| Recently developed direct methanol fuel cell (DMFC) has been received widespread attention due to the abundant source, the low price, the safety of the storage and transportation of the fuel. Nevertheless, the step toward the practical application has not been developed as fast as had been expected. Mainly, there are some problems, such as low electrocatalytic activity of the anodic catalyst, the poisoning of the anode catalysts by the adsorbed carbonyl species derived from methanol oxidation, methanol permeation from anode to cathode and demand for methanol-tolerant oxygen reduction catalyst. In this thesis, in order to reducing the amount of the Pt catalyst, improving the electrocatalytic activity of the Pt catalysts and utilization ratio of Pt, the electrochemical codeposition method by cyclic voltammetry (CV) was used to prepare a series Pt/MoOx/glassy carbon (GC) composite electrodes with high dispersibility. The composite electrode, Pt/MoOx/GC, was characterized to study its composition and its electrochemical behavior by CV. Using the XRD and SEM techniques, the size and the dispersion degree of the catalyst particles were studied in presence or absence of MoOx in the catalyst. The quantitatively Pt or Mo analyses of the catalyst were made by ICP-AES technique. The electrocatalytic activities and stability for the mathanol oxidation and the electrocatalystic activition of the electrode for the oxygen reduction were evaluated with the electrochemical techniques, respectively. The main result obtained are as follows:It was found that methanol oxidation was catalyzed on the Molybdenum oxide-modified platinum by lowering methanol oxidation potential and promoting methanol oxidation current. SEM results and XRD results indicated that thePt/MoOx microparticles were uniformly high dispersed on the GC electrode, theaverage diameter of its microparticles was smaller than that of Pt microparticle in the Pt/GC electrode which was prepared in the same fashion as in the Pt/MoOx/GC system. MoOx decreased catalytic agglomeration rate. All these made the Pt/MoOx samples higher specific surface area of Pt/MoOx microparticles in the Pt/MoOx/GC composite electrode than Pt microparticles in the Pt/GC electrode. The Pt/MoOx/GC composite electrodes were prepared by cycling the potential between 550 and -700mV versus Hg/Hg2SO4, at a scan rate of 20mV/s, in a solution of 3.0mM in K2PtCl6, 300mM in Na2MoO4, and 2.5M in H2SO4. In this case, methanol oxidation took place on the MoOx-modified platinum at the potential 400mV more negatively than on the non-modified platinum, the steady mass specific oxidation current of methanol on this modified platinum at 250mV versus Hg/Hg2SO4 was 10-20% more than on the non-modified platinum, and the current density (geometric basis) was 10.9 times higher than that on a Pt wire. Chronoamperometry response and CV result for the Pt/MoOx/GC composite electrode, compared with the Pt/GC electrode, showed slightly a better CO tolerant perfomance, a performance for methanol oxidation from poisoning by the adsorbed carbonyl species deroved from methanol oxidation. The reaction mechanism for methanol oxidation at Pt/MoOx/GC composite electrode involved the proton spillover effect from hydrogen molybdenum bronze, and a bifunctional reation mechanism for methanol oxidation by providing a hydrous Molybdenum oxide to oxidize the intermediates , COads, for keeping cleaning platinum surface and make it easier for methanol to be oxidized on the clean platinum. So, the Pt/MoOx catalyst can be used as anodic CO tolerant catalyst for methanol oxidation. Presence of Vulcan XC-72 active carbon powder in the Pt/MoOx/GC composite electrode by electrochemical codeposition made peak potential of methanol oxidation a further negative shift of about 50mV and a further promotion of CO-tolerant performance for methanol oxidation.Also, the steady mass specific peak current of oxygen reduction methanol on this modified platinum was 20% more than that on the non-modified platinum, the Overpoten...
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