Preparation And Electrocatalytic Properties Of Pd - Nanoparticles Supported On MWCNTs Modified By NH4 +

Direct methanol fuel cell (DMFC) is viewed as a promising power sources for various portable deivces due to its simplicity,convenience and higher energy density of the system. Anode catalyst performance is one of the bottlenecks for the commercialization of direct methanol fuel cell. Currently, Pt-based catalysts is sill the most efficient anode catalysts for DMFC. However, many factors will severely limit the commercial application of DMFC, such as high costs, scarce resources and easy to be poisoned. Therefore, in order to promote the development of commercial DMFC as soon as possible,developing a high efficient and low toxic non-platinum catalyst or decreasing the cost by an appropriate supporting material, it may be the main research methods to solve the above problems. In recent years, researchers found that the Pd metal for methanol electro-oxidation showed higher activity in alkaline solution,and based on Pd cost is low and rich in resources as well as for CO adsorption ability is low. Thus,Pd can replace Pt as anode catalyst in DMFCs have attracted extensive attention of the researchers.To increase the utilization rate of noble metal,nanoparticles often were loaded onto multi-walled carbon nanotube (MWCNTs). Carbon nanotube are considered to be the most promising catalyst supporting material,because of its outstanding pHysical and chemical properties such as special geometric structure, good electronic conductivity and high external surfaces. However,the inert surface of MWCNTs make them diffcult to disperse in polar solvent and in nonpolar solvent. Generally, MWCNTs modified has usually been proposed to solve this problem.The functionalization of MWCNTs can be carried out as follows:HNO3 or HNO3/H2SO4 oxidation treatment, covalent organic modification and surfactant treatment. These modification methods have been developed for the surface modification of MWCNTs by introduce functional groups and amounts of defect sites. Although electric catalytic activity of noble metal nanoparticles has been improved in a certain extent, these methods lead to uneven distribution on MWCNTs and aggregation of nanoparticles, and even destroyed the original structure of MWCNTs. In addition, these modification methods were against the analysis of the catalytic mechanism.In this paper, multi-walled carbon nanotubes (MWCNTs) were firstly pretreated with sodium hydroxide solution (f1-MWCNTs),and then f1-MWCNTs were covalently modified by ammonium fluoride (f2-MWCNTs),which were used as a new support for Pd nanoparticles. The new catalysts (Pd/f2-MWCNTs) were prepared by one-step pHotochemical reduction technique. Additionally,systematically studied using ammonium chloride and sodium fluoridec modified MWCNTs to explore the effects of N,F element for functionalization of fluorine of MWCNTs. Also research MWCNTs as Pd nanoparticles carrier catalyst preparation conditions. Mainly includes that modified concentration and preparation methods as well as alkaline and acidity in the synthesis system. FT-IR was used to analyze the funcyionalized MWCNTs,finding that the C-F(1180cm-1),C-N(1093cm-1) and N-H(667cm-1)groups existed in f2-MWCNTs. XPS analysis showed that there were N,F elements exised in f2-MWCNTs. And the electronic structure of Pd nanoparticles was changed in Pd/f2-MWCNTs. TEM,EDS and XRD analysis showed that the Pd nanoparticles with the uniformly dispersed on the surface of f2-MWCNTs were 2-6nm in diameter,and Pd nanoparticles load rate reached 16.7%,close to ideal value (20%). Cyclic electrochemical experiments indicated that electro-catalytic activity of Pd/f2-MWCNTs catalyst for methanol in alkaline medium was about 1.92 times and 2.87 times higher than that of the Pd/f1-MWCNTs catalyst and commercial Pd/C (JM) catalyst at the same conditions.In order to further analyze the influence factors of catalyst,Systematically studied to Pd/MWCNTs catalyst factors affecting for electric catalytic performance,and these factors mainly include:modification, modification of carbon nanotubes concentration of pH, synthesis methods and synthesis system. Its great significance for improve the activity of catalyst and prolong the catalyst life.