetic route from potentially inexpensive precursors. 2-2PEAQ has the lowest molecular weight (MW = 296.07 g/mol) among the anthraquinone derivatives reported to date that can deliver an extremely low capacity fade rate (<0.02%/day), low membrane permeability (<1 x 10 -13 cm 2 /s), high solubility (≥1 M transferrable electrons) and acceptable redox potential (OCV >~1.0 V vs. Fe(CN) 6 3-/4- ) for use in aqueous organic flow batteries. Having a smaller MW per mole transferrable electrons in species that can be synthesized via simple synthesis routes is highly preferable because both attributes correlate with low mass production cost. We will discuss the degradation mechanisms of 2-2PEAQ and report its performance in the negolyte of a redox flow battery under practically relevant conditions, advancing the prospects for commercialization of grid-scale aqueous organic redox flow batteries.