Defect-ligand-based atomically dispersed non-noble metal catalysts, methods of making and using the same

Abstract

The application relates to an atomic dispersion non-noble metal catalyst based on a defect ligand and a preparation method and application thereof, and relates to an atomic dispersion non-noble metal catalyst and a preparation method and application thereof. The application aims to solve the technical problem of low catalytic activity of existing single-atom transition metal carbon-based catalysts, and the catalyst is composed of MN4 embedded in a carbon carrier, wherein M is coordinated with N in two different M-N bond lengths, and a 2N t =M=2N c coordination structure is formed. The preparation method is as follows: a three-dimensional nitrogen-doped porous defect type flower-shaped carbon carrier is prepared by utilizing the thermal instability of a defect ligand, then a catalyst is obtained by impregnation adsorption and heat treatment. The carbon carrier of the catalyst has a hierarchical porous structure of micropores and mesopores, the catalyst has asymmetric sites, and the maximum power density of a fuel cell assembled by using the catalyst as a cathode reaches 862 mW cm ‑2 , and the catalyst can be applied to the fields of proton exchange membrane fuel cells and metal air batteries.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of preparation and application of oxygen reduction electrocatalysts, and particularly relates to an atomically dispersed non-noble metal catalyst and a preparation method and application thereof. BACKGROUND

[0002] With the global energy crisis and climate change, the demand for sustainable energy technology is increasingly urgent. Proton exchange membrane fuel cells (PEMFCs) are considered as a leading energy technology, but its wide application is still hindered by the slow kinetics of the oxygen reduction reaction (ORR). Among them, single-atom transition metal carbon-based catalysts (Fe, Mn, Co, Ni) M-NC overcome the limitations of traditional Pt-based catalysts and become a promising ORR catalyst. Generally speaking, M-N4 sites with symmetrical electronic structure are not conducive to the adsorption-desorption of oxygen-containing intermediates, thereby hindering the ORR kinetics.

[0003] At the same time, the high-activity Fe-NC catalyst is limited in further practical application due to the lack of active site utilization and low stability. In order to achieve high catalytic performance, Fe-N-C catalysts often have high loading and thick catalytic layer. However, too high loading may lead to mutual shielding between active sites and affect mass transfer, thereby affecting the efficiency of catalytic reaction. SUMMARY

[0004] The present application is to solve the technical problem of low catalytic activity of existing single-atom transition metal carbon-based catalysts, and provides an atomically dispersed non-noble metal catalyst based on defect ligand and a preparation method and application thereof. The catalyst is a strain-regulated transition metal-based single-atom catalyst with high activity and high stability, and can be applied to cathode oxygen reduction in new energy fields such as proton exchange membrane fuel cells and metal-air batteries.

[0005] The atomically dispersed non-noble metal catalyst based on defect ligand of the present application is composed of MN4 embedded in a carbon carrier, wherein M is coordinated with N in two different M-N bond lengths, showing 2N t = M = 2N c coordination structure, wherein t represents tensile, c represents compressive, the mass fraction of M is 0.5% to 1%, and M is Fe, Mn, Co or Ni.

[0006] The preparation method of the atomically dispersed non-noble metal catalyst based on defect ligand described above is carried out according to the following steps:

[0007] I. Preparation of a three-dimensional nitrogen-doped porous defect-type flower-like carbon support precursor: Zinc source and nitrogen source were dissolved in methanol, then mixed and stirred rapidly and vigorously for 2-2.5 h, and then kept at 60-65℃ for 2-2.5 h, resulting in a white suspension in the solution; then centrifuged, washed, and dried to obtain a three-dimensional nitrogen-doped porous defect-type flower-like carbon support precursor, which is a white powder; wherein the nitrogen source is 5-aminotetrazolium monohydrate (5-ATZ) and 2-methylimidazolium (2-MIM) in a molar ratio of 1:(3-5);

[0008] II. Preparation of nitrogen-doped porous carbon support: The precursor prepared in step one was subjected to a step-by-step high-temperature heat treatment under an inert atmosphere and cooled to room temperature to obtain nitrogen-doped porous carbon support (NC); the step-by-step high-temperature heat treatment was as follows: first, the temperature was raised to 200-220℃ and held for 0.5-0.6 h, then raised to 400-420℃ and held for 0.5-0.6 h, then raised to 700-720℃ and held for 1-1.3 h, and finally raised to 1000-1050℃ and held for 2-2.5 h;

[0009] III. Preparation of single-atom catalyst precursor: First, nitrogen-doped porous carbon support is immersed in a solution of metal M soluble salt, stirred vigorously for 2-2.5 h under an inert atmosphere, then ultrasonically dispersed for 2-2.5 h, filtered or centrifuged, and the solid phase is dried to obtain single-atom catalyst precursor;

[0010] IV. Preparation of single-atom catalysts: The single-atom catalyst precursors were placed in a furnace and heated to 950–1050 °C in an argon atmosphere for 2–3 h to obtain a non-noble metal catalyst based on defect ligands with atomically dispersed structure, denoted as MN4-SM.

[0011] Furthermore, the zinc source mentioned in step one is zinc acetate dihydrate ((CH3COO)2Zn), anhydrous zinc nitrate (Zn(NO3)2), or zinc nitrate hexahydrate (Zn(NO3)2·6H2O).

[0012] Furthermore, the inert atmosphere described in steps two and three is either Ar or N2.

[0013] Furthermore, the drying described in steps one and three is performed under vacuum at a temperature of 60–80°C for 6–8 hours.

[0014] Furthermore, the solvent for the metal M soluble salt solution in step three is N,N-dimethylformamide.

[0015] Furthermore, the vigorous stirring described in step three involves a stirring speed of 500–700 rpm.

[0016] Furthermore, the heating rate described in step four is 5–20 °C / min. -1 .

[0017] The aforementioned application of non-precious metal catalysts based on atomically dispersed defective ligands is to use these catalysts as cathode catalysts in proton exchange membrane fuel cells or metal-air batteries.

[0018] The method for preparing strain-modulated single-atom catalysts of this invention achieves two effects through the pyrolysis of the defective ligand 5-aminotetrazolium: First, a one-step porosification process significantly reduces the complexity and cost of single-atom catalyst preparation, generating a hierarchical porous structure that improves pore size and pore structure, thereby enhancing the accessibility and utilization of active sites and mass transport capacity. Second, induced CN cracking regulates atomic strain, ensuring the efficient preparation of single-atom sites. This method is applicable to Fe, Mn, Co, and Ni metals, demonstrating good versatility.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0020] 1. This invention uses 5-aminotetrazole as a defect ligand to prepare three-dimensional porous defect-type flower-like spheres for use as nitrogen-doped carbon supports in oxygen reduction reactions, resulting in CN cracking. The induced hierarchical porous structure is beneficial to promoting the mass transfer of O2 and H2O, without the need for secondary porousing treatment.

[0021] 2. The one-step porousing heat treatment produces a multi-level porous structure, which helps to increase defects and thus increase the density of M-N4 centers; the two-step graphitization heat treatment enhances the corrosion resistance of the carbon substrate, thereby improving the stability of the catalyst under operating conditions.

[0022] 3. Compared with single-atom Fe-based catalysts, strain-regulated MN4-SM (M = Fe, Mn, Co, Ni) can mitigate the adsorption affinity for intermediates and effectively promote the desorption of oxygen-containing intermediates, thereby effectively increasing the rate of oxygen reduction reaction of the catalyst.

[0023] 4. The atomically dispersed Fe-based catalyst prepared by this invention exhibits a high half-wave potential in both acidic and alkaline electrolytes, and the half-wave potential decreases by only 16 mV after 60,000 cycles of aging in acidic media.

[0024] The atomically dispersed catalyst of this invention uses 5-aminotetrazole as a defect ligand and dimethylimidazolium as a synergistic diligand to prepare a porous defective carbon support. Utilizing the thermal instability of 5-aminotetrazole during pyrolysis, gas is generated leading to CN cracking. While replenishing the nitrogen source, the resulting asymmetric strain helps regulate Fe sites, and the content is low. Simultaneously, the carbon support possesses a hierarchical porous structure with micropores and mesopores, wherein the micropores have a pore size of 0.5–2 nm, the mesopores have a pore size of 2–30 nm, and the pore volume is 1.383 cm³. 3 g -1 The specific surface area of ​​the catalyst particles is 400–1000 m². 2 g -1 This catalyst, with its three-dimensional hierarchical porous structure, exhibits high intrinsic activity and a high density of accessible active sites, effectively promoting mass transport. Fuel cells assembled using this catalyst as the cathode achieve a maximum power density of 862 mW / cm². -2 It can be used in the cathode oxygen reduction reaction of proton exchange membrane fuel cells and metal-air batteries. Attached Figure Description

[0025] Figure 1 XRD spectra of FeN4-SM prepared in Example 1, FeN4-SM3, FeN4-SM5 and FeN4 prepared in Comparative Examples 2, 3 and 4, and their corresponding precursors.

[0026] Figure 2 High-resolution transmission electron microscope images of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4. The columns from left to right represent FeN4, FeN4-SM3, FeN4-SM, and FeN4-SM5, respectively.

[0027] Figure 3 This is a scanning electron microscope image of FeN4-SM from Example 1.

[0028] Figure 4 This is a transmission electron microscope image of FeN4-DH in Comparative Example 5.

[0029] Figure 5 These are energy-dispersive X-ray spectroscopy (EDS) surface scan images of FeN4-SM prepared in Example 1. From left to right, they are: EDS surface scan image of C element distribution, EDS surface scan image of N element distribution, and EDS surface scan image of Fe element distribution.

[0030] Figure 6 These are nitrogen adsorption-desorption isotherms of FeN4-SM prepared in Example 1 and FeN4 prepared in Comparative Example 4.

[0031] Figure 7 These are pore size distribution curves of FeN4-SM in Example 1 and FeN4 in Comparative Example 4.

[0032] Figure 8 This is a spherical aberration electron microscope image of FeN4-SM prepared in Example 1.

[0033] Figure 9 The high-resolution C1s X-ray photoelectron spectra of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4 are shown. The columns from left to right represent FeN4, FeN4-SM3, FeN4-SM, and FeN4-SM5, respectively.

[0034] Figure 10 The high-resolution Fe 2p X-ray photoelectron spectra of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5 and FeN4 prepared in Comparative Examples 2, 3 and 4 are shown.

[0035] Figure 11 It is the FeN4-SM prepared in Example 1 and the FeN4 prepared in Comparative Example 4. 13 C10 NMR spectrum.

[0036] Figure 12 The images show the X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis of Fe element in FeN4-SM in Example 1.

[0037] Figure 13 This is a structural model diagram of FeN4-SM in Example 1;

[0038] Figure 14 The images show the in-situ Raman spectra of FeN4-SM in Example 1 and FeN4 in Comparative Example 1 at different potentials.

[0039] Figure 15 This is a comparison of the oxygen reduction performance test curve of FeN4-SM in oxygen-saturated 0.1M KOH solution in Example 1 with that of other catalysts.

[0040] Figure 16 This is a comparison of the oxygen reduction performance test curve of FeN4-SM in oxygen-saturated 0.1M HClO4 solution in Example 1 with that of other catalysts.

[0041] Figure 17 The graph shows the polarization curve of FeN4-SM after 60,000 cycles of accelerated cyclic voltammetry testing in oxygen-saturated 0.1M HClO4 solution in Example 1.

[0042] Figure 18This is a comparison chart of the discharge power curves of the fuel cells assembled with FeN4-SM in Example 1 and FeN4 catalyst in Comparative Example 1.

[0043] Figure 19 The images shown are transmission electron microscopy (TEM) EDS scans of MnN4-SM in Example 2; from left to right, they are: EDS scan image of C element distribution, EDS scan image of N element distribution, and EDS scan image of Mn element distribution.

[0044] Figure 20 The graph shows the oxygen reduction performance test curve of MnN4-SM in oxygen-saturated 0.1M KOH solution in Example 2. Detailed Implementation

[0045] The technical solutions and applications of the present invention will be described in detail below through specific examples, but the scope of protection of the present invention is not limited thereto.

[0046] Example 1: The preparation method of the non-noble metal catalyst based on atomically dispersed defect ligands in this example is carried out according to the following steps:

[0047] I. Preparation of a three-dimensional nitrogen-doped porous defect-type flower-like carbon support precursor: 428 mg of zinc acetate dihydrate was dissolved in 150 mL of methanol to obtain a zinc acetate solution; 492 mg of 2-methylimidazole and 154 mg of 5-aminotetrazole monohydrate were dissolved in 150 mL of methanol to obtain a nitrogen source solution; then the zinc acetate solution and the nitrogen source solution were mixed and stirred vigorously at a stirring speed of 500-700 rpm for 2 h, and then placed in an oven at 65 °C for 2 h, resulting in a white suspension in the solution; after centrifugation, the solid phase was washed three times with methanol and then vacuum dried in a vacuum drying oven at 65 °C for 8 h to obtain a nitrogen-doped porous carbon support precursor, which is a white powder;

[0048] II. Preparation of nitrogen-doped porous carbon support: The precursor prepared in step one was placed in a high-temperature furnace and heated at 5°C for 1 minute under an argon atmosphere. -1 The heating rate was first increased to 200℃ and held for 0.5 hours, then increased at 5℃ per minute. -1 The temperature was increased to 400℃ at a heating rate and held for 0.5 hours, then increased at a rate of 5℃ per minute. -1 The temperature was increased to 700℃ at a heating rate and held for 1 hour, and finally increased to 5℃ per minute. -1 The temperature was increased to 1000℃ and held for 2 hours to obtain nitrogen-doped porous carbon support (NC);

[0049] III. Preparation of single-atom catalyst precursor: 50 mg of ferrous sulfate heptahydrate was dissolved in 40 mL of N,N-dimethylformamide liquid to obtain ferrous sulfate solution; 100 mg of nitrogen-doped porous carbon support was impregnated in ferrous sulfate solution and stirred vigorously at a stirring speed of 500-700 rpm for 2 h under argon atmosphere, then ultrasonically dispersed in an ultrasonic cleaner for 2 h, filtered, and the separated solid components were placed in a vacuum drying oven at 65℃ and vacuum dried for 8 h to obtain single-atom catalyst precursor;

[0050] IV. Preparation of single-atom catalysts: The single-atom catalyst precursor was placed in a high-temperature furnace and heated to 1000℃ in an argon atmosphere and held for 3 hours for heat treatment to obtain a non-noble metal catalyst based on defect ligands with atomically dispersed structure, denoted as FeN4-SM.

[0051] Comparative Example 1: This comparative example is for the preparation of FeN4-SM0 catalyst. The difference between this comparative example and Example 1 is that "492 mg 2-methylimidazole" in step one is replaced with "773 mg 5-aminotetrazolium monohydrate". The other steps and parameters are the same as in Example 1. The resulting catalyst is denoted as FeN4-SM0.

[0052] In this comparative example, 5-aminotetrazole (5-ATZ) was used to completely replace 2-methylimidazole (2-MIM). Since the only ligand was 5-aminotetrazole, it almost entirely pyrolyzed into gaseous volatilization during the high-temperature treatment in step two, resulting in a very low yield that was difficult to collect. This suggests that in precursor structures prepared based on defective ligands, 2-methylimidazole serves as the backbone, while 5-aminotetrazole primarily functions as the defective ligand.

[0053] Comparative Example 2: This comparative example is for the preparation of FeN4-SM3 catalyst. The difference between this comparative example and Example 1 is that in step one, "492 mg 2-methylimidazole and 154 mg 5-aminotetrazole monohydrate" is replaced with "461 mg 2-methylimidazole and 193 mg 5-aminotetrazole monohydrate", so that the molar ratio of 5-aminotetrazole monohydrate to 2-methylimidazole is 1:3. Other steps and parameters are the same as in Example 1. The resulting catalyst is denoted as FeN4-SM3.

[0054] Comparative Example 3: This comparative example is for the preparation of FeN4-SM5 catalyst. The difference between this comparative example and Example 1 is that in step one, "492 mg 2-methylimidazole and 154 mg 5-aminotetrazole monohydrate" is replaced with "129 mg 2-methylimidazole and 512 mg 5-aminotetrazole monohydrate", so that the molar ratio of 5-aminotetrazole monohydrate to 2-methylimidazole is 1:5. Other steps and parameters are the same as in Example 1. The resulting catalyst is denoted as FeN4-SM5.

[0055] Comparative Example 4: This comparative example is for the preparation of FeN4 catalyst. The difference between this comparative example and Example 1 is that step one is replaced by the following operation:

[0056] 1. Dissolve 320 mg of 2-methylimidazole (2-MIM) in 300 mL of methanol to obtain a 2-methylimidazole solution; dissolve 290 mg of Zn(NO3)2·6H2O in 300 mL of methanol to obtain a zinc nitrate solution; mix the 2-methylimidazole solution and the zinc nitrate solution and stir for 1 day to react; then centrifuge to separate the solid phase, wash the solid phase three times with ethanol, and place it in a vacuum drying oven at 65℃ for 12 h to obtain a nitrogen-doped carbon support;

[0057] The other steps and parameters were the same as in Example 1, and the FeN4 catalyst was obtained.

[0058] Comparative Example 5: This comparative example is for the preparation of FeN4-DH (Direct heating) catalyst. The difference between this comparative example and Example 1 is that step two is replaced with the following operation: II. The precursor prepared in step one is placed in a high-temperature furnace and heated at 5°C for 1 minute under an argon atmosphere. -1 The temperature was directly increased to 1000℃ and held for 2 hours to obtain a nitrogen-doped porous carbon support; other steps and parameters were the same as in Example 1, and the resulting catalyst was denoted as FeN4-DH.

[0059] X-ray diffraction patterns of FeN4-SM prepared in Example 1, FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4, and their corresponding precursors were analyzed. The obtained X-ray diffraction patterns are shown below. Figure 1 As shown, from Figure 1 As shown in Figure a, the precursor of FeN4-SM is the same as that of FeN4-SM3 and FeN4-SM5, and shows a high degree of similarity to the precursor of FeN4, further highlighting the inheritance of its main framework. This indirectly proves that 2-methylimidazolium serves as the framework of the precursor structure, and 5-aminotetrazole acts as a defective ligand, which is consistent with the extremely low yield of Comparative Example 1. Figure 1 As can be seen from b, in the X-ray diffraction patterns of FeN4, FeN4-SM3, FeN4-SM, and FeN4-SM5, only the (002) and (101) crystal plane diffraction peaks of carbon appeared at 26° and 44°, which preliminarily indicates that there are no iron nanoparticles.

[0060] High-resolution transmission electron microscopy (TEM) images of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4 are shown below. Figure 2 As shown, Figure 2The columns in the middle, from left to right, are FeN4-SM, FeN4, FeN4-SM3, and FeN4-SM5, from... Figure 2 It can be seen that the introduction of 5-ATZ leads to the gradual appearance of pores in the prepared catalyst, eventually forming porosity. The pore size increases with increasing 5-ATZ concentration. The formation of pores originates from the thermal instability of the 5-ATZ linker as a defect ligand in the nitrogen-doped carbon support. Micropores in the crystal will generate crystal defects under high temperature conditions, subsequently forming mesopores with independent open pores, which enhances the transfer of oxygen-containing species and electrolytes, thus proving the possibility of CN cracking. It also demonstrates that an excessively high proportion of 5-aminotetrazole ligand leads to the collapse of the catalyst's pore structure, which is detrimental to the exposure of active sites. The FeN4-SM prepared in Example 1 is shown in the scanning electron microscope as follows: Figure 3 The prepared FeN4-SM was shown to be a three-dimensional defect sphere assembled from nanosheets.

[0061] High-resolution transmission electron microscopy of FeN4-DH prepared in Comparative Example 5, as shown in Figure 5. Figure 4 As shown, from Figure 4 As can be seen in the direct heating process, the catalyst does not exhibit obvious pores. This indicates that the direct pyrolysis of 5-aminotetrazole results in insufficient gas generation, leaving insufficient time for pore formation and thus preventing the formation of a stable porous structure.

[0062] The high-angle annular dark-field scanning transmission electron microscope and elemental surface scan analysis of FeN4-SM prepared in Example 1 are shown below. Figure 5 As shown. By Figure 5 It can be seen that there are no metal-containing nanoparticles in the prepared catalyst. Energy dispersive X-ray spectroscopy (EDS) results show that the Fe element is uniformly distributed in the carbon substrate, and no metal nanoclusters or particles are present. This indicates that the iron element is atomically dispersed rather than aggregated.

[0063] The nitrogen adsorption-desorption isotherms of FeN4-SM prepared in Example 1 and FeN4 prepared in Comparative Example 4 are as follows: Figure 6 As shown, the corresponding pore size distribution curve is as follows: Figure 7 As shown, FeN4-SM exhibits a distinct type IV hysteresis ring characteristic, demonstrating its hierarchical porous structure with both micropores and mesopores. The specific surface area of ​​FeN4-SM is 477.12 m². 2 g -1 It has a large accessible surface area, which can expose a large number of single-atom Fe sites and allow rapid mass transfer of reactants.

[0064] The aberration-corrected high-angle annular dark-field scanning transmission electron microscope of FeN4-SM prepared in Example 1 is shown below. Figure 8As shown, many isolated bright spots were precisely identified, indicating that iron atoms are dispersed rather than clustered together.

[0065] The high-resolution C1s X-ray photoelectron spectra of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4 are shown below. Figure 9 As shown, the high-resolution spectrum of Fe 2p is as follows: Figure 10 As shown. Peak fitting processing of the high-resolution XPS spectrum of C1s revealed three N species in the deconvolutioned high-resolution C1s spectrum, corresponding to CC (284.6 eV), CN (285.5 eV), and C=O (288.0 eV). Compared to FeN4, Fe-N... X The significant positive shift of the peak indicates a change in the electronic structure of the atomically dispersed Fe sites, which is also confirmed by the high-resolution Fe 2p spectrum. The breaking of the CN bond adjacent to Fe-N4 may be the reason for the increase in the Fe-N bond binding energy, which is consistent with the TEM image. Notably, during the pore expansion process, a simultaneous decrease in CN and pyridine N content can be observed, suggesting that the gaseous products generated during the pyrolysis of 5-ATZ may trigger selective cleavage of the CN bond, which first occurs on the pyridine N.

[0066] The FeN4-SM prepared in Example 1, and the FeN4 prepared in Comparative Example 4... 13 C nuclear magnetic resonance spectrum as Figure 11 As shown, two broad peaks were observed in FeN4 and FeN4-SM at δ = 110-190 and 70-100 ppm, respectively, corresponding to sp... 2 - Hybrid graphite carbon structure and N-alkyl carbon (denoted as C*). Conversely, the peak intensity of N-alkyl carbon (C*) in FeN4-SM begins to decrease, and a new N-alkyl carbon peak (denoted as C) appears at δ = 45-70 ppm. # This is related to the cleavage of C=N and CN bonds in graphite N and pyridine N. Due to the cleavage of the CN bonds, FeN4-SM exhibits sp(20-40 ppm) at δ = 20-40 ppm. 3 The signal peaks of the hybrid carbon structure, in turn, weaken the resonance of the N-alkyl carbon. The results indicate that the CN bonds undergo selective cleavage throughout the pore expansion process, consistent with X-ray photoelectron spectroscopy findings.

[0067] The X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis of FeN4-SM prepared in Example 1 are as follows: Figure 12 As shown. From Figure 12 As can be seen from a, the near-absorption edge of FeN4-SM is located between FeO and Fe2O3, thus proving that the positively charged Fe...δ+ Species (3>δ>2). To obtain reliable structural information, further least-squares EXAFS curve fitting analysis was performed, such as... Figure 12 As shown in b. The best fit results indicate that, with The peak centered on the center was well decomposed into Fe-N2. t and Fe-N2 c Two scattering paths, with coordination numbers of 2.33 and 1.98, and distances of 1.75 and 1.98, respectively. These results indicate that the Fe-NC configuration has different bond lengths, consistent with the theoretical calculation model of FeN4-SM. The structural model, derived by combining synchrotron radiation and aberration-corrected electron microscopy data, is as follows: Figure 13 As shown in the differential charge density plot, the asymmetric electronic structure leads to charge differences in the ligand N atoms, resulting in an asymmetric electron cloud at the Fe site. The subsequent tensile and compressive strain modulates the dp orbital hybridization of Fe / O and reduces the adsorption affinity for intermediates. All of the above evidence confirms that it is feasible to improve the acidic oxygen reduction activity and reduce the adsorption strength of *OH by selectively modulating the atomic strain environment of the iron metal center through CN cleavage.

[0068] The in-situ Raman spectra of FeN4-SM prepared in Example 1 and FeN4 prepared in Comparative Example 4 are as follows: Figure 14 As shown in figures a and b, as the applied potential decreases, peak voltages at 1150 and 1550 cm⁻¹ are detected in FeN₄ and FeN₄-SM, respectively. -1 The peak centered at [value] corresponds to the stretching vibrations of *OO and *OOH, confirming that the catalyst initiates the oxygen reduction reaction via a correlated mechanism. Due to the short lifetime of oxygen-containing intermediates, their formation mainly occurs at low potentials. Therefore, Raman signals from the intermediates are typically only observed after the ORR has begun. Figure 14 Analysis revealed that the increased redshift position and main peak height indicate a weakening of the interaction strength between the Fe atom centers and *OOH in FeN4-SM. Therefore, the result that asymmetric atomic strain causes a change in the Fe-O bond stretching vibration frequency is verified, which is beneficial for the desorption of oxygen-containing intermediates.

[0069] The electrocatalytic activity of FeN4-SM prepared in Example 1, and FeN4-SM3, FeN4-SM5, and FeN4 prepared in Comparative Examples 2, 3, and 4, was evaluated using a rotating ring-disc electrode method in 0.1 M KOH electrolyte. A three-electrode test system was used, with a glassy carbon electrode as the working electrode, Ag / AgCl as the reference electrode, and a Pt mesh as the counter electrode. Cyclic voltammetry was performed at a rotation speed of 1600 rpm and a voltage range of 1.20–0.05 V (vs. RHE). Figure 15As shown in the figure, the oxygen reduction polarization curves show that FeN4-SM has the optimal half-wave potential, reaching 0.948V (vs. RHE), which is higher than that of FeN4 (0.927V (vs. RHE), and its limiting current density is much higher than that of FeN4.

[0070] The electrocatalytic activity of the FeN4-SM prepared in Example 1 and the catalyst in the comparative example was evaluated using a rotating ring-disk electrode method in 0.1M HClO4 electrolyte. The resulting staged cyclic voltammetry curves are shown below. Figure 16 As shown. From Figure 16 The cyclic voltammetry curves in section a show that the half-wave potential of FeN4-SM is 0.83V (vs. RHE). From... Figure 16 As can be seen from b, the kinetic current density of the FeN4-SM catalyst at 0.8 V is 12.94 mA / cm². -2 The value is more than 2.15 times higher than that of FeN4, which indicates that geometric structure modulation has an enhancement effect.

[0071] The electrochemical stability of the FeN4-SM prepared in Example 1 was evaluated by accelerated cyclic voltammetry, and the obtained polarization curves are shown below. Figure 17 As shown. From Figure 17 It can be seen that after 60,000 accelerated aging cycles, the half-wave potential of FeN4-SM only shifted negatively by 16mV, proving that the catalyst has excellent stability.

[0072] The FeN4-SM prepared in Example 1 and the FeN4 prepared in the comparative example were used in proton exchange membrane fuel cells to assemble proton exchange membrane fuel cells (PEMFCs) with Pt / C as the anode. The application prospects of FeN4-SM were evaluated, and the obtained polarization curves are shown in the figure. Figure 18 As shown. From Figure 18 It can be seen that under H2 / O2 conditions with a back pressure of 2.0 bar, the peak power density of the FeN4-SM-based fuel cell reaches 862 mW / cm². -2 It exceeded the 640mW cm⁻¹ of FeN₄. -2 For FeN4-SM, the current density reaches 418 mA cm⁻¹ at 0.7 V. -2 It exceeded the 383 mA cm of FeN4. -2 This indicates that FeN4-SM with an asymmetric atomic strain environment exhibits excellent PEMFC performance and has promising prospects for commercial applications.

[0073] Example 2: This example is for the preparation of MnN4-SM. The difference between this example and Example 1 is that the "50 mg ferrous sulfate heptahydrate" in step 3 is replaced with "12 mg manganese chloride tetrahydrate". The other steps and parameters are the same as in Example 1, and an atomically dispersed non-noble metal catalyst based on defect ligands is obtained, which is represented by MnN4-SM.

[0074] The transmission EDS surface scan analysis image of the MnN4-SM prepared in Example 2 is shown below. Figure 19 As shown. By Figure 19 It can be seen that there are no metal-containing nanoparticles in the prepared catalyst. Energy dispersive X-ray spectroscopy (EDS) results show that the Mn element is uniformly distributed in the carbon support, and the Mn element is atomically dispersed rather than aggregated, which preliminarily proves that no metal nanoclusters and particles are present.

[0075] The MnN4-SM catalyst prepared in Example 2 was evaluated for electrocatalytic activity in 0.1 M KOH electrolyte using a rotating ring-disc electrode method. A three-electrode system was employed, with a glassy carbon electrode as the working electrode, Ag / AgCl as the reference electrode, and a Pt mesh as the counter electrode. Cyclic voltammetry (CV) was first used to activate the catalyst, followed by staged cyclic voltammetry at a rotation speed of 1600 rpm and a voltage range of 1.20–0.05 V (vs. RHE). The obtained oxygen reduction polarization curves are shown below. Figure 20 As shown. From Figure 20 It can be seen that MnN4-SM also exhibits excellent oxygen reduction performance in alkaline electrolyte, with a half-wave potential of 0.933V.

[0076] This invention utilizes the strain effect of CN cracking to break the electronic symmetry of the square planar transition metal MN4 active center, and uses the asymmetric electronic structure to improve the adsorption between the M site and the oxygen-containing intermediate to enhance ORR activity. At the same time, it uses step-by-step high-temperature heat treatment to generate a multi-level porous structure, improve the accessibility of single-atom metal sites, thereby enhancing the stability and reaction rate of the catalyst, and promoting the application of nitrogen-doped porous carbon-supported single-atom transition metal catalysts (MNC) in energy conversion and storage.

Claims

1. A method for preparing a non-noble metal catalyst based on atomically dispersed defect ligands, characterized in that, This method is performed according to the following steps: I. Preparation of a three-dimensional nitrogen-doped porous defect-type flower-like carbon support precursor: Zinc source and nitrogen source were dissolved in methanol, then mixed and stirred rapidly and vigorously for 2–2.5 h, and then kept at 60–65 °C for 2–2.5 h, resulting in a white suspension in the solution; then centrifuged, washed, and dried to obtain a three-dimensional nitrogen-doped porous defect-type flower-like carbon support precursor, which is a white powder; wherein the nitrogen source is 5-aminotetrazole and 2-methylimidazole in a molar ratio of 1:(3–5); II. Preparation of nitrogen-doped porous carbon support: The precursor prepared in step one was subjected to a step-by-step high-temperature heat treatment under an inert atmosphere and cooled to room temperature to obtain a nitrogen-doped porous carbon support; wherein the step-by-step high-temperature heat treatment was as follows: first, the temperature was raised to 200-220℃ and held for 0.5-0.6 h, then the temperature was raised to 400-420℃ and held for 0.5-0.6 h, then the temperature was raised to 700-720℃ and held for 1-1.3 h, and finally the temperature was raised to 1000-1050℃ and held for 2-2.5 h; III. Preparation of single-atom catalyst precursor: First, nitrogen-doped porous carbon support is immersed in a solution of metal M soluble salt, stirred vigorously for 2-2.5 h under an inert atmosphere, then ultrasonically dispersed for 2-2.5 h, filtered or centrifuged, and the solid phase is dried to obtain single-atom catalyst precursor; IV. Preparation of Single-Atom Catalysts: The single-atom catalyst precursor was placed in a furnace and heated to 950–1050 °C in an argon atmosphere for 2–3 hours to obtain an atomically dispersed non-noble metal catalyst based on defect ligands. This catalyst is composed of MN4 embedded in a carbon support, where M is coordinated with N with two different sets of MN bond lengths, exhibiting a 2N configuration. t =M=2N c The coordination structure is defined as follows: t represents tension, c represents compression, and the mass fraction of M is 0.5% to 1%, where M is Fe, Mn, Co, or Ni.

2. The method for preparing a non-noble metal catalyst based on atomically dispersed defective ligands according to claim 1, characterized in that, The zinc source mentioned in step one is zinc acetate dihydrate, anhydrous zinc nitrate, or zinc nitrate hexahydrate.

3. The method for preparing a non-noble metal catalyst based on atomically dispersed defective ligands according to claim 1 or 2, characterized in that, The inert atmosphere mentioned in steps two and three is either Ar or N2.

4. The method for preparing a non-noble metal catalyst based on atomically dispersed defective ligands according to claim 1 or 2, characterized in that, The drying described in steps one and three is vacuum drying at a temperature of 60–80°C for 6–8 hours.

5. A method for preparing a non-noble metal catalyst based on atomically dispersed defect ligands according to claim 1 or 2, characterized in that, The solvent for the metal M soluble salt solution mentioned in step three is N,N-dimethylformamide.

6. The method for preparing a non-noble metal catalyst based on atomically dispersed defective ligands according to claim 1 or 2, characterized in that, The vigorous stirring described in step three is performed at a speed of 500–700 rpm.

7. A method for preparing a non-noble metal catalyst based on atomically dispersed defect ligands according to claim 1 or 2, characterized in that, The heating rate described in step four is 5–20 °C / min. -1 .

8. The application of a non-noble metal catalyst based on atomically dispersed defective ligands prepared by the method of claim 1, characterized in that... This application involves using atomically dispersed non-precious metal catalysts based on defective ligands as cathode catalysts in proton exchange membrane fuel cells or metal-air batteries.

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