JP7702239B2 - Diaphragm for alkaline water electrolysis and manufacturing method thereof - Google Patents

Description

The present invention relates to a diaphragm for alkaline water electrolysis. More specifically, the present invention relates to a diaphragm for alkaline water electrolysis in which retention of generated gas is effectively suppressed, and a method for producing the same.

Water electrolysis (also called "electrolysis") is known as one of the industrial methods for producing hydrogen, and is generally carried out by applying an electric current to water to which an electrolyte such as sodium hydroxide or potassium hydroxide has been added to increase the electrical conductivity. For this type of water electrolysis, an electrolytic cell is used that has an anode chamber and a cathode chamber, each containing an anode and a cathode, separated by a diaphragm.

Water electrolysis is carried out by the transfer of electrons (or ions). Therefore, the diaphragm must have high ion permeability to ensure efficient electrolysis. It must also have gas barrier properties that can block oxygen molecules generated in the anode chamber and hydrogen molecules generated in the cathode chamber. Furthermore, water electrolysis is carried out using alkaline water with a high concentration of about 30%, at 80 to 100°C, and in some cases under a pressure of 1 MPa, so it must also have high temperature resistance, alkali resistance, and mechanical strength.

Various diaphragms used in water electrolysis have been known to date. For example, Patent Document 1 discloses a diaphragm for alkaline water electrolysis that has a polymer porous membrane containing a polymer resin and inorganic particles, and in which the porosity of the polymer porous membrane, the average pore size on the surface, and the ratio of the mode particle size of the inorganic particles to the average pore size are controlled within specific ranges.

International Publication No. 2016/148302

However, in the electrolysis of water, if gas bubbles generated at each electrode remain on the electrode surface, the active area of the electrode is reduced, the cell voltage increases, and the electrolysis efficiency decreases. Therefore, various electrode designs that make it difficult for gas bubbles generated to remain on the electrode surface have been investigated.
In recent years, a zero-gap structure, which is a cell structure in which a diaphragm and an electrode are in contact with each other to reduce the distance between the electrodes, has been known as a structure with good electrolysis efficiency in water electrolysis devices. In the zero-gap structure, air bubbles are more likely to remain on the surfaces of the electrodes and the diaphragm, and the decrease in electrolysis efficiency due to the diaphragm becomes more noticeable.

The present invention was made in consideration of the above-mentioned current situation, and aims to provide a diaphragm for alkaline water electrolysis that effectively suppresses the retention of air bubbles and achieves high electrolysis efficiency even when used in an electrolysis device with a zero-gap structure.

The inventors have conducted various investigations into the causes of air bubbles remaining on the surface of a diaphragm for alkaline water electrolysis and have found that unevenness on the surface of the diaphragm makes it easier for air bubbles to remain on the surface of the diaphragm. The inventors have then found that by setting the average area of the depressed portions on one or both surfaces of the diaphragm and the area ratio of the depressed portions within a predetermined range, air bubble retention is significantly suppressed, resulting in a diaphragm for alkaline water electrolysis that can achieve high electrolysis efficiency even when used in a water electrolysis device with a zero gap structure, and have completed the present invention.

That is, the present invention relates to a diaphragm for alkaline water electrolysis, characterized in that, on at least one diaphragm surface, the average area of the depressed portions is 7 ^µm2 or less, and the area ratio of the depressed portions to the diaphragm surface is 20% or less.

The diaphragm for alkaline water electrolysis preferably has an arithmetic mean roughness Ra of the diaphragm surface of 0.8 μm or less.

The diaphragm for alkaline water electrolysis preferably contains an organic polymer resin and inorganic particles.

The inorganic particles are preferably metal hydroxide particles and/or metal oxide particles.

The organic polymer resin is preferably at least one resin selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone.

The present invention also relates to a method for producing the above-mentioned diaphragm for alkaline water electrolysis, the method comprising the steps of: (1) preparing a dispersion solution containing an organic polymer resin, inorganic particles, and a solvent; (2) forming a coating film using the dispersion solution; (3) contacting the coating film with a non-solvent for the organic polymer resin to solidify the coating film; and (4) drying the solidified coating film to obtain a porous membrane, wherein in the step (3), the contact speed of the coating film with the non-solvent is 0.3 m/min or more.

In the method for producing a diaphragm for alkaline water electrolysis, the step (3) is preferably performed under conditions of an absolute humidity of 20 g/ ^m3 or less.

In the method for producing a diaphragm for alkaline water electrolysis, the step (2) is preferably performed under conditions of an absolute humidity of 20 g/ ^m3 or less.

The diaphragm for alkaline water electrolysis of the present invention effectively prevents retention of bubbles of oxygen gas and hydrogen gas generated during water electrolysis. By using the diaphragm for alkaline water electrolysis of the present invention, water electrolysis can be performed extremely efficiently, and a highly efficient water electrolysis device can be provided.

FIG. 1 is an image of a diaphragm surface for alkaline water electrolysis in Example 1 observed with a laser microscope (objective magnification: 150 times).

The present invention will be described in detail below.
In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

1. Diaphragm for alkaline water electrolysis The diaphragm for alkaline water electrolysis of the present invention is characterized in that on at least one of the diaphragm surfaces, the average area of the depressed portions is 7 ^µm2 or less and the area ratio of the depressed portions on the diaphragm surface is 20% or less. By setting the state of at least one of the diaphragm surfaces within a specific range, the diaphragm for alkaline water electrolysis of the present invention can effectively suppress retention of oxygen gas and hydrogen gas bubbles generated during electrolysis in the diaphragm, thereby improving the electrolysis efficiency of an electrolysis device using the diaphragm. It is believed that the reason why the diaphragm for alkaline water electrolysis of the present invention is excellent in suppressing retention of bubbles is that by setting the surface state of the diaphragm for alkaline water electrolysis of the present invention within the above specific range, the diaphragm surface becomes relatively smooth and there is less space for the retention of bubbles generated during alkaline water electrolysis, thereby effectively suppressing retention of oxygen gas and hydrogen gas bubbles.

In the present invention, the "depressed portion" on the diaphragm surface refers to the following portion: When one surface (first surface) or both surfaces (first surface and second surface) of the diaphragm for alkaline water electrolysis of the present invention are observed using a laser microscope such as VK9700 (manufactured by Keyence Corporation), a plane obtained by subjecting the diaphragm surface to a least squares method of Z-direction height data when the diaphragm surface is defined as an XY plane is used as a reference plane, and a portion whose Z-direction height is −1.5 μm or less with respect to the reference plane is defined as a "depressed portion A."
Furthermore, if there is a protruding portion relative to the reference surface, a recessed portion surrounded by protruding portions with a Z-direction height of +1.5 μm or more has a space with respect to the reference surface when in contact with an electrode, and therefore the recessed portion can also be considered as a depressed portion, which is referred to as "depressed portion B." The "depressed portion" in this invention includes both the above-mentioned "depressed portion A" and "depressed portion B."
The reference plane can be determined by measurement analysis in the observation field of a laser microscope. Specifically, the observation image obtained with a laser microscope VK9700 (manufactured by Keyence Corporation) at 150x objective magnification is analyzed by specifying 15,000 μm ² as the measurement area using analysis software VK Analyzer VK-H1A1 (manufactured by Keyence Corporation) and performing least squares analysis.

The shape of the recessed portion is not particularly limited and may be any concave shape, such as a (substantially) hemisphere, (substantially) polygonal pyramid, (substantially) cone, (substantially) elliptical cone, or a combination of these shapes, or an indefinite shape. The shape of the opening of the recessed portion is also not particularly limited and may be a polygon, circle, ellipse, or a modified version of these, or an indefinite shape. The bottom surface of the recessed portion may be curved.

The average area of the depressed portions is 7 ^μm2 or less. The depressed portions include the above-mentioned "depressed portion A" and "depressed portion B." Therefore, "the average area of the depressed portions is 7 ^μm2 or less" means that the average areas of "depressed portion A" and "depressed portion B" are both 7 ^μm2 or less.
The average area of the above-mentioned depressed portions is preferably 5 μm ² or less, and more preferably 4 μm ² or less, in order to further suppress the retention of air bubbles.
The average area of the depressed portions can be determined by image analysis of an observation image (150x objective) obtained by a laser microscope (e.g., VK9700, manufactured by Keyence Corporation) using analysis software (e.g., VK Analyzer VK-H1A1, manufactured by Keyence Corporation); specifically, the average area can be determined by measurement using the method described in the Examples.

In the diaphragm for alkaline water electrolysis of the present invention, the area ratio of the depressed portions on the diaphragm surface is further 20% or less. When the average area of the depressed portions on the diaphragm surface of the diaphragm for alkaline water electrolysis of the present invention is within the above-mentioned range and the area ratio of the depressed portions is within the above-mentioned range, the diaphragm surface becomes smooth and the diaphragm can be provided in which retention of gas bubbles generated during electrolysis is significantly suppressed.
As described above, the depressed portions include “depressed portion A” and “depressed portion B.” Therefore, the area ratio of the depressed portions is the sum of the area ratio of depressed portion A and the area ratio of depressed portion B.
The area ratio of the depressed portions is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.
The area ratio of the depressed portions can be determined by calculating the ratio (%) of the total area of the depressed portions (A and B) present in the observation field to the entire area of the observation field of the diaphragm surface by image analysis of an observation image (150x objective) obtained by a laser microscope (e.g., VK9700, manufactured by Keyence Corporation) using analysis software (e.g., VK Analyzer VK-H1A1, manufactured by Keyence Corporation); specifically, the area ratio can be determined by measurement using the method described in the Examples.

The diaphragm for alkaline water electrolysis preferably has an arithmetic mean roughness Ra of the diaphragm surface of 0.8 µm or less. When the arithmetic mean roughness Ra is 0.8 µm or less, retention of gas bubbles can be further suppressed. In terms of further suppressing retention of gas bubbles, the arithmetic mean roughness Ra is more preferably 0.6 µm or less, and even more preferably 0.5 µm or less. There is no particular limitation on the lower limit of the arithmetic mean roughness Ra of the diaphragm surface, but it is preferably 0.01 µm or more, more preferably 0.05 µm or more, and even more preferably 0.08 µm or more.
The arithmetic mean roughness Ra of the diaphragm surface is a value that can be determined by measurement using a laser microscope or the like in accordance with JIS B0601:2001, and specifically, can be determined by the method described in the examples below.

The diaphragm for alkaline water electrolysis contains an organic polymer resin and inorganic particles. The diaphragm for alkaline water electrolysis preferably has a porous membrane containing an organic polymer resin and inorganic particles. The presence of a porous membrane provides ion permeability.

(Organic polymer resin)
The organic polymer resin is not particularly limited as long as it is an organic polymer resin that is typically used in a diaphragm for alkaline water electrolysis, and examples thereof include fluorine-based resins, olefin-based resins, aromatic hydrocarbon-based resins, etc. The organic polymer resin may be one type alone or a combination of two or more types. In particular, the organic polymer resin preferably includes an aromatic hydrocarbon-based resin in terms of excellent heat resistance and alkali resistance.

Examples of the fluorine-based resin include ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer, etc.

Examples of the olefin resin include polyethylene, polypropylene, polybutene, polymethylpentene, etc.

Examples of the aromatic hydrocarbon resin include polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyarylate, polyetherimide, polyimide, polyamideimide, and the like. Among these, at least one selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone is preferred in terms of excellent alkali resistance, and polysulfone is more preferred in terms of ease of producing a diaphragm.

The content of the organic polymer resin is preferably 5 to 40 mass% relative to 100 mass% of the diaphragm for alkaline water electrolysis. When the content of the organic polymer resin is within the above range, elution of inorganic components from the diaphragm in an alkaline solution can be suppressed. The content of the organic polymer resin is more preferably 7 mass% or more relative to 10 mass% of the diaphragm for alkaline water electrolysis, more preferably 10 mass% or more, more preferably 35 mass% or less, and even more preferably 30 mass% or less.

(Inorganic particles)
The diaphragm for alkaline water electrolysis contains inorganic particles, which makes the diaphragm hydrophilic and can suppress adhesion of oxygen gas or hydrogen gas bubbles to the diaphragm surface.
Examples of the inorganic particles include metal hydroxides or oxides such as magnesium, zirconium, titanium, zinc, aluminum, and tantalum, sulfates such as calcium, barium, lead, and strontium, nitrides such as titanium, zirconium, and hafnium, and carbides such as titanium, zirconium, and hafnium. The inorganic particles may contain only one type, or two or more types.
Among these, in that the diaphragm can be hydrophilized to provide excellent ion permeability and suppress gas adhesion, metal hydroxides or metal oxides are preferred, magnesium hydroxide, zirconium hydroxide, titanium hydroxide, zirconium oxide and titanium oxide are more preferred, magnesium hydroxide, zirconium hydroxide, titanium hydroxide and titanium oxide are even more preferred, magnesium hydroxide, zirconium hydroxide and titanium hydroxide are even more preferred, and magnesium hydroxide is particularly preferred.

The inorganic particles may be surface-untreated or surface-treated. Examples of the surface treatment include known surface treatments using silane coupling agents, stearic acid, oleic acid, phosphoric acid esters, etc.

The shape of the inorganic particles is not particularly limited, and may be any shape such as irregular, granular, flaky, hexagonal plate, plate, fiber, etc. Among these, in terms of excellent adhesion to the resin, the shape of the inorganic particles is preferably granular, flaky, or plate-like, more preferably plate-like or flaky, and even more preferably flaky.

The inorganic particles preferably have an average particle size of 0.05 μm or more and 2.0 μm or less, from the viewpoint of increasing the hydrophilic surface area and efficiently forming a permeation path for the electrolyte in the diaphragm, and more preferably have an average particle size of 0.1 μm or more and even more preferably have an average particle size of 0.2 μm or more, more preferably have an average particle size of 1.5 μm or less and even more preferably have an average particle size of 1.0 μm or less.
The above average particle size is the volume average particle size (D50) obtained by particle size distribution measurement by laser diffraction method. Specifically, the average particle size is measured by using a laser diffraction/scattering type particle size distribution measuring device (manufactured by Horiba, Ltd., Model No. LA-920), and the median diameter (D50) in the volume-based particle size distribution is taken as the average particle size. Note that the particles are mixed in ethanol and dispersed by ultrasonic irradiation to prepare a measurement sample.

Among the above inorganic particles, magnesium hydroxide is preferred because it has particularly excellent alkali resistance and durability, and can provide a diaphragm for alkaline water electrolysis at a relatively low cost. The preferred form of magnesium hydroxide in the present invention is described below.

The magnesium hydroxide used in the present invention preferably has an aspect ratio of 2.0 to 8.0. When the aspect ratio is within the above range, a diaphragm having even more excellent ion permeability and excellent uniformity can be obtained. The aspect ratio is more preferably 2.5 to 7.0, and further preferably 3.0 to 6.0.
The aspect ratio means the ratio [(a)/(b)] of the longest diameter (a) to the shortest diameter (b), and can be obtained by observing magnesium hydroxide particles with a SEM, measuring the ratio [(a)/(b)] of the longest diameter (a) to the shortest diameter (b) of each particle for any 10 particles in the obtained image using analysis software or the like, and calculating the simple average value of these ratios as the aspect ratio of the particle. Usually, it is preferable to use the shortest diameter (b) as the shortest diameter among the diameters that pass through the midpoint of the longest diameter (a) and are perpendicular to the longest diameter.
As the above-mentioned longest diameter (a), for example, when the particle has a plate-like shape such as a flaky or hexagonal plate-like shape, the longest diameter of the plate surface of the particle is used, and when the particle has a fibrous shape, the length of the fiber is used.
As the shortest diameter (b), for example, when the particle shape is a plate shape such as a flaky or hexagonal plate shape, the thickness of the particle is used, and when the particle shape is a fiber shape, the thickness of the fiber is used. As the thickness of the particle and the thickness of the fiber, it is preferable to use the thickness and thickness at the midpoint of the longest diameter a, respectively.

The magnesium hydroxide preferably has a crystallite diameter of 35 nm or more in a direction perpendicular to the (110) plane as measured by X-ray diffraction. When the crystallite diameter in the direction perpendicular to the (110) plane is in the above-mentioned range, the ion permeability and uniformity of the diaphragm are further improved.
The crystallite size in the direction perpendicular to the (110) plane is preferably 40 nm or more, more preferably 50 nm or more, further preferably 60 nm or more, and particularly preferably 65 nm or more.
The upper limit of the crystallite size in the direction perpendicular to the (110) plane is not particularly limited, but is usually, for example, 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less.

The magnesium hydroxide preferably has a crystallite size of 15 nm or more in a direction perpendicular to the (001) plane as measured by X-ray diffraction.
The crystallite size in the direction perpendicular to the (001) plane is more preferably 18 nm or more, further preferably 21 nm or more, and particularly preferably 24 nm or more.
The upper limit of the crystallite size in the direction perpendicular to the (001) plane is not particularly limited, but is usually, for example, 300 nm or less, preferably 250 nm or less, and more preferably 200 nm or less.

The above crystallite size can be determined by measuring the X-ray diffraction pattern of magnesium hydroxide particles using powder X-ray diffraction method, and calculating the crystallite size (crystallite size perpendicular to the above lattice plane) using Scherrer's formula from the spread (half-width) of the diffraction line assigned to the target lattice plane.

As a method for obtaining magnesium hydroxide having the above-mentioned specific crystallite size range, for example, the following method can be mentioned.
Magnesium hydroxide is prepared by hydration reaction using an aqueous solution of magnesium salt (magnesium chloride, magnesium nitrate, etc.) or an aqueous dispersion of magnesium oxide obtained by a conventional method as a raw material and adding an alkaline substance (lithium hydroxide, sodium hydroxide, calcium hydroxide, ammonia water, etc.). At this time, by adding an organic acid such as formic acid, acetic acid, propionic acid, etc., a polybasic acid such as nitric acid, sulfuric acid, or a mixture thereof, the solubility of the generated magnesium hydroxide can be adjusted, or by appropriately adjusting the temperature (e.g., 150°C to 270°C) and time (e.g., 30 minutes to 10 hours) of the hydrothermal reaction, particles with different crystallite sizes can be prepared. The more the amount of acid added, the more the crystal growth advances and the larger the crystallite size. Also, the higher the temperature of the hydrothermal reaction and the longer the time, the more the crystal growth advances and the larger the crystallite size.

In the present invention, general commercially available magnesium hydroxide can also be used. Examples of commercially available magnesium hydroxide that can be used in the present invention include 200-06H manufactured by Kyowa Chemical Industry Co., Ltd., UP650-1 manufactured by Ube Materials Co., Ltd., MAGSTAR #20 manufactured by Tateho Chemical Industry Co., Ltd., and #200 manufactured by Konoshima Chemical Co., Ltd.

The content of the inorganic particles is preferably 30 to 90 mass% relative to 100 mass% of the diaphragm for alkaline water electrolysis. When the content of the inorganic particles is within the above range, the diaphragm for alkaline water electrolysis has excellent ion permeability. The content of the inorganic particles is more preferably 35 mass% or more relative to 100 mass% of the diaphragm for alkaline water electrolysis, more preferably 40 mass% or more, more preferably 85 mass% or less, and even more preferably 80 mass% or less.

The diaphragm for alkaline water electrolysis preferably contains 20 to 60 parts by mass of the organic polymer resin per 100 parts by mass of the inorganic particles. When the content ratio of the inorganic particles to the organic polymer resin is within the above-mentioned range, the diaphragm for alkaline water electrolysis has excellent ion permeability, gas barrier property, heat resistance, and alkali resistance. The diaphragm for alkaline water electrolysis more preferably contains 22 to 55 parts by mass, and even more preferably contains 25 to 50 parts by mass, of the organic polymer resin per 100 parts by mass of the inorganic particles.

(Porous support)
The diaphragm for alkaline water electrolysis may further comprise a porous support. The porous support is porous and ion permeable, and can serve as a support for the diaphragm for alkaline water electrolysis. The inclusion of the porous support improves the strength of the porous membrane, thereby improving the strength of the diaphragm for alkaline water electrolysis and preventing damage to the ion permeable membrane during electrolysis. The porous support is preferably a sheet-like member.

Examples of the material for the porous support include resins such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyketone, polyimide, polyetherimide, and fluororesin. These may be used alone or in combination of two or more. Among them, in terms of excellent heat resistance and alkali resistance, it is preferable to include at least one resin selected from the group consisting of polypropylene, polyethylene, and polyphenylene sulfide, and it is more preferable to include at least one resin selected from the group consisting of polypropylene and polyphenylene sulfide.

The form of the porous support may be, for example, a nonwoven fabric, a woven fabric, a mesh, a porous membrane, or a mixture of a nonwoven fabric and a woven fabric, but is preferably a nonwoven fabric, a woven fabric, or a mesh, more preferably a nonwoven fabric or a mesh, and even more preferably a nonwoven fabric.

As the porous support, a nonwoven fabric, a woven fabric, or a mesh containing at least one resin selected from the group consisting of polypropylene, polyethylene, and polyphenylene sulfide is preferable.Furthermore, as the porous support, a nonwoven fabric or a mesh containing polyphenylene sulfide is preferable.
The above-mentioned porous support is preferably one which has been subjected to a hydrophilization treatment such as gas treatment or application of an oil to fibers in order to improve adhesion to the coating film.

When the porous support is in the form of a sheet, the thickness of the porous support is not particularly limited as long as the diaphragm for alkaline water electrolysis can exhibit the effects of the present invention, but is, for example, preferably 30 to 300 μm, more preferably 50 to 250 μm, and even more preferably 100 to 200 μm.

In the diaphragm for alkaline water electrolysis, the porous membrane may be laminated on one or both sides of the porous support, or the porous support and the porous membrane may be integrated. The integration refers to a state in which the porous membrane contains a part or the whole of the porous support. In terms of increasing the strength and toughness of the diaphragm for alkaline water electrolysis, the diaphragm for alkaline water electrolysis is preferably a composite in which the porous support and the porous membrane are integrated.

The porosity of the diaphragm for alkaline water electrolysis is preferably 20 to 80 volume%, more preferably 25 to 75 volume%, and even more preferably 30 to 70 volume%. When the porosity is within the above range, the pores in the diaphragm are continuously filled with the electrolytic solution, thereby providing a layer with excellent ion permeability and excellent gas barrier property.
The porosity can be determined by immersing the diaphragm for alkaline water electrolysis in the electrolytic solution overnight and measuring the mass of the diaphragm before and after absorbing the electrolyte. Specifically, the porosity can be determined by the following formula:
Porosity (volume %)=(mass of diaphragm after immersion−mass of diaphragm before immersion)/density of electrolyte/volume of diaphragm×100

The pore size of the diaphragm for alkaline water electrolysis is preferably 0.01 to 1 μm, more preferably 0.05 to 0.9 μm, and even more preferably 0.1 to 0.8 μm. When the pore size is within the above range, ion permeability is even more excellent.
The pore size can be determined from a surface observation image (magnification × 25,000) of the diaphragm for alkaline water electrolysis by FE-SEM measurement. Specifically, for any ten pores in the FE-SEM image of the diaphragm for alkaline water electrolysis, a diameter passing through the center of gravity of each selected pore is measured using analysis software (Image-Pro Premier, manufactured by Nippon Roper Co., Ltd.) and the pore size is determined by calculating an average value.

The thickness of the diaphragm for alkaline water electrolysis is preferably 50 to 1000 μm in terms of excellent electrolysis efficiency and durability. The thickness of the diaphragm for alkaline water electrolysis is more preferably 100 μm or more, even more preferably 200 μm or more, more preferably 500 μm or less, and even more preferably 400 μm or less.

2. Method for producing the diaphragm for alkaline water electrolysis A method for producing the diaphragm for alkaline water electrolysis of the present invention will be described.
The method for producing the diaphragm for alkaline water electrolysis of the present invention is not particularly limited and any known method can be applied. However, the non-solvent induced phase separation method is preferred in that a diaphragm having the above-described surface state can be efficiently produced. Specifically, a production method including the following steps (1) to (4) is preferred:
(1) A step of preparing a dispersion solution containing an organic polymer resin, inorganic particles, and a solvent; (2) A step of forming a coating film using the dispersion solution; (3) A step of contacting the coating film with a non-solvent for the organic polymer resin to solidify the coating film; (4) A step of drying the solidified coating film to obtain a porous film.

In step (3) of the production method, the contact speed of the coating with the non-solvent is preferably 0.3 m/min or more. When the contact speed of the coating with the non-solvent is within the above-mentioned range, a diaphragm having the above-mentioned surface condition can be easily produced. Such a method for producing a diaphragm for alkaline water electrolysis, comprising the above-mentioned steps (1) to (4), and characterized in that in step (3), the contact speed of the coating with the non-solvent is 0.3 m/min or more, also constitutes one aspect of the present invention.
Each step in the method for producing a diaphragm for alkaline water electrolysis of the present invention will be described below.

Process (1)
The method for producing a diaphragm for alkaline water electrolysis of the present invention includes a step (1) of preparing a dispersion solution containing an organic polymer resin, inorganic particles, and a solvent. The dispersion solution is a solution for forming a porous membrane containing the above-mentioned organic polymer resin and inorganic particles. The organic polymer resin and inorganic particles are the same as the organic polymer resin and inorganic particles described in "1. Diaphragm for alkaline water electrolysis", respectively.

The preparation of the dispersion solution is not particularly limited, and can be performed by mixing the organic polymer resin, inorganic particles, and a solvent. When mixing the organic polymer resin, inorganic particles, and a solvent, the three components may be mixed simultaneously, or a dispersion solution (slurry) in which the inorganic particles are dispersed in a solvent may be prepared in advance, and then the dispersion solution and the organic polymer resin may be mixed. Alternatively, a dispersion solution (slurry) or solution in which the inorganic particles and the organic polymer resin are each dispersed or dissolved in a solvent may be prepared in advance, and then the dispersion solution and the solution may be mixed. Among these, a method in which a dispersion solution is prepared by dispersing or dissolving the inorganic particles and the organic polymer resin in a solvent, respectively, in a uniform manner and easily producing a membrane with a smooth surface, is preferred in that it allows the organic polymer resin and the inorganic particles to be uniformly mixed, and then the dispersion solution is mixed with the solution to prepare the dispersion solution.

The solvent to be mixed with the organic polymer resin or inorganic particles is preferably one that has the property of being able to dissolve the organic polymer resin, and examples of such solvents include organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. These solvents may be used alone or in combination of two or more. Of these, N-methyl-2-pyrrolidone is preferred because it easily dissolves the organic polymer resin. The solvent may contain other solvents in addition to the organic solvents mentioned above.

The above-mentioned mixing and dispersion methods are not particularly limited, and include known mixing and dispersion means such as methods using a mixer, ball mill, jet mill, disperser, sand mill, roll mill, pot mill, paint shaker, etc.

The concentration of the organic polymer resin in the solution in which the organic polymer resin is dissolved is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 30% by mass, in order to facilitate mixing.

The solution containing the organic polymer resin and the dispersion containing the inorganic particles are preferably mixed so that the organic polymer resin is present in an amount of 20 to 60 parts by weight, more preferably 22 to 55 parts by weight, and even more preferably 25 to 50 parts by weight per 100 parts by weight of the inorganic particles.

Process (2)
The method for producing a diaphragm for alkaline water electrolysis of the present invention subsequently includes a step (2) of forming a coating film using the dispersion solution obtained in the step (1).
Examples of the method for forming the coating film include a method in which the dispersion solution is applied onto a substrate.
The coating method is not particularly limited, and examples thereof include known coating means such as die coating, spin coating, gravure coating, curtain coating, spraying, and methods using an applicator or coater.

The substrate is not particularly limited as long as it can be coated with the dispersion solution to form a coating film, and examples of the substrate include films or sheets made of resins such as polytetraethylene terephthalate, polyethylene naphthalate, polypropylene, polyethylene, polyvinyl chloride, polyvinyl acetal, polymethyl methacrylate, and polycarbonate, and glass plates. Among these, polytetraethylene terephthalate films or sheets are preferred.

When the diaphragm for alkaline water electrolysis includes a porous support, the dispersion solution may be applied to the porous support. Examples of the application method include a method of directly applying the dispersion solution to the porous support, a method of immersing the porous support in the dispersion solution, and a method of applying the dispersion solution to the substrate and contacting the porous support with the applied material to impregnate the porous support with the dispersion solution. By impregnating the porous support with the dispersion solution, a composite in which the porous membrane and the porous support are integrated can be produced.

The amount of the dispersion solution applied is not particularly limited, and may be appropriately set so that the resulting membrane has the desired thickness that can achieve the above-mentioned effects.

The step (2) of forming the coating film is preferably carried out under conditions of an absolute humidity of 20 g/ ^m3 or less. By carrying out the step (2) under the above conditions, a membrane having the above surface condition can be produced more efficiently. The step (2) is more preferably carried out under conditions of an absolute humidity of 20 g/ ^m3 or less, and even more preferably carried out under conditions of an absolute humidity of 10 g/ ^m3 or less.
The lower limit of the absolute humidity is not particularly limited and may be 0 g/ ^m3. From the viewpoint of excellent economic efficiency, however, it is usually preferable that the lower limit is 0.5 g/ ^m3 or more, and more preferably 1.0 g/ ^m3 or more.
The above absolute humidity can be determined by multiplying the relative humidity at the working atmosphere temperature for forming the coating film by the amount of saturated water vapor.

Process (3)
The method for producing a diaphragm for alkaline water electrolysis of the present invention includes a step (3) of contacting the coating film formed in the step (2) with a non-solvent for the organic polymer resin to solidify the coating film.
By contacting the coating with a non-solvent for the organic polymer resin, the non-solvent diffuses into the coating, and the organic polymer resin that is not soluble in the non-solvent solidifies. Meanwhile, the solvent in the coating that is soluble in the non-solvent dissolves from the coating. Due to this phase separation, the organic polymer resin solidifies, and a film having pores (porous film) is formed.

Examples of a method for contacting the coating film with the non-solvent include a method in which the coating film is immersed in the non-solvent (coagulation bath).

The non-solvent for the organic polymer resin may be a solvent that does not substantially dissolve the organic polymer resin. The term "not substantially dissolving the organic polymer resin" refers to a case where the solubility of the organic polymer resin in 100 g of the solvent is 100 mg or less.
Examples of the non-solvent include water such as pure water, distilled water, and ion-exchanged water; lower alcohols such as methanol, ethanol, and propyl alcohol; and mixed solvents thereof, among which water is preferred from the viewpoint of economy and wastewater treatment, and ion-exchanged water is more preferred. In addition, the non-solvent in which the coating film is immersed may contain a small amount of the same solvent as the solvent contained in the coating film, in addition to the above-mentioned components.

In the production method of the present invention, when the coating film is brought into contact with the non-solvent, the contact speed between the coating film and the non-solvent is preferably 0.3 m/min or more. When the contact speed is in the above-mentioned range, a membrane having a surface with the above-mentioned depressed portions within a predetermined range can be obtained. The contact speed is more preferably 0.5 m/min or more, and even more preferably 0.7 m/min or more. There is no particular upper limit to the contact speed, but it is preferably 20 m/min or less, and more preferably 10 m/min or less.
The contact speed can be set by the peripheral speed of the roller that transports the coating film, or the like.

In step (3) of contacting the coating film with the non-solvent to solidify the coating film, the atmosphere before contacting the coating film with the non-solvent is preferably carried out under conditions of an absolute humidity of 20 g/ ^m3 or less. By carrying out step (3) under the above conditions, a membrane having the above surface condition can be produced more easily. Step (3) is more preferably carried out under conditions of 15 g/m3 or less, and even more preferably under conditions of an absolute humidity of ¹⁰ g/ ^m3 or less. The absolute humidity can be calculated by multiplying the relative humidity at the working atmosphere temperature for forming the coating film by the amount of saturated water vapor.
The lower limit of the absolute humidity is not particularly limited and may be 0 g/ ^m3. From the viewpoint of excellent economic efficiency, however, it is usually preferable that the lower limit is 0.5 g/ ^m3 or more, and more preferably 1.0 g/ ^m3 or more.

The temperature conditions in step (3) above are preferably 10 to 30°C, more preferably 15 to 25°C, and even more preferably 20 to 25°C, in that it is easier to control the absolute humidity constant.

Process (4)
The method for producing a diaphragm for alkaline water electrolysis of the present invention further includes a step (4) of drying the coating film solidified in the step (3) to obtain a porous membrane. The coating film solidified in the step (3) is dried to remove the non-solvent, thereby obtaining a porous membrane.
The drying temperature is preferably from 60 to 120°C, and more preferably from 70 to 100°C.
The drying time is preferably from 2 to 120 minutes, more preferably from 5 to 60 minutes, and even more preferably from 10 to 30 minutes.

The diaphragm for alkaline water electrolysis of the present invention can be easily produced by the above-mentioned steps (1) to (4). The method for producing the diaphragm for alkaline water electrolysis may include other known steps in addition to the above-mentioned steps (1) to (4).

3. Applications The diaphragm for alkaline water electrolysis of the present invention suitably suppresses retention of gas bubbles generated during electrolysis. Furthermore, the diaphragm for alkaline water electrolysis of the present invention is excellent in ion permeability, gas barrier property and alkali resistance. The diaphragm for alkaline water electrolysis of the present invention can be suitably used as a diaphragm for water electrolysis using an alkaline aqueous solution as the electrolyte.
An electrolysis apparatus and an electrolysis method using the diaphragm for alkaline water electrolysis of the present invention are described below.

(Electrolyzer)
The diaphragm for alkaline water electrolysis of the present invention is used as a component of an alkaline water electrolysis apparatus. The alkaline water electrolysis apparatus may, for example, include an anode, a cathode, and the diaphragm for alkaline water electrolysis disposed between the anode and the cathode. More specifically, the alkaline water electrolysis apparatus has an electrolytic cell including an anode chamber in which the anode is present, and a cathode chamber in which the cathode is present, separated by the diaphragm for alkaline water electrolysis.

The alkaline water electrolysis diaphragm is preferably installed so as to be in contact with the anode or the cathode, and more preferably so as to be in contact with the anode and the cathode. When the distance between the electrodes is smaller, the electrical resistance is smaller, and the electrolysis efficiency of the electrolysis device can be increased. When the alkaline water electrolysis diaphragm of the present invention is used, it is possible to suppress retention of generated air bubbles and achieve high electrolysis efficiency even in an electrolysis cell having a so-called "zero gap structure" in which the diaphragm is installed so as to be in contact with each electrode so as to minimize the distance between the electrodes. Therefore, the alkaline water electrolysis diaphragm of the present invention can be suitably used in an electrolysis device having a zero gap structure.

The above anode and cathode are not particularly limited as long as they are known electrodes, and examples include electrodes containing known conductive substrates such as copper, lead, nickel, chromium, titanium, gold, platinum, iron, metal compounds thereof, metal oxides, and alloys containing two or more of these metals.

The electrode may be one in which a catalyst layer is formed on the conductive substrate. The catalyst layer is not particularly limited, and examples thereof include known catalyst layers including metal compounds, metal oxides, and alloys containing nickel, cobalt, palladium, iridium, platinum, and the like.

The shape of the electrodes is not particularly limited, and may be any known shape such as a sheet, a rod, or a prism. However, a sheet shape is preferred since it has a large contact area with the alkaline water electrolysis diaphragm and can further improve the electrolysis efficiency of the electrolysis device.

The electrolysis device may further include other commonly used components, such as a gas-liquid separation tank for separating the generated gas from the electrolytic solution, a condenser for stably performing electrolysis, and a mist separator.
The diaphragm for alkaline water electrolysis of the present invention effectively suppresses retention of gas bubbles and can therefore be suitably used in a high-pressure system in which the size of gas bubbles becomes small.

(Electrolysis method)
The method for electrolyzing water using an alkaline water electrolysis apparatus comprising the diaphragm for alkaline water electrolysis of the present invention is not particularly limited and can be performed by a known method. For example, water can be electrolyzed by filling an alkaline water electrolysis apparatus comprising the above-mentioned diaphragm for alkaline water electrolysis of the present invention with an electrolytic solution and applying a current in the electrolytic solution.

As the electrolyte, an alkaline aqueous solution in which an electrolyte such as potassium hydroxide or sodium hydroxide is dissolved is preferably used. The concentration of the electrolyte in the electrolyte is not particularly limited, but is preferably 20 to 40% by mass in order to further increase the electrolysis efficiency.

The temperature at which electrolysis is carried out is preferably 50 to 120°C, more preferably 80 to 90°C, in that the ionic conductivity of the electrolyte is further improved and the electrolysis efficiency can be further increased. The current application conditions can be performed under known conditions and methods, and are usually 0.2 A/ ^cm2 or more, preferably 0.3 A/ ^cm2 or more. The higher the applied current density, the more hydrogen gas and oxygen gas can be obtained in a short period of time, and therefore hydrogen can be produced efficiently.
The electrolysis voltage is preferably adjusted to about 2 V, for example within a range not exceeding 1.5 to 2.5 V, so that the current density is high.

As described above, the diaphragm for alkaline water electrolysis of the present invention effectively suppresses the retention of air bubbles generated during water electrolysis. It also has excellent ion permeability, gas barrier properties, and alkali resistance. By using the diaphragm for alkaline water electrolysis of the present invention, air bubble retention is suppressed and electrolysis can be performed with high electrolysis efficiency even in an electrolysis device with a zero gap structure.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

In the examples, various evaluations were carried out by the following methods.
(Method of Measuring Film Thickness)
The thickness of the obtained diaphragm for alkaline water electrolysis was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation). Measurements were taken at 10 random points on a 5 cm square diaphragm sample, and the average value was defined as the film thickness.

(Method of measuring the average area and area ratio of depressions)
Using a laser microscope VK9700 (manufactured by Keyence Corporation), observation images of the diaphragm surface were obtained at 150x objective magnification for 10 arbitrary fields of view of the diaphragm sample of 5 cm square. For each obtained image, analysis software VK Analyzer VK-H1A1 (manufactured by Keyence Corporation) was used to perform height analysis of line roughness measurement on the diagonal line of the observation field, and a point that was -1.5 μm in the Z direction (height direction) from the reference plane in the obtained cross-sectional profile was defined as reference point A. It is preferable for the analysis that there are three or more reference points A. Then, using image analysis software (Image-Pro Premier, manufactured by Nippon Roper Co., Ltd.), the obtained image was used to show points farther from the reference plane than the reference point A (points ≦-1.5 μm in the Z direction) in dark color, and the points that were darker than the reference point A defined above were automatically extracted and binarized. The area of each depression in the dark parts was determined and the "average area of depression A in one visual field" was calculated from the simple average (number average) of the areas, and the ratio of the total area of each depression A to the area of the entire visual field observed, i.e., the "area proportion of depression A in one visual field" was calculated. Similar image analysis was performed on a total of 10 visual fields, and simple averages (number averages) were obtained for the average area and area proportion of depression A in each visual field, which were defined as the "average area of depression A" and "area proportion of depression A" of the diaphragm sample.

Furthermore, a point located +1.5 μm from the reference plane in the Z direction (height direction) from the cross-sectional profile obtained in the same manner was determined as reference point B. It is preferable for the number of reference points B to be three or more points for analysis. After that, image analysis software was used for the acquired image to display points (points located ≧1.5 μm in the Z direction) farther from the reference plane than the reference point B in a light color, and points that were lighter in color than the reference point B determined above were automatically extracted and binarized. Then, the areas (depressed areas B) surrounded by the light color were each specified to determine their areas, and the "average area of the depressed areas B in one visual field" was calculated from the simple average (number average) of the areas. In addition, the ratio of the total area of each depressed area B to the area of the entire visual field of observation, i.e., the "area ratio of the depressed areas B in one visual field" was calculated. A similar image analysis was performed for a total of 10 visual fields, and the simple average values (number averages) of the average area and area ratio of the depressed areas B in each visual field were calculated, and these were determined as the "average area of the depressed areas B" and the "area ratio of the depressed areas B" of the diaphragm sample.

(Method of measuring surface roughness)
Using a VK9700 (manufactured by Keyence Corporation), observation images of the diaphragm surface were obtained at 150x objective magnification for 10 arbitrary fields of view of a diaphragm sample of 5 cm square. For each obtained image, analysis software VK Analyzer VK-H1A1 (manufactured by Keyence Corporation) was used to specify the entire observation field and perform measurements according to a method conforming to JIS B0601:2001. A total of 10 fields of view were measured, and the simple average value was taken as the representative value of the surface roughness of the diaphragm.

(Electrical property evaluation)
The obtained alkaline water electrolysis diaphragm was evaluated for alkaline water electrolysis as follows. A platinum mesh (manufactured by Nilaco Corporation, product number PT-358056/55 mesh) cut to 3 cm x 3 cm was used as the anode electrode. A nickel mesh (manufactured by Nilaco Corporation, product number NI-318040/40 mesh) cut to 3 cm x 3 cm was used as the cathode electrode. The platinum mesh was placed in contact with the obtained alkaline water electrolysis diaphragm (zero gap structure) and fixed so as not to shift when assembling the electrolytic cell. The electrolytic cell was assembled so that the cathode electrode chamber and the anode electrode chamber were separated by the diaphragm. An aqueous potassium hydroxide solution with a concentration of 30% by weight was used as the electrolytic solution. First, the electrolytic cell was filled with the electrolytic solution, and then the solution was circulated and heated, and the solution temperature was adjusted to 40°C as measured by a thermometer installed immediately before the solution flowed into the electrolytic cell. After the electrolyte reached 40°C and 30 minutes had passed, a constant current density of 0.3 A/ ^cm2 was applied continuously for 10 minutes. The current density was then increased to 0.5 A/ ^cm2 , and the voltage was recorded every minute. The collected voltages were held until they stabilized within ±3% of the average value of the five consecutive points. After the voltage was stabilized, 10 voltage measurements were taken every minute, and the average of the 10 measured values was calculated.

Example 1
(1. Preparation of Magnesium Hydroxide Dispersion)
Magnesium hydroxide (average particle size 0.20 μm, plate-like, aspect ratio 6.21) and N-methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a mass ratio of 1:1, and a dispersion treatment was carried out at room temperature for 6 hours in a pot mill containing zirconia media balls to prepare a magnesium hydroxide dispersion.

(2. Preparation of polysulfone resin solution)
A polysulfone resin (manufactured by BASF, product number Ultrason S3010) was dissolved in N-methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a concentration of 30% by mass.

(3. Preparation of Coating Fluid)
The magnesium hydroxide dispersion and polysulfone resin solution obtained above were weighed out so that the solid content was 48% by mass and the polysulfone resin (PSU) was 25 parts by mass per 100 parts by mass of magnesium hydroxide, and mixed at room temperature and 1000 rpm for about 10 minutes in a planetary centrifugal mixer (Thinky Corporation, product number: Awatori Rentaro ARE-500). The resulting mixture was filtered through a 200 mesh SUS filter to obtain a coating liquid.

(4. Formation of Coating Film)
In an atmosphere of absolute humidity of 12.7 g/ ^m3 , a polyphenylene sulfide nonwoven fabric (manufactured by Toray Industries, Inc., Torcon Paper #100) was directly applied to a running sheet of the fabric with the peripheral speed of an automatic conveying roller set to give a line speed of 3.0 m/min, and the coating liquid obtained was applied to the nonwoven fabric so that the diaphragm had a total thickness of 250 µm after drying, thereby impregnating the nonwoven fabric with the coating liquid. The nonwoven fabric impregnated with the coating liquid was immersed vertically into the water surface of a water tank and then subjected to a water bath for 5 minutes to solidify the coating liquid and form a membrane. After the water bath, the obtained membrane was dried in a dryer at 80°C for 10 minutes to obtain a diaphragm for alkaline water electrolysis composed of a composite of a nonwoven fabric and a membrane containing magnesium hydroxide and a polysulfone resin.
The average area of the depressed portions A of the obtained diaphragm was 3.3 ^μm2 , the area ratio of the depressed portions A was 9.0%, the average area of the depressed portions B was 0.8 ^μm2 , the area ratio of the depressed portions B was 0.7%, and the arithmetic mean roughness Ra was 0.47 μm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 1.81 V.
FIG. 1 shows an image of the surface of the obtained diaphragm for alkaline water electrolysis observed with a laser microscope (objective magnification: 150 times).

Example 2
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Example 1 (3. Preparation of coating solution), except that the amount of PSU was 50 parts by mass per 100 parts by mass of magnesium hydroxide. The obtained diaphragm had an average area of depressed portions A of 2.1 ^µm2 , an area ratio of depressed portions A of 12.4%, an average area of depressed portions B of 0.9 ^µm2 , an area ratio of depressed portions B of 0.5%, and an arithmetic mean roughness Ra of 0.39 µm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 1.88 V.

Example 3
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Example 1 (4. Formation of coating film), except that the absolute humidity was changed to 3.5 g/ ^m3 . The average area of the depressed portions A of the obtained diaphragm was 0.9 ^µm2 , the area ratio of the depressed portions A was 8.5%, there was no depressed portion B, and the arithmetic mean roughness Ra was 0.34 µm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 1.80 V.

Example 4
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Example 1 (4. Formation of coating film), except that the line speed was changed to 0.3 m/min and the absolute humidity was changed to 19.5 g/ ^m3 . The obtained diaphragm had an average area of depressed portions A of 5.9 ^µm2 , an area ratio of depressed portions A of 12.7%, an average area of depressed portions B of 0.9 ^µm2 , an area ratio of depressed portions B of 6.8%, and an arithmetic mean roughness Ra of 0.77 µm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 1.89 V.

<Comparative Example 1>
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Example 1 (4. Formation of coating film), except that the absolute humidity was changed to 20.9 g/ ^m3 . The obtained diaphragm had an average area of depressed portions A of 10.1 ^µm2 , an area ratio of depressed portions A of 23.8%, an average area of depressed portions B of 3.1 ^µm2 , an area ratio of depressed portions B of 1.2%, and an arithmetic mean roughness Ra of 0.82 µm. Electrical characteristics were evaluated, and the cell voltage at 0.5 A/ ^cm2 was 2.03 V.

<Comparative Example 2>
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Example 1 (4. Formation of coating film), except that the line speed was changed to 0.2 m/min. The obtained diaphragm had an average area of depressed portions A of 8.2 ^µm2 , an area ratio of depressed portions A of 21.4%, an average area of depressed portions B of 2.7 ^µm2 , an area ratio of depressed portions B of 2.8%, and an arithmetic mean roughness Ra of 0.96 µm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 2.08 V.

<Comparative Example 3>
A diaphragm for alkaline water electrolysis was prepared in the same manner as in Comparative Example 1, except that the line speed was changed to 0.2 m/min. The obtained diaphragm had an average area of depressed portions A of 8.6 ^µm2 , an area ratio of depressed portions A of 21.4%, an average area of depressed portions B of 5.0 ^µm2 , an area ratio of depressed portions B of 3.7%, and an arithmetic mean roughness Ra of 1.25 µm. Electrical characteristics were evaluated and the cell voltage at 0.5 A/ ^cm2 was 2.08 V.

Claims (6)

A method for using a diaphragm for alkaline water electrolysis, comprising installing a diaphragm for alkaline water electrolysis having an average area of depressed portions on at least one surface of the diaphragm of 7 ^µm2 or less and an area ratio of the depressed portions on the diaphragm surface of 20% or less in an electrolysis device having an anode and a cathode, comprising:
The diaphragm for alkaline water electrolysis comprises a porous membrane containing an organic polymer resin and inorganic particles, and a porous support, in which the porous membrane is laminated on only one side of the porous support,
a diaphragm for alkaline water electrolysis comprising: The method for using the diaphragm for alkaline water electrolysis according to claim 1, characterized in that the arithmetic mean roughness Ra of the diaphragm surface is 0.8 μm or less. The method for using the diaphragm for alkaline water electrolysis according to claim 1 or 2, characterized in that the diaphragm for alkaline water electrolysis contains an organic polymer resin and inorganic particles. The method for using the diaphragm for alkaline water electrolysis according to claim 3, characterized in that the inorganic particles are metal hydroxide particles and/or metal oxide particles. The method for using the diaphragm for alkaline water electrolysis according to claim 3 or 4, characterized in that the organic polymer resin is at least one resin selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone. An alkaline water electrolysis apparatus comprising an anode, a cathode, and a diaphragm for alkaline water electrolysis disposed between the anode and the cathode,
the diaphragm for alkaline water electrolysis comprises a porous membrane containing an organic polymer resin and inorganic particles, and a porous support, the porous membrane being laminated on only one side of the porous support, and the average area of depressed portions on at least one surface of the diaphragm is 7 ^µm2 or less and the area ratio of the depressed portions on the diaphragm surface is 20% or less, and the alkaline water electrolysis apparatus is installed in contact with the anode and the cathode.