Studies On Anode Catalysts Supported On Carbon Nanotubes For Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) is one of promising candidates as power sources in mobile electronic products, electric vehicle etc., due to its advantages of easy transport and storage of the fuel, low weight, volume and high energy efficiency. The poor kinetics of anode reaction and catalysts readily poisoned by intermediate species produced during methanol oxidation are the two key issues hindering DMFC commercial application. It is important techniques in DMFC to find the complex catalysts with good electro-catalytic activity and resistant ability to poisoning for the methanol oxidation. In this dissertation, a novel synthesis method of this kind of electro-catalysts was explored, and we mainly investigate the preparation and the catalytic properties of multi-walled carbon nanotubes supported platinum based catalysts. The main results obtained are as followed:Part one: At first, the MWCNTs supported highly dispersed Pt elctro-catalyst was prepared by microwave radiation method. The Pt/MWCNTs was characterized by XRD and TEM techniques. The results shows the Pt nanoparticles were uniform and highly dispersed on MWCNTs surfaces. The mean size of the Pt particles was about 3 nm. And Pt/MWCNTs displayed the characteristic diffraction peaks of Pt face-centered cubic (fcc) crystal structure. The measurements results of cyclic voltammetry (CV) and chronoamperometry (CA) demonstrated that the Pt/MWCNTs catalysts prepared in this way exhibited a higher electro-catalytic activity for methanol electro-oxidation than that of Pt/Vulcan XC-72. Pt-Ru/MWCNTs and Pt-Sn/MWCNTs alloy catalysts were firstly prepared respectively by a hydrothermal method and characterized by TEM, XRD and EDS techniques. The results shows the PtRu and PtSn nanoparticles were uniform and highly dispersed on MWCNTs surfaces. The mean size of the PtRu and PtSn particles were about 3.5 nm and 3.2 nm respectively. And Pt-Ru/MWCNTs and Pt-Sn/MWCNTs all displayed the characteristic diffraction peaks of Pt fcc crystal structure. The electro-oxidation of methanol on the synthesized Pt-Ru/MWCNTs and Pt-Sn/MWCNTs were studied by CV and CA measurements. It was found that both Pt-Ru/MWCNTs and Pt-Sn/MWCNTs catalysts have higher and durable electro-catalytic activities for methanol oxidation. Meanwhile the electro-catalytic activities for methanol oxidation of PtRu/MWCNTs and PtSn/MWCNTs synthesized by hydrothermal method were higher than that of PtRu/MWCNTs and PtSn/MWCNTs synthesized by microwave heating method. At last, the differences in electrochemical performance of Pt-Ru/MWCNTs and Pt-Ru/C were obtained by electrochemical impedance spectra (EIS).Part two: The PtSnPb/MWCNTs and PtRuNi/MWCNTs nanostructural electro-catalysts were prepared by a hydrothermal synthesis method for the first time and characterized by TEM, XRD and EDS techniques. It was found that both the PtSnPb nanoparticle uniformly and highly dispersed on MWCNTs surfaces. The mean size of the alloy metal particles was about 5 nm. CV, CA and EIS electrochemical measurements demonstrated that the PtSnPb/MWCNTs catalysts prepared in this way exhibited a higher electrocatalytic activity for methanol electro-oxidation than that of PtSn/MWCNTs and PtRu/MWCNTs in alkaline solution. The results of XRD and TEM techniques measurement displays PtRuNi nanoparticles uniformly and highly dispersed on MWCNTs surfaces, were 4.5 nm in size. PtRuNi/MWCNTs catalysts showed higher electro-catalytic performances for methanol electro-oxidation than Pt-Ru/MWCNTs in acidic media. The possible reasons of enhanced catalytic performances of PtSnPb/MWCNTs and PtRuNi/MWCNTs were proposed.Some electro-catalysts with higher electro-catalytic activity and stability were prepared in this thesis, and it reduces the amount of the Pt catalysts at the same time. Presence of Ru, Sn, Pb and Ni in the composite elctro-catalysts prepared by hydrothermal method made a further promotion of CO-tolerant performance and enhanced electro-catalytic activity for methanol oxidation, and some reasonable explanation were presented. The results of investigation prove hydrothermal method and microwave heating method are efficient method for preparing electro-catalysts. The synthesized nanostructure elctro-catalysts present good catalytic activity; and all these results provide rich information for understanding the methanol electro-oxidation mechanism, and could be attractive for the application in DMFC.