Highly Water-Soluble 6-Quinoxalinecarboxylic Acid for High-Voltage Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (AORFBs) are promising for grid-scale energy storage, but the aqueous solubility and stability of redox-active organic molecules are usually low. Herein, we report scalable and convenient synthesis of 6-quinoxalinecarboxylic acid (QCA) anolyte material with high solubility (5.5 M) and ultralow redox potential (−0.79 V vs SHE). When coupling with K4Fe(CN)6 catholyte, the QCA||K4Fe(CN)6 AORFBs show a cell voltage of 1.28 V, a power density of 199 mW cm–2, and a capacity retention of 99.9% cycle–1. This work highlights the reasonable construction of redox-active organic species to develop advanced AORFBs toward large-scale energy storage applications.