Electrochemical performance of poly(arylene piperidinium) membranes and ionomers in anion exchange membrane fuel cells

Abstract

Awakening interest in anion exchange membrane fuel cells (AEMFC) for low temperature applications has led to an increased demand for high-performing polymers stable under alkaline conditions. In this study a poly(p-terphenylene piperidinium)-based membrane and ionomer was synthesized and applied in membrane electrode assemblies (MEAs), with porous gas-diffusion electrodes based on Pt catalysts supported by VULCAN® and high surface area carbon, respectively. The MEAs were evaluated in AEMFC single-cell tests. In order to identify specific beneficial characteristics of the polymer, the results were compared to reference tests using a commercial Aemion™-polymer. Steady-state polarisation performance measurements were carried out as well as electrode characterisations via cyclic voltammetry and electrochemical impedance spectroscopy, in addition to ex-situ characterisation of the polymer and the membrane electrode assemblies. Poly(p-terphenylene piperidinium)-based (PAP) membranes showed great potential with an in-situ measured average ohmic resistance of 0.09 Ωcm2. Mass transport limitations at higher current densities were observed for high surface area carbon electrodes, leading to an overall higher performance with the use of VULCAN®. Properties of the ionomer related to water uptake capabilities were observed to inhibit performance as well. The higher water uptake of PAP-based ionomers appears to be a key property for increasing electrode performance.