Research ArticleELECTROCHEMICAL SCIENCES

Ultrastable atomic copper nanosheets for selective electrochemical reduction of carbon dioxide

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Science Advances  06 Sep 2017:
Vol. 3, no. 9, e1701069
DOI: 10.1126/sciadv.1701069
  • Fig. 1 Microscopic characterizations of the hybrid Cu/Ni(OH)2 nanosheets.

    (A) Low-magnification TEM image. Inset: Photograph of a dispersion of the nanosheets in ethanol. (B) TEM image of the cross-sectional nanosheets obtained by microtoming. (C) AFM image (top) and the height profile (bottom) of the nanosheets. (D) HRTEM image of an individual nanosheet.

  • Fig. 2 Detailed structure characterizations of the Cu/Ni(OH)2 nanosheets.

    (A) XRD pattern of the Cu/Ni(OH)2 nanosheets. a.u., arbitrary units. (B to E) XANES and EXAFS fitting spectra of Cu/Ni(OH)2 for Ni K-edge (B and C) and Cu K-edge (D and E). (F) HS-LEISS spectra for the nanosheets with different detected depths.

  • Fig. 3 The proposed formation mechanism of the hybrid Cu/Ni(OH)2 nanosheets.

    Color codes: cyan, Cu; green, Ni; red, O; gray, C; white, H.

  • Fig. 4 Stability in air and surface species identification of the Cu/Ni(OH)2 nanosheets.

    (A) TEM image of the Cu/Ni(OH)2 nanosheets after being stored in air at room temperature for 90 days. (B) XRD patterns of the nanosheets after storing in air at room temperature for 7 to 90 days. (C) TPD-MS profiles of the Cu/Ni(OH)2 nanosheets heated in vacuum. Whereas the bottom shows relative ionization intensities of the main decomposition products at different temperatures, the top displays the accumulative ionization intensity. m/z, mass/charge ratio. (D) FTIR spectrum of the nanosheets. (E) Adsorption model of formate on Cu. Color codes: cyan, Cu; red, O; gray, C; white, H.

  • Fig. 5 Catalytic performances of the Cu/Ni(OH)2 nanosheets in the electroreduction of CO2.

    (A) Normalized polarization curves in N2-saturated and CO2-saturated 0.5 M NaHCO3 aqueous solution by the electrode surface area of electrocatalysts. The scan rate was 10 mV/s. (B) FEs of CO and H2 at different potentials. (C) Chronoamperometric current at −0.5 V versus RHE. The loading of the Cu/Ni(OH)2 nanosheets on carbon paper was 0.5 mg/cm2.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/9/e1701069/DC1

    fig. S1. Large-scale SEM and TEM images and SAED pattern of the Cu/Ni(OH)2 nanosheets.

    fig. S2. EDX spectrum of the Cu/Ni(OH)2 nanosheets.

    fig. S3. UV-vis absorption spectrum of the dispersion of the Cu/Ni(OH)2 nanosheets in ethanol.

    fig. S4. STEM and EDX mapping images of the Cu/Ni(OH)2 nanosheets.

    fig. S5. XPS spectra of the Cu/Ni(OH)2 nanosheets.

    fig. S6. Experimental FT-EXAFS spectrum and the best fits of the as-prepared Cu/Ni(OH)2 nanosheets and Cu foil.

    fig. S7. Three structural models of Cu to simulate their FT-EXAFS using the FEFF 8 program: bulk Cu, two-atomic-layer Cu, and one-atomic-layer Cu.

    fig. S8. TEM, AFM, XRD, and XPS characterizations of the Cu nanosheets.

    fig. S9. TEM images of the products obtained with the different heating time at 160°C.

    fig. S10. XRD patterns of the products obtained with the different heating time at 160°C: 0, 1, 3, 5, and 15 hours.

    fig. S11. Relative contents of Cu and Ni in the products obtained with different heating time at 160°C.

    fig. S12. TEM images and XRD patterns of the products obtained at different hydrothermal temperatures.

    fig. S13. Two possible pathways for the deposition of Cu2+ onto premade Ni(OH)2 nanosheets subsequent deposition with Cu(OH)2 continually grown on Ni(OH)2 (pathway I) and substitution deposition (pathway II) with surface Ni2+ replaced by Cu2+.

    fig. S14. TEM and AFM images of Ni(OH)2 nanosheets before and after Cu2+ substitution, and HS-LEISS spectra for Cu(OH)2/Ni(OH)2 nanosheets.

    fig. S15. TEM, XRD, and EDX characterizations of Cu2O intermediates and Cu nanosheets using β-Ni(OH)2 as the template.

    fig. S16. TEM images and XRD of the α-Ni(OH)2 and Cu/α-Ni(OH)2 nanosheets.

    fig. S17. TEM and HR-TEM images and XRD pattern of the Cu nanoparticles synthesized in the absence of Ni.

    fig. S18. TEM image of the Cu/Ni(OH)2 nanosheets after being heated at 280°C in N2 for 3 hours.

    fig. S19. XPS and Auger electron spectra of the Cu/Ni(OH)2 nanosheets after storing in air at room temperatures for 90 days.

    fig. S20. Thermal stability of the hybrid Cu/Ni(OH)2 nanosheets at 100°C in air.

    fig. S21. N2 adsorption isotherm of the Cu/Ni(OH)2 nanosheets at 77 K.

    fig. S22. Effect of surface formate modification on the stability of Cu foils against oxidation.

    fig. S23. Air instability of the Cu/Ni(OH)2 nanosheets after surface ligand exchange by acetate.

    fig. S24. TPD-MS profiles of the species released from the acetate-exchanged Cu/Ni(OH)2 nanosheets under the TPD-MS measuring condition.

    fig. S25. Photograph of the reaction mixture without the addition of HCOONa after being heated at the same conditions as those for the synthesis of the Cu/Ni(OH)2 nanosheets.

    fig. S26. Electrocatalytic performances of pure Cu nanoparticles and Ni(OH)2 nanosheets in the CO2 reduction.

    fig. S27. 1H NMR spectra of products after bulk electrolysis at different potentials for 2 hours on the Cu/Ni(OH)2 nanosheets modified carbon paper electrode.

    fig. S28. TEM image and electrocatalytic performance of the Cu nanosheets in CO2 reduction.

    fig. S29. Loading-dependent chronoamperometric currents at −0.5 V versus RHE.

    fig. S30. TEM images of the Cu and Cu/Ni(OH)2 nanosheets after electrochemical tests.

    fig. S31. Room-temperature CO2 adsorption isotherms of the Cu/Ni(OH)2 nanosheets, Cu nanosheets obtained from the Cu/Ni(OH)2 nanosheets by etching away Ni(OH)2, Cu nanoparticles made with the same conditions of Cu/Ni(OH)2 except that no Ni was introduced, and Ni(OH)2 nanosheets prepared with the same conditions of Cu/Ni(OH)2 except that no Cu was introduced.

    fig. S32. Nyquist plots of the four different samples under the potential of −0.5 V (versus RHE).

    fig. S33. Scheme of the setup for the electrochemical reduction of CO2.

    table S1. EXAFS parameters of the Cu foil and Cu/Ni(OH)2 nanosheets.

    table S2. The elemental analysis results of two different Cu/Ni(OH)2 nanosheets.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Large-scale SEM and TEM images and SAED pattern of the Cu/Ni(OH)2 nanosheets.
    • fig. S2. EDX spectrum of the Cu/Ni(OH)2 nanosheets.
    • fig. S3. UV-vis absorption spectrum of the dispersion of the Cu/Ni(OH)2 nanosheets in ethanol.
    • fig. S4. STEM and EDX mapping images of the Cu/Ni(OH)2 nanosheets.
    • fig. S5. XPS spectra of the Cu/Ni(OH)2 nanosheets.
    • fig. S6. Experimental FT-EXAFS spectrum and the best fits of the as-prepared Cu/Ni(OH)2 nanosheets and Cu foil.
    • fig. S7. Three structural models of Cu to simulate their FT-EXAFS using the FEFF 8 program: bulk Cu, two-atomic-layer Cu, and one-atomic-layer Cu.
    • fig. S8. TEM, AFM, XRD, and XPS characterizations of the Cu nanosheets.
    • fig. S9. TEM images of the products obtained with the different heating time at 160°C.
    • fig. S10. XRD patterns of the products obtained with the different heating time at 160°C: 0, 1, 3, 5, and 15 hours.
    • fig. S11. Relative contents of Cu and Ni in the products obtained with different heating time at 160°C.
    • fig. S12. TEM images and XRD patterns of the products obtained at different hydrothermal temperatures.
    • fig. S13. Two possible pathways for the deposition of Cu2+ onto premade Ni(OH)2 nanosheets subsequent deposition with Cu(OH)2 continually grown on Ni(OH)2 (pathway I) and substitution deposition (pathway II) with surface Ni2+ replaced by Cu2+.
    • fig. S14. TEM and AFM images of Ni(OH)2 nanosheets before and after Cu2+ substitution, and HS-LEISS spectra for Cu(OH)2/Ni(OH)2 nanosheets.
    • fig. S15. TEM, XRD, and EDX characterizations of Cu2O intermediates and Cu nanosheets using β-Ni(OH)2 as the template.
    • fig. S16. TEM images and XRD of the α-Ni(OH)2 and Cu/α-Ni(OH)2 nanosheets.
    • fig. S17. TEM and HR-TEM images and XRD pattern of the Cu nanoparticles synthesized in the absence of Ni.
    • fig. S18. TEM image of the Cu/Ni(OH)2 nanosheets after being heated at 280°C in N2 for 3 hours.
    • fig. S19. XPS and Auger electron spectra of the Cu/Ni(OH)2 nanosheets after storing in air at room temperatures for 90 days.
    • fig. S20. Thermal stability of the hybrid Cu/Ni(OH)2 nanosheets at 100°C in air.
    • fig. S21. N2 adsorption isotherm of the Cu/Ni(OH)2 nanosheets at 77 K.
    • fig. S22. Effect of surface formate modification on the stability of Cu foils against oxidation.
    • fig. S23. Air instability of the Cu/Ni(OH)2 nanosheets after surface ligand exchange by acetate.
    • fig. S24. TPD-MS profiles of the species released from the acetate-exchanged Cu/Ni(OH)2 nanosheets under the TPD-MS measuring condition.
    • fig. S25. Photograph of the reaction mixture without the addition of HCOONa after being heated at the same conditions as those for the synthesis of the Cu/Ni(OH)2 nanosheets.
    • fig. S26. Electrocatalytic performances of pure Cu nanoparticles and Ni(OH)2 nanosheets in the CO2 reduction.
    • fig. S27. 1H NMR spectra of products after bulk electrolysis at different potentials for 2 hours on the Cu/Ni(OH)2 nanosheets modified carbon paper electrode.
    • fig. S28. TEM image and electrocatalytic performance of the Cu nanosheets in CO2 reduction.
    • fig. S29. Loading-dependent chronoamperometric currents at −0.5 V versus RHE.
    • fig. S30. TEM images of the Cu and Cu/Ni(OH)2 nanosheets after electrochemical tests.
    • fig. S31. Room-temperature CO2 adsorption isotherms of the Cu/Ni(OH)2 nanosheets, Cu nanosheets obtained from the Cu/Ni(OH)2 nanosheets by etching away Ni(OH)2, Cu nanoparticles made with the same conditions of Cu/Ni(OH)2 except that no Ni was introduced, and Ni(OH)2 nanosheets prepared with the same conditions of Cu/Ni(OH)2 except that no Cu was introduced.
    • fig. S32. Nyquist plots of the four different samples under the potential of −0.5 V (versus RHE).
    • fig. S33. Scheme of the setup for the electrochemical reduction of CO2.
    • table S1. EXAFS parameters of the Cu foil and Cu/Ni(OH)2 nanosheets.
    • table S2. The elemental analysis results of two different Cu/Ni(OH)2 nanosheets.

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