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

Abstract

An ion exchange membrane comprising: a sulfonic-acid-type membrane body containing a polymer having a sulfonic-acid group; and a reinforcement material disposed in the sulfonic-acid-type membrane body, wherein the surface roughness R1 of a first surface of the sulfonic-acid-type membrane body is lower than the surface roughness R2 of a second surface of the sulfonic-acid-type membrane body.

Description

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

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

[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 has the property of being highly variable, as its output depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy (hereinafter referred to as "variable power source") to the general power grid, raising concerns about the social impact of imbalances in power supply and demand and instability in the power grid. It is also well known that imbalances between the electricity generated by renewable energy and the electricity 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.As one example, consideration is being given to generating storable and transportable hydrogen through electrolysis (hereinafter also referred to as "electrolysis") using electricity generated from renewable energy, specifically through the electrolysis of water (hereinafter also referred to as "water electrolysis"), and using the generated hydrogen as an energy source or raw material.

[0005] Hydrogen is widely used industrially in petroleum refining, chemical synthesis, metal refining, etc., and in recent years, its potential use has expanded to include 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 ion exchange membrane is thinned to a thickness of 25 to 70 μm, and the ion exchange capacity is adjusted, thereby enabling the electrolysis voltage to be kept low even at high current densities and reducing the likelihood of delamination.

[0008] Furthermore, in order to reduce the electrolysis voltage in alkaline water electrolysis and improve the power consumption rate for hydrogen production, progress has been made in introducing a structure known as a zero-gap structure, in which the gap between the diaphragm and the electrode is substantially eliminated (see, for example, Patent Documents 2 and 3). In the zero-gap structure, generated gas is quickly released to the side of the electrode opposite the diaphragm through 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.

[0009] Japanese Patent No. 6981421, U.S. Patent No. 4,530,743, Japanese Patent Laid-Open No. 59-173281

[0010] When a current flows through the electrodes, a pressure difference (differential pressure) can occur between the anode chamber and the cathode chamber. The pressure difference 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 apparatus also fluctuates. In such power fluctuation operation, the fluctuation in the pressure difference may damage the diaphragm, which may result in mixing of oxygen gas and hydrogen gas. Thus, the diaphragm is required to be resistant to fluctuations in the pressure difference (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 keep the electrolysis voltage low, has excellent stability in electrolysis operation, and is particularly excellent in resistance to differential pressure fluctuations.

[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 encompasses the following aspects. [1] An ion exchange membrane comprising 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. [2] The ion exchange membrane according to [1], wherein the surface roughness R1 of the first surface is less than 10 μm, and the surface roughness R2 of the second surface is 10 μm or more. [3] The ion exchange membrane according to [1] or [2], wherein, in a cross section of the ion exchange membrane, the thickness h1 of the ion exchange membrane at a position P1 where the reinforcing material is present and the thickness h2 of the ion exchange membrane at a position P2 where the reinforcing material is not present satisfy the relationship 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] The ion exchange membrane according to any one of [1] to [5], wherein a plurality of the reinforcing members are present along the surface direction of the ion exchange membrane, and 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 contains 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 ３M)]- (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 comprises a reinforcing yarn and / or a sacrificial yarn.

[11] The ion exchange membrane according to

[10] , wherein the reinforcing yarn comprises at least one selected from the group consisting of PTFE and PFA, and the sacrificial yarn comprises PET.

[12] The ion exchange membrane according to

[10] or

[11] , wherein the deniers of the reinforcing yarn and the sacrificial yarn are each independently 20 to 150 denier.

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

[10] to

[12] , wherein the weave density of the reinforcing yarn is 20 to 150 threads 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] , wherein the inorganic particles are SiO ２ , SiC, ZrO ２and 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 electrolytic cell comprising: an anode; a cathode facing the anode; and the ion exchange membrane according to any one of [1] to

[19] , which is disposed between the anode and the cathode.

[21] The electrolytic cell according to

[20] , in which the first surface of the ion exchange membrane is disposed on the electrode surface side of the anode or the cathode, whichever is more rigid.

[22] The electrolytic cell according to

[20] or

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

[23] The electrolytic cell according to any one of

[20] to

[22] , which has a zero-gap structure.

[24] A method for producing hydrogen using the electrolytic cell according to any one of

[20] to

[23] , comprising a step of supplying an electrolytic solution to the electrolytic cell and performing water electrolysis.

[25] 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 is more rigid.

[26] The method for producing hydrogen according to

[24] or

[25] , wherein the water electrolysis is alkaline water electrolysis.

[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 fluctuations in differential pressure.

[0017] 5 is a schematic diagram showing an example of a top view of an ion exchange membrane according to the present embodiment. It is a schematic diagram showing the X-X' cross section of FIG. 1. It is an explanatory diagram showing a method for measuring 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. It is a conceptual diagram showing an example of an electrolytic cell according to the present embodiment. It is a side view showing the entirety of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. It is a cross-sectional view showing a partially enlarged zero gap structure of the bipolar electrolytic cell for alkaline water electrolysis within the dashed rectangular frame (A) of FIG. 5.

[0018] Hereinafter, a detailed description will be given of an embodiment of the present invention (also referred to as "the present embodiment" in this specification). The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. 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 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. 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 visible. 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 warp and weft yarns, 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, although the ion exchange membrane 10 in the example of FIG. 2 includes a hydrophilic layer 3, the ion exchange membrane 10 does not necessarily have to include a 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. As described above, the surface texture of the hydrophilic layer 3 tends to correspond to that 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 side, regardless of the presence or absence of the hydrophilic layer 3. Assuming electrolysis operation, the flat surface of the ion exchange membrane of this embodiment contributes to adhesion with the electrode, 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 electrode. Ensuring such a gap also facilitates dispersion of gas (oxygen or hydrogen) generated by electrolysis from the vicinity of the electrode to the offshore side, which, in turn, tends to further reduce the electrolysis voltage. As described above, the ion exchange membrane of this embodiment has both a flat surface and a rough surface, and therefore, compared to a diaphragm having flat surfaces on both sides, it can improve electrolysis performance while suppressing membrane damage. In recent years, there have been many cases where electrolysis is carried out 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 differential pressure fluctuates, the ion exchange membrane is pressed against the electrodes, and therefore, electrolysis using a variable power supply is likely to cause 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 be demonstrated 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 therefore can 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. Furthermore, 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 but less than 80 μm, more preferably 10 μm or more but less than 50 μm, even more preferably 10 μm or more but less than 40 μm, and even more preferably 10 μm or more but less than 30 μm. 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. In other words, 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 be 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. Furthermore, 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 the above-mentioned ranges, for example, as follows. In the manufacturing process of the ion exchange membrane described below, after forming a film from the precursor of 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 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 the reinforcing material is present and the thickness h2 of the ion exchange membrane at position P2 where the reinforcing material is not 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. On the other hand, 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 the procedure 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 absent is determined as a portion excluding position P1. Also, as shown in FIG. 3, the thickness h1 is determined by the portion of the ion exchange membrane thickness (perpendicular to the in-plane direction D1) that gives the maximum value as determined at position P1. The thickness h2 is determined by the portion of the ion exchange membrane thickness that gives the minimum value as determined at 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, and 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 any 100 points, and the value of the thickness h1 is determined as the average value.Similarly, the thickness h2 is measured at 100 random points, and the average value of the measurements is determined as the value of thickness h2. More specifically, thicknesses h1 and h2 can be measured based on the method described in the Examples below. Thicknesses h1 and 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 the thickness h1 was measured to the adjacent position where the thickness h1 was measured. Using this measurement method, the distance L1 is measured at any 50 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 layers, can be said to have sulfonic acid groups on the first and second surfaces and therefore corresponds to a 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 a 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] As the polymer S, various polymers having sulfonic acid groups can be used. The polymer S preferably further contains, for example, a fluorine atom, i.e., a fluorine-containing polymer. In this case, the polymer S preferably contains at least one of a polymer P1 having a unit represented by the following formula (1) and a polymer P2 having a unit represented by the following formula (2), and more preferably contains a polymer P1. -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｍ -SO ３ M)] - (1) - [CF ２ -CF(-O-(CF ２ ) ｍ -SO ３ M)]-(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 viewpoint, 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] (Reinforcing 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 reinforcing yarns and sacrificial yarns. That is, the reinforcing material preferably includes reinforcing yarns and / or sacrificial yarns. Examples of reinforcing materials include, but are not limited to, a woven fabric woven with reinforcing yarns and sacrificial yarns. 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, the phrase "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 is disposed so as to penetrate 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] Examples of the reinforcing yarn 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 the present embodiment, from the viewpoint of heat resistance and chemical resistance, the reinforcing yarn preferably contains 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 the present embodiment, from the viewpoints of stability during weaving and solubility in acid or alkali, it is preferable that the sacrificial yarn contains PET.

[0033] The denier numbers (thread diameters) of the reinforcing yarns and the 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 above-mentioned denier numbers. 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 tends to be suppressed, and the electrolysis voltage tends to be further reduced.

[0036] The hydrophilic layer preferably contains inorganic particles, and the inorganic particles preferably contain at least one selected from the group consisting of oxides, nitrides, and carbides of Group 4 elements or Group 14 elements from the viewpoint of hydrophilicity, and SiO ２ , SiC, ZrO ２and ZrC. The hydrophilic layer may contain a binder polymer. Examples of the binder polymer include vinyl compounds having a functional group that can be converted into a sulfone-type ion exchange group, and materials similar to those used for polymer S may also be used.

[0037] [Method for Producing 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-described 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 the 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 hydrolyzing the precursor of polymer S in the precursor of the sulfonic acid type membrane body to obtain a sulfonic acid type membrane body containing polymer S (hydrolysis step); and (4) a step of optionally forming a hydrophilic layer on at least one surface of the sulfonic acid type membrane body (hydrophilic layer formation 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. The vinyl fluoride compound is preferably one represented by the following formula (3): CF ２ =CX １ X ２ ... (3) (In the above formula (3), X １ and X ２ are each independently F, Cl, H or CF ３ Represents.)

[0041] The vinyl fluoride compound represented by the above formula (3) is not limited to the following, but examples thereof include vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, etc. In this embodiment, the vinyl fluoride compound is preferably a perfluoromonomer, more preferably a perfluoromonomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene. Even more preferably, it is tetrafluoroethylene (TFE).

[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 compound having a functional group that can be converted into a sulfonic acid type ion exchange group is preferably represented by the following formula (4): CF ２ = CFO-(CF ２ CYFO) ａ -(CF ２ ) ｂ -SO ２ F (4) (In the above formula (4), a is an integer of 0 to 2, b is an integer of 1 to 6, and Y is F or CF ３ , R is CH ３ , C ２ H ５ or C ３ H ７ Represents.)

[0043] Specific examples of these include the following monomers: CF ２ = CFOCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ SO ２ F, CF ２=CF(CF ２ ) ２ SO ２ F, CF ２ = CFO [CF ２ CF (CF ３ ) O] ２ CF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ２ OCF ３ ) OCF ２ CF ２ SO ２ F. Among the above, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ SO ２ F and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F is preferred, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F 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 may contain 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 step) 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 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 the precursor film of polymer S are laminated in this order on a flat plate or drum having a heating source and / or vacuum source inside and a large number of pores on the surface, via a flat substrate (for example, a release paper having air permeability and heat resistance), and the film is 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 the precursor film 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). In addition, for example, when two types of precursors of polymer S are used in the form of films, a method in which the release paper, the reinforcing material, the precursor film of polymer S, and the precursor film of polymer S (different type) are laminated in this order on a drum and integrated under heating and reduced pressure can be mentioned. 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 type membrane body having a rough 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 be formed on the release paper side. On the other hand, on the atmospheric side, the part without the reinforcing material (the part with only the resin part) flows relative to the part with the reinforcing material due to heating and decompression, and as a result, a rough surface tends to be formed. The lower the embedding temperature at this time, the smaller h2 and the greater the surface roughness tend to be. The higher the embedding temperature, the larger h2 and the smaller the surface roughness tend to be.

[0048] (Hydrolysis Step) 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, when sacrificial yarn is included as the reinforcing material, the sacrificial yarn can be dissolved and removed with an acid or alkali in addition to the introduction of the ion exchange group, thereby forming interconnected pores inside the sulfonic acid type membrane body. 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 an electrolytic solution.

[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 Forming Step) 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 forming step is an optional step. If the hydrophilic layer forming step is not performed, a composite membrane of the sulfonic acid type membrane body and reinforcing material obtained through the above-mentioned 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 according to 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 has higher rigidity 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 further such that 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 it is preferable that these are 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 in 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, each including 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, are stacked with a diaphragm 44 sandwiched between them.

[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 current plates 46 arranged parallel to a given direction D2 along the partition wall (see FIG. 6 ).

[0060] (Bipolar 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. In the example shown in Fig. 5 , the 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, and further includes 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. In this case, the bipolar element 60 is positioned such 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 anode side gasket portion 47 through the bipolar element 60 a desired number of times, 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 a tie rod 51r (see FIG. 5 ) or a hydraulic cylinder, thereby forming the bipolar electrolytic cell 50 for alkaline water electrolysis. The arrangement of the bipolar electrolytic cell 50 for alkaline water electrolysis can be selected as desired, either from the anode 42a side or the cathode 42c side, and is not limited to the above-mentioned 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 , 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.

[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 FIGS. 5 and 6 , the rectangular partition wall 41 and the rectangular diaphragm 44 are arranged in parallel to each other, 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 electrode chamber 45 has a rectangular parallelepiped shape.

[0067] The bipolar electrolytic cell 50 for alkaline water electrolysis is typically equipped with headers, which are pipes for distributing or collecting the electrolyte, and includes 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, 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, located at the upper part of the outer frame 43 at the edge of the partition wall 41. Representative header arrangements for the headers attached to the bipolar electrolytic cell 50 for alkaline water electrolysis shown in Figs. 5 and 6 are an internal header type and an external header type; however, either type may be employed in the present embodiment, and there is no particular limitation.

[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, and 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 a constant interval (pitch) in a direction perpendicular to a given direction D2 along the partition wall 41 (in the illustrated example, the electrolyte flow direction).

[0072] In the example of the bipolar electrolytic cell 50 for alkaline water electrolysis, the current 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 (the direction in which the electrolytic solution passes in the illustrated example).

[0073] In the present embodiment, the shape of the electrode chamber 45 is not limited to the rectangular parallelepiped shape of the example shown in FIGS. 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 partition wall 41 and the inner surface of the outer frame 43 on the partition wall 41 side, and the partition wall 41, etc.

[0074] Furthermore, in this embodiment, the arrangement of the rectifying plates 46 in the electrode chamber 45 is not limited to the examples shown in FIGS. 5 and 6 . In this embodiment, the number of rectifying plates 46 and the constant intervals (pitch) of 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. Also, in this 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 intervals (pitch) of the through holes in the given direction D2 along the partition wall 41 may be determined as appropriate. Here, the intervals between the through holes do not have to be constant.

[0075] In the examples shown in FIGS. 5 and 6 , the partition wall 41, the anode 42 a, and the cathode 42 c all have a plate-like shape with a predetermined thickness. However, the present invention is not limited to this, and the cross section of each of the partition walls 41, the anode 42 a, and the cathode 42 c may all or partly have a zigzag or wavy shape, or may have rounded ends.

[0076] [Method for Producing Hydrogen] 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 method for producing hydrogen 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. 7,353,494, 7,136,580, 6,826,243, and 3,696,137.

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

[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 below was in a wet state, a 10 cm x 10 cm piece of the wet ion exchange membrane was cut out. To prevent the center from drying and undulating, 500 g weights were placed on the four edges of the membrane, and the ion exchange membrane was dried by leaving it in a dryer (YAMATO constant temperature blower dryer DKM400) controlled at 50 °C for 5 hours (drying process). When the ion exchange membrane obtained in the examples and comparative examples described below was in a dry state, the drying process was omitted. The dried ion exchange membrane was placed in a laser microscope (KEYENCE shape analysis laser microscope). A laser measurement was performed at a magnification of 50x, with a 12 horizontal grid x 7 vertical grid (each grid was 282 μm wide x 211 μm long). 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) according to the following procedure, and the surface roughness was calculated. First, the waviness of the film itself was removed using waviness removal (correction strength 5) in the shape correction of the image processing tool. Then, the entire area was selected using the surface roughness analysis tool, and the surface roughness R was calculated. This was measured for each of the cathode-facing surface and the anode-facing surface of the composite film, and R1 and R2 were calculated. If there was a magnitude relationship between the surface roughness of the cathode-facing surface and the anode-facing surface, the larger value was designated R2, and that surface was identified as the second surface, and the smaller value was designated R1, and that surface was identified as the first surface. If there was no such magnitude relationship, it was evaluated as if the first and second surfaces could not be distinguished.

[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, position P1 where the reinforcing material was present was identified as a portion containing at least one of the reinforcing yarn and the sacrificial yarn (see P1 in Figure 3). Furthermore, position P2 where no reinforcing material was present within the observation field of view was identified as a portion containing neither the reinforcing yarn nor the sacrificial yarn (see P2 in Figure 3). Among the measured membrane thickness values ​​at position P1 within the observation field of one 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 one 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 L1 Between Reinforcing Materials] 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. In the field of view, a position P1 where the reinforcing material was located was identified, similar to the above-described [thicknesses h1 and h2]. In all examples, as shown in FIG. 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 to exist within the observation field. For each of the multiple positions P1, the portion Pmax giving the largest value among the measured membrane thickness values ​​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 FIG. 3, three measured values ​​of L1 were obtained). This was repeated, and the average value of the measurement results for a total of 100 points was identified 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 precursors of ion exchange groups) described below was collected and press-molded at a temperature about 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 CF of the obtained infrared peak was ２ , C.F., C.H. ３ , OH, SO ２ The ratio of the infrared peaks of F was calculated. The ratio of the structural units having sulfonic acid / carboxylic acid functional groups obtained by hydrolyzing each of these polymers was used as the ratio, and the ion exchange capacity was determined using a calibration curve of samples whose ion exchange capacity was known as calculated by titration.

[0083] [Evaluation of Delamination Resistance] The electrolytic cell used for electrolysis had a structure in which an ion exchange membrane was placed between an anode and a cathode, and three pairs of forced circulation zero-gap electrolytic cells were arranged in series. A plain-woven mesh electrode was used as the cathode, which was made of 40-mesh woven nickel fine wires with a diameter of 0.15 mm and 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 surface and a 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 Electrical current was passed at a current density of 1000 kJ / s for a total of 6 days. Table 1 shows the difference in voltage loss compared to the initial voltage loss of the corresponding film. That is, it shows the value calculated from the following formula, and if delamination is present, the difference will be a positive value. Difference in voltage loss before and after evaluation of delamination resistance ΔV = (Voltage loss after evaluation of delamination resistance) [mV] - (Voltage loss before evaluation of delamination resistance) [mV] In Table 1, if the difference in voltage loss before and after evaluation of delamination resistance ΔV is negative to 0, there is no delamination and the sample is evaluated as A. If the above ΔV is positive, there is delamination and the sample is evaluated as B. In addition to the change in voltage, the presence or absence of delamination was confirmed by observing the removed film under a microscope.

[0084] [Evaluation of Initial Voltage Loss] The electrolytic cell used for electrolysis had a structure in which an ion exchange membrane was placed between the anode and cathode, and three pairs of forced circulation zero-gap electrolytic cells were arranged in series. A plain-woven mesh electrode woven with 0.15 mm diameter nickel fine wires coated with platinum and palladium as catalysts was placed as the cathode. Ni expanded metal was used as the anode. A conductive cushion mat made of 0.15 mm nickel wires was placed as an elastic body on the cathode side. When the ion exchange membrane had a first surface and a second surface, the first surface was placed 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 a current of 6 kA / m was applied. ２ Current was passed for a total of 10 hours at a current density of 1000 kJ / s. Impedance was measured after 10 hours. The membrane resistance was calculated for each of the three pairs of cells arranged in series, and the average value was determined as the voltage loss. Table 1 shows the difference compared to the initial voltage loss in Comparative Example 1. That is, it shows the value calculated from the following formula, and if the membrane voltage loss is reduced compared to Comparative Example 1, it is marked as -, and if it is increased, it is marked as +. Initial membrane voltage loss (difference from Comparative Example 1) ΔV = (membrane voltage loss in Comparative Examples and Examples) [mV] - (membrane voltage loss in Comparative Example 1) [mV]

[0085] [Differential Pressure Fluctuation Resistance] The following accelerated test was conducted to accelerate the evaluation of the effect on the ion exchange membrane of the pressure difference between the anode and cathode chambers observed during electrolysis (when current flows through the electrodes). 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 fabricate a zero-gap electrolysis 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 woven nickel fine wires with a diameter of 0.15 mm and 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 surface and a second surface, the first surface was positioned on the anode side. In this electrolytic cell, the cell was filled with water, and a pressure swing was performed by controlling the gas pressure to create a pressure difference between the anode chamber and the cathode chamber. Specifically, a pressure swing from 0 kPa to 80 kPa was repeated approximately 100 times per hour. In each pressure swing, the pressure was first increased to 80 kPa over 15 seconds, then maintained at 80 kPa for 3 seconds, and then decreased to 0 kPa over 15 seconds and maintained at 0 kPa for 3 seconds. This series of operations constituted one pressure swing. During the pressure swing, 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 were likely 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 the outer edge) and near the openings in the anode (expanded metal). After repeating the above pressure swings a predetermined number of times, the appearance of the ion exchange membrane was visually inspected 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 was observed even after 10,000 or more pressure swings.B: Damage was observed at pressure swings of 7000 to 9999. C: Damage was observed at pressure swings of 5000 to 6999. D: Damage was observed at pressure swings of 2500 to 4999. E: Damage was observed at pressure swings of 1 to 2500.

[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. CF ２ =CF ２ ... (5) CF ２ = CFO-CF ２ CF (CF ３ )O-(CF ２ ) ２ -SO ２ F... (6)

[0087] Polymer S-2 was prepared by copolymerizing the monomer represented by the above formula (5) and the 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 the monomer represented by the above formula (5) and the 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 prepared by copolymerizing the monomer represented by the above formula (5) and the 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 prepared by copolymerizing the monomer represented by the above formula (5) and the 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. ２ = CFO-CF ２ CF (CF ３ )O-(CF ２ ) ２ -COOCH ３ ... (7)

[0092] [Reinforcing Material] A polytetrafluoroethylene (PTFE) monofilament yarn with a thread diameter of 90 denier was prepared as the reinforcing yarn. A multifilament yarn made by twisting together six polyethylene terephthalate (PET) yarns with a thread diameter of 6.7 denier was prepared as the sacrificial yarn. The reinforcing yarn was 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. Furthermore, a commercially available Teflon woven fabric (made of PTFE) was used as 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 film A and film B was 70 μm. A drum having a heating source and a vacuum source inside and having micropores on its surface was prepared. On this drum, unembossed release paper, reinforcing material 1, film B, and film A were stacked in this order, and integrated at 230 ° C. under heating and reduced pressure (reduced pressure of -650 mmHg) while removing air between each material to obtain a composite membrane (a membrane containing a precursor of a sulfonic acid type membrane body and a reinforcing material). In this process, the membrane was heated and reduced pressure on the unembossed release paper side, so that a flat surface was formed on the unembossed release paper side. On the other hand, on the atmospheric side, only the resin portion flowed due to heating and reduced pressure relative to the portion with the reinforcing material, resulting in the formation of a rough surface. (Hydrolysis) In the hydrolysis step, the obtained 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 therein to prepare a suspension. This suspension was sprayed onto both sides of the composite membrane that had undergone the above hydrolysis by a spray method, and the membrane was dried to obtain a hydrophilic layer of 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] Film C (thickness 110 μm) was obtained from polymer S-3 by the T-die method. The ion exchange membrane of Example 8 was obtained in the same manner as in Example 7, except that Film C was used instead of 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 Films D and E were obtained from polymers S-4 and S-5, respectively, by the T-die method. The total film thickness of Films D and E was 150 μm. Using Films D and E and Reinforcement 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 at 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 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 the preparation of 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. An ion exchange membrane of Comparative Example 1 was obtained by the same production method as in Example 3, except for the above points.

[0104] Comparative Example 2 Film F was obtained from polymer S-2 and Film G from polymer C-1 by the T-die method. 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 production method as in Comparative Example 2, except that in the preparation of the composite membrane in Comparative Example 2, the unembossed release paper, reinforcing material 1, film F, and film G were laminated in this order.

[0106] Comparative Example 4 The ion exchange membrane of Comparative Example 4 was obtained by carrying out the same hydrolysis step and hydrophilic layer formation step as in Example 1 on 110 μm film B without carrying out the integration step in Example 1.

[0107]

[0108] The Examples and Comparative Examples showed that the use of a sulfonic acid type membrane body (without 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 this reason is not intended to be limited, 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.

[0109] 1... sulfonic acid type membrane body, 1a... first surface, 1b... second surface, 2... reinforcing material, 2a... reinforcing yarn, 2b... sacrificial yarn, 3... hydrophilic layer, 10... ion exchange membrane, 21... anode, 31... cathode, 41... partition wall, 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 wall (electrolyte passage direction), Z... zero gap structure

Claims

1. An ion exchange membrane comprising 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.

2. The ion exchange membrane according to claim 1, wherein the surface roughness R1 of the first surface is less than 10 μm, and the surface roughness R2 of the second surface is 10 μm or more.

3. 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.

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

5. The ion exchange membrane according to claim 3, wherein the thickness h1 is 100 μm or more and 200 μm or less.

6. The ion exchange membrane according to claim 3, wherein a plurality of the reinforcing members are present along the surface direction of the ion exchange membrane, and 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 claim 1, 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 claim 1, wherein the polymer is a fluorine-containing polymer.

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

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

12. The ion exchange membrane of claim 10, wherein the denier of said reinforcing yarns and said sacrificial yarns is each independently from 20 to 150 denier.

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

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

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

16. The ion exchange membrane according to claim 15, 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.

17. The inorganic particles are SiO ２ , SiC, ZrO ２ The ion exchange membrane according to claim 15, comprising at least one selected from the group consisting of ZrC and ZrC.

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

19. The ion exchange membrane according to any one of claims 1 to 17, which is used in alkaline water electrolysis.

20. An electrolytic cell comprising: an anode; a cathode facing the anode; and the ion exchange membrane according to any one of claims 1 to 17, disposed between the anode and the cathode.

21. The electrolytic cell according to claim 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.

22. The electrolytic cell according to claim 20, which is used for alkaline water electrolysis.

23. The electrolytic cell of claim 20, having a zero-gap configuration.

24. A method for producing hydrogen using the electrolytic cell according to claim 20, comprising the step of supplying an electrolyte to the electrolytic cell and performing water electrolysis.

25. The method for producing hydrogen according to claim 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 greater rigidity.

26. The method for producing hydrogen according to claim 24, wherein the water electrolysis is alkaline water electrolysis.

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