SEBS-Based Anion Exchange Membrane Grafted with N-Spirocyclic Quaternary Ammonium Cations for Fuel Cells

To balance the water absorption, alkali stability, and ion conductivity of anion exchange membranes, we synthesize high-performance anion exchange membranes (AEMs) based on 3-(3-(piperidin-4-yl)propyl)-6-azaspiro[5.5]undecan-6-ium bromide (p-ASU), 3-amino-6-azaspiro[5.5]undecan-6-ium (a-ASU), and trimethylamine (TMA). By fully grafting ASU and TMA cations onto poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), obvious microphase separation structures are well-developed in the anion exchange membranes. The swelling ratio of SEBS-ASU-TMA membranes is less than 39% on account of the introduction of larger sterically hindered ASU cations. In addition, the SEBS-p-ASU-TMA-40 membrane with an alkyl spacer chain exhibits a higher efficiency for ion transport channels and higher ionic conductivity compared to SEBS-a-ASU-TMA-40 without the alkyl spacer chain. The SEBS-p-ASU-TMA-40 attained a OH– conductivity of 96.6 mS cm–1 at 80 °C. Furthermore, stable N-spirocyclic quaternary ammonium cations contributed to the good chemical stability of SEBS-p-ASU-TMA-40, which exhibits 17% degradation in OH– conductivity after 1000 h of alkali stability testing. The H2/O2 fuel cell assembled by SEBS-p-ASU-TMA-40 exhibits a maximum power density of 286 mW cm–2 at 80 °C.