Indolo[2,3-<i>b</i>]quinoxaline as a Low Reduction Potential and High Stability Anolyte Scaffold for Nonaqueous Redox Flow Batteries
Wenhao Zhang, Ryan Walser-Kuntz, Jacob S. Tracy, Tim K. Schramm, James Shee, Martin Head‐Gordon, Gan Chen, Brett A. Helms, Melanie S. Sanford, F. Dean Toste
Abstract
High Resolution Image Download MS PowerPoint Slide Redox flow batteries (RFBs) are a promising stationary energy storage technology for leveling power supply from intermittent renewable energy sources with demand. A central objective for the development of practical, scalable RFBs is to identify affordable and high-performance redox-active molecules as storage materials. Herein, we report the design, synthesis, and evaluation of a new organic scaffold, indolo[2,3- b ]quinoxaline, for highly stable, low-reduction potential, and high-solubility anolytes for nonaqueous redox flow batteries (NARFBs). The mixture of 2- and 3-( tert -butyl)-6-(2-methoxyethyl)-6 H -indolo[2,3- b ]quinoxaline exhibits a low reduction potential (−2.01 V vs Fc/Fc + ), high solubility (>2.7 M in acetonitrile), and remarkable stability (99.86% capacity retention over 49.5 h (202 cycles) of H-cell cycling). This anolyte was paired with N -(2-(2-methoxyethoxy)-ethyl)phenothiazine (MEEPT) to achieve a 2.3 V all-organic NARFB exhibiting 95.8% capacity retention over 75.1 h (120 cycles) of cycling.