CN111554941A - Bifunctional catalyst, preparation method thereof and metal-air battery - Google Patents

Abstract

The invention belongs to the technical field of catalysts, and in particular relates to a bifunctional catalyst, a preparation method thereof, and a metal-air battery. In the bifunctional catalyst of the present invention, transition metal oxides and transition metal single atoms have high stability under the synergistic effect of carbon nanotubes, which can avoid the agglomeration of transition metal oxides and transition metal single atoms; The impurities bring a large number of crystal defects, which provide more active sites for the catalyst in the catalytic reaction, which is beneficial to promote the occurrence of the oxygen reduction reaction and the oxygen evolution reaction. The bifunctional catalyst of the invention can promote the occurrence of the oxygen reduction reaction and the oxygen evolution reaction, and has the advantages of good stability and low cost while improving the catalytic efficiency. The application of the bifunctional catalyst of the invention to a metal-air battery can improve the electrochemical performance of the obtained metal-air battery, promote the large-scale production of the metal-air battery, and has a good application prospect.

Description

Bifunctional catalyst and preparation method thereof, metal-air battery

technical field

The invention belongs to the technical field of catalysts, and in particular relates to a bifunctional catalyst, a preparation method thereof, and a metal-air battery.

Background technique

After the second industrial revolution, the improvement in the level of science and technology and medical care has led to a surge in the world population, and the demand for energy due to the improvement of living standards has also reached an all-time high. However, the limited reserves of traditional fossil energy and its exploitation and use easily lead to environmental pollution, so it is urgent to develop new green energy. Lithium batteries and metal-air batteries have the advantages of light pollution, low cost and high energy density, and are considered to be the main force in the development of new energy in the future. Compared with lithium batteries, zinc-air batteries have higher energy density; compared with fuel cells, they have higher safety and practicability. At present, zinc-air batteries have been studied and applied to electric vehicles. For example, from 2016 to 2017, Dongfeng Special Automobile (Shiyan) Bus Co., Ltd. produced more than 500 zinc-air battery electric vehicles. The weight of the zinc-air battery in the battery vehicle is 50% of that of lithium battery, and the driving range is 200% of that of lithium battery. Only 40% off the initial price. Tesla's latest Model S has a battery mass of more than 500 kilograms and a cruising range of less than 600 kilometers. It can be seen that metal-air batteries have great prospects in the field of battery vehicles.

The main reasons hindering the large-scale application of metal-air batteries are the high cost of platinum-based catalysts and the low catalytic activity and poor stability of non-platinum-based catalysts. Therefore, the development of highly active non-platinum catalysts is the primary work to promote metal-air batteries. Both transition metal oxides and metal single-atom catalysts have high catalytic activity for oxygen reduction, but the stability of these catalysts cannot meet the requirements of metal-air batteries. Therefore, the preparation of high-performance, high-stability and low-cost catalysts through efficient processes has become a current research focus.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a bifunctional catalyst, a preparation method thereof, and a metal-air battery, aiming at solving the technical problems of high cost of platinum-based catalysts, low activity and poor stability of non-platinum-based catalysts in existing metal-air batteries.

In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is as follows:

One aspect of the present invention provides a preparation method of a bifunctional catalyst, which comprises the following steps:

Provide organometallic frameworks and transition metal compounds;

Mixing the organic metal framework and the transition metal compound to make the transition metal compound adsorb on the organic metal framework to obtain the organic metal framework adsorbed with the transition metal compound;

The carbon source is introduced, and the organic metal framework adsorbed with the transition metal compound is treated by chemical vapor deposition, so that the transition metal oxide and the single atom of the transition metal are simultaneously supported on the nitrogen-doped carbon nanotube to obtain the bifunctional catalyst.

As a preferred technical solution of the present invention, in the step of mixing the organometallic framework and the transition metal compound, the mass ratio of the organometallic framework to the transition metal compound is (0.1-2): (0.1-1.5).

As a preferred technical solution of the present invention, in the step of treating the organometallic framework with the transition metal compound adsorbed by the chemical vapor deposition method, the temperature of the chemical vapor deposition method is 650°C-1100°C.

As a preferred technical solution of the present invention, before the step of treating the transition metal compound-adsorbed organometallic framework by the chemical vapor deposition method, the method further includes: performing ultraviolet ozone on the transition metal compound-adsorbed organometallic framework. Irradiation treatment.

As a further preferred technical solution of the present invention, the time of the ultraviolet ozone irradiation treatment is 1min-30min.

As a preferred technical solution of the present invention, the organic metal framework is selected from Prussian blue, MIF-47, MIL-53(Fe), MIF-101(Cr), MIL-88(Fe), MOF-5, HKUST -1. At least one of CMK-3, Ni-Me4bpz, IRMOF-3, Mn-BTC, Al-MOFs, ZIF-8, ZIF-67.

As a preferred technical solution of the present invention, in the step of mixing the organic metal framework and the transition metal compound, the mixing treatment method is a solvent method or a deposition method.

As a further preferred technical solution of the present invention, the solvent method is to mix the organometallic framework, the transition metal compound and the solvent, and the mass ratio of the organometallic framework, the transition metal compound, and the solvent is is (0.1-2):(0.1-1.5):(0.3-10).

Another aspect of the present invention provides a bifunctional catalyst comprising nitrogen-doped carbon nanotubes, and transition metal oxides and transition metal single atoms supported on the nitrogen-doped carbon nanotubes.

Still another aspect of the present invention provides a metal-air battery comprising the above-mentioned bifunctional catalyst.

The preparation method of the bifunctional catalyst of the present invention utilizes the structural features of porosity, high specific surface area and modifiability of the organometallic frame, and processes the organometallic frame with the transition metal compound adsorbed by chemical vapor deposition. The metal framework undergoes pyrolysis to generate transition metal single atoms, transition metal oxides and nitrogen sources. The nitrogen source is used to grow nitrogen-doped carbon nanotubes, and the transition metal compounds adsorbed on the organometallic framework react to generate transition metal oxides; due to nitrogen doping Heterocarbon nanotubes have a hollow structure, so the transition metal oxides generated above are supported on the inner and outer walls of nitrogen-doped carbon nanotubes (CNTs), and the single atoms of transition metals generated above are anchored in the nitrogen-doped carbon nanotubes. In the tube wall, nitrogen-doped carbon nanotubes loaded with transition metal oxides and transition metal single atoms at the same time are obtained. The preparation method of the bifunctional catalyst of the present invention has the advantages of simple steps and easy control of the reaction process.

The bifunctional catalyst of the invention is a nitrogen-doped carbon nanotube supporting transition metal oxide and transition metal single atom at the same time, wherein the transition metal oxide and transition metal single atom have higher stability under the synergistic effect of carbon nanotube. It can avoid the agglomeration of transition metal oxides and transition metal single atoms; in addition, nitrogen doping brings a large number of crystal defects, providing more active sites for bifunctional catalysts in catalytic reactions, which is conducive to promoting oxygen The reduction reaction and the oxygen evolution reaction take place. In addition, compared with the traditional platinum-based catalyst, the bifunctional catalyst of the present invention has significantly lower cost and higher stability.

Since the metal-air battery of the present invention includes the above-mentioned bifunctional catalyst with high catalytic efficiency, the occurrence of oxygen reduction reaction and oxygen evolution reaction is promoted. Therefore, the metal-air battery of the present invention has high reaction efficiency, good stability and low cost, which is beneficial to the realization of Industrialization development, has a good application prospect.

Description of drawings

Fig. 1 is the scanning electron microscope image of the bifunctional catalyst obtained in Example 1 of the present invention;

Fig. ² is the metal-air battery obtained in Example 1 of the present invention at a current density of 5mA/cm 20min test results of alternate charging and discharging;

Fig. 3 is the scanning electron microscope image of the bifunctional catalyst obtained in Example 2 of the present invention;

Fig. 4 is the scanning electron microscope image of the bifunctional catalyst obtained in Example 3 of the present invention;

Fig. 5 is the scanning electron microscope image of the bifunctional catalyst obtained in Example 4 of the present invention;

6 is a scanning electron microscope image of the bifunctional catalyst obtained in Example 5 of the present invention.

Detailed ways

In order to make the purposes, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. The embodiments described below are part of the embodiments of the present invention, rather than all implementations. example. In combination with the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. If the specific conditions are not indicated in the examples, the routine conditions or the conditions suggested by the manufacturer are used; if the reagents or instruments used are not indicated by the manufacturer, they are all conventional products that can be purchased from the market.

In the description of the present invention, it is to be understood that expressions in the singular form of a word should be understood to include the plural form of the word unless the context clearly uses otherwise. The terms "comprising" or "having" are intended to specify the presence of features, components, quantities, steps, operations, elements, parts, or combinations thereof, but not to exclude the presence or possible addition of one or more other features, components, quantities , steps, operations, elements, parts or combinations thereof.

In addition, the weight of the relevant components mentioned in the embodiments of the present invention can not only refer to the specific content of each component, but also can represent the proportional relationship between the weights of the components. Therefore, as long as the relevant components are according to the embodiments of the present invention It is within the scope of the disclosure of the present invention that the content of the ingredients is scaled up or down. Specifically, the weight described in the embodiments of the present invention may be a mass unit known in the chemical industry, such as μg, mg, g, and kg.

The embodiment of the present invention provides a preparation method of a bifunctional catalyst, which comprises the following steps:

S1. Provide organometallic frameworks and transition metal compounds;

S2, mixing the organometallic framework with the transition metal compound, so that the transition metal compound is adsorbed on the organometallic framework to obtain the organometallic framework adsorbed with the transition metal compound;

S3, feeding carbon source and nitrogen source, chemical vapor deposition method to process the organometallic framework adsorbed with transition metal compounds, so that transition metal oxides and transition metal single atoms are simultaneously supported on nitrogen-doped carbon nanotubes to obtain bifunctional catalysts .

The preparation method of the bifunctional catalyst of the present invention utilizes the structural features of porosity, high specific surface area and modifiability of the organometallic frame, and processes the organometallic frame with the transition metal compound adsorbed by chemical vapor deposition. The metal framework undergoes pyrolysis to generate transition metal single atoms, transition metal oxides and nitrogen sources. The nitrogen source is used to grow nitrogen-doped carbon nanotubes, and the transition metal compounds adsorbed on the organometallic framework react to generate transition metal oxides; due to nitrogen doping The heterocarbon nanotube is a hollow structure, so the transition metal oxide generated above is supported on the inner and outer walls of the nitrogen-doped carbon nanotube, and the single atom of the transition metal generated above is anchored in the tube wall of the nitrogen-doped carbon nanotube. , and then obtain nitrogen-doped carbon nanotubes loaded with transition metal oxides and transition metal single atoms at the same time. The preparation method of the bifunctional catalyst of the present invention has the advantages of simple steps and easy control of the reaction process.

Specifically, in the above S1, organometallic frameworks (MOFs) are a new class of porous crystalline materials, which are hybrid materials formed by organic ligands and transition metal ions through coordination bonds. The porosity of the organometallic framework makes it have a high specific surface area, and the unique structural characteristics of the organometallic framework make it have switchable ligands and metal centers, and can be modified. In addition, the organometallic framework also has the advantages of low cost and good thermal stability. Oxygen evolution reaction (OER) is a four-electron transfer process, and its reaction kinetics is relatively slow. Therefore, by using organometallic frameworks as reaction raw materials, transition metal single atoms with high catalytic activity of oxygen evolution reaction can be generated by pyrolysis. , used to increase the rate of oxygen evolution reaction.

In some embodiments, the organometallic framework is selected from the group consisting of Prussian Blue, MIF-47, MIL-53(Fe), MIF-101(Cr), MIL-88(Fe), MOF-5, HKUST-1, CMK-3 , at least one of Ni-Me4bpz, IRMOF-3, Mn-BTC, Al-MOFs, ZIF-8, ZIF-67.

The oxygen reduction reaction (ORR) is the cathodic reaction in metal-air batteries. As catalysts for the oxygen reduction reaction, transition metal oxides have very good physical and electrochemical properties and generally low cost, which can accelerate the occurrence and efficiency of the oxygen reduction reaction for providing metal oxidation during the preparation of bifunctional catalysts thing.

In S2, various methods can be used to mix the organometallic framework and the transition metal compound, so that the transition metal compound is adsorbed on the organometallic framework. In some embodiments, the adsorption of the transition metal compound on the organometallic framework is performed using a solvent method. Specifically, the organometallic framework can be dispersed in the solvent first, and then the transition metal compound is added and mixed, so that the transition metal compound is adsorbed on the organometallic framework, and then the solvent is removed. Wherein, the solvent can be a conventional polar or non-polar solvent, such as water, ethanol, methanol, diethyl ether, isopropanol, dichloromethane, benzene, carbon tetrachloride, hexane, DMSO, DMF, acetone at least one.

In some embodiments, the organometallic framework adsorbs the transition metal compound using a deposition method. Optionally, the deposition method is atomic layer deposition and/or pulsed laser deposition to improve deposition efficiency.

By optimizing the addition amount of the organometallic framework and the transition metal compound, it is favorable for the transition metal compound to be uniformly dispersed in the organometallic framework. Therefore, in some embodiments, the mass ratio of the organometallic framework to the transition metal compound is controlled within (0.1-2 ): (0.1～1.5). When the transition metal compound is adsorbed on the organometallic framework by the solvent method, the mass ratio of the organometallic framework to the transition metal compound and the solvent is preferably controlled at (0.1-2):(0.1-1.5):(0.3-10).

In some embodiments, after obtaining the organometallic framework adsorbed with the transition metal compound, it is also subjected to ozone irradiation treatment to modify the surface groups of the organometallic framework and increase its surface binding energy, so as to further improve the subsequent transition metal Binding effect of compounds with nitrogen-doped carbon nanotubes. Specifically, an ultraviolet ozone cleaning machine can be used for irradiation, and the irradiation time is preferably 1min-30min. Specifically, typical and non-limiting irradiation times are 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min.

In S3, when the organometallic framework adsorbed with transition metal compounds is treated by chemical vapor deposition, the organometallic framework can be pyrolyzed to generate transition metal oxides and metal single atoms due to the reaction temperature of chemical vapor deposition. The deposition method can also make transition metal compounds react to generate transition metal oxides. During this process, the introduced carbon source and nitrogen source grow into nitrogen-doped carbon nanotubes, and then simultaneously load transition metal oxides and transition metal single atoms are obtained. of nitrogen-doped carbon nanotubes.

In some embodiments, the chemical vapor deposition treatment of the organometallic framework adsorbed with the transition metal compound can be carried out in a plasma enhanced chemical vapor deposition apparatus with the introduction of a carbon source.

In some embodiments, low cost methane is preferred as the carbon source for growing carbon nanotubes.

Further, the flow rate of the carbon source is 5 sccm-200 sccm. Introducing an appropriate amount of carbon source can avoid problems such as increasing impurities caused by excess carbon source on the premise of ensuring the growth of carbon nanotubes. Specifically, typical non-limiting carbon source flow rates are 5 sccm, 10 sccm, 50 sccm, 100 sccm, 150 sccm, 200 sccm.

In some embodiments, hydrogen gas may also be introduced during the growth of carbon nanotubes. Hydrogen can control the cracking reaction rate of the carbon source, and avoid a large number of cracked carbon atoms caused by the accelerated decomposition of the carbon source at high temperature. It is too late to arrange regularly, and it is only deposited as amorphous carbon or carbon particles, resulting in fewer carbon nanotubes.

Further, the flow rate of introducing hydrogen is 5 sccm-200 sccm. Introducing an appropriate amount of hydrogen can control the cracking reaction rate of the carbon source, and at the same time avoid the cost increase caused by excessive infusion. Specifically, typical and non-limiting nitrogen flow rates are 5 sccm, 10 sccm, 50 sccm, 100 sccm, 150 sccm, 200 sccm.

In some embodiments, the flow rate of the nitrogen gas is 0 sccm-300 sccm. It can be understood that although the organometallic framework contains a certain amount of nitrogen, which can be used as a nitrogen source for nitrogen-doped carbon nanotubes, adding an appropriate amount of nitrogen can make the obtained bifunctional catalyst have a moderate doping nitrogen content, which is beneficial to Sufficient sites are provided for metal oxides and metal single atoms. Specifically, typical non-limiting nitrogen flow rates are 0 sccm, 5 sccm, 10 sccm, 50 sccm, 100 sccm, 150 sccm, 200 sccm, 250 sccm, 300 sccm.

Plasma radio frequency power, ventilation time and heating time can be adjusted according to the actual situation, for example: plasma radio frequency power is 10W-300W; ventilation time is 1h-24h; heating temperature is 350℃-1100℃.

Embodiments of the present invention also provide a bifunctional catalyst comprising nitrogen-doped carbon nanotubes, and transition metal oxides and transition metal single atoms supported on the nitrogen-doped carbon nanotubes.

The bifunctional catalyst of the invention is a nitrogen-doped carbon nanotube supporting transition metal oxide and transition metal single atom at the same time, wherein the transition metal oxide and transition metal single atom have higher stability under the synergistic effect of carbon nanotube. It can avoid the agglomeration of transition metal oxides and transition metal single atoms; in addition, nitrogen doping brings a large number of crystal defects, providing more active sites for bifunctional catalysts in catalytic reactions, which is conducive to promoting oxygen The reduction reaction and the oxygen evolution reaction take place. In addition, compared with the traditional platinum-based catalyst, the bifunctional catalyst of the present invention has significantly lower cost and higher stability.

The embodiment of the present invention also provides a metal-air battery, which includes the above-mentioned bifunctional catalyst.

Metal-air batteries use metals such as magnesium, aluminum, zinc, mercury, and iron as the negative electrode, and oxygen or pure oxygen in the air as the positive electrode. Oxygen side reactions in metal-air batteries include oxygen reduction reaction and oxygen evolution reaction. Since the electrochemical processes of oxygen reduction reaction and oxygen evolution reaction are multi-step electron transfer reactions with slow kinetics, catalysts are often used to reduce electrochemical polarization, Accelerates the electrochemical reaction rate of oxygen. The invention has the advantages of high reaction efficiency, good stability and low cost by replacing the platinum-based catalyst with the bifunctional catalyst of nitrogen-doped carbon nanotubes simultaneously supporting transition metal oxides and transition metal single atoms as the catalyst in the metal-air battery. advantage.

In some embodiments, the bifunctional catalyst of the present invention is mixed with a binder and a conductive agent in a mass ratio of (6-10):(0.2-3):(0-3), and used together with a current collector to assemble the metal Air battery.

Preferably, the binder is selected from polytetrafluoroethylene (PTFE) and/or polyvinylidene fluoride (PVDF).

Preferably, the conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, and graphene.

Preferably, the current collector is selected from carbon paper, carbon cloth, and nickel foam. At least one of nickel sheet, stainless steel sheet, aluminum foil and titanium sheet.

In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art, as well as the bifunctional catalyst of the present invention, its preparation method, and the remarkable performance of the improved performance of the metal-air battery, the following examples illustrate the above technical solutions. .

Example 1

(1) Take 2g of MIF-53(Fe) ultrasonically in 100mL of ethanol solution, add 50mg of cobalt tetroxide particles, stir for 30min, heat and dry in air to obtain powder;

(2) get the gained powder and illuminate 10min in the ultraviolet ozone cleaning machine;

(3) The powder after irradiation was placed in a plasma-enhanced chemical vapor deposition device with 5 sccm of hydrogen, 10 sccm of methane and 0 sccm of nitrogen, a plasma radio frequency power of 50 W, a ventilation time of 4 h, and a heating temperature of 800 °C in a tube furnace to obtain Co ₃ O ₄ @Fe@CNT;

(4) Co ₃ O ₄ @Fe@CNT:PTFE:super-P mass ratio = 9:0.7:0.3, pressed on foam nickel current collector, assembled zinc-air battery, and charged and discharged at a constant current of 5mA/ ^cm2 .

The scanning electron microscope image of Co ₃ O ₄ @Fe@CNT obtained in step (3) is shown in FIG. 1 , and the charging and discharging test results of step (4) are shown in FIG. 2 .

Example 2

(1) take 2g of ZIF-8 ultrasonic in 300mL methanol solution, then add 50mg nickel chloride particles, stir for 30min, rotary vacuum drying to obtain powder;

(2) get the gained powder and illuminate 20min in the ultraviolet ozone cleaning machine;

(3) In the plasma enhanced chemical vapor deposition device, the powder after irradiation was fed with 30 sccm hydrogen, 20 sccm methane and 20 sccm nitrogen, the plasma radio frequency power was 100 W, the ventilation time was 8 h, and the heating temperature of the tube furnace was 1100 °C to obtain NiO@ Ni@CNT;

(4) NiO@Ni@CNT:PVDF:graphene mass ratio=8.5:1.2:0.3, coated on stainless steel current collector, assembled zinc-air battery, and charged and discharged at a constant current of 30 mA/cm ² .

The scanning electron microscope image of the NiO@Ni@CNT obtained in step (3) is shown in FIG. 3 .

Example 3

(1) take 5g of ZIF-67 ultrasonic in 100mL aqueous solution, then add 100mg of ferric nitrate particles, stir for 30min, spin vacuum drying to obtain powder;

(2) get the gained powder and illuminate 20min in the ultraviolet ozone cleaning machine;

(3) The powder after irradiation was placed in a plasma-enhanced chemical vapor deposition device with 30 sccm hydrogen, 20 sccm methane and 20 sccm nitrogen, the plasma radio frequency power was 100 W, the ventilation time was 8 h, and the heating temperature of the tube furnace was 1100 ° C to obtain Fe ₂ O ₃ @Co@CNT;

(4) Fe ₂ O ₃ @Co@CNT:PTFE:super-P=6:3:1, press the sheet on the carbon paper current collector, assemble the zinc-air battery, and conduct the charge-discharge test at a constant current of 20mA/cm ² .

The scanning electron microscope image of Fe ₂ O ₃ @Co@CNT obtained in step (3) is shown in FIG. 4 .

Example 4

(1) Take 10g of MIF-101(Cr) to deposit iron-based catalyst by ALD to obtain powder;

(2) get the gained powder and illuminate 30min in ultraviolet ozone cleaning machine;

(3) The powder after irradiation was placed in a plasma-enhanced chemical vapor deposition device with 100 sccm of hydrogen, 200 sccm of methane and 5 sccm of nitrogen, plasma radio frequency power of 300 W, ventilation time of 24 hours, and a heating temperature of 900 ℃ in a tube furnace to obtain Fe ₃ O ₄ @Cr@CNT;

(4) Fe ₃ O ₄ @Cr@CNT: PTFE mass ratio=9.8:0.2, press the sheet on the carbon cloth current collector, assemble the zinc-air battery, and conduct the charge-discharge test at a constant current of 10mA/cm ² .

The scanning electron microscope image of Fe ₃ O ₄ @Cr@CNT obtained in step (3) is shown in FIG. 5 .

Example 5

(1) get 10g HKUST-1 to deposit cobalt-based catalyst successively by ALD and PLD to obtain powder;

(2) get the gained powder and illuminate 15min in ultraviolet ozone cleaning machine;

(3) The powder after irradiation was placed in a plasma-enhanced chemical vapor deposition device with 7 sccm hydrogen, 30 sccm methane and 50 sccm nitrogen, the plasma radio frequency power was 10 W, the ventilation time was 9 h, and the heating temperature of the tube furnace was 650 ℃ to obtain Co ₃ O ₄ @Cu@CNT;

(4) Co ₃ O ₄ @Cu@CNT:PTFE:CNT mass ratio=8.6:1.1:0.3, press the sheet on the carbon cloth current collector, assemble the zinc-air battery, and conduct the charge-discharge test at a constant current of 3 mA/cm ² .

The scanning electron microscope image of Co ₃ O ₄ @Cu@CNT obtained in step (3) is shown in FIG. 6 .

Comparative Example 1

Traditionally using Pt/C@IrO ₂ catalyst, the potential difference between charge and discharge at 10 mA/cm ² is 0.79 mV.

After mixing and grinding Pt@C, IrO ₂ , PTFE, and super-P according to the mass ratio of 9:9:0.5:0.5 for 30 minutes, they were pressed on the carbon cloth current collector to assemble the zinc ^- air battery. Charge and discharge test under constant current of 10mA/ ^cm2 .

Comparative Example 2

1.10mg graphene ultrasonically dispersed in 100ml alcohol solution;

2. Add 15mg cobalt acetate, 2ml, 30% ammonia water and 5ml water to the dispersion, stir for 5 minutes, put it in a hydrothermal kettle for reaction at 150°C for 10h, and centrifuge to obtain Co ₃ O ₄ @N-graphene catalyst.

3. Co ₃ O ₄ @N-graphene: PTFE: CNT mass ratio=8.5:1.3:0.2, pressed on nickel foam, assembled a zinc-air battery, and charged and discharged at a constant current of 5 mA/cm ² .

Table 1 shows the results of the charge-discharge test potential difference of the air batteries obtained in Examples 1-5 and Comparative Examples 1-2 of the present invention.

Table 1 Potential difference of zinc-air batteries obtained in Example 1-5 and Comparative Example 1-2

It can be seen from Table 1 that the zinc-air battery assembled with the bifunctional catalyst obtained in the embodiment of the present invention can be charged and discharged, so the bifunctional catalyst obtained in the embodiment of the present invention has the catalytic effect of oxygen reduction and oxygen evolution. Under the same current density, the smaller the potential difference, the better the electrochemical performance of the zinc-air battery. Therefore, the zinc-air batteries obtained in Example 1 and Example 5 of the present invention have better electrochemical performance than other examples.

Fig. 1 and Fig. 3-6 show the scanning electron microscope images of the bifunctional catalyst obtained in Example 1-5 of the present invention. It can be seen that the main structure of the bifunctional catalyst obtained in Example 1-5 of the present invention is a carbon nanotube structure, Among them, the granular bright spots are transition metal oxides, which are supported on the inner and outer walls of carbon nanotubes; transition metal single atoms are in the tube walls of carbon nanotubes. Therefore, it can be seen that the bifunctional catalyst of the present invention is a nitrogen-doped carbon nanotube supporting both transition metal oxide and transition metal single atom.

The above-mentioned embodiments only represent individual embodiments of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. A preparation method of a bifunctional catalyst is characterized by comprising the following steps:

providing an organometallic framework, a transition metal compound;

mixing the organic metal framework and the transition metal compound to enable the transition metal compound to be adsorbed on the organic metal framework, so as to obtain the organic metal framework adsorbed with the transition metal compound;

and introducing a carbon source, and treating the organic metal framework adsorbed with the transition metal compound by a chemical vapor deposition method to simultaneously load transition metal oxide and transition metal single atoms on the nitrogen-doped carbon nanotube to obtain the bifunctional catalyst.

2. The method for preparing a bifunctional catalyst as claimed in claim 1, wherein in the step of subjecting the organometallic framework and the transition metal compound to mixing treatment, the mass ratio of the organometallic framework to the transition metal compound is (0.1-2): 0.1-1.5.

3. The method for preparing a bifunctional catalyst according to claim 1, wherein in the step of treating the organometallic framework adsorbed with the transition metal compound by chemical vapor deposition, the temperature of the chemical vapor deposition treatment is 650 ℃ to 1100 ℃.

4. The method for preparing a bifunctional catalyst according to claim 1, wherein the step of treating the organometallic framework adsorbed with the transition metal compound by chemical vapor deposition further comprises: and carrying out ultraviolet ozone irradiation treatment on the organic metal framework adsorbed with the transition metal compound.

5. The method for preparing the bifunctional catalyst according to claim 4, wherein the time of the ultraviolet ozone irradiation treatment is 1min to 30 min.

6. The method for preparing the bifunctional catalyst according to any one of claims 1-5, wherein the organometallic framework is selected from at least one of Prussian blue, MIF-47, MIL-53(Fe), MIF-101(Cr), MIL-88(Fe), MOF-5, HKUST-1, CMK-3, Ni-Me4bpz, IRMOF-3, Mn-BTC, Al-MOFs, ZIF-8, ZIF-67.

7. The method for preparing a bifunctional catalyst as claimed in any one of claims 1 to 5, wherein the step of mixing the organometallic framework and the transition metal compound is a solvent method or a deposition method.

8. The method for preparing a bifunctional catalyst as defined in claim 7, wherein the solvent method comprises mixing the organometallic framework, the transition metal compound and a solvent, and the mass ratio of the organometallic framework, the transition metal compound and the solvent is (0.1-2): (0.1-1.5): (0.3-10).

9. A bifunctional catalyst comprising nitrogen-doped carbon nanotubes, and transition metal oxides and transition metal monatomics supported on the nitrogen-doped carbon nanotubes.

10. A metal-air battery comprising the bifunctional catalyst prepared by the method for preparing a bifunctional catalyst according to any one of claims 1 to 8, or the bifunctional catalyst according to claim 9.

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