A diatomic copper-doped catalyst, a preparation method and application thereof

Abstract

The application provides a diatomic copper-doped catalyst and a preparation method and application thereof, and the catalyst is a carbon material doped with a structural unit shown in formula I in a molecular structure. The diatomic metal catalyst copper catalyst constructed by the application can adjust the adsorption / desorption energy of an electrocatalytic reaction intermediate through metal-metal synergistic effect, so that the selectivity of the electrocatalytic reaction is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials chemistry, specifically relating to a diatomic copper catalyst embedded in a nitrogen-doped porous carbon support, its preparation method, and its application. Background Technology

[0002] Nitrate pollution in water bodies is widespread. Converting nitrates into high-value chemicals such as hydroxylamine (NH₂OH) can simultaneously achieve pollution control and resource recovery. Hydroxylamine is a crucial raw material in semiconductor manufacturing, organic synthesis, pharmaceuticals, biomedicine, and nylon-6 production, and also shows potential as a hydrogen carrier in clean energy applications. Traditional industrial routes for hydroxylamine production, such as ammonia oxidation and nitric oxide reduction, suffer from harsh operating conditions, high energy consumption, and significant greenhouse gas emissions. Therefore, developing a green and energy-efficient hydroxylamine synthesis route is crucial for advancing sustainable chemistry.

[0003] The electrochemical nitrate reduction reaction (NO3RR) at ambient temperature and pressure shows promising application prospects. However, the polar NH2OH intermediate binds tightly to the active sites on the catalyst surface and is easily further reduced to NH3, resulting in low selectivity for hydroxylamine. Furthermore, the competitive hydrogen evolution reaction further reduces efficiency. Therefore, advanced electrocatalysts are needed to achieve the sustainable production of hydroxylamine. Summary of the Invention

[0004] Single-atom catalysts (SA) have well-defined active sites, but may cause over-stabilization of intermediates. The diatomic catalyst (DA) constructed in this invention can modulate the adsorption / desorption energy of reaction intermediates through metal-metal synergistic effects, thereby breaking the proportional relationship of intermediate adsorption energy and improving the high selectivity of electrocatalytic reactions.

[0005] To address the problems in the prior art, this invention provides a diatomic copper-doped catalyst, its preparation method, and its application. This catalyst does not require organic promoters and can achieve stable and highly selective electrochemical synthesis of NH2OH under mild conditions, showing promising prospects for industrial applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A diatomic copper-doped catalyst, wherein the catalyst is a carbon material whose molecular structure is doped with structural units represented by Formula I: ,in This indicates that the structural unit connects to other parts of the carbon material.

[0007] The catalyst has a structure similar to nitrogen-doped graphene or nitrogen-doped carbon nanotubes, where Cu is doped and embedded in the framework structure of the carbon material, unlike supported materials.

[0008] The carbon material includes pure carbon materials (e.g., graphene, carbon nanotubes), doped carbon materials (e.g., N-doped graphene, N-doped carbon nanotubes), or carbon materials with other functional groups attached (e.g., graphene oxide). When the carbon material is pure carbon, it means that, apart from the structural units described above, all other parts of the catalyst are composed of carbon (C). Similarly, when the carbon material is doped carbon or has other functional groups attached, it means that, apart from the structural units described above, all other parts of the catalyst are either doped carbon or have other functional groups attached.

[0009] Preferably, there are multiple structural units.

[0010] Preferably, the Cu element content in the catalyst is 3.0~3.5% by mass.

[0011] The second objective of this invention is to provide a method for preparing the above-mentioned diatomic copper-doped catalyst, comprising the following steps: (1) A carbon source and a pore-forming agent are prepared into a mixed solution, and then copper salt and NH3 source are added to the mixed solution and ultrasonically treated to form a precursor, wherein the molar ratio of NH3 to Cu in the NH3 source is greater than or equal to 3:1; (2) After drying the precursor, it is pyrolyzed at 650~850°C under an inert atmosphere to obtain the catalyst.

[0012] Preferably, the carbon source is glucose.

[0013] Preferably, the pore-forming agent is hydroxylamine hydrochloride.

[0014] Preferably, the solvent of the mixed solution is a mixture of water and ethanol. More preferably, the volume ratio of water to ethanol in the mixed solvent is 1:1.

[0015] Preferably, the copper salt and NH3 source is a mixture of copper salt and ammonia water, or copper salt and [Cu(NH3)4]. 2+ A mixture of salts. More preferably, the copper salt and NH3 source are a mixture of CuCl2 and [Cu(NH3)4]Cl2.

[0016] Preferably, the heating rate of the pyrolysis in step (2) is 3~7℃ / min.

[0017] A third objective of this invention is to provide the above-mentioned catalyst for the electrochemical conversion of NO3. - For the application of hydroxylamine.

[0018] The applications include: Using an electrode modified with the catalyst as the working electrode, and containing NO3 -An acidic aqueous solution is used as the electrolyte, and a voltage is applied at a potential of -0.1 V to -0.5 V relative to the reversible hydrogen electrode (RHE), preferably -0.4 V.

[0019] Preferably, the cation of the electrolyte is selected from H. + and Li + Na + K + or Cs + One or more of the following. More preferably, the cation of the electrolyte is H. + and Li + In this case, Faraday efficiency (FE) is at its highest.

[0020] When the electrolyte's cation is H + and Li + When using a voltage of -0.4 V relative to RHE, the yield of hydroxylamine can reach 7.0 mg•h. −1 •mgcat −1 above.

[0021] The beneficial effects of this invention are as follows: The catalyst of this invention does not require an organic promoter and can achieve stable and highly selective electrochemical synthesis of NH2OH under mild conditions. Its preparation method is simple, has good reproducibility and stability, and has good prospects for industrial application. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the synthesis route of the catalyst of this invention.

[0023] Figure 2 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF STEM) image of SA obtained in Example 1.

[0024] Figure 3 This is a HAADF STEM image of DA obtained in Example 1.

[0025] Figure 4 yes Figure 3 Intensity distribution along the XY plane marked by the blue rectangles (numbered 1-4).

[0026] Figure 5 These are HAADF-STEM images of DA and energy-dispersive X-ray spectra (EDX) of the corresponding elements.

[0027] Figure 6 This is a XANES diagram of DA, SA, copper foil, copper oxide (CuO), and cuprous oxide (Cu2O).

[0028] Figure 7These are the copper Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectra of DA, SA, and copper foil.

[0029] Figure 8 It is the N2 adsorption-desorption isotherm of DA.

[0030] Figure 9 These are the HR-XPS plots for SA(A) and DA(B).

[0031] Figure 10 These are HR-XPS N 1s spectra of different materials, where A is the NC part of DA (i.e., the region outside the formula I structure in the DA catalyst), B is the formula I structure region of DA, and C is the NC part of SA.

[0032] Figure 11 The cyclic voltammetry (LSV) curves obtained in Example 1 (3) with different catalyst-modified electrodes as working electrodes, under conditions of adding and not adding 0.05 MHNO3.

[0033] Figure 12 It is the Faraday efficiency (FE) value of various NO3RR products on DA under different applied potentials in Example 1 (3).

[0034] Figure 13 The FE and yield of NH2OH on DA under different applied potentials in Example 1 (3) are the results.

[0035] Figure 14 This is a comparison diagram of FE of NH2OH on SA and DA under different applied potentials in Example 1 (3).

[0036] Figure 15 The ATR-SEIRAS spectra (calibrated baselines) of the DA catalyst in Example 1 (3) under different applied potentials are shown, where A is 3000-2750 cm⁻¹. -1 The spectrum of the region, B is 1500-900 cm⁻¹ -1 Spectra of the region. The reference spectrum was acquired at 0 V vs. RHE. C is the free energy diagram of NO3RR on SA and DA. The ∆G value represents the potential-determining step (PDS). D is the calculated free energy diagram of HER on SA and DA.

[0037] Figure 16 This diagram illustrates the effect of cations on the formation of NH2OH on DA. Figure A shows the yield as a function of proton flux, and Figure B shows the Faraday efficiency (FE) as a function of the electrical double layer (EDL) relaxation time in different electrolytes.

[0038] Figure 17 This is a characterization of the repeatability and stability of DA in Example 1 (3).

[0039] Figure 18 The image is a HAADF-STEM image of DA-2 obtained in Example 2.

[0040] Figure 19 The image is a HAADF-STEM image of DA-3 obtained in Example 3. Detailed Implementation

[0041] Example 1 Example 1 (1) Preparation of catalyst: Glucose (0.576 g) and NH₂OH•HCl (2.760 g) were dissolved in 200 mL of water / ethanol (1:1 v / v). 0.04 mmol CuCl₂ and 0.04 mmol [Cu(NH₃)₄]Cl₂ were added, and the mixture was then sonicated for 1 h. The mixture was dried at approximately 70 °C, and the resulting solid precursor was pyrolyzed under argon: the temperature was increased to 800 °C at a rate of 5 °C / min, held for 4 h, and then cooled under argon; the resulting powder was named DA.

[0042] The activity and loading of atomic sites can be adjusted by modifying the nitrogen source, precursor stoichiometry, pyrolysis temperature (650~850 ℃), residence time (2~6 h), and heating rate (3~7 ℃ / min).

[0043] As a comparison, a single-atom control catalyst (SA) was prepared: glucose (0.576 g), melamine (2.522 g), and cuprous chloride (CuCl2, 0.07 mmol) were mixed in 200 mL of a 1:1 (v / v) water-ethanol mixture. A few drops of glacial acetic acid were added to fully dissolve the components, resulting in a clear solution, which was then sonicated for 1 h. The solvent was then evaporated at 70 °C. The resulting solid was placed in an alumina crucible and annealed at 800 °C at a heating rate of 5 °C per minute for 4 h to obtain SA Cu1NC.

[0044] (2) Catalyst characterization: Figure 2 -~4 shows the characterization results of DA and SA using high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), where DA shows paired Cu atom bright spots, while SA shows isolated single atoms.

[0045] Figure 4 yes Figure 3 The intensity distribution along the XY plane in the area marked by the blue rectangle shows that the distance between the two Cu atoms is approximately 0.3 ± 0.02 nm.

[0046] Figure 5 These are the HAADF-STEM images of DA and the corresponding energy-dispersive X-ray spectra (EDX) of the elements. The images show that all elements are uniformly distributed within the catalyst.

[0047] Figure 6 -~7 shows the XANES and EXAFS characterization results. XANES analysis of the Cu K-edge between CuO and Cu2O indicates that the oxidation states of atomically dispersed Cu are between +1 and +2. DA shows a slight lower energy shift compared to SA. FT EXAFS analysis of DA shows Cu-N and Cu-Cu characteristics, consistent with the N3CuCuN3 model. Fitting data indicate that the configurations of DA and N3CuCuN3 / graphene, and SA and CuN4 / graphene, are matched.

[0048] XPS ( Figure 9 The results show that, compared to SA, the Cu 2p peak in DA shifts towards lower binding energies; the N 1s spectrum ( Figure 10 It shows pyridine / pyrrole / graphite components and Cu-N characteristics.

[0049] ICP AES: Taking copper as an example, its content is approximately 3.27 wt%.

[0050] BET Figure 8 This confirms its porous morphology.

[0051] (3) Electrocatalytic performance: The electrochemical cell is an H-type cell, separated by a Nafion 117 membrane. The working electrode is modified with a catalyst (a solution containing 10 mg of catalyst, 1 ml of isopropanol, and 20 μL of 5% Nafion was drop-coated onto carbon cloth and dried). The reference electrode is Ag / AgCl (saturated KCl), converted to RHE via E(RHE) = E(Ag / AgCl) + 0.198 + 0.059•pH. The counter electrode is a Pt mesh. The electrolyte volume is 35 mL.

[0052] The electrochemical catalytic performance of DA and SA was tested using a 0.05 M H2SO4 Ar saturated solution as the electrolyte.

[0053] Figure 11 Linear scan voltammetry (LSV) curves of NO3RR performance on SA and DA with and without the addition of 0.05 M HNO3 in the electrolyte are shown at a scan rate of 10 mV / s.

[0054] Figure 12 The Faraday efficiency (FE) values ​​of various NO3RR products on DA at different applied potentials are shown. Figure 13The excision potential (FE) and yield of NH2OH on DA at different applied potentials are shown. This indicates that the DA-modified electrode exhibits high yield and selectivity for NH2OH, along with a high FE, in the range of -0.1V to -0.7V relative to RHE.

[0055] At the optimal potential of −0.4 V relative to RHE, the Faraday efficiency (FE) of NH2OH on DA is approximately 83.7%, and the yield is approximately 7.5 mg•h. −1 •mgcat −1 A more negative potential (≤ −0.6 V) will increase the hydrogen evolution reaction and decrease the selectivity of NH2OH.

[0056] Figure 14 This indicates that DA has a significantly higher FE compared to SA.

[0057] In argon-saturated solutions of 0.05 M HNO3 and 0.05 M H2SO4, ATR-SEIRAS spectra of the DA catalyst were collected under different applied potentials. It can be seen that the potential-dependent infrared absorption peaks are attributed to the N-O stretching vibrations of activated *NO3, *NO2, *NOOH and NH2OH, as well as the N-H bending vibrations of metal-bonded *NH2OH.

[0058] In-situ ATR-SEIRAS and density functional theory (DFT) indicate that the DA Cu2 site favors the desorption of *NH2OH (e.g., desorption free energy ΔG). desorb ≈ −0.29 eV), and raise the energy barrier for further reduction to NH3; electrolyte cation selection (H + Li + Na + K + Cs + The interfacial electrobilayer environment is adjusted, thereby altering the desorption capacity of *NH2OH and affecting selectivity (the observed Faraday efficiency (FE) order is Li). + >H + >Cs + >Na + >K + ).

[0059] Catalyst stability: SA is more conducive to the formation of ammonia (NH3). DA still exhibits stable structure and activity after long-term electrolysis (characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) and X-ray photoelectron spectroscopy (XPS).

[0060] Example 2 Glucose and NH₂OH•HCl were dissolved in 200 mL of water / ethanol (1:1 v / v). 0.04 mmol of CuCl₂ and excess NH₃ were added, and the mixture was then sonicated for 1 h. The mixture was dried at approximately 70 °C, and the resulting solid precursor was pyrolyzed under argon: the temperature was increased to 850 °C at a rate of 5 °C / min, held for 4 h, and then cooled under argon; the resulting powder was named DA-2.

[0061] Figure 18 The prepared DA-2 catalyst was shown to have a paired double copper atom structure.

[0062] Example 3 Glucose and NH₂OH•HCl were dissolved in 200 mL of water / ethanol (1:1 v / v). 0.04 mmol CuCl₂ and 0.04 mmol [Cu(NH₃)₄]Cl₂ were added, and the mixed solution was sonicated for 1 h. The mixture was dried at approximately 70 °C, and the resulting solid precursor was pyrolyzed under argon: the temperature was increased to 650 °C at a rate of 5 °C / min, held for 4 h, and then cooled under argon; the resulting powder was named DA-3.

[0063] Figure 19 The prepared DA-3 catalyst was shown to have a paired double copper atom structure.

Claims

1. A diatomic copper-doped catalyst, characterized in that, The catalyst is a carbon material whose molecular structure is doped with structural units represented by Formula I: ,in This indicates that the structural unit connects to other parts of the carbon material.

2. The catalyst according to claim 1, characterized in that, The catalyst contains 3.0 to 3.5% Cu by mass.

3. The method for preparing the diatomic copper-doped catalyst according to any one of claims 1-2, characterized in that, Includes the following steps: (1) A carbon source and a pore-forming agent are prepared into a mixed solution, and then copper salt and NH3 source are added to the mixed solution and ultrasonically treated to form a precursor, wherein the molar ratio of NH3 to Cu in the NH3 source is greater than or equal to 3:1; (2) After drying the precursor, it is pyrolyzed at 650~850°C under an inert atmosphere to obtain the catalyst.

4. The preparation method according to claim 3, characterized in that, The carbon source is glucose.

5. The preparation method according to claim 3, characterized in that, The pore-forming agent is hydroxylamine hydrochloride.

6. The preparation method according to claim 3, characterized in that, The solvent of the mixed solution is a mixture of water and ethanol; preferably, the volume ratio of water to ethanol in the mixed solvent is 1:

1.

7. The preparation method according to claim 3, characterized in that, The copper salt and NH3 source are a mixture of copper salt and ammonia water, or copper salt and [Cu(NH3)4]. 2+ A mixture of salts; preferably, the copper salt and NH3 source are a mixture of CuCl2 and [Cu(NH3)4]Cl2.

8. The preparation method according to claim 3, characterized in that, The heating rate of the pyrolysis described in step (2) is 3~7℃ / min.

9. The diatomic copper-doped catalyst according to any one of claims 1-2 in the electrochemical conversion of NO3 - For the application of hydroxylamine.

10. The application according to claim 9, characterized in that, The applications include: Using an electrode modified with the catalyst as the working electrode, and containing NO3 - An acidic aqueous solution is used as the electrolyte, and a voltage is applied at a potential of -0.1 V to -0.5 V relative to the reversible hydrogen electrode, preferably -0.4 V.

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