Composite proton exchange membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of proton exchange membranes, and discloses a composite proton exchange membrane as well as a preparation method and application thereof. The composite proton exchange membrane comprises perfluorinated sulfonic acid resin and M-acid-rich nano particles, the M-acid-rich nano particles are distributed in the perfluorinated sulfonic acid resin, the M-acid-rich nano particles are prepared from metal M oxide through acid activation, the surfaces of the M-acid-rich nano particles contain metal M-hydroxyl functional groups, and the surface of the M-acid-rich nano particles contain metal M-hydroxyl functional groups. The metal M comprises at least one of niobium, tantalum, hafnium, tin, cerium, tungsten, yttrium and lanthanum. The composite proton exchange membrane provided by the invention not only can remarkably inhibit the cross permeation of vanadium ions, but also can synchronously improve the proton conductivity, thereby fundamentally solving the problem of proton conductivity-selectivity tradeoff.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of proton exchange membranes, and particularly relates to a composite proton exchange membrane and a preparation method and application thereof. BACKGROUND

[0002] Vanadium redox flow battery (VRFB) is one of the ideal choices for large-scale energy storage technology due to its flexible power and capacity design, long cycle life, high safety and other advantages. As the core component of VRFB, the proton exchange membrane (PEM) plays a key role in isolating the positive and negative electrolytes and simultaneously conducting protons to form a loop. The currently widely used perfluorosulfonic acid membrane (such as Nafion) has high proton conductivity and chemical stability, but the size of the hydrophilic ion cluster channel in it is relatively large (about 4 nm), which has limited blocking effect on vanadium ions (such as VO 2+ , with a hydrated ion radius of about 0.6 nm), resulting in serious vanadium ion penetration, causing the decrease of coulombic efficiency and capacity decay, and restricting the long-term performance of the battery.

[0003] In order to overcome this problem, researchers often use inorganic nanoparticles (such as SiO2, TiO2, ZrO2) or porous materials (such as COF, MOF) to dope and modify Nafion, aiming to limit the migration of vanadium ions through the size screening effect or tortuous path effect of nanoparticles. However, this kind of physical doping method often hinders the transmission of protons to varying degrees while improving the selectivity, resulting in increased surface resistance and limited performance improvement. Therefore, developing a proton exchange membrane that can simultaneously and cooperatively improve proton conductivity and ion selectivity has become a research hotspot and difficulty in this field. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a composite proton exchange membrane and a preparation method and application thereof. The composite proton exchange membrane of the present application can not only significantly inhibit the cross-penetration of vanadium ions, but also simultaneously improve the proton conductivity, thereby fundamentally solving the trade-off problem between proton conductivity and selectivity.

[0005] In a first aspect, the present application provides a composite proton exchange membrane, comprising a perfluorosulfonic acid resin and M-rich acid-type nanoparticles, wherein the M-rich acid-type nanoparticles are distributed in the perfluorosulfonic acid resin, the M-rich acid-type nanoparticles are prepared by acid activation of a metal M oxide, the surface of the M-rich acid-type nanoparticles contains metal M-hydroxyl functional groups, and the metal M includes at least one of niobium, tantalum, hafnium, tin, cerium, tungsten, yttrium and lanthanum.

[0006] Specifically, the above technical solution of the present application discards the traditional physical screening concept and introduces a kind of dopant with surface preferential adsorption and proton conduction function, i.e. M-rich acid type nanoparticles, the M hydroxyl group (M-OH) on the surface of the material is a very strong Bronsted acid site, which has very strong adsorption and dissociation capacity for protons (H + ) and can provide efficient surface hopping (Surface Hopping) transmission path for protons, like building a "proton highway". For hydrated vanadium ions, the interaction with M-OH is much weaker than that of protons, and the huge volume has a very high energy barrier for surface migration, so it is effectively blocked. This is a chemical selection mechanism based on the difference in surface chemical properties, rather than simple size exclusion.

[0007] In some embodiments, the metal M includes at least one of niobium, tantalum, and hafnium.

[0008] In some embodiments, in the composite proton exchange membrane, the mass fraction of the M-rich acid type nanoparticles is 0.5%-20%.

[0009] In some embodiments, in the composite proton exchange membrane, the mass fraction of the M-rich acid type nanoparticles is 5%-20%.

[0010] In some embodiments, the particle size of the M-rich acid type nanoparticles is 10-200 nm.

[0011] In some embodiments, the metal M oxide includes at least one of Nb2O5, Ta2O5, and HfO2.

[0012] In the second aspect of the present application, a preparation method of the composite proton exchange membrane of the first aspect of the present application is provided, which comprises the following steps: (1) dispersing the metal M oxide in an acid solution, hydrothermal reaction, collecting the precipitate after solid-liquid separation, washing the precipitate to neutral, drying, grinding, to obtain M-rich acid type nanoparticles containing metal M-hydroxyl functional groups on the surface; (2) mixing the M-rich acid type nanoparticles obtained in step (1), perfluorosulfonic acid resin and solvent to obtain a casting solution; (3) forming a film of the casting solution obtained in step (2) to obtain the composite proton exchange membrane.

[0013] In some embodiments, in step (1), the amount ratio of the metal M oxide to the acid solution is 1g:(10-70)mL.

[0014] In some embodiments, in step (1), the acid solution includes at least one of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, and phosphoric acid solution.

[0015] In some embodiments, the concentration of the acid solution in step (1) is 0.5-5 mol / L.

[0016] In some embodiments, the temperature of the hydrothermal reaction in step (1) is 80-120°C.

[0017] In some embodiments, the hydrothermal reaction time in step (1) is 6-12 hours.

[0018] In some embodiments, in step (2), the mass ratio of M-rich acid nanoparticles, perfluorosulfonic acid resin and solvent is (3-12):50:(1000-2000).

[0019] In some embodiments, in step (2), the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and ethanol.

[0020] In some embodiments, the specific process of step (2) includes: mixing the M-rich acid nanoparticles obtained in step (1) with a solvent, ultrasonically dispersing them, then adding a perfluorosulfonic acid resin solution and stirring to mix them evenly to obtain a casting solution.

[0021] In some embodiments, the stirring temperature in step (2) is 25-60°C.

[0022] In some embodiments, the stirring time in step (2) is 2-12 hours.

[0023] In some embodiments, the specific process of step (3) includes: casting the casting liquid obtained in step (2) onto a flat substrate, drying and annealing it to solidify the film, peeling it off from the substrate to obtain an initial composite film; immersing the initial composite film in an acid solution for activation treatment, and finally washing and drying it to obtain the composite proton exchange membrane.

[0024] In some embodiments, the drying temperature in step (3) is 40-80°C.

[0025] In some embodiments, the drying time in step (3) is 4-12 hours.

[0026] In some embodiments, the annealing temperature in step (3) is 100-150°C.

[0027] In some implementations, the annealing time in step (3) is 1-4 hours.

[0028] In some embodiments, in step (3), the acid solution used for the activation treatment is a sulfuric acid, hydrochloric acid, or nitric acid solution, and the concentration of the acid solution is 0.5-2.0 mol / L.

[0029] In some embodiments, in step (3), the activation treatment temperature is 25-80°C and the activation time is 1-6h.

[0030] In a third aspect, the present invention provides a flow battery comprising the composite proton exchange membrane described in the first aspect of the present invention.

[0031] In some embodiments, the flow battery is an all-vanadium redox flow battery.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Mechanism innovation: This invention is the first to use M-rich acid nanoparticles with strong surface acidity in the proton exchange membrane of flow battery. It achieves high-speed and high-selectivity transport of protons through the chemical mechanism of surface proton jumping, which is different from the traditional physical sieving mechanism. It has a unique idea and strong innovation.

[0033] (2) Synergistic performance improvement: Thanks to the unique conduction mechanism, the composite proton exchange membrane provided by the present invention can simultaneously achieve a significant improvement in proton conductivity and ion selectivity, effectively overcoming the performance trade-off effect.

[0034] (3) Simple process and easy to promote: The raw materials used in this invention are readily available, the preparation process does not require complex equipment or harsh conditions, it is compatible with traditional doping film formation processes, and is easy to apply in large-scale production. Detailed Implementation

[0035] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional means or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0036] Room temperature: 25±3℃.

[0037] Example 1 A composite proton exchange membrane includes a perfluorosulfonic acid resin and niobate-rich nanoparticles. The niobate-rich nanoparticles are distributed in the perfluorosulfonic acid resin and are prepared by acid activation of niobium oxide. The surface of the niobate-rich nanoparticles contains niobium-hydroxyl functional groups (Nb-OH).

[0038] The method for preparing the composite proton exchange membrane in this example includes the following steps: (1) Preparation of niobate-rich nanoparticles: Weigh 1.0 g of Nb₂O₅ powder and disperse it in 40 mL of 1.0 mol / L sulfuric acid solution. Stir magnetically for 30 minutes to obtain a mixed suspension. Transfer the mixed suspension to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene and react at 100 °C for 8 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation. Wash the precipitate repeatedly with deionized water until the pH of the supernatant is neutral. Then dry it in a vacuum oven at 80 °C for 12 hours. After drying, grind it to obtain niobate-rich nanoparticles with a particle size of 20 nm (denoted as A-NbO).

[0039] (2) Preparation of casting solution: Weigh 30 mg of the above A-NbO and disperse it in 5 g of N,N-dimethylacetamide. Sonicate the solution for 30 minutes, then add 5 g of 5 wt% Nafion solution (equivalent to 250 mg of solid resin, DuPont D520) to make the doping amount of A-NbO 10.7 wt% (30 mg / (250 mg + 30 mg)). Stir magnetically at 50 °C for 8 hours to obtain a uniform casting solution.

[0040] (3) Membrane preparation and activation: The above casting solution was cast onto a flat glass plate, and the thickness was controlled to 200 μm using a doctor blade. The glass plate was dried in a 60°C oven for 12 hours, and then annealed in a 120°C oven for 2 hours. After cooling, the membrane was peeled off the glass plate to obtain the initial composite membrane. The initial composite membrane was immersed in a 1.0 mol / L sulfuric acid solution and kept at 60°C for 3 hours. After removal, it was rinsed with deionized water until neutral, and finally vacuum dried at 80°C for 4 hours to obtain the final composite proton exchange membrane, denoted as A-NbO-10.7%.

[0041] Example 2 A composite proton exchange membrane includes a perfluorosulfonic acid resin and tantalic acid-rich nanoparticles. The tantalic acid-rich nanoparticles are distributed in the perfluorosulfonic acid resin and are prepared by acid activation of tantalum oxide. The surface of the tantalic acid-rich nanoparticles contains tantalum-hydroxyl functional groups (Ta-OH).

[0042] The method for preparing the composite proton exchange membrane in this example includes the following steps: (1) Preparation of tantalic acid-rich nanoparticles: Weigh 1.0 g of Ta2O5 powder and disperse it in 40 mL of 1.0 mol / L sulfuric acid solution. Stir magnetically for 30 minutes to obtain a mixed suspension. Transfer the mixed suspension to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene and react at 100 °C for 8 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation. Wash the precipitate repeatedly with deionized water until the pH of the supernatant is neutral. Then dry it in a vacuum oven at 80 °C for 12 hours. After drying, grind it to obtain tantalic acid-rich nanoparticles with a particle size of 30 nm (denoted as A-TaO).

[0043] (2) Preparation of casting solution: Weigh 15 mg of the above A-TaO and disperse it in 5 g of N,N-dimethylacetamide. Sonicate the solution for 30 minutes, then add 5 g of 5 wt% Nafion solution (equivalent to 250 mg of solid resin, DuPont D520) to make the doping amount of A-TaO 5.7 wt% (15 mg / (250 mg + 15 mg)). Stir magnetically at 50 °C for 8 hours to obtain a uniform casting solution.

[0044] (3) Membrane preparation and activation: The above casting solution was cast onto a flat glass plate, and the thickness was controlled to 200 μm using a doctor blade. The glass plate was dried in a 60°C oven for 12 hours, and then annealed in a 120°C oven for 2 hours. After cooling, the membrane was peeled off the glass plate to obtain the initial composite membrane. The initial composite membrane was immersed in a 1.0 mol / L sulfuric acid solution and kept at 60°C for 3 hours. After removal, it was rinsed with deionized water until neutral, and finally vacuum dried at 80°C for 4 hours to obtain the final composite proton exchange membrane, denoted as A-TaO-5.7%.

[0045] Example 3 A composite proton exchange membrane includes a perfluorosulfonic acid resin and hafnium-rich nanoparticles. The hafnium-rich nanoparticles are distributed in the perfluorosulfonic acid resin and are prepared by acid activation of metal hafnium oxide. The surface of the hafnium-rich nanoparticles contains metal hafnium-hydroxyl functional groups (Hf-OH).

[0046] The method for preparing the composite proton exchange membrane in this example includes the following steps: (1) Preparation of hafnium-rich nanoparticles: Weigh 1.0 g of Hf2O5 powder and disperse it in 40 mL of 1.0 mol / L sulfuric acid solution. Stir magnetically for 30 minutes to obtain a mixed suspension. Transfer the mixed suspension to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene and react at 100 °C for 8 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation. Wash the precipitate repeatedly with deionized water until the pH of the supernatant is neutral. Then dry it in a vacuum oven at 80 °C for 12 hours. After drying, grind it to obtain hafnium-rich acid nanoparticles (denoted as A-HfO) with a particle size of 30 nm.

[0047] (2) Preparation of casting solution: Weigh 60 mg of the above A-HfO and disperse it in 5 g of N,N-dimethylacetamide. Sonicate the solution for 30 minutes, then add 5 g of 5 wt% Nafion solution (equivalent to 250 mg of solid resin, DuPont D520) to make the doping amount of A-HfO 19.4 wt% (60 mg / (250 mg + 60 mg)). Stir magnetically at 50 °C for 8 hours to obtain a uniform casting solution.

[0048] (3) Membrane preparation and activation: The above casting solution was cast onto a flat glass plate, and the thickness was controlled to 200 μm using a doctor blade. The glass plate was dried in a 60°C oven for 12 hours, and then annealed in a 120°C oven for 2 hours. After cooling, the membrane was peeled off the glass plate to obtain the initial composite membrane. The initial composite membrane was immersed in a 1.0 mol / L sulfuric acid solution and kept at 60°C for 3 hours. After removal, it was rinsed with deionized water until neutral, and finally vacuum dried at 80°C for 4 hours to obtain the final composite proton exchange membrane, denoted as A-HfO-19.4%.

[0049] Comparative Example 1 The difference from Example 1 is that no nanoparticles are added. Instead, 5g of 5wt% Nafion solution is stirred at 50°C for 2 hours and then a pure Nafion film is prepared by the same casting, drying, annealing and activation process, which is denoted as Recast-Nafion.

[0050] Comparative Example 2 The difference from Example 1 is that Nb2O5 powder that has not been acid-activated is used.

[0051] The specific preparation method is as follows: (1) Preparation of casting solution: Weigh 30 mg of Nb2O5 powder and disperse it in 5 g of N,N-dimethylacetamide. Sonicate the solution for 30 minutes, then add 5 g of 5 wt% Nafion solution (equivalent to 250 mg of solid resin, DuPont D520) to make the Nb2O5 powder doping amount 10.7 wt% (30 mg / (250 mg + 30 mg)). Stir magnetically at 50 °C for 8 hours to obtain a uniform casting solution.

[0052] (2) Membrane preparation and activation: The above casting solution was cast onto a flat glass plate, and the thickness was controlled to 200 μm using a doctor blade. The glass plate was dried in a 60°C oven for 12 hours, and then annealed in a 120°C oven for 2 hours. After cooling, the membrane was peeled off the glass plate to obtain the initial composite membrane. The initial composite membrane was immersed in a 1.0 mol / L sulfuric acid solution and kept at 60°C for 3 hours. After removal, it was rinsed with deionized water until neutral, and finally vacuum dried at 80°C for 4 hours to obtain the final composite proton exchange membrane, denoted as Nb2O5-10.7%.

[0053] Comparative Example 3 The difference from Example 1 is that Nb2O5 is replaced with attapulgite.

[0054] The specific preparation method is as follows: (1) Preparation of acid-activated attapulgite nanofibers: Weigh 1.0 g of attapulgite and disperse it in 40 mL of 1.0 mol / L sulfuric acid solution. Stir magnetically for 30 minutes to obtain a mixed suspension. Transfer the mixed suspension to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene and react at 100 °C for 8 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation. Wash the precipitate repeatedly with deionized water until the pH of the supernatant is neutral. Then dry it in a vacuum oven at 80 °C for 12 hours. After drying, grind it to obtain acid-activated attapulgite nanofibers (denoted as A-OT) with a diameter of 30 nm and a length of 500 nm.

[0055] (2) Preparation of casting solution: Weigh 30 mg of the above A-OT and disperse it in 5 g of N,N-dimethylacetamide. Sonicate the solution for 30 minutes, then add 5 g of 5 wt% Nafion solution (equivalent to 250 mg of solid resin, DuPont D520) to make the doping amount of A-OT 10.7 wt% (30 mg / (250 mg + 30 mg)). Stir magnetically at 50 °C for 8 hours to obtain a uniform casting solution.

[0056] (3) Membrane preparation and activation: The above casting solution was cast onto a flat glass plate, and the thickness was controlled to 200 μm using a doctor blade. The glass plate was dried in a 60°C oven for 12 hours, and then annealed in a 120°C oven for 2 hours. After cooling, the membrane was peeled off the glass plate to obtain the initial composite membrane. The initial composite membrane was immersed in a 1.0 mol / L sulfuric acid solution and kept at 60°C for 3 hours. After removal, it was rinsed with deionized water until neutral, and finally vacuum dried at 80°C for 4 hours to obtain the final composite proton exchange membrane, denoted as A-OT-10.7%.

[0057] Performance testing 1. Proton conductivity Test method (extra-position test - four-electrode AC impedance method): 1. Sample preparation: Cut the membrane into the specified size (circle) and accurately measure its thickness (L) and the effective area (A) covered by the electrode.

[0058] 2. Pretreatment: According to the test requirements, the membrane is acid-treated (e.g., immersed in dilute sulfuric acid) and washed with deionized water to ensure that the proton exchange sites are in H+ ionization. + state.

[0059] 3. Installation: Install the wet membrane sample in the test cell and tighten the screws evenly to ensure good contact without damaging the membrane.

[0060] 4. Environmental equilibration: Place the entire test cell into an environmental chamber and maintain it at the set temperature (e.g., 80℃) and relative humidity (e.g., 80%RH) for a sufficient period of time (usually 30-60 minutes) to allow the membrane to fully hydrate and reach equilibrium.

[0061] 5. Impedance measurement: Apply a small sinusoidal AC disturbance (e.g., 10mV) using an electrochemical workstation and scan within a set frequency range (e.g., 1MHz to 1Hz) to obtain the Nyquist plot.

[0062] 6. Data Analysis: On the Nyquist plot, the real intercept in the high-frequency region represents the bulk resistance (R) of the membrane. The proton conductivity can be calculated by substituting the obtained R value, along with the measured L and A values, into the formula σ = L / (R × A).

[0063] 2. Vanadium ion permeability Test method (diffusion cell method): 1. Sample preparation: Cut the membrane to a suitable size and pretreat it (e.g., acid washing, soaking in deionized water). Accurately measure its effective area (A) and thickness (L).

[0064] 2. Prepare the solution: Left side (donor cell): Inject a sulfuric acid solution (e.g., 2.0 mol / L H2SO4) containing a certain concentration (e.g., 1.5 mol / L) of VOSO4, simulating the positive electrode electrolyte in the charging state (mainly VOSO4). 2+ ).

[0065] Right side (acceptor pool): Inject an equal volume of sulfuric acid solution of the same concentration (but without vanadium ions), or use MgSO4 solution to balance ionic strength and osmotic pressure, simulating the negative electrode side.

[0066] 3. Assembly and initialization: Clamp the membrane in the middle of the diffusion cell and seal it to ensure no leakage. Inject the solution into both sides, turn on the agitator and water bath, and bring the system to the set temperature (e.g., 25°C).

[0067] 4. Sampling and Testing: At the start of the experiment (t=0) and at a series of subsequent time points (e.g., every 1, 2, 4, 8 hours...), a small amount of solution (e.g., 100 μL) was taken from the acceptor pool. The VO in the sample was measured using a UV-Vis spectrophotometer. 2+ The characteristic absorption peak intensity (typically around 760 nm) is measured. The absorbance values ​​are converted to vanadium ion concentration (Ct) based on a pre-plotted concentration-absorbance standard curve. Note: After each sampling, an equal volume of blank sulfuric acid solution must be reinjected into the acceptor cell to maintain a constant volume.

[0068] 5. Data Analysis: A graph was plotted with the vanadium ion concentration (Ct) in the acceptor pool on the ordinate and time (t) on the abscissa. In the initial stage, Ct and t usually show a good linear relationship. The slope of this line (dCt / dt) is the rate of concentration change.

[0069] According to Fick's first law, the formula for calculating vanadium ion permeability (P) is: P = (dCt / dt) × Vr × L / (A × Cd); Wherein, P: Vanadium ion permeability (unit: cm) 2 ·min -1 ); dCt / dt: Rate of change of receptor pool concentration (mol / L / s); Vr: Volume of the acceptor pool solution (L); L: Membrane thickness (cm); A: Effective diffusion area of ​​the membrane (cm²) 2 ); Cd: The initial vanadium ion concentration (mol / L) in the donor pool can be considered to remain essentially constant throughout the experiment.

[0070] The performance test results of the samples prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0071] Table 1

[0072] The ion selectivity in Table 1 is the ratio of proton conductivity to vanadium ion permeability, i.e., proton conductivity / vanadium ion permeability.

[0073] As shown in Table 1, Comparative Example 1 (pure Nafion membrane) has a worse water retention capacity because it is not doped with any nanoparticles. In contrast, Examples 1-3 of this invention, doped with M-rich acid-type nanoparticles, can provide additional proton hopping sites and optimize the hydrophilic channel structure. Therefore, the proton conductivity of Comparative Example 1 is significantly lower than that of the examples. Comparative Example 2 is doped with untreated nanoparticles. These nanoparticles lack strongly acidic M-hydroxyl (M-OH) sites on their surface, resulting in a significantly lower proton conductivity compared to the examples. Comparative Example 3 is doped with acid-activated attapulgite nanofibers. The addition of attapulgite dilutes the concentration of sulfonic acid groups in Nafion itself, and since attapulgite is non-conductive, its proton conductivity is even worse.

[0074] Comparative Example 1 (pure Nafion membrane) lacks physical sieving and Donnan repulsion effects due to the absence of any nanoparticles, resulting in significantly higher vanadium ion permeability and poor ion selectivity compared to the examples. Comparative Example 2 is doped with untreated nanoparticles, which lack strong acidic M-hydroxyl (M-OH) sites on their surface. Therefore, hydrated vanadium ions cannot be effectively blocked due to weak interaction with M-OH sites and high migration barriers, resulting in poor ion selectivity. Comparative Example 3 is doped with acid-activated attapulgite nanofibers, which can only block vanadium ions physically, while the examples can effectively block vanadium ions through chemical selection mechanisms. Therefore, Comparative Example 3 has even worse ion selectivity than the examples.

[0075] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A composite proton exchange membrane, characterized in that, The invention comprises perfluorosulfonic acid resin and M-rich acid nanoparticles, wherein the M-rich acid nanoparticles are distributed in the perfluorosulfonic acid resin and are prepared by acid activation of metal M oxides. The surface of the M-rich acid nanoparticles contains metal M-hydroxyl functional groups, and the metal M includes at least one of niobium, tantalum, hafnium, tin, cerium, tungsten, yttrium, and lanthanum.

2. The composite proton exchange membrane according to claim 1, characterized in that, In the composite proton exchange membrane, the mass percentage of M-rich acid nanoparticles is 0.5%-20%.

3. The composite proton exchange membrane according to claim 1, characterized in that, The particle size of the M-rich acid-type nanoparticles is 10-200 nm.

4. The composite proton exchange membrane according to claim 1, characterized in that, The metal M oxide includes at least one of Nb2O5, Ta2O5, and HfO2.

5. The method for preparing the composite proton exchange membrane according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Disperse metal M oxide in an acid solution, perform hydrothermal reaction, collect the precipitate after solid-liquid separation, wash the precipitate with water until neutral, dry, grind, and obtain M-rich acid nanoparticles with metal M-hydroxyl functional groups on the surface. (2) Mix the M-rich acid nanoparticles obtained in step (1), perfluorosulfonic acid resin and solvent to obtain casting solution; (3) The casting solution obtained in step (2) is used to form a film to obtain the composite proton exchange membrane.

6. The preparation method according to claim 5, characterized in that, In step (1), the ratio of metal M oxide to acid solution is 1g:(10-70)mL; and / or, the acid solution includes at least one of sulfuric acid solution, hydrochloric acid solution, nitric acid solution and phosphoric acid solution; and / or, the concentration of the acid solution is 0.5-5mol / L.

7. The preparation method according to claim 5, characterized in that, In step (1), the temperature of the hydrothermal reaction is 80-120℃; and / or the time of the hydrothermal reaction is 6-12h.

8. The preparation method according to claim 5, characterized in that, In step (2), the mass ratio of M-rich acid nanoparticles, perfluorosulfonic acid resin and solvent is (3-12):50:(1000-2000).

9. The preparation method according to claim 5, characterized in that, In step (2), the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and ethanol.

10. A flow battery, characterized in that, Includes the composite proton exchange membrane according to any one of claims 1-4.

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