Metal / carbon coated iron-chromium flow battery electrode material and preparation method thereof

Abstract

The invention provides a multi-metal / carbon coated iron-chromium flow battery electrode material and a preparation method thereof, and belongs to the technical field of iron-chromium flow battery energy storage. The preparation method comprises the following steps: carrying out pre-oxidation treatment, carbonization treatment and graphitization treatment on a precursor fiber felt to obtain a graphite felt; the preparation method comprises the following steps: dipping a graphite felt in a potassium hydroxide solution, then drying and carrying out primary calcination treatment, dipping an activated felt in a metal salt solution, then drying and carrying out secondary calcination treatment, dipping a multi-metal loaded activated felt in a dopamine solution containing a conductive agent, then adding a buffer solution until the pH value of the solution is 8-10 so as to enable dopamine to be self-polymerized, and then carrying out tertiary calcination treatment so as to obtain the multi-metal loaded activated felt. The multi-metal / carbon coated iron-chromium flow battery electrode material is obtained. The multi-metal / carbon coated iron-chromium flow battery electrode material disclosed by the invention has high hydrophilicity, high hydrogen evolution overpotential, high specific surface area, high energy efficiency and long cycle stability.

Description

Technical Field

[0001] This invention relates to the field of iron-chromium redox flow battery energy storage technology, and in particular to a multi-metal / carbon-coated iron-chromium redox flow battery electrode material and its preparation method. Background Technology

[0002] Energy storage technology is a key means to alleviate the imbalance between energy demand and supply, improve the efficiency of renewable energy utilization, and enhance the security and flexibility of energy system supply. Among them, flow batteries have a strong competitive advantage in the field of large-scale, long-term energy storage due to their advantages such as safety and reliability, long cycle life, flexible structural design, and environmental friendliness. Because iron and chromium are widely available, have high solubility, are inexpensive, and have low corrosiveness, and because iron-chromium mixed electrolytes can be used for both positive and negative electrodes, thus avoiding cross-contamination of active ions during battery charging and discharging, iron-chromium redox flow batteries have become a promising flow battery technology.

[0003] As the site of electrochemical reactions in flow batteries, the electrode's response rate directly impacts battery performance. Electrode materials should possess excellent chemical stability for acid and corrosion resistance, high specific surface area and porosity to ensure sufficient electrochemical reaction area, low resistance to minimize ohmic losses caused by current flow, and high overpotential for hydrogen evolution and oxygen evolution side reactions. However, the carbon felt electrodes used in traditional iron-chromium flow batteries often suffer from poor electrochemical activity and high charge transfer resistance due to their poor hydrophilicity and low specific surface area. Furthermore, in iron-chromium flow batteries, the slow kinetics of the Cr anode and the severe hydrogen evolution side reactions further affect the electrodes, increasing battery polarization and impacting efficiency and cycle life.

[0004] Therefore, modifying the electrode material of iron-chromium redox flow batteries is an important means to improve performance. Providing a multi-metal / carbon-coated iron-chromium redox flow battery electrode material and its preparation method is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-metal / carbon-coated iron-chromium flow battery electrode material and its preparation method, which alleviates the serious hydrogen evolution side reaction problem on the surface of the iron-chromium flow battery electrode, thereby significantly improving energy efficiency and cycle stability.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a multi-metal / carbon-coated iron-chromium flow battery electrode material, comprising the following steps: 1) The raw filament fiber felt is pre-oxidized to obtain pre-oxidized fiber felt; 2) The pre-oxidized fiber felt is carbonized in an inert gas atmosphere to obtain carbon fiber felt; 3) Graphitize the carbon fiber felt in an inert gas atmosphere to obtain graphite felt; 4) The graphite felt is impregnated in potassium hydroxide solution and then dried, and then calcined once under an inert gas atmosphere to obtain activated felt; 5) The activated felt is immersed in a metal salt solution and then dried. It is then subjected to a second calcination treatment under an inert gas atmosphere to obtain a multi-metal loaded activated felt. 6) After impregnating the multi-metal-loaded activated felt with a dopamine solution containing a conductive agent, a buffer solution was added to the dopamine solution to adjust the pH value to 8-10 to allow the dopamine to self-polymerize. Then, the solution was subjected to three calcination treatments under an inert gas atmosphere to obtain the multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0007] Preferably, the precursor fiber mat in step 1) comprises polyacrylonitrile-based precursor fiber mat and / or viscose-based precursor fiber mat; the temperature of the pre-oxidation treatment is 200~320℃, the time of the pre-oxidation treatment is 1~4h, and the pre-oxidation treatment is carried out in an air atmosphere.

[0008] Preferably, the carbonization temperature in step 2) is 900~1700℃ and the carbonization time is 0.5~5h; the graphitization temperature in step 3) is 1900~2800℃ and the graphitization time is 0.5~5h.

[0009] Preferably, in step 4), the mass fraction of the potassium hydroxide solution is 2-10%; the soaking time is 10-30 min; the drying temperature is 80-120℃; the drying time is 0.5-3 h; and the temperature of the first calcination treatment is 500-1000℃; the first calcination treatment time is 0.5-3 h.

[0010] Preferably, the metal salt solution in step 5) comprises a metal salt and an acid solution. The metal salt includes two or more of tin nitrate, bismuth nitrate, lead nitrate, tin sulfate, bismuth sulfate and lead sulfate. The concentration of the acid solution is 0.8~1.2 mol / L. The acid solution includes one or more of sulfuric acid, hydrochloric acid and nitric acid solutions. The mass fraction of each metal salt in the acid solution is independently 0.2~4%.

[0011] Preferably, the soaking time in step 5) is 5-10 min; the drying temperature is 80-150℃ and the drying time is 0.5-3 h; the temperature of the secondary calcination treatment is 400-800℃ and the secondary calcination treatment time is 0.5-3 h.

[0012] Preferably, the concentration of the dopamine solution in step 6) is 0.01~0.05mol / L, the mass fraction of the conductive agent in the dopamine solution is 0.5~10%, and the conductive agent includes one or more of carbon black, reduced graphene oxide and polyaniline; The buffer solution contains Tris buffer and / or borate-borax buffer, with a concentration of 0.01~0.1 mol / L.

[0013] Preferably, the temperature of the three calcination treatments in step 6) is 600~900℃, and the time of the three calcination treatments is 0.5~3h; the inert gas atmosphere in steps 2) to 6) is nitrogen and / or argon.

[0014] The present invention also provides a multi-metal / carbon-coated iron-chromium redox flow battery electrode material prepared by the aforementioned preparation method.

[0015] The beneficial effects of this invention are: This invention pre-oxidizes, carbonizes, and graphitizes the raw fiber felt, promoting the regular arrangement of graphite microcrystals on the fiber surface and improving fiber conductivity. Activation with potassium hydroxide introduces oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the fiber surface to improve hydrophilicity, while simultaneously increasing specific surface area and porosity. This facilitates the uniform and stable binding of metal oxides generated from the subsequent carbothermal decomposition of metal salts within the fiber pores. The metal oxides generated from the carbothermal decomposition of metal salts, bound to the fiber surface, provide additional active sites and significantly increase the hydrogen evolution overpotential, effectively suppressing the occurrence of hydrogen evolution side reactions. Furthermore, the self-polymerization of dopamine on the fiber surface and the subsequent carbon layer coating of the metal oxides during calcination further ensure the stable binding of the metal oxides to the fiber surface, preventing them from detaching after long-term cycling.

[0016] The multi-metal / carbon-coated iron-chromium flow battery electrode material prepared by the method of the present invention possesses both high hydrophilicity and high hydrogen evolution overpotential (≤-0.6V, 20mA / cm). 2 High specific surface area (≥6.0m²) 2 / g), high energy efficiency (≥75%, 80mA / cm²) 2 ) and long-cycle stability. Attached Figure Description

[0017] Figure 1 The multi-metal / carbon-coated iron-chromium flow battery electrode material of Example 1 was applied in an iron-chromium flow battery at a current density of 80 mA / cm². 2 Cyclic performance graph under the given conditions; Figure 2 The graph shows the rate performance of the multi-metal / carbon-coated iron-chromium flow battery electrode material from Example 1 applied to an iron-chromium flow battery. Detailed Implementation

[0018] This invention provides a method for preparing a multi-metal / carbon-coated iron-chromium flow battery electrode material, comprising the following steps: 1) The raw filament fiber felt is pre-oxidized to obtain pre-oxidized fiber felt; 2) The pre-oxidized fiber felt is carbonized in an inert gas atmosphere to obtain carbon fiber felt; 3) Graphitize the carbon fiber felt in an inert gas atmosphere to obtain graphite felt; 4) The graphite felt is impregnated in potassium hydroxide solution and then dried, and then calcined once under an inert gas atmosphere to obtain activated felt; 5) The activated felt is immersed in a metal salt solution and then dried. It is then subjected to a second calcination treatment under an inert gas atmosphere to obtain a multi-metal loaded activated felt. 6) After impregnating the multi-metal-loaded activated felt with a dopamine solution containing a conductive agent, a buffer solution was added to the dopamine solution to adjust the pH value to 8-10 to allow the dopamine to self-polymerize. Then, the solution was subjected to three calcination treatments under an inert gas atmosphere to obtain the multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0019] In this invention, the precursor fiber felt in step 1) preferably comprises polyacrylonitrile-based precursor fiber felt and / or viscose-based precursor fiber felt; the temperature of the pre-oxidation treatment is preferably 200~320℃, more preferably 220~300℃, and even more preferably 260~280℃; the time of the pre-oxidation treatment is preferably 1~4h, more preferably 2~3h; and the pre-oxidation treatment is preferably carried out in an air atmosphere.

[0020] In this invention, the carbonization temperature in step 2) is preferably 900~1700℃, more preferably 1000~1500℃, and even more preferably 1100~1200℃, and the carbonization time is preferably 0.5~5h, more preferably 1~4h, and even more preferably 2~3h; the graphitization temperature in step 3) is preferably 1900~2800℃, more preferably 2000~2300℃, and even more preferably 2100~2200℃, and the graphitization time is preferably 0.5~5h, more preferably 1~4h, and even more preferably 2~3h.

[0021] In this invention, the mass fraction of the potassium hydroxide solution in step 4) is preferably 2-10%, more preferably 4-9%, and even more preferably 5-8%; the soaking time is preferably 10-30 min, more preferably 15-28 min, and even more preferably 20-25 min; the drying temperature is preferably 80-120℃, more preferably 90-110℃, and even more preferably 95-100℃, and the drying time is preferably 0.5-3 h, more preferably 1-2.5 h, and even more preferably 1.5-2 h; the temperature of the first calcination treatment is preferably 500-1000℃, more preferably 600-900℃, and even more preferably 700-800℃, and the first calcination treatment time is preferably 0.5-3 h, more preferably 1-2.5 h, and even more preferably 1.5-2 h.

[0022] In this invention, the metal salt solution in step 5) preferably comprises a metal salt and an acid solution. The metal salt preferably includes two or more of tin nitrate, bismuth nitrate, lead nitrate, tin sulfate, bismuth sulfate, and lead sulfate. The concentration of the acid solution is preferably 0.8-1.2 mol / L, more preferably 0.9-1.1 mol / L, and more preferably 1 mol / L. The acid solution preferably includes one or more of sulfuric acid, hydrochloric acid, and nitric acid solutions. The mass fraction of each metal salt in the acid solution is preferably 0.2-4%, more preferably 1-2.5%, and more preferably 1.5-2%.

[0023] In this invention, the soaking time in step 5) is preferably 5-10 min, more preferably 6-9 min, and even more preferably 7-8 min; the drying temperature is preferably 80-150℃, more preferably 100-140℃, and even more preferably 120-130℃, and the drying time is preferably 0.5-3 h, more preferably 1-2.5 h, and even more preferably 1.5-2 h; the temperature of the secondary calcination treatment is preferably 400-800℃, more preferably 500-750℃, and even more preferably 600-700℃, and the secondary calcination treatment time is preferably 0.5-3 h, more preferably 1-2.5 h, and even more preferably 1.5-2 h.

[0024] In this invention, the concentration of the dopamine solution in step 6) is preferably 0.01~0.05 mol / L, more preferably 0.02~0.04 mol / L, and even more preferably 0.03 mol / L. The mass fraction of the conductive agent in the dopamine solution is preferably 0.5~10%, more preferably 2~8%, and even more preferably 4~6%. The conductive agent preferably includes one or more of carbon black, reduced graphene oxide, and polyaniline. The buffer solution preferably comprises Tris buffer and / or borate-borax buffer, and the concentration of the buffer solution is preferably 0.01~0.1 mol / L, more preferably 0.02~0.08 mol / L, and even more preferably 0.04~0.06 mol / L.

[0025] In this invention, the temperature of the three calcination treatments in step 6) is preferably 600~900℃, more preferably 700~850℃, and even more preferably 750~800℃; the time of the three calcination treatments is preferably 0.5~3h, more preferably 1~2.5h, and even more preferably 1.5~2h; the inert gas atmosphere in steps 2) to 6) is preferably nitrogen and / or argon.

[0026] The present invention also provides a multi-metal / carbon-coated iron-chromium redox flow battery electrode material prepared by the aforementioned preparation method.

[0027] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0028] In the embodiments, the method for assembling the multi-metal / carbon-coated iron-chromium flow battery electrode materials into an iron-chromium flow battery can be any method well known in the art.

[0029] Example 1

[0030] Polyacrylonitrile-based filament felt was pre-oxidized in air at a temperature of 220°C for 1 hour to obtain polyacrylonitrile-based pre-oxidized felt.

[0031] Polyacrylonitrile-based pre-oxidized felt was carbonized under a nitrogen atmosphere at a temperature of 1200℃ for 1 hour to obtain polyacrylonitrile-based carbon felt.

[0032] Polyacrylonitrile-based carbon felt was graphitized under an argon atmosphere at a temperature of 2000℃ for 2 hours to obtain polyacrylonitrile-based graphite felt.

[0033] Polyacrylonitrile-based graphite felt was immersed in a 5% potassium hydroxide aqueous solution for 30 minutes and then dried at 80°C for 3 hours. Subsequently, the polyacrylonitrile-based graphite felt was calcined once under a nitrogen atmosphere at a temperature of 700°C for 0.5 hours to obtain polyacrylonitrile-based activated felt.

[0034] The polyacrylonitrile-based activated felt was immersed in a mixed solution of bismuth nitrate and lead nitrate (the solvent was a 1 mol / L nitric acid solution, and the mass fraction of bismuth nitrate and lead nitrate in the nitric acid solution was 1%). After immersion for 5 min, it was dried at 80 °C for 3 h. Subsequently, the polyacrylonitrile-based activated felt was subjected to a second calcination treatment under a nitrogen atmosphere at a temperature of 600 °C for 0.5 h to obtain a multi-metal-supported polyacrylonitrile-based activated felt.

[0035] A multi-metal-supported polyacrylonitrile-based activated felt was impregnated in a 0.02 mol / L dopamine aqueous solution containing reduced graphene oxide (1% by mass). Tris buffer (0.02 mol / L) was added to the dopamine aqueous solution until the pH of the solution was 9, allowing the dopamine to self-polymerize. Subsequently, the solution was subjected to three calcination treatments under a nitrogen atmosphere at a temperature of 700 °C for 1 h to obtain a multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0036] The specific surface area and hydrogen evolution overpotential of the multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 1 were tested. The test results showed that the specific surface area of ​​the electrode material prepared in Example 1 was 7.5 m². 2 / g, the hydrogen evolution overpotential is -0.68V.

[0037] The multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 1 was assembled into an iron-chromium flow battery and subjected to charge-discharge tests. The multi-metal / carbon-coated iron-chromium flow battery electrode material of Example 1 was applied in an iron-chromium flow battery, and the charge-discharge test was performed at a current density of 80 mA / cm². 2 The cyclic performance under the conditions is shown in the figure. Figure 1 As shown; the rate performance of the multi-metal / carbon-coated iron-chromium flow battery electrode material of Example 1 applied to an iron-chromium flow battery is shown in the figure. Figure 2 As shown. By Figure 1 It can be seen that the assembled battery operates at a current density of 80 mA / cm². 2 At that time, the obtained coulombic efficiency was 96.63%, voltage efficiency was 81.98%, and energy efficiency was 79.23%. Figure 2 It can be seen that the electrode material of the multi-metal / carbon-coated iron-chromium flow battery is at 60 mA / cm 2 80mA / cm 2 100mA / cm 2 Under current density charge and discharge conditions, the energy efficiencies are 83.67%, 79.61%, and 76.54%, respectively, and the voltage efficiencies are 85.22%, 80.80%, and 77.41%, respectively, indicating that it has good rate performance.

[0038] Example 2

[0039] The viscose-based filament felt was pre-oxidized in air at a temperature of 250°C for 1 hour to obtain the viscose-based pre-oxidized felt.

[0040] The viscose-based pre-oxidized felt was carbonized in a nitrogen atmosphere at a temperature of 1100℃ for 1 hour to obtain viscose-based carbon felt.

[0041] The viscose-based carbon felt was graphitized under an argon atmosphere at a temperature of 2000℃ for 3 hours to obtain the viscose-based graphite felt.

[0042] The viscose-based graphite felt was immersed in a 4% potassium hydroxide aqueous solution for 20 minutes and then dried at 80°C for 3 hours. Subsequently, the viscose-based graphite felt was calcined once under a nitrogen atmosphere at 800°C for 2 hours to obtain viscose-based activated felt.

[0043] The viscose-based activated felt was immersed in a mixed solution of bismuth nitrate and tin nitrate (the solvent was a 1 mol / L nitric acid solution, and the mass fraction of bismuth nitrate and tin nitrate in the nitric acid solution was 2%), and then dried at 80℃ for 3 hours. Subsequently, the viscose-based activated felt was subjected to a second calcination treatment under a nitrogen atmosphere at a temperature of 600℃ for 1 hour to obtain a multi-metal-loaded viscose-based activated felt.

[0044] A multi-metal-loaded viscose-based activated felt was impregnated in a 0.03 mol / L dopamine aqueous solution containing reduced graphene oxide (5% by mass). Tris buffer (0.05 mol / L) was added to the dopamine aqueous solution until the pH of the solution was 8, allowing the dopamine to self-polymerize. Subsequently, the solution was subjected to three calcination treatments under a nitrogen atmosphere at a temperature of 700 °C for 1 h to obtain a multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0045] The specific surface area and hydrogen evolution overpotential of the multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 2 were tested. The test results showed that the specific surface area of ​​the electrode material prepared in Example 2 was 6.9 m². 2 / g, the hydrogen evolution overpotential is -0.62V.

[0046] The multi-metal / carbon-coated iron-chromium flow battery electrode materials prepared in Example 2 were assembled into an iron-chromium flow battery and subjected to charge-discharge tests. The current density was 80 mA / cm². 2 At that time, the obtained coulombic efficiency was 97.24%, voltage efficiency was 80.49%, and energy efficiency was 78.27%.

[0047] Example 3

[0048] The viscose-based filament felt was pre-oxidized in air at a temperature of 220°C for 1 hour to obtain the viscose-based pre-oxidized felt.

[0049] The viscose-based pre-oxidized felt was carbonized in a nitrogen atmosphere at a temperature of 1000℃ for 1 hour to obtain viscose-based carbon felt.

[0050] The viscose-based carbon felt was graphitized under an argon atmosphere at a temperature of 1900℃ for 2 hours to obtain the viscose-based graphite felt.

[0051] The viscose-based graphite felt was immersed in an 8% potassium hydroxide aqueous solution for 15 minutes and then dried at 80°C for 3 hours. Subsequently, the viscose-based graphite felt was calcined once under a nitrogen atmosphere at a temperature of 600°C for 2 hours to obtain viscose-based activated felt.

[0052] The viscose-based activated felt was immersed in a mixed solution of lead nitrate and tin nitrate (the solvent was a 1 mol / L nitric acid solution, and the mass fraction of lead nitrate and tin nitrate in the nitric acid solution was 2%), and then dried at 80°C for 3 hours. Subsequently, the viscose-based activated felt was subjected to a second calcination treatment under a nitrogen atmosphere at a temperature of 600°C for 1 hour to obtain a multi-metal-loaded viscose-based activated felt.

[0053] A multi-metal-loaded viscose-based activated felt was impregnated in a 0.03 mol / L dopamine aqueous solution containing polyaniline (the relative molecular mass of polyaniline is 20000 g / mol, and its mass fraction in the dopamine aqueous solution is 5%). Tris buffer (concentration of 0.05 mol / L) was added to the dopamine aqueous solution until the pH of the solution was 10 to induce dopamine self-polymerization. Subsequently, the solution was subjected to three calcination treatments under a nitrogen atmosphere at a temperature of 600 °C for 1 h to obtain a multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0054] The specific surface area and hydrogen evolution overpotential of the multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 3 were tested. The test results showed that the specific surface area of ​​the electrode material prepared in Example 3 was 7.8 m². 2 / g, the hydrogen evolution overpotential is -0.68V.

[0055] The multi-metal / carbon-coated iron-chromium flow battery electrode materials prepared in Example 3 were assembled into an iron-chromium flow battery and subjected to charge-discharge tests. The current density was 80 mA / cm². 2At that time, the obtained coulombic efficiency was 96.28%, voltage efficiency was 79.26%, and energy efficiency was 76.31%.

[0056] Example 4

[0057] Polyacrylonitrile-based filament felt was pre-oxidized in air at a temperature of 250°C for 1 hour to obtain polyacrylonitrile-based pre-oxidized felt.

[0058] Polyacrylonitrile-based pre-oxidized felt was carbonized under a nitrogen atmosphere at a temperature of 1200℃ for 1 hour to obtain polyacrylonitrile-based carbon felt.

[0059] Polyacrylonitrile-based carbon felt was graphitized under an argon atmosphere at a temperature of 2200℃ for 2 hours to obtain polyacrylonitrile-based graphite felt.

[0060] Polyacrylonitrile-based graphite felt was immersed in a 6% potassium hydroxide aqueous solution for 20 minutes and then dried at 80°C for 3 hours. Subsequently, the polyacrylonitrile-based graphite felt was calcined once under a nitrogen atmosphere at 800°C for 1 hour to obtain polyacrylonitrile-based activated felt.

[0061] The polyacrylonitrile-based activated felt was immersed in a mixed solution of bismuth nitrate and tin nitrate (the solvent was a 1 mol / L nitric acid solution, and the mass fraction of bismuth nitrate and tin nitrate in the nitric acid solution was 1.5%). After immersion for 10 min, it was dried at 80 °C for 3 h. Subsequently, the polyacrylonitrile-based activated felt was subjected to a second calcination treatment under a nitrogen atmosphere at a temperature of 700 °C for 1 h to obtain a multi-metal-supported polyacrylonitrile-based activated felt.

[0062] A multi-metal-supported polyacrylonitrile-based activated felt was impregnated in a 0.05 mol / L dopamine aqueous solution containing reduced graphene oxide (5% by mass). Tris buffer (0.05 mol / L) was added to the dopamine aqueous solution until the pH of the solution was 9, allowing the dopamine to self-polymerize. Subsequently, the solution was subjected to three calcination treatments under a nitrogen atmosphere at a temperature of 800 °C for 1 h to obtain a multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0063] The specific surface area and hydrogen evolution overpotential of the multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 4 were tested. The test results showed that the specific surface area of ​​the electrode material prepared in Example 4 was 6.3 m². 2 / g, the hydrogen evolution overpotential is -0.65V.

[0064] The multi-metal / carbon-coated iron-chromium flow battery electrode materials prepared in Example 4 were assembled into an iron-chromium flow battery and subjected to charge-discharge tests. The current density was 80 mA / cm². 2 At that time, the obtained coulombic efficiency was 97.39%, voltage efficiency was 81.83%, and energy efficiency was 79.69%.

[0065] Example 5

[0066] The viscose-based filament felt was pre-oxidized in air at a temperature of 250°C for 1 hour to obtain the viscose-based pre-oxidized felt.

[0067] The viscose-based pre-oxidized felt was carbonized in a nitrogen atmosphere at a temperature of 1100℃ for 1 hour to obtain viscose-based carbon felt.

[0068] The viscose-based carbon felt was graphitized under an argon atmosphere at a temperature of 2300℃ for 1 hour to obtain the viscose-based graphite felt.

[0069] The viscose-based graphite felt was immersed in a 2% potassium hydroxide aqueous solution for 20 minutes and then dried at 80°C for 3 hours. Subsequently, the viscose-based graphite felt was calcined once under a nitrogen atmosphere at a temperature of 600°C for 1 hour to obtain viscose-based activated felt.

[0070] The viscose-based activated felt was immersed in a mixed solution of lead nitrate and tin nitrate (the solvent was a 1 mol / L nitric acid solution, and the mass fraction of lead nitrate and tin nitrate in the nitric acid solution was 2%), and then dried at 80°C for 3 hours. Subsequently, the viscose-based activated felt was subjected to a second calcination treatment under a nitrogen atmosphere at a temperature of 700°C for 1 hour to obtain a multi-metal-loaded viscose-based activated felt.

[0071] A multi-metal-loaded viscose-based activated felt was impregnated in a 0.02 mol / L dopamine aqueous solution containing carbon black (5% by mass). A boric acid-borax buffer solution (0.05 mol / L) was added to the dopamine aqueous solution until the pH of the solution was 9, allowing the dopamine to self-polymerize. Subsequently, the solution was subjected to three calcination treatments under a nitrogen atmosphere at a temperature of 700 °C for 1 h to obtain a multi-metal / carbon-coated iron-chromium flow battery electrode material.

[0072] The specific surface area and hydrogen evolution overpotential of the multi-metal / carbon-coated iron-chromium flow battery electrode material prepared in Example 5 were tested. The test results showed that the specific surface area of ​​the electrode material prepared in Example 5 was 8.3 m². 2 / g, the hydrogen evolution overpotential is -0.67V.

[0073] The multi-metal / carbon-coated iron-chromium flow battery electrode materials prepared in Example 5 were assembled into an iron-chromium flow battery and subjected to charge-discharge tests. The current density was 80 mA / cm². 2 At that time, the obtained coulombic efficiency was 96.71%, voltage efficiency was 78.24%, and energy efficiency was 75.67%.

[0074] The multi-metal / carbon-coated iron-chromium flow battery electrode material of this invention is applied to iron-chromium flow batteries. The introduction of multiple metal elements can effectively suppress the hydrogen evolution side reaction during the redox reaction of chromium ions at the negative electrode of the iron-chromium flow battery, and the layered carbon coating structure can effectively avoid the performance degradation caused by the shedding of metal elements during the charge and discharge process of the flow battery, thereby improving energy efficiency and long-cycle stability. 2 At current density, the energy efficiency is higher than 75%, the voltage efficiency is higher than 78%, and the coulombic efficiency is higher than 96%, remaining stable in a 50-cycle long test.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-metal / carbon-coated iron-chromium flow battery electrode material, characterized in that, It includes the following steps: 1) The raw filament fiber felt is pre-oxidized to obtain pre-oxidized fiber felt; 2) The pre-oxidized fiber felt is carbonized in an inert gas atmosphere to obtain carbon fiber felt; 3) Graphitize the carbon fiber felt in an inert gas atmosphere to obtain graphite felt; 4) The graphite felt is impregnated in potassium hydroxide solution and then dried, and then calcined once under an inert gas atmosphere to obtain activated felt; 5) The activated felt is immersed in a metal salt solution and then dried. It is then subjected to a second calcination treatment under an inert gas atmosphere to obtain a multi-metal loaded activated felt. 6) After impregnating the multi-metal-loaded activated felt with a dopamine solution containing a conductive agent, a buffer solution was added to the dopamine solution to adjust the pH value to 8-10 to allow the dopamine to self-polymerize. Then, the solution was subjected to three calcination treatments under an inert gas atmosphere to obtain the multi-metal / carbon-coated iron-chromium flow battery electrode material.

2. The preparation method according to claim 1, characterized in that, Step 1) The precursor fiber felt comprises polyacrylonitrile-based precursor fiber felt and / or viscose-based precursor fiber felt; the pre-oxidation treatment temperature is 200~320℃, the pre-oxidation treatment time is 1~4h, and the pre-oxidation treatment is carried out in an air atmosphere.

3. The preparation method according to claim 1 or 2, characterized in that, Step 2) The carbonization temperature is 900~1700℃ and the carbonization time is 0.5~5h; Step 3) The graphitization temperature is 1900~2800℃ and the graphitization time is 0.5~5h.

4. The preparation method according to claim 3, characterized in that, Step 4) The mass fraction of the potassium hydroxide solution is 2-10%; the soaking time is 10-30 min; the drying temperature is 80-120℃; the drying time is 0.5-3 h; the temperature of the first calcination treatment is 500-1000℃; and the time of the first calcination treatment is 0.5-3 h.

5. The preparation method according to claim 4, characterized in that, Step 5) The metal salt solution comprises a metal salt and an acid solution. The metal salt includes two or more of tin nitrate, bismuth nitrate, lead nitrate, tin sulfate, bismuth sulfate and lead sulfate. The concentration of the acid solution is 0.8~1.2 mol / L. The acid solution includes one or more of sulfuric acid, hydrochloric acid and nitric acid solutions. The mass fraction of each metal salt in the acid solution is independently 0.2~4%.

6. The preparation method according to claim 5, characterized in that, Step 5) The soaking time is 5~10 min; the drying temperature is 80~150℃ and the drying time is 0.5~3 h; the secondary calcination temperature is 400~800℃ and the secondary calcination time is 0.5~3 h.

7. The preparation method according to any one of claims 4 to 6, characterized in that, Step 6) The concentration of the dopamine solution is 0.01~0.05mol / L, the mass fraction of the conductive agent in the dopamine solution is 0.5~10%, and the conductive agent includes one or more of carbon black, reduced graphene oxide and polyaniline; The buffer solution contains Tris buffer and / or borate-borax buffer, with a concentration of 0.01~0.1 mol / L.

8. The preparation method according to claim 7, characterized in that, Step 6) The temperature of the three calcination treatments is 600~900℃, and the time of the three calcination treatments is 0.5~3h; the inert gas atmosphere in steps 2) to 6) is nitrogen and / or argon.

9. The multi-metal / carbon-coated iron-chromium redox flow battery electrode material prepared by the preparation method according to any one of claims 1 to 8.

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