A long-lifetime aqueous organic redox flow battery utilizing multi-redox anolyte

Abstract

High-volumetric-capacity and long-lifetime aqueous organic redox flow batteries (AORFBs) have received considerable attention for electrochemical energy storage. Here, we report a six-electron transfer π-conjugated heteroaromatic hexaazatrinaphthalene tricarboxylic acid (HATNTA) as a promising anolyte for AORFBs. HATNTA, synthesized by a straightforward and scalable one-step condensation reaction of cyclic carbonyl molecules, can undergo a reversible three-step six-electron redox process of -0.69, -0.87, and -0.94 V (versus Ag/AgCl) at pH=14. The redox reactions of HATNTA are unveiled by combining ultraviolet-visible spectrophotometry and density functional theory calculations. When paired with ferrocyanide catholyte, HATNTA-based AORFB with 1.5 M electron concentration exhibits high open-circuit voltage of 1.24 V, impressive specific capacity of 37.2 Ah L−1, high output power density of 238 mW cm−2 and superior cycling stability with a capacity fade rate of 0.021% per cycle. The outstanding battery performance substantiates that multi-redox HATNTA breaks a novel pathway to develop advanced AORFBs for large-scale energy storage.