Abstract: A redox flow battery, comprising a first electrolyte storage (1), a second electrolyte storage (2), an electrochemical cell connected to said first and second electrolyte storages (1, 2), wherein said electrochemical cell comprises a first half-cell and a second half-cell, wherein said first half-cell comprises a cathode (7), wherein said second half-cell comprises an anode (8), wherein said first and second half-cells are separated from each other by an ion exchange membrane (9), wherein said first electrolyte storage comprises an aqueous solution comprising an iron complex of a compound of formula I and stereoisomers of compound of formula I.