Heteroatom-doped oxygen reduction catalyst with asymmetric coordination structure as well as preparation method and application of heteroatom-doped oxygen reduction catalyst

Abstract

The invention relates to a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst as well as a preparation method and application thereof, and belongs to the technical field of electrochemical oxygen reduction catalysis. The preparation method of the catalyst comprises the following steps: S1, dissolving an iron source and a zinc source in an organic solvent, stirring and dissolving, and performing ultrasonic treatment to obtain a solution A; s2, dissolving 2-methylimidazole and a ligand containing heteroatoms in an organic solvent to obtain a solution B; s3, pouring the solution B into the solution A, reacting at room temperature, centrifugally collecting a product, and drying to obtain precursor powder; and S4, performing pyrolysis treatment on the precursor powder to obtain the catalyst. The MOF carrier has the advantages of good ligand modifiability, coordination topology and the like, and high-dispersion, high-load and high-precision doping of heteroatoms can be achieved by adjusting the types, proportion and number of the ligands containing the heteroatoms in the synthesis process.

Description

Technical Field

[0001] The present application relates to the technical field of electrochemical oxygen reduction catalysis, and in particular to a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst and a preparation method and application thereof. Background Art

[0002] The hydrogen energy industry is one of my country's six major future energy industries, and the development of proton exchange membrane fuel cells (PEMFC) is in line with this major national strategic need. Proton exchange membrane fuel cells have attracted widespread attention in the industry due to their advantages such as high energy conversion efficiency, strong endurance, and environmental friendliness. However, the cathode oxygen reduction reaction (ORR) kinetics of proton exchange membrane fuel cells are slow, and a large amount of additional catalysts are required to increase the reaction rate of the cathode, which limits its commercialization process for large-scale applications. At present, precious metal platinum-based catalysts are still the most effective catalysts for ORR, but they are expensive and susceptible to poisoning. Therefore, low-cost, highly active, and highly stable non-platinum ORR catalysts are widely studied and developed as the most potential candidates.

[0003] So far, iron-nitrogen-carbon single-atom catalysts have made some progress in ORR activity, but there are still many shortcomings that hinder them from meeting the needs of practical applications. Among them, the adsorption strength of the iron-nitrogen coordination structure center to oxygen-containing intermediates determines the ORR activity of the catalyst. The active center of the typical iron-nitrogen four-coordinate structure has D4h local symmetry, which is inconsistent with the asymmetric ORR reaction kinetics, increases the desorption barrier of the active site to the intermediate, and leads to insufficient catalytic activity. In contrast, the asymmetric coordination Fe-N / X (such as P, S, O, Cl, etc.) structure with precise heteroatom doping has unique advantages. On the one hand, the precise first shell doping of heteroatoms can break the local symmetry of the active site, improve the local coordination environment and geometric electronic structure of the active center, optimize the adsorption energy to oxygen-containing intermediates, and improve the ORR catalytic activity; on the other hand, due to the difference in electronegativity between heteroatoms and nitrogen atoms, the doping of the first shell can not only affect the valence state of the iron active center, but also regulate the bond length and bond energy of the iron-nitrogen bond, increase the dissolution barrier of the iron atom, and thus improve the ORR stability. At present, inorganic salts, simple substances (such as sodium chloride, ammonium bromide, sulfur powder, etc.) are generally used as sources of heteroatom-doped asymmetric coordination iron-based catalysts. However, the introduction of such heteroatoms cannot accurately or even effectively dope the coordination layer of the active center, which weakens the regulation of the electronic structure of the active center by the doped heteroatoms to a certain extent, resulting in very limited improvement in catalyst activity and stability. Therefore. It is necessary to further develop effective and accurate methods for preparing heteroatom-doped ORR catalysts to realize the practical application of non-platinum catalysts in fuel cells. Summary of the invention

[0004] In view of this, the present application provides a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst and its preparation method and application, utilizing the advantages of MOF carriers such as good ligand modifiability and coordination topology. During the synthesis, the type, proportion and number of heteroatom-containing ligands can be adjusted to achieve high dispersion, high loading and high precision doping of heteroatoms, providing a good universal method for the subsequent preparation of other efficient ORR catalysts with precise heteroatom doping, which can effectively overcome the defects of the above-mentioned prior art.

[0005] The first aspect of the present application provides a method for preparing a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, comprising the following steps:

[0006] S1, dissolving the iron source and the zinc source in an organic solvent, stirring and dissolving, and then ultrasonically treating to obtain a solution A;

[0007] S2, dissolving 2-methylimidazole and a heteroatom-containing ligand in an organic solvent to obtain a solution B;

[0008] S3, pouring the B solution into the A solution, reacting at room temperature, collecting the product by centrifugation, and drying to obtain a precursor powder;

[0009] S4. The precursor powder is subjected to pyrolysis treatment to obtain a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst.

[0010] Specifically, the steps include:

[0011] S1, dissolving anhydrous ferric chloride and zinc acetate nonahydrate in an organic solvent, stirring and dissolving, and then ultrasonically treating to obtain solution A;

[0012] S2, dissolving 2-methylimidazole and a heteroatom-containing ligand in an organic solvent to obtain a solution B;

[0013] S3, pouring the B solution into the A solution, reacting at room temperature, collecting the product by centrifugation, and drying to obtain a precursor powder;

[0014] S4. The precursor powder is subjected to pyrolysis treatment to obtain a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst.

[0015] Preferably, in step S2, the heteroatom-containing ligand is selected from one of thiazole, 2-aminooxazole, and 4,5-dichloroimidazole; or

[0016] In step S1, the iron source is selected from one of anhydrous ferric chloride, ferric nitrate nonahydrate, and ferrocene; or

[0017] In step S1, the zinc source is selected from one of zinc acetate nonahydrate, zinc chloride and zinc sulfate.

[0018] Preferably, in step S4, the pyrolysis conditions are: in an argon atmosphere, at 5°C min -1 The temperature was raised to 800-1100°C at a heating rate and pyrolyzed at this temperature for 1 h.

[0019] Preferably, in step S3, the specific conditions for drying are: carried out in a vacuum drying oven, the drying time is 24 hours, and the drying temperature is 65°C.

[0020] Preferably, in step S1, the usage ratio of anhydrous ferric chloride, zinc acetate nonahydrate and organic solvent is (0.2-1g):(0.3-0.6g):50ml; or

[0021] In step S2, the usage ratio of the 2-methylimidazole, the heteroatom-containing ligand and the organic solvent is (0.5-1.5 g):(0.1-1.2 g):50 ml.

[0022] The second aspect of the present application also provides a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, which is a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst prepared by the above method.

[0023] The third aspect of the present application also provides the use of the above-mentioned heteroatom-doped asymmetric coordination structure oxygen reduction catalyst in battery cathode materials.

[0024] The fourth aspect of the present application also provides a working electrode, which includes the above-mentioned heteroatom-doped asymmetric coordination structure oxygen reduction catalyst.

[0025] The fifth aspect of the present application also provides a method for preparing the above-mentioned working electrode, comprising the following steps:

[0026] The heteroatom-doped asymmetric coordination structure oxygen reduction catalyst is dispersed in a mixed solvent of isopropanol and Nafion, and a uniformly dispersed slurry is obtained after ultrasonic treatment. The slurry is then transferred with a pipette and evenly coated on the surface of a glassy carbon electrode, and dried in air to obtain a working electrode.

[0027] Specifically, the steps include:

[0028] 10 mg of the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst was dispersed in a mixed solvent of 1 mL of isopropanol and 20 μL of Nafion (5 wt%), and ultrasonicated for 2 h to obtain a uniformly dispersed slurry. Then, 15 μL of the slurry was transferred with a pipette and evenly coated on the surface of the glassy carbon electrode, and dried in air to obtain a working electrode.

[0029] Compared with the prior art, this application has the following beneficial effects:

[0030] The present application aims to design a heteroatom-doped, precisely asymmetric coordinated iron-based ORR catalyst, using a metal organic framework (MOF) as a carrier, selecting heteroatom-containing ligands (such as thiazole, oxazole, 4,5-dichloroimidazole, etc.), taking sulfur and chlorine as examples, introducing thiazole / 4,5-dichloroimidazole as ligands into zeolite imidazole MOFs, partially replacing with 2-methylimidazole ligands, and coordinating with zinc to achieve atomic-level precise coordination regulation of sulfur and chlorine atoms. The present application method utilizes the advantages of MOF carriers such as good ligand modifiability and coordination topology. During the synthesis, the type, proportion and number of heteroatom-containing ligands can be adjusted to achieve high dispersion, high loading and high precision doping of heteroatoms, providing a good universal method for the subsequent preparation of other efficient ORR catalysts precisely doped with various heteroatoms. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present application or the prior art, the drawings required for use in the description of the present application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is a SEM image of the Fe-N / SC catalyst prepared in Example 1;

[0033] Figure 2 CV comparison diagram of Fe-N / XC catalyst and Fe-NC catalyst prepared with different ligands;

[0034] Figure 3 SCV comparison diagram of Fe-N / XC catalyst and Fe-NC catalyst prepared with different ligands;

[0035] Figure 4 XRD comparison diagrams of Fe-N / XC catalyst and Fe-NC catalyst prepared with different ligands. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] Unless otherwise specified, the experimental methods used in the examples of this application are all conventional methods.

[0038] In the following examples and comparative examples, unless otherwise specified, all raw materials can be obtained by commercial purchase or conventional methods.

[0039] Example 1

[0040] Dissolve 0.5g of anhydrous ferric chloride and 0.6g of zinc acetate nonahydrate in 50ml of methanol, stir and dissolve, and then ultrasonicate for 30min, which is recorded as solution A. Then, dissolve 1.5g of 2-methylimidazole and 0.5g of thiazole in 50ml of methanol to obtain solution B; pour solution B into solution A, react at room temperature, collect the product by centrifugation, and place it in a vacuum drying oven to dry for 24h at a drying temperature of 65℃. Then, under an argon atmosphere, heat for 5℃min -1 The catalyst was pyrolyzed at 1000 °C for 1 h at a rate of 1.5 wt %. The final catalyst was used for testing and was recorded as Fe-N / SC catalyst.

[0041] Example 2

[0042] Except for the following steps which are different from those in Implementation Case 1, other preparation and testing methods are exactly the same as those in Implementation Case 1.

[0043] Then, 1.5 g of 2-methylimidazole and 0.8 g of 2-aminooxazole were dissolved in 50 ml of methanol to obtain solution B. Solution B was poured into solution A, and the product was collected by centrifugation after reaction at room temperature and placed in a vacuum drying oven for 24 h at a drying temperature of 65 °C. Then, the product was heated to 40 °C for 24 h in an argon atmosphere at 5 °C min. -1 The catalyst was pyrolyzed at 1000 °C for 1 h at a rate of 1.5 wt %. The final catalyst was used for testing and was recorded as Fe-N / OC catalyst.

[0044] Example 3

[0045] Except for the following steps which are different from those in Implementation Case 1, other preparation and testing methods are exactly the same as those in Implementation Case 1.

[0046] Then, 1.5 g of 2-methylimidazole and 1.2 g of 4,5-dichloroimidazole were dissolved in 50 ml of methanol to obtain solution B. Solution B was poured into solution A, and the product was collected by centrifugation after reaction at room temperature and placed in a vacuum drying oven for 24 h at a drying temperature of 65 °C. Then, the product was dried at 5 °C min under an argon atmosphere. -1 The catalyst was pyrolyzed at 1000 °C for 1 h at a rate of 1.5 wt %. The final catalyst was used for testing and was recorded as Fe-N / Cl-C catalyst.

[0047] Comparative Example 1

[0048] Dissolve 0.5g of anhydrous ferric chloride and 0.6g of zinc acetate nonahydrate in 50ml of methanol, stir and dissolve, and then sonicate for 30min, which is recorded as solution A. Then, dissolve 1.5g of 2-methylimidazole in 50ml of methanol to obtain solution B; pour solution B into solution A, react at room temperature, collect the product by centrifugation, and place it in a vacuum drying oven to dry for 24h at a drying temperature of 65℃. Then, under an argon atmosphere, heat for 5℃min -1 The catalyst was pyrolyzed at 1000 °C for 1 h at a rate of 1.5 wt %. The final catalyst was used for testing and was recorded as Fe-NC catalyst.

[0049] Test Case

[0050] 10 mg of the catalysts of Examples 1-3 and Comparative Example 1 were respectively dispersed in a mixed solvent of 1 mL of isopropanol and 20 μL of Nafion (5 wt%), and ultrasonicated for 2 h to obtain a uniformly dispersed slurry. Then, 15 μL of the slurry was transferred with a pipette and evenly coated on the surface of the glassy carbon electrode, and dried in air to prepare a working electrode.

[0051] Figure 1 The SEM images show that the prepared Fe-N / SC catalyst has a porous structure; Figure 2 The CV plots show that the heteroatom-doped catalyst has a higher electrochemical active area than Fe-NC; Figure 3 The polarization curves show that the heteroatom-doped catalyst has a higher half-wave potential than Fe-NC, that is, it has better oxygen reduction performance; Figure 4 XRD tests show that the prepared catalyst has diffraction peaks only at 26 and 44 degrees, corresponding to the (002) and (100) crystal planes of graphite carbon, respectively, proving that the prepared catalyst is at the atomic dispersion level.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, characterized in that: The following steps are involved: S1, dissolving the iron source and the zinc source in an organic solvent, stirring and dissolving, and then ultrasonically treating to obtain a solution A; S2, dissolving 2-methylimidazole and a heteroatom-containing ligand in an organic solvent to obtain a solution B; S3, pouring the B solution into the A solution, reacting at room temperature, collecting the product by centrifugation, and drying to obtain a precursor powder; S4. The precursor powder is subjected to pyrolysis treatment to obtain a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst.

2. The method for preparing the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst according to claim 1, characterized in that: In step S2, the heteroatom-containing ligand is selected from one of thiazole, 2-aminooxazole, and 4,5-dichloroimidazole; or In step S1, the iron source is selected from one of anhydrous ferric chloride, ferric nitrate nonahydrate, and ferrocene; or In step S1, the zinc source is selected from zinc acetate nonahydrate, zinc chloride, and zinc sulfate.

3. The method for preparing the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst according to claim 1, characterized in that: In step S4, the pyrolysis conditions are: under an argon atmosphere, at 5°C min -1 The temperature was raised to 800-1100°C at a heating rate and pyrolyzed at this temperature for 1 h.

4. The method for preparing the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst according to claim 1, characterized in that: In step S3, the specific drying conditions are: carried out in a vacuum drying oven, the drying time is 24 hours, and the drying temperature is 65°C.

5. The method for preparing the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst according to claim 1, characterized in that: In step S1, the usage ratio of anhydrous ferric chloride, zinc acetate nonahydrate and organic solvent is (0.2-1g):(0.3-0.6g):50ml; or In step S2, the usage ratio of the 2-methylimidazole, the heteroatom-containing ligand and the organic solvent is (0.5-1.5 g):(0.1-1.2 g):50 ml.

6. A heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, characterized in that: A heteroatom-doped asymmetric coordination structure oxygen reduction catalyst prepared by the method according to any one of claims 1 to 5.

7. Use of the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst according to claim 6 in battery cathode materials.

8. A working electrode, characterized in that It comprises the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst as claimed in claim 6.

9. A method for preparing the working electrode according to claim 8, characterized in that: The following steps are involved: The heteroatom-doped asymmetric coordination structure oxygen reduction catalyst is dispersed in a mixed solvent of isopropanol and Nafion, and a uniformly dispersed slurry is obtained after ultrasonic treatment. The slurry is then transferred with a pipette and evenly coated on the surface of a glassy carbon electrode, and dried in air to obtain a working electrode.

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