Enhancement of hydroxide conductivity by the di-quaternization strategy for poly(ether ether ketone) based anion exchange membranes
Enhancement of hydroxide conductivity by the di-quaternization strategy for poly(ether ether ketone) based anion exchange membranes
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DOI：
10.1039/c4ta01397b
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发表时间：
2014-07
影响因子：
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通讯作者：
Xuemei Wu;Wanting Chen;Xiaoming Yan;G. He;Junjun Wang;Ying Zhang;Xiaoping Zhu
中科院分区：
文献类型：
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作者：
Xuemei Wu;Wanting Chen;Xiaoming Yan;G. He;Junjun Wang;Ying Zhang;Xiaoping Zhu
以双官能团1，4-二氮杂双环[2，2，2]辛烷(DABCO)为季铵化试剂，采用氯甲基化二季铵化法合成了侧链上含有多个季铵基团的聚醚醚酮(PEEK)。采用溶剂浇铸法制备了坚韧透明的阴离子交换膜。其目的是促进高效的氢氧离子传导通道，由于氢氧离子本身的低迁移率，这对提高AEMS的氢氧化物导电性尤为重要和具有挑战性。透射电子显微镜(TEM)图像显示，与单季铵盐膜相比，双季铵盐膜中的离子团簇具有更大尺寸的散射。在离子交换容量相近的情况下，双季铵盐膜的有效氢离子迁移率(∼3.5×10−4cm2 S−1 V−1)远高于单季铵盐膜(∼1.7×10−4 cm2 S−1 V−1)。侧链上的多个季铵盐基的结构促进了膜的亲水疏水微相分离和高效的氢氧化物离子传导通道。结果表明，与相同离子交换容量的单季铵盐膜相比，双季铵盐膜的氢氧化物电导率提高了约2~3倍，在25℃时达到了35.3ms cm−-1的高值。在一定的离子交换容量下，双季铵盐基膜的侧链较少，这也有利于膜的机械和化学稳定性。
Poly(ether ether ketone) (PEEK) with multiple quaternary ammonium groups on pendent side chains is synthesized through the chloromethylation di-quaternization route, using bi-functional 1,4-diazabicyclo[2,2,2]octane (DABCO) as quaternization reagent. The materials are made into tough and transparent anion exchange membranes (AEMs) by solvent casting. The purpose is to promote efficient hydroxide ion conductive channels, which are particularly important and challenging to improve hydroxide conductivity of AEMs due to the inherently low mobility of hydroxide ions. Transmission electron microscopy (TEM) images show ionic clusters of bigger size scattering in the di-quaternized membranes compared with the mono-quaternized membranes. Given similar ion exchange capacities (IECs), the di-quaternized membranes exhibit much higher values of effective hydroxide ion mobility (∼3.5 × 10−4 cm2 s−1 V−1) than the mono-quaternized membranes (∼1.7 × 10−4 cm2 s−1 V−1). The structure of multiple quaternary ammonium groups on the pendent side chain promotes hydrophilic–hydrophobic micro-phase separation and efficient hydroxide ion conductive channels in the membranes. As a result, hydroxide conductivity of the di-quaternized membranes is about 2 to 3 fold higher than that of the mono-quaternized membranes with similar IEC, exhibiting a high value of about 35.3 mS cm−1 at 25 °C. At a certain IEC, the di-quaternized membranes have fewer pendent side chains on the polymer backbone, which also benefits the mechanical and chemical stabilities of the AEMs.