A dry gel composite graphite felt electrode and a preparation method and application thereof

Abstract

The application relates to the technical field of electrodes of all-vanadium redox flow batteries, and discloses a dry gel composite graphite felt electrode and a preparation method and application thereof. Taurine is used to modify MOF-808, the MOF-808 modified graphite felt is prepared, MnO2 is in-situ synthesized on the MOF-808 modified graphite felt through a gel impregnation method, three-dimensional hydrogel is formed by relying on MnO2 nanocolloid + silicate ion crosslinking, the graphite felt fiber is in-situ coated, and the dry gel composite graphite felt electrode is obtained through calcination. The MOF-808 is modified by taurine, the electrocatalytic activity of the MOF-808 is improved, the carbon on the graphite felt is etched by KMnO4, the surface of the etched graphite felt forms a porous and defect structure, more reaction active sites are generated, the silicon acid molecules are dehydrated and condensed with each other, a continuous silicon-oxygen inorganic network is formed, the MnO2 colloid is tightly wrapped, and the dry gel composite graphite felt electrode has conductivity, redox activity and ion transmission channels.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode technology, and in particular to a dry gel composite graphite felt electrode, its preparation method, and its application. Background Technology

[0002] In recent years, vanadium redox flow batteries have become the focus of new energy storage batteries. They have advantages such as independent capacity, high power, long life, deep discharge capability and no emission pollution. They can be used as supporting energy storage devices in the power generation process of renewable energy sources such as wind and solar energy, and can also play a role in frequency regulation and peak shaving in the power grid system. They are suitable for large-scale electrochemical energy storage devices.

[0003] Currently, the most electrically superior electrode materials used in vanadium redox flow batteries are porous carbon three-dimensional electrode materials such as graphite felt or carbon felt. Made from woven carbon fibers, these materials possess excellent mechanical strength, and their actual specific surface area is far greater than their geometric surface area, providing a large electrochemical reaction area. Combined with their good chemical stability and conductivity, this makes them a research hotspot for vanadium redox flow battery electrode materials. However, graphite felt also has some drawbacks, particularly low energy efficiency due to low electrode material activity and high contact resistance between the electrode and the plate. To address these issues, scientists have been seeking methods to improve battery energy efficiency and design a simple yet high-performance electrode. Furthermore, employing high-performance electrode materials and improving electrode structure are effective ways to reduce the investment cost of vanadium redox flow batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a dry gel composite graphite felt electrode, its preparation method, and its application.

[0005] In a first aspect, a method for preparing a dry gel composite graphite felt electrode is disclosed, comprising the following steps: Step S1: Mix MOF-808 and taurine solution evenly, heat and react. After the reaction is complete, centrifuge and wash to obtain taurine-modified MOF-808. Step S2: Disperse the taurine-modified MOF-808 in a mixture of anhydrous ethanol and Nafion solution, ultrasonically treat it, coat it on the surface of graphite felt and dry it to obtain MOF-808 modified graphite felt. Step S3: Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, carry out a water bath reaction, wash and dry to obtain the precursor graphite felt. Step S4: The precursor graphite felt is calcined under a protective atmosphere to obtain a dry gel composite graphite felt electrode.

[0006] In one implementation, in step S1: The concentration of the taurine solution is 20~50g / L; The mass ratio of MOF-808 to taurine in the taurine solution is 1:1.

[0007] Introducing sulfonic acid groups onto the surface of MOF-808 can act as VO 2+ / VO2 + and V 2+ / V 3+ The active sites of redox reactions accelerate the diffusion and mass transfer of active substances on the surface of electrode materials, thereby improving the reactivity of the electrode.

[0008] In one implementation, in step S1: The heating reaction is carried out at a temperature of 60~100℃ for a time of 1~5h; The centrifuge speed is 8000 r / min; The washing process involves washing the precipitate with deionized water until the washing liquid is neutral.

[0009] In one implementation, in step S2: The mass ratio of the taurine-modified MOF-808, the Nafion solution, and the anhydrous ethanol is 1:1:(100~500); The Nafion solution has a mass concentration of 5%; The ultrasonic treatment frequency is 50~100Hz, and the time is 30~60min; The drying temperature is 60~100℃, and the time is 8~24h.

[0010] In one implementation, in step S3: The concentration of potassium permanganate in the mixed sol is 0.01~0.05 mol / L; The concentration of manganese sulfate in the mixed sol is 0.02~0.1 mol / L; The concentration of calcium silicate in the mixed sol is 0.01~0.05 mol / L; The molar ratio of potassium permanganate, manganese sulfate, and calcium silicate in the mixed solution is 1:2:1.

[0011] KMnO4 can etch carbon from graphite felt to generate MnO2, which then grows in situ on the graphite felt surface. The etched surface forms a porous and defective structure, increasing the specific surface area and providing more reactive sites. Silicic acid molecules undergo dehydration and condensation to form a continuous silicon-oxygen inorganic network, firmly encapsulating the MnO2 colloid. This results in a three-dimensional structure of MnO2 nanoparticles + silica-silicon-oxygen framework, possessing conductivity, redox activity, and ion transport channels.

[0012] In one implementation, in step S3: The water bath reaction is carried out at a temperature of 30-40°C for 2-5 hours. The drying temperature is 40~60℃, and the time is 12~24.

[0013] In one implementation, in step S4: The calcination conditions are as follows: under a nitrogen atmosphere, the temperature is increased to 250-350°C at a heating rate of 5-10°C / min, and held for 2-4 hours.

[0014] Secondly, a dry gel composite graphite felt electrode is disclosed, which is prepared by the preparation method described above.

[0015] In one embodiment, the dry gel composite graphite felt electrode comprises a graphite felt and a dry gel layer loaded on the surface of the graphite felt; wherein, The dry gel layer comprises taurine-modified MOF-808, manganese dioxide nanoparticles, and a silicon-oxygen inorganic network.

[0016] MnO2 was generated in situ on MOF-808 modified graphite felt, and a three-dimensional hydrogel was formed by cross-linking of MnO2 nanocolloids and silicate ions. The hydrogel was then used to in situ coat the graphite felt fibers and calcined to obtain GF@MnO2-SiO3 dry gel composite graphite felt, which further improved the conductivity of the graphite felt.

[0017] Thirdly, an application of a dry gel composite graphite felt electrode is disclosed, wherein the dry gel composite graphite felt electrode prepared by the above-described preparation method or the dry gel composite graphite felt electrode described above is applied to vanadium batteries; wherein... The contact resistance of the dry gel composite graphite felt electrode in the vanadium battery is no higher than 35.2 mΩ; The energy efficiency of the dry gel composite graphite felt electrode in the vanadium battery is not less than 89.1%; The voltage efficiency of the dry gel composite graphite felt electrode in the vanadium battery is not less than 91.9%.

[0018] The beneficial effects of this invention are: 1. This invention modifies MOF-808 with taurine, introducing sulfonic acid groups onto the surface of MOF-808. The hydrophilic sulfonic acid groups on the surface of the graphite felt can act as VO 2+ / VO2 + and V 2+ / V 3+ The active sites of redox reactions accelerate the diffusion and mass transfer of active substances on the surface of graphite felt, thereby improving the reactivity of graphite felt.

[0019] 2. In this invention, KMnO4 is used to etch carbon on graphite felt to generate MnO2, which is then grown in situ on the surface of graphite felt. After etching, the surface of graphite felt forms a porous and defective structure, which increases the specific surface area and thus provides more reactive sites.

[0020] 3. In this invention, silicic acid molecules undergo dehydration and condensation to form a continuous silicon-oxygen inorganic network, which firmly encapsulates the MnO2 colloid, forming a three-dimensional structure of MnO2 nanoparticles + silicic acid-silicon-oxygen framework. This structure possesses conductivity, redox activity, and ion transport channels, further improving the conductivity of the graphite felt. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of a method for preparing a dry gel composite graphite felt electrode according to the present invention. Detailed Implementation

[0022] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0023] See Figure 1 A method for preparing a dry gel composite graphite felt electrode includes the following steps: Step S1: Mix MOF-808 and a taurine solution with a concentration of 20-50 g / L at a mass ratio of 1:1 until homogeneous. Place the mixture in a constant temperature magnetic stirrer and heat at 60-100℃ for 1-5 hours. After the reaction is complete, centrifuge at 8000 r / min. Then wash the precipitate with deionized water until the washing liquid is neutral to obtain taurine-modified MOF-808.

[0024] Step S2: Add the taurine-modified MOF-808 to anhydrous ethanol solution, then add 5% Nafion solution, and ultrasonically disperse at a frequency of 50~100Hz for 30~60min. Coat the graphite felt surface evenly with a dropper, and dry in a constant temperature oven at 60~100℃ for 8~24h to obtain MOF-808 modified graphite felt; the mass ratio of the modified MOF-808, the Nafion solution and the anhydrous ethanol is 1:1:(100~500).

[0025] Step S3: Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate, and calcium silicate, and bathe it in a low-temperature water bath at 30-40℃ for 2-5 hours. After the reaction, remove the graphite felt, rinse it with deionized water, and vacuum dry it at 40-60℃ for 12-24 hours to obtain GF@MOF-MnO2-SiO3 inorganic hydrogel graphite felt, i.e., precursor graphite felt. The concentration of potassium permanganate in the mixed sol is 0.01-0.05 mol / L; the concentration of manganese sulfate in the mixed sol is 0.02-0.1 mol / L; the concentration of calcium silicate in the mixed sol is 0.01-0.05 mol / L; and the concentration ratio of potassium permanganate, manganese sulfate, and calcium silicate in the mixed solution is 1:2:1.

[0026] Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode in a tube furnace under a nitrogen atmosphere and heat it to 250-350℃ at a heating rate of 5-10℃ / min. Hold the temperature for 2-4 hours to obtain a dry gel composite graphite felt electrode.

[0027] Example 1: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 20 g / L, add 2 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 60 °C for 5 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 100g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 50Hz for 60min, then evenly coat the graphite felt surface with a dropper, and dry in a 60℃ constant temperature oven for 24h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.02 mol / L manganese sulfate solution, add 0.58 g of calcium silicate and stir to form a suspension, then add 0.79 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 30°C in a low-temperature water bath for 5 h, then remove the graphite felt and rinse it with deionized water. Dry it at 40°C under vacuum for 24 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 250°C at a heating rate of 5°C / min and hold it for 4 hours to obtain a dry gel composite graphite felt electrode.

[0028] Example 2: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 30 g / L, add 3 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 70 °C for 4 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 200g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 60Hz for 40min, then evenly coat the graphite felt surface with a dropper, and dry in a 70℃ constant temperature oven for 20h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.04 mol / L manganese sulfate solution, add 1.16 g of calcium silicate and stir to form a suspension, then add 1.58 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 35°C in a low-temperature water bath for 4 h, then remove the graphite felt and rinse it with deionized water. Dry it under vacuum at 50°C for 16 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 300°C at a heating rate of 6°C / min and hold it for 3 hours to obtain a dry gel composite graphite felt electrode.

[0029] Example 3: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 40 g / L, add 4 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 80℃ for 3 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 300g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 70Hz for 50min, then evenly coat the graphite felt surface with a dropper, and dry in an 80℃ constant temperature oven for 16h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.06 mol / L manganese sulfate solution, add 1.74 g of calcium silicate and stir to form a suspension, then add 2.37 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate. After reacting in a water bath at 40°C for 3 h, remove the graphite felt and rinse it with deionized water. Dry it in a vacuum at 60°C for 12 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 350°C at a heating rate of 7°C / min and hold it at that temperature for 2 hours to obtain a dry gel composite graphite felt electrode.

[0030] Example 4: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 50 g / L, add 5 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 90 °C for 2 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 400g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 80Hz for 30min, then evenly coat the graphite felt surface with a dropper, and dry in a 90℃ constant temperature oven for 12h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.08 mol / L manganese sulfate solution, add 2.32 g of calcium silicate and stir to form a suspension, then add 3.16 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate. After reacting in a water bath at 30°C for 2 h, remove the graphite felt and rinse it with deionized water. Dry it under vacuum at 40°C for 24 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 280℃ at a heating rate of 8℃ / min and hold it for 3.5h to obtain the dry gel composite graphite felt electrode.

[0031] Example 5: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 25 g / L. Add 2.5 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 100℃ for 1 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 500g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 90Hz for 30min, then evenly coat the graphite felt surface with a dropper, and dry in a 100℃ constant temperature oven for 84h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.1 mol / L manganese sulfate solution, add 2.9 g of calcium silicate and stir to form a suspension, then add 3.95 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 35°C in a low-temperature water bath for 5 h, then remove the graphite felt and rinse it with deionized water. Dry it under vacuum at 50°C for 16 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 320℃ at a heating rate of 9℃ / min and hold it for 2.5h to obtain the dry gel composite graphite felt electrode.

[0032] Example 6: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 35 g / L. Add 3.5 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 60 °C for 5 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 100g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 100Hz for 30min, then evenly coat the graphite felt surface with a dropper, and dry in a 60℃ constant temperature oven for 24h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.02 mol / L manganese sulfate solution, add 0.58 g of calcium silicate and stir to form a suspension, then add 0.79 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate. After reacting in a water bath at 40°C for 4 h, remove the graphite felt and rinse it with deionized water. Dry it in a vacuum at 60°C for 12 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 250℃ at a rate of 10℃ / min and hold it for 4 hours to obtain a dry gel composite graphite felt electrode.

[0033] Example 7: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 45 g / L. Add 4.5 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 70 °C for 4 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 200g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 50Hz for 50min, then evenly coat the graphite felt surface with a dropper, and dry in a 70℃ constant temperature oven for 20h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.04 mol / L manganese sulfate solution, add 1.16 g of calcium silicate and stir to form a suspension, then add 1.58 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 30°C in a low-temperature water bath for 3 h, then remove the graphite felt and rinse it with deionized water. Dry it at 45°C under vacuum for 15 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 300℃ at a rate of 5℃ / min and hold it for 3 hours to obtain a dry gel composite graphite felt electrode.

[0034] Example 8: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 50 g / L, add 5 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 80℃ for 3 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 300g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 70Hz for 60min, then evenly coat the graphite felt surface with a dropper, and dry in an 80℃ constant temperature oven for 16h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.03 mol / L manganese sulfate solution, add 1.74 g of calcium silicate and stir to form a suspension, then add 2.37 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 35°C in a low-temperature water bath for 2 h, then remove the graphite felt and rinse it with deionized water. Dry it under vacuum at 55°C for 15 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 350℃ at a heating rate of 6℃ / min and hold it for 2 hours to obtain a dry gel composite graphite felt electrode.

[0035] Example 9: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 30 g / L, add 3 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer at 90℃ for 2 h. After the reaction is complete, centrifuge at 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 400g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 80Hz for 40min, then evenly coat the graphite felt surface with a dropper, and dry in a 90℃ constant temperature oven for 12h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.08 mol / L manganese sulfate solution, add 2.32 g of calcium silicate and stir to form a suspension, then add 3.16 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 40℃ in a low-temperature water bath for 2.5 h, then remove the graphite felt and rinse it with deionized water. Dry it at 45℃ under vacuum for 18 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode in a tube furnace and calcine it under nitrogen. Heat the electrode to 280℃ at a heating rate of 7℃ / min and hold it for 3.5h to obtain the dry gel composite graphite felt electrode.

[0036] Example 10: The following technical solution is adopted. Step S1: Prepare 100 mL of taurine solution with a concentration of 20 g / L, add 2 g of MOF-808 to the solution and mix well. Then heat the mixture in a constant temperature magnetic stirrer, set the heating temperature to 100℃ and the reaction time to 1 h. After the reaction is completed, centrifuge at a speed of 8000 r / min. Wash MOF-808 with deionized water until the washing liquid is neutral to obtain organic acid modified MOF-808. Step S2: Add 1g of taurine-modified MOF-808 to 1500g of anhydrous ethanol solution, then add 1g of 5% Nafion solution, sonicate at 100Hz for 45min, then evenly coat the graphite felt surface with a dropper, and dry in a 100℃ constant temperature oven for 8h to obtain MOF-808 modified graphite felt. Step S3: Prepare 500 ml of 0.1 mol / L manganese sulfate solution, add 2.9 g of calcium silicate and stir to form a suspension, then add 3.95 g of potassium permanganate. Immerse the MOF-808 modified graphite felt in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate, react at 30°C in a low-temperature water bath for 2.5 h, then remove the graphite felt and rinse it with deionized water. Dry it under vacuum at 55°C for 18 h to obtain the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode. Step S4: Place the GF@MOF-MnO2-SiO3 inorganic hydrogel electrode into a tube furnace and calcine it under nitrogen. Heat the electrode to 320℃ at a heating rate of 10℃ / min and hold it for 2.5h to obtain the dry gel composite graphite felt electrode.

[0037] Comparative Example 1: The following technical solution is adopted. The only difference between the preparation process of this comparative example and Example 1 is that MOF-808 was not modified with taurine.

[0038] Comparative Example 2: The following technical solution is adopted. The only difference between the preparation process of this comparative example and that of Example 1 is that MnO2 was not synthesized in situ on the MOF-808 modified graphite felt using the gel impregnation method.

[0039] Comparative Example 3: The following technical solution is adopted. The only difference between the preparation process of this comparative example and that of Example 1 is that calcium silicate was not added to the graphite felt impregnation sol.

[0040] Comparative Example 4: The following technical solution is adopted. This comparative example is a blank control group, that is, using untreated blank graphite felt electrodes.

[0041] Contact resistance test: The graphite felt electrodes obtained in Examples 1-10 and Comparative Examples 1-4 were cut into 3cm*3cm sizes, and copper plates were placed at both ends. A low resistance tester was used to clamp the electrodes at both ends and the resistance value was tested under 20% deformation. Contact resistance = resistance value - material bulk resistance.

[0042] Battery performance testing: The graphite felt electrodes prepared in Examples 1-10 and Comparative Examples 1-4 were respectively assembled into vanadium battery stacks, and charge-discharge cycle tests were conducted under the same test conditions. The coulombic efficiency, voltage efficiency, and energy efficiency were recorded. The test results are shown in Table 1. Table 1. Battery performance test results using the assembled stacks of the examples and comparative examples.

[0043] Therefore, as can be seen from the comparison between Example 1 and Comparative Example 1, due to the taurine modification of MOF-808, sulfonic acid groups are introduced onto the surface of MOF-808. The hydrophilic sulfonic acid groups on the surface of the graphite felt can act as VO 2+ / VO2 + and V 2+ / V 3+ The active sites of the oxidative epoxy reaction accelerate the diffusion and mass transfer of active substances on the graphite felt surface, thereby improving the reactivity of the graphite felt. However, in Comparative Example 1, MOF-808 was not modified with taurine, so the voltage efficiency decreased slightly. Comparing Example 1 and Comparative Example 2, it can be seen that KMnO4 etches carbon on the graphite felt to generate MnO2, which grows in situ on the graphite felt surface. After etching, the graphite felt surface forms a porous and defective structure, increasing the specific surface area and thus providing more reactive sites, resulting in better stack performance. Comparing Example 1 and Comparative Example 3, it can be seen that adding calcium silicate to the graphite felt impregnation sol causes silica molecules to dehydrate and condense, forming a continuous silicon-oxygen inorganic network that firmly encapsulates the MnO2 colloid, forming a three-dimensional structure of MnO2 nanoparticles + silicate-siloxane framework. This structure combines conductivity, redox activity, and ion transport channels, further improving the conductivity of the graphite felt. In Comparative Example 3, the absence of calcium silicate caused the MnO2 colloid to detach, affecting the voltage efficiency.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dry gel composite graphite felt electrode, characterized in that, Includes the following steps: Step S1: Mix MOF-808 and taurine solution evenly, heat and react, centrifuge and wash after the reaction to obtain taurine-modified MOF-808; the heating reaction temperature is 60~100℃ and the time is 1~5h. Step S2: Disperse the taurine-modified MOF-808 in a mixture of anhydrous ethanol and Nafion solution, ultrasonically treat it, coat it on the surface of graphite felt and dry it to obtain MOF-808 modified graphite felt. Step S3: The MOF-808 modified graphite felt is immersed in a mixed sol of potassium permanganate, manganese sulfate and calcium silicate for a water bath reaction, then washed and dried to obtain the precursor graphite felt; the water bath reaction temperature is 30~40℃ and the time is 2~5h. Step S4: The precursor graphite felt is calcined under a protective atmosphere to obtain a dry gel composite graphite felt electrode; the calcination conditions are: under a nitrogen atmosphere, the temperature is increased to 250-350℃ at a heating rate of 5-10℃ / min, and held for 2-4 hours.

2. The preparation method according to claim 1, characterized in that, In step S1: The concentration of the taurine solution is 20~50g / L; The mass ratio of MOF-808 to taurine in the taurine solution is 1:

1.

3. The preparation method according to claim 1, characterized in that, In step S1: The washing process involves washing the precipitate with deionized water until the washing liquid is neutral.

4. The preparation method according to claim 1, characterized in that, In step S2: The mass ratio of the taurine-modified MOF-808, the Nafion solution, and the anhydrous ethanol is 1:1:(100~500); The Nafion solution has a mass concentration of 5%; The ultrasonic treatment frequency is 50~100Hz, and the time is 30~60min; The drying temperature is 60~100℃, and the time is 8~24h.

5. The preparation method according to claim 1, characterized in that, In step S3: The concentration of potassium permanganate in the mixed sol is 0.01~0.05 mol / L; The concentration of manganese sulfate in the mixed sol is 0.02~0.1 mol / L; The concentration of calcium silicate in the mixed sol is 0.01~0.05 mol / L; The molar ratio of potassium permanganate, manganese sulfate, and calcium silicate in the mixed sol is 1:2:

1.

6. The preparation method according to claim 1, characterized in that, In step S3: The drying temperature is 40~60℃, and the time is 12~24h.

7. A dry gel composite graphite felt electrode, characterized in that, The dry gel composite graphite felt electrode is prepared using the preparation method described in any one of claims 1 to 6.

8. The dry gel composite graphite felt electrode as described in claim 7, characterized in that, The dry gel composite graphite felt electrode consists of a graphite felt and a dry gel layer loaded on the surface of the graphite felt; wherein, The dry gel layer comprises taurine-modified MOF-808, manganese dioxide nanoparticles, and a silicon-oxygen inorganic network.

9. An application of a dry gel composite graphite felt electrode, characterized in that, The dry gel composite graphite felt electrode prepared by the preparation method according to any one of claims 1 to 6, or the dry gel composite graphite felt electrode according to any one of claims 7 to 8, is applied to a vanadium battery; wherein, The contact resistance of the dry gel composite graphite felt electrode in the vanadium battery is no higher than 35.2 mΩ; The energy efficiency of the dry gel composite graphite felt electrode in the vanadium battery is not less than 89.1%; The voltage efficiency of the dry gel composite graphite felt electrode in the vanadium battery is not less than 91.9%.

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