【作者】 曾松军；

【导师】 徐伟箭；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2011， 博士

【摘要】 质子交换膜燃料电池是第五代燃料电池,相对于其他燃料电池具有转化效率高、启动快、比功率和比能量高等优点,是公认的最有发展前景的电化学能量转化装置之一,非常适宜用做便携式电源和分散型电站。质子交换膜作为其关键部件之一,直接影响到其制作成本及工作效率。研究低成本、高效率的质子交换膜将会对质子交换膜燃料电池的大规模应用产生巨大的推进作用。杂化材料是近年来材料研究的热点之一,它将有机物和无机物的优点相结合,因此具备普通材料所不具备的优异性能。而聚倍半硅氧烷是杂化材料中非常重要的一类,一般通过简便的溶胶-凝胶法进行制备。聚倍半硅氧烷基材料通常具有耐热性好、耐腐蚀性强、易于功能化等优点,将其应用于高温质子交换膜领域是一项既有意义也富有挑战性的工作。本文以碱性聚倍半硅氧烷为基体制备了一系列酸-碱型高温质子交换膜,并对其各种性能进行了研究,尤其对其质子传导机理进行了深入的阐释,具体内容如下：(1)以N-(2-氨乙基)-3-氨丙基三甲氧基硅烷(AAS)为单体,通过其在硫酸或者磷酸的水溶液中的溶胶-凝胶反应制备了PAAS-R质子交换膜。通过FTIR和29Si CP NMR对其化学结构进行了表征。这种酸-碱型杂化质子交换膜具有良好的热稳定性(高达300℃),在不同的温度范围内表现出不同的电导率。光学显微镜和SEM分析发现PAAS-HSO4膜中原位生成了大量的纳米粒子。AFM和EDS分析表明此种纳米颗粒的表面富集了软性的有机链段。AFM的RMS分析表明加水量越少,PAAS-HSO4膜的粗糙度越大,并且质子电导率越高。但是PAAS-H2PO4膜的表面非常光滑均一,其质子电导率也对粗糙度和加水量并不敏感。以上结果均表明,PAAS-HSO4膜较高的电导率是由于硫酸本身的电离能力较强,还因为其拥有着不同于PAAS-H2PO4的结构。最后,推测了一种能够很好的解释以上现象的质子传导机理,并且为在交联型无水质子交换膜中构造有效的质子传递通道提供了一种方法。(2)首先通过环氧基团的开环反应制备了一种有机链段含有三唑基团的新型硅氧烷单体,然后通过溶胶-凝胶法制备了PGA-xH3PO4系列质子交换膜。通过FTIR表征了其分子结构。通过SEM对其断面形貌进行了分析。TGA表明这种类型的质子交换膜在250℃下能够稳定工作。所有膜的质子电导率对温度都呈现出Arrhenius(阿尔尼乌斯)行为。膜的质子电导率随着酸含量的增加而增加,随着温度的升高而升高。在无水环境中,PGA-1H3PO4,PGA-2H3PO4与PGA-3 H3PO4在200℃时的电导率分别为1.48×10-3,1.07×10-2与1.43×10-2 S/cm.FTIR结果表明,加入的磷酸破坏了原有的PGA的氢键网络,将更加有利于三唑环的取向,从而促进了质子的跳跃。在PGA-2H3P04中,多余的磷酸会产生“桥”的作用,也有利于质子的有效传递。(3)以AAS为单体,在PVA与磷酸的水溶液中通过溶胶-凝胶法制备了PAAS-P-xPVA薄膜。用FTIR表征了其化学结构,并研究了其成膜性与酸含量之间的关系。PAAS-P-xPVA系列质子交换膜具有非常好的热稳定性,能够在300℃下稳定工作。此系列膜的无水质子电导率与温度之间的关系呈现出阿尔尼乌斯行为。当PVA含量从10%增加到15%时,质子电导率骤然下降。通过AFM与SEM分析发现,PVA含量在15%和20%时,膜中出现了较大尺度的相分离。这种现象不仅导致了膜质子电导率的下降,也导致了膜的机械性能出现了较大程度的下降。以上结果均表明,PVA含量在≤10%时,有利于提高体系酸含量、成膜性和机械性能,而且对质子电导率的影响较小。(4)以GA为单体,通过在PVA与磷酸的水溶液中的溶胶-凝胶反应制备了一种既能够在干燥环境中使用,也能够在潮湿环境中使用的“双栖”质子交换膜。此种新型的质子交换膜由三个部分构成：1.具有两个碱性位点的聚硅氧烷(侧链中的-N-,三唑环中的=N-)；2.作为质子源的磷酸；3.具有良好成膜性的并且能够在有水环境中锚定磷酸的PVA,所有的膜均在200℃下稳定。断面SEM表明PVA与聚硅氧烷之间在PVA含量较高时会发生一个相转变。此系列膜的质子电导率均在无水和有水两种环境中进行了测量。在25℃到120℃之间测试了有水质子电导率,未经水浸泡和经水浸泡过后的膜的质子电导率分别在0.019～0.068和0.009～0.031 S/cm范围内。在干燥环境中150℃时,这些膜的质子电导率在0.0047～0.021 S/cm范围内。以上结果表明所得膜在无水和有水环境下均表现出较好的质子电导率,有潜力应用于聚合物电解质燃料电池中,因此也称之为“双栖质子交换膜”。更多还原

【Abstract】 Proton exchange membrane fuel cells (PEMFCs) are the fifth generation of the fuel cells. There are a lot of advantages of the PEMFCs, such as efficient energy transformation, fast initiation, high power density and high specific energy. It is accepted that PEMFCs are one of the most promising electrochemical energy conversion devices. PEMFCs are suitable for portable and distributed power applications. PEM is one of the key items of the PEMFCs. It directly influences the cost and the efficiency of the PEMFCs. The research on the PEM will be helpful to the wide application of the PEMFCs.Hybrid materials is one of the hot materials in recent years, it combines the advantages of the organic and inorganic materials. So, hybrid materials have the excellent performance comparing with common materials. The Polysilsesquioxane is an important class in the hybrid materials. It is usually synthesized by sol-gel method. Polysilsesquioxane based materials typically have good heat resistance, corrosion resistance, easy functionalization, and so on. Thus, application of polysilsesquioxane to areas of high temperature proton exchange membrane is a meaningful and challenging work. In this paper, a series of acid-base type of high temperature proton exchange membranes based on basic polysilsesquioxane system were studied. Particularly the mechanism of the proton conduction in these membranes, as follows:(1) Inorganic-organic hybrid proton exchange membranes were prepared via sol-gel reaction of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AAS) in a sulfuric or phosphoric acid aqueous solution. The chemical structures of these membranes are characterized by means of Fourier transform infrared (FTIR) and 29Si cross polarization nuclear magnetic resonance (29Si CP NMR). Those acid-doped membranes were stable at temperatures up to about 300℃and showed varied conductivities at different temperature ranges. Optical Microscopy and Scan Electron Microscopy (SEM) analysis revealed that the introduction of H2SO4 led to the generation of nanoparticles in situ. Atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS) results indicated that these nanoparticles were wrapped by the soft organic side chains. Root-mean-square (RMS) roughness measured by AFM demonstrated that lower water addition during synthesis led to rougher surface and higher conductivity of H2SO4-doped membrane, while the surface of H3PO4-doped membrane remained smooth and clean, and the conductivity did not show significant change by varying water additions. All those results demonstrated that the higher conductivity of the H2SO4-doped membrane achieved was contributed to not only the dissociation of the counter anion but also the morphology of the membrane. Finally, we proposed a potential mechanism for the proton conduction in such acid-doped membranes. This mechanism could possibly provide a method to construct effective proton channels in the cross-linked anhydrous proton exchange membranes.(2) In the present work, H3PO4-doped 1,2,4-triazole-polysiloxane proton conducting membrane is successfully prepared by sol-gel reaction. The molecular structure of the PGA-xH3PO4 is confirmed via FTIR. Thermogravimetry (TG) analysis shows that the samples were thermally stable up to approximately 250℃. The fracture surface morphology of the materials is characterized by SEM. The temperature dependence of proton conductivity of all the membranes exhibits an Arrhenius behavior. The proton conductivities of these membranes increase with dopant concentration and the temperature. In an anhydrous state, the proton conductivity of PGA-1H3PO4,PGA-2H3PO4 and PGA-3H3PO4 is 1.48×10-3 1.07×10-2,1.43×10-2 S/cm at 200℃, respectively. According to FTIR results, the added H3PO4 is presumed to break up the hydrogen-bonding network of pure PGA, facilitating ring-reorientation and thus Grotthus mechanism proton transport. In PGA-2H3PO4, the extra H3PO4 may act as a bridge providing effective proton conduction. Therefore the proton conductivity of PGA-2H3PO4 is greatly improved compared with PGA-1H3PO4.(3) The development of anhydrous proton exchange membrane is critical for the polymer electrolyte membrane fuel cell PEMFC operating at intermediate temperature (100～200℃). In the present work, inorganic-organic hybrid proton exchange membranes were prepared via sol-gel reaction of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AAS) and PVA in a phosphoric acid aqueous solution. The chemical structure of the hybrid membrane was confirmed by FTIR. The film-forming capacity and acid content of these membranes were enhanced by the introduction of the PVA. Those PVA-doped acid-base membranes were stable at temperatures up to about 300℃.The proton conductivities of the membranes were measured under anhydrous conditions. The dependence of proton conductivity to temperature of all membranes showed an Arrehnius behavior. There was a visible drop of conductivity from 10% to 15% PVA content. The surface and fracture surface morphology of the membrane was observed by AFM and SEM, respectively. A large scale phase separation was appeared at 15% or 20% PVA content which led to the decreased tensile strength and proton conductivity of the membranes. All the results suggest that appropriate PVA doping level (≤10%) was helpful to the membrane formation and improved the mechanical property of the membrane but with little effect on the proton conductivity.(4) Amphibious proton exchange membranes which could be used under both wet and dry conditions were prepared by sol-gel method in this work. Those novel hybrid PEMs were constructed by three parts:1) Polysiloxane with two basic sites (-NH-on the pendant and=N-in the triazole); 2) H3PO4 as the proton source; 3) Poly(vinyl alcohol) (PVA) which had good film-forming capacity and ability to anchor the H3PO4 under wet conditions. The resulting hybrid membranes were thermally stabilized up to 200℃. A matrix-change between polysiloxane and PVA could be observed at a high PVA doping level. The proton conducting property of these membranes was investigated under both hydrous and anhydrous conditions. From 25 to 120℃, the non-soaked and soaked (soaked in the water) membranes showed the proton conductivity of 0.019～0.068 and 0.009～0.031 S/cm at 100% relative humidity (RH), respectively. Under completely dry conditions, the proton conductivity of these membranes showed large dependence on the temperature and the proton conductivity of 0.0047～0.021 S/cm was achieved at 150℃for these membranes. The excellent performance of these hybrid membranes under both wet and dry conditions demonstrated that they have potential use as electrolytes in PEMFCs operating either in a watery or in a water-free environment and so called "amphibious" proton conducting membranes.更多还原