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

Abstract

The present invention provides: a solid polymer electrolyte membrane which is excellent in terms of low gas permeability; a membrane electrode assembly; and a water electrolysis device.　A solid polymer electrolyte membrane according to the present disclosure comprises: a first membrane which contains a fluorine-containing polymer that has an ion exchange group, and a platinum-containing material; and a second membrane which contains a fluorine-containing polymer that has an ion exchange group, and which has a lower concentration of the platinum-containing material than the first membrane. If a ratio X is the ratio of the thickness of the first membrane to the total thickness of the thickness of the first membrane and the thickness of the second membrane at an end of the solid polymer electrolyte membrane, and a ratio Y is the ratio of the thickness of the first membrane to the total thickness of the thickness of the first membrane and the thickness of the second membrane at the central part of the solid polymer electrolyte membrane, the ratio X is greater than the ratio Y.

Description

Solid polymer electrolyte membrane, membrane electrode assembly, water electrolysis device, and hydrogen production method

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

[0002] From the viewpoint of power-to-gas, i.e., converting surplus electricity into gas for storage and utilization, the use of a polymer electrolyte membrane (PEM-type water electrolysis device) has been considered. For example, Patent Document 1 discloses a polymer electrolyte membrane (PEM-type water electrolysis device) having a membrane electrode assembly including an anode and a cathode each having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode, wherein the solid polymer electrolyte membrane includes a second region, a first region, and a third region, which are disposed in this order at equal intervals along the thickness direction, and the second region contains platinum or platinum oxide.

[0003] U.S. Patent No. 1,141,470

[0004] In recent years, there has been a demand for further improvements in the performance of water electrolysis devices, specifically, a demand for reducing hydrogen crossover. Here, hydrogen crossover refers to the movement of hydrogen gas generated at the cathode to the anode side through a solid polymer electrolyte membrane in a water electrolysis device. The occurrence of hydrogen crossover poses a problem of reduced hydrogen gas recovery efficiency. Therefore, a solid polymer electrolyte membrane is required to be able to suppress the permeation of hydrogen gas generated in the system, i.e., to have low gas permeability. The present inventors evaluated a water electrolysis device having a solid polymer electrolyte membrane as described in Patent Document 1 and found that there is room for improvement in the low gas permeability of the solid polymer electrolyte membrane.

[0005] The present disclosure has been made in view of the above problems, and an object of one embodiment of the present invention is to provide a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis device, and a method for producing hydrogen, which are excellent in low gas permeability.

[0006] The present disclosure has the following aspects. [1] A solid polymer electrolyte membrane comprising: a first membrane containing a fluorine-containing polymer having ion exchange groups and a platinum-containing substance; and a second membrane containing a fluorine-containing polymer having ion exchange groups and having a lower concentration of the platinum-containing substance than the first membrane, wherein, when a ratio of the thickness of the first membrane to the total thickness of the first membrane and the second membrane at an end of the solid polymer electrolyte membrane is defined as ratio X, and a ratio of the thickness of the first membrane to the total thickness of the first membrane and the second membrane at a central portion of the solid polymer electrolyte membrane is defined as ratio Y, the ratio X is larger than the ratio Y. [2] The solid polymer electrolyte membrane according to [1], wherein a value obtained by subtracting the thickness of the first membrane at the central portion of the solid polymer electrolyte membrane from the thickness of the first membrane at the end of the solid polymer electrolyte membrane is larger than 0. [3] The solid polymer electrolyte membrane according to [1] or [2], wherein the second membrane is substantially free of a platinum-containing substance. [4] The solid polymer electrolyte membrane according to any one of [1] to [3], wherein the ratio X is 0.04 to 0.50 and the ratio Y is 0.01 to 0.50. [5] The solid polymer electrolyte membrane according to any one of [1] to [4], wherein the value obtained by subtracting the ratio Y from the ratio X is 0.10 or more. [6] The solid polymer electrolyte membrane according to any one of [1] to [5], wherein the ion exchange groups of the fluoropolymer contained in the first membrane and the ion exchange groups of the fluoropolymer contained in the second membrane are both sulfonic acid type functional groups. [7] The solid polymer electrolyte membrane according to any one of [1] to [6], wherein the ion exchange capacities of the fluoropolymer contained in the first membrane and the fluoropolymer contained in the second membrane are both 0.90 to 2.00 meq / g dry resin. [8] The solid polymer electrolyte membrane according to any one of [1] to [7], wherein the fluoropolymers contained in the first membrane and the second membrane each contain a unit having an ion exchange group represented by the following formula (1): Formula (1) -[CF ２ -CF(-L-(SO ３M))]--In the above formula (1), L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, and M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. [9] The solid polymer electrolyte membrane according to any one of [1] to [8], wherein the total thickness of the first membrane and the second membrane is 30 μm or more and 90 μm or less.

[10] A membrane electrode assembly comprising the solid polymer electrolyte membrane according to any one of [1] to [9], a cathode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and an anode catalyst layer disposed on the other side of the solid polymer electrolyte membrane.

[11] A water electrolysis device comprising: the membrane electrode assembly according to

[10] ; a power supply unit connected to the cathode catalyst layer side and the anode catalyst layer side of the membrane electrode assembly; a water supply unit that supplies water to the anode catalyst layer side; and an electrolytic cell to which water is supplied from the water supply unit, wherein the membrane electrode assembly is disposed inside the electrolytic cell such that an end portion of the solid polymer electrolyte membrane included in the membrane electrode assembly, which exhibits the ratio X, is located above the electrolytic cell relative to a central portion of the solid polymer electrolyte membrane, which exhibits the ratio Y.

[12] A hydrogen production method, comprising producing hydrogen by electrolyzing water using the water electrolysis device according to

[11] .

[0007] According to one embodiment of the present invention, it is possible to provide a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis device, and a method for producing hydrogen, which are excellent in low gas permeability.

[0008] Fig. 1 is a partial schematic plan view showing one embodiment of a solid polymer electrolyte membrane of the present invention. Fig. 2 is a schematic cross-sectional view showing one embodiment of a solid polymer electrolyte membrane of the present invention. Fig. 3 is a schematic cross-sectional view showing one embodiment of a solid polymer electrolyte membrane of the present invention. Fig. 4 is a schematic cross-sectional view showing one embodiment of a solid polymer electrolyte membrane of the present invention. Fig. 5 is a schematic cross-sectional view showing one embodiment of a membrane electrode assembly of the present invention.

[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 based on one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, 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.

[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] [Electrolyte Membrane] The solid polymer electrolyte membrane (hereinafter also simply referred to as "electrolyte membrane") of the present disclosure comprises: a first membrane containing a fluoropolymer having ion exchange groups and a platinum-containing substance; and a second membrane containing a fluoropolymer having ion exchange groups and having a lower concentration of the platinum-containing substance than the first membrane, wherein, when the ratio of the thickness of the first membrane to the total thickness of the first membrane and the second membrane at an end of the solid polymer electrolyte membrane is taken as ratio X, and the ratio of the thickness of the first membrane to the total thickness of the first membrane and the second membrane at a central portion of the solid polymer electrolyte membrane is taken as ratio Y, the ratio X is larger than the ratio Y. Hereinafter, the fluoropolymer having ion exchange groups contained in the first membrane and the fluoropolymer having ion exchange groups contained in the second membrane may be collectively referred to as "fluoropolymer (I)".

[0013] When an electrolyte membrane contains a platinum-containing material, hydrogen generated on the cathode side reacts with oxygen generated on the anode side on the platinum-containing material in the electrolyte membrane to form water, thereby suppressing hydrogen crossover (the movement of hydrogen to the anode side). However, the inventors have found that even when an electrolyte membrane containing a platinum-containing material is used, there is room for improvement in the occurrence of hydrogen crossover. The inventors believe that this is due to the fact that hydrogen generated on the cathode side of a water electrolysis device tends to collect above the electrolytic cell of the water electrolysis device, and crossover of hydrogen collected above the electrolytic cell is not sufficiently suppressed. To address this issue, the inventors have found that hydrogen crossover can be significantly suppressed when the membrane thickness ratios X and Y at predetermined locations on the electrolyte membrane satisfy a predetermined relationship. It is presumed that the occurrence of crossover of hydrogen collected above the electrolytic cell can be effectively suppressed by positioning the end showing the ratio X above the electrolytic cell, i.e., by installing the electrolyte membrane in a water electrolysis device so that the platinum-containing material is concentrated above the electrolytic cell.

[0014] When the electrolyte membrane of the present disclosure is applied to a water electrolysis device, it is preferable to place the surface of the first membrane on the anode side, since this can further suppress the occurrence of hydrogen crossover.

[0015] Fig. 1 is a partial schematic plan view showing one embodiment of the electrolyte membrane of the present invention. Fig. 1 shows only a portion where the electrolyte membrane 1A functions effectively when a membrane electrode assembly including the electrolyte membrane 1A is installed in a water electrolysis device. Here, the portion where the electrolyte membrane functions effectively refers to a portion where the electrolyte membrane overlaps both the cathode catalyst layer and the anode catalyst layer when the membrane electrode assembly is viewed from above. Note that when the membrane electrode assembly is installed in a water electrolysis device after its peripheral edge is sandwiched between mounting members (e.g., gaskets), the portion where the electrolyte membrane functions effectively does not include the portion covered by the mounting members.

[0016] 1 shows the case where the planar shape of the electrolyte membrane 1A is rectangular, but the planar shape of the electrolyte membrane is not particularly limited and may be, for example, circular, elliptical, polygonal other than rectangular, etc. Among these, the planar shape of the electrolyte membrane is preferably rectangular or circular, and more preferably rectangular.

[0017] The electrolyte membrane 1A includes an end E1 including a side e1 of the electrolyte membrane 1A, a central portion C1 adjacent to the end E1 and including the center of gravity c of the electrolyte membrane 1A, and an end E2 adjacent to the central portion C1 and including a side e2 facing the side e1. When a membrane electrode assembly including the electrolyte membrane 1A is installed in a water splitting apparatus, it is preferable that either the end E1 or the end E2 be located above the central portion C1. For example, if the electrolyte membrane 1A is elongated and the shortest distance from the side e1 to the side e2 is defined as the short side direction (width direction) and the direction intersecting the short side direction is defined as the longitudinal direction, the central portion in the width direction is the central portion C1, the range from the side e1 to the boundary with the central portion C1 is the end E1, and the range from the side e2 to the boundary with the central portion C1 is the end E2.

[0018] The end E1, central portion C1, and end E2 will be described using an example in which a membrane electrode assembly including the electrolyte membrane 1A is installed in a water electrolysis device so that the highest point of the electrolyte membrane 1A is at side e1. End E1 is in the range from side e1 to position D1. Position D1 is a position obtained by advancing a length d1 (the shortest distance from side e1 to position D1) from side e1 toward side e2. If the shortest distance from side e1 (i.e., the highest point of the electrolyte membrane 1A installed in the water electrolysis device) to side e2 (i.e., the lowest point of the electrolyte membrane 1A when installed in the water electrolysis device) is length D, length d1 is one-third of length D. Central portion C1 is in the range from position D1 to position D2. Position D2 is a position obtained by advancing a length d2 (the shortest distance from position D1 to position D2) from position D1 toward side e2. Length d2 is one-third of length D. End E2 is in the range from position D2 to side e2. Length d3, which is the shortest distance from position D2 to side e2, is one-third of length D. In the example of FIG. 1, length D is the sum of lengths d1, d2, and d3. Length D is preferably 20 to 200 cm, more preferably 30 to 180 cm, and even more preferably 40 to 160 cm.

[0019] FIG. 2 is a cross-sectional schematic diagram showing one embodiment of the electrolyte membrane of the present invention, specifically a cross-section that appears when the electrolyte membrane 1A of FIG. 1 is cut along a straight line along A-A'. In FIG. 2, the electrolyte membrane 1A includes an end E1, a central portion C1 adjacent to the first end E1, and a second end E2 adjacent to the central portion C1. In FIG. 2, the electrolyte membrane 1A has a first membrane 11A and a second membrane 12A laminated so as to be in contact with the first membrane 11A. The first membrane 11A contains a fluorine-containing polymer having ion exchange groups and a platinum-containing substance. The second membrane 12A contains a fluorine-containing polymer having ion exchange groups and has a lower concentration of the platinum-containing substance than the first membrane 11A.

[0020] In the example of Figure 2, the thickness of the first film 11A remains constant from the end E1 toward the center C1, then gradually decreases, reaches a minimum somewhere in the center, gradually increases from the center C1 toward the end E2, and then becomes constant. Specifically, the cross-sectional shape of the first film 11A in Figure 2 is a concave shape with the thinnest thickness at the center C1. Also, in the example of Figure 2, the thickness of the second film 12A remains constant from the end E1 toward the center C1, then gradually increases, reaches a maximum somewhere in the center, then gradually decreases from the center C1 toward the end E2, and then becomes constant. Specifically, the cross-sectional shape of the second film 12A in Figure 2 is a convex shape with the thickest thickness at the center C1.

[0021] <Thickness of First Membrane> The thickness T11 of the first membrane 11A at the end E1 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, in order to achieve better effects of the present disclosure. The thickness T11 of the first membrane 11A at the end E1 is preferably 60 μm or less, more preferably 45 μm or less, and even more preferably 30 μm or less, in order to achieve better formability during the manufacture of the electrolyte membrane. The thickness T11 of the first membrane 11A at the end E1 is measured using an enlarged image (e.g., 100x magnification) of the cross section of the electrolyte membrane 1A taken with an optical microscope (product name "BX-51" manufactured by Olympus Corporation). Specifically, in the portion of the enlarged image of the cross section corresponding to the first membrane 11A, with one end of the end E1 as the starting point and the other end as the end point, the thickness is measured at a total of 10 equally spaced locations including the starting point and the end point, and the arithmetic average of the thicknesses of the 10 locations is defined as the thickness T11.

[0022] The thickness T12 of the first membrane 11A in the central portion C1 is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, from the viewpoint of better formability during production of the electrolyte membrane. The thickness T12 of the first membrane 11A in the central portion C1 is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, from the viewpoint of better effects of the present disclosure. The thickness T12 of the first membrane 11A in the central portion C1 is measured at a portion corresponding to the first membrane 11A in an enlarged image of the cross section of the electrolyte 1A used to measure the thickness T11, by measuring the thickness at a total of 10 equally spaced points including the starting point and the end point, with one end of the central portion C1 as the starting point and the other end as the end point, and the arithmetic average of the thicknesses at the 10 points is defined as the thickness T12.

[0023] The thickness T13 of the first membrane 11A at the end E2 is preferably greater than 0 μm, more preferably 1 μm or greater, even more preferably 5 μm or greater, and even more preferably 10 μm or greater, in order to achieve better effects of the present disclosure. The thickness T13 of the first membrane 11A at the end E2 is preferably 60 μm or less, more preferably 45 μm or less, and even more preferably 30 μm or less, in order to reduce the electrolysis voltage. The thickness T13 of the first membrane 11A at the end E2 is determined by measuring the thickness at 10 equally spaced points, including the starting point and the ending point, in the portion corresponding to the first membrane 11A in an enlarged image of the cross section of the electrolyte 1A used to measure the thickness T11. The thickness T13 is calculated by measuring the thickness at 10 equally spaced points, including the starting point and the ending point, in the portion corresponding to the first membrane 11A in an enlarged image of the cross section of the electrolyte 1A used to measure the thickness T11. The thickness T11 and the thickness T13 may be the same or different.

[0024] The value (T11-T12) obtained by subtracting the thickness T12 from the thickness T11 is preferably greater than 0 μm, more preferably 5 μm or greater, and even more preferably 10 μm or greater, in order to achieve better effects of the present disclosure. The value (T11-T12) obtained by subtracting the thickness T12 from the thickness T11 is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, in order to achieve better formability during production of the electrolyte membrane.

[0025] 2 shows an example in which T13 is greater than T12, but this is not limiting. The value (T13 - T12) obtained by subtracting thickness T12 from thickness T13 is preferably -20 μm or greater, more preferably -15 μm or greater, and even more preferably -10 μm or greater, in terms of superior effects of the present disclosure. The value (T13 - T12) obtained by subtracting thickness T12 from thickness T13 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less, in terms of formability during production of the electrolyte membrane.

[0026] <Thickness of Second Film> The thickness T21 of the second film 12A at the end E1 is preferably 15 μm or more, more preferably 30 μm or more, even more preferably 45 μm or more, and particularly preferably 60 μm or more, from the viewpoint of achieving superior effects of the present disclosure. The thickness T21 of the second film 12A at the end E1 is preferably 115 μm or less, more preferably 100 μm or less, and even more preferably 85 μm or less, from the viewpoint of reducing the electrolysis voltage. The thickness T21 of the second film 12A at the end E1 is measured at a portion corresponding to the second film 12A in an enlarged image of the cross section of the electrolyte 1A used to measure the thickness T11, starting from one end of the end E1 and ending at the other end, at a total of 10 equally spaced locations including the starting point and the ending point, and the arithmetic average of the thicknesses at the 10 locations is defined as the thickness T21.

[0027] The thickness T22 of the second membrane 12A in the central portion C1 is preferably 40 μm or more, more preferably 45 μm or more, even more preferably 50 μm or more, and particularly preferably 80 μm or more, from the viewpoint of achieving superior effects of the present disclosure. The thickness T22 of the second membrane 12A in the central portion C1 is preferably 120 μm or less, more preferably 110 μm or less, and even more preferably 90 μm or less, from the viewpoint of reducing the electrolysis voltage. The thickness T22 of the second membrane 12A in the central portion C1 is measured at a portion corresponding to the second membrane 12A in an enlarged image of the cross section of the electrolyte 1A used in measuring the thickness T11, with one end of the central portion C1 as the starting point and the other end as the end point, at a total of 10 equally spaced thicknesses including the starting point and the end point, and the arithmetic average of the thicknesses at the 10 points is defined as the thickness T22.

[0028] The thickness T23 of the second membrane 12A at the end E2 is preferably 15 μm or more, more preferably 30 μm or more, even more preferably 45 μm or more, and particularly preferably 60 μm or more, in order to achieve better effects of the present disclosure. The thickness T23 of the second membrane 12A at the end E2 is preferably 115 μm or less, more preferably 110 μm or less, and even more preferably 85 μm or less, in order to reduce the electrolysis voltage. The thickness T23 of the second membrane 12A at the end E2 is determined by measuring the thickness at a total of 10 equally spaced locations, including the starting point and the ending point, in the portion corresponding to the second membrane 12A in the enlarged cross-sectional image of the electrolyte 1A used to measure the thickness T11. The thickness T23 is the arithmetic mean value of the thicknesses at the 10 locations. The thicknesses T21 and T23 may be the same or different.

[0029] The value (T22-T21) obtained by subtracting the thickness T21 from the thickness T22 is preferably greater than 0 μm, more preferably 5 μm or greater, and even more preferably 10 μm or greater, in order to achieve better effects of the present disclosure. The value (T22-T21) obtained by subtracting the thickness T21 from the thickness T22 is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, in order to achieve better formability during production of the electrolyte membrane.

[0030] 2 shows an example in which T22 is greater than T23, but this is not limiting. The value (T22-T23) obtained by subtracting thickness T23 from thickness T22 is preferably −20 μm or greater, more preferably −15 μm or greater, and even more preferably −10 μm or greater, in terms of achieving better effects of the present disclosure. The value (T22-T23) obtained by subtracting thickness T23 from thickness T22 is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less, in terms of achieving better formability during production of the electrolyte membrane.

[0031] <Thickness of Electrolyte Membrane> The thickness T1 of the electrolyte membrane 1A is the sum of the thickness of the first membrane and the thickness of the second membrane. The thickness T1 of the electrolyte membrane 1A is preferably 30 μm or more, and preferably 400 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, particularly preferably 90 μm or less, and most preferably 60 μm or less. The thickness T1 of the electrolyte membrane 1A is determined by measuring the thickness T11 at a total of 30 equally spaced points, including the starting point and the ending point, in a cross-sectional image of the electrolyte membrane 1A used to measure the thickness T11. If the surface of the electrolyte membrane is uneven, the thicknesses of 15 recessed portions and 15 protruding portions of the electrolyte membrane are measured, and the arithmetic mean value of the thicknesses of the total 30 points is defined as the thickness of the electrolyte membrane. However, if the convex portion contains a thread that constitutes the woven fabric, the thickness of the convex portion is the value obtained by subtracting the thickness of the thread present in the convex portion. While Fig. 2 shows the case where thickness T1, the sum of thickness T11 and thickness T21, the sum of thickness T12 and thickness T22, and the sum of thickness T13 and thickness T23 are the same, this is not limitative and they may be different from each other. However, it is preferable that the thickness T1, the sum of thickness T11 and thickness T21, the sum of thickness T12 and thickness T22, and the sum of thickness T13 and thickness T23 are the same for the electrolyte membrane.

[0032] <Thickness Relationship> At the end E1, the ratio X1 of the thickness T11 to the total thickness of the thickness T11 and the thickness T21 (i.e., T11 / (T11+T21)) is preferably 0.04 or more, more preferably 0.06 or more, and even more preferably 0.08 or more, in terms of better effects of the present disclosure. The ratio X1 is preferably 0.50 or less, more preferably 0.33 or less, and even more preferably 0.25 or less, in terms of better formability during production of the electrolyte membrane.

[0033] In the central portion C1, the ratio Y of the thickness T12 to the total thickness of the thickness T12 and the thickness T22 (i.e., T12 / (T12+T22)) is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.08 or more, in order to improve the effects of the present disclosure. In order to improve the formability during production of the electrolyte membrane, the ratio Y is preferably 0.50 or less, more preferably 0.42 or less, even more preferably 0.33 or less, and particularly preferably 0.17 or less.

[0034] At the end E2, the ratio X2 of the thickness T13 to the total thickness of the thickness T13 and the thickness T23 (i.e., T13 / (T13+T23)) is preferably 0.04 or more, more preferably 0.06 or more, and even more preferably 0.08 or more, in order to obtain better effects of the present disclosure. The ratio X2 is preferably 0.50 or less, more preferably 0.33 or less, and even more preferably 0.25 or less, in order to reduce the electrolysis voltage.

[0035] In FIG. 2 , the ratio X1 is greater than the ratio Y (i.e., the value obtained by subtracting the ratio Y from the ratio X1 is greater than 0). In this case, since the layer containing the platinum-containing material is thinner in the center compared to the edges, it is thought that the electrolysis voltage will be lower if the total platinum content is equal compared to when the thickness of the center and edges of the layer containing the platinum-containing material are the same. From the viewpoint of achieving superior effects of the present disclosure, the value obtained by subtracting the ratio Y from the ratio X1 (X1-Y) is preferably 0.03 or greater, more preferably 0.04 or greater, even more preferably 0.10 or greater, particularly preferably 0.16 or greater, and most preferably 0.22 or greater. From the viewpoint of achieving superior formability during production of the electrolyte membrane, the value obtained by subtracting the ratio Y from the ratio X1 is preferably 0.42 or less, more preferably 0.33 or less, and even more preferably 0.25 or less.

[0036] FIG. 2 shows a case where the ratio X2 is greater than the ratio Y (i.e., the value obtained by subtracting the ratio Y from the ratio X1 is greater than 0), but the present invention is not limited to this. For example, as shown in FIGS. 3 and 4 described below, the ratio X1 may be greater than the ratio Y and the ratio X2 may be equal to or less than the ratio Y. The value obtained by subtracting the ratio Y from the ratio X2 (X2-Y) is preferably equal to or greater than -0.17, and more preferably equal to or greater than -0.08. The value obtained by subtracting the ratio Y from the ratio X2 is preferably equal to or less than 0.33, and more preferably equal to or less than 0.25.

[0037] <Other Aspects of Cross-Sectional Shape> In the example of FIG. 2 , the thicknesses of the end portions E1 and E2 of the first membrane 11A are thicker than the thickness of the central portion C1. However, this is not limited to this as long as the relationship between the ratio X1 and the ratio Y satisfies the above-described relationship. Specifically, the electrolyte membrane 1A may have a cross-sectional shape as shown in FIG. 3 or a cross-sectional shape as shown in FIG. 4. FIG. 3 is a cross-sectional schematic diagram showing another example of the cross-sectional shape of the electrolyte membrane of the present disclosure. In the example of FIG. 3 , the thickness of the first membrane 11A gradually decreases from the end portion E1 to the end portion E2. Furthermore, the thickness of the second membrane 12A gradually increases from the end portion E1 to the end portion E2. FIG. 4 is a cross-sectional schematic diagram showing another example of the cross-sectional shape of the electrolyte membrane of the present disclosure. In the example of FIG. 4 , the thickness of the first membrane 11A gradually decreases from the end portion E1 to the central portion C1 and remains constant from the central portion C1 to the end portion E2. The thickness of the second film 12A gradually increases from the end E1 toward the center C1 and becomes constant from the center C1 toward the end E2.

[0038] <Fluorine-containing polymer (I)> The fluoropolymer (I) contained in the first membrane and the fluoropolymer (I) contained in the second membrane may be the same or different. If they are the same, there is an advantage that the occurrence of curling of the electrolyte membrane can be suppressed. If they are different, by making the ion exchange capacity of the fluoropolymer (I) contained in the first membrane higher than the ion exchange capacity of the fluoropolymer (I) contained in the second membrane, the effect of increasing resistance due to the platinum-containing material contained in the first membrane can be reduced, and the occurrence of hydrogen crossover can also be further suppressed.

[0039] 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 splitting apparatus. 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, even more preferably 1.43 milliequivalents / gram dry resin or less, from the viewpoint of the strength of the membrane electrode assembly when water is contained. Only one type of fluoropolymer (I) may be used, or two or more types may be used in combination.

[0040] The first and second films may contain polymers other than the fluorine-containing polymer (I), but it is preferable that the polymer in the first and second films essentially consists of the fluorine-containing polymer (I). "Essentially consisting of the fluorine-containing polymer (I)" means that the content of the fluorine-containing polymer (I) is 95% by mass or more relative to the total mass of the polymers in the first film (or the second film). The upper limit of the content of the fluorine-containing polymer (I) can be 100% by mass relative to the total mass of the polymers in the first film (or the second film). Specific examples of other polymers than the fluorine-containing polymer (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. In view of the oxidation resistance of the electrolyte membrane, other polymers include polyphenylene sulfide resin and polyphenylene ether resin.

[0041] 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 further reducing the electrolysis voltage when the electrolyte membrane is applied to a water electrolysis device. 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.

[0042] 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.

[0043] 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 )]-

[0044] 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, more preferably 10 or less.

[0045] L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, more 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.

[0046] M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. n Ms may be the same or different. n is 1 or 2, preferably 1.

[0047] 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) ]-

[0048]

[0049]

[0050] 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, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0051] 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, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0052] 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, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0053] r is 0 or 1. m is 0 or 1. M is as defined above.

[0054] 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 M is as described above.

[0055] 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) ]-

[0056] 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. The definition of M in the formula is as described above. -[CF ２ -CF(-(CF２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0057] The unit represented by formula (1-3) is preferably a unit represented by formula (1-3-1), where M is defined as above.

[0058]

[0059] 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 the carbon atoms. The definitions of r and M are as described above.

[0060] Specific examples of the unit represented by formula (1-3-1) include the following.

[0061]

[0062] 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.

[0063]

[0064] Specific examples of the unit represented by formula (1-4-1) include the following.

[0065]

[0066] The unit having a sulfonic acid type functional group and a fluorine atom may be used alone or in combination of two or more.

[0067] 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 CF ２= 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.

[0068] The content of the fluoropolymer (I) is preferably from 95 to 100% by mass based on the total mass of the first film (or second film).

[0069] <Platinum-containing material> The platinum-containing material may contain platinum atoms. Specific examples of the platinum-containing material include platinum itself, platinum oxide, platinum-containing composite metal oxides, and platinum alloys. Specific examples of platinum-containing composite oxides include M ｘ Pt ３ O ４ (M is at least one metal atom selected from the group consisting of Li, Na, Mg, Ca, Zn, Cd, Co, Ni, Mn, Cu, Ag, Bi, and Ce, and x is greater than 0 and equal to or less than 1.) Specific examples of platinum alloys include alloys containing platinum and at least one metal selected from the group consisting of transition metals and noble metals other than platinum.

[0070] Specific examples of the shape of the platinum-containing material include particles and sheets. When the platinum-containing material is particulate, it may be a core-shell type particle. An example of a core-shell type particle is a particle in which the core is carbon or contains a metal other than platinum, and the shell contains platinum atoms. When the platinum-containing material is particulate, the average particle diameter (D50) of the platinum-containing material is preferably 1 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, particularly preferably 100 nm or more, and preferably 50 μm or less, more preferably 30 μm or less, even more preferably 14 μm or less, particularly preferably 7 μm or less. The average particle diameter of the platinum-containing material is measured as follows. The average particle size of the platinum-containing material can be obtained by measuring the particle sizes of 40,000 particles in a dry state using an image particle size distribution analyzer (for example, the "Morphologi (registered trademark)" series manufactured by Malvern Panalytical) and determining the cumulative 50% diameter (D50) of the volume-based particle size distribution cumulative curve.

[0071] Electrolyte membrane 1cm ２ The mass of platinum content per unit area is 0.005 mg / cm ２ More than 0.010 mg / cm ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm ２ Preferably, 0.040 mg / cm or less ２ The mass of the platinum-containing material is preferably 0.005 mg / cm or less. ２ If the mass of the platinum-containing material is 0.050 mg / cm or more, the occurrence of hydrogen crossover can be further suppressed. ２ If the above ratio is less than 1, the electrolysis voltage can be reduced, and a low-cost membrane electrode assembly and water electrolysis device can be provided.

[0072] 1 cm of the first membrane ２ The mass of platinum content per unit area is 0.005 mg / cm ２ More than 0.010 mg / cm ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm２ Preferably, 0.040 mg / cm or less ２ The mass of the platinum-containing material is preferably 0.005 mg / cm or less. ２ If the mass of the platinum-containing material is 0.050 mg / cm or more, the occurrence of hydrogen crossover can be further suppressed. ２ If the mass ratio is 0.0005 or more, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.024 or less, the electrolysis voltage can be further reduced, and a low-cost membrane electrode assembly and water electrolysis apparatus can be provided. In the first membrane, the mass ratio of the platinum-containing material to the fluoropolymer (I) (mass of the platinum-containing material / mass of the fluoropolymer (I)) is preferably 0.0005 or more, more preferably 0.004 or more, and even more preferably 0.007 or more, and is preferably 0.024 or less, and preferably 0.014 or less. If the mass ratio is 0.0005 or more, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.024 or less, the electrolysis voltage can be further reduced, and a low-cost membrane electrode assembly and water electrolysis apparatus can be provided. In the first membrane, the platinum-containing material is preferably uniformly dispersed.

[0073] The second film has a lower concentration of platinum-containing material than the first film. The second film may contain platinum-containing material, or may be substantially free of platinum-containing material. Here, "substantially free of platinum-containing material" means that 1 cm of the second film is free of platinum-containing material. ２ The mass of platinum content per unit area is 0.001 mg / cm ２ When the second film contains a platinum-containing material, the second film is ２ The mass of platinum content per unit area is 0.005 mg / cm ２ More than 0.010 mg / cm ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm ２ Preferably, 0.040 mg / cm or less ２or less is preferred. In the second membrane, the mass ratio of the platinum-containing material to the fluoropolymer (I) (mass of platinum-containing material / mass of fluoropolymer (I)) is preferably 0.024 or less, more preferably 0.014 or less, even more preferably 0.007 or less, particularly preferably 0.004 or less. The lower limit is usually 0. When the second membrane contains a platinum-containing material, it is preferred that the platinum-containing material be uniformly dispersed in the second membrane.

[0074] The platinum-containing material may be supported on a carrier. Specific examples of the carrier include carbon carriers such as carbon black powder, graphitized carbon, carbon fiber, and carbon nanotubes. When the platinum-containing material is supported on a carrier, the amount of the platinum-containing material supported is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 50% by mass or less, based on the total mass of the platinum-containing material and the carrier.

[0075] <Cerium oxide> The electrolyte membrane may contain cerium oxide. This suppresses decomposition of the fluoropolymer in the electrolyte membrane, thereby further improving the chemical durability of the electrolyte membrane. Cerium oxide may be contained in at least one of the first membrane and the second membrane, or may be contained in both.

[0076] Cerium oxide is CeO ２ (cerium (IV) oxide), Ce ２ O ３ (cerium (III) oxide) may be used, but from the viewpoint of stability, CeO ２ Cerium oxide may be doped with polyvalent metal ions such as zirconium and praseodymium.

[0077] The cerium oxide is preferably in particulate form. When the cerium oxide is in particulate form, the average particle size (D50) of the cerium oxide is preferably 10 nm or more, more preferably 100 nm or more, even more preferably 1 μm or more, particularly preferably 3 μm or more, and is preferably 30 μm or less, more preferably 14 μm or less, and even more preferably 10 μm or less. When the average particle size of cerium oxide is 10 nm or more, aggregation of cerium oxide is suppressed, and it is easy to achieve a stable dispersion state. When the average particle size of cerium oxide is 30 μm or less, the chemical durability of the electrolyte membrane can be further improved. The method for measuring the average particle size of cerium oxide is as follows. The average particle size of cerium oxide can be obtained by measuring the particle sizes of 40,000 particles in a dry state using an image particle size distribution analyzer (e.g., the "Morphologi (registered trademark)" series manufactured by Malvern Panalytical) and determining the cumulative 50% diameter on a volume-based particle size distribution cumulative curve.

[0078] Electrolyte membrane 1cm ２ The mass of cerium oxide per ２ More than 0.029 mg / cm ２ More preferably, 0.043 mg / cm or more ２ More preferably, 0.088 mg / cm ２ More than 0.132 mg / cm is particularly preferred. ２ More than 1.000 mg / cm is most preferred. ２ Preferably, 0.500 mg / cm or less ２ More preferably, 0.300 mg / cm or less ２ It is more preferable that the mass of cerium oxide is 0.010 mg / cm ２ If the mass of cerium oxide is 1.000 mg / cm or more, the electrolyte membrane will have a whitish color, making it easier to find foreign matter present in the electrolyte membrane. As a result, when the electrolyte membrane is used in a water electrolysis device, it can be used while avoiding the portion of the electrolyte membrane where foreign matter is present, thereby suppressing the occurrence of pinholes in the electrolyte membrane due to foreign matter. ２If the electrolyte membrane contains cerium oxide, it is preferable that the cerium oxide is uniformly dispersed in the electrolyte membrane.

[0079] <Woven Fabric> The electrolyte membrane may contain a woven fabric. The woven fabric serves to improve the dimensional stability, strength, and handleability of the electrolyte membrane. 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 terms of further reducing the electrolysis voltage. The upper limit of the aperture ratio of the woven fabric is preferably 90% or less, particularly preferably 80% or less, in terms of further improving the strength of the membrane-electrode assembly. The aperture ratio of the woven fabric is calculated using the following formula (ε) based on the average diameter R1 of the threads constituting the woven fabric and the average spacing P1 between adjacent threads (hereinafter also referred to as "pitch P1") among the threads constituting the woven fabric. Here, the average diameter R1 of the threads 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 woven fabric surface obtained using a microscope. The pitch P1 refers to the arithmetic mean value of 10 different intervals arbitrarily selected based on a magnified image (for example, 100x) of the woven fabric surface obtained using a microscope. Opening ratio of woven fabric (%) = [P1 / (P1+R1)] ２ × 100 (ε)

[0080] The denier number of the yarn constituting the woven fabric is preferably 2 or more, and from the viewpoint of achieving better strength and dimensional stability of the membrane electrode assembly, more preferably 10 or more, and particularly preferably 15 or more. The upper limit of the denier number of the yarn constituting the woven fabric is preferably 60 or less, more preferably 50 or less, and particularly preferably 20 or less, from the viewpoint of further reducing the electrolysis voltage. The denier number is the value expressed in grams of the mass of 9000 m of yarn (g / 9000 m).

[0081] The density of the threads constituting the woven fabric is preferably 50 threads / inch or more, more preferably 70 threads / inch or more, and particularly preferably 90 threads / inch or more, in terms of excellent strength and dimensional stability of the membrane electrode assembly, and is preferably 200 threads / inch or less, more preferably 150 threads / inch or less, and particularly preferably 100 threads / inch or less, in terms of further reducing the electrolysis voltage.

[0082] The yarn constituting the woven fabric may be either a monofilament consisting of one filament or a multifilament consisting of two or more filaments, with monofilament being preferred.

[0083] The yarns constituting the woven fabric are preferably each independently 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 view of superior yarn durability. The yarns constituting the woven fabric are preferably made of slit yarns in view of superior yarn durability and strength.

[0084] When the material constituting the woven fabric is PTFE, the basis weight of the woven fabric is 20 g / m2, which provides an excellent balance between the strength of the electrolyte membrane and ease of handling. ２ More than 30 g / m ２ More than 40 g / m ２ When the material constituting the woven fabric is PFA, the weight of the woven fabric is preferably 10 g / m2 or less, in view of an excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 30 g / m ２ Preferably, 20 g / m or less ２ When the material constituting the woven fabric is PEEK, the weight of the woven fabric is preferably 5 g / m2 or less, in view of the excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 40 g / m ２ Preferably, 30 g / m or less ２When the material constituting the woven fabric is PPS, the weight per unit area of ​​the woven fabric is preferably 5 g / m2 or less, in view of the excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 40 g / m ２ More than 30 g / m ２ The following is more preferred:

[0085] The content of the woven fabric is preferably 3 mass % or more, more preferably 5 mass % or more, and is preferably 50 mass % or less, more preferably 40 mass % or less, and even more preferably 30 mass % or less, based on the total mass of the electrolyte membrane.

[0086] <Method for Producing Electrolyte Membrane> The electrolyte membrane is preferably produced by melt extrusion. Melt extrusion facilitates the production of an electrolyte membrane including a first membrane in which the platinum-containing material is uniformly dispersed and which has a desired thickness. The following method can be given as an example of a method for producing an electrolyte membrane. First, a kneaded material 1 is prepared, which includes a polymer (hereinafter also referred to as "fluoropolymer (I')") of a fluorine-containing monomer having a group convertible to an ion-exchange group (hereinafter also referred to as fluorine-containing monomer (I')) and a platinum-containing material. Furthermore, the fluorine-containing polymer (I') and a kneaded material 2 that does not contain the platinum-containing material or has a lower platinum-containing material concentration than the kneaded material 1 are prepared. Next, the kneaded materials 1 and 2 are co-extruded by a T-die method as a melt extrusion method to obtain a precursor membrane in which a film P1 formed from the kneaded material 1 and a film P2 formed from the kneaded material 2 are laminated. Here, the T-die temperature and discharge rate are adjusted so that the thickness of the end portions of the membrane P1 in the width direction (at least one of the end portions E1 and E2 in FIG. 1) is thicker than the thickness of the central portion of the membrane P1 in the width direction (the central portion C1 in FIG. 1). Next, groups convertible to ion-exchange groups in the obtained precursor membrane are converted into ion-exchange groups to obtain an electrolyte membrane.

[0087] The fluoropolymer (I') is preferably a polymer (hereinafter also referred to as "fluoropolymer (S')") of a fluoromonomer having a group that can be converted into a sulfonic acid type functional group (hereinafter also referred to as "fluoromonomer (S')"), and particularly preferably a copolymer of a fluorine-containing olefin and a monomer having a group that can be converted into a sulfonic acid type functional group and a fluorine atom. The fluoropolymer (S') will be described in detail below.

[0088] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted.

[0089] 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.

[0090] 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. The n A's may be the same or different.

[0091] 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

[0092]

[0093] R in the formula ｆ１ , R ｆ２ , r and A are as defined above.

[0094]

[0095] R in the formula ｆ１ , R ｆ２ , R ｆ３ , r, m and A are as defined above.

[0096] 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 ３ The definitions of x, y, z and Y in the formula F are as described above.

[0097] 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

[0098] 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

[0099] The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

[0100]

[0101] R in the formula ｆ４ , R ｆ５ , r and A are as defined above.

[0102] Specific examples of the compound represented by formula (2-3-1) include the following.

[0103]

[0104] The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

[0105]

[0106] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0107] Specific examples of the compound represented by formula (2-4-1) include the following.

[0108]

[0109] 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'), in addition to the fluorine-containing olefin and the fluorine-containing monomer (S'), other monomers may be further used. Examples of other monomers include those exemplified above.

[0110] 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').

[0111] 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.

[0112] Specific examples of the method for contacting the precursor film with the alkaline aqueous solution include immersing the precursor film in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the surface of the precursor film. The temperature of the alkaline aqueous solution is preferably 30° C. or higher, more preferably 40° C. or higher, and preferably 100° C. or lower. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 minutes or longer, more preferably 5 minutes or longer, and preferably 150 minutes or shorter, more preferably 50 minutes or shorter.

[0113] 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 1000 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 may be used in combination.

[0114] 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.

[0115] The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The content of the water-soluble organic solvent in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The concentration of water in the alkaline aqueous solution is preferably 39 to 80% by mass.

[0116] 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.

[0117] 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.

[0118] [Membrane Electrode Assembly] The membrane electrode assembly of the present disclosure includes the electrolyte membrane, a cathode catalyst layer disposed on one side of the electrolyte membrane, and an anode catalyst layer disposed on the other side of the electrolyte membrane.

[0119] 5 is a cross-sectional view schematically illustrating an example of a membrane electrode assembly according to the present disclosure. In the example of Fig. 5, the membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having the catalyst layer 26 and the gas diffusion layer 28, and an electrolyte membrane 1A disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26.

[0120] 5 includes a first membrane 11A and a second membrane 12A arranged in this order from the anode 22 side toward the cathode 24 side. The details of the electrolyte membrane 1A are as described above, and therefore will not be described again.

[0121] <Anode and Cathode> The anode and cathode each have a catalyst layer. In the example of Figure 2, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28.

[0122] 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 catalyst containing platinum, a platinum alloy, or a platinum having a core-shell structure is supported on a carbon support, an iridium oxide catalyst, a composite oxide catalyst containing iridium and other metal elements, an alloy containing iridium oxide, and a catalyst containing iridium oxide having a core-shell structure.An example of the carbon support is carbon black powder.An example of the polymer having an ion exchange group is a fluorine-containing polymer having an ion exchange group, and for example, the above-mentioned fluorine-containing polymer (I) can be used.

[0123] Catalyst layer 1cm ２ The mass of the catalytic metal per ２ More than 0.05 mg / cm ２ More preferably, 0.2 mg / cm ２ More preferably, 4 mg / cm ２ Preferably, 2 mg / cm or less２ More preferably, 1 mg / cm or less ２ The following is more preferred: The mass ratio of the catalyst to the polymer having an ion-exchange group in the catalyst layer (mass of catalyst / mass of polymer having an ion-exchange group) is preferably 2 to 6.

[0124] The gas diffusion layer functions to rapidly diffuse gas generated from the catalyst layer out of the catalyst layer and also functions as a current collector. Specific examples of gas diffusion layers include carbon paper, carbon cloth, carbon felt, sintered titanium oxide fibers, and sintered titanium oxide particles. The anode side has a high potential, and using carbon materials would result in oxidation. Therefore, it is preferable to use sintered titanium oxide fibers or sintered titanium oxide particles. The sintered titanium oxide may be plated with platinum or other metals as needed. The cathode gas diffusion layer may be treated with PTFE or other materials for water repellency. While the membrane electrode assembly in FIG. 5 includes a gas diffusion layer 28, the gas diffusion layer is an optional component and may not be included in the membrane electrode assembly.

[0125] The film thickness of the anode and the cathode is preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 15 μm or less, from the viewpoint of obtaining superior effects of the present disclosure. The film thickness of the anode and the cathode is measured using an image obtained by measuring a cross section of the membrane electrode assembly cut in the film thickness direction with a laser microscope, and is an arithmetic average value at any 20 points.

[0126] <Method for Manufacturing a Membrane Electrode Assembly> The method for manufacturing a membrane electrode assembly involves forming the cathode catalyst layer on one side of an electrolyte membrane and the anode catalyst layer on the other side of the electrolyte membrane. One example of a method for manufacturing a membrane electrode assembly involves using a laminate having an anode catalyst layer and a releasable substrate (e.g., an ETFE sheet) and another laminate having a cathode catalyst layer and a releasable substrate (e.g., an ETFE sheet), bonding catalyst layers to both sides of the electrolyte membrane, and then peeling off the releasable substrate. The laminate may have a gas diffusion layer between the catalyst layer and the releasable substrate. In this case, the gas diffusion layer can be formed on the catalyst layer opposite the electrolyte membrane. The catalyst layer can be manufactured by applying a catalyst layer-forming coating liquid to a predetermined position (e.g., the surface of the releasable substrate) and drying it as necessary. The catalyst layer-forming coating liquid is a liquid in which a polymer having an ion-exchange group and a catalyst are dispersed in a dispersion medium.

[0127] <Applications> The membrane electrode assembly of the present disclosure is suitably used in a solid polymer water electrolysis device.

[0128] [Water Electrolysis Apparatus] The water electrolysis apparatus of the present disclosure includes the above-described membrane electrode assembly, a water supply unit that supplies water to the anode catalyst layer side, and an electrolytic cell to which water is supplied from the water supply unit. The membrane electrode assembly is disposed inside the electrolytic cell such that an end portion of the solid polymer electrolyte membrane included in the membrane electrode assembly, which exhibits a ratio X, is located higher than a central portion of the solid polymer electrolyte membrane, which exhibits a ratio Y. In the water electrolysis apparatus of the present disclosure, when a DC voltage is applied by the power supply unit while water is supplied to the anode catalyst layer side by the water supply unit, water is decomposed at the anode catalyst layer side to generate oxygen and protons. At the cathode catalyst layer side, protons that have migrated to the cathode catalyst layer side through the electrolyte membrane gain electrons to generate hydrogen. The water electrolysis apparatus of the present disclosure may have the same configuration as known water electrolysis devices (e.g., an oxygen recovery member that recovers the generated oxygen, a hydrogen recovery member that recovers the generated hydrogen), except for the components described above.

[0129] [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.

[0130] The present invention will be described in detail below with reference to examples. Examples 1 to 5 are working examples, and Example 6 is a comparative example. However, the present invention is not limited to these examples.

[0131] [Ion exchange capacity of fluoropolymer] The fluoropolymer was placed in a glove box purged 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, then removed, and 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 (milliequivalents / gram dry resin) of the fluoropolymer. In the tables shown below, IEC (meq / g) means ion exchange capacity (milliequivalents / gram dry resin).

[0132] [Thickness of Electrolyte Membrane, Thickness of Each Location of First Membrane, Thickness of Each Location of Second Membrane] The thickness of the electrolyte membrane (corresponding to thickness T1 in FIG. 2 ), the thickness of each location of the first membrane (thickness T11, thickness T12, thickness T13 in FIG. 2 ), and the thickness of each location of the second membrane (thickness T21, thickness T22, thickness T23 in FIG. 2 ) were calculated by the method described above based on an enlarged image (objective lens magnification: 100x) of a cross section of the electrolyte membrane photographed using a laser microscope (product name "VK-X1000", manufactured by Keyence Corporation) under conditions of a temperature of 23°C and a relative humidity of 50% RH.

[0133] [Hydrogen concentration in oxygen] A membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekaert) with a thickness of 0.25 mm and a porosity of 60%, and a platinum-plated titanium plate with a straight flow path was used as a separator. The electrode area was 16 cm. ２The membrane electrode assembly was incorporated into a single cell and evaluated. The membrane electrode assembly was clamped so that a pressure of 1.5 MPa was applied to the electrode portions. The membrane electrode assembly incorporated into the single cell was placed inside the electrolytic cell so that the end E1 of the electrolyte membrane was located above the center C1. Next, to sufficiently hydrate the electrolyte membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 60°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 8 hours. Thereafter, pure water with a conductivity of 1.0 μS / cm or less and a temperature of 60°C was supplied to the anode side at a flow rate of 50 mL / min, and while maintaining the back pressure at both the anode and cathode at atmospheric pressure, a current of 16 A (current density 1 A / cm) was applied using a large current potentio / galvanostat HCP-803 (manufactured by Biologic). ２ ) for 4 hours as a break-in operation, water electrolysis was carried out. After that, the main measurement was carried out at a current density of 0 to 32 A (current density 0 to 2 A / cm ２ The current was increased stepwise by 2 A in the range of 0.2 A / cm. Thereafter, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 60°C, and atmospheric pressure was supplied to the cell at 50 mL / min. The back pressure was kept at atmospheric pressure for both the anode and cathode. A current of 3.2 A (current density 0.2 A / cm) was applied using a large current potentio / galvanostat HCP-803 (manufactured by Biologic). ２ After 12 hours had passed, water was separated from the gas discharged from the anode side, and the hydrogen concentration in the gas was measured using a micro GC (Agilent 490, manufactured by Agilent). ２ Medium H ２ The density was evaluated according to the following criteria: ２ Medium H ２ The smaller the concentration value, the better the low gas permeability of the electrolyte membrane. A: Less than 0.03 vol% B: 0.03 vol% or more and less than 0.05 vol% C: 0.05 vol% or more and less than 0.10 vol% D: 0.10 vol% or more

[0134] [Example 1] First, CF ２ =CF ２and a monomer (X) represented by the following formula (X) were copolymerized to obtain a fluoropolymer (I'-1) (ion exchange capacity: 1.25 meq / g dry resin). The ion exchange capacity in parentheses represents the ion exchange capacity of the fluoropolymer obtained when the fluoropolymer (I'-1) is hydrolyzed by the procedure described below. CF ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F...(X)

[0135] Next, a kneaded product 1 containing a fluoropolymer (I'-1) and platinum black ("TEC90300" manufactured by Tanaka Kikinzoku Co., Ltd., a platinum-containing material) and a kneaded product 2 containing a fluoropolymer (I'-1) but no platinum-containing material were prepared. Next, using the kneaded products 1 and 2, co-extrusion was performed by a T-die method as a melt extrusion method to obtain a precursor membrane 1 in which a membrane P1 formed from the kneaded product 1 and a membrane P2 formed from the kneaded product 2 were laminated. Here, in an electrolyte membrane 1 (described below) obtained using the precursor membrane 1, the T-die temperature was adjusted and the extrusion rate was controlled so that the thickness of the electrolyte membrane 1, the thickness of each portion of the first membrane, and the thickness of each portion of the second membrane would be the values ​​listed in Table 1 below. Specifically, for the T-die used to form membrane P1, the set temperature was adjusted in the width direction of the T-die so that the temperatures at both ends of the T-die were higher than the temperature at the center of the T-die. Furthermore, the set temperature of the T-die for forming the film P2 was adjusted so that the temperature of the T-die was constant in the width direction of the T-die.

[0136] Next, 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, and the groups convertible to sulfonic acid functional groups in the precursor membrane were hydrolyzed to convert 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 electrolyte membrane 1 of Example 1. Electrolyte membrane 1 has a first membrane corresponding to membrane P1 and a second membrane corresponding to membrane P2.

[0137] CF ２ =CF２ and the above-mentioned monomer (X), and the resulting polymer (ion exchange capacity: 1.10 meq / g dry resin) was converted to an acid form through hydrolysis and acid treatment, and the resulting polymer was dispersed in a water / ethanol solvent of 40 / 60 (mass%) at a solids concentration of 26.0% to obtain a dispersion (hereinafter also referred to as "Dispersion Y"). Ethanol (18.06 g) and Zeorola-H (manufactured by Zeon Corporation) (10.58 g) were added to the resulting dispersion Y (33.0 g), and the mixture was mixed for 5 minutes at 2200 rpm using a planetary centrifugal mixer (Thinky, Awatori Rentaro). Ethanol (46.44 g) and water (75.75 g) were added to the mixed composition (54.06 g), and a mixture of 74.8 mass% iridium and a specific surface area of ​​100 m was obtained. ２ 40.0 g of an iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd.) was added to the mixture. The resulting mixture was processed in a planetary bead mill (rotational speed: 300 rpm) for 90 minutes to obtain an anode catalyst ink with a solids concentration of 22 mass %. The anode catalyst ink was applied to an ETFE sheet so that the iridium concentration was 1.0 mg / cm. ２ The anode catalyst layer decal was obtained by applying the coating with an applicator so that the coating became smooth, followed by drying at 80° C. for 10 minutes and then heat treating at 150° C. for 15 minutes.

[0138] 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 Y (20.1 g), ethanol (11 g), and Zeorola-H (manufactured by Zeon Corporation) (6.3 g) was premixed and kneaded. Furthermore, water (3.66 g) and ethanol (7.63 g) were added to the resulting dispersion and mixed for 60 minutes using a paint conditioner to obtain a cathode catalyst ink with a solids concentration of 10.0% by mass. 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.

[0139] The surface of the anode catalyst layer decal on which the catalyst layer is located is placed facing the first membrane side of the electrolyte membrane 1, and the surface of the cathode catalyst layer decal on which the catalyst layer is located is placed facing the second membrane side of the electrolyte membrane 1. The anode catalyst layer, electrolyte membrane 1, and cathode catalyst layer are bonded together by hot pressing under conditions of a pressing temperature of 150°C and a pressure of 3 MPa for 10 minutes. After the temperature is lowered to 70°C, the pressure is released and the assembly is taken out. The ETFE sheets of the anode catalyst layer decal and the cathode catalyst layer decal are peeled off, and an electrode with an area of ​​16 cm is obtained. ２ The membrane electrode assembly thus obtained was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0140] [Examples 2 to 5] Electrolyte membranes 2 to 5 of Examples 2 to 5 were obtained in the same manner as in Example 1, except that the T-die temperature and discharge rate were adjusted during the production of the precursor membrane so that the thicknesses of electrolyte membranes 2 to 5 obtained using the precursor membrane, the thicknesses of each portion of the first membrane, and the thicknesses of each portion of the second membrane would be the values ​​listed in Table 1 below. In each of Examples 2 to 5, the temperature setting in the T-die for forming the membrane corresponding to the first membrane was adjusted in the width direction of the T-die so that the temperature at both ends of the T-die was higher than the temperature at the center of the T-die. The temperature setting in the T-die for forming the membrane corresponding to the second membrane was adjusted so that the temperature of the T-die was constant in the width direction of the T-die. Membrane electrode assemblies of Examples 2 to 5 were obtained in the same manner as in Example 1, except that electrolyte membranes 2 to 5 were used instead of electrolyte membrane 1. The membrane electrode assemblies of Examples 2 to 5 were used for the above-described evaluations. The results are shown in Table 1.

[0141] [Example 6] The electrolyte membrane 6 of Example 6 was obtained in the same manner as in Example 1, except that the T-die temperature and discharge rate were adjusted during the production of the precursor membrane so that the thickness of the electrolyte membrane 6 obtained using the precursor membrane, the thickness of each portion of the first membrane, and the thickness of each portion of the second membrane would be the values ​​listed in Table 1 below. Specifically, in Example 6, the set temperature of the T-die for forming a membrane corresponding to the first membrane was adjusted so that the temperature of the T-die was constant in the width direction of the T-die. Furthermore, the set temperature of the T-die for forming a membrane corresponding to the second membrane was adjusted so that the temperature of the T-die was constant in the width direction of the T-die. The membrane electrode assembly of Example 6 was obtained in the same manner as in Example 1, except that electrolyte membrane 6 was used instead of electrolyte membrane 1. The membrane electrode assembly of Example 6 was used for the above-mentioned evaluations. The results are shown in Table 1.

[0142]

[0143] As shown in Table 1, when an electrolyte membrane having a ratio X greater than the ratio Y was used, it was confirmed that the low gas permeability was excellent (Examples 1 to 5). The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-221141 filed on December 27, 2023 are hereby incorporated by reference as the disclosure of the present invention.

[0144] 1A Electrolyte membrane 11A First membrane 12A Second membrane E1, E2 Ends C1 Center e1, e2 Side c Center of gravity d1, d2, d3 Length D1, D2 Position T1, T11, T12, T13, T21, T22, T23 Thickness 20 Membrane electrode assembly 22 Anode 24 Cathode 26 Catalyst layer 28 Gas diffusion layer

Claims

1. A solid polymer electrolyte membrane comprising: a first membrane including a fluorine-containing polymer having an ion-exchange group and a platinum-containing substance; and a second membrane including a fluorine-containing polymer having an ion-exchange group and having a lower concentration of the platinum-containing substance than the first membrane. The ratio of the thickness of the first membrane to the total thickness of the thicknesses of the first membrane and the second membrane at the end of the solid polymer electrolyte membrane is defined as ratio X, and the ratio of the thickness of the first membrane to the total thickness of the thicknesses of the first membrane and the second membrane at the center of the solid polymer electrolyte membrane is defined as ratio Y. The solid polymer electrolyte membrane in which ratio X is greater than ratio Y.

2. The solid polymer electrolyte membrane according to claim 1, wherein the value obtained by subtracting the thickness of the first membrane at the center of the solid polymer electrolyte membrane from the thickness of the first membrane at the end of the solid polymer electrolyte membrane is greater than 0.

3. The solid polymer electrolyte membrane according to claim 1, wherein the second membrane substantially does not contain a platinum-containing substance.

4. The solid polymer electrolyte membrane according to claim 1, wherein ratio X is 0.04 to 0.50 and ratio Y is 0.01 to 0.

50.

5. The solid polymer electrolyte membrane according to claim 1, wherein the value obtained by subtracting ratio Y from ratio X is 0.10 or more.

6. The solid polymer electrolyte membrane according to claim 1, wherein both the ion-exchange group of the fluorine-containing polymer contained in the first membrane and the ion-exchange group of the fluorine-containing polymer contained in the second membrane are sulfonic acid type functional groups.

7. The solid polymer electrolyte membrane according to claim 1, wherein both the ion-exchange capacity of the fluorine-containing polymer contained in the first membrane and the ion-exchange capacity of the fluorine-containing polymer contained in the second membrane are 0.90 to 2.00 milliequivalents / gram of dry resin.

8. The solid polymer electrolyte membrane according to claim 1, wherein both the first film and the second film contain a unit having an ion-exchange group represented by the following formula (1). Formula (1): -[CF ２ -CF(-L-(SO ３ M))]- In the formula (1), L is an (n + 1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom, and M is a hydrogen atom, an alkali metal or a quaternary ammonium cation.

9. The solid polymer electrolyte membrane according to claim 1, wherein the total thickness of the thicknesses of the first membrane and the second membrane is 30 μm or more and 90 μm or less.

10. A membrane electrode assembly comprising: the solid polymer electrolyte membrane according to any one of claims 1 to 9; a cathode catalyst layer disposed on one surface side of the solid polymer electrolyte membrane; and an anode catalyst layer disposed on the other surface side of the solid polymer electrolyte membrane.

11. The membrane electrode assembly according to claim 10, a power supply unit connected to the cathode catalyst layer side and the anode catalyst layer side in the membrane electrode assembly, a water supply unit for supplying water to the anode catalyst layer side, and an electrolytic cell to which water is supplied from the water supply unit, wherein an end portion indicating the ratio X in the solid polymer electrolyte membrane included in the membrane electrode assembly is located above the electrolytic cell than a central portion indicating the ratio Y in the solid polymer electrolyte membrane, and the membrane electrode assembly is disposed inside the electrolytic cell. A water electrolysis device.

12. A method for producing hydrogen, which electrolyzes water by the water electrolysis device according to claim 11 to produce hydrogen.

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