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

• Published in: Journal of power sources 2012-11, Vol.217, p.373-380
• Main Authors: Lin, Xiaocheng, Wu, Liang, Liu, Yanbo, Ong, Ai Lien, Poynton, Simon D., Varcoe, John R., Xu, Tongwen
• Format: Article
• Language: English
• Subjects: Alkali stability; Anion-exchange membrane fuel cells; Applied sciences; Carbon; Density; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Guanidinium groups; Hydroxides; Ionic conductivity; Jewelry; Membranes; Nitrogen atoms; Stems
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2012.05.062

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 pKa) 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−3) solution for 192 h at 25 °C. A H2/O2 fuel cell test at 50 °C with a GPPO AAEM yielded a beginning-of-life peak power density of 16 mW cm−2. ► Alkaline anion exchange membranes (AAEMs) with guanidium groups were prepared. ► The ionic conductivity of AAEMs can attain as high as 71 mS cm−1. ► 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.