Reinforced composite membrane for hydrogen fuel cell and manufacturing method therefor

Abstract

The present invention relates to a reinforced composite membrane for a hydrogen fuel cell and a manufacturing method therefor. One embodiment provides a technique for controlling the thickness of a reinforced composite membrane for a hydrogen fuel cell, manufactured by adjusting the thickness of a PTFE membrane and the coating thickness of an ionomer. The manufacturing method for a reinforced composite film for a hydrogen fuel cell, according to the present invention, comprises the steps of: preparing a polytetrafluoroethylene (PTFE) membrane; coating both sides of the PTFE membrane with an ionomer to form an ionomer-coated layer; and drying the coated PTFE membrane.

Description

Reinforced composite membrane for hydrogen fuel cells and method for manufacturing the same

[0001] The present invention relates to a reinforced composite membrane for a hydrogen fuel cell and a method for manufacturing the same. In one embodiment, a technique for controlling the thickness of a reinforced composite membrane for a hydrogen fuel cell manufactured by controlling the thickness of a PTFE film and the coating thickness of an ionomer is provided.

[0002] The present invention is the result of the Local Government-University Cooperation-based Regional Innovation Project (2021RIS-004), conducted with funding from the Ministry of Education and support from the National Research Foundation of Korea in 2024; the 2023 SME Tech-Bridge Utilization Commercialization Technology Development Project (00218647), conducted with funding from the Ministry of SMEs and Startups and support from the Korea Technology Information Promotion Agency for SMEs in 2023; and the National Core Materials Research Group (Platform Type) (2023M3H4A3091698), conducted with funding from the Ministry of Science and ICT and support from the National Research Foundation of Korea in 2023.

[0003] Hydrogen fuel cells are attracting attention as next-generation energy systems due to their high energy efficiency and low environmental pollution, serving as an eco-friendly energy source. In particular, one of the critical factors significantly determining the performance and durability of hydrogen fuel cells is the Polymer Electrolyte Membrane (PEM) used in the Membrane Electrode Assembly (MEA). This PEM facilitates the movement of hydrogen ions to ensure smooth electrochemical reactions within the fuel cell, and requires electrical conductivity, durability, and chemical stability. Reinforced composite membranes are a technology developed to enhance the mechanical strength of the electrolyte membrane and increase resistance to mechanical damage or thermal stress occurring during fuel cell operation.

[0004] Polymer electrolyte membranes manufactured by conventional methods have low mechanical strength, which can lead to damage or tearing during prolonged use. Furthermore, since hydrogen fuel cells operate at high temperatures, electrolyte membranes lacking thermal stability degrade during long-term operation, resulting in increased hydrogen permeability and performance degradation. Due to these issues, there is a growing need to improve the durability and enhance the thermal stability of electrolyte membranes.

[0005] Related prior art includes Korean Published Patent Application No. 10-2014-0085885.

[0006] The present invention aims to provide a reinforced composite membrane for a hydrogen fuel cell capable of improving the current density and maximum power density of the fuel cell, and a method for manufacturing the same.

[0007] In addition, the present invention allows for the easy manufacture of a reinforced composite membrane having uniform thickness and performance.

[0008] In addition, the reinforced composite membrane of the present invention has a reduced permeability density for gases such as hydrogen.

[0009] In addition, the reinforced composite membrane of the present invention has improved durability and an increased lifespan.

[0010] A method for manufacturing a reinforced composite membrane for a hydrogen fuel cell according to an embodiment of the present invention comprises the steps of: preparing a PTFE (Polytetrafluoroethylene) membrane; coating both sides of the PTFE membrane with an ionomer to form an ionomer coating layer; and drying the coated PTFE membrane.

[0011] In the step of preparing the above PTFE film, the thickness of the above PTFE film may be 19 to 21 µm.

[0012] The step of forming the ionomer coating layer may be such that the thickness of the ionomer coating layer is 40 to 55 µm.

[0013] The drying step may include a first drying step for removing the solvent of the ionomer and a second drying step for shrinking the PTFE film.

[0014] The first drying step may be performed at less than 100℃, and the second drying step may be performed at 100℃ or higher.

[0015] The thickness of the reinforced composite membrane for hydrogen fuel cells manufactured above may be 9 to 11 µm.

[0016] Among the reinforced composite membranes for hydrogen fuel cells manufactured above, the thickness of the PTFE membrane may be 5 to 7 µm, and the thickness of the ionomer coating layer may be 1.5 to 2.5 µm.

[0017]

[0018] A reinforced composite membrane for a hydrogen fuel cell according to an embodiment of the present invention comprises a PTFE membrane and an ionomer coating layer disposed on each side of the PTFE membrane, and is manufactured by the method described above.

[0019] The reinforced composite membrane for a hydrogen fuel cell and the method for manufacturing the same according to an embodiment of the present invention can improve the current density and maximum output density of the fuel cell.

[0020] In addition, the present invention allows for the easy manufacture of a reinforced composite membrane having uniform thickness and performance.

[0021] In addition, the reinforced composite membrane of the present invention has a reduced permeability density for gases such as hydrogen.

[0022] In addition, the reinforced composite membrane of the present invention has improved durability and an increased lifespan.

[0023] FIGS. 1 and 2 are a flowchart and a conceptual diagram of a method for manufacturing a reinforced composite membrane for a hydrogen fuel cell according to an embodiment of the present invention.

[0024] Figures 3 to 5 are SEM cross-sectional views of ePTFE films with thicknesses of 10µm, 20µm, and 30µm, respectively.

[0025] Figure 6(a) is a reinforced composite membrane made of an ePTFE film with a thickness of 10 µm, and (a) is a reinforced composite membrane made of an ePTFE film with a thickness of 30 µm.

[0026] FIGS. 7 to 9 are SEM cross-sectional views of reinforced composite membranes fabricated using ePTFE membranes with thicknesses of 10 µm and 20 µm, respectively. (a) is a cross-sectional view of the ePTFE membrane fabricated to have a thickness of 10 µm after fabrication, and (b) is a cross-sectional view of the ePTFE membrane fabricated to have a thickness of 15 µm after fabrication.

[0027] Figure 10 shows the voltage and power density according to current density of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 10 µm after fabrication.

[0028] Figure 11 shows the voltage and power density according to current density of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 15 µm after fabrication.

[0029] Figure 12 shows the hydrogen gas permeability density of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 10 µm after fabrication.

[0030] Figure 13 shows the hydrogen gas permeability density of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 15 µm after fabrication.

[0031] Figure 14 shows the measured OCV according to the operating time of a hydrogen fuel cell.

[0032] Figure 15 shows the hydrogen permeation current density measured over the operating time of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 10 µm after fabrication.

[0033] Figure 16 shows the hydrogen permeation current density measured over time of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 15 µm after fabrication.

[0034] Figure 17 shows the voltage and power density according to current density before operation and after 100 hours of operation of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 10 µm.

[0035] Figure 18 shows the voltage and power density according to current density before operation and after 100 hours of operation of a hydrogen fuel cell fabricated using a reinforced composite membrane with an ePTFE film thickness of 15 µm.

[0036] Hereinafter, preferred embodiments of the present invention are described as follows with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0037]

[0038] A method for manufacturing a reinforced composite membrane for a hydrogen fuel cell according to an embodiment of the present invention comprises the steps of: preparing a PTFE (Polytetrafluoroethylene) membrane; coating both sides of the PTFE membrane with an ionomer to form an ionomer coating layer; and drying the coated PTFE membrane. A reinforced composite membrane for a hydrogen fuel cell according to an embodiment of the present invention comprises a PTFE membrane and ionomer coating layers disposed on each side of the PTFE membrane, and is manufactured by the method described above.

[0039]

[0040] In the step of preparing the above PTFE (Polytetrafluoroethylene) membrane, the PTFE membrane is a membrane or layer made of PTFE that possesses excellent chemical resistance and heat resistance, thereby maintaining membrane stability even in strongly acidic or alkaline environments during the operation of the fuel cell, providing mechanical strength to the reinforced composite membrane, and, since it does not have ion conductivity, does not hinder ion conduction in the fuel cell, and combines with other materials acting as electrolytes to maintain the functionality of the composite membrane.

[0041] In one embodiment, the PTFE film may be an ePTFE (Expanded Polytetrafluoroethylene) film. ePTFE is a porous material made by expanding PTFE. ePTFE has a very fine porous structure, which is advantageous for ionomer impregnation, and possesses excellent chemical resistance, mechanical strength, and lightweight properties.

[0042] In this step, the thickness of the PTFE film may be 19 to 21 µm. If the thickness of the PTFE film is too small, problems such as tearing of the film may occur during the manufacturing process of the reinforced composite film, reduced durability, and gas permeability may occur. Conversely, if the thickness of the PTFE film is too large, flexibility may decrease, increasing the likelihood of defects occurring during the manufacturing process and hindering ion transfer through the electrolyte.

[0043]

[0044] Next, a step of forming an ionomer coating layer is performed. An ionomer is a polymeric material containing ionic groups (mainly anionic or cationic) in a polymer chain and possesses electrical properties. These ionic groups are immobilized on the polymer chain and provide an environment that allows ions to move easily. More specifically, the ionomer enables ions such as hydrogen ions (H⁺) to move through a membrane in an electrochemical device. In one embodiment, the ionomer may be any one of Nafion, Flemion, Aquivion, 3MTMPFSA ionomer, and Aciplex.

[0045] This step can be performed using various types of coaters, such as slot die coaters. Referring to FIG. 2, an ionomer is spread and applied to a uniform thickness on the working surface of the coater, and the PTFE film is placed thereon. Next, by using the coater to apply an ionomer to a uniform thickness on the upper surface of the PTFE film, the ionomer can be coated and impregnated on both sides of the PTFE film.

[0046] In this step, the thickness of the ionomer coated on both sides of the PTFE film may be 40 to 55 µm. If the ionomer is coated too thinly, the thickness of the manufactured reinforced composite film becomes thin, resulting in poor electrical properties, and problems such as tearing may occur when separating from the base film (a film covering the working surface to protect the working surface of the coater) during the manufacturing process. Conversely, if the thickness of the ionomer is too thick, characteristics such as current density and lifespan deteriorate.

[0047]

[0048] The step of drying the coated PTFE film is a step of removing the solvent of the ionomer and shrinking the PTFE film. This step can be performed by heating to a constant temperature. In this step, the thickness of the PTFE film can be shrunk to 5 to 7 µm, the thickness of the ionomer coating layer can be shrunk to 1.5 to 2.5 µm, and the total thickness of the reinforced composite film can be 9 to 11 µm. Through this, characteristics as a hydrogen fuel cell, such as current density and OCV, can be optimized.

[0049] This step may include a first drying step for removing the solvent of the ionomer and a second drying step for shrinking the PTFE film.

[0050] The first drying step described above can be performed at a temperature below 100°C, more specifically at 75 to 85°C. The first drying step is a step that gradually removes the solvent to ensure uniform physical and electrical properties throughout. Ionomers generally contain solvent, and if evaporated rapidly at too high a temperature, bubbles or cracks may form in the coating layer. Additionally, since ionomers have a low glass transition temperature (Tg), drying at this temperature allows the material to remain in a glass state while the solvent gradually evaporates and interlayer bonding is slowly formed. If the temperature of the first drying step is too low, the solvent does not evaporate properly, resulting in partially different properties. Conversely, if the temperature is too high, as previously explained, bubbles or cracks may form, and the solvent does not evaporate evenly, resulting in partially different properties.

[0051]

[0052] The second drying step described above can be performed at 100°C or higher, preferably at 145 to 155°C. This step is a step for curing the ionomer and shrinking the PTFE film. Therefore, it is necessary to have a sufficient temperature for the ionomer to undergo thermal curing and stabilization. If the temperature is too low, the ionomer curing may be insufficient, and the PTFE film may not shrink sufficiently, resulting in poor electrical properties and durability. Conversely, if the temperature is too high, problems such as cracking may occur.

[0053]

[0054] In one embodiment, a step of treating the dried reinforced composite membrane with an acidic solution may be further performed after the drying step. The treatment may be washing and pretreatment, wherein the washing is performed using hydrogen peroxide (H2O2) and the pretreatment is performed using sulfuric acid (H2SO4).

[0055]

[0056] Example: Preparation of a reinforced composite membrane

[0057] Example 1 (PEM-10, ePTFE-10): SN10 from Commtech Co., Ltd. (thickness 10.07 µm, pore size 0.415 µm, porosity 43.79%, see Fig. 3) was prepared as the ePTFE membrane, and D2021 from Chemours was prepared as the ionomer. The ionomer was applied to the working surface of a bar coater to a thickness of 50 µm, and the ePTFE membrane was placed on top of it. Next, the ionomer was applied to the upper surface of the ePTFE membrane to a thickness of 50 µm. The ionomer-coated ePTFE was placed in an oven and dried at 80°C for 8 hours, followed by annealing at 150°C for 2 hours. The annealed membrane was washed with a hydrogen peroxide solution and then treated with a sulfuric acid solution. A reinforced composite membrane was manufactured through this process.

[0058]

[0059] Example 2 (PEM-10, ePTFE-20): The ePTFE film was prepared in the same manner as Example 1, except that SN20 from Commtech Co., Ltd. (thickness 20.24 µm, pore size 0.422 µm, porosity 43.54%, see Fig. 4) was used, and the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 45 µm.

[0060]

[0061] Comparative Example 1 (PEM-5, ePTFE-10): Prepared in the same manner as Example 1, except that the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 60 µm each. During the manufacturing process, the coated ePTFE film was damaged while separating it from the coater, so no further experiments were conducted.

[0062]

[0063] Comparative Example 2 (PEM-10, ePTFE-30): This example was prepared in the same manner as Example 1, except that the ePTFE film used was SN30 from Commtech Co., Ltd. (thickness 30.16 µm, pore size 0.408 µm, porosity 44.19%, see Fig. 5), and the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 40 µm. As shown in Fig. 6, in the case of Example 1, the surface of the reinforced composite film was formed smoothly and uniformly, whereas in Comparative Example 2, the surface was rough and non-uniform. No further experiments were conducted on Comparative Example 2.

[0064]

[0065] Comparative Example 3 (PEM-15, ePTFE-0): A film was made with only ionomer without using an ePTFE film to a thickness of 90 µm, and then processes such as drying, annealing, and washing were performed under the same conditions as in Example 1.

[0066]

[0067] Comparative Example 4 (PEM-15, ePTFE-10): Prepared in the same manner as Example 1, except that the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 85 µm each.

[0068]

[0069] Comparative Example 5 (PEM-15, ePTFE-20): It was prepared in the same manner as Comparative Example 4, except that SN20 from Commtech Co., Ltd. (thickness 20.24µm, pore size 0.422µm, porosity 43.54%) was used as the ePTFE film, and the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 80µm.

[0070]

[0071] Comparative Example 6 (PEM-15, ePTFE-30): This example was prepared in the same manner as Comparative Example 4, except that the ePTFE film used was the SN30 product from Commtech Co., Ltd. (thickness 30.16 µm, pore size 0.408 µm, porosity 44.19%), and the thickness of the ionomer applied to the working surface of the coater and the ePTFE film was 75 µm. Similar to Comparative Example 2, the surface of Comparative Example 6 was rough and non-uniform. No additional experiments were conducted on Comparative Example 2.

[0072]

[0073] Experimental Example: Cross-sectional analysis of a reinforced composite membrane

[0074] The reinforced composite membranes of the examples and comparative examples were cut, and their cross-sections were photographed using SEM. Figure 7 (a) shows Comparative Example 1, (b) shows Comparative Example 3, Figure 8 (a) shows Example 1, (b) shows Comparative Example 4, Figure 9 (a) shows Example 2, and (b) shows Comparative Example 5.

[0075]

[0076] Preparation Example: Preparation of a hydrogen fuel cell

[0077] Catalytic electrodes were placed on the top and bottom of the reinforced composite membranes of Examples 1 and 2 and Comparative Examples 1, 4, 5, and 6, and an MEA was prepared by pressurizing at a pressure of 15 MPa at a temperature of 140°C for 5 minutes. A hydrogen fuel cell was prepared by placing the MEA inside a unit cell and tightening it at a pressure of 80 lb·in. The experiment was conducted under conditions of 70°C and 100% RH while injecting hydrogen and air into the hydrogen fuel cell. In addition, the result graphs were classified and displayed as ePTFE-0, ePTFE-10, and ePTFE-20 according to the initial ePTFE thickness, and as PEM-10 and PEM-15 according to the final reinforced composite membrane thickness.

[0078]

[0079] Experimental Example: Open-circuit voltage (OCV) measurement

[0080] The previously manufactured hydrogen fuel cells were connected to a circuit, and the voltage was measured using a voltmeter. Figure 10 shows the measurement results of hydrogen fuel cells manufactured with the reinforced composite membranes of Comparative Example 1, Example 1, and 2, and Figure 11 shows the measurement results of hydrogen fuel cells manufactured with the reinforced composite membranes of Comparative Examples 3 to 5. In both Figures 10 and 11, it can be seen that the thicker the ePTFE film, the better the OCV characteristics.

[0081]

[0082] Experimental Example: Measurement of hydrogen gas permeability density

[0083] Current density and voltage were measured while injecting hydrogen gas into the previously manufactured hydrogen fuel cells. Figure 12 shows the measurement results of hydrogen fuel cells manufactured with the reinforced composite membranes of Comparative Example 1, Example 1, and 2, and Figure 13 shows the measurement results of hydrogen fuel cells manufactured with the reinforced composite membranes of Comparative Examples 3 to 5. Referring to Figures 12 and 13, it can be seen that the thicker the ePTFE membrane, the better the hydrogen permeation inhibition effect.

[0084]

[0085] Experimental Example: Analysis of OCV Characteristics According to Operating Time

[0086] The OCV of hydrogen fuel cells manufactured using the reinforced composite membranes of Example 2 and Comparative Example 5 was measured while operating for 100 hours, and the results are shown in FIG. 14. Referring to FIG. 14, it can be seen that the OCV of Example 2 remains constant, while the OCV of Comparative Example 5 decreases after 75 hours. Therefore, it can be seen that a reinforced composite membrane with a thickness of 10 µm is superior.

[0087]

[0088] Experimental Example: Measurement of current density according to operating time

[0089] The voltage and power density according to current density were measured while operating hydrogen fuel cells manufactured using the reinforced composite membranes of Example 2 and Comparative Example 5 for 100 hours. Figure 15 shows the results of Example 2, and Figure 16 shows the results of Comparative Example 5. Referring to Figures 15 and 16, it can be seen that Example 2 does not show significant changes over time, whereas Comparative Example 5 shows a rapid change after 75 hours.

[0090]

[0091] Experimental Example: Analysis of Voltage and Current Density Characteristics Before and After Operation

[0092] The voltage and current density characteristics of hydrogen fuel cells manufactured using the reinforced composite membranes of Example 2 and Comparative Example 5 were analyzed before operation and after 100 hours of operation. Figure 17 shows the measurement results of Example 2, and Figure 18 shows the measurement results of Comparative Example 5. Referring to Figures 17 and 18, it can be seen that Example 2 does not show a significant difference before and after operation, whereas Comparative Example 5 shows poor electrical characteristics after operation.

[0093]

[0094] The present invention is not limited by the embodiments described above and the attached drawings, but is intended to be limited by the appended claims. Accordingly, various substitutions, modifications, and changes may be made by those skilled in the art within the scope of the technical concept of the present invention as described in the claims, without departing from the technical spirit of the invention, and such are also to be considered to fall within the scope of the present invention.

[0095]

[0096]

Claims

1. Step of preparing a PTFE (Polytetrafluoroethylene) membrane; A step of forming an ionomer coating layer by coating both sides of the above PTFE film with an ionomer; and A step comprising drying the above-mentioned coated PTFE film, Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

2. In Paragraph 1, In the step of preparing the above PTFE film, the thickness of the above PTFE film is 19 to 21 µm, Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

3. In Paragraph 1, The step of forming the ionomer coating layer is such that the thickness of the ionomer coating layer is 40 to 55 µm. Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

4. In Paragraph 1, The drying step comprises a first drying step for removing the solvent of the ionomer and a second drying step for shrinking the PTFE film. Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

5. In Paragraph 4, The first drying step is performed at less than 100℃, and the second drying step is performed at 100℃ or higher. Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

6. In Paragraph 1, The thickness of the reinforced composite membrane for a hydrogen fuel cell manufactured above is 9 to 11 µm, Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

7. In Paragraph 1, Among the reinforced composite membranes for hydrogen fuel cells manufactured above, the thickness of the PTFE membrane is 5 to 7 µm and the thickness of the ionomer coating layer is 1.5 to 2.5 µm, Method for manufacturing a reinforced composite membrane for a hydrogen fuel cell.

8. Includes a PTFE film and an ionomer coating layer disposed on each side of the PTFE film, and Manufactured by the method of paragraph 1, Reinforced composite membrane for hydrogen fuel cells.

9. In Paragraph 8, The thickness is 9 to 11 µm, Reinforced composite membrane for hydrogen fuel cells.

10. In Paragraph 8, The thickness of the PTFE film is 5 to 7 µm, and the thickness of the ionomer coating layer is 1.5 to 2.5 µm, Reinforced composite membrane for hydrogen fuel cells.

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