Homogeneous graphene oxide modified graphite felt and preparation method thereof

Abstract

The invention discloses a preparation method of a homogeneous graphene oxide modified graphite felt. According to the preparation method disclosed by the invention, a highly uniformly dispersed graphene oxide dispersion liquid is prepared by adopting a staged ultrasonic-heat treatment mode, and the bonding strength between graphene oxide and a graphite felt is improved through a Nafion solution; and immersing the pretreated graphite felt to prepare the homogeneous graphene oxide modified graphite felt electrode material. The graphene oxide modified graphite felt electrode material prepared by the invention has the advantages of high charge-discharge energy efficiency, high voltage efficiency, long cycle life and the like when being used for an ICRFB battery; meanwhile, the raw materials are easy to obtain, the cost is low, and the method is suitable for large-scale industrial development.

Description

Technical Field

[0001] This invention relates to the field of electrode materials for iron-chromium redox flow batteries (ICRFB), specifically to a homogeneous graphene oxide modified graphite felt electrode material and its preparation method. Background Technology

[0002] With rapid global population growth and economic development, the energy crisis is becoming increasingly severe. Developing and utilizing green energy is an effective way to solve this crisis. Renewable and clean energy sources such as wind and solar power are currently hot topics in scientific research and industrial development due to their environmental friendliness and sustainability. However, factors such as wind speed, solar radiation intensity, and time of day can cause unstable and intermittent unsteady power output during power generation, posing significant risks to the quality and safe operation of the power grid. Therefore, there is an urgent need to develop efficient, environmentally friendly, low-cost, and safe large-scale energy storage technologies. Among existing large-scale energy storage technologies, redox flow batteries, or flow batteries for short, have become an emerging high-efficiency energy-saving technology due to their advantages such as high safety, long cycle life, flexible design, and low maintenance costs.

[0003] Flow batteries utilize soluble active materials in various oxidation states to store and release chemical energy through reversible redox reactions. One of the most important characteristics of flow batteries is their ability to independently expand both the power source (electrochemical cell) and the electrochemical energy storage component (external storage tank). Iron-chromium flow batteries possess advantages such as high efficiency, wide operating temperature range, modular power, customizable capacity, high safety, environmental friendliness, and low cost, making them a highly promising large-scale energy storage technology. Among them, iron-chromium flow batteries, as one of the earliest flow battery technologies, use inexpensive metallic iron and chromium ions as active materials, and are expected to become cost-effective energy storage equipment. However, in practical applications, they encounter challenges related to Cr... 3+ Low electrochemical activity and susceptibility to hydrogen evolution reactions are problems that limit the widespread application of flow batteries. Current flow battery technology, due to performance and cost issues, is far from meeting the stringent requirements of commercialization. Therefore, developing cheaper and higher-performance flow batteries has become the primary task for flow battery researchers.

[0004] Electrodes, as the site of battery reactions, play a crucial role in the degree and rate of electrolyte reaction, and are the core determinants of battery energy conversion efficiency and power density. Graphite felt is the most commonly used electrode material in iron-chromium batteries, characterized by its wide availability, good chemical stability, good conductivity, rich surface states, and diverse structures. It has long been an ideal electrode material for various electrochemical energy storage batteries, but its electrochemical activity and hydrophilicity still cannot meet the requirements of flow batteries.

[0005] Graphene oxide, with its abundant oxygen-containing groups on its surface and edges, is easily modified and functionalized, exhibiting good chemical stability. When dispersed in solution, graphene oxide can be mixed with polymer monomers to form composite material systems, enabling multifunctional composites that not only possess excellent mechanical and electrical properties but also superior processing performance, thus broadening the application areas of composite materials. Currently, researchers mainly use a hydrothermal method to modify graphene felt with graphene oxide. However, this method is prone to agglomeration of graphene oxide into small particles due to electrostatic interactions during processing, resulting in insufficient exposure of the active sites of graphene oxide and affecting the performance of the modified electrode. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a homogeneous graphene oxide-modified graphite felt material and its preparation method. This invention solves the problem of graphene oxide agglomeration into small particles caused by existing modification methods, thereby improving the utilization rate of graphene oxide and enhancing the electrochemical activity of the graphite felt. Using this method, a low-cost, high-performance composite graphite felt material can be obtained, which has advantages such as a large number of active sites, high electrochemical activity, and good stability in ICRFB battery applications.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing homogeneous graphene oxide modified graphite felt.

[0008] Specifically, the preparation method of the homogeneous graphene oxide modified graphite felt of the present invention includes the following steps:

[0009] (1) Clean the graphite felt with organic solvent and deionized water, and then dry it;

[0010] (2) The cleaned graphite felt obtained in step (1) is subjected to heat pretreatment to increase the oxygen-containing functional groups therein.

[0011] (3) Weigh out graphene oxide and add it to a mixed solution consisting of isopropanol, deionized water and Nafion. Disperse the solution by sonication to obtain a graphene oxide dispersion.

[0012] (4) Impregnate the graphite felt after heat pretreatment in step (2) with the graphene oxide dispersion obtained in step (3), wherein ultrasonication is performed during the impregnation process and then the material is left to stand.

[0013] (5) Repeat step (4) 0 to 5 times;

[0014] (6) The graphite felt obtained after the last ultrasonic impregnation treatment is dried to obtain a homogeneous graphite felt loaded with graphene oxide.

[0015] Furthermore, the cleaning in step (1) is a standard procedure in the art. The cleaning process typically includes organic solvent cleaning and deionized water cleaning. The organic solvent is selected from one or more of ethanol, acetone, trichloroethylene, dichloromethane, and carbon tetrachloride. During organic solvent cleaning, ultrasonic treatment is preferably performed simultaneously. After immersion in deionized water, ultrasonic treatment is preferably performed to remove organic solutions and inorganic impurities.

[0016] Furthermore, the heat pretreatment in step (2) employs an operating procedure well known to those skilled in the art. For example, the conditions for heat pretreatment are generally: a treatment temperature of 400–600°C and a treatment time of 3–6 hours.

[0017] Furthermore, the mixed solution in step (3) consists of isopropanol, deionized water, and Nafion. Preferably, in the mixed solution, the volume fraction of isopropanol is 5%-25%, the volume fraction of Nafion is 0.5%-5%, and the remainder is deionized water.

[0018] Furthermore, the graphene oxide is a general-purpose sheet-like graphene, a highly conductive graphene, or a composite material of various types of graphene.

[0019] Furthermore, the concentration of graphene oxide in the dispersion obtained in step (4) is generally 0.5-5 mg / mL, the concentration of isopropanol is 10-20 mg / mL, and the concentration of Nafion is 0.04-0.13 mg / mL. The ultrasonic impregnation operation is as follows: ultrasonic treatment is performed at a temperature of 20-60℃ for 1-6 hours, followed by static soaking for 1-12 hours.

[0020] Furthermore, in step (5), it is preferable to repeat step (4) 1-5 times. Specifically, the ultrasonic impregnation operation in step (5) is as follows: ultrasonic treatment is performed for 2-4 hours each time at a temperature of 40-50°C, followed by static soaking for 3-5 hours.

[0021] Furthermore, the drying process described in step (6) employs conventional procedures in the art. The drying conditions are as follows: the drying temperature is generally 60–80°C, and the drying time is generally 8–12 hours.

[0022] According to a second objective of the present invention, a second aspect of the present invention also provides a homogeneous graphene oxide modified graphite felt, which is prepared by the method described above.

[0023] Furthermore, the homogeneous graphene oxide-supported graphite felt of the present invention can be used to manufacture electrode materials in the field of iron-chromium redox flow batteries.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention uses commercial graphite felt, graphene oxide, deionized water, etc. as raw materials and employs a staged ultrasonic-thermal treatment method to prepare a homogeneous graphene oxide modified graphite felt electrode material. This composite electrode material has advantages such as high conductivity, large specific surface area, good catalytic performance, good stability, and high electrochemical catalytic activity.

[0026] 2. The key to the method of the present invention lies in the process of strengthening the modification with Nafion solution. Nafion has a large number of sulfonic acid groups, which can crosslink with oxygen-containing functional groups on graphene oxide and graphite felt, acting as a binder to improve the bonding strength, while also having good conductivity.

[0027] 3. The key to this invention lies in the use of a novel multi-frequency ultrasonic-variable-temperature heat treatment method. Heating accelerates the adhesion of graphene oxide, while ultrasound allows for the re-attachment of weak sites. Each ultrasonic-heat treatment increases the ultrasonic frequency and heat treatment temperature, gradually increasing the loading of graphene oxide and making its distribution more uniform. This repeated process can greatly increase the number of active sites and improve the activity of the electrode.

[0028] 4. This invention uses commercially available graphene as a raw material and employs a staged ultrasonic-thermal treatment method to prepare a highly uniformly dispersed graphene oxide dispersion. Nafion solution is used to enhance the bonding strength between the graphene oxide and the graphite felt. The pretreated graphite felt is then immersed in the dispersion to prepare a homogeneous graphene oxide-loaded graphite felt. This improves the conductivity, effective active area, and electrochemical catalytic performance of the graphite felt. Therefore, compared to a single ICRFB battery containing only commercially available graphene oxide, a single ICRFB battery containing homogeneously loaded graphene oxide exhibits advantages such as higher charge-discharge energy efficiency, higher voltage efficiency, and longer cycle life. By utilizing the high conductivity of graphene and controlling the duration of specific stages of ultrasonic-thermal treatment to regulate the loading and dispersion of the graphene oxide, an electrode material with optimal catalytic performance can be prepared. This method uses readily available and inexpensive raw materials, making it suitable for large-scale industrialization and promising the development of a low-cost, high-performance commercially available graphene oxide felt for iron-chromium batteries. Attached Figure Description

[0029] Figure 1 Comparative analysis of infrared spectra of graphite felt, heat-pretreated graphite felt, and homogeneous graphene oxide-supported graphite felt prepared in Example 4.

[0030] Figure 2 Cyclic voltammetry curves for graphite felt, heat-pretreated graphite felt, and homogeneous graphene oxide-supported graphite felt prepared in Example 4.

[0031] Figure 3EIS curves of graphite felt, heat-pretreated graphite felt, and graphite felt electrodes with different graphene oxide loadings in Examples 2, 4, and 5.

[0032] Figure 4 The graphite felt, the heat-pretreated graphite felt, and the homogeneous graphene oxide-supported graphite felt electrode prepared in Example 4 (1.5 mg·cm⁻¹) are examples of graphite felt electrodes. -2 The charge and discharge curves of ).

[0033] Figure 5 The homogeneous graphene oxide-loaded graphene felt electrode (1.5 mg·cm⁻¹) prepared in Example 4 -2 The efficiency curve of ).

[0034] Figure 6 The graphite felt, the heat-pretreated graphite felt, and the homogeneous graphene oxide-supported graphite felt electrode prepared in Example 4 (1.5 mg·cm⁻¹) are examples of graphite felt electrodes. -2 The energy efficiency curve of ). Detailed Implementation

[0035] The present invention will be described in detail below through specific embodiments. However, the purpose and use of these exemplary embodiments are only for illustrating the present invention and do not constitute any limitation on the actual protection scope of the present invention, nor are they intended to limit the protection scope of the present invention to these embodiments.

[0036] Example 1:

[0037] 10g of graphite felt was soaked in a 95% ethanol solution and then sonicated for 1 hour. It was then repeatedly rinsed and soaked in deionized water, followed by sonication for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt was dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 3 hours at a heating rate of 5℃ / min.

[0038] Weigh 1 mg of graphene oxide and add 1.5 mL of isopropanol, 6 mL of deionized water, and 0.1 mL of a 5% Nafion solution. Sonicate the mixture for 2 hours to ensure uniform dispersion. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: sonicate at 40°C for 2 hours, followed by soaking for 10 hours. Finally, place the finished graphene felt in a vacuum oven and dry at 60°C for 24 hours to obtain homogeneous graphene oxide-modified graphene felt, which is then packaged and stored.

[0039] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2Cyclic tests were conducted at a current density, and the average energy efficiency was 76.3%, the coulombic efficiency was 92.6%, and the voltage efficiency was 82.4%.

[0040] Example 2:

[0041] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 4 hours at a heating rate of 5℃ / min.

[0042] Weigh 5 mg of graphene oxide and add 1.6 mL of isopropanol, 0.7 mL of deionized water, and 0.1 mL of a 5% Nafion solution. Sonicate the mixture for 2 hours to ensure uniform dispersion. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: ultrasonic treatment at 40°C for 2 hours, followed by stopping the ultrasonic treatment and allowing it to stand for 10 hours. Repeat the ultrasonic-soaking process twice. Finally, place the finished graphene felt in a vacuum oven and dry it at 60°C for 24 hours to obtain homogeneous graphene oxide-modified graphene felt, which is then packaged and stored.

[0043] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 75.9%, the coulombic efficiency was 92.7%, and the voltage efficiency was 81.9%.

[0044] Example 3:

[0045] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 500℃ for 5 hours at a heating rate of 5℃ / min.

[0046] Weigh 10 mg of graphene oxide and add 1.75 mL of isopropanol, 0.8 mL of deionized water, and 0.15 mL of a 5% Nafion solution. Sonicate the mixture for 2 hours to disperse it evenly. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: ultrasonic treatment at 50°C for 3 hours, followed by stopping the ultrasonic treatment and allowing it to stand for 11 hours. Repeat the ultrasonic-soaking process twice. Finally, place the finished graphene felt in a vacuum oven and dry it at 60°C for 24 hours to obtain homogeneous graphene oxide-modified graphene felt, which is then packaged and stored.

[0047] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 76.8%, the coulombic efficiency was 93.1%, and the voltage efficiency was 82.5%.

[0048] Example 4:

[0049] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 500℃ for 5 hours at a heating rate of 5℃ / min.

[0050] Weigh 15 mg of graphene oxide and add 1.85 mL of isopropanol, 8 mL of deionized water, and 0.15 mL of a 5% Nafion solution. Sonicate the mixture for 2 hours to ensure uniform dispersion. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: ultrasonic treatment at 40°C for 3 hours, followed by stopping the ultrasonic treatment and allowing it to stand for 11 hours. Repeat the ultrasonic-soaking process twice. Finally, place the finished graphene felt in a vacuum oven and dry it at 80°C for 24 hours to obtain homogeneous graphene oxide-modified graphene felt, which is then packaged and stored.

[0051] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 77.9%, the coulombic efficiency was 93.2%, and the voltage efficiency was 83.6%.

[0052] Example 5:

[0053] The graphite felt blocks were immersed in a 95% ethanol solution and then sonicated for 1 hour. They were then repeatedly rinsed and immersed in deionized water, followed by sonication for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 3 hours at a heating rate of 5℃ / min.

[0054] Weigh 45 mg of graphene oxide and add 1.9 mL of isopropanol, 9 mL of deionized water, and 0.15 mL of a 5% Nafion solution. Sonicate the mixture for 2 hours to ensure uniform dispersion. Place the prepared heat-pretreated graphene felt into the resulting dispersion. Then, uniformly load graphene oxide onto the heat-pretreated graphene felt using a multi-frequency staged ultrasonic-heat treatment method: ultrasonic treatment was performed at 60°C for 3 hours, followed by stopping the ultrasonic treatment and allowing the material to stand and soak for 12 hours. This ultrasonic-soaking process was repeated four times at ultrasonic frequencies of 20 kHz, 30 kHz, 40 kHz, 50 kHz, and 60 kHz. Finally, the finished graphene felt was placed in a vacuum oven and dried at 80°C for 24 hours to obtain homogeneous graphene oxide-modified graphene felt, which was then packaged and stored.

[0055] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 76.8%, the coulombic efficiency was 91.4%, and the voltage efficiency was 84.1%.

[0056] Comparative Example 1:

[0057] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 3 hours at a heating rate of 5℃ / min.

[0058] Weigh 1 mg of graphene oxide and add 7.6 mL of deionized water. Sonicate the mixture for 2 h to disperse it evenly and obtain a dispersion. Place the prepared heat-pretreated graphene felt into the obtained mixed dispersion and then perform ultrasonic-heat treatment: sonicate at 40 °C for 2 h, and then let it stand and soak for 10 h. Finally, place the finished graphene felt in a vacuum oven and dry it at 60 °C for 24 h to obtain graphene oxide modified graphene felt, which is then packaged and stored.

[0059] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 73.5%, the coulombic efficiency was 90.2%, and the voltage efficiency was 81.5%.

[0060] Comparative Example 2:

[0061] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 4 hours at a heating rate of 5℃ / min.

[0062] Weigh 5 mg of graphene oxide and add 7.6 mL of deionized water. Sonicate the mixture for 2 h to disperse it evenly and obtain a dispersion. Place the prepared heat-pretreated graphene felt into the obtained mixed dispersion and then perform ultrasonic-heat treatment: ultrasonic treatment at 40℃ for 2 h, then stop ultrasonic treatment and let it stand for 10 h. Repeat the ultrasonic-soaking process twice. Finally, place the finished graphene felt in a vacuum oven and dry it at 60℃ for 24 h to obtain homogeneous graphene oxide modified graphene felt, which is then packaged and stored.

[0063] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 74.2%, the coulombic efficiency was 92.0%, and the voltage efficiency was 80.7%.

[0064] Comparative Example 3:

[0065] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 3 hours at a heating rate of 5℃ / min.

[0066] Weigh 1 mg of graphene oxide and add 1 mL of isopropanol, 6 mL of deionized water, and 0.03 mL of a 3% Nafion solution. Sonicate the mixture for 2 hours to disperse it evenly. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: sonicate at 40°C for 2 hours, followed by standing soaking for 10 hours. Finally, place the finished graphene felt in a vacuum oven and dry it at 60°C for 24 hours to obtain graphene oxide-modified graphene felt, which is then packaged and stored.

[0067] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 71.7%, the coulombic efficiency was 90.3%, and the voltage efficiency was 79.4%.

[0068] Comparative Example 4:

[0069] The graphite felt was immersed in a 95% ethanol solution and then ultrasonically treated for 1 hour. It was then repeatedly rinsed and immersed in deionized water, followed by ultrasonic treatment for 2 hours to remove the ethanol solution and impurities. Finally, the cleaned graphite felt blocks were dehydrated and dried. The cleaned and dried graphite felt blocks were neatly arranged in a quartz tube and preheated in a high-temperature tube furnace at 400℃ for 3 hours at a heating rate of 5℃ / min.

[0070] Weigh 1 mg of graphene oxide and add 3 mL of isopropanol, 6 mL of deionized water, and 0.3 mL of a 10% Nafion solution. Sonicate the mixture for 2 hours to ensure uniform dispersion. Place the prepared heat-pretreated graphene felt into the resulting dispersion and then perform ultrasonic-heat treatment: sonicate at 40°C for 2 hours, followed by standing soaking for 10 hours. Finally, place the finished graphene felt in a vacuum oven and dry at 60°C for 24 hours to obtain graphene oxide-modified graphene felt, which is then packaged and stored.

[0071] The modified electrode prepared in Example 1 was assembled into an iron-chromium flow battery and tested at 60 mA cm⁻¹. -2 Cyclic tests were conducted at a current density, and the average energy efficiency was 72.0%, the coulombic efficiency was 89.1%, and the voltage efficiency was 80.8%.

[0072] Attached Figure Analysis

[0073] Figure 1 Comparative infrared spectral analysis of graphite felt, heat-pretreated graphite felt, and the homogeneous graphene oxide-supported graphite felt prepared in Example 4. Figure 1 It can be seen that after treatment with adsorbed graphene oxide, the temperature range is 2900°~3000°cm.-1 The strong and broad peak enhancement observed within the range is due to the overlap between the -OH stretching vibration peak of graphene oxide and the original groups of graphite felt; 2344°cm -1 The peak at 1231 cm⁻¹ shows a slight enhancement, which is a result of the superposition of C=O peaks in the graphene-loaded graphene felt; -1 The vibration peaks around 1391 cm⁻¹ and 1391 cm⁻¹ -1 The significant increase in peak intensity is due to the overlap of the alkoxy-CO stretching vibration peaks of graphene oxide. Based on the above analysis, graphene oxide was successfully adsorbed on the surface of the heat-treated graphite felt carbon fibers, and a large number of oxygen-containing functional groups were added to the surface. This helps to improve the hydrophilicity of the fiber surface, allowing for better contact with the electrolyte and further enhancing the catalytic activity of the electrode.

[0074] Figure 2 Cyclic voltammetry (CV) curves of graphite felt, heat-pretreated graphite felt, and homogeneous graphene oxide-supported graphite felt prepared in Example 4, at a fixed scan rate (5 mV·s). -1 The electrocatalytic performance of the materials was evaluated using a traditional three-electrode system. The curves of all tested electrode materials showed a clear pair of redox peaks, with the oxidation peak matching Equation (1) and the reduction peak corresponding to Equation (2).

[0075]

[0076] The peak spacing (E) between oxidation and reduction peaks pp The oxidation and reduction peak currents are used to describe the level of electrochemical performance. According to... Figure 2 It can be seen that, under the same testing conditions, the oxidation peak current of the graphene oxide-loaded graphite felt fiber electrode reached 142 mA. pp The voltage is 220mV, while the thermally pretreated graphite felt electrode is 118mA. pp The peak current density of graphite felt is 434mV, while E is lower. pp The larger value indicates that the graphene oxide-loaded graphene felt fiber electrode has better redox reversibility and improved stability, and can provide a larger discharge voltage during battery discharge, further proving that the graphene oxide-loaded graphene felt fiber electrode has better electrochemical performance.

[0077] Figure 3 EIS curves are shown for graphite felt, heat-pretreated graphite felt, and graphite felt electrodes with different graphene oxide loadings prepared in Examples 2, 4, and 5. The test results show that, compared to graphite felt loaded with graphene oxide, both ordinary graphite felt and heat-pretreated graphite felt have larger impedance values ​​R0. ctThe resistances were 8.82Ω and 3.88Ω, respectively. Meanwhile, the resistances of graphite felt electrodes with different graphene oxide loadings were 0.892Ω (0.5 mg·cm⁻¹). -2 ), 0.325Ω (1.5mg·cm -2 ) and 0.481Ω (4.5mg·cm -2 All graphite felt electrodes have similar R... s The Ω value is approximately 2.23 Ω. This result further demonstrates the excellent electrochemical reaction kinetics of the graphene oxide-loaded graphene felt electrode cathode reaction, which helps to reduce electrochemical polarization and is superior to that of graphene felt electrodes under the same conditions and thermally pretreated graphene felt electrodes.

[0078] Figure 4 The graphite felt, the heat-pretreated graphite felt, and the homogeneous graphene oxide-supported graphite felt electrode prepared in Example 4 (1.5 mg·cm⁻¹) were used. -2 The charge-discharge curves of the iron-chromium redox flow battery were obtained. In the charge-discharge test of the iron-chromium redox flow battery, under the same conditions, a homogeneously loaded graphene oxide graphite felt electrode (1.5 mg·cm⁻¹) was used. -2 It exhibited the best performance, with the lowest charging voltage (~1.02V) and the highest discharging voltage (~0.94V) among the three.

[0079] Figure 5 The homogeneous graphene oxide-loaded graphene felt electrode (1.5 mg·cm⁻¹) prepared in Example 4 -2 The energy efficiency, coulombic efficiency, and voltage efficiency curves are shown in the figure. As shown in the figure, the average energy efficiency (EE) of the homogeneous graphene oxide-loaded graphite felt electrode after five cycles is 78%, which is higher than that of graphite felt and thermally pretreated graphite felt. This proves that the loading of graphene oxide increases the number of active sites and enhances the electrochemical activity of the electrode.

[0080] Figure 6 The graphite felt, the heat-pretreated graphite felt, and the homogeneous graphene oxide-supported graphite felt electrode prepared in Example 4 (1.5 mg·cm⁻¹) are examples of graphite felt electrodes. -2 The energy efficiency curves are shown in the figure. As can be seen from the figure, the energy efficiency of the homogeneously loaded graphene oxide graphite felt electrode is significantly higher than that of the unloaded graphite felt and the heat-pretreated graphite felt, further demonstrating the excellent performance of the prepared electrode.

Claims

1. A method for preparing homogeneous graphene oxide-modified graphite felt, characterized in that, Includes the following steps: (1) Clean the graphite felt with organic solvent and deionized water, and then dry it; (2) The cleaned graphite felt obtained in step (1) is subjected to heat pretreatment to increase the oxygen-containing functional groups therein; (3) Weigh out graphene oxide and add it to a mixed solution consisting of isopropanol, deionized water and Nafion. Disperse the solution by sonication to obtain a graphene oxide dispersion. (4) Impregnate the graphite felt after heat pretreatment in step (2) with the graphene oxide dispersion obtained in step (3), wherein ultrasonication is performed during the impregnation process and then the material is left to stand. (5) Repeat step (4) 0 to 5 times; (6) The graphite felt obtained after the last ultrasonic impregnation treatment is dried to obtain a homogeneous graphite felt loaded with graphene oxide.

2. The preparation method according to claim 1, characterized in that, The cleaning process described in step (1) includes organic solvent cleaning and deionized water cleaning.

3. The preparation method according to claim 1, characterized in that, The conditions for the heat pretreatment in step (2) are: treatment temperature of 400 ~ 600 ℃ and treatment time of 3 ~ 6 h.

4. The preparation method according to claim 1, characterized in that, In the mixed solution described in step (3), the volume fraction of isopropanol is 5%-25%, the volume fraction of Nafion is 0.5%-5%, and the remainder is deionized water.

5. The preparation method according to claim 1, characterized in that, The graphene oxide is a general-purpose sheet-like graphene, a highly conductive graphene, or a composite material of various types of graphene.

6. The preparation method according to claim 1, characterized in that, In step (4), the mass percentage concentration of graphene oxide in the resulting dispersion is 0.5-5 mg / mL.

7. The preparation method according to claim 1, characterized in that, The ultrasonic impregnation operation conditions in step (4) are: ultrasonic treatment for 1 to 6 hours at a temperature of 20 to 60 ℃, followed by static soaking for 1 to 12 hours.

8. The preparation method according to claim 1, characterized in that, In step (5), step (4) is repeated 1-5 times.

9. The preparation method according to claim 1, characterized in that, The ultrasonic impregnation operation described in step (5) is as follows: at a temperature of 40 ~ 50 ℃, ultrasonic treatment is performed for 2 ~ 4 h each time, followed by static soaking for 3 ~ 5 h.

10. The preparation method according to claim 1, characterized in that, The drying conditions described in step (6) are: a drying temperature of 60 ~ 80 ℃ and a drying time of 8-12 h.

11. The homogeneous graphene oxide modified graphite felt obtained by any of the preparation methods described in claims 1-10.

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