Anion Exchange Membranes of Alkaline Resistance Based on Acrylonitrile-Styrene Copolymer with N-Spirocyclic Ammonium

The N-spirocyclic ammonium with exceptional alkaline stability is employed to fabricate anion exchange membranes (AEMs) suitable for long-lasting fuel cell applications. In this paper, two types of N-spirocyclic ammonium, namely 3-(2-(piperidine-4-yl)ethyl)-6-azaspiro[5.5]undecan-6-ium (ASU) and 3,6-diazaspiro[5.5]undecan-6-ium (DSU), are incorporated into an acrylonitrile-styrene copolymer (SAN) to enhance the alkaline stability of AEMs. The introduction of N-spirocyclic ammonium results in AEMs exhibiting excellent alkaline tolerance, particularly the SAN resin membranes incorporating the ASU group (SAN-ASU-OH), which retain 95.0% of their initial conductivity after undergoing a 720-h alkaline treatment at 80 °C, and 1H NMR shows that almost no β-elimination occurred in the SAN-ASU-OH membranes. The utilization of SAN resin as the primary structural component provides a reasonable tensile strength (8.51 MPa) for SAN-ASU-OH, enhances the ion conductivity of AEMs significantly, and ensures a certain water uptake (WU) at the same time to ensure a low swelling ratio (SR). For instance, hydroxide conductivity of the membranes reached 67.7 mS cm–1 at 80 °C for the SAN-ASU-OH membrane while WU reached 81.65% and SR was limited to only 18.42% at 80 °C. The results indicate that the membranes based on SAN resins incorporating N-spirocyclic ammonium are expected to be promising candidates for future fuel cell applications.