Crosslinked poly(m-terphenyl N-methyl piperidinium)-SEBS membranes with aryl-ether free and kinked backbones as highly stable and conductive anion exchange membranes

Abstract

The aryl-ether free polymer backbones containing ion-conducting head groups have drawn recent interest as high-performance anion exchange membrane (AEM) materials because of their excellent chemical stability against hydroxide ions. However, a relatively high ion exchange capacity (IEC) is required to ensure high ion conductivity and cell performance. In this study, new AEMs based on crosslinked poly(m-terphenyl N-methyl piperidinium)- poly(styrene-b-ethylene-co-butylene-b-styrene), x-PmTP-SEBS, were developed by crosslinking two aryl-ether free polymers with different structures: poly(m-terphenyl N-methyl piperidine) (PmTP) and SEBS. The crosslinked x-PmTP-SEBS membranes showed excellent mechanical properties (tensile strength of 28.5 MPa and elongation of break of 170.3% for the sample with 50% crosslinking degree, 50xPmTP-SEBS), as well as high dimensional stability (swelling ratio of around 30%) despite its high water uptake. In addition, despite its relatively low IEC value (1.68 meq g−1), this membrane also exhibited excellent ionic conductivity (116 mS cm−1 at 80 °C) and hydration number (λ = 42), which are higher than representative AEMs. This is due to the high content of bound water, which originates from the excellent phase separation of the SEBS unit and the kinked structure of the m-terphenyl unit. The AEM fuel cell using this membrane had a peak power density of 642 mW cm−2 with H2/O2 gas flow at 60 °C and 95% room humidity (RH). Moreover, the 50x-PmTP-SEBS membrane retained around 99% of its original conductivity and IEC after immersion in 2 M KOH solution at 80 °C for 600 h, exceeding the alkaline stability of most reported AEMs.