A heteroatom-doped asymmetric coordination structure oxygen reduction catalyst and a preparation method and application thereof

Abstract

The application relates to a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst and 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, ultrasonic treatment after stirring and dissolving to obtain an A solution; S2, dissolving 2-methyl imidazole and a heteroatom-containing ligand in an organic solvent to obtain a B solution; S3, pouring the B solution into the A solution, centrifugally collecting the product after room-temperature reaction, and obtaining a precursor powder after drying; and S4, pyrolyzing the precursor powder to obtain the catalyst. The MOF carrier has the advantages of good ligand modifiability and coordination topology, and in the synthesis, the types, proportions and quantities of the heteroatom-containing ligands can be adjusted to achieve high dispersion, high loading and high-precision doping of the heteroatoms.

Description

Technical Field

[0001] This application relates to the field of electrochemical oxygen reduction catalysis technology, and in particular to a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is one of my country's six major future energy industries, and the development of proton exchange membrane fuel cells (PEMFCs) aligns with this significant national strategic need. PEMFCs have attracted widespread attention due to their advantages such as high energy conversion efficiency, long driving range, and environmental friendliness. However, the slow kinetics of the oxygen reduction reaction (ORR) at the cathode of PEMFCs necessitate the use of large amounts of additional catalysts to increase the reaction rate, limiting their large-scale commercial application. Currently, platinum-based catalysts remain the most effective catalysts for ORR, but their high cost and susceptibility to poisoning make inexpensive, highly active, and stable non-platinum ORR catalysts the most promising candidates, leading to extensive research and development.

[0003] To date, iron-nitrogen-carbon single-atom catalysts have made some progress in ORR activity, but many shortcomings still exist, hindering their ability to meet practical application requirements. The adsorption strength of oxygen-containing intermediates by the iron-nitrogen coordination center determines the catalyst's ORR activity. The active center of a typical iron-nitrogen tetracoordinate structure exhibits D4h local symmetry, which is incompatible with the asymmetric ORR reaction kinetics, increasing the desorption barrier of the active site for intermediates and leading to insufficient catalytic activity. In contrast, asymmetric coordination Fe-N / X structures (such as P, S, O, Cl, etc.) with precise heteroatom doping have unique advantages. On the one hand, 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 for oxygen-containing intermediates, and improve ORR catalytic activity. On the other hand, due to the electronegativity difference between heteroatoms and nitrogen atoms, first-shell doping 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, increasing the dissolution barrier of the iron atom and thus improving ORR stability. Currently, heteroatom-doped asymmetric coordinated iron-based catalysts commonly use inorganic salts and elemental substances (such as sodium chloride, ammonium bromide, and sulfur powder) as sources. However, the introduction of these heteroatoms cannot precisely or even effectively dope the coordination layer of the active center, thus weakening the control 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 precise 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, this application provides a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, its preparation method and application. Utilizing the advantages of MOF support such as good ligand modifiability and coordination topology, the synthesis process can achieve high dispersion, high loading and high precision doping of heteroatoms by adjusting the type, ratio and number of heteroatom-containing ligands. This provides a good and universal method for the subsequent preparation of other highly efficient ORR catalysts with precise heteroatom doping, and can effectively overcome the defects of the existing technologies.

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

[0006] S1. Dissolve the iron source and zinc source in an organic solvent, stir to dissolve, and then sonicate to obtain solution A;

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

[0008] S3. Pour the B solution into the A solution, react at room temperature, centrifuge to collect the product, and dry to obtain the precursor powder;

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

[0010] Specifically, it includes the following steps:

[0011] S1. Dissolve anhydrous ferric chloride and zinc acetate nonahydrate in an organic solvent, stir to dissolve, and then sonicate to obtain solution A;

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

[0013] S3. Pour the B solution into the A solution, react at room temperature, centrifuge to collect the product, and dry to obtain the precursor powder;

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

[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: under an argon atmosphere, at 5°C for 1 minute. -1 The temperature was increased to 800-1100℃ at a heating rate, and then pyrolyzed for 1 hour at this temperature.

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

[0020] Preferably, in step S1, the 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 ratio of the amount of 2-methylimidazole, the heteroatom-containing ligand, and the organic solvent is (0.5-1.5g):(0.1-1.2g):50ml.

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

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

[0024] A fourth aspect of this application also provides a working electrode comprising the aforementioned heteroatom-doped asymmetric coordination structure oxygen reduction catalyst.

[0025] The fifth aspect of this 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 after sonication, a uniformly dispersed slurry is obtained. Then, the slurry is transferred with a pipette and uniformly coated on the surface of a glassy carbon electrode, and dried in air to obtain the working electrode.

[0027] Specifically, it includes the following steps:

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

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

[0030] This application aims to design a heteroatom-doped, precisely asymmetric coordinated iron-based ORR catalyst. Using a metal-organic framework (MOF) as the support, heteroatom-containing ligands (such as thiazole, oxazole, and 4,5-dichloroimidazole) are selected. Taking sulfur and chlorine as examples, thiazole / 4,5-dichloroimidazole is introduced as a ligand into a zeolite imidazole MOF, partially replacing the 2-methylimidazole ligand and coordinating with zinc, achieving atomic-level precise coordination control of sulfur and chlorine atoms. This method utilizes the advantages of MOF supports, such as good ligand modifiability and coordination topology. During synthesis, the type, ratio, and number of heteroatom-containing ligands can be adjusted to achieve high heteroatom dispersion, high loading, and high-precision doping, providing a good and universal method for the subsequent preparation of other heteroatom-doped, highly efficient ORR catalysts. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

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

[0033] Figure 2 Comparison of CV values ​​for Fe-N / XC and Fe-NC catalysts prepared with different ligands;

[0034] Figure 3 Comparison of SCV values ​​for Fe-N / XC and Fe-NC catalysts prepared for different ligands;

[0035] Figure 4 Comparison of XRD patterns of Fe-N / XC catalysts and Fe-NC catalysts prepared for different ligands. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

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

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

[0039] Example 1

[0040] 0.5 g of anhydrous ferric chloride and 0.6 g of zinc acetate nonahydrate were dissolved in 50 ml of methanol. After stirring and sonicating for 30 min, this solution was labeled A. Then, 1.5 g of 2-methylimidazole and 0.5 g of thiazole were dissolved in 50 ml of methanol to obtain solution B. Solution B was added to solution A, and the mixture was reacted at room temperature. The product was collected by centrifugation and dried in a vacuum oven at 65 °C for 24 h. Subsequently, under an argon atmosphere, the product was dried at 5 °C for 1 min. -1 The catalyst was pyrolyzed at 1000℃ for 1 h to obtain the final catalyst for testing, denoted as Fe-N / SC catalyst.

[0041] Example 2

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

[0043] Subsequently, 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, reacted at room temperature, and the product was collected by centrifugation and dried in a vacuum drying oven for 24 h at 65 °C. Then, under an argon atmosphere, the product was dried at 5 °C for 1 minute. -1 The catalyst was pyrolyzed at 1000℃ for 1 hour to obtain the final catalyst for testing, denoted as Fe-N / OC catalyst.

[0044] Example 3

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

[0046] Subsequently, 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 then added to solution A, and the mixture was reacted at room temperature. The product was collected by centrifugation and dried in a vacuum oven at 65 °C for 24 h. Subsequently, the product was dried under an argon atmosphere at 5 °C for 1 minute. -1 The catalyst was pyrolyzed at 1000℃ for 1 hour to obtain the final catalyst for testing, denoted as Fe-N / Cl-C catalyst.

[0047] Comparative Example 1

[0048] 0.5 g of anhydrous ferric chloride and 0.6 g of zinc acetate nonahydrate were dissolved in 50 ml of methanol. After stirring and sonicating for 30 min, this solution was labeled A. Then, 1.5 g of 2-methylimidazole was dissolved in 50 ml of methanol to obtain solution B. Solution B was added to solution A, and the mixture was reacted at room temperature. The product was collected by centrifugation and dried in a vacuum oven at 65 °C for 24 h. Subsequently, under an argon atmosphere, the product was dried at 5 °C for 1 min. -1 The catalyst was pyrolyzed at 1000℃ for 1 hour to obtain the final catalyst for testing, which was denoted as Fe-NC catalyst.

[0049] Test case

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

[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, which means it has better oxygen reduction performance. Figure 4 XRD tests showed that the prepared catalyst had 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 was atomically dispersed.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a heteroatom-doped asymmetric coordination structure oxygen reduction catalyst, characterized in that, Includes the following steps: S1. Dissolve the iron source and zinc source in an organic solvent, stir to dissolve, and then sonicate to obtain solution A; S2. Dissolve 2-methylimidazole and a heteroatom-containing ligand in an organic solvent to obtain solution B; S3. Pour the B solution into the A solution, react at room temperature, centrifuge to collect the product, and dry to obtain the precursor powder; S4. The precursor powder is subjected to pyrolysis to obtain an oxygen reduction catalyst with asymmetric coordination structure doped with heteroatoms. In step S2, the heteroatom-containing ligand is selected from one of thiazole, 2-aminooxazole, and 4,5-dichloroimidazole; In step S1, the iron source is selected from one of anhydrous ferric chloride, ferric nitrate nonahydrate, and ferrocene; In step S1, the zinc source is selected from one of zinc acetate nonahydrate, zinc chloride, and zinc sulfate; In step S4, the pyrolysis conditions are: under an argon atmosphere, at 5 °C for 1 minute. -1 The temperature was increased to 800-1100℃ at a heating rate, and then pyrolyzed for 1 hour at this temperature.

2. 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 as follows: the drying is carried out in a vacuum drying oven for 24 hours at a temperature of 65°C.

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

4. A heteroatom-doped asymmetric coordination structure oxygen reduction catalyst prepared by the method according to any one of claims 1-3.

5. The application of the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst of claim 4 in battery cathode materials.

6. A working electrode, characterized in that, It includes the heteroatom-doped asymmetric coordination structure oxygen reduction catalyst as described in claim 4.

7. A method for preparing the working electrode according to claim 6, characterized in that, Includes the following steps: The heteroatom-doped asymmetric coordination structure oxygen reduction catalyst is dispersed in a mixed solvent of isopropanol and Nafion, and after sonication, a uniformly dispersed slurry is obtained. Then, the slurry is transferred with a pipette and uniformly coated on the surface of a glassy carbon electrode, and dried in air to obtain the working electrode.

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