Iron diatomic catalyst, its preparation method and application

Abstract

The application provides an iron diatomic catalyst and a preparation method and application thereof, and belongs to the technical field of zinc-air batteries, and aims to solve the technical problem of low oxygen electrocatalytic activity of a catalyst in a zinc-air battery. The iron diatomic catalyst with high loading capacity and high catalytic activity is prepared through a two-step anchoring strategy. In the first step, single Fe sites are first anchored on the surface of highly porous helical carbon spheres. The second step introduces dense and uniformly dispersed Fe atoms, which can greatly shorten the distance between adjacent atoms and promote the formation of iron diatomic pairs. The synthesized Fe-DAC exhibits excellent oxygen reduction electrochemical performance, has a good half-wave potential, fast reaction kinetics and good durability. In addition, the Fe-DAC also exhibits good performance in a zinc-air battery. Our research provides a foundation and practical insight for developing advanced DAC catalysts to simply and practically convert energy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of zinc-air batteries, and particularly relates to a Fe double-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] Single-atom catalysts (SACs) with nitrogen-coordinated metal centers have become a research hotspot in the field of catalysis, attracting widespread attention from academia and industry. SACs have 100% atom utilization efficiency, can effectively reduce the amount of metal used in the preparation of catalysts, and can provide independent active sites coordinated with adjacent non-metallic functional sites, ultimately achieving excellent catalytic performance. So far, SACs have shown good catalytic performance due to their unique atomic structure and have been proven to have good catalytic performance in photocatalysis, thermal catalysis and electrocatalysis.

[0003] However, due to the inherent electronic structure of M-N4 and the single active metal atom, SACs can usually catalyze single-molecule elementary reactions. For example, patent publication CN111384407A discloses a preparation method of metal single-atom dispersed ordered mesoporous carbon spheres, which uses histidine and dopamine hydrochloride as a nitrogen source and a carbon source, utilizes the chelation of histidine with metal, and through a simple microemulsion polymerization method and high-temperature calcination, atomically dispersed metal-loaded ordered mesoporous microspheres are prepared. However, two or more sites often need to be involved in the catalytic reaction of air batteries, and single-atom catalysts are not suitable for complex reactions involving multiple molecules and intermediates. To address this challenge, designing double-atom centers (DACs) with exposed atomic interfaces and optimized electronic structures has been proven to be an effective way to improve catalytic activity. The high efficiency of DACs depends largely on its structure, including the configuration, coordination state and morphology of the support. For DACs, the precise distance between the two metal sites and its stable atomic structure are the basis for the occurrence of atomic interactions in catalytic reactions. Therefore, it is of great significance to develop double-atom catalysts with high activity and high stability. SUMMARY

[0004] In order to solve the technical problem of low oxygen electrocatalytic activity of the catalyst in the zinc-air battery, the application provides a Fe double-atom catalyst and a preparation method and application thereof. The distance between the two iron atoms in the Fe double-atom catalyst is shortened, promoting mass transfer, and the synergistic effect of the Fe double-atom pair effectively improves the catalytic activity.

[0005] In order to achieve the above purpose, the technical scheme of the application is as follows:

[0006] A preparation method of a Fe double-atom catalyst, comprising the following steps:

[0007] S1: Dissolve the block copolymer P123, F127 and dopamine hydrochloride in a mixed solution of water and ethanol, and add 1,3,5-trimethylbenzene under strong stirring to obtain a white emulsion solution; then, add concentrated ammonia solution to the reaction mixture to obtain a carbon nanosphere precursor.

[0008] S2: Wash the carbon nanosphere precursor by centrifugation, and wash with ethanol and deionized water for at least 3 times, respectively; then, dry in a vacuum oven at 70°C; finally, perform calcination and carbonization to obtain mesoporous carbon nanospheres, which have a large specific surface area and a large highly curved continuous channel, and can expose more active sites.

[0009] S3: Dissolve iron salt and urea in a molar ratio of 1:5 in methanol to prepare iron salt solution I, and then introduce the obtained helical carbon nanospheres into the iron salt solution I, and the concentration of mesoporous carbon nanospheres in the iron salt solution is 1-2 mg mL -1 , the concentration of iron ions in the iron salt solution I is 1.5-3 mmol L -1 , the iron salt is ferric acetylacetonate, ferric chloride hexahydrate or ferric nitrate, and the mixture is reacted at room temperature for 4-6 h; the product is dried in a vacuum oven at 70°C overnight, and then carbonized in a tube furnace filled with Ar atmosphere at 700-900°C for 2-3 h, the heating rate is 3-5°C min -1 , to obtain a single-atom iron catalyst (Fe-SAC).

[0010] S4: Dissolve iron salt and melamine ligand in a molar ratio of 1:6 in methanol solution to prepare iron salt solution II, the concentration of iron ions in the iron salt solution II is 2.25-4.5 mmol L -1 , the iron salt is ferric acetylacetonate, ferric chloride hexahydrate or ferric nitrate, and a uniform solution is formed under vigorous stirring, and the stirring is continued for 30 min. Then, the single-atom iron catalyst synthesized in the above step is added to the solution, and the mixture is continuously reacted under magnetic stirring for 4-6 h, and the concentration of the single-atom iron catalyst in the iron salt solution is 1-2 mg mL -1 .

[0011] S5: The product obtained in step S4 is dried in a vacuum oven at 70°C. Finally, the sample is annealed in a tube furnace Ar atmosphere at 700-900°C for 2-3 h, and the heating rate during high-temperature calcination is 3-5°C min -1 , to obtain a double-atom iron catalyst (Fe-DAC) bridged by two nitrogen atoms.

[0012] Preferably, the mass ratio between the block copolymer P123, poloxamer F127 and dopamine hydrochloride in step S1 is in the range of 1:(1.5-3):(3-6), and the volume ratio of the mixed solution of water and ethanol is 1:1. The concentration of dopamine hydrochloride in the white emulsion solution is 10-20 mg / mL -1 ; After adding an equal volume of concentrated ammonia solution to the white emulsion solution, the reaction is continued at room temperature for 2-4 h, and the volume ratio of 1, 3, 5-trimethylbenzene to solvent ethanol is 1:(10-12.5).

[0013] Preferably, in step S2, the calcination is first preheated at 300-350°C for 2-3 h, and then further heated at 700-900°C under argon atmosphere for 2-3 h, with a heating rate of 3-5°C / min -1 .

[0014] Preferably, in step S3, the methanol mixed solution containing iron salt and urea is continuously stirred at room temperature for 30 min before adding the mesoporous carbon nanospheres.

[0015] The iron diatomic catalyst prepared by the above method has a diameter of 250-300 nm, a highly porous helical wall and a large continuous curved channel, and the coordination center has a Fe diatomic pair bridged by two N atoms.

[0016] The iron diatomic catalyst is coated on carbon cloth as a zinc-air battery cathode catalyst.

[0017] The beneficial effects of the present application are:

[0018] (1) The present application proposes a "two-step anchoring" strategy to prepare an iron diatomic catalyst (Fe-DAC) with high loading capacity and high catalytic activity; in the first step, a single Fe site is first anchored on the surface of a highly porous helical carbon sphere. The second step introduces densely and uniformly dispersed Fe atoms, which can greatly shorten the distance between adjacent atoms and promote the formation of iron diatomic pairs. Therefore, the distance between the two iron atoms in the Fe-DAC catalyst prepared by the present application is short (0.25-0.38 nm), which is beneficial to accelerate the mass transfer speed; the adjacent iron atoms produce a synergistic effect in the catalytic process, optimize the adsorption energy of the oxygen-containing intermediate, and reduce the energy barrier in the rate-determining step, thereby improving the oxygen electrocatalytic activity.

[0019] (2) The Fe-DAC diatomic catalyst prepared by the application has faster reaction kinetics, a half-wave potential of 0.882 V, and the smallest Tafel slope value (60 mV / dec). In the practical application of a disposable zinc-air battery, it exhibits excellent performance; the zinc-air battery with Fe-DAC as the cathode has a maximum power density of 169.78 mW cm -2 , which is much higher than the 98 mW cm -2 of the zinc-air battery with a cathode assembled by a Pt / C catalyst.

[0020] (3) The application provides a method for improving the catalytic performance by regulating the coordination environment of the active center metal atom and increasing the loading of the metal, which provides a new idea for developing high-activity diatomic catalysts. Meanwhile, the catalyst developed in the work has a wide application prospect in energy storage and conversion devices. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0022] Figure 1 It is a scanning electron microscope image of Fe-DAC.

[0023] Figure 2 It is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of Fe-DAC.

[0024] Figure 3 a is the Fourier transform of the extended X-ray absorption fine structure (EXAFS) of Fe-DAC and a control sample; Figure 3 b is the R-space fitting curve of Fe-DAC and the corresponding structure model.

[0025] Figure 4 It is the ORR linear cyclic voltammetry curve of the Fe-DAC oxygen reduction catalyst.

[0026] Figure 5 It is the Tafel slope curve of the Fe-DAC oxygen reduction catalyst.

[0027] Figure 6 It is the polarization discharge and power density curve of the Fe-DAC catalyst as a zinc-air battery cathode material. DETAILED DESCRIPTION

[0028] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0029] Embodiment 1

[0030] A diatomic iron catalyst, the preparation method comprising the following steps:

[0031] 1) 0.25 g P123, 0.75 g F127 and 1.5 g dopamine hydrochloride were dissolved in 100 mL of a 1:1 water and ethanol mixed solution, 4 mL of 1,3,5-trimethylbenzene was added under strong stirring to obtain a white emulsion solution. Subsequently, a 25% concentrated ammonia solution (4 mL) was added to the reaction mixture, and in other embodiments, the concentration of the concentrated ammonia solution can be 25-28%. After stirring at room temperature for 3 h, a carbon nanosphere precursor was obtained.

[0032] 2) The carbon nanosphere precursor was washed by centrifugation, and washed with ethanol and deionized water for 3 times respectively. Subsequently, drying was performed in a vacuum oven at 70°C. Calcination was performed in a high-temperature tube furnace, first preheating at 350°C for 2 h, and then further heating at 800°C under an argon atmosphere for 2 h, with a heating rate of 5°C / min -1 , to obtain mesoporous carbon nanospheres with spiral pore structure and large continuous channels.

[0033] 3) 53 mg of ferric trisacetylacetone and 45 mg of urea were dissolved in 100 mL of methanol, and after the reaction for 30 min, the obtained mesoporous carbon nanospheres (100 mg) were introduced into the above-mentioned system solution and continuously stirred for 5 h. The product was dried in a vacuum oven at 70°C overnight, and then carbonized in a tube furnace filled with Ar atmosphere at 800°C for 2 h, with a heating rate of 5°C / min -1 , to obtain a single-atomic iron catalyst (Fe-SAC).

[0034] 4) 80 mg of ferric trisacetylacetone and 170 mg of melamine ligand were dissolved in 100 mL of methanol solution, and under strong stirring, a uniform solution was formed, and the stirring was continued for 30 min. Then, the single-atomic iron catalyst (100 mg) synthesized in the above-mentioned step was added to the solution, and the mixture was continuously reacted for 5 h under magnetic stirring.

[0035] 5) The residual methanol was removed by a rotary evaporator, and the obtained product was dried in a vacuum oven at 70°C. Finally, the sample was annealed in a tube furnace Ar atmosphere at 800°C for 2 h, with a heating rate controlled at 5°C / min -1, to obtain a high loading of iron diatomic catalyst (Fe-DAC).

[0036] The prepared iron diatomic catalyst was scanned by electron microscopy, and the results are shown in Figure 1 From Figure 1 it can be seen that the Fe-DAC catalyst has highly porous helical walls and large continuous curved channels with a diameter of about 250-300 nm. Figure 2 is the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of Fe-DAC, from Figure 2 it can be seen that Fe exists in the form of single bright spots without agglomeration, and the distance between adjacent Fe atoms is short. In the EXAFS spectrum Figure 3 a), the Fe-DAC catalyst has a strong peak at , indicating that the main coordination structure of Fe is Fe-N bond; at the same time, a peak is observed at , which can be attributed to Fe-Fe coordination, indicating that Fe monomers are coordinated with Fe and N atoms, respectively. Figure 3 b is the R-space fitting curve of Fe-DAC and the corresponding structure model, indicating that the coordination center has a Fe diatomic pair bridged by two N atoms.

[0037] Example 2

[0038] An iron diatomic catalyst, the preparation method comprising the following steps:

[0039] 1) 0.66 g P123, 1.5 g F127 and 2 g dopamine hydrochloride were dissolved in 100 mL of a 1:1 mixture of water and ethanol solution, and 5 mL of 1,3,5-trimethylbenzene was added under vigorous stirring to obtain a white emulsion solution. Subsequently, concentrated ammonia solution (5 mL) was added to the reaction mixture, and after stirring at room temperature for 4 h, carbon nanosphere precursors were obtained.

[0040] 2) The carbon nanosphere precursors were washed by centrifugation, and washed with ethanol and deionized water for 3 times, respectively. Subsequently, drying was carried out in a vacuum oven at 70°C. Calcination in a high-temperature tube furnace, first preheating at 300°C for 2.5 h, then further heating at 700°C under argon atmosphere for 2.5 h, with a heating rate of 3°C min -1 , to obtain mesoporous carbon nanospheres with helical pore structure and large continuous channels.

[0041] 3) 81 mg of iron trichloride hexahydrate and 90 mg of urea were dissolved in 100 mL of methanol, after 30 min of reaction, the mesoporous carbon nanospheres (150 mg) obtained were introduced into the above system solution with continuous stirring for 4 h. The product was dried in a vacuum oven at 70 °C overnight, and then carbonized in a tube furnace filled with Ar atmosphere at 700 °C for 2.5 h with a heating rate of 3 °C / min -1 , to obtain a single-atom iron catalyst (Fe-SAC).

[0042] 4) 91.2 mg of iron trichloride hexahydrate and 255 mg of melamine ligand were dissolved in 100 mL of methanol solution, under vigorous stirring, a uniform solution was formed, and the stirring was continued for 30 min. Then the single-atom iron catalyst (150 mg) synthesized in the above step was added to the solution, and the mixture was continuously reacted for 4 h under magnetic stirring.

[0043] 5) The residual methanol was removed with a rotary evaporator, and the product was dried in a vacuum oven at 70 °C. Finally, the sample was annealed in a tube furnace Ar atmosphere at 700 °C for 2.5 h with a heating rate controlled at 3 °C / min -1 , to obtain a double-atom iron catalyst (Fe-DAC) with high loading.

[0044] Example 3

[0045] A double-atom iron catalyst, the preparation method comprising the following steps:

[0046] 1) 0.22 g of P123, 0.33 g of F127 and 1 g of dopamine hydrochloride were dissolved in 100 mL of a 1:1 mixture of water and ethanol solution, 4.5 mL of 1,3,5-trimethylbenzene was added under strong stirring to obtain a white emulsion solution. Subsequently, a concentrated ammonia solution (4.5 mL) was added to the reaction mixture, and after stirring at room temperature for 2 h, carbon nanosphere precursors were obtained.

[0047] 2) The carbon nanosphere precursors were washed by centrifugation, and washed with ethanol and deionized water for 3 times respectively. Subsequently, drying was performed in a vacuum oven at 70 °C. Calcination was performed in a high-temperature tube furnace, first preheated at 325 °C for 3 h, and then further heated at 900 °C under argon atmosphere for 3 h with a heating rate of 4 °C / min -1 , to obtain mesoporous carbon nanospheres with spiral pore structure and large continuous channels.

[0048] 3) 54.4 mg of iron nitrate and 67.6 mg of urea were dissolved in 100 mL of methanol, after 30 min of reaction, the mesoporous carbon nanospheres (200 mg) obtained were introduced into the above system solution with continuous stirring for 6 h. The product was dried in a vacuum oven at 70 °C overnight, and then carbonized in a tube furnace filled with Ar atmosphere at 900 °C for 3 h with a heating rate of 4 °C / min -1, to obtain the iron single-atom catalyst (Fe-SAC).

[0049] 4) 108.8 mg of iron nitrate and 340 mg of melamine ligand were dissolved in 100 mL of methanol solution, under vigorous stirring, a homogeneous solution was formed, and the stirring was continued for 30 min. Then, the iron single-atom catalyst (200 mg) synthesized in the above step was added to the solution, and the mixture was continuously reacted under magnetic stirring for 6 h.

[0050] 5) The residual methanol was removed by a rotary evaporator, and the obtained product was dried in a vacuum oven at 70 °C. Finally, the sample was annealed in an Ar atmosphere at 900 °C for 3 h, with a heating rate of 4 °C min -1 , to obtain the iron double-atom catalyst (Fe-DAC) with a high loading amount.

[0051] Comparative Example 1

[0052] Under the same conditions, an equal amount of metallic iron was loaded by using a one-step anchoring method to obtain the iron cluster (Fe-Cluster). The specific content is as follows:

[0053] 1) 0.25 g of P123, 0.75 g of F127 and 1.5 g of dopamine hydrochloride were dissolved in 100 mL of a 1:1 water and ethanol mixed solution, 4 mL of 1,3,5-trimethylbenzene was added under vigorous stirring to obtain a white emulsion solution. Subsequently, a concentrated ammonia solution (4 mL) was added to the reaction mixture to obtain a carbon nanosphere precursor.

[0054] 2) The carbon nanosphere precursor was washed by centrifugation, and was washed with ethanol and deionized water at least three times, respectively. Subsequently, it was dried in a vacuum oven at 70 °C. Calcination was carried out in a high-temperature tube furnace, first preheated at 350 °C for 2 h, and then further heated at 800 °C under an argon atmosphere for 2 h, with a heating rate of 5 °C min -1 , to obtain mesoporous carbon nanospheres with a spiral pore structure and large continuous channels.

[0055] 3) Catalysts were prepared using an equal amount of iron salt and ligand as in Example 1. 53 mg of iron trisacetylacetonate and 45 mg of urea were dissolved in 100 mL of methanol as solution A, and 80 mg of iron trisacetylacetonate and 170 mg of melamine ligand were dissolved in 100 mL of methanol solution as solution B. After solution A and solution B were fully mixed and reacted for 30 min, the above-obtained spiral carbon nanospheres (100 mg) were added and stirred for 5 h. The product was dried in a vacuum oven at 70 °C overnight, and finally carbonized in an 800 °C tube furnace filled with Ar atmosphere for 2 h, with a heating rate of 5 °C min -1 , to obtain Fe-Cluster.

[0056] Application Example

[0057] Example 1 prepared iron biatomic catalyst (Fe-DAC) coated on carbon cloth as zinc-air battery cathode catalyst, zinc-air battery was assembled. At the same time, the performance test was carried out on the iron monatomic catalyst (Fe-SAC) prepared in Example 1 as Comparative Example 2, the commercially available Pt / C catalyst as Comparative Example 3 and the iron cluster (Fe-Cluster) prepared in Comparative Example 1. The ORR test and oxygen reduction test results are shown in Figures 4-5 The prepared Fe-DAC has excellent catalytic activity for ORR, and the half-wave potential (0.882V) is higher than that of Fe-Cluster (0.806V), Fe-SAC (0.858V) and commercial Pt / C (0.843V). Fe-DAC shows faster reaction kinetics with the smallest Tafel slope value (60 mV / dec). The performance comparison of Fe-DAC, Fe-SAC prepared in Example 1 and Fe-Cluster synthesized in Comparative Example 1 is shown in Table 1. The Fe-DAC catalyst was used as a disposable zinc-air battery cathode material, and its polarization discharge test was carried out at room temperature Figure 6 The test results show that it has a larger power density of 169.78 mW cm -2 , which is much higher than that of the zinc-air battery assembled by the Pt / C catalyst (98 mW cm -2 ).

[0058] Table 1 Performance comparison of different samples

[0059]

[0060]

[0061] In summary, the "two-step anchoring" strategy proposed in the application effectively increases the loading of Fe atoms, shortens the atomic distance between adjacent Fe atoms, and promotes the formation of Fe atomic pairs. The iron biatomic pair produces a synergistic effect in the catalytic process, optimizes the adsorption energy of the oxygen-containing intermediate, and thus improves the ORR catalytic performance. In addition, the helical wall mesoporous carbon nanospheres as the support matrix have excellent mesoporous structure and highly curved helical structure, which undoubtedly helps to fully expose the metal active sites and fast mass transfer in the catalytic process. Thanks to these characteristics, the prepared Fe-DAC has excellent catalytic activity for ORR, and the half-wave potential (0.882V) is higher than that of commercial Pt / C (0.843V), and has faster reaction kinetics with a Tafel slope of 60 mV / dec. The zinc-air battery assembled with Fe-DAC as the air cathode shows a maximum power density of 169.78 mW cm -2 , which is much higher than that of the zinc-air battery assembled by the Pt / C catalyst (98 mW cm -2), which indicates that the catalyst has good potential in practical application. The application prepares a diatomic catalyst with high loading by adopting a two-step doping strategy to regulate the coordination environment and electronic structure of the active metal center, and the synergistic effect between adjacent iron diatoms can effectively improve the catalytic performance. This strategy can be popularized to other metal catalytic systems, and provides a new way for accurately designing and constructing atomically dispersed single metal / dual metal center catalysts.

[0062] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an iron diatomic catalyst, characterized in that, Includes the following steps: S1: Mesoporous carbon nanospheres were added to iron salt solution I for reaction. After the reaction was completed, the product was calcined to obtain an iron single-atom catalyst. S2: Add the iron single-atom catalyst to iron salt solution II for reaction. After the reaction is completed, calcine the product to obtain an iron diatom catalyst with two nitrogen atoms bridging it. The iron salt solution I in S1 is prepared by dissolving iron salt and urea in methanol in a molar ratio of 1:

5. The iron salt is ferric triacetylacetone, ferric chloride hexahydrate, or ferric nitrate. The iron salt solution II in S2 is prepared by dissolving iron salt and melamine in methanol at a molar ratio of 1:

6. The iron salt is iron triacetylacetone, ferric chloride hexahydrate, or ferric nitrate.

2. The method for preparing the iron diatomic catalyst according to claim 1, characterized in that, The method for preparing the mesoporous carbon nanospheres includes the following steps: (1) Block copolymer P123, poloxamer F127 and dopamine hydrochloride were dissolved in a solvent, and then 1,3,5-trimethylbenzene was added to obtain a white emulsion; concentrated ammonia solution was added to the white emulsion solution and the reaction was continued until complete to obtain carbon nanosphere precursor; (2) The carbon nanosphere precursor is calcined and carbonized to obtain mesoporous carbon nanospheres.

3. The method for preparing the iron diatomic catalyst according to claim 2, characterized in that, In step (1), the mass ratio of block copolymer P123, poloxamer F127, and dopamine hydrochloride is 1:(1.5-3):(3-6), the solvent is water and ethanol in a volume ratio of 1:1, and the concentration of dopamine hydrochloride in the white emulsion is 10-20 mg / mL. -1 The volume ratio of 1,3,5-trimethylbenzene to concentrated ammonia solution is 1:1, and the volume ratio of 1,3,5-trimethylbenzene to ethanol in the solvent is 1:(10-12.5).

4. The method for preparing the iron diatomic catalyst according to claim 2, characterized in that, In step (2), the calcination and carbonization process involves preheating at 300-350 °C for 2-3 hours, followed by further heating at 700-900 °C in an argon atmosphere for 2-3 hours, with a heating rate of 3-5 °C / min. -1 .

5. The method for preparing the iron diatomic catalyst according to any one of claims 1-4, characterized in that, The iron ion concentration in the iron salt solution I is 1.5-3 mmol / L. -1 The reaction conditions were: 4-6 h at room temperature, with the concentration of mesoporous carbon nanospheres in the iron salt solution being 1-2 mg / mL. -1 .

6. The method for preparing the iron diatomic catalyst according to claim 5, characterized in that, The iron ion concentration in the iron salt solution II was 2.25-4.5 mmol / L. -1 The reaction conditions were: reaction at room temperature for 4-6 h; and the concentration of the iron single-atom catalyst in the iron salt solution was 1-2 mg / mL. -1 .

7. The method for preparing the iron diatomic catalyst according to claim 6, characterized in that, In step S1, the calcination atmosphere is argon, the calcination temperature is 700-900 ℃, and the heating rate is 3-5 ℃ min. -1 The calcination time is 2-3 hours.

8. The method for preparing the iron diatomic catalyst according to claim 7, characterized in that, In step S2, the calcination atmosphere is argon, the calcination temperature is 700-900 ℃, and the heating rate is 3-5 ℃ min. -1 The calcination time is 2-3 hours.

9. The iron diatomic catalyst prepared by the method according to any one of claims 1-4 and 6-8, characterized in that, The iron diatomic catalyst has a diameter of 250~300 nm, with highly porous spiral walls and large continuous tortuous channels. The coordination center has two Fe diatomic pairs formed by two N atoms bridging each other.

10. The application of the iron diatomic catalyst of claim 9 in the preparation of high-power-density zinc-air batteries.

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