Self-assembling And Crystalline Control Of Pt-based Nanocrystals

Platinum?Pt?based nanocrystals have been widely used in the catalysis of organic small molecule oxidation and oxygen reduction?ORR?reactions due to their excellent catalytic properties.The performance of catalysts can significantly be improved through controlling the morphology,size and compositions of the nanostructures.In recent years,the self-assembled and twinned nanostructures have received intensive research attention for their unique collective electronic,optical,magnetic properties and effect of twin defect.The nanostructure with self-assembled and twinned features can further improve the catalytic activity and stability.Moreover,polyaniline is considered to be a new strategy to improve the activity and stability of the catalyst,owning to its large surface area,high conductivity and strong stability.Therefore,it is of great significance for the self-assembling and twin defect control of Pt-based nanomaterials.In this thesis,we have developed strategies to control the self-assembling and twinned structure of Pt-based nanocrystals,and successfully prepared Pt nanocube assemblies,polyaniline-coated Pt nanocube assemblies and multiply-twinned Pt₃Cu icosahedra.The structural analysis,growth mechanism and the catalytic properties of these Pt-based nanocrystals are investigated.The main contents are as following:Chapter 1.The progress of regulation and control of Pt-based nanomaterials were briefly introduced,and expounds the basis,research contents and significance of this thesis.Chapter 2.The highly monodisperse and uniquely assembled Pt nanocubes were selectively producedin one-potsynthesis.The synthesis strategy is based on the combined introduction of formaldehyde and Fe³⁺into the synthesis,which is mostcritical to the successful formation of unique Pt nanocube assemblies.The unique Pt nanocube assemblies exhibit high activity for methanol electrooxidation reaction?MOR?with much better performance than those of the monodisperse Pt nanocubes and also the commercial Pt black due to their unique assembling characteristic.Chapter 3.The Pt nanocube assemblies?NCAMs?have been prepared by introducing glyoxal in one-pot method.The synthesized Pt NCAMs are used as cores and directly coated with polyaniline?PANI?on their surface.The Pt NCAMs@PANI with self-assembled coreand PANI shell shows enhanced electrocatalytic activities and stability towards MOR compared with the Pt NCAMs and the commercial Pt/C.Chapter 4.Two distinct{111}-bounded shapes,namely,multiply-twinned Pt₃Cu icosahedra and single-crystalline Pt₃Cu octahedra,are successfully prepared by simply changing the types of Cu precursors with the other growth parameters unchanged.Electrocatalytic studies show that the{111}-terminated Pt₃Cu nanocrystals exhibit the very interesting crystalline nature-dependent electrocatalytic activities toward both the oxygen reduction reaction?ORR?and MOR with multiply-twinned Pt₃Cu icosahedra demonstrating enhanced electrocatalytic activities compared to the single-crystalline Pt₃Cu octahedra due to their additional yet important effect of twin defect.