Supporting Information
Controlling the morphology of CuO to construct rich Cu0/Cu+ interfaces for CO2 electroreduction to multi-carbon products
Weiren Chen, Xixiong Jin,* Min Wang, Bohan A, Zixuan Wei, Guobao Jiang, Hongqi Shi,* and Lingxia Zhang*
W. R. Chen, X. X. Jin, M. Wang, B. H. A, Z. X. Wei, L. X. Zhang
State Key Laboratory of High Performance Ceramics, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, P. R. China
E-mail: jinxixiong@mail.sic.ac.cn (Xixiong Jin); zhlingxia@mail.sic.ac.cn (Lingxia Zhang)
W. R. Chen, X. X. Jin, M. Wang, B. H. A, Z. X. Wei, L. X. Zhang
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, P. R. China
G. B. Jiang, H. Q. Shi
Wuhan Second Ship Design and Research Institute, 19 Yangqiao Lake Avenue, Wuhan 430205, P. R. China
E-mail: flags_s@163.com (Hongqi Shi)
L. X. Zhang
School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, 1 Sub-lane Xiangshan, Hangzhou 310024, P. R. China
Experiment Section
Material and chemicals. Copper(Ⅱ) acetate monohydrate (Cu(CH3COO)2·H2O, ≥98%) and deuterium oxide (D2O, 99.9%) were purchased from Admas. Sodium hydroxide (NaOH, ≥98%), hexamethylenetetramine ((CH2)6N4, ≥ 98%), potassium hydroxide (KOH, ≥98%), potassium bicarbonate (KHCO3, ≥99.5%), and polyethylene glycol (PEG, M = 6000) were purchased from Sinopharm Group Co., LTD. Ammonia solution (NH3·H2O, 25~28%), isopropyl alcohol (C3H8O, ≥99.7%), and ethanol absolute (C2H5OH, ≥99.7%) were purchased from Shanghai LingFeng Chemical Reagent Co., LTD. Dimethyl Sulfoxide (C2H6OS, ≥99.5%) was purchased from Sigma-Aldrich.
Synthesis of S-CuO. The synthesis of CuO catalysts with diverse morphologies was referenced from previous literature and modified accordingly.[1] Firstly, 1.20 g of Cu(CH3COO)2·H2O and 0.15 g of PEG-6000 were dissolved in 150 mL of deionized water to obtain a homogeneous precursor solution. Subsequently, 0.96 g of NaOH was dissolved in 30 mL of deionized water. After a complete ultrasonic dispersion, NaOH solution was added dropwise to the precursor solution. Finally, the precursor solution with NaOH was transferred to a water bath at 85 °C for 15 h. Stirring was maintained throughout the whole synthesis process. After the reaction, the product was collected through a centrifuge at 11000 rpm and washed with deionized water and ethanol for three times, respectively, then transferred to an oven at 60 °C for 24 h. The final gray powder obtained was nanosheet-like CuO (denoted as S-CuO). The reaction equation is as follows:
Synthesis of F-CuO. The synthesis procedure of F-CuO was consistent with that of S-CuO, while 3.6 mL of NH3·H2O substituted for NaOH. The final black powder obtained was nanoflower-like CuO (denoted as F-CuO). The reaction equation is as follows:
Synthesis of R-CuO. The synthesis procedure of R-CuO was consistent with that of S-CuO, while 1.68 g of HMTA substituted for NaOH. The final brown powder obtained was nanorod-like CuO (denoted as R-CuO). The reaction equation is as follows:
Preparation of CuO catalysts supported on gas diffusion electrode (GDE). The homogeneous ink of the catalysts was firstly prepared. 20 mg of CuO catalyst to be tested was dispersed into 120 μL of Nafion solution (5 wt%, Dupont) and 3.88 mL of isopropyl alcohol. Then the ink after complete ultrasonic would be sprayed onto a hydrophobic carbon-modified GDL (2×2 cm2, TGP-H-060) with an airbrush. The mass loading amount was controlled at 1.00 mg·cm-2.
Electrochemical measurement and product analysis. Electrochemical CO2 reduction reaction (CO2RR) was conducted in a flow-cell (working area 1×1 cm2) with a three-electrode system, in which previously prepared CuO catalysts supported on the GDL acted as the working electrode, a solid Ag/AgCl electrode acted as the reference electrode, and a titanium mesh loaded with iridium oxide (Ti/IrO2) acted as the counter electrode. The cathode chamber and the anode chamber were separated by an anion exchange membrane (2×2 cm2, Fumasep FAB-PK-130). 30 mL of 1 M KOH (pH = 14) was employed as electrolyte for both the cathode and the anode, and the flow rate was controlled at 20 mL·min-1 with two peristaltic pumps. All potential units in this paper have been converted into the reversible hydrogen electrode (RHE), and there is no iR correction. The specific formula is as follows:
During the measurement, Chenhua CHI1140C was employed as the electrochemical workstation, and the flow rate of introduced CO2 or Ar atmosphere was controlled at 20 sccm (standard cubic centimeter per minute). The Linear sweep voltammetry (LSV) curves were conducted from 0 to -2.0 V vs RHE at a scan rate of 50 mV·cm-2 under CO2- and Ar-fed environments, respectively. The performance of CO2RR was evaluated through a constant current test. The testing range was selected for the total current density (jtotal, mA·cm-2) from 100 to 600 mA·cm-2 with an interval of 100 mA·cm-2. At each testing current density, those gas-phase products were directly introduced into online gas chromatography (Shimadzu, GC2030) equipped with a barrier discharge ionization detector (BID) and a flame ionization detector (FID). The gas-phase products included C2H4, CH4, CO, and H2. The cathodic electrolyte was also collected at each testing point, and liquid-phase products (HCOOH, CH3COOH, and CH2CH3OH) could be detected through 1H-nuclear magnetic resonance (1H-NMR, Bruker 500 MHz) with DMSO as the internal standard. The test was conducted on 100 μL D2O mixed with 500 μL cathodic electrolyte after CO2RR, and the quantitative analysis of liquid products was carried out by calculating the corresponding peak area.
The long-term stability of 30 h was conducted with the same equipment, and the total current density was set at 400 mA·cm-2. The gas-phase product was detected through online gas chromatography with an interval of 2 h and the corresponding cathodic electrolyte was also collected to be detected through 1H-nuclear magnetic resonance.
Faradaic efficiency (FE) of each product can be calculated through following formula:
c represents the concentration of each product (ppm); t represents the time of the reaction (min); v represents the velocity of input CO2 flow (sccm, standard cubic centimeter per minute, cm3·min-1); Z represents the number of transferred electrons required for reducing CO2 to each product (2 for CO, HCOOH, and H2; 8 for CH4, and CH3COOH; 12 for C2H4, and CH2CH3OH); F represents Faraday constant (96485 C·mol-1); Q represents the coulombic quantities during CO2RR (C); Vm represents gas standard molar volume.
The partial current density of each product (jproduct, mA·cm-2) can be calculated through the following formula:
FEproduct represents FE for each C2+ product; jtotal represents the total applied current density (mA·cm-2).
The average potential (E, V vs RHE) can be calculated through the following formula:
Ei represents the potential at each second during CO2RR; t represents the reaction time (s).
The half-cell power conversion efficiency (HPCE) for C2 products (C2H4, CH2CH3OH, and CH3COOH) was calculated according to former literature[2]:
E represents the calculated average potential (V vs RHE) at each testing point; EC2 product represents the equilibrium potential (V vs RHE) during CO2RR for each C2 product (0.47 V vs RHE for C2H4; 0.48 V vs RHE for CH3CH2OH; 0.15 V vs RHE for CH3COOH). FEproduct represents FE for each C2 product.
Cyclic voltammetry (CV) was conducted in a flow-cell after feeding Ar for 15 min with 1 M KHCO3 as the electrolyte. Double-layer capacitor (Cdl, mF·cm-2) of three CuO catalysts before CO2RR could be obtained from CV curves with different scan rates (10 ~ 80 mV·s-1) from 0.40 to 0.50 V vs RHE with an interval of 10 mV·s-1. Cdl of CuO catalysts after CO2RR could be obtained with different scan rates (5 ~ 40 mV·s-1) from 0.20 to 0.30 V vs RHE with an interval of 5 mV·s-1. The graph was plotted with double-layer charging current density (Δj) as the vertical axis and scan rates as the horizontal axis, and half of the slope of the obtained line would be the value of Cdl:
With the electropolished Cu foil (Cdl = 29 μF·cm-2) as the reference, electrochemically active surface area (ECSA) could be directed calculated through the following formula[3]. Cdl and ECSA was calculated before and after CO2RR, respectively:
Electrochemical impedance spectroscopy (EIS) was conducted at -0.7 V vs RHE in an H-cell with CO2-saturated 0.1 м KHCO3 as electrolyte. The testing frequency was set from 10-1 to 105 Hz. Bio-logic VSP was employed as the electrochemical workstation. The plots of the Nyquist curves, solution resistance (Rs), and charge-transfer resistance (Rct) of three catalysts could be fitted through the Z-view software package.
The OH- adsorption experiment was conducted in a flow-cell with 1 M KOH as the electrolyte. Firstly, Ar gas was bubbled into the flow-cell for 15 min to remove the adsorbed oxygen in the electrolyte. Secondly, the OH- adsorption curves could be obtained through conducting CV with 50 mV·s-1 for the loop from -0.5 to 1.5 V vs RHE. The OH- adsorption experiment was conducted before and after CO2RR, respectively.
The CO stripping experiment was conducted in an H-cell with 1 M KHCO3 as the electrolyte. Firstly, all three CuO catalysts had been completely reduced under CO2-fed environments. Secondly, the gas composed of 50% CO and 50% N2 was bubbled into the electrolyte for 45 min. Then, a constant current measurement was conducted at 100 mA·cm-2 for 10 min. After that, Ar gas was bubbled into the electrolyte for 45 min to fully remove the residual CO. Finally, the LSV curve from 0.00 to 1.5 V vs RHE with the scan rate of 50 mV·s-1 was conducted. Bio-logic VSP was employed as the electrochemical workstation.
Characterization. The particle size of CuO catalysts was analyzed by Zetasizer Nano ZS90. X-ray diffraction (XRD) was obtained from Rigaku D/Max2200PC X-ray diffractometer (Cu Kα radiation) to detect the crystal plane of CuO catalysts. The testing range is from 30° to 60° with the scan rate of 5 degree·min-1. Raman spectroscopy was conducted with a Laser confocal Raman spectrometer, Horiba LabRam HR Evolution-HRDLS20. Scanning electron microscope (SEM) images and high-resolution transmission electron microscope (HR-TEM) images to observe the morphology of CuO catalysts were obtained from SU8220 and JEM-2100F, respectively. To discover the surface component of CuO catalysts, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were collected from Thermo Scientific ESCALAB 250 photoelectron spectrometer (Al Kα radiation, 1486 eV), and the binding energy was corrected according to C1s 284.8 eV. The surface areas of CuO catalysts were measured with nitrogen adsorption and desorption isotherms on Micrometrics Tristar 3020 and calculated through the Brunauer-Emmett-Teller (BET) method. The electron paramagnetic resonance (EPR) spectrum was measured on a Bruker A300 spectrometer. The contact angle test was conducted on Dataphysics DCAT21. Ex-situ XRD was conducted during CO2RR at 0, 15, 30, and 60 min, respectively. The current density was set at 100 mA·cm-2. The Cu K-edge data were collected on BL14W1 beamline in Shanghai Synchrotron Radiation Facility. The data were analyzed by the ATHENA and ARTEMIS modules of the Demeter software package.[4]
In-situ Raman spectroscopy measurement. Time-dependent in-situ Raman spectroscopy was also conducted with a Laser confocal Raman spectrometer, Horiba LabRam HR Evolution-HRDLS20 with a laser of 785 nm and a custom-designed three-electrode cell. During the measurement, CuO catalysts supported on the GDL, a KCl-saturated Ag/AgCl electrode, and a Pt wire acted as the working electrode, the reference electrode, and the counter electrode, respectively. The cathode chamber and anode chamber were separated by a proton exchange membrane (Dupont N117). 30 mL of 1 M KHCO3 (pH = 8.4) was employed as the electrolyte for both the cathode and anode. Before the measurement, the electrolyte had been bubbled with high-purity CO2 gas for at least 45 min. During the measurement, the electrolyte would be pumped into the cell with two peristaltic pumps. All Raman spectra were collected at open circuit potential (OCP) and at reaction times from 10 to 60 min with an interval of 5 min.
In-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The Potential-dependent ATR-FTIR spectroscopy was conducted on Thermo Scientific Nicolet iS10 with an HgCdTe (MCT) detector. The ink of the CuO catalysts to be tested would be added dropwise onto the Au film supported on a silicon prism. The obtained electrode acted as the working electrode. A KCl-saturated Ag/AgCl electrode and a Pt wire acted as the reference electrode and the counter electrode, respectively. 30 mL of 1 M KHCO3 was employed as the electrolyte and bubbled with high-purity CO2 gas for at least 45 min before the measurement. During the measurement, the electrolyte would be pumped into the cell with one peristaltic pump. All FTIR spectra were collected at OCP and negative potential from -1.0 to -2.0 V vs RHE with an interval of 0.1 V.
Scheme S1. Illustration of the synthesis procedure of three CuO catalysts with different morphologies.
Scheme S2. Illustration of the growth process of S-CuO.
Scheme S3. Illustration of the growth process of F-CuO.
Scheme S4. Illustration of the growth process of R-CuO.
Scheme S5. Illustration of the electrochemical reconstruction process of S-CuO and F-CuO.
Scheme S6. Illustration of the electrochemical reconstruction process of R-CuO.
Figure S1. The digital photographs during catalyst synthesis. (a) Initial Cu2+ precursor solutions; (b) Cu2+ precursor solution after being dropped with different precipitants; Powder of (c) S-CuO, (d) F-CuO, and (e) R-CuO.
Figure S2. The pH values of the initial Cu2+ precursor solution and those different precipitants.
Figure S3. SEM images of nanowire-like Cu(OH)2 after the initial Cu2+ precursor solution was dropped with NaOH solution.
Figure S4. SEM (a, b) and TEM (c, d) images of S-CuO.
Figure S5. SEM (a, b) and TEM (c, d) images of F-CuO.
Figure S6. SEM (a, b) and TEM (c, d) images of R-CuO.
Figure S7. SEM image of R-CuO without adding PEG-6000 during synthesis.
Figure S8. HR-TEM (a, b, c) images of S-CuO; (d) Enlarged local image within the red box and its (e) fast Fourier transform (FFT) pattern; Interplanar spacing patterns of (f) CuO (002) crystal plane.
Figure S9. HR-TEM (a, b, c) images of F-CuO; (d) Enlarged local image within the yellow box and its (e) fast Fourier transform (FFT) pattern; Interplanar spacing patterns of (f) CuO (002) crystal plane and (g) CuO (111) crystal plane.
Figure S10. Interplanar spacing pattern of CuO (111) crystal plane on R-CuO.
Figure S11. The particle size distributions of (a) S-CuO, (b) F-CuO, and (c) R-CuO.
Figure S12. Raman spectra of all three CuO catalysts.
Figure S13. FTIR spectra of all three CuO catalysts.
Figure S14. CO2-TPD curves of all three CuO catalysts.
Figure S15. EDS mapping of R-CuO. (a) The original image; (b) Cu element; (c) O element.
Figure S16. a) XPS survey spectra; b) Cu 2p spectra; c) O 1s spectra of all three CuO catalysts.
Figure S17. EPR spectra of all three CuO catalysts.
Figure S18. LSV curves of all three CuO catalysts under an Ar-fed environment.
Figure S19. The Faradaic Efficiency towards each product (H2, CO, CH4, HCOOH, C2H4, CH3CH2OH, and CH3COOH) at different applied current densities: (a) S-CuO; (b) F-CuO. Every error bar is obtained through three parallel experiments.
Figure S20. Partial current density towards each C2 product (C2H4, CH3CH2OH, and CH3COOH) at different applied current densities: (a) S-CuO, (b) F-CuO, and (c) R-CuO. Every error bar is obtained through three parallel experiments.
Figure S21. (a) The Faradaic Efficiency towards C1 products and (b) C1 current densities at different applied current densities on all three CuO catalysts. Partial current density towards each C1 products (CO, CH4, and HCOOH) at different applied current densities: (c) S-CuO, (d) F-CuO, and (e) R-CuO. Every error bar is obtained through three parallel experiments.
Figure S22. (a) The Faradaic Efficiency towards H2 and (b) H2 current densities at different applied current densities on all three CuO catalysts. Every error bar is obtained through three parallel experiments.
Figure S23. The contact angle test of all three CuO catalysts.
Figure S24. The HPCE towards C2 products at different applied current densities: (a) S-CuO, (b) F-CuO, and (c) R-CuO. Every error bar is obtained through three parallel experiments.
Figure S25. The p-t curves of all three CuO catalysts at different applied current densities: (a) S-CuO; (b) F-CuO; (c) R-CuO.
Figure S26. The calculated average potential of all three CuO catalysts at different applied current densities during CO2RR.
Figure S27. The Faradaic efficiency towards each product (H2, CO, CH4, HCOOH, C2H4, CH3CH2OH, and CH3COOH) at 400 mA·cm-2 on R-CuO during long-term stability test with an interval of 2 h. Digital photograph of (b) carbon paper; (b) cathode electrolyte, and (d) CO2 gas channel.
Figure S28. (a) LSV curves of all three CuO catalysts after CO2RR under (a) a CO2-fed environment and (b) an Ar-fed environment.
Figure S29. The Nyquist curves of all three CuO catalysts.
Figure S30. CV curves of (a) S-Cuo, (b) F-CuO, and (c) R-CuO before CO2RR. CV curves of (d) S-CuO, (e) F-CuO, and (f) R-CuO after CO2RR.
Figure S31. The calculated Cdl of all three CuO catalysts (a) before and (b) after CO2RR.
Figure S32. Ex-situ XRD pattern of R-CuO during CO2RR at 100 mA·cm-2.
Figure S33. Raman spectra of all three CuO catalysts after CO2RR.
Figure S34. (a) Cu 2p, (b) O 1s, (c) Cu LMM, and (d) XPS survey spectra of all three CuO catalysts without Ar+ etching after CO2RR.
Figure S35. Peak fitting of Cu species in Cu LMM spectra of (a) S-CuO, (b) F-CuO, and (c) R-CuO without Ar+ etching after CO2RR. (d) Ratio of Cu species on the surface of all three CuO catalysts without Ar+ etching after CO2RR.
Figure S36. XPS (a) Cu 2p, (b) O 1s, and (c) survey spectra of all three CuO catalysts with Ar+ etching after CO2RR.
Figure S37. Ratio of Cu species on the surface of all three CuO catalysts with Ar+ etching after CO2RR.
Figure S38. EPR spectra for detecting the existence of hydroxyl radical (·OH) in 1 M KOH.
Figure S39. SEM images of S-CuO after CO2RR.
Figure S40. TEM images of S-CuO after CO2RR.
Figure S41. SEM images of F-CuO after CO2RR.
Figure S42. TEM images of F-CuO after CO2RR.
Figure S43. SEM images of R-CuO after CO2RR.
Figure S44. TEM images of R-CuO after CO2RR.
Figure S45. Time-dependent in-situ Raman spectra of S-CuO during CO2RR.
Figure S46. Time-dependent in-situ Raman spectra of F-CuO during CO2RR.
Figure S47. Time-dependent in-situ Raman spectra of R-CuO during CO2RR.
Figure S48. The color mapping of time-dependent in-situ Raman spectra of (a, b) S-CuO, (c) F-CuO, and (d) R-CuO.
Figure S49. The Cu K-edge normalized XANES spectra of all three CuO catalysts after CO2RR. The Cu foil, Cu2O std., and CuO std. were used as references.
Figure S50. The wavelet transforms of Cu K-edge EXAFS spectra of (a) Cu foil; (b) Cu2O std.; (c) CuO std.; (d) S-CuO after CO2RR; (d) F-CuO after CO2RR; (f) R-CuO after CO2RR.
Figure S51. Cu K-edge EXAFS fitting curves: (a) R-space; (b) Im(R)-space; (c) K-space of Cu foil. (d) R-space; (e) Im(R)-space; (f) K-space of S-CuO after CO2RR. (h) R-space; (i) Im(R)-space; (j) K-space of F-CuO after CO2RR. (k) R-space; (l) Im(R)-space; (m) K-space of R-CuO after CO2RR.
Figure S52. Coordination number of the first shell Cu-O scattering of all three CuO catalysts after CO2RR.
Figure S53. CV curves on all three CuO catalysts before CO2RR.
Figure S54. LSV curves for CO stripping experiments for all three CuO catalysts.
Figure S55. The potential-dependent in-situ ATR-FTIR spectra of S-CuO.
Table S1. Faradaic Efficiency of S-CuO, F-CuO, and R-CuO during CO2RR at different applied current densities in a flow-cell. Every error bar was obtained through three parallel experiments.
| Sample | jtotal (mA·cm-2) | H2 (%) | CO (%) | HCOOH (%) | CH4 (%) | C2H4 (%) | CH3CH2OH (%) | CH3COOH (%) |
|---|---|---|---|---|---|---|---|---|
| S-CuO | 100 | 25.5±4.8 | 17.7±7.8 | 19.3±10.8 | 0.0±0.0 | 26.4±2.6 | 6.5±0.6 | 5.1±1.9 |
| S-CuO | 200 | 20.9±3.7 | 10.6±7.1 | 13.7±7.3 | 0.1±0.2 | 43.8±1.6 | 8.6±1.3 | 3.1±0.5 |
| S-CuO | 300 | 24.0±5.8 | 4.1±1.7 | 7.2±1.9 | 0.1±0.2 | 51.5±4.0 | 10.3±2.3 | 2.8±0.3 |
| S-CuO | 400 | 20.2±2.8 | 3.2±0.4 | 6.5±1.5 | 0.1±0.2 | 56.3±1.9 | 11.0±3.4 | 2.5±0.8 |
| S-CuO | 500 | 24.5±0.9 | 3.2±0.6 | 3.7±0.7 | 0.3±0.4 | 56.3±4.2 | 9.0±3.9 | 2.3±0.5 |
| S-CuO | 600 | 27.8±3.3 | 3.2±0.7 | 2.7±0.7 | 0.6±0.7 | 56.7±3.2 | 7.5±3.7 | 2.1±0.9 |
| F-CuO | 100 | 31.6±5.4 | 13.5±4.3 | 11.5±8.4 | 0.2±0.2 | 27.9±5.1 | 10.7±4.1 | 4.8±2.0 |
| F-CuO | 200 | 21.2±3.7 | 7.6±0.8 | 10.7±0.6 | 1.1±0.8 | 36.9±7.3 | 18.1±3.4 | 4.3±0.8 |
| F-CuO | 300 | 23.4±4.6 | 5.7±1.6 | 5.2±2.3 | 1.1±0.8 | 40.7±7.7 | 17.6±1.7 | 5.9±3.0 |
| F-CuO | 400 | 27.8±5.5 | 5.2±1.8 | 3.7±1.3 | 4.0±3.9 | 35.6±6.2 | 18.6±2.1 | 6.8±3.7 |
| F-CuO | 500 | 30.5±4.7 | 5.0±1.8 | 2.2±0.7 | 4.7±4.7 | 36.3±6.3 | 14.1±2.6 | 6.8±3.2 |
| F-CuO | 600 | 41.1±6.6 | 5.2±2.6 | 1.9±0.4 | 8.9±3.8 | 29.2±5.6 | 9.6±5.8 | 4.5±3.9 |
| R-CuO | 100 | 10.1±2.6 | 11.6±0.9 | 18.5±1.3 | 0 | 45.4±3.2 | 10.6±0.3 | 3.8±1.9 |
| R-CuO | 200 | 8.7±1.1 | 11.4±1.0 | 19.1±1.9 | 0 | 49.9±1.6 | 10.5±0.5 | 1.6±0.6 |
| R-CuO | 300 | 7.9±0.9 | 7.9±1.3 | 14.0±2.9 | 0 | 55.5±1.4 | 12.5±1.3 | 1.7±0.2 |
| R-CuO | 400 | 8.4±0.8 | 4.2±0.4 | 3.9±1.7 | 0.6±0.2 | 65.5±2.9 | 12.8±0.4 | 3.2±0.9 |
| R-CuO | 500 | 7.6±1.9 | 5.0±1.3 | 8.2±0.5 | 0.4±0.2 | 63.3±2.1 | 17.4±0.5 | 3.3±0.6 |
| R-CuO | 600 | 9.8±1.9 | 3.7±0.9 | 4.2±1.0 | 0.4±0.2 | 56.3±4.2 | 19.0±1.9 | 6.3±2.1 |
Table S2. Comparison of R-CuO with those reported Cu-based catalysts with superior performance on CO2RR towards C2 products.
| Sample | Main product | Faradaic efficiency (%) | Partial current density (mA·cm-2) | Reference |
|---|---|---|---|---|
| R-CuO | C2 | 84.0 | 489.6 | This work |
| NS-Cu2O | C2 | 81.7 | 286.0 | [2] |
| Cu2O/CuO | C2 | 80.0 | 320.0 | [5] |
| ON−CuO | C2 | 77.0 | 26.6 | [6] |
| Cu0.25@Cu2O convex sphere | C2 | 90.5 | 14.8 | [7] |
| Zn-CuO-5% | C2H4 | 61.0 | 500 | [8] |
| p-CuSiO3/CuO | C2 | 91.7 | 366.8 | [9] |
| HA-Cu-OD | C2 | 64.5 | 129.0 | [10] |
| GA-capped Cu2O | C2 | 81.5 | 285.0 | [11] |
| Cu=N | CH3CH2OH | 45.0 | 406 | [12] |
Table S3. The fitting Rs and Rct of all three CuO catalysts according to EIS results.
| Catalyst | Rs (Ω) | Rct (Ω) |
|---|---|---|
| S-CuO | 93.5 | 305.5 |
| F-CuO | 84.4 | 493.6 |
| R-CuO | 88.9 | 164.3 |
Table S4. Fitting parameter for Cu K-edge EXAFS spectra of Cu foil and all three CuO catalysts after CO2RR.
| Sample | Path | CN | R (Å) | σ2 (10-3·Å2) | ΔE0 (eV) | R factor |
|---|---|---|---|---|---|---|
| Cu foil | Cu-Cu | 12 | 2.548±0.008 | 12.97±1.02 | -7.55±1.11 | 0.013 |
| S-CuO | Cu-Cu | 9.68±1.20 | 2.549±0.009 | 11.40±1.15 | 5.45±1.28 | 0.007 |
| S-CuO | Cu-O | 0.46±0.23 | 1.825±0.020 | 3.84±2.07 | 5.45±1.28 | 0.007 |
| F-CuO | Cu-Cu | 10.59±1.54 | 2.548±0.010 | 10.52±1.89 | 4.76±1.48 | 0.010 |
| F-CuO | Cu-O | 0.33±0.24 | 1.831±0.025 | 4.79±4.21 | 4.76±1.48 | 0.010 |
| R-CuO | Cu-Cu | 8.71±1.60 | 2.553±0.013 | 11.30±1.75 | 5.16 ± 1.91 | 0.013 |
| R-CuO | Cu-O | 0.72±0.37 | 1.825±0.026 | 5.21±0.34 | 5.16 ± 1.91 | 0.013 |
Fitting range: S02 = 0.91; k(Å): 2.5 ~ 12; R(Å): 1~2.8
CN: coordination number
R: distance between absorber and backscatter atoms
σ2: Debye-Waller factor
ΔE0: inner potential correction
R factor: goodness of the fitting
Table S5. Comparison of the parameters of the three CuO catalysts after CO2RR.
| Samples | ECSA | Cu0 coordination number | Cu+ content (at%) | FEC2 (%) | jC2 (mA·cm-2) |
|---|---|---|---|---|---|
| S-CuO after CO2RR | 180.3 | 9.68 | 61.4 | 69.8 | 398.1 |
| F-CuO after CO2RR | 74.1 | 10.59 | 56.5 | 64.1 | 286.0 |
| R -CuO after CO2RR | 271.4 | 8.71 | 73.8 | 84.0 | 489.5 |
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