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.
Graphene oxide (GO) is a potential material in the electrode and membrane of polymer electrolyte membrane fuel cells due to its unique structure and various oxygen-containing functional groups. A class of three-layered GO/poly (phenylene oxide) for AEMs was prepared in this work. GO was functionalized with highly stable 6-azonia-spiro [5.5]undecane groups and used as a fast hydroxide conductor, named ASU-GO. Functionalized by N-spirocyclic cations, poly (phenylene oxide) (PIPPO) was then combined with ASU-GO and GO to fabricate the ASU-GO/PIPPO and GO/PIPPO. Notably, the maximum hydroxide conductivity of the ASU-GO/PIPPO was 73.7 mS cm −1 at 80 °C, which was 3 times higher than that of the GO/PIPPO. The enhancement in hydroxide conductivity was due to the changes in the hydroxide transport mechanism and the poor stacked structure of the ASU-GO layer. Only 10.8% drops in hydroxide conductivity of ASU-GP/PIPPO after the alkaline test (1 M KOH at 80 °C for 700 h). Furthermore, the ASU-GO/PIPPO-50 membrane showed a maximum peak power density of 102 mW cm −2 , demonstrating the prepared membrane was promising in the AEM applications.
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