Method for manufacturing diaphragm for alkaline water electrolysis, and diaphragm for alkaline water electrolysis

Abstract

The present invention provides a method for producing a diaphragm for alkaline water electrolysis use, in which the formation of macrovoids is prevented. The present invention is a method for producing a diaphragm for alkaline water electrolysis use which is provided with a porous layer, the method including a step for producing the porous layer using a composition comprising an organic polymer, inorganic particles, a compound represented by general formula (1) and a solvent. (1): R-X (In formula (1), R represents a hydrocarbon group having 6 or more carbon atoms; and X represents a hydrophilic functional group.)

Description

[Technical Field]

[0001] The present invention relates to a method for producing a diaphragm for alkaline water electrolysis, and a diaphragm for alkaline water electrolysis. [Background technology]

[0002] Alkaline water electrolysis (electrolysis of alkaline water) is known as one of the industrial methods for producing hydrogen gas. It is generally carried out by applying an electric current to water to which sodium hydroxide, potassium hydroxide, or the like has been added. For such alkaline water electrolysis, an electrolytic cell is used, which has an anode chamber in which an anode is placed and a cathode chamber in which a cathode is placed, separated by a diaphragm for alkaline water electrolysis (hereinafter also referred to as a diaphragm).

[0003] In the electrolysis of alkaline water, electrons (or ions) move from the cathode chamber to the anode chamber. Therefore, the diaphragm must have high ionic conductivity. Furthermore, the electrolysis of alkaline water is carried out using alkaline water with a high concentration of about 30%, at 80 to 100°C, and in some cases under high pressure of 1 MPa or more. Therefore, heat resistance, alkali resistance, etc. are also required.

[0004] Known membranes include porous membranes made of organic polymers such as polysulfone, which contain inorganic particles such as magnesium hydroxide. One known method for producing such membranes is the non-solvent induced phase separation (NIPS) method (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 021774 Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of extensive investigation, it was found that membranes obtained by non-solvent induced phase separation (NIPS) are prone to the formation of macrovoids, which may be a cause of fluctuations in ionic conductivity.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a diaphragm for alkaline water electrolysis in which the formation of macrovoids is suppressed. [Means for solving the problem]

[0008] The present invention provides a method for producing a diaphragm for alkaline water electrolysis having a porous layer, the method comprising the step of obtaining the porous layer using a composition comprising an organic polymer, inorganic particles, a compound represented by the following general formula (1), and a solvent: RX (1) (In formula (1), R represents a hydrocarbon group having 6 or more carbon atoms, and X represents a hydrophilic functional group.)

[0009] In the composition, the content of the compound represented by the general formula (1) is preferably 2 to 30% by mass relative to 100% by mass of the total content of the organic polymer and the inorganic particles.

[0010] The present invention also provides a diaphragm for alkaline water electrolysis comprising a porous layer containing an organic polymer and inorganic particles, comprising: the pair of main surfaces of the porous layer form the front and back surfaces of the diaphragm for alkaline water electrolysis; In the three cross-sectional layers obtained by dividing the cross section of the porous layer into three equal parts in the thickness direction, when two cross-sectional layers including the front and back surfaces are defined as a front layer and a back layer, and the other cross-sectional layers are defined as an internal layer, The inner layer is a diaphragm for alkaline water electrolysis, having an average pore size larger than that of at least one of the surface layer and the back surface layer.

[0011] The present invention also provides a diaphragm for alkaline water electrolysis, comprising: a porous layer containing an organic polymer and inorganic particles; and a porous support, the porous layer includes a non-impregnated layer that is not impregnated into the porous support; When the cross section of the non-impregnated layer is divided into three equal sections in the thickness direction to obtain three cross-sectional layers, one cross-sectional layer including the surface of the diaphragm for alkaline water electrolysis is designated as a surface layer, and the other two cross-sectional layers are designated as internal layers, The diaphragm for alkaline water electrolysis has an average pore size larger than that of the surface layer.

[0012] The present invention also provides a diaphragm for alkaline water electrolysis, comprising: a porous layer containing an organic polymer and inorganic particles; and a porous support, the porous layer includes an impregnated layer that impregnates the porous support and a non-impregnated layer that does not impregnate the porous support, When the cross section of the non-impregnated layer is divided into three equal sections in the thickness direction to obtain three cross-sectional layers, one cross-sectional layer including the surface of the diaphragm for alkaline water electrolysis is designated as a surface layer, and the other two cross-sectional layers are designated as internal layers, At least one of the inner layers is a diaphragm for alkaline water electrolysis, the average pore size of which is larger than that of the impregnated layer.

[0013] At least one of the inner layers preferably has a larger average pore size than the surface layer. [Effects of the Invention]

[0014] According to the present invention, a diaphragm for alkaline water electrolysis including a porous layer in which macrovoid formation is suppressed can be produced. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a photograph (observation image) of a cross section of a diaphragm for alkaline water electrolysis (mainly of the non-impregnated layer portion) taken using a scanning electron microscope, with reference lines and the like added. [Figure 2] FIG. 1 is a photograph (observation image) of a cross section (mainly of the impregnation layer portion) of a diaphragm for alkaline water electrolysis, taken using a scanning electron microscope, with reference lines and the like added. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention is described in detail below. In this specification, a numerical range indicated as "〇 to △" means "〇 or more and △ or less." For example, "35 to 400 nm" means "35 nm or more and 400 nm or less."

[0017] 1. Manufacturing method of diaphragm for alkaline water electrolysis The method for producing a diaphragm for alkaline water electrolysis of the present invention will now be described. The method for producing a diaphragm for alkaline water electrolysis of the present invention is a method for producing a diaphragm for alkaline water electrolysis having a porous layer, and includes a step of obtaining the porous layer using a composition comprising an organic polymer, inorganic particles, a compound represented by general formula (1) below, and a solvent: RX (1) (In formula (1), R represents a hydrocarbon group having 6 or more carbon atoms, and X represents a hydrophilic functional group.) The method for producing a diaphragm for alkaline water electrolysis of the present invention is also referred to as the production method of the present invention. The compound represented by general formula (1) is also referred to as compound (A), and the composition is also referred to as composition (P).

[0018] The organic polymer is a fluorine-based resin, an olefin-based resin, an aromatic hydrocarbon-based resin, or the like.

[0019] Fluorine-based resins 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.

[0020] The olefin resins include polyethylene, polypropylene, polybutene, polymethylpentene, and the like.

[0021] The aromatic hydrocarbon resins include polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyether sulfone, polyphenylene sulfide, polyphenyl sulfone, polyarylate, polyether imide, polyimide, and polyamide imide.

[0022] The organic polymer may contain only one or two or more of the listed fluorine-based resins, olefin-based resins, aromatic hydrocarbon-based resins, etc. Aromatic hydrocarbon-based resins are preferred in terms of excellent heat resistance, pressure resistance, and alkali resistance, and at least one selected from polysulfone, polyethersulfone, and polyphenylsulfone is more preferred, with polysulfone being even more preferred in terms of ease of solubility in solvents.

[0023] 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.

[0024] The inorganic particles may contain only one kind or two or more kinds of the listed metal hydroxides, metal oxides, sulfates, nitrides, carbides, etc. In order to improve the ionic conductivity of the diaphragm for alkaline water electrolysis, 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 still more preferred, and magnesium hydroxide is particularly preferred.

[0025] The inorganic particles may be surface-treated by known methods, such as with a silane coupling agent, stearic acid, oleic acid, or phosphoric acid ester.

[0026] The shape of the inorganic particles is not limited. They may be any shape, such as irregular, granular, flaky, or plate-like (e.g., hexagonal plate-like), or fibrous. From the viewpoint of improving adhesion to the organic polymer, granular, flaky, or plate-like shapes are preferred, flaky or plate-like shapes are more preferred, and flaky shapes are even more preferred. From the viewpoint of improving the strength of the diaphragm for alkaline water electrolysis, flaky or plate-like shapes are preferred, and flaky shapes are more preferred.

[0027] The average particle size of the inorganic particles is not limited. To enhance the strength of the diaphragm for alkaline water electrolysis, the average particle size is preferably 0.05 μm or more and 2.0 μm or less, more preferably 0.08 μm or more and 1.5 μm or less, and even more preferably 0.1 μm or more and 1 μm or less.

[0028] The average particle size refers to the volume-average particle size (D50) determined by particle size distribution measurement using a laser diffraction method. Specifically, the particle size distribution is measured using a laser diffraction / scattering particle size distribution analyzer (e.g., Horiba, Ltd., Model 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.

[0029] The aspect ratio of the inorganic particles is not limited. To improve the ionic conductivity of the diaphragm for alkaline water electrolysis, the aspect ratio is preferably 2.0 or more and 8.0 or less, more preferably 2.5 or more and 7.0 or less, and even more preferably 3.0 or more and 6.0 or less.

[0030] The aspect ratio refers to the ratio [(a) / (b)] of the longest diameter (a) to the shortest diameter (b). Inorganic particles are observed with a scanning electron microscope (SEM), and the ratio [(a) / (b)] is measured for each of any 10 inorganic particles in the resulting image using analysis software. The average value of the ratios [(a) / (b)] for the 10 inorganic particles is taken as the aspect ratio of the inorganic particle. Usually, the shortest diameter (b) is taken as the diameter that is perpendicular to the longest diameter.

[0031] Again, magnesium hydroxide is preferred among the inorganic particles in that it has excellent alkali resistance and durability and allows a diaphragm for alkaline water electrolysis to be obtained relatively inexpensively. As described above, the average particle size of magnesium hydroxide is preferably 0.05 μm or more and 2.0 μm or less. As described above, the aspect ratio of magnesium hydroxide is preferably 2.0 or more and 8.0 or less.

[0032] The magnesium hydroxide preferably has a crystallite size of 35 nm or more in the direction perpendicular to the (110) plane as measured by X-ray diffraction. This further enhances the ionic conductivity of the diaphragm for alkaline water electrolysis. In particular, a crystallite size of 40 nm or more is more preferred, 50 nm or more is even more preferred, 60 nm or more is even more preferred, and 65 nm or more is particularly preferred. There is no upper limit, but it is usually 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less.

[0033] That is, the crystallite diameter of magnesium hydroxide in the direction perpendicular to the (110) plane measured by X-ray diffraction is preferably 35 to 400 nm, more preferably 40 to 350 nm, even more preferably 50 to 300 nm, still more preferably 60 to 300 nm, and particularly preferably 65 to 300 nm.

[0034] The magnesium hydroxide preferably has a crystallite size of 15 nm or more in the direction perpendicular to the (001) plane as measured by X-ray diffraction. This further enhances the ionic conductivity of the diaphragm for alkaline water electrolysis. In particular, a crystallite size of 18 nm or more is more preferable, a crystallite size of 21 nm or more is even more preferable, and a crystallite size of 24 nm or more is even more preferable. The upper limit is not limited, but is usually 300 nm or less, preferably 250 nm or less, and more preferably 200 nm or less.

[0035] That is, the crystallite diameter in the direction perpendicular to the (001) plane of magnesium hydroxide measured by X-ray diffraction is preferably 15 to 300 nm, more preferably 18 to 250 nm, even more preferably 21 to 200 nm, and still more preferably 24 to 200 nm.

[0036] The crystallite size is determined by powder X-ray diffraction. The X-ray diffraction pattern of magnesium hydroxide particles is measured, and the crystallite size (crystallite size perpendicular to the lattice plane) is calculated using the Scherrer equation from the broadening (half-width) of the diffraction lines assigned to the target lattice plane.

[0037] Examples of methods for obtaining magnesium hydroxide within the specific crystallite size range described above include the following. Specifically, magnesium hydroxide is prepared by hydrating an aqueous solution of a magnesium salt (e.g., magnesium chloride, magnesium nitrate, etc.) or an aqueous dispersion of magnesium oxide obtained by a conventional method using an alkaline substance (e.g., lithium hydroxide, sodium hydroxide, calcium hydroxide, aqueous ammonia, etc.) as a raw material. The solubility of the resulting magnesium hydroxide can be adjusted by adding an organic acid such as formic acid, acetic acid, or propionic acid, a polybasic acid such as nitric acid or sulfuric acid, or a mixture thereof, or by appropriately adjusting the hydrothermal reaction temperature (e.g., 150°C to 270°C) and time (e.g., 30 minutes to 10 hours). The greater the amount of acid added, the more rapidly the crystal growth progresses, resulting in a larger crystallite size. Furthermore, the higher the hydrothermal reaction temperature and the longer the reaction time, the more rapidly the crystal growth progresses and the larger the crystallite size.

[0038] The inorganic particles may be commercially available products. For example, commercially available magnesium hydroxide products such as 200-06H manufactured by Kyowa Chemical Industry Co., Ltd., UP650-1 manufactured by Ube Materials Co., Ltd., MAGSTAR #20 manufactured by Tateho Chemical Industries Co., Ltd., and #200 manufactured by Konoshima Chemical Co., Ltd. may be used.

[0039] The compound (A) is represented by the following general formula (1). RX (1)

[0040] In general formula (1), R is a hydrocarbon group having 6 or more carbon atoms. The hydrocarbon group is not limited and may be an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a saturated hydrocarbon group, an unsaturated hydrocarbon group, a chain hydrocarbon group, a cyclic hydrocarbon group, or the like.

[0041] The hydrocarbon group is preferably an alkyl group, an alkenyl group, an aryl group, or an aromatic alkyl group.

[0042] The alkyl group may be a chain alkyl group such as hexyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, heptyl, octyl, 1-methylheptyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, or octadecyl; or a cyclic alkyl group such as cyclohexyl. An alkyl group having 6 to 18 carbon atoms is preferred, an alkyl group having 6 to 12 carbon atoms is more preferred, and an alkyl group having 6 to 10 carbon atoms is even more preferred.

[0043] The alkenyl group is a group in which one CC single bond in the enumerated alkyl groups is replaced with a double bond, etc. Alkenyl groups having 6 to 18 carbon atoms are preferred, and alkenyl groups having 6 to 12 carbon atoms are more preferred.

[0044] The aryl group includes a phenyl group, a tolyl group, a xylyl group, a naphthyl group, an anthryl group, a biphenyl group, a triphenyl group, etc. A phenyl group, a tolyl group, or a xylyl group is preferred. An aryl group having 6 to 18 carbon atoms is preferred, and an aryl group having 6 to 12 carbon atoms is more preferred.

[0045] The aromatic alkyl group is a benzyl group, a phenethyl group, a phenylpropyl group, a phenylpentyl group, a phenylhexyl group, a phenyloctyl group, etc. An aromatic alkyl group having 6 to 18 carbon atoms is preferred, an aromatic alkyl group having 6 to 12 carbon atoms is more preferred, and an aromatic alkyl group having 6 to 10 carbon atoms is even more preferred.

[0046] The hydrocarbon group is preferably a hydrocarbon group having 6 to 12 carbon atoms. More preferably, it is at least one selected from an alkyl group having 6 to 12 carbon atoms, an alkenyl group having 6 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aromatic alkyl group having 6 to 12 carbon atoms. The hydrocarbon group is preferably at least one selected from an alkyl group and an aromatic alkyl group, more preferably at least one selected from an alkyl group having 6 to 12 carbon atoms and an aromatic alkyl group having 6 to 12 carbon atoms, even more preferably at least one selected from an alkyl group having 6 to 10 carbon atoms and an aromatic alkyl group having 6 to 10 carbon atoms, and even more preferably at least one selected from an alkyl group having 6 to 10 carbon atoms.

[0047] The hydrocarbon group may have a substituent. The substituent is a halogen atom, an alkoxy group, or the like. The halogen atom is a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, or the like. A fluorine atom, a chlorine atom, or a bromine atom is preferred. The alkoxy group is a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an s-butoxy group, a t-butoxy group, a pentyloxy group, a phenoxy group, a cyclohexyloxy group, a benzyloxy group, or the like. An alkoxy group having 1 to 18 carbon atoms is preferred, an alkoxy group having 1 to 6 carbon atoms is more preferred, and a methoxy group is even more preferred.

[0048] X in general formula (1) is a hydrophilic functional group. The hydrophilic functional group is not limited. It may be an acidic functional group such as a carboxyl group (-COOH), a phosphate group (-OPO(OH)), a hydroxyl group (-OH), a sulfonic acid group (-SOH), a phosphonic acid group (-PO(OH)), a phosphinic acid group (-PO(OH)-), or a mercapto group (-SH); or a basic functional group such as an amino group, an ammonium group, an imino group, an amide group, an imide group, or a maleimide group.

[0049] During the process of forming the porous layer of the diaphragm for alkaline water electrolysis using composition (P), compound (A) is thought to interact with the organic polymer at the R (hydrocarbon group) portion and with the inorganic particles at the X (hydrophilic functional group) portion. It is presumed that this interaction suppresses the formation of macrovoids. The reason for this presumption will be explained later.

[0050] The compound (A) is preferably removed after the formation of the porous layer in order to increase the ionic conductivity of the resulting porous layer. From this viewpoint, the hydrophilic functional group is preferably a hydroxyl group or a carboxyl group, which has a moderate interaction force with inorganic particles, and more preferably a hydroxyl group.

[0051] From the same viewpoint, it is also preferable that the compound (A) is easily volatile. The boiling point of the compound (A) at normal pressure is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0052] Considering all the above, compound (A) is preferably a saturated aliphatic alcohol having 6 to 10 carbon atoms. For example, at least one selected from primary alcohols such as cyclohexanol, 1-hexanol, 2-hexanol, 2-methyl-1-pentanol, 1-heptanol, 1-octanol, 2-octanol (1-methylheptanol), 2-ethylhexanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol; secondary alcohols such as 2-hexanol and 3-methyl-2-pentanol; and tertiary alcohols such as 2-methyl-2-pentanol are preferred.

[0053] The solubility of the compound (A) in water at 25° C. is preferably 0.001 to 5% by mass. This makes it easier to suppress the formation of macrovoids. In particular, the solubility is more preferably 0.01 to 3% by mass, and even more preferably 0.05 to 2% by mass.

[0054] The solvent is an organic solvent capable of dissolving the organic polymer. Examples include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide. The solvent may contain one or more of these solvents. N-methyl-2-pyrrolidone is preferred because it has excellent solubility for organic polymers and excellent dispersibility for inorganic particles. The solvent may also contain a non-organic solvent such as water.

[0055] The total content of the organic polymer, inorganic particles, and compound (A) in composition (P) is preferably 20% by mass or more, based on 100% by mass of composition (P). In particular, 30% by mass or more is more preferable, and 40% by mass or more is even more preferable. There is no upper limit, but it is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. That is, the total content of the organic polymer, inorganic particles, and compound (A) in composition (P) is preferably 20 to 80% by mass, more preferably 30 to 60% by mass, and even more preferably 40 to 50% by mass, based on 100% by mass of composition (P).

[0056] The content of inorganic particles in composition (P) is preferably 50 to 90% by mass relative to 100% by mass of the total content of the organic polymer and inorganic particles. In particular, the upper limit is more preferably 85% by mass, and even more preferably 80% by mass. The lower limit is more preferably 55% by mass, and even more preferably 60% by mass. The content of inorganic particles in composition (P) is more preferably 55 to 85% by mass, and even more preferably 60 to 80% by mass relative to 100% by mass of the total content of the organic polymer and inorganic particles.

[0057] The content of compound (A) in composition (P) is preferably 2 to 30% by mass relative to 100% by mass of the total content of the organic polymer and inorganic particles. It is particularly preferably 2.5% by mass or more, even more preferably 3% by mass or more, and even more preferably 5% by mass or more. It is also more preferably 20% by mass or less, and even more preferably 15% by mass or less. The content of compound (A) in composition (P) is more preferably 2.5 to 20% by mass, even more preferably 3 to 15% by mass, and even more preferably 5 to 15% by mass relative to 100% by mass of the total content of the organic polymer and inorganic particles.

[0058] The composition (P) may contain a dispersant. The dispersant is a cationic surfactant, an anionic surfactant, a polymer dispersant, or the like. The cationic surfactant preferably has a hydrocarbon chain having 5 or more carbon atoms. The anionic surfactant preferably has a hydrocarbon chain having 5 or more carbon atoms. The polymer dispersant preferably contains a hydrocarbon chain having 5 or more carbon atoms as a constituent unit (repeating unit) and has a hydrophilic functional group. The hydrophilic functional group is an acidic functional group such as a carboxy group, a phosphate group, or a sulfonic acid group; or a basic functional group such as an amino group. In particular, a carboxy group or a phosphate group is preferred.

[0059] The content of the dispersant in composition (P) is preferably more than 0.01 mass% and not more than 8.0 mass%, more preferably 0.1 mass% or more and 6.0 mass% or less, and even more preferably 1.0 mass% or more and 5.0 mass% or less, relative to 100 mass% of the inorganic particles contained in composition (P).

[0060] The composition (P) may contain a hydrophilic additive. The hydrophilic additive may be an organic or inorganic hydrophilic additive. Organic hydrophilic additives include water-soluble polymers such as polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyethyleneimine having a molecular weight of less than 100,000, polyacrylic acid, and dextran; surfactants; glycerin; and sugars. Polyethyleneimine and polyacrylic acid are particularly preferred. Inorganic hydrophilic additives include metal chlorides such as calcium chloride, magnesium chloride, lithium chloride, sodium chloride, and potassium chloride. Metal chlorides are particularly preferred.

[0061] The content of the hydrophilic additive in composition (P) is preferably 0.001 to 20% by mass relative to 100% by mass of the inorganic particles. When the hydrophilic additive is a metal chloride, the content is preferably 0.001 to 15% by mass, more preferably 0.01 to 12% by mass, and even more preferably 0.05 to 10% by mass, relative to 100% by mass of the inorganic particles.

[0062] The composition (P) may contain other additives as required.

[0063] The process of obtaining a porous layer using the composition (P) includes the following steps (1) to (3). (1) A step of preparing the composition (P). (2) A step of forming the composition (P) into a coating film. (3) A process for making the coating film into a porous layer.

[0064] Step (1) is a step of preparing composition (P) by mixing an organic polymer, inorganic particles, compound (A), and a solvent. The mixing method and procedure are not limited. Any known mixing method may be used. For example, a mixer, ball mill, jet mill, disperser, sand mill, roll mill, pot mill, or paint shaker may be used. The mixing procedure may be arbitrary. For example, the three components of organic polymer, inorganic particles, and compound (A) may be mixed into a solvent simultaneously or in any order. Alternatively, the organic polymer, inorganic particles, and compound (A) may be mixed separately into a solvent, and then the resulting mixture may be mixed.

[0065] Step (2) is a step of applying the composition (P) obtained in step (1) to a substrate or a porous support to form a coating film.

[0066] The coating method for the substrate includes die coating, spin coating, gravure coating, curtain coating, spraying, using an applicator, coater, and the like.

[0067] The substrate is a film or sheet made of a resin such as polytetraethylene terephthalate, polyethylene naphthalate, polypropylene, polyethylene, polyvinyl chloride, polyvinyl acetal, polymethyl methacrylate, polycarbonate, etc., or a glass plate, etc. A polytetraethylene terephthalate film or sheet is preferred.

[0068] Step (2) is preferably a step of applying composition (P) to a porous support. The application method is not limited. It may be a method of directly applying composition (P) to a porous support, a method of immersing a porous support in composition (P), or a method of applying composition (P) to the above-mentioned substrate to form a coating film, bringing the porous support into contact with the coating film, and impregnating the porous support with composition (P).

[0069] The coating film may be provided on one side or both sides of the porous support. The entire coating film may be laminated on the surface of the porous support, or a portion of the coating film may be impregnated into the porous support and the remainder may be laminated on the surface of the porous support. In a form in which the coating film is impregnated into the porous support, the coating film may be impregnated into a portion of the porous support in the thickness direction, or may be impregnated throughout the entire thickness direction of the porous support. The degree to which the coating film is impregnated into the porous support can be adjusted by appropriately adjusting the application method, the viscosity of the composition (P), etc.

[0070] The porous support is a resin such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyketone, polyimide, polyetherimide, or fluorine-based resin. It may contain only one of these, or two or more. From the viewpoint of excellent heat resistance and alkali resistance, at least one selected from polypropylene, polyethylene, and polyphenylene sulfide is preferred, and at least one selected from polypropylene and polyphenylene sulfide is more preferred.

[0071] The form of the porous support is not limited. It may be a nonwoven fabric, a woven fabric, a mesh, a porous membrane, or a mixture of a nonwoven fabric and a woven fabric. Nonwoven fabric, a woven fabric, or a mesh is preferred, nonwoven fabric and mesh are more preferred, and nonwoven fabric is even more preferred.

[0072] The porous support is preferably a nonwoven fabric, woven fabric, or mesh containing at least one resin selected from polypropylene, polyethylene, and polyphenylene sulfide, and more preferably a nonwoven fabric or mesh containing polyphenylene sulfide.

[0073] When the porous support is in the form of a sheet, there are no limitations on its thickness. For example, it is 30 to 2000 μm. It is preferably 50 to 1000 μm, more preferably 80 to 500 μm, and even more preferably 80 to 250 μm.

[0074] The thickness of the porous support can be determined by observing the cross section with a field emission scanning electron microscope (FE-SEM). For example, the average value of thicknesses at any five points may be used as the thickness of the porous support.

[0075] Step (3) is a step of forming a porous layer from the coating film obtained in step (2). In the present invention, at least a non-solvent induced phase separation method is carried out.

[0076] In the non-solvent-induced phase separation method, a liquid containing a non-solvent for the organic polymer contained in the coating film obtained in step (2) (non-solvent-containing liquid) is used. When this non-solvent-containing liquid is brought into contact with the coating film, the non-solvent diffuses into the coating film. At this time, the solvent in the coating film that is soluble in the non-solvent dissolves from the coating film. As a result, the organic polymer that is not soluble in the non-solvent solidifies, forming a porous layer.

[0077] In conventional methods, many macrovoids are formed in the porous layer, but in the manufacturing method of the present invention, the formation of macrovoids is suppressed. In other words, the number of macrovoids formed is reduced compared to conventional methods. The reason for this is presumed to be as follows.

[0078] When the coating film does not contain compound (A), the interaction between the organic polymer and the inorganic particles in the coating film is not very strong. Therefore, when the coating film is contacted with a non-solvent-containing liquid, the non-solvent-containing liquid tends to penetrate the coating film quickly and in large quantities. The areas occupied by the mixture of the non-solvent-containing liquid and the solvent that constitutes the coating film become voids, and many macrovoids tend to form.

[0079] In contrast, in the manufacturing method of the present invention, the coating film contains a compound (A) having a hydrophobic hydrocarbon group (R) and a hydrophilic functional group (X). It is believed that the hydrocarbon group (R) interacts with the organic polymer, and the hydrophilic functional group (X) of the compound (A) interacts with the inorganic particles. This interaction may extend two-dimensionally or three-dimensionally, like the hydrogen bonding of water molecules. When such a coating film is contacted with a non-solvent-containing liquid, the hydrophobic component is dispersed throughout the coating film, reducing the water diffusion rate compared to when the compound (A) is not included. As a result, it is believed that the formation of macrovoids is suppressed.

[0080] The method for bringing the coating film into contact with the non-solvent-containing liquid is, for example, a method in which the coating film is immersed in the non-solvent-containing liquid (coagulation bath).

[0081] The non-solvent has the property of not substantially dissolving the organic polymer. "Not substantially dissolving the organic polymer" means that the solubility of the organic polymer in 100 g of the solvent at 25°C is 100 mg or less. The non-solvent may be water such as pure water, distilled water, or ion-exchanged water; lower alcohols such as methanol, ethanol, or propyl alcohol; or a mixture thereof. From the viewpoint of wastewater treatment, water is preferred, and ion-exchanged water is more preferred.

[0082] The non-solvent-containing liquid may contain a non-solvent, and the concentration of the non-solvent in the non-solvent-containing liquid may be 100% by mass or a value close to 100% by mass.

[0083] The non-solvent-containing liquid may contain a solvent other than the non-solvent. The solvent other than the non-solvent is not limited. For example, it is preferably the same solvent as the solvent contained in the coating film. When a solvent other than the non-solvent is contained, the concentration of the non-solvent in the non-solvent-containing liquid is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 40% by mass or more. Also, it is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 60% by mass or less. That is, the concentration of the non-solvent in the non-solvent-containing liquid is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 40 to 60% by mass.

[0084] The temperature of the non-solvent-containing liquid when brought into contact with the coating film is not limited. From the viewpoint of uniformly solidifying the coating film, a temperature of 5 to 70°C is preferred. In particular, a temperature of 10 to 50°C is more preferred, and a temperature of 15 to 30°C is even more preferred. The time for which the coating film is immersed in the non-solvent-containing liquid is not limited. A temperature of 0.5 to 30 minutes is preferred, a temperature of 1 to 20 minutes is more preferred, and a temperature of 2 to 15 minutes is even more preferred.

[0085] In step (3), it is preferable to perform a vapor-induced phase separation method before the non-solvent-induced phase separation method. In the vapor-induced phase separation method, the coating film obtained in step (2) is exposed to vapor containing a non-solvent for the organic polymer (non-solvent-containing gas). The method for exposing the coating film obtained in step (2) to the non-solvent-containing gas is not limited. It may be a method of spraying the non-solvent-containing gas onto the surface of the coating film, or a method of exposing the coating film to the gas phase of a storage tank containing a heated non-solvent-containing liquid, etc.

[0086] The non-solvent in the vapor-induced phase separation method is the same as the non-solvent in the non-solvent-induced phase separation method. The non-solvent-containing gas may contain gases normally contained in air, such as oxygen, nitrogen, or carbon dioxide, or may contain vapor of a solvent similar to the solvent contained in the coating film.

[0087] The non-solvent-containing gas may contain a non-solvent. The concentration of the non-solvent in the non-solvent-containing gas is preferably 50 to 100% by volume, more preferably 70 to 100% by volume, and even more preferably 80 to 100% by volume, in terms of the proportion of non-solvent molecules relative to 100% by volume of the non-solvent-containing gas.

[0088] The temperature of the non-solvent-containing gas when brought into contact with the coating film is not limited. In order to solidify the coating film uniformly, a temperature of 50 to 80°C is preferred. In particular, a temperature of 55 to 75°C is more preferred, and a temperature of 60 to 70°C is even more preferred. The time for which the coating film is brought into contact with the non-solvent-containing gas is preferably 1 to 60 seconds, more preferably 2 to 30 seconds, and even more preferably 3 to 15 seconds.

[0089] Steps (1) to (3) provide a porous layer containing an organic polymer and inorganic particles. This porous layer may be used as a diaphragm for alkaline water electrolysis. However, the porous layer obtained in step (3) may contain a non-solvent contained in the non-solvent-containing solution or a solvent component contained in the coating film formed in step (2). These substances may affect the performance of the diaphragm for alkaline water electrolysis. From this perspective, the method for producing a diaphragm for alkaline water electrolysis of the present invention preferably further includes the following step (4): (4) A step of drying the porous layer.

[0090] Step (4) is a drying step for removing the non-solvent, compound (A), and the like contained in the porous layer obtained in step (3). The drying temperature is preferably 60 to 150°C, more preferably 60 to 130°C. The drying time is preferably 2 to 60 minutes, more preferably 2 to 30 minutes, and even more preferably 5 to 30 minutes. Drying may be carried out at normal pressure or under reduced pressure. In order to promote the removal of volatile components, drying under reduced pressure at 0.03 to 0.06 atmospheres is preferred.

[0091] Furthermore, in addition to the above-mentioned steps (1) to (4), known steps such as a pressing step for making the density of the membrane uniform may be included.

[0092] By the method described above, a diaphragm for alkaline water electrolysis in which macrovoid formation is suppressed can be produced.

[0093] 2. Diaphragms for alkaline water electrolysis The diaphragm for alkaline water electrolysis of the present invention can be obtained by, for example, the production method described above in "1. Production method of diaphragm for alkaline water electrolysis."

[0094] The diaphragm for alkaline water electrolysis comprises a porous layer containing an organic polymer and inorganic particles, and preferably further comprises a porous support.

[0095] The organic polymer, inorganic particles, and porous support are the same as those described in "1. Manufacturing method of a diaphragm for alkaline water electrolysis." For example, the organic polymer is preferably polysulfone. The inorganic particles are preferably magnesium hydroxide. The porous support is preferably a nonwoven fabric or mesh containing polyphenylene sulfide.

[0096] The content of the organic polymer is not limited. It is preferably 10 to 50% by mass relative to 100% by mass of the porous layer. Within this range, excellent ion conductivity and mechanical strength are achieved. In particular, 15% by mass or more is more preferable, and 20% by mass or more is even more preferable. Also, 45% by mass or less is more preferable, and 40% by mass or less is even more preferable. In other words, the content of the organic polymer is more preferably 15 to 45% by mass, and even more preferably 20 to 40% by mass relative to 100% by mass of the porous layer.

[0097] The content of inorganic particles is not particularly limited. It is preferably 50 to 90% by mass relative to 100% by mass of the porous layer. This range provides excellent ion conductivity. In particular, it is more preferably 55% by mass or more, and even more preferably 60% by mass or more. It is also more preferably 85% by mass or less, and even more preferably 80% by mass or less. That is, the content of inorganic particles is more preferably 55 to 85% by mass, and even more preferably 60 to 80% by mass relative to 100% by mass of the porous layer.

[0098] The porous layer may contain compound (A). Compound (A) is the same as that described in "1. Production method of diaphragm for alkaline water electrolysis." The content of compound (A) is not limited. It is preferably 10% by mass or less, relative to 100% by mass of the porous layer. In particular, it is more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0099] The porous layer may contain a dispersant. The dispersant may be the same as that described in "1. Manufacturing method of a diaphragm for alkaline water electrolysis." The content of the dispersant is not limited. It is preferably more than 0.01 mass% and not more than 8.0 mass%, more preferably 0.1 mass% to 6.0 mass%, and even more preferably 1.0 mass% to 5.0 mass%, relative to 100 mass% of the inorganic particles in the porous layer.

[0100] The porous layer may naturally contain impurities, and the term "impurities" used here refers to components that are not intentionally mixed in, regardless of whether they are unavoidable or not.

[0101] When the diaphragm for alkaline water electrolysis includes a porous support, the content of the porous layer in the diaphragm for alkaline water electrolysis is not limited. It is preferably 10 to 80 mass% relative to 100 mass% of the diaphragm for alkaline water electrolysis. In particular, it is more preferably 15 mass% or more, and even more preferably 20 mass% or more. It is also more preferably 75 mass% or less, and even more preferably 70 mass% or less. That is, the content of the porous layer in the diaphragm for alkaline water electrolysis is more preferably 15 to 75 mass%, and even more preferably 20 to 70 mass%, relative to 100 mass% of the diaphragm for alkaline water electrolysis.

[0102] The porous layer may be provided on one side of the porous support, or on both sides. The entire porous layer may be laminated on the surface of the porous support, or a portion may be impregnated into the porous support and the remainder may be laminated on the surface of the porous support. In a form in which the porous layer is impregnated into the porous support, the porous layer may be impregnated into a portion of the porous support in the thickness direction, or may be impregnated over the entire thickness direction of the porous support. Therefore, for example, a form in which two porous layers laminated on the front and back sides of the porous support are integrated by the porous layer impregnated into the porous support may be used.

[0103] The porous layer constituting the diaphragm for alkaline water electrolysis of the present invention has a content of macrovoids having a major axis of at least 30 μm and a minor axis of at least 5 μm of not more than 50%. From the viewpoint of improving the mechanical strength of the diaphragm for alkaline water electrolysis, the content is more preferably at most 30%, further preferably at most 20%, and even more preferably at most 10%. For example, it may be at least 0% and at most 18%, and preferably at least 0% and at most 12%.

[0104] The macrovoid content refers to the ratio of the total area of ​​macrovoids to the area of ​​the porous layer in a cross section of the porous layer in the thickness direction. When the diaphragm for alkaline water electrolysis does not include a porous support, the macrovoid content in the porous layer falls within the above range. When the diaphragm for alkaline water electrolysis includes a porous support, the macrovoid content in unimpregnated parts of the porous layer that are not impregnated with the porous support falls within the above range. The method for measuring the macrovoid content is described in detail in the Examples.

[0105] The diaphragms for alkaline water electrolysis of the present invention are characterized by the morphology of the porous layer. Hereinafter, each morphology of the porous layer will be described as a diaphragm for alkaline water electrolysis (S1), a diaphragm for alkaline water electrolysis (S2), and a diaphragm for alkaline water electrolysis (S3).

[0106] <Diaphragm for alkaline water electrolysis (S1)> The diaphragm (S1) for alkaline water electrolysis is a diaphragm for alkaline water electrolysis comprising a porous layer containing an organic polymer and inorganic particles, wherein a pair of main surfaces of the porous layer form the front and back surfaces of the diaphragm for alkaline water electrolysis, and wherein when a cross section of the porous layer is divided into three equal parts in the thickness direction to obtain three cross-sectional layers, two cross-sectional layers including the front and back surfaces are defined as a front layer and a back layer, and the other cross-sectional layer is defined as an internal layer, the internal layer has an average pore size larger than that of at least one of the surface layer and the back layer.

[0107] The above configuration provides excellent ion conductivity and gas barrier properties. The diaphragm (S1) for alkaline water electrolysis is also referred to as the diaphragm (S1).

[0108] The diaphragm (S1) is a diaphragm for alkaline water electrolysis of the present invention that does not include a porous support. Because it does not include a porous support, the pair of main surfaces of the porous layer form the front and back surfaces of the diaphragm for alkaline water electrolysis. The front and back surfaces of the diaphragm for alkaline water electrolysis are not particularly distinguished from one another, and for the sake of convenience of explanation, one of the pair of main surfaces of the diaphragm for alkaline water electrolysis is simply referred to as the front surface, and the other as the back surface.

[0109] Dividing the cross section of the porous layer into three equal parts in the thickness direction results in a cross-sectional layer (surface layer) including the surface of the diaphragm for alkaline water electrolysis, a cross-sectional layer (internal layer) not including the front or back surface of the diaphragm for alkaline water electrolysis, and a cross-sectional layer (back surface layer) including the back surface of the diaphragm for alkaline water electrolysis. The average pore size of the internal layer is larger than the average pore size of at least one of the surface layer and the back surface layer. From the viewpoint of improving mechanical strength, the average pore size of the internal layer is preferably larger than the average pore sizes of both the surface layer and the back surface layer.

[0110] The ratio of the average pore size of the inner layer to the average pore size of at least one of the surface layer and the back layer (average pore size ratio r 11 ) is greater than 1.0. In particular, it is preferably 1.1 or more, and more preferably 1.2 or more. It is also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less.

[0111] The average pore size of the inner layer is not particularly limited. From the viewpoint of improving mechanical strength, it is preferably 0.1 to 5.0 μm. In particular, it is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. It is also more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. That is, the average pore size of the inner layer is more preferably 0.2 to 4.0 μm, and even more preferably 0.3 to 3.0 μm.

[0112] The average pore size of the front and back layers is not particularly limited. From the viewpoint of improving mechanical strength, it is preferably 0.05 to 3.0 μm. In particular, it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. It is also more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. It is preferable that both the front and back layers have such average pore sizes. That is, the average pore size of the front and back layers is more preferably 0.1 to 2.5 μm, and even more preferably 0.2 to 2.0 μm.

[0113] <Alkaline water electrolysis membrane (S2)> The diaphragm (S2) for alkaline water electrolysis is a diaphragm for alkaline water electrolysis comprising a porous layer containing an organic polymer and inorganic particles, and a porous support, the porous layer includes a non-impregnated layer that is not impregnated into the porous support; The diaphragm for alkaline water electrolysis is such that, when the cross section of the non-impregnated layer is divided into three equal sections in the thickness direction, the cross section including the surface of the diaphragm for alkaline water electrolysis is designated as a surface layer and the other two cross section sections are designated as internal layers, at least one of the two internal layers has a larger average pore size than the surface layer.

[0114] The above-described configuration provides excellent ion conductivity and gas barrier properties. The diaphragm (S2) for alkaline water electrolysis is also referred to as the diaphragm (S2).

[0115] The diaphragm (S2) is a diaphragm for alkaline water electrolysis of the present invention that includes a porous support. Because the diaphragm (S2) includes a porous support, one of the pair of main surfaces of the porous layer forms the surface of the diaphragm for alkaline water electrolysis.

[0116] When the cross section of the porous layer is divided into three equal parts in the thickness direction, one cross-sectional layer (surface layer) including the surface of the diaphragm for alkaline water electrolysis and two cross-sectional layers (internal layers) not including the surface of the diaphragm for alkaline water electrolysis are obtained. In the diaphragm (S2), at least one of the two internal layers has a larger average pore size than the surface layer. The diaphragm (S2) may have a porous layer having this configuration on at least one main surface of the porous support.

[0117] The ratio of the average pore size of the inner layer, which has a larger average pore size, to the average pore size of the surface layer (average pore size ratio r 11 ) is greater than 1.0. In particular, it is preferably 1.1 or more, and more preferably 1.2 or more. It is also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. That is, the average pore size ratio r 11 is preferably more than 1.0 and not more than 3.0, more preferably 1.1 or more and 2.5 or less, and even more preferably 1.2 or more and 2.0 or less.

[0118] The average pore size of the inner layer having the larger average pore size is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.1 to 5.0 μm. In particular, it is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. It is also more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. In other words, the average pore size of the inner layer having the larger average pore size is more preferably 0.2 to 4.0 μm, and even more preferably 0.3 to 3.0 μm. It is preferable that the inner layer having a smaller average pore size also has such an average pore size.

[0119] The average pore size of the surface layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.05 to 3.0 μm. In particular, it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. It is also more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. That is, the average pore size of the surface layer is more preferably 0.1 to 2.5 μm, and even more preferably 0.2 to 2.0 μm.

[0120] It is also preferable that the inner layer adjacent to the surface layer has a larger average pore size than the surface layer, and it is also preferable that both of the two inner layers have a larger average pore size than the surface layer.

[0121] The diaphragm (S2) preferably has a porous layer in which a part of the porous layer is impregnated into the porous support. That is, the porous layer preferably includes an impregnated layer in which the porous support is impregnated and an unimpregnated layer in which the porous support is not impregnated. At least one of the two inner layers in the unimpregnated layer preferably has a larger average pore size than the impregnated layer.

[0122] The ratio of the average pore size of the inner layer with a larger average pore size in the non-impregnated layer to the average pore size of the impregnated layer (average pore size ratio r 12 ) is preferably greater than 1.0, more preferably 1.2 or greater, and even more preferably 1.4 or greater. It is also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. That is, the average pore size ratio r 12 is preferably more than 1.0 and not more than 3.0, more preferably 1.2 or more and 2.5 or less, and even more preferably 1.4 or more and 2.0 or less.

[0123] The average pore size of the impregnated layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.05 to 3.0 μm. In particular, it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. It is also more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. That is, the average pore size of the impregnated layer is more preferably 0.1 to 2.5 μm, and even more preferably 0.2 to 2.0 μm.

[0124] The thickness of the non-impregnated layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 20 to 150 μm. In particular, it is more preferably 30 μm or more, and even more preferably 40 μm or more. It is also more preferably 120 μm or less, and even more preferably 100 μm or less. When non-impregnated layers are present on both sides of the porous support, the thickness refers to the thickness of each non-impregnated layer. That is, the thickness of the non-impregnated layer is more preferably 30 to 120 μm, and even more preferably 40 to 100 μm.

[0125] The thickness of the impregnated layer is not particularly limited. From the viewpoint of excellent strength and low resistance, it is preferably 50 to 300 μm. In particular, it is more preferably 80 μm or more, and even more preferably 130 μm or more. Also, it is more preferably 250 μm or less. Note that when the impregnated layer is present on both sides of the porous support, the thickness refers to the thickness of each non-impregnated layer. That is, the thickness of the impregnated layer is more preferably 80 to 250 μm, and even more preferably 130 to 250 μm.

[0126] <Alkaline water electrolysis membrane (S3)> The diaphragm (S3) for alkaline water electrolysis is a diaphragm for alkaline water electrolysis comprising a porous layer containing an organic polymer and inorganic particles, and a porous support, wherein the porous layer comprises an impregnated layer in which the porous support is impregnated, and a non-impregnated layer in which the porous support is not impregnated, and wherein when a cross section of the non-impregnated layer is divided into three equal sections in the thickness direction to obtain three cross-sectional layers, one cross-sectional layer including a surface of the diaphragm for alkaline water electrolysis is designated as a surface layer, and the other two cross-sectional layers are designated as internal layers, at least one of the internal layers has an average pore size larger than that of the impregnated layer.

[0127] The above-described configuration provides a diaphragm for alkaline water electrolysis that is excellent in both ion conductivity and gas barrier property. The diaphragm for alkaline water electrolysis (S3) is also referred to as the diaphragm (S3).

[0128] The diaphragm (S3) is a diaphragm for alkaline water electrolysis of the present invention that includes a porous support. Because the diaphragm (S3) includes a porous support, one of the pair of main surfaces of the porous layer forms the surface of the diaphragm for alkaline water electrolysis.

[0129] When the cross section of the porous layer is divided into three equal parts in the thickness direction, one cross-sectional layer (surface layer) including the surface of the diaphragm for alkaline water electrolysis and two cross-sectional layers (internal layers) not including the surface of the diaphragm for alkaline water electrolysis are obtained. In the diaphragm (S3), at least one of the two internal layers has a larger average pore size than the impregnation layer. The diaphragm (S3) may have a porous layer having this configuration on at least one main surface of the porous support.

[0130] The ratio of the average pore size of the inner layer with a larger average pore size in the non-impregnated layer to the average pore size of the impregnated layer (average pore size ratio r 22 ) is preferably greater than 1.0. In particular, it is more preferably 1.2 or more, and even more preferably 1.4 or more. It is also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. That is, the average pore size ratio r 22 is preferably more than 1.0 and not more than 3.0, more preferably 1.2 or more and 2.5 or less, and even more preferably 1.4 or more and 2.0 or less.

[0131] The average pore size of the inner layer having a larger average pore size in the non-impregnated layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.1 to 5.0 μm. In particular, it is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. It is also more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. That is, the average pore size of the inner layer having a larger average pore size in the non-impregnated layer is more preferably 0.2 to 4.0 μm, and even more preferably 0.3 to 3.0 μm. It is preferable that the average pore size of the inner layer having a smaller average pore size in the non-impregnated layer also has such an average pore size.

[0132] The average pore size of the impregnated layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.05 to 3.0 μm. In particular, it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. It is also more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. That is, the average pore size of the impregnated layer is more preferably 0.1 to 2.5 μm, and even more preferably 0.2 to 2.0 μm.

[0133] The thickness of the non-impregnated layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 20 to 150 μm. In particular, it is more preferably 30 μm or more, and even more preferably 40 μm or more. It is also more preferably 120 μm or less, and even more preferably 100 μm or less. That is, the thickness of the non-impregnated layer is more preferably 30 to 120 μm, and even more preferably 40 to 100 μm. When non-impregnated layers are present on both sides of the porous support, the thickness refers to the thickness of each non-impregnated layer.

[0134] The thickness of the impregnated layer is not particularly limited. From the viewpoint of excellent strength and low resistance, it is preferably 50 to 300 μm. It is more preferably 80 μm or more, and even more preferably 130 μm or more. It is more preferably 250 μm or less, and even more preferably 200 μm or less. That is, the thickness of the impregnated layer is more preferably 80 to 250 μm, and even more preferably 130 to 200 μm. When the impregnated layer is present on both sides of the porous support, it is the thickness of each non-impregnated layer.

[0135] In the diaphragm (S3), it is preferable that the average pore size of the inner layer, which has a larger average pore size among the non-impregnated layers, is larger than the average pore size of the surface layer.

[0136] The ratio of the average pore size of the inner layer, which has a larger average pore size, to the average pore size of the surface layer (average pore size ratio r 21 ) is preferably greater than 1.0. In particular, it is more preferably 1.1 or more, and even more preferably 1.2 or more. It is also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. That is, the average pore size ratio r 21 is preferably more than 1.0 and not more than 3.0, more preferably 1.1 or more and 2.5 or less, and even more preferably 1.2 or more and 2.0 or less.

[0137] The average pore size of the surface layer is not particularly limited. From the viewpoint of improving the balance of strength, it is preferably 0.05 to 3.0 μm. In particular, it is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. It is also more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. That is, the average pore size of the surface layer is more preferably 0.1 to 2.5 μm, and even more preferably 0.2 to 2.0 μm. It is preferable that the average pore size of the inner layer, which has a smaller average pore size, also has such an average pore size.

[0138] It is also preferable that the inner layer adjacent to the surface layer has a larger average pore size than the surface layer, and it is also preferable that both of the two inner layers have a larger average pore size than the surface layer.

[0139] <<How to determine the average pore size in the non-impregnated layer>> An example of how to determine the average pore size in the non-impregnated layer of diaphragms (S1) to (S3) will be described. Note that since diaphragm (S1) is a porous support body in which a porous layer is not impregnated, it is treated here as a non-impregnated layer. Hereinafter, when there is no need to distinguish between diaphragms (S1) to (S3), they will simply be referred to as diaphragms.

[0140] (1) Obtaining observation images A diaphragm for alkaline water electrolysis is cut in the thickness direction to obtain a cross section. The cross section is observed using a field emission scanning electron microscope (FE-SEM) to obtain an observation image. An example of an observation image is shown in FIG. 1. The observation image 100 in FIG. 1 is a rectangle having a horizontal length L1 and a vertical length L2. The imaging magnification is selected to obtain the observation image 100 so that the entire thickness of the non-impregnated layer 110 is included. The vertical direction of the observation image 100 is the thickness direction of the non-impregnated layer 110, and the horizontal direction is the surface direction of the non-impregnated layer 110. In the form of the diaphragm (S1), any main surface of the non-impregnated layer 110 is considered to be the upper side. In the forms of the diaphragms (S2) to (S3), the side opposite to the impregnated layer 120 is considered to be the upper side. Five observation images 100 are obtained in this manner.

[0141] The length L1 in the horizontal direction is not particularly limited, and is, for example, about 50 to 150 μm. The length L2 in the vertical direction may be selected depending on the thickness of the non-impregnated layer 110, and is, for example, about 20 to 150 μm.

[0142] (2) Determining the surface, inner, and back layers of the non-impregnated layer The cross section of the non-impregnated layer 110 is divided into three equal parts in the thickness direction to determine the surface layer, the internal layer, and the back layer. This method will be explained with reference to Figure 1. Figure 1 shows an observation image 100 surrounded by a dotted line. The observation image 100 includes the non-impregnated layer 110. A center line XL1 parallel to the vertical direction is drawn in the horizontal center of the observation image 100. The area to the left of the center line XL1 is the left area AL1, and the area to the right of the center line XL1 is the right area AR1.

[0143] (2-1) Determining the upper reference line UL1 On the upper contour line of the non-impregnated layer 110 in the observation image 100, a straight line connecting the uppermost position 101 in the left region AL1 and the uppermost position 102 in the right region AR1 is defined as the upper reference line UL1. Hereinafter, the upper reference line UL1 is regarded as the upper contour line of the non-impregnated layer 110. The uppermost position refers to the position that is the shortest distance from the top edge of the observation image 100.

[0144] (2-2) Determining the lower reference line LL1 On the lower contour line of the non-impregnated layer 110 in the observed image 100, a straight line connecting the uppermost position 103 in the left area AL1 and the uppermost position 104 in the right area AR1 is defined as a lower reference line LL1. Hereinafter, the lower reference line LL1 is regarded as the lower contour line of the non-impregnated layer 110. The uppermost position refers to the position that is farthest from the bottom side of the observed image 100.

[0145] (2-3) Determining interior dividing lines An intersection 11 between the upper reference line UL1 and the left side of the observation image 100 is determined. An intersection 12 between the lower reference line LL1 and the left side of the observation image 100 is determined. An intersection 15 between the upper reference line UL1 and the right side of the observation image 100 is determined. An intersection 16 between the lower reference line LL1 and the right side of the observation image 100 is determined. Next, the shorter of the distance from intersection 11 to intersection 12 and the distance from intersection 15 to intersection 16 is selected. If the distance from intersection 11 to intersection 12 is shorter as shown in FIG. 1, intersections 13 and 14 are determined on the left side of the observation image 100, starting from intersection 11, so as to divide the distance from intersection 11 to intersection 12 into thirds. Then, an upper interior dividing line UIL1 is drawn that is parallel to the upper reference line UL1 and passes through intersection 13, and a lower interior dividing line LIL1 is drawn that is parallel to the upper reference line UL1 and passes through intersection 14. If the distance from intersection 15 to intersection 16 is shorter, intersections 17 and 18 are determined on the right side of the observed image 100, starting from intersection 15, so as to divide the distance from intersection 15 to intersection 16 into thirds. Then, an upper internal dividing line UIL1 that is parallel to the upper reference line UL1 and passes through intersection 17, and a lower internal dividing line LIL1 that is parallel to the upper reference line UL1 and passes through intersection 18 are drawn.

[0146] (2-4) Determining the surface layer, inner layer, and back layer By the method described above, the non-impregnated layer 110 is divided into a region 111 sandwiched between the upper reference line UL1 and the upper inner division line UIL1, a region 112 sandwiched between the upper inner division line UIL1 and the lower inner division line LIL1, and a region 113 sandwiched between the lower inner division line LIL1 and the lower reference line LL1. In the diaphragm (S1), the region 111 is the surface layer, the region 112 is the inner layer, and the region 113 is the back layer. In the diaphragms (S2) to (S3), the region 111 is the surface layer, and the regions 112 and 113 are inner layers.

[0147] (3) Measurement of average pore size The average pore size of each layer (surface layer, inner layer, back layer) in the non-impregnated layer 110 can be determined by image analysis of each layer. It is preferable to use commercially available image analysis software, such as Scion Image (manufactured by Sciion) or Image-Pro Premier (manufactured by Media Cybernetics).

[0148] The average pore size in the surface layer is determined as follows. First, a measurement area is selected so that it contains at least 50 pores. Next, the pore size of each pore observed within the measurement area is calculated. The pore size is calculated using the image analysis software as the average length of the line segment passing through the center of gravity and two points on the periphery of the pore. Note that pores are openings formed by the absence of organic polymers or inorganic particles.

[0149] Then, the average diameter of each pore is calculated for 50 pores, with only pores with a diameter of 0.1 μm or more being the target.

[0150] This measurement is performed in five different measurement areas. The average value of the values ​​obtained in the five locations is taken as the average pore size of the surface layer. The average pore sizes of the inner layer and back layer are calculated in the same way.

[0151] <<How to determine the average pore size in the impregnated layer>> An example of how to determine the average pore size in the impregnation layer of the diaphragms (S2) to (S3) will be described below. Hereinafter, when the diaphragms (S2) to (S3) are not distinguished from one another, they will simply be referred to as diaphragms. (1) Acquisition of cross-sectional observation images The diaphragm for alkaline water electrolysis is cut in the thickness direction to obtain a cross section. The cross section is observed using a field emission scanning electron microscope (FE-SEM) to obtain an observation image. An example of an observation image is shown in FIG. 2. The observation image 200 in FIG. 2 is a rectangle having a horizontal length L1 and a vertical length L2. The imaging magnification is selected to obtain the observation image 200 so that the entire thickness of the impregnated layer 220 is included. The vertical direction of the observation image 200 is the thickness direction of the impregnated layer 220, and the horizontal direction is the surface direction of the impregnated layer 220. The side on which the non-impregnated layer 210 is provided is defined as the upper side. When two non-impregnated layers 210 are connected by one impregnated layer 220, any of the non-impregnated layers 210 is defined as the upper side. Five observation images 200 are obtained in this manner.

[0152] The length L1 in the horizontal direction is not particularly limited, and is, for example, about 50 to 150 μm. The length L2 in the vertical direction may be selected depending on the thickness of the non-impregnated layer, and is, for example, about 20 to 150 μm.

[0153] (2) Determining the impregnation layer A method for determining the impregnated layer will be described with reference to Figure 2. Figure 2 shows an observed image 200 surrounded by a dotted line. The observed image 200 includes a non-impregnated layer 210 and an impregnated layer 220. A center line XL2 parallel to the vertical direction is drawn in the horizontal center of the observed image 200. The area to the left of the center line XL2 is defined as a left area AL2, and the area to the right of the center line XL2 is defined as a right area AR2.

[0154] (2-1) Determining the upper reference line UL2 On the upper contour line of the impregnated layer 220 in the observation image 200, a straight line connecting the uppermost position 201 in the left area AL2 and the uppermost position 202 in the right area AR2 is defined as the upper reference line UL2. Hereinafter, the upper reference line UL2 is regarded as the upper contour line of the impregnated layer 220. The uppermost position refers to the position that is the shortest distance from the top side of the observation image 200.

[0155] (2-2) Determining the lower reference line LL2 On the lower contour line of the impregnated layer 220 in the observation image 200, a straight line connecting the uppermost position 203 in the left area AL2 and the uppermost position 204 in the right area AR2 is defined as a lower reference line LL2. Hereinafter, the lower reference line LL2 is regarded as the lower contour line of the impregnated layer 220. The uppermost position refers to the position that is farthest from the bottom side of the observation image 200.

[0156] (3) Measurement of average pore size The average pore size of the impregnated layer 220 can be determined by image analysis. It is preferable to use commercially available image analysis software, such as Scion Image (manufactured by Sciion) or Image-Pro Premier (manufactured by Media Cybernetics).

[0157] The average pore size in the impregnated layer is determined as follows. First, a measurement area is selected so that it contains at least 50 pores. Next, the pore size of each pore observed within the measurement area is calculated. The pore size is calculated using the image analysis software as the average length of the line segment passing through the center of gravity and two points on the periphery of the pore. Note that pores are openings formed by the absence of organic polymer or inorganic particles.

[0158] Then, the average diameter of each pore is calculated for 50 pores, with only pores with a diameter of 0.1 μm or more being the target.

[0159] This measurement is carried out at five different measurement areas, and the average value of the values ​​obtained at the five locations is taken as the average pore size of the impregnated layer.

[0160] <Preferred embodiments of the diaphragms (S1) to (S3)> Preferred embodiments of the diaphragms (S1) to (S3) will be explained below. Hereinafter, when the diaphragms (S1) to (S3) are not to be distinguished from one another, they will be simply referred to as diaphragms.

[0161] The membrane (S1) preferably has an inner layer with a content of macrovoids having a major axis of 30 μm or more and a minor axis of 5 μm or more of 50% or less. The surface layer and back layer also preferably have a content of macrovoids of 50% or less. The membranes (S2) to (S3) preferably have an inner layer with a content of macrovoids having a major axis of 30 μm or more and a minor axis of 5 μm or more of 50% or less in at least one of the two inner layers of the non-impregnated layer. The surface layer also preferably has a content of macrovoids of 50% or less.

[0162] The diaphragm preferably has a mass loss rate of 2% or less in an ultrasonic test. Within this range, the diaphragm is prevented from losing its constituent components, resulting in excellent mechanical strength. The mass loss rate is more preferably 1.5% or less, even more preferably 1.2% or less, and even more preferably 1% or less. The method for measuring the mass loss rate will be described in detail in the Examples.

[0163] The membrane resistance is 0.30Ωcm 2 Within this range, ion conduction in alkaline water electrolysis is good, resulting in excellent electrolysis efficiency. The method for measuring the membrane resistance will be described in detail in the Examples.

[0164] In a hot alkali durability test, the membrane preferably has a ratio (membrane resistance ratio) of membrane resistance after 240 hours of durability to membrane resistance after 24 hours of durability of 0.7 or more. Within this range, the membrane is less affected by hot alkali and therefore has excellent alkali resistance. The method for measuring the membrane resistance ratio will be described in detail in the Examples.

[0165] The membrane preferably has an air permeability of 50 to 5000 seconds. Within this range, gas is less likely to permeate the membrane, resulting in excellent gas barrier properties. The air permeability is more preferably 100 to 1000 seconds, and even more preferably 150 to 800 seconds. The method for measuring air permeability will be described in detail in the Examples.

[0166] The thickness of the diaphragm is preferably 50 to 2000 μm. Within this range, it is easy to balance mechanical strength, gas barrier properties, and ion conductivity. The thickness is more preferably 100 to 1000 μm, even more preferably 100 to 500 μm, and most preferably 150 to 350 μm. The method for measuring the thickness of the diaphragm will be described in detail in the Examples.

[0167] The diaphragm preferably has an air permeability per unit thickness, i.e., the value obtained by dividing the air permeability of the diaphragm by the thickness of the diaphragm, of 0.6 or more. Within this range, gas is less likely to permeate the diaphragm, resulting in excellent gas barrier properties. The air permeability per unit thickness is more preferably 0.65 or more, even more preferably 0.70 or more, and even more preferably 0.75 or more. There is no upper limit to the air permeability per unit thickness, but it is preferably 4.00 or less, and more preferably 3.50 or less. That is, the air permeability per unit thickness is preferably 0.6 or more and 4.00 or less, more preferably 0.65 or more and 3.50 or less, even more preferably 0.70 or more and 3.50 or less, and even more preferably 0.75 or more and 3.50 or less.

[0168] 3.Applications The diaphragm for alkaline water electrolysis of the present invention can be used for the electrolysis of alkaline water. An alkaline water electrolysis apparatus including the diaphragm for alkaline water electrolysis of the present invention and a method for alkaline water electrolysis will now be described.

[0169] (Alkaline water electrolysis equipment) The alkaline water electrolysis device includes an anode, a cathode, and a diaphragm for alkaline water electrolysis. Specifically, the alkaline water electrolysis device has an electrolytic cell in which an anode chamber containing an anode and a cathode chamber containing a cathode are separated by a diaphragm for alkaline water electrolysis.

[0170] The diaphragm for alkaline water electrolysis is preferably installed near the anode or the cathode, and more preferably installed so as to be in contact with the anode and the cathode (so-called zero-gap structure). As the distance between the electrodes decreases, the electrical resistance decreases, improving the efficiency of electrolysis.

[0171] The anode and cathode are not particularly limited. They may be, for example, a conductive substrate with a catalytic layer provided thereon. The conductive substrate may be copper, lead, nickel, chromium, titanium, gold, platinum, iron, metal compounds thereof, metal oxides, or alloys containing two or more of these metals. The catalytic layer may be a metal compound, metal oxide, or alloy containing nickel, cobalt, palladium, iridium, platinum, or the like. The catalytic layer may be omitted. The electrode may have any known shape, such as a sheet, rod, or prism, but a sheet shape is preferred in terms of increasing the contact area with the diaphragm and improving the efficiency of electrolysis.

[0172] The electrolysis device may 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.

[0173] (Alkaline water electrolysis method) The alkaline water electrolysis method is carried out by filling the alkaline water electrolysis apparatus described above with an electrolyte (an alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, or the like) and applying a current to the electrolyte. The concentration of the alkali metal hydroxide in the electrolyte is preferably 20 to 40 mass %. The temperature during electrolysis is preferably 50 to 120°C, more preferably 80 to 90°C. The current density during electrolysis is usually 0.2 A / cm 2 More than 0.3A / cm, preferably 0.3A / cm 2 That's all. A high current density allows large amounts of hydrogen gas and oxygen gas to be produced in a short time. The voltage during electrolysis is, for example, 1.5 to 2.5 V. The voltage is adjusted so that the current density is high within this range. The pressure during electrolysis is not particularly limited. It may be normal pressure or pressurized pressure. The diaphragm for alkaline water electrolysis of the present invention has excellent gas barrier properties and can therefore be used even under high pressures of 1 MPa or more (for example, 3 MPa). [Example]

[0174] The method for producing a diaphragm for alkaline water electrolysis and the diaphragm for alkaline water electrolysis of the present invention will be described below with reference to examples. However, the present invention is not limited to these examples.

[0175] <Measurement of macrovoid content> The produced diaphragm for alkaline water electrolysis was cut approximately at the center in the thickness direction, and a cross section obtained was observed using an FE-SEM (Model S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain an observation image. The magnification was 300x. In the observation image, a region extending from the outermost surface of the non-impregnated layer of the diaphragm for alkaline water electrolysis in the depth direction to a range of 60 µm and a range of approximately 400 µm in the direction perpendicular to the depth direction was defined as the measurement region. Void images were extracted from the measurement region using image analysis software (Scion Image, manufactured by Scion Corporation). For each void image, the longitudinal length (Lt) along the thickness direction of the diaphragm for alkaline water electrolysis and the lateral length (Lf) perpendicular to the thickness direction were determined. The thickness direction is the opposing direction between the pair of main surfaces of the diaphragm for alkaline water electrolysis. Therefore, the longitudinal length (Lt) was defined as the distance along the opposing direction between the outermost and outermost points of the outline of the void image in the opposing direction. The horizontal length (Lt) was defined as the distance between the most distant point on the contour of the void image in the direction perpendicular to the opposing direction and the most distant point on the other side. The larger of the (Lt) and (Lf) values ​​thus determined was defined as the void's major axis (Lb), and the smaller was defined as the void's minor axis (Ls). Using this method, the major axis (Lb) and minor axis (Ls) of each extracted void image were determined. The individual areas (S) of void images with a major axis (Lb) of 30 μm or more and a minor axis (Ls) of 5 μm or more were calculated, and these areas were summed. This total area was defined as the total area (Sy) of macrovoids. The area (St) of the measurement region was determined, and the ratio of (Sy) to (St) (Sy / St × 100 (%)) was calculated. The same procedure was performed on five randomly selected visual fields spaced approximately equally apart, and the average value was defined as the content of macrovoids with a major axis of 30 μm or more and a minor axis of 5 μm or more.

[0176] <Measurement of mass loss rate in ultrasonic testing> The manufactured alkaline water electrolysis diaphragm was cut into a 5 x 5 cm piece to prepare a test piece. The test piece and 6 cc of ion-exchanged water were placed in a zippered plastic bag (Unipack C-4, manufactured by Seisan Nippon Sha) and sealed. An ultrasonic cleaner (manufactured by SND Corporation, model US-103) with a water bath temperature adjusted to 30°C was prepared, and the zippered plastic bag was left to stand in the water bath for 1 hour. After that, ultrasonic waves (high-frequency output: 100 W, transmission frequency: 38 kHz) were irradiated for 3 minutes. The weight of the test piece was measured before and after the ultrasonic test using a precision balance (manufactured by A&D Co., Ltd., model GH-200), and the mass loss rate was calculated using the following formula. Mass reduction rate (%) = 100 - (mass after ultrasonic test (g) / mass before ultrasonic test (g) × 100).

[0177] <Measurement of film resistance> (Measurement method) The membrane resistance of the produced diaphragms for alkaline water electrolysis was measured as follows. That is, two diaphragm samples for measurement were prepared by cutting out one produced diaphragm. Cells formed using each diaphragm sample with the following cell configuration were allowed to stand in a thermostatic bath at 25°C for 30 minutes, and then AC impedance measurements were performed under the following measurement conditions. The membrane resistance was calculated according to the following formula using the intercept component (Ra) of the real part of the AC impedance measured when the diaphragm sample was set and the intercept component (Rb) of the real part of the AC impedance measured when the diaphragm sample was not set. The above measurement was performed on two diaphragm samples, and the average of the obtained measured values ​​(at two points) was calculated, and this was defined as the membrane resistance of the diaphragm. [Membrane resistance (Ωcm 2 )] = (Ra - Rb) × 1.77 (Measurement conditions) Cell configuration. Working electrode: Ni plate. Counter electrode: Ni plate. Electrolyte: 30% by mass potassium hydroxide aqueous solution. Sample pretreatment: Immerse in the above electrolyte overnight. Effective measurement area: 1.77cm 2 . AC impedance measurement conditions. Applied voltage: 10mV vs. open circuit voltage. Frequency range: 100kHz~100Hz.

[0178] <Measurement of membrane resistance ratio in hot alkaline durability test> The produced diaphragm for alkaline water electrolysis was cut into a 3 cm square to prepare a test specimen. Two test specimens were prepared. These two test specimens were placed in a fluororesin container (made of PFA), immersed in 30 g of a 30% KOH aqueous solution, and maintained at 90°C. 24 hours and 240 hours after the start of maintaining the specimen at 90°C, the test specimens were removed, and the membrane resistance was measured at room temperature. The membrane resistance ratio after the hot-alkali durability test was calculated as (membrane resistance after 240 hours / membrane resistance after 24 hours).

[0179] <Thickness measurement> The thickness of the produced diaphragm for alkaline water electrolysis was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation). Measurements were taken at 10 randomly selected points spaced approximately equally apart, and the average value was used.

[0180] <Air permeability measurement> The air permeability of the produced diaphragms for alkaline water electrolysis was measured using an Oken air permeability tester (manufactured by Asahi Seiko Co., Ltd., model number: EGBO). Measurements were taken at three randomly selected points spaced approximately equally apart, and the average value was used.

[0181] <Air permeability per unit thickness> The air permeability Z per unit thickness of the produced diaphragm for alkaline water electrolysis was calculated according to the following formula using the air permeability and thickness determined by the above methods. Z = membrane air permeability (seconds) / membrane thickness (μm)

[0182] <Measurement of average pore size> The average pore size of the produced diaphragms for alkaline water electrolysis was measured according to the methods described above in <<Method for determining the average pore size in a non-impregnated layer>> and <<Method for determining the average pore size in an impregnated layer>>. Image-Pro Premier (manufactured by Media Cybernetics) was used as image analysis software.

[0183] [Example 1] (1. Preparation of Inorganic Particle 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 at a mass ratio of 1:1. This mixture was dispersed in a pot mill containing zirconia media balls at room temperature for 6 hours to obtain a magnesium hydroxide dispersion.

[0184] 2. Preparation of the Composition 100 parts by weight of the resulting magnesium hydroxide dispersion, 57 parts by weight of a polysulfone resin solution obtained by thermally dissolving a 35% by weight concentration of polysulfone resin (BASF, Ultrason S3010) (PSU) in N-methyl-2-pyrrolidone (Mitsubishi Chemical Corporation) at 80°C, and 31 parts by weight of N-methyl-2-pyrrolidone (Mitsubishi Chemical Corporation) were mixed, and 20 parts by weight of 2-ethyl-1-hexanol was added per 100 parts by weight of the combined magnesium hydroxide and polysulfone to prepare a mixture. The resulting mixture was mixed at room temperature for approximately 30 minutes at 1000 rpm in a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro ARE-500).

[0185] (3. Formation of diaphragm for alkaline water electrolysis) Polyphenylene sulfide nonwoven fabric (film thickness 130 μm, basis weight 60 g / m 2 ) and the composition was applied (22 mg / cm 2 ) and impregnated. Thereafter, the nonwoven fabric impregnated with the composition was bathed in a water tank filled with ion-exchanged water at room temperature for 5 minutes. The obtained membrane was dried at 120°C for 10 minutes to obtain a diaphragm for alkaline water electrolysis (1).

[0186] Example 1 was partially modified to obtain diaphragms for alkaline water electrolysis (2) to (13) of Examples 2 to 13 and a diaphragm for alkaline water electrolysis (C1) of Comparative Example 1. Only the modifications are described below.

[0187] [Example 2] In (1. Preparation of inorganic particle dispersion), zirconium oxide (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd., product number UEP) was used instead of magnesium hydroxide.

[0188] [Example 3] In (1. Preparation of inorganic particle dispersion), titanium oxide (average particle diameter: 0.5 μm) was used instead of magnesium hydroxide.

[0189] [Example 4] In (2. Preparation of composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was further added in an amount of 0.7 parts by mass relative to 100 parts by mass of magnesium hydroxide.

[0190] [Example 5] In (2. Preparation of Composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K30) were further added. The amount of lithium chloride added was 0.7 parts by mass per 100 parts by mass of magnesium hydroxide. The amount of polyvinylpyrrolidone added was 14 parts by mass per 100 parts by mass of magnesium hydroxide.

[0191] [Example 6] In (2. Preparation of Composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and polyvinylpyrrolidone (K15 manufactured by Kishida Chemical Co., Ltd.) were further added. The amount of lithium chloride added was 0.7 parts by mass per 100 parts by mass of magnesium hydroxide. The amount of polyvinylpyrrolidone added was 14 parts by mass per 100 parts by mass of magnesium hydroxide.

[0192] [Example 7] In (2. Preparation of composition), 1-dodecanol was used instead of 2-ethyl-1-hexanol. The amount of 1-dodecanol added was 3 parts by mass per 100 parts by mass of the total content of magnesium hydroxide and polysulfone.

[0193] [Example 8] In (2. Preparation of Composition), the amount of 2-ethyl-1-hexanol added was changed to 42 parts by mass per 100 parts by mass of the total content of magnesium hydroxide and polysulfone.

[0194] [Example 9] In (2. Preparation of composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and polyvinylpyrrolidone (K30, manufactured by Nippon Shokubai Co., Ltd.) were further added. The amount of lithium chloride added was 0.7 parts by mass relative to 100 parts by mass of magnesium hydroxide. The amount of polyvinylpyrrolidone added was 14 parts by mass relative to 100 parts by mass of magnesium hydroxide. In (3. Formation of diaphragm for alkaline water electrolysis), a PET film was used instead of a polyphenylene sulfide nonwoven fabric. A diaphragm for alkaline water electrolysis was formed on the PET film, and then peeled off from the PET film to provide a diaphragm for alkaline water electrolysis (9).

[0195] [Example 10] In (2. Preparation of Composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K30) were further added. The amount of lithium chloride added was 0.7 parts by mass per 100 parts by mass of magnesium hydroxide. The amount of polyvinylpyrrolidone added was 14 parts by mass per 100 parts by mass of magnesium hydroxide.

[0196] In (3. Formation of diaphragm for alkaline water electrolysis), the application method was changed as follows: The composition was placed in a SUS tray, and then a polyphenylene sulfide nonwoven fabric (thickness: 130 μm, basis weight: 60 g / m) was applied. 2 ) was immersed in the composition. After that, the polyphenylene sulfide nonwoven fabric was lifted out of the SUS tray. In this way, the composition was applied to both sides of the nonwoven fabric.

[0197] [Example 11] In (1. Preparation of inorganic particle dispersion), the mixing ratio of magnesium hydroxide (average particle diameter 0.20 μm, plate-like, aspect ratio 6.21) to N-methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was changed to a mass ratio of 3:2. Furthermore, 3 parts by mass of a polyphosphate ester dispersant was added per 100 parts by mass of magnesium hydroxide.

[0198] In (2. Preparation of Composition), lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K30) were further added. The amount of lithium chloride added was 0.7 parts by mass per 100 parts by mass of magnesium hydroxide. The amount of polyvinylpyrrolidone added was 14 parts by mass per 100 parts by mass of magnesium hydroxide.

[0199] [Example 12] In (1. Preparation of inorganic particle dispersion), the mixing ratio of magnesium hydroxide (average particle diameter 0.20 μm, plate-like, aspect ratio 6.21) to N-methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was changed to a mass ratio of 3:2. Furthermore, 2 parts by mass of phosphate polyester was added as a dispersant per 100 parts by mass of magnesium hydroxide.

[0200] In (2. Preparation of composition), 100 parts by mass of the magnesium hydroxide dispersion, 80 parts by mass of a 30% by mass solution of polysulfone resin (manufactured by BASF, product number Ultrason S3010) dissolved in N-methyl-2-pyrrolidone, 7.5 parts by mass of 2-ethyl-1-hexanol, 4.3 parts by mass of polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., Epomin SP-200), and 18.2 parts by mass of N-methyl-2-pyrrolidone were mixed.

[0201] [Example 13] In (1. Preparation of inorganic particle dispersion), the mixing ratio of magnesium hydroxide (average particle diameter 0.20 μm, plate-like, aspect ratio 6.21) to N-methyl-2-pyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was changed to a mass ratio of 3:2. Furthermore, 2 parts by mass of phosphate polyester was added as a dispersant per 100 parts by mass of magnesium hydroxide.

[0202] In (2. Preparation of composition), 100 parts by mass of magnesium hydroxide dispersion, 80 parts by mass of a 30% by mass solution of polysulfone resin (manufactured by BASF, product number Ultrason S3010) dissolved in N-methyl-2-pyrrolidone, 12.5 parts by mass of 2-ethyl-1-hexanol, 1.3 parts by mass of polyacrylic (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., molecular weight 250,000), and 16.2 parts by mass of N-methyl-2-pyrrolidone were mixed.

[0203] [Comparative Example 1] In (2. Preparation of Composition), 2-ethyl-1-hexanol was not added.

[0204] For the diaphragms (1) to (13), and (C1) for alkaline water electrolysis in Examples 1 to 13 and Comparative Example 1, the macrovoid content, mass loss rate in an ultrasonic test, membrane resistance, membrane resistance ratio in a hot alkaline durability test, diaphragm thickness, air permeability per unit thickness, average pore size of the surface layer, average pore size of the internal layer, average pore size of the back layer, and average pore size of the impregnation layer were measured. The results are shown in Table 1. In Table 1, internal layer 1 refers to the internal layer closer to the surface layer. In Table 1, internal layer 2 refers to the internal layer farther from the surface layer. Example 9 does not include a porous support, and therefore does not include internal layer 2, but does include a back layer. Example 10 includes porous layers on both sides of the porous support, and therefore one of the two porous layers is referred to as porous layer 1 and the other as porous layer 2.

[0205] [Table 1]

[0206] The diaphragms (1) to (13) for alkaline water electrolysis of Examples 1 to 13 showed significantly reduced macrovoid formation compared to Comparative Example 1. This was thought to be because 2-ethyl-1-hexanol and the like were contained in the composition in Example 1 during production of the diaphragm for alkaline water electrolysis.

[0207] The diaphragms for alkaline water electrolysis (1) to (8) and (10) to (13) of Examples 1 to 8 and 10 to 13 each had an internal layer with a larger average pore size than the surface layers in the non-impregnated layers. The diaphragm for alkaline water electrolysis (9) of Example 9 had an internal layer with a larger average pore size than the two surface layers. On the other hand, the diaphragm for alkaline water electrolysis (C1) of Comparative Example 1 did not have an internal layer with a larger average pore size than the surface layers in the non-impregnated layers.

[0208] The diaphragms for alkaline water electrolysis (1) to (13) of Examples 1 to 13 had higher air permeabilities per unit thickness than the diaphragm for alkaline water electrolysis (C1) of Comparative Example 1 and therefore had excellent gas barrier properties. Similarly, a comparison of membrane resistance revealed excellent ion conductivity. A comparison of membrane resistance ratios in a hot alkaline durability test revealed excellent alkali resistance. A comparison of mass loss rates in an ultrasonic test revealed excellent mechanical strength. [Explanation of symbols]

[0209] 100, 200 observation images 110, 210 non-impregnated layer 111, 112, 113 areas 120, 220 impregnated layer

Claims

1. A method for producing a diaphragm for alkaline water electrolysis provided with a porous layer, comprising: A method for producing a diaphragm for alkaline water electrolysis, comprising: obtaining the porous layer using a composition comprising an organic polymer, inorganic particles, a compound represented by general formula (1) below, and a solvent: R-X (1) (In formula (1), R represents a hydrocarbon group having 6 or more carbon atoms, and X represents a hydroxyl group.)

2. 2. The method for producing a diaphragm for alkaline water electrolysis according to claim 1, wherein the content of the compound represented by general formula (1) in the composition is 2 to 30 mass%, relative to 100 mass% of the total content of the organic polymer and the inorganic particles.

3. A diaphragm for alkaline water electrolysis comprising: a porous layer containing an organic polymer and inorganic particles; and a porous support, the inorganic particles are composed of at least one kind selected from the group consisting of magnesium hydroxide, zirconium hydroxide, titanium hydroxide, zirconium oxide, and titanium oxide, the porous layer includes an impregnated layer that is impregnated into the porous support and a non-impregnated layer that is not impregnated into the porous support, When the cross section of the non-impregnated layer is divided into three equal sections in the thickness direction to obtain three cross-sectional layers, one cross-sectional layer including the surface of the diaphragm for alkaline water electrolysis is designated as a surface layer, and the other two cross-sectional layers are designated as internal layers, a diaphragm for alkaline water electrolysis, wherein at least one of the inner layers has an average pore size larger than that of the impregnated layer.

4. The diaphragm for alkaline water electrolysis according to claim 3, wherein at least one of the inner layers has a larger average pore size than the surface layer.

5. 5. The diaphragm for alkaline water electrolysis according to claim 3 or 4, wherein the porous layer has a content of macrovoids having a major axis of 30 µm or more and a minor axis of 5 µm or more of 50% or less.

6. The diaphragm for alkaline water electrolysis according to claim 5, wherein the macrovoid content is 30% or less.

7. The diaphragm for alkaline water electrolysis according to claim 6, wherein the macrovoid content is 20% or less.

8. The diaphragm for alkaline water electrolysis according to claim 7, wherein the macrovoid content is 10% or less.

9. A diaphragm for alkaline water electrolysis as described in claim 3, wherein the inorganic particles consist solely of magnesium hydroxide, zirconium oxide or titanium oxide.

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