Porous separator and method for using same

Abstract

Provided is a porous separator selected from (a) to (c). (a) Porous membranes containing hydrophilic inorganic particles, an aromatic porous support, and an organic polymer including a hydrophilic organic polymer that has a sulfo group and / or a carboxy group and has an acid value of 0.3 mmol / g or higher; (b) porous membranes containing no porous support and containing hydrophilic inorganic particles and an organic polymer including a hydrophilic organic polymer that has a sulfo group and / or a carboxy group and has an acid value of 0.3 mmol / g or higher, the hydrophilic inorganic particle content of said porous membranes being 10 mass% or greater; (c) porous membranes containing no hydrophilic inorganic particles and containing an aromatic porous support and an organic polymer including a hydrophilic organic polymer that has a sulfo group and / or a carboxy group and has an acid value of 0.3 mmol / g or higher.

Description

Porous separator and method of using same

[0001] The present invention relates to a porous separator having a porous structure and a method for using the same.

[0002] Hydrogen is a clean energy source that does not emit carbon dioxide and is used, for example, as fuel for fuel cell vehicles and household fuel cells. Water electrolysis is a well-known method for producing hydrogen. Hydrogen can be produced without carbon dioxide emissions by electrolyzing water using a renewable energy power generation system as a power source. Therefore, hydrogen is increasingly attracting attention as a fundamental energy source for a sustainable society.

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

[0004] Such porous separators can be formed by a wet phase separation method. In this method, a dope solution is prepared by dissolving the organic polymer, which is the material for the porous membrane, in a solvent (good solvent) that dissolves the organic polymer. A coating film is then formed from this dope 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, the separator can be supported by a porous support. For example, a porous support can be placed in the dope solution, and the porous membrane can be formed integrally with the porous support. Furthermore, by incorporating hydrophilic inorganic particles into the separator, the gas barrier properties and mechanical strength can be improved, while an alkaline aqueous solution can be efficiently infiltrated into the separator, further increasing ionic conductivity.

[0005] For example, Patent Document 1 describes such a porous separator, which includes a porous support and first and second porous layers provided on one and the other sides of the porous support, respectively. In this separator, the porous support has a thickness of 150 μm or less, the separator has a thickness of less than 250 μm, and the porous layers may contain hydrophilic inorganic particles. The technology described in Patent Document 1 is said to provide a separator with sufficient mechanical quality and improved ionic conductivity.

[0006] Special Publication No. 2023-531792

[0007] As mentioned above, porous separators are required to have both high gas barrier properties and high ionic conductivity, but achieving these properties is still in the early stages. Recently, attempts have been made to further improve the ionic conduction efficiency between the cathode and anode electrodes by using a porous separator in a cell (zero-gap cell) in which a cathode electrode is attached to one side and an anode electrode is attached to the other side. The inventors' investigations of such zero-gap cells have revealed that the ionic conduction efficiency is not necessarily improved, and even if the ionic conduction efficiency is improved, the level of improvement may be limited. Zero-gap cells generally maintain the zero-gap state by applying pressure to the porous separator sandwiched between the electrodes. This pressure is thought to cause some kind of change in the porous structure of the porous separator, which is one of the factors hindering the ionic conduction efficiency.

[0008] An object of the present invention is to provide a porous separator that can achieve both gas barrier properties and ionic conductivity at a higher level and can achieve highly efficient ionic conductivity even when used under pressure.

[0009] The present invention provides the following porous separator.

[0010] [1] A porous separator selected from the following (a) to (c): (a) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, hydrophilic inorganic particles, and an aromatic porous support; (b) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and hydrophilic inorganic particles, but not containing a porous support, wherein the content of the hydrophilic inorganic particles in the porous separator is 10 mass % or more; (c) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and an aromatic porous support, but not containing hydrophilic inorganic particles. [2] The porous separator according to [1], wherein the porous separator (a) is a porous membrane in which a porous body containing an organic polymer at least containing the hydrophilic organic polymer and the hydrophilic inorganic particles is supported by the aromatic porous support, or a porous membrane having a laminate structure of a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer and the hydrophilic inorganic particles is supported by the aromatic porous support, and a layer of the hydrophilic organic polymer. [3] The porous separator according to [1] or [2], wherein the porous separator (b) is a porous membrane in which a porous body containing an organic polymer at least containing the hydrophilic organic polymer and the hydrophilic inorganic particles is supported by the aromatic porous support, and a layer of the hydrophilic organic polymer. [4] The porous separator (c) described in any one of [1] to [3], wherein the porous separator (c) is a porous membrane in which a porous body containing an organic polymer at least containing the hydrophilic organic polymer is supported by the aromatic porous support, or a porous membrane having a laminate structure of a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer is supported by the aromatic porous support, and a layer of the hydrophilic organic polymer.[5] The porous separator according to any one of [1] to [4], wherein in (a) and (b) above, the content of the hydrophilic inorganic particles in the porous separator is 20 mass% or more. [6] The porous separator according to any one of [1] to [5], wherein in (a) to (c) above, the hydrophilic organic polymer has a sulfo group. [7] The porous separator according to any one of [1] to [6], wherein the hydrophilic organic polymer has a benzene ring. [8] The porous separator according to any one of [1] to [7], wherein the hydrophilic organic polymer is an organic polymer selected from polysulfone, polyethersulfone, and polyetheretherketone, into which a sulfo group has been introduced. [9] The porous separator according to any one of [1] to [8], wherein the hydrophilic organic polymer is an organic polymer selected from polysulfone and polyethersulfone, into which a sulfo group has been introduced.

[10] The porous separator according to any one of [1] to [9] above, wherein the hydrophilic inorganic particles in (a) and (b) comprise at least one of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, magnesium oxide, zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, magnesium hydroxide, and barium sulfate.

[11] The porous separator according to any one of [1] to

[10] above, wherein the aromatic porous support in (a) and (c) is composed of polyphenylene sulfide or polyether ether ketone.

[12] The porous separator according to any one of [1] to

[11] above, wherein the porous separator is a porous separator for alkaline water electrolysis.

[13] A method for using the porous separator according to any one of [1] to

[11] above, comprising using the porous separator as a separator disposed between a cathode electrode and an anode electrode in alkaline water electrolysis.

[0011] The porous separator of the present invention can achieve both gas barrier properties and ionic conductivity at a higher level, and can exhibit highly efficient ionic conductivity even when used in a zero-gap cell state.

[0012] FIG. 1 is a diagram schematically illustrating an embodiment of an alkaline water electrolysis system. FIG. 2 is a diagram schematically illustrating another embodiment of an alkaline water electrolysis system. FIG. 3 is a diagram schematically illustrating yet another embodiment of an alkaline water electrolysis system. FIG. 4 is a cross-sectional view schematically illustrating an embodiment of a porous separator of the present invention. FIG. 5 is a cross-sectional view schematically illustrating another embodiment of a porous separator of the present invention. FIG. 6 is a cross-sectional view schematically illustrating yet another embodiment of a porous separator of the present invention. FIG. 7 is a cross-sectional view schematically illustrating yet another embodiment of a porous separator of the present invention.

[0013] [Porous Separator] The porous separator of the present invention is selected from the following (a) to (c): (a) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, hydrophilic inorganic particles, and an aromatic porous support; (b) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and hydrophilic inorganic particles, but not containing a porous support, wherein the content of the hydrophilic inorganic particles in the porous separator is 10 mass % or more; (c) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and an aromatic porous support, but not containing hydrophilic inorganic particles.

[0014] The porous separator of the present invention is suitable as a separator to be disposed between a cathode electrode and an anode electrode in alkaline water electrolysis. The porous separator of the present invention can also be used as a separator for anion exchange membrane water electrolysis.

[0015] In the following description, the porous separator (a) above will be referred to as porous separator (a), the porous separator (b) above will be referred to as porous separator (b), and the porous separator (c) above will be referred to as porous separator (c). Furthermore, simply referring to the "porous separator of the present invention" means porous separators (a) to (c). The porous separators (a) to (c) will be described in order.

[0016] <Porous separator (a)> The porous separator (a) is a porous membrane comprising an organic polymer containing at least a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and an acid value of 0.3 mmol / g or more, hydrophilic inorganic particles, and an aromatic porous support. The porous separator (a) is preferably a porous membrane in which a porous body containing an organic polymer containing at least the hydrophilic organic polymer and hydrophilic inorganic particles (meaning a porous structure (porous material) consisting of a mixture containing an organic polymer containing at least the hydrophilic organic polymer and hydrophilic inorganic particles) is supported by an aromatic porous support. Figure 4 is an explanatory diagram schematically showing the cross section of an example of this porous membrane. In Figure 4, 1a is a porous body containing an organic polymer containing at least the hydrophilic organic polymer and hydrophilic inorganic particles, and 2 is an aromatic porous support. Furthermore, the porous separator (a) is preferably a porous membrane having a laminated structure including a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer and hydrophilic inorganic particles is supported by an aromatic porous support, and a layer of the hydrophilic organic polymer (meaning a layer formed using an organic polymer containing at least the hydrophilic organic polymer). In this case, the porous layer constituting the laminated structure may contain the hydrophilic organic polymer. Figure 5 is an explanatory diagram showing a cross section of an example of this porous membrane. In Figure 5, 1b is a porous body containing an organic polymer other than the hydrophilic organic polymer and hydrophilic inorganic particles, 2 is an aromatic porous support, and 3 is the layer of the hydrophilic organic polymer. Note that the drawings referred to in this specification are schematic diagrams for facilitating understanding of the present invention, and the sizes or relative magnitude relationships of the respective components do not directly represent actual relationships. Furthermore, matters other than those specified in the present invention are not limited to the external shapes and configurations shown in these drawings.

[0017] (Hydrophilic Organic Polymer) The hydrophilic organic polymer is an organic polymer whose hydrophilicity is enhanced by having at least one group selected from sulfo and carboxy groups, and its acid value is 0.3 mmol / g or more. The hydrophilic organic polymer itself can form a porous structure in a state where it is mixed with at least hydrophilic inorganic particles to form the porous body of the porous separator (a). Furthermore, the porous separator (a) may be formed as a layer of hydrophilic organic polymer separate from the porous layer containing the organic polymer and hydrophilic inorganic particles. The porous separator (a) can contain one or more hydrophilic organic polymers.

[0018] The sulfo groups of the hydrophilic organic polymer may be at least partially (partially or entirely) in the form of a salt. Therefore, the hydrophilic organic polymer having sulfo groups means that the hydrophilic organic polymer has a sulfo group represented by -SO ３ It means that the hydrophilic organic polymer has X. X is a hydrogen atom or a monovalent cation. The monovalent cation is preferably an alkali metal cation, and is preferably a cation selected from lithium ion, sodium ion, potassium ion and cesium ion, and more preferably a cation selected from sodium ion and potassium ion. Similarly, at least a portion (partially or entirely) of the carboxy groups contained in the hydrophilic organic polymer may be in a salt state. Therefore, the hydrophilic organic polymer having a carboxy group means that it has -COOX. X in -COOX is -SO ３ The meaning and preferred embodiments of X are the same as those of X.

[0019] The acid value of the hydrophilic organic polymer is not measured when the sulfo group and carboxy group are in a salt state, but when all of the sulfo group and carboxy group have hydrogen atoms (a structure in which all of the X's are hydrogen atoms). For example, the acid value of the hydrophilic organic polymer can be measured in a state in which the pH of the solution of the hydrophilic organic polymer is acidified to pH 5 or less with a 0.1 M aqueous HCl solution. The acid value of the hydrophilic organic polymer can be measured in accordance with JIS K0070:1992. An acid value of 1 mmol / g is equivalent to 56.1 mg KOH / g. In addition, １The structure can also be identified by H NMR, and the amount of sulfo group and carboxy group introduced can be calculated to determine the acid value. The acid value of the hydrophilic organic polymer is preferably 0.3 to 10 mmol / g, more preferably 0.3 to 9 mmol / g, even more preferably 0.3 to 8 mmol / g, and still more preferably 0.4 to 6 mmol / g.

[0020] The hydrophilic organic polymer preferably has a sulfo group. It is also preferable that the hydrophilic organic polymer has a sulfo group but does not have a carboxy group. The hydrophilic organic polymer preferably has a benzene ring in the polymer structure. The benzene ring may constitute a part of a condensed ring. For example, when the hydrophilic organic polymer has a naphthalene ring, a fluorene ring, or the like, the hydrophilic organic polymer has a benzene ring in the polymer structure.

[0021] The hydrophilic organic polymer is not particularly limited in type to the organic polymer before hydrophilization (the organic polymer before at least one of a sulfo group and a carboxy group is introduced). For example, it can be selected from polysulfone, polyethersulfone, polyetheretherketone, fluororesin, olefin resin, polyester resin, aromatic hydrocarbon resin, etc. Among these, an organic polymer selected from polysulfone, polyethersulfone, and polyetheretherketone is preferred, and an organic polymer selected from polysulfone and polyethersulfone is more preferred. That is, the hydrophilic organic polymer is preferably an organic polymer selected from polysulfone, polyethersulfone, and polyetheretherketone into which at least one of a sulfo group and a carboxy group has been introduced, and more preferably an organic polymer selected from polysulfone and polyethersulfone into which at least one of a sulfo group and a carboxy group has been introduced. The sulfo group and the carboxy group in the hydrophilic organic polymer are preferably introduced into the polymer structure via an alkylene group. The alkylene group preferably has 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, even more preferably 1 to 12 carbon atoms, still more preferably 1 to 10 carbon atoms, and particularly preferably 1 to 8 carbon atoms.

[0022] When the hydrophilic organic polymer itself is mixed with at least hydrophilic inorganic particles to form a porous structure and is incorporated into the porous separator (a), the hydrophilic organic polymer is preferably a non-crosslinked polymer (linear or chain polymer). The porous structure formed when the hydrophilic organic polymer is mixed with at least hydrophilic inorganic particles may contain an organic polymer other than the hydrophilic organic polymer. When the hydrophilic organic polymer is a non-crosslinked polymer, the weight average molecular weight (Mw) is preferably 10,000 to 500,000, more preferably 20,000 to 300,000. In the present invention, Mw can be determined according to the following conditions. NMP: Wako Pure Chemical Industries 138-12103 NMP for GPC (containing 10 mM LiBr, manufactured by Kojundo Chemical Laboratory) Column: TOSOH TSKgel Super AWM-H (6.0 mm ID x 15 cm) x 3 Detector: RI detector UV detector (STD: 270 nm, Sample: 280 nm) Flow rate: Sample pump side (0.5 ml / min.), Reference pump side (0.25 ml / min.) Measurement time: 37 min. Temperature control: 40°C

[0023] When the hydrophilic organic polymer is incorporated into the porous separator (a) in a state where it is laminated with another porous layer, the porous separator (a) is preferably a porous membrane having a laminate structure of a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer and at least hydrophilic inorganic particles is supported by an aromatic porous support, and a layer of the hydrophilic organic polymer. When the porous separator (a) has such a laminate structure, the hydrophilic organic polymer layer can be provided on one or both sides of the porous layer, preferably on one side of the porous layer, and more preferably on one side of the porous layer. The thickness of the hydrophilic organic polymer layer (the total thickness of all layers in the case of multiple layers) is preferably 0.1 to 500 μm, more preferably 0.5 to 300 μm, and even more preferably 1 to 100 μm. It is preferable that the hydrophilic organic polymer layer is not porous (non-porous). Furthermore, the hydrophilic organic polymer constituting the hydrophilic organic polymer layer is preferably a crosslinked hydrophilic organic polymer having a crosslinked structure. The crosslinked hydrophilic organic polymer can be obtained, for example, by polymerizing a monomer A having at least one vinyl group and at least one sulfo group as crosslinkable groups and a monomer B having at least two or more vinyl groups. Monomer A and monomer B may be the same. In addition to the hydrophilic organic polymer, the hydrophilic organic polymer layer may contain an organic polymer other than the hydrophilic organic polymer, as necessary. In the hydrophilic organic polymer layer, the amount of the organic polymer other than the hydrophilic organic polymer is preferably 1,000 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and may also be 5 parts by mass or less, or may be 1 part by mass or less, per 100 parts by mass of the hydrophilic organic polymer.When the hydrophilic organic polymer layer contains an organic polymer other than the hydrophilic organic polymer, the range of the ratio of the hydrophilic organic polymer to the organic polymer other than the hydrophilic organic polymer in the hydrophilic organic polymer layer can be, for example, a mass ratio of [the hydrophilic organic polymer] / [the organic polymer other than the hydrophilic organic polymer] of 1000 / 1 to 1 / 1000, 100 / 1 to 1 / 100, or 10 / 1 to 1 / 10. Alternatively, the range can be 1000 / 1 to 1 / 10, 100 / 1 to 1 / 1, or 10 / 1 to 1 / 1.

[0024] (Organic Polymer Other Than Hydrophilic Organic Polymer) As described above, the porous separator (a) can contain an organic polymer other than the hydrophilic organic polymer in combination with the hydrophilic organic polymer, if necessary. For example, the porous structure of the porous separator (a) can be formed from a mixture containing the hydrophilic organic polymer, an organic polymer other than the hydrophilic organic polymer, and hydrophilic inorganic particles. In this form of porous separator (a), the amount of the organic polymer other than the hydrophilic organic polymer in the porous membrane is preferably 1,000 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and even preferably 5 parts by mass or less, and may be 1 part by mass or less, per 100 parts by mass of the hydrophilic organic polymer. When the porous separator (a) is constructed by forming a porous structure using a mixture containing the hydrophilic organic polymer, an organic polymer other than the hydrophilic organic polymer, and hydrophilic inorganic particles, the ratio of the hydrophilic organic polymer to the organic polymer other than the hydrophilic organic polymer in the porous body is not particularly limited and can be appropriately adjusted within a range that does not impair the intended effect. For example, the mass ratio of [the hydrophilic organic polymer] / [the organic polymer other than the hydrophilic organic polymer] can be 1000 / 1 to 1 / 1000, 100 / 1 to 1 / 100, or 10 / 1 to 1 / 10. It can also be 1000 / 1 to 1 / 10, 100 / 1 to 1 / 1, or 10 / 1 to 1 / 1.

[0025] As described above, the porous separator (a) is preferably a porous membrane having a laminate structure of a porous layer in which a porous body comprising an organic polymer other than the hydrophilic organic polymer and at least hydrophilic inorganic particles is supported by an aromatic porous support, and a layer of the hydrophilic organic polymer. This porous layer may contain the hydrophilic organic polymer. In this form of porous separator (a), the amount of the hydrophilic organic polymer in the porous layer is preferably 1,000 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the organic polymer other than the hydrophilic organic polymer. When the porous layer contains the hydrophilic organic polymer in addition to the organic polymer other than the hydrophilic organic polymer, the ratio of the organic polymer other than the hydrophilic organic polymer to the hydrophilic organic polymer in the porous layer is not particularly limited and may be appropriately adjusted within a range that does not impair the intended effect. For example, the mass ratio of [organic polymer other than the hydrophilic organic polymer] / [the hydrophilic organic polymer] can be 1000 / 1 to 1 / 1000, 100 / 1 to 1 / 100, or 10 / 1 to 1 / 10. Also, it can be 1000 / 1 to 1 / 10, 100 / 1 to 1 / 1, or 10 / 1 to 1 / 1.

[0026] The organic polymer other than the hydrophilic 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.

[0027] Other preferred organic polymers besides the above hydrophilic organic polymers include polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamideimide.

[0028] The organic polymers other than the hydrophilic organic polymers may be used singly or in combination of two or more.

[0029] The organic polymer other than the hydrophilic organic polymer that can constitute the dope solution is more preferably a polymer selected from polysulfone, polyethersulfone, and polyphenylsulfone, with polysulfone being particularly preferred.

[0030] The molecular weight (Mw) of the organic polymer other than the hydrophilic organic polymer is not particularly limited. Taking into consideration the handleability of the dope solution 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. The Mw can be determined under the same conditions as for the hydrophilic organic polymer.

[0031] (Hydrophilic Inorganic Particles) The porous separator (a) contains one or more types of hydrophilic inorganic particles, which are preferably particles selected from metal oxides and metal hydroxides.

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

[0033] The metal hydroxide is preferably selected from the group consisting of zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide and magnesium hydroxide.

[0034] As the hydrophilic inorganic particles, in addition to metal oxides and metal hydroxides, for example, barium sulfate can also be used.

[0035] The hydrophilic inorganic particles constituting the porous separator (a) preferably contain at least one of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, magnesium oxide, zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, magnesium hydroxide, and barium sulfate.

[0036] The particle size of the hydrophilic inorganic particles is preferably 0.05 to 2.00 μm, more preferably 0.1 to 1.50 μm, even more preferably 0.15 to 1.00 μm, and still more preferably 0.20 to 0.80 μm. This particle size is the median diameter (D50), which means the particle size at 50% cumulative when the total volume of particles is taken as 100% in the cumulative distribution measured by a laser diffraction / scattering method.

[0037] The content of the hydrophilic inorganic particles in the porous separator (a) (based on the total mass of the porous separator (a)) is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 70% by mass or more. This proportion is usually 95% by mass or less, preferably 92% by mass or less, more preferably 90% by mass or less, even more preferably 88% by mass or less, and even more preferably 85% by mass or less. The content of the hydrophilic inorganic particles in the porous separator (a) is preferably in the range of 20 to 95% by mass, more preferably 30 to 92% by mass, even more preferably 40 to 90% by mass, even more preferably 50 to 88% by mass, even more preferably 60 to 85% by mass, and even more preferably 70 to 85% by mass. The content of the hydrophilic inorganic particles in the porous separator (a) is determined by drying the porous separator (a) in advance with air at 40°C for 12 hours, and then measuring the proportion (mass %) of the content of the hydrophilic inorganic particles in the total mass of the porous separator (a) after drying.

[0038] (Aromatic Porous Support) In the present invention, the term "aromatic porous support" refers to a porous support composed of an organic polymer, and the organic polymer has an aromatic ring in its molecular structure. The porous separator has a structure in which a porous material (porous body) formed from a mixture of an organic polymer and hydrophilic inorganic particles is supported by a porous support, thereby improving mechanical strength, etc. The porous separator (a) uses an aromatic porous support as the porous support. The use of an aromatic porous support can further improve heat resistance and chemical resistance. In a preferred embodiment, the porous separator (a) is composed of an aromatic porous support and a porous material containing an organic polymer containing at least a hydrophilic organic polymer and hydrophilic inorganic particles, which is disposed on at least one of the outer surface and pores of the aromatic porous support. In this case, the organic polymer contained in the porous material is preferably a hydrophilic organic polymer. The "outer surface of the aromatic porous support" refers to the surface of the film when the aromatic porous support is viewed as a single-layer membrane. Furthermore, the "pores of the aromatic porous support" refer to the gaps between the fibers of the organic polymer having an aromatic ring that constitute the aromatic porous support. The structure in which a porous material containing an organic polymer containing at least a hydrophilic organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of an aromatic porous support can be appropriately adjusted within the range that exhibits the desired performance. For example, the structure in which the porous material is disposed only on the outer surface of the aromatic porous support may be used. In this case, the structure in which the porous material is disposed on only one side of the aromatic porous support may be used, or the structure in which the porous material is disposed on both sides may be used. Also, the structure in which the porous material is disposed only in the pores of the aromatic porous support may be used. Furthermore, the structure in which the porous material is disposed on part of the outer surface and part of the pores of the aromatic porous support may be used. In the present invention, such a form is also included in the structure in which a porous material containing an organic polymer containing at least a hydrophilic organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of an aromatic porous support.The porous separator (a) preferably has a structure in which the porous material is disposed on the entire outer surface and in the entire pores of the aromatic porous support. The porous separator (a) preferably does not include any porous support other than the aromatic porous support.

[0039] The opening ratio of the aromatic porous support is preferably 30 to 80%, more preferably 40 to 70%. The opening ratio is the ratio of the area of ​​voids to a unit area when the aromatic porous support is viewed in a plane. The aromatic porous support is preferably a woven fabric or a nonwoven fabric.

[0040] The organic polymer constituting the aromatic porous support is not particularly limited as long as it has an aromatic ring. Suitable examples of the aromatic porous support include polysulfone, polyphenylene sulfide, polyether sulfone, polyphenyl sulfone, polyethylene terephthalate, polyether ether ketone, sulfonated polyether ether ketone, polyimide, polyether imide, and m-aramid. Among these, polyphenylene sulfide and polyether ether ketone are preferred.

[0041] The thickness of the aromatic porous support is preferably 30 to 150 μm, more preferably 30 to 100 μm, and even more preferably 30 to 75 μm. The thickness of the porous support can be measured using a dot-type thickness meter.

[0042] The preferred ranges of the thickness, pore size, and porosity of the porous separator are common to the porous separators (a) to (c), and will be described below.

[0043] <Porous Separator (b)> The porous separator (b) is a porous membrane that contains hydrophilic inorganic particles and an organic polymer containing at least one of a sulfo group and a carboxy group and an acid value of 0.3 mmol / g or more, but does not contain a porous support. That is, the porous separator (b) does not contain the aromatic porous support, and does not contain any porous support other than the aromatic porous support. The content of the hydrophilic inorganic particles in the porous separator (b) is 10% by mass or more. The content of the hydrophilic inorganic particles in the porous separator (b) is determined by previously drying the porous separator (b) with air at 40°C for 12 hours, and then measuring the proportion (mass%) of the hydrophilic inorganic particles in the total mass of the porous separator (b) after drying. The porous separator (b) is preferably a porous membrane made of a porous body containing an organic polymer at least containing the hydrophilic organic polymer and hydrophilic inorganic particles (meaning a porous structure consisting of a mixture containing an organic polymer at least containing the hydrophilic organic polymer and hydrophilic inorganic particles). FIG. 6 is an explanatory diagram showing a cross section of an example of this porous membrane. In FIG. 6, 1a is a porous body containing an organic polymer at least containing the hydrophilic organic polymer and hydrophilic inorganic particles. It is also preferable that the porous separator (b) is a porous membrane made of a laminated structure including a porous layer that is a porous body containing an organic polymer other than the hydrophilic organic polymer and hydrophilic inorganic particles, and a layer of the hydrophilic organic polymer (meaning a layer formed using an organic polymer at least containing the hydrophilic organic polymer). In this case, the porous layer constituting the laminated structure may contain the hydrophilic organic polymer. FIG. 7 is an explanatory diagram showing a cross section of an example of this porous membrane. In FIG. 7, 1b denotes a porous body containing an organic polymer other than the hydrophilic organic polymer and hydrophilic inorganic particles, and 3 denotes a layer of the hydrophilic organic polymer.

[0044] The hydrophilic organic polymer, the organic polymer other than the hydrophilic organic polymer, and the hydrophilic inorganic particles constituting the porous separator (b) are respectively synonymous with the hydrophilic organic polymer, the organic polymer other than the hydrophilic organic polymer, and the hydrophilic inorganic particles described in the porous separator (a), and the preferred forms are also the same. Except for not including an aromatic porous support, the matters described in the porous separator (a) (all matters such as the configuration of the porous body, the configuration of the hydrophilic organic polymer layer, the mode of the laminated structure, the amount of components, and the ratio of component amounts) can be applied as they are to the porous separator (b).

[0045] <Porous Separator (c)> The porous separator (c) is a porous membrane comprising an aromatic porous support and an organic polymer containing at least one of a sulfo group and a carboxy group and a hydrophilic organic polymer having an acid value of 0.3 mmol / g or more, and no hydrophilic inorganic particles. The porous membrane of the porous separator (c) preferably does not contain inorganic particles, and more preferably does not contain particulate components. The porous separator (c) is preferably a porous membrane in which a porous body containing an organic polymer at least including the hydrophilic organic polymer is supported by an aromatic porous support. An example of the structure of this porous membrane is the porous body shown in FIG. 4 as 1a, but without the hydrophilic inorganic particles. The porous separator (c) is also preferably a porous membrane having a laminate structure comprising a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer is supported by an aromatic porous support, and a layer of the hydrophilic organic polymer (meaning a layer formed using an organic polymer containing at least the hydrophilic organic polymer). In this case, the porous layer constituting the laminate structure may contain the hydrophilic organic polymer. An example of the structure of this porous membrane is the porous body shown as 1b in FIG. 5, from which the hydrophilic inorganic particles have been removed.

[0046] The hydrophilic organic polymer, the organic polymer other than the hydrophilic organic polymer, and the aromatic porous support constituting the porous separator (c) are respectively synonymous with the hydrophilic organic polymer, the organic polymer other than the hydrophilic organic polymer, and the hydrophilic inorganic particles described in the porous separator (a), and the preferred forms are also the same. The porous separator (c) can be applied to the porous separator (a) as described above (all matters such as the structure of the porous body, the structure of the hydrophilic organic polymer layer, the form of the laminated structure, the amount of components, and the ratio of the amount of components). It is preferable that the porous separator (c) does not contain a porous support other than the aromatic porous support.

[0047] The thickness of the porous separator of the present invention (porous separators (a) to (c)) is preferably 60 to 1000 μm, more preferably 60 to 800 μm, even more preferably 60 to 600 μm, and even more preferably 60 to 400 μm. This thickness is also preferably 60 to 300 μm, also preferably 70 to 260 μm, and also preferably 80 to 220 μm. This thickness is measured by obtaining a cross-sectional SEM (scanning electron microscope) image of a cross-section cut out of the porous separator with a razor at a magnification (e.g., 400x) that fits the separator cross-section in one field of view. More specifically, assuming that no pores exist in the obtained cross-sectional SEM image (assuming that the pores are filled with an organic polymer), the thickness is measured at 20-point intervals, and the arithmetic mean value of the 20 measured values ​​is used.

[0048] In the porous separator of the present invention, the pore size of the pores of the porous material containing an organic polymer and, optionally, hydrophilic inorganic particles (pore size formed by wet phase separation) is preferably 50 to 1,000 nm, more preferably 100 to 800 nm, and even more preferably 150 to 600 nm. This pore size is the average pore size and can be determined by the following method. A porous separator punched to a diameter of 1 cm is immersed in pure water for 24 hours at room temperature (25°C). Next, the mean flow pores are calculated using perm-porometry by Porometer, and this mean flow pore is taken as the average pore size.

[0049] The porosity of the porous separator of the present invention is preferably 30 to 70%, more preferably 40 to 60%, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier properties. This porosity can be calculated by the following method. First, the separator is placed over a predetermined area (S, unit: cm ２ ) and immerse in pure water at room temperature (25°C) for 24 hours. After that, wipe off any excess water droplets on the surface and measure the weight (w1, unit: g) and thickness (d, unit: cm). Dry in an oven at 90°C for 24 hours and measure the weight (w2, unit: g) again. Calculate the porosity using the following formula: Porosity (%) = {1 - [(w1 - w2) / (S x d)]} x 100

[0050] In the porous separators (a) and (b) of the present invention, when the porous separator does not have the above-mentioned hydrophilic organic polymer layer (when the porous separator does not have a laminate structure of a porous layer and a hydrophilic organic polymer layer), the ratio of the content of the hydrophilic inorganic particles to the content of the hydrophilic organic polymer in the porous separator (porous membrane) (hydrophilic inorganic particles / hydrophilic 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, in mass ratio.

[0051] The porous separator of the present invention has a base polymer forming a porous structure that includes a hydrophilic organic polymer containing at least one of sulfo and carboxy groups in an amount such that the polymer has an acid value of 0.3 mmol / g or more, or a layer of a hydrophilic organic polymer containing at least one of sulfo and carboxy groups in an amount such that the polymer has an acid value of 0.3 mmol / g or more superposed on a porous layer. This enhances gas repellency and gas barrier properties. Furthermore, the enhanced affinity for water facilitates penetration of the electrolyte into the pores of the porous structure, effectively enhancing ionic conductivity. Furthermore, the hydrophilic organic polymer interacts with hydrophilic inorganic particles and contributes to improved adhesion to the aromatic porous support, thereby increasing mechanical strength and enabling the porous separator of the present invention to have even higher ionic conductivity, even when used in a zero-gap cell configuration. The above description is merely speculative and does not fully explain the effects of the present invention. However, the effects of the present invention are supported by experimental evidence, as described below.

[0052] [Method for Producing Porous Separator] The method for producing the porous separator of the present invention is not particularly limited. For example, the porous separator of the present invention can be produced through a process of forming a porous body or porous membrane by wet phase separation. When the porous separator does not have a layer of the hydrophilic organic polymer described above, for example, a coating film formed with a dope solution containing at least the hydrophilic organic polymer and, if necessary, the hydrophilic inorganic particles is dissolved, and the aromatic porous support is optionally disposed in the coating film, and a porous structure is formed by wet phase separation to obtain the desired porous separator. Furthermore, when the porous separator has a layer of the hydrophilic organic polymer described above, for example, a curable composition composed of a monomer having a crosslinkable group and a hydrophilic group, which is the raw material for the hydrophilic organic polymer, is applied to the porous layer, and the coating layer is then cured by photopolymerization or thermal polymerization using radicals, a strong acid, or the like to form a layer of the hydrophilic organic polymer, thereby obtaining the desired porous separator.

[0053] <Dope Solution> The dope solution may be a solution of an organic polymer containing at least the hydrophilic organic polymer, and may contain an organic polymer containing at least the hydrophilic organic polymer and a solvent, and may further contain hydrophilic inorganic particles, etc., as necessary. Note that the hydrophilic inorganic particles are particles that are dispersed in the dope solution without dissolving, and such a dispersion state is also referred to as the dope solution in the present invention. In other words, the "solution" in the dope solution means that the hydrophilic organic polymer is dissolved in the solvent.

[0054] (Solvent) The dope solution in the wet phase separation may be any solvent (good solvent) capable of dissolving at least the organic polymer containing the hydrophilic 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, N,N-dimethylpropionamide, γ-valerolactone, Rhodiasolv PolarClean, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, 3-methyl-2-oxazolidone, Cyrene, and mixtures thereof, and more preferably at least one of NMP, NBP, N,N-dimethylpropionamide, and 3-methoxy-N,N-dimethylpropanamide.

[0055] The content of the solvent in the dope solution is appropriately set in consideration of the presence or absence of hydrophilic inorganic particles, etc. The content of the solvent in the dope solution can be, for example, 20 to 95% by mass, may be 25 to 90% by mass, and is also preferably 30 to 80% by mass.

[0056] The content of the organic polymer containing at least the hydrophilic organic polymer in the dope solution is also appropriately set in consideration of the presence or absence of hydrophilic inorganic particles, etc. The content of the organic polymer containing at least the hydrophilic organic polymer in the dope solution can be, for example, 2 to 50% by mass, or may be 4 to 40% by mass, or preferably 5 to 30% by mass, or preferably 6 to 25% by mass.

[0057] When the dope solution contains the hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the solid content (components excluding the solvent) of the dope solution is preferably 20 to 95 mass%, more preferably 25 to 92 mass%, still more preferably 30 to 90 mass%, and particularly preferably 35 to 88 mass%.

[0058] The dope solution may contain components (other components) other than the components described above (solvent, organic polymer containing at least a hydrophilic organic polymer, and hydrophilic inorganic particles). For example, to control pore formation during wet phase separation, the dope solution may contain polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohol, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, calcium chloride, magnesium chloride, lithium chloride, etc. The content of the other components in the dope solution is appropriately determined taking into account the presence or absence of hydrophilic inorganic particles, etc. The total content of the other components in the dope solution may be, for example, 0.1 to 25% by mass, 0.1 to 20% by mass, 0.1 to 15% by mass, 0.2 to 10% by mass, or preferably 0.5 to 5% by mass.

[0059] <Formation of Porous Membrane by Wet Phase Separation> The porous separator of the present invention can be obtained by a process of forming a porous body or porous membrane by wet phase separation using the dope solution. In wet phase separation, a membrane (coating) is formed using the dope solution, and then the membrane is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent. The temperature during this immersion is preferably 0 to 90°C, more preferably 5 to 70°C. When the proportion of the good solvent in the membrane decreases during this immersion, the organic polymer and the solvent undergo phase separation (liquid-induced phase separation), causing the organic polymer to gel (coagulate), resulting in the formation of a porous body or porous membrane. Examples of the poor solvent that can be used include water or a mixed solvent of water and a hydrophilic organic solvent (a water-miscible organic solvent), with water being preferred. Before immersing the membrane in the poor solvent, the membrane may be exposed to the vapor of the poor solvent to induce vapor-induced phase separation (vapor-induced phase separation). The steam-induced phase separation can prevent the formation of a dense skin layer on the surface, so the wet phase separation can be performed in combination with the steam-induced phase separation and the liquid-induced phase separation.

[0060] The porous separator 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 separator of the present invention may also be preserved or stored by immersing it in a preservative solution such as pure water.

[0061] [Alkaline water electrolysis] The porous separator of the present invention (also referred to as "separator of the present invention") is suitable as a separator for alkaline water electrolysis. That is, it is preferably disposed between the cathode and anode in alkaline water electrolysis. Preferred embodiments of an alkaline water electrolysis system (also referred to as "alkaline water electrolysis system of the present invention") suitable for use of the porous separator of the present invention will be described below; however, the form of alkaline water electrolysis is not limited thereto.

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

[0063] Figure 2 schematically illustrates another preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (20) illustrated in Figure 2 is the same as the alkaline water electrolysis system (10) illustrated in Figure 1 , except that the porous separator (11) and the electrodes (12, 13) are arranged in contact with each other (zero-gap type). The alkaline water electrolysis system (20) illustrated in Figure 2 is advantageous in terms of ion conduction efficiency because the porous separator (11) and the electrodes (12, 13) are pressurized and tightly attached to each other.

[0064] FIG. 3 schematically illustrates another preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (30) illustrated in FIG. 3 includes a membrane electrode assembly. That is, a cathode catalyst layer (32) is disposed on one side of a separator (31) of the present invention, and an anode catalyst layer (33) is disposed on the other side. These catalyst layers are composed of a catalyst and a binder. Gas diffusion layers (34) are further formed on the outer surfaces of these catalyst layers to form a membrane electrode assembly. In FIG. 3 , a bipolar plate (35) is further 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 is generated from the anode catalyst layer (33).

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

[0066] Thus, in one embodiment, the present invention provides an alkaline water electrolysis system incorporating the porous separator of the present invention as a separator in the alkaline water electrolysis system. Furthermore, in one embodiment, the present invention provides a method for producing an alkaline water electrolysis system, comprising incorporating the porous separator of the present invention as a separator in the alkaline water electrolysis system. Furthermore, in one aspect, the present invention provides an alkaline water electrolysis member comprising the porous separator of the present invention. The alkaline water electrolysis member is a member comprising a combination of the porous separator of the present invention with a catalyst, an anode electrode, and / or a cathode electrode. A cell formed by closely contacting the porous separator of the present invention with a cathode electrode on one surface and an anode electrode on the other surface (a zero-gap cell for alkaline water electrolysis) is a preferred alkaline water electrolysis member provided by the present invention.

[0067] The present invention will be described in more detail based on examples, but the present invention should not be construed as being limited by these examples except as defined in the present invention.

[0068] [Preparation of Hydrophilic Organic Polymer] <Hydrophilic Organic Polymer 1> With reference to Example 1 of Japanese Patent No. 5824734, polyethersulfone (Mw 90,000) was sulfonated with chlorosulfonic acid (0.8 equivalents relative to the repeating units of polyethersulfone) using sulfolane as a solvent to obtain sulfonated polyethersulfone having the following structure. The Mw was 120,000. １ The results of H NMR showed that the molar ratio of m to n was m:n=85:15, and the acid value was 0.6 mmol / g.

[0069] <Hydrophilic Organic Polymer 2> With reference to Example 1 of Japanese Patent No. 5824734, polyethersulfone (Mw 90,000) was sulfonated with chlorosulfonic acid (1.7 equivalents relative to the repeating units of polyethersulfone) using sulfolane as a solvent to obtain sulfonated polyethersulfone having the following structure. The Mw was 130,000. １ The results of H NMR showed that the molar ratio of m to n was m:n=70:30, and the acid value was 1.2 mmol / g.

[0070]

[0071] [Fabrication of Porous Separator] Example 1 8.5 g of the hydrophilic organic polymer 1 and 41.6 g of 3-methoxy-N,N-dimethylpropanamide (Tokyo Chemical Industry Co., Ltd.) were mixed and stirred at 60°C for 5 hours to completely dissolve the hydrophilic organic polymer 1. Next, 2.4 g of polyvinylpyrrolidone (trade name: PVP K90, Merck) was added, and the mixture was stirred at 60°C for 1 hour. Next, 47.9 g of zirconium oxide particles (trade name: High Purity Monoclinic Zirconias E101, Luxfer MEL Technologies, D50: approximately 0.8 μm) were added as hydrophilic inorganic particles, and the mixture was stirred for 3 hours to obtain a dope solution. The resulting dope solution was cast onto a glass plate using a 250 μm-thick applicator to form a coating film. A woven fabric support made of polyether ether ketone (PEEK) (manufactured by Safer, opening ratio 70%, thickness 54 μm) was placed on top of the coating film as an aromatic porous support, and this woven fabric support was completely immersed in the coating film. The coating film and the glass plate were gently immersed in a water tank containing water (poor solvent) cooled to 10 ° C., and phase separation between the sulfonated polyethersulfone and the solvent occurred, forming a porous membrane containing sulfonated polyethersulfone on the glass plate. The resulting porous membrane with aromatic porous support was washed with water together with the glass plate at 50 ° C. for 10 minutes, and then the porous membrane with aromatic porous support was peeled off from the glass plate. Subsequently, the porous membrane with aromatic porous support was washed with water at 90 ° C. for 1 hour to obtain porous separator (a-1). The thickness of porous separator (a-1) was 160 μm.

[0072] Example 2 A porous separator (a-2) was obtained in the same manner as in Example 1, except that the hydrophilic organic polymer 2 was used instead of the hydrophilic organic polymer 1. The thickness of the porous separator (a-2) was 160 μm.

[0073] Example 3 A porous separator (b-1) was obtained in the same manner as in Example 1, except that the PEEK woven fabric support (porous support) was not used. The thickness of the porous separator (b-1) was 160 μm.

[0074] Example 4 A porous separator (b-2) was obtained in the same manner as in Example 2, except that the PEEK woven fabric support (porous support) was not used. The thickness of the porous separator (b-2) was 160 μm.

[0075] Example 5 A porous separator (c-1) was obtained in the same manner as in Example 1, except that the hydrophilic inorganic particles were not used. The thickness of the porous separator (c-1) was 160 μm.

[0076] Example 6 A porous separator (c-2) was obtained in the same manner as in Example 2, except that the hydrophilic inorganic particles were not used. The thickness of the porous separator (c-2) was 160 μm.

[0077] Example 7 A porous layer was formed by wet phase separation in the same manner as in Example 1, except that polysulfone (a non-hydrophilic organic polymer, acid value 0.0 mmol / g, Mw 90,000) was used instead of the hydrophilic organic polymer 1 in Example 1. The thickness of this porous layer was 160 μm. The porous layer was formed on a glass plate as described above, with the side of the porous layer that had been in contact with the glass plate being the lower side and the side that had been in contact with air being the upper side.

[0078] A curable composition was prepared by mixing sodium p-styrenesulfonate and sodium 1,4-divinylbenzenesulfonate at a mass ratio of sodium p-styrenesulfonate:sodium 1,4-divinylbenzenesulfonate = 8:2 as raw materials for forming hydrophilic organic polymer 3. This curable composition was applied to the top side of the porous layer and subjected to a polymerization reaction to form a 10 μm thick layer composed of hydrophilic organic polymer 3, which is a crosslinked polymer, to form porous separator (a-3). The acid value of hydrophilic organic polymer 3 was 4.7 mmol / g.

[0079] Comparative Example 1 A sulfonated polyether ether ketone (hydrophilic organic polymer h1, organic polymer acid value 3.1 mol / g) was prepared with reference to Journal of Power Sources, February 1, 2014, Vol. 247, pp. 967-974. A porous separator (h-1) was obtained in the same manner as in Example 1, except that the hydrophilic organic polymer h1 was used instead of the hydrophilic organic polymer 1 in Example 1, no hydrophilic inorganic particles were used, and no porous support was used. The thickness of the porous separator (h-1) was 160 μm.

[0080] Comparative Example 2 Zirfon Perl 500 (manufactured by Agfa) was used as the porous separator (h-2). Zirfon Perl 500 is a porous separator (thickness 500 μm) in which the polysulfone forming the porous structure does not have a hydrophilized structural portion in its molecular structure (the acid value of the organic polymer is 0.0 mmol / g), contains zirconium oxide as hydrophilic inorganic particles, and is supported by a porous support made of polyphenylene sulfide.

[0081] Comparative Example 3 A porous separator (h-3) was obtained in the same manner as in Example 1, except that polyethersulfone (a non-hydrophilic organic polymer having a molecular structure in which the sulfo group has been removed from the structure of the hydrophilic organic polymer 1, acid value 0.0 mmol / g, Mw 90,000) was used instead of the hydrophilic organic polymer 1. The thickness of the porous separator (h-3) was 160 μm.

[0082] <Comparative Example 4> A porous separator (h-4) was obtained in the same manner as in Comparative Example 3, except that no porous support was used. The thickness of the porous separator (h-4) was 160 μm.

[0083] Comparative Example 5 A porous separator (h-5) was obtained in the same manner as in Comparative Example 3, except that the hydrophilic inorganic particles were not used. The thickness of the porous separator (h-5) was 160 μm.

[0084] Comparative Example 6 A porous separator (h-6) was obtained in the same manner as in Example 5, except that the porous support was changed from a woven fabric support made of polyether ether ketone (PEEK) (manufactured by Safer, opening ratio 70%, thickness 54 μm) to a polypropylene-polyethylene nonwoven fabric (manufactured by Ube Exsymo, film thickness approximately 100 μm, 7 cm × 7 cm) which was not an aromatic porous support. The thickness of the porous separator (h-6) was 160 μm.

[0085] [Test Example] <Ionic Conductivity Test> A two-compartment cell having a nickel electrode at the current control terminal and a Luggin capillary filled with 3M-KCl at the voltage control terminal was filled with a 30% by mass aqueous solution of potassium hydroxide as an electrolyte and maintained at 30°C. ２ The ionic resistance was measured under the conditions of 0.05 Ω cm to obtain a blank value (the ionic resistance value when no separator was installed between the two chambers). Next, the porous separators produced in the above examples and comparative examples were installed between the two chambers, and a 30% by mass aqueous potassium hydroxide solution was added as above, and the ionic resistance was measured under the same conditions as above. The difference between the obtained ionic resistance value and the blank value was taken as the ionic resistance value of the porous separator. The ionic resistance value of each porous separator was applied to the following evaluation criteria and used as an index of ionic conductivity. (Evaluation criteria for ionic resistance value) A: 0.05 Ω cm ２ Less than B: 0.05 Ω cm ２ 0.07Ω・cm or more ２ Less than C: 0.07 Ω cm ２ 0.09Ω・cm or more ２ Less than D: 0.09 Ω cm ２ End

[0086] <Zero Gap Resistance Test> A gas diffusion layer with an anode catalyst layer (manufactured by Dioxide Material) and a gas diffusion layer with a cathode catalyst layer (manufactured by Dioxide Material) were each separated by 1 cm. ２The porous separators were punched out to the same shape, and stacked with each catalyst layer facing inward, sandwiching each other, and then pressurized at a surface pressure of 4 MPa (the porous separator (a-3) of Example 7 was arranged so that the hydrophilic organic polymer layer faced the cathode side). The pressurized stack was sandwiched between two Ni bipolar plates having flow channels and constrained with bolts to apply a constraining pressure of 1 MPa. In this way, a water electrolysis cell having a layer structure of bipolar plate / gas diffusion layer / anode catalyst layer / porous separator / cathode catalyst layer / gas diffusion layer / bipolar plate was obtained. A 30 mass % potassium hydroxide aqueous solution heated to 95°C was supplied to the cathode catalyst layer and anode catalyst layer of each of the water electrolysis cells obtained above at a flow rate of 10 mL / min, while a current of 0.1 A / cm was applied. ２ Using these water electrolysis cells after initial energization, a 30 mass % potassium hydroxide aqueous solution heated to 95°C was supplied to the cathode catalyst layer and the anode catalyst layer at a flow rate of 10 mL / min, and the cell resistance (Ω cm ２ ) was measured. The ratio of the obtained cell resistance to the ionic resistance obtained in the above <Ionic Conductivity Test> (cell resistance / ionic resistance) was calculated, and the calculated value was applied to the following evaluation criteria to evaluate the zero gap resistance. (Evaluation criteria for zero gap resistance) A: Cell resistance / ionic resistance less than 0.5 B: Cell resistance / ionic resistance 0.5 or more and less than 1.0 C: Cell resistance / ionic resistance 1.0 or more and less than 1.5 D: Cell resistance / ionic resistance 1.5 or more

[0087] <Gas Barrier Property Test> In the above <Zero Gap Resistance Test>, the gas generated on the anode side was measured by gas chromatography simultaneously with the measurement of the cell resistance value, and the amount of hydrogen gas contamination relative to oxygen gas (%, 100 × [volume % of hydrogen gas / volume % of oxygen gas]) was evaluated using the following index: A: Less than 0.10% B: 0.10% or more and less than 0.15% C: 0.15% or more and less than 0.20% D: 0.20% or more

[0088] The results of each of the above tests are shown in the table below.

[0089]

[0090] As shown in the table above, even if the porous separator contained a hydrophilic organic polymer, when the porous separator did not contain either hydrophilic inorganic particles or an aromatic porous support, the results showed at least inferior zero-gap resistance (Comparative Examples 1 and 6). The difference between the porous separators of Example 5 and Comparative Example 6 is whether the porous support was an aromatic porous support or not. However, the porous separator of Comparative Example 6, which used a porous support that was not an aromatic porous support, showed significantly inferior performance compared to the porous separator of Example 5, possibly because effective adhesion with the hydrophilic organic polymer was not achieved. Furthermore, when the porous separator did not contain a hydrophilic organic polymer, the ionic conductivity and gas barrier properties were inferior, regardless of the presence or absence of the porous separator and hydrophilic inorganic particles (Comparative Examples 2 to 5). In contrast, the porous separators of Examples 1 to 7, which satisfied the requirements of the present invention, all exhibited excellent ionic conductivity, excellent zero-gap resistance, and even excellent gas barrier properties.

[0091] 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.

[0092] This application claims priority based on Japanese Patent Application No. 2024-070318, filed on April 24, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0093] REFERENCE SIGNS LIST 10 Alkaline water electrolysis system 11 Porous separator 12 Cathode electrode 13 Anode electrode 14 Alkaline aqueous solution 20 Alkaline water electrolysis system 30 Alkaline water electrolysis system 31 Porous separator 32 Cathode catalyst layer 33 Anode catalyst layer 34 Gas diffusion layer 35 Bipolar plate 1a Porous body containing an organic polymer containing at least a hydrophilic organic polymer and hydrophilic inorganic particles 1b Porous body containing an organic polymer other than a hydrophilic organic polymer and hydrophilic inorganic particles 2 Aromatic porous support 3 Layer of hydrophilic organic polymer

Claims

1. A porous separator selected from the following (a) to (c): (a) a porous separator consisting of a porous membrane comprising an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, hydrophilic inorganic particles, and an aromatic porous support; (b) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and hydrophilic inorganic particles, but not containing a porous support, wherein the content of the hydrophilic inorganic particles in the porous separator is 10 mass% or more; (c) a porous separator consisting of a porous membrane containing an organic polymer at least containing a hydrophilic organic polymer having at least one of a sulfo group and a carboxy group and having an acid value of 0.3 mmol / g or more, and an aromatic porous support, but not containing hydrophilic inorganic particles.

2. The porous separator according to claim 1, wherein the porous separator (a) is a porous membrane in which a porous body containing an organic polymer at least containing the hydrophilic organic polymer and the hydrophilic inorganic particles is supported by the aromatic porous support, or a porous membrane having a laminate structure of a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer and the hydrophilic inorganic particles is supported by the aromatic porous support, and a layer of the hydrophilic organic polymer.

3. The porous separator according to claim 1, wherein the porous separator (b) is a porous membrane made of a porous body containing an organic polymer containing at least the hydrophilic organic polymer and the hydrophilic inorganic particles, or a porous membrane made of a laminated structure of a porous layer that is a porous body containing an organic polymer other than the hydrophilic organic polymer and the hydrophilic inorganic particles, and a layer of the hydrophilic organic polymer.

4. The porous separator according to claim 1, wherein the porous separator (c) is a porous membrane in which a porous body containing an organic polymer at least containing the hydrophilic organic polymer is supported by the aromatic porous support, or a porous membrane having a laminate structure of a porous layer in which a porous body containing an organic polymer other than the hydrophilic organic polymer is supported by the aromatic porous support, and a layer of the hydrophilic organic polymer.

5. The porous separator according to claim 1, wherein in (a) and (b), the content of the hydrophilic inorganic particles in the porous separator is 20 mass % or more.

6. The porous separator according to claim 5, wherein in (a) to (c), the hydrophilic organic polymer has a sulfo group.

7. The porous separator according to claim 6, wherein the hydrophilic organic polymer has a benzene ring.

8. The porous separator according to claim 7, wherein the hydrophilic organic polymer is an organic polymer selected from the group consisting of polysulfone, polyethersulfone, and polyetheretherketone, into which the sulfo group has been introduced.

9. The porous separator according to claim 8, wherein the hydrophilic organic polymer is an organic polymer selected from polysulfone and polyethersulfone into which the sulfo group has been introduced.

10. The porous separator according to claim 7, wherein in (a) and (b), the hydrophilic inorganic particles comprise at least one of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, magnesium oxide, zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, magnesium hydroxide, and barium sulfate.

11. The porous separator according to claim 7, wherein in (a) and (c), the aromatic porous support is made of polyphenylene sulfide or polyether ether ketone.

12. The porous separator according to any one of claims 1 to 11, which is a porous separator for alkaline water electrolysis.

13. A method for using the porous separator according to any one of claims 1 to 11, comprising using the porous separator as a separator disposed between a cathode electrode and an anode electrode in alkaline water electrolysis.

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