节点文献
燃料电池用阴离子交换膜的制备与性能研究
Preparation and Characterization of Anion Exchange Membranes for Fuel Cells
【作者】 熊鹰；
【导师】 刘庆林；
【作者基本信息】 厦门大学 ， 工业催化， 2009， 博士
【摘要】 直接甲醇燃料电池（direct methanol fuel cell，DMFC）具有燃料廉价易得、储运方便、高效无污染等特点，作为便携式移动电源在通信、军事、交通运输等领域有广阔应用前景。但是，DMFC面临两大主要难题：一是DMFC所用的质子交换膜阻醇性能较差，甲醇渗透严重；二是阳极催化剂对甲醇氧化活性低。碱性阴离子交换膜直接甲醇燃料电池（AMDMFC）采用了阴离子交换膜作为电解质，整个体系为碱性。在碱性介质中甲醇氧化速度比在酸性介质中要快，而且也不存在反应中间产物使电极催化剂中毒现象；在AMDMFC中，氢氧根基团与甲醇传递方向相反，可消除电渗析产生的甲醇渗透，从而可降低甲醇渗透速度。因此，AMDMFC能够克服DMFC的缺点。阴离子交换膜是碱性直接甲醇燃料电池的关键部件，本文在新型阴离子交换膜的制备方面进行了尝试，并对膜在AMDMFC的应用进行了评估。聚乙烯醇（PVA）是优先透水材料，具有良好的阻醇性和成膜性。我们通过亲电取代反应，采用2，3-环氧丙基三甲基氯化铵作为醚化剂，将季铵基团引入PVA主链，制备了季铵化聚乙烯醇（QAPVA）。添加戊二醛（GA）作为交联剂，制备了交联度不同的交联QAPVA膜。交联QAPVA膜的甲醇渗透率随交联度的增加而减少，优于Nafion117。由于QAPVA羟基收缩产生的尺度效应和羟基亲水性，使得QAPVA的甲醇渗透率随甲醇浓度的升高而降低。制备了带有季铵基团的季铵化壳聚糖（HACC），将不同量的HACC与QAPVA混合，GA作为交联剂，制备了交联度不同、组成不同的两种系列的QAPVA／HACC共混膜。复合膜的甲醇渗透率在5．68×10-7-4．42×10-6cm2·s-1，均小于Nafion117膜，且具有良好的电导率，膜的电导率为10-3-10-2S·cm-1。以正硅酸乙酯（TEOS）为前驱物，通过溶胶-凝胶反应，制备了二氧化硅（SiO2）含量不同的QAPVA／SiO2有机-无机杂化膜。无机粒子的加入，不仅增强了膜的热稳定性，降低了甲醇渗透率，而且膜的电导率也增强。杂化膜的甲醇渗透率比Nafion117低一个数量级，电导率最高可达1．4×10-2S·cm-1。通过氯甲基化、季铵化、碱化等反应，制备了OH型季铵化酚酞型聚醚酮（QPEK-C）阴离子交换膜。QPEK-C膜的热稳定性良好，抗氧化性能强，在3％H2O2溶液中浸泡1周，膜的质量和电导率变化较小。膜的阻醇性能良好，甲醇渗透率低于10-9mol·cm-2·min-1。但是由于接枝上去的季铵基团数量较少，使得膜的离子交换容量IEC仅为0．11mmol·g-1，电导率为1．6×10-3-1．4×10-2·cm-1。
【Abstract】 Direct methanol fuel cells （DMFC） have numerous benefits such as fuel cheapand available, easy fuel carriage, high efficiency, high power density and environmentfriendly. DMFC are expected to find wide application in communication, military andtransportation as a mobile power. However, there are two major technology problemsin DMFC. One is that the methanol diffusion resistance of proton exchangemembrane is poor. The other is slow methanol oxidation kinetics on the anodecatalyst.Alkaline anion exchange membranes for direct methanol fuel cells （AMDMFC）use an anion exchange membrane as polyelectrolyte and the whole system is basic.The methanol oxidative rate is faster in alkaline media than in acid. And there is noreaction intermediate which can make electrode catalyst poisoned. In AMDMFC, thedirection of OH- anion motion opposes that of the methanol flux through themembrane leading to an intrinsic reduction in methanol permeability. AMDMFC canovercome the drawback of DMFC.Anion exchange membrane is one of the key parts of AMDMFC. In this study,novel anion exchange membranes were synthesized and their application inAMDMFC evaluated.Poly （vinyl alcohol） （PVA） is a water-permselective polymer, which hasexcellent methanol resistant ability and film forming property. We used（2,3-epoxypropyl） trimethylammonium chloride （EPTMAC） as etherifying agent tointroduce quaternary ammonium groups into the structure of PVA throughelectrophilic reaction and produced quaternized PVA （QAPVA）. GA was added as across-linking agent and produced cross-linked QAPVA membranes with differentcross-linking degree. The methanol permeability of the cross-linked QAPVAmembranes decreased with increasing cross-linking degree, which is better thanNafion117 membrane. Because of dimensional effect caused by hydroxyl groups shrinking and water-permselective performance, the methanol permeability of thecross-linked QAPVA membranes decreased with increasing the methanolconcentration.Quaternized chitosan （HACC） which contains quaternary ammonium groups wassynthesized. Cross-linked composite membranes were synthesized with differentcontent HACC and QAPVA, and GA as a cross-linking agent. The methanolpermeability of composite membranes was 5.68×10-7-4.42×10-6 cm2·s-1. whichwas lower than that of Nafionl17 membrane. The conductivity of the compositemembranes is 10-3-10-2 S·cm-1.The QAPVA/SiO2 hybrid membranes with different SiO2 content weresynthesized with QAPVA and TEOS as precursor through a sol-gel reaction. Theintroducing of inorganic particles increased the thermal stability and conductivity, anddecreased the methanol permeability of the hybrid membranes. The methanolpermeability of the hybrid membranes was one order of magnitude lower than that ofNafionl 17 membrane. The best conductivity of the hybrid membranes is 1.4×10-2S·cm-1.OH-form quaternized PEK-C （QPEK-C） membranes were synthesized throughchloromethylation, quaternization and alkalization reaction. QPEK-C membraneshave good thermal stability, excellent anti-oxidative performance. After staying in 3%H2O2 solution for one week, the mass and conductivity of the QPEK-C membraneschanged little. Methanol permeability of the QPEK-C membranes is lower than 10-9mol·cm-2·min-1. The quantity of introduced quaternary ammonium groups is small,which caused little IEC (0.11 mmol·g-1). The conductivity of the QPEK-C membraneswas from 1.6×10-3 to 1.4×10-2 S·cm-1.