Reinforced composite polymer electrolyte membrane with improved thermal and dimensional stability

Abstract

The present invention relates to a reinforced composite polymer electrolyte membrane having assured mechanical, structural, and thermal stability.

Description

Reinforced composite polymer electrolyte membrane with improved thermal and dimensional stability

[0001] The present invention relates to a reinforced composite polymer electrolyte membrane that ensures mechanical, structural, and thermal stability. The polymer electrolyte membrane according to the present invention can be applied, for example, to hydrogen fuel cells or water electrolysis systems, and can additionally be utilized in energy devices or components such as flow batteries (Redox flow batteries) and reverse electrodialysis (RED).

[0002] A polymer electrolyte membrane is a solid-state electrolyte in the form of a film, which selectively transmits cations (hydrogen ions) and blocks hydrogen gas. It can be used in water electrolysis systems that produce hydrogen or fuel cell systems that generate power using hydrogen.

[0003] In both water electrolysis systems and fuel cell systems, the electrolyte membrane is introduced in the form of a membrane-electrode assembly (MEA) coated with electrode layers that cause electrochemical reactions on both surfaces. The main function of the polymer electrolyte membrane or cation exchange membrane is to effectively transfer hydrogen ions generated through the catalytic reaction of the electrode layers.

[0004] The role of cation-conducting polymer electrolyte membranes in water electrolysis / fuel cell systems is to exhibit performance through hydrogen ion transport, separate reaction / product gases, and ensure mechanical robustness as an engineering plastic in the system.

[0005] Among these, since the hydrogen ion transport ability is considered a fundamental role, electrolyte membranes have been manufactured in the form of a single membrane (single-layer film) using only electrolytes with high ion exchange capacity (IEC) to minimize resistance in the thickness direction, and this trend has been particularly prominent in the field of water electrolysis systems.

[0006] In order to increase the hydrogen ion conductivity of polymer electrolyte membranes, i.e., maximize the IEC, when manufactured in the form of a single membrane or a single layer of film, there is a problem that the hydrogen gas permeability also increases as the mass transport characteristics increase. In water electrolysis systems, there is a constant risk of fire or explosion due to the mixing of oxygen and hydrogen gas. In fuel cell systems, there are safety issues and the problem of the open circuit voltage of the stack decreasing due to the mixing of reactant gases.

[0007] In addition, the single-layer film form can be problematic in terms of mechanical stability. Specifically, there is a problem with thermal and tensile stability in that the MEA structure can be damaged due to thermal expansion when exposed to an environment where a certain level of heat and tension is applied during the post-process MEA transfer process. In addition, both fuel cells and water electrolysis systems operate at temperatures above 60℃, so thermal deformation occurs during long-term operation or when local hot spots occur, making it difficult to maintain selectivity (hydrogen ion conductivity compared to hydrogen gas permeability), and in serious cases, there is a concern that pin holes may occur, making it difficult to guarantee stability during system operation.

[0008] Therefore, it can be seen that securing thermal and structural stability at the fuel cell / water electrolysis process temperature or operating temperature is an essential element.

[0009] The present invention was conceived to solve the above-described problem, and aims to provide a reinforced composite polymer electrolyte membrane having a composite structure that can secure thermal and structural expansion stability.

[0010] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011] The present invention provides a reinforced composite polymer electrolyte membrane, characterized in that, according to a preferred embodiment, an ionomer dispersion is applied to a support, wherein the ionomer includes a sulfonic group for conducting protons, the support is a porous substrate having a higher melting point than the ionomer, the polymer electrolyte membrane comprises a composite layer in which the ionomer is impregnated inside the support, and an electrolyte layer formed of the ionomer on the upper and lower portions of the composite layer, and a gradient of sulfur (S) element content (wt%) is measured when analyzing the upper electrolyte layer, the composite layer, and the lower electrolyte layer in the cross section using an energy dispersive spectrometer (EDS).

[0012] At this time, the sulfur element content (wt%) of the upper electrolyte layer, composite layer, and lower electrolyte layer may be an average value of the sulfur element content calculated when EDS line-scanning the point where the vertical thickness of each layer is the thickest - the longest among the vertical lines connecting the top and bottom points of each layer - based on a specific cross-section of the polymer electrolyte membrane.

[0013] At this time, the sulfur (S) element content of the upper electrolyte layer or the lower electrolyte layer may be 1.5 to 5.0 times the sulfur (S) element content of the composite layer, and preferably 1.5 to 3.5 times.

[0014] The above ionomer may be a fluorine-based ionomer or a hydrocarbon-based ionomer mixed with a compound containing a sulfone group.

[0015] The polymer electrolyte membrane may have a total dimension change of 2,000 ㎛ or less at 200°C according to thermomechanical analysis (TMA), and preferably 1,500 ㎛ or less.

[0016] The polymer electrolyte membrane may have a total dimension change at 200°C as measured by thermomechanical analysis (TMA) that is 20 to 60% smaller than that of a single membrane - unlike the polymer electrolyte membrane, which is composed only of the ionomer without the support, and has the same membrane thickness and ionomer material type.

[0017] Additionally, the polymer electrolyte membrane may have a thermal transition temperature according to thermomechanical analysis (TMA) that is 5 to 20% higher than that of a single membrane - unlike the polymer electrolyte membrane, which is composed only of the ionomer without the support, and has the same membrane thickness and ionomer material type.

[0018] In addition, the slope of the straight line connecting the point at the thermal transition temperature and the point at 200°C on the temperature-dependent dimensional change curve according to the thermomechanical analysis (TMA) of the polymer electrolyte membrane may be 20 to 60% of the slope of the equivalent straight line in a single membrane - unlike the polymer electrolyte membrane, which is composed only of the ionomer without the support, and has the same membrane thickness and ionomer material type.

[0019] The hydrogen gas permeability of the above polymer electrolyte membrane may be 2.0 mA / cm2 or less, and the above polymer electrolyte membrane may be applied as a PEM for a water electrolysis system or a PEM for a fuel cell.

[0020] The present invention provides a membrane-electrode assembly for a fuel cell or a water electrolysis system comprising a polymer electrolyte membrane as described above, according to another preferred embodiment, and provides a fuel cell or a water electrolysis system comprising the polymer electrolyte membrane as described above.

[0021] The reinforced composite polymer electrolyte membrane according to the present invention as described above has the effect of ensuring high thermodynamic stability and thus maintaining high performance even under the manufacturing process temperature or operating temperature conditions of a water electrolysis / fuel cell system.

[0022] The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned, although they can be clearly understood by those skilled in the art from the description throughout the specification.

[0023] Figure 1 is a cross-sectional SEM photograph showing the target points of EDS analysis in the thickness direction of a reinforced composite polymer electrolyte membrane according to a preferred embodiment of the present invention.

[0024] FIG. 2 is a cross-section EDS analysis graph for spectra 27-29 according to Example 2 of the present invention.

[0025] Figure 3 is a TMA curve (temperature-dependent dimensional change graph) for samples 1 to 3 according to an embodiment of the present invention.

[0026] Figure 4 is a cross-sectional schematic diagram of a reinforced composite polymer electrolyte membrane of the present invention.

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described in detail below together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

[0028] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise.

[0029] The terms "comprises" and / or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations and / or elements.

[0030]

[0031] First, the present invention provides a reinforced composite polymer electrolyte membrane in which an ionomer dispersion is applied to a support, wherein the ionomer includes a sulfonic group for conducting hydrogen ions, the support is a porous substrate having a higher melting point than the ionomer, the polymer electrolyte membrane comprises a composite layer in which the ionomer is impregnated inside the support, and an electrolyte layer formed of the ionomer on the upper and lower portions of the composite layer, and wherein a gradient of sulfur (S) element content (wt%) is measured when analyzing the upper electrolyte layer, the composite layer, and the lower electrolyte layer in the cross section using an energy dispersive spectrometer (EDS).

[0032] At this time, the sulfur element content (wt%) of the upper / lower electrolyte layers and composite layer can be defined and calculated through various approaches that can be utilized in EDS analysis. Specifically, EDS analysis can measure and calculate the element content for a specific point, line, or area.

[0033] In the following examples of the present invention, the values ​​obtained through EDS analysis at specific points of each layer were experimentally measured, but as another example, the average value of the sulfur element content obtained when performing an EDS line scan on a point with the thickest vertical thickness of each layer based on a specific cross-section of a polymer electrolyte membrane - the longest vertical line connecting the top and bottom points of each layer - can be defined as the sulfur element content (wt%) value of the upper / lower electrolyte layer composite layer.

[0034] Specifically, with reference to FIG. 4, the sulfur element content value of the upper electrolyte layer based on a specific cross-section can be defined as the average value of the sulfur element content calculated when performing an EDS line-scan for the point where the thickness of the upper electrolyte layer is the thickest, that is, the length of the vertical line vertically connecting the upper line (y3) of the upper electrolyte layer and the boundary line (y2) with the lower composite layer is the longest.

[0035] Likewise, the sulfur element content of each layer can be calculated in the same manner for the composite layer at the point where the vertical thickness in the y2-y1 direction is the thickest, and for the lower electrolyte layer at the point where the vertical thickness in the y1-y0 direction is the thickest.

[0036]

[0037] 1. Electrolyte (ionomer) and composite layer application material

[0038] Any material with a functional group capable of transporting hydrogen ions can be used as the ionomer, and preferably includes a sulfonic group. Specifically, a fluorine-based ionomer or a hydrocarbon-based ionomer mixed with a compound containing a sulfonic group can be used.

[0039] The support used in the composite structure must have a higher melting point than the ionomer, preferably at least 1.2 times higher, and any type of porous material can be applied, and typically a material with a melting point of 300°C or higher is suitable.

[0040] Polytetrafluoroethylene (PTFE, melting point approximately 327°C) or e-PTFE, cerium oxide (ceria, melting point approximately 2,400°C), polyimide (polyimide, melting point approximately 247 to 388°C), etc. can be adopted as the support material forming the composite layer.

[0041] The support is a porous material, and a material with a porosity of at least 70% is suitable, and preferably 80% or more is good.

[0042]

[0043] 2. Composite layer

[0044] The formation of a reinforced composite electrolyte membrane having a composite layer in the depth can be confirmed through SEM cross-section analysis, and the difference in the thickness direction distribution of functional elements (sulfur, S) contained in the ionomer can be confirmed through energy dispersive spectrometer (EDS) analysis of the upper electrolyte layer, composite layer, and lower electrolyte layer in the thickness direction (cross section).

[0045] In the composite layer region, the sulfur (S) element content of the sulfone group is lower than that of the pure ionomer layer (electrolyte layer) on the upper and lower parts of the composite layer, and in order for the effect of the reinforced composite type to actually be expressed in the electrolyte membrane characteristics, the sulfur element content of the electrolyte layer must be at least 1.5 times that of the composite layer region, and more effectively, at least 2.0 times.

[0046] The sulfur element content of the electrolyte layer compared to the composite layer is determined by a complex interplay of variables such as the porosity of the support, the level of porosity reduction due to thickness-wise shrinkage during the composite process through ionomer coating, the filling ratio of the electrolyte (ionomer) to the pores of the support, and the volume ratio of the electrolyte layer and the composite layer. These variables become factors that determine the thermal, mechanical, and dimensional stability of the polymer electrolyte membrane.

[0047] For example, the fact that the sulfur element content of the electrolyte layer is higher than that of the composite layer can be seen as a result of a complex combination of factors, including the high content of a support material with relatively high material thermal stability within the composite layer, the occurrence of high-strength shrinkage in the thickness direction during the electrolyte coating process, which leads to a large decrease in the porosity of the support, and the relatively low filling rate of the electrolyte in the pores of the support, which leaves residual pores, so that during the moisture absorption process of the electrolyte membrane, moisture is primarily filled in the residual pores, thereby reducing the swelling phenomenon or external dimensional change of the membrane itself due to moisture absorption.

[0048] Accordingly, the sulfur element content of the electrolyte layer can be increased compared to the composite layer, but if it exceeds 5 times, preferably 3.5 times, this means that the equivalent weight of the sulfonic acid group in the composite layer is significantly reduced, which means that the equivalent weight exceeds the range of use as an electrolyte, and the hydrogen ion transport ability of the composite layer is excessively reduced, resulting in a problem in that the hydrogen ion transport ability in the thickness direction, i.e. the Effective Conductivity, is lowered compared to the hydrogen ion transport ability of the entire volume of the electrolyte membrane.

[0049]

[0050] 3. Thermal and dimensional stability

[0051] The thermodynamic stability of a material can be confirmed through thermomechanical analysis (TMA). After fixing the electrolyte membrane to a TMA device, the temperature is raised to 200°C, the decomposition temperature of the sulfonic acid functional group in the electrolyte. This process allows the determination of the material's thermal transition temperature (T), the temperature at which mobility begins to develop, and its final thermal expansion dimension.

[0052] A single membrane formed only with a pure electrolyte and a reinforced composite polymer electrolyte membrane according to the present invention were manufactured through the same process and subjected to a comparative experiment. Compared to the single membrane, the thermal transition temperature was found to be 5 to 20% higher (specifically 5°C or higher, preferably 10°C or higher), and the thermal expansion dimension was found to be 20 to 60% smaller (specifically 2,000 μm or less, preferably 1,500 μm or less), confirming that the thermal and dimensional stability was greatly improved.

[0053]

[0054] Example 1: Preparation of a reinforced composite polymer electrolyte membrane (Sample 1)

[0055] The electrolyte (ionomer) used was 3M's Middle Side Chain structure PFSA (Perfluorosulfonic acid) with an equivalent weight of 720. The ionomer dispersion had a solid content of 20 wt%, and the solvent was water and 1-Propanol in a 1:1 ratio, prepared using a rotary mixer.

[0056] The support used e-PTFE (Expanded Polytetrafluoroethylene) with a porosity of 85%, and the e-PTFE was filled with the above-mentioned electrolyte and coated on the top and bottom using an applicator so that the composite layer occupies 50% of the total volume in the thickness direction. To remove the electrolyte solvent, drying at 70°C for 1 hour and heat treatment (annealing) at 170°C for 10 minutes were performed to obtain a film-type reinforced composite membrane.

[0057]

[0058] Example 2: EDS analysis

[0059] To verify the composite structure of the reinforced composite polymer electrolyte membrane, EDS (Energy Dispersive Spectrometer) analysis was performed using JSM-7600F equipment from JEOL. The amounts of C, S, F, and O elements were measured at an accelerating voltage of 15 kV, and the element distributions in the upper electrolyte layer, deep composite layer, and lower electrolyte layer were confirmed. The ratio of S element in the pure electrolyte layer and composite layer at the upper and lower parts was confirmed to be 2 to 3 times higher than that of the electrolyte layer. In Fig. 1, Spectrum 27 represents the upper electrolyte layer, Spectrum 28 represents the composite layer, and Spectrum 29 represents the lower electrolyte layer.

[0060]

[0061] Spectrum 27Spectrum 28Spectrum 29ElementWt%Wt% SigmaAtomic%Wt%Wt% SigmaAtomic%Wt%Wt% SigmaAtomic%C34.050.2545.3835.580.2546.8937.530.3149.64O2.880.122.890.670.110.660.880.130.88F58.970.24 49.6961.830.2551.5055.670.3046.55S4.100.082.051.920.080.955.920.132.93 Total 100.0-100.0100.0100.0100.0-100.0

[0062] In Table 1 above, Wt% is weight percent, which indicates the percentage of each component of the material by weight, Wt% Sigma means the standard deviation of weight percent, and Atomic% means the percentage of the number of atoms. Figure 2 is a cross-section EDS analysis graph for spectra 27-29.

[0063]

[0064] Referring to Table 1 and Figure 2 above, the gradient of sulfur (S) element content (wt%) in the thickness direction between the upper and lower electrolyte layers and the deep composite layer can be clearly confirmed, and in particular, the content of sulfur (S) element is the most significant indicator in terms of ease of measurement, representativeness for composite structuring as a key element constituting the ionomer functional group, and linkage between the composition of the composite layer and porosity / filling ratio control.

[0065]

[0066] Example 3: TMA analysis

[0067] To investigate the thermal behavior of the reinforced composite membrane, the change in sample dimensions according to temperature was measured using the Discovery TMA 450EM equipment of WATERS. The specimens with a width of 5 mm and a length of at least 20 mm were fastened and the dimensional change was observed while the temperature was increased by 5 °C per minute from 25 °C to 200 °C. The temperature at which the material mobility begins (thermal transition temperature) was first observed to confirm the transition delay section of the composite membrane structure compared to the single membrane, and the change in length at the final temperature (200 °C) was confirmed.

[0068] Three samples were used for analysis by thermomechanical analysis (TMA). Sample 1 is a reinforced composite polymer electrolyte membrane according to Example 1 described above.

[0069] The manufacturing example of Sample 2 is as follows. 3M's Middle Side Chain structure PFSA (Perfluorosulfonic acid) was used as the electrolyte, and its equivalent weight is about 720. The first ionomer dispersion had a solid content of 20 wt%, and the solvent was water and 1-propanol in a 1:1 ratio, and was manufactured using a rotating mixer. The second ionomer dispersion applied to the composite layer was further dispersed using a rotating mixer by adding 8000 ppm of cerium oxide (Ceria) to the previously manufactured one based on the solid content.

[0070] In the film forming process, the first ionomer dispersion was first applied using an applicator, dried at 70°C for 30 minutes to remove the solvent, and then the second ionomer dispersion was equally applied on the top of the first application surface, dried at 70°C for 30 minutes to form a second layer, and then the first ionomer dispersion was additionally applied, and finally dried at 70°C for 1 hour and heat-treated at 170°C for 10 minutes to produce a total of three-layer structure.

[0071] Sample 3 served as a control group, and its manufacturing method was as follows. 3M's Middle Side Chain structure PFSA (Perfluorosulfonic acid) was used as the electrolyte, with an equivalent weight of 720. The ionomer dispersion had a solids content of 20 wt%, and the solvent was water and 1-Propanol in a 1:1 ratio, prepared using a rotary mixer.

[0072] The manufactured ionomer dispersion was applied only once using the same coating method as that of Samples 1 and 2, and drying and heat treatment were also performed under the same final drying conditions as those of Samples 1 and 2: drying at 70°C for 1 hour and heat treatment at 170°C for 10 minutes.

[0073] The results of the sulfur (S) element content ratio of the electrolyte layer compared to the composite layer, the thermal transition temperature, and the total dimension change at 200°C according to the EDS analysis results of Samples 1 to 3 are shown in Table 2 below, and the dimension change curve according to the temperature change is shown in Fig. 3 (Sample 1 is red 0628C-MD, Sample 2 is blue 0628D-MD, and Sample 3 is black Single membrane).

[0074]

[0075] S element content ratio (electrolyte layer / composite layer) Thermal Transition Temperature (℃) Thermal Expansion (mm, @200℃) Sample 13.11 19.7 1.14 Sample 22.5 117.7 1.49 Sample 31.11 0 7.12.45

[0076]

[0077] In the case of Sample 1, which corresponds to the reinforced composite polymer electrolyte membrane according to the present invention, and Sample 2, which is a form in which cerium oxide is added, the thermal conversion temperature, which is the temperature at which fluidity begins, is about 10℃ higher than that of Sample 3, which is a single membrane, and while Sample 3 experiences rapid dimensional changes as the temperature increases thereafter, Sample 1 and 2 form a gentle delay section, and it can be confirmed that the dimensional change at 200℃ (this temperature is the temperature at which sulfonic groups begin to detach and decompose, and is the upper limit of the process temperature such as the heat treatment process or the MEA electrode process) is about half that of Sample 3 (see Fig. 3).

[0078] The reason why Samples 1 and 2, unlike Sample 3, show a so-called "delayed section" in which the full-scale thermal expansion occurs is delayed to a relatively higher temperature section. This is because, during the manufacturing process of the reinforced composite membrane, the electrolyte and support are exposed to the solvent during the membrane forming process, and the internal structure of the membrane is rearranged during the drying-annealing process. During drying, the forces acting differently on the inside of the composite layer and the surface of the electrolyte membrane during the drying process cause the forces between the two layers to compete with each other, increasing the thermal and physical resistance of the material.

[0079] Meanwhile, Sample 2 has a slightly lower thermal transition temperature and a slightly larger total dimension change at 200℃ than Sample 1, despite being reinforced by the addition of cerium oxide, which has a higher melting temperature. In the case of Sample 1, it was reinforced by infiltrating the electrolyte into the three-dimensional structure between the nodes and fibrils of the e-PTFE reinforcement itself, but Sample 2 was manufactured by dispersing cerium oxide in an electrolyte dispersion and applying it, so it appears that the cerium oxide is absorbed into the aggregated electrolyte polymer unit structure to reinforce it. If the metal oxide is manufactured in the form of a network structure and similarly impregnated with electrolyte, it can exhibit higher reinforcing properties than Sample 1.

[0080]

[0081] In conclusion, when the composite is implemented as a reinforced composite and an appropriate level of sulfur (S) element content gradient is formed in the thickness direction, the composite effect can be maximized and the thermal and dimensional stability can be increased.

[0082] When a composite layer is implemented so that an appropriate level of sulfur element content gradient is formed, a polymer electrolyte membrane can be manufactured such that the total dimension change at 200°C according to thermomechanical analysis (TMA) is 2,000 μm or less, preferably 1,500 μm or less, which is 20 to 60% less than the total dimension change for a single membrane.

[0083] In addition, the temperature at which fluidity begins to occur, i.e. the thermal transition temperature, is also 5 to 20% higher than that of a single film, so the starting point of thermal expansion is also relatively delayed to a high temperature range, and thermal-dimensional stability can be obtained throughout the entire range from the operating / manufacturing temperature to the upper limit temperature (200°C).

[0084] In particular, the low thermal expansion dimension at 200°C is a result of the aforementioned delay section, and this physical characteristic is a property of a reinforced composite polymer electrolyte membrane having a sulfur element content gradient in the thickness direction. In the temperature-dependent dimensional change curve according to TMA analysis, the slope of the straight line connecting the point at the thermal transition temperature and the point at 200°C is smaller than the slope of the single membrane, and can preferably be at the level of 20% to 60%.

[0085]

[0086] Although embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. In a polymer electrolyte membrane in which an ionomer dispersion is applied to a support, The above ionomer contains a sulfonic group for hydrogen ion conduction, The above support is a porous substrate having a higher melting point than the ionomer, The polymer electrolyte membrane comprises a composite layer impregnated with the ionomer inside the support, and an electrolyte layer formed of the ionomer on the upper and lower portions of the composite layer, wherein a gradient of sulfur (S) element content (wt%) is measured when analyzing the upper electrolyte layer, the composite layer, and the lower electrolyte layer in the cross section using an energy dispersive spectrometer (EDS).

2. In paragraph 1, The sulfur element content (wt%) of the upper electrolyte layer, composite layer and lower electrolyte layer is A reinforced composite polymer electrolyte membrane characterized in that the average value of the sulfur element content is calculated when EDS line-scanning the point where the vertical thickness of each layer is the thickest - the longest of the vertical lines connecting the top and bottom points of each layer - based on a specific cross-section of the polymer electrolyte membrane.

3. In paragraph 1, A reinforced composite polymer electrolyte membrane, characterized in that the sulfur (S) element content of the upper electrolyte layer or the lower electrolyte layer is 1.5 to 5.0 times the sulfur (S) element content of the composite layer.

4. In paragraph 1, A reinforced composite polymer electrolyte membrane, characterized in that the sulfur (S) element content of the upper electrolyte layer or the lower electrolyte layer is 1.5 to 3.5 times the sulfur (S) element content of the composite layer.

5. In paragraph 1, A reinforced composite polymer electrolyte membrane characterized in that the above ionomer is a hydrocarbon ionomer mixed with a fluorine-based ionomer or a compound containing a sulfone group.

6. In paragraph 1, The above polymer electrolyte membrane is a reinforced composite polymer electrolyte membrane characterized in that the total dimension change at 200°C according to thermomechanical analysis (TMA) is 2,000 ㎛ or less.

7. In paragraph 1, The above polymer electrolyte membrane is a reinforced composite polymer electrolyte membrane characterized in that the total dimension change at 200°C according to thermomechanical analysis (TMA) is 1,500 ㎛ or less.

8. In paragraph 1, The polymer electrolyte membrane is a reinforced composite polymer electrolyte membrane characterized in that the total dimension change at 200°C according to thermomechanical analysis (TMA) is 20 to 60% smaller than that of a single membrane - unlike the polymer electrolyte membrane, it is composed only of the ionomer without the support, and the membrane thickness and ionomer material type are the same.

9. In paragraph 1, The polymer electrolyte membrane is a reinforced composite polymer electrolyte membrane characterized in that the thermal transition temperature according to the thermomechanical analysis (TMA) is 5 to 20% higher than that of a single membrane - unlike the polymer electrolyte membrane, it is composed only of the ionomer without the support, and the membrane thickness and ionomer material type are the same.

10. In paragraph 1, The polymer electrolyte membrane is a reinforced composite polymer electrolyte membrane characterized in that the slope of a straight line connecting a point at the thermal transition temperature and a point at 200°C on a temperature-dependent dimensional change curve according to thermomechanical analysis (TMA) is 20 to 60% of the slope of an equivalent straight line in a single membrane - unlike the polymer electrolyte membrane, which is composed only of the ionomer without the support, and has the same membrane thickness and ionomer material type.

11. In paragraph 1, A reinforced composite polymer electrolyte membrane, characterized in that the hydrogen gas permeability of the polymer electrolyte membrane is 2.0 mA / cm2 or less.

12. In paragraph 1, A reinforced composite polymer electrolyte membrane characterized in that the polymer electrolyte membrane is a PEM for a water electrolysis system or a PEM for a fuel cell.

13. A membrane-electrode assembly for a fuel cell comprising a reinforced composite polymer electrolyte membrane according to any one of claims 1 to 12.

14. A membrane-electrode assembly for a water electrolysis system comprising a reinforced composite polymer electrolyte membrane according to any one of claims 1 to 12.

15. A fuel cell comprising a reinforced composite polymer electrolyte membrane according to any one of claims 1 to 12.

16. A water electrolysis system comprising a reinforced composite polymer electrolyte membrane according to any one of claims 1 to 12.

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