Scheme of the first report of a fully Symmetric Redox Flow Battery based on a innovative [4]helicenium with pegylateg arms ( ^PEG C⁺ ). This organic redox active molecule offers a theoretical energy density of 15 Wh/L, enabling pole-free operation and the use of a cost-effective porous membrane.

Abstract

Long duration storage batteries such as Redox Flow Batteries (RFBs) are promising storage system to address the energy storage requirement that our society will require in the years to come. Recent effort has been focused on the development of metal free and high energy density system such as all-organic non-aqueous redox flow batteries (NAORFBs). However high-voltage NAORFBs currently use distinct anolytes and catholytes, which are separated by a membrane sensitive to osmotic pressure, resulting in rapid capacity and energy density degradation over time. To address this issue, symmetric organic redox flow batteries (SORFBs) have been proposed as an elegant solution. We have introduced dimethoxyquinacridiniums (DMQA⁺) ions as efficient bipolar redox molecules (BRMs) in static H-cell conditions. In this study, we present the first application of DMQA⁺ ions in a complete flow RFB prototype, showcasing their ability to operate with polarity reversal. Key kinetic properties were evaluated through cyclic voltammetry and DFT calculations. While coulombic and energy efficiency metrics were moderate, pegylated DMQA⁺ demonstrated impressive capacity retention of over 99.99 % and the capability to operate under polarity inversion, making it a highly attractive choice for grid-scale, long-lifespan energy storage applications.