【作者】 李冬杰；

【导师】 王宇新；

【作者基本信息】 天津大学 ， 化学工程， 2009， 博士

【摘要】 质子交换膜燃料电池(PEMFC)以其能量转化率高、低排放、能量和功率密度高等优点被认为是适应未来能源和环境要求的理想动力源之一。双极板是PEMFC的重要组成部分,它为电池分配燃料与氧化剂并串联相邻电池,其成本可占总成本的约40%,而高成本正是其走向实用化的一大障碍。寻找性能优良的材料和成本低廉的加工方法已成为燃料电池产业化技术研究中的重要课题。本论文着眼于PEMFC双极板的现实需要和未来发展,在开发高性能、耐高温的燃料电池双极板材料和工艺方面进行了新的探索和尝试。我们建立了石墨/聚苯硫醚复合双极板成型的烧结工艺。与采用较多的注塑成型工艺相比,其优势在于降低了生产上的设备投入,而且可以采用注塑工艺所不允许的高石墨含量,从而使双极板的材料费用更低而导电率更高;与模压工艺相比其优势在于提高了生产率。我们以价格低廉的天然鳞片石墨为板主体,选取耐高温的工程塑料聚苯硫醚为粘结剂,制备了石墨/聚苯硫醚复合板。考察了烧结工艺四要素、树脂含量对复合板导电性能、阻气性能、机械性能和耐腐蚀性能等性质的影响,对比了烧结制备复合板与模压制备复合板的性能。并首次考察了石墨/聚苯硫醚复合板导电性能与温度的关系以及复合板长时间置于高温下的导电性能。通过对工艺条件的探索,使烧结复合板的综合性能达到公认的PEMFC双极板技术指标。对于模压工艺制备的石墨/聚苯硫醚复合板,在适当的工艺条件下,PPS含量高于10wt%时,复合板的各种性能均能达到美国能源部提出的PEMFC双极板要求,而当PPS含量小于30wt%时,复合板的导电率都高于100S·cm-1。在相同树脂含量下,烧结复合板的导电性能和阻气性能低于模压复合板,机械性能高于模压复合板。烧结复合板和模压复合板的电阻都随着环境温度的升高而减小。在200℃时,两种复合板的导电性能都很稳定且都高于室温下的导电性能。复合材料双极板中的聚合物与扩散层接触的地方会产生较大的接触电阻,而且随聚合物含量增加接触电阻成快速增大的趋势,虽然有很多对复合材料双极板改性的研究,但往往降低了接触电阻,却又增大了体积电阻。为了解决这一问题,我们首次在石墨/酚醛树脂复合板的表面覆盖一层导电的膨胀石墨,采用模压工艺制备了膨胀石墨表面改性复合板。研究表明:不但改性复合板的接触电阻大大降低,而且随复合板中树脂含量的增加改性复合板接触电阻保持不变。膨胀石墨厚度较小时,改性复合板不但可以降低复合板接触电阻,而且可以降低复合板体积电阻。改性复合板在几乎没有降低复合板的阻气性和强度的情况下,大大降低了复合板的接触电阻和体积电阻。改性复合板耐腐蚀性达到了美国能源部的要求。氧化石墨烯具有较高的比表面能、良好的亲水性、良好的机械性能以及在水中较好的分散性,是一种优良的纳米材料,可以用于纳米复合材料的制备。目前对氧化石墨烯的研究还处于起步阶段,且关于氧化石墨烯和氧化石墨具体区别的研究还未见文献报道。因此我们制备了氧化石墨和氧化石墨烯,并通过对二者的表征首次总结出了氧化石墨烯和氧化石墨的异同。同时制备了氧化石墨烯/聚乙烯醇纳米复合膜,并考察了氧化石墨烯含量、热处理温度对复合膜机械性能和溶胀性能的影响。氧化石墨烯表面官能团的形式和氧化石墨的基本没有区别,但是通过元素分析可知超声会使氧化石墨表面的含氧官能团部分减少。氧化石墨烯的热稳定性较低,在高于170℃时官能团开始分解,而且氧化石墨烯的热稳定性略低于氧化石墨。与氧化石墨相比,氧化石墨烯在水中的分散性更好。氧化石墨烯能提高聚乙烯醇膜的玻璃化温度、拉伸强度以及断裂伸长率。氧化石墨烯/聚乙烯醇复合膜出现了各向异性的溶胀性能,而热处理以后复合膜的这种性能消失。复合膜热处理以后,氧化石墨烯上的含氧官能团与聚乙烯醇上的羟基发生脱水反应。当氧化石墨烯含量为0.1wt%,150℃热处理复合膜的弹性模量提高了168.59%。更多还原

【Abstract】 Polymer electrolyte membrane fuel cell (PEMFC) is recognized as a new alternative to the present power sources because of its high efficiency, low emission, high energy and power density. Bipolar plate is an important part in FC, which distributes fuel and oxidant to the electrodes of FC and provides electronic connection between single cells. Its cost can account for as high as 40% of a FC stack, while the high cost of FC is a key obstacle to its wide application. Therefore, searching materials and manufacturing methods for high performance and low cost bipolar plate has been very important. With the above background, new materials and manufacturing methods for bipolar plates are explored in this study.The nature graphite/polyphenylene sulfide (NG/PPS) composite plates were manufactured using a sintering process. Compared with injection process commonly used, our method is more competitive for much lower equipment cost and high graphite content allowed in the plate, which then leads to lower cost of the plate and higher conductivity. Compared with moulding process, our method has higher efficiency.The heat-resistant PPS were selected to mix with the low-cost natural graphite. The variation of electrical properties, gas tightness, mechanical properties and corrosion resistance with sintering technological conditions and polymer content was studied. The property of sintered composite plates was compared with the property of molded composite plates, and the conductivity in high temperature was also studied. The sintered composite plate with PPS content 20wt% can meet the demand for the bipolar plate materials. The molded composite plate with PPS content 10～30wt% can meet the demand of the American DOE. Compared with the molded composite plates, the sintered composite plates have lower H2 permeability, higher flexural strength and lower conductivity, when the PPS content is the same in the tow type of composite plates. The conductivity of the tow kinds of composite plates at 200℃is higher than the conductivity at the room temperature.The contact resistance between the composite plate and the gas diffusion layer is high because of the nonconducting polymer in the composite plate, and the contact resistance increases rapidly with the polymer content increasing. In order to decrease the contact resistance, expanded graphite (EG) was used to modify the natural graphite/phenol formaldehyde (NG/PF) resin composite plate. Results show that the modification considerably reduced contact resistance versus bare NG/PF plates. The extant of the decrease in contact resistance is influenced by the expanded volume of EG used. The total electrical resistance, as expressed by volume resistance, can be reduced by applying EG layers to NG/PF composite plates. The reduction of total resistance is more remarkable for the composite plates with high PF content because the bulk resistance of the EG layer can be well compensated by the decrease of contact resistance at a proper range of EG layer thickness.Graphene oxide with high surface energy, high hydrophilic properties, good mechanical strength, can be used for preparation of nano composite membrane. So far, the study of graphen oxide is still in primary stage, and we have not seen the article about the difference between grapheme oxide and graphite oxide. For the fist time, we prepared grapheme oxide and graphite oxide and obtained the same and the difference by characterized them. We also adopted the graphene oxide in preparation of graphene oxide/polyvinyl alcohol (PVA) composite membrane, and investigated the properties.The surface functional groups of graphene oxide are the same as that of the graphite oxide. Ultrasonication can destroy the surface functional groups of the graphite oxide, as revealed by elemental analysis. The surface functional groups of the graphene oxide decomposed at 170℃, and the thermal stability of graphene oxide is lower than that of graphite oxide. Compared with graphite oxide, graphene oxide is much easier to distribute in water.Graphene oxide increases the glass temperature and the tensile strength of the PVA membrane. Graphene oxide/PVA composite membrane has anisotropic swelling property, but heat treatment would destroy this property. The oxygen functional groups of graphene oxide react with the hydroxyl groups of PVA after the composite membrane heated. Compared with the no heat treatment composite membrane (graphene oxide 0.1wt%), the elastic modulus of the heat treatment composite membrane at 150℃increases 168.59%.更多还原