All-Organic Redox Targeting with a Single Redox Moiety: Combining Organic Radical Batteries and Organic Redox Flow Batteries

The volumetric capacities and the lifetime of organic redox flow batteries (RFBs) are strongly dependent on the concentrations of the redox-active molecules in the electrolyte. Single-molecule redox targeting represents an efficient approach toward realizing viable organic RFBs with low to moderate electrolyte concentrations. For the first time, an all-organic Nernstian potential-driven redox targeting system is investigated that directly combines a single-electrode material from organic radical batteries (ORBs) with a single redox couple of an aqueous, organic RFB, which are based on the same redox moiety. Namely, poly(TEMPO-methacrylate) (PTMA) is utilized as the redox target ("solid booster") and <i>N</i>,<i>N</i>,<i>N</i>-2,2,6,6-heptamethylpiperidinyloxy-4-ammonium chloride (TMATEMPO) is applied as the sole redox mediator to demonstrate the redox targeting mechanisms between the storage materials of both battery types. The formal potentials of both molecules are investigated, and the targeting mechanism is verified by cyclic voltammetry and state-of-charge measurements. Finally, battery cycling experiments demonstrate that 78-90% of the theoretical capacity of the ORB electrode material can be addressed when this material is present as the redox target in the electrolyte tank of an operating, aqueous organic RFB.