High-performance membrane electrode for electrolyzed water as well as preparation method and application of high-performance membrane electrode

Abstract

The invention relates to the field of fuel cells, in particular to a high-performance membrane electrode for electrolyzed water as well as a preparation method and application of the high-performance membrane electrode. The membrane electrode comprises a proton exchange membrane and catalyst layers coating the two sides of the proton exchange membrane, and the proton exchange membrane comprises a sulfonated polyethersulfone base membrane, a reinforcing layer covering the sulfonated polyethersulfone base membrane and a sulfonated polyethersulfone top layer membrane covering the reinforcing layer; the enhancement layer is an expanded polytetrafluoroethylene porous membrane; and the catalyst layer contains sulfonated polyethersulfone. Meanwhile, an integrated thermal crosslinking strategy is adopted in the preparation method, and the ionomer layer and the membrane substrate are jointly crosslinked, so that the body proton conductivity is remarkably improved, and the interface contact resistance is reduced.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more particularly to a high-performance membrane electrode for water electrolysis, its preparation method, and its application. Background Technology

[0002] High-temperature proton exchange membrane electrolysis (ET-PEMWE) raises the operating temperature of PEMWE to 100-200℃, effectively improving electrode reaction kinetics and reducing thermodynamic decomposition voltage, thus decreasing energy consumption and the amount of precious metal catalysts required. It represents a significant development direction for next-generation green hydrogen production technology. The core component of this technology is the membrane electrode assembly (MEA), which typically consists of a central proton exchange membrane and two flanking layers coated with anolyte (OER) and cathode (HER) catalysts, sometimes including a current collector or gas diffuser layer. The entire electrochemical reaction process and the transfer of protons, electrons, water, and gas are highly dependent on the structural integrity and functionality of the MEA. However, the low saturated vapor pressure of water vapor under high-temperature conditions leads to severe water loss in the MEA, increasing the internal resistance of the proton exchange membrane, causing dehydration and shrinkage of the catalyst layer, and potentially disrupting gas selective permeability (GTR). This results in a sharp increase in ohmic overpotential and concentration polarization, limiting the practical application of this technology.

[0003] Studies have shown that by increasing the feed pressure to achieve liquid water supply under high-temperature conditions, the membrane and catalyst layer can be kept fully hydrated, thereby significantly improving electrolysis performance. Therefore, high-temperature, high-pressure liquid water operation is considered a promising operating mode for ET-PEMWE.

[0004] Under these conditions, to obtain a membrane electrode with good electrolysis performance, on the one hand, the proton exchange membrane, one of the important components of the membrane electrode, must simultaneously possess high proton conductivity, good thermomechanical stability, and resistance to high-pressure liquid water erosion; on the other hand, the interface between the membrane and the catalyst layer must achieve low proton transport resistance.

[0005] In summary, the current research and development focus is on how to enable membrane electrodes to achieve high current density and high efficiency under high temperature and high pressure conditions, and to ensure stable and efficient operation. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance membrane electrode for water electrolysis, its preparation method, and its application. By designing the proton exchange membrane and the catalyst layer, an integrated interface structure is constructed by thermally crosslinking the membrane matrix and the ionomer. This helps to improve the continuity of the proton conduction channel and reduce the contact resistance of the membrane / catalyst layer interface, thereby enabling the membrane electrode to achieve high current density and efficient operation under high temperature and high pressure liquid water conditions.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A first aspect of the present invention provides a membrane electrode comprising a proton exchange membrane and a catalyst layer coated on both sides of the proton exchange membrane. The proton exchange membrane comprises a sulfonated polyethersulfone base membrane, a reinforcing layer covering the sulfonated polyethersulfone base membrane, and a sulfonated polyethersulfone top membrane covering the reinforcing layer. The reinforcing layer is an expanded polytetrafluoroethylene porous membrane. The catalyst layer contains sulfonated polyethersulfone.

[0009] Furthermore, the degree of sulfonation of the sulfonated polyether sulfone in the proton exchange membrane is 80-99%; The expanded polytetrafluoroethylene porous membrane has a porosity of 30-90% and an average pore size of 100-200 nm. The thickness of the sulfonated polyethersulfone base film is 10-50 μm, the thickness of the reinforcing layer is 3-20 μm, and the thickness of the sulfonated polyethersulfone top film is 10-50 μm.

[0010] Furthermore, the degree of sulfonation of the sulfonated polyether sulfone in the catalyst layer is 60-70%.

[0011] Furthermore, the thickness of the anode catalyst layer is 5-12 μm, and the thickness of the cathode catalyst layer is 3-8 μm.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned membrane electrode, comprising the following steps: S1. Dissolve sulfonated polyethersulfone in an alcohol solvent to prepare a casting solution. Pour the casting solution onto the substrate and dry it to form a sulfonated polyethersulfone substrate film. S2. Cover one side of the expanded polytetrafluoroethylene porous membrane wetted with alcohol solvent onto the sulfonated polyethersulfone base membrane obtained in step S1, and pour the casting solution obtained in step S1 onto the other side of the expanded polytetrafluoroethylene porous membrane. After drying, the SPES / PTFE composite primary membrane is obtained. S3. Prepare cathode catalyst slurry and anode catalyst slurry, and coat the cathode catalyst slurry and anode catalyst slurry onto both sides of the SPES / PTFE composite primary membrane to obtain the initial membrane electrode. S4. Perform a staged thermal crosslinking treatment on the initial membrane electrode obtained in step S4 to obtain the membrane electrode.

[0013] Further, in step S1, the mass concentration of sulfonated polyethersulfone in the casting solution is 2-20 wt%. In step S2, the drying temperature is 30-60℃ and the drying time is 12-15h; The second drying method is as follows: first, dry at 50-80℃ for 12-15 hours, and then dry at 70-120℃ for 12-15 hours.

[0014] Further, in step S3, the cathode catalyst slurry includes a Pt / C catalyst and a sulfonated polyethersulfone solution; The anode catalyst slurry includes an Ir Black catalyst sulfonated polyethersulfone solution; The mass concentration of the sulfonated polyethersulfone solution is 2-8%; In the anode catalyst slurry, the mass ratio of carbon to sulfonated polyether sulfone in the Pt / C catalyst is 1:0.5-0.8; In the anode catalyst slurry, the mass ratio of Ir Black catalyst to sulfonated polyether sulfone is 1:0.5-0.8; The cathode catalyst slurry is prepared by mixing Pt / C catalyst and sulfonated polyethersulfone solution, diluting with isopropanol, and ultrasonically dispersing for 60-80 minutes to prepare the cathode catalyst slurry. The anode catalyst slurry is prepared by mixing Ir Black catalyst and sulfonated polyethersulfone solution, diluting with isopropanol, and ultrasonically dispersing for 60-80 minutes to prepare the anode catalyst slurry. In the membrane electrode, the anolyte Ir Black loading is 0.1-1.5 mg / cm³. 2 The cathode Pt / C loading is 0.1-0.45 mg / cm³. 2 .

[0015] Further, in step S3, the cathode catalyst slurry and the anode catalyst slurry are both sprayed onto both sides of the SPES / PTFE composite primary film. The spraying parameters are: spraying temperature 40-60℃, flow rate 0.1-2mL / min, and spacing 5-10mm.

[0016] Furthermore, in step S4, the staged thermal crosslinking treatment is carried out in a nitrogen-filled environment, with an initial temperature of 120°C, and the temperature is gradually increased to 180-200°C in 4-8 stages, with each stage held for 2 hours.

[0017] A third aspect of the present invention provides an application of the above-mentioned membrane electrode in medium-high temperature PEM water electrolysis, wherein the medium-high temperature is 90-140°C.

[0018] The beneficial effects of this invention are as follows: 1. In the membrane electrode of the present invention, SPES with high sulfonation degree is first used as the base membrane and top membrane, which can significantly improve IEC and proton conduction performance and reduce cost. Then, pretreated expanded polytetrafluoroethylene (ePTFE) porous membrane is used as the intermediate reinforcement layer. On the one hand, it greatly enhances the mechanical strength and tear resistance of the entire membrane, effectively maintains excellent dimensional stability, and prevents membrane deformation, wrinkling or cracking, thereby improving the reliability and life of the battery. On the other hand, although porous, non-conductive ePTFE is embedded in the middle of the membrane, the SPES layers on both sides fill and cover the pores of the ePTFE. These SPES layers are continuous phases, providing efficient proton transport channels, thereby ensuring that protons are mainly conducted through sulfonic acid groups on the polymer chain. Secondly, regarding the catalyst layer, the same material as the proton exchange membrane is used in the catalyst layer slurry. Through thermal cross-linking, the SPES ionomer in the catalyst layer chemically bonds with the SPES on the top layer of the proton exchange membrane, forming a continuous sulfonic acid group network at the interface. This gives the membrane electrode excellent physical and chemical compatibility. Simultaneously, the molecular-level bonding between the two materials is tighter, forming a low-defect, continuous, and seamless transition interface. This significantly reduces the proton transport resistance at the catalyst layer / proton exchange membrane interface, making the transport of protons from the membrane surface to the catalyst active sites smoother and more efficient in a homogeneous interface. Furthermore, the transport path of the membrane electrode forms a relatively homogeneous sulfonated polyethersulfone matrix environment. This homogeneous system reduces interfacial stress or gradient changes caused by differences in swelling ratio, hydrophilicity / hydrophobicity, and conductivity between different polymers, thereby improving the overall structural stability and durability.

[0019] 2. In the membrane electrode of the present invention, both the proton exchange membrane and the catalyst layer are made of SPES. The degree of sulfonation of SPES can be adjusted, thereby controlling the water management of the membrane electrode. That is, the catalyst layer uses a medium degree of sulfonation ionomer with moderate water absorption. The pores formed are more conducive to the discharge of produced water or the transport of reaction water / generated bubbles, reducing the risk of flooding or local drying. Therefore, compared with high degree of sulfonation ionomer, medium degree of sulfonation has a smaller volume change when humidity changes, which helps to maintain the stability of the microstructure of the catalyst layer and reduce micropore blockage or cracking. That is, under the premise of ensuring low resistance and high degree of sulfonation in the membrane region, the medium degree of sulfonation in the ionomer region of the catalyst layer can bring about mass transfer optimization, structural stability and better water management capabilities.

[0020] 3. The proton exchange membrane in the membrane electrode of this invention uses SPES with a high degree of sulfonation. To address the problem of excessive swelling in such membranes, a combination of thermal crosslinking and a composite reinforcement layer is used to effectively control the membrane structure. On the one hand, thermal crosslinking introduces covalent bonds between molecular chains, thereby significantly improving the structural stability of the membrane. Since expanded polytetrafluoroethylene (ePTFE) porous membranes possess excellent mechanical strength, high-temperature resistance, and chemical inertness, their introduction as a reinforcement layer effectively limits the volume swelling of the membrane and improves dimensional stability. On the other hand, combining thermal crosslinking with the ePTFE porous membrane, the ePTFE porous membrane acts as a rigid framework. When SPES is filled into the interior, it physically supports and inhibits the swelling and deformation of the polymer, thereby improving tensile strength. Crosslinking allows polymer segments to be connected by covalent bonds to form a three-dimensional network structure, thereby inhibiting segment slippage and improving tensile strength and creep resistance. Therefore, the composite proton exchange membrane prepared by this invention can effectively inhibit excessive swelling of highly sulfonated SPES while maintaining high proton conductivity, achieving synergistic optimization of structural stability and electrochemical performance. Furthermore, the thermal crosslinking method proposed in this invention targets the synergistic integration of the proton exchange membrane and the catalyst layer. Specifically, after the catalyst layer is coated onto both sides of the SPES / PTFE composite primary membrane, a thermal crosslinking treatment is performed. This addresses the delamination phenomenon at the interface caused by swelling differences, mechanical stress, or electrochemical corrosion, which is common in traditional physical bonding or hot-pressing of the catalyst layer and proton exchange membrane. In this invention, the SPES on the membrane surface and the SPES ionomer in the catalyst layer are homogeneous materials, allowing the crosslinking reaction to penetrate both, transforming the interface from "adhesion" to "molecular-level fusion," significantly suppressing dry-wet cycling. The invention addresses two main issues: firstly, the failure of the catalyst layer under high humidity or high pressure due to delamination; secondly, the cross-linking of SPES ionomers in the catalyst layer forms a three-dimensional network, which fixes the ionomer chains and reduces the phenomenon of water flooding in the pores of the catalyst layer caused by excessive swelling under high humidity or shrinkage and cracking under low humidity; and thirdly, the cross-linking structure further enhances the mechanical strength of the ionomers, preventing catalyst particles from detaching from the carbon support or agglomerating under high pressure. Therefore, by combining the advantages of the above-mentioned thermal cross-linking and composite reinforcement layer, the present invention utilizes a synergistic integrated thermal cross-linking method between the catalyst layer and the proton exchange membrane to simultaneously optimize the structural stability of the catalyst layer and the membrane under high humidity and high pressure conditions.

[0021] 4. In the preparation method of the present invention, an alcohol solvent is used as the solvent, which has the dual characteristics of being able to dissolve highly sulfonated SPES and efficiently wet expanded polytetrafluoroethylene porous membrane. The alcohol solvent acts as a carrier, allowing the SPES solution to fully penetrate into the porous network of the expanded polytetrafluoroethylene porous membrane. The partially penetrated solvent can also locally dissolve the pre-deposited SPES, thereby promoting the mutual diffusion and entanglement of polymer chains at the interface. This achieves a tight wrapping and firm bonding between the SPES matrix and the fiber skeleton of the expanded polytetrafluoroethylene porous membrane, forming a dense "sandwich" composite structure, which effectively improves the interlayer bonding force.

[0022] 5. In the process of preparing the composite membrane, this invention addresses the low surface energy and strong hydrophobicity of expanded polytetrafluoroethylene (ePTFE) porous membranes by pre-wetting them with alcohol solvents. Compared to conventional polar solvent modification methods, this invention employs simple, mild, near-zero residue alcohol solvents that are highly compatible with the casting solution. Firstly, after pre-wetting with an alcohol solvent, the subsequent casting solution using an alcohol solvent as the solvent can more easily wet and cover the ePTFE porous membrane. This alcohol solvent acts as a "transition solvent" for the casting solution, promoting better "mixing" and contact between the two originally incompatible materials (SPES and ePTFE) at the interface, and penetrating into its porous structure, further strengthening the robust physical interlocking structure between the membrane layers. Secondly, using an alcohol solvent... The solvent wets the expanded PTFE porous membrane, effectively displacing and expelling air from the PTFE pores. This allows the casting solution to flow smoothly into and fill the liquid-occupied pores when poured onto the membrane, significantly reducing the possibility of gas entrainment. Consequently, the surface area of ​​the membrane wetted by the solvent is temporarily enhanced, facilitating more uniform spreading and leveling of the casting solution poured in step S4. This results in a smoother, less defective, and more uniform coating layer, preventing droplets from shrinking and agglomerating on hydrophobic surfaces.

[0023] 6. This invention employs a staged thermal crosslinking strategy, effectively resolving the contradiction between water absorption and swelling rate of PEM membranes in electrolysis applications. This strategy constructs a moderately stable crosslinking network, enabling the membrane to maintain a high water absorption rate to meet proton conduction requirements while effectively suppressing excessive dimensional expansion caused by excessive water absorption. Simultaneously, the resulting controllable swelling rate significantly reduces the risk of catalyst layer detachment due to repeated swelling and contraction of the membrane, and significantly enhances the membrane's mechanical strength and dimensional stability, fundamentally avoiding the pinhole effect caused by decreased mechanical properties. Attached Figure Description

[0024] Figure 1 The polarization curves of the membrane electrodes prepared in Example 3 and Comparative Example 1 are shown. Figure 2 Electrochemical impedance spectroscopy of the membrane electrodes prepared in Example 3 and Comparative Example 1. Detailed Implementation

[0025] 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.

[0026] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0027] Example 1 A method for preparing a membrane electrode specifically includes the following steps: (1) Place 10 g of polyethersulfone (PES) in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 5 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the acid on the surface. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyethersulfone (SPES) with a sulfonation degree of 80%. (2) Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 3 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the acid on the surface. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone with a sulfonation degree of 60%. Then, the 60% sulfonated polyether sulfone is mixed and dispersed with polypyrrolidone to form a SPES solution with a concentration of 5%. (3) Dissolve the SPES obtained in step (1) in n-propanol to prepare a 2wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 30℃ for 15 h to form a sulfonated polyethersulfone substrate film. (4) Purchase expanded polytetrafluoroethylene (ePTFE) porous membrane with a porosity of 30% and a pore size of 200 nm, and lay one side of the ePTFE porous membrane rinsed with ethanol on the sulfonated polyethersulfone substrate membrane obtained in step (3) to form a reinforcing layer. Then, cast the film solution obtained in step (1) on the other side of the ePTFE porous membrane to complete the second casting. After that, dry the composite membrane at 50 °C for 15 h, and then maintain it at 70 °C for 15 h to remove excess solution, and obtain the SPES / PTFE composite initial membrane. S5. Preparation of cathode catalyst slurry: Weigh 30 ml of 5% SPES solution with 60% sulfonation degree and 0.4 g of commercially available Pt / C (Pt loading of 70%) catalyst, add 30 mL of isopropanol for dilution, and then disperse by ultrasonication for 60 min. S6. Preparation of anode catalyst slurry: Weigh 60 ml of 5% SPES solution with 60% sulfonation degree and 0.6 g of commercially available IrBlack catalyst, add 60 mL of isopropanol for dilution, and then sonicate for 60 min to disperse. S7. The cathode catalyst slurry and the anode catalyst slurry are sprayed onto both sides of the SPES / PTFE composite primary membrane obtained in step (4) by electrostatic spraying to form the initial membrane electrode. In this step, the electrostatic spraying parameters are: spraying temperature 40℃, flow rate 0.1mL / min, and spacing 5mm. S8. The initial membrane electrode is subjected to a staged thermal crosslinking treatment in a nitrogen-filled oven, i.e., the treatment is sequentially maintained at 120℃ for 2 hours, 140℃ for 2 hours, 160℃ for 2 hours, and 180℃ for 2 hours. A platinum-plated titanium felt is used as the anode gas diffusion layer (20×25 mm), and carbon paper is used as the cathode diffusion layer (20×25 mm). Finally, the membrane electrode (MEA) is assembled between the anode and cathode gas diffusion layers, with each electrode having an effective area of ​​5 cm². 2 The cathode Pt / C loading is 0.3 mg / cm³. 2 The anolyte Ir Black loading was 1.0 mg / cm³. 2 The thickness of the sulfonated polyethersulfone base film is 10.9 μm, the thickness of the reinforcing layer is 3.2 μm, the thickness of the sulfonated polyethersulfone top film is 11 μm, the thickness of the cathode catalyst layer is 3.3 μm, and the thickness of the anode catalyst layer is 5.1 μm.

[0028] Example 2 A method for preparing a membrane electrode specifically includes the following steps: (1) Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 70 °C for 6 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the acid on the surface. Then the polymer is washed through a dialysis membrane until pH=7.3. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone (SPES) with a sulfonation degree of 88%. (2) 10 g of PES was placed in a vacuum drying oven and dried overnight. The dried PES and 100 mL of sulfuric acid were mechanically stirred at 80 °C for 4.2 h under a nitrogen atmosphere. After the reaction was completed, the polymer solution was poured into an ice-water mixture to obtain a white precipitate. The precipitate was washed with a large amount of ice water to remove the surface acid. Then the polymer was washed through a dialysis membrane until pH=7. Finally, the dialysis solution was dried to obtain sulfonated polyethersulfone with a sulfonation degree of 70%. Then, 65% of the sulfonated polyethersulfone was mixed and dispersed with isopropanol to form a 5% SPES solution. (3) Dissolve the SPES obtained in step (1) in n-propanol to prepare a 20wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 40 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 60℃ for 12 h to form a sulfonated polyethersulfone substrate film. (4) Purchase an ePTFE porous membrane with a porosity of 90% and a pore size of 100 nm. Spread one side of the ePTFE porous membrane, which has been rinsed with ethanol, on the sulfonated polyethersulfone substrate membrane obtained in step (3) to form a reinforcing layer. Then, cast the casting solution obtained in step (1) on the other side of the ePTFE porous membrane to complete the second casting. After that, dry the composite membrane at 80 °C for 12 h and then maintain it at 120 °C for 12 h to remove excess solution, and obtain the SPES / PTFE composite initial membrane. (5) Preparation of cathode catalyst slurry: Weigh 60 ml of 5% SPES solution with 70% sulfonation degree and 1.3 g of commercially available Pt / C (Pt loading of 70%) catalyst, add 30 mL of isopropanol for dilution, and then disperse by ultrasonication for 60 min; (6) Preparation of anode catalyst slurry: Weigh 120 ml of 5% SPES solution with 70% sulfonation degree and 2 g of commercially available IrBlack catalyst, add 50 mL of isopropanol for dilution, and then disperse by ultrasonication for 60 min; (7) The cathode catalyst slurry and the anode catalyst slurry are sprayed onto both sides of the SPES / PTFE composite primary membrane obtained in step (4) by electrostatic spraying to form the initial membrane electrode. In this step, the electrostatic spraying parameters are: spraying temperature 60℃, flow rate 2mL / min, and spacing 10mm. (8) The initial membrane electrode was subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, namely, thermal crosslinking treatment was carried out sequentially at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, and 200℃ for 2h. Platinum-plated titanium felt was used as the anode gas diffusion layer (20×25 mm), and carbon paper was used as the cathode diffusion layer (20×25 mm). Finally, the MEA was assembled between the anode and cathode gas diffusion layers, with each electrode having an effective area of ​​5 cm². 2 The cathode Pt / C loading is 0.3 mg / cm³. 2 The anolyte Ir Black loading was 1.0 mg / cm³. 2 The thickness of the sulfonated polyethersulfone base film is 48.1 μm, the thickness of the reinforcing layer is 18.6 μm, the thickness of the sulfonated polyethersulfone top film is 49.2 μm, the thickness of the cathode catalyst layer is 7.8 μm, and the thickness of the anode catalyst layer is 11.7 μm.

[0029] Example 3 A method for preparing a membrane electrode specifically includes the following steps: (1) Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 7 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the acid on the surface. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone (SPES) with a sulfonation degree of 95%. (2) Place 10 g of PES in a vacuum drying oven and dry overnight. The dried PES and 100 mL of sulfuric acid are mechanically stirred at 80 °C for 3 h under a nitrogen atmosphere. After the reaction is complete, the polymer solution is poured into an ice-water mixture to obtain a white precipitate. The precipitate is washed with a large amount of ice water to remove the acid on the surface. Then the polymer is washed through a dialysis membrane until pH=7. Finally, the dialysis solution is dried to obtain sulfonated polyether sulfone with a sulfonation degree of 60%. Then, 65% sulfonated polyether sulfone is mixed and dispersed with N,N-dimethylacetamide to form a SPES solution with a concentration of 5%. (3) Dissolve the SPES obtained in step S1 in n-propanol to prepare a 6wt% casting solution. Filter the casting solution with a 0.45μm needle filter and then degas for 30 min. Then pour the casting solution onto a glass plate and dry it in a vacuum oven at 50℃ for 12 h to form a sulfonated polyethersulfone substrate film. (4) Purchase an ePTFE porous membrane with a porosity of 60% and a pore size of 150nm. Spread one side of the ePTFE porous membrane, which has been rinsed with ethanol, on the sulfonated polyethersulfone substrate membrane obtained in step (3) to form a reinforcing layer. Then, cast the casting solution obtained in step (1) on the other side of the ePTFE porous membrane to complete the second casting. After that, dry the composite membrane at 50 °C for 12h and then maintain it at 70 °C for 12h to remove excess solution, and obtain the SPES / PTFE composite initial membrane. (5) Preparation of cathode catalyst slurry: Weigh 35 ml of 5% SPES solution with 65% sulfonation degree and 0.8 g of commercially available Pt / C (Pt loading of 70%) catalyst, add 56 mL of isopropanol for dilution, and then disperse by ultrasonication for 60 min; (6) Preparation of anode catalyst slurry: Weigh 70 ml of 5% SPES solution with 65% sulfonation degree and 1.2 g of commercially available IrBlack catalyst, add 100 mL of isopropanol for dilution, and then sonicate for 60 min to disperse; (7) The cathode catalyst slurry and the anode catalyst slurry are sprayed onto both sides of the SPES / PTFE composite primary membrane in step (3) by electrostatic spraying to form the initial membrane electrode. In this step, the electrostatic spraying parameters are: spraying temperature 50℃, flow rate 1.5mL / min, and spacing 8mm. S8. The initial membrane electrode is subjected to a staged thermal crosslinking treatment in a nitrogen-filled oven, i.e., the thermal crosslinking treatment is maintained sequentially at 120℃ for 2 hours, 140℃ for 2 hours, 160℃ for 2 hours, 180℃ for 2 hours, and 200℃ for 2 hours. A platinum-plated titanium felt is used as the anode gas diffusion layer (20×25 mm), and carbon paper is used as the cathode diffusion layer (20×25 mm). Finally, the MEA is assembled between the anode and cathode gas diffusion layers, with each electrode having an effective area of ​​5 cm². 2 The cathode Pt / C loading is 0.3 mg / cm³. 2 The anolyte Ir Black loading was 1.0 mg / cm³. 2 The thickness of the sulfonated polyethersulfone base film is 30.8 μm, the thickness of the reinforcing layer is 11.3 μm, the thickness of the sulfonated polyethersulfone top film is 32.5 μm, the thickness of the cathode catalyst layer is 6.6 μm, and the thickness of the anode catalyst layer is 8.9 μm.

[0030] Comparative Example 1 A method for preparing a membrane electrode specifically includes the following steps: S1. Use commercial Nafion-115 membrane as a proton exchange membrane; S2. Preparation of cathode catalyst slurry: Weigh 35 ml of Nafion-115 solution (5 wt%) and 0.8 g of commercially available Pt / C (Pt loading of 70%) catalyst, add 56 mL of isopropanol for dilution, and then disperse by ultrasonication for 60 min. S3. Preparation of anode catalyst slurry: Weigh 70 ml of Nafion-115 solution (5 wt%) and 1.2 g of commercially available IrBlack catalyst, add 100 mL of isopropanol for dilution, and then sonicate for 60 min to disperse. S4. The cathode catalyst slurry and the anode catalyst slurry are respectively sprayed onto both sides of the commercial Nafion-115 membrane in step S1 by electrostatic spraying to form the initial membrane electrode. In this step, the electrostatic spraying parameters are: spraying temperature 50℃, flow rate 1.5mL / min, and spacing 8mm. S5. The initial membrane electrode is subjected to staged thermal crosslinking treatment in a nitrogen-filled oven, i.e., thermal crosslinking treatment is carried out sequentially at 120℃ for 2h, 140℃ for 2h, 160℃ for 2h, 180℃ for 2h, and 200℃ for 2h. Platinum-plated titanium felt is used as the anode gas diffusion layer (20×25 mm), and carbon paper is used as the cathode diffusion layer (20×25 mm). Finally, the MEA is assembled between the anode and cathode gas diffusion layers, with each electrode having an effective area of ​​5 cm². 2 The cathode Pt / C loading is 0.3 mg / cm³. 2 The anolyte Ir Black loading was 1.0 mg / cm³. 2The thickness of the sulfonated polyethersulfone base film is 31.2 μm, the thickness of the reinforcing layer is 11.6 μm, the thickness of the sulfonated polyethersulfone top film is 31.9 μm, the thickness of the cathode catalyst layer is 6.3 μm, and the thickness of the P anode catalyst layer is 9.1 μm.

[0031] Comparative Example 2 A method for preparing a membrane electrode is adopted, which is the same as the preparation method in Example 3. The difference is that the staged thermal crosslinking is not used, and the electrode is directly dried. That is, step (8) is changed to: the initial membrane electrode is dried at 180°C for 10 hours in a nitrogen-filled oven. The other conditions are the same as in Example 3.

[0032] Comparative Example 3 A method for preparing a membrane electrode is adopted, which is the same as the preparation method in Example 3, except that step (8) is changed to: the initial membrane electrode is subjected to a staged thermal crosslinking treatment in a nitrogen-filled oven, that is, the thermal crosslinking treatment is maintained at 120°C for 2h, 140°C for 2h, 160°C for 2h, 180°C for 2h, 200°C for 2h, 220°C for 2h, and 240°C for 2h in sequence. The remaining conditions are the same as in Example 3.

[0033] Comparative Example 4 A method for preparing a membrane electrode is provided, which uses the same preparation method as in Example 3, except that an ePTFE porous membrane is not used: that is, step (4) in Example 3 is omitted. The remaining conditions are the same as in Example 3.

[0034] Test Example 1 To ensure that water remains liquid above 100 °C, all tests were conducted in a high-pressure water electrolysis test apparatus, with the test pressure maintained at 200 kPa. The water electrolysis performance of the membrane electrodes prepared in Example 3 and Comparative Example 1 was characterized using a high-pressure electrolysis test bench, with the test pressure maintained at 200 kPa. The same pressure was maintained on both the anode inlet and cathode sides. Electrolysis tests were conducted at 110 °C with an inlet water flow rate of 45 mL / min. -1 The test results are as follows Figure 1 As shown.

[0035] Figure 1 The electrolytic performance of the membrane electrode prepared in Example 3 was compared with that of the commercial Nafion-115 membrane electrode in Comparative Example 1 under high pressure liquid water conditions at 110 °C. Throughout the entire test current density range, the membrane electrode of Example 3 exhibited a lower operating voltage: at 110 °C and 1.9 V, the maximum current density of the membrane electrode of Example 3 reached 7.5 A / cm². 2 Under the same conditions, the current density of the Nafion-115 film electrode is only 3.3 A / cm². 2Furthermore, the membrane electrode of Example 3 still exhibits a significant advantage in the low current density region. Since both membrane electrodes use the same type and loading of catalyst system, this difference is difficult to attribute to changes in intrinsic catalyst activity.

[0036] Further analysis of its impedance characteristics was performed using electrochemical impedance spectroscopy (EIS). Figure 2 The Nyquist curves show that the real intercept of the membrane electrode in Example 3 is significantly smaller than that of the Nafion-115 membrane electrode in the high-frequency region, with an ohmic impedance (HFR) of approximately 0.040 Ω, compared to approximately 0.10 Ω for the Nafion-115 membrane electrode, the former being only about 40% of the latter. In contrast, the diameters of the first semicircles of the two membrane electrodes are similar, indicating that their charge transfer-related impedances are not significantly different. These results suggest that the performance improvement of the membrane electrode in Example 3 mainly stems from a significant reduction in ohmic polarization, while no significant change was observed in the charge transfer process. This advantage can be attributed to the integrated interface structure constructed by the co-thermal crosslinking of the membrane matrix and the ionomer, which helps to improve the continuity of the proton conduction channel and reduce the interfacial contact resistance of the membrane / catalyst layer, thereby reducing the electrolysis voltage across the entire current density range.

[0037] Test Example 2 To simulate an electrolysis environment, the membrane electrodes of Examples 1-3 and Comparative Examples 2-4 were placed in a high-pressure reactor and maintained at 110°C for 12 hours. The test results are shown in Table 1.

[0038] Test Example 3 Tensile strength tests were conducted on Examples 1-3 and Comparative Examples 2-4. The tensile strength and elongation at break of the membrane electrode were characterized using a universal testing machine (WDW-100) at a tensile rate of 2 mm / min. The test results are recorded in Table 1.

[0039] Table 1

[0040] As shown in Table 1, Comparative Example 2, without staged thermal crosslinking, exhibits free swelling of the molecular chains and lacks interfacial reinforcement, resulting in low strength. Comparative Example 3 shows excessive thermal crosslinking, with no significant changes in water absorption and swelling before and after PTFE reinforcement. Comparative Example 4, lacking the rigid support of the ePTFE porous membrane, exhibits high swelling and weak strength. The data in Table 1 indicate that the significant improvements in Examples 1-3 are mainly attributed to the strong physical constraint effect of the ePTFE network. Its hydrophobic, high-strength microfiber framework effectively limits the expansion of the hydrophilic SPES matrix during hydration, thereby significantly improving the dimensional stability of the composite membrane. This confirms that introducing an ePTFE porous membrane reinforcement layer is an effective strategy to suppress excessive swelling of high-sulfonation SPES.

[0041] The above studies demonstrate that the "integrated" thermal crosslinking strategy proposed in this invention, which co-crosslinks the ionomer layer and the membrane matrix, significantly improves the bulk proton conductivity and reduces the interfacial contact resistance. The membrane electrode of this invention has outstanding application potential in the field of high-temperature PEM water electrolysis.

[0042] 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 membrane electrode, comprising a proton exchange membrane and a catalytic layer coated on both sides of the proton exchange membrane, characterized in that: The proton exchange membrane includes a sulfonated polyethersulfone base membrane, a reinforcing layer covering the sulfonated polyethersulfone base membrane, and a sulfonated polyethersulfone top membrane covering the reinforcing layer; the reinforcing layer is an expanded polytetrafluoroethylene porous membrane; and the catalyst layer contains sulfonated polyethersulfone.

2. The membrane electrode according to claim 1, characterized in that: The degree of sulfonation of the sulfonated polyether sulfone in the proton exchange membrane is 80-99%; The expanded polytetrafluoroethylene porous membrane has a porosity of 30-90% and an average pore size of 100-200 nm. The thickness of the sulfonated polyethersulfone base film is 10-50 μm, the thickness of the reinforcing layer is 3-20 μm, and the thickness of the sulfonated polyethersulfone top film is 10-50 μm.

3. The membrane electrode according to claim 1, characterized in that: The sulfonated polyether sulfones in the catalyst layer all have a sulfonation degree of 60-70%.

4. The membrane electrode according to claim 1, characterized in that: The thickness of the anode catalyst layer is 5-12 μm, and the thickness of the cathode catalyst layer is 3-8 μm.

5. A method for preparing a membrane electrode as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve sulfonated polyethersulfone in an alcohol solvent to prepare a casting solution. Pour the casting solution onto the substrate and dry it to form a sulfonated polyethersulfone substrate film. S2. Cover one side of the expanded polytetrafluoroethylene porous membrane wetted with alcohol solvent onto the sulfonated polyethersulfone base membrane obtained in step S1, and pour the casting solution obtained in step S1 onto the other side of the expanded polytetrafluoroethylene porous membrane. After drying, the SPES / PTFE composite primary membrane is obtained. S3. Prepare cathode catalyst slurry and anode catalyst slurry, and coat the cathode catalyst slurry and anode catalyst slurry onto both sides of the SPES / PTFE composite primary membrane to obtain the initial membrane electrode. S4. Perform a staged thermal crosslinking treatment on the initial membrane electrode obtained in step S4 to obtain the membrane electrode.

6. The preparation method according to claim 5, characterized in that: In step S1, the mass concentration of sulfonated polyethersulfone in the casting solution is 2-20 wt%. In step S2, the drying temperature is 30-60℃ and the drying time is 12-15h; The second drying method is as follows: first, dry at 50-80℃ for 12-15 hours, and then dry at 70-120℃ for 12-15 hours.

7. The preparation method according to claim 5, characterized in that: In step S3, the cathode catalyst slurry includes a Pt / C catalyst and a sulfonated polyethersulfone solution; The anode catalyst slurry includes an Ir Black catalyst sulfonated polyethersulfone solution; The mass concentration of the sulfonated polyethersulfone solution is 2-8%; In the anode catalyst slurry, the mass ratio of carbon to sulfonated polyether sulfone in the Pt / C catalyst is 1:0.5-0.8; In the anode catalyst slurry, the mass ratio of Ir Black catalyst to sulfonated polyether sulfone is 1:0.5-0.

8.

8. The preparation method according to claim 5, characterized in that: In step S3, the cathode catalyst slurry and the anode catalyst slurry are both sprayed onto both sides of the SPES / PTFE composite primary film. The spraying parameters are: spraying temperature 40-60℃, flow rate 0.1-2mL / min, and spacing 5-10mm.

9. The preparation method according to claim 5, characterized in that: In step S4, the staged thermal crosslinking treatment is carried out in a nitrogen-filled environment with an initial temperature of 120°C. The temperature is gradually increased to 180-200°C in 4-8 stages, and each stage is held for 2 hours.

10. An application of a membrane electrode prepared by any one of claims 1-4 or by any one of claims 5-9, characterized in that: Application in medium-high temperature PEM water electrolysis, wherein the medium-high temperature is 90-140℃.

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