High-performance fluorinated poly(aryl-piperidine) anion exchange membranes containing flexible biphenyls: Realize effective regulation between ionic conductivity and dimensional stability

Abstract

The anion exchange membranes (AEMs) face many challenges, and drawbacks such as poor alkali resistance stability, low ionic conductivity, and poor dimensional stability have hindered widespread applications. Herein, a series of fluorinated poly(aryl-piperidine) anion exchange membranes (QPTPF₆D-x) containing flexible biphenyls (1,2-diphenylethanes) were successfully prepared by using an ultra-strong acid-catalyzed polycondensation reaction. Flexible biphenyl is an aromatic monomer containing a collapsible rotary alkyl chain. It promotes the aggregation of piperidinium cationic groups and the construction of a more obvious microphase separated structure with fluorinated groups, effectively improving the conduction. At 80 °C, the ionic conductivity of QPTPF₆D-25% AEM reached 151.02 mS cm⁻¹. Incorporation of hydrophobic fluorinated groups and rigid aryl rings to maintain high mechanical properties (above 40 MPa under hydrated condition) and low swelling ratio (below 22.69%). Ether-free main-chain type AEMs were prepared to have better alkali resistance, and QPTPF₆D-25% AEM was soaked in 2 M NaOH for 1800 h, and the ion retention rate remained above 95%. In addition, the QPTPF₆D-25% AEM's peak power density (PPD) was 616.93 mW cm⁻² under 100 % RH and 1.75 bar test conditions. Meanwhile, the advantages of introducing flexible biphenyl and fluorinated groups were confirmed by density functional theory (DFT).