Water Vapor Induced Preparing Polyethersulfone Anion Exchange Membranes

Alkaline anion exchange membrane fuel cells (AAEMFCs) have been considered as one of clean and efficient power sources, because of their higher reaction kinetics, cheap non-noble metal catalysts,and low fuel permeability. As one of the key components of AAEMFCs, alkaline anion exchange membranes (AAEMs) conduct hydroxide and separate fuel/oxidant. In the conventional quaternary-ammonium anion exchange membranes, it’s hard to form continuous ion transport channels due to the lack of hydrophilic-hydrophobic micro-phase separation, resulting into low conductivity. In order to improve ion conductivity of AAEMs, in the present work, water vapor is used as driving force to promote self-assembly of the hydrophilic quaternary-ammonium groups into the surface of the micro-phase separated aggregations, and build up ion conducting pathway in the membranes.With the reaction of CMPES and1-methylimidazole, imidazolium-functionalized PES(PES-ImCl)were synthesized, and then the WPES-ImOH membranes and PES-ImOH membranes were prepared by the water vapor induced method and the casting method respectively, testing membranes hydroxide conductivity changes. Based on a series of tentative experiments, the reasonable water vapor temperature was70℃, the reasonable solution was1-methylimidazole, the reasonable proportion of CMPES was10%.Different DCs of WPES-ImOH membranes and PES-ImOH membranes were prepared. And as the temperature rose, the ionic exchange capacity (IEC), water uptake, swelling ratio and hydroxide conductivity of two membranes increased. Due to the hydrophilic imidazolium groups into the surface of the micro-phase separated aggregations, the hydroxide conductivity of WPES-ImOH membranes was obviously higher than that of PES-ImOH membranes. The hydroxide conductivity of WPES-ImOH61%membranes was up to30.69mS/cm at20℃, and PES-ImOH40%membranes was25.85mS/cm. The hydroxide conductivity of WPES-ImOH61%membranes reached40.68mS/cm at50℃, and PES-ImOH61%membranes was36.53mS/cm. The ionic exchange capacity, water uptake and swelling ratio of WPES-ImOH membranes were slightly above PES-ImOH membranes. In addition, TGA manifested that the WPES-ImOH membranes and PES-ImOH membranes posses good thermal stability (the initial decomposition temperature were197℃and185℃respectively). For further studying the effect of water vapor on membranes’ preparation process, quaternized PES (QAPES) was obtained by dissolving CMPES and strong basic trimethylamine aqueous solution into N, N-dimethyl acetamide (DMAC)to complete homogeneous quaternization. After precipitation, the WPES-QaOH membranes and PES-QaOH membranes were prepared by the water vapor induced method and the casting method respectively. Due to the hydrophilic trimethylamine groups into the surface of the micro-phase separated aggregations, the hydroxide conductivity of WPES-QaOH membranes was above that of PES-QaOH membranes. The hydroxide conductivity of WPES-QaOH50%membranes arrived at27mS/cm at20℃, and PES-QaOH50%membranes was21.51mS/cm. The hydroxide conductivity of WPES-QaOH50%membranes was up to38.23mS/cm at50℃,and PES-QaOH50%membranes was31.71mS/cm.