High-performance carbon felt electrode for flow battery as well as preparation method and application of high-performance carbon felt electrode

Abstract

The invention discloses a high-performance carbon felt electrode for a flow battery as well as a preparation method and application of the high-performance carbon felt electrode. The preparation method comprises the following steps: 1) impregnating a pre-oxidized felt in a metal compound solution or dispersion liquid to obtain an impregnated pre-oxidized felt; and 2) carbonizing and activating the impregnated pre-oxidized felt to obtain the carbon felt electrode, and the pre-oxidized felt is a polyacrylonitrile-based pre-oxidized felt. Coordination bonds are formed through a large number of nitrogen-containing groups and metal ions in the felt pre-oxidation stage, the combination effect of an electrode material and a catalyst is enhanced, the advantage of improving the electrode activity and stability is achieved, meanwhile, no additional carbon-nitrogen material is introduced, no negative influence is generated on the pore channel structure of the electrode, and the service life of the electrode is prolonged. And the mass transfer effect of the carbon felt electrode material in battery operation is ensured. The carbon felt electrode can simultaneously realize high electrode activity such as high electrode mass transfer efficiency and excellent catalyst stability, and the service life of the carbon felt electrode is prolonged.

Description

Technical Field

[0001] This invention relates to a high-performance carbon felt electrode for flow batteries, its preparation method, and its application. Background Technology

[0002] In recent years, the installed capacity of new energy power generation such as photovoltaic and wind power has been increasing year by year, and the demand for energy storage has also been growing. In the field of energy storage, vanadium redox flow batteries, as a type of aqueous battery, have significant advantages over lithium-ion batteries, such as high safety, long-term energy storage (>8 hours), long lifespan, and capacity flexibility. Therefore, as the global "new energy + energy storage" trend moves towards large-scale and long-term applications, vanadium redox flow batteries are gradually becoming an important technology in the field of large-scale energy storage, especially possessing irreplaceable competitiveness in the "long-term energy storage" sector.

[0003] As an electrode material for vanadium redox flow batteries, carbon felt offers advantages such as low cost, high porosity, and good chemical stability, ensuring good mass transfer efficiency and stability during battery operation. However, due to its low intrinsic catalytic activity and sensitivity to side reactions, it results in significant polarization losses (100-200 mV), leading to relatively low current and energy efficiencies. Therefore, surface modification of the electrodes is typically performed in practical applications.

[0004] To improve the activity of carbon felt electrodes and reduce their sensitivity to side reactions (hydrogen evolution reaction / oxygen evolution reaction), existing technologies typically employ a catalyst-supported method, depositing metal-based (manganese, bismuth, tungsten, etc.) or non-metal-based (graphene, carbon nanotubes, etc.) catalysts on the electrode surface.

[0005] Chinese patent CN120432554A discloses a method for preparing a Bi-Co diatomic catalyst-modified carbon felt electrode. By utilizing the synergistic effect of BiCo bimetallic sites and a nitrogen-doped carbon substrate, the catalytic activity and cycle stability of the electrode are significantly improved. The BiCo diatomic catalyst optimizes the battery reaction pathway through electronic coupling, reducing overpotential and improving reaction kinetic efficiency. However, in this type of electrode, the catalyst and the substrate electrode material are not tightly bonded, and the catalyst is prone to detachment during battery cycling, weakening the electrode stability. Furthermore, the carbon-nitrogen materials introduced through urea easily fill the pore structure of the electrode, clogging the pores and affecting the mass transfer of the electrode. In other words, this type of electrode has low mass transfer and poor stability.

[0006] Chinese patent CN116779883A introduces resin as a binder to increase the adhesion of the catalyst to the electrode. Simultaneously, the resin carbonization process generates resin carbon, which does not affect the electrode's conductivity. While this method increases catalyst adhesion to some extent, the carbonized resin carbon particles easily clog the pore structure of the carbon felt electrode, reducing its mass transfer efficiency. In other words, the mass transfer efficiency of this type of electrode is significantly insufficient, and its stability needs further improvement.

[0007] The challenge lies in significantly improving the stability of the catalyst supported on the carbon felt electrode while ensuring its high electrode activity, such as high electrode mass transfer efficiency. Summary of the Invention

[0008] To address the shortcomings and deficiencies of existing technologies, this invention provides an improved carbon felt electrode. This carbon felt electrode can simultaneously achieve high electrode activity, such as high electrode mass transfer efficiency, and excellent catalyst stability, thereby extending the service life of the carbon felt electrode.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a carbon felt electrode, the method comprising the following steps: 1) impregnating a pre-oxidized felt with a solution or dispersion of a metal compound to obtain an impregnated pre-oxidized felt; 2) carbonizing and activating the impregnated pre-oxidized felt to obtain the carbon felt electrode; wherein the pre-oxidized felt is a polyacrylonitrile-based pre-oxidized felt.

[0010] In some embodiments, the metal compound is selected from one or more combinations of metal nitrates, sulfates, and chlorides; the metal is selected from one or more combinations of bismuth, manganese, copper, and tungsten. Carbon felt electrodes with bismuth, manganese, and copper exhibit better performance than those with tungsten.

[0011] In some embodiments, the metal is selected from manganese and / or copper, and in step 1), the pre-oxidized felt is impregnated with an aqueous solution of the metal compound.

[0012] In some embodiments, the metal is bismuth. In step 1), the pre-oxidized felt is impregnated with an alcohol solution of the metal compound. The preparation method further includes adding water dropwise to the alcohol solution of the metal compound during the impregnation process to hydrolyze the metal compound. Bismuth metal compounds such as bismuth nitrate have low water solubility and are more readily soluble in alcohol. However, they cannot ionize into bismuth ions in alcohol. Therefore, the process involves adding water dropwise and hydrolyzing to generate bismuth oxide ions.

[0013] In some embodiments, the alcohol is ethanol.

[0014] In some embodiments, the mass ratio of the metal compound to the water is 1:0.07-3.0, preferably 1:1-3.

[0015] In some embodiments, the hydrolysis time is 0.5-2 hours.

[0016] In some embodiments, the mass percentage concentration of the metal element in the solution or dispersion of the metal compound is 1%-10%.

[0017] In some implementations, the immersion time in step 1) is 5-40 minutes.

[0018] In some embodiments, in step 2), the carbonization temperature is 1500-1700°C. At this temperature, the metal compound decomposes, producing a metal active component that can act as a catalyst.

[0019] In some implementations, during step 2), the heating rate is 5-10°C / min when carbonization is performed.

[0020] In some implementations, the carbonization time in step 2) is 1-2 hours.

[0021] In some embodiments, in step 2), the carbonization is carried out in an inert atmosphere.

[0022] In some embodiments, in step 2), the activation is selected from one or more combinations of steam activation, air activation, or carbon dioxide activation. Activation can cause oxygen-containing active groups to form on the surface of the carbon felt electrode, which is beneficial to improving electroactivity.

[0023] In some embodiments, the activation temperature in step 2) is 300-500°C.

[0024] In some implementations, during step 2), the heating rate is 1-5°C / min during activation.

[0025] In some implementations, the activation time in step 2) is 0.5-4 hours.

[0026] The present invention also provides a carbon felt electrode prepared by the aforementioned method. This carbon felt electrode can simultaneously achieve high electrode activity, such as high electrode mass transfer efficiency, and excellent catalyst stability, thereby extending the service life of the carbon felt electrode.

[0027] The present invention also provides an application of the aforementioned carbon felt electrode in a flow battery.

[0028] Compared with the prior art, the present invention has the following advantages: The carbon felt electrode of this invention can simultaneously achieve high electrode activity, such as high electrode mass transfer efficiency, and excellent catalyst stability, thus extending the service life of the carbon felt electrode. The carbon felt electrode of this invention exhibits high current efficiency, voltage efficiency, and energy efficiency, and its electroactivity remains essentially stable after 2000 cycles. Attached Figure Description

[0029] Figure 1 The results of the cycle stability test of the carbon felt electrode in Example 1 of the present invention are shown, where CE is the current efficiency, VE is the voltage efficiency, EE is the energy efficiency, and the horizontal axis is the number of cycles.

[0030] Figure 2 The results of the cycle stability test of the carbon felt electrode in Comparative Example 1 are shown, where CE is the current efficiency, VE is the voltage efficiency, EE is the energy efficiency, and the horizontal axis represents the number of cycles. Detailed Implementation

[0031] To improve the activity of carbon felt electrodes and reduce their sensitivity to side reactions (hydrogen evolution reaction / oxygen evolution reaction), existing technologies typically employ catalyst loading methods, depositing metal-based (manganese, bismuth, tungsten, etc.) or non-metal-based (graphene, carbon nanotubes, etc.) catalysts on the electrode surface. However, such electrodes may suffer from poor catalyst-to-substrate bonding, leading to catalyst detachment during battery cycling and reduced electrode stability. Alternatively, attempts to increase catalyst adhesion may result in blockage of the carbon felt electrode's pore structure, reducing mass transfer efficiency. In short, it is difficult to simultaneously achieve high electrode activity (e.g., high mass transfer efficiency) and catalyst stability.

[0032] This invention uses PAN-based pre-oxidized felt and metal catalyst precursor impregnation treatment to form coordination bonds between the metal precursor and the components in the pre-oxidized felt (through the metal element forming coordination bonds with N in the pre-oxidized felt, which is a chemical bonding effect), thereby enhancing the binding force between the catalyst components and the pre-oxidized felt. After carbonization and activation, the catalyst can be stably loaded in the electrode material without any negative impact on the pore structure of the electrode. Therefore, it can simultaneously achieve high electrode activity and high catalyst loading stability of carbon felt electrodes.

[0033] This invention enhances the bonding between the electrode material and the catalyst by forming coordination bonds with metal ions through a large number of nitrogen-containing groups during the pre-oxidation felt stage, thereby improving the electrode activity and stability. At the same time, it does not introduce additional carbon and nitrogen materials, has no negative impact on the pore structure of the electrode itself, and ensures the mass transfer function of the carbon felt electrode material during battery operation.

[0034] This invention involves impregnating a metal catalyst precursor with a PAN-based pre-oxidized felt. The nitrogen element in the PAN-based pre-oxidized felt forms coordination bonds with the metal ions in the precursor, strengthening the chemical bonding between the catalyst precursor and the pre-oxidized felt. After high-temperature carbonization, a carbon felt electrode is obtained. Therefore, in the electrode, the metal ions and nitrogen element have formed MN coordination bonds (M represents a metal element, such as Bi, Mn, Cu, W, etc.), making it difficult for the metal-based catalyst to detach from the electrode, thus resulting in high electrode material stability. Simultaneously, due to the anchoring effect of nitrogen, the metal catalyst particles are small and do not clog the electrode's own pore structure, thereby ensuring a high level of electrode mass transfer efficiency.

[0035] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0036] Example 1 This embodiment provides a carbon felt electrode, which is prepared by the following method: 1) Weigh 10g of manganese nitrate (approximately 3g of manganese) and dissolve it in 300mL of water to obtain a precursor solution with a manganese content of 1wt%; 2) After cutting the PAN-based pre-oxidized felt into 10cm*10cm pieces, immerse them in the aforementioned precursor solution with a manganese content of 1wt% for 30 minutes. After removing them, dry them at 60°C to obtain the impregnated manganese-doped pre-oxidized felt material. 3) The impregnated manganese-doped pre-oxidized felt material is placed in a carbonization furnace and heated to 1700℃ at a heating rate of 10℃ / min, and held at this temperature for 1h to obtain manganese-doped carbon felt electrode material. 4) Place the manganese-doped carbon felt electrode material into a box furnace and heat it to 500°C at a heating rate of 5°C / min. Hold it in air for 2 hours to obtain the final carbon felt electrode.

[0037] During the carbonization process in step 3) above, the manganese nitrate precursor is decomposed.

[0038] Example 2 This embodiment provides a carbon felt electrode, which is prepared by the following method: 1) Weigh 70g of bismuth nitrate pentahydrate (about 30g of bismuth element) and dissolve it in 35mL of ethanol to obtain a precursor suspension with a bismuth element content of 30.7wt%; 2) After cutting the PAN-based pre-oxidized felt into 10cm*10cm pieces, it was immersed in the aforementioned precursor with a bismuth content of 30.7wt%. After sonication for 20min, it was stirred and set aside. 202mL of deionized water was slowly added dropwise to the bismuth precursor solution to allow the bismuth nitrate to undergo a hydrolysis reaction, forming bismuth oxyions (at this time, the bismuth content in the suspension was 10wt%). After stirring for 1h, it was taken out and dried at 60℃ to obtain the impregnated bismuth-doped pre-oxidized felt electrode material. 3) The impregnated bismuth-doped pre-oxidized felt electrode material is placed in a carbonization process and heated to 1700℃ at a heating rate of 10℃ / min, and held at this temperature for 1.5h to obtain bismuth-doped carbon felt electrode material. 4) Place the bismuth-doped carbon felt electrode material into a box furnace and heat it to 500°C at a heating rate of 5°C / min. Hold it in air for 3 hours to obtain the final carbon felt electrode.

[0039] Example 3 This embodiment provides a carbon felt electrode, which is prepared by the following method: 1) Weigh 30g of anhydrous copper sulfate (approximately 11.9g of copper) and dissolve it in 200mL of water to obtain a precursor solution with a copper content of 5.2wt%; 2) After cutting the PAN-based pre-oxidized felt into 10cm*10cm pieces, immerse it in a precursor solution with a copper content of 5.2wt% for 30min. After removing it, dry it at 60℃ to obtain the copper-doped pre-oxidized felt material after immersion. 3) The impregnated copper-doped pre-oxidized felt material is placed in a carbonization furnace and heated to 1700℃ at a heating rate of 10℃ / min, and held at this temperature for 1 hour to obtain copper-doped carbon felt electrode material. 4) Place the copper-doped carbon felt electrode material into a box furnace and heat it to 400°C at a heating rate of 5°C / min. Hold it in air for 3 hours to obtain the final carbon felt electrode.

[0040] Comparative Example 1 This comparative example demonstrates the preparation of a carbon felt electrode that is first carbonized and then doped with manganese ions, as detailed below: 1) Cut out PAN-based pre-oxidized felt material in the size of 10cm*10cm (the same material as in Example 1), put it into a carbonization furnace, raise the temperature to 1700℃ at a heating rate of 10℃ / min, and keep it at this temperature for 1h to obtain carbon felt electrode material. 2) The obtained carbon felt electrode material was placed in a box furnace and heated to 500°C at a heating rate of 5°C / min. The temperature was then maintained in air for 2 hours to obtain the activated carbon felt electrode material. 3) Weigh 10g of manganese nitrate and dissolve it in 300mL of water to obtain a precursor solution with a manganese content of 1wt%; 4) Immerse the activated carbon felt electrode material in a precursor solution containing 1 wt% manganese for 30 min, and then dry it at 60°C. 5) Place the dried carbon felt material into a box furnace, heat it to 300°C at a rate of 5°C / min under a nitrogen protective atmosphere, and hold it at that temperature for 1.5 hours to obtain a manganese-doped carbon felt electrode.

[0041] Step 5) involves heating to decompose the manganese nitrate precursor.

[0042] The electrode materials prepared in Examples 1-3 and Comparative Example 1 were assembled into single cells for battery electrical performance (current efficiency, voltage efficiency, and energy efficiency) and stability testing.

[0043] The specifications of the tested single cell are: effective active area of ​​48 cm². 2 The electrode compression ratio is 27-32%, the electrolyte is a commercial electrolyte with a total vanadium ion concentration of 1.7 mol / L, the volume of the positive and negative electrode electrolytes is 60 mL, and the diaphragm is a commercial perfluorosulfonic acid ion membrane.

[0044] The test conditions were as follows: constant current test was used, with a current density of 160 mA / cm². 2 or 200 mA / cm 2 The test results for current efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are shown in Tables 1-3, respectively.

[0045] During the cyclic stability test, Example 1 and Comparative Example 1 were compared using a constant current test with a current density of 200 mA / cm². 2 The upper limit of the charging voltage is 1.55V, the lower limit of the discharging voltage is 1.0V, the upper limit of the cyclic charging voltage is 1.55V, the lower limit of the discharging voltage is 1.0V, and the number of cycles is approximately 2000. The results are as follows: Figure 1-2 As shown. As shown in Tables 1-3, the carbon felt electrodes prepared by loading metal catalysts during the pre-oxidation stage in this invention (Examples 1-3) exhibit superior voltage and energy efficiency compared to Comparative Example 1. This may be because, during metal ion loading after carbonization and activation of the pre-oxidized felt (Comparative Example 1), the carbon felt surface has fewer and unevenly distributed defect sites. After metal ion adsorption by these defects, high-temperature annealing leads to the formation of larger and uneven metal particles, causing partial blockage of the pore structure of the carbon felt electrode, reducing the mass transfer efficiency of the reaction, increasing concentration polarization, and decreasing the voltage efficiency of the battery, ultimately resulting in low energy efficiency. In contrast, during the pre-oxidation stage of this invention, when the PAN-based pre-oxidized felt contacts and is impregnated with metal ions, the abundant nitrogen-containing groups can combine with metal ions to form coordination bonds. Therefore, the metal ions can be uniformly distributed in the carbon felt electrode, avoiding the formation of larger particles during carbonization. This ensures high electroactivity without blocking the microporous structure of the carbon felt electrode surface, achieving higher voltage efficiency and thus higher energy efficiency.

[0046] In Comparative Example 1, when the PAN-based pre-oxidized felt material is first carbonized and then impregnated with a catalyst precursor solution, the nitrogen element in the PAN-based pre-oxidized felt is basically decomposed in the form of nitrogen oxides during carbonization. Therefore, the carbonized material contains very little nitrogen element and cannot bond with metal ions. The small amount of metal ions can only be adsorbed on the defects of the carbon felt electrode in the form of electrostatic adsorption. The binding effect is not strong, which makes them easy to fall off.

[0047] In the PAN-based pre-oxidized felt material of this application, N forms coordinate bonds with metal ions, making it difficult for N to decompose during the subsequent carbonization process. Therefore, in the formed carbon felt electrode, N still forms coordinate bonds with the metal, playing the role of fixing the metal catalyst.

[0048] Depend on Figure 1-2 It can be seen that the carbon felt electrode prepared in Example 1 exhibits significantly better overall stability than the carbon felt electrode prepared in Comparative Example 1 (the VE and EE curves of Example 1 remain stable after approximately 2000 cycles, showing virtually no decrease, while the VE and EE curves of Comparative Example 1 show a significant decrease after approximately 2000 cycles). Furthermore, the voltage efficiency (VE) in the stability curve of Comparative Example 1 shows two significant fluctuations, which may be due to catalyst particles on the surface of the carbon felt electrode in Comparative Example 1 detaching from the electrode surface during battery cycling under prolonged acidic cycling conditions, causing fluctuations in voltage efficiency. The carbon felt electrode of Example 1, however, demonstrates significantly superior stability. Therefore, the carbon felt electrode of the present invention possesses both high electrode activity and high catalyst stability and cycling performance.

[0049] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0050] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method of making a carbon felt electrode, characterized by: The preparation method comprises the following steps: 1) impregnating a pre-oxidized felt into a solution or dispersion of a metal compound to obtain an impregnated pre-oxidized felt; 2) carbonizing and activating the impregnated pre-oxidized felt to obtain the carbon felt electrode; the pre-oxidized felt is a polyacrylonitrile-based pre-oxidized felt.

2. The method of claim 1, wherein: The metal compound is selected from a combination of one or more of nitrates, sulfates and chlorides of metals; the metal is selected from a combination of one or more of bismuth, manganese, copper and tungsten.

3. The method of claim 2, wherein: The metal is selected from manganese and / or copper, and in step 1), the pre-oxidized felt is impregnated into an aqueous solution of the metal compound.

4. The method of claim 2, wherein: The metal is bismuth, and in step 1), the pre-oxidized felt is impregnated into an alcoholic solution of the metal compound, and the preparation method further comprises a step of adding water dropwise to the alcoholic solution of the metal compound to hydrolyze the metal compound when the impregnation is performed.

5. The method of claim 4, wherein: The alcohol is ethanol; and / or, the mass ratio of the metal compound to the water is 1:0.07-3.0; and / or, the hydrolysis time is 0.5-2h.

6. The method of claim 1, wherein: The mass percentage concentration of the metal element in the solution or dispersion of the metal compound is 1%-10%.

7. The method of claim 1, wherein: In step 1), the impregnation time is 5-40min; and / or, in step 2), the carbonization temperature is 1500-1700℃; and / or, in step 2), the heating rate is 5-10℃ / min when the carbonization is performed; and / or, in step 2), the carbonization time is 1-2h; and / or, in step 2), the carbonization is performed in an inert atmosphere.

8. The method of claim 1, wherein: In step 2), the activation is selected from a combination of one or more of steam activation, air activation or carbon dioxide activation; and / or, in step 2), the activation temperature is 300-500℃; and / or, in step 2), the heating rate is 1-5℃ / min when the activation is performed; and / or, in step 2), the activation time is 0.5-4h.

9. A carbon felt electrode prepared by the preparation method of the carbon felt electrode according to any one of claims 1-8.

10. Use of the carbon felt electrode according to claim 9 for a flow battery.

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