SEBS-Based Anion Exchange Membrane Grafted with <i>N</i>-Spirocyclic Quaternary Ammonium Cations for Fuel Cells
Jing Sang, Lincan Yang, Fanghui Wang, Zhihua Wang, Hong Zhu
Abstract
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.