Method for regulating coordination environment of metal monatomic catalyst by nitrogen-containing organic ligand and application thereof

Abstract

This application discloses a method and its application for regulating the coordination environment of a metal single-atom catalyst using nitrogen-containing organic ligands. The structure of the metal single-atom catalyst is M-N. x -C and M are metal atoms, and x is selected from 4 or 5. The preparation method includes: S1. Mixing a metal salt, a nitrogen-containing organic ligand, and an activated support to obtain a metal-nitrogen co-doped carbon precursor; S2. Pyrolyzing and acid washing the metal-nitrogen co-doped carbon precursor to obtain the metal single-atom catalyst; wherein: the total mass ratio of the metal salt and the nitrogen-containing organic ligand to the activated support is 1:(2.3-3), and the cutoff temperature of the pyrolysis treatment is 500-700℃. This application achieves pyrolysis at a relatively mild temperature by directionally controlling the coordination environment of the catalyst through nitrogen-containing organic ligands.

Description

Technical Field

[0001] This application belongs to the field of single-atom catalyst preparation and CO2 electroreduction technology, specifically relating to a method for regulating the coordination environment of a metal single-atom catalyst using nitrogen-containing organic ligands. Background Technology

[0002] Currently, CO2 activation and conversion has become a hot topic. Among various electrochemical activation and conversion methods, CO2 electroreduction to CO is considered a technology with great application potential due to its mild reaction conditions, ability to couple renewable electrical energy, and excellent conversion performance. However, due to the strong chemical bonding of CO2 and its competition for hydrogen evolution reaction, it is necessary to design and develop ideal electrocatalysts with excellent activity and high stability to achieve rapid reaction, low overpotential, high current density, and maintain long-term electrolysis stability under industrial conditions.

[0003] Among numerous CO2 electroreduction catalysts, single-atom catalysts have become a research hotspot in recent years due to their near 100% atom utilization, unique electronic structure, and coordination environment. Studies have shown that precisely controlling the local coordination environment of single-atom catalysts can modify the electronic state of the central active metal atom, thereby regulating catalytic performance and revealing the influence of single-atom coordination number on CO2 electroreduction performance. For example, Miao et al. (… ACS Catalysis. (2026, 16, 1656-1664) By changing the ratio of the ligand nitrogen source, three CuN with different coordination ratios were prepared at 700℃. x N' y O-type porous catalysts improve CO2 electroreduction performance by modulating the electronic structure of catalytic active sites through local coordination environment regulation. Pan et al. Journal of the American Chemical Society (2018, 140, 4218-4221) Atomic-scale dispersed nitrogen-doped hollow porous carbon spheres (Co-N) with different coordination numbers were prepared at 700℃ using a nitrogen coordination regulation strategy. x (x=4 or 5) catalysts were used, and it was found that Co-N5 catalysts with high coordination number and significant spin polarization exhibited significantly better catalytic performance than Co-N4 catalysts with low coordination number. Wang et al. ( Angewandte Chemie-International Edition Zhang et al. (2018, 57, 1944-1948) precisely controlled the coordination number of cobalt single atoms by adjusting the pyrolysis temperature (800℃, 900℃, 1000℃), and prepared three catalysts: Co-N3, Co-N4, and Co-N5. Experimental and theoretical calculations showed that a low coordination number is beneficial for activation into an intermediate and enhances the electroreduction activity of CO2, providing a new approach for catalyst design. Carbon Energy(2026, 8, e70111) The coordination number was controllably regulated at 850℃ by simply changing the order of metal precursor feeding, thus optimizing the performance of CO electroreduction to CO. Compared with the symmetrically coordinated Co-N4 configuration, the asymmetrically coordinated Co-N3 configuration strengthens the Co-N bond interaction, causing the 3d orbital energy level of the Co atom to shift towards the Fermi level. This promotes the activation of the CO2 molecule and the formation of the key intermediate *COOH (adsorbed carboxyl intermediate), achieving efficient CO electroreduction to CO. Nevertheless, current methods for directionally controlling the coordination environment of single-atom catalysts still rely on relatively complex synthetic steps or high-temperature pyrolysis conditions (≥900℃), lacking a preparation strategy that can flexibly and precisely control the coordination environment in single-atom catalysts.

[0004] Therefore, it is of great significance to find a simple and mild way to directionally control the coordination environment of single-atom catalysts to obtain better CO2 electroreduction performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for regulating the coordination environment of a metal single-atom catalyst using nitrogen-containing organic ligands.

[0006] To achieve this objective, the present application adopts the following technical solution: In a first aspect, this application provides a method for regulating the coordination environment of a metal single-atom catalyst using a nitrogen-containing organic ligand, wherein the structure of the metal single-atom catalyst is MN. x -C, M are metal atoms, x is selected from 4 or 5, and the preparation method includes: S1. Mix metal salt, nitrogen-containing organic ligand and activation support to obtain metal-nitrogen co-doped carbon precursor; S2. The metal-nitrogen co-doped carbon precursor is subjected to pyrolysis and acid washing to obtain the metal single-atom catalyst; Wherein: the cutoff temperature of the pyrolysis treatment is 500-700℃.

[0007] This application describes a process where metal salts, nitrogen-containing organic ligands, and an activated support are uniformly mixed and doped at a specific mass ratio, then pyrolyzed at 500-700℃, followed by acid washing to obtain MN with different coordination environments. x -C (x selected from 4 or 5) single-atom catalysts. By controlling the number of π-bonded N atoms in nitrogen-containing organic ligands, the orbital hybridization mode with metal atoms during pyrolysis is altered, thereby achieving the directional preparation of MN catalysts with different coordination environments at relatively mild pyrolysis temperatures. x -C single-atom catalyst.

[0008] Compared with existing methods that regulate the coordination number of MN by driving the volatilization of NC fragments through high-temperature pyrolysis (≥900℃), this application has advantages such as simple operation, mild conditions, and good directionality. Compared with the M-N4-C coordinated single-atom catalyst prepared by this method, the M-N5-C highly coordinated single-atom catalyst obtained in this application has a lower reaction energy barrier and a stronger adsorption capacity for reaction intermediates, exhibiting superior current density and CO selectivity in the electrochemical reduction reaction of CO2.

[0009] In some embodiments, the cutoff temperature of the pyrolysis treatment is 500-700°C, such as 500°C, 550°C, 600°C, 650°C, or 700°C.

[0010] In some embodiments, the MN x -C refers to nitrogen-doped carbon as a support, with a metal single atom (M) anchored on the support. The metal single atom has MN... x Coordination structure, single-atom catalyst with coordination number (x) of 4 or 5.

[0011] In some embodiments, the preparation method further includes S1': activating the carrier.

[0012] In some embodiments, the carrier comprises a carbon-based conductive material, more preferably comprising any one or a combination of at least two of conductive carbon black, polyaniline, carbon nanotubes, or graphene.

[0013] This application enables the one-step preparation of single-atom catalysts with different coordination environments by controlling the type of support and calcining under mild pyrolysis conditions of 500-700℃. This method can effectively achieve the directional anchoring of metal ions and ligands and the uniform dispersion of precursors on the support surface, thereby enhancing the catalyst's reactivity and structural stability during CO2 electroreduction.

[0014] In some embodiments, the activation treatment method includes heating activation using a nitric acid solution.

[0015] In some embodiments, after the heating activation treatment is completed, the product is washed and then freeze-dried under vacuum.

[0016] This application introduces oxygen-containing functional groups onto the surface of the support by activating the support, thereby anchoring metal ions in subsequent steps and preventing them from migrating and agglomerating into large particles during pyrolysis.

[0017] In some embodiments, the concentration of the nitric acid solution is 8-10 mol / L, such as 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L, or 10 mol / L.

[0018] This application utilizes nitric acid solution and controls its concentration within the aforementioned preferred range to effectively oxidize the carrier carbon-based conductive material, increasing the number of metal anchoring points on its surface. This is more conducive to the stable anchoring of metal ions and prevents them from agglomerating into large particles during subsequent pyrolysis.

[0019] In some embodiments, the heating temperature is 80-100°C, such as 80°C, 85°C, 90°C, 95°C, or 100°C.

[0020] In some embodiments, the stirring speed during heating is 600-800 rpm, such as 600 rpm, 650 rpm, 700 rpm, 750 rpm, or 800 rpm.

[0021] In some embodiments, the heating time is 6-10 hours, such as 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, or 10 hours.

[0022] In some embodiments, the metal salt includes any one of Ni salt, Fe salt, Co salt, Cu salt or Zn salt, preferably Ni salt.

[0023] In some embodiments, the metal salt is a metal chloride salt.

[0024] The use of chloride salts in this application does not introduce impurities, and chloride ions will form HCl gas that volatilizes out of the system during subsequent pyrolysis. If sulfate salts are used, the sulfur species therein are prone to coordinate with the target metal center, changing its coordination environment and causing the active site to be poisoned, thereby reducing catalytic activity. If nitrate salts are used, additional nitrogen elements will be introduced during pyrolysis, interfering with the precise control of N content in the catalyst and resulting in uncontrollable product composition.

[0025] In some embodiments, the nitrogen-containing organic ligand includes any one or a combination of at least two of melamine, 2-NH2-1,3,5-triazine, 5-NH2-1,2,4-triazole, 2-NH2-imidazole, or dicyandiamide, preferably melamine.

[0026] In some embodiments, the molar ratio of the metal salt to the nitrogen-containing organic ligand is (0.6-1.5):1, for example, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, etc.

[0027] In this application, by controlling the molar ratio of metal salt and nitrogen-containing organic ligand within the above-mentioned preferred range, it is more beneficial to adjust the coordination environment between nitrogen-containing organic ligand and metal to form a stable complex.

[0028] In some embodiments, the mass ratio of the activation carrier is 1:(2.3-3), such as 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3.0, etc.

[0029] In some embodiments, the nitrogen-containing organic ligand is any one or a combination of at least two of melamine, 2-NH2-1,3,5-triazine, or 5-NH2-1,2,4-triazole, and the structure of the metal single-atom catalyst is M-N5-C.

[0030] In some embodiments, the nitrogen-containing organic ligand is 2-NH2-imidazolium and / or dicyandiamide, and the structure of the metal single-atom catalyst is M-N4-C.

[0031] This application can form two different metal single-atom catalysts by selecting different nitrogen-containing organic ligands. Among them, the M-N5-C high-coordination single-atom catalyst has a lower reaction energy barrier and a stronger adsorption capacity for reaction intermediates, and exhibits better current density and CO selectivity in the electrochemical reduction reaction of CO2.

[0032] In some embodiments, the metal salt, nitrogen-containing organic ligand, and activation support are mixed and dispersed in a solvent, and dried to obtain a metal-nitrogen co-doped carbon precursor.

[0033] In some embodiments, the solvent includes water.

[0034] In some embodiments, the dispersion is performed using ultrasound.

[0035] In some embodiments, the power of the ultrasound is 300-350W, such as 300W, 310W, 320W, 330W, 340W, or 350W.

[0036] In some embodiments, the duration of the ultrasound is 2-4 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0037] In some embodiments, the drying includes vacuum freeze drying.

[0038] In some embodiments, the pyrolysis process is carried out in an inert gas.

[0039] In some embodiments, the flow rate of the inert gas is 80-120 sccm, such as 80 sccm, 90 sccm, 100 sccm, 110 sccm or 120 sccm.

[0040] In some embodiments, the heating rate of the pyrolysis treatment is 4-6℃ / min, such as 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, or 6℃ / min.

[0041] In some embodiments, the heat treatment holding time is 1-3 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0042] In some embodiments, the solution used for pickling is a hydrochloric acid solution.

[0043] In some embodiments, the concentration of the hydrochloric acid solution is 1-4 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0044] In some embodiments, the amount of hydrochloric acid solution used is 30-60 mL, such as 30 mL, 35 mL, 40 mL, 45 mL, 50 mL, 55 mL, or 60 mL.

[0045] In some embodiments, the pickling temperature is 40-60°C, such as 40°C, 45°C, 50°C, 55°C, or 60°C.

[0046] In some embodiments, the pickling time is 48-96 hours, such as 48 hours, 60 hours, 72 hours, 84 hours, or 96 hours.

[0047] In this application, acid washing is used to remove unstable metal particles, etch amorphous carbon, and clear pores so that active sites are exposed as much as possible. If acid washing is not performed, nanoparticles with uneven particle size will be formed, making it impossible to form a single-atom catalyst.

[0048] As a specific embodiment, this application provides a method for preparing Ni metal single atoms, the preparation process as follows: Figure 1 As shown, taking NiCl2 as the metal salt, dicyandiamide or melamine as the nitrogen-containing organic ligand, and conductive carbon black as the support as an example, the steps include: S1. Mix the metal salt, nitrogen-containing organic ligand and activation support (the total mass ratio of the metal salt and nitrogen-containing organic ligand to the activation support is 1:(2.3-3)) to obtain a metal-nitrogen co-doped carbon precursor; S2. The metal-nitrogen co-doped carbon precursor is subjected to pyrolysis (pyrolysis temperature of 600℃) and acid washing (using 1-4 mol / L hydrochloric acid solution, acid washing at 40-60℃ for 48-96 h) to obtain the metal single-atom catalyst.

[0049] Secondly, this application provides a metal single-atom catalyst obtained by the preparation method described in the first aspect.

[0050] In some embodiments, the metal atom includes any one of Ni, Fe, Co, Cu or Zn, preferably Ni.

[0051] Thirdly, this application provides the application of a metal single-atom catalyst as described in the second aspect in the electrochemical reduction of carbon dioxide.

[0052] Compared with the prior art, this application has the following advantages: (1) This application modifies the orbital hybridization mode of nitrogen-containing organic ligands with metal atoms during pyrolysis by regulating the number of π-bonded N atoms in the nitrogen-containing organic ligands, thereby achieving directional regulation of the coordination environment of the catalyst at a mild pyrolysis temperature. Compared with traditional high-temperature pyrolysis (≥900℃), the preparation method provided in this application has the advantages of simple synthesis method, mild conditions and good directionality.

[0053] (2) The M-N5-C single-atom catalyst prepared in this application is more conducive to improving the overall performance of the catalyst than the M-N4-C single-atom catalyst. The M-N5-C single-atom catalyst has a lower reaction energy barrier and a stronger intermediate adsorption capacity in the CO2 electroreduction to CO reaction, and can achieve better CO2 electrochemical reduction performance. It solves the problem that the coordination environment of traditional single-atom catalysts is difficult to be directionally controlled and the catalytic activity and stability are difficult to balance. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating the preparation process of the Ni metal single-atom catalyst provided in this application.

[0055] Figure 2 The images show XRD comparisons of the metal single-atom catalysts with different coordination environments prepared in Examples 1.1-1.5.

[0056] Figure 3 The images show a comparison of HAADF-STEM images of metal single-atom catalysts with different coordination environments prepared in Examples 1.1-1.5.

[0057] Figure 4 The above are comparison diagrams of EXAFS fitting of metal single-atom catalysts with different coordination environments prepared in Examples 1.1-1.5. Detailed Implementation

[0058] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0059] This application does not limit the specific application environment. For example, the electrolyte can be 1M KOH or 0.5M KHCO3, the anode and cathode electrolyte chambers are separated by anion exchange membranes, and the anode catalyst can be any one of nickel foam, platinum sheet or iridium oxide.

[0060] Unless otherwise specified, the raw materials involved in the following specific embodiments of this application are all conventional materials in the art, and can be purchased from commercially available products. Some raw material information is as follows: 2-NH2-1,3,5-triazine: purchased from Beijing Kepujia Experimental Instrument Co., Ltd., brand name Aladdin; 5-NH2-1,2,4-triazole: purchased from Beijing Kepujia Experimental Instrument Co., Ltd., brand name Aladdin; 2-NH2-imidazole: purchased from Beijing Kepujia Experimental Instrument Co., Ltd., brand name Aladdin.

[0061] Example 1.1 This embodiment provides a method for preparing a Ni metal single-atom catalyst, including the following steps: (1) 2g of conductive carbon black was dispersed in 250mL of 9mol / L nitric acid, then heated under reflux at 90℃ and stirred for 8h at a stirring rate of 700rpm. After the reaction was completed, the carbon black was washed 5 times with deionized water and then freeze-dried under vacuum to obtain activated conductive carbon black.

[0062] (2) 132.7 mg of NiCl2·6H2O, 47.3 mg of melamine and 450 mg of activated conductive carbon black were mixed in ultrapure water and then ultrasonicated for 3 h in an ultrasonic machine with an ultrasonic power of 320 W to disperse them evenly. After ultrasonication, the precursor was obtained by vacuum freeze drying.

[0063] (3) The nickel-nitrogen co-doped carbon precursor was placed in a tube furnace (heating rate of 5℃ / min) and pyrolyzed at 600℃ for 2h under an argon atmosphere (flow rate of 100sccm) to obtain the pyrolysis product; the pyrolysis product was transferred to a 3mol / L hydrochloric acid solution for acid washing for 72h, then washed 5 times with ultrapure water and then freeze-dried under vacuum to obtain Ni-N5-C.

[0064] Example 1.2 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that in this embodiment, 128.18 mg of NiCl2·6H2O and 51.82 mg of 2-NH2-1,3,5-triazine are added in step (2), and Ni-N5-C is prepared in step (3).

[0065] Example 1.3 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that in this embodiment, 132.88 mg of NiCl2·6H2O and 47.12 mg of 5-NH2-1,2,4-triazole are added in step (2), and Ni-N5-C is prepared in step (3).

[0066] Example 1.4 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that in this embodiment, 122.77 mg of NiCl2·6H2O and 57.23 mg of 2-NH2-imidazole are added in step (2), and Ni-N4-C is prepared in step (3).

[0067] Example 1.5 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that in this embodiment, 132.88 mg of NiCl2·6H2O and 47.12 mg of dicyandiamide are added in step (2), and Ni-N4-C is prepared in step (3).

[0068] Example 2 This embodiment provides a method for preparing a Ni metal single-atom catalyst, including the following steps: (1) 2g of carbon nanotubes were dispersed in 200mL of 9mol / L nitric acid, and then heated under reflux at 85℃ and stirred at a stirring rate of 700rpm for 8h. After the reaction was completed, the carbon nanotubes were washed with deionized water 5 times and then freeze-dried under vacuum to obtain activated carbon nanotubes.

[0069] (2) 132.7 mg of NiCl2·6H2O, 47.3 mg of melamine and 420 mg of activated carbon nanotubes were mixed in ultrapure water and then sonicated in an ultrasonic machine with an ultrasonic power of 300 W for 4 h to disperse them evenly. After sonication, the nickel-nitrogen co-doped carbon precursor was obtained by vacuum freeze drying.

[0070] (3) The nickel-nitrogen co-doped carbon precursor was placed in a tube furnace (heating rate of 4℃ / min) and pyrolyzed at 550℃ for 3h under an argon atmosphere (flow rate of 80sccm) to obtain the pyrolysis product. The pyrolysis product was transferred to a 3mol / L hydrochloric acid solution for acid washing for 72h, then washed 5 times with ultrapure water and freeze-dried under vacuum to obtain Ni-N5-C. The catalyst uses nitrogen-doped carbon as a support, and Ni single atoms are anchored on the support.

[0071] Example 3 This embodiment provides a method for preparing a Ni metal single-atom catalyst, including the following steps: (1) 2g of graphene was dispersed in 200mL of 10mol / L nitric acid, then heated to reflux at 95℃ and stirred at a stirring rate of 700rpm for 12h. After the reaction was completed, the carbon black was washed 5 times with deionized water and then freeze-dried under vacuum to obtain activated conductive carbon black.

[0072] (2) 132.7 mg of NiCl2·6H2O, 47.3 mg of melamine and 500 mg of activated graphene were mixed in ultrapure water and then ultrasonicated in an ultrasonic machine with an ultrasonic power of 350 W for 2 hours to disperse them evenly. After ultrasonication, the nickel-nitrogen co-doped carbon precursor was obtained by vacuum freeze drying.

[0073] (3) The nickel-nitrogen co-doped carbon precursor was placed in a tube furnace (heating rate of 6℃ / min) and pyrolyzed at 650℃ for 1h under an argon atmosphere (flow rate of 120sccm) to obtain the pyrolysis product. The pyrolysis product was transferred to a 3mol / L hydrochloric acid solution for acid washing for 72h, then washed 5 times with ultrapure water and freeze-dried under vacuum to obtain Ni-N5-C. The catalyst uses nitrogen-doped carbon as a support, and Ni single atoms are anchored on the support.

[0074] Example 4 This embodiment provides a method for preparing a Co metal single-atom catalyst. The difference between this method and that of Example 1.1 is that 132.7 mg of NiCl2·6H2O and 47.3 mg of melamine in step (2) of Example 1.1 are replaced with 133 mg of CoCl2·6H2O and 47 mg of melamine, respectively; and the catalyst Co-N5-C is prepared in step (3).

[0075] Example 5 This embodiment provides a method for preparing a Fe metal single-atom catalyst. The difference between this method and that of Example 1.1 is that in step (2) of Example 1.1, 132.7 mg of NiCl2·6H2O and 47.3 mg of melamine are replaced with 112.8 mg of FeCl2·4H2O and 567.2 mg of melamine, respectively; and in step (3), the catalyst Fe-N5-C is prepared.

[0076] Example 6 This embodiment provides a method for preparing a Cu metal single-atom catalyst. The difference between this method and that of Example 1.1 is that 132.7 mg of NiCl2·6H2O and 47.3 mg of melamine in step (2) of Example 1.1 are replaced with 120.5 mg of CuCl2·2H2O and 59.5 mg of melamine, respectively; and the catalyst Cu-N5-C is prepared in step (3).

[0077] Example 7 This embodiment provides a method for preparing a Zn metal single-atom catalyst. The difference between this method and that of Example 1.1 is that 132.7 mg of NiCl2·6H2O and 47.3 mg of melamine in step (2) of Example 1.1 are replaced with 111.3 mg of ZnCl2 and 78.7 mg of melamine, respectively; and the catalyst Zn-N5-C is prepared in step (3).

[0078] Example 8 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that the concentration of nitric acid in step (1) is 4 mol / L.

[0079] Example 9 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that, in this embodiment, 132.7 mg of NiCl2·6H2O in step (2) is replaced with 146.7 mg of NiSO4·6H2O, and the amount of activated conductive carbon black added is changed to 465 mg.

[0080] Examples 10.1-10.2 Examples 10.1-10.2 provide a method for preparing a Ni metal single-atom catalyst. The difference between the preparation method and that in Example 1.1 is that Example 10.1 uses a pyrolysis temperature of 500℃, while Example 10.2 uses a pyrolysis temperature of 700℃.

[0081] Examples 11.1-11.2 Examples 11.1-11.2 provide a method for preparing a Co metal single-atom catalyst. The difference between the preparation method and that in Example 4 is that Example 11.1 uses a pyrolysis temperature of 500℃, while Example 11.2 uses a pyrolysis temperature of 700℃.

[0082] Examples 12.1-12.2 Examples 12.1-12.2 provide a method for preparing an Fe metal single-atom catalyst. The difference between the preparation method and that in Example 5 is that Example 12.1 uses a pyrolysis temperature of 500℃, while Example 12.2 uses a pyrolysis temperature of 700℃.

[0083] Examples 13.1-13.2 Examples 13.1-13.2 provide a method for preparing a Cu metal single-atom catalyst. The difference between the preparation method and Example 6 is that Example 13.1 uses a pyrolysis temperature of 500℃, while Example 13.2 uses a pyrolysis temperature of 700℃.

[0084] Examples 14.1-14.2 Examples 14.1-14.2 provide a method for preparing a Zn metal single-atom catalyst. The difference between the preparation method and that in Example 7 is that Example 14.1 uses a pyrolysis temperature of 500℃, while Example 14.2 uses a pyrolysis temperature of 700℃.

[0085] Example 15 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that 250 mg of activated conductive carbon black is added in step (2) of this embodiment.

[0086] Example 16 This embodiment provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and that in Example 1.1 is that 600 mg of activated conductive carbon black is added in step (2) of this embodiment.

[0087] Comparative Example 1 This comparative example provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and Example 1.1 is that step (1) is not performed in this comparative example.

[0088] Comparative Example 2 This comparative example provides a method for preparing a Ni metal single-atom catalyst. The difference between this method and Example 1.1 is that a pyrolysis temperature of 800℃ is used in this comparative example.

[0089] Comparative Example 3 This comparative example provides a method for preparing a Co metal single-atom catalyst. The difference between this method and Example 4 is that a pyrolysis temperature of 800°C is used in this comparative example.

[0090] Comparative Example 4 This comparative example provides a method for preparing an Fe metal single-atom catalyst. The difference between this method and Example 5 is that a pyrolysis temperature of 800°C is used in this comparative example.

[0091] Comparative Example 5 This comparative example provides a method for preparing a Cu metal single-atom catalyst. The difference between this method and Example 6 is that a pyrolysis temperature of 800°C is used in this comparative example.

[0092] Comparative Example 6 This comparative example provides a method for preparing a Zn metal single-atom catalyst. The difference between this method and Example 7 is that a pyrolysis temperature of 800°C is used in this comparative example.

[0093] Performance Test 1 The Ni metal single-atom catalysts with different coordination environments prepared in Examples 1.1-1.5 were subjected to XRD, HAADF-STEM (high-angle annular dark-field imaging-scanning transmission electron microscopy) and EXAFS fitting (extended X-ray absorption fine structure spectrum fitting analysis) tests, and the results are as follows: Figure 2 The images show the XRD patterns of the single-atom catalysts with different coordination environments prepared in Examples 1.1-1.5. Figure 2 As shown, the characteristic crystal plane peaks of graphitic carbon (002) and (100) can only be observed at ~24.6° and ~43.5° in the catalysts under the three coordination conditions. This indicates that there is no obvious aggregation of nickel metal nanoparticles in the catalysts and the nickel metal single atom dispersion is good.

[0094] Figure 3 The HAADF-STEM results are for the atomic cluster-single atom catalysts with different coordination environments prepared in Examples 1.1-1.5. Figure 3 As shown, only single-atom sites exist in the catalysts under the three coordination conditions, indicating that this series of catalysts are single-atom catalysts of metallic nickel.

[0095] Figure 4The EXAFS fitting results are for the atomic cluster-single atom catalysts prepared in different coordination environments in Examples 1.1-1.5. The fitting results show that Ni in the catalysts under the three coordination environments mainly coordinates with N atoms in the first shell. Furthermore, the Ni-N coordination number fitting result for the catalyst prepared in Example 1.1 is 4.9±0.2, with a Ni-N5-C structure; the Ni-N coordination number fitting result for the catalyst prepared in Example 1.2 is 4.9±0.4, with a Ni-N5-C structure; the Ni-N coordination number fitting result for the catalyst prepared in Example 1.3 is 4.7±0.1, with a Ni-N5-C structure; the Ni-N coordination number fitting result for the catalyst prepared in Example 1.4 is 3.9±0.2, with a Ni-N4-C structure; and the Ni-N coordination number fitting result for the catalyst prepared in Example 1.5 is 4.1±0.2, with a Ni-N4-C structure. These results indicate that the coordination environment of the catalyst can be effectively controlled by changing the content of conductive carbon black on the support.

[0096] Performance Test 2 The CO Faraday efficiency and current density of the examples and comparative examples were tested. The test method was as follows: 6 mg of the catalyst prepared in the examples and comparative examples above was mixed with 500 μL of isopropanol and 100 μL of Nafion solution and ultrasonically prepared to obtain a catalyst slurry. The slurry was then completely coated on a 2 0.5cm 2 The carbon paper was dried and used as the working electrode. The electrochemical reduction performance of CO2 was evaluated in a gas diffusion flow cell. The cathode and anode electrolytes were 1M KOH. Nickel foam was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The cathode gaseous products were quantitatively analyzed by gas chromatography. Some test results are shown in Tables 1 and 2.

[0097] It should be noted that, for ease of comparison, Table 1 only shows the CO Faradaic efficiency and current density data of the catalysts prepared in Examples 1.1-1.5 (different types of supports), Examples 10.1-10.2, and Comparative Example 2 (only the temperature was changed compared to Example 1.1) at different voltages; Table 2 shows the CO Faradaic efficiency and current density data of Examples 2-3, Examples 8-9, Examples 15-16, and Comparative Example 1 at a voltage of -2.4V (vs. Ag / AgCl); while the other examples, such as Examples 4-7, Examples 11-14, and the corresponding Comparative Examples 3-6, show similar trends to those of Examples 1 and Comparative Example 2.

[0098] Table 1 Table 2 The test results show that: 1. As shown in Table 1, under the same reaction conditions, the Ni-N5-C catalysts obtained in Examples 1.1-1.3 of this application exhibit superior CO2 electroreduction performance compared to the Ni-N4-C catalysts obtained in Examples 1.4-1.5. Specifically, at -2.4V (vs. Ag / AgCl), the Ni-N5-C catalyst in Example 1.1 achieves a CO Faradaic efficiency of 97.98% and a CO electroreduction efficiency of 484.92 mA cm⁻¹. -2 The industrial-grade current density is superior to that of the Ni-N4-C catalyst in Examples 1.4-1.5, and it has broad prospects for industrial applications.

[0099] 2. As can be seen from the comparison of data from Examples 1.1 and 8-9, in this application, the concentration of acid solution and the type of metal salt during the activation process also affect the performance of the catalyst. By controlling them within the preferred range of this application, it is more conducive to improving the overall performance of the catalyst.

[0100] 3. As can be seen from the comparison of the data of Example 1.1 with Examples 15-16 and Comparative Example 1, the activation treatment in step (1) and the amount of carrier added in step (2) will have a significant impact on the performance of the catalyst, and they must be controlled within the conditions specified in this application.

[0101] 4. As can be seen from the comparison of the data of Example 1.1 and Comparative Examples 2-6, the coordination environment of single atoms in the catalyst can also be controlled by adjusting the temperature, but the controllability is poor and it is impossible to accurately prepare the desired coordination structure.

[0102] This application illustrates its technical solution through the above embodiments, but it is not limited to the above process steps, meaning that this application does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this application.

Claims

1. A method for regulating the coordination environment of a metal single-atom catalyst using nitrogen-containing organic ligands, characterized in that, The structure of the metal single-atom catalyst is MN. x -C, M are metal atoms, x is selected from 4 or 5, and the preparation method includes: S1. Mix metal salt, nitrogen-containing organic ligand and activation support to obtain metal-nitrogen co-doped carbon precursor; S2. The metal-nitrogen co-doped carbon precursor is subjected to pyrolysis and acid washing to obtain the metal single-atom catalyst; Wherein: the cutoff temperature of the pyrolysis treatment is 500-700℃.

2. The preparation method according to claim 1, characterized in that, The preparation method further includes S1': activating the carrier; Preferably, the carrier comprises a carbon-based conductive material, and more preferably comprises any one or a combination of at least two of conductive carbon black, polyaniline, carbon nanotubes or graphene; Preferably, the activation treatment method includes heating activation treatment using nitric acid solution; Preferably, the concentration of the nitric acid solution is 8-10 mol / L; Preferably, the heating temperature is 80-100℃; Preferably, the stirring speed during heating is 600-800 rpm; Preferably, the heating time is 6-10 hours.

3. The preparation method according to claim 1 or 2, characterized in that, The metal salt includes any one of Ni salt, Fe salt, Co salt, Cu salt or Zn salt, preferably Ni salt; And / or, the metal salt is a metal chloride salt; And / or, the nitrogen-containing organic ligand includes any one or a combination of at least two of melamine, 2-NH2-1,3,5-triazine, 5-NH2-1,2,4-triazole, 2-NH2-imidazolium or dicyandiamide, preferably melamine; And / or, the molar ratio of the metal salt to the nitrogen-containing organic ligand is (0.6-1.5):1; And / or, the total mass ratio of the metal salt and nitrogen-containing organic ligand to the mass ratio of the activated support is 1:(2.3-3).

4. The preparation method according to any one of claims 3, characterized in that, The nitrogen-containing organic ligand is any one or a combination of at least two of melamine, 2-NH2-1,3,5-triazine or 5-NH2-1,2,4-triazole, and the structure of the metal single-atom catalyst is M-N5-C; And / or, the nitrogen-containing organic ligand is 2-NH2-imidazolium and / or dicyandiamide, and the structure of the metal single-atom catalyst is M-N4-C.

5. The preparation method according to any one of claims 1-4, characterized in that, The metal salt, nitrogen-containing organic ligand and activation support are mixed and dispersed in a solvent, and dried to obtain a metal-nitrogen co-doped carbon precursor. Preferably, the solvent includes water; Preferably, the dispersion is carried out in the form of ultrasound; Preferably, the power of the ultrasound is 300-350W; Preferably, the ultrasound duration is 2-4 hours; Preferably, the drying process includes vacuum freeze drying.

6. The preparation method according to any one of claims 1-5, characterized in that, The pyrolysis process is carried out in an inert gas. Preferably, the flow rate of the inert gas is 80-120 sccm; Preferably, the heating rate of the pyrolysis treatment is 4-6℃ / min; Preferably, the heat treatment holding time is 1-3 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The pickling solution used is hydrochloric acid solution; Preferably, the concentration of the hydrochloric acid solution is 1-4 mol / L; Preferably, the amount of hydrochloric acid solution used is 30-60 mL; Preferably, the pickling temperature is 40-60°C; Preferably, the pickling time is 48-96 hours.

8. A metal single-atom catalyst obtained by the preparation method according to any one of claims 1-7.

9. The metal single-atom catalyst according to claim 8, characterized in that, The metal atoms include any one of Ni, Fe, Co, Cu or Zn, preferably Ni.

10. The application of a metal single-atom catalyst as described in claim 8 or 9 in the electrochemical reduction of carbon dioxide.

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