Preparation method of ultrathin gel composite proton exchange membrane with three-dimensional nanofiber skeleton

Abstract

The invention discloses a preparation method of an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber skeleton. According to the proton exchange membrane, a PTFE-based three-dimensional nanofiber skeleton prepared by an electrostatic spinning technology is used as a mechanical support body, and SPEEK-based semi-crosslinked gel is compounded in pores of the skeleton through vacuum impregnation, so that a stable skeleton-gel interpenetrating network structure is formed. The preparation method is characterized in that an ultrathin high-strength nanofiber skeleton membrane with high porosity and the thickness of only 3-10 microns is obtained through a low-solid-content and high-orientation electrostatic spinning and light sintering technology; further preparing an SPEEK gel precursor solution, and carrying out vacuum impregnation, controllable membrane scraping, hydration expansion and post-treatment to form a continuous proton conduction gel phase with the thickness of 2-8 microns in the skeleton, so as to finally obtain the composite membrane with the total thickness of 5-15 microns. The composite membrane has the advantages of ultrathin structure, high mechanical strength, low swelling ratio, excellent interface stability and high proton conductivity, and is especially suitable for high-temperature proton exchange membrane fuel cells.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of proton exchange membrane fuel cells, and particularly relates to a preparation method of an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber skeleton. BACKGROUND

[0002] Proton exchange membrane (PEM) is the core component of proton exchange membrane fuel cell (PEMFC), and its performance directly determines the energy conversion efficiency, power density and service life of the cell. An ideal proton exchange membrane should have high proton conductivity, excellent mechanical strength, dimensional stability (low swelling) and durability.

[0003] At present, the most widely used proton exchange membrane in commercial applications is perfluorosulfonic acid (PFSA) membrane (such as Nafion®), which exhibits excellent proton conductivity under normal temperature and high humidity conditions. However, PFSA membrane has problems such as high cost, rapid decrease in proton conductivity under low humidity conditions at high temperature (> 80℃), and excessive water absorption and swelling, which limits its application in a wider range of scenarios.

[0004] In order to overcome the limitations of PFSA membrane, hydrocarbon polymers such as sulfonated polyether ether ketone (SPEEK) with lower cost and better thermal stability are considered as promising alternative materials. However, SPEEK membrane itself has a key contradiction: high sulfonation degree (DS) is a prerequisite for obtaining high proton conductivity, but high DS will cause excessive water absorption and swelling of the membrane, resulting in rapid deterioration of mechanical strength and dimensional instability. In order to solve this contradiction, researchers have developed various composite modification strategies, but all have different degrees of limitations: At present, the enhancement strategies for proton exchange membranes mainly include organic-inorganic blending, porous matrix filling and fiber skeleton reinforcement. For example, Foshan Qingji Energy Technology Co., Ltd. discloses a sulfonated polyether ether ketone-based proton exchange membrane and a preparation method thereof (CN114883618A), which specifically grafts a polymer containing imidazole groups on the surface of silica particles, then blends with SPEEK, uses ion crosslinking to inhibit the swelling of the membrane, and improves the high-temperature proton conductivity. Jiangsu Runmem Material Co., Ltd. discloses a composite proton exchange membrane and a preparation method thereof (CN113416982A), which specifically blends perfluorosulfonic acid resin with partially fluorinated or non-fluorinated sulfonated resin (such as SPEEK, PVDF-g-PSSA), and dopes metal oxides (such as CeO2) or noble metal nanoparticles (such as Pt), uses metal oxides to scavenge free radicals to prolong the service life, and uses noble metal to catalyze composite crossover gas to improve safety. Both methods improve the performance of the proton exchange membrane, but the essence is homogeneous blending structure, the mechanical strength of the membrane is limited, and the membrane cannot be thinned, which is difficult to meet the requirements of fuel cells for high power density.

[0005] Zhengzhou University discloses a method for preparing sandwich structure proton exchange membrane for hydrogen fuel cell based on electrospinning (CN117558955A), which specifically uses electrospinning to prepare PVDF-HFP / Ti3C2T x -SO3H fiber membrane as a sandwich layer, and a SPEEK membrane is compounded to form a sandwich structure, thereby improving the mechanical properties and proton conductivity of the membrane, but the structure is macroscopic lamination, the interfacial bonding force is insufficient, and there is a risk of delamination.

[0006] Shanghai Boyuan Energy Technology Co., Ltd. discloses a method for improving the fiber characteristics of a PTFE microporous membrane substrate (CN110459790A), which specifically coats a mixed additive coating on the surface of the PTFE microporous membrane fiber to improve its tensile strength and oxidation resistance, but does not solve the swelling problem of the SPEEK filler phase, and the overall membrane is relatively thick.

[0007] The same point is that both introduce reinforcing phases or modified fillers to improve the mechanical properties, dimensional stability or proton conductivity of the proton exchange membrane; the difference is that one composite proton exchange membrane and a preparation method thereof (CN113416982A) and one sulfonated polyether ether ketone matrix proton exchange membrane and a preparation method thereof (CN114883618A) are both blending structures of a base resin and a functional filler, one method for improving the fiber characteristics of a PTFE microporous membrane substrate (CN110459790A) is all based on a commercial PTFE microporous membrane as a support body, and one method for preparing a sandwich structure proton exchange membrane for hydrogen fuel cell based on electrospinning (CN117558955A) is a sandwich layered structure.

[0008] In summary, the existing technology has not yet been able to well solve the following key problems: how to realize the ultra-thin (<15 μm) of the proton exchange membrane to reduce the proton transmission impedance while ensuring that it has high mechanical strength, excellent dimensional stability (low swelling) and firm interface bonding sufficient to cope with the operating environment of the fuel cell, especially long-term durability under high temperature conditions. Most composite membranes either sacrifice thickness for strength or have difficulty balancing conductivity and stability at an ultra-thin scale. Therefore, developing a new type of composite proton exchange membrane structure with ultra-thin thickness, intrinsic high strength, stable interface and high proton conductivity at low humidity under high temperature is of great importance to the development of high-performance fuel cell technology. SUMMARY

[0009] The present application aims to provide an ultra-thin three-dimensional nanofiber skeleton gel composite proton exchange membrane with a total thickness of 5-15 μm. In view of the problem that the existing composite membrane has a large thickness (20-60 μm) and is difficult to have low swelling, low impedance and high mechanical strength under high temperature conditions, the present application realizes the balance between ultra-thin structure and high strength through the technical route of reducing the solid content of the spinning system, improving the fiber orientation, adopting light melting sintering technology and constructing a thickness-limited gel layer.

[0010] 1. A preparation method of an ultra-thin gel composite proton exchange membrane with a three-dimensional nanofiber skeleton, characterized by comprising the following steps: Step 1: preparing a three-dimensional nanofiber skeleton, mixing polytetrafluoroethylene emulsion (hereinafter referred to as PTFE), nano-inorganic filler modified by a silane coupling agent and a spinning aid in a proportion to obtain a nanofiber skeleton spinning solution (hereinafter referred to as spinning solution) under ultrasonic and stirring; carrying out electrospinning of the spinning solution under specific low solid content and high orientation electrospinning conditions, and forming a cohesive micro-cage structure by mutual adhesion of the spinning fibers to obtain a nanofiber base material; placing the nanofiber base material in an inert gas atmosphere for heat treatment, so that the spinning aid is gasified and removed, the inorganic nano-filler particles are exposed, and the PTFE particles are melted to obtain an ultra-thin high-strength nanofiber skeleton membrane with a thickness of 3-10 μm; Step 2: gel treatment pre-treating the nanofiber skeleton membrane obtained in step 1, then immersing it in a prepared SPEEK gel precursor solution, forming a semi-crosslinked gel layer with a thickness of 2-8 μm by vacuum impregnation and film thickness control, then soaking in deionized water for hydration and expansion, and finally performing post-treatment, to finally obtain an ultra-thin gel composite proton exchange membrane with a three-dimensional nanofiber skeleton with a total thickness of 5-15 μm.

[0011] 2. Further, the step 1 of preparing an ultra-thin high-strength nanofiber skeleton is characterized by: The polytetrafluoroethylene emulsion is DuPont Teflon DISP 30. PTFE is the main component of the three-dimensional nanofiber skeleton, which provides the mechanical skeleton and hydrophobic framework of the composite proton exchange membrane, supports the doping of inorganic nano-filler and the coating of SPEEK gel.

[0012] The silane coupling agent is one of γ-aminopropyl triethoxysilane (KH-550), γ-glycidoxypropyl trimethoxysilane (KH-560), and γ-methacryloyloxypropyl trimethoxysilane (KH-570). The silane coupling agent has three functions in the system: first, it improves compatibility, enhances the interfacial compatibility of inorganic nano-filler and PTFE and SPEEK gel, reduces the agglomeration of inorganic nano-filler in the spinning solution, and improves the uniformity and stability of the spinning solution; second, it enhances adhesion and dispersion, promotes the uniform dispersion of inorganic nano-filler in the spinning solution, and improves the mechanical strength, peel strength, and durability of the three-dimensional inorganic nanofiber skeleton.

[0013] The nano-inorganic filler is one or more of SiO2, TiO2, and ZrO2, and the particle size is 20-50 nm. The inorganic nano-filler can increase the hydrophilicity of the three-dimensional nanofiber skeleton, improve the compatibility of the three-dimensional nanofiber skeleton and the SPEEK gel, and make the SPEEK better coat on the three-dimensional nanofiber skeleton.

[0014] The spinning aid is a PVA aqueous solution, and the molecular weight of PVA is 8500-12400. The preparation process of the spinning aid is as follows: PVA is dissolved in water at 70-85°C and stirred for 1.5-3 h, and the stirring speed of the magnetic stirrer is 800-1000 rpm. When the PVA content is less than 3 wt%, the spinning solution viscosity is insufficient, and when the PVA content is higher than 20 wt%, the needle is easily blocked. Therefore, the PVA content is preferably 3-20 wt%. The preparation process of the spinning solution is as follows: The modified nano-inorganic filler is placed in deionized water, ultrasonically dispersed for 30-60 min, and then the spinning aid and PTFE emulsion are added and stirred for 1-3 h at a stirring speed of 800-1000 rpm of the magnetic stirrer to obtain a nanofiber skeleton spinning solution. The solid content of the final nanofiber skeleton spinning solution is PTFE 10-35 wt%, nano-inorganic filler 2-5 wt%, and PVA 3-20 wt%. The specific parameters of electrospinning are as follows: the positive and negative voltages of spinning are +10 kV to +20 kV and -2.5 kV to -5 kV, the spinning distance is 10-15 cm, the inner diameter of the needle is 0.5-1 mm, the solution advancing speed is 0.6-2.0 mL·h -1 , the spinning receiving surface is a metal cylinder wrapped with silicone oil paper, the rotating speed of the metal cylinder is 300-1200 rpm, the environmental temperature is 20-30°C, and the environmental humidity is <60%; The key of the cohesive micro-cage structure lies in the local aggregation of nano-inorganic filler particles at the microscale, which causes the adhesion between fibers and forms a stable space skeleton, thereby improving the mechanical strength and locking the gel.

[0015] The inert gas atmosphere is a nitrogen or argon atmosphere.

[0016] The key to the heat treatment is to place the nanofiber substrate obtained by spinning into a muffle furnace and heat it at 1~5 °C·min under a nitrogen or argon atmosphere. - ¹Heating to 320~400 ℃ and holding for 5~45 min, slight sintering allows PVA to decompose and volatilize, causing PTFE to undergo surface melting and bonding without complete collapse. This maintains high porosity (≥60%) within a thickness of 3~10 μm, forming a porous but continuous structure, thus forming a robust nanofiber framework membrane. At the same time, inorganic nanofillers are exposed, providing anchor points for subsequent SPEEK gel coating, increasing the compatibility between the nanofiber framework membrane and the SPEEK gel, and reducing the risk of phase separation. 3. Furthermore, the gelation treatment in step 2 is characterized by: The pretreatment involves soaking the nanofiber framework membrane obtained in step 1 in ethanol for 15-45 minutes to enhance the hydrophilicity of the nanofiber framework membrane. The key to preparing the SPEEK gel precursor solution is to dissolve sulfonated polyether ether ketone (hereinafter referred to as SPEEK) with a sulfonation degree of 50%~90% in dimethyl sulfoxide (hereinafter referred to as DMSO) to prepare a 5~15 wt% solution, and stir at 50~80℃ for 2~12 h until transparent; then add 0.5~2 wt% carboxymethyl cellulose (hereinafter referred to as CMC), 1~5 wt% ethylene glycol dimethacrylate (hereinafter referred to as PEGMA), 0.1~0.5 wt% ammonium persulfate (hereinafter referred to as APS), 0.1~0.5 wt% methylethylenediamine (hereinafter referred to as TEMED) and 0.5~7 wt% glycerol in sequence, and disperse by ultrasonication for 15~45 min; let stand until no bubbles are present to ensure the homogeneity of the solution; SPEEK, as the main polymer, provides a proton conduction channel; CMC, as a reversible crosslinking agent, forms a dynamic hydrogen bond network; PEGMA, as a hydrophilic monomer, enhances water uptake and gel flexibility, supporting water retention and swelling; APS and TEMED, as an initiator pair, initiate room temperature polymerization to form semi-crosslinked junctions; glycerol, as a plasticizer, enhances gel flexibility and mechanical durability, preventing embrittlement; DMSO, as a solvent, ensures uniform mixing of components. The specific conditions for forming the semi-crosslinked gel composite membrane are as follows: the pretreated nanofiber skeleton membrane is vacuum-immersed in a gel precursor solution for 5-15 min to ensure that the gel precursor solution penetrates into the fiber network of the nanofiber skeleton membrane; the membrane thickness is limited to 5-30 μm or centrifuged at 800-1200 rpm for 1-10 min to remove excess solution from the surface of the nanofiber skeleton membrane so that the final thickness of the gel layer is controlled at 2-8 μm; and the membrane is allowed to stand at 10-35 ℃ for 3-4 h, where APS / TEMED initiates the reaction between CMC / PEGMA and SPEEK side chains to form a semi-crosslinked gel. The key to the hydration expansion is to immerse the gel in deionized water for 12-36 h to induce a 1-8% expansion, so that the gel completely fills the pores of the nanofiber skeleton membrane and expands to both sides, while avoiding the thickening of the ultrathin film structure and enhancing the interfacial bonding between the gel and the nanofiber skeleton to obtain a semi-crosslinked gel composite membrane. The key to the post-processing is to vacuum dry the semi-crosslinked gel composite membrane at 60~100 ℃ for 12~24 h to accelerate DMSO volatilization, gently remove residual DMSO solvent, and avoid excessive chain segment shrinkage leading to cracks; then place it in an oven at 100~120 ℃ for 1~3 h to allow thermal energy to rearrange the network, enhance the stability of hydrogen bonds and covalent bonds in the system, fix the proton channels, and finally obtain an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber skeleton.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The PTFE inorganic filler nanofiber skeleton prepared by electrospinning provides a high-porosity mechanical support structure. After sintering, a stable hydrophobic skeleton is obtained, which significantly improves the mechanical strength and dimensional stability of the membrane. 2. SPEEK-based semi-crosslinked three-dimensional gels serve as a continuous proton-conducting phase, providing a large number of exchangeable sulfonic acid groups, which significantly improves proton conductivity. The gels are formed at room temperature or under mild conditions using APS and TEMED, balancing the continuity of conductive channels with controllable swelling. 3. By employing a micro-mechanical interlocking strategy induced by surface-modified inorganic fillers and hydration expansion, the interfacial bonding between the gel and the fiber skeleton can be enhanced, reducing the risk of delamination and improving cycle stability. 4. The composite structure combines water-retaining sites (inorganic filler, glycerol) and a continuous conductive phase (SPEEK) under high temperature and low humidity conditions, which is beneficial for maintaining proton conduction performance at operating conditions above 80 °C; 5. The composite membrane of this invention achieves an ultrathin structure with a total thickness of only 5~15 μm, which significantly reduces the proton transport impedance and achieves a balance between thin film and high strength and high stability, which is significantly better than the existing thick film SPEEK composite membrane system.

[0018] 6. The method can be implemented using a water-based system and room temperature initiation, is suitable for roll-to-roll mass production, and has a lower cost than the pure perfluorosulfonic acid membrane system, thus possessing industrialization potential. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process of this invention.

[0020] Figure 2 This is a schematic diagram of the structure of an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber framework according to the present invention.

[0021] Figure 3 This is a scanning electron microscope image of the three-dimensional nanofiber skeleton of the present invention. Specific Implementation Example 1: Step 1: Fabrication of a three-dimensional nanofiber framework PVA powder was dissolved in water at 80°C and stirred for 2.5 h with a magnetic stirrer at 900 rpm to prepare a 20 wt% PVA aqueous solution.

[0023] Inorganic nanofillers SiO2 (2.75 wt%) and ZrO2 (2.75 wt%) modified with KH-550 were ultrasonically dispersed in deionized water for 40 min. Then, a spinning aid (PVA solution, molecular weight 10000) and PTFE emulsion were added, and the mixture was stirred for 2 h to obtain the spinning solution. The solid content of this solution was PTFE 34 wt%, nano-inorganic filler 5.5 wt%, and PVA 7 wt%.

[0024] The spinning solution was placed in an electrospinning apparatus, with the positive and negative electrode voltages set to +18 kV and -4 kV, respectively. The spinning distance was 10 cm, the needle inner diameter was 0.5 mm, and the solution propulsion speed was 1.0 mL·h. - ¹ The spinning receiving surface is a metal roller wrapped with silicone paper, and the roller speed is 300 rpm. The spinning environment temperature is 25°C and the relative humidity is 40%.

[0025] The nanofiber substrate obtained by spinning was placed in a nitrogen atmosphere and heated in a muffle furnace at 5 °C·min. - The temperature was increased to 385 °C at a heating rate of ¹, held for 30 min, and then allowed to cool naturally to room temperature. This step allowed the PTFE particles to melt and fuse, forming a stable nanofiber framework membrane, while simultaneously removing PVA and exposing the inorganic filler particles, providing a good substrate for subsequent gelation treatment.

[0026] Step 2: Gelation treatment The nanofiber framework membrane obtained in step 1 was pretreated by soaking it in ethanol for 25 min to enhance its hydrophilicity.

[0027] Sulfonated polyether ether ketone (SPEEK) with a sulfonation degree of 60% was dissolved in DMSO to prepare a 12 wt% solution. The solution was stirred for 8 h until it became clear. Then, 1.5 wt% CMC, 3 wt% PEGMA, 0.5 wt% APS, 0.5 wt% TEMED, and 3 wt% glycerol were added. The solution was ultrasonically dispersed for 30 min, allowed to stand to remove air bubbles, and ensured to be homogeneous.

[0028] The pretreated nanofiber framework membrane was vacuum-impregnated in a gel precursor solution for 30 min to ensure full penetration of the fiber network. Excess solution was then removed from the surface using a scraper, and the membrane was allowed to stand at room temperature for 3 h. A polymerization reaction was then initiated via APS / TEMED to form a semi-crosslinked gel.

[0029] The semi-crosslinked gel membrane was immersed in deionized water for 24 hours to allow the gel to swell by 8%, thereby enhancing the interfacial bonding between the gel and the nanofiber framework membrane.

[0030] Finally, the gel composite membrane was vacuum dried at 80 °C for 24 h to remove residual solvent. The membrane was then heated in an oven at 120 °C for 2 h to enhance the stability of hydrogen and covalent bonds, ensuring the fixation of proton channels, thus obtaining the final composite proton exchange membrane.

[0031] The proton conductivity of the prepared composite proton exchange membrane was tested using the four-probe method: at 80 °C, the values ​​at 0%, 20%, 40%, 80%, and 100% relative humidity were 0.8 mS / cm, 5 mS / cm, 12 mS / cm, 79 mS / cm, and 125 mS / cm, respectively. At 90 °C, the values ​​at 0%, 20%, 40%, 80%, and 100% relative humidity were 1.1 mS / cm, 6.6 mS / cm, 15.6 mS / cm, 101 mS / cm, and 154 mS / cm, respectively. Specific Implementation Example 2: Step 1: Fabrication of a three-dimensional nanofiber framework PVA powder was dissolved in water at 80°C and stirred for 2.5 h with a magnetic stirrer at 900 rpm to prepare a 20 wt% PVA aqueous solution.

[0033] Inorganic nanofillers SiO2 (3 wt%) and ZrO2 (2 wt%) modified with KH-550 were ultrasonically dispersed in deionized water for 40 min. Then, a spinning aid (PVA solution, molecular weight 10000) and PTFE emulsion were added, and the mixture was stirred for 2 h to obtain the spinning solution. The solid content of this solution was PTFE 12 wt%, nano-inorganic filler 5 wt%, and PVA 8 wt%.

[0034] The spinning solution was placed in an electrospinning apparatus, with the positive and negative electrode voltages set to +12 kV and -3 kV, respectively. The spinning distance was 10 cm, the needle inner diameter was 0.5 mm, and the solution propulsion speed was 1.5 mL·h. - ¹ The spinning receiving surface is a metal roller wrapped with silicone paper, and the roller speed is 800 rpm. The spinning environment temperature is 25 °C and the relative humidity is 40%.

[0035] The nanofiber substrate obtained by spinning was placed in a nitrogen atmosphere and heated in a muffle furnace at 5 °C·min. - The temperature was increased to 325 °C at a heating rate of ¹, lightly sintered, held for 30 min, and then naturally cooled to room temperature. This step allowed the PTFE particles to melt and fuse, forming a stable nanofiber framework membrane, while simultaneously removing PVA and exposing the inorganic filler particles, providing a good substrate for subsequent gelation treatment.

[0036] Step 2: Gelation treatment The nanofiber framework membrane obtained in step 1 was pretreated by soaking it in ethanol for 25 min to enhance its hydrophilicity.

[0037] Sulfonated polyether ether ketone (SPEEK) with a sulfonation range of 65% was dissolved in DMSO to prepare a 6 wt% solution. The solution was stirred for 8 hours until it became clear. Then, 0.5 wt% CMC, 2 wt% PEGMA, 0.3 wt% APS, 0.3 wt% TEMED, and 2 wt% glycerol were added. The solution was ultrasonically dispersed for 30 minutes and allowed to stand to remove air bubbles, ensuring the homogeneity of the solution.

[0038] The pretreated nanofiber framework membrane was vacuum-impregnated in a gel precursor solution for 30 min to ensure full penetration of the fiber network. Excess solution was then removed from the surface using a scraper, and the membrane was allowed to stand at room temperature for 3 h. A polymerization reaction was then initiated via APS / TEMED to form a semi-crosslinked gel.

[0039] The semi-crosslinked gel membrane was immersed in deionized water for 18 hours to allow the gel to swell by 4%, thereby enhancing the interfacial bonding between the gel and the nanofiber framework membrane.

[0040] Finally, the gel composite membrane was vacuum dried at 80 °C for 24 h to remove residual solvent. The membrane was then heated in an oven at 120 °C for 2 h to enhance the stability of hydrogen and covalent bonds, ensuring the fixation of proton channels, thus obtaining the final composite proton exchange membrane.

[0041] The proton conductivity of the prepared composite proton exchange membrane was tested using the four-probe method: at 80 °C, the values ​​at 0%, 20%, 40%, 80%, and 100% relative humidity were 1.0 mS / cm, 6.2 mS / cm, 18.5 mS / cm, 105 mS / cm, and 155 mS / cm, respectively. At 90 °C, the values ​​at 0%, 20%, 40%, 80%, and 100% relative humidity were 1.35 mS / cm, 8.2 mS / cm, 24.1 mS / cm, 134 mS / cm, and 191 mS / cm, respectively.

Claims

1. A method for preparing an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber framework, characterized in that, Includes the following steps: Step 1: Prepare a three-dimensional nanofiber framework. Polytetrafluoroethylene emulsion (hereinafter referred to as PTFE), nano-inorganic fillers modified with silane coupling agent and spinning aids are mixed in proportion and ultrasonically and stirred to obtain nanofiber skeleton spinning solution (hereinafter referred to as spinning solution). Electrospinning is performed on the spinning solution under specific low solid content and high orientation electrospinning conditions. The spun fibers bond together to form an adhesive microcage structure, thus obtaining a nanofiber substrate. The nanofiber substrate is placed in an inert gas atmosphere for heat treatment, which causes the spinning aid to be vaporized and removed, the inorganic nanofiller particles to be exposed, and the PTFE particles to be melted, resulting in an ultrathin high-strength nanofiber skeleton membrane with a thickness of 3–10 μm. Step 2: Gelation treatment The nanofiber framework membrane obtained in step 1 was pretreated and then immersed in a pre-prepared SPEEK gel precursor solution. A semi-crosslinked gel layer with a thickness of 2–8 μm was formed by vacuum impregnation and membrane scraping. The membrane was then immersed in deionized water for hydration and expansion. Finally, post-treatment was performed to obtain an ultrathin gel composite proton exchange membrane with a total thickness of 5–15 μm and a three-dimensional nanofiber framework.

2. The method for preparing an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber framework according to claim 1, characterized in that, In step 1: The polytetrafluoroethylene emulsion is designated as DuPont Teflon DISP 30. The silane coupling agent is one of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-methacryloyloxypropyltrimethoxysilane (KH-570); The nano-inorganic filler is one or more of SiO2, TiO2, and ZrO2, with a particle size of 20~50 nm; The spinning aid is an aqueous solution of PVA, with a molecular weight of 8500~12400. The preparation process of the spinning aid is to dissolve PVA in water at 70℃~85℃ and stir for 1.5~3 hours with a magnetic stirrer speed of 800 rpm~1000 rpm. The preparation process of the spinning solution is as follows: The modified nano-inorganic filler was placed in deionized water and ultrasonically dispersed for 30-60 min. Then, spinning aids and PTFE emulsion were added, and the mixture was stirred for 1-3 h at a magnetic stirrer speed of 800-1000 rpm until homogeneous to obtain a spinning solution. The solid content of the spinning solution was 10-35 wt% PTFE, 2-5 wt% nano-inorganic filler, and 3-20 wt% PVA. The specific parameters for electrospinning are: positive and negative electrode voltages of +10 kV to +20 kV and -2.5 kV to -5 kV, respectively; spinning distance of 10 to 15 cm; needle inner diameter of 0.5 to 1 mm; and solution propulsion speed of 0.6 to 2.0 mL / h. -1 The spinning receiving surface is a metal roller wrapped with silicone paper. The metal roller rotates at 300~1200 rpm, the ambient temperature is 20~30 ℃, and the ambient humidity is <60%. The inert gas atmosphere is a nitrogen or argon atmosphere; The heat treatment involves placing the spun nanofiber substrate into a muffle furnace and heating it at 1-5°C / min under a nitrogen or argon atmosphere. - ¹Heating to 320~400 ℃ and holding for 5~45 min, slight sintering allows PVA to decompose and volatilize, causing PTFE to undergo surface melting and bonding without complete collapse. This maintains high porosity (≥60%) within a thickness of 3~10 μm, forming a porous but continuous structure, thus creating a robust nanofiber framework membrane. At the same time, inorganic nanofillers are exposed, providing anchor points for subsequent SPEEK gel coating, increasing the compatibility between the nanofiber framework membrane and the SPEEK gel, and reducing the risk of phase separation.

3. The method for preparing an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber framework according to claim 1, characterized in that, In step 2: The pretreatment involves soaking the nanofiber framework membrane obtained in step 1 in ethanol for 15-45 minutes to enhance the hydrophilicity of the nanofiber framework membrane. The SPEEK gel precursor solution is prepared by dissolving sulfonated polyether ether ketone (hereinafter referred to as SPEEK) with a sulfonation degree of 50%~90% in dimethyl sulfoxide (hereinafter referred to as DMSO) to prepare a 5~15 wt% solution, stirring at 50~80 ℃ for 2~12 h until transparent; then adding 0.5~2 wt% carboxymethyl cellulose (hereinafter referred to as CMC), 1~5 wt% ethylene glycol dimethacrylate (hereinafter referred to as PEGMA), 0.1~0.5 wt% ammonium persulfate (hereinafter referred to as APS), 0.1~0.5 wt% methylethylenediamine (hereinafter referred to as TEMED) and 0.5~7 wt% glycerol sequentially, and ultrasonically dispersing for 15~45 min; allowing to stand until air bubbles are removed to ensure solution homogeneity; SPEEK serves as the main polymer, providing a proton conduction channel; CMC acts as a reversible crosslinking agent, forming a dynamic hydrogen bond network; PEGMA, as a hydrophilic monomer, enhances water uptake and gel flexibility, supporting water retention and swelling; APS and TEMED act as an initiator pair, initiating room temperature polymerization to form semi-crosslinked junctions. Glycerin acts as a plasticizer, enhancing gel flexibility and mechanical durability and preventing embrittlement; DMSO acts as a solvent, ensuring uniform mixing of components. The specific conditions for forming the semi-crosslinked gel composite membrane are as follows: the pretreated nanofiber framework membrane is vacuum-immersed in a gel precursor solution for 5-15 min to ensure that the gel precursor solution penetrates the fiber network of the nanofiber framework membrane; the membrane thickness is limited to 5-30 μm or the excess solution on the surface of the nanofiber framework membrane is removed by centrifugation at 800-1200 rpm for 1-10 min, so that the final thickness of the gel layer is controlled at 2-8 μm; and the membrane is allowed to stand at 10-35 ℃ for 3-4 h, where APS / TEMED initiates the reaction between CMC / PEGMA and SPEEK side chains to form a semi-crosslinked gel. The hydration expansion involves immersing the gel in deionized water for 12-36 hours to induce a 1-8% expansion, allowing the gel to completely fill the pores of the nanofiber framework membrane and expand to both sides. This process avoids thickening of the ultrathin film structure and enhances the interfacial bonding between the gel and the nanofiber framework, resulting in a semi-crosslinked gel composite membrane. The post-processing involves vacuum drying the semi-crosslinked gel composite membrane at 60-100 °C for 12-24 h to accelerate DMSO volatilization, gently remove residual DMSO solvent, and prevent excessive chain segment shrinkage leading to cracks; then, it is placed in an oven at 100-120 °C for 1-3 h to allow thermal rearrangement of the network, enhance the stability of hydrogen bonds and covalent bonds in the system, fix the proton channels, and finally obtain an ultrathin gel composite proton exchange membrane with a three-dimensional nanofiber framework.

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