High-Power Near-Neutral Aqueous All Organic Redox Flow Battery Enabled with a Pair of Anionic Redox Species.

Aqueous organic redox flow batteries (AORFBs) are regarded as a promising alternative for low-cost and durable grid-scale energy storage. However, the narrow potential gap, chemical lability and membrane fouling in most AORFBs constitute formidable roadblocks for practical applications. Herein, a pair of anionic organic molecules, namely (PPBPy)Br2 and PSS-TEMPO, are proposed. The (PPBPy)Br2 in anolyte reveals remarkable electrochemical stability without degradation after 1000 cycles, while PSS-TEMPO in catholyte presents a capacity decay rate as low as 0.012 %/cycle. At near-neutral conditions, the (PPBPy)Br2 /PSS-TEMPO flow cell exhibits a high voltage of 1.61 V, extremely low permeability across cation-exchange membrane and thus excellent cycling stability. Notably, a highest peak power density of 509 mW cm-2 has been achieved among reported all-organic aqueous RFBs. The molecular engineering strategies demonstrated here could provide a credible example of high-performance AORFBs.