Porous carbon fiber paper electrode material for vanadium redox flow batteries, its preparation and application

Abstract

This invention relates to porous carbon fiber paper electrode materials for vanadium redox flow batteries, their preparation, and applications, comprising the following steps: First, niobium chloride is dissolved in ethanol and stirred; then, a diisopropyl di(acetylacetonate)titanate solution is added and stirred again to obtain a precursor solution; the precursor solution is deposited on the surface of a rough electrode using a horizontal ultrasonic spray pyrolysis deposition process; the rough electrode is prepared by heat-treating porous carbon fiber paper, then immersing it in a liquid culture medium containing fungi for a period of time, and finally annealing it. In this invention, the double-layer structure achieves the coating of wrinkled carbon, preventing the wrinkled carbon from leaching out in the flowing electrolyte. The anode is manufactured using a simple and low-cost horizontal ultrasonic spray pyrolysis deposition process. The laminated structure prevents the carbon layer from falling off, which helps improve energy storage efficiency during charging / discharging.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to porous carbon fiber paper electrode materials for vanadium redox flow batteries and their preparation and application. Background Technology

[0002] The ever-increasing global energy consumption has accelerated the demand for sustainable energy. With increasing restrictions on fossil fuels, the growth of the rechargeable energy storage market, including redox flow batteries, fuel cells, and lithium-ion batteries, has received significant attention. Therefore, it is essential to improve the performance of electrochemical energy storage technologies to address future energy challenges. Electrochemical energy storage devices offer key advantages such as high efficiency, environmental friendliness, and controllable energy density. To date, various types of flow batteries have been developed due to their long-term cyclicability, including iron-chromium flow batteries, zinc-bromine flow batteries, and vanadium redox flow batteries.

[0003] In particular, vanadium redox flow batteries (VRFBs) are considered a key candidate for next-generation energy storage systems. VRFBs offer advantages such as flexible capacity design, high safety, high efficiency, and long cycle life. The capacity of a VRFB can be easily controlled according to the application type by adjusting the amount of electrolyte. Furthermore, the use of vanadium chemicals in both the anolyte and catholyte (vanadium content in the anolyte) contributes to its superior performance. 2+ / V 3+ VO2 in solution, cathode electrolyte + / VO 2+ In the context of lithium-ion batteries (solutions), VRFB systems mitigate cross-contamination issues. As a field of application for large-scale energy storage systems, VRFB is rapidly replacing traditional lithium-ion batteries due to its non-flammability, long-term cyclicability, and favorable levelized cost of electricity (LCOE). These advantages have promoted the commercialization of the VRFB market and the development of related technologies.

[0004] Electrode materials are a crucial component of vanadium redox flow batteries (VRFBs). To improve the energy storage performance of VRFBs, electrode materials must possess high porosity, mechanical and chemical stability, and high electrical conductivity. Porous carbon fiber paper has become a representative electrode material due to its high porosity, good electronic conductivity, low cost, and excellent electrochemical stability. The morphology of the electrode material influences the kinetic properties during electrochemical reactions occurring on the electrode surface. However, because porous carbon fiber paper electrodes are hydrophobic, their catalytic activity for vanadium redox reactions is unsatisfactory. Summary of the Invention

[0005] The purpose of this invention is to provide porous carbon fiber paper electrode materials for vanadium redox flow batteries, as well as their preparation and application. By impregnating porous carbon fiber paper with Aspergillus niger, the polysaccharides produced by Aspergillus niger during its growth process encapsulate the spores, which have a large spraying speed and a large critical movement distance. After annealing, wrinkled carbon is generated in the pores of the porous carbon fiber paper, which improves the catalytic activity of vanadium ion redox. Furthermore, carbon, oxygen, nitrogen, phosphorus, and sulfur elements are introduced to increase the electrolyte wettability of the porous carbon fiber paper. By loading the wrinkled carbon onto the porous carbon fiber paper with an Nb-doped TiO2 laminate, the problem of wrinkled carbon falling off in the flowing electrolyte is avoided, and the wettability of the porous carbon fiber paper is further increased.

[0006] It solves the problems existing in the current technology.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The preparation of porous carbon fiber paper electrode material for vanadium redox flow batteries includes the following steps:

[0009] S1. First, 2.025 g of niobium chloride (purity > 99%) was dissolved in 300 mL of ethanol and stirred for 2 h. Then, 9 mL of diisopropyl di(acetylacetonyl)titanate (purity 75 wt.% inisopropanol) solution was added and stirred for another 2 h to obtain the precursor solution;

[0010] S2. The precursor solution is deposited on the surface of the rough electrode using a horizontal ultrasonic spray pyrolysis deposition process.

[0011] For the horizontal ultrasonic spray pyrolysis deposition process, the coarse electrode is placed on a clean glass support, and the ultrasonic atomized (1.6MHz) precursor solution is thermally deposited on the coarse electrode substrate in a heating chamber at 420℃. Air is used as the carrier gas with a flow rate of 15L / min, and the support rotation speed is fixed at 5rpm. Niobium-doped TiO2 particles are deposited on the coarse electrode substrate for 60 minutes to obtain porous carbon fiber paper electrode material for vanadium redox flow batteries.

[0012] During the above operation, due to the indirect droplet supply mechanism with a rotating disk, the precursor droplets can be deposited more uniformly on the substrate. A layer of niobium-doped TiO2 composite material is deposited on the surface of porous carbon fiber paper. After heat treatment at 420℃, the surface exhibits a rough porous structure, which provides sufficient active sites for redox reactions. The increase in oxygen-containing functional groups also increases the wettability of the material.

[0013] Furthermore, the thickness of the niobium-doped TiO2 layer is less than 32 nm.

[0014] Furthermore, the method for preparing the rough electrode specifically includes the following steps:

[0015] A1. Heat treatment of porous carbon fiber paper:

[0016] Porous carbon fiber paper (3×4cm) was ultrasonically cleaned for 30 minutes using a 1:3 mixture of ethanol and deionized water. Then, it was washed with deionized water for 10 minutes. After cleaning, the porous carbon fiber paper was dried at 80°C for 12 hours. To increase surface area and electrochemical activity, facilitating subsequent wrinkled carbon deposition, the dried porous carbon fiber paper was heat-treated in an air-atmosphere box furnace at 420°C for 10 hours to obtain heat-treated porous carbon fiber paper.

[0017] S2. Preparation of liquid culture medium:

[0018] Take an appropriate amount of wheat bran and water and mix them in an enamel cup. Heat the mixture in an induction cooker and stir constantly for 15 minutes until it boils. Finally, filter to remove the solids and obtain the liquid culture medium.

[0019] S3. Preparation of porous carbon fiber paper loaded with wrinkled carbon:

[0020] Heat-treated porous carbon fiber paper was immersed in liquid culture medium and ultrasonically dispersed for 15 min, dried in an oven at 90℃ for 12 h, inoculated with 7 mL of Aspergillus niger seed liquid with OD600=0.5, and cultured in an incubator at 30℃ for 72 h to obtain precursor material. Then, the precursor material was dried in a drying oven for 12 h, annealed at 800℃ for 1 h under argon atmosphere, washed five times with deionized water, and dried in an oven to constant weight to obtain crude electrode.

[0021] Furthermore, the thickness of the porous carbon fiber paper is 0.4 mm.

[0022] Furthermore, the ratio of wheat bran to water is 50g:500mL.

[0023] During the aforementioned process, *Aspergillus niger* produces a large number of polysaccharide-encapsulated spores with rapid ejection speed and long critical movement distance, which are precursors to wrinkled carbon. These spores are uniformly distributed and attached to the carbon fiber surface of the porous carbon fiber paper. The spores possess a large effective specific surface area and a microcellular structure composed of wrinkled cell walls. This cellular structure is mainly composed of an organic framework containing carbon, oxygen, nitrogen, phosphorus, and sulfur. During annealing, the carbon in the organic framework is chemically transformed into wrinkled carbon material. Due to its uniformly distributed heteroatoms, wrinkled structure, and abundant edge carbon, the wrinkled carbon material exhibits rapid electron transfer between the interface and surface, demonstrating high electrocatalytic activity for the vanadium ion redox pair. This significantly reduces the overpotential during oxidation and reduction, and the doping of these elements also improves the wettability of the porous carbon fiber paper electrode material.

[0024] Among them, due to the doping of nitrogen atoms, the carbon atoms around the nitrogen atoms are positively charged, and the nitrogen functional group acts as a catalyst to accelerate the reduction and oxidation reactions.

[0025] Phosphorus doping facilitates an increase in the content of oxygen-containing functional groups via PO bonds, which increases the number of catalytic binding sites for the vanadium redox reaction using wrinkled carbon, and ultimately improves the performance of the vanadium redox flow battery.

[0026] Sulfur doping can induce uneven electron distribution, thereby promoting redox reactions.

[0027] Furthermore, compared to basal carbon, wrinkled carbon exhibits faster charge transfer and higher electrocatalytic activity, as the wrinkles in wrinkled carbon provide sufficient reaction sites for vanadium ions.

[0028] Furthermore, porous carbon fiber paper is prepared by the following steps:

[0029] After degumming in acetone solution, polyacrylonitrile-based chopped carbon fibers are slurried in an aqueous solution containing 0.1% polyethylene oxide dispersant to form a polyacrylonitrile-based carbon fiber slurry. This slurry is then formed into a sheet with a unit area weight of 40 g / m² using a wet forming machine. 2 The carbon paper precursor was prepared by immersing it in a 1% ethanol solution of phenolic resin for 30 minutes, then drying it and hot-pressing it at 200℃ to obtain carbon paper base paper with a pressure of 6MPa. The carbon paper base paper was placed in an electric furnace and heated to 1600℃ at a heating rate of 10℃ / min under N2 atmosphere, and held at that temperature for 1 hour. Then it was cooled to 1300℃, and a mixture of CO2 and N2 was introduced with flow rates of 40mL / min and 200mL / min, respectively, and the reaction was held at that temperature for 30 minutes. Finally, it was cooled to room temperature to obtain porous carbon fiber paper.

[0030] A porous carbon fiber paper electrode material is also disclosed.

[0031] The application of porous carbon fiber paper electrode material in vanadium redox flow batteries was also disclosed.

[0032] The beneficial effects of this invention are:

[0033] 1. In the technical solution of this invention, heat treatment of porous carbon fiber paper generates additional active sites, thereby maximizing the discharge capacity by fixing the electrolyte. Secondly, the structure of the niobium-doped TiO2 laminate increases the number of oxygen-containing functional groups, thereby increasing the wettability of the porous carbon fiber paper electrode, resulting in excellent cycle stability. Thirdly, the double-layer structure achieves coating of wrinkled carbon, preventing the wrinkled carbon from leaching out in the flowing electrolyte. This anode is manufactured using a simple and low-cost horizontal ultrasonic spray pyrolysis deposition process. The laminate structure prevents the carbon layer from falling off, which helps to improve energy storage efficiency during charging / discharging.

[0034] 2. Wrinkled carbon originates from the abundant polysaccharide-encapsulated spores produced by *Aspergillus niger* during its growth process. These spores, characterized by rapid ejection speed and long critical movement distance, are uniformly distributed and attached to the surface of porous carbon fiber paper. The spores possess a large effective specific surface area and a microcellular structure composed of wrinkled cell walls. This cellular structure is primarily composed of an organic framework containing carbon, oxygen, nitrogen, phosphorus, and sulfur. During annealing, the carbon in the organic framework is chemically transformed into wrinkled carbon material. Due to its uniformly distributed heteroatoms, wrinkled structure, and abundant edge carbon, wrinkled carbon material exhibits rapid electron transfer between the interface and surface, demonstrating high electrocatalytic activity for the vanadium ion redox pair, significantly reducing the overpotential during oxidation and the reduction process. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the cross-sectional structure of the porous carbon fiber paper electrode material for the all-vanadium redox flow battery of the present invention. Detailed Implementation

[0037] 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, and 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.

[0038] In this invention, porous carbon fiber paper is prepared by the following steps:

[0039] 10mm long polyacrylonitrile-based short carbon fibers were prepared, degummed in acetone solution, and then pulped in an aqueous solution containing 0.1% polyethylene oxide dispersant to form polyacrylonitrile-based carbon fiber slurry. This slurry was then formed into a carbon paper precursor with a unit area weight of 40g / m2 using a wet forming equipment. The precursor was then immersed in a 1% phenolic resin ethanol solution for 30 minutes, dried, and then hot-pressed at 200℃ to obtain carbon paper base paper at a pressure of 6MPa. The carbon paper base paper was placed in an electric furnace and heated to 1600℃ at a heating rate of 10℃ / min under a N2 atmosphere, and held at that temperature for 1 hour. The temperature was then lowered to 1300℃, and a mixture of CO2 and N2 was introduced at flow rates of 40mL / min and 200mL / min, respectively, and the reaction was held at that temperature for 30 minutes. Finally, the mixture was cooled to room temperature to obtain porous carbon fiber paper.

[0040] Example 1

[0041] The preparation of porous carbon fiber paper electrode material for vanadium redox flow batteries includes the following steps:

[0042] S1. Pretreatment of porous carbon fiber paper:

[0043] 0.4 mm porous carbon fiber paper (3×4 cm) was ultrasonically cleaned for 30 minutes using a 1:3 ratio of ethanol and deionized water. Then, the porous carbon fiber paper was washed with deionized water for 10 minutes. After cleaning, the porous carbon fiber paper was dried at 80°C for 12 hours, and then heat-treated in an air-atmosphere box furnace at 420°C for 10 hours to obtain heat-treated porous carbon fiber paper.

[0044] S2. Preparation of liquid culture medium:

[0045] Take an appropriate amount of wheat bran 50g and water 500mL and put them in an enamel cup. Heat the mixture in an induction cooker and stir constantly for 15 minutes until boiling. Finally, filter to remove the solids and obtain the liquid culture medium.

[0046] S3. Preparation of porous carbon fiber paper loaded with wrinkled carbon:

[0047] Heat-treated porous carbon fiber paper was immersed in liquid culture medium and ultrasonically dispersed for 15 min, dried in an oven at 90℃ for 12 h, inoculated with 7 mL of Aspergillus niger seed liquid with OD600=0.5, and cultured in an incubator at 30℃ for 72 h to obtain precursor material. Then, the precursor material was dried in a drying oven for 12 h, annealed at 800℃ for 1 h under argon atmosphere, washed five times with deionized water, and dried in an oven to constant weight to obtain crude electrode.

[0048] S4. Preparation of layered coarse electrodes:

[0049] Preparation of precursor solution: First, 2.025 g of niobium chloride (purity > 99%) was dissolved in 300 mL of ethanol and stirred for 2 h. Then, 9 mL of diisopropyl di(acetylacetonyl)titanate (purity 75 wt.% in isopropanol) solution was added and stirred for another 2 h.

[0050] Horizontal ultrasonic spray pyrolysis deposition process: The coarse electrode is placed on a clean glass support, and the ultrasonic atomized (1.6MHz) precursor solution is thermally deposited on the coarse electrode substrate in a heating chamber at 420℃. Air is used as the carrier gas with a flow rate of 15L / min and the support rotation speed is fixed at 5rpm. Niobium-doped TiO2 particles are deposited on the coarse electrode substrate for 60 minutes to obtain porous carbon fiber paper electrode material for vanadium redox flow batteries.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the preparation of wrinkled carbon loaded on porous carbon fiber paper is not performed. Porous carbon fiber paper is used as the coarse electrode, and the following steps are included:

[0053] S1. Pretreatment of porous carbon fiber paper:

[0054] 0.4 mm porous carbon fiber paper (3×4 cm) was ultrasonically cleaned for 30 minutes using a 1:3 ratio of ethanol and deionized water. Following this, the porous carbon fiber paper was washed with deionized water for 10 minutes. After cleaning, the porous carbon fiber paper was dried at 80°C for 12 hours. The dried porous carbon fiber paper was then heat-treated in an air-atmosphere box furnace at 420°C for 10 hours to obtain heat-treated porous carbon fiber paper, i.e., the rough electrode.

[0055] S2. Preparation of layered coarse electrodes:

[0056] Preparation of precursor solution: First, 2.025 g of niobium chloride (purity > 99%) was dissolved in 300 mL of ethanol and stirred for 2 h. Then, 9 mL of diisopropyl di(acetylacetonyl)titanate (purity 75 wt.% in isopropanol) solution was added and stirred for another 2 h.

[0057] Horizontal ultrasonic spray pyrolysis deposition process: The coarse electrode is placed on a clean glass support, and the ultrasonic atomized (1.6MHz) precursor solution is thermally deposited on the coarse electrode substrate in a heating chamber at 420℃. Air is used as the carrier gas with a flow rate of 15L / min and the support rotation speed is fixed at 5rpm. Niobium-doped TiO2 particles are deposited on the coarse electrode substrate for 60 minutes to obtain porous carbon fiber paper electrode material for vanadium redox flow batteries.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is that niobium chloride is not added during the preparation of the precursor solution, while the remaining steps and raw materials are the same as in Example 1.

[0060] Comparative Example 3

[0061] The difference between this comparative example and Example 1 is that the porous carbon fiber paper loaded with wrinkled carbon is not used for niobium-doped TiO2 particle deposition, but is directly used as the electrode material.

[0062] To test the electrochemical activity of the vanadium ion redox couple on the surface of porous carbon fiber paper, cyclic voltammetry was performed on the porous carbon fiber paper prepared in Example 1. Nafion 115 (Dupont, USA) was used as the membrane. Electrolytes with concentrations of 0.05MV(II) + 0.05MV(III) + 3M H2SO4 and 0.05MV(IV) + 0.05MV(V) + 3M H2SO4 were prepared. A porous carbon fiber paper electrode, a graphite felt electrode, and an Ag / AgCl electrode with dimensions of 5×5 mm were used as the working electrode, counter electrode, and reference electrode, respectively. The test results are shown in Table 1 below.

[0063] Table 1

[0064]

[0065]

[0066] As shown in Table 1 above, the peak potential difference between the cathode and anode of the electrode material prepared in Example 1 of this invention is lower than that of the graphite felt, indicating that the electrochemical activity is significantly improved by doping with carbon and other heteroatoms and by the structure of the niobium-doped TiO2 laminate.

[0067] The electrode materials prepared in Example 1 and Comparative Examples 1-3 were assembled into single cells, and their charge-discharge performance was tested. The positive electrode electrolyte was 1.5M VOC. 2+ 40 mL of 3M H₂SO₄ solution and 1.5 MV negative electrode electrolyte. 3+ 40 mL of 3M H2SO4 solution was used; the current efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of each single cell at different current densities are shown in Table 2 below:

[0068] Table 2

[0069] project Current efficiency (CE) Voltage efficiency (VE) Energy efficiency (EE) Example 1 83.5 76.5 81.6 Comparative Example 1 73.6 71.4 77.4 Comparative Example 2 75.2 73.6 78.6 Comparative Example 3 70.3 68.7 74.2

[0070] As shown in Table 2 above, the high energy efficiency of the single cell prepared in Example 1 compared to Comparative Example 3 is mainly attributed to the enhanced catalytic activity caused by the conductive niobium-doped TiO2 laminate, accompanied by abundant oxygen functional groups. During cell operation, the improved electrochemical catalytic performance of the single cell anode and the additional reaction sites promote the redox reaction.

[0071] As can be seen from the data in Comparative Example 1, the uniform distribution of heteroatom doping can provide sufficient active defect sites, a larger specific surface area, and improved conductivity.

[0072] Comparative Example 2 shows that the electrochemical performance of the electrode material is improved due to the doping of niobium.

[0073] First, vanadium redox flow batteries made from the electrode materials prepared in Example 1 and Comparative Examples 1-3 were tested at 150 mA / cm². 2 The voltage windows for charging / discharging at the specified current density are 1.6V and 0.7V. Charge / discharge cycle tests were conducted using a battery cycle tester (WonATech, WBCS 3000L), and the coulombic efficiency after 100 cycles is shown in Table 3 below.

[0074] Table 3

[0075] project Coulomb efficiency Example 1 97.6 Comparative Example 1 95.5 Comparative Example 2 95.1 Comparative Example 3 94.6

[0076] As shown in Table 3 above, the vanadium redox flow battery prepared in Example 1 of this invention maintains a higher coulombic efficiency after 100 cycles due to the addition of a niobium-doped TiO2 laminate.

[0077] The electrode materials prepared in Example 1 and Comparative Examples 1-3 were subjected to wetting performance tests. The prepared electrode materials and electrolyte (0.15 MV) were evaluated using a contact angle meter (KSV200). 3+ The interface characteristics between the interface and 3M H2SO4 are shown in Table 4 below:

[0078] Table 4

[0079] project Contact angle (°) Example 1 ＜0.5° Comparative Example 1 ＜0.5° Comparative Example 2 ＜0.5° Comparative Example 3 115°

[0080] As shown in Table 4 above, the poor wettability of the electrode in Comparative Example 3 leads to low charge transfer efficiency during continuous charging / discharging, and also restricts reaction sites. The electrode prepared in Example 1 completely absorbed the electrolyte (contact angle < 0.5°), indicating excellent wettability compared to other samples. This excellent wettability is mainly attributed to the abundant oxygen-related functional groups on the surface of the niobium-doped TiO2 laminate.

[0081] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0082] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon fiber paper electrode material for vanadium redox flow batteries, characterized in that, Includes the following steps: S1. First, niobium chloride was dissolved in ethanol and stirred for 2 hours. Then, a diisopropyl di(acetylacetonyl)titanate solution was added and stirred for another 2 hours to obtain the precursor solution. S2. The precursor solution is deposited on the surface of the coarse electrode using a horizontal ultrasonic spray pyrolysis deposition process to form a niobium-doped TiO2 laminate structure. The thickness of the niobium-doped TiO2 layer is less than 32 nm; The coarse electrode is made by heat-treating porous carbon fiber paper, then immersing it in a liquid culture medium containing fungi for a period of time, and finally annealing it. The method for preparing the crude electrode specifically includes the following steps: A1. Heat treatment of porous carbon fiber paper: The porous carbon fiber paper was ultrasonically cleaned with ethanol and deionized water. Then, the porous carbon fiber paper was washed with deionized water for 10 minutes. After cleaning, the porous carbon fiber paper was dried at 80°C. The dried porous carbon fiber paper was then heat-treated in an air atmosphere box furnace at 420°C for 10 hours to obtain heat-treated porous carbon fiber paper. A2. Preparation of liquid culture medium: Take an appropriate amount of wheat bran and water and mix them in an enamel cup. Heat the mixture in an induction cooker and stir constantly for 15 minutes until it boils. Finally, filter to remove the solids and obtain the liquid culture medium. A3. Preparation of porous carbon fiber paper loaded with wrinkled carbon: Heat-treated porous carbon fiber paper was immersed in liquid culture medium and ultrasonically dispersed for 15 min. After removal, it was placed in a 90℃ oven and dried for 12 h. It was then inoculated with Aspergillus niger seed liquid with OD600=0.5 and cultured in a 30℃ incubator for 72 h to obtain the precursor material. Subsequently, the precursor material was dried in a drying oven for 12 h and annealed at 800℃ for 1 h under an argon atmosphere. It was washed five times with deionized water and dried in an oven to constant weight to obtain the crude electrode.

2. The method for preparing a porous carbon fiber paper electrode material for a vanadium redox flow battery according to claim 1, wherein the fungus is Aspergillus niger.

3. The method for preparing a porous carbon fiber paper electrode material for a vanadium redox flow battery according to claim 1, characterized in that, In step A1, the volume ratio of ethanol to deionized water is 1:

3.

4. The method for preparing a porous carbon fiber paper electrode material for an all-vanadium redox flow battery according to claim 1, characterized in that, The porous carbon fiber paper has a thickness of 0.4 mm.

5. The method for preparing a porous carbon fiber paper electrode material for a vanadium redox flow battery according to claim 1, characterized in that, The ratio of wheat bran to water is 50g:500mL.

6. The method for preparing a porous carbon fiber paper electrode material for a vanadium redox flow battery according to claim 1, characterized in that, Porous carbon fiber paper is prepared by the following steps: After degumming in acetone solution, polyacrylonitrile-based chopped carbon fibers are slurried in an aqueous solution containing 0.1% polyethylene oxide dispersant to form a polyacrylonitrile-based carbon fiber slurry. This slurry is then formed into a sheet with a unit area weight of 40 g / m² using a wet forming machine. 2 The carbon paper precursor was prepared by immersing it in a 1% ethanol solution of phenolic resin for 30 minutes, then drying it and hot-pressing it at 200℃ to obtain carbon paper base paper with a pressure of 6MPa. The carbon paper base paper was placed in an electric furnace and heated to 1600℃ at a heating rate of 10℃ / min under N2 atmosphere, and held at that temperature for 1 hour. Then it was cooled to 1300℃, and a mixture of CO2 and N2 was introduced with flow rates of 40mL / min and 200mL / min, respectively, and the reaction was held at that temperature for 30 minutes. Finally, it was cooled to room temperature to obtain porous carbon fiber paper.

7. The method for preparing a porous carbon fiber paper electrode material for a vanadium redox flow battery according to claim 1, characterized in that, The horizontal ultrasonic spray pyrolysis deposition process is as follows: a coarse electrode is placed on a clean glass support, and an ultrasonic atomized precursor solution is thermally deposited on the coarse electrode substrate in a heating chamber at 420°C. Air is used as the carrier gas with a flow rate of 15 L / min, and the support rotation speed is fixed at 5 rpm. Niobium-doped TiO2 particles are deposited on the coarse electrode substrate for 60 minutes.

8. A porous carbon fiber paper electrode material for vanadium redox flow batteries prepared by the preparation method according to any one of claims 1-7.

9. The application of the porous carbon fiber paper electrode material for an all-vanadium redox flow battery according to claim 8, characterized in that, The porous carbon fiber paper electrode material can be used in vanadium redox flow batteries.

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