A method for preparing a highly active electrode for an iron-chromium redox flow battery

Abstract

This invention discloses a method for preparing a highly active electrode for an iron-chromium redox flow battery. The method is as follows: 1) A nanosheet template is prepared by precipitating Fe(OH)3 on the surface of carbon felt fibers; 2) Pyrrole is self-polymerized on the Fe(OH)3 nanosheet layer using a hydrothermal synthesis method; 3) The carbon felt is placed in a tube furnace and subjected to isothermal heat treatment in an air atmosphere to convert Fe(OH)3 into Fe2O3. The template is then washed away with HCl to obtain a carbon felt with a defective carbon layer loaded with N doping; 4) Finally, in a three-electrode system, a constant voltage deposition method is used, with cleverly designed deposition potential and time, so that Sn is uniformly and preferentially anchored at the defective sites of N doping on the carbon layer, thereby preparing a highly active carbon felt electrode with dual catalytic sites on its surface. This can effectively improve the electrochemical activity and kinetics of the chromium anode and suppress the hydrogen evolution side reaction, thereby improving the energy efficiency and cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and more specifically, to a method for preparing a highly active electrode for an iron-chromium flow battery system. Background Technology

[0002] Energy storage technology is an important means to alleviate the imbalance between energy demand and supply, improve the utilization efficiency of renewable energy, and enhance the security and flexibility of energy system supply. Among them, flow batteries have significant advantages in large-scale energy storage technology due to their strong scalability, long lifespan, high efficiency, high safety, and high renewability.

[0003] As the sole site of electrochemical reactions in a flow battery, the electrode's response rate directly impacts battery performance. Traditional carbon felt electrodes used in flow batteries often suffer from slow electrochemical response rates and high internal resistance due to their poor electrochemical activity and low specific surface area, ultimately affecting battery efficiency and power. Furthermore, in iron-chromium flow batteries, the slow kinetics of the Cr anode and the severe hydrogen evolution side reaction further affect the electrode, increasing battery polarization and reducing efficiency and cycle life. Based on these two points, modifying the electrode materials for iron-chromium flow batteries is a direct means to improve battery performance. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing a highly active electrode for iron-chromium flow batteries by anchoring metal atoms on a defective carbon layer doped with nitrogen using a sacrificial template method. The diatomic doping on the carbon felt surface serves as dual catalytic sites, exhibiting higher catalytic activity and selectivity. This effectively increases the number of reactive sites on the electrode surface, provides strong chemisorption, improves electrochemical reaction kinetics, suppresses side reactions, thereby reducing battery polarization and improving battery energy efficiency and cycle life.

[0005] The objective of this invention is achieved through the following technical solution: a method for preparing a highly active carbon felt electrode for an iron-chromium redox flow battery, characterized by comprising the following steps:

[0006] Step 1) Immerse the carbon felt in FeCl3 solution at room temperature, perform ultrasonic vibration treatment, and then slowly drop in NaOH solution with a concentration of 0.1-1.0 mol / L to allow it to react fully with FeCl3 with a concentration of 0.1-1.0 mol / L. Then, centrifuge the carbon felt to generate Fe(OH)3 precipitate which is fully loaded onto the carbon felt for later use.

[0007] Step 2) The carbon felt from Step 1) is soaked again in a pyrrole solution with a concentration of 0.01-0.5 Wt%, and then placed in a hydrothermal reactor for hydrothermal synthesis, so that pyrrole self-polymerizes on the surface of Fe(OH)3 nanosheets. The carbon felt is then removed, washed, and dried for later use.

[0008] Step 3) Place the carbon felt from Step 2) in a quartz tube furnace and heat it in air at a rate of 5 min / min. o The temperature rises at a rate of C to 250-300. o C is subjected to heat preservation treatment for 0.5-3 hours, followed by natural cooling to room temperature;

[0009] Step 4) Remove the carbon felt and soak it in an HCl solution with a concentration of 2.0-6.0 mol / L, and shake it to fully dissolve the template, then wash it with deionized water;

[0010] Step 5) The washed carbon felt is immersed in a SnCl4 solution with a concentration of 0.01-1.0 mol / L. Tin is deposited on the surface of the carbon felt electrode by constant voltage deposition method. After washing with deionized water, it is vacuum dried to obtain the finished high-activity carbon felt electrode used in iron-chromium redox flow batteries.

[0011] Preferably, in step 1), the concentration of FeCl3 is 0.1-0.5 mol / L; the concentration of NaOH is 0.5-1.0 mol / L.

[0012] Preferably, in step 1), the ultrasonic treatment time is 10-20 min.

[0013] Preferably, in step 1), the centrifugation speed is 1000-2000 rpm and the time is 5-10 min.

[0014] Preferably, in step 2), the pyrrole concentration is 0.2-0.5 wt%, and the hydrothermal synthesis temperature is 120-160 °C. o C, process for 10-12 hours.

[0015] Preferably, in step 3), the heat preservation treatment time is 1-2 h, so that Fe(OH)3 is fully oxidized to Fe2O3.

[0016] Preferably, in step 4), the concentration of HCl is 2.0-4.0 mol / L, and the ultrasonic oscillation treatment time is 30-60 min to fully react and consume Fe2O3.

[0017] Preferably, in step 5), the SnCl4 solution with a concentration of 0.1-0.5 mol / L is used as the electrolyte, and a constant voltage deposition process is performed using a three-electrode system with a Pt sheet as the counter electrode, saturated calomel as the reference electrode, and the carbon felt as the working electrode. The deposition voltage is -1.0 V to -1.6 V (vs. SCE), and the deposition time is 30-60 s.

[0018] This invention first uses chemical deposition to prepare Fe(OH)3 nanosheets on the surface of carbon felt fibers as a sacrificial template. Then, a self-polymerized pyrrole carbon layer is coated onto the nanosheets via hydrothermal synthesis to introduce an N source. Next, the template is washed away with hydrochloric acid, leaving an N-doped defect carbon layer on the carbon felt surface. Finally, an electrochemical deposition method is used, with a relatively low deposition voltage, to allow Sn in the system to... 2+ With a smaller deposition driving force, it is preferentially anchored at defect sites doped with N atoms, forming dual catalytic sites on the carbon layer on the carbon felt surface. On the other hand, setting a shorter deposition time allows the deposited Sn to be uniformly dispersed on the electrode surface, effectively preventing the deposited Sn from accumulating on the carbon felt surface and covering the original carbon layer, thus reducing the catalytic activity of the carbon felt.

[0019] The carbon felt electrode prepared by this invention, supported on a defective carbon layer co-doped with N and Sn, exhibits high defect levels, good catalytic effect, and structural stability. On one hand, the pyrrole self-polymerization layer on the carbon felt surface significantly increases the electrode's specific surface area, thereby enhancing its electrochemical activity. On the other hand, by directionally depositing Sn atoms at pyrrole N defect sites, the carbon felt surface possesses multiple catalytic sites. Electrochemical reaction kinetics are faster at sites rich in N defects, thus addressing the slow Cr kinetics on the negative electrode side of iron-chromium flow batteries. Simultaneously, the metallic Sn deposited at the defect sites effectively suppresses the hydrogen evolution side reaction, further improving battery capacity and efficiency. Attached Figure Description

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These descriptions are for illustrative and explanatory purposes only and do not constitute any limitation on the present invention. The accompanying drawings are merely schematic diagrams of one embodiment of the present invention. Those skilled in the art can obtain other drawings based on this drawing without any creative effort.

[0021] Figure 1 This is the SEM morphology of the original carbon felt used in Embodiment 1 of the present invention;

[0022] Figure 2 This is the SEM morphology of the highly active carbon felt electrode prepared in Example 1 of the present invention;

[0023] Figure 3This is a comparison chart of Raman test results between the highly active carbon felt electrode and the original carbon felt electrode in Embodiment 2 of the present invention;

[0024] Figure 4 This is a comparison diagram of the contact angles between the highly activated carbon felt electrode and the original carbon felt electrode in Embodiment 3 of the present invention;

[0025] Figure 5 This is a comparison chart of CV tests between the highly active carbon felt electrode and the original carbon felt electrode in Example 4 of this invention;

[0026] Figure 6 This is a comparison chart of EIS tests between the highly active carbon felt electrode and the original carbon felt electrode in Embodiment 4 of the present invention;

[0027] Figure 7 This is a comparison chart of the rate test results of the iron-chromium redox flow battery assembled with the high-activity carbon felt electrode and the original carbon felt electrode in Embodiment 5 of the present invention. Detailed Implementation Example 1

[0028] 1) Prepare 50 ml of 0.1 mol / L FeCl3 solution, fully immerse the original carbon felt electrode in it, and sonicate for 10 min to ensure thorough wetting of the carbon felt electrode with FeCl3 solution. Immediately afterwards, add 0.5 mol / L NaOH solution dropwise to the FeCl3 solution until no obvious precipitate forms, then centrifuge at 1000 rpm for 5 min. Remove the carbon felt electrode afterward.

[0029] 2) Prepare 50 ml of pyrrole solution (0.2 wt%) and immerse the carbon felt in it, then transfer it to a 100 mL reaction vessel. o The carbon was treated at C for 12 h to allow pyrrole to fully self-polymerize on the surface of Fe(OH)3 nanosheets. After the reaction, the carbon was cooled to room temperature, removed, washed, and dried.

[0030] 3) Place the carbon felt into the tube furnace at 5... o Heating to 250°C at a constant rate of C / min o The carbon felt was then kept at a constant temperature for 1 hour to fully oxidize Fe(OH)3 to Fe2O3. After that, it was naturally cooled to room temperature and the carbon felt was removed.

[0031] 4) Immerse the carbon felt completely in a 3 mol / L hydrochloric acid solution and sonicate for 30 min to ensure that the Fe2O3 is fully consumed.

[0032] 5) The carbon felt electrode was immersed in a 0.1 mol / L SnCl4 solution and used as the working electrode. In a three-electrode system with a Pt sheet and a saturated calomel electrode as the counter electrode and reference electrode, respectively, a constant voltage deposition was performed for 60 s at a voltage of -1.6 V (vs. SCE) to obtain a highly active carbon felt electrode loaded with metal Sn.

[0033] The highly activated carbon felt prepared by the above method and the original carbon felt were characterized by SEM morphology, and the results are as follows: Figure 1-2 As shown, compared to the original carbon felt with a smooth surface, the prepared carbon felt has a defect carbon layer with obvious nanosheet morphology on its surface, in which Sn is loaded in the form of tiny nanospheres on the defect carbon layer. The presence of these defect carbon layers, which are rich in N and Sn, can significantly increase the specific surface area of ​​the carbon felt electrode and improve the electrochemical activity of the electrode. Example 2

[0034] To simplify the description, Example 2 uses the same operating method as Example 1, except that the FeCl3 solution concentration is 0.3 mol / L, and Raman spectroscopy analysis is performed. The results are as follows: Figure 3 As shown. The results indicate that the I on the surface of the prepared carbon felt electrode... D / I G The value of 1.57 is greater than the I value of the original carbon felt surface. D / I G The value (1.47) indicates that the carbon felt electrode prepared by the method of this invention has abundant defect sites on its surface, which are mainly caused by N and Sn doping. The presence of these abundant catalytic sites can improve the electrocatalytic activity of the electrode, giving it better reaction kinetics. Example 3

[0035] To simplify the description, Example 3 used the same operating method as Example 1, except that a FeCl3 solution concentration of 0.5 mol / L was used, and contact angle tests were performed. The results are as follows: Figure 4 As shown, the prepared carbon felt electrode has a smaller contact angle than the original carbon felt electrode, indicating that it has higher electrolyte wettability and can further improve the electrochemical activity of the electrode. Example 4

[0036] For simplicity, Example 4 uses the same operating method as Example 1, except that a SnCl4 solution concentration of 0.2 mol / L is used, and electrochemical measurements are performed. In a three-electrode electrolytic cell consisting of a carbon felt, a Pt sheet, and a saturated calomel electrode as the working electrode, counter electrode, and reference electrode, respectively, an electrolyte solution of 0.1 mol / L Cr was prepared. 3++ 3 mol / L HCl, and perform cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. Figure 5 As shown, compared to the original felt electrode, the highly active carbon felt electrode prepared by the method of this invention exhibits a more significant oxidation peak and a larger peak current, indicating that the prepared carbon felt electrode has higher electrochemical activity and can effectively promote Cr... 2+ The oxidation reaction. EIS results ( Figure 6 This also indicates that the prepared carbon felt electrode exhibits stronger reaction kinetics. The above experiments fully demonstrate that the prepared highly active carbon felt electrode with dual catalytic sites is effective for Cr... 2+ / Cr 3+ It exhibits excellent catalytic activity. Example 5

[0037] To simplify the description, Example 5 uses the same operating method as Example 1, except that the SnCl4 solution concentration is 1.0 mol / L, the constant voltage deposition time is 30 s, and the full-cell rate performance is tested. The positive and negative electrodes of the full cell use 0.5 mol / L CrCl3 / FeCl2 + 3 mol / L HCl as the electrolyte, and charge-discharge cycles are performed between 0.6 V and 1.3 V. The results are as follows. Figure 7 As shown. At 60-120 mA cm⁻¹ -2 Within this range, cells assembled with highly active carbon felt electrodes possessing dual catalytic sites exhibit higher coulombic efficiency and energy efficiency. Furthermore, after 20 cycles, the efficiency returns to 60 mA cm⁻¹. -2 Under the conditions of charging and discharging, the battery can still produce stable and efficient output, further proving the stable catalytic characteristics of the prepared highly active carbon felt electrode.

[0038] It is foreseeable that although the above embodiments only list a few implementation methods of the present invention, other modifications can still be made based on them. Therefore, other modifications derived from the present invention that do not depart from the principle of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly active carbon felt electrode for an iron-chromium redox flow battery, characterized in that... Includes the following steps: Step 1) Immerse the carbon felt in FeCl3 solution at room temperature, perform ultrasonic vibration treatment, and then slowly drop in NaOH solution with a concentration of 0.1-1.0 mol / L to allow it to react fully with FeCl3 with a concentration of 0.1-1.0 mol / L. Then, centrifuge the carbon felt to generate Fe(OH)3 precipitate which is fully loaded onto the carbon felt for later use. Step 2) The carbon felt from Step 1) is soaked again in a pyrrole solution with a concentration of 0.01-0.5 wt%, and then placed in a hydrothermal reactor for hydrothermal synthesis, so that pyrrole self-polymerizes on the surface of Fe(OH)3 nanosheets. The carbon felt is then removed, washed, and dried for later use. Step 3) Place the carbon felt from Step 2) in a quartz tube furnace and heat it to 250-300℃ at a rate of 5 min / ℃ in air atmosphere for heat treatment. The heat treatment time is 0.5-3 h, and then it is naturally cooled to room temperature. Step 4) Remove the carbon felt and soak it in an HCl solution with a concentration of 2.0-6.0 mol / L, and shake it to fully dissolve the template, then wash it with deionized water; Step 5) The washed carbon felt is immersed in a SnCl4 solution with a concentration of 0.01-1.0 mol / L. Tin is deposited on the surface of the carbon felt electrode by constant voltage deposition method. After washing with deionized water, it is vacuum dried to obtain the finished high-activity carbon felt electrode used in iron-chromium redox flow batteries.

2. The preparation method according to claim 1, characterized in that: In step 1), the FeCl3 concentration is 0.1-0.5 mol / L; the NaOH concentration is 0.5-1.0 mol / L.

3. The preparation method according to claim 1, characterized in that: The ultrasonic treatment time in step 1) is 10-20 min.

4. The preparation method according to claim 1, characterized in that: In step 1), the centrifugation speed is 1000-2000 rpm and the time is 5-10 min.

5. The preparation method according to claim 1, characterized in that: Step 2) The concentration of the pyrrole solution is 0.2-0.5wt%, the hydrothermal synthesis conditions are 120-160 ℃, and the treatment time is 10-12 h.

6. The preparation method according to claim 1, characterized in that: The heat preservation treatment time in step 3) is 1-2 hours.

7. The preparation method according to claim 1, characterized in that: Step 4) The concentration of the HCl solution is 2.0-4.0 mol / L, and the ultrasonic vibration treatment time is 30-60 min.

8. The preparation method according to claim 1, characterized in that: Step 5) Using the SnCl4 solution with a concentration of 0.1-0.5 mol / L as the electrolyte, a constant voltage deposition process is carried out using a three-electrode system with a Pt sheet as the counter electrode, saturated calomel as the reference electrode, and carbon felt as the working electrode. The deposition voltage is -1.0 V to -1.6 V vs. SCE, and the deposition time is 30-60 s.

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