A high-performance all-iron non-aqueous redox flow battery

An all-iron non-aqueous redox flow battery (NARFB) based on iron acetylacetonate (Fe(acac)3) anolyte and N-(ferrocenylmethyl)-N,N-dimethyl -N-ethylammonium bis(trifluoromethane-sulfonyl)imide (Fc1N112-TFSI) catholyte with an open circuit voltage of 1.34 V is designed. Due to the high electrochemical activity of the active species, the resultant battery demonstrates fairly high cycling performance and rate capability with anion exchange membrane FAP-375-PP. The Coulombic efficiency (CE) of 98.7%, voltage efficiency (VE) of 84.5%, and energy efficiency (EE) of 83.4% are achieved over 100 cycles at the current density of 10 mA cm−2. VE and EE can be further enhanced by employing mixed-reactant electrolyte as both anolyte and catholyte, which are 89.2% and 85.2%, respectively. The underlying reasons for the capacity decay are discussed for future optimization.