Single-atom catalyst based on metal-organic framework electrochemical reconstitution and synthesis method and application thereof

Abstract

The application provides a single-atom catalyst based on metal organic framework electrochemical reconstruction and a synthesis method and application thereof, the synthesis method comprising: (1) obtaining a carbon-nitrogen base by mixing melamine with conductive carbon black and then heat treating; (2) synthesizing Ni-MOF-74 by a hydrothermal method; and (3) drop-coating the Ni-MOF-74 on the carbon-nitrogen base and using the same for electrocatalytic CO2 reduction, to generate nickel single atoms in situ under constant-voltage electrolysis. The nickel single atom catalyst synthesized in situ at-0.9 V vs. RHE (relative reversible hydrogen electrode) can electrocatalytically reduce CO2 into CO, and the faradic efficiency (FE) of the product can reach 96.4%, the preparation method is simple in process, low in process cost and energy consumption, and can be widely applied to CO2 electrochemical reduction (CER).

Description

Technical Field

[0001] This invention relates to electrochemistry, and more particularly to a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework, its synthesis method, and its applications. Background Technology

[0002] Research on converting CO2 into high-value-added chemicals or fuels such as carbon monoxide, formate, ethanol, and ethylene using renewable energy has become a major focus of attention. Among these, CO2 electrochemical reduction (CER) is a promising energy recycling technology due to its mild reaction conditions, enabling intermittent storage of renewable energy and zero carbon emissions. However, the conversion efficiency of CER is limited by slow kinetics and is often accompanied by severe hydrogen evolution side reactions, leading to reduced CER reactivity and product selectivity. Therefore, there is an urgent need to develop novel CER catalysts with high target product selectivity / conversion efficiency, low cost, and high atom utilization.

[0003] Single-atom catalysts (SACs) are widely used in the electrocatalytic reduction of CO2 due to their high atom utilization and uniform active sites. Carbon-based supported SACs, in particular, offer advantages such as high specific surface area, high conductivity, and potentially low manufacturing costs. Furthermore, carbon-based support materials often contain heteroatoms such as N, O, and S, which not only improve the dispersion of single atoms but also further enhance the catalytic activity of the SACs. Currently, there are two main strategies for synthesizing carbon-based supported SACs: "top-down" and "bottom-up." However, both methods typically require high-temperature pyrolysis during synthesis, resulting in high energy consumption and low safety. Additionally, the synthesized single atoms often exhibit particle aggregation, leading to low Faradaic efficiency and significantly reduced catalytic performance in the CO2 reduction reaction.

[0004] Patent CN114289065A discloses a method for preparing a metal ion-doped X-MOF-74 photocatalyst and its application in gas-phase photocatalytic CO2 reduction. Doping with metal ions can effectively reduce the conduction band bottom of X-MOF-74, thereby decreasing its band gap and increasing its light absorption, thus enhancing its photocatalytic activity for carbon dioxide reduction. However, this method is complex, offers limited improvement to catalyst performance, and results in insufficient catalytic performance.

[0005] Developing a new type of SACs that meets the requirements of a simple process flow and high Faraday efficiency in catalytic CO2 reduction reaction is a technical problem that needs to be solved. Summary of the Invention

[0006] To address the aforementioned technical issues, this application provides a nickel single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework and its synthesis method, and uses the obtained catalyst for electrocatalytic CO2 reduction.

[0007] This application is achieved through the following technical solution:

[0008] On the one hand, this application provides a method for synthesizing single-atom catalysts based on the electrochemical reconstruction of metal-organic frameworks, comprising the following steps:

[0009] S1. Add conductive carbon black and melamine to ethanol, stir evenly at room temperature, heat and continue stirring, and vacuum dry to obtain a mixed powder;

[0010] S2. The mixed powder is heated and reacted under an inert atmosphere to obtain a carbon-nitrogen substrate material;

[0011] S3. Dissolve the metal precursor nitrate hexahydrate and 2,5-dihydroxyterephthalic acid in a mixed solution of N,N-dimethylformamide (DMF), methanol and water, stir evenly at room temperature, heat to react, cool to room temperature, and collect the crude product powder of X-MOF-74 by centrifugation.

[0012] S4. Wash the crude X-MOF-74 powder with N,N-dimethylformamide and methanol. Soak the crude X-MOF-74 powder in methanol, filter, and vacuum dry to obtain X-MOF-74.

[0013] S5. Add the carbon-nitrogen substrate material to a mixed solution of isopropanol and water, add Nafion binder and mix evenly, centrifuge ultrasonically, and drop-coat the centrifuged carbon-nitrogen substrate material onto carbon paper.

[0014] S6. Add the X-MOF-74 to a mixed solution of isopropanol and water, add Nafion binder and mix evenly, centrifuge ultrasonically, drop-coat the centrifuged X-MOF-74 onto carbon paper loaded with carbon-nitrogen substrate material, dry, and obtain a single-atom catalyst based on electrochemical reconstruction of metal-organic framework.

[0015] Preferably, the metal precursor is nickel, cadmium, magnesium, or cobalt; more preferably, nickel.

[0016] Further, in step S1, the mass ratio of melamine to conductive carbon black is 1:2 to 3; the temperature for heating and stirring is 50 to 70°C, and the stirring time is 0.5 to 1 hour; the vacuum drying time is 8 to 24 hours.

[0017] Furthermore, in step S2, the temperature at which the mixed powder is heated to react under an inert atmosphere is 600–700°C, the heating rate is 3–6°C / min, and the heating time is 1–2 h.

[0018] Further, in step S3, the molar ratio of the metal precursor hexahydrate nitrate to 2,5-dihydroxyterephthalic acid is 3:1, the volume ratio of N,N-dimethylformamide, methanol, and water is 15:1:1, and the heating reaction is carried out at a temperature of 80–120°C for 12–36 hours.

[0019] Furthermore, the Nafion binder has a mass fraction of 5%; the ultrasonic centrifugation time is 30 min; and the mass ratio of X-MOF-74 to carbon-nitrogen substrate material is 0.125–0.625:1.

[0020] On the other hand, this application provides a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework, which is prepared by the above-described synthesis method.

[0021] Finally, this application also provides an application of the above-mentioned single-atom catalyst based on electrochemical reconstruction of metal-organic framework in the electrocatalytic CO2 reduction reaction.

[0022] Furthermore, the electrocatalytic CO2 reduction reaction includes the following steps:

[0023] Electrocatalytic CO2 reduction was performed using a three-electrode system. The reference electrode was a saturated Ag / AgCl electrode, the counter electrode was a platinum mesh, and the working electrode was the single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework. The cathode electrolyte was a KHCO3 solution, and the anolyte was a H2SO4 solution. The anode and cathode chambers were separated by a Nafion 117 membrane. Under constant voltage (-0.7V to -1.1V vs. RHE), in-situ electrochemical reconstruction was carried out to generate a single-atom metal, and the electrocatalytic CO2 reduction reaction was carried out to generate CO.

[0024] Compared with the prior art, this application has the following advantages:

[0025] 1) The method for synthesizing single-atom catalysts is simple and the conditions are mild. By drop-coating Ni-MOF-74 onto a carbon-nitrogen substrate, single-atom metal catalysts are synthesized in situ using constant voltage electrolysis. The process is simple and easy to operate, can be completed at room temperature, has low energy consumption and is safe, and does not require the high-temperature treatment in general single-atom synthesis processes.

[0026] 2) The synthesized nickel single-atom catalyst has good CER performance and can generate CO with high activity and high selectivity. The Farada efficiency (FE) of CO can reach more than 90% and can reach up to 96.4% at -0.7V to -1.1V (relative to the reversible hydrogen electrode), which is significantly better than existing CER single-atom catalysts.

[0027] The synthesis and catalytic methods provided in this application are simple and have high catalytic efficiency, offering a new approach for the synthesis and application of single-atom catalysts. Attached Figure Description

[0028] The following is a brief explanation of the content depicted in the accompanying drawings:

[0029] Figure 1 This is a scanning electron microscope image of the nickel single-atom catalyst prepared in Example 1 of this application;

[0030] Figure 2 Aberration-corrected transmission electron microscope image of the nickel single-atom catalyst prepared in Example 1 of this application;

[0031] Figure 3 The XRD pattern of the nickel single-atom catalyst prepared in Example 1 of this application;

[0032] Figure 4 The overall XPS spectrum of the nickel single-atom catalyst prepared in Example 1 of this application;

[0033] Figure 5 This is a fine XPS image of the nickel single-atom catalyst prepared in Example 1 of this application;

[0034] Figure 6 Synchrotron radiation diagram of the nickel single-atom catalyst prepared in Example 1 of this application;

[0035] Figure 7 Synchrotron radiation diagram of the nickel single-atom catalyst prepared in Example 1 of this application;

[0036] Figure 8 Synchrotron radiation diagram of the nickel single-atom catalyst prepared in Example 1 of this application;

[0037] Figure 9 Gibbs free energy diagrams of the CER reaction pathways calculated for different configurations of the nickel single-atom catalyst prepared in Example 1 of this application;

[0038] Figure 10 This is a graph showing the electrocatalytic CO2 reduction performance of the nickel single-atom catalyst prepared in Example 1 of this application;

[0039] Figure 11 This is a stability test diagram of the nickel single-atom catalyst prepared in Example 1 of this application;

[0040] Figure 12 The graph shows the electrocatalytic CO2 reduction performance of the nickel single-atom catalyst prepared in Example 2 of this application.

[0041] Figure 13 This is a graph showing the electrocatalytic CO2 reduction performance of the nickel single-atom catalyst prepared in Example 3 of this application;

[0042] Figure 14 This is a Faraday efficiency diagram of the single-atom catalyst prepared in Example 4 of this application for the electrocatalytic reduction of CO from CO2 to obtain CO;

[0043] Figure 15 This is a graph showing the electrocatalytic CO2 reduction performance of the single-atom catalyst prepared in Example 5 of this application. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] Step 1: At room temperature, conductive carbon black and melamine are stirred in ethanol at a mass ratio of 1:2.5 for 1 hour to ensure uniform distribution. The mixture is then heated to 60°C and stirred for another hour. Finally, it is placed in an oven and vacuum-dried at 60°C overnight. The resulting mixed powder is placed in a tube furnace and heated to 650°C at a rate of 5°C / min under a N2 atmosphere, and maintained for 2 hours to obtain a carbon-nitrogen substrate material.

[0047] Step 2: At room temperature, weigh out 0.036 mmol of nickel nitrate hexahydrate and 0.012 mmol of 2,5-dihydroxyterephthalic acid, and dissolve them in 10 mL of LMF, methanol, and water (volume ratio V). DMF ∶V 甲醇 ∶V 水 The mixture was stirred at room temperature for 10 min in a 15:1:1 ratio solution, then placed in a 20 mL stainless steel reactor lined with polytetrafluoroethylene (PTFE). The reactor was then placed in an oven at 100 °C for 24 h. After cooling to room temperature, the solid powder product was collected by centrifugation. The product was washed multiple times with DMF and methanol, and then soaked in methanol for 24 h. Finally, the solid powder was placed in a vacuum oven at 120 °C and evacuated for 12 h to obtain Ni-MOF-74.

[0048] Step 3: Weigh 1.2 mg of the carbon-nitrogen substrate material obtained in Step 1. Use a pipette to measure 240 μL of a mixed solution of isopropanol and water (volume ratio 1:1). Measure 1.2 μL of Nafion (5% by mass) binder into a 2 mL centrifuge tube. After sonicating for 30 min, drop the mixture at 30 μL per drop onto a 1.2 × 1 cm plate. -2 The catalyst was dried on carbon paper at 60°C to achieve a catalyst loading of 1 mg / cm³. -2Weigh 0.45 mg of Ni-MOF-74 obtained in step two. Use a pipette to measure 90 μL of a mixed solution of isopropanol and water (volume ratio 1:1). Measure 0.45 μL of Nafion (5% by mass) binder into a 2 mL centrifuge tube. After sonicating for 30 min, drop the mixture at 30 μL per drop onto a 1.2 × 1 cm substrate loaded with carbon-nitrogen. -2 Nickel single-atom catalyst (labeled NiSAs / NC) was obtained by drying on carbon paper at 60°C, with a catalyst loading of 0.375 mg / cm³. -2 .

[0049] Step 4: In-situ electrochemical reconstruction and electrocatalytic CO2 reduction were performed using a three-electrode system. The reference electrode was a saturated Ag / AgCl electrode, the counter electrode was a platinum mesh, and the working electrode was the carbon paper loaded with NiSAs / NC prepared in Step 3. The cathode electrolyte was 0.1 MkHCO3, and the anolyte was 0.1 Mh2SO4. The anode and cathode chambers were separated by a Nafion 117 membrane. Nickel single atoms were generated in-situ under a constant voltage (-0.7V to -1.1V (relative to the reversible hydrogen electrode)) and directly used for electrocatalytic CO2 reduction. The resulting product was analyzed by an Agilent 7890B gas chromatograph.

[0050] The NiSACs / NC catalyst prepared in Example 1 was subjected to scanning electron microscopy (STEM), as shown below. Figure 1 As shown, the NiSACs / NC catalyst was subjected to aberration-corrected transmission electron microscopy (HAADF-STEM), as shown. Figure 2 As shown, from Figure 1 and Figure 2 Highly dispersed nickel single atoms can be seen, thus proving that the method in Example 1 successfully synthesized nickel single atoms loaded on a carbon-nitrogen substrate.

[0051] Figure 3 The image shows the XRD pattern of the NiSACs / NC catalyst prepared in Example 1. Figure 3 As can be seen from Example 1, Ni-MOF-74 was successfully synthesized. Furthermore, characteristic peaks of Ni-MOF-74 also appeared in the synthesized nickel single atoms, proving that the nickel single atoms generated after reconstruction still contain some Ni-MOF-74.

[0052] Figure 4 and Figure 5 The image shows the XPS plot of the NiSACs / NC catalyst prepared in Example 1. Figure 4 For the general spectrum, Figure 5 Fine XPS spectra of C, O, Ni, and N. From Figure 4As can be seen from Example 1, the nickel single atoms supported on the carbon-nitrogen material have C, N, Ni, and O elements, and combined with... Figure 5 The detailed spectra of each element suggest that new coordination structures were formed during the electrochemical reconstruction process.

[0053] Figure 6-8 The image shows the NiSACs / NC synchrotron radiation pattern prepared in Example 1, where... Figure 6 The fine structure spectrum of Ni's k-edge X-ray absorption is shown. Figure 7 The FT-EXAFS spectrum of the k-edge of Ni is shown below. Figure 8 Wavelet transform diagrams for Ni-MOF-74 and NiSAs / NC. From Figure 6 It can be seen that the valence state of NiSAs / NC is slightly higher than that of Ni-MOF-74, combined with... Figure 7 FT-EXAFS, Figure 8 Wavelet transform and EXAFS-fitted catalyst structural parameters suggest that the coordination structure in NiSAs / NC is Ni-N2-O2. The EXAFS-fitted catalyst structural parameters are shown in Table 1.

[0054] Table 1 Catalyst structural parameters fitted by EXAFS

[0055]

[0056] Figure 9 The Gibbs free energy diagrams for the CER reaction pathways calculated in different configurations of NiSACs / NC prepared in Example 1 are shown below. Figure 9 It can be seen that for the NiN4, NiN3O1, and NiN2O2 configurations, the rate-determining step is the step of generating the *COOH intermediate. As the O coordination number increases, the ΔG for generating the *COOH intermediate further decreases, further verifying that the possible coordination structure in NiSACs / NC is NiN2O2.

[0057] Figure 10 The image shows the electrocatalytic carbon dioxide reduction performance of the NiSACs / NC prepared in Example 1, including the partial current density and Faradaic efficiency. Figure 10 It can be seen that, compared with pure carbon-nitrogen materials and Ni-MOF-74, the synthesized NiSAs / NC exhibits superior performance in the electrocatalytic reduction of carbon dioxide to carbon monoxide, maintaining product selectivity of over 90% across a voltage range of -0.7 to -1.1 V (relative to the reversible hydrogen electrode). Furthermore, the nickel single-atom catalyst prepared at -0.9 V (relative to the reversible hydrogen electrode) achieves a Faradaic efficiency of up to 96.4% in the electrocatalytic production of CO from CO2.

[0058] The stability of the NiSACs / NC prepared in Example 1 at -0.9V (relative to the reversible hydrogen electrode) was tested, and the results are as follows: Figure 11 As shown. By Figure 11 It can be seen that the synthesized NiSAs / NC has good stability, with activity decay only occurring after 15 hours, indicating that NiSAs / NC can serve as a good catalyst for electrocatalytic carbon dioxide reduction and has the potential for industrial application.

[0059] Example 2

[0060] The procedures of Example 1 were repeated, except that the mass ratio of conductive carbon black to melamine in step one of Example 1 was changed to 1:2 and 1:3. NiSAs / NC were prepared and applied to electrocatalytic CO2 reduction.

[0061] The electrocatalytic performance of the single-atom catalyst prepared in Example 2 for CO2 is as follows: Figure 12 As shown. From Figure 12 As can be seen from the data, when the mass ratio of conductive carbon black to melamine is within the parameter range provided by the technical solution of this application, the prepared nickel single-atom catalysts all have relatively ideal CO Faradaic efficiency and bias current density.

[0062] Example 3

[0063] Repeat the operation steps of Example 1, except that the heat treatment temperature in step one of Example 1 is changed to 600℃ and 700℃ respectively. Figure 13 This diagram shows the electrocatalytic CO2 performance of single-atom catalysts synthesized at different temperatures. Based on... Figure 13 It can be seen that when the heat treatment temperature increases from 600℃ to 700℃, the bias current density and Faraday efficiency of CO show relatively ideal performance. Among them, the performance of NiSAs / NC reaches the optimal when the heat treatment temperature is 650℃.

[0064] Example 4

[0065] Repeat the steps of Example 1, except that the nickel source in step two of Example 1 is changed to a cadmium source, a cobalt source, and a magnesium source, respectively. Figure 14 This is a Faraday efficiency diagram for CO obtained from the electrocatalytic reduction of CO2 by Ni / Cd / Mg / CoSAs / NC. Based on... Figure 14 As can be seen, the CER performance of different types of SAs / NCs is improved compared with that of pure carbonitriding materials.

[0066] Example 5

[0067] Repeat the steps of Example 1, except that the proportion of Ni-MOF-74 loaded on the carbonitridium material substrate in step three of Example 1 is changed to 0.125, 0.25, 0.5 and 0.625, respectively. Figure 15 The diagram shows the partial current density and Faraday efficiency of nickel single-atom catalysts catalyzing CO production with different loadings. Figure 15 As can be seen from the above, when the proportion of Ni-MOF-74 loaded on the carbonitridium material substrate is within the range provided in this application, the Faraday efficiency can reach over 90, with the highest reaching 96.4%.

[0068] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for synthesizing single-atom catalysts based on electrochemical reconstruction of metal-organic frameworks, characterized in that, Includes the following steps: S1. Add conductive carbon black and melamine to ethanol, stir evenly at room temperature, heat and continue stirring, and vacuum dry to obtain a mixed powder; S2. The mixed powder is heated and reacted under an inert atmosphere to obtain a carbon-nitrogen substrate material; S3. Dissolve the metal precursor nitrate hexahydrate and 2,5-dihydroxyterephthalic acid in a mixed solution of N,N-dimethylformamide, methanol and water, stir evenly at room temperature, heat to react, cool to room temperature, and centrifuge to collect the crude product powder of X-MOF-74. S4. Wash the crude X-MOF-74 powder with N,N-dimethylformamide and methanol. Soak the crude X-MOF-74 powder in methanol, filter, and vacuum dry to obtain X-MOF-74. S5. Add the carbon-nitrogen substrate material to a mixed solution of isopropanol and water, add Nafion binder and mix evenly, centrifuge ultrasonically, and drop-coat the centrifuged carbon-nitrogen substrate material onto carbon paper. S6. Add the X-MOF-74 to a mixed solution of isopropanol and water, add Nafion binder and mix evenly, centrifuge ultrasonically, drop-coat the centrifuged X-MOF-74 onto carbon paper loaded with carbon-nitrogen substrate material, dry, and obtain carbon paper loaded with X-MOF-74 and carbon-nitrogen substrate material. S7. In-situ electrochemical reconstruction and electrocatalytic CO2 reduction were performed using a three-electrode system. The reference electrode was a saturated Ag / AgCl electrode, the counter electrode was a platinum mesh, and the working electrode was carbon paper supported on X-MOF-74 and a carbon-nitrogen substrate. The cathode electrolyte was KHCO3, and the anolyte was H2SO4. The anode and cathode chambers were separated by a Nafion 117 membrane. Metal single atoms were generated in-situ under constant voltage electrolysis and directly used for electrocatalytic CO2 reduction, resulting in a single-atom catalyst based on metal-organic framework electrochemical reconstruction.

2. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 1, characterized in that, The metal precursor is nickel, cadmium, magnesium, or cobalt.

3. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 2, characterized in that, The metal precursor is nickel.

4. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 1, characterized in that, In step S1, the mass ratio of melamine to conductive carbon black is 1:2-3; the temperature for heating and stirring is 50-70°C, and the stirring time is 0.5-1h; the vacuum drying time is 8-24h.

5. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 1, characterized in that, In step S2, the temperature at which the mixed powder is heated to react under an inert atmosphere is 600–700°C, the heating rate is 3–6°C / min, and the heating time is 1–2 h.

6. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 1, characterized in that, In step S3, the molar ratio of the metal precursor hexahydrate nitrate to 2,5-dihydroxyterephthalic acid is 3:1, the volume ratio of N,N-dimethylformamide, methanol, and water is 15:1:1, and the heating reaction is carried out at a temperature of 80–120°C for 12–36 hours.

7. The method for synthesizing a single-atom catalyst based on the electrochemical reconstruction of a metal-organic framework according to claim 1, characterized in that, In steps S5 and S6, the mass fraction of the Nafion binder is 5%; the ultrasonic centrifugation time is 30 min; and the mass ratio of the X-MOF-74 to the carbon-nitrogen substrate material is 0.125 to 0.625:

1.

8. A single-atom catalyst based on electrochemical reconstruction of a metal-organic framework, prepared by the synthesis method according to any one of claims 1 to 7.

9. The application of a single-atom catalyst based on electrochemical reconstruction of a metal-organic framework prepared by any one of the synthesis methods described in claims 1 to 7 in the electrocatalytic CO2 reduction reaction.

10. The application of a single-atom catalyst based on electrochemical reconstruction of a metal-organic framework according to claim 9 in the electrocatalytic CO2 reduction reaction, characterized in that, The electrocatalytic CO2 reduction reaction includes the following steps: A three-electrode system was used for electrocatalytic CO2 reduction. The reference electrode was a saturated Ag / AgCl electrode, the counter electrode was a platinum mesh, and the working electrode was carbon paper loaded with X-MOF-74 and a carbon-nitrogen substrate. The cathode electrolyte was a KHCO3 solution, and the anolyte was an H2SO4 solution. A Nafion 117 membrane was used to separate the anode and cathode chambers. Under constant voltage, in-situ electrochemical reconstruction was carried out to generate single-atom metals, and the electrocatalytic reduction of CO2 was carried out to generate CO.

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