Abstract
Novel alkaline anion-exchange membranes (AAEMs) containing pendant guanidinium groups are synthesized from poly(2, 6-dimethyl-1,4-phenylene oxide) (PPO) by benzyl bromination and subsequent reaction with 1,1,2,3,3- pentamethylguanidine (PMG). The performances of the resultant guanidinium-functionalized-PPO (GPPO) AAEMs are controlled by tailoring the amount of guanidinium groups in the membrane matrix. The AAEMs exhibit high ionic conductivities (up to 71 mS cm at room temperature); this stems from the high alkalinity (high pK ) of guanidinium hydroxide, which leads to an augmentation of both the number of dissociated hydroxides and water molecules. Furthermore, the GPPO AAEMs exhibit excellent thermal and alkali stabilities due to the presence of the π electron conjugated systems of the pendant guanidinium head-groups permitting the positive charge to be delocalized over one carbon and three nitrogen atoms. Specifically, the initial decomposition temperatures, from thermogravimmetric analyses of the GPPO AAEMs, are high at 270 °C, while the hydroxide conductivity of the AAEM with the most optimal properties remains stable in aqueous KOH (1 mol dm ) solution for 192 h at 25 °C. A H /O fuel cell test at 50 °C with a GPPO AAEM yielded a beginning-of-life peak power density of 16 mW cm . Highlights: Alkaline anion exchange membranes (AAEMs) with guanidium groups were prepared. The ionic conductivity of AAEMs can attain as high as 71 mS cm . The membranes are stable after immersion in 1 M KOH solution at 25 °C for 8 d. The membranes show promise for application in alkaline polymer electrolyte fuel cells. © 2012 Elsevier B.V. All rights reserved.