Benzotriazoles As Low-Potential Anolytes for Non-aqueous Redox Flow Batteries

Non-aqueous redox flow batteries hold promise as a technology for electrochemical energy storage based on the large potential window of organic solvents compared to that of their aqueous counterparts. However, to date, the realization of this promise has been limited by a dearth of redox active molecules that leverage the full potential window of non-aqueous solvents. This report addresses this challenge through the development of an organic storage material based on the benzotriazole scaffold. Using a combination of iterative molecular design, organic synthesis, electrochemical evaluation, and density functional theory, a 2-aryl benzotriazole derivative is developed that exhibits a redox potential below -2 V (-2.3 V vs ferrocene/ferrocenium), a >= 0.4 M solubility in the electrolyte solution in all oxidation states, and stable electrochemical cycling in a prototype flow battery (<= 90% capacity retention over 100 cycles, which represents approximately 505 h of cycling).