Flow battery electrode for improving cycling stability and electrochemical performance and preparation method

Abstract

The invention belongs to the technical field of flow battery energy storage, and particularly relates to a flow battery electrode for improving cycling stability and electrochemical performance and a preparation method. The preparation method comprises the following steps: carrying out alkali treatment and acid treatment on a pretreated graphite felt to obtain a porous electrode material, carrying out dipping treatment, and carrying out polymerization reaction and heating curing treatment to obtain a thermal response self-repairing and nano reinforced material coating modified electrode material; treating the tantalum oxide nanostructure substrate with a precursor solution to obtain an electrode material with the tantalum oxide nanostructure substrate; a mixed solution of neodymium nitrate hexahydrate, cerium nitrate hexahydrate and an ethylene glycol deionized water solution is used for dipping an electrode material with a tantalum oxide nanostructure substrate, and the flow battery electrode with improved cycle stability and electrochemical performance is obtained through sectional heating treatment. The electrode has high activity and long service life, and is favorable for improving the energy efficiency, the power density and the long-term cycling stability of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flow battery energy storage, and particularly relates to a flow battery electrode with improved cycle stability and electrochemical performance and a preparation method thereof. BACKGROUND

[0002] At present, porous carbon materials are mainly used as electrodes in flow batteries, but such materials have inherent defects of low intrinsic electrochemical activity and limited specific surface area, resulting in slow reaction kinetics and high overpotential. Although physical or chemical activation methods can partially increase the active sites on the electrode surface, they often exacerbate corrosion in strong oxidizing electrolyte while improving activity, causing structural damage and performance degradation, making it difficult to achieve high activity and long life.

[0003] Surface modification and nano-engineering are important directions to break through the above bottleneck. By constructing a nano-coating or depositing a catalytic substance, the electrochemical performance can be optimized while protecting the carbon fiber matrix. However, existing technologies mainly focus on single function improvement, which limits the overall breakthrough of the comprehensive performance of the electrode. SUMMARY

[0004] The technical purpose of the present application is to at least solve the problem of low intrinsic activity and limited specific surface area of the existing porous carbon electrode of the flow battery, and to provide a preparation technology of a flow battery electrode that can simultaneously achieve high specific surface area, excellent corrosion resistance and high catalytic activity, taking into account the high activity and long life of the flow battery electrode, which is conducive to the improvement of the energy efficiency, power density and long-term cycle stability of the battery.

[0005] The first aspect of the present application is to provide a preparation method of a flow battery electrode with improved cycle stability and electrochemical performance, comprising: pretreating a graphite felt, treating the pretreated graphite felt with alkali and acid to obtain a porous electrode material; performing immersion treatment on the porous electrode material, and performing polymerization reaction and heating solidification treatment to obtain an electrode material coated with a thermal response self-repairing and nano-enhancing material coating; treating the electrode material coated with the thermal response self-repairing and nano-enhancing material coating with a precursor solution to obtain an electrode material with a tantalum oxide nano-structure substrate; immersing the electrode material with the tantalum oxide nano-structure substrate in a mixed solution of neodymium nitrate hexahydrate, cerium nitrate hexahydrate and ethylene glycol deionized water, and performing stepwise heating treatment to obtain a flow battery electrode with improved cycle stability and electrochemical performance. The electrode prepared by the preparation method simultaneously improves the cycle stability and electrochemical performance of the flow battery, which is conducive to the consideration of high activity and long life of the flow battery.

[0006] In some embodiments of the present application, the alkali treatment comprises: sequentially using potassium hydroxide solutions with molar concentrations of 0.4 mol / L to 0.8 mol / L and 1 mol / L to 1.4 mol / L to perform alkali treatment on the pretreated graphite felt; and the acid treatment comprises: using concentrated sulfuric acid to perform acidification treatment on the pretreated graphite felt to introduce oxygen-containing functional groups. Through step-by-step alkali treatment with potassium hydroxide solution and acidification with concentrated sulfuric acid, oxygen-containing functional groups are introduced, and the surface properties and reaction basis of the electrode are optimized.

[0007] In some embodiments of the present application, the impregnation treatment comprises: using a mixture of graphene quantum dots, concentrated nitric acid, N-isopropyl acrylamide, and N,N'-methylene bisacrylamide in deionized water to perform impregnation treatment on the porous electrode material; the proportions of graphene quantum dots, concentrated nitric acid, N-isopropyl acrylamide, N,N'-methylene bisacrylamide, and deionized water are (0.81 mg to 1.21 mg):(18 mL to 22 mL):(1.35 g to 1.55 g):(0.035 g to 0.045 g):(80 mL to 120 mL). Using the mixture for impregnation, the electrode is endowed with thermal response self-repairing and nano-enhancing functions, and the structural stability and conductivity are strengthened.

[0008] In some embodiments of the present application, the polymerization reaction and heat curing treatment comprise: using ammonium persulfate and polytriacetic acid aqueous solution to treat the porous electrode material, washing with deionized water, heating to 120°C to 130°C at a temperature rise rate of 2°C / min to 3°C / min, and keeping the temperature for 1.5 h to 2.5 h to complete the polymerization reaction and heat curing treatment; the mass concentration of ammonium persulfate in the ammonium persulfate and polytriacetic acid aqueous solution is 9.5 g / L to 10.5 g / L, and the mass concentration of polytriacetic acid is 0.87 g / L to 0.93 g / L. Using ammonium persulfate and polytriacetic acid aqueous solution for treatment and curing is conducive to fully performing the polymerization reaction and enhancing the firmness of the coating combination.

[0009] In some embodiments of the present application, the precursor solution comprises a mixed solution of tantalum oxide, hydrofluoric acid, and oxalic acid; the proportions of tantalum oxide, hydrofluoric acid, and oxalic acid are (0.117 g to 0.121 g):(0.05 mol / L to 0.06 mol / L):(0.45 mol / L to 0.49 mol / L). The precursor solution is conducive to constructing a high-activity tantalum oxide nanostructure substrate and improving the catalytic capacity of the electrode.

[0010] In some embodiments of the present application, the precursor solution further comprises a mixed solution of ammonia water and hydrogen peroxide with a volume ratio of 3:1 to 4:1; the molar concentration of the ammonia water is 1 mol / L to 1.1 mol / L, and the mass fraction of the hydrogen peroxide is 30%. The mixed solution is conducive to optimizing the performance of the precursor solution and improving the uniform formation of the tantalum oxide nanostructure substrate.

[0011] In some embodiments of the present application, the ratio of neodymium nitrate hexahydrate, cerium nitrate hexahydrate and ethylene glycol deionized water solution is (0.32g-0.52g):(0.76g-0.96g):(20mL-25mL); the volume ratio of ethylene glycol and deionized water in the ethylene glycol deionized water solution is 1.2:1-1:1. This ratio is conducive to providing high-quality raw materials for the co-deposition of the composite oxide and enhancing catalytic synergy.

[0012] In some embodiments of the present application, the staged temperature rising treatment includes a first temperature rising treatment and a second temperature rising treatment; the first temperature rising treatment includes: heating to 350℃-360℃ at a temperature rising rate of 2℃ / min-3℃ / min in an argon-hydrogen mixed atmosphere, and holding for 1h-1.5h; the second temperature rising treatment includes: heating to 450℃-460℃ at a temperature rising rate of 4℃ / min-4.5℃ / min in an argon-hydrogen mixed atmosphere, and holding for 2h-2.5h. The staged temperature rising and the atmosphere are conducive to the removal of residues and the activation of the composite oxide, further improving the catalytic activity and stability of the electrode.

[0013] The second aspect of the present application is to provide a liquid flow battery electrode with improved cycle stability and electrochemical performance, which is prepared by the preparation method of the first aspect. The electrode has high cycle stability and excellent electrochemical performance.

[0014] In some embodiments of the present application, the liquid flow battery electrode has an energy efficiency of greater than or equal to 86.7% and a stability of greater than or equal to 1645 times when the current density is 100mA / cm 2

[0015] The beneficial effects of the present application include at least one of the following: Compared with the prior art, the preparation method of the liquid flow battery electrode provided by the present application uses pore-forming and etching treatment to construct rich micro-nano pores and defect structures in situ on the surface of the carbon fiber, the pores with a diameter of greater than or equal to 1μm are used for electrolyte flow, and the pores with a diameter of less than 10nm are used for chemical reaction, which greatly increases the electrochemical active specific surface area and active sites, optimizes the electrolyte transport kinetics, reduces the concentration polarization, and lays a structural foundation for improving the power density of the battery.

[0016] The nano coating uniformly covers the surface and inner wall of the activated carbon fiber, which not only fills the structural weaknesses caused by etching, but also forms a dense physical and chemical barrier to isolate the strong corrosive electrolyte from the carbon matrix, inhibit the structural corrosion and performance degradation in long-term cycling, and the coating has excellent conductivity, which ensures efficient electron conduction in the electrode.

[0017] ​The tantalum oxide is deposited on the surface of the nano coating, and the tantalum-oxygen atoms form a rich single-double bond structure, which significantly improves the electrocatalytic performance; the co-deposition of neodymium and cerium composite oxides further enhances the conductivity and catalytic activity, and the neodymium oxide catalyzes the positive electrode and the cerium oxide catalyzes the negative electrode, realizing hierarchical catalysis and forming oxygen defects, so that the oxygen binder is stably attached, accelerating the redox reaction kinetics and reducing the electrochemical activation overpotential. After the above treatment, the energy efficiency of the electrode is more than 86.7%, and the stability is more than 1645 times. BRIEF DESCRIPTION OF DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of preferred embodiments and are not meant to limit the scope of the present application. In the drawings: Figure 1 Preparation method flowchart of the liquid flow battery electrode provided by the present application; Figure 2 Scanning electron microscope micrograph of the liquid flow battery electrode, wherein (a) is the SEM image of the liquid flow battery electrode in Example 1 of the present application, and (b) is the SEM image of the liquid flow battery electrode in Comparative Example 6 of the present application; Figure 3 Current-voltage curve diagram of the liquid flow battery electrode provided by the present application at different scanning rates; Figure 4 Energy efficiency change curve of the liquid flow battery electrode provided by the present application after multiple cycles at a current density of 100 mA / cm 2 DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present application. Furthermore, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application; the description and claims of the present application as well as the above description of the drawings herein are intended to cover all alternatives, modifications and equivalents of elements falling within the true scope of the present application.

[0021] ​In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is more than two, unless otherwise explicitly and specifically limited.

[0022] Reference herein to "embodiments" means that a particular feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of the application. The occurrence of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as generally understood by those skilled in the art to which the present application belongs. The experimental reagents used in the following embodiments, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments and equipment used in the following embodiments can be purchased or obtained by existing methods; the amount of the experimental reagents, unless otherwise specified, is the amount of reagents in conventional experimental operations; the experimental methods, unless otherwise specified, are conventional methods.

[0024] Large-scale energy storage technology is the core guarantee for supporting the rapid development of new energy and the stable operation of power grid. Flow batteries show broad application prospects in this field due to their independent design of power and capacity, high safety, long service life and other outstanding advantages. However, the commercialization process of flow batteries is limited by energy efficiency, power density and long-term cycle stability, and these key performances mainly depend on the characteristics of electrode materials. The porous carbon electrode currently used in mainstream flow batteries has inherent defects of low intrinsic electrochemical activity and limited specific surface area, resulting in slow reaction kinetics and high overpotential. Even if the surface active sites are increased by physical or chemical activation, corrosion in strong oxidizing electrolyte is also easily intensified, causing structural damage and performance degradation, which is difficult to balance high activity and long life. Surface modification and nano-engineering are effective ways to break through the above bottlenecks, but existing technologies mainly focus on single functional improvement and fail to systematically solve the problem of simultaneous improvement of intrinsic activity, structural stability and durability of electrodes. In particular, there is a lack of integrated design of activation, protection and enhancement steps, which limits the overall breakthrough of the comprehensive performance of the electrode. Therefore, it is of great significance to develop an electrode and a preparation method thereof which can simultaneously realize high specific surface area, excellent corrosion resistance and high catalytic activity, to promote the development of high-performance and long-life flow batteries and accelerate the commercialization process of large-scale energy storage technology.

[0025] In a first aspect, the present application provides a preparation method of a flow battery electrode with improved cycle stability and electrochemical performance, such asFigure 1 The method comprises the following steps: (1) Pretreatment and pore size adjustment A graphite felt with a size of 5 cm x 5 cm x 0.5 cm is used as a sample. The sample is immersed in 50 mL of anhydrous ethanol for 20 min to 30 min and cleaned with deionized water for 3 to 4 times. 1.5 g to 2 g of the treated sample is completely immersed in 170 mL to 190 mL of a 0.4 mol / L to 0.8 mol / L potassium hydroxide solution and magnetically stirred for 20 min to 30 min. The obtained sample is placed in a nitrogen atmosphere tube furnace and heated to 680°C to 720°C at a rate of 4°C / min to 6°C / min and kept for 1.5 h to 2.5 h, and after natural cooling, it is ready for use. All the above samples are completely immersed in 170 mL to 190 mL of a 1 mol / L to 1.4 mol / L potassium hydroxide solution and magnetically stirred for 20 min to 30 min. The obtained sample is placed in a nitrogen atmosphere tube furnace and heated to 680°C to 720°C at a rate of 4°C / min to 6°C / min and kept for 1.5 h to 2.5 h. After cooling to room temperature, it is cleaned with deionized water for 3 to 4 times, and immersed in 80 mL to 100 mL of concentrated sulfuric acid for acidification treatment for 2 h to 3 h to introduce oxygen-containing functional groups, enhance hydrophilicity and coating adhesion. Then, it is washed with a large amount of deionized water until the washing liquid is neutral (pH value is greater than or equal to 6.8), and then dried in a 80°C vacuum oven for 10 h to 12 h to obtain a porous electrode material. After pore size testing, two different pore channels with a pore size greater than or equal to 1 μm are formed for electrolyte flow, and a pore size less than 10 nm is used for chemical reaction, thereby increasing the reaction specific surface area by more than 4.6 times through pore forming and etching.

[0026] (2) Preparation of a thermally responsive self-repairing and nano-enhanced material coating This step is to compensate for the electrode corrosion and structure degradation caused by step (1), to a certain extent, to increase the electrical conductivity and improve the cycle stability.

[0027] 90 mL to 110 mL of graphene quantum dot aqueous dispersion (0.9 mg / mL to 1.1 mg / mL) is mixed with 18 mL to 22 mL of concentrated nitric acid, and stirred at 78°C to 80°C for 6 h to 8 h. The mixture is dialyzed using a dialysis bag until the outside liquid is neutral. The dialyzed graphene quantum dot aqueous dispersion is concentrated to a concentration of 4.5 mg / mL to 5.5 mg / mL at 60°C to 64°C by rotary evaporation, and 18 mL to 22 mL of concentrated solution is obtained for standby use.

[0028] In a three-necked flask, 18 mL ~ 22 mL of the concentrated solution, 80 mL ~ 120 mL of deionized water, 1.35 g ~ 1.55 g of N-isopropyl acrylamide and 0.035 g ~ 0.045 g of N, N'-methylene bisacrylamide were added in turn. The mechanical stirring method was used and it was completely dissolved. The pretreated step (1) graphite felt was immersed in the above reaction solution, the condenser was installed, high-purity nitrogen was continuously introduced into the system for 30 min ~ 40 min to remove oxygen, the water bath temperature was raised to 65 ℃ ~ 70 ℃ and kept constant, and ammonium persulfate (9.5 g / L ~ 10.5 g / L) and polytriacetic acid (0.87 g / L ~ 0.93 g / L) aqueous solution dissolved in 4 mL ~ 6 mL of deionized water were quickly added and reacted at this temperature for 6 h ~ 8 h. After the reaction was completed, the graphite felt was taken out, rinsed with deionized water for 2 ~ 3 times and dried in a 40 ℃ vacuum oven for 12 h ~ 16 h to obtain a thermally responsive self-repairing and nano-enhanced material coating modified electrode material. The sample obtained was placed in a nitrogen atmosphere tube furnace and heated to 120 ℃ ~ 130 ℃ at a rate of 2 ℃ / min ~ 3 ℃ / min and kept for 1.5 h ~ 2.5 h, which was beneficial to trigger repair and bonding. After natural cooling, it was ready for use.

[0029] After this step, the conductivity and stability of the thermally responsive self-repairing and nano-enhanced material coating modified electrode material were greatly improved, and the stable cycle number was increased by more than 580 times compared with step (1).

[0030] (3) Tantalum oxide nanostructure substrate construction 0.117 g ~ 0.121 g of tantalum oxide powder was added to 15 mL ~ 18 mL of a mixed acid solution of 0.05 mol / L ~ 0.06 mol / L hydrofluoric acid and 0.45 mol / L ~ 0.49 mol / L oxalic acid, and a mixed solution composed of 1 mol / L ~ 1.1 mol / L ammonia water and 30% hydrogen peroxide with a volume ratio of 3:1 ~ 4:1 was slowly added to form a clear solution to prepare a precursor solution.

[0031] 1 g ~ 1.1 g of the electrode sample obtained in step (2) was immersed in the above precursor solution for 30 min ~ 40 min, and the mixture was transferred to a 50 mL polytetrafluoroethylene lined high-pressure reaction kettle. The reaction kettle was placed in an oven and reacted at 190 ℃ ~ 200 ℃ for 9 h ~ 10 h. After the reaction was completed, it was naturally cooled to room temperature, the graphite felt was taken out, washed with deionized water and anhydrous ethanol alternately for 5 ~ 6 times, and the sample was dried in a 80 ℃ vacuum drying oven for 6 h ~ 8 h to obtain an electrode material with a tantalum oxide nanostructure substrate.

[0032] The step is to prepare and introduce in-situ fluorine doping by precursor to preform partial oxygen vacancies, improve the conductivity of the substrate and improve the catalytic activity, voltage efficiency and energy efficiency are all improved by more than 4% compared with the electrode material in step (2) which is modified by thermal response self-repairing and nano-enhanced material coating.

[0033] (4) Co-deposition and activation of neodymium and cerium composite oxides 0.32g~0.52g of neodymium nitrate hexahydrate and 0.76g~0.96g of cerium nitrate hexahydrate were weighed respectively and dissolved in 20mL~25mL of ethylene glycol deionized water solution (volume ratio 1.2:1~1:1). Ammonia water was slowly added to the above system, and the pH value was adjusted to 9~10.

[0034] 1g~1.1g of the electrode sheet obtained in step (3) was immersed in the above prepared solution. The whole system was transferred to a high-pressure reaction kettle, and the reaction kettle was placed in an oven and reacted at 110~120℃ for 6h~7h. After the reaction was completed, it was naturally cooled to room temperature, and the sample was taken out and washed with deionized water and anhydrous ethanol alternately for 5~6 times. The sample was dried in a vacuum drying oven at 80℃ for 6h~8h. After the reaction was completed, the electrode material was washed with ethanol and dried. The dried electrode material was subjected to programmed temperature heat treatment in a tube furnace under argon-hydrogen mixed gas atmosphere. First, heat to 350℃~360℃ at a rate of 2℃ / min~3℃ / min and keep for 1h~1.5h to remove residual organic matter and crystals. Then heat to 450℃~460℃ at a rate of 4℃ / min~4.5℃ / min and keep for 2h~2.5h. Wash with deionized water several times. Dry the sample in a vacuum drying oven at 80℃ for 6h~8h and test its performance.

[0035] After this step, the conductivity of the electrode material is further enhanced, oxygen defects are introduced, and the positive and negative electrode catalysis is realized. The energy efficiency is greatly improved to more than 86.7%, and the stability is also improved to more than 1645 times.

[0036] It should be noted that those skilled in the art can adjust the above parameters as needed. For example, taking the molar concentration of potassium hydroxide solution as an example, the above range is 0.4mol / L~0.8mol / L, i.e. the molar concentration of potassium hydroxide solution can be, for example, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, or any one of the ranges of any two of the foregoing. Similarly, the remaining parameters can also be any one of the parameter ranges or any one of the ranges of any two of the foregoing. Those skilled in the art can select the required experimental materials as needed, for example, the specific surface area of the selected graphite felt can be 3.7m 2The dialysis bag has a molecular weight cut-off of 1000 Da to 1500 Da, and the concentrated sulfuric acid has a mass fraction of 98%, and the concentrated nitric acid has a mass fraction of 68%.

[0037] In a second aspect, the application provides a flow battery electrode with improved cycle stability and electrochemical performance, which is prepared by the preparation method of the first aspect.

[0038] Example 1 In this embodiment, the preparation method specifically comprises the following steps: Step (1) Pretreatment and pore size adjustment A graphite felt with a size of 5 cm x 5 cm x 0.5 cm was used as a sample, immersed in 50 mL of anhydrous ethanol for 25 min, and cleaned with deionized water for 3 times.

[0039] Take 1.75g treated sample completely immersed in 180mL of 0.6mol / L potassium hydroxide solution, and magnetic stirring for 25min. Put the obtained sample into a nitrogen atmosphere tube furnace and heat to 700℃ at a rate of 5℃ / min and keep for 2h, and cool naturally after cooling, standby.

[0040] The above sample was completely immersed in 180mL of 1.2mol / L potassium hydroxide solution and magnetically stirred for 25min, and was put into a nitrogen atmosphere tube furnace and heated to 700℃ at a rate of 5℃ / min and kept for 2h; cooled to room temperature, washed with deionized water for 4 times, immersed in 90mL of concentrated sulfuric acid for acidification treatment for 2.5h, introduced oxygen-containing functional groups, enhanced hydrophilicity and coating adhesion; washed with a large amount of deionized water until the cleaning liquid is neutral (pH value is greater than or equal to 6.8), and dried in a vacuum oven at 80℃ for 11h.

[0041] After pore size testing, two kinds of pores with different pore sizes were formed, the pores with a pore size greater than or equal to 1μm were used for electrolyte flow, and the pores with a pore size less than 10nm were used for chemical reaction.

[0042] Step (2) Thermal response self-repairing and nano-enhanced material coating preparation Mix 100mL graphene quantum dot aqueous dispersion (1mg / mL) with 20mL concentrated nitric acid, stir and reflux at 79℃ for 7h. Use a dialysis bag to dialyze the above mixture until the outside liquid is neutral. The dialyzed graphene quantum dot aqueous dispersion is concentrated to a concentration of 5mg / mL at 62℃ by rotary evaporation and concentrated to 20mL of concentrated solution for standby. In a three-necked flask, add 20mL of concentrated solution, 100mL of deionized water, 1.45g of N-isopropyl acrylamide and 0.04g of N,N'-methylene bisacrylamide in turn. Mechanical stirring method is adopted and it is completely dissolved.

[0043] The pretreated graphite felt of step (1) was immersed in the above prepared solution. The condenser was installed and high purity nitrogen was continuously bubbled into the system for 35 min to remove oxygen. The temperature of the water bath was raised to 67°C and kept constant. The ammonium persulfate (10 g / L) and polyacetic acid (0.9 g / L) solution dissolved in 5 mL deionized water was quickly added and the reaction was carried out at this temperature for 7 h. After the reaction was completed, the graphite felt was taken out, rinsed with deionized water for 3 times and dried in a vacuum oven at 40°C for 14 h to obtain the electrode material coated with the thermal response self-repairing and nano-enhanced material. The sample was heated to 125°C at a rate of 3°C / min in a nitrogen atmosphere tube furnace and kept for 2 h to trigger the repair and bonding. After natural cooling, it was ready for use.

[0044] Step (3) construction of tantalum oxide nanostructure substrate Firstly, 0.119 g of tantalum oxide powder was added to 16 mL of 0.055 mol / L hydrofluoric acid and 0.47 mol / L oxalic acid mixed acid solution. A mixed solution composed of 1.05 mol / L ammonia water and 30% hydrogen peroxide with a volume ratio of 3:1 was slowly added to the above suspension to form a clear solution.

[0045] The electrode sample of 1.05 g obtained in step (2) was completely immersed in the above prepared precursor solution for 35 min, and the mixture was transferred to a 50 mL polytetrafluoroethylene lined high-pressure reaction kettle. The reaction kettle was placed in an oven and reacted at 195°C for 9 h. After the reaction was completed, it was naturally cooled to room temperature, and the graphite felt was washed with deionized water and anhydrous ethanol alternately for 6 times. The sample was dried in a vacuum drying oven at 80°C for 7 h.

[0046] Step (4) co-deposition and activation of neodymium and cerium composite oxides 0.42 g of neodymium nitrate hexahydrate and 0.86 g of cerium nitrate hexahydrate were weighed respectively and dissolved in 23 mL of ethylene glycol deionized water solution (volume ratio 1.1:1). Ammonia water was slowly added to the above system to adjust the pH value to 9.5.

[0047] Immerse 1.05 g of the electrode sheet obtained in step (3) entirely in the prepared solution. Transfer the entire system to a high-pressure reactor. Place the reactor in an oven and react at 115 °C for 6.5 h. After the reaction, allow it to cool naturally to room temperature, remove the sample, and wash it 6 times alternately with deionized water and anhydrous ethanol. Dry the sample in an 80 °C vacuum drying oven for 7 h. After the reaction, remove the electrode material, wash it with ethanol, and then dry it. Place the dried sample in a tube furnace and perform programmed temperature heat treatment under an argon-hydrogen mixed atmosphere. First, heat it to 355 °C at a rate of 3 °C / min and hold it for 1.25 h to remove residual organic matter and crystals. Then, heat it to 455 °C at a rate of 4 °C / min and hold it for 2.25 h, wash it multiple times with deionized water, and dry the sample in an 80 °C vacuum drying oven for 7 h.

[0048] The SEM image of the electrode is as follows: Figure 2 As shown in (a), the surface exhibits numerous grooves and folds, with a specific surface area of ​​29.7 m². 2 / g, which is beneficial for promoting catalytic activity. Performance testing of this electrode showed that the energy efficiency was significantly improved to 87.5%, such as... Figure 4 As shown, the stability has been improved to 1730 times, as... Figure 3 As shown, the VO of this electrode 2+ / VO2 + and V 3+ / V 2+ It has the lowest peak potential and the best electrochemical performance.

[0049] Example 2 Step (1) Pretreatment and aperture adjustment Graphite felt with size of 5 cm x 5 cm x 0.5 cm was used as sample, immersed in 50 mL of absolute ethanol for 30 min, and cleaned with deionized water for 3 times. 2 g of the treated sample was completely immersed in 170 mL of 0.4 mol / L potassium hydroxide solution, and magnetically stirred for 20 min. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 680℃ at a rate of 4℃ / min and kept for 2.5 h, and after natural cooling, it was ready for use. All the above samples were completely immersed in 170 mL of 1.4 mol / L potassium hydroxide solution, and magnetically stirred for 30 min. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 720℃ at a rate of 6℃ / min and kept for 1.5 h. After cooling to room temperature, it was cleaned with deionized water for 4 times, and immersed in 80 mL of concentrated sulfuric acid for acidification treatment for 3 h to introduce oxygen-containing functional groups, enhance hydrophilicity and coating adhesion. Then it was rinsed with a large amount of deionized water until the cleaning solution was neutral (pH value greater than or equal to 6.8). Subsequently, it was dried in an 80℃ vacuum oven for 10 h. After pore size testing, two different pore sizes were formed, the pores with a pore size greater than or equal to 1 μm were used for electrolyte flow, and the pores with a pore size less than 10 nm were used for chemical reaction.

[0050] Step (2) Preparation of thermally responsive self-healing and nano-enhanced material coating The 110 mL graphene quantum dot aqueous dispersion (0.9 mg / mL) was mixed with 22 mL of concentrated nitric acid, and stirred at 78℃ for 8 h. The above mixture was dialyzed using a dialysis bag until the dialysate was neutral. The dialyzed graphene quantum dot aqueous dispersion was concentrated to a concentration of 5.5 mg / mL at 64℃ by rotary evaporation and concentrated to 18 mL of concentrated solution for standby. In a three-necked flask, 18 mL of concentrated solution, 80 mL of deionized water, 1.55 g of N-isopropyl acrylamide and 0.035 g of N,N'-methylene bisacrylamide were added in turn. Mechanical stirring method was used and it was completely dissolved. The pretreated graphite felt of step (1) was immersed in the above reaction solution. The condenser tube was installed, high-purity nitrogen was continuously introduced into the system for 40 min to remove oxygen, the water bath temperature was raised to 65℃ and kept constant, and ammonium persulfate (9.5 g / L) and polytriacetic acid (0.93 g / L) aqueous solution dissolved in 6 mL of deionized water were quickly added and reacted at this temperature for 6 h. After the reaction was completed, the graphite felt was taken out, rinsed with deionized water for 2 times and dried in a 40℃ vacuum oven for 16 h to obtain an electrode material modified with a thermally responsive self-healing and nano-enhanced material coating. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 120℃ at a rate of 2℃ / min and kept for 2.5 h to trigger repair and bonding, and after natural cooling, it was ready for use.

[0051] Step (3) Construction of tantalum oxide nanostructure substrate Firstly, 0.121 g of tantalum oxide powder was added into 18 mL of 0.05 mol / L hydrofluoric acid and 0.49 mol / L oxalic acid mixed acid solution. A mixed solution composed of 1 mol / L ammonia water and 30% hydrogen peroxide with a volume ratio of 3:1 was slowly added into the above suspension until a clear solution was formed. 1 g of the electrode sample obtained in step (2) was completely immersed in the prepared precursor solution for 40 min, and the mixture was transferred to a 50 mL polytetrafluoroethylene lined autoclave. The autoclave was placed in an oven and reacted at 190°C for 10 h. After the reaction was completed, it was naturally cooled to room temperature, and the graphite felt was taken out and washed with deionized water and anhydrous ethanol alternately for 5 times. The sample was dried in a vacuum drying oven at 80°C for 8 h.

[0052] Step (4) Co-deposition and activation of neodymium and cerium composite oxides 0.52 g of neodymium nitrate hexahydrate and 0.76 g of cerium nitrate hexahydrate were weighed respectively and dissolved in 20 mL of ethylene glycol deionized water solution (volume ratio 1:1). Ammonia water was slowly added to the above system to adjust the pH value to 9. 1 g of the electrode sample obtained in step (3) was completely immersed in the prepared solution. The whole system was transferred to an autoclave. The autoclave was placed in an oven and reacted at 120°C for 6 h. After the reaction was completed, it was naturally cooled to room temperature, and the sample was taken out and washed with deionized water and anhydrous ethanol alternately for 6 times. The sample was dried in a vacuum drying oven at 80°C for 6 h. After the reaction was completed, the electrode material was washed with ethanol and dried. The dried sample was subjected to programmed temperature heat treatment in a tube furnace under argon-hydrogen mixed gas atmosphere. Firstly, it was heated to 360°C at a rate of 3°C / min and kept for 1 h to remove residual organic matter and crystallization. Then it was heated to 450°C at a rate of 4°C / min and kept for 2.5 h. It was washed with deionized water several times. The sample was dried in a vacuum drying oven at 80°C for 8 h.

[0053] The material was used as an electrode and tested for performance, and the test results were: the energy efficiency was increased to 86.7%, and the stability was also increased to 1645 times.

[0054] Example 3 Step (1) Pretreatment and pore size adjustment A graphite felt with a size of 5 cm x 5 cm x 0.5 cm was used as a sample. The sample was immersed in 50 mL of anhydrous ethanol for 20 min and cleaned with deionized water four times. 1.5 g of the treated sample was completely immersed in 190 mL of a 0.8 mol / L potassium hydroxide solution and magnetically stirred for 30 min. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 720°C at a rate of 6°C / min and kept for 1.5 h, and after natural cooling, it was reserved. The above sample was completely immersed in 190 mL of a 1 mol / L potassium hydroxide solution and magnetically stirred for 20 min. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 680°C at a rate of 4°C / min and kept for 2.5 h. After cooling to room temperature, it was cleaned with deionized water three times, and immersed in 100 mL of concentrated sulfuric acid for acidification treatment for 2 h to introduce oxygen-containing functional groups, enhance hydrophilicity and coating adhesion. Then it was washed with a large amount of deionized water until the cleaning liquid was neutral (pH value greater than or equal to 6.8). Subsequently, it was dried in a vacuum oven at 80°C for 12 h. After pore size testing, two different pore sizes were formed, the pores with a pore size greater than or equal to 1 μm were used for electrolyte flow, and the pores with a pore size less than 10 nm were used for chemical reaction.

[0055] Step (2) preparation of a thermal response self-repairing and nano-enhanced material coating A mixture of 90 mL of graphene quantum dot aqueous dispersion (1.1 mg / mL) and 18 mL of concentrated nitric acid was stirred and refluxed at 80°C for 6 h. The mixture was dialyzed using a dialysis bag until the outside liquid was neutral. The dialyzed graphene quantum dot aqueous dispersion was concentrated to a concentration of 4.5 mg / mL at 60°C by rotary evaporation and concentrated to 22 mL of concentrated solution for later use. In a three-necked flask, 22 mL of concentrated solution, 120 mL of deionized water, 1.35 g of N-isopropyl acrylamide and 0.045 g of N,N'-methylene bisacrylamide were sequentially added. Mechanical stirring was used and complete dissolution was achieved. The pretreated graphite felt of step (1) was immersed in the above reaction solution. A condenser tube was installed, high-purity nitrogen was continuously introduced into the system for 30 min to remove oxygen, the water bath temperature was raised to 70°C and kept constant, and ammonium persulfate (10.5 g / L) and polytriacetic acid (0.87 g / L) dissolved in 4 mL of deionized water were quickly added and reacted at this temperature for 8 h. After the reaction was completed, the graphite felt was taken out, rinsed with deionized water three times and dried in a vacuum oven at 40°C for 12 h to obtain an electrode material modified with a thermal response self-repairing and nano-enhanced material coating. The obtained sample was placed in a nitrogen atmosphere tube furnace and heated to 130°C at a rate of 3°C / min and kept for 1.5 h to trigger repair and bonding, and after natural cooling, it was reserved.

[0056] Step (3) construction of a tantalum oxide nanostructure substrate First, 0.117 g of tantalum oxide powder was added to 15 mL of a mixed acid solution of 0.06 mol / L hydrofluoric acid and 0.45 mol / L oxalic acid. A mixed solution composed of 1.1 mol / L ammonia water and 30% hydrogen peroxide in a volume ratio of 4:1 was slowly added to the above suspension until a clear solution was formed. 1.1 g of the electrode sample obtained in step (2) was completely immersed in the above prepared precursor solution for 30 min, and the mixture was transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in an oven and reacted at 200°C for 9 h. After the reaction was completed, it was naturally cooled to room temperature, and the graphite felt was taken out and washed with deionized water and anhydrous ethanol alternately for 6 times. The sample was dried in a vacuum drying oven at 80°C for 6 h.

[0057] Step (4) Co-deposition and activation of neodymium and cerium composite oxides 0.32 g of neodymium nitrate hexahydrate and 0.96 g of cerium nitrate hexahydrate were weighed separately and dissolved in 25 mL of ethylene glycol deionized water solution (volume ratio 1.2:1). Ammonia water was slowly added to the above system to adjust the pH value to 10. 1.1 g of the electrode sample obtained in step (3) was completely immersed in the above prepared solution. The whole system was transferred to a high-pressure reactor. The reactor was placed in an oven and reacted at 110°C for 7 h. After the reaction was completed, it was naturally cooled to room temperature, and the sample was taken out and washed with deionized water and anhydrous ethanol alternately for 5 times. The sample was dried in a vacuum drying oven at 80°C for 8 h. After the reaction was completed, the electrode material was washed with ethanol and dried. The dried sample was subjected to programmed temperature heat treatment in a tube furnace under an argon-hydrogen mixed gas atmosphere. First, heated to 350°C at a rate of 2°C / min and kept for 1.5 h to remove residual organic matter and crystallization. Then heated to 460°C at a rate of 4.5°C / min and kept for 2 h. Washed with deionized water several times. The sample was dried in a vacuum drying oven at 80°C for 6 h.

[0058] The material was used as an electrode and performance test was carried out, and the test results were as follows: the energy efficiency was increased to 87.0%, and the stability was also increased to 1659 times.

[0059] Comparative Example 1 Compared with Example 1, the only difference is that the step of constructing a tantalum oxide nanostructure substrate is not performed in Comparative Example 1, and the rest of the steps and parameters are the same.

[0060] The material was used as an electrode and performance test was carried out, and the test results were as follows: the electrode voltage efficiency was 88.1%, the energy efficiency was 86.3%, the specific surface area was 29.8 m 2 / g, and the stable cycle number was 1680 times.

[0061] Comparative Example 2 The difference between Example 1 and Comparative Example 2 is that the step of co-deposition and activation of neodymium and cerium composite oxide is not performed in Comparative Example 2, and the rest of the steps and parameters are the same as those in Example 1.

[0062] The material is used as an electrode and performance test is performed, and the test results are: the voltage efficiency of the electrode is 87.5%, the energy efficiency is 85.1%, the specific surface area is 29.1 m 2 / g, and the stable cycle number is 1612 times.

[0063] Comparative Example 3 The difference between Example 1 and Comparative Example 3 is that the step of heat response self-repairing and nano-enhanced material coating preparation is not performed in Comparative Example 3, and the rest of the steps and parameters are the same as those in Example 1.

[0064] The material is used as an electrode and performance test is performed, and the test results are: the voltage efficiency of the electrode is 85.3%, the energy efficiency is 82.2%, the specific surface area is 26.2 m 2 / g, and the stable cycle number is 778 times.

[0065] Comparative Example 4 The difference between Example 1 and Comparative Example 4 is that the step of pretreatment and pore size adjustment is not performed in Comparative Example 4, and the rest of the steps and parameters are the same as those in Example 1.

[0066] The material is used as an electrode and performance test is performed, and the test results are: the voltage efficiency of the electrode is 85.6%, the energy efficiency is 83.1%, the specific surface area is 11.4 m 2 / g, and the stable cycle number is 1364 times.

[0067] Comparative Example 5 The difference between Example 1 and Comparative Example 5 is that the step of constructing a tantalum oxide nanostructure substrate and the step of co-deposition and activation of neodymium and cerium composite oxide are not performed in Comparative Example 5, and the rest of the steps and parameters are the same as those in Example 1.

[0068] The electrode is tested for performance, and the test results are: the voltage efficiency of the electrode is 84.1%, the energy efficiency is 81.9%, the specific surface area is 27.5 m 2 / g, as shown in Figure 4 , the stable cycle number is 1512 times, as shown in Figure 3 , the VO 2 + / VO2 + and V 3+ / V 2+ indicate poor electrochemical performance.

[0069] Comparative Example 6 Compared with Example 1, the only difference is that Comparative Example 6 did not perform the pretreatment and pore size adjustment steps, nor the thermal response self-healing and nano-reinforced material coating preparation steps. All other steps and parameters are the same as in Example 1.

[0070] The SEM image of the electrode is as follows: Figure 2 As shown in (b), the surface is relatively smooth, with a specific surface area of ​​6.8 m². 2 The electrode was tested for performance (g / g), and the results were as follows: electrode voltage efficiency was 83.0%, energy efficiency was 79.8%, and specific surface area was 6.8 m² / g. 2 / g, such as Figure 4 As shown, the stable cycle count is 676.

[0071] Comparative Example 7 Compared with Example 1, Comparative Example 7 only performed pretreatment and pore size adjustment to obtain electrode materials.

[0072] The electrode was subjected to performance testing, and the results were as follows: electrode voltage efficiency of 81.8%, energy efficiency of 75.9%, and specific surface area of ​​20.8 m². 2 / g, with a stable cycle count of 594.

[0073] Comparative Example 8 Using a graphite felt measuring 5cm×5cm×0.5cm as a sample, the sample was immersed in 50mL of anhydrous ethanol for 25min and then cleaned three times with deionized water.

[0074] The electrode underwent performance testing, and the results were as follows: electrode voltage efficiency of 80.2%, energy efficiency of 73.6%, and specific surface area of ​​3.7 m². 2 / g, such as Figure 4 As shown, the stable cycle count is 308. Figure 3 As shown, the VO of this electrode 2+ / VO2 + and V 3 + / V 2+ This indicates poor electrochemical performance.

[0075] The electrodes prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0076] Table 1

[0077] Based on the various embodiments and comparative examples, as well as Table 1, the electrode material prepared by the preparation method provided in this application has an increased specific surface area, which improves the cycle stability, voltage efficiency, and energy efficiency of flow batteries.

[0078] In combination with the test results of Comparative Example 1 and Example 1, it can be seen that in the test results of the electrode material of Comparative Example 1, the voltage efficiency is decreased by 1.1% compared with Example 1, the energy efficiency is decreased by 1.2%, the stable cycle number is reduced by 50 times, and there is no obvious difference in the specific surface area. This is because the step of constructing the nanometer structure of tantalum oxide introduces in-situ doping by precursor preparation, pre-generates part of oxygen vacancies, and forms abundant single bond and double bond structures between tantalum and oxygen atoms, which greatly improves the electrocatalytic performance of the electrode. The lack of oxygen vacancies in Comparative Example 1 hinders the improvement of subsequent metal loading efficiency and active site number, directly leading to performance degradation, fully proving that this step is an important support for high performance of the electrode.

[0079] In combination with the test results of Comparative Example 2 and Example 1, it can be seen that in the test results of the electrode material of Comparative Example 2, the voltage efficiency is decreased by 1.7%, the energy efficiency is decreased by 2.4%, and the stable cycle number is reduced by 118 times. The step of co-deposition and activation of neodymium and cerium composite oxides forms a hierarchical catalytic system with the catalytic effect of neodymium oxide on the positive electrode and the catalytic effect of cerium oxide on the negative electrode, and introduces oxygen defects, which makes the oxygen binder stably adhere to the surface of the electrode, not only improves the cycle stability, but also speeds up the redox reaction kinetics rate and reduces the electrochemical activation overpotential. The absence of this step directly leads to insufficient electrode catalytic activity and conductivity, verifying its indispensability in the process.

[0080] In combination with the test results of Comparative Example 3 and Example 1, it can be seen that in the test results of the electrode material of Comparative Example 3, the voltage efficiency is decreased by 3.9%, the energy efficiency is decreased by 5.3%, the specific surface area is decreased by 12.5%, and the stable cycle number is sharply reduced by 55.0%. This is because the step of preparing the nano-enhanced material coating constructs a nano-coating uniformly coated on the surface and inner wall of the activated carbon fiber, which not only fills the structural defects generated by etching, but also forms a dense physical and chemical barrier to effectively isolate the corrosion of the strong corrosive electrolyte to the carbon matrix and inhibit the structural degradation and performance decay in long-term cycling; at the same time, the coating has excellent conductivity, which guarantees the efficient conduction of electrons inside the electrode. After lacking the protection of the coating, the electrode quickly deteriorates in the corrosive environment, fully highlighting its dual protection effect on structural stability and electrochemical performance.

[0081] From the test results of Comparative Example 4 and Example 1, it can be seen that in the test results of the electrode material of Comparative Example 4, the voltage efficiency decreased by 3.6%, the energy efficiency decreased by 4.4%, the specific surface area decreased by 61.6%, and the stable cycle number decreased by 21.2%. This step constructs rich micro-nano pores (pore diameter greater than or equal to 1 μm for electrolyte flow and less than 10 nm for chemical reaction) on the surface of the carbon fiber in situ through etching and pore making, so that the reaction specific surface area is increased by more than 4.6 times, which not only provides sufficient active sites for the redox reaction, but also optimizes the electrolyte transmission kinetics and reduces the concentration polarization. After the step is omitted, the insufficient specific surface area directly affects the uniform loading of the subsequent catalytic metal, resulting in a decline in overall performance, confirming that it is the structural basis for improving the power density of the electrode.

[0082] Comparative Example 5 omits steps 3 and 4 at the same time, and the voltage efficiency, energy efficiency, specific surface area and cycle stability are lower than those of Comparative Examples 1 and 2 which omit only one step. This is because the step 3 constructs a tantalum oxide substrate and the step 4 forms a synergistic catalytic system of neodymium cerium composite oxide: the former improves the basic electrocatalytic performance through oxygen vacancies, and the latter supplements activity and enhances conductivity through hierarchical catalysis, and the two synergistically support the high-efficiency and stable operation of the electrode.

[0083] Comparative Example 6 omits steps 1 and 2 at the same time, and the voltage efficiency and energy efficiency are lower than those of Comparative Examples 3 and 4 which omit only one step, and the specific surface area is only 26.0% of that of Comparative Example 3. This is because the pore making process of step 1 and the coating protection of step 2 form a synergistic effect: the former constructs a high specific surface area pore structure, and the latter fills in structural defects, improves stability, and provides a stable attachment substrate for subsequent metal loading. After the two steps are omitted, the catalytic metal cannot be stably dispersed and attached, resulting in overall performance degradation.

[0084] Comparative Example 7 only retains step 1, and compared with Comparative Example 5, the voltage efficiency decreases by 2.3%, the energy efficiency decreases by 6.0%, and the stable cycle number decreases by 60.7%, but the specific surface area is still higher than that of Comparative Example 6. This shows that the high specific surface area provided by step 1 is the basis for performance improvement, but after lacking the coating protection of step 2, the cycle stability of the electrode is greatly attenuated, confirming that the synergistic effect of the two is crucial for balancing high specific surface area and long life.

[0085] Comparative Example 8 only performs a simple ethanol cleaning pretreatment on the original graphite felt, and the specific surface area is only 12.5% of that of Example 1. Due to the lack of sufficient active sites, the electrochemical performance and cycle stability are the worst among all groups, and the energy efficiency is 13.9% lower than that of Example 1. This comparison directly reflects the significant advantages of the four-step optimization process, verifying that the preparation method adopted in Example 1 can achieve a qualitative leap in the performance of the original electrode.

[0086] In summary, through precise optimization of the parameters of the four-step integrated process, the electrode achieves a synergistic improvement in high specific surface area, high catalytic activity, strong corrosion resistance, and long cycle stability. Specifically, in step (1), by adjusting and optimizing the amount of potassium hydroxide used, the electrode material forms abundant micro-nano channels, reducing the phenomenon of insufficient micro-nano channel formation due to insufficient potassium hydroxide, which affects the subsequent performance improvement effect; or the phenomenon of excessive corrosion of the electrode due to excessive potassium hydroxide, which affects the performance. In step (2), the mass ratio of graphene quantum dot aqueous dispersion and N-isopropyl acrylamide is adjusted and optimized, which is beneficial to the dual protection of the structural stability and electrochemical performance of the electrode material. A suitable mass ratio of graphene quantum dot aqueous dispersion and N-isopropyl acrylamide is beneficial to reducing the phenomenon of insufficient N-isopropyl acrylamide, which cannot effectively coat the carbon material and is not conducive to the self-repairing process; or excessive N-isopropyl acrylamide, which occupies too much of the pore structure of the carbon material, reducing the performance of the electrode; or insufficient graphene quantum dots, which cannot provide sufficient stability; or excessive graphene quantum dots, which increase the occupation of active sites and reduce the performance of the electrode. In step (3), the loading amount of tantalum oxide is adjusted and optimized, and the tantalum and oxygen atoms form abundant single and double bond structures, which is beneficial to improving the electrocatalytic performance of the electrode. A suitable loading amount of tantalum oxide is beneficial to reducing the phenomenon of insufficient loading of tantalum oxide, which cannot effectively improve the performance of the electrode, or excessive loading of tantalum oxide, which forms too many single and double bond structures, resulting in a decrease in defect sites and affecting the subsequent performance optimization, which is not conducive to the electrocatalytic performance of the electrode. In step (4), by optimizing the mass ratio of neodymium nitrate hexahydrate and cerium nitrate hexahydrate, neodymium oxide catalyzes the positive electrode and cerium oxide catalyzes the negative electrode, achieving graded catalysis of different half-reactions and improving the catalytic activity and conductivity of the electrode. As two different catalytic metals for half-reactions, if the mass ratio is not suitable, the rates of the half-reactions will not match, affecting the catalytic activity and conductivity of the electrode. In addition, the high-temperature treatment temperature and time in each processing step should be within a suitable range to avoid the phenomenon of insufficient performance improvement due to insufficient treatment temperature or time, or the destruction of the carbon material or catalytic structure due to excessive temperature or time, resulting in a loss of electrode performance. The above steps interact with and synergize with each other, achieving a synergistic improvement in high specific surface area, high catalytic activity, strong corrosion resistance, and long cycle stability of the electrode, breaking through the technical bottleneck of traditional liquid flow battery electrodes that high activity and long life are difficult to achieve, and providing a reliable electrode preparation scheme for the large-scale application of high-performance long-life liquid flow batteries.

[0087] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a flow battery electrode that improves cycle stability and electrochemical performance, characterized in that, include: The pretreated graphite felt is then subjected to alkali treatment and acid treatment to obtain a porous electrode material. The porous electrode material is impregnated, and then subjected to polymerization and heat curing to obtain an electrode material modified with a thermally responsive self-healing and nano-reinforced material coating. The electrode material modified with the thermally responsive self-healing and nano-reinforced material coating is treated with a precursor solution to obtain an electrode material with a tantalum oxide nanostructure substrate. The electrode material with the tantalum oxide nanostructure substrate was impregnated with a mixture of neodymium nitrate hexahydrate, cerium nitrate hexahydrate, and ethylene glycol deionized water, and then subjected to a segmented heating process to obtain a flow battery electrode with improved cycle stability and electrochemical performance.

2. The preparation method according to claim 1, characterized in that, The alkaline treatment includes: sequentially applying potassium hydroxide solutions with molar concentrations of 0.4 mol / L to 0.8 mol / L and 1 mol / L to 1.4 mol / L to the pretreated graphite felt; The acid treatment includes: acidifying the pretreated graphite felt with concentrated sulfuric acid to introduce oxygen-containing functional groups.

3. The preparation method according to claim 1, characterized in that, The impregnation treatment includes: impregnating the porous electrode material with a deionized water mixture of graphene quantum dots, concentrated nitric acid, N-isopropylacrylamide, and N,N'-methylenebisacrylamide. The ratio of graphene quantum dots, concentrated nitric acid, N-isopropylacrylamide, N,N'-methylenebisacrylamide, and deionized water is (0.81 mg~1.21 mg): (18 mL~22 mL): (1.35 g~1.55 g): (0.035 g~0.045 g): (80 mL~120 mL).

4. The preparation method according to claim 1, characterized in that, The polymerization reaction and heat curing treatment include: treating the porous electrode material with an aqueous solution of ammonium persulfate and polytriacetic acid, washing with deionized water, heating to 120℃~130℃ at a heating rate of 2℃ / min~3℃ / min, and holding at that temperature for 1.5h~2.5h to complete the polymerization reaction and heat curing treatment; The mass concentration of ammonium persulfate in the aqueous solution of ammonium persulfate and polytriacetic acid is 9.5 g / L to 10.5 g / L, and the mass concentration of polytriacetic acid is 0.87 g / L to 0.93 g / L.

5. The preparation method according to claim 1, characterized in that, The precursor solution includes a mixed solution of tantalum oxide, hydrofluoric acid, and oxalic acid; The ratio of tantalum oxide, hydrofluoric acid, and oxalic acid is (0.117g~0.121g): (0.05mol / L~0.06mol / L): (0.45mol / L~0.49mol / L).

6. The preparation method according to claim 5, characterized in that, The precursor solution also includes a mixed solution of ammonia and hydrogen peroxide in a volume ratio of 3:1 to 4:

1. The ammonia solution has a molar concentration of 1 mol / L to 1.1 mol / L, and the hydrogen peroxide has a mass fraction of 30%.

7. The preparation method according to claim 1, characterized in that, The ratio of neodymium nitrate hexahydrate, cerium nitrate hexahydrate, and deionized ethylene glycol aqueous solution is (0.32g~0.52g): (0.76g~0.96g): (20mL~25mL); The volume ratio of ethylene glycol to deionized water in the ethylene glycol deionized aqueous solution is 1.2:1 to 1:

1.

8. The preparation method according to claim 1, characterized in that, The segmented heating process includes a first heating process and a second heating process; The first heating process includes: heating to 350°C to 360°C in a mixed atmosphere of argon and hydrogen at a heating rate of 2°C / min to 3°C / min, and holding at that temperature for 1 hour to 1.5 hours; The second heating process includes: heating to 450°C to 460°C in a mixed atmosphere of argon and hydrogen at a heating rate of 4°C / min to 4.5°C / min, and holding at that temperature for 2 hours to 2.5 hours.

9. A flow battery electrode for improving cycle stability and electrochemical performance, characterized in that, The flow battery electrode is prepared using the preparation method described in any one of claims 1 to 8.

10. The flow battery electrode according to claim 9, characterized in that, The flow battery electrode operates at a current density of 100 mA / cm². 2 At that time, the energy efficiency was greater than or equal to 86.7%, and the stability was greater than or equal to 1645 cycles.

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