【作者】 张伟；

【导师】 王荣方； 雷自强；

【作者基本信息】 西北师范大学 ， 高分子化学与物理， 2011， 硕士

【摘要】 高分子燃料电池是一种直接以电化学反应方式将燃料的化学能转变为电能的发电装置,是一种绿色能源技术。对解决目前世界面临的“能源短缺”和“环境污染”这两大难题具有重要意义,被认为是21世纪的最为重要的能源动力之一。其中,低温燃料电池如质子交换膜燃料电池（PEMCF）、直接甲醇燃料电池（DMFC）,具有工作温度低,启动快,能量转化率高等特点,是未来电动汽车、野外电站、便携式电源的理想替代电源,是燃料电池优先发展的类型。而实际上,燃料电池的性能与理论性能还有很大的差距,存在着一些技术上的难题,如:醇氧化的动力学过程非常缓慢;液体醇通过聚合物电解质膜渗透到阴极产生混合电位导致电池系统效率降低;燃料电池阴极氧还原动力学过程缓慢,具有较高的过电位等。因此制备和寻找高活性的电催化剂是提高燃料电池性能降低其使用成本的重要途径,也成为研究者们孜孜以求的目标。本论文的工作主要围绕如何获得高活性低铂催化剂这一主题,制备低铂催化剂。采用X-射线粉末衍射（XRD）、透射电镜（TEM）、X-射线能量色散谱（EDX）等手段对催化剂结构进行了表征。采用循环伏安法、线性扫描法、计时电流法等电化学方法研究了催化剂在酸性溶液中的氧还原反应及甲醇氧化反应。具体见如下的三部分:第一部分高活性碳载PdSn@Pt核壳结构催化剂催化氧还原通过两步合成法制得一种低成本高活性的核壳结构催化剂。X-射线衍射（XRD）和透射电子显微镜（TEM）测试结果表明,该催化剂微粒分散良好,具有大的比表面积,平均粒径为5.6 nm。循环伏安及线性扫描结果表明,该催化氧还原活性明显高于商业Pt/C催化剂。其具有如此好的催化性能源于金属Pt和PdSn之间的协同效应。第二部分高效碳载PdSn@Pt核壳结构催化剂催化甲醇氧化改良的方法制得了一种用贵金属铂量最低,同时具有高活性的核壳结构的催化剂PdSn@Pt/C催化甲醇。这种核壳结构通过透射电子显微镜,X-射线衍射,X-射线光电子能谱以及循环伏安得以确认。其催化甲醇的活性是商业PtRu/C活性的3.64倍,PdSn@Pt/C催化剂具有这么好的催化活性归因于几种金属间的协同作用。该合成方法简单经济,适合于大规模的工业生产。第三部分高效Pt/Ag-C催化剂催化甲醇氧化Pt/Ag-C催化剂的制备与表征。采用置换反应的方法将铂沉积到碳载Ag/C上,得到了一种低价、高活性的甲醇氧化催化剂。电化学测试结果发现:Pt/Ag-C催化剂具有比PtAg/C和Pt/C催化剂更大的电化学活性。此外,Pt/Ag-C电极在催化氧化甲醇过程中产生的单位质量峰电流更是高达1.20 A·mg^-1Pt,是PtRu/C催化剂的3.2倍,是Pt/C催化剂的18.5倍。该研究进一步改进了制备低铂催化剂方法,对减小铂用量制备优异的燃料电池催化剂带来了希望。更多还原

【Abstract】 High Polymer Fuel cell is adevice that can turn chemical energy into electrieal energy through eleetroehemieal reaetion without combustion and is of great importance in solving the seareity of energy sourees and environmental pollution,so it is regarded as one of the most important power resources in the 21 century. Low temperature fuel cells such as PEMFC、DMFC can work at low temperature with the adventages of quiek start and high energy effieieney. They can be potentially used for eleetric car、field power plant and potable equipment.However,there is large distance between the practical DMFC performance and the theoretieal performance. For example, the crossover of liquid alcohol through the polymer electrolyte membrane into the cathodic compartment results in a decrease in the efficiency of the system. At the same time, oxygen reduction reaction (ORR) has a sluggish kinetics and results in high overpotential. Synthesizing and searehing for eleetroeatlasyts with high activity are the mportant aooroach to improve DMFC performance, which also become to be the endlessly goal for researehers.The thesis mainly focuses on high utilization of platinum in the catalysts. To match this requirement, a series of low-Pt catalysts for ORR and methanol oxidation are designed and prepared by several methods. And the catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX), etc. It was found that these catalysts showed quite good activity for ORR and methanol oxidation in fuel cells. The thesis is consists of three parts and the research details are as follows:PartⅠ: High performance carbon-supported core@shell PdSn@Pt electrocatalysts for oxygen reduction reactionA low-cost and high performance PdSn@Pt/C catalyst with core–shell structure is prepared by two-stage route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations show that the composite catalyst particles distribution is quite homogeneous and has a high surface area and the PdSn@Pt/C catalyst has an average diameter of ca. 5.6 nm. The oxygen reduction reaction (ORR) activity of PdSn@Pt/C was higher than commercial Pt/C catalyst. Catalytic activity is studied by cyclic voltammetry. High electrocatalytic activities could be attributed to the synergistic effect between Pt and PdSnPartⅡ: An effective carbon-supported pseudo-core@shell electrocatalysts for methanol oxidationA core-shell nanostructure of PdSn@Pt/C catalyst is synthesized with minimal use of Pt and shows exceptionally high catalytic activity towards the electrooxidation of methanol. The core@shell nanostructure is confirmed by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammetry. The Pt mass activity of PdSn@Pt/C catalyst for methanol oxidation is about 3.64 times as large as the PtRu/C catalyst. High electrocatalytic activities could be attributed to the synergistic effect between Pt and PdSn. The present synthesis route is very facile and economical, which may be suitable for large-scale production of catalysts with low-cost and high activity.PartⅢ: An effective carbon supported Pt-Ag catalyst for methanol oxidationA high performance Pt/Ag-C catalyst for methanol oxidation is prepared by deposited Pt onto the carbon supported Ag/C nanoparticles using replacement reaction. Electrochemical results show that the Pt/Ag-C catalyst has much larger Pt active than that of the PtAg/C and Pt/C catalyst. Furthermore, the mass specific anodic peak current is 1.20 A mg-1Pt for methanol oxidation on the Pt/Ag-C electrode, an increase by a factor of 3.2 times and 18.5 times as compared to Pt/C and PtAg/C, respectively. The studies sheds light on the advanced way to reducing Pt loading while has excellent electrocatalysts activities for polymer fuel cells.更多还原