Electrolyte membrane and method for manufacturing the same

Abstract

The present invention provides at least one of the following: an electrolyte membrane with superior proton conductivity and gas shielding properties compared to conventional electrolyte membranes using hydrocarbon-based electrolyte polymers, and a method for manufacturing the same. [Solution] An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, The contact layer comprises at least a hydrocarbon-based electrolyte polymer, The reinforcing layer is characterized by comprising at least a porous substrate, a surfactant, and a hydrocarbon-based electrolyte polymer.

Description

[Technical Field]

[0001] This disclosure relates to an electrolyte membrane and a method for manufacturing the same. [Background technology]

[0002] In polymer electrolyte fuel cells, the temperature inside the battery changes depending on the power generation state, and the resulting increase or decrease in the water content in the electrolyte membrane causes repeated expansion and contraction of the electrolyte membrane. On the other hand, in polymer electrolyte water electrolysis, a differential pressure is generated on the front and back of the electrolyte membrane due to the gas generated during electrolysis, resulting in a constant state of stress. Therefore, in both fuel cells and water electrolysis, the electrolyte membrane used must have not only functions such as proton conductivity and gas shielding properties, but also mechanical strength.

[0003] In response to such demands, studies are generally being conducted to improve the mechanical properties by using a porous substrate made of fluororesin, such as polytetrafluoroethylene (PTFE), as a reinforcing substrate, and by using a composite membrane in which a fluororesin electrolyte polymer is impregnated into the porous structure as the electrolyte membrane.

[0004] Furthermore, with the aim of reducing environmental impact, the use of hydrocarbon-based electrolyte polymers instead of fluorine-based electrolyte polymers is being considered. For example, Patent Document 1 discloses an electrolyte membrane that does not use fluorine-based electrolyte polymers, by impregnating and fixing a hydrocarbon-based electrolyte polymer into a fluorine-based porous substrate. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-094934 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, hydrocarbon-based electrolyte polymers and porous substrates made of PTFE have poor wettability. Therefore, in the electrolyte membrane described in Patent Document 1, the electrolyte polymer was difficult to impregnate into the porous substrate, and the two materials did not adhere well to each other. As a result, the basic functions of the electrolyte membrane, such as proton conductivity and gas shielding properties, were significantly low.

[0007] The present disclosure aims to provide at least one of the following: an electrolyte membrane with superior proton conductivity and gas shielding properties compared to conventional electrolyte membranes using hydrocarbon-based electrolyte polymers, and a method for manufacturing the same. [Means for solving the problem]

[0008] In this disclosure, we investigated an electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, focusing on the structure of the electrolyte membrane and the reinforcing layer. As a result, we found that the above objective can be achieved by incorporating a surfactant into the reinforcing layer.

[0009] In other words, the present invention is as described in the claims, and the gist of this disclosure is as follows. [1] An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, The contact layer comprises at least a hydrocarbon-based electrolyte polymer, The reinforcing layer is characterized by comprising at least a porous substrate, a surfactant, and a hydrocarbon-based electrolyte polymer. [2] The electrolyte membrane according to [1] above, wherein the hydrocarbon electrolyte polymer is one or more selected from the group consisting of polysulfone, polyphenylene oxide, polyethersulfone, polyphenylene sulfide, polyparaphenylene, polybenzthiazole, polybenzimidazole, polyamide, polyimide, polyaliene polymer, polyetherimide, and polyetherketone. [3] The electrolyte membrane according to [1] or [2], wherein the hydrocarbon electrolyte polymer is one or more selected from the group P1 to P5.

[0010] [Chemical formula]

[0011] [4] The electrolyte membrane according to any one of [1] to [3] above, wherein the surfactant is one or more compounds selected from the group consisting of anionic, cationic, and nonionic compounds. [5] The electrolyte membrane according to any one of [1] to [4] above, which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis. [6] A method for producing an electrolyte membrane according to any one of [1] to [5] above, comprising a first impregnation step of impregnating a porous substrate with a surfactant solution, a drying step of removing a solvent from the porous substrate, and a second impregnation step of impregnating the porous substrate with a hydrocarbon-based electrolyte polymer solution. [7] The method for producing an electrolyte membrane according to [6] above, wherein the second impregnation step includes a process of filling the pores of the porous substrate with a solution of the electrolyte polymer, a process of drying the filled solution of the electrolyte polymer, and a process of applying the solution of the electrolyte polymer to the surface of the porous substrate. [Advantages of the Invention]

[0012] According to the present disclosure, it is possible to provide at least one of an electrolyte membrane excellent in proton conductivity and gas barrier properties and a method for producing the same, as compared with an electrolyte membrane using a conventional hydrocarbon-based electrolyte polymer. [Brief Description of the Drawings]

[0013] [Figure 1] It is a schematic diagram showing a cross section of the electrolyte membrane of the present disclosure. [Figure 2] It is a schematic diagram showing a cross section of the reinforcing layer of the present disclosure. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, an example of an embodiment of the present disclosure will be shown and described. The present disclosure includes any combination of each configuration and parameter disclosed in this specification, and also includes any combination range of the upper limit and the lower limit of the values disclosed in this specification. In this specification, "~" includes the lower end and the upper end values. <Electrolyte membrane> This embodiment is an electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, wherein the contact layer contains at least a hydrocarbon-based electrolyte polymer, and the reinforcing layer is an electrolyte membrane containing at least a porous substrate, a surfactant, and a hydrocarbon-based electrolyte polymer.

[0015] The electrolyte membrane of this embodiment has a structure in which a reinforcing layer is sandwiched between contact layers. That is, it is a structure in which both surfaces of the reinforcing layer are sandwiched by contact layers, and the contact layer, the reinforcing layer, and the contact layer are laminated in this order and integrated. The electrolyte membrane of this embodiment has a higher affinity and adhesion between the electrolyte polymer and the porous substrate compared to an electrolyte membrane that does not contain a surfactant. As a result, even after a thermal history such as temperature increase and high-temperature cycles, the electrolyte membrane is less likely to deteriorate.

[0016] The contact layer contains at least a hydrocarbon-based electrolyte polymer, and preferably has the hydrocarbon-based electrolyte polymer as a main component. The contact layer exhibits high flexibility and is likely to adhere to catalyst particles. Thereby, when used as an electrolyte membrane of a fuel cell or water electrolysis, a sufficient proton conduction path is ensured. In this specification, the main component means the component having the largest content among the contained components. The content of the main component is, for example, 60% by mass or more, and may be 80% by mass or more or 90% by mass or more. The contact layer may contain a surfactant or may contain inevitable impurities and the like.

[0017] Furthermore, the thickness of the contact layer is 1 μm or more, or 2 μm or more, and preferably 10 μm or less. The contact layer on the surface and the contact layer on the back surface (the two contact layers sandwiching the reinforcing layer) may have the same thickness or they may be different. A contact layer thickness of 1 μm or more prevents the porous support from being exposed on the surface of the electrolyte membrane, and the contact layer has appropriate flexibility, allowing it to adhere closely to the catalyst particles and increase the contact area between the electrolyte polymer and the catalyst particles, thereby expanding the proton conduction pathway. A contact layer thickness of 10 μm or less suppresses swelling of the contact layer and prevents a decrease in the mechanical strength of the electrolyte membrane. The thickness of the contact layer is 1 μm or more and 10 μm or 2 μm or more and 10 μm or less.

[0018] The hydrocarbon electrolyte polymer contained in the contact layer is preferably a hydrocarbon resin having ionic groups. The hydrocarbon resin is any hydrocarbon resin having at least one of aliphatic alkyl chains and aromatic molecular structures in its main chain and side chain skeleton, and may have heterobonds. On the other hand, it is preferable that the hydrocarbon resin does not contain fluorine atoms (F) in its molecule (fluorine content is below the detection limit). Examples of hydrocarbon electrolyte polymers include one or more selected from the group consisting of polysulfone, polyphenylene oxide, polyethersulfone, polyphenylene sulfide, polyparaphenylene, polybenzthiazole, polybenzimidazole, polyamide, polyimide, polyaliene polymer, polyetherimide, and polyetherketone.

[0019] The ionic group can be any ionic group that can be used in electrolyte polymers used in solid polymer fuel cells and water electrolysis, and a sulfonic acid group is preferred.

[0020] The hydrocarbon electrolyte polymer is preferably a hydrocarbon electrolyte polymer having hydrophilic constituent units (hydrophilic portion) and hydrophobic constituent units (hydrophobic portion). More preferably, the hydrocarbon electrolyte polymer is one or more selected from the following group P1 to P5.

[0021] [ka]

[0022] In P1 through P5, n represents the number of repetitions.

[0023] The number-average molecular weight (Mn) of the electrolyte polymer can be any value depending on its molecular structure, but it can be 50,000 or more or 70,000 or more, or 300,000 or less or 250,000 or less, or 50,000 to 300,000 or 70,000 to 250,000.

[0024] In this embodiment, the number-average molecular weight of the electrolyte polymer is a standard polyethylene glycol / oxide (PEG / PEO) equivalent value measured by gel permeation chromatography (GPC).

[0025] The specific gravity of electrolyte polymers varies depending on the repeating units and structure, but for example, it is 1.0 g / cm³. 3 More than 2.4g / cm 3 Furthermore, 1.5 g / cm³ 3 More than 2.2g / cm 3 The following are listed:

[0026] The electrolyte polymer may have a cross-linked structure. Having a cross-linked structure increases the molecular weight, which can lead to improved mechanical properties.

[0027] The crosslinked structure may be any structure derived from a known crosslinkable compound, and from the viewpoint of chemical stability, it is preferable that it is a structure having one or more aromatic rings. The crosslinked structure may include aromatic rings, and hydrocarbons having hydrophilic and hydrophobic parts may be bonded to the aromatic rings directly or via -O-, -S-, or -SO2-.

[0028] The reinforcing layer comprises at least a porous substrate, a surfactant, and a hydrocarbon-based electrolyte polymer.

[0029] The porous substrate included in the reinforcing layer may be any substrate having pores and having lower flexibility than the contact layer, and examples include porous membranes, more specifically, porous membranes made of resin, more specifically, porous membranes made of fluororesin, and more specifically, porous membranes made of hydrocarbon resin. The hydrocarbon resin is preferably one or more selected from the group consisting of polyolefins, polyesters, polyphenylene sulfide, polyetherimide, polyimide, polyurethane, and polyethersulfone, and more preferably polyolefin. The fluororesin is preferably one or more selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkanes, and polyvinylidene fluoride, and more preferably polytetrafluoroethylene (PTFE).

[0030] The porous substrate has pores, and preferably has pores that communicate at least in the thickness direction. In the porous substrate constituting the reinforcing layer, it is sufficient if at least one of the electrolyte polymer and the surfactant fills at least some, preferably all, of the pores.

[0031] The average pore size of the porous substrate may be 0.1 nm or larger, 0.5 nm or larger, or 1 nm or larger, or 300 μm or smaller, 250 nm or smaller, or 200 μm or smaller, or 0.1 nm to 300 μm or smaller, 0.5 nm to 250 μm or smaller, or 1 nm or larger or 200 μm or smaller.

[0032] The thickness of the porous substrate may be 1 μm or more or 2 μm or more, or 100 μm or less or 30 μm or less, or 1 μm or more and 100 μm or less, or 2 μm or more and 30 μm or less.

[0033] The porosity of the porous substrate is preferably 60% or more, or 70% or more, and preferably 98% or less, or 95% or less. For example, it may be 60% to 98% or 70% to 95%. The porosity of the porous substrate can be calculated from the specific gravity of the material constituting the porous support and the mass of the apparent volume as follows.

[0034] Porosity (%) = 100 × [Mass of porous support (g)] / [Volume of porous support (cm³)] 3 ) × Specific gravity (g / cm³) of the material constituting the porous support 3 )] The electrolyte polymer contained in the reinforcing layer may be the same as or different from the electrolyte polymer contained in the contact layer. It is preferable that the electrolyte polymer contained in the reinforcing layer and the electrolyte polymer contained in the contact layer be the same, as this eliminates the difference in proton conductivity due to differences in polymer species.

[0035] The surfactant contained in the reinforcing layer may be any compound that exhibits a surfactant effect on the porous substrate, and is preferably one or more compounds selected from the group of anionic, cationic, and nonionic compounds, with nonionic compounds being more preferable. Furthermore, it is preferable that the surfactant does not contain metal ions. This makes side reactions between the surfactant and the electrolyte polymer less likely to occur, and the proton conductivity of the electrolyte membrane is more easily improved.

[0036] The surfactant only needs to have heat resistance so as not to decompose during the manufacturing process of the electrolyte membrane or at the operating temperature of the fuel cell or water electrolysis. Furthermore, it is preferable that the surfactant has acid resistance in order to exhibit resistance when in contact with acidic electrolyte polymers.

[0037] Specific examples of surfactants include the Softanol series (manufactured by Nippon Shokubai Co., Ltd.), the Emulmin series (manufactured by Sanyo Chemical Industries, Ltd.), the Newpol series (manufactured by Sanyo Chemical Industries, Ltd.), the MEGAFACE series (manufactured by DIC Corporation), and the Stahome series (manufactured by NOF Corporation).

[0038] The reinforcing layer preferably has a structure in which at least a portion of the hydrocarbon-based electrolyte polymer is contained within the pores of the porous substrate, and more preferably, a structure in which at least a portion of the hydrocarbon-based electrolyte polymer is contained within the pores of the porous substrate via a surfactant. Having such a structure ensures that the surfactant is present only in the vicinity of the porous substrate of the electrolyte polymer in the reinforcing layer. This makes it less likely for the surfactant to inhibit the movement of protons and water generated in the electrolyte polymer.

[0039] Furthermore, the electrolyte of this embodiment exhibits higher affinity and adhesion between the electrolyte polymer and the porous substrate compared to electrolyte membranes without surfactants. As a result, degradation of the electrolyte membrane is more easily suppressed, even after thermal histories such as heating and high-temperature cycling.

[0040] The electrolyte membrane of this embodiment can be used for known applications as an electrolyte membrane, and may be used as an electrolyte membrane for electrochemical devices, but it is preferable to use it as at least one of an electrolyte membrane for fuel cells and an electrolyte membrane for electrolysis, and more preferably as an electrolyte membrane for polymer electrolyte fuel cells or an electrolyte membrane for water electrolysis. <Method for manufacturing electrolyte membranes> The method for manufacturing the electrolyte membrane of this embodiment is arbitrary as long as it satisfies the above-described configuration. A preferred manufacturing method includes a step of impregnating a porous substrate with a surfactant solution (hereinafter also referred to as the "first impregnation step"), a step of removing the solvent from the porous membrane (hereinafter also referred to as the "drying step"), and a step of impregnating the porous substrate with a hydrocarbon-based electrolyte polymer solution (hereinafter also referred to as the "second impregnation step").

[0041] In the first impregnation step, at least a porous substrate and a surfactant solution are used. This allows the surfactant to be retained in the porous substrate, and in the subsequent second impregnation step, the electrolyte polymer can be impregnated into the porous substrate, making it easier to improve the affinity between the porous substrate and the electrolyte polymer.

[0042] A surfactant solution is a solution containing a surfactant and a solvent. The surfactant can be the same as the surfactant described above. The solvent in the surfactant solution can be any solvent having a boiling point lower than the melting point of the porous substrate, and also any solvent having a boiling point lower than the thermal decomposition temperature of the surfactant. Furthermore, since the solvent in the surfactant solution is more easily removed from the solution containing the hydrocarbon electrolyte polymer (hereinafter also referred to as the "polymer solution"), it is preferable that the solvent in the surfactant solution has a boiling point lower than the boiling point of the solvent in the polymer solution. Specific examples of solvents include one or more selected from the group consisting of alcohols, dimethyl sulfoxide, N-methyl-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, butyl acetate, ethyl acetate diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, tetramethylurea, methyl ethyl ketone, propylene glycol monomethyl ether acetate, and ethyl ether. Since the drying time is shortened, the solvent in the surfactant solution is preferably a lower alcohol (alcohol with 5 or fewer carbon atoms), and at least one of methanol and ethanol is more preferable.

[0043] It should be noted that commercially available surfactants are sometimes distributed in a state mixed with a diluent solvent. Therefore, when using a commercially available surfactant, the surfactant solution may contain a diluent solvent in addition to the solvent mentioned above. The diluent solvent is preferably the same as the solvent mentioned above, and more preferably a solvent with a boiling point lower than that of the diluent solvent. For example, if the solvent is butyl acetate, the diluent solvent is preferably butyl acetate, and more preferably a solvent with a boiling point lower than that of butyl acetate.

[0044] Furthermore, the surfactant solution may also contain an electrolyte polymer. The concentration of the electrolyte polymer can be between 0.1% by mass and 0.5% by mass.

[0045] The impregnation method in the first impregnation step can be any method that retains the surfactant in the porous substrate after the drying step, and examples include one or more selected from the group consisting of the solution casting method, the dispersion casting method, the solution spraying method and the dipping method, with the solution casting method being preferred.

[0046] The surfactant should be included in an amount sufficient to improve its affinity with the electrolyte polymer. The lower limit of the ratio of the surfactant to the mass of the electrolyte polymer impregnated into the porous substrate (hereinafter also referred to as the "surfactant ratio") is 0.5% by mass or more, or 1.0% by mass or more, when the surfactant solution is impregnated into the porous substrate. The upper limit is 4.0% by mass or less, or 3.0% by mass or less. The surfactant ratio is preferably 0.5% by mass or more and 4.0% by mass or less, and more preferably 1.0% by mass or more and 3.0% by mass or less.

[0047] Note that the "mass of electrolyte polymer impregnated into the porous substrate" is the porosity [cm²] obtained by multiplying the volume of the porous substrate by its porosity. 3 ] is the specific gravity of the electrolyte polymer [g / cm³ 3 It can be found by dividing by [ ].

[0048] In the drying process, the porous substrate is impregnated with a surfactant solution, and then dried, which allows the surfactant to be retained on the porous substrate, particularly on the pore surface of the porous substrate.

[0049] The drying conditions in the drying process can be any method and conditions that remove the solvent from the surfactant solution. Examples of drying methods include placement in a constant temperature bath, hot air drying, heat breathing, or infrared irradiation. Examples of drying conditions include drying in a constant temperature bath at 60°C to 120°C.

[0050] Depending on the surfactant content, the first impregnation step and the drying step may be repeated multiple times (for example, two to five times).

[0051] Alternatively, an electrolyte polymer may be added to the surfactant solution beforehand. In this case, setting the concentration of the electrolyte polymer in the solution to 0.1% to 0.5% by mass will improve the impregnation of the electrolyte polymer in the next step.

[0052] In the second impregnation step, the polymer solution is impregnated into the porous substrate. By impregnating the substrate with the polymer solution after the first impregnation step and drying step, it becomes easier to impregnate the porous substrate with the electrolyte polymer.

[0053] The method for impregnating the porous substrate with a polymer solution can be any method that allows the hydrocarbon electrolyte polymer to fill the surface and pores of the porous substrate. Examples include bringing the porous substrate into contact with the polymer solution, or dropping the polymer solution onto the porous substrate.

[0054] The polymer solution comprises a hydrocarbon electrolyte polymer and a solvent. The hydrocarbon electrolyte polymer may be the same as that described above. The solvent in the polymer solution may be any solvent in which the hydrocarbon electrolyte polymer can dissolve or disperse, but it is preferable that the solvent has a boiling point at the decomposition temperature of the hydrocarbon electrolyte polymer and a boiling point below the melting point of the porous substrate. Specific examples of solvents include N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO), with dimethyl sulfoxide being preferred.

[0055] The concentration of the hydrocarbon electrolyte polymer in the polymer solution can be adjusted as appropriate, but for example, it can be 1% by mass or more, or 5% by mass or more, and 20% by mass or less, or 15% by mass or less, preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less.

[0056] In the second impregnation step, the filled hydrocarbon electrolyte polymer solution may be dried. The drying method may be the same as the drying method in the above drying step, and it is preferable to dry in an air atmosphere at a temperature of 60°C to 120°C.

[0057] Furthermore, the second impregnation step may be repeated multiple times (for example, two to five times) depending on the content of the target hydrocarbon electrolyte polymer.

[0058] In this embodiment, the electrolyte membrane can be manufactured by simultaneously producing the reinforcing layer and the contact layer, or by forming the reinforcing layer first and then forming the contact layer on top of the reinforcing layer to produce the electrolyte membrane. It is preferable to manufacture the reinforcing layer and the contact layer simultaneously because this reduces the number of steps required to manufacture the electrolyte membrane.

[0059] Furthermore, when using hydrocarbon-based electrolyte polymers with different molecular structures for the reinforcing layer and the contact layer, or when the hydrocarbon-based electrolyte polymers for the reinforcing layer and the contact layer are the same and it is necessary to prevent solvent residue in the reinforcing layer, the second impregnation step can be performed in two stages. Specifically, a hydrocarbon-based electrolyte polymer solution is filled into the pores of a porous substrate and dried to create a reinforcing layer, and then the hydrocarbon-based electrolyte polymer solution is applied to the surface of the porous substrate. Finally, the contact layer is dried to create an electrolyte film.

[0060] Alternatively, the reinforcing layer and the contact layer may be fabricated separately, and the contact layer may be bonded to both sides of the reinforcing layer to create an electrolyte membrane. [Examples]

[0061] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples. (molecular weight) The number-average molecular weight of the electrolyte polymer was measured by GPC. The electrolyte polymer was dissolved at a concentration of 1 mg / mL in an eluent (N,N-dimethylformamide solvent containing 10 mmol / L lithium bromide) to prepare the sample solution. A Tosoh HLC-8320GPC was used as the apparatus. Two Tosoh TSKgel SuperAWM-H columns (6.0 mm inner diameter, 15 cm length) were used. A differential refractometer was used as the detector. The flow rate was 0.6 mL / min and the temperature was 40°C. The number-average molecular weight was determined by converting it to standard polyethylene glycol / oxide (PEG / PEO). (film thickness) The thickness of the electrolyte membrane was measured using a commercially available micrometer at five points: the four corners and the center of a 30mm x 30mm square-shaped electrolyte membrane. The average of these measurements was taken as the thickness of the electrolyte membrane. (Proton conductivity) The proton conductivity of the electrolyte membrane was measured using the AC impedance method under conditions of 80°C, a hydrogen atmosphere, and 90% RH relative humidity. A rectangular piece of electrolyte membrane measuring 1 cm x 3 cm was cut out, and four 1 mm diameter platinum wires were placed at equal intervals. The two outer wires were connected to current terminals and the two inner wires to voltage terminals. After connecting the terminals, the resistance was measured by measuring the current under constant potential conditions. The proton conductivity was calculated from the obtained resistance values. (Gas shielding rate) The gas shielding efficiency of the electrolyte membrane was measured according to the JIS K 7126B method (isobaric method). Specifically, hydrogen gas was supplied to one side of the electrolyte membrane under the following conditions, and the amount of hydrogen gas that permeated from the opposite side was quantified by chromatography.

[0062] Electrolyte membrane: 40mm diameter circular shape Relative humidity: 90%RH Measurement temperature: 80℃ A reference sample consisting of a 12 μm thick electrolyte membrane (single membrane) was obtained by forming and drying the film in the same manner as in Example 1, except that a commercially available fluorine-based electrolyte polymer dispersion (Nafion DE2020CS, manufactured by Fujifilm Wako Chemical Co., Ltd.) was used as the electrolyte polymer.

[0063] The gas shielding efficiency of the electrolyte membrane was defined as the ratio of the quantitative value of the electrolyte membrane to the quantitative value of the obtained reference sample. (swelling rate) The swelling rate of the electrolyte membrane was measured by the following method. A rectangular electrolyte membrane measuring 4 cm in length and 2 cm in width was used as the sample, and its length and width were measured to three decimal places (cm) using a caliper. Then, the sample was sandwiched between 2 mm thick slides and immersed in 100 mL of pure water at room temperature for 1 hour. After immersion, any droplets adhering to the surface of the sample were removed, and its length and width were measured again. The swelling rate in the in-plane direction was calculated from the obtained measurements using the following formula, and this was defined as the swelling rate of the electrolyte membrane.

[0064] Swelling rate [%]=[{(X2-X1) / X1+(X2-X1) / X1} / 2]×100 In the above equation, X1 and X2 are the lengths of the vertical sides before and after immersion, respectively, and Y1 and Y2 are the lengths of the horizontal sides before and after immersion, respectively. <Preparation of electrolyte polymers> (Synthesis of hydrophilic monomer (M1)) A 10 L flask equipped with a dropping funnel, reflux condenser, and mechanical stirrer was purged with nitrogen. Then, 101 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl and 4 L of anhydrous tetrahydrofuran were added to the flask to form a reaction solution, which was then stirred. Next, the flask was placed in a methanol-dry ice bath and cooled to -70°C. After that, 320 mL of 2.6 mol / L n-butyllithium-hexane solution was added dropwise to the reaction solution, and the mixture was stirred for a further 1 hour. Then, 40 mL of sulfur dioxide gas was introduced into the flask using nitrogen gas as a carrier gas. After the introduction, the reaction solution was stirred for a further 30 minutes, and then the flask was removed from the bath and the temperature was raised to 0°C to obtain the refined product.

[0065] The obtained precipitate was filtered off by suction filtration, washed with 200 mL of tetrahydrofuran, and then dissolved in 2 L of pure water. 260 mL of 35% hydrogen peroxide solution was added to the precipitate solution and stirred for 18 hours to obtain a reprecipitate. 600 g of sodium chloride was added to the filtrate after removing the reprecipitate by suction filtration, and a white solid was precipitated. The obtained white solid was recovered by suction filtration, recrystallized from water / isopropyl alcohol, and dried under reduced pressure to obtain a hydrophilic monomer represented by the following formula (M1). The yield of the hydrophilic monomer was 65%.

[0066] [ka]

[0067] (Synthesis of hydrophobic monomer (M2)) In a 200 mL flask equipped with a stirring bar, a Dean-Stark tube, a reflux condenser, and a calcium chloride tube, 4.0 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl, 14.8 g of [1,1'-biphenyl]-4,4'-diol, and 13.2 g of potassium carbonate were added. Further, 50 mL of N,N-dimethylacetamide (DMAc) and 50 mL of toluene were added to obtain the reaction solution. The flask was placed in an oil bath, and the reaction solution was heated to 160°C while stirring, and then stirred for a further 4 hours. Next, the toluene was removed from the Dean-Stark tube, and the reaction solution was heated to 180°C. After heating, the mixture was stirred for a further 8 hours. The reaction solution was allowed to cool to room temperature, and the reaction solution was added to 200 mL of 10% hydrochloric acid to precipitate a white solid, which was then filtered and recovered.

[0068] The recovered white solid was washed with 300 mL of ethanol, dried, and then purified by recrystallization from NMP / ethanol, followed by vacuum drying to obtain the hydrophobic monomer (M2) represented by the following formula (M2). The yield of the hydrophilic monomer was 50%.

[0069] [ka]

[0070] (Synthesis of electrolyte polymer (P1)) 0.983 g of hydrophobic monomer (M2), 1.181 g of hydrophilic monomer (M1), and 0.507 g of potassium carbonate were added to a 100 mL three-necked flask equipped with a nitrogen inlet tube, a stirrer, and a Dean-Stark tube to obtain a reaction solution, and then nitrogen substitution was performed. Then, 10 mL of dimethyl sulfoxide (DMSO) and 10 mL of cyclohexane were added to the reaction solution. After heating the reaction solution after addition to 130 °C and performing reflux dehydration for 4 hours, cyclohexane was extracted from the Dean-Stark tube, and polymerization was carried out by holding at 130 °C for 150 hours. After allowing the reaction solution after polymerization to cool to room temperature, precipitation purification was performed with 300 mL of isopropyl alcohol (IPA) to obtain a precipitate.

[0071] The precipitate was collected by suction filtration, immersed in 1 M hydrochloric acid for 24 hours to replace metal ions (Na + or K + ) with protons (H + ), washed by immersion in pure water, and then dried under reduced pressure to obtain an electrolyte polymer (a polymer (P1) with proton substitution). The number average molecular weight of the electrolyte polymer was 50,000, and its yield was 97%.

[0072] [Chemical formula]

[0073] [Example 1] A porous substrate (PTFE porous film; porosity 70%, thickness 8 μm) was cut into 30 × 30 mm shapes and placed on a horizontal glass plate measuring 150 × 150 mm and 2 mm thick. 0.002 g of surfactant (nonionic surfactant MEGAFACE®, manufactured by DIC Corporation; surfactant concentration 20% by mass) was mixed with 5 mL of ethanol to obtain a surfactant solution. The surfactant solution was applied to the porous substrate so that the mass ratio of the surfactant to the mass of the electrolyte polymer impregnated into the porous substrate (0.081 g) was 0.5% by mass. The resulting porous substrate was dried by leaving it on the glass plate in a constant temperature bath at 80°C for 30 minutes.

[0074] Furthermore, electrolyte polymer (P1; specific gravity = 1.6 g / cm³) 3 The solution was dissolved in DMSO to obtain a polymer solution in which the electrolyte polymer (P1) was concentrated at 10% by mass.

[0075] A porous substrate, initially placed on a glass plate, was positioned on the applicator stage. 2 g of polymer solution was dropped onto one surface of the porous substrate, and then the polymer solution was spread over the substrate using an applicator with a 15 μm gap. This state was held for 30 seconds. The same procedure was then performed on the other surface of the porous substrate.

[0076] Subsequently, the porous substrate containing the electrolyte polymer, which was placed on a glass plate, was maintained in an air atmosphere at 60°C for 8 hours to dry the porous substrate containing the electrolyte polymer and obtain an electrolyte membrane.

[0077] After drying, the electrolyte membrane, which was placed on a glass plate, was immersed in 2 L of pure water for 30 minutes. Then, the electrolyte membrane was removed from the glass plate, and the burrs consisting only of electrolyte polymer that protruded from the porous substrate (30 mm x 30 mm) were removed to obtain the electrolyte membrane of this embodiment.

[0078] In this embodiment, an electrolyte membrane was obtained in which an electrolyte polymer was impregnated into the porous substrate, and a contact layer totaling 4 μm was formed on both the front and back surfaces of the porous substrate. [Example 2] An electrolyte membrane was obtained in the same manner as in Example 1. The obtained electrolyte membrane was made into a 30 mm x 30 mm square shape, and this was stacked in the order of glass plate, electrolyte membrane, glass plate. The obtained stack was placed in a constant temperature bath and subjected to a process in which the temperature was raised from room temperature to 100°C in 1 hour, and then lowered from 100°C to 30°C in 2 hours, with this cycle being repeated a total of 5 times (hereinafter also referred to as "heat cycle treatment") to obtain the electrolyte membrane of this example. [Example 3] An electrolyte membrane was prepared in the same manner as in Example 1, except that a surfactant solution was used, obtained by adding 5 mL of ethanol to 0.004 g of surfactant so that the ratio of surfactant to the mass of the electrolyte polymer impregnated in the porous substrate was 1.0% by mass, and the surfactant solution was applied. The prepared electrolyte membrane was subjected to a heat cycle treatment to obtain the electrolyte membrane of this example. [Example 4] An electrolyte membrane was prepared in the same manner as in Example 1, except that a surfactant solution was used, obtained by adding 5 mL of ethanol to 0.0084 g of surfactant so that the ratio of surfactant to the mass of the electrolyte polymer impregnated into the porous substrate was 2.1% by mass, and the surfactant solution was applied. The prepared electrolyte membrane was subjected to a heat cycle treatment to obtain the electrolyte membrane of this example. [Example 5] An electrolyte membrane was prepared in the same manner as in Example 1, except that a surfactant solution was used, obtained by adding 5 mL of ethanol to 0.016 g of surfactant so that the ratio of surfactant to the mass of the electrolyte polymer impregnated into the porous substrate was 4.2% by mass, and the surfactant solution was applied. The prepared electrolyte membrane was subjected to a heat cycle treatment to obtain the electrolyte membrane of this example. [Comparative Example 1] The electrolyte membrane of this comparative example was prepared in the same manner as in Example 1, except that the porous substrate was not impregnated with a surfactant solution.

[0079] [Table 1]

[0080] In Examples 1 to 5, an electrolyte membrane having a contact layer was obtained. In contrast, in Comparative Example 1, which did not contain a surfactant, an electrolyte membrane could not be obtained, and numerous through-holes were visually confirmed after drying. From this, it was confirmed that pre-impregnating a porous substrate with a surfactant makes it easier to impregnate it with an electrolyte polymer.

[0081] Examples 1 and 2 confirmed that the change in proton conductivity before and after the heat cycle was less than 2%, and that the changes in gas shielding properties and film swelling were also minimal.

[0082] Examples 2 to 4 confirmed that increasing the amount of surfactant improved the swelling rate while maintaining equivalent gas barrier properties.

[0083] In Examples 3 and 4, where the amount of surfactant was increased compared to Example 2, a slight decrease in the film swelling rate was observed. This suggests that the improved affinity between the electrolyte polymer and the porous substrate is contributing to the improved function of the porous substrate in suppressing the swelling of the electrolyte membrane. [Explanation of Symbols]

[0084] 1 Electrolyte membrane 2a contact layer 2b Contact layer 3. Reinforcement layer 31 Electrolyte Polymers 32 Porous substrate 33 Surfactants

Claims

1. An electrolyte membrane having a structure in which a reinforcing layer is sandwiched between contact layers, The contact layer comprises at least a hydrocarbon-based electrolyte polymer, The reinforcing layer is characterized by comprising at least a porous substrate, a surfactant, and a hydrocarbon-based electrolyte polymer.

2. The electrolyte membrane according to claim 1, wherein the hydrocarbon-based electrolyte polymer is one or more selected from the group consisting of polysulfone, polyphenylene oxide, polyethersulfone, polyphenylene sulfide, polyparaphenylene, polybenzthiazole, polybenzimidazole, polyamide, polyimide, polyarilene-based polymer, polyetherimide, and polyetherketone.

3. The electrolyte membrane according to claim 1, wherein the hydrocarbon electrolyte polymer is one or more selected from the group P1 to P5. 【Chemistry 1】

4. The electrolyte membrane according to claim 1, wherein the surfactant is one or more compounds selected from the group consisting of anionic, cationic, and nonionic compounds.

5. The electrolyte membrane according to any one of claims 1 to 4, which is an electrolyte membrane for fuel cells or an electrolyte membrane for water electrolysis.

6. A method for producing an electrolyte membrane according to claim 1, comprising: a first impregnation step of impregnating a porous substrate with a surfactant solution; a drying step of removing the solvent from the porous substrate; and a second impregnation step of impregnating the porous substrate with a hydrocarbon-based electrolyte polymer solution.

7. The method for producing an electrolyte membrane according to claim 6, wherein the second impregnation step includes filling the pores of the porous substrate with a solution of the electrolyte polymer, drying the filled electrolyte polymer solution, and applying the electrolyte polymer solution to the surface of the porous substrate.

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