The Study On Synthesis Of Novel Nano-structural Pt/Au Based Catalysts By Hydrothermal And Microwave Methods And Electrocatalytic Performance

Due to the combination of unique nature of Platinum/Gold and special properties of nanomaterials,Pt/Au based nanomaterials have been widely used as catalysts in industry catalysis,energy environment,and fuel cell.The morphology of Pt/Au based nanocrystals(NCs)can affect their catalytic performance strongly and has been widely concerned by researchers.The researchers studied shape-controlled synthesis of Pt/Au based NCs to improve their catalytic activity and many advances in this field have been achieved.Through an in-depth literature survey,the issues including how synthetic atmosphere affect the shape of NCs,is it possible to prepare Pt based alloy NCs with high-index facets(HIFs)distributed on graphene by one-pot hydrothermal method,and whether can we synthesize multiply-twinned structural Au based alloy NCs under microwave irradiation,have not been studied deeply.Herein,we have carried out works to study the three issues,and summarized the work:1.The influence between Synthestic atmosphere and morphology of Pt-Co NCs prepared by hydrothermal method has not been investigated deeply.Therefore,it is of great significance to study the effect of atmosphere on the shape-controlled synthesis of Pt based NCs.Pt-Co NCs have been prepared by hydrothermal method under various atmospheres(air,H2,N2)at ambient pressure(AP).Form the images of TEM,we found that three different shapes of Pt-Co NCs were prepared under various atmosphere at AP.It was demonstrated that the shape of Pt–Co NCs were sensitive to the synthetic atmosphere and we can shape-controlled synthesize Pt-Co NCs by changing atmosphere.From the results of composition of Pt–Co NCs,we found that there was a significant difference in the composition of Pt–Co NCs prepared in various atmospheres.It was demonstrated that synthetic atmosphere also affected the composition of Pt–Co NCs.Then we increased the pressure of synthetic atmosphere from AP to 1 MPa to prepare Pt–Co NCs.We found that the morphology of NCs changed.Because the amount of O2 increased when the pressure of air increased to 1 MPa,Pt/Co precursors could not be reduced and the Pt-Co alloy NCs were not obtained.Pt–Co dendritic NCs were also prepared in H2 at 1 MPa,but the structure is more open and the size of dendritic cluster decreased obviously.Nanochain-like Pt–Co NCs were prepared in N2 at 1 MPa and there were abundant porous and defect sites in single NCs.Form the results of composition of Pt–Co NCs,we found that the pressure of atmosphere affected the composition weakly.The as-synthesized Pt–Co alloy NCs have been measured in the electro-oxidation of methanol to probe the structure effects on electro-catalytic properties.The Pt–Co nanochain with abundant porous and defect sites prepared in N2 at 1 MPa exhibited the highest catalytic activity and durability.2.Recent studies showed that Pt NCs exposed high-index facets(HIF)exhibited superior activity in the field of electrocatalysis.To further improve the catalytic activity,graphene was employed as the support to loading Pt based alloy NCs by in situ growth.Based on the synthetic method of Pt-Co NCs in previous chapter,to further improve the electrocatalytic activtiy,Pt-Co NCs with HIFs grew in situ on reduced graphene oxide(rGO)by hydrothermal method.RGO immobilized concave nanocubic(CNC)Pt-Co NCs exposed {410},{510} and {720} facets and rGO immobilized concave polyhedra bounded by {411} facets.Form the analysis of growth mechanism,we found that GO played the key role in morphology controlling of Pt–Co binary alloys,rather than as a support.Through the study of electronic structure of Pt–Co/rGO,we found that the contact between rGO and Pt–Co NCs affects strongly the electronic structure of Pt–Co/rGO hybrids.The strong interaction between rGO and Pt–Co NCs can facilitate p-electron polarization from rGO to Pt–Co NCs,accelerating the electron transfer.Thanks to the synergy of the HIFs and the electronic effect of the intimate contact/interaction between Pt–Co alloy and rGO,these as-prepared Pt–Co NCs/rGO hybrids presents enhanced catalytic properties for the electrooxidation of formic acid,as well as for the oxygen reduction reaction(ORR).3.Twinned structure and Au based alloy NCs possess great potential in the field of electrocatalysis in recent studies.Therefore,twinned structural Au based alloy NCs was expected to be a novel non-Pt catalyst.To further improve the electrocatalysis activity and stability,these Au based NCs with twinned structure was grown directly on the surface of graphene.Au-Ag decahedron and icosahedron grew in situ on rGO under microwave irradiation.Through the analysis of structure of Au–Ag NCs,we found that Au–Ag decahedra and icosahedra were both multiply-twinned structure.From the survey of growth mechanism,we found that the size of Au–Ag decahedron and icosahedron could be tuned.The evolution of r GO immobilized Au–Ag decahedron and icosahedron are a typical crystal growth controlling,and these NCs could be formed in one-pot method under microwave irradiation for a very short time(≤ 4 min).The morphology of Au-Ag NCs could be tuned by controlling the reduction rate in this synthetic system.RGO immobilized Au–Ag decahedron could be obtained in faster reduction rate and rGO immobilized Au–Ag icosahedron could be prepared in slower reduction rate.Thanks to the high density of twin defects and the electronic effect of the intimate contact/interaction between Au–Ag NCs and reduced graphene oxide,these Au–Ag/rGO hybrids exhibit excellent electrocatalytic activity towards HER.Especially,Au–Ag icosahedra/r GO present Pt-like activity and is even more stable than the commercial Pt/C in the HER.