Octopus-like side chain grafted poly(arylene piperidinium) membranes for fuel cell application

Abstract

Octopus-like side chains are introduced in poly(arylene piperidinium)-based alkaline anion exchange membranes (AEMs) to enhance the conductivity and stability. This type of side chain consists of a bulky rigid β-cyclodextrin (β-CD) as the “octopus head”, and long flexible piperidinium ionic liquids as the “arms”. The β-CD unit can enlarge internal free volume of the AEM to reduce ion transport resistance; the “arms” can interact with adjacent hydrophilic ionic groups and water, constructing continuous ion transport channels. The prepared poly(biphenyl piperidinium) AEM with “octopus” side chains at an ion exchange capacity (IEC) of 1.29 mmol g−1 exhibits higher hydroxide conductivity (121.5 mS cm−1 at 80 °C) than that without the “octopus” structure (57.4 mS cm−1) although the latter has a larger IEC (1.55 mmol g−1). This “octopus” AEM retains 87.2% of its conductivity after being treated in a 1 M NaOH at 80 °C for 480 h. The alkaline H2/O2 fuel cell constructed with this “octopus” AEM produces a peak power density of 469 mW cm−2; the cell voltage can be maintained by 85% during 16 h operation. This work illustrates the advantage of “octopus” side chain for enhancement of AEM performance.