A functionalized carbon material modified electrode, its preparation method and application

Abstract

This application relates to the field of vanadium redox flow battery electrodes, and discloses a functionalized carbon material modified electrode and its preparation method and application, including the following steps: preparing hydroxylated carbon material and hydroxylated graphite felt; dispersing the hydroxylated carbon material in an organic solvent, stirring in an ice bath, adding a sulfonating agent and an activator, and reacting to obtain sulfonated carbon material; dispersing the sulfonated carbon material, nitrogen source, and additives in an ethanol solution, grinding, and gradient heat treatment to obtain functionalized carbon material; dispersing the functionalized carbon material, Nafion solution, and dispersant in a mixture of ethanol and water, ultrasonically dispersing to obtain a drop-coating slurry; and drop-coating the hydroxylated graphite felt electrode to obtain the functionalized carbon material modified electrode. By forming a uniform and continuous catalytic layer on the electrode surface, which is tightly bonded to the graphite felt substrate and not easily detached, the battery maintains structural stability and slow performance degradation during long-term cycling.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery electrode technology, specifically relating to a functionalized carbon material modified electrode and its preparation method and application. Background Technology

[0002] Vanadium redox flow batteries, as a core technology in the field of long-term energy storage, have become key equipment for large-scale storage of intermittent renewable energy sources such as wind power and photovoltaics, grid peak shaving and frequency regulation, and distributed energy storage due to their outstanding advantages of inherent safety, long cycle life, independent power and capacity expansion, environmental friendliness, and no cross-contamination. They have broad application prospects in grid-side energy storage and supporting energy storage for new energy bases. Electrodes, as the core component of vanadium battery stacks, are the key sites for vanadium ion redox reactions, electron transfer, and ion migration conversion. Their catalytic activity, conductivity, stability, and surface structure directly determine the battery's energy efficiency, power density, and long-term cycle stability, and are one of the core bottlenecks restricting the performance improvement and large-scale commercial application of vanadium redox flow batteries.

[0003] Currently, carbon materials are the mainstream electrode material, but they still suffer from problems such as insufficient catalytic activity, a lack of surface active sites, and poor hydrophilicity. Furthermore, the bonding between carbon materials and the electrode substrate is not strong, leading to easy detachment. This results in slow redox reactions of vanadium ions on the electrode surface and high charge transfer resistance, thus affecting the battery's charge-discharge efficiency and long-term cycle stability. Existing electrode modification processes struggle to precisely control the functionalization effect of carbon materials, resulting in uneven distribution of active sites on the modified electrode surface, which fails to meet the demands of large-scale commercial applications of vanadium batteries for high-performance, low-cost electrodes. Therefore, developing a modification process that can precisely optimize the modification effect of carbon materials, improve electrode stability, and optimize overall electrode performance is crucial for driving the technological upgrade of all-vanadium redox flow batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a functionalized carbon material modified electrode, its preparation method and application, to solve the problems of poor hydrophilicity and low electroactivity of existing graphite felt electrodes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a functionalized carbon material modified electrode, comprising the following steps: Step S1: The vacuum-dried carbon material and graphite felt are respectively immersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. They are stirred at low temperature, then filtered, washed and dried to obtain hydroxylated carbon material and hydroxylated graphite felt. Step S2: Disperse the hydroxylated carbon material in an organic solvent, stir in an ice bath, then slowly add an activator and then slowly add a sulfonating agent, sonicate, filter and wash, and dry at low temperature to obtain sulfonated carbon material; Step S3: Disperse the sulfonated carbon material, nitrogen source and additives in an ethanol solution, grind and dry, grind the dried solid, and then transfer the dried solid to a tube furnace for gradient heat treatment under nitrogen protection to obtain functionalized carbon material. Step S4: Disperse the functionalized carbon material, Nafion solution and dispersant in a mixture of ethanol and water, and ultrasonically disperse to obtain a drop coating slurry; place the hydroxylated graphite felt on a heating stage to drop-coat the drop coating slurry to obtain a functionalized carbon material modified electrode.

[0006] In one implementation, in step S1: The carbon material is one of acetylene black, graphene, carbon aerogel, carbon nanotubes, activated carbon, and conductive carbon black. The vacuum drying temperature is 80~120℃, and the time is 4~8h; The low-temperature stirring is carried out at a temperature of -5 to 5°C for 2 to 8 hours. The washing and drying temperature is 60~80℃, and the time is 6~8h.

[0007] Drying carbon materials removes adsorbed water, facilitating subsequent oxidation processes.

[0008] In one implementation, in step S1: The volume ratio of saturated ozone water to hydrogen peroxide in the mixed solution is 1:(0.5~3). The hydrogen peroxide in the hydrogen peroxide solution has a mass fraction of 3% to 6%.

[0009] Hydroxylation modification of carbon materials is achieved through the synergistic oxidation effect of ozone and hydrogen peroxide, introducing hydroxyl active groups on the surface of carbon materials to provide reaction sites for subsequent reactions.

[0010] In one implementation, in step S2: The mass ratio of the hydroxylated carbon material, sulfonating agent, activator, and organic solvent is 1:(5~10):(0.5~5):(200~400). The organic solvent is one of 1,2-dichloroethane, carbon tetrachloride, dichloromethane, chloroform, and nitrobenzene; The sulfonating agent is one of chlorosulfonic acid, p-toluenesulfonic acid, benzenesulfonyl chloride, aminosulfonic acid, and sulfur trioxide pyridine complex; The activator is one of acetic anhydride, silver sulfate, anhydrous aluminum chloride, benzoic anhydride, and succinic anhydride.

[0011] In one implementation, in step S2: The temperature of the ice bath stirring is -5~5℃, and the time is 2~8 h; The frequency of the ultrasonic treatment is 20~50 kHz, and the duration is 5~15 min; The low-temperature drying process is carried out at a temperature of 50-60°C for 90-150 minutes.

[0012] In one implementation, in step S3: The nitrogen source is one of urea, melamine, dicyandiamide, ammonium chloride, and ethylenediamine; The additive is one of polyethylene glycol, polyvinylpyrrolidone, sucrose, and sodium chloride; The mass ratio of the sulfonated carbon material, nitrogen source, additives and ethanol solution is 1:(0.2~0.8):(0.1~0.3):(2~4).

[0013] Sulfonation of hydroxylated carbon materials under low-temperature conditions can effectively suppress the sulfonation reaction rate, avoid excessively vigorous reactions that could lead to corrosion and structural collapse of the carbon materials, and achieve uniform and stable grafting of sulfonic acid groups.

[0014] In one implementation, in step S3: The drying process is carried out at a temperature of 80~100℃ for 4~6 hours. The gradient heat treatment method is as follows: first, maintain a low temperature of 250~350℃ for 30-60 min, then raise the temperature to a high temperature of 550~700℃ at a rate of 2-8℃ / min, maintain for 4~6 h, and then naturally cool to room temperature.

[0015] In one implementation, in step S4: The Nafion solution has a mass concentration of 3% to 5%; The dispersant is one of isopropanol, polyethylene glycol, and polyvinylpyrrolidone; The mass ratio of ethanol to water in the mixture is (5~10):1; The mass ratio of the functionalized carbon material, Nafion solution, dispersant, and mixture is (0.2~1):(0.1~0.5):(1~3):10; The temperature of the heating platform is 100-130℃.

[0016] Secondly, the present invention provides a functionalized carbon material modified electrode, which is prepared by the above-described method for preparing a functionalized carbon material modified electrode.

[0017] Thirdly, this invention provides an application of a functionalized carbon material-modified electrode, wherein the functionalized carbon material-modified electrode prepared by the above-described preparation method or the functionalized carbon material-modified electrode described above is applied to a vanadium battery; wherein... The energy efficiency of the functionalized carbon material-modified electrode in the vanadium battery is not less than 83.0%; After the vanadium battery has been operated for 200 cycles, the energy efficiency retention rate of the functionalized carbon material modified electrode is not less than 83.0%. The voltage efficiency of the functionalized carbon material-modified electrode in the vanadium battery is not less than 85.9%.

[0018] The beneficial effects of this invention patent are as follows: 1. Controllable oxidation of the surface of clean carbon materials is achieved under mild conditions through the synergistic effect of ozone and hydrogen peroxide, thereby introducing a large number of hydroxyl groups as active reaction sites without excessively damaging the carbon material skeleton structure. This effectively preserves its high conductivity and structural stability, providing sufficient reaction anchors for subsequent sulfonation and nitrogen doping, and improving the uniformity and loading of functional group grafting.

[0019] 2. By sulfonating hydroxylated carbon materials under low-temperature conditions, the sulfonation reaction rate can be effectively suppressed, avoiding excessively vigorous reactions that could lead to corrosion and structural collapse of the carbon materials. This achieves uniform and stable grafting of sulfonic acid groups, thereby significantly improving the hydrophilicity and ion conductivity of the electrode. Subsequent activator and ultrasonic-assisted treatment can promote the full exfoliation and dispersion of the carbon materials, breaking the agglomeration phenomenon, and also promote the penetration of sulfonated functional groups into the internal pores of the carbon materials, achieving deep and uniform sulfonation modification.

[0020] 3. By grinding the sulfonated carbon material with a nitrogen source and additives to form a uniform paste, sufficient contact between the nitrogen source and the carbon material surface is ensured, achieving uniform nitrogen doping and preferentially forming highly active pyridine nitrogen and pyrrole nitrogen. This effectively avoids problems such as insufficient local nitrogen content and low catalytic activity caused by uneven mixing. Simultaneously, the combination of secondary grinding and gradient heat treatment effectively retains the sulfonic acid groups, preventing their decomposition due to sudden heating or local overheating. This ensures that the functionalized carbon material possesses both excellent ion conductivity and electrocatalytic activity. Furthermore, the combination of secondary grinding and gradient heat treatment results in a carbon material with synergistic modification of sulfonated / nitrogen functional groups, i.e., the functionalized carbon material. The resulting stable slurry, formed subsequently with binders and dispersants, can be drop-coated onto the electrode surface to form a uniform and continuous catalytic layer. This layer adheres tightly to the graphite felt substrate, preventing detachment and ensuring structural stability and slow performance degradation of the battery during long-term cycling. Attached Figure Description

[0021] Figure 1This is a schematic diagram illustrating the preparation method of a functionalized carbon material modified electrode.

[0022] Figure 2 This is a SEM image of the functionalized carbon material modified electrode prepared in Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 invention.

[0024] like Figure 1 As shown, a method for preparing a functionalized carbon material modified electrode includes the following steps: Step S1: Immerse the vacuum-dried carbon material and graphite felt separately in a mixed solution of saturated ozone water and 3%~6% hydrogen peroxide at a volume ratio of 1:(0.5~3) and keep sealed. Stir at -5~5℃ for 2~8 h, then filter and wash, and dry at 60~80℃ for 6~8 h to obtain hydroxylated carbon material and hydroxylated graphite felt; the carbon material is one of acetylene black, graphene, carbon aerogel, carbon nanotubes, activated carbon and conductive carbon black; the vacuum drying temperature is 80~120℃ and the time is 4~8 h; Step S2: Disperse the hydroxylated carbon material in an organic solvent, stir in an ice bath at -5~5℃ for 2~8 h, then slowly add the activator and then slowly add the sulfonating agent, sonicate at a frequency of 20~50 kHz for 5~15 min, filter and wash, and dry at 50~60℃ for 90~150 min to obtain the sulfonated carbon material; the mass ratio of the hydroxylated carbon material, sulfonating agent, activator and organic solvent is 1:(5~10):(0.5~5):(200~400); the organic solvent is one of 1,2-dichloroethane, carbon tetrachloride, dichloromethane, chloroform and nitrobenzene; the sulfonating agent is one of chlorosulfonic acid, p-toluenesulfonic acid, benzenesulfonyl chloride, aminosulfonic acid and sulfur trioxide pyridine complex; the activator is one of acetic anhydride, silver sulfate, anhydrous aluminum chloride, benzoic anhydride and succinic anhydride.

[0025] Step S3: Disperse the sulfonated carbon material, nitrogen source, and additives in an ethanol solution, grind them, and dry them at 80~100℃ for 4~6 hours. Grind the dried solid and then transfer it to a tube furnace. Under nitrogen protection, first maintain the temperature at 250~350℃ for 30~60 minutes, then raise the temperature to 550~700℃ at a rate of 2~8℃ / min and maintain it for 4~6 hours. Allow it to cool naturally to room temperature to obtain the functionalized carbon material. The nitrogen source is one of urea, melamine, dicyandiamide, ammonium chloride, and ethylenediamine. The additives are one of polyethylene glycol, polyvinylpyrrolidone, sucrose, and sodium chloride. The mass ratio of the sulfonated carbon material, nitrogen source, additives, and ethanol solution is 1:(0.2~0.8):(0.1~0.3):(2~4).

[0026] Step S4: Disperse the functionalized carbon material, a 3%~5% Nafion solution, and a dispersant in a mixture of ethanol and water at a mass ratio of (5~10):1, and ultrasonically disperse to obtain a drop-coating slurry; place the hydroxylated graphite felt electrode on a heating stage at 100~130℃ for drop-coating treatment to obtain a functionalized carbon material modified electrode. The dispersant is one of isopropanol, polyethylene glycol, and polyvinylpyrrolidone; the mass ratio of the functionalized carbon material, Nafion solution, dispersant, and the mixture of ethanol and water is (0.2~1):(0.1~0.5):(1~3):10; Example 1: The following technical solution is adopted. Step S1: Graphene was treated under vacuum drying at 80℃ for 8 hours to remove surface-adsorbed moisture and impurities. The dried graphene was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:0.5, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 3%. The solution was transferred to an ice bath at -5℃ and stirred continuously for 2 hours. After that, the graphene was filtered, washed, and dried at 60℃ for 6 hours to obtain hydroxylated graphene. Step S2: The hydroxylated graphene is dispersed in carbon tetrachloride solvent and continuously stirred in an ice bath. Then, silver sulfate is slowly added dropwise to the above solution, followed by benzenesulfonyl chloride. The mass ratio of hydroxylated graphene, benzenesulfonyl chloride, silver sulfate, and carbon tetrachloride solvent is 1:5:0.5:200. The solution is then subjected to ultrasonic treatment at a frequency of 20 kHz for 15 min. The resulting graphene is then filtered and washed with deionized water and anhydrous ethanol, and then dried at 60°C for 150 min to obtain sulfonated graphene. Step S3: Sulfonated graphene, melamine, and polyvinylpyrrolidone are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of sulfonated graphene, melamine, polyvinylpyrrolidone, and ethanol solution is 1:0.2:0.1:2. The resulting paste-like slurry is ground to disperse it, then transferred to an 80℃ oven for drying for 6 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. The temperature is first held at 250℃ for 30 minutes, then increased to 550℃ at a rate of 2℃ / min and held for 4 hours. After naturally cooling to room temperature, the functionalized graphene is obtained. The functionalized graphene, with a mass concentration of 3%, is then... Nafion solution and polyethylene glycol are dispersed in a mixture of ethanol and water at a mass ratio of 5:1. The mass ratio of the functionalized graphene, Nafion solution, polyethylene glycol and the mixture of ethanol and water is 0.2:0.1:1:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 100°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Example 2: The following technical solution is adopted. Step S1: The activated carbon was treated under vacuum drying at 90℃ for 7 hours to remove surface-adsorbed moisture and impurities. The dried activated carbon was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:1 and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 4%. The solution was transferred to an ice bath at 0℃ and stirred continuously for 4 hours. The activated carbon was then filtered, washed, and dried at 70℃ for 7 hours to obtain hydroxylated activated carbon. Step S2: The hydroxylated activated carbon is dispersed in 1,2-dichloroethane solvent and continuously stirred in an ice bath. Then, anhydrous aluminum chloride is added dropwise to the above solution, followed by slow addition of chlorosulfonic acid. The mass ratio of hydroxylated activated carbon, chlorosulfonic acid, anhydrous aluminum chloride, and 1,2-dichloroethane solvent is 1:8:2:300. The solution is then subjected to ultrasonic treatment at a frequency of 30 kHz for 10 min. The resulting activated carbon is then filtered and washed with deionized water and anhydrous ethanol, and then dried at 70°C for 100 min to obtain sulfonated activated carbon. Step S3: Sulfonated activated carbon, urea, and sodium chloride are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of sulfonated activated carbon, urea, sodium chloride, and ethanol solution is 1:0.8:0.3:4. The resulting paste-like slurry is ground to disperse it, then transferred to a 90℃ oven for drying for 5 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. The temperature is first maintained at 300℃ for 45 minutes, then increased to 700℃ at a rate of 5℃ / min and maintained for 4 hours. After naturally cooling to room temperature, the functionalized activated carbon is obtained. The functionalized activated carbon, with a mass concentration of 4%, is then... Nafion solution and isopropanol are dispersed in a mixture of ethanol and water at a mass ratio of 8:1. The mass ratio of the functionalized activated carbon, Nafion solution, isopropanol and the mixture of ethanol and water is 1:0.5:3:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 110°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Example 3: The following technical solution is adopted. Step S1: Acetylene black was treated under vacuum drying at 100℃ for 6 hours to remove surface-adsorbed moisture and impurities. The dried acetylene black was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:2, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 5%. The solution was transferred to an ice bath at 5℃ and stirred continuously for 8 hours. After that, the acetylene black was filtered, washed, and dried at 80℃ for 8 hours to obtain hydroxylated acetylene black. Step S2: Disperse hydroxylated acetylene black in chloroform solvent and stir continuously in an ice bath. Then, slowly add acetic anhydride to the solution, followed by slowly adding aminosulfonic acid. The mass ratio of hydroxylated acetylene black, aminosulfonic acid, acetic anhydride, and chloroform solvent is 1:10:5:400. The solution is then subjected to ultrasonic treatment at a frequency of 40 kHz for 5 min. The resulting acetylene black is then filtered and washed with deionized water and anhydrous ethanol, and dried at 80°C for 90 min to obtain sulfonated acetylene black. Step S3: Sulfonated acetylene black, dicyandiamide, and polyethylene glycol are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of sulfonated acetylene black, dicyandiamide, polyethylene glycol, and ethanol solution is 1:0.5:0.2:3. The resulting paste-like slurry is ground to disperse it, then transferred to a 100℃ oven for drying for 4 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. First, it is held at 350℃ for 60 minutes, then heated to 600℃ at a rate of 8℃ / min and held for 5 hours. After naturally cooling to room temperature, it is removed to obtain functionalized acetylene black. The functionalized acetylene black, with a mass concentration of 5%, is then further processed. Nafion solution and polyethylene glycol are dispersed in a mixture of ethanol and water at a mass ratio of 10:1. The mass ratio of functionalized acetylene black, Nafion solution, polyethylene glycol and the mixture of ethanol and water is 0.5:0.3:2:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 120°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Example 4: The following technical solution is adopted. Step S1: The carbon aerogel was treated under vacuum drying at 110℃ for 5 hours to remove surface-adsorbed moisture and impurities. The dried carbon aerogel was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:3, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 6%. The solution was transferred to an ice bath at 0℃ and stirred continuously for 8 hours. The carbon aerogel was then filtered, washed, and dried at 80℃ for 6 hours to obtain hydroxylated carbon aerogel. Step S2: The hydroxylated carbon aerogel is dispersed in dichloromethane solvent and continuously stirred in an ice bath. Then, succinic anhydride is slowly added dropwise to the solution, followed by the slow addition of p-toluenesulfonic acid. The mass ratio of hydroxylated carbon aerogel, p-toluenesulfonic acid, succinic anhydride, and dichloromethane solvent is 1:5:0.5:200. The mixture is then subjected to ultrasonic treatment at a frequency of 50 kHz for 5 min. The resulting carbon aerogel is then filtered and washed with deionized water and anhydrous ethanol, and dried at 70°C for 120 min to obtain sulfonated carbon aerogel. Step S3: Sulfonated carbon aerogel, ethylenediamine, and sucrose are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of the sulfonated carbon aerogel, ethylenediamine, sucrose, and ethanol solution is 1:0.8:0.1:2. The resulting paste-like slurry is ground to disperse it, then transferred to an 80℃ oven for drying for 5 hours. The dried slurry is then ground again to obtain well-dispersed carbon powder. This powder is transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. First, it is held at 350℃ for 45 minutes, then heated to 650℃ at a rate of 5℃ / min and held for 4 hours. After naturally cooling to room temperature, the functionalized carbon aerogel is obtained. The functionalized carbon aerogel, with a mass concentration of 4%, is then... Nafion solution and polyvinylpyrrolidone were dispersed in a mixture of ethanol and water at a mass ratio of 5:1. The mass ratio of the functionalized carbon aerogel, Nafion solution, polyvinylpyrrolidone and the mixture of ethanol and water was 0.2:0.5:3:10. The mixture was ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode was placed on a heating stage at 130°C for drop-coating to obtain a functionalized carbon material modified electrode. Example 5: The following technical solution is adopted. Step S1: The conductive carbon black was treated under vacuum drying at 120℃ for 4 hours to remove surface-adsorbed moisture and impurities. The dried conductive carbon black was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:1.5, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 5%. The solution was transferred to an ice bath at -5℃ and stirred continuously for 8 hours. After that, the conductive carbon black was filtered, washed, and dried at 80℃ for 7 hours to obtain hydroxylated conductive carbon black. Step S2: The hydroxylated conductive carbon black is dispersed in carbon tetrachloride solvent and continuously stirred in an ice bath. Then, benzoic anhydride is slowly added dropwise to the solution, followed by the slow addition of chlorosulfonic acid. The mass ratio of hydroxylated conductive carbon black, chlorosulfonic acid, benzoic anhydride, and carbon tetrachloride solvent is 1:10:0.5:400. The mixture is then subjected to ultrasonic treatment at a frequency of 50 kHz for 15 min. The resulting conductive carbon black is then filtered and washed with deionized water and anhydrous ethanol, and dried at 80°C for 100 min to obtain sulfonated conductive carbon black. Step S3: Sulfonated conductive carbon black, urea, and polyethylene glycol are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of the sulfonated conductive carbon black, urea, polyethylene glycol, and ethanol solution is 1:0.4:0.3:3. The resulting paste-like slurry is ground to disperse it, then transferred to a 100℃ oven for drying for 6 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. First, it is held at 350℃ for 30 minutes, then heated to 600℃ at a rate of 2℃ / min and held for 6 hours. After naturally cooling to room temperature, the functionalized conductive carbon black is obtained. The functionalized conductive carbon black has a mass concentration of 3%. Nafion solution and isopropanol are dispersed in a mixture of ethanol and water at a mass ratio of 10:1. The mass ratio of the functionalized conductive carbon black, Nafion solution, isopropanol and the mixture of ethanol and water is 0.8:0.3:3:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 120°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Example 6: The following technical solution is adopted. Step S1: The activated carbon was treated under vacuum drying at 120℃ for 5 hours to remove adsorbed moisture and impurities from the surface. The dried activated carbon was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:2.5, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 3%. The solution was transferred to an ice bath at 0℃ and stirred continuously for 2 hours. The activated carbon was then filtered, washed, and dried at 60℃ for 7 hours to obtain hydroxylated activated carbon. Step S2: Hydroxylated activated carbon is dispersed in nitrobenzene solvent and continuously stirred in an ice bath. Then, anhydrous aluminum chloride is slowly added dropwise to the above solution, followed by the slow addition of sulfur trioxide pyridine complex. The mass ratio of hydroxylated activated carbon, sulfur trioxide pyridine complex, anhydrous aluminum chloride, and nitrobenzene solvent is 1:10:1:300. Ultrasonic treatment is then performed at a frequency of 20 kHz for 10 min. The obtained activated carbon is then filtered and washed with deionized water and anhydrous ethanol, and then dried at 60°C for 90 min to obtain sulfonated activated carbon. Step S3: Sulfonated activated carbon, urea, and sodium chloride are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of sulfonated activated carbon, urea, sodium chloride, and ethanol solution is 1:0.2:0.2:2. The resulting paste-like slurry is ground to disperse it, then transferred to a 90℃ oven for drying for 4 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. First, it is held at 300℃ for 60 minutes, then heated to 550℃ at a rate of 2℃ / min and held for 5 hours. After naturally cooling to room temperature, the functionalized activated carbon is obtained. The functionalized activated carbon, with a mass concentration of 5%, is then... Nafion solution and polyvinylpyrrolidone are dispersed in a mixture of ethanol and water at a mass ratio of 8:1. The mass ratio of the functionalized activated carbon, Nafion solution, polyvinylpyrrolidone and the mixture of ethanol and water is 1:0.5:2:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a heating stage at 110°C for drop-coating to obtain a functionalized carbon material modified electrode. Comparative Example 1: The following technical solution is adopted. Using untreated blank graphite felt electrodes Comparative Example 2: The following technical solution is adopted. The only difference from Example 1 is that the carbon material is not hydroxylated. Step S1: Graphene is dispersed in carbon tetrachloride solvent and continuously stirred in an ice bath. Then, silver sulfate is slowly added dropwise to the solution, followed by benzenesulfonyl chloride. The mass ratio of hydroxylated graphene, benzenesulfonyl chloride, silver sulfate, and carbon tetrachloride solvent is 1:5:0.5:200. The solution is then subjected to ultrasonic treatment at a frequency of 20 kHz for 15 min. The resulting graphene is then filtered and washed with deionized water and anhydrous ethanol, and then dried at 60°C for 150 min to obtain sulfonated graphene. Step S2: Sulfonated graphene, melamine, and polyvinylpyrrolidone are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of sulfonated graphene, melamine, polyvinylpyrrolidone, and ethanol solution is 1:0.2:0.1:2. The resulting paste-like slurry is ground to disperse it, then transferred to an 80℃ oven for drying for 6 hours. After drying, the slurry is ground again to obtain well-dispersed carbon powder. This powder is then transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. The temperature is first held at 250℃ for 30 minutes, then increased to 550℃ at a rate of 2℃ / min and held for 4 hours. After naturally cooling to room temperature, the functionalized graphene is obtained. The functionalized graphene, with a mass concentration of 3%, is then... Nafion solution and polyethylene glycol are dispersed in a mixture of ethanol and water at a mass ratio of 5:1. The mass ratio of the functionalized graphene, Nafion solution, polyethylene glycol and the mixture of ethanol and water is 0.2:0.1:1:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 100°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Comparative Example 3: The following technical solution is adopted. The only difference from Example 1 is that the carbon material is not subjected to sulfonation treatment. Step S1: Graphene was treated under vacuum drying at 80℃ for 8 hours to remove surface-adsorbed moisture and impurities. The dried graphene was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:0.5, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 3%. The solution was transferred to an ice bath at -5℃ and stirred continuously for 2 hours. After that, the graphene was filtered, washed, and dried at 60℃ for 6 hours to obtain hydroxylated graphene. Step S2: Hydroxylated graphene, melamine, and polyvinylpyrrolidone are dispersed in an ethanol solution to obtain a paste-like slurry. The mass ratio of the hydroxylated graphene, melamine, polyvinylpyrrolidone, and ethanol solution is 1:0.2:0.1:2. The resulting paste-like slurry is ground to disperse it, then transferred to an 80℃ oven for drying for 6 hours. The dried slurry is then ground again to obtain well-dispersed carbon powder. This powder is transferred to a tube furnace and subjected to gradient heat treatment under nitrogen protection. The temperature is first held at 250℃ for 30 minutes, then increased to 550℃ at a rate of 2℃ / min and held for 4 hours. After natural cooling to room temperature, the functionalized graphene is obtained. The functionalized graphene, with a mass concentration of 3%, is then... Nafion solution and polyethylene glycol are dispersed in a mixture of ethanol and water at a mass ratio of 5:1. The mass ratio of the functionalized graphene, Nafion solution, polyethylene glycol and the mixture of ethanol and water is 0.2:0.1:1:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 100°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Comparative Example 4: The following technical solution is adopted. The only difference from Example 1 is that the carbon material is not nitrided. Step S1: Graphene was treated under vacuum drying at 80℃ for 8 hours to remove surface-adsorbed moisture and impurities. The dried graphene was dispersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The volume ratio of saturated ozone water to hydrogen peroxide was 1:0.5, and the mass fraction of hydrogen peroxide in the hydrogen peroxide was 3%. The solution was transferred to an ice bath at -5℃ and stirred continuously for 2 hours. After that, the graphene was filtered, washed, and dried at 60℃ for 6 hours to obtain hydroxylated graphene. Step S2: The hydroxylated graphene was dispersed in carbon tetrachloride solvent and continuously stirred in an ice bath. Then, silver sulfate was slowly added dropwise to the solution, followed by benzenesulfonyl chloride. The mass ratio of hydroxylated graphene, benzenesulfonyl chloride, silver sulfate, and carbon tetrachloride solvent was 1:5:0.5:200. The solution was then subjected to ultrasonic treatment at a frequency of 20 kHz for 15 min. The resulting graphene was then filtered and washed with deionized water and anhydrous ethanol, and then dried at 60°C for 150 min to obtain sulfonated graphene. Step S3: Sulfonated graphene, a 3% Nafion solution, and polyethylene glycol are dispersed in a mixture of ethanol and water at a mass ratio of 5:1. The mass ratio of the functionalized graphene, Nafion solution, polyethylene glycol, and the ethanol and water mixture is 0.2:0.1:1:10. The mixture is then ultrasonically dispersed to obtain a drop-coating slurry. The graphite felt electrode is then placed on a 100°C heating stage for drop-coating to obtain a functionalized carbon material modified electrode. Test method: The graphite felt electrodes obtained in Examples 1-6 and Comparative Examples 1-4 were assembled into a small battery stack as working electrodes, and charge-discharge cycle tests were performed under the same operating conditions. The coulombic efficiency, energy efficiency, and voltage efficiency of the battery were recorded. The test results are shown in Table 1. Table 1 Summary of Battery Test Results

[0027] As shown in Table 1, compared with Comparative Example 1, the blank graphite felt has a strong chemical inertness and a lack of electrochemical active sites, resulting in weak catalytic ability for vanadium ion redox reactions and low voltage efficiency. In Examples 1-6, functionalized carbon materials were prepared by hydroxylation modification, sulfonation modification and nitrogen functional doping. These materials can effectively synergistically construct a composite modification system with high conductivity, high hydrophilicity and high catalytic activity. The nitrogen active sites provide abundant electrocatalytic active centers, the sulfonic acid groups accelerate ion transport, and the stable electrode modification structure can withstand electrolyte erosion for a long time. Thus, it has the advantages of lower polarization, higher reactivity and longer cycle life, and comprehensively improves the overall electrochemical performance of the vanadium redox flow battery. In Example 2, due to the lack of hydroxylation modification, the graphene surface is highly inert with few reaction sites, making it difficult to stabilize the grafted sulfonic acid groups in subsequent processes. Furthermore, the binding force of the nitrogen source doping is significantly weakened, resulting in poor hydrophilicity of the material surface, high resistance to vanadium ion redox reactions, and severe electrode polarization. This indicates that hydroxylation is a key pre-anchoring process for subsequent sulfonation and nitridation modifications. In Example 3, without sulfonation modification, the material surface lacks strongly hydrophilic sulfonic acid functional groups, significantly reducing proton conductivity and vanadium ion migration and diffusion rates, exacerbating battery concentration polarization. Simultaneously, the lack of synergistic effect of sulfonic acid groups limits the effectiveness of single nitrogen doping modification, leading to decreased electrocatalytic activity. This demonstrates that sulfonation modification can endow the material with excellent hydrophilicity and proton transport capabilities, and is a core key step in optimizing vanadium ion reaction kinetics and reducing electrode polarization. Compared to Comparative Example 4, nitrogen functional group doping can generate active sites such as pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen on the surface of carbon materials, effectively reducing the reaction energy barrier of vanadium ion redox reaction and improving electrocatalytic performance. At the same time, the polarity of nitrogen functional groups can improve the surface wettability of graphite felt substrates, alleviate concentration polarization, and synergize with the previously introduced hydroxyl and sulfonic acid groups. The sulfonic acid groups are responsible for rapid proton conduction, while the nitrogen functional groups provide catalytic activity. The synergistic effect of multiple functional groups significantly improves the voltage efficiency and cycle stability of vanadium batteries, thereby comprehensively improving the working efficiency of vanadium batteries.

[0028] 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 a functionalized carbon material modified electrode, characterized in that, Includes the following steps: Step S1: The vacuum-dried carbon material and graphite felt are respectively immersed in a mixed solution of saturated ozone water and hydrogen peroxide and kept sealed. The mixture is stirred at low temperature, then filtered, washed and dried to obtain hydroxylated carbon material and hydroxylated graphite felt. The low-temperature stirring temperature is -5~5℃ and the time is 2~8h. Step S2: Disperse the hydroxylated carbon material in an organic solvent, stir in an ice bath, then slowly add an activator followed by a slow addition of a sulfonating agent, sonicate, filter and wash, and dry at low temperature to obtain sulfonated carbon material; the activator is one of acetic anhydride, silver sulfate, anhydrous aluminum chloride, benzoic anhydride, and succinic anhydride; Step S3: Disperse the sulfonated carbon material, nitrogen source, and additives in an ethanol solution, grind them, dry them, grind the dried solid, and then transfer the dried solid to a tube furnace for gradient heat treatment under nitrogen protection to obtain functionalized carbon material; the nitrogen source is one of urea, melamine, dicyandiamide, ammonium chloride, and ethylenediamine; the additives are one of polyethylene glycol, polyvinylpyrrolidone, sucrose, and sodium chloride; the gradient heat treatment method is as follows: first, maintain a low temperature of 250~350℃ for 30-60 min, then raise the temperature to a high temperature of 550~700℃ at a rate of 2-8℃ / min, maintain for 4~6 h, and then cool naturally to room temperature; Step S4: Disperse the functionalized carbon material, Nafion solution and dispersant in a mixture of ethanol and water, and ultrasonically disperse to obtain a drop coating slurry; place the hydroxylated graphite felt on a heating stage to drop-coat the drop coating slurry to obtain a functionalized carbon material modified electrode.

2. The production method according to claim 1, wherein In step S1: The carbon material is one of graphene, carbon aerogel, carbon nanotubes, activated carbon, and conductive carbon black. The vacuum drying temperature is 80~120℃, and the time is 4~8h; The washing and drying process takes place at a temperature of 60-80°C for 6-8 hours.

3. The production method according to claim 1, wherein In step S1: The volume ratio of saturated ozone water to hydrogen peroxide in the mixed solution is 1:(0.5~3). The hydrogen peroxide in the hydrogen peroxide solution has a mass fraction of 3% to 6%.

4. The production method according to claim 1, wherein In step S2: The mass ratio of the hydroxylated carbon material, sulfonating agent, activator, and organic solvent is 1:(5~10):(0.5~5):(200~400). The organic solvent is one of 1,2-dichloroethane, carbon tetrachloride, dichloromethane, chloroform, and nitrobenzene; The sulfonating agent is one of chlorosulfonic acid, p-toluenesulfonic acid, benzenesulfonyl chloride, aminosulfonic acid, and sulfur trioxide pyridine complex.

5. The production method according to claim 1, wherein In step S2: The temperature of the ice bath stirring is -5~5℃, and the time is 2~8h; The frequency of the ultrasonic treatment is 20~50 kHz, and the duration is 5~15 min; The low-temperature drying process is carried out at a temperature of 50-60°C for 90-150 minutes.

6. The production method according to claim 1, wherein In step S3: The mass ratio of the sulfonated carbon material, nitrogen source, additives and ethanol solution is 1:(0.2~0.8):(0.1~0.3):(2~4).

7. The preparation method according to claim 1, characterized in that, In step S3: The drying temperature is 80~100℃, and the time is 4~6 hours.

8. The preparation method according to claim 1, characterized in that, In step S4: The mass concentration of the Nafion solution is 3%~5%; The dispersant is one of isopropanol, polyethylene glycol, and polyvinylpyrrolidone; The mass ratio of ethanol to water in the mixture is (5~10):1; The mass ratio of the functionalized carbon material, Nafion solution, dispersant, and mixture is (0.2~1):(0.1~0.5):(1~3):10; The temperature of the heating platform is 100~130℃.

9. A functionalized carbon material modified electrode, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. An application of a functionalized carbon material-modified electrode, characterized in that, The functionalized carbon material modified electrode prepared by the preparation method according to any one of claims 1-8 or the functionalized carbon material modified electrode according to claim 9 is applied to a vanadium battery; wherein, The energy efficiency of the functionalized carbon material-modified electrode in the vanadium battery is not less than 83.0%; After the vanadium battery has been operated for 200 cycles, the energy efficiency retention rate of the functionalized carbon material modified electrode is not less than 83.0%. The voltage efficiency of the functionalized carbon material-modified electrode in the vanadium battery is not less than 85.9%.

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