Studies On The Control Synthesis And Catalytic Property Of Platinum-Cobalt Alloy Nanocrystals

Precious metal Pt is a very important catalyst in the industrial field,which widely used in fuel cell cathode and anode catalyst and organic small molecule catalytic reaction.But the rare source of Pt and poor tolerance of CO poisoning in the catalytic reaction process hinder its commercialization applications.So,how to improve the efficiency of precious metal Pt and find the relevant substitutes have become a very meaningful research topic.Materials scientists have found that the Pt-M alloys(M=Fe,Co,Ni,Cu and etc.)not only effectively reduce the amount of precious metal Pt,but also exhibit enhanced catalytic activity in many catalytic reactions due to the changing of electronic structure of Pt-based alloy nanocrystals(NCs).Therefore,the development of highly efficient Pt-based alloy catalysts becomes a very effective method to alleviate the energy crisis.Because the catalytic properties of Pt-based nanocrystals are closely related to their size,composition and surface structure,we can improve the catalytic performance of Pt-based bimetallic alloys by regulating these factors.From the aspect of the regulation of the surface structure,the nanocrystals with high surface energy provide more catalytic active sites due to the high density of lower coordination of atoms,step bits,and kink atoms than the nanocrystals with low surface energy.However,the crystal tends to form a convex polyhedron with a low surface energy crystal surface during the growth process.Thermodynamically,the nanocrystals with a high surface energy are far instable than the nanocrystals with low surface energy,which led to the formation of concave nanocrystals is very difficult.From the aspect of component regulation,it is very difficult to control the synthesis of Pt-based bimetallic alloys with specific composition due to the large difference between atomic radius and atomic electronegativity of different metal element.In this paper,the work was focused on controlling surface structure and composition of Pt-Co bimetallic alloy,the main research progress and results are as follows:(1)In the oleylamine and oleic acid system,the Pt-Co bimetallic alloy with the highly concave rhombic dodecahedral structure were successfully synthesized by the regulation of the amounts of formaldehyde and initio molar ratio of precursors.We have learned through a series of experiments and comed to the conclution that formaldehyde plays a key role in the formation of highly concave structure.The electrocatalytic activity has been investigated on Pt-Co alloy NCs with different morphology and the commercial Pt/C as a reference catalyst.The specific surface activities of Pt-Co bimetallic alloys with rhombic dodecahedron structure and highly concave rhombic dodecahedron structure were 1.43 mA/cm2 and 2.68 mA/cm2,respectively,7.2 times and 13.4 times of commercial Pt/C(0.2 mA/cm2),respectively.The mass activity of Pt-Co bimetallic alloy with rhombic dodecahedron structure and highly concave rhombic dodecahedron structure was 0.54 mA/mg and 0.94 mA/mg,respectively,which were 3.2 times and 5.5 times of commercial Pt/C(0.17 mA/mg),respectively.(2)The Pt-Co bimetallic alloy with truncated octahedral structure was successfully synthesized in benzyl alcohol and DMF system.By changing the ratio of precursors Pt(acac)2 and CoCl2,the morphology transition from truncated octahedron to octahedron and concave octahedron can be achieved.By changing the volume ratio of benzyl alcohol and DMF,we obtained truncated octahedral Pt-Co bimetallic alloy with different composition.And the electrocatalytic activity of truncated octahedral Pt-Co alloy NCs with different composition and commercial Pt black was compared with the electrocatalytic oxidation of methanol as the probe reaction.We found that the specific surface activities of the truncated octahedral Pt-Co bimetallic alloy with three different components(Pt86Co14,Pt74CO26,Pt69CO31),are higher than that of commercial Pt black.By comparing the electrocatalytic activity of the truncated octahedral Pt-Co bimetallic alloys with different composition(Pt86Co14,Pt74Co26 and Pt69Co31),it was found that the higher the composition of Co in the alloy,the better the catalytic activity.