【作者】 郭未宽；

【导师】 牛林；

【作者基本信息】 山东大学 ， 物理化学， 2009， 硕士

【摘要】 直接甲醇燃料电池由于结构简单、能量转化率高、适用范围广、无污染等优点,有望在许多应用领域替代化石能源,而备受重视。然而如何进一步提高Pt催化剂活性及利用率,开发高性能、低成本的催化剂,仍是甲醇燃料电池商业化中亟待解决的问题。本论文着重开展针对直接甲醇燃料电池阳极催化剂的优化制备、及其相关的载体材料的前期处理和功能化研究。主要内容如下:（1）对Vulcan XC-72炭黑载体材料进行有针对性的化学处理,改变其表面性能,以利于高分散、高活性Pt催化剂的制备。由于化学处理后的炭黑载体表面以氧化基团为主,难以有效吸附催化剂前驱体[PtCl₆]^2-离子,我们提出并实施了改变载体荷电性质的研究方案。结果表明,以氧化处理后的炭黑为载体所制备的Pt催化剂,其催化活性及稳定性明显提高。同时,通过对比实验发现,以经过不同程度氧化处理的炭黑为载体,所制备催化剂的催化性能有明显差别。氧化程度越高,催化剂催化活性越强。这不仅是因为氧化程度高的载体吸附[PtCl₆]^2-离子能力增强,导致Pt催化剂的分散性提高,同时也在一定程度上证实,这些氧化基团的存在对甲醇催化氧化有更好的促进作用。（2）利用多壁碳纳米管（MWCNTs）作Pt催化剂载体材料,首先对其进行电化学氧化处理,以增加碳管表面的亲水性和活性基团。然后采用先在氧化电位下聚集Pt（Ⅳ）络合物,再在酸性溶液中电化学还原的步骤,制备了分散性良好的Pt催化剂,并通过TEM、XRD等表面物理分析手段,对Pt催化剂微粒的粒径、分散状态及晶体结构等特点进行了表征。（3）使用具有富含羟、氨基结构特征的壳聚糖对多壁碳纳米管进行表面功能化,制备了壳聚糖包覆的多壁碳纳米管（c-MWCNTs）材料,并以此作载体通过浸渍法和溶胶法制备了Pt/c-MWCNTs催化剂。通过对比MWCNTs及c-MWCNTs作载体制备的催化剂的形貌及催化性能,结果发现用c-MWCNTs作载体制备的Pt催化剂,其分散性、催化活性等性能指标明显优于用未功能化的MWCNTs作载体的情况。同时对比两种不同方法制备的催化剂的形貌及催化活性,结果表明使用溶胶法制备的催化剂的分散性更好,催化活性更高。更多还原

【Abstract】 As a promising alternative for fossil energy,direct methanol fuel cell（DMFC） has attracted much attention in the past decades due to its intrinsic advantages of structural simplicity,high energy conversion efficiency and non pollution,etc.However,how to enhance the catalytic activity and utilization efficiency of platinum catalyst and develop high-performance,low-cost catalysts are still the technological keys to the commercialization of DMFC.As a matter of fact,this thesis focuses on the pre-treatment and functionlization of different kinds of catalyst supporters,such as carbon black and carbon nanotube,as well as the optimum preparation and characterization of anode catalysts for DMFC.The main work of the thesis is summarized as follows:（1） In order to effectively prepare Pt catalysts with excellent performance of high dispersion and activity,the Vulcan XC-72 carbon black,which was employed as a catalyst supporter,has been chemically treated to purposefully modify its surface properties.Due to the fact that the oxidized groups existing in the carbon black,which was subjected to chemical pre-treatment,will play a dominant role,and lead to low efficient adsorption of catalyst precursor,[PtCl₆]^2- ions,we have therefore proposed a novel scheme to change the electrical property of carbon supporters.The results showed that the catalytic activity and stability of Pt catalyst supported on carbon black has been improved significantly if the carbon black was treated by an oxidation step.Meanwhile,it was found that the catalytic performances of the Pt catalysts supported on carbon black varied greatly with the extent of oxidation treatments for the carbon black support. Generally,the higher the oxidation treatment,the better the catalytic activity.The reason is that,on one hand,the highly oxidized support has a higher adsorption capacity to [PtCl₆]^2- ions,resulting in an ideal dispersion of Pt catalyst;On the other hand,it verified that the oxidation group in the carbon black support could to some extent promote the electrocatalytic oxidation process of methanol.（2） Multi-wall carbon nanotubes（MWCNTs） were utilized as a supporter material to support the Pt catalyst.Firstly,the MWCNTs were electrochemically oxidized to enhance their surface hydrophilicity and active groups.Afterwards,the Pt catalysts with high dispersion on the surface of MWCNTs supporter were prepared by an initial oxidation step to deposit Pt（Ⅳ） complexes on the surface of MWCNTs and followed by a subsequent reduction in acid solution to form Pt particles.Moreover,the size, morphology and dispersion state of Pt catalyst supported on the MWCNTs have been characterized by means of transmission electron microscope（TEM） and X-ray diffraction （XRD） techniques.（3） Since there exist many-OH and -NH₂ groups in the chitosan molecule,it was used to modify MWCNTs for preparing chitosan-coated MWCNTs（denoted by c-MWCNTs）. The c-MWCNTs were employed as support to prepare Pt/C-MWCNTs catalysts by impregnation and sol methods,respectively.By comparing the catalytic performances of Pt catalysts supported on MWCNTs and c-MWCNTs,respectively,it was found that the dispersion degree,catalytic activity and long term stability of Pt catalysts supported on c-MWCNTs showed significant advantages compared with that of Pt catalysts supported on MWCNTs.Moreover,the results demonstrated that the dispersion degree and catalytic activity of Pt catalysts prepared by sol method were better than that of Pt catalysts prepared by impregnation method.更多还原