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

Abstract

Provided is a solid polymer electrolyte membrane that has high durability during electrolysis.　Provided is a solid polymer electrolyte membrane which contains a fluorine-containing polymer that comprises a unit represented by a specific formula (1). In the infrared spectrum of the fluorine-containing polymer, the ratio of the maximum absorbance I1690 at 1690 ± 10 cm-1 to the maximum absorbance I2350 at 2350 ± 30 cm-1 is 0.150 or less. By Raman spectroscopy, when a cross section in the thickness direction is irradiated with polarized light orthogonal to the thickness direction to obtain a spectrum chart, A1 is the ratio of the peak area a2 of 680 to 760 cm-1 to the peak area a1 of 1025 to 1095 cm-1, and when the cross section in the thickness direction is irradiated with polarized light parallel to the thickness direction to obtain a spectrum chart, B1 is the ratio of the peak area b2 of 680 to 760 cm-1 to the peak area b1 of 1025 to 1095 cm-1, and the ratio of B1 to A1 is 1.05 or more.

Description

Solid polymer electrolyte membrane, method for manufacturing a solid polymer electrolyte membrane, membrane electrode assembly, water electrolysis apparatus, and method for producing hydrogen

[0001] This disclosure relates to a solid polymer electrolyte membrane. Furthermore, this disclosure also relates to a method for producing the solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis apparatus including the membrane electrode assembly, and a method for producing hydrogen using the water electrolysis apparatus.

[0002] Solid polymer electrolyte membranes can be applied to a variety of uses, and various studies have been conducted on them. For example, solid polymer electrolyte membranes are applied as membrane electrode assemblies with catalyst layers and electrodes on both sides to polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. For example, polymer electrolyte water electrolyzers are used to produce hydrogen gas and are particularly useful from the viewpoint of leveling the amount of electricity supplied from renewable energy sources, and can be said to contribute to the reduction of greenhouse gases. An example of such a solid polymer electrolyte membrane is the one described in Patent Document 1.

[0003] Patent Document 1 discloses a solid polymer electrolyte membrane formed using a copolymer of tetrafluoroethylene and a vinyl fluoride compound having a sulfonic acid group. The disclosed solid polymer electrolyte membrane has an equivalent mass of 790 g / eq.

[0004] International Publication No. 2018 / 047925

[0005] When the solid polymer electrolyte membrane described in Patent Document 1 was applied to a water electrolysis apparatus, it was found that its durability during electrolysis did not meet the standards required today, indicating that there is room for improvement.

[0006] This disclosure has been made in view of the above-mentioned problems, and one embodiment of the present invention aims to provide a solid polymer electrolyte membrane with high durability during electrolysis. Another embodiment of the present invention also aims to provide a method for manufacturing a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis apparatus, and a method for manufacturing hydrogen.

[0007] This disclosure includes the following aspects: [1] A solid polymer electrolyte membrane for a water electrolysis apparatus, wherein the solid polymer electrolyte membrane contains a fluorine-containing polymer containing a unit represented by formula (1) described later, and the infrared spectrum obtained by measuring the fluorine-containing polymer by infrared spectroscopy contains 2350 ± 30 cm⁻¹ －１ Maximum absorbance I ２３５０ 1690 ± 10 cm －１ Maximum absorbance I １６９０ The ratio is 0.150 or less, and by Raman spectroscopy, a spectral chart is obtained by irradiating the cross-section of the solid polymer electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction, and the Raman shift is 1025 to 1095 cm⁻¹. －１ Raman shift of 680–760 cm² relative to peak area a1 －１ The ratio of the peak areas a2 is taken as A1. By Raman spectroscopy, polarized light parallel to the thickness direction is irradiated onto the cross-section of the solid polymer electrolyte membrane in the thickness direction, and a spectral chart is obtained, with a Raman shift of 1025–1095 cm⁻¹. －１ Raman shift of 680–760 cm² relative to peak area b1 －１When the ratio of the peak area b2 is B1, a solid polymer electrolyte membrane in which the ratio of B1 to A1 is 1.05 or more. 〔2〕 The solid polymer electrolyte membrane according to 〔1〕, wherein the ion exchange capacity of the fluorine-containing polymer is 0.90 to 1.50 milliequivalents / gram of dry resin. 〔3〕 The solid polymer electrolyte membrane according to 〔1〕, wherein the ion exchange capacity of the fluorine-containing polymer is 1.20 to 1.50 milliequivalents / gram of dry resin. 〔4〕 The solid polymer electrolyte membrane according to 〔1〕, wherein the ion exchange capacity of the fluorine-containing polymer is 0.90 to 1.20 milliequivalents / gram of dry resin. 〔5〕 The solid polymer electrolyte membrane according to any one of 〔1〕 to 〔4〕, wherein the fluorine-containing polymer further contains a unit based on tetrafluoroethylene. 〔6〕 The content of the unit represented by the above formula (1) in the fluorine-containing polymer is 8 to 35 mol% with respect to all the units in the fluorine-containing polymer, and the content of the unit based on tetrafluoroethylene in the fluorine-containing polymer is 65 to 92 mol% with respect to all the units in the fluorine-containing polymer. The solid polymer electrolyte membrane according to any one of 〔1〕 to 〔5〕. 〔7〕 The solid polymer electrolyte membrane according to any one of 〔1〕 to 〔6〕, wherein the film thickness of the solid polymer electrolyte membrane is 20 to 150 μm. 〔8〕 The solid polymer electrolyte membrane according to any one of 〔1〕 to 〔7〕, wherein the amount of fluorine ion eluted in the Fenton test of the solid polymer electrolyte membrane is 0.02 mass% or less with respect to the mass of all the fluorine atoms in the electrolyte membrane. 〔9〕 The ratio of the peak area a3 to the peak area a1 at Raman shift 920 to 1025 cm －１ is A2, and when the ratio of the peak area b3 at Raman shift 920 to 1025 cm －１ to the peak area b1 is B2, a solid polymer electrolyte membrane according to any one of 〔1〕 to 〔8〕, wherein the ratio of B2 to A2 is more than 1.05. 〔10〕 By Raman spectroscopy, polarized light orthogonal to the thickness direction is irradiated on a cross section in the thickness direction of the electrolyte membrane to obtain a spectrum chart, and the height h1 of the highest peak existing in the range of Raman shift 1025 to 1095 cm －１ is compared with the peak height at Raman shift 920 to 1025 cm－１ Taking H1 as the ratio of the heights h2 of the highest peaks present in the range, a spectral chart is obtained by irradiating the cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction using Raman spectroscopy, and the Raman shift is 1025–1095 cm⁻¹. －１ Raman shift of 920–1025 cm relative to the height h3 of the highest peak in the range －１ A solid polymer electrolyte membrane according to any one of [1] to [9], wherein when the ratio of the heights h4 of the highest peaks in the range is taken as H2, the ratio of H2 to H1 is 1.05 or more.

[11] A membrane electrode assembly comprising an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane according to any one of [1] to

[10] disposed between the anode and the cathode.

[12] A water electrolysis apparatus comprising the membrane electrode assembly according to

[11] .

[13] 2 A / cm when water is electrolyzed. ２ The hydrogen permeability coefficient in is 2.8 × 10⁻⁶. －６ cc・cm / cm ２ - A water electrolysis apparatus as described in

[12] , wherein the temperature is sec·atm or less.

[14] A method for producing hydrogen by electrolyzing water using the water electrolysis apparatus described in

[12] or

[13] .

[15] A method for producing a solid polymer electrolyte membrane, comprising copolymerizing a fluorine-containing olefin with a monomer represented by formula (2), which will be described later and has a group that can be converted to a sulfonic acid type functional group, then contacting the copolymer with a gas containing 5% to 40% by volume of fluorine gas to form a film of the obtained polymer to obtain a precursor film, then contacting the precursor film with an alkaline aqueous solution to obtain a wet solid polymer electrolyte membrane in which the group that can be converted to a sulfonic acid type functional group has been converted to a sulfonic acid type functional group, and then drying the wet solid polymer membrane while constraining its periphery, or drying the wet solid polymer membrane while fixing its periphery, to obtain a solid polymer electrolyte membrane as described in any one of [1] to

[10] .

[0008] According to one embodiment of the present invention, a solid polymer electrolyte membrane with high durability during electrolysis can be provided. Furthermore, according to one embodiment of the present invention, a method for manufacturing a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis apparatus, and a method for producing hydrogen can be provided.

[0009] This figure illustrates the relationship between the irradiation direction of polarized light by Raman spectroscopy and the orientation direction of the fluorine-containing polymer. This figure illustrates the measurement method by Raman spectroscopy. This is an example of a spectral chart obtained when polarized light is irradiated onto a cross-section of a solid polymer electrolyte membrane in the thickness direction, in a direction perpendicular to the thickness direction. This is a cross-sectional view showing an example of a membrane electrode assembly of this disclosure.

[0010] The following definitions of terms apply throughout this specification and the claims unless otherwise specified. “Ion exchange group” means a group capable of exchanging at least some of the ions it contains with other ions, such as the sulfonic acid type functional group and the carboxylic acid type functional group described below. “Sulfonic acid type functional group” means a sulfonic acid group (-SO ３ H), or sulfonic acid base (-SO ３ M ２ However, M ２ (is an alkali metal or quaternary ammonium cation.) Here, the form of the sulfonic acid base 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＋ It 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. "Carboxylic acid-type functional group" refers to a carboxylic acid group (-COOH) or a carboxylic acid base (-COOM). １ However, M１ (is an alkali metal or quaternary ammonium cation.) Here, the form of the carboxylic acid base is, 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＋ It 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 that has groups that can be converted into ion exchange groups. "Groups that can be converted into ion exchange groups" means groups that can be converted into ion exchange groups by treatments such as hydrolysis and acidification. "Groups that can be converted into sulfonic acid-type functional groups" means groups that can be converted into sulfonic acid-type functional groups by treatments such as hydrolysis and acidification. "Groups that can be converted into carboxylic acid-type functional groups" means groups that can be converted into carboxylic acid-type functional groups by known treatments such as hydrolysis and acidification.

[0011] In polymers, a "unit" refers to an atomic group derived from a single monomer molecule, formed by the polymerization of monomers, and is also called a "monomer-based unit." A monomer-based unit may be an atomic group directly formed by the polymerization reaction of monomers, 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 of monomers.

[0012] Numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. 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. Also, 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] [Solid Polymer Electrolyte Membrane] The solid polymer electrolyte membrane of this disclosure (hereinafter also simply referred to as "electrolyte membrane") contains a fluorine-containing polymer (hereinafter also referred to as "fluorine-containing polymer (I)") which includes a unit represented by formula (1) described later. Furthermore, in the infrared spectrum obtained by measuring the above fluorine-containing polymer by infrared spectroscopy, the infrared spectrum is 2350 ± 30 cm⁻¹. －１ Maximum absorbance I ２３５０ 1690 ± 10 cm －１ Maximum absorbance I １６９０ The ratio is 0.150 or less. Below, in the infrared spectrum, 2350 ± 30 cm⁻¹ －１ Maximum absorbance I ２３５０ 1690 ± 10 cm －１ Maximum absorbance I １６９０ The ratio of is simply called "I １６９０ / I ２３５０ It is also called "[...]." Furthermore, the ratio of B1 to A1, determined by the following method, is 1.05 or greater. A1 is the Raman shift of 1025–1095 cm in the spectral chart obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction using Raman spectroscopy. －１ Raman shift of 680–760 cm² relative to peak area a1 －１ This is the ratio of the peak areas a2. B1 is the Raman shift of 1025–1095 cm in the spectral chart obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction using Raman spectroscopy. －１ Raman shift of 680–760 cm² relative to peak area b1 －１This is the ratio of the peak areas b2. Hereafter, the ratio of B1 to A1 will also simply be referred to as "B1 / A1".

[0014] The mechanism by which the electrolyte membrane of this disclosure exhibits high durability during electrolysis is not entirely clear, but the inventors speculate as follows: The fluorine-containing polymer contained in the electrolyte membrane of this disclosure is I １６９０ / I ２３５０ This is within the specified range. １６９０ / I ２３５０ This will be explained in detail later, but it is thought to correspond to the amount of COOH groups contained in the fluorine-containing polymer. COOH groups are unstable end groups located at the ends of the main chain of the fluorine-containing polymer and are thought to be the starting point for the decomposition of the fluorine-containing polymer during electrolysis, so it is preferable to keep it at 0.150 or less. Furthermore, regarding B1 and A1 above, as will be described later, the peaks used in the calculation are, in order from the low wavenumber region, -CF ２ - Structure, and - SO ３ This peak is thought to originate from the group represented by M. Here, when obtaining a Raman spectrum by incident polarized light, as will be described later, -CF ２ -Raman scattering is likely to occur with polarized light in a direction perpendicular to the direction in which the structures are linked. Therefore, the above B1 / A1 being within the above range is due to -CF in a direction perpendicular to the thickness direction of the electrolyte membrane. ２ -This is thought to correspond to an increase in the proportion of the structure that is elongated. Here, -CF ２ - In directions perpendicular to the direction in which the structure extends, the amount of gas permeation, such as oxygen, is thought to be less. Oxygen that permeates to the cathode side can become a source of radicals that attack fluorine-containing polymers, and if the amount of oxygen permeation is reduced, I １６９０ / I ２３５０ It is believed that the durability during electrolysis will be enhanced through a synergistic effect with the fact that the value is below a predetermined level.

[0015] The configuration of the electrolyte membrane in this disclosure will be described below.

[0016] <Fluorine-containing polymer> The electrolyte membrane contains a fluorine-containing polymer (fluorine-containing polymer (I)) containing units represented by formula (1) described later. The ion exchange capacity of fluorine-containing polymer (I) is preferably 0.70 milliequivalents / gram dry resin or more, more preferably 0.90 milliequivalents / gram dry resin or more, even more preferably 1.00 milliequivalents / gram dry resin or more, particularly preferably 1.15 milliequivalents / gram dry resin or more in terms of superior proton conductivity, especially preferably 1.20 milliequivalents / gram dry resin or more, and most preferably 1.25 milliequivalents / gram dry resin or more. The ion exchange capacity of fluorine-containing polymer (I) is preferably 1.70 milliequivalents / gram dry resin or less, more preferably 1.50 milliequivalents / gram dry resin or less, and even more preferably 1.48 milliequivalents / gram dry resin or less. The ion exchange capacity of the fluorine-containing polymer (I) is preferably 0.70 to 1.70 milliequivalents / gram dry resin, and more preferably 0.90 to 1.50 milliequivalents / gram dry resin. From the viewpoint of hydrogen permeability of the electrolyte membrane, the ion exchange capacity of the fluorine-containing polymer (I) is preferably 0.70 to 1.20 milliequivalents / gram dry resin, more preferably 0.90 to 1.20 milliequivalents / gram dry resin, and even more preferably 0.90 to 1.15 milliequivalents / gram dry resin. From the viewpoint of conductivity of the electrolyte membrane, 1.15 to 1.70 milliequivalents / gram dry resin is preferred, more preferably 1.20 to 1.50 milliequivalents / gram dry resin, and even more preferably 1.25 to 1.48 milliequivalents / gram dry resin. The ion exchange capacity of the fluorine-containing polymer (I) can be determined by the method described in the examples below.

[0017] The fluorine-containing polymer (I) is preferably a copolymer polymer comprising a unit represented by formula (1) described later and a unit based on a fluorine-containing olefin described later, and more preferably a copolymer polymer consisting of a unit represented by formula (1) described later and a unit based on a fluorine-containing olefin described later.

[0018] The fluorine-containing polymer (I) contains a unit represented by the following formula (1). The unit represented by the following formula (1) has an ion exchange group (sulfonic acid type functional group). Formula (1) - [CF ２ -CF(-L-(SO３ M)))]- L is a divalent perfluorohydrocarbon group which may contain an etheric oxygen atom. M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation.

[0019] The etheric oxygen atom contained in the divalent perfluorohydrocarbon group may be located at the terminal end of the perfluorohydrocarbon group or between carbon atoms. The number of carbon atoms in the divalent perfluorohydrocarbon group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

[0020] For L, a divalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom is preferred.

[0021] The unit represented by formula (1) is preferably the unit represented by formula (1-1) or the unit represented by formula (1-2), and from the viewpoint of dimensional change, the unit represented by formula (1-1) is preferred. Formula (1-1) - [CF ２ -CF(-OR-R) ｆ１ -SO ３ M)] - Formula (1-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0022] R ｆ１ This is a perfluoroalkylene group which may contain oxygen atoms between carbon atoms. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, particularly preferably 4 or more, preferably 20 or less, and particularly preferably 10 or less. The number of carbon atoms in the above perfluoroalkylene group is preferably 1 to 20, more preferably 2 to 10, even more preferably 3 to 10, and particularly preferably 4 to 10. M is as described above.

[0023] Of the units represented by formula (1-1) and formula (1-2), the unit represented by formula (1-5) is more preferable. Formula (1-5) - [CF ２ -CF (-(CF ２ ) ｘ - (OCF ２ CFY) ｙ -O-(CF２ ) 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, Y is F or CF ３ and, when y = 2, the two Ys may be the same or different. M is as described above.

[0024] Specific examples of the unit represented by formula (1-1) include the following units. In the formula, w is an integer from 1 to 8, x is an integer from 1 to 5, and M 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)] -

[0025] Specific examples of the unit represented by formula (1-2) include the following units. In the formula, w is an integer from 1 to 8, and M is as described above. -[CF ２ -CF(-(CF ２ )) ｗ -SO ３ M)] - -[CF ２ -CF(-CF ２ -O-(CF ２ )) ｗ -SO ３ M)] -

[0026] The unit represented by formula (1) may be used alone or in combination of two or more.

[0027] The fluorine-containing polymer (I) may contain units having ion exchange groups other than the unit represented by formula (1) described above. Examples of such units include units having carboxylic acid-type functional groups. From the viewpoint of applicability to water electrolysis, it is also preferable that the ion exchange group does not contain units having carboxylic acid-type functional groups.

[0028] The fluorine-containing polymer (I) preferably contains units based on a fluorine-containing olefin. Examples of fluorine-containing olefins include fluoroolefins having 2 to 3 carbon atoms and containing 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 (I). The fluorine-containing olefin may be used alone or in combination of two or more types.

[0029] When the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of units based on fluorinated olefins is preferably 65 mol% or more, more preferably 68 mol% or more, and even more preferably 71 mol% or more, relative to the total units in the fluorinated polymer (I). Furthermore, when the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of units based on fluorinated olefins is preferably 92 mol% or less, more preferably 90 mol% or less, even more preferably 87 mol% or less, and particularly preferably 80 mol% or less, relative to the total units in the fluorinated polymer (I). When the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of units based on fluorinated olefins is preferably 65 to 92 mol%, more preferably 68 to 90 mol%, and even more preferably 71 to 87 mol%, relative to the total units in the fluorinated polymer (I). From the viewpoint of hydrogen permeability of the electrolyte membrane, it is preferably 80 to 92 mol%, and more preferably 80 to 90 mol%. From the viewpoint of conductivity of the electrolyte membrane, it is preferably 68 to 82 mol%, more preferably 71 to 82 mol%, and even more preferably 75 to 80 mol%.

[0030] When the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of the units represented by formula (1) is preferably 35 mol% or less, more preferably 32 mol% or less, and even more preferably 29 mol% or less, relative to the total units in the fluorinated polymer (I). Furthermore, when the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of the units represented by formula (1) is preferably 8 mol% or more, more preferably 10 mol% or more, even more preferably 13 mol% or more, and particularly preferably 20 mol% or more, relative to the total units in the fluorinated polymer (I). When the fluorinated polymer (I) contains units represented by formula (1) and units based on fluorinated olefins, the content of the units represented by formula (1) is preferably 8 to 35 mol%, more preferably 10 to 32 mol%, and even more preferably 13 to 29 mol%, relative to the total units in the fluorinated polymer (I). From the viewpoint of hydrogen permeability of the electrolyte membrane, it is preferably 8 to 20 mol%, and more preferably 10 to 20 mol%. From the viewpoint of conductivity of the electrolyte membrane, it is preferably 18 to 32 mol%, more preferably 18 to 29 mol%, and even more preferably 15 to 20 mol%.

[0031] The fluorine-containing polymer (I) may or may not contain units based on other monomers other than the unit represented by formula (1) and the unit based on the fluorine-containing olefin. Specific examples of other monomers include CF ２ = CF - OR ｆ７ (However, R ｆ７ (These are perfluoroalkyl groups having 1 to 10 carbon atoms.) CF ２ = CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer from 1 to 3.) are examples. The content of units based on other monomers is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 1% by mass or less, relative to the total units in the fluorine-containing polymer (I), from the viewpoint of maintaining ion exchange performance.

[0032] <Infrared Spectroscopy Measurement> As described above, in the infrared spectrum obtained by measuring the fluorine-containing polymer (I) by infrared spectroscopy, the infrared spectrum of 2350 ± 30 cm⁻¹ －１ Maximum absorbance I ２３５０ 1690 ± 10 cm －１ Maximum absorbance I １６９０ The ratio (I １６９０ / I ２３５０ ) is 0.150 or less. Below, the above I １６９０ / I ２３５０ I will explain how to calculate it.

[0033] First, a measurement film with a thickness of 50 to 150 μm is obtained, made of the fluorine-containing polymer (I) to be measured. If the electrolyte membrane is made of the fluorine-containing polymer (I), the electrolyte membrane may be used as the measurement film. Next, prior to measurement, the measurement film is immersed in a 2.5% by mass potassium hydroxide aqueous solution at 20°C for 30 minutes to convert the sulfonic acid groups contained in the fluorine-containing polymer into K salts. Then, to minimize the influence of adsorbed water on the infrared spectrum, the film is dried using a vacuum dryer or the like. The dried measurement film is measured by infrared spectroscopy to obtain the infrared spectrum. Detailed measurement and analysis methods are shown in the examples below. Note: 2350 ± 30 cm －１ The region (2320-2380 cm) －１ The absorption peak observed in the range of 1690 ± 10 cm is absorption originating from CF stretching, and is －１ The region (1680-1700 cm) －１ The absorption peak observed in the range of () can be said to be absorption originating from the COOK group.

[0034] Fluorine-containing polymer of electrolyte membrane １６９０ / I ２３５０ The value is 0.150 or less, preferably 0.100 or less, more preferably 0.070 or less, and even more preferably 0.050 or less. １６９０ / I ２３５０ There is no particular lower limit, but it is often 0.003 or higher.

[0035] <Raman Spectroscopy Measurement> The electrolyte membrane has a ratio of B1 to A1 (B1 / A1) of 1.05 or higher, calculated from the spectral chart obtained by Raman spectroscopy. As mentioned above, B1 / A1 is -CF ２ - This parameter is thought to be related to the direction in which the structure extends. This point will be explained with reference to the drawings.

[0036] Figure 1 is a diagram illustrating the relationship between the irradiation direction of polarized light by Raman spectroscopy and the orientation direction of the fluorine-containing polymer. In Figure 1, a cross-section 12 in a direction parallel to the thickness direction of the electrolyte membrane 10 is shown. In Figure 1, the main chain M1 of the fluorine-containing polymer is oriented along a direction 12A perpendicular to the thickness direction T of the electrolyte membrane 10. In this case, measurements taken with polarized light PB along the direction parallel to the thickness direction T are more effective than measurements taken with polarized light PA along the direction 12A perpendicular to the thickness direction T, as it allows for better detection of the -CF present in the main chain. ２ - It is thought that the Raman scattering efficiency of peaks originating from the structure will be higher. In other words, a ratio of B1, which is calculated by obtaining a spectral chart by irradiating with polarized light parallel to the thickness direction, to A1, which is calculated by irradiating with polarized light perpendicular to the thickness direction, to 1.05 or higher indicates that the main chain of the fluorine-containing polymer tends to be oriented in a direction perpendicular to the thickness direction of the electrolyte membrane. This point will be explained in detail later. When the main chain of the fluorine-containing polymer is oriented in a direction perpendicular to the thickness direction, gas permeability is reduced, and as mentioned above, it is thought that it has excellent durability during electrolysis.

[0037] B1 / A1 is preferably 1.10 or higher, may be 1.13 or higher, or 1.25 or higher, as this provides better durability during electrolysis. B1 / A1 is usually 3.00 or lower, and preferably 2.00 or lower.

[0038] The method for calculating A1, which is calculated based on the spectral chart obtained by Raman spectroscopy, will be described in detail below using Figures 2 and 3.

[0039] Figure 2 is a diagram illustrating the measurement method using Raman spectroscopy. Figure 3 is an example of a spectral chart obtained when polarized light is irradiated onto a cross-section of the electrolyte membrane in the thickness direction, perpendicular to the thickness direction.

[0040] In calculating A1 above, first, the electrolyte membrane 10 is cut along an axial direction parallel to the thickness direction T of the electrolyte membrane 10, exposing the cross-section 12 of the electrolyte membrane 10. For example, the cutting method can be done using a razor. Next, polarized light is irradiated onto the cross-section 12 in a direction 12A perpendicular to the thickness direction T, and the spectral chart shown in Figure 3 is obtained by Raman spectroscopy. The polarized light irradiated onto the electrolyte membrane 10 is linearly polarized, and linearly polarized light can be obtained using a known polarizer. For measurement by Raman spectroscopy, for example, a Raman spectrometer (product name "LabRAM HR-800", manufactured by Horiba, Ltd.) is used.

[0041] The spectral chart shown in Figure 3 has the intensity (Raman scattering intensity) on the vertical axis and the Raman shift (unit: cm) on the horizontal axis. －１ This represents a Raman shift of 1025–1095 cm². In this disclosure, the Raman shift is 1025–1095 cm². －１ The peak area a1 within the range is used. In the example in Figure 3, the Raman shift is 1060 cm². －１ A peak is observed at this position. Here, the peak area a1 is 1025 cm², as shown in Figure 3. －１ The point (coordinate) representing the intensity at 1095 cm, and －１ The baseline is the point (coordinate) connecting two points representing the intensity in the region, and the distance between 1025 and 1095 cm. －１ It is calculated as the area of ​​the region enclosed by the spectrum in the range of . In this disclosure, the Raman shift is 680 to 760 cm⁻¹. －１ The peak area a2 within the range is used. In the example in Figure 3, the Raman shift is 730 cm². －１ A peak is observed at this position. Here, the peak area a2 is 680 cm², as shown in Figure 3. －１ The point (coordinate) representing the intensity at 760 cm －１ The baseline is the point (coordinate) connecting two points representing the intensity in that region, and the range is 680-760 cm. －１The area of ​​the region enclosed by the spectrum within the range is calculated. Based on the value obtained as described above, A1(a2 / a1), which is the ratio of peak area a2 to peak area a1, is calculated.

[0042] As described above, A1 is a value calculated from the spectral chart obtained by irradiating the cross-section 12 of the electrolyte membrane 10 in the thickness direction T with polarized light in a direction 12A perpendicular to the thickness direction T. Therefore, A1 is the value of -CF present in the main chain. ２ The C-F bond of the group represented by - is oriented along the direction 12A perpendicular to the thickness direction T of the electrolyte membrane 10, and this is considered an indicator that the main chain (C-C) bond is oriented along the thickness direction T of the electrolyte membrane 10. In other words, when the main chain is oriented along the thickness direction T of the electrolyte membrane 10, the value of A1 is considered to be large.

[0043] On the other hand, B1 (b2 / b1) is calculated in the same manner as A1, except that a spectral chart obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction is used. Specifically, in the example in Figure 2, B1 is a value calculated from the spectrum measured by irradiating the cross-section 12 with polarized light in the direction 12B parallel to the thickness direction T. Therefore, B1 is the -CF present in the main chain. ２ The C-F bond of the group represented by - is oriented along the direction 12B parallel to the thickness direction T of the electrolyte membrane 10, and the main chain (C-C bond) is oriented along the direction 12A perpendicular to the thickness direction T of the electrolyte membrane 10. This is considered to be an indicator of this orientation. In other words, if the main chain is oriented along the direction 12A perpendicular to the thickness direction T of the electrolyte membrane 10, the value of B1 is considered to be large.

[0044] Therefore, it is considered that the higher the ratio of B1 to A1 (B1 / A1), the more likely the main chain of the fluorine-containing polymer is to be oriented perpendicular to the thickness direction of the electrolyte membrane. Furthermore, by using peak area in calculating the above ratio, the influence of spectral noise variations can be reduced.

[0045] The fluorine-containing polymer contained in the electrolyte membrane of this disclosure preferably further has ether-binding sites (specifically, partial bonds represented by C-O-C) in its side chains. In this case, the electrolyte membrane of this disclosure preferably satisfies the following characteristics: First, the Raman shift relative to the peak area a1 is 920 to 1025 cm². －１ Let A2 be the ratio of the peak areas a3. Also, the Raman shift of 920–1025 cm⁻¹ to the above peak area b1. －１ Let B2 be the ratio of the peak areas b3. Here, the ratio of B2 to A2 (B2 / A2) is preferably greater than 1.05, may be 1.10 or greater, or 1.15 or greater. B2 / A2 is usually 3.00 or less, and preferably 2.00 or less. Note that the Raman shift is 920 to 1025 cm⁻¹. －１ The peaks present in this range are thought to originate from ether bonding sites in the side chains of fluorine-containing polymers.

[0046] The method for calculating A2 will be explained with reference to Figure 3, in the case where the fluorine-containing polymer contained in the electrolyte membrane of this disclosure has ether-binding sites in its side chains. In the example in Figure 3, the Raman shift is 975 cm⁻¹. －１ A peak exists at this position. The peak area a3 is 920 cm², as shown in Figure 3. －１ The point (coordinate) representing the intensity at 1025 cm, and 1025 cm －１ A baseline connecting two points (coordinates) representing the intensity in that region, and 920–1025 cm －１ The area is calculated as the region enclosed by the spectrum within this range. The peak area a3 is obtained by obtaining a spectral chart by irradiating the cross-section of the electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction using Raman spectroscopy, as described above, with a Raman shift of 920–1025 cm⁻¹. －１ This is calculated as the peak area. Based on the value obtained in this way, A2(a3 / a1), which is the ratio of peak area a3 to peak area a1, is calculated.

[0047] Similarly, the peak area b3 is obtained by Raman spectroscopy, where a spectral chart is obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction, and the Raman shift is 920–1025 cm⁻¹. －１ This is calculated as the peak area. Based on the value obtained in this way, B2 (b3 / b1), which is the ratio of peak area b3 to peak area b1, is calculated.

[0048] As described above, A2 is a value calculated by irradiating the cross-section of the electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction. Therefore, when ether binding sites are present in the side chains of the fluorinated polymer, it is an indicator that the main chain of the fluorinated polymer is oriented in a direction parallel to the thickness direction. More specifically, when a fluorinated polymer has side chains containing ether binding sites, the side chains tend to be oriented in a direction perpendicular to the main chain (in particular, the unit represented by equation (1) tends to show this tendency). Therefore, it is considered that the value of A2 will be large when the main chain, which is located perpendicular to the side chains of the fluorinated polymer, is oriented in a direction parallel to the thickness direction of the electrolyte membrane. On the other hand, B2 is a value calculated by irradiating the cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction. Therefore, when ether binding sites are present in the side chains of the fluorinated polymer, it is an indicator that the main chain of the fluorinated polymer is oriented in a direction perpendicular to the thickness direction. Therefore, it is thought that the value of B2 increases when the main chain of the fluorinated polymer, which is located perpendicular to the side chains, is oriented perpendicular to the thickness direction of the electrolyte membrane. In other words, the greater the ratio of B2 to A2 (B2 / A2), the stronger the tendency for the main chain of the fluorinated polymer to be oriented perpendicular to the thickness direction of the electrolyte membrane. Therefore, when B2 / A2 is greater than 1.05, the gas permeability of the electrolyte membrane tends to be lower, and it is thought that the durability during electrolysis is superior.

[0049] When the fluorine-containing polymer contained in the electrolyte membrane of this disclosure has ether-binding sites in its side chains, the electrolyte membrane of this disclosure preferably satisfies the following characteristics. First, by Raman spectroscopy, a spectral chart is obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction, and the Raman shift is 1025 to 1095 cm. －１ Raman shift of 920–1025 cm for the height h1 of the highest peak in the range －１ H1 is defined as the ratio of the heights h2 of the highest peaks present in the range (h2 / h1). Furthermore, by Raman spectroscopy, a spectral chart is obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction, and the Raman shift is 1025–1095 cm⁻¹. －１ Raman shift of 920–1025 cm relative to the height h3 of the highest peak in the range －１ H2 is defined as the ratio (h4 / h3) of the highest peak heights h4 present in the range. Here, in the electrolyte membrane of this disclosure, the ratio of H2 to H1 (H2 / H1) is preferably 1.05 or higher, may be 1.10 or higher, or 1.15 or higher, in terms of superior durability during electrolysis. The above ratio (H2 / H1) is not particularly limited, but is usually 3.00 or lower, and more preferably 2.00 or lower.

[0050] As mentioned above, the Raman shift is 1025-1095 cm. －１ The peaks in the range are -SO ３ This peak is thought to originate from the group represented by M, and its Raman shift is 920–1025 cm. －１ The peaks present in this range are thought to originate from ether binding sites in the side chains. H1 and H2, like A2 and B2, are thought to reflect the orientation of the polymer main chain and side chains. A larger ratio of H2 to H1 (H2 / H1) suggests that the main chain of the fluorine-containing polymer tends to be oriented perpendicular to the thickness direction of the electrolyte membrane. Therefore, the gas permeability of the electrolyte membrane tends to be lower, resulting in superior durability during electrolysis.

[0051] The height of the highest peak in the above wavenumber range is determined by the following procedure. First, a baseline is created using the same procedure as when determining the peak area. Next, at the wavenumber of the Raman shift that represents the maximum value of the peak whose height is to be determined, the peak height is obtained by subtracting the baseline intensity from the maximum value of the above peak. Raman shift 1025–1095 cm －１ The highest peak height h1 in the range, and the Raman shift 920–1025 cm －１ An example of how to determine the height h2 of the highest peak in the range is shown in Figure 3. Based on the value obtained in this way, H1(h2 / h1), which is the ratio of the peak height h2 to the peak height h1, is calculated. Similarly, h3 and h4 are determined from the spectral chart by irradiating with polarized light parallel to the thickness direction, and H2(h4 / h3) is calculated.

[0052] The electrolyte membrane may have a single-layer structure or a multilayer structure. In the case of a multilayer structure, for example, one embodiment may involve stacking multiple layers containing a fluorine-containing polymer (I) with different ion exchange capacities.

[0053] The fluorine-containing polymer (I) used in the electrolyte membrane may be of one type, or two or more types may be used in a laminated or mixed form. 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 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 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. In addition, from the standpoint of oxidation resistance of the electrolyte membrane, other polymers such as polyphenylene sulfide resins and polyphenylene ether resins can also be mentioned.

[0054] The electrolyte membrane preferably has a fluoride ion elution amount of 0.02% by mass or less, and more preferably 0.01% by mass or less, relative to the total mass of fluorine atoms in the electrolyte membrane, in order to improve durability during electrolysis. The Fenton test is performed by the method described in the examples below.

[0055] <Reinforcement Material> The electrolyte membrane may be reinforced with a reinforcement material. Examples of reinforcement materials include porous materials, fibers, woven fabrics, and nonwoven fabrics. Examples of materials for the reinforcement material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, polyphenylene sulfide, and polyether ether ketone.

[0056] <Film Thickness (Film Thickness of Electrolyte Membrane When Drying)> The film thickness of the electrolyte membrane is preferably 20 μm or more, more preferably 40 μm or more, even more preferably 50 μm or more, and particularly preferably 60 μm or more. The film thickness of the electrolyte membrane is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 100 μm or less, from the viewpoint that the electrolysis voltage can be further reduced when applied to an electrolytic device. The film thickness of the electrolyte membrane is preferably 20 to 150 μm, more preferably 40 to 150 μm, even more preferably 50 to 130 μm, particularly preferably 60 to 130 μm, and most preferably 60 to 100 μm. The film thickness of the electrolyte membrane is measured by the method described in the examples below.

[0057] [Method for Manufacturing Electrolyte Membranes] One method for manufacturing electrolyte membranes involves producing a membrane (hereinafter also referred to as a "precursor membrane") containing a polymer of a fluorine-containing monomer (hereinafter also referred to as "fluorine-containing monomer (I')") having a group that can be converted to a sulfonic acid-type functional group (hereinafter also referred to as "fluorine-containing polymer (I')"), then converting the groups in the precursor membrane that can be converted to a sulfonic acid-type functional group into sulfonic acid-type functional groups to obtain a wet electrolyte membrane, and finally drying the wet electrolyte membrane to produce the electrolyte membrane. Note that a wet electrolyte membrane refers to an electrolyte membrane that has been swollen in a liquid medium. The method for manufacturing electrolyte membranes will be described below.

[0058] As the fluorine-containing polymer (I'), 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.

[0059] Methods for copolymerizing fluorine-containing polymers (I') can include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.

[0060] 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 polymers (I) and (I'). Fluorine-containing olefins may be used individually or in combination of two or more types.

[0061] The content of units based on fluorinated olefins in the fluorinated polymer (I') is preferably 65 mol% or more, more preferably 68 mol% or more, and even more preferably 71 mol% or more, relative to the total units in the fluorinated polymer (I'). Furthermore, the content of units based on fluorinated olefins is preferably 92 mol% or less, more preferably 90 mol% or less, even more preferably 87 mol% or less, and particularly preferably 80 mol% or less, relative to the total units in the fluorinated polymer (I').

[0062] Examples of fluorine-containing monomers (I') include compounds having one or more fluorine atoms in the molecule, having an ethylenically active double bond, and having a group that can be converted to a sulfonic acid-type functional group. As the fluorine-containing monomer (I'), 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 (I). Formula (2) CF ２ =CF-L-A The definition of L in formula (2) is as described above. A is a group that can be converted to a sulfonic acid type functional group. The group that can be converted to a sulfonic acid type functional group is preferably a functional group that can be converted to a sulfonic acid type functional group by hydrolysis. A specific example of a group that can be converted to a sulfonic acid type functional group is -SO ２ F, -SO ２ Cl, -SO ２ Br is one example.

[0063] The compound represented by formula (2) is preferably the compound represented by formula (2-1) or the compound represented by formula (2-2). Formula (2-1) CF ２ =CF-O-R ｆ１ -A Formula (2-2) CF ２ =CF-R ｆ１ -A

[0064] R in the formula ｆ１ The definition of A is as stated above.

[0065] 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. CF ２ =CF - O - (CF ２ )ｗ -SO ２ F CF ２ = CF - O - CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ F CF ２ =CF - [O - CF ２ CF (CF ３ )] ｘ -SO ２ F

[0066] Specific examples of compounds represented by formula (2-2) include the following compounds. In the formula, w is an integer from 1 to 8. CF ２ = CF - (CF ２ ) ｗ -SO ２ F CF ２ = CF - CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0067] The fluorine-containing monomer (I') may be used alone or in combination of two or more types.

[0068] The content of the unit represented by formula (1) in the fluorinated polymer (I') is preferably 35 mol% or less, more preferably 32 mol% or less, and even more preferably 29 mol% or less, relative to the total units in the fluorinated polymer (I'). Furthermore, the content of the unit represented by formula (1) is preferably 8 mol% or more, more preferably 10 mol% or more, even more preferably 13 mol% or more, and particularly preferably 20 mol% or more, relative to the total units in the fluorinated polymer (I').

[0069] In the production of the fluorine-containing polymer (I'), other monomers may be used in addition to the fluorine-containing olefin and the fluorine-containing monomer (I'). Examples of other monomers include those exemplified above. The content of units based on other monomers is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 1% by mass or less, relative to the total units in the fluorine-containing polymer (I').

[0070] The TQ value of the fluorine-containing polymer (I') is preferably 180°C or higher, more preferably 200°C or higher, and even more preferably 220°C or higher. Furthermore, the TQ value of the fluorine-containing polymer (I') is preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower. The TQ value is a value related to the molecular weight of the polymer, and the volumetric flow rate is 100 mm. ３ This is expressed as temperature per second and is determined by the method described in the Examples section below.

[0071] It is preferable to perform a fluorination treatment on the fluorine-containing polymer (I') used in the manufacture of electrolyte membranes. A preferred fluorination treatment is one in which the polymer is brought into contact with a gas containing fluorine gas. When the fluorination treatment is performed, the above-mentioned I' １６９０ / I ２３５０ An electrolyte membrane with the above range is easily obtained.

[0072] The gas used in the fluorination treatment may contain gases other than fluorine gas. Examples of gases other than fluorine gas include inert gases, such as nitrogen gas and argon gas. The fluorine gas content in the gas used in the fluorination treatment is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 15% by volume or more. Furthermore, the fluorine gas content in the gas used in the fluorination treatment is preferably 40% by volume or less, and more preferably 30% by volume or less. The fluorine gas content is preferably 5 to 40% by volume, more preferably 10 to 30% by volume, and even more preferably 15 to 30% by volume.

[0073] The atmospheric pressure during fluorination treatment is often -0.02 MPa or higher, and preferably 0.1 MPa or higher, as measured by gauge pressure (differential pressure relative to ambient pressure). Furthermore, the atmospheric pressure during fluorination treatment is preferably 1.0 MPa or lower, as measured by gauge pressure. A positive gauge pressure indicates a pressure higher than the ambient pressure.

[0074] The temperature at which the fluorination treatment is carried out (fluorination treatment temperature) is preferably 0°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher, from the viewpoint of ensuring that the fluorination treatment proceeds sufficiently. Furthermore, from the viewpoint of the handling properties of the fluorinated polymer (I'), the temperature is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. The above fluorination treatment temperature is preferably 0 to 250°C, more preferably 30 to 200°C, even more preferably 50 to 100°C, and particularly preferably 50 to 90°C.

[0075] The duration of the fluorination treatment (fluorination treatment time) is preferably 0.1 hours or more, more preferably 1 hour or more, and even more preferably 3 hours or more. Furthermore, it is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 7 hours or less. The above fluorination treatment time is preferably 0.1 to 24 hours, more preferably 1 to 12 hours, and even more preferably 3 to 7 hours.

[0076] The fluorination treatment may be carried out in multiple stages to suppress the decomposition of the fluorine-containing polymer (I'). For example, the number of fluorination treatments may be two or more, and may be three or more, but is usually five or less. In this case, the fluorination treatment time per stage is preferably 7 hours or less, and more preferably 5 hours or less. When the number of fluorination treatments is two or more, the total fluorination treatment time is preferably 3 to 24 hours, and more preferably 7 to 22 hours.

[0077] In the fluorination treatment, a hydrogen fluoride adsorbent may be used to reduce the hydrogen fluoride concentration in the gas used in the fluorination treatment. The hydrogen fluoride adsorbent is preferably substantially inert to the fluorinating agent and has the property of reacting with or adsorbing hydrogen fluoride; inorganic fluorides are preferred. Examples of hydrogen fluoride adsorbents include alkali metal fluorides and ammonium fluoride, with alkali metal fluorides being preferred. As the alkali metal fluoride, at least one selected from the group consisting of KF, NaF, and CsF is preferred, with NaF being more preferred.

[0078] Furthermore, it is preferable to perform vacuum drying of the fluorine-containing polymer (I') before the fluorination treatment described above. The pressure used for vacuum drying is preferably 0.02 MPa or less in absolute pressure, and more preferably 0.01 MPa or less. The temperature used for vacuum drying is preferably 0°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher. In addition, the temperature used for vacuum drying is preferably 300°C or lower, and more preferably 250°C or lower.

[0079] Methods for forming precursor films include melt extrusion and hot press molding. For hot press molding, known hot press equipment such as flat plate presses and roll presses can be used.

[0080] A specific example of a method for converting groups in a precursor film that can be converted to sulfonic acid-type functional groups is to subject the precursor film to hydrolysis. As for the hydrolysis treatment, a method of contacting the precursor film with an alkaline aqueous solution is preferred.

[0081] Specific examples of methods for bringing the precursor film into contact with an 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 to 100°C, and more preferably 40 to 100°C. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 to 150 minutes, and more preferably 5 to 50 minutes.

[0082] 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, and specifically, an organic solvent with a solubility of 0.1 g or more in 1,000 ml of water (20°C) is preferred, and an organic solvent with a solubility of 0.5 g or more is more 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 more preferably contains an aprotic organic solvent. The water-soluble organic solvent may be used alone or in combination of two or more.

[0083] 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.

[0084] The concentration of alkali metal hydroxide is preferably 1 to 60% by mass, and more preferably 3 to 55% by mass, in the alkaline aqueous solution. The content of water-soluble organic solvent is preferably 1 to 60% by mass, and more preferably 3 to 55% by mass, in the alkaline aqueous solution. The concentration of water is preferably 39 to 80% by mass, in the alkaline aqueous solution.

[0085] 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.

[0086] After contact between the precursor film and the alkaline aqueous solution, the resulting film may be subjected to an acidification treatment by contacting it with an acidic aqueous solution to convert the ion exchange groups to the acidic form. Specific examples of the acidification treatment include immersing the precursor film in an acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor film. The acidic aqueous solution preferably contains an acid component and water. Specific examples of the acid component include hydrochloric acid and sulfuric acid.

[0087] When the precursor film is brought into contact with an alkaline aqueous solution, a wet electrolyte film is obtained in which the groups that can be converted to sulfonic acid-type functional groups have been converted to sulfonic acid-type functional groups. The electrolyte film after hydrolysis or acidification treatment is usually wet with the medium used in the hydrolysis or acidification treatment, and the water used for subsequent washing. This wet electrolyte film may be used as is and then dried.

[0088] In a wet electrolyte membrane, a higher liquid medium content is preferable. When the degree of swelling of the fluorine-containing polymer (I) by the liquid medium is higher, the gas permeability of the electrolyte membrane obtained after drying tends to be lower. The degree of swelling of the fluorine-containing polymer (I) by the liquid medium is influenced by the polymer structure of the fluorine-containing polymer (I), the ion exchange capacity, the type of counterion of the sulfonic acid-type functional group, and the membrane composition of the wet electrolyte membrane. For example, the higher the ion exchange capacity, the higher the degree of swelling of the fluorine-containing polymer (I) tends to be. Although also influenced by the conditions mentioned above, the liquid medium content of the wet electrolyte membrane is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the wet electrolyte membrane. It is presumed that by increasing the degree of swelling of the fluorine-containing polymer (I) and drying it from a state where the internal stress is further relaxed, the residual internal stress due to drying in the dried electrolyte membrane is reduced, and the above-mentioned effects are obtained.

[0089] As described above, the wet electrolyte membrane after hydrolysis or acidification treatment may be dried as is as a wet electrolyte membrane. However, in order to obtain a wet electrolyte membrane with a high liquid medium content, it is preferable to perform an operation to increase the liquid medium content. Examples of such operations include heating while in contact with a liquid medium, and immersing for a certain period of time in a liquid medium that has a higher affinity for the fluorine-containing polymer (I). Among these, the method of heating while in contact with a liquid medium (hereinafter also referred to as "contact heating treatment") is preferred because it is easy to perform.

[0090] The electrolyte membrane used in the contact heat treatment (hereinafter also referred to as the "untreated membrane") may be a wet electrolyte membrane after hydrolysis or conversion of ion exchange groups to an acid type, or it may be a dried electrolyte membrane. Methods for contacting the untreated membrane with the liquid medium include, for example, immersing the untreated membrane in the liquid medium, and coating the untreated membrane with the liquid medium. The heating temperature in the contact heat treatment is preferably 60°C or higher, and more preferably 90°C or higher, in order to facilitate the penetration of the liquid medium into the untreated membrane. Furthermore, the heating temperature is preferably below the boiling point of the liquid medium. The contact heat treatment time can be appropriately adjusted, for example, so that the liquid medium content in the wet electrolyte membrane falls within the above range.

[0091] In the above-described method for manufacturing an electrolyte membrane, a step is performed to dry the wet electrolyte membrane to remove the liquid medium and obtain a dry solid polymer electrolyte membrane (hereinafter also referred to as the "drying step"). In the drying step, it is preferable to perform the drying step such that the dimensional change of the dry solid polymer electrolyte membrane from the wet solid polymer electrolyte membrane is -5% or more in both the MD direction and the TD direction. When the drying step is performed under the above-described preferred conditions, it is easy to obtain an electrolyte membrane with a B1 / A1 of 1.05 or more. In the following, "dimensional change of the dry electrolyte membrane from the wet electrolyte membrane during the drying step" may be abbreviated as "dimensional change of the wet electrolyte membrane before and after drying". Furthermore, "MD direction" refers to the transport direction of the wet electrolyte membrane during the manufacture of the dry electrolyte membrane, and when a long wet electrolyte membrane is used to manufacture the dry electrolyte membrane, it refers to the length direction. "TD direction" refers to the direction intersecting the MD direction in the plane of the wet electrolyte membrane (the width direction of the wet electrolyte membrane).

[0092] The dimensional changes of the wet electrolyte membrane in the MD and TD directions before and after drying can be calculated specifically for each direction using the following formula (L1): Dimensional change of wet electrolyte membrane (%) = 100 × {(Length of dry electrolyte membrane) - (Length of wet electrolyte membrane)} / (Length of wet electrolyte membrane) (L1)

[0093] The dimensional changes in the MD and TD directions of the wet electrolyte membrane before and after drying are preferably -5% or more, and it is preferable that there is little shrinkage. However, even if there is no dimensional change or the membrane is stretched while drying, an electrolyte membrane with low gas permeability can be obtained. Specifically, a preferred dimensional change is preferably 0% or more, more preferably 5% or more, even more preferably 10% or more, and particularly preferably 20% or more. When the dimensional change exceeds 0%, i.e., when stretching, there is no particular upper limit, but the dimensional changes in the MD and TD directions of the wet electrolyte membrane before and after drying are preferably 250%, more preferably 200%, even more preferably 150%, and particularly preferably 50%, respectively.

[0094] Methods for ensuring that the dimensional changes in the MD and TD directions of the wet electrolyte membrane before and after drying are within the above range include drying while constraining the periphery of the wet electrolyte membrane, and drying while fixing the periphery of the wet electrolyte membrane. More specifically, methods for drying while constraining the periphery of the wet electrolyte membrane include fixing the periphery of the wet electrolyte membrane by sandwiching it with a metal frame, and fixing the periphery of the wet electrolyte membrane by inserting needles into it. Methods for drying while fixing the periphery of the wet electrolyte membrane include applying a load to the periphery of the wet electrolyte membrane. Here, the production of the dried electrolyte membrane may be carried out by roll-to-roll. In this case, a long roll of wet electrolyte membrane is unwound, and after each of the above steps is performed, the dried electrolyte membrane is wound into a roll. At this time, the dimensional change in the MD direction during drying of the wet electrolyte membrane can also be controlled, for example, by adjusting the winding speed of the dried electrolyte membrane.

[0095] Drying of the wet electrolyte membrane may be done by natural drying or by using a known drying apparatus, but drying by heating is preferred from the viewpoint of drying efficiency. When heating is performed when drying the wet electrolyte membrane, the heating temperature of the wet electrolyte membrane is preferably 50 to 300°C, and more preferably 90 to 280°C. In particular, the heating temperature of the wet electrolyte membrane is preferably above the softening point of the fluorine-containing polymer (I), more preferably 10°C or more above the softening point of the fluorine-containing polymer, and especially preferably 20°C or more above the softening point of the fluorine-containing polymer (I), from the viewpoint of minimizing residual internal stress during drying. In this specification, the softening point of the fluorine-containing polymer (I) is measured using a dynamic viscoelasticity measuring device in the following procedure. First, dynamic viscoelasticity measurement is performed using a dynamic viscoelasticity measuring device (DVA-225, manufactured by IT Measurement Control Co., Ltd.) under the conditions of sample width: 5.0 mm, gripping distance: 15 mm, measurement frequency: 1 Hz, heating rate: 2°C / min, and tensile mode. Next, the tanδ (loss tangent) is calculated from the ratio of the loss modulus E'' to the storage modulus E' (E'' / E'), and a tanδ-temperature curve is created. From the created tanδ-temperature curve, the peak temperature between -100 and 300°C is read, and this value is taken as the softening point.

[0096] [Membrane Electrode Assembly] The membrane electrode assembly of this disclosure includes an anode having a catalyst layer, a cathode having a catalyst layer, and an electrolyte membrane disposed between the anode and the cathode. The electrolyte membrane is as described above, so its explanation is omitted.

[0097] Figure 4 is a cross-sectional view showing an example of a membrane electrode assembly according to the present disclosure. The membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having a catalyst layer 26 and a gas diffusion layer 28, and an electrolyte membrane 10 disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26. In Figure 4, the laminate of the catalyst layer 26 of the anode 22, the electrolyte membrane 10, and the catalyst layer 26 of the cathode 24 is the electrolyte membrane with a catalyst layer.

[0098] <Anode and Cathode> The anode and cathode each have a catalyst layer. In the example in Figure 4, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28. In at least one of the anode 22 and cathode 24, there may be a region where a portion of the gas diffusion layer 28 and the catalyst layer 26 overlap in the thickness direction. Also, in at least one of the anode 22 and cathode 24, the catalyst layer 26 may be omitted, and the gas diffusion layer 28 may perform the role of the catalyst layer 26.

[0099] Specific examples of catalyst layers include layers 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, ruthenium oxide catalysts, iridium oxide catalysts, ruthenium-containing composite oxides, iridium-containing composite oxides, catalysts containing ruthenium oxide having a core-shell structure, and catalysts containing iridium oxide having a core-shell structure. Carbon black powder can be used as the carbon support. The polymer having ion exchange groups is not particularly limited, and for example, known fluorine-containing polymers having ion exchange groups can be used. The catalyst included in the anode-side catalyst layer is preferably one or more catalysts selected from the group consisting of ruthenium oxide catalysts, iridium oxide catalysts, ruthenium-containing composite oxides, iridium-containing composite oxides, catalysts containing ruthenium oxide having a core-shell structure, and catalysts containing iridium oxide having a core-shell structure. The supported catalyst is preferred as the catalyst included in the cathode-side catalyst layer.

[0100] The gas diffusion layer has the function of uniformly diffusing gas into the catalyst layer and also functions as a current collector. Specific examples of the gas diffusion layer include carbon paper, carbon cloth, carbon felt, and metal mesh. For the anode-side gas diffusion layer, a metal mesh is preferably used. The metal material constituting the metal mesh is preferably a metal with high corrosion resistance, such as titanium, zirconium, niobium, and tantalum, with titanium being preferred. The gas diffusion layer may be treated to be water-repellent with PTFE or the like. If the gas diffusion layer is a metal mesh, its surface may be coated with a precious metal such as platinum. In the membrane electrode assembly shown in Figure 4, the gas diffusion layer 28 is included, but the gas diffusion layer is an arbitrary component and does not necessarily have to be included in the membrane electrode assembly. Furthermore, as described above, the gas diffusion layer may also contain the catalyst mentioned above.

[0101] The film thickness of the anode and cathode is preferably 5 to 100 μm, more preferably 5 to 50 μm, even more preferably 5 to 30 μm, and particularly preferably 5 to 15 μm, independently of each other. The film thickness of the anode and cathode is measured using an image obtained by measuring a cross-section of the film electrode assembly cut in a plane parallel to the film thickness direction with an optical microscope, and is the arithmetic mean value at any 20 locations.

[0102] [Method for Manufacturing Membrane Electrode Assembly] Examples of methods for manufacturing a membrane electrode assembly include forming a catalyst layer on an electrolyte membrane and then sandwiching the resulting assembly between gas diffusion layers, and forming a catalyst layer on a gas diffusion layer to form electrodes (anode, cathode) and sandwiching the electrolyte membrane between these electrodes. Methods for manufacturing the catalyst layer include applying a catalyst layer forming coating solution to a predetermined position on the electrolyte membrane and drying it as needed. Alternatively, a catalyst layer forming coating solution may be applied to a substrate and dried to form the catalyst layer on the substrate, after which the formed catalyst layer is transferred to the electrolyte membrane. The catalyst layer forming coating solution may be a liquid in which a polymer having ion exchange groups and a catalyst are dispersed in a dispersion medium.

[0103] <Applications> The membrane electrode assembly of this disclosure can be used in a water electrolysis apparatus (specifically, a polymer electrolyte water electrolysis apparatus).

[0104] [Water Electrolyzer] The water electrolyzer of the present disclosure includes the membrane electrode assembly described above. Because the water electrolyzer of the present disclosure includes the membrane electrode assembly described above (the electrolyte membrane of the present disclosure), it has excellent durability during electrolysis. The water electrolyzer of the present disclosure may have the same configuration as known water electrolyzers, except that it includes the membrane electrode assembly described above. For example, the water electrolyzer of the present disclosure has a water supply unit that supplies water to the anode catalyst layer and a power supply unit that is electrically connected to the anode catalyst layer and the cathode catalyst layer. In the water electrolyzer of the present disclosure, when a DC voltage is applied by the power supply unit while water is supplied to the anode catalyst layer by the water supply unit, water decomposes on the anode catalyst layer side, generating oxygen and protons. On the cathode catalyst layer side, protons that have moved to the cathode catalyst layer side via the electrolyte membrane gain electrons, generating hydrogen. The water electrolyzer of the present disclosure may also have an oxygen recovery member for recovering the generated oxygen and a hydrogen recovery member for recovering the generated hydrogen.

[0105] The water electrolysis apparatus disclosed herein provides a flow rate of 2 A / cm² when water is electrolyzed. ２ The hydrogen permeability coefficient in is 2.8 × 10⁻⁶. －６ cc・cm / cm ２ It is preferable that it be sec·atm or less, and 2.0 × 10 －６ cc・cm / cm ２ It is more preferable that the temperature is sec·atm or less. Since the water electrolysis apparatus of this disclosure includes the electrolyte membrane of this disclosure, it is thought that the outflow of fluoride ions is reduced, the hydrogen permeability coefficient during water electrolysis is lower, and the durability during electrolysis is improved. The hydrogen permeability coefficient is determined by the method described in the Examples section below.

[0106] [Method for Producing Hydrogen] The method for producing hydrogen according to this disclosure is a method for producing hydrogen by electrolyzing water (electrolyte) using the water electrolysis apparatus described above. With the method for producing hydrogen according to this disclosure, hydrogen can be produced efficiently because the water electrolysis apparatus of this disclosure is used.

[0107] The present disclosure will be described in detail below with reference to examples. Examples 1-3, 6 and 7 are examples, and Examples 4 and 5 are comparative examples. However, the present disclosure is not limited to these examples.

[0108] [Measurement Method] <Raman Spectroscopy> Raman spectroscopy was performed using the method described above to obtain spectral charts, and B1 / A1, B2 / A2, and H2 / H1 were obtained. A LabRAM HR-800 manufactured by Horiba, Ltd. was used as the measuring device. The irradiation light used for Raman spectroscopy was a laser light with a wavelength of 532 nm.

[0109] <Ion exchange capacity of fluorine-containing polymers> After weighing the fluorine-containing polymer after vacuum drying, it is placed in a polycarbonate container and subjected to a 0.7 mol / L NaOH solution (solvent: H2). ２ O / CH ３ Immerse in OH = 10 / 90 (mass ratio) at 60°C for 72 hours or more to obtain -SO in fluorine-containing polymers. ２ The F group was completely converted to the Na salt form. The NaOH solution after immersion was back-titrated with 0.1 mol / L HCl using phenolphthalein as an indicator, and the amount of NaOH in the solution was determined to calculate the ion exchange capacity (milliequivalents / g dry resin). Note that "meq / g" refers to "milliequivalents / g dry resin," which is the unit of ion exchange capacity.

[0110] <Infrared Spectroscopy Measurement> Using the electrolyte membrane obtained in the subsequent procedure as the measurement sample, infrared spectroscopy was performed according to the procedure described above. In the obtained infrared spectrum, the infrared spectrum at 2350 ± 30 cm⁻¹ was observed. －１ Maximum absorbance I ２３５０ 1690 ± 10 cm －１ Maximum absorbance I １６９０ The ratio (I １６９０ / I ２３５０ The following was calculated: For infrared spectroscopy, a Nicolet iS20 FT-IR spectrophotometer manufactured by Thermo Fisher Scientific was used. The measurement conditions were 32 integration cycles and a resolution of 4 cm. －１ That's what I decided.

[0111] From the obtained infrared spectrum, the maximum absorbance I ２３５０ The following procedure was used to calculate the value: 2350 ± 30 cm⁻¹ of the infrared spectrum. －１Absorption in the vicinity is often relatively broad. Therefore, in this specification, 2740 ± 20 cm －１ The point showing the minimum absorbance within the range, and 2070 ± 20 cm －１ The baseline is defined as the line connecting the point showing the minimum absorbance within the range, and from the baseline, 2350 ± 30 cm －１ The difference between the points showing the highest absorbance within the range is the maximum absorbance I. ２３５０ That's what I decided.

[0112] Furthermore, from the obtained infrared spectrum, the maximum absorbance I １６９０ The following procedure was used to calculate the value: First, the measured wavefrequency was 1690 ± 10 cm. －１ At the absorption peak, 1690 cm －１ It is closest to and 1690 cm －１ The point at the wavelength that shows a minimum value on the high wavenumber side, and 1690 cm －１ It is closest to and 1690 cm －１ The baseline was defined as a straight line connecting points at wavelengths showing minimum values ​​on the low wavenumber side. From the above baseline, 1690 ± 10 cm －１ The difference between the points showing the maximum absorbance within the range is called the maximum absorbance I. １６９０ That's what I decided.

[0113] <TQ Value> Using a flow tester (Shimadzu Corporation, CFT-500D) equipped with a nozzle 1 mm in length and 1 mm in inner diameter, particles containing a fluorine-containing polymer after vacuum drying were melt-extruded at an extrusion pressure of 2.94 MPa (gauge pressure) while varying the temperature. The polymer extrusion volume was 100 mm. ３ The TQ value, which is the temperature at which the temperature is measured per second, was calculated.

[0114] <Film thickness of electrolyte membrane during drying> The electrolyte membrane was placed on a dial gauge stand 7002 (manufactured by Mitutoyo Corporation), and the thickness was measured at nine points using a digital gauge 543-250 (manufactured by Mitutoyo Corporation) with a flat terminal of 5 mm in diameter attached to its tip. The arithmetic mean was taken as the film thickness of the electrolyte membrane during drying.

[0115] <Hydrogen Permeation Coefficient during Water Electrolysis> The hydrogen concentration in the gas at the anode of each membrane electrode assembly was measured according to the following procedure, and the hydrogen crossover was evaluated. First, a membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekalt Co., Ltd.) with a thickness of 0.25 mm and a porosity of 60 volume%, and a platinum-plated titanium plate with a straight channel was used as a separator, resulting in an electrode area of ​​16 cm². ２ A membrane electrode assembly was incorporated into the single cell. When the membrane electrode assembly was clamped, it was fastened so that a pressure of 1.3 MPa was applied to the electrode portion. Next, in order to sufficiently hydrate the electrolyte membrane and the fluorine-containing polymer of both electrodes, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 4 hours. After that, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C was supplied to the anode side at a flow rate of 50 mL / min, and while the back pressure was kept at atmospheric pressure for both the anode and cathode, a high-current potentio / galvanostat HCP-803 (manufactured by Biologic) was used to apply 32 A (current density 2 A / cm²). ２ While maintaining the current, a 4-hour water electrolysis was performed as a break-in period. Subsequently, 0-48A (current density 0-3A / cm²) was used. ２ IV (current-voltage) measurements were performed by gradually increasing the current within the specified range. Four IV measurements were taken. Subsequently, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the cell 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 measure 3.2 A (current density 0.2 A / cm²). ２ ) for 11 hours at 8A (current density 0.5A / cm²) ２ ) for 7 hours at 16A (current density 1A / cm²) ２ ) for 4 hours, and 32A (current density 2A / cm²) ２The gas was held at the specified current for 4 hours. After the holding time for each current, water was separated from the gas discharged from the anode side. The hydrogen concentration in the gas on the anode side was then measured using a micro GC (Agilent 490, manufactured by Agilent Corporation), and the hydrogen concentration in the gas at the final measurement point (volume %) was measured (hydrogen content / gas content). From the current and gas concentration at the time of measurement, the amount of hydrogen permeating from the cathode side to the anode side was calculated, and by multiplying this by the film thickness during drying, the result was obtained as 2 A / cm². ２ The hydrogen permeability coefficient of the electrolyte membrane during water electrolysis was calculated at the given current density. Based on the calculated hydrogen permeability coefficient, evaluation was performed according to the following criteria: A+: 2 A / cm ２ The hydrogen permeability coefficient in is 1.5 × 10 －６ Below A: 2A / cm ２ The hydrogen permeability coefficient in is 1.5 × 10 －６ Super 2.0×10 －６ Below B: 2A / cm ２ The hydrogen permeability coefficient in is 2.0 × 10 －６ Super 2.8×10 －６ Below C: 2A / cm ２ The hydrogen permeability coefficient in is 2.8 × 10 －６ Furthermore, the unit of hydrogen permeability coefficient is "cc・cm / cm" ２ It is "sec.atm".

[0116] <Fenton Test> For each example, the electrolyte membrane was cut to approximately 2.5 cm x 2.5 cm and held in a glove box with nitrogen gas flowing through it for 24 hours. Approximately 0.1 g was weighed in the glove box. Then, the electrolyte membrane was immersed in 50 g of Fenton's reagent containing 3% by mass of hydrogen peroxide and 200 ppm of divalent iron ions at 40°C for 16 hours. After removing the electrolyte membrane after immersion, the mass of the Fenton's reagent was measured, the fluoride ion concentration in the Fenton's reagent was measured with an ion meter, and the amount of fluoride ions eluted relative to the total amount of fluoride atoms in the immersed electrolyte membrane was calculated. A: Fluoride ion elution amount is 0.01% by mass or less B: Fluoride ion elution amount is greater than 0.01% by mass and 0.02% or less C: Fluoride ion elution amount is greater than 0.02% by mass

[0117] <Fluorine Release Rate> The fluoride ion concentration in the water discharged from the cathode side of each membrane electrode assembly was measured according to the following procedure, and the fluorine release rate was evaluated. First, a break-in operation was performed in the same manner as the measurement method for the hydrogen permeability coefficient during water electrolysis described above. Then, the water supply rate to the anode catalyst layer was changed to 150 mL / min, and the back pressure was changed to 50 kPa for both the anode and cathode, resulting in a current density of 2 A / cm². ２ The system was operated for 500 hours. Between 300 and 500 hours after the break-in period, wastewater discharged from the cathode catalyst layer was sampled. The amount of fluoride ions contained in this wastewater was quantified by ion chromatography and averaged to calculate the average amount of fluoride ions per unit electrode area and per unit time, and evaluated as the fluorine release rate according to the following criteria. A smaller fluorine release rate indicates that the decomposition of the fluorine-containing polymer is suppressed and the electrolyte membrane has superior durability during electrolysis. In practical terms, an A or B rating is preferable, with an A rating being more preferable. A: 1.0 × 10 －６ mg / (h·cm) ２ ) Less than B: 1.0 × 10 －６ mg / (h·cm) ２ ) Above, 3.0 x 10 －６ mg / (h·cm) ２ ) Less than C: 3.0 x 10 －６ mg / (h·cm) ２ ) That's all.

[0118] <Conductivity> A substrate with four-terminal electrodes arranged at 5 mm intervals was placed in close contact with a 5 mm wide electrolyte membrane. The resistance of the electrolyte membrane H was measured using a known four-terminal method under constant temperature and humidity conditions of 80°C and 50% relative humidity, with AC: 10 kHz and voltage: 1 V, and the conductivity was calculated. The standard dimensions and thickness of the membrane used in the calculation were measured under conditions of 23°C and 50% relative humidity RH. Based on the calculated conductivity, the conductivity was evaluated according to the following criteria. The measured conductivity can be considered an indicator of proton conductivity. For practical purposes, an A or B evaluation of conductivity (proton conductivity) is preferable, with an A evaluation being more preferable. A: Conductivity of 0.1 S / cm or more B: Conductivity of 0.05 S / cm or more and less than 0.1 S / cm C: Conductivity of less than 0.05 S / cm

[0119] [Abbreviations] The manufacturing procedures for the electrolyte membranes in each example are described below. The abbreviations used in the procedures for each example are as follows:

[0120] <Monomers> ・TFE: Tetrafluoroethylene monomer ・m: CF ２ = CFOCF ２ CF (CF ３ ) O (CF ２ ) ２ SO ２ F

[0121]

[0122] <Radical polymerization initiators> ・V-601: Dimethyl 2,2'-azobis (2-methylpropionate) ・AIBN: 2,2'-Azobis (isobutyrinitrile)

[0123] <Solvent> ・HFE-347pc-f: HCF ２ CF ２ OCH ２ CF ３ ・HFC-52-13p:CF ３ (CF ２ ) ４ CF ２ H ・HCFC-225cb: CClF ２ CF ２ CHClF ・HCFC-141b:CH ３CCl ２ F

[0124] [Production of Fluorine-Containing Polymers] <Fluorine-Containing Polymer F1> Fluorine-containing polymer A1 was produced using TFE and the above monomer m, with reference to the description in paragraph 0093 of Japanese Patent Publication No. 5168903. The ion exchange capacity of fluorine-containing polymer A1 was 1.00 meq / g, and the TQ value was 225°C. The ratio of units based on TFE to units based on monomer m was 85:15 in molar ratio.

[0125] <Fluorination Treatment> 20.0 g of powder of fluorine-containing polymer A1 obtained by the above procedure was uniformly dispersed on a PFA petri dish in a nickel reactor and placed in the 1.1 L reactor. Then, a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at -0.01 MPa (gauge pressure), and the reactor was held at 70°C for 2 hours to perform the first fluorination treatment. After the treatment, the gas in the reactor was evacuated, and a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at -0.01 MPa (gauge pressure), and the reactor was held at 70°C for 2 hours to perform the second fluorination treatment. After the treatment, the gas in the reactor was evacuated, and a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at -0.01 MPa (gauge pressure), and the reactor was held at 70°C for 18 hours to perform the third fluorination treatment. After the treatment, the gas in the reactor was evacuated, the polymer was removed, and it was pulverized in a pulverizer. In the procedure described above, the precursor group of the fluorinated sulfonic acid group is -SO ２ A fluorine-containing polymer F1 having an F group was obtained.

[0126] <Fluorine-containing polymer F2> Fluorine-containing polymer A2 was produced using TFE and the above monomer m, with reference to the description in paragraph 0197 of Japanese Patent Publication No. 2015-099772. The ion exchange capacity of fluorine-containing polymer A2 was 1.25 meq / g, and the TQ value was 232°C. The ratio of units based on TFE to units based on monomer m was 78:22 in molar ratio.

[0127] <Fluorination Treatment> 20.0 g of the fluorine-containing polymer A2 powder obtained by the above procedure was uniformly dispersed on a PFA petri dish in a nickel reactor and placed in a 1.1 L reactor. Then, a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at -0.01 MPa (gauge pressure), and the fluorination treatment was carried out by holding it at 70°C for 4 hours. After the treatment, the gas in the reactor was evacuated, the polymer was removed, and it was pulverized in a pulverizer. The precursor group of the sulfonic acid group fluorinated by the above procedure was -SO ２ A fluorine-containing polymer F2 having an F group was obtained.

[0128] <Fluorine-containing polymer F3> Fluorine-containing polymer A3 was produced using TFE and the above monomer m, with reference to the description in paragraph 0200 of Japanese Patent Publication No. 2015-099772. The ion exchange capacity of fluorine-containing polymer A3 was 1.43 meq / g, and the TQ value was 230°C. The ratio of units based on TFE to units based on monomer m was 72:28 in molar ratio.

[0129] <Fluorination Treatment> Except for using fluorine-containing polymer A3 instead of fluorine-containing polymer A2, the fluorination treatment was carried out in the same procedure as for fluorine-containing polymer F2, and the precursor group of the fluorinated sulfonic acid group was -SO ２ A fluorine-containing polymer F3 having an F group was obtained.

[0130] <Fluorine-containing polymer F4> <Fluorination treatment> 20.0 g of powder of fluorine-containing polymer A1 obtained by the above procedure was uniformly dispersed on a PFA petri dish in a nickel reactor and placed in a 1.1 L reactor. Then, a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at 0.15 MPa (gauge pressure), and the reactor was held at 70°C for 4 hours to perform the first fluorination treatment. After the treatment, the gas in the reactor was evacuated, and a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at 0.15 MPa (gauge pressure), and the reactor was held at 70°C for 4 hours to perform the second fluorination treatment. After the treatment, the gas in the reactor was evacuated, the polymer was removed, and it was pulverized in a pulverizer. The precursor group of the sulfonic acid group fluorinated in the above procedure was -SO ２ A fluorine-containing polymer F4 having an F group was obtained.

[0131] <Fluorine-containing polymer F5> <Fluorination treatment> 20.0 g of powder of fluorine-containing polymer A2 obtained by the above procedure was uniformly dispersed on a PFA petri dish in a nickel reactor and placed in a 1.1 L reactor. Then, a mixed gas of 20% fluorine gas and 80% nitrogen gas was introduced into the reactor at 0.15 MPa (gauge pressure), and the fluorination treatment was carried out by holding it at 70°C for 4 hours. After the treatment, the gas in the reactor was evacuated, the polymer was removed, and it was pulverized in a pulverizer. The precursor group of the sulfonic acid group fluorinated by the above procedure was -SO ２ A fluorine-containing polymer F5 having an F group was obtained.

[0132] <Film Manufacturing> [Manufacturing of Film α1] Fluorine-containing polymer F1 was molded by melt extrusion to obtain film α1 (film thickness: 90 μm) made of fluorine-containing polymer F1.

[0133] [Production of film α2] A fluorine-containing polymer F2 was molded by melt extrusion to obtain film α2 (film thickness: 90 μm) made of the fluorine-containing polymer F2.

[0134] [Manufacturing of Film α3] Fluorine-containing polymer F3 was molded by melt extrusion to obtain film α3 (film thickness: 90 μm) made of fluorine-containing polymer F3.

[0135] [Manufacturing of Film α4] Fluorine-containing polymer A2 was molded by melt extrusion to obtain film α4 (film thickness: 90 μm) made of fluorine-containing polymer A2.

[0136] [Manufacturing of Film α5] Fluorine-containing polymer F4 was molded by melt extrusion to obtain film α5 (film thickness: 90 μm) made of fluorine-containing polymer F4.

[0137] [Manufacturing of film α6] Fluorine-containing polymer F5 was molded by melt extrusion to obtain film α6 (film thickness: 90 μm) made of fluorine-containing polymer F5.

[0138] <Manufacture of Electrolyte Membrane> [Example 1] Film α1 as a precursor membrane was immersed in a solution of dimethyl sulfoxide / potassium hydroxide / water = 30 / 5.5 / 64.5 (mass ratio) at 95°C for 30 minutes to hydrolyze the groups in the precursor membrane that can be converted to sulfonic acid type functional groups. After hydrolysis converted the groups in the precursor membrane that can be converted to sulfonic acid type functional groups to K-type sulfonic acid type functional groups, it was washed with water. Then, the obtained membrane was immersed in 1M sulfuric acid to convert the ends of the sulfonic acid type functional groups from K-type to H-type. The obtained membrane (undried membrane) was immersed in water at 100°C for 1 hour to obtain a wet electrolyte membrane (contact heat treatment). With the obtained wet electrolyte membrane fixed around the periphery with a metal restraint frame, the wet electrolyte membrane was dried at a temperature above the softening point of the fluorine-containing polymer (105°C) (drying step) to obtain the electrolyte membrane of Example 1 (dried electrolyte membrane). Furthermore, the wet electrolyte membrane was thoroughly dried until the liquid medium content in the electrolyte membrane was 10% by mass or less. In the above drying process, the dimensional change of the dried electrolyte membrane from the wet electrolyte membrane was -5% or more in both the MD and TD directions.

[0139] [Example 2] An electrolyte membrane of Example 2 was obtained in the same manner as in Example 1, except that film α2 was used as the precursor membrane.

[0140] [Example 3] The electrolyte membrane of Example 3 was obtained in the same manner as in Example 1, except that film α3 was used as the precursor membrane.

[0141] [Example 4] The electrolyte membrane of Example 4 was obtained in the same manner as in Example 1, except that film α4 was used as the precursor membrane.

[0142] [Example 5] An electrolyte membrane for Example 5 was obtained in the same manner as in Example 1, except that film α2 was used as the precursor membrane and the drying process was carried out without fixing the periphery of the wet electrolyte membrane with a metal restraint frame. When obtaining the electrolyte membrane for Example 5 (dry electrolyte membrane), the dimensional change of the dry electrolyte membrane from the wet electrolyte membrane was less than -5% in both the MD and TD directions.

[0143] [Example 6] The electrolyte membrane of Example 6 was obtained in the same manner as in Example 1, except that film α5 was used as the precursor membrane.

[0144] [Example 7] The electrolyte membrane of Example 7 was obtained in the same manner as in Example 1, except that film α6 was used as the precursor membrane.

[0145] <Manufacturing of Membrane Electrode Assembly> A polymer (ion exchange capacity: 1.10 mm equivalent / gram dry resin) obtained by copolymerizing TFE and monomer m, hydrolysis, and acid treatment was dispersed in a water / ethanol = 40 / 60 (mass%) solvent at a solid content concentration of 26.0% to obtain a dispersion (hereinafter also referred to as "dispersion Y"). Ethanol (18.06 g) and Zeolora-H (manufactured by Nippon Zeon) (10.58 g) were added to dispersion Y (33.0 g), and the mixture was mixed at 2,200 rpm for 5 minutes using a rotation-orbit mixer (manufactured by Thinky, Awatori Rentaro). Ethanol (46.44 g) and water (75.75 g) were added to the mixed composition (54.06 g), and further a specific surface area of ​​100 m² containing 74.8 mass% iridium was added. ２ 40.0 g of iridium oxide catalyst (manufactured by Tanaka Kikinzoku Kogyo 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. The anode catalyst ink was then placed on an ETFE sheet at an iridium concentration of 1.0 mg / cm³. 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.

[0146] 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) and mixed and pulverized using an ultrasonic homogenizer to obtain a catalyst dispersion. To the catalyst dispersion, a mixture (29.2 g) was added, which consisted of dispersion Y (20.1 g), ethanol (11 g), and Zeolora-H (manufactured by Nippon Zeon Co., Ltd.) (6.3 g) that had been pre-mixed and kneaded. Furthermore, water (3.66 g) and ethanol (7.63 g) were added to the obtained dispersion and mixed with paint conditioner for 60 minutes to obtain a cathode catalyst ink with a solid content 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 then heat-treated at 150°C for 15 minutes to obtain a platinum content of 0.4 mg / cm². ２A cathode catalyst layer decal was obtained.

[0147] One side of each electrolyte membrane cut to 7.0 cm x 7.0 cm was placed opposite the side with the catalyst layer of a 4.0 cm x 4.0 cm anode catalyst layer decal, and the other side of the electrolyte membrane was placed opposite the side with the catalyst layer of a 4.0 cm x 4.0 cm cathode catalyst layer decal. The two were then bonded by heating and pressing at a press temperature of 160°C for 10 minutes at a pressure of 2.6 MPa. After lowering the temperature to 70°C, the pressure was released and the decals were removed. The ETFE sheets of the anode catalyst layer decal and cathode catalyst layer decal were peeled off, resulting in an electrode area of ​​16 cm². ２ A membrane electrode assembly was obtained. The hydrogen permeability coefficient and fluorine release rate were measured using the obtained membrane electrode assembly. The results are shown in Table 1.

[0148] [Results] The fluorine-containing polymer used for the electrolyte membrane, and the various measurements and evaluation results of the obtained electrolyte membrane are shown in Table 1. In Table 1, the "IR intensity ratio" column shows the I measured by the method described above. １６９０ / I ２３５０ This is shown. In Table 1, the "Raman: B1 / A1" column contains the B1 / A1 values ​​measured using the method described above. Similarly, the "Raman: B2 / A2" column contains the B2 / A2 values ​​measured using the method described above. The "Raman: H2 / H1" column contains the H2 / H1 values ​​measured using the method described above.

[0149]

[0150] From the results shown in Table 1, it is found that the polymer contains a fluorine-containing polymer that includes the unit represented by the above formula (1), and I １６９０ / I ２３５０ The electrolyte membranes of Examples 1 to 3 and Examples 6 to 7, in which the ratio was 0.150 or less and B1 / A1 was 1.05 or more, were confirmed to have excellent durability during electrolysis (evaluation of fluorine release rate). On the other hand, I １６９０ / I ２３５０ The electrolyte membrane in Example 4, where B1 / A1 was greater than 0.150, had poor durability during electrolysis. On the other hand, the electrolyte membrane in Example 5, where B1 / A1 was less than 1.05, had poor durability during electrolysis. １６９０ / I ２３５０The value was within the range of 0.150 or less, which was excellent in the Fenton test but poor in durability during electrolysis. From the results of Examples 1 to 7, in order to improve durability during electrolysis, a fluorine-containing polymer containing the unit represented by the above formula (1) is required, １６９０ / I ２３５０ It is found that the ratio must be 0.150 or less, and B1 / A1 must be 1.05 or more. Furthermore, from a comparison of Example 1 with Example 2 and Example 3, it was confirmed that when the ion exchange capacity is 1.20 to 1.50 milliequivalents / gram dry resin, the conductivity (proton conductivity) of the electrolyte membrane is excellent.

[0151] 10 Electrolyte membrane (solid polymer electrolyte membrane) 12 Cross-section 12A, 12B Direction T Thickness direction a1, a2, a3 Peak area PA, PB Polarization M1 Main chain of fluorine-containing polymer 20 Membrane electrode assembly 22 Anode 24 Cathode 26 Catalyst layer 28 Gas diffusion layer

[0152] Furthermore, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-227387, filed on December 24, 2024, are incorporated herein by reference as disclosure of the present invention.

Claims

1. A solid polymer electrolyte membrane for a water electrolysis device, wherein the solid polymer electrolyte membrane contains a fluorine-containing polymer including a unit represented by the following formula (1), and in an infrared spectrum obtained by measuring the fluorine-containing polymer by infrared spectroscopy, the maximum absorbance I at 2,350 ± 30 cm ２ , －１ with respect to the maximum absorbance I at 1,690 ± 10 cm ２３５０ is 0.150 or less. By Raman spectroscopy, polarized light orthogonal to the thickness direction is irradiated onto a cross-section in the thickness direction of the solid polymer electrolyte membrane to obtain a spectrum chart, and the ratio of the peak area a2 at a Raman shift of 680 to 760 cm －１ to the peak area a1 at a Raman shift of 1,025 to 1,095 cm １６９０ is defined as A1. By Raman spectroscopy, polarized light parallel to the thickness direction is irradiated onto a cross-section in the thickness direction of the solid polymer electrolyte membrane to obtain a spectrum chart, and when the ratio of the peak area b2 at a Raman shift of 680 to 760 cm －１ to the peak area b1 at a Raman shift of 1,025 to 1,095 cm －１ is defined as B1, the ratio of B1 to A1 is 1.05 or more. A solid polymer electrolyte membrane. Formula (1) -[CF －１ -CF(-L-(SO －１ M))]- L is a divalent perfluorohydrocarbon group which may contain an etheric oxygen atom. M is a hydrogen atom, an alkali metal or a quaternary ammonium cation.​​​​ 2. The solid polymer electrolyte membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer is 0.90 to 1.50 milliequivalents / gram dry resin.

3. The solid polymer electrolyte membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer is 1.20 to 1.50 milliequivalents / gram dry resin.

4. The solid polymer electrolyte membrane according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer is 0.90 to 1.20 milliequivalents / gram dry resin.

5. The solid polymer electrolyte membrane according to claim 1, wherein the fluorine-containing polymer further comprises units based on tetrafluoroethylene.

6. The solid polymer electrolyte membrane according to claim 5, wherein the content of the unit represented by formula (1) in the fluorine-containing polymer is 8 to 35 mol% of the total units in the fluorine-containing polymer, and the content of the tetrafluoroethylene-based unit in the fluorine-containing polymer is 65 to 92 mol% of the total units in the fluorine-containing polymer.

7. The solid polymer electrolyte membrane according to claim 1, wherein the thickness of the solid polymer electrolyte membrane is 20 to 150 μm.

8. The solid polymer electrolyte membrane according to claim 1, wherein the amount of fluoride ions eluted in the Fenton test of the solid polymer electrolyte membrane is 0.02% by mass or less relative to the total mass of fluorine atoms in the electrolyte membrane.

9. Raman shift of 920–1025 cm² relative to the peak area a1. －１ Let A2 be the ratio of the peak areas a3, and the Raman shift relative to the peak area b1 be 920-1025 cm². －１ The solid polymer electrolyte membrane according to claim 1, wherein, when the ratio of the peak areas b3 is denoted as B2, the ratio of B2 to A2 is greater than 1.

05.

10. By Raman spectroscopy, a spectral chart is obtained by irradiating a cross-section of the electrolyte membrane in the thickness direction with polarized light perpendicular to the thickness direction, and the Raman shift is 1025–1095 cm. －１ Raman shift of 920–1025 cm for the height h1 of the highest peak in the range －１ Taking H1 as the ratio of the heights h2 of the highest peaks present in the range, a spectral chart is obtained by irradiating the cross-section of the electrolyte membrane in the thickness direction with polarized light parallel to the thickness direction using Raman spectroscopy, and the Raman shift is 1025-1095 cm. －１ Raman shift of 920–1025 cm relative to the height h3 of the highest peak in the range －１ The solid polymer electrolyte membrane according to claim 1, wherein when the ratio of the heights h4 of the highest peaks in the range is taken as H2, the ratio of H2 to H1 is 1.05 or more.

11. A membrane electrode assembly comprising an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane according to any one of claims 1 to 10, disposed between the anode and the cathode.

12. A water electrolysis apparatus comprising the membrane electrode assembly described in claim 11.

13. 2 A / cm² when water is electrolyzed. ２ The hydrogen permeability coefficient in is 2.8 × 10⁻⁶. －６ cc・cm / cm ２ The water electrolysis apparatus according to claim 12, wherein the temperature is less than or equal to sec·atm.

14. A method for producing hydrogen, comprising producing hydrogen by electrolyzing water using the water electrolysis apparatus described in claim 12.

15. A method for producing a solid polymer electrolyte film, comprising copolymerizing a fluorine-containing olefin with a monomer represented by the following formula (2) having a group that can be converted to a sulfonic acid type functional group, then contacting the copolymer with a gas containing 5% to 40% by volume of fluorine gas to form a film of the resulting polymer to obtain a precursor film, then contacting the precursor film with an alkaline aqueous solution to obtain a wet solid polymer electrolyte film in which the group that can be converted to a sulfonic acid type functional group has been converted to a sulfonic acid type functional group, and then drying the wet solid polymer film while constraining its periphery, or drying the wet solid polymer film while fixing its periphery, to obtain the solid polymer electrolyte film according to any one of claims 1 to 10. Formula (2) CF ２ =CF-L-A L is a divalent perfluorohydrocarbon group which may contain an etheric oxygen atom. A is a group which can be converted to a sulfonic acid type functional group.

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