Symmetric, Robust, and High-voltage Organic Redox Flow Battery Model Based on a Helical Carbenium Ion Electrolyte

Redox flow batteries (RFBs) represent a promising technology for grid-scale integration of renewable energy. Redox-active molecular pairs with large potential windows have been identified as key components of these systems. However, cross-contamination problems encountered by the use of different catholyte and anolyte species still limits the development of reliable organic RFBs. Herein, we report the first use of a helical carbenium ion, with three stable oxidation states, as electrolyte for the development of symmetric cells. Cyclic voltammo-amperometric studies were conducted in acetonitrile to assess the essential kinetic properties for flow battery performance and cycling stability of this molecule. The selected [4]helicenium ion was then evaluated by using mono- and bi-electronic cycling experiments, resulting in 745 and 80 cycles respectively, with near-perfect capacity retention. This helical carbenium ion based electrolyte achieved a proof-of-principle 2.12 V open circuit potential as an all-organic symmetric RFB.