Universal complexing agent enabling advanced iron-cerium redox flow batteries

The development of a safe and affordable redox flow battery technology is important for storing intermittent renewable energy. Here, we design a stable aqueous organic iron-cerium redox flow battery based on the inexpensive metal iron and the abundant rare earth metal cerium, enabled by the universal complexing agent diethylenetriamine pentaacetic acid. Molecular dynamics simulations are employed to screen for carboxyl-containing ligands with different electron donating capacities, revealing that diethylenetriamine pentaacetic acid is an effective candidate to chelate iron and cerium in the negolyte and posolyte, respectively, as verified by experimental characterization. The complexing agent enhances the redox characteristics of iron and cerium and reduces osmotic water migration between the negative and positive chambers by allowing the same ligand in both electrolytes. Our iron-cerium redox flow battery achieves an energy efficiency of 87.7% at 40 mA cm^-2 and 80.6% at 100 mA cm^-2, while retaining 95.3% of its initial capacity and maintaining around 86.3% energy efficiency after 500 cycles under neutral environments (100% of state-of-charge). The capacity is still preserved after 1779 cycles even when cycled at high-rates (80 mA·cm^-2, 70% of state-of-charge).