Preparation method of cross-temperature-zone stable proton exchange membrane

Abstract

The invention relates to the field of fuel cells, in particular to a preparation method of a temperature-crossing stable proton exchange membrane. The preparation method comprises the following steps: by taking sulfonated polybenzimidazole as a matrix, firstly grafting MOFs nanoparticles, then forming SPBI / ZrP-MOFs hybrid sol by combining a sol-gel method with a zirconium phosphate precursor, then constructing a three-dimensional interpenetrating structure by doping dynamic disulfide bonds and utilizing ultraviolet light to initiate a cross-linking reaction, and then forming a membrane by a tape casting method. And finally, sequentially forming and growing a vertically arranged carbon nanotube array layer on the surface of the gt, dipping to form a sulfonated COFs gradient hydrogen resistance layer, and finally endowing an Al2O3 protection layer with the sulfonated COFs gradient hydrogen resistance layer. According to the present invention, the technical bottlenecks of high swelling rate under the working condition of 100 DEG C and life attenuation caused by easy loss of the phosphoric acid dopant are overcome, the synergistic improvement of the proton channel stability and the gas barrier property can be effectively achieved, the low swelling rate under the film thickness of 50-100 [mu] m and the phosphoric acid retention rate are achieved, and the crack self-repairing rate is provided.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more particularly to a method for preparing a transtemperature-stable proton exchange membrane. Background Technology

[0002] As a core component of proton exchange membrane fuel cells (PEMFC) and water electrolysis for hydrogen production (PEMWE), the proton exchange membrane (PEM) must meet requirements such as high proton conductivity, low gas permeability, excellent chemical stability, high mechanical strength, and long lifespan.

[0003] Traditional perfluorosulfonic acid membranes (such as Nafion) hold an important position in some current applications due to their good chemical stability and high proton conductivity. However, at high temperatures (>80°C), the increased thermal motion of water molecules within the membrane leads to swelling, with swelling rates exceeding 3%. This not only alters the membrane's microstructure, distorting the proton conduction channels and causing a sharp drop in proton conductivity, thus affecting the battery's power generation efficiency, but also increases the membrane thickness, making it easier for gas molecules to permeate, increasing hydrogen permeability, causing fuel loss, and reducing the battery's energy conversion efficiency. Furthermore, under high-temperature conditions, the stability of the phosphate dopant within the membrane deteriorates, resulting in significant loss, exceeding 10% / 1000h, further weakening the membrane's proton conductivity at high temperatures. This severely limits the long-term stable operation of the battery in high-temperature environments and shortens its lifespan.

[0004] To improve high-temperature performance, researchers have modified existing composite membranes. Most composite membranes are reinforced with a single material, such as MOFs or carbon materials. However, while improving one property, a single reinforcing material may negatively impact other properties. For example, adding MOFs may increase the membrane's proton conductivity, but its improvement on the membrane's mechanical properties is limited. Furthermore, in high-temperature swelling environments, the interfacial compatibility issues between MOFs and the polymer matrix become prominent, leading to a decline in the overall membrane performance. On the other hand, carbon-reinforced composite membranes may be insufficient in hydrogen barrier properties, failing to effectively prevent hydrogen permeation and thus failing to meet the comprehensive high-performance requirements of proton exchange membranes in practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a cross-temperature stable proton exchange membrane and its preparation method. Its advantage is that it can synergistically solve problems such as high-temperature swelling, hydrogen inhibition and self-repair.

[0006] This invention provides a method for preparing a proton exchange membrane, comprising the following steps: Step 1: Dissolve sulfonated polybenzimidazole in N-methylpyrrolidone, add amino-functionalized MOF nanoparticles for grafting reaction to obtain composite solution; Step 2: Using the sol-gel method, the zirconium phosphate precursor solution is mixed with the composite solution obtained in Step 1, and the pH is adjusted to 1.5-2.0 with hydrochloric acid, and then adjusted to 2.5-3.0 with ammonia to form SPBI / ZrP-MOFs hybrid sol. Step 3: Add a dynamic crosslinking agent to the hybrid sol obtained in Step 2 to obtain a mixed solution, then form a film by casting, and then use ultraviolet light to initiate a crosslinking reaction to obtain a film with a three-dimensional interpenetrating network structure; the dynamic crosslinking agent is a crosslinking agent containing disulfide bonds or a crosslinking agent containing siloxane; Step 4: A vertically aligned carbon nanotube array layer is grown on the surface of the film obtained in Step 3 using chemical vapor deposition, followed by sequential impregnation with sulfonated COFs solution with larger pore size and sulfonated COFs solution with smaller pore size. Step 5: The membrane material obtained in Step 4 is first activated with phosphoric acid solution, and then annealed. Step 6: An Al2O3 protective layer is formed on the surface of the membrane material obtained in step 5 by atomic layer deposition to obtain the proton exchange membrane.

[0007] The present invention is further configured such that step 1 specifically includes: a) Dissolve sulfonated polybenzimidazole with a sulfonation degree of 30-50% in N-methylpyrrolidone to obtain a mixed solution, wherein the concentration of sulfonated polybenzimidazole in the mixed solution is 5-15 wt%. b) Add amino-functionalized MOF S Nanoparticles were reacted at 30-80℃ for 6-12 hours under nitrogen protection; the amino-functionalized MOF S The nanoparticles are selected from at least one of NH2-UiO-66 and NH2-MIL-125(Ti), and their pore size is 0.6-3.4 nm; c) After centrifugation, a composite solution was obtained, containing amino-functionalized MOFs. S The content of nanoparticles is 10-25 wt%.

[0008] The present invention is further configured such that the sulfonated polybenzimidazole and the amino-functionalized MOF S The mass ratio of the nanoparticles is (3:1) - (10:1); The water content of the reaction system should be controlled to be less than 500 ppm.

[0009] The present invention is further configured such that step 2 specifically comprises: 1) Mix ZrOCl2·8H2O and H3PO4 at a molar ratio of 1:1.25-1:3 and age for 24-48 h to obtain a zirconium phosphate precursor solution; 2) Mix the zirconium phosphate precursor solution with the composite solution obtained in step 1 at a mass ratio of sulfonated polybenzimidazole to zirconium phosphate precursor of (1:0.5)-(1:4); 3) First, add hydrochloric acid to adjust the pH to 1.5-2.0, then add ammonia to adjust the pH to 2.5-3.0, forming SPBI / ZrP-MOF. S Hybrid sol.

[0010] The present invention is further configured such that, in step 3, the crosslinking agent containing disulfide bonds is selected from one or two of 4,4'-dimercaptobenzophenone and dithiodipropionic acid, and the amount added is 5-10% of the mass of the mixed solution; the 4,4'-dimercaptobenzophenone is prepared by reacting 4,4'-diaminobenzophenone with thioacetic acid and then hydrolyzing; the dithiodipropionic acid is prepared by oxidative coupling of 2-mercaptopropionic acid; The siloxane-containing crosslinking agent is a tetraethoxysilane-mercaptopropyltrimethoxysilane copolymer with a molecular weight of 1000-5000 g / mol, and the amount added is 3-8% of the mass of the mixed solution; the tetraethoxysilane-mercaptopropyltrimethoxysilane copolymer is prepared by the sol-gel method: tetraethoxysilane and γ-mercaptopropyltrimethoxysilane are mixed in a molar ratio of 1:1-1:2 and reacted at pH 3-4 and temperature 80-90°C for 2-4 hours; The conditions for the crosslinking reaction are: ultraviolet wavelength 365nm, irradiation dose 500-2000mJ / cm2, and oxygen concentration <100ppm; The coating flow rate of the casting method is 1-10 mL / min, and the heating temperature is 30-90℃.

[0011] The present invention is further configured such that, in step 4, the step of growing a vertically aligned array of carbon nanotubes on the substrate surface using CVD is as follows: 1) Chamber pretreatment: Place the membrane in the CVD reaction chamber and evacuate to 2×10⁻⁶. -3 -5×10 -3 Torr; 2) Reduction activation: Introduce a mixture of Ar and H2 gas with a volume ratio of Ar:H2=3:1, heat to 250-280℃, and maintain for 5-10 min to activate the catalyst; 3) Carbon nanotube growth: Apply radio frequency power in pulse mode at a frequency of 30-40 Hz and a duty cycle of 50%-60%. The plasma radio frequency power is 180-220 W. Introduce a mixture of C2H2 and Ar gas with a volume ratio of Ar:C2H2=3:1 and adjust the flow rate to 45-55 sccm. Control the substrate temperature at 250-300℃ to start carbon nanotube growth. The carbon nanotube growth time is 10-20 min to obtain a vertical array with a height of 5-10 μm. 4) Cooling: Turn off C2H2 and plasma, and cool to room temperature at a rate of ≤5℃ / min in a pure Ar atmosphere; The vertically aligned carbon nanotube array layer has a tube length of 5-10 μm and an array density of 102. 8 -10 10 root / cm 2 .

[0012] The present invention is further configured such that, in step 4, the concentration of the sulfonated COFs solution with larger pore size is 2-3 wt% of the DMSO solution of SA-TFP COF, the pore size of the SA-TFP COF is 1.2-1.8 nm, the sulfonic acid group density is 1.2-2.0 mmol / g, and the impregnation time is 5-8 min. The smaller pore size sulfonated COFs solution is an N,N-dimethylformamide solution of SO3H-COF-300 or an N,N-dimethylformamide solution of SO3H-COF-316, with a concentration of 4-5 wt% for the DMF solution of SO3H-COF-300 or SO3H-COF-316. The pore size of SO3H-COF-300 and SO3H-COF-316 is 0.65-1.0 nm, the sulfonic acid group density is 2.8-4.2 mmol / g, and the impregnation time is 10-15 min. The pore size of SO3H-COF-300 and SO3H-COF-316 is 0.65-1.0 nm, and the sulfonic acid group density is 2.8-4.2 mmol / g. SA-TFP... COF, SO3H-COF-300, and SO3H-COF-316 were prepared by a solvothermal method: the monomers were reacted in NMP solvent at 120-150℃ for 24-48h, followed by sulfonation with concentrated sulfuric acid to introduce SO3H groups. After impregnation, dry at 70-90℃ for 3-5 minutes.

[0013] The present invention is further configured such that, in step 5, the phosphoric acid solution activation treatment is: immersing in a phosphoric acid solution at 70-85°C for 1-3 hours to achieve a phosphoric acid doping amount of 180-220 wt%; the concentration of the phosphoric acid solution is 85 wt%.

[0014] The present invention is further configured such that, in step 5, the gradient annealing is performed as follows: under the protection of nitrogen or argon atmosphere, at a heating rate of 1-3℃ / min, the internal stress is first released by treating at 120-130℃ for 1.5-2.5h, and then by treating at 160-170℃ for 0.8-1.2h to enhance the crosslinking density.

[0015] The present invention is further configured such that, in step 6, the parameters for depositing the Al2O3 layer using atomic layer deposition technology include: deposition temperature of 100-140℃, TMA pulse time of 0.15-0.25s, H2O pulse time of 0.15-0.25s, purging with N2 or Ar for 20-30s / cycle, and the thickness of the Al2O3 protective layer is 1-3nm.

[0016] In summary, the present invention has the following beneficial effects: 1. High-temperature swelling: This invention uses sulfonated polybenzimidazole as the main chain. On the one hand, it constructs high-density phosphate anchoring points by grafting amino-functionalized MOFs. Since MOFs contain regular channels, they can form a certain physical constraint on the movement of polymer chain segments, thus effectively reducing chain segment migration at high temperatures. On the other hand, the composite membrane of this invention also constructs a zirconium phosphate inorganic network through the sol-gel method. ZrP has the characteristics of a rigid skeleton, thus effectively inhibiting high-temperature swelling and phosphate loss. Furthermore, the dynamic cross-linked network containing disulfide bonds forms a reversible three-dimensional network after ultraviolet light cross-linking, giving the membrane material self-healing ability. When high temperature causes local structural deformation, the dynamic bond dissociation-recombination equilibrium can absorb some stress, further preventing the swelling from intensifying. 2. Hydrogen barrier effect: The composite membrane prepared by this invention has a vertically arranged carbon nanotube array layer. This structure forms a maze-like pattern with tortuous paths, which forces hydrogen to diffuse along the tortuous paths, thus effectively forming a hydrogen barrier effect. In addition, the composite membrane prepared by this invention also has a gradient gas barrier layer formed by sulfonated COFs. Through the dual effects of size sieving and polar adsorption of sulfonate groups, the hydrogen permeability is further reduced. 3. Self-healing aspect: The composite membrane of the present invention is provided with a dynamic crosslinking agent containing disulfide bonds, which can form a dynamic crosslinking network. The disulfide bonds in this network will promote the bonding and regeneration of the microcrack interface after being triggered by ultraviolet light, that is, it has the function of microcrack self-healing. In addition, the high temperature treatment stage of the present invention is set to gradient temperature control (120→160℃), which can also effectively avoid the thermal decomposition of the dynamic crosslinking agent. 4. The proton exchange membrane of this invention is based on sulfonated polybenzimidazole (SPBI) and is constructed by combining phosphate and MOF nanoparticles to form a three-dimensional interpenetrating network structure. The SPBI main chain first provides mechanical support, the MOF nanopores inhibit chain segment migration, the rigid framework of the phosphate glass network further inhibits high-temperature swelling and phosphate loss, and the dynamic cross-linked network realizes the self-healing of the membrane material. In addition, the vertical carbon nanotube array and sulfonated COFs work together to effectively achieve the hydrogen barrier effect of the proton exchange membrane. Finally, the top layer of the proton exchange membrane of this invention is covered with an Al2O3 protective layer. Al2O3 is a chemically inert material that can resist the corrosion and high-temperature oxidation of phosphoric acid in fuel cells, protecting the internal structure of the membrane from damage. Therefore, it can greatly improve the service life of the proton exchange membrane in fuel cells. In addition, Al2O3 can also slow down the migration of phosphoric acid molecules from the inside of the membrane to the outside, further reducing phosphoric acid loss. The thickness of the Al2O3 layer in this invention is set to a thin layer of 1-3 nm, which effectively avoids the problem of proton conduction being blocked due to an excessively thick protective layer. Detailed Implementation

[0017] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0018] Example 1 Step 1: Prepare the composite solution: a) Dissolve 15g SPBI (sulfonation degree of 50%) in 85mL NMP, the concentration of sulfonated polybenzimidazole is 15wt%, stir until completely transparent to obtain a mixed solution; b) Add 5 g of NH2-UiO-66 with a pore size of 1.1 nm to the mixed solution obtained in step a), and react at 80 °C for 12 h under nitrogen protection. During this process, the oxygen and moisture content in the system is reduced to below 500 ppm by nitrogen replacement method (the process of increasing the vacuum in the flask to ≤100 Pa and then filling it with nitrogen to atmospheric pressure is repeated more than 3 times). c) Centrifuge at 8000 rpm for 20 min to remove ungrafted MOFs. S Obtain MOF S A composite solution with a loading of 25 wt%; In the above preparation method, NMP, NH2-UiO-66 and SPBI are first pre-dried. The drying method can be a common method in the existing field, such as calcination, nitrogen bubbling, or vacuum drying oven dehydration, so that the water content of the reaction system is <500ppm. Step 2: Preparation of SPBI / ZrP-MOF hybrid sol: 1) Mix 3.63 g ZrOCl2·8H2O (12 mol) with 0.94 mL H3PO4 (15 mol) and age for 48 h to obtain a zirconium phosphate precursor solution; 2) Mix 2.78g of zirconium phosphate precursor solution with 5mL of the composite solution obtained in step one; 3) First, add hydrochloric acid to adjust the pH to 1.5, then add ammonia to adjust the pH to 3.0 to form a uniform sol; Step 3: Construct a membrane with a three-dimensional interpenetrating network structure. 1) Preparation of dynamic crosslinking agent: A crosslinking agent containing disulfide bonds (4,4'-dimercaptobenzophenone) is used, which is prepared by reacting 4,4'-diaminobenzophenone with thioacetic acid and then hydrolyzing it, with a purity ≥99%; 2) Addition of dynamic crosslinking agent: Take 100g of the hybrid sol obtained in step 2 and add 10g of dynamic crosslinking agent; 3) Casting film formation: The casting method is used, with a coating flow rate of 10 mL / min and a heating temperature of 90℃ to form a film material; 4) Ultraviolet crosslinking: Under nitrogen protection (oxygen concentration <100ppm), irradiated with 365nm ultraviolet light at a dose of 2000mJ / cm². 2 The cross-linking time is 5 minutes, which triggers a dynamic disulfide bond exchange reaction and forms a three-dimensional interpenetrating network structure membrane. Step 4: Vertically aligned carbon nanotubes are grown on the surface of the base film using CVD. The membrane material that has completed step 3 is placed in the CVD reaction chamber, and a vacuum of 5 × 10⁻⁶ is drawn. -3 Torr was used to introduce a mixture of Ar and H2 gas (volume ratio Ar:H2 = 3:1), and the temperature was raised to 280℃ and held for 10 min to activate the catalyst. The plasma was then activated in pulse mode with a frequency of 40 Hz, a duty cycle of 60%, and a plasma RF power of 220 W. A mixture of C2H2 and Ar gas (volume ratio Ar:C2H2 = 3:1) was introduced, and the flow rate was adjusted to 55 sccm. The substrate temperature was controlled at 300℃ to begin carbon nanotube growth, which lasted for 20 min, resulting in nanotubes with a height of 10 μm and a density of 10⁻⁶. 10 root / cm 2 After the vertically arranged carbon nanotube array was grown, C2H2 and plasma were turned off, and the array was naturally cooled to room temperature at a cooling rate of 5℃ / min in a pure Ar atmosphere. Step 5, Prepare the sulfonated COFs layer: 1) Dissolve 3 g of SA-TFP COF (sulfonic acid group density 2.0 mmol / g, pore size 1.2 nm) in 97 g of DMSO to obtain a 3 wt% SA-TFP COF DMSO solution; dissolve 5 g of SO3H-COF-300 (sulfonic acid group density 4.2 mmol / g, pore size 0.65 nm) in 95 g of DMF to obtain a 5 wt% SO3H-COF-300 DMF solution. 2) Immerse the polybenzimidazole-based film on which the carbon nanotube array is grown in a 3 wt% SA-TFP COF DMSO solution and keep it for 8 min to allow the large-pore SA-TFP COF to preferentially fill the bottom of the CNT array. 3) Remove the membrane material and immediately transfer it to a 5 wt% DMF solution of SO3H-COF-300. Immerse it for 15 min to induce the self-assembly of small-pore SO3H-COF-300 on the surface. 4) After impregnation, dry at 90℃ for 5 min. The COFs are driven by solvent evaporation and concentration gradient to form a continuous gradient structure of pore size from the bottom layer to the surface layer, thus obtaining a hydrogen barrier layer of sulfonated covalent organic framework with pore size gradient distribution. Step 6: Activation with phosphoric acid solution and gradient annealing. Heating an 85 wt% phosphoric acid solution to 85°C and maintaining the temperature, immersing the membrane from step 4 into the phosphoric acid solution for 3 hours to achieve a phosphoric acid doping concentration of 180 wt%, rinsing with deionized water until neutral, drying with nitrogen, and then placing the membrane in a vacuum oven, first heating it to 130°C at a rate of 3°C / min and holding it for 2.5 hours to release internal stress, then continuing to heat it to 170°C at a rate of 3°C / min and holding it for 1.2 hours to enhance the chemical crosslinking density between COFs and CNTs; Step 7, Prepare an Al2O3 protective layer A protective Al2O3 layer with a thickness of 3 nm was formed on the surface of the membrane material obtained in step 5 by atomic layer deposition. The deposition parameters were: temperature 140℃, TMA pulse 0.25s-N2 purge 30s-H2O pulse 0.25s-N2 purge 30s, cycled 25 times to obtain the proton exchange membrane.

[0019] Example 2 Step 1: Prepare the composite solution: a) Dissolve 10g SPBI (sulfonation degree of 50%) in 90mL NMP, the concentration of sulfonated polybenzimidazole is 10wt%, stir until completely transparent to obtain a mixed solution; b) Add 2 g of NH2-UiO-66 with a pore size of 1.1 nm to the mixed solution obtained in step a), and react at 60 °C for 9 h under nitrogen protection. During this process, reduce the oxygen and moisture content in the system to below 500 ppm by nitrogen replacement method (increasing the vacuum in the flask to ≤100 Pa and then filling it with nitrogen to atmospheric pressure and repeating this process more than 3 times). c) Centrifuge at 7000 rpm for 20 min to remove ungrafted MOFs. S Obtain MOF S A composite solution with a loading of 18 wt%; In the above preparation method, NMP, NH2-UiO-66 and SPBI are first pre-dried. The drying method can be a common method in the existing field, such as calcination, nitrogen bubbling, or vacuum drying oven dehydration, so that the water content of the reaction system is <500ppm. Step 2: Preparation of SPBI / ZrP-MOF S Hybrid sol: 1) Mix 2.42 g ZrOCl2·8H2O (8 mol) with 1.63 mL H3PO4 (16 mol) and age for 48 h to obtain a zirconium phosphate precursor solution; 2) Mix 5.48 g of zirconium phosphate precursor solution with 10.54 mL of the composite solution obtained in step one; 3) First, add hydrochloric acid to adjust the pH to 1.8, then add ammonia to adjust the pH to 2.8 to form a homogeneous sol; Step 3, construct a membrane with a three-dimensional interpenetrating network structure. 1) Preparation of dynamic crosslinking agent: Tetraethoxysilane and γ-mercaptopropyltrimethoxysilane were mixed at a molar ratio of 1:1.5 and dissolved in 10 mL of ethanol; a sol-gel reaction was adopted: the pH was adjusted to 3.5 (with 0.1 M HCl), and the mixture was stirred at 85 °C for 3 hours to generate a tetraethoxysilane-mercaptopropyltrimethoxysilane copolymer with a molecular weight of 3000 g / mol; 2) Addition of dynamic crosslinking agent: Take 100g of the hybrid sol obtained in step 2 and add 5.5g of the above-mentioned dynamic crosslinking agent; 3) Casting film formation: The casting method is used, with a coating flow rate of 10 mL / min and a heating temperature of 90℃ to form a film material; 4) Ultraviolet crosslinking: Under nitrogen protection (oxygen concentration <100ppm), irradiated with 365nm ultraviolet light at a dose of 1200mJ / cm². 2 The cross-linking time is 3 minutes, which triggers a dynamic disulfide bond exchange reaction to form a three-dimensional interpenetrating network structure membrane.

[0020] Step 4: Growing a vertically aligned array of carbon nanotubes on the film surface using CVD: Place the membrane material that has completed step 3 into the CVD reaction chamber and evacuate it to 4×10⁻⁶. -3 Torr was introduced, followed by the introduction of a mixture of Ar and H2 gas (volume ratio Ar:H2 = 3:1), and the temperature was raised to 260℃ and held for 8 min to activate the catalyst. The plasma was then activated in pulse mode with a frequency of 35 Hz, a duty cycle of 55%, and a plasma RF power of 200 W. A mixture of C2H2 and Ar gas (volume ratio Ar:C2H2 = 3:1) was introduced, and the flow rate was adjusted to 50 sccm. The substrate temperature was controlled at 280℃, and carbon nanotube growth began. The growth time was 15 min, yielding nanotubes with a height of 8 μm and a density of 10⁻⁶. 9 root / cm 2 After the vertically arranged carbon nanotube array was grown, C2H2 and plasma were turned off, and the array was naturally cooled to room temperature at a cooling rate of 2.5℃ / min in a pure Ar atmosphere. Step 5, Prepare the sulfonated COFs layer: 1) Dissolve 2.5 g of SA-TFP COF (sulfonic acid group density 1.6 mmol / g, pore size 1.5 nm) in 97.5 g of DMSO to obtain a 2.5 wt% SA-TFP COF DMSO solution; dissolve 4.5 g of SO3H-COF-300 (sulfonic acid group density 3 mmol / g, pore size 0.8 nm) in 95.5 g of DMF to obtain a 4.5 wt% SO3H-COF-300 DMF solution. 2) Immerse the polybenzimidazole film on which the carbon nanotube array is grown in a 2.5 wt% SA-TFP COF DMSO solution and keep it for 6 min to allow the large-pore SA-TFP COF to preferentially fill the bottom of the CNT array. 3) Remove the membrane material and immediately transfer it to a 4.5 wt% DMF solution of SO3H-COF-300. Immerse it for 12 min to induce the self-assembly of small-pore SO3H-COF-300 on the surface. 4) After impregnation, the membrane material is dried at 80°C for 4 minutes. The COFs are driven by solvent evaporation and concentration gradient to form a continuous gradient structure of pore size from the bottom layer to the surface layer, thus obtaining a sulfonated covalent organic framework hydrogen barrier layer with pore size gradient distribution. Step 6: Activation with phosphoric acid solution and gradient annealing. Heating an 85 wt% phosphoric acid solution to 80°C and maintaining the temperature, immersing the membrane from step b into the phosphoric acid solution for 2 hours to achieve a phosphoric acid doping concentration of 200 wt%, rinsing with deionized water until neutral, drying with nitrogen, and then placing the membrane in a vacuum oven, first heating it to 125°C at a rate of 2°C / min and holding it for 2 hours to release internal stress, then continuing to heat it to 165°C at a rate of 2°C / min and holding it for 1 hour to enhance the chemical crosslinking density between COFs and CNTs; Step 7, Prepare an Al2O3 protective layer Atomic layer deposition was used to form a 2nm thick Al2O3 protective layer on the surface of the membrane material obtained in step 5. The deposition parameters were: temperature 120℃, TMA pulse 0.2s-N2 purge 25s-H2O pulse 0.2s-N2 purge 25s, cycled 18 times to obtain a 2nm thick Al2O3 layer, and finally the desired proton exchange membrane was obtained.

[0021] Example 3 Step 1: Prepare the composite solution: a) Dissolve 5g SPBI (sulfonation degree of 50%) in 80mL NMP, the concentration of sulfonated polybenzimidazole is 5wt%, stir until completely transparent to obtain a mixed solution; b) Add 1.5 g of NH2-MIL-125(Ti) with a pore size of 0.9 nm to the mixed solution obtained in step a), and react at 30 °C for 6 h under nitrogen protection. During this process, the oxygen and moisture content in the system is reduced to below 500 ppm by nitrogen replacement method (increasing the vacuum in the flask to ≤100 Pa and then filling it with nitrogen to atmospheric pressure and repeating this process more than 3 times). c) Centrifuge at 5000 rpm for 12 min to remove ungrafted MOFs. S Obtain MOF S A composite solution with a loading of 10 wt%; In the above preparation method, NMP, NH2-MIL-125(Ti) and SPBI are first pre-dried. The drying method can be a common method in the existing field, such as calcination, nitrogen bubbling, or vacuum drying oven dehydration, so that the water content of the reaction system is <500ppm. Step 2: Preparation of SPBI / ZrP-MOF hybrid sol: 1) Mix 5.04 g of 4 mol ZrOCl2·8H2O with 1.63 mL of 12 mol H3PO4 and age for 48 h to obtain a zirconium phosphate precursor solution; 2) Mix 4.27 g of zirconium phosphate precursor solution with 20.2 mL of the composite solution obtained in step one; 3) First add hydrochloric acid to adjust to pH 2, then add ammonia to adjust to pH 2.5 to form a uniform sol; Step 3: Construct a membrane with a three-dimensional interpenetrating network structure. 1) Preparation of dynamic crosslinking agent: Tetraethoxysilane and γ-mercaptopropyltrimethoxysilane were mixed in a 1:1 molar ratio and dissolved in 10 mL of ethanol; a sol-gel reaction was adopted: the pH was adjusted to 4 (with 0.1 M HCl), and the mixture was stirred at 80 °C for 4 hours to generate a tetraethoxysilane-mercaptopropyltrimethoxysilane copolymer with a molecular weight of 1000 g / mol; 2) Addition of dynamic crosslinking agent: Take 100g of the hybrid sol obtained in step 2 and add 3g of the above-mentioned dynamic crosslinking agent; 3) Casting film formation: The casting method is used, with a coating flow rate of 1 mL / min and a heating temperature of 30℃ to form a film material; 4) Ultraviolet crosslinking: Under nitrogen protection (oxygen concentration <100ppm), irradiate with 365nm ultraviolet light at a dose of 500mJ / cm2 for 2 minutes to trigger a dynamic disulfide bond exchange reaction and form a three-dimensional interpenetrating network structure film.

[0022] Step 4: A vertically aligned array of carbon nanotubes is grown on the surface of the film obtained in Step 3 using CVD. Place the membrane material that has completed step 3 into the CVD reaction chamber and evacuate it to a vacuum of 2×10⁻⁶. -3 Torr was introduced, followed by the introduction of a mixture of Ar and H2 gas (volume ratio Ar:H2 = 3:1), and the temperature was raised to 250℃ and held for 5 min to activate the catalyst. The plasma was then activated in pulse mode with a frequency of 30 Hz, a duty cycle of 50%, and a plasma RF power of 180 W. A mixture of C2H2 and Ar gas (volume ratio Ar:C2H2 = 3:1) was introduced, and the flow rate was adjusted to 45 sccm. The substrate temperature was controlled at 250℃, and carbon nanotube growth began. The growth time was 10 min, yielding nanotubes with a height of 5 μm and a density of 10⁻⁶. 8 root / cm 2 After the vertically arranged carbon nanotube array was grown, C2H2 and plasma were turned off, and the array was naturally cooled to room temperature at a cooling rate of 2℃ / min in a pure Ar atmosphere. Step 4, sulfonation of COFs layer: 1) Dissolve 2 g of SA-TFP COF (sulfonic acid group density 1.2 mmol / g, pore size 1.8 nm) in 98 g of DMSO to obtain a 2 wt% SA-TFP COF DMSO solution; dissolve 4 g of SO3H-COF-316 (sulfonic acid group density 4.2 mmol / g, pore size 0.65 nm) in 96 g of DMF to obtain a 4 wt% SO3H-COF-316 DMF solution. 2) Immerse the polybenzimidazole film with carbon nanotube arrays in a 2wt% SA-TFP COF DMSO solution and keep it for 5 min to allow the large-pore SA-TFP COF to preferentially fill the bottom of the CNT array. 3) Remove the membrane material and immediately transfer it to a 4 wt% SO3H-COF-316 DMF solution. Immerse it for 10 min to induce the self-assembly of small-pore SO3H-COF-316 on the surface. 4) After impregnation, the membrane material is dried at 70°C for 3 minutes. The COFs are driven by solvent evaporation and concentration gradient to form a continuous gradient structure of pore size from the bottom layer to the surface layer, thus obtaining a hydrogen barrier layer of sulfonated covalent organic framework with pore size gradient distribution. Step 6: Activation with phosphoric acid solution and gradient annealing. Heating an 85 wt% phosphoric acid solution to 70°C and maintaining the temperature, immersing the membrane from step 4 into the phosphoric acid solution for 1 hour to achieve a phosphoric acid doping concentration of 180 wt%, rinsing with deionized water until neutral, drying with nitrogen, and then placing the membrane in a vacuum oven, first heating it to 120°C at a rate of 1°C / min and holding it for 1.5 hours to release internal stress, then continuing to heat it to 160°C at a rate of 1°C / min and holding it for 0.8 hours to enhance the chemical crosslinking density between COFs and CNTs; Step 7, Prepare an Al2O3 protective layer Atomic layer deposition was used to form an Al2O3 protective layer with a thickness of 1 nm on the surface of the film material obtained in step 5. The deposition parameters were: temperature 100℃, TMA pulse 0.15s - N2 purge 20s - H2O pulse 0.15s - N2 purge 20s, cycled 11 times to obtain a 1 nm thick Al2O3 layer. Finally, the desired proton exchange membrane is obtained.

[0023] Comparative Example 1 The preparation method is the same as in Example 1, except that amino-functionalized MOFs are not added. S The nanoparticles undergo a grafting reaction. Steps 1-2 are changed, while the remaining parameters and steps are the same as in Example 1. The specific steps of steps 1-2 are as follows: Step 1: Prepare SPBI solution: Dissolve 15g of SPBI (sulfonation degree of 50%) in 85mL of NMP, the concentration of sulfonated polybenzimidazole is 15wt%, and stir until completely transparent to obtain SPBI solution; Step 2: Preparation of SPBI / ZrP-MOF hybrid sol: 1) Mix 3.63 g of 12 mol ZrOCl2·8H2O with 0.83 mL of 15 mol H3PO4 and age for 48 h to obtain zirconium phosphate precursor; 2) Mix the zirconium phosphate precursor with the SPBI solution obtained in step one; 3) First, add hydrochloric acid to adjust the pH to 1.5, then add ammonia to adjust the pH to 3.0 to form a uniform sol.

[0024] Comparative Example 2 The preparation method is the same as in Example 1, except that no zirconium phosphate glass network is used, step 1 is changed, and step 2 is omitted. That is, a dynamic crosslinking agent is added to the composite solution obtained in step 1 below, and then the solution is placed in a casting equipment for casting film formation. The parameters of the remaining steps are the same as in Example 1. The specific steps of step 1 are as follows: Step 1: Preparation of SPBI@MOFs composite solution: a) Dissolve 15g SPBI (sulfonation degree of 50%) in 85mL NMP, the concentration of sulfonated polybenzimidazole is 15wt%, stir until completely transparent to obtain a mixed solution; b) Add 5 g of NH2-UiO-66 with a pore size of 3.4 nm to the mixed solution obtained in step a), and react at 80 °C for 12 h under nitrogen protection. During this process, the oxygen and moisture content in the system is reduced to below 500 ppm by nitrogen replacement method (the process of increasing the vacuum in the flask to ≤100 Pa and then filling it with nitrogen to atmospheric pressure is repeated more than 3 times). c) Add 1.14 g PVP to increase viscosity, and mechanically stir at 500 rpm for 1 h to ensure complete dissolution of PVP; d) Remove ungrafted MOFs by centrifuging at 8000 rpm for 20 min. S Obtain MOF S A composite solution with a loading of 25 wt%.

[0025] Comparative Example 3 The preparation method is the same as in Example 1, except that no dynamic crosslinking agent is added, that is, the addition of the dynamic crosslinking agent in step 3 is omitted, and the SPBI / ZrP-MOFs hybrid sol in step 2 is directly used for casting film. The parameters of the remaining steps are the same as in Example 1.

[0026] Comparative Example 4 The preparation method is the same as in Example 1, except that after step 3, the vertically aligned carbon nanotube array is not grown, i.e., step 4 is omitted, and the COFs solution is directly impregnated. The parameters of the remaining steps are the same as in Example 1.

[0027] Comparative Example 5 The preparation method is the same as in Example 1, except that after step 4, the COFs solution is not impregnated, i.e. step 5 is omitted, and the parameters of the remaining steps are the same as in Example 1.

[0028] Comparative Example 6 The preparation method is the same as in Example 1, except that phosphoric acid activation is not performed after step 5, i.e. step 6 is omitted, and the parameters of the remaining steps are the same as in Example 1.

[0029] Comparative Example 7 The preparation method is the same as in Example 1, except that a single-stage annealing process is used and the annealing parameters in step 6 are changed to 130°C for 2 hours. The parameters of the other steps are the same as in Example 1.

[0030] Comparative Example 8 The preparation method is the same as in Example 1, except that the Al2O3 layer in step 7 is omitted, while the parameters of the remaining steps are the same as in Example 1.

[0031] Test Example 1 The membranes of Examples 1-3 and Comparative Examples 1-8 were subjected to performance tests: A laser thickness gauge and a non-contact imaging instrument were used to detect the three-dimensional dimensional changes of the samples under conditions of 25℃ / 50% RH and 80℃ / 95% RH, respectively, to obtain the swelling rate; the initial phosphorus content of the samples was measured using ICP-MS, followed by an aging test, and then the residual phosphorus content was measured again to obtain the phosphoric acid retention rate; the samples were immersed in 68℃ 3% H2O2 + 4 ppm Fe 2+The solution was kept at a constant temperature and shaken. The reagents were changed every 24 hours. The samples were then taken out periodically, dried, weighed, and the tensile strength was tested to determine the oxidation stability. The hydrogen permeability was measured at a constant temperature of 120℃±1℃ using a CS2350 four-electrode electrochemical workstation or a differential pressure gas permeameter.

[0032] The test results are shown in Table 1.

[0033] Table 1 Comparison of High Temperature Stability and Chemical Durability

[0034] Conclusions: Comparative Example 1, without the grafting reaction of amino-functionalized MOF nanoparticles, lacks the high-density phosphate anchoring sites and physical confinement of MOF channels. This leads to increased migration of SPBI segments at high temperatures, resulting in significant high-temperature swelling and easy phosphate loss. Comparative Example 2, without the zirconium phosphate glass network, lacks the structural confinement of the rigid ZrP framework. Therefore, the film lacks sufficient support in the high-temperature phosphate environment, resulting in increased swelling, poor phosphate retention, and poor Fenton lifetime. Comparative Example 3, without the addition of a dynamic crosslinking agent, lacks a self-healing mechanism, leading to increased swelling and reduced lifetime under high-temperature cycling. Comparative Example 4, without the growth of vertically aligned carbon nanotube arrays... The hydrogen barrier effect of Comparative Example 5 was significantly reduced because it was not impregnated with sulfonated COFs solution, i.e., it had no gradient hydrogen barrier layer. Comparative Example 6 was not activated with phosphoric acid, and its phosphoric acid doping was insufficient and unevenly distributed, resulting in discontinuous proton conduction channels and reduced chemical stability. Comparative Example 7 was subjected to single-stage annealing, which made it difficult to eliminate residual stress and had insufficient cross-linking density. Therefore, it was prone to microcracks and significant swelling at high temperatures, resulting in reduced durability. Comparative Example 8 had no Al2O3 layer, which lacked a dense protective layer on the outer surface. It suffered severe acid loss and oxidative erosion, resulting in the worst long-term chemical stability, the highest swelling rate, and a further shortened Fenton lifetime.

[0035] Test Example 2 The membranes of Examples 1-3 and Comparative Examples 1-8 were subjected to performance tests: the crack width before and after repair was measured using a laser confocal microscope, the hardness of the repaired area before and after repair was tested using a nanoindenter, and the self-repair efficiency was determined; the maximum load of the sample was recorded using a universal testing machine, the thickness and width were measured using a laser thickness gauge, and the tensile strength was obtained; the gauge length elongation at the time of sample breakage was recorded, and the elongation at break was calculated.

[0036] The test results are shown in Table 2.

[0037] Table 2 Comparison of Dynamic Self-Healing and Mechanical Properties

[0038] Conclusions: Examples 1-3 introduced a dynamic crosslinking network containing disulfide bonds / siloxanes, which significantly improved the self-healing ability and also improved the tensile strength under gradient annealing, while maintaining a suitable elongation at break. Comparative Example 3 did not have the addition of a dynamic crosslinking agent, and lacked a fracture-reorganization mechanism, making it difficult for microcracks to self-close, thus Comparative Example 3 had the worst self-healing performance. Secondly, Comparative Example 2 did not have a zirconium phosphate glass network, and lacked the structural support of the ZrP rigid skeleton and the inhibition of polymer swelling, thus making it difficult to form a stable self-healing structure. Comparative Example 8 did not have an Al2O3 layer, and lacked a protective layer, making the surface more prone to aging and embrittlement and inducing cracks, thus having the worst long-term mechanical reliability and self-healing retention. Comparative Example 7 used a single-stage annealing treatment, which made it difficult to eliminate residual stress and had insufficient crosslinking density, thus making it prone to microcracks and significant swelling at high temperatures, resulting in decreased durability.

[0039] Test Example 3 The membranes of Examples 1-3 and Comparative Examples 1-8 were subjected to performance tests: the samples were placed in a constant temperature bath of -30℃±0.5℃ and a humidity test cell of 95% RH, and a 10mV AC disturbance was applied. The impedance spectrum was fitted to the bulk resistance. The membrane surface temperature was monitored in real time using a four-electrode system, and the membrane thickness and effective area were recorded simultaneously to obtain the low-temperature proton conductivity. The samples were aged in a nitrogen atmosphere of 120℃±2℃ and 50% RH for 1000h. Samples were taken every 180h, and the proton conductivity (25℃ standard method) and ion exchange capacity were tested according to GB / T 20042.3 to obtain the high-temperature conductivity stability.

[0040] The test results are shown in Table 3.

[0041] Table 3 Comparison of wide temperature range adaptability (-30℃~120℃)

[0042] Conclusion: The data in the table show that Comparative Examples 1, 2, and 6 performed poorly in terms of proton conductivity. Comparative Example 1 lacks the phosphate anchoring sites and nanopore confinement provided by amino-functionalized MOFs, resulting in insufficient active sites and wettability of phosphate and proton conduction channels at low temperatures, thus exhibiting poor conductivity at -30℃ and weak phosphate fixation at high temperatures. Comparative Example 2 lacks the physical restriction of polymer chain swelling and stable fixation of phosphate by the rigid ZrP framework at high temperatures, resulting in even lower conductivity at -30℃ and poor conductivity stability at 120℃. Comparative Example 6 has insufficient phosphate doping and distribution, resulting in low conductivity at low temperatures and poor conductivity at high temperatures.

[0043] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a proton exchange membrane, characterized in that, Includes the following steps: Step 1: Dissolve sulfonated polybenzimidazole in N-methylpyrrolidone, add amino-functionalized MOF nanoparticles for grafting reaction to obtain composite solution; Step 2: Using the sol-gel method, the zirconium phosphate precursor solution is mixed with the composite solution obtained in Step 1, and the pH is adjusted to 1.5-2.0 with hydrochloric acid, and then adjusted to 2.5-3.0 with ammonia to form SPBI / ZrP-MOFs hybrid sol. Step 3: Add a dynamic crosslinking agent to the hybrid sol obtained in Step 2 to obtain a mixed solution, then form a film by casting, and then use ultraviolet light to initiate a crosslinking reaction to obtain a film with a three-dimensional interpenetrating network structure; the dynamic crosslinking agent is a crosslinking agent containing disulfide bonds or a crosslinking agent containing siloxane; Step 4: A vertically aligned carbon nanotube array layer is grown on the surface of the film obtained in Step 3 using chemical vapor deposition, followed by sequential impregnation with sulfonated COFs solution with larger pore size and sulfonated COFs solution with smaller pore size. Step 5: The membrane material obtained in Step 4 is first activated with phosphoric acid solution, and then annealed. Step 6: An Al2O3 protective layer is formed on the surface of the membrane material obtained in step 5 by atomic layer deposition to obtain the proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: Step 1 specifically includes: a) Dissolve sulfonated polybenzimidazole with a sulfonation degree of 30-50% in N-methylpyrrolidone to obtain a mixed solution, wherein the concentration of sulfonated polybenzimidazole in the mixed solution is 5-15 wt%. b) Add amino-functionalized MOF S Nanoparticles were reacted at 30-80℃ for 6-12 hours under nitrogen protection; the amino-functionalized MOF S The nanoparticles are selected from at least one of NH2-UiO-66 and NH2-MIL-125(Ti), and their pore size is 0.6-3.4 nm; c) After centrifugation, a composite solution was obtained, containing amino-functionalized MOFs. S The content of nanoparticles is 10-25 wt%.

3. The preparation method according to claim 1 or 2, characterized in that: The sulfonated polybenzimidazole and amino-functionalized MOF S The mass ratio of the nanoparticles is (3:1) - (10:1); The water content of the reaction system should be controlled to be less than 500 ppm.

4. The preparation method according to claim 1, characterized in that: Step 2 is as follows: 1) Mix ZrOCl2·8H2O and H3PO4 at a molar ratio of 1:1.25-1:3 and age for 24-48 h to obtain a zirconium phosphate precursor solution; 2) Mix the zirconium phosphate precursor solution with the composite solution obtained in step 1 at a mass ratio of sulfonated polybenzimidazole to zirconium phosphate precursor of (1:0.5)-(1:4); 3) First, add hydrochloric acid to adjust the pH to 1.5-2.0, then add ammonia to adjust the pH to 2.5-3.0, forming SPBI / ZrP-MOF. S Hybrid sol.

5. The preparation method according to claim 1, characterized in that: In step 3, the disulfide-containing crosslinking agent is selected from one or two of 4,4'-dimercaptobenzophenone and dithiodipropionic acid, and the amount added is 5-10% of the mass of the mixed solution; the siloxane-containing crosslinking agent is a tetraethoxysilane-mercaptopropyltrimethoxysilane copolymer with a molecular weight of 1000-5000 g / mol, and the amount added is 3-8% of the mass of the mixed solution. The conditions for the crosslinking reaction are: ultraviolet wavelength 365nm, irradiation dose 500-2000mJ / cm2, and oxygen concentration <100ppm; The coating flow rate of the casting method is 1-10 mL / min, and the heating temperature is 30-90℃.

6. The preparation method according to claim 1, characterized in that: Step 4, which involves growing a vertically aligned array of carbon nanotubes on the substrate surface using CVD, is as follows: 1) Chamber pretreatment: Place the membrane in the CVD reaction chamber and evacuate to 2×10⁻⁶. -3 -5×10 -3 Torr; 2) Reduction activation: Introduce a mixture of Ar and H2 gas with a volume ratio of Ar:H2=3:1, heat to 250-280℃, and maintain for 5-10 min to activate the catalyst; 3) Carbon nanotube growth: Apply radio frequency power in pulse mode at a frequency of 30-40 Hz and a duty cycle of 50%-60%. The plasma radio frequency power is 180-220 W. Introduce a mixture of C2H2 and Ar gas with a volume ratio of Ar:C2H2=3:1 and adjust the flow rate to 45-55 sccm. Control the substrate temperature at 250-300℃ to start carbon nanotube growth. The carbon nanotube growth time is 10-20 min to obtain a vertical array with a height of 5-10 μm. 4) Cooling: Turn off C2H2 and plasma, and cool to room temperature at a rate of ≤5℃ / min in a pure Ar atmosphere; The vertically aligned carbon nanotube array layer has a tube length of 5-10 μm and an array density of 102. 8 -10 10 root / cm 2 .

7. The preparation method according to claim 1, characterized in that: In step 4, the sulfonated COFs solution with larger pore size is a DMSO solution of SA-TFP COF with a concentration of 2-3 wt%, the SA-TFP COF has a pore size of 1.2-1.8 nm, a sulfonic acid group density of 1.2-2.0 mmol / g, and an impregnation time of 5-8 min. The smaller pore size sulfonated COFs solution is an N,N-dimethylformamide solution of SO3H-COF-300 or an N,N-dimethylformamide solution of SO3H-COF-316, with a concentration of 4-5 wt% for the DMF solution of SO3H-COF-300 or SO3H-COF-316. The pore size of SO3H-COF-300 and SO3H-COF-316 is 0.65-1.0 nm, the sulfonic acid group density is 2.8-4.2 mmol / g, and the impregnation time is 10-15 min. The pore size of SO3H-COF-300 and SO3H-COF-316 is 0.65-1.0 nm, and the sulfonic acid group density is 2.8-4.2 mmol / g. After impregnation, dry at 70-90℃ for 3-5 minutes.

8. The preparation method according to claim 1, characterized in that: In step 5, the phosphoric acid solution activation treatment is as follows: immersion in a phosphoric acid solution at 70-85℃ for 1-3 hours to achieve a phosphoric acid doping amount of 180-220wt%; the concentration of the phosphoric acid solution is 85wt%.

9. The preparation method according to claim 1, characterized in that: In step 5, the gradient annealing is performed by first treating at 120-130℃ for 1.5-2.5h under nitrogen or argon atmosphere protection, with a heating rate of 1-3℃ / min, followed by treatment at 160-170℃ for 0.8-1.2h.

10. The preparation method according to claim 1, characterized in that: In step 6, the parameters for depositing the Al2O3 layer using atomic layer deposition technology include: deposition temperature of 100-140℃, TMA pulse time of 0.15-0.25s, H2O pulse time of 0.15-0.25s, purging with N2 or Ar for 20-30s / cycle, and the thickness of the Al2O3 protective layer of 1-3nm.

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