Solid polymer type water electrolysis membrane electrode assembly (water electrolysis device)

Abstract

Provided are a solid polymer-type water electrolysis membrane-electrode joint body and a water electrolysis device which enable suppression of crossover of hydrogen and can achieve low electrolysis voltage.　A solid polymer-type water electrolysis membrane-electrode joint body according to the present invention is provided with: a solid polymer electrolytic membrane including a platinum-containing substance and a fluorine-containing polymer that has an ion exchange group having an ion-exchange capacity of 1.25-2.00 mm equivalent / g dry resin; an anode that has a catalyst layer disposed on one surface of the solid polymer electrolytic membrane; and a cathode that has a catalyst layer disposed on the other surface of the solid polymer electrolytic membrane.

Description

[Technical Field]

[0001] The present invention relates to a membrane electrode assembly for solid polymer type water electrolysis and a water electrolysis apparatus. [Background technology]

[0002] From the perspective of power-to-gas technology, that is, technology that converts surplus electricity into gas for storage and utilization, the use of polymer electrolyte membrane (PEM) water electrolysis devices is being considered. For example, Patent Document 1 discloses a solid polymer water electrolysis apparatus having a membrane electrode assembly comprising an anode and a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2020 / 162511 [Overview of the project] [Problems that the invention aims to solve]

[0004] In recent years, there has been a growing demand for further performance improvements in water electrolysis equipment. Specifically, this includes the ability to lower the electrolysis voltage and reduce hydrogen crossover. Here, hydrogen crossover refers to the movement of hydrogen gas generated at the cathode to the anode side through the solid polymer electrolyte membrane in a water electrolysis device. When hydrogen crossover occurs, there is a problem in that the hydrogen gas that has moved to the anode side mixes with the oxygen gas already present at the anode, potentially producing an explosive gas. When the inventors evaluated a water electrolysis apparatus including a membrane electrode assembly as described in Patent Document 1, they found that while a low electrolysis voltage could be achieved, there was room for improvement regarding the hydrogen crossover.

[0005] The present invention has been made in view of the above problems and aims to provide a solid polymer membrane electrode assembly and a water electrolysis apparatus that can suppress hydrogen crossover and achieve a low electrolysis voltage. [Means for solving the problem]

[0006] As a result of diligent research into the above-mentioned problems, the present inventors have found that in a membrane electrode assembly for solid polymer water electrolysis, which comprises an anode and a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode, the desired effect can be obtained if the solid polymer electrolyte membrane contains a fluorine-containing polymer having ion exchange groups with an ion exchange capacity of 1.25 to 2.00 milliequivalents / gram dry resin and a platinum-containing material, leading to the present invention.

[0007] In other words, the inventors found that the above problem could be solved by the following configuration. [1] A membrane electrode assembly for solid polymer water electrolysis, comprising a fluorine-containing polymer having ion exchange groups with an ion exchange capacity of 1.25 to 2.00 milliequivalents / gram dry resin, and a platinum-containing material, an anode having a catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode having a catalyst layer disposed on the other side of the solid polymer electrolyte membrane. [2] The solid polymer type membrane electrode assembly for water electrolysis according to [1], wherein the platinum-containing material in the solid polymer electrolyte membrane is present only from the surface of the plane on which the anode of the solid polymer electrolyte membrane is located to a thickness corresponding to 20% of the total thickness of the solid polymer electrolyte membrane. [3] When measured by X-ray fluorescence analysis from the surface of the solid polymer electrolyte membrane on which the anode is located, the platinum atom content is 0.005 to 0.050 mg / cm³. 2 The solid polymer membrane electrode assembly for water electrolysis described in [2]. [4] A solid polymer type membrane electrode assembly for water electrolysis according to any one of [1] to [3], wherein the platinum-containing material is supported on a carrier. [5] The solid polymer electrolyte membrane further comprises a reinforcing material as described in any of [1] to [4]. [6] The fluorine-containing polymer comprising at least one unit selected from the group consisting of units represented by formula (1-3) and units represented by formula (1-4) described below, according to any one of [1] to [5]. In equations (1-3) and (1-4) described below, R f1 R is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms, f2 R is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms, f3 is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms, r is 0 or 1, m is 0 or 1, and M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. [7] The solid polymer electrolyte membrane has a multilayer structure in which a plurality of electrolyte layers are stacked, wherein at least one of the plurality of electrolyte layers contains the fluoropolymer and the platinum-containing material, as described in any of [1] to [6]. [8] The solid polymer type membrane electrode assembly for water electrolysis according to [7], wherein the plurality of electrolyte layers contain the platinum-containing material, and the platinum-containing material content of the electrolyte layer closer to the anode is greater than the platinum-containing material content of the electrolyte layer closer to the cathode. [9] The solid polymer type membrane electrode assembly for water electrolysis according to [7] or [8], wherein the ion exchange capacities of the plurality of electrolyte layers are different from each other.

[10] The polymer electrolyte membrane electrode assembly for water electrolysis according to [7] or [9], wherein the plurality of electrolyte layers include an electrolyte layer containing a platinum-containing material and an electrolyte layer not containing a platinum-containing material, and the ratio of the thickness of the electrolyte layer containing a platinum-containing material to the thickness of the electrolyte layer not containing a platinum-containing material is 0.02 or more and 0.50 or less.

[11] A solid polymer type membrane electrode assembly for water electrolysis according to any one of [1] to

[10] , wherein the thickness of the solid polymer electrolyte membrane is 30 μm or more and 400 μm or less.

[12] The solid polymer type membrane electrode assembly for water electrolysis according to any one of [1] to

[11] , wherein the mass ratio of the platinum-containing substance to the fluorine-containing polymer in the solid polymer electrolyte membrane is 0.005 or more and 0.030 or less.

[13] A water electrolysis apparatus comprising a solid polymer membrane electrode assembly for water electrolysis described in any of [1] to

[12] . [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a solid polymer membrane electrode assembly and a water electrolysis apparatus that can suppress hydrogen crossover and achieve a low electrolysis voltage. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing an example of a solid polymer membrane electrode assembly for water electrolysis according to the present invention. [Figure 2] This is a schematic cross-sectional view showing another example of the solid polymer type membrane electrode assembly for water electrolysis of the present invention. [Figure 3] Figure 2 is a partially enlarged view of a membrane electrode assembly for solid polymer electrolyte water electrolysis. [Modes for carrying out the invention]

[0010] The following definitions of terms apply throughout this specification and the claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least some of the ions it contains with other ions. Examples include the sulfonic acid type functional group and the carboxylic acid type functional group described below. A "sulfonic acid type functional group" refers to a sulfonic acid group (-SO3H) or a sulfonic acid base (-SO3M). 2 )(However, M 2 It means an alkali metal or quaternary ammonium cation. A "carboxylic acid-type functional group" refers to a carboxylic acid group (-COOH) or a carboxylic acid base (-COOH). 1 )(However, M 1It means an alkali metal or quaternary ammonium cation. A "precursor membrane" is a membrane containing a polymer that has groups that can be converted into ion exchange groups. "Groups that can be converted into ion exchange groups" refers to groups that can be converted into ion exchange groups through treatments such as hydrolysis or acidification. "A group that can be converted to a sulfonic acid type functional group" refers to a group that can be converted to a sulfonic acid type functional group through treatments such as hydrolysis or acidification.

[0011] In polymers, a "unit" refers to an atomic group derived from one monomer molecule, formed by the polymerization of monomers. A unit may be an atomic group directly formed by a polymerization reaction, or it may be an atomic group in which a portion of the atomic group is converted to a different structure by processing the polymer obtained by the polymerization reaction.

[0012] Numerical ranges expressed using "~" represent a range that includes the numbers before and after "~" as the lower and upper limits, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0013] [Membrane electrode assembly] The solid polymer type membrane electrode assembly for water electrolysis of the present invention (hereinafter also simply referred to as "membrane electrode assembly") comprises a solid polymer electrolyte membrane (hereinafter also simply referred to as "electrolyte membrane") containing a fluorine-containing polymer (hereinafter also simply referred to as "fluorine-containing polymer (I)") having ion exchange groups with an ion exchange capacity of 1.25 to 2.00 milliequivalents / gram dry resin and a platinum-containing material, an anode having a catalyst layer disposed on one side of the electrolyte membrane, and a cathode having a catalyst layer disposed on the other side of the electrolyte membrane. The membrane electrode assembly of the present invention, when applied to a water electrolysis apparatus, can suppress hydrogen crossover and achieve a low electrolysis voltage. While the detailed reasons for this are not yet clear, it is presumed to be due to the following reasons. The electrolyte membrane in this invention contains a platinum-containing material. It is hypothesized that this suppresses the movement of hydrogen to the anode (hydrogen crossover) by causing hydrogen generated on the cathode side to react with oxygen generated on the anode side on the platinum-containing material in the electrolyte membrane to form water. Furthermore, since the electrolyte membrane in this invention contains a fluorine-containing polymer with high ion exchange capacity, a low electrolytic voltage can be achieved.

[0014] Figure 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly of the present invention, and shows the case where the electrolyte membrane has a single-layer structure. In the example of Figure 1, the membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having a catalyst layer 26 and a gas diffusion layer 28, and an electrolyte membrane 10 disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26.

[0015] In the example shown in Figure 1, the electrolyte membrane has a single-layer structure, but the electrolyte membrane may also have a multilayer structure. Specific embodiments of the multilayer electrolyte membrane include an embodiment in which multiple electrolyte layers are stacked, and at least one of the multiple electrolyte layers contained in the electrolyte membrane contains a fluorine-containing polymer (I) and a platinum-containing material. Furthermore, embodiments include an embodiment in which multiple electrolyte layers contain a platinum-containing material, with the platinum-containing material content being different from that of the other, and an embodiment in which multiple electrolyte layers with different ion exchange capacities are stacked. In particular, a configuration in which multiple electrolyte layers with different platinum content are stacked is preferred in terms of the superior effects of the present invention, and it is even more preferable that the electrolyte layer closer to the anode has a higher platinum content than the electrolyte layer closer to the cathode. Note that the “electrolyte layer closer to the anode” includes not only the electrolyte layer in contact with the anode, but also electrolyte layers in which other thin film layers exist between the anode and the electrolyte layer. The same applies to the “electrolyte layer closer to the cathode.”

[0016] Figure 2 is a schematic cross-sectional view showing another example of the membrane electrode assembly of the present invention, where the electrolyte membrane has a multilayer structure. The structure of the membrane electrode assembly 120 in Figure 2 is the same as the structure of the membrane electrode assembly 20 in Figure 1, except that it has an electrolyte membrane 100 instead of the electrolyte membrane 10 in Figure 1. In the electrolyte membrane 100 in Figure 2, the first electrolyte layer 100A and the second electrolyte layer 100B are arranged in this order from the anode 22 side to the cathode 24 side. In the example shown in Figure 2, the electrolyte membrane has a two-layer structure, but the electrolyte membrane may also have a structure of three or more layers.

[0017] The platinum-containing material in the electrolyte membrane is preferably present only from the surface of the anode-facing side of the electrolyte membrane up to a thickness equivalent to 20% of the total thickness of the electrolyte membrane, as this can further suppress hydrogen crossover. More preferably, the platinum-containing material in the electrolyte membrane is present only from the surface of the anode-facing side of the electrolyte membrane up to a thickness equivalent to 18% of the total thickness of the electrolyte membrane, and even more preferably, it is present only from the surface of the anode-facing side of the electrolyte membrane up to a thickness equivalent to 10% of the total thickness of the electrolyte membrane. The detailed reasons for this are not yet clear, but it is presumed to be due to the following reasons. In other words, when hydrogen generated on the cathode side moves to the anode side during the operation of a water electrolysis device, the hydrogen concentration at the interface between the anode and the electrolyte membrane, which is far from the hydrogen generation site, is lower than the hydrogen concentration at the interface between the cathode and the electrolyte membrane, which is closer to the hydrogen generation site. Therefore, it is presumed that the decomposition or adsorption of hydrogen by platinum-containing materials is more effective when performed near the interface between the anode and the electrolyte membrane, where the hydrogen concentration is lower, than near the interface between the cathode and the electrolyte membrane, where the hydrogen concentration is higher.

[0018] The case where platinum-containing material exists at a thickness equivalent to X% of the total thickness of the electrolyte membrane, from the surface of the plane where the anode of the electrolyte membrane is located, will be specifically explained using the example in Figure 3. Figure 3 is a partially enlarged view of the membrane electrode assembly of Figure 2. As shown in Figure 3, the first electrolyte layer 100A contains a plurality of particulate platinum-containing substances 112, and the second electrolyte layer 100B does not contain the platinum-containing substance 112. The distance T1, which is the shortest distance from the surface S0 on one side of the electrolyte membrane 100 to the surface S1 on the other side, corresponds to the membrane thickness of the electrolyte membrane 100. The platinum-containing substance 112 is dispersed in the first electrolyte layer 100A and exists from the surface S0 to the surface S on the cathode side of the first electrolyte layer 100A X up to. From the surface S0 to the surface S X The shortest distance up to is the distance T X which is X% of the length of the distance T1. Therefore, when the distance T X is 20% of the length of the distance T1, the surface S X corresponds to the position of the membrane thickness corresponding to 20% of the total membrane thickness (distance T1) of the electrolyte membrane 100 from the surface S0 on one side of the electrolyte membrane 100.

[0019] The position where the platinum-containing substance exists in the electrolyte membrane can be specified, for example, using an enlarged image of a cross section along the membrane thickness direction of the membrane electrode assembly taken by a scanning electron microscope (product name "SU8230", manufactured by Hitachi High-Technologies Corporation). If necessary, an energy dispersive X-ray analyzer (product name "QUANTAX FlatQUAD", manufactured by Bruker) may be used to obtain the elemental distribution. Based on the position where the platinum-containing substance exists in the enlarged image, the distance Tx in FIG. 3 described above can be calculated.

[0020] As an example of a method of making it exist only from the surface of the anode-side surface of the electrolyte membrane to the position of the membrane thickness corresponding to 20% of the total membrane thickness of the electrolyte membrane, as shown in FIG. 3, a method using an electrolyte membrane including an electrolyte layer containing a platinum-containing substance and an electrolyte layer not containing a platinum-containing substance can be mentioned. As other methods, a method of immersing a solution containing platinum ions or the like from one surface of an electrolyte membrane not containing a platinum-containing substance and depositing a platinum-containing substance between the surface of the anode-side surface of the electrolyte membrane and the position of the membrane thickness corresponding to 20% of the total membrane thickness of the electrolyte membrane can be mentioned.

[0021] If the platinum content in the electrolyte membrane is present only from the surface where the anode of the electrolyte membrane is located to a thickness equivalent to 20% of the total thickness of the electrolyte membrane, then when measured by X-ray fluorescence analysis (XRF) from the surface where the anode of the solid polymer electrolyte membrane is located, the platinum atom content will be 0.050 mg / cm³. 2 The following is preferred: 0.04 mg / cm³ 2 The following is more preferable: 0.03 mg / cm³ 2 The following are even more preferable, and also 0.005 mg / cm³ 2 The above is preferable, and 0.008 mg / cm³ 2 The above is more preferable, 0.010 mg / cm³ 2 The above is even more preferable. The platinum atom content is 0.050 mg / cm³. 2 If the following is achieved, the electrolysis voltage can be further reduced, providing a lower-cost membrane electrode assembly and water electrolysis device, with a voltage of 0.005 mg / cm³. 2 If the above conditions are met, the occurrence of hydrogen crossover can be further suppressed. The specific method for measuring the platinum atom content using the XRF method is shown in the Examples section below.

[0022] <Electrolyte membrane> The electrolyte membrane contains a fluorine-containing polymer (I) and a platinum-containing material.

[0023] The thickness of the electrolyte membrane is preferably 30 μm or more, more preferably 400 μm or less, more preferably 300 μm or more, and even more preferably 200 μm or less. If the electrolyte membrane has a multilayer structure, the thickness of the electrolyte membrane refers to the total thickness of each layer. When the electrolyte membrane has a multilayer structure and comprises an electrolyte layer containing a platinum-containing material and an electrolyte layer not containing a platinum-containing material, the ratio of the thickness of the electrolyte layer containing a platinum-containing material to the thickness of the electrolyte layer not containing a platinum-containing material (thickness of the electrolyte layer containing a platinum-containing material / thickness of the electrolyte layer not containing a platinum-containing material) is preferably 0.02 or more, more preferably 0.05 or more, even more preferably 0.06 or more, and also preferably 0.50 or less, more preferably 0.20 or less, and even more preferably 0.15 or less. The thickness of the electrolyte membrane (electrolyte layer) is measured using a magnified image of the cross-section of the electrolyte membrane taken with a laser microscope (product name "VK-X1000", manufactured by Keyence Corporation) (for example, objective lens magnification of 50x).

[0024] (Fluorine polymer (I)) The ion exchange capacity of fluorine-containing polymer (I) is 1.25 to 2.00 milliequivalents / gram dry resin. The ion exchange capacity of the fluorine-containing polymer (I) is more preferably 1.40 milliequivalents / gram dry resin or higher, and even more preferably 1.80 milliequivalents / gram dry resin or higher, since this allows for a further reduction in the electrolysis voltage when applied to a water electrolysis device. The ion exchange capacity of the fluorine-containing polymer (I) is more preferably 1.90 milliequivalents / gram dry resin or less, and even more preferably 1.80 milliequivalents / gram dry resin or less, from the viewpoint of the strength of the membrane electrode assembly when hydrated. The fluorine-containing polymer (I) may be used alone, or two or more types may be used in a layered or mixed configuration.

[0025] The electrolyte membrane may contain polymers other than fluorine-containing polymer (I), but it is preferable that the polymers in the electrolyte membrane consist substantially of fluorine-containing polymer (I). "Substantially consisting of fluorine-containing polymer (I)" means that the content of fluorine-containing polymer (I) is 95% by mass or more of the total mass of polymers in the electrolyte membrane. An upper limit for the content of fluorine-containing polymer (I) is 100% by mass of the total mass of polymers in the electrolyte membrane. Specific examples of polymers other than fluorine-containing polymers (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 and / or sulfur atoms in the ring. Specific examples of polyazole compounds include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds. Furthermore, from the standpoint of oxidation resistance of the electrolyte membrane, other polymers that can be mentioned include polyphenylene sulfide resin and polyphenylene ether resin.

[0026] The fluorine-containing polymer (I) has ion exchange groups. Specific examples of ion exchange groups include sulfonic acid-type functional groups and carboxylic acid-type functional groups. Sulfonic acid-type functional groups are preferred because they can further reduce the electrolysis voltage when an electrolyte membrane is applied to a water electrolysis device. The following will mainly describe in detail the embodiments of fluorine-containing polymers having sulfonic acid-type functional groups (hereinafter also referred to as "fluorine-containing polymers (S)").

[0027] The fluorine-containing polymer (S) preferably contains units based on fluorine-containing olefins, as well as units having sulfonic acid-type functional groups and fluorine atoms. Examples of fluorine-containing olefins include fluoroolefins with 2 to 3 carbon atoms and one or more fluorine atoms in the molecule. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred due to its superior monomer production cost, reactivity with other monomers, and the characteristics of the resulting fluorine-containing polymer (S). Fluorine-containing olefins may be used individually or in combination of two or more types.

[0028] As a unit having a sulfonic acid-type functional group and a fluorine atom, the unit represented by formula (1) is preferred. Formula (1) -[CF2-CF(-L-(SO3M) n )]-

[0029] L is an n+1 valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at the terminal end of the perfluorohydrocarbon group or between carbon atoms. The number of carbon atoms in the n+1 valent perfluorohydrocarbon group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

[0030] As L, an n+1 valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom is preferred, and in the n=1 embodiment, a divalent perfluoroalkylene group which may contain an etheric oxygen atom, or in the n=2 embodiment, a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, is particularly preferred. The above-mentioned divalent perfluoroalkylene group may be in either a linear or branched chain configuration.

[0031] M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. n is either 1 or 2.

[0032] The units represented by formula (1) are preferably those represented by formula (1-1), formula (1-2), formula (1-3), or formula (1-4). Equation (1-1) -[CF2-CF(-OR f1 -SO3M)]- Equation (1-2) -[CF2-CF(-R f1 -SO3M)]-

[0033] [ka]

[0034] [ka]

[0035] R f1This is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

[0036] R f2 This is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

[0037] R f3 This is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

[0038] r is either 0 or 1. m is either 0 or 1. M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation.

[0039] The units represented by formula (1-1) and formula (1-2) are more preferably those represented by formula (1-5). Equation (1-5) -[CF2-CF(-(CF2) x -(OCF2CFY) y -O-(CF2) z -SO3M)]- x is 0 or 1, y is an integer between 0 and 2, z is an integer between 1 and 4, and Y is either F or CF3. M is as described above.

[0040] The following are specific examples of units represented by equation (1-1). In the equation, w is an integer from 1 to 8, and x is an integer from 1 to 5. The definition of M in the equation is as described above. -[CF2-CF(-O-(CF2) w -SO3M)]- -[CF2-CF(-O-CF2CF(CF3)-O-(CF2) w -SO3M)]- -[CF2-CF(-(O-CF2CF(CF3)) x -SO3M)]-

[0041] The following are specific examples of units represented by equation (1-2). w in the equation is an integer between 1 and 8. The definition of M in the equation is as described above. -[CF2-CF(-(CF2) w -SO3M)]- -[CF2-CF(-CF2-O-(CF2) w -SO3M)]-

[0042] The unit represented by formula (1-3-1) is preferred over the unit represented by formula (1-3-3). The definition of M in the formula is as described above.

[0043] [ka]

[0044] R f4 R is a linear perfluoroalkylene group having 1 to 6 carbon atoms, f5 is a linear perfluoroalkylene group having 1 to 6 carbon atoms, which may contain single bonds or oxygen atoms between carbon atoms. The definitions of r and M are as described above.

[0045] The following are specific examples of units that can be represented by equation (1-3-1):

[0046] [ka]

[0047] The unit represented by formula (1-4) is preferably the unit represented by formula (1-4-1). f1 , R f2 The definitions of M and other factors are as described above.

[0048] [ka]

[0049] The following are specific examples of units represented by equation (1-4-1):

[0050] [ka]

[0051] The units having a sulfonic acid-type functional group and a fluorine atom may be used individually or in combination of two or more types.

[0052] The fluorine-containing polymer (I) may contain units based on fluorine-containing olefins, as well as units based on other monomers other than those having sulfonic acid-type functional groups and fluorine atoms. Other specific examples of monomers include CF2 = CFR f6 (However, R f6 CF2=CF-OR f7 (However, R f7 ) is a perfluoroalkyl group having 1 to 10 carbon atoms. ), CF2 = CFO(CF2) v One example is CF = CF² (where v is an integer between 1 and 3). The content of units based on other monomers is preferably 30% by mass or less relative to the total units in the fluorine-containing polymer (I) in order to maintain ion exchange performance.

[0053] The content of fluorine-containing polymer (I) is preferably 95 to 100% by mass relative to the total mass of the electrolyte membrane.

[0054] (Platinum-containing material) Platinum-containing materials only need to contain platinum atoms. Specific examples of platinum-containing materials include platinum itself, platinum oxides, platinum-containing composite metal oxides, and platinum alloys. A specific example of a platinum-containing composite oxide is M x Pt3O4 is an example (where 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 less than or equal to 1). Specific examples of platinum alloys include alloys containing platinum and at least one metal selected from the group consisting of transition metals and other precious metals.

[0055] Specific examples of the shape of platinum-containing materials include particulate and sheet forms. When the platinum-containing material is in particulate form, it may be a core-shell type particle. When the platinum-containing material is in particulate form, the average particle size (D50) of the platinum-containing material is preferably 1 nm or more, more preferably 10 nm or more, even more preferably 100 nm or more, and also preferably 10,000 nm or less, more preferably 5,000 nm or less, and even more preferably 3,000 nm or less. The average particle size of the platinum-containing material is the volume-based cumulative 50% diameter (D50), obtained by measuring the particle size distribution using a particle size analyzer after dispersion treatment in a dispersion liquid containing the platinum-containing material. The detailed measurement conditions are as described in the examples.

[0056] If the electrolyte membrane has a single-layer structure, then 1 cm of the electrolyte membrane 2 The amount of platinum content per unit is 0.010 mg / cm³. 2 The above is preferable, and 0.030 mg / cm³ 2 The above is more preferable, 0.040 mg / cm³ 2 The above is even more preferable, and also 0.050 mg / cm³ 2 The following is preferable: The mass of the platinum-containing material is 0.030 mg / cm³. 2 If the above is true, the occurrence of hydrogen crossover can be further suppressed. (Mass of platinum-containing material: 0.050 mg / cm³) 2 The following conditions allow for a lower electrolysis voltage, enabling the provision of low-cost membrane electrode assemblies and water electrolysis devices. If the electrolyte membrane has a multilayer structure, at least one electrolyte layer contained in the electrolyte membrane is the electrolyte layer 1 cm 2The amount of platinum content per unit is 0.005 mg / cm³. 2 The above is preferable, and 0.008 mg / cm³ 2 The above is more preferable, 0.010 mg / cm³ 2 The above is even more preferable, and also 0.050 mg / cm³ 2 The following is preferred: 0.040 mg / cm³ 2 The following is more preferable: Electrolyte layer 1 cm 2 The mass of platinum content per unit is 0.005 mg / cm³. 2 If the above conditions are met, the occurrence of hydrogen crossover can be further suppressed. Electrolyte layer 1 cm 2 The mass of platinum content per unit is 0.050 mg / cm³. 2 The following conditions allow for a lower electrolysis voltage, enabling the provision of low-cost membrane electrode assemblies and water electrolysis devices.

[0057] When the electrolyte membrane has a single-layer structure, the mass ratio of the platinum-containing material to the fluorine-containing polymer (I) in the electrolyte membrane (mass of platinum-containing material / mass of fluorine-containing polymer (I)) is preferably 0.001 to 0.003. If the mass ratio is 0.001 or higher, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.003 or lower, the electrolysis voltage can be lowered, and a low-cost membrane electrode assembly and water electrolysis device can be provided. When the electrolyte membrane has a multilayer structure, the mass ratio of platinum-containing material to fluorine-containing polymer (I) in at least one electrolyte layer contained in the electrolyte membrane (mass of platinum-containing material / mass of fluorine-containing polymer (I)) is preferably 0.005 or higher, more preferably 0.010 or higher, and preferably 0.030 or lower. If the mass ratio is 0.005 or higher, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.030 or lower, the electrolysis voltage can be lowered, and a low-cost membrane electrode assembly and water electrolysis device can be provided.

[0058] The platinum-containing material may be supported on a carrier. Specific examples of carriers include carbon carriers such as carbon black powder, graphitized carbon, carbon fibers, and carbon nanotubes. When a platinum-containing material is supported on a carrier, the amount of 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.

[0059] (Reinforcement material) The electrolyte membrane may also contain reinforcing materials. This can improve the strength of the electrolyte membrane. Specific examples of reinforcing materials include porous materials, fibers, woven fabrics, and nonwoven fabrics. The reinforcing material is preferably composed of at least one 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").

[0060] If the electrolyte membrane contains a reinforcing material, the reinforcing material content is preferably 3% by mass or more, more preferably 5% by mass or more, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the electrolyte membrane.

[0061] (Method for manufacturing electrolyte membranes) One example of a method for manufacturing a single-layer electrolyte membrane is as follows: First, a polymer of a fluorine-containing monomer (hereinafter also referred to as "fluorine-containing monomer (I')") having a group that can be converted into an ion-exchange group (hereinafter also referred to as "fluorine-containing polymer (I')") is prepared by converting the group that can be converted into an ion-exchange group to an ion-exchange group to obtain a fluorine-containing polymer (I). Next, the dispersion obtained by dispersing the fluorine-containing polymer (I) and a platinum-containing material in a solvent is applied to a substrate, and the solvent is removed to obtain a single-layer electrolyte membrane (an electrolyte layer containing a platinum-containing material). When applying the dispersion to the substrate, a reinforcing material can be used as needed, and an electrolyte layer containing the reinforcing material can be obtained by impregnating the dispersion with the reinforcing material. The type of solvent used is not particularly limited, but examples include water and organic solvents. Furthermore, water alone may be used as the solvent, organic solvent alone may be used, or a mixed solvent of water and organic solvent may be used, but a mixed solvent of water and organic solvent is preferred. Another example of a method for manufacturing a single-layer electrolyte membrane is as follows: First, an electrolyte layer is obtained that contains reinforcing materials as needed but does not contain platinum. Next, a solution containing platinum ions is applied to the obtained electrolyte layer, and then the electrolyte layer is dried to precipitate platinum in the electrolyte layer. This yields a single-layer electrolyte membrane (an electrolyte layer containing platinum). Another example of a method for manufacturing a single-layer electrolyte membrane involves producing a membrane (hereinafter also referred to as a "precursor membrane") containing a fluorine-containing polymer (I'), a platinum-containing material, and a reinforcing material used as needed, and then converting the groups in the precursor membrane that can be converted into ion-exchange groups into ion-exchange groups. This yields a single-layer electrolyte membrane (an electrolyte layer containing a platinum-containing material). Another example of a method for manufacturing a single-layer electrolyte membrane is as follows: First, a precursor membrane containing reinforcing materials as needed but without platinum content is manufactured, and a membrane (an electrolyte layer without platinum content) is obtained by converting the groups in the precursor membrane that can be converted into ion exchange groups into ion exchange groups. Next, a solution containing platinum ions is attached to the obtained membrane, and then the membrane is dried to precipitate platinum content within the membrane. This yields a single-layer electrolyte membrane (an electrolyte layer containing platinum content). One example of a method for manufacturing a multilayer electrolyte membrane is to laminate an electrolyte layer containing the aforementioned platinum-containing material with an electrolyte layer that does not contain the aforementioned platinum-containing material, and then heat-press the layers. This yields a multilayer electrolyte membrane. Another example involves coating the aforementioned electrolyte layer that does not contain the aforementioned platinum-containing material with a dispersion of a fluorine-containing polymer (I) and a platinum-containing material, and then removing the solvent to obtain a multilayer electrolyte membrane.

[0062] As the fluorine-containing polymer (I'), a polymer of a fluorine-containing monomer having a group that can be converted to a sulfonic acid-type functional group (hereinafter also referred to as "fluorine-containing polymer (S')") is preferred, and a copolymer polymer of a fluorine-containing olefin and a monomer having a group that can be converted to a sulfonic acid-type functional group and a fluorine atom is particularly preferred. The following provides a detailed explanation of fluorine-containing polymers (S').

[0063] Methods for copolymerizing fluorine-containing polymers (S') can include known methods such as solution polymerization, suspension polymerization, and emulsion polymerization.

[0064] Examples of fluorine-containing olefins include those exemplified above, and TFE is preferred due to its superior monomer production cost, reactivity with other monomers, and the characteristics of the resulting fluorine-containing polymer (S). Fluorine-containing olefins may be used individually or in combination of two or more types.

[0065] Examples of fluorine-containing monomers (S') include compounds that have one or more fluorine atoms in the molecule, have an ethylenically active double bond, and have a group that can be converted to a sulfonic acid-type functional group. As the fluorine-containing monomer (S'), the compound represented by formula (2) is preferred due to its superior manufacturing cost, reactivity with other monomers, and the characteristics of the resulting fluorine-containing polymer (S). Equation (2) CF2 = CF - L - (A) n The definitions of L and n in equation (2) are as described above. A is a group that can be converted to a sulfonic acid type functional group. Preferably, the group can be converted to a sulfonic acid type functional group by hydrolysis. Specific examples of groups that can be converted to a sulfonic acid type functional group include -SO2F, -SO2Cl, and -SO2Br. If there are multiple A groups, they may be the same or different.

[0066] The compounds represented by formula (2) are preferably those represented by formula (2-1), formula (2-2), formula (2-3), and formula (2-4). Equation (2-1) CF2 = CF - OR f1 -A Equation (2-2) CF2 = CF - R f1 -A

[0067] [ka]

[0068] R in the formula f1 , R f2 The definitions of r and A are as described above.

[0069] [ka]

[0070] R in the formula f1 , R f2 , R f3 The definitions of r, m, and A are as described above.

[0071] Of the compounds represented by formula (2-1) and formula (2-2), the compound represented by formula (2-5) is preferred. Equation (2-5) CF2 = CF - (CF2) x -(OCF2CFY) y -O-(CF2) z -SO3 M The definitions of M, x, y, z, and Y in the formula are as described above.

[0072] Specific examples of compounds represented by formula (2-1) include the following compounds. In the formula, w is an integer from 1 to 8, and x is an integer from 1 to 5. CF2 = CF - O - (CF2) w -SO2F CF2 = CF - O - CF2CF(CF3) - O - (CF2) w -SO2F CF2 = CF - [O - CF2CF(CF3)] x -SO2F

[0073] Specific examples of compounds represented by formula (2-2) include the following compounds. In the formula, w is an integer from 1 to 8. CF2 = CF - (CF2) w -SO2F CF2 = CF - CF2 - O - (CF2) w -SO2F

[0074] Of the compounds represented by formula (2-3), the compound represented by formula (2-3-1) is preferred.

[0075] [ka]

[0076] R in the formula f4 , R f5 The definitions of r and A are as described above.

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

[0078] [ka]

[0079] Of the compounds represented by formula (2-4), the compound represented by formula (2-4-1) is preferred.

[0080] [ka]

[0081] R in the formula f1 , R f2 The definition of A is as described above.

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

[0083] [ka]

[0084] Fluorine-containing monomers (S') may be used individually or in combination of two or more. In addition to fluorine-containing olefins and fluorine-containing monomers (S'), other monomers may also be used in the production of fluorine-containing polymers (S'). Examples of other monomers include those exemplified above.

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

[0086] A specific example of a method for producing a precursor film is the extrusion method. A specific example of a manufacturing method when the precursor film contains a reinforcing material is as follows: First, a film (I') is formed containing a fluorine-containing polymer (I') and, if necessary, a platinum-containing material. Then, the film (I'), reinforcing material, and film (I') are arranged in that order and stacked using a lamination roll or a vacuum lamination apparatus.

[0087] Specific examples of methods for converting groups in a precursor membrane that can be converted into ion exchange groups include methods of subjecting the precursor membrane to hydrolysis treatment or acidification treatment. Among these methods, the method of contacting the precursor film with an alkaline aqueous solution is preferred.

[0088] Specific examples of methods for bringing a precursor film into contact with an alkaline aqueous solution include immersing the precursor film in an 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 more, more preferably 5 minutes or more, more preferably 150 minutes or less, and more preferably 50 minutes or less.

[0089] 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, a water-soluble organic solvent is an organic solvent that dissolves readily in water. Specifically, an organic solvent with a solubility of 0.1 g or more in 1000 ml of water (20°C) is preferred, and an organic solvent with 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 amino alcohols, and is particularly preferred to contain an aprotic organic solvent. Water-soluble organic solvents may be used individually or in combination of two or more types.

[0090] 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 amino alcohols 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.

[0091] The concentration of alkali metal hydroxide in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass, more preferably 60% by mass or less, and more preferably 55% by mass or less. The content of the water-soluble organic solvent is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, and more preferably 55% by mass or less, in the alkaline aqueous solution. The water concentration is preferably 39-80% by mass in the alkaline aqueous solution.

[0092] After contact between the precursor film and the alkaline aqueous solution, a treatment to remove the alkaline aqueous solution may be performed. One method for removing the alkaline aqueous solution is to wash the precursor film that has been in contact with the alkaline aqueous solution with water.

[0093] After contacting the precursor film with an alkaline aqueous solution, the resulting film may be brought into contact with an acidic aqueous solution to convert the ion exchange groups to the acidic form. Specific examples of methods for bringing a precursor film into contact with an acidic aqueous solution include immersing the precursor film in an acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor film. An acidic aqueous solution preferably contains an acidic component and water. Specific examples of acidic components include hydrochloric acid and sulfuric acid.

[0094] <Anode and Cathode> The anode and cathode each have a catalyst layer. In the examples in Figures 1 and 2, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28.

[0095] A specific example of a catalyst layer is a layer containing a catalyst and a polymer having ion exchange groups. Specific examples of catalysts include supported catalysts in which a catalyst containing platinum, a platinum alloy, or platinum having a core-shell structure is supported on a carbon support, iridium oxide catalysts, composite oxide catalysts containing iridium and other metal elements, alloys containing iridium oxide, and catalysts containing iridium oxide having a core-shell structure. Carbon black powder can be used as a carbon support. Examples of polymers having ion exchange groups include fluorine-containing polymers having ion exchange groups, and for example, the above-mentioned fluorine-containing polymer (I) can be used.

[0096] Catalyst layer 1cm 2 The mass of catalyst metal per unit is 0.05 mg / cm³. 2 The above is preferable, and 0.2 mg / cm³ 2 The above is more preferable, and also 4 mg / cm³ 2 The following is preferred: 2 mg / cm³ 2 The following is more preferable: 1 mg / cm³ 2 The following are even more preferable. The mass ratio of the catalyst to the polymer having ion exchange groups in the catalyst layer (mass of catalyst / mass of polymer having ion exchange groups) is preferably 2 to 6.

[0097] The gas diffusion layer has the function of rapidly diffusing the gas generated from the catalyst layer to the outside of the catalyst layer and also functions as a current collector. Specific examples of the gas diffusion layer include carbon paper, carbon cloth, carbon felt, titanium fiber sintered body, and titanium particle sintered body. The anode side has a high potential, and since carbon materials would oxidize there, it is preferable to use a titanium fiber sintered body or a titanium particle sintered body. The titanium sintered body may be plated with platinum or the like as needed. The cathode gas diffusion layer may be treated with a water-repellent material such as PTFE. In the membrane electrode assemblies shown in Figures 1 and 2, a gas diffusion layer 28 is included, but the gas diffusion layer is an optional component and does not necessarily have to be included in the membrane electrode assemblies.

[0098] The film thickness of the anode and cathode can be independently set to 5 μm or more, more 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 achieving superior effects of the present invention. The film thicknesses of the anode and cathode were measured using images obtained by measuring a cross-section of the film electrode assembly cut in the direction of film thickness with a laser microscope, and the arithmetic mean value is calculated at any 20 locations.

[0099] <Method for manufacturing a membrane electrode assembly> One method for manufacturing a membrane electrode assembly is to use a laminate having an anode catalyst layer and a release substrate (e.g., an ETFE sheet) and a laminate having a cathode catalyst layer and a release substrate (e.g., an ETFE sheet), to bond the catalyst layers to both sides of the electrolyte membrane, and then peel off the release substrate. The above laminate may have a gas diffusion layer between the catalyst layer and the release substrate. In this case, the gas diffusion layer can be formed on the side of the catalyst layer opposite to the electrolyte membrane. The method for manufacturing the catalyst layer involves applying a catalyst layer forming coating liquid to a predetermined location (for example, the surface of a release-resistant substrate) and drying it as necessary. The catalyst layer forming coating liquid is a liquid in which a polymer having ion exchange groups and a catalyst are dispersed in a dispersion medium.

[0100] <Application> The membrane electrode assembly of the present invention is used in a solid polymer water electrolysis apparatus.

[0101] [Water electrolysis device] The water electrolysis apparatus of the present invention includes the membrane electrode assembly described above. Because the water electrolysis apparatus of the present invention includes the membrane electrode assembly described above, hydrogen crossover can be suppressed and a low electrolysis voltage can be achieved. The water electrolysis apparatus of the present invention can have the same configuration as a known water electrolysis apparatus, except that it includes the membrane electrode assembly described above. [Examples]

[0102] The present invention will be described in detail below with reference to examples. Examples 1-1 to 1-5 and Examples 2-1 to 2-2 are preparation examples, Examples 3-1 to 3-10 are examples, and Examples 4-1 to 4-3 are comparative examples. However, the present invention is not limited to these examples. In the Examples section, the first electrolyte layer refers to a general term for electrolyte layers containing fluorine-containing polymers and platinum-containing materials, while the second electrolyte layer refers to a general term for electrolyte layers containing fluorine-containing polymers but not platinum-containing materials.

[0103] [Ion exchange capacity of fluorine-containing polymers] Fluorine-containing polymers were placed in a glove box circulating dry nitrogen for 24 hours, and their dry mass was measured. Subsequently, the fluorine-containing polymers were immersed in a 2 mol / L sodium chloride aqueous solution at 60°C for 1 hour. After washing the fluorine-containing polymers with ultrapure water, they were removed, and the ion exchange capacity (milliequivalents / gram dry resin) of the fluorine-containing polymers was determined by titrating the immersion solution with a 0.1 mol / L sodium hydroxide aqueous solution. In the table below, IEC (meq / g) refers to the ion exchange capacity (milliequivalents / gram dry resin).

[0104] [Average particle size of platinum-containing material (D50)] After dispersing a platinum-containing / fluorinated polymer dispersion (using a bead mill), the particle size distribution was measured using a laser diffraction particle size distribution analyzer (Microtrac Bell, MT3300EXII-SDC) to determine the volume-based cumulative 50% diameter of the platinum-containing material. The arithmetic mean of the three obtained cumulative 50% diameters was adopted as D50.

[0105] [Thickness of the electrolyte layer] The thickness of each electrolyte layer was measured using a laser microscope (product name "VK-X1000", manufactured by Keyence Corporation) to capture magnified images of the cross-section of the electrolyte layer (objective lens magnification 50x) under conditions of temperature: 23°C and relative humidity: 50%RH.

[0106] [Maximum Depth from the Anode-Side Surface of the Solid Polymer Electrolyte Membrane Containing Platinum Inclusions] The "maximum depth from the anode-side surface of the solid polymer electrolyte membrane containing platinum inclusions" means the ratio (%) of the distance (distance T in FIG. 3) from the anode-side surface of the solid polymer electrolyte membrane containing platinum inclusions to the membrane thickness (distance T1 in FIG. 3) of the solid polymer electrolyte membrane. X ) of the solid polymer electrolyte membrane. The above maximum depth was calculated as follows. First, based on the enlarged image of the cross-section along the membrane thickness direction of the membrane electrode assembly taken by a scanning electron microscope (product name "SU8230", manufactured by Hitachi High-Technologies Corporation) and the elemental distribution obtained using an energy dispersive X-ray analyzer (product name "QUANTAX FlatQUAD", manufactured by Bruker), the positions where platinum inclusions exist in the solid polymer electrolyte membrane were identified, and the distance Tx in FIG. 3 described above was measured. The maximum depth was calculated using the distance T X thus obtained and the membrane thickness (distance T1 in FIG. 3) of the solid polymer electrolyte membrane.

[0107] [Mass of Platinum Atoms Measured by Incident X-Rays from the Anode Side of the Solid Polymer Electrolyte Membrane] Using a fluorescence X-ray analyzer ("Supermini200" manufactured by Rigaku), X-rays were incident from the surface on the side where the anode of the solid polymer electrolyte membrane is placed, and the mass of platinum atoms (mg / cm 2 ) was measured. A circle with a diameter of 30 mm was used as the measurement surface, and quantitative analysis was performed using a calibration curve created in advance.

[0108] [Electrolysis Voltage] A membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekkarto) 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 to evaluate a single cell with an electrode area of 16 cm 2 . When sandwiching the membrane electrode assembly, it was fastened so that a pressure of 1.5 MPa was applied to the electrode part. Next, to ensure sufficient water absorption of the solid polymer electrolyte membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, at 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. Subsequently, pure water with a conductivity of 1.0 μS / cm or less and at a temperature of 60°C was supplied to the anode side at a flow rate of 50 mL / min, while maintaining atmospheric pressure at both the anode and cathode. A high-current potentio / galvanostat HCP-803 (manufactured by Biologic) was used to conduct a test at 16 A (current density 1 A / cm²). 2 While maintaining the current, water electrolysis was performed for 4 hours as a break-in period. After that, for the main measurement, current was set to 0-32A (current density 0-2A / cm²). 2 The current was gradually increased in increments of 2A within the range of ). The current was held for 5 minutes in each increment, resulting in a total current of 32A (current density 2A / cm²). 2 The electrolytic voltage at the following conditions was evaluated according to the following criteria. Good: 1.70V or less Defective: Greater than 1.70V

[0109] [Hydrogen concentration in oxygen] After evaluating the electrolysis voltage, pure water was supplied to the cell at a conductivity of 1.0 μS / cm or less, at a temperature of 60°C, at a rate of 50 mL / min, with the back pressure at both the anode and cathode at atmospheric pressure. A high-current potentio / galvanostat HCP-803 (manufactured by Biologic) was used to draw 3.2 A (current density 0.2 A / cm²). 2 The mixture was held in place for 12 hours. After 12 hours, water was separated from the gas discharged from the anode, and the hydrogen concentration in the gas was measured using a micro GC (Agilent 490). The hydrogen concentration in oxygen (H2 concentration in O2) was evaluated according to the following criteria. Excellent: Less than 0.05% by volume Good: 0.05% by volume or more and less than 0.1% by volume Acceptable: 0.1% or more and less than 0.5% by volume Defective: 0.5% or more by volume

[0110] [Abbreviation] TFE: Tetrafluoroethylene PSVE:CF2=CFOCF2CF(CF3)OCF2CF2SO2F P2SVE: Monomer represented by the following formula m32-1

[0111] [ka]

[0112] [Preparation of platinum / electrolyte polymer dispersion] <Example 1-1> A dispersion (hereinafter also referred to as "dispersion X") was obtained by copolymerizing TFE and PSVE, and then hydrolyzing and acid treating the resulting acid-type fluorine-containing polymer (ion exchange capacity: 1.25 milliequivalents / gram dry resin) in a water / ethanol = 40 / 60 (mass%) solvent at a solid content concentration of 20.0%. To the obtained dispersion X (1.75 g), ethanol (4.00 g) and water (6.70 g) were added, and then a platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd., a catalyst in which platinum, which is a platinum-containing substance, is supported on a carbon support) (1.30 g) containing 45.6 mass% platinum in the dispersion was added. To the obtained mixture, 150 g of 5 mm diameter beads were added and processed in a planetary bead mill (rotation speed 300 rpm) for 30 minutes. Then, water (4.87 g) and dispersion X (113.65 g) were added and processed in a planetary bead mill (rotation speed 200 rpm) for 60 minutes to obtain platinum-containing / fluorinated polymer dispersion D-1 with a solid content concentration of 18.4% by mass.

[0113] <Examples 1-2 and 1-3> Platinum-containing / fluorinated polymer dispersions D-2 and D-3 were obtained in the same manner as in Example 1-1, except that the ratio of platinum to fluorinated polymer contained in the dispersion was adjusted to match the ratio shown in Table 1.

[0114] <Example 1-4> A fluorine-containing polymer obtained by copolymerizing TFE and P2SVE and converting it to an acid form through hydrolysis and acid treatment (ion exchange capacity: 1.95 meq / g of dry resin) was dispersed in a solvent of water / propanol = 30 / 70 (mass%) at a solid content concentration of 13.0% to obtain a dispersion (hereinafter also referred to as "dispersion Z"). Ethanol (5.24 g) and water (7.27 g) were added to the obtained dispersion (2.72 g), and further, a platinum-supported carbon catalyst (manufactured by Tanaka Kikinzoku Kogyo K.K., "TEC10E50E", a catalyst in which platinum as a platinum-containing substance is supported on a carbon carrier) (1.30 g) containing 45.6% by mass of platinum in the dispersion was added. Further, 150 g of beads with a diameter of 5 mm were added to the obtained mixture, and after treating with a planetary bead mill (rotation speed: 300 rpm) for 30 minutes, water (33.39 g), ethanol (73.81 g), and the dispersion (356.05 g) were added, and further treated with a planetary bead mill (rotation speed: 200 rpm) for 60 minutes to obtain a platinum-containing substance / fluorine-containing polymer dispersion D-4 with a solid content concentration of 10.0% by mass.

[0115] <Example 1-5> As the platinum-containing substance, platinum powder (manufactured by Tanaka Kikinzoku Kogyo K.K.) containing 96.5% platinum and having a specific surface area of 50 m 2 / g was used, and a platinum-containing substance / fluorine-containing polymer dispersion D-5 was obtained in the same manner as in Example 1-1 except that the ratio of the platinum-containing substance to the fluorine-containing polymer was adjusted as shown in Table 1.

[0116] <Example 2-1> As a dispersion containing a fluorine-containing polymer, commercially available Nafion (D2020) (manufactured by Chemours, ion exchange capacity: 1.0 meq / g of dry resin) was used, and a platinum-containing substance / fluorine-containing polymer dispersion D'-1 was obtained in the same manner as in Example 1-1 except that the ratio of the platinum-containing substance to the fluorine-containing polymer was adjusted as shown in Table 1.

[0117] <Example 2-2> Platinum-containing / fluorine-containing polymer dispersion D'-2 was obtained in the same manner as in Example 1-1, except that a fluorine-containing polymer (ion exchange capacity: 1.10 milliequivalents / gram dry resin) obtained by copolymerizing TFE and PSVE and then hydrolyzing and acidifying it to an acidic type was dispersed in a water / ethanol = 40 / 60 (mass%) solvent at a solid content concentration of 26.0% (hereinafter also referred to as "dispersion Y") as the fluorine-containing polymer dispersion, and the ratio of platinum-containing material to fluorine-containing polymer was prepared as shown in Table 1.

[0118] [Table 1]

[0119] <Example 3-1> (Formation of solid polymer electrolyte membranes) Dispersion D-1 was applied to an ETFE sheet using an applicator to a thickness of 10 μm after drying. The sheet was dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to obtain the first electrolyte layer. Dispersion X was coated onto a 100 μm thick ethylene-tetrafluoroethylene copolymer (ETFE) sheet using a die coater to form a film. This film was dried at 80°C for 15 minutes, and then heat-treated at 160°C for 30 minutes to obtain a second electrolyte layer. The amount of liquid composition coated was adjusted so that the film thickness of the second electrolyte layer after drying was 100 μm. The first and second electrolyte layers were stacked and hot-pressed at 150°C and 1.5 MPa for 2 minutes. After removal from the press, the mixture was heat-treated in an oven at 150°C for 30 minutes to obtain a solid polymer electrolyte membrane.

[0120] (Fabrication of anode catalyst layer decal) Dispersion Y (33.0g) was mixed with ethanol (18.06g) and Zeolora-H (manufactured by Zeon Corporation) (10.58g) and mixed at 2200 rpm for 5 minutes using a rotational and revolving mixer (manufactured by Shinky, Awatori Rentaro). Ethanol (46.44g) and water (75.75g) were added to the mixed composition (54.06g), and further a mixture containing 74.8% by mass of iridium with a specific surface area of ​​100m² was prepared. 240.0 g of iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd.) was added. The resulting mixture was treated with a planetary bead mill (rotation speed 300 rpm) for 90 minutes to obtain an anode catalyst ink with a solid content concentration of 22% by mass. On an ETFE sheet, an anode catalyst ink containing iridium at a concentration of 1.0 mg / cm³ is applied. 2 The material was coated using an applicator, dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to obtain an anode catalyst layer decal.

[0121] (Fabrication of cathode catalyst layer decal) A supported catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) (11 g), in which 46% by mass of platinum was supported on carbon powder, was mixed with water (59.4 g) and ethanol (39.6 g). The mixture was then mixed and pulverized using an ultrasonic homogenizer to obtain a catalyst dispersion. To the catalyst dispersion, a mixture (29.2g) was added, which consisted of dispersion Y (20.1g), ethanol (11g), and Zeolora-H (manufactured by Zeon Corporation) (6.3g), all of which had been pre-mixed and kneaded. Furthermore, water (3.66g) and ethanol (7.63g) were added to the resulting dispersion, and the mixture was mixed for 60 minutes using paint conditioner to obtain a cathode catalyst ink with a solid content concentration of 10.0% by mass. A cathode catalyst ink was applied to an ETFE sheet using a die coater, dried at 80°C, and then heat-treated at 150°C for 15 minutes, resulting in a platinum content of 0.4 mg / cm³. 2 A cathode catalyst layer decal was obtained.

[0122] (Fabrication of membrane electrode assemblies) The side of the anode catalyst layer decal containing the catalyst layer is placed facing the first electrolyte layer side of the solid polymer electrolyte membrane, and the side of the cathode catalyst layer decal containing the catalyst layer is placed facing the other side of the electrolyte membrane. The membrane is heated and pressed at a press temperature of 150°C for 10 minutes at a pressure of 3 MPa to bond the anode catalyst layer, solid polymer electrolyte membrane 1, and cathode catalyst layer. After the temperature is lowered to 70°C, the pressure is released and the assembly is removed. The ETFE sheets of the anode catalyst layer decal and cathode catalyst layer decal are peeled off, resulting in an electrode area of ​​16 cm². 2A membrane electrode assembly was obtained. The obtained membrane electrode assembly was subjected to evaluation of its electrolytic voltage and hydrogen concentration in oxygen. The results are shown in Table 2.

[0123] <Examples 3-2 and 3-3> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that dispersions D-2 and D-3 were used instead of dispersion D-1 as the dispersion for forming the first electrolyte layer. The evaluation results are shown in Table 2.

[0124] <Example 3-4> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that dispersion D-4 was used instead of dispersion D-1 as the dispersion forming the first electrolyte layer, dispersion Z was used as the dispersion for the electrolyte layer, and the thickness of the electrolyte layer was adjusted to 50 μm. The evaluation results are shown in Table 2.

[0125] <Example 3-5> A membrane electrode assembly was obtained in the same manner as in Example 3-2, except that the electrolyte membrane described in Example 1 of WO2020 / 162511 was used as the second electrolyte layer. The evaluation results are shown in Table 2.

[0126] <Example 3-6> Dispersion D-2 was applied to an ETFE sheet using an applicator to a thickness of 100 μm after drying. The sheet was dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to obtain the first electrolyte layer. A membrane electrode assembly was obtained in the same manner as in Example 3-2, except that this first electrolyte layer was a solid polymer electrolyte membrane. The evaluation results are shown in Table 2.

[0127] <Example 3-7> The second electrolyte layer prepared by the method described in Example 3-1 was immersed in ultrapure water for 16 hours, then immersed in a 0.1N sodium hydroxide aqueous solution for 30 minutes, washed with ultrapure water, and then immersed in a 0.1N sodium hydroxide aqueous solution for another hour. After removing the immersed electrolyte layer, it was washed with ultrapure water, immersed in a 3mM tetraammineplatinum(II) chloride aqueous solution for 2 minutes, and washed with ultrapure water. Subsequently, it was immersed for 3 hours in a 0.1N sodium hydroxide aqueous solution prepared to have a sodium borohydride concentration of 1% by mass, to form platinum nanoparticles in the electrolyte layer. After further washing this electrolyte layer with ultrapure water, the procedure of immersing it in 3N hydrochloric acid at 80°C for 30 minutes, followed by immersion in ultrapure water at 80°C for another 30 minutes, was repeated 8 times. Subsequently, the procedure of immersing it in ultrapure water at 80°C for 30 minutes was repeated 3 times, and then air-dried to obtain a first electrolyte layer in which platinum nanoparticles had formed inside. A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that the first electrolyte layer was used as a solid polymer electrolyte membrane. The evaluation results are shown in Table 2.

[0128] <Example 3-8> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that dispersion D-5 was used instead of dispersion D-1 as the dispersion forming the first electrolyte layer. The evaluation results are shown in Table 2.

[0129] <Example 3-9> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that a first electrolyte layer was sandwiched between two 50 μm second electrolyte layers prepared from dispersion X, hot-pressed at 150°C and 1.5 MPa for 2 minutes, and after removal from the press, heat-treated in an oven at 150°C for 30 minutes to obtain a solid polymer electrolyte membrane. Since this solid polymer electrolyte membrane has no front or back side, the bonding surface between the anode and cathode does not need to be considered when bonding the catalyst layer. The evaluation results are shown in Table 2.

[0130] <Example 3-10> A membrane electrode assembly was fabricated in the same manner as in Example 3-1, except that the side of the cathode catalyst layer decal containing the catalyst layer was placed opposite the first electrolyte layer side of the solid polymer electrolyte membrane, and the side of the anode catalyst layer decal containing the catalyst layer was placed opposite the other side of the solid polymer electrolyte membrane. The evaluation results are shown in Table 2.

[0131] <Example 4-1> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that dispersion D'-1 was used instead of dispersion D-1 as the dispersion forming the first electrolyte layer, and commercially available Nafion 115 (manufactured by Chemours) was used as the second electrolyte layer. The evaluation results are shown in Table 2.

[0132] <Example 4-2> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that dispersion D'-2 was used instead of dispersion D-1 as the dispersion forming the first electrolyte layer, and dispersion Y was used as the dispersion forming the second electrolyte layer. The evaluation results are shown in Table 2.

[0133] <Example 4-3> A membrane electrode assembly was obtained in the same manner as in Example 3-1, except that the first electrolyte layer was not formed and only the second electrolyte layer was a solid polymer electrolyte membrane. The evaluation results are shown in Table 2.

[0134] [Table 2]

[0135] As shown in Table 2, in a solid polymer type water electrolysis membrane electrode assembly having an anode and cathode having a catalyst layer and a solid polymer electrolyte membrane disposed between the anode and cathode, it was confirmed that hydrogen crossover can be suppressed and a low electrolysis voltage can be achieved if the solid polymer electrolyte membrane contains a fluorine-containing polymer having ion exchange groups with an ion exchange capacity of 1.25 to 2.00 milliequivalents / gram dry resin and a platinum-containing material (Examples 3-1 to 3-10). [Explanation of Symbols]

[0136] 10,100 Electrolyte membrane 20,120 Membrane electrode assembly 22 Anodes 24 Cathode 26 Catalyst layer 28 Gas diffusion layer 100A 1st electrolyte layer 100B 2nd electrolyte layer 112 Platinum-containing substances S0,S X ,S1 surface T X T1 distance

[0137] Furthermore, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2021-107925, filed on June 29, 2021, are incorporated herein by reference as the disclosure of the specification of this invention.

Claims

1. A solid polymer electrolyte membrane containing a fluorine-containing polymer having ion exchange groups with an ion exchange capacity of 1.25 to 2.00 milliequivalents / gram dry resin, and a platinum-containing material, An anode having a catalyst layer is disposed on one side of the solid polymer electrolyte membrane, The solid polymer electrolyte membrane comprises a cathode having a catalyst layer, disposed on the other side of the solid polymer electrolyte membrane. A solid polymer electrolyte membrane electrode assembly for water electrolysis, wherein the platinum atom content is 0.005 to 0.050 mg / cm² as measured by X-ray fluorescence analysis from the surface on which the anode of the solid polymer electrolyte membrane is located.

2. The solid polymer type membrane electrode assembly for water electrolysis according to claim 1, wherein the platinum-containing material contained in the solid polymer electrolyte membrane is present only from the surface of the plane on which the anode of the solid polymer electrolyte membrane is located to a position corresponding to 20% of the total thickness of the solid polymer electrolyte membrane.

3. The solid polymer type membrane electrode assembly for water electrolysis according to claim 1, wherein the platinum-containing material is supported on a carrier.

4. The solid polymer electrolyte membrane further comprises a reinforcing material, as described in claim 1, for the solid polymer type water electrolysis membrane electrode assembly.

5. The solid polymer type membrane electrode assembly for water electrolysis according to claim 1, wherein the fluorine-containing polymer comprises at least one unit selected from the group consisting of units represented by formula (1-3) and units represented by formula (1-4). 【Chemistry 1】 In equations (1-3) and (1-4), R ｆ１ R is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms, ｆ２ R is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms, ｆ３ is a perfluoroalkylene group which may contain a single bond or an oxygen atom between carbon atoms, where r is 0 or 1, m is 0 or 1, and M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation.

6. The solid polymer electrolyte membrane has a multilayer structure in which a plurality of electrolyte layers are stacked, and at least one of the plurality of electrolyte layers contains the fluoropolymer and the platinum-containing material, as described in claim 1.

7. The polymer electrolyte membrane electrode assembly for water electrolysis according to claim 6, wherein the plurality of electrolyte layers contain the platinum-containing material, and the platinum-containing material content in the electrolyte layer closest to the anode is greater than the platinum-containing material content in the electrolyte layer closest to the cathode.

8. The solid polymer type membrane electrode assembly for water electrolysis according to claim 6, wherein the ion exchange capacities of the plurality of electrolyte layers are different from each other.

9. The solid polymer type membrane electrode assembly for water electrolysis according to claim 6, wherein the plurality of electrolyte layers include an electrolyte layer containing a platinum-containing material and an electrolyte layer not containing a platinum-containing material, and the ratio of the thickness of the electrolyte layer containing a platinum-containing material to the thickness of the electrolyte layer not containing a platinum-containing material is 0.02 or more and 0.50 or less.

10. The solid polymer type membrane electrode assembly for water electrolysis according to claim 1, wherein the thickness of the solid polymer electrolyte membrane is 30 μm or more and 400 μm or less.

11. The solid polymer type membrane electrode assembly for water electrolysis according to claim 1, wherein the mass ratio of the platinum-containing substance to the fluorine-containing polymer in the solid polymer electrolyte membrane is 0.005 or more and 0.030 or less.

12. A water electrolysis apparatus comprising a solid polymer membrane electrode assembly for water electrolysis according to any one of claims 1 to 11.

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