Nitrogen-doped metal monatomic graphite felt and preparation method thereof

Abstract

The application discloses a preparation method of a medium-nitrogen-doped metal monatomic graphite felt. The method comprises the following steps: cleaning and heat pretreating the graphite felt; preparing a Tris buffer solution, adding dopamine hydrochloride into the Tris buffer solution, adjusting the pH value, and obtaining a mixed solution; placing the heat pretreated graphite felt into the mixed solution, and passing oxygen-containing gas to form a polydopamine layer on the heat pretreated graphite felt; placing the obtained polydopamine graphite felt into a metal salt solution to react, forming a polydopamine graphite felt doped with metal; and performing calcination in a nitrogen atmosphere to obtain a nitrogen-doped metal monatomic graphite felt. The polydopamine is used as a complexing agent, and the modified metal is fixed on the graphite felt in a complexing manner, so that the stability of the metal catalyst loading is greatly improved, and the energy efficiency of a flow battery is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of electrode materials and applies to an iron-chromium redox flow battery (ICRFB), in particular to a preparation method of a high-performance nitrogen-doped metal monatomic graphite felt electrode material suitable for an iron-chromium redox flow battery. BACKGROUND

[0002] In recent years, since the carbon peak and carbon neutral targets were proposed, China has been developing clean energy at a great speed. Renewable energy such as wind energy and solar energy will become the main force of future energy. However, the intermittency and instability of renewable energy bring great challenges to the stable operation of the power system, and energy storage technology is an effective means to help realize the efficient use of renewable energy and the stable operation of the power system. Compared with physical energy storage technologies such as pumped storage, battery energy storage technology with higher flexibility gradually attracts people's attention. Among various battery energy storage technologies, flow batteries have become a large-scale battery energy storage technology with great development potential due to their long service life, high safety and high energy efficiency.

[0003] Flow batteries mainly use the change of the oxidation-reduction state of active substances in the solutions on the positive and negative sides to realize charging and discharging. A flow battery mainly consists of an electric pile and two electrolyte storage tanks. The electrolyte is stored in the liquid storage tank outside the electric pile and is delivered to the inside of the electric pile by a pump to perform oxidation-reduction reaction at the electrode. The active substances after the reaction flow back to the external storage tank with the electrolyte. Between the anode and the cathode is a diaphragm that can selectively allow the supporting electrolyte to pass through to maintain electrolyte balance. Among them, the iron-chromium flow battery is widely concerned due to its low cost and high cost performance, and is expected to become the next generation of emerging large-scale energy storage equipment. However, the low activity of Cr 3+ The lack of electrochemical activity and the occurrence of hydrogen evolution reaction (HER) restrict its large-scale application. Therefore, the modification of the electrode, electrolyte and membrane structure to assemble a flow battery with better performance has become the primary goal.

[0004] Carbon felt and graphite felt have the advantages of good electrical conductivity, good stability, high specific surface area, and pore structure conducive to improving the catalytic activity of the electrode. However, the specific surface area of graphite felt is small, the hydrophilic ability is poor, and the electrochemical activity and reversibility still cannot meet the demand of flow battery electrode materials. Therefore, surface modification must be carried out to improve the electrochemical activity of the electrode reaction, increase the wettability of the electrode, reduce the resistivity of the electrode, and prolong the service life of the electrode, which has become a research hotspot in recent years.

[0005] Patent CN112160156A discloses a preparation method of a modified carbon felt electrode material for a vanadium redox flow battery. The method includes the following steps: ultrasonicating and drying polyacrylonitrile-based graphite felt in anhydrous ethanol solution and deionized water, respectively, then heat treating under air conditions; soaking in a bismuth trioxide (Bi2O3) solution, then heating and drying to obtain a Bi-doped carbon felt, then soaking in a dopamine solution, adding a buffer, allowing the dopamine to polymerize, stirring for a period of time, then washing with deionized water, and placing in a tube furnace to carbonize under a nitrogen atmosphere to obtain a modified carbon felt electrode. The electrode prepared by the method increases the surface oxygen-containing functional groups and loads Bi, improving the electrochemical activity and electrical conductivity; in addition, the Bi2O3 is coated on the surface of the carbon felt by dopamine, making the loading more secure; and finally, high-temperature calcination carbonizes the dopamine as a carbon source and nitrogen source, further improving the electrochemical performance and electrical conductivity. However, the Bi2O3 is coated on the surface of the carbon felt by physical action, and the degree of firmness needs to be improved; and the dopamine coating prevents the Bi2O3 from being effectively exposed, limiting the catalytic effect; nitrogen doping helps to improve the electrochemical activity of the electrode, and the nitrogen doping treatment method and conditions still need to be further investigated. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a method for synthesizing an electrode material suitable for iron-chromium redox flow battery technology, to prepare a high-performance nitrogen-doped metal monatomic graphite felt electrode material. The method can obtain a low-cost high-performance composite graphite felt material, nitrogen-doping modification can improve the electrochemical activity of Cr 3+ , and the addition of functional metal monatomic atoms can inhibit the occurrence of hydrogen evolution reaction, achieving high energy efficiency of the redox flow battery.

[0007] To achieve the above-mentioned purposes, the first aspect of the present application provides a method for preparing a nitrogen-doped metal monatomic graphite felt.

[0008] A method for preparing a nitrogen-doped metal monatomic graphite felt, comprising the following steps:

[0009] (1) washing the graphite felt to remove various impurities inside the graphite felt, then removing water and drying;

[0010] (2) heat pretreating the graphite felt block obtained in step (1);

[0011] (3) preparing a Tris buffer solution, adding dopamine hydrochloride to the Tris buffer solution, adjusting the pH value, and stirring to make it uniform to obtain a mixed solution;

[0012] (4) placing the heat pretreated graphite felt of step (2) into the mixed solution obtained in step (3), and passing oxygen-containing gas, and fully and continuously stirring to form a polydopamine layer on the heat pretreated graphite felt;

[0013] (5) putting the polydopamine graphite felt prepared in step (4) into a metal salt solution to react, forming a metal-doped polydopamine graphite felt;

[0014] (6) baking the graphite felt prepared in step (5) in a nitrogen atmosphere to obtain a nitrogen-doped metal monatomic graphite felt.

[0015] Further, the cleaning of the graphite felt in step (1) is a routine operation in the art, which generally includes acetone cleaning and deionized water cleaning. Preferably, the graphite felt is first soaked in acetone for 1-4 h and ultrasonically treated for 0.2-1 h; then soaked in ethanol for 1-4 h and ultrasonically treated for 0.2-1 h; and then soaked in deionized water and ultrasonically treated for 0.2-1 h.

[0016] Further, the thermal pretreatment in step (2) is a routine operation in the art. For example, the graphite felt is subjected to thermal pretreatment in an oxygen-containing atmosphere, the thermal pretreatment temperature is generally 400-600 ℃, and the thermal pretreatment time is generally 3-6 h.

[0017] Further, the preparation of the Tris buffer solution in step (3) is a routine operation in the art. The concentration of the Tris buffer solution is generally 1.0-1.3 g / L.

[0018] Further, in step (3), the preparation of the dopamine hydrochloride solution is a routine operation in the art. For example, the concentration of the dopamine hydrochloride is generally 0.5-5 mg / mL Tris buffer solution, and preferably 1-3 mg / mL. The pH value of the obtained mixture (i.e., the Tris solution of dopamine hydrochloride) is adjusted to 8-9.

[0019] Further, in step (4), the oxygen-containing gas is preferably oxygen or air, and after the oxygen or air is introduced, the reaction temperature is generally 10-40 ℃; and the reaction time is 4-24 h.

[0020] Further, in step (5), the reaction temperature is generally 10-60 ℃, and the reaction time is generally 4-24 h.

[0021] Further, in step (6), the baking can be a routine operation in the art. For example, the graphite felt can be heated to 600-900 ℃ in a nitrogen atmosphere, and the baking time is 2-6 h. In the present application, a staged baking process is recommended. Specifically, the metal-doped polydopamine graphite felt obtained in step (5) is first heated to 300-500 ℃ in a nitrogen atmosphere, and the baking time is 0.5-2 h; and then heated to 600-900 ℃, and the baking time is 2-6 h.

[0022] Further, the metal salt in step (5) includes, but is not limited to, bismuth nitrate (Bi(NO3)3), cobalt nitrate (Co(NO3)2), indium nitrate (In(NO3)3), and the like nitrate compounds. The concentration of the metal salt solution is generally 0.5-3.0 mol / L.

[0023] The preparation method of the nitrogen-doped metal monatomic graphite felt provided by the application can be widely applied to the field of iron-chromium redox flow batteries to manufacture electrode materials.

[0024] According to the purposes of the application, the second aspect of the application provides a nitrogen-doped metal monatomic graphite felt prepared by the method described above.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. The application uses commercial graphite felt, dopamine hydrochloride, nitrate and the like as raw materials, realizes stable loading of metal catalysts on the graphite felt electrode based on the complexation between polydopamine and metals, and then obtains a nitrogen-doped metal monatomic graphite felt electrode material through calcination in a nitrogen atmosphere. Further preferably, nitrogen doping of the graphite felt is realized through staged calcination, the first stage of calcination mainly helps to form metal-N bonds, and the second stage of calcination at a higher temperature can form more active N on the surface of the graphite felt electrode, further improving the activity of the electrode. Through nitrogen doping modification, the composite electrode material prepared by the application can effectively improve the electrical conductivity and the electrochemical activity of Cr 3+ , and the addition of functional metal monatomic atoms can inhibit the occurrence of hydrogen evolution reaction, thereby realizing high energy efficiency of the flow battery.

[0027] 2. The most important advantage of the application lies in that polydopamine is used as a complexing agent to fix the modified metal on the graphite felt in a complexed manner, and the metal is mainly loaded in the form of adsorption and coating in traditional methods. The application greatly improves the stability of the metal catalyst loading, and compared with coating, the metal catalyst can be exposed on the surface of the electrode, thereby realizing the improvement of the energy efficiency of the flow battery.

[0028] 3. The preparation method of the modified graphite felt proposed by the application can batch produce graphite felt electrodes of a size for industrial application, and the raw materials are cheap and easy to obtain, the operation process is simple, and the method is green and pollution-free. Embodiments

[0029] The application will be described in detail below through specific embodiments, but the purposes and objectives of these exemplary embodiments are only used to exemplify the application, and do not constitute any form of any limitation on the actual protection scope of the application, and still less limit the protection scope of the application.

[0030] The graphite felt used in the examples and comparative examples of the present application is from Liaoyang Jingu Carbon Fiber Technology Co., Ltd.

[0031] In the examples and comparative examples, the test method of energy efficiency refers to the standard NB / T 42081-2016. Only the electrolyte used in the test is changed from VO 2+ sulfuric acid solution and V 3+ sulfuric acid solution is changed to Fe 2+ hydrochloric acid solution and Cr 3+ hydrochloric acid solution. Example 1

[0032] The polyacrylonitrile-based graphite felt is sequentially cleaned with acetone, anhydrous ethanol and deionized water for 30 min, and then placed in a muffle furnace for drying at 120°C in air for 4h, and then heated to 500°C at a heating rate of 2°C / min, and heat treated in air for 6h.

[0033] A Tris buffer solution with a concentration of 1.3 g / L is prepared; hydrochloric acid dopamine is added with a concentration of 2 mg / mL Tris buffer solution, and the pH value is adjusted to 9 to obtain a mixed solution. The graphite felt is placed in the mixed solution and oxygen is introduced, and the reaction is stirred at 40°C for 4h to obtain polydopamine / graphite felt.

[0034] The prepared polydopamine graphite felt is placed in a 1 mol / L bismuth nitrate solution and reacted at 40°C for 12h to form a metal-doped polydopamine graphite felt.

[0035] Finally, the modified electrode is obtained by calcining at 600°C for 2h under N2 atmosphere in a tube furnace.

[0036] The prepared modified graphite felt electrode is used in an iron-chromium flow battery for charge-discharge performance test, and the results show that the energy efficiency can reach 75.4%. Example 2

[0037] The polyacrylonitrile-based graphite felt is sequentially cleaned with acetone, anhydrous ethanol and deionized water for 30 min, and then placed in a muffle furnace for drying at 120°C in air for 4h, and then heated to 500°C at a heating rate of 2°C / min, and heat treated in air for 6h.

[0038] A Tris buffer solution with a concentration of 1.3 g / L is prepared; hydrochloric acid dopamine is added with a concentration of 2 mg / mL Tris buffer solution, and the pH value is adjusted to 9 to obtain a mixed solution. The graphite felt is placed in the mixed solution and oxygen is introduced, and the reaction is stirred at 40°C for 4h to obtain polydopamine / graphite felt.

[0039] The prepared polydopamine graphite felt is placed into a 1 mol / L bismuth nitrate solution and reacted at 40℃ for 12h to form a metal-doped polydopamine graphite felt.

[0040] Finally, under the protection of N2 atmosphere, the temperature is first increased to 400℃, and calcined for 1h, and then the temperature is continuously increased to 700℃, and calcined for 4h to obtain a nitrogen-doped metal monatomic graphite felt.

[0041] The prepared modified graphite felt electrode is used in an iron-chromium flow battery to perform charge-discharge performance test, and the results show that the energy efficiency can reach 77.8%. Example Three

[0042] The polyacrylonitrile-based graphite felt is sequentially ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30min, and then placed in a muffle furnace and dried at 120℃ in air for 4h, and then heated to 500℃ at a heating rate of 2℃ / min, and heat-treated in air for 6h.

[0043] A Tris buffer solution with a concentration of 1.3 g / L is prepared; hydrochloric acid dopamine is added to the Tris buffer solution with a concentration of 2 mg / mL, and the pH value is adjusted to 9 to obtain a mixed solution. The graphite felt is placed in the mixed solution, and oxygen is introduced, and the reaction is stirred at 40℃ for 24h to obtain a polydopamine / graphite felt.

[0044] The prepared polydopamine graphite felt is placed into a bismuth nitrate solution and reacted at 60℃ for 24h to form a metal-doped polydopamine graphite felt.

[0045] Finally, under the protection of N2 atmosphere, the temperature is first increased to 400℃, and calcined for 1h, and then the temperature is continuously increased to 700℃, and calcined for 4h to obtain a nitrogen-doped metal monatomic graphite felt.

[0046] The prepared modified graphite felt electrode is used in an iron-chromium flow battery to perform charge-discharge performance test, and the results show that the energy efficiency can reach 78.1%. Example Four

[0047] The polyacrylonitrile-based graphite felt is sequentially ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30min, and then placed in a muffle furnace and dried at 120℃ in air for 4h, and then heated to 500℃ at a heating rate of 2℃ / min, and heat-treated in air for 6h.

[0048] A Tris buffer solution with a concentration of 1.3 g / L was prepared; hydrochloric acid dopamine was added at a concentration of 2 mg / mL Tris buffer solution, and the pH value was adjusted to 9 to obtain a mixed solution. The graphite felt was placed in the mixed solution and oxygen was introduced, and the reaction was stirred at 40℃ for 4h to obtain polydopamine / graphite felt.

[0049] The prepared polydopamine graphite felt was placed in a 1 mol / L bismuth nitrate solution and reacted at 40℃ for 12h to form a metal-doped polydopamine graphite felt.

[0050] Finally, under the protection of N2 atmosphere, the temperature was first raised to 500℃ and calcined for 2h, and then the temperature was continuously raised to 900℃ and calcined for 6h to obtain nitrogen-doped metal monatomic graphite felt.

[0051] The prepared modified graphite felt electrode was used in an iron-chromium flow battery for charge-discharge performance test, and the results showed that the energy efficiency could reach 77.4%. Example Five

[0052] The polyacrylonitrile-based graphite felt was sequentially ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30min, and then placed in a muffle furnace and dried at 120℃ in air for 4h, and then heated to 500℃ at a rate of 2℃ / min, and heat-treated in air for 6h.

[0053] A Tris buffer solution with a concentration of 1.3 g / L was prepared; hydrochloric acid dopamine was added at a concentration of 2 mg / mL Tris buffer solution, and the pH value was adjusted to 9 to obtain a mixed solution. The graphite felt was placed in the mixed solution and oxygen was introduced, and the reaction was stirred at 40℃ for 4h to obtain polydopamine / graphite felt.

[0054] The prepared polydopamine graphite felt was placed in a 1 mol / L bismuth nitrate solution and reacted at 40℃ for 12h to form a metal-doped polydopamine graphite felt.

[0055] Finally, under the protection of N2 atmosphere, the temperature was first raised to 500℃ and calcined for 2h, and then the temperature was continuously raised to 900℃ and calcined for 6h to obtain nitrogen-doped metal monatomic graphite felt.

[0056] The prepared modified graphite felt electrode was used in an iron-chromium flow battery for charge-discharge performance test, and the results showed that the energy efficiency could reach 77.4%.

[0057] Comparative Example 1: (using the method disclosed in CN112160156A)

[0058] The polyacrylonitrile-based graphite felt was sequentially cleaned with acetone, anhydrous ethanol and deionized water for 30 min, and then was placed in a muffle furnace and dried at 120°C in air for 4 h, and then was heated to 500°C at a heating rate of 2°C / min, and was heat-treated in air for 6 h.

[0059] The graphite felt was immersed in a 1 mol / L bismuth nitrate solution for 10 h, and then was heated and dried in an oven at 90°C for 4 h to obtain a metal-doped graphite felt.

[0060] A tris (hydroxymethyl) aminomethane (Tris) buffer solution having a concentration of 1.3 g / L was prepared, and hydrochloric acid dopamine was added to the Tris buffer solution to have a concentration of 2 mg / mL Tris buffer solution, and the pH value was adjusted to 9 to obtain a mixed solution. The metal-doped graphite felt was immersed in the dopamine solution for 4 h, and then a tris (hydroxymethyl) aminomethane (Tris) buffer was added to coat the metal catalyst with dopamine. The Tris buffer solution had a concentration of 1.3 g / L, and the dopamine had a concentration of 2 mg / mL Tris buffer solution.

[0061] Finally, the modified electrode was calcined at 600°C in a tube furnace under N2 atmosphere for 2 h.

[0062] The prepared modified graphite felt electrode was used in an iron-chromium flow battery to test the charge-discharge performance, and the results showed that the energy efficiency could reach 73.2%.

[0063] Comparative Example 2:

[0064] The polyacrylonitrile-based graphite felt was sequentially cleaned with acetone, anhydrous ethanol and deionized water for 30 min, and then was placed in a muffle furnace and dried at 120°C in air for 4 h, and then was heated to 500°C at a heating rate of 2°C / min, and was heat-treated in air for 6 h.

[0065] The graphite felt was immersed in a 1 mol / L bismuth nitrate solution for 10 h, and then was heated and dried in an oven at 90°C for 4 h to obtain a metal-doped graphite felt.

[0066] A tris (hydroxymethyl) aminomethane (Tris) buffer solution having a concentration of 1.3 g / L was prepared, and hydrochloric acid dopamine was added to the Tris buffer solution to have a concentration of 2 mg / mL Tris buffer solution, and the pH value was adjusted to 9 to obtain a mixed solution. The metal-doped graphite felt was immersed in the dopamine solution for 4 h, and then a tris (hydroxymethyl) aminomethane (Tris) buffer was added to coat the metal catalyst with dopamine. The Tris buffer solution had a concentration of 1.3 g / L, and the dopamine had a concentration of 2 mg / mL Tris buffer solution.

[0067] Finally in the tube furnace, under the protection of N2 atmosphere, first heated to 400 ℃, calcined 1h, continue to heat to 700 ℃, calcination time is 4h, get modified electrode.

[0068] The prepared modified graphite felt electrode is used in iron-chromium flow battery, and charge-discharge performance test is carried out, and the results show that the energy efficiency can reach 74.7%.

Claims

1. A method for preparing nitrogen-doped metal single-atom graphite felt, characterized in that, Includes the following steps: (1) Clean the graphite felt to remove various impurities inside the graphite felt, and then remove water and dry it; (2) The graphite felt block obtained in step (1) is subjected to heat pretreatment; (3) Prepare Tris buffer solution, add dopamine hydrochloride to Tris buffer solution, adjust pH value, stir to make it uniform, and obtain a mixture; (4) Place the graphite felt after heat pretreatment in step (2) into the mixture obtained in step (3), introduce oxygen-containing gas, and stir thoroughly and continuously to form a polydopamine layer on the graphite felt after heat pretreatment. (5) The polydopamine graphite felt obtained in step (4) is placed in a metal salt solution for reaction to form a metal-doped polydopamine graphite felt; the metal salt is selected from one or more of bismuth nitrate, cobalt nitrate and indium nitrate, and the concentration of the metal salt solution is 0.5-3.0 mol / L; (6) The graphite felt obtained in step (5) is calcined in a nitrogen atmosphere to obtain nitrogen-doped metal single-atom graphite felt; the calcination is carried out in stages: the polydopamine graphite felt doped with metal obtained in step (5) is first heated to 300 ~ 500 ℃ in a nitrogen atmosphere, and the calcination time is 0.5 ~ 2 h; then the temperature is further increased to 600 ~ 900 ℃, and the calcination time is 2 ~ 6 h.

2. The preparation method according to claim 1, characterized in that, The heat pretreatment process in step (2) is as follows: the graphite felt is placed in an oxygen-containing atmosphere for heat pretreatment. The heat pretreatment temperature is 400~600 ℃ and the heat pretreatment time is 3~6 h.

3. The preparation method according to claim 1, characterized in that, The concentration of the Tris buffer solution in step (3) is 1.0-1.3 g / L.

4. The preparation method according to claim 1, characterized in that, The concentration of the mixture obtained in step (3) is 0.5-5 mg / mL Tris buffer solution, and the pH value of the mixture is 8-9.

5. The preparation method according to claim 1, characterized in that, In step (4), after oxygen or air is introduced, the reaction temperature is 10-40℃ and the reaction time is 4-24 h.

6. The preparation method according to claim 1, characterized in that, The reaction temperature in step (5) is 10-60 ℃ and the reaction time is 4-24 h.

7. The nitrogen-doped metal single-atom graphite felt obtained by any of the preparation methods described in claims 1-6.