Supported PtCu alloys have been broadly applied in heterogeneous catalysis and electrocatalysis owing to their excellent catalytic performance and high CO tolerance. It is important to analyze the outermost surface c...Supported PtCu alloys have been broadly applied in heterogeneous catalysis and electrocatalysis owing to their excellent catalytic performance and high CO tolerance. It is important to analyze the outermost surface composition of the supported alloy nanoparticles to understand the nature of the catalytically active sites. In this paper, homogeneous face-centered cubic PtCu nanoparticles with a narrow particle size distribution were successfully fabricated and dispersed on a high-surface-area Ti〇2 powder support. The samples were oxidized and reduced in situ and then introduced into the ultrahigh vacuum chamber to measure the topmost surface composition by high-sensitivity low-energy ion scattering spectroscopy, and to determine the oxidation states of the elements by X-ray photoelectron spectroscopy. The surface composition and morphology, elemental distribu-tion, and oxidation states of the components were found to be significantly affected by the support and treatment conditions. The PtCu is de-alloyed upon oxidation with CuO wetting on the TiO2 sur-face and re-alloyed upon reduction. Phase diagrams of the surface composition and the bulk com-position were plotted and compared for the supported and unsupported materials.展开更多
The stability and oxygen reduction reaction （ORR） activity of the Pt-segregated surface in various Pt-M alloys （M： transition metals） are investigated through systematic DFT calculations on the thermodynamic （al...The stability and oxygen reduction reaction （ORR） activity of the Pt-segregated surface in various Pt-M alloys （M： transition metals） are investigated through systematic DFT calculations on the thermodynamic （alloy formation energy and Pt surface segregation energy）, surface chemical property （oxygen binding energy） and electronic （d-band center） properties. Factors af- fecting these properties, such as the atomic radii and surface energy of M and the electronic ligand interaction between Pt and M are analyzed as a function of outmost d electron numbers of M. It is shown that the electronic ligand interaction plays de- termining role in the alloy formation energy of various Pt-M alloys; the formation of Pt-segregated surface in Pt-M alloys is faw）red when alloying metals have higher surface energy and smaller radii than Pt; the oxygen binding energy on the Pt-segregated surface in Pt-M alloys varies approximately linearly with the d-band center of surface Pt atoms; the lattice strain and electronic ligand effects are simply additive in Pt-M alloys; the stain effect in Pt-M alloys nearly linearly affects the d-band center of the Pt-segregated surface in Pt-M alloys; transition metals with less than 10 d electrons mostly exhibit electron ligand effects which result in downshift of the d-band center of the segregated surface Pt atoms, while those with ten d electrons exhibit electron ligand effect upshifting the d-band center of the segregated Pt atoms.展开更多
We have successfully employed metal-organic chemical vapor deposition （MOCVD） technique to simultaneously deposit double-sided YBa2Cu3O7-δ （YBCO） films on both sides of YzO3/yttria-stabilized zirconia （YSZ）/Ce...We have successfully employed metal-organic chemical vapor deposition （MOCVD） technique to simultaneously deposit double-sided YBa2Cu3O7-δ （YBCO） films on both sides of YzO3/yttria-stabilized zirconia （YSZ）/CeO2 （YYC） buffered biaxially textured Ni-5 at.% W substrates, which is of great prospect to cut the production cost of YBCO coated conductors. X-ray diffraction analysis revealed that both sides of YBCO film were purely c-axis oriented and highly textured. The co-scan of （005） YBCO and Ф-scan of （103） YBCO yielded full width at half maximum （FWHM） values of 4.9° and 6.6° for one side of double-sided YBCO film, respectively, as well as 4.4° and 6.4° for the other side. The current transportation measurements performed on such double-sided 500 nm-thickness YBCO films showed the self-field critical current density （Jc） at 77 K of 0.6 MA/cm^2 and 1.2 MA/cm^2, respectively. Further research is in the process of exploring new solution to improve the Jc in practice.展开更多
基金supported by the National Basic Research Program of China(973 Program,2013CB933102)the National Natural Science Foundation of China(21273178,21573180,91545204)Xiamen-Zhuoyue Biomass Energy Co.Ltd~~
文摘Supported PtCu alloys have been broadly applied in heterogeneous catalysis and electrocatalysis owing to their excellent catalytic performance and high CO tolerance. It is important to analyze the outermost surface composition of the supported alloy nanoparticles to understand the nature of the catalytically active sites. In this paper, homogeneous face-centered cubic PtCu nanoparticles with a narrow particle size distribution were successfully fabricated and dispersed on a high-surface-area Ti〇2 powder support. The samples were oxidized and reduced in situ and then introduced into the ultrahigh vacuum chamber to measure the topmost surface composition by high-sensitivity low-energy ion scattering spectroscopy, and to determine the oxidation states of the elements by X-ray photoelectron spectroscopy. The surface composition and morphology, elemental distribu-tion, and oxidation states of the components were found to be significantly affected by the support and treatment conditions. The PtCu is de-alloyed upon oxidation with CuO wetting on the TiO2 sur-face and re-alloyed upon reduction. Phase diagrams of the surface composition and the bulk com-position were plotted and compared for the supported and unsupported materials.
基金supported by the National Basic Research Program of China(2012CB932800)the National Natural Science Foundation of China(21303048)the Natural Science Foundation of Hunan Province(13JJ4101)
文摘The stability and oxygen reduction reaction （ORR） activity of the Pt-segregated surface in various Pt-M alloys （M： transition metals） are investigated through systematic DFT calculations on the thermodynamic （alloy formation energy and Pt surface segregation energy）, surface chemical property （oxygen binding energy） and electronic （d-band center） properties. Factors af- fecting these properties, such as the atomic radii and surface energy of M and the electronic ligand interaction between Pt and M are analyzed as a function of outmost d electron numbers of M. It is shown that the electronic ligand interaction plays de- termining role in the alloy formation energy of various Pt-M alloys; the formation of Pt-segregated surface in Pt-M alloys is faw）red when alloying metals have higher surface energy and smaller radii than Pt; the oxygen binding energy on the Pt-segregated surface in Pt-M alloys varies approximately linearly with the d-band center of surface Pt atoms; the lattice strain and electronic ligand effects are simply additive in Pt-M alloys; the stain effect in Pt-M alloys nearly linearly affects the d-band center of the Pt-segregated surface in Pt-M alloys; transition metals with less than 10 d electrons mostly exhibit electron ligand effects which result in downshift of the d-band center of the segregated surface Pt atoms, while those with ten d electrons exhibit electron ligand effect upshifting the d-band center of the segregated Pt atoms.
基金supported by the National Natural Science Foundation of China(Grant No.51002024)Sichuan Youth Science and Technology Innovation Research Team Funding(Grant No.2011JTD0006)Fundamental Research Funds for the Central Universities(Grant Nos.ZYGX2012J039 and ZYGX2011Z002)
文摘We have successfully employed metal-organic chemical vapor deposition （MOCVD） technique to simultaneously deposit double-sided YBa2Cu3O7-δ （YBCO） films on both sides of YzO3/yttria-stabilized zirconia （YSZ）/CeO2 （YYC） buffered biaxially textured Ni-5 at.% W substrates, which is of great prospect to cut the production cost of YBCO coated conductors. X-ray diffraction analysis revealed that both sides of YBCO film were purely c-axis oriented and highly textured. The co-scan of （005） YBCO and Ф-scan of （103） YBCO yielded full width at half maximum （FWHM） values of 4.9° and 6.6° for one side of double-sided YBCO film, respectively, as well as 4.4° and 6.4° for the other side. The current transportation measurements performed on such double-sided 500 nm-thickness YBCO films showed the self-field critical current density （Jc） at 77 K of 0.6 MA/cm^2 and 1.2 MA/cm^2, respectively. Further research is in the process of exploring new solution to improve the Jc in practice.
