Formation of Copper Catalysts for CO2 Reduction with High Ethylene ...
Supporting Information for
Formation of Copper Catalysts for CO2 Reduction with High Ethylene/Methane Product Ratio Investigated with In Situ X-ray Absorption Spectroscopy André Eilert,†,‡,ǁ F. Sloan Roberts,†,‡,ǁ Daniel Friebel,†,‡ and Anders Nilsson*,†,‡,§ †SLAC
National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
‡SUNCAT
Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, 443 Via Ortega, Stanford, CA 95305, USA
§Department
of Physics, AlbaNova University Center, Stockholm University, Roslagstullsbacken 21, S-10691 Stockholm, Sweden.
AUTHOR INFORMATION Corresponding Author *mailing address: Anders Nilsson, Stockholms universitet, Kemisk Fysik, 106 91 Stockholm, email: [email protected] Author Contributions ǁ(A.E.,
F.S.R.) These authors contributed equally to this work. S1
Fig. S1. Comparison of the Cu K-edge XAS of the pristine sample and the reduced sample after oxidation with Cl- at 0.7 V vs. RHE (2 scans). The latter one was reduced at -0.4 V vs. RHE. Spectra measured at ocp. Full spectrum and three zooms. Fig. S2. Lattice strain analysis using the „bond length with a ruler“ concept ES = E0 + (Eexp – E0)(1+s)2 with the energy under strain ES, the absorption energy E0, the experimentally observed energy Eexp and the lattice strain s. The experimentally observed spectrum of the reduced sample was stretched for different s and the square deviation to the spectrum of the pristine sample was plotted. The minimum of the curve shows the apparent lattice strain. The results show now significant lattice strain, an apparent lattice strain of -0.12 % for CuCubes corresponds to a change of 0.003 Å in Cu-Cu nearest neighbor distance, which is below the EXAFS detection limit of 0.01 Å.
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1.9
1.4
0.9 reduced oxidized
0.4
CuCl ref. -0.1 2815
2825
2835 2845 Energy / eV
2855
Difference oxidized-reduced / a.u.
Normalized absorbance / a.u.
0.06 0.04 0.02 0.00 -0.02 -0.04 -0.06 2815
2825
2835 2845 Energy / eV
2855
Fig. S3. Left: Comparison of the Cl K-edge XAS of the reduced sample before oxidation at -0.28 V and of the oxidized sample at 0.65 V. The spectrum is dominated by hydrated Cl- in the solution. The CuCl reference spectrum was taken from Drake et al.1 The yellow line marks the region with the largest difference between measured spectra and the CuCl reference. Right: Difference spectrum. From the difference spectrum, a maximum spectral concentration of CuCl of 3 % can be assumed, which corresponds to a layer thickness of ca. 0.3 nm CuCl (attenuation length of Cl Kα in water: 34.6 µm).
Fig. S4. Results from Figure 2 (main text) in the top row and corresponding edge jumps (height of step edge) in the bottom row. A decreasing edge jump corresponds to dissolving Cu.
S3
Fig. S5. Spectrum of the experimentally observed Cu(II) species (Cu(II) Exp) and of several reference compounds. The lack of a feature at 8987 eV in the experimental spectrum points towards CuCO3, Cu(OH)2 or a [Cu(H2O)6]-salt. A mixed carbonate/hydroxide such as malachite or azurite is possible. References of CuO, CuCl2∙2H2O, CuCl2, Cu2OCl and Cu2Cl(OH)3 from Ferrandon et al.2, of the solid [Cu(H2O)6]∙2ClO4 from Frank et al.3, of Cu(OH)2 from Chang et al.4 and of CuCO3 from Liu et al.5
S4
Fig. S6. Comparison of the Cu K-edge XAS of the pristine, reduced sample and the reduced sample after oxidation without Cl- at 0.7 V vs. RHE (2 scans). Both samples were reduced at -0.9 V vs. RHE. Spectra measured at ocp. Full spectrum and three zooms. 0
J / mA/cm2
-5 -10 - Cu(II)-derived - CuCubes - Polycrystalline Cu
-15 -20 -25 -30
-1.0
-0.8 E / V vs. RHE
-0.6
-0.4
Fig. S7. Current densities during CO2RR for the investigated samples in OLEMS (Fig. 3a main text). The reductive wave for CuCubes at -0.4 V is due to the reduction of Cu2O.
S5
Fig. S8. Sketch of the setup used for in situ Cu K-edge XAS. The setup for Cl K-edge XAS was the same except for the thickness of the glassy carbon window (~8 µm, self-made by heating Kapton to 1000 °C for one hour in a nitrogen atmosphere).
References (1)
(2)
(3) (4) (5)
Drake, I.; Fujdala, K.; Bell, A.; Tilley, T. Dimethyl Carbonate Production via the Oxidative Carbonylation of Methanol over Cu/SiO2 Catalysts Prepared via Molecular Precursor Grafting and Chemical Vapor Deposition Approaches. J. Catal. 2005, 230, 14–27. Ferrandon, M.; Daggupati, V.; Wang, Z.; Naterer, G.; Trevani, L. Using XANES to Obtain Mechanistic Information for the Hydrolysis of CuCl2 and the Decomposition of Cu2OCl2 in the Thermochemical Cu–Cl Cycle for H2 Production. J. Therm. Anal. Calorim. 2015, 119, 975–982. Frank, P.; Benfatto, M.; Hedman, B.; Hodgson, K. O. The XAS Model of Dissolved Cu(II) and Its Significance to Biological Electron Transfer. J. Phys. Conf. Ser. 2009, 190, 012059. Chang, P.-C.; Wei, Y.-L.; Chang, S.-H.; Wang, H. P. XAS Study of the Residual Copper after Desorption from Rice Husk Ash. J. Electron Spectrosc. Relat. Phenom. 2007, 156–158, 224–227. Liu, S.-H.; Wang, H. P.; Huang, C.-H.; Hsiung, T.-L. In Situ X-Ray Absorption Spectroscopic Studies of Copper in a Copper-Rich Sludge during Electrokinetic Treatments. J. Synchrotron Radiat. 2010, 17, 202–206.
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Formation of Copper Catalysts for CO2 Reduction with High Ethylene/Methane Product Ratio Investigated with In Situ X-ray Absorption Spectroscopy André Eilert,†,‡,ǁ F. Sloan Roberts,†,‡,ǁ Daniel Friebel,†,‡ and Anders Nilsson*,†,‡,§ †SLAC
National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
‡SUNCAT
Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, 443 Via Ortega, Stanford, CA 95305, USA
§Department
of Physics, AlbaNova University Center, Stockholm University, Roslagstullsbacken 21, S-10691 Stockholm, Sweden.
AUTHOR INFORMATION Corresponding Author *mailing address: Anders Nilsson, Stockholms universitet, Kemisk Fysik, 106 91 Stockholm, email: [email protected] Author Contributions ǁ(A.E.,
F.S.R.) These authors contributed equally to this work. S1
Fig. S1. Comparison of the Cu K-edge XAS of the pristine sample and the reduced sample after oxidation with Cl- at 0.7 V vs. RHE (2 scans). The latter one was reduced at -0.4 V vs. RHE. Spectra measured at ocp. Full spectrum and three zooms. Fig. S2. Lattice strain analysis using the „bond length with a ruler“ concept ES = E0 + (Eexp – E0)(1+s)2 with the energy under strain ES, the absorption energy E0, the experimentally observed energy Eexp and the lattice strain s. The experimentally observed spectrum of the reduced sample was stretched for different s and the square deviation to the spectrum of the pristine sample was plotted. The minimum of the curve shows the apparent lattice strain. The results show now significant lattice strain, an apparent lattice strain of -0.12 % for CuCubes corresponds to a change of 0.003 Å in Cu-Cu nearest neighbor distance, which is below the EXAFS detection limit of 0.01 Å.
S2
1.9
1.4
0.9 reduced oxidized
0.4
CuCl ref. -0.1 2815
2825
2835 2845 Energy / eV
2855
Difference oxidized-reduced / a.u.
Normalized absorbance / a.u.
0.06 0.04 0.02 0.00 -0.02 -0.04 -0.06 2815
2825
2835 2845 Energy / eV
2855
Fig. S3. Left: Comparison of the Cl K-edge XAS of the reduced sample before oxidation at -0.28 V and of the oxidized sample at 0.65 V. The spectrum is dominated by hydrated Cl- in the solution. The CuCl reference spectrum was taken from Drake et al.1 The yellow line marks the region with the largest difference between measured spectra and the CuCl reference. Right: Difference spectrum. From the difference spectrum, a maximum spectral concentration of CuCl of 3 % can be assumed, which corresponds to a layer thickness of ca. 0.3 nm CuCl (attenuation length of Cl Kα in water: 34.6 µm).
Fig. S4. Results from Figure 2 (main text) in the top row and corresponding edge jumps (height of step edge) in the bottom row. A decreasing edge jump corresponds to dissolving Cu.
S3
Fig. S5. Spectrum of the experimentally observed Cu(II) species (Cu(II) Exp) and of several reference compounds. The lack of a feature at 8987 eV in the experimental spectrum points towards CuCO3, Cu(OH)2 or a [Cu(H2O)6]-salt. A mixed carbonate/hydroxide such as malachite or azurite is possible. References of CuO, CuCl2∙2H2O, CuCl2, Cu2OCl and Cu2Cl(OH)3 from Ferrandon et al.2, of the solid [Cu(H2O)6]∙2ClO4 from Frank et al.3, of Cu(OH)2 from Chang et al.4 and of CuCO3 from Liu et al.5
S4
Fig. S6. Comparison of the Cu K-edge XAS of the pristine, reduced sample and the reduced sample after oxidation without Cl- at 0.7 V vs. RHE (2 scans). Both samples were reduced at -0.9 V vs. RHE. Spectra measured at ocp. Full spectrum and three zooms. 0
J / mA/cm2
-5 -10 - Cu(II)-derived - CuCubes - Polycrystalline Cu
-15 -20 -25 -30
-1.0
-0.8 E / V vs. RHE
-0.6
-0.4
Fig. S7. Current densities during CO2RR for the investigated samples in OLEMS (Fig. 3a main text). The reductive wave for CuCubes at -0.4 V is due to the reduction of Cu2O.
S5
Fig. S8. Sketch of the setup used for in situ Cu K-edge XAS. The setup for Cl K-edge XAS was the same except for the thickness of the glassy carbon window (~8 µm, self-made by heating Kapton to 1000 °C for one hour in a nitrogen atmosphere).
References (1)
(2)
(3) (4) (5)
Drake, I.; Fujdala, K.; Bell, A.; Tilley, T. Dimethyl Carbonate Production via the Oxidative Carbonylation of Methanol over Cu/SiO2 Catalysts Prepared via Molecular Precursor Grafting and Chemical Vapor Deposition Approaches. J. Catal. 2005, 230, 14–27. Ferrandon, M.; Daggupati, V.; Wang, Z.; Naterer, G.; Trevani, L. Using XANES to Obtain Mechanistic Information for the Hydrolysis of CuCl2 and the Decomposition of Cu2OCl2 in the Thermochemical Cu–Cl Cycle for H2 Production. J. Therm. Anal. Calorim. 2015, 119, 975–982. Frank, P.; Benfatto, M.; Hedman, B.; Hodgson, K. O. The XAS Model of Dissolved Cu(II) and Its Significance to Biological Electron Transfer. J. Phys. Conf. Ser. 2009, 190, 012059. Chang, P.-C.; Wei, Y.-L.; Chang, S.-H.; Wang, H. P. XAS Study of the Residual Copper after Desorption from Rice Husk Ash. J. Electron Spectrosc. Relat. Phenom. 2007, 156–158, 224–227. Liu, S.-H.; Wang, H. P.; Huang, C.-H.; Hsiung, T.-L. In Situ X-Ray Absorption Spectroscopic Studies of Copper in a Copper-Rich Sludge during Electrokinetic Treatments. J. Synchrotron Radiat. 2010, 17, 202–206.
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