Bipolar Isoindoline Nitroxide for Nonaqueous Symmetrical Redox Flow Battery

Abstract

AbstractCrossover in non‐aqueous redox flow batteries remains a critical challenge to the cycle stability of these devices. The use of bipolar redox‐active organic materials (ROM) is an emerging strategy for mitigating crossover. Herein we report the first example of a bipolar ROM derived from an isoindoline nitroxide, a ring class which gives a number of advantages over the more commonly employed piperidines, including greater stability and a 200 mV higher oxidation potential. Through facile synthetic transformation, the unsubstituted isoindoline nitroxide was nitrated to give a novel bipolar molecule, 5‐nitro‐1,1,3,3‐tetramethylisoindoline‐2‐yloxyl (NTMIO). This material was investigated electrochemically, revealing a reversible oxidation and quasi‐reversible reduction giving a cell potential of 2.07 V. NTMIO was then assessed as an active material in both a static and flow battery model, where cycling was observed for both oxidative and reductive redox couples for over 70 and 20 cycles respectively.