Organic Redox Targeting Flow Battery Utilizing a Hydrophilic Polymer and Its In‐Operando Characterization via State‐of‐Charge Monitoring of The Redox Mediator

Abstract

The hydrophilic poly(2,2,6,6-tetramethylpiperdinyloxy-4-ylmethacrylamide) (PTMAm) was utilized as redox target material in an aqueous organic redox targeting flow battery (RTFB). This polymer is processed into granules, which contain a conductive agent and an alginate binder. By this, a hydrophilic, yet waterinsoluble redox target can be obtained. The target was combined with the redox mediator molecule N,N,N-trimethyl-2oxo-2-[(2,2,6,6-tetramethylpiperidin-4-yloxyl)amino]ethan-1ammonium chloride (TEMPOAmide), that has been reported earlier as flow battery active material. This target/mediator combination has been characterized electrochemically and flow battery testing has been done. Furthermore, in-operando characterization of the redox target via electrolyte state-ofcharge (SOC) monitoring has been performed for the first time.The approach provides estimates for the redox target's SOC changes during cycling. In addition, a figure of merit -the "redox targetivity" -is proposed, which provides insights into the efficiency of the targeting reaction and supports the future optimization of materials, cell designs, and operational parameters for RTFBs.

Beyond conventional batteries: a review on semi-solid and redox targeting flow batteries-LiFePO4 as a case study

“…The first polymers reported as charge storage materials were polyaniline (PANI), poly (vinylbenzylethylviologene) and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), this opened the door to further develop new high-performance polymers for RFBs application. 18,104–113…”