Enabling high Anion-selective conductivity in membrane for High-performance neutral organic based aqueous redox flow battery by microstructure design

Neutral aqueous organic redox flow battery (NAORFB) has been considered as a promising energy-storage device in the stationary storage field. Yet the insufficient Cl− conductivity of anion exchange membrane (AEM) has become a crucial obstacle for neutral energy systems compared to their counterparts, such as H+ and OH– in acidic and alkaline conditions, respectively. Here, by proper microstructure design in AEM, a membrane with high Cl− conductivity is constructed by coupling the hydrophobic fluorinated poly(arylene ether) backbone and hydrophilic piperazinium groups, which exhibits excellent Cl− conductivity up to 55.9 mS cm−1 at room temperature. Moreover, the developed piperazinium functional fluorinated poly(arylene ether) (QPFPAE) membrane exhibits excellent low swelling, low organic redox-active species permeability, and high chemical stability. The constructed NAORFB using QPFPAE membrane shows a remarkable energy efficiency (85.6% at 80 mA cm−2), which has outperformed the other best-performing membranes. In addition, the membrane demonstrates outstanding stability and state-of-the-art performance over 1000 charge–discharge cycles. This work provides a rational design strategy toward high anion-selective conductivity in the membrane for large-scale NAORFB development.