Study On The Preparation And Electrocatalytic Properties Of Pt Catalysts Supported On Carbon Black And Carbon Nanotube

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(â…£) 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.