Preparation And Properties Of Alkaline Anion Exchange Membranes Based On Quaternary Ammonium Poly(Ether Sulfone)S

Anion exchange membrane fuel cells (AEMFC) have great development prospects due to its combination of advantages for the simple structure for proton exchange membrane fuel cell, fast oxidation for traditional alkaline fuel cell and high energy density for direct methanol fuel cells. Anion exchange membrane (AEM), as a crucial component of AEMFC, serves as the hydroxide ion carrier and separator fuel/oxidant simultaneously. In this paper, several types of novel AEMs derived from quarternized poly(ether sulfone)s were successfully prepared and their fundamental properties were evaluated in details.Firstly, two different poly(ether sulfone)s were prepared through random polymerization, then chloromethyl groups were introduced to the main chain and side chain of the polymer backbones by Friedel-Crafts chloromethylation reaction, afterwards, quaternized random poly(ether sulfone)s anion exchange membranes (rQPES) were prepared by quaternization and alkalization. The results indicated that the selection of monomer for synthesizing polymer have significant influence on the prepared AEMs. rQPES(A) membranes consisting of rigid9,9’-bis(4-hydroxyphenyl) fluorine units showed good mechanical properties and alkaline stability, and were favorable to form hydrophilic-hydrophobic micro-phase separation structure since chloromethyl groups were mainly introduced to the side chain in polymer backbones, which would facilitate the transfer of OH". For example, the membrane of rQPES(A)-2(IEC=1.33mmol/g) exhibited hydroxide ion conductivity of10.6mS/cm at30℃and41.4mS/cm at80℃, respectively. The reduction of hydroxide ion conductivity for the rQPES(A)-2membrane was about40%after soaking in4M NaOH for168h. On the other hand, the membranes consist of flexible4,4’-(1-methylethyliden)bisphenol unit, such as rQPES(B)-2(IEC=1.26mmol/g) exhibited hydroxide ion conductivity of6.7mS/cm at30℃and36.1mS/cm at80℃, respectively, and the reduction of hydroxide ion conductivity was about50%after the same stability test.Secondly, a series of sequenced quaternized poly(ether sulfone)s AEMs were successfully prepared through changing the polymerization method from the step-feeding methods. The results indicated that at similar IEC levels, the AEMs derived from sequenced quaternary poly(ether sulfone)s have higher hydroxide ion conductivity, better mechanical properties and alkaline stability compared with the random ones. For example, the membrane of sQPES(20/20)-A2(IEC=1.72mmol/g) exhibited hydroxide ion conductivity of27.8mS/cm at30℃. The reduction of hydroxide ion conductivity was about30%after soaking in4M NaOH for168h. In contrast, the random membrane of rQPES(A)-4(IEC=1.78mmol/g) exhibited hydroxide ion conductivity of23.0mS/cm and the lost of hydroxide ion conductivity about40%under the same conditions.Finally, a series of titanium nanotubes composite anion exchange membranes were obtained using quaternized random poly(ether sulfone) as the starting material through ball milling method. The results indicated that the compositing of appropriate amount of TiO2nanotubes could improve the hydroxide ion conductivity as well as inhibit the swelling of the membrane effectively, improve the dimensional stability and mechanical properties at the same time. For example, the membrane of QPES(A)-TNT-2.0%exhibited dimensional changes in the in-plane and through-plane directions of0.20and0.19, respectively, water uptake of98%, and hydroxide ion conductivity of25.7mS/cm at30℃in water. In contrast, the pristine membrane of QPES(A) exhibited dimensional changes in the in-plane and through-plane directions of0.25and0.23, respectively, water uptake of92%, and hydroxide ion conductivity of23.2mS/cm under the same conditions. It suggests that nanomaterial composite modification is an effective method to prepare high performance AEMs.