Increased Performance of an all-Organic Redox Flow Battery model by Nitration of the [4]Helicenium Ion Electrolyte

Redox Flow Batteries (RFBs) through their scalable design and virtually unlimited capacity, are promising candidates for large-scale energy storage. While recent advances in the development of redox-active bipolar organic molecules satisfy the prerequisites for the pioneering Symmetrical all-Organic Redox Flow Batteries (SORFBs) emerging, problems of low durability or low energy density remain a bottleneck for their wide-spread application. The present work reports that nitration of the [4]helicenium ion core (DMQA+) result in a significant enhancement of the electrochemical performance of DMQA as electrolyte for SORFBs. The physical and kinetic properties of NO2C+ were evaluated by cyclic voltammetry (CV) and UV-visible spectroscopy in acetonitrile and compared to those of its precursor HC+. The electrons storage ability of NO2C+ was investigated in three differents type of static H-cell experiments. In the first experiment, NO2C+ provided an open circuit voltage (OCV) of 2.24 V and demonstrated good stability, as well as high coulombic (>98%) efficiencies, over more than 200 charge/discharge cycles. In the second experiment, a charge-discharge cycling over the entire redox window of NO2C+ (OCV > 3 V) resulted in 80 cycles at a potential energy density above 12 Wh/L. During the last epxeriment, a bipolarization stress-test was performed during which NO2C+ demonstrated a remarkable durability of 90 cycles at 100% load with a perfect retention of capacity and coulombic efficiency. The electrochemical performance results of this enhanced redox material highlights that DMQA+ ions are robust and versatile materials for the emergence of symmetrical all-Organic ORFB