Quaternary ammonium-functionalized hexyl bis(quaternary ammonium)-mediated partially crosslinked SEBSs as highly conductive and stable anion exchange membranes

Abstract

We chemically modify a commercially available elastomeric triblock copolymer, poly(styrene-b-ethylene-co-butylene-b-styrene) SEBS, to produce quaternary ammonium-functionalized hexyl bis(quaternary ammonium)-mediated partially-crosslinked SEBSs with different grafting degree of the conducting head groups as highly conductive and stable anion exchange membranes (AEMs). In an attempt to achieve a high ion exchange capacity and hence conductivity of the corresponding membranes without causing ‘gelation’, which these types of SEBS polymers typically experience, we use a SEBS with a high content (57%) of styrene, and graft the quaternary ammonium (QA) as both a crosslinker and the conducting head group on the side chain of the SEBS. The partial crosslinking approach, in combination with introducing these QA-conducting head groups as the side chain of the SEBS, helps to form larger ion clusters, and also to form a nano-phase morphology with long-range connecting channels. This induced the highest ion conductivity, 174.8 mS cm−1 at 80 °C, reported to date among these types of SEBS series. In addition, we obtain excellent cell performance with a current density of 450 mA cm−2 at 0.6 V and a peak power density of 315 mW cm−2 at 95% RH and 60 °C using the corresponding AEM.