A redox flow battery having a supporting solution that includes Cl− anions is characterized by an anolyte having V2+ and V3+ in the supporting solution, a catholyte having Fe2+ and Fe3+ in the supporting solution, and a membrane separating the anolyte and the catholyte. The anolyte and catholyte can have V cations and Fe cations, respectively, or the anolyte and catholyte can each contain both V and Fe cations in a mixture. Furthermore, the supporting solution can contain a mixture of SO42− and Cl− anions.