Study On The Structure, Composition Regulation And Oxygen Reduction Performance Of AuPd Binary Nanocrystals

AuPd bimetallic nanocrystals demonstrate potential application value in the field of electrocatalysis due to their unique structural characteristics.Since Au component has excellent electrochemical stability and corrosion resistance,and the intrinsic catalytic activity of Pd is only inferior to Pt,the construction of Au and Pd bimetallic nanostructures can not only exert the quality properties of the two metals themselves,but also induce synergistic effects to further improve the electrocatalytic performance.In addition,by accurately designing the size,structure and surface properties of AuPd bimetallic nanocrystals,their area specific activity and mass specific activity can be effectively improved.Therefore,this paper intends to construct a series of AuPd bimetallic nanocrystals with controllable dimensions and size,and quantitatively study the effects of various experimental parameters in the reaction system on its dynamic growth rate,and observe the synergistic effect and electronic coupling effect between Au and Pd.Then,oxygen reduction reaction(ORR)is regarded as probe reaction to investigate the internal relationships among the structure,composition,electronic state and catalytic activity of AuPd bimetallic nanocrystals.Specifically,this paper mainly carries out the following three works:1.In this chapter,we synthesize a series of PdAu nanocrystals with the same building blocks and surface composition but with different dimensions by one-step hydrothermal method,including 1D ultrathin PdAu nanowires(1D PdxAu1-x NWs,x≧0.5),2D freestanding PdAu nanosheets with large porosity and rough surfaces(2D PdxAu1-x PNSs,x≧ 0.5),and 3D penetrative PdAu nanoflowers(3D PdxAu1-x NFs,x<0.5).This series of PdAu nanoalloys with definite morphology and dimension demonstrate excellent activity and stability for ORR.Comparing with other samples and commercial Pd black,the 2D PdAu PNSs has the best ORR performance(Eonset=1.040 V,E1/2=0.932 V)due to their abundant surface atoms and full range of mass transfer channels.2.In this chapter,we construct the Au@Pd core-shell nanowires with ultrathin Pd layer employing 1D Au(111)NWs as seeds by seed growth method.The relatively slow reduction rate contributes to the diffusion of Pd2+ on the surface of 1D Au(111)NWS,which drives to the epitaxial growth mode of Pd.The obtained Au@Pd coreshell NW has an ultrathin Pd shell layer(about 4 atomic layers),which can induce a synergistic effect with Au nanowires,thus exhibiting excellent ORR performance.The relatively slow reduction rate is conducive to the diffusion of Pd2+ on the surface of 1D Au(111)NWs,which drives Pd atoms to the epitaxial growth mode and obtains an ultrathin shell layer with 4 atomic layers thickness,effectively inducing the synergistic effect between Pd layer and 1D Au(111)NWs,thus exhibiting excellent ORR performance.Compared with Pd Black and 1D Au(111)NWs,the E1/2(0.880 V)of Au@Pd core-shell NWs exhibit a positive shift of 30 mV and 20 mV,respectively.After the chronograph current test of 40,000 s,the current only attenuates by 7.2%,which reflects the excellent oxygen reduction activity and stability of Au@Pd core-shell NWs.This chapter indicate that the surface properties of 1D Au(111)NWs regulated by Pd is an effective strategy to improve the electrocatalytic performance.3.In this chapter,1D Au(111)NWs are served as seeds to investigate the effect of Pd atoms growth behavior on ORR activity.Based on the synthesis system described in the previous chapter,Au@Pd core-islands NWs can be obtained by adjusting pH to 11.Quantitative analysis demonstrates that the pivotal factor of Pd atoms growth mode from epitaxial growth to island growth is the faster kinetic reduction rate(1.2×10-2 s1)induced by pH value,which promotes the rapid reduction of Pd2+ and forming the unique nano island structure.The segmented oxyphilic-anaerobic interface of the Au@Pd core-islands NWs directly balances the adsorbability of the intermediates;meanwhile,the interleaved lattice orientations favor multi-directional electron transmissions to promote ORR kinetics.Therefore,Au@Pd core-islands NWs showed significantly superior oxidation reduction activity(E1/2=0.91V)and stability(4.2%current decay)of compared to Au NWs and commercial Pd Black.