Facile construction of a highly proton-conductive matrix-mixed membrane based on a –SO3H functionalized polyamide

Abstract

Developing a facile strategy to construct low-cost and efficient proton-conductive electrolytes is pivotal in the practical application of proton exchange membrane (PEM) fuel cells. Herein, a polyamide with in-built –SO₃H moieties, PA(PhSO₃H)₂, was synthesized via a simple one-pot polymeric acylation process. Investigations via electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA(PhSO₃H)₂ displays a proton conductivity of up to 5.54 × 10⁻² S cm⁻¹ at 353 K under 98% relative humidity (RH), which is more than 2 orders of magnitude higher than that of its –SO₃H-free analogue PA(Ph)₂ (2.38 × 10⁻⁴ S cm⁻¹) under the same conditions. Therefore, after mixing with polyacrylonitrile (PAN) at different ratios, PA(PhSO₃H)₂-based matrix-mixed membranes were subsequently made and the analysis results revealed that the proton conductivity can reach up to 5.82 × 10⁻² S cm⁻¹ at 353 K and 98% RH when the weight ratio of PA(PhSO₃H)₂ : PAN is in 3 : 1 (labeled as PA(PhSO₃H)₂–PAN(3 : 1)), the value of which is comparable even to those of commercially available electrolytes that are used in PEM fuel cells. In addition, continuous testing shows that PA(PhSO₃H)₂–PAN(3 : 1) possesses long-life reusability. This work demonstrates that, utilizing the simple reaction of polymeric acylation with a sulfonated module as a precursor, highly effective proton-conductive membranes for PEM fuel cells can be achieved in a facile manner.