Studies on Metal Complexes as Active Materials in Redox-flow Battery Using Ionic Liquids as Electrolyte: Cyclic Voltammetry of Betainium Bis(Trifluoromethylsulfonyl)Imide Solution Dissolving Na[Fe^III(edta)(H₂O)] as an Anode Active Material

Abstract

As a part of studies for finding metal complexes as an active material in the redox-flow battery system using ionic liquids (ILs) as an electrolyte, we have measured cyclic voltammograms (CVs) of betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf₂N]) (H₂O content: 11 wt%) dissolving Na[Fe^III(edta)(H₂O)] (edta = ethylenediamine-N,N,N′,N′-tetraacetate). Two peaks corresponding to one redox couple were observed around 50 and 220 mV vs. Ag/AgCl and assigned as a quasi-reversible redox reaction based on electrochemical data. Furthermore, the CVs were found to be cycled stably. From these results, the Na[Fe^III(edta)(H₂O)] is expected to be used as anode active material for the redox-flow batteries using [Hbet][Tf₂N] containing 11 wt% H₂O as the electrolyte.