Dextrosil-Viologen: A Robust and Sustainable Anolyte for Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (RFBs) are promising for grid-scale energy storage. However, identifying stable and inexpensive organic redox couples suitable for practical applications has been challenging. Herein, we report a robust anolyte species, dextrosil-viologen (Dex-Vi), that demonstrates record overall RFB performance for anolyte redox species in neutral aqueous media, including ultralow anion-exchange membrane permeability, high volumetric capacity capability, and outstanding chemical stability. Remarkably, at a high concentration of 1.5 M (40.2 Ah·L –1 theoretical anolyte volumetric capacity), Dex-Vi shows extremely stable cycling performance without observable capacity decay over one month of cycling. We present a high-yield hydrothermal synthetic approach for this viologen chloride salt with a low-cost precursor. These results not only establish a new benchmark organic anolyte species that is promising for practical RFB applications but also show that the properties of organic redox species can be enhanced with minute performance trade-offs through rationalized structural and synthetic design.