Porous film, method for producing same, alkaline water electrolysis member, alkaline water electrolysis cell, alkaline water electrolysis device, and method for producing hydrogen

Abstract

Provided are: a porous film for water electrolysis, the porous film containing an organic polymer that has a porous structure, wherein both surfaces of the porous film each have five or more pores that have a diameter of 1 µm or more in a 10 μm square area, the average pore diameter is 0.3 µm or less as measured by a bubble point method, and the thickness is 200 µm or less; a method for producing the same; an alkaline water electrolysis member; an alkaline water electrolysis cell; an alkaline water electrolysis device; and a method for producing hydrogen.

Description

Porous membrane and method for producing same, alkaline water electrolysis member, alkaline water electrolysis cell, alkaline water electrolysis device, and method for producing hydrogen

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

[0002] Hydrogen is a clean energy source that does not emit carbon dioxide and is used, for example, as a fuel for fuel cell vehicles and household fuel cells. Alkaline water electrolysis, which uses a highly concentrated alkaline aqueous solution as the electrolyte, is a well-known method for producing hydrogen. Alkaline water electrolysis, which uses a renewable energy power generation system as a power source, 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 － ) from migrating to the cathode side, a gas-barrier separator (diaphragm) is disposed between the cathode and the anode. In alkaline water electrolysis devices, water is consumed on the cathode side and generated on the anode side, which would cause an imbalance in the electrolyte solution across the separator if left as is. To suppress this, the flow rate of the electrolyte solution is adjusted for each of the cathode and anode electrodes during alkaline water electrolysis. In this case, if the separator has high liquid permeability, the effect of the flow rate adjustment is reduced, so it is also required to suppress the permeation of the electrolyte solution (hereinafter referred to as "suppression of liquid permeability"). Furthermore, in addition to gas barrier properties and suppression of liquid permeability, the separator must also have the ability to prevent OH from moving from the cathode side to the anode side. －Ion conductivity that allows the permeation of ions (hydroxy ions) is also required. Therefore, porous membranes (microporous membranes) made of organic polymer materials are used as separators for alkaline water electrolysis. That is, the separators are required to achieve two contradictory properties: the porous membrane provides liquid permeability to ensure ionic conductivity, while suppressing liquid permeability.

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

[0005] As an example of such a porous separator, Patent Document 1 describes a method for producing an ion-permeable web-reinforced separator, which includes preparing a web (corresponding to a porous support) and an appropriate paste, guiding the web in a vertical position, evenly coating both sides of the web with the paste, and subjecting the obtained paste-coated web to a symmetrical surface pore-forming step and a symmetrical solidification step; and a web-reinforced separator obtained by this method, in which the web is disposed in the middle of the membrane and both sides of the membrane have the same pore size characteristics.

[0006] On the other hand, it is also known that a separator for water electrolysis comprising a porous membrane obtained by a symmetric surface pore formation step and a coagulation step as described in Patent Document 1 has insufficient electrolyte permeability (also referred to as electrolyte impregnation) into the pores in the membrane, and air (air bubbles) remaining in the pores of the porous membrane hinders ion conduction, resulting in a decrease in electrolysis efficiency. As a technology to address this problem, research is being conducted on separators having asymmetric pore structures, a departure from conventional separators having symmetric pore structures. For example, Patent Document 2 describes a separator having an asymmetric pore structure, which includes a porous support and porous polymer layers on both sides of the porous support, in which the ratio (PDmax(2)) of the maximum pore size (PDmax(1)) of the outer surface of the porous polymer layer on one side of the separator surface to the maximum pore size (PDmax(2)) of the outer surface of the porous polymer layer on the other side (PDmax(1)) is between 1.25 and 10. The separator described in Patent Document 2 is said to be able to ensure electrolyte permeability while also achieving the low liquid permeability required of a separator.

[0007] Special table 2008-508997 publication Special table 2020-527193 publication

[0008] In recent years, separators have been thinned to improve the electrolyte impregnation of porous separators and thereby enhance electrolysis efficiency. Technological development is underway to develop separators that are approximately half the thickness of conventional separators, or even thinner, compared to the thickness of approximately 500 μm. However, as a result of research by the present inventors, it has been found that porous separators thinned to 200 μm or less warp when immersed in pure water, resulting in problems such as an inability to maintain flatness and increased electrolyte impregnation and even liquid permeability. The above-mentioned warping problem will be explained in detail. When incorporating a porous separator into a water electrolysis device (cell), a pretreatment is performed in which the porous separator is immersed in pure water to replace the air in the pores with water. If warping occurs in the porous separator during this pretreatment, multiple workers are required to unwarp the separator when incorporating it into the water electrolysis device, reducing work efficiency. Furthermore, the separator may be accidentally bent during unwarping, which poses a risk of reducing electrolysis performance. In recent years, increasing the area of ​​electrolysis cells has also been considered from the viewpoint of reducing manufacturing costs. The problem of warping becomes more pronounced when porous separators are thinned to 200 μm or less and have an increased area. In particular, porous separators are now commonly handled in the form of long sheets with widths of 1.1 m or more and lengths of 1 m or more, and addressing the problem of warping has become an urgent issue in the manufacture of porous separators.

[0009] As a result of extensive investigations into the above-mentioned problems, the present inventors have found that in a separator having an asymmetric pore structure described in Patent Document 2, which describes that it is possible to achieve both improved electrolyte permeability and suppressed liquid permeability, when the separator is thinned to 200 μm or less, significant warping occurs due to the above-mentioned pretreatment. Also, in a separator having a symmetric pore structure described in the comparative example of Patent Document 2, warping is unlikely to occur even when the separator is thinned to 200 μm or less, but liquid permeability increases.

[0010] Therefore, an object of the present invention is to provide a porous membrane having a thickness of 200 μm or less, which exhibits excellent electrolyte impregnation property, is resistant to warping even when immersed in pure water, and has low liquid permeability, and a method for producing the same. Another object of the present invention is to provide an alkaline water electrolysis element, an alkaline water electrolysis cell, an alkaline water electrolysis apparatus, and a hydrogen production method, which use the porous membrane of the present invention.

[0011] The above-mentioned problems of the present invention have been solved by the following means. [1] A porous membrane for water electrolysis, comprising a porous organic polymer, wherein both surfaces of the porous membrane have five or more pores with a diameter of 1 μm or more within a 10 μm square area, the average pore size measured by a bubble point method is 0.3 μm or less, and the thickness is 200 μm or less. [2] The porous membrane according to [1], wherein the porous membrane contains hydrophilic inorganic particles. [3] The porous membrane according to [1] or [2], wherein the porous membrane contains a porous support. [4] The porous membrane according to any one of [1] to [3], which is a separator for water electrolysis. [5] A method for producing the porous membrane according to any one of [1] to [4], comprising: performing steam-induced phase separation on a surface of a laminate comprising a membrane-forming support and a coating film containing a constituent material of the porous membrane formed on the membrane-forming support, the surface of the coating film side; and immersing the laminate that has undergone steam-induced phase separation in a condensation bath. [6] The method for producing the porous membrane according to [5], wherein the steam-induced phase separation is performed under conditions of a relative humidity of 85 to 99% and a temperature of 60 to 80°C. [7] An alkaline water electrolysis device comprising the porous membrane according to any one of [1] to [4]. [8] An alkaline water electrolysis cell comprising the porous membrane according to any one of [1] to [4] or the alkaline water electrolysis device according to [7]. [9] An alkaline water electrolysis apparatus comprising the alkaline water electrolysis cell according to [8].

[10] A method for producing hydrogen using the alkaline water electrolysis apparatus according to [9].

[0012] In the present invention, when describing physical properties and the like by showing a numerical range, if the upper and lower limits of the numerical range are described separately, any of the upper and lower limits can be appropriately combined to form a specific numerical range. On the other hand, when describing multiple numerical ranges expressed using "to", the upper and lower limits forming the numerical range are not limited to the combination of the specific upper and lower limits written before and after "to" as a specific numerical range, but can be a numerical range obtained by appropriately combining the upper and lower limits of each numerical range. Note that in the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits.

[0013] The porous membrane of the present invention has a thickness of 200 μm or less, exhibits excellent electrolyte impregnation, is resistant to warping even when immersed in pure water, and has low liquid permeability. Furthermore, the porous membrane of the present invention can be suitably produced by the porous membrane production method of the present invention. Furthermore, the alkaline water electrolysis member, alkaline water electrolysis cell, and alkaline water electrolysis apparatus of the present invention each include the porous membrane of the present invention. Furthermore, the hydrogen production method of the present invention allows hydrogen to be produced using the alkaline water electrolysis apparatus of the present invention.

[0014] Figure 1 shows the surface SEM (scanning electron microscope) images of the front and back of the porous membrane produced in Example 1. Figure 1 (a) shows the surface SEM image of the front of the porous membrane produced in Example 1, and Figure 1 (b) shows the surface SEM image of the back of the porous membrane produced in Example 1. Also, Figure 1 (c) is a surface SEM image in which a white circle with a diameter of 1 μm is drawn on the hole with a maximum Feret diameter of 1 μm or more (including the hole that does not form a closed curve in the surface SEM image shown in the figure) in the surface SEM image of Figure 1 (a). Figure 1 (d) is a surface SEM image in which a black circle with a diameter of 1 μm is drawn on the hole with a maximum Feret diameter of 1 μm or more (including the hole that does not form a closed curve in the surface SEM image shown in the figure) in the surface SEM image of Figure 1 (b). Figure 2 shows the surface SEM (scanning electron microscope) images of the front and back of the porous membrane produced in Comparative Example 1. Fig. 2(a) shows a surface SEM image of the front surface of the porous membrane produced in Comparative Example 1, and Fig. 2(b) shows a surface SEM image of the back surface of the porous membrane produced in Comparative Example 1. Fig. 3 shows a schematic cross-sectional view of an alkaline water permeation amount measuring device used in the Examples. Hatching indicating a cross-sectional view is omitted in Fig. 3. Fig. 4 is a drawing schematically illustrating one embodiment of an alkaline water electrolysis device. Fig. 5 is a drawing schematically illustrating another embodiment of an alkaline water electrolysis device. Fig. 6 is a drawing schematically illustrating yet another embodiment of an alkaline water electrolysis device.

[0015] [Porous membrane] The porous membrane of the present invention is a porous membrane for water electrolysis comprising an organic polymer with a porous structure, wherein both surfaces of the porous membrane each have five or more pores with a diameter of 1 μm or more within a 10 μm square area, the average pore size measured by the bubble point method is 0.3 μm or less, and the thickness is 200 μm or less.

[0016] (Number of pores with a diameter of 1 μm or more present within a 10 μm square area on the surface) On both surfaces of the porous membrane of the present invention, the number of pores with a diameter of 1 μm or more present within a 10 μm square area on the surface is 5 or more, and from the viewpoint of further suppressing the occurrence of warping, it is preferably 7 or more, more preferably 9 or more. The practical upper limit is usually 20 or less. That is, the preferred range is preferably 5 to 20, more preferably 7 to 20, and even more preferably 9 to 20. In the porous membrane of the present invention, the number of pores with a diameter of 1 μm or more present within a 10 μm square area on the surface is preferably about the same on one side and the other side of both surfaces of the porous membrane, from the viewpoint of further suppressing the occurrence of warping. Specifically, the absolute value of the difference between the number of pores with a diameter of 1 μm or more present within a 10 μm square area on one of the two surfaces of the porous membrane and the number of pores with a diameter of 1 μm or more present within a 10 μm square area on the other surface is preferably 0 to 15, more preferably 0 to 13, even more preferably 0 to 11, particularly preferably 0 to 7, and most preferably 0 to 5. The number of pores with a diameter of 1 μm or more present within a 10 μm square area on the surface is determined by observing surface SEM (scanning electron microscope) images at a 10 μm square viewing angle on each surface of the porous membrane from three different fields of view, counting the number of pores with a diameter of 1 μm or more present within each 10 μm square area, calculating the arithmetic mean value of the three obtained numbers of pores, and rounding off the value to the nearest tenth to obtain the "number of pores with a diameter of 1 μm or more present within a 10 μm square area on the surface." Note that pores with a diameter of 1 μm or more refer to pores with a maximum Feret diameter of 1 μm or more as determined by binary analysis of an SEM image, and only pores with a diameter of 1 μm or more that form a closed curve within a 10 μm square field of view are counted. Other detailed conditions can be applied as described in the examples below.

[0017] (Average Pore Diameter (Average Value of Through-pores)) The average pore diameter of the porous membrane of the present invention measured by the bubble point method (also simply referred to as "average pore diameter" in the present invention) is 0.3 μm or less, and from the viewpoint of further suppressing liquid permeability, it is preferably 0.2 μm or less. The practical lower limit is usually 0.01 μm or more. That is, the preferred range is 0.01 to 0.3 μm, and more preferably 0.01 to 0.2 μm. The average pore diameter corresponds to the average value of the through-pores of the porous membrane. The average pore diameter is measured using a porometer manufactured by PMI based on the bubble point method described in ASMT (American Society for Testing and Materials) F316-86. Using a measurement porous membrane completely wetted with Galwick (trade name, manufactured by Porous Materials, fluorine-based solvent, surface tension 15.6 dyn / cm) as the immersion liquid, the applied pressure and air permeation rate were measured in a pressure increase mode. From the measured pore size distribution, the most frequent pore size (the pore size with the highest proportion in the pore size distribution) was determined, and the value rounded to one decimal place in μm was defined as the "average pore size." Note that if the most frequent pore size is 0.0X μm (X is a number from 0 to 9), this value (0.0X μm) was defined as the "average pore size." For other detailed conditions, the description of the examples below can be applied.

[0018] (Thickness of porous membrane) The thickness of the porous membrane of the present invention is 200 μm or less. The lower limit of the thickness of the porous membrane of the present invention is usually 30 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. That is, a preferred range is 30 to 200 μm, more preferably 50 to 200 μm, and even more preferably 100 to 200 μm. This thickness is determined by taking a cross-section cut out of the porous membrane with a razor at a magnification (for example, 400 times) that fits the porous membrane cross-section in one field of view, obtaining a cross-sectional SEM (scanning electron microscope) image, assuming that no pores exist in the obtained cross-sectional SEM image (assuming that the pores are filled with an organic polymer), measuring the thickness at 20 points at equal intervals, calculating the arithmetic average of the obtained 20 measured values, and rounding off the value to one decimal place in μm.

[0019] The reasons why the porous membrane of the present invention, despite its thin thickness of 200 μm or less, exhibits excellent electrolyte impregnation, is resistant to warping even when immersed in pure water, and has low liquid permeability, are thought to be as follows. The porous membrane of the present invention is a porous membrane for water electrolysis containing an organic polymer with a porous structure and having a thickness of 200 μm or less, and therefore exhibits excellent electrolyte impregnation. Furthermore, both surfaces of the porous membrane of the present invention have five or more pores with a diameter of 1 μm or more within a 10 μm square (10 μm long x 10 μm wide square) (excluding pores with a diameter of 1 μm or more that are partially outside the periphery of the square) ([Specification A]), so that shrinkage stress is less likely to act on the membrane surface and warping is less likely to occur even when immersed in pure water. Furthermore, the porous membrane of the present invention has an average pore size of 0.3 μm or less as measured by the bubble point method ([Specification B]), so that its liquid permeability is low. In the combination of the thickness of the porous membrane of the present invention, [specified A] and [specified B], the thickness of the porous membrane, the number of the holes with diameter of 1 μm or more that exist in the area of ​​10 μm square on the surface and the numerical range of the average pore diameter that is measured by bubble point method can suitably adopt the above-mentioned preferred range (at least one of upper limit and lower limit), more preferred range (at least one of upper limit and lower limit), further more preferred range (at least one of upper limit and lower limit).Below, based on the comparison between the porous membrane of the present invention and the porous membrane that does not meet [specified A] or [specified B] (for example, comparative example 1 and 2), more detailed explanation will be given.

[0020] The warpage of porous membrane after being impregnated with water such as pure water occurs due to the evaporation of the water applied to the hydrophilic membrane surface, which causes shrinkage stress on the surface.This shrinkage is thought to occur easily under the condition that the surface is smooth and dense, and the water film is likely to remain.The porous membrane of the present invention satisfies the above-mentioned [Requirement A], and a certain number of pores with a diameter of 1 μm or more are distributed on both surfaces of the porous membrane, so that it is not a smooth and dense surface, shrinkage stress is not likely to occur, and warping is not likely to occur.Furthermore, the porous membrane of the present invention has a small average diameter of through-pores so as to satisfy the above-mentioned [Requirement B], so that the liquid permeability is kept low.As will be described in detail in the examples below, the configuration of the present invention that satisfies the above-mentioned [Requirement A] and [Requirement B] can be realized by carrying out steam-induced phase separation and liquid-induced phase separation under the condition that a membrane-forming support is used on one side when preparing the porous membrane.

[0021] As the porous membrane that does not satisfy [specification A], for example, as shown in comparative example 1, on both surfaces of membrane, the number of holes with diameter of 1 μm or more that exist in 10 μm square area on one side (surface in table) is less than 5, and as shown in the surface SEM image of Fig. 2 (a), it is smooth and dense surface.Therefore, this smooth and dense surface side is larger in shrinkage stress caused by water evaporation than the other surface (reverse surface in table) that the number of holes with diameter of 1 μm or more that exist in 10 μm square area is 5 or more (not smooth and dense surface shown in the surface SEM image of Fig. 2 (b)).In the porous membrane with thickness of 200 μm or less and thin film, the shrinkage stress difference between both sides of membrane causes warpage. Furthermore, as shown in Comparative Example 2, for example, a porous membrane that does not satisfy [Requirement B] satisfies [Requirement A], and as a result the pore size near both surfaces of the membrane becomes large, accelerating the penetration of water from both sides in the condensation bath, and the average pore size (average value of the through pores) measured by the bubble point method becomes large at 0.4 μm, thereby increasing the liquid permeability.

[0022] The specific configuration of the porous membrane of the present invention is not particularly limited, as long as it is a porous membrane for water electrolysis containing a porous organic polymer, has a thickness of 200 μm or less, and satisfies the above [Specification A] and [Specification B]. For example, the porous membrane of the present invention may or may not contain a porous support. When the porous membrane of the present invention contains a porous support, the porous membrane of the present invention is preferably configured to include a porous support and a porous organic polymer (hereinafter also referred to as a "porous material") disposed on at least one of the outer surface and pores of the porous support. Furthermore, regardless of whether the porous support is contained, the porous material preferably further contains hydrophilic inorganic particles in addition to the organic polymer. Note that the "outer surface of the porous support" refers to the surface of the porous support when viewed macroscopically as a membrane having a single thickness, and the "pores of the porous support" refer to the gaps between the fibers, metal, and ceramic that constitute the porous support. The structure in which a porous material containing an organic polymer (preferably further containing hydrophilic inorganic particles) is disposed on at least one of the outer surface and pores of a porous support can be appropriately adjusted within the range in which the porous membrane satisfies the above [Specification A] and [Specification B]. For example, the structure may be such that the porous material is disposed only on the outer surface of the porous support. In this case, the structure may be such that the porous material is disposed on only one side of the porous support, or on both sides. Alternatively, the structure may be such that the porous material is disposed only in the pores of the porous support. Furthermore, the structure may be such that the porous material is disposed on part of the outer surface and part of the pores of the porous support. In the present invention, such a structure is also included in the structure in which a porous material containing an organic polymer (preferably further containing hydrophilic inorganic particles) is disposed on at least one of the outer surface and pores of the porous support. In particular, a structure in which the porous material is disposed on the entire outer surface and in all the pores of the porous support is preferred. Below, the porous support, porous material, and the organic polymer and hydrophilic inorganic particles that are constituent materials of the porous material are described in detail.

[0023] (Porous Support) The porous support is not particularly limited as long as it is applicable to a porous membrane for water electrolysis, and is preferably applicable to a porous separator for alkaline water electrolysis. For example, a porous support selected from a porous cloth, a porous metal plate, and a porous ceramic plate can be used. The aperture ratio of the porous support is preferably 30 to 80%, more preferably 40 to 70%. The aperture ratio is the ratio of the area of ​​voids to a unit area when the porous support is viewed in a plane. The porous support is preferably a porous cloth, and more preferably a porous polymer cloth. The porous polymer cloth is a woven fabric or a nonwoven fabric.

[0024] The polymer constituting the porous polymer fabric is not particularly limited, and examples thereof include polypropylene, polyethylene, polysulfone, polyphenylene sulfide, polyamide, polyethersulfone, polyphenylsulfone, polyethylene terephthalate, polyetheretherketone, sulfonated polyetheretherketone, monochlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene or chlorotrifluoroethylene, polyimide, polyetherimide, m-aramid, etc. Among the above, the polymer constituting the porous polymer fabric preferably contains at least one of polypropylene, polyphenylene sulfide, and polyetheretherketone, and more preferably contains at least one of polyphenylene sulfide and polyetheretherketone.

[0025] The thickness of the porous support is preferably 30 to 150 μm, more preferably 30 to 100 μm, and even more preferably 30 to 75 μm. The thickness of the porous support is a value measured using a dot-type thickness meter. The thickness of the porous support in the porous membrane can be measured and calculated by removing the porous support from the porous membrane using a solvent that dissolves the organic polymer contained in the porous material, and then measuring and calculating the thickness of the removed porous support using the above-mentioned method.

[0026] (Porous Material) The porous material may be any material that can turn the porous membrane of the present invention into a porous membrane that satisfies the above-mentioned [Specification A] and [Specification B], and preferably has a function as a separator for water electrolysis that blocks permeation of gases (preferably hydrogen gas and oxygen gas) and allows permeation of ions (preferably hydroxy ions). The porous material contains at least an organic polymer and may further contain other components such as hydrophilic inorganic particles.

[0027] - Organic Polymer - As the organic polymer contained in the porous material, various organic polymers applicable to the wet phase separation described below can be used.

[0028] 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.

[0029] Other preferred organic polymers include polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamideimide.

[0030] The organic polymers may be used alone or in combination of two or more.

[0031] The organic polymer more preferably contains at least one of polyvinylidene fluoride, polysulfone, polyethersulfone, and polyphenylsulfone, and further preferably contains at least one of polysulfone, polyethersulfone, and polyphenylsulfone.

[0032] The weight average molecular weight (Mw) of the organic polymer is not particularly limited. Taking into consideration the handleability of the membrane-forming solution described below and the mechanical strength of the resulting porous membrane, it can be, for example, 10,000 to 500,000, and preferably 20,000 to 300,000. Mw can be determined under the following conditions. Apparatus: HLC-8220GPC (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI (Refractive Index) detector) Precolumn: TSKGUARDCOLUMN HXL-L 6 mm x 40 mm (manufactured by Tosoh Corporation) Sample side columns: The following three columns were directly connected in order (all manufactured by Tosoh Corporation): TSK-GEL GMHXL 7.8 mm x 300 mm TSK-GEL G4000HXL 7.8 mm x 300 mm TSK-GEL G2000HXL 7.8 mm x 300 mm Reference side column: TSK-GEL G1000HXL 7.8 mm x 300 mm Thermostatic bath temperature: 40°C Mobile phase: THF (tetrahydrofuran) Sample side mobile phase flow rate: 1.0 mL / min Reference side mobile layer flow rate: 1.0 mL / min Sample concentration: 0.1 mass% Sample injection amount: 100 μL Data collection time: 5 to 45 minutes after sample injection Sampling pitch: 300 milliseconds

[0033] The content of the organic polymer in the porous material is preferably 5.00 to 49.99% by mass, more preferably 5.00 to 40.00% by mass, still more preferably 7.00 to 30.00% by mass, and particularly preferably 9.00 to 25.00% by mass.

[0034] - Hydrophilic Inorganic Particles - The porous material may contain hydrophilic inorganic particles, preferably particles selected from metal oxides and metal hydroxides.

[0035] The metal oxide is preferably selected from the group consisting of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide and magnesium oxide.

[0036] The metal hydroxide is preferably selected from the group consisting of zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide and magnesium hydroxide.

[0037] As the hydrophilic inorganic particles, in addition to particles selected from metal oxides and metal hydroxides, barium sulfate particles can also be used.

[0038] The hydrophilic inorganic particles may be used alone or in combination of two or more kinds.

[0039] The particle size of the hydrophilic inorganic particles is preferably 0.05 to 2.00 μm, more preferably 0.1 to 1.50 μm, even more preferably 0.15 to 1.00 μm, and still more preferably 0.20 to 1.00 μm. This particle size is the median diameter (D50), which means the particle size at 50% cumulative when the total volume of the particles is taken as 100% in the cumulative distribution measured by a laser diffraction / scattering method.

[0040] When the porous material contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the porous material is preferably 50.00 to 94.99 mass%, more preferably 60.00 to 94.99 mass%, still more preferably 70.00 to 93.00 mass%, and particularly preferably 75.00 to 91.00 mass%.

[0041] When the porous material contains hydrophilic inorganic particles, the ratio of the content of the hydrophilic inorganic particles to the content of the organic polymer in the porous material (hydrophilic inorganic particles / organic polymer) is preferably 10 / 1 to 1 / 1, more preferably 9 / 1 to 2 / 1, even more preferably 8 / 1 to 3 / 1, still more preferably 7 / 1 to 4 / 1, and still more preferably 6.5 / 1 to 4 / 1, by mass.

[0042] When the porous membrane of the present invention is produced by the porous membrane production method of the present invention described below, a certain amount of good solvent, which will be described later in the membrane-forming solution, inevitably remains in the porous material. As a result, the total content of the good solvent in the porous material is usually 0.01 to 5.00 mass%.

[0043] (Average pore diameter in membrane surface region) The average pore diameter in the membrane surface region of the porous membrane of the present invention is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.8 μm, and even more preferably 0.1 to 0.5 μm, on both the front and back surfaces of the membrane. The average pore diameter in the membrane surface region is a value measured and calculated as follows. A porous membrane is impregnated with methanol and frozen in liquid nitrogen. A cross section is cut out from the porous membrane using a microtome (e.g., manufactured by Leica, trade name: EM UC6). Using a scanning electron microscope (e.g., manufactured by Hitachi High-Technologies Corporation, model number: S4700), a region from the surface to 10% of the thickness of the porous membrane (e.g., in a porous membrane with a thickness of 200 μm, a region 20 μm thick from the surface) is measured so that the region fits within one field of view. The arithmetic average value of the pore diameter in the region from the surface to 10% of the thickness of the porous membrane is calculated, and the value rounded to one decimal place is defined as the "average pore diameter in the membrane surface region." When the arithmetic mean value is 0.0X μm (X is a number from 0 to 9), the value (0.0X μm) is defined as the "average pore size in the membrane surface region." For other detailed conditions, the descriptions in the examples below can be applied.

[0044] From the viewpoint of the gas barrier property required for a separator for water electrolysis, the porous membrane of the present invention preferably has a bubble point of more than 1 bar, more preferably more than 2 bar. The bubble point is measured using a perm porometer based on the bubble point method described in ASMT (American Society for Testing and Materials) F316-86, and the pressure at which the first bubble appears in the obtained wetting curve is defined as the bubble point.

[0045] The porosity of the porous membrane 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 is a value calculated from an insertion curve by mercury intrusion porosimetry.

[0046] In view of the ion permeability required for a separator for water electrolysis, the porous membrane of the present invention has an ionic resistance of 0.01 to 0.30 Ω cm ２is preferably 0.01 to 0.15 Ω cm ２ The ionic resistance is a value measured by setting a circular punched-out porous membrane of the present invention in a cell and measuring it by an AC impedance method at 30° C. Details are as described in the Examples below.

[0047] The porous membrane of the present invention has a water permeability of 100 L / (bar m) from the viewpoint of suppressing electrolyte permeability and satisfying the gas barrier properties required for a separator for water electrolysis. ２ ・hr) or more 1000L / (bar・m ２ ·hr), and preferably less than 100 L / (bar·m ２ ・hr) or more 500L / (bar・m ２ The water permeation rate is a value calculated by setting a circular punched-out porous membrane of the present invention in a filter holder, supplying a 30 mass % electrolyte solution (for example, a 30 mass % aqueous potassium hydroxide solution for alkaline water electrolysis) heated to 85°C from above the porous membrane under a pressurized condition of 50 mbar to a circular separator, and measuring the amount (mL) of electrolyte solution that permeates in 8 minutes. Details are as described in the Examples below.

[0048] The porous membrane of the present invention exhibits a high level of suppression of warpage. For example, the "warpage" measured as described below can be suppressed to 4 mm or less, preferably 2 mm or less, in the porous membrane of the present invention. (Warpage) A 10 mm square sample cut from the porous membrane is immersed in pure water for 1 hour, then placed on a flat surface. The height of warpage after 3 minutes is measured with a ruler, and the maximum height of warpage is defined as the "warpage." When the "warpage" is suppressed to 4 mm or less, the workability of incorporating the porous membrane into a separator for water electrolysis can be improved. For example, when incorporating the porous membrane as a separator into an electrolysis cell with a separator width of 1.8 m, good workability can be achieved without the need for an assistant to perform the warpage correction operation.

[0049] The porous membrane of the present invention is a porous membrane for water electrolysis, and can be preferably used as a separator for water electrolysis, such as a separator in an alkaline water electrolysis apparatus (alkaline water electrolysis separator) or a separator in a sodium chloride electrolysis apparatus that produces hydrogen by electrolyzing brine in an electrolysis cell (sodium chloride electrolysis separator). From the viewpoint of use as a separator for water electrolysis, the porous membrane of the present invention preferably has a desired ion permeability (preferably hydroxy ion permeability) as a basic property for water electrolysis applications.

[0050] The porous membrane 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. The porous membrane of the present invention is preferably in the form of a long sheet and has a thickness distribution in which the thickness of the central part of the sheet is greater than the thickness of both ends in at least one of the width direction and the length direction, from the viewpoint of production efficiency. The porous membrane of the present invention may also be stored by immersing it in a storage solution such as pure water. The porous membrane of the present invention may also be stored as a dry membrane without being immersed in a storage solution.

[0051] [Method for producing porous membrane] The method for producing a porous membrane is not particularly limited, but porous membranes are usually produced by a method comprising forming a porous material by wet phase separation. In this way, in the method for forming a porous material by wet phase separation, an organic polymer is contained as a constituent material of the porous material. Through this wet phase separation process, the porous membrane of the present invention can be obtained, which is composed of a porous material containing an organic polymer. In particular, the porous membrane of the present invention that satisfies the above [Requirement A] and [Requirement B] can be obtained by performing steam-induced phase separation and liquid-induced phase separation as wet phase separation under conditions using a membrane-forming support. Specifically, the porous membrane of the present invention can be preferably produced by a method comprising: performing steam-induced phase separation on the surface of a laminate comprising a membrane-forming support and a coating film containing the constituent material of the porous membrane of the present invention formed on the membrane-forming support, and immersing the laminate that has undergone the steam-induced phase separation in a condensation bath. In wet phase separation using a membrane-forming support, the coating film on the membrane-forming support side takes time to penetrate water from the surface of the coating film on the side not having the membrane-forming support in the condensation bath, which increases the pore growth time and the pore size. The pore size near the surface of the coating film on the side not having the membrane-forming support can be adjusted by the conditions of steam-induced phase separation performed before immersion in the condensation bath. The higher the temperature and humidity of the steam in steam-induced phase separation, the larger the pore size near the surface of the coating film on the side not having the membrane-forming support can be adjusted. For example, a method can be used in which a membrane-forming solution containing the above-mentioned organic polymer is cast onto a membrane-forming support to form a coating film, and then a laminate of the membrane-forming support and the coating film is formed by wet phase separation with the membrane-forming support attached to the coating film. This process provides the porous membrane of the present invention, which is composed of a porous material containing at least an organic polymer and does not include a porous support. Furthermore, by further including a step of impregnating a porous support into the coating film, the porous membrane of the present invention can be obtained, which contains a porous support and a porous material.

[0052] (Membrane-forming solution) The membrane-forming solution may be a solution of an organic polymer that is a constituent material of the porous material, and may contain an organic polymer and a solvent, and may further contain hydrophilic inorganic particles. The organic polymer contained in the membrane-forming solution can be described in the above description of the organic polymer in the porous membrane. Furthermore, the hydrophilic inorganic particles that may be contained in the membrane-forming solution can be described in the above description of the hydrophilic inorganic particles in the porous membrane.

[0053] - Solvent - The membrane-forming solution used in wet phase separation may be any solvent (good solvent) capable of dissolving the organic polymer, and is preferably miscible with water. The solvent is preferably selected from 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, γ-valerolactone, Compounds (2) and (3) shown below, and mixtures thereof, with at least one of NMP, NBP, γ-valerolactone, and Compounds (2) and (3) shown below being more preferred.

[0054] When the membrane-forming solution contains hydrophilic inorganic particles, the content of the solvent in the membrane-forming solution is preferably 10 to 85% by mass, more preferably 15 to 80% by mass, even more preferably 25 to 70% by mass, even more preferably 30 to 65% by mass, even more preferably 32 to 60% by mass, and even more preferably 35 to 50% by mass. When the membrane-forming solution does not contain hydrophilic inorganic particles, the content of the solvent in the membrane-forming solution is preferably 20 to 95% by mass, more preferably 25 to 90% by mass, even more preferably 30 to 80% by mass, even more preferably 40 to 80% by mass, even more preferably 45 to 75% by mass, and even more preferably 50 to 75% by mass.

[0055] - Organic Polymer - When the membrane-forming solution contains hydrophilic inorganic particles, the content of the organic polymer in the membrane-forming solution is preferably 2 to 30 mass%, more preferably 4 to 20 mass%, even more preferably 5 to 15 mass%, and still more preferably 6 to 15 mass%. When the membrane-forming solution does not contain hydrophilic inorganic particles, the content of the organic polymer in the membrane-forming solution is preferably 2 to 30 mass%, more preferably 4 to 30 mass%, even more preferably 6 to 25 mass%, and still more preferably 8 to 20 mass%.

[0056] - Hydrophilic inorganic particles - Hydrophilic inorganic particles are particles that are dispersed in the membrane-forming solution without dissolving, and this state of dispersion is also referred to as the membrane-forming solution in the present invention. In other words, the "solution" of the membrane-forming solution means that an organic polymer is dissolved in a solvent. When the membrane-forming solution contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the membrane-forming solution is preferably 10 to 85% by mass, more preferably 15 to 80% by mass, even more preferably 20 to 70% by mass, and particularly preferably 25 to 60% by mass.

[0057] Other Components—The membrane-forming solution may contain components (other components) other than the components described above (solvent, organic polymer, and hydrophilic inorganic particles). For example, in order to control pore formation during wet phase separation, other components may be included, such as polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohol, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid, neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, calcium chloride, magnesium chloride, and lithium chloride. When the membrane-forming solution contains other components and hydrophilic inorganic particles, the total content of the other components in the membrane-forming solution is preferably 0.1 to 15% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 5% by mass. When the membrane-forming solution contains other components but does not contain hydrophilic inorganic particles, the total content of the other components in the membrane-forming solution is preferably 1 to 25 mass%, more preferably 5 to 25 mass%, and even more preferably 7 to 20 mass%.

[0058] <Formation of porous material by wet phase separation> (Water vapor-induced phase separation) In a preferred method for producing the porous membrane of the present invention, water vapor-induced phase separation is carried out on the surface of a laminate consisting of a membrane-forming support and a coating film containing the constituent materials of the porous membrane of the present invention formed on the membrane-forming support, on the coating film side (hereinafter simply referred to as the "coating film side of the laminate"). The laminate can be formed, for example, by casting a membrane-forming solution containing the organic polymer dissolved on the membrane-forming support and appropriately drying the surface to form a coating film. When the porous membrane of the present invention contains a porous support, the membrane-forming solution is cast on the membrane-forming support, and then a woven fabric support is placed on top of the woven fabric support and immersed in the membrane obtained by casting, thereby impregnating the woven fabric support with the membrane-forming solution, preferably completely impregnated.

[0059] In steam-induced phase separation, it is preferable to use high-temperature, high-humidity steam as the poor solvent vapor in steam-induced phase separation. The relative humidity in the region where steam-induced phase separation is performed is preferably 80 to 99%, more preferably 85 to 99%, and even more preferably 90 to 99%, from the viewpoint of controlling the pore size of the pores on the coated surface of the laminate. Furthermore, the temperature in the region where steam-induced phase separation is performed is preferably 55 to 85°C, more preferably 60 to 80°C, and even more preferably 60 to 75°C, from the viewpoint of controlling the pore size of the pores on the coated surface of the laminate. The temperature range in the region where steam-induced phase separation is performed (at least one of the upper and lower limits in the preferred range, more preferred range, and even more preferred range) can be appropriately set to at least one of the upper and lower limits of the above-mentioned temperature ranges. Specifically, steam-induced phase separation is preferably performed under conditions of a relative humidity of 85 to 99% and 60 to 80°C. In this combination, the numerical ranges of the relative humidity and temperature (at least one of the upper and lower limits) can be appropriately selected from the above-mentioned more preferred ranges (at least one of the upper and lower limits) and even more preferred ranges (at least one of the upper and lower limits). The time for steam-induced phase separation is preferably 1 to 35 seconds, more preferably 1 to 30 seconds, and even more preferably 1 to 25 seconds, from the viewpoint of controlling the average pore size measured by the bubble point method. The space in which steam-induced phase separation is performed is not particularly limited in terms of the specific adjustment method, equipment, etc., as long as it can be a space in which the predetermined temperature and humidity can be maintained. It is preferable that the space be provided so as to be continuous with the coagulation bath in which liquid-induced phase separation is performed after steam-induced phase separation.

[0060] (Liquid-induced phase separation) In a preferred method for producing the porous membrane of the present invention, the laminate that has undergone the steam-induced phase separation is immersed in a coagulation bath while still laminated with the membrane-forming support, and liquid-induced phase separation is carried out, thereby producing the porous membrane of the present invention that satisfies the above [Requirement A] and [Requirement B].For liquid-induced phase separation, the laminate that has undergone the steam-induced phase separation is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent.By this immersion, the proportion of the good solvent in the coating of the membrane-forming solution is further reduced, and the organic polymer and the solvent undergo phase separation (liquid-induced phase separation), and the organic polymer gels (coagulates), forming a porous material, and the porous membrane of the present invention can be obtained.

[0061] The poor solvent can be, for example, water, or a mixed solvent of water with a hydrophilic organic solvent (an organic solvent miscible with water) or a water-soluble polymer. Examples of hydrophilic organic solvents include aprotic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC), and alcohol solvents such as ethanol, propanol, and isopropanol. Examples of water-soluble polymers include water-soluble polymers such as polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA). Of the above, water is preferred as the poor solvent.

[0062] The temperature of the coagulation bath is preferably 20 to 90° C., more preferably 40 to 70° C. The time for carrying out the coagulation bath is preferably 1 to 15 minutes, more preferably 1 to 12 minutes, and even more preferably 3 to 10 minutes, from the viewpoint of controlling the pore size of the coating film on the membrane-forming support side.

[0063] In the liquid-induced phase separation, after the membrane is immersed in the poor solvent to form a porous material (porous membrane), the membrane may be immersed in a glycol such as ethylene glycol or diethylene glycol, or water, or washed with the glycol, water, or the like. This process can remove the solvent remaining in the membrane.

[0064] In the porous membrane obtained by the above-mentioned method for producing a porous membrane, a certain amount of good solvent in the membrane-forming solution used in the production inevitably remains. As a result, a porous membrane is provided in which the total content of good solvent in the porous material is 0.01 to 5.00 mass %. The amount of residual solvent is measured by air-dried the porous membrane at 40°C for 12 hours, and then analyzed by gas chromatography or １ The amount can be quantified as % by mass relative to 100% by mass of the porous membrane after drying by H-NMR (nuclear magnetic resonance) measurement.

[0065] The porous membrane of the present invention can be used as a separator in a method for producing hydrogen by electrolyzing an alkaline aqueous solution using an electrolytic cell or a method for producing hydrogen by electrolyzing saline water using an electrolytic cell. In particular, the porous membrane can be suitably used as a separator for alkaline water electrolysis in an alkaline water electrolysis apparatus described below.

[0066] [Alkaline water electrolysis] When the porous membrane of the present invention is used as a separator for alkaline water electrolysis, the porous membrane of the present invention (hereinafter also simply referred to as the "separator of the present invention") is disposed between the cathode and the anode in alkaline water electrolysis. Preferred embodiments of an alkaline water electrolysis apparatus to which the separator of the present invention is applied (also referred to as the "alkaline water electrolysis apparatus of the present invention") will be described, but the alkaline water electrolysis of the present invention is not limited to these embodiments.

[0067] Fig. 4 is a schematic diagram of a preferred embodiment of an alkaline water electrolysis apparatus of the present invention. The alkaline water electrolysis apparatus (10) shown in Fig. 4 has a cathode electrode (12) on one side of a separator (11) of the present invention and an anode electrode (13) on the other side, 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 comprise 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 device (10) shown in FIG. 4 , the separator (11) and the electrodes (12, 13) are separated from each other, resulting in a long migration distance of hydroxy ions, which limits the improvement of ion conduction efficiency.

[0068] FIG. 5 is a schematic diagram of another preferred embodiment of the alkaline water electrolysis apparatus of the present invention. The alkaline water electrolysis apparatus (20) shown in FIG. 5 is the alkaline water electrolysis apparatus (10) shown in FIG. 4 , except that the separator (11) and the electrodes (12, 13) are arranged in contact with each other (zero-gap type). In the alkaline water electrolysis apparatus (20) shown in FIG. 5 , the separator (11) and the electrodes (12, 13) are in contact with each other, thereby shortening the migration distance of hydroxy ions and providing an advantage in terms of ion conduction efficiency. Since the separator (11) of the present invention satisfies the above [Requirement A], in the zero-gap type alkaline water electrolysis apparatus (20) shown in FIG. 5 , small gaps are formed between the separator (11) of the present invention and the electrodes (12, 13), and hydrogen bubbles (H ) generated on the surfaces of the electrodes (12, 13) can be easily condensed. ２ ), oxygen (O ２ ) can be more easily released, which is thought to improve ion permeability. Among alkaline water electrolysis devices, pressurized alkaline water electrolysis devices that are operated under a pressure of 10 bar or more relative to atmospheric pressure (about 1 bar) are also known from the standpoint of imparting renewable energy suitability. Examples of such pressurized alkaline water electrolysis devices include the alkaline water electrolysis device shown in Fig. 5 , with the configuration, components, etc. appropriately adjusted to enable pressurized operation (e.g., operation under a pressurized condition of 10 bar or more).

[0069] FIG. 6 is a schematic diagram illustrating yet another preferred embodiment of the alkaline water electrolysis device of the present invention. The alkaline water electrolysis device (30) illustrated in FIG. 6 includes a membrane electrode assembly. That is, a cathode catalyst layer (32) is disposed on one side of a separator (31) of the present invention, and an anode catalyst layer (33) is disposed on the other side. These catalyst layers are composed of a catalyst and a binder. Furthermore, a gas diffusion layer (34) is formed on the outer surface of these catalyst layers (the surface opposite to the side on which the separator (33) is disposed) to form a membrane electrode assembly. In FIG. 6 , a bipolar plate (35) is formed on the outer side of the membrane electrode assembly. An alkaline aqueous solution is supplied to the cathode catalyst layer (32) and the anode catalyst layer (33) of this membrane electrode assembly, and the cathode catalyst layer (32) and the anode catalyst layer (33) are electrically connected and energized, whereby hydrogen bubbles are generated from the cathode catalyst layer (32) and oxygen bubbles are generated from the anode catalyst layer (33).

[0070] In the alkaline water electrolysis device, the configuration of the cathode electrode, cathode catalyst layer, anode electrode, anode catalyst layer, etc., other than the separator, is not particularly limited, and typical members used in alkaline water electrolysis devices can be applied as appropriate.

[0071] Thus, one embodiment of the present invention provides an alkaline water electrolysis apparatus incorporating the separator of the present invention as a separator for the alkaline water electrolysis apparatus. Also, one embodiment of the present invention provides a method for producing an alkaline water electrolysis apparatus, comprising incorporating the separator of the present invention as a separator for the alkaline water electrolysis apparatus.

[0072] [Alkaline Water Electrolysis Member] The alkaline water electrolysis member of the present invention includes the separator of the present invention. Specifically, the alkaline water electrolysis member of the present invention includes the separator of the present invention and at least one of a catalyst, an anode electrode, and a cathode electrode. Note that an embodiment including the separator of the present invention and an anode electrode and a cathode electrode is classified as the alkaline water electrolysis cell of the present invention, which will be described later. Examples of an alkaline water electrolysis member of the present invention that does not include an electrode and includes a catalyst include a structure in which the catalyst is located only on one side of the separator of the present invention, and a structure in which the catalyst is located on both sides of the separator of the present invention. Examples of an alkaline water electrolysis member of the present invention that does not include a cathode electrode and includes an anode electrode include a structure in which the anode electrode is located on one side of the separator of the present invention. In this structure, the catalyst may or may not be located. When a catalyst is located, the catalyst may be located only on one side of the separator of the present invention, or may be located on both sides of the separator of the present invention. An example of a configuration in which the alkaline water electrolysis device of the present invention does not include an anode electrode but includes a cathode electrode is a configuration in which the cathode electrode is located on one side of the separator of the present invention. In this configuration, a catalyst may or may not be included. When a catalyst is included, the catalyst may be located on only one side of the separator of the present invention, or may be located on both sides of the separator of the present invention.

[0073] [Alkaline Water Electrolysis Cell] The alkaline water electrolysis cell of the present invention comprises the separator of the present invention or the alkaline water electrolysis member of the present invention. The "alkaline water electrolysis cell" comprises a separator and two electrodes (an anode electrode and a cathode electrode) separated by the separator. In this configuration, an alkaline aqueous solution may be present as an electrolyte between both electrodes (including the separator of the present invention), and the anode electrode and the cathode electrode may each further comprise a catalyst. For example, when the alkaline water electrolysis cell of the present invention comprises the separator of the present invention, the alkaline water electrolysis cell of the present invention can be obtained by combining the separator of the present invention with the anode electrode and the cathode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. Alternatively, when the alkaline water electrolysis cell of the present invention does not comprise electrodes but comprises the separator of the present invention and a catalyst, the alkaline water electrolysis cell of the present invention can be obtained by combining the separator of the present invention with the anode electrode and the cathode electrode. In this case, the catalyst may be contained in the alkaline water electrolysis element of the present invention, or may be separately contained in the alkaline water electrolysis element of the present invention and combined with it, similar to the anode electrode or cathode electrode. In the alkaline water electrolysis cell of the present invention, the catalyst may be contained on at least one side of the separator of the present invention, or may be contained on both sides. When the alkaline water electrolysis cell of the present invention does not include a cathode electrode but includes the separator of the present invention and an anode electrode, the alkaline water electrolysis cell of the present invention can be produced by combining the separator with the cathode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. The catalyst may be contained in the alkaline water electrolysis element of the present invention, or may be separately contained in the alkaline water electrolysis element of the present invention and combined with it, similar to the cathode electrode. When the alkaline water electrolysis cell of the present invention does not include an anode electrode but includes the separator and cathode electrode of the present invention, the alkaline water electrolysis cell of the present invention can be produced by combining the separator with the anode electrode. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst.The catalyst may be contained in the alkaline water electrolysis device of the present invention, or may be separately contained in the alkaline water electrolysis device of the present invention in combination with it, similar to the anode electrode.

[0074] [Alkaline water electrolysis device] The alkaline water electrolysis device of the present invention includes the alkaline water electrolysis cell of the present invention. The alkaline water electrolysis device of the present invention can produce hydrogen as described for the alkaline water electrolysis device described above by supplementing necessary components, configuration, etc. depending on the configuration of the alkaline water electrolysis cell of the present invention.

[0075] [Method for Producing Hydrogen] The method for producing hydrogen according to the present invention is the same as a conventional method for producing hydrogen (water electrolysis) except that the alkaline water electrolysis apparatus according to the present invention is used.

[0076] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited thereto. The water used is deionized water. RH means relative humidity, sec means seconds, min means minutes, and hr means hours. The thickness of the porous support is a value measured by the method described above.

[0077] [Preparation of Porous Film] Example 1 8.5 g of polysulfone (trade name: Udel P-3500 LCD MB7, manufactured by Solvay, Mw: 80000) was added to 20.8 g of γ-valerolactone (manufactured by Merck) and 20.8 g of PolarClean (trade name, manufactured by Solvay, a mixture of the aforementioned compounds (2) and (3)), and the mixture was stirred at 60°C for 5 hours to achieve complete dissolution. Next, 2.4 g of PVP K90 (trade name, manufactured by Merck, polyvinylpyrrolidone) was added, and the mixture was stirred at 60°C for 1 hour. After that, 47.9 g of zirconium oxide particles (trade name: E101, manufactured by Luxfer, median diameter (D50) 0.80 μm) were added, and the mixture was stirred for 3 hours to obtain a coating solution. The obtained coating solution was cast onto a membrane support made of a PET (polyethylene terephthalate) film using an applicator with a clearance thickness set to 230 μm. A PEEK (polyether ether ketone) woven fabric support (manufactured by Safer, thickness 54 μm, aperture ratio 60%) was placed on top of it as a porous support and completely impregnated with the coating solution. The membrane-side surface of the coating solution impregnated with the woven fabric support (the surface opposite to the side where the membrane support is attached (the side in contact with the membrane support)) was exposed to a water vapor environment of 65 ° C and 98% relative humidity for 20 seconds (water vapor-induced phase separation process). Subsequently, it was gently immersed in a condensation bath of pure water at 50 ° C for 5 minutes to form a porous structure (condensation bath phase separation process). After further washing with water at 50 ° C for 10 minutes, the porous membrane was peeled off from the PET film. Subsequently, it was washed with water at 90 ° C for 1 hour to obtain the porous membrane of Example 1. The thickness of this porous membrane was 180 μm.

[0078] <Example 2> A porous membrane of Example 2 was obtained in the same manner as in Example 1, except that the time of exposure to the water vapor environment was changed from 20 seconds to 30 seconds in Example 1. <Example 3> A porous membrane of Example 3 was obtained in the same manner as in Example 1, except that the PEEK woven fabric support (manufactured by Safer) in Example 1 was not used. <Example 4> A porous membrane of Example 4 was obtained in the same manner as in Example 1, except that the coating process in Example 1 was adjusted so that the thickness of the obtained porous membrane was 100 μm.

[0079] Comparative Example 1 Based on the separator manufacturing method schematically shown in Figure 3 of JP-A 2020-527193, the porous membrane of Comparative Example 1 was produced as follows. The coating solution prepared in Example 1 above was coated on both sides of a 1.8 m wide PEEK (polyether ether ketone) woven fabric support (manufactured by Safer, thickness 54 μm, aperture ratio 60%) as a porous support using a slot die coating technique at 3 m / min, so that the finished porous membrane had a thickness of 180 μm. Next, while the coated woven fabric support was transported to a water bath (coagulation bath) maintained at 50 ° C, a steam-induced phase separation process was carried out in a region (a region 7 cm away from the water bath after coating). The steam-induced phase separation process was carried out by exposing one side of the coated woven fabric support to conditions of 25 ° C and 70% relative humidity, and the other side to conditions of 65 ° C and 98% relative humidity for 10 seconds. The coated and steam-induced phase-separated woven fabric support was then immersed in a water bath at 50° C. for 5 minutes to carry out liquid-induced phase separation, followed by an in-line washing step in water at 80° C. for 30 minutes to produce the porous membrane of Comparative Example 1.

[0080] Comparative Example 2 Based on the separator manufacturing method schematically shown in Figure 2 of JP-A 2020-527193, a porous membrane of Comparative Example 2 was produced as follows. The coating solution prepared in Example 1 above was coated on both sides of a 1.8 m wide PEEK (polyether ether ketone) woven fabric support (manufactured by Safer, thickness 54 μm, aperture ratio 60%) using a slot die coating technique at 3 m / min, so that the finished porous membrane would have a thickness of 180 μm. Next, while the coated woven fabric support was transported to a water bath (coagulation bath) maintained at 50 °C, both sides of the coated woven fabric support were exposed to water vapor for 20 seconds within a region (a 7 cm distance from coating to the water bath, 65 °C, relative humidity 98%), thereby carrying out a steam-induced phase separation process. Next, the woven fabric support that had been coated and subjected to steam-induced phase separation was immersed in a 50 °C water bath for 5 minutes, thereby carrying out liquid-induced phase separation. Further, an in-line washing step was carried out in water at 80° C. for 30 minutes to prepare a porous membrane of Comparative Example 2.

[0081] <Comparative Example 3> The porous membrane of Comparative Example 3 was obtained in the same manner as in Comparative Example 1, except that the coating step in Comparative Example 1 was adjusted so that the thickness of the resulting porous membrane was 220 μm. <Comparative Example 4> The porous membrane of Comparative Example 4 was obtained in the same manner as in Comparative Example 2, except that the coating step in Comparative Example 2 was adjusted so that the thickness of the resulting porous membrane was 220 μm, and the time of exposure to steam-induced phase separation was changed from 20 seconds to 10 seconds. <Comparative Example 5> The porous membrane of Comparative Example 5 was obtained in the same manner as in Comparative Example 1, except that the coating step in Comparative Example 1 was adjusted so that the thickness of the resulting porous membrane was 500 μm. <Comparative Example 6> The porous membrane of Comparative Example 6 was obtained in the same manner as in Comparative Example 2, except that the coating step in Comparative Example 2 was adjusted so that the thickness of the resulting porous membrane was 500 μm, and the time of exposure to steam-induced phase separation was changed from 20 seconds to 10 seconds.

[0082] The following measurements and evaluations were carried out for each porous membrane. These results are shown in Tables 1-1 and 1-2 (hereinafter collectively referred to as "Table 1"). FIG. 1 shows surface SEM images of the front and back surfaces of the porous membrane of Example 1, and FIG. 2 shows surface SEM images of the front and back surfaces of the porous membrane prepared in Comparative Example 1. These FIGS. 1 and 2 are reference images for showing the surface morphology of the porous membrane, and neither is an image with a 10 μm square field of view. FIG. 1 shows surface SEM images of the front and back surfaces of the porous membrane of Example 1 (FIGS. 1(a) and (b)), and in these surface SEM images, circles with a diameter of 1 μm are drawn at the locations of pores with a maximum Feret diameter of 1 μm or more (including pores that do not form a closed curve in the surface SEM images shown in the figures) (FIGS. 1(c) and (d)). In addition, when performing each evaluation, the obtained porous membrane was rolled up without drying, unless otherwise specified, and the porous membrane cut into the desired shape was used as is for the evaluation described below.

[0083] (Thickness of Porous Film) A cross-section cut from a porous film with a razor blade was imaged with a cross-section SEM (scanning electron microscope) at a magnification (e.g., 400x) that allowed the porous film cross-section to fit in one field of view. Assuming that no pores were present in the obtained cross-sectional SEM image (assuming that the pores were filled with an organic polymer), the thickness was measured at 20 points at equal intervals, and the arithmetic mean of the 20 measurements was calculated. The value, rounded to the nearest decimal place in μm, was used as the thickness of the porous film. The following equipment was used for cross-sectional SEM observation. The same applies to subsequent SEM observations. Conductivity treatment device: manufactured by Meiwafosis Co., Ltd., model number: HPC-1SW type osmium coater / source Os / film thickness 5 nm. CIS device: manufactured by JEOL Ltd., model number: IB-09060CIS / accelerating voltage 4 kV / processing temperature -130°C / pretreatment: the sample cut with the razor blade was attached and fixed to a Si wafer (100 μm thick) with epoxy resin. FE-SEM (field emission scanning electron microscope) observation device: Carl Zeiss, model number: Ultra5, measurement conditions: secondary / backscattered electron image, acceleration voltage 2 kV, aperture 30 μm, W.D. (working distance) 3.0 mm (cross section)

[0084] (Mean pore size in membrane surface region) Porous membrane is impregnated with methanol, and the porous membrane is frozen in liquid nitrogen. The cross section is cut out from the porous membrane using a microtome (manufactured by Leica, trade name: EM UC6). Using a scanning electron microscope (model number: S4700, manufactured by Hitachi High-Technologies Corporation), the area of ​​10% thickness of the porous membrane from the surface (for example, in the case of a porous membrane with a thickness of 200 μm, the area of ​​20 μm thickness from the surface) is set in one field of view, and the arithmetic mean value of the pore size in the area of ​​10% thickness of the porous membrane from the surface is calculated, and the value is rounded off to one decimal place and is defined as "the mean pore size in membrane surface region".

[0085] (Average pore size measured by bubble point method) The average pore size was measured using a porometer manufactured by PMI, based on the bubble point method described in ASMT (American Society for Testing and Materials) F316-86. Using a measurement porous membrane completely wetted with Galwick (trade name, manufactured by Porous Materials, fluorine-based solvent, surface tension 15.6 dyn / cm) as an immersion liquid, the applied pressure and air permeation rate were measured in a pressure increase mode, and the value of the most frequent pore size (the pore size having the highest proportion in the pore size distribution) in μm notation, rounded to one decimal place, was taken as the "average pore size."

[0086] (The number of holes with diameter of 1 μm or more that exist in the 10 μm square area of ​​membrane surface) The surface SEM image of the 10 μm square viewing angle for each surface of porous membrane is observed in three different fields, and the number of holes with diameter of 1 μm or more that exist in each 10 μm square area is counted, and the arithmetic mean value of the number of obtained three holes is calculated, and the value obtained by rounding off to the first decimal place is defined as "the number of holes with diameter of 1 μm or more that exist in the 10 μm square area of ​​surface".It should be noted that the hole with diameter of 1 μm or more means that the maximum Feret diameter that is calculated by binary analysis from SEM image is 1 μm or more, and only the hole with diameter of 1 μm or more that forms a closed curve within the viewing angle of 10 μm square is counted.

[0087] (Warpage) A 10 mm square sample was cut out from the porous membrane, and the sample was immersed in pure water for 1 hour. The sample was then placed on a flat surface, and the height of warpage that occurred after 3 minutes was measured with a ruler. The maximum height of warpage was defined as "warpage." The smaller the warpage, the more efficiently the porous membrane that had been immersed in pure water for 1 hour could be incorporated into an electrolysis cell as a separator.

[0088] (Measurement of ionic resistance and evaluation of electrolyte impregnation) A 30% by mass aqueous solution of potassium hydroxide was added as an electrolyte to a two-compartment cell having a nickel electrode at the current control terminal and a Luggin capillary filled with a 3M aqueous solution of KCl at the voltage control terminal, and the cell was maintained at 30°C. ２The ionic resistance was measured under the conditions of 0.01 to 0.01, and a blank value for the measurement was obtained. Next, the sample prepared as described below was sandwiched between separators, and a 30% by mass aqueous potassium hydroxide solution was filled in the same manner as in the measurement of the blank value. The ionic resistance was measured under the same conditions as in the measurement of the blank value. The difference between the resistance value of each obtained porous membrane and the blank value (i.e., the value calculated by [resistance value of porous membrane] - [blank value]) was used as the ionic resistance value of the porous membrane. Since the ionic resistance is affected by the electrolyte impregnation property, the electrolyte impregnation property was evaluated according to the following evaluation criteria. The porous membranes used in the measurement were punched out into a circle with a diameter of 10 mm and dried to prepare a sample before impregnation, and immersed in a 30% by mass aqueous potassium hydroxide solution (manufactured by Kanto Chemical Co., Inc.) at room temperature (25°C) for 2 hours, 8 hours, or 20 hours, and then punched out into a circle with a diameter of 10 mm to prepare a sample after impregnation (three types of impregnation samples with different immersion times). - Evaluation criteria - A: Compared to the ionic resistance value of the sample before impregnation, the ionic resistance values ​​of all samples after 2-hour immersion, 8-hour immersion, and 20-hour immersion were smaller, and the electrolyte impregnated and the ionic resistance decreased within 2 hours. B: Compared to the ionic resistance value of the sample before impregnation, the ionic resistance values ​​of the samples after 8-hour immersion and 20-hour immersion were smaller than the ionic resistance value of the sample before impregnation, and it took 8 hours for the electrolyte to impregnate and the ionic resistance to decrease. C: Compared to the ionic resistance value of the sample before impregnation, the ionic resistance value of the sample after 20 hours immersion was smaller than the ionic resistance value of the sample before impregnation, and it took 20 hours for the electrolyte to impregnate and the ionic resistance to decrease.

[0089] (Suppression of Liquid Permeability) Sample 4, prepared by cutting a porous membrane into a circle with a diameter of 47 mm, was set in an alkaline water permeation measurement device as shown in the schematic cross-sectional view of Figure 3. Specifically, a stainless steel mesh support 5 and sample 4 were placed in this order on top of a sample holder lower part 2, and a rubber O-ring packing 3 was further sandwiched between them and then a sample holder upper part 1 was placed on top of the sample holder lower part 2 and the sample holder upper part 1. Sample 4 was fixed by the sample holder lower part 2 and the sample holder upper part 1. A 30 mass% potassium hydroxide aqueous solution heated to 85°C was supplied from above the sample (the position indicated by the arrow in Figure 3), and a pressure of 50 mbar was applied. The time when droplets were visually confirmed to emerge from below the sample was set as 0 minutes, and the pressure was maintained for 8 minutes. The amount of potassium hydroxide aqueous solution that permeated the sample in 8 minutes was quantified and converted into units to calculate the alkaline water permeation amount, and the liquid permeation suppression effect was evaluated according to the following criteria. Note that, when the alkaline water permeation amount in this test was 1000 L / (bar m ２ When the permeation rate is less than 100 L / (bar·m), the gas barrier property required for the separator is also satisfied. ２ ・hr) or more, 500L / (bar・m ２ B: The alkaline water permeation rate is less than 500 L / (bar·m ２ ・hr) or more, 1000L / (bar・m ２ C: Alkaline water permeation rate is less than 1000 L / (bar·m ２ ・hr) or more.

[0090]

[0091]

[0092] Polysulfone: UDEL P-3500 LCD MB7 (trade name, manufactured by Solvay, Mw: 80000) Zirconium oxide: E101 (trade name, manufactured by Luxfer, median diameter (D50) 0.80 μm) Polyvinylpyrrolidone: PVP K90 (trade name, manufactured by Merck) γ-valerolactone: manufactured by Merck PolarClean: trade name, manufactured by Solvay, a mixture of the above-mentioned compounds (2) and (3) The unit for the content of each component constituting the coating solution is "g". PEEK: woven fabric support made of polyether ether ketone (manufactured by Safer, thickness 54 μm, opening ratio 60%) The unit is written in [ ] for each item. ＊１ In Examples 1, 2 and 4, and Comparative Examples 1 to 6, the properties and evaluation of the porous membrane obtained using a PPS (polyphenylene sulfide) woven fabric support (manufactured by NBC Mesh Tec, thickness 70 μm) instead of the PEEK woven fabric support were the same as those of the porous membrane using a PEEK woven fabric support. When Zirfon UTP 220 (trade name) manufactured by Agfa was used, the same evaluation results as the porous membrane of Comparative Example 3 (same evaluation results for suppression of warpage, electrolyte impregnation, and liquid permeability) were obtained. The terms "front surface" and "back surface" are used to identify which side of the membrane surface, and there is no particular limitation as to which side of both sides of the porous membrane of the present invention is the front surface and the back surface. In Examples 1 to 4, the surface of the membrane on the side where the membrane-forming support was arranged was designated as the back surface. The "-" in the column for temperature and humidity on the back side of steam-induced phase separation means that a membrane-forming support was placed on the back side of the porous membrane to perform steam-induced phase separation, and steam-induced phase separation was not performed on the back side.

[0093] The following can be seen from Table 1 above. As shown in Comparative Examples 3 to 6, when the porous membrane had a thickness of 500 μm (Comparative Examples 5 and 6) and when the porous membrane had a thickness of 220 μm (Comparative Examples 3 and 4), the electrolyte solution impregnation was poor. It should be noted that the porous membranes of Comparative Examples 3 to 6 were produced by the conventional manufacturing method described in JP-A-2020-527193, and it can be seen that when the porous membrane had a thickness of 220 μm or 500 μm, problems with warping and liquid permeability did not occur. In contrast, as shown in Comparative Examples 1 and 2, when the porous membrane had a thickness as thin as 180 μm, warping occurred at a level that was unacceptable from the standpoint of workability when incorporating the porous membrane into a separator for water electrolysis, or even if warping could be suppressed, liquid permeability increased and was not suppressed low. The porous membrane of Comparative Example 1 having a thickness of 180 μm had only two pores with a diameter of 1 μm or more in a 10 μm square area on one surface of the porous membrane, and did not satisfy the requirements of the present invention. The porous membrane of Comparative Example 1 had a large warp of 6 mm, which exceeded the allowable level from the viewpoint of workability when incorporating the porous membrane into an electrolysis cell as a separator for water electrolysis. Furthermore, the porous membrane of Comparative Example 2 having a thickness of 180 μm had an average pore size of 0.4 μm as measured by the bubble point method, and therefore did not satisfy the requirements of the present invention. The porous membrane of Comparative Example 2 had an alkaline water permeation rate of 1000 L / (bar m ２ In contrast, the porous membranes of Examples 1 to 3, which satisfy the requirements of the present invention, exhibited excellent electrolyte impregnation, and despite the porous membrane having a thin thickness of 180 μm, the warpage was kept small at 2 mm in all cases, which is a level that indicates good workability when the porous membrane is incorporated into a separator for water electrolysis, and the alkaline water permeation rate was 1000 L / (bar·m ２The porous membrane of Example 4, which satisfies the requirements of the present invention, exhibited excellent electrolyte impregnation, and despite the porous membrane having a thickness as thin as 100 μm, the warpage was suppressed to a small level of 4 mm, which is a level that indicates good workability when the porous membrane is incorporated into a separator for water electrolysis, and the alkaline water permeation rate was 500 L / (bar·m ２ hr), and thus the liquid permeability was suppressed to a desired level required for water electrolysis. Furthermore, a comparison between Examples 1 and 3 shows that, regardless of the presence or absence of a porous support, excellent electrolyte impregnation was exhibited, and the occurrence of warping was suppressed to the same level, and the liquid permeability was suppressed to a desired level required for water electrolysis.

[0094] 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.

[0095] This application claims priority based on Japanese Patent Application No. 2024-100851, filed on June 21, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0096] REFERENCE SIGNS LIST 1 Upper sample holder 2 Lower sample holder 3 Rubber O-ring packing 4 Sample 5 Stainless steel mesh support 10 Alkaline water electrolysis device 11 Separator 12 Cathode electrode 13 Anode electrode 14 Highly concentrated alkaline aqueous solution 20 Alkaline water electrolysis device 30 Alkaline water electrolysis device 31 Separator 32 Cathode catalyst layer 33 Anode catalyst layer 34 Gas diffusion layer 35 Bipolar plate O ２ Bubble oxygen H ２ Bubble hydrogen OH － Hydroxy ion e － electronic

Claims

1. A porous membrane for water electrolysis comprising an organic polymer with a porous structure, wherein both surfaces of the porous membrane have five or more pores with a diameter of 1 μm or more within a 10 μm square area, the average pore diameter measured by the bubble point method is 0.3 μm or less, and the thickness is 200 μm or less.

2. The porous membrane of claim 1, wherein said porous membrane contains hydrophilic inorganic particles.

3. The porous membrane of claim 1, wherein the porous membrane comprises a porous support.

4. The porous membrane according to claim 1, which is a separator for water electrolysis.

5. A method for producing a porous membrane according to any one of claims 1 to 4, comprising: subjecting a laminate comprising a support for membrane formation and a coating film containing a constituent material of the porous membrane formed on the support for membrane formation to steam-induced phase separation on the surface of the coating film side; and immersing the laminate that has undergone steam-induced phase separation in a condensation bath.

6. The method for producing a porous membrane according to claim 5, wherein the steam-induced phase separation is carried out under conditions of a relative humidity of 85 to 99% and a temperature of 60 to 80°C.

7. An alkaline water electrolysis element comprising the porous membrane according to claim 4.

8. An alkaline water electrolysis cell comprising the porous membrane according to any one of claims 1 to 4 or the alkaline water electrolysis member according to claim 7.

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

10. A method for producing hydrogen using the alkaline water electrolysis device according to claim 9.

Images