Synthesis Of Palladium Nanoflower With Special Morphology And Preparation Of Core-shell Structured Low Platinum Catalyst Based On Palladium Nanoflower

Catalyst is one of the most important materials of fuel cells, and platinum based catalystis widely used for proton exchange membrane (PEM) fuel cells. It is recognized as a type ofmost important fuel cell catalysts. However, the high cost of platinum based catalyst actuallyhas become one of the obstacles for the commercialization of PEM fuel cells. Thus,investigation and exploring of low platinum catalyst has become the important object in thefield of fuel cells.Core-shell structured low platinum catalyst attracts great attention recently, because itcan enhance the utilization of Pt in catalyst greatly, and thus decrease the usage of Pt sharply.This type of catalyst is widely recognized as the most promising catalyst for the practicalapplication in fuel cells.In this thesis, we have synthesized the Pd nanoflower. Furthermore, using this type ofnanoflower as substrate, core-shell structured Pd@Pt nanoparticles with monolayer of Pt asshell have been prepared successfully by an underpoteantial deposition method (UPD). Weinvestigate the influences of synthesis conditions on the morphology of the Pd nanoparticles,the electrochemical activity of Pd@Pt for the oxygen reduction reaction (ORR) and thecharacterization of the Pd@Pt nanoparticles.The main works are presented here:1. Pd nanoflower particles have been synthesized with a hydrothermal approach witholeic acid and oleylamine as template. We systematically investigate the influences oftemperature and template on the morphology of the Pd nanoparticles with the characterizationtechnologies of X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM).2. Using this type of Pd nanoflower as substrate, core-shell structured Pd@Ptnanoparticles with monolayer of Pt as shell have been prepared successfully by anunderpoteantial deposition method. We investigate the electrochemical activity of Pd@Pt forthe oxygen reduction reaction. The Pd@Pt nanoparticles exhibit enhanced activity towardsthe ORR. The mass activity of Pt in the Pd@Pt nanospheres (1.03A mg-1Pt) is3.3timeshigher than that of commercial Pt/C (0.24Amg-1Pt).3. We have characterized the Pd@Pt nanoparticles with the technologies of Transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM),X-ray spectroscopy mapping, and X-ray photoelectron spectra (XPS). The analytical resultsshow that the Pt is highly distributed on the Pd nanospherical surface, and the core-shellstructured Pd@Pt nanoparticles are formed. The Pd@Pt nanoparticles still remain themorphology of Pd nanoflower.4. The catalytic mechanism of Pd@Pt nanoparticles is discussed. We suggest that theenhancement of the mass activity of Pt is due to two factors: the flower morphology ofPd@Pt, and the interaction between this Pt in the shell and the Pd in the core.5. We synthesize the cubic structured Platinum nanoparticles with the hydrothermalorganic sol synthesis technology, and examine the ORR catalytic performance.The study result of this thesis is important for the low platinum catalyst fuel cellresearch and development. It may provide a new and important ways for the low platinumcatalyst fuel cell research.