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

Abstract

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 °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 °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 . • Ether-free fluoropolymers functionalized with multi-piperidine cationic groups. • More obvious microphase separation by grafting side-chain close to the fluorine-contained groups. • High ionic conductivity of 156.4 mS cm -1 and high alkaline stability were realized.