A redox flow battery using V4+/V5+ vs. V2+/V3+ and Fe2+/Fe3+ vs. V2+/V3+ redox couples in chloric/sulfuric mixed acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V hybrid redox flow cell using mixed reactant solutions and operated within a voltage window of 0.5–1.7 V demonstrated stable cycling over 100 cycles with energy efficiency ∼80% and negligible capacity fading at room temperature. A 66% improvement in the energy density of the Fe/V hybrid cell was achieved compared with the previously reported Fe/V cell using only Fe2+/Fe3+ vs. V2+/V3+ redox couples.