A method for modifying a proton exchange membrane

Abstract

The present invention relates to the field of all-vanadium redox flow batteries and discloses a method for modifying a proton exchange membrane. The method comprises the following steps: synthesizing a hollow TiO2-SO3H nanomaterial, comprising: mixing tetrabutyl titanate (TNB) and polyvinyl pyrrolidone (PVP) in a solvent of ethanol and anhydrous acetic acid, vigorously stirring, and then calcining to obtain solid TiO2; subjecting the solid TiO2 to a hydrothermal reaction in a NaOH solution to form a hollow TiO2; and subjecting the hollow TiO2 to a sulfonation reaction in a H2SO4 solution. By introducing the TiO2-SO3H@PMoA nanocomposite into a Nafion membrane, the proton conductivity of the membrane is significantly improved, reaching a proton conductivity of 200-300 mS / cm. This method maintains efficient proton conduction while ensuring the membrane's overall vanadium resistance, making it suitable for all-vanadium redox flow battery applications at high current densities.

Description

Technical Field

[0001] The present invention relates to the field of all-vanadium redox flow batteries, and in particular to a method for modifying a proton exchange membrane. Background Art

[0002] Vanadium redox flow batteries (VRBs) are an important energy storage system, widely used in large-scale energy storage scenarios due to their renewable, environmentally friendly, and long-life characteristics. As a core component of vanadium redox flow batteries, the proton exchange membrane primarily separates the positive and negative electrolytes and promotes proton conduction, directly determining the battery's coulombic efficiency, energy efficiency, and service life. Currently, Nafion membrane is the most widely used proton exchange membrane material, offering excellent proton conductivity. However, its high vanadium ion permeability limits the battery's overall performance.

[0003] The proton conductivity of Nafion membranes comes from the hydrophilic ion channels formed within them, which can effectively conduct protons. However, the ion cluster structure of Nafion membranes is large, and vanadium ions can easily diffuse through these channels to the other side of the membrane, resulting in cross-contamination of the positive and negative electrolytes, which seriously reduces the coulombic efficiency and voltage efficiency of the battery. In addition, although some studies have improved the vanadium resistance of Nafion membranes by doping them with inorganic nanomaterials, these modification methods usually sacrifice proton conductivity and cannot simultaneously achieve high proton conductivity and low vanadium ion permeability.

[0004] The high vanadium ion permeability of Nafion membranes currently limits the efficiency and service life of all-vanadium flow batteries. While existing technologies have proposed doping the membranes with inorganic materials to enhance vanadium resistance, these modification methods often struggle to effectively balance proton conductivity and mechanical stability. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a method for modifying a proton exchange membrane. The present invention introduces a TiO2-SO3H@PMoA nanocomposite material into the Nafion membrane, thereby significantly improving the proton conductivity to 200-300 mS / cm and significantly reducing the vanadium ion permeability to 1×10 -9 cm² / s. This membrane has both excellent vanadium resistance and proton conductivity, effectively solving the problem of high vanadium ion permeability, proton conductivity and mechanical stability of existing Nafion membranes, and significantly improving the coulombic efficiency, energy efficiency and service life of all-vanadium redox flow batteries.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for modifying a proton exchange membrane comprises the following steps:

[0007] Synthesis of hollow TiO2-SO3H nanomaterials, including:

[0008] Tetrabutyl titanate (TNB) and polyvinyl pyrrolidone (PVP) were mixed and dissolved in a solvent of ethanol and anhydrous acetic acid, stirred vigorously and calcined to obtain solid TiO2;

[0009] Solid TiO2 is subjected to hydrothermal reaction in NaOH solution to form hollow TiO2;

[0010] The hollow TiO2 is subjected to sulfonation reaction in H2SO4 solution to obtain hollow TiO2-SO3H;

[0011] Hollow TiO2-SO3H composites anchored with PMoA were prepared by reacting hollow TiO2-SO3H with phosphomolybdic acid (PMoA) solution.

[0012] The prepared hollow TiO2-SO3H@PMoA nanocomposite was added into Nafion solution, and a modified proton exchange membrane was obtained through stirring, film formation and drying steps.

[0013] Preferably, the synthesis of hollow TiO2-SO3H nanomaterials further comprises the following specific steps:

[0014] 5 g of TNB and 2 g of PVP were added to a mixed solvent of 10 g of ethanol and 2 g of anhydrous acetic acid and stirred vigorously at room temperature for 4 h to obtain a yellow solution;

[0015] Centrifuging the solution to obtain a solid material;

[0016] The solid material was placed in a muffle furnace, heated to 320° C. at a heating rate of 5° C. / min, and calcined in air for 6 h to obtain solid TiO 2 .

[0017] Preferably, the centrifugal separation of the solution specifically includes: a centrifugal speed of 10000 rpm and a duration of 10 minutes.

[0018] Preferably, the average particle size of the solid TiO2 particles after calcination is 50 to 100 nm.

[0019] Preferably, the centrifugal separation of the solution further comprises the step of subjecting the solid TiO2 to a hydrothermal reaction in an aqueous NaOH solution, the step being specifically as follows:

[0020] 0.1 g of solid TiO2 was soaked in 1 M NaOH solution;

[0021] Transferring the soaked solid TiO2 into a stainless steel autoclave lined with polytetrafluoroethylene;

[0022] Hydrothermal reaction at 180 °C for 36 h;

[0023] The obtained product was repeatedly washed with deionized water until the pH value reached 7.

[0024] Preferably, the calcination further comprises:

[0025] Add 0.1g of hollow TiO2 into 10MH2SO4 solution;

[0026] Heat at 60°C for 8 hours;

[0027] The mixture was washed repeatedly with deionized water until the pH value reached 7.

[0028] Preferably, the formation of the hollow TiO2 comprises:

[0029] 5 g of PMoA was dissolved in 45 g of N,N-dimethylformamide (DMF) solution and stirred for 5 hours to obtain a 10% PMoA solution;

[0030] Using the vacuum impregnation method, 0.08 g of hollow TiO2-SO3H nanomaterials were immersed in the 10% PMoA solution;

[0031] The mixture was kept in a vacuum oven at 70 °C for 4 h to anchor PMoA on the TiO2-SO3H surface.

[0032] Preferably, the vacuum degree of the vacuum impregnation step is controlled below 0.05 MPa.

[0033] Preferably, the formation of the hollow TiO2-SO3H comprises:

[0034] Add 5g of Nafion resin to 95g of N,N-dimethylformamide solution;

[0035] Heat and stir in a water bath at 150°C for 5 h to ensure that the Nafion resin is completely dissolved;

[0036] 0.04 g of hollow TiO2-SO3H@PMoA nanomaterials were added to 80 ml of 5% Nafion solution and stirred in a 60 °C water bath for 5 h;

[0037] The uniformly stirred solution was poured into a mold and heated at 100° C. for 6 h to form a film;

[0038] The formed proton exchange membrane is repeatedly rinsed with deionized water to remove residual solvent.

[0039] Preferably, the proton conductivity of the prepared modified proton exchange membrane is 200-300 mS / cm, and the vanadium ion permeability is less than 1×10 -9 cm² / s.

[0040] The present invention provides a method for modifying a proton exchange membrane, which has the following beneficial effects:

[0041] 1. The present invention significantly improves the proton conductivity of the Nafion membrane by introducing the TiO2-SO3H@PMoA nanocomposite material into the membrane, so that the proton conductivity of the membrane reaches 200-300 mS / cm. While maintaining efficient proton conduction, it ensures the overall electrochemical performance of the membrane and is suitable for all-vanadium redox flow battery applications at high current density.

[0042] 2. The present invention significantly reduces the vanadium ion permeability of the proton exchange membrane through the ion selectivity and physical barrier effect of TiO2-SO3H, and the permeability is as low as 1×10 -9 cm² / s, effectively reducing vanadium ion cross-contamination, improving the coulombic efficiency and voltage efficiency of the all-vanadium redox flow battery, and extending the battery life.

[0043] 3. The proton exchange membrane of this invention possesses excellent mechanical strength and long-term stability, demonstrating exceptional corrosion resistance and structural stability in strong acid environments. Its combination of efficient vanadium resistance and high proton conductivity significantly improves the overall efficiency of all-vanadium redox flow batteries, making it suitable for long-term, stable operation in practical industrial energy storage systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the specification of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0046] Please see the attached Figure 1 , an embodiment of the present invention provides a method for modifying a proton exchange membrane, comprising the following steps:

[0047] Synthesis of hollow TiO2-SO3H nanomaterials, including:

[0048] 1. Tetrabutyl titanate (TNB) and polyvinyl pyrrolidone (PVP) are mixed and dissolved in a solvent of ethanol and anhydrous acetic acid, stirred vigorously, and then calcined to obtain solid TiO2. First, tetrabutyl titanate (TNB) and polyvinyl pyrrolidone (PVP) are mixed and dissolved in a solvent of ethanol and anhydrous acetic acid, and stirred vigorously to ensure that the two chemicals can be fully mixed to form a uniform solution. After calcination, solid TiO2 particles are obtained. The high temperature during the calcination process causes tetrabutyl titanate to decompose and generate nano-sized TiO2 particles. These particles can be regulated during the reaction to eventually form the desired solid form. This solid structure prepares for the subsequent NaOH solution treatment, and its uniform structural characteristics help to improve the uniformity of the final hollow structure.

[0049] 2. Solid TiO2 is hydrothermally reacted in a NaOH solution to form hollow TiO2. The hollow TiO2 obtained in this step has a large specific surface area and a unique hollow structure, which helps to improve the barrier effect of vanadium ions and provide more active sites for subsequent functionalization. This hollow structure can also reduce the density of the material, making it more evenly distributed in the proton exchange membrane, thereby further optimizing the overall performance of the membrane;

[0050] 3. Sulfonation of hollow TiO2 in H2SO4 solution to obtain hollow TiO2-SO3H. Sulfonation of hollow TiO2 not only provides ion selectivity for the material, but also blocks the positively charged vanadium ions (V n+ ) through the membrane, thereby significantly reducing the permeability of vanadium ions;

[0051] By reacting hollow TiO2-SO3H with a phosphomolybdic acid (PMoA) solution, a PMoA-anchored hollow TiO2-SO3H composite material was prepared. This step effectively maintained the proton donor function of PMoA. At the same time, the hollow TiO2-SO3H served as a matrix, further improving the vanadium resistance of the membrane. Through this material composite, proton conductivity was fully maintained, avoiding the problem of decreased proton conductivity in traditional modification processes.

[0052] The prepared hollow TiO2-SO3H@PMoA nanocomposite material was incorporated into a Nafion solution, and a modified proton exchange membrane was obtained through stirring, film formation and drying steps. The modified proton exchange membrane has a significant vanadium ion barrier effect. The introduction of hollow TiO2-SO3H nanomaterials forms a stable structural barrier, effectively preventing vanadium ions from passing through the membrane. At the same time, the presence of phosphomolybdic acid maintains the proton conductivity of the membrane, ensuring the efficient operation of the battery. Through this modification process, the overall performance of the membrane has been significantly improved, thereby improving the coulombic efficiency and voltage efficiency of the all-vanadium redox flow battery and extending the battery life.

[0053] Please see the attached Figure 1 In a preferred embodiment of the present invention, the synthesis of hollow TiO2-SO3H nanomaterials further comprises the following specific steps:

[0054] 5g of TNB and 2g of PVP were added to a mixed solvent of 10g of ethanol and 2g of anhydrous acetic acid, and vigorously stirred at room temperature for 4h to obtain a yellow solution. This uniform stirring ensured the uniformity of the reaction solution, which helped to improve the uniformity and structural stability of the subsequently generated TiO2 particles, providing a guarantee for achieving a good nanoscale structure.

[0055] The solution is centrifuged to obtain a solid material. Centrifugation can effectively remove the solvent and impurities that have not participated in the reaction, and obtain pure TiO2 particles. This step ensures the purity of subsequent materials and improves the structural consistency of TiO2;

[0056] The solid material was placed in a muffle furnace, heated to 320°C at a heating rate of 5°C / min, and calcined in air for 6 hours to obtain solid TiO2. The calcination process completely decomposed the organic matter and formed solid TiO2 particles with a stable crystal structure, providing a stable structural foundation. The uniformity and purity of the particles provided favorable conditions for subsequent reactions and improved the mechanical strength and thermal stability of the material.

[0057] Please see the attached Figure 1 In a preferred embodiment of the present invention, the solution centrifugal separation specifically includes: a centrifugal speed of 10,000 rpm for 10 minutes. The centrifuge rotates at high speed, utilizing centrifugal force to deposit solid particles in the solution toward the bottom of the tube. Particularly at high speeds, TiO2 particles, due to their relatively large mass, are rapidly pushed toward the bottom of the tube by the centrifugal force, forming a precipitate. Centrifugal speed and time are key parameters influencing the separation effect. A centrifugal speed of 10,000 rpm provides sufficient centrifugal force to rapidly separate nanoscale TiO2 particles from the solution. A duration of 10 minutes ensures sufficient sedimentation of the solution during the centrifugation process, preventing particles from being suspended in the supernatant. After centrifugation is complete, the solid precipitate in the centrifuge tube is collected, and the supernatant is carefully removed. This operation removes unreacted solvent and impurities, ensuring a high-purity solid material. Furthermore, a reasonable combination of centrifugal speed and time prevents particle aggregation or damage to the particle structure, ensuring that the resulting TiO2 particles maintain good dispersion and nanostructure.

[0058] Please see the attached Figure 1In a preferred embodiment of the present invention, the average particle size of the solid TiO2 particles after calcination is 50-100 nm. This particle size provides a sufficiently large surface area for the subsequent sulfonation reaction while ensuring uniform dispersion of the TiO2 particles within the membrane, preventing large particle agglomerations. Particles within this size range exhibit high reactivity, enabling better binding with phosphomolybdic acid (PMoA) during subsequent processing, ensuring the integrity of the proton conduction pathway.

[0059] Please see the attached Figure 1 In a preferred embodiment of the present invention, the centrifugal separation of the solution further comprises the step of subjecting the solid TiO2 to a hydrothermal reaction in an aqueous NaOH solution, the step being specifically as follows:

[0060] 0.1g of solid TiO2 was immersed in a 1M NaOH solution. The NaOH concentration during the immersion process was controlled to 1M, which ensured the effective dissolution of the core without causing excessive damage to the external structure, thereby maintaining the integrity of the TiO2 shell. The immersion time is closely related to the solution concentration. Reasonable control can avoid excessive damage to the internal and external structures. By immersing the solid TiO2 in a 1M NaOH aqueous solution, the core structure can be effectively dissolved, and the framework of the hollow structure can be initially formed. This ensures the stability of the shell and is conducive to the formation of hollow TiO2 in subsequent reactions.

[0061] The soaked solid TiO2 is transferred to a stainless steel autoclave lined with polytetrafluoroethylene. The closed environment of the stainless steel autoclave can generate high pressure under high temperature conditions. Under these conditions, the erosion effect of the NaOH solution is significantly enhanced, which helps to further dissolve the core of the TiO2 particles. At the same time, the use of polytetrafluoroethylene lining can prevent NaOH from corroding the equipment and extend the service life of the equipment, thereby ensuring the smooth progress of the reaction under high temperature and high pressure conditions, providing a strong alkaline environment and chemical stability, and improving the efficiency of the reaction;

[0062] The hydrothermal reaction was carried out at 180°C for 36 hours. Under this temperature condition, the hollowing of the TiO2 particles was gradually completed, the internal structure was completely eroded, and the outer shell was retained due to its high mechanical strength. The 36-hour reaction time ensured the full dissolution of the interior of the TiO2 particles, obtaining a uniform and stable hollow structure. By carrying out the hydrothermal reaction at 180°C for 36 hours, the interior of the solid TiO2 particles could be completely dissolved by NaOH, ultimately forming hollow TiO2 particles with a high specific surface area and good structural stability, which helped to improve the reactivity and dispersibility of the material.

[0063] The obtained product was repeatedly washed with deionized water to a pH of 7. By repeatedly washing with deionized water, the purity of the hollow TiO2 particles was ensured and the pH value was neutral, providing excellent basic conditions for the subsequent sulfonation reaction and avoiding any adverse effects of incompletely removed alkaline residues on subsequent reactions.

[0064] Please see the attached Figure 1 In a preferred embodiment of the present invention, the calcination further comprises:

[0065] 0.1g of hollow TiO2 was added to a 10MH2SO4 solution. Sulfonation treatment in 10MH2SO4 successfully introduced sulfonic acid groups (SO3H) onto the surface of the hollow TiO2. This step gave the TiO2 particles better ion selectivity and significantly enhanced their ability to block vanadium ions while maintaining good proton conductivity.

[0066] Heating at 60°C for 8h, the 10MH2SO4 solution containing hollow TiO2 was heated at 60°C for 8h. This temperature condition can not only accelerate the reaction rate, but also avoid damage to the TiO2 structure caused by high temperature. The heating process promotes the chemical bonding of SO3H groups with the TiO2 surface, so that the sulfonic acid groups can be more firmly anchored on the surface of the TiO2 particles, so that the SO3H groups can be evenly and firmly bonded to the surface of the hollow TiO2, forming a stable TiO2-SO3H structure. The heating treatment ensures the full progress of the sulfonation process, so that the modified TiO2 particles have better stability and ion selectivity, especially the vanadium barrier effect in the proton exchange membrane is significantly enhanced;

[0067] Repeated washing with deionized water to a pH of 7 ensures that no excess acid residue remains on the surface of the TiO2-SO3H particles, resulting in a pure and stable material. This step further ensures the chemical stability and dispersibility of the TiO2-SO3H particles, providing high-quality material for the subsequent proton exchange membrane modification step, ensuring the membrane's vanadium resistance and proton conductivity.

[0068] Please see the attached Figure 1 In a preferred embodiment of the present invention, the formation of hollow TiO2 comprises:

[0069] 5g of PMoA was dissolved in 45g of N,N-dimethylformamide (DMF) solution and stirred for 5 hours to obtain a 10% PMoA solution. Prolonged stirring ensured that the PMoA was fully dispersed in the DMF solution, forming a uniform and stable solution. This uniform dispersion ensured that during the subsequent vacuum impregnation process, the PMoA could be evenly anchored on the surface of the TiO2-SO3H, improving proton conductivity. By fully dissolving the PMoA in the DMF solution, the uniformity and stability of the solution were ensured, providing a good foundation for the subsequent PMoA anchoring step. The high proton conductivity of PMoA can provide an effective proton conduction path in the membrane, helping to improve the overall performance of the proton exchange membrane.

[0070] Using a vacuum impregnation method, 0.08g of hollow TiO2-SO3H nanomaterials were immersed in a 10% PMoA solution. The vacuum treatment ensured full contact between the TiO2-SO3H surface and the PMoA. This method can avoid the uneven solution coverage problem that occurs in traditional impregnation processes and effectively improve the utilization rate of PMoA. PMoA molecules are evenly distributed on the surface of the hollow TiO2-SO3H, providing more transmission paths for proton conduction while maintaining the ion selectivity of TiO2-SO3H. The vacuum impregnation method ensures that the PMoA molecules can be evenly and stably attached to the surface of the TiO2-SO3H, avoiding the problem of uneven coverage of the material during use and further improving the conductive performance of the proton exchange membrane.

[0071] The PMoA was anchored to the TiO2-SO3H surface by maintaining it in a vacuum oven at 70°C for 4 hours. This step, through the synergistic effect of temperature and vacuum, effectively accelerated the binding of PMoA to the TiO2-SO3H surface, forming a stable chemical bond. The 70°C temperature condition not only promoted the movement of PMoA molecules and improved anchoring efficiency, but also did not damage the structural integrity of the TiO2-SO3H. The vacuum environment helped to further remove impurities from the air, ensuring that the anchoring process was not affected by external factors. After 4 hours of treatment, the PMoA molecules were firmly anchored to the TiO2-SO3H surface and were not easily detached, ensuring the long-term stability of the nanocomposite in the proton exchange membrane, thereby improving the performance of the nanocomposite, ensuring its stable performance in the proton exchange membrane, and enhancing the conductivity efficiency and ion selectivity without sacrificing structural integrity.

[0072] Please see the attached Figure 1In a preferred embodiment of the present invention, the vacuum degree of the vacuum impregnation step is controlled below 0.05 MPa. By controlling the vacuum degree below 0.05 MPa, it is possible to ensure that the PMoA molecules are evenly and firmly anchored on the surface of TiO2-SO3H, avoiding the problem of rapid evaporation of the solution or residual bubbles on the surface of the material under high vacuum. This step improves the surface modification effect of the nanomaterial, ensures the uniformity of the distribution of the material in the proton exchange membrane, and further improves the proton conductivity and vanadium resistance of the membrane. In addition, another major advantage of controlling the vacuum degree is to prevent the occurrence of excessive adsorption and material agglomeration. When the vacuum degree is too high, the adhesion of the material surface is too strong, which can easily lead to excessive deposition in local areas, resulting in uneven distribution of PMoA and affecting the performance of the material. Appropriate vacuum degree can ensure that the solution evenly covers the TiO2-SO3H surface and improves the performance consistency of the final modified membrane.

[0073] Please see the attached Figure 1 In a preferred embodiment of the present invention, the formation of hollow TiO2-SO3H comprises:

[0074] Add 5g of Nafion resin to 95g of N,N-dimethylformamide solution. 95g of N,N-dimethylformamide solution can effectively dissolve the Nafion resin, making it evenly distributed in the solution. Nafion is a fluorine-containing proton exchange membrane material with excellent proton conductivity. The dissolved Nafion resin is the basis for preparing the proton exchange membrane. By dissolving the Nafion resin in DMF solution, the uniformity and stability of the Nafion membrane matrix can be guaranteed, providing a good solution environment for the dispersion of nanomaterials in subsequent steps, ensuring the overall performance of the proton exchange membrane.

[0075] Heat and stir in a 150°C water bath for 5 hours to ensure that the Nafion resin is completely dissolved. The 150°C water bath temperature is high enough to effectively accelerate the dissolution of Nafion, but will not cause excessive evaporation of the solvent or degradation of the resin. Continuous stirring for 5 hours can prevent precipitation of the resin in the solution and ensure that the formed solution has high uniformity. The completely dissolved Nafion solution lays the foundation for the uniform dispersion and membrane formation of nanomaterials in the subsequent steps. By heating and stirring the Nafion solution in a 150°C water bath, the complete dissolution of the resin can be accelerated, the uniformity of the solution can be ensured, and the stable physical and chemical properties of the solution can be ensured, providing good conditions for the subsequent dispersion of nanomaterials and membrane preparation.

[0076] 0.04 g of hollow TiO2-SO3H@PMoA nanomaterials were added to 80 ml of 5% Nafion solution and stirred in a 60°C water bath for 5 hours. During this process, the control of temperature and stirring speed is the key to ensuring the uniform dispersion of the nanomaterials in the Nafion solution. The 60°C water bath temperature can maintain the fluidity of the solution and ensure the dispersibility of the nanomaterials, while avoiding excessively high temperatures that may lead to the agglomeration of the nanomaterials or the degradation of the Nafion solution. By stirring at 60°C, the hollow TiO2-SO3H@PMoA nanomaterials are uniformly dispersed in the Nafion solution, ensuring the full combination of the composite material and the matrix, forming a composite matrix with excellent vanadium resistance and proton conductivity.

[0077] The evenly stirred solution was poured into a mold and heated at 100°C for 6 hours to form a membrane. Heating at 100°C for 6 hours ensured uniform and dense membrane formation, forming a proton exchange membrane with stable mechanical strength and good electrical conductivity, providing high-quality membrane samples for subsequent performance testing.

[0078] The proton exchange membrane after membrane formation is repeatedly rinsed with deionized water to remove residual solvent. Repeated rinsing with deionized water can effectively remove residual solvent and impurities, ensure the purity and stability of the proton exchange membrane, further improve the conductivity and durability of the membrane, and enable it to have good performance in electrochemical applications.

[0079] Please see the attached Figure 1 In a preferred embodiment of the present invention, the proton conductivity of the prepared modified proton exchange membrane is 200-300 mS / cm, and the vanadium ion permeability is less than 1×10 -9 cm² / s. Through the synergistic effect of Nafion matrix and TiO2-SO3H@PMoA composite material, the modified proton exchange membrane can reach a high conductivity level of 200-300mS / cm, ensuring the efficient operation of the battery and significantly improving the electrochemical performance of the all-vanadium redox flow battery. The modified proton exchange membrane has significant vanadium resistance and the vanadium ion permeability is less than 1×10 -9 cm² / s. Through the physical and chemical synergistic effect of nanomaterials, the membrane effectively prevents the penetration of vanadium ions while maintaining high proton conductivity, thereby improving the efficiency and life of the all-vanadium redox flow battery, thereby ensuring the efficient and long-term operation of the all-vanadium redox flow battery and improving the coulombic efficiency and energy efficiency of the battery.

[0080] In order to better understand the present invention, the above contents are described in detail below in conjunction with specific embodiments.

[0081] Example 1: Preparation of TiO2-SO3H@PMoA nanomaterials

[0082] Preparation of solid TiO2

[0083] 5g of tetrabutyl titanate (TNB) and 2g of polyvinyl pyrrolidone (PVP) were added to a mixture of 10g of ethanol and 2g of anhydrous acetic acid and stirred for 4 hours to obtain a yellow solution. The solution was centrifuged to obtain a solid material, which was then calcined in air at 320°C for 6 hours to obtain solid TiO2.

[0084] Preparation of hollow TiO2

[0085] 0.1g of solid TiO2 particles were immersed in a 1M NaOH solution and transferred to a Teflon-lined stainless steel autoclave for a hydrothermal reaction at 180°C for 36 hours to form hollow TiO2. The solution was then repeatedly washed with deionized water and adjusted to pH 7.

[0086] Preparation of TiO2-SO3H

[0087] The hollow TiO2 particles were immersed in 10MH2SO4 solution, heated at 60°C for 8 h, and then washed repeatedly until the pH reached 7 to obtain hollow TiO2-SO3H nanomaterials.

[0088] PMoA anchored TiO2-SO3H

[0089] 5g of phosphomolybdic acid (PMoA) was dissolved in 45g of N,N-dimethylformamide (DMF) and stirred for 5h to obtain a 10% PMoA solution. 0.08g of TiO2-SO3H nanomaterials was immersed in the PMoA solution and kept in a vacuum oven at 70°C for 4h to anchor the PMoA on the TiO2-SO3H surface.

[0090] Preparation of proton exchange membrane

[0091] 5g of Nafion resin was added to 95g of N,N-dimethylformamide, stirred, and heated in a 150°C water bath for 5 hours to ensure complete dissolution of the Nafion. 0.04g of TiO2-SO3H@PMoA nanomaterial was added to 80ml of a 5% Nafion solution, stirred, and heated in a 60°C water bath for 5 hours. This solution was then poured into a mold and heated at 100°C for 6 hours to form a membrane. Finally, the proton exchange membrane was repeatedly rinsed with deionized water to remove any residual solvent.

[0092] Performance Testing

[0093] The test results show that the proton conductivity of the proton exchange membrane is 241mS / cm and the vanadium ion permeability is 6.55×10 -10 cm² / s.

[0094] Example 2: Changes in modification temperature conditions

[0095] Preparation of TiO2-SO3H Nanomaterials

[0096] The steps are the same as those in Example 1.

[0097] PMoA anchored TiO2-SO3H

[0098] The PMoA anchoring procedure remained unchanged, but the temperature of the vacuum oven was set to 80 °C and the duration was extended to 8 h to ensure a more secure anchoring of PMoA.

[0099] Preparation of proton exchange membrane

[0100] The process of preparing Nafion solution was the same as that in Example 1, but when introducing TiO2-SO3H@PMoA nanomaterial into Nafion solution, the water bath temperature was lowered to 50°C and the stirring time was maintained for 6 h. Subsequently, the film forming temperature was still 100°C and the heating time was 6 h.

[0101] Performance Testing

[0102] The proton conductivity of the modified proton exchange membrane is 207mS / cm, and the vanadium ion permeability is 6.82×10 -10 cm² / s.

[0103] Example 3: Modification under different sulfonation conditions

[0104] Preparation of TiO2-SO3H

[0105] 0.1 g of hollow TiO2 particles were added to 15 MH2SO4 solution, heated at 60 °C for 8 h, and then repeatedly washed with deionized water until the pH reached 7.

[0106] PMoA anchored TiO2-SO3H and preparation of proton exchange membrane

[0107] The anchoring steps of PMoA were the same as those in Example 1, and the preparation steps of the proton exchange membrane were also the same.

[0108] Performance Testing

[0109] The proton conductivity of this modified membrane is 165 mS / cm, and the vanadium ion permeability is 7.17×10 -10 cm² / s.

[0110] Example 4: Changing TiO2 hydrothermal reaction conditions

[0111] Preparation of solid TiO2

[0112] Same as Example 1.

[0113] Preparation of hollow TiO2

[0114] 0.1 g of solid TiO2 particles were immersed in a 1 M NaOH solution, transferred to a stainless steel autoclave, and hydrothermally reacted at 260°C for 36 h to form hollow TiO2 particles. The particles were then washed with deionized water and adjusted to pH 7.

[0115] TiO2-SO3H and PMoA anchoring steps

[0116] Same as Example 1.

[0117] Preparation of proton exchange membrane

[0118] The film forming steps are kept consistent with those in Example 1.

[0119] Performance Testing

[0120] Under these conditions, the proton conductivity is 219 mS / cm and the vanadium ion permeability is 6.74×10 -10 cm² / s.

[0121] Example 5

[0122] PMoA solution concentration adjustment

[0123] Preparation of TiO2-SO3H Nanomaterials

[0124] Same as Example 1.

[0125] Preparation of PMoA solution and anchoring

[0126] 5 g of PMoA was dissolved in 20 g of N,N-dimethylformamide and stirred for 5 h to obtain a 20% PMoA solution; 0.08 g of TiO2-SO3H nanomaterial was immersed in the 20% PMoA solution and treated in a vacuum oven at 70 °C for 4 h.

[0127] Preparation of proton exchange membrane This step is consistent with Example 1.

[0128] Performance Testing

[0129] The proton conductivity is 234 mS / cm and the vanadium ion permeability is 1.17×10 -9 cm² / s

[0130] Example 6

[0131] Increase the amount of nanomaterials incorporated

[0132] Preparation of TiO2-SO3H Nanomaterials

[0133] Same as Example 1.

[0134] Preparation of proton exchange membrane

[0135] 0.12 g TiO2-SO3H@PMoA nanocomposite was added to 5% Nafion solution and stirred for 5 h. The film formation steps remained unchanged.

[0136] Performance Testing

[0137] The proton conductivity is 274 mS / cm and the vanadium ion permeability is 5.28×10 -10 cm² / s.

[0138] Comparative experiment 1: Proton conductivity test

[0139] Experimental purpose: To evaluate the proton conductivity of the proton exchange membrane of the present invention.

[0140] Experimental setup

[0141] Experimental group and control group:

[0142] Experimental group: using the proton exchange membrane of the present invention, containing TiO2-SO3H@PMoA nanocomposite material.

[0143] Control group 1: traditional Nafion membrane without any modification.

[0144] Control group 2: Nafion membrane doped with only TiO2-SO3H nanomaterials.

[0145] Control group 3: Nafion membrane doped with PMoA only.

[0146] Test conditions:

[0147] Temperature: Room temperature (25°C)

[0148] Electrolyte: 3mol / LH2SO4

[0149] Test equipment: AC impedance meter

[0150] Film size: 1cm×1cm

[0151] Experimental procedures

[0152] Membrane pretreatment:

[0153] The proton exchange membranes of the experimental group and each control group were cut into small squares of 1 cm × 1 cm and immersed in 3 mol / L H2SO4 solution for 30 min to activate the proton exchange membranes and ensure that all samples were under the same test conditions.

[0154] Resistance measurement:

[0155] Each sample was clamped into a conductivity test device and the resistance value (R) of the membrane was measured using an AC impedance meter.

[0156] Calculate proton conductivity:

[0157] Proton conductivity is calculated according to the formula:

[0158]

[0159] Where β is the thickness of the membrane (in μm), R is the membrane resistance (in Ω), and α is the proton conductivity unit (mS / cm)

[0160] Repeat the test:

[0161] The membrane was tested three times and the average value was taken to ensure the reliability of the data.

[0162] The comparative experimental data are shown in Table 1:

[0163] Table 1 Proton conductivity data of different proton exchange membranes

[0164]

[0165] From the data in Table 1, we can get:

[0166] The proton conductivity of the experimental group reached 245.7 mS / cm, approximately 57% higher than that of the pure Nafion membrane, demonstrating that the present invention optimizes the overall performance of the membrane while maintaining proton conductivity. Control groups 2 and 3 respectively demonstrated the effects of TiO2-SO3H and PMoA when used alone, but both were inferior to the performance of the membrane of the present invention, indicating that the present invention achieves the best effect through the combination of the two materials.

[0167] Comparative experiment 2: Vanadium ion permeability test

[0168] Experimental purpose: By comparing the vanadium ion permeability of the proton exchange membrane of the present invention (experimental group) with that of the existing Nafion membrane and different modified membranes (control group), the significant effect of the present invention in preventing the penetration of vanadium ions was verified.

[0169] Experimental setup

[0170] Experimental group and control group:

[0171] Experimental group: the proton exchange membrane of the present invention, containing the TiO2-SO3H@PMoA nanocomposite material.

[0172] Control group 1 (pure Nafion membrane): traditional Nafion membrane without any modification.

[0173] Control group 2 (only doped with TiO2-SO3H): Only TiO2-SO3H nanomaterials were doped into the Nafion membrane.

[0174] Control group 3 (PMoA only): only PMoA was doped into the Nafion membrane.

[0175] Test conditions:

[0176] Left container: 1.5mol / LMgSO4+3mol / LH2SO4 mixed solution, 50ml.

[0177] Right container: 1.5mol / LVOSO4+3mol / LH2SO4 mixed solution, 50ml.

[0178] Stir continuously to prevent the solution from polarizing.

[0179] The vanadium ion concentration was measured using a UV spectrophotometer.

[0180] Test time: Sampling every 1 hour for 8 hours.

[0181] Experimental procedures

[0182] Membrane installation:

[0183] The proton exchange membrane of the present invention and the membranes of each control group were respectively installed in a vanadium ion permeation test device to ensure that the membranes separated the solutions in the two containers.

[0184] Experiment begins:

[0185] A mixed solution of 1.5 mol / LMgSO4 and 3 mol / LH2SO4 was placed on one side (left side), and a mixed solution of 1.5 mol / LVOSO4 and 3 mol / LH2SO4 was placed on the other side (right side).

[0186] Sample collection:

[0187] Samples were taken from the left container every hour, and the vanadium ion concentration in the solution was measured using an ultraviolet spectrophotometer.

[0188] Data processing:

[0189] The vanadium ion permeability is calculated by the formula:

[0190]

[0191] in P Represents the permeability coefficient of VO²+ (unit: cm2·s -1 ); L and A Represent the thickness and area of the membrane (in μm, cm 2 ); Indicates the volume of the solution in the right reservoir (unit: cm 3 ); and is the VO²+ concentration in the left and right reservoirs (in mmol / L)

[0192] Repeat test: Test each film sample three times and take the average value to ensure the data is reliable.

[0193] The comparative experimental data are shown in Table 2:

[0194] Table 2 Vanadium ion permeability data of different proton exchange membranes

[0195]

[0196] From the data in Table 2, we can get:

[0197] The vanadium ion permeability of the experimental group (the present invention) was significantly reduced, reaching 6.05×10 -10 cm² / s, compared to the permeability of pure Nafion membrane (7.76×10 -9 cm² / s), is reduced by an order of magnitude, which indicates that the vanadium resistance performance of the film of the present invention is significantly improved.

[0198] Comparative Experiment 3: All-vanadium flow battery performance test

[0199] Experimental purpose: To verify the advantages of the proton exchange membrane of the present invention in improving battery performance, extending battery life and reducing vanadium ion cross contamination.

[0200] Experimental setup

[0201] Experimental group and control group:

[0202] Experimental group: the proton exchange membrane of the present invention, containing the TiO2-SO3H@PMoA nanocomposite material.

[0203] Control group 1 (pure Nafion membrane): traditional Nafion membrane without any modification.

[0204] Control group 2 (only doped with TiO2-SO3H): Only TiO2-SO3H nanomaterials were doped into the Nafion membrane.

[0205] Control group 3 (PMoA only): only PMoA was doped into the Nafion membrane.

[0206] Test conditions:

[0207] Electrolyte: a mixed solution of 1.5 mol / L VOSO4 and 3 mol / L H2SO4.

[0208] Battery configuration: The working area of each battery pack is 25cm².

[0209] Current density: set to 50mA / cm² and 100mA / cm² respectively during testing.

[0210] Test equipment: Battery test system, used to record parameters such as voltage and current during charging and discharging.

[0211] Test indicators: Coulombic efficiency (CE), voltage efficiency (VE).

[0212] Experimental procedures

[0213] Battery Assembly:

[0214] All-vanadium redox flow battery systems were assembled using different proton exchange membranes (experimental and control groups). The positive and negative electrode solutions in each group were the same (1.5 mol / L VOSO4 + 3 mol / L H2SO4).

[0215] Charge and discharge test:

[0216] The vanadium redox flow battery was cycled at current densities of 50 mA / cm² and 100 mA / cm². The current and voltage data were recorded during charge and discharge.

[0217] Calculation of Coulombic efficiency and voltage efficiency:

[0218] Repeat the test:

[0219] Each group of batteries was tested three times and the average value was taken to ensure the reliability of the data.

[0220] The comparative experimental data are shown in Table 3 and Table 4:

[0221] Table 3 All-vanadium redox flow battery performance test data

[0222]

[0223] Table 3 All-vanadium redox flow battery performance test data

[0224]

[0225] From the data in Table 3, we can get:

[0226] The present invention (experimental group) demonstrated significant advantages, achieving coulombic efficiencies of 95.4% and 94.8% at high current densities of 50 mA / cm² and 100 mA / cm², respectively, and voltage efficiencies of 85.3% and 84.7%, respectively. This demonstrates that the proton exchange membrane of the present invention can maintain high proton conductivity while inhibiting vanadium ion permeation, enabling the battery to maintain efficient charge and discharge even under high load conditions.

[0227] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for modifying a proton exchange membrane, characterized in that: The following steps are involved: Synthesis of hollow TiO2-SO3H nanomaterials, including: (1) Tetrabutyl titanate and polyvinyl pyrrolidone were mixed and dissolved in a solvent of ethanol and anhydrous acetic acid, stirred vigorously, and then calcined to obtain solid TiO2; (2) solid TiO2 is subjected to hydrothermal reaction in NaOH solution to form hollow TiO2; (3) The hollow TiO2 is subjected to sulfonation reaction in H2SO4 solution to obtain hollow TiO2-SO3H; Hollow TiO2-SO3H@phosphomolybdic acid nanocomposites anchored with phosphomolybdic acid were prepared by vacuum impregnation of hollow TiO2-SO3H with phosphomolybdic acid solution. The prepared hollow TiO2-SO3H@phosphomolybdic acid nanocomposite material was added into Nafion solution, and a modified proton exchange membrane was obtained through stirring, film forming and drying steps.

2. The method for modifying a proton exchange membrane according to claim 1, wherein: The synthesis of hollow TiO2-SO3H nanomaterials further comprises the following specific steps: 5 g of tetrabutyl titanate and 2 g of polyvinyl pyrrolidone were added to a mixed solvent of 10 g of ethanol and 2 g of anhydrous acetic acid, and stirred vigorously at room temperature for 4 h to obtain a yellow solution; The yellow solution was centrifuged to obtain a solid material; The solid material was placed in a muffle furnace, heated to 320° C. at a heating rate of 5° C. / min, and calcined in air for 6 h to obtain solid TiO 2 .

3. The method for modifying a proton exchange membrane according to claim 2, characterized in that: The yellow solution is centrifuged and separated at a speed of 10,000 rpm for 10 minutes.

4. The method for modifying a proton exchange membrane according to claim 3, wherein: The average particle size of the solid TiO2 particles is 50 to 100 nm.

5. The method for modifying a proton exchange membrane according to claim 4, characterized in that: The step of hydrothermally reacting solid TiO2 in a NaOH aqueous solution: 0.1 g of solid TiO2 was soaked in 1 M NaOH solution; Transferring the soaked solid TiO2 into a stainless steel autoclave lined with polytetrafluoroethylene; After hydrothermal reaction at 180 °C for 36 h, hollow TiO2 nanomaterials were obtained; The obtained hollow TiO2 nanomaterials were repeatedly washed with deionized water until the pH value reached 7.

6. The method for modifying a proton exchange membrane according to claim 5, characterized in that: The formation of the hollow TiO2-SO3H nanomaterial includes: 0.1 g of hollow TiO2 nanomaterials was added to 10 MH2SO4 solution; Heating at 60 °C for 8 h yielded hollow TiO2-SO3H nanomaterials; The mixture was washed repeatedly with deionized water until the pH value reached 7.

7. The method for modifying a proton exchange membrane according to claim 6, characterized in that: The formation of the hollow TiO2-SO3H@phosphomolybdic acid nanocomposite material anchored with phosphomolybdic acid comprises: Dissolve 5 g of phosphomolybdic acid in 45 g of N,N-dimethylformamide solution and stir for 5 h to obtain a 10% phosphomolybdic acid solution; Using a vacuum impregnation method, 0.08 g of hollow TiO2-SO3H was immersed in the 10% phosphomolybdic acid solution; The mixture was kept in a vacuum oven at 70°C for 4 h to anchor the phosphomolybdic acid on the surface of TiO2-SO3H, and hollow TiO2-SO3H@phosphomolybdic acid nanomaterials were obtained.

8. The method for modifying a proton exchange membrane according to claim 7, characterized in that: The vacuum degree of the vacuum impregnation step is controlled below 0.05 MPa.

9. The method for modifying a proton exchange membrane according to claim 8, characterized in that: The formation of the proton exchange membrane comprises: Add 5g of Nafion resin to 95g of N,N-dimethylformamide solution; Heat and stir in a water bath at 150°C for 5 h to ensure that the Nafion resin is completely dissolved; 0.04 g of hollow TiO2-SO3H@phosphomolybdic acid nanomaterials were added to 80 ml of 5% Nafion solution and stirred in a 60 °C water bath for 5 h; The stirred solution was poured into a mold and heated at 100 °C for 6 h to form a film; The formed proton exchange membrane is repeatedly rinsed with deionized water to remove residual solvent, thereby obtaining a proton exchange membrane.

10. The method for modifying a proton exchange membrane according to claim 9, characterized in that: The proton conductivity of the prepared modified proton exchange membrane is 200-300 mS / cm, and the vanadium ion permeability is less than 1×10 -9 cm² / s.

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