Solid polymer electrolyte membrane, membrane-electrode assembly, water electrolysis device, method for producing hydrogen, and method for producing solid polymer electrolyte membrane

Abstract

Provided is a solid polymer electrolyte membrane that resists tearing and, when employed in a water electrolysis device, resists the generation of pinholes.　The solid polymer electrolyte membrane contains an ion-exchange group-bearing fluoropolymer and a woven fabric composed of a warp and a weft. When the solid polymer electrolyte membrane is observed from the direction normal to a surface of the solid polymer electrolyte membrane, the standard deviation on the area of regions delimited by the warp and the weft is 0.10 × 104 to 2.0 × 104 μm2.

Description

Solid polymer electrolyte membrane, membrane electrode assembly, water electrolysis device, method for producing hydrogen, and method for producing solid polymer electrolyte membrane

[0001] The present disclosure relates to a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis device, a method for producing hydrogen, and a method for producing a solid polymer electrolyte membrane.

[0002] Solid polymer electrolyte membranes can be applied to various applications, and various studies have been conducted on them. For example, a membrane electrode assembly in which an anode including a catalyst layer, a solid polymer electrolyte membrane, and a cathode including a catalyst layer are arranged in this order is used in, for example, a solid polymer water electrolysis device. In a solid polymer water electrolysis device, electrolysis is performed by supplying water to the membrane electrode assembly from the anode side, and therefore the solid polymer electrolyte membrane may include a woven fabric for the purpose of improving mechanical strength, etc. For example, Patent Document 1 describes using a woven fabric as a support material for the solid polymer electrolyte membrane and adjusting the water contact angle of the support material.

[0003] Japanese Patent Application Laid-Open No. 2000-195333

[0004] The present inventors have found that pinholes may occur when a solid polymer electrolyte membrane is applied to a solid polymer water electrolysis device (hereinafter also simply referred to as a "water electrolysis device"). Furthermore, the present inventors have studied the solid polymer electrolyte membrane described in Patent Document 1 and found that the solid polymer electrolyte membrane may be easily torn.

[0005] The present disclosure has been made in view of the above-described circumstances, and an object of one embodiment of the present invention is to provide a solid polymer electrolyte membrane that is resistant to tearing and that is resistant to pinholes when applied to a water electrolysis device. Another object of one embodiment of the present invention is to provide a membrane electrode assembly, a water electrolysis device, a method for producing hydrogen, and a method for producing a solid polymer electrolyte membrane.

[0006] The present disclosure has the following aspects: [1] A solid polymer electrolyte membrane comprising a fluoropolymer having an ion exchange group and a woven fabric composed of warp yarns and weft yarns, wherein when observed from a normal direction to a surface of the solid polymer electrolyte membrane, the standard deviation of the area of ​​the region defined by the warp yarns and the weft yarns is 0.10 × 10４ ~2.0 x 10 ４ μm ２ [2] The solid polymer electrolyte membrane according to [1], wherein the denier of the warp yarns and the denier of the weft yarns are each independently 15 to 50. [3] The average area of ​​the regions partitioned by the warp yarns and the weft yarns is 1.0 × 10 ４ ~10.0 x 10 ４ μm ２ [4] The solid polymer electrolyte membrane according to [1] or [2], wherein the standard deviation of the area of ​​the region defined by the warp yarns and the weft yarns is 0.30 × 10 ４ ~1.0 x 10 ４ μm ２ [5] The solid polymer electrolyte membrane according to any one of [1] to [4], wherein the density of the warp and the weft is independently 70 to 150 threads / inch. [6] The solid polymer electrolyte membrane according to any one of [1] to [5], wherein the warp and the weft are independently made of a material selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyether ether ketone, and polyphenylene sulfide. [7] The solid polymer electrolyte membrane according to any one of [1] to [6], wherein the ion exchange group is a sulfonic acid type functional group. [8] The solid polymer electrolyte membrane according to any one of [1] to [7], wherein the ion exchange capacity of the fluoropolymer is 0.90 to 2.00 meq / g dry resin. [9] The solid polymer electrolyte membrane according to any one of [1] to [8], wherein the fluorine-containing polymer contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid type functional group and a fluorine atom.

[10] The solid polymer electrolyte membrane according to [9], wherein the fluorine-containing olefin is a fluoroolefin having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule.

[11] The solid polymer electrolyte membrane according to [9] or

[10] , wherein the unit having a sulfonic acid type functional group and a fluorine atom is a unit represented by formula (1): Formula (1) -[CF ２ -CF(-L-(SO ３M) ｎ ))]- L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, n is 1 or 2, and multiple Ms may be the same or different.

[12] A membrane electrode assembly for a water electrolysis system, comprising: an anode having a catalyst layer; a cathode having a catalyst layer; and the solid polymer electrolyte membrane according to any one of [1] to

[11] disposed between the anode and the cathode.

[13] A water electrolysis system, comprising the membrane electrode assembly according to

[12] .

[14] A method for producing hydrogen, comprising producing hydrogen by electrolyzing water using the water electrolysis system according to

[13] .

[15] A method for producing a solid polymer electrolyte membrane, comprising: (a) a substrate having a difference between the maximum and minimum membrane thicknesses of 5 to 30 μm; (b) a film made of a fluoropolymer having groups convertible to ion-exchange groups; and (c) a woven fabric composed of warp and weft yarns.

[16] A method for producing a solid polymer electrolyte membrane, comprising: (a) a substrate having a difference between the maximum and minimum membrane thicknesses of 5 to 30 μm; (b) a film made of a fluoropolymer having groups convertible to ion-exchange groups; and (c) a woven fabric composed of warp yarns and weft yarns.

[0007] According to one embodiment of the present invention, it is possible to provide a solid polymer electrolyte membrane that is resistant to tearing and that is resistant to pinholes when applied to a water electrolysis device. Also, according to one embodiment of the present invention, it is possible to provide a membrane electrode assembly, a water electrolysis device, an electrolytic hydrogenation device, a method for producing hydrogen, and a method for producing a solid polymer electrolyte membrane.

[0008] 1 is a plan view of a solid polymer electrolyte membrane of the present disclosure, observed from a direction normal to its surface. 2 is a cross-sectional view of the solid polymer electrolyte membrane of the present disclosure, taken along line BB'. 3 is a diagram for explaining how to determine the area of ​​a region partitioned by warp yarns and weft yarns. 4 is a schematic cross-sectional view of a membrane electrode assembly of the present disclosure.

[0009] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group with other ions, and examples thereof include the sulfonic acid functional group and carboxylic acid functional group shown below. A "sulfonic acid functional group" is a sulfonic acid group (-SO ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. "Carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid salt group. Here, the form of the carboxylic acid salt group can be, for example, (-COO － ) Ma ＋ , (-COO － ) ２ Mb ２＋ , and (-COO － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋is a trivalent metal ion.) Note that when there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. A "precursor membrane" is a membrane containing a polymer having a group that can be converted into an ion exchange group. A "group that can be converted into an ion exchange group" means a group that can be converted into an ion exchange group by treatment such as hydrolysis or acidification. A "group that can be converted into a sulfonic acid functional group" means a group that can be converted into a sulfonic acid functional group by treatment such as hydrolysis or acidification. A "group that can be converted into a carboxylic acid functional group" means a group that can be converted into a carboxylic acid functional group by known treatment such as hydrolysis or acidification.

[0010] The term "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer, and is also referred to as a unit based on the monomer. The unit based on the monomer may be an atomic group formed directly by the polymerization reaction of the monomer, or may be an atomic group in which a part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction of the monomer.

[0011] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0012] <Solid polymer electrolyte membrane> The solid polymer electrolyte membrane of the present disclosure (hereinafter also simply referred to as "electrolyte membrane") contains a fluoropolymer having ion exchange groups (hereinafter also referred to as "fluoropolymer (I)"), and a woven fabric composed of warp yarns and weft yarns. Here, when observed from the normal direction to the surface of the electrolyte membrane, the standard deviation of the area of ​​the region partitioned by the warp yarns and the weft yarns is 0.10 × 10 ４ ~2.0 x 10 ４ μm ２The areas defined by the warp and weft will be described with reference to the drawings.

[0013] FIG. 1 is a plan view of a solid polymer electrolyte membrane 10 (hereinafter also simply referred to as "electrolyte membrane 10") of the present disclosure, observed from a direction normal to its surface. FIG. 1 shows a portion of the electrolyte membrane 10. The electrolyte membrane 10 has an electrolyte 12 containing a fluoropolymer (I) and a woven fabric 14 composed of warp yarns 16 and weft yarns 18. The woven fabric 14 is plain woven. FIG. 1 shows warp yarns V1 to V4 and weft yarns H1 to H4. FIG. 2 is a cross-sectional view of the electrolyte membrane 10 shown in FIG. 1 taken along line B-B'. As shown in FIG. 2, the warp yarns 16 (i.e., the woven fabric 14) are disposed in the electrolyte 12. Here, region A33 shown in FIG. 1 is a region defined by warp yarns V3, V4, weft yarns H3, and weft yarn H4. 1, when the electrolyte membrane 10 is observed from the normal direction to the surface of the electrolyte membrane 10, the region A33 refers to a region surrounded by the warp yarns V3, V4, weft yarns H3, and H4, but not including the warp yarns V3, V4, weft yarns H3, and weft yarns H4. The electrolyte membrane 10 has a region, such as the region A33, that is partitioned by adjacent warp yarns 16 and adjacent weft yarns 18. In the present disclosure, the standard deviation of the area of ​​the region is 0.10×10 ４ ~2.0 x 10 ４ μm ２ The detailed method for calculating the standard deviation will be explained later.

[0014] Although the mechanism by which the standard deviation of the area of ​​the above region within the above range makes the electrolyte membrane less likely to tear and less likely to develop pinholes when applied to a water electrolysis device is not entirely clear, the inventors speculate as follows: If the standard deviation of the area of ​​the above region is equal to or greater than the lower limit of the above range, this indicates that there is a certain degree of variation in the area of ​​the region defined by the warp and weft. This suggests that there are non-linear portions in at least one of the warp and weft, and that there are also portions of the above region that are not linearly arranged. When a tear occurs in the polymer electrolyte membrane, it is presumed that the tear propagates linearly between the above regions. If there are portions where the above regions are not linearly arranged, the propagation of the tear is likely to stop at those portions, resulting in the electrolyte membrane being less likely to tear. Furthermore, if the standard deviation of the area of ​​the above region is equal to or less than the upper limit of the above range, this indicates that the variation in the area of ​​the above region is equal to or less than a certain degree. If the variation in the area is too large, there is likely to be a portion defined by the warp and weft that is larger in area than the surrounding area. In such a portion, the restraining force of the woven fabric is likely to be weak, and therefore swelling is more likely to occur when the electrolyte membrane swells during water electrolysis, resulting in bulging in that portion. When such swelling occurs, the swelling may come into contact with other components in the water electrolysis apparatus, which is thought to result in pinholes (holes in the membrane) being more likely to occur.

[0015] The configuration of the electrolyte membrane of the present disclosure (hereinafter also simply referred to as "electrolyte membrane") will be described below.

[0016] [Fluoropolymer] The above-mentioned electrolyte contains a fluoropolymer (I). That is, the electrolyte membrane contains a fluoropolymer (I). The ion exchange capacity of the fluoropolymer (I) is preferably 0.90 milliequivalents / gram dry resin or more, more preferably greater than 1.10 milliequivalents / gram dry resin, even more preferably 1.15 milliequivalents / gram dry resin or more, particularly preferably 1.20 milliequivalents / gram dry resin or more, and most preferably 1.25 milliequivalents / gram dry resin or more, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device. The upper limit of the ion exchange capacity of the fluoropolymer (I) is preferably 2.00 milliequivalents / gram dry resin or less, more preferably 1.50 milliequivalents / gram dry resin or less, particularly preferably 1.43 milliequivalents / gram dry resin or less.

[0017] The fluoropolymer (I) used in the electrolyte membrane may be one type, or two or more types may be laminated or mixed and used. The electrolyte membrane may contain a polymer other than the fluoropolymer (I), but it is preferable that the polymer in the electrolyte membrane essentially consists of the fluoropolymer (I). "Substantially consisting of the fluoropolymer (I)" means that the content of the fluoropolymer (I) is 95 mass% or more relative to the total mass of the polymers in the electrolyte membrane. The upper limit of the content of the fluoropolymer (I) is 100 mass% relative to the total mass of the polymers in the electrolyte membrane. Specific examples of polymers other than the fluoropolymer (I) include one or more polyazole compounds selected from the group consisting of polymers of heterocyclic compounds containing one or more nitrogen atoms in the ring, and polymers of heterocyclic compounds containing one or more nitrogen atoms and oxygen atoms and / or sulfur atoms in the ring. Specific examples of the polyazole compound include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds. Furthermore, in terms of the oxidation resistance of the electrolyte membrane, examples of other polymers that can be used include polyphenylene sulfide resins and polyphenylene ether resins.

[0018] The fluoropolymer (I) has an ion exchange group. Specific examples of the ion exchange group include a sulfonic acid type functional group and a carboxylic acid type functional group, and the sulfonic acid type functional group is preferred from the viewpoint of being able to further reduce the electrolysis voltage. Below, mainly, embodiments of the fluoropolymer having a sulfonic acid type functional group (hereinafter also referred to as "fluoropolymer (S)") will be described in detail.

[0019] The fluorine-containing polymer (S) preferably contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid functional group and a fluorine atom. Examples of the fluorine-containing olefin include fluoroolefins having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule. Specific examples of the fluoroolefin include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred from the viewpoints of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0020] As the unit having a sulfonic acid type functional group and a fluorine atom, a unit represented by formula (1) is preferred. ２ -CF(-L-(SO ３ M) ｎ )]-

[0021] L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at a terminal of the perfluorohydrocarbon group or between carbon atoms. The (n+1)-valent perfluorohydrocarbon group preferably has 1 or more carbon atoms, more preferably 2 or more carbon atoms, and preferably 20 or less, and more preferably 10 or less carbon atoms.

[0022] L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and particularly preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom, where n = 1, or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, where n = 2. The divalent perfluoroalkylene group may be either linear or branched.

[0023] M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. Multiple Ms may be the same or different. n is 1 or 2.

[0024] The unit represented by formula (1) is preferably a unit represented by formula (1-1), a unit represented by formula (1-2), a unit represented by formula (1-3), or a unit represented by formula (1-4). ２ -CF(-O-R ｆ１ -SO ３ M)] - Formula (1-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0025]

[0026]

[0027] R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0028] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0029] R ｆ３is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, and is preferably 20 or less, particularly preferably 10 or less.

[0030] r is 0 or 1. m is 0 or 1. M is defined as above.

[0031] As the unit represented by formula (1-1) and the unit represented by formula (1-2), a unit represented by formula (1-5) is more preferred. ２ -CF(-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ M)]—x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ The definition of M is as described above.

[0032] Specific examples of the unit represented by formula (1-1) include the following units. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. The definition of M in the formula is as described above. -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M) ]-

[0033] Specific examples of the unit represented by formula (1-2) include the following units. In the formula, w is an integer of 1 to 8. M in the formula is as defined above. -[CF ２ -CF(-(CF２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0034] The unit represented by formula (1-3) is preferably a unit represented by formula (1-3-1), where M is defined as above.

[0035]

[0036] R ｆ４ is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ is a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between carbon atoms. The definitions of r and M are as described above.

[0037] Specific examples of the unit represented by formula (1-3-1) include the following.

[0038]

[0039] As the unit represented by formula (1-4), a unit represented by formula (1-4-1) is preferred. ｆ１ , R ｆ２ and M are defined as above.

[0040]

[0041] Specific examples of the unit represented by formula (1-4-1) include the following.

[0042]

[0043] The unit having a sulfonic acid type functional group and a fluorine atom may be used alone or in combination of two or more.

[0044] The fluoropolymer (I) may contain units based on other monomers other than the units based on fluorine-containing olefin and the units having a sulfonic acid functional group and a fluorine atom. Specific examples of other monomers include CF２ = CFR ｆ６ (However, R ｆ６ is a perfluoroalkyl group having 2 to 10 carbon atoms, CF ２ =CF-OR ｆ７ (However, R ｆ７ is a perfluoroalkyl group having 1 to 10 carbon atoms, CF ２ = CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer of 1 to 3.) The content of units based on other monomers is preferably at most 30 mass % based on all units in the fluoropolymer (I) from the viewpoint of maintaining ion exchange performance.

[0045] The electrolyte membrane may have a single layer structure or a multilayer structure. In the case of a multilayer structure, for example, a mode in which a plurality of layers containing the fluoropolymer (I) and having different ion exchange capacities are laminated is mentioned.

[0046] [Woven Fabric] The electrolyte membrane has a woven fabric composed of warp yarns and weft yarns. The denier numbers of the warp yarns and weft yarns constituting the woven fabric are each independently preferably 2 or more, more preferably 10 or more, and even more preferably 15 or more, in terms of achieving better strength and dimensional stability of the electrolyte membrane. The upper limit values ​​of the denier numbers of the warp yarns and weft yarns constituting the woven fabric are each independently preferably 60 or less, more preferably 50 or less, and particularly preferably 20 or less, in terms of further reducing the electrolysis voltage when applied to a water electrolysis device. The denier number is the mass in grams of 9,000 m of yarn (g / 9,000 m).

[0047] The densities of the warp and weft yarns are each independently preferably 50 yarns / inch or more, more preferably 70 yarns / inch or more, and particularly preferably 90 yarns / inch or more, from the viewpoint of achieving excellent strength and dimensional stability of the electrolyte membrane, and are preferably 200 yarns / inch or less, more preferably 150 yarns / inch or less, and particularly preferably 100 yarns / inch or less, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device.

[0048] The warp and weft threads may be made of either monofilaments consisting of one filament or multifilaments consisting of two or more filaments, with monofilaments being preferred.

[0049] The warp and weft yarns are preferably made of a material selected from the group consisting of polytetrafluoroethylene (hereinafter also referred to as "PTFE"), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA"), polyether ether ketone (hereinafter also referred to as "PEEK"), and polyphenylene sulfide (hereinafter also referred to as "PPS"), in order to provide superior durability and strength of the yarns. The warp and weft yarns are preferably made of slit yarns in order to provide superior durability and strength of the yarns.

[0050] In the woven fabric, the warp and weft threads are preferably substantially perpendicular to each other (see FIG. 1). "Substantially perpendicular" means that the angle between the warp and weft threads is 90±10 degrees. The weave of the woven fabric is not particularly limited, and examples thereof include plain weave, twill weave, and satin weave, with plain weave being preferred.

[0051] When the material constituting the woven fabric is PTFE, the weight of the woven fabric is 20 to 40 g / m, in order to obtain an excellent balance between the strength of the electrolyte membrane and the ease of handling. ２ is preferred, and 30 to 40 g / m ２ When the material constituting the woven fabric is PFA, the weight per unit area of ​​the woven fabric is preferably 10 to 30 g / m2, in view of the excellent balance between the strength and the handling properties of the electrolyte membrane. ２ is preferably 10 to 20 g / m ２ When the material constituting the woven fabric is PEEK, the weight per unit area of ​​the woven fabric is preferably 5 to 40 g / m2, in view of the excellent balance between the strength and the handling properties of the electrolyte membrane. ２ is preferred, and 5 to 30 g / m ２ When the material constituting the woven fabric is PPS, the weight per unit area of ​​the woven fabric is preferably 5 to 40 g / m2, in view of the excellent balance between the strength and the handling properties of the electrolyte membrane. ２ is preferred, and 5 to 30 g / m ２ is particularly preferred.

[0052] The aperture ratio of the woven fabric is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 70% or more, in order to further reduce the electrolysis voltage when applied to a water electrolysis device. The upper limit of the aperture ratio of the woven fabric is preferably 90% or less, particularly preferably 80% or less, in order to further improve the strength of the electrolyte membrane. The aperture ratio of the woven fabric is calculated using the following formula (ε) based on the average thread diameter R1 and the average spacing P1 between adjacent threads (hereinafter also referred to as "pitch P1"). Here, the average thread diameter R1 refers to the arithmetic mean value of the diameters of 10 different threads arbitrarily selected based on a magnified image (e.g., 100x magnification) of the electrolyte membrane obtained using a microscope. The pitch P1 refers to the arithmetic mean value of the spacing between 10 different points arbitrarily selected based on a magnified image (e.g., 100x magnification) of the woven fabric surface obtained using a microscope. Opening ratio of woven fabric (%) = [P1 / (P1+R1)] ２ × 100 (ε)

[0053] [Area divided by warp and weft yarns] In the electrolyte membrane of the present disclosure, when observed from the normal direction to the surface of the electrolyte membrane, the standard deviation of the area of ​​the region divided by the warp and weft yarns is 0.10 × 10 ４ ~2.0 x 10 ４ μm ２The standard deviation of the above area can be calculated using the following procedure. Note that the following procedure assumes a configuration in which the warp and weft yarns are approximately perpendicular to each other, but the same procedure can be used to approximate a configuration in which they are not approximately perpendicular to each other. First, the electrolyte membrane is observed using an optical microscope from the normal direction to the surface. The observation is performed at a magnification of 5 to 10 times. Note that the normal direction to the surface of the electrolyte membrane corresponds to the thickness direction of the electrolyte membrane. Next, the area of ​​each region defined by the warp and weft yarns (see region A33 in Figure 1) is measured. The area of ​​the above region is calculated using the following method. The method for calculating the area of ​​the above region will be explained with reference to Figure 3. Figure 3 illustrates only one region A defined by the warp and weft yarns. In Figure 3, the upper side (side HX1) and lower side (side HX2) of region A are the sides of region A defined by the weft yarns, and the left side (side VX1) and right side (side VX2) of region A are the sides of region A defined by the warp yarns. In FIG. 3 , point CH1 represents the midpoint of side HX1, point CH2 represents the midpoint of side HX2, point CV1 represents the midpoint of side VX1, and point CV2 represents the midpoint of side VX2. Here, a straight line segment L1 is drawn with its endpoints at points CH1 and CH2, and a straight line segment L2 is drawn with its endpoints at points CV1 and CV2. Furthermore, the longer of the line segments L1 and L2 (line segment L1 in FIG. 3 ) is identified and its length is measured. The width of region A (width D1 in FIG. 3 ) is measured in a direction passing through the midpoint of the identified line segment (line segment L1) and perpendicular to the identified line segment. In the present disclosure, the area of ​​region A is calculated by multiplying the length of the identified line segment (line segment L1) by the width of region A (width D1) in a direction perpendicular to the identified line segment. If line segment L2 is longer than line segment L1, the width of region A is measured in a direction passing through the midpoint of line segment L2 and perpendicular to line segment L2, and the area is calculated in the same manner as above. The area measurements are carried out at 30 locations. If the number of regions for which area measurements have been carried out in the above observation field does not reach the above number, area measurements are carried out in a field different from the above observation field, and area measurements are continued until the above number is reached. From the area values ​​of each region calculated, an average value (unit: μm ２ ), and standard deviation (unit: μm２ The above average value is an arithmetic average value.

[0054] The standard deviation of the area calculated using the above procedure is 0.10 x 10 ４ ~2.0 x 10 ４ μm ２ When applied to a water electrolysis device, pinholes are less likely to occur, which is 1.5 × 10 ４ μm ２ Preferably, the value is 1.0 x 10 or less. ４ μm ２ More preferably, 0.50 x 10 or less ４ μm ２ Furthermore, the standard deviation of the area is preferably 0.15×10 or less, since tearing becomes more difficult. ４ μm ２ More than 0.20 × 10 ４ μm ２ More preferably, 0.30 × 10 ４ μm ２ The above is more preferable.

[0055] The average area obtained by the above procedure is 1.0 × 10 ４ μm ２ More than 3.0 × 10 ４ μm ２ More preferably, the strength of the electrolyte membrane is increased to 10.0×10 ４ μm ２ Preferably, the following is 7.0 x 10 ４ μm ２ The following is more preferred:

[0056] [Thickness of Membrane] The thickness of the electrolyte membrane of the present disclosure is preferably 20 μm or more, more preferably 40 μm or more, and particularly preferably 70 μm or more. The upper limit of the thickness of the electrolyte membrane is preferably 150 μm, more preferably 130 μm, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device. The thickness of the electrolyte membrane is measured using an image obtained by measuring a cross section cut along a plane parallel to the membrane thickness direction with an optical microscope, and is the arithmetic average value at any 20 points.

[0057] [Method for producing electrolyte membrane] Examples of methods for producing an electrolyte membrane include the following. A laminate containing (a), (b), and (c) in this order, with (b) and (c) in contact with each other, is subjected to thermocompression bonding using a thermocompression bonding apparatus preheated at a thermocompression bonding temperature for 30 to 600 seconds, and then (a) is peeled off to obtain a membrane containing fluoropolymer (I') and a woven fabric (hereinafter also referred to as "precursor membrane"). Next, groups in the precursor membrane that can be converted to ion-exchange groups are converted to ion-exchange groups to obtain an electrolyte membrane. (a) A substrate having a difference between the maximum and minimum membrane thicknesses of 5 to 30 μm. (b) A film made of a fluoropolymer having groups that can be converted to ion-exchange groups (hereinafter also referred to as "fluoropolymer (I')"). (c) A woven fabric composed of warp and weft yarns.

[0058] An example of a method for producing the fluorine-containing polymer is a method for producing a membrane (hereinafter also referred to as a "precursor membrane") comprising a polymer (hereinafter also referred to as a "fluoropolymer (I')") of a fluorine-containing monomer having a group convertible to an ion-exchange group (hereinafter also referred to as a "fluorine-containing monomer (I')") and a woven fabric, and then converting the group convertible to an ion-exchange group in the precursor membrane into an ion-exchange group.

[0059] A preferred embodiment of the method for producing the precursor membrane is a method in which both sides of a laminate in which the fluoropolymer (I') is disposed on both sides of a woven fabric are sandwiched between transfer substrates (hereinafter also simply referred to as "substrates") such as films having a melting point of 70 to 180°C, followed by heat and pressure bonding. Specific examples of the substrate include polyethylene film, polypropylene film, polystyrene film, and polyethylene terephthalate film. The substrate may be a substrate having a single layer structure, or a substrate having a multi-layer structure having two or more layers. When the substrate has a multi-layer structure, each layer may be made of the same material or may be made of different materials. Specific examples of the materials constituting each layer are as described above.

[0060] In the preferred embodiment described above, it is preferable to use a substrate having a predetermined variation in thickness, since this facilitates the standard deviation of the area defined by the warp and weft yarns to fall within the above-described range, thereby facilitating the production of an electrolyte membrane according to the present disclosure. Specifically, when the thickness of the substrate is measured using a contact-type film thickness meter, the difference between the maximum and minimum film thickness is preferably 5 to 30 μm, more preferably 5 to 20 μm, and even more preferably 5 to 10 μm. It is also preferable that the two substrates satisfy the above requirements. The method of thermocompression (hot pressing) is not particularly limited, and examples include flat pressing and roll pressing. Furthermore, since it is easy to adjust the standard deviation of the area defined by the warp and weft yarns to fall within the above-described range, it is preferable to use the substrate that satisfies the requirement for the difference between the maximum and minimum film thicknesses, while adjusting the hot pressing conditions. For example, the hot pressing involves inserting a press laminate, which is made up of a metal plate, a cushion sheet, a substrate, the laminate, the substrate, a cushion sheet, and a metal plate, between a pair of heaters, and applying force to the pair of heaters to press the press laminate. Examples of adjustments to the hot pressing conditions include adjustment of the press pressure, press time, press temperature, and preheating time. Among these, adjusting the preheating time is preferred, as it allows for easier adjustment of the standard deviation of the area defined by the warp and weft yarns within the above-mentioned range. The preheating time refers to the time during which the press laminate is inserted between a pair of heaters, no press pressure is applied, and the heater and metal plate are in contact before hot pressing. In this state, the heater and metal plate are in contact, so the metal plate is preheated before pressing. A preferred preheating time is 30 seconds or more, more preferably 60 seconds or more, and even more preferably 120 seconds or more, as it allows for easier adjustment of the standard deviation of the area defined by the warp and weft yarns to the upper limit of the above-mentioned range or less. It may also be held for 150 seconds or more. Furthermore, a preferred preheating time is 600 seconds or less, more preferably 300 seconds or less, and even more preferably 240 seconds or less, from the viewpoint of making it easier to adjust the standard deviation of the area defined by the warp and weft yarns to be equal to or greater than the lower limit of the above-mentioned range.Furthermore, it is also preferable to apply the above preheating time while satisfying the requirement for the difference between the maximum and minimum film thicknesses of the substrate, since the standard deviation of the area defined by the warp and weft yarns can be easily adjusted within the above range. The thermocompression bonding temperature is preferably 100°C to 200°C.

[0061] The configuration of the woven fabric is as described above, and therefore will not be described further. Note that the standard deviation of the area defined by the warp and weft yarns in the woven fabric can be adjusted, for example, by adopting the preferred embodiment of the above-described method for producing the precursor membrane.

[0062] The fluoropolymer (I') is preferably a polymer containing units based on a fluoromonomer having a group convertible into an ion-exchange group (hereinafter also referred to as fluoromonomer (I')), more preferably a polymer containing units based on a fluoromonomer having a group convertible into a sulfonic acid type functional group (hereinafter also referred to as "fluoromonomer (S')") (hereinafter also referred to as "fluoropolymer (S')"), and particularly preferably a copolymer of a fluorine-containing olefin and a monomer having a group convertible into a sulfonic acid type functional group and a fluorine atom. The fluoropolymer (S') will be described in detail below.

[0063] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted.

[0064] Examples of the fluorine-containing olefin include those exemplified above, and TFE is preferred from the viewpoints of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0065] The fluorine-containing monomer (S') may be a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group that can be converted into a sulfonic acid functional group. As the fluorine-containing monomer (S'), a compound represented by formula (2) is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). Formula (2) CF ２ =CF-L-(A)ｎ The definitions of L and n in formula (2) are as described above. A is a group that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of groups that can be converted into a sulfonic acid functional group include -SO ２ F, -SO ２ Cl, —SO ２ Br. A plurality of A's may be the same or different.

[0066] The compound represented by formula (2) is preferably a compound represented by formula (2-1), a compound represented by formula (2-2), a compound represented by formula (2-3), or a compound represented by formula (2-4). ２ =CF-O-R ｆ１ -A Formula (2-2) CF ２ =CF-R ｆ１ -A

[0067]

[0068] R in the formula ｆ１ , R ｆ２ , r and A are as defined above.

[0069]

[0070] R in the formula ｆ１ , R ｆ２ , R ｆ３ , r, m and A are as defined above.

[0071] The compound represented by formula (2-1) and the compound represented by formula (2-1) are preferably compounds represented by formula (2-5): Formula (2-5) CF ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ２ The definitions of x, y, z and Y in the formula F are as described above.

[0072] Specific examples of the compound represented by formula (2-1) include the following compounds. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｘ -SO ２ F

[0073] Specific examples of the compound represented by formula (2-2) include the following compounds: In the formula, w is an integer of 1 to 8. CF ２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0074] The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

[0075]

[0076] R in the formula ｆ４ , R ｆ５ , r and A are as defined above.

[0077] Specific examples of the compound represented by formula (2-3-1) include the following.

[0078]

[0079] The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

[0080]

[0081] R in the formulaｆ１ , R ｆ２ and A are defined as above.

[0082] Specific examples of the compound represented by formula (2-4-1) include the following.

[0083]

[0084] The fluorine-containing monomer (S') may be used alone or in combination of two or more. In the production of the fluorine-containing polymer (S'), other monomers may be used in addition to the fluorine-containing olefin and the fluorine-containing monomer (S'). Examples of other monomers include those exemplified above.

[0085] The ion exchange capacity of the fluoropolymer (I') can be adjusted by changing the content of groups that can be converted into ion exchange groups in the fluoropolymer (I').

[0086] Specific examples of methods for converting groups in the precursor membrane that can be converted to ion-exchange groups into ion-exchange groups include methods of subjecting the precursor membrane to hydrolysis treatment, acidification treatment, etc. Among these, a method of contacting the precursor membrane with an alkaline aqueous solution is preferred.

[0087] Specific examples of the method for contacting the precursor film with the alkaline aqueous solution include a method of immersing the precursor film in the alkaline aqueous solution and a method of spraying the alkaline aqueous solution onto the surface of the precursor film. The temperature of the alkaline aqueous solution is preferably 30 to 100°C, and more preferably 40 to 100°C. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 to 150 minutes, and more preferably 5 to 50 minutes.

[0088] The alkaline aqueous solution preferably contains an alkali metal hydroxide, a water-soluble organic solvent, and water. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. In this specification, the water-soluble organic solvent refers to an organic solvent that is easily soluble in water. Specifically, an organic solvent having a solubility of 0.1 g or more in 1,000 ml of water (20°C) is preferred, and an organic solvent having a solubility of 0.5 g or more is particularly preferred. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols, and aminoalcohols, and particularly preferably contains an aprotic organic solvent. One water-soluble organic solvent may be used alone, or two or more water-soluble organic solvents may be used in combination.

[0089] Specific examples of aprotic organic solvents include dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone, with dimethyl sulfoxide being preferred. Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol, and ethylene glycol. Specific examples of aminoalcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol, 2-aminothioethoxyethanol, and 2-amino-2-methyl-1-propanol.

[0090] The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1 to 60% by mass, and particularly preferably 3 to 55% by mass. The content of the water-soluble organic solvent in the alkaline aqueous solution is preferably 1 to 60% by mass, and particularly preferably 3 to 55% by mass. The concentration of water in the alkaline aqueous solution is preferably 39 to 80% by mass.

[0091] After the precursor film is brought into contact with the alkaline aqueous solution, a treatment for removing the alkaline aqueous solution may be carried out. As a method for removing the alkaline aqueous solution, for example, a method for washing the precursor film that has been brought into contact with the alkaline aqueous solution with water may be mentioned.

[0092] After contacting the precursor membrane with the alkaline aqueous solution, the resulting membrane may be contacted with an acidic aqueous solution to convert the ion exchange groups to an acid form. Specific examples of methods for contacting the precursor membrane with the acidic aqueous solution include immersing the precursor membrane in the acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor membrane. The acidic aqueous solution preferably contains an acid component and water. Specific examples of the acid component include hydrochloric acid and sulfuric acid.

[0093] <Membrane Electrode Assembly> The membrane electrode assembly of the present disclosure includes an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. The electrolyte membrane is as described above, and therefore will not be described here.

[0094] 4 is a cross-sectional view showing an example of a membrane electrode assembly according to the present disclosure. The membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having a catalyst layer 26 and a gas diffusion layer 28, and an electrolyte membrane 10 disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26.

[0095] [Anode and Cathode] The anode and cathode each have a catalyst layer. In the example of Fig. 4, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28. At least one of the anode 22 and cathode 24 may have a region where the gas diffusion layer 28 and the catalyst layer 26 partially overlap in the thickness direction. Alternatively, at least one of the anode 22 and cathode 24 may omit the catalyst layer 26, and the gas diffusion layer 28 may function as the catalyst layer 26.

[0096] Specific examples of the catalyst layer include a layer containing a catalyst and a polymer having an ion exchange group. Specific examples of the catalyst include a supported catalyst in which a carbon support supports a catalyst containing platinum, a platinum alloy, or a platinum catalyst having a core-shell structure; a ruthenium oxide catalyst; an iridium oxide catalyst; a ruthenium-containing composite oxide; an iridium-containing composite oxide; a ruthenium oxide-containing catalyst having a core-shell structure; and an iridium oxide-containing catalyst having a core-shell structure. Examples of the carbon support include carbon black powder. Examples of the polymer having an ion exchange group include a fluorine-containing polymer having an ion exchange group. The catalyst contained in the anode-side catalyst layer is preferably one or more catalysts selected from the group consisting of a ruthenium oxide catalyst, an iridium oxide catalyst, a ruthenium-containing composite oxide, an iridium-containing composite oxide, a ruthenium oxide-containing catalyst having a core-shell structure, and an iridium oxide-containing catalyst having a core-shell structure. The catalyst contained in the cathode-side catalyst layer is preferably the supported catalyst described above.

[0097] The gas diffusion layer functions to uniformly diffuse gas into the catalyst layer and as a current collector. Specific examples of gas diffusion layers include carbon paper, carbon cloth, carbon felt, and metal mesh. A metal mesh is preferably used as the anode-side gas diffusion layer. The metal mesh is preferably made of a highly corrosion-resistant metal, such as titanium, zirconium, niobium, and tantalum, with titanium being preferred. The gas diffusion layer may be treated with PTFE or the like to be water-repellent. When the gas diffusion layer is a metal mesh, its surface may be coated with a precious metal such as platinum. While the membrane electrode assembly of FIG. 4 includes a gas diffusion layer 28, the gas diffusion layer is an optional component and may not be included in the membrane electrode assembly. As described above, the gas diffusion layer may also include the catalyst described above.

[0098] The thicknesses of the anode and cathode are each independently preferably 5 to 100 μm, more preferably 5 to 50 μm, even more preferably 5 to 30 μm, and particularly preferably 5 to 15 μm, from the viewpoint of achieving superior effects of the present disclosure. The thicknesses of the anode and cathode are measured using images obtained by measuring, with an optical microscope, a cross section of the membrane electrode assembly cut along a plane parallel to the thickness direction, and are the arithmetic average values ​​at any 20 points.

[0099] [Method for Manufacturing Membrane Electrode Assembly] Examples of methods for manufacturing a membrane electrode assembly include a method in which a catalyst layer is formed on an electrolyte membrane and the resulting assembly is further sandwiched between gas diffusion layers, and a method in which a catalyst layer is formed on a gas diffusion layer to form electrodes (anode, cathode) and the electrolyte membrane is sandwiched between these electrodes. Examples of methods for manufacturing a catalyst layer include a method in which a catalyst layer-forming coating liquid is applied to a predetermined position on the electrolyte membrane and dried as necessary. Another example is a method in which a catalyst layer-forming coating liquid is applied to a substrate and dried to form a catalyst layer on the substrate, and then the formed catalyst layer is transferred to the electrolyte membrane. Examples of the catalyst layer-forming coating liquid include a liquid in which a polymer having an ion exchange group and a catalyst are dispersed in a dispersion medium.

[0100] <Applications> The membrane electrode assembly of the present disclosure can be used in a water electrolysis device (specifically, a solid polymer water electrolysis device). The membrane electrode assembly of the present disclosure can also be used in an electrolytic hydrogenation device for aromatic compounds (e.g., toluene).

[0101] [Water electrolysis device] The water electrolysis device of the present disclosure includes the above-described membrane electrode assembly. Because the water electrolysis device of the present disclosure includes the above-described membrane electrode assembly (electrolyte membrane of the present disclosure), pinholes are less likely to occur in the electrolyte membrane. The water electrolysis device of the present disclosure can have the same configuration as known water electrolysis devices, except for including the above-described membrane electrode assembly.

[0102] [Method for Producing Hydrogen] The method for producing hydrogen according to the present disclosure is a method for producing hydrogen by electrolyzing water (electrolyte) using the water electrolysis device described above. The method for producing hydrogen according to the present disclosure is thought to be able to efficiently produce hydrogen because it uses the water electrolysis device described above.

[0103] [Electrolytic hydrogenation apparatus] The electrolytic hydrogenation apparatus of the present disclosure includes the above-described membrane electrode assembly. The electrolytic hydrogenation apparatus of the present disclosure can have the same configuration as known electrolytic hydrogenation apparatuses, except that it includes the above-described membrane electrode assembly.

[0104] The present invention will be described in detail below with reference to examples. Examples 1 to 5 are working examples, and Examples 6 to 10 are comparative examples. However, the present invention is not limited to these examples.

[0105] <Measurement Method> The method for measuring the values ​​in each example will be described below.

[0106] [Ion exchange capacity of fluoropolymer] The fluoropolymer was placed in a glove box filled with dry nitrogen for 24 hours, and the dry mass of the fluoropolymer was measured. Thereafter, the fluoropolymer was immersed in a 2 mol / L aqueous sodium chloride solution at 60°C for 1 hour. The fluoropolymer was washed with ultrapure water and then removed. The solution in which the fluoropolymer had been immersed was titrated with a 0.1 mol / L aqueous sodium hydroxide solution to determine the ion exchange capacity X of the fluoropolymer (milliequivalents / gram of dry resin (also referred to as "meq / g" in the tables below)).

[0107] [Weight of Woven Fabric] The raw woven fabric used was cut into a size of 20 x 20 cm, and the mass was measured. The above measurement was carried out five times, and the weight of the woven fabric (g / m) was calculated based on the average value. ２ The density of the warp and weft yarns constituting the woven fabric was calculated according to the following method. For each warp and weft yarn, the length of 10 yarns was measured five times from an image observed under an optical microscope, and the average value was converted into the density (threads / inch).

[0108] [Opening ratio of woven fabric] The raw woven fabric used was cut into a sample of 20 x 20 cm, and the opening ratio was calculated according to the method described in the description of the woven fabric above.

[0109] [Area divided by warp and weft] The standard deviation of the area divided by the warp and weft and the average value of the area divided by the warp and weft were calculated using the method described above.

[0110] Example 1 The electrolyte membrane used in Example 1 was obtained by the following procedure.

[0111] [Production of Fluorine-Containing Polymer (S'-1)] CF ２ =CF ２ and a monomer (X) represented by the following formula (X) were copolymerized to obtain a fluorine-containing polymer (S'-1) (ion exchange capacity: 1.25 meq / g dry resin): CF ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F...(X)

[0112] The ion exchange capacity described in the above [Production of Fluoropolymer (S'-1)] represents the ion exchange capacity of the fluoropolymer obtained when the fluoropolymer (S'-1) is hydrolyzed by the procedure described below.

[0113] [Production of film-attached substrate Y1] Next, a fluoropolymer (S'-1) was adhered by melt extrusion to a substrate made of a linear low-density polyethylene (LLDPE) film (melting point: 110 to 120°C), to obtain a film-attached substrate Y1 in which a film α1 (film thickness: 45 µm) made of the fluoropolymer (S'-1) was formed on the substrate. The difference between the minimum and maximum film thicknesses of the substrate was 10 µm. The film thickness was measured using a contact film thickness meter (thickness gauge, SMD-565J-L, manufactured by Teclock Corporation), and film thickness measurements were made at 20 locations.

[0114] [Production of woven fabric] 18.6 denier PFA yarns were used as warp and weft yarns, and plain weaving was performed so that the density of the PFA yarns was 100 threads / inch to obtain woven fabric A1. The weight of woven fabric A1 was 16.3 g / m ２ The aperture ratio was 74%.

[0115] [Production of electrolyte membrane] A laminate was obtained by stacking the film-attached substrate Y1 / woven fabric A1 / film-attached substrate Y1 in this order. The film-attached substrate Y1 was positioned so that the film α1 of the film-attached substrate Y1 was in contact with the woven fabric A1. The laminate was then heated at a temperature of 160°C and a surface pressure of 30 MPa / m２ After the substrates were heated and pressed for 10 minutes using a plate press, the substrates on both sides were peeled off at a temperature of 50° C. to obtain a precursor film. The preheating time before the above-mentioned heating and pressing (heat pressing) was 120 seconds.

[0116] The precursor membrane was immersed in a solution of dimethyl sulfoxide / potassium hydroxide / water = 30 / 5.5 / 64.5 (mass ratio) at 95 ° C for 30 minutes to hydrolyze the groups in the precursor membrane that can be converted to sulfonic acid functional groups, converting them to K-type sulfonic acid functional groups, and then washed with water. The resulting membrane was then immersed in 1 M sulfuric acid to convert the terminal groups from K-type to H-type, and then dried to obtain an electrolyte membrane.

[0117] [Production of Membrane Electrode Assembly] TFE and the above-mentioned monomer (X) were copolymerized, and the resulting polymer (ion exchange capacity: 1.10 meq / g dry resin) was converted to an acid form through hydrolysis and acid treatment. This polymer was dispersed in a water / ethanol solvent (40 / 60 mass%) at a solids concentration of 25.8% to obtain a dispersion (hereinafter also referred to as "Dispersion X"). Ethanol (0.52 g) and water (3.34 g) were added to the resulting Dispersion X (19.0 g), followed by the addition of 13.0 g of an iridium oxide catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) containing 76 mass% iridium. The resulting mixture was milled in a planetary bead mill (rotation speed: 300 rpm) for 30 minutes, after which water (4.49 g) and ethanol (4.53 g) were added. This mixture was then milled in a planetary bead mill (rotation speed: 200 rpm) for 60 minutes to obtain an anode catalyst ink with a solids concentration of 40 mass%. On one surface of the electrolyte membrane obtained by the above procedure, an anode catalyst ink was applied to a thickness of 2.0 mg / cm of iridium. ２ The coated film was dried at 80° C. for 10 minutes, and then subjected to a heat treatment at 150° C. for 15 minutes to obtain an electrolyte membrane with an anode catalyst layer.

[0118] Water (59.4 g) and ethanol (39.6 g) were added to 11 g of a supported catalyst ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which 46% by mass of platinum was supported on carbon powder, and the mixture was mixed and pulverized using an ultrasonic homogenizer to obtain a catalyst dispersion. To the catalyst dispersion, a mixture (29.2 g) of Dispersion X (20.1 g), ethanol (11 g), and Zeorola-H (manufactured by Zeon Corporation) (6.3 g) was premixed and kneaded. Water (3.66 g) and ethanol (7.63 g) were then added to the resulting dispersion and mixed for 60 minutes using a paint conditioner to adjust the solids concentration to 10.0% by mass, thereby obtaining a cathode catalyst ink. The cathode catalyst ink was applied to an ETFE sheet using a die coater, dried at 80°C, and further heat-treated at 150°C for 15 minutes, resulting in a platinum content of 0.4 mg / cm. ２ As a result, a cathode catalyst layer decal of 1000 nm was obtained.

[0119] The surface of the electrolyte membrane with an anode catalyst layer on which no anode catalyst layer was formed was placed opposite the surface of the cathode catalyst layer decal on which the catalyst layer was present, and the membrane was hot-pressed at a press temperature of 150°C for 2 minutes under a pressure of 3 MPa to bond the electrolyte membrane with an anode catalyst layer to the cathode catalyst layer. After the temperature was lowered to 70°C, the pressure was released and the membrane was removed. The ETFE sheet of the cathode catalyst layer decal was peeled off, and the membrane was then bonded to an electrode with an area of ​​25 cm. ２ As a result, a membrane electrode assembly of 1000 .mu.m was obtained.

[0120] [Electrolysis Test] The membrane electrode assembly obtained by the above procedure was heat-treated at 150°C for 15 minutes and then set in a water electrolysis evaluation jig EH50-25 (manufactured by Greenlight Innovation). Next, first, to sufficiently hydrate the electrolyte membrane and the ionomers of both electrodes, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 12 hours. The cathode side was then purged with nitrogen. After the nitrogen purging, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode side at a flow rate of 50 mL / min. While the generated gas pressure on the cathode side was kept at 1 MPa, a current of 0 to 50 A (current density 0 to 2 A / cm) was supplied from a DC power supply PWR1600L manufactured by Kikusui Electronics Co., Ltd. ２The current was increased stepwise by 2.5 A in the range of 50 A (current density 2 A / cm ２ ) and operated for 300 hours.

[0121] After the electrolysis test, the membrane electrode assembly was removed from the water electrolysis evaluation jig, and the number of pinholes (holes) in the electrolyte membrane of the membrane electrode assembly was counted using a pinhole inspection device (product name "TRS-70", manufactured by Sanko Electronics Laboratory Co., Ltd.). Based on the above results, the resistance to pinhole formation was evaluated according to the following criteria. A rating, B rating, or C rating is preferable. A: No pinholes were found. B: There were 1 or 2 pinholes. C: There were 3 or 4 pinholes. D: There were 5 or more pinholes.

[0122] [Tensile Test] A tensile test was carried out on the electrolyte membrane obtained by the above procedure using the following procedure. The tear strength was determined using a dumbbell-shaped test piece (test piece type 1B, width of narrowest parallel part: 10 mm, distance between gauge lines: 50 mm) described in JIS K 7127:1999. This tear strength was designated as σ1. In addition, a 1 mm incision was made in the test piece at the midpoint in the longitudinal direction between the gauge lines, and the tear strength was determined in the same manner. This tear strength was designated as σ2. The tear resistance of the electrolyte membrane was evaluated based on the ratio of σ2 to σ1 (σ2 / σ1) using the following criteria. Note that a larger ratio indicates greater tear resistance. A rating of A, B, or C is preferred. A: The ratio is 0.6 or more. B: The ratio is 0.5 or more but less than 0.6. C: The ratio is 0.4 or more but less than 0.5. D: The ratio is less than 0.4.

[0123] Examples 2 to 9 Except for changing the type of substrate used in producing the film-attached substrate to the substrate shown in the table below and changing the preheating time before thermocompression bonding as shown in the table below, electrolyte membranes were produced in the same manner as in Example 1, and measurements and evaluations were carried out in the same manner as in Example 1. Note that in Example 6, when an electrolyte membrane was produced without a preheating time, no pinholes were observed in the above-mentioned electrolysis evaluation test when the gas pressure generated on the cathode side was atmospheric pressure, whereas pinholes were confirmed to occur when the gas pressure generated on the cathode side was 1 MPa in the same manner as in the above-mentioned electrolysis evaluation test.

[0124] <Results> Table 1 shows the conditions for producing the electrolyte membrane, the various measurements of the obtained electrolyte membrane, and the evaluation results.

[0125]

[0126] From the results shown in Table 1, it can be seen that the standard deviation of the area of ​​the region defined by the warp and weft yarns is 0.10 × 10 ４ μm ２ The electrolyte membranes of Examples 6 and 8, in which the standard deviation was less than 2.0 × 10, were easily torn. ４ μm ２ The electrolyte membranes of Examples 7 and 9, where the standard deviation was greater than 0.15×10, were prone to pinholes. On the other hand, it was confirmed that the electrolyte membranes of Examples 1 to 5, where the standard deviation was within the predetermined range, were less prone to pinholes and were less prone to tearing. From a comparison of Example 2 with Examples 1 and 4, it was found that the standard deviation was 0.15×10 ４ μm ２ or more (more preferably 0.20 × 10 ４ μm ２ More preferably, 0.30×10 ４ μm ２ It was confirmed that when the standard deviation was 1.5 × 10 or more, the electrolyte membrane was less likely to be torn. ４ μm ２ or less (more preferably 1.0 × 10 ４ μm ２ More preferably, 0.50 × 10 ４ μm ２It was confirmed that the occurrence of pinholes was further suppressed when the thickness was 100 μm or less (hereinafter referred to as "100 μm").

[0127] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-221084, filed on December 27, 2023, are hereby incorporated by reference as the disclosure of the present invention.

[0128] REFERENCE SIGNS LIST 10 Solid polymer electrolyte membrane 12 Electrolyte 14 Woven fabric 16, V1, V2, V3, V4 Warp yarns 18, H1, H2, H3, H4 Weft yarns 20 Membrane electrode assembly 22 Anode 24 Cathode 26 Catalyst layer 28 Gas diffusion layer

Claims

1. A solid polymer electrolyte membrane comprising a fluorine-containing polymer having an ion-exchange group and a woven fabric composed of warp and weft, wherein when observed from the normal direction to the surface of the solid polymer electrolyte membrane, the standard deviation of the area of the region partitioned by the warp and the weft is 0.10×10 ４ ~2.0×10 ４ μm ２ A solid polymer electrolyte membrane.

2. The solid polymer electrolyte membrane according to claim 1, wherein the denier of the warp and the denier of the weft are each independently 15 to 50.

3. The average value of the area of the region partitioned by the warp and weft yarns is 1.0×10 ４ to 10.0×10 ４ μm ２ The solid polymer electrolyte membrane according to claim 1.

4. The standard deviation of the area of the region partitioned by the warp threads and the weft threads is 0.30×10 ４ to 1.0×10 ４ μm ２ The solid polymer electrolyte membrane according to claim 1, wherein the standard deviation is in the above range.

5. The solid polymer electrolyte membrane according to claim 1, wherein the densities of the warp and the weft are each independently 70 to 150 threads per inch.

6. The solid polymer electrolyte membrane according to claim 1, wherein the warp and the weft are each independently composed of a material selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyether ether ketone, and polyphenylene sulfide.

7. The solid polymer electrolyte membrane according to claim 1, wherein the ion exchange group is a sulfonic acid type functional group.

8. The solid polymer electrolyte membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer is 0.90 to 2.00 milliequivalents per gram of dry resin.

9. The solid polymer electrolyte membrane according to claim 1, wherein the fluorine-containing polymer contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid type functional group and a fluorine atom.

10. The solid polymer electrolyte membrane according to claim 9, wherein the fluorine-containing olefin is a fluoroolefin having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule.

11. The solid polymer electrolyte membrane according to claim 9, wherein the unit having a sulfonic acid type functional group and a fluorine atom is a unit represented by the formula (1). Formula (1) -[CF ２ -CF(-L-(SO ３ M) ｎ )]- L is an (n + 1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, n is 1 or 2, and a plurality of M's may be the same or different.

12. A membrane electrode assembly for a water electrolysis device, comprising an anode having a catalyst layer, a cathode having a catalyst layer, and the solid polymer electrolyte membrane according to claim 1 or 2 disposed between the anode and the cathode.

13. A water electrolysis device comprising the membrane electrode assembly according to claim 12.

14. A method for producing hydrogen, comprising electrolyzing water with the water electrolysis device according to claim 13 to produce hydrogen.

15. A method for producing a solid polymer electrolyte membrane, comprising sequentially including the following (a), (b), and (c), heat-pressing with a heat-pressing device preheated at a heat-pressing temperature for 30 to 600 seconds a laminate in which (b) and (c) are in contact, then peeling (a) to obtain a precursor membrane, and then converting a group convertible to an ion exchange group in the precursor membrane to an ion exchange group to obtain the solid polymer electrolyte membrane according to any one of claims 1 to 11. (a) A base material having a difference between the maximum value and the minimum value of the film thickness of 5 to 30 μm; (b) A film made of a fluorine-containing polymer having a group convertible to an ion exchange group; (c) A woven fabric composed of a warp and a weft

Images