A transition metal diatomic catalyst, preparation method and application thereof

Abstract

The present invention relates to a transition metal dual-atom catalyst, a preparation method thereof and an application thereof, belonging to the technical field of electrocatalytic technology. The catalyst uses nitrogen-doped carbon as a carrier, and transition metals M1 and M2 form a bimetallic site. M1 and M2 are any two of manganese, iron, cobalt, nickel, copper and zinc. The configuration of the metal dual-atom site is M1M2N5O. M1 and M2 are coordinated with 5 nitrogen atoms in the plane direction, and 2 of the nitrogen atoms are shared by M1 and M2. A metal bond is formed between M1 and M2, and M1 or M2 is coordinated with 1 oxygen atom. It is prepared by one-step pyrolysis of impregnating dual-ligand MOFs in a solvent containing two active metals. The catalyst is used as an ORR catalyst and can exhibit excellent electrochemical performance and stability.

Description

Technical Field

[0001] The invention relates to a transition metal diatomic catalyst, a preparation method and application thereof, and belongs to the technical field of electrochemical catalysis. Background Art

[0002] Oxygen reduction reaction (ORR) is the core reaction of important sustainable energy storage and conversion technologies such as metal-air batteries and fuel cells, and determines the performance of the above batteries. However, ORR involves multi-step electron and proton coupling reactions, and the slow kinetic process is difficult to meet application requirements, so catalysts are needed to accelerate the reaction.

[0003] At present, commercial ORR catalysts are mainly precious metal-based catalysts, such as platinum group (PGM) catalysts with high catalytic activity. However, precious metal reserves are scarce, costly, and have poor performance, making them difficult to apply on a large scale. Therefore, it is urgent to use transition metals, which are more abundant in resources and cheaper in price, as raw materials to develop transition metal-based ORR catalysts.

[0004] In recent years, atomic-level transition metal catalysts have been recognized as one of the most promising ORR catalysts due to their unique electronic structure of active sites, ultra-high atomic utilization and strong site-substrate interactions, and are expected to replace PGM catalysts.

[0005] At present, the most effective way to improve the activity of atomic-level catalysts is to optimize the electronic structure of the site by regulating the site coordination environment. Among them, the construction of diatomic catalysts, the use of the coordination unsaturation of the bimetallic sites, and the coordinated regulation of the conversion behavior of the reaction intermediates to accelerate the catalytic process are the current research focuses. However, the controllable preparation of diatomic catalysts still faces great challenges, and the reported diatomic catalysts have a single configuration, which is not conducive to further improvement of catalytic performance. As reported in the literature Angew.Chem.Int.Ed.2019,58,6972–6976., the diatomic catalyst obtained by pyrolysis of ZIF-8 loaded with Fe and Ni contains a large number of Ni single-atom sites in addition to FeNi diatomic sites. Summary of the invention

[0006] In view of this, an object of the present invention is to provide a transition metal diatomic catalyst, a preparation method and application thereof.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A transition metal diatomic catalyst, wherein the catalyst uses nitrogen-doped carbon as a carrier, transition metals M1 and M2 form a dimetallic site, M1 and M2 are any two of manganese, iron, cobalt, nickel, copper and zinc, the configuration of the metal diatomic site is M1M2N5O, M1 and M2 are coordinated with five nitrogen atoms in a planar direction, two of which are shared by M1 and M2, a metallic bond is formed between M1 and M2, and M1 or M2 is coordinated with one oxygen atom.

[0009] Preferably, the total metal content of the diatomic catalyst is 0.1 to 5.0 wt% of the total mass of the catalyst; the specific surface area of ​​the diatomic catalyst is 600 to 800 m 2 More preferably, the total metal content of the diatomic catalyst is 0.5-2 wt%.

[0010] A method for preparing the transition metal diatomic catalyst of the present invention, the method steps comprising:

[0011] (1) adding M1 salt and M2 salt into organic solvent 1 and completely dissolving them to obtain a mixed solution A;

[0012] (2) adding a dual-ligand metal organic framework (dual-ligand MOFs) into an organic solvent 2, mixing and dispersing the mixture uniformly to obtain a mixture B; wherein the organic solvent 1 and the organic solvent 2 are miscible;

[0013] (3) Pour the mixed solution A into the mixture B under stirring and soak for more than 24 hours;

[0014] (4) After the impregnation is completed, the solid and liquid are separated, the solid is collected, washed, and vacuum dried to obtain a catalyst precursor;

[0015] (5) placing the catalyst precursor in a tubular furnace, raising the temperature to 900-1000° C. for high-temperature pyrolysis for 2-4 hours under a protective gas purge, and obtaining a transition metal diatomic catalyst after the pyrolysis is completed.

[0016] Preferably, the M1 salt is a chloride and / or nitrate of M1; and the M2 salt is a chloride and / or nitrate of M2.

[0017] Preferably, the organic solvent 1 is one or more of methanol, ethanol and N,N-dimethylformamide; the organic solvent 2 is one or more of methanol, ethanol and N,N-dimethylformamide.

[0018] Preferably, the dual-ligand MOFs are one or more of IISERP-MOF27, ZnBDCA and JXNU-4.

[0019] Preferably, the mass ratio of the M1 salt, the M2 salt and the metal organic framework is 1:1-2:50-60.

[0020] Preferably, the total molar concentration of the metal salt in the mixed solution A is 0.1 to 0.3 mmol / mL.

[0021] Preferably, the molar concentration of the dual-ligand MOFs in the mixture B is 0.1 to 0.3 mmol / mL.

[0022] Preferably, the vacuum drying pressure is less than or equal to -0.1 MPa, the temperature is 100 to 120° C., and the time is 12 to 18 hours.

[0023] Preferably, the protective gas is nitrogen or an inert gas, and the purge flow rate is 100-200 sccm.

[0024] Preferably, the heating rate of pyrolysis is 5 to 10°C / min.

[0025] An application of the transition metal diatomic catalyst of the present invention, wherein the catalyst is used as an ORR catalyst.

[0026] Beneficial Effects

[0027] (1) The present invention provides a transition metal diatomic catalyst, which is a MOF-derived carbon skeleton material with a dimetallic heteronuclear site. The two metal active sites in the material are covalently bonded, which can give full play to the synergistic effect of the two heteronuclear atoms. The orbital coupling between the two metal atoms induces interaction between internal electrons, making the ORR activity of the material much higher than that of MOF-derived materials with a single component metal.

[0028] (2) The present invention provides a method for preparing a transition metal diatomic catalyst, the core of which is a bi-ligand MOF-derived heteronuclear diatomic ORR catalyst. Through a simple and scalable impregnation strategy, the bi-ligand MOFs are impregnated in a solvent containing two active metals, and a heteronuclear diatomic carbon skeleton material can be prepared by a one-step pyrolysis.

[0029] In the above method, the dual-ligand MOF material has a rich and regular pore structure, which can accelerate the mass transfer process. At the same time, the pores have abundant coordination unsaturated sites (such as amino, carboxyl and pyridinic nitrogen), which can anchor a large number of active metal precursors (such as Fe 3+ and Cu 2+ ), achieving large-scale and stable coordination of metal active centers.

[0030] In the above method, in addition to utilizing the porous and site unsaturated characteristics of MOF, the dual ligands used make MOF also have compositional diversity, such as O-containing ligands (terephthalic acid and 2,3,5,6-tetrafluoroterephthalic acid, etc.) and N-ligands (such as adenine, imidazole, etc.). ORR catalysts derived from dual-ligand MOFs inherit their own compositional diversity, giving the catalyst configuration diversity and novelty, which is different from the zeolitic imidazolate frameworks (ZIFs) that have been reported so far, which are limited to the N element, and drive the diversified development of atomic-level catalysts.

[0031] In the above method, the MOF pores are exposed to abundant functional groups (amino and carboxyl groups, etc.) and metal ions (Fe 3+ and Cu 2+ This interaction enables the high dispersion of metal active centers in the catalyst, thereby realizing the preparation of atomic-level catalysts.

[0032] (3) The present invention provides an application of a transition metal diatomic catalyst, which is used as an ORR catalyst and can exert excellent electrochemical performance and stability, and has good application potential. Specifically, it can be used as a cathode material for a metal-air battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the spherical aberration correction-high-angle annular dark field scanning transmission electron microscope image of Comparative Example 1.

[0034] Figure 2 This is the spherical aberration correction-high-angle annular dark field scanning transmission electron microscope image of comparative example 2.

[0035] Figure 3 This is the spherical aberration correction-high-angle annular dark field scanning transmission electron microscope image of Example 1.

[0036] Figure 4 The specific surface area test results of Examples 1 to 3 are shown.

[0037] Figure 5 The detailed spectra of Fe 2p, Cu 2p and O1s in X-ray photoelectron spectra of Comparative Examples 1-2 and Example 1 are shown in FIG.

[0038] Figure 6 It is the chemical coordination environment diagram of Fe and Cu in the X-ray photoelectron spectra of Comparative Examples 1-2 and Example 1.

[0039] Figure 7 It is the K-space Fourier transform spectrum of the X-ray absorption fine structure spectrum of Fe K-edge and Cu K-edge of Comparative Examples 1-2 and Example 1.

[0040] Figure 8 2 are the ORR polarization current curves of Comparative Examples 1 to 2 and Example 1.

[0041] Fig. 9 The following are the test results of the discharge performance of zinc-air batteries using Example 1.

[0042] Fig.10 The following are the test results of the charge-discharge performance of zinc-air batteries using Example 1.

[0043] Fig.11 It is a schematic diagram of the structure of the catalyst of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with specific embodiments.

[0045] In the following comparative examples and embodiments:

[0046] (1) Spherical aberration correction - high-angle annular dark-field scanning transmission electron microscope: Titan 80-300 scanning / projection electron microscope.

[0047] (2) Inductively coupled plasma optical emission spectrometer: Shimadzu ICPE-9800 (OES), Japan.

[0048] (3) X-ray photoelectron spectroscopy test: Thermo Scientific K-Alpha.

[0049] (4) X-ray absorption fine structure spectrum test: Beijing Synchrotron Radiation Center 1W1B workstation.

[0050] (5) Specific surface area test: Kubo-X1000 Kubo adsorption analyzer, Beijing Biode Electronics.

[0051] (6) The ORR polarization current curves of Comparative Examples 1 to 3, Example 1 and commercially available Pt / C catalysts were tested by the Shanghai Chenhua electrochemical workstation to evaluate the ORR performance of each catalyst. The specific test conditions are as follows: the electrolyte is 0.1 mol / L potassium hydroxide solution, the working electrode is a rotating ring disk electrode, the Ag / AgCl electrode is a reference electrode, and the graphite rod is a counter electrode. The catalysts were respectively prepared into electrode slurries, and the slurry preparation method was as follows: 2.5 mg of the catalyst was dispersed in a mixed solution of ethanol, isopropanol and 5 wt% Nafion solution (DuPont) with a volume ratio of 1:2:0.06, so that the mass concentration of the catalyst in the slurry was 12.5 mg / mL. Then 10 μL of the slurry was measured and dripped on the surface of the disk electrode (the disk electrode area was 0.19625 cm 2). After the slurry is naturally dried to form a film, the working electrode is prepared. The rotating ring disk electrode, Ag / AgCl electrode and graphite rod are placed in an electrolyte saturated with oxygen for electrochemical activation. The specific parameters are set as follows: the rotating ring disk electrode speed is set to 1600rpm, and the electrochemical workstation parameters are: cyclic voltammetry, scanning speed 100mV / s, scanning voltage range 0.2~-1V (equivalent to 1.151~-0.049V vs RHE). When the signals of the first and last two consecutive scans do not change, the electrochemical activation process is considered to be completed. The parameters of the electrochemical workstation are adjusted to linear voltammetry scanning method, scanning speed 50mV / s, scanning voltage range 0.2~-1V (equivalent to 1.151~-0.049V vs RHE), and the ORR polarization current curve test is carried out.

[0052] (7) Preparation of zinc-air battery: Example 1 and commercially available Pt / C catalyst were respectively prepared as cathodes of zinc-air batteries. The anode of the zinc-air battery was a clean zinc sheet (0.5 mm thick), the electrolyte was a mixed solution of 6 mol / L potassium hydroxide and 0.2 mol / L zinc acetate, and the cathode was a gas diffusion electrode (model YLS30T) coated with a catalyst. The preparation method of the cathode was as follows: 5 mg of Example 1 or commercially available Pt / C catalyst was weighed, ultrasonically dispersed in a mixed solution prepared by 950 μL of 50% ethanol solution and 50 μL of 5 wt% Nafion solution to prepare an electrode slurry. The electrode slurry was dripped on the hydrophilic surface of the gas diffusion electrode, and after natural drying to form a film, the cathode preparation was completed.

[0053] (8) Discharge performance test of zinc-air batteries: At room temperature, the discharge polarization current curves of the two zinc-air batteries were tested by an electrochemical workstation. The test parameters were: linear voltammetry, scan rate 5 mV / s, scan voltage range 1.47 ~ 0.2 V (vs Zn).

[0054] (9) Charge-discharge stability test of zinc-air batteries: At room temperature, the charge-discharge curves of two zinc-air batteries were tested using a blue battery test system. The test parameters were: charge-discharge current density 5 mA / cm 2 .

[0055] Comparative Example 1

[0056] A method for preparing a single-atom catalyst Fe-S comprises the following steps:

[0057] Step 1: Measure 5 mL of ethanol in two 20 mL glass containers respectively;

[0058] Step 2: Add 8.6 mg of ferric nitrate nonahydrate into one of the glass containers and stir at 500 rpm for 30 min to completely dissolve it, to obtain solution A;

[0059] Step 3: 0.25 g of IISERP-MOF27 was added to another glass container, and after ultrasonication for 30 min, it was stirred at 500 rpm for 30 min to disperse it into a turbid liquid to obtain a mixture B;

[0060] Step 4: Pour solution A into mixture B under stirring at 500 rpm, and stir at 500 rpm for 48 h to load Fe;

[0061] Step 5: After loading, the solid part was collected by filtration, washed with 20 mL of ethanol, and dried at 120 °C for 16 h under -0.1 MPa vacuum to obtain a catalyst precursor;

[0062] Step 6: Place the above catalyst precursor in a tubular furnace and perform high-temperature pyrolysis on the precursor under a N2 purge with a flow rate of 100 ccm. The pyrolysis heating rate is 5°C / min, the pyrolysis temperature is 900°C, and the pyrolysis time is 3 hours. A single atom catalyst is obtained, which is recorded as Fe-S.

[0063] Comparative Example 2

[0064] A method for preparing a single-atom catalyst Cu-S comprises the following steps:

[0065] Step 1: Measure 5 mL of ethanol in two 20 mL glass containers respectively;

[0066] Step 2: Add 14 mg of copper nitrate trihydrate into one of the glass containers and stir at 500 rpm for 30 min to completely dissolve it to obtain solution A;

[0067] Step 3: 0.25 g of IISERP-MOF27 was added to another glass container, and after ultrasonication for 30 min, it was stirred at 500 rpm for 30 min to disperse it into a turbid liquid to obtain a mixture B;

[0068] Step 4: Pour solution A into mixture B under stirring at 500 rpm and stir for 48 h to load Cu;

[0069] Step 5: After loading, the solid was collected by filtration, washed with 20 mL of ethanol, and dried at 120 °C for 16 h under -0.1 MPa vacuum to obtain a catalyst precursor;

[0070] Step 6: Place the above catalyst precursor in a tubular furnace and perform high-temperature pyrolysis on the precursor under a N2 purge with a flow rate of 100 ccm. The pyrolysis heating rate is 5°C / min, the pyrolysis temperature is 900°C, and the pyrolysis time is 3 hours. A single atom catalyst is obtained, which is recorded as Cu-S.

[0071] Comparative Example 3

[0072] A method for preparing a nitrogen-doped graphite catalyst comprises the following steps:

[0073] Step 1: Measure 10 mL of ethanol in a 20 mL glass container;

[0074] Step 2: 0.25 g of IISERP-MOF27 was added into a glass container, ultrasonicated for 30 min, and then stirred at 500 rpm for 48 h to disperse into a turbid liquid;

[0075] Step 3: Collect the solid by filtration, rinse with 20 mL of ethanol, and dry at 120 °C under -0.1 MPa vacuum for 16 h;

[0076] Step 4: Place the dried solid in a tubular furnace and perform high-temperature pyrolysis on the precursor under a N2 purge with a flow rate of 100 ccm. The pyrolysis heating rate is 5°C / min, the pyrolysis temperature is 900°C, and the pyrolysis time is 3 hours. The obtained nitrogen-doped graphite catalyst is recorded as NC.

[0077] Example 1

[0078] A method for preparing a transition metal diatomic catalyst FeCu-D comprises the following steps:

[0079] Step 1: Measure 5 mL of ethanol in two 20 mL glass containers respectively;

[0080] Step 2: 4.3 mg of ferric nitrate nonahydrate and 7 mg of copper nitrate trihydrate were added into one of the glass containers in sequence, and stirred at 500 rpm for 30 min to completely dissolve them, to obtain a mixed solution A;

[0081] Step 3: 0.25 g of IISERP-MOF27 was added to another glass container, and ultrasonicated for 30 min at 500 rpm and then stirred for 30 min to disperse it into a turbid liquid to obtain mixture B;

[0082] Step 4: Pour mixture A into mixture B under stirring at 500 rpm and stir for 48 h to load Fe and Cu;

[0083] Step 5: After loading, the solid part is collected by filtration, washed with 20 mL of ethanol, and dried at 120° C. under a vacuum of -0.1 MPa to obtain a catalyst precursor;

[0084] Step 6: Place the above catalyst precursor in a tubular furnace and perform high-temperature pyrolysis on the precursor under a N2 purge with a flow rate of 100 ccm. The pyrolysis heating rate is 5°C / min, the pyrolysis temperature is 900°C, and the pyrolysis time is 3 hours. A transition metal diatomic catalyst is obtained, which is denoted as FeCu-D.

[0085] Example 2

[0086] In this embodiment, the pyrolysis temperature of step (6) is 950° C., and the remaining operations are the same as those in Example 1.

[0087] Example 3

[0088] In this embodiment, the pyrolysis temperature of step (6) is 1000° C., and the remaining operations are the same as those in Example 1.

[0089] The catalysts described in the comparative examples and the examples were tested as follows:

[0090] (1) The atomic-level morphologies of Comparative Example 1, Comparative Example 2, and Example 1 were observed using a spherical aberration-corrected high-angle annular dark field scanning transmission electron microscope. The results are as follows: Figure 1-3 shown. Figure 1-2 A single white bright spot can be observed in Comparative Examples 1 and 2, indicating that there are dispersed Fe single atom sites and Cu single atom sites. Figure 3 In Example 1, pairs of white bright spots appear, with a spacing of about This distance is close to the bond length of the Fe-Cu bond, indicating that there are Fe and Cu bimetallic sites dispersed in Example 1.

[0091] (2) The metal contents in Example 1 and Comparative Examples 1-2 were measured by inductively coupled plasma emission spectrometry, and the results are shown in Table 1. Table 1 shows that Example 1 and Comparative Examples 1-2 contain similar total metal contents.

[0092] Table 1

[0093] Sample name Fe(wt%) Cu(wt%) Comparative Example 1 0.42 - Comparative Example 2 - 0.43 Example 1 0.36 0.23

[0094] (3) The specific surface areas of Examples 1 to 3 were tested using a physical adsorption instrument. The results are as follows Figure 4 Example 1 shows a higher specific surface area, with a value of 804 m 2 / g, and the rich pore structure accelerates the ORR mass transfer process.

[0095] (4) The valence states of Fe and Cu in Example 1 and Comparative Examples 1-2 were characterized by X-ray photoelectron spectroscopy (XPS). The results are as follows: Figure 5 shown. Figure 5It shows that the valence state of Fe in Example 1 is between +2 and +3, and the valence state of Cu is between +1 and +2. At the same time, the binding energy of Fe and Cu is shifted relative to Comparative Example 1 and Comparative Example 2, indicating that there is electron transfer between Fe and Cu in Example 1.

[0096] (5) Furthermore, the chemical coordination environments of Fe and Cu in Example 1 and Comparative Examples 1-2 were tested by XPS. The results are as follows: Figure 6 As shown. From the XPS spectrum of N1s, it can be seen that Example 1 and Comparative Examples 1 to 2 contain Fe-N chemical bonds and Cu-N chemical bonds. From the XPS spectrum of O1s, it can be seen that Example 1 and Comparative Example 1 contain Fe-O chemical bonds.

[0097] (6) The coordination configuration of the metal center of Example 1 and Comparative Examples 1-2 was further characterized by X-ray absorption fine structure spectroscopy. The K-space spectrum of the extended X-ray near-edge absorption structure obtained by Fourier transformation using Athena software is shown in FIG. Figure 7 As shown in Table 2. Figure 7 As shown in Table 2, the coordination configuration of Fe in Comparative Example 1 is Fe-N3O. The coordination configuration of Cu in Comparative Example 2 is Cu-N4. The coordination configuration of Fe and Cu in Example 1 is FeN3O-CuN4. Specifically, the bond length of the Fe-Cu metal bond is Consistent with the spherical aberration-corrected high-angle annular dark field scanning transmission electron microscopy results in test (1), it was successfully demonstrated that Example 1 is a heteronuclear bimetallic catalyst with a FeN3O-CuN4 configuration.

[0098] Table 2 Extended X-ray near-edge absorption structure fitting results of Example 1 and Comparative Examples 1-2

[0099]

[0100] According to the results of tests (1) to (6), it can be confirmed that the configuration of the prepared heteronuclear bimetal is FeN3O-CuN4; Fe and Cu are coordinated with 5 nitrogen atoms in the plane direction, 2 of which are shared by Fe and Cu; a metallic bond is formed between Fe and Cu; Fe is coordinated with 1 oxygen atom, and its structure is as follows Fig.11 In addition, the results of Example 2 and Example 3 are similar to those of Example 1.

[0101] (7) The linear voltammetric curves of the catalyst measured in an oxygen-saturated electrolyte and in a nitrogen-saturated KOH electrolyte are the ORR polarization current curves of the catalyst. The test results are shown in Figure 8 .according to Figure 8It can be seen that the potential values ​​(half-wave potential values) of Comparative Examples 1 to 3 at half the limiting current density value are significantly lower than those of commercially available Pt / C catalysts. The half-wave potential values ​​of Examples 1 to 3 are all higher than those of commercially available Pt / C catalysts, indicating that the catalysts described in the Examples have excellent ORR catalytic performance.

[0102] (8) The discharge polarization current curve of the zinc-air battery assembled with the catalyst described in Example 1 and the commercially available Pt / C catalyst is as follows: Fig. 9 As shown in Figure 2, the maximum power density of a zinc-air battery using a commercially available Pt / C catalyst as the cathode is 121 mW / cm 2 , and the maximum power density of the zinc-air battery using Example 1 as the cathode is as high as 199.7 mW / cm 2 , indicating that Example 1 has excellent zinc-air battery performance.

[0103] (9) The charge-discharge stability test results of the zinc-air battery assembled with the catalyst described in Example 1 and the commercially available Pt / C catalyst are as follows: Fig.10 As shown, the zinc-air battery using the commercially available Pt / C catalyst and the commercially available RuO2 catalyst as the cathode has an irreversible decrease in discharge potential after several hours of charge and discharge cycles, while the zinc-air battery using Example 1 and the commercially available RuO2 catalyst as the cathode has no significant decrease in discharge potential after 400 hours of charge and discharge cycles, indicating that the zinc-air battery using Example 1 and the commercially available RuO2 catalyst as the cathode has good charge-discharge stability, and Example 1 is very promising for use as a cathode material for zinc-air batteries.

[0104] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A transition metal diatomic catalyst, characterized in that: The catalyst uses nitrogen-doped carbon as a carrier, transition metals M1 and M2 form a bimetallic site, M1 and M2 are any two of manganese, iron, cobalt, nickel, copper and zinc, the configuration of the metal diatomic site is M1M2N5O, M1 and M2 are coordinated with 5 nitrogen atoms in the planar direction, 2 nitrogen atoms are shared by M1 and M2, a metallic bond is formed between M1 and M2, and M1 or M2 is coordinated with 1 oxygen atom.

2. A transition metal diatomic catalyst as claimed in claim 1, characterized in that: The total metal content of the diatomic catalyst is 0.1-5.0 wt% of the total mass of the catalyst; the specific surface area of ​​the diatomic catalyst is 600-800 m 2 / g.

3. A transition metal diatomic catalyst as claimed in claim 2, characterized in that The total metal content of the diatomic catalyst is 0.5-2 wt %.

4. A method for preparing a transition metal diatomic catalyst as claimed in any one of claims 1 to 3, characterized in that: The method steps include: (1) adding M1 salt and M2 salt into organic solvent 1 and completely dissolving them to obtain a mixed solution A; (2) adding the dual-ligand MOFs to the organic solvent 2, mixing and dispersing them uniformly, and obtaining a mixture B; wherein the organic solvent 1 and the organic solvent 2 are miscible; (3) Pour the mixed solution A into the mixture B under stirring and soak for more than 24 hours; (4) After the impregnation is completed, the solid and liquid are separated, the solid is collected, washed, and vacuum dried to obtain a catalyst precursor; (5) placing the catalyst precursor in a tubular furnace, raising the temperature to 900-1000° C. for high-temperature pyrolysis for 2-4 hours under a protective gas purge, and obtaining a transition metal diatomic catalyst after the pyrolysis is completed.

5. The method for preparing a transition metal diatomic catalyst according to claim 4, characterized in that: The M1 salt is a chloride and / or nitrate of M1; the M2 salt is a chloride and / or nitrate of M2; The organic solvent 1 is one or more of methanol, ethanol and N,N-dimethylformamide; the organic solvent 2 is one or more of methanol, ethanol and N,N-dimethylformamide; The dual-ligand MOFs are one or more of IISERP-MOF27, ZnBDCA and JXNU-4.

6. The method for preparing a transition metal diatomic catalyst according to claim 5, characterized in that: The mass ratio of the M1 salt, the M2 salt and the metal organic framework is 1:1-2:50-60; The total molar concentration of the metal salt in the mixed solution A is 0.1 to 0.3 mmol / mL; The molar concentration of the dual-ligand MOFs in the mixture B is 0.1-0.3 mmol / mL.

7. The method for preparing a transition metal diatomic catalyst according to claim 4, characterized in that: The vacuum drying pressure is less than or equal to -0.1MPa, the temperature is 100-120°C, and the time is 12-18h.

8. The method for preparing a transition metal diatomic catalyst according to claim 4, characterized in that: The protective gas is nitrogen or an inert gas, and the purge flow rate is 100-200 sccm.

9. The method for preparing a transition metal diatomic catalyst according to claim 4, characterized in that: The heating rate of pyrolysis is 5-10°C / min.

10. Use of the transition metal diatomic catalyst according to any one of claims 1 to 3, characterized in that: The catalyst acts as an ORR catalyst.

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