CN114976042A - Composite material and preparation method and application thereof - Google Patents

Abstract

The present application discloses a composite material and a preparation method and application thereof. The composite material comprises carbon nanofibers, nanosheets and transition metal nanoparticles; the nanosheets comprise carbon elements; the nanosheets are supported on the carbon nanosheets. on the fibers; the transition metal nanoparticles are dispersed on the carbon nanofibers and the nanosheets. The invention obtains a fiber structure in which the catalytic active site is anchored on the surface of the carbon fiber in situ through the electrospinning technology, which is beneficial to improve the long-term stability of the catalyst during the operation of the metal-air battery.

Description

A kind of composite material and its preparation method and application

technical field

The present application relates to a composite material, a preparation method and application thereof, and belongs to the field of metal-air batteries.

Background technique

The economy based on fossil energy brings social progress and also brings environmental pollution problems. Therefore, the development and utilization of sustainable new energy such as wind energy, solar energy and tidal energy has become a major strategic goal of national development. However, due to geographical restrictions and environmental impacts, this new energy is intermittent and cannot be supplied continuously and stably, resulting in limited utilization. Therefore, it is necessary to develop better energy storage and conversion equipment, in which electrochemical energy storage systems realize the mutual conversion of electrical energy and chemical energy through electrochemical oxidation-reduction reactions, such as lithium-ion batteries, lead-acid batteries, metal-air batteries, etc. Metal-air batteries, especially zinc-air batteries, are considered to be promising devices for next-generation portable devices due to their high energy density and low cost. Currently, metal-air batteries face challenges such as low energy conversion efficiency and poor stability due to the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the multi-electron transfer process. Although noble metal-based electrocatalysts (Pt, Ru, Ir and their alloys) are currently the best oxygen electrocatalysts, their insufficient bifunctional catalytic ability and high scarcity cost hinder large-scale commercial applications. Therefore, the research and development of an efficient non-precious metal bifunctional electrocatalyst is imminent.

SUMMARY OF THE INVENTION

The invention aims at the problems of poor performance and stability of the existing metal-air battery air cathode catalyst, and provides an efficient air cathode catalyst and a preparation method thereof. Through the electrospinning technique, a fibrous structure with catalytic active sites anchored in situ on the surface of carbon fibers was prepared, which is beneficial to improve the long-term stability of the catalyst during the operation of metal-air batteries.

The spinning solution in this application is obtained by dissolving ligands and polymers in organic solvents, and setting appropriate spinning environment and parameters to obtain ligand-polymer non-woven fabrics; immersing the obtained non-woven fabrics in the nucleation-growth metal organic framework In the solution, a uniform layer of organometallic framework material is grown on the surface of the non-woven fabric using the coordination binding force between the ligand and the metal ion to obtain the organometallic framework-ligand-polymer non-woven fabric; the above-mentioned materials are placed in an inert atmosphere. Metal nanoparticle-doped carbon fibers are obtained through high-temperature carbonization in a tube furnace. The zinc-air battery was selected as the test system, and its discharge capacity was measured as high as 165.5mW cm ^-2 , and the performance did not deteriorate significantly after running for 1000 cycles (>160h).

According to a first aspect of the present application, a composite material is provided, the composite material includes carbon nanofibers, nanosheets and transition metal nanoparticles; the nanosheets include carbon elements;

The nanosheets are supported on the carbon nanofibers.

Preferably, the carbon nanofibers penetrate the nanosheets.

Optionally, the nanosheets are arranged at an angle to the carbon nanofibers.

Preferably, the angle is greater than or equal to zero.

The transition metal nanoparticles are dispersed on the carbon nanofibers and the nanosheets.

Optionally, the composite material is two-dimensional nanosheets grown on one-dimensional carbon nanofibers, and zero-dimensional metal nanoparticles are uniformly dispersed on the one-dimensional carbon nanofibers and the two-dimensional nanosheets.

Optionally, in the composite material, the mass content of the transition metal nanoparticles is 10-15%.

Preferably, in the nanosheet, nitrogen element is also included.

Optionally, the transition metal nanoparticles are selected from at least one of cobalt nanoparticles and zinc nanoparticles.

Optionally, in the nanosheet, the mass content of the nitrogen element is 1-5%.

According to a second aspect of the present application, a method for preparing the above composite material is provided, the method comprising:

(1) obtaining a spinning solution containing polymer and ligand I, spinning to obtain ligand I-polymer nonwoven;

(2) mixing the ligand I-polymer non-woven fabric, the transition metal nanoparticle source and the ligand II obtained in the step (1), and growing, to obtain growth on the ligand I-polymer non-woven fabric Intermediate products of metal-organic framework materials;

(3) Heat treatment of the intermediate product obtained in the step (2) in an inactive atmosphere to obtain the composite material.

Optionally, the method includes:

(1) after the ligand I is completely dissolved in the solvent, add the polymer powder, stir until the liquid is transparent and clear, and obtain a mixed spinning solution;

(2) the spinning solution is loaded in the syringe, the stainless steel needle is used, the spinning environment is controlled, the spinning parameters are set, and the ligand I-polymer non-woven fabric is obtained;

(3) Immerse the non-woven fabric obtained in (2) into a nucleation-growth metal organic framework solution containing ligand II and metal ions, and grow a uniform layer of organic metal framework material on the surface of the non-woven fabric to obtain an organic metal framework - ligand-polymer nonwoven;

(4) The non-woven fabric obtained in (3) is carbonized at high temperature in a tube furnace under an inert atmosphere to obtain metal nanoparticle-doped carbon fibers (M-N-CNFs).

Optionally, if the Ligand I or the polymer used contains nitrogen, during the heat treatment, most of the nitrogen in the Ligand I-polymer nonwoven fabric will be carbonized to disappear.

Optionally, when the ligand II does not contain nitrogen, the prepared nanosheets do not contain nitrogen, and when the ligand II contains nitrogen, the prepared nanosheets contain nitrogen. element.

Optionally, the gas used in the heat treatment process is N ₂ or Ar.

Optionally, the step (3) includes: dissolving the transition metal salt and the ligand respectively in a solvent, mixing after being completely dissolved, immersing the above-mentioned non-woven fabric in it, growing an ordered MOF layer on the surface of the fiber, taking out the After cleaning, drying was performed to obtain MOF-polymer non-woven fabric (MOF@PAMN).

Optionally, both the ligand I and the ligand II are independently selected from at least one of trimesic acid, terephthalic acid, benzimidazole, and 2-methylimidazole;

The polymer is selected from at least one of polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, polyimide, asphalt, polyvinylidene fluoride, and cellulose.

Optionally, the source of transition metal nanoparticles is at least one selected from transition metal salts.

Optionally, the transition metal salt is selected from at least one of cobalt salt and zinc salt.

Optionally, the cobalt salt is selected from at least one of cobalt acetate, cobalt nitrate, cobalt sulfate, and cobalt chloride;

The zinc salt is selected from at least one of zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride.

Optionally, in the step (1), the mass ratio of the ligand I to the polymer is 1:12-1:4.

Optionally, the upper limit of the mass ratio of the ligand I and the polymer is independently selected from 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and the lower limit is independently selected from From 1:12, 1:10, 1:5, 1:6, 1:7, 1:8, 1:9.

Optionally, in the step (1), the spinning conditions are: the inner diameter of the needle used for spinning is 0.5-2.0 mm; the temperature is 20-35° C.; the relative humidity of the environment is 10-30%; The spinning voltage is 20-30 kV; the advancing speed of the injector is 0.5-2.0 ml h ^-1 ; the spinning distance is 15-30 cm.

Optionally, the spinning receiver is a flat receiver or a drum receiver.

Optionally, in the step (1), the volume of the syringe used for spinning is 5ml, 10ml or 20ml.

Optionally, the step (2) includes: mixing the ligand I-polymer nonwoven fabric obtained in the step (1), the solution A containing the transition metal nanoparticle source, and the solution B containing the ligand II, growing to obtain an intermediate product of growing a metal-organic framework material on the ligand I-polymer nonwoven fabric;

Optionally, the concentration of the solution A containing the transition metal nanoparticle source is 0.02 mol/L to 0.1 mol/L.

Optionally, the concentration of the solution B containing the ligand II is 0.2 mol/L to 0.8 mol/L.

Optionally, the upper limit of the concentration of the transition metal nanoparticle source-containing solution A is independently selected from 0.1 mol/L, 0.09 mol/L, 0.08 mol/L, 0.07 mol/L, 0.06 mol/L, 0.04 mol/L L, 0.03mol/L, the lower limit is independently selected from 0.02mol/L, 0.09mol/L, 0.08mol/L, 0.07mol/L, 0.06mol/L, 0.04mol/L, 0.03mol/L.

Optionally, the upper limit of the concentration of the solution B containing ligand II is independently selected from 0.8mol/L, 0.7mol/L, 0.6mol/L, 0.5mol/L, 0.4mol/L, 0.3mol/L, The lower limit is independently selected from 0.7 mol/L, 0.6 mol/L, 0.5 mol/L, 0.4 mol/L, 0.3 mol/L, 0.2 mol/L.

Optionally, the solvent in the solution A is selected from at least one of ethanol, methanol and water.

Optionally, the solvent in the solution B is selected from at least one of ethanol, methanol and water.

Preferably, the molar ratio of the transition metal nanoparticle source and the ligand II is 1:1 to 1:10; the mass of the transition metal nanoparticle source is based on its own mass; the mass of the ligand II is Ligand II self mass meter.

Preferably, the growth conditions are: the temperature is 20-30° C.; the time is 1-2 h.

Optionally, the upper limit of the molar ratio of the transition metal nanoparticle source and the ligand II is independently selected from 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1 : 4, 1:3, 1:2, the lower limit is independently selected from 1:1, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1: 2.

Optionally, the Ligand I and the Ligand II are the same.

Optionally, in the step (1), the spinning solution also includes a solvent; the solvent is selected from water, ethanol, acetone, dimethylformamide, dimethylacetamide, N-methyl At least one of pyrrolidones.

Optionally, the mass content of the polymer in the spinning solution is 8-12%.

Optionally, the upper limit of the mass content of the polymer in the spinning solution is independently selected from 12%, 11%, and 10%, and the lower limit is independently selected from 8%, 11%, and 10%.

Optionally, in the step (3), the conditions of the heat treatment are: the heating rate is 1-5°C/min; the temperature is 700-1000°C; and the time is 1-3h.

Optionally, the upper limit of the temperature of the heat treatment is independently selected from 1000°C, 900°C, and 800°C, and the lower limit is independently selected from 700°C, 900°C, and 800°C.

Optionally, in the step (3), the upper limit of the heating rate of the heat treatment is independently selected from 5°C/min, 4°C/min, 3°C/min, and 2°C/min, and the lower limit is independently selected from 1 °C/min, 4 °C/min, 3 °C/min, 2 °C/min.

According to a third aspect of the present application, a catalyst is provided, the catalyst comprising at least one of the above-mentioned composite material and the composite material prepared according to the above-mentioned method.

According to a fourth aspect of the present application, there is provided a metal-air battery, wherein the air electrode catalyst of the metal-air battery is selected from at least one of the above catalysts.

Optionally, the method for preparing the cathode of the metal-air battery includes: mixing the binder, ethanol and water in a volume ratio of 1:2:7 to 1:7:2 and ultrasonically uniformly, and the air electrode catalyst concentration is 5 ～12mg/ml was added to the above solution, sonicated for 20～40min, and uniformly coated on carbon paper according to the catalyst loading of 0.5mg cm ^-2 to 2mg cm ^-2 to obtain an air cathode of a metal-air battery.

The beneficial effects that this application can produce include:

(1) The preparation mechanism of the transition metal-doped carbon nanofiber catalyst in the present invention is as follows: the ligand and the polymer are added to the solvent to configure the spinning solution, wherein the polymer is used as the carbon source, and the ligand is successfully doped during the electrospinning process. into the interior and surface of polymer fibers. When immersed in a solution containing MOF, the interior and surface of the fiber are coated with a uniform layer of MOF by means of the interfacial effect. Carbonized under high temperature and inert atmosphere, the carbon of the polymer itself and the MOF material form transition metal-doped carbon nanofibers, and the nano-sized metal nanoparticles are uniformly dispersed on its surface. Due to the stable and porous properties of the MOF framework, the agglomeration of active sites can be reduced, the specific surface area of the material can be increased, and more active sites can be obtained with enhanced dispersion.

(2) The transition metal-doped carbon nanofiber catalyst prepared by the present invention has a fibrous structure, and the interconnected fibers are beneficial to accelerate electron or ion transport. When thermally decomposed, the polymer will generate gas so that the fiber has a large number of pore structures, which is conducive to gas diffusion and improves the reaction efficiency.

(3) The preparation process of the present invention is simple and easy to obtain, the production cost is low, and large-scale preparation is possible.

(4) The present invention obtains a fiber structure with catalytic active sites anchored on the surface of carbon fibers in situ through electrospinning technology, which is beneficial to improve the long-term stability of the catalyst during the operation of the metal-air battery.

Description of drawings

Fig. 1 is the schematic flow chart of composite material preparation;

Fig. 2 is the SEM image of the ligand-polymer nonwoven fabric prepared in Example 1;

Fig. 3 is the SEM image of the ligand-polymer nonwoven fabric of in-situ growth of three-dimensional MOF nanosheets prepared in Example 1;

Fig. 4 is the SEM image of the composite material prepared in Example 1;

Figure 5 and Figure 6 are TEM images of the catalyst obtained in Example 1;

7 is an EDS-Mapping diagram of the ligand-polymer nonwoven fabric of the in-situ grown three-dimensional MOF nanosheets prepared in Example 1;

8 is the EDS diagram of the ligand-polymer nonwoven fabric of in-situ grown three-dimensional MOF nanosheets prepared in Example 1 and the weight percentage of each element.

Fig. 9 is the discharge performance test curve of the catalyst in the zinc-air battery in Example 2;

10 is a test curve of the long-term charge-discharge cycle stability of the catalyst in Example 2 in a zinc-air battery.

Detailed ways

The present application will be described in detail below with reference to the examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials and reagents in the examples of this application are purchased through commercial channels.

The analytical method in the embodiment of the application is as follows:

Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS-Mapping) of the samples were characterized by a Hitachi SU-8020 field emission scanning electron microscope;

The linear sweep voltammetry of the electrode was measured on the CHI760E electrochemical workstation of Shanghai Chenhua Company;

The cycle stability test of the battery was determined on the CT3001A LAND system of Wuhan Landian Electronics Co., Ltd.

Figure 1 is a schematic flow chart of the preparation of composite materials. It can be seen from Figure 1 that the application first prepares the ligand I-polymer non-woven fabric, and then places it in a solution containing metal salt and ligand II to obtain the The intermediate product of growing nanosheets on Ligand I-polymer nonwoven fabric is finally carbonized to obtain a composite material.

Example 1 Preparation of three-dimensional nanosheets of cobalt-nitrogen-carbon catalyst carbon fibers grown in situ

(1) Dissolving 0.2 g of dimethylimidazole and 1 g of polyacrylonitrile in 9 g of dimethylformamide under magnetic stirring to obtain a spinning solution with a mass content of polyacrylonitrile of 10%.

(2) Put the spinning solution in a 10ml syringe, use a stainless steel needle with a diameter of 1.8mm, control the ambient temperature to 25°C, and the relative humidity to be lower than 30%. Set the spinning parameters: advancing speed 0.6ml/h, voltage 21kV, spinning The silk distance was 25 cm and collected using a roller. After spinning, take off the obtained ligand-polymer non-woven fabric.

(3) Dissolving dimethylimidazole and cobalt nitrate in water to form solutions with concentrations of 0.4 mol/L and 0.05 mol/L, respectively, the molar ratio of dimethylimidazole and cobalt nitrate is 8:1, and rapidly dissolving the cobalt nitrate The aqueous solution was poured into the dimethylimidazole aqueous solution and mixed, and after stirring for 25 s, the ligand-polymer non-woven fabric obtained in (2) was soaked in it for 1 hour. Due to the coordination between cobalt ions and dimethylimidazole, a uniformly distributed nanosheet MOF can be formed on the surface of the fiber, which can be taken out and dried at 60 °C in a vacuum drying oven to obtain ligand-polymerization of in-situ growth of three-dimensional MOF nanosheets. non-woven fabric.

(4) The ligand-polymer non-woven fabric of the in-situ growth of three-dimensional MOF nanosheets was first raised to 250 °C at a heating rate of 1 °C/min in a tube furnace in an argon atmosphere, kept for 1 h, and then heated at a temperature of 2 °C. The heating rate of ℃/min is increased to 800 ℃, the temperature is kept for 1.5 hours, and then cooled to room temperature to obtain the final electrode material, which is the cobalt-nitrogen-carbon metal-air battery air cathode material.

Fig. 2 is the SEM image of the ligand-polymer nonwoven fabric prepared in Example 1; Fig. 3 is the SEM image of the ligand-polymer nonwoven fabric prepared in Example 1 for in-situ growth of three-dimensional MOF nanosheets; Figure 4 is the SEM image of the composite material prepared in Example 1; it can be seen from the figure that the surface of the ligand-polymer non-woven fabric is smooth and flat, and the ligands are uniformly dispersed therein, which is conducive to the in-situ growth of three-dimensional MOF nanosheets. Figure 3 The medium MOF nanosheets were uniformly grown on the non-woven fabric, and after carbonization (Fig. 4), it was found that cobalt nanoparticles were anchored on the nanosheets to form cobalt-nitrogen-carbon catalytic active sites. Figures 5 and 6 are the TEM images of the catalyst obtained in Example 1. It can be seen from the figures that the nanosheet arrays are uniformly arranged, and the cobalt nanoparticles are anchored in the nanosheets and carbon fibers at the same time, that is, cobalt nitrogen carbon is also present in the fibers. Catalytic active sites, increasing active sites is beneficial to catalyst activity.

Fig. 7 is the EDS-Mapping diagram of the ligand-polymer non-woven fabric of the in-situ growth of three-dimensional MOF nanosheets prepared in Example 1. It can be seen from the figure that it further proves that the three elements of cobalt, nitrogen and carbon are uniformly distributed, The overlap is good, proving the existence of cobalt-nitrogen-carbon active sites.

Fig. 8 is the EDS diagram of the ligand-polymer nonwoven fabric of the in-situ growth of three-dimensional MOF nanosheets prepared in Example 1 and the weight percentage of each element. It can be seen from the figure that the weight percentage of cobalt, nitrogen and carbon elements were 12.12%, 2.07% and 65.90%, respectively.

Example 2: Preparation of metal-air battery air cathode

The cobalt-nitrogen-carbon metal-air battery air cathode material prepared in Example 1 was ground into powder, and the catalyst concentration was 10mg/ml ultrasonically dispersed in a binder:water:ethanol volume ratio of 1:4.5:4.5 solution Slurry is made, coated on carbon paper, dried and used as an air cathode.

An aqueous alkaline zinc-air battery was assembled and tested using a zinc sheet as the negative electrode, the above-mentioned air cathode as the positive electrode, and a mixed solution of 6 mol/L potassium hydroxide and 0.2 mol/L zinc acetate as the electrolyte.

Figure 9 shows the discharge polarization curve and discharge capacity curve of the catalyst in the zinc-air battery test system in Example 2. It can be seen from Figure 9 that the zinc-air battery with cobalt nanoparticles and nitrogen-doped carbon fiber as the air cathode material has a discharge capacity of up to 165.5 mW cm ^-2 ; Figure 10 is the charge-discharge stability test of the catalyst in the zinc-air battery test system in Example 2. It can be seen from Figure 10 that after 1000 cycles (>160h) of operation, the difference in the charge-discharge potential of the zinc-air battery The value is slightly larger, and the performance is not significantly degraded.

Example 3 Preparation of in-situ growth of porous nitrogen-doped carbon fiber catalyst and air electrode

(1) 0.12g of dimethylimidazole, 0.6g of polyvinylpyrrolidone and 0.6g of polyacrylonitrile were dissolved in 6.8g of dimethylformamide under magnetic stirring to obtain a spinning solution with a polymer mass content of 12%.

(2) Put the spinning solution in a 20ml syringe, use a stainless steel needle with a diameter of 2mm, control the ambient temperature to 25°C, the relative humidity to be lower than 30%, and set the spinning parameters: advancing speed 2.0ml/h, voltage 30kV, spinning The distance is 30cm, and the rollers are used to collect. After spinning, take off the obtained ligand-polymer non-woven fabric.

(3) Dissolving dimethylimidazole and zinc nitrate in water to form solutions with concentrations of 0.8 mol/L and 0.1 mol/L respectively, the molar ratio of dimethyl imidazole and zinc nitrate is 8:1, and quickly pour the aqueous solution of zinc nitrate. Mixed with dimethylimidazole aqueous solution, and after stirring for 25s, the ligand-polymer non-woven fabric obtained in (2) was soaked in it for 1h. Due to the coordination between zinc ions and dimethylimidazole, a uniformly distributed MOF nanosheet can be formed on the surface of the fiber, which is then taken out and dried in a vacuum drying oven at 60 °C to obtain a ligand-polymerization of in-situ growth of three-dimensional MOF nanosheets. non-woven fabric.

(4) The ligand-polymer non-woven fabric for in situ growth of three-dimensional MOF nanosheets was first raised to 250 °C at a heating rate of 1 °C/min in a tube furnace in an argon atmosphere, and after holding for 1 h, the temperature was 5 °C. The heating rate of ℃/min was increased to 700 ℃, the temperature was maintained for 3 h, and then cooled to room temperature to obtain the final electrode material, which was the porous nitrogen-doped carbon fiber catalyst.

(5) Mix the binder, ethanol and water in a volume ratio of 1:7:2 and ultrasonically evenly, add the above solution according to the air electrode catalyst concentration of 5mg/ml, ultrasonicate for 20min, and press the catalyst load to 0.5mg cm ^-2 It is uniformly coated on carbon paper to obtain the air cathode of metal-air battery.

Example 4 In situ growth of double MOF nitrogen-doped carbon fiber catalyst and preparation of its air electrode

(1) 0.1 g of terephthalic acid and 0.4 g of polyimide were dissolved in 4.6 g of dimethylformamide under magnetic stirring to obtain a spinning solution with a polymer mass content of 8%.

(2) Put the spinning solution in a 5ml syringe, use a stainless steel needle with a diameter of 0.5mm, control the ambient temperature to 25°C, and the relative humidity to be lower than 30%. Set the spinning parameters: advancing speed 0.5ml/h, voltage 25kV, spinning The filaments were 15 cm apart and collected using a roller. After spinning, take off the obtained ligand-polymer non-woven fabric.

(3) The methanol solution of 0.2mol/L dimethylimidazole and the methanol solution of 0.04mol/L zinc acetate and cobalt acetate (the molar ratio of dimethylimidazole, zinc acetate and cobalt acetate is 10:1:1) are rapidly After mixing, the ligand-polymer non-woven fabric obtained in (2) was soaked in it for 2 hours. Due to the coordination of zinc ion, cobalt ion, terephthalic acid and dimethylimidazole, a uniformly distributed MOF can be formed on the surface of the fiber. After taking it out, it is dried at 60 °C in a vacuum drying oven to obtain an in-situ growth of double MOF. Ligand-polymer nonwoven.

(4) The ligand-polymer non-woven fabric of in-situ growth of double MOF was first raised to 250 °C at a heating rate of 1 °C/min in a nitrogen atmosphere in a tube furnace, and after 1 h of heat preservation, the temperature was 2 °C/min. The heating rate was increased to 1000°C, kept for 1 h, and cooled to room temperature to obtain the final electrode material, which was the porous nitrogen-doped carbon fiber catalyst.

(5) Mix the binder, ethanol and water in a volume ratio of 1:7:2 and ultrasonically uniformly, add the above solution according to the air electrode catalyst concentration of 15mg/ml, ultrasonicate for 40min, and uniformly according to the catalyst loading amount of 2mg cm ^-2 Coated on carbon paper to obtain metal-air battery air cathode.

Example 5 In situ growth of double MOF carbon fiber catalyst and preparation of its air electrode

(1) Dissolve 0.1g of terephthalic acid and 1.2g of cellulose in a mixed solution of 10.8g of dimethylacetamide and acetone (the volume ratio of dimethylpropionamide and acetone is 1:2) under magnetic stirring, A spinning solution with a polymer mass content of 12% was obtained.

(2) Put the spinning solution in a 10ml syringe, use a stainless steel needle with a diameter of 0.8mm, control the ambient temperature to 25°C, and the relative humidity to be lower than 30%. Set the spinning parameters: advancing speed 1.0ml/h, voltage 20kV, spinning The filaments were 18 cm apart and collected using a roller. After spinning, take off the obtained ligand-polymer non-woven fabric.

(3) An aqueous solution of 0.2 mol/L terephthalic acid and an aqueous solution of 0.1 mol/L zinc acetate and 0.1 mol/L cobalt acetate (the molar ratio of terephthalic acid, zinc acetate and cobalt acetate is 2:1:1 , that is, the molar ratio of ligand to metal is 1:1) After rapid mixing, the ligand-polymer non-woven fabric obtained in (2) was soaked in it for 2h. Due to the coordination of zinc ion, cobalt ion and terephthalic acid, a uniformly distributed MOF can be formed on the surface of the fiber, which is then taken out and dried in a vacuum drying oven at 60 °C to obtain a ligand-polymer of in-situ growth of dual MOFs. Non-woven.

(4) The ligand-polymer non-woven fabric of in-situ growth of double MOF was first raised to 250°C at a heating rate of 1°C/min in a tube furnace in a nitrogen atmosphere, and after holding for 1 h, the temperature was increased to 2°C/min. The heating rate was raised to 700 °C, the temperature was kept for 1.5 h, and then cooled to room temperature to obtain the final electrode material, which is the porous carbon fiber catalyst.

(5) Mix the binder, ethanol and water in a volume ratio of 1:5:5 and ultrasonically uniformly, add the above solution according to the air electrode catalyst concentration of 10mg/ml, ultrasonicate for 30min, and uniformly according to the catalyst loading amount of 1mg cm ^-2 Coated on carbon paper to obtain metal-air battery air cathode.

The above are only a few embodiments of the present application, and are not intended to limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Without departing from the scope of the technical solution of the present application, any changes or modifications made by using the technical content disclosed above are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims (10)

1. A composite material, characterized in that the composite material comprises carbon nanofibers, nanosheets and transition metal nanoparticles; the nanosheets comprise carbon; the nanosheets are supported on the carbon nanofibers; The transition metal nanoparticles are dispersed on the carbon nanofibers and the nanosheets. 2 . The composite material according to claim 1 , wherein, in the composite material, the mass content of the transition metal nanoparticles is 10-15%; 3 . Preferably, the transition metal nanoparticles are selected from at least one of cobalt nanoparticles and zinc nanoparticles; Preferably, in the nanosheets, nitrogen is also included; Further preferably, in the nanosheet, the mass content of the nitrogen element is 1-5%. 3. The preparation method of the composite material according to claim 1 or 2, wherein the method comprises: (1) obtaining a spinning solution containing polymer and ligand I, spinning to obtain ligand I-polymer nonwoven; (2) mixing the ligand I-polymer non-woven fabric, the transition metal nanoparticle source and the ligand II obtained in the step (1), and growing, to obtain growth on the ligand I-polymer non-woven fabric Intermediate products of metal-organic framework materials; (3) Heat treatment of the intermediate product obtained in the step (2) in an inactive atmosphere to obtain the composite material. 4. preparation method according to claim 3, is characterized in that, described part I and described part II are all independently selected from trimesic acid, terephthalic acid, benzimidazole, 2-methyl at least one of imidazoles; The polymer is selected from at least one of polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, polyimide, asphalt, polyvinylidene fluoride, and cellulose. 5 . The preparation method according to claim 3 , wherein the source of transition metal nanoparticles is at least one selected from transition metal salts. 6 . 6 . The preparation method according to claim 5 , wherein the transition metal salt is selected from at least one of cobalt salt and zinc salt. 7 . 7. The preparation method according to claim 6, wherein the cobalt salt is selected from at least one of cobalt acetate, cobalt nitrate, cobalt sulfate, and cobalt chloride; The zinc salt is selected from at least one of zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride. 8. The preparation method according to claim 3, wherein in the step (1), the mass ratio of the ligand I to the polymer is 1:12～1:4; Preferably, in the step (1), the spinning conditions are: the inner diameter of the needle used for spinning is 0.5-2.0 mm; the temperature is 20-35°C; the relative humidity of the environment is 10-30%; The silk voltage is 20～30kV; the injector advancing speed is 0.5～2.0ml h ^-1 ; the spinning distance is 15cm～30cm; Preferably, the step (2) includes: mixing the ligand I-polymer nonwoven fabric obtained in the step (1), the solution A containing the transition metal nanoparticle source, and the solution B containing the ligand II, and growing , to obtain an intermediate product of growing metal-organic framework materials on the ligand I-polymer non-woven fabric; The concentration of the solution A containing the transition metal nanoparticle source is 0.02mol/L～0.1mol/L; The concentration of the solution B containing the ligand II is 0.2mol/L～0.8mol/L; Preferably, the molar ratio of the transition metal nanoparticle source and the ligand II is 1:1 to 1:10; The mass of the transition metal nanoparticle source is based on its own mass; the mass of the ligand II is based on the own mass of the ligand II; Preferably, the growth conditions are: the temperature is 20-30°C; the time is 1-2h; Preferably, in the step (1), the spinning solution further includes a solvent; the solvent is selected from water, ethanol, acetone, dimethylformamide, dimethylacetamide, N-methylpyrrolidone at least one of; Preferably, the mass content of the polymer in the spinning solution is 8-12%; Preferably, in the step (3), the conditions of the heat treatment are: the heating rate is 1-5°C/min; the temperature is 700-1000°C; and the time is 1-3h. 9 . A catalyst, characterized in that the catalyst comprises at least one of the composite material of claim 1 or 2 and the composite material prepared by the method of any one of claims 3 to 8 . 10 . A metal-air battery, wherein the air electrode catalyst of the metal-air battery is selected from at least one of the catalysts of claim 9 .

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