High-performance hierarchical pore carbon felt electrode for flow battery and preparation method of high-performance hierarchical pore carbon felt electrode

Abstract

The invention belongs to the technical field of redox flow batteries, and particularly discloses a high-performance hierarchical pore carbon felt electrode for a flow battery and a preparation method of the high-performance hierarchical pore carbon felt electrode for the flow battery. Zinc salt or bismuth salt is dissolved in a solvent, and a precursor solution is obtained through stirring and ultrasonic treatment; dipping the pre-oxidized felt into the precursor solution, performing ultrasonic treatment, taking out and drying; and carbonizing the dried carbon felt at a high temperature in a protective atmosphere, treating with nitric acid, cleaning with deionized water, and drying to obtain the hierarchical porous carbon felt electrode with high activity and high specific surface area. The prepared high-performance hierarchical pore carbon felt electrode has a multi-scale pore structure and rich active sites, the specific surface area, the conductivity and the catalytic activity are remarkably improved, meanwhile, the hydrophilicity is optimized, and the electrolyte wettability is enhanced. The method is short in technological process, high in efficiency, low in cost and suitable for large-scale production and industrial application of the high-performance carbon felt electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of redox flow batteries, and in particular to a high-performance multi-level porous carbon felt electrode for a flow battery and a preparation method thereof. Background Art

[0002] With the rapid development of renewable energy sources such as wind and solar, the inherent dispersion, intermittency, and randomness of these sources have led to increasingly volatile power generation, posing a significant challenge to the stable operation and regulation of power systems. To improve the flexible regulation capabilities of power systems and alleviate issues such as insufficient power supply during peak periods and difficulty absorbing power during off-peak periods, the development of efficient and cost-effective large-scale energy storage technologies has become a key task in the energy sector.

[0003] Redox flow batteries (RFBs), as a new electrochemical energy storage technology, have garnered widespread attention in areas such as grid peak regulation, renewable energy integration, and distributed energy storage due to their advantages, including high safety, long cycle life, ease of scalability, and independent power and capacity adjustment. Among them, the vanadium redox flow battery (VRFB), with its unique single-component vanadium electrolyte, dominates existing flow battery technologies. However, limitations in energy efficiency, material cost, and long-term operational stability hinder its large-scale commercial application.

[0004] Electrodes are the core sites of electrochemical reactions in flow batteries, and their structure and performance directly affect the battery's overall energy conversion efficiency and operating life. Currently, carbon-based porous materials (such as carbon cloth, carbon felt, carbon paper, and graphite felt) are widely used as flow battery electrode materials due to their high electrical conductivity, chemical stability, and mechanical strength. Among them, carbon felt has become an extremely common electrode material in commercial flow battery systems due to its excellent electrical conductivity, chemical stability, and cost advantages.

[0005] However, traditional carbon felt materials still have many performance bottlenecks, mainly including: limited specific surface area, surface functional groups and catalytic active sites, resulting in slow redox reaction kinetics; unreasonable internal pore structure, resulting in poor electrolyte permeability and low mass transfer efficiency; in addition, the carbon felt has strong intrinsic hydrophobicity, which further reduces the contact efficiency between the electrode and the electrolyte.

[0006] Existing carbon felt modification methods (such as high-temperature heat treatment, chemical doping, and electrochemical activation) increase the surface activity of electrodes to a certain extent, improving their electrochemical activity and reaction kinetics. However, these modification technologies are generally subject to technical bottlenecks such as cumbersome processes, high costs, environmental unfriendliness, and difficulty in scalable production, making them difficult to meet the needs of industrialized development of redox flow batteries. In view of this, the present invention proposes a simple, scalable method for preparing high-performance, multi-level porous carbon felt electrodes to increase their specific surface area and catalytic activity, thereby reducing battery polarization, increasing output power density, and lowering the overall cost of redox flow battery systems. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a high-performance multi-level porous carbon felt electrode for liquid flow batteries and a preparation method thereof, which overcomes the problems of complex processes and difficulty in scalability in the prior art, and effectively improves the catalytic activity and specific surface area of ​​the carbon felt electrode, thereby optimizing the redox reaction kinetics, improving the overall performance of the battery, and solving the problems mentioned in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery, comprising the following steps:

[0009] S1. Clean the commercial polypropylene pre-oxidized felt with anhydrous ethanol to remove surface impurities;

[0010] S2. dissolving an appropriate amount of zinc salt or bismuth salt in a solvent, stirring and ultrasonically treating the solvent at a certain temperature to fully dissolve the solvent to obtain a precursor solution;

[0011] S3, immersing the cleaned pre-oxidized felt into the precursor solution and ultrasonically treating it, taking it out and drying it to obtain a base carbon felt;

[0012] S4. Carbonizing the base carbon felt at high temperature under a protective atmosphere, soaking it in nitric acid, washing it with deionized water, and drying it to obtain a carbon felt electrode with high activity and high specific surface area.

[0013] Preferably, the commercial polypropylene pre-oxidized felt has a thickness of 2.5 to 5 mm.

[0014] Preferably, the zinc salt is selected from zinc chloride and / or zinc nitrate.

[0015] Preferably, the bismuth salt is selected from bismuth chloride and / or bismuth nitrate.

[0016] Preferably, the solvent is selected from ethylene glycol.

[0017] Preferably, the dissolving temperature in step S2 is 20-60°C.

[0018] Preferably, the stirring method in step S2 is magnetic stirring, and the stirring speed is 200-600 rpm.

[0019] Preferably, the stirring method in step S2 is magnetic stirring, and the stirring time is 10 to 20 minutes.

[0020] Preferably, the ultrasonic treatment time in step S2 is 5 to 10 minutes.

[0021] Preferably, the mass concentration of the precursor solution is 0.1% to 5%.

[0022] Preferably, the ultrasonic treatment time in step S3 is 20 to 30 minutes.

[0023] Preferably, the specific process of the carbonization treatment is: placing the dried pre-oxidized felt in a tubular furnace and continuously introducing a nitrogen atmosphere, the gas flow rate is about 0.2 to 1.0 m / s, the tubular furnace heating rate is 2 to 8°C / min, the carbonization temperature is 1000 to 1200°C, and the carbonization time is 1 to 3 hours.

[0024] Preferably, the specific process of nitric acid soaking and deionized water cleaning is: immersing the carbonized carbon felt in a nitric acid solution with a concentration of 50% to 70%, and ultrasonically treating it for 5 to 10 minutes, and then rinsing it with deionized water for 3 to 5 times.

[0025] Preferably, the specific method of the drying treatment is: placing the carbon felt in a vacuum drying oven at 80-120° C. and drying for 0.5-3 hours.

[0026] To achieve the above object, the present invention provides the following technical solution: a high-performance multi-level porous carbon felt electrode for liquid flow battery prepared by the preparation method of the high-performance multi-level porous carbon felt electrode for liquid flow battery.

[0027] The beneficial effects of the present invention are:

[0028] 1) The present invention carbonizes the composite carbon felt at 1000-1200°C to maintain excellent electrical conductivity of the electrode material and retain some catalytically active nitrogen-doped functional groups during the carbonization process, effectively optimizing the redox reaction kinetics and significantly improving the electrochemical performance of the battery.

[0029] 2) This invention loads zinc nitrate onto the surface of carbon felt and utilizes its thermal decomposition and carbothermal reduction reaction at high temperatures to etch the carbon fibers, creating a rich oxygen vacancy and multi-scale pore structure. This significantly increases the specific surface area of ​​the carbon felt, facilitating electrolyte penetration and diffusion of active materials, thereby enhancing the reactivity of the electrode.

[0030] 3) The present invention removes organic impurities on the surface of the carbon felt through nitric acid treatment and introduces oxygen-containing functional groups, which significantly improves the hydrophilicity of the electrode, helps improve the permeability and wetting effect of the electrolyte, thereby enhancing the ion transmission rate and the electrochemical reaction efficiency of the electrode.

[0031] 4) The present invention adopts a short and efficient preparation process, avoiding the traditional complex modification steps, significantly reducing process costs and improving preparation efficiency, which is conducive to the large-scale production and industrial application of high-performance carbon felt electrodes. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] The present invention provides a technical solution: a short-process preparation method for a high-performance multi-level porous carbon felt electrode for a redox flow battery, comprising the following steps:

[0034] S1. Clean the commercial polypropylene pre-oxidized felt with anhydrous ethanol to remove surface impurities;

[0035] S2. dissolving an appropriate amount of zinc salt or bismuth salt in a solvent, stirring and ultrasonically treating the solvent at a certain temperature to fully dissolve the solvent to obtain a precursor solution;

[0036] S3, immersing the cleaned pre-oxidized felt into the precursor solution and ultrasonically treating it, taking it out and drying it to obtain a base carbon felt;

[0037] S4. Carbonizing the base carbon felt at high temperature under a protective atmosphere, soaking it in nitric acid, washing it with deionized water, and drying it to obtain a carbon felt electrode with high activity and high specific surface area.

[0038] As an optional embodiment, the commercial polypropylene pre-oxidized felt has a thickness of 2.5 to 5 mm, for example, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, etc.

[0039] As an optional embodiment, the zinc salt is selected from zinc chloride and / or zinc nitrate.

[0040] As an optional embodiment, the bismuth salt is selected from bismuth chloride and / or bismuth nitrate.

[0041] As an optional embodiment, the solvent is selected from ethylene glycol.

[0042] As an optional embodiment, the stirring temperature in step S2 is 20-60°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, etc.

[0043] As an optional embodiment, the stirring method in step S2 is magnetic stirring, and the stirring speed is 200-600 rpm, for example, it can be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, etc.

[0044] As an optional embodiment, the stirring method in step S2 is magnetic stirring, and the stirring time is 10 to 20 minutes, for example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, etc.

[0045] As an optional embodiment, the ultrasonic treatment time in step S2 is 5 to 10 minutes, for example, 5 minutes, 7.5 minutes, 10 minutes, etc.

[0046] As an optional embodiment, the mass concentration of the precursor solution is 0.1% to 5%, for example, it can be 0.1%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc.

[0047] As an optional embodiment, the ultrasonic treatment time in step S3 is 20 to 30 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, etc.

[0048] As an optional embodiment, the specific process parameters of the carbonization treatment include the following conditions: a gas flow rate of approximately 0.2 to 1.0 m / s, a tubular furnace heating rate of 2 to 8°C / min, a carbonization temperature of 1000 to 1200°C, and a carbonization time of 1 to 3 hours.

[0049] As an optional embodiment, the gas introduced into the tube furnace during the carbonization treatment is nitrogen.

[0050] As an optional embodiment, the parameters of the specific process of nitric acid soaking and deionized water cleaning include the following conditions: the concentration of the nitric acid solution is 50% to 70%, the ultrasonic treatment time is 5 to 10 minutes, and the number of deionized water rinses is 3 to 5 times.

[0051] As an optional embodiment, the parameters of the specific method of the drying treatment include the following conditions: the temperature of the vacuum drying oven is 80 to 120° C., and the drying time is 0.5 to 3 hours.

[0052] Example 1

[0053] This embodiment provides a high specific surface area, high activity, multi-level porous carbon felt, and the specific steps of the carbon felt preparation method are as follows:

[0054] S1. Cut commercial polyacrylonitrile (PAN)-based pre-oxidized felt (thickness 2.5 mm, area 12 cm2) of appropriate size and wash it with anhydrous ethanol 2 to 3 times to remove surface impurities.

[0055] S2. Weigh an appropriate amount of anhydrous zinc nitrate and dissolve it in ethylene glycol to prepare a 0.5% zinc nitrate solution. The solution is magnetically stirred at room temperature (25°C) for 10 minutes (at a stirring speed of 300 rpm) and then ultrasonically treated for 10 minutes to ensure that the zinc nitrate is fully dissolved and evenly dispersed.

[0056] S3. Vertically immerse the cleaned pre-oxidized felt in a zinc nitrate solution and ultrasonically treat it at a frequency of 20 kHz for 30 minutes to allow it to fully absorb the solution. Subsequently, remove the sample and dry it in a vacuum drying oven at 80°C for 10 hours to remove the solvent.

[0057] S4. The dried sample was carbonized at 1100°C under a nitrogen protective atmosphere (flow rate 0.5m / s). The carbonization process adopted a heating rate of 3°C / min and maintained at a constant temperature for 1.5h to ensure the high temperature stability and microstructure optimization of the carbon felt. After carbonization, the sample was immersed in a 50% nitric acid solution and ultrasonically treated for 10min to remove possible residual impurities and amorphous carbon. Then, it was rinsed with deionized water 3 to 5 times and finally dried in a vacuum drying oven at 120°C for 1h to obtain a carbon felt electrode with a high specific surface area.

[0058] Example 2

[0059] This embodiment provides a high specific surface area, high activity, multi-level porous carbon felt, and the specific steps of the carbon felt preparation method are as follows:

[0060] In this example, the loading amount of zinc nitrate was adjusted based on Example 1 to further optimize the microstructure and electrochemical performance of the carbon felt.

[0061] S1. Pretreatment: completely consistent with S1 described in Example 1.

[0062] S2. Preparation of zinc nitrate solution: The mass concentration of the zinc nitrate solution was increased to 1.0%, and the other preparation conditions were exactly the same as those of S2 described in Example 1.

[0063] S3, impregnation and drying: All setting conditions are consistent with S3 described in Example 1.

[0064] S4, carbonization treatment and washing and drying: All setting conditions are consistent with S4 described in Example 1.

[0065] Example 3

[0066] This embodiment provides a high specific surface area, high activity, multi-level porous carbon felt, and the specific steps of the carbon felt preparation method are as follows:

[0067] In this example, the loading amount of zinc nitrate was further increased on the basis of Example 2 to explore its effect on the regulation of carbon felt structure.

[0068] S1. Pretreatment: completely consistent with S1 described in Example 1.

[0069] S2. Preparation of zinc nitrate solution: The mass concentration of the zinc nitrate solution was increased to 1.5%, and the other preparation conditions were completely consistent with those of S2 described in Example 1.

[0070] S3, impregnation and drying: All setting conditions are consistent with S3 described in Example 1.

[0071] S4, carbonization treatment and washing and drying: All setting conditions are consistent with S4 described in Example 1.

[0072] Comparative Example 1

[0073] This comparative example adopts the same process as Example 1, but without the zinc nitrate solution impregnation treatment, and directly carbonizes the pre-oxidized felt to study the structure and electrochemical properties of the carbon felt without etching treatment. The specific preparation steps are as follows:

[0074] S1. Cut commercial polyacrylonitrile (PAN)-based pre-oxidized felt (thickness 2.5 mm, area 12 cm2) of appropriate size and wash it with anhydrous ethanol 2 to 3 times to remove surface impurities.

[0075] S2. Place the sample in a vacuum drying oven at 80°C and dry for 10 h.

[0076] S3. The dried sample was carbonized at 1100°C under a nitrogen protective atmosphere (flow rate 0.5m / s). The carbonization process adopted a heating rate of 3°C / min and maintained at a constant temperature for 1.5h to ensure the high temperature stability and microstructure optimization of the carbon felt. After carbonization, the sample was immersed in a 50% nitric acid solution and ultrasonically treated for 10min to remove possible residual impurities and amorphous carbon. Then, it was rinsed with deionized water 3 to 5 times and finally dried in a vacuum drying oven at 120°C for 1h to obtain a carbon felt electrode with a high specific surface area.

[0077] Comparative Example 2

[0078] This comparative example provides a method for preparing carbon felt using a graphitization process, and the specific steps are as follows:

[0079] S1. Cut commercial polyacrylonitrile (PAN)-based pre-oxidized felt (thickness 2.5 mm, area 12 cm2) of appropriate size and wash it with anhydrous ethanol 2 to 3 times to remove surface impurities.

[0080] S2. Place the sample in a vacuum drying oven at 80°C and dry for 10 h.

[0081] S3. Graphitization: The dried pre-oxidized felt was placed in a tube furnace and heated to 1800°C at a rate of 5°C / min under a nitrogen atmosphere (flow rate 0.5 m / s) for 1.5 hours to complete the graphitization process. The sample was then immersed in a 50% nitric acid solution for 10 minutes and ultrasonically treated. The sample was then rinsed 3-5 times with deionized water. Finally, the sample was dried in a vacuum drying oven at 120°C for 1 hour.

[0082] S4. Oxidation treatment: The graphitized carbon felt was heated to 400° C. at a heating rate of 5° C. / min in a muffle furnace and heat treated in an air atmosphere for 72 h to increase its oxidation activity.

[0083] Performance Testing

[0084] Test samples: the high specific surface area and high activity multi-level porous carbon felt electrodes provided in Examples 1 to 3, the carbonized carbon felt electrode without etching provided in Comparative Example 1, and the carbon felt electrode prepared by graphitization process provided in Comparative Example 2.

[0085] In order to evaluate the electrochemical performance of different carbon felt materials in all-vanadium redox flow batteries, the carbon felts and graphite felts prepared in Examples 1-3 and Comparative Examples 1-2 were selected as electrode materials and tested at 100 mA / cm 2 Carry out charge and discharge test under current density. The specific test method is as follows:

[0086] The battery assembly adopts a symmetrical structure of all-vanadium redox flow battery with an electrode area of ​​25cm 2 The electrolyte used was 1.6M VOS04 + 3M H2SO4. In constant current charge and discharge mode, the cutoff voltage range was set to 1.65V-0.8V, and the test environment temperature was controlled at 25±1°C. The battery's coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were recorded, and the battery's stability and cycle performance were calculated.

[0087] The test results are shown in Table 1 below:

[0088] Table 1 Performance test results of examples and comparative examples

[0089] sample Coulombic efficiency (%) Voltage efficiency (%) Energy efficiency (%) Discharge capacity (mAh) Example 1 97.06 82.91 80.47 434.3 Example 2 96.90 86.88 84.20 437.3 Example 3 97.10 83.31 80.90 434.9 Comparative Example 1 94.96 76.66 72.80 317.9 Comparative Example 2 95.11 85.37 81.20 392.5

[0090] As shown in Table 1, the high-performance multi-level porous carbon felt electrode prepared by the present invention exhibits excellent electrochemical performance. Examples 1 to 3 are preferred embodiments of the present invention, and the high-specific surface area and high-activity multi-level porous carbon felt provided by the present invention have excellent electrochemical performance at 100 mA / cm 2 The coulombic efficiency at the current density is 96.90% to 97.10%, the voltage efficiency is 82.91% to 86.88%, the energy efficiency is 80.47% to 84.20%, and the discharge capacity is 434.3 to 437.3. In particular, Example 2 has an energy efficiency of up to 84.20% and exhibits a high discharge capacity. All performance indicators are significantly better than those of the comparative example samples. This shows that the short-process preparation method for a high-performance multi-level porous carbon felt electrode for a redox flow battery proposed in the present invention not only significantly simplifies the preparation process, but also effectively optimizes the microstructure and electrochemical activity of the electrode material, thereby improving the overall performance of the flow battery. This technical solution has obvious advantages in improving energy conversion efficiency, reducing electrode polarization loss, and enhancing cycle stability, and shows good market application prospects.

[0091] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery, characterized in that: The steps include: S1. Clean the commercial polypropylene pre-oxidized felt with anhydrous ethanol to remove surface impurities; S2. dissolving an appropriate amount of zinc salt or bismuth salt in a solvent, stirring and ultrasonically treating the mixture at a certain temperature to fully dissolve the mixture to obtain a precursor solution; S3, immersing the cleaned pre-oxidized felt into the precursor solution and ultrasonically treating it, taking it out and drying it to obtain a base carbon felt; S4. Carbonizing the base carbon felt at high temperature under a protective atmosphere, soaking it in nitric acid, washing it with deionized water, and drying it to obtain a multi-level porous carbon felt electrode with high activity and high specific surface area.

2. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, characterized in that: The thickness of the preoxidized felt is 2.5 to 5 mm.

3. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, characterized in that: In step S2, the zinc salt is selected from zinc chloride and / or zinc nitrate; the bismuth salt is selected from bismuth chloride and / or bismuth nitrate; the solvent is selected from ethylene glycol; the dissolution temperature is 20-60°C; the stirring method is magnetic stirring, the stirring speed is 200-600 rpm, and the stirring time is 10-20 min; the ultrasonic treatment time is 5-10 min; and the mass concentration of the precursor solution is 0.1%-5%.

4. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, wherein: In step S3, the ultrasonic treatment time is 20 to 30 minutes.

5. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, characterized in that: In step S4, the carbonization treatment is specifically as follows: placing the dried pre-oxidized felt in a tubular furnace and continuously introducing a nitrogen atmosphere with a gas flow rate of 0.2 to 1.0 m / s; the heating rate of the tubular furnace is 2 to 8°C / min; the carbonization temperature is 1000 to 1200°C, and the carbonization time is 1 to 3 hours.

6. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, characterized in that: In step S4, the specific process of the nitric acid soaking and deionized water cleaning is: immersing the carbonized carbon felt in a nitric acid solution, ultrasonically treating it, and then rinsing it with deionized water for 3 to 5 times.

7. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 6, characterized in that: The nitric acid concentration is 50% to 70%; and the ultrasonic treatment time is 5 to 10 minutes.

8. The method for preparing a high-performance multi-level porous carbon felt electrode for a flow battery according to claim 1, characterized in that: In step S4, the specific drying method is: placing the carbon felt in a vacuum drying oven to obtain dried carbon felt after a period of time; the temperature of the vacuum drying oven is 80-120° C.; and the drying time is 0.5-3 hours. 9 . A high-performance multi-level porous carbon felt electrode for a liquid flow battery prepared according to the method for preparing a high-performance multi-level porous carbon felt electrode for a liquid flow battery according to any one of claims 1 to 8 .