A method for preparing porous carbon-modified graphite felt and its application

Abstract

This invention relates to the field of vanadium redox flow batteries, and more particularly to a method for preparing and applying porous carbon-modified graphite felt. The method includes: mixing a polymer resin, a pore-forming agent, a solvent, and a catalyst to prepare a catalyst resin slurry; mixing a surfactant, an inorganic salt, and deionized water to prepare a coagulation bath; impregnating graphite felt with the catalyst resin slurry and then performing solvent-inducing phase separation to prepare an asymmetric graphite felt precursor; graphitizing the asymmetric graphite felt precursor to prepare a porous graphite-coated graphite felt; and finally, oxidizing and activating the porous graphite-coated graphite felt to prepare a porous carbon-modified graphite felt. This invention, through a solvent-inducing phase separation method, coats and fixes the catalyst onto the porous structure on the surface and between the graphite felt fibers, resulting in a modified graphite felt with catalyst-supported porous graphite after graphitization, significantly improving the battery's voltage efficiency and energy efficiency.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode technology, and in particular to a method for preparing porous carbon-modified graphite felt and its application. Background Art

[0002] Vanadium redox flow batteries (VFBs), also known as vanadium batteries, are a new type of energy storage device with broad application prospects in photovoltaic power generation, wind power generation, emergency power supplies, and grid peak shaving and valley filling. The electrodes are one of the key components of a VFB, serving the following functions: 1) providing a reaction site for the redox reactions of active materials; 2) acting as catalysts to increase the reaction rate of redox reactions; and 3) achieving rapid charge transfer during redox reactions. During operation, the electrodes operate in a highly acidic and oxidizing environment, and their stability and electrochemical activity significantly affect the overall performance of the VFB. Therefore, the electrode materials for vanadium redox flow batteries need to possess the following characteristics: 1) Good chemical stability, acid and oxidation resistance, to ensure a long service life; 2) Superior electrocatalytic activity to improve the electrochemical reaction rate and ensure high current density operating efficiency; 3) High specific surface area / effective electrochemical surface area to ensure sufficient contact between the electrode and the electrolyte, increasing the total electrochemical reaction volume per unit volume of electrolyte, i.e., improving electrolyte utilization; 4) Good conductivity to reduce battery internal resistance and decrease electrochemical polarization during charging and discharging.

[0003] Currently, commercially used electrode materials are mainly graphite felt, which has relatively low electrochemical reactivity and poor conductivity. The contact resistance between graphite felt and the electrode plate is also relatively high, thus limiting its application at high current densities. Therefore, developing electrode materials with high activity, high conductivity, and low contact resistance has become crucial. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing porous carbon material modified graphite felt and its application. The prepared porous carbon material modified graphite felt has a high specific surface area, a large number of reactive sites, excellent electrical conductivity, and low contact resistance with the electrode plate. It is suitable for operation under high current density, enabling high-power vanadium batteries to have high energy efficiency and voltage efficiency.

[0005] In a first aspect, the present invention provides a method for preparing porous carbon material modified graphite felt, the method comprising:

[0006] Step S1: Mix 10-30 parts by weight of polymer resin, 1-5 parts by weight of pore-forming agent, and 65-89 parts by weight of solvent, heat and stir to dissolve, and obtain a resin solution; then add 0.1-1 parts by weight of catalyst to the resin solution, stir and disperse, and ball mill to obtain catalyst resin slurry;

[0007] Step S2: Mix 0.5-3 parts by weight of surfactant, 1-5 parts by weight of inorganic salt, and 92-98.5 parts by weight of deionized water, stir and dissolve to obtain a coagulation bath;

[0008] Step S3: Immerse the graphite felt in the catalyst resin slurry, remove it, use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt, then place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath to perform non-solvent-induced phase separation, to obtain an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side.

[0009] Step S4: The asymmetric graphite felt precursor is pre-oxidized, carbonized, and graphitized to obtain a porous graphite-coated graphite felt.

[0010] Step S5: The porous graphite-coated graphite felt is oxidized in potassium permanganate solution, taken out and cleaned, and then immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide for activation treatment to obtain porous carbon material modified graphite felt.

[0011] Preferably, in step S1:

[0012] The polymer resin is selected from at least one of polyacrylonitrile, polyethersulfone, polybenzimidazole, and polyurethane;

[0013] The pore-forming agent is selected from at least one of polyethylene glycol-400, polypropylene glycol-400, and polyvinylpyrrolidone;

[0014] The solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0015] The catalyst is selected from at least one of lead dioxide, tungsten trioxide, manganese tetroxide, and zirconium dioxide.

[0016] Polymer resin can uniformly and firmly coat the surface of graphite felt fibers and fill the spaces between the fibers. After graphitization, it forms conductive pathways between the graphite felt fibers, improving the mechanical strength and structural stability of the graphite felt, reducing electron transfer resistance, and enhancing the voltage efficiency, stability, and lifespan of vanadium batteries.

[0017] Preferably, in step S1:

[0018] The heating and stirring dissolution process takes place at a temperature of 50-70°C for 30-90 minutes.

[0019] The stirring and dispersion time is 30~90 min, and the rotation speed is 2000~4000 r / min;

[0020] The ball milling time is 60~180min, and the rotation speed is 500~1000r / min.

[0021] Preferably, in step S2:

[0022] The surfactant is selected from at least one of sodium dioctyl succinate sulfonate, bis(decyl)dimethylammonium bromide, and stilbene phenol polyoxyethylene ether.

[0023] The inorganic salt is selected from at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium nitrate.

[0024] Preferably, in step S2:

[0025] The stirring and dissolving time is 30-60 minutes, and the rotation speed is 1000-2000 r / min.

[0026] Preferably, in step S3:

[0027] The time for the graphite felt to be impregnated in the catalyst resin slurry is 30~120 min;

[0028] The graphite felt impregnated with catalyst resin slurry is immersed in deionized water for 5 to 15 minutes.

[0029] By impregnating graphite felt with a catalyst-supported resin slurry and then performing non-solvent-induced phase separation, the catalyst can be coated and fixed in the porous structure on the surface of the graphite felt fibers and between the fibers. The graphitized and fixed catalyst not only has strong mechanical strength but also further increases the reactivity of the graphite felt, thereby improving the battery voltage efficiency.

[0030] Preferably, in step S4:

[0031] The pre-oxidation process is as follows: the asymmetric graphite felt precursor is placed in a muffle furnace, and the temperature is raised from 200°C to 300°C in an air atmosphere within 60-90 minutes, and then naturally cooled to room temperature before being removed.

[0032] The carbonization process is as follows: the asymmetric graphite felt precursor after pre-oxidation is placed in an atmosphere furnace, and under a nitrogen atmosphere, it is first carbonized at a low temperature of 300~800℃ for 5~15 minutes, and then carbonized at a high temperature of 1000~1500℃ for 5~15 minutes.

[0033] The graphitization process is as follows: the carbonized asymmetric graphite felt precursor is placed in an atmosphere furnace and held at 2500~3000℃ for 10~25s under an argon atmosphere.

[0034] Preferably, in step S5:

[0035] The concentration of the potassium permanganate solution is 0.5~1.5 mol / L;

[0036] The oxidation treatment lasts for 5-10 hours at a temperature of 80-100°C.

[0037] The volume ratio of concentrated sulfuric acid to hydrogen peroxide in the mixed solution is 5:2;

[0038] The activation treatment lasts for 3 to 6 hours and is performed at a temperature of 80 to 100°C.

[0039] Secondly, the present invention provides an application of porous carbon material modified graphite felt, wherein the porous carbon material modified graphite felt prepared by the above-described preparation method is applied to an all-vanadium redox flow battery.

[0040] Preferably, during use, the porous carbon material modified graphite felt has its flat and dense side in contact with the electrode plate, and its rough and loose side in contact with the ion membrane.

[0041] Porous carbon material modified graphite felt has an asymmetric structure. The flat and dense side contacts the electrode plate, which can effectively increase the contact area between the graphite felt and the electrode plate and reduce the contact resistance. The rough and loose side contacts the ion membrane, which can reduce the ion transport resistance at the membrane-electrode interface and effectively improve the battery voltage efficiency.

[0042] In summary, the beneficial effects of this invention are as follows:

[0043] 1. This invention uses a method of impregnating graphite felt with polymer resin slurry to uniformly coat the surface of graphite felt fibers and fill the spaces between them, so that the graphitized resin forms conductive pathways between the graphite felt fibers, which can effectively reduce electron transfer resistance and improve battery voltage efficiency.

[0044] 2. This invention loads polymer resin onto graphite felt using a non-solvent-induced phase separation method to form a porous structure. The porous morphology is retained after graphitization, which increases the reactive surface area of ​​the graphite felt and provides sufficient reactive sites for redox reactions. This can effectively improve the redox reaction rate and increase the battery voltage efficiency.

[0045] 3. This invention adds the catalyst to the polymer resin solution and combines it with a graphite felt impregnated with a catalyst-supported resin slurry. Non-solvent-induced phase separation can coat and fix the catalyst in the porous structure on the surface of the graphite felt fibers and between the fibers. The graphitized and fixed catalyst can further increase the reactivity of the graphite felt and improve the battery voltage efficiency.

[0046] 4. This invention involves placing a graphite felt impregnated with catalyst resin slurry onto a smooth, flat glass plate and immersing it in water for non-solvent-induced phase separation. This allows the graphite felt precursor to form an asymmetric structure: one side near the glass has a smooth, dense sponge-like porous layer structure, while the other side has a rough, loose, finger-like porous layer structure. The porous carbon-modified graphite felt obtained after graphitization and activation has a smooth, dense surface that reduces contact resistance with the bipolar plate, and a rough, loose surface that reduces ion transport resistance at the membrane-electrode interface, effectively improving battery voltage efficiency. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the preparation method of porous carbon material modified graphite felt according to this application;

[0048] Figure 2 These are scanning electron microscope images of the modified graphite felt in Comparative Example 1 and Example 1 of this application;

[0049] Figure 3 The cyclic voltammetry curves are for the modified graphite felt of Comparative Example 1 and Example 1 of this application. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the present invention.

[0051] See Figure 1This invention discloses a method for preparing porous carbon-modified graphite felt, specifically comprising the following steps: First, a catalyst resin slurry is prepared by mixing a polymer resin, a pore-forming agent, a solvent, and a catalyst; second, a coagulation bath is prepared by mixing a surfactant, an inorganic salt, and deionized water; further, graphite felt is impregnated with the catalyst resin slurry and then subjected to non-solvent-induced phase separation to prepare an asymmetric graphite felt precursor; further still, the asymmetric graphite felt precursor is pre-oxidized, carbonized, and graphitized to prepare a porous graphite-coated graphite felt; finally, the porous graphite-coated graphite felt is subjected to oxidation and activation treatments to prepare porous carbon-modified graphite felt. During battery assembly, the flat, dense side of the porous carbon-modified graphite felt contacts the electrode plate, and the rough, porous side contacts the ion-exchange membrane.

[0052] Example 1: The following technical solution is adopted.

[0053] Step S1: Mix 10 parts by weight of polyacrylonitrile, 1 part by weight of polyethylene glycol-400, and 65 parts by weight of N,N-dimethylformamide, heat and stir at 50°C for 30 min to dissolve, and obtain a resin solution. Then add 0.1 parts by weight of lead dioxide to the resin solution, stir and disperse at 2000 r / min for 30 min, and ball mill at 500 r / min for 60 min to obtain a catalyst resin slurry.

[0054] Step S2: Mix 0.5 parts by weight of sodium dioctyl succinate sulfonate, 1 part by weight of sodium chloride, and 92 parts by weight of deionized water, and stir at 1000 r / min for 30 min to dissolve and obtain a coagulation bath;

[0055] Step S3: Immerse the graphite felt in the catalyst resin slurry for 30 minutes, remove it, and use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt. Place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath for 5 minutes to perform non-solvent-induced phase separation, obtaining an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side;

[0056] Step S4: The asymmetric graphite felt precursor is pre-oxidized (air is introduced, the heating temperature is increased from 200℃ to 300℃, and the heating time is 60min), carbonized (nitrogen is introduced, the temperature is heated at 300℃ for 5min, and then at 1000℃ for 5min), and graphitized (argon is introduced, the temperature is heated at 2500℃ for 10s) to obtain porous graphite-coated graphite felt.

[0057] Step S5: The porous graphite-coated graphite felt is oxidized in a 0.5 mol / L potassium permanganate solution at 80℃ for 5 hours. After cleaning, it is then activated by immersing in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80℃ for 3 hours. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining the porous carbon material modified graphite felt.

[0058] Example 2: The following technical solution is adopted.

[0059] Step S1: Mix 15 parts by weight of polyethersulfone, 2 parts by weight of polypropylene glycol-400, and 73 parts by weight of N,N-dimethylacetamide, heat and stir at 55°C for 50 min to dissolve, and obtain a resin solution. Then add 0.4 parts by weight of tungsten trioxide to the resin solution, stir and disperse at 2500 r / min for 50 min, and ball mill at 650 r / min for 100 min to obtain a catalyst resin slurry.

[0060] Step S2: Mix 1.5 parts by weight of didecyldimethylammonium bromide, 2 parts by weight of potassium chloride, and 94 parts by weight of deionized water, and stir at 1300 r / min for 40 min to dissolve, thus obtaining a coagulation bath;

[0061] Step S3: Immerse the graphite felt in the catalyst resin slurry for 60 minutes, remove it, and use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt. Place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath for 9 minutes to perform non-solvent-induced phase separation, obtaining an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side;

[0062] Step S4: The asymmetric graphite felt precursor is pre-oxidized (air is passed through, the heating temperature is increased from 200℃ to 300℃, and the heating time is 70min), carbonized (nitrogen is passed through, the temperature is heated at 450℃ for 9min, and then at 1150℃ for 9min), and graphitized (argon is passed through, the temperature is heated at 2650℃ for 15s) to obtain porous graphite-coated graphite felt.

[0063] Step S5: The porous graphite-coated graphite felt is oxidized in a 0.9 mol / L potassium permanganate solution at 87℃ for 6.5 h. After cleaning, it is then activated by immersing in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 87℃ for 4 h. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining porous carbon material modified graphite felt.

[0064] Example 3: The following technical solution is adopted.

[0065] Step S1: Mix 25 parts by weight of polybenzimidazole, 3 parts by weight of polyvinylpyrrolidone, and 80 parts by weight of dimethyl sulfoxide, heat and stir at 65°C for 70 min to dissolve, and obtain a resin solution. Then add 0.7 parts by weight of manganese tetroxide to the resin solution, stir and disperse at 3500 r / min for 70 min, and ball mill at 850 r / min for 140 min to obtain a catalyst resin slurry.

[0066] Step S2: Mix 2.5 parts by weight of stilbene phenol polyoxyethylene ether, 4 parts by weight of sodium sulfate, and 96 parts by weight of deionized water, and stir at 1700 r / min for 50 min to dissolve and obtain a coagulation bath;

[0067] Step S3: Immerse the graphite felt in the catalyst resin slurry for 90 minutes, remove it, and use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt. Place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath for 12 minutes to perform non-solvent-induced phase separation, obtaining an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side;

[0068] Step S4: The asymmetric graphite felt precursor is pre-oxidized (air is introduced, the heating temperature is increased from 200℃ to 300℃, and the heating time is 80min), carbonized (nitrogen is introduced, the temperature is heated at 650℃ for 12min, and at 1350℃ for 12min), and graphitized (argon is introduced, the temperature is heated at 2850℃ for 20s) to obtain porous graphite-coated graphite felt.

[0069] Step S5: The porous graphite-coated graphite felt is oxidized in a 1.2 mol / L potassium permanganate solution at 93℃ for 8.5 h. After cleaning, it is then immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 93℃ for 5 h for activation treatment. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2 to obtain porous carbon material modified graphite felt.

[0070] Example 4: The following technical solution is adopted.

[0071] Step S1: Mix 30 parts by weight of polyurethane, 5 parts by weight of polyethylene glycol-400, and 89 parts by weight of N-methylpyrrolidone, heat and stir at 70°C for 90 min to dissolve, and obtain a resin solution. Then add 1 part by weight of zirconium dioxide to the resin solution, stir and disperse at 4000 r / min for 90 min, and ball mill at 1000 r / min for 180 min to obtain a catalyst resin slurry.

[0072] Step S2: Mix 3 parts by weight of sodium dioctyl succinate sulfonate, 5 parts by weight of potassium nitrate, and 98.5 parts by weight of deionized water, and stir at 2000 r / min for 60 min to dissolve and obtain a coagulation bath;

[0073] Step S3: Immerse the graphite felt in the catalyst resin slurry for 120 min, remove it, and use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt. Place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath for 15 min to perform non-solvent-induced phase separation, obtaining an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side;

[0074] Step S4: The asymmetric graphite felt precursor is pre-oxidized (air is passed through, the heating temperature is increased from 200℃ to 300℃, and the heating time is 90min), carbonized (nitrogen is passed through, the temperature is heated at 800℃ for 15min, and then at 1500℃ for 15min), and graphitized (argon is passed through, the temperature is heated at 3000℃ for 25s) to obtain porous graphite-coated graphite felt;

[0075] Step S5: The porous graphite-coated graphite felt is oxidized in a 1.5 mol / L potassium permanganate solution at 100℃ for 10 h. After cleaning, it is then immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 100℃ for 6 h for activation treatment. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining porous carbon material modified graphite felt.

[0076] Comparative Example 1: The following technical solution is adopted.

[0077] Step S1: Pre-oxidize the untreated graphite felt (pass through air, heat the temperature from 200℃ to 300℃ for 60 min), carbonize (pass through nitrogen, heat at 300℃ for 5 min, then heat at 1000℃ for 5 min), and graphitize (pass through argon, heat at 2500℃ for 10 s) to obtain heat-treated graphite felt.

[0078] Step S2: The heat-treated graphite felt is oxidized in a 0.5 mol / L potassium permanganate solution at 80℃ for 5 hours. After cleaning, it is then immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80℃ for 3 hours for activation treatment. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2 to obtain modified graphite felt.

[0079] Comparative Example 2: The following technical solution is adopted.

[0080] Step S1: Mix 10 parts by weight of polyacrylonitrile, 1 part by weight of polyethylene glycol-400, and 65 parts by weight of N,N-dimethylformamide, heat and stir at 50°C for 30 minutes to dissolve and obtain a resin solution.

[0081] Step S2: Immerse the graphite felt in the resin solution for 30 minutes, remove it, and use a scraper to remove excess resin solution from the surface of the graphite felt. Dry at 70℃ to obtain the graphite felt precursor;

[0082] Step S3: The graphite felt precursor is pre-oxidized (air is passed through, the heating temperature is increased from 200℃ to 300℃, and the heating time is 60min), carbonized (nitrogen is passed through, the temperature is heated at 300℃ for 5min, and then at 1000℃ for 5min), and graphitized (argon is passed through, the temperature is heated at 2500℃ for 10s) to obtain porous graphite-coated graphite felt.

[0083] Step S4: The porous graphite-coated graphite felt is oxidized in a 0.5 mol / L potassium permanganate solution at 80℃ for 5 hours. After cleaning, it is then activated by immersing in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80℃ for 3 hours. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining porous carbon material modified graphite felt.

[0084] Comparative Example 3: The following technical solution is adopted.

[0085] Step S1: Mix 10 parts by weight of polyacrylonitrile, 1 part by weight of polyethylene glycol-400, and 65 parts by weight of N,N-dimethylformamide, heat and stir at 50°C for 30 minutes to dissolve and obtain a resin solution.

[0086] Step S2: Mix 0.5 parts by weight of sodium dioctyl succinate sulfonate, 1 part by weight of sodium chloride, and 92 parts by weight of deionized water, and stir at 1000 r / min for 30 min to dissolve and obtain a coagulation bath;

[0087] Step S3: Immerse the graphite felt in the resin solution for 30 minutes, remove it, and use a scraper to remove excess resin solution from the surface of the graphite felt. Immerse the graphite felt impregnated with the resin solution in a coagulation bath for 5 minutes to perform non-solvent-induced phase separation to obtain the graphite felt precursor;

[0088] Step S4: The graphite felt precursor is pre-oxidized (air is passed through, the heating temperature is increased from 200℃ to 300℃, and the heating time is 60min), carbonized (nitrogen is passed through, the temperature is heated at 300℃ for 5min, and then at 1000℃ for 5min), and graphitized (argon is passed through, the temperature is heated at 2500℃ for 10s) to obtain porous graphite-coated graphite felt.

[0089] Step S5: The porous graphite-coated graphite felt is oxidized in a 0.5 mol / L potassium permanganate solution at 80℃ for 5 hours. After cleaning, it is then activated by immersing in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80℃ for 3 hours. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining the porous carbon material modified graphite felt.

[0090] Comparative Example 4: The following technical solution is adopted.

[0091] Step S1: Mix 10 parts by weight of polyacrylonitrile, 1 part by weight of polyethylene glycol-400, and 65 parts by weight of N,N-dimethylformamide, heat and stir at 50°C for 30 minutes to dissolve and obtain a resin solution.

[0092] Step S2: Mix 0.5 parts by weight of sodium dioctyl succinate sulfonate, 1 part by weight of sodium chloride, and 92 parts by weight of deionized water, and stir at 1000 r / min for 30 min to dissolve and obtain a coagulation bath;

[0093] Step S3: Immerse the graphite felt in the resin solution for 30 minutes, remove it, and use a scraper to remove excess resin solution from the surface of the graphite felt. Place the graphite felt impregnated with the resin solution on a smooth and flat glass plate, and immerse it together in a coagulation bath for 5 minutes to perform non-solvent-induced phase separation, obtaining an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side;

[0094] Step S4: The graphite felt precursor is pre-oxidized (air is passed through, the heating temperature is increased from 200℃ to 300℃, and the heating time is 60min), carbonized (nitrogen is passed through, the temperature is heated at 300℃ for 5min, and then at 1000℃ for 5min), and graphitized (argon is passed through, the temperature is heated at 2500℃ for 10s) to obtain porous graphite-coated graphite felt.

[0095] Step S5: The porous graphite-coated graphite felt is oxidized in a 0.5 mol / L potassium permanganate solution at 80℃ for 5 hours. After cleaning, it is then activated by immersing in a mixed solution of concentrated sulfuric acid and hydrogen peroxide at 80℃ for 3 hours. The volume ratio of concentrated sulfuric acid to hydrogen peroxide is 5:2, thus obtaining the porous carbon material modified graphite felt.

[0096] Experimental Procedure and Data:

[0097] The modified graphite felts prepared in the examples and comparative examples were cut into 3cm*3cm pieces. Using a resistance tester, the modified graphite felts were clamped onto copper plates at both ends, and the contact resistance under 20% deformation was measured. The modified graphite felts prepared in the examples and comparative examples were then assembled into fuel cells and subjected to charge-discharge tests under the same test conditions. The test charge-discharge current density was 150mA / cm². 2 300mA / cm 2 The battery coulombic efficiency, voltage efficiency, and energy efficiency were recorded, and the test results are shown in Table 1.

[0098] Table 1 Test results of modified graphite felt

[0099]

[0100] As shown in Table 1, Comparative Example 1, as a blank sample, only underwent heat treatment and oxidation activation treatment. Its corresponding voltage and energy efficiencies were relatively low. Comparative Example 2, compared to Comparative Example 1, added the immersion of graphite felt in a polymer resin solution, resulting in increased voltage and energy efficiencies in the charge-discharge tests of the modified graphite felt. This indicates that uniformly coating the graphite felt fiber surface with polymer resin and filling the spaces between the fibers, allowing for the formation of conductive pathways between the graphite felt fibers after graphitization, can effectively reduce electron transfer resistance and improve battery voltage and energy efficiency. Comparative Example 3, compared to Comparative Example 2, added a non-solvent-induced phase separation step after impregnating the graphite felt with a polymer resin solution, increasing the reactivity of the graphite felt and improving the voltage and energy efficiencies in the charge-discharge tests. This indicates that loading polymer resin onto the graphite felt using a non-solvent-induced phase separation method forms a porous structure, and the porous morphology is retained after graphitization, increasing the reactive surface area of ​​the graphite felt and providing sufficient reactive sites for redox reactions, effectively improving the redox reaction rate and thus improving battery voltage and energy efficiency. Figure 2 As shown, the scanning electron microscope (SEM) images of the modified graphite felt in Comparative Example 1 and Example 1 demonstrate the porous morphology of Example 1, indicating the formation of porous graphite. Compared to Comparative Example 3, Comparative Example 4 adds a step of "placing the graphite felt impregnated with catalyst resin slurry on a smooth, flat glass plate and immersing it together in water for solvent-induced phase separation" during the non-solvent-induced phase separation process. This results in an asymmetric structure for the graphite felt precursor: a smooth, dense sponge-like porous layer on the side closest to the glass, and a rough, loose, finger-like porous layer on the other side. The porous carbon material modified graphite felt obtained after graphitization and activation exhibits reduced contact resistance when the smooth, dense surface contacts the bipolar plate, and reduced ion transport resistance at the membrane-electrode interface when the rough, loose surface contacts the ion exchange membrane, effectively improving battery voltage efficiency. Examples 1-4, compared to Comparative Example 1, combined the beneficial effects of Comparative Examples 2-4. Furthermore, the addition of a metal oxide catalyst to the polymer resin solution further enhanced the reactivity of the graphite felt, improving the voltage efficiency and energy efficiency in charge-discharge tests. Figure 3 As shown in the cyclic voltammetry curves of the modified graphite felt, Example 1 exhibits a higher peak current density than Comparative Example 1, indicating that the graphite felt possesses higher catalytic activity. This demonstrates that adding the catalyst to the polymer resin solution, combined with the graphite felt impregnated with the catalyst-supported resin slurry, and using solvent-induced phase separation, can encapsulate and fix the catalyst within the porous structure on the surface of the graphite felt fibers and between the fibers. The graphitized and fixed catalyst can further increase the reactivity of the graphite felt, thereby improving the battery voltage efficiency and energy efficiency.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon material modified graphite felt, characterized in that, The preparation method includes: Step S1: Mix 10-30 parts by weight of polymer resin, 1-5 parts by weight of pore-forming agent, and 65-89 parts by weight of solvent, heat and stir to dissolve, and obtain a resin solution; then add 0.1-1 parts by weight of catalyst to the resin solution, stir and disperse, and ball mill to obtain a catalyst resin slurry; Step S2: Mix 0.5-3 parts by weight of surfactant, 1-5 parts by weight of inorganic salt, and 92-98.5 parts by weight of deionized water, stir and dissolve to obtain a coagulation bath; Step S3: Immerse the graphite felt in the catalyst resin slurry, remove it, use a scraper to remove excess catalyst resin slurry from the surface of the graphite felt, then place the graphite felt impregnated with the catalyst resin slurry on a smooth and flat glass plate, and immerse it together in a coagulation bath to perform non-solvent-induced phase separation, to obtain an asymmetric graphite felt precursor with a smooth and flat side near the glass plate and a rough and loose side on the other side. Step S4: The asymmetric graphite felt precursor is pre-oxidized, carbonized, and graphitized to obtain a porous graphite-coated graphite felt. Step S5: The porous graphite-coated graphite felt is oxidized in potassium permanganate solution, taken out and cleaned, and then immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide for activation treatment to obtain porous carbon material modified graphite felt.

2. The preparation method according to claim 1, characterized in that, In step S1: The polymer resin is selected from at least one of polyacrylonitrile, polyethersulfone, polybenzimidazole, and polyurethane; The pore-forming agent is selected from at least one of polyethylene glycol-400, polypropylene glycol-400, and polyvinylpyrrolidone; The solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; The catalyst is selected from at least one of lead dioxide, tungsten trioxide, manganese tetroxide, and zirconium dioxide.

3. The preparation method according to claim 1, characterized in that, In step S1: The heating and stirring dissolution process takes place at a temperature of 50-70°C for 30-90 minutes. The stirring and dispersion time is 30~90 min, and the rotation speed is 2000~4000 r / min; The ball milling time is 60~180min, and the rotation speed is 500~1000r / min.

4. The preparation method according to claim 1, characterized in that, In step S2: The surfactant is selected from at least one of sodium dioctyl succinate sulfonate, bis(decyl)dimethylammonium bromide, and stilbene phenol polyoxyethylene ether. The inorganic salt is selected from at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium nitrate.

5. The preparation method according to claim 1, characterized in that, In step S2: The stirring and dissolving time is 30-60 minutes, and the rotation speed is 1000-2000 r / min.

6. The preparation method according to claim 1, characterized in that, In step S3: The time for the graphite felt to be impregnated in the catalyst resin slurry is 30~120 min; The graphite felt impregnated with catalyst resin slurry is immersed in deionized water for 5 to 15 minutes.

7. The preparation method according to claim 1, characterized in that, In step S4: The pre-oxidation process is as follows: the asymmetric graphite felt precursor is placed in a muffle furnace, and the temperature is raised from 200°C to 300°C in an air atmosphere within 60-90 minutes, and then naturally cooled to room temperature before being removed. The carbonization process is as follows: the asymmetric graphite felt precursor after pre-oxidation is placed in an atmosphere furnace, and under a nitrogen atmosphere, it is first carbonized at a low temperature of 300~800℃ for 5~15 minutes, and then carbonized at a high temperature of 1000~1500℃ for 5~15 minutes. The graphitization process is as follows: the carbonized asymmetric graphite felt precursor is placed in an atmosphere furnace and held at 2500~3000℃ for 10~25s under an argon atmosphere.

8. The preparation method according to claim 1, characterized in that, In step S5: The concentration of the potassium permanganate solution is 0.5~1.5 mol / L; The oxidation treatment lasts for 5-10 hours at a temperature of 80-100°C. The volume ratio of concentrated sulfuric acid to hydrogen peroxide in the mixed solution is 5:2; The activation treatment lasts for 3 to 6 hours and is performed at a temperature of 80 to 100°C.

9. An application of a porous carbon material modified graphite felt, characterized in that, The porous carbon-modified graphite felt prepared by the preparation method according to any one of claims 1-8 is applied to an all-vanadium redox flow battery.

10. The application as described in claim 9, characterized in that, During use, the porous carbon material modified graphite felt has its flat and dense side in contact with the electrode plate, and its rough and loose side in contact with the ion membrane.

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