Ion exchange membrane, electrolytic cell, and method for producing hydrogen

Abstract

A sulfonic acid type membrane body containing a polymer having sulfonic acid groups, and a reinforcing material disposed within the sulfonic acid type membrane body, An ion exchange membrane, wherein a surface roughness R1 of a first surface of the sulfonic acid type membrane body is smaller than a surface roughness R2 of a second surface of the sulfonic acid type membrane body.

Description

[Technical Field]

[0001] The present invention relates to an ion exchange membrane, an electrolytic cell, and a method for producing hydrogen. [Background technology]

[0002] In recent years, technologies such as wind power generation and solar power generation that utilize renewable energy sources such as wind and sunlight have been attracting attention in order to solve problems such as global warming caused by greenhouse gases such as carbon dioxide and dwindling fossil fuel reserves.

[0003] Renewable energy output is highly variable because it depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy sources (hereinafter referred to as "variable power sources") to the general power grid, raising concerns about the potential for imbalances in power supply and demand and the instability of the power grid. It is also well known that imbalances between the power generated by renewable energy sources and power demand occur not only throughout the day but also depending on the season.

[0004] Therefore, research is being conducted into converting electricity generated from renewable energy into a form that can be stored and transported and utilizing it.One example is the use of electricity generated from renewable energy to generate storable and transportable hydrogen through electrolysis (hereinafter also referred to as "electrolysis"), specifically the electrolysis of water (hereinafter also referred to as "water electrolysis"), and the use of the generated hydrogen as an energy source or raw material.

[0005] Hydrogen is widely used industrially in oil refining, chemical synthesis, metal refining, etc., and in recent years, the possibility of its use has expanded in hydrogen stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. For this reason, there are high expectations for the development of technology to obtain particularly high-purity hydrogen from renewable energy sources.

[0006] Water electrolysis methods include solid polymer water electrolysis, high-temperature steam electrolysis, alkaline water electrolysis, etc. Among these, alkaline water electrolysis is considered to be one of the most promising methods because it has been industrialized for more than several decades, can be carried out on a large scale, and is inexpensive compared to other water electrolysis devices.

[0007] In alkaline water electrolysis, water is electrolyzed by supplying current to an anode and a cathode in the presence of an alkaline electrolyte. During this process, hydrogen is generated from the cathode, and oxygen is generated from the anode. Alkaline water electrolysis equipment includes a diaphragm between the cathode and the anode, which is configured to prevent mixing of hydrogen and oxygen. Patent Document 1 discloses an alkaline water electrolysis diaphragm containing a polymer having a sulfonic acid functional group as a specific example of a diaphragm used in alkaline water electrolysis. Specifically, Patent Document 1 discloses an alkaline water electrolysis diaphragm containing an ion exchange membrane containing a polymer having a sulfonic acid functional group but not a polymer having a carboxylic acid functional group, and a hydrophilic layer provided as at least one outermost layer of the diaphragm. The document describes that by reducing the thickness of the ion exchange membrane to 25 to 70 μm and adjusting the ion exchange capacity, the electrolysis voltage can be kept low even at high current densities, and delamination is unlikely to occur.

[0008] Furthermore, in order to reduce the electrolysis voltage in alkaline water electrolysis and improve the power consumption rate for hydrogen production, the introduction of a structure known as a zero-gap structure, in which the gap between the diaphragm and the electrode is essentially eliminated, is being promoted (see, for example, Patent Documents 2 and 3). In the zero-gap structure, the generated gas is quickly released to the side of the electrode opposite the diaphragm through the pores in the electrode, thereby reducing the distance between the electrodes and minimizing the occurrence of gas accumulation near the electrodes, thereby reducing the electrolysis voltage. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6981421 [Patent Document 2] U.S. Patent No. 4,530,743 [Patent Document 3] Japanese Patent Application Publication No. 59-173281 Summary of the Invention [Problem to be solved by the invention]

[0010] When a current flows through the electrodes, a pressure difference (differential pressure) can occur between the anode chamber and the cathode chamber. This differential pressure presses the diaphragm against one of the electrodes. In particular, when the supply of electricity from renewable energy fluctuates significantly, the power supplied to the water electrolysis device also fluctuates. In such power fluctuation operation, the fluctuation in the differential pressure can damage the diaphragm, potentially causing mixing of oxygen gas and hydrogen gas. Thus, the diaphragm is required to be resistant to fluctuations in differential pressure (differential pressure fluctuation resistance).

[0011] In order to ensure the resistance of the diaphragm to differential pressure fluctuations, it may be considered to increase the thickness of the diaphragm; however, as the diaphragm becomes thicker, voltage loss in a zero gap structure tends to become more pronounced, and electrolysis efficiency tends to be impaired.

[0012] As described above, in the prior art, there is a trade-off between resistance to differential pressure fluctuations and electrolysis efficiency, and no diaphragm having both high resistance to differential pressure fluctuations and high electrolysis efficiency has been obtained.

[0013] In view of the above, an object of the present invention is to provide an ion exchange membrane or the like that can suppress electrolysis voltage to a low level, has excellent stability in electrolysis operation, and is particularly excellent in resistance to differential pressure fluctuations. [Means for solving the problem]

[0014] As a result of extensive research into solving the above problems, the present inventors have discovered that the above problems can be solved by an ion exchange membrane having a specific configuration, and have thus completed the present invention.

[0015] That is, the present invention includes the following aspects. [1] A sulfonic acid type membrane body containing a polymer having sulfonic acid groups, and a reinforcing material disposed within the sulfonic acid type membrane body, An ion exchange membrane, wherein a surface roughness R1 of a first surface of the sulfonic acid type membrane body is smaller than a surface roughness R2 of a second surface of the sulfonic acid type membrane body. [2] The surface roughness R1 of the first surface is less than 10 μm, The ion exchange membrane according to [1], wherein the second surface has a surface roughness R2 of 10 μm or more. [3] The ion exchange membrane according to [1] or [2], wherein in a cross section of the ion exchange membrane, a thickness h1 of the ion exchange membrane at a position P1 where the reinforcing material is present and a thickness h2 of the ion exchange membrane at a position P2 where the reinforcing material is not present satisfy 1.3≦h1 / h2≦10. [4] The ion exchange membrane according to [3], wherein the thickness h2 is 10 μm or more and 100 μm or less. [5] The ion exchange membrane according to [3] or [4], wherein the thickness h1 is 100 μm or more and 200 μm or less. [6] a plurality of the reinforcing members are present along the surface direction of the ion exchange membrane, The ion exchange membrane according to any one of [1] to [5], wherein the distance L1 between adjacent reinforcing members is 1 / 150 inch or more and 1 / 10 inch or less. [7] The ion exchange membrane according to any one of [1] to [6], wherein the ion exchange capacity of the polymer is 0.90 meq / g or more and 2.00 meq / g or less. [8] The ion exchange membrane according to any one of [1] to [7], wherein the polymer is a fluorine-containing polymer. [9] The ion exchange membrane according to any one of [1] to [8], wherein the polymer comprises a polymer P1 having a unit represented by the following formula (1): -[CF2-CF(-O-CF2CF(CF3)-O-(CF2) m -SO3M)]- (1) (In formula (1), m is an integer of 1 to 6, and M is an alkali metal.)

[10] The ion exchange membrane according to any one of [1] to [9], wherein the reinforcing material includes a reinforcing thread and / or a sacrificial thread.

[11] the reinforcing yarn comprises at least one selected from the group consisting of PTFE and PFA, The ion exchange membrane according to

[10] , wherein the sacrificial yarn comprises PET.

[12] The ion exchange membrane according to

[10] or

[11] , wherein the reinforcing yarn and the sacrificial yarn each have a denier of 20 to 150 denier.

[13] The ion exchange membrane according to any one of

[10] to

[12] , wherein the reinforcing yarns have a weave density of 20 to 150 yarns per inch.

[14] The ion exchange membrane according to any one of [1] to

[13] , further comprising a hydrophilic layer disposed on the first surface and / or the second surface.

[15] The ion exchange membrane according to

[14] , wherein the hydrophilic layer contains inorganic particles.

[16] The ion exchange membrane according to

[15] , wherein the inorganic particles contain at least one selected from the group consisting of oxides, nitrides, and carbides of Group 4 elements or Group 14 elements.

[17] The ion exchange membrane according to

[15] or

[16] , wherein the inorganic particles contain at least one selected from the group consisting of SiO2, SiC, ZrO2, and ZrC.

[18] The ion exchange membrane according to any one of [1] to

[17] , which is used for water electrolysis.

[19] The ion exchange membrane according to any one of [1] to

[18] , which is used for alkaline water electrolysis.

[20] an anode; a cathode facing the anode; The ion exchange membrane according to any one of [1] to

[19] , which is disposed between the anode and the cathode; An electrolytic cell comprising: [twenty one] The electrolytic cell according to

[20] , wherein the first surface of the ion exchange membrane is disposed on the electrode surface side of the anode or the cathode, whichever has greater rigidity. [twenty two] The electrolytic cell according to

[20] or

[21] , which is used for alkaline water electrolysis. [twenty three] The electrolytic cell according to any one of

[20] to

[22] , which has a zero-gap structure. [twenty four] A method for producing hydrogen using the electrolytic cell according to any one of

[20] to

[23] , A method for producing hydrogen, comprising the steps of supplying an electrolytic solution to the electrolytic cell and performing water electrolysis. [twenty five] The method for producing hydrogen according to

[24] , wherein the first surface of the ion exchange membrane is disposed on the electrode surface side of the anode or the cathode, whichever has higher rigidity.

[26] The method for producing hydrogen according to

[24] or

[25] , wherein the water electrolysis is alkaline water electrolysis. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an ion exchange membrane or the like which can suppress the electrolysis voltage to a low level, has excellent stability in electrolysis operation, and is particularly excellent in resistance to differential pressure fluctuations. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing an example of the ion exchange membrane of the present embodiment as viewed from above. FIG. [Figure 2] FIG. 2 is a schematic diagram showing the XX′ cross section of FIG. [Figure 3] 3 is an explanatory diagram showing how to measure the thickness h1 of the ion exchange membrane, the thickness h2 of the ion exchange membrane, and the distance L1 between adjacent reinforcing members, based on the example of FIG. 2.

[0023] FIG. [Figure 4]FIG. 1 is a conceptual diagram showing an example of an electrolytic cell according to an embodiment of the present invention. [Figure 5] FIG. 1 is a side view illustrating an example of an entire bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. [Figure 6] FIG. 6 is a partially enlarged cross-sectional view showing the zero-gap structure of the bipolar electrolytic cell for alkaline water electrolysis within the dashed square frame (A) in FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a mode for carrying out the present invention (also referred to as "the present embodiment" in this specification) will be described in detail. Note that the present invention is not limited to the following present embodiment, and various modifications can be made within the scope of the gist of the present invention. Note that in the drawings, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0019] [Ion exchange membrane] The ion exchange membrane of this embodiment comprises a sulfonic acid type membrane body containing a polymer having sulfonic acid groups, and a reinforcing material disposed within the sulfonic acid type membrane body, wherein the surface roughness R1 of a first surface of the sulfonic acid type membrane body is smaller than the surface roughness R2 of a second surface of the sulfonic acid type membrane body. Because the ion exchange membrane of this embodiment is configured as described above, it is possible to keep the electrolysis voltage low, resulting in excellent stability of electrolysis operation and, in particular, excellent resistance to differential pressure fluctuations.

[0020] FIG. 1 is a schematic diagram showing an example of the top view of the ion exchange membrane of this embodiment. In this embodiment, when the ion exchange membrane 10 is viewed from the top, typically, an optional hydrophilic layer 3 that may be disposed on one side of the sulfonic acid type membrane body 1 or on the sulfonic acid type membrane body 1 is visible. However, in the example of FIG. 1, these are omitted for convenience of explanation. That is, in the example of FIG. 1, a portion of the sulfonic acid type membrane body 1 and the hydrophilic layer 3 are omitted, and the reinforcing material 2 (reinforcing yarns 2a and sacrificial yarns 2b) disposed within the sulfonic acid type membrane body 1 is shown. Note that in the example of FIG. 1, both reinforcing yarns 2a and sacrificial yarns 2b are disposed as the reinforcing material 2, but this is not limited thereto; only one of them may be disposed. Furthermore, in the example of FIG. 1, both reinforcing yarns 2a and sacrificial yarns 2b are disposed at predetermined intervals as the warp and weft, but this is not limited thereto. Furthermore, although the sacrificial yarns 2b are shown as an aggregate of four fiber cross sections, this is not limited thereto.

[0021] FIG. 2 is a schematic diagram showing the X-X' cross section of FIG. 1. As shown in FIG. 2, in a sulfonic acid type membrane body 1 having a first surface 1a and a second surface 1b, the surface roughness R1 of the first surface 1a is smaller than the surface roughness R2 of the second surface 1b. That is, the first surface 1a is flatter than the second surface 1b (hereinafter also referred to as the "flat surface"), and the second surface 1b is rougher than the first surface 1a (hereinafter also referred to as the "rough surface"). As shown in FIG. 2, a hydrophilic layer 3 is disposed on each of the first surface 1a and the second surface 1b. Note that in the example of FIG. 2, the ion exchange membrane 10 includes the hydrophilic layer 3, but the ion exchange membrane 10 does not necessarily have to include the hydrophilic layer 3. In the example of FIG. 2, the surface 3a of the hydrophilic layer 3 is flat to correspond to the surface texture of the first surface 1a, and the surface 3b of the hydrophilic layer 3 is rough to correspond to the surface texture of the second surface 1b. Thus, the surface properties of the hydrophilic layer 3 tend to correspond to the surface properties of the sulfonic acid type membrane body 1, and therefore the surface of the ion exchange membrane 10 tends to be flat on one side and rough on the other, regardless of whether the hydrophilic layer 3 is present or not. When considering electrolysis operation, the flat surface of the ion exchange membrane of this embodiment contributes to adhesion with the electrodes, thereby making it easier to ensure a zero-gap structure in the electrolytic cell. Ensuring a zero-gap structure tends to reduce the electrolysis voltage. Furthermore, the rough surface of the ion exchange membrane contributes to ensuring a gap between the ion exchange membrane and the electrodes. Ensuring such a gap also makes it easier for gas (oxygen or hydrogen) generated by electrolysis to disperse from the vicinity of the electrodes to the offshore side, which also tends to further reduce the electrolysis voltage. Thus, the ion exchange membrane of this embodiment has both a flat surface and a rough surface, and therefore can improve electrolysis performance while suppressing membrane damage, compared to a diaphragm having flat surfaces on both sides. In recent years, electrolysis has been carried out in many cases using electricity obtained from renewable energy sources, and the use of such variable power sources differs from electrolysis using conventional power sources in the following respects: As the amount of electricity fluctuates, the amount of hydrogen generated also changes over time, resulting in frequent fluctuations in the pressure difference between the cathode chamber and the anode chamber. When the pressure difference fluctuates, the ion exchange membrane is pressed against the electrodes, and therefore electrolysis using a variable power source can be said to be prone to physical damage to the ion exchange membrane. As described above, the ion exchange membrane of this embodiment not only can reduce the electrolysis voltage but also contributes to suppressing membrane damage, and therefore its performance is likely to become apparent when applied to electrolysis using a variable power supply. As such, the ion exchange membrane of this embodiment can suppress membrane damage even when used in electrolysis using a variable power supply, and can therefore be said to have excellent resistance to differential pressure fluctuations. Therefore, the ion exchange membrane of this embodiment can be preferably used for water electrolysis, and more preferably for alkaline water electrolysis, and particularly preferably for alkaline water electrolysis using a variable power supply.

[0022] In this embodiment, from the viewpoint of electrolysis performance, the surface roughness R1 is preferably less than 10 μm, more preferably less than 9 μm, and even more preferably less than 7 μm. Also, in this embodiment, from the viewpoint of differential pressure fluctuation resistance, the surface roughness R2 is preferably 10 μm or more, preferably 10 μm or more and less than 80 μm, more preferably 10 μm or more and 50 μm or less, even more preferably 10 μm or more and 40 μm or less, and still more preferably 10 μm or more and 30 μm or less. From the same viewpoint as above, it is preferable that the surface roughness R1 is less than 10 μm and the surface roughness R2 is 10 μm or more. That is, when the flat surface has a surface roughness of less than 10 μm and the rough surface has a surface roughness of 10 μm or more, the differential pressure fluctuation resistance of the ion exchange membrane tends to become more pronounced. From the same viewpoint as above, the difference between the surface roughness R2 and the surface roughness R1, R2-R1, is preferably 0.5 μm or more, more preferably 1.0 μm or more, even more preferably 3 μm or more, and even more preferably 5 μm or more. Also, the difference between the surface roughness R2 and the surface roughness R1, R2-R1, is preferably 75 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and even more preferably 20 μm or less. The surface roughness R1 and the surface roughness R2 can be measured based on the method described in the examples below. The surface roughness R1 and the surface roughness R2 can be adjusted to fall within the above-mentioned ranges, for example, as follows. In the ion exchange membrane production process described below, after forming a film from a precursor of the polymer S, a flat substrate (e.g., unembossed release paper) is placed on one side of the film (the side of the first surface 1a of the sulfonic acid type membrane body 1), and the reinforcing material is heated and vacuum-embedded using a heating source and a vacuum source arranged on the substrate side, thereby adjusting the surface roughness to fall within the above-mentioned ranges. More specifically, for example, increasing the heating and decompression temperature (embedding temperature) during embedding tends to decrease the surface roughness, while decreasing the embedding temperature tends to increase the surface roughness.

[0023] In the cross section of the ion exchange membrane of this embodiment, as shown in FIG. 3 (described later), the thickness h1 of the ion exchange membrane at position P1 where a reinforcing material is present and the thickness h2 of the ion exchange membrane at position P2 where no reinforcing material is present preferably satisfy 1.3≦h1 / h2≦10, more preferably satisfy 3≦h1 / h2≦10, and even more preferably satisfy 5≦h1 / h2≦10, from the viewpoint of electrolysis performance and differential pressure fluctuation resistance. Furthermore, in this embodiment, from the viewpoint of differential pressure fluctuation resistance, the lower limit of the thickness h2 is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. Meanwhile, from the viewpoint of low voltage, the upper limit of h2 is preferably 100 μm or less, more preferably 90 μm or less, even more preferably 50 μm or less, and even more preferably 40 μm. Furthermore, in this embodiment, from the viewpoint of differential pressure fluctuation resistance, the lower limit of the thickness h1 is preferably 100 μm or more, more preferably 110 μm or more, and even more preferably 120 μm or more. From the viewpoint of low voltage, the upper limit of h1 is preferably 200 μm or less, more preferably 180 μm or less, and even more preferably 160 μm or less. These values ​​can be measured as follows. FIG. 3 is an explanatory diagram showing a method for measuring the thickness h1 and the thickness h2 of the ion exchange membrane 10 based on the example of FIG. 2. In the example of FIG. 3, the reinforcing yarns 2a and the sacrificial yarns 2b corresponding to the reinforcing material 2 are arranged along the in-plane direction D1 of the ion exchange membrane 10. As shown in FIG. 3, the position P1 where the reinforcing material 2 is present is determined based on the width of each of the reinforcing yarns 2a and the sacrificial yarns 2b in the in-plane direction D1, and the position P2 where the reinforcing material 2 is not present is determined as a portion excluding the position P1. Also, as shown in FIG. 3, the thickness h1 is determined by the portion of the ion exchange membrane that gives the maximum thickness (perpendicular to the in-plane direction D1) measured at the position P1. The thickness h2 is determined by the portion of the ion exchange membrane that gives the minimum thickness measured at the position P2. When measuring the maximum and minimum values, if the ion exchange membrane 10 has a hydrophilic layer 3, the measurement is made to be the total thickness including the hydrophilic layer 3. If the ion exchange membrane 10 does not have a hydrophilic layer 3, the measurement is made to be the thickness of the sulfonic acid type membrane body 1 (and possibly the reinforcing material 2, depending on the position). Using this measurement method, the thickness h1 is measured at 100 arbitrary points, and the value of thickness h1 is determined as the average value. Similarly, the thickness h2 is measured at 100 arbitrary points, and the value of thickness h2 is determined as the average value. More specifically, the thickness h1 and the thickness h2 can be measured based on the method described in the examples below. The thickness h1 and the thickness h2 can be adjusted to fall within the above-mentioned ranges by, for example, adjusting the method of embedding the reinforcing material and the temperature in the manufacturing process of the ion exchange membrane.

[0024] In this embodiment, a plurality of reinforcing materials are present along the in-plane direction of the ion exchange membrane, and the distance L1 between adjacent reinforcing materials is preferably 1 / 150 inch or more and 1 / 10 inch or less, more preferably 1 / 100 inch or more and 1 / 20 inch or less, and even more preferably 1 / 100 inch or more and 1 / 50 inch or less. The method for measuring the distance L1 will also be described with reference to FIG. 3. As shown in FIG. 3, adjacent reinforcing materials 2 may be a reinforcing yarn 2a and a sacrificial yarn 2b, or two sacrificial yarns 2b. Note that adjacent reinforcing materials 2 may also be two reinforcing yarns 2a. In the example shown in FIG. 3, the distance L1 can be measured as the distance between adjacent reinforcing yarns 2a and sacrificial yarns 2b, and the distance between two sacrificial yarns 2b. In this measurement, the distance is specified as the distance along the in-plane direction D1 from the position where thickness h1 was measured to the adjacent position where thickness h1 was measured. Using this measurement method, the distance L1 is measured at 50 arbitrary points, and the thickness h1 value is determined as the average value. More specifically, the distance L1 can be measured based on the method described in the examples below.

[0025] (sulfonic acid type membrane body) The sulfonic acid type membrane body contains a polymer having sulfonic acid groups (hereinafter also referred to as "polymer S"). In this embodiment, the sulfonic acid type membrane body refers to one having sulfonic acid groups on the first and second surfaces. Typically, a membrane body formed by laminating a single polymer layer composed of polymer S, or two or more polymer layers, can be said to have sulfonic acid groups on the first and second surfaces and therefore corresponds to the sulfonic acid type membrane body. In contrast, for example, a composite membrane with a two-layer structure in which a polymer layer composed of a polymer having carboxylic acid groups (hereinafter also referred to as "polymer C") and a polymer layer composed of polymer S are laminated can be said to have no sulfonic acid groups on at least one surface (the surface on the polymer layer composed of polymer C) and therefore does not correspond to the sulfonic acid type membrane body. In this embodiment, from the viewpoint of preventing delamination within the sulfonic acid type membrane body, it is preferable that the sulfonic acid type membrane body does not have a polymer layer composed of polymer C.

[0026] Various polymers having sulfonic acid groups can be used as the polymer S. Preferably, the polymer S further contains fluorine atoms, i.e., a fluorine-containing polymer. In this case, the polymer S preferably contains at least one of a polymer P1 having units represented by the following formula (1) and a polymer P2 having units represented by the following formula (2), and more preferably contains polymer P1. -[CF2-CF(-O-CF2CF(CF3)-O-(CF2) m -SO3M)]- (1) -[CF2-CF(-O-(CF2) m -SO3M)]- (2) (In the above formulas (1) and (2), m is an integer of 1 to 6, and M is an alkali metal.)

[0027] In this embodiment, from the viewpoint of ensuring electrolysis performance and preventing delamination within the sulfonic acid type membrane body, when the thickness (thickness in the direction perpendicular to the plane direction of the first surface) of the sulfonic acid type membrane body (excluding the reinforcing material disposed inside) is taken as 100%, the total thickness of the polymer layers composed of polymer S is preferably 99.9% or more, more preferably 99.99% or more, and even more preferably 100%. From the same viewpoint, when the thickness of the sulfonic acid type membrane body is taken as 100%, the total thickness of the polymer layers composed of polymer C is preferably less than 0.1%, more preferably less than 0.01%, and even more preferably below the detection limit.

[0028] The ion exchange capacity of polymer S is preferably 0.90 meq / g or more and 2.00 meq / g or less. When the ion exchange capacity is 0.90 meq / g or more, the electrolysis voltage tends to be lower. When the ion exchange capacity is 2.00 meq / g or less, the strength of the sulfonic acid type membrane body tends to be improved. From the above viewpoints, the ion exchange capacity is more preferably 0.95 meq / g or more and 1.50 meq / g or less, even more preferably 0.97 meq / g or more and 1.25 meq / g or less, and even more preferably 1.00 meq / g or more and 1.15 meq / g or less. The ion exchange capacity can be measured based on the method described in the examples below.

[0029] (reinforcement material) The reinforcing material is disposed within the sulfonic acid type membrane body. In this embodiment, the reinforcing material can function as at least one of a reinforcing thread and a sacrificial thread. That is, the reinforcing material preferably includes a reinforcing thread and / or a sacrificial thread. Examples of the reinforcing material include, but are not limited to, a woven fabric woven with a reinforcing thread and a sacrificial thread. By disposing the reinforcing material within the sulfonic acid type membrane body, it is possible to control the expansion and contraction of the ion exchange membrane within a desired range. Such an ion exchange membrane does not expand and contract more than necessary during electrolysis, etc., and can maintain excellent dimensional stability for a long period of time. In this specification, "disposed within the sulfonic acid type membrane body" means that at least a portion of the reinforcing material is disposed within the sulfonic acid type membrane body, and also includes an embodiment in which a portion of the reinforcing material penetrates from the inside to the outside of the sulfonic acid type membrane body.

[0030] The configuration of the reinforcing material is not particularly limited, and may be formed, for example, by spinning a thread called a reinforcing thread. The reinforcing thread referred to here is a component constituting the reinforcing material, and refers to a thread that can impart the desired dimensional stability and mechanical strength to the ion exchange membrane and can exist stably within the ion exchange membrane. By using a reinforcing material spun from such a reinforcing thread, it is possible to impart even better dimensional stability and mechanical strength to the ion exchange membrane.

[0031] The reinforcing yarns may include, but are not limited to, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), vinylidene fluoride polymer (PVDF), polyphenylene sulfide (PPS), nylon, etc. In this embodiment, from the viewpoint of heat resistance and chemical resistance, the reinforcing yarns preferably include at least one selected from the group consisting of PTFE and PFA.

[0032] The sacrificial yarn may be, but is not limited to, polyethylene terephthalate (PET), polyvinyl alcohol (PVA), rayon, cellulose, polyamide, etc. In this embodiment, from the viewpoint of stability during weaving and solubility in acid or alkali, the sacrificial yarn preferably contains PET.

[0033] The denier numbers (thread diameters) of the reinforcing yarns and sacrificial yarns are not particularly limited, but are preferably each independently 20 to 150 denier. When a woven fabric woven with reinforcing yarns and sacrificial yarns is used as a reinforcing material, the warp and weft of the reinforcing yarns and sacrificial yarns may each independently have the denier numbers described above. In this case, the weaving density (number of threads per unit length) is preferably 20 to 150 threads per inch. When the reinforcing material is a woven fabric, the thickness is preferably 50 μm or more and 150 μm or less. The form of the reinforcing material is not limited to a woven fabric, and may be, for example, a nonwoven fabric, a knitted fabric, or the like.

[0034] For the woven or knitted fabric, monofilament, multifilament, or yarns thereof, slit yarn, etc. can be used, and the weaving method may be various, such as plain weave, leno weave, knit weave, cord weave, shear sack, etc.

[0035] (hydrophilic layer) The ion exchange membrane may further include a hydrophilic layer disposed on the first surface and / or the second surface of the sulfonic acid type membrane body. When the ion exchange membrane includes a hydrophilic layer, gas adhesion to the ion exchange membrane surface during electrolysis operation tends to be suppressed, and the electrolysis voltage tends to be further reduced.

[0036] The hydrophilic layer preferably contains inorganic particles. From the viewpoint of hydrophilicity, the inorganic particles preferably contain at least one selected from the group consisting of oxides, nitrides, and carbides of Group 4 or Group 14 elements, and more preferably at least one selected from the group consisting of SiO2, SiC, ZrO2, and ZrC. The hydrophilic layer may contain a binder polymer. Examples of binder polymers include vinyl compounds having functional groups that can be converted to sulfone-type ion-exchange groups, and materials similar to those used for polymer S may also be used.

[0037] [Method of manufacturing ion exchange membrane] The method for producing the ion exchange membrane of this embodiment is not particularly limited as long as it can produce an ion exchange membrane having the above-mentioned configuration. Suitable methods for producing the ion exchange membrane of this embodiment include, for example, the following methods (1) to (4). (1) a step of obtaining a precursor of polymer S; (2) A step of embedding the reinforcing material in a film using a precursor of polymer S to obtain a precursor of a sulfonic acid type membrane body having the reinforcing material disposed therein (integration step); (3) A step of obtaining a sulfonic acid type membrane body containing polymer S by hydrolyzing a precursor of polymer S in a precursor of the sulfonic acid type membrane body (hydrolysis step); (4) Optionally, a step of forming a hydrophilic layer on at least one surface of the sulfonic acid type membrane body (hydrophilic layer forming step).

[0038] Each step will be described in more detail below.

[0039] The precursor of polymer S can be produced, for example, but not limited to, by copolymerizing the following first group monomer and second group monomer, or by homopolymerizing the second group monomer.

[0040] The first group of monomers includes, but is not limited to, a vinyl fluoride compound, and is preferably a vinyl fluoride compound represented by the following formula (3). CF2=CX1X2 (3) (In the above formula (3), X1 and X2 each independently represent F, Cl, H, or CF3.)

[0041] Examples of the vinyl fluoride compound represented by the above formula (3) include, but are not limited to, vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, and chlorotrifluoroethylene. In this embodiment, the vinyl fluoride compound is preferably a perfluoromonomer, more preferably a perfluoromonomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene. Tetrafluoroethylene (TFE) is even more preferred.

[0042] The second group of monomers includes, but is not limited to, vinyl compounds having a functional group that can be converted into a sulfonic acid type ion exchange group. The vinyl compounds having a functional group that can be converted into a sulfonic acid type ion exchange group are preferably those represented by the following formula (4): CF2=CFO-(CF2CYFO) a -(CF2) b -SO2F (4) (In the above formula (4), a represents an integer of 0 to 2, b represents an integer of 1 to 6, Y represents F or CF3, and R represents CH3, C2H5, or C3H7.)

[0043] Specific examples of these include the monomers shown below: CF2=CFOCF2CF2SO2F, CF2=CFOCF2CF(CF3)OCF2CF2SO2F, CF2=CFOCF2CF(CF3)OCF2CF2CF2SO2F, CF2 = CF(CF2)2SO2F, CF2=CFO〔CF2CF(CF3)O〕2CF2CF2SO2F, CF2=CFOCF2CF(CF2OCF3)OCF2CF2SO2F. Among the above, CF2=CFOCF2CF(CF3)OCF2CF2CF2SO2F and CF2=CFOCF2CF(CF3)OCF2CF2SO2F are preferred, and CF2=CFOCF2CF(CF3)OCF2CF2SO2F is more preferred.

[0044] The type, ratio, and degree of polymerization of the combination of monomers constituting the precursor of polymer S are not particularly limited. That is, the type, ratio, and degree of polymerization of the combination of monomers constituting polymer S are not particularly limited. The ion exchange membrane may contain one type of polymer S alone or two or more types of polymer S. The ion exchange capacity of polymer S can be adjusted to the above-mentioned range by, for example, changing the ratio of the monomers represented by the above formulas (3) and (4). More specifically, for example, the monomer represented by formula (3) and the monomer represented by formula (4) may be copolymerized in a ratio of 3:1 to 7:1.

[0045] (integration process) The precursor of polymer S can be formed into a film using an extruder or the like. The film may be a single layer or may have a structure of two or more layers. When a structure of two or more layers is used, for example, films of the precursor of polymer S constituting each layer are formed separately and then subjected to the integration process described below.

[0046] The structure of the ion exchange membrane can be controlled by adjusting the shape and arrangement of the reinforcing material, such as the reinforcing threads and sacrificial threads. For example, if the sacrificial threads are made thicker, they tend to be located near the surface of the precursor of the sulfonic acid-type membrane body, and the sacrificial threads are eluted, making it easier to form openings in the ion exchange membrane. Furthermore, the density of openings can be controlled by controlling the number of sacrificial threads. Similarly, if the reinforcing threads are made thicker, openings tend to form more easily.

[0047] Methods for integrating the precursor of polymer S and the reinforcing material include, but are not limited to, a method in which the reinforcing material and a film of the precursor of polymer S are laminated in this order on a flat substrate (e.g., air-permeable and heat-resistant release paper) on a flat plate or drum having an internal heating and / or vacuum source and a large number of fine holes on its surface, and the layers are integrated while removing air between each layer by reducing the pressure at a temperature at which the film melts. Specific examples include, but are not limited to, a method in which the release paper, the reinforcing material, and a film of the precursor of polymer S are laminated in this order on a drum, and integrated under heating and reduced pressure (the reinforcing material is embedded in the film). Furthermore, for example, when two types of precursor of polymer S are used in the form of films, a method in which the release paper, the reinforcing material, a film of the precursor of polymer S, and a film of a (different) precursor of polymer S are laminated in this order on a drum, and integrated under heating and reduced pressure is included. Here, the release paper has a smooth surface and is gas permeable and heat resistant. By adjusting the temperature of heating and decompression (embedding temperature), a sulfonic acid-based membrane body having a roughened surface and a flat surface can be easily obtained. For example, when the membrane is heated and decompressed on the side of the release paper without embossing, a flat surface tends to form on the release paper side. On the other hand, on the atmospheric side, the part without the reinforcing material (the part containing only the resin) flows relative to the part with the reinforcing material due to heating and decompression, and as the embedding temperature decreases, h2 tends to decrease and the surface roughness tends to increase. On the other hand, as the embedding temperature increases, h2 tends to increase and the surface roughness tends to decrease.

[0048] (Hydrolysis process) By hydrolyzing the precursor of polymer S, the precursor of the ion exchange group can be converted into the ion exchange group. In this way, a composite membrane of a sulfonic acid type membrane body containing polymer S and a reinforcing material can be obtained. Here, if sacrificial yarn is included as the reinforcing material, interconnected pores can be formed inside the sulfonic acid type membrane body by dissolving and removing the sacrificial yarn with acid or alkali in addition to the introduction of the ion exchange group. Note that the sacrificial yarn may not be completely dissolved and removed, but may remain in the interconnected pores. Furthermore, when electrolysis is performed, the sacrificial yarn remaining in the interconnected pores may be dissolved and removed with the electrolyte.

[0049] The acid or alkali may be any acid or alkali capable of dissolving the sacrificial yarn, and the type of acid or alkali is not particularly limited. Examples of acids include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and fluorine-containing acetic acid. Examples of alkalis include, but are not limited to, potassium hydroxide and sodium hydroxide.

[0050] The hydrolysis conditions are not particularly limited, and can be carried out, for example, in an aqueous solution of 2.5 to 4.0 normal (N) potassium hydroxide (KOH) and 20 to 40 mass % DMSO (dimethyl sulfoxide), at 40 to 95°C for 10 minutes to 24 hours.

[0051] (Hydrophilic layer formation process) A hydrophilic layer may be formed on at least one surface of the sulfonic acid type membrane body. The material for the hydrophilic layer is not particularly limited, and the method for forming the hydrophilic layer on the sulfonic acid type membrane body is not particularly limited, and known methods can be used. For example, a method in which a liquid in which inorganic oxide particles are dispersed in a binder polymer solution is applied by spraying or the like can be used. The application conditions are not particularly limited, and spraying can be used at 30 to 90°C, for example. Methods other than the spraying method include roll coating, for example. The hydrophilic layer formation step is an optional step. If the hydrophilic layer formation step is not performed, a composite membrane of a sulfonic acid type membrane body and a reinforcing material obtained through the aforementioned hydrolysis step can also be used as the ion exchange membrane of this embodiment.

[0052] [Electrolytic cell] The ion exchange membrane of this embodiment can be used as a component of an electrolytic cell. That is, the electrolytic cell of this embodiment includes the ion exchange membrane of this embodiment. The electrolytic cell of this embodiment typically includes an anode, a cathode facing the anode, and the ion exchange membrane of this embodiment disposed between the anode and the cathode. Since the electrolytic cell of this embodiment includes the ion exchange membrane of this embodiment, it can be preferably used as an electrolytic cell for water electrolysis, and more preferably as an electrolytic cell for alkaline water electrolysis. Furthermore, from the viewpoint of further demonstrating the performance of the ion exchange membrane of this embodiment, the electrolytic cell of this embodiment preferably has a zero-gap structure.

[0053] Fig. 4 is a conceptual diagram showing an example of an electrolytic cell of this embodiment. In Fig. 4, the electrolytic cell 100 includes an anode 21, a cathode 31 facing the anode 21, and an ion exchange membrane 10 disposed between the anode 21 and the cathode 31. The electrolytic cell 100 is separated by the ion exchange membrane 10 into an anode chamber 20 containing the anode 21 and a cathode chamber 30 containing the cathode 31.

[0054] The surface 10a of the ion exchange membrane 10 may be disposed on the electrode surface side of the anode 21 or the cathode 31, whichever has greater rigidity. When the ion exchange membrane 10 has a hydrophilic layer 3, the surface 10a of the ion exchange membrane 10 is the surface 3a of the hydrophilic layer 3. When the ion exchange membrane 10 does not have a hydrophilic layer 3, the surface 10a of the ion exchange membrane 10 is the first surface 1a of the sulfonic acid type membrane body 1. Thus, the surface 10a of the ion exchange membrane 10 is a flat surface, whereas the surface 10b of the ion exchange membrane 10 is a rough surface. When the surface 10a of the ion exchange membrane 10, i.e., the flat surface, is disposed on the electrode surface side of the anode 21 or the cathode 31, whichever has greater rigidity, resistance to pressure on the ion exchange membrane from the electrode tends to be ensured, and therefore membrane damage tends to be further suppressed.

[0055] FIG. 4 shows an example in which the anode 21 is more rigid than the cathode 31. That is, in the electrolytic cell 100, the ion exchange membrane 10 is arranged such that the surface 10a of the ion exchange membrane 10 faces the surface 21a of the anode 21, and the surface 10b of the ion exchange membrane 10 faces the surface 31b of the cathode 31. In FIG. 4, for convenience of explanation, the anode 21, the ion exchange membrane 10, and the cathode 31 are shown spaced apart, but these are preferably arranged so that adjacent members are in contact with each other, that is, the electrolytic cell 100 has a zero-gap structure. In alkaline water electrolysis, oxygen is generated from the anode 21, and hydrogen is generated from the cathode 31. Because the amount of hydrogen generated at the cathode 31 is greater than the amount of oxygen generated at the anode 21, when the surface 10b of the ion exchange membrane 10 is arranged in contact with the surface 31b of the cathode 31, the effect of reducing the electrolysis voltage by dispersing the gas tends to be more pronounced.

[0056] In this embodiment, other device configurations of the electrolytic cell are not particularly limited and may be similar to the device configurations of various known electrolytic cells. Furthermore, the operating conditions of the electrolytic cell are also not particularly limited and may be similar to the operating conditions of various known electrolytic cells. For example, they may be similar to the operating conditions of Japanese Patent No. 6826243 and Japanese Patent No. 3696137.

[0057] (Bipolar electrolytic cell for alkaline water electrolysis) The electrolytic cell of this embodiment may be a bipolar electrolytic cell for alkaline water electrolysis. Fig. 5 shows an overall side view of an example of a bipolar electrolytic cell for alkaline water electrolysis of this embodiment. Fig. 6 is a partially enlarged cross-sectional view showing the zero-gap structure of the bipolar electrolytic cell for alkaline water electrolysis within the dashed square frame (A) in Fig. 5. As shown in Figs. 5 and 6 , the bipolar electrolytic cell for alkaline water electrolysis of this embodiment may be a bipolar electrolytic cell 50 for alkaline water electrolysis in which a plurality of bipolar elements 60 are stacked with a diaphragm 44 sandwiched between them. The bipolar elements 60 include an anode 42a, a cathode 42c, a partition wall 41 separating the anode 42a and the cathode 42c, and an outer frame 43 bordering the partition wall 41.

[0058] In the example of Fig. 6, a bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment has a zero-gap structure Z in which the diaphragm 44 is in contact with the anode 42a and the cathode 42c. When the ion exchange membrane 10 of this embodiment (see Fig. 2) is used as the diaphragm 44, as described above, the rough surface 10b of the ion exchange membrane 10 is arranged to be in contact with the surface of the cathode 42c, which tends to more significantly reduce the electrolysis voltage due to gas dispersion.

[0059] In the bipolar electrolytic cell 50 for alkaline water electrolysis in this embodiment, an electrode chamber 45 through which the electrolytic solution passes is defined by the partition wall 41, the outer frame 43, and the diaphragm 44, and the electrode chamber 45 is preferably provided with a plurality of rectifying plates 46 arranged parallel to a given direction D2 along the partition wall (see FIG. 6 ).

[0060] (multi-pole element) As shown in Fig. 6 , a bipolar element 60 used in an example bipolar electrolytic cell 50 for alkaline water electrolysis includes a partition wall 41 that separates an anode 42a and a cathode 42c, and an outer frame 43 that borders the partition wall. More specifically, the partition wall 41 is conductive, and the outer frame 43 is provided along the outer edge of the partition wall 41 so as to surround the partition wall 41.

[0061] In this embodiment, the bipolar element 60 may be used so that the given direction D2 along the partition wall 41 is normally the vertical direction. Specifically, when the partition wall 41 has a rectangular shape in a plan view as shown in FIG. 6, the bipolar element 60 may be used so that the given direction D2 along the partition wall 41 is the same direction as the direction of one of two pairs of opposing sides (see FIGS. 5 and 6). In this specification, the vertical direction is also referred to as the electrolyte passage direction.

[0062] In this embodiment, as shown in FIG. 5, a bipolar electrolytic cell 50 for alkaline water electrolysis is configured by stacking a desired number of bipolar elements 60. 5, a bipolar electrolytic cell 50 for alkaline water electrolysis includes, from one end, a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in this order, followed by an anode-side gasket 47 (anode-side gasket portion 47), a diaphragm 44, a cathode-side gasket 47 (cathode-side gasket portion 47), and a bipolar element 60 arranged in this order. The bipolar element 60 is positioned so that the cathode 42c faces the anode terminal element 51a. The components from the anode-side gasket portion 47 to the bipolar element 60 are repeatedly arranged as many times as necessary for the designed production volume. After repeatedly arranging the desired number of components from the anode side gasket portion 47 to the bipolar element 60, the anode side gasket portion 47, the diaphragm 44, and the cathode side gasket portion 47 are again arranged side by side, and finally the cathode terminal element 51c, the insulating plate 51i, and the loose head 51g are arranged in this order. The bipolar electrolytic cell 50 for alkaline water electrolysis is integrated by clamping the entire cell using a clamping mechanism such as tie rods 51r (see FIG. 5 ) or a hydraulic cylinder type, to form the bipolar electrolytic cell 50 for alkaline water electrolysis. The arrangement of the bipolar electrolytic cell 50 for alkaline water electrolysis can be arbitrarily selected from either the anode 42a side or the cathode 42c side, and is not limited to the above order.

[0063] As shown in FIG. 5 , in a bipolar electrolytic cell 50 for alkaline water electrolysis, a bipolar element 60 is disposed between an anode terminal element 51 a and a cathode terminal element 51 c, and diaphragms 44 are disposed between the anode terminal element 51 a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51 c.

[0064] In the bipolar electrolytic cell 50 for alkaline water electrolysis according to this embodiment, as shown in FIG. 6, the partition wall 41, the outer frame 43, and the diaphragm 44 define an electrode chamber 45 through which the electrolyte passes.

[0065] Specifically, the electrode chambers 45 have, at the boundary with the outer frame 43, an electrolyte inlet for introducing the electrolyte into the electrode chambers 45 and an electrolyte outlet for discharging the electrolyte from the electrode chambers 45. More specifically, the anode chamber 45a is provided with an anolyte inlet for introducing the electrolyte into the anode chamber 45a and an anolyte outlet for discharging the electrolyte discharged from the anode chamber 45a, and the cathode chamber 45c is provided with a catholyte inlet for introducing the electrolyte into the cathode chamber 45c and a catholyte outlet for discharging the electrolyte discharged from the cathode chamber 45c.

[0066] In the example shown in Figures 5 and 6, the rectangular partition wall 41 and the rectangular diaphragm 44 are arranged in parallel, and the inner surface of the rectangular outer frame 43 provided on the edge of the partition wall 41, facing the partition wall 41, is perpendicular to the partition wall 41, so that the shape of the electrode chamber 45 is rectangular.

[0067] The bipolar electrolytic cell 50 for alkaline water electrolysis is usually fitted with headers, which are pipes for distributing or collecting the electrolyte, and is provided with an anode inlet header for introducing the electrolyte into the anode chamber 45a and a cathode inlet header for introducing the electrolyte into the cathode chamber 45c, both located at the lower part of the outer frame 43 at the edge of the partition wall 41. Similarly, an anode outlet header for discharging the electrode solution from the anode chamber 45a and a cathode outlet header for discharging the electrolyte from the cathode chamber 45c are provided at the upper part of the outer frame 43 at the edge of the partition wall 41. The arrangement of the headers attached to the bipolar electrolytic cell 50 for alkaline water electrolysis shown in Figs. 5 and 6 is typically an internal header type or an external header type, but either type may be employed in the present embodiment, and is not particularly limited.

[0068] In the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment, the electrolyte distributed in the anode inlet header is introduced into the anode chamber 45a through the anolyte inlet, passes through the anode chamber 45a, is discharged from the anode chamber 45a through the anolyte outlet, and is collected in the anode outlet header.

[0069] As shown in FIG. 6, the electrode chamber in this embodiment includes a plurality of current plates 46 arranged parallel to a given direction D2 along the partition wall 41.

[0070] The current plate 46 reduces convection that occurs in the electrode chamber 45 due to turbulence in the gas-liquid flow within the electrode chamber 45, thereby suppressing a local increase in the temperature of the electrolyte.

[0071] In particular, in the example shown in Figures 5 and 6, multiple rectifying plates 46 are provided at regular intervals (pitch) in a direction perpendicular to a given direction D2 (in the illustrated example, the electrolyte flow direction) along the partition wall 41.

[0072] In the example of the bipolar electrolytic cell 50 for alkaline water electrolysis, the rectifying plate 46 has a length substantially equal to the height of the electrode chambers 45, is provided perpendicular to the partition wall 41, and has through-holes at a predetermined pitch in a given direction D2 along the partition wall 41 (in the illustrated example, the direction in which the electrolytic solution passes).

[0073] In this embodiment, the shape of the electrode chamber 45 is not limited to the rectangular parallelepiped shape of the example shown in Figures 5 and 6, and may be modified as appropriate depending on the planar shapes of the partition wall 41 and the diaphragm 44, the angle between the inner surface of the outer frame 43 on the partition wall 41 side and the partition wall 41, etc.

[0074] In this embodiment, the arrangement of the current plate 46 in the electrode chamber 45 is not limited to the example shown in FIGS. In the present embodiment, the number of the rectifying plates 46 and the constant intervals (pitch) between the rectifying plates 46 in the direction perpendicular to the given direction D2 along the partition wall 41 may be determined as appropriate. Here, the intervals between the rectifying plates 46 do not have to be constant. In the present embodiment, the length of the rectifying plate 46, the angle between the rectifying plate 46 and the partition wall 41, the number of through holes, and the constant interval (pitch) of the through holes in a given direction D2 along the partition wall 41 may be determined as appropriate. Here, the interval between the through holes does not have to be constant.

[0075] In the example shown in FIGS. 5 and 6, the partition wall 41, the anode 42a, and the cathode 42c all have a plate-like shape with a predetermined thickness, but are not limited thereto, and may have a shape in which all or part of the cross section is zigzag or wavy, or may have rounded ends.

[0076] [Hydrogen production methods] When the electrolytic cell of this embodiment is used as an electrolytic cell for water electrolysis, hydrogen can be obtained as described above. That is, the hydrogen production method of this embodiment is a hydrogen production method using an electrolytic cell including an anode, a cathode facing the anode, and the ion exchange membrane of this embodiment disposed between the anode and the cathode, and includes a step of supplying an electrolytic solution to the electrolytic cell and performing water electrolysis. From the viewpoint of further demonstrating the performance of the ion exchange membrane of this embodiment, the water electrolysis is preferably alkaline water electrolysis. The conditions for the above step are also not particularly limited and may be similar to the operating conditions of various known electrolytic cells. For example, the conditions may be similar to those described in Japanese Patent Nos. 7353494, 7136580, 6826243, and 3696137.

[0077] In this embodiment, the first surface of the ion exchange membrane may be disposed on the side of the electrode having a higher rigidity, either the anode or the cathode. As described above, the first surface of the ion exchange membrane is a flat surface, and when the flat surface of the ion exchange membrane is disposed on the side of the electrode having a higher rigidity, either the anode or the cathode, resistance to pressure from the electrode to the ion exchange membrane tends to be ensured, and therefore membrane damage tends to be further suppressed. [Example]

[0078] The present embodiment will be described in detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0079] [Surface roughness] When the ion exchange membrane obtained in the Examples and Comparative Examples described later was in a wet state, a piece of the wet ion exchange membrane cut into a length of 10 cm and a width of 10 cm was placed with 500 g weights on the four edges to prevent the center of the membrane from drying and undulating, and the ion exchange membrane was dried by leaving it to stand for 5 hours in a dryer (YAMATO constant temperature blower dryer DKM400) adjusted to 50°C (drying step). When the ion exchange membrane obtained in the Examples and Comparative Examples described later was in a dry state, the above-mentioned drying step was omitted. The dried ion exchange membrane was placed in a laser microscope (KEYENCE shape analysis laser microscope). The laser measurement was set to 50x magnification, and a 12-by-7 grid (each grid was 282 μm wide by 211 μm long) measurement was performed. Then, a basic measurement was performed at a pitch of 0.12 μm. The measurement results were analyzed using the KEYENCE multi-file analysis application (version 2.2.0.93) using the following procedure to calculate the surface roughness. First, the waviness of the membrane itself was removed using the waviness removal (correction strength 5) in the shape correction section of the image processing tool. The entire area was then selected using the surface roughness analysis tool, and the surface roughness R was calculated. This measurement was performed on both the cathode-facing and anode-facing surfaces of the composite membrane, and R1 and R2 were calculated. If there was a relationship between the surface roughness of the cathode-facing surface and the surface roughness of the anode-facing surface, the surface with the larger value was designated R2 and identified as the second surface, and the surface with the smaller value was designated R1 and identified as the first surface. If there was no such relationship, it was evaluated as being impossible to distinguish between a first surface and a second surface.

[0080] [Thickness h1 and h2] The dried ion exchange membrane was cut perpendicular to the first surface 1a to obtain a sample with a long side of 6 mm or more and a short side of 100 μm. The cross section of the sample was fixed facing upward, and the cross section was observed using an optical microscope. Within the field of view, a position P1 where a reinforcing material was present was identified as a portion containing at least one of a reinforcing yarn and a sacrificial yarn (see P1 in Figure 3). Furthermore, a position P2 where a reinforcing material was absent within the observation field of view was identified as a portion containing neither a reinforcing yarn nor a sacrificial yarn (see P2 in Figure 3). Among the measured membrane thickness values ​​at position P1 within the observation field of a single cross section, the largest and second largest values ​​were recorded. This measurement was performed on 50 cross sections, and the average value of a total of 100 points was identified as h1. Furthermore, among the measured membrane thickness values ​​at position P2 within the observation field of a single cross section, the smallest and second smallest values ​​were recorded. Such measurements were carried out on 50 cross sections, and the average value of the measurement results of a total of 100 points was determined as h2.

[0081] [Distance between reinforcements L1] A dried ion exchange membrane was cut perpendicular to the first surface 1a to obtain a sample with a long side of 6 mm or more and a short side of 100 μm. The sample was fixed with its cross section facing upward, and the cross section was observed using an optical microscope. Within the field of view, a position P1 where the reinforcing material was present was identified, similar to the above-described [thicknesses h1 and h2]. In all examples, as shown in Figure 3, multiple reinforcing materials 2 were observed along the in-plane direction D1 of the ion exchange membrane 10. That is, multiple positions P1 were confirmed within the observation field. For each of the multiple positions P1, the portion Pmax that gave the largest measured membrane thickness value was identified. Next, the distance between two adjacent portions Pmax was recorded. The above measurement was performed on all reinforcing materials within the observation field of a single cross section (in the example of Figure 3, three measured values ​​of L1 were obtained). This process was repeated, and the average of the 100 measurement results was determined as L1.

[0082] [Ion exchange capacity] Approximately 1 g of each of the polymers S-1 to S-5 and C-1 (fluorine-containing polymers having ion-exchange group precursors) described below was collected and press-molded at a temperature approximately 30°C higher than the pseudo-melting point of the polymer to obtain a polymer film. Each of the obtained films was subjected to transmission infrared spectroscopy. The proportions of the infrared peaks of CF2, CF, CH3, OH, and SO2F were calculated. The ion-exchange capacity was determined by hydrolyzing each of these polymers to obtain the proportion of structural units having sulfonic acid / carboxylic acid functional groups, using a calibration curve of samples with known ion-exchange capacities calculated by titration.

[0083] [Delamination resistance evaluation] The electrolytic cell used for electrolysis had an ion exchange membrane between the anode and cathode, and three pairs of forced circulation zero-gap electrolytic cells were arranged in series. The cathode was a plain-woven mesh electrode made of 40-mesh 0.15 mm diameter nickel fine wires coated with platinum and palladium as catalysts. Ni expanded metal was used as the anode. A conductive cushion mat made of 0.15 mm nickel wire was placed on the cathode side as an elastic body. When the ion exchange membrane had a first and second surface, the first surface was positioned on the anode side. Using the above electrolytic cell, a 26 wt% aqueous sodium hydroxide solution was supplied to the anode and cathode sides. The temperature of the electrolytic cell was set to 70°C, and the current was 10 kA / m 2 The current density was applied for a total of six days. Table 1 shows the difference in voltage loss compared to the initial voltage loss of the film. In other words, it shows the value calculated using the following formula, and if there is delamination, the difference will be positive. Difference in voltage loss before and after the delamination resistance evaluation ΔV = (voltage loss after the delamination resistance evaluation) [mV] - (voltage loss before the delamination resistance evaluation) [mV] In Table 1, when the difference in voltage loss ΔV before and after the evaluation of delamination resistance was negative to 0, there was no delamination and the sample was evaluated as A. When the above ΔV was positive, there was delamination and the sample was evaluated as B. In addition to the change in voltage, the presence or absence of delamination was also confirmed by observing the removed film under a microscope.

[0084] [Initial voltage loss evaluation] The electrolytic cell used for electrolysis had an ion exchange membrane between the anode and cathode, and three pairs of forced circulation zero-gap electrolytic cells were arranged in series. The cathode was a plain-woven mesh electrode woven with 0.15 mm diameter nickel fine wires coated with platinum and palladium as catalysts. Ni expanded metal was used as the anode. A conductive cushion mat made of 0.15 mm nickel wire was placed on the cathode side as an elastic body. Here, when the ion exchange membrane had a first surface and a second surface, it was positioned so that the first surface was on the anode side. Using the above electrolytic cell, a 20 wt% aqueous sodium hydroxide solution was supplied to the anode and cathode sides. The temperature of the electrolytic cell was set to 90°C, and 6 kA / m 2 The current was passed for a total of 10 hours at a current density of 100 kJ / s. The impedance was measured after 10 hours. The membrane resistance was calculated for each of the three series-connected cells, and the average value was calculated as the voltage loss. Table 1 shows the difference in the initial voltage loss compared to Comparative Example 1. That is, it shows the value calculated by the following formula, and indicates a decrease in membrane voltage loss compared to Comparative Example 1 with a negative sign, and an increase with a positive sign. Initial membrane voltage loss (difference from Comparative Example 1) ΔV = (membrane voltage loss of Comparative Example and Example) [mV] - (membrane voltage loss of Comparative Example 1) [mV]

[0085] [Differential pressure fluctuation resistance] The following accelerated test was conducted to evaluate the effect of the pressure difference between the anode and cathode chambers, as observed during electrolysis (when current flows through the electrodes), on the ion-exchange membrane in an accelerated manner. First, a 65 mm x 69 mm square anode and cathode were prepared, and the ion-exchange membrane of each example was placed between them to create a zero-gap electrolytic cell equipped with an anode chamber and a cathode chamber. The anode was a Ni expanded metal with a center-to-center distance of 3 mm in the short direction and 4.5 mm in the long direction. The cathode was a plain-woven mesh electrode made of 40-mesh 0.15 mm diameter nickel fine wires coated with platinum and palladium as catalysts. A conductive cushion mat made of 0.15 mm nickel wire was placed on the cathode side as an elastic body. Furthermore, when the ion-exchange membrane had a first and second surface, the first surface was positioned on the anode side. In this electrolytic cell, the cell was filled with water, and pressure swings were performed by controlling the gas pressure to create a pressure difference between the anode and cathode chambers. Specifically, pressure swings from 0 kPa to 80 kPa were repeated approximately 100 times per hour. In each pressure swing, the pressure was first increased to 80 kPa over 15 seconds, then held at 80 kPa for 3 seconds, and then decreased to 0 kPa over 15 seconds, then held at 0 kPa for 3 seconds. This series of operations constituted one pressure swing. During the pressure swings, it was observed that the ion-exchange membrane fixed in the zero-gap electrolytic cell tended to be more strongly affected by pressure, particularly in the following areas that tended to become free. Specifically, it was observed that pressure was more likely to be applied to the ion-exchange membrane near the frame (the gap between the anode and the frame) used to fix the ion-exchange membrane in the electrolytic cell (fixing the ion-exchange membrane in the electrolytic cell at its outer edge) and near the openings in the anode (expanded metal). After repeating the above pressure swing a predetermined number of times, the appearance of the ion exchange membrane was visually observed to check for damage. This procedure was repeated until damage was observed on the appearance or a predetermined number of times. The above test was carried out on the ion exchange membrane of each example, and the differential pressure fluctuation resistance was evaluated according to the following criteria. (Evaluation criteria) A: No damage even after more than 10,000 pressure swings. B: Damage was observed at pressure swings of 7,000 to 9,999. C: Damage was observed at pressure swings of 5,000 to 6,999. D: Damage was observed at pressure swings of 2500 to 4999. E: Damage was observed at pressure swings of 1 to 2,500.

[0086] [Polymer] Polymer S-1 was prepared by copolymerizing a monomer represented by the following formula (5) and a monomer represented by the following formula (6) to obtain a polymer having an ion exchange capacity of 1.03 meq / g. CF2=CF2 (5) CF2=CFO-CF2CF(CF3)O-(CF2)2-SO2F ···(6)

[0087] Polymer S-2 was prepared by copolymerizing a monomer represented by the above formula (5) and a monomer represented by the above formula (6) to obtain a polymer having an ion exchange capacity of 1.05 meq / g.

[0088] Polymer S-3 was prepared by copolymerizing a monomer represented by the above formula (5) and a monomer represented by the above formula (6) to obtain a polymer having an ion exchange capacity of 1.15 meq / g.

[0089] Polymer S-4 was obtained by copolymerizing a monomer represented by the above formula (5) and a monomer represented by the above formula (6) to obtain a polymer having an ion exchange capacity of 0.74 meq / g.

[0090] Polymer S-5 was obtained by copolymerizing a monomer represented by the above formula (5) and a monomer represented by the above formula (6) to obtain a polymer having an ion exchange capacity of 0.9 meq / g.

[0091] Polymer C-1 was prepared by copolymerizing a monomer represented by the above formula (5) with a monomer represented by the following formula (7) to obtain a polymer having an ion exchange capacity of 0.87 meq / g. CF2=CFO-CF2CF(CF3)O-(CF2)2-COOCH3...(7)

[0092] [Reinforcement material] A polytetrafluoroethylene (PTFE) monofilament yarn with a diameter of 90 denier was prepared as the reinforcing yarn. A multifilament yarn made by twisting together six polyethylene terephthalate (PET) yarns with a diameter of 6.7 denier was prepared as the sacrificial yarn. The reinforcing yarns were woven in a plain weave with a weave density of 24 threads / inch, with two sacrificial yarns positioned between adjacent reinforcing yarns. The resulting woven fabric was pressed with a roll at 125°C to obtain Reinforcing Material 1. The thickness of Reinforcing Material 1 was 80 μm. In addition, a commercially available Teflon woven fabric (made of PTFE) was used as the reinforcing material 2.

[0093] [Example 1] (Integration of each material) Using the T-die method, films A and B were obtained from polymer S-1 and polymer S-2, respectively. The total film thickness of films A and B was 70 μm. A drum with an internal heating source and vacuum source and micropores on its surface was prepared. Unembossed release paper, reinforcing material 1, film B, and film A were stacked on this drum in this order, and then heated and decompressed at 230 °C (a vacuum of -650 mmHg) to remove air from between the materials, resulting in a composite membrane (a membrane containing a precursor of the sulfonic acid-type membrane body and a reinforcing material). In this process, the membrane was heated and decompressed on the unembossed release paper side, forming a flat surface on the unembossed release paper side. On the other hand, on the atmospheric side, the resin portion alone flowed relative to the reinforcing material due to the heating and decompression, forming a rough surface. (hydrolysis) The resulting composite membrane was hydrolyzed by immersing it in an aqueous solution containing 30% by mass of DMSO and 15% by mass of potassium hydroxide (KOH) at 90°C for 1 hour, followed by washing with water and drying. In this way, a composite membrane containing a sulfonic acid type membrane body and a reinforcing material was obtained. (Formation of hydrophilic layer) Furthermore, zirconium oxide having a primary particle size of 1 μm was added to a 5% by mass ethanol solution of the acid type polymer of polymer S-2 so as to have a ratio of 20% by mass, and dispersed to prepare a suspension. This suspension was sprayed onto both sides of the composite membrane that had been subjected to the hydrolysis described above by a spray method, and then dried to obtain a 0.5 mg / cm 2 A hydrophilic layer of the above formula was formed on the surface of the composite membrane to obtain an ion exchange membrane.

[0094] The ion exchange membrane obtained as described above was subjected to various measurements and evaluations as described above. The results are shown in Table 1.

[0095] [Examples 2 to 5] The total film thickness of Film A and Film B was changed from 70 μm in Example 1 to 90 μm in Example 2, 110 μm in Example 3, 120 μm in Example 4, and 150 μm in Example 5. Except for the above points, the ion exchange membranes of Examples 2 to 5 were obtained by the same production method as in Example 1.

[0096] [Example 6] An ion exchange membrane of Example 6 was obtained in the same manner as in Example 3, except that the heating and decompression temperature during the preparation of the composite membrane in Example 3 was changed from 230°C to 240°C.

[0097] [Example 7] Film A was not used when preparing the composite membrane in Example 3, and the non-embossed release paper, reinforcing material 1, and film B (thickness 110 μm) were laminated on the drum in this order. Except for the above points, the ion exchange membrane of Example 7 was obtained by the same production method as in Example 3.

[0098] [Example 8] A film C (thickness: 110 μm) was obtained from the polymer S-3 by the T-die method. An ion exchange membrane of Example 8 was obtained in the same manner as in Example 7, except that the film C was used instead of the film B in Example 7.

[0099] [Example 9] An ion exchange membrane of Example 9 was obtained in the same manner as in Example 5, except that the heating and decompression temperature during the preparation of the composite membrane in Example 5 was changed from 230°C to 200°C.

[0100] [Example 10] Using the T-die method, films D and E were obtained from polymer S-4 and polymer S-5, respectively. The total film thickness of films D and E was 150 μm. Using films D and E and reinforcing material 2, an ion exchange membrane was obtained in the same manner as in Example 1. Only one side of this ion exchange membrane was roughened by the following method. That is, a 3 mm thick silicone rubber sheet (upper part), cotton cloth, the ion exchange membrane (the ion exchange membrane was wetted and the rough surface was placed on the cotton cloth side), a 3 mm thick silicone rubber sheet, and a 60 mesh wire mesh (lower part) were laminated in this order, and the laminate was heated to 250° C. while applying a pressure of 10 kg / cm 2 After pressing for 10 minutes under a pressure of 0.05g, the membrane was treated with a hot aqueous solution of sodium hypochlorite to remove the cotton cloth adhering to the membrane, and an ion exchange membrane of Example 10 was obtained.

[0101] [Example 11] An ion exchange membrane of Example 11 was obtained in the same manner as in Example 10, except that the surface roughening treatment in Example 10 was not carried out.

[0102] [Example 12] An ion exchange membrane of Example 12 was obtained in the same manner as in Example 3, except that embossed release paper was used instead of the non-embossed release paper used in Example 2.

[0103] [Comparative Example 1] In preparing the composite membrane in Example 3, the unembossed release paper, reinforcing material 1, film B, film A, and unembossed release paper were laminated in this order, and the layers were embedded by thermocompression. Except for the above points, the ion exchange membrane of Comparative Example 1 was obtained by the same method as in Example 3.

[0104] Comparative Example 2 Using the T-die method, film F was obtained from polymer S-2 and film G from polymer C-1. The total film thickness of film F and film G was 110 μm. Next, an ion exchange membrane of Comparative Example 2 was obtained by the same production method as in Example 3, except that in the preparation of the composite membrane in Example 3, unembossed release paper, reinforcing material 1, film F, film G, and unembossed release paper were laminated in this order and embedded by thermocompression bonding.

[0105] Comparative Example 3 The ion exchange membrane of Comparative Example 3 was obtained by the same manufacturing method as in Comparative Example 2, except that in preparing the composite membrane in Comparative Example 2, the unembossed release paper, reinforcing material 1, film F, and film G were laminated in that order.

[0106] Comparative Example 4 The integration step in Example 1 was not carried out, and the same hydrolysis step and hydrophilic layer formation step as in Example 1 were carried out on 110 μm Film B to obtain an ion exchange membrane of Comparative Example 4.

[0107] [Table 1]

[0108] The Examples and Comparative Examples showed that the use of a sulfonic acid type membrane body (not containing a carboxylic acid type layer) and the fact that such a membrane body has a flat surface and a rough surface make it possible to keep the electrolysis voltage low, resulting in excellent stability of electrolysis operation, and in particular excellent resistance to differential pressure fluctuations. The reason why the ion exchange membranes of the Examples have excellent resistance to differential pressure fluctuations is not necessarily clear, and although it is not intended to limit the reason, it is presumed to be as follows. That is, it is thought that the sulfonic acid type membrane body having a rough surface and a flat surface has the effect of releasing the pressure at the contact point between the rough surface and the electrode to the part of the rough surface that does not contact the electrode when pressure is applied while in contact with the electrode. [Explanation of symbols]

[0109] 1...sulfonic acid type membrane body, 1a...first surface, 1b...second surface, 2...reinforcing material, 2a...reinforcing thread, 2b...sacrificial thread, 3...hydrophilic layer, 10...ion exchange membrane, 21...anode, 31...cathode, 41...diaphragm, 42...electrode, 42a...anode, 42c...cathode, 42e...conductive elastic body, 42r...current collector, 43...outer frame, 44...diaphragm, 45...electrode chamber, 45a...anode chamber, 45c...cathode chamber, 46...rectifier Plate (rib), 47...gasket, 50...bipolar electrolytic cell for alkaline water electrolysis, 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, 100...electrolytic cell, D1...surface direction, D2...given direction along the partition (direction of electrolyte passage), Z...zero gap structure

Claims

1. A sulfonic acid type membrane body containing a polymer having sulfonic acid groups, and a reinforcing material disposed within the sulfonic acid type membrane body, the surface roughness R1 of the first surface of the sulfonic acid type membrane body is smaller than the surface roughness R2 of the second surface of the sulfonic acid type membrane body; The surface roughness R1 of the first surface is less than 10 μm, An ion exchange membrane, wherein the second surface has a surface roughness R2 of 10 μm or more.

2. 2. The ion exchange membrane according to claim 1, wherein, in a cross section of the ion exchange membrane, a thickness h1 of the ion exchange membrane at a position P1 where the reinforcing material is present and a thickness h2 of the ion exchange membrane at a position P2 where the reinforcing material is not present satisfy 1.3≦h1 / h2≦10.

3. The ion exchange membrane according to claim 2 , wherein the thickness h2 is 10 μm or more and 100 μm or less.

4. The ion exchange membrane according to claim 2 , wherein the thickness h1 is 100 μm or more and 200 μm or less.

5. a plurality of the reinforcing members are present along the surface direction of the ion exchange membrane, The ion exchange membrane according to claim 2 , wherein the distance L1 between adjacent reinforcing members is 1 / 150 inch or more and 1 / 10 inch or less.

6. 2. The ion exchange membrane according to claim 1, wherein the ion exchange capacity of the polymer is 0.90 meq / g or more and 2.00 meq / g or less.

7. The ion exchange membrane according to claim 1 , wherein the polymer is a fluorine-containing polymer.

8. The ion exchange membrane according to claim 1 , wherein the polymer comprises a polymer P1 having a unit represented by the following formula (1): -[CF ２ -CF(-O-CF ２ CF(CF ３ )-O-(CF ２ ) ｍ -SO ３ M)]- (1) (In formula (1), m is an integer of 1 to 6, and M is an alkali metal.)

9. The ion exchange membrane of claim 1 , wherein the reinforcement material comprises reinforcing yarns and / or sacrificial yarns.

10. The reinforcing yarn comprises at least one selected from the group consisting of PTFE and PFA, The ion exchange membrane of claim 9 , wherein the sacrificial yarn comprises PET.

11. 10. The ion exchange membrane of claim 9, wherein the reinforcing yarns and the sacrificial yarns each independently have a denier of 20 to 150 denier.

12. 10. The ion exchange membrane according to claim 9, wherein the reinforcing yarns have a weave density of 20 to 150 threads per inch.

13. The ion exchange membrane of claim 1 , further comprising a hydrophilic layer disposed on the first surface and / or the second surface.

14. The ion exchange membrane of claim 13 , wherein the hydrophilic layer comprises inorganic particles.

15. 15. The ion exchange membrane according to claim 14, wherein the inorganic particles contain at least one selected from the group consisting of oxides, nitrides, and carbides of Group 4 or Group 14 elements.

16. The inorganic particles are SiO ２ , SiC, ZrO ２ The ion exchange membrane according to claim 14, comprising at least one selected from the group consisting of ZrC and ZrC.

17. The ion exchange membrane according to any one of claims 1 to 16, which is used for water electrolysis.

18. The ion exchange membrane according to any one of claims 1 to 16, which is used for alkaline water electrolysis.

19. an anode; a cathode facing the anode; The ion exchange membrane according to any one of claims 1 to 16, which is disposed between the anode and the cathode; An electrolytic cell comprising:

20. 20. The electrolytic cell according to claim 19, wherein the first surface of the ion exchange membrane is disposed on the electrode surface side of the anode or the cathode, whichever has greater rigidity.

21. The electrolytic cell according to claim 19, which is used for alkaline water electrolysis.

22. 20. The electrolytic cell of claim 19 having a zero gap configuration.

23. 20. A method for producing hydrogen using the electrolytic cell of claim 19, comprising: A method for producing hydrogen, comprising the steps of supplying an electrolytic solution to the electrolytic cell and performing water electrolysis.

24. 24. The method for producing hydrogen according to claim 23, wherein the first surface of the ion exchange membrane is disposed on the electrode surface side of the anode or the cathode, whichever has higher rigidity.

25. The method for producing hydrogen according to claim 23, wherein the water electrolysis is alkaline water electrolysis.

Images