Raw source: Supporting Information — Strain Regulation Enhances the CO Coverage on Cu2O Surface for CO2 Electroreduction
Supporting Information
Strain Regulation Enhances the *CO Coverage on Cu2O Surface for CO2 Electroreduction to Ethylene under Industrial-level Current Density
Zhiqing Yan1, Peng Gao1, Zhong Li, Dong Cao*, Daojian Cheng*
State Key Laboratory of Organic-Inorganic Composites and College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
*Corresponding author: Dong Cao (caod@mail.buct.edu.cn); Daojian Cheng (chengdj@mail.buct.edu.cn)
1 Contributed equally to this work.
Chemicals and Reagents
Copper chloride dihydrate (CuCl2·2H2O, AR), ascorbic acid (C6H8O6, ＞99.0%), potassium hydroxide (KOH, 95%), Nafion (117 solution, ~5%) were purchased from Shanghai Macklin Biochemical Co., Ltd. Sodium hydroxide (NaOH, 96%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Isopropanol (C3H8O, AR, 99.5%) was purchased from Shanghai Yien Chemical Technology Co., Ltd.
Experimental Section
Synthesis of Cu2O catalyst
A dilute CuCl2 solution was obtained by pouring 7 mL of 0.1 M CuCl2 into a beaker and adding 300 mL of deionized water. Then 21 mL of 0.2 M NaOH solution was added drop by drop to the diluted CuCl2 solution and stirred for 10 minutes to obtain a solution with small light blue particles. After adding 14 mL of 0.1 M ascorbic acid solution dropwise to the above solution, the color of the solution changed to orange and stirred for 1 hour. Finally, the catalyst was washed three times with deionized water and ethanol by centrifugation and dried under vacuum at 60°C for 12 h to obtain Cu2O catalyst.
Synthesis of LS3.7%Cu2O, LS17.6%Cu2O and LS18.3%Cu2O
Cu2O catalysts with different strain levels were prepared by pre-reduction of Cu2O at -2.47 V vs. RHE for different times. The pre-reduction times for LS3.7%Cu2O, LS17.6%Cu2O and LS18.3%Cu2O were 10 min, 30 min and 60 min, respectively.
Synthesis of Cu
The synthesis method of Cu was similar to that of Cu2O. The difference was that the amount of ascorbic acid added was increased to two times and the stirring time was extended to 5 hours. It was washed three times by centrifugation with deionized water and ethanol, and then dried under vacuum at 60℃ for 12 hours to obtain Cu catalyst.
Catalysts characterization
The morphology of the catalyst was obtained by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) images were collected on a Talos F200X G2 equipped with a ring dark field detector and an energy dispersive X-ray spectrometer (EDS) operating at 200 kV. High resolution TEM (HRTEM) and high angle annular dark field STEM (HAADF-STEM) images were also recorded on the same equipment. Scanning electron microscope (SEM) images were acquired on a ZEISS Gemini SEM 300 in Germany. Aberration-corrected high-angle annular dark field scanning transmission electron microscopy (AC HAADF-STEM) images were performed on JEM-ARM300F (JEOL) with accelerating voltage of 300 kV. X-ray diffraction (XRD) pattern was recorded using an Ultima IV diffractometer equipped with a high speed detector D/teX-Ultra using Cu Kα radiation from 10° to 90° with 0.02° step at a scan speed of 10°/min. Chemical compositions and elemental valence of as-synthesized catalyst were analyzed by X-ray photoelectron spectroscopy (XPS) based on Thermo Scientific K-Alpha with a monochromatic Al Kα (1486.6 eV) X-ray source at an operating source power of 12 kV × 6 mA. All XPS peaks were calibrated with the surface contamination C1s binding energy at 284.8 eV. The X-ray absorption spectroscopy (XAS) measurements were performed at 4B9A beamline at the Beijing Synchrotron Radiation Facility (BSRF). The Cu K-edge X-ray absorption spectra were collected for the samples before and after electrolysis. The Cu K-edge X-ray absorption spectra of Cu foil, Cu2O and CuO were also used as references. The obtained Extended X-ray Absorption Fine Structure (EXAFS) data were processed according to standard procedures using the ATHENA module in the IFEFFIT software. Quantitative structural parameters around the central atom were obtained by least-squares curve fitting using the ARTEMIS module in the IFEFFIT software packages.
In-situ characterization
INVENIO R FTIR spectrometer equipped with an MCT detector for in-situ attenuated total reflection-surface-enhanced IR absorption spectroscopy (ATR-SEIRAS) spectroscopy testing, and all spectra are obtained in absorbance (-log(R/R0)). The silicon prism was mounted in a three-electrode electrochemical cell with a Ag/AgCl reference electrode and a platinum foil counter electrode. Catalyst ink was dropped on ATR crystals with a gold film. The in situ ATR-SEIRAS test used 1 M KOH as the electrolyte and CO2 was continuously purged during the test. In electrochemical CO2RR, tests were performed stepwise for -0.2 V to -1.2 V vs. RHE. Spectra at open circuit potential (OCP) was recorded for comparison.
In situ Raman spectroscopy was tested in 1 M KOH aqueous solution. It operated in the ranges of 100 to 2000 cm-1 and -0.2 V to -1.2 V vs.RHE, respectively, with the aim of monitoring the formation of intermediates.
Catalytic performance evaluation
The CO2RR performance was tested in a membrane electrode assembly cell consisting of a cathode chamber and an anode chamber, and using gaskets with an area of 11 to ensure a reaction area of 11 cm2. Catalyst ink droplets on Toray YLS30T gas diffusion layer (GDL). Ag/AgCl and itanium felt coated with iridium dioxide were used as the reference electrode and anode, respectively. The cathode and anode chambers were separated by a proton exchange membrane (Nafion117). During the measurements, carbon dioxide was introduced into the cathode chamber at a flow rate of approximately 20 mL/min. A peristaltic pump continuously circulated the catholyte and anolyte (both 1 M KOH) at a flow rate of 10 mL/min-1.All the CO2 electroreduction performance tests were done on a Shanghai Chenhua workstation (CHI1140C) using a membrane electrode assembly cell. Linear scanning voltammetry (LSV) tests with a scan rate of 10 mV s-1 in an electrolyte of 1 M KOH. The measured potential was converted to a reversible hydrogen electrode according to the Nernst equation: E (vs. RHE) = E (vs. Ag/AgCl) + 0.197 + 0.0591×pH.
The CO2 gas was continuously passed at a rate of 30 mL/min during the reaction, and the reacted gas was directly fed into the gas chromatography for on-line detection. The gas-phase products, such as H2, CO, C2H4, and so on, were analyzed by a gas chromatograph with a thermal conductivity detector (TCD) and a flame ionization detector.
The formula for calculating the Faraday efficiency of the gas phase product is as follows:
FE (%)
where V is the relative gas content read directly from the gas chromatograph; v is the flow rate of CO2 output (L/s), z is the number of electrons transferred by the electrocatalytic reduction of CO2 (different reduction products have different numbers of electrons transferred), F is the Faraday’s constant (96485 C/mol), Vm is the molar volume of the gas, Vm = 22.4 L/mol, I is the standard condition of the current (A).
The cathode energy efficiency (CEE) of C2H4 is calculated using the following formula: CEE
where E is the applied voltage (vs. RHE), EC2H4 is the thermodynamic potential of ethylene (vs. RHE), and FEC2H4 is the Faradaic efficiency of ethylene.
The energy efficiency (EE) of the full cell for ethylene is calculated using the following formula:
EE
where Eʹ is the experimentally measured cell voltage, and E’C2H4 represents the theoretical cell voltage of ethylene derived from thermodynamic calculations (1.15 V), FEC2H4 is the Faradaic efficiency of ethylene.
Computational calculations
The Cu2O and LS17.6%Cu2O related models were established. To avoid physical interactions between neighboring plates due to periodic boundary conditions, the vacuum space exceeds 15 Ǻ. All calculations are performed within the framework of plane-wave density functional theory (DFT), which is implemented in the Vienna Ab-initio Simulation Package (VASP). The electron wave function is extended using a plane wave basis set with a cutoff energy of 450 eV. The Brillouin zone consists of 3 × 3 × 1 and 5 × 5 × 1 k grids, which are used for geometric optimization and electronic characteristics calculation respectively. The adsorption energy of CO molecule on the catalyst structure is defined by equation:
Where Esalb is the total energy of the catalyst structure, ECO is the energy of a single CO molecule, and Etotal is the total energy of a single CO molecule adsorbed on the surface of the catalyst structure. The zero-point energy (ZPE)and entropy corrections were taken into account for free energies calculations, ∆G=ΔEDFT + ΔEZPE – TΔS. The Climbing Image - Nudged Elastic Band (CI-NEB) method is used to locate the transition state of the CO coupling reaction.
Figure S1. HRTEM image of Cu2O.
Figure S2. Elemental mapping of Cu2O.
Figure S3. a) HRTEM image, b) inverse FFT image and c) lattice spacing of the catalyst with a reconstruction potential of -2.17 V (vs. RHE).
Figure S4. Elemental mapping of the catalyst with a reconstruction potential of -2.17 V (vs. RHE).
Figure S5. a) HRTEM image, b) inverse FFT image and c) lattice spacing of the catalyst with a reconstruction potential of -2.27 V (vs. RHE).
Figure S6. Elemental mapping of the catalyst with a reconstruction potential of -2.27 V (vs. RHE).
Figure S7. a) HRTEM image, b) inverse FFT image and c) lattice spacing of the catalyst with a reconstruction potential of -2.37 V (vs. RHE).
Figure S8. Elemental mapping of the catalyst with a reconstruction potential of -2.37 V (vs. RHE).
Figure S9. HRTEM image of LS3.7%Cu2O.
Figure S10. HRTEM image of LS17.6%Cu2O.
Figure S11. HRTEM image of LS18.3%Cu2O.
Figure S12. Elemental mapping of LS3.7%Cu2O.
Figure S13. Elemental mapping of LS18.3%Cu2O.
Figure S14. a) SEM image of the surface of LS17.6%Cu2O. b) TOF-SIMS depth profiling diagram of LS17.6%Cu2O.
Figure S15. High-resolution XPS spectra of a) Cu 2p, b) Cu LMM and c) O1s for Cu2O.
Figure S16. High-resolution XPS spectra of a) Cu 2p, b) Cu LMM and c) O1s for LS3.7%Cu2O.
Figure S17. High-resolution XPS spectra of a) Cu 2p, b) Cu LMM and c) O1s for LS17.6%Cu2O.
Figure S18. High-resolution XPS spectra of a) Cu 2p, b) Cu LMM and c) O1s for LS18.3%Cu2O.
Figure S19. a) CV curve and b) Cdl of Cu2O.
Figure S20. a) CV curve and b) Cdl of LS3.7%Cu2O.
Figure S21. a) CV curve and b) Cdl of LS17.6%Cu2O.
Figure S22. a) CV curve and b) Cdl of LS18.3%Cu2O.
Figure S23. a) Product distribution and b) FEC2H4 of Cu2O at different current densities.
Figure S24. a) Product distribution and b) FEC2H4 of LS3.7%Cu2O at different current densities.
Figure S25. a) Product distribution and b) FEC2H4 of LS18.3%Cu2O at different current densities.
Figure S26. a) Ethylene partial current density of Cu2O, LS3.7%Cu2O, LS17.6%Cu2O and LS18.3%Cu2O at different current densities.
Figure S27. a) Product distribution and b) FEC2H4 of Cu at different current densities
Figure S28. CEEC2H4 and EEC2H4 of Cu at different current densities.
Figure S29. CEEC2H4 and EEC2H4 of Cu2O at different current densities.
Figure S30. CEEC2H4 and EEC2H4 of LS3.7%Cu2O at different current densities.
Figure S31. CEEC2H4 and EEC2H4 of LS17.6%Cu2O at different current densities.
Figure S32. CEEC2H4 and EEC2H4 LS18.3%Cu2O at different current densities.
Figure S33. In situ ATR-SEIRSA spectra of electrochemical CO2 reduction on Cu2O.
Figure S34. In situ ATR-SEIRSA spectra of electrochemical CO2 reduction on LS3.7%Cu2O.
Figure S35. In situ ATR-SEIRSA spectra of electrochemical CO2 reduction on LS18.3%Cu2O.
Figure S36. *COOH intermediates (1250 cm-1) at different strain rates.
Figure S37. *COCO intermediates (1440 cm-1) at different strain rates.
Figure S38. a) TEM image, b) HRTEM image of LS17.6%Cu2O after reaction. The inset at the bottom right shows a SAED graph. c) Inverse FFT image and d) lattice spacing of LS17.6%Cu2O after reaction.
Figure S39. a) TEM image and b) HRTEM image of Cu2O after reaction. c) Inverse FFT image and d) lattice spacing of Cu2O after reaction.
Figure S40. a) TEM image and b) HRTEM image of LS3.7%Cu2O after reaction. c) Inverse FFT image and d) lattice spacing of LS3.7%Cu2O after reaction.
Figure S41. a) TEM image and b) HRTEM image of LS18.3%Cu2O after reaction. c) Inverse FFT image and d) lattice spacing of LS18.3%Cu2O after reaction.
Figure S42. EPR spectra of four samples after reaction.
Figure S43. XRD pattern of LS17.6%Cu2O after reaction.
Figure S44. High-resolution XPS spectra of a) Cu 2p, b) Cu LMM and c) O1s for LS17.6%Cu2O after reaction.
Table S1. The oxygen vacancy content in different samples obtained by integrating the O1s XPS spectrum shown in Figure 2f. O vacancy contents of Cu2O, LS3.7%Cu2O, LS17.6%Cu2O and LS18.3%Cu2O. The oxygen vacancy content of 4 samples were estimated from O1s spectra.
Table S2. EXAFS fitting parameters at the Cu K-edge for various samples
a N: coordination numbers; b R: bond distance; c σ2: Debye-Waller factors; d ΔE0: the inner potential correction. R factor: goodness of fit. Ѕ02 were set as 0.85 for Cu-O/Cu-Cu, which was obtained from the experimental EXAFS fit of reference Cu foil/Cu2O by fixing CN as the known crystallographic value and was fixed to all the samples.
Table S3. Performance comparison of various reported Cu2O catalysts for CO2RR to C2H4.
“/” indicates that there are no relevant data present in the literature.
References
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Table 1
Sample | Peak (eV) | Fraction (at%)
Cu2O | 531.8 | 28.06
LS3.7%Cu2O | 531.9 | 53.48
LS17.6%Cu2O | 532.1 | 71.94
LS18.3%Cu2O | 532.1 | 81.30
Table 2
Sample | Shell | N a | R (Å) b | σ2 (Å2·10-3) c | ΔE0 (eV) d | R factor (%)
LS17.6%Cu2O | Cu-O | 1.0 | 1.85 | 3.4 | 7.5 | 0.8
LS17.6%Cu2O | Cu-Cu | 5.5 | 2.56 | 9.2 | 7.5 | 0.8
Table 3
Catalysts | Electrolyte | jC2H4 /mA·cm-2 | FEC2H4/% | References
LS17.6%Cu2O | 1 M KOH | 615.7 | 76.97 | This work
Cu2O homojunction | 0.1 M K2SO4 | 38.2 | 73.7 | [1]
Cu2O nanoparticles | 1 M KOH | 416.4 | 56.3 | [2]
Cu2O polyhedrons | 1 M KOH | 576 | 72 | [3]
Nano-Cu2O | 0.1 M KHCO3 | / | 74.1 | [4]
t-Cu2O | 0.5 M KHCO3 | 22 | 59 | [5]
Octahedral Cu2O with 500 nm | 0.5 M CsHCO3 | 12.5 | 50.6 | [6]
Cu2O/NCS | 0.1 M KHCO3 | / | 24.7 | [7]
HQ-Cu | 0.1 M KHCO3 | / | 39 | [8]
Cu2O/ILGS | 0.1 M KHCO3 | / | 31.1 | [9]
Cu-Cu2O | 0.1 M KHCO3 | 4.2 | 36.3 | [10]
Cuy-Cu2O | 0.1 M KHCO3 | 15.7 | 51 | [11]