Porous separator for alkaline water electrolysis, alkaline water electrolysis member using same, alkaline water electrolysis cell, alkaline water electrolysis device, and hydrogen production method

Abstract

Provided are: a porous separator which is for alkaline water electrolysis and satisfies <Condition I> below; an alkaline water electrolysis member using the same; an alkaline water electrolysis cell; an alkaline water electrolysis device; and a hydrogen production method. <Condition I> The porous separator for alkaline water electrolysis has a thickness unevenness of 15% or less, obtained by immersing the separator in a 90°C 7 mol / L KOH aqueous solution and treating the separator under a pressurizing condition of 5 MPa for 60 minutes.

Description

Porous separator for alkaline water electrolysis, alkaline water electrolysis component using the same, alkaline water electrolysis cell, alkaline water electrolysis device, and method for producing hydrogen

[0001] The present invention relates to a porous separator for alkaline water electrolysis, an alkaline water electrolysis member using the same, an alkaline water electrolysis cell, an alkaline water electrolysis apparatus, and a method for producing hydrogen.

[0002] Hydrogen is a clean energy source that does not emit carbon dioxide and is used, for example, as a fuel for fuel cell vehicles and household fuel cells. Alkaline water electrolysis, which uses a highly concentrated alkaline aqueous solution as the electrolyte, is a well-known method for producing hydrogen. Alkaline water electrolysis, powered by a renewable energy power generation system, can produce hydrogen without emitting carbon dioxide. Therefore, hydrogen is increasingly attracting attention as a fundamental energy source for a sustainable society.

[0003] In alkaline water electrolysis, hydrogen bubbles (2H ２ O + 2e － →H ２ +2OH － ) to the anode side, and also prevents the bubble-like oxygen (4OH) generated at the anode (positive electrode). － →O ２ +2H ２ O+4e － In order to prevent OH from migrating to the cathode side, a gas barrier separator (membrane) is placed between the cathode and the anode. In addition to the gas barrier properties, this separator also has the function of preventing OH from migrating from the cathode side to the anode side. － The separator used in alkaline water electrolysis is therefore a porous membrane (microporous membrane) made of an organic polymer material.

[0004] Porous separators used in alkaline water electrolysis can be formed by wet phase separation. In wet phase separation, a dope solution is prepared by dissolving an organic polymer, which is a constituent material of the porous membrane, in a solvent (good solvent) that dissolves the organic polymer. A coating of the dope solution is then formed. The coating is then immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer but is compatible (miscible) with the good solvent. This immersion reduces the proportion of the good solvent in the coating, causing phase separation between the organic polymer and the solvent, resulting in gelation (coagulation) of the organic polymer, resulting in the formation of a porous membrane. To enhance the mechanical strength of the porous separator, a porous support, such as a nonwoven fabric or woven fabric, is placed in the dope solution. The phase separation is then carried out in the presence of the porous support, resulting in the organic polymer in the impregnated dope solution forming a porous structure. This results in a porous separator in which the porous support and the porous structure of the organic polymer are integrated. Furthermore, by including hydrophilic inorganic particles in the separator, the gas barrier properties can be improved, and the alkaline aqueous solution can be efficiently permeated into the separator, thereby further increasing the ionic conductivity.

[0005] As such a porous separator, for example, Patent Document 1 describes a separator including a porous support and first and second porous layers provided on one and the other sides of the porous support, where the porous support has a thickness of 150 μm or less, the separator has a thickness of less than 250 μm, and the porous layers may contain hydrophilic inorganic particles.

[0006] Special Publication No. 2023-531792

[0007] In recent years, with a view to improving the efficiency of hydrogen production and making alkaline water electrolysis systems suitable for renewable energy, research and development has been progressing on high-pressure alkaline water electrolysis systems (also referred to as "pressurized alkaline water electrolysis systems" because they are operated under a pressure of 10 bar or more compared to atmospheric pressure (approximately 1 bar)). However, studies by the present inventors have revealed that when the separator described in Patent Literature 1 is used in a pressurized alkaline water electrolysis system to perform alkaline water electrolysis under pressure, a problem occurs in that the electrolysis voltage increases. As a result of repeated studies by the present inventors on this problem, it has been found that the application of pressure causes thickness unevenness in the separator, and that this thickness unevenness traps air bubbles in recessed surface portions, resulting in an increase in the initial resistance. Furthermore, it has been found that continued operation under pressure causes deterioration due to heat generation, oxidation, etc. in the portions where air bubbles are trapped, accelerating separator deterioration and further increasing the electrolysis voltage.

[0008] An object of the present invention is to provide a porous separator for alkaline water electrolysis that, when used as a separator for pressurized alkaline water electrolysis, can suppress an increase in initial resistance (electrolysis voltage) due to pressurization and also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions. Another object of the present invention is to provide an alkaline water electrolysis member, an alkaline water electrolysis cell, an alkaline water electrolysis apparatus, and a method for producing hydrogen, all of which use the porous separator for alkaline water electrolysis of the present invention.

[0009] The above-described problems of the present invention have been solved by the following means. [1] A porous separator for alkaline water electrolysis that satisfies the following <Condition I>. <Condition I>: The thickness unevenness of the separator obtained by immersing the porous separator for alkaline water electrolysis in a 7 mol / L KOH aqueous solution at 90°C and treating it under a pressurized condition of 5 MPa for 60 minutes is 15% or less. [2] The porous separator for alkaline water electrolysis according to [1], which comprises a porous support and a porous material that is disposed on at least one of the outer surface and voids of the porous support and that contains an organic polymer and hydrophilic inorganic particles, and the porous material has an inorganic particle concentration of 50 vol% or more. [3] The porous separator for alkaline water electrolysis according to [1] or [2], which comprises a porous support and a porous material that is disposed on at least one of the outer surface and voids of the porous support and that contains an organic polymer and hydrophilic inorganic particles, and the thickness of the porous separator for alkaline water electrolysis is 210 µm or less. [4] The porous separator for alkaline water electrolysis according to any one of [1] to [3], comprising a porous support and a porous material comprising an organic polymer and hydrophilic inorganic particles disposed on at least one of the outer surface and pores of the porous support, wherein the organic polymer has a storage modulus of 850 MPa or more at 90°C. [5] The porous separator for alkaline water electrolysis according to [1], comprising a porous material comprising an organic polymer and not including a porous support. [6] An alkaline water electrolysis member comprising the porous separator for alkaline water electrolysis according to any one of [1] to [5]. [7] An alkaline water electrolysis cell comprising the porous separator for alkaline water electrolysis according to any one of [1] to [5] or the alkaline water electrolysis member according to [6]. [8] An alkaline water electrolysis apparatus comprising the alkaline water electrolysis cell according to [7]. [9] A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to [8] at a pressure of 10 bar or more.

[10] A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to [8] by applying a pressure of 5 bar or more from the hydrogen generation side to the oxygen generation side.

[0010] In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] When used as a separator for pressurized alkaline water electrolysis, the porous separator for alkaline water electrolysis of the present invention can suppress a pressurized increase in initial resistance (electrolysis voltage) and can also suppress a temporal increase in electrolysis voltage due to operation under pressurized conditions. Furthermore, when used as a component for pressurized alkaline water electrolysis, the alkaline water electrolysis member of the present invention can suppress a pressurized increase in initial resistance (electrolysis voltage) and can also suppress a temporal increase in electrolysis voltage due to operation under pressurized conditions. Furthermore, the alkaline water electrolysis cell and alkaline water electrolysis device of the present invention can suppress both a pressurized increase in initial resistance (electrolysis voltage) and a pressurized increase in electrolysis voltage. Furthermore, according to the hydrogen production method of the present invention, hydrogen can be efficiently produced using the alkaline water electrolysis device of the present invention.

[0012] Fig. 1 is a diagram schematically illustrating an embodiment of an alkaline water electrolysis system, Fig. 2 is a diagram schematically illustrating another embodiment of an alkaline water electrolysis system, and Fig. 3 is a diagram schematically illustrating yet another embodiment of an alkaline water electrolysis system.

[0013] [Porous separator for alkaline water electrolysis] The porous separator for alkaline water electrolysis of the present invention is a porous separator that satisfies the following <Condition I>. <Condition I> The porous separator for alkaline water electrolysis is immersed in a 7 mol / L KOH aqueous solution at 90°C and treated under a pressure of 5 MPa for 60 minutes, resulting in a separator with a thickness variation of 15% or less. The porous separator for alkaline water electrolysis to be treated (pressure treatment) as specified in <Condition I> above is immersed in pure water at 25°C overnight before use. The thickness variation of the separator is measured and calculated as follows. The separator that has been subjected to the pressure alkali treatment as specified in <Condition I> above is dried, and a cross-section is cut out using a razor. A cross-sectional SEM (scanning electron microscope) image is obtained at a magnification (e.g., 400x) that fits the entire separator cross-section in one field of view. In the obtained cross-sectional SEM image, the thickness was measured at 20-point intervals, and the arithmetic mean, maximum value, and minimum value were determined from the obtained 20 measurement values. The thickness unevenness X was calculated using the following formula: Thickness unevenness X = {(maximum value - minimum value) / arithmetic mean value} × 100 (unit: %). The arithmetic mean value of five thickness unevenness X values ​​obtained using five cross-sectional SEM images with different fields of view was defined as the "thickness unevenness." Other detailed conditions can be applied as described in the Examples below. The porous separator for alkaline water electrolysis of the present invention is a porous separator suitable for use in alkaline water electrolysis. This separator has the desired gas barrier properties and hydroxy ion permeability as basic properties for alkaline water electrolysis. The porous separator for alkaline water electrolysis of the present invention may be used as a separator for alkaline water electrolysis operated under any pressure condition from normal pressure to pressurized pressure. The effects of the porous separator for alkaline water electrolysis of the present invention are particularly evident when used as a separator for pressurized alkaline water electrolysis operated under pressurized conditions. Pressurized alkaline water electrolysis refers to alkaline water electrolysis performed under pressurized conditions of 10 bar or more.

[0014] The reasons why the use of the porous separator for alkaline water electrolysis of the present invention as a separator for pressurized alkaline water electrolysis can suppress an increase in initial resistance (electrolysis voltage) due to pressurization and also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions are thought to be as follows: Conventional porous separators such as those described in Patent Document 1 have porous layers formed on both sides of a porous support, each of which is made of a porous material containing an organic polymer and hydrophilic inorganic particles. Furthermore, because they are formed by a wet phase separation method, voids in the porous support (gaps between the fibers, metal, and ceramic constituting the porous support) are also filled with the porous material. In a pressurized alkaline water electrolysis system, pressure is applied, and therefore pores in the porous material are crushed by the pressure, while the fibers, metal, and ceramic constituting the porous support themselves are hardly deformed. When viewed in the thickness direction, the porous separator has a portion where the fibers, metal, or ceramic constituting the porous support are present and where a porous material is present on the outer surface of the porous support, and a portion where the fibers, metal, or ceramic constituting the porous support are not present and where the porous material is present. This is thought to result in different compressibility rates under pressure depending on the location of the porous separator, resulting in thickness unevenness. As a result, conventional porous separators suffer from significant thickness unevenness when an alkaline water electrolysis cell is operated under pressure, and oxygen gas and hydrogen gas bubbles are trapped in depressions on the separator surface caused by this thickness unevenness, which is thought to increase the initial resistance (electrolysis voltage) due to pressure and also cause an increase in the electrolysis voltage over time during operation under pressure. In contrast, the porous separator for alkaline water electrolysis of the present invention has thickness unevenness of the separator caused by the pressurized alkaline treatment specified in the above <Condition I> suppressed to 15% or less. Therefore, thickness unevenness is unlikely to occur even when the separator is incorporated into a pressurized alkaline water electrolysis system and the electrolysis cell is operated under pressure (under a pressure of 10 bar or more). As a result, it is believed that it is possible to effectively suppress the increase in initial resistance (electrolysis voltage) due to pressurization and the increase in electrolysis voltage over time due to operation under pressurized conditions.

[0015] The thickness unevenness specified by the above <Condition I> is preferably 12% or less, more preferably 9% or less, and even more preferably 5% or less, from the viewpoint of further suppressing an increase in initial resistance (electrolysis voltage) due to pressurization and an increase in electrolysis voltage over time due to operation under pressurized conditions. The practical lower limit of the thickness unevenness specified by the above <Condition I> is usually 1% or more.

[0016] The specific configuration of the porous separator for alkaline water electrolysis of the present invention is not particularly limited, as long as it satisfies the above <Condition I> and has the desired gas barrier properties and hydroxy ion permeability required of a porous separator for alkaline water electrolysis. Examples of the configuration include the following. For example, when the porous separator for alkaline water electrolysis of the present invention is configured to include a porous support and a porous material containing an organic polymer and hydrophilic inorganic particles, which is disposed on at least one of the outer surface and pores of the porous support, the porous separator for alkaline water electrolysis can be configured to satisfy the above <Condition I> by adjusting the type of organic polymer constituting the porous material, the inorganic particle concentration in the porous material, and the thickness of the porous separator for alkaline water electrolysis. The "outer surface of the porous support" refers to the surface of the porous support when viewed as a membrane having a single thickness from a macroscopic perspective, and the "pores of the porous support" refer to the gaps between the fibers, metal, and ceramic constituting the porous support. The structure in which a porous material containing an organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of a porous support can be appropriately adjusted within a range in which the separator for alkaline water electrolysis has the desired gas barrier properties and ionic conductivity. For example, the porous material may be disposed only on the outer surface of the porous support. In this case, the porous material may be disposed on only one side of the porous support, or on both sides. The porous material may also be disposed only in the pores of the porous support. Furthermore, the porous material may be disposed in part of the outer surface and in part of the pores of the porous support. In the present invention, such a configuration is also included in the structure in which a porous material containing an organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of a porous support. Among these, a structure in which the porous material is disposed on the entire outer surface and in all the pores of the porous support is preferred.When the porous separator for alkaline water electrolysis of the present invention has a structure in which a woven fabric support is used as the porous support and a porous material containing an organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of the woven fabric support, properties that satisfy the above <Condition I> can be achieved, for example, by Production Method I in the production method for a porous separator for alkaline water electrolysis of the present invention described below. Specifically, a porous separator for alkaline water electrolysis that satisfies the above <Condition I> can be obtained by satisfying at least one of the following requirements (A-1) to (A-3). In particular, from the viewpoint of further suppressing the thickness unevenness specified in the above <Condition I>, it is preferable to satisfy at least two of the following requirements (A-1) to (A-3), more preferably to satisfy at least two of the following requirements (A-1) to (A-3) including (A-2), and even more preferably to satisfy all of the following requirements (A-1) to (A-3). The effects of these configurations of the porous separator for alkaline water electrolysis of the present invention are generally more pronounced when used as a porous separator for pressurized alkaline water electrolysis. (A-1): The inorganic particle concentration in the porous material is 50% by volume or more. (A-2): The thickness of the porous separator for alkaline water electrolysis is 210 μm or less. (A-3): The storage modulus of the organic polymer at 90°C is 850 MPa or more. Furthermore, even when the porous separator for alkaline water electrolysis of the present invention is configured using a porous material containing an organic polymer and does not include a porous support, it can still satisfy the above-mentioned <Condition I>. A porous separator for alkaline water electrolysis of the present invention that is configured using a porous material containing an organic polymer and does not include a porous support can be obtained, for example, by Production Method II in the production method for a porous separator for alkaline water electrolysis of the present invention described below. The effects of this configuration of the porous separator for alkaline water electrolysis of the present invention are generally more pronounced when used as a porous separator for pressurized alkaline water electrolysis. The porous support, porous material, and the organic polymer and hydrophilic inorganic particles that are constituent materials of the porous material are described in detail below. The above (A-1) to (A-3) are also described in detail below.

[0017] (Porous Support) The porous support is not particularly limited as long as it is applicable to a porous separator for alkaline water electrolysis. For example, a porous support selected from a porous cloth, a porous metal plate, and a porous ceramic plate can be used. The aperture ratio of the porous support is preferably 30 to 80%, more preferably 40 to 70%. The aperture ratio is the ratio of the area of ​​voids to a unit area when the porous support is viewed in a plane. The porous support is preferably a porous cloth, more preferably a porous polymer cloth. The porous polymer cloth is a woven fabric or a nonwoven fabric.

[0018] The polymer constituting the porous polymer fabric is not particularly limited, and examples thereof include polypropylene, polyethylene, polysulfone, polyphenylene sulfide, polyamide, polyethersulfone, polyphenylsulfone, polyethylene terephthalate, polyetheretherketone, sulfonated polyetheretherketone, monochlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene or chlorotrifluoroethylene, polyimide, polyetherimide, m-aramid, etc. Among the above, the polymer constituting the porous polymer fabric preferably contains at least one of polypropylene, polyphenylene sulfide, and polyetheretherketone, and more preferably contains at least one of polyphenylene sulfide and polyetheretherketone.

[0019] The thickness of the porous support is preferably 30 to 150 μm, more preferably 30 to 100 μm, and even more preferably 30 to 75 μm. The thickness of the porous support is a value measured using a constant pressure thickness measuring device in accordance with JIS (Japanese Industrial Standards) K6250 (2019). The thickness of the porous support in the porous separator for alkaline water electrolysis can be measured and calculated by the above-mentioned method after removing the porous support from the porous separator for alkaline water electrolysis using a solvent that dissolves the organic polymer contained in the porous material.

[0020] (Porous material) The porous material is disposed on at least one of the outer surface and pores of the porous support, and has the function of blocking permeation of hydrogen gas and oxygen gas and allowing permeation of hydroxy ions. When the porous separator for alkaline water electrolysis of the present invention does not contain a porous support, the porous separator for alkaline water electrolysis of the present invention is made of a porous material containing an organic polymer and has the function of blocking permeation of hydrogen gas and oxygen gas and allowing permeation of hydroxy ions. The porous material contains at least an organic polymer and may further contain other components such as hydrophilic inorganic particles.

[0021] - Organic Polymer - As the organic polymer contained in the porous material, various organic polymers applicable to the wet phase separation described below can be used.

[0022] The organic polymer can be selected from, for example, fluororesins, olefin resins, polyester resins, aromatic hydrocarbon resins, etc. The fluororesins are preferably resins selected from polyvinylidene fluoride and polytetrafluoroethylene. The olefin resins are preferably polypropylene resins. The polyester resins are preferably resins selected from polyethylene terephthalate, polybutylene terephthalate, and polybutylene naphthalate. The aromatic hydrocarbon resins are preferably polystyrene resins.

[0023] Other preferred organic polymers include polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamideimide.

[0024] The organic polymers may be used alone or in combination of two or more.

[0025] The organic polymer more preferably contains at least one of polyvinylidene fluoride, polysulfone, polyethersulfone, and polyphenylsulfone, and further preferably contains at least one of polysulfone, polyethersulfone, and polyphenylsulfone.

[0026] The storage modulus of the organic polymer at 90°C may be, for example, 750 MPa or more, preferably 800 MPa or more, and as defined in the above-mentioned (A-3), more preferably 850 MPa or more, and even more preferably 900 MPa or more. There is no particular limitation on the upper limit, and for example, it is preferably 4000 MPa or less, more preferably 2000 MPa or less, and even more preferably 1500 MPa or less. That is, preferred ranges include 750 to 4000 MPa, more preferably 800 to 2000 MPa, even more preferably 850 to 2000 MPa, and particularly preferably 900 to 1500 MPa. The storage modulus at 90°C was measured using a cone-plate rheometer by increasing the temperature from 30°C (measurement start temperature) at a rate of 10°C / min to 150°C (measurement end temperature). ２ The storage modulus is a value obtained by measuring in an ambient atmosphere. Note that the storage modulus of an organic polymer contained in a porous material constituting a porous separator for alkaline water electrolysis can be measured by eluting and extracting the organic polymer from the porous separator for alkaline water electrolysis using a solvent (both solvents) in which the organic polymer dissolves, removing inorganic particles using a filter, and then drying the resulting solution to prepare a measurement sample. Details are as described in the Examples below.

[0027] The mass average molecular weight (Mw) of the organic polymer is not particularly limited. Taking into consideration the handleability of the dope solution described below and the mechanical strength of the resulting porous separator for alkaline water electrolysis, it can be, for example, 10,000 to 500,000, and preferably 20,000 to 300,000. Mw can be determined under the following conditions. Apparatus: HLC-8220GPC (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI (Refractive Index) detector) Precolumn: TSKGUARDCOLUMN HXL-L 6 mm x 40 mm (manufactured by Tosoh Corporation) Sample side columns: The following three columns were directly connected in order (all manufactured by Tosoh Corporation): TSK-GEL GMHXL 7.8 mm x 300 mm TSK-GEL G4000HXL 7.8 mm x 300 mm TSK-GEL G2000HXL 7.8 mm x 300 mm Reference side column: TSK-GEL G1000HXL 7.8 mm x 300 mm Thermostatic bath temperature: 40°C Mobile phase: THF (tetrahydrofuran) Sample side mobile phase flow rate: 1.0 mL / min Reference side mobile layer flow rate: 1.0 mL / min Sample concentration: 0.1 mass% Sample injection amount: 100 μL Data collection time: 5 to 45 minutes after sample injection Sampling pitch: 300 milliseconds

[0028] The content of the organic polymer in the porous material is preferably from 5 to 50% by mass, more preferably from 5 to 40% by mass, even more preferably from 7 to 30% by mass, and particularly preferably from 9 to 25% by mass.

[0029] - Hydrophilic Inorganic Particles - The porous material may contain hydrophilic inorganic particles, preferably particles selected from metal oxides and metal hydroxides.

[0030] The metal oxide is preferably selected from the group consisting of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide and magnesium oxide.

[0031] The metal hydroxide is preferably selected from the group consisting of zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide and magnesium hydroxide.

[0032] As the hydrophilic inorganic particles, in addition to particles selected from metal oxides and metal hydroxides, barium sulfate particles can also be used.

[0033] The hydrophilic inorganic particles may be used alone or in combination of two or more kinds.

[0034] The particle size of the hydrophilic inorganic particles is preferably 0.05 to 2.00 μm, more preferably 0.1 to 1.50 μm, even more preferably 0.15 to 1.00 μm, and still more preferably 0.20 to 1.00 μm. This particle size is the median diameter (D50), which means the particle size at 50% cumulative when the total volume of the particles is taken as 100% in the cumulative distribution measured by a laser diffraction / scattering method.

[0035] When the porous material contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the porous material is preferably 50 to 95 mass%, more preferably 60 to 95 mass%, still more preferably 70 to 93 mass%, and particularly preferably 75 to 91 mass%.

[0036] When the porous material contains hydrophilic inorganic particles, the inorganic particle concentration of the porous material is typically 35 vol% or more, preferably 40 vol% or more, more preferably 45 vol% or more, and even more preferably 50 vol% or more, as defined in (A-1) above. There is no particular upper limit, and for example, 85 vol% or less is preferred, 75 vol% or less is more preferred, and 65 vol% or less is even more preferred. That is, preferred ranges include 35 to 85 vol%, more preferably 40 to 75 vol%, even more preferably 45 to 65 vol%, and particularly preferably 50 to 65 vol%. The "inorganic particle concentration of the porous material" refers to the concentration (unit: vol%) of all inorganic particles contained in the porous material. The inorganic particle concentration of the porous material can be calculated by scraping the porous material from the porous separator, collecting the porous material other than the porous support, quantifying the weight of the organic material and the inorganic material (inorganic particles) by thermal analysis, and using the densities of the organic and inorganic materials described in publicly available documents. Details are as described in the Examples below.

[0037] When the porous material contains hydrophilic inorganic particles, the ratio of the content of the hydrophilic inorganic particles to the content of the organic polymer in the porous material (hydrophilic inorganic particles / organic polymer) is preferably 10 / 1 to 1 / 1, more preferably 9 / 1 to 2 / 1, even more preferably 8 / 1 to 3 / 1, still more preferably 7 / 1 to 4 / 1, and still more preferably 6.5 / 1 to 4 / 1, by mass.

[0038] When the porous separator for alkaline water electrolysis of the present invention is produced by the method for producing a porous separator for alkaline water electrolysis of the present invention described below, a certain amount of good solvent, which will be described later in relation to the dope solution, inevitably remains in the porous material. As a result, the total content of the good solvent in the porous material is usually 0.01 to 5.00 mass%.

[0039] The thickness of the porous separator for alkaline water electrolysis of the present invention may typically be 600 μm or less, preferably 300 μm or less, and more preferably 210 μm or less, as specified in (A-2) above. When the porous separator for alkaline water electrolysis of the present invention is made of a porous material containing an organic polymer and does not include a porous support, the thickness is more preferably 210 μm or less. The lower limit of the thickness of the porous separator for alkaline water electrolysis of the present invention may typically be 30 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. That is, a preferred range includes 30 to 600 μm, more preferably 50 to 300 μm, and even more preferably 100 to 210 μm. The thickness is determined by taking a cross-sectional SEM (scanning electron microscope) image of a cross-section cut out of a porous separator for alkaline water electrolysis with a razor at a magnification (e.g., 400x) such that the separator cross-section fits in a single field of view, measuring the thickness at 20 intervals in the obtained cross-sectional SEM image, assuming that no pores are present (i.e., that the pores are filled with an organic polymer). The thickness is the arithmetic mean of 20 measured values. The porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 30 to 600 μm and a thickness variation of 1 to 12% as specified in <Condition I>, preferably a thickness of 30 to 600 μm and a thickness variation of 1 to 9%, and more preferably a thickness of 30 to 600 μm and a thickness variation of 1 to 5%. The porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 50 to 300 μm and a thickness variation of 1 to 12% as specified in the above <Condition I>, preferably a thickness of 50 to 300 μm and a thickness variation of 1 to 9% as specified in the above <Condition I>, and preferably a thickness of 50 to 300 μm and a thickness variation of 1 to 5% as specified in the above <Condition I>. Furthermore, the porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 100 to 210 μm and a thickness variation of 1 to 12% as specified in the above <Condition I>, preferably a thickness of 100 to 210 μm and a thickness variation of 1 to 9% as specified in the above <Condition I>, and preferably a thickness of 100 to 210 μm and a thickness variation of 1 to 5% as specified in the above <Condition I>.

[0040] From the viewpoint of the gas barrier properties required of porous separators for alkaline water electrolysis, the porous separator for alkaline water electrolysis of the present invention preferably has a bubble point of more than 1 bar, and more preferably more than 2 bar. The pore size and porosity of the pores in the porous separator for alkaline water electrolysis of the present invention may be adjusted to ranges that satisfy the above-mentioned bubble point. The bubble point is measured using a perm porometer based on the bubble point test method described in ASMT (American Society for Testing and Materials) F316-86, and the pressure at which the first bubble appears in the obtained wetting curve is defined as the bubble point. Details are as described in the Examples below.

[0041] The pore size of the pores in the porous separator for alkaline water electrolysis of the present invention is preferably 10 to 1,000 nm, more preferably 20 to 700 nm, and even more preferably 30 to 500 nm, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier properties. This pore size is determined as the average value of the pore size distribution obtained from an insertion curve obtained by mercury intrusion porosimetry.

[0042] The porosity of the porous separator for alkaline water electrolysis of the present invention is preferably 30 to 70%, more preferably 40 to 60%, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier property. This porosity is a value calculated from an insertion curve obtained by mercury intrusion porosimetry.

[0043] In view of the hydroxy ion permeability required for a porous separator for alkaline water electrolysis of the present invention, the ionic resistance of the porous separator for alkaline water electrolysis of the present invention is 0.01 to 0.30 Ω cm ２ is preferably 0.01 to 0.15 Ω cm ２ The ionic resistance is a value measured by setting a circular punched porous separator for alkaline water electrolysis of the present invention in a cell and measuring it by an AC impedance method at 90°C. Details are as described in the Examples below.

[0044] The porous separator for alkaline water electrolysis of the present invention has a water permeability of 100 to 2000 mL / (h m) from the viewpoint of the mass balance between the cathode side and the anode side of the electrolyte required for the porous separator for alkaline water electrolysis. ２ From the viewpoint that it is not necessary to devise an operation of the alkaline water electrolysis cell such as changing the amount of electrolyte permeated on the anode side and the cathode side, it is preferable that the electrolysis capacity is 100 to 1000 mL / (h m ２ The water permeation rate is a value calculated by measuring the amount of liquid (mL) when a circular punched-out porous separator for alkaline water electrolysis of the present invention is set in a filter holder and a 30 mass% aqueous potassium hydroxide solution is allowed to pass through the circular separator for 30 seconds under conditions of 90°C and a gauge pressure of 1 bar. Details are as described in the Examples below.

[0045] The porous separator for alkaline water electrolysis of the present invention can be preferably used as a separator in a pressurized alkaline water electrolysis system (pressurized alkaline water electrolysis separator). The porous separator for alkaline water electrolysis of the present invention can also be used as a separator in an alkaline water electrolysis system used under normal pressure (alkaline water electrolysis separator). The porous separator for alkaline water electrolysis of the present invention may be in the form of a long sheet wound into a roll, or may be pre-cut into a predetermined shape depending on the intended use, device, etc. The porous separator for alkaline water electrolysis of the present invention may be stored immersed in a storage solution such as pure water. The porous separator for alkaline water electrolysis of the present invention may also be stored as a dried film without being immersed in a storage solution.

[0046] [Method for producing porous separator for alkaline water electrolysis] The method for producing the porous separator for alkaline water electrolysis of the present invention is not particularly limited. Typically, the porous separator for alkaline water electrolysis of the present invention is produced by a method comprising forming a porous material by wet phase separation. For example, a method comprising forming the porous material by wet phase separation in a state in which the woven fabric support is disposed in a coating film formed from a dope solution containing the organic polymer dissolved therein (hereinafter referred to as "Production Method I") is included. This process results in a porous separator for alkaline water electrolysis of the present invention, in which a porous material containing at least an organic polymer is disposed on at least one of the outer surface and pores of the woven fabric support. Another example is a method comprising forming the porous material by wet phase separation, in which the porous material is formed by casting a membrane-forming solution containing the organic polymer dissolved therein onto a release film, and then performing liquid-induced phase separation on the coating film in a state in which the release film is peeled off (hereinafter referred to as "Production Method II"). This process results in a porous separator for alkaline water electrolysis of the present invention, which is composed of a porous material containing at least an organic polymer and does not include a porous support.

[0047] (Dope solution) The dope solution may be a solution of an organic polymer that is a constituent material of the porous material, and may contain an organic polymer and a solvent, and may further contain hydrophilic inorganic particles. The organic polymer contained in the dope solution may be the same as that described above for the organic polymer in the porous separator for alkaline water electrolysis. Furthermore, the hydrophilic inorganic particles that may be contained in the dope solution may be the same as that described above for the hydrophilic inorganic particles in the porous separator for alkaline water electrolysis.

[0048] The dope solution used in the wet phase separation may be any solvent (good solvent) capable of dissolving the organic polymer, and is preferably miscible with water. The solvent is preferably selected from the group consisting of N-methyl-pyrrolidone (NMP), N-ethyl-pyrrolidone (NEP), N-butyl-pyrrolidone (NBP), N,N-dimethylformamide (DMF), formamide, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), acetonitrile, and mixtures thereof, with at least one of NMP and NBP being more preferred.

[0049] When the dope solution contains hydrophilic inorganic particles, the content of the solvent in the dope solution is preferably 20 to 95% by mass, more preferably 25 to 90% by mass, even more preferably 30 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 32 to 60% by mass, and even more preferably 35 to 50% by mass. When the dope solution does not contain hydrophilic inorganic particles, the content of the solvent in the dope solution is preferably 20 to 95% by mass, more preferably 25 to 90% by mass, even more preferably 30 to 80% by mass, even more preferably 40 to 80% by mass, even more preferably 45 to 75% by mass, and even more preferably 50 to 75% by mass.

[0050] - Organic Polymer - When the dope solution contains hydrophilic inorganic particles, the content of the organic polymer in the dope solution is preferably 2 to 30 mass %, more preferably 4 to 20 mass %, even more preferably 5 to 15 mass %, and still more preferably 6 to 15 mass %. When the dope solution does not contain hydrophilic inorganic particles, the content of the organic polymer in the dope solution is preferably 2 to 30 mass %, more preferably 4 to 30 mass %, even more preferably 6 to 25 mass %, and still more preferably 8 to 20 mass %.

[0051] - Hydrophilic inorganic particles - Hydrophilic inorganic particles are particles that are dispersed in the dope solution without dissolving, and such a dispersion state is also referred to as the dope solution in the present invention. In other words, the "solution" in the dope solution means that the organic polymer is dissolved in the solvent. When the dope solution contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the dope solution is preferably 20 to 95% by mass, more preferably 25 to 92% by mass, even more preferably 30 to 90% by mass, and particularly preferably 35 to 88% by mass.

[0052] Other Components The dope solution may contain components (other components) other than the components described above (solvent, organic polymer, and hydrophilic inorganic particles). For example, in order to control pore formation during wet phase separation, other components may include polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohol, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, calcium chloride, magnesium chloride, and lithium chloride. When the dope solution contains other components and hydrophilic inorganic particles, the total content of the other components in the dope solution is preferably 0.1 to 15% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 5% by mass. When the dope solution contains other components but does not contain hydrophilic inorganic particles, the total content of the other components in the dope solution is preferably 1 to 25 mass%, more preferably 5 to 25 mass%, and even more preferably 7 to 20 mass%.

[0053] <Formation of Porous Material by Wet Phase Separation> In the above-described production method I, a porous material is formed by wet phase separation in a state in which a woven fabric support is disposed in a coating film formed from a dope solution containing an organic polymer dissolved therein. This allows the production of a porous separator for alkaline water electrolysis of the present invention, in which a porous material containing at least an organic polymer is disposed on at least one of the outer surface and pores of the woven fabric support. In the wet phase separation, the woven fabric support is placed on a coating film formed by casting the dope solution on a substrate, and the woven fabric support is immersed in the coating film to impregnate, preferably completely impregnate, the woven fabric support with the dope solution. Next, the woven fabric support impregnated with the dope solution is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent. When the proportion of the good solvent in the coating film of the dope solution decreases during this immersion, the organic polymer and the solvent undergo phase separation (liquid-induced phase separation), causing the organic polymer to gel (coagulate), forming a porous material. This allows the porous separator for alkaline water electrolysis of the present invention to be obtained, in which the porous material is disposed on at least one of the outer surface and pores of the woven fabric support. In the above-mentioned Production Method II, a membrane-forming solution containing an organic polymer dissolved therein is cast onto a release film to form a coating film, and the coating film is then subjected to wet phase separation, which includes performing liquid-induced phase separation while the release film is peeled off, thereby producing the porous separator for alkaline water electrolysis of the present invention, which is composed of a porous material containing at least an organic polymer and does not include a porous support. In the wet phase separation, the membrane-forming solution is cast onto a release film, and the surface is appropriately dried to form a coating film. Next, the laminate, in which the coating film of the membrane-forming solution has been formed on the release film, is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent, and the release film is peeled off during immersion. When the proportion of the good solvent in the coating of the membrane-forming solution is reduced by this immersion, phase separation occurs between the organic polymer and the solvent (liquid-induced phase separation), causing the organic polymer to gel (solidify), forming a porous material, and the porous separator for alkaline water electrolysis of the present invention, which is composed of the porous material and does not include a porous support, can be obtained.

[0054] The poor solvent can be, for example, water, or a mixed solvent of water with a hydrophilic organic solvent (an organic solvent miscible with water) or a water-soluble polymer. Examples of hydrophilic organic solvents include aprotic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC), and alcohol solvents such as ethanol, propanol, and isopropanol. Examples of water-soluble polymers include water-soluble polymers such as polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA). Of the above, water is preferred as the poor solvent.

[0055] The temperature of the coagulation bath is preferably 20 to 90°C, more preferably 40 to 70°C.

[0056] It is also preferable to expose the membrane to the vapor of the poor solvent before immersing it in the poor solvent to cause phase separation by vapor (vapor-induced phase separation). By performing vapor-induced phase separation, it is possible to prevent the formation of a dense skin layer on the surface. Therefore, the wet phase separation can be performed by combining vapor-induced phase separation and liquid-induced phase separation. After the wet phase separation, preferably after the liquid-induced phase separation, it is preferable to perform a washing step using pure water or the like.

[0057] In steam-induced phase separation, a porous support coated with a dope solution is exposed to non-solvent vapor, preferably moist air. For methods of performing steam-induced phase separation, see, for example, Figure 2 and the accompanying description in JP-A No. 2023-531792, as appropriate, and can be applied to the present invention. The antisolvent vapor used in steam-induced phase separation is preferably moist air. The space in which steam-induced phase separation is performed can be, for example, provided between the step of coating the porous support with a dope solution and the step of performing liquid-induced phase separation, so as to be continuous with the apparatuses performing each step, and can be further shielded from the external environment using an insulating metal plate. The degree and rate of water movement in the steam-induced phase separation step can be adjusted by adjusting the air velocity, relative humidity and temperature of the air, exposure time, etc. The relative humidity in the region where steam-induced phase separation is performed can be adjusted by the temperature of the coagulation bath and by shielding the steam-induced phase separation region from the environment. Steam-induced phase separation performed on a porous support coated with a dope solution can be performed on both sides under the same conditions or different conditions. The relative humidity and temperature in the region where steam-induced phase separation is performed can be adjusted using an insulating metal plate, for example, when using the apparatus described in Figure 2 of JP-A 2023-531792. When the apparatus is completely shielded from the external environment by the metal plate, the relative humidity and temperature are determined by the temperature of the coagulation bath used in the subsequent liquid-induced phase separation. The higher the relative humidity in the region where steam-induced phase separation is performed and the higher the air velocity, the larger the maximum pores in the resulting porous material. The relative humidity in the region where steam-induced phase separation is performed can be, for example, in the range of 50 to 99%, preferably 60 to 98%, and more preferably 70 to 98%.

[0058] In the above-mentioned production method II, after the membrane is immersed in the poor solvent to form a porous material (porous membrane), the membrane may be immersed in a glycol such as ethylene glycol or diethylene glycol, water, etc. This step can remove the solvent remaining in the membrane.

[0059] In the porous separator for alkaline water electrolysis obtained by the above-mentioned method for producing a porous separator for alkaline water electrolysis, a certain amount of good solvent in the dope solution used in its production inevitably remains. As a result, a porous separator for alkaline water electrolysis is provided in which the total content of good solvent in the porous material is 0.01 to 5.00 mass%. The amount of residual solvent can be determined by measuring the amount of residual solvent by air-blowing the separator at 40°C for 12 hours and then analyzing the amount of residual solvent by gas chromatography or １ Using H-NMR, the amount can be quantified as mass % based on 100 mass % of the porous separator for alkaline water electrolysis after drying.

[0060] The porous separator for alkaline water electrolysis of the present invention can be used as a separator in a method for producing hydrogen by electrolyzing an alkaline aqueous solution using an electrolytic cell, and is particularly suitable for use as a separator for alkaline water electrolysis in the alkaline water electrolysis system described below.

[0061] [Alkaline water electrolysis] The porous separator for alkaline water electrolysis of the present invention (hereinafter also simply referred to as the "separator of the present invention") is disposed between the cathode and the anode for use in alkaline water electrolysis. Preferred embodiments of an alkaline water electrolysis system to which the separator of the present invention is applied (also referred to as the "alkaline water electrolysis system of the present invention") will be described, but the alkaline water electrolysis of the present invention is not limited to these embodiments.

[0062] FIG. 1 schematically illustrates a preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (10) illustrated in FIG. 1 includes a separator (11) of the present invention, a cathode electrode (12) on one side thereof, and an anode electrode (13) on the other side thereof, and the separator (11) and the electrodes (12, 13) are immersed in a highly concentrated alkaline aqueous solution (14, preferably a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution). When a current flows between the electrodes, electrons are supplied to the cathode side, and hydrogen bubbles (H ２ ) occurs (2H ２ O + 2e － →H ２ +2OH －) Hydroxy ions (OH － ) passes through the separator (11) and moves to the anode side, where electrons are taken away and oxygen (O ２ ) is generated (4OH － →O ２ +2H ２ O+4e － The cathode electrode (12) and the anode electrode (13) preferably include an electrode substrate (conductive material) and a catalyst layer on the electrode substrate. When a catalyst layer is included, the catalyst species may be the same or different between the cathode electrode (12) and the anode electrode (13). In the alkaline water electrolysis system (10) shown in FIG. 1 , the separator (11) and the electrodes (12, 13) are separated from each other, resulting in a long migration distance of hydroxy ions, which limits improvement in ion conduction efficiency.

[0063] FIG. 2 schematically illustrates another preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (20) illustrated in FIG. 2 is the same as the alkaline water electrolysis system (10) illustrated in FIG. 1 , except that the separator (11) and the electrodes (12, 13) are arranged in contact with each other (zero-gap type). The alkaline water electrolysis system (20) illustrated in FIG. 2 has a short migration distance of hydroxy ions due to the separator (11) and the electrodes (12, 13) being in contact with each other, which is advantageous in terms of ion conduction efficiency. Examples of pressurized alkaline water electrolysis systems include the alkaline water electrolysis system illustrated in FIG. 2 , where the configuration, components, etc. of the alkaline water electrolysis system are appropriately adjusted to accommodate pressurized operation (e.g., operation under a pressurized condition of 10 bar or more). The separator (11) of the present invention can suppress a pressurized increase in initial resistance (electrolysis voltage) and can also suppress a temporal increase in electrolysis voltage due to operation under pressurized conditions, thereby demonstrating its effects in pressurized alkaline water electrolysis systems. Furthermore, with regard to other members, ordinary members used in pressurized alkaline water electrolysis systems can be applied as appropriate.

[0064] FIG. 3 is a schematic diagram illustrating yet another preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (30) illustrated in FIG. 3 includes a membrane electrode assembly. That is, a cathode catalyst layer (32) is disposed on one side of a separator (31) of the present invention, and an anode catalyst layer (33) is disposed on the other side. These catalyst layers are composed of a catalyst and a binder. Furthermore, a gas diffusion layer (34) is formed on the outer surface of these catalyst layers (the surface opposite to the side on which the separator (33) is disposed) to form a membrane electrode assembly. In FIG. 3 , a bipolar plate (35) is formed further outside the membrane electrode assembly. An alkaline aqueous solution is supplied to the cathode catalyst layer (32) and the anode catalyst layer (33) of this membrane electrode assembly, and the cathode catalyst layer (32) and the anode catalyst layer (33) are electrically connected and energized, whereby hydrogen bubbles are generated from the cathode catalyst layer (32) and oxygen bubbles are generated from the anode catalyst layer (33).

[0065] In the alkaline water electrolysis system, the configurations of the cathode electrode, cathode catalyst layer, anode electrode, anode catalyst layer, etc., other than the separator, are not particularly limited, and typical components used in alkaline water electrolysis systems can be applied as appropriate.

[0066] Thus, one embodiment of the present invention provides an alkaline water electrolysis system incorporating the separator of the present invention as the separator in the alkaline water electrolysis system. Furthermore, one embodiment of the present invention provides a method for producing an alkaline water electrolysis system, the method comprising incorporating the separator of the present invention as the separator in the alkaline water electrolysis system. The effects of the separator of the present invention are more pronounced when the separator is incorporated as the separator in a pressurized alkaline water electrolysis system, among other separators for alkaline water electrolysis systems.

[0067] [Alkaline Water Electrolysis Member] The alkaline water electrolysis member of the present invention includes the separator of the present invention. Specifically, the alkaline water electrolysis member of the present invention includes the separator of the present invention and at least one of a catalyst, an anode electrode, and a cathode electrode. Note that an embodiment including the separator of the present invention and an anode electrode and a cathode electrode is classified as the alkaline water electrolysis cell of the present invention, which will be described later. Examples of an alkaline water electrolysis member of the present invention that does not include an electrode and includes a catalyst include a structure in which the catalyst is located only on one side of the separator of the present invention, and a structure in which the catalyst is located on both sides of the separator of the present invention. Examples of an alkaline water electrolysis member of the present invention that does not include a cathode electrode and includes an anode electrode include a structure in which the anode electrode is located on one side of the separator of the present invention. In this structure, the catalyst may or may not be located. When a catalyst is located, the catalyst may be located only on one side of the separator of the present invention, or may be located on both sides of the separator of the present invention. An example of a configuration in which the alkaline water electrolysis device of the present invention does not include an anode electrode but includes a cathode electrode is a configuration in which the cathode electrode is located on one side of the separator of the present invention. In this configuration, a catalyst may or may not be included. When a catalyst is included, the catalyst may be located on only one side of the separator of the present invention, or may be located on both sides of the separator of the present invention.

[0068] [Alkaline Water Electrolysis Cell] The alkaline water electrolysis cell of the present invention comprises the separator of the present invention or the alkaline water electrolysis member of the present invention. The "alkaline water electrolysis cell" comprises a separator and two electrodes (an anode electrode and a cathode electrode) separated by the separator. In this configuration, an alkaline aqueous solution may be present as an electrolyte between both electrodes (including the separator of the present invention), and the anode electrode and the cathode electrode may each further comprise a catalyst. For example, when the alkaline water electrolysis cell of the present invention comprises the separator of the present invention, the alkaline water electrolysis cell of the present invention can be obtained by combining the separator of the present invention with the anode electrode and the cathode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. Alternatively, when the alkaline water electrolysis cell of the present invention does not comprise electrodes but comprises the separator of the present invention and a catalyst, the alkaline water electrolysis cell of the present invention can be obtained by combining the separator with the anode electrode and the cathode electrode. In this case, the catalyst may be contained in the alkaline water electrolysis element of the present invention, or may be separately contained in the alkaline water electrolysis element of the present invention and combined with it, similar to the anode electrode or cathode electrode. In the alkaline water electrolysis cell of the present invention, the catalyst may be contained on at least one side of the separator of the present invention, or may be contained on both sides. When the alkaline water electrolysis cell of the present invention does not include a cathode electrode but includes the separator of the present invention and an anode electrode, the alkaline water electrolysis cell of the present invention can be produced by combining the separator with the cathode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. The catalyst may be contained in the alkaline water electrolysis element of the present invention, or may be separately contained in the alkaline water electrolysis element of the present invention and combined with it, similar to the cathode electrode. When the alkaline water electrolysis cell of the present invention does not include an anode electrode but includes the separator and cathode electrode of the present invention, the alkaline water electrolysis cell of the present invention can be produced by combining the separator with the anode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst.The catalyst may be contained in the alkaline water electrolysis device of the present invention, or may be separately contained in the alkaline water electrolysis device of the present invention in combination with it, similar to the anode electrode.

[0069] [Alkaline water electrolysis device] The alkaline water electrolysis device of the present invention includes the alkaline water electrolysis cell of the present invention. The alkaline water electrolysis device of the present invention can produce hydrogen as described in the alkaline water electrolysis system described above by supplementing necessary components, configuration, etc. depending on the configuration of the alkaline water electrolysis cell of the present invention.

[0070] [Hydrogen production method] A preferred example of the hydrogen production method of the present invention is a method comprising operating the alkaline water electrolysis apparatus of the present invention described above at a pressure of 10 bar or more. In the present invention, "operating at a pressure of 10 bar or more" means operating while controlling the pressure of the gas flow generated from each electrode chamber using a pressure control valve so that a pressure of 10 bar or more is applied to at least one of the cathode electrode chamber and the anode electrode chamber (or both). In an alkaline water electrolysis system, of the electrolytic cells separated by a separator, the electrolytic cell containing the cathode electrode is referred to as the cathode electrode chamber, and the electrolytic cell containing the anode electrode is referred to as the anode electrode chamber. The pressure applied to at least one of the cathode electrode chamber and the anode electrode chamber is preferably 10 to 500 bar, more preferably 20 to 300 bar, and even more preferably 30 to 100 bar. It is also preferable that the above pressure is applied to both the cathode electrode chamber and the anode electrode chamber. The separator of the present invention included in the alkaline water electrolysis device of the present invention can be suitably applied to a pressurized alkaline water electrolysis system and can therefore be used in a hydrogen production method in which the alkaline water electrolysis device is operated at a pressure of 10 bar or more, enabling efficient hydrogen production.

[0071] Another preferred example of the hydrogen production method of the present invention includes adjusting the pressure control valve of the alkaline water electrolysis device of the present invention to operate the device under conditions in which the hydrogen generation side is at a pressure 1 bar or more higher than the oxygen generation side (operating under conditions in which the pressure difference obtained by subtracting the pressure on the oxygen generation side from the pressure on the hydrogen generation side is 1 bar or more). Operating the device under this condition, applying a pressure of 1 bar or more from the hydrogen generation side to the oxygen generation side, can increase the purity of the produced hydrogen. The pressure difference obtained by subtracting the pressure on the hydrogen generation side (i.e., the pressure applied to the anode electrode chamber) from the pressure on the hydrogen generation side (i.e., the pressure applied to the cathode electrode chamber) is preferably 1 to 10 bar, more preferably 2 to 10 bar, and even more preferably 2 to 8 bar. The separator of the present invention included in the alkaline water electrolysis device of the present invention is suitable for use in pressurized alkaline water electrolysis systems and can therefore be used in a hydrogen production method in which a pressure of 5 bar or more is applied from the hydrogen generation side to the oxygen generation side of the alkaline water electrolysis device, enabling efficient production of higher purity hydrogen. In this case, the pressure difference obtained by subtracting the pressure on the oxygen generation side from the pressure on the hydrogen generation side is preferably 5 to 10 bar, and more preferably 5 to 8 bar.

[0072] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited thereto. The water used is deionized water. wt% means mass % and vol% means volume %. The thickness of the porous support is a value measured by the method described above.

[0073] [Fabrication of porous separator for alkaline water electrolysis] Example 1 (1) The following materials were prepared. Porous support: polyphenylene sulfide woven fabric (manufactured by NBC meshtec) with a thickness of 300 μm and an opening ratio of 65%. Hydrophilic inorganic particles: zirconium oxide particles with a median diameter (D50) of 0.70 μm. Organic polymer: polysulfone UDEL P1700 (storage modulus at 90° C. 900 MPa, Mw: 72000) manufactured by SOLVAY. Additives: glycerol, pore expander sold by MOSSELMAN. Solvent: N-butyl-pyrrolidone (NBP) sold by Taminco. (2) Preparation of Dope Solution: A dope solution was prepared by mixing and stirring 50 wt % hydrophilic inorganic particles, 10 wt % organic polymer, 1 wt % additive, and 39 wt % solvent (inorganic particle concentration: 51 vol%). (3) Fabrication of Porous Separator for Alkaline Water Electrolysis: A porous separator for alkaline water electrolysis was fabricated as follows, based on the separator manufacturing method schematically shown in FIG. 2 of JP-A 2023-531792. The obtained dope solution was coated on both sides of a 1.8 m wide porous support using a slot die coating technique at 3 m / min to a finished film thickness of 500 μm. The coated porous support was then transported to a water bath (coagulation bath) maintained at 65°C, during which a steam-induced phase separation (VIPS) process was carried out in a closed area (a 7 cm distance from the coating to the water bath, a relative humidity of 98%, and ventilation). Next, the porous support that had been subjected to the coating and VIPS process was immersed in a water bath at 65°C for 2 minutes to perform liquid induced phase separation (LIPS).Furthermore, an in-line washing step was performed in water at 70°C for 5 minutes to produce a porous separator for alkaline water electrolysis of Example 1.

[0074] Example 2 A porous separator for alkaline water electrolysis of Example 2 was prepared in the same manner as in Example 1, except that the organic polymer in Example 1 was changed to polyphenylsulfone ULTRASON P3010 (storage modulus at 90°C: 800 MPa, Mw: 55,000) manufactured by BASF.

[0075] Example 3 A porous separator for alkaline water electrolysis of Example 3 was prepared in the same manner as in Example 1, except that the porous support was changed to a polyphenylene sulfide woven fabric (manufactured by Kureha Co., Ltd.) with a thickness of 100 µm and an opening ratio of 50%, and the thickness of the porous separator for alkaline water electrolysis was changed to 200 µm.

[0076] Example 4 A porous separator for alkaline water electrolysis of Example 4 was prepared in the same manner as in Example 3, except that the contents of the materials in the dope solution were changed to 45 wt % for hydrophilic inorganic particles, 15 wt % for organic polymer, 1 wt % for additive, and 39 wt % for solvent (inorganic particle concentration: 39 vol%), and the thickness of the separator was changed to 150 µm.

[0077] Example 5 A porous separator for alkaline water electrolysis of Example 5 was prepared in the same manner as in Example 6, except that the dope solution prepared in Example 1 was used instead of the membrane-forming solution and casting was performed so that the completed membrane thickness would be 200 µm.

[0078] Example 6 A membrane-forming solution was prepared by dissolving 15 wt % of polysulfone (manufactured by SOLVAY, trade name: UDEL P1700, storage modulus at 90°C: 900 MPa, Mw: 72,000) as an organic polymer, 15 wt % of polyvinylpyrrolidone (manufactured by Merck, trade name: PVP K-30) as a pore control agent, 1 wt % of lithium chloride as a pore control agent, 2 wt % of water, and 67 wt % of N-methyl-2-pyrrolidone (NMP). The resulting membrane-forming solution was cast onto the surface of a PET (polyethylene terephthalate) film so that the completed film thickness would be 130 μm. Air adjusted to 25°C and a relative humidity of 80% was blown onto the surface of the cast liquid film at a speed of 2 m / s for 5 seconds. The film was then immediately immersed in a 50°C water bath (coagulation bath), and the PET film was peeled off to obtain a porous membrane. The obtained porous membrane was immersed in a diethylene glycol bath at 80°C for 120 seconds and then thoroughly washed with pure water to prepare a porous separator for alkaline water electrolysis of Example 6.

[0079] <Comparative Example 1> Zirfon Perl UTP-500 (product name) manufactured by Agfa was used as the porous separator for alkaline water electrolysis in Comparative Example 1. <Comparative Example 2> The separator (S-1) described in Example 1 of JP-A 2023-531792 was prepared and used as the porous separator for alkaline water electrolysis in Comparative Example 2. <Comparative Example 3> A porous separator for alkaline water electrolysis in Comparative Example 3 was prepared in the same manner as in Example 5, except that the thickness of the membrane after completion was changed to 500 μm. <Comparative Example 4> A porous separator for alkaline water electrolysis in Comparative Example 4 was prepared in the same manner as in Example 6, except that the thickness of the membrane after completion was changed to 300 μm.

[0080] The following measurements and evaluations were carried out for each porous separator for alkaline water electrolysis (hereinafter also simply referred to as "separator"). For each evaluation, the obtained porous separator for alkaline water electrolysis was rolled up without drying, and cut into a desired shape for the evaluations described below, and used as is, unless otherwise specified. The configuration of each porous separator for alkaline water electrolysis is shown in Table 1-A, and the properties and evaluation results are shown in Tables 1-A and 1-B, respectively.

[0081] (Thickness Unevenness) A separator was immersed overnight in pure water at 25°C, and then cut into a 5 cm x 5 cm square. The resulting separator was immersed in a 7 mol / L KOH aqueous solution at 90°C and treated under a pressure of 5 MPa for 60 minutes to obtain a pressure-treated separator. The pressure-treated separator was dried, and a cross section was cut out using a razor. A cross-sectional SEM (scanning electron microscope) image was obtained at a magnification (e.g., 400x) that allowed the separator cross section to fit within a single field of view. In the obtained cross-sectional SEM image, the thickness was measured at 20-point intervals. The arithmetic mean, maximum, and minimum values ​​were determined from the 20 measurements, and the thickness unevenness X was calculated using the following formula: Thickness Unevenness X = {(Maximum - Minimum) ÷ Arithmetic Mean} × 100 (Unit: %). The arithmetic mean value of the five thickness unevenness X values ​​obtained using five cross-sectional SEM images with different fields of view was defined as "thickness unevenness." The following equipment was used for cross-sectional SEM observation. Conductive treatment device: Meiwafosis Co., Ltd., model number: HPC-1SW type osmium coater / source Os / film thickness 5 nm. CIS device: JEOL Ltd., model number: IB-09060CIS / acceleration voltage 4 kV / processing temperature -130 ° C / pretreatment. The sample cut with a razor was attached and fixed to a Si wafer (100 μm thick) with epoxy resin. FE-SEM (field emission scanning electron microscope) observation device: Carl Zeiss, model number: Ultra5, measurement conditions: secondary / backscattered electron image, acceleration voltage 2 kV, aperture (aperture) 30 μm, W.D. (working distance) 3.0 mm (cross section).

[0082] (Separator Thickness) In the measurement and calculation of the thickness unevenness described above, the obtained separator (not subjected to pressure treatment) was used instead of the pressure-treated separator, and the thickness was measured at intervals of 20 points, assuming that no pores were present in the obtained cross-sectional SEM image (assuming that the pores were filled with an organic polymer). The arithmetic mean value of the obtained 20 measurement values ​​was taken as the thickness of the separator.

[0083] (Inorganic particle concentration) The porous material was scraped off from the separator to remove the porous support, and about 10 mg of components other than the porous support were packed into an alumina pan. Thermal analysis was performed using the following temperature profile, and the decomposed weight was determined as the weight of the organic material, and the remaining weight was determined as the weight of the inorganic material. The density of the organic material and the inorganic material described in publicly known documents (for example, the density of zirconium oxide is 5.68 g cm) was used. －３ , density of polysulfone 1.24 g cm －３ ) was used to calculate the inorganic particle concentration from the following formula: Volume of organic substance = Weight of organic substance ÷ Density Volume of inorganic substance = Weight of inorganic substance ÷ Density Inorganic particle concentration = {Volume of inorganic substance ÷ (Volume of inorganic substance + Volume of organic substance)} × 100 (unit: %). The following apparatus was used for the thermal analysis measurements. Apparatus: Hitachi High-Tech Corporation, Model No.: TG-DTA STA7300 Measurement conditions: The temperature was increased from 30°C (measurement start temperature) at a rate of 10°C / min to 800°C (measurement end temperature), and measurements were performed in an air atmosphere.

[0084] (Storage Modulus) The porous material was scraped off from the separator, and the organic polymer in the porous material was dissolved in a good solvent for the organic polymer (for example, N-butyl-2-pyrrolidone for polysulfone). After removing the inorganic particles using a filter, the solution was dried and solidified to extract the organic polymer. The storage modulus of the extracted organic polymer at 90°C was measured using a cone-plate rheometer. The following device was used as the cone-plate rheometer, and the measurement was performed under the following measurement conditions. Device: Model MCR301 manufactured by Anton Paar. Measurement conditions: The temperature was increased from 30°C (measurement start temperature) at a rate of 10°C / min to 150°C (measurement end temperature), and N ２ It was measured in the atmosphere.

[0085] (Ionic Resistance) A separator was immersed in a 30% by mass aqueous solution of potassium hydroxide (manufactured by Kanto Chemical Co., Inc.) overnight (20 hours) at room temperature (25°C), and then punched out into a circular shape with a diameter of 10 mm to prepare a measurement sample. A 30% by mass aqueous solution of potassium hydroxide was added as an electrolyte to a two-compartment cell having a nickel electrode at the current control terminal and a Luggin capillary filled with a 3M aqueous solution of KCl at the voltage control terminal, and the cell was maintained at 90°C. A current density of 10 mA / cm was measured in galvanostat mode. ２ The ionic resistance was measured under the conditions of 0.015 MPa and 0.015 MPa, and a blank value was obtained. Next, the measurement sample prepared above was sandwiched between two separators, and a 30% by mass aqueous potassium hydroxide solution was similarly filled, and the ionic resistance was measured under the same conditions. The difference between the resistance value of the measurement sample and the blank value was taken as the ionic resistance value of the separator.

[0086] (Bubble Point) Measurement was performed using a perm porometer (Porolux 1000, manufactured by Polometer) based on the bubble point test method described in ASMT (American Society for Testing and Materials) F316-86. Using perfluoropolyester (trade name "Galwick", surface tension 15.6 dyn / cm) as the immersion liquid, a measurement separator was completely wetted. The applied pressure and air permeation rate were measured in a pressure increase mode, and the bubble point was determined as the pressure at which the first bubble appeared on the obtained wetting curve. Those for which no bubble appeared even at a pressure of 2 bar were represented in the tables as ">2 (unit: bar)." A bubble point of >2 bar can be said to satisfy the gas barrier properties required for a porous separator for alkaline water electrolysis.

[0087] (Electrolyte Permeability) The separator was punched into a circle with a diameter of 47 mm. The obtained circular separator was set in a filter holder (product number XX4004700, manufactured by Merck). A 30% by mass aqueous potassium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) was passed through the circular separator for 30 seconds under conditions of 90°C and a gauge pressure of 1 bar, and the liquid volume (mL) was measured. The water permeability (mL / (h·m)) was calculated by converting the unit. ２ ・bar) was sought.

[0088] (Electrolytic Cell Evaluation) Both sides of the separator were sandwiched with Ni foam (thickness 160 μm, porosity 110 PPI (Pore per inch)) manufactured by Goodfellow Corp. as electrodes, and the separator was sandwiched between two Ni bipolar plates having flow channels and restrained with bolts. A 7.0 M potassium hydroxide (KOH) aqueous solution heated to 90° C. was supplied to the cathode and anode sides of the water electrolysis cell obtained above at a flow rate of 10 mL / min, while a current of 0.1 A / cm was applied. ２ A current of 0.8 A / cm was applied for 4 hours to obtain a water electrolysis cell after initial current application. ２ The electrolysis cell was evaluated by adjusting the pressure in the anode electrode chamber and the cathode electrode chamber to desired values ​​using the pressure regulating valves. Specifically, the initial resistance (electrolysis voltage) of the water electrolysis cell after the initial energization was 0.8 A / cm. ２ The voltage at 1 bar (normal pressure) is shown in the table as "Voltage at 1 bar @ 0.8 A cm －２ In the "Voltage at 50 bar @ 0.8 A cm" column, enter the voltage when a pressure of 50 bar is applied. －２ " column, these voltage changes are recorded as "50 bar voltage @ 0.8 A cm －２ " to "Voltage of 1 bar @ 0.8 A cm －２ The values ​​obtained by subtracting "Voltage change at 1 bar and 50 bar" are shown in the "Change in voltage at 1 bar and 50 bar" column. The electrolysis voltage after operation was 0.8 A / cm for the water electrolysis cell obtained after the initial energization. ２ The voltage after 1000 hours of operation at 1 bar (normal pressure) is shown in the column "Voltage increase after 1000 hours of operation at 1 bar" in the table, and the voltage after 1000 hours of operation while applying a pressure of 50 bar is shown in the column "Voltage increase after 1000 hours of operation at 50 bar" in the table. Note that "applying a pressure of 50 bar" means that a pressure of 50 bar was applied to both the cathode electrode chamber and the anode electrode chamber.

[0089]

[0090] PSU: Polysulfone PPSU: Polyphenylsulfone PPS: Polyphenylene sulfide The units are listed in brackets [ ] for each item.

[0091] The porous separators for alkaline water electrolysis of Comparative Examples 1 to 4 all had thickness unevenness, as defined in <Condition I>, of more than 15%, and therefore did not satisfy the requirements of the present invention. In the alkaline water electrolysis cells comprising the porous separators for alkaline water electrolysis of Comparative Examples 1 to 4, when a pressure of 50 bar was applied, the voltage increased by 0.11 to 0.15 V compared to when the pressure was 1 bar (atmospheric pressure), indicating that the initial resistance (electrolysis voltage) increased due to the application of pressure. Furthermore, when operated at 50 bar for 1,000 hours, the voltage increased by 0.21 to 0.30 V compared to the initial state before operation, indicating poor durability to operation under pressurized conditions. In contrast, the porous separators for alkaline water electrolysis in Examples 1 to 6 all had thickness unevenness, as defined by <Condition I>, of 15% or less, and the increase in initial resistance (electrolysis voltage) due to pressurization from 1 bar to 50 bar was suppressed to 0.06 V or less. Moreover, even after operation at 50 bar for 1000 hours, the increase in voltage relative to the initial state before operation was suppressed to 0.15 V or less. Thus, it was found that when used as a separator in a pressurized alkaline water electrolysis cell, the porous separator for alkaline water electrolysis of the present invention can suppress the increase in initial resistance (electrolysis voltage) due to pressurization, and can also suppress the increase in electrolysis voltage over time due to operation under pressurized conditions. Among them, when the porous support and the porous material containing an organic polymer and hydrophilic inorganic particles arranged on at least one of the outer surface and pores of the porous support are used, and the inorganic particle concentration of the porous material is 50% by volume or more, when the thickness of the separator is 210 μm or less, or when the storage modulus of the organic polymer at 90 ° C. is 850 MPa or more, the initial resistance (electrolysis voltage) is suppressed by pressure, and the increase in electrolysis voltage over time due to operation under pressure conditions is suppressed. (See Example 3 for Example 4, Example 3 for Example 1, and Example 1 for Example 2, respectively.) Furthermore, when the porous material is composed of an organic polymer and does not include a porous support, the initial resistance (electrolysis voltage) is suppressed by pressure, and the increase in electrolysis voltage over time due to operation under pressure conditions is suppressed. It was even more superior (see Examples 5 and 6 for Examples 1 to 4).

[0092] This application claims priority based on Japanese Patent Application No. 2024-055616, filed on March 29, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0093] REFERENCE SIGNS LIST 10 Alkaline water electrolysis system 11 Porous separator for alkaline water electrolysis 12 Cathode electrode 13 Anode electrode 14 Highly concentrated alkaline aqueous solution 20 Alkaline water electrolysis system 30 Alkaline water electrolysis system 31 Porous separator for alkaline water electrolysis 32 Cathode catalyst layer 33 Anode catalyst layer 34 Gas diffusion layer 35 Bipolar plate O ２ Bubble oxygen H ２ Bubble hydrogen OH － Hydroxy ion e － electronic

Claims

1. A porous separator for alkaline water electrolysis that satisfies the following <Condition I>: <Condition I> The porous separator for alkaline water electrolysis is immersed in a 7 mol / L aqueous KOH solution at 90°C and treated under a pressure of 5 MPa for 60 minutes, and the resulting separator has a thickness variation of 15% or less.

2. The porous separator for alkaline water electrolysis according to claim 1, comprising: a porous support; and a porous material containing an organic polymer and hydrophilic inorganic particles, the porous material being disposed on at least one of the outer surface and pores of the porous support, wherein the inorganic particle concentration in the porous material is 50 vol % or more.

3. The porous separator for alkaline water electrolysis according to claim 1, comprising: a porous support; and a porous material containing an organic polymer and hydrophilic inorganic particles, which is disposed on at least one of the outer surface and pores of the porous support; and the thickness of the porous separator for alkaline water electrolysis is 210 μm or less.

4. The porous separator for alkaline water electrolysis according to claim 1, comprising: a porous support; and a porous material, which is disposed on at least one of the outer surface and pores of the porous support, and which contains an organic polymer and hydrophilic inorganic particles, wherein the organic polymer has a storage modulus at 90°C of 850 MPa or more.

5. The porous separator for alkaline water electrolysis according to claim 1, which is made of a porous material containing an organic polymer and does not include a porous support.

6. An alkaline water electrolysis component comprising the porous separator for alkaline water electrolysis according to claim 1.

7. An alkaline water electrolysis cell comprising the porous separator for alkaline water electrolysis according to any one of claims 1 to 5 or the alkaline water electrolysis member according to claim 6.

8. An alkaline water electrolysis device comprising the alkaline water electrolysis cell according to claim 7.

9. A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to claim 8 at a pressure of 10 bar or more.

10. A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to claim 8 while applying a pressure of 5 bar or more from the hydrogen generation side to the oxygen generation side.

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