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 chloride (TMA-TEMPO) has been intensively studied for its usage in aqueous organic redox flow batteries. Straightforward synthesis, reliable electrochemistry, fast kinetics and high cycling stability are the advantages of this active material. Nevertheless, it has been shown that elevated temperatures and high states of charge accelerate the decomposition of this material. Hence, a comparative study was performed with five new and one known TEMPO derivatives, to elucidate the structure–stability relationship of the TEMPO scaffold and to investigate the influence on the battery performance. The results show that the introduction of linkers between the solubility-promoting group and the piperidyl core or enhanced shielding of the radical has a great impact on the stability during cycling.