A metal oxide-modified electrode for flow batteries and its preparation method

Abstract

This invention belongs to the field of vanadium redox flow batteries and relates to a metal oxide-modified electrode for flow batteries and its preparation method. The preparation method of the metal oxide-modified electrode for flow batteries includes the following steps: S1: Dissolving soluble tungsten salt, soluble cobalt salt, and soluble bismuth salt in water, adding a reducing agent, a template agent, and a surfactant to obtain a reaction precursor solution. S2: Performing a hydrothermal reaction on the reaction precursor solution to obtain a catalyst precursor. S3: Adding the catalyst precursor and conductive carbon material to a dispersion medium containing a binder to obtain a suspension. S4: Loading the suspension onto the surface of an electrode substrate material, and drying it to obtain an electrode precursor with a modified layer. S5: Performing a hot-pressing treatment on the electrode precursor to obtain the electrode. The electrode prepared by this invention possesses the characteristics of high catalytic activity, high structural stability, and low hydrogen evolution side reactions, achieving uniform distribution and efficient utilization of active sites.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, specifically to a metal oxide-modified electrode for flow batteries and its preparation method. Background Technology

[0002] Vanadium redox flow batteries, as a large-scale, long-term energy storage technology, have shown broad application prospects in areas such as smoothing renewable energy output and ensuring stable grid operation due to their outstanding advantages, including high safety, long lifespan, high energy conversion efficiency, and strong scalability. To ensure efficient electrochemical reactions within the battery, the electrode materials of vanadium redox flow batteries typically require modification to enhance their electrochemical activity and reaction reversibility.

[0003] Currently, common methods for modifying vanadium redox flow battery electrode materials include high-temperature oxidation to introduce oxygen-containing functional groups, etching to increase the specific surface area of ​​the electrode, in-situ growth of carbon nanotubes on the surface of the electrode carbon material, and electrochemical deposition to introduce metal catalysts such as bismuth. However, these existing technologies often have their own limitations. For example, high-temperature oxidation and etching methods may affect the structural strength of the electrode bulk, while the introduction of metal catalysts faces problems such as high cost, uneven or insufficient distribution of active sites, poor catalyst stability or insufficient catalytic activity, and the potential to induce side reactions such as hydrogen evolution. These problems limit further improvement of electrode performance and commercialization.

[0004] Therefore, there is a need for an electrode modification method that can achieve uniform active sites, high catalytic activity and high structural stability, and fewer hydrogen evolution side reactions. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the problems of insufficient catalytic activity, poor structural stability, uneven distribution of active sites, and easy induction of hydrogen evolution side reactions when modifying electrode materials for vanadium redox flow batteries in the prior art, this invention provides a metal oxide-modified electrode for flow batteries and its preparation method.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] A method for preparing a metal oxide-modified electrode for a flow battery includes the following steps:

[0010] S1: Dissolve soluble tungsten salt, soluble cobalt salt and soluble bismuth salt in water, add reducing agent, template agent and surfactant to obtain reaction precursor solution;

[0011] S2: Perform a hydrothermal reaction on the precursor liquid to obtain the catalyst precursor;

[0012] S3: Add the catalyst precursor and conductive carbon material to a dispersion medium containing a binder to obtain a suspension;

[0013] S4: Load the suspension onto the surface of the electrode substrate material and dry it to obtain an electrode precursor with a modified layer;

[0014] S5: The electrode precursor is subjected to hot pressing to obtain a metal oxide-modified flow battery electrode.

[0015] In the preparation method described above, preferably, in step S1, the soluble tungsten salt is sodium tungstate, potassium tungstate, or ammonium tungstate; the soluble cobalt salt is cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt acetate; and the soluble bismuth salt is bismuth nitrate, bismuth sulfate, or bismuth chloride.

[0016] In soluble tungsten salts, soluble cobalt salts, and soluble bismuth salts, the molar ratio of tungsten, cobalt, and bismuth is (0.5-1.5):(0.5-1.5):(1.5-2.5).

[0017] In the preparation method described above, preferably, in step S1, the reducing agent is ethylene glycol, the template agent is urea, and the surfactant is at least one of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium fatty acid methyl ester sulfonate, and sodium di-(2-ethylhexyl)succinate sulfonate.

[0018] The volume ratio of water to ethylene glycol is 1:(1-3);

[0019] In the reaction precursor solution obtained in step S1, the urea concentration is 0.02-0.1 mol / L, the surfactant concentration is 5-12 g / L, and the sum of the concentrations of soluble tungsten salt, soluble cobalt salt, and soluble bismuth salt is 0.02-0.2 mol / L.

[0020] In the preparation method described above, preferably, in step S2, the precursor solution is subjected to hydrothermal reaction at 150-190°C for 18-22 hours to obtain the catalyst precursor.

[0021] In the preparation method described above, preferably, in step S3, the catalyst precursor is ground to 500-1000 nm, and then added to a dispersion medium containing a binder along with a conductive carbon material. After stirring and ultrasonic treatment, a suspension is obtained.

[0022] In the preparation method described above, preferably, in step S3, the conductive carbon material is at least one of graphene, carbon nanotubes, carbon black, and graphyne; the mass ratio of the catalyst precursor to the conductive carbon material is 5:1 to 1:1; the binder is polyvinylidene fluoride; and the dispersion medium containing the binder is an aqueous dispersion medium of polyvinylidene fluoride, wherein the solid content of polyvinylidene fluoride is 30-55%wt.

[0023] In the preparation method described above, preferably, in step S4, the electrode substrate material is immersed in a suspension and dried to obtain the electrode precursor.

[0024] Alternatively, the suspension can be sprayed onto the surface of the electrode substrate material and dried to obtain the electrode precursor.

[0025] The electrode substrate material is carbon felt, graphite felt, carbon cloth, or carbon paper.

[0026] In the preparation method described above, preferably, in step S4, when the electrode substrate material is immersed in the suspension for 10-30 minutes, and when the suspension is sprayed onto the surface of the electrode substrate material, the spraying thickness is 0.1-0.5 mm.

[0027] In the preparation method described above, preferably, in step S5, the hot pressing temperature is 170-180℃, the pressure is 0.05-0.3MPa, and the time is 10-20min.

[0028] The present invention also provides a metal oxide-modified flow battery electrode prepared according to the above preparation method.

[0029] (III) Beneficial Effects

[0030] This invention utilizes a hydrothermal reaction of tungsten salt, cobalt salt, and bismuth salt to achieve a uniform reaction of the three metal elements and form a perovskite-structured tungsten-cobalt-bismuth composite metal oxide catalyst precursor. This specific configuration allows bismuth and cobalt to exist stably in a doped form within the tungsten-oxygen anion framework, achieving a uniform distribution and synergistic effect of the three elements at the atomic level. Specifically, bismuth ions effectively suppress the hydrogen evolution side reaction on the negative electrode side of the flow battery, while cobalt ions help improve Vg. 3+ / V 2+ The reversibility of the redox couple and the synergistic effect between them and the tungsten oxide ion group significantly enhance the catalytic activity of the electrode, solving the problems of insufficient catalytic activity and uneven distribution of active sites in existing modification methods.

[0031] This invention involves dispersing a perovskite-structured catalyst precursor and conductive carbon material together in a dispersion medium containing a binder to form a suspension. This suspension is then loaded onto the surface of an electrode substrate and subjected to hot pressing, ensuring a robust composite modification layer formed by the catalyst and conductive carbon material adheres firmly to the electrode substrate. The perovskite structure itself possesses excellent resistance to strong acid corrosion, ensuring high structural stability of the catalyst during long-term cycling in vanadium redox flow battery electrolytes. The conductive carbon material constructs a highly efficient electron conduction network within the modification layer, compensating for potential conductivity losses due to the binder and significantly reducing charge transfer impedance. This effectively improves the battery's voltage efficiency, energy efficiency, and capacity retention.

[0032] The modified layer prepared by this invention has a uniform and firmly bonded catalyst distribution. The hot pressing treatment further enhances the interfacial bonding force, giving the electrode the characteristics of high catalytic activity, high structural stability and low hydrogen evolution side reaction. It achieves uniform distribution and efficient utilization of active sites. At the same time, the preparation method of this invention has simple process steps, readily available raw materials, and is suitable for large-scale production applications. Detailed Implementation

[0033] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0034] This invention provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0035] S1: Dissolve soluble tungsten salt, soluble cobalt salt and soluble bismuth salt in water, add reducing agent, template agent and surfactant to obtain reaction precursor solution.

[0036] S2: Perform a hydrothermal reaction on the precursor liquid to obtain the catalyst precursor.

[0037] S3: Add the catalyst precursor and conductive carbon material to a dispersion medium containing a binder to obtain a suspension.

[0038] S4: Load the suspension onto the surface of the electrode substrate material and dry it to obtain an electrode precursor with a modified layer.

[0039] S5: The electrode precursor is subjected to hot pressing to obtain a metal oxide-modified flow battery electrode.

[0040] This invention utilizes a hydrothermal reaction of tungsten salt, cobalt salt, and bismuth salt to achieve a uniform reaction of the three metal elements and form a perovskite-structured tungsten-cobalt-bismuth composite metal oxide catalyst precursor. This specific configuration allows bismuth and cobalt to exist stably in a doped form within the tungsten-oxygen anion framework, achieving a uniform distribution and synergistic effect of the three elements at the atomic level. Specifically, bismuth ions effectively suppress the hydrogen evolution side reaction on the negative electrode side of the flow battery, while cobalt ions help improve Vg.3+ / V 2+ The reversibility of the redox couple and the synergistic effect between them and the tungsten oxide ion group significantly enhance the catalytic activity of the electrode, solving the problems of insufficient catalytic activity and uneven distribution of active sites in existing modification methods.

[0041] This invention involves dispersing a perovskite-structured catalyst precursor and conductive carbon material together in a dispersion medium containing a binder to form a suspension. This suspension is then loaded onto the surface of an electrode substrate and subjected to hot-pressing, ensuring a robust composite modification layer formed by the catalyst and conductive carbon material adheres firmly to the electrode substrate. The perovskite structure itself possesses excellent resistance to strong acid corrosion, ensuring high structural stability of the catalyst during long-term cycling in the electrolyte of a vanadium redox flow battery. The conductive carbon material constructs a highly efficient electron conduction network within the modification layer, compensating for potential conductivity losses due to the binder and significantly reducing charge transfer impedance, thereby effectively improving the battery's voltage and energy efficiency.

[0042] The modified layer prepared by this invention has a uniform and firmly bonded catalyst distribution. The hot pressing treatment further enhances the interfacial bonding force, giving the electrode the characteristics of high catalytic activity, high structural stability and low hydrogen evolution side reaction. It achieves uniform distribution and efficient utilization of active sites. At the same time, the preparation method of this invention has simple process steps, readily available raw materials, and is suitable for large-scale production applications.

[0043] Preferably, in step S1 above, the soluble tungsten salt is sodium tungstate, potassium tungstate, or ammonium tungstate; the soluble cobalt salt is cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt acetate; and the soluble bismuth salt is bismuth nitrate, bismuth sulfate, or bismuth chloride. The molar ratio of tungsten, cobalt, and bismuth in the soluble tungsten salt, soluble cobalt salt, and soluble bismuth salt is (0.5-1.5):(0.5-1.5):(1.5-2.5). The reducing agent is ethylene glycol, the template agent is urea, and the surfactant is at least one selected from sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium fatty acid methyl ester sulfonate, and sodium di-(2-ethylhexyl)succinate sulfonate. The volume ratio of water to ethylene glycol is 1:(1-3). More preferably, in the reaction precursor solution obtained in step S1, the urea concentration is 0.02-0.1 mol / L, the surfactant concentration is 5-12 g / L, and the sum of the concentrations of soluble tungsten salt, soluble cobalt salt, and soluble bismuth salt is 0.02-0.2 mol / L.

[0044] The aforementioned soluble salts are all industrially common and readily available metal source compounds. They are fully soluble in water and provide the corresponding metal ions, thus providing a raw material basis for the subsequent hydrothermal reaction to form a homogeneous composite metal oxide. Among them, sodium tungstate, potassium tungstate, and ammonium tungstate serve as tungsten sources, providing WO4 in aqueous solution. 2-Cobalt ions participate in the construction of perovskite structures. Cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt acetate can all serve as cobalt sources, providing Co. 2+ Bismuth ions, including bismuth nitrate, bismuth sulfate, and bismuth chloride, can all provide Bi. 3+ Ions. The range of salts described above provides those skilled in the art with flexible options based on raw material availability and cost considerations.

[0045] The molar ratio of tungsten, cobalt, and bismuth is a key control parameter for forming the target perovskite-structured composite metal oxide. If the tungsten ratio is too low, a stable tungsten-oxygen anionic framework may not form. Furthermore, since the tungsten-oxygen ion group is the main component of this type of perovskite catalyst, providing the anionic framework structure for supporting bismuth and cobalt cations, the target catalyst cannot be obtained if tungsten is not added at all. Conversely, if the cobalt ratio is too high or too low, it will affect the Co content. 2+ The amount of doping in the crystal lattice, and thus its effect on V 3+ / V 2+ The catalytic activity of the redox couple may be affected if the bismuth ratio deviates from the preferred range mentioned above, as this could impact its ability to suppress the hydrogen evolution side reaction and the stability of the perovskite structure. Controlling the molar ratio of the three elements within the above range ensures the formation of a tungsten-cobalt-bismuth composite metal oxide with a good crystal structure after the hydrothermal reaction, achieving uniform distribution and synergistic catalytic effect of the three elements in the crystal lattice.

[0046] Ethylene glycol, as a reducing agent, can promote the formation of tungsten oxide anion groups, which is beneficial for increasing V. 3+ / V 2+ Regarding the reactivity of the redox couple, urea, acting as a template agent, can balance the charge and promote the orderly growth of catalyst products, which is beneficial to the formation of perovskite structures. The use of surfactants can effectively reduce interfacial energy, promote the forward reaction, and effectively control the morphology and particle size of the products, inducing orderly and directional growth of the products and preventing the catalyst from agglomerating and causing a decline in activation performance. The aforementioned surfactants are all common anionic or cationic surfactants in this field, possessing good dispersing and regulating effects.

[0047] Preferably, in step S2 above, the precursor solution can be subjected to hydrothermal reaction at 150-190°C for 18-22 hours to obtain the catalyst precursor. These reaction conditions ensure that the reaction proceeds fully, generating a perovskite-configured composite metal oxide catalyst precursor with good crystallinity and uniform particle size.

[0048] Furthermore, in step S2, after the hydrothermal reaction is completed, post-processing steps such as cooling, filtration, washing, and drying are typically included. Specifically, after the reaction is completed, the product is cooled and filtered to obtain a solid product. The product is then washed with deionized water and ethanol to remove unreacted raw materials and byproducts, and then dried at 80-90°C for 1-2 hours to obtain a pure catalyst precursor powder. These post-processing steps help improve the purity and performance stability of the catalyst.

[0049] Preferably, in step S3 above, the catalyst precursor is ground to 500-1000 nm, and then added to a dispersion medium containing a binder along with the conductive carbon material. After stirring and ultrasonic treatment, a suspension is obtained. In step S3, the conductive carbon material is at least one of graphene, carbon nanotubes, carbon black, and graphylene; the mass ratio of the catalyst precursor to the conductive carbon material is 5:1 to 1:1; the binder is polyvinylidene fluoride; and the dispersion medium containing the binder is an aqueous dispersion medium of polyvinylidene fluoride, wherein the solid content of polyvinylidene fluoride is 30-55% wt.

[0050] Grinding the catalyst precursor to submicron particle size improves its dispersion uniformity in the suspension and avoids uneven distribution of active sites caused by large particle agglomeration. The combined use of stirring and ultrasonic treatment further promotes the uniform dispersion of catalyst powder and conductive carbon materials in the dispersion medium, forming a stable suspension and creating conditions for subsequent uniform loading on the electrode substrate surface.

[0051] The aforementioned conductive carbon material possesses a high specific surface area and excellent electrical conductivity. As an electron conduction bridge in the modification layer, it can establish an efficient electron transport channel between the catalyst and the electrode substrate, compensating for potential conductivity losses caused by the binder. Its high specific surface area also helps increase the exposure of active sites. By controlling the mass ratio of catalyst precursor to conductive carbon material within the range of 5:1 to 1:1, a highly efficient electron conduction network can be constructed while ensuring sufficient catalytic activity, achieving a balanced optimization of catalytic performance and electrical conductivity.

[0052] Polyvinylidene fluoride (PVDF) possesses excellent corrosion resistance and adhesion, enabling it to form a stable dispersion system in aqueous media, firmly immobilizing the catalyst and conductive carbon material on the electrode substrate surface. Using an aqueous dispersion medium is more environmentally friendly and safer, avoiding the use and recycling costs of organic solvents. The solid content of PVDF is controlled within the range of 30-55%wt, ensuring sufficient adhesive strength without excessive binder that could over-encapsulate the catalyst's active sites or affect conductivity.

[0053] Preferably, in step S4 above, the electrode substrate material can be immersed in a suspension and dried to obtain the electrode precursor. Alternatively, the suspension can be sprayed onto the surface of the electrode substrate material and dried to obtain the electrode precursor.

[0054] The two loading methods described above offer flexible options for actual production: the immersion method is simple to operate, suitable for batch processing, and allows the suspension to fully penetrate into the porous electrode substrate. The spraying method is suitable for precise control of the loading amount, and can form a uniformly thick modification layer on the electrode surface. Both methods ensure that the solids in the suspension adhere uniformly to the electrode substrate surface, and after drying to remove moisture, a uniform modification layer is formed.

[0055] Preferably, the electrode substrate material used in this invention is carbon felt, graphite felt, carbon cloth, or carbon paper. These carbon-based materials possess good conductivity, corrosion resistance, and porous structure, providing ample surface area and channels for electrolyte flow and electrochemical reactions. All of the above materials can serve as substrates for catalyst loading in this invention, and their electrochemical performance can be significantly improved through modification.

[0056] Preferably, in step S4, when the electrode substrate material is immersed in the suspension, the immersion time is 10-30 minutes. This immersion time ensures that the suspension fully wets the electrode substrate, allowing the catalyst and conductive carbon material to effectively adhere to the fiber surface. Too short an immersion time may result in insufficient loading, while too long an immersion time may cause overloading or a decrease in production efficiency. When the suspension is sprayed onto the surface of the electrode substrate material, the spray thickness is 0.1-0.5 mm. This thickness range allows for the formation of a uniform and suitable modification layer. Too thin a layer may result in insufficient catalytic activity, while too thick a layer may increase mass transfer resistance or cause the modification layer to peel off.

[0057] Preferably, in step S5 above, the hot-pressing temperature is 170-180℃, the pressure is 0.05-0.3MPa, and the time is 10-20min. Hot-pressing is a crucial step in ensuring a firm bond between the modified layer and the electrode substrate. Under heating conditions, the polyvinylidene fluoride (PVDF) binder softens or melts, enabling it to tightly bond the catalyst and conductive carbon material to the electrode substrate surface under pressure. Simultaneously, hot-pressing helps to further improve the density and adhesion of the modified layer and reduce interfacial resistance. Controlling the hot-pressing temperature at 170-180℃, slightly higher than the melting temperature range of PVDF, ensures sufficient softening without excessive flow. Controlling the pressure at 0.05-0.3MPa guarantees a tight fit without damaging the porous structure of the electrode due to excessive pressure. Controlling the hot-pressing time at 10-20min ensures the full realization of the hot-pressing effect while also considering production efficiency.

[0058] This invention also provides a metal oxide-modified flow battery electrode prepared according to the above-described method. The electrode surface is uniformly loaded with a composite modification layer formed by a perovskite-structured tungsten-cobalt-bismuth composite metal oxide catalyst and a conductive carbon material. The catalyst is firmly bonded to the electrode substrate, exhibiting high catalytic activity, high structural stability, and low hydrogen evolution side reaction characteristics. Using this electrode in an all-vanadium redox flow battery can significantly improve the battery's voltage efficiency, energy efficiency, and capacity retention, demonstrating promising commercial application prospects.

[0059] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0060] Example 1:

[0061] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0062] S1: Sodium tungstate, cobalt nitrate, and bismuth nitrate were dissolved in a mixed solution of deionized water and ethylene glycol (volume ratio 1:2) at a molar ratio of 1:1:2. Urea and sodium dodecyl sulfate were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.05 mol / L, the concentration of the surfactant was 8 g / L, and the sum of the concentrations of sodium tungstate, cobalt nitrate, and bismuth nitrate was 0.1 mol / L.

[0063] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 170°C for 20 hours. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 85°C for 1 hour to obtain the catalyst precursor.

[0064] S3: The catalyst precursor is ball-milled to 500 nm, and then the milled powder and graphene are added together in a 3:1 mass ratio to a polyvinylidene fluoride aqueous emulsion with a solid content of 40% wt. After thorough stirring and ultrasonic treatment, a suspension is obtained.

[0065] S4: Immerse the carbon felt electrode in the suspension for 20 minutes and stir the suspension slowly. After removing and rinsing it, dry it at 105°C for 1 hour to obtain the electrode precursor.

[0066] S5: The electrode precursor was hot-pressed at 175℃ and 0.08MPa for 15 min to obtain a metal oxide-modified flow battery electrode.

[0067] Example 2:

[0068] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0069] S1: Potassium tungstate, cobalt sulfate, and bismuth sulfate were dissolved in a 1:1 volume ratio of deionized water and ethylene glycol, with a molar ratio of 0.5:0.5:1.5 for tungsten, cobalt, and bismuth. Urea and hexadecyltrimethylammonium bromide were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.02 mol / L, the concentration of the surfactant was 5 g / L, and the sum of the concentrations of potassium tungstate, cobalt sulfate, and bismuth sulfate was 0.02 mol / L.

[0070] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 150°C for 18 hours. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 80°C for 2 hours to obtain the catalyst precursor.

[0071] S3: The catalyst precursor is ball-milled to 800 nm, and then the milled powder and carbon nanotubes are added together in a 5:1 mass ratio to a polyvinylidene fluoride aqueous emulsion with a solid content of 30% wt. After thorough stirring and ultrasonic treatment, a suspension is obtained.

[0072] S4: The suspension is uniformly sprayed onto the surface of the carbon paper electrode to form a surface modification layer of electrode substrate with a thickness of 0.3 mm, and dried at 105℃ for 1 h to obtain the electrode precursor.

[0073] S5: The electrode precursor was hot-pressed at 170℃ and 0.05MPa for 10 min to obtain a metal oxide-modified flow battery electrode.

[0074] Example 3:

[0075] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0076] S1: Following a molar ratio of tungsten, cobalt, and bismuth of 1.5:1.5:2.5, ammonium tungstate, cobalt chloride, and bismuth chloride were dissolved in a mixed solution of deionized water and ethylene glycol at a volume ratio of 1:1.5. Urea and sodium fatty acid methyl ester sulfonate were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.1 mol / L, the concentration of the surfactant was 12 g / L, and the sum of the concentrations of ammonium tungstate, cobalt chloride, and bismuth chloride was 0.2 mol / L.

[0077] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 190°C for 22 hours. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 90°C for 1 hour to obtain the catalyst precursor.

[0078] S3: The catalyst precursor was ball-milled to 750 nm, and then the milled powder and graphylene were added together in a mass ratio of 4:3 to a polyvinylidene fluoride aqueous emulsion with a solid content of 55% wt. After thorough stirring and ultrasonic treatment, a suspension was obtained.

[0079] S4: The suspension is uniformly sprayed onto the surface of the carbon cloth electrode to form a surface modification layer of electrode substrate with a thickness of 0.1 mm, and dried at 105℃ for 1 h to obtain the electrode precursor.

[0080] S5: The electrode precursor was hot-pressed at 180℃ and 0.3MPa for 20 min to obtain a metal oxide-modified flow battery electrode.

[0081] Example 4:

[0082] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0083] S1: Sodium tungstate, cobalt acetate, and bismuth nitrate were dissolved in a mixed solution of deionized water and ethylene glycol in a volume ratio of 1:2.5, according to a molar ratio of tungsten, cobalt, and bismuth of 1:1:2. Urea and sodium di-(2-ethylhexyl)succinate sulfonate were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.08 mol / L, the concentration of surfactant was 10 g / L, and the sum of the concentrations of sodium tungstate, cobalt acetate, and bismuth nitrate was 0.15 mol / L.

[0084] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 170°C for 20 hours. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 85°C for 1 hour to obtain the catalyst precursor.

[0085] S3: The catalyst precursor was ball-milled to 600 nm, and then the milled powder and graphene were added together in a 5:4 mass ratio to a polyvinylidene fluoride aqueous emulsion with a solid content of 40% wt. After thorough stirring and ultrasonic treatment, a suspension was obtained.

[0086] S4: The suspension is uniformly sprayed onto the surface of the carbon paper electrode to form a surface modification layer of electrode substrate with a thickness of 0.5 mm, and dried at 105℃ for 1 h to obtain the electrode precursor.

[0087] S5: The electrode precursor was hot-pressed at 175℃ and 0.2MPa for 15 min to obtain a metal oxide-modified flow battery electrode.

[0088] Example 5:

[0089] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0090] S1: Sodium tungstate, cobalt nitrate, and bismuth nitrate were dissolved in a mixed solution of deionized water and ethylene glycol in a volume ratio of 1:1.5, according to a molar ratio of tungsten, cobalt, and bismuth of 1:1:2. Urea and sodium dodecyl sulfate were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.12 mol / L, the concentration of surfactant was 6 g / L, and the sum of the concentrations of sodium tungstate, cobalt nitrate, and bismuth nitrate was 0.08 mol / L.

[0091] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 170°C for 21 h. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 85°C for 1.5 h to obtain the catalyst precursor.

[0092] S3: The catalyst precursor is ball-milled to 700 nm, and then the milled powder and carbon nanotubes are added together in a 3:2 mass ratio to a polyvinylidene fluoride aqueous emulsion with a solid content of 45% wt. After thorough stirring and ultrasonic treatment, a suspension is obtained.

[0093] S4: Immerse the carbon felt electrode in the suspension for 10 min and stir the suspension slowly. After removing and rinsing it, dry it at 105℃ for 1 h to obtain the electrode precursor.

[0094] S5: The electrode precursor was hot-pressed at 175℃ and 0.1MPa for 15 min to obtain a metal oxide modified flow battery electrode.

[0095] Example 6:

[0096] This embodiment provides a method for preparing a metal oxide-modified electrode for a flow battery, comprising the following steps:

[0097] S1: Sodium tungstate, cobalt nitrate, and bismuth nitrate were dissolved in a mixed solution of deionized water and ethylene glycol at a volume ratio of 1:3, according to a molar ratio of tungsten, cobalt, and bismuth of 1.2:1.4:2.2. Urea and hexadecyltrimethylammonium bromide were added, and the mixture was continuously stirred and dispersed to obtain the reaction precursor solution. In the reaction precursor solution, the concentration of urea was 0.11 mol / L, the concentration of surfactant was 7 g / L, and the sum of the concentrations of sodium tungstate, cobalt nitrate, and bismuth nitrate was 0.12 mol / L.

[0098] S2: The reaction precursor liquid was transferred to a reaction vessel with a polytetrafluoroethylene liner and hydrothermally reacted at 165°C for 19 hours. After the reaction was completed, the product was cooled, filtered, washed with deionized water and ethanol, and then dried at 85°C for 1 hour to obtain the catalyst precursor.

[0099] S3: The catalyst precursor is ball-milled to 1000 nm, and then the milled powder and graphylene are added together in a 1:1 mass ratio to a polyvinylidene fluoride aqueous emulsion with a solid content of 43% wt. After thorough stirring and ultrasonic treatment, a suspension is obtained.

[0100] S4: The suspension is uniformly sprayed onto the surface of the graphite felt electrode to form a surface modification layer of electrode substrate with a thickness of 0.1 mm. The electrode precursor is then dried at 105 °C for 1 h.

[0101] S5: The electrode precursor was hot-pressed at 175℃ and 0.15MPa for 12 min to obtain a metal oxide modified flow battery electrode.

[0102] Comparative Example 1:

[0103] This comparative example provides a carbon felt electrode that has not been modified with a catalyst and has only undergone normal aerobic activation treatment.

[0104] Comparative Example 2:

[0105] This comparative example provides a method for preparing an electrode for a flow battery, comprising the following steps:

[0106] S1: Bismuth nitrate and carbon black are added together in a mass ratio of 3:1 to a polyvinylidene fluoride aqueous emulsion with a solid content of 30%wt. After thorough stirring and ultrasonic treatment, a suspension is obtained.

[0107] S2: Immerse the carbon felt electrode substrate in the suspension obtained in step S1 for 20 min, remove it, rinse it dry, and dry it at 105℃ for 1 h to obtain the electrode prepreg.

[0108] S3: The electrode pre-impregnated body is hot-pressed at 175℃ and 0.08MPa for 15min to obtain the bismuth-modified electrode product.

[0109] Comparative Example 3:

[0110] This comparative example provides a method for preparing an electrode for a flow battery. In step S1, cobalt nitrate is not added, and the other steps are the same as in Example 1.

[0111] To characterize the performance parameters of the modified electrode prepared in this invention during actual operation of a flow battery, electrodes prepared in Examples 1-6 and Comparative Examples 1-3 were selected as experimental subjects for battery assembly and related performance tests. The test conditions were constant current charge-discharge mode with a current density of 200 mA / cm². 2 The test was repeated 3000 times. The test results are shown in Table 1.

[0112] Table 1. Statistical table of performance test results of electrodes prepared in Examples 1-6 and Comparative Examples 1-3

[0113] As shown in Table 1, the electrodes prepared in Examples 1-6 of this invention exhibit significant advantages in various electrochemical performance aspects. Regarding voltage efficiency, Examples 1-6 are significantly higher than Comparative Examples 1-3, indicating that this invention effectively reduces the charge transfer impedance on the electrode surface and improves the electrochemical reaction kinetics by utilizing the synergistic effect of the tungsten-cobalt-bismuth ternary metals and the electron conduction network constructed from conductive carbon materials, thus significantly enhancing the catalytic activity of the electrode. In terms of energy efficiency, Examples 1-6 are also superior to Comparative Examples 1-3, confirming the improvement effect of the modification strategy of this invention on the overall battery performance. Furthermore, energy efficiency is also a reflection of the overall charge-discharge performance of the battery, and its level depends not only on catalytic activity but also closely related to the uniformity of the distribution of active sites on the electrode surface. Only when the catalyst is uniformly distributed on the electrode surface can the reaction be consistent and mass transfer smooth throughout the electrode region, thereby achieving higher energy efficiency. The high energy efficiency of the examples fully demonstrates that this invention, by grinding the catalyst precursor to submicron particle size and combining it with the regulatory effect of surfactants, achieves uniform distribution and efficient utilization of the catalyst on the electrode substrate surface, effectively solving the problem of uneven distribution of active sites. Of particular note is the significantly higher capacity retention rate of Examples 1-6 compared to Comparative Examples 1-3. Capacity retention rate is the most direct indicator of the long-term cycling stability of an electrode, comprehensively reflecting its ability to maintain catalytic activity, structural integrity, and resistance to side reactions. The composite metal oxide formed by the hydrothermal reaction in this invention possesses a stable structure. Combined with hot-pressing, the modified layer is tightly bonded to the electrode substrate, ensuring that the catalyst is not easily detached or deactivated in the electrolyte, providing structural protection for the long-term stable operation of the electrode. The high capacity retention rate of the examples fully demonstrates that, based on this stable structure, bismuth ions effectively suppress the hydrogen evolution side reaction, and cobalt ions effectively inhibit V... 3+ / V 2+ The improved reversibility of the redox reaction and the structural stability of the composite metal oxide in a strong acid environment work together to enable the electrode to maintain excellent catalytic activity and structural integrity during long-term cycling, thereby significantly delaying the battery capacity decay. In contrast, Comparative Example 1 did not undergo hydrogen evolution suppression and electrochemical catalyst modification, resulting in insufficient active sites and a lack of hydrogen evolution suppression capability. Although Comparative Example 2 introduced a single bismuth source, which suppressed the hydrogen evolution side reaction to some extent, it lacked the catalytic effect of a cobalt source and the synergistic effect of the tungsten oxide ion group anion framework. Furthermore, the uniformity of bismuth source distribution was limited, so the performance improvement was significantly lower than that of the embodiments of the present invention. Comparative Example 3, due to the absence of a cobalt source, V 3+ / V 2+The insufficient reversibility of the redox reaction and the lower voltage efficiency compared to the embodiments of the present invention also affect the capacity retention performance. In summary, the electrode modification scheme of the present invention has the advantages of low cost, high efficiency, and ease of implementation, making it suitable for industrial mass production.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a metal oxide-modified electrode for a flow battery, characterized in that, Includes the following steps: S1: Dissolve soluble tungsten salt, soluble cobalt salt and soluble bismuth salt in water, add reducing agent, template agent and surfactant to obtain reaction precursor solution; S2: Perform a hydrothermal reaction on the precursor liquid to obtain the catalyst precursor; S3: Add the catalyst precursor and conductive carbon material to a dispersion medium containing a binder to obtain a suspension; S4: Load the suspension onto the surface of the electrode substrate material and dry it to obtain an electrode precursor with a modified layer; S5: The electrode precursor is subjected to hot pressing to obtain a metal oxide-modified flow battery electrode.

2. The preparation method according to claim 1, characterized in that, In step S1, the soluble tungsten salt is sodium tungstate, potassium tungstate, or ammonium tungstate; the soluble cobalt salt is cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt acetate; and the soluble bismuth salt is bismuth nitrate, bismuth sulfate, or bismuth chloride. In soluble tungsten salts, soluble cobalt salts, and soluble bismuth salts, the molar ratio of tungsten, cobalt, and bismuth is (0.5-1.5):(0.5-1.5):(1.5-2.5).

3. The preparation method according to claim 1, characterized in that, In step S1, the reducing agent is ethylene glycol, the template agent is urea, and the surfactant is at least one of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium fatty acid methyl ester sulfonate, and sodium di-(2-ethylhexyl)succinate sulfonate. The volume ratio of water to ethylene glycol is 1:(1-3); In the reaction precursor solution obtained in step S1, the urea concentration is 0.02-0.1 mol / L, the surfactant concentration is 5-12 g / L, and the sum of the concentrations of soluble tungsten salt, soluble cobalt salt, and soluble bismuth salt is 0.02-0.2 mol / L.

4. The preparation method according to claim 1, characterized in that, In step S2, the reaction precursor liquid is subjected to hydrothermal reaction at 150-190℃ for 18-22h to obtain the catalyst precursor.

5. The preparation method according to claim 1, characterized in that, In step S3, the catalyst precursor is ground to 500-1000 nm, and then added to a dispersion medium containing a binder along with conductive carbon material. After stirring and ultrasonic treatment, a suspension is obtained.

6. The preparation method according to claim 1, characterized in that, In step S3, the conductive carbon material is at least one of graphene, carbon nanotubes, carbon black, and graphyne. The mass ratio of the catalyst precursor to the conductive carbon material is 5:1 to 1:

1. The binder is polyvinylidene fluoride (PVDF). The dispersion medium containing the binder is an aqueous dispersion medium of PVDF, wherein the solid content of PVDF is 30-55%wt.

7. The preparation method according to claim 1, characterized in that, In step S4, the electrode substrate material is immersed in a suspension and dried to obtain the electrode precursor. Alternatively, the suspension can be sprayed onto the surface of the electrode substrate material and dried to obtain the electrode precursor. The electrode substrate material is carbon felt, graphite felt, carbon cloth, or carbon paper.

8. The preparation method according to claim 7, characterized in that, In step S4, the electrode substrate material is immersed in a suspension for 10-30 minutes, and the suspension is sprayed onto the surface of the electrode substrate material with a thickness of 0.1-0.5 mm.

9. The preparation method according to claim 1, characterized in that, In step S5, the hot pressing temperature is 170-180℃, the pressure is 0.05-0.3MPa, and the time is 10-20min.

10. A metal oxide-modified flow battery electrode prepared by the preparation method according to any one of claims 1-9.

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