Studies on Iron (Fe[sup 3+]∕Fe[sup 2+])-Complex/Bromine (Br[sub 2]∕Br[sup −]) Redox Flow Cell in Sodium Acetate Solution

The formal potential of the couple shifts markedly in the negative direction by complexation with ethylenediamine tetraacetate (EDTA), oxalate, and citrate. The potentials of the complexes with EDTA and oxalate are less pH-dependent than with citrate. But, the relatively high pH of around 6.0 is favorable electrochemically due to high corresponding currents. Complexation of couple can provide fast electrode kinetics except for the complex with citrate. But, the solubility of the complex with citrate is up to . Charge–discharge measurements were conducted with the iron-complex/ redox cells. The results show that performance of the cells with -oxalate or -citrate is relatively poor due to slow kinetics for the -citrate and the unstability of the ferric form for the -oxalate, whereas performance of the iron-citrate/ cell is improved considerably by increasing concentration of the -citrate complex. Also, energy efficiencies of up to approximately 80 and 70% could be obtained for the cell with -EDTA and -citrate, respectively. The preliminary study shows that novel /iron-complex cells are technically feasible in redox flow batteries but need further investigation.