Redox flow batteries (RFBs) are membrane-separated rechargeable flow cells with redox electrolytes, offering the potential for large-scale energy storage and supporting renewable energy grids. Yet, creating a cost-effective, high-performance RFB system is challenging. In this work, we investigate an Fe/Mn RFB alkaline system based on the [(TEA)Fe-O-Fe(TEA)]3-/4- and MnO4-/2- redox couples with a theoretical cell voltage of ∼1.43 V. This combination has not been systematically studied previously, but it can lead to a very low-cost and sustainable materials for high energy storage. Constant current cycling tests were performed at ±41 mA cm-2 between 20% and 80% SOC over 800 h (400 cycles) with an apparent Coulombic efficiency (CE) approaching 100%, while the voltage efficiency (VE) gradually decreased from ∼75.3% to ∼61.4% due to increasing internal resistances. The voltage efficiency loss can be mitigated through a periodic acid treatment to remove MnO2 deposits from the separator.
Keywords: all-soluble; iron triethanolamine complex; large-scale energy storage; low-cost; permanganate ion; resistance analysis.