A new redox-active conjugated polymer containing anthraquinone pendants as anode material for aqueous all-organic hybrid-flow battery

Organic redox polymers have attracted extensive research interest due to tunable redox potential and high theoretical capacity. However, sluggish redox kinetics, poor electronic conductivity and low electrochemical stability derived from dissolution of polymers into the electrolyte and/or unexpected side reactions limit their use in batteries and electrochemical capacitors. To overcome these drawbacks, a conjugated redox polymer (Poly (N-anthraquinoyl pyrrole, PAQPy) with electronically conductive polypyrrole backbone and redox-active anthraquinone pendants was synthesized and then utilized as active anode materials for aqueous all-organic hybrid-flow batteries. The PAQPy shows highly reversible redox reaction at -0.2 V vs SHE with good stability in weakly acidic aqueous electrolytes. It is also found that when PAQPy is combined with graphene nanosheets through n-n stacking interactions, their redox capacity can be dramatically increased due to substantial weakening of hydrogen bonding interaction of anthraquinone groups. An aqueous all-organic hybrid-flow battery employing the PAQPy/Graphene composite (PAQPy/G) as the anode and 4-NH 2 -TEMPO as the flowing catholyte, respectively, displays a discharge capacity of ca. 62.2 mAh g(-1) at the current density of 0.2 A g(-1), a peak power density of 1.41 W g(-1) at 100% SOC and a round-trip energy efficiency of around 74.5% during 100 charge-discharge cycles.