[4]Helicenium Ion as Bipolar Redox Material for Symmetrical Fully Organic Pole-less Redox Flow Battery

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. This configuration results in permanent capacity and energy density fading rapidly with time. As an elegant solution, symmetric organic redox flow batteries (SORFB) have been proposed to address this issue. We recently reported the use of dimethoxyquinacridiniums (DMQA+) ions as efficient bipolar redox molecule (BRM) in static H-cell conditions. Herein, we are reporting the use of dimethoxyquinacridinium (DMQA+) ion, with a Egap of 2.1V and a theoretical energy density (Ed) to 14.9 Wh/L in CH3CN, as a bipolar redox molecule (BRM) in a full in flow RFB prototype and its ability to operate under polarity reversal. Essential kinetic properties of this molecule were assessed by cyclic voltammetry and correlated to DFT calculation. Its stability has been evaluated in static H-cell at two different concentration and then in full SORFB prototype. Although the coulombic and energy efficiency metrics were moderate, this pegylated DMQA+ exhibited a capacity retention of over 99.99%, and the property of operating under polarity inversion making it highly attractive for grid-scale long lifespan energy storage applications.

Development of the Squaramide Scaffold for High Potential and Multielectron Catholytes for Use in Redox Flow Batteries

“…The majority of previously reported catholyte scaffolds, including TEMPO derivatives, dialkoxybenzenes, ferrocenes, phenothiazines, and phenazines, as shown in Figure a, exhibit oxidation potentials below 0.6 V vs Fc/Fc + . − N-ORFB catholyte materials, which exhibit potentials above 0.8 V vs Fc/Fc + , however, are primarily limited to the cyclopropenium scaffolds developed by the Sanford group, [4]­helicinium scaffolds pioneered by the Gianetti group, and tetrathiafulvalene derivatives, which have seen use in hybrid Li/organic RFBs. ,− We therefore aimed at the outset of our research to expand the chemical space of these high-oxidation potential catholyte scaffolds.…”