Method for producing porous separator for alkaline water electrolysis, porous separator for alkaline water electrolysis, method for producing porous membrane, and porous membrane

Abstract

Provided are: a method for producing a porous separator for alkaline water electrolysis, said method using a dope solution to form a porous membrane by wet phase separation, wherein the dope solution is obtained by dissolving an organic polymer in a solvent which contains at least one of compounds (1)-(7); and a porous separator for alkaline water electrolysis which is obtained by this production method. Also provided are: a method for producing a porous membrane, said method using a dope solution to form a porous membrane by wet phase separation, wherein the dope solution is obtained by dissolving an organic polymer in a solvent which contains at least one of compounds (1), (5), and (6); and a porous membrane which is obtained by this production method. In the compound (1), R represents an alkyl group.

Description

Manufacturing method of porous separator for alkaline water electrolysis, porous separator for alkaline water electrolysis, manufacturing method of porous membrane, and porous membrane

[0001] The present invention relates to a method for producing a porous separator for alkaline water electrolysis, a porous separator for alkaline water electrolysis, a method for producing a porous membrane, and a porous membrane.

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

[0003] In alkaline water electrolysis, hydrogen bubbles (2H ２ O + 2e － →H ２ +2OH － ) to the anode side, and also prevents the bubble-like oxygen (4OH) generated at the anode (positive electrode). － →O ２ +2H ２ O+4e － In order to prevent OH from migrating to the cathode side, a gas barrier separator (membrane) is placed between the cathode and the anode. In addition to the gas barrier properties, this separator also has the function of preventing OH from migrating from the cathode side to the anode side. － Ion conductivity that allows permeation of hydroxy ions (hydroxy ions) is also required. For this reason, porous membranes (microporous membranes) formed using organic polymer materials have come to be widely adopted as separators for alkaline water electrolysis. Furthermore, porous membranes formed using organic polymers are not only used as separators for alkaline water electrolysis, but are also widely used in fields such as reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, and dialysis membranes.

[0004] Such porous membranes can be formed by wet phase separation. In wet phase separation, first, an organic polymer, which is a constituent material of the porous membrane, is dissolved in a solvent (good solvent) that dissolves the organic polymer to prepare a dope solution, and then this dope solution is applied to a substrate or the like to form a coating. Next, the coating is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer but is compatible (miscible) with the good solvent. This immersion reduces the proportion of the good solvent in the coating, causing phase separation between the organic polymer and the solvent, resulting in gelation (coagulation) of the organic polymer, resulting in the formation of a porous membrane. Techniques for imparting strength and functionality to porous membranes obtained by wet phase separation are also known. For example, to increase the mechanical strength of the porous membrane, a porous support is placed in the dope solution, and the porous membrane is formed integrally with the porous support. Furthermore, adding hydrophilic inorganic particles to the dope solution can improve the water compatibility of the resulting porous membrane and enhance its gas barrier properties.

[0005] As an example of such a porous membrane, Patent Document 1 describes a separator including a porous support and first and second porous layers provided on one and the other sides of the porous support, respectively. In this separator, the porous support has a thickness of 150 μm or less, the separator has a thickness of less than 250 μm, and the porous layers may contain hydrophilic inorganic particles. Patent Document 1 also describes that a solvent selected from N-methyl-pyrrolidone (NMP), N-ethyl-pyrrolidone (NEP), N-butyl-pyrrolidone (NBP), N,N-dimethylformamide (DMF), formamide, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), acetonitrile, and mixtures thereof may be used as a good solvent for the dope solution. The technology described in Patent Document 1 is said to provide a separator with sufficient mechanical quality and improved ionic conductivity. Patent Document 2 also describes the formation of a porous membrane by wet phase separation using a dope solution containing at least one sulfone polymer, at least one water-soluble polymer, and gamma-valerolactone. Patent Document 2 also describes the formation of a porous membrane by wet phase separation using a dope solution in which gamma-valerolactone is used as a good solvent and water as a poor solvent, and the use of the obtained porous membrane as an ultrafiltration membrane or a dialysis membrane.

[0006] Special table 2023-531792 publication Special table 2023-529999 publication

[0007] The present invention relates to providing a porous separator and a porous membrane for alkaline water electrolysis with improved functionality, and the configurations thereof are as shown below.

[0008] [1] A method for producing a porous separator for alkaline water electrolysis, comprising forming a porous membrane by wet phase separation using a dope solution obtained by dissolving an organic polymer in a solvent containing at least one of the following compounds (1) to (7): In the compound (1), R represents an alkyl group. [2] The method for producing a porous separator for alkaline water electrolysis according to [1], wherein the dope solution further contains hydrophilic inorganic particles. [3] The method for producing a porous separator for alkaline water electrolysis according to [1] or [2], comprising forming a coating film from the dope solution, and then performing wet phase separation with a porous support disposed in the coating film to form the porous membrane. [4] The method for producing a porous separator for alkaline water electrolysis according to any of [1] to [3], wherein the solvent contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (2), (3) and (4): [5] The method for producing a porous separator for alkaline water electrolysis according to [4], wherein the solvent contains at least one of the compounds (1)-1, (1)-2, and (1)-3. [6] A porous separator for alkaline water electrolysis comprising an organic polymer with a porous structure, the porous separator for alkaline water electrolysis containing at least one of the following compounds (1) to (7), and the total content of the compounds (1) to (7) in the porous separator for alkaline water electrolysis is 0.0001 to 5 mass%: In the above compound (1), R represents an alkyl group.

[0009] [7] A method for producing a porous membrane, comprising forming a porous membrane by wet phase separation using a dope solution obtained by dissolving an organic polymer in a solvent containing at least one of the following compounds (1), (5), and (6): In the compound (1), R represents an alkyl group. [8] The method for producing a porous membrane according to [7], wherein the dope solution further contains hydrophilic inorganic particles. [9] The method for producing a porous membrane according to [7] or [8], wherein a coating film is formed from the dope solution, and a porous support is disposed in the coating film, and the wet phase separation is performed to form the porous membrane.

[10] The method for producing a porous membrane according to any one of [7] to [9], wherein the solvent contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (5), and (6).

[11] The method for producing a porous membrane according to

[10] , wherein the solvent contains at least one of the compounds (1)-1, (1)-2, and (1)-3.

[12] A porous membrane comprising an organic polymer having a porous structure, wherein the porous membrane contains at least one of the following compounds (1), (5), and (6), and the total content of the compounds (1), (5), and (6) in the porous membrane is 0.0001 to 5% by mass. In the compound (1), R represents an alkyl group.

[13] An alkaline water electrolysis system having a structure in which the porous separator for alkaline water electrolysis obtained by the production method according to any one of [1] to [5] is disposed between a cathode electrode and an anode electrode.

[14] An alkaline water electrolysis system having a structure in which the porous separator for alkaline water electrolysis according to [6] is disposed between a cathode electrode and an anode electrode.

[15] A method for producing an alkaline water electrolysis system, comprising disposing the porous separator for alkaline water electrolysis obtained by the production method according to any one of [1] to [5] between a cathode electrode and an anode electrode.

[0010] FIG. 1 is a diagram schematically illustrating an embodiment of an alkaline water electrolysis system. FIG. 2 is a diagram schematically illustrating another embodiment of an alkaline water electrolysis system. FIG. 3 is a diagram schematically illustrating yet another embodiment of an alkaline water electrolysis system.

[0011] [Method for producing porous separator for alkaline water electrolysis] The method for producing a porous separator for alkaline water electrolysis of the present invention (hereinafter also referred to as "Production method-1 of the present invention") includes forming a porous membrane by wet phase separation. A characteristic technical element of Production method-1 of the present invention is the use of a specific type of solvent as a solvent (good solvent) for dissolving the organic polymer in the dope solution (a solution of an organic polymer that is a constituent material of the porous membrane) used in this wet phase separation. This makes it possible to sufficiently improve the gas barrier properties of the obtained separator for alkaline water electrolysis while also increasing the ionic conductivity.

[0012] <Dope Solution> (Solvent) In Production Method-1 of the present invention, the dope solution in the wet phase separation contains at least one solvent (good solvent) selected from the following compounds (1) to (7).

[0013]

[0014] In the compound (1), R represents an alkyl group, and the alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, even more preferably 1 to 6 carbon atoms, and still more preferably 1 to 5 carbon atoms.

[0015] It is also preferable that the alkyl group has an alkoxy group or a hydroxyl group as a substituent. When the alkyl group has an alkoxy group as a substituent, the number of carbon atoms of the alkyl group is the total number of carbon atoms including the alkoxy group. The alkoxy group is preferably an unsubstituted alkoxy group. When the alkyl group has a hydroxyl group as a substituent, the number of hydroxyl groups in the alkyl group is preferably one or two, more preferably one. The alkyl group is preferably a straight-chain alkyl group. Furthermore, when the alkyl group has an alkoxy group as a substituent, it is preferable that the entire structure including the alkoxy group is a straight-chain alkyl group. Note that when the straight-chain alkyl group has only a hydroxyl group as a substituent, this alkyl group is a straight-chain alkyl group.

[0016] By including at least one of the compounds (1) to (7) as a solvent in the dope solution used in the wet phase separation method, the resulting porous film can have excellent ionic conductivity and gas barrier properties. While the reason for this is unclear, it is believed that the unique polar group arrangement, molecular shape, and molecular size of the compounds (1) to (7) effectively enhance their ability to absorb and diffuse into poor solvents (e.g., water). This allows for the formation of finer voids at a higher density during phase separation between the organic polymer and the solvent, which is believed to enhance ionic conductivity while adequately suppressing gas barrier properties.

[0017] The total content of the solvent selected from the compounds (1) to (7) in the solvent constituting the dope solution (the content of the solvent when one solvent selected from the compounds (1) to (7) is used, or the total content of the two or more solvents when two or more solvents are used) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. When the solvent constituting the dope solution contains a solvent other than the solvent selected from the compounds (1) to (7), the other solvent is preferably a solvent miscible with the solvent selected from the compounds (1) to (7). For example, NMP, NEP, NBP, DMF, formamide, DMSO, DMAC, acetonitrile, etc. may be contained as the other solvent. The solvent constituting the dope solution may contain a small amount of water as an unavoidable impurity.

[0018] The solvent selected from the above compounds (1) to (7) preferably contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (2), (3) and (4), and more preferably contains at least one of the following compounds (1)-1, (1)-2 and (1)-3.

[0019] The solvent selected from the above compounds (1) to (7) is preferably at least one of the following compounds (1)-1, (1)-2, (1)-3, (2), (3) and (4), more preferably at least one of the compounds (1)-1, (1)-2 and (1)-3, and even more preferably at least one of the compounds (1)-1 and (1)-2.

[0020]

[0021] The content of the solvent in the dope solution is preferably 20 to 95% by mass, more preferably 25 to 90% by mass, even more preferably 30 to 80% by mass, still more preferably 30 to 70% by mass, still more preferably 32 to 60% by mass, and still more preferably 35 to 50% by mass.

[0022] The preferred embodiments of the components other than the solvent that make up the dope solution will be described below.

[0023] (Organic Polymer) The dope solution is a solution containing an organic polymer dissolved therein, which is a constituent material of the porous membrane. As the organic polymer, various organic polymers applicable to wet phase separation can be used.

[0024] The organic polymer can be selected from, for example, fluororesins, olefin resins, polyester resins, aromatic hydrocarbon resins, etc. The fluororesins are preferably resins selected from polyvinylidene fluoride and polytetrafluoroethylene. The olefin resins are preferably polypropylene resins. The polyester resins are preferably resins selected from polyethylene terephthalate, polybutylene terephthalate, and polybutylene naphthalate. The aromatic hydrocarbon resins are preferably polystyrene resins.

[0025] Other preferred organic polymers include polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamideimide.

[0026] The organic polymers may be used alone or in combination of two or more.

[0027] The organic polymer constituting the dope solution is more preferably a polymer selected from polysulfone, polyethersulfone and polyphenylsulfone, with polysulfone being particularly preferred.

[0028] The weight-average molecular weight (Mw) of the organic polymer is not particularly limited. Taking into consideration the handleability of the dope solution and the mechanical strength of the resulting porous separator for alkaline water electrolysis, it can be, for example, 10,000 to 500,000, and preferably 20,000 to 300,000. Mw can be determined under the following conditions. NMP: Wako Pure Chemical Industries 138-12103 NMP for GPC (containing 10 mM LiBr, manufactured by Kojundo Chemical Laboratory Co., Ltd.) Column: TOSOH TSKgel Super AWM-H (6.0 mm ID x 15 cm) x 3 Detector: RI detector UV detector (STD: 270 nm, Sample: 280 nm) Flow rate: Sample pump side (0.5 ml / min.), reference pump side (0.25 ml / min.) Measurement time: 37 min Temperature control: 40°C

[0029] The content of the organic polymer in the dope solution is preferably 2 to 50% by mass, more preferably 4 to 40% by mass, even more preferably 5 to 30% by mass, and still more preferably 6 to 25% by mass.

[0030] (Hydrophilic inorganic particles) The dope solution may contain hydrophilic inorganic particles. The hydrophilic inorganic particles are particles that are dispersed in the dope solution without dissolving, and such a dispersion state is also referred to as a dope solution in the present invention. In other words, the "solution" of the dope solution means that the organic polymer is dissolved in the solvent. The hydrophilic inorganic particles are preferably particles selected from metal oxides and metal hydroxides. One or more types of hydrophilic inorganic particles can be used as the hydrophilic inorganic particles.

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

[0032] The metal hydroxide is preferably selected from the group consisting of zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide and magnesium hydroxide.

[0033] As the hydrophilic inorganic particles, in addition to metal oxides and metal hydroxides, for example, barium sulfate can also be used.

[0034] The particle size of the hydrophilic inorganic particles is preferably 0.05 to 2.00 μm, more preferably 0.1 to 1.50 μm, even more preferably 0.15 to 1.00 μm, and still more preferably 0.20 to 0.80 μm. This particle size is the median diameter (D50), which means the particle size at 50% cumulative when the total volume of the particles is taken as 100% in the cumulative distribution measured by a laser diffraction / scattering method.

[0035] The content of the hydrophilic inorganic particles in the solid content of the dope solution (components excluding the solvent) is usually 95% by mass or less, preferably 92% by mass or less, more preferably 90% by mass or less, even more preferably 88% by mass or less, and still more preferably 85% by mass or less. When the dope solution contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the solid content of the dope solution (components excluding the solvent) is preferably 20 to 95% by mass, more preferably 30 to 92% by mass, even more preferably 40 to 90% by mass, even more preferably 50 to 88% by mass, even more preferably 60 to 85% by mass, and still more preferably 70 to 85% by mass.

[0036] When the dope solution contains hydrophilic inorganic particles, the ratio of the content of the hydrophilic inorganic particles to the content of the organic polymer in the dope solution (hydrophilic inorganic particles / organic polymer) is preferably 10 / 1 to 1 / 1, more preferably 9 / 1 to 2 / 1, even more preferably 8 / 1 to 3 / 1, still more preferably 7 / 1 to 4 / 1, and still more preferably 6.5 / 1 to 4 / 1, by mass.

[0037] The dope solution may contain one or more components (other components) other than the components described above (solvent, organic polymer, and hydrophilic inorganic particles). For example, to control pore formation during wet phase separation, the dope solution may contain polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohol, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, calcium chloride, magnesium chloride, lithium chloride, etc. The content of the other components in the dope solution is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the dope solution contains other components, the total content of the other components in the dope solution is preferably 0.1 to 15% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 5% by mass.

[0038] <Formation of Porous Membrane by Wet Phase Separation> In Production Method 1 of the present invention, a porous membrane is formed by wet phase separation using the dope solution. The porous membrane thus obtained can be suitably used as a porous separator for alkaline water electrolysis. In wet phase separation, a membrane (coating) is formed using the dope solution, and then the membrane is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent. When the proportion of the good solvent in the membrane decreases during this immersion, the organic polymer and the solvent undergo phase separation (liquid-induced phase separation), causing the organic polymer to gel (coagulate), thereby obtaining a porous membrane. As the poor solvent, for example, water or a mixed solvent of water and a hydrophilic organic solvent (a water-miscible organic solvent) can be used, with water being preferred. Before immersing the membrane in the poor solvent, the membrane may be exposed to the vapor of the poor solvent to induce steam-induced phase separation (steam-induced phase separation). By performing steam-induced phase separation, the formation of a dense skin layer on the surface layer can be suppressed. Therefore, the wet phase separation can be carried out by combining vapor-induced phase separation and liquid-induced phase separation.

[0039] The membrane formed from the dope solution may include a porous support. For example, by forming a porous membrane by incorporating a porous support into a membrane formed from a dope solution and then causing phase separation, the resulting porous membrane contains a porous support, and its mechanical strength is further enhanced. For example, a porous support is placed on a coating film formed by casting a dope solution on a substrate, and the porous support is immersed in the coating film. Thereafter, phase separation is caused by a poor solvent, thereby obtaining a porous membrane supported by a porous support. In addition, when the porous membrane has a structure supported by a porous support, the entire structure including the porous support is the "porous membrane" specified in the present invention.

[0040] (Porous support)

[0041] The porous support is not particularly limited as long as it is applicable to a porous separator for alkaline water electrolysis. For example, a porous support selected from a porous cloth, a porous metal plate, and a porous ceramic plate can be used. The porous support preferably has an aperture ratio of 30 to 80%, more preferably 40 to 70%. The aperture ratio is the ratio of the area of ​​voids to a unit area when the porous support is viewed in a plane. The porous support is preferably a porous cloth, more preferably a porous polymer cloth. The porous polymer cloth is a woven fabric or a nonwoven fabric.

[0042] The polymer constituting the porous polymer fabric is not particularly limited, and examples thereof include polypropylene, polyethylene, polysulfone, polyphenylene sulfide, polyamide, polyethersulfone, polyphenylsulfone, polyethylene terephthalate, polyetheretherketone, sulfonated polyetheretherketone, monochlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene or chlorotrifluoroethylene, polyimide, polyetherimide, and m-aramid.

[0043] The thickness of the porous support is preferably 30 to 150 μm, more preferably 30 to 100 μm, and even more preferably 30 to 75 μm. The thickness of the porous support can be measured using a dot-type thickness meter.

[0044] The thickness of the porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention is preferably 60 to 200 μm, more preferably 70 to 170 μm, and even more preferably 80 to 120 μm. This thickness is measured by obtaining a cross-sectional SEM (scanning electron microscope) image of a cross-section cut out of the porous separator with a razor at a magnification (e.g., 400x) that fits the separator cross-section in a single field of view. More specifically, assuming that no pores are present in the obtained cross-sectional SEM image (assuming that the pores are filled with an organic polymer), the thickness is measured at 20-point intervals, and the thickness is the arithmetic mean of the 20 measured values.

[0045] From the above viewpoints, the pore size of the pores in the porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention is preferably 50 to 1,000 nm, more preferably 100 to 800 nm, and even more preferably 150 to 600 nm. This pore size is the average pore size and can be determined by the following method. A 1 cm diameter punched-out piece of the porous separator is immersed in pure water for 24 hours at room temperature (25°C). Subsequently, the mean flow pores are calculated using perm-porometry by Porometer Corporation, and this mean flow pore is taken as the average pore size.

[0046] The porosity of the porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention is preferably 30 to 70%, more preferably 40 to 60%, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier properties. This porosity can be calculated by the following method. First, the porous separator is cut to a predetermined area (S, unit: cm ２ ) and immerse in pure water at room temperature (25°C) for 24 hours. After that, wipe off any excess water droplets on the surface and measure the weight (w1, unit: g) and thickness (d, unit: cm). Dry in an oven at 90°C for 24 hours and measure the weight (w2, unit: g) again. Calculate the porosity using the following formula: Porosity (%) = {1 - [(w1 - w2) / (S x d)]} x 100

[0047] A certain amount of good solvent in the dope solution used in the production of the porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention inevitably remains in the porous separator for alkaline water electrolysis. That is, the present invention provides the following porous separator for alkaline water electrolysis: A porous separator for alkaline water electrolysis comprising an organic polymer with a porous structure, the porous separator for alkaline water electrolysis containing at least one of the compounds (1) to (7), and the total content of the compounds (1) to (7) in the porous separator for alkaline water electrolysis (amount of residual solvent) is 0.0001 to 5 mass% (0.0001 to 5.0000 mass%). The amount of residual solvent can be determined by measuring the amount of residual solvent in the separator for alkaline water electrolysis using a gas chromatograph or a chromatograph after previously drying the separator for alkaline water electrolysis with air at 40°C for 12 hours. １ Using H-NMR, the amount can be quantified as mass % based on 100 mass % of the porous separator for alkaline water electrolysis after drying.

[0048] The porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention may be in the form of a long sheet wound into a roll, or may be pre-cut into a predetermined shape according to the intended use, device, etc. Furthermore, the porous separator for alkaline water electrolysis obtained by Production Method-1 of the present invention may be preserved or stored by immersing it in a storage liquid such as pure water.

[0049] [Alkaline water electrolysis] The porous separator for alkaline water electrolysis obtained by Production method-1 of the present invention (also referred to as the "separator of the present invention") is disposed between the cathode and the anode for use in alkaline water electrolysis. Preferred embodiments of an alkaline water electrolysis system to which the separator of the present invention is applied (also referred to as the "alkaline water electrolysis system of the present invention") will be described, but the alkaline water electrolysis of the present invention is not limited to these embodiments.

[0050] FIG. 1 schematically illustrates a preferred embodiment of an alkaline water electrolysis system to which the separator of the present invention can be applied. The alkaline water electrolysis system (10) illustrated in FIG. 1 includes a separator (11) of the present invention, a cathode electrode (12) on one side thereof, and an anode electrode (13) on the other side thereof, and the separator (11) and the electrodes (12, 13) are immersed in a highly concentrated alkaline aqueous solution (14, preferably a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution). When a current flows between the electrodes, electrons are supplied to the cathode side, and hydrogen bubbles (H ２ ) occurs (2H ２ O + 2e － →H ２ +2OH － ) Hydroxy ions (OH － ) passes through the separator (11) and moves to the anode side, where electrons are taken away and oxygen (O ２ ) is generated (4OH － →O ２ +2H ２ O+4e － The cathode electrode (12) and the anode electrode (13) preferably include an electrode substrate (conductive material) and a catalyst layer on the electrode substrate. When a catalyst layer is included, the catalyst species may be the same or different between the cathode electrode (12) and the anode electrode (13). In the alkaline water electrolysis system (10) shown in FIG. 1 , the separator (11) and the electrodes (12, 13) are separated from each other, resulting in a long migration distance of hydroxy ions, which limits improvement in ion conduction efficiency.

[0051] Figure 2 schematically illustrates another preferred embodiment of an alkaline water electrolysis system to which the separator of the present invention can be applied. The alkaline water electrolysis system (20) illustrated in Figure 2 is the same as the alkaline water electrolysis system (10) illustrated in Figure 1 , except that the separator (11) and the electrodes (12, 13) are arranged in contact with each other (zero gap type). The alkaline water electrolysis system (20) illustrated in Figure 2 is advantageous in terms of ion conduction efficiency because the separator (11) and the electrodes (12, 13) are in contact with each other, thereby shortening the migration distance of hydroxy ions.

[0052] FIG. 3 is a schematic diagram illustrating yet another preferred embodiment of an alkaline water electrolysis system to which the separator of the present invention can be applied. The alkaline water electrolysis system (30) illustrated in FIG. 3 includes a membrane electrode assembly. That is, a cathode catalyst layer (32) is disposed on one side of a separator (31) of the present invention, and an anode catalyst layer (33) is disposed on the other side. These catalyst layers are composed of a catalyst and a binder. Furthermore, gas diffusion layers (34) are formed on the outer surfaces of these catalyst layers to form a membrane electrode assembly. In FIG. 3 , a bipolar plate (35) is formed further outside the membrane electrode assembly. An alkaline aqueous solution is supplied to the cathode catalyst layer (32) and the anode catalyst layer (33) of this membrane electrode assembly, and the cathode catalyst layer (32) and the anode catalyst layer (33) are electrically connected and energized, whereby hydrogen bubbles are generated from the cathode catalyst layer (32) and oxygen is generated from the anode catalyst layer (33).

[0053] In the alkaline water electrolysis system, the configurations of the cathode electrode, cathode catalyst layer, anode electrode, anode catalyst layer, etc., other than the separator, are not particularly limited, and typical components used in alkaline water electrolysis systems can be applied as appropriate.

[0054] Thus, one embodiment of the present invention provides an alkaline water electrolysis system in which the separator of the present invention is incorporated as a separator in the alkaline water electrolysis system. Also, one embodiment of the present invention provides a method for producing an alkaline water electrolysis system, which includes incorporating the separator of the present invention as a separator in the alkaline water electrolysis system.

[0055] [Method for producing porous membrane] Next, the invention of the method for producing a porous membrane according to the present invention will be described. The applications of the porous membrane obtained by this production method are not limited to separators for alkaline water electrolysis, but can also be used as reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, dialysis membranes (e.g., membranes for desalination), etc. Therefore, the invention of the method for producing a porous membrane according to the present invention is aimed at solving the technical problems common to porous membranes intended for the above-mentioned various applications, as described below.

[0056] When forming a porous membrane by wet phase separation using a dope solution containing an organic polymer, it is usually necessary to apply the dope solution to a substrate or the like to form a coating film. Forming this coating film with high surface smoothness is directly related to the surface smoothness of the resulting porous membrane. Poor surface smoothness of the porous membrane may result in contamination adhering to the surface, leading to clogging and other problems, preventing the porous membrane from fully demonstrating its functionality. Furthermore, an uneven surface of the porous membrane may result in unstable performance or poor performance due to defects. Therefore, the surface smoothness of the coating film formed from the dope solution is an important factor in improving the quality of the resulting porous membrane. The porous membrane manufacturing method of the present invention (hereinafter also referred to as "Manufacturing Method-2 of the Present Invention") involves forming a porous membrane by wet phase separation. A characteristic technical element of the present invention is the use of a specific type of solvent as a solvent (good solvent) for dissolving the organic polymer in the dope solution (a solution containing the organic polymer that constitutes the porous membrane) used in this wet phase separation. This allows the resulting porous membrane to have excellent surface smoothness.

[0057] <Dope Solution> (Solvent) In Production Method-2 of the present invention, the dope solution in the wet phase separation contains at least one solvent (good solvent) for the above compounds (1), (5), and (6). Specifically, it contains at least one solvent having the following chemical structure:

[0058]

[0059] R in the above compound (1) has the same definition as R in the compound (1) in the above-mentioned Production Method-1 of the present invention, and the preferred structure is also the same.

[0060] The dope solution in the wet phase separation method contains at least one of the compounds (1), (5), and (6) as a solvent, which can effectively improve the surface smoothness of the resulting porous film. Although the reason for this is unclear, it is thought that one of the reasons is that the polar groups, molecular shape, molecular size, etc. specific to the compounds (1), (5), and (6) ensure the solubility of the organic polymer while adequately suppressing the interaction with the organic polymer, thereby improving the fluidity of the dope solution.

[0061] The total content of the solvent selected from the compounds (1), (5), and (6) in the solvent constituting the dope solution (the content of the solvent when one solvent selected from the compounds (1), (5), and (6) is used, or the total content of the two or more solvents when two or more solvents are used) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. When the solvent constituting the dope solution contains a solvent other than the solvent selected from the compounds (1), (5), and (6), the other solvent is preferably a solvent miscible with the solvent selected from the compounds (1), (5), and (6). For example, the other solvent may include NMP, NEP, NBP, DMF, formamide, DMSO, DMAC, acetonitrile, etc. The solvent constituting the dope solution may contain a small amount of water as an unavoidable impurity.

[0062] The solvent selected from the above compounds (1), (5), and (6) preferably contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (5), and (6), and more preferably contains at least one of the following compounds (1)-1, (1)-2, and (1)-3.

[0063]

[0064] The content of the solvent in the dope solution is preferably 20 to 95% by mass, more preferably 25 to 90% by mass, even more preferably 30 to 80% by mass, still more preferably 30 to 70% by mass, still more preferably 32 to 60% by mass, and still more preferably 35 to 50% by mass.

[0065] The dope solution preferably contains an organic polymer as a component other than the solvent, and also contains hydrophilic inorganic particles. The types of these organic polymers and hydrophilic inorganic particles are the same as those described in the above-mentioned Production Method-1 of the present invention. That is, the description of the types of organic polymers and hydrophilic inorganic particles in the above-mentioned Production Method-1 of the present invention also applies to Production Method-2 of the present invention. Furthermore, the contents and content ratios of the organic polymers and hydrophilic inorganic particles in the dope solution are also the same as those of the organic polymers and hydrophilic inorganic particles in the dope solution or its solid content described in the above-mentioned Production Method-1 of the present invention. That is, the description of the contents and content ratios of the organic polymers and hydrophilic inorganic particles in the dope solution or its solid content described in the above-mentioned Production Method-1 of the present invention also applies to Production Method-2 of the present invention.

[0066] The dope solution may contain one or more components (other components) other than the components described above (solvent, organic polymer, and hydrophilic inorganic particles). For example, to control pore formation during wet phase separation, the dope solution may contain polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohol, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, calcium chloride, magnesium chloride, lithium chloride, etc. The content of the other components in the dope solution is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the dope solution contains other components, the total content of the other components in the dope solution is preferably 0.1 to 15% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 5% by mass.

[0067] <Formation of porous membrane by wet phase separation> As described above, the method for forming a porous membrane by wet phase separation in Production Method-2 of the present invention is the same as the method for forming a porous membrane by wet phase separation in Production Method-1 of the present invention, except that the essential solvent species used in the dope solution are more limited than in Production Method-1 of the present invention. In other words, for matters other than the essential solvent species, including the type and structure of a usable porous support, the method described in "<Formation of porous membrane by wet phase separation>" in the explanation of Production Method-1 of the present invention above can be directly applied.

[0068] The thickness of the porous membrane obtained by Production Method-2 of the present invention is preferably 60 to 200 μm, more preferably 70 to 170 μm, and even more preferably 80 to 120 μm. This thickness can be determined in the same manner as the above-mentioned method for measuring the thickness of the porous separator for alkaline water electrolysis.

[0069] From the above viewpoints, the pore size of the pores in the porous membrane obtained by Production Method-2 of the present invention is preferably 50 to 1,000 nm, more preferably 100 to 800 nm, and even more preferably 150 to 600 nm. This pore size is an average pore size, and can be determined in the same manner as the above-mentioned method for measuring the pore size of the porous separator for alkaline water electrolysis.

[0070] The porosity of the porous membrane obtained by Production method-2 of the present invention is preferably 30 to 70%, more preferably 40 to 60%. This porosity can be determined in the same manner as the above-mentioned method for measuring the porosity of the porous separator for alkaline water electrolysis.

[0071] A certain amount of good solvent in the dope solution used in the production of the porous membrane obtained by Production Method-2 of the present invention inevitably remains in the porous membrane. That is, according to the present invention, the following porous membrane is provided: A porous membrane comprising an organic polymer with a porous structure, the porous membrane containing at least one of the compounds (1), (5), and (6), and the total content of the compounds (1), (5), and (6) in the porous membrane (residual solvent amount) is 0.0001 to 5 mass% (0.0001 to 5.0000 mass%). The residual solvent amount in the porous membrane can be determined in the same manner as the method for measuring the residual solvent amount in a porous separator for alkaline water electrolysis described above.

[0072] The porous membrane obtained by Production Method-2 of the present invention can be used as a reverse osmosis membrane, a nanofiltration membrane, an ultrafiltration membrane, a separator for alkaline water electrolysis, a dialysis membrane, etc.

[0073] The porous membrane obtained by the production method of the present invention may be in the form of a long sheet wound into a roll, or may be cut into a predetermined shape in advance according to the intended use, device, etc. Furthermore, the porous membrane obtained by the production method of the present invention may be preserved or stored by immersing it in a preservative solution such as pure water.

[0074] The present invention will be described in more detail based on examples, but the present invention should not be construed as being limited to these examples except as defined in the present invention.

[0075] Examples and Comparative Examples Related to Manufacturing Method-1 of the Present Invention [Fabrication of Porous Separator] Example 1-1 8.5 g of polysulfone (trade name: Udel LCD3500 MB7, manufactured by Solvay, weight average molecular weight Mw: 80,000), 20.8 g of gamma-valerolactone (manufactured by Merck) which is compound (4), and 20.8 g of PolarClean (manufactured by Solvay, mass ratio of compound (2) / compound (3) = 95 / 5) were mixed and stirred at 60°C for 5 hours to completely dissolve the polysulfone. Next, 2.4 g of polyvinylpyrrolidone (trade name: PVP K90, manufactured by Merck) was added, and the mixture was stirred at 60°C for 1 hour. Next, 47.9 g of zirconium oxide particles (trade name: High Purity Monoclinic Zirconias E101, manufactured by Luxfer MEL Technologies, D50: approximately 0.8 μm) were added as hydrophilic inorganic particles, and the mixture was stirred for 3 hours to obtain a dope solution. The obtained dope solution was cast onto a glass plate using a 250 μm thick applicator to form a coating film. A woven fabric support made of polyether ether ketone (PEEK) (manufactured by Safer, aperture ratio 70%, thickness 54 μm) was placed on top of the coating film as a porous support, and this support was completely immersed in the coating film. The coating film together with the glass plate was gently immersed in a water tank containing water (poor solvent) cooled to 10°C, and phase separation between the polysulfone and the solvent occurred, forming a porous film containing polysulfone on the glass plate. The obtained porous membrane with a porous support was washed together with the glass plate with water at 50°C for 10 minutes, and then the porous membrane with a porous support was peeled off from the glass plate. Subsequently, the porous membrane with a porous support was washed with water at 90°C for 1 hour to obtain a porous separator (1-a). The thickness of the porous separator (1-a) was 160 μm. Furthermore, the amount of residual solvent in the porous separator (1-a) (the total amount of compounds (2), (3), and (4)) measured by gas chromatography was 4 mass%.

[0076] Example 1-2 A porous separator (1-b) was obtained in the same manner as in Example 1-1, except that 41.6 g of N,N-dimethylpropionamide (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (1)-1, was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-b) was 160 μm. The amount of residual solvent (amount of compound (1)-1) in the porous separator (1-b) measured by gas chromatography was 1% by mass.

[0077] Example 1-3 A porous separator (1-c) was obtained in the same manner as in Example 1-1, except that 41.6 g of 3-methoxy-N,N-dimethylpropanamide (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (1)-2, was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-c) was 160 μm. The amount of residual solvent (amount of compound (1)-2) in the porous separator (1-c) measured by gas chromatography was 2 mass%.

[0078] Example 1-4 A porous separator (1-d) was obtained in the same manner as in Example 1-1, except that 41.6 g of 3-butoxy-N,N-dimethylpropanamide (manufactured by KJ Chemicals), which is compound (1)-3, was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution in Example 1. The thickness of the porous separator (1-d) was 160 μm. The amount of residual solvent (amount of compound (1)-3) in the porous separator (1-d) measured by gas chromatography was 3 mass%.

[0079] Example 1-5 A porous separator (1-e) was obtained in the same manner as in Example 1-1, except that 41.6 g of 3-methyl-2-oxazolidone (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (5), was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-e) was 160 μm. The amount of residual solvent (amount of compound (5)) in the porous separator (1-e) measured by gas chromatography was 4% by mass.

[0080] Example 1-6 A porous separator (1-f) was obtained in the same manner as in Example 1-1, except that 41.6 g of N-formylpiperidine (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (6), was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-f) was 160 μm. The amount of residual solvent (amount of compound (6)) in the porous separator (1-f) measured by gas chromatography was 4 mass%.

[0081] Example 1-7 A porous separator (g) was obtained in the same manner as in Example 1-1, except that 41.6 g of Cyrene (manufactured by Merck) which is compound (7) was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-g) was 160 μm. The amount of the remaining solvent (amount of compound (7)) in the porous separator (1-g) measured by gas chromatography was 3 mass%.

[0082] Example 1-8 A porous separator (1-h) was obtained in the same manner as in Example 1-1, except that 41.6 g of PolarClean, a mixture of compounds (2) and (3), was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-h) was 160 μm. The amount of residual solvent in the porous separator (1-h) (the total amount of compounds (2) and (3)) measured by gas chromatography was 4% by mass.

[0083] Example 1-9 A porous separator (1-i) was obtained in the same manner as in Example 1-1, except that 41.6 g of gamma-valerolactone (compound (4)) was used instead of gamma-valerolactone and PolarClean as the solvent for the dope solution. The thickness of the porous separator (1-i) was 160 μm. The amount of residual solvent (amount of compound (4)) in the porous separator (1-i) measured by gas chromatography was 3 mass%.

[0084] Example 1-10 A porous separator (1-j) was obtained in the same manner as in Example 1-3, except that a porous support was not used. The thickness of the porous separator (1-j) was 200 μm. The amount of residual solvent (amount of compound (1)-2) in the porous separator (1-j) measured by gas chromatography was 2 mass%.

[0085] Comparative Example 1-1 A porous separator (1-k) was obtained in the same manner as in Example 1-1, except that 41.6 g of 1-butyl-2-pyrrolidone (NBP, manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the solvent for the dope solution instead of gamma-valerolactone and PolarClean. The thickness of the porous separator (1-k) was 160 μm.

[0086] Comparative Example 1-2: 11.86 g of polysulfone (product name: Udel LCD3500 MB7, manufactured by Solvay) and 39.7 g of 1-butyl-2-pyrrolidone (NBP, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed and stirred at 60°C for 5 hours to completely dissolve the polysulfone. Next, 1.0 g of glycerol was added, and the mixture was stirred at 60°C for 1 hour. Next, 47.44 g of zirconium oxide particles (product name: E101, manufactured by Luxfer) as hydrophilic inorganic particles were added, and the mixture was stirred for 3 hours to obtain a dope solution. Using this dope solution, a porous separator (1-1) was obtained in the same manner as in Example 1-1. The thickness of the porous separator (1-1) was 160 μm.

[0087] Comparative Example 1-3 A porous separator (1-m) was obtained in the same manner as in Example 1-1, except that 41.6 g of N-methyl-2-pyrrolidone (NMP, manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the solvent for the dope solution instead of gamma-valerolactone and PolarClean. The thickness of the porous separator (1-m) was 160 μm.

[0088] Comparative Example 1-4 A porous separator (1-n) was obtained in the same manner as in Example 1-1, except that 41.6 g of N,N-dimethylacetamide (DMAC, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the solvent for the dope solution instead of gamma-valerolactone and PolarClean. The thickness of the porous separator (1-n) was 160 μm.

[0089] Comparative Example 1-5 In Example 1-1, the solvent for the dope solution was changed to 41.6 g of dimethyl sulfoxide (DMSO, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) instead of gamma-valerolactone and PolarClean, and an attempt was made to prepare a porous separator. However, the solubility of polysulfone was insufficient, and a dope solution in which polysulfone was completely dissolved could not be obtained.

[0090] Comparative Example 1-6 In Example 1-1, the solvent for the dope solution was changed to 41.6 g of acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) instead of gamma-valerolactone and PolarClean, and an attempt was made to prepare a porous separator. However, the solubility of polysulfone was insufficient, and a dope solution could not be obtained.

[0091] [Test Example] <Ionic Conductivity> A two-compartment cell having a nickel electrode at the current control terminal and a Luggin capillary filled with 3M-KCl at the voltage control terminal was filled with a 30% by mass aqueous solution of potassium hydroxide as an electrolyte and maintained at 30°C. ２The ionic resistance was measured under the conditions of 0.05 Ω cm to obtain a blank value (the ionic resistance value when no separator was installed between the two chambers). Next, the porous separators produced in the above examples and comparative examples were installed between the two chambers, and a 30% by mass aqueous potassium hydroxide solution was added as above, and the ionic resistance was measured under the same conditions as above. The difference between the obtained ionic resistance value and the blank value was taken as the ionic resistance value of the porous separator. The ionic resistance value of each porous separator was applied to the following evaluation criteria and used as an index of ionic conductivity. (Evaluation criteria for ionic resistance value) A: 0.05 Ω cm ２ Less than B: 0.05 Ω cm ２ 0.07Ω・cm or more ２ Less than C: 0.07 Ω cm ２ End

[0092] <Gas Barrier Properties> Since the gas barrier properties of a porous separator correlate with the liquid permeability, the gas barrier properties were evaluated using the liquid permeability as an index. Each of the porous separators was punched into a circular shape with a diameter of 47 mm. Each of the obtained circular porous separators was set in a pressure-resistant filter holder (product number XX4004700, manufactured by Merck). A 30% by mass aqueous solution of potassium hydroxide heated to 85°C was supplied to the circular porous separator from above, and a gauge pressure of 50 mbar was applied from above the circular porous separator. The time when droplets began to emerge from the bottom of the circular porous separator was set to 0 minutes, and the pressure was maintained for 8 minutes. The amount of aqueous potassium hydroxide solution that had escaped to the bottom of the circular porous separator over 8 minutes was quantified to calculate the liquid permeability, which was then used as an index of gas barrier properties according to the following evaluation criteria. (Evaluation Criteria for Liquid Permeability) A: 800 mL / bar m ２ Less than hr B: 800 mL / bar m ２ ・HR or more 1000mL / bar・m ２ Less than hr C: 1000 mL / bar m ２ ・Over hr

[0093] The results are shown in the table below.

[0094]

[0095] As shown in the above table, by preparing the dope solution using the solvent specified in Production Method-1 of the present invention, the resulting porous separator was able to achieve both gas barrier properties and ionic conductivity at a higher level.

[0096] Examples and Comparative Examples of Manufacturing Method-2 of the Present Invention [Fabrication of Porous Membrane] Example 2-1 8.5 g of polysulfone (trade name: Udel LCD3500 MB7, manufactured by Solvay, weight average molecular weight Mw: 80,000) and 41.6 g of N,N-dimethylpropionamide (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (1)-1, were mixed and stirred at 60°C for 5 hours to completely dissolve the polysulfone. Next, 2.4 g of polyvinylpyrrolidone (trade name: PVP K90, manufactured by Merck) was added, and the mixture was stirred at 60°C for 1 hour. Next, 47.9 g of zirconium oxide particles (trade name: High Purity Monoclinic Zirconias E101, manufactured by Luxfer MEL Technologies, D50: approximately 0.8 μm) were added as hydrophilic inorganic particles, and the mixture was stirred for 3 hours to obtain a dope solution. The obtained dope solution was cast onto a glass plate using a 250 μm thick applicator to form a coating film. A woven fabric support made of polyether ether ketone (PEEK) (manufactured by Safer, aperture ratio 70%, thickness 54 μm) was placed on top of the coating film as a porous support, and this support was completely immersed in the coating film. The coating film together with the glass plate was gently immersed in a water tank containing water (poor solvent) cooled to 10°C, and phase separation between the polysulfone and the solvent occurred, forming a porous film containing polysulfone on the glass plate. The obtained porous membrane with a porous support was washed together with the glass plate with water at 50°C for 10 minutes, and then the porous membrane with a porous support was peeled off from the glass plate. Subsequently, the porous membrane with a porous support was washed with water at 90°C for 1 hour to obtain porous membrane (2-a). The thickness of porous membrane (2-a) was 160 μm. Furthermore, the amount of residual solvent in porous membrane (2-a) (amount of compound (1)-1) measured by gas chromatography was 1 mass%. This porous membrane (2-a) was produced by the same production method as the porous separator (1-b).

[0097] Example 2-2 A porous membrane (2-b) was obtained in the same manner as in Example 2-1, except that 41.6 g of 3-methoxy-N,N-dimethylpropanamide (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (1)-2, was used instead of N,N-dimethylpropionamide as the solvent for the dope solution in Example 2-1. The thickness of the porous membrane (2-b) was 160 μm. The amount of the remaining solvent (amount of compound (1)-2) in the porous membrane (2-b) measured by gas chromatography was 2 mass%. This porous membrane (2-b) was produced by the same method as the porous separator (1-c).

[0098] Example 2-3 A porous membrane (c) was obtained in the same manner as in Example 2-1, except that 41.6 g of 3-butoxy-N,N-dimethylpropanamide (manufactured by KJ Chemicals), which is compound (1)-3, was used instead of N,N-dimethylpropionamide as the solvent for the dope solution in Example 2-1. The thickness of the porous membrane (2-c) was 160 μm. The amount of the remaining solvent (amount of compound (1)-3) in the porous membrane (2-c) measured by gas chromatography was 3 mass%. This porous membrane (2-c) was produced by the same method as the porous separator (1-d).

[0099] Example 2-4 A porous membrane (2-d) was obtained in the same manner as in Example 2-1, except that 41.6 g of 3-methyl-2-oxazolidone (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (5), was used instead of N,N-dimethylpropionamide as the solvent for the dope solution. The thickness of the porous membrane (2-d) was 160 μm. The amount of the remaining solvent (amount of compound (2)) in the porous membrane (2-d) measured by gas chromatography was 4 mass%. This porous membrane (2-d) was produced by the same method as the porous separator (1-e).

[0100] Example 2-5 A porous membrane (2-e) was obtained in the same manner as in Example 2-1, except that 41.6 g of N-formylpiperidine (manufactured by Tokyo Chemical Industry Co., Ltd.), which is compound (6), was used instead of N,N-dimethylpropionamide as the solvent for the dope solution. The thickness of the porous membrane (2-e) was 160 μm. The amount of the remaining solvent (amount of compound (3)) in the porous membrane (2-e) measured by gas chromatography was 4 mass%. This porous membrane (2-e) was produced by the same method as the porous separator (1-f).

[0101] Example 2-6 A porous membrane (2-f) was obtained in the same manner as in Example 2-2, except that a porous support was not used. The thickness of the porous membrane (2-f) was 200 μm. The amount of residual solvent (amount of compound (1)-2) in the porous membrane (2-f) measured by gas chromatography was 2 mass%. This porous membrane (2-f) was produced by the same method as the porous separator (1-j).

[0102] Comparative Example 2-1 A porous membrane (2-g) was obtained in the same manner as in Example 2-1, except that 41.6 g of 1-butyl-2-pyrrolidone (NBP, manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of N,N-dimethylpropionamide as the solvent for the dope solution. The thickness of the porous membrane (2-g) was 160 μm. This porous membrane (2-g) was produced by the same method as the porous separator (1-k).

[0103] Comparative Example 2-2: 11.86 g of polysulfone (product name: Udel LCD3500 MB7, manufactured by Solvay) and 39.7 g of 1-butyl-2-pyrrolidone (NBP, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed and stirred at 60°C for 5 hours to completely dissolve the polysulfone. Next, 1.0 g of glycerol was added, and the mixture was stirred at 60°C for 1 hour. Next, 47.44 g of zirconium oxide particles (product name: E101, manufactured by Luxfer) as hydrophilic inorganic particles were added, and the mixture was stirred for 3 hours to obtain a dope solution. Using this dope solution, a porous membrane (2-h) was obtained in the same manner as in Example 2-1. The thickness of the porous membrane (2-h) was 160 μm. This porous membrane (2-h) was produced by the same method as the porous separator (1-l) described above.

[0104] Comparative Example 2-3 A porous membrane (2-i) was obtained in the same manner as in Example 2-1, except that 41.6 g of N-methyl-2-pyrrolidone (NMP, manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of N,N-dimethylpropionamide as the solvent for the dope solution. The thickness of the porous membrane (2-i) was 160 μm. This porous membrane (2-i) was produced by the same method as that for the porous separator (1-m).

[0105] Comparative Example 2-4 A porous membrane (2-j) was obtained in the same manner as in Example 2-1, except that 41.6 g of N,N-dimethylacetamide (DMAC, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of N,N-dimethylpropionamide as the solvent for the dope solution. The thickness of the porous membrane (2-j) was 160 μm. This porous membrane (2-j) was produced by the same method as that for the porous separator (1-n).

[0106] Comparative Example 2-5: In Example 2-1, the solvent for the dope solution was changed from N,N-dimethylpropionamide to 41.6 g of dimethyl sulfoxide (DMSO, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and an attempt was made to prepare a porous membrane. However, the solubility of polysulfone was insufficient, and a dope solution in which polysulfone was completely dissolved could not be obtained (the same results as in Comparative Example 1-5 were reproduced).

[0107] Comparative Example 2-6: In Example 2-1, the solvent for the dope solution was changed from N,N-dimethylpropionamide to 41.6 g of acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and an attempt was made to prepare a porous membrane. However, the solubility of polysulfone was insufficient, and a dope solution could not be obtained (the same results as in Comparative Example 1-6 were reproduced).

[0108] [Test Example] <Surface Smoothness of Porous Membrane> The surface smoothness of the porous membrane was evaluated by observing its surface. Specifically, a 7 cm x 7 cm square area was visually inspected in the coating direction (casting direction) of the dope solution to determine whether or not there were any coating streaks during coating, and if there were any, the number of coating streaks. The surface smoothness was evaluated according to the following evaluation criteria. A has the highest surface smoothness, followed by B, C, and D in order of poor surface smoothness. (Evaluation criteria for surface smoothness) A: No coating streaks B: Only one coating streak was observed, and this coating streak was barely visible to the naked eye C: Only one coating streak was observed, and this coating streak was clearly visible to the naked eye D: Two or more coating streaks were observed, and these coating streaks were clearly visible to the naked eye

[0109] <Ionic Conductivity> Assuming that the porous membrane would be used as an ion-conductive membrane, the ionic resistance was measured by the method described in "<Ionic Conductivity>" in "[Test Example]" above, and the ionic conductivity was evaluated based on the "(Evaluation Criteria for Ionic Resistance)" above.

[0110] The results are shown in the table below.

[0111]

[0112] As shown in the table above, by forming the dope solution using the solvent specified in Manufacturing Method-2 of the present invention, the surface smoothness of the obtained porous membrane was clearly improved. Furthermore, these porous membranes also had excellent ionic conductivity. Furthermore, by comparing Tables 1 and 2, it was confirmed that the evaluation results of ionic conductivity were reproduced.

[0113] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0114] This application claims priority based on Japanese Patent Application Nos. 2024-51302 and 2024-51303 filed in Japan on March 27, 2024, and Japanese Patent Application No. 2024-209632 filed in Japan on December 2, 2024, the contents of which are incorporated herein by reference.

[0115] REFERENCE SIGNS LIST 10 alkaline water electrolysis system 11 separator 12 cathode electrode 13 anode electrode 14 alkaline aqueous solution 20 alkaline water electrolysis system 30 alkaline water electrolysis system 31 separator 32 cathode catalyst layer 33 anode catalyst layer 34 gas diffusion layer 35 bipolar plate

Claims

1. A method for producing a porous separator for alkaline water electrolysis, comprising forming a porous membrane by wet phase separation using a dope solution obtained by dissolving an organic polymer in a solvent containing at least one of the following compounds (1) to (7): In the compound (1), R represents an alkyl group.

2. The method for producing a porous separator for alkaline water electrolysis according to claim 1, wherein the dope solution further contains hydrophilic inorganic particles.

3. The method for producing a porous separator for alkaline water electrolysis according to claim 2, wherein a coating film is formed from the dope solution, and the porous film is formed by carrying out the wet phase separation in a state where a porous support is disposed in the coating film.

4. The method for producing a porous separator for alkaline water electrolysis according to claim 2 or 3, wherein the solvent contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (2), (3) and (4):

5. The method for producing a porous separator for alkaline water electrolysis according to claim 4, wherein the solvent contains at least one of the compounds (1)-1, (1)-2, and (1)-3.

6. A porous separator for alkaline water electrolysis comprising a porous organic polymer, the porous separator for alkaline water electrolysis comprising at least one of the following compounds (1) to (7), and the total content of the compounds (1) to (7) in the porous separator for alkaline water electrolysis is 0.0001 to 5 mass%: In the compound (1), R represents an alkyl group.

7. A method for producing a porous membrane, comprising forming a porous membrane by wet phase separation using a dope solution obtained by dissolving an organic polymer in a solvent containing at least one of the following compounds (1), (5), and (6): In the compound (1), R represents an alkyl group.

8. The method for producing a porous membrane according to claim 7, wherein the dope solution further contains hydrophilic inorganic particles.

9. The method for producing a porous membrane according to claim 8, wherein a coating film is formed from the dope solution, and the wet phase separation is carried out with a porous support disposed in the coating film to form the porous membrane.

10. The method for producing a porous membrane according to claim 8 or 9, wherein the solvent contains at least one of the following compounds (1)-1, (1)-2, (1)-3, (5) and (6):

11. The method for producing a porous membrane according to claim 10, wherein the solvent contains at least one of the compounds (1)-1, (1)-2, and (1)-3.

12. A porous membrane comprising an organic polymer having a porous structure, the porous membrane containing at least one of the following compounds (1), (5), and (6), and the total content of the compounds (1), (5), and (6) in the porous membrane is 0.0001 to 5% by mass. In the compound (1), R represents an alkyl group.

13. An alkaline water electrolysis system having a structure in which a porous separator for alkaline water electrolysis obtained by the manufacturing method according to any one of claims 1 to 3 is disposed between a cathode electrode and an anode electrode.

14. An alkaline water electrolysis system having a structure in which the porous separator for alkaline water electrolysis according to claim 6 is disposed between a cathode electrode and an anode electrode.

15. A method for producing an alkaline water electrolysis system, comprising disposing a porous separator for alkaline water electrolysis obtained by the production method according to any one of claims 1 to 3 between a cathode electrode and an anode electrode.

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