Preparation method of Bi-loaded graphite felt electrode

Abstract

The invention discloses a preparation method of a Bi-loaded graphite felt electrode, which comprises the following steps: (1) loading bismuth and zinc on a pretreated graphite felt in the form of oxide to obtain a Bi2O3 / ZnO / graphite felt; and (2) carrying out carbon thermal reduction reaction on the Bi2O3 / ZnO / graphite felt obtained in the step (1), and then washing and drying to obtain the high-dispersion Bi-loaded graphite felt electrode. The Bi-loaded graphite felt electrode prepared by the method is large in specific surface area, uniform in dispersion and high in electrochemical activity, and has a wide application prospect as an electrode material.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to a highly dispersed Bi-loaded graphite felt electrode and its preparation method. Technical Background

[0002] Iron-chromium redox flow batteries are one of the preferred technologies for large-scale energy storage. Flow batteries offer advantages such as high safety, long cycle life, recyclable electrolyte, high cost-effectiveness over their lifecycle, and environmental friendliness, making them a top choice for large-scale energy storage. Iron-chromium flow batteries, in particular, use abundant and relatively inexpensive iron and chromium ions as active materials, with the iron-chromium electrolyte accounting for only 9% of the system cost, giving them a cost advantage. They can be applied to various fields, including solar and wind power generation, smart microgrids, and user-side applications, demonstrating promising development prospects.

[0003] As one of the key components of a flow battery, the electrode is the main site of electrochemical reactions. During charging and discharging, the structure and characteristics of the electrode material directly affect the uniformity of the distribution of active materials, the ion diffusion state, the electrochemical reaction rate, the battery internal resistance, and its polarization degree, thereby affecting the battery performance. The electrode material of the iron-chromium flow battery needs to have the following characteristics: (1) The electrode material has good chemical stability, is resistant to acid and oxidation, to ensure that the electrode has a long service life; (2) Superior electrocatalytic activity, which can improve the electrochemical reaction rate, that is, improve the rate performance of the iron-chromium flow battery; (3) High specific surface area / effective electrochemical surface area, to ensure that the electrode and electrolyte are in full contact, and increase the total amount of electrochemical reaction per unit volume of electrolyte, that is, improve the electrolyte utilization rate; (4) Good conductivity, which can reduce the battery internal resistance and reduce electrochemical polarization during charging and discharging.

[0004] Many researchers have focused on modifying graphite felt electrodes. Traditional intrinsic treatment methods include acid treatment, alkali treatment, and heat treatment. Other methods include loading nanomaterials, metals and metal oxides, and heteroatom doping. While traditional intrinsic treatment methods are simple to operate, they offer limited improvement in electrochemical activity and have been less studied in recent years. Although modifying graphite felt electrodes with metal nanoparticles in a specific way can improve battery performance, carbon fiber electrodes modified with metal nanoparticles for flow batteries are still in the early stages of development. Further research is needed to control the size, shape, and distribution of these nanoparticles to further enhance their catalytic activity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a Bi-supported graphite felt electrode. The Bi-supported graphite felt electrode prepared by this invention has a large specific surface area, uniform dispersion, and high electrochemical activity, and has broad application prospects as an electrode material.

[0006] The method for preparing the Bi-supported graphite felt electrode of the present invention includes the following steps: (1) Bismuth and zinc were loaded onto pretreated graphite felt in the form of oxides to obtain Bi2O3 / ZnO / graphite felt; (2) The Bi2O3 / ZnO / graphite felt obtained in step (1) is subjected to carbothermal reduction reaction, and then washed and dried to obtain a highly dispersed Bi-loaded graphite felt electrode.

[0007] In the method of this invention, the pretreatment described in step (1) is a conventional operation in the art. Generally, it involves degreasing and removing impurities. The specific process is as follows: the graphite felt is immersed in an ethanol-water solution and ultrasonically treated, followed by multiple washing and drying to obtain degreased and impurity-removed graphite felt. The ultrasonic treatment time is generally 0.5-1 h. The drying temperature is 80-120℃, and the drying time is 12-36 h.

[0008] In the method of this invention, the loading process in step (1) is carried out by impregnation, generally using an ethylene glycol solution containing bismuth nitrate and zinc nitrate, with a concentration of 5-15 g / L, wherein the molar ratio of bismuth nitrate to zinc nitrate is 1:3-3:1; the impregnation time is 0.5-1.5 h, and shaking is preferably used during the impregnation process. The impregnated material is dried and calcined to obtain Bi2O3 / ZnO / graphite felt. The drying temperature is 80-120℃, and the drying time is 12-36 h; the calcination temperature is 400-500℃, and the calcination time is 1-2 h, and the calcination is carried out under an inert atmosphere, wherein the inert atmosphere is nitrogen and / or an inert gas. In the method of this invention, the carbothermic reduction reaction conditions in step (2) are: the reaction temperature is 1000-1100℃, the reaction time is 1-2 h, and the reaction is carried out under an inert atmosphere, wherein the inert atmosphere is nitrogen and / or an inert gas.

[0009] In the method of the present invention, the washing in step (2) is carried out in a dilute hydrochloric acid solution with a concentration of 1~2 M; the drying conditions are: drying temperature of 80-120℃ and drying time of 12-36h.

[0010] According to a second aspect of the invention, a highly dispersed Bi-supported graphite felt electrode is also provided, which is prepared by the method described above. The resulting product properties include a specific surface area of ​​1.9 m². 2 / g~7.6m 2 / g, Bi nanoparticles are uniformly distributed on the surface of carbon fibers.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first loads the graphite felt electrode with bismuth nitrate and zinc nitrate in an ethylene glycol solution, and then obtains a highly dispersed graphite felt electrode through a carbothermal reduction reaction. During the carbothermal reduction process, the following reactions occur: 3C + Bi₂O₃ → 2Bi + 3CO, C + ZnO → Zn + CO. At the same time, elemental Zn evaporates at this reaction temperature. The sites of Bi₂O₃ and ZnO originally loaded on the surface of the graphite felt are replaced by Bi nanoparticles, which are highly dispersed.

[0012] In this invention, zinc evaporates onto the graphite felt surface after the carbothermic reaction, forming highly dispersed bismuth nanoparticles. This increases the specific surface area (5-10 times) and the number of activation sites, providing a favorable environment for the attachment of chromium ions, improving the electrochemical activity of chromium ions, and inhibiting the occurrence of hydrogen evolution side reactions. Attached Figure Description

[0013] Figure 1 SEM image of the graphite felt prepared in Example 1.

[0014] Figure 2 SEM image of the graphite felt prepared in Example 2.

[0015] Figure 3 SEM image of the graphite felt prepared in Example 3.

[0016] Figure 4 SEM image of the graphite felt prepared for Comparative Example 1.

[0017] Figure 5 SEM image of the graphite felt prepared for Comparative Example 2.

[0018] Figure 6 The results of HER tests on graphite felt electrodes in the examples and comparative examples are shown. Detailed Implementation

[0019] This invention provides a modification method for highly dispersed Bi-loaded graphite felt electrodes, effectively solving the technical defects of current graphite felt electrodes, such as small specific surface area, low electrochemical activity, and uneven Bi catalyst loading on the graphite felt electrode surface. The electrode morphology was characterized using a JSM-7500F scanning electron microscope manufactured by JEOF Corporation of Japan.

[0020] The method of the present invention will be described in more detail below with reference to specific embodiments and comparative examples.

[0021] The original graphite felt used in the examples and comparative examples was purchased from Liaoning Jingu Carbon Materials Co., Ltd. Example 1

[0022] Pre-treated graphite felt: The graphite felt was cut into 3 cm × 3 cm pieces, placed in a 20% ethanol aqueous solution and ultrasonically washed for 0.5 h to remove impurities from the surface of the graphite felt. After drying at 100 ℃ for 24 h, the graphite felt was de-oiled and impurity-removed. Impregnated graphite felt: 4.101 g of bismuth nitrate and 5.899 g of zinc nitrate (the molar ratio of bismuth nitrate to zinc nitrate is 1:3) were dissolved in 1 L of ethylene glycol solution. The pretreated graphite felt was immersed in the above-obtained bismuth nitrate and zinc nitrate solution (30 mL), shaken in a shaker for 1 h, and then dried at 100 °C for 24 h to obtain graphite felt coated with bismuth nitrate and zinc nitrate. Heat-treated graphite felt: The impregnated graphite felt is transferred to a tube furnace and heated at 5 °C for 5 min under a N2 atmosphere. -1 The temperature of the quartz tube was heated from room temperature to 500℃ to promote the decomposition of Bi(NO3)3 and Zn(NO3)2, and the heating was continued for 2 h to ensure complete decomposition, resulting in graphite felt with ZnO and Bi2O3 distributed in it. Continue heating to 1050℃ and hold for 2 h. At this time, ZnO and Bi2O3 undergo carbothermic reduction reaction to generate Bi particles and Zn particles, but Zn will evaporate together with CO to obtain a highly dispersed Bi-supported graphite felt electrode. Acid washing: The highly dispersed Bi-supported graphite felt electrode was washed with 1 M HCl aqueous solution and deionized water and dried at 100℃ for 12 h. The electrode properties are shown in Table 1.

[0023] Example 2

[0024] (1) Pre-treatment of graphite felt: The graphite felt was cut into 3 cm × 3 cm pieces, placed in 20% ethanol aqueous solution and ultrasonically washed for 0.5 h to remove impurities from the surface of the graphite felt. After drying at 100 ℃ for 24 h, the graphite felt was degreased and impurities removed. (2) Impregnated graphite felt: 6.759 g of bismuth nitrate and 3.241 g of zinc nitrate (the molar ratio of bismuth nitrate and zinc nitrate is 1:1) were dissolved in 1 L of ethylene glycol solution. The pretreated graphite felt was immersed in the bismuth nitrate and zinc nitrate solution (30 mL) obtained above, shaken in a shaker for 1 h, and then dried at 100 °C for 24 h to obtain graphite felt coated with bismuth nitrate and zinc nitrate. (3) Heat treatment of graphite felt: The impregnated graphite felt is transferred to a tube furnace and heated at 5 °C for 5 min under N2 atmosphere. -1 The temperature of the quartz tube was heated from room temperature to 500℃ to promote the decomposition of Bi(NO3)3 and Zn(NO3)2, and the heating was continued for 2 h to ensure complete decomposition, resulting in graphite felt with ZnO and Bi2O3 distributed in it. (4) Continue heating to 1050℃ and hold for 2 h. At this time, ZnO and Bi2O3 undergo carbothermic reduction reaction to generate Bi particles and Zn particles, but Zn will evaporate together with CO to obtain a highly dispersed Bi-supported graphite felt electrode. (5) Acid washing: Wash the highly dispersed Bi-supported graphite felt electrode with 1 M HCl aqueous solution and deionized water, and dry it at 100℃ for 12 h. The electrode properties are shown in Table 1. Example 3

[0025] (1) Pre-treatment of graphite felt: The graphite felt was cut into 3 cm × 3 cm pieces, placed in 20% ethanol aqueous solution and ultrasonically washed for 0.5 h to remove impurities from the surface of the graphite felt. After drying at 100 ℃ for 24 h, the graphite felt was degreased and impurities removed. (2) Impregnated graphite felt: 8.622 g of bismuth nitrate and 1.378 g of zinc nitrate (the molar ratio of bismuth nitrate to zinc nitrate is 3:1) were dissolved in 1 L of ethylene glycol solution. The pretreated graphite felt was immersed in the bismuth nitrate and zinc nitrate solution (30 mL) obtained above, shaken in a shaker for 1 h, and then dried at 100 °C for 24 h to obtain graphite felt coated with bismuth nitrate and zinc nitrate. (3) Heat treatment of graphite felt: The impregnated graphite felt is transferred to a tube furnace and heated at 5 °C for 5 min under N2 atmosphere. -1 The temperature of the quartz tube was heated from room temperature to 500℃ to promote the decomposition of Bi(NO3)3 and Zn(NO3)2, and the heating was continued for 2 h to ensure complete decomposition, resulting in graphite felt with ZnO and Bi2O3 distributed in it. (4) Continue heating to 1050℃ and hold for 2 h. At this time, ZnO and Bi2O3 undergo carbothermic reduction reaction to generate Bi particles and Zn particles, but Zn will evaporate together with CO to obtain a highly dispersed Bi-supported graphite felt electrode. (5) Acid washing: Wash the highly dispersed Bi-supported graphite felt electrode with 1 M HCl aqueous solution and deionized water, and dry it at 100℃ for 12 h. The electrode properties are shown in Table 1.

[0026] Comparative Example 1 (1) Pre-treatment of graphite felt: The graphite felt was cut into 3 cm × 3 cm pieces, placed in 20% ethanol aqueous solution and ultrasonically washed for 0.5 h to remove impurities from the surface of the graphite felt. After drying at 100 ℃ for 24 h, the graphite felt was degreased and impurities removed. (2) Impregnated graphite felt: Dissolve 10 g of bismuth nitrate in 1 L of ethylene glycol solution, immerse the pretreated graphite felt in the bismuth nitrate solution (30 mL) obtained above, shake in a shaker for 1 h, and then dry at 100 °C for 24 h to obtain graphite felt with bismuth nitrate coating. (3) Heat treatment of graphite felt: The impregnated graphite felt is transferred to a tube furnace and heated at 5 °C for 5 min under N2 atmosphere. -1 The temperature of the quartz tube was heated from room temperature to 500℃ to promote the decomposition of Bi(NO3)3 by heating the tube at a certain rate, and the heating was continued for 2 hours to ensure complete decomposition, resulting in graphite felt with Bi2O3 distributed in it. (4) Continue heating to 1050℃ and hold for 2 h. At this time, Bi2O3 undergoes carbothermic reduction reaction to generate Bi particles, and Bi-supported graphite felt electrode is obtained. (5) Acid washing: The Bi-supported graphite felt electrode was washed with 1 M HCl aqueous solution and deionized water and dried at 100℃ for 12 h. The electrode properties are shown in Table 1.

[0027] Comparative Example 2 (1) Pre-treatment of graphite felt: The graphite felt was cut into 3 cm × 3 cm pieces, placed in 20% ethanol aqueous solution and ultrasonically washed for 0.5 h to remove impurities from the surface of the graphite felt. After drying at 100 ℃ for 24 h, the graphite felt was degreased and impurities removed. (2) Impregnated graphite felt: 2.943 g of bismuth nitrate and 7.057 g of zinc nitrate (the molar ratio of bismuth nitrate and zinc nitrate is 1:5) were dissolved in 1 L of ethylene glycol solution. The heat-treated graphite felt was immersed in the solution (30 mL) obtained above, shaken in a shaker for 1 h, and then dried at 100 °C for 24 h to obtain graphite felt coated with bismuth nitrate and zinc nitrate. (3) Heat treatment of graphite felt: The impregnated graphite felt is transferred to a tube furnace and heated at 5 °C for 5 min under N2 atmosphere. -1 The temperature of the quartz tube was heated from room temperature to 500℃ to promote the decomposition of Bi(NO3)3 and Zn(NO3)2, and the heating rate was increased to ensure complete decomposition for 2 h, resulting in graphite felt with ZnO distributed in it. (4) Continue heating to 1050℃ and hold for 2 h. At this time, ZnO undergoes carbothermic reduction reaction to generate Zn particles, but Zn will evaporate together with CO to obtain porous graphite felt electrode. (5) Acid washing: The porous graphite felt electrode was washed with 1 M HCl aqueous solution and deionized water and dried at 100℃ for 12 h. The electrode properties are shown in Table 1.

[0028] By comparing the SEM images, it can be seen that by controlling the molar ratio of bismuth nitrate and zinc nitrate, the particle size and dispersion of the generated bismuth particles can be controlled. In the graphite felt electrodes prepared in Examples 1-3 and Comparative Examples 1-2, when the molar ratio of bismuth nitrate and zinc nitrate is 1:1 (Example 2), the surface of the prepared graphite felt electrode is uniformly distributed with bismuth particles.

[0029] Test case The testing process for iron-chromium redox flow batteries is as follows: Electrolyte preparation: The electrolyte composition is 1 mol / L FeCl2 + 1 mol / L CrCl3 + 3 mol / L HCl. It is prepared by dissolving FeCl2·4H2O and CrCl3·6H2O in concentrated hydrochloric acid solution, and then diluting with deionized water to a final volume at room temperature.

[0030] The main components of the single cell are: a perfluorinated ion exchange membrane as the separator, graphite felt as the positive and negative electrodes (the graphite felt has a compression ratio of 25%), and a graphite plate as the bipolar plate. The positive and negative electrolytes are stored in an external reservoir and are pumped into the single cell at a rate of 80 mL / min by a magnetic circulation pump for internal circulation.

[0031] Testing process: Test parameters set: current density 80 mA / cm² 2 The charge / discharge cutoff voltage was 0.8-1.2V, and the battery operating temperature was controlled at 55℃. A charge / discharge tester was used to monitor the battery, and the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of a single cell were calculated, where EE = CE × VE. The charge / discharge tester was purchased from Wuhan Landian Electronics Co., Ltd. The battery test results for the graphite felt prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 2. It can be seen that Example 2 has the highest coulombic efficiency, voltage efficiency, and energy efficiency.

[0032] The HER test process is as follows: The graphite felt electrodes prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to HER testing. The testing method was linear sweep voltammetry (LSV), and HER performance was tested in 0.1 mol / L HCl at a scan rate of 2 mV / s, with a scan potential range of 0.2 to -0.2 V. The test results are shown in [Figure number missing]. Figure 6 By comparing the current signals of different electrodes at the same potential (-0.2 V), it can be seen that the current signal of Example 2 is the smallest, indicating that Example 2 has excellent performance in suppressing hydrogen evolution compared to Examples 1-3 and Comparative Examples 1-2.

[0033] Table 1. BET specific surface area of ​​graphite felt electrodes prepared in Examples 1-3 and Comparative Examples 1-2, obtained by measuring with a Mack ASAP-2420 physical adsorption instrument.

[0034] electrode <![CDATA[Specific surface area (m 2 / g)]]> Example 1 1.917 Example 2 5.127 Example 3 2.241 Comparative Example 1 0.995 Comparative Example 2 1.097 Table 2 Test Results of Iron-Chromium Redox Flow Batteries Different electrodes Coulomb efficiency (CE) / % Voltage efficiency (VE) / % Energy efficiency (EE) / % Example 1 98.4 80.7 80.6 Example 2 98.8 85.2 84.2 Example 3 98.1 83.1 81.5 Comparative Example 1 95.8 76.8 73.6 Comparative Example 2 95.7 75.9 72.6

Claims

1. A method for preparing a Bi-loaded graphite felt electrode, characterized by The application comprises the following contents: (1) loading bismuth and zinc in the form of oxides onto pretreated graphite felt to obtain Bi2O3 / ZnO / graphite felt; (2) performing carbon thermal reduction reaction on the Bi2O3 / ZnO / graphite felt obtained in step (1), and then washing and drying to obtain a Bi-loaded graphite felt electrode.

2. The method of claim 1, wherein: The pretreatment process in step (1) is specifically as follows: graphite felt is immersed in an ethanol aqueous solution and ultrasonically treated, and the oil-removed and impurity-removed graphite felt is obtained through multiple washing and drying.

3. The method of claim 1, wherein: The loading process in step (1) is performed by the impregnation method, and a glycol solution containing bismuth nitrate and zinc nitrate is used, the concentration of the solution is 5-15 g / L, and the molar ratio of bismuth nitrate to zinc nitrate is 1:3-3:

1.

4. The method of claim 3, wherein: The impregnation time is 0.5-1.5 h, and the shaking table oscillation is preferably used during the impregnation process.

5. The method according to claim 3 or 4, characterized in that: The impregnated material is dried and calcined to obtain Bi2O3 / ZnO / graphite felt.

6. The method of claim 5, wherein: The drying temperature is 80-120 DEG C, and the drying time is 12-36 h; the calcination temperature is 400-500 DEG C, the calcination time is 1-2 h, and the calcination is performed in an inert atmosphere, and the inert atmosphere is nitrogen and / or inert gas.

7. The method of claim 1, wherein: The carbon thermal reduction reaction condition in step (2) is as follows: the reaction temperature is 1000-1100 DEG C, the time is 1-2 h, and the reaction is performed in an inert atmosphere, and the inert atmosphere is nitrogen and / or inert gas.

8. The method of claim 1, wherein: The washing in step (2) is performed in a dilute hydrochloric acid solution, and the concentration of the dilute hydrochloric acid is 1-2 M; and the drying condition is as follows: the drying temperature is 80-120 DEG C, and the drying time is 12-36 h.

9. The Bi-loaded graphite felt electrode prepared according to the method of claim 1, characterized in that: Specific surface area 1.9 m 2 / g 7.6 m 2 / g, Bi nanoparticles are distributed on the surface of carbon fibers in a uniform dispersed manner.

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