Hydrogen ion conductive multilayer composite membrane

Abstract

The present invention provides a hydrogen ion conductive multilayer composite membrane comprising an inner reinforced membrane comprising a porous PTFE layer impregnated with an ionomer composition, and outer reinforced membranes on both sides of the inner reinforced membrane, the outer reinforced membranes comprising a porous PTFE layer impregnated with an ionomer composition.

Description

Technical Field

[0001] The present invention relates to a multilayer composite membrane with hydrogen ion conductivity. Background Art

[0002] Water electrolysis is a technology for obtaining hydrogen by electrolyzing water, which can produce hydrogen in an environmentally friendly manner. The types of water electrolysis are divided into cation exchange membrane (PEM; Proton Exchange Membrane), anion exchange membrane (AEM; Anion Exchange Membrane), alkaline solution, solid oxide, etc.

[0003] On the other hand, a fuel cell is a highly efficient power generation device. Compared with existing internal combustion engines, it has the advantages of high efficiency, less fuel consumption, and being a pollution-free energy source that does not produce environmental pollutants such as SOx, NOx, and VOC. In addition, it has additional advantages such as less floor area required for production equipment and short construction time. Its application fields are diverse, including mobile power sources such as portable devices, transportation power sources such as automobiles, and distributed power generation for household and power utility use.

[0004] Fuel cells are roughly divided into 5 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, the polymer electrolyte fuel cell with excellent mobility has attracted much attention.

[0005] The electrolyte membranes for cation exchange membrane water electrolysis and polymer electrolyte fuel cells mainly include fluorocarbon-based electrolyte membranes. A representative example is the perfluorinated hydrogen ion exchange membrane Nafion developed by DuPont in the early 1960s. In addition to Nafion, similar commercial perfluoropolymer electrolyte membranes include Aciplex-S membrane of Asahi Kasei, Dow membrane of Dow Chemical, Flemion membrane of Asahi Glass, etc.

[0006] This single membrane (Casting Membrane) is composed only of an ion-conductive electrolyte and is easy to manufacture, so it is widely used as an experimental and mass-produced product.

[0007] However, under the operating conditions of the water electrolysis system and the fuel cell system, fatigue of the material accumulates due to volume changes, resulting in durability problems. In addition, as the thickness of the membrane increases, the membrane resistance increases and the electrochemical performance decreases, and when the membrane thickness becomes thinner, the performance deteriorates due to problems of hydrogen permeation and durability.

[0008] Therefore, improvements to the above problems are needed.

[0009] Prior art documents

[0010] Patent documents

[0011] (Patent Document 1) Korean Patent No. 10-1995527 Summary of the Invention

[0012] An object of the present invention is to provide a hydrogen ion conductive multilayer composite film having excellent durability, ionic conductivity, and reduced hydrogen transmission effect.

[0013] In addition, an object of the present invention is to provide a water electrolysis system and a fuel cell using the hydrogen ion conductive multilayer composite film as a separator.

[0014] However, the object of the present invention is not limited to the above objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

[0015] As a means for solving the above problems,

[0016] The present invention provides a hydrogen ion conductive multilayer composite film, which includes an internal reinforcing film and external reinforcing films located on both sides of the internal reinforcing film. The internal reinforcing film includes a porous PTFE layer impregnated with an ionomer composition. The external reinforcing film includes a porous PTFE layer impregnated with an ionomer composition.

[0017] In addition, the average pore diameter and porosity of the porous PTFE layer of the external reinforcing film can be smaller than those of the PTFE layer of the internal reinforcing film.

[0018] In addition, the average pore diameter of the PTFE of the external reinforcing film 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 film is in the range of 0.2 μm to 0.4 μm, and the porosity is in the range of 80% to 90%.

[0019] In addition, the internal reinforcing film can be one layer, or can be stacked in the range of two to five layers.

[0020] In addition, the external reinforcing film includes a PTFE layer internally impregnated with an ionomer; 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 formed on the above outer surface or both sides.

[0021] In addition, the internal reinforcing film includes a PTFE layer impregnated with an ionomer therein; 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 formed on the above outer surface or both sides.

[0022] In addition, the viscosity and the ionomer concentration of the ionomer composition used when coating the ionomer layer on the surface modification layer can be higher than those of the ionomer composition used when impregnating the ionomer inside the PTFE layer.

[0023] In addition, the viscosity difference at 25 °C can be in the range of 10 cp to 100 cp, and the concentration difference can be in the range of 30 wt% to 80 wt%.

[0024] In addition, one or more of the inner reinforcing film and the outer reinforcing film can be treated with an acid to reduce voids.

[0025] In addition, before bonding the inner reinforcing film and the outer reinforcing film, the surface to be bonded is first subjected to plasma pretreatment, and a separate ionomer coating can be present between the inner reinforcing film and the outer reinforcing film by applying and adhering the ionomer composition to the pretreated surface.

[0026] In addition, a catalyst mesh layer can be bonded between the at least one or more outer reinforcing films and the at least one or more inner reinforcing films, and a catalyst layer is present.

[0027] The present invention also provides a water electrolysis system and a fuel cell including the hydrogen ion-conducting multilayer composite film as a separator.

[0028] The hydrogen ion-conducting multilayer composite film according to the present invention has excellent durability, ion conductivity, and the effect of reducing hydrogen transmission, and thus can be effectively used as a separator for a water electrolysis system and a fuel cell.

[0029] The above effects and additional effects will be described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 and Figure 2 are schematic diagrams of the structure and manufacturing process of a hydrogen ion-conducting multilayer composite film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] Before explaining the present invention in detail, it should be understood that the terms used in this specification are only for describing specific embodiments and are not intended to limit the scope of the present invention. The scope of the present invention should only be defined by the scope of the appended claims. Unless otherwise clearly stated, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by those with ordinary knowledge.

[0032] Throughout this specification and the claims, unless otherwise expressly stated, the term "comprise", "comprises" or "comprising" is used to indicate the inclusion of the recited elements, steps or groups of elements and steps, and does not preclude the inclusion of any other elements, steps or groups of elements or steps.

[0033] On the other hand, various embodiments of the present invention may be combined with other embodiments, unless there is a clear contrary opinion.

[0034] The present invention will be described in more detail below.

[0035] According to an embodiment of the present invention, a hydrogen ion-conducting multilayer composite film includes an internal reinforcing film and external reinforcing films on both sides of the internal reinforcing film. The internal reinforcing film includes a porous PTFE layer impregnated with an ionomer composition. The external reinforcing films include porous PTFE layers impregnated with an ionomer composition. The internal reinforcing film may be one, as Figure 1 shown, or may be two or more. Preferably, it is stacked in a form within the range of two to five. The thickness of the hydrogen ion-conducting multilayer composite film may be in the range of 20 μm to 100 μm, and considering thin film formation, durability, hydrogen ion conductivity, reduction of hydrogen transmission, etc., it may be in the range of 30 μm to 60 μm.

[0036] The porous PTFE membrane can achieve porosity through a stretching process. The porous PTFE membrane can be obtained and used as a commercial product meeting the required performance, or can be directly manufactured.

[0037] The manufacturing method of the porous PTFE membrane can use known methods. For example, the porous PTFE membrane can be manufactured through the following steps. First, tetrafluoroethylene powder and a lubricant are mixed and then subjected to the next forming to obtain a preform. The above preform is extruded to obtain a rod-shaped primary formed body. The above primary formed body is processed into a sheet to obtain a secondary formed body. The above secondary formed body is dried to remove the above lubricant and then stretched in the transverse and longitudinal directions. The PTFE membrane with desired performance can be manufactured by controlling the type, content of the powder used, and the stretching process conditions.

[0038] The porous PTFE layer of the above external reinforcing film and the PTFE layer of the above internal reinforcing film can use the same PTFE membrane. More preferably, the average pore size and porosity of the porous PTFE layer of the above external reinforcing film are smaller than the average pore size and porosity of the PTFE of the above internal membrane reinforcement. By using a relatively small PTFE pore size and porosity for the external reinforcing film, hydrogen that may be introduced from the outside can be blocked, thereby reducing the hydrogen transmission rate and improving durability. The PTFE of the internal reinforcing film has a relatively large pore size and porosity, which can increase the impregnation property of the ionomer, impregnate the ionomer into a high content, and thus improve the hydrogen ion conductivity.

[0039] Specifically, the average pore size of the PTFE layer of the above external reinforcing film is in the range of 0.1 μm to 0.2 μm, and the porosity is in the range of 70% to 80%. The average pore size of the PTFE layer of the above internal reinforcing film is in the range of 0.2 μm to 0.4 μm, and the porosity is in the range of 80% to 90%. The difference in the average pore size between the two PTFE layers can be in the range of 0.05 to 0.3 μm, and the difference in porosity can be in the range of 5% to 20%.

[0040] The above ionomer composition may include a conductive ionomer, a solvent, and a surfactant. Optionally, it may also include a radical scavenger and the like.

[0041] As the conductive ionomer, any hydrogen ion conductive polymer can be used. For example, a polymer resin having a cation exchange group selected from sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups, and their derivatives can be used, and the cation exchange group has hydrogen ion conductivity.

[0042] For example, it may include one or more hydrogen ion conductive polymers selected from fluorine-based polymers, benzimidazole-based polymers, polyamide-based polymers, polyetherimide-based polymers, polyphenylene sulfide-based polymers, polysulfone-based polymers, polyethersulfone-based polymers, polyether ketone-based polymers, polyether ketone-like polymers, or polyphenylquinoxaline-based polymers.

[0043] Preferably, a perfluorosulfonated ionomer can be used as the conductive ionomer. Specifically, polyfluorosulfonate (trade name Nafion, Dupont) can be used as the perfluorosulfonated ionomer. In addition, commercial products such as Aciplex (Asahi Kasei Chemical), Flemion (Asahi Glass), and Fumion (fumatech) can also be used.

[0044] As the solvent, commonly used solvents such as N-methylpyrrolidone, isopropyl alcohol, and n-propanol can be used.

[0045] In consideration of the affinity with PTFE and environmental issues, the surfactant preferably contains a hydrophobic group in which hydrogen in the hydrocarbon is partially substituted by fluorine. The hydrophilic group of the above surfactant is preferably a hydrophilic group having an affinity for an ionomer having a sulfonic acid group.

[0046] Known surfactants can be used. For example, one selected from the group consisting of Zonyl series of DuPont, Novec series of 3M, or a mixture thereof can be used. Specifically, the above Zonyl series surfactants can include Zonyl TBS (RfCH2CH2SO3X (X = H or NH4), Rf = F(CF2CF2)3-8), Zonyl FSN (RfCH2CH2O(CH2CH20)xH)), and Zonyl FSP (RfCH2CH2O)P(O)(ONH4)2. In addition, Novec-based surfactants that can be used include Novec 4200 (fluoroalkylsulfonamide ammonium), Novec 4300 (fluoroalkylsulfonic acid ammonium), Novec 4430 (polymer fluorinated compound activator), and Novec 4432 (polymer fluorinated compound activator).

[0047] The method of impregnating the ionomer composition into porous PTFE is not limited. Examples include a method of coating the ionomer composition on porous PTFE or impregnating PTFE in the ionomer composition. Through impregnation, the ionomer composition penetrates into the interior of the porous PTFE. In addition, the ionomer composition can remain on the surface of the PTFE.

[0048] Before the impregnation process, the impregnability of the ionomer composition can be further improved by pretreating the porous PTFE with plasma. The plasma treatment can be performed on one or both sides of the PTFE.

[0049] The surface modification technology of plasma treatment is to apply various energies and particles to the surface. Physical impacts are applied to the surface, increasing roughness, cutting polymer chains, or forming new chemical bonds, resulting in an increase in hydrophilic groups.

[0050] Plasma treatment methods include a low-pressure plasma method that generates plasma by discharging under low pressure and an atmospheric pressure plasma method that generates plasma by discharging under atmospheric pressure. It is preferably to use the atmospheric pressure plasma method at normal temperature. The atmospheric pressure plasma technology can generate efficient, stable, and uniform plasma discharge at atmospheric pressure (760 Torr) without using a high-cost vacuum system, improving economy and productivity.

[0051] After impregnation, the support is heat-treated to crystallize the ionomer, and two heat sources are preferably used for the heat treatment. During the heat treatment, if the generated gas is not removed stepwise, cracks will occur after the heat treatment, leading to problems with hydrogen transmittance and durability. Specifically, the first heat treatment is performed at 150 to 210 °C by hot air, and the second heat treatment is performed at 50 to 100 °C by near-infrared rays (NIR).

[0052] On the other hand, the PTFE membrane impregnated with the ionomer is subjected to plasma treatment again to form a surface modification layer, and then an ionomer layer is coated to further improve the durability and hydrogen permeability reduction performance.

[0053] Specifically, as Figure 2 shown, the external reinforcement membrane may include a PTFE layer impregnated with an internal ionomer, a surface modification layer formed by heat treatment after plasma surface treatment on the outer surface or both surfaces of the above PTFE layer, and an ionomer layer coated on the surface modification layer formed on the outer surface or both sides (the drawing showing both sides treated is omitted).

[0054] Similarly, the above internal reinforcement membrane may include a PTFE layer impregnated with an internal ionomer, a surface modification layer formed by heat treatment after plasma surface treatment on the outer surface or both surfaces of the above PTFE layer, and an ionomer layer coated on the surface modification layer formed on the outer surface or both sides.

[0055] Here, the viscosity and ionomer concentration of the ionomer composition used when coating the ionomer layer on the surface modification layer may be higher than those of the ionomer composition used when impregnating the ionomer inside the PTFE layer. Since the inside of the PTFE has been impregnated with the ionomer, the ionomer composition used for coating the surface modification layer can use a relatively high viscosity and ionomer concentration to ensure coatability, film stability and uniformity, rather than impregnability.

[0056] The viscosity difference between the above two ionomer compositions is in 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 viscosity of the low-viscosity ionomer composition can reach 10 cp to 30 cp at 25 °C, and the viscosity of the high-viscosity polyionomer composition can reach 40 cp to 110 cp at 25 °C. In addition, 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%.

[0057] One or more of the above-mentioned internally reinforced film and externally reinforced film can be post-treated with an acid to reduce voids that impede ion conduction and increase hydrogen transmission. The acid solution is not limited, and common acids such as sulfuric acid, hydrochloric acid, and nitric acid can be used. The acid solution concentration can be used in the range of 0.01 - 5 mol concentration. The acid treatment can be in the form of coating the acid solution on the reinforced film or immersing the reinforced film in the acid solution, without limitation. After acid treatment, it is washed with deionized water, pressure is applied to the reinforced film, and a reinforced film with a thickness in the range of 10 - 15 μm is manufactured. The reinforced film can be manufactured by heat treatment.

[0058] The internally reinforced film and externally reinforced film prepared in this way can be stacked as Figure 1 shown to form a hydrogen ion-conducting multilayer composite film. Before stacking, the stacking surface of the reinforced film can be pretreated by plasma, and stacking can be carried out after coating the pretreated surface with an ionomer composition. In this way, there may be a separate ionomer coating between the internally reinforced film and the externally reinforced film. The above-mentioned separate ionomer coating can form an interface different from the plasma-pretreated surface, or when the ionomer is coated, the ionomer composition penetrates into a part of the interface and the interior of the reinforced film, so that the interface is not visible to the naked eye.

[0059] As shown in the following examples, the hydrogen ion-conducting multilayer composite film can contain a more catalyst layer inside, and can also selectively contain more other functional layers.

[0060] For the hydrogen ion-conducting multilayer composite film according to an embodiment of the present invention, based on the thickness, the externally reinforced film is in the range of 15% to 40%, and the internally reinforced film is in the range of 60% to 85%. Within the above range, the effects of durability, ion conductivity, and reduction of hydrogen transmission can be excellent.

[0061] The hydrogen ion-conducting multilayer composite film of the present invention can be very effectively used as a separator for a water electrolysis system and a separator for a fuel cell.

[0062] The hydrogen ion-conducting multilayer composite film of the present invention is not limited to the type and structure of the water electrolysis system and fuel cell used as a separator. The details have been published, so the description is omitted. If the water electrolysis system and fuel cell are in a mode where hydrogen ions are conducted through the separator, it can be applied without limitation.

[0063] Hereinafter, the present invention will be described in more detail according to examples. In addition, the scope of the present invention is not limited to the following examples.

[0064] Preparation Example 1-1: Preparation of Ionomer Composition A

[0065] This manufacturing example uses perfluorosulfonate (trade name Nafion, Dupont) as the conductive ionomer, which is 12% by weight in the whole composition, and isopropyl alcohol (IPA) as the solvent. To improve the impregnation property, 0.5% by weight of a surfactant is added to the whole composition.

[0066] The ionomer composition was dispersed at 1000 to 2000 rpm for 1 hour using a ShearStress device, and then secondarily dispersed at 30% to 50% amplitude for 1 hour using an Ultra-Sonic device to uniformly distribute the ionomer molecules in the composition. This is to facilitate immersion into the pores of the PTFE membrane by adjusting the rheological particle size.

[0067] The final viscosity of the ionomer composition was measured to be 20 cp at 25 °C.

[0068] Preparation Example 1-2: Preparation of Ionomer Composition B

[0069] It was prepared in the same manner as Preparation Example 1-1, except that the ionomer was 60% by weight of the total solution. The viscosity of the ionomer was measured to be 68 cp at 25 °C.

[0070] Preparation Example 2-1: Preparation of PTFE / Ionomer Impregnated Membrane A

[0071] Expandable porous PTFE A was prepared. The average pore size and porosity of porous PTFE A were 0.15 μm and 75%, respectively.

[0072] First, at room temperature and atmospheric pressure, porous PTFE A was subjected to a primary plasma treatment under conditions of 220 V and 2 - 10 A. After that, the ionomer composition A prepared in Preparation Example 1-1 was impregnated into the support on the surface of PTFE A modified by the primary plasma treatment. After impregnation, the carrier was heat-treated to enable the ionomer to crystallize. Heat treatment was carried out at 100 to 150 °C by hot air to prepare PTFE / ionomer impregnated membrane A.

[0073] Preparation Example 2-2: Preparation of PTFE / Ionomer Impregnated Membrane B

[0074] Expandable porous PTFE B was prepared. The average pore size and porosity of porous PTFE B were 0.30 μm and 85%, respectively.

[0075] PTFE / ionomer impregnated membrane B was prepared in the same manner as Preparation Example 2-1, except that porous PTFE B was used instead of porous PTFE A.

[0076] Preparation Example 3-1: Preparation of PTFE / Ionomer Reinforced Membrane A

[0077] The surface modification was carried out by subjecting the upper surface of the impregnated film A of Preparation Example 2-1 to a second plasma treatment under the conditions of 220 V and 1-4 A, room temperature, and atmospheric pressure. Thereafter, the ionomer composition B prepared in Preparation Example 1-2 was coated on the newly formed surface modification layer. After coating, dual-source heat treatment was performed under hot air at 150-210 °C and near-infrared (NIR) at 0-100 °C.

[0078] Then, under the same conditions as above, the opposite side of the impregnated film A was also subjected to plasma surface modification layer formation treatment, ionomer composition B coating, and heat treatment to prepare the PTFE / ionomer reinforced film A.

[0079] Preparation Example 3-2: Preparation of PTFE / ionomer reinforced film B

[0080] The PTFE / ionomer reinforced film B was prepared in the same manner as Preparation Example 3-1, except that the impregnated film B of Preparation Example 2-2 was used instead of the impregnated film A of Preparation Example 2-1.

[0081] Preparation Example 3-1-1: Post-treatment of PTFE / ionomer reinforced film A

[0082] The reinforced film A of Preparation Example 3-1 was post-treated by acid treatment. As the acid solution, an aqueous sulfuric acid solution with a concentration of 1.0 mol was used to treat the reinforced film A, and it was washed with deionized water to reduce the pores that might appear during the impregnation and drying processes. Thereafter, the reinforced film was pressurized to prepare a reinforced film A with a thickness of 8 μm, and heat treatment was performed at 180 °C to 200 °C.

[0083] Preparation Example 3-2-1: Post-treatment of PTFE / ionomer reinforced film B

[0084] Using the reinforced film B of Preparation Example 3-2 instead of the reinforced film A of Preparation Example 3-1, a reinforced film B with a thickness of 15 μm was manufactured by performing post-treatment in the same manner.

[0085] Preparation Example 4-1: Preparation of PTFE / ionomer multilayer composite film A

[0086] One side of the PTFE / ionomer reinforced film A of Preparation Example 3-1-1 was subjected to plasma treatment under the conditions of 220 V and 2-10 A, room temperature, and atmospheric pressure to modify the surface.

[0087] On the other hand, one side of the PTFE / ionomer reinforced film B of Preparation Example 3-2-1 was subjected to plasma treatment under the same conditions to modify the surface.

[0088] Thereafter, the plasma-treated surface of the PTFE / ionomer reinforced film A was coated with the ionomer composition B of Preparation Example 1-2, and the plasma-treated surface of the PTFE / ionomer reinforced film B was brought into contact with the coating of the ionomer composition B, and then thermally laminated to prepare a PTFE / ionomer multilayer composite film having two layers of PTFE. Thereafter, heat treatment was carried out at 150-210 °C by hot air, and NIR heat treatment was carried out at 50-100 °C.

[0089] Two PTFE / ionomer multilayer composite films having the two PTFE layers prepared above were prepared, and the exposed surfaces of each PTFE / ionomer reinforced film B were plasma-treated in the same manner as above to modify the surfaces. Thereafter, the ionomer composition B of Preparation Example 1-2 was coated on the plasma-treated surface of any one of the reinforced films B, and thermally bonded in the same manner as above to prepare a PTFE / ionomer multilayer composite film having four layers of PTFE, and heat treatment was carried out in the same manner as above, and finally a PTFE / ionomer composite film having four layers of PTFE was prepared. The thickness of the multilayer composite film was measured to be about 50 μm.

[0090] Preparation Example 4-2: Preparation of PTFE / ionomer multilayer composite film B

[0091] Plasma treatment, ionomer coating and thermal lamination were carried out in the same manner as in Preparation Example 4-1, except that the reinforced film A / reinforced film B / reinforced film A structure was stacked and thermally laminated to prepare a PTFE / ionomer multilayer composite film B having three layers of PTFE and one inner reinforced film B. The thickness of the multilayer composite film was measured to be about 35 μm.

[0092] Preparation Example 4-3: Preparation of PTFE / ionomer multilayer composite film C

[0093] Plasma treatment, ionomer coating and thermal lamination were carried out in the same manner as in Preparation Example 4-1, but the reinforced film A / catalyst layer / reinforced film B / reinforced film B / reinforced film A structure was thermally laminated. A PTFE / ionomer multilayer composite film C having three layers of PTFE was prepared by lamination. The thickness of the multilayer composite film C was measured to be about 53 μm.

[0094] The catalyst layer was composed of a reticulated layer coated with cerium oxide, and was carried out by stacking the catalyst layer between the reinforced film A and the reinforced film B before thermal lamination in Preparation Example 4-1. The catalyst layer was to prevent side reactions due to gas penetration phenomena that may occur during driving, thereby improving performance and durability.

[0095] Preparation Example 4-4: Preparation of PTFE / ionomer multilayer composite film D

[0096] Plasma treatment, ionomer coating, and thermal lamination were carried out in the same manner as in Preparation Example 4-1, except that the structure of Reinforcing Film A / Reinforcing Film A / Reinforcing Film A / Reinforcing Film A / Reinforcing Film A was stacked and thermally laminated to prepare a PTFE / ionomer multilayer composite film D having four layers of PTFE. The thickness of the multilayer composite film D was measured to be about 50 μm.

[0097] Preparation Example 4-5: Preparation of PTFE / ionomer Multilayer Composite Film E

[0098] Plasma treatment, ionomer coating, and thermal lamination were carried out in the same manner as in Preparation Example 4-1, except that the structure of Reinforcing Film B / Reinforcing Film B / Reinforcing Film B / Reinforcing Film B / Reinforcing Film B was stacked and thermally laminated to prepare a PTFE / ionomer multilayer composite film E having four layers of PTFE. The thickness of the multilayer composite film E was measured to be about 50 μm.

[0099] Experimental Example 1: Tensile Strength Evaluation

[0100] Samples of the preparation examples were prepared to have a width and length of 1 cm × 10 cm in the MD (machine direction) and TD (transverse direction), respectively, and the samples were fixed to a universal material tester fixture, and the tensile strength was evaluated by setting the distance between the upper and lower fixtures to 5 cm.

[0101] The results are shown in Table 1.

[0102] Experimental Example 2: Evaluation of Ionic Conductivity

[0103] Samples of the preparation examples were prepared to have a composite film size of 4 cm × 1 cm, and the samples were fixed to an ionic conductivity fixture. Using a thermo-hygrostat, the measurement environment was maintained at a temperature of 80°C and a humidity of 95%, and the measurement was carried out using an impedance analyzer in the measurement range of 0.001 Hz to 100,000 Hz (based on the through-plane). The results are shown in Table 1.

[0104] Experimental Example 3: Hydrogen Permeability Evaluation

[0105] The hydrogen permeability of the samples of the preparation examples was measured at 60°C and 9 bar by the bubble flowmeter measurement method, and the results are shown in Table 1.

[0106] Experimental Example 4: Accelerated Durability Evaluation

[0107] After preparing a membrane electrode assembly (MEA) using the membranes prepared in the preparation examples, the OCV was monitored. The battery temperature was set to 90°C, 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.

[0108]

Table 1

[0109]

[0110] As shown in Table 1, it can be seen that the hydrogen permeability of the reinforced membranes of Preparation Examples 3-1 and 3-2 is significantly reduced compared with the impregnated membranes of Preparation Examples 2-1 and 2-2. In addition, in the case of post-treatment with an acid solution, as shown in Preparation Examples 3-1-1 and 3-2-1, the pores are reduced, whereby the ionic conductivity is increased and the hydrogen permeability is reduced.

[0111] In addition, it can be seen from Preparation Examples 4-1 to 4-5 that the PTFE layer for the outer multi-layer composite membrane has a smaller pore diameter and porosity, while the PTFE layer for the inner multi-layer composite membrane has a larger pore diameter and porosity, which can improve the durability and ionic conductivity and reduce the hydrogen permeation rate.

[0112] [Table 2]

[0113] Preparation Example Initial OCV Value Final OCV Value Preparation Example 4-1 0.96 0.76 Preparation Example 4-3 0.97 0.82

[0114] In addition, it can be seen from Table 2 that by using a catalyst layer such as in Preparation Example 4-3, the durability of the multi-layer composite membrane is further improved and the driving performance is excellent.

Claims

1. A hydrogen ion conductive multilayer composite membrane, comprising: An internal reinforcing membrane; and External reinforcing membranes located on both sides of the internal reinforcing membrane; Wherein the internal reinforcing membrane comprises a porous PTFE layer impregnated with an ionomer composition, Wherein the external reinforcing membrane comprises a porous PTFE layer impregnated with an ionomer composition.

2. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, The average pore size and porosity of the porous PTFE layer of the external reinforcing membrane are smaller than those of the PTFE layer of the internal reinforcing membrane. Among them, the average pore size of the PTFE of the external reinforcing membrane is in the range of 0.1 μm to 0.2 μm, and the porosity is in the range of 70% to 80%. Among them, the average pore size of the PTFE of the internal reinforcing membrane is in the range of 0.2 μm to 0.4 μm, and the porosity is in the range of 80% to 90%.

3. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, The internal reinforcing membranes are stacked in the range of one or two layers to five layers.

4. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, The external reinforcing membrane includes: A PTFE layer internally impregnated with an ionomer; A surface modification layer formed by plasma surface treatment of one or both outer surfaces of the PTFE layer; and an ionomer layer coated on the surface modification layer formed on the above outer surface or both sides.

5. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, The internal reinforcing membrane includes: A PTFE layer impregnated with an ionomer therein; A surface modification layer formed by plasma surface treatment of one or both outer surfaces of the PTFE layer; and an ionomer layer coated on the surface modification layer formed on the above outer surface or both sides.

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

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

8. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, One or more layers of the internal reinforcing membrane and the external reinforcing membrane are treated with acid to reduce voids.

9. The hydrogen ion conductive multilayer composite membrane according to claim 1, wherein, Before joining the internal reinforcing membrane and the external reinforcing membrane, the surface to be joined is first subjected to plasma pretreatment. By applying and adhering an ionomer composition to the pretreated surface, a separate ionomer coating exists between the internal reinforcing membrane and the external reinforcing membrane.

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

11. A water electrolysis system comprising the hydrogen ion conductive multilayer composite membrane according to claim 1 as a diaphragm.

12. A fuel cell comprising the hydrogen ion conductive multilayer composite membrane according to claim 1 as a diaphragm.

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