Structural alterations on the TEMPO scaffold and their impact on the performance as active materials for redox flow batteries

Abstract

Trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl chlorid (TMA-TEMPO) has been intensively studied for the usage in aqueous organic redox flow batteries. A straightforward synthesis, a reliable electrochemistry, fast kinetics and high cyc¬ling stability are the...

Oxidation of N,N,N,2,2,6,6‐Heptamethyl‐piperidine‐4‐ammonium Chloride to Water‐Soluble N‐Oxyl Radicals: A Comparative Study

“…This value can be considered as high and suggests that larger reaction times will yield quantitative yields. This is in good accordance with the literature, where often reaction times of one to five days, depending on the structure, are proposed for obtaining high yields [4,23] . As highly concentrated hydrogen peroxide solutions can represent a potential risk in large‐scale processes, the reaction was repeated exemplarily with six and ten equivalents of a 35 % H 2 O 2 solution.…”

“…This is in good accordance with the literature, where often reaction times of one to five days, depending on the structure, are proposed for obtaining high yields. [4,23] As highly concentrated hydrogen peroxide solutions can represent a potential risk in large-scale processes, the reaction was repeated exemplarily with six and ten equivalents of a 35 % H 2 O 2 solution. For six equivalents, a DoO of 85 % was obtained at room temperature.…”

“…Redox titrations were performed according to a literature procedure. [23] Standard solution preparation: The purchased 0.1 M cerium(IV)sulphate solution was diluted with water to receive a 0.025 M solution.…”

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

“…Both the TEMPOAmide and the PTMAm investigated as RM and RT in this study, respectively, are available through straight forward lab-scale synthesis. [12,14] They are structurally closely related, as both show an amide bond in the 4-position of the redox-active TEMPO-moiety. In case of the PTMAm, the amide connects the TEMPO to the crosslinked polymer backbone, that mediates the insolubility while maintaining the hydrophilic character of the amide bond.…”

“…[13] As this chemical modification also leads to a change of the standard potential of the RT, another N,N,N-trimethyl-2-oxo-2-[(2,2,6,6-tetramethylpiperidin-4-yloxyl)amino]ethan-1ammonium chloride (TEMPOAmide) was investigated as RM, since it was presented earlier as a stable TEMPO-based redoxactive material for aqueous organic redox flow batteries. [14] Flow batteries have been constructed and the material combination was evaluated in a fully operating quasi-symmetrical flow battery setup, where the non-capacity limiting side contained a large amount of TMATEMPO-based electrolyte and no RT. Furthermore, a new figure of merit is mathematically derived in this study based on the charge transfer in the flow cell and the state-of-charge (SOC) change of the RM and it is demonstrated that the SOC change of the RT can be inferred from the data.…”