Diaphragm for alkaline water electrolysis, alkaline water electrolysis tank, and method for using porous film

Abstract

The purpose of the present invention is to provide a diaphragm for alkaline water electrolysis that realizes a diaphragm which, even when used as a diaphragm for alkaline water electrolysis for a long time, can maintain high ion permeability and high gas barrier property and enables stable water electrolysis. This diaphragm for alkaline water electrolysis is characterized by comprising a porous film containing a polyolefin, wherein the peel strength in the film thickness direction of the porous film is 2.0 N or more.

Description

Diaphragm for alkaline water electrolysis, alkaline water electrolytic cell and method of using porous membrane

[0001] The present disclosure relates to a diaphragm for alkaline water electrolysis, an alkaline water electrolytic cell, and a method for using the porous membrane.

[0002] In recent years, CO ２ Hydrogen produced using renewable energy is attracting attention as a clean energy source that can solve problems such as global warming caused by CO2 and dwindling fossil fuel reserves. Hydrogen production using renewable energy requires low costs comparable to those of conventional hydrogen production by reforming fossil fuels. Therefore, hydrogen production using renewable energy requires high levels of energy efficiency and inexpensive equipment that could not be achieved with conventional technologies.

[0003] One of the industrial methods for producing hydrogen is water electrolysis. This method has the advantage of producing hydrogen with higher purity than hydrogen production methods that involve reforming fossil fuels. In water electrolysis, an aqueous solution containing an electrolyte such as sodium hydroxide or potassium hydroxide is generally used as the electrolyte to increase conductivity. Water is electrolyzed by applying a direct current to this electrolyte between the cathode and anode.

[0004] Among these, alkaline water electrolysis can be carried out on a large scale and is inexpensive compared to other water electrolysis devices, and therefore has already been proven in commercial plants. Therefore, the development of a large-scale hydrogen production device using alkaline water electrolysis is expected. For example, several concepts have been proposed for producing large amounts of hydrogen by electrolysis of alkaline water using power generated by natural energy such as wind power or solar power, and then transporting and supplying the hydrogen to consumption areas.

[0005] An electrolytic cell for performing electrolysis (hereinafter sometimes referred to as "electrolysis") is divided into an anode chamber and a cathode chamber via a diaphragm, and oxygen gas is produced in the anode chamber, while hydrogen gas is produced in the cathode chamber. The diaphragm is required to have gas barrier properties to prevent mixing of the oxygen gas and hydrogen gas. Furthermore, in water electrolysis, the medium that carries electricity (electrons) is ions, and therefore, to perform electrolysis efficiently, the diaphragm is required to have high ion permeability. From this perspective, a diaphragm having a porous structure (hereinafter sometimes referred to as "porous membrane") has been proposed as a diaphragm that has gas barrier properties and ion permeability.

[0006] In addition, in order to efficiently perform electrolysis, it is desirable to reduce the electrical resistance of the solution between the anode, cathode, and diaphragm, and it is considered preferable to have a structure in which the diaphragm is sandwiched between both electrodes (hereinafter, sometimes referred to as a "zero gap structure").

[0007] As technologies relating to such diaphragms, Patent Documents 1 and 2 disclose diaphragms for alkaline water electrolysis, which are porous membranes formed by mixing zirconium oxide or magnesium oxide into polysulfone, an aromatic polymer resin, and by a non-solvent-induced phase separation method.

[0008] International Publication No. WO 93 / 15529 French Patent Application Publication No. 2546535 International Publication No. 2018-182006 International Publication No. 2014-119207 International Publication No. 2014-119208

[0009] However, the above-mentioned techniques still have room for improvement. For example, polyethersulfone and polysulfone, which are commonly used as diaphragms, contain ether groups in their repeating units and are therefore gradually hydrolyzed in acidic or alkaline environments. As the hydrolysis progresses, the membrane structure changes, which can lead to a decrease in the membrane's functionality and mechanical strength. In particular, the hydrolysis rate increases in high-temperature, high-concentration acidic or alkaline environments, making this problem even more pronounced.

[0010] On the other hand, the ion permeation efficiency is expressed by the electrical conductivity, which is closely related to the concentration and temperature of the electrolyte. For example, in a high temperature range of 80°C or higher, the electrical conductivity of an aqueous potassium hydroxide solution reaches a maximum at a concentration of approximately 30 mass%. Therefore, using a diaphragm under high electrical conductivity conditions in order to improve ion permeability may exacerbate the problem of the hydrolysis rate.

[0011] In addition, controlling the porous structure of a diaphragm is extremely important in optimizing the ion permeability of the diaphragm. In particular, when used as a diaphragm for water electrolysis, high ion permeability and high gas barrier properties must be compatible. Therefore, an optimal diaphragm made of a material with high hydrolysis resistance and capable of achieving high electrolysis efficiency is required. Furthermore, in order to perform electrolysis continuously and efficiently, it is considered necessary to impart sufficient wettability to the electrolyte to the diaphragm. For this reason, as disclosed in Patent Documents 3, 4, and 5, hydrophilization treatments have been performed, such as introducing hydrophilic substances such as inorganic oxides into the pores or introducing hydrophilic resins or hydrophilic groups into the pore surfaces. However, introducing such substances into the pores causes considerable clogging of the pore structure, resulting in a problem of reduced ion permeability.

[0012] Meanwhile, polyethylene (hereinafter, sometimes referred to as "PE"), a polyolefin resin, is widely used as a highly chemical-resistant material and is known to have extremely high resistance even in alkaline environments. PE porous membranes made from PE maintain the properties of PE and are therefore used in applications such as filters in environments where mechanical strength and chemical resistance are required.

[0013] A PE porous membrane can be produced, for example, by the method described in Japanese Patent No. 6,596,329, i.e., by extruding, rolling, stretching, or the like of a PE powder and a pore-forming material, and it is known that porous membranes with various controlled pore structures and physical properties can be produced, and this method has the potential to realize a pore structure that can achieve both high ion permeability and high gas barrier properties. The present inventors investigated the use of a porous membrane containing polyolefin as a diaphragm for alkaline water electrolysis and found a new problem in that the diaphragm may be deformed or broken in the early stages of operation, making it impossible to maintain high ion permeability and high gas barrier properties for an extended period of time.

[0014] An object of the present invention is to provide a diaphragm for alkaline water electrolysis that maintains high ion permeability and high gas barrier properties even after long-term use, and enables stable water electrolysis.

[0015] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by, for example, using a diaphragm for alkaline water electrolysis including a porous membrane containing a polyolefin and having a peel strength of 2.0 N or more in the membrane thickness direction, thereby maintaining high ion permeability and high gas barrier properties and enabling stable long-term water electrolysis, and have completed the present invention.

[0016] That is, the present disclosure is as follows. [1] A diaphragm for alkaline water electrolysis, comprising a porous membrane containing a polyolefin, the porous membrane having a peel strength of 2.0 N or more in the thickness direction. [2] The diaphragm for alkaline water electrolysis according to [1], wherein the porous membrane comprises the polyolefin as a main component. [3] The diaphragm for alkaline water electrolysis according to [1], wherein the porous membrane comprises 90 mass% or more of the polyolefin. [4] The diaphragm for alkaline water electrolysis according to any of [1] to [3], wherein the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more. [5] The diaphragm for alkaline water electrolysis according to any of [1] to [4], wherein the porous membrane has a peel strength of 3.0 N or more in the thickness direction. [6] The diaphragm for alkaline water electrolysis according to any of [1] to [5], wherein the porous membrane has a thickness of 25 μm or more and 500 μm or less. [7] The diaphragm for alkaline water electrolysis according to any of [1] to [6], wherein the porous membrane has a porosity of 30% or more and 80% or less. [8] The diaphragm for alkaline water electrolysis according to any one of [1] to [7], wherein the air permeability of the porous membrane is 10 seconds or more and 2,000 seconds or less, calculated on a 100 μm basis. [9] The diaphragm for alkaline water electrolysis according to any one of [1] to [8], wherein the pin puncture strength of the porous membrane is 200 gf or more and 10,000 gf or less.

[10] An alkaline water electrolytic cell comprising: the diaphragm for alkaline water electrolysis according to any one of [1] to [9]; an anode; and a cathode, wherein the diaphragm for alkaline water electrolysis is disposed between the anode and the cathode.

[11] A method of use, wherein a porous membrane comprising a polyolefin and having a peel strength of 2.0 N or more in the membrane thickness direction is used as a diaphragm for alkaline water electrolysis.

[12] The method of use according to

[11] , wherein the porous membrane comprises the polyolefin as a main component.

[13] The method of use according to

[11] , wherein the porous membrane comprises the polyolefin in 90 mass% or more.

[14] The method for use according to any one of

[11] to

[13] , wherein the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more.

[15] The method for use according to any one of

[11] to

[14] , wherein the porous membrane has a peel strength of 3.0 N or more in the thickness direction.

[16] The method for use according to any one of

[11] to

[15] , wherein the porous membrane has a thickness of 25 μm or more and 500 μm or less.

[17] The method for use according to any one of

[11] to

[16] , wherein the porosity of the porous membrane is 30% or more and 80% or less.

[18] The method for use according to any one of

[11] to

[17] , wherein the air permeability of the porous membrane is 10 seconds or more and 2000 seconds or less in terms of 100 μm conversion.

[19] The method for use according to any one of

[11] to

[18] , wherein the pin puncture strength of the porous membrane is 200 gf or more and 10,000 gf or less.

[0017] The present disclosure makes it possible to provide a diaphragm for alkaline water electrolysis that maintains high ion permeability and high gas barrier properties and is capable of stably electrolyzing water for a long period of time.

[0018] Fig. 1 is a side view showing the entirety of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. Fig. 2 is a side view showing the zero-gap structure of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, focusing on the part enclosed by a dashed square frame. Fig. 3 is a plan view showing an electrode chamber part of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. Fig. 4 is a diagram showing an outline of an alkaline water electrolysis device including an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. Fig. 5 is an explanatory diagram of a test piece for measuring the peel strength in the film thickness direction of a porous membrane according to the present embodiment.

[0019] Hereinafter, an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described in detail. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0020] The diaphragm for alkaline water electrolysis according to the present embodiment is characterized by comprising a porous membrane containing polyolefin and having a peel strength in the membrane thickness direction of 2.0 N or more. The diaphragm for alkaline water electrolysis comprises at least the porous membrane according to the present embodiment and may further comprise other members such as a support. In particular, the diaphragm for alkaline water electrolysis preferably consists solely of the porous membrane. In this specification, the diaphragm for alkaline water electrolysis may also be referred to simply as the "diaphragm".

[0021] In an electrolytic cell, the diaphragm is disposed between the anode and the cathode and serves to allow an ion-containing electrolyte to pass through while blocking gas generated at both electrodes. The diaphragm for alkaline water electrolysis of the present embodiment is preferably formed from a resin composition containing the polyolefin. The resin composition may further contain other components such as additives described below in addition to the polyolefin. In particular, the resin composition is preferably a resin composition whose only resin component is polyolefin, and more preferably a resin composition consisting solely of polyolefin.

[0022] The porous membrane preferably contains a polyolefin as a main component, and the mass proportion of the polyolefin relative to 100 mass% of the porous membrane is more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 99 mass% or more. The porous membrane may consist solely of a polyolefin. The resin component contained in the porous membrane preferably contains a polyolefin as a main component, and the mass proportion of the polyolefin relative to 100 mass% of the resin component is more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 99 mass% or more. The resin component may consist solely of a polyolefin. The diaphragm for alkaline water electrolysis of this embodiment comprises a porous membrane containing a polyolefin. The polyolefin used in this embodiment is not particularly limited and examples include polymers (e.g., homopolymers, copolymers, multistage polymers) obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, among others. Polyethylene is preferred. These polymers can be used alone or in combination of two or more.

[0023] Furthermore, examples of the polyolefin include low-density PE (density 0.910 g / cm ３ 0.930g / cm or more ３ less than 0.910 g / cm ３ 0.940g / cm or more ３ less than 0.930 g / cm ３0.942g / cm or more ３ less than 0.942 g / cm ３ Examples of suitable polyolefins include polypropylene (PP) and polybutene (PP), isotactic PP, atactic PP, and polybutene. These may be used alone or in combination. Among these, using PE alone is preferred from the viewpoint of obtaining a membrane with uniform physical properties. From the viewpoint of enhancing resistance to decomposition under high-temperature conditions in a concentrated alkaline aqueous solution, the polyolefin preferably contains PE resin as the main component, preferably 70% by mass or more of PE, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 99% by mass or more. In this specification, "containing" a specific component as the main component means that the content of the specific component is 50% by mass or more. The proportion of the resin contained in the porous membrane can be measured, for example, by measuring the weight change using a thermogravimetric analyzer or by combining a pyrolysis GC-MS and a thermogravimetric analyzer.

[0024] The viscosity average molecular weight of the polyolefin is preferably 900,000 or more, more preferably 2,000,000 or more, and even more preferably 4,000,000 or more, from the viewpoint of achieving both ion permeability and the mechanical strength of the membrane. Furthermore, from the viewpoint of film-forming properties, it is preferably 10,000,000 or less, more preferably 7,500,000 or less. As for PE, from the viewpoint of achieving both ion permeability and the mechanical strength of the membrane, it is preferable to use PE having a viscosity average molecular weight of 900,000 or more, more preferably PE having a viscosity average molecular weight of 2,000,000 or more, and even more preferably PE having a viscosity average molecular weight of 4,000,000 or more. On the other hand, from the viewpoint of film-forming properties, it is preferable to use PE having a viscosity average molecular weight of 10,000,000 or less, and more preferably PE having a viscosity average molecular weight of 7,500,000 or less. Setting the viscosity average molecular weight to 900,000 or more is preferable from the viewpoint of maintaining high melt tension during melt molding to ensure good moldability, or from the viewpoint of imparting sufficient entanglement to the resin to increase the mechanical strength of the porous membrane. On the other hand, a viscosity average molecular weight of 10 million or less is preferable from the viewpoint of realizing uniform melt-kneading and improving sheet formability, particularly thickness formability. Furthermore, a viscosity average molecular weight of 7.5 million or less is preferable from the viewpoint of further improving thickness formability. The viscosity average molecular weight Mv of PE can be calculated by determining the intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent based on ASTM-D4020 and using the following formula: [η] = 6.77 × 10 -４ Mv ０．６７ The viscosity average molecular weight of PP can be calculated by the following formula: [η] = 1.10 × 10 -４ Mv ０．８

[0025] In addition, various known additives such as phenolic, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments may be mixed into the resin composition containing the resin, as needed.

[0026] The diaphragm for alkaline water electrolysis according to this embodiment is characterized by comprising a porous membrane containing a polyolefin, the porous membrane having a peel strength in the thickness direction of 2.0 N or more. The present inventors have found that a porous membrane containing a polyolefin and having a peel strength in the thickness direction of 2.0 N or more can maintain a low cell voltage and high gas barrier property and perform stable water electrolysis even when used as a diaphragm for alkaline water electrolysis for a long period of time, and have completed the present invention. During alkaline water electrolysis, ions and the electrolyte move within the diaphragm as the water electrolysis reaction progresses. It is believed that the pressure caused by this mass transfer causes deformation or destruction of the diaphragm. In order to suppress deformation of the diaphragm and obtain a diaphragm that can maintain a low cell voltage and high gas barrier property for a long period of time, it is important to increase the peel strength in the thickness direction of the porous membrane. The peel strength in the thickness direction is preferably 2.0 N or more, more preferably 2.5 N or more, and even more preferably 3.0 N or more. Although the reason for this is not clear, if the peel strength in the thickness direction is 2.0 N or more, the diaphragm is less likely to deform even when pressure is applied to the diaphragm due to mass transfer during water electrolysis, and a low cell voltage and high gas barrier property can be maintained for a long period of time. On the other hand, if the peel strength in the thickness direction is less than 2.0 N, the diaphragm will deform or break in a short period of time, leading to an increase in cell voltage and a decrease in gas barrier property, making it difficult to continue water electrolysis. Furthermore, the peel strength in the thickness direction is preferably less than 20.0 N, and more preferably less than 15.0 N. If the peel strength in the thickness direction is less than 20.0 N, the balance between the peel strength in the thickness direction and the puncture strength is good, and the membrane can be used for water electrolysis stably for a long period of time.

[0027] The method for producing a polyolefin porous membrane having a peel strength of 2.0 N or more in the film thickness direction is not particularly limited, but the product of the MD stretching ratio and the TD stretching ratio in the primary stretching step (d) described below is preferably less than 100, more preferably less than 64, and even more preferably less than 36. When the product of the MD stretching ratio and the TD stretching ratio is 100 or more, the crystal orientation in the in-plane direction perpendicular to the film thickness direction proceeds, and the peel strength in the film thickness direction decreases. Furthermore, the product of the MD stretching ratio and the TD stretching ratio is preferably 4 or more, more preferably 9 or more, and even more preferably 16 or more. When the product of the MD stretching ratio and the TD stretching ratio is 4 or more, the balance between the peel strength in the film thickness direction and the pin puncture strength is good, and the porous membrane has high durability.

[0028] The diaphragm for alkaline water electrolysis according to this embodiment may be used after the pores of the porous membrane are filled with a solvent such as water. The method for filling the pores of the porous membrane with a solvent such as water is not particularly limited. A preferred method involves impregnating the porous membrane with a hydrophilic solvent to fill the pores with the hydrophilic solvent, and then impregnating the porous membrane with a solvent such as water to replace the hydrophilic solvent in the pores with the solvent such as water, thereby filling the pores with the solvent such as water. A hydrophilic solvent with a high surface tension makes it difficult to sufficiently fill the pores of the resin with the solvent. Therefore, it is more preferable to use a hydrophilic solvent with a surface tension of 34 mN / m or less. Examples of the hydrophilic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and butanol, as well as acetone and acetonitrile. Alternatively, a method in which the hydrophilic solvent is used not alone but as an aqueous solution mixed with water is also preferred. The hydrophilic solvent preferably contains one or more solvents selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone, and acetonitrile. The hydrophilic solvent is preferably an aqueous solution containing 30% by mass or more of one or more solvents selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone, and acetonitrile. In this case, an aqueous solution having a surface tension of 34 mN / m or less is preferably used. For example, a 30% by mass aqueous solution of ethanol (surface tension: 33 mN / m) or a 50% by mass aqueous solution of ethanol (surface tension: 28 mN / m) can be used. The hydrophilic solvent is not particularly limited, but is preferably an organic solvent having a solubility in water of 50 g / L or more at 20°C. The solubility of the organic solvent in water is more preferably 100 g / L or more, and even more preferably 200 g / L or more, from the viewpoint of rapid substitution with water.

[0029] The diaphragm for alkaline water electrolysis of the present embodiment can perform continuous water electrolysis for long periods of time at a low cell voltage without substantially damaging the original porous structure, as long as the pores of the porous membrane are pre-filled with a solvent at a certain volume fraction or more, even without any special hydrophilization treatment. Although not particularly limited, for example, pre-filling 40% or more of the pores of the porous membrane with a solvent such as water is preferable because, even if ions or the electrolyte move as the water electrolysis reaction progresses, a continuous layer of the electrolyte in the pores is maintained without interruption, allowing for more continuous water electrolysis. In particular, a porous membrane having a porous structure with high ion permeability is considered to enable water electrolysis at a low cell voltage. From the viewpoint of high ion permeability, it is more preferable to pre-fill 54% or more of the pores of the porous membrane with a solvent (e.g., water), even more preferably to pre-fill 68% or more of the pores with a solvent (e.g., water), and even more preferably to pre-fill 88% or more of the pores with a solvent (e.g., water).

[0030] The proportion of the solvent (e.g., water) filling the pores of the porous membrane can be adjusted by appropriately adjusting the time for impregnating the porous membrane with the hydrophilic solvent or the time for impregnating the porous membrane with water. In some cases, the proportion of the solvent filling the pores may be adjusted by impregnating the porous membrane with a solvent (e.g., water) and then drying the porous membrane. Examples of the solvent filling the pores of the porous membrane include water; the hydrophilic solvent (preferably a hydrophilic solvent having a surface tension of 34 mN / m or less); alkaline aqueous solutions such as NaOH aqueous solution and KOH aqueous solution (e.g., alkaline aqueous solutions having an alkali salt concentration of more than 0 mass% and less than 40 mass% (preferably more than 0 mass% and less than 35 mass%)); and combinations thereof. Among these, hydrophilic solvents and water are preferred from the viewpoint of facilitating replacement with an electrolyte during alkaline water electrolysis and further extending the period during which continuous electrolysis is possible. Furthermore, hydrophilic solvents (more preferably hydrophilic solvents having a surface tension of 34 mN / m or less) are preferred, and water is also preferred.

[0031] The porous membrane may contain an inorganic compound to exhibit high ion permeability and high gas barrier property. Here, the inorganic compound is preferably one that does not dissolve or decompose in an alkaline environment. In addition, the inorganic compound may be attached to the surface of the porous membrane, or may be partially or entirely embedded in the resin that constitutes the porous membrane.

[0032] Examples of the inorganic compound include at least one inorganic substance selected from the group consisting of oxides or hydroxides of zirconium, titanium, bismuth, and cerium; oxides of Group IV elements of the periodic table; hydroxides of Group IV elements of the periodic table; nitrides of Group IV elements of the periodic table; and carbides of Group IV elements of the periodic table. Among these, from the viewpoint of chemical stability, oxides of zirconium, titanium, bismuth, and cerium, and oxides or hydroxides of Group IV elements of the periodic table are preferred, and zirconium oxide (ZrO ２ ), zirconium hydroxide (Zr(OH) ４ ), titanium oxide (TiO ２ ), titanium hydroxide (Ti(OH) ４ ) is more preferred. These may be used alone or in combination of two or more. As the electrolyte for alkaline water electrolysis, alkaline aqueous solutions such as aqueous NaOH solutions and aqueous KOH solutions are often used. When titanium oxide is exposed to such an environment, it may change into titanates such as sodium titanate and potassium titanate. Therefore, titanates may be used in advance.

[0033] The size of the inorganic compound is not particularly limited, but in the case of a particulate substance, the average primary particle size is preferably 10 nm or more and 300 nm or less, and more preferably 25 nm or more and 250 nm or less. The average primary particle size of the particulate inorganic compound in the porous membrane (hereinafter sometimes referred to as "inorganic particles") can be determined by the following method. The measurement sample is observed with a scanning electron microscope (SEM) from the direction perpendicular to the porous membrane surface, and an image is taken at a magnification at which the particulate inorganic compound can be observed. The image is binarized using image analysis software (ImageJ), and the absolute maximum length is measured for each of 10 non-aggregated points of the particulate inorganic compound, and the number average is determined. Note that if the particulate inorganic compound is present only inside the porous membrane and not on the surface, the cut cross section can be observed with an SEM.

[0034] The diaphragm for alkaline water electrolysis of the present embodiment may have a layered structure including other layers in addition to the porous membrane.

[0035] The diaphragm for alkaline water electrolysis of this embodiment may include a support. The support may be porous or may not have pores as long as it has ion permeability. Among these, a porous support is preferred from the viewpoint of not substantially reducing ion permeability. The porous support mainly serves as a core material in the diaphragm for alkaline water electrolysis and improves the mechanical strength of the diaphragm. The porous support preferably does not substantially reduce ion permeability. The material of the porous support is not particularly limited, and examples include polyphenylene sulfide, polyethylene, polypropylene, fluorine-based resin, polyparaphenylene benzobisoxazole, polyketone, polyimide, and polyetherimide. These may be used alone, or two or more types may be used simultaneously. The porous support may have a shape such as a sheet. Examples of the porous support include a membrane-like porous body, a nonwoven fabric, a woven fabric, and a composite fabric containing a nonwoven fabric and a woven fabric embedded in the nonwoven fabric. These may be used alone, or two or more types may be used simultaneously. On the other hand, from the viewpoint of ion permeability, the diaphragm for alkaline water electrolysis of the present embodiment preferably does not have a porous support, and more preferably does not have a support. When the diaphragm does not have a support, the area that can contribute to ion permeability increases by the volume of the support, and water electrolysis with high ion permeability and low cell voltage may be achieved.

[0036] <Method of using porous membrane> The method of using the porous membrane is a method of using a porous membrane containing a polyolefin and having a peel strength in the membrane thickness direction of 2.0 N or more as a diaphragm for alkaline water electrolysis. The porous membrane used in the method of use is preferably the porous membrane described in this specification. The diaphragm for alkaline water electrolysis preferably does not contain a porous support. The porous membrane is preferably a porous membrane containing a polyolefin as a main component, and more preferably a porous membrane consisting of only a polyolefin. The porous membrane contains polyolefin (preferably as a main component, and the mass ratio of polyolefin to 100% by mass of the porous membrane is more preferably 70% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 99% by mass or more, and the porous membrane may consist of only polyolefin), the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more (may be 2,000,000 or more and 10,000,000 or less, or 4,000,000 or more and 7,500,000 or less), and the peel strength in the thickness direction is 2.0 N or more (2.5 N or more and less than 20.0 N, or 3.0 N or more and less than 15.0 N), It is preferable that the film thickness is 25 μm or more and 500 μm or less (which may be 50 μm or more and 400 μm or less, 80 μm or more and 300 μm or less, or 100 μm or more and 250 μm or less), the porosity is 30% or more and 80% or less (which may be 40% or more and 70% or less, or 45% or more and 65% or less), the air permeability per 100 μm is 10 seconds or more and 2000 seconds or less (which may be 50 seconds or more and 1500 seconds or less, or 100 seconds or more and 1000 seconds or less), and the pin puncture strength is 200 gf or more and 10,000 gf or less (which may be 500 gf or more and 8,000 gf or less, or 800 gf or more and 6,000 gf or less).

[0037] <Method for producing diaphragm for alkaline water electrolysis> The diaphragm for alkaline water electrolysis of the present embodiment can be produced by any known method without any particular limitation, but preferably includes the following steps. The order of these steps is not limited and can be selected as appropriate.

[0038] Hereinafter, as an example, a method for producing a porous film containing polyolefin will be mentioned, but the method is not limited thereto, and the production method can be variously changed, for example, it can be produced by a known dry film-forming method, a melt film-forming method, a wet film-forming method, etc.

[0039] [Method for producing a porous film containing polyolefin] The method for producing a porous film containing polyolefin (sometimes referred to as "polyolefin porous film" in this specification) is not particularly limited. For example, a method including: a mixing step (a) of mixing a resin composition containing polyolefin and a pore-forming material; an extrusion step (b) of melt-kneading and extruding the mixture obtained in the step (a); a sheet-forming step (c) of forming the extrudate obtained in the step (b) into a sheet; a primary stretching step (d) of stretching the sheet-shaped product obtained in the step (c) at least once in at least one axial direction; an extraction step (e) of extracting the pore-forming material from the stretched film obtained in the step (d); and a heat-setting step (f) of heat-setting the extracted film obtained in the step (e) at a predetermined temperature. In addition, in the above method, a secondary stretching step (g) may be performed after the extraction step (e) before the heat-setting step (f). The sheet forming step (c) may be immediately followed by the extraction step (e), followed by the primary stretching step (d) and the heat setting step (f).

[0040] The above-mentioned method for producing a polyolefin porous membrane can provide a polyolefin porous membrane that exhibits excellent performance in a high-temperature, high-concentration alkaline environment when used as a diaphragm for an alkaline water electrolytic cell or other electrochemical device. Among these, the method of stretching in MD and TD in the first stretching step (d), followed by heat setting in TD in the heat setting step (f) after the extraction step (e) tends to produce a membrane capable of water electrolysis at a low cell voltage. Note that MD refers to the machine direction of continuous molding, and TD refers to the direction perpendicular to MD. Other examples include a method (so-called dry method) in which a polyolefin alone or a mixture of a polyolefin and a crystal nucleating agent is melt-kneaded and extruded, and then uniaxially stretched and oriented at a high draw ratio immediately after extrusion, followed by heat treatment and stretching to produce a porous membrane. Note that the method for producing the porous membrane is not limited to the above-mentioned method, and various modifications are possible within the scope of the invention.

[0041] [Mixing step (a)] The mixing step (a) is a step of mixing a resin composition containing a polyolefin and a pore-forming material. In the mixing step (a), other components may be mixed as necessary.

[0042] The pore-forming material may be any material as long as it is distinguishable from the polyolefin and inorganic particle materials. Examples of the pore-forming material include non-volatile solvents capable of forming a homogeneous solution at or above the melting point of the polyolefin, such as hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate, dibutyl phthalate, and diisononyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. These pore-forming materials may be recovered and reused by operations such as distillation after extraction. Among the pore-forming materials, liquid paraffin is preferred because, when the polyolefin is PE or polypropylene, it has high compatibility with these, so that even when the molten kneaded product is stretched, interfacial peeling between the resin and the pore-forming material is unlikely to occur, making it easier to perform uniform stretching.

[0043] In step (a), the resin composition containing polyolefin may contain any additive. The additive is not particularly limited, but examples thereof include polymers other than polyolefin; antioxidants such as phenolic compounds, phosphorus compounds, and sulfur compounds; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; coloring pigments; etc. The total amount of these additives added is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of polyolefin.

[0044] The mixing method in step (a) is not particularly limited, but examples thereof include a method in which some or all of the raw materials are premixed as necessary using a Henschel mixer, ribbon blender, tumbler blender, etc. Among these, a method in which mixing is performed using a Henschel mixer is preferred.

[0045] Alternatively, the step (a) may be omitted and each raw material may be fed separately to the next step (b). For example, the polyolefin and the porous material may be fed separately to the twin-screw extruder from separate feeders or liquid addition pumps, or a mixture may be prepared from the polyolefin and any additives, and this mixture and other components may be fed to the twin-screw extruder from separate feeders.

[0046] [Extrusion step (b)] The extrusion step (b) is a step of melt-kneading and extruding the resin composition containing the polyolefin and the pore-forming material. In the extrusion step (b), other components may be mixed with the resin composition as needed.

[0047] The method of melt-kneading in step (b) is not particularly limited, and examples thereof include a method in which all raw materials including the mixture mixed in step (a) are melt-kneaded using a screw extruder such as a single-screw extruder or a twin-screw extruder, a kneader, a mixer, etc. Among these, it is preferable to perform the melt-kneading using the screws of a twin-screw extruder.

[0048] The mass fraction of polyolefin in the resin composition consisting of polyolefin and pore-forming material is preferably 12% by mass or more and less than 40% by mass, more preferably 15% by mass or more and less than 35% by mass, and even more preferably 18% by mass or more and less than 33% by mass. When the mass fraction is less than 40% by mass, the energy during kneading does not increase too much, and the molecular weight reduction due to excessive entanglement between polymers can be suppressed, so the properties of the polyolefin porous film are not impaired. On the other hand, when the mass fraction of polyolefin is 12% by mass or more, sufficient energy can be applied during melt kneading, and the polymers are entangled uniformly, so even when the mixture of polyolefin and pore-forming material is stretched at a high ratio, the polyolefin molecular chains do not become entangled, and it is easy to form a uniform and fine pore structure, and the mechanical strength is also easy to increase.

[0049] Furthermore, when melt-kneading, the pore-forming material may be added in its entirety at once using a liquid addition pump, or may be added in portions at multiple locations using multiple liquid addition pumps. When adding the additive in portions multiple times, it is preferable to adjust the amount added in the first portion to 80 mass % or less of the total amount added, from the viewpoint of suppressing aggregation of the polyolefin and inorganic particles and dispersing them uniformly.

[0050] As described above, uniform dispersion of polyolefin or inorganic particles improves the viscosity of the polyolefin-containing porous membrane near its melting point, making pore clogging less likely to occur, leading to a lower cell voltage during alkaline water electrolysis and improved output characteristics, etc. Furthermore, uniform dispersion of polyolefin or inorganic particles reduces variation in membrane properties. This makes it possible to suppress performance variations within a cell even in a diaphragm with a large area, and also makes it possible to suppress performance variations among individual cells when electrolysis is performed by combining multiple cells to form a stack, which is preferable from the viewpoint of improving the uniformity of cell performance.

[0051] When a pore-forming material is used in step (b), the temperature of the melt-kneading section is preferably 250° C. or lower, more preferably 230° C. or lower, and even more preferably 210° C. or lower, from the viewpoint of dispersibility of polyolefins and suppression of molecular weight reduction. The lower limit of the temperature of the melt-kneading section is preferably equal to or higher than the melting point of the polyolefin used, from the viewpoint of uniformly dissolving the polyolefin in the pore-forming material.

[0052] In this embodiment, although not particularly limited, it is preferable to mix the raw polyolefin with an antioxidant at a predetermined concentration, then replace the atmosphere around the mixture with a nitrogen atmosphere, and perform melt-kneading while maintaining the nitrogen atmosphere. The temperature during melt-kneading is preferably 160°C or higher, more preferably 180°C or higher, and preferably lower than 300°C.

[0053] In step (b), the kneaded product obtained through the above kneading is extruded using an extruder such as a T-die, a circular die, or a slit nozzle. The conditions for extrusion are not particularly limited, and known methods can be used, for example. When a T-die is used to obtain the extrudate, from the viewpoint of easy control of the thickness of the diaphragm of the final product, the die slit gap is preferably 1.2 to 7 mm, more preferably 1.5 to 6 mm, and even more preferably 2 to 5 mm, and the extrusion is preferably heated to 150 to 250°C.

[0054] In step (b), moisture and volatile components contained in the raw materials may be mixed into the molten mixture during melt-kneading and adversely affect the mixture extruded from the extruder. Therefore, it is preferable to provide the extruder with a degassing vent and a vacuum pump to remove moisture and volatile components vaporized during melt-kneading.

[0055] [Sheet molding step (c)] The sheet molding step (c) is a step of molding the extrudate obtained in the extrusion step (b) into a sheet. The sheet-shaped molded product obtained by the sheet molding step (c) may be a single layer or a laminate, but is preferably a single layer. The sheet molding method is not particularly limited, but for example, a method of solidifying the extrudate by compression cooling is mentioned. The compression cooling method is not particularly limited, but for example, a method of directly contacting the extrudate with a cooling medium such as cold air or cooling water; a method of contacting the extrudate with a metal roll, a press, etc. cooled with a refrigerant, etc. Among these, the method of contacting the extrudate with a metal roll, a press, etc. cooled with a refrigerant is preferred in terms of easy film thickness control. After the melt-kneading in step (b), the set temperature in the step of molding the molten material into a sheet is preferably set to the same or higher than the set temperature of the extruder. From the viewpoint of thermal degradation of polyolefins, the upper limit of the set temperature is preferably 300 ° C or less, more preferably 260 ° C or less, and even more preferably 240 ° C or less. For example, when continuously producing a sheet-shaped product using an extruder, if the set temperatures of the path from the extruder outlet to the T-die and the T-die in the sheet-forming step after the melt-kneading step, i.e., the set temperatures of the path from the extruder outlet to the T-die, are set higher than the set temperatures in the extrusion step, this is preferred because it makes it possible to form the molten product into a sheet without re-aggregation of the inorganic particles finely dispersed in the melt-kneading step. In particular, when inorganic particles having a small average primary particle size are added, the effect of suppressing aggregation is remarkable.

[0056] [Primary Stretching Step (d)] The primary stretching step (d) is a step of stretching the sheet-like molded product obtained in the sheet molding step (c) at least once in at least one axial direction. This stretching step (a stretching step performed before the next extraction step (e)) is referred to as "primary stretching," and the film obtained by primary stretching is referred to as "primary stretched film." In the primary stretching, the sheet-like molded product can be stretched in at least one direction, and may be performed in both MD and TD, or only in MD or TD. MD refers to the machine direction of continuous molding, and TD refers to the direction perpendicular to MD.

[0057] The stretching method of the first stretching is not particularly limited, and examples thereof include uniaxial stretching using a roll stretching machine; TD uniaxial stretching using a tenter; sequential biaxial stretching using a roll stretching machine and a tenter or a combination of a plurality of tenters; simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding, etc. Among them, in order to balance the ion permeability and mechanical strength of the resulting porous membrane, sequential biaxial stretching or simultaneous biaxial stretching is preferred.

[0058] The stretching ratio in MD and / or TD of the primary stretching is preferably 2 times or more, more preferably 3 times or more, and even more preferably 4 times or more. When the stretching ratio in MD and / or TD of the primary stretching is 2 times or more, the mechanical strength of the obtained porous film tends to be further improved. Furthermore, the stretching ratio in MD and / or TD of the primary stretching is preferably 10 times or less, more preferably 8 times or less, and even more preferably 6 times or less. When the stretching ratio in MD and / or TD of the primary stretching is 10 times or less, stretching breakage tends to be further suppressed. When performing biaxial stretching, either sequential stretching or simultaneous biaxial stretching may be used, and the stretching ratio in each axial direction is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 8 times or less, and even more preferably 4 times or more and 6 times or less.

[0059] In the simultaneous biaxial or sequential biaxial stretching of the primary stretching, the stretching strain rate in MD and TD is preferably 0.5% / sec or more and 50% / sec or less, more preferably 1% / sec or more and 45% / sec or less, even more preferably 1.5% / sec or more and 40% / sec or less, and most preferably 2% / sec or more and 35% / sec or less. Without wishing to be bound by theory, it is presumed that if the stretching strain rate in MD and TD is 0.5% / sec or more, the entanglement of the polymers in the sheet-like molded body is maintained while stretching, so the porous film has high mechanical strength and uniform pore size, and the occurrence of large pores that may cause a decrease in gas purity during electrolysis can be suppressed. If the stretching strain rate in MD and TD is 50% / sec or less, the residual stress of the resulting polyolefin porous film is reduced, which tends to reduce the shrinkage rate, which is preferable.

[0060] The primary stretching temperature is not particularly limited and can be selected with reference to the raw material resin composition and concentration contained in the resin composition. The stretching temperature is preferably in the range from a temperature 30°C lower than the melting point Tm of the porous membrane to the melting point Tm (Tm-30°C to Tm°C) from the viewpoint of preventing breakage due to excessive stretching stress and balancing mechanical strength and thermal shrinkage. When the resin that is the main component of the porous membrane is PE, the stretching temperature is preferably 100°C or higher, and from the viewpoint of increasing the mechanical strength of the porous membrane, it is preferably 135°C or lower. Specifically, the stretching temperature is preferably 100 to 135°C, more preferably 110 to 130°C, and even more preferably 120 to 128°C.

[0061] [Extraction step (e)] The extraction step (e) is a step of extracting the pore-forming material from the first stretched membrane obtained in the first stretching step (d) to obtain an extracted membrane. As a method for removing the pore-forming material, for example, a method of immersing the first stretched membrane in an extraction solvent to extract the pore-forming material and then thoroughly drying it can be mentioned. The method for extracting the pore-forming material may be either a batch method or a continuous method. In addition, it is preferable that the amount of the pore-forming material, particularly the amount of the pore-forming material remaining in the porous membrane, is less than 1 mass%.

[0062] The extraction solvent used to extract the pore-forming material is preferably a poor solvent for polyolefin, a good solvent for the pore-forming material, and has a boiling point lower than the melting point of polyolefin. Examples of such extraction solvents include, but are not limited to, hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by distillation or other procedures.

[0063] [Heat setting step (f)] The heat setting step (f) is a step of heat setting the extracted film obtained in the extraction step (e) at a predetermined temperature. The heat treatment method at this time is not particularly limited, but may be a heat setting method using a tenter or a roll stretching machine to perform stretching and relaxation operations.

[0064] The stretching operation in the heat-setting step (f) is an operation of stretching the porous membrane in at least one direction of MD and TD, and may be performed in both MD and TD, or only in MD or TD. The stretching ratios in MD and TD in the heat-setting step (f) are preferably 1.0 times or more, more preferably 1.1 times or more, even more preferably 1.2 times or more, and even more preferably 1.5 times or more. The upper limit of the stretching ratios in MD and TD in the heat-setting step (f) is not particularly limited, but is preferably 2.5 times or less. If the stretching ratio is outside the above range, shrinkage stress near the melting point tends to remain, which tends to worsen heat shrinkage. In addition, when the stretching ratio is within the above range, the mechanical strength and porosity of the porous membrane tend to be further improved.

[0065] The stretching temperature in this stretching operation is not particularly limited, but is preferably a temperature 30°C lower than the melting point Tm of the porous membrane (i.e., stretching temperature ≥ Tm - 30°C), more preferably a temperature higher than the melting point Tm - 25°C of the porous membrane, and even more preferably a temperature in the range from the melting point Tm - 20°C of the porous membrane to the melting point Tm (i.e., Tm - 20°C to Tm). When the resin that is the main component of the porous membrane is PE, the stretching temperature is preferably 110°C or higher, and from the viewpoint of increasing the mechanical strength of the porous membrane, it is preferably 136°C or lower. Specifically, the stretching temperature is 110 to 136°C, more preferably 115 to 134°C, and even more preferably 120 to 133°C. When the stretching temperature is within the above range, the heat shrinkage rate of the obtained porous membrane tends to be further reduced, and the porosity and mechanical strength tend to be further improved.

[0066] The relaxation operation in the heat setting step (f) is an operation of shrinking the porous membrane in at least one direction of MD and TD, and may be performed in both MD and TD, or only in MD or TD. The relaxation rate in the heat setting step (f) is preferably 2% or more, more preferably 3% or more, even more preferably 4% or more, and even more preferably 5% or more. A relaxation rate of 2% or more in the heat setting step (f) tends to improve the heat shrinkage rate. In addition, from the viewpoint of membrane quality, the relaxation rate is preferably 30% or less, and more preferably 25% or less is preferred from the viewpoint of increasing the relaxation temperature. Here, the "relaxation rate" refers to the value obtained by subtracting the dimension of the membrane after the relaxation operation from the dimension of the membrane before the relaxation operation, divided by the dimension of the membrane before the relaxation operation. When both MD and TD are relaxed, it refers to the value obtained by multiplying the relaxation rate in MD and the relaxation rate in TD. Relaxation rate (%)=(membrane dimension (m) before relaxation operation−membrane dimension (m) after relaxation operation) / (membrane dimension (m) before relaxation operation)×100

[0067] The relaxation ratio in the heat setting step (f) is not particularly limited, but is preferably 1.0 to 1.8 times, more preferably 1.1 to 1.7 times, and even more preferably 1.2 to 1.6 times. When the relaxation ratio in the heat setting step (f) is 1.0 times or more, the cell voltage becomes good, and when it is 1.8 times or less, excessive increase in pore size can be suppressed. Here, the relaxation ratio is the value obtained by dividing the dimension of the membrane after the relaxation operation by the dimension of the membrane before stretching.

[0068] The relaxation temperature in the relaxation operation is not particularly limited, but in order to obtain a porous membrane according to the present embodiment and a diaphragm for alkaline water electrolysis including the same, the relaxation temperature is preferably equal to or lower than the melting point (Tm) of the porous membrane, more preferably in the range from the melting point (Tm) - 7°C to the melting point (Tm) of the porous membrane (i.e., Tm - 7°C to Tm), and even more preferably in the range from the melting point (Tm) - 6°C to the melting point (Tm) - 2°C of the porous membrane (i.e., Tm - 6°C to Tm - 2°C). When the temperature in the relaxation operation is within the above range, not only can residual stress due to the stretching step be removed but also the orientation of molecular chains can be firmly fixed, which is preferable from the viewpoints of preventing a decrease in ion permeability near the melting point of the porous membrane and improving the performance of the electrochemical device.

[0069] The final thickness of the porous membrane is preferably 25 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, still more preferably 100 μm or more, and preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and most preferably 250 μm or less. The diaphragm for alkaline water electrolysis according to this embodiment has a thickness of preferably 25 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, still more preferably 100 μm or more, and preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and most preferably 250 μm or less. A thickness of 25 μm or more is suitable from the viewpoint of improving the mechanical strength of the diaphragm. On the other hand, a thickness of 500 μm or less of the diaphragm is preferred because it is advantageous for reducing the distance between electrodes and tends to reduce the cell voltage during electrolysis.

[0070] The porosity of the porous membrane is preferably 30% or more, more preferably 40% or more, even more preferably 45% or more, and preferably 80% or less, more preferably 70% or less, and even more preferably 65% ​​or less. A porosity of 30% or more is preferable from the viewpoint of reducing the cell voltage when the porous membrane is used for alkaline water electrolysis. On the other hand, a porosity of 80% or less is preferable from the viewpoint of ensuring high pin puncture strength and from the viewpoint of avoiding a decrease in ion permeability due to excessive stretching of the membrane in the stretching and / or heat setting steps. The porosity can be adjusted by adjusting the stretching temperature, stretch ratio, and stretching strain rate in the step (d) and / or by adjusting the temperature, stretch ratio, and strain rate in the heat setting and heat relaxing steps (f), or the like.

[0071] The air permeability of the porous membrane is preferably 10 seconds or more and 2000 seconds or less, more preferably 50 seconds or more and 1500 seconds or less, and even more preferably 100 seconds or more and 1000 seconds or less, calculated in terms of 100 μm. An air permeability of 10 seconds or more is preferable from the viewpoint of maintaining the mechanical strength of the porous membrane and gas barrier properties. On the other hand, an air permeability of 2000 seconds or less is preferable from the viewpoint of reducing the cell voltage during electrolysis. The air permeability can be adjusted by adjusting the temperature, magnification, strain rate, etc., of the heat treatment step (f) above.

[0072] The pin puncture strength of the porous membrane is preferably 200 gf or more and 10,000 gf or less, more preferably 500 gf or more and 8,000 gf or less, and even more preferably 800 gf or more and 6,000 gf or less. A pin puncture strength of 200 gf or more is preferred from the viewpoint of preventing membrane rupture during assembly of the electrolytic cell. This is also preferred from the viewpoint of preventing the risk of short-circuiting due to contact between the electrodes and the diaphragm caused by vibrations occurring during electrolysis. On the other hand, a pin puncture strength of 10,000 gf or less is preferred from the viewpoint of reducing width contraction of the diaphragm during electrolysis. The pin puncture strength can be adjusted by adjusting the molecular weight of the resin, the proportion of polyolefin, and the stretching temperature and stretch ratio in the step (d) above and / or by adjusting the temperature, stretch ratio, and strain rate in the heat setting and heat-relaxing steps (f) above.

[0073] The porous membrane contains polyolefin (preferably as a main component, and the mass ratio of polyolefin to 100% by mass of the porous membrane is more preferably 70% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 99% by mass or more, and the porous membrane may consist of only polyolefin), the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more (may be 2,000,000 or more and 10,000,000 or less, or 4,000,000 or more and 7,500,000 or less), and the peel strength in the thickness direction is 2.0 N or more (2.5 N or more and less than 20.0 N, or 3.0 N or more and less than 15.0 N), It is preferable that the film thickness is 25 μm or more and 500 μm or less (which may be 50 μm or more and 400 μm or less, 80 μm or more and 300 μm or less, or 100 μm or more and 250 μm or less), the porosity is 30% or more and 80% or less (which may be 40% or more and 70% or less, or 45% or more and 65% or less), the air permeability per 100 μm is 10 seconds or more and 2000 seconds or less (which may be 50 seconds or more and 1500 seconds or less, or 100 seconds or more and 1000 seconds or less), and the pin puncture strength is 200 gf or more and 10,000 gf or less (which may be 500 gf or more and 8,000 gf or less, or 800 gf or more and 6,000 gf or less).

[0074] The various parameters described above are measured according to the measurement methods in the examples described below, unless otherwise specified.

[0075] (Bipolar electrolytic cell for alkaline water electrolysis) The alkaline water electrolytic cell of this embodiment is an electrolytic cell comprising the diaphragm for alkaline water electrolysis of this embodiment described above, an anode, and a cathode, with the diaphragm for alkaline water electrolysis disposed between the anode and the cathode. Hereinafter, an example of a bipolar electrolytic cell for alkaline water electrolysis of this embodiment comprising the cathode, anode, and diaphragm described above will be described with reference to the drawings. The bipolar electrolytic cell for alkaline water electrolysis of this embodiment is not limited to the one described below. Furthermore, members included in the bipolar electrolytic cell for alkaline water electrolysis other than the anode, cathode, and diaphragm are not limited to those listed below, and known members can be appropriately selected, designed, etc.

[0076] The alkaline water electrolysis cell of this embodiment is a bipolar electrolysis cell formed by stacking the diaphragm for alkaline water electrolysis of this embodiment described above and a bipolar element holding an anode and a cathode. In other words, the alkaline water electrolysis cell of this embodiment is a bipolar electrolysis cell comprising a plurality of combinations (also referred to as "electrolytic cells") of an anode, a cathode, and the diaphragm for alkaline water electrolysis according to this embodiment disposed between the anode and the cathode. The diaphragm for alkaline water electrolysis of this embodiment is characterized by comprising a porous membrane containing a polyolefin and having a peel strength of 2.0 N or more in the membrane thickness direction, and is capable of maintaining high ion permeability and high gas barrier properties and performing stable water electrolysis for an extended period of time.

[0077] As described above, the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment is characterized by including the diaphragm for alkaline water electrolysis of the present embodiment described above, and other configurations are not particularly limited. Hereinafter, the configuration of one example of a bipolar electrolytic cell for alkaline water electrolysis of the present embodiment will be described with reference to the drawings.

[0078] Fig. 1 shows a side view of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. Fig. 2 shows a side view of the zero gap structure of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, focusing on the portion enclosed by the dashed square frame in Fig. 1. Fig. 3 shows a plan view of an electrode chamber portion of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. As shown in Fig. 1, the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment is a bipolar electrolytic cell 50 in which a plurality of electrolytic cells 65, each including an anode 2a, a cathode 2c, a partition wall 1 separating the anode 2a and the cathode 2c, and an outer frame 3 bordering the partition wall 1, are stacked one on top of the other with a diaphragm 4 sandwiched between them.

[0079] Although not particularly limited, the bipolar electrolytic cell for alkaline water electrolysis of this embodiment preferably has a zero-gap structure Z in which the diaphragm 4 is in contact with the anode 2 a and the cathode 2 c (see FIG. 2 ).

[0080] In the bipolar electrolytic cell 50 of the present embodiment, the partition wall 1, the outer frame 3, and the diaphragm 4 define an electrode chamber 5 through which the electrolytic solution passes, and the electrode chamber 5 is provided with a plurality of current plates 6 arranged parallel to a given direction D1 along the partition wall 1 (see FIGS. 2 and 3 ).

[0081] 2 and 3 , a bipolar element 60 used in an example bipolar electrolytic cell for alkaline water electrolysis includes a partition wall 1 that separates an anode 2a from a cathode 2c, and an outer frame 3 that borders the partition wall. More specifically, the partition wall 1 is conductive, and the outer frame 3 is provided along the outer edge of the partition wall 1 so as to surround the partition wall 1.

[0082] In this embodiment, the bipolar element 60 may be used so that the given direction D1 along the partition wall 1 is normally the vertical direction. Specifically, when the partition wall 1 has a rectangular shape in a plan view as shown in Figures 2 and 3, the bipolar element 60 may be used so that the given direction D1 along the partition wall 1 is the same direction as the direction of one of two pairs of opposing sides (see Figures 1 to 3). In this specification, the vertical direction is also referred to as the electrolyte passage direction.

[0083] In this embodiment, as shown in Fig. 1 , the bipolar electrolytic cell 50 is configured by stacking the required number of bipolar elements 60. In the example shown in Fig. 1 , the bipolar electrolytic cell 50 includes a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in this order from one end, and further includes an anode side gasket portion 7, a diaphragm 4, a cathode side gasket portion 7, and a bipolar element 60 arranged in this order. At this time, the bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a. The anode side gasket portion 7 to the bipolar element 60 are arranged repeatedly the number of times required for the designed production volume. After the required number of arrangements of the anode side gasket portion 7 to the bipolar element 60 are repeated, the anode side gasket portion 7, the diaphragm 4, and the cathode side gasket portion 7 are again arranged in a row, and finally the cathode terminal element 51c, the insulating plate 51i, and the loose head 51g are arranged in this order. The bipolar electrolytic cell 50 is integrated by clamping the entire cell together using a clamping mechanism such as a tie rod 51r (see FIG. 1) or a hydraulic cylinder, to form the bipolar electrolytic cell 50. The arrangement of the bipolar electrolytic cell 50 can be selected arbitrarily, either from the anode 2a side or the cathode 2c side, and is not limited to the above-mentioned order.

[0084] As shown in FIG. 1 , in a bipolar electrolytic cell 50, a bipolar element 60 is disposed between an anode terminal element 51 a and a cathode terminal element 51 c, and diaphragms 4 are disposed between the anode terminal element 51 a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51 c.

[0085] In the bipolar electrolytic cell 50 of this embodiment, as shown in FIGS. 2 and 3, the partition wall 1, the outer frame 3, and the diaphragm 4 define an electrode chamber 5 through which the electrolyte passes.

[0086] Specifically, the electrode chambers 5 have, at the boundary with the outer frame 3, an electrolyte inlet for introducing the electrolyte into the electrode chambers 5 and an electrolyte outlet for discharging the electrolyte from the electrode chambers 5. More specifically, the anode chamber 5a is provided with an anolyte inlet for introducing the electrolyte into the anode chamber 5a and an anolyte outlet for discharging the electrolyte discharged from the anode chamber 5a, and the cathode chamber 5c is provided with a catholyte inlet for introducing the electrolyte into the cathode chamber 5c and a catholyte outlet for discharging the electrolyte discharged from the cathode chamber 5c.

[0087] In the example shown in FIGS. 1 to 3 , the rectangular partition wall 1 and the rectangular diaphragm 4 are arranged in parallel to each other, and the inner surface of the rectangular parallelepiped outer frame 3 provided on an edge of the partition wall 1, facing the partition wall 1, is perpendicular to the partition wall 1, and therefore the electrode chamber 5 has a rectangular parallelepiped shape.

[0088] The bipolar electrolytic cell 50 is usually fitted with headers, which are pipes for distributing or collecting the electrolyte, and is provided with an anode inlet header for introducing the electrolyte into the anode chamber 5a and a cathode inlet header for introducing the electrolyte into the cathode chamber 5c, located at the lower part of the outer frame 3 at the edge of the partition wall 1. Similarly, an anode outlet header for discharging the electrode solution from the anode chamber 5a and a cathode outlet header for discharging the electrolyte from the cathode chamber 5c are provided at the upper part of the outer frame 3 at the edge of the partition wall 1. Representative arrangements of headers fitted to the bipolar electrolytic cell 50 shown in Figures 1 to 3 include an internal header type and an external header type, but either type may be adopted in the present disclosure and are not particularly limited.

[0089] In the bipolar electrolytic cell 50 of this embodiment, the electrolyte distributed in the anode inlet header is introduced into the anode chamber 5a through the anolyte inlet, passes through the anode chamber 5a, is discharged from the anode chamber 5a through the anolyte outlet, and is collected in the anode outlet header.

[0090] As shown in FIGS. 2 and 3, the electrode chamber in this embodiment includes a plurality of current plates 6 arranged parallel to a given direction D1 along the partition wall 1.

[0091] The current plate 6 reduces convection that occurs in the electrode chamber 5 due to turbulence in the gas-liquid flow within the electrode chamber 5, thereby suppressing a local increase in the temperature of the electrolyte.

[0092] In particular, in the example shown in FIGS. 1 to 3 , a plurality of rectifying plates 6 are provided at a constant interval (pitch) in a direction perpendicular to a given direction D1 along the partition wall 1 (in the illustrated example, the electrolyte solution passing direction).

[0093] In addition, in one example of a bipolar electrolytic cell 50, the current plate 6 has approximately the same length as the height of the electrode chamber 5, is provided perpendicular to the partition wall 1, and has through-holes at a predetermined pitch in a given direction D1 along the partition wall 1 (in the illustrated example, the direction in which the electrolyte passes). In the present disclosure, the shape of the electrode chamber 5 is not limited to the rectangular parallelepiped of the example shown in Figs. 1 to 3 , and may be modified as appropriate depending on the planar shapes of the partition wall 1 and the diaphragm 4, the angle between the partition wall 2 and the inner surface of the outer frame 3 on the partition wall 2 side, and the like, and may have any shape as long as the effects of the present disclosure are obtained.

[0094] In the present disclosure, the arrangement of the current plate 6 in the electrode chamber 5 is not limited to the examples shown in FIGS.

[0095] In the present disclosure, the number of rectifying plates 6 and the constant intervals (pitch) of the rectifying plates 6 in the direction perpendicular to the given direction D1 along the partition wall 1 may be determined as appropriate, as long as the effects of the present invention are obtained. Here, the intervals between the rectifying plates 6 do not have to be constant. In the present disclosure, the length of the rectifying plates 6, the angle between the rectifying plates 6 and the partition wall 1, the number of through holes, and the constant intervals (pitch) of the through holes in the given direction D1 along the partition wall 1 may be determined as appropriate, as long as the effects of the present invention are obtained. Here, the intervals between the through holes do not have to be constant.

[0096] In the examples illustrated in FIGS. 1 to 3 , the partition wall 1, the anode 2 a, and the cathode 2 c all have a plate-like shape with a predetermined thickness; however, the present disclosure is not limited thereto, and the cross section may entirely or partially have a zigzag or wavy shape, or may have rounded edges.

[0097] [Diaphragm for alkaline water electrolysis] The diaphragm 4 used in the electrolytic cell for alkaline water electrolysis of this embodiment is the diaphragm for alkaline water electrolysis of this embodiment described above, and therefore further description will be omitted.

[0098] [Electrodes (anode, cathode)] In the alkaline water electrolysis reaction, alkaline water is electrolyzed in an electrolytic cell equipped with an electrode pair (i.e., an anode and a cathode) connected to a power source, generating oxygen gas at the anode and hydrogen gas at the cathode. The electrode 2 included in the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment will be described in detail below. In this specification, the term "electrode" refers to either or both of the anode 2a and the cathode 2c.

[0099] In the case of a zero gap electrolytic cell described below, it is necessary to degas the gas generated from the back side of the surface in contact with the diaphragm 4, and therefore the porous electrode is preferably perforated on the surface opposite to the surface in contact with the diaphragm 4.

[0100] The porous electrode in this embodiment is not particularly limited, but examples thereof include electrodes having a mesh structure such as a plain weave mesh type, a punched type, and an expanded type, and metal foams, from the viewpoint of controlling the average pore size. Among these, from the viewpoint of controlling the size and shape of the pores, it is preferable to have a mesh structure selected from the group consisting of a plain weave mesh type, a punched type, and an expanded type.

[0101] The porous electrode in this embodiment may be the substrate itself, or may have a highly reactive catalyst layer on the surface of the substrate, but it is preferable that the porous electrode has a highly reactive catalyst layer on the surface of the substrate.

[0102] The material of the substrate is not particularly limited, and examples thereof include conductive substrates made of at least one selected from the group consisting of nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group metals, graphite, and chromium. A conductive substrate made of an alloy of two or more metals or a mixture of two or more conductive materials may also be used. Among these, nickel and nickel-based alloys are preferred from the viewpoints of the conductivity of the substrate and durability to the usage environment.

[0103] Examples of methods for forming a catalyst layer on a substrate include plating methods, thermal spraying methods such as plasma spraying, thermal decomposition methods in which a precursor layer solution is applied to a substrate and then heat is applied, methods in which a catalyst substance is mixed with a binder component and then fixed to the substrate, and vacuum film formation methods such as sputtering.

[0104] In the zero-gap configuration described below, the diaphragm 4 is pressed against the electrode more strongly than in conventional electrolytic cells. For example, in an electrode using an expanded base material, the diaphragm 4 may be damaged at the edge of the opening, or may be embedded in the opening, creating a gap between the cathode 2c and the diaphragm 4 and resulting in an increase in voltage.

[0105] In order to solve the above problems, it is preferable to make the electrode shape as flat as possible. For example, a method can be applied in which an expanded substrate (e.g., an expanded substrate) is pressed with a roller to form a flat shape. In this case, it is desirable to press the expanded substrate to 95% to 110% of the original thickness of the metal plate before the expanding process to flatten it.

[0106] The electrode 2 manufactured by the above-mentioned treatment not only prevents damage to the diaphragm 4 but also, unexpectedly, reduces the voltage. The reason for this is not clear, but it is thought to be because the surface of the diaphragm 4 and the electrode surface come into uniform contact, resulting in a more uniform current density.

[0107] The size of the electrode 2 is not particularly limited and can be determined according to the shape and size of the bipolar electrolytic cell for alkaline water electrolysis, the electrolytic cell, the bipolar element, the partition wall, etc., and also according to the desired electrolysis capacity, etc. For example, when the partition wall has a plate shape, the size of the electrode 2 may be determined according to the size of the partition wall.

[0108] [Gasket] In the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment, the sealing region (b) of the diaphragm and the bipolar element are preferably stacked together via a gasket 7. The gasket 7 is used to seal the space between the bipolar element 60 and the diaphragm 4 and the space between the bipolar elements 60 against the electrolytic solution and the generated gas, and can prevent leakage of the electrolytic solution or the generated gas to the outside of the cell and mixing of gases between the two electrode chambers.

[0109] The material of the gasket 7 is not particularly limited, and may be selected from known insulating rubber materials, resin materials, etc. Specific examples of the rubber material or resin material include natural rubber (NR), styrene butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated PE rubber (CSM); fluororesin materials such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE); and resin materials such as polyphenylene sulfide (PPS), PE, polyimide, and polyacetal. Among these, ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) are particularly suitable from the viewpoint of elastic modulus and alkali resistance.

[0110] The gasket 7 may have a reinforcing material embedded therein. This prevents the gasket 7 from being crushed when sandwiched and pressed by the frame during stacking, making it easier to prevent breakage. Known metal materials, resin materials, and carbon materials can be used for such reinforcing materials. Specific examples include metals such as nickel and stainless steel; resins such as nylon, polypropylene, PVDF, PTFE, and PPS; and carbon materials such as carbon particles and carbon fibers. Suitable shapes of the reinforcing material include woven fabric, nonwoven fabric, short fiber, and porous film. Furthermore, a protective layer may be provided on the surface of the gasket 7. This can improve adhesion between the gasket 7 and the element and can also improve the alkali resistance of the gasket 7. The material for such a protective layer can be selected from the materials used for the gasket 7.

[0111] The size of the gasket 7 is not particularly limited and may be designed to match the dimensions of the electrode chamber 5 and the membrane, but it is preferable that the width be 10 mm to 40 mm.

[0112] The thickness of the gasket 7 is not particularly limited and is designed depending on the material, elastic modulus, and cell area of ​​the gasket 7. A preferable range of the thickness is 1 mm to 10 mm, and more preferably 1.5 mm to 10 mm.

[0113] Furthermore, when the gasket 7 has a rectangular slit structure (a structure having a U-shaped cross section) capable of accommodating the diaphragm 4, the spacing of the slit portion that sandwiches the diaphragm 4 is preferably 0.2 mm to 1.2 mm, preferably 0.25 mm to 1.1 mm, more preferably 0.3 mm to 1.0 mm, and even more preferably 0.35 mm to 0.8 mm. Furthermore, the depth of the slit portion of the slit structure into which the diaphragm 4 is inserted is preferably 4.0 mm to 90 mm, more preferably 4.5 mm to 85 mm, and even more preferably 5.0 mm to 80 mm.

[0114] Furthermore, the height of the protrusions when provided is not particularly limited, but is preferably 0.5 mm to 5 mm in order to exert a sufficient pressing force.

[0115] The elastic modulus of the gasket 7 is not particularly limited and is designed depending on the material of the electrode 2 and the cell area. A preferred range of the elastic modulus is a tensile stress at 100% deformation of 0.20 MPa to 20 MPa, more preferably 1.0 MPa to 10 MPa from the viewpoint of sealing characteristics and cell strength when stacked. The tensile stress can be measured in accordance with JIS K6251. For example, an Autograph AG manufactured by Shimadzu Corporation may be used.

[0116] An adhesive may be used when attaching the gasket 7 to the bipolar element 60. The adhesive may be applied to one side of the gasket 7 and then attached to the outer frame 3 on one side of the element. After the adhesive has dried, it is preferable to spray water on the electrode surfaces of the bipolar alkaline water bipolar element 60 to moisten the electrodes 2. In the case of a gasket 7 having a slit that accommodates the edge of the diaphragm 4 so that it can hold the diaphragm 4, the gasket 7 may be attached while holding the diaphragm 4, or the diaphragm 4 may be held after being attached.

[0117] [Zero gap structure] The bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment is preferably, but not particularly limited to, a so-called "zero gap structure" Z in which the diaphragm 4 is in contact with the anode 2a and the cathode 2c, as shown in Fig. 2 . The "zero gap structure" Z is a structure that can maintain a state in which the anode 2a and the diaphragm 4 are in contact with each other and the cathode 2c and the diaphragm 4 are in contact with each other over the entire electrode surfaces, or a state in which the inter-electrode distance is substantially the same as the thickness of the diaphragm 4 and there is almost no gap between the anode 2a and the diaphragm 4 and between the cathode 2c and the diaphragm 4 over the entire electrode surfaces. During alkaline water electrolysis, if there is a gap between the diaphragm 4 and the anode 2a or the cathode 2c, in addition to the electrolytic solution, a large amount of gas bubbles generated during electrolysis will remain in this portion, resulting in a very high electrical resistance. On the other hand, when the zero gap structure Z is formed, the generated gas is quickly released to the side of the electrode 2 opposite to the diaphragm 4 side through the pores in the electrode 2, thereby reducing the distance between the anode 2 a and the cathode 2 c (hereinafter also referred to as the "inter-electrode distance"), minimizing voltage loss due to the electrolytic solution and the occurrence of gas accumulation near the electrodes, and keeping the electrolysis voltage low.

[0118] Several means for constructing the zero gap structure Z have already been proposed, including a method in which the anode 2a and cathode 2c are processed to be completely smooth and then pressed together so as to sandwich the diaphragm 4, and a method in which an elastic body such as a spring is disposed between the electrode 2 and the partition wall 4 and the electrode 2 is supported by this elastic body. Note that preferred embodiments of the means for constructing the zero gap structure Z in the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment will be described later.

[0119] In the bipolar element 60 of the zero-gap cell, a means for reducing the inter-electrode distance is preferably provided by disposing an elastic spring between the electrode 2 and the partition wall 1, and supporting the electrode 2 with this spring. For example, in a first example, a spring made of a conductive material may be attached to the partition wall 1, and the electrode 2 may be attached to this spring. In a second example, a spring may be attached to the electrode rib 6 attached to the partition wall 1, and the electrode 2 may be attached to this spring. When adopting such a configuration using an elastic body, the strength, number, shape, etc. of the spring must be appropriately adjusted as necessary to prevent uneven contact pressure between the electrode 2 and the diaphragm 4.

[0120] Furthermore, by increasing the rigidity of the other electrode 2 that is paired with the electrode 2 supported via the elastic body (for example, by making the rigidity of the anode stronger than that of the cathode), a structure is achieved in which deformation is small even when pressed. Meanwhile, the electrode 2 supported via the elastic body has a flexible structure that deforms when the diaphragm 4 is pressed against it, which makes it possible to absorb unevenness due to tolerances in the manufacturing precision of the electrolytic cell 50 and deformation of the electrode 2, thereby maintaining the zero gap structure Z.

[0121] In the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment, as shown in FIG. 2 , a conductive elastic body 2 e and a current collector 2 r are provided between the cathode 2 c or the anode 2 a and the partition wall 1, such that the conductive elastic body 2 e is sandwiched between the cathode 2 c or the anode 2 a and the current collector 2 r.

[0122] (Alkaline water electrolysis apparatus) An example of an alkaline water electrolysis apparatus in which the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment can be used is shown in Fig. 4. In addition to the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment, the alkaline water electrolysis apparatus 70 may include a liquid feed pump 71, a gas-liquid separation tank 72, a water supply device 73, a rectifier 74, an oxygen concentration meter 75, a hydrogen concentration meter 76, a flow meter 77, a pressure meter 78, a heat exchanger 79, a pressure control valve 80, etc.

[0123] (Alkaline water electrolysis) By performing electrolysis by circulating the electrolytic solution in an alkaline water electrolysis device including the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, excellent electrolysis efficiency and high purity of the generated gas can be maintained even after high density current operation or variable power supply operation, and highly efficient alkaline water electrolysis can be performed.

[0124] The electrolyte solution that can be used for the alkaline water electrolysis of this embodiment may be an alkaline aqueous solution in which an alkali salt is dissolved, such as an aqueous NaOH solution or an aqueous KOH solution. The concentration of the alkali salt is not particularly limited, but is preferably 20% by mass to 50% by mass, and more preferably 25% by mass to 40% by mass. Among these, a 25% by mass to 40% by mass aqueous KOH solution is particularly preferred from the viewpoints of ionic conductivity, kinetic viscosity, and freezing at low temperatures.

[0125] The temperature of the electrolytic solution in the electrolytic cell is not particularly limited, but is preferably 60°C to 100°C. Within this temperature range, it is possible to effectively prevent thermal deterioration of electrolytic device components such as gaskets and diaphragms while maintaining high electrolysis efficiency. The temperature of the electrolytic solution is more preferably 65°C to 95°C, and particularly preferably 70°C to 90°C.

[0126] In the alkaline water electrolysis of this embodiment, the current density applied to the electrolytic cell is not particularly limited, but is preferably 3 kA / m ２ ~20 kA / m ２ Preferably, it is 6 kA / m ２ ~15kA / m ２ In particular, when a variable power supply is used, it is preferable that the upper limit of the current density be within the above range.

[0127] In alkaline water electrolysis of this embodiment, the pressure inside the electrolytic cell is not particularly limited, but is preferably 3 kPa to 1000 kPa, and more preferably 3 kPa to 300 kPa.

[0128] The flow rate of the electrolyte per electrode chamber and other conditions may be appropriately controlled depending on the configuration of the bipolar electrolytic layer for alkaline water electrolysis.

[0129] The bipolar electrolytic cell for alkaline water electrolysis according to the embodiment of the present invention has been described above with reference to the drawings. However, the bipolar electrolytic cell for alkaline water electrolysis according to the present invention is not limited to the above example, and appropriate modifications can be made to the above embodiment.

[0130] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0131] [Methods for measuring and evaluating physical properties] The analytical and evaluation methods used in the examples and comparative examples are as follows.

[0132] (1) Film Thickness (μm) A diaphragm was cut into a size of 10 cm in MD×10 cm in TD, and 9 points (3 points×3 points) were selected in a grid pattern and measured at room temperature of 23° C. using a Digimatic Indicator (manufactured by Mitutoyo Corporation, Code No. 543-390B). The average value of the measurements at the 9 points was taken as the film thickness.

[0133] (2) Porosity (%) A 10 cm x 10 cm square sample was cut out from the diaphragm, and its volume (cm ３ ) and mass (g), and compare them with the film density (g / cm ３ ), the porosity was calculated using the following formula: ３ ) = 10 (cm) × 10 (cm) × film thickness Porosity (%) = (volume - mass / film density) × 100 / volume The film density was calculated from the following formula: film density (g / cm) = (volume - mass / film density) × 100 / volume The membrane or raw material resin used was heated to above its melting point in a heat press, press-molded into a sheet, cut into a certain size (e.g., 10 mm × 10 mm), measured for film thickness to calculate the sheet volume, and then measured for sheet mass. ３ ) = sheet mass (g) / sheet volume (cm ３ )

[0134] (3) Peel Strength in the Thickness Direction (N) A strip of sample A measuring 2 cm in the TD direction and 9 cm in the MD direction was cut from the diaphragm, and a line C was drawn parallel to the TD direction with a ballpoint pen 5 cm from the end B in the MD direction. A slit was made along line C with a razor (76 razor, manufactured by Nisshin EM Co., Ltd.), and a peel starting point was created using tweezers or the like. Double-sided tape D (No. 5015, 20 mm wide, manufactured by Nitto Denko Corporation) cut to a length of 5 cm was attached to the area from line C to end B. To create a gripping portion, a PE porous membrane E (Hipore ND416Z, manufactured by Asahi Kasei Corporation, film thickness 16 μm) was cut into a strip measuring 2 cm x 10 cm square and attached to the side of double-sided tape D opposite the side in contact with sample A, overlapping sample A. This was used as a test specimen. The configuration of the test specimen is shown in Figure 5. The PE porous membrane E serves as a reinforcing material for the double-sided tape D, and other PE porous membranes may be used as long as they do not break during the measurement. Using a tensile tester (Autograph AG, manufactured by Shimadzu Corporation), the sample end F (the end opposite the MD end B) was positioned on the bottom, and the PE porous membrane end G was positioned on the top, with the chuck distance of 5 cm and the chuck length of 2 cm. The tensile test was performed in a 25°C atmosphere, with the test speed set to 10 cm / min and the stroke set to a range of 0 cm to 10 cm. The minimum test force (N) in the stroke range of 2 cm or more and less than 9 cm was taken as the peel strength (N) in the film thickness direction. The razor cut along line C and the peeled portion of sample A resulting from the tensile test are shown by dashed lines in Figure 5. If the sample broke at a stroke of less than 2 cm and the minimum test force (N) in the range of 2 cm or more and less than 9 cm could not be measured, the peel strength was recorded as 0 (N).

[0135] (4) Air Permeability (Seconds) Using a digital Oken air permeability tester (EG01 type, measuring nozzle diameter 12.82φ mm, manufactured by Asahi Seiko Co., Ltd.) conforming to JIS P-8117:2009, the time (seconds) required for 100 ml of air to pass through was measured, and this was defined as the air permeability of the diaphragm.

[0136] (5) Puncture Strength (gf) Using a puncture tester "NDG5" (manufactured by Kato Tech Co., Ltd.), a diaphragm was fixed with a sample holder having an opening diameter of 11.3 mm. A puncture test was performed on the center of the fixed diaphragm in an atmosphere of 25°C under conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec, to measure the puncture strength (gf) as the maximum puncture load.

[0137] (6) Gas Purity As one of the evaluation indices for the gas barrier properties of the membrane of this embodiment, gas purity during electrolysis was evaluated. In this evaluation, the O ２ H in gas ２ The gas concentration was taken as the gas purity.

[0138] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0139] <<Production of Porous Membrane>> [Example 1] 27.3 parts by mass of PE with a viscosity average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the liquid paraffin content in the total mixture (100 parts by mass) after melt-kneading was 72.7 parts by mass. The addition ratio of the two batches was 1st / 2nd = 5 / 3, and the temperature of the liquid paraffin at the time of addition was 120°C. The melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 11 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. Subsequently, the molten kneaded product emerging from the 7 mm slit nozzle was air-cooled on a mesh conveyor to obtain a kneaded product. The kneaded mixture was then pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd.) and cooled to 20°C to produce a 2 mm thick raw sheet. The raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched 3.0 × 3.0 times at 125°C, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 133°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis of this PE membrane demonstrated that it could be continuously electrolyzed for more than 1,000 hours.

[0140] Example 2: 27.3 parts by mass of PE with a viscosity-average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the liquid paraffin content was 72.7 parts by mass in the total mixture (100 parts by mass) melt-kneaded and extruded. The addition ratio of the two batches was 5 / 3, and the liquid paraffin temperature at the time of addition was 120°C. The melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 11 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded product. The kneaded mixture was then pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd.) and cooled to 20°C to produce a 3 mm thick raw sheet. The raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched 4.0 × 4.0 times at 126°C, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 133°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis of this PE membrane demonstrated that it could be continuously electrolyzed for more than 1,000 hours.

[0141] Example 3: 23.2 parts by mass of PE with a viscosity-average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the liquid paraffin content was 76.8 parts by mass relative to the total mixture (100 parts by mass) melt-kneaded and extruded. The addition ratio of the two batches was 5.1 / 2.2, and the liquid paraffin temperature at the time of addition was 120°C. The melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 13 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded product. The kneaded mixture was then pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd.) and cooled to 20°C to produce a 3 mm thick raw sheet. The raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched 4.5 × 4.5 times at 126°C, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 133°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis of this PE membrane demonstrated that it could be continuously electrolyzed for more than 1,000 hours.

[0142] Example 4: 20 parts by mass of PE with a viscosity-average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the liquid paraffin content was 80 parts by mass in the total mixture (100 parts by mass) melt-kneaded and extruded. The addition ratio of the two batches was 3 / 1, and the liquid paraffin temperature at the time of addition was 120°C. The melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 15 kg / h. The set temperatures were 200°C for the kneading zone and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded product. The kneaded mixture was then pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd.) and cooled to 20°C to produce a 1.5 mm thick raw sheet. The raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched 3.0 × 3.0 times at 123°C, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 130°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis of this PE membrane demonstrated that it could be continuously electrolyzed for more than 1,000 hours.

[0143] Example 5: 20 parts by mass of PE with a viscosity-average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two separate additions so that the liquid paraffin content was 80 parts by mass in the total mixture (100 parts by mass) extruded after melt-kneading. The addition ratio of the two additions was 3 / 1, and the liquid paraffin temperature at the time of addition was 120°C. The melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 15 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded product. The kneaded mixture was then pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd.) and cooled to 20°C to produce a 2.5 mm thick raw sheet. The raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched 4.0 × 4.0 times at 123°C, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 130°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis evaluation of this PE membrane showed that it could be used for more than 720 hours, but it became unusable within 1000 hours.

[0144] Example 6: 24 parts by mass of PE with a viscosity-average molecular weight of 2,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the total amount of liquid paraffin in the melt-kneaded and extruded mixture (100 parts by mass) was 76 parts by mass. The addition ratio of the two batches was 8 / 5, and the temperature of the liquid paraffin at the time of addition was 138°C. The melt-kneading was performed under conditions of a screw rotation speed of 280 rpm and an extrusion rate of 10 kg / h. The set temperatures were 200°C for the kneading zone and 220°C for the die holder. The molten mixture emerging from the T-die was then cooled with a cooling roll to obtain a raw sheet with a thickness of 2.8 mm. The raw sheet was then placed in a sequential biaxial stretching machine and stretched 4.0 times in the MD direction at 110°C, followed by 6.0 times in the TD direction at 130°C. The stretched polyolefin membrane was then removed, clipped on all four sides to a stainless steel frame, and immersed in methylene chloride to extract the plasticizer. The membrane was then dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 130°C for 0.5 hours to obtain a PE membrane. The evaluation results of the resulting PE membrane are shown in Table 1. Long-term electrolysis of this PE membrane demonstrated that electrolysis could be continued for more than 1,000 hours.

[0145] Example 7 PE with a viscosity average molecular weight of 900,000, tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant (0.3 wt % relative to the total amount of PE), and liquid paraffin with a kinematic viscosity at 38 ° C of 82 cSt as a plasticizer were mixed in a weight ratio of 30 / 70 (total amount of PE / plasticizer) and kneaded at 200 ° C using a Labo Plastomill (manufactured by Toyo Seiki Seisaku-sho). Next, the kneaded mixture was pressed and molded at 200 ° C at a pressure of 15 MPa using a Mini Test Press (manufactured by Toyo Seiki Seisaku-sho). After cooling at 20 ° C, a raw sheet with a thickness of 3 mm was produced. The raw sheet was placed in a biaxial stretching machine and simultaneously biaxially stretched to 4.0 × 4.0 times in a 125 ° C environment, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched raw sheet was then taken out and, while secured to a stainless steel frame with clips on all four sides, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 130°C for 0.5 hours to obtain a PE diaphragm. The evaluation results of the obtained PE diaphragm are shown in Table 1. Long-term electrolysis evaluation of this PE diaphragm showed that electrolysis could be continued for more than 1,000 hours.

[0146] Comparative Example 1: 21 parts by mass of PE with a viscosity-average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Furthermore, liquid paraffin was added to the twin-screw extruder cylinder via side feed in two batches so that the liquid paraffin ratio was 79 parts by mass in the total mixture (100 parts by mass) extruded after melt-kneading. The addition ratio for the two batches was 3 / 1 (first batch / second batch), and the temperature of the liquid paraffin at the time of addition was 120°C. Melt-kneading was performed under conditions of a screw rotation speed of 250 rpm and an extrusion rate of 11 kg / h. The set temperature of the kneading section was 200°C. Subsequently, the molten mixture emerging from the T-die was cooled with a cooling roll to obtain a raw sheet with a thickness of 2 mm. Next, the raw sheet was placed in a sequential biaxial stretching machine and simultaneously biaxially stretched to 4.4x MD and 8.0x TD in a 123°C environment, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched polyolefin membrane was then taken out and, while secured to a stainless steel frame with clips on all four sides, immersed in methylene chloride to extract the plasticizer, dried at room temperature to remove the methylene chloride, and then heat-set in an oven at 133°C for 0.5 hours to obtain a PE membrane. The evaluation results of the obtained PE membrane are shown in Table 1. As a result of long-term electrolysis evaluation of this PE membrane, it was found that electrolysis could not be continued in less than 720 hours.

[0147] [Comparative Example 2] 25 parts by mass of PE having a viscosity average molecular weight of 2,000,000, 25 parts by mass of finely powdered silica, 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant, and 50 parts by mass of dioctyl phthalate as a plasticizer were mixed and kneaded using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.) at 200 ° C. Next, the kneaded product was pressed and molded at 200 ° C. at a pressure of 15 MPa using a Mini Test Press (manufactured by Toyo Seiki Co., Ltd.), and then cooled to 20 ° C. to produce a raw sheet having a thickness of 2.5 mm. The raw sheet, secured on all four sides by clips in a stainless steel frame, was immersed in methylene chloride to extract the plasticizer, then immersed in ethanol, and then in a 30% aqueous potassium hydroxide solution heated to 90°C to extract and remove the finely divided silica. The sheet was then washed to remove the alkali and dried in an oven to remove moisture, yielding a raw sheet for stretching. The raw sheet for stretching was placed in a biaxial stretching machine and simultaneously biaxially stretched at 125°C and a stretch ratio of 6.0x4.0x. After relaxation at a relaxation rate of 3.2%, it was placed in an oven at 130°C for 0.5 hours for heat setting to obtain a PE diaphragm. The evaluation results of the resulting PE diaphragm are shown in Table 1. Long-term electrolysis of this PE diaphragm revealed that it could not be continued for less than 720 hours.

[0148] [Comparative Example 3] PE with a viscosity average molecular weight of 2,000,000 and PE with a viscosity average molecular weight of 300,000 were mixed at a weight ratio of 1 / 1, and tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane was used as an antioxidant at 0.3 wt% relative to the total amount of PE, and liquid paraffin with a kinematic viscosity at 38 ° C. of 82 cSt was used as a plasticizer at a weight ratio of 25 / 75 PE total amount / plasticizer, and the mixture was kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded mixture was pressed and molded at 200 ° C. at a pressure of 15 MPa using a Mini Test Press (manufactured by Toyo Seiki Co., Ltd.), and then cooled to 20 ° C. to produce a 3 mm thick raw sheet. The sheet was fixed on all four sides with clips in a stainless steel frame, immersed in methylene chloride to extract the plasticizer, and then dried at room temperature to remove the methylene chloride. This raw sheet was set in a biaxial stretching machine and simultaneously biaxially stretched to 4.0 × 4.0 times in an environment of 130°C, followed by a relaxation operation at a relaxation rate of 5.4%, and then placed in an oven at 130°C for 0.5 hours for heat setting to obtain a PE diaphragm. The evaluation results of the obtained PE diaphragm are shown in Table 1. As a result of long-term electrolysis evaluation of this PE diaphragm, it became impossible to continue electrolysis within 720 hours.

[0149] <Evaluation of Water Electrolysis> The monoelectrode electrolytic cell and electrolysis system used in the evaluation of water electrolysis will be described below.

[0150] [Monopolar electrolytic cell] A bipolar electrolytic cell is an electrolytic cell with a bipolar zero-gap structure, as shown in Figure 1, which is composed of an anode terminal element, a cathode terminal element, and multiple bipolar elements. In this evaluation, a monopolar electrolytic cell composed of an anode terminal element and a cathode terminal element was prepared and used. Each electrolytic cell was similarly equipped with the anode, cathode, and diaphragm of each example and comparative example. The header pipe of the electrolytic cell was an external header type.

[0151] The electrodes (anode, cathode) used in the water electrolysis evaluation were prepared as follows. The diaphragms used were those produced in the Examples and Comparative Examples. <Anode> A nickel expand-type substrate was used as the anode, with a mesh center-to-center distance in the long direction (LW) of 4.6 mm, a mesh center-to-center distance in the short direction (SW) of 3.1 mm, and a substrate thickness of 0.75 mm. <Cathode> An electrode prepared by the following procedure was used as the cathode. The conductive substrate was a plain-woven mesh-type substrate in which nickel fine wires with a diameter of 0.15 mm were woven into 40 meshes. The substrate was blasted with alumina powder with a weight-average particle size of 100 μm or less, then acid-treated in 6 N hydrochloric acid at room temperature for 5 minutes, washed with water, and dried. <Conductive Elastic Body> The conductive elastic body was prepared by woven nickel wires with a wire diameter of 0.15 mm and corrugated to a wave height of 5 mm. The thickness was 5 mm, and the repulsive force at 50% compression deformation was 150 g / cm. ２ The mesh count was approximately 5. <Element> The element was a rectangle measuring 70 mm x 90 mm, with the anode and cathode dimensions being 48 mm x 58 mm. The anode was used by bending 3 mm from each edge at a 45-degree angle. The anode chamber depth (anode chamber depth) was 10 mm, and the cathode chamber depth (cathode chamber depth) was 10 mm, and the material was nickel. A nickel anode receiver measuring 9 mm in height and 10 mm in diameter was attached to the anode terminal element by welding, and a nickel current collector receiver measuring 6 mm in height and 10 mm in diameter was attached to the cathode terminal element by welding. A nickel expand metal current collector was used as the current collector, with a thickness of 1.3 mm and an opening measuring 4.6 mm in width and 3.1 mm in length. The current collector was fixed to the current collector receiver of the cathode terminal element with nickel screws. The conductive elastic body described above was placed on the current collector, and the cathode described above was placed on the conductive elastic body. Next, the above-mentioned anode was fixed to the anode receiver of the anode terminal element with a nickel screw. The cathode element and the anode element were then stacked together via a 70 mm × 90 mm diaphragm and an EPDM gasket with outer dimensions of 90 mm × 70 mm and inner dimensions of 70 mm × 50 mm, thereby forming a zero-gap structure in which the cathode and anode were pressed against the diaphragm.

[0152] [Electrolysis System] The monopolar electrolytic cell was incorporated into an electrolysis device 70 shown in FIG. 4 and used for alkaline water electrolysis. The electrolysis system will now be outlined with reference to FIG. 4. A 30% KOH aqueous solution was sealed as the electrolyte in the gas-liquid separation tank 72 and the external header-type monopolar electrolytic cell 50. This electrolyte was circulated between the anode chamber and the anode gas-liquid separation tank (oxygen separation tank 72o) and between the cathode chamber and the cathode gas-liquid separation tank (hydrogen separation tank 72h) by a liquid feed pump 71. The flow rate of the electrolyte was measured with a flow meter 77 and adjusted to 0.3 L / min, and the temperature was adjusted to 80°C with a ribbon heater 79. SUS316 10AA piping was used for the electrolyte-contacting parts of the circulation flow path. The gas-liquid separation tanks 72 (72h and 72o) had a height of 240 mm and a volume of 2.3 L. The liquid volume in each of the gas-liquid separation tanks 72h and 72o was approximately 50% of the design volume. A current was applied from the rectifier 74 to the cathode and anode of each electrolysis cell at a predetermined electrode density. The rectifier 74 used was a ZX-S-800LAN manufactured by Takasago Machinery Works, Ltd. The hydrogen concentration meter 76 used was an SD-1D manufactured by Riken Keiki Co., Ltd. The pressure gauge 78 used was a KP15-17G manufactured by Nagano Keiki Co., Ltd. The flow meter 77, ribbon heater 79, liquid feed pump 71, gas-liquid separation tanks 72 (72h and 72o), water supply unit 73, and the like were all devices commonly used in the relevant technical field.

[0153] [Electrolysis Test] Using the diaphragms of Examples 1 to 7 and Comparative Examples 1 to 3, electrolysis was carried out at an electrolyte temperature of 80°C and a current density of 10 kA / m ２ Alkaline water electrolysis was performed continuously at a current density of 1000 s. Each diaphragm was immersed in ethanol for 30 seconds and then in water for 4 minutes before use in water electrolysis. When the gas purity reached 1% or more or the cell voltage reached 2.4 V or more, it was determined that electrolysis could not be continued and electrolysis was stopped. The electrolysis time was the time from the start of electrolysis until electrolysis became impossible to continue and electrolysis was stopped, and this was used as the evaluation standard for the long-term stability of the diaphragm. An electrolysis time of 1000 hours or more was assigned an evaluation of A, a time of 720 hours or more but less than 1000 hours was assigned an evaluation of B, and a time of less than 720 hours was assigned an evaluation of C. The results are shown in Table 1.

[0154]

[0155] [Results of Electrolysis Test] In Examples 1 to 7, the electrolysis time exceeded 720 hours, and it was possible to maintain high ion permeability and high gas barrier properties and perform stable water electrolysis for a long period of time.

[0156] On the other hand, in Comparative Examples 1 to 3, the gas purity reached 1% or more or the cell voltage reached 2.4 V or more within a short period of time, and the electrolysis time was less than 720 hours.

[0157] According to the present disclosure, by using a porous membrane containing a polyolefin and having a peel strength in the membrane thickness direction of 2.0 N or more as a diaphragm for alkaline water electrolysis, high ion permeability and high gas barrier properties can be maintained, and water electrolysis can be performed stably for a long period of time, and the porous membrane can be suitably used for hydrogen production by water electrolysis.

[0158] REFERENCE SIGNS LIST 1 Partition wall 2a Anode 2c Cathode 2e Conductive elastic body 2r Current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c Cathode chamber 50 Electrolytic cell 51a Anode terminal element 51c Cathode terminal element 51g Fast head, loose head 51i Insulating plate 51r Tie rod 6 Rectifier plate 60 Element 65 Electrolytic cell 7 Gasket part 70 Alkaline water electrolysis device 71 Liquid feed pump 72h Cathode side gas-liquid separation tank (hydrogen separation tank) 72o Anode side gas-liquid separation tank (oxygen separation tank) 73 Water supply device 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure gauge 79 Heat exchanger 80 Pressure control valve Z Zero gap structure D1 Given Direction

Claims

1. A diaphragm for alkaline water electrolysis, comprising a porous membrane containing polyolefin, the porous membrane having a peel strength of 2.0 N or more in the membrane thickness direction.

2. The diaphragm for alkaline water electrolysis according to claim 1, wherein the porous membrane contains the polyolefin as a main component.

3. The diaphragm for alkaline water electrolysis according to claim 1, wherein the porous membrane contains 90 mass% or more of the polyolefin.

4. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more.

5. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the porous membrane has a peel strength in the thickness direction of 3.0 N or more.

6. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the porous membrane has a thickness of 25 μm or more and 500 μm or less.

7. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the porosity of the porous membrane is 30% or more and 80% or less.

8. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the porous membrane has an air permeability of 10 seconds or more and 2,000 seconds or less, calculated as 100 μm.

9. The diaphragm for alkaline water electrolysis according to claim 1 or 2, wherein the porous membrane has a pin puncture strength of 200 gf or more and 10,000 gf or less.

10. An alkaline water electrolytic cell comprising: the diaphragm for alkaline water electrolysis according to claim 1 or 2; an anode; and a cathode, wherein the diaphragm for alkaline water electrolysis is disposed between the anode and the cathode.

11. A method of using a porous membrane containing polyolefin and having a peel strength of 2.0 N or more in the membrane thickness direction as a diaphragm for alkaline water electrolysis.

12. The method according to claim 11, wherein the porous membrane comprises the polyolefin as a main component.

13. The method according to claim 11, wherein the porous membrane contains 90% by mass or more of the polyolefin.

14. The method according to claim 11 or 12, wherein the polyolefin is polyethylene having a viscosity average molecular weight of 900,000 or more.

15. The method of use according to claim 11 or 12, wherein the porous membrane has a peel strength of 3.0 N or more in the thickness direction.

16. The method of claim 11 or 12, wherein the thickness of the porous membrane is 25 μm or more and 500 μm or less.

17. The method according to claim 11 or 12, wherein the porosity of the porous film is 30% or more and 80% or less.

18. The method of use according to claim 11 or 12, wherein the porous membrane has an air permeability of 10 seconds or more and 2000 seconds or less in terms of 100 μm.

19. The method of use according to claim 11 or 12, wherein the puncture strength of the porous membrane is 200 gf or more and 10,000 gf or less.

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