【作者】 张淑贤；

【导师】 田燕妮；

【作者基本信息】 山西大学 ， 无机化学， 2010， 硕士

【摘要】 甲酸作为甲醇和氢气的替代燃料,在聚合物电解质膜燃料电池中的应用,越来越受到关注。特别是作为便携式电源装置,燃料甲酸具有很多不可比拟的优点：甲酸无毒,常温下不易燃；由于HCOO-离子和SO3-离子之间存在排斥作用,所以甲酸透过Nafion膜的渗透率远低于甲醇；在DFAFCs中甲酸的最高操作浓度可达到20 M,使得整个体系的能量密度增大,弥补了甲酸单位体积能量密度比甲醇小的缺点,提高了燃料电池的性能；此外,甲酸的理论开路电位(1.45 V)高于氢气和甲醇。有研究显示,Pd催化甲酸氧化反应的电活性高于Pt,这是因为甲酸在Pd催化剂上是通过直接途径被氧化的,不生成COads毒性中间产物,提高了催化剂的效率。所以,近年来,有一些课题组致力于Pd和Pd基复合金属催化剂对甲酸氧化的催化性能研究。在本论文的工作中,以Au和Ru为第二种金属,分别加入到Pd催化剂中,用浸渍法合成了Pd/MWCNTs, PdAu/MWCNTs, PdRu/MWCNTs三种不同组分的纳米催化剂。与Pd催化剂做对比,研究Pd-Au、Pd-Ru复合催化剂对甲酸氧化反应的催化性能。(1)以功能化的多壁碳纳米管为载体,采用温和的液相还原法合成了不同质量比的PdAu纳米催化剂,并研究了其对甲酸氧化反应的催化性能。制得的电催化剂用XRD和TEM表征了其元素组成、形态、分散度和粒径大小。电化学方法测试了其催化活性,数据显示,4Pd1Au/f-MWCNTs催化剂比单一金属Pd/f-MWCNTs催化剂拥有更高的电化学活性表面积、更好的催化氧化性能和更优的催化稳定性。(2)以羧化的多壁碳纳米管为载体,采用传统的浸渍还原法合成了纳米Pd、纳米Pd-Ru催化剂。TEM图显示出Pd和Ru纳米粒子很好的附着在碳纳米管的侧壁,分散状况良好。XRD图谱证实了Pd和Ru两种金属粒子以合金的形式共存。而电化学测试结果显示,4Pd1Ru/MWCNTs催化剂的电催化活性和稳定性都好于Pd/MWCNTs催化剂。更多还原

【Abstract】 As an attractive candidate to replace methanol and hydrogen, formic acid (FA) has considerable advantages in polymer electrolyte membrane (PEM) fuel cells for powering portable devices. FA is nontoxic, nonflammable and has lower penetration efficiency through the Nafion membrane to methanol due to the repulsion between HCOO- and SO3- ions. These extraordinary properties of FA make it possible to use highly concentrated fuel solutions in DFAFCs, which compensates the low volumetric energy density of FA and improves the overall cell efficiency. In addition, FA has a higher electronic motive force (EMF,1.45 V) than either hydrogen or methanol. Recent studies showed that the electrocatalytic activity of Pd for FA oxidation is higher than that of Pt, because Pd catalysts can overcome the CO poisoning effect mainly through the direct pathway. In many studies, considerable effort has been made to develop the Pd and Pd-based binary metallic catalyst.In present work, Pd/f-MWCNTs, a series of bimetallic PdAu/f-MWCNTs catalysts and Pd/MWCNTs, PdRu/MWCNTs were synthesized by a mild impregnation reduction method. FA oxidation reaction of the catalysts were investigated, and compared with that of Pd catalyst.(1) PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4PdlAu/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. So the suitable addition of Au to Pd/f-MWCNTs can promote the catalytic activity and poisoning tolerance of Pd catalyst for the electrooxidation of formic acid. The Au nanoparticles show potential in further improving the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).(2) We have developed nano-Pd, nano-PdRu catalysts supported on multi-walled carbon nanotubes. TEM and XRD studies indicated that so many fine Pd and Ru nanoparticles with well uniformed dispersion formed on the outer walls of the CNTs, and the coexistence of Pd and Ru particles in the catalyst. Further more, electrochemical results showed that the 4Pd1Ru/MWCNTs catalyst, weight ratio of 4Pd to 1Ru, exhibited distinctly higher catalytic activity and better stability on formic acid electrooxidation than the Pd/MWCNTs catalyst. So the nano-Ru improves potentially the performance of Pd-based electrocatalysts for the DFAFCs.更多还原