Adjusting the perfluorinated side chain length in dual-grafted anion exchange membranes for high performance fuel cells

Abstract

The high hydroxide conductivity and alkali stability of anion exchange membranes (AEMs) is the guarantee for high-performance anion exchange membrane fuel cells. Introducing perfluorinated hydrophobic side chains has emerged as an effective strategy to promote microphase separation and ion transport. However, the effect of the perfluorinated side chain length on the evolution of membrane microstructure needs to be further elucidated. In this work, we design a series of AEMs by grafting perfluorinated side chains of different lengths, and ether-containing quaternized hydrophilic side chains, onto poly(aryl piperidine). The PAP-ON-pF6 membrane with the most suitable length (pF6) of perfluorinated side chain shows the best microphase separation; shorter (pF4) perfluorinated side chains contribute little to this behavior due to their insufficient hydrophobicity while longer (pF8 and pF10) chains play an inhibitory role because they impede the hydrophilic side chain aggregation. As a result, the PAP-ON-pF6 membrane shows a hydroxide conductivity of 134.2 mS cm⁻¹ at 80 °C at an ion exchange capacity of 2.17 mmol g⁻¹ and retains 90.1% and 80.8% of its conductivity after being treated in 1 M and 2 M NaOH at 80 °C for 1600 h. The H₂/O₂ fuel cell assembled with this membrane yields a peak power density of 1066 mW cm⁻² and works stably at 200 mA cm⁻² for 140 h without appreciable voltage decay. This work provides a new idea for regulating microphase separation in AEMs.