三维开骨架杂化固态质子导体多晶薄膜制备和导电性质

A fuel cell, a device that converts the chemical energy from fuel into electricity through a chemical reaction with oxygen or another oxidizing agent, has high energy efficiency and less pollutant emission. The wide applications of full cell promote to explore new types of solid state proton conducting materials. Lots of proton conductors, including Nafion and other organic polymer as well as perovskite-type ceramic oxides and phosphates and so on, have been reported so far and some of them have been commercially used, however, it has made little progress to discover the proton conducting materials operating at the temperatures between 100 and 500 C, so-called the intermediate temperature proton conductors. In this study, we will design and prepare three classes of open-framework coordination polymers, including Prussian blue analogues, phosphates-based and clustered chalcogenides-based hybrids, and select ones with high thermal stability and stable to water, acidic and basic environments as new types of intermediate temperature proton conductors, furthermore, we will fabricate their crystalline films/membranes on the porous supports, such as alumina, titanium dioxide, glass and non-woven fabrics using the layer-by-layer growth, the solvothermal reaction growth in situ or the secondary growth on seeding layer approaches. We will characterize the films/membranes using the modern techniques, such as SEM, AFM, XPS, EDS, X-ray powder diffraction and electron diffraction, and investigate the binding interactions between the film and the surface of support combined the experimental and theoretical approaches to better understand the relationship between the surface nature of support and morphology of film/membrane. Our target is to get the integrated, highly crystalline and stable in water and acidic and basic environment open-framework films/membranes of proton conducting materials, which are probably applied in a fuel cell operating at the intermediate temperature region.

燃料电池是一种将化学能直接转化为电能的电化学装置，具有高能量转换效率和低污染物排放等优点，其快速发展促进了固态质子导体深入研究。尽管一些高分子、钙钛矿陶瓷和酸式含氧酸盐质子导体已被商业化使用，但是工作温度在100-500度之间高性能质子导体仍然匮乏。在本项目中，我们从类普鲁士蓝、磷酸盐和金属硫簇等三个系列三维开骨架杂化晶体中选择高热稳定性、对水、酸和碱环境稳定、高质子电导率杂化质子导体，拟通过原位反应、预置晶种、二次晶体生长等多晶薄膜制备方法，在氧化铝、无纺布和石英玻璃等多孔支撑体上，制备形貌和微结构可控、晶粒分布均匀、致密和规整质子导体薄膜。结合电子显微、原子力显微、电子能谱、X-射线粉末衍射和电子衍射等材料表征技术与界面结构模拟理论手段，研究支撑体表面性质（化学组成、界面键等）与质子导电薄膜形貌之间相关性，为制备形貌可控、薄膜与支撑体结构匹配、高质子电导率的中温质子导体奠定应用基础。

固态质子导体能选择性允许质子传输，在燃料电池、液流电池、电化学显示、电化学传感和电化学反应等器件中，固态质子导体被广泛应用。近十年来，晶态多孔质子导体受到极大关注，这类材料包括MOFs、COFs、开骨架磷酸盐和金属硫族化合物等，其孔道结构便于质子迁移。在本项目研究中，我们对Zr-MOFs、开骨架磷酸盐和金属硫族化合物等三个系列多孔质子导体的晶体结构、热稳定性、耐酸性、质子导电性以及成膜性能等展开了系统和深入研究。我们研究了以Zr6O4(OH)4(-CO2)n（其中，-CO2代表羧基；n = 6, 8, 10, or 12）多酸锆氧簇为次级结构单元的MOF-801、MOF-802和MOF-808的晶体结构、质子导电性及其传输机理等。此类Zr-MOFs框架热稳定性高（~400度）；在6 M盐酸中稳定好；在98% RH环境中，其室温质子电导率达10-3~10-2 S cm-1，是性能优异的多酸型质子导体。其纳米晶易于制备，且与聚偏氟乙烯、聚乙烯吡咯烷酮等高分子可形成混合基质膜，当其质量百分比高达60%时，膜仍具较高机械强度；在98% RH环境中，室温膜质子电导率达10-3 S cm-1量级。尽管如此，其混合基质膜构建的H2/O2燃料电池却表现出较低功率密度，其内在原因值得进一步探索。开骨架磷酸盐质子导体虽然热稳定性高（>300度），但是在强酸性环境中，其化学稳定性差。在98% RH环境中，其室温质子电导率仅达10-5 S cm-1量级，甚至更低。开骨架金属硫族质子导体热稳定性高（>220度），耐酸性好（3 M硫酸中稳定）。在98% RH环境中，其室温质子电导率达10-3 S cm-1量级。在玻璃和二氧化硅支撑体表面，MOF-802能生长连续、结构致密的、微米厚度晶态薄膜。开骨架磷酸盐能生长连续、结构致密的晶态薄膜，然而，开骨架金属硫族质子导体难以形成连续、结构致密晶态薄膜。对挥发性酸（HCl、甲酸、乙酸）以及挥发性有机物（甲醇、乙醇、丙酮、二氯甲烷和硝基苯等），MOF-802晶态薄膜叉指电极表现灵敏的阻抗响应，可用于上述挥发性物质传感与检测。本项目研究揭示，多孔质子导体的导电性强烈依赖环境湿度，故而不适合应用于中温燃料电池，但在液流电池中具有潜在应用。