Study On The Preparation Of PdSn@Pt/C,Pt/Ag-C Electrocatalysts For Polymer Fuel Cells

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.