Pyridine nitrogen-doped regular dodecahedron supported transition metal catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalytic oxygen reduction reaction, and particularly relates to a pyridine nitrogen-doped regular dodecahedron supported transition metal catalyst as well as a preparation method and application thereof. Soluble transition metal salt and an organic ligand are used as raw materials and are mixed and coordinated in a solvent system to obtain a pyridine nitrogen-doped N-C skeleton precursor; and calcining in a nitrogen atmosphere to obtain the pyridine nitrogen doped regular dodecahedron loaded transition metal catalyst. The oxygen reduction performance of the transition metal catalyst is improved by increasing the content of pyridine nitrogen, metal agglomeration is effectively prevented, meanwhile, pyridine nitrogen can effectively adjust the electron cloud density of center metal, adsorption of an active center to O2 is improved, and then the intrinsic activity of an electrocatalytic oxygen reduction reaction is improved. The preparation method is simple, the raw material source is wide, the preparation cost is low, the catalyst activity is high, the performance is only attenuated by 4.1% when the stability CA of the oxygen reduction reaction is tested for 40 hours, and the activity is still maintained by 95.9%.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic oxygen reduction reaction technology, specifically relating to a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, its preparation method, and its application. Background Technology

[0002] With continuous technological advancements and a significant improvement in people's quality of life, the demand for energy continues to rise. Currently, energy consumption is dominated by non-renewable fossil fuels, leading to a sustained increase in carbon emissions. These massive carbon emissions exacerbate climate problems, and the use of fossil fuels is a major source of increased greenhouse gases such as carbon dioxide. Therefore, exploring clean and renewable energy sources, such as wind, solar, and hydropower, and developing related power storage and conversion technologies, is an inevitable choice for ensuring a secure and sustainable future.

[0003] Compared to traditional energy utilization methods, fuel cells have significant advantages such as stable operation, low energy loss, high conversion efficiency, long service life, and environmental friendliness. These advantages make the development of fuel cells a highly practical approach to alleviating the energy crisis and environmental pollution. Currently, Pt-based noble metal catalysts are used in both the oxygen reduction reaction at the cathode and the hydrogen oxidation reaction at the anode of fuel cells, accounting for about 40% of the total cost of the battery. However, the high price and low reserves of noble metals limit their commercial development. Therefore, transition metal-based catalysts have been studied as the best potential alternative. Among them, Fe, Co, and Ni have been applied in ORR (Organic Reduction) due to their tunable 3d orbitals. Currently, transition metal-based catalysts are often in the form of single metals or carbon-supported transition metals. However, single metals are prone to dissolution or detachment during long-term cycling stability tests, while the binding force between carbon supports and transition metal sites is insufficient, which easily leads to transition metal agglomeration and deactivation of active sites. Summary of the Invention

[0004] The present invention aims to provide a pyridine nitrogen-doped dodecahedral supported transition metal catalyst, its preparation method, and its application. The catalyst is obtained by coordination with a transition metal salt and an organic ligand, followed by high-temperature calcination. Increasing the pyridine nitrogen content improves the oxygen reduction performance of the transition metal catalyst and effectively prevents metal aggregation. Simultaneously, pyridine nitrogen can effectively regulate the electron cloud density of the central metal, enhancing the adsorption of O2 by the active center and thus improving the intrinsic activity of the electrocatalytic oxygen reduction reaction. The preparation method is simple, the raw materials are widely available, the preparation cost is low, and the catalyst activity is high.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] The first objective of this invention is to provide a method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, comprising the following steps: S1. Using soluble transition metal salts and organic ligands as raw materials, a mixture is formed in a solvent system and coordinated under stirring to obtain a pyridine nitrogen-doped NC framework precursor.

[0007] S2. In a nitrogen atmosphere, the pyridine nitrogen-doped NC framework precursor is calcined to coordinate the metal atoms with the nitrogen atoms in the NC framework, thereby obtaining a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst.

[0008] Furthermore, the transition metal in the soluble transition metal salt is at least one of zinc, iron, manganese, and cobalt. When the transition metal contains zinc, the transition metal is at least two of them.

[0009] Furthermore, the organic ligand is at least one of 2-methylimidazole, methylimidazole, and bipyridine.

[0010] Furthermore, the molar ratio of transition metal to organic ligand in soluble transition metal salts is 1:5 to 8.

[0011] Furthermore, the concentration of organic ligands in the mixture is 0.3 mol / L to 0.5 mol / L.

[0012] Furthermore, the coordination temperature is 25℃~30℃, and the time is 4h~6h.

[0013] Furthermore, the calcination temperature is 900℃~1000℃, and the holding time is 2h~3h.

[0014] The second objective of this invention is to provide a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, which is prepared using the above-described preparation method.

[0015] A third objective of this invention is to provide the application of the above-mentioned pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst in the electrocatalytic oxygen reduction reaction of fuel cells.

[0016] Compared with the prior art, the present invention has the following advantages: This invention provides a preparation method in which transition metals and organic ligands are coordinated in a certain ratio and under controlled synthesis conditions, followed by high-temperature calcination to obtain a regular dodecahedral supported transition metal catalyst. Specifically, the transition metal ions coordinate with nitrogen atoms in the organic ligands to form coordination units that link the metal to nitrogen-containing molecules. These units self-assemble through intermolecular forces to form a regular dodecahedral catalyst precursor. After high-temperature calcination, the metal atoms coordinate with nitrogen atoms in the NC carbon framework to form a stable M–N matrix. XThe –C coordination structure yields a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst. Increasing the pyridine nitrogen content enhances the activity of the oxygen reduction reaction (ORR). The lone pair electrons of pyridine nitrogen can coordinate with the empty orbitals of the transition metal, effectively preventing metal aggregation. Simultaneously, pyridine nitrogen effectively modulates the electron cloud density of the central metal, increasing the adsorption of O2 by the active center and thus improving the intrinsic activity of the electrocatalytic ORR. The ORR stability was demonstrated by CA testing, showing only a 4.1% performance degradation after 40 hours, maintaining 95.9% of the activity. Attached Figure Description

[0017] Figure 1 This is a microstructure diagram of the FeMn / NC catalyst prepared in Example 1 of the present invention, wherein, Figure 1 In the image, (a) is a SEM image, (b) is a magnified view of (a), (c) is a TEM image, and (d) to (g) are the elemental distribution maps of the X-ray spectrum.

[0018] Figure 2 X-ray diffraction patterns of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention.

[0019] Figure 3 Raman scattering patterns of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention.

[0020] Figure 4 The image shows the adsorption performance and pore size distribution of the FeMn / NC catalyst prepared in Example 1 of this invention.

[0021] Figure 5 The image shows the adsorption performance and pore size distribution of the Mn / NC catalyst prepared in Example 2 of this invention.

[0022] Figure 6 The image shows the adsorption performance and pore size distribution of the Fe / NC catalyst prepared in Example 3 of this invention.

[0023] Figure 7 The graph shows a comparison of linear sweep voltammetry tests of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3.

[0024] Figure 8 Tafel slope diagrams of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention.

[0025] Figure 9Comparison of linear sweep voltammetry tests of the FeMn / NC catalyst prepared in Example 1, the FeMn / NC-2 catalyst prepared in Example 4, the FeMn / NC-3 catalyst prepared in Example 5, and the FeMn / NC-4 catalyst prepared in Example 6 of this invention.

[0026] Figure 10 This is a comparison chart of cyclic voltammetry and capacitance density analysis of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 10 In the figure, (a) is the cyclic voltammetry test diagram of the Fe / NC catalyst prepared in Example 3, (b) is the cyclic voltammetry test diagram of the Mn / NC catalyst prepared in Example 2, (c) is the cyclic voltammetry test diagram of the FeMn / NC catalyst prepared in Example 1, and (d) is a comparison diagram of capacitance density analysis of Examples 1 to 3.

[0027] Figure 11 This is a durability test graph of the current-time curve of the FeMn / NC catalyst prepared in Example 1 of the present invention.

[0028] Figure 12 X-ray photoelectron spectra of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 12 In the figure, (a) is the full spectrum of the catalysts of Examples 1 to 3, (b) is the fine N1s spectrum and peak fitting diagram of the catalysts of Examples 1 to 3, and (c) is the bar chart of the relative N content analysis of the catalysts of Examples 1 to 3. Detailed Implementation

[0029] 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.

[0030] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0031] The present invention provides a method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, comprising the following steps: S1. Using soluble transition metal salts and organic ligands as raw materials, a mixture is formed in a solvent system and coordinated at 25℃~30℃ for 4h~6h under stirring to obtain a pyridine nitrogen-doped NC framework precursor.

[0032] In this invention, the soluble transition metal salt and the organic ligand are mixed in solution. The soluble transition metal salt and the organic ligand are each dissolved in a solvent solution, which can be one or more of water, methanol, and ethanol mixed in any proportion. The mixture is then stirred to allow coordination, where the metal ions in the solution coordinate with the nitrogen atoms in the organic ligand, forming coordination units that link the metal to the nitrogen-containing molecule. During stirring, the aforementioned coordination units self-assemble through intermolecular forces to form a regular dodecahedral catalyst precursor. The molar ratio of the transition metal to the organic ligand in the soluble transition metal salt is 1:5–8. The concentration of the organic ligand in the mixture is 0.3 mol / L–0.5 mol / L. The transition metal in the soluble transition metal salt is at least one of zinc, iron, manganese, and cobalt. When the transition metal contains zinc, there are at least two transition metals. In a preferred embodiment, the soluble transition metal salt can be zinc nitrate, iron nitrate, manganese nitrate, or cobalt nitrate. When the soluble transition metal salt contains zinc nitrate, its transition metal needs to be combined with at least one of iron nitrate, manganese nitrate, or cobalt nitrate. The organic ligand is one or more of 2-methylimidazole, methylimidazole, and bipyridine mixed in any proportion.

[0033] It should be noted that after coordination is completed, centrifugation, washing and drying are required. The centrifugation speed is 8000 r / min to 10000 r / min. The washing solvent is the same as the solvent, which is one or more of water, methanol and ethanol in any proportion. The drying temperature is 50℃ to 60℃ and the time is 6h to 12h.

[0034] S2. In a nitrogen atmosphere, the pyridine nitrogen-doped NC framework precursor is calcined at 900℃~1000℃ for 2h~3h to coordinate the metal atoms with the nitrogen atoms in the NC carbon framework, thereby obtaining a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst.

[0035] In this invention, during the low-temperature stage of calcination of the pyridine nitrogen-doped NC framework precursor, the physically adsorbed water, solvent, and some uncoordinated organic matter in the precursor begin to decompose. As the temperature rises, the organic ligands begin to carbonize, releasing reducing carbon and nitrogen-containing small molecule gases, reducing high-valence metal ions to low-valence or zero-valence metal clusters, and the carbon atoms rearrange to form a nitrogen-doped organic carbon framework. At high temperatures, the metal atoms coordinate with the nitrogen atoms in the carbon framework to form a stable M–N matrix. X–C coordination structure. Ultimately, a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst was obtained.

[0036] In summary, this invention coordinates transition metal salts and organic ligands in a specific ratio under controlled synthesis conditions, followed by high-temperature calcination to obtain a regular dodecahedral supported transition metal catalyst. Increasing the pyridine nitrogen content enhances the activity of the oxygen reduction reaction. The lone pair electrons of pyridine nitrogen can coordinate with the empty orbitals of the transition metal, effectively preventing metal aggregation. Simultaneously, pyridine nitrogen can effectively regulate the electron cloud density of the central metal, increasing the adsorption of O2 by the active center and thus improving the intrinsic activity of the electrocatalytic oxygen reduction reaction.

[0037] The following specific examples will provide further explanation.

[0038] Example 1 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate, 61.8 mg of manganese nitrate and 99.4 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0039] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0040] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as FeMn / NC.

[0041] Example 2 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, differing from Example 1 in that ferric nitrate is not added, includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate and 61.8 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0042] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0043] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as Mn / NC.

[0044] Example 3 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, differing from Example 1 in that manganese nitrate is not added, includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate and 99.4 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0045] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0046] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as Fe / NC.

[0047] Example 4 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, differing from Example 1 in that the molar ratio of metallic iron to manganese is 3:2, includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate, 49.4 mg of manganese nitrate and 119.3 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0048] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0049] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as FeMn / NC-2.

[0050] Example 5 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, differing from Example 1 in that the molar ratio of metallic iron to manganese is 2:3, includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate, 74.1 mg of manganese nitrate and 79.6 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0051] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0052] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as FeMn / NC-3.

[0053] Example 6 A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, differing from Example 1 in that the molar ratio of metallic iron to manganese is 3:7, includes the following steps: S1. Preparation of pyridine nitrogen-doped NC framework precursor: Dissolve 8.4 g of 2-methylimidazole in 150 mL of methanol to obtain a 2-methylimidazole solution; dissolve 3.7 g of zinc nitrate, 86.5 mg of manganese nitrate and 59.7 mg of ferric nitrate in 150 mL of methanol. After complete dissolution, a transition metal solution is obtained.

[0054] The transition metal solution was poured into the 2-methylimidazole solution to form a mixture. The mixture was stirred at 400 rpm for 4 h at 25 °C to form a precipitate. After precipitation, it was treated at 9000 rpm for 3 min, washed three times with methanol solution, and dried at 60 °C for 12 h to obtain the pyridine nitrogen-doped NC framework precursor for later use.

[0055] S2. Preparation of pyridine nitrogen-doped NC framework: The pyridine nitrogen-doped NC framework precursor was calcined at 950℃ under N2 atmosphere for 2 hours to obtain pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, abbreviated as FeMn / NC-4.

[0056] The structure and performance of the pyridine nitrogen-doped regular dodecahedral supported transition metal catalysts prepared in Examples 1 to 6 were tested, and the results are shown below.

[0057] Figure 1 This is a microstructure diagram of the FeMn / NC catalyst prepared in Example 1 of the present invention, wherein, Figure 1 In the image, (a) is a SEM image, (b) is a magnified view of (a), (c) is a TEM image, and (d) to (g) are elemental distribution maps of the X-ray spectrum. Figure 1 As shown in (a) and (b), after calcination at 950℃, a catalyst with regular dodecahedral morphology was obtained, exhibiting uniform particle morphology, no obvious agglomeration, and a particle size of approximately 100 nm. Figure 1 As shown in (c), the FeMn / NC catalyst particles have a regular dodecahedral nanostructure, which is consistent with the characteristics of the SEM morphology image. Figure 1 As can be seen from (d) to (g), the metal elements are evenly distributed in the material particles without agglomeration, proving that Fe and Mn elements were successfully doped into the NC substrate and the doping uniformity is excellent.

[0058] Figure 2 X-ray diffraction patterns of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 2 As shown, the FeMn / NC catalyst prepared in Example 1, after carbonization, mainly exhibits characteristic peaks of carbon, without any related diffraction peaks or impurity peaks of Fe and Mn metals, and no crystal form is observed. Figure 1 The structural characterization results show good agreement; the Mn / NC catalyst prepared in Example 2, after carbonization, mainly shows characteristic peaks of carbon, without any related diffraction peaks or impurity peaks of Mn metal, and no crystal form appears; the Fe / NC catalyst prepared in Example 3, after carbonization, mainly shows characteristic peaks of carbon, without any related diffraction peaks or impurity peaks of Fe metal, and no crystal form appears.

[0059] Figure 3 Raman scattering patterns of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 3 As shown, the I of the FeMn / NC catalyst D :I G The value is 0.924, indicating a high degree of graphitization, and sp 2 The higher proportion of ordered hybrid carbon structures increases the electron conduction rate of the FeMn / NC catalyst, accelerates the electron transfer rate in the ORR process, and improves the catalyst's electrochemical performance; the I of the Mn / NC catalyst... D :I G The value is 0.926, indicating a low degree of graphitization, and sp 2 The ordered structure of hybrid carbon accounts for a smaller proportion, resulting in slower electron transfer during the ORR process; the I of Fe / NC catalysts D :I G The value is 0.937, indicating a low degree of graphitization, and sp 2 Hybrid carbon has a smaller proportion of ordered structures, resulting in slower electron transfer during the ORR process.

[0060] The adsorption performance and pore size distribution of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 were characterized.

[0061] Figure 4 This is a diagram showing the adsorption performance and pore size distribution of the FeMn / NC catalyst prepared in Example 1 of this invention. Figure 4 As shown, the specific surface area of ​​the prepared catalyst reaches 848.52 m². 2 / g, mesopores exist at 2nm.

[0062] Figure 5 This is a diagram showing the adsorption performance and pore size distribution of the Mn / NC catalyst prepared in Example 2 of this invention. Figure 5 As shown, the specific surface area of ​​the prepared catalyst reaches 1054.86 m². 2 / g, mesopores exist at 2nm.

[0063] Figure 6 This is a diagram showing the adsorption performance and pore size distribution of the Fe / NC catalyst prepared in Example 3 of this invention. Figure 6 As shown, the specific surface area of ​​the prepared catalyst reaches 758.00 m². 2 / g, mesopores exist at 2nm.

[0064] The electrochemical performance of the pyridine nitrogen-doped regular dodecahedral supported transition metal catalysts prepared in Examples 1 to 6 was tested, specifically including the following steps: The pyridine nitrogen-doped regular dodecahedral supported transition metal catalysts prepared in Examples 1 to 6 were tested using a three-electrode system in O2-saturated 0.1M KOH medium at a rotation speed of 1600 rpm. The FeMn / NC catalyst, 0.5% naphthol solution, and anhydrous ethanol were mixed, ultrasonically dispersed for 2 h, coated with electrodes, and then tested.

[0065] Figure 7 The graph shows a comparison of linear sweep voltammetry results for the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3. Figure 7 As shown, the FeMn / NC catalyst prepared in Example 1 has an onset potential of 0.92 V and a half-wave potential of 0.77 V for the oxygen reduction reaction; the Mn / NC catalyst prepared in Example 2 has an onset potential of 0.85 V and a half-wave potential of 0.69 V for the oxygen reduction reaction; and the Fe / NC catalyst prepared in Example 3 has an onset potential of 0.91 V and a half-wave potential of 0.74 V for the oxygen reduction reaction.

[0066] Table 1. Comparison of the electrochemical performance of catalysts in the oxygen reduction reaction As shown in Table 1, the FeMn / NC catalyst prepared in Example 1 exhibited the best performance, with an onset potential of 0.92 V and a half-wave potential of 0.77 V, indicating its high catalytic activity. The Mn / NC catalyst prepared in Example 2 and the Fe / NC catalyst prepared in Example 3 showed weaker performance, indicating that the bimetals exhibited a synergistic effect, enhancing the catalyst activity. The FeMn / NC-2 catalyst prepared in Example 4, the FeMn / NC-3 catalyst prepared in Example 5, and the FeMn / NC-4 catalyst prepared in Example 6 all showed poor performance, indicating that different ratios of bimetals have a significant impact on catalytic performance.

[0067] The linear sweep voltammetry curves from the tests were analyzed and plotted as Tafel slope diagrams. Figure 8 The Tafel slope diagrams are for the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 8 As shown, the Tafel slope of FeMn / NC is 65.1 mV·dec -1 The pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst exhibited excellent electrocatalytic kinetics; the Tafel slope of Mn / NC was 62.5 mV·dec. -1The pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst exhibited good electrocatalytic kinetics; the Tafel slope of Fe / NC was 63.8-62.5 mV·dec. -1 The pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst exhibits excellent electrocatalytic kinetics.

[0068] Figure 9 A comparison graph of linear sweep voltammetry tests for the FeMn / NC catalyst prepared in Example 1, the FeMn / NC-2 catalyst prepared in Example 4, the FeMn / NC-3 catalyst prepared in Example 5, and the FeMn / NC-4 catalyst prepared in Example 6 of this invention. The results are as follows... Figure 9 As shown, the FeMn / NC-2 catalyst prepared in Example 4 had an onset potential of 0.87 V and a half-wave potential of 0.69 V for the oxygen reduction reaction; the FeMn / NC-3 catalyst prepared in Example 5 had an onset potential of 0.86 V and a half-wave potential of 0.63 V for the oxygen reduction reaction; and the FeMn / NC-4 catalyst prepared in Example 6 had an onset potential of 0.92 V and a half-wave potential of 0.68 V for the oxygen reduction reaction.

[0069] Figure 10 This is a comparison chart of cyclic voltammetry and capacitance density analysis of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 10 In the diagram, (a) shows the cyclic voltammetry results of the Fe / NC catalyst prepared in Example 3, (b) shows the cyclic voltammetry results of the Mn / NC catalyst prepared in Example 2, (c) shows the cyclic voltammetry results of the FeMn / NC catalyst prepared in Example 1, and (d) is a comparison diagram of the capacitance density analysis of Examples 1 to 3. Figure 10 As shown, the FeMn / NC catalyst prepared in Example 1 has a capacitance density of 33.2 mF·cm⁻¹. -2 The capacitance density of the Mn / NC catalyst prepared in Example 2 reached 26.1 mF·cm. -2 The Fe / NC catalyst prepared in Example 3 achieved a capacitance density of 23.3 mF·cm⁻¹. -2 .

[0070] The oxygen reduction reaction stability of the FeMn / NC catalyst prepared in Example 1 was tested. Figure 11 This is a current-time durability test graph of the FeMn / NC catalyst prepared in Example 1 of this invention. Figure 11 As shown, the oxygen reduction reaction stability test showed that the performance decreased by only 4.1% after 40 hours, still maintaining 95.9% of the activity.

[0071] For the stability test of oxygen reduction reaction (ORR) with catalysts containing non-transition metals, when only Mn or Fe is used (as in Examples 2 and 3), the stability of ORR shows increased performance degradation and decreased activity after 40 hours of CA test compared to Example 1. When the molar ratio of Fe to Mn is changed (as in Examples 4 to 6), the activity of FeMn / NC-2, FeMn / NC-3, and FeMn / NC-4 catalysts decreases, and the stability of ORR shows increased performance degradation after 40 hours of CA test, similar to the activity of single Mn or Fe catalysts. This indicates that different ratios of bimetallic catalysts have a significant impact on catalytic performance.

[0072] Figure 12 X-ray photoelectron spectra of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3 of this invention. Figure 12 In the table, (a) is the full spectrum of the catalysts in Examples 1 to 3, (b) is the fine N1s spectrum and peak fitting diagram of the catalysts in Examples 1 to 3, and (c) is the bar chart of the relative N content analysis of the catalysts in Examples 1 to 3. Table 2 shows the relative N content distribution of the FeMn / NC catalyst prepared in Example 1, the Mn / NC catalyst prepared in Example 2, and the Fe / NC catalyst prepared in Example 3.

[0073] Table 2. Relative N content distribution of the catalyst like Figure 12 As shown in Table 2, the FeMn / NC catalyst exhibits characteristic photoelectron peaks of C1s, N1s, O1s, Zn2p, Fe2p, and Mn2p, confirming the presence of these elements in the material. The clear signals of each element indicate successful preparation of FeMn / NC. The FeMn / NC catalyst contains 4.43% pyridine nitrogen. The Mn / NC catalyst also exhibits characteristic photoelectron peaks of C1s, N1s, O1s, Zn2p, and Mn2p, with a pyridine nitrogen content of 4.15%. This is lower than the FeMn / NC catalyst prepared in Example 1, demonstrating that the introduction of Fe increases the pyridine nitrogen content, effectively regulating the electron cloud density of the central metal, improving the adsorption of O2 by the active center, and thus enhancing the intrinsic activity of the electrocatalytic oxygen reduction reaction. The Fe / NC catalyst also exhibits characteristic photoelectron peaks of C1s, N1s, O1s, Zn2p, and Fe2p. Compared to the FeMn / NC prepared in Example 1, which had a lower pyridine nitrogen content, this demonstrates that the introduction of Mn increases the pyridine nitrogen content, effectively regulating the electron cloud density of the central metal, improving the adsorption of O2 by the active center, and thus enhancing the intrinsic activity of the electrocatalytic oxygen reduction reaction.

[0074] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, characterized in that, Includes the following steps: Soluble transition metal salts and organic ligands were mixed in a solvent system to form a mixture, and coordination was carried out under stirring to obtain a pyridine nitrogen-doped NC framework precursor. In a nitrogen atmosphere, the pyridine nitrogen-doped NC framework precursor is calcined to coordinate the metal atoms with the nitrogen atoms in the NC framework, thereby obtaining a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst.

2. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The molar ratio of transition metal to organic ligand in soluble transition metal salts is 1:5 to 8.

3. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The organic ligand is at least one of 2-methylimidazole, methylimidazole, and bipyridine.

4. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The transition metal in a soluble transition metal salt is at least one of zinc, iron, manganese, and cobalt. When the transition metal contains zinc, the transition metal is at least two of them.

5. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The concentration of organic ligands in the mixture is 0.3 mol / L to 0.5 mol / L.

6. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The coordination temperature is 25℃~30℃, and the time is 4h~6h.

7. The method for preparing a pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst according to claim 1, characterized in that, The calcination temperature is 900℃~1000℃, and the holding time is 2h~3h.

8. A pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the pyridine nitrogen-doped regular dodecahedral supported transition metal catalyst of claim 8 in the electrocatalytic oxygen reduction reaction of a fuel cell.

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