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

Abstract

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.<br>

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

“…14 31 and it is 8 times higher compared to its alkyl parent (1.8 Wh.L -1 ). 45 It is noteworthy that this pegylated carbenium ion approaches the energy density range observed in applied VRFB systems, which typically lie between 15 and 25 Wh.L -1 at their best. Consequently, the singlet description likely predominates as the principal contributing spin state to the anionic redox state.…”

“…57 Upon scanning to the cathodic region of potential, an oxidation event is observed at E1/2 Ox = 0.94 V vs AgNO3, corresponding to the formation of the dication radical PEG C •++ . 45 The event taking place at E red2 = -1.98 V vs AgNO3…”

“…54 To a solution of tris(2,6 dimethoxyphenyl)carbenium tetrafluoroborate salt 49 Electrochemical studies. In this investigation, acetonitrile was selected as the preferred solvent owing to its ability to stabilize the various oxidation states of DMQA + , 45,46,55 its significant electrochemical window (~6.0 V), and its potential to enhance energy density. 42,56 During cyclic voltammetry experiments in acetonitrile (0.5M TBABF4), PEG C + exhibited three single-electron redox events (Figure 1).…”

“…[41][42][43][44] In this growing field of SORFB, our research team has recently played a role in emphasizing the properties of helical carbenium ions, more specifically the [4]heliceniums ions dimethoxyquinacridiniums (DMQA + ). 45,46 Through the three stable redox states possessed by these carbocations, we were able to point out remarkable performances as electrolytic material for SORFB with Ecell voltages higher than 2.0 V. However our previous studies were only performed in a H-cell, the static RFB models. 33,47 Herein, we report the use of this DMQA platform in a flow RFB model for the first time.…”