Preparation method and application of graded pore channel nitrogen and fluorine co-doped carbon fiber loaded manganese difluoride nanoparticle composite material

Abstract

The invention discloses a preparation method and application of a graded-channel nitrogen and fluorine co-doped carbon fiber loaded manganese difluoride nanoparticle composite material in the field of preparation of new materials, dicyandiamide and manganese chloride tetrahydrate are dissolved in a polyvinyl alcohol aqueous solution, a polytetrafluoroethylene dispersion liquid is added, and a MnCl2 / DCD / PTFE / PVA spinning solution is prepared; initiating the spinning solution to form a film through an electrostatic spinning technology, and carrying out pre-oxidation and calcination treatment to obtain a MnF2 / NF-CNF composite material; according to the invention, polytetrafluoroethylene is used as a fluorine source and a pore-forming agent, a through macroporous structure of the material is constructed, a gas diffusion path is optimized, the oxygen mass transfer efficiency is greatly improved, the effective area of a three-phase interface of a reaction is increased, and the limiting current density of the reaction is improved; dicyandiamide is adopted as a nitrogen source cross-linking agent, so that a catalytic activity center electronic structure is optimized, and the stability and the mechanical strength of the material are improved through a three-dimensional cross-linked network formed by the dicyandiamide and polyvinyl alcohol; when the MnF2 / NF-CNF is used as the air positive electrode of the zinc-air battery, excellent discharge efficiency and cycle performance are shown.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new material preparation, and particularly relates to a preparation method and application of a hierarchical pore nitrogen and fluorine co-doped carbon fiber loaded manganese difluoride nanoparticle composite (MnF2 / NF-CNF). BACKGROUND

[0002] As an important part of renewable energy, electrochemical energy storage has gradually moved from the laboratory to industrialization, forming a diversified development pattern with multiple new energy storage technologies parallel to lithium ion batteries. Currently, the energy density of lithium ion batteries (LIBs) has approached its theoretical energy density (about 350 Wh / kg), but the organic electrolyte of LIBs has problems such as flammability, explosion and thermal runaway, and an effective solution has not been found, resulting in an increasing number of energy storage safety accidents. Therefore, a safer energy storage technology is needed to replace LIBs. Under this background, the rechargeable zinc-air battery has become an ideal substitute for LIBs due to its ultra-high theoretical energy density (>1000 Wh / kg), high safety, environmental friendliness and low cost. Compared with LIBs, zinc-air batteries fundamentally eliminate the risk of thermal runaway of organic electrolyte, and the electrolyte is usually water-based, which will not cause explosion and other safety accidents even in high-temperature or open flame environments. At the same time, zinc-air batteries can achieve free oxygen breathing charge-discharge cycles through their open air electrodes, making them have advantages in manufacturing cost and environmental friendliness. In addition, the unique dual-function catalytic mechanism of the zinc-air battery cathode catalyst gives the battery fast response capability, making it highly adaptable to dynamic scenarios such as grid frequency regulation. The high theoretical capacity of the zinc anode and the unlimited oxygen supply characteristics of the air cathode complement each other, enabling the energy density to break through the physical limitations of traditional closed batteries and showing potential in the fields of electric vehicle power batteries and portable electronic devices.

[0003] However, the oxygen reduction reaction (ORR) in the discharge process of zinc-air batteries requires oxygen consumption, which changes the reaction from a general solid-liquid reaction interface to a gas-liquid-solid three-phase interface, resulting in problems such as blocked oxygen diffusion path and reduced active site utilization. Especially in carbon-based and metal-based catalysts, factors such as the microstructure, wettability, electrical conductivity and pore structure of the three-phase interface determine the adsorption and diffusion path of oxygen and the stability of reaction intermediates. Therefore, there is an urgent need for a catalyst with a reasonable structure and hydrophobicity to improve its oxygen capture capacity and reaction activity, and to reduce side reactions and improve the service life of zinc-air batteries. SUMMARY

[0004] In view of the above deficiencies of the prior art, the application aims to provide a kind of with application, the prepared MnF2 / NF-CNF composite material is used as the air positive electrode catalyst of zinc-air battery, and it shows good battery performance, improves oxygen mass transfer efficiency, reduces electrolyte infiltration rate, prevents the accumulation of electrolyte, enhances the stability of battery, and improves the limiting current density of reaction.

[0005] To achieve the above object, the technical scheme adopted by the preparation method of the hierarchical pore nitrogen and fluorine co-doped carbon fiber loaded manganese difluoride nanoparticle composite material is as follows: MnCl2 / DCD / PTFE / PVA spinning solution is prepared by dissolving dicyandiamide and manganese chloride tetrahydrate in polyvinyl alcohol aqueous solution and adding polytetrafluoroethylene dispersion liquid; the spinning solution is initiated to form a film by electrospinning technology, and MnF2 / NF-CNF composite material is obtained after pre-oxidation and calcination treatment.

[0006] Further, the preparation is carried out according to the following steps:

[0007] (1) polyvinyl alcohol powder is added to deionized water to prepare a polyvinyl alcohol aqueous solution; then dicyandiamide and manganese chloride tetrahydrate are added to the polyvinyl alcohol aqueous solution, and heating and stirring are carried out until a transparent viscous solution is formed; finally, polytetrafluoroethylene dispersion liquid is added to the transparent viscous solution, and stirring is carried out at room temperature until it becomes a brown viscous solution, which is the MnCl2 / DCD / PTFE / PVA spinning solution;

[0008] (2) the brown viscous solution is electrospun to obtain an electrospun film, and the electrospun film is dried;

[0009] (3) the dried electrospun film is heated and pre-oxidized in a muffle furnace;

[0010] (4) the pre-oxidized sample is transferred to a tube furnace, heated and calcined under inert atmosphere, and MnF2 / NF-CNF composite material is obtained after the tube furnace is cooled to room temperature.

[0011] The prepared MnF2 / NF-CNF composite material is applied to the air positive electrode of zinc-air battery.

[0012] The beneficial effects of the application after adopting the above technical scheme are:

[0013] 1、The preparation method of the MnF2 / NF-CNF composite material of the application, through electrostatic spinning technology, using polytetrafluoroethylene as a fluorine source and a pore-forming agent, a honeycomb-shaped macroporous fiber structure with a hydrophobic surface, a through macroporous structure of the building material, significantly increasing the specific surface area of the material, improving the effective area of the three-phase interface of the reaction, and improving the limiting current density of the reaction. Then using dicyandiamide as a nitrogen source crosslinking agent, not only optimizes the electronic structure of the catalytic active center, forms a three-dimensional crosslinked network with polyvinyl alcohol, and significantly improves the stability and mechanical strength of the material. At the same time, the hierarchical pore system constructed can optimize the gas diffusion path and greatly improve the oxygen mass transfer efficiency. The hydrophobic interface of the composite material reduces the electrolyte wetting rate, prevents the accumulation of electrolyte, and enhances the stability of the battery. Dicyandiamide as a nitrogen source not only optimizes the electronic structure of the catalytic active center, but also improves the oxygen reduction capacity of the catalyst active site by co-doping with fluorine, and forms a three-dimensional crosslinked network with polyvinyl alcohol, which significantly improves the stability and mechanical strength of the material and improves the application prospect.

[0014] 2、When the prepared MnF2 / NF-CNF composite material is used as an air positive electrode catalyst of a zinc-air battery, not only the through macroporous structure produced by the high-temperature decomposition of polytetrafluoroethylene is used together with mesopores and micropores to construct a hierarchical pore system and a hydrophobic interface, but also the specific surface area of the material is increased, the gas diffusion path is optimized, and the oxygen mass transfer efficiency is greatly improved, thereby further improving the limiting current density of the ORR reaction. Due to the hierarchical pore system, the through macroporous structure, and the reasonable hydrophilic and hydrophobic interfaces, the air positive electrode of the zinc-air battery has good oxygen mass transfer efficiency, high three-phase reaction area, and sufficient catalytic active sites. Experiments prove that when MnF2 / NF-CNF is used as an air positive electrode catalyst of a zinc-air battery, it shows a very high power density of 181 mW / cm 2 and a specific capacity of 812.2 mAh g Zn -1 Under different current densities of 5, 10, 15, and 20 mA / cm 2 , the MnF2 / NF-CNF-based zinc-air battery has excellent rate performance and cycle performance, especially at a high current density of 20 mA / cm 2 , it shows better discharge stability and excellent discharge efficiency than commercial Pt / C. In the long cycle test, the MnF2 / NF-CNF-based zinc-air battery exhibits a charge-discharge voltage gap of 0.88 V, which is much lower than that of the zinc-air battery assembled by Pt / C (1.25 V). Therefore, it has good application prospect.

[0015] 3、The application can realize three key optimizations: (1) By the hierarchical pore system, the gas diffusion path is optimized, which greatly improves the oxygen mass transfer efficiency; (2) The hydrophobic interface reduces the electrolyte wetting rate, prevents the accumulation of electrolyte, and enhances the stability of the battery; (3) The through-hole structure significantly increases the specific surface area of the material, further increases the effective area of the three-phase interface of the reaction, and improves the limiting current density of the reaction. At the same time, when it is used as an air positive electrode catalyst of a zinc-air battery, it shows good battery performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A scanning electron microscope (SEM) image of the MnF2 / NF-CNF composite material prepared in Example 1 of the application;

[0017] Figure 2 Transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images of the MnF2 / NF-CNF prepared in Example 1 of the application;

[0018] Figure 3 Scanning transmission electron microscope (STEM) images and element distribution images of the MnF2 / NF-CNF prepared in Example 1 of the application;

[0019] Figure 4 SEM images of the MnF2 / NF-CNF composite material prepared in Examples 2, 3, 4, 5, and 6 of the application;

[0020] Figure 5 SEM images of the MnF2 / NF-CNF composite material prepared in Examples 7, 8, 9, 10, and 11 of the application;

[0021] Figure 6 SEM images of the MnO / CNF composite material prepared in Comparative Example 1;

[0022] Figure 7 SEM images of the Mn / N-CNF composite material prepared in Comparative Example 2;

[0023] Figure 8 SEM images of the MnF2 / F-CNF composite material prepared in Comparative Example 3;

[0024] Figure 9 X-ray diffraction (XRD) spectra of the composite materials prepared in Example 1 of the application and Comparative Examples 1, 2, and 3;

[0025] Figure 10 Raman spectra of the composite materials prepared in Example 1 of the application and Comparative Examples 1, 2, and 3;

[0026] Figure 11Nitrogen adsorption-desorption curves and pore size distribution graphs of the composite materials prepared in Example 1 and Comparative Examples 1, 2, 3 of the present application;

[0027] Figure 12 Dynamic contact angle change graphs of the composite materials prepared in Example 1 and Comparative Examples 1, 2, 3 of the present application;

[0028] Figure 13 Linear sweep voltammetry (LSV) graphs of the composite materials prepared in Example 1 and Comparative Examples 1, 2, 3, 4 of the present application;

[0029] Figure 14 LSV graphs of the composite materials prepared in Example 2, 3, 4, 5, 6 of the present application;

[0030] Figure 15 LSV graphs of the composite materials prepared in Example 7, 8, 9, 10, 11 of the present application;

[0031] Figure 16 LSV graphs of the composite materials prepared in Example 12, 13, 14 of the present application at different calcination temperatures;

[0032] Figure 17 Tafel slope graphs of the composite materials prepared in Example 1 and Comparative Examples 1, 2, 3, 4 of the present application;

[0033] Figure 18 Peroxide yield and number of electron transfer graphs of the composite materials prepared in Example 1 and Comparative Examples 1, 2, 3, 4 of the present application at different potentials;

[0034] Figure 19 Chronoamperometric response graphs of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the commercial Pt / C composite material of Comparative Example 4;

[0035] Figure 20 Methanol tolerance test graphs of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the commercial Pt / C composite material of Comparative Example 4;

[0036] Figure 21 Performance graphs of the zinc-air battery assembled with the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the commercial Pt / C composite material of Comparative Example 4 as the air cathode; wherein Figure 21 (a) is the polarization curve and power density graph, Figure 21 (b) is the open circuit voltage graph, Figure 21 (c) is the discharge specific capacity graph, Figure 21 (d) is the rate curve graph, Figure 21 (e) is the charge-discharge long cycle graph;

[0037] Figure 22 Digital image of a zinc-air battery lighting LED signboard assembled with MnF2 / NF-CNF composite material prepared for Example 1 of the present application as an air positive electrode. DETAILED DESCRIPTION

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described.

[0039] The preparation method of the hierarchical pore nitrogen and fluorine co-doped carbon fiber loaded manganese difluoride nanoparticle composite material of the present application is divided into four steps. Polyvinyl alcohol is used as the spinning polymer, dicyandiamide is used as the nitrogen source and crosslinking agent, and polytetrafluoroethylene is used as the fluorine source and pore-forming agent. MnCl2 / DCD / PTFE / PVA composite film is prepared by electrospinning technology, and then pre-oxidized and calcined to obtain a honeycomb-shaped macroporous carbon nanofiber catalyst with a hydrophobic surface. First, MnCl2 / DCD / PTFE / PVA spinning solution is prepared, then MnCl2 / DCD / PTFE / PVA electrospinning film is prepared, then MnCl2 / DCD / PTFE / PVA electrospinning film is pre-oxidized, and finally MnF2 / NF-CNF is prepared. The specific process is as follows:

[0040] (1) Preparation of MnCl2 / DCD / PTFE / PVA spinning solution

[0041] Polyvinyl alcohol (PVA) powder is added to deionized water to prepare a polyvinyl alcohol aqueous solution. Then dicyandiamide (DCD) and manganese chloride tetrahydrate (MnCl2·4H2O) are added to the polyvinyl alcohol aqueous solution, and then heated and stirred until a transparent viscous solution is formed. Finally, polytetrafluoroethylene (PTFE) dispersion is added to the transparent viscous solution, and stirred at room temperature until it becomes a brown viscous solution. The brown viscous solution is the MnCl2 / DCD / PTFE / PVA spinning solution.

[0042] The mass concentration of the polyvinyl alcohol aqueous solution is 12wt%, the mass ratio of manganese chloride tetrahydrate to polyvinyl alcohol aqueous solution is 6:125, the mass ratio of dicyandiamide to polyvinyl alcohol aqueous solution is 6:125, and the mass ratio of polytetrafluoroethylene dispersion to polyvinyl alcohol aqueous solution is 9:22.

[0043] (2) Preparation of MnCl2 / DCD / PTFE / PVA electrospinning film

[0044] The obtained brown viscous MnCl2 / DCD / PTFE / PVA spinning solution was used as a precursor solution for electrospinning. During electrospinning, the fibers were collected on a drum collector in the electrospinning equipment with silicon oil paper, and an electrospinning film was obtained.

[0045] During electrospinning, the plastic needle in the equipment was 20G, the flow rate of the spinning solution was 0.01 mL / min, the electrostatic voltage was 20 kV, and the distance between the needle and the drum collector was 15 cm.

[0046] After electrospinning, the obtained electrospinning film was placed in a vacuum drying oven together with the silicon oil paper for drying.

[0047] (3) Pre-oxidation of the MnCl2 / DCD / PTFE / PVA electrospinning film

[0048] The dried electrospinning film was separated from the silicon oil paper, and the electrospinning film was placed in a muffle furnace for heating and pre-oxidation.

[0049] The heating temperature was 250℃, the pre-oxidation heating rate was 2℃ / min, and the pre-oxidation holding time was 2h.

[0050] (4) Preparation of MnF2 / NF-CNF composite material

[0051] The pre-oxidized sample was transferred to a tube furnace, heated and held for calcination under an inert atmosphere, and the MnF2 / NF-CNF composite material was obtained after the tube furnace was cooled to room temperature.

[0052] Heating and holding for calcination under an inert atmosphere to 850℃, the calcination heating rate was 3℃ / min, and the calcination holding time was 2h.

[0053] The obtained MnF2 / NF-CNF composite material was applied to the air positive electrode of a zinc-air battery.

[0054] The following provides 14 examples and 4 comparative examples of the present application:

[0055] Example 1

[0056] The preparation method of the MnF2 / NF-CNF composite material is as follows:

[0057] (1) Preparation of MnCl2 / DCD / PTFE / PVA spinning solution

[0058] 0.6 g of polyvinyl alcohol powder was added to 4.4 mL of deionized water, stirred until completely dissolved to obtain a polyvinyl alcohol aqueous solution; 240 mg of dicyandiamide and 240 mg of manganese chloride tetrahydrate were poured into the polyvinyl alcohol aqueous solution, and heated to 45°C and stirred until a transparent viscous solution was formed; 1.8 mL of polytetrafluoroethylene dispersion was added to the transparent viscous solution, and stirred at room temperature until it became a brown viscous solution.

[0059] (2) Preparation of MnCl2 / DCD / PTFE / PVA electrospun membrane

[0060] The obtained brown viscous precursor solution was loaded into a plastic syringe, and assembled into a spinner with a 20G plastic needle, a luer joint and a spinning hose. The assembled spinner was installed on an electrospinning machine, and electrospinning was carried out at a pushing speed of 0.01 mL / min. At the same time, the fibers were collected on a drum collector with silicone paper, and the distance between the needle and the drum collector was kept at 15 cm. After electrospinning, the obtained electrospun membrane was placed in a vacuum drying oven together with the silicone paper and dried at 60°C for 12 h.

[0061] (3) Pre-oxidation of MnCl2 / DCD / PTFE / PVA electrospun membrane

[0062] The alumina ceramic pressed with the electrospun membrane was covered with a pressed tablet cover and placed in a muffle furnace, and heated to 250°C at a heating rate of 2°C / min for 2h pre-oxidation.

[0063] (4) Preparation of MnF2 / NF-CNF composite material

[0064] The pre-oxidized sample was transferred to a tube furnace, heated to 850°C at a heating rate of 3°C / min under argon atmosphere and calcined for 2h, and the MnF2 / NF-CNF composite material was obtained after the tube furnace was cooled to room temperature.

[0065] Figure 1 SEM images of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application, wherein, Figure 1 (a) is a low magnification SEM image of the MnF2 / NF-CNF composite material, Figure 1 (b) is a high magnification SEM image of the MnF2 / NF-CNF composite material, and Figure 1 It can be seen from the above that there are a large number of pores on the surface of the fibers, the fiber morphology remains complete, and a certain degree of cross-linking appears in some areas, but overall most of the fibers remain independent and complete. The fiber surface has large pores with a diameter of 100 nm, which can optimize the diffusion path of the gas and improve the oxygen mass transfer efficiency.

[0066] Figure 2TEM images of MnF2 / NF-CNF composite prepared for Example 1 of the present application, wherein, Figure 2 (a) and Figure 2 (b) are TEM images of MnF2 / NF-CNF, Figure 2 (c) HRTEM image of MnF2 / NF-CNF. The three-dimensional interconnected channels inside the fiber and the presence of partial nanoparticles can be seen. These through-hole structures can greatly increase the specific surface area of the material, further increase the effective area of the gas-liquid-solid three-phase interface of the reaction, and improve the limiting current density of the reaction. The HRTEM image exhibits the lattice fringes of the MnF2 / NF-CNF composite material, and the lattice spacings of 0.273 nm and 0.182 nm can be seen, corresponding to the (101) and (211) planes of MnF2 (PDF # 27-0727), respectively, proving that the particles in the fiber are MnF2 nanoparticles.

[0067] Figure 3 STEM images and element distribution images of MnF2 / NF-CNF composite prepared for Example 1 of the present application, Figure 3 (a) is a STEM image of MnF2 / NF-CNF, Figure 3 (b), Figure 3 (c), Figure 3 (d) are element Mn, N, F distribution images, respectively. It shows that the material has a good three-dimensional network structure, which is beneficial to the diffusion of reactants and the conduction of electrons. The bright area mainly corresponds to the MnF2 particles, indicating that the MnF2 particles are successfully dispersed on the surface or in the pores of the MnF2 / NF-CNF composite material.

[0068] Figure 9The XRD spectra of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the MnO / CNF, Mn / N-CNF and MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2 and 3 can be seen to have three sharp main peaks at 34.9°, 40.5° and 58.7° for the MnO / CNF curve, which completely correspond to the (111), (200) and (220) crystal faces of the standard substance of MnO (PDF # 07-0230), indicating that the MnO / CNF contains manganous oxide. The Mn / N-CNF added with dicyanediamine exhibits an amorphous state, because the decomposition of dicyanediamine during pyrolysis generates a large amount of gas, which destroys the stable environment required for the growth of manganous oxide crystals, ultimately resulting in no obvious crystallization peak for the Mn / N-CNF. The three sharp main peaks at 25.8°, 32.6° and 50.1° for the MnF2 / F-CNF curve are well matched with the characteristic peaks of the (110), (101) and (211) faces of the reported MnF2 (PDF # 70-2499) crystal, confirming the presence of manganese fluoride molecules. The three sharp peaks at 25.8°, 32.6° and 50.1° can also be observed for the MnF2 / NF-CNF, but the three characteristic peaks of the MnF2 / NF-CNF composite material are much weaker than those of the MnF2 / F-CNF. This is because the nitrogen-containing organic fragments formed by dicyanediamine at the same time as the nitrogen source may coordinate with MnF2, inhibiting the ordered aggregation of MnF2 crystal nuclei. 2+

[0069] Figure 10 The Raman spectra of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the MnO / CNF, Mn / N-CNF and MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2 and 3 can be seen to have two wide bands at about 1350 cm -1 (D band) and 1600 cm -1 (G band), which reflect the disordered sp 3 carbon atoms at the edges and the crystallization of sp 2 hybrid carbon atoms in the ideal graphene layer, respectively. The I D / I G of the MnF2 / NF-CNF is higher than that of the MnO / CNF, and the many defect sites can act as active centers to reduce the reaction energy barrier, enhance the adsorption and activation ability of oxygen molecules, and also promote the occurrence of the multi-electron reaction path of ORR, etc.

[0070] Figure 11 The nitrogen adsorption-desorption curves and pore size distribution graphs of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the MnO / CNF, Mn / N-CNF and MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2 and 3 can be seen to have a hysteresis loop, which indicates that the materials have a large number of mesopores. The pore size distribution of the MnF2 / NF-CNF is mainly concentrated in the range of 2-4 nm, and the pore size distribution of the MnO / CNF is mainly concentrated in the range of 2-3 nm. The pore size distribution of the Mn / N-CNF is mainly concentrated in the range of 2-3 nm, and the pore size distribution of the MnF2 / F-CNF is mainly concentrated in the range of 2-4 nm. Figure 11 ​(a) is a nitrogen adsorption-desorption curve, Figure 11 (b) is a pore size distribution graph. Due to the cross-linking effect of dicyandiamide, the specific surface area (100.4 m 2 g 1 ) of the MnF2 / NF-CNF composite is lower than that of Mn / F-CNF (148.8 m 2 g 1 ). Mn / NF-CNF and Mn / F-CNF form a large number of micropores and mesopores due to the pore-forming effect of polytetrafluoroethylene. Their specific surface area is much larger than that of Mn / CNF (22.3 m 2 g 1 ) and Mn / N-CNF (13.0 m 2 / g 1 ). The MnF2 / NF-CNF composite forms a hierarchical pore system with a larger specific surface area and more micropores, mesopores and macropores. This structure provides more contact interfaces for gas-liquid-solid three-phase interface reactions, which helps oxygen adsorption and diffusion on the surface of the catalyst, thereby improving the limiting current density.

[0071] Figure 12The dynamic contact angle change diagram of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the MnO / CNF, Mn / N-CNF, MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2 and 3 reveals the evolution law of the hydrophilic and hydrophobic properties of the surfaces of the MnO / CNF, Mn / N-CNF, MnF2 / F-CNF and MnF2 / NF-CNF composite materials through different contact time with water droplets. With the increase of time, the contact angles of all the catalysts are gradually decreasing. Among them, the MnO / CNF exhibits superhydrophilicity due to the rich oxygen-containing functional groups, and its contact angle is only 23.5° at 0s. The Mn / N-CNF has a contact angle of 78.2° at 0s due to the absence of pore-forming agent and the decrease of the surface roughness of the catalyst caused by the cross-linking of the fibers induced by DICY, which is greatly improved compared with the MnO / CNF. The MnF2 / F-CNF composite material becomes extremely hydrophobic due to the addition of F, which greatly reduces the surface energy of the catalyst, so its contact angle does not decrease much even after 120s. The contact angle of the MnF2 / NF-CNF composite material decreases from 110.4° at the beginning to 82.2° at the end, which has a large decrease. This is because the F-containing MnF2 / NF-CNF composite material is hydrophobic as a whole. However, the addition of N improves the hydrophilicity of the MnF2 / NF-CNF composite material to some extent, and the fibers also have a hierarchical pore structure, so that the water droplets gradually infiltrate the inside of the material after contacting the surface of the material. This special structure not only enables the electrolyte to quickly infiltrate along the hydrophilic pore channel, but also ensures the smooth oxygen diffusion channel of the hydrophobic surface, so it has a fast oxygen mass transfer process.

[0072] The MnF2 / NF-CNF composite material prepared in Example 1 and 2mg and 1mg of acetylene black conductive agent were each taken and added into a 2ml sample tube, and 290ul of ethanol, 100ul of water and 15ul of 5wt% Nafion (perfluorosulfonic acid-based polymer) were measured and added into the sample tube in turn, and the catalyst was dispersed uniformly by ultrasonic for 2h to form a MnF2 / NF-CNF composite material ink. An Al2O3 polished glassy carbon electrode (diameter 4mm) was used as a substrate, and 10ul of the MnF2 / NF-CNF ink was dropped twice. After natural drying at room temperature, a working electrode with a MnF2 / NF-CNF composite material loading of 0.4mg / cm 2 was obtained. Under O2 saturation conditions, a Hg / HgO (1.0mol / L KOH) electrode was used as a reference electrode, a carbon rod electrode was used as a counter electrode, and all potentials were converted by the Nernst equation (E RHE = E Hg / HgOThe pH values ​​(+0.098 +0.0592) were uniformly converted to the reversible hydrogen electrode potential (vs. RHE) for performance testing.

[0073] Figure 13 The LSV curves of the MnF2 / NF-CNF composite material prepared in Example 1 of this invention, and the MnO / CNF, Mn / N-CNF, and MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2, and 3 are shown. The MnF2 / NF-CNF composite material exhibits a higher onset potential (0.96 V) and limiting current density (6.23 mA / cm²). 2 It exhibits an extremely high half-wave potential (0.867V), and except for the initial potential, its performance is superior to that of Pt / C (0.97V, 5.72mA / cm). 2 The half-wave potential of Mn / N-CNF increased significantly compared to MnO / CNF, from 0.754V to 0.844V, indicating that DICY, as a nitrogen source, greatly enhanced the half-wave potential of the sample. The limiting current density of MnF2 / F-CNF increased significantly compared to MnO / CNF, from 5.04 mA / cm². -2 Increased to 6.07 mA / cm 2 This indicates that polytetrafluoroethylene (PTFE), as a pore-forming agent, not only increases the specific surface area but also adds many active sites. While single F doping can increase the limiting current density, its effect on overall ORR activity is limited. In contrast, N and F co-doping can simultaneously increase both the limiting current density and half-wave potential, thus enhancing catalytic performance.

[0074] Figure 17 The Tafel slope diagrams are for the MnF2 / NF-CNF composite material prepared in Example 1 of this invention and the MnO / CNF, Mn / N-CNF, and MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2, and 3. The MnF2 / NF-CNF composite material exhibits a Tafel slope of 55.54 mV / dec, which is much lower than that of Pt / C (60.26 mV / dec), MnO / CNF (89.01 mV / dec), Mn / N-CNF (65.73 mV / dec), and MnF2 / F-CNF (84.37 mV / dec), indicating that the MnF2 / NF-CNF composite material has the most active sites and possesses faster ORR reaction kinetics.

[0075] Figure 18The graph of peroxide production rate and electron transfer number of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the MnO / CNF, Mn / N-CNF, MnF2 / F-CNF composite materials prepared in Comparative Examples 1, 2, and 3 at different potentials; the average n value of the MnF2 / NF-CNF composite material in the potential range of 0.2-0.7 V is 3.98, and the production rate of hydrogen peroxide (H2O2) is less than 1.5%, indicating that the MnF2 / NF-CNF composite material mainly passes through a 4-electron transfer pathway in the ORR process, and almost no H2O2 is produced. This not only helps to improve the energy efficiency and reduce the corrosion of carbon materials in the ORR process.

[0076] Figure 19 The graph of chronoamperometric response curves of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the commercial Pt / C composite material of Comparative Example 4; the MnF2 / NF-CNF composite material s and the commercial Pt / C were subjected to a long-time i-t test at a potential of 0.6 V for 30000 s. From Figure 19 It can be seen that the current retention rate of the MnF2 / NF-CNF composite material after 30000 s of testing is 89.26%, while that of the commercial Pt / C is attenuated to 85.31%.

[0077] Figure 20 The graph of methanol tolerance test curves of the MnF2 / NF-CNF composite material prepared in Example 1 of the present application and the commercial Pt / C composite material of Comparative Example 4; when the test time is 400 s, a certain amount of methanol is added to the electrolyte, and the current density of the commercial Pt / C catalyst is rapidly attenuated to 1 mA / cm 2 , while the MnF2 / NF-CNF does not show obvious fluctuation, indicating that it has much better methanol tolerance than Pt / C.

[0078] The MnF2 / NF-CNF composite material prepared in Example 1 and acetylene black conductive agent were each taken 1 mg and 0.25 mg, and added into a 2 mL sample tube, followed by injecting 250 μL of anhydrous ethanol and 10 μL of a 5 wt% Nafion solution. After 1 h of ultrasonic dispersion, a stable MnF2 / NF-CNF catalyst ink was formed. Using a 20 mL pipette, the ink was coated on the carbon paper of a commercial composite electrode in multiple times (controlled within the effective area of 1×1 cm 2 , and dried at room temperature to obtain 1.0 mg / cm 2An air electrode with MnF2 / NF-CNF loading was used. A zinc-air battery was assembled using a composite electrode loaded with the MnF2 / NF-CNF catalyst as the air positive electrode, a 0.5 mm high-purity zinc foil (99.99%) as the negative electrode, and a mixed solution of 6.0 mol / L KOH and 0.2 mol / L Zn(Ac)2 as the electrolyte. Battery performance was then tested.

[0079] Figure 21 The graph shows the performance of zinc-air batteries assembled using the MnF2 / NF-CNF composite material prepared in Example 1 of this invention and the commercial Pt / C composite material in Comparative Example 4 as air cathodes. Figure 21 (a) shows the polarization curve and power density curve; Figure 21 (b) is the open-circuit voltage diagram; Figure 21 (c) is the discharge specific capacity diagram; Figure 21 (d) is the multiplier curve; Figure 21 (e) is a long-cycle charge-discharge diagram. Figure 21 It can be seen that the liquid zinc-air battery assembled with MnF2 / NF-CNF as the air cathode exhibits excellent energy storage characteristics. (See...) Figure 21 (a) The peak power density of MnF2 / NF-CNF based zinc-air cells reaches 181 mW / cm². 2 Compared to Pt / C-based zinc-air cells (125mW / cm²), 2 The efficiency was improved by 44.8%, thanks to the unique hierarchical porous structure of the MnF2 / NF-CNF composite catalyst. Notably, the MnF2 / NF-CNF-based zinc-air battery exhibited excellent stability in the 60-minute open-circuit voltage test, maintaining a high potential of 1.48V throughout the 60-minute test period. Figure 21 (b)). At 10 mA / cm 2 At the discharge current density, no significant voltage decay was observed in the MnF2 / NF-CNF based zinc-air battery, with a corresponding specific capacity of 812.2 mAh g⁻¹. Zn -1 ( Figure 21 (c)). Compared to commercially available Pt / C-based zinc-air batteries (799.2 mAh g⁻¹). Zn -1 MnF2 / NF-CNF-based zinc-air batteries improved by 13 mAh g. Zn -1 This indicates that the MnF2 / NF-CNF composite material has a higher energy conversion efficiency. To further evaluate the stability of the MnF2 / NF-CNF-based zinc-air battery, measurements were performed at 5, 10, 15, and 20 mA / cm². 2 Discharging at different current densities, MnF2 / NF-CNF-based zinc-air batteries exhibit excellent rate performance. Figure 21(d)), especially at high current density of 20 mA / cm 2 The results of multiple tests prove that the high specific surface area porous MnF2 / NF-CNF composite catalyst has good stability and rate performance under the working conditions of the actual zinc-air battery. In order to explore the charge-discharge capacity of the MnF2 / NF-CNF-based zinc-air battery, long-time charge-discharge cycle test is carried out on it Figure 21 (e)). Compared with the charge / discharge voltage gap of 1.25V of the Pt / C-based zinc-air battery, the charge / discharge voltage gap of the MnF2 / NF-CNF-based zinc-air battery is reduced by 0.37V, which has a smaller charge / discharge voltage gap. And the MnF2 / NF-CNF-based zinc-air battery is superior to the Pt / C-based zinc-air battery both in the charge voltage platform and the discharge voltage platform. It shows that the MnF2 / NF-CNF composite material as the air positive electrode assembled alkaline liquid zinc-air battery is superior to the commercial Pt / C both in the energy storage and the energy release capacity. And after 400 complete charge-discharge cycles, the charge / discharge voltage gap of the Pt / C-based zinc-air battery is expanded to 1.71V, while the MnF2 / NF-CNF-based zinc-air battery still has a smaller charge / discharge voltage gap (0.99V), which shows that the MnF2 / NF-CNF composite material has more stable charge-discharge capacity than Pt / C.

[0080] Figure 22 The digital photo of the zinc-air battery assembled by the MnF2 / NF-CNF composite material prepared in Example 1 as the air positive electrode lighting the LED lamp card.

[0081] Example 2

[0082] The difference from Example 1 is that the amount of dicyandiamide added in the preparation process of MnCl2 / DCD / PTFE / PVA spinning solution is 180mg (mass ratio is 9:250). The prepared material is recorded as Example 2.

[0083] Figure 4 The SEM images of samples obtained by different amounts of dicyandiamide are Figure 4 (a) is the amount of 0.18g; Figure 4 (b) is the amount of 0.22g; Figure 4 (c) is the amount of 0.24g; Figure 4 (d) is the amount of 0.26g; Figure 4 (e) is the amount of 0.30g; Figure 4 (f) is the amount of 0.34g. From Figure 4It can be seen that the micro-morphology of the prepared composite material is similar to that of the implementation case 1, and has a large-pore fiber structure. At the same time, compared with the implementation case 1, the cross-linking degree between the fibers is weakened.

[0084] Figure 14 is the LSV curve of the sample obtained by different amounts of dicyandiamide addition, and Figure 14 It can be seen that the limiting current density of the composite material prepared in Example 2 is 6.2 mA / cm 2 , and the half-wave potential is 0.82 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density difference is not obvious, but the half-wave potential is reduced more.

[0085] Example 3

[0086] The difference from Example 1 is that the amount of dicyandiamide added in the preparation process of the MnF2 / NF-CNF spinning solution is 220 mg. The prepared material is recorded as Example 3.

[0087] is the LSV curve of the sample obtained by different amounts of dicyandiamide addition, and Figure 4 It can be seen that the micro-morphology of the prepared composite material is basically the same as that of the implementation case 1, and the fiber still has a large-pore structure. But with the increase of dicyandiamide content, the cross-linking degree between the fibers increases.

[0088] is the LSV curve of the sample obtained by different amounts of dicyandiamide addition, and Figure 14 It can be seen that the limiting current density of the composite material prepared in Example 3 is 6.3 mA / cm 2 , and the half-wave potential is 0.839 V. Compared with the implementation case 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density is not obviously improved, but the half-wave potential is reduced more.

[0089] Example 4

[0090] The difference from Example 1 is that the amount of dicyandiamide added in the preparation process of the MnF2 / NF-CNF spinning solution is 260 mg. The prepared material is recorded as Example 4.

[0091] is the LSV curve of the sample obtained by different amounts of dicyandiamide addition, and Figure 4 It can be seen that the micro-morphology of the prepared composite material is quite different from that of the implementation case 1, but still has a certain large-pore fiber structure. At the same time, compared with the implementation case 1, the cross-linking degree between the fibers is enhanced.

[0092] is the LSV curve of the sample obtained by different amounts of dicyandiamide addition, and Figure 14 It can be seen that the limiting current density of the composite material prepared in Example 4 is 6.23 mA / cm 2 , and the half-wave potential is 0.86 V. Compared with the implementation case 1 (6.23 mA / cm 2The half-wave potential is slightly reduced compared to 0.867 V. The overall ORR performance is close to that of Example 1, but the half-wave potential is still less than that of Example 1.

[0093] Example 5

[0094] The difference from Example 1 is that the amount of dicyandiamide added in the preparation of the MnF2 / NF-CNF spinning solution is 300 mg. The prepared material is recorded as Example 5.

[0095] From the SEM images of the prepared composite material, it can be seen that the micro-morphology of the prepared composite material is quite different from that of Example 1. The fiber structure cannot be observed, but the macroporous structure can still be observed. At the same time, compared with Example 1, the degree of cross-linking between the fibers is greatly enhanced. Figure 4 From the SEM images of the prepared composite material, it can be seen that the micro-morphology of the prepared composite material is quite different from that of Example 1. The fiber structure cannot be observed, but the macroporous structure can still be observed. At the same time, compared with Example 1, the degree of cross-linking between the fibers is greatly enhanced.

[0096] Figure 14 It can be seen that the limiting current density of the composite material prepared in Example 5 is 6.23 mA / cm 2 , and the half-wave potential is 0.85 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density is close to that of Example 1, but the half-wave potential is reduced more.

[0097] Example 6

[0098] The difference from Example 1 is that the amount of dicyandiamide added in the preparation of the MnCl2 / DCD / PTFE / PVA spinning solution is 340 mg. The prepared material is recorded as Example 6.

[0099] From the SEM images of the prepared composite material, it can be seen that the micro-morphology of the prepared composite material is quite different from that of Example 1. The fiber structure cannot be observed, but the macroporous structure can still be observed. At the same time, compared with Example 1, the degree of cross-linking between the fibers is greatly enhanced. Figure 4 From the SEM images of the prepared composite material, it can be seen that the micro-morphology of the prepared composite material is quite different from that of Example 1. The fiber structure cannot be observed, but the macroporous structure can still be observed. At the same time, compared with Example 1, the degree of cross-linking between the fibers is greatly enhanced.

[0100] Figure 14 It can be seen that the limiting current density of the composite material prepared in Example 6 is 6.03 mA / cm 2 , and the half-wave potential is 0.852 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the overall ORR performance of Example 6 is quite different from that of Example 1.

[0101] Example 7

[0102] The difference from Example 1 is that the amount of polytetrafluoroethylene dispersion added in the preparation of the MnCl2 / DCD / PTFE / PVA spinning solution is 0.8 mL. The prepared material is recorded as Example 7. ​​

[0103] Figure 5 SEM images of samples obtained with different PTFE dispersion liquid Figure 5 (a) is the dispersion liquid is 0.8 mL; Figure 5 (b) is the dispersion liquid is 1.2 mL, Figure 5 (c) is the dispersion liquid is 1.6 mL, Figure 5 (d) is the dispersion liquid is 1.8 mL, Figure 5 (e) is the dispersion liquid is 2.0 mL; Figure 5 (f) is the dispersion liquid is 2.4 mL. From Figure 5 It can be seen that the microstructure of the prepared composite material is similar to that of Example 1, with a fiber structure. At the same time, compared with Example 1, the pore size of the fiber becomes smaller. Among them, due to the small amount of polytetrafluoroethylene dispersion liquid added, the viscosity of the solution is too high, and the fiber appears to be inconsistent in thickness.

[0104] Figure 15 LSV curve of samples obtained with different PTFE dispersion liquid addition amount, from Figure 15 It can be seen that the limiting current density of the composite material prepared in Example 7 is 5.62 mA / cm 2 , and the half-wave potential is 0.81 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density and half-wave potential are greatly reduced.

[0105] Example 8

[0106] The difference between Example 8 and Example 1 is that the amount of polytetrafluoroethylene dispersion liquid added in the preparation process of MnCl2 / DCD / PTFE / PVA spinning solution is 1.2 mL. The prepared material is recorded as Example 8.

[0107] From Figure 5 It can be seen that the microstructure of the prepared composite material is similar to that of Example 1, with a fiber structure. At the same time, compared with Example 1, the pore size of the fiber becomes smaller. Among them, due to the small amount of polytetrafluoroethylene dispersion liquid added, the viscosity of the solution is too high, and the fiber appears to be inconsistent in thickness.

[0108] From Figure 15 It can be seen that the limiting current density of the composite material prepared in Example 8 is 5.72 mA / cm 2 , and the half-wave potential is 0.82 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density and half-wave potential are still greatly reduced, but relative to Example 7, it has improved.

[0109] Example 9

[0110] The difference between Example 1 is that the amount of polytetrafluoroethylene dispersion liquid added in the preparation process of MnCl2 / DCD / PTFE / PVA spinning solution is 1.6 mL. The prepared material is recorded as Example 9.

[0111] From Figure 5 It can be seen that the micro-morphology of the prepared composite material is similar to that of Example 1, and the fiber hole is increased. And because of the increase of the amount of polytetrafluoroethylene, the viscosity of the spinning solution decreases, and the diameter of the spinning fiber decreases.

[0112] From Figure 15 It can be seen that the limiting current density of the composite material prepared in Example 9 is 5.9 mA / cm 2 , and the half-wave potential is 0.861 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), the limiting current density is greatly reduced, but the half-wave potential is slightly reduced.

[0113] Example 10

[0114] The difference between Example 1 is that the amount of polytetrafluoroethylene dispersion liquid added in the preparation process of MnCl2 / DCD / PTFE / PVA spinning solution is 2.0 mL. The prepared material is recorded as Example 10.

[0115] From Figure 5 It can be seen that the micro-morphology of the prepared composite material is similar to that of Example 1, the fiber hole is increased, and the cross-linking degree of the fiber is weakened.

[0116] From Figure 15 It can be seen that the limiting current density of the composite material prepared in Example 10 is 6.33 mA / cm 2 , and the half-wave potential is 0.837 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), although the limiting current density is improved, the half-wave potential is greatly reduced, and the overall ORR performance is not as good as Example 1.

[0117] Example 11

[0118] The difference between Example 1 is that the amount of polytetrafluoroethylene dispersion liquid added in the preparation process of MnCl2 / DCD / PTFE / PVA spinning solution is 2.4 mL. The prepared material is recorded as Example 11.

[0119] From Figure 5 It can be seen that the micro-morphology of the prepared composite material is similar to that of Example 1, but due to the large increase in the amount of polytetrafluoroethylene, the viscosity of the spinning solution decreases, the fiber diameter decreases, and the fiber diameter is inconsistent.

[0120] From Figure 15 It can be seen that the limiting current density of the composite material prepared in Example 11 is 6.45 mA / cm 2 , and the half-wave potential is 0.821 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), although the excessive addition of polytetrafluoroethylene greatly improves the limiting current density, the half-wave potential is greatly reduced, and the overall ORR performance is not as good as that of Example 1.

[0121] Example 12

[0122] The difference from Example 1 is that in the preparation process of the MnF2 / NF-CNF composite material, it is heated to 800°C at a heating rate of 3°C / min under an argon atmosphere and calcined for 2 h. The prepared material is recorded as Example 12.

[0123] Figure 16 is the LSV curve of the sample prepared at different calcination temperatures, from Figure 16 It can be seen that the limiting current density of Example 12 prepared by calcining at 800°C for 2 h is 6.6 mA / cm 2 , and the half-wave potential is 0.845 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), its limiting current density has increased to a certain extent, and the half-wave potential has decreased more, and the overall ORR performance is not as good as that of Example 1.

[0124] Example 13

[0125] The difference from Example 1 is that in the preparation process of the MnF2 / NF-CNF composite material, it is heated to 900°C at a heating rate of 3°C / min under an argon atmosphere and calcined for 2 h. The prepared material is recorded as Example 13.

[0126] From Figure 16 It can be seen that the limiting current density of Example 13 prepared by calcining at 900°C for 2 h is 6.1 mA / cm 2 , and the half-wave potential is 0.867 V. Compared with Example 1 (6.23 mA / cm 2 , 0.867 V), its half-wave potential is the same, but the limiting current density is reduced, and the overall ORR performance is comparable to that of Example 1.

[0127] Example 14

[0128] The difference from Example 1 is that in the preparation process of the MnF2 / NF-CNF composite material, it is heated to 1000°C at a heating rate of 3°C / min under an argon atmosphere and calcined for 2 h. The prepared material is recorded as Example 14.

[0129] Depend on Figure 16 It can be seen that the limiting current density of Example 14, prepared by calcination at 1000℃ for 2 hours, is 5.9 mA / cm². 2 The half-wave potential is 0.870V. This is similar to Example 1 (6.23mA / cm). 2 Compared to 0.867V, its half-wave potential is improved, but the limiting current density is reduced significantly. The overall ORR performance is comparable to that of Example 1.

[0130] Comparative Example 1

[0131] The difference from Example 1 is that dicyandiamine and polytetrafluoroethylene dispersion were not added in the preparation of the spinning solution. The prepared MnO / CNF composite material is designated as Comparative Example 1. The electrochemical performance testing method for the MnO / CNF composite material is the same as that for Example 1. Figure 6 SEM images of MnO / CNF composites, from Figure 6 It can be seen that the fiber distribution is uniform, but the consistency in thickness is poor. Due to the absence of polytetrafluoroethylene (PTFE), the fiber surface is smooth and no large pores are present. Basic parameters: Ig of the MnO / CNF composite material. D / I G The strength ratio of 1.00 indicates that although the carbon in the material has a high degree of graphitization, which helps to improve the conductivity of the material, its structural defects are relatively few, resulting in less exposure of active sites. Consequently, its electrochemical performance is extremely poor compared to Example 1, with a significantly lower ORR performance.

[0132] Comparative Example 2

[0133] The difference from Example 1 is that no polytetrafluoroethylene dispersion was added in the preparation of the spinning solution. The prepared Mn / N-CNF composite material is designated as Comparative Example 2. The electrochemical performance testing method for the Mn / N-CNF composite material is the same as that in Example 1. Figure 7 SEM images of Mn / N-CNF composite materials, such as Figure 7 As shown, the fibers are extensively cross-linked, making it impossible to observe a complete fiber morphology. Some pores can be observed in incompletely cross-linked areas, while only partial fiber outlines are visible in fully cross-linked areas. Basic parameters: The addition of dicyandiamine instead of polytetrafluoroethylene significantly disrupts the fiber morphology, resulting in a substantial reduction in the material's specific surface area. Furthermore, the material was not treated to be hydrophobic. Consequently, compared to Example 1, its electrochemical performance shows a good half-wave potential but a poor limiting current density.

[0134] Comparative Example 3

[0135] The difference from Example 1 is that dicyandiamine was not added in the preparation of the spinning solution. The prepared MnF2 / F-CNF composite material is designated as Comparative Example 3.

[0136] The method for testing the electrochemical performance of the MnF2 / F-CNF composite material and assembling the battery is the same as that of Example 1. Figure 8 The SEM image of the MnF2 / F-CNF composite material is as shown in FIG. 4B. Figure 8 As can be seen from FIG. 4B, the fiber morphology is clear, the overall thickness is relatively uniform, the distribution is also relatively uniform, and no obvious cross-linking phenomenon is observed. The fiber surface presents a rich macroporous structure, effectively improving the specific surface area of the material and providing more active sites for the reaction. However, due to the absence of dicyandiamide for cross-linking, part of the fiber has a fracture phenomenon. Basic parameters: due to the addition of polytetrafluoroethylene, dicyandiamide is not added, although the fiber has a larger specific surface area, but its active sites are insufficient. Compared with Example 1, its electrochemical performance has a better limiting current density, but a poorer half-wave potential.

[0137] Comparative Example 4

[0138] The difference from Example 1 is that the commercial Pt / C composite material is recorded as Comparative Example 2, and the electrochemical performance test is carried out in the same way as Example 1. Basic parameters: the ORR performance of Pt / C is excellent, but the methanol tolerance is extremely poor. The charge-discharge voltage gap of the assembled zinc air battery is large.

Claims

1. A method for preparing a hierarchical porous carbon fiber-supported manganese difluoride nanoparticle composite material, characterized in that: Dicyandiamine and manganese chloride tetrahydrate were dissolved in an aqueous solution of polyvinyl alcohol, and polytetrafluoroethylene dispersion was added to prepare a spinning solution of MnCl2 / DCD / PTFE / PVA. The spinning solution was then used to initiate film formation by electrospinning technology, and after pre-oxidation and calcination treatment, MnF2 / NF-CNF composite material was obtained.

2. The method for preparing the composite material according to claim 1, characterized in that... Follow these steps: (1) Add polyvinyl alcohol powder to deionized water to prepare a polyvinyl alcohol aqueous solution; then add dicyandiamine and manganese chloride tetrahydrate to the polyvinyl alcohol aqueous solution, and heat and stir until a transparent viscous solution is formed; finally, add polytetrafluoroethylene dispersion to the transparent viscous solution and stir at room temperature until it becomes a brown viscous solution, which is the spinning solution of MnCl2 / DCD / PTFE / PVA. (2) Electrospinning the brown viscous solution, collecting the electrospun membrane, and drying the electrospun membrane; (3) The dried electrospun film is placed in a muffle furnace for pre-oxidation; (4) The pre-oxidized sample was transferred to a tube furnace, heated and calcined under an inert atmosphere, and the MnF2 / NF-CNF composite material was obtained after the tube furnace cooled to room temperature.

3. The method for preparing the composite material according to claim 2, characterized in that: In step (1), the mass concentration of the polyvinyl alcohol aqueous solution is 12wt%, the mass ratio of manganese chloride tetrahydrate to the polyvinyl alcohol aqueous solution is 6:125, the mass ratio of dicyandiamine to the polyvinyl alcohol aqueous solution is 6:125, and the mass ratio of polytetrafluoroethylene dispersion to the polyvinyl alcohol aqueous solution is 9:

22.

4. The method for preparing the composite material according to claim 2, characterized in that: In step (2), during electrospinning, the flow rate of the spinning solution is 0.01 mL / min and the electrostatic voltage is 20 kV.

5. The method for preparing the composite material according to claim 2, characterized in that: In step (3), the heating temperature is 250℃, the heating rate of pre-oxidation is 2℃ / min, and the holding time of pre-oxidation is 2h.

6. The method for preparing the composite material according to claim 2, characterized in that: In step (4), the temperature is raised to 850°C and kept at that temperature for calcination. The calcination heating rate is 3°C / min and the calcination holding time is 2h.

7. The method for preparing the composite material according to claim 4, characterized in that: The plastic needle used in electrospinning is 20G, and the distance between the needle and the roller collector is 15cm.

8. The application of a MnF2 / NF-CNF composite material prepared by any one of claims 1 to 7, characterized in that: The MnF2 / NF-CNF composite material is used in the air cathode of zinc-air batteries.

9. The application of the MnF2 / NF-CNF composite material according to claim 8, characterized in that: The MnF2 / NF-CNF composite material and acetylene black conductive agent were added to the sample tube, and then ethanol, water and Nafion were added to the sample tube in sequence. The mixture was uniformly dispersed by ultrasound to form MnF2 / NF-CNF catalyst ink. Using an Al2O3 polished glassy carbon electrode as a substrate, the ink was repeatedly drop-coated and dried at room temperature to obtain a composite electrode. The composite electrode loaded with the MnF2 / NF-CNF catalyst was used as the air positive electrode.

10. The application of the MnF2 / NF-CNF composite material according to claim 9, characterized in that: A zinc-air battery was assembled by using high-purity zinc foil as the negative electrode and a mixed solution of KOH and Zn(Ac)2 as the electrolyte.

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