Mofs derived iron / nitrogen-doped porous carbon nanofibers, and preparation method and application thereof

Abstract

The application relates to a MOFs derived iron / nitrogen doped porous carbon nanofiber and a preparation method and application thereof. The preparation method is as follows: polyacrylonitrile and 2-methyl imidazole are subjected to electrostatic spinning and pre-oxidation treatment to obtain a pre-oxidized nanofiber film; the pre-oxidized nanofiber film is placed in a mixed solution of zinc nitrate, iron chloride and 2-methyl imidazole to perform a solvothermal reaction, thereby obtaining a nanofiber film coated with irregular ZnFe-ZIF; and high-temperature annealing is performed to obtain an iron / nitrogen doped porous carbon nanofiber film material. The film material preparation method is simple, the process flow is short, the cost is low, and the structure is uniform. Benefited from the high-conductivity carbon nanofiber film, the rich Fe-N active species and the porous structure, the nanofiber provided by the application exhibits excellent oxygen reduction (ORR) and oxygen evolution (OER) catalytic performance and zinc-air battery performance, and has a good application prospect in the field of energy conversion and storage.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials, and more specifically, relates to a MOFs-derived iron / nitrogen-doped porous carbon nanofiber, its preparation method, and its application. Background Technology

[0002] With the continuous consumption of fossil fuels and the rapid development of electric vehicles, developing renewable and environmentally friendly new clean energy sources is considered an effective way to solve these problems. Zinc-air batteries have advantages such as high theoretical energy density, high conversion efficiency, and safety and environmental friendliness, and have broad application prospects in supplying sustainable clean and low-carbon energy. Although noble metal catalysts (Pt / C, RuO2, IrO2, etc.) exhibit significant oxygen reduction (ORR) and oxygen evolution (OER) performance, their high cost and low reserves severely limit their large-scale commercial application. Therefore, developing low-cost, efficient, and stable ORR / OER non-noble metal catalysts is of great significance to the development of zinc-air batteries.

[0003] Transition metal-nitrogen-carbon (MNC) materials are a class of highly promising non-noble metal catalysts, possessing abundant MN active species and exhibiting excellent catalytic activity and stability. Metal-organic frameworks (MOFs), composed of metal ions and organic ligands, are important precursors for MNC preparation. During high-temperature pyrolysis, the metal center transforms into a transition metal, and the nitrogen in the organic ligands can be in-situ doped and dispersed within the carbon material. Electrospun nanofibers, with their advantages of large aspect ratio, high porosity, convenient preparation, and low cost, have attracted widespread attention from researchers. Combining MOFs and electrospun nanofibers can fully leverage the advantages of both MOF derivatives and nanofibers to obtain non-noble metal MNC catalysts with good catalytic performance and high stability.

[0004] In recent years, researchers have combined MOFs and nanofibers using electrospinning assembly technology to prepare porous carbon nanofibers. These nanofibers expose more active sites, provide rapid mass transfer and charge transfer channels, and exhibit superior electrochemical performance. However, the electrospinning assembly technique involves pre-synthesizing regular dodecahedral MOF particles, then assembling them into polymer nanofibers using electrospinning, followed by high-temperature annealing to obtain porous carbon nanofibers. This method of pre-synthesizing regular MOF particles requires steps such as centrifugation, separation, and drying, making the operation complex and the process lengthy. Therefore, there is a need to find a simpler and shorter preparation method to obtain MOF-derived porous carbon nanofibers with excellent catalytic performance. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides MOFs-derived iron / nitrogen-doped porous carbon nanofibers, their preparation method, and applications, solving the problems of complex operation and long process flow in the preparation of MOFs-derived porous carbon nanofibers.

[0006] This invention employs electrospinning and pre-oxidation treatment to obtain a pre-oxidized PAN nanofiber membrane. Then, a solvothermal reaction is carried out in a mixed solution of zinc nitrate, ferric chloride, and 2-methylimidazole to obtain a nanofiber membrane loaded with irregular ZnFe-ZIF. After high-temperature annealing, a MOF-derived iron / nitrogen-doped porous carbon nanofiber membrane material is obtained. The membrane material preparation method provided by this invention is simple and effective, with a short process flow, low cost, and uniform structure. It exhibits excellent ORR and OER catalytic activity, as well as zinc-air battery performance, and has significant application value in the field of electrochemistry.

[0007] The specific technical solution for preparing MOF-derived iron / nitrogen-doped porous carbon nanofibers according to this invention is as follows:

[0008] Step (1): Polyacrylonitrile and 2-methylimidazole were dissolved in N,N-dimethylformamide (DMF) to obtain a spinning solution. Pre-oxidized electrospun nanofibers PAN / M were prepared by electrospinning technology and pre-oxidation treatment.

[0009] Step (2): The pre-oxidized electrospun nanofibers PAN / M obtained in step (1) are placed in a solution of transition metal zinc iron salt and 2-methylimidazole and subjected to a solvothermal reaction to prepare irregular ZnFe-ZIF-coated pre-oxidized nanofibers ZnFe-ZIF@PAN / M;

[0010] Step (3): The irregular ZnFe-ZIF coated pre-oxidized nanofiber membrane ZnFe-ZIF@PAN / M obtained in step (2) and urea are placed in the middle and upstream of a tube furnace, respectively, and subjected to high-temperature annealing under a nitrogen atmosphere to obtain iron / nitrogen doped porous carbon nanofibers Fe / N@PCNF.

[0011] Furthermore, in step (1), the mass ratio of polyacrylonitrile, 2-methylimidazole and DMF is (1-2):(0.1-1):(5-10).

[0012] Furthermore, the electrospinning conditions in step (1) are as follows: the spinning temperature is room temperature, the spinning voltage is 15-20kV, the distance from the nozzle to the receiving roller is 10-18cm, the receiving speed is 100-180r / min, and the injection speed is 0.04-0.10mm / min.

[0013] Furthermore, the pre-oxidation treatment conditions in step (1) are as follows: the pre-oxidation temperature is 200-250℃, the heating rate is 1-5℃ / min, and the holding time is 1-2h.

[0014] Further, in step (2), the transition metal zinc salt is one or more of the divalent zinc salts zinc nitrate, zinc chloride, and zinc acetate, and the transition metal iron salt is one or more of the trivalent iron salts ferric chloride, ferric nitrate, and ferric acetylacetone. The mass ratio of the transition metal zinc salt to the transition metal iron salt is (9:1):(1:9), the mass ratio of PAN / M to the total mass of the transition metal zinc salt and transition metal iron salt is 1:(50-200), the mass ratio of 2-methylimidazole to the total mass of the transition metal zinc salt and transition metal iron salt is 1:(1-3), the solution is a 1:1 volume mixture of DMF and methanol, the reaction temperature is 100-120℃, and the reaction time is 1-12h.

[0015] Furthermore, in step (3), the mass ratio of ZnFe-ZIF@PAN / M to urea is 1:(10-30), and the high-temperature annealing conditions are: heating rate of 1-10℃ / min, holding temperature of 600-1000℃, and holding time of 1-5h.

[0016] The present invention also provides a MOFs-derived iron / nitrogen-doped porous carbon nanofiber membrane material prepared by the above preparation method. The material has the following structure: transition metal Fe nanoparticles are uniformly loaded on porous carbon nanofibers, the diameter of the porous carbon nanofibers is 300-600 nm, the size of the nanoparticles is 5 nm-50 nm, and the MOFs are irregular ZnFe-ZIF.

[0017] The present invention also provides the application of the aforementioned MOFs-derived iron / nitrogen-doped porous carbon nanofibers as ORR and OER catalysts and cathode materials in zinc-air batteries.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0019] (1) The preparation method of the present invention has the advantages of simple and efficient operation, short process flow, high yield and uniform structure.

[0020] (2) In the preparation method of the present invention, since the nitrogen atom of 2-methylimidazole has a strong coordination and complexation effect with the ferric ion, the growth process of ZnFe-ZIF is changed during the solvothermal reaction, so that irregular ZnFe-ZIF is uniformly coated on the nanofiber.

[0021] (3) During the high-temperature annealing process, zinc volatilizes and polymer nanofibers are transformed into porous carbon nanofibers; ferric ions are reduced to Fe nanoparticles, which are uniformly distributed in the porous carbon nanofibers; nitrogen in organic ligands not only forms abundant Fe-N active species, but also does it into carbon nanofibers, which regulates the charge density and electron distribution of carbon and enhances the electrocatalytic performance of the material.

[0022] (4) The MOFs-derived iron / nitrogen-doped porous carbon nanofibers prepared in this invention are low-cost non-precious metal catalysts with excellent ORR and OER catalytic performance. They are used as positive electrode catalysts in zinc-air batteries and have broad application prospects in other energy conversion and storage fields. Attached Figure Description

[0023] Figure 1 These are scanning electron microscope images of (ab)PAN / M, (cd)ZnFe-ZIF@PAN / M-2 and (ef)Fe / N@PCNF-2 provided in Embodiment 1 of the present invention;

[0024] Figure 2 These are scanning electron microscope (SEM) images of (a) ZIF-8@PAN / M, (b) ZnFe-ZIF@PAN / M-1, (c) ZnFe-ZIF@PAN / M-3, and (d) ZnFe-ZIF@PAN / M-4 provided in Embodiments 2-5 of the present invention.

[0025] Figure 3 These are scanning electron microscope images of (a) NCNF, (b) Fe / N@PCNF-1, (c) Fe / N@PCNF-3, and (d) Fe / N@PCNF-4 provided in Embodiments 2-5 of the present invention;

[0026] Figure 4 These are the XRD patterns of ZIF-8@PAN / M, ZnFe-ZIF@PAN / M-2, NCNF, and Fe / N@PCNF-2 provided in Embodiments 1 and 2 of the present invention;

[0027] Figure 5 These are the oxygen reduction LSV curves of NCNF, Fe / N@PCNF-1, 2, 3, 4 and Pt / C provided in Examples 1-5 of this invention;

[0028] Figure 6 The LSV curves of oxygen evolution of NCNF, Fe / N@PCNF-1, 2, 3, 4 and RuO2 provided in Examples 1-5 of this invention are shown.

[0029] Figure 7The graph shows the cycle stability test results of Fe / N@PCNF-2 and the comparative material (a mixture of Pt / C and RuO2) provided in Example 1 of this invention as positive electrode materials for liquid zinc-air batteries.

[0030] Figure 8 This is a test chart showing the cycle stability of Fe / N@PCNF-2 and the comparative material (a mixture of Pt / C and RuO2) provided in Example 1 of this invention as cathode materials for solid zinc-air batteries. Detailed Implementation

[0031] The present invention will be further described clearly and completely below with reference to specific embodiments. The embodiments are only some embodiments of the present invention and are used to illustrate the present invention, and do not limit the scope of the invention.

[0032] Example 1

[0033] The preparation method of MOFs-derived iron / nitrogen-doped porous carbon nanofibers in this embodiment is as follows:

[0034] Step (1): Dissolve 1.6g of polyacrylonitrile and 0.5g of 2-methylimidazole in 8.4g of DMF and stir magnetically for 24h to obtain a transparent and uniform precursor spinning solution. Electrospinning was performed under the following conditions: spinning voltage of 18kV, distance from nozzle to receiving roller of 18cm, receiving speed of 150r / min, and injection speed of 0.05mm / min, to obtain electrospun nanofibers. These nanofibers were then placed in a muffle furnace for pre-oxidation treatment under the following conditions: in an air atmosphere, the temperature was increased from room temperature to 210℃ at a rate of 5℃ / min and held for 1h to obtain pre-oxidized electrospun nanofibers, named PAN / M.

[0035] Step (2): Dissolve 0.5 g of Zn(NO3)2·6H2O and FeCl3·6H2O in a 1:1 mass ratio in a 5 ml DMF and 5 ml methanol mixture to prepare a metal salt solution. Place 0.005 g of PAN / M and 0.25 g of 2-methylimidazole obtained in step (1) into the above metal salt solution, react at 120 °C for 5 h, cool to room temperature, rinse and dry to prepare an irregular ZnFe-ZIF coated pre-oxidized nanofiber membrane material, named: ZnFe-ZIF@PAN / M-2;

[0036] Step (3): The ZnFe-ZIF@PAN / M-2 obtained in step (2) and urea were placed in the middle and upstream of a tube furnace, respectively. The mass ratio of ZnFe-ZIF@PAN / M-2 to urea was 1:30. Under a nitrogen atmosphere, the temperature was increased from room temperature to 800℃ at a heating rate of 3℃ / min and held for 2 hours for high-temperature annealing. Iron / nitrogen doped porous carbon nanofiber membrane material was prepared and named: Fe / N@PCNF-2.

[0037] Electrocatalytic performance testing of Fe / N@PCNF-2: Fe / N@PCNF-2 was cut into small fragments, ground, and 5 mg was weighed into a centrifuge tube. 4.75 mL of DMF and 0.25 mL of naphthol solution were added, and the mixture was ultrasonically dispersed to form a catalyst solution. A glassy carbon electrode coated with the catalyst was used as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The ORR and OER performance of the material were tested using a PINE rotating disk electrode apparatus and a CHI 760E electrochemical workstation. In the ORR test, the scan rate was 5 mV / s, and the voltage range was 0.5–1.2 V vs. RHE. In the OER test, the scan rate was 5 mV / s, and the voltage range was 1.2–1.7 V vs. RHE. The preparation process and testing methods for Pt / C and RuO2 slurries were the same as described above.

[0038] Zinc-air battery performance testing: A two-electrode system was used during battery testing. The positive electrode was Fe / N@PCNF-2, and the negative electrode was a polished zinc sheet. The liquid electrolyte was 6M KOH, and the solid electrolyte was a gel polymer electrolyte. The LAND battery testing system was used for testing. For liquid cycle stability testing, the test current density was 5 mA cm⁻¹. -2 For solid-state cycling stability testing, the test current density is 1 mA cm⁻¹. -2 A cycle consists of charging for 10 minutes and discharging for 10 minutes.

[0039] Examples 2-5

[0040] The preparation steps are the same as in Example 1, except that the mass ratios of Zn(NO3)2·6H2O and FeCl3·6H2O in step (2) of Examples 2-5 are different, namely 1:0, 7:3, 3:7, and 0:1.

[0041] The materials obtained in step (2) of Examples 2-5 are named as follows: ZIF-8@PAN / M, ZnFe-ZIF@PAN / M-1, ZnFe-ZIF@PAN / M-3, and ZnFe-ZIF@PAN / M-4.

[0042] Correspondingly, the materials obtained in step (3) of Examples 2-5 are named as follows: NCNF, Fe / N@PCNF-1, Fe / N@PCNF-3, Fe / N@PCNF-4.

[0043] The electrocatalytic performance testing methods for Examples 2-5 are the same as those for Example 1.

[0044] Figure 1 Scanning electron microscope (SEM) images of PAN / M, ZnFe-ZIF@PAN / M-2, and Fe / N@PCNF-2 prepared in Example 1. From... Figure 1 (ab) shows that pre-oxidized electrospun nanofibers PAN / M were prepared using electrospinning technology and pre-oxidation treatment, and the fiber surface is smooth. Figure 1 (cd) shows that a solvothermal reaction in a mixed solution of zinc nitrate, ferric chloride, and 2-methylimidazole yielded irregularly coated ZnFe-ZIF nanofibers with a roughened fiber surface. Figure 1 (ef) shows that after high-temperature annealing, the metallic zinc in this irregular ZnFe-ZIF volatilizes, the polymer nanofibers are transformed into porous carbon nanofibers, and the ferric ions are reduced to Fe nanoparticles, which are uniformly distributed in the porous carbon nanofibers.

[0045] Figure 2 Scanning electron microscope (SEM) images of ZIF-8@PAN / M, ZnFe-ZIF@PAN / M-1, ZnFe-ZIF@PAN / M-3, and ZnFe-ZIF@PAN / M-4 prepared in Examples 2-5. From... Figure 2 (a) It can be seen that when the mass ratio of Zn(NO3)2·6H2O and FeCl3·6H2O is 1:0, the nanofibers are loaded with particulate ZIF-8, and ZIF-8@PAN / M is obtained. Figure 2 (b) is a scanning electron microscope image of a sample with a mass ratio of Zn(NO3)2·6H2O and FeCl3·6H2O of 7:3. When a certain amount of FeCl3·6H2O is added, the growth process of ZnFe-ZIF is changed due to the strong coordination and complexation between the nitrogen atom of 2-methylimidazolium and the ferric ion, so that the irregular ZnFe-ZIF is uniformly coated on the nanofiber, resulting in ZnFe-ZIF@PAN / M-1. Figure 2 (c) and (d) are scanning electron microscope images of Zn(NO3)2·6H2O and FeCl3·6H2O with mass ratios of 3:7 and 0:1, respectively. As the amount of FeCl3·6H2O gradually increases, the amount of material loaded on the fiber surface gradually increases and thickens, resulting in ZIF@PAN / M-3 and ZnFe-ZIF@PAN / M-4.

[0046] Figure 3Scanning electron microscope (SEM) images of NCNF, Fe / N@PCNF-1, Fe / N@PCNF-3, and Fe / N@PCNF-4 prepared in Examples 2-5. From... Figure 3 (a) It can be seen that NCNF was obtained after high-temperature pyrolysis of ZIF-8@PAN / M, the polymer nanofibers were transformed into carbon nanofibers, and ZIF-8 was transformed into particulate nitrogen-doped carbon material. From Figure 3 (b) It can be seen that after high-temperature pyrolysis of ZnFe-ZIF@PAN / M-1, no particulate matter exists on the surface of the nanofibers, and the polymer nanofibers loaded with ZnFe-ZIF become iron / nitrogen-doped porous carbon nanofibers (Fe / N@PCNF-1). From Figure 3 As can be seen from (c) and (d), with the gradual increase of FeCl3·6H2O, ZIF@PAN / M-3 and ZnFe-ZIF@PAN / M-4 also transformed into iron / nitrogen-doped porous carbon nanofibers (Fe / N@PCNF-3 and Fe / N@PCNF-4) after high-temperature pyrolysis.

[0047] Figure 4 XRD patterns of ZIF-8@PAN / M, ZnFe-ZIF@PAN / M-2, NCNF, and Fe / N@PCNF-2 prepared in Examples 1 and 2. Figure 4 (a) It can be seen that the diffraction peaks of ZIF-8@PAN / M correspond to those of the ZIF-8 standard card, proving that the polymer nanofibers are loaded with ZIF-8 particles. The diffraction peaks of ZnFe-ZIF@PAN / M-2 correspond to the main characteristic peaks of the ZIF-8 standard card, and are weaker than those of granular ZIF-8, which also indirectly indicates the formation of irregular ZnFe-ZIF. From Figure 4 (b) It can be seen that the characteristic peaks of carbon are present in NCNF, indicating the formation of carbon materials. Compared with the XRD pattern of NCNF, Fe / N@PCNF-2 also has diffraction peaks of elemental Fe, which are consistent with the standard card PDF#87-0722, proving the formation of iron / nitrogen-doped porous carbon nanofibers.

[0048] Figure 5 Oxygen reduction LSV curves for NCNF, Fe / N@PCNF-1, 2, 3, 4, and Pt / C prepared in Examples 1-5. From... Figure 5 As can be seen, compared with NCNF, Fe / N@PCNF-1, 3, 4 and Pt / C, Fe / N@PCNF-2 has an earlier onset potential and half-wave potential, and has the best catalytic activity.

[0049] Figure 6 Oxygen evolution LSV curves for NCNF, Fe / N@PCNF-1, 2, 3, 4, and RuO2 prepared in Examples 1-5. From... Figure 6 As can be seen, Fe / N@PCNF-2 has an earlier onset potential, reaching 10 mA cm⁻¹. -2 The requirement for a smaller overpotential indicates that Fe / N@PCNF-2 exhibits superior OER catalytic activity.

[0050] Figure 7 Cycle stability test results for Fe / N@PCNF-2 prepared in Example 1 and a comparative material (a mixture of Pt / C and RuO2) as positive electrode materials in a liquid zinc-air battery. Figure 7 As can be seen, Fe / N@PCNF-2 has a smaller charge-discharge potential difference than Pt / C+RuO2 and also has better cycle stability, which can be maintained for 1500 hours and 4500 cycles, and the charge-discharge potential difference hardly decays.

[0051] Figure 8 Cycle stability test results for Fe / N@PCNF-2 provided in Example 1 and the comparative material (a mixture of Pt / C and RuO2) as cathode materials in a solid-state zinc-air battery. Figure 8 As can be seen, compared with the rapid decay of Pt / C+RuO2 cycling performance, Fe / N@PCNF-2 has good cycling stability and can maintain a cycle life of more than 225 cycles for 75 hours.

[0052] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers, characterized in that, Includes the following steps: Step (1): Polyacrylonitrile and 2-methylimidazole were dissolved in N,N-dimethylformamide (DMF) to obtain a spinning solution. Pre-oxidized electrospun nanofibers PAN / M were prepared by electrospinning technology and pre-oxidation treatment. Step (2): The pre-oxidized electrospun nanofibers PAN / M obtained in step (1) are placed in a solution of transition metal zinc salt, transition metal iron salt and 2-methylimidazole and subjected to a solvothermal reaction to prepare irregular ZnFe-ZIF coated pre-oxidized nanofibers ZnFe-ZIF@PAN / M; Step (3): The irregular ZnFe-ZIF coated pre-oxidized nanofiber membrane ZnFe-ZIF@PAN / M obtained in step (2) and urea are placed in the middle and upstream of a tube furnace, respectively, and subjected to high-temperature annealing under a nitrogen atmosphere to obtain iron / nitrogen doped porous carbon nanofibers Fe / N@PCNF.

2. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, In step (1), the mass ratio of polyacrylonitrile, 2-methylimidazole and DMF is (1-2):(0.1-1):(5-10).

3. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, The electrospinning conditions in step (1) are as follows: the spinning temperature is room temperature, the spinning voltage is 15-20 kV, the distance from the nozzle to the receiving roller is 10-18 cm, the receiving speed is 100-180 r / min, and the injection speed is 0.04-0.10 mm / min.

4. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, The pre-oxidation conditions in step (1) are as follows: the pre-oxidation temperature is 200-250 °C, the heating rate is 1-5 °C / min, and the holding time is 1-2 h.

5. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, In step (2), the transition metal zinc salt is one or more of the divalent zinc salts zinc nitrate, zinc chloride, and zinc acetate, and the transition metal iron salt is one or more of the trivalent iron salts ferric chloride, ferric nitrate, and ferric acetylacetone. The solution is a mixed solution of DMF and methanol in a volume ratio of 1:

1.

6. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, The mass ratio of transition metal zinc salt to transition metal iron salt is (9:1):(1:9), the mass ratio of PAN / M to the total mass of transition metal zinc salt and transition metal iron salt is 1:(50-200), and the mass ratio of 2-methylimidazole to the total mass of transition metal zinc salt and transition metal iron salt is 1:(1-3).

7. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, The temperature of the solvothermal reaction in step (2) is 100-120 °C and the reaction time is 1-12 h.

8. The method for preparing MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 1, characterized in that, In step (3), the mass ratio of ZnFe-ZIF@PAN / M to urea is 1:(10-30), and the high-temperature annealing conditions are: heating rate of 1-10 °C / min, holding temperature of 600-1000 °C, and holding time of 1-5 h.

9. The MOFs-derived iron / nitrogen-doped porous carbon nanofibers prepared by any one of the preparation methods according to claims 1-8, characterized in that... It has the following structure: transition metal Fe nanoparticles are uniformly loaded on porous carbon nanofibers, the diameter of the porous carbon nanofibers is 300-600 nm, the size of the nanoparticles is 5 nm-50 nm, and the MOFs are irregular ZnFe-ZIF.

10. The application of MOFs-derived iron / nitrogen-doped porous carbon nanofibers according to claim 9, characterized in that, It is used as an ORR and OER catalyst, as well as a cathode material for zinc-air batteries.

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