Modified graphite felt, method for preparing the same, and application of the same in vanadium flow battery

Abstract

The present application relates to modified graphite felt and its preparation method, and its application in vanadium flow battery, and belongs to the technical field of flow battery electrode. The method comprises the following steps: mixing graphite felt and mixed solution, carrying out thermal reaction to obtain metal organic framework two-dimensional nanosheet loaded graphite felt; sintering the metal organic framework two-dimensional nanosheet loaded graphite felt to obtain modified graphite felt; wherein the mixed solution comprises nitrogen-containing organic ligand and metal salt. In the modified graphite felt of the present application, the surface of the modified graphite felt is coated with a layer of metal nitrogen-carbon two-dimensional nanosheet. Since the metal organic framework two-dimensional nanosheet is formed by the coordination reaction of nitrogen-containing organic ligand and metal salt, the metal is uniformly dispersed in the organic framework two-dimensional nanosheet, and then the metal is uniformly dispersed in the metal nitrogen-carbon two-dimensional nanosheet, so that the surface of the obtained modified graphite felt not only uniformly distributes a large number of metal active sites, but also forms nitrogen element doping at the same time, thereby improving the electrochemical performance of the modified graphite felt electrode.

Description

Technical Field

[0001] This invention belongs to the field of flow battery electrode technology, and specifically relates to modified graphite felt and its preparation method, and its application in vanadium redox flow batteries. Background Technology

[0002] Vanadium redox flow batteries (VRBs) have become a promising electrochemical energy storage system due to their scalability to medium and large-scale systems, durability, fast response, low maintenance costs, and good safety. Electrode materials are a crucial component affecting their energy storage performance. Currently, VRB electrode materials generally suffer from insufficient stability and durability, need for improved catalytic activity, and require optimization of conductivity. Specifically, the surface structure and chemical properties of electrode materials limit the adsorption of vanadium ions and the provision of reactive sites. Insufficient number or low activity of active sites in commonly used electrode materials leads to incomplete and slow redox reactions of vanadium ions on the electrode surface, affecting battery efficiency and performance.

[0003] Modifying graphite felt electrodes can effectively solve the aforementioned problems of vanadium redox flow batteries. In recent years, research hotspots in graphite felt electrode modification have included discovering new materials and loading them onto the graphite felt surface or directly synthesizing second-phase catalysts in situ on the graphite felt surface, as well as etching carbon-based materials to create pores, regulate chemical structure, and modify catalysts, thereby increasing the electrode's specific surface area, hydrophilicity, and active sites. However, etching weakens the electrode's mechanical properties and conductivity, affecting its long-term stability. Chemical structure regulation, such as group modification and heteroatom doping, has poor tolerance in strongly acidic electrolyte environments. Loading highly active catalysts, such as metal-based and carbon-based active materials, can directly improve electrode activity, offering advantages such as high catalytic activity, wide selectivity, and high stability. Common second-phase catalysts include carbon-based catalysts, metals and metal oxides, and single-atom catalysts. Carbon-based catalysts generally possess excellent pore structure, defects, and high conductivity, providing sites for redox reactions; however, carbon-based materials have poor wettability, affecting the mass transfer process of electrochemical reactions, and have fewer active sites on their surface. Metal nanoparticle catalysts in single-atom catalysts can effectively improve the electrocatalytic activity of electrodes, but due to their low hydrogen evolution overpotential, they can produce hydrogen evolution side reactions. Metal nitrogen-carbon catalysts, on the other hand, not only increase the number of active sites but also incorporate the characteristics of nitrogen doping, including maximized atom utilization, well-defined active sites, and a stable electronic structure.

[0004] In existing technologies, heteroatom doping is a simple and effective method to improve electrode performance. Typically, elements such as B, N, P, and S are introduced into the carbon layer through physical or chemical means to disperse the charge density on the electrode surface. Jin et al. (LEE ME, JINH-J, YUN YS. Synergistic catalytic effects of oxygen and nitrogen functional groups on active carbon electrodes for all-vanadium redox flow batteries[J]. RSC Advances, 2017, 7(68): 43227-43232.) coated a thin layer of pyritin containing oxygen and nitrogen functional groups onto the surface of carbon felt to obtain oxygen- and nitrogen-rich pyritin carbon felt (P-CF). Vanadium batteries based on P-CF achieved higher energy efficiency and stable cycling performance. This is attributed to the pyridine structure in P-CF and the synergistic effect of nitrogen and oxygen functional groups at the carbon skeleton edge. However, this technique cannot increase the specific surface area of ​​the electrode material, and its effect on improving active sites is limited. In summary, current technologies still face challenges: slow negative electrode reactions and limitations imposed by the surface structure and chemical properties of electrode materials on the adsorption of vanadium ions and the provision of reactive sites. Insufficient number or low activity of active sites in the electrode material leads to incomplete and slow redox reactions of vanadium ions on the electrode surface, affecting battery efficiency and performance. Summary of the Invention

[0005] To address the above problems, this invention provides modified graphite felt, its preparation method, and its application in vanadium redox flow batteries.

[0006] The first objective of this invention is to provide a method for preparing modified graphite felt, comprising:

[0007] Graphite felt and a mixed solution were mixed and subjected to a thermal reaction to obtain graphite felt supported on two-dimensional nanosheets of a metal-organic framework.

[0008] Graphite felt supported on metal-organic framework two-dimensional nanosheets was sintered to obtain modified graphite felt.

[0009] The mixed solution includes nitrogen-containing organic ligands and metal salts.

[0010] Furthermore, the mass ratio of the nitrogen-containing organic ligand to the metal salt is 1-80:1.

[0011] Furthermore, the nitrogen-containing organic ligand is one of formamide, folic acid, ethylenediamine, urea, 2-methylimidazole, and aniline;

[0012] Preferably, the nitrogen-containing organic ligand is formamide or folic acid.

[0013] More preferably, the nitrogen-containing organic ligand is formamide.

[0014] Furthermore, the metal salt is one of cobalt salt, nickel salt, iron salt, ferrous salt, manganese salt, chromium salt, and molybdenum (Mo) salt.

[0015] Furthermore, the temperature of the thermal reaction is 120-190℃, and the time is 10-24h.

[0016] Furthermore, the sintering temperature is 750-850℃, and the time is 2-4 hours.

[0017] Furthermore, the atmosphere during sintering is an inert atmosphere.

[0018] Furthermore, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere, preferably a nitrogen atmosphere.

[0019] Furthermore, the mixed solution also includes an organic solvent, which facilitates the thorough mixing of the nitrogen-containing organic ligand and the metal salt, thereby increasing the coordination reaction rate between the nitrogen-containing organic ligand and the metal ions in the subsequent thermal reaction.

[0020] A second objective of this invention is to provide a modified graphite felt prepared using the aforementioned method.

[0021] A third objective of this invention is to provide a method for preparing modified graphite felt, which is then used as an electrode material in vanadium redox flow batteries.

[0022] The beneficial effects of this invention are:

[0023] This invention relates to a modified graphite felt, its preparation method, and its application in vanadium redox flow batteries. The invention introduces graphite felt into a coordination reaction solution of nitrogen-containing organic ligands and metal salts, and synthesizes in situ a graphite felt supported on metal-organic framework (MOF) two-dimensional nanosheets. The MOF-supported graphite felt is further sintered to form a modified graphite felt. It is understood that the modified graphite felt of this invention has a layer of metal-nitrogen-carbon two-dimensional nanosheets coated on its surface. These metal-nitrogen-carbon two-dimensional nanosheets are obtained by sintering MOF two-dimensional nanosheets, with the nitrogen and carbon originating from nitrogen-containing organic ligands. Because the MOF two-dimensional nanosheets are formed by the coordination reaction of nitrogen-containing organic ligands and metal salts, the metal is uniformly dispersed within the MOF two-dimensional nanosheets, and further uniformly dispersed within the metal-nitrogen-carbon two-dimensional nanosheets. This results in a modified graphite felt surface with numerous uniformly distributed metal active sites and simultaneous nitrogen doping, improving the electrochemical performance of the modified graphite felt electrode.

[0024] Furthermore, this invention can further increase the number of single-atom metal active sites by controlling the size of nitrogen-containing organic ligands to synthesize tunable electrode surface defects and a larger specific surface area, thereby further improving the electrochemical performance of the modified graphite felt electrode and meeting the requirements for higher battery energy efficiency.

[0025] Furthermore, the modified graphite felt of this invention, with its surface coated with two-dimensional metal-nitrogen-carbon nanosheets, not only possesses numerous metal active sites and nitrogen doping, but also exhibits the high hydrophilicity characteristic of single-atom metal materials, which is beneficial for mass transfer during electrochemical reactions. Its application as an electrode material in vanadium redox flow batteries can significantly improve the efficiency and performance of vanadium redox flow batteries. Subsequent tests on vanadium redox flow batteries show that, compared to the original graphite felt, the modified graphite felt of this invention, as an electrode material, improves voltage efficiency by approximately 3.5-8.6% and energy efficiency by approximately 3.2-7.2%.

[0026] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A scanning electron microscope image of the modified graphite felt obtained according to Example 1 of the present invention is shown. Figure 1 Image (a) is a scanning electron microscope image of the blank graphite felt in Comparative Example 1. Figure 1 (b) is a scanning electron microscope image of the modified graphite felt obtained in Example 1;

[0029] Figure 2 A comparison diagram of the contact angles of the modified graphite felt obtained according to Example 1 and Comparative Example 1 of the present invention is shown. Figure 2 Figure (a) shows the contact angle diagram of the blank graphite felt in Comparative Example 1. Figure 2 (b) is a contact angle diagram of the modified graphite felt obtained in Example 1;

[0030] Figure 3Cyclic voltammetry curves of electrode materials obtained according to Embodiments 1, 2, 3, 4, 5, and Comparative Example 1 are shown.

[0031] Figure 4 Cyclic voltammetry curves of electrode materials obtained according to Embodiments 6, 7, 8 and Comparative Example 1 of the present invention are shown.

[0032] Figure 5 A comparison diagram of charge-discharge curves of electrode materials obtained according to Embodiment 1 and Comparative Example 1 is shown.

[0033] Figure 6 A comparison graph showing the capacity of the electrode materials obtained according to Embodiment 1 and Comparative Example 1 under different current densities is presented. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1:

[0036] (1) Dissolve 0.5 parts of cobalt nitrate in 40 parts of formamide, sonicate for 0.5 h to obtain a homogeneous solution, add it to the reaction vessel, and then add blank graphite felt (3×3 cm). 2 The mixture was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 180 °C and the holding time was 12 h. The mixture was purified three times with deionized water and dried overnight at 60 °C to obtain graphite felt supported on two-dimensional nanosheets of a small molecule metal-organic framework.

[0037] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a constant temperature for 2 hours and then sintered at a high temperature of 800 °C for 2 hours in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 1).

[0038] Example 2

[0039] (1) Dissolve 1 part cobalt nitrate in 40 parts formamide, sonicate for 0.5 h to obtain a homogeneous solution, add it to the reaction vessel, and then add blank graphite felt (3×3 cm) 2The sample was placed in a reaction vessel, sealed, kept at a temperature of 180℃, and then cooled and removed. The temperature was 180℃ and the holding time was 12 h. The sample was purified three times with deionized water and dried overnight at 60℃ to obtain graphite felt supported on two-dimensional nanosheets of small molecule metal-organic framework.

[0040] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 °C for 2 h in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 2).

[0041] Example 3

[0042] (1) Dissolve 1.5 parts cobalt nitrate in 40 parts formamide, sonicate for 0.5 h to obtain a homogeneous solution, add it to the reaction vessel, and then add blank graphite felt (3×3 cm). 2 The mixture was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 180 °C and the holding time was 12 h. The mixture was purified three times with deionized water and dried overnight at 60 °C to obtain graphite felt supported on two-dimensional nanosheets of a small molecule metal-organic framework.

[0043] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 ℃ in a tube furnace for 2 h. After calcination, the graphite felt was naturally cooled to 25 ℃ under a nitrogen atmosphere to obtain the modified graphite felt (Example 3).

[0044] Example 4

[0045] (1) Dissolve 1 part nickel nitrate in 40 parts formamide, sonicate for 0.5 h to obtain a homogeneous solution, add it to the reaction vessel, and then add blank graphite felt (3×3 cm) 2 The sample was placed in a reaction vessel, sealed, kept at a temperature of 180℃, and then cooled and removed. The temperature was 180℃ and the holding time was 12 h. The sample was purified three times with deionized water and dried overnight at 60℃ to obtain graphite felt supported on two-dimensional nanosheets of small molecule metal-organic framework.

[0046] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 ℃ in a tube furnace for 2 h. After calcination, the graphite felt was naturally cooled to 25 ℃ under a nitrogen atmosphere to obtain the modified graphite felt (Example 4).

[0047] Example 5

[0048] (1) Dissolve 1 part ferric citrate in 40 parts formamide, sonicate for 0.5 h to obtain a homogeneous solution, add it to the reaction vessel, and then add blank graphite felt (3×3 cm) 2 The mixture was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 180 °C and the holding time was 12 h. The mixture was purified three times with deionized water and dried overnight at 60 °C to obtain graphite felt supported on two-dimensional nanosheets of a small molecule metal-organic framework.

[0049] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 °C for 2 h in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 5).

[0050] Example 6

[0051] (1) Add 1 part cobalt chloride hexahydrate and 1 part folic acid to a mixed solution of 20 mL deionized water and 20 mL ethanol, and control the solution concentration to 0.0020 mol·L⁻¹. -1 After sonication for 0.5 h, a homogeneous solution was obtained and added to the reaction vessel. Then, a blank graphite felt (3×3 cm) was added. 2 The sample was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 140℃ and the holding time was 4 h. The sample was purified three times with deionized water and then freeze-dried in a petri dish to obtain graphite felt supported on two-dimensional nanosheets of a metal-organic framework.

[0052] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 °C for 2 h in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 6).

[0053] Example 7

[0054] (1) Add 1 part nickel chloride hexahydrate and 1 part folic acid to a mixed solution of 20 mL deionized water and 20 mL ethanol, and control the solution concentration to 0.0020 mol·L⁻¹. -1 After sonication for 0.5 h, a homogeneous solution was obtained and added to the reaction vessel. Then, a blank graphite felt (3×3 cm) was added. 2 The sample was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 140℃ and the holding time was 4 h. The sample was purified three times with deionized water and then freeze-dried in a petri dish to obtain graphite felt supported on two-dimensional nanosheets of a metal-organic framework.

[0055] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 °C for 2 h in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 7).

[0056] Example 8

[0057] (1) Add 1 part ferrous chloride tetrahydrate and 1 part folic acid to a mixed solution of 20 mL deionized water and 20 mL ethanol, and control the solution concentration to 0.0020 mol·L⁻¹. -1 After sonication for 0.5 h, a homogeneous solution was obtained and added to the reaction vessel. Then, a blank graphite felt (3×3 cm) was added. 2 The sample was placed in a sealed reactor, kept at a constant temperature, cooled, and removed. The temperature was 140℃ and the holding time was 4 h. The sample was purified three times with deionized water and then freeze-dried in a petri dish to obtain graphite felt supported on two-dimensional nanosheets of a metal-organic framework.

[0058] (2) The graphite felt supported on the metal-organic framework two-dimensional nanosheets was placed in an atmosphere furnace, evacuated, and then purged with nitrogen. The furnace was kept at a temperature of 2 h and then sintered at a high temperature of 800 °C for 2 h in a tube furnace. After calcination, the graphite felt was naturally cooled to 25 °C under a nitrogen atmosphere to obtain the modified graphite felt (Example 8).

[0059] Comparative Example 1:

[0060] This comparative example is a blank control group, that is, using untreated blank graphite felt.

[0061] test:

[0062] Scanning electron microscopy (SEM) tests were performed on the graphite felt in Example 1 and Comparative Example 1. The test results are as follows: Figure 1 As shown, Figure 1 Image (a) is a scanning electron microscope image of the blank graphite felt in Comparative Example 1. Figure 1 Image (b) is a scanning electron microscope image of the modified graphite felt obtained in Example 1. Figure 1 As can be seen, the original graphite felt fiber surface is clean and smooth, while the modified graphite felt fiber surface has a uniform layer of two-dimensional nanosheets, which increases the specific surface area of ​​the electrode surface and adds more active sites.

[0063] Contact angle tests were performed on Example 1 and Comparative Example 1, and the test results are as follows: Figure 2 As shown, Figure 2 Figure (a) shows the contact angle diagram of Comparative Example 1. Figure 2 (b) is a contact angle diagram of Example 1, from... Figure 2 As can be seen, the original graphite felt had a relatively large contact angle (77.1°C).o The vanadium ions exhibit hydrophobicity. Example 1, with a contact angle of 0, demonstrates excellent hydrophilicity, which facilitates the diffusion of vanadium ions and thus promotes the redox reaction of vanadium ions.

[0064] Cyclic voltammetry tests were performed on Examples 1-8 and Comparative Example 1, and the test results are as follows: Figure 3 and Figure 4 As shown. Figure 3 The graph shows the cyclic voltammetry test results of Examples 1-5 and Comparative Example 1. Figure 4 The figures show the cyclic voltammetry results for Examples 6-8 and Comparative Example 1. Compared to Comparative Example 1, the redox peak currents of Examples 1-8 were all increased, and the peak separation potentials were decreased. This is attributed to the modified graphite felt having a larger surface area and better hydrophilicity, providing more active sites for the reaction and promoting the redox reaction kinetics of vanadium ions.

[0065] Examples 1-8 and Comparative Example 1 were assembled with fuel cells and subjected to charge-discharge tests under the same test conditions. The coulombic efficiency, voltage efficiency, and energy efficiency of the cells were recorded. The charge-discharge curves of the electrode materials (graphite felt or modified graphite felt) provided in Examples 1 and Comparative Example 1 are shown below. Figure 5 As shown in the figure, the capacity comparison diagram of the electrode materials provided in Example 1 and Comparative Example 1 at different current densities is as follows. Figure 6 As shown in Table 1 (Test Results of Carbon Fiber Cloth in Examples and Comparative Examples):

[0066] Table 1

[0067]

[0068] As shown in Table 1, compared with Comparative Example 1, Examples 1-8 exhibit higher energy efficiency, mainly due to the coating of a layer of metal nitrogen-carbon two-dimensional nanosheets on the surface of the modified graphite felt prepared by the method of this invention. The metal nitrogen-carbon two-dimensional nanosheets increase the specific surface area of ​​the graphite felt, providing more reaction sites for vanadium ion reactions and improving the electrolyte utilization rate of the battery. Compared with Comparative Example 1, Examples 1-8 exhibit higher voltage efficiency, mainly because the single-atom metal in the metal nitrogen-carbon two-dimensional nanosheets can catalyze the interconversion of vanadium ions, enhancing the catalytic activity of carbon fibers and improving the voltage and energy efficiency of the battery. The metal nitrogen-carbon two-dimensional nanosheets have good conductivity and wettability, effectively improving the conductivity of the graphite felt, reducing charge transfer resistance, and improving the voltage and energy efficiency of the battery. The ligand in Examples 1-5 is formamide, and the ligand in Examples 6-8 is folic acid. Formamide is a small molecule ligand, avoiding the problem of shielding active sites caused by the encapsulation effect. While maintaining structural stability, it can also increase the specific surface area of ​​the composite electrode and increase more active sites. Therefore, the metal nitrogen-carbon material formed by small molecule organic ligands has superior performance.

[0069] Depend on Figure 5 As shown in the charge-discharge curves of Example 1 and Comparative Example 1, compared with the blank graphite felt, the charging voltage of the modified graphite felt decreased and the discharging voltage increased, indicating that the electrode of Example 1 reduced the polarization of the battery and improved the energy density of the battery. Figure 6 The discharge capacity at different current densities shows that the discharge capacity of both Comparative Example 1 and Example 1 decreases with increasing current density, but the discharge capacity of Example 1 is always higher than that of Comparative Example 1. This is because the good hydrophilicity of the modified graphite felt allows it to adsorb more vanadium ions on the electrode surface, providing more active sites for vanadium ions and accelerating the redox reaction of more vanadium ions, thereby improving the discharge capacity of the battery.

[0070] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing modified graphite felt, characterized in that, include: Graphite felt and a mixed solution were mixed and subjected to a thermal reaction to obtain graphite felt supported on two-dimensional nanosheets of a metal-organic framework. Graphite felt supported on metal-organic framework two-dimensional nanosheets was sintered to obtain modified graphite felt. The mixed solution includes nitrogen-containing organic ligands and metal salts; The metal salt is one of cobalt salt, nickel salt, iron salt, ferrous salt, manganese salt, chromium salt, and molybdenum salt; The sintering temperature is 750-850℃, and the time is 2-4 hours; The modified graphite felt is coated with a layer of two-dimensional metal nitrogen-carbon nanosheets.

2. The method for preparing a modified graphite felt according to claim 1, characterized in that, The mass ratio of the nitrogen-containing organic ligand to the metal salt is 1-80:

1.

3. The method for preparing a modified graphite felt according to claim 1, characterized in that, The nitrogen-containing organic ligand is one of formamide, folic acid, ethylenediamine, urea, 2-methylimidazole, and aniline.

4. The method for preparing a modified graphite felt according to claim 1, characterized in that, The nitrogen-containing organic ligand is formamide.

5. The method for preparing a modified graphite felt according to claim 1, characterized in that, The temperature of the thermal reaction is 120-190℃.

6. The method for preparing a modified graphite felt according to claim 1, characterized in that, The thermal reaction takes 10-24 hours.

7. A method for preparing a modified graphite felt according to any one of claims 1-6, characterized in that, The sintering process is carried out in an inert atmosphere.

8. Modified graphite felt prepared according to any one of claims 1-7.

9. The modified graphite felt prepared by the method according to any one of claims 1-7 is used as an electrode material in vanadium redox flow batteries.

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