Modification of Hydrophobic Diacid Units for Enhanced Poly(crown ether) Anion-Exchange Membrane Performance

Abstract

Ideal anion-exchange membranes (AEMs) for anion-exchange membrane fuel cells (AEMFCs) must possess high OH − conductivity, excellent alkaline resistance, good thermal stability, and improved dimensional stability. In this study, four types of poly(crown ether) (PCE) cross-linked AEMs containing different aromatic or alicyclic dicarboxylic acids were prepared for AEMFCs. The hydrophilic/hydrophobic polarity discrimination of AEMs can be adjusted by the introduction of various diacids into the polymer backbones. As a result, an obvious microphase-separated structure will form in AEMs, which may aid the movement of hydroxide ions. The as-prepared QAPCE-1.4P membranes with 1,4-phenylenediacetic acid as the dicarboxylic acid exhibit a distinct micromorphology separation, as confirmed by morphology characterization using small-angle X-ray scattering, atomic force microscopy, as well as transmission electron microscopy. The highest hydroxide ion conductivity of QAPCE-1.4P at 80 °C in ultrapure water is 133.25 mS cm −1 . Meanwhile, QAPCE-1.4P shows an improved dimensional stability at 80 °C with a swelling ratio of 10.83%. In addition, QAPCE-1.4P shows good chemical stability (96.1% ionic conductivity retention) even after being put in harsh alkali conditions at 80 °C for 40 days. Furthermore, the maximum power density of a single cell using QAPCE-1.4P as the polymer electrolyte membranes can reach 689 mW cm −2 in hydrogen/oxygen (80 °C).

Anion Exchange Membrane Based on Cross-Linked Poly(2,6-dimethyl-1,4-phenylene oxide)/Poly(dimethylaminophenyl bisdiphenol) for Fuel Cell Applications

“…5 Fuel cells based on conventional quaternary amine aromatic polymers typically exhibit good fuel cell performance, long-term durability, hydroxide conductivity, adequate ion exchange capacity, and stability in alkaline environments. 6 While these characteristics contribute to satisfactory AEMFC performance, they may also result in higher water uptake and less controlled dimensional stability. Consequently, a common approach involves the development and synthesis of quaternary amine aromatic polymers with tailored molecular structures to address these issues in AEMFCs.…”

“…Many polymers have been investigated as alternatives to PFSA in PEMFC fuel cells to provide low cost, high fuel resistance, excellent physicochemical and thermal stability, and outstanding mechanical properties . Fuel cells based on conventional quaternary amine aromatic polymers typically exhibit good fuel cell performance, long-term durability, hydroxide conductivity, adequate ion exchange capacity, and stability in alkaline environments . While these characteristics contribute to satisfactory AEMFC performance, they may also result in higher water uptake and less controlled dimensional stability.…”