Fluorine-nitrogen-doped carbon-based oxygen reduction electrocatalyst for zinc-air battery and preparation method of fluorine-nitrogen-doped carbon-based oxygen reduction electrocatalyst

Abstract

The invention discloses a fluorine-nitrogen-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery and a preparation method of the fluorine-nitrogen-doped carbon-based oxygen reduction electrocatalyst, and belongs to the technical field of catalysts. According to the method, a fluorocarbon mixture is rapidly treated through Joule heat to achieve efficient fluorine doping, then nitrogen doping is conducted through an ammonia gas plasma technology, and therefore an original carbon precursor is converted into fluorine-nitrogen-doped carbon. The catalyst material is short in preparation time and high in production efficiency, the content configuration of fluorine and nitrogen doped in fluorine-nitrogen-doped carbon finally formed by accurately controlling the temperature and time of Joule heat treatment and the power and time of plasma treatment is controllable, the morphology and the pore structure are controllable, high electro-catalytic performance is guaranteed, and the catalyst material is suitable for industrial production. The preparation method is high in production efficiency and low in cost, and has large-scale amplification potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for zinc-air batteries and a preparation method thereof. Background Art

[0002] Zinc-air batteries (ZABs) are clean energy storage devices that convert chemical energy into electrical energy through redox reactions by means of a zinc negative electrode and a catalyst positive electrode. At present, the performance of zinc-air batteries is mainly limited by two major problems: insufficient power density and short cycle life. The insufficient power density is directly related to the insufficient catalytic activity caused by the poor reaction kinetics of the positive electrode catalyst. The short cycle life is related to factors such as the weak catalytic stability of the positive electrode catalyst, the dendritic corrosion and passivation of the zinc negative electrode, and the failure of the electrolyte composition. Therefore, there is an urgent need to develop non-precious metal catalysts with high activity and high stability to replace precious metal catalysts (such as Pt / C) in order to improve the power density, cycle life, and rate performance of ZABs.

[0003] However, in the process of industrial application, the following technical problems exist: (1) Carbon-based materials are generally prepared by heating and carbonizing in a tube furnace, which has a long carbonization time and low production efficiency; (2) Non-precious metal heteroatom carbon-based catalysts have insufficient active sites, manifested as insufficient catalytic activity of the catalyst, especially when applied to devices such as actual zinc-air batteries, which is related to the insufficient controllability of the quantity and position of heteroatom doping, and also related to the pore structure and morphology of the carbon-based material itself; (3) The cycle stability of heteroatom carbon-based catalysts still needs to be improved, which is related to the stability of the doped heteroatoms and the stability of the carbon material itself. Summary of the Invention

[0004] An object of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for zinc-air batteries and a preparation method thereof, so as to solve the problems of long heating and carbonization preparation time of carbon-based materials and insufficient catalytic activity of the catalyst in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for zinc-air batteries, comprising the following steps: S1, mixing a carbon source and a fluorine dopant to obtain a mixed slurry, coating the mixed slurry on carbon cloth, and drying to obtain carbon cloth loaded with the carbon source and the fluorine dopant; S2, subjecting the carbon cloth loaded with the carbon source and the fluorine dopant to Joule heat treatment, and after completion, obtaining powder on the carbon cloth, and performing post-treatment on the powder to obtain fluorine-doped carbon; S3, performing plasma treatment on the fluorine-doped carbon in an ammonia atmosphere to obtain fluorine and nitrogen co-doped carbon.

[0006] A further improvement of the present invention lies in: Preferably, in S1, the specific process of mixing the mixed carbon source and the fluorine dopant is as follows: successively through solid-phase grinding, ultrasonic mixing, and stirring and dispersing treatments.

[0007] Preferably, in S1, the mixing mass ratio of the carbon source and the fluorine dopant is 1:(0.1 - 2).

[0008] Preferably, in S1, the carbon source is one or several of carbon black, Ketjen black, sodium alginate, sodium citrate, sucrose, lactose, cellulose, hemicellulose, starch, and dextrin.

[0009] Preferably, in S1, the fluorine dopant is one or more of PTFE, PVDF, and ammonium fluoride.

[0010] Preferably, in S2, during the Joule heat treatment process, the charging voltage is 5 - 100V, the energization time is 100 - 10000ms, and the Joule heat temperature is 500 - 2000°C.

[0011] Preferably, in S2, the process of post-treating the powder is as follows: the powder is subjected to pickling, filtration, water washing, and drying treatments.

[0012] Preferably, in S3, the temperature of the plasma treatment process is 25 - 400°C, the treatment time is 1 - 180s, and the power is 10 - 200W.

[0013] A fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery prepared by any one of the above preparation methods, which is composed of aggregated carbon particles. The surface of the carbon particles has roughness, and the interior has a pore structure. Fluorine and nitrogen are doped on the carbon particles; among them, carbon and fluorine are connected by ionic carbon-fluorine bonds and semi-ionic carbon-fluorine bonds, and the nitrogen includes graphitic nitrogen and pyridinic nitrogen.

[0014] Preferably, the total specific surface area of the fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst is 200 - 250 m 2 g –1 .

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery. In this method, fluorine doping is first achieved by rapidly treating a carbon-fluorine mixture through Joule heating, and then nitrogen doping is carried out through ammonia plasma, thereby converting the original carbon precursor into fluorine and nitrogen co-doped carbon. This preparation method combines Joule heating and plasma treatment. Fluorine doping is realized through Joule heat treatment; by ammonia plasma treatment, additional edge and defect sites are created on the carbon material surface, and nitrogen doping mainly composed of pyridine nitrogen and graphitic nitrogen is achieved simultaneously. Moreover, since ammonia plasma can reshape the carbon skeleton, ionic carbon-fluorine bonds and semi-ionic carbon-fluorine bonds are finally obtained, ensuring the synergistic catalytic activity of fluorine and nitrogen species. The catalyst material prepared by the present invention has a short preparation time, high production efficiency, and the potential for large-scale amplification. The synthesized fluorine and nitrogen co-doped carbon has regular morphology and pore structure, and the doping components are controllable.

[0016] Further, the carbon source and the fluorine dopant are successively subjected to solid-phase grinding, ultrasonic mixing, and stirring and dispersion treatments, so that the two can be fully mixed and then uniformly coated on the carbon cloth.

[0017] Further, by adjusting the ratio of the carbon source to the fluorine dopant, the fluorine doping content in the subsequent carbon and the pore structure on the carbon can be adjusted. If the ratio of the fluorine dopant is too small, the fluorine doping content is insufficient; if the ratio of the fluorine dopant is too large, the pore structure is insufficient.

[0018] Further, the carbon source can be common types such as carbon black and sucrose, indicating that the method has a wider applicability.

[0019] Further, the fluorine dopant is polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ammonium fluoride, etc. During the heating process, the fluorine dopant decomposes and releases fluorine-containing free radicals or gaseous fluorine. During the reaction process between the released fluorine and carbon, carbon-fluorine bonds are formed, enabling fluorine to firmly adhere to carbon.

[0020] Further, by precisely controlling the temperature and time of Joule heat treatment, ionic carbon-fluorine bonds and semi-ionic carbon-fluorine bonds can be obtained.

[0021] Further, by precisely controlling the plasma treatment atmosphere, power, and time, a nitrogen configuration mainly composed of pyridine nitrogen and graphitic nitrogen is obtained.

[0022] The present invention also discloses a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery. The prepared fluorine and nitrogen co-doped carbon (FNC) has appropriate amounts of doped fluorine and nitrogen, a large specific surface area, pore volume, and a relatively regular morphology. By regulating the micro-nano size of the carbon material, the number of active sites and the catalytic "three-phase interface" are increased. The precise site doping and synergistic effect of fluorine atoms and nitrogen atoms significantly improve the electrocatalytic activity. The catalyst has a relatively regular micro-spherical morphology, abundant edge sites, and a high specific surface area (up to 213.0 m 2 g –1 ), an excellent micropore to mesopore ratio (the specific surface areas of micropores and mesopores can reach 150.5 m 2 g –1 and 62.5 m 2 g –1 ), ensuring good mass transfer; an effective doped nitrogen content (1.26 at%) and doped fluorine content (0.25 at%), an optimized pyridine nitrogen and graphite nitrogen configuration (34.1%, 26.2%) and doped fluorine configuration, ensuring sufficient catalytic active sites and intrinsic catalytic activity; the above advantages enable the material to show good catalytic performance as an oxygen reduction reaction electrocatalyst in alkaline electrolyte, making the zinc-air battery have good power density, rate performance, and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a scanning electron microscope (SEM) image of the FNC prepared in Example 2 of the present invention.

[0024] Figure 2 FIG. is a fluorine deconvolution peak diagram of the X-ray photoelectron spectroscopy (XPS) of the FNC prepared in Example 2 of the present invention.

[0025] Figure 3 FIG. is a nitrogen deconvolution peak diagram of the X-ray photoelectron spectroscopy (XPS) of the FNC prepared in Example 2 of the present invention.

[0026] Figure 4 FIG. is a linear sweep voltammetry (LSV) diagram of the products prepared in Comparative Example 1, Comparative Example 2, and Example 2 of the present invention at various rotation speeds in 0.1 mol L –1 KOH solution at 10 mV s –1 .

[0027] Figure 5 FIG. is a power density diagram measured in a zinc-air battery with the FNC prepared in Example 2 of the present invention as the electrolyte in 6.0 mol L –1 KOH + 0.2 M Zn(CH3COO)2 solution.

[0028] Figure 6The FNC prepared in Example 2 of the present invention in 6.0 mol L –1 The constant current discharge curve diagram at different current densities measured in a zinc-air battery with a KOH + 0.2M Zn(CH3COO)2 solution as the electrolyte.

[0029] Figure 7 The FNC prepared in Example 2 of the present invention in 6.0 mol L –1 The charge-discharge cycle curve diagram of a zinc-air battery with a KOH + 0.2M Zn(CH3COO)2 solution as the electrolyte. Detailed implementation manners

[0030] The present invention will be further described in detail below with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0031] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar expressions cover the meanings of "consisting of" and "mainly consisting of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0032] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0033] Conventional instrument equipment in the art is used in the following embodiments. The experimental methods without specific conditions indicated in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0034] The first aspect of the present invention discloses a preparation method of a fluorine-nitrogen doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery, comprising the following steps: S1. First, grind and uniformly mix a carbon source and a fluorine dopant at a mass ratio of 1:(0.1 - 2), then ultrasonically disperse, and then obtain a mixed slurry through magnetic stirring. Uniformly coat the mixed slurry on carbon cloth and dry it to obtain carbon cloth loaded with a mixed material.

[0035] Exemplarily, the ratio can be 1:0.1, 1:0.5, 1:1, 1:1.5, and 1:2. In this process, by adjusting the ratio of the carbon source to the fluorine dopant, the fluorine doping content in carbon and the pore structure on the carbon can be adjusted. If the ratio of the fluorine dopant is too small, the fluorine doping content is insufficient; if the ratio of the fluorine dopant is too large, the pore structure is insufficient.

[0036] S2. Perform fluorine doping through Joule heat: Connect the carbon cloth loaded with the mixed material to an electrode through a conductive fixture, pass in direct current, instantaneously energize in a nitrogen atmosphere, control the charging voltage to 5 - 100 V, control the energization time within 100 - 10,000 ms, and control the Joule heat temperature at 500 - 2,000 °C. After the treatment, scrape off the powder on the carbon cloth, and obtain fluorine-doped carbon through pickling, filtering, washing with water, and drying.

[0037] Exemplarily, the charging voltage can be 5 V, 10 V, 20 V, 30 V, 40 V, 50 V, 60 V, 70 V, 80 V, 90 V, or 100 V. The energization time can be 100 ms, 200 ms, 300 ms, 400 ms, 500 ms, 600 ms, 700 ms, 800 ms, 900 ms, or 1,000 ms. The Joule heat temperature can be 500 °C, 800 °C, 1,000 °C, 1,200 °C, 1,500 °C, 1,800 °C, or 2,000 °C.

[0038] S3. Perform nitrogen doping through plasma treatment: Transfer the fluorine-doped carbon to a plasma furnace chamber, treat it at 25 - 400 °C for 1 - 180 s in an ammonia atmosphere, and control the plasma treatment power at 10 - 200 W to obtain fluorine and nitrogen co-doped carbon.

[0039] Exemplarily, when performing nitrogen doping with ammonia, the temperature can be 25 °C, 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, or 400 °C, the treatment time can be 1 s, 5 s, 10 s, 20 s, 50 s, 80 s, 100 s, 120 s, 150 s, or 180 s. The plasma treatment power can be 10 W, 50 W, 100 W, 150 W, or 200 W.

[0040] In this step, the plasma can dope nitrogen on the carbon material with ammonia as a precursor, and the ammonia plasma can etch additional edges and defects at the edges of the carbon material, synchronously realizing the introduction of nitrogen atoms and the remodeling of the carbon skeleton.

[0041] The preparation method of the present invention uses rapid Joule heat treatment to dope fluorine into micro-carbon spheres. Due to the short treatment time, the morphology of the carbon material can be kept intact, and the stability of the morphology of the micro-carbon spheres can be maintained. Ammonia plasma further creates additional edges and defect sites on the surface of the micro-carbon spheres, achieving controllable doping positions of nitrogen atoms and fluorine atoms, and the doped nitrogen and doped fluorine at the edges and defects have higher catalytic activity.

[0042] The present invention generates ionic CF (ionic) and semi-ionic CF (semi-ionic) of specified configurations by controlling the process parameters of the Joule heat-ammonia plasma integration technology. Simple Joule heat treatment cannot produce a sufficient proportion of semi-ionic CF (semi-ionic) configurations. Etching of the carbon structure by ammonia plasma treatment creates additional edges and defects, driving the transformation of ionic CF to semi-ionic CF (semi-ionic). Finally, the integration of Joule heat and ammonia plasma technology realizes that the doped fluorine in the fluorine-nitrogen doped carbon material has two configurations, in which the atomic ratio of ionic CF and semi-ionic CF can be controlled to be 1: (0.9-1.1).

[0043] At the same time, by controlling the process parameters of the Joule heat-ammonia plasma integrated technology, a doped nitrogen configuration with pyridinic nitrogen and graphitic nitrogen as the main body was generated. Ammonia plasma can etch additional edges and defects at the edges of the carbon material, so that the nitrogen doping is mainly doped at the edges and defect positions of the carbon structure, thereby forming pyridinic nitrogen. At the same time, a rich graphitic nitrogen configuration can also be formed under medium temperature conditions of 200°C. In the final nitrogen configuration, the content ratio of pyridinic nitrogen to the total nitrogen content can be controlled to be 30-40%, the content ratio of graphitic nitrogen to the total nitrogen content can be controlled to be 20-30%, and the rest is pyrrolic nitrogen and graphitic nitrogen.

[0044] As a preferred solution, in S1, the mixing method of the carbon source and the fluorine dopant is a three-stage mixing method of solid phase grinding, ultrasonic mixing, and finally stirring dispersion. The solid phase grinding is 5-10 minutes, the ultrasonic time is 0.1-0.5 hours, and the stirring time is 0.5-2 hours.

[0045] As a preferred embodiment, in S1, the carbon source is one or more of carbon black, Ketjen black, sodium alginate, sodium citrate, sucrose, lactose, cellulose, hemicellulose, starch and dextrin.

[0046] As a preferred solution, in S1, the fluorine dopant is one or more of PTFE, PVDF and ammonium fluoride.

[0047] As a preferred solution, in S1, the mass ratio of the carbon source to the fluorine dopant is 1:0.5.

[0048] As a preferred solution, in S2, the charging voltage is controlled at 50V, the energization time is controlled at 3000ms, and the joule heat temperature is controlled at 750°C.

[0049] As a preferred solution, in S3, the plasma treatment conditions are an ammonia atmosphere, the treatment temperature is 200°C, the treatment time is 20s, and the treatment power is 30W.

[0050] In a specific embodiment of the present invention, in S1, the mass ratio of the carbon source to the fluorine dopant is 1:0.5; in S2, the charging voltage is controlled at 50V, the energization time is controlled at 3000ms, and the joule heat temperature is controlled at 750°C; in S3, the plasma treatment conditions are an ammonia atmosphere, the treatment temperature is 200°C, the treatment time is 20s, and the treatment power is 30W.

[0051] The second aspect of the present invention discloses a fluorine and nitrogen doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery prepared by the above preparation method. The main structure of the catalyst consists of composite carbon spheres, which are doped with fluorine and nitrogen, and the carbon spheres have a pore structure, including micropores and mesopores The fluorine-doped carbon (FNC) prepared by the above steps can control the fluorine doping amount and nitrogen doping amount to 0.2-0.3at% and 1-1.5at% respectively, the ratio of ionic bond type C-F to semi-ionic bond type C-F can be controlled to 1:(0.9-1.1), the content ratio of pyridine nitrogen to the total nitrogen content is 30-40%, the content ratio of graphitic nitrogen to the total nitrogen content is 20-30%, and it also includes some pyrrole nitrogen and nitrogen oxides; the total specific surface area of the composite material is 200-250 m 2 g –1 , the micropore surface area can be controlled to 140-200m 2 g –1 , the mesopore surface area can be controlled to 50-110m 2 g –1 . At the same time, the catalyst has a morphology in which micro carbon spheres are interconnected, and the surface of the carbon spheres has rich roughness.

[0052] The following is further illustrated with specific examples. The natural mineral-based raw materials used in the following examples are all subjected to the same pretreatment.

[0053] Example 1 First, carbon black and PTFE were ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere, the charging voltage was controlled at 50V, the power-on time was 3000ms, and the Joule heat temperature was 500°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 200°C for 20s in an ammonia atmosphere with a power of 30W, thereby obtaining fluorine and nitrogen co-doped carbon.

[0054] Example 2 First, carbon black and PTFE were ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere, the charging voltage was controlled at 50V, the power-on time was 3000ms, and the Joule heat temperature was 750°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 200°C for 20s in an ammonia atmosphere with a power of 30W, thereby obtaining fluorine and nitrogen co-doped carbon. Example 3 First, carbon black and PTFE were ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere, the charging voltage was controlled at 50V, the power-on time was 3000ms, and the Joule heat temperature was 1000°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 200°C for 20s in an ammonia atmosphere with a power of 30W, thereby obtaining fluorine and nitrogen co-doped carbon.

[0055] Example 4 First, carbon black and PTFE were ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere. The charging voltage was controlled at 50 V, the power-on time was 3000 ms, and the Joule heat temperature was 750 °C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 200 °C for 20 s in an ammonia atmosphere with a power of 10 W to obtain fluorine and nitrogen co-doped carbon.

[0056] Example 5 First, carbon black and PTFE were ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere. The charging voltage was controlled at 50 V, the power-on time was 3000 ms, and the Joule heat temperature was 750 °C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 200 °C for 20 s in an ammonia atmosphere with a power of 50 W to obtain fluorine and nitrogen co-doped carbon.

[0057] Example 6 First, Ketjen black and PVDF were ground and uniformly mixed at a mass ratio of 1:0.1. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out in a nitrogen atmosphere. The charging voltage was controlled at 30 V, the power-on time was 100 ms, and the Joule heat temperature was 1000 °C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 25 °C for 180 s in an ammonia atmosphere with a power of 100 W to obtain fluorine and nitrogen co-doped carbon.

[0058] Example 7 Sodium citrate and PVDF were first ground and uniformly mixed at a mass ratio of 1:1. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out under a nitrogen atmosphere, the charging voltage was controlled at 5V, the power-on time was 10000ms, and the Joule heat temperature was 1000°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 100°C for 100s under an ammonia atmosphere with a power of 200W to obtain fluorine and nitrogen co-doped carbon.

[0059] Example 8 Lactose and PTFE were first ground and uniformly mixed at a mass ratio of 1:1.5. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out under a nitrogen atmosphere, the charging voltage was controlled at 80V, the power-on time was 500ms, and the Joule heat temperature was 1000°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 300°C for 50s under an ammonia atmosphere with a power of 150W to obtain fluorine and nitrogen co-doped carbon.

[0060] Example 9 Cellulose and PVDF were first ground and uniformly mixed at a mass ratio of 1:0.2. After ultrasonic dispersion, magnetic stirring was carried out to obtain a mixed slurry. The mixed slurry was uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material was connected to the electrode through a conductive fixture, and instantaneous direct current was passed through. Instantaneous power-on was carried out under a nitrogen atmosphere, the charging voltage was controlled at 100V, the power-on time was 800ms, and the Joule heat temperature was 1000°C. After the treatment, the powder on the carbon cloth was scraped off, and fluorine-doped carbon was obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon was transferred to a plasma furnace chamber and treated at 400°C for 1s under an ammonia atmosphere with a power of 50W to obtain fluorine and nitrogen co-doped carbon.

[0061] Comparative Example 1 The carbon source and the fluorine dopant are first ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring is carried out to obtain a mixed slurry. The mixed slurry is uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material is connected to the electrode through a conductive fixture, and instantaneous direct current is passed through. Under a nitrogen atmosphere, instantaneous power-on is carried out, the charging voltage is controlled at 50V, the power-on time is 3000ms, and the Joule heat temperature is 750°C. After the treatment, the powder on the carbon cloth is scraped off, and fluorine-doped carbon is obtained through pickling, filtration, water washing, and drying. Then, the fluorine-doped carbon is transferred to a plasma furnace chamber and treated at 200°C for 20s under a nitrogen atmosphere with a power of 30W to obtain fluorine and nitrogen co-doped carbon, and electrocatalytic tests are carried out to verify the effect.

[0062] Comparative Example 2 The carbon source and the fluorine dopant are first ground and uniformly mixed at a mass ratio of 1:0.5. After ultrasonic dispersion, magnetic stirring is carried out to obtain a mixed slurry. The mixed slurry is uniformly coated on carbon cloth and dried. Then, the carbon cloth loaded with the mixed material is connected to the electrode through a conductive fixture, and instantaneous direct current is passed through. Under a nitrogen atmosphere, instantaneous power-on is carried out, the charging voltage is controlled at 50V, the power-on time is 3000ms, and the Joule heat temperature is 750°C. After the treatment, the powder on the carbon cloth is scraped off, and fluorine-doped carbon is obtained through pickling, filtration, water washing, and drying. Electrocatalytic tests are carried out to verify the effect.

[0063] The fluorine and nitrogen co-doped carbon materials obtained in Examples 1-9 and Comparative Examples 1-2 are characterized and tested according to the following scheme.

[0064] 1) SEM test The representative FNC prepared in Example 2 exhibits relatively regular carbon microspheres under a scanning electron microscope (SEM), with a particle size of 200-500nm, and has rich surface roughness. As Figure 1 shown, the FNC with this morphology can provide rich edges and defect positions for the embedding of active sites, and is also conducive to electron transfer and the transport of related substances.

[0065] 2) X-ray photoelectron spectroscopy test The surface elements and contents of the samples in Example 2 are tested using an X-ray photoelectron spectroscopy (XPS) analyzer. FNC has a high carbon content and some nitrogen, phosphorus, and oxygen contents. Figure 2 is the high-resolution fluorine partial peak diagram of FNC. FNC has two typical C-F bonds, C-F (ionic) and C-F (semi-ionic). Fluoride ions can change the electronegativity around the doping environment, thereby optimizing the catalyst reaction energy barrier. Figure 3High-resolution nitrogen peak figure of FNC. FNC contains 1.26 at% nitrogen atoms respectively. Through peak fitting calculation, the contents of pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen and oxidized nitrogen in FNC are 0.43, 0.29, 0.33 and 0.21 at% respectively; the doping content and type of fluorine and nitrogen atoms in FNC are precisely controllable (see Table 1). The C-F bond, pyridine nitrogen and graphitic nitrogen change the charge density and spin density of adjacent carbon, thereby improving the catalytic activity.

[0066] Table 1 Composition and content of fluorine and nitrogen atom doping in FNC in Example 2

[0067] It should be noted that the doping of fluorine and nitrogen dual atoms with controllable configuration and content must be achieved by precisely controlling the process parameters of the Joule heat-ammonia plasma integration technology within the protection scope. Simply combining the two technologies cannot achieve the controllable doping of the two atoms simultaneously.

[0068] 3) Nitrogen physical adsorption test Use a nitrogen physical adsorption instrument to test the specific surface area and pore structure of the sample in Example 2. Table 2 shows the specific surface area information of FNC. The total specific surface area is 213.0 m 2 g -1 , the micropore surface area can be controlled to 150.5 m 2 g -1 , the mesopore surface area can be controlled to 62.5 m 2 g -1 . It can be seen that FNC has micropores with larger pore size and a certain proportion of mesopores. The micropores can provide an actual reaction site for the catalytic reaction, and the mesopores can facilitate mass transfer and the transfer of related substances. The synergistic effect of micropores and mesopores enables the function of more active sites to be exerted, ensuring excellent catalytic efficiency.

[0069] Table 2 Specific surface area information of FNC in Example 2

[0070] 4) Alkaline catalytic performance test The preparation process of the working electrode is as follows: Weigh 3 mg of the fluorine and nitrogen doped carbon material prepared in Example 2 and put it into a centrifuge tube, then add 80 μL of isopropanol, 160 μL of water and 10 μL of perfluorosulfonic acid-polytetrafluoroethylene copolymer to prepare a 250 μL suspension and ultrasonicate it for 30 min to form a well-dispersed black mucus. Then take 10 μL of the mucus and drop it on the glassy carbon electrode and dry it to prepare the working electrode. Use a carbon rod electrode as the reference electrode and a platinum wire as the counter electrode to conduct oxygen reduction electrocatalytic performance test on the workstation. Under the condition of a constant temperature water bath at 25 °C, 0.1 mol L –1The sample FNC of Example 2 was subjected to LSV testing in a KOH solution.

[0071] Figure 4 Figure 4 shows the LSV curves of the catalysts in Example 2, Comparative Example 1, and Comparative Example 2 at a typical rotation speed of 1600 rpm. It can be seen from the figure that the carbon precursor basically has no catalytic activity. The fluorine-doped carbon in Comparative Example 2 has certain catalytic activity, confirming the catalytic effect of the doped fluorine introduced by Joule heat treatment of the carbon-fluorine mixture. FNC in Example 2 has the most excellent catalytic performance, with a half-wave potential of 0.87 V and a limiting current density of 6.80 mA cm –2 . The excellent catalytic performance of FNC benefits from the balanced improvement of active sites, pore structure, and surface roughness caused by fluorine-nitrogen doping brought about by the two-step preparation method of first fluorine doping by Joule heat method and then nitrogen doping by plasma method, further demonstrating the catalytic improvement of the doped nitrogen introduced by the second-step ammonia plasma. In contrast, in Comparative Example 1, the plasma atmosphere in the second step was changed from ammonia to nitrogen, and the obtained catalyst material has catalytic activity superior to that of the fluorine-doped carbon in Comparative Example 2 but weaker than that of the FNC catalyst in Example 2. This further illustrates the positive effect of ammonia plasma. Ammonia plasma can create additional edge and defect sites on the surface of micro-carbon spheres, realizing the controllable doping of nitrogen atoms at the edge / defect positions. Finally, the content ratio of pyridine nitrogen to the total nitrogen content can be controllably achieved to be 30 - 40%, and the content ratio of graphitic nitrogen to the total nitrogen content can be 20 - 30%. At the same time, ammonia plasma reshapes the carbon skeleton, making the fluorine atoms doped in the first step fully exposed and then undergoing a transformation of the doped fluorine configuration. Finally, the ratio of ionic bond type C-F to semi-ionic bond type C-F atoms in the doped fluorine can be controllably achieved to be 1:(0.9 - 1.1), thus the optimal catalytic activity of FNC in Example 2.

[0072] 5) Performance test of zinc-air battery Using FNC in Example 2 as the cathode catalyst in an alkaline zinc-air battery, the maximum power density of the battery can reach 306 mW cm –2 , as shown in Figure 5 . In addition, the battery can stably discharge for a long time at different current densities, with a maximum current density of 200 mW cm -2 , as shown in Figure 6 ; at the same time, the ZABs show a long cycle stability of 1600 times, with a charge-discharge cycle time of 1.5 h per cycle and a total time of up to 2400 h, as shown in Figure 7 .

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery, characterized in that, It includes the following steps: S1. Mix a carbon source and a fluorine dopant to obtain a mixed slurry, coat the mixed slurry on carbon cloth, and obtain carbon cloth loaded with the carbon source and the fluorine dopant after drying; S2. Perform Joule heat treatment on the carbon cloth loaded with the carbon source and the fluorine dopant, and obtain powder on the carbon cloth after completion. Post-treat the powder to obtain fluorine-doped carbon; S3. Under an ammonia atmosphere, perform plasma treatment on the fluorine-doped carbon to obtain fluorine and nitrogen co-doped carbon.

2. The preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, wherein, In S1, the specific process of mixing the carbon source and the fluorine dopant is: successively perform solid-phase grinding, ultrasonic mixing, and stirring and dispersion treatment.

3. The preparation method of a fluorine and nitrogen doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S1, the mixing mass ratio of the carbon source to the fluorine dopant is 1:(0.1 - 2).

4. The preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S1, the carbon source is one or more of carbon black, Ketjen black, sodium alginate, sodium citrate, sucrose, lactose, cellulose, hemicellulose, starch, and dextrin.

5. The preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S1, the fluorine dopant is one or more of PTFE, PVDF, and ammonium fluoride.

6. The preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S2, during the Joule heat treatment process, the charging voltage is 5 - 100 V, the energization time is 100 - 10000 ms, and the Joule heat temperature is 500 - 2000 °C.

7. The preparation method of a fluorine and nitrogen doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S2, the process of post-treating the powder is: subject the powder to pickling, filtration, water washing, and drying treatment.

8. The preparation method of a fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery according to claim 1, characterized in that, In S3, the temperature of the plasma treatment process is 25 - 400 °C, the treatment time is 1 - 180 s, and the power is 10 - 200 W.

9. A fluorine and nitrogen doped carbon-based oxygen reduction electrocatalyst for a zinc-air battery prepared by the preparation method according to any one of claims 1-8, characterized in that, It is composed of polymerized carbon particles. The surface of the carbon particles has roughness, and the interior has a pore structure. Fluorine and nitrogen are doped on the carbon particles; among them, carbon and fluorine are connected by ionic carbon-fluorine bonds and semi-ionic carbon-fluorine bonds, and the nitrogen includes graphitic nitrogen and pyridinic nitrogen.

10. The fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst for zinc-air battery according to claim 9, wherein, The total specific surface area of the fluorine and nitrogen co-doped carbon-based oxygen reduction electrocatalyst is 200-250 m 2 g –1 .

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