Pyridinium ferrocene sulfonate salts: Highly soluble materials for electrochemical applications

Abstract

Aqueous redox flow batteries (ARFBs) are devices that use water-soluble electroactive compounds for scalable energy storage. Energy storage capacity is maximized when anolytes and catholytes are highly soluble. In this paper, we present a series of pyridinium salts of the ferrocene bis(sulfonate) dianion as highly soluble candidates for ARFB applications. Four compounds with different alkyl chains on pyridinium cations were synthesized and evaluated for their electrochemical properties as well as their efficacy in ARFB devices. Although these compounds were highly soluble, resulting in potentially large energy densities, they suffer from the same stability issues as seen in the related imidazolium ferrocene bis(sulfonate) salt systems.