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Adsorbate-driven reactive interfacial Pt-NiO1−x nanostructure formation on the Pt3Ni(111) alloy surface

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Science Advances  13 Jul 2018:
Vol. 4, no. 7, eaat3151
DOI: 10.1126/sciadv.aat3151
  • Fig. 1 STM images on the Pt3Ni(111) surface in UHV or ambient pressure condition at 300 K.

    (A) Formation of a topmost Pt-skin layer after several cycles of Ar+ sputtering, followed by annealing at UHV and 1100 K (Vs = 0.32 V; It = 0.25 nA). (Inset) Atom-resolved STM image of the Pt-skin layer (Vs = 0.20 V; It = 0.20 nA). (B) CO adsorption on the terrace of the Pt-skin layer under 120 mtorr of CO (Vs = 0.45 V; It = 0.21 nA). (C) Disintegrated step and terrace structures of the Pt-skin layer under 135 mtorr of O2 (Vs = 1.40 V; It = 0.31 nA). (D) Evolution of the interfacial Pt-NiO1−x structure under 120 mtorr of mixed CO/O2 (1:5 ratio) (Vs = 1.25 V; It = 0.22 nA).

  • Fig. 2 AP-STM images and AP-XPS spectra on the Pt3Ni(111) surface under mixed CO/O2 gas (1:5 ratio) at 300 K.

    Time-lapse in situ AP-STM images of the segregated Ni oxide clusters on the Pt-skin layer (Vs = 1.40 V; It = 0.21 nA) at (A) 0 s, (B) 5 s, and (C) 108 s under 120 mtorr of mixed CO/O2 (1:5 ratio) gas at 300 K. (D) AP-XPS core-level spectra for Ni 2p (hν = 1200 eV) and for Pt 4f (hν = 180 eV) on the Pt-skin covered Pt3Ni(111) surface at 300 K under 100 mtorr of mixed CO/O2 (1:5 ratio) gas and at UHV. a.u., arbitrary units.

  • Fig. 3 Mass spectrometry profiles of the residual gas and AP-XPS spectra of the Pt3Ni(111) surface under 40 mtorr of CO and 100 mtorr of O2 mixed gas (1:2.5 ratio) at elevated temperatures.

    (A) Time-lapse mass fragment profiles for m/z = 28 (CO; black solid line), m/z = 32 (O2; green solid line), and m/z = 44 (CO2; blue solid line) in the second differential pumping stage of the photoelectron analyzer. (B) O 1s core-level AP-XPS spectra (hν = 650 eV) for (i) 300 K, (ii) 393 K, (iii) 420 K, and (iv) 543 K.

  • Fig. 4 DFT calculation results of the chemical reaction pathway for CO oxidation.

    Energy profiles for (A) the interfacial Pt-NiO1−x and (B) the fully oxidized NiO on the stoichiometric Pt3Ni structure. The optimized minimum and transition state (TS) structures are shown, and their relative energies are summarized by the solid black and red lines, respectively. For the energy barrier (ETS) of the rate-determining step, the results for Pt(111) are also shown (blue) for comparison. The adsorbed species are denoted with asterisks (*). The colors for each atom in the model: Pt (light gray), Ni (green), O (red), and C (brown).

  • Table 1 Calculated molecular adsorption energies and activation energy barriers.

    DFT calculation results for the molecular adsorption of CO, O2, and O on the surface of each theoretically designed model and their apparent activation energy barriers.

    Eads(CO), eVEads(O2), eVEads(O), eVEa, eV/mol
    Interfacial Pt-NiO1−x−1.30−0.88+0.37
    NiO/Pt3NiUnboundUnbound+1.08
    Pt(111)−1.41−0.31−0.53+0.86

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/7/eaat3151/DC1

    Supplementary Text

    Fig. S1. Formation of the bimetallic domain structures.

    Fig. S2. Oxygen-induced surface restructuring.

    Fig. S3. Statistical analysis plots for NiO1−x clusters.

    Fig. S4. Direct observation of the Pt3Ni(111) after CO/O2 gas evacuation.

    Fig. S5. AP-XPS analysis at 100 mtorr of O2.

    Fig. S6. Tracking the mass profiles at room temperature.

    Fig. S7. AP-XPS analysis in mixed CO/O2 gas at elevated temperature.

    Fig. S8. Arrhenius plots for catalytic activity measurements.

    Fig. S9. Model structures of the interfacial Pt-NiO1−x and NiO/Pt3Ni.

    Fig. S10. Energy profile for CO oxidation on the Pt(111).

    Fig. S11. Activation barriers for the CO oxidation reaction (CO* + O* → CO2) for different O* configurations on the model surfaces.

    Fig. S12. Energy profile for O2 dissociation on the Pt(111) surface and on the interfacial Pt-NiO1−x nanostructure.

    Movie S1. Time-lapse AP-STM movie on the Pt3Ni(111) surface under mixed CO/O2 (1:5 ratio) gas at 300 K.

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Text
    • Fig. S1. Formation of the bimetallic domain structures.
    • Fig. S2. Oxygen-induced surface restructuring.
    • Fig. S3. Statistical analysis plots for NiO1− x clusters.
    • Fig. S4. Direct observation of the Pt3Ni(111) after CO/O2 gas evacuation.
    • Fig. S5. AP-XPS analysis at 100 mtorr of O2.
    • Fig. S6. Tracking the mass profiles at room temperature.
    • Fig. S7. AP-XPS analysis in mixed CO/O2 gas at elevated temperature.
    • Fig. S8. Arrhenius plots for catalytic activity measurements.
    • Fig. S9. Model structures of the interfacial Pt-NiO1− x and NiO/Pt3Ni.
    • Fig. S10. Energy profile for CO oxidation on the Pt(111).
    • Fig. S11. Activation barriers for the CO oxidation reaction (CO* + O* → CO2) for different O* configurations on the model surfaces.
    • Fig. S12. Energy profile for O2 dissociation on the Pt(111) surface and on the interfacial Pt-NiO1− x nanostructure.
    • Legend for movie S1

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Time-lapse AP-STM movie on the Pt3Ni(111) surface under mixed CO/O2 (1:5 ratio) gas at 300 K.

    Files in this Data Supplement:

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