advances.sciencemag.org/cgi/content/full/3/9/e1701069/dc1 Supplementary Materials for Ultrastable atomic copper nanosheets for selective electrochemical reduction of carbon dioxide Lei Dai, Qing Qin, Pei Wang, Xiaojing Zhao, Chengyi Hu, Pengxin Liu, Ruixuan Qin, Mei Chen, Daohui Ou, Chaofa Xu, Shiguang Mo, Binghui Wu, Gang Fu, Peng Zhang, Nanfeng Zheng This PDF file includes: Published 6 September 2017, Sci. Adv. 3, e1701069 (2017) DOI: 10.1126/sciadv.1701069 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 Cu 2+ 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 Ni 2+ replaced by Cu 2+.
fig. S14. TEM and AFM images of Ni(OH)2 nanosheets before and after Cu 2+ 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. 1 H 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.
fig. S1. Large-scale SEM and TEM images and SAED pattern of the Cu/Ni(OH) 2 nanosheets. (A) Large-scale SEM image of the Cu/Ni(OH)2 nanosheets. (B to C) TEM images of the Cu/Ni(OH)2 nanosheets. (D) 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 Cu/Ni(OH) 2 nanosheets in ethanol. The SPR peak of Cu is highlighted by circle. fig. S4. STEM and EDX mapping images of the Cu/Ni(OH) 2 nanosheets. (A) STEM and (B) EDX mapping images of the Cu/Ni(OH)2 nanosheets.
fig. S5. XPS spectra of the Cu/Ni(OH) 2 nanosheets. (A) Complete survey spectrum of the nanosheets. (B) High-resolution XPS spectrum of Ni 2p. (C) High-resolution XPS spectrum of Cu 2p. (D) Auger electron spectra of Cu.
fig. S6. Experimental FT-EXAFS spectrum and the best fits of the as-prepared Cu/Ni(OH) 2 nanosheets and Cu foil. (A) The k-space and corresponding Fourier transformed R-space EXAFS spectra of Cu in Cu/Ni(OH)2 nanosheets. (B) Cu-Cu path considered, (C) Cu-Cu and Cu-O paths correlated. (D) 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. (A) Low-magnification, (B) High-magnification TEM, and (C) AFM images of the Cu nanosheets obtained from the Cu/Ni(OH)2 nanosheets by etching away Ni(OH)2, (D) XRD patterns of the Cu nanosheets. Due to the weakening of the orientation effect, only the diffraction peaks of (111) was appear. (E) XPS (top) and Ager electron spectra (bottom) of the Cu nanosheets. The inset in (A) shows a photograph of the ethanol dispersion of Cu nanosheets.
fig. S9. TEM images of the products obtained with the different heating time at 160 C. (A) 0 hour, (B) 1 hour, (C) 3 hours, (D) 5 hours, (E) 15 hours. Insets show the photographs of ethanol dispersions of the as-prepared nanosheets corresponding to the TEM images.
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 the different heating time at 160 C. The elemental contents were measured by ICP-MS.
fig. S12. TEM images and XRD patterns of the products obtained at different hydrothermal temperature. (A, B) 140 o C; (C, D) 180 o C.
fig. S13. Two possible pathways for the deposition of Cu 2+ 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 Ni 2+ replaced by Cu 2+. While Pathway 1 should result in an increment in the thickness of the nanosheets, pathway 2 should not change the thickness. Color codes: Cyan, Cu; green, Ni; red, C; white, H.
fig. S14. TEM and AFM images of the Ni(OH) 2 nanosheets before and after Cu 2+ substitution, and HS-LEISS spectra for the Cu(OH) 2 /Ni(OH) 2 nanosheets. TEM and AFM images of Ni(OH)2 nanosheets (A) before and (B) after Cu 2+ substitution. The photographs of their ethanol dispersions are given as insets. (C) High-sensitivity LEISS spectra for the Cu(OH)2/Ni(OH)2 nanosheets with Cu and Ni references.
fig. S15. TEM, XRD, and EDX characterizations of the Cu 2 O intermediates and Cu nanosheets using β-ni(oh) 2 as the template. TEM images of the as-prepared (A) β-ni(oh)2, (B) Cu2O/β-Ni(OH)2 and (C) Cu/β-Ni(OH)2 nanosheets. (D) HR- TEM image of Cu/β-Ni(OH)2 nanosheets. (E) XRD patterns of β-ni(oh)2, Cu2O/β- Ni(OH)2 and Cu/β-Ni(OH)2 nanosheets. (F) STEM/EDX-mapping image of the asprepared Cu/β-Ni(OH)2 nanosheets. The Cu/β-Ni(OH)2 nanosheets were prepared with the same conditions of Cu/Ni(OH)2 nanosheets except that the Ni 2+ precursors was prepared by β-ni(oh)2 nanosheets.
fig. S16. TEM images and XRD of the α-ni(oh) 2 and Cu/α-Ni(OH) 2 nanosheets. TEM images of the as-prepared (A) α-ni(oh)2 nanosheets and (B) Cu/α- Ni(OH)2 nanosheets. (C) HR-TEM image of the Cu/α-Ni(OH)2 nanosheets, (D) XRD pattern, and (E) STEM/EDS-mapping image of the as-prepared Cu/α-Ni(OH)2 nanosheets. The Cu/α-Ni(OH)2 nanosheets were prepared with the same conditions of Cu/Ni(OH)2 nanosheets except that the Ni 2+ precursors was prepared by 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. (A) TEM, (B) HR-TEM image, and (C) XRD pattern of the Cu nanoparticles prepared in the same conditions as Cu/Ni(OH)2 nanosheets except that no Ni was introduced. fig. S18. TEM image of the Cu/Ni(OH) 2 nanosheets after being heated at 280 C in N 2 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. (A) High-resolution XPS spectrum of Cu 2p. (B) Auger electron spectrum of Cu. fig. S20. Thermal stability of the hybrid Cu/Ni(OH) 2 nanosheets at 100 o C in air. (A, B) Photographs of the nanosheets (A) before and (B) after being heated for 48 h. (C) TEM image and (D) XRD pattern of the nanosheets after the 48-h thermal treatment.
fig. S21. N 2 adsorption isotherm of the Cu/Ni(OH) 2 nanosheets at 77 K. Based on the analysis, the BET surface area of the Cu/Ni(OH)2 nanosheets was calculated to be 200.5 m 2 /g.
fig. S22. Effect of surface formate modification on the stability of Cu foils against oxidation. (A) Color change of Cu foils after being stored in air at room temperature for 5 months with and without surface HCOO - modification. (B) Cyclic voltammetry of Cu foils in 0.5 M NaHCO3 before and after HCOO - treatment. The scan rate was set at 1 mv/s. The inset is the images of Cu foil before (left) and after (right) HCOO - modification.
fig. S23. Air instability of the Cu/Ni(OH) 2 nanosheets after surface ligand exchange by acetate. Color change of Cu/Ni(OH)2 nanosheets after being mixed with an acetate solutionin air to induce the surface ligand exchange for different time: (A) 0 h, (B) 48 h, (C) 120 h. (D) XRD patternsof Cu/Ni(OH)2 nanosheets obtained at 48 h and 120h. The conditions for the formate-acetate exchange process: 20 mg Cu/Ni(OH)2 nanosheets were mixed 50 mg CH3COONa in 10 ml deionized water, and the solution was stirred in air at room temperature.
fig. S24. TPD-MS profiles of the species released from the acetate-exchanged Cu/Ni(OH) 2 nanosheets under the TPD-MS measuring condition. The acetateexchanged Cu/Ni(OH)2 nanosheets were obtained by mixing the as-prepared formatestabilized Cu/Ni(OH)2 nanosheets with a CH3COONa solution at room temperature for 120 h. The peak at 59.1 was corresponding to CH3COO -, suggesting that the HCOO - has been replaced by CH3COO -. 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 CO 2 reduction. (A) The normalized polarization curves of three samples in CO2-saturated 0.5 M NaHCO3 aqueous solution by the electrode surface area of electrocatalysts and the scan rate was 10 mv/s. (B) Faradaic efficiencies of CO and H2 at each given potential for 2 h on Cu nanoparticles. (C) Faradaic efficiencies of CO and H2 at each given potential for 2 h on Ni(OH)2 nanosheets. (D) Chronoamperometric current of Cu nanoparticles and Ni(OH)2 nanosheets at -0.5 V vs. RHE. The catalyst s loading on carbon paper electrode was 0.5 mg/cm 2.
fig. S27. 1 H NMR spectra of products after bulk electrolysis at different potentials for 2 hours on Cu/Ni(OH) 2 nanosheets modified carbon paper electrode.
fig. S28. TEM image and electrocatalytic performance of the Cu nanosheets in CO 2 reduction. (A) TEM image of Cu nanosheets made from nanosheets obtained Cu/Ni(OH)2 by etching away Ni(OH)2. (B) The polarization curves of Cu-rich nanosheets in N2-saturated and CO2-saturated 0.5 M NaHCO3 aqueous solution. The current densities were normalized by the electrode surface area. And the scan rate was 10 mv/s. (C) Faradaic efficiencies of CO and H2 at different potentials. (D) Chronoamperometric current at -0.5V vs. RHE. The catalyst s loading on carbon paper electrode was 0.5 mg/cm 2.
fig. S29. Loading-dependent chronoamperometric currents at -0.5 V versus RHE. The loading of Cu/Ni(OH)2 nanosheets on carbon paper was 0.2 or 1.0 mg/cm 2. fig. S30. TEM images of the Cu and Cu/Ni(OH) 2 nanosheets after electrochemical tests. (A) Cu nanosheets; (B) Cu/Ni(OH)2 nanosheets.
fig. S31. Room-temperature CO 2 adsorption isotherms of the Cu/Ni(OH) 2 nanosheets, Cu nanosheets obtained from 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). Z is real impedance and -Z is imaginary impedance. Cu/Ni(OH)2 nanosheets exhibited superior electrical conductivity and ion transport kinetics over other three samples. The mass loading was 0.5 mg/cm 2. The electrochemical interface was modeled by an equivalent circuit containing the total Ohmic resistance of the cell (R Ω ); charge-transfer resistance (Rct) and the double-layer capacitance (Cdl). The catalyst s loading on carbon paper electrode was 0.5 mg/cm 2.
fig. S33. Scheme of the setup for the electrochemical reduction of CO 2.
table S1. EXAFS parameters of Cu foil and Cu/Ni(OH) 2 nanosheets. sample Path CN R / Å σ 2 / x10-3 Å ΔE 0 / ev S 0 2 Cu foil Cu-Cu 12 2.539±0.003 8.7±0.6 2.6±0.5 Cu/Ni(OH) 2 only Cu- Cu path Correlate Cu-Cu 6.6±0.6 2.546±0.004 9.3±0.8 3.6±0.6 Cu-Cu 6.5±0.9 2.549±0.006 9.2±1.3 4.0±1.1 Cu-O 0.5±0.2 1.961±0.041 0.87 It should be noted that, based on all our careful experimental results that the Cu-O shell in Cu/Ni(OH)2 nanosheets is due to the interaction between Cu(0) and the HCOO -, but not caused by the Cu oxidation. table S2. The elemental analysis results of two different Cu/Ni(OH) 2 nanosheet s. No # Mass (mg) Element Mass content (%) 1 6.08 2 6.76 N C H N C H 0.02 2.01 2.49 0.02 2.05 2.49