Preparation And Properties Of Platinum-based Catalysts For Potential Use In PEMFCs

In recent years, with the increasing environmental concerns and accelerated depletion of fossil fuels, there are resurgent research interests for the development of new technology using alternative energy sources other than fossil fuel, most noticeably hydrogen in polymer electrolyte membrane (or proton exchange membrane) fuel cells(PEMFCs) for automobiles. However, cost, durability and fuel supply infrastructure remain the key problems barricading the successful commercialization of PEMFCs. As for the PEMFCs, the cost and durability of key materials comes from Pt catalyst used in the fuel cell. Due to the various cost and resource issues regarding Pt, it is important for researchers to develop low-Pt or non-Pt as fuel cell anode/cathode catalysts.This thesis focuses on the preparation and characterization of Pt-CeO2/C, Pt-Ce0.8Zr0.2O2/C and Au@Pt/C catalyst, and makes the following progress:(1)The morphology, dispersion, HOR activity and CO oxidation activity of Pt-CeO2/C catalysts with different CeO2 content were examined in detail using transmission electron microscopy(TEM), X-Ray Diffraction(XRD), cyclic voltammetry(CV), liner cyclic voltammetry(LSV), CO-Stripping and other methods. The results indicate that Pt-20%CeO2/C shows the best performance. CO oxidation peak of Pt-20%CeO2/C catalyst starts at about 653 mV and the maximum value is at about 772 mV. The CO oxidation peak of Pt-20%CeO2/C negatively shifts 60 mV compared to the commercial Pt/C. The homemade Pt-20%CeO2/C catalyst was also tested for 5 ppm CO tolerance, and the results shows that the Pt-20%CeO2/C has much better CO tolerance than commercial Pt/C catalyst.(2) A series of Pt-Ce0.8Zr0.2O2/C with various content of Ce0.8Zr0.2O2 were synthesized by one-pot synthesis process by ethylene glycol (EG) method. High-surface area nanosized Ce0.8Zr0.2O2 was prepared by a surfactant-templated method beforehand. Effect of the addition of Ce0.8Zr0.2O2 for the electro-catalytic activities of Pt/C catalysts were detected by CV, LSV and CO-stripping techniques. It is found that Pt-20%Ce0.8Zr0.2O2 exhibits a better activity among these catalysts for hydrogen oxidation and CO oxidation reaction. The membrane-electrode assembly(MEA) fabricated with Pt-20%Ce0.8Zr0.2O2 as anode exhibits the excellent catalytic activity toward hydrogen oxidation reaction (HOR) and reaches 490 mW/cm2 at 0.49 V in a single cell test.(3) Carbon-supported Au@Pt core shell nanostructured catalysts were synthesized by seed mediate method. The nanostructured catalysts were characterized by UV-vis spectroscopy, X-ray photoelectron spectra (XPS) and TEM. Investigation of the ORR activity of the Au@Pt/C by means of LSV employing a rotating disk electrode (RDE) has revealed that Au@Pt(2:4)/C (atomic ratio) catalyst exhibits the best catalytic activity. The ORR of Au@Pt(2:4)/C in acid solution proceeds by an approximately four-electron pathway, through which molecular oxygen is directly reduced to water. The performance of a membrane electrode assembly prepared with the most active Au@Pt(2:4)/C as the cathode catalyst in a single PEMFC generate a maximum power density of 479 mW/cm2 at 0.431V.