Alkaline-Stable Poly(phenylene-co-arylene ether) Block Copolymer-Based Anion Exchange Membranes with Alkyl Side Chain

Abstract

Proton exchange membranes (PEMs) are desirable materials as they can be applied to their potential and wide range of electrochemical applications. However, in most electrochemical applications of PEMs for energy production, precious metals such as platinum are essential as catalysts due to the highly acidic media of the system. Anion exchange membranes (AEMs) have been studied recently to replace these PEMs. However, AEM-based electrochemical devices mainly operate under strongly basic conditions. Under those conditions, AEM is prone to decomposition. As a result, membrane scientists have adopted polymers of ether-free backbone, but their IEC is generally more than 2.0 meq/g to achieve high conductivity. The high IEC results in excessive water uptake, making the AEM fail chemically and mechanically during long-term operations.To develop high-performance AEMs, we have synthesized new phenylene-based block copolymers. They have phenylene chains as hydrophilic segments for high chemical stability, in which hydrophobic parts are composed of arylene ether. This configuration is beneficial in solubility because the hydrophobic arylene ether block mitigates the poor solubility of phenylene. Moreover, a flexible alkyl chain was introduced as conducting moiety into hydrophilic phenylene. Thus, the enhanced solubility promoted the membrane’s efficient hydrophilic/hydrophobic morphological separation. The block copolymer-based AEM showed lower HFR (141 mΩ·cm2) than the Fumatech membrane (168 mΩ·cm2) in single-cell performance at 70 °C.