The Preparation Of Core-Shell(Pd,Pt) Nano-Particles And Their Electro-Catalytic Performance

Energy crisis and environmental pollution have become more serious.Being a sustainable energy,directly feed methanol fuel cell(DMFC)has the advantages of high efficient,clean and portable,and is concerned recently.However,methanol crossover and cost problem have prevented the development of DMFC.Meanwhile higher requirement was put forward to the materials of cathode and anode.Core-shell type nanoparticles have become a hot research topic for DMFC electrode materials as they have core-shell dual-metal physical and chemical property,can effectively increase the surface area of noble metals and activity,avoid instability caused by the dissolution of transition metal.Core-shell type nanoparticles not only raise the utilization rate of noble metals,but also reduce the cost of the catalyst.Because of chaotic arrangement of surface atoms and increasement of surface atoms ligand unsaturaton and bond bit density,amorphous material shows unique catalytic properties and gradually applied to DMFC fields.At present,noble metal Pt is considered to be an ideal electrode material although of its limited resources and expensive price.Therefore,the introduction of core-shell structure and amorphous concept,exploring non-Pt catalyst or improve the utilization and catalytic properties of Pt series catalyst have been an urgent issue need to be solved in DMFC research field.In this research,based on the analysis of research status of the anode and cathode catalysts,guided by the research direction of current electrode materials,according to the differences of DMFC electrode reaction mechanism and problems,the cathode and anode electrode materials were prepared and their eletro-catalytic properties were investigated by experimental study.Firstly,a series of non-Pt core-shell nanoparticles were synthesized,then combined with the amorphous concent,different amorphous core-shell type nanoparticles were prepared;the composition,structure and morphology of core-shell nanoparticles were characterized by means of XRD,HRTEM,aberration-corrected,EDS and XPS etc.;the regularity of experimental research for the preparation of core-shell nanoparticles was investigated roughly;Using zeta potential,AC impedance,timing current,cyclic voltammetry and in situ FTIR technology and other electrochemical methods,the electro-catalytic properties of nanoparticles were evaluated;finally the effect of different elements,shell thickness,different atomic ratio and other factors on the electro catalytic properties was investigated.The above research provides the experimental foundation for its potential application.The main contents and conclusions are:1.A series of Co series core-shell nanoparticles Co@M(M = Pd,Pt,Ag,Au),whose core Co was about 5nm in diameter and shell thickness can be controlled,were prepared by the method of colloid particle template.According to the difference of M:Co atomic ratio,the shell thickness can be regulated 1～5nm.In the cases of same atomic ratio,the electro-catalytic activity sequence of Co-based noble metal core-shell type catalyst was:Pd>Pt>Au>Ag;Co@Pd/C catalytic experiments results show that the oxygen reduction activity was"Volcano" trend(first increased and then decreased)with the increase of Pd thickness of the shell.Among them,Col@Pd2/C catalyst had the highest activity and its oxygen reduction peak current density was about 175.5 mA/mg,but had no activity to methanol oxidation.Col@Pd2/C was a kind of cathode material with good performance of anti oxidation of methanol.2.A series of amorphous Pt coated Ni@Pt core-shell nanoparticles,whose average particle size was about 12nm,were synthesized by consecutive two-step chemical reduction method.The test results showed that the shell thickness was only 1～2nm,the core metal Ni presented a face-center cubic(FCC)crystal structure,the surface was mainly Ni(111)crystal surfcae.The electrochemical experiments results showed that:the adsorption of oxygen-containing inter-mediates on the surface reduced with Pt shell thickness incresing;Ni15@Pt1/C had a high ability of resistance to CO poisoning;the methanol oxidation reaction on Ni15@Pt1/C was consistant with "two-way mechanism".3.Introduction of Fe metal,a series of nearly spherical,amorphous core-shell Fe2O3@Pt nanoparticles were prepared by two step chemical reduction method.When Fe/Pt atomic ratio was more than 1:0.5,the diffraction peak of shell Pt was disappeared and became amorphous.The electrochemical test results showed that:the oxidation peak potential of core-shell Fe2O3@Pt nanoparticles(Fe:Pt =1:0.5)was decreased;Fe2O3@Pt nanoparticles had higher selectivity to C02 and showed higher structural stability to carbonaceous intermediate.Compared with E-TEK 40%Pt/C catalyst,Fe2O3@Pt core-shell nanoparticles was a better anode matrial.