Supplementary Information for
Phosphorus-Doped Cu/Fe2O3 Electrocatalysts with Optimized Synergy between the Different Sites for Efficient Urea Electrosynthesis
Ting Deng1,2, Shuaiqiang Jia1,2*, Cheng Xue1,2, Hailian Cheng1,2, Jiapeng Jiao1,2, Xiao Chen1,2, Zhanghui Xia1,2, Mengke Dong1,2, Chunjun Chen1,2, Haihong Wu1,2*, Mingyuan He1,2, Buxing Han1,2,3*
1 Shanghai Key Laboratory of Green Chemistry and Chemical Processes, State Key Laboratory of Petroleum Molecular & Process Engineering, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062 (China) 2 Institute of Eco-Chongming, Shanghai, 202162 (China) 3 Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid and Interface and Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100049 (China)
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Experimental Section Materials: Cupric acetate anhydrous (C4H6CuO4, 98%), Diacetylmonoxime (C4H7NO2, 99%), Sodium nitroferricyanide(III) dihydrate (C5H4FeN6Na2O3, 99%), Sulfanilamide (C6H8N2O2S, 99%) were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. Iron acetate anhydrous (C4H7FeO5, 95%) was obtained from Shanghai yuanye Bio-Technology Co., Ltd. Sodium pyrophosphate (Na4O7P2, 99%) provided by Bide Pharmatech Ltd. Sulfuric acid (H2SO4, 98%), Phosphoric acid (H3PO4, 85%), Sodium hydroxide (NaOH, 96%) were supplied by Sinopharm Chemical Reagent Co., Ltd. Potassium nitrate (KNO3, 99%), Potassium nitrate-15N (K15NO3, 99.8%), N-(1-naphthyl) ethylenediamine dihydrochloride (C12H14N2·2HCl, 98%) were purchased from Aladdin Ltd. Urease (C2H5O-S-C(O)-NH-CONH2) were provided by Shanghai Titan Scientific Co., Ltd. Thiosemicarbazide (CH5N3S, 98.5%), Iron(III) chloride hexahydrate (CHCl3Fe, 98.5%), Salicylic acid (C7H6O3, 99%), Sodium citrate anhydrous (Na3C6H5O7, 99%), Sodium hypochlorite (NaClO, >10% active chlorine) were obtained from Beijing InnoChem Science & Technology Co., Ltd. Toray Carbon Paper (CP, TGP-H-60, 19×19 cm), Nafion N-117 membrane (0.180 mm thick, ≥0.90 meg/g exchange capacity) and Nafion D-521 dispersion (5% w/w in water and 1-propanol, ≥ 0.92 meg/g exchange capacity) were supplied by Alfa Aesar China Co., Ltd. Both CO2 and Ar had a purity of 99.999%, which were provided by Shanghai Chemistry Industrial Zone Pujiang Special Type Gas Co., Ltd. All the chemical reagents were used directly without further purification. Catalyst Preparation: Preparation of P-Cu/Fe2O3: In general, 4 mmol of copper acetate and 2 mmol of iron acetate were dissolved in 20 mL of deionized water and stirred for 1 h. Subsequently, a slight excess (15 mmol) of NaOH was added, and the mixture was stirred for 1 h. Then, 15 mmol of sodium pyrophosphate was introduced, and the solution volume was adjusted to 50 mL with deionized water, followed by stirring for 24 h. The resulting mixture was transferred into a 100 mL Teflon autoclave and
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subjected to hydrothermal reaction at 160 °C for 8 h. After the reaction, the products were centrifuged and washed several times with deionized water and ethanol to remove any residual impurities. Finally, the samples were dried overnight at 60 °C under vacuum. To obtain electrocatalysts with different P-doped, the molar amount of sodium pyrophosphate was varied (5, 10, 15, 20, 25 mmol). The final P-Cu/Fe2O3 electrocatalysts were prepared by calcining the precursors in a tubular furnace under a hydrogen atmosphere at a heating rate of 3 °C min−1 to 300 °C, holding at this temperature for 2 h, and then cooling to room temperature. Preparation of Cu/Fe2O3: In general, 4 mmol of copper acetate and 2 mmol of iron acetate were dissolved in 20 mL of deionized water and stirred for 1 h. Subsequently, a slight excess (15 mmol) of NaOH was added, and the mixture was stirred for 1 h. The solution volume was adjusted to 50 mL with deionized water, followed by stirring for 24 h. The resulting mixture was transferred into a 100 mL Teflon autoclave and subjected to hydrothermal reaction at 160 °C for 8 h. After the reaction, the products were centrifuged and washed several times with deionized water and ethanol to remove any residual impurities. Finally, the samples were dried overnight at 60 °C under vacuum. The final Cu/Fe2O3 electrocatalysts were prepared by calcining the precursors in a tubular furnace under a hydrogen atmosphere at a heating rate of 3 °C min−1 to 300 °C, holding at this temperature for 2 h, and then cooling to room temperature. Catalyst Characterizations: The morphologies of the samples were observed by field-emission scanning electron microscopy (SEM) (ZEISS Sigma 300). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) measurements were performed on a FEI Talos F200x instrument equipped with Energy Dispersive Spectroscopy (EDS) operated at 200 kV to characterize the morphology of samples. The Agilent 5100 SVDV model of Inductively coupled plasma-atomic emission spectrometer (ICP-AES) was employed to quantify the relative content of copper and iron. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was operated at 300 kV by FEI 3 Talos F200x. X-ray photoelectron spectroscopy (XPS) analysis was performed on the Thermo Scientific ESCA Lab 250Xi using 200 W monochromatic Al Kα radiation. X-ray diffraction (XRD) patterns were collected on a Rigaku Ultima IV X-ray diffractometer using Cu Kα radiation at 35 kV and 25mA (λ=1.5405 Å) over a 2θ ranging from 5 to 90° at a scanning speed of 5° min. The X-ray absorption spectroscopy (XAS) measurements were carried out at the BL13SSW beamline at Shanghai Synchrotron Radiation Facility (SSRF), China. The EXAFS data were processed according to the standard procedures using the ATHENA module implemented in the IFEFFIT software packages. The Cu K-edge X-ray absorption spectra of P-Cu/Fe2O3 and Cu/Fe2O3 electrodes were collected before and after electrolysis. The Cu K-edge X-ray absorption spectra of Cu foil, Cu2O, and CuO were collected for reference. The Fe K-edge X-ray absorption spectra of P-Cu/Fe2O3 and Cu/Fe2O3 electrodes were collected before and after electrolysis. The Fe K-edge X-ray absorption spectra of Fe foil and Fe2O3 were collected for reference. Pre-edge and post-edge backgrounds were subtracted from the XAS spectra, and the resulting spectra were normalized by edge height. In situ Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) testing was performed using a PerkinElmer Spectrum-3 at Hefei in situ technology Co. In situ Raman was conducted on a Renishaw in Via Reflex Raman spectrometer with a 785 nm solid laser as an excitation source. The measurements were performed in a custom-built flow cell with a similar configuration as the flow cell electrolytic reactor. The spectra were obtained in CO2-saturated 0.1 M KNO3, respectively, to avoid scattering of the Raman signal generated by bubbles at high currents. Cathode Preparation: To fabricate the working electrode, 5 mg of the as-prepared electrocatalyst was dispersed in 950 µL of isopropanol. Subsequently, 50 µL of a 5 wt.% Nafion solution was added to the suspension. This mixture was then subjected to ultrasonic treatment for 30 min to ensure a homogeneous ink formulation. Afterward, the prepared ink was precisely deposited onto a 1×1.5 cm2 carbon paper electrode. It was noteworthy that this specific catalyst loading was consistently maintained across all experimental 4 measurements. Electrochemical study: All the electrochemical experiments were conducted on the potentiostat workstation (CHI 6081E, Shanghai CH Instruments Co., China), and the experiment was conducted at room temperature. The linear sweep voltammetry (LSV) measurements were carried out in a typical H-type cell with three electrodes configuration, which consisted of a working electrode, a counter electrode (Pt gauze), and a reference electrode. Aqueous solutions of 0.1 M KNO3 and 0.1 M K2SO4 were utilized as cathodic and anodic electrolytes, respectively. Before each set experiment, the catholyte was bubbled with CO2 or Ar for at least 30 min to form a CO2-saturated or Ar-saturated solution. Slight magnetic stirring was employed to acquire uniform electrolytes. The LSV measurements in gas-saturated electrolytes were conducted at a scan rate of 20 mV s−1 in the potential range of −0 to −0.80 V vs. RHE. In all measurements, we used Ag/AgCl (saturated KCl solution) as the reference electrode, and the potential (vs. Ag/AgCl) was converted to RHE using the following equations:
ERHE = EAg/AgCl + E0Ag/AgCl + 0.0591 × pH
E0Ag/AgCl (Saturated KCl) = 0.197 V (25 ℃)
where ERHE is the potential of the reversible hydrogen electrode, EAg/AgCl is the applied potential, and pH is the value of the catholyte. Online Differential Electrochemical Mass Spectrometry (DEMS): During the electrosynthesis of urea, intermediate products were detected by online DEMS measurement. Specifically, Ag/AgCl and Pt electrodes were used as the reference and counter electrodes, respectively. The working electrode was P-Cu/Fe2O3. For the DEMS measurements, a mass spectrometer (QAS 100) and an electrochemical workstation were used for online DEMS measurements (GAS100-Li, Shanghai Linlu Co., China). CO2-saturated 0.1 M KNO3 was used as the electrolyte. Data were collected every 10 minutes under a constant potential of −0.68 V vs. RHE for a total duration of 100 minutes. This ensured that the mass signal returned to baseline levels after each electrochemical test before initiating the next test cycle. 5 Electrochemical measurement of the Urea Electrosynthesis: The performance of the prepared electrocatalysts for urea electrosynthesis from co-electrolysis of CO2 and NO3−(UECN) was measured in a typical H-type cell, which was divided into two compartments by a Nafion 117 proton exchange membrane. This membrane facilitated the transfer of H+ ions from the anode compartment to the cathode compartment, serving as the proton source. For the experiment, P-Cu/Fe2O3 and Cu/Fe2O3 were used as working electrodes, while an Ag/AgCl electrode was used as the reference electrode and Pt gauze as the counter electrode. Prior to conducting the UECN, the apparatus was thoroughly cleaned to prevent contamination. In the electrolysis experiment, the electrolyte volume was 30 mL and it was bubbled with CO2 for at least 30 min to form a CO2-saturated solution. The potentiostatic electrochemical reduction was carried out under a steady stream of CO2 (15 sccm). To further ensure accuracy and prevent contamination or changes in surface state, a fresh working electrode sample was utilized at each applied potential. Products analysis: Quantification of Urea: The Urease Decomposition Method: This method was used for urea detection, which quantitatively analyzes the variation in NH3 concentration before and after enzymatic decomposition of urea. Specifically, urease solution was introduced into the urea solutions, facilitating the enzymatic breakdown of urea at 40 °C for 30 min. Upon completion of the decomposition process, the NH3 content was quantified, and the change in the molar quantity of ammonia (Δn = n2–n1) was used to calculate the molar content of the decomposed urea as (Δn/2). The Diacetyl-monoxime Method: 2 mL of acidic-iron solution (the acidic-iron solution was prepared by mixing 300 mL concentrated sulfuric acid (H2SO4, 98%), 100 mL concentrated phosphoric acid (H3PO4, 85%), 600 mL deionized water, and 100 mg ferric chloride (FeCl3·6H2O)); and 1 mL of DAMO-TSC solution (the DAMO-TSC solution was containing 5 g L−1 diacetylmonoxime (DAMO) and 0.1 g L−1 thiourea (TSC)), then were added in sequence to 1 mL of the cathode solution after electrolysis and mixed evenly. The mixture was then reacted at 100°C in a water 6 bath for 30 min, cooled down to room temperature, and its absorbance at 525 nm was determined. When using this method, the concentration of NO2− should be controlled within 15 ppm. Nuclear Magnetic Resonance (NMR) Method: Urea was analyzed using a high-field nuclear magnetic resonance spectrometer (Bruker AscendTM 800 MHz; Bruker Company) with deuterated dimethyl sulfoxide (DMSO-d) as the solvent and 1H NMR spectra were acquired with 1024 scans. High-Performance Liquid Chromatography (HPLC) Method: HPLC analyses were performed on Shimadzu LC-2050 equipment. Chromatographic separation was achieved using a NH2-column (250 × 4.6 mm, 5 μm particle size) with an isocratic mobile phase comprising acetonitrile and ultrapure water (75:25 v/v). Operational parameters were optimized as follows: flow rate 0.7 mL min−1, column temperature 40°C, injection volume 10 μL, and detection wavelength 195 nm. NH3 quantification: To measure the concentration of ammonia (NH3), the indophenol blue method was employed using UV-vis spectrophotometry. In this method, a series of reagents were sequentially added to a 2 mL diluted electrolyte obtained from cathode chamber. Firstly, 2 mL of 1 M sodium hydroxide aqueous solution containing 5% salicylic acid and 5% sodium citrate was added. Next, 1 mL of a 0.05 M sodium hypochlorite solution and 0.2 mL of a 1% mass fraction of sodium nitroprusside aqueous solution were added. The resulting mixture was thoroughly mixed and placed in a dark environment to react for 2 hours. After the reaction, the absorbance of the solution was measured at a wavelength of 662 nm. The quantification of ammonia was based on a standard curve obtained through the indophenol blue method. NO2− quantification: The colorimetric reagent for NO2− was prepared by dissolving 20 g of sulfanilamide and 1 g N-(1-naphthyl) ethylenediamine dihydrochloride in a solution containing 250 mL of distilled water and 50 mL of phosphoric acid. Subsequently, 1 g of N-(1-naphthyl) ethylenediamine dihydrochloride was added to the mixture. For analytical detection, 0.1 mL of the NO2−-specific color reagent was introduced into 5 7 mL of the electrolyte solution and left to stand for 20 min. UV–Vis spectroscopic analysis was then conducted, with an absorbance peak at 540 nm attributed to NO2−. A standard calibration curve was used for quantification of NO2−. Gaseous products: Following the electrolysis process, the gaseous byproducts were collected and subjected to gas chromatography (GC) analysis using an Agilent-8890 instrument. Through the evaluation of GC peak areas and the utilization of calibration curves pertinent to the TCD detector, the molar quantities of the gaseous product could be determined. Liquid products: The liquid products were quantified by a nuclear magnetic resonance (NMR) spectrometer. 1H NMR spectra of freshly acquired samples were collected on an NMR spectrometer (Bruker; Ascend 400–400 MHz) in deuterated water (D2O) with phenol as an internal standard. Faradaic Efficiency Calculation: After the quantification, the FE of each product was calculated as follows: FE = (n × F × moles of product)/Q ×100% (Q: the amount of charge passed through the working electrode; F: The Faraday constant (96485 C mol−1); n: the number of electrons transferred for product formation.) Production yield of urea: The production yield of urea (Rurea) was calculated using the following formula: Rurea = (Curea × V)/(t × m) (Curea: the amount of substance of urea (mmol L−1); V: the volume of electrolyte (L); t: the testing time (h); m: the amount of the electrocatalyst (g).). Double-layer capacitances (Cdl) measurement: The value of Cdl is proportional to the electrochemically active surface area. The value of Cdl was determined by measuring the capacitive current associated with double-layer charging from the scan-rate dependence of CV in an H-type cell. The CV was obtained from 0.14 V to 0.24 V vs. RHE. Cdl values for each electrode were 8 estimated using cyclic voltammetry over 3 cycles in the non-Faradaic region with various scan rates, which included 10 mV s−1, 20 mV s−1, 40 mV s−1, 60 mV s−1, 80 mV s−1, 100 mV s−1, 150 mV s−1 and 200 mV s−1. The Cdl was estimated by plotting the Δ(ja–jc) at 0.19 V vs. RHE (in 0.1 M KNO3 solution) against the scan rates, where ja and jc were the anodic and cathodic current densities, respectively. Computational details: In model construction, Cu (111) 2×5×1 supercell was constructed based on Cu FCC bulk structure. Fe2O3 (110) unitcell was constructed based on Fe2O3 spinel phase bulk structure. Cu (111)/Fe2O3 (110) heterostructure was constructed based on Cu (111) 2×5×1 supercell and Fe2O3 (110) unitcell. Cu (111)/ Fe2O3 (110) interface was constructed based on Cu (111)/Fe2O3 (110) superlattice. Cu (111)/Fe2O3 (110)-2P interface was constructed by replacing two oxygen atoms with phosphorous atoms, and then introducing one oxygen vacancy in Cu (111)/Fe2O3 (110). In Cu (111)/Fe2O3 (110) and Cu (111)/Fe2O3 (110)-2P interface, thickness along z direction was set at 30 Å to avoid weak interactions between images. In Density Functional Theory (DFT) calculations, structural optimizations were performed by Vienna Ab-initio Simulation Package (VASP)1 with the Projector Augmented Wave (PAW) method.2 The exchange-functional was treated using the Perdew-Burke-Ernzerhof (PBE)3 functional, in combination with the DFT-D3 correction.4 The cut-off energy of the plane-wave basis was set at 450 eV in structural optimizations. For optimization of lattice size of Cu (111)/Fe2O3 (110) superlattice, the Brillouin Zone integration was performed with a Monkhorst-Pack5 k-point mesh of 2×2×1. For optimization of geometry of Cu (111)/Fe2O3 (110) and Cu (111)/Fe2O3 (110)-2P interface, the Brillouin Zone integration was performed with a k-point mesh of 2×1×1. The equilibrium geometries and lattice constants were optimized with maximum stress on each atom within 0.02 eV Å-1. Spin polarization method was adopted to describe magnetism of models. Specifically, equal and opposite magnetic moments were set for Fe atoms to keep antiferromagnetism from Fe2O3. Hubbard U correction was introduced to describe Fe-3d orbitals, where UFe = 4.0 eV.6 In Gibbs free energy calculation, we built the hydrogen adsorption model by 9 employing the computational hydrogen electrode (CHE) model developed by Nørskov et al.7 Elementary steps of CO2 reduction reaction (CO2RR) to CO were described as: * + CO2(aq) + H2O(l) + e- → *COOH + OH-(aq) *COOH + e- → *CO + OH-(aq) Elementary steps of nitrate reduction reaction (NO3RR) were described as: * + NO3-(aq) + H2O(l) + e- → *NO2 + 2OH-(aq) *NO2 + H2O(l) + 2e- → *NO + 2OH-(aq) Elementary steps of H2O dissociation were described as: * + H2O(l) → *H2O *H2O → *H + *OH Elementary steps of desorption free energy from *NO—CO to *CO + NO (aq) or *CO
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NO (aq) were described as: *NO—CO → *CO + NO(aq) *NO—CO → *NO + CO(aq) Elementary steps of N-C coupling were described as: * + NO3-(aq) + H2O(l) + e- → *NO2 + 2OH-(aq) *NO2 + H2O(l) + 2e- → *NO(aq) + 2OH-(aq) *NO + CO(aq) → *NO + *CO *NO + *CO(aq) → *NO-CO *NO-CO(aq) + NO(aq) → *NO-CO + *NO *NO-CO + *NO → *NO-CO-NO *NO-CO-NO + H2O(l) + e- → *NO-CO-NOH + OH-(aq) In reaction pathways, * represents the bare surface of interface. *i represents the adsorption configuration of intermediate i on interface. Gibbs free energy of intermediates were calculated as G = E + G(T) + 0.0592pH + eU. E represents the total energy of *i. G(T) represents the thermal correction of *i. G(T) of *i was obtained by vaspkit interface, as same as G(T) of H2, H2O in their gas phase.8 G(T) contains two terms of correction, including zero-point energy (ZPE), product of temperature T and entropy S (TS). The Kelvin temperature T was set at 298.15K. 10 Gibbs free energy of OH-, CO2, CO, NO3-, NO in their aqueous phase, H2O in its liquid phase were referenced to Standard Hydrogen Electrode (SHE), and then corrected under specific pH value. PH value was set at 7 to simulate neutral medium for reactions. Besides, the applied potential was set at 0 V vs. RHE.
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Supplementary Figures
Figure S1. SEM images of a) P-Cu/Fe2O3 and b) Cu/Fe2O3.
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Figure S2. TEM image of Cu/Fe2O3 and the corresponding EDS elemental mappings, with Cu in red, Fe in green, O in blue.
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Figure S3. XPS spectra comparison of P-Cu/Fe2O3 and Cu/Fe2O3; a) Cu 2p XPS spectra; b) Fe 2p XPS spectra.
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Figure S4. WT-EXAFS plots of a) Cu foil, b) Cu2O; c) CuO, d) Cu/Fe2O3 and e) P-Cu/Fe2O3.
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Figure S5. WT-EXAFS plots of a) Fe foil, b) Fe2O3, c) Cu/Fe2O3 and d) P-Cu/Fe2O3.
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Figure S6. ECSA of P-Cu/Fe2O3 and Cu/Fe2O3
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Figure S7. (a) UV-Vis absorption curves of diacetyl-monoxime method with varied concentrations of urea after heating at 100 °C for 20 min; (b) Calibration curve used for urea estimation.
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Figure S8. (a) UV-Vis absorption curves of indophenol-blue colorimetry method with varied concentrations of NH4+ after in the dark for 2 h; (b) Calibration curve used for NH4+ estimation.
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Figure S9. (a) HPLC curve of urea dissolved in 0.1 M KNO3 solution with various concentrations. (b) Corresponding linear curve fitting for different urea concentrations.
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Figure S10. (a) 1H NMR curve of urea dissolved in 0.1 M KNO3 solution with various concentrations. (b) Corresponding linear curve fitting for different urea concentrations.
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Figure S11. Interference experiment of 1, 2, 4, 8, and 15 ppm of NO2− on different ppm levels of urea: (a) 1 ppm; (b) 3 ppm; (c) 5 ppm.
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Figure S12. Quantitative results of different test methods for UECN at −0.68V vs. RHE of P-Cu/Fe2O3. As shown in Figure S13, the test results of these four methods are within the margin of error about urea yield rate and FEs.
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Figure S13. (a) UV-Vis curves of Griess’s regent with varied concentrations of NO2− at room temperature for 20 min. (b) Calibration curve used for estimation of NO2−.
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Figure S14. The FEs and yield rate of urea on P-Cu/Fe2O3 with the different amounts of sodium pyrophosphate additive at –0.68 V vs. RHE.
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Figure S15. The relationship of urea yield rates and urea FEs with the different concentrations of NO3– at –0.68 V vs. RHE. The optimal concentrations of NO3– in urea electrosynthesis were screened. As shown in Figure S15, the urea yield rates and urea FEs increased as the concentrations of NO3– increased before 0.1 mol L–1. After that the urea yield rate and urea FE began to decrease which may be caused by the mismatching reduction rate of CO2RR and NO3RR.
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Figure S16. The UECN performance of P-Cu/Fe2O3 in different electrolytes. a) 0.1 M KNO3 + 0.05 M KHCO3; b) 0.1 M KNO3 + 0.05 M K2SO4. The results show that when the electrolyte is 0.1 M KNO3, the performance of UECN is the best. The results show that when KHCO3 is added to the solution, the amount of the C-byproduct increases. When K2SO4 is added to the solution, the Faraday efficiency of NO2− and NH4+ increases.
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Figure S17. 1H NMR spectra of the electrolyte obtained in isotope labeling experiments.
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Figure S18. 13C NMR spectra of P-Cu/Fe2O3 obtained in 13CO2 isotope labeling experiments.
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Figure S19. (a) Cu K-edge XANES data and (b) Cu K-edge EXAFS data in R space of P-Cu/Fe2O3 after UENC. Note that no substantial changes in the electronic state of Cu were observed for the P-Cu/Fe2O3 in UECN.
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Figure S20. Wavelet transforms of EXAFS (WT-EXAFS) of P-Cu/Fe2O3 electrode after UECN. The catalyst is in a Cu metallic elemental state during UECN, similar results are found from the wavelet transforms of EXAFS (WT-EXAFS) of the Cu K-edge.
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Figure S21. (a) Fe K-edge XANES data and (b) Fe K-edge EXAFS data in R space of P-Cu/Fe2O3 after UECN. Note that no substantial changes in the electronic state of Fe were observed for the P-Cu/Fe2O3 in UECN. It demonstrated that the P-Cu/Fe2O3 structure appears unchanged after the UECN and it existed in the form of Fe2O3.
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Figure S22. Wavelet transforms of EXAFS (WT-EXAFS) of P-Cu/Fe2O3 electrode after UECN. The catalyst is in a similar Fe2O3 state during UECN, similar results are found from the wavelet transforms of EXAFS (WT-EXAFS) of the Fe K-edge.
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Figure S23. P 2p XPS spectra of P-Cu/Fe2O3 before and after electrochemical testing.
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Figure S24. Schematic illustration of the electrochemical cell for in situ ATR-SEIRAS measurement.
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Figure S25. a-b) In situ ATR-SEIRAS spectra of 3000-3800 cm−1 on P-Cu/Fe2O3 and Cu/Fe2O3 without 0.1 M KNO3; The OH stretching bands attributed to ice-like water, liquid-like water, and isolated water, as determined by Gaussian fitting, are shown in blue, yellow, and red, respectively; c) Plot of the population of different types of interfacial water vs potential on P-Cu/Fe2O3 and Cu/Fe2O3. (The one filled with diagonal lines in the pattern is Cu/Fe2O3.)
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Figure S26. CO2RR and HER on P-Cu and P-Fe2O3.
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Figure S27. NO3RR and HER on P-Cu and P-Fe2O3.
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Supplementary Tables: Table S1. ICP results of P-Cu/Fe2O3 and Cu/Fe2O3.
Electrocatalysts Cu content wt(%) Fe content wt(%) Molar ratio of Cu/Fe
P-Cu/Fe2O3 68.97 % 31.03 % 1.96
Cu/Fe2O3 69.29 % 30.71 % 1.99
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Table S2. The actual content of P in the electrocatalysts.
Electrocatalysts Method P elemental content (wt%)
EDS mapping 0.14
P(5mmol)-Cu/Fe2O3
XPS peak areas 0.16
EDS mapping 0.23
P(10mmol)-Cu/Fe2O3
XPS peak areas 0.24
EDS mapping 0.35
P(15mmol)-Cu/Fe2O3
XPS peak areas 0.37
EDS mapping 0.46
P(20mmol)-Cu/Fe2O3
XPS peak areas 0.46
EDS mapping 0.57
P(25mmol)-Cu/Fe2O3
XPS peak areas 0.57
EDS mapping 0.37
Ele-P(15mmol)-Cu/Fe2O3 XPS peak areas 0.39
Note: The parentheses following “P” indicate the amount of sodium hypophosphite added;
Ele-P(15mmol)-Cu/Fe2O3 represents P(15mmol)-Cu/Fe2O3 after the electrochemical testing.
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Table S3. Comparison of the results of urea synthesis composite electrocatalysts in H-cell. Potential / FE (CO(NH2)2) Y (CO(NH2)2) Electrocatalyst Electrolyte Ref. V vs. RHE /% /mmol h-1 gcat.-1 97.11 P-Cu/Fe2O3 −0.68 0.1 M KNO3 73.81 This work (−0.88 V) 0.1 M KHCO3 + 9 CuPd1Rh1–DAA −0.50 72.10 53.20 0.1 M KNO3 10 a-SnBi NS/rGO −0.40 0.1M KNO3 78.36 7.70
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TiO2−C 0.90 0.1 M KNO3 45.14 19.53
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Cu1/NC −0.50 0.1 M KNO3 62.00 9.93
0.2 M Na2SO4 + 13
Mo2C/C −0.50 44.80 9.64
0.05 M NO3-
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Ru-Cu9Bi/CNT −0.40 0.01~1 M KNO3 75.60 40.00 0.1 M KHCO3 + 38.20 15 FeNC-Fe1N4 −0.60 66.50 0.1 M KNO3 (−0.90 V) 20.56 16 Cu–MoSe2 −0.60 0.1 M KNO3 23.43 (−0.70 V) In2O3-NT −0.52 0.1 M KNO3 60.30 24.00 17
CuSiOx −0.20 0.1 M KNO3 79.01 26.74 18
0.1 M KHCO3 + 19
Mo-PCN-222(Co) 0.40 33.90 14.05 50 mM KNO3 20 Bi2Se3 −0.40 0.1 M KNO3 32.00 4.60 0.2 M KHCO3 + 21 O–BiM/CuOX −0.60 23.50 36.31 0.1 M KNO3 0.05 M KNO3 + 22 Cu-MnO2 −0.50 54.70 80.00 0.1 M KHCO3 0.1 M KNO3 + 23 Cu1/In2O3 −0.60 50.88 28.97 0.1 M KHCO3 0.1 M KNO3 + 24 FeN4/B2CuN2@NC −0.40 71.90 34.52 0.1 M KHCO3 0.1 M KNO3 + 135.60 25 PCOF-34-Fe −0.50 90.00 0.1 M KHCO3 (−0.60 V) 1 M KNO3 + 0.1 26 FeNC-Ce −0.50 89.30 349.14 M KHCO3 0.1 M KNO3 + 27 RP-AuCu −0.60 88.50 22.90 0.1 M KHCO3
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Table S4. Control experiments using different C-sources and N-sources at −0.68 V vs. RHE.
Catalysts C-source N-source Urea? Electrolyte
CO2 NO3− Yes 0.1 M KNO3
CO2 NO Yes 0.1 M KHCO3
CO2 NO2− Yes 0.1 M KNO2
CO2 NH4+ NO 0.05 M NH4Cl + 0.1 M KHCO3
P-Cu/Fe2O3 CO NO3− Yes 0.1 M KNO3
CO NO2− Yes 0.1 M KNO2
CO NH4+ NO 0.05 M NH4Cl + 0.1 M KCl
CH3OH NO3− NO 0.05 M CH3OH + 0.1 M KNO3
0.1 M phosphate buffered solution
CO NO Yes
(PH=6.8)
CO2 NO3− Yes 0.1 M KNO3
CO2 NO Yes 0.1 M KHCO3
CO2 NO2− Yes 0.1 M KNO2
CO2 NH4+ NO 0.05 M NH4Cl + 0.1 M KHCO3
Cu/Fe2O3 CO NO3− Yes 0.1 M KNO3
CO NO2− Yes 0.1 M KNO2
CO NH4+ NO 0.05 M NH4Cl + 0.1 M KCl
CH3OH NO3− NO 0.05 M CH3OH + 0.1 M KNO3
0.1 M phosphate buffered solution
CO NO Yes
(PH=6.8)
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Table S5. The optimized adsorption configurations of reaction intermediates on the simulated interface structures of Cu/Fe2O3.
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Table S6. The optimized adsorption configurations of reaction intermediates on the simulated interface structures of P-Cu/Fe2O3.
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Table S7 Free energy change of all proton-coupled electron transfer steps (PCET) along urea pathways on active sites of Cu/Fe2O3. PCET Reaction along NO pathway （1） ΔG(U=0) (eV)
(Ⅰ) *+NO3−(aq)+H2O(l)+e−→*NO2+2OH−(aq) −1.5517
(Ⅱ) *NO2+H2O(l)+2e−→*+NO(aq)+2OH−(aq) 0.3531
Reaction along CO pathway （2）
(Ⅰ) *+CO2(aq)+H2O(l)+e−→*COOH+OH−(aq) 1.0396
(Ⅱ) COOH*+e−→*+CO(aq)+ OH−(aq) −0.0038
Reaction along C-N pathway （3）
(Ⅰ) *+NO3−(aq)+H2O(l)+e−→*NO2+2OH−(aq) −1.5517
(Ⅱ) *NO2+H2O(l)+2e−→*+NO(aq)+2OH−(aq) 0.0744
(Ⅲ) *NO+CO(aq)→*NO--CO −0.9067
(Ⅳ) *NO—CO(aq)→*NO-CO 0.7547
(Ⅴ) *NO-CO(aq)+NO(aq)→*NO-CO--NO −1.7192
(Ⅵ) *NO-CO--NO→*NO-CO-NO 0.7530
(Ⅶ) *NO-CO-NO+H2O(l)+e−→*NO-CO-NOH+OH−(aq) 0.1299
Reaction along H2O dissociation （4）
(Ⅰ) *H2O+e−→*H+OH−(aq) 0.2204
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Table S8. Free energy change of all proton-coupled electron transfer steps (PCET) along urea pathways on active sites of P-Cu/Fe2O3. PCET Reaction along NO pathway （1） ΔG(U=0) (eV)
(Ⅰ) *+NO3−(aq)+H2O(l)+e−→*NO2+2OH−(aq) −2.7537
(Ⅱ) *NO2+H2O(l)+2e−→*+NO(aq)+2OH−(aq) 1.5552
Reaction along CO pathway （2）
(Ⅰ) *+CO2(aq)+H2O(l)+e−→*COOH+OH−(aq) 0.9598
(Ⅱ) COOH*+e−→*+CO(aq)+ OH−(aq) 0.0760
Reaction along C-N pathway （3）
(Ⅰ) *+NO3−(aq)+H2O(l)+e−→*NO2+2OH−(aq) −2.7537
(Ⅱ) *NO2+H2O(l)+2e−→*+NO(aq)+2OH−(aq) −0.4420
(Ⅲ) *NO+CO(aq)→*NO--CO −0.0572
(Ⅳ) *NO—CO(aq)→*NO-CO 0.3185
(Ⅴ) *NO-CO(aq)+NO(aq)→*NO-CO--NO −0.9886
(Ⅵ) *NO-CO--NO→*NO-CO-NO 0.3669
(Ⅶ) *NO-CO-NO+H2O(l)+e−→*NO-CO-NOH+OH−(aq) −0.2267
Reaction along H2O dissociation （4）
(Ⅰ) *H2O+e−→*H+OH−(aq) −0.0236
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