Structure–Property Relationship in Poly(Terphenylene)-Based Anion Exchange Membranes; The Impact of Backbone Structure for the Free Volume Control in Alkaline Fuel Cell Application

Abstract

The commercial application of anion exchange membrane fuel cells (AEMFCs) has been impeded by the lack of high ion conductivity and mechanical/chemical stability of the currently used anion exchange membranes (AEMs). A new class of aromatic polymers, which contain conducting head groups directly onto the polymer backbone were developed to attain long-term stability along with high conductivity. Inspired from this, a series of poly(terphenylene)-based anion exchange membranes devoid of benzylic sites or aryl-ether bonds, that are vulnerable to attack by hydroxide ion, were synthesized and were investigated for their physicochemical properties for alkaline fuel cell applications. The polymer backbones having N,N-dimethylpiperidinium conducting head group were synthesized using acid-catalyzed Friedel-Crafts polycondensation reaction between N-methyl-4-piperidone and meta/para-terphenyl monomers. Along with meta-terphenyl homopolymer, another three sets of copolymers were synthesized by introducing the kink structured meta-terphenyl in different ratios with para-terphenyl to control the free volume. The copolymer membrane, m-p-CoP-50, prepared from meta/para terphenyl monomers with a 1:1 molar ratio displayed a well-balanced water uptake, dimensional stability and the highest conductivity. The experimental procedures and the results will be discussed in detail.