The Economically Sustainable Hydrothermal Synthesis of Dextrosil-Viologen as a Robust Anolyte in Aqueous Redox Flow Batteries

Aqueous organic redox flow batteries (RFBs) are promising for grid-scale energy storage, but identifying stable and inexpensive organic redox couples suitable for practical applications has been challenging. Here we report a new, inexpensive, and robust anolyte, Dextrosil-Viologen (Dex-Vi), that demonstrates a 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 cycling. Furthermore, by rationalizing a high-yield hydrothermal synthetic approach that has never been applied to viologen RFB molecules along with a low-cost precursor, the predicted mass production cost of Dex-Vi is below $10/kAh. These results not only establish a new benchmark organic anolyte promising for practical RFB applications but also shows that the properties of organic redox species can be enhanced with minute performance tradeoffs through rationalized structural and synthetic design.