A Highly Soluble Iron‐Based Posolyte Species with High Redox Potential for Aqueous Redox Flow Batteries

Abstract

AbstractA novel iron‐based posolyte redox species are presented for an aqueous redox flow battery, (Tetrakis(2‐pyridylmethyl)ethylenediamine)iron(II) dichloride, which is obtained by a simple synthetic route, shows a high redox potential of 0.788 V versus SHE, and exhibits exceptional aqueous solubility of 1.46 M. Paired with bis(3‐trimethylammonio)propyl viologen tetrachloride at neutral pH, the battery demonstrates an open‐circuit voltage of 1.19 V and delivers good cycling performance, with a capacity fade rate of 0.28% per day and coulombic efficiency of 99.3%. Postmortem chemical and electrochemical analyses of the posolyte species suggest future routes for stabilization of the complex. Among all the iron complexes with a redox potential above 0.4 V versus SHE, this compound exhibits the highest solubility. These results offer valuable insights that can be applied to the development of future posolyte species for sustainable energy storage solutions.