基于螺环季铵盐的阴离子交换膜的制备与性能

Preparation and properties of anion exchange membranes based on spirocyclic quaternary ammonium salts

合成了N,N-二烯丙基吡咯烷溴盐([DAPy][Br]),采用光引发聚合的方式制备了基于[DAPy][Br]的聚合物膜,经过离子交换后得到OH^-型阴离子交换膜.改变原料配比调控膜的离子交换容量,发现膜的溶胀度、吸水率、离子交换容量与电导率都随着[DAPy][Br]含量的增加而增大.该阴离子交换膜具有良好的机械性能和热稳定性,拉伸强度在室温下为10.6～19.8 MPa. 80℃下最高离子电导率可达7.29×10^(-2) S/cm.在成膜过程中[DAPy][Br]发生交联,形成拥有两个五元环的N-螺环结构阳离子,有效提高了膜的耐碱性能,[PSAN]_(70^-)[DAPy][OH]_(30)膜浸泡于80℃下1mol/LKOH溶液中240h,电导率仅下降了11%.上述结果表明,拥有N-螺环季铵盐的脂肪主链的阴离子交换膜有望应用于燃料电池.

Among various types of fuel cells, alkaline anion exchange membrane fuel cells(AEMFCs) have attracted enormous attention as clean and highly efficient energy conversion devices for vehicles and portable electronic applications. As the key component of AEMFCs, anion exchange membranes(AEMs) act both as a barrier to separate the fuel and an electrolyte to transport hydroxide anion. To fulfill the application of AEMFCs, an AEM should possess good thermal stability, good mechanical properties, high conductivity and excellent alkaline stability. The lack of commercially available AEMs with excellent alkaline stability is limited the application of AEMs in the AEMFCs. In the recent years, a variety of AEMs based on poly(sulfone)s, poly(styrene)s, polypropylene, poly(arylene ether)s, poly(phenylene)s, poly(phenylene oxide)s and poly(olefin)s, have been synthesized for the application of AEMs. Most of these AEMs showed a similar chemical structure that a polymer backbone with with pendent quaternary ammonium cations. However, quaternary ammonium cations are unstable in alkaline environment due to the Hofmann degradation, the nucleophilic substitution and the ylide reaction, even in high temperature. Therefore, various types of AEMs based on some potential alternative cations, including imidazolium, guanidinium, phosphonium, metal-cation, pyridinium, tertiary sulfonium, and pyrrolidinium cations have been prepared and investigated in the last few years. Recently, different quaternary ammonium small molecules were synthesized and their alkaline stability was thoroughly investigated by Marino and Kreuer. Their study showed that spirocyclic quaternary ammonium have good stability in alkaline condition. To date, there is few work on spirocyclic quaternary ammonium-based AEMs, and to understand the properties of this type of AEMs, a systematic study is needed. In the present work, N,N-diallylpyrrolidinium bromide [DAPy][Br] was synthesized and used as hydrophilic phase in the polymeric membranes. The purity and chemical structure of [DAPy][Br] were confirmed by 1H NMR measurements. However, poly(N,N-diallylpyrrolidinium bromide), the homopolymer of [DAPy][Br], shows poor film forming properties, and it is very soluble in water. Therefore, styrene and acrylonitrile were chosed to synthesize the copolymers with [DAPy][Br] due to the ease of processing, good mechanical properties and chemical resistance. A mixture of styrene/acrylonitrile, [DAPy][Br], divinylbenzene and benzoin ethyl ether was stirred to obtain a homogeneous solution. Then, the mixture was casted onto a glass mold irradiation with UV light. The prepared spirocyclic quaternary ammonium-based membranes were immersed in 1 mol/L KOH solution at 60°C for 24 h to convert the anion of membrane from Br-to OH-. Then the membranes was immersed in deionized water and washed with deionized water until the pH of residual water was neutral. In summary, a series of spirocyclic quaternary ammonium-based AEMs were successfully designed and prepared via a simple synthetic strategy. The resultant AEMs demonstrated great potential for alkaline anion exchange membrane fuel cell applications based on its good thermal stability, sufficient mechanical properties and high conductivity. The ion exchange capacity can be controlled by change the mixture ratio, and the swelling ratio, water uptake and ion exchange capacity of the spirocyclic quaternary ammonium-based membranes increase with the increasement of the content of [DAPy][Br] in the membranes. The transparent and mechanically robust spirocyclic quaternary ammonium-based AEMs show high conductivity up to 7.29×10-2 S/cm at 80°C, and all the membranes showed conductivity up to 1×10-2 S/cm at room temperature. In addition, all the AEMs synthesize in this work showed excellent long-term alkaline stability at elevated temperature. The spirocyclic quaternary ammonium-based AEMs with an aliphatic backbone exhibit high alkaline stability, which will open up new prospects for the preparation of AEMs with excellent alkaline stability and high conductivity.