Research On The Synthesis Of Au,Pt,Pd And Alloy Nanowires As Well As The Electrocatalytic Performance For Methanol

Noble metal nanomaterials with special optical,electrical,and catalytic properties,can be applied potentially in many fields.Their properties can be obviously influenced by their morphologies,structures,sizes,compositions,and surface state.One-dimensional nanostructures not only offer opportunities to form high surface-to-volume ratio and achieve attractive catalytic activity,make electron transfer easier as their better connectivity,reduce the possibility of Ostwald ripening and aggregation,but also serve as self-supported electrocatalysts,thus making the mass transfer easier and avoiding the possible support corrosion.In this dissertation,according to the different characteristic of precursors,we employed different reaction conditions to prepare one-dimensional noble metal nanowires with different compositions and structures by using ultrafine Te NWs as sacrifice templates.Their morphologies,structures,compositions,surface,and electrocatalytic activity for catalytic oxidation of methanol were characterized by the modern detection techniques,such as SEM,TEM,EDX,XRD,XPS,electrochemical method etc.And their detailed formation methanism was also presented.The main achievements of this dissertation are summarized as follows:?1?Through optimization and control of the key parameters influencing the formation mechanism of Te NWs,the highly-dispersed ultrafine Te NWs with a diameter about 12 nm were synthesized in order to serve as sacrificial template for the preparation of high quality nobel nanowires.?2?When a small amount of Br-ions was introduced into the solution,Au precursor with a lower reduction potential was formed.In this case,the galvanic replacement reaction rate could be reduced.The key parameters that influence the formation of Au NWs,such as,reation time,concentration of Au precursor and Br-,were discussed.An aggregative growth mechanism in terms of ID and 3D growth pathways for the NW length and diameter,respectively,was revealed to be operative in the template-directed Au NW formation process.In contrast to the use of various organic surfactants in most previous synthesis of Au NWs and catalysts,the surfactant-free Au NWs synthesized in this work have been demonstrated to exhibit enhanced electrocatalytic activities for methanol oxidation reaction.The preparation method and mechanism study of Au NWs in this paper shine some fresh insight on the controllability of other alloy nanowires.?3?The ultrafine porous nanowires were synthesized by employing Te NWs and NaCIO as the template and etching agents,respectively.And the composition for as-prepared nanowires could be tuned easily by controlling feeding ratios of H2PdCl4,H2PtCl6 and HAUCl4 added in the synthesis,such as the synthesis of Pd,Pd₈₀Pt₂₀,Pd₄₅Pt55,Pd₂₁Pt₇₉,Pt,Au₂₈Pt₇₂,Au₅₂Pt₄₈,Au₇₁Pt₂₉,Au₂₉Pd₇₁,and Au₅₃Pd₄₇ porous nanowires.The feeding ratios and concentration of precursors were the key parameters influencing the formation of porous nanowires.The nanowires with porous structure can produce more active sites,which was advantageous to enhance the electrocatalytic property.?4?In order to evaluate the electrocatalytic properties of porous nanowires with different composition,methanol oxidation reaction?MOR?was examined as a model reaction.It was found that the electrocatalytic activity of porous nanowires depended on their composition.In the cyclic voltammetry curves of methanol oxidation reaction catalyzed by porous nanowires of Pd,Pd₈₀Pt₂₀,Pd₄₅Pt₅₅,Pd₂₁Pt₇₉,Pt,Au₂₈Pt₇₂,Au₅₂Pt₄₈,Au₇₁Pt₂₉,Au₂₉Pd₇₁,and Au₅₃Pd₄₇,the maximum mass current density of Pd₂₁Pt₇₉ porous nanowires reached 1.13A·mg^-1,which was about 1.09,1.91 and 1.13 times than that of Pt porous nanowires,Pd porous nanowires and commercial Pt/C,respectively.The maximum mass current density of Au₂₈Pt₇₂ porous nanowires reached 1.278 A·mg^-1,which was about 1.22 and 1.65 times than that of Pt porous nanowires and commercial Pt/C,respectively.The maximum mass current density of Au₂₉Pd₇₁ porous nanowires reached 0.8624 A·mg^-1,which was about 1.45 and 1.12 times than that of Pd porous nanowires and commercial Pt/C,respectively.Among all of the above mentioned porous nanowires,Au₂₈Pt₇₂ porous nanowires showed the highest electrocatalytic activities for methanol oxidation,and can be used as a potential anode catalyst in fuel cells.