WO2018182006A1

WO2018182006A1 - Diaphragm, electrolytic bath, and method for producing hydrogen

Info

Publication number: WO2018182006A1
Application number: PCT/JP2018/013957
Authority: WO
Inventors: 稔幸平野; 悠介鈴木; 一洋大海; 則和藤本
Original assignee: 旭化成株式会社
Priority date: 2017-03-31
Filing date: 2018-03-30
Publication date: 2018-10-04
Also published as: JPWO2018182006A1

Abstract

The present invention is characterized by including at least polytetrafluoroethylene (PTFE) and an inorganic compound, by having an average water-permeable pore diameter of 0.02 µm to 1.0 µm, a maximum pore diameter of 0.2 µm to 2.0 µm, a porosity of 30% to 90%, and a thickness of 100 µm to 600 µm, and in that the content of the inorganic compound therein is 70% by mass to 95% by mass with respect to a total amount of 100% by mass of PTFE and the inorganic compound.

Description

Diaphragm, electrolytic cell, and hydrogen production method

The present invention relates to a diaphragm, an electrolytic cell, and a hydrogen production method.

Separation membranes are used in various fields such as concentration, purification, filtration, and dialysis, and are being actively developed to optimize their materials, pore size, thickness, and the like. In recent years, aiming for higher performance and functional specialization for each purpose, both safety and performance have been achieved, particularly in new energy fields such as fuel cells and renewable energy, and storage battery fields such as lithium ion secondary batteries. The demand for diaphragms is increasing day by day. In particular, there is a high demand for developing a diaphragm that can be used in a wide range of temperatures, pressures, and pHs.

Hydrogen is widely used industrially, such as petroleum refining, chemical synthesis materials, metal refining, and stationary fuel cells. In recent years, the possibility of use in hydrogen stations, smart communities, hydrogen power plants, etc. for fuel cell vehicles (FCVs) has also expanded. Furthermore, as the introduction of renewable energy has progressed, it has become necessary to maintain a balance between the supply and demand of the power grid, and there is an increasing need for hydrogen storage that can store a large amount of power for a long period of time. From this point of view, attention has been focused on high-purity hydrogen production technology.

One of the industrial methods for producing hydrogen is electrolysis of water (hereinafter sometimes simply referred to as “electrolysis”). This method has an advantage that high-purity hydrogen can be obtained as compared with a hydrogen production method for reforming fossil fuels. In the electrolysis of water, an aqueous solution to which an electrolyte such as sodium hydroxide or potassium hydroxide is added is generally used as an electrolytic solution in order to increase conductivity. Water is electrolyzed by applying a direct current to the electrolytic solution through a cathode and an anode.

The electrolytic cell for performing electrolysis is divided into an anode chamber and a cathode chamber through a diaphragm. Oxygen gas is generated in the anode chamber, and hydrogen gas is generated in the cathode chamber. The diaphragm is required to have a gas barrier property so that the oxygen gas and the hydrogen gas are not mixed.

The medium that carries electricity (electrons) in the electrolysis of water is ions. Therefore, in order to perform electrolysis efficiently, the diaphragm is required to have high ion permeability. From this viewpoint, Patent Document 1 proposes a diaphragm having a diaphragm structure as a diaphragm that exhibits high ion permeability.

In addition, in order to perform electrolysis efficiently and stably for a long period of time, physical and chemical stability are required for the anode, cathode and diaphragm constituting the electrolytic cell. From such a viewpoint, the diaphragm is required to satisfy both gas barrier properties and high ion permeability using a material having excellent durability.

International Publication No. 2013/183584

However, there are still some points to be improved on the above technology. For example, polyethersulfone and polysulfone, which are widely used as a diaphragm, have an ether group in the repeating unit, and therefore are gradually hydrolyzed in an acidic or alkaline environment. As hydrolysis proceeds, the pore size and porosity change, which may cause a decrease in function as a diaphragm and a decrease in mechanical strength. In particular, under a high temperature, high concentration acidic and alkaline environment, the hydrolysis rate increases, and this problem becomes more remarkable.

On the other hand, the ion transmission efficiency is expressed in terms of conductivity and is closely related to the concentration and temperature of the electrolyte. For example, in a high temperature range of 80 ° C. or higher, the conductivity of the potassium hydroxide aqueous solution is maximum at a concentration of about 30% by mass. For this reason, the use of a diaphragm under high electrical conductivity conditions for the purpose of improving ion transmission efficiency may cause the problem of the hydrolysis rate.

In addition, in order to optimize the ion transmission efficiency of the diaphragm, it is very important to control the porous structure of the diaphragm. In particular, when used as a diaphragm for water electrolysis, it is necessary to achieve both high ion permeability and high gas barrier properties. Therefore, there is a demand for an optimum diaphragm that is a material having high hydrolysis resistance and that can obtain high electrolysis efficiency.

By the way, polytetrafluoroethylene (PTFE) which is a fluorine-based polymer is widely used as a material having high heat resistance and chemical resistance, and has extremely high resistance even in an alkaline environment. It has been known. In particular, porous PTFE called ePTFE is used for applications such as filters and seals in environments that require heat resistance and chemical resistance because it is porous while maintaining the properties of PTFE.

EPTFE can be produced, for example, by the method described in International Publication No. 1997/20881, that is, extrusion, rolling and stretching of PTFE fine powder mixed with a lubricant. However, PTFE is a hydrophobic material and there is still no diaphragm suitable for use in alkaline water electrolysis.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a diaphragm having a high function stably for a long period of time. In particular, an object of the present invention is to provide a diaphragm that has high hydrolysis resistance in a high temperature and high concentration acidic or alkaline environment and that has both high separation ability and ion permeability.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a material containing a hydrophilic inorganic compound and polytetrafluoroethylene (PTFE) has an appropriate average water-permeable pore diameter, maximum pore diameter, porosity, thickness. And it discovered that the said subject could be solved by implement | achieving the diaphragm which has content of a hydrophilic inorganic compound, and came to complete this invention.

That is, the present invention is as follows.
[1]
At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
The content of the inorganic compound is 70% by mass or more and 95% by mass or less, where the total amount of the PTFE and the inorganic compound is 100% by mass,
diaphragm.
[2]
At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
The content of the inorganic compound is 70% by mass or more and 95% by mass or less, where the total amount of the PTFE and the inorganic compound is 100% by mass,
A diaphragm for alkaline water electrolysis.
[3]
The diaphragm according to [1] or [2], wherein the average water-permeable pore diameter is 0.1 μm or more and 1.0 μm or less.
[4]
The diaphragm according to any one of [1] to [3], wherein the inorganic compound is a hydrophilic inorganic particle or a hydrophilic inorganic porous material.
[5]
The diaphragm according to any one of [1] to [4], wherein a primary particle size of the hydrophilic inorganic particles is 10 nm or more and 300 nm or less.
[6]
The hydrophilic inorganic particles include at least one of TiO ₂ , Ti (OH) ₄ , ZrO ₂ , and Zr (OH) ₄ , according to any one of [1] to [5] diaphragm.
[7]
The diaphragm according to any one of [1] to [6], wherein the water contact angle is greater than 10 ° and 90 ° or less.
[8]
Any of [1] to [7], wherein the tensile breaking strength in the flow (MD) direction is 10 MPa or more and 30 MPa or less and the tensile breaking strength in the (TD) direction orthogonal to the flow direction is 10 MPa or more and 30 MPa or less The diaphragm according to the above.
[9]
[1] to the diaphragm according to any one of [8],
A plurality of elements including a cathode and an anode are stacked with the diaphragm interposed therebetween,
An electrolytic cell, wherein the diaphragm is in contact with the cathode and the anode to form a zero gap structure.
[10]
Using the electrolytic cell according to [9], electrolyte temperature 85 ° C. ~ 125 ° C., and wherein the electrolysis of an aqueous solution of potassium hydroxide or sodium hydroxide at a current density of ^{^{4kA / m 2 ~ 20kA / m}} 2 A method for producing hydrogen.
[11]
In a hydrogen production method for producing hydrogen by electrolyzing water containing an alkali with an electrolytic cell,
The electrolytic cell has a diaphragm at least between an anode and a cathode,
The diaphragm is
At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
Content of the said inorganic compound is 70 mass% or more and 95 mass% or less characterized by the total amount of the said PTFE and the said inorganic compound being 100 mass%, The hydrogen manufacturing method characterized by the above-mentioned.

According to the present invention, it is possible to provide a diaphragm for alkaline water electrolysis that has good gas barrier properties and ion permeability, and has high electrolysis efficiency even in high-temperature and long-term electrolysis.

It is a side view shown about the whole example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment. It is a side view which shows the zero gap structure of an example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment about the part of a broken-line square frame. It is a top view shown about the electrode chamber part of an example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment. It is a figure which shows the outline | summary of the alkaline water electrolysis apparatus provided with an example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment. A plan view showing a network portion of an expanded base material as an example of a porous electrode of a bipolar electrolytic cell for alkaline water electrolysis according to this embodiment, and when cut by a plane along line AA in the plan view. It is sectional drawing. It is a top view shown about the mesh part of the plain-woven mesh type | mold base material of an example of the porous body electrode of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment. It is a top view shown about a punching type substrate of an example of a porous body electrode of a bipolar electrolytic cell for alkaline water electrolysis of this embodiment.

(Membrane for alkaline water electrolysis)
Hereinafter, embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The alkaline water electrolysis diaphragm of this embodiment contains at least polytetrafluoroethylene (PTFE) and a hydrophilic inorganic compound, and has an average water-permeable pore diameter of 0.02 μm to 1.0 μm and a maximum pore diameter of 0.2 μm to 2.0 μm. Hereinafter, the porosity is 30% or more and 90% or less, the thickness is 100 μm or more and 600 μm or less, and the content of the hydrophilic inorganic compound is 70% by mass or more and 95% by mass, where the total amount of PTFE and hydrophilic inorganic compound is 100% by mass. It is characterized by being not more than mass%.

-PTFE-
The diaphragm for alkaline water electrolysis in the present embodiment is a porous film containing polytetrafluoroethylene. The PTFE contained in the diaphragm may be appropriately selected from various PTFEs, and among them, PTFE fine powder is preferable. By using PTFE fine powder, the tensile strength of the diaphragm can be increased. PTFE fine powder is obtained by coagulating and drying an aqueous dispersion (PTFE dispersion) of PTFE fine particles (for example, PTFE fine particles having an average particle size of 0.1 to 0.5 μm) obtained by emulsion polymerization of tetrafluoroethylene. PTFE powder produced by The average particle size of the PTFE powder is, for example, 200 to 1000 μm.

As PTFE, pure PTFE made of a homopolymer obtained by polymerizing only tetrafluoroethylene can be used, or modified PTFE which is a copolymer containing a small amount of other monomers can also be used. As a component to be copolymerized with tetrafluoroethylene, for example, one or both of hexafluoropropylene and perfluoropropyl vinyl ether can be used. As PTFE used in the present embodiment, one of these may be used alone, or two or more may be used in combination.
Specific examples of the above-mentioned PTFE fine powder include “Algoflon (trademark, the same applies hereinafter)” of SOLVAY, “Teflon (trademark; same applies hereinafter)” of Mitsui DuPont Fluorochemical Co., “Polyflon” of Daikin (Trademark, the same shall apply hereinafter) ".

By using a copolymer containing tetrafluoroethylene in the main chain skeleton as PTFE, resistance to high temperature and high concentration alkaline solution is further improved. Moreover, a PTFE porous film can be produced by using a known general production method as described in, for example, Japanese Patent No. 2810869.

The standard specific gravity of the PTFE of the present invention is preferably 2.00 or more and 2.30 or less. If the specific gravity is 2.00 or more, the mechanical strength can be ensured in a wide temperature range, and the function of the diaphragm can be stably expressed. If the specific gravity is 2.30 or less, the workability is good and the pore diameter during film formation can be easily controlled.

PTFE may be subjected to a crosslinking treatment. The method for the crosslinking treatment is not particularly limited, and examples thereof include crosslinking by irradiation with radiation such as electron beams and γ rays and thermal crosslinking using a crosslinking agent. These crosslinking treatments are more preferably performed after imparting a porous structure.

-Hydrophilic inorganic compounds-
The diaphragm for alkaline water electrolysis in the present embodiment contains an inorganic compound in order to exhibit high electrolyte solution permeability, high ion permeability, and high gas barrier properties. Here, the inorganic compound may adhere to the surface of the diaphragm, or a part thereof may be buried in a polymer material constituting the porous film. In addition, when the inorganic compound is encapsulated in the gap of the diaphragm, it becomes difficult to detach from the diaphragm, and the performance of the diaphragm can be maintained for a long time. As the inorganic compound, a hydrophilic inorganic compound is preferable, and a hydrophilic inorganic particle or a hydrophilic inorganic porous body in the form of fine particles is more preferable.

--- Hydrophilic inorganic particles--
Examples of hydrophilic inorganic particles include zirconium, titanium, bismuth, cerium oxide or hydroxide; periodic table group IV element oxide; periodic table group IV element nitride, and periodic table. And at least one inorganic substance selected from the group consisting of carbides of Group IV elements. Among these, from the viewpoint of chemical stability, oxides of zirconium, titanium, bismuth, cerium, oxides or hydroxides of group IV elements of the periodic table are preferable, and zirconium oxide (ZrO ₂ ), zirconium hydroxide (Zr (OH) ₄ ), titanium oxide (TiO ₂ ), and titanium hydroxide (Ti (OH) ₄ ) are more preferable. These hydrophilic inorganic particles may be used alone or in combination of two or more. As an electrolytic solution for alkaline water electrolysis, alkaline solutions such as NaOH aqueous solution and KOH aqueous solution are often used. When titanium oxide is exposed to such an environment, it may change to a titanate such as sodium titanate or potassium titanate. Therefore, titanate may be used in advance as the hydrophilic inorganic particles. The particle surface of the hydrophilic inorganic particles is polar. Considering the affinity between oxygen molecules and hydrogen molecules with a small polarity and water molecules with a large polarity in an electrolyte solution that is an aqueous solution, water molecules with a large polarity are more easily adsorbed to hydrophilic inorganic particles. Conceivable. Therefore, when such hydrophilic inorganic particles are present on the surface of the diaphragm, water molecules are preferentially adsorbed on the surface of the diaphragm, and bubbles such as oxygen molecules and hydrogen molecules are not adsorbed on the surface of the diaphragm. As a result, it is possible to effectively suppress the adhesion of bubbles to the diaphragm surface.

The average primary particle size of the hydrophilic inorganic particles is not particularly limited, but is preferably 10 nm or more and 300 nm or less, and more preferably 25.0 nm or more and 250 nm or less. When the average primary particle size of the hydrophilic inorganic particles is within this range, when the particles are taken into the pores of the membrane, the particle size of the secondary particles formed by aggregation is larger than the pore size of the membrane, so Of the inorganic particles can be suppressed. In addition, the surface area of the secondary particles of the hydrophilic inorganic particles can be increased to make the pores of the diaphragm more hydrophilic. Moreover, it is possible to prevent the hydrophilic inorganic particles dropped from the diaphragm from blocking the pores of the porous electrode, thereby preventing an increase in overvoltage.
The average primary particle size of the hydrophilic inorganic particles in the diaphragm can be determined by the following method. The measurement sample is observed with a scanning electron microscope (SEM) from the direction perpendicular to the diaphragm surface, and is imaged at a magnification at which the hydrophilic inorganic particles can be observed. The image is binarized using image analysis software, the absolute maximum length is measured for each of the 10 non-aggregated inorganic particles, and the number average is obtained.

The average secondary particle size of the hydrophilic inorganic particles is not particularly limited, but is preferably 0.2 μm or more and 10 μm or less, and preferably 0.5 μm or more, from the viewpoint of preventing falling off from the diaphragm and hydrophilization in the pores of the porous membrane. More preferably, it is 8.0 μm or less. The average secondary particle size is an average particle size in a state of secondary particles formed by hydrophilic inorganic particles in the diaphragm.
The average secondary particle size can be measured from the volume distribution by laser diffraction / scattering method using the hydrophilic inorganic particles remaining after dissolving and removing the polymer resin from the diaphragm as a measurement sample. it can. More specifically, it can be determined by the method described in Examples described later.

--- Hydrophilic inorganic porous material--
Examples of the hydrophilic inorganic porous material include oxides or hydroxides of zirconium, titanium, bismuth, and cerium; oxides of group IV elements of the periodic table; nitrides of group IV elements of the periodic table; and periodic rules Examples include at least one inorganic substance selected from the group consisting of carbides of Group IV elements. Among these, from the viewpoint of chemical stability, oxides of zirconium, titanium, bismuth, cerium, oxides or hydroxides of group IV elements of the periodic table are preferable, and zirconium oxide (ZrO ₂ ), zirconium hydroxide (Zr _{(OH) 4),} titanium oxide _(TiO 2), titanium hydroxide (Ti _{(OH) 4)} is more preferable. These hydrophilic inorganic porous materials may be used alone or in combination of two or more. As an electrolytic solution for alkaline water electrolysis, alkaline solutions such as NaOH aqueous solution and KOH aqueous solution are often used. When titanium oxide is exposed to such an environment, it may change to a titanate such as sodium titanate or potassium titanate. Therefore, titanate may be used in advance as the hydrophilic inorganic porous body. The surface of the hydrophilic inorganic porous body is polar. Considering the affinity between oxygen molecules and hydrogen molecules with a small polarity and water molecules with a large polarity in an electrolyte solution that is an aqueous solution, water molecules with a large polarity are more easily adsorbed to the hydrophilic inorganic porous material. it is conceivable that. Therefore, when such a hydrophilic inorganic porous material exists on the surface of the diaphragm, water molecules are preferentially adsorbed on the surface of the diaphragm, and bubbles such as oxygen molecules and hydrogen molecules are not adsorbed on the surface of the diaphragm. As a result, it is possible to effectively suppress the adhesion of bubbles to the diaphragm surface.

The average pore size of the hydrophilic inorganic porous material is not particularly limited, but is preferably 10 nm or more and 500 nm or less, and more preferably 20 nm or more and 300 nm or less. When the average pore size of the hydrophilic inorganic porous material is within this range, both high gas barrier properties and high ion permeability can be achieved. *

In this embodiment, the total amount of PTFE and hydrophilic inorganic compound contained in the diaphragm is 100% by mass, and the content of the hydrophilic inorganic compound is 70% by mass to 95% by mass. When the content of the hydrophilic inorganic compound is 70% by mass or more, for example, the hydrophilicity inside the diaphragm can be increased even during electrolysis, and it is easy to prevent the generated gas from passing through the diaphragm to the opposite electrode chamber. Furthermore, since the electrolytic solution can permeate into the diaphragm, the voltage loss of the diaphragm can be kept lower. On the other hand, when the content of the hydrophilic inorganic particles is 95% by mass or less, it is easy to control the porosity of the diaphragm higher.

[Hydrolysis resistance]
In the present embodiment, the diaphragm preferably has high hydrolysis resistance from the viewpoint of obtaining stable performance for a long period of time. During diaphragm electrolysis, since it is always immersed in a high-temperature and high-concentration alkaline solution, if the hydrolyzability is insufficient, the diaphragm may gradually deteriorate and become brittle. The fragile diaphragm is eroded by the circulating electrolyte and generated gas, and the pores become larger and the porosity becomes larger. As a result, the gas barrier property is lowered, and the gas generated from both electrodes is mixed to easily reduce the gas purity.

The diaphragm in the present embodiment may contain a substance other than PTFE as long as the function of the diaphragm is not inhibited for the purpose of imparting further functions. For example, an additive such as an antioxidant or a heat stabilizer may be contained, or a coating such as a fluorine resin may be applied.

[Diaphragm pore size]
In the present embodiment, the pore diameter must be controlled in order to obtain appropriate membrane properties such as separation ability and strength. In alkaline water electrolysis, the pore diameter of the diaphragm must be controlled from the viewpoint of preventing mixing of oxygen gas generated from the anode and hydrogen gas generated from the cathode and reducing voltage loss in electrolysis.

The larger the average water permeability pore size of the diaphragm, the better the ion permeability of the diaphragm, and the more likely it is to reduce the voltage loss. Moreover, since the surface area of contact with the alkaline solution is smaller as the average water-permeable pore diameter of the diaphragm is larger, the deterioration of the polymer tends to be suppressed.

On the other hand, the smaller the average water-permeable pore diameter of the diaphragm, the higher the resolution of the diaphragm, and the better the gas barrier property of the diaphragm in electrolysis. Furthermore, when a hydrophilic inorganic compound having a small particle size, which will be described later, is supported on the diaphragm, it can be held firmly without being lost. Thereby, the high retention capability of a hydrophilic inorganic compound can be provided, and the effect can be maintained over a long period of time.

Also, the maximum pore size of the diaphragm must be controlled to increase the separation accuracy of the diaphragm. Specifically, the separation performance tends to be higher as the difference between the average water-permeable pore diameter and the maximum pore diameter is smaller. In particular, in electrolysis, since the variation in the hole diameter in the diaphragm can be kept small, it is possible to reduce the possibility that the purity of the gas generated from both electrode chambers due to the generation of pinholes is lowered.

From such a viewpoint, in the diaphragm of the present invention, the average water-permeable pore diameter of the diaphragm must be in the range of 0.02 μm to 1.0 μm and the maximum pore diameter is in the range of 0.2 μm to 2.0 μm. If the pore diameter is within this range, both excellent gas barrier properties and high ion permeability can be achieved. Further, the pore diameter of the diaphragm is preferably controlled in the temperature range in which it is actually used. Therefore, for example, when used as a diaphragm for electrolysis in an environment of 90 ° C., it is necessary to satisfy the above pore diameter range at 90 ° C. In addition, as a diaphragm for alkaline water electrolysis, an average water-permeable pore diameter of 0.1 μm or more and 1.0 μm or less and a maximum pore diameter of 0.5 μm or more and 1.8 μm can be exhibited as a better gas barrier property and high ion permeability. Or less, more preferably 0.1 μm or more and 0.5 μm or less, and a maximum pore diameter of 0.5 μm or more and 1.8 μm or less.

The pore diameter of the diaphragm is preferably controlled approximately symmetrically in the thickness direction from the center of the diaphragm to both surfaces. When the pore size distribution of the diaphragm is symmetric, for example, when the diaphragm is incorporated into an electrolytic cell, the same function can be exhibited on both the front and back sides, and handling properties are improved. In addition, foreign matter is less likely to be clogged inside the diaphragm during electrolysis. Furthermore, it is more preferable that the pore diameter of the diaphragm gradually decreases from the surface of the diaphragm toward the inside in the thickness direction. When the pore diameter is gradually reduced toward the inside, high separation ability can be maintained even when, for example, the surface of the diaphragm is damaged by foreign matter during use.

The average water permeability pore diameter and the maximum pore diameter of the diaphragm can be measured by the following methods.
The average water-permeable pore diameter of the diaphragm means an average water-permeable pore size measured by the following method using an integrity tester (“Sartochcheck Junior BP-Plus” manufactured by Sartorius Stedim Japan). First, the diaphragm is cut into a predetermined size including the core material, and this is used as a sample. This sample is set in an arbitrary pressure vessel, and the inside of the vessel is filled with pure water. Next, the pressure vessel is held in a thermostatic chamber set at a predetermined temperature, and measurement is started after the pressure vessel reaches a predetermined temperature. When the measurement starts, the upper surface side of the sample is pressurized with nitrogen, and the pressure and the permeate flow rate when pure water permeates from the lower surface side of the sample are recorded. The average water-permeable pore diameter can be obtained from the following Hagen-Poiseuille equation using a pressure between 10 kPa and 30 kPa and a gradient of the water flow rate.

Average water-permeable pore diameter (m) = {32ηLμ ₀ / (εP)} ^0.5
Here, η is the viscosity of water (Pa · s), L is the thickness of the diaphragm (m), μ ₀ is the apparent flow velocity, and μ ₀ (m / s) = flow rate (m ³ / s) / flow channel area. (M ² ). Further, ε is the porosity, and P is the pressure (Pa).

The maximum pore diameter of the diaphragm can be measured by the following method using an integrity tester (manufactured by Sartorius Stedim Japan, “Sartochcheck Junior BP-Plus”). First, the diaphragm is cut into a predetermined size including the core material, and this is used as a sample. This sample is wetted with pure water, impregnated with pure water in the pores of the diaphragm, and set in a pressure-resistant container for measurement. Next, the pressure vessel is held in a thermostatic chamber set at a predetermined temperature, and measurement is started after the pressure vessel reaches a predetermined temperature. When the measurement starts, the upper surface side of the sample is pressurized with nitrogen, and the nitrogen pressure when bubbles are continuously generated from the lower surface side of the sample is defined as a bubble point pressure. The maximum pore diameter can be obtained from the following bubble point equation obtained by modifying the Young-Laplace equation.

Maximum pore diameter (m) = 4γ cos θ / P
Here, γ is the surface tension (N / m) of water, cos θ is the contact angle (rad) of the diaphragm surface and water, and P is the bubble point pressure (Pa).

[Porosity of diaphragm]
From the viewpoint of appropriate separation ability and prevention of shortening of the life due to clogging, the porosity of the diaphragm must be controlled. In addition, when a diaphragm is used for electrolysis, it is possible to maintain gas barrier properties, maintain hydrophilicity, prevent ion permeability from being reduced due to air bubbles, and obtain stable electrolysis performance (low voltage loss, etc.) for a long time. , The porosity of the diaphragm must be controlled. It can be said that the porosity of the diaphragm is related to the ratio of the pores having the average pore diameter and the maximum pore diameter within the above ranges to the diaphragm. In order to exhibit the high function of the diaphragm, in particular the compatibility of gas barrier properties and low voltage loss in the diaphragm for alkaline water electrolysis, the lower limit of the porosity of the diaphragm needs to be 30% or more, and 35% or more. Is more preferable, and it is still more preferable that it is 40% or more. Moreover, the upper limit of porosity needs to be 80% or less, and it is more preferable that it is 70% or less. If the porosity of the diaphragm is not more than the above upper limit value, the porous structure can be maintained.

Here, the porosity ε of the diaphragm refers to the open porosity determined by the Archimedes method and can be determined by the following equation.
Porosity ε (%) = (ρ1-ρ2) × 100
ρ1 represents the saturated water density (g / cm ³ ), that is, the density of the sample in a state where the open pores are saturated with water. ρ2 represents the dry density (g / cm ³ ), that is, the density of the sample in a state where water is sufficiently removed from the open pores and dried. ρ1 and ρ2 are w: weight (g), d: thickness (cm), s: area (cm ² ) of a plane perpendicular to the thickness direction, and ρ = w / (d Xs).
If the water contact surface of the diaphragm sample is low in water absorption and the thickness or area of the sample does not change significantly between the water-containing state and the dry state, d and s may be regarded as constant values. it can.
Specifically, the porosity ε can be measured in a room set at 25 ° C. by the following procedure. The diaphragm washed with pure water is cut into three pieces having a size of 3 cm × 3 cm, and the thickness d is measured with a thickness gauge. These measurement samples are immersed in pure water for 24 hours, excess water is removed, and the weight w1 (g) is measured. Subsequently, the sample taken out is allowed to stand for 12 hours or more in a dryer set at 50 ° C. and dried, and the weight w2 (g) is measured. And a porosity is calculated | required from the value of w1, w2, and d. The porosity is obtained for three samples, and the arithmetic average value thereof is defined as the porosity ε of the diaphragm.

And there is a correlation between the porosity of the diaphragm and the degree of opening of the membrane surface. For example, the degree of opening tends to increase as the porosity increases. Moreover, it is easy to receive the effect of the hydrophilic inorganic compound mentioned later, and there exists a tendency to maintain higher hydrophilicity, so that opening degree is high. For these reasons, it is preferable to control the opening degree of the diaphragm according to the present embodiment after controlling the porous structure within the above-described range of the pore diameter. From the viewpoint of maintaining high hydrophilicity, the opening degree needs to be 20% or more, more preferably 25% or more, and still more preferably 30% or more. On the other hand, in order to maintain the support of the hydrophilic inorganic compound and the strength of the diaphragm surface, the opening degree needs to be 80% or less, more preferably 75% or less, and still more preferably 70% or less.

The opening degree of the diaphragm in the present embodiment can be obtained by the following method. First, a diaphragm surface image is captured by SEM. Next, this image is binarized by image analysis software (“WinROOF”, manufactured by Mitani Corporation), and the holes and portions other than the holes are separated. Subsequently, the obtained binarized image is analyzed to determine the ratio of holes to the entire image, and this is used as the opening degree. As the aperture, an average value of apertures obtained from three or more SEM images with different observation locations is used.

By forming a diaphragm having the above pore diameter and porosity with a polyphenylene copolymer, it is possible to realize a diaphragm structure having higher mechanical strength and higher strength than other polymers. In addition, it has been found that the diaphragm stably exhibits its function over a long period of time in a wide range of temperature, pressure and pH.

[Thickness of diaphragm]
The thickness of the diaphragm of this embodiment must be controlled in order to obtain appropriate film properties and electrolysis performance. In alkaline water electrolysis, it must be properly controlled to increase the mechanical strength and electrolysis efficiency of the diaphragm.

From such a viewpoint, the thickness of the diaphragm must be 100 μm or more and 600 μm or less. If the thickness of the diaphragm is 100 μm or more, the diaphragm is hardly broken and the strength against impact is further improved. From this viewpoint, the thickness of the diaphragm is more preferably 200 μm or more, and further preferably 300 μm or more.
On the other hand, if the thickness of the diaphragm is 600 μm or less, thickness unevenness can be reduced during film formation, and the pore diameter can be easily controlled. In addition, when the diaphragm is used for electrolysis, the ion permeability is hardly hindered by the resistance of the electrolytic solution contained in the pores, and a further excellent ion permeability can be maintained. From this viewpoint, the thickness of the diaphragm is more preferably 500 μm or less, and further preferably 450 μm or less.

[Mechanical strength]
The tensile strength at break of the diaphragm of the present embodiment is preferably controlled in each of the MD direction and the TD direction. Specifically, the tensile breaking strength in the MD direction is preferably 10 MPa or more and 30 MPa or less, and the tensile breaking strength in the TD direction is preferably 10 MPa or more and 30 MPa or less. If it is a diaphragm which has the tensile fracture strength of each range, it will become a diaphragm with high handling property at the time of incorporating in an electrolytic cell, and a tear and a pinhole are hard to generate | occur | produce. In addition, the tensile strength at break of the diaphragm is preferably controlled in the temperature range in which it is actually used. Therefore, for example, when used as a diaphragm for electrolysis in an environment of 90 ° C., it is necessary to satisfy the above-described range of tensile strength at 90 ° C. The tensile strength at break can be measured by a method according to JIS K 7161. In this specification, unless otherwise specified, the MD (Machine Direction) direction is a flow direction during film formation, and the TD (Transverse Direction) direction is a direction orthogonal to the MD direction.

When a notch or a pinhole is generated in the diaphragm of the present embodiment, tear strength is given as one of indices indicating the ease of fracture starting from the notch or pinhole. The tear strength of the diaphragm can be measured by a method according to JIS L 1096. If the tear strength of the diaphragm is high, for example, even when notches or pinholes are generated due to contact with the electrode during electrolysis, it is possible to more effectively suppress the problem that the diaphragm is broken by its own weight. The tear strength of the diaphragm is not particularly limited, but is preferably 10N or more and 100N or less. If the tear strength is 10 N or more, even when a notch, a pinhole, or the like is generated in the diaphragm, it is possible to more effectively suppress the wound from being enlarged. When the tear strength is 100 N or less, the adhesion with the electrode is improved during water electrolysis, and the electrolysis efficiency can be increased. Here, the tear strength of the diaphragm is the tear strength in each of the MD direction and the TD direction.

[Water contact angle]
Although the water contact angle of the porous membrane is not particularly limited, it can be 10 ° or more and 90 ° or less, preferably 20 ° or more and 80 ° or less, from the viewpoint of gas barrier properties and electrolyte permeability. It is more preferable that the angle is not less than 70 ° and not more than 70 °. When the water contact angle is within this range, it is possible to prevent the gas generated at the electrode from adhering to the electrode surface and hindering the electrode reaction, and the electrolysis efficiency can be further enhanced.
The water contact angle of the porous membrane can be controlled by controlling the hydrophilicity of a material such as a polymer constituting the surface of the porous membrane. Here, the water contact angle of the porous electrode refers to the tangent and the surface of the porous electrode when water is dropped on the surface of the porous electrode and a tangent is drawn from the portion where the water droplet contacts the porous electrode to the surface of the water droplet. This is the angle formed by
The water contact angle of the porous electrode can be measured by the θ / 2 method using a commercially available contact angle meter.

<Method for producing diaphragm (1)>
Although the diaphragm for alkaline water electrolysis of this embodiment is not specifically limited, It can form into a film by a well-known method, However, It is preferable to provide the following processes. These steps do not limit the procedure and can be appropriately selected.
<< Step A >> Step of mixing PTFE fine powder, hydrophilic inorganic particles and lubricant << Step B >> Step of preforming the mixture obtained in Step A and extruding the paste << Step C >> Step of rolling the sheet between a pair of rolls << step D >> step of removing the lubricant from the rolled sheet << step E >> step of stretching the obtained sheet in the MD or TD direction << Step F >> Step of firing the stretched sheet at a temperature equal to or higher than the melting point of PTFE

Hereinafter, each step will be described in detail.
<< Step A >>
As a raw material, it is preferable to use PTFE fine powder having a standard specific gravity of 2.19 or less, particularly 2.16 or less. The standard specific gravity is a specific gravity measured according to JIS K6892.
The lubricant is not particularly limited as long as it can wet the surface of the PTFE fine powder and can be removed by means such as evaporation or extraction after the mixture is formed into a sheet. The lubricant is, for example, a hydrocarbon oil such as liquid paraffin, naphtha, white oil, toluene, xylene, and various alcohols, ketones, esters, and the like can be used. Among them, when liquid paraffin is used, the affinity with PTFE is good, the moldability is good, and the product that completely evaporates in Step F is preferable. Specifically, those having a boiling point of 100 ° C. or higher and 160 ° C. or lower are more preferable. Examples of such liquid paraffin include “Isopar E” and “Isopar M” manufactured by TonenGeneral.

The amount of lubricant added to PTFE is not particularly limited, but is preferably 20 parts by mass or more and 200 parts by mass or less when the total of PTFE and hydrophilic inorganic particles is 100 parts by mass. If it is this range, since a lubricant will fully osmose | permeate PTFE and the dispersion state of a hydrophilic inorganic particle will also become favorable, a diaphragm without a spot can be obtained.

In order to uniformly disperse the hydrophilic inorganic particles in the lubricant, it is preferable to carry out a dispersion treatment in the presence of the dispersant in the lubricant to obtain a dispersion (dispersion paste). The dispersant is not particularly limited, but is a long-chain carboxylic acid having low water solubility such as stearic acid, lauric acid, decanoic acid, octanoic acid, 2-ethylhexanoic acid, and a polar having a chain length of 6 or more carbon atoms. An organic solvent is mentioned. A known apparatus can be used for the dispersion treatment, and specific examples include a bead mill, a ball mill, a planetary mixer, a disper, and a homogenizer.

The amount of the dispersant added is not particularly limited as long as the surface of the hydrophilic inorganic particles can be hydrophobized, but is preferably 1% by mass or more and 10% by mass or less with respect to the hydrophilic inorganic particles. If it is this range, the surface of a hydrophilic inorganic particle can fully be hydrophilized, and it will be supersaturated in a lubricant and will not precipitate.

The mixing temperature is not particularly limited, but is preferably 19 ° C. or lower, which is the PTFE transition point. Moreover, in order to fully infiltrate PTFE into PTFE between the process A and the process B, it is preferable to age | cure | ripen. For aging, it is preferable to ripen PTFE at a temperature not lower than the transition point of PTFE, that is, not lower than 20 ° C. and not higher than 30 ° C. A uniform extruded sheet can be obtained in Step B after the aging step.

<< Step B >>
The mixture obtained in step A is extruded into a sheet using a T-die after preforming in step B. Although it does not specifically limit for extrusion, It is preferable to use a flat die. The thickness of the extruded PTFE sheet is preferably 0.5 to 5.0 mm.

It is preferable to perform preforming for the purpose of reducing the bulk of the paste and eliminating excess air. In molding, the physical properties of the obtained sheet can be made uniform by appropriately controlling the molding pressure, compression speed, and holding time.

The extrusion temperature is not particularly limited, but is preferably 20 ° C or higher and 100 ° C or lower. If it is this range, an appropriate shear can be given to PTFE and a moldability becomes favorable in a latter process. From this viewpoint, the extrusion temperature is more preferably 30 ° C. or higher and 80 ° C. or lower.

<< Step C >>
In step C, the sheet extruded from the die is rolled through the pair of rolls along the MD direction. At this time, the TD direction is preferably rolled while maintaining the width of the sheet. That is, the sheet is stretched only in the MD direction. Specifically, this rolling is performed by passing the sheet between the pair of rolling rolls while pulling the sheet with a pulling roll disposed downstream of the pair of rolling rolls in the sheet flow direction. Can be implemented. At this time, if the rotational speed of the pulling roll is set slightly higher than the rotational speed of the rolling roll, the sheet is rolled in the MD direction while keeping the length in the TD direction constant.

In step C, the PTFE sheet is rolled in a state containing a liquid lubricant, and the PTFE sheet is stretched thinner than at the time of extrusion, and the thickness is leveled.

Although the temperature of the rolled sheet is affected by the temperature of the roll and the atmosphere, it may be lower than 19 ° C. which is the phase transition point of PTFE. However, when the temperature of the PTFE sheet is so low, the film thickness distribution in the width direction of the obtained PTFE porous film becomes large. Therefore, the PTFE sheet at a temperature of less than 19 ° C. is heated to a temperature of 19 ° C. or higher. That is, in Step C, the PTFE sheet at a temperature lower than the phase transition point of PTFE is heated so as to have a temperature equal to or higher than the phase transition point of PTFE. However, it is preferable to heat the PTFE sheet so as to be less than the boiling point of the lubricant to be used.

The rolling of the PTFE sheet is preferably performed such that the length in the width direction after rolling relative to the length in the width direction before rolling is in the range of 90% to 110%. In this specification, when the change in the length in the width direction is within the above range, the sheet is rolled “while maintaining the length in the width direction”. In step C, the thickness of the PTFE sheet after rolling is preferably 50 μm or more and 2000 μm. In Step C, the thickness of the PTFE sheet is preferably 5% or more and 60% or less compared to the thickness before rolling. The thickness of the PTFE sheet in step B is preferably 30% or less as compared with the thickness before rolling. The rolling in step C is preferably performed in a state where the liquid lubricant is held on the PTFE sheet. For this reason, it is preferable to carry out while keeping the temperature of the PTFE sheet below the boiling point of the liquid lubricant.

<< Step D >>
In step D, the lubricant is removed by heating or extracting the sheet. At this time, if the heating is performed at a temperature equal to or higher than the boiling point of the dispersant, the dispersant can also be removed. When removing by drying, the temperature is preferably 100 ° C. or higher and 300 ° C. or lower.

<< Step E >>
In step E, the sheet is stretched in the MD direction and the TD direction to produce a porous film containing PTFE. The stretching is preferably carried out at a temperature below the melting point of PTFE.

The stretching in the longitudinal direction is preferably performed by a roll stretching method, and the stretching in the width direction is preferably performed by a tenter stretching method. Either stretching in the longitudinal direction or stretching in the width direction may be performed first. In the step E, the draw ratio is appropriately adjusted so that desired characteristics can be obtained. The stretch plane magnification calculated by the product of the stretch ratio in the longitudinal direction and the stretch ratio in the width direction is appropriately adjusted according to the desired electrolytic performance. The stretching in step F is preferably performed at a temperature lower than the melting point of PTFE. Thin fibrils are produced by stretching in Step F.

<< Step F >>
In step F, the stretched porous membrane is heated to a temperature equal to or higher than the melting point of PTFE and baked. This heating step improves the strength of the PTFE porous sheet.

<Method for producing diaphragm (2)>
It can also be manufactured by a method comprising the following steps, which is different from the above-described method (1) for manufacturing a diaphragm. These steps do not limit the procedure and can be appropriately selected.
<< Step G >> Step of impregnating PTFE porous membrane with solution of inorganic compound << Step H >> Step of depositing inorganic compound from inorganic compound solution in PTFE porous membrane

Hereinafter, each step will be described in detail.
<< Process G >>
The form of the PTFE porous membrane is not particularly limited, and examples thereof include papermaking, non-woven fabric, and stretched aperture membrane, but stretched aperture membranes are preferable. The thickness is 100 μm or more and 600 μm or less, the average pore diameter is 1.0 μm or less, and the porosity is 50% or more. 90% or less is preferable.

The solvent of the solution to be impregnated is not particularly limited as long as it permeates PTFE. However, since it needs to be removed by drying, low molecular weight alcohols such as ethanol, propanol, and butanol having a low boiling point and volatile, acetone, Ketones and esters such as butanone are preferred.

As the inorganic compound, titanium, bismuth, zirconium, cesium salts and organic compounds are used. From the viewpoint of solubility and stability, an alcohol solution of an alkoxide compound of titanium or zirconium is preferably used.
Examples of the step of impregnating the PTFE porous membrane with the inorganic compound solution include dip coating, slit coating, roll coating, blade coating, and the like.

<< Step H >>
The inorganic compound impregnated in the PTFE porous membrane can be precipitated in the PTFE porous membrane by synthesizing a compound having low solubility by drying or chemical reaction. Hydrolysis is an example of a method for synthesizing a compound having low solubility by a chemical reaction. Acid chlorides and alkoxide compounds react with water, and are deposited by replacing some or all of chlorine and alkoxyl groups with hydroxyl groups. The form of water to be reacted is not limited and may be liquid or gas. In order to obtain a more stable compound such as an oxide after depositing a compound having low solubility by a chemical reaction, a heating step may be added. The heating temperature is preferably 400 ° C. or lower at which PTFE does not decompose. The heating environment may be liquid or gas. The liquid is not particularly limited, and examples thereof include acidic solutions such as hydrochloric acid, nitric acid, and sulfuric acid, and alkaline aqueous solutions containing ammonia, sodium hydroxide, and potassium hydroxide. Furthermore, for example, a stable compound can be obtained in a short time by hydrothermal synthesis by exposure to high temperature and high pressure in a liquid.

(Bipolar electrolytic cell for alkaline water electrolysis)
Hereinafter, an example of a bipolar electrolytic cell for alkaline water electrolysis according to this embodiment, which includes the above-described cathode, anode, and diaphragm, will be described with reference to the drawings.
In addition, the bipolar electrolytic cell for alkaline water electrolysis of this embodiment is not limited to what is demonstrated below. Further, members other than the anode, the cathode and the diaphragm included in the bipolar electrolytic cell for alkaline water electrolysis are not limited to those listed below, and known members can be appropriately selected, designed and used. .

The electrolytic cell for alkaline water electrolysis of this embodiment is a bipolar electrolytic cell formed by stacking (stacking) the above-described diaphragm for alkaline water electrolysis of the present invention and a bipolar element holding a cathode and an anode. is there. In other words, the electrolytic cell for alkaline water electrolysis according to the present embodiment is a combination of an anode, a cathode, and the above-described diaphragm for alkaline water electrolysis according to the present invention disposed between the anode and the cathode (“electrolysis cell”). Is also a bipolar electrolyzer having a plurality. The diaphragm for alkaline water electrolysis of the present invention is a material containing a hydrophilic inorganic compound and polytetrafluoroethylene (PTFE), and has an appropriate average water-permeable pore diameter, maximum pore diameter, porosity, thickness, and content of the hydrophilic inorganic compound. Have. As a result, it is possible to provide a diaphragm for alkaline water electrolysis that has good gas barrier properties and ion permeability, and has high electrolysis efficiency even in high-temperature and long-term electrolysis.

Thus, the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment is characterized by including the above-described diaphragm for alkaline water electrolysis according to the present invention, and other configurations are not particularly limited. Hereinafter, the configuration of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment will be described with reference to the drawings.

In FIG. 1, the side view about the whole example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment is shown.
In FIG. 2, the side view about the part of the broken-line square frame which shows the zero gap structure of an example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment to (A) is shown.
In FIG. 3, the top view about the electrode chamber part of an example of the bipolar electrolytic cell for alkaline water electrolysis of this embodiment is shown.
As shown in FIG. 1, the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment includes an anode 2 a, a cathode 2 c, a partition wall 1 that separates the anode 2 a and the cathode 2 c, and an outer frame 3 that borders the partition wall 1. Is a bipolar electrolytic cell 50 in which a plurality of electrolytic cells 65 are stacked with the diaphragm 4 interposed therebetween.

In the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment, although not particularly limited, it is preferable that a zero gap structure Z in which the diaphragm 4 is in contact with the anode 2a and the cathode 2c is formed (see FIG. 2).

In the bipolar electrolytic cell 50 according to this embodiment, an electrode chamber 5 through which an electrolytic solution passes is defined by the partition wall 1, the outer frame 3, and the diaphragm 4 (see FIGS. 2 and 3).

((Bipolar element))
A bipolar element 60 used in a bipolar electrolytic cell for alkaline water electrolysis as an example, as shown in FIGS. 2 to 3, includes a partition wall 1 that separates an anode 2a and a cathode 2c, and an outer edge that surrounds the partition wall. A frame 3 is provided. More specifically, the partition wall 1 has conductivity, and the outer frame 3 is provided so as to surround the partition wall 1 along the outer edge of the partition wall 1.

In the present embodiment, the bipolar element 60 may be used so that a given direction D1 along the partition wall 1 is normally a vertical direction. Specifically, as shown in FIGS. 2 and 3, when the partition wall 1 has a rectangular shape in plan view, a given direction D1 along the partition wall 1 is a set of two sides facing each other. The direction may be the same as the direction (see FIGS. 1 to 3). And in this specification, the said perpendicular direction is also called electrolyte solution passage direction.

In the present embodiment, as shown in FIG. 1, the bipolar electrolytic cell 50 is configured by stacking a necessary number of bipolar elements 60.
In the example shown in FIG. 1, the bipolar electrolytic cell 50 has a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in order from one end, and further, an anode side gasket portion 7, a diaphragm 4, and a cathode side gasket portion. 7. Bipolar elements 60 are arranged in this order. At this time, the bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a side. The anode gasket portion 7 to the bipolar element 60 are repeatedly arranged as many times as necessary for the design production amount. After the necessary number of anode-side gasket portions 7 to the bipolar element 60 are repeatedly arranged, the anode-side gasket portion 7, the diaphragm 4, and the cathode-side gasket portion 7 are arranged again, and finally, the cathode terminal element 51c and the insulation The plate 51i and the loose head 51g are arranged in this order. The bipolar electrolyzer 50 is formed into a body by tightening the entire body with a tightening mechanism such as a tie rod 51r (see FIG. 1) or a hydraulic cylinder system.
The arrangement constituting the bipolar electrolytic cell 50 can be arbitrarily selected from the anode 2a side or the cathode 2c side, and is not limited to the order described above.

As shown in FIG. 1, in the bipolar electrolytic cell 50, the bipolar element 60 is disposed between the anode terminal element 51a and the cathode terminal element 51c, and the diaphragm 4 is connected to the anode terminal element 51a and the bipolar terminal element. It is disposed between the element 60, between the adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51c.

In the bipolar electrolytic cell 50 according to the present embodiment, as shown in FIGS. 2 and 3, an electrode chamber 5 through which an electrolytic solution passes is defined by the partition wall 1, the outer frame 3, and the diaphragm 4.

Specifically, the electrode chamber 5 has an electrolyte inlet for introducing the electrolyte into the electrode chamber 5 and an electrolyte outlet for extracting the electrolyte from the electrode chamber 5 at the boundary with the outer frame 3. More specifically, the anode chamber 5a is provided with an anode electrolyte inlet for introducing an electrolyte into the anode chamber 5a and an anode electrolyte outlet for extracting an electrolyte led out from the anode chamber 5a. Are provided with a cathode electrolyte inlet for introducing an electrolyte into the cathode chamber 5c and a cathode electrolyte outlet for extracting an electrolyte led out from the cathode chamber 5c.

In the example shown in FIGS. 1 to 3, the rectangular partition wall 1 and the rectangular diaphragm 4 are arranged in parallel, and the partition wall of the rectangular parallelepiped outer frame 3 provided at the edge of the partition wall 1. Since the inner surface on one side is perpendicular to the partition wall 1, the shape of the electrode chamber 5 is a rectangular parallelepiped.

The bipolar electrolytic cell 50 is usually provided with a header which is a pipe for distributing or collecting the electrolytic solution. The electrolytic solution is placed in the anode chamber 5 a below the outer frame 3 at the edge of the partition wall 1. An anode inlet header and a cathode inlet header into which the electrolyte solution is placed in the cathode chamber 5c. Similarly, an anode outlet header for discharging the electrode solution from the anode chamber 5a and a cathode outlet header for discharging the electrolyte solution from the cathode chamber 5c are provided above the outer frame 3 at the edge of the partition wall 1. .
Note that typical arrangements of headers attached to the bipolar electrolytic cell 50 shown in FIGS. 1 to 3 include an internal header type and an external header type. In the present invention, either type is used. You may employ | adopt and it does not specifically limit.

In the bipolar electrolytic cell 50 of the present embodiment, the electrolytic solution distributed at the anode inlet header is introduced into the anode chamber 5a through the anode electrolyte inlet, passes through the anode chamber 5a, and passes through the anode electrolyte outlet. It is led out from the anode chamber 5a and collected at the anode outlet header.

[Diaphragm for alkaline water decomposition]
The diaphragm 4 used in the alkaline water decomposition electrolytic cell of the present embodiment is the above-described alkaline water electrolysis diaphragm of the present invention, and the description thereof is omitted.

[Electrodes (Anode, Cathode)]
In the alkaline water electrolysis reaction, alkaline water is electrolyzed in an electrolytic cell having an electrode pair (that is, an anode and a cathode) connected to a power source, oxygen gas is generated at the anode, and hydrogen gas is generated at the cathode. .
Hereinafter, the electrode 2 included in the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment will be described in detail.
In the present specification, the term “electrode” means one or both of the anode 2a and the cathode 2c.

In the case of a zero gap electrolytic cell described later, since it is necessary to degas the gas generated from the back side of the contact surface with the diaphragm 4, the surface of the porous electrode located opposite to the surface in contact with the diaphragm 4 penetrates. It is preferable.

Although it does not specifically limit as a porous body electrode in this embodiment, From a viewpoint of control of an average hole diameter, the electrode, metal foam, etc. which have net | network (mesh) structure, such as a plain woven mesh type, a punching type, and an expanded type, are mentioned. It is done. Among these, from the viewpoint of controlling the size and shape of the pores, it is preferable to have a network structure selected from the group consisting of plain weave mesh type, punching type, and expanded type.

The porous body electrode in the present embodiment may be the base material itself or may have a catalyst layer with high reaction activity on the surface of the base material, but may have a catalyst layer with high reaction activity on the surface of the base material. preferable.

The material of the substrate is not particularly limited and is a conductive substrate made of at least one selected from the group consisting of nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group, graphite, chromium, and the like. Is mentioned. You may use the electroconductive base material which consists of an alloy which consists of 2 or more types of metals, or a mixture of 2 or more types of electroconductive substances. Among these, nickel and nickel-based alloys are preferable from the viewpoint of the conductivity of the base material and the resistance to the use environment.

As a method for forming a catalyst layer on a substrate, a thermal spraying method such as a plating method or a plasma spraying method, a thermal decomposition method in which heat is applied after applying a precursor layer solution on the substrate, a catalyst substance is mixed with a binder component And a method such as a method of fixing to a substrate and a vacuum film forming method such as a sputtering method.

In the zero gap configuration described later, the diaphragm 4 is pressed against the electrode more strongly than the conventional electrolytic cell. For example, in an electrode using an expanded type substrate, the diaphragm 4 is damaged at the end of the opening, or the diaphragm 4 bites into the opening, and a gap is formed between the cathode 2c and the diaphragm 4 to increase the voltage. There is a case.

In order to solve the above problems, it is preferable to make the electrode shape as planar as possible. For example, a method in which an expanded base material (for example, an expanded base material) is pressed with a roller and processed into a flat shape can be applied. At this time, it is desirable to press from 95% to 110% with respect to the original thickness of the metal flat plate before the expansion process to planarize.

The electrode 2 manufactured by performing the above treatment not only can prevent the diaphragm 4 from being damaged, but also can surprisingly reduce the voltage. The reason for this is not clear, but it is expected that the current density is equalized because the surface of the diaphragm 4 and the electrode surface are in uniform contact.

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

[gasket]
In the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment, it is preferable that the sealing region (B) of the diaphragm and the bipolar element are further stacked via the gasket 7.
The gasket 7 is used to seal between the bipolar element 60 and the diaphragm 4 and between the bipolar element 60 against the electrolytic solution and the generated gas. Gas mixing between the chambers can be prevented.

The material of the gasket 7 is not particularly limited, and a known rubber material or resin material having insulating properties can be selected.

The gasket 7 may be embedded with a reinforcing material. Thereby, when it is pinched | interposed and pressed by the frame at the time of stacking, it can suppress that the gasket 7 is crushed and can make it easy to prevent a failure | damage.

[[Zero gap structure]]
In the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment, although not particularly limited, as shown in FIG. 2, a so-called “zero gap structure” Z in which the diaphragm 4 is in contact with the anode 2a and the cathode 2c is formed. It is preferable. In the “zero gap structure” Z, the anode 2a and the diaphragm 4 are in contact with each other over the entire surface of the electrode, and the cathode 2c and the diaphragm 4 are in contact with each other, or the distance between the electrodes is the diaphragm over the entire surface of the electrode. 4 is a structure that can be maintained at a distance that is substantially the same as the thickness of 4, with almost no gap between the anode 2 a and the diaphragm 4 and between the cathode 2 c and the diaphragm 4.
In alkaline water electrolysis, when there is a gap between the diaphragm 4 and the anode 2a or the cathode 2c, a large amount of gas bubbles generated by electrolysis stay in this portion in addition to the electrolytic solution, so that the electric resistance is very high. Get higher.
On the other hand, when the zero gap structure Z is formed, the generated gas is quickly released to the side opposite to the diaphragm 4 side of the electrode 2 through the pores of the electrode 2, whereby the distance between the anode 2 a and the cathode 2 c (hereinafter referred to as “distance between electrodes”). ")", The voltage loss due to the electrolytic solution and the occurrence of gas accumulation in the vicinity of the electrode can be suppressed as much as possible, and the electrolysis voltage can be suppressed low.

Several means for forming the zero gap structure Z have already been proposed. For example, the anode 2a and the cathode 2c are processed completely smoothly and pressed so as to sandwich the diaphragm 4, or the electrode 2 and the partition 4 There is a method in which an elastic body such as a spring is disposed between and the electrode 2 is supported by this elastic body.
In addition, preferable embodiment of the means which comprises the zero gap structure Z in the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment is mentioned later.

In the bipolar element 60 in the zero gap type cell, as a means for reducing the distance between the electrodes, a spring which is an elastic body is disposed between the electrode 2 and the partition wall 1, and the electrode 2 is supported by this spring. It is preferable. For example, in the 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 the 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 the spring. When adopting a form using such an elastic body, the strength of the springs, the number of springs, the shape, etc. are adjusted as necessary so that the pressure at which the electrode 2 contacts the diaphragm 4 is not uneven. There is a need to.

In addition, by strengthening the rigidity of the other electrode 2 that forms a pair of electrodes 2 supported via an elastic body (for example, by making the rigidity of the anode stronger than the rigidity of the cathode), the structure is less deformed even when pressed. It is said. On the other hand, the electrode 2 supported via the elastic body has a flexible structure that is deformed when the diaphragm 4 is pressed, thereby absorbing tolerances in manufacturing accuracy of the electrolytic cell 50 and irregularities due to deformation of the electrode 2 and the like. Thus, the zero gap structure Z can be maintained.

In the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment, as shown in FIG. 2, the conductive elastic body 2 e and the current collector 2 r are electrically conductive between the cathode 2 c or the anode 2 a and the partition wall 1. The elastic body 2e is provided so as to be sandwiched between the cathode 2c or the anode 2a and the current collector 2r.

(Alkaline water electrolyzer)
FIG. 4 shows an example of an alkaline water electrolysis apparatus that can use the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment.
The alkaline water electrolyzer 70 includes a rectifier 74, an oxygen concentration meter, in addition to the liquid feed pump 71, the gas-liquid separation tank 72, and the water replenisher 73, in addition to the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment. 75, a hydrogen concentration meter 76, a flow meter 77, a pressure gauge 78, a heat exchanger 79, a pressure control valve 80, and the like.

(Alkaline water electrolysis)
Electrolysis is performed by circulating the electrolyte in the alkaline water electrolysis apparatus equipped with the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, so that excellent electrolytic efficiency can be achieved even after high-density current operation or variable power supply operation. In addition, it is possible to carry out highly efficient alkaline water electrolysis while maintaining high gas purity.

The electrolytic solution that can be used for the alkaline water electrolysis of the present embodiment may be an alkaline aqueous solution in which an alkali salt is dissolved, and examples thereof include an aqueous NaOH solution and 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, from the viewpoint of ionic conductivity, kinematic viscosity, and freezing at low temperature, a 25% to 40% by weight aqueous KOH solution is particularly preferable.

The temperature of the electrolytic solution in the electrolytic cell is not particularly limited, but is preferably 80 ° C. to 130 ° C.
If it is set as the said temperature range, it can suppress effectively that the members of electrolysis apparatuses, such as a gasket and a diaphragm, deteriorate with heat, maintaining high electrolysis efficiency.
The temperature of the electrolytic solution is more preferably 85 ° C. to 125 ° C., and particularly preferably 90 ° C. to 115 ° C.

In alkaline water electrolysis of the present embodiment, it as the current density applied to the electrolytic cell is not particularly ^limited, is preferably ^{4kA / m 2 ~ 20kA / m} 2, a ^{6kA / m 2 ~ 15kA / m} 2 Is more preferable.
In particular, when using a variable power source, it is preferable to set the upper limit of the current density within the above range.

In the alkaline water electrolysis of the present embodiment, the pressure in the electrolytic cell is not particularly limited, but is preferably 3 kPa to 1000 kPa, and more preferably 3 kPa to 300 kPa.

The flow rate of the electrolytic solution per electrode chamber and other conditions may be appropriately controlled according to each configuration of the bipolar electrolytic layer for alkaline water electrolysis.

The bipolar electrolytic cell for alkaline water electrolysis according to the embodiment of the present invention has been illustrated and described with reference to the drawings, but the bipolar electrolytic cell for alkaline water electrolysis of the present invention is limited to the above example. However, the above embodiment can be modified as appropriate.

(Evaluation of gas barrier properties)
One evaluation index of the gas barrier property of the diaphragm of the present embodiment is evaluation of the bubble point of the diaphragm. The bubble point in this evaluation method is that the diaphragm is sufficiently wetted with pure water, the inside of the hole is filled with pure water, one side of the diaphragm is pressurized with nitrogen, and from the opposite side of the diaphragm at a rate of 150 mL / min. This is the pressure when bubbles are continuously generated. The lower the gas barrier property of the diaphragm, the smaller the value of the bubble point. The higher the gas barrier property of the diaphragm, the more difficult it is for gas to pass through, so the value of the bubble point increases.

The bubble point of the diaphragm is not particularly limited, but is preferably 10 kPa or more. If the bubble point of the diaphragm is 10 kPa or more, since there is no pinhole of 0.2 μm or more, the separation ability of the diaphragm can be secured. In addition, when the diaphragm is used for electrolysis, even when a differential pressure is applied between the cathode chamber and the anode chamber, the generated gas cannot easily pass through the diaphragm, so that mixing of oxygen and hydrogen can be effectively suppressed. . From this viewpoint, the bubble point of the diaphragm is more preferably 100 kPa or more.

(Ion permeability evaluation)
One of the cell voltage evaluation indices when electrolysis is performed using the alkaline water electrolysis diaphragm of the present embodiment is the ion permeability of the diaphragm. If the ion permeability is high, the electrical resistance during electrolysis can be reduced, and accordingly, the voltage loss caused by the diaphragm for alkaline water electrolysis can also be reduced. In this respect, since the diaphragm for alkaline water electrolysis of the present embodiment can maintain high ion permeability, the cell voltage during electrolysis can be reduced by using this.

The cell voltage at the time of performing electrolysis using the diaphragm for alkaline water electrolysis of this embodiment can be evaluated by the following method, for example. A diaphragm is installed between the nickel electrodes, and both electrode chambers separated by the diaphragm are filled with a 30% by mass KOH aqueous solution at 90 ° C. A direct current having a current density of 0.60 A / cm ² is applied between both electrodes, and electrolysis is performed for a long time. The potential difference between both electrodes is measured 24 hours after the start of electrolysis, and the potential difference between both electrodes is defined as the cell voltage. During electrolysis, water in the KOH aqueous solution is consumed by electrolysis. Therefore, pure water is periodically added so that the KOH concentration becomes constant. Further, the electrolytic solution in both electrode chambers is circulated by a pump so that oxygen and hydrogen generated from the electrodes do not stay in the electrolytic cell. When operated under such conditions, the cell voltage when the diaphragm of the present embodiment is used is not particularly limited, but a suitable example is 1.80 V at a current density of 0.60 A / cm ² . The voltage can be further reduced to 1.75 V or less, and the cell voltage can be further reduced depending on the operating conditions. If the voltage loss in the diaphragm can be reduced, water can be electrolyzed efficiently with a small amount of electric power. Furthermore, even when operating at a high current density for a long period of time, the risk of overheating the electrolyte in the electrolytic cell due to heat generation due to voltage loss, the risk of premature deterioration of the material of the electrolytic cell and electrodes, etc. are reduced. be able to.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

The electrodes (anode and cathode) and diaphragm used in Examples and Comparative Examples were prepared as follows.

[Example 1]
Zirconium oxide (“UEP zirconium oxide”, manufactured by Daiichi Rare Element Chemical Industries, Ltd.) in 300 g of Isopar M (manufactured by TonenGeneral Co., Ltd., hereinafter the same) in which 10 g of n-decanoic acid (manufactured by Kanto Chemical Co., Ltd.) was dissolved, 475 g (hereinafter referred to as ZrO ₂ ) was previously uniformly dispersed with a ball mill (Universal Ball Mill Base BKFD-203 manufactured by Terraoka Co., Ltd.) to prepare a ZrO ₂ dispersion solution. Subsequently, 25 g of PTFE (“Teflon PTFE fine powder 6-J”, manufactured by Mitsui DuPont Fluoro Chemical Co., Ltd., hereinafter referred to as PTFE-A) was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore size of 0.2 μm and an average water-permeable pore size of 0.1 μm. The thickness was 360 μm, the porosity was 30%, and the water contact angle was 30 °. And the tensile fracture strength of MD direction and TD direction was 20 MPa and 16 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Example 2]
350 g of ZrO ₂ was uniformly dispersed in 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved to prepare a ZrO ₂ dispersion solution. Subsequently, 150 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore size of 2.0 μm and an average water-permeable pore size of 1.0 μm. The thickness was 360 μm, the porosity was 80%, and the water contact angle was 85 °. And the tensile fracture strength of MD direction and TD direction was 28 MPa and 24 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Example 3]
In 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved, 425 g of ZrO ₂ was uniformly dispersed to prepare a ZrO ₂ dispersion solution. Subsequently, 75 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore diameter of 1.4 μm and an average water-permeable pore diameter of 0.6 μm. The thickness was 110 μm, the porosity was 40%, and the water contact angle was 15 °. And the tensile breaking strength of MD direction and TD direction was 25 MPa and 19 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Example 4]
In 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved, 425 g of titanium oxide (“TTO-51A”, manufactured by Ishihara Sangyo Co., Ltd., hereinafter referred to as TiO ₂ ) was uniformly dispersed to prepare a TiO ₂ dispersion solution. Subsequently, 75 g of PTFE-A was mixed with the TiO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore diameter of 1.4 μm and an average water-permeable pore diameter of 0.6 μm. The thickness was 480 μm, the porosity was 40%, and the water contact angle was 90 °. And the tensile breaking strength of MD direction and TD direction was 25 MPa and 19 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Example 5]
A PTFE porous membrane having a thickness of 300 μm, a porosity of 80%, and a pore diameter of 200 nm was obtained by a biaxial stretching opening method. The obtained PTFE porous membrane was immersed in an 80 wt% zirconium tetrabutoxide 1-butanol solution (manufactured by Sigma Aldrich), and the porous membrane was impregnated with zirconium tetrabutoxide. The PTFE porous membrane was taken out from the 1-butanol solution, and the zirconium compound was precipitated in the PTFE porous membrane by immersing it in distilled water after removing the excess solution using a PE spatula. The PTFE porous membrane on which the zirconium compound was deposited was dried at 60 ° C. for 1 hour and then heated in a heating furnace at 200 ° C. for 1 hour to obtain a diaphragm for alkaline water electrolysis.
The maximum pore diameter of the obtained diaphragm was 0.8 μm, and the average water-permeable pore diameter was 0.025 μm. The thickness was 300 μm, the porosity was 40%, and the water contact angle was 80 °.
And the tensile fracture strength of MD direction and TD direction was 25 MPa and 22 MPa, respectively. The details of the obtained diaphragm for alkaline water electrolysis are shown in Table 2.

[Example 6]
A PTFE porous film having a thickness of 300 μm, a porosity of 80%, and a pore diameter of 100 nm was obtained by a biaxial stretching opening method. The obtained PTFE porous membrane was immersed in an 80 wt% zirconium tetrabutoxide 1-butanol solution (manufactured by Sigma Aldrich), and the porous membrane was impregnated with zirconium tetrabutoxide. The PTFE porous membrane was taken out from the 1-butanol solution, and the excess solution was removed using a PE spatula and then immersed in distilled water to precipitate a zirconium compound in the PTFE porous membrane. The PTFE porous membrane on which the zirconium compound was deposited was dried at 60 ° C. for 1 hour and then heated at 200 ° C. for 1 hour. Furthermore, it put into the container made from PTFE with an internal volume of 100 mL with 80 mL 30% potassium hydroxide aqueous solution, and it heated at 150 degreeC * 24 hours in the pressure | voltage resistant container made from SUS, and obtained the diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore size of 1.0 μm and an average water-permeable pore size of 0.03 μm. The thickness was 300 μm, the porosity was 45%, and the water contact angle was 80 °.
And the tensile fracture strength of MD direction and TD direction was 11 MPa and 24 MPa, respectively. The details of the obtained diaphragm for alkaline water electrolysis are shown in Table 2.

[Example 7]
A PTFE porous film having a thickness of 300 μm, a porosity of 80%, and a pore diameter of 100 nm was obtained by a biaxial stretching opening method. The obtained PTFE porous membrane was immersed in an 80 wt% zirconium tetrabutoxide 1-butanol solution, and the porous membrane was impregnated with zirconium tetrabutoxide. The PTFE porous membrane was taken out from the 1-butanol solution, and the excess solution was removed using a PE spatula and then immersed in distilled water to precipitate a zirconium compound in the PTFE porous membrane. The PTFE porous membrane on which the zirconium compound was deposited was dried at 60 ° C. for 1 hour and then heated at 200 ° C. for 1 hour. Furthermore, it put into the container made from PTFE with an internal capacity of 100 mL with 80 mL 30% potassium hydroxide aqueous solution, and it heated at 200 degreeC x 24 hours in the pressure | voltage resistant container made from SUS, and obtained the diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore size of 1.6 μm and an average water-permeable pore size of 0.03 μm. The thickness was 300 μm, the porosity was 45%, and the water contact angle was 80 °.
And the tensile breaking strength of MD direction and TD direction was 12 MPa and 22 MPa, respectively. The details of the obtained diaphragm for alkaline water electrolysis are shown in Table 2.

[Comparative Example 1]
In 300 g of Isopar M in which 10 g of n-decanoic acid (manufactured by Kanto Chemical Co., Inc.) was dissolved, 485 g of ZrO ₂ was uniformly dispersed to prepare a ZrO ₂ dispersion solution. Subsequently, 15 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The maximum pore diameter of the obtained diaphragm was 0.1 μm, and the average water-permeable pore diameter was smaller than 0.1 μm, and could not be measured. The thickness was 300 μm, the porosity was 15%, and the water contact angle was 20 °. And the tensile breaking strength of MD direction and TD direction was 6 MPa and 5 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 2]
In 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved, 300 g of ZrO ₂ was uniformly dispersed to prepare a ZrO ₂ dispersion solution. Subsequently, 200 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm had a maximum pore diameter of 2.5 μm and an average water-permeable pore diameter of 1.4 μm. The thickness was 300 μm, the porosity was 85%, and the water contact angle was 110 °. And the tensile fracture strength of MD direction and TD direction was 12 MPa and 9 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 3]
In 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved, 385 g of ZrO ₂ was uniformly dispersed to prepare a ZrO ₂ dispersion solution. Subsequently, 125 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained membrane had a maximum pore size of 0.9 μm and an average water-permeable pore size of 0.4 μm. The thickness was 30 μm, the porosity was 50%, and the water contact angle was 45 °. The tensile breaking strengths in the MD direction and TD direction were 27 MPa and 20 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 4]
In 300 g of Isopar M in which 10 g of n-decanoic acid was dissolved, 385 g of ZrO ₂ was uniformly dispersed to prepare a ZrO ₂ dispersion solution. Subsequently, 125 g of PTFE-A was mixed with the ZrO ₂ dispersion adjusted to 15 ° C. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained membrane had a maximum pore size of 0.9 μm and an average water-permeable pore size of 0.4 μm. The thickness was 800 μm, the porosity was 50%, and the water contact angle was 50 °. The tensile breaking strengths in the MD direction and TD direction were 27 MPa and 20 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 5]
300 g of Isopar M adjusted to 15 ° C. and 125 g of PTFE-A were mixed. The resulting mixture was extruded into a sheet at 70 ° C. after preforming. The sheet was rolled through a pair of rolls set at 120 ° C. The rolled sheet was heated to 200 ° C. to remove the lubricant, and stretched in the MD and TD directions with a stretcher set at 320 ° C. The stretched sheet was fired at 350 ° C. to obtain a diaphragm for alkaline water electrolysis.
The obtained membrane had a maximum pore size of 0.8 μm and an average water-permeable pore size of 0.3 μm. The thickness was 110 μm, the porosity was 70%, and the water contact angle was 125 °. And the tensile breaking strength of MD direction and TD direction was 30 MPa and 26 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 6]
As the PTFE porous membrane, a commercially available PTFE membrane filter ("Omnipore JGWP" manufactured by Merck Millipore) was used, and details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 7]
ZrO ₂ and N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter referred to as NMP) were charged into a ball mill pot containing SUS balls having a particle diameter of 0.5 mm. These were stirred at a rotational speed of 70 rpm for 3 hours and dispersed to obtain a mixture. The resulting mixture was filtered through a stainless steel sieve (mesh 30 mesh) to separate the balls from the mixture. Polyethersulfone ("Ultrason E7020" (trademark), manufactured by BASF, hereinafter PES) and polyvinylpyrrolidone (weight average molecular weight (Mw) 900000, manufactured by Wako Pure Chemical Industries, Ltd., hereinafter PVP) are added to the mixture from which the balls have been separated. Then, the mixture was stirred and dissolved at 60 ° C. for 12 hours using a three-one motor to obtain a coating solution having the following component composition.
PES: 15 parts by mass PVP: 6 parts by mass NMP: 70 parts by mass ZrO ₂ : 45 parts by mass

Apply this coating solution to both surfaces of polyphenylene sulfide mesh (Kuraba Co., Ltd., film thickness: 280 μm, mesh opening: 358 μm, thread diameter: 150 μm, hereinafter referred to as PPS mesh) using a comma coater. Coating was performed so that the thickness was 150 μm on each side. Immediately after coating, the supporting base material coated with the coating liquid is placed under the steam of a coagulation bath in which 40 ° C. pure water / NMP mixed liquid (pure water / NMP = 50/50 (v / v)) is stored. I was exposed. Immediately after that, the supporting substrate coated with the coating solution was immersed in a coagulation bath. And the coating film was formed in the support base material surface by solidifying PES. Thereafter, the coating film was sufficiently washed with pure water.
The obtained diaphragm had a maximum pore size of 1.2 μm and an average water-permeable pore size of 0.2 μm. The thickness was 600 μm, the porosity was 40%, and the water contact angle was 25 °. The tensile breaking strengths in the MD direction and TD direction were 16 MPa and 17 MPa, respectively. The details of the obtained membrane for alkaline water electrolysis are shown in Table 1.

[Comparative Example 8]
A diaphragm for alkaline water electrolysis was obtained in the same manner as in Example 7, except that a PTFE porous membrane having a thickness of 200 μm, a porosity of 55%, and a pore diameter of 1000 nm obtained by the uniaxial stretching opening method was used.
The obtained diaphragm had a maximum pore size of 2.5 μm and an average water-permeable pore size of 0.1 μm. The thickness was 200 μm, the porosity was 20%, and the water contact angle was 90 °.
And the tensile breaking strength of MD direction and TD direction was 20 MPa and 10 MPa, respectively. The details of the obtained diaphragm for alkaline water electrolysis are shown in Table 2.

[Measurement and evaluation method of physical properties]
Hereinafter, a method for measuring and evaluating physical properties of the diaphragm will be described.

(1) Average water-permeable pore diameter The average water-permeable pore size of the diaphragm is the average water-permeable pore size obtained by measurement of the following method using an integrity tester (manufactured by Sartorius Stedim Japan, "Sartochcheck Junior BP-Plus"). did. First, the diaphragm was cut into a predetermined size including the core material, and this was used as a sample. This sample was set in a pressure-resistant container for measurement (permeation area: 12.57 cm ² ), and the inside of the container was filled with 150 mL of pure water. Next, the pressure vessel was held in a thermostat set at 90 ° C., and the measurement was started after the inside of the pressure vessel reached 90 ° C. When the measurement started, the upper surface side of the sample was pressurized with nitrogen, and pure water permeated from the lower surface side of the sample, so the numerical values of pressure and permeation flow rate were recorded. The average water permeable pore diameter was determined from the following Hagen-Poiseuille equation using the gradient between the pressure between 10 kPa and 30 kPa and the water flow rate.
Average water-permeable pore diameter (m) = {32ηLμ ₀ / (εP)} ^0.5
Here, η is the viscosity of water (Pa · s), L is the thickness of the diaphragm (m), μ ₀ is the apparent flow velocity, and μ ₀ (m / s) = flow rate (m ³ / s) / flow channel area. (M ² ). Further, ε is the porosity, and P is the pressure (Pa).

(2) Maximum pore diameter The maximum pore diameter of the diaphragm was measured by the following method using an integrity tester ("Sartochcheck Junior BP-Plus" manufactured by Sartorius Stedim Japan). First, the diaphragm was cut into a predetermined size including the core material, and this was used as a sample. This sample was wetted with pure water, impregnated with pure water in the pores of the membrane, and set in a pressure-resistant container for measurement. Next, the pressure vessel was held in a thermostat set at a predetermined temperature, and measurement was started after the pressure vessel reached the predetermined temperature. When the measurement was started, the upper surface side of the sample was pressurized with nitrogen, and the nitrogen pressure when bubbles were continuously generated from the lower surface side of the sample at a rate of 150 mL / min was defined as the bubble point pressure. The maximum pore diameter was obtained from the following bubble point equation obtained by modifying the Young-Laplace equation.
Maximum pore diameter (m) = 4γ cos θ / P
Here, γ is the surface tension (N / m) of water, cos θ is the contact angle (rad) between the diaphragm surface and water, and P is the bubble point pressure (Pa).

(3) Average primary particle size of hydrophilic inorganic particles The average primary particle size of the hydrophilic inorganic particles of the diaphragm is measured using a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation, “Miniscope TM3000”). It was. First, the diaphragm was cut into a predetermined size including the core material, and this was used as a sample. This sample was subjected to metal coating for 1 minute using a magnetron sputtering apparatus (“MSP-1S type” manufactured by Vacuum Device Inc.). Next, this sample was set on an SEM observation sample stage, and measurement was started. At this time, the diaphragm which is a measurement sample was set so that observation by SEM could be performed from the direction perpendicular to the film surface to be measured. The measurement was started, the magnification was adjusted (preferably 20,000 times or more) so that the inorganic particles to be observed can be seen, and the imaging screen was stored as an image. The obtained image was binarized using image analysis software (“WinROOF”, manufactured by Mitani Corporation), the absolute maximum length was measured for each of the 10 non-aggregated inorganic particles, and the number average was calculated. Calculated. This average was taken as the primary particle size of the inorganic particles.

(4) Porosity The porosity of the diaphragm was measured in a room kept at 25 ° C. using an electronic balance.
The diaphragm was cut into three pieces of 3 cm × 3 cm (9 cm ² ) to make measurement samples, and the thickness d (cm) was measured with a thickness gauge. Next, the measurement sample was immersed in pure water for 24 hours to remove excess water, and the weight w1 (g) was measured. Then, these were left still for 12 hours or more in the dryer set to 50 degreeC, and were dried, and the weight w2 (g) was measured.
The diaphragm to be measured had a very low water-absorbing surface on the water contact surface, and the thickness and area did not change significantly between the state in which the measurement sample contained water and the dry state. Therefore, considering the thickness d and the area as constant values, the porosity was determined from the values of w1 and w2 by the following formula.
Porosity (%) = {(w1-w2) / (d × 9)} × 100
The porosity was obtained for each of the three measurement samples, and the arithmetic average value thereof was defined as the porosity ε of the diaphragm.

(5) Water contact angle The water contact angle of the diaphragm was measured using “Drop Master DM-701” (manufactured by Kyowa Interface Chemical Co., Ltd.). 3 μL of pure water was dropped on the surface of the measurement target (diaphragm or porous electrode), and the water contact angle was measured by the θ / 2 method. The measurement atmosphere conditions were a temperature of 23 ° C. and a humidity of 65% RH.

(6) Tensile rupture stress It measured by the method according to JISK7161 in the atmosphere of temperature 23 degreeC and humidity 65% RH. A specimen cut into a width of 10 mm and a length of 100 mm along the MD direction and the TD direction of the diaphragm for alkaline water electrolysis was used as a test piece. Using “Autograph AGS-1kNX” (manufactured by Shimadzu Corporation), a tensile test was performed on the test piece under the conditions of a length between chucks of 50 mm and a pulling speed of 100 mm / min, and an arithmetic average of five measured values was calculated. It was set as the measured value of tensile breaking strength. This was calculated for each of the MD and TD directions.

[Electrolysis test]
Using the diaphragms of Examples 1 to 7 and Comparative Examples 1 to 8, energization was continuously performed for 2500 hours under a high current density of 10 kA / m ² to perform alkaline water electrolysis.
After 2500 hours, the average value of the counter voltage of the four electrolytic cells was calculated for each Example and Comparative Example and evaluated as the cell voltage (V).
In addition, gas was sampled from the gas-liquid separation tank on the cathode side and the anode side, the hydrogen concentration (%) on the cathode side and the oxygen concentration (%) on the anode side were measured by gas chromatography, and the hydrogen purity (% ) And oxygen purity (%). Table 1 shows the results of Examples 1 to 4 and Comparative Examples 1 to 7, and Table 2 shows the results of Examples 5 to 7 and Comparative Example 8.

Hereinafter, the used bipolar electrolytic cell and electrolytic system will be described.

[Bipolar electrolytic cell]
An electrolytic cell having a bipolar zero-gap structure as shown in FIG. 1 was prepared, which was composed of an anode terminal element, a cathode terminal element, and four bipolar elements. The diaphragms of the respective examples and comparative examples are incorporated in each electrolytic cell. The header pipe of the electrolytic cell was an external header type.

<Anode>
As the anode, a nickel expanded base material that had been blasted in advance was used, and a granulated product of nickel oxide was sprayed on both surfaces of the conductive base material by plasma spraying.

<Cathode>
As the conductive substrate, a material in which platinum was supported on a plain woven mesh substrate obtained by knitting a fine nickel wire having a diameter of 0.15 mm with a mesh of 40 mesh was used.

<Gasket>
The gasket used was a rectangular shape having an inner dimension of 60 mm × 50 mm with a thickness of 4.0 mm and having a slit structure for holding by inserting a diaphragm inside. The slit structure was a structure in which a gap of 0.4 mm was provided inside the gasket in the width direction of 6 mm in order to accommodate the edge of the diaphragm. This gasket was made of fluorine-based rubber and had an elastic modulus of 4.0 MPa at 100% deformation.

<Conductive elastic body>
As the conductive elastic body, one obtained by corrugating a woven nickel wire having a wire diameter of 0.15 mm so as to have a wave height of 5 mm was used.

<Bipolar element>
The bipolar element was a 90 mm × 70 mm rectangle, and the area of the anode and cathode was 58 mm × 48 mm. The depth of the anode chamber (anode chamber depth) was 10 mm, the depth of the cathode chamber (cathode chamber depth) was 10 mm, and the material was nickel. The thickness of a nickel partition wall in which a nickel anode rib having a height of 11 mm and a thickness of 1.5 mm and a nickel cathode rib having a height of 11 mm and a thickness of 1.5 mm were attached by welding was 2 mm.

As the current collector, a nickel expanded metal having a thickness of 1 mm, a lateral length of the opening of 4.5 mm, and a longitudinal length of 3.2 mm was used. The conductive elastic body described above was fixed by spot welding on a current collector. The zero gap bipolar element was stacked through a 60 mm × 50 mm diaphragm to form a zero gap structure in which the cathode and the anode were pressed against the diaphragm.

[Electrolysis system]
The above bipolar electrolytic cell was incorporated into an electrolysis apparatus 70 shown in FIG. 4 and used for alkaline water electrolysis. Hereinafter, an outline of the electrolysis system will be described with reference to FIG.
The gas-liquid separation tank 72 and the external header type bipolar electrolytic cell 50 are filled with 30% KOH aqueous solution as an electrolytic solution. The electrolyte solution is fed 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 the liquid feed pump 71, respectively. It is circulating. The flow rate of the electrolyte was measured with a flow meter 77 to 10 L / min, and the temperature was adjusted to 120 ° C. with a heat exchanger 79. For the electrolyte solution wetted part of the circulation channel, a 20A pipe obtained by subjecting an SGP carbon steel pipe to a Teflon lining inner surface treatment was used.
A gas-liquid separation tank 72 (72h and 72o) having a height of 500 mm and a volume of 0.02 m ³ was used. The amount of liquid in each gas-liquid separation tank 72h and 72o was about 50% of the design volume. From the rectifier 74, electricity was supplied at a predetermined electrode density to the cathode and anode of each electrolytic cell.
The pressure in the cell after the start of energization was measured with a pressure gauge 78 and adjusted so that the cathode side pressure was 301 kPa and the oxygen side pressure was 300 kPa. The pressure was adjusted by installing a pressure control valve 80 downstream of the pressure gauge 78.

The rectifier 74, oxygen concentration meter 75, hydrogen concentration meter 76, pressure gauge 78, flow meter 77, heat exchanger 79, liquid feed pump 71, gas-liquid separation tank 72 (72h and 72o), water replenisher 73, etc. All of those used in the art are used.

[Results of electrolysis test]
In Examples 1 to 7, the cell voltage after electrolysis for 2500 hours was 2.00 V or less, and the low voltage was maintained. The gas purity was 99.0% or more for both oxygen and hydrogen, and the gas barrier property of the diaphragm was good.

On the other hand, in Comparative Examples 1 to 6 and 8, the cell voltage after 2500 hours of electrolysis was 2.20 V or higher, the cell voltage was high, and the electrolysis efficiency was low. In Comparative Example 7, the diaphragm deteriorated and the gas purity was less than 98.5% for both oxygen and hydrogen.

DESCRIPTION OF SYMBOLS 1 Partition 2 Electrode 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 6 Current plate (rib)
7 Gasket 50 Bipolar electrolytic cell 51g Fast head, loose head 51i Insulating plate 51a Anode terminal element 51c Cathode terminal element 51r Tie rod 60 Bipolar element 65 Electrolytic cell 70 Electrolytic device 71 Feed pump 72 Gas-liquid separation tank 72h Hydrogen separation Tank 72o Oxygen separation tank 73 Water replenisher 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure meter 79 Heat exchanger 80 Pressure control valve D1 A given direction along the partition (electrolyte passage direction)
Z Zero gap structure SW Center distance in the short direction of the mesh LW Distance between centers in the long direction of the mesh C Mesh opening TE Mesh thickness B Mesh bond length T Plate thickness W Feed width (step width)
A Opening of plain weave mesh type d Wire diameter of plain weave mesh type D Hole diameter of punching type P Pitch between holes of punching type

Claims

At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
The content of the inorganic compound is 70% by mass or more and 95% by mass or less, where the total amount of the PTFE and the inorganic compound is 100% by mass,
diaphragm.
At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
The content of the inorganic compound is 70% by mass or more and 95% by mass or less, where the total amount of the PTFE and the inorganic compound is 100% by mass,
A diaphragm for alkaline water electrolysis.
The diaphragm according to claim 1 or 2, wherein the average water-permeable pore diameter is 0.1 µm or more and 1.0 µm or less.
The diaphragm according to any one of claims 1 to 3, wherein the inorganic compound is a hydrophilic inorganic particle or a hydrophilic inorganic porous material.
The diaphragm according to any one of claims 1 to 4, wherein a primary particle size of the hydrophilic inorganic particles is 10 nm or more and 300 nm or less.
6. The hydrophilic inorganic particles according to any one of claims 1 to 5, wherein the hydrophilic inorganic particles include at least one of TiO 2 , Ti (OH) 4 , ZrO 2 , and Zr (OH) 4 . diaphragm.
The diaphragm according to any one of claims 1 to 6, wherein the water contact angle is greater than 10 ° and 90 ° or less.
The tensile breaking strength in the flow (MD) direction is 10 MPa or more and 30 MPa or less, and the tensile breaking strength in the (TD) direction orthogonal to the flow direction is 10 MPa or more and 30 MPa or less. The diaphragm according to item.
A diaphragm according to any one of claims 1 to 8,
A plurality of elements including a cathode and an anode are stacked with the diaphragm interposed therebetween,
An electrolytic cell, wherein the diaphragm is in contact with the cathode and the anode to form a zero gap structure.
And characterized by using the electrolytic cell according to claim 9, electrolyte temperature of 85 ° C. ~ 125 ° C., electrolysis of an aqueous solution of potassium hydroxide or sodium hydroxide at a current density of 4kA / m 2 ~ 20kA / m 2 A method for producing hydrogen.
In a hydrogen production method for producing hydrogen by electrolyzing water containing an alkali with an electrolytic cell,
The electrolytic cell has a diaphragm at least between an anode and a cathode,
The diaphragm is
At least polytetrafluoroethylene (PTFE) and an inorganic compound,
The average water permeable pore diameter is 0.02 μm or more and 1.0 μm or less,
The maximum pore size is 0.2 μm or more and 2.0 μm or less,
Porosity is 30% or more and 90% or less,
The thickness is 100 μm or more and 600 μm or less,
Content of the said inorganic compound is 70 mass% or more and 95 mass% or less characterized by the total amount of the said PTFE and the said inorganic compound being 100 mass%, The hydrogen manufacturing method characterized by the above-mentioned.