Highly Soluble Imidazolium Ferrocene Bis(sulfonate) Salts for Redox Flow Battery Applications.

Redox flow batteries (RFBs) are scalable devices that employ solution-based redox active components for scalable energy storage. To maximize energy density, new highly soluble catholytes and anolytes need to be synthesized and evaluated for their electrochemical performance. To that end, we synthesized a series of imidazolium ferrocene bis(sulfonate) salts as highly soluble catholytes for RFB applications. Six salts with differing alkyl chain lengths on the imidazolium cation were synthesized, characterized, and electrochemically analyzed. While aqueous solubility was significantly improved, the reactivity of the imidazolium cation and the increased viscosities of the salt solutions in water (which increase with increasing imidazolium chain length) limit the applicability of these materials to RFB design.