Advanced rigid carbazole-based membranes assembled with flexible piperidine alkyl chains for neutral aqueous organic redox flow battery

Neutral aqueous organic redox flow battery (NAORFB) represents a highly promising energy storage device. However, one of its challenges is the need for high Cl− conductivity, highly stable ion-selective membranes. In this work, N-methylpiperidine-modified carbazole-based long side chain anion exchange membranes (QPCEP-x) were designed and prepared. The rigidity and hydrophobicity provided by the carbazole on the main chain, in conjunction with the flexibility and hydrophilicity provided by the alkyl-piperidine groups on the side chains, resulted in the observed excellent microphase separation properties of the prepared membranes. The prepared membranes exhibited excellent overall performance, with QPCEP-1 achieving a Cl− conductivity of 20.33 mS cm−1 at 25 °C. In NAORFB, the energy efficiency of QPCEP-1 ranges from 91.7 % to 62.4 % at 20–160 mA cm−2, far exceeding the 89.1 %–38.4 % of commercial AMVN. Furthermore, long-term cell cycling tests demonstrate that the energy efficiency of QPCEP-1 remains unchanged at 82.7 % at 60 mA cm−2 after 10,000 complete charge and discharge cycles, exceeding the majority of cycles reported in literatures. These findings suggest that QPCEP-x has significant potential for use in NAORFB.