【作者】 李野；

【导师】 王策； 刘新才；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2014， 博士

【摘要】 由于低排放和高转换效率,燃料电池技术已被认为是最有前景能源技术之一。聚合物电解质膜（PEM）作为燃料电池的关键部件，它起着隔绝燃料和氧化剂，从阳极至阴极传导质子的作用。这就要求聚合物电解质膜具有下列性质：优异的质子传导性，良好的电绝缘性，高的化学稳定性和机械性能，低的燃料透过性和成本。目前，已经商品化用于燃料电池中的PEM主要是全氟磺酸系列膜，如Dupont公司的Nafion系列膜，因为它的质子传导性和化学稳定性十分优异。然而，高成本，低工作温度和高甲醇透过，限制了Nafion膜的广泛应用。目前已经开发出多种PEM材料如磺化聚芳醚酮，磺化聚芳醚砜，磺化聚酰亚胺，磺化聚芳醚腈和酸掺杂的聚苯并咪唑等。磺化聚芳醚酮类聚合物膜材料由于其具有良好的机械性能，优异的耐热性和质子传导性能，已经被作为聚合物电解质膜广泛地研究。然而，为了获得更高的质子传导率，就需要提高聚合物的磺化度，随之而来的，高磺化度聚合物膜在水中会过度吸水溶胀，严重影响机械性能，限制了它的进一步发展。本论文针对传统结构磺化聚芳醚酮材料存在的缺点，分别通过分子设计新结构、交联改性以及有机-无机复合等方法来制备新型聚合物电解质膜材料。首先，通过两步法将1,3,5-三氟苯羰基苯作为支化单体引入到聚合反应中，制备了一系列支化结构含量不同的支化磺化聚醚醚酮。支化磺化聚醚醚酮表现出了良好的溶解性，通过溶剂挥发法可以容易地制备出致密的膜材料。与线性聚合物膜相比，支化聚合物膜表现出增强的机械强度和更好的尺寸稳定性。虽然质子传导率由于支化结构的引入有所降低，但是甲醇渗透率降低的更多。相对于线性聚合物膜来说，支化聚合物膜表现出更高的化学稳定性。在80oC的Fenton试剂中，BSPEEK-10膜的破碎时间是267min，时长是相同磺化度的LSPEEK膜的4倍。采用磺酰氯作为磺化试剂，制备了磺化二氧化硅纳米粒子（SSA）。通过EDX和TEM，证实了这种简单方法的成功修饰，同时并没有导致二氧化硅微观形貌的改变。随后将磺化二氧化硅纳米粒子混入到支化磺化聚醚醚酮材料中，制备了一系列有机-无机复合膜材料。SSA纳米粒子的引入，增强了膜材料的热稳定性，提高了吸水率和质子传导率。同时，甲醇渗透率也有一定的升高，但不显著，这是因为存在亲水相中的SSA可以弯曲甲醇传递通道，阻碍其透过。选用带有胺基和巯基的两种硅烷偶联剂掺杂到支化聚醚醚酮中，并利用硅烷偶联剂的水解交联反应，制备了一系列硅烷交联膜材料。随后，将硅烷交联结构中的巯基氧化为磺酸基团。硅烷交联结构的引入，使得膜材料的吸水率下降，质子传导率有所降低。随着MPTMS引入量的增加，质子传导率有所提高，甚至高于纯膜。在80oC，BSPEEK/AP/MP膜的质子传导率达0.177S cm-1，高于相同磺化度的LSPEEK膜（0.152S cm-1）。而甲醇渗透率增加则不明显，并且低于相同磺化度的线性磺化聚醚醚酮膜。通过两步法成功制备了一系列不同磺化度含丙烯基的支化磺化聚醚醚酮。随后，在BPO的催化作用下，通过点击化学反应将苯并咪唑磺酸钠基团接枝到聚合物链段当中，并利用核磁和红外光谱确认了聚合物的结构。引入苯并咪唑磺酸钠基团，膜材料的质子传导性能显著增强。在80oC，最高的质子传导率达0.215S cm-1，远高于相同测试条件下的Nafion117膜（0.146S cm-1）。同时，吸水率和甲醇渗透率低于相同磺化度的线性聚合物膜材料，这主要是因为支化结构和磺酸基团与苯并咪唑之间的相互作用，使得膜结构更为致密。利用点击化学反应将可以与磺酸基团形成离子交联的苯并噁唑基团接枝到支化聚醚醚酮链段中。引入苯并噁唑基团，膜材料的热稳定性有所提高，因为苯并噁唑结构是一种耐热等级非常高的结构。这种离子交联膜材料表现出了很好的机械强度和尺寸稳定性，这主要是因为引入苯并噁唑基团后所形离子键限制了分子链段的运动。相对于未修饰的BSPEEK膜，BSPEEK-BO膜显示出了更好的氧化稳定性，在80oC的Fenton试剂中的破碎时间从165min增加到255min。此外，相对于纯BSPEEK膜，离子交联膜表现出了更好的阻醇性能，BSPEEK-BO膜的甲醇渗透率在3.25×10-7cm2S-1与5.18×10-7cm2S-1之间。更多还原

【Abstract】 Fuel cells have been regarded as one of the most promising alternative powersources due to its low emission and high conversion efficiency. The heart and key partof fuel cell is the proton electrolyte membrane (PEM) that separates fuel and oxidantand transports protons from anode side to cathode side. It is required that the PEMshould have the following properties: high proton conductivity under operatingconditions; good electrical insulation; high chemical and mechanical stability; lowpermeability of fuel, and low cost. Currently, the commercially availableperfluorinated acid membranes, such as Dupont’ Nafion membranes arepredominantly used in direct methanol fuel cell system as the PEM owing to theirhigh proton conductivity and excellent chemical stability. However, Nafon is limitedin extensive scale due to its high cost, low operating temperature and high methanolcrossover. A variety of alternative PEMs have been developed in the last decades forPEMFCs: such as sulfonated poly(arylene ether ketone)s, sulfonated poly(aryleneether sulfone)s, sulfonated polyimides, sulfonated poly(arylene ether nitrile)s andacid-doped poly(benzimidazole)s, and so on.In recent years, sulfonated poly(arylene ether ketone)s have attracted a great dealof attentions due to their remarkable properties, such as good mechanical property,excellent thermal stability, and high proton conductivity that can be controlled by thedegree of sulfonation. However, SPEEK with a high sulfonation degree (DS) aremuch swelling in water and low mechanical property under humid circumstance,which limit the end-use in fuel cells. In order to solve the shortcomings of thetraditional sulfonated poly(arylene ether ketone)s material, we have prepared newmolecular structure, cross-linked structure and organic-inorganic hybrid compositematerial to further improve their properties.First, novel branched sulfonated poly(ether ether ketone)s (BSPEEK) containingdifferent sulfonated degrees have been successfully prepared via a two-steppolymerization method. A series of BSPEEK were obtained by changing the amounts of branching agents. The branched polymers exhibited good solubilities, and could beeasily made into tough and smooth films by casting from the common polar aproticsolvents. Compared with linear polymer membrane, the branched polymer membraneshowed improved mechanical strength and better dimensional stability. Although theproton conductivity decreased upon the addition of the branching agent, lowermethanol permeability value was found. Incorporation of the branching structure, themembrane showed enhanced oxidative stability. The BSPEEK-10showed the bestoxidative stability and the elapsed time in Fenton’s reagent at80oC was267min,which was4times longer than that of LSPEEK.The silica sulfonic acid nanoparticles (SSA) were successfully prepared via thesimple sulfonation with sulfuryl chloride. The EDX analysis and TEM imagesindicated that the sulfonic acid groups were successfully grafted on the silica and thesulfonation process didn’t alter the morphological characteristics. Then theas-prepared nanoparticles were used as fillers to prepare nanocomposite hybridmembranes. The presence of SSA improved thermal property, water uptake andproton conductivity of hybrid membranes as compared with pure BSPEEK membrane.The methanol permeabilities of BSPEEK-SSA hybrid membranes were slightly higherthan that of pristine BSPEEK, because the hydrophilic inorganic filler existed aroundhydrophilic ion-cluster and could not react with methanol molecules, increasing thetortuosity of methanol transport channels.A novel series of silane-cross-linked membranes based on branched sulfonatedpoly(ether ether ketone)s were successfully prepared by hydrolysis-condensationreaction of silane coupling agents. The silane coupling agents were(3-Mercaptopropyl)trimethoxysilane (MPTMS) and (3-Aminopropyl)triethoxysilane(APTES). Subsequently, the thiol groups were easily oxidized to sulfonic acid groupsvia hydrogen peroxide oxidation. Due to the silane-cross-linked network structure, thecomposite membrane showed lower proton conductivity than BSPEEK. However, theproton conductivities of silane-cross-linked membranes increased with the increasingcontent of MPTMS, even higher than the pure polymer membrane. The highest protonconductivity of silane-cross-linked membranes was0.177S cm-1at80oC, which was much higher than that of LSPEEK (0.152S cm-1). The methanol permeabilities ofBSPEEK/AP/MP membranes were slightly higher than that of pristine BSPEEKmembrane due to the dense structure formed by the silane-crosslinking.A series of branched sulfonated poly(ether ether ketone)s containing propenylgroups have been synthesized using a nucleophilic polycondensation reaction.Subsequently, a thiol-ene click chemistry reaction between propenyl and thiol groupsresulted in a new series of copolymers containing benzimidazole sulfonic acid groups.The expected structures of the copolymers were confirmed by1H NMR and Fouriertransform infrared spectroscopy. By introducing benzimidazole sulfonic acid groupsonto the pendant position, the proton conductivity of BSPEEK membrane improvedsignificantly. The highest proton conductivity was0.215S cm-1at80oC, which wasmuch higher than that of Nafion117measured at the same condition (0.146S cm-1).Meanwhile, the water uptake values and methanol permeabilities of BSPEEK-BISmembranes were lower than those of LSPEEK with the same DS, due to the densestructure formed by branching structure and interaction between sulfonic acid andbenzimidazole groups.A series of novel branched sulfonated poly(ether ether ketone)s containingintermolecular ionic cross-linkable groups, benzoxazole groups, have been preparedfor direct methanol fuel cells. The benzoxazole groups (BO) were grafted onto thepolymer chain via a thiol-ene click chemistry reaction. Introduced BO groups, themembrane showed enhanced thermal stability due to the benzoxazole ring washeat-resistant structure. The ionic cross-linked membranes showed improvedmechanical properties and good dimensional stabilities, due to the compact membranestructure by the introduction of benzoxazole groups. Compared to BSPEEKmembrane, the oxidative stabilities of BSPEEK-BO membranes increased from165min to255min. Furthermore, compared with that of pure BSPEEK, the ioniccross-linked membranes exhibited extremely improved methanol resistance properties,from3.25×10-7cm2S-1to5.18×10-7cm2S-1, due to the branching structure and the interaction between sulfonic acid and benzi midazole groups.更多还原