Studies on Metal Complexes as Active Materials in Redox-flow Battery Using Ionic Liquids as Electrolyte

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[FeIII(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[FeIII(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.