Electrochemical Characterization and EPR Studies of TEMPO-Based Electrolytes for Redox Flow Batteries

Redox flow batteries are energy storage devices capable of holding large amounts of energy in comparison with traditional batteries. These batteries utilize redox species that are dissolved in an electrolyte and stored in two external tanks, making it possible to decouple power and energy, making them ideal for storing electricity produced solar and eolic technologies, where the energy production depends greatly on the fluctuations of the source. State-of-the-art redox flow batteries use vanadium solutions as electrolytes. However, vanadium is expensive and has to be dissolved in concentrated acid solutions to obtain the best performance, which poses safety concerns. In this study, we investigated the physical properties and electrochemical behavior of the newly synthesized (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) derivatives. Electron paramagnetic resonance (EPR) gave us insight into the molecular dynamics of the TEMPO derivatives, while cyclic voltammetry and the rotating disk electrode techniques helped us to determine the electron transfer kinetic process of the molecules and the stability of reaction products. The results show that the studied TEMPO-based electrolytes are promising candidates for redox flow battery applications.