Highly conductive fluorinated poly(biphenyl piperidinium) anion exchange membranes with robust durability

To prepare anion exchange membranes (AEMs) that possess an excellent alkaline resistance, a competitive conductivity and a low swelling ratio (SR), a reasonable molecular structure design is particularly important. Herein, we synthesized ether-free fluoropolymers via a superacid catalyzed polyhydroxyalkylation reaction in one pot, and grafted long flexible multipiperidine cation side chains to different positions of the backbone through Menshutkin reaction. We investigated the effect of hydrophilic-hydrophobic polarity difference on the microphase separation. When the ionic liquid is grafted closer to the fluorine-contained group, AEMs exhibit a more obvious microphase separated structure and larger ion clusters as confirmed by morphology observation. Molecular dynamics simulations also confirmed that the construction of ion channels in PBPip-QAPBF-30% is more efficient than in QAPBPip-PBF-30%. The resulting PBPip-QAPBF-30% AEM exhibits the highest OH- conductivity of 156.4 mS cm(-1) with a low SR of 12.9% at 80 degrees C. The QAPBPip-PBF-30% and PBPip-QAPBF-30% AEMs both show an excellent alkaline stability with the OH- conductivity retention of 93.2% and 95.0% correspondingly after being treated in a 2 M NaOH solution at 80 degrees C for 1080 h. Moreover, the peak power density of a single cell equipped with PBPip-QAPBF-30% reaches 324.5 mW cm(-2) at a current density of 550 mA cm(-2).

Automated summary

Reasonable molecular structure design is particularly important for preparing anion exchange membranes (AEMs) with excellent alkaline resistance, competitive conductivity, and low swelling ratio (SR). In this study, ether-free fluoropolymers were synthesized via a superacid catalyzed reaction and long flexible multipiperidine cation side chains were grafted to different positions of the backbone. The position of the grafted ionic liquid affected the microphase separation structure and ion cluster size in the AEMs.