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Surface states in bulk single crystal of topological semimetal Co3Sn2S2 toward water oxidation

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Science Advances  16 Aug 2019:
Vol. 5, no. 8, eaaw9867
DOI: 10.1126/sciadv.aaw9867
  • Fig. 1 Crystal and band structure of bulk single-crystal Co3Sn2S2.

    (A) Crystal structure of Co3Sn2S2 obtained from single-crystal XRD and the Kagome lattice structure constructed by Co atoms in the a-b plane. (B) The 3D BZ projected in the (001) direction. Three pairs of nodal lines are shown in the first BZ. (C) Band structure of Co3Sn2S2 in a paramagnetic state without the consideration of SOC effect. The band linear crossing near the Fermi energy can be found around the point L. (D) Band structure of Co3Sn2S2 with the inclusion of SOC effect. The band linear crossing is open, resulting in the band gap. (E) The nontrivial surface states on (001) facet of Co3Sn2S2 crystal with Sn termination, which is not fully occupied and located just above the Fermi level. (F) The contribution of Co atoms to the nontrivial surface states shown in (E). Nearly all the states originate from the surface Co Kagome layer.

  • Fig. 2 Electrochemical performance of Co3Sn2S2 single-crystal catalyst.

    (A) OER polarization curves for Ni foam, Co3Sn2S2 single crystal, and Co3Sn2S2 micropowder crushed from the single crystal. (B) Overpotential of Co3Sn2S2 single-crystal catalyst at 10 mA cm−2 compared with some recently reported results for OER electrocatalysts. (C) Tafel plot of Ni foam, Co3Sn2S2 single crystal and Co3Sn2S2 micropowder Koutecky-Levich plots in O2-saturated 1 M KOH solution. The wide linear regime indicates the excellent electron transfer kinetics even at large overpotential. RHE, reverse hydrogen electrode. (D) Multicurrent process with the current density increased from 10 to 85 mA cm−2 without iR correction.

  • Fig. 3 Phase structure and physical properties of Co3Sn2S2 single-crystal catalyst.

    (A) Single-crystal XRD pattern of Co3Sn2S2. The pattern was recorded by rocking by 32° about the b axis of the rhombohedral cell. The high quality of the crystal is proven by the clear and sharp diffraction spots. The faint rings may be attributed to distortions and contaminations on the crystal surface. A typical SEM image of the single crystal is shown in the upper left corner. (B) HRTEM image of the Co3Sn2S2 single crystal prepared using the FIB technique and the SAED pattern recorded along the [001] crystal orientation. (C) Temperature dependence of electric resistivity of Co3Sn2S2 single crystal in zero field. The current was applied along the a and c axes. (D) Reciprocal susceptibility as a function of temperature. The magnetic moments are derived from Co atoms in the Kagome lattice. Using Curie Weiss law, an effective Bohr magneton μeff of 0.31 μB/Co is obtained.

  • Fig. 4 Surface structure and OER mechanism.

    (A) Detailed XPS analysis of the prepared single crystal. High-resolution XPS spectra for (A) S 2p and (B) Co 3d. (C) STM topography of a cleaved Co3Sn2S2 single-crystal thin flake showing an area of 8 nm by 8 nm. The Kagome lattice is highlighted by yellow lines in the circle. (D) Schematic representation of the favored OH uptake with the Co 3d orbitals. The exfoliation between the S-Sn plane break the octahedral symmetry of the surface Co atoms in the Kagome lattice (highlighted by yellow triangle). The empty 3dz2 orbital points to the p orbital of the OH group, resulting in a strong bonding between them. (E) Contour plots of the total charge distribution of Co3Sn2S2 single crystal with one OH group bonded to the Co atoms. Electronic charges are distributed in the vicinity of Sn atoms. However, for Co atoms, one can see the electron transfer through the Co─O bonding. a.u., arbitrary units.

  • Table 1 Z2 numbers (1; 000) of Co3Sn2S2 crystal.

    The product of parity of occupied bands at each time reversal invariant momenta (TRIM) points.

    TRIM points𝚪 (0,0,0)L (0.5,0,0) × 3F (0.5,0.5,0) × 3T (0.5,0.5,0.5)
    Parity+

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaaw9867/DC1

    Calculation details

    Single-crystal XRD measurements

    Fig. S1. Band structure of Co3Sn2S2 with different strength of SOC.

    Fig. S2. Surface band structure of Co3Sn2S2 with different strength of SOC.

    Fig. S3. The surface states contributed by S atoms, and Sn atoms, respectively.

    Fig. S4. The surface states of Co3Sn2S2 with S termination.

    Fig. S5. Polarization curves of a Cu wire with silver paint and Co3Sn2S2 crystal.

    Fig. S6. Stability test of the crushed single-crystal catalyst on Ni foam.

    Fig. S7. SEM image of the crystal.

    Fig. S8. EDS spectra of the Co3Sn2S2 single crystal.

    Fig. S9. Powder XRD measurement of the crushed single crystal.

    Fig. S10. Crystal structure of Co3Sn2S2 at 100 K.

    Fig. S11. TEM image of the single crystal prepared using the FIB technique.

    Fig. S12. ZFC/FC curves for the single crystal.

    Fig. S13. XPS survey spectrum of the bulk single crystal.

    Fig. S14. High-resolution XPS spectra of Sn 3d.

    Fig. S15. The Co atoms (red) in Co3Sn2S2 are octahedrally coordinated.

    Fig. S16. The adsorption position of OH group on the crystal surface.

    Fig. S17. The adsorption position of H atom on the Co3Sn2S2 single-crystal surface.

    Table S1. Crystallographic and refinement parameters of Co3Sn2S2.

    Table S2. Fractional atomic coordinates of the crystal.

    Table S3. Selected interatomic distances.

    Data S1. Crystallographic information file obtained at 100 K.

    Data S2. Crystallographic information file obtained at 300 K.

    References (4447)

  • Supplementary Materials

    The PDF file includes:

    • Calculation details
    • Single-crystal XRD measurements
    • Fig. S1. Band structure of Co3Sn2S2 with different strength of SOC.
    • Fig. S2. Surface band structure of Co3Sn2S2 with different strength of SOC.
    • Fig. S3. The surface states contributed by S atoms, and Sn atoms, respectively.
    • Fig. S4. The surface states of Co3Sn2S2 with S termination.
    • Fig. S5. Polarization curves of a Cu wire with silver paint and Co3Sn2S2 crystal.
    • Fig. S6. Stability test of the crushed single-crystal catalyst on Ni foam.
    • Fig. S7. SEM image of the crystal.
    • Fig. S8. EDS spectra of the Co3Sn2S2 single crystal.
    • Fig. S9. Powder XRD measurement of the crushed single crystal.
    • Fig. S10. Crystal structure of Co3Sn2S2 at 100 K.
    • Fig. S11. TEM image of the single crystal prepared using the FIB technique.
    • Fig. S12. ZFC/FC curves for the single crystal.
    • Fig. S13. XPS survey spectrum of the bulk single crystal.
    • Fig. S14. High-resolution XPS spectra of Sn 3d.
    • Fig. S15. The Co atoms (red) in Co3Sn2S2 are octahedrally coordinated.
    • Fig. S16. The adsorption position of OH group on the crystal surface.
    • Fig. S17. The adsorption position of H atom on the Co3Sn2S2 single-crystal surface.
    • Table S1. Crystallographic and refinement parameters of Co3Sn2S2.
    • Table S2. Fractional atomic coordinates of the crystal.
    • Table S3. Selected interatomic distances.
    • References (4447)

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    Other Supplementary Material for this manuscript includes the following:

    • Data S1 (.cif file). Crystallographic information file obtained at 100 K.
    • Data S2 (.cif file). Crystallographic information file obtained at 300 K.

    Files in this Data Supplement:

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