Nanoarchitectonics and electrochemical properties of redox-active nanogels for redox flow battery electrolytes

In this paper, we provide a thorough electrochemical study of redox-active nanosized cationic gels which are promising materials for redox flow battery electrolytes. We use two-step synthesis under mild aqueous conditions: precipitation polymerization of nanogels based on poly-(N-isporopylacrylamide-co-N-(3-aminopropyl) methacrylamide hydrochloride) (PNIPAM-co-APMA), and grafting of redox-active 4-(3-carboxypropanamido)TEMPO units to the nanogels. We demonstrate stable reduction-oxidation behavior of such nanogels and suggest a universal approach to evaluate the "effective" concentration and diffusion coefficient of redox-active groups grafted to nanogel particles. For the TEMPO-grafted PNIPAM-co-APMA nanogels we find the "effective" concentration of TEMPO-groups to be approximately 50 % of their total concentration and demonstrate an increase of the "effective" concentration upon electrode rotation. Also, we investigate electron transfer kinetics of redoxactive nanogels and provide an evidence that the adsorbed layer of nanogels facilitates electron transfer.