Theoretical Design And Electrochemical Performance Control Of Platinum And Palladium Based Nanoalloy Catalysts

In recent years,catalysis plays a more and more important role in the rapid development of the national economy.Then new requirements for the research and development of high performance nanometallic catalysts are put forward.An array of novel features will arise when bulk metals are transformed into nanocrystals,including drastically increased specific surface areas,higher densities of lowcoordination atoms on the surface,changes to phase stability and miscibility,quantum-confinement effects,and novel magnetic phenomena such as superparamagnetism.Upgrading the simplest monometallic nanocrystals to bimetallic or more complex compositions would greatly enhance their properties,often making them superior to their monometallic counterparts.At present,the most widely studied metal nanoalloy catalysts are mainly platinum group metals,and platinum based and palladium based nanoalloy catalysts are typical catalysts.The catalytic properties of platinum based and palladium based nanoalloy catalysts are related to their structure,size,composition,morphology and chemical ordering.In this paper,platinum based and palladium based nanoalloy catalysts were chosen as research objects.In order to design and prepare high-performance catalysts for oxygen reduction and CO2 adsorption,we carried out systematic research on its electrocatalytic performance control.The main innovation points are as follows:(1)Density functional theory(DFT)computations predicted Au-Pd cluster-functionalized ionic liquid complex.We investigated the interaction of CO2 with Au-Pd cluster-functionalized ionic liquid complex by using DFT calculations.It was found that single Au or Pd atom interact strongly with ionic liquids with Au showing the more significant interaction of the two metals.In addition it was found that Au-Pd cluster-functionalized ionic liquid complex exhibit a significant enhancement for interaction with CO2.It was found that the composition and size of the cluster can be used to tune the capture performance for CO2 by Au-Pd cluster-functionalized ionic liquid complex.Our calculation results show that the larger size of Au-Pd cluster benefits the interaction with CO2 in complex,which was confirmed by localized orbital locator(LOL)map and natural bond orbital(NBO)analysis.Among the systems investigated the Au1Pd2 Au-Pd cluster-functionalized ionic liquid complex possesses the strongest interaction with CO2.It is anticipated that the results can provide useful insights for the design and development of metal cluster-functionalized ionic liquid complex for the capture of CO2 and help to mitigate the greenhouse effect.(2)DFT computations predicted binary(Pt42-M13,M =Fe,Co,Ni,Cu)and ternary(Pt42-M12-N1,M,N =Fe,Co,Ni,Cu)Pt-shelled electrocatalysts.The activity of binary and ternary platinum shelled electrocatalysts with inexpensive metals for the ORR has been screened by means of DFT computations.Trends of the ORR activity of the binary Pt-M and ternary Pt-M-N(M,N = Fe,Co,Ni,Cu)Pt shelled electrocatalysts are described by the adsorption strength of O on a 55-atom nanoalloy cluster model.For the binary Pt-M(M = Fe,Co,Ni,Cu)shelled electrocatalysts,the ORR activity follows the order of Pt42Fe13>Pt42Ni13>Pt42Co13>Pt42Cu13,meaning that Pt42Fe13 is of the strongest ORR activity among these binary systems.For the ternary(Pt42-M12-N1,M,N =Fe,Co,Ni,Cu)Pt-shelled electrocatalysts,the ORR activity follows the order of Pt42Cu12N1<Pt42Ni,2N1<Pt42Co12N1<Pt42Fe,2N,(N = Fe,Co,Ni,Cu).Therefore,Pt42Fe12Cu1 is found to be the most optimal catalysts for the ORR among these ternary Pt-M-N(M,N = Fe,Co,Ni,Cu)systems,which is expected to be validated in future experiments.Our results can provide useful insights for the design and development of binary and ternary platinum shelled electrocatalysts with inexpensive metals for the ORR.(3)The new structure of three-layer core/shell PtCu nanoparticles(NPs)control for enhanced electrochemical performance.We have prepared unique three-layer core/shell PtCu NPs by a one-pot synthesis method in an organic solution system.All the reaction reagents were optimized in order to produce high-quality three-layer core/shell PtCu NPs.Our results show that the uniform three-layer core/shell PtCu NPs can be obtained by adding benzyl ether(BE)in the synthesis process of mixed PtCu NPs.The resulting three-layer core/shell PtCu NPs/C exhibit much higher performance for electrocatalytic activities in the ORR,FAOR,MOR,and EOR than those of mixed PtCu NPs/C and commercial Pt/C,due to the ligand(BE)-induced surface segregation of Pt on the surface of the NP.Our results suggest that advanced core-shell segregated electrocatalysts can be developed by engineering the surface composition by an easy preparation strategy,such as adding ligands.(4)The size control of PdCu NPs for enhanced electrochemical performance.We have created a new class of PdCu nanoparticle(NPs)as electrocatalysts with interesting tunable size for enhancing the ORR activity.The amount of TPP plays a crucial role in controlling the size of PdCu NPs.With the increasing amount of TPP,the size of PdCu NPs decreases.As a general trend,ORR activity decreases as bimetallic particle size increases.It is found that the 5.8 nm-PdCu NPs/C with the smallest size is of the best catalytic activity for ORR among these NPs,which is much larger than that of the commercial Pt/C catalyst.DFT calculations confirm that,with the increase of particle size,the adsorption energy upon O atom and charge distribution of particle are closer to the bulk phase,and the edges and corners become less,which explains the reason for the decrease of ORR catalytic performance.Our results provide useful size controlled strategy and reveal the relationship between bimetallic particle size and reaction activity,which will be useful in the development of new nanoalloy catalysts.(5)The transition metal doping control of PtCu NPs for enhanced electrochemical performance.PtCu nanooctahedrons(PtCu NOs)were successfully prepared by one pot method of CO released from W(CO)6 as a ligand.If W(CO)6 was not added,PtCu nanospheres(PtCu NSs)could be prepared.Through the electrocatalytic performance test of oxygen reduction reaction(ORR),it was found that PtCu NOs/C had higher activity than commercial Pt/C and PtCu NSs/C.To further improve the electrocatalytic performance of PtCu NOs,We dopted little nonnoble metal elements in PtCu NOs.Five PtCuM(M = Sc,Y,La,Gd,Fe)NOs catalyst were successfully prepared.Compared to commercial Pt/C and PtCu NOs/C,PtCuSc NOs/C catalyst show higher electrocatalytic performance for ORR and better stability.Our results provide a new method for the synthesis of trimetallic platinum based catalysts under controlled morphology,which will greatly promote the development of new trimetallic nanoparticle catalysts.