Cation‐Anion Redox Switching in an All‐Ferrocene Salt

Abstract

An “all‐ferrocene” salt comprised of two ferrocene cations and one ferrocene dianion exhibits an unusual reversing of oxidation‐reduction potentials between the cationic and the anionic components. This redox switching can be controlled via the solvent, and is not greatly affected by the supporting electrolyte.

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

“…The syntheses of the imidazolium ferrocene sulfonate salts were based on our previous work in which we generated "allferrocene" salts via simple ion metatheses. 41 Bis(ferrocene sulfonic acid) is generated via the reaction of ferrocene and chlorosulfonic acid. 42 Our group has used this reagent in the past to make sulfonamide conjugates containing amino acids and biomolecules as well as various electrochemically active sulfonate salts.…”

“…The obtained diffusion coefficient in water was comparable with the value published previously for ferrocene sulfonate salts. 40,41,44 The electrochemical data for imidazolium 1,1′-FcDS compound 3 are summarized in Table 1.…”

“…The syntheses of the imidazolium ferrocene sulfonate salts were based on our previous work in which we generated “all-ferrocene” salts via simple ion metatheses . Bis­(ferrocene sulfonic acid) is generated via the reaction of ferrocene and chlorosulfonic acid .…”

Investigations Into Aqueous Redox Flow Batteries Based on Ferrocene Bisulfonate

“…1,1′-bis(sulfonate)ferrocene dianion disodium salt (1,1′-FcDS) was found to be oxidized at a more positive potential than (ferrocenylmethyl)trimethylammonium cations because of the higher electron withdrawing strength of the sulfonate functional group. 22 Thus, RFB using 1,1′-FcDS as the catholyte is expected to generate a larger working voltage. Moreover, it opens up the possibility of adopting neutral or negatively charged redox species as the anolyte such as, for example, anthraquinones.…”

“…Both of these compounds are highly soluble in water due to the presence of the sulfonate functional groups. 1,1′-bis­(sulfonate)­ferrocene dianion disodium salt (1,1′-FcDS) was found to be oxidized at a more positive potential than (ferrocenylmethyl)­trimethylammonium cations because of the higher electron withdrawing strength of the sulfonate functional group . Thus, RFB using 1,1′-FcDS as the catholyte is expected to generate a larger working voltage.…”