N-alkyl-carboxylate-functionalized anthraquinone for long-cycling aqueous redox flow batteries

Aqueous redox flow batteries (ARFBs) are regarded as promising candidates for large-scale energy storage. In particular, ARFBs based on organic redox-active species can largely reduce the capital cost and mineral resource requirements. However, the design of redox-active organic materials with desirable electrochemical performances needs to be further explored. Herein, we report a green and low-cost synthesis of a highly soluble N-alkyl-carboxylate-functionalized derivative of 2,6-diaminoanthraquinone, namely, N,N'-(9,10-anthraquinone-2,6-diyl)-di-β-alanine (DAEAQ), which exhibits a high voltage plateau and long cycling life when serving as an anolyte in ARFBs. The alkaline ARFBs based on DAEAQ anolyte and potassium ferrocyanide (K 4 Fe(CN) 6 ) catholyte deliver a high open-circuit voltage of 1.12 V at pH ≥12. When sandwiched with a custom highly-sulfonated and nonfluorinated cation exchange membrane , the as-prepared ARFBs achieve an excellent maximum power density of 0.34 W cm −2 and an optimal capacity retention rate of 99.86% day −1 . This work highlights the great potential of rationally designed anthraquinone derivatives in ARFBs for grid-scale renewable and sustainable energy storage applications .