Preparation method and application of a zinc-air battery bifunctional catalyst

Abstract

The invention discloses a preparation method and application of a zinc-air battery bifunctional catalyst, which uses a spatiotemporal gradient assembly strategy and combines the dynamic response characteristics of a buffer system and an inducer to temperature, and adopts a synchronous control technology to achieve uniform distribution of NiFe2O4 nanoparticles in ZIF-8 growth, thereby forming a NiFe2O4 / ZIF-8 precursor; and then the precursor is pyrolyzed in a tubular furnace under the protection of a nitrogen-hydrogen-helium mixed gas to obtain a uniformly distributed NiFe2O4 / ZIF-8 bifunctional catalyst. The NiFe2O4 / ZIF-8 bifunctional catalyst prepared by the invention can replace expensive and scarce precious metal catalysts, and shows a wide range of application prospects in energy storage and conversion fields such as electrocatalytic oxygen reduction reaction and zinc-air batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of rechargeable zinc-air battery catalysts, and in particular relates to a preparation method and application of a zinc-air battery bifunctional catalyst. Background Art

[0002] Zinc-air batteries (ZABs) have attracted much attention as an environmentally friendly, low-cost and high-energy-density energy system. However, the air cathode oxygen reaction kinetics of zinc-air batteries are relatively slow, which limits their energy efficiency and cycle stability. With the development of metal-air battery technology and the country's continuous advancement of the new energy industry, how to improve the overall performance and cycle stability of ZABs is the core issue of current research. So far, noble metals and their alloys are considered to be the most effective catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), but their application is limited due to high cost and limited reserves. Therefore, transition metal catalysts have attracted much attention due to their high catalytic activity, structural stability, abundant reserves and low cost.

[0003] MOF (metal organic framework) is a porous crystalline material formed by the combination of metal ions (or clusters) and organic ligands through coordination chemical bonds. In recent years, due to its porosity, adjustability, high specific surface area and functionality, it has become an important research direction in the field of materials science and application, and has shown broad application prospects in many fields such as gas storage, separation, catalysis, drug delivery and sensors. However, existing MOF-based catalysts may have the following deficiencies in regulating the distribution of nanoparticles: during the reaction, the MOF framework may experience structural degradation or pore blockage, thereby affecting the catalytic performance, and in terms of the uniformity of nanoparticle distribution, MOF-based catalysts may find it difficult to ensure the uniform distribution of nanoparticles in the MOF pores, resulting in uneven distribution of reaction active sites, which may affect the overall catalytic efficiency. Based on this, the present invention provides a method for preparing a catalyst based on regulated assembly under time and space gradients. The catalyst is prepared by in-situ assembling NiFe2O4 nanoparticles in the MOF material ZIF-8, and then synthesizing a high-performance NiFe2O4 / ZIF-8 bifunctional catalyst by thermal decomposition. The catalyst has good catalytic activity and stability in catalyzing oxygen reduction and oxygen evolution reactions, and exhibits excellent bifunctional catalytic activity and cycle stability when used to prepare zinc-air batteries, which points out the direction for the application of non-precious metal catalysts in zinc-air batteries. There are currently no related reports in this regard. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for preparing a bifunctional catalyst for a zinc-air battery. The NiFe2O4 / ZIF-8 bifunctional catalyst prepared by the method is used to catalyze the ORR and OER reactions of a rechargeable zinc-air battery, thereby effectively improving the electrochemical performance and cycle stability of the rechargeable zinc-air battery.

[0005] The present invention adopts the following technical scheme to solve the above technical problems, which is a preparation method of a zinc-air battery bifunctional catalyst. The specific process is: firstly, NiFe2O4 nanoparticles are synthesized, and then the ZIF-8 generation process is regulated under a time-space gradient, that is, the temperature of the reaction environment is precisely regulated and the hydrophilicity of the multifunctional inducer is used to improve the dispersion and uniformity of the NiFe2O4 nanoparticles in the ZIF-8 generation process, effectively avoid particle aggregation, and realize ZIF-8 uniformly coating the NiFe2O4 nanoparticles, and finally successfully synthesize the NiFe2O4 / ZIF-8 bifunctional catalyst. The uniform dispersion of the NiFe2O4 nanoparticles in the ZIF-8 makes the prepared NiFe2O4 / ZIF-8 bifunctional catalyst have ultra-high performance, including excellent catalytic activity, stability and mass transfer efficiency, and effectively improves the electrocatalytic activity and cycle stability of the NiFe2O4 / ZIF-8 bifunctional catalyst in practical applications. The high-performance NiFe2O4 / ZIF-8 bifunctional catalyst prepared by the present invention exhibits excellent oxygen reduction and oxygen evolution catalytic activity in catalyzing ORR and OER reactions, and exhibits excellent practicality in zinc-air batteries.

[0006] The preparation method of the zinc-air battery bifunctional catalyst of the present invention is characterized by the following specific steps:

[0007] Step S1, adding ferric acetylacetonate, nickel acetylacetonate and 1,2-hexadecanediol into a reaction container, then adding oleylamine, oleic acid and dibenzene ether and mixing them evenly, heating to react under an inert gas environment, and after the reaction is completed, centrifuging and washing the product, and then freeze-drying it to obtain NiFe2O4 nanoparticles;

[0008] Step S2: Add the NiFe2O4 nanoparticles and Zn(NO3)2·6H2O obtained in step S1 into a reaction container, then add Tris-HCl buffer and copolymer PNIPAM-PAA and dilute with deionized water to obtain a mixed solution A, dissolve different masses of 2-methylimidazole in methanol to obtain solutions B1 and B2, wherein the concentration of solution B1 is greater than that of solution B2;

[0009] Step S3: placing the mixed solution A obtained in step S2 in a constant temperature reactor and setting the temperature for staged changes, the whole change process includes a heating stage, a constant temperature stage and a cooling stage, in the heating stage, adding solution B1 dropwise to the mixed solution A, the duration of adding solution B1 is consistent with the duration of heating in the heating stage, in the constant temperature stage, adding solution B2 dropwise to the mixed solution A, the duration of adding solution B2 is consistent with the duration of heating in the constant temperature stage, in the cooling stage, cooling reaction is performed, and the product is collected by centrifugation, and the product is vacuum dried and ground to obtain a NiFe2O4 / ZIF-8 precursor;

[0010] Step S4: The NiFe2O4 / ZIF-8 precursor obtained in step S3 is pyrolyzed at 700-900°C under the protection of a nitrogen, hydrogen and helium mixed gas to obtain a NiFe2O4 / ZIF-8 bifunctional catalyst.

[0011] It is further defined that in step S1, the feed ratio of ferric acetylacetonate, nickel acetylacetonate, 1,2-hexadecanediol, oleylamine, oleic acid and dibenzene ether is 2mmol:1mmol:8~12mmol:4~8mmol:4~8mmol:20~40mL.

[0012] It is further defined that the reaction conditions of the heating reaction process in step S1 are an oxygen-free N2 environment, and the heating reaction process is a programmed temperature increase, specifically, first heating the temperature to 100~120°C at a heating rate of 6~10°C / min and maintaining for 1~2h, then heating the temperature to 200~220°C at a heating rate of 2~5°C / min and maintaining for 1~3h, and then continuing to heat the temperature to 290~300°C at a heating rate of 2~5°C / min and maintaining for 1~2h.

[0013] It is further defined that in step S1, the centrifugation conditions are 8000-10000 rpm, the centrifugation time is 3-15 min, the washing conditions are n-hexane ultrasonic dispersion followed by ethanol precipitation, and the freeze-drying time is 24-60 h; in step S3, the centrifugation conditions are 7000-9000 rpm, the centrifugation time is 2-8 min, the washing solvent is ethanol, the vacuum drying temperature is 50-70°C, and the vacuum drying time is 10-15 h.

[0014] It is further defined that in step S2, the feed ratio of Zn(NO3)2·6H2O, NiFe2O4 nanoparticles, Tris-HCl buffer and copolymer PNIPAM-PAA is 600~800mg:1mg:1~2mL:0.8~1.5mg; the feed mass ratio of Zn(NO3)2·6H2O and dimethylimidazole is 1:0.5~1.5; and the concentration ratio of solution B1 and solution B2 is 1.5~2.5:1.

[0015] It is further defined that the specific process of the heating stage in step S3 is heating from 30°C to 70°C, and the heating duration is 30 minutes; the specific process of the constant temperature stage is maintaining a constant temperature of 70°C for 30 minutes; the specific process of the cooling stage is cooling from 70°C to 30°C, and the cooling duration is 30 minutes.

[0016] It is further defined that the specific process of pyrolysis in step S4 is to heat the mixture to 800°C at a heating rate of 5°C / min and maintain for 2 hours under the protection of a nitrogen, hydrogen and helium mixed gas, and then cool naturally to obtain a NiFe2O4 / ZIF-8 bifunctional catalyst, wherein the volume fraction of hydrogen in the nitrogen, hydrogen and helium mixed gas is 10%, the volume fraction of helium is 1%~2%, and the remainder is nitrogen.

[0017] The invention discloses an application of the zinc-air battery bifunctional catalyst in catalyzing oxygen reduction and oxygen evolution reactions. The zinc-air battery bifunctional catalyst has a catalytic oxygen reduction performance in a 0.1M KOH solution with a half-wave potential of 0.88V, and a catalytic oxygen evolution performance in a 1M KOH solution with a half-wave potential of 10mA cm -2 The overpotential is 330mV.

[0018] The invention discloses an application of the zinc-air battery bifunctional catalyst in preparing a zinc-air battery cathode.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. The present invention realizes spontaneous pH regulation and additive hydrophilicity regulation under temperature changes by using a temperature-dependent buffer system (Tris-HCl buffer) and a temperature-responsive copolymer (PNIPAM-PAA). Compared with the addition of acid-base regulators, which easily changes the reaction system and introduces other substances, the use of Tris-HCl buffer can achieve pH regulation without adding additional acid or base, which simplifies the experimental operation and improves the dispersion and uniformity of NiFe2O4 nanoparticles during the growth process of ZIF-8.

[0021] 2. The present invention achieves uniform distribution of NiFe2O4 nanoparticles during the growth of ZIF-8 by regulating the staged change of temperature during the reaction and introducing a buffer system, thereby avoiding the instability of the reaction environment.

[0022] 3. The present invention uses an automatic titration device to accurately control the stage-by-stage change of 2-methylimidazole concentration during the reaction process, thereby controlling the slowness and uniformity of the ZIF-8 growth process, thereby promoting the uniform distribution of NiFe2O4 nanoparticles in ZIF-8.

[0023] 4. The present invention achieves dynamic regulation of NiFe2O4 nanoparticles by designing a multifunctional inducer and combining temperature and pH responsiveness. The copolymer PNIPAM-PAA exhibits different hydrophilicity and hydrophobicity under different temperature and pH conditions, and the NiFe2O4 nanoparticles are in the best dispersion state at different stages by regulating the reaction environment. The weak acidity of the initial reaction system inhibits the hydrolysis of zinc ions and promotes the formation of ZIF-8 crystal nuclei. The inducer is hydrophilic, which promotes the rapid and uniform dispersion of NiFe2O4 nanoparticles in the solvent system and the combination with the generated ZIF-8. As the temperature increases, the pH of the reaction solution system decreases and the acidity increases. At the same time, the inducer is hydrophobic, which can better disperse the NiFe2O4 nanoparticles in the solution system to avoid agglomeration. As the acidity of the solution increases, the crystal growth of ZIF-8 is inhibited due to coordination instability, forming a defective structure or an incomplete framework structure. The incomplete growth of ZIF-8 will lead to more defects and voids in its structure. These defects and voids help NiFe2O4 nanoparticles to be loaded more and more evenly. The uniformly dispersed NiFe2O4 nanoparticles can provide more active sites, thereby improving the reaction efficiency. This is of great significance for the preparation of bifunctional catalysts with high dispersibility and good catalytic performance.

[0024] 5. The present invention achieves the optimal distribution and structural stability of NiFe2O4 nanoparticles in the ZIF-8 framework through multi-dimensional comprehensive regulation and protection measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray powder diffraction pattern of the NiFe2O4 nanoparticles obtained in Example 1.

[0026] Figure 2 This is a scanning electron microscope image of the NiFe2O4 / ZIF-8 precursor obtained in Example 1.

[0027] Figure 3 The linear voltammetric scanning curves of the NiFe2O4 / ZIF-8 catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 1 and 3 to 5 in 0.1 M KOH solution.

[0028] Figure 4 The linear voltammetric scanning curves of the NiFe2O4 / ZIF-8 catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 2 to 5 in 1M KOH solution. DETAILED DESCRIPTION

[0029] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example 1

[0030] Step S1: Accurately weigh 2 mmol of ferric acetylacetonate, 1 mmol of nickel acetylacetonate and 10 mmol of 1,2-hexadecanediol, then add 6mmol oleylamine and 6mmol oleic acid and measure 25mL dibenzene with a pipette. After adding a magnet, place the three-necked flask in a temperature-controllable magnetic stirrer. In a N2 atmosphere, heat it to 110℃ at a heating rate of 8℃ / min and keep it for 60min, then heat it to 210℃ at a heating rate of 3℃ / min and keep it for 2h, continue to heat it to 295℃ at a heating rate of 3℃ / min and keep it for 1h, then cool it naturally to room temperature, transfer the product to a centrifuge tube containing 20mL ethanol, centrifuge it at 8000rpm for 8min, add 15mL n-hexane to the precipitate obtained after centrifugation for ultrasonic dispersion, then add 20mL ethanol to precipitate the product, and then centrifuge it at 9000rpm for 5min. After centrifugation, freeze-dry the product for 48h to obtain NiFe2O4 nanoparticles with a particle size of 10~20nm.

[0031] Step S2: Weigh 50 mg of NiFe2O4 nanoparticles and add them to a beaker containing 33.9 g of Zn(NO3)2·6H2O, then add 75 mL of Tris-HCl buffer and 50 mg of copolymer PNIPAM-PAA, and then add 300 mL of deionized water for ultrasonic dispersion to obtain a mixed solution A after dispersion; 26.4 g of 2-methylimidazole and 13.2 g of 2-methylimidazole are respectively added to 187.5 mL of methanol and ultrasonically dispersed to obtain solutions B1 and B2.

[0032] Step S3: placing the mixed solution A in a constant temperature reactor, and adding solution B1 and solution B2 to the mixed solution A using an automatic titrator while changing the temperature of the mixed solution A in stages; in the heating stage (heating from 30°C to 70°C, heating duration 30min), adding solution B1 using an automatic titrator (dropping duration 30min); in the constant temperature stage (maintained at 70°C, constant temperature duration 30min), adding solution B2 using an automatic titrator (dropping duration 30min); in the cooling stage (cooling from 70°C to 30°C, cooling duration 30min), the product is cooled and then centrifuged at 8000rpm for 3min, then washed with ethanol 3 times, and the washed product is dried in a vacuum drying oven at 60°C for 12h, and then ground to obtain a NiFe2O4 / ZIF-8 precursor.

[0033] Step S4: The NiFe2O4 / ZIF-8 precursor was transferred to a quartz boat and placed in a tubular furnace, and a nitrogen-hydrogen-helium mixed gas (hydrogen 10Vol%, helium 1Vol%, and the balance nitrogen) was introduced as a protective gas, and then the temperature was increased to 800°C at a heating rate of 5°C / min and maintained for 2h, and then naturally cooled to obtain a NiFe2O4 / ZIF-8 catalyst.

[0034] Comparative Example 1

[0035] This comparative example uses 20 wt % commercial Pt / C as a control.

[0036] Comparative Example 2

[0037] This comparative example uses commercial Ir / C as a control.

[0038] Comparative Example 3 (pH Control without Tris-HCl Buffer)

[0039] Step S1: Accurately weigh 2 mmol of ferric acetylacetonate, 1 mmol of nickel acetylacetonate and 10 mmol of 1,2-hexadecanediol, then add 6mmol oleylamine and 6mmol oleic acid and measure 25mL dibenzene with a pipette. After adding a magnet, place the three-necked flask in a temperature-controllable magnetic stirrer. In a N2 atmosphere, heat it to 110℃ at a heating rate of 8℃ / min and keep it for 60min, then heat it to 210℃ at a heating rate of 3℃ / min and keep it for 2h, continue to heat it to 295℃ at a heating rate of 3℃ / min and keep it for 1h, then cool it naturally to room temperature, transfer the product to a centrifuge tube containing 20mL ethanol, centrifuge it at 8000rpm for 8min, add 15mL n-hexane to the precipitate obtained after centrifugation for ultrasonic dispersion, then add 20mL ethanol to precipitate the product, and then centrifuge it at 9000rpm for 5min. After centrifugation, freeze-dry the product for 48h to obtain NiFe2O4 nanoparticles with a particle size of 10~20nm.

[0040] Step S2: Weigh 50 mg of NiFe2O4 nanoparticles and add them to a beaker containing 33.9 g of Zn(NO3)2·6H2O, then add 50 mg of copolymer PNIPAM-PAA and 300 mL of deionized water for ultrasonic dispersion to obtain a mixed solution A; add 26.4 g of 2-methylimidazole and 13.2 g of 2-methylimidazole to 187.5 mL of methanol, respectively, and perform ultrasonic dispersion to obtain solutions B1 and B2.

[0041] Step S3: placing the mixed solution A in a constant temperature reactor, and adding solution B1 and solution B2 to the mixed solution A using an automatic titrator while changing the temperature of the mixed solution A in stages; in the heating stage (heating from 30°C to 70°C, heating duration 30min), adding solution B1 using an automatic titrator (dropping duration 30min); in the constant temperature stage (maintained at 70°C, constant temperature duration 30min), adding solution B2 using an automatic titrator (dropping duration 30min); in the cooling stage (cooling from 70°C to 30°C, cooling duration 30min), the product is cooled and then centrifuged at 8000rpm for 3min, then washed with ethanol 3 times, and the washed product is dried in a vacuum drying oven at 60°C for 12h, and then ground to obtain a NiFe2O4 / ZIF-8 precursor.

[0042] Step S4: The NiFe2O4 / ZIF-8 precursor was transferred to a quartz boat and placed in a tubular furnace, and a nitrogen-hydrogen-helium mixed gas (hydrogen 10Vol%, helium 1Vol%, and the balance nitrogen) was introduced as a protective gas, and then the temperature was increased to 800°C at a heating rate of 5°C / min and maintained for 2h, and then naturally cooled to obtain a NiFe2O4 / ZIF-8 catalyst.

[0043] Comparative Example 4 (without adding copolymer PNIPAM-PAA)

[0044] Step S1: Accurately weigh 2 mmol of ferric acetylacetonate, 1 mmol of nickel acetylacetonate and 10 mmol of 1,2-hexadecanediol, then add 6mmol oleylamine and 6mmol oleic acid and measure 25mL dibenzene with a pipette. After adding a magnet, place the three-necked flask in a temperature-controllable magnetic stirrer. In a N2 atmosphere, heat it to 110℃ at a heating rate of 8℃ / min and keep it for 60min, then heat it to 210℃ at a heating rate of 3℃ / min and keep it for 2h, continue to heat it to 295℃ at a heating rate of 3℃ / min and keep it for 1h, then cool it naturally to room temperature, transfer the product to a centrifuge tube containing 20mL ethanol, centrifuge it at 8000rpm for 8min, add 15mL n-hexane to the precipitate obtained after centrifugation for ultrasonic dispersion, then add 20mL ethanol to precipitate the product, and then centrifuge it at 9000rpm for 5min. After centrifugation, freeze-dry the product for 48h to obtain NiFe2O4 nanoparticles with a particle size of 10~20nm.

[0045] Step S2: Weigh 50 mg of NiFe2O4 nanoparticles and add them to a beaker containing 33.9 g of Zn(NO3)2·6H2O, then add 75 mL of Tris-HCl buffer and then add 300 mL of deionized water for ultrasonic dispersion to obtain a mixed solution A after dispersion; 26.4 g of 2-methylimidazole and 13.2 g of 2-methylimidazole are respectively added to 187.5 mL of methanol and ultrasonically dispersed to obtain solutions B1 and B2.

[0046] Step S3: placing the mixed solution A in a constant temperature reactor, and adding solution B1 and solution B2 to the mixed solution A using an automatic titrator while subjecting the mixed solution A to a step-by-step temperature change. In the heating stage (from 30°C to 70°C, the heating duration is 30 minutes), the solution B1 is added using an automatic titrator. In the constant temperature stage (maintained at 70°C, the constant temperature duration is 30 minutes), the solution B2 is added using an automatic titrator. After cooling in the cooling stage (from 70°C to 30°C, the cooling duration is 30 minutes), the product is centrifuged at 8000 rpm for 3 minutes, and then washed with ethanol 3 times. The washed product is dried in a vacuum drying oven at 60°C for 12 hours, and then ground to obtain a NiFe2O4 / ZIF-8 precursor.

[0047] Step S4: The NiFe2O4 / ZIF-8 precursor was transferred to a quartz boat and placed in a tubular furnace, and a nitrogen-hydrogen-helium mixed gas (hydrogen 10Vol%, helium 1Vol%, and the balance nitrogen) was introduced as a protective gas, and then the temperature was increased to 800°C at a heating rate of 5°C / min and maintained for 2h, and then naturally cooled to obtain a NiFe2O4 / ZIF-8 catalyst.

[0048] Comparative Example 5 (without using automatic titration device for staged addition)

[0049] Step S1: Accurately weigh 2 mmol of ferric acetylacetonate, 1 mmol of nickel acetylacetonate and 10 mmol of 1,2-hexadecanediol, then add 6mmol oleylamine and 6mmol oleic acid and measure 25mL dibenzene with a pipette. After adding a magnet, place the three-necked flask in a temperature-controllable magnetic stirrer. In a N2 atmosphere, heat it to 110℃ at a heating rate of 8℃ / min and keep it for 60min, then heat it to 210℃ at a heating rate of 3℃ / min and keep it for 2h, continue to heat it to 295℃ at a heating rate of 3℃ / min and keep it for 1h, then cool it naturally to room temperature, transfer the product to a centrifuge tube containing 20mL ethanol, centrifuge it at 8000rpm for 8min, add 15mL n-hexane to the precipitate obtained after centrifugation for ultrasonic dispersion, then add 20mL ethanol to precipitate the product, and then centrifuge it at 9000rpm for 5min. After centrifugation, freeze-dry the product for 48h to obtain NiFe2O4 nanoparticles with a particle size of 10~20nm.

[0050] Step S2: Weigh 50 mg of NiFe2O4 nanoparticles and add them to a beaker containing 33.9 g of Zn(NO3)2·6H2O, then add 75 mL of Tris-HCl buffer and 50 mg of copolymer PNIPAM-PAA, and then add 300 mL of deionized water for ultrasonic dispersion to obtain a mixed solution A; add 39.6 g of 2-methylimidazole to 375 mL of methanol and perform ultrasonic dispersion to obtain a solution B.

[0051] Step S3: Pour solution B into mixed solution A and heat to 70°C for 60 minutes. After the reaction is cooled, the product is centrifuged at 8000 rpm for 3 minutes, and then washed with ethanol three times. The washed product is dried in a vacuum drying oven at 60°C for 12 hours, and then ground to obtain a NiFe2O4 / ZIF-8 precursor.

[0052] Step S4: The NiFe2O4 / ZIF-8 precursor was transferred to a quartz boat and placed in a tubular furnace, and a nitrogen-hydrogen-helium mixed gas (hydrogen 10Vol%, helium 1Vol%, and the balance nitrogen) was introduced as a protective gas, and then the temperature was increased to 800°C at a heating rate of 5°C / min and maintained for 2h, and then naturally cooled to obtain a NiFe2O4 / ZIF-8 catalyst.

[0053] The rechargeable zinc-air battery bifunctional catalyst prepared by the present invention has good ORR and OER bifunctional catalytic activity. Figure 3 and Figure 4It can be seen from the electrical performance test results that the NiFe2O4 / ZIF-8 catalyst prepared in Example 1 has a larger limiting current density and half-wave potential, and the NiFe2O4 / ZIF-8 catalyst prepared in Example 1 has the best bifunctional catalytic activity.

[0054] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a zinc-air battery bifunctional catalyst, characterized in that The specific steps are: Step S1, adding ferric acetylacetonate, nickel acetylacetonate and 1,2-hexadecanediol into a reaction container, then adding oleylamine, oleic acid and dibenzene ether and mixing them evenly, heating and reacting in an inert gas or oxygen-free N2 environment, and after the reaction is completed, centrifuging and washing the product, and then freeze-drying it to obtain NiFe2O4 nanoparticles; Step S2: Add the NiFe2O4 nanoparticles and Zn(NO3)2·6H2O obtained in step S1 into a reaction container, then add Tris-HCl buffer and copolymer PNIPAM-PAA and dilute with deionized water to obtain a mixed solution A, dissolve different masses of 2-methylimidazole in methanol to obtain solutions B1 and B2, wherein the concentration of solution B1 is greater than that of solution B2; Step S3: placing the mixed solution A obtained in step S2 in a constant temperature reactor and setting the temperature for staged changes, the whole change process includes a heating stage, a constant temperature stage and a cooling stage, in the heating stage, adding solution B1 dropwise to the mixed solution A, the duration of adding solution B1 is consistent with the duration of heating in the heating stage, in the constant temperature stage, adding solution B2 dropwise to the mixed solution A, the duration of adding solution B2 is consistent with the duration of heating in the constant temperature stage, cooling reaction is performed in the cooling stage, centrifugation and washing are performed to collect the product, and the product is vacuum dried and ground to obtain a NiFe2O4 / ZIF-8 precursor; Step S4: The NiFe2O4 / ZIF-8 precursor obtained in step S3 is pyrolyzed at 700-900° C. under the protection of a nitrogen-hydrogen-helium mixed gas to obtain a zinc-air battery bifunctional catalyst.

2. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: In step S1, the feed ratio of ferric acetylacetonate, nickel acetylacetonate, 1,2-hexadecanediol, oleylamine, oleic acid and dibenzene ether is 2mmol:1mmol:8~12mmol:4~8mmol:4~8mmol:20~40mL.

3. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: The reaction conditions of the heating reaction process in step S1 are an oxygen-free N2 environment, and the heating reaction process is a programmed temperature increase, specifically, first heating to 100~120°C at a heating rate of 6~10°C / min and maintaining for 1~2h, then heating to 200~220°C at a heating rate of 2~5°C / min and maintaining for 1~3h, and then continuing to heat to 290~300°C at a heating rate of 2~5°C / min and maintaining for 1~2h.

4. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: In step S1, the centrifugal condition is 8000-10000 rpm, the centrifugal time is 3-15 min, the washing condition is n-hexane ultrasonic dispersion followed by ethanol precipitation, and the freeze-drying time is 24-60 h; in step S3, the centrifugal condition is 7000-9000 rpm, the centrifugal time is 2-8 min, the washing solvent is ethanol, the vacuum drying temperature is 50-70° C., and the vacuum drying time is 10-15 h.

5. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: In step S2, the feed ratio of Zn(NO3)2·6H2O, NiFe2O4 nanoparticles, Tris-HCl buffer and copolymer PNIPAM-PAA is 600~800mg:1mg:1~2mL:0.8~1.5mg; the feed mass ratio of Zn(NO3)2·6H2O and dimethylimidazole is 1:0.5~1.5; the concentration ratio of solution B1 and solution B2 is 1.5~2.5:

1.

6. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: The specific process of the heating stage in step S3 is heating from 30°C to 70°C, and the heating duration is 30 minutes; the specific process of the constant temperature stage is maintaining a constant temperature of 70°C for 30 minutes; the specific process of the cooling stage is cooling from 70°C to 30°C, and the cooling duration is 30 minutes.

7. The method for preparing a zinc-air battery bifunctional catalyst according to claim 1, characterized in that: The specific process of pyrolysis in step S4 is to heat the mixture to 800°C at a heating rate of 5°C / min and maintain for 2 hours under the protection of nitrogen, hydrogen and helium mixed gas, and then cool naturally to obtain a zinc-air battery bifunctional catalyst, wherein the volume fraction of hydrogen in the nitrogen, hydrogen and helium mixed gas is 10%, the volume fraction of helium is 1%~2%, and the remainder is nitrogen.

8. The use of a zinc-air battery bifunctional catalyst prepared by the method according to any one of claims 1 to 7 in catalytic oxygen reduction and oxygen evolution reactions, wherein the catalytic oxygen reduction performance of the zinc-air battery bifunctional catalyst in a 0.1M KOH solution is shown as a half-wave potential of 0.88V, and the catalytic oxygen evolution performance in a 1M KOH solution is shown as a half-wave potential of 10mAcm -2 The overpotential is 330mV.

9. Use of the zinc-air battery bifunctional catalyst prepared by the method according to any one of claims 1 to 7 in preparing a zinc-air battery cathode.

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