Novel Ethylene Glycol Substituted Benzoxadiazole and Benzothiadiazole as Anolytes for Nonaqueous Organic Redox Flow Batteries

The design of new organic materials for redox‐flow batteries is an actively developing topic in the field of energy storage. Herein, two novel redox‐active organic molecules were presented, based on benzoxadiazole and benzothiadiazole cores bearing ethylene glycol substituents, which were first synthesized and evaluated as anolytes in nonaqueous all organic redox flow batteries. These two molecules were compared with their unsubstituted analogs in terms of electrochemistry, solubility and RFB cycling behavior. Substituted benzoxadiazole and benzothiadiazole possess low redox potentials near −2.1 V vs. Fc/Fc⁺, increased solubility in organic solvents, reduced permeability through the membrane and higher stability under charge‐discharge cycling in laboratory RFB cells than unsubstituted counterparts.