Controllable Preparation And Electrocatalytic Study Of Pd And Pt Based Nanocrystals

In the past decades,the Pd and Pt based nanocrystals have attracted considerable attention owing to their wide applications in many areas of modern science and technology,including catalysis,plasmonics,electronics and biomedicine.The properties of these nanocrystals are highly dependent on the size,shape,composition and structure.In principle,one can tailor and fine-tune the electrocatalytic properties of a metal nanocrystal by controlling any one of these of parameters.On the other hand,featuring the excellent electronic properties,huge surface and unique graphitized basal plane structure,graphene is an ideal two-dimensional material to act as a kind of support material to load theses metal nanocrystals,which would be an effective strategy to maximize the electrocatalytic activity of nanocrystals.In this dissertation,we have developed a wet-chemical method for the shape controlled synthesis of Pt and Pd based nanocrystals,and successfully prepared graphene supported Pt based nanocrystals with superb monodispersity and homogeneity.The growth mechanism as well as the structure and shape dependent electrocatalytic properties of the nanocrystals are also investigated.The main results are as follows:Chapter 1:Recent progress of fuel cell catalysts has been briefly reviewed and the research purpose and significance during my master period are also clarified.Chapter 2:We have demonstrated a water-based surfactant-free synthesis of three-dimensional porous Pd@Pt core-shell nanoflowers on graphene with superb monodispersity and homogeneity.The Pd@Pt nanoflower is composed of a Pd interior and porous dendritic Pt shell,which would offer three-dimensional molecular accessibility and thereby dramatically diminish the number of buried nonfunctional precious metal atoms and increase the atomic utilization efficiency.Benefiting from this attractive architecture and unique characteristic,the as-prepared Pd@Pt-graphene hybrids exhibited substantially enhanced electrocataltic activity and stability towards methanol oxidation relative to the PdPt alloy-graphene,Pt-graphene and commercial Pt/C catalyst.Chapter 3:Monodisperse PdCo nanocrystals enclosed by(100)facets have been synthesized by a wet-chemical method.We have investigated the influence of capping agents,temperature,and composition on the shape evolution of PdCo nanocrystals.Compared with other halides,we found the use of NaI played a key role in the synthesis process.We also found the proper temperature was crucial for the synthesis of high-quality nanocrystals.We have explored the optimal conditions for the synthesis of PdCo nanocrystals with superb monodispersity and homogeneity,which is of significance for investigating the shape-dependent properties in the future.