Fluorenone Based Anolyte for an Aqueous Organic Redox-Flow Battery

As renewable energy sources (e.g. solar, wind) are increasingly incorporated into our electrical grid, adequate large-scale energy storage is necessary to smooth out the intermittency of these renewable sources. Redox-flow batteries (RFBs) are an attractive energy storage solution with several attributes, most notably their decoupling of power and energy. Recently, organic RFBs have gained widespread attention over their inorganic counterparts due to the ability to synthetically tune and tailor the molecular structure of the active material for improved performance. Here, we present the first aqueous organic RFB utilizing a fluorenone based negative electrolyte (anolyte). With the addition of a carboxylic acid functional group, solubility of the fluorenone anolyte is enabled under alkaline conditions with a maximum solubility of 1M. Paired with a ferro/ferricyanide redox couple in the positive electrolyte (catholyte), this RFB can achieve an open circuit potential of 1.18V which rivals many other aqueous organic RFB chemistries that have previously been reported. Galvanostatic charge/discharge cycling has shown coulombic efficiencies in excess of 90% with energy and voltaic efficiencies above 80%. Moreover, the cost of this material has been quoted to be as low as $2/kg compared with the current state-of-the-art inorganic vanadium RFBs at greater than $80/kg. This work will show the potential for fluorenone based anolytes as promising candidates to further promote widespread commercialization of RFBs.