Synthesis and NMR Studies of Electron and Proton Conducting Mesoporous Nb, Ta and Ti Oxide Composites for Alternative Energy Applications

在中尺度（即20-500埃范围）上具有周期性孔隙率的材料的合成是当前研究的最活跃的领域之一。通过改变中孔之间的壁的结构的组成，可以针对各种应用定制各种各样的物理性质，例如选择性气体吸附或催化或不寻常的电子、光学或磁性。通过用改变介孔复合材料的性质的第二客体相浸渍这些材料的孔结构，可以产生在纯介孔固体中未观察到的协同效应。任何材料最基本的特性之一是其电荷传输行为，因为在无数催化或电子应用中，移动电子和质子通过固体是关键步骤。虽然存在无数具有周期性介观结构的无机材料的例子，但它们中很少有具有高电子传导性。这是因为介观结构的壁通常很薄，以具有任何程度的规则结构，这导致电子在陷阱中的定位，或者制造导电介观结构的合成条件与导致无机相中的导电性质的条件不相容。这是有问题的，因为具有高电导率和可变氧化态的高表面积多孔材料对于在Li电池中使用或作为用于需要电子迁移率的反应的催化剂载体材料是理想的。通过固体的质子传导性也很重要，特别是对于调节电荷从电化学电池一侧流到另一侧的燃料电池膜，但是作为最常用的燃料电池膜材料的具有质子传导磺酸盐基团的氟化聚合物Nafion具有低的脱水稳定性，这导致在超过120 ℃的温度下质子传导性降低。全氟磺酸也容易受到酒精通过结构的扩散，这是一个问题，因为许多燃料电池的设计使用酒精作为原料。由于这个原因，许多研究人员已经转向探索介孔材料/聚合物复合膜，这有望克服Nafion的问题。该提案中的研究旨在用各种试剂修改中孔Nb，Ta和Ti氧化物的结构，这些材料具有可变的氧化态和高酸度/质子传导性，以产生在一种情况下具有高电子传导性或金属行为的复合材料，以及在另一种情况下具有高质子传导性的复合材料，这取决于所使用的试剂。因此，中孔Nb、Ta和Ti氧化物将用试剂处理，以用S或Se取代表面氧化物，从而在材料的内表面上产生导电的硫化物或硒化物相，这将允许电子传输到金属氧化物下层。还将进行用聚苯胺或聚噻吩的电子传导聚合物纳米线浸渍孔以尝试利用这些单链聚合物作为通向孔通道壁上的金属氧化物中心的电子通路。然后将测试这些材料是否用作锂电池中的阴极材料，预计通过孔隙的电子迁移率将导致上级的充电和放电动力学，这是锂电池通常存在的一个问题。该提议的第二部分涉及用具有高质子传导性的磺化聚合物浸渍介孔Nb、Ta和Ti氧化物。在这里，预计中孔通道将通过在性能温度下保持水分来帮助克服Nafion的脱水问题，同时还限制醇通过膜的扩散。一旦合成，这些材料将在操作条件下作为燃料电池膜进行测试。

The synthesis of materials with periodic porosity on the mesoscale (ie 20-500 Angstrom range) is one of the most active areas of current research. By varying the composition of the structure of the walls between the mesopores it is possible to tailor in an enormous variety of physical properties for various applications such as selective gas sorption or catalysis or unusual electronic, optical or magnetic, properties. By impregnating the pore structure of these materials with secondary guest phases that modify the properties of the mesoporous composite, it is possible to create cooperative effects not observed in the pure mesoporous solid. One of the most fundamental properties of any material is its charge transport behavior because moving electrons and protons through a solid is a key step in myriad catalytic or electronic applications. While countless examples of inorganic materials with a periodic mesostructure exist, very few of them possess high electron conductivity. This is because the walls of the mesostructure are often two thin to possess any degree of regular structure, which leads to localization of the electrons in traps, or that the synthesis conditions to fabricate the conducting mesostructure are not compatible with the conditions that lead to conducting properties in the inorganic phase. This is problematic because a high surface area porous material with high conductivity and variable oxidation states would be ideal for use in a Li battery or as a catalyst support material for reactions requiring electron mobility. Proton conductivity through a solid is also important, especially for fuel cell membranes which regulate the flow of charge from one side of the electrochemical cell to the other, but Nafion, a fluorinated polymer with proton conducting sulfonate groups that is the most commonly used fuel cell membrane materials, possess low stability to dehydration, which leads to a decrease in proton conductivity at temperatures over 120 C. Nafion is also vulnerable to alcohol diffusion through the structure, which is problematic since many fuel cells are designed to use alcohol as a feedstock. For this reason many researchers have turned to the exploration of mesoporous material/polymer composite membranes, which promise to overcome the problems with Nafion. The research in this proposal sets out to modify the structure of mesoporous Nb, Ta and Ti oxides, materials possessing variable oxidation states and high acidities/proton conductivity with various agents to create composites with high electronic conductivity or metallic behavior in the one instance, and high proton conductivity in the other, depending on the agent used. Hence, mesoporous Nb, Ta and Ti oxides will be treated with reagents to replace the surface oxides with S or Se, hence creating a conducting sulfide or selenide phase on the inner surface of the material which will allow electron transport to the metal oxide under layer. Impregnation of the pores with electron conducting polymer nanowires of polyaniline or polythiophene will also be carried out to try to exploit these single strand polymers as electron pathways to the metal oxide centers on the walls of the pore channels. These materials will then be tested for use as cathode materials in Li batteries, where it is anticipated that electron mobility through the pores will lead to superior charge and discharge kinetics, an area of performance that is often a problem with Li batteries. The second part of this proposal involves the impregnation of mesoporous Nb, Ta and Ti oxides with sulfonated polymers with high proton conductivity. Here it is anticipated that the mesoporous channels will help overcome dehydration problems of Nafion by holding onto moisture at performance temperatures, while also limiting alcohol diffusion through the membrane. Once synthesized these materials will be tested as fuel cell membranes in operating conditions.