Sulfur-doped iron fe-s-n-c cathode oxygen reduction catalyst and preparation method and application thereof

Abstract

The application provides a Fe-S-N-C cathode oxygen reduction catalyst doped with sulfur and a preparation method and application thereof, and belongs to the field of catalysts and preparation technologies thereof. The preparation method comprises the following steps: mixing and pyrolyzing ZIF-8 with a framework structure of a regular dodecahedron and a nitrogen-containing ligand to form a nitrogen-coated nitrogen-carbon base, wherein the nitrogen-carbon base has a framework structure of a regular dodecahedron; and performing chemical vapor deposition on the precursor iron salt, the precursor sulfur salt and the nitrogen-coated nitrogen-carbon base to obtain the Fe-S-N-C cathode oxygen reduction catalyst doped with sulfur. The application reduces the electrons around the Fe active center, improves the interaction with oxygen compounds, promotes the four-electron transfer oxygen reduction process in subsequent application, reduces the dissolution of Fe, and improves the cycle stability of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalysts and their preparation technology, and in particular to a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are a novel type of energy conversion device that has attracted widespread attention due to their environmental friendliness, low cost, and high theoretical energy density. The oxygen reduction reaction (ORR) is a crucial electrochemical reaction in fuel cell applications. Because this reaction involves four electron transfers and has slow kinetics, developing high-performance and stable ORR electrocatalysts is a key focus in the development of PEMFCs.

[0003] Traditional platinum-based catalysts have hindered the widespread application of proton exchange membrane fuel cells (PEMFCs) due to the scarcity and high cost of platinum. Therefore, developing alternative catalysts made of non-precious metals is considered key to realizing the large-scale application of PEMFCs.

[0004] Single-atom catalysts possess advantages such as high atom utilization efficiency, tunable coordination structures, and designable geometries. Furthermore, they exhibit ORR catalytic activity comparable to platinum-based catalysts in acidic media. However, in proton exchange membrane fuel cells, there remains a significant gap in membrane electrode performance between single-atom and platinum-based catalysts. Summary of the Invention

[0005] In view of the above, in order to at least partially solve at least one of the aforementioned technical problems, the present invention provides a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst, its preparation method, and its application.

[0006] According to one aspect of the present invention, a method for preparing a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst is provided, comprising: mixing and pyrolyzing ZIF-8 having a dodecahedral framework structure with a nitrogen-containing ligand to form a nitrogen-coated nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a dodecahedral framework structure; and performing chemical vapor deposition on a precursor iron salt, a precursor sulfur salt, and the nitrogen-coated nitrogen-carbon substrate to obtain the sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst.

[0007] According to an embodiment of the present invention, the temperature of chemical vapor deposition is 750~900℃ and the time is 2~4h; wherein, the atmosphere of chemical vapor deposition is a mixture of argon and hydrogen, or argon.

[0008] According to an embodiment of the present invention, the process of mixing and pyrolyzing ZIF-8 with a nitrogen-containing ligand to form a nitrogen-coated nitrogen-carbon substrate comprises: dissolving ZIF-8 and the nitrogen-containing ligand in a solvent and mixing to obtain a suspension; subjecting the suspension to rotary evaporation, drying, and grinding in sequence to obtain nitrogen-coated ZIF-8; and pyrolyzing the nitrogen-coated ZIF-8 under a protective atmosphere to obtain a nitrogen-coated nitrogen-carbon substrate; wherein the nitrogen-containing ligand includes at least one of o-phenanthroline and dopamine.

[0009] According to an embodiment of the present invention, the pyrolysis temperature is 900~1000℃ and the time is 0.5~1.5h; the solvent includes a mixed solution of water and ethanol.

[0010] According to an embodiment of the present invention, when the nitrogen-containing ligand is o-phenanthroline, the mass ratio of ZIF-8 to the nitrogen-containing ligand is (3~5):1.

[0011] According to an embodiment of the present invention, the precursor iron salt includes at least one of ferrocene, ferrous chloride, and ferrous chloride hydrate; the precursor sulfur salt includes at least one of thiourea and sublimed sulfur; and the molar ratio of the precursor iron salt, the precursor sulfur salt, and the nitrogen-coated nitrogen-carbon substrate is 1:1:(1.6~3.2).

[0012] According to an embodiment of the present invention, ZIF-8 is prepared by the following process: zinc nitrate and dimethylimidazole are dissolved in methanol solution and mixed to obtain a mixture; the mixture is then centrifuged and dried sequentially to obtain ZIF-8.

[0013] According to an embodiment of the present invention, the mass ratio of zinc nitrate to dimethylimidazole is (4~8):(11~15).

[0014] According to another aspect of the present invention, a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst prepared by the preparation method described above is provided, comprising: a nitrogen-coated nitrogen-carbon substrate having a dodecahedral framework structure, wherein sulfur is loaded on the nitrogen-coated nitrogen-carbon substrate, the sulfur interacts with the nitrogen-coated nitrogen-carbon substrate, the sulfur doping changes the bond energy of the iron-nitrogen bond, and inhibits the dissolution of iron; and an active center comprising Fe-N4 loaded inside the nitrogen-coated nitrogen-carbon substrate.

[0015] According to another aspect of the present invention, an application of the above-described Fe-SNC cathode oxygen reduction catalyst in the field of proton exchange membrane fuel cell cathode technology is provided.

[0016] According to embodiments of the present invention, a nitrogen-coated nitrogen-carbon substrate is formed by pyrolyzing a nitrogen-containing ligand mixed with ZIF-8. The introduction of nitrogen provides an electron donor, which helps to anchor more iron and enhance the electron density around the iron active center. In the oxygen reduction reaction, the introduction of nitrogen helps to promote the adsorption and activation of oxygen molecules by changing the local electronic structure, thereby accelerating the reaction rate. Furthermore, iron and sulfur are introduced into the nitrogen-coated nitrogen-carbon substrate by chemical vapor deposition. The sulfur doping breaks the symmetry structure of the Fe-N4 sites, changing the spin and charge density of the Fe-N4 active center. When applied to the oxygen reduction reaction, this helps to improve the adsorption energy between the Fe-N4 active sites and oxygen intermediates, thereby improving the catalytic activity of the Fe-SNC cathode oxygen reduction catalyst. In addition, the addition of sulfur causes the nitrogen-carbon substrate to form a thiophene-like structure (C@S@C), which helps to change the bond energy of the iron-nitrogen bond, inhibits the process of iron forming particulate dissolution, and improves the stability of the Fe-SNC cathode oxygen reduction catalyst. Attached Figure Description

[0017] Figure 1 A flowchart illustrating the preparation method of the Fe-SNC cathode oxygen reduction catalyst according to an embodiment of the present invention is shown;

[0018] Figure 2 The image shown is a scanning electron microscope image of ZIF-8 prepared in Example 1 of the present invention;

[0019] Figure 3 The image shows a scanning electron microscope (SEM) image of the nitrogen-coated nitrogen-carbon substrate prepared in Example 1 of the present invention.

[0020] Figure 4 The cyclic voltammetry curves of Fe-SNC cathode oxygen reduction catalyst 1, platinum-based catalyst, and FeNC oxygen reduction catalyst 1' prepared in Comparative Example 1 are shown in 0.1M perchloric acid solution.

[0021] Figure 5 The half-wave potential curves of the Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 of the present invention before and after accelerated aging tests in 0.1M perchloric acid solution at 0.6~0.9V for 0, 10000, 30000 and 50000 cycles are shown.

[0022] Figure 6 The following are hydrogen-oxygen polarization curves measured in an 850e fuel cell test system when the Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 and the FeNC oxygen reduction catalyst 1' prepared in Comparative Example 1 were applied to the cathodes of proton exchange membrane fuel cells; and...

[0023] Figure 7The half-wave potential curve of the Fe-SNC cathode oxygen reduction catalyst 6 prepared by calcination under argon atmosphere in Example 6 of the present invention is shown. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0026] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). When using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0027] Traditionally, platinum-based catalysts are commonly used as cathode catalysts in proton exchange membrane fuel cells. However, platinum-based catalysts require expensive precious metals, resulting in high application costs. Related technologies often use non-precious metal catalysts to selectively replace platinum-based catalysts. However, the catalytic activity and stability of non-precious metal catalysts are inferior to those of platinum-based catalysts.

[0028] In realizing the concept of this invention, it was discovered that Fe-NC single-atom catalysts with Fe-N4 can more easily achieve oxygen reduction catalytic activity comparable to Pt-based catalysts in acidic media. However, in proton exchange membrane fuel cells, there is still a significant gap in membrane electrode performance between Fe-NC catalysts and Pt-based catalysts.

[0029] Furthermore, to address the aforementioned issues, sulfur atoms with different atomic radii and electronegativity are doped into the Fe-N4 active sites. This disrupts the symmetry of the Fe-N4 active sites, altering the spin and charge density of the Fe-N4 active centers, thereby improving the adsorption energy between the active sites and oxygen intermediates and enhancing the catalytic activity of the Fe-SNC cathode oxygen reduction catalyst. Additionally, the addition of sulfur causes the ZIF-8 support to form a thiophene-like structure (C@S@C), reducing the number of electrons around the Fe-N4 active centers and improving the interaction between the Fe-N4 active centers and oxygen compounds. This promotes a complete four-electron transfer oxygen reduction process in acidic solution, reduces iron dissolution, and improves the stability of the Fe-SNC cathode oxygen reduction catalyst.

[0030] Specifically, according to one embodiment of the present invention, a method for preparing a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst is provided. Figure 1 A flowchart illustrating the preparation method of the Fe-SNC cathode oxygen reduction catalyst according to an embodiment of the present invention is shown, as follows: Figure 1 As shown, the preparation method includes operations S101 to S102.

[0031] In operation S101, ZIF-8 with a dodecahedral framework structure is mixed with nitrogen-containing ligands and pyrolyzed to form a nitrogen-coated nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a dodecahedral framework structure.

[0032] According to embodiments of the present invention, ZIF-8 with a dodecahedral framework structure is used as a support, which maintains a high specific surface area and abundant pore structure after pyrolysis, helping to increase the number of active sites for subsequent catalyst formation, thereby improving the catalytic effect. The nitrogen-coated nitrogen-carbon substrate not only increases the nitrogen content of the nitrogen-carbon substrate but also forms a uniform distribution of nitrogen on the surface of the nitrogen-carbon substrate, thus providing more active sites. The nitrogen-coated structure may contain multiple nitrogen species, such as pyridine nitrogen, pyrrole nitrogen, or graphitic nitrogen. These different nitrogen species can form Fe-N4 coordination structures with iron active centers, improving the catalytic activity and stability of the Fe-SNC cathode oxygen reduction catalyst.

[0033] In operation S102, precursor iron salt, precursor sulfur salt and nitrogen-coated nitrogen-carbon substrate are subjected to chemical vapor deposition to obtain sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst.

[0034] According to embodiments of the present invention, iron and sulfur are uniformly dispersed on a nitrogen-coated nitrogen-carbon substrate via chemical vapor deposition, ensuring a uniform distribution of active sites for iron and sulfur, and improving the utilization rate of Fe single atoms and catalytic activity. The introduction of nitrogen improves the conductivity of the carbon substrate material, while the introduction of sulfur further optimizes the electron transport path. Sulfur atoms act as bridges for electron transport, enhancing the internal electronic conductivity of the catalyst material.

[0035] For example, the chemical vapor deposition process can be understood as follows: Iron and sulfur precursors are placed in the lower part of a container, and a nitrogen-coated carbon-nitrogen substrate is placed in the upper part of the container. A vapor phase film separates the upper and lower parts of the container; the container could be, for example, a ceramic boat. Then, pyrolysis is performed, causing the iron and sulfur precursors to form gaseous states, which are then deposited onto the nitrogen-coated carbon-nitrogen substrate after passing through the vapor phase film.

[0036] According to embodiments of the present invention, when using chemical vapor deposition, due to the different diffusion rates of iron and sulfur atoms, voids or pores may appear at the diffusion interface. In other words, when sulfur doping is used, the Kirkendall effect (forming voids or pores) occurs, etching the nitrogen-coated nitrogen-carbon substrate and making the nitrogen-carbon substrate have more abundant micropores and mesopores, thereby increasing the active site density of the Fe-SNC cathode oxygen reduction catalyst. When applied in the oxygen reduction process, it facilitates the reach of oxygen to the Fe-N4 active centers, thereby enhancing the oxygen reduction catalytic activity of the catalyst. The introduction of sulfur atoms alters the electronic structure of iron, improving the catalytic activity of iron and enhancing the intrinsic activity of each Fe-N4 active site. Furthermore, the preparation method of the present invention is simple and easy to operate, suitable for large-scale production and promotion.

[0037] According to embodiments of the present invention, the temperature for chemical vapor deposition is 750~900°C, for example, 750°C, 800°C, 850°C or 900°C, preferably 900°C. The time is 2~4 hours, for example, 2 hours, 3 hours or 4 hours, preferably 3 hours. Setting the temperature and time of chemical vapor deposition within the above range helps to promote the complete conversion of precursor iron salts and precursor sulfur salts into a gaseous state, so that iron and sulfur can be uniformly loaded on the nitrogen-coated nitrogen-carbon substrate. The atmosphere for chemical vapor deposition is a mixture of argon and hydrogen, or argon alone. Preferably, the atmosphere for chemical vapor deposition is a mixture of 10% by volume of hydrogen and argon. Adding the above-mentioned mass percentage of hydrogen to the argon helps to provide a reducing atmosphere, which can reduce iron salts to metallic iron, so that iron atoms exist in the Fe-SNC cathode oxygen reduction catalyst in the form of Fe-N4 active sites. At the same time, 10% hydrogen can etch the nitrogen-coated nitrogen-carbon substrate, thereby further increasing the specific surface area of ​​the nitrogen-carbon substrate and helping to improve the catalytic activity of the Fe-SNC cathode oxygen reduction catalyst.

[0038] According to an embodiment of the present invention, operation S101 includes sub-operations S1011 to S1013.

[0039] In suboperation S1011, ZIF-8 and its nitrogen-containing ligands are dissolved in a solvent and mixed to obtain a suspension.

[0040] In sub-operation S1012, the suspension is sequentially subjected to rotary evaporation, drying, and grinding to obtain nitrogen-coated ZIF-8.

[0041] In sub-operation S1013, under a protective atmosphere, nitrogen-coated ZIF-8 is pyrolyzed to obtain a nitrogen-coated nitrogen-carbon substrate.

[0042] According to embodiments of the present invention, the nitrogen-containing ligand includes at least one of o-phenanthroline and dopamine, preferably o-phenanthroline. Nitrogen coating helps improve the chemical and thermal stability of ZIF-8, helping it maintain structural integrity even at higher temperatures (1000°C). By mixing the nitrogen-containing ligand with ZIF-8 and rotary evaporating it, a relatively large number of nitrogen atoms can be introduced into the ZIF-8 structure. These introduced nitrogen atoms are fixed on ZIF-8 during subsequent pyrolysis, thereby increasing the nitrogen doping level, providing more N active sites, and enabling subsequent bonding with more Fe, thus enhancing catalytic efficiency.

[0043] Specifically, in sub-operation S1011, the mixing time is 12 hours. The solvent includes a mixed solution of water and ethanol, more specifically, the volume ratio of ethanol to water in the mixed solution is 2:1. Mixing water and ethanol helps to lower the boiling point of the mixed solution, reducing it to about 70°C, which makes solvent removal easier and more convenient during subsequent rotary evaporation. In sub-operation S1013, the pyrolysis temperature is 900~1000°C, for example, 900°C, 950°C, or 1000°C, preferably 1000°C, and the pyrolysis time is 0.5~1.5 hours, for example, 0.5 hours, 1 hour, or 1.5 hours, preferably 1 hour. The pyrolysis method can be, for example, roasting in a tube furnace, and the pyrolysis atmosphere can be, for example, argon.

[0044] In sub-operation S1012, the rotary evaporation temperature is 70~80°C, for example, 70°C, 75°C or 80°C, preferably 70°C, and the rotary evaporation speed is, for example, 121 rpm. Adjusting the temperature and speed within the above range helps to remove the solvent by rotary evaporation.

[0045] According to embodiments of the present invention, when the nitrogen-containing ligand is o-phenanthroline, the mass ratio of ZIF-8 to the nitrogen-containing ligand is (3~5):1, preferably 4:1. O-phenanthroline contains two nitrogen atoms, and compared to other nitrogen-containing ligands, it can introduce more nitrogen atoms under the same mass ratio conditions, thereby increasing the nitrogen doping level. In related experiments, when the mass ratio is lower than the above range, the resulting nitrogen-carbon substrate has poor conductivity; when the mass ratio is higher than the above range, the nitrogen doping amount in the resulting nitrogen-carbon substrate is lower, which is detrimental to subsequent bonding with Fe.

[0046] According to embodiments of the present invention, the precursor iron salt includes at least one selected from ferrocene, ferrous chloride, and ferrous chloride hydrate; the precursor sulfur salt includes at least one selected from thiourea and sublimed sulfur. The boiling points of the aforementioned precursor iron salt and precursor sulfur salt are between 100 and 200°C, allowing for relatively uniform mixing during vapor deposition, thereby forming a uniform distribution of iron and sulfur. The molar ratio of the precursor iron salt, precursor sulfur salt, and nitrogen-coated nitrogen-carbon substrate is 1:1:(1.6~3.2), for example, it can be 1:1:1.6, 1:1:2, 1:1:2.5, 1:1:3, or 1:1:3.2. During the screening process for the molar ratio of the three components, it was found that adjusting the molar ratio to the above range helps to adequately load iron and sulfur onto the nitrogen-carbon substrate.

[0047] According to an embodiment of the present invention, ZIF-8 is prepared by the following process: zinc nitrate and dimethylimidazole are dissolved in methanol solution and mixed to obtain a mixture; the mixture is then centrifuged and dried sequentially to obtain ZIF-8.

[0048] In one embodiment, zinc nitrate is dissolved in methanol to obtain a zinc nitrate solution. Dimethylimidazole is dissolved in methanol to obtain a dimethylimidazole solution. The zinc nitrate solution is added to the dimethylimidazole solution and stirred to obtain a mixture. Zinc nitrate and dimethylimidazole have high solubility in methanol, and zinc ions and dimethylimidazole molecules are formed during dissolution. During mixing, the two interact through electrostatic attraction to form a complex. If necessary, the mixture can be allowed to stand for a period of time after mixing to promote the assembly of the complex into a ZIF-8 crystal structure. Unreacted raw materials and byproducts are then removed by centrifugation, and residual solvent is removed by drying.

[0049] According to embodiments of the present invention, the mass ratio of zinc nitrate to dimethylimidazole is (4~8):(11~15), preferably 6:13. For example, 6g of zinc nitrate can be dissolved in 80mL of methanol solution to form a zinc nitrate solution, and 13g of dimethylimidazole can be dissolved in 160mL of methanol solution to form a dimethylimidazole solution.

[0050] Preferably, the mixing time for obtaining the mixture is (22~26) h, more preferably 24 h, the centrifugation speed is 10000 rpm, and the centrifugation time is (3~5) min, more preferably 5 min. The drying method can be, for example, vacuum drying, at a drying temperature of 55~60℃, for a drying time of 6 h.

[0051] In one specific embodiment, the preparation process of the Fe-SNC cathode oxygen reduction catalyst is as follows:

[0052] Zinc nitrate is dissolved in methanol solution to obtain zinc nitrate solution.

[0053] Dimethylimidazole is dissolved in methanol solution to obtain dimethylimidazole solution.

[0054] Zinc nitrate solution was added to dimethylimidazole solution and stirred to obtain a mixture.

[0055] The mixture was subjected to centrifugation, methanol washing, and vacuum drying to obtain ZIF-8.

[0056] ZIF-8 and nitrogen-containing ligands were dissolved in a mixed solution of ethanol and water, and then subjected to rotary evaporation, grinding, and pyrolysis to obtain a nitrogen-coated nitrogen-carbon substrate.

[0057] In an atmosphere of 10% by volume hydrogen mixed with argon, precursor iron salt, precursor sulfur salt and nitrogen-coated nitrogen-carbon substrate were subjected to chemical vapor deposition to obtain sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst.

[0058] According to another aspect of the present invention, a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst prepared by the preparation method described above is provided, comprising: a nitrogen-coated nitrogen-carbon substrate having a dodecahedral framework structure, wherein sulfur is uniformly dispersed on the nitrogen-coated nitrogen-carbon substrate and interacts with the nitrogen-coated nitrogen-carbon substrate, the doping of sulfur alters the bond energy of the iron-nitrogen bond and inhibits the dissolution of iron; and an active center comprising Fe-N4 loaded inside the nitrogen-coated nitrogen-carbon substrate.

[0059] According to embodiments of the present invention, the single-atom center of iron is tightly bonded to the nitrogen-carbon substrate via Fe-N bonds to form the active center Fe-N4, which exhibits high catalytic activity and high stability in the oxygen reduction reaction. Sulfur doping enhances the oxygen conductivity of the Fe-SNC cathode oxygen reduction catalyst and the catalytic activity of the Fe single atom at the active site, while also suppressing the dissolution of iron in particulate form and improving the single-atom stability of Fe.

[0060] According to embodiments of the present invention, the mass fraction of Fe single atoms is 3-6%, for example, it can be 3%, 4%, 5% or 6%. This illustrates that coating nitrogen on a nitrogen-carbon substrate helps to fix more Fe, thereby optimizing the electronic structure of the Fe-N4 active center and improving catalytic efficiency.

[0061] According to another aspect of the present invention, an application of the Fe-SNC cathode oxygen reduction catalyst as described above in the field of proton exchange membrane fuel cell cathode technology is provided.

[0062] According to embodiments of the present invention, the formed Fe-N4 active centers possess high intrinsic activity and can efficiently catalyze the oxygen reduction reaction. Nitrogen doping and thiocyanate doping on the carbon substrate further optimize the electronic structure of the Fe-N4 active centers, improving catalytic efficiency. This results in the Fe-SNC cathode oxygen reduction catalyst having a high half-wave potential, enabling effective catalysis of the oxygen reduction reaction at lower potentials, improving the voltage output and energy efficiency of the fuel cell, while also exhibiting high catalytic activity and stability, significantly improving fuel cell performance and extending battery life.

[0063] In one embodiment, the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst can reach 0.86V, which has wide applicability in the field of proton exchange membrane fuel cell technology.

[0064] The present invention will be further illustrated below through embodiments and related test experiments and results. In the following detailed description, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present invention. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict.

[0065] It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this invention is not limited thereto. The chemicals and raw materials used in the following embodiments are all commercially available or prepared using recognized processing methods.

[0066] Example 1:

[0067] 6 g of zinc nitrate was dissolved in 80 mL of methanol to obtain a zinc nitrate solution. 13 g of dimethylimidazole was dissolved in 160 mL of methanol to obtain a dimethylimidazole solution. Under stirring, zinc nitrate solution was added to the dimethylimidazole solution, and the mixture was stirred for 24 h to obtain a first suspension. The first suspension was centrifuged at 10000 rpm for 5 min, washed three times with methanol, and then dried in a vacuum oven at 60 °C to obtain ZIF-8.

[0068] Figure 2 A scanning electron microscope (SEM) image of ZIF-8 prepared in Example 1 of this invention is shown. Figure 2 As shown, the ZIF-8 prepared in Example 1 has a regular dodecahedral structure.

[0069] ZIF-8 and o-phenanthroline were dissolved in a mixed solution at a mass ratio of 4:1. The mixed solution was prepared by mixing ethanol and water at a volume ratio of 2:1. After stirring for 12 hours, the mixture was stirred until homogeneous to obtain a second suspension. The second suspension was subjected to rotary evaporation, vacuum drying and grinding to obtain a composite solid. The composite solid was pyrolyzed at 1000℃ under argon for one hour to obtain a nitrogen-coated nitrogen-carbon substrate.

[0070] Figure 3 A scanning electron microscope (SEM) image of the nitrogen-coated nitrogen-carbon substrate prepared in Example 1 of this invention is shown. Figure 3 As shown, it can be seen that the nitrogen-carbon substrate is coated with a nitrogen layer without much change in its basic structure.

[0071] Chemical vapor deposition process: Ferrocene and thiourea were placed in the lower part of a ceramic boat, and a nitrogen-coated nitrogen-carbon substrate was placed in the upper part of the ceramic boat. The molar ratio of the three was 1:1:1.6. The mixture was pyrolyzed at 750℃ in an atmosphere of 10% hydrogen mixed with argon for 3 hours to obtain sulfur-doped FeSNC single-atom oxygen reduction catalyst 1.

[0072] Comparative Example 1:

[0073] The preparation process of Comparative Example 1 is largely the same as that of Example 1, except that only ferrocene is loaded into the lower part of the ceramic boat, and the addition ratio of ferrocene to nitrogen-coated nitrogen-carbon substrate is 1:2, resulting in FeNC oxygen reduction catalyst 1'.

[0074] Figure 4 Cyclic voltammetry curves of Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 of the present invention, a commercially available platinum-based catalyst, and Fe-NC oxygen reduction catalyst 1' prepared in Comparative Example 1 are shown in 0.1 M perchloric acid solution. Figure 4 As shown, the Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 exhibits excellent acidic oxygen reduction activity, with a half-wave potential reaching 0.86V, which is far superior to Fe-NC oxygen reduction catalyst 1', and has better oxygen reduction activity than commercially available platinum-based catalysts.

[0075] Figure 5The diagram shows the half-wave potential curves of the Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 of this invention before and after accelerated aging tests in 0.1M perchloric acid solution at 0~0.9V, including 0 cycles, 10000 cycles, 30000 cycles, and 50000 cycles. Figure 5 As shown, Fe-SNC cathode oxygen reduction catalyst 1 exhibits superior acidic oxygen reduction stability.

[0076] Figure 6 The diagram shows the hydrogen-oxygen polarization curves obtained by applying the Fe-SNC cathode oxygen reduction catalyst 1 prepared in Example 1 of the present invention and the FeNC oxygen reduction catalyst 1' prepared in Comparative Example 1 to the cathodes of proton exchange membrane fuel cells, respectively, and measuring them in an 850e fuel cell test system. Figure 6 As shown, Fe-SNC cathode oxygen reduction catalyst 1 exhibits superior battery performance compared to FeNC oxygen reduction catalyst 1'. ICP results indicate that the iron content in the FeSNC catalyst is 5.6 wt%, while the iron content in the FeNC catalyst is 4.6 wt%.

[0077] Example 2:

[0078] The preparation process of Example 2 is largely the same as that of Example 1, except that the pyrolysis temperature in the chemical vapor deposition process is adjusted to 800℃, and Fe-SNC cathode oxygen reduction catalyst 2 is prepared.

[0079] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 2 prepared in Example 2, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 2 was found to be 0.853V.

[0080] Example 3:

[0081] The preparation process of Example 3 is largely the same as that of Example 1, except that the pyrolysis temperature in the chemical vapor deposition process is adjusted to 900℃, and Fe-SNC cathode oxygen reduction catalyst 3 is prepared.

[0082] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 3 prepared in Example 3, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 3 was found to be 0.856V.

[0083] Example 4:

[0084] The preparation process of Example 4 is largely the same as that of Example 3, except that the stirring time of the dimethylimidazole solution and zinc nitrate solution is adjusted to 22 h during the preparation of ZIF-8, thus preparing Fe-SNC cathode oxygen reduction catalyst 4.

[0085] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 4 prepared in Example 4, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 4 was found to be 0.849 V.

[0086] Example 5:

[0087] The preparation process of Example 5 is largely the same as that of Example 3, except that the stirring time of the dimethylimidazole solution and zinc nitrate solution is adjusted to 26 h during the preparation of ZIF-8, thus preparing Fe-SNC cathode oxygen reduction catalyst 5.

[0088] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 5 prepared in Example 5, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 5 was found to be 0.851V.

[0089] Example 6:

[0090] The preparation process of Example 6 is largely the same as that of Example 3, except that the atmosphere in the chemical vapor deposition process is adjusted to an argon atmosphere, and Fe-SNC cathode oxygen reduction catalyst 6 is prepared.

[0091] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 6 prepared in Example 6, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 6 was found to be 0.842V.

[0092] Figure 7 The half-wave potential curve of the Fe-SNC cathode oxygen reduction catalyst 6 prepared by calcination under an argon atmosphere in Example 6 of the present invention is shown. Figure 7 As shown, it can be seen that the Fe-SNC cathode oxygen reduction catalyst 3 prepared under the mixed atmosphere of 10% volume hydrogen and argon has a higher half-wave potential compared to the argon atmosphere. This is because the 10% volume hydrogen not only provides a reducing atmosphere but also etches the nitrogen-coated nitrogen-carbon substrate, thereby increasing the specific surface area of ​​the nitrogen-carbon substrate.

[0093] Example 7:

[0094] The preparation process of Example 7 is largely the same as that of Example 3, except that the pyrolysis time in the chemical vapor deposition process is adjusted to 1 hour, and Fe-SNC cathode oxygen reduction catalyst 7 is prepared.

[0095] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 7 prepared in Example 7, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 7 was found to be 0.848V.

[0096] Example 8:

[0097] The preparation process of Example 8 is largely the same as that of Example 3, except that the molar ratio of ferrocene, thiourea, and nitrogen-coated nitrogen-carbon substrate in the chemical vapor deposition process is adjusted to 1:1:2.4, thus preparing Fe-SNC cathode oxygen reduction catalyst 8.

[0098] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 8 prepared in Example 8, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 8 was found to be 0.852V.

[0099] Example 9:

[0100] The preparation process of Example 9 is largely the same as that of Example 3, except that the molar ratio of ferrocene, thiourea, and nitrogen-coated nitrogen-carbon substrate in the chemical vapor deposition process is adjusted to 1:1:3.2, thus preparing Fe-SNC cathode oxygen reduction catalyst 9.

[0101] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 9 prepared in Example 9, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 9 was found to be 0.848V.

[0102] Example 10:

[0103] The preparation process of Example 10 is largely the same as that of Example 9, except that the temperature of the vacuum oven is adjusted to 50°C during the preparation of ZIF-8, and Fe-SNC cathode oxygen reduction catalyst 10 is obtained.

[0104] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 10 prepared in Example 10, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 10 was found to be 0.850 V.

[0105] Example 11:

[0106] The preparation process of Example 11 is largely the same as that of Example 9, except that the mass ratio of ZIF-8 to o-phenanthroline is adjusted to 8:1 when preparing the nitrogen-coated nitrogen-carbon substrate, thus preparing Fe-SNC cathode oxygen reduction catalyst 11.

[0107] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 11 prepared in Example 11, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 11 was found to be 0.857V.

[0108] Example 12:

[0109] The preparation process of Example 12 is largely the same as that of Example 9, except that the pyrolysis temperature in the chemical vapor deposition process is adjusted to 1000℃, and Fe-SNC cathode oxygen reduction catalyst 12 is prepared.

[0110] Cyclic voltammetry was performed on the Fe-SNC cathode oxygen reduction catalyst 12 prepared in Example 12, and the half-wave potential of the Fe-SNC cathode oxygen reduction catalyst 12 was found to be 0.853V.

[0111] As can be seen from the preparation results of Examples 1 to 12 of the present invention, the above steps can enable the prepared Fe-SNC cathode oxygen reduction catalyst to have high oxygen reduction catalytic activity while maintaining high cycle stability, and can be applied to proton exchange membrane fuel cells.

[0112] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst, comprising: ZIF-8, which has a dodecahedral framework structure, is mixed with nitrogen-containing ligands and pyrolyzed to form a nitrogen-coated nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a dodecahedral framework structure; The precursor iron source, the precursor sulfur source, and the nitrogen-coated nitrogen-carbon substrate were subjected to chemical vapor deposition to obtain a sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst. The symmetry structure of the Fe-N4 site was broken by sulfur doping, which changed the spin and charge density of the Fe-N4 active center. The temperature of chemical vapor deposition was 750~900℃ and the time was 2~4h. The precursor iron source and the precursor sulfur source are deposited together in the gas phase to form a uniform distribution of iron and sulfur. The precursor iron source is ferrocene; the precursor sulfur source is thiourea; and the molar ratio of the precursor iron source, the precursor sulfur source, and the nitrogen-coated nitrogen-carbon substrate is 1:1:(1.6~3.2). The process of mixing and pyrolyzing ZIF-8 with a dodecahedral framework structure with nitrogen-containing ligands to form a nitrogen-coated nitrogen-carbon substrate includes: ZIF-8 and the nitrogen-containing ligand were dissolved in a solvent and mixed to obtain a suspension; The suspension was sequentially subjected to rotary evaporation, drying, and grinding to obtain nitrogen-coated ZIF-8. Under a protective atmosphere, the nitrogen-coated ZIF-8 is pyrolyzed to obtain the nitrogen-coated nitrogen-carbon substrate; The nitrogen-containing ligand includes at least one of o-phenanthroline and dopamine; The pyrolysis temperature is 900~1000℃, and the time is 0.5~1.5h; The solvent includes a mixed solution of water and ethanol.

2. The preparation method according to claim 1, wherein, The atmosphere for the chemical vapor deposition is a mixture of argon and hydrogen, or argon alone.

3. The preparation method according to claim 1, wherein, When the nitrogen-containing ligand is o-phenanthroline, the mass ratio of ZIF-8 to the nitrogen-containing ligand is (3~5):

1.

4. The preparation method according to claim 1, wherein, ZIF-8 is prepared through the following process: Zinc nitrate and dimethylimidazole were dissolved in methanol solution and mixed to obtain a mixture. The mixture was centrifuged and dried sequentially to obtain ZIF-8.

5. The preparation method according to claim 4, wherein, The mass ratio of zinc nitrate to dimethylimidazole is (4~8):(11~15).

6. A sulfur-doped iron Fe-SNC cathode oxygen reduction catalyst prepared by the preparation method according to any one of claims 1 to 5, comprising: A nitrogen-coated nitrogen-carbon substrate having a dodecahedral framework structure, wherein sulfur is loaded on the nitrogen-coated nitrogen-carbon substrate, and the sulfur interacts with the nitrogen-coated nitrogen-carbon substrate; and The active center includes Fe-N4 loaded inside the nitrogen-coated nitrogen-carbon substrate.

7. The application of the Fe-SNC cathode oxygen reduction catalyst as described in claim 6 in the cathode of a proton exchange membrane fuel cell.

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