Carbon felt electrode for all-vanadium redox flow battery and preparation process and application thereof
By constructing a bismuth composite layer and growing a MOF framework structure on a carbon felt electrode, the problems of few active sites and poor hydrophilicity were solved, thereby improving the energy efficiency and long-term stability of the all-vanadium redox flow battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ENERFLOW TECH CO LTD
- Filing Date
- 2026-04-02
- Publication Date
- 2026-06-09
Smart Images
Figure CN121964680B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of flow batteries, and in particular to a carbon felt electrode for an all-vanadium redox flow battery, its preparation process, and its application. Background Technology
[0002] Vanadium redox flow batteries, as a large-scale energy storage technology, have broad application prospects in renewable energy grid integration and grid peak shaving due to their advantages such as long cycle life, high safety, and high energy efficiency. Electrode materials, as the core sites for electrochemical reactions, directly affect the battery's energy efficiency and long-term stability. Carbon felt is widely used as an electrode material due to its good conductivity and chemical stability.
[0003] During the operation of a vanadium redox flow battery, vanadium ions store and release energy through redox reactions on the electrodes. Although the porous structure of carbon felt can provide a large specific surface area, carbon felt electrodes have the disadvantages of few active sites and poor hydrophilicity. This not only leads to a lower electrochemical reaction rate but also results in a higher overall internal resistance of the battery, affecting the battery's energy efficiency and long-term stability, making it difficult to meet the application requirements of high-power scenarios. Summary of the Invention
[0004] The main purpose of this application is to propose a carbon felt electrode for all-vanadium redox flow batteries, its preparation process and application, aiming to solve the problems of few active sites and poor hydrophilicity of existing carbon felt electrodes.
[0005] In a first aspect, this application provides a process for fabricating a carbon felt electrode for an all-vanadium redox flow battery, comprising the following steps:
[0006] S1. Provide carbon felt, immerse the carbon felt in urea solution, and sonicate to obtain a first mixture containing carbon felt; mix bismuth source, polyvinylpyrrolidone and nitric acid aqueous solution to obtain a second mixture, and mix the second mixture with the first mixture containing carbon felt to obtain a first reaction solution;
[0007] S2. Under sealed conditions, the first reaction solution obtained in step S1 is reacted at a first temperature, cooled, the carbon felt is removed and washed to obtain a carbon felt loaded with a bismuth composite layer.
[0008] S3. Dissolve the transition metal source and organic ligand in a solvent to obtain a third mixture. Immerse the carbon felt with bismuth composite layer obtained in step S2 into the third mixture to obtain a second reaction solution. Under sealed conditions, react the second reaction solution at a second temperature, cool it, remove the carbon felt, wash it, filter it and dry it to obtain the carbon felt electrode for the all-vanadium redox flow battery.
[0009] In step S3, the transition metal source is selected from at least one of cobalt source and iron source; the molar ratio of transition metal source to organic ligand is 1:(1.5~4.0).
[0010] By employing the above technical solution, carbon felt is immersed in urea solution. The cavitation effect generated during ultrasonic treatment effectively promotes the urea solution's penetration into the porous structure of the carbon felt, significantly improving the penetration depth and uniformity of the urea solution within the porous structure, thus laying the foundation for uniform loading of functional components. The bismuth source, polyvinylpyrrolidone (PVP), and nitric acid aqueous solution are mixed to promote the complete dissolution of the bismuth source. Furthermore, the coordination and steric hindrance effects of PVP improve the dispersion stability of the bismuth source, preventing agglomeration and ensuring uniform deposition of bismuth on the carbon felt during subsequent heating reactions.
[0011] The first reaction solution was placed under sealed conditions and heated to generate autogenous pressure, driving the hydrolysis of urea and slowly alkalizing the system. This gradually increased the pH of the system, creating suitable conditions for the bonding of bismuth and carbon felt. Combined with the coordination and steric hindrance effects of PVP, this guided the stable, uniform, and directional deposition of bismuth on the carbon felt, ultimately forming a porous bismuth composite layer on the carbon felt, enhancing its active sites and hydrophilicity. After the reaction, the mixture was allowed to cool naturally to room temperature. The carbon felt was then removed and washed to remove loose deposits and impurities.
[0012] A carbon felt loaded with a bismuth composite layer is immersed in a third mixture formed by a transition metal source (cobalt source, iron source, etc.) and organic ligands to obtain a second reaction solution. Under sealed conditions and heating, cobalt (Co) or iron (Fe) grows in situ on the bismuth composite layer through the organic ligands, forming a Co-MOF framework structure or a Fe-MOF framework structure. This further improves the specific surface area, active sites, and hydrophilicity of the material, and also facilitates ion diffusion, improving ion transport efficiency. After the reaction, the material is naturally cooled to room temperature, and the carbon felt is removed, washed, filtered, and dried to obtain a carbon felt electrode for vanadium redox flow batteries. The prepared carbon felt electrode for vanadium redox flow batteries possesses abundant active sites and excellent hydrophilicity, effectively improving the electrochemical performance of vanadium redox flow batteries.
[0013] It should be noted that in step S3, the drying conditions are: drying under vacuum at 50~70℃ for 15~24h.
[0014] Preferably, in step S3, the drying conditions are: drying under vacuum at 60°C for 24 hours.
[0015] Optionally, in step S3, the molar ratio of the transition metal source to the organic ligand is 1:(2~3).
[0016] By adopting the above technical solution and further controlling the molar ratio of transition metal source to organic ligand, the loading effect of transition metal source can be further improved, which helps to further improve the active sites and hydrophilicity of the prepared material.
[0017] Optionally, in step S3, the organic ligand is selected from at least one of pyromellitic acid and 2-methylimidazole.
[0018] By adopting the above technical solution and using specific organic ligands, it is possible to ensure that the transition metal source can be loaded onto the bismuth composite layer more fully and stably.
[0019] Optionally, in step S3, the organic ligand includes pyromellitic acid and 2-methylimidazole, and the molar ratio of pyromellitic acid and 2-methylimidazole is (1.5~2.5):1.
[0020] By adopting the above technical solution and further optimizing the composition and ratio of organic ligands, the loading effect of transition metal sources can be improved.
[0021] Preferably, the molar ratio of pyromellitic acid to 2-methylimidazole is 2:1.
[0022] Optionally, in step S3, the cobalt source is cobalt nitrate, and the iron source is ferrous nitrate; and / or,
[0023] In step S3, the solvent is N,N-dimethylformamide, and the preparation method of the third mixture includes: adding a transition metal source to the solvent, stirring, adding an organic ligand, stirring, and obtaining the third mixture.
[0024] By adopting the above technical solution, the transition metal source and the organic ligand are added to the solvent in sequence, and each addition is accompanied by stirring to ensure that the transition metal source and the organic ligand are fully dissolved.
[0025] It should be noted that magnetic stirring can be used, with a stirring speed of 300-600 rpm and a stirring time of 30-60 minutes per session. Preferably, the stirring speed is 400 rpm and the stirring time is 30 minutes per session.
[0026] Optionally, in step S2, the first temperature is 120~160℃, and the reaction time at the first temperature is 2~5h;
[0027] In step S3, the second temperature is 150~180℃, and the reaction time at the second temperature is 10~15h.
[0028] By adopting the above technical solution, the reaction conditions of this application are mild, and the two reactions are carried out at specific temperatures and times to deposit a bismuth composite layer on the carbon felt, and to grow a Co-MOF framework structure in situ on the bismuth composite layer, or to grow an Fe-MOF framework structure in situ on the bismuth composite layer, so as to improve the active sites and hydrophilicity of the obtained material.
[0029] Preferably, in step S2, the first temperature is 150°C, and the reaction time at the first temperature is 3 hours.
[0030] In step S3, the second temperature is 180°C, and the reaction time at the second temperature is 12 hours.
[0031] Optionally, in step S1, the bismuth source is bismuth trichloride, the concentration of the nitric acid aqueous solution is 1~2 mol / L, and the mass ratio of the bismuth source, the mass of the polyvinylpyrrolidone, and the volume ratio of the nitric acid aqueous solution is (0.4~0.5) g : (6~7) g : (15~30) mL.
[0032] By adopting the above technical solution and controlling the amounts of bismuth source, polyvinylpyrrolidone, and nitric acid, it is possible to ensure that bismuth is sufficiently loaded onto the carbon felt.
[0033] Preferably, in step S1, the bismuth source is bismuth trichloride, the concentration of the nitric acid aqueous solution is 1 mol / L, and the mass ratio of the bismuth source, the mass of the polyvinylpyrrolidone, and the volume ratio of the nitric acid aqueous solution is 0.47 g: 6.75 g: 20 mL.
[0034] Optionally, in step S1, the preparation method of the first mixture containing carbon felt includes: dissolving urea in ethylene glycol to obtain a urea solution, immersing the carbon felt in the urea solution, and ultrasonically treating it with 100~300W for 5~30min to obtain the first mixture containing carbon felt.
[0035] The mass ratio of urea to the volume of ethylene glycol is (0.3~0.4) g : (90~110) mL.
[0036] By adopting the above technical solution and using ethylene glycol as a solvent, the reaction temperature is kept in a liquid state, providing a homogeneous environment.
[0037] Preferably, the mass ratio of urea to the volume of ethylene glycol is 0.32 g: 100 mL.
[0038] Preferably, in step S1, the preparation method of the first mixture containing carbon felt includes: dissolving urea in ethylene glycol to obtain a urea solution, immersing the carbon felt in the urea solution, and ultrasonically treating it with 200W for 15 minutes to obtain the first mixture containing carbon felt.
[0039] Secondly, this application provides a carbon felt electrode for an all-vanadium redox flow battery prepared using any of the above-described preparation processes.
[0040] By adopting the above technical solution, the carbon felt electrode produced has abundant active sites and good hydrophilicity, which helps to improve the energy efficiency and long-term stability of the battery.
[0041] Thirdly, this application also provides an all-vanadium redox flow battery, including a positive electrode and a negative electrode, both of which are made of the aforementioned carbon felt electrode.
[0042] By adopting the above technical solution, using carbon felt electrodes with abundant active sites and good hydrophilicity as positive and negative electrodes, it is helpful to improve the energy efficiency and long-term stability of the battery.
[0043] In summary, this application includes at least the following beneficial technical effects:
[0044] 1. This application constructs a bismuth composite layer on a carbon felt and grows an MOF framework structure in situ on the bismuth composite layer, which significantly increases the specific surface area and the number of active sites of the carbon felt electrode, effectively reduces the water contact angle on the electrode surface, and improves the hydrophilicity of the electrode.
[0045] 2. The bismuth composite layer provides a stable anchoring substrate for the MOF framework structure, enhances the bonding strength of MOF on carbon felt, and is beneficial to the long-term cycling stability of the electrode.
[0046] 3. When the prepared carbon felt electrode is applied to a vanadium redox flow battery, the average energy efficiency and capacity retention of the battery are significantly improved. Attached Figure Description
[0047] Figure 1 This is the energy efficiency diagram corresponding to Embodiment 3 of this application;
[0048] Figure 2 This is the capacity retention rate diagram corresponding to Embodiment 3 of this application. Detailed Implementation
[0049] The present application will be further described in detail below with reference to the embodiments. All raw materials involved in this application are commercially available, wherein:
[0050] Carbon felt, polyacrylonitrile-based carbon felt, Liaoning Jingu Carbon Materials Co., Ltd., length 8cm, width 6cm, thickness 5mm;
[0051] Polyvinylpyrrolidone K60, Shanghai Aladdin Biochemical Technology Co., Ltd. Example 1
[0052] A process for fabricating a carbon felt electrode for an all-vanadium redox flow battery includes the following steps:
[0053] S1. Add 0.32g of urea to 100mL of ethylene glycol and stir magnetically at 400rpm for 10min to obtain a urea solution. Provide two carbon felt pieces and immerse them in the urea solution. Sonicate at 200W for 15min to obtain a first mixture containing carbon felt. Add 0.47g of bismuth trichloride and 6.75g of polyvinylpyrrolidone K60 to 20mL of 1mol / L nitric acid aqueous solution and stir magnetically at 400rpm for 10min to obtain a second mixture. Add the second mixture to the first mixture and stir magnetically at 500rpm for 10min to obtain a first reaction solution.
[0054] S2. Add the first reaction solution obtained in step S1 into the hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, control the temperature inside the reactor to 150℃, maintain this temperature for 3 hours, and allow it to cool naturally to room temperature (25℃). Take out the carbon felt, wash it 5 times with deionized water and 3 times with anhydrous ethanol to obtain the carbon felt loaded with the bismuth composite layer.
[0055] S3. Add 2 mmol of cobalt nitrate hexahydrate to 40 mL of N,N-dimethylformamide and stir magnetically at 400 rpm for 30 min. Add 4 mmol of trimesic acid and stir magnetically at 400 rpm for 30 min to obtain the third mixture. Immerse the carbon felt with bismuth composite layer obtained in step S2 into the third mixture to obtain the second reaction solution. Add the second reaction solution to the hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, and control the temperature inside the reactor at 180℃. Maintain this temperature for 12 h and allow it to cool naturally to room temperature (25℃). Remove the carbon felt, wash it three times with deionized water, filter to remove the solvent, and dry the filtered carbon felt under vacuum at 60℃ for 24 h to obtain the carbon felt electrode.
[0056] Examples 2-4
[0057] Examples 2-4 are based on Example 1, the difference being that the molar amount of pyromellitic acid in step S3 is different, while the other steps remain the same as in Example 1. Specifically,
[0058] In Example 2, the molar amount of pyromellitic acid was 3 mmol.
[0059] In Example 3, the molar amount of pyromellitic acid was 6 mmol.
[0060] In Example 4, the molar amount of pyromellitic acid was 8 mmol. Comparative Example 1
[0061] The carbon felt electrode provided in this comparative example is a commercially available polyacrylonitrile-based carbon felt, i.e., an unmodified carbon felt electrode. Comparative Example 2
[0062] A process for fabricating a carbon felt electrode for an all-vanadium redox flow battery includes the following steps:
[0063] S1. Add 0.32g of urea to 100mL of ethylene glycol and stir magnetically at 400rpm for 10min to obtain a urea solution. Provide two carbon felt pieces and immerse them in the urea solution. Sonicate at 200W for 15min to obtain a first mixture containing carbon felt. Add 0.47g of bismuth trichloride and 6.75g of polyvinylpyrrolidone K60 to 20mL of 1mol / L nitric acid aqueous solution and stir magnetically at 400rpm for 10min to obtain a second mixture. Add the second mixture to the first mixture and stir magnetically at 500rpm for 10min to obtain a first reaction solution.
[0064] S2. Add the first reaction solution obtained in step S1 to the hydrothermal synthesis reactor, seal the hydrothermal synthesis reactor, control the temperature inside the reactor to 150℃, maintain this temperature for 3 hours, and allow it to cool naturally to room temperature (25℃). Take out the carbon felt, wash it 5 times with deionized water and 3 times with anhydrous ethanol to obtain a carbon felt loaded with a bismuth composite layer. Place the washed carbon felt under vacuum at 60℃ for 24 hours to dry it to obtain a carbon felt electrode. Comparative Example 3
[0065] This comparative example is based on Example 1, except that in step S3, the molar amount of pyromellitic acid is 2 mmol, and the other steps are the same as in Example 1.
[0066] Performance Test 1
[0067] Contact angle tests were conducted on the carbon felt electrodes obtained in Examples 1-4 and Comparative Examples 1-3. The carbon felt electrodes obtained in Examples 1-4 and Comparative Examples 1-3 were then used as positive and negative electrodes to assemble vanadium redox flow batteries, and constant current charge-discharge performance tests were performed. The test results are shown in Table 1 below.
[0068] The contact angle test involved cutting a 2cm x 2cm effective area of the carbon felt electrode as the test sample. After removing surface dust, residual solvent, and loose attachments, the sample was horizontally fixed on the test platform. A vanadium sulfate-based electrolyte (Dalian Borong High-Tech Materials Co., Ltd., with a total vanadium ion concentration of 1.8 mol / L and a sulfuric acid concentration of 3 mol / L) was used as the test solution. Under an environment of 25±1℃ and 50±10% relative humidity, 3μL of the test solution was slowly added by a micropipette 2mm directly above the sample surface. After 4 seconds, an image was acquired using a contact angle measuring instrument. Five different areas of each sample were tested, and the average value of the test results was taken (the results were retained to the nearest integer). If the droplet was completely immersed in the electrode surface instantly, it was determined to be superhydrophilic.
[0069] Electrochemical performance testing: An 8cm × 6cm carbon felt electrode (effective area 48cm²) was cut as the test sample, and a 160mA / cm² electrode was used. 2 The current density was tested for 100 effective charge-discharge cycles at a constant current of 8A, with charge and discharge cutoff voltages of 1.55V and 1V, respectively. Nitrogen was used as the protective gas. The average energy efficiency (%) of the battery after 100 effective charge-discharge cycles and the capacity retention rate (%) of the battery after 100 effective charge-discharge cycles were tested.
[0070] in, In the formula, Ei refers to the energy efficiency corresponding to the i-th effective cycle, and the value of i is an integer from 1 to 100.
[0071] Battery capacity retention rate = (Q 100 / Q)*100%, where Q 100 Q refers to the discharge energy at the 100th effective cycle, while Q refers to the maximum discharge energy obtained in 100 effective cycles.
[0072] Table 1. Test Results
[0073] Example 5
[0074] This embodiment is based on Example 3, except that 2 mmol of cobalt nitrate hexahydrate [Fe(NO3)2·6H2O] is used instead of 2 mmol of cobalt nitrate hexahydrate [Co(NO3)2·6H2O]. The other steps are the same as in Example 3. Example 6
[0075] This embodiment is based on Example 3, except that 6 mmol of 2-methylimidazole is used instead of 6 mmol of trimesic acid, while the other steps are the same as in Example 3. Example 7
[0076] This embodiment is based on Example 3, except that: a mixture of 4 mmol of trimellitic acid and 2 mmol of 2-methylimidazole is used instead of 6 mmol of trimellitic acid, while the other steps are the same as in Example 3.
[0077] Performance Test 2
[0078] Using the same experimental methods as performance test 1, the carbon felt electrodes obtained in Examples 5-7 were subjected to contact angle and electrochemical performance tests. The test results are shown in Table 2 below.
[0079] Table 2 Test Results
[0080]
[0081] As shown in Tables 1 and 2, the experimental results of this application, by constructing a bismuth composite layer on the carbon felt and then growing a MOF framework structure in situ on the bismuth composite layer, significantly increased the specific surface area and the number of active sites of the carbon felt electrode, effectively reduced the water contact angle of the electrode surface, and improved the hydrophilicity of the electrode. Furthermore, the bismuth composite layer provides a stable anchoring substrate for the MOF framework structure, enhancing the bonding strength of the MOF framework on the carbon felt and contributing to the long-term cycling stability of the electrode. When the prepared carbon felt electrode is applied to an all-vanadium redox flow battery, the average energy efficiency and capacity retention of the battery are significantly improved.
[0082] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the principles of this application should be covered within the scope of protection of this application.
Claims
1. A fabrication process for a carbon felt electrode for an all-vanadium redox flow battery, characterized in that, Includes the following steps: S1. Dissolve urea in ethylene glycol to obtain a urea solution. Provide carbon felt and immerse the carbon felt in the urea solution. Sonicate the solution to obtain a first mixture containing carbon felt. Mix bismuth source, polyvinylpyrrolidone and nitric acid aqueous solution to obtain a second mixture. Mix the second mixture with the first mixture containing carbon felt to obtain a first reaction solution. S2. Under sealed conditions, the first reaction solution obtained in step S1 is reacted at a first temperature, cooled, the carbon felt is removed and washed to obtain a carbon felt loaded with a bismuth composite layer. S3. Dissolve the transition metal source and organic ligand in a solvent to obtain a third mixture. Immerse the carbon felt with the bismuth composite layer obtained in step S2 into the third mixture to obtain a second reaction solution. Under sealed conditions, react the second reaction solution at a second temperature, cool, remove the carbon felt, wash, filter, and dry to obtain the carbon felt electrode for the vanadium redox flow battery. In step S3, the transition metal source is selected from at least one of cobalt source and iron source. The molar ratio of the transition metal source to the organic ligand is 1:(1.5~4.0). In step S3, the organic ligand is selected from at least one of pyromellitic acid and 2-methylimidazole; in step S1, the bismuth source is bismuth trichloride, the concentration of the nitric acid aqueous solution is 1~2 mol / L, and the mass ratio of the bismuth source, the mass of the polyvinylpyrrolidone, and the volume ratio of the nitric acid aqueous solution is (0.4~0.5) g : (6~7) g : (15~30) mL; in step S2, the first temperature is 120~160℃, and the reaction time at the first temperature is 2~5 h; in step S3, the second temperature is 150~180℃, and the reaction time at the second temperature is 10~15 h.
2. The fabrication process of the carbon felt electrode for an all-vanadium redox flow battery according to claim 1, characterized in that, In step S3, the molar ratio of the transition metal source to the organic ligand is 1:(2~3).
3. The fabrication process of the carbon felt electrode for an all-vanadium redox flow battery according to claim 1, characterized in that, In step S3, the organic ligands include pyromellitic acid and 2-methylimidazole, and the molar ratio of pyromellitic acid to 2-methylimidazole is (1.5~2.5):
1.
4. The fabrication process of the carbon felt electrode for an all-vanadium redox flow battery according to claim 1, characterized in that, In step S3, the cobalt source is cobalt nitrate, and the iron source is ferrous nitrate; and / or, In step S3, the solvent is N,N-dimethylformamide, and the preparation method of the third mixture includes: adding a transition metal source to the solvent, stirring, adding an organic ligand, stirring, and obtaining the third mixture.
5. The fabrication process of the carbon felt electrode for an all-vanadium redox flow battery according to claim 1, characterized in that, In step S1, the preparation method of the first mixture containing carbon felt includes: dissolving urea in ethylene glycol to obtain a urea solution, immersing the carbon felt in the urea solution, and ultrasonically treating it with 100~300W for 5~30min to obtain the first mixture containing carbon felt. The mass ratio of urea to the volume of ethylene glycol is (0.3~0.4) g : (90~110) mL.
6. A carbon felt electrode for an all-vanadium redox flow battery, prepared using the process described in any one of claims 1 to 5.
7. A vanadium redox flow battery, characterized in that, It includes a positive electrode and a negative electrode, both of which are carbon felt electrodes as described in claim 6.