Hydrogen ion conductive multilayer composite membrane

Abstract

To provide a hydrogen ion conductive multi-layer composite membrane having excellent durability, ion conductivity, and hydrogen permeation reduction effect.SOLUTION: The present invention provides a hydrogen ion conductive multilayer composite membrane comprising: inner reinforced membranes comprising a porous PTFE layer impregnated with an ionomer composition and outer reinforced membranes positioned on both sides of the inner reinforced membrane, wherein the outer reinforced membranes comprise a porous PTFE layer impregnated with an ionomer composition.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention

[0001]

Technical Field

[0002] The present invention relates to a hydrogen ion conductive multilayer composite membrane.

Background Art

[0003] Water electrolysis is a technology for electrolyzing water to obtain hydrogen, and can produce environmentally friendly hydrogen. Types of water electrolysis are classified into cation exchange membranes (PEM; Proton Exchange Membrane), anion exchange membranes (AEM; Anion Exchange Membrane), alkaline, solid oxide, etc.

[0004] On the other hand, fuel cells, as high-efficiency power generation devices, have the advantages of being more efficient and using less fuel compared to existing internal combustion engines, and being a pollution-free energy source that does not generate environmental pollutants such as SOx, NOx, and VOC. There are also additional advantages such as less floor area required for production facilities and a short construction period, and the application fields are diverse, ranging from mobile power sources for portable devices to distributed power generation that can be used for transportation power sources such as automobiles, household use, and power utilities.

[0005] Fuel cells are roughly classified into five types according to the operating temperature and electrolyte. Specifically, there are alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), polymer electrolyte fuel cells (PEMFC), and direct methanol fuel cells (DMFC). Among them, polymer electrolyte fuel cells with excellent mobility have attracted great attention.

[0006] The electrolyte membranes used in cation exchange membrane water electrolysis and polymer electrolyte fuel cells are mainly fluorinated carbon-based electrolyte membranes. A typical example is Nafion, a perfluorinated hydrogen ion exchange membrane developed by DuPont in the United States in the early 1960s. In addition to Nafion, other similar perfluorinated polymer electrolyte commercial membranes include Aciplex-S membrane from Asahi Kasei Corporation, Dow membrane from Dow Chemicals, and Flemion membrane from Asahi Glass Company, Ltd.

[0007] Such a casting membrane is composed only of an ion-conductive electrolyte, is easy to manufacture, and is widely applied as experimental and mass-produced products. However, under the driving conditions of the water electrolysis system and the fuel cell system, fatigue of the material due to volume change accumulates, and there are problems with durability. Also, as the thickness of the membrane increases, the membrane resistance increases while the electrochemical performance decreases, and when the membrane thickness is decreased, the performance deteriorates due to hydrogen permeation problems and durability problems. Therefore, improvement against the above problems is required.

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a hydrogen ion-conductive multilayer composite membrane excellent in durability, ion conductivity, and hydrogen permeation reduction effect. Another object is to provide a water electrolysis system and a fuel cell using the hydrogen ion-conductive multilayer composite membrane as a separation membrane. However, the object of the present invention is not limited to the above objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0009] As means for solving the above problems, The present invention provides a hydrogen ion conductive multilayer composite membrane including an internal reinforcing membrane containing a porous PTFE layer impregnated with an ionomer composition, and external reinforcing membranes located on both sides of the internal reinforcing membrane, wherein the external reinforcing membrane includes a porous PTFE layer impregnated with an ionomer composition.

[0010] In addition, the average pore size and porosity of the porous PTFE layer of the external reinforcing membrane can be smaller than the average pore size and porosity of the PTFE of the internal reinforcing membrane.

[0011] In addition, the average pore diameter of the PTFE of the external reinforcing membrane is in the range of 0.1 μm to 0.2 μm, the porosity is in the range of 70% to 80%, the average pore diameter of the PTFE of the internal reinforcing membrane is in the range of 0.2 μm to 0.4 μm, and the porosity can be in the range of 80% to 90%. In addition, the internal reinforcing membrane can be laminated within a range of 1 or 2 to 5.

[0012] In addition, the external reinforcing membrane can include a PTFE layer impregnated with an ionomer inside, a surface modification layer formed by plasma surface treatment on one or both outer surfaces of the PTFE layer, and an ionomer layer coated on the surface modification layer. In addition, the internal reinforcing membrane can include a PTFE layer impregnated with an ionomer inside, a surface modification layer formed by plasma surface treatment on one or both outer surfaces of the PTFE layer, and an ionomer layer coated on the surface modification layer.

[0013] In addition, the viscosity and ionomer concentration of the ionomer composition used when coating the ionomer layer on the surface modification layer can be higher than the viscosity and ionomer concentration of the ionomer composition used when impregnating the ionomer inside the PTFE layer. In addition, the viscosity difference is in the range of 10 cp to 100 cp from 25 °C, and the concentration difference can be in the range of 30 wt% to 80 wt%. In addition, one or more of the internal reinforcing membrane and the external reinforcing membrane can be treated with an acid to reduce voids.

[0014] Further, before the above-mentioned inner reinforcing film and the above-mentioned outer reinforcing film are joined together, the surfaces to be joined are pretreated with plasma first, and after coating the surfaces pretreated with the ionomer composition, they are joined together, and a separate ionomer coating layer can be present between the inner reinforcing film and the outer reinforcing film. Also, a catalyst mesh layer can be joined between the above-mentioned at least one or more outer reinforcing films and the above-mentioned at least one or more inner reinforcing films so that a catalyst layer can be present. Further, the present invention provides a water electrolysis system and a fuel cell including the hydrogen ion conductive multilayer composite membrane as a separation membrane.

Advantages of the Invention

[0015] The hydrogen ion conductive multilayer composite membrane according to the present invention is excellent in durability, ion conductivity, and hydrogen permeation reduction effect, and can be usefully used as a separation membrane for a water electrolysis system and a fuel cell. The above effects and additional effects will be described in detail below.

Brief Description of the Drawings

[0016] FIG. 1 and FIG. 2 are schematic views of the structure and manufacturing process of a hydrogen ion conductive multilayer composite membrane according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0017] Before explaining the present invention in detail below, it should be understood that the terms used in this specification are for explaining specific embodiments and do not limit the scope of the present invention, which is limited only by the appended claims. All technical terms and scientific terms used in this specification have the same meaning as generally understood by those having ordinary skill in the art, unless otherwise described.

[0018] Unless otherwise indicated throughout this specification and the claims, the term "comprising" means including the recited item, step, or group of items and steps and is not meant to be construed as excluding any other item, step, or group of items or steps. On the other hand, various embodiments of the present invention can be combined with any other embodiments unless there is a clear indication to the contrary.

[0019] The present invention will be described in more detail below. The hydrogen ion conductive multilayer composite membrane according to an embodiment of the present invention includes an internal reinforcing membrane including a porous PTFE layer impregnated with an ionomer composition and an external reinforcing membrane located on both sides of the internal reinforcing membrane and including a porous PTFE layer impregnated with an ionomer composition. There is one internal reinforcing membrane, and as shown in FIG. 1, there can be two or more. In terms of advantages, it can be in a stacked form within the range of two to five. The thickness of the hydrogen ion conductive multilayer composite membrane may be in the range of 20 μm to 100 μm, and considering comprehensively factors such as thinning, durability, hydrogen ion conductivity, and reduction of hydrogen permeation, it may be in the range of 30 μm to 60 μm.

[0020] The porous PTFE layer can be a PTFE membrane having porosity by stretching. A commercially available product that meets the required performance can be obtained and used for the porous PTFE membrane, or it can be directly manufactured.

[0021] As a method for manufacturing the porous PTFE membrane, a publicly known method can be used. As an example, the porous PTFE membrane can be manufactured through the following steps. First, after mixing tetrafluoroethylene powder and a lubricant, perform the following primary molding to obtain a preform, extrude the preform to obtain a rod-shaped primary molded body, process the above primary molded body into a sheet shape to obtain a secondary molded body, and after drying the above secondary molded body to remove the lubricant, perform stretching in the lateral and longitudinal directions of the above secondary shaped body. By controlling the type, content of the powder used, and the conditions of the stretching process, a PTFE membrane with desired performance can be manufactured.

[0022] The porous PTFE layer of the external reinforcing film and the PTFE layer of the internal reinforcing film can use the same PTFE film. More preferably, the average pore size and porosity of the porous PTFE layer of the external reinforcing film can be smaller than the average pore size and porosity of the PTFE layer of the internal reinforcing film. By using a PTFE layer of the external reinforcing film with relatively small pore size and porosity, hydrogen flowing in from the outside can be blocked, the hydrogen permeability can be reduced, and the durability can be improved. For the PTFE layer of the internal reinforcing film, those with relatively large pore size and porosity can be used to enhance the impregnation property of the ionomer, and the ionomer can be impregnated with a high content to improve the hydrogen ion conductivity. Specifically, the PTFE layer of the external reinforcing film can have an average pore size of 0.1 to 0.2 μm and a porosity within the range of 70% to 80%, and the PTFE of the internal reinforcing film can have an average pore size of 0.2 to 0.4 μm and a porosity within the range of 80% to 90%. The difference in the average pore size between the two PTFE layers may be in the range of 0.05 to 0.3 μm, and the difference in porosity may be in the range of 5% to 20%.

[0023] The ionomer composition can include a conductive ionomer, a solvent, and a surfactant. Optionally, a radical scavenger or the like can be further included.

[0024] As the conductive ionomer, any hydrogen ion conductive polymer can be used. For example, a cation exchanger selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphinic acid groups, and derivatives thereof in the side chain, that is, a polymer resin having a hydrogen ion conductor can be used.

[0025] As an example, it can contain one or more hydrogen ion conductive polymers selected from fluoride-based polymers, benzimidazole-based polymers, polyimide-based polymers, polyphenylene sulfide-based polymers, polysulfone-based polymers, polyether ketone-based polymers, polyether-ether-ketone-based polymers, or polyphenylquinoxaline-based polymers.

[0026] Desirably, a perfluorosulfonated ionomer may be used as the conductive ionomer. Specifically, polyperfluorosulfonate (trade name Nafion, Dupont) can be used as the perfluorosulfonated ionomer. In addition, commercially available products such as Aciplex (Asahi Kasei Chemical), Flemion (Asahi Glass), and Fumion (fumatech) can also be used. As the solvent, commonly used solvents such as N-methylpyrrolidone, isopropyl alcohol, and normal propyl alcohol can be used.

[0027] Considering both the affinity with PTFE and environmental issues, the surfactant preferably contains a hydrophobic group in which the hydrogen of the hydrocarbon is partially substituted by fluorine. The hydrophilic group of the surfactant is preferably a hydrophilic group having an affinity with an ionomer having a sulfonic acid group.

[0028] Known surfactants can be used. For example, one selected from the group consisting of Du Pont's Zonyl series, 3M's Novec series, or a mixture thereof is used. Specifically, as the above Zonyl surfactant, Zonyl TBS (RfCH2CH2SO3X (X = H or NH4), Rf = F(CF2CF2)3-8), Zonyl FSN (RfCH2CH2O(CH2CH20)xH)), Zonyl FSP (RfCH2O)P(O)(ONH4) can be used. Also, as the Novec surfactant, Novec 4200 (Ammonium Fluoroalkylsulfonamide), Novec 4300 (Ammonium Fluoroalkylsulfonate), Novec 4430 (polymeric fluorochemical active), Novec 4432 (polymeric fluor), etc. can be mentioned.

[0029] The method of impregnating the porous PTFE with the ionomer composition is not limited, and examples include applying the ionomer composition to the porous PTFE or immersing the PTFE in the ionomer composition. By impregnation, the ionomer composition penetrates into the interior of the porous PTFE and can also remain on the surface of the PTFE.

[0030] Before the impregnation step, the porous PTFE can be pre-treated with plasma to further enhance the impregnability of the ionomer composition. The plasma treatment can be performed on one or both sides of the PTFE.

[0031] The surface modification technology by plasma treatment adds various types of energy and particles to the surface, applies a physical impact to the surface to increase roughness, cuts the polymer chain, or forms new chemical bonds to cause an increase in hydrophilic functional groups.

[0032] There are a low-pressure plasma (low pressure plassma) method of generating plasma by discharging at low pressure as plasma and an atmospheric-pressure plasma (atomspheric pressure plassma) method of generating plasma by discharging at atmospheric pressure. In terms of advantages, the normal-temperature and normal-pressure plasma method is good. The atmospheric-pressure plasma technology can generate efficient, stable, and uniform plasma discharge at atmospheric pressure, that is, 760 Torr, without using a high-cost vacuum system, and can improve economy and productivity.

[0033] After impregnation, it is better to perform a two-step heat treatment by applying heat to the support so that the ionomer can crystallize. If the generated gas during heat treatment is not removed step by step, problems such as cracks may occur after heat treatment, which can cause problems with hydrogen permeability and durability. Specifically, the heat treatment can proceed first at 150 to 210 °C through hot air and then secondarily at 50 to 100 °C with near-infrared (NIR).

[0034] On the other hand, the PTFE impregnated membrane impregnated with ionomer can be plasma-treated again to form a surface modified layer, and by coating the ionomer layer again, the durability and the performance of reducing hydrogen permeability can be further improved.

[0035] Specifically, as shown in FIG. 2, the external reinforcing film can include a PTFE layer impregnated with ionomer inside, a surface modified layer formed by heat treatment after plasma surface treatment on the outer surface or both surfaces of the PTFE layer, and an ionomer layer coated on the surface modified layer formed on the outer surface or both surfaces (drawings with both surfaces treated are omitted).

[0036] Similarly, the internal reinforcing film can also include a PTFE layer impregnated with ionomer inside, a surface modified layer formed by heat treatment after plasma surface treatment on the outer surface or both surfaces of the PTFE layer, and an ionomer layer coated on the surface modified layer formed on the outer surface or both surfaces.

[0037] Here, the viscosity and ionomer concentration of the ionomer composition used during the ionomer layer coating of the surface modification layer can be higher than those of the ionomer composition used during the ionomer impregnation inside the PTFE layer. Since the inside of the PTFE already contains impregnated ionomer, an ionomer composition with relatively higher viscosity and ionomer concentration can be used for the surface modification layer coating to ensure coating property, coating film stability, and uniformity rather than impregnation property.

[0038] The viscosity difference between the two ionomer compositions can be within the range of 10 cp to 100 cp at 25°C, and the concentration difference can be in the range of 30 wt% to 80 wt%. Specifically, the low-viscosity ionomer composition can have a viscosity of 10 cp to 30 cp at 25°C, and the high-viscosity ionomer composition can have a viscosity of 40 cp to 110 cp at 25°C. Also, the low-concentration ionomer composition can have a concentration of 5 wt% to 25 wt%, and the high-concentration ionomer composition can have a concentration of 40 to 85 wt%.

[0039] Among the manufactured internal reinforcement film and external reinforcement film, one or more can be post-treated with an acid to reduce voids that impede ion conduction and increase hydrogen permeation. The acid solution is not limited, and commonly used acids such as sulfuric acid, hydrochloric acid, and nitric acid can be used. The concentration of the acid solution can be used within the range of 0.01 - 5 mol concentration. The acid treatment can be in the form of applying the acid solution to the reinforcement film or immersing the reinforcement film in the acid solution, without limitation. After the acid treatment, it can be washed using deionized water, pressure can be applied to the reinforcement film to manufacture the reinforcement film with a thickness in the range of 10 - 15 μm, and heat treatment can be performed to manufacture the reinforcement film.

[0040] The internally reinforced film and the externally reinforced film manufactured in this way are joined together as shown in Fig. 1 to form a hydrogen ion conductive multilayer composite film. Before joining, the surface of the reinforced film to be joined can be pretreated with plasma first, and after coating the surface pretreated with the ionomer composition, they can be joined. In this case, a separate ionomer coating layer can exist between the internally reinforced film and the externally reinforced film. The above-mentioned separate ionomer coating layer can also form an interface that is distinguished from the plasma-pretreated surface, and sometimes the ionomer composition penetrates into a part of the interface and inside the reinforced film during ionomer coating, making the interface invisible to the naked eye. As can be seen in the examples described later, the hydrogen ion conductive multilayer composite film can further include a catalyst layer inside, and can also selectively further include other functional layers.

[0041] In the hydrogen ion conductive multilayer composite film according to the examples of the present invention, the externally reinforced film can be in the range of 15% to 40% and the internally reinforced film can be in the range of 60 - 85% based on the thickness. It can be excellent in durability, ion conductivity, and hydrogen permeation reduction effect within the above range. The hydrogen ion conductive multilayer composite film of the present invention can be very usefully used as a separation membrane for a water electrolysis system and a separation membrane for a fuel cell.

[0042] The types and structures of the water electrolysis system and the fuel cell to which the hydrogen ion conductive multilayer composite film of the present invention is applied as a separation membrane can be applied without limitation as long as hydrogen ions are conducted through the separation membrane, and since they are publicly known in detail, the description is omitted.

Examples

[0043] Hereinafter, the present invention will be described in more detail based on examples. Also, the scope of the present invention is not limited to the following examples.

[0044] Production Example 1 - 1: Production of Ionomer Composition A As the conductive ionomer, polyperfluorosulfonate (trade name Nafion, Dupont) was used as a perfluorinated sulfonated ionomer. As the solvent, isopropyl alcohol (IPA) was used, and the ionomer was adjusted to 12% by weight in the overall composition. A surfactant was added at 0.5% by weight in the overall composition to improve impregnation.

[0045] The ionomer composition was dispersed for 1 hour at 1000 - 2000 rpm using a Shear Stress device, and then secondarily dispersed for 1 hour at an amplitude of 30 - 50% using an Ultra - Sonic device so that the ionomer molecules were uniformly distributed within the composition. This was to adjust the size of the electrochemically active particles to facilitate impregnation into the pores of the PTFE membrane. The final viscosity of the ionomer composition was measured to be 20 cp at 25°C.

[0046] Production Example 1 - 2: Production of Ionomer Composition B Although carried out in the same manner as Production Example 1 - 1, it was carried out in the same way except that the ionomer was adjusted to 60% by weight in the overall solution, and the viscosity of the ionomer was measured to be 68 cp at 25°C.

[0047] Production Example 2 - 1: Production of PTFE / Ionomer Impregnated Membrane A Stretched porous PTFEA was prepared. The average pore size of the porous PTFEA was 0.15 μm and the porosity was 75%. First, the porous PTFEA was subjected to a primary plasma treatment at normal temperature and pressure with a plasma at 220 V and 2 - 10 A. Then, the ionomer composition A produced in Production Example 1 - 1 was impregnated into the interior of the support on the surface of the PTFEA surface - modified by the primary plasma treatment. After impregnation, the support was heat - treated so that the ionomer could crystallize. The heat - treatment was carried out at 100 - 150°C through hot air, and PTFE / ionomer impregnated membrane A was produced.

[0048] Production Example 2 - 2: Production of PTFE / Ionomer Impregnated Membrane B An extended porous PTFE B was prepared. The average pore size (poresize) of the porous PTFE B was 0.30 μm, and the porosity was 85%. Although carried out in the same manner as in Production Example 2-1, a PTFE / ionomer impregnated membrane B was produced in the same manner except that porous PTFE B was used instead of porous PTFE A.

[0049] Production Example 3-1: Production of PTFE / ionomer reinforced membrane A The upper surface of the impregnated membrane A of Production Example 2-1 was surface-modified by performing a secondary plasma treatment at 220 V and 1 to 4 A under normal temperature and pressure plasma. Thereafter, the ionomer composition B produced in Production Example 1-2 was coated on the newly formed surface-modified layer. After coating, a binary heat treatment was performed at 150 to 210 °C with hot air and 0 to 100 °C with near-infrared (NIR). Thereafter, the opposite surface of the impregnated membrane A was also subjected to plasma surface modification layer formation treatment, coating of the ionomer composition B, and heat treatment under the same conditions as above to produce a PTFE / ionomer reinforced membrane A.

[0050] Production Example 3-2: Production of PTFE / ionomer reinforced membrane B Although carried out in the same manner as in Production Example 3-1, a PTFE / ionomer reinforced membrane B was produced identically except that the impregnated membrane B of Production Example 2-2 was used instead of the impregnated membrane A of Production Example 2-1.

[0051] Production Example 3-1-1: Post-treatment of PTFE / ionomer reinforced membrane A The reinforced membrane A of Production Example 3-1 was treated with an acid for post-treatment. As the acid solution, a 1.0 molar concentration sulfuric acid aqueous solution was used to treat the reinforced membrane A, and it was washed with deionized water to reduce the voids that could occur during the impregnation and drying processes. Thereafter, the reinforced membrane was pressed to produce a 8-μm thick reinforced membrane A, and a heat treatment was carried out at 180 to 200 °C.

[0052] Production Example 3-2-1: Post-treatment of PTFE / ionomer reinforced membrane B Although the procedure was the same as in Production Example 3-1-1, a 15-μm thick Reinforcement Film B was produced by proceeding with the post-treatment in the same manner using Reinforcement Film B of Production Example 3-2 instead of Reinforcement Film A of Production Example 3-1.

[0053] Production Example 4-1: Production of PTFE / Ionomer Multilayer Composite Film A One surface of the PTFE / ionomer Reinforcement Film A of Production Example 3-1-1 was surface-modified by performing a normal-temperature and normal-pressure plasma treatment under the conditions of 220 V and 2 - 10 A. On the other hand, one surface of the PTFE / ionomer Reinforcement Film B of Production Example 3-2-1 was plasma-treated under the same conditions as above to modify the surface. Thereafter, the ionomer composition B of Production Example 1-2 was coated on the plasma-treated surface of the PTFE / ionomer Reinforcement Film A. After bringing the plasma-treated surface of the PTFE / ionomer Reinforcement Film B into contact with the coating layer of the ionomer composition B, heat bonding was performed to produce a PTFE / ionomer multilayer composite film having two PTFEs. Thereafter, heat treatment was carried out at 150 - 210 °C through hot air, and heat treatment was advanced at 50 - 100 °C for NIR.

[0054] Two PTFE / ionomer multilayer composite films having two PTFEs produced above were prepared, and the exposed surfaces of the PTFE / ionomer Reinforcement Film B were each plasma-treated in the same manner as above to modify the surface. Thereafter, the ionomer composition B of Production Example 1-2 was coated on the plasma-treated surface of any one of the Reinforcement Films B, and heat bonding was performed in the same manner as above to produce a PTFE / ionomer multilayer composite film having four PTFEs. Heat treatment was advanced in the same manner as above to finally produce a PTFE / ionomer multilayer composite film having four PTFEs. The thickness of the multilayer composite film was measured to be approximately 50 μm.

[0055] Production Example 4-2: Production of PTFE / Ionomer Multilayer Composite Film B Although plasma treatment, ionomer coating, and thermal bonding were carried out in the same manner as in Production Example 4-1, a PTFE / ionomer multilayer composite film B with three PTFEs, in which the internal reinforcing film B is one and is laminated and thermally bonded in a reinforcing film A / reinforcing film B / reinforcing film A structure, was produced. The thickness of the multilayer composite film was measured to be about 35 μm.

[0056] Production Example 4-3: Production of PTFE / ionomer multilayer composite film C Although plasma treatment, ionomer coating, and thermal bonding were carried out in the same manner as in Production Example 4-1, a PTFE / ionomer multilayer composite film C with three PTFEs, in which the layers were laminated and thermally bonded in a reinforcing film A / catalyst layer / reinforcing film B / reinforcing film B / reinforcing film A structure, was produced. The thickness of the multilayer composite film was measured to be about 53 μm. The catalyst layer is composed of a mesh layer coated with cerium oxide and was laminated and carried out between the reinforcing film A and the reinforcing film B before thermal bonding in Production Example 4-1. The catalyst layer is for preventing side reactions due to the gas crossover phenomenon that may occur during driving, enhancing the driving performance, and enhancing the durability.

[0057] Production Example 4-4: Production of PTFE / ionomer multilayer composite film D Although plasma treatment, ionomer coating, and thermal bonding were carried out in the same manner as in Production Example 4-1, a PTFE / ionomer multilayer composite film D with four PTFEs, in which the layers were laminated and thermally bonded in a reinforcing film A / reinforcing film A / reinforcing film A / reinforcing film A structure, was produced. The thickness of the multilayer composite film was measured to be about 50 μm.

[0058] Production Example 4-5: Production of PTFE / ionomer multilayer composite film E Although plasma treatment, ionomer coating, and thermal bonding were carried out in the same manner as in Production Example 4-1, a PTFE / ionomer multilayer composite film E with four PTFEs, in which the layers were laminated and thermally bonded in a reinforcing film B / reinforcing film B / reinforcing film B / reinforcing film B structure, was produced. The thickness of the multilayer composite film was measured to be about 50 μm.

[0059] Experimental Example 1: Tensile strength evaluation Samples were prepared by taking the products manufactured in the production examples and cutting them into a size of 1 cm * 10 cm in the MD (Machine Direction) and TD (Transverse Direction) directions, with the horizontal and vertical lengths being 1 cm and 10 cm respectively. The corresponding samples were fixed to a jig of a universal material testing machine, and the tensile strength was evaluated with a distance of 5 cm between the upper jig and the lower jig. The results are shown in Table 1.

[0060] Experimental Example 2: Ionic Conductivity Evaluation Samples were prepared by taking the products manufactured in the production examples and cutting them into a size of 4 cm * 1 cm for the composite membrane. The corresponding samples were fastened to an ionic conductivity jig. The measurement environment was maintained at a temperature of 80 °C and a humidity of 95% in a constant temperature and humidity-resistant chamber, and the measurement was performed with an impedance analyzer in the measurement range of 0.001 Hz to 100,000 Hz (Through-plane standard). The results are shown in Table 1.

[0061] Experimental Example 3: Hydrogen Permeability Evaluation of the Impregnated Membrane The hydrogen permeability of the products manufactured in the production examples was measured through the Bubble Flowmeter measurement method. The measurement was carried out at 60 °C and 9 bar, and the results are shown in Table 1.

[0062] Experimental Example 4: Accelerated Durability Evaluation Test After manufacturing the products manufactured in the production examples with MEA, the OCV was monitored. The cell temperature was set to 90 °C, and the relative humidity was set to 0% (dry, 30 seconds) - 100% (wet, 45 seconds), and about 10,000 cycles were performed. The results are shown in Table 2.

[0063]

Table 1

[0064] As can be seen from Table 1 above, it can be confirmed that the hydrogen permeability of the reinforced membranes in Production Examples 3-1 and 3-2 decreased significantly compared to the impregnated membranes in Production Examples 2-1 and 2-2. Also, when post-treatment is carried out using an acid solution as in Production Examples 3-1-1 and 3-2-1, it can be confirmed that the voids decrease, the ionic conductivity improves, and the hydrogen permeability decreases.

[0065] Also, as seen in Production Examples 4-1 to 4-5, PTFE used for the external multilayer composite membrane is one with small pore size and porosity, and PTFE used for the internal multilayer composite membrane is one with relatively large pore size and porosity, and it can be confirmed that ion conductivity performance, durability, and hydrogen permeability performance can be achieved simultaneously.

[0066]

Table 2

Claims

1. An internally reinforced membrane comprising a porous PTFE layer impregnated with an ionomer composition; and An externally reinforced membrane located on both sides of the internally reinforced membrane and comprising a porous PTFE layer impregnated with an ionomer composition; A hydrogen ion conductive multilayer composite membrane.

2. The average pore size and porosity of the porous PTFE layer of the externally reinforced membrane are smaller than the average pore size and porosity of the PTFE of the internally reinforced membrane, The average pore size of the PTFE of the externally reinforced membrane is 0.1 to 0.2 μm, and the porosity is in the range of 70% to 80%, The average pore size of the PTFE of the internally reinforced membrane is 0.2 to 0.4 μm, and the porosity is in the range of 80% to 90%. The hydrogen ion conductive multilayer composite membrane according to Claim 1.

3. The internally reinforced membrane is laminated within a range of 1 or 2 to 5. The hydrogen ion conductive multilayer composite membrane according to Claim 1.

4. The externally reinforced membrane is A PTFE layer impregnated with an ionomer inside; A surface modified layer formed by plasma surface treatment on the outer surface or both surfaces of the PTFE layer; and An ionomer layer coated on the surface modified layer formed on the outer surface or both surfaces; The hydrogen ion conductive multilayer composite membrane according to Claim 1.

5. The internally reinforced membrane is A PTFE layer impregnated with an ionomer inside; A surface modified layer formed by plasma surface treatment on the outer surface or both surfaces of the PTFE layer; and An ionomer layer coated on the surface modified layer formed on the outer surface or both surfaces; The hydrogen ion conductive multilayer composite membrane according to Claim 1.

6. The viscosity and ionomer concentration of the ionomer composition used when coating the ionomer layer on the surface modified layer are higher than the viscosity and ionomer concentration of the ionomer composition used when impregnating the ionomer inside the PTFE layer. The hydrogen ion conductive multilayer composite membrane according to Claim 4.

7. The viscosity difference is in the range of 10 cp to 100 cp from 25 °C, and the concentration difference is in the range of 30 wt% to 80 wt%. The hydrogen ion conductive multilayer composite membrane according to Claim 6.

8. One or more of the internally reinforced membrane and the externally reinforced membrane are treated with an acid to reduce voids. The hydrogen ion conductive multilayer composite membrane according to Claim 1.

9. Before the above-mentioned internal reinforcing film and the above-mentioned external reinforcing film are laminated, the surfaces to be laminated are pretreated with plasma first, and after coating the surfaces pretreated with the ionomer composition, they are laminated. There is a separate ionomer coating layer between the internal reinforcing film and the external reinforcing film. The hydrogen ion conductive multilayer composite membrane according to claim 1.

10. The hydrogen ion conductive multilayer composite membrane according to claim 9, wherein a catalyst mesh layer is laminated between the at least one or more external reinforcing films and the at least one or more internal reinforcing films, and a catalyst layer is present.

11. A water electrolysis system including the hydrogen ion conductive multilayer composite membrane of claim 1 as a separation membrane.

12. A fuel cell including the hydrogen ion conductive multilayer composite membrane of claim 1 as a separation membrane.

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