WO2025205501A1 - Porous separator for alkaline water electrolysis, alkaline water electrolysis member using same, alkaline water electrolysis cell, alkaline water electrolysis device, and hydrogen production method - Google Patents

Abstract

Provided are: a porous separator which is for alkaline water electrolysis and satisfies <Condition I> below; an alkaline water electrolysis member using the same; an alkaline water electrolysis cell; an alkaline water electrolysis device; and a hydrogen production method. <Condition I> The porous separator for alkaline water electrolysis has a thickness unevenness of 15% or less, obtained by immersing the separator in a 90°C 7 mol/L KOH aqueous solution and treating the separator under a pressurizing condition of 5 MPa for 60 minutes.

Description

Porous separator for alkaline water electrolysis, alkaline water electrolysis component using the same, alkaline water electrolysis cell, alkaline water electrolysis device, and method for producing hydrogen

The present invention relates to a porous separator for alkaline water electrolysis, an alkaline water electrolysis component using the same, an alkaline water electrolysis cell, an alkaline water electrolysis device, and a method for producing hydrogen.

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. One known method of producing hydrogen is alkaline water electrolysis, which uses a highly concentrated alkaline aqueous solution as the electrolyte. If alkaline water electrolysis is performed using a power generation system that uses renewable energy as the power source, hydrogen can be produced without emitting carbon dioxide, and hydrogen is therefore attracting increasing attention as a fundamental energy source for a sustainable society.

In alkaline water electrolysis, a gas barrier separator (diaphragm) is placed between the cathode and anode to prevent hydrogen bubbles (2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ ) generated at the cathode (negative electrode) from migrating to the anode side, and to prevent oxygen bubbles (4OH ⁻ → O ₂ + 2H ₂ O + 4e ⁻ ) generated at the anode (positive electrode) from migrating to the cathode side. In addition to gas barrier properties, this separator is also required to have ionic conductivity that allows OH ⁻ (hydroxy ions) to pass from the cathode side to the anode side. For this reason, porous membranes (microporous membranes) made of organic polymer materials are used as separators for alkaline water electrolysis.

Porous separators used in alkaline water electrolysis can be formed by a wet phase separation method. In wet phase separation, first, an organic polymer, which is a constituent material of the porous membrane, is dissolved in a solvent (good solvent) that dissolves the organic polymer to prepare a dope solution, and a coating of this dope solution is formed. Next, the coating is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer but is compatible (miscible) with the good solvent. When the proportion of the good solvent in the coating is reduced by this immersion, the organic polymer and the solvent phase separate, causing the organic polymer to gel (coagulate), thereby obtaining a porous membrane.
To enhance the mechanical strength of the porous separator, a porous support such as a nonwoven fabric or a woven fabric is placed in the dope solution, and the phase separation is carried out in the presence of the porous support, so that the organic polymer in the impregnated dope solution forms a porous structure, thereby forming a porous separator in which the porous support and the porous structure of the organic polymer are integrated. Furthermore, by incorporating hydrophilic inorganic particles into the separator, the gas barrier properties can be enhanced while the alkaline aqueous solution can be efficiently infiltrated into the separator, thereby further enhancing ionic conductivity.

For example, Patent Document 1 describes an example of such a porous separator, which includes a porous support and first and second porous layers provided on one and the other side of the porous support. 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.

Special Publication No. 2023-531792

In recent years, with a view to improving the efficiency of hydrogen production and making alkaline water electrolysis systems suitable for renewable energy, research and development has been progressing on high-pressure alkaline water electrolysis systems (which are also called "pressurized alkaline water electrolysis systems" because they are operated under a pressure of 10 bar or more compared to atmospheric pressure (approximately 1 bar)).
However, studies by the present inventors have revealed that when the separator described in Patent Document 1 is used in a pressurized alkaline water electrolysis system to perform alkaline water electrolysis under pressure, a problem occurs in which the electrolysis voltage increases.
As a result of extensive research into the above problem, the inventors have found that the application of pressure causes uneven thickness in the separator, and that this uneven thickness traps bubbles in the recessed surface areas, causing an increase in initial resistance. Furthermore, they have found that continued operation under pressure causes deterioration due to heat generation, oxidation, etc. in the areas where bubbles are trapped, accelerating separator deterioration and further increasing the electrolysis voltage.

An object of the present invention is to provide a porous separator for alkaline water electrolysis that, when used as a separator for pressurized alkaline water electrolysis, can suppress an increase in initial resistance (electrolysis voltage) due to pressurization and also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions.
Another object of the present invention is to provide an alkaline water electrolysis member, an alkaline water electrolysis cell, an alkaline water electrolysis apparatus, and a method for producing hydrogen, which use the porous separator for alkaline water electrolysis of the present invention.

The above-mentioned problems of the present invention have been solved by the following means.
[1]
A porous separator for alkaline water electrolysis, which satisfies the following <Condition I>:
<Condition I>
The porous separator for alkaline water electrolysis is immersed in a 7 mol/L aqueous KOH solution at 90°C and treated under a pressure of 5 MPa for 60 minutes, and the resulting separator has thickness variation of 15% or less.
[2]
The porous separator for alkaline water electrolysis according to [1], comprising: a porous support; and a porous material, which is disposed on at least one of an outer surface and pores of the porous support, and which contains an organic polymer and hydrophilic inorganic particles, and wherein a concentration of the inorganic particles in the porous material is 50 vol% or more.
[3]
The porous separator for alkaline water electrolysis according to [1] or [2], comprising: a porous support; and a porous material, which is disposed on at least one of the outer surface and pores of the porous support and which contains an organic polymer and hydrophilic inorganic particles; and the thickness of the porous separator for alkaline water electrolysis is 210 µm or less.
[4]
The porous separator for alkaline water electrolysis according to any one of [1] to [3], comprising: a porous support; and a porous material that is disposed on at least one of the outer surface and pores of the porous support and that contains an organic polymer and hydrophilic inorganic particles, wherein the organic polymer has a storage modulus at 90°C of 850 MPa or more.
[5]
The porous separator for alkaline water electrolysis according to [1], which is made of a porous material containing an organic polymer and does not include a porous support.
[6]
An alkaline water electrolysis element comprising the porous separator for alkaline water electrolysis according to any one of [1] to [5].
[7]
An alkaline water electrolysis cell comprising the porous separator for alkaline water electrolysis according to any one of [1] to [5] or the alkaline water electrolysis member according to [6].
[8]
An alkaline water electrolysis device comprising the alkaline water electrolysis cell according to [7].
[9]
A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to [8] at a pressure of 10 bar or more.
[10]
A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus according to [8], applying a pressure of 5 bar or more from the hydrogen generation side to the oxygen generation side.

In addition, in this invention, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

When used as a separator for pressurized alkaline water electrolysis, the porous separator for alkaline water electrolysis of the present invention can suppress an increase in initial resistance (electrolysis voltage) due to pressurization, and can also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions.
Furthermore, when used as a component for pressurized alkaline water electrolysis, the alkaline water electrolysis device of the present invention can suppress an increase in initial resistance (electrolysis voltage) due to pressurization, and can also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions.
Furthermore, the alkaline water electrolysis cell and alkaline water electrolysis device of the present invention can suppress both an increase in initial resistance (electrolysis voltage) due to pressurization and an increase in electrolysis voltage due to operation under pressurized conditions.
Furthermore, according to the hydrogen production method of the present invention, hydrogen can be efficiently produced using the alkaline water electrolysis apparatus of the present invention.

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.

[Porous separator for alkaline water electrolysis]
The porous separator for alkaline water electrolysis of the present invention is a porous separator that satisfies the following <Condition I>:
<Condition I>
The porous separator for alkaline water electrolysis is immersed in a 7 mol/L aqueous KOH solution at 90°C and treated under a pressure of 5 MPa for 60 minutes, and the resulting separator has thickness variation of 15% or less.

The porous separator for alkaline water electrolysis to be subjected to the treatment (pressure treatment) specified in the above <Condition I> is immersed in pure water at 25°C overnight before use.
The thickness unevenness of the separator is measured and calculated as follows.
The separator subjected to the pressure alkali treatment specified in the above <Condition I> is dried, and a cross section is cut out using a razor, and a cross-sectional SEM (scanning electron microscope) image is taken at a magnification (e.g., 400x) that fits the separator cross section in one field of view. In the obtained cross-sectional SEM image, the thickness is measured at intervals of 20 points, and the arithmetic mean, maximum value, and minimum value are calculated from the obtained 20 measurement values, and the thickness unevenness X is calculated using the following formula.

Thickness unevenness X = {(maximum value - minimum value) ÷ arithmetic mean value} x 100 (unit: %)

The arithmetic mean value of five thickness variations X obtained using five cross-sectional SEM images with different fields of view is defined as the "thickness variation."
For other detailed conditions, the description in the Examples below can be applied.
The porous separator for alkaline water electrolysis of the present invention is a porous separator suitable for alkaline water electrolysis. This separator has the desired basic properties for alkaline water electrolysis, namely, gas barrier property and hydroxy ion permeability.
The porous separator for alkaline water electrolysis of the present invention may be used as a separator for alkaline water electrolysis operated under any pressure condition ranging from normal pressure to pressurized pressure, and the effects become particularly apparent when used as a separator for pressurized alkaline water electrolysis operated under pressurized conditions. Pressurized alkaline water electrolysis refers to alkaline water electrolysis operated under pressurized conditions of 10 bar or more.

The reasons why use of the porous separator for alkaline water electrolysis of the present invention as a separator for pressurized alkaline water electrolysis can suppress an increase in initial resistance (electrolysis voltage) due to pressurization and also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions are thought to be as follows.
A conventional porous separator such as that described in Patent Document 1 has porous layers formed on both sides of a porous support, the porous layers being made of a porous material containing an organic polymer and hydrophilic inorganic particles. Furthermore, because the porous separator is formed by a wet phase separation method, the voids in the porous support (gaps between the fibers, metal, and ceramic constituting the porous support) are also filled with the porous material. In an alkaline water electrolysis system under pressure, pores in the porous material are crushed by the pressure, while the fibers, metal, and ceramic constituting the porous support themselves are hardly deformed. When viewed in the thickness direction, the porous separator has a portion where the fibers, metal, or ceramic constituting the porous support are present and where the porous material is present on the outer surface of the porous support, and a portion where the fibers, metal, or ceramic constituting the porous support are not present and where the porous material is present. This is thought to result in different compressibility under pressure depending on the location of the porous separator, resulting in thickness unevenness. As a result, with conventional porous separators, significant thickness unevenness occurs when an alkaline water electrolysis cell is operated under pressure, and oxygen gas and hydrogen gas bubbles are trapped in depressions on the separator surface caused by this thickness unevenness, which is thought to result in an increase in initial resistance (electrolysis voltage) due to pressure application and an increase in electrolysis voltage over time due to operation under pressure conditions.
In contrast, in the porous separator for alkaline water electrolysis of the present invention, the thickness unevenness of the separator caused by the pressurized alkaline treatment specified in the above <Condition I> is suppressed to 15% or less. Therefore, thickness unevenness is unlikely to occur even when the electrolytic cell is incorporated into a pressurized alkaline water electrolysis system and operated under pressure (under a pressure of 10 bar or more). As a result, it is believed that the increase in initial resistance (electrolysis voltage) due to pressurization and the increase in electrolysis voltage over time due to operation under pressurized conditions can be effectively suppressed.

The thickness unevenness specified in the above <Condition I> is preferably 12% or less, more preferably 9% or less, and even more preferably 5% or less, from the viewpoint of further suppressing the increase in initial resistance (electrolysis voltage) due to pressurization and the increase in electrolysis voltage over time due to operation under pressurized conditions. The practical lower limit of the thickness unevenness specified in the above <Condition I> is usually 1% or more.

The specific configuration of the porous separator for alkaline water electrolysis of the present invention is not particularly limited, as long as it satisfies the above <Condition I> and has the desired gas barrier properties and hydroxy ion permeability required of a porous separator for alkaline water electrolysis. For example, the following configurations can be mentioned.
For example, when the porous separator for alkaline water electrolysis of the present invention is configured to include a porous support and a porous material that is disposed on at least one of the outer surface and pores of the porous support and contains an organic polymer and hydrophilic inorganic particles, the porous separator for alkaline water electrolysis that satisfies the above <Condition I> can be obtained by adjusting the type of organic polymer that constitutes the porous material, the inorganic particle concentration in the porous material, and the thickness of the porous separator for alkaline water electrolysis.
The term "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 term "pores of the porous support" refers 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 and hydrophilic inorganic particles is disposed on at least one of the outer surface and pores of the porous support can be appropriately adjusted within a range in which the separator for alkaline water electrolysis has the desired gas barrier properties and ionic conductivity. For example, the porous material may be disposed only on the outer surface of the porous support. In this case, the porous material may be disposed on only one side of the porous support, or on both sides. Alternatively, the porous material may be disposed only in the pores of the porous support. Furthermore, the porous material may be 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 encompassed in the structure in which a porous material containing an organic polymer and 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 over the entire outer surface and in all pores of the porous support is preferred.
When the porous separator for alkaline water electrolysis of the present invention has a structure in which a woven fabric support is used as the porous support and a porous material containing an organic polymer and hydrophilic inorganic particles is disposed on at least one of the outer surface and voids of the woven fabric support, properties that satisfy the above <Condition I> can be achieved by, for example, Production Method I in the production method for a porous separator for alkaline water electrolysis of the present invention described below.
Specifically, a porous separator for alkaline water electrolysis that satisfies the above <Condition I> can be obtained by satisfying at least one of the following requirements (A-1) to (A-3). In particular, from the viewpoint of further suppressing the thickness unevenness specified in the above <Condition I>, it is preferable to satisfy at least two of the following requirements (A-1) to (A-3), more preferably to satisfy at least two of the following requirements (A-1) to (A-3) including requirement (A-2), and even more preferably to satisfy all of the following requirements (A-1) to (A-3). The effects of these embodiments of the porous separator for alkaline water electrolysis of the present invention are generally more pronounced when used as a porous separator for pressurized alkaline water electrolysis.
(A-1): the inorganic particle concentration in the porous material is 50 vol% or more; (A-2): the thickness of the porous separator for alkaline water electrolysis is 210 μm or less; (A-3): the storage modulus of the organic polymer at 90°C is 850 MPa or more. Furthermore, even when the porous separator for alkaline water electrolysis of the present invention is made of a porous material containing an organic polymer and does not contain a porous support, it can still satisfy the above-mentioned <Condition I>. A porous separator for alkaline water electrolysis of the present invention made of a porous material containing an organic polymer and not containing a porous support can be obtained, for example, by Production Method II in the production method for a porous separator for alkaline water electrolysis of the present invention described below. The effects of this form of the porous separator for alkaline water electrolysis of the present invention are generally more pronounced when used as a porous separator for pressurized alkaline water electrolysis.
The porous support, the porous material, and the organic polymer and hydrophilic inorganic particles constituting the porous material will be described in detail below. (A-1) to (A-3) will also be described in detail below.

(Porous support)
The porous support is not particularly limited as long as it is applicable to a porous separator for alkaline water electrolysis. For example, a material 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 fabric, more preferably a porous polymer fabric, which may be a woven or nonwoven fabric.

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

The thickness of the porous support is preferably from 30 to 150 μm, more preferably from 30 to 100 μm, and even more preferably from 30 to 75 μm.
The thickness of the porous support is a value measured using a constant pressure thickness measuring instrument in accordance with JIS (Japanese Industrial Standards) K6250 (2019).
The thickness of the porous support in the porous separator for alkaline water electrolysis can be measured and calculated by removing the porous support from the porous separator for alkaline water electrolysis using a solvent that dissolves the organic polymer contained in the porous material, and measuring and calculating the thickness of the removed porous support using the method described above.

(Porous material)
The porous material is disposed on at least one of the outer surface and pores of the porous support, and has the function of blocking the permeation of hydrogen gas and oxygen gas, but allowing the permeation of hydroxy ions.
When the porous separator for alkaline water electrolysis of the present invention does not contain a porous support, the porous separator for alkaline water electrolysis of the present invention is made of a porous material containing an organic polymer and has the function of blocking permeation of hydrogen gas and oxygen gas and allowing permeation of hydroxy ions.
The porous material contains at least an organic polymer, and may further contain other components such as hydrophilic inorganic particles.

- 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.

The organic polymer can be selected from, for example, fluororesins, olefin resins, polyester resins, aromatic hydrocarbon resins, and the like.
The fluororesin is preferably a resin selected from polyvinylidene fluoride and polytetrafluoroethylene.
The olefin resin is preferably a polypropylene resin.
The polyester resin is preferably a resin selected from polyethylene terephthalate, polybutylene terephthalate, and polybutylene naphthalate.
The aromatic hydrocarbon resin is preferably a polystyrene resin.

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

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

The organic polymer more preferably includes at least one of polyvinylidene fluoride, polysulfone, polyethersulfone, and polyphenylsulfone, and even more preferably includes at least one of polysulfone, polyethersulfone, and polyphenylsulfone.

The storage modulus of the organic polymer at 90°C may be, for example, 750 MPa or more, preferably 800 MPa or more, and as defined in (A-3) above, more preferably 850 MPa or more, and even more preferably 900 MPa or more. There is no particular upper limit, and for example, it is preferably 4000 MPa or less, more preferably 2000 MPa or less, and even more preferably 1500 MPa or less. That is, a preferred range is 750 to 4000 MPa, more preferably 800 to 2000 MPa, even more preferably 850 to 2000 MPa, and particularly preferably 900 to 1500 MPa.
The storage modulus at 90°C is a value obtained by measuring in a _N2 atmosphere using a cone-plate rheometer, raising the temperature from 30°C (measurement start temperature) at a rate of 10°C/min to 150°C (measurement end temperature).
The storage modulus of the organic polymer contained in the porous material constituting the porous separator for alkaline water electrolysis can be measured by eluting and extracting the organic polymer from the porous separator for alkaline water electrolysis using a solvent in which the organic polymer dissolves (both solvents), removing inorganic particles using a filter, and then drying the organic polymer to prepare a measurement sample. Details are as described in the Examples below.

The mass average molecular weight (Mw) of the organic polymer is not particularly limited. Taking into consideration the handleability of the dope solution described below and the mechanical strength of the resulting porous separator for alkaline water electrolysis, it can be, for example, 10,000 to 500,000, and preferably 20,000 to 300,000. Mw can be determined under the following conditions.

Apparatus: HLC-8220GPC (manufactured by Tosoh Corporation)
Detector: differential refractometer (RI (Refractive Index) detector)
Precolumn: TSKGUARD COLUMN HXL-L 6 mm x 40 mm (manufactured by Tosoh Corporation)
Sample column: The following three columns are connected in order (all manufactured by Tosoh Corporation)
・TSK-GEL GMHXL 7.8mm x 300mm
・TSK-GEL G4000HXL 7.8mm x 300mm
・TSK-GEL G2000HXL 7.8mm x 300mm
Reference column: TSK-GEL G1000HXL 7.8 mm x 300 mm
Constant temperature bath temperature: 40℃
Mobile phase: THF (tetrahydrofuran)
Sample side mobile layer flow rate: 1.0 mL/min Reference side mobile layer flow rate: 1.0 mL/min Sample concentration: 0.1% by mass
Sample injection volume: 100 μL
Data collection time: 5 to 45 minutes after sample injection Sampling pitch: 300 milliseconds

The organic polymer content in the porous material is preferably 5 to 50% by mass, more preferably 5 to 40% by mass, even more preferably 7 to 30% by mass, and particularly preferably 9 to 25% by mass.

- Hydrophilic inorganic particles -
The porous material may contain hydrophilic inorganic particles, preferably particles selected from metal oxides and metal hydroxides.

The metal oxide is preferably selected from zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide.

The metal hydroxide is preferably selected from zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, and magnesium hydroxide.

In addition to particles selected from metal oxides and metal hydroxides, barium sulfate particles can also be used as hydrophilic inorganic particles.

Hydrophilic inorganic particles may be used alone or in combination of two or more types.

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 even more preferably 0.20 to 1.00 μm. This particle size is the median diameter (D50), and refers to the particle size at which the cumulative distribution reaches 50% when the total volume of particles is taken as 100% when the particle size distribution is measured using a laser diffraction/scattering method.

When the porous material contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in the porous material is preferably 50 to 95% by mass, more preferably 60 to 95% by mass, even more preferably 70 to 93% by mass, and particularly preferably 75 to 91% by mass.

When the porous material contains hydrophilic inorganic particles, the inorganic particle concentration of the porous material is usually 35% by volume or more, preferably 40% by volume or more, more preferably 45% by volume or more, and even more preferably 50% by volume or more, as defined in the above-mentioned (A-1). There is no particular upper limit, and for example, 85% by volume or less is preferred, 75% by volume or less is more preferred, and 65% by volume or less is even more preferred. That is, a preferred range is 35 to 85% by volume, more preferably 40 to 75% by volume, even more preferably 45 to 65% by volume, and particularly preferably 50 to 65% by volume.
The "concentration of inorganic particles in a porous material" means the concentration (unit: volume %) of all inorganic particles contained in the porous material.
The inorganic particle concentration of the porous material can be calculated by scraping the porous material off the porous separator, collecting the porous material other than the porous support, quantifying the weight of the organic material and the weight of the inorganic material (inorganic particles) by thermal analysis, and using the densities of the organic material and the inorganic material described in publicly known materials. Details are as described in the Examples below.

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

When the porous separator for alkaline water electrolysis of the present invention is produced by the method for producing a porous separator for alkaline water electrolysis of the present invention described below, a certain amount of good solvent, which will be described later in the dope solution, will inevitably remain in the porous material. As a result, the total content of good solvent in the porous material is typically 0.01 to 5.00 mass%.

The thickness of the porous separator for alkaline water electrolysis of the present invention may usually be 600 μm or less, preferably 300 μm or less, and more preferably 210 μm or less as specified in (A-2) above. When the porous separator for alkaline water electrolysis of the present invention is made of a porous material containing an organic polymer and does not include a porous support, the thickness is more preferably 210 μm or less.
The lower limit of the thickness of the porous separator for alkaline water electrolysis of the present invention is usually 30 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. That is, the preferred range is 30 to 600 μm, more preferably 50 to 300 μm, and even more preferably 100 to 210 μm.
This thickness is the arithmetic mean value of 20 measurement values obtained by obtaining a cross-sectional SEM (scanning electron microscope) image of a cross-section cut out from a porous separator for alkaline water electrolysis with a razor at a magnification (for example, 400x) such that the separator cross-section is included in a single field of view, and measuring the thickness at 20-point intervals on the assumption that no pores are present in the obtained cross-sectional SEM image (assuming that the pores are filled with an organic polymer).
The porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 30 to 600 μm and a thickness variation of 1 to 12% as specified in the above <Condition I>, preferably has a thickness of 30 to 600 μm and a thickness variation of 1 to 9% as specified in the above <Condition I>, and preferably has a thickness of 30 to 600 μm and a thickness variation of 1 to 5% as specified in the above <Condition I>.
Furthermore, the porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 50 to 300 μm and a thickness variation of 1 to 12% as specified in the above <Condition I>, preferably has a thickness of 50 to 300 μm and a thickness variation of 1 to 9% as specified in the above <Condition I>, and preferably has a thickness of 50 to 300 μm and a thickness variation of 1 to 5% as specified in the above <Condition I>.
Furthermore, the porous separator for alkaline water electrolysis of the present invention preferably has a thickness of 100 to 210 μm and a thickness variation of 1 to 12% as specified in the above <Condition I>, preferably has a thickness of 100 to 210 μm and a thickness variation of 1 to 9% as specified in the above <Condition I>, and preferably has a thickness of 100 to 210 μm and a thickness variation of 1 to 5% as specified in the above <Condition I>.

From the viewpoint of the gas barrier properties required of porous separators for alkaline water electrolysis, the porous separator for alkaline water electrolysis of the present invention preferably has a bubble point of more than 1 bar, and more preferably more than 2 bar. The pore size and porosity of the pores in the porous separator for alkaline water electrolysis of the present invention may be adjusted to ranges that satisfy the above-mentioned bubble point.
The bubble point is measured using a perm porometer in accordance with the bubble point test 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. Details are as described in the Examples below.

The pore size of the pores in the porous separator for alkaline water electrolysis of the present invention is preferably 10 to 1,000 nm, more preferably 20 to 700 nm, and even more preferably 30 to 500 nm, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier properties. This pore size is determined as the average value of the pore size distribution obtained from an insertion curve obtained by mercury intrusion porosimetry.

The porosity of the porous separator for alkaline water electrolysis of the present invention is preferably 30 to 70%, and more preferably 40 to 60%, from the viewpoint of exhibiting excellent ion permeability and excellent gas barrier properties. This porosity is the value calculated from an insertion curve obtained by mercury intrusion porosimetry.

The porous separator for alkaline water electrolysis of the present invention preferably has an ionic resistance of 0.01 to 0.30 Ω ^cm2 , and more preferably 0.01 to 0.15 Ω ^cm2 , from the viewpoint of the hydroxy ion permeability required for a porous separator for alkaline water electrolysis.
The ionic resistance is a value measured by setting a circular punched porous separator for alkaline water electrolysis of the present invention in a cell and measuring it by an AC impedance method at 90° C. Details are as described in the Examples below.

The porous separator for alkaline water electrolysis of the present invention preferably has a water permeability of 100 to 2000 mL/(h ^m2 bar) from the viewpoint of the mass balance between the cathode and anode sides of the electrolyte required for the porous separator for alkaline water electrolysis, and more preferably 100 to 1000 mL/(h ^m2 bar) from the viewpoint of eliminating the need for special measures in the operation of the alkaline water electrolysis cell, such as changing the amount of electrolyte permeation between the anode and cathode sides.
The water permeation rate is a value calculated by measuring the amount of liquid (mL) when a circular punched-out porous separator for alkaline water electrolysis of the present invention is set in a filter holder and a 30 mass% aqueous potassium hydroxide solution is allowed to pass through the circular separator for 30 seconds under conditions of 90°C and a gauge pressure of 1 bar. Details are as described later in the Examples.

The porous separator for alkaline water electrolysis of the present invention can be preferably used as a separator in a pressurized alkaline water electrolysis system (separator for pressurized alkaline water electrolysis). The porous separator for alkaline water electrolysis of the present invention can also be used as a separator in an alkaline water electrolysis system used under normal pressure (separator for alkaline water electrolysis).
The porous separator for alkaline water electrolysis of the present invention may be in the form of a long sheet wound into a roll, or may be cut in advance to a predetermined shape according to the intended use, device, etc.
The porous separator for alkaline water electrolysis of the present invention may be preserved or stored by immersing it in a storage liquid such as pure water, or may be preserved or stored as a dried membrane without being immersed in a storage liquid.

[Method for manufacturing porous separator for alkaline water electrolysis]
The method for producing the porous separator for alkaline water electrolysis of the present invention is not particularly limited, and the porous separator for alkaline water electrolysis of the present invention is usually produced by a method including forming a porous material by wet phase separation.
For example, there may be mentioned a method (hereinafter referred to as "production method I") comprising forming the porous material by wet phase separation in a state in which the woven fabric support is disposed in a coating formed from a dope solution obtained by dissolving the organic polymer. This step provides the porous separator for alkaline water electrolysis of the present invention, in which a porous material comprising at least an organic polymer is disposed on at least one of the outer surface and pores of the woven fabric support.
Another example is a method (hereinafter referred to as "production method II") that includes forming the porous material by wet phase separation, which includes casting a membrane-forming solution containing the organic polymer dissolved therein onto a release film to form a coating film, and performing liquid-induced phase separation on the coating film while the release film is peeled off. This step provides the porous separator for alkaline water electrolysis of the present invention, which is made of a porous material containing at least an organic polymer and does not include a porous support.

(Dope solution)
The dope 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 dope solution can be the same as that described above for the organic polymer in the porous separator for alkaline water electrolysis.
The hydrophilic inorganic particles that may be contained in the dope solution can be described in the same manner as for the hydrophilic inorganic particles in the porous separator for alkaline water electrolysis.

- Solvent -
The dope solution in the wet phase separation may be any solvent (good solvent) that can dissolve 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, and mixtures thereof, with at least one of NMP and NBP being more preferred.

When the dope solution contains hydrophilic inorganic particles, the content of the solvent in the dope solution is preferably 20 to 95 mass%, more preferably 25 to 90 mass%, further preferably 30 to 80 mass%, further preferably 30 to 70 mass%, further preferably 32 to 60 mass%, and further preferably 35 to 50 mass%.
When the dope solution does not contain hydrophilic inorganic particles, the content of the solvent in the dope solution is preferably 20 to 95 mass%, more preferably 25 to 90 mass%, further preferably 30 to 80 mass%, further preferably 40 to 80 mass%, further preferably 45 to 75 mass%, and further preferably 50 to 75 mass%.

- Organic polymer -
When the dope solution contains hydrophilic inorganic particles, the content of the organic polymer in the dope 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 dope solution does not contain hydrophilic inorganic particles, the content of the organic polymer in the dope 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 %.

- Hydrophilic inorganic particles -
The hydrophilic inorganic particles are particles that are dispersed in the dope solution without dissolving, and such a dispersion state is also called the dope solution in the present invention. That is, the "solution" in the dope solution means that the organic polymer is dissolved in the solvent.
When the dope solution contains hydrophilic inorganic particles, the content of the hydrophilic inorganic particles in 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 %.

- Other ingredients -
The dope solution may contain components (other components) other than the components described above (solvent, organic polymer, and hydrophilic inorganic particles), such as 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, and lithium chloride, in order to control pore formation during wet phase separation.
When the dope solution contains other components and hydrophilic inorganic particles, the total content of the other components in the dope solution is preferably 0.1 to 15 mass%, more preferably 0.2 to 10 mass%, and even more preferably 0.5 to 5 mass%.
When the dope solution contains other components but does not contain hydrophilic inorganic particles, the total content of the other components in the dope solution is preferably 1 to 25 mass%, more preferably 5 to 25 mass%, and even more preferably 7 to 20 mass%.

<Formation of porous materials by wet phase separation>
In the above-mentioned production method I, a porous material is formed by disposing a woven fabric support in a coating film formed from a dope solution containing an organic polymer, and then wet phase separation is performed to form the porous material. This allows the production of a porous separator for alkaline water electrolysis of the present invention, in which a porous material containing at least an organic polymer is disposed on at least one of the outer surface and pores of the woven fabric support. In the wet phase separation, the woven fabric support is placed on a coating film formed by casting the dope solution on a substrate, and the woven fabric support is immersed in the coating film to impregnate, preferably completely impregnate, the woven fabric support with the dope solution. Next, the woven fabric support impregnated with the dope solution is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent. When the proportion of the good solvent in the coating film of the dope solution is reduced by this immersion, phase separation occurs between the organic polymer and the solvent (liquid-induced phase separation), causing the organic polymer to gel (solidify), forming a porous material, and the porous material is disposed on at least one of the outer surface and pores of the woven fabric support, thereby providing the porous separator for alkaline water electrolysis of the present invention.
In the above-mentioned production method II, a membrane-forming solution containing an organic polymer dissolved therein is cast onto a release film to form a coating, and the coating is then subjected to wet phase separation, which involves performing liquid-induced phase separation while the release film is peeled off, to form the porous material. This allows the production of a porous separator for alkaline water electrolysis of the present invention, which is composed of a porous material containing at least an organic polymer and does not include a porous support. In the wet phase separation, the membrane-forming solution is cast onto a release film, and the surface is appropriately dried to form a coating. Next, the laminate, in which the coating of the membrane-forming solution on the release film has been formed, is immersed in a solvent (poor solvent, coagulation bath) that does not dissolve the organic polymer and is compatible (miscible) with the good solvent, and the release film is peeled off during immersion. When the proportion of the good solvent in the coating of the membrane-forming solution decreases during this immersion, the organic polymer and the solvent undergo phase separation (liquid-induced phase separation), causing the organic polymer to gel (coagulate), forming a porous material. This allows the production of a porous separator for alkaline water electrolysis of the present invention, which is composed of a porous material and does not include a porous support, to be obtained.

The poor solvent may 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 the hydrophilic organic solvent include aprotic solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC), and alcoholic solvents such as ethanol, propanol, and isopropanol. Examples of the water-soluble polymer include water-soluble polymers such as polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA).
Of the above, water is preferred as the poor solvent.

The temperature of the coagulation bath is preferably 20 to 90°C, more preferably 40 to 70°C.

It is also preferable to expose the membrane to the vapor of the poor solvent before immersing it in the poor solvent to induce phase separation by vapor (vapor-induced phase separation). By performing vapor-induced phase separation, it is possible to prevent the formation of a dense skin layer on the surface. Therefore, the wet phase separation can be performed by combining vapor-induced phase separation and liquid-induced phase separation.
After the wet phase separation, preferably after the liquid-induced phase separation, it is preferable to carry out a washing step using pure water or the like.

In the vapor-induced phase separation, the porous support coated with the dope solution is exposed to non-solvent vapor, preferably humid air. For the method of vapor-induced phase separation, see, for example, FIG. 2 of JP-A-2023-531792 and the description therein, which can be applied to the present invention.
The anti-solvent vapor used in the vapor-induced phase separation is preferably moist air.
The space for performing vapor-induced phase separation can be provided, for example, between the step of coating the porous support with a dope solution and the step of performing liquid-induced phase separation, so as to be continuous with the apparatuses for performing each step, and can be further shielded from the external environment by an insulating metal plate.
The degree and rate of water movement in the steam-induced phase separation process can be controlled by adjusting the air velocity, the relative humidity and temperature of the air, the exposure time, and the like.
The relative humidity within the region where the vapor-induced phase separation occurs can be controlled by the temperature of the coagulation bath as well as by shielding the vapor-induced phase separation region from the environment.
The vapor-induced phase separation carried out on the porous support coated with the dope solution may be carried out on both sides under the same conditions or under different conditions.
The relative humidity and air temperature in the region where the vapor-induced phase separation is carried out can be adjusted using an insulating metal plate, for example, when using the apparatus described in FIG. 2 of JP-A-2023-531792. When the apparatus is completely shielded from the external environment by the metal plate, the relative humidity and air temperature are determined by the temperature of the coagulation bath used in the subsequent liquid-induced phase separation.
The higher the relative humidity and the higher the air velocity in the region where the vapor-induced phase separation occurs, the larger the maximum pores in the resulting porous material.
The relative humidity in the region where the vapor-induced phase separation takes place can be, for example, in the range of 50 to 99%, preferably 60 to 98%, and more preferably 70 to 98%.

In addition, in the above-mentioned manufacturing method II, after immersing the membrane in the above-mentioned poor solvent to form a porous material (porous membrane), it may be immersed in a glycol such as ethylene glycol or diethylene glycol, or water. This step allows the solvent remaining in the membrane to be removed.

A certain amount of good solvent in the dope solution used in the production of a porous separator for alkaline water electrolysis obtained by the above-described method for producing a porous separator for alkaline water electrolysis inevitably remains in the porous separator for alkaline water electrolysis. As a result, a porous separator for alkaline water electrolysis is provided in which the total content of good solvents in the porous material is 0.01 to 5.00 mass%.
The amount of residual solvent can be quantified as mass % based on 100 mass % of the porous separator for alkaline water electrolysis after drying the separator in advance with air at 40°C for 12 hours using gas chromatography or ^1H -NMR.

The porous separator for alkaline water electrolysis of the present invention can be used as a separator in a method for producing hydrogen by electrolyzing an alkaline aqueous solution in an electrolytic cell. In particular, it can be suitably used as a separator for alkaline water electrolysis in the alkaline water electrolysis system described below.

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

Fig. 1 schematically illustrates a preferred embodiment of an alkaline water electrolysis system according to the present invention. The alkaline water electrolysis system (10) shown in Fig. 1 includes a separator (11) according to the present invention, a cathode electrode (12) on one side thereof, and an anode electrode (13) on the other side thereof. 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, generating hydrogen (H ₂ ) bubbles from water (2H ₂ O + 2e ^- → H ₂ + 2OH ^- ). Hydroxy ions (OH ^- ) generated with the hydrogen generation pass through the separator (11) and migrate to the anode side, where electrons are removed to generate oxygen (O ₂ ) bubbles (4OH ^- → O ₂ + 2H ₂ O + 4e ^- ). The cathode electrode (12) and the anode electrode (13) are preferably composed of an electrode substrate (conductive material) and a catalyst layer on the electrode substrate. When a catalyst layer is included, the catalyst species may be the same or different between the cathode electrode (12) and the anode electrode (13).
In the alkaline water electrolysis system (10) shown in FIG. 1, the separator (11) and the electrodes (12, 13) are spaced apart, resulting in a long migration distance of hydroxy ions, which limits the improvement of ion conduction efficiency.

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 separator (11) and the electrodes (12, 13) are arranged in contact with each other (zero gap type). The alkaline water electrolysis system (20) illustrated in Figure 2 is advantageous in terms of ion conduction efficiency because the separator (11) and the electrodes (12, 13) are in contact with each other, thereby shortening the migration distance of hydroxy ions.
An example of a pressurized alkaline water electrolysis system is the alkaline water electrolysis system shown in Fig. 2 , with the configuration, components, etc. appropriately adjusted to enable pressurized operation (e.g., operation under a pressurized condition of 10 bar or more). The separator (11) of the present invention can suppress an increase in initial resistance (electrolysis voltage) due to pressurization and also suppress an increase in electrolysis voltage over time due to operation under pressurized conditions, thereby enabling the effects of the separator (11) to be manifested in a pressurized alkaline water electrolysis system. Furthermore, typical components used in pressurized alkaline water electrolysis systems can also be applied, as appropriate, to other components.

Figure 3 schematically illustrates another preferred embodiment of the alkaline water electrolysis system of the present invention. The alkaline water electrolysis system (30) shown in Figure 3 includes a membrane electrode assembly. That is, a cathode catalyst layer (32) is disposed on one side of a separator (31) of the present invention, and an anode catalyst layer (33) is disposed on the other side. These catalyst layers are composed of a catalyst and a binder. Furthermore, 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), thereby constituting a membrane electrode assembly. In Figure 3, a bipolar plate (35) is formed further outside the membrane electrode assembly. An alkaline aqueous solution is supplied to the cathode catalyst layer (32) and anode catalyst layer (33) of this membrane electrode assembly, and the cathode catalyst layer (32) and anode catalyst layer (33) are electrically connected and electrified, whereby hydrogen bubbles are generated from the cathode catalyst layer (32) and oxygen bubbles are generated from the anode catalyst layer (33).

In the alkaline water electrolysis system described above, 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 components used in alkaline water electrolysis systems can be applied as appropriate.

As such, in one embodiment, the present invention provides an alkaline water electrolysis system incorporating the 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 manufacturing an alkaline water electrolysis system, which includes incorporating the separator of the present invention as a separator in the alkaline water electrolysis system. The effects of the separator of the present invention are more pronounced when incorporated as a separator in a pressurized alkaline water electrolysis system, among other alkaline water electrolysis systems.

[Alkaline water electrolysis components]
The alkaline water electrolysis device of the present invention includes the separator of the present invention.
Specifically, the alkaline water electrolysis device 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 a configuration including the separator of the present invention, an anode electrode, and a cathode electrode is categorized as an alkaline water electrolysis cell of the present invention, which will be described later.
Examples of the alkaline water electrolysis device of the present invention that does not include an electrode but includes a catalyst include a device in which the catalyst is provided on only one side of the separator of the present invention, and a device in which the catalyst is provided 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 a cathode electrode but includes an anode electrode is a configuration in which the anode 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.
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.

[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.
An "alkaline water electrolysis cell" includes 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 include a catalyst.
For example, when the alkaline water electrolysis cell of the present invention includes 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 an anode electrode and a cathode electrode, in which case the anode electrode and the cathode electrode may each independently contain a catalyst.
Furthermore, when the alkaline water electrolysis cell of the present invention does not include electrodes but includes the separator of the present invention and a catalyst, the separator and a catalyst can be combined with an anode electrode and a cathode electrode to produce the alkaline water electrolysis cell of the present invention. In this case, the catalyst may be contained in the alkaline water electrolysis member of the present invention, or may be separately contained in the alkaline water electrolysis member of the present invention and combined with the separator, 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.
Furthermore, 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 separator and the anode electrode can be combined with the cathode electrode to form the alkaline water electrolysis cell of the present invention. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. Furthermore, the catalyst may be contained in the alkaline water electrolysis element of the present invention, or, similar to the cathode electrode, may be separately contained in the alkaline water electrolysis element of the present invention and combined with it.
Furthermore, when the alkaline water electrolysis cell of the present invention does not include an anode electrode but includes the separator of the present invention and a cathode electrode, the separator and the cathode electrode can be combined with the anode electrode to form the alkaline water electrolysis cell of the present invention. In this case, the anode electrode and the cathode electrode may each independently contain a catalyst. Furthermore, the catalyst may be contained in the alkaline water electrolysis member of the present invention, or, similar to the anode electrode, may be separately contained in the alkaline water electrolysis member of the present invention and combined with the alkaline water electrolysis member of the present invention.

[Alkaline water electrolysis device]
The alkaline water electrolysis apparatus 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 in the alkaline water electrolysis system above by supplementing necessary components, configurations, etc. depending on the configuration of the alkaline water electrolysis cell of the present invention.

[Hydrogen production method]
A preferred example of the method for producing hydrogen of the present invention is a method comprising operating the alkaline water electrolysis apparatus of the present invention described above at a pressure of 10 bar or more.
In the present invention, "operating at a pressure of 10 bar or more" means operating while controlling the pressure of the gas flow generated from each electrode chamber using a pressure control valve so that a pressure of 10 bar or more is applied to at least one of the cathode electrode chamber and the anode electrode chamber (or both). In an alkaline water electrolysis system, of electrolytic cells separated by a separator, the electrolytic cell containing the cathode electrode is referred to as the cathode electrode chamber, and the electrolytic cell containing the anode electrode is referred to as the anode electrode chamber.
The pressure applied to at least one of the cathode electrode chamber and the anode electrode chamber is preferably 10 to 500 bar, more preferably 20 to 300 bar, and even more preferably 30 to 100 bar. It is also preferable that the above pressure is applied to both the cathode electrode chamber and the anode electrode chamber.
The separator of the present invention included in the alkaline water electrolysis device of the present invention can be suitably applied to a pressurized alkaline water electrolysis system and can therefore be used in a hydrogen production method in which the alkaline water electrolysis device is operated at a pressure of 10 bar or more, enabling efficient hydrogen production.

Another preferred example of the hydrogen production method of the present invention includes adjusting the pressure control valve of the alkaline water electrolysis device of the present invention to operate the device under conditions in which the pressure on the hydrogen generation side is 1 bar or more higher than that on the oxygen generation side (operating the device under conditions in which the pressure difference obtained by subtracting the pressure on the oxygen generation side from the pressure on the hydrogen generation side is 1 bar or more). By operating the device under such conditions in which a pressure of 1 bar or more is applied from the hydrogen generation side to the oxygen generation side, the purity of the produced hydrogen can be increased.
The pressure difference obtained by subtracting the pressure on the hydrogen generation side (i.e., the pressure applied to the cathode electrode chamber) from the pressure on the oxygen generation side (i.e., the pressure applied to the anode electrode chamber) is preferably 1 to 10 bar, more preferably 2 to 10 bar, and even more preferably 2 to 8 bar.
The separator of the present invention included in the alkaline water electrolysis apparatus of the present invention can be suitably applied to pressurized alkaline water electrolysis systems and can therefore be used in a hydrogen production method in which a pressure of 5 bar or more is applied from the hydrogen generation side to the oxygen generation side of the alkaline water electrolysis apparatus, thereby enabling efficient production of hydrogen with higher purity. In this case, the pressure difference obtained by subtracting the pressure on the oxygen generation side from the pressure on the hydrogen generation side is preferably 5 to 10 bar, and more preferably 5 to 8 bar.

The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited thereby. The water used was deionized water. wt% means mass % and vol% means volume %. The thickness of the porous support is a value measured using the method described above.

[Fabrication of porous separator for alkaline water electrolysis]
Example 1
(1) The following materials were prepared:
Porous support: Polyphenylene sulfide woven fabric (manufactured by NBC meshtec) with a thickness of 300 μm and an opening ratio of 65%.
Hydrophilic inorganic particles: zirconium oxide particles with a median diameter (D50) of 0.70 μm.
Organic polymer: Polysulfone UDEL P1700 (storage modulus at 90°C: 900 MPa, Mw: 72000) manufactured by SOLVAY.
Additive: Glycerol, a pore expander sold by MOSSELMAN.
Solvent: N-butyl-pyrrolidone (NBP) available from Taminco.
(2) Preparation of Dope Solution A dope solution was prepared by mixing and stirring 50 wt % of hydrophilic inorganic particles, 10 wt % of organic polymer, 1 wt % of additive, and 39 wt % of solvent (inorganic particle concentration: 51 vol %).
(3) Fabrication of porous separator for alkaline water electrolysis Based on the separator fabrication method schematically shown in FIG. 2 of JP-A 2023-531792, a porous separator for alkaline water electrolysis was fabricated as follows.
The resulting dope solution was coated onto both sides of a 1.8 m wide porous support using a slot die coating technique at 3 m/min to a finished film thickness of 500 μm.
Next, the coated porous support was transported to a water bath (coagulation bath) maintained at 65°C, during which time it was subjected to a vapor-induced phase separation (VIPS) process in a closed area (a 7 cm distance from the coating to the water bath, a relative humidity of 98%, ventilation). Next, the porous support that had been subjected to the coating and VIPS process was immersed in a water bath at 65°C for 2 minutes to perform liquid-induced phase separation (LIPS). Further, an in-line washing process was performed in water at 70°C for 5 minutes to produce a porous separator for alkaline water electrolysis of Example 1.

Example 2
A porous separator for alkaline water electrolysis of Example 2 was prepared in the same manner as in Example 1, except that the organic polymer in Example 1 was changed to polyphenylsulfone ULTRASON P3010 (storage modulus at 90°C: 800 MPa, Mw: 55,000) manufactured by BASF.

Example 3
A porous separator for alkaline water electrolysis of Example 3 was prepared in the same manner as in Example 1, except that the porous support was changed to a polyphenylene sulfide woven fabric (manufactured by Kureha Corporation) with a thickness of 100 µm and an opening ratio of 50%, and the thickness of the porous separator for alkaline water electrolysis was changed to 200 µm.

Example 4
A porous separator for alkaline water electrolysis of Example 4 was prepared in the same manner as in Example 3, except that the contents of the materials in the dope solution were changed to 45 wt % for the hydrophilic inorganic particles, 15 wt % for the organic polymer, 1 wt % for the additive, and 39 wt % for the solvent (inorganic particle concentration: 39 vol%) and that the thickness of the separator was changed to 150 µm.

Example 5
The porous separator for alkaline water electrolysis of Example 5 was prepared in the same manner as in Example 6, except that the dope solution prepared in Example 1 was used instead of the membrane-forming solution and casting was performed so that the completed membrane thickness would be 200 µm.

Example 6
A membrane-forming solution was prepared by dissolving 15 wt % of polysulfone (manufactured by SOLVAY, trade name: UDEL P1700, storage modulus at 90°C: 900 MPa, Mw: 72,000) as an organic polymer, 15 wt % of polyvinylpyrrolidone (manufactured by Merck, trade name: PVP K-30) as a pore control agent, 1 wt % of lithium chloride as a pore control agent, 2 wt % of water, and 67 wt % of N-methyl-2-pyrrolidone (NMP).
The obtained membrane-forming solution was cast onto the surface of a PET (polyethylene terephthalate) film so that the finished film thickness would be 130 μm. Air adjusted to 25°C and a relative humidity of 80% was blown onto the surface of the cast liquid film at 2 m/s for 5 seconds. Thereafter, the film was immediately immersed in a water bath (coagulation bath) at 50°C, and the PET film was peeled off to obtain a porous membrane. The obtained porous membrane was immersed in a diethylene glycol bath at 80°C for 120 seconds and then thoroughly washed with pure water to produce a porous separator for alkaline water electrolysis of Example 6.

<Comparative Example 1>
Zirfon Perl UTP-500 (product name) manufactured by Agfa was used as the porous separator for alkaline water electrolysis in Comparative Example 1.
<Comparative Example 2>
A separator (S-1) described in Example 1 of JP-A No. 2023-531792 was prepared and used as a porous separator for alkaline water electrolysis in Comparative Example 2.
<Comparative Example 3>
A porous separator for alkaline water electrolysis of Comparative Example 3 was produced in the same manner as in Example 5, except that the thickness of the completed membrane was changed to 500 µm.
<Comparative Example 4>
A porous separator for alkaline water electrolysis of Comparative Example 4 was produced in the same manner as in Example 6, except that the thickness of the completed membrane was changed to 300 µm.

Each porous separator for alkaline water electrolysis (hereinafter also simply referred to as "separator") was subjected to the following measurements and evaluations. In each evaluation, the obtained porous separator for alkaline water electrolysis was rolled up without drying, and cut into a desired shape for the evaluations described below was used as is, unless otherwise specified.
The structure of each porous separator for alkaline water electrolysis is shown in Table 1-A, and the characteristics and evaluation results are shown in Tables 1-A and 1-B, respectively.

(Thickness unevenness)
A separator was immersed overnight in pure water at 25°C, and then cut into a 5 cm x 5 cm square. The separator was then immersed in a 7 mol/L KOH aqueous solution at 90°C and treated under a pressure of 5 MPa for 60 minutes to obtain a pressure-treated separator.
The pressure-treated separator was dried, and a cross section was cut out using a razor, and a cross-sectional SEM (scanning electron microscope) image was taken at a magnification (e.g., 400x) such that the separator cross section was captured in one field of view. In the obtained cross-sectional SEM image, the thickness was measured at intervals of 20 points, and the arithmetic mean, maximum value, and minimum value were calculated from the obtained 20 measurement values, and the thickness unevenness X was calculated using the following formula.

Thickness unevenness X = {(maximum value - minimum value) ÷ arithmetic mean value} x 100 (unit: %)

The arithmetic mean value of five thickness variations X obtained using five cross-sectional SEM images with different fields of view was defined as "thickness variation."

The following equipment was used for cross-sectional SEM observation.
Conductive treatment device: manufactured by Meiwafosis Co., Ltd., model number: HPC-1SW type Osmium coater / source Os / film thickness 5 nm
CIS device: JEOL Ltd., model number: IB-09060CIS/accelerating voltage 4 kV/processing temperature -130°C/pretreatment A sample cut out with a razor 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)

(Separator thickness)
In the measurement and calculation of the thickness unevenness described above, the obtained separator (not subjected to pressure treatment) was used instead of the pressure-treated separator, and the thickness was measured at intervals of 20 points, assuming that no pores were present in the obtained cross-sectional SEM image (assuming that the pores were filled with an organic polymer). The arithmetic mean value of the obtained 20 measurement values was taken as the thickness of the separator.

(Inorganic particle concentration)
The porous material was scraped off from the separator to remove the porous support, and about 10 mg of the components other than the porous support were packed into an alumina pan. Thermal analysis was performed using the temperature profile below, and the decomposed weight was determined as the weight of the organic material, and the remaining weight was determined as the weight of the inorganic material. The inorganic particle concentration was calculated using the densities of the organic and inorganic materials described in publicly known documents (for example, the density of zirconium oxide is 5.68 g cm ^-3 and the density of polysulfone is 1.24 g cm ^-3 ) using the following formula:
Volume of organic matter = weight of organic matter ÷ density Volume of inorganic matter = weight of inorganic matter ÷ density Inorganic particle concentration = {volume of inorganic matter ÷ (volume of inorganic matter + volume of organic matter)} x 100 (unit: %)

The following equipment was used for the thermal analysis measurements.
Device: Hitachi High-Tech, model number: TG-DTA STA7300
Measurement conditions: The temperature was raised from 30° C. (measurement start temperature) at a rate of 10° C./min up to 800° C. (measurement end temperature) in an air atmosphere.

(Storage modulus)
The porous material was scraped off from the separator, and the organic polymer in the porous material was dissolved in a good solvent for the organic polymer (for example, N-butyl-2-pyrrolidone for polysulfone). After removing the inorganic particles using a filter, the organic polymer was extracted by drying.
The storage modulus of the organic polymer taken out was measured at 90° C. using a cone-plate type rheometer.

The following device was used as a cone-plate type rheometer, and measurements were carried out under the following measurement conditions.
Apparatus: Model MCR301 manufactured by Anton Paar Measurement conditions: The temperature was raised from 30°C (measurement start temperature) at a rate of 10°C/min to 150°C (measurement end temperature) in a _N2 atmosphere.

(ionic resistance)
The separator was immersed in a 30% by mass aqueous solution of potassium hydroxide (manufactured by Kanto Chemical Co., Inc.) at room temperature (25° C.) overnight (20 hours), and then punched out into a circle with a diameter of 10 mm to prepare a measurement sample.
A 30% by mass aqueous potassium hydroxide solution 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 KCl aqueous solution at the voltage control terminal, and the cell was maintained at ⁹⁰ °C. The ionic resistance was measured in galvanostat mode at a current density of 10 mA/cm² to obtain a measurement blank value. Next, the measurement sample prepared above was sandwiched between two separators, and similarly filled with a 30% by mass aqueous potassium hydroxide solution, and the ionic resistance was measured under the same conditions. The difference between the resistance value of the obtained measurement sample and the blank value was taken as the ionic resistance value of the separator.

(Bubble Point)
Measurements were performed using a perm porometer (Porolux 1000, manufactured by Polometer) based on the bubble point test method described in ASMT (American Society for Testing and Materials) F316-86. Using perfluoropolyester (trade name "Galwick", surface tension 15.6 dyn/cm) as the immersion liquid, a completely wetted measuring separator was used to measure the applied pressure and air permeability in a pressure increase mode. The bubble point was determined as the pressure at which the first bubble appeared on the obtained wetting curve. Those for which no bubble generation was observed even at a pressure of 2 bar were represented in the tables as ">2 (unit: bar)." A bubble point of >2 bar can be said to satisfy the gas barrier properties required for porous separators for alkaline water electrolysis.

(Electrolyte permeability)
The separator was punched into a circle with a diameter of 47 mm. The resulting circular separator was set in a filter holder (product number XX4004700, manufactured by Merck). A 30% by mass aqueous potassium hydroxide solution (manufactured by Kanto Chemical Co., Inc.) was passed through the circular separator for 30 seconds under conditions of 90°C and a gauge pressure of 1 bar. The liquid volume (mL) was measured, and the water permeation rate (mL/(h ^m2 bar)) was calculated by converting the unit.

(Electrolytic cell evaluation)
The separator was sandwiched between two Ni foam electrodes (160 μm thick, 110 PPI (pore per inch)) manufactured by Goodfellow Corp., and the resulting electrode was sandwiched between two Ni bipolar plates having flow channels and secured with bolts. A 7.0 M potassium hydroxide (KOH) aqueous solution heated to 90°C was supplied to each of the cathode and anode sides of the water electrolysis cell obtained above at a flow rate of 10 mL/min, while a current of 0.1 A/ ^cm2 was applied for 4 hours to obtain a water electrolysis cell after initial energization.
Using the obtained water electrolysis cell after initial energization, an electric current of 0.8 A/cm ² was applied, and the pressure in the anode electrode chamber and the cathode electrode chamber was adjusted to desired values using the pressure regulating valve, and the electrolysis cell was evaluated.
Specifically, for the initial resistance (electrolysis voltage), a current of 0.8 A/ ^cm2 was applied to the resulting water electrolysis cell after initial energization, and the voltage at 1 bar (normal pressure) was recorded in the column "Voltage at 1 bar @ 0.8 A cm ^-2 " in the table, the voltage when a pressure of 50 bar was applied was recorded in the column "Voltage at 50 bar @ 0.8 A cm ^-2 " in the table, and the change in these voltages, obtained by subtracting "Voltage at 1 bar @ 0.8 A cm ^-2 " from "Voltage at 50 bar @ 0.8 A cm ^-2 ", was recorded in the column "Change in voltage between 1 bar and 50 bar."
Furthermore, with regard to the electrolysis voltage after operation, a current of 0.8 A/ ^cm2 was applied to the obtained water electrolysis cells after initial energization, and the voltage after operation at 1 bar (normal pressure) for 1000 hours was recorded in the column titled "Voltage increase after 1000-hour operation at 1 bar" in the table, and the voltage after operation at a pressure of 50 bar for 1000 hours was recorded in the column titled "Voltage increase after 1000-hour operation at 50 bar" in the table.
The phrase "a pressure of 50 bar was applied" means that a pressure of 50 bar was applied to both the cathode electrode chamber and the anode electrode chamber.

<Table notes>
PSU: Polysulfone PPSU: Polyphenylsulfone PPS: Polyphenylene sulfide The units are listed in brackets [ ] for each item.

The porous separators for alkaline water electrolysis of Comparative Examples 1 to 4 all had thickness unevenness, as defined in <Condition I>, of more than 15%, and therefore did not satisfy the requirements of the present invention. In the alkaline water electrolysis cells comprising the porous separators for alkaline water electrolysis of Comparative Examples 1 to 4, when a pressure of 50 bar was applied, the voltage increased by 0.11 to 0.15 V compared to when the pressure was 1 bar (atmospheric pressure), indicating that the initial resistance (electrolysis voltage) increased due to the application of pressure. Furthermore, when operated at 50 bar for 1,000 hours, the voltage increased by 0.21 to 0.30 V compared to the initial state before operation, indicating poor durability to operation under pressurized conditions.
In contrast, the porous separators for alkaline water electrolysis in Examples 1 to 6 all had thickness unevenness, as defined by <Condition I>, of 15% or less, and the increase in initial resistance (electrolysis voltage) due to pressurization from 1 bar to 50 bar was suppressed to 0.06 V or less. Moreover, even after operation at 50 bar for 1000 hours, the increase in voltage relative to the initial state before operation was suppressed to 0.15 V or less. Thus, it was found that when used as a separator in a pressurized alkaline water electrolysis cell, the porous separator for alkaline water electrolysis of the present invention can suppress the increase in initial resistance (electrolysis voltage) due to pressurization, and can also suppress the increase in electrolysis voltage over time due to operation under pressurized conditions.
Among them, when the porous support and the porous material containing an organic polymer and hydrophilic inorganic particles arranged on at least one of the outer surface and pores of the porous support are used, and the inorganic particle concentration of the porous material is 50% by volume or more, when the thickness of the separator is 210 μm or less, or when the storage modulus of the organic polymer at 90 ° C. is 850 MPa or more, the initial resistance (electrolysis voltage) is suppressed by pressure, and the increase in electrolysis voltage over time due to operation under pressure conditions is suppressed. (See Example 3 for Example 4, Example 3 for Example 1, and Example 1 for Example 2, respectively.) Furthermore, when the porous material is composed of an organic polymer and does not include a porous support, the initial resistance (electrolysis voltage) is suppressed by pressure, and the increase in electrolysis voltage over time due to operation under pressure conditions is suppressed. It was even more superior (see Examples 5 and 6 for Examples 1 to 4).

This application claims priority to Japanese Patent Application No. 2024-055616, filed on March 29, 2024, the contents of which are incorporated herein by reference as part of the present specification.

10 alkaline water electrolysis system 11 porous separator for alkaline water electrolysis 12 cathode electrode 13 anode electrode 14 highly concentrated alkaline aqueous solution 20 alkaline water electrolysis system 30 alkaline water electrolysis system 31 porous separator for alkaline water electrolysis 32 cathode catalyst layer 33 anode catalyst layer 34 gas diffusion layer 35 bipolar plate O ₂ oxygen bubbles H ₂ hydrogen bubbles OH ^- hydroxy ion e ^- electron

Claims (10)

A porous separator for alkaline water electrolysis, which satisfies the following <Condition I>:
<Condition I>
The porous separator for alkaline water electrolysis is immersed in a 7 mol/L aqueous KOH solution at 90°C and treated under a pressure of 5 MPa for 60 minutes, and the resulting separator has thickness variation of 15% or less. The porous separator for alkaline water electrolysis according to claim 1, comprising a porous support and a porous material containing an organic polymer and hydrophilic inorganic particles, the porous material being disposed on at least one of the outer surface and pores of the porous support, and the inorganic particle concentration of the porous material being 50% by volume or more. The porous separator for alkaline water electrolysis according to claim 1, which is composed of a porous support and a porous material containing an organic polymer and hydrophilic inorganic particles, which is disposed on at least one of the outer surface and pores of the porous support, and which has a thickness of 210 μm or less. The porous separator for alkaline water electrolysis according to claim 1, which is composed of a porous support and a porous material containing an organic polymer and hydrophilic inorganic particles, which is disposed on at least one of the outer surface and pores of the porous support, and wherein the storage modulus of the organic polymer at 90°C is 850 MPa or greater. The porous separator for alkaline water electrolysis according to claim 1, which is composed of a porous material containing an organic polymer and does not include a porous support. An alkaline water electrolysis component comprising the porous separator for alkaline water electrolysis according to claim 1. An alkaline water electrolysis cell comprising the porous separator for alkaline water electrolysis described in any one of claims 1 to 5, or the alkaline water electrolysis member described in claim 6. An alkaline water electrolysis device comprising the alkaline water electrolysis cell of claim 7. A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus described in claim 8 at a pressure of 10 bar or more. A method for producing hydrogen, comprising operating the alkaline water electrolysis apparatus described in claim 8 by applying a pressure of 5 bar or more from the hydrogen generation side to the oxygen generation side.