A carbon-based electrode for a flow battery and its preparation method and application

Abstract

The present invention relates to a carbon-based electrode for a liquid flow battery, a preparation method thereof, and an application thereof. The preparation method comprises the following steps: dissolving a cobalt salt and an alkali in a polar organic solvent respectively, and mixing them uniformly to form a precursor solution; placing a carbon-based material in the precursor solution, performing a hydrothermal reaction, and obtaining a carbon-based electrode precursor; performing high-temperature carbonization on the carbon-based electrode precursor under an inert atmosphere, cooling the carbon-based electrode precursor to room temperature after the reaction is completed, and then washing and removing impurities from the product to obtain the carbon-based electrode; the polar organic solvent is at least one of formamide, acetonitrile, and N,N-dimethylformamide; and the present invention achieves surface modification of the carbon-based material by depositing cobalt cyanide on the surface of the carbon-based material and then performing surface etching and nitrogen doping on the carbon-based material under high-temperature conditions, thereby increasing the contact area between the carbon-based electrode surface and the electrolyte and improving the electrochemical performance of the carbon-based electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow battery electrode materials, and more specifically, to a liquid flow battery carbon-based electrode and a preparation method and application thereof. Background Art

[0002] Amidst the global energy transition, developing efficient energy storage technologies has become crucial for addressing the intermittent nature of renewable energy sources, such as solar and wind power. Flow batteries, with their power-capacity decoupling design, long cycle life, and high safety, are considered a promising option for large-scale energy storage systems. While vanadium redox flow batteries (VRFBs) have achieved commercial demonstration applications after over four decades of development, their energy conversion efficiency and cycling stability remain constrained by bottlenecks in electrode material performance.

[0003] Carbon-based materials (such as graphite felt and carbon cloth), as mainstream electrodes for all-vanadium redox flow batteries (VRFBs), offer advantages such as low cost and excellent chemical stability. However, they face three inherent drawbacks: a scarcity of active sites (insufficient effective surface area, resulting in sluggish reaction kinetics), low intrinsic activity (a lack of catalytically active centers and high charge transfer impedance), and a structure-function imbalance (traditional modification methods often enhance activity at the expense of mechanical strength). Existing electrode modification techniques have significant limitations: while thermal activation can introduce oxygen-containing functional groups, the increase in active site density is limited; strong acid oxidation severely erodes the carbon fiber lattice structure, resulting in a decrease in tensile strength and affecting the electrode's mechanical properties; while noble metal modification can enhance catalytic activity, it is costly and poses metal dissolution contamination issues; and plasma treatment relies on specialized equipment and has a low processing rate, making it difficult to scale up. These limitations severely restrict the widespread application and performance improvement of electrode modification techniques in all-vanadium redox flow batteries.

[0004] Therefore, the development of electrode modification technology that combines high activity, strong durability and low cost has become a core issue to break through the bottleneck of the industrialization of all-vanadium liquid flow batteries. Summary of the Invention

[0005] Based on the above-mentioned technical problems existing in the prior art, the present invention provides a method for preparing a carbon-based electrode for a liquid flow battery. This method forms a nitrogen-doped porous carbon fiber surface on the surface of the carbon-based material by in-situ etching and doping the carbon-based material under high temperature conditions. This can effectively increase the contact area between the electrode and the electrolyte, and promote the sufficient diffusion of electrons and ions at the interface. At the same time, the porous defects and nitrogen doping help to enhance the electrocatalytic activity of the electrochemical active sites, so that the obtained carbon-based electrode exhibits excellent electrochemical performance.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for preparing a carbon-based electrode for a flow battery comprises the following steps:

[0008] S1, dissolving the cobalt salt and the base in a polar organic solvent respectively, and mixing them evenly to form a precursor solution;

[0009] S2. placing the carbon-based material in the precursor solution and performing a hydrothermal reaction to obtain a carbon-based electrode precursor;

[0010] S3, carbonizing the carbon-based electrode precursor at high temperature under an inert gas atmosphere, cooling the product to room temperature after the reaction is completed, and then washing and removing impurities to obtain the carbon-based electrode;

[0011] Wherein, the polar organic solvent is at least one of formamide, dimethyl sulfoxide, acetonitrile, N,N-dimethylformamide, and ethanol.

[0012] In some embodiments, in step S2, the temperature of the hydrothermal reaction is 80-200°C.

[0013] In some embodiments, in step S2, the hydrothermal reaction time is 8-15 hours.

[0014] In some embodiments, in step S3, the carbonization temperature is 400-1200°C.

[0015] In some embodiments, in step S3, the carbonization reaction time is 1-24 hours.

[0016] In some embodiments, in step S3, the heating rate is 1-10°C / min.

[0017] In some embodiments, the cobalt salt is at least one of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate.

[0018] In some embodiments, the base is at least one of sodium hydroxide and potassium hydroxide.

[0019] In some embodiments, the carbon-based material includes at least one of graphite felt, carbon cloth, and carbon paper.

[0020] In some embodiments, the mass ratio of the carbon-based material to the cyanide generated in the precursor solution is 1-100:1-100.

[0021] In some embodiments, in step S1, the molar concentrations of the cobalt salt and the base in the precursor solution are 0.01-0.1 mol / L, respectively.

[0022] In some embodiments, in step S3, the cleaning and impurity removal method is acid washing and / or water washing; the acid washing treatment uses at least one of dilute sulfuric acid, hydrochloric acid or nitric acid, and the acid concentration is 0.5-3.0 mol / L.

[0023] In some embodiments, in step S3, the acid washing treatment is performed by soaking the carbon-based electrode obtained after sintering in an acid solution for 6-20 hours.

[0024] In some embodiments, the inert gas is one of argon, nitrogen, and helium; and the gas flow rate is 50-200 mL / min.

[0025] The present invention also provides a carbon-based electrode obtained by the preparation method of any of the above embodiments, wherein the surface of the carbon-based electrode has a micron-nano graded porous structure.

[0026] In some embodiments, the carbon-based electrode has a porosity of 5.5 to 7.0 mL / g and a specific surface area of 0.2 to 0.45 m 2 / g.

[0027] The present invention also provides a liquid flow battery, which includes the above-mentioned carbon-based electrode.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The solution of the present invention is to deposit cobalt cyanide on the surface of a carbon-based material by reacting a cobalt salt, an alkali and a specific nitrogen-containing organic solvent under hydrothermal conditions. Then, under high-temperature sintering conditions, the cobalt cyanide and the carbon-based material undergo etching and doping reactions, etching the surface of the carbon-based material and nitrogen-doping while generating cobalt carbide, CO and N2. Finally, the generated cobalt carbide, CO and N2 substances are removed by cleaning and impurity removal, thereby forming a nano-micrometer-scale porous structure on the surface of the carbon-based material, realizing etching and doping modification of the carbon-based material, and forming a nitrogen-doped porous carbon-grade electrode, which can effectively increase the contact area between the electrode and the electrolyte, promote the full diffusion of electrons and ions at the interface, and at the same time, the porous defects and nitrogen doping help to enhance the electrocatalytic activity of the electrochemically active sites.

[0030] The carbon-based material obtained by the method of the present invention is applied to a liquid flow battery, which can enable the liquid flow battery to have excellent voltage efficiency and energy efficiency.

[0031] The preparation method of the present invention has simple process, low cost and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1The figures are scanning electron microscope images of the graphite felt electrode prepared in Example 1 and a blank graphite felt electrode before etching reaction; wherein (a) is a scanning electron microscope image of the graphite felt without any treatment; (b) is a scanning electron microscope image of the graphite felt electrode prepared in Example 1;

[0033] Figure 2 cyclic voltammograms of the graphite felt electrode prepared in Example 1 and a blank graphite felt electrode before etching reaction;

[0034] Figure 3 The AC impedance diagram of the graphite felt electrode prepared in Example 1 and the blank graphite felt electrode before etching reaction;

[0035] Figure 4 The graph is a charge-discharge curve diagram of the graphite felt electrode prepared in Example 1 and the blank graphite felt electrode before the etching reaction after being assembled into an all-vanadium redox flow battery. DETAILED DESCRIPTION

[0036] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified. Example 1

[0039] A method for chemical etching and surface modification of a graphite felt electrode comprises the following steps:

[0040] S1. Dissolve 1.0 mmol of Co(NO3)2·6H2O and 1.0 mmol of KOH in 20 mL of formamide to obtain solution A and solution B, respectively. Mix and stir for 30 min until completely dissolved to obtain a mixed solution.

[0041] S2. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined autoclave and place four 2×2 cm 2The graphite felt was ultrasonically treated for 30 minutes, and then the reactor was sealed and heated at 170 °C for 12 hours. After the reaction was completed, the graphite felt was cooled to room temperature, collected, washed with ethanol, and dried at 80 °C for 12 hours to obtain a graphite felt electrode precursor.

[0042] S3, placing the graphite felt electrode precursor in a tube furnace, heating it to 900 °C at a heating rate of 5 °C / min under an argon atmosphere and annealing it for 2 h, cooling it, cleaning it, and drying it to obtain a composite electrode;

[0043] S4. Soak the composite electrode in 3.0 mol / L H2SO4 solution for 6 h, wash and dry to obtain the final graphite felt electrode.

[0044] The prepared graphite felt electrode and the blank graphite felt electrode (graphite felt without any treatment) were subjected to SEM examination. The results are as follows: Figure 1 As shown. Figure 1 The carbon fiber surface of the untreated graphite felt electrode is smooth and has no porous structure, while the carbon fiber surface of the graphite felt electrode treated by the scheme of this embodiment has an obvious porous structure.

[0045] The graphite felt electrode prepared in Example 1 and a blank graphite felt electrode (graphite felt without any treatment) were assembled into an all-vanadium redox flow battery, and the electrochemical performance test was carried out. The test results are as follows: Figure 2-Figure 4 As shown. Among them:

[0046] Figure 2 1 is a cyclic voltammogram of the graphite felt electrode in situ etched with cobalt cyanide and a blank graphite felt electrode in Example 1, which shows that the modified graphite felt electrode exhibits excellent positive and negative electrode catalytic performance.

[0047] Figure 3 3 is an AC impedance diagram of the graphite felt electrode in situ etched with cobalt cyanide and a blank graphite felt electrode in Example 1, which shows that the modified graphite felt electrode has a smaller charge transfer impedance.

[0048] Figure 4 The graphs show the charge and discharge curves of the graphite felt electrode in situ etched with cobalt cyanide and the blank graphite felt electrode after being assembled into an all-vanadium liquid flow battery in Example 1, indicating that the modified electrode exhibits smaller polarization during the charge and discharge process and exerts a higher capacity.

[0049] After testing, at 200 mA / cm 2 At the current density, the all-vanadium redox flow battery assembled with the graphite felt electrodes prepared in this embodiment has a voltage efficiency of 75% and an energy efficiency of 72%. Example 2

[0050] A method for chemical etching and surface modification of a carbon felt electrode comprises the following steps:

[0051] S1. Dissolve 1.0 mmol of Co(NO3)2·6H2O and 1.0 mmol of KOH in 20 mL of formamide to obtain solution A and solution B, respectively. Mix and stir for 30 min until completely dissolved to obtain a mixed solution.

[0052] S2. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined autoclave and place four 2×2 cm 2 After ultrasonic treatment for 30 minutes, the reactor was sealed and heated at 170 °C for 12 hours. After the reaction was completed, the graphite felt was cooled to room temperature, collected, washed with ethanol and dried at 80 °C for 12 hours to obtain a carbon felt electrode precursor.

[0053] S3, placing the carbon felt precursor in a tube furnace, heating to 900 °C at a heating rate of 5 °C / min under an argon atmosphere and annealing for 2 h, cooling, washing, and drying to obtain a carbon felt electrode;

[0054] S4. Soak the carbon felt electrode in 3.0 mol / L H2SO4 solution for 6 h, wash and dry to obtain the final carbon felt electrode.

[0055] In order to test the electrochemical performance of the electrode, the electrode was assembled into an all-vanadium redox flow battery for charge and discharge tests. 2 At the current density, the voltage efficiency of the all-vanadium flow battery is 73% and the energy efficiency is 70%. Example 3

[0056] A method for chemical etching and surface modification of a graphite felt electrode comprises the following steps:

[0057] S1. Dissolve 1.0 mmol of Co(NO3)2·6H2O and 1.0 mmol of KOH in 20 mL of formamide to obtain solution A and solution B, respectively. Mix and stir for 30 min until completely dissolved to obtain a mixed solution.

[0058] S2. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined autoclave and place four 2×2 cm 2 The graphite felt was ultrasonically treated for 30 minutes, and then the reactor was sealed and heated at 170 ° C for 12 hours. After the reaction was completed, the graphite felt was cooled to room temperature, collected, washed with ethanol, and dried at 80 ° C for 12 hours to obtain a graphite felt electrode precursor.

[0059] S3, placing the graphite felt precursor in a tube furnace, heating it to 1000 °C at a heating rate of 5 °C / min under an argon atmosphere and annealing it for 2 h, cooling it, washing it, and drying it to obtain a graphite felt electrode;

[0060] S4. Soak the graphite felt electrode in 3.0 mol / L H2SO4 solution for 6 h, and then wash and dry to obtain the final graphite felt electrode.

[0061] In order to test the electrochemical performance of the electrode, the electrode was assembled into an all-vanadium redox flow battery for charge and discharge tests. 2 At the current density, the voltage efficiency of the all-vanadium redox flow battery is 72.1% and the energy efficiency is 69.7%. Example 4

[0062] A method for chemical etching and surface modification of a graphite felt electrode comprises the following steps:

[0063] S1. Dissolve 5.0 mmol of Co(NO3)2·6H2O and 5.0 mmol of KOH in 20 mL of formamide to obtain solution A and solution B, respectively. Mix and stir for 30 min until completely dissolved to obtain a mixed solution.

[0064] S2. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined autoclave and place four 2×2 cm 2 The graphite felt was ultrasonically treated for 30 min, and then the reactor was sealed and heated at 170 ° C for 12 h. After the reaction was completed, it was cooled to room temperature, and the graphite felt was collected, washed with ethanol, and dried at 80 ° C for 12 h to obtain a graphite felt electrode precursor;

[0065] S3, placing the graphite felt precursor in a tube furnace, heating it to 900°C at a heating rate of 5°C / min under an argon atmosphere and annealing it for 2 hours, cooling it, washing it, and drying it to obtain a graphite felt electrode;

[0066] S4. Soak the graphite felt electrode in 3.0 mol / L H2SO4 solution for 6 h, and then wash and dry to obtain the final graphite felt electrode.

[0067] In order to test the electrochemical performance of the electrode, the electrode was assembled into a battery for charge and discharge tests at 200 mA / cm 2 At the current density, the voltage efficiency of the all-vanadium redox flow battery is 70.1% and the energy efficiency is 65.7%.

[0068] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a carbon-based electrode for a flow battery, characterized in that: The following steps are involved: S1, dissolving the cobalt salt and the base in a polar organic solvent respectively, and mixing them evenly to form a precursor solution; S2. placing the carbon-based material in the precursor solution and performing a hydrothermal reaction to generate cobalt cyanide to obtain a carbon-based electrode precursor; S3, carbonizing the carbon-based electrode precursor at high temperature under an inert gas atmosphere to generate cobalt carbide. After the reaction is completed, cooling the product to room temperature, and then washing the product to remove the cobalt carbide to obtain the carbon-based electrode; Wherein, in step S1, the polar organic solvent is at least one of formamide, acetonitrile, and N,N-dimethylformamide; In step S2, the temperature of the hydrothermal reaction is 80-200°C; In step S3, the carbonization temperature is 400-1200°C.

2. The method for preparing a carbon-based electrode for a flow battery according to claim 1, wherein: The cobalt salt is at least one of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate; and / or the base is at least one of sodium hydroxide and potassium hydroxide.

3. The method for preparing a carbon-based electrode for a flow battery according to claim 1, wherein: The carbon-based material includes at least one of graphite felt, carbon cloth, and carbon paper.

4. The method for preparing a carbon-based electrode for a flow battery according to claim 1, wherein: In step S1, in the precursor solution, the molar concentrations of the cobalt salt and the base are 0.01-0.1 mol / L, respectively.

5. The method for preparing a carbon-based electrode for a flow battery according to claim 1, wherein: In step S3, the cleaning method is acid washing; the acid washing uses at least one of dilute sulfuric acid, hydrochloric acid or nitric acid, and the acid concentration is 0.5-3.0 mol / L.

6. The method for preparing a carbon-based electrode for a flow battery according to claim 1, wherein: The inert gas is one of argon and helium; the gas flow rate is 50-200 mL / min.

7. The carbon-based electrode obtained by the preparation method according to any one of claims 1 to 6, wherein the surface of the carbon-based electrode has a micron-nano hierarchical porous structure.

8. A flow battery, characterized in that: Comprising the carbon-based electrode according to claim 7.

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