A method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst and its application.

Abstract

This invention discloses a method for preparing LDH-induced M@N-CNT bifunctional electrocatalysts. Two-dimensional ultrathin LDH nanosheets are prepared using a co-precipitation method and a liquid-phase exfoliation method. By changing the types and ratios of metal ions, the types of metal ions and the structure of the layers are adjusted. An LDH-ZIF-8 composite material is synthesized via in-situ growth and further subjected to high-temperature pyrolysis. LDH is used as a sacrificial template to catalyze the growth of the M@N-CNT bifunctional catalyst. By optimizing the synthesis conditions, the obtained M@N-CNT bifunctional electrocatalyst is rich in high-density ORR / OER bifunctional catalytic active sites. This catalyst exhibits a hierarchical porous structure with a high specific surface area, achieving ORR / OER catalytic activity comparable to commercial noble metal catalysts Pt / C and IrO2, and possesses good cycle stability, resulting in higher power density and cycle life for zinc-air batteries.

Description

Technical Field

[0001] This invention relates to the field of zinc-air battery catalyst technology, specifically to a method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst and its application. Background Technology

[0002] Rechargeable metal-air batteries have attracted widespread attention due to their advantages such as low cost, environmental friendliness, and high safety performance. Among them, rechargeable zinc-air batteries are considered the most promising next-generation new energy battery due to their high specific energy density, with a theoretical energy density of 1086 kWh / kg. -1 It is 2 to 5 times that of current lithium-ion battery technology.

[0003] Generally, the catalyst layer in a zinc-air battery largely determines the performance of the entire battery system. Developing highly efficient ORR / OER bifunctional catalysts to address the slow kinetics of oxygen in the oxygen reduction and oxygen evolution reactions, thereby improving charge-discharge efficiency and reducing energy loss, plays a crucial role in advancing the commercialization of zinc-air batteries. In addition, efforts are being made to find non-precious metal catalytic materials to reduce the cost of zinc-air battery catalysts.

[0004] Significant progress has been made in bifunctional non-precious metal catalysts, including transition metal compound materials (oxides, chalcogenides, nitrides, and carbides), heteroatom-doped carbon nanomaterials, and composite materials composed of both. However, the mechanisms and reaction kinetics of ORR and OER differ among different catalyst materials and electrolytes. Therefore, the catalytic mechanisms of bifunctional non-precious metal catalysts remain unclear, and their stability still falls short of requirements, greatly limiting the cycle life of zinc-air batteries.

[0005] Layered double hydroxides (LDHs) are a class of anionic clay minerals with a structure similar to brucite, formed by the overlapping of a main layer of metal hydroxide composed of two or more metal elements and anions and water molecules between the layers. Due to their low cost, simple synthesis methods, ease of modification of composition (types and ratios of metal ions on the layers, types of anions, etc.), ease of tailoring of structure (number of layers, interlayer spacing, etc.), and ease of functionalization through combination with other materials, LDHs show promising application prospects in secondary batteries and electrocatalysis. LDHs possess excellent OER performance, but lack high-performance ORR active sites and have poor conductivity.

[0006] Zeolitic imidazolate frameworks (ZIFs) are a class of metal-organic framework materials with zeolite framework structures. ZIF-derived Fe-NC catalysts are considered to be promising ORR electrocatalysts, but their OER catalytic activity is generally low and their stability is insufficient. Summary of the Invention

[0007] In view of this, this invention proposes a method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst and its application. Two-dimensional ultrathin LDH nanosheets are prepared using a co-precipitation method and a liquid-phase exfoliation method. The types and ratios of metal ions are changed to adjust the metal ion types and layer structure. An LDH-ZIF-8 composite material is synthesized via in-situ growth and further thermally activated. Using LDH as a sacrificial template, an M@N-CNT nanotube bifunctional catalyst is catalyzed for growth. By optimizing the synthesis conditions, the electrocatalytic activity of this catalyst for ORR / OER in an alkaline system is controlled. The prepared bifunctional catalyst is used to assemble a rechargeable zinc-air battery. Using this catalyst as the positive electrode material, the battery exhibits superior charge-discharge performance and cycle stability compared to commercial catalysts.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst, which exhibits both ORR and OER electrocatalytic activities, specifically includes the following steps:

[0010] Step 1, Preparation of two-dimensional ultrathin LDH nanosheets

[0011] Step 1.1: Add the aqueous solution containing metal ions to the formamide solution and stir magnetically. At the same time, add potassium hydroxide solution dropwise to the solution to ensure that the pH value of the solution is maintained at 8-12 and the reaction continues. The metal ions are any two of nickel nitrate hexahydrate, ferric nitrate nonahydrate, and cobalt nitrate hexahydrate, and the metal ion ratio is 1:1-3:1.

[0012] Step 1.2: After cooling the reaction solution obtained in Step 1.1 to room temperature, collect the generated LDH nanosheets by centrifugation;

[0013] Step 1.3: Wash the LDH nanosheets obtained in Step 1.2 with a mixed solvent of ethanol and water, and keep the LDH nanosheets in a moist state for subsequent use. In the prepared two-dimensional ultrathin LDH nanosheets, the LDH is one of NiFe-LDH, NiCo-LDH, and CoFe-LDH.

[0014] Step 2, Preparation of LDH@Fe-ZIF-8

[0015] The LDH nanosheets, ferric nitrate nonahydrate, and zinc nitrate hexahydrate prepared in step 1 were completely dissolved in methanol and labeled as solution A. 2-methylimidazole was weighed and dissolved in methanol and labeled as solution B. Solution A and solution B were then mixed evenly, sealed, and magnetically stirred for reaction. After the reaction was completed, the mixture was cooled to room temperature, and the product was collected using a high-speed centrifuge. The product was washed with anhydrous ethanol, vacuum dried, and finally ground to obtain LDH@Fe-ZIF-8 powder.

[0016] Step 3, Preparation of catalyst M@N-CNT

[0017] The LDH@Fe-ZIF-8 prepared in step 2 was placed in a clean quartz boat and then placed in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. After natural cooling, the pyrolysis products were ground to obtain the final powder material, which is denoted as M@N-CNT. In the M@N-CNT bifunctional electrocatalyst, M is one of NiFe, NiCo, or CoFe. The high-temperature pyrolysis conditions are as follows: under a nitrogen atmosphere, the heating rate is 5-10 ℃ / min, and the temperature is held at 800-1200℃ for 1-3 h.

[0018] Furthermore, in step 1.1, magnetic stirring is performed at 20-80°C for a continuous reaction time of 10-60 minutes.

[0019] Further, step 2 is performed as follows: the LDH nanosheets, ferric nitrate nonahydrate, and zinc nitrate hexahydrate prepared in step 1 are completely dissolved in 300-900 mL of methanol, denoted as solution A; 2-methylimidazole is weighed and dissolved in 300-900 mL of methanol, denoted as solution B; then solution A and solution B are mixed evenly, sealed, and reacted with magnetic stirring at 20-60℃ for 12-36 h. After the reaction is completed, the mixture is cooled to room temperature, collected using a high-speed centrifuge, washed three times with anhydrous ethanol, and then vacuum dried at 40-80℃ for 10-24 h. Finally, the mixture is ground to obtain LDH@Fe-ZIF-8 powder.

[0020] The M@N-CNT bifunctional electrocatalyst prepared according to the above-described method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst is used to assemble a rechargeable zinc-air battery, with the M@N-CNT bifunctional electrocatalyst serving as the cathode material.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The LDH-induced M@N-CNT bifunctional electrocatalyst has M as a highly efficient OER active site and retains the highly efficient ORR active site of the MNC catalyst, and also endows it with a large specific surface area, thus enabling the material to exhibit excellent discharge performance in zinc-air batteries.

[0023] 2. In the LDH-induced M@N-CNT bifunctional electrocatalyst, the metal particles generated in situ by LDH promote the growth of carbon nanotubes, improve the graphitization degree of the catalyst, and enable it to have bifunctional catalytic activity, exhibiting good cycle stability in zinc-air batteries.

[0024] 3. The LDH-induced M@N-CNT bifunctional electrocatalyst prepared in this invention exhibits superior ORR and OER activity / stability under alkaline conditions compared to commercial noble metal catalysts. Attached Figure Description

[0025] Figure 1 This is a TEM image of the M@N-CNT bifunctional electrocatalyst prepared in Example 1 of this invention;

[0026] Figure 2 This is a CV diagram of the M@N-CNT bifunctional electrocatalyst prepared in Example 1 of this invention;

[0027] Figure 3 This is the SCV diagram of ORR of the M@N-CNT bifunctional electrocatalyst prepared in Example 1 of this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] A method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst, specifically including the following steps:

[0030] Step 1, Preparation of two-dimensional ultrathin LDH nanosheets

[0031] Step 1.1: Add the aqueous solution containing metal ions to the formamide solution and stir magnetically at 20-80℃. At the same time, add potassium hydroxide solution dropwise to the solution to ensure that the pH value of the solution is maintained at 8-12 and continue to react for 10-60 min. The metal ions are any two of nickel nitrate hexahydrate, ferric nitrate nonahydrate, and cobalt nitrate hexahydrate, and the metal ion ratio is 1:1-3:1.

[0032] Step 1.2: After cooling the reaction solution obtained in Step 1.1 to room temperature, collect the generated LDH nanosheets by centrifugation. The LDH is one of NiFe-LDH, NiCo-LDH, and CoFe-LDH.

[0033] Step 1.3: Wash the LDH nanosheets obtained in Step 1.2 with a mixed solvent of ethanol and water, and keep the LDH nanosheets moist for subsequent use;

[0034] Step 2, Preparation of LDH@ZIF-8

[0035] The LDH nanosheets, ferric nitrate nonahydrate, and zinc nitrate hexahydrate prepared in step 1 were completely dissolved in 300-900 mL of methanol, denoted as solution A; 2-methylimidazole was weighed and dissolved in 300-900 mL of methanol, denoted as solution B; then solutions A and B were mixed evenly, sealed, and reacted with magnetic stirring at 20-60℃ for 12-36 h. After the reaction was completed, the mixture was cooled to room temperature, the product was collected using a high-speed centrifuge, washed three times with anhydrous ethanol, and then vacuum dried at 40-80℃ for 10-24 h. Finally, the mixture was ground to obtain LDH@ZIF-8 powder.

[0036] Step 3, Preparation of catalyst M@N-CNT

[0037] The LDH@ZIF-8 prepared in step 2 was placed in a clean quartz boat and then placed in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions were: nitrogen atmosphere, heating rate of 5-10 ℃ / min, holding at 800-1200℃ for 1-3 h, and natural cooling. The pyrolysis products were then ground, and the final powder material was denoted as M@N-CNT. In the prepared M@N-CNT bifunctional electrocatalyst, M is one of NiFe, NiCo, or CoFe.

[0038] Example 1

[0039] Step 1: Add 20 mL of an aqueous solution containing 0.218 g nickel nitrate hexahydrate and 0.101 g ferric nitrate nonahydrate to 20 mL of a 23 vol% formamide solution. Stir magnetically at 80 °C while simultaneously adding 50 mL of 0.25 mol∙L⁻¹ formamide dropwise. -1A potassium hydroxide solution was used to maintain the pH at approximately 10, and the reaction was continued for 10 minutes. After cooling the reaction solution to room temperature, the generated NiFe-LDH nanosheets were collected by centrifugation. Subsequently, the NiFe-LDH nanosheets were washed three times with a mixture of ethanol and water (volume ratio 1:1), and kept moist for subsequent use.

[0040] Step 2: Take a certain amount of NiFe-LDH nanosheets, 0.178 g of ferric nitrate nonahydrate and 3.39 g of zinc nitrate hexahydrate and completely dissolve them in 600 mL of methanol, which is recorded as solution A; weigh 3.94 g of 2-methylimidazole and dissolve it in 600 mL of methanol, which is recorded as solution B; then mix solution A and solution B evenly, seal, and react with magnetic stirring at 60℃ for 24 h. After the reaction is completed, cool to room temperature, collect the solution using a high-speed centrifuge, wash it three times with anhydrous ethanol, and then vacuum dry it at 60℃ for 10 h. Finally, grind it to obtain NiFe-LDH@Fe-ZIF-8 powder.

[0041] Step 3: Weigh a portion of the NiFe-LDH@Fe-ZIF-8 prepared in Step 2 and place it in a clean quartz boat. Then, place it in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions are: nitrogen atmosphere, heating rate of 5℃ / min, holding at 1100℃ for 1 h, and natural cooling. Grind the pyrolysis product to obtain the final powder material, denoted as NiFe@N-CNT. Its transmission electron microscopy image is shown below. Figure 1 As shown. From Figure 1 It can be seen that the prepared catalyst is a uniform carbon nanotube.

[0042] Electrochemical tests were performed on the NiFe@N-CNT bifunctional catalyst in a three-electrode electrolytic cell, and the CV results are as follows: Figure 2 As shown, from Figure 2 It can be seen that the catalyst has a distinct oxygen reduction peak.

[0043] Figure 3 This is the SCV plot of the NiFe@N-CNT bifunctional catalyst for ORR. The SCV test window is 1.1 - 0 V (vs. RHE), with a potential increment of 0.05 V, a sampling width of 15 s, and a settling time of 300 s. Figure 3 It can be seen that the half-wave potential of NiFe@N-CNT for ORR is 0.884 V.

[0044] The catalyst operates at a current density of 10 mA cm⁻¹ -2The overpotential at the open circuit potential (OER) was 0.304 V. Further assembly into a zinc-air battery was conducted to test its charge-discharge performance. The open circuit potential was 1.42 V, and the maximum power density was 127.1 mW / cm². -2 With a charging and discharging current density of 10 mA cm⁻¹ -1 Under these conditions, it exhibits better cycle stability compared to the noble metal catalyst Pt / C+IrO2.

[0045] Example 2

[0046] Step 1: Add 20 mL of an aqueous solution containing 0.218 g of cobalt nitrate hexahydrate and 0.101 g of ferric nitrate nonahydrate to 20 mL of a 23 vol% formamide solution. Stir magnetically at 80 °C while simultaneously adding 50 mL of 0.25 mol·L⁻¹ formamide dropwise. -1 A potassium hydroxide solution was used to maintain the pH at approximately 10, and the reaction was continued for 10 minutes. After cooling the reaction solution to room temperature, the generated CoFe-LDH nanosheets were collected by centrifugation. Subsequently, the CoFe-LDH nanosheets were washed three times with a mixture of ethanol and water (volume ratio 1:1), and kept moist for subsequent use.

[0047] Step 2: Take a certain amount of CoFe-LDH nanosheets, 0.178 g of ferric nitrate nonahydrate and 3.39 g of zinc nitrate hexahydrate and completely dissolve them in 600 mL of methanol, which is recorded as solution A; weigh 3.94 g of 2-methylimidazole and dissolve it in 600 mL of methanol, which is recorded as solution B; then mix solution A and solution B evenly, seal, and react with magnetic stirring at 60℃ for 24 h. After the reaction is completed, cool to room temperature, collect the solution using a high-speed centrifuge, wash it three times with anhydrous ethanol, and then vacuum dry it at 60℃ for 10 h. Finally, grind it to obtain powder CoFe-LDH@Fe-ZIF-8.

[0048] Step 3: Weigh a portion of the CoFe-LDH@Fe-ZIF-8 prepared in Step 2 and place it in a clean quartz boat. Then, place it in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions are: nitrogen atmosphere, heating rate of 5℃ / min, holding at 1100℃ for 1 h, and natural cooling. Grind the pyrolysis product and the resulting catalyst is denoted as CoFe@N-CNT.

[0049] In this embodiment, the half-wave potential of CoFe@N-CNT for ORR is 0.876 V, at a current density of 10 mA cm⁻¹. -2The overpotential at the open circuit potential (OER) was 0.314 V. Further assembly into a zinc-air battery was conducted to test its charge-discharge performance. The open circuit potential was 1.43 V, and the maximum power density was 115.6 mW / cm². -2 With a charging and discharging current density of 10 mA cm⁻¹ -1 Under these conditions, it exhibits better cycle stability compared to the noble metal catalyst Pt / C+IrO2.

[0050] Example 3

[0051] Step 1: Add 20 mL of an aqueous solution containing 0.436 g nickel nitrate hexahydrate and 0.051 g ferric nitrate nonahydrate to 20 mL of a 23 vol% formamide solution. Stir magnetically at 80 °C while simultaneously adding 50 mL of 0.25 mol∙L⁻¹ formamide dropwise. -1 A potassium hydroxide solution was used to maintain the pH at approximately 10, and the reaction was continued for 30 minutes. After cooling the reaction solution to room temperature, the resulting product, Ni2Fe-LDH, was collected by centrifugation. Subsequently, the product was washed three times with a mixture of ethanol and water (volume ratio 1:1) and kept moist for subsequent use.

[0052] Step 2: Take a certain amount of Ni2Fe-LDH nanosheets, 0.178 g of ferric nitrate nonahydrate and 3.39 g of zinc nitrate hexahydrate and dissolve them completely in 600 mL of methanol, which is recorded as solution A; weigh 3.94 g of 2-methylimidazole and dissolve it in 600 mL of methanol, which is recorded as solution B; then mix solution A and solution B evenly, seal, and react with magnetic stirring at 20℃ for 36 h. After the reaction is completed, cool to room temperature, collect the solution using a high-speed centrifuge, wash it three times with anhydrous ethanol, and then vacuum dry it at 60℃ for 10 h. Finally, grind it to obtain Ni2Fe-LDH@Fe-ZIF-8 powder.

[0053] Step 3: Weigh a portion of the Ni2Fe-LDH@Fe-ZIF-8 prepared in Step 2 and place it in a clean quartz boat. Then, place the boat in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions are: nitrogen atmosphere, heating rate of 5 °C / min, holding at 1200 °C for 1 h, and natural cooling. Grind the pyrolysis product to obtain the final powder material, which is denoted as Ni2Fe@N-CNT.

[0054] Example 4

[0055] Step 1: Add 20 mL of an aqueous solution containing 0.218 g nickel nitrate hexahydrate and 0.101 g ferric nitrate nonahydrate to 20 mL of a 23 vol% formamide solution. Stir magnetically at 60 °C while simultaneously adding 50 mL of 0.25 mol∙L⁻¹ formamide dropwise. -1 A potassium hydroxide solution was used to maintain the pH at approximately 10, and the reaction was continued for 30 minutes. After cooling the reaction solution to room temperature, the generated NiFe-LDH nanosheets were collected by centrifugation. Subsequently, the NiFe-LDH nanosheets were washed three times with a mixed solvent of ethanol and water (volume ratio 1:1), and kept moist for subsequent use.

[0056] Step 2: Take a certain amount of NiFe-LDH nanosheets, 0.178 g of ferric nitrate nonahydrate and 3.39 g of zinc nitrate hexahydrate and completely dissolve them in 600 mL of methanol, which is recorded as solution A; weigh 3.94 g of 2-methylimidazole and dissolve it in 600 mL of methanol, which is recorded as solution B; then mix solution A and solution B evenly, seal, and react with magnetic stirring at 40℃ for 24 h. After the reaction is completed, cool to room temperature, collect the solution using a high-speed centrifuge, wash it three times with anhydrous ethanol, and then vacuum dry it at 80℃ for 12 h. Finally, grind it to obtain NiFe-LDH@Fe-ZIF-8 powder.

[0057] Step 3: Weigh a portion of the NiCo-LDH@Fe-ZIF-8 prepared in Step 2 and place it in a clean quartz boat. Then, place it in a tube-type high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions are: nitrogen atmosphere, heating rate of 10 ℃ / min, holding at 800℃ for 3 h, and natural cooling. Grind the pyrolysis product to obtain the final powder material, which is denoted as NiFe@N-CNT.

[0058] Example 5

[0059] Step 1: Add 20 mL of an aqueous solution containing 0.218 g of nickel nitrate hexahydrate and 0.218 g of cobalt nitrate hexahydrate to 20 mL of a 23 vol% formamide solution. Stir magnetically at 20 °C while simultaneously adding 50 mL of 0.25 mol·L⁻¹ formamide dropwise. -1 A potassium hydroxide solution was used to maintain the pH at approximately 10, and the reaction was continued for 60 minutes. After cooling the reaction solution to room temperature, the generated NiCo-LDH nanosheets were collected by centrifugation. Subsequently, the NiCo-LDH nanosheets were washed three times with a mixture of ethanol and water (volume ratio 1:1), and kept moist for subsequent use.

[0060] Step 2: Take a certain amount of NiCo-LDH nanosheets, 0.178 g of ferric nitrate nonahydrate and 3.39 g of zinc nitrate hexahydrate and dissolve them completely in 600 mL of methanol, which is recorded as solution A; weigh 3.94 g of 2-methylimidazole and dissolve it in 600 mL of methanol, which is recorded as solution B; then mix solution A and solution B evenly, seal, and react with magnetic stirring at 60℃ for 12 h. After the reaction is completed, cool to room temperature, collect the solution using a high-speed centrifuge, wash it three times with anhydrous ethanol, and then vacuum dry it at 40℃ for 24 h. Finally, grind it to obtain NiCo-LDH@Fe-ZIF-8 powder.

[0061] Step 3: Weigh a portion of the NiCo-LDH@Fe-ZIF-8 prepared in Step 2 and place it in a clean quartz boat. Then, place the boat in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis. The pyrolysis conditions are: nitrogen atmosphere, heating rate of 10 °C / min, holding at 1000 °C for 2 h, and natural cooling. Grind the pyrolysis product to obtain the final powder material, which is denoted as NiCo@N-CNT.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A method for preparing an LDH-induced M@N-CNT bifunctional electrocatalyst having ORR and OER electrocatalytic activity, characterized in that, Specifically comprising the following steps: Step 1, preparation of two-dimensional ultrathin LDH nanosheets Step 1.1, an aqueous solution containing metal ions is added to a formamide solution for magnetic stirring, and at the same time, a potassium hydroxide solution is added dropwise to the solution to ensure that the pH value of the solution is maintained at 8-12, and the reaction is continued; wherein the metal ions are from any two of nickel nitrate hexahydrate, iron nitrate nonahydrate, and cobalt nitrate hexahydrate, and the ratio of metal ions is 1:1-3:1; Step 1.2, after the reaction solution obtained in step 1.1 is cooled to room temperature, the generated LDH nanosheets are collected by centrifugation; Step 1.3, the LDH nanosheets obtained in step 1.2 are washed with a mixed solvent of ethanol and water, and the LDH nanosheets are kept in a wet state for subsequent use, and the prepared two-dimensional ultrathin LDH nanosheets are one of NiFe-LDH, NiCo-LDH, and CoFe-LDH; Step 2, preparation of LDH@Fe-ZIF-8 The LDH nanosheets, iron nitrate nonahydrate, and zinc nitrate hexahydrate prepared in step 1 are completely dissolved in methanol, denoted as A liquid; 2-methylimidazole is weighed and dissolved in methanol, denoted as B liquid; then A liquid and B liquid are mixed uniformly, sealed, and magnetically stirred for reaction, and after the reaction is completed, the product is collected by a high-speed centrifuge, and after the product is washed with anhydrous ethanol, vacuum drying is performed, and finally the powder LDH@Fe-ZIF-8 is obtained by grinding; Step 3, preparation of catalyst M@N-CNT The LDH@Fe-ZIF-8 prepared in step 2 is placed in a clean quartz boat, which is placed in a tubular high-temperature atmosphere furnace for high-temperature pyrolysis, and after natural cooling, the pyrolysis product is ground to obtain the final powder material denoted as M@N-CNT, and M in the M@N-CNT bifunctional electrocatalyst is one of NiFe, NiCo, or CoFe; wherein the high-temperature pyrolysis conditions are: under a nitrogen atmosphere, the heating rate is 5-10 ℃ / min, and the temperature is kept at 800-1200 ℃ for 1-3 h.

2. The method for preparing LDH-induced M@N-CNT bifunctional electrocatalyst according to claim 1, characterized in that, In step 1.1, magnetic stirring is performed at 20-80 ℃, and the reaction time is 10-60 min.

3. The method for preparing LDH-induced M@N-CNT bifunctional electrocatalyst according to claim 1, characterized in that, The specific method of step 2 is as follows: the LDH nanosheets, iron nitrate nonahydrate, and zinc nitrate hexahydrate prepared in step 1 are completely dissolved in 300-900 mL of methanol, denoted as A liquid; 2-methylimidazole is weighed and dissolved in 300-900 mL of methanol, denoted as B liquid; then A liquid and B liquid are mixed uniformly, sealed, and magnetically stirred at 20-60 ℃ for 12-36 h, and after the reaction is completed, the product is collected by a high-speed centrifuge, and after being washed with anhydrous ethanol for 3 times, vacuum drying is performed at 40-80 ℃ for 10-24 h, and finally the powder LDH@Fe-ZIF-8 is obtained by grinding.

4. The M@N-CNT bifunctional electrocatalyst prepared by the method according to any one of claims 1-3, characterized in that, The M@N-CNT bifunctional electrocatalyst is used to assemble a rechargeable zinc air battery, and the M@N-CNT bifunctional electrocatalyst is used as a positive electrode material.

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