A method for modifying a graphite felt electrode with flaky graphene and applications thereof

Abstract

The application discloses a method for modifying a graphite felt electrode by using flaky graphene and application. The graphite felt is treated by an electrochemical treatment method to increase the content of oxygen-containing functional groups of the graphite felt, so that the electrolyte accessibility of graphite fibers is increased; then, flaky graphene is sprayed on the surface of the graphite felt to enhance the catalytic activity of the graphite felt, so that the battery performance is improved. It can be seen from the application of the modified electrode in a flow battery that the graphite felt electrode can not only improve the reaction active sites of the electrode, but also improve the electrochemical activity of the electrode material by spraying flaky graphene material on the surface of the graphite felt matrix. Meanwhile, the method has a simple technological process, low cost and is easier to popularize in industry.

Description

Technical Field

[0001] This invention relates to the field of organic battery technology in electrochemical energy storage, and specifically to a method and application of modifying graphite felt electrodes with flake-like graphene. Background Technology

[0002] With the continuous development of new energy technologies, especially clean energy represented by solar and wind power, the volatility and randomness of power generation mean that traditional energy storage methods cannot meet the requirements. Flow battery energy storage technology is a very effective energy storage method. Its advantages, such as spatial separation of electrolyte and electrodes, lack of restriction by geographical or other external conditions, flexible configuration, and fast response speed, effectively solve the unstable characteristics of solar and wind power generation. Among them, graphite felt electrodes, as a traditional electrode material, have a high specific surface area, excellent conductivity, and strong oxidation resistance, making them a relatively ideal electrode material. However, when used as an electrode material, they still have drawbacks such as poor hydrophilicity and low electrochemical activity, which limit the improvement of battery energy conversion efficiency and power density.

[0003] To address the issues of poor hydrophilicity and electrochemical activity in graphite felt, two main methods are employed. One method involves intrinsic treatments such as heat treatment, acid treatment, electro-oxidation, ammonia oxidation, and plasma treatment to introduce functional groups (-COOH, -OH, -C=O, etc.) into the graphite felt electrode. This enhances the electrochemical activity and wettability, improving cycle performance, ion diffusion rate, and specific capacitance. Some of these modification methods can also increase the surface roughness of the graphite felt fibers, thereby increasing the number of active reaction sites and improving the electrode's electrochemical performance. The other method involves surface-decorating the graphite felt electrode with nanoparticles possessing excellent conductivity or electrocatalytic activity. These nanoparticles primarily include carbon-based and metal-based materials. Carbon-based materials, such as carbon nanotubes, graphene oxide, and biomass-based carbon materials, are used to modify the graphite felt electrode due to their high specific surface area, good stability, and low cost.

[0004] Graphene and graphene oxide have become hot topics in scientific research due to their unique electronic, optical, and mechanical properties. However, the elemental composition of graphene oxide is not fixed compared to graphene. It is generally believed that graphene oxide contains oxygen-containing functional groups such as hydroxyl (-OH), epoxy (-C(O)C-), carbonyl (-C=O), carboxyl (-COOH), and ester (-COO-). Due to the presence of these functional groups, the thickness of graphene oxide can reach (1.1±0.2) nm, far exceeding the 0.3354 nm of graphene. This presence of oxygen-containing functional groups, on the one hand, makes some physical properties of graphene oxide lower than those of graphene, but on the other hand, it endows it with good dispersibility. Graphite felt, as a key electrode material in flow batteries, is the site of ion electrode reactions, but its limited electrocatalytic activity and reaction area severely restrict the improvement of battery performance. Considering that graphene oxide has abundant oxygen-containing functional groups and good hydrophilicity, graphene oxide can be modified onto the surface of graphite felt through a simple physical adsorption method. If graphene oxide is modified on graphite felt, the conductivity of the material will be improved to a certain extent, the specific surface area of ​​the material will also increase, there will be more active sites during the entire reaction process, and the electrochemical activity of the electrode will also be enhanced. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the purpose of this invention is to provide a method and application for modifying graphite felt electrodes with flake-like graphene.

[0006] This invention protects a method for modifying graphite felt electrodes using flake-like graphene, specifically comprising the following steps:

[0007] Step 1: Take a certain amount of 98% concentrated sulfuric acid and add it dropwise to deionized water. Stir and mix evenly at room temperature and set aside. Separately, prepare a KOH solution of a certain concentration and set aside.

[0008] Step 2: Mix the two solutions prepared in Step 1 in a 1:1 ratio and use them as the electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, apply a certain voltage to the two ends of the positive and negative graphite felt electrodes, electrolyze for a certain time, and after the electrolysis is completed, take the positive and negative graphite felts, ultrasonically rinse them with deionized water, dry them, and set them aside.

[0009] Step 3: Take a certain amount of flake graphite powder and place it in DMF solution. Use an ultrasonic disperser to stir and pulverize the flake graphite powder at high speed. After the treatment is completed, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in Step 2. Then place it in an oven to dry, and you will get the graphite felt electrode modified with flake graphene.

[0010] Furthermore, in step 1, take 2-5g of 98% concentrated sulfuric acid and add it dropwise to 200mL of deionized water, stir and mix evenly at room temperature, and set aside; separately take 22.22-85.71g of KOH and prepare 200mL of 10-30% KOH solution, and set aside.

[0011] Furthermore, in step 2, the voltage applied across the positive and negative graphite felt electrodes is 8–10V, and the electrolysis time is 30s–2min.

[0012] Furthermore, in step 3, 2-6g of flake graphite powder is placed in 20ml of LDM solution; the power of the ultrasonic disperser is 300-600W, and the processing time is 10-20min.

[0013] Furthermore, in step 3, the drying temperature in the oven is 80°C, and the drying time is 10–12 hours.

[0014] The present invention also protects the application of the above-mentioned flake-shaped graphene-modified graphite felt electrode, which is used in organic aqueous phase flow batteries.

[0015] Furthermore, the positive electrode active material of the organic aqueous phase flow battery is 0.2-0.4 mol / L TEMPO, the negative electrode active material is 0.2-0.4 mol / L methyl viologen (MV), the supporting electrolyte is 1.5-2 mol / L NaCl solution, and the battery separator is an anion exchange membrane.

[0016] Compared with existing technologies, the present invention has the following beneficial effects:

[0017] The method of this invention utilizes a mixture of concentrated sulfuric acid and KOH solution as the electrolyte for electrochemical pretreatment of graphite felt. By controlling appropriate voltage and time, the surface roughness and hydrophilicity of the carbon fibers in the graphite felt electrode are effectively improved, thereby effectively activating the carbon fiber surface and facilitating the subsequent adsorption and deposition of flake graphite powder on its surface. Furthermore, flake graphite powder possesses excellent conductivity, and the use of an ultrasonic disperser to pulverize the flake graphite powder reduces its thickness and size. The reduced thickness enhances the conductivity of the flake graphite powder, while the smaller size facilitates better adsorption and deposition on the carbon fiber surface. The electrode modification method of this invention is simple, highly efficient, and produces graphite felt electrodes with excellent electrochemical activity and stable performance. It has the following advantages:

[0018] (1) The electrochemical method used in this invention pretreats the graphite felt. By controlling the solute, concentration, voltage and time of the electrolyte, the surface of the graphite felt electrode can be effectively activated to facilitate the adsorption and deposition of graphite powder. Moreover, it will not cause the carbon fiber inside the graphite felt electrode material to break, thus avoiding the disadvantage of increased internal resistance of the electrode material due to fiber breakage.

[0019] (2) The present invention uses an ultrasonic disperser to reduce the thickness and size of flake graphite powder. The process is controllable and highly operable. The flakes of the treated graphite powder are attached to the rough surface of the carbon fiber after pretreatment, which enhances the conductivity of the graphite felt and increases the specific surface area of ​​the graphite felt. This increases the number of electrochemical active sites on the electrode material surface, which is conducive to the occurrence of redox reactions on the electrode surface, thereby improving the performance of the battery.

[0020] (3) The present invention uses an electrochemical method to pretreat graphite felt and modify flake graphite powder. The process is simple, the cost is low, and it is easier to promote industrialization. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the surface of the graphite felt electrode before modification in Embodiment 1 of the present invention;

[0022] Figure 2 This is a scanning electron microscope image of the modified graphite felt electrode surface in Embodiment 1 of the present invention;

[0023] Figure 3 This is a graph showing the current-voltage cycle test curves of the graphite felt electrode before and after modification in Embodiment 1 of the present invention;

[0024] Figure 4 This is a graph showing the relationship between the specific capacity and voltage of a battery after the graphite felt electrode of the present invention is used in a flow battery and subsequently cycled. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] This invention provides a method for modifying graphite felt electrodes using flake-like graphene, with the optimization objectives of each step as follows:

[0028] (1) Take a certain amount of concentrated sulfuric acid with a concentration of 98% and add it dropwise to deionized water. Stir and mix evenly at room temperature and set aside. Separately, prepare a KOH solution with a certain concentration and set aside. After parameter optimization, take 2-5g of concentrated sulfuric acid with a concentration of 98% and add it dropwise to 200mL of deionized water. Stir and mix evenly at room temperature and set aside. Separately, take 22.22-85.71g of KOH and prepare 200mL of KOH solution with a concentration of 10-30%.

[0029] (2) Mix the two solutions prepared in step 1 in a 1:1 ratio and use them as electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, apply a certain voltage to the two ends of the positive and negative graphite felt electrodes, electrolyze for a certain time, and after the electrolysis is completed, take the positive and negative graphite felts, ultrasonically rinse them with deionized water, dry them, and set them aside.

[0030] This pretreatment step increases the roughness of the graphite felt to enhance its hydrophilicity, and also facilitates the adsorption of flake graphene powder on the rough carbon fiber surface in subsequent steps. Key control steps include electrolyte concentration, voltage applied across the electrodes, and time, ensuring that the graphite felt acquires a certain level of hydrophilicity while maintaining its original structure and properties. After parameter optimization, the voltage applied across the positive and negative graphite felt electrodes was 8–10 V, and the electrolysis time was 30 s–2 min.

[0031] (3) Take a certain amount of flake graphite powder and place it in DMF solution. Use an ultrasonic disperser to stir and crush the flake graphite powder at high speed. After the treatment is completed, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in step 2. Then place it in an oven to dry, and you will get the graphite felt electrode modified with flake graphene.

[0032] In this step, the flake-shaped graphene powder is first pulverized using an ultrasonic disperser to reduce its size, making it easier to adsorb onto the rough carbon fiber surface. Then, the dispersion is applied to both sides of the graphite felt electrode via solution spraying, ensuring full contact between the flake-shaped graphene powder and the carbon fiber. After drying, a graphite felt electrode modified with flake-shaped graphene is obtained. The key to this step is twofold: firstly, using appropriately sized flake-shaped graphene; and secondly, controlling the concentration of graphene powder in the dispersion to ensure uniform adsorption onto the carbon fiber surface. After parameter optimization, 2–6 g of flake-shaped graphene powder is placed in a 20 mL LDM solution; the ultrasonic disperser power is 300–600 W; the processing time is 10–20 min; and the drying temperature in the oven is 80℃, with a drying time of 10–12 h.

[0033] Example 2

[0034] A method for modifying graphite felt electrodes using flake-like graphene specifically includes the following steps:

[0035] Step 1: Take 4.8g of 98% concentrated sulfuric acid and add it dropwise to 200mL of deionized water. Stir and mix thoroughly at room temperature and set aside. Separately, take 85.71g of KOH and prepare 200mL of 30% KOH solution and set aside.

[0036] Step 2: Mix the two solutions prepared in Step 1 in a 1:1 ratio and use them as the electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, apply a voltage of 10V to the two ends of the positive and negative graphite felt electrodes, electrolyze for 30s, and after the electrolysis is completed, take the positive and negative graphite felts, ultrasonically rinse them with deionized water, dry them, and set them aside.

[0037] Step 3: Take 4g of flake graphite powder and place it in 20ml of DMF solution. Use an ultrasonic disperser to stir and pulverize the flake graphite powder at high speed. The ultrasonic disperser has a power of 400W and a processing time of 20min. After processing, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in Step 2, and then dry it in an oven at 80℃ for 10h to obtain the flake graphene-modified graphite felt electrode. The scanning electron microscope (SEM) image of the modified graphite felt electrode surface is shown in the appendix. Figure 2 ).

[0038] Cyclic voltammetry tests were performed on the graphite felt electrodes before and after modification, using TEMPO solution as the electrolyte. The test results are attached. Figure 3 As shown, the polarization overpotential of the modified graphite felt electrode is significantly smaller than that of the unmodified graphite felt electrode.

[0039] Using modified graphite felt as electrode materials, and TEMPO solution and MV solution as positive and negative electrolytes respectively, organic aqueous phase flow single cells were assembled. The performance of the two electrode cells was compared, as shown in the appendix. Figure 4 As shown, the specific capacity of the single cell assembled with the modified graphite felt electrode is 8.95 Ah / L, which is higher than the specific capacity of the single cell assembled with the unmodified graphite felt electrode (7.29 Ah / L).

[0040] The graphene-modified flake-like graphene electrode obtained by the above method was assembled in an organic aqueous phase flow single cell. The positive electrode active material was 0.4 mol / L TEMPO, the negative electrode active material was 0.4 mol / L methyl viologen (MV), the supporting electrolyte was a 2 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The current density was 20 mA / cm². 2 At that time, the coulombic efficiency was 96%, the voltage efficiency was 75%, and the energy efficiency was 73%.

[0041] Example 3

[0042] A method for modifying graphite felt electrodes using flake-like graphene specifically includes the following steps:

[0043] Step 1: Take 2g of 98% concentrated sulfuric acid and add it dropwise to 200mL of deionized water. Stir and mix well at room temperature and set aside. Separately, take 22.22g of KOH and prepare 200mL of 10% KOH solution and set aside.

[0044] Step 2: Mix the two solutions prepared in Step 1 in a 1:1 ratio and use them as the electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, apply a voltage of 10V to the two ends of the positive and negative graphite felt electrodes, electrolyze for 2 minutes, and after the electrolysis is completed, take the positive and negative graphite felts, ultrasonically rinse them with deionized water, dry them, and set them aside.

[0045] Step 3: Take 2g of flake graphite powder and place it in 20ml of DMF solution. Use an ultrasonic disperser to stir and pulverize the flake graphite powder at high speed. The power of the ultrasonic disperser is 300W and the processing time is 20min. After the processing is completed, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in Step 2. Then place it in an 80℃ oven to dry for 12h to obtain the flake graphene modified graphite felt electrode.

[0046] Using modified graphite felt as electrode material, organic aqueous phase flow single cells were assembled with TEMPO solution and MV solution as positive and negative electrolytes, respectively. The performance of the two electrode cells was compared. The specific capacity of the single cell assembled with the modified graphite felt electrode was 8.39 Ah / L.

[0047] The graphene-modified flake-like graphene felt electrode obtained by the above method was assembled in an organic aqueous phase flow single cell. The positive electrode active material was 0.2 mol / L TEMPO, the negative electrode active material was 0.2 mol / L methyl viologen (MV), the supporting electrolyte was a 2 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The current density was 20 mA / cm². 2 At that time, the coulombic efficiency was 94%, the voltage efficiency was 73%, and the energy efficiency was 71%.

[0048] Example 4

[0049] A method for modifying graphite felt electrodes using flake-like graphene specifically includes the following steps:

[0050] Step 1: Take 5g of 98% concentrated sulfuric acid and add it dropwise to 200mL of deionized water. Stir and mix thoroughly at room temperature. Set aside. Separately, take 85.71g of KOH and prepare 200mL of 30% KOH solution. Set aside.

[0051] Step 2: Mix the two solutions prepared in Step 1 in a 1:1 ratio and use them as the electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, apply a voltage of 8V to the two ends of the positive and negative graphite felt electrodes, electrolyze for 2 minutes, and after the electrolysis is completed, take the positive and negative graphite felt electrodes, ultrasonically rinse them with deionized water, dry them, and set them aside.

[0052] Step 3: Take 6g of flake graphite powder and place it in 20ml of DMF solution. Use an ultrasonic disperser to stir and pulverize the flake graphite powder at high speed. The power of the ultrasonic disperser is 600W and the processing time is 10min. After the processing is completed, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in Step 2. Then place it in an 80℃ oven to dry for 10h to obtain the graphite felt electrode modified with flake graphene.

[0053] Using modified graphite felt as electrode material, organic aqueous phase flow single cells were assembled with TEMPO solution and MV solution as positive and negative electrolytes, respectively. The performance of the two electrode cells was compared. The specific capacity of the single cell assembled with the modified graphite felt electrode was 8.39 Ah / L.

[0054] The graphene-modified flake-like graphene electrode obtained by the above method was assembled in an organic aqueous phase flow single cell. The positive electrode active material was 0.4 mol / L TEMPO, the negative electrode active material was 0.4 mol / L methyl viologen (MV), the supporting electrolyte was 1.5 mol / L NaCl solution, and an anion exchange membrane was selected as the battery separator. The current density was 20 mA / cm². 2 At that time, the coulombic efficiency was 93%, the voltage efficiency was 72%, and the energy efficiency was 71%.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for modifying graphite felt electrodes using flake-like graphene, characterized in that, Specifically, the steps include the following: Step 1: Take 2-5g of 98% concentrated sulfuric acid and add it dropwise to 200mL of deionized water. Stir and mix thoroughly at room temperature. Set aside. Separately, take 22.22-85.71g of KOH and prepare 200mL of 10-30% KOH solution. Set aside. Step 2: Mix the two solutions prepared in Step 1 in a 1:1 ratio and use them as the electrolyte for electrochemical pretreatment of graphite felt; take two graphite felts as positive and negative electrodes respectively, and apply a voltage of 8-10V to the two ends of the positive and negative graphite felt electrodes, electrolyze for 30s-2min. After electrolysis is completed, take the positive and negative graphite felts and ultrasonically rinse them with deionized water, and dry them to obtain graphite felt with roughened surface and effective activation. The carbon fiber surface of this graphite felt has improved hydrophilicity and is ready for use. Step 3: Take 2-6g of flake graphite powder and place it in 20mL of DMF solution. Use an ultrasonic disperser at a power of 300-600W to stir and pulverize the flake graphite powder at high speed for 10-20 minutes to reduce the thickness and size of the flake graphite powder. After the treatment, take the DMF dispersion of the flake graphene powder and place it in a spray bottle. Spray it evenly on both sides of the graphite felt treated in Step 2, and then place it in an oven to dry, thus obtaining the graphite felt electrode modified with flake graphene.

2. The method for modifying a graphite felt electrode using flake-like graphene according to claim 1, characterized in that, In step 3, the drying temperature in the oven is 80℃, and the drying time is 10-12 hours.

3. An application of graphite felt electrodes modified with flake-like graphene, characterized in that, The graphene-modified flake-shaped graphene-modified graphite felt electrode is prepared by the method described in claim 1 or 2, and the graphene-modified flake-shaped graphene-modified graphite felt electrode is used in an organic aqueous phase flow battery.

4. The application of a graphite felt electrode modified with flake-like graphene according to claim 3, characterized in that, The positive electrode active material of the organic aqueous phase flow battery is 0.2-0.4 mol / L LTEMPO, the negative electrode active material is 0.2-0.4 mol / L methyl viologen MV, the supporting electrolyte is 1.5-2 mol / L NaCl solution, and the battery separator is an anion exchange membrane.

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