Anthraquinone-based anode material for aqueous redox flow batteries operating in nondemanding atmosphere

Organic materials are promising alternatives to inorganic counterparts in redox flow batteries (RFBs) owing to the good resource sustainability and tunable electrochemical characteristics. However, their practical implementation in most cases is hampered by the unsatisfactory chemical stability. This is particularly severe for anode materials that usually need to be operated in specified conditions. In this work, we report a molecular-engineering strategy to promote the stability of anthraquinone-based anode material through the synergy effect of steric hindrance and electron delocalization regulation by the introduction of armed-shaped quaternary ammonium groups. A quaternary ammonium protected anthraquinone derivative (denoted as QAAQ) is designed and used as anode material for aqueous RFBs that are able to operate in neutral NaCl electrolyte without inert-gas protection and interference-ion elimination. When paired with ferrocene-based catholyte, the cell displayed a stable cyclability for 500 cycles under nondemanding atmosphere, and good tolerance with the co-existence of interfering ions, which make QAAQ a competing candidate for practical organic RFBs.