Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells

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(-1) at room temperature): this stems from the high alkalinity (high pK(a)) 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 pi 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 degrees C, while the hydroxide conductivity of the AAEM with the most optimal properties remains stable in aqueous KOH (1 mol dm(-3)) solution for 192 h at 25 degrees C. A H-2/O-2 fuel cell test at 50 degrees C with a GPPO AAEM yielded a beginning-of-life peak power density of 16 mW cm(-2). (C) 2012 Elsevier B.V. All rights reserved.