Method for repairing diaphragm for alkaline water electrolysis

Abstract

To provide a method for repairing a diaphragm when a slight defect such as a crack, a dent, or abrasion occurs in the diaphragm for alkaline water electrolysis having a porous structure.SOLUTION: The gas barrier property of a defective part is recovered by welding the defective part reducing the gas barrier property of the diaphragm for alkaline water electrolysis made of a polymer porous membrane to change the porous structure of the defective part into a bulk structure.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for repairing a diaphragm for alkaline water electrolysis. [Background technology]

[0002] In recent years, hydrogen has been attracting attention as an environmentally friendly, clean energy source because it does not produce CO2 during combustion or reaction. Alkaline water electrolysis is a well-known method for producing hydrogen. Alkaline water electrolysis generates hydrogen and oxygen by electrolyzing water using an alkaline aqueous solution as the electrolyte.

[0003] A known electrolytic cell used in alkaline water electrolysis has a structure in which a porous diaphragm made of an organic polymer is placed between the anode chamber and the cathode chamber. Oxygen is produced in the anode chamber of the electrolytic cell, and hydrogen is produced in the cathode chamber. The diaphragm is required to have gas barrier properties to prevent the permeation of oxygen gas and hydrogen gas so that these gases do not mix.

[0004] Because the diaphragm is a thin sheet with a porous structure made of an organic polymer, it may be subject to physical damage such as breakage. If the diaphragm is physically damaged, the gas barrier properties of the diaphragm will decrease, requiring immediate maintenance. Therefore, the diaphragm for alkaline water electrolysis described in Patent Document 1 includes a sheet-like porous support and a microporous membrane containing an organic polymer resin laminated on one or both sides of the porous support, and is designed to maintain gas barrier properties even if physical damage occurs to the membrane surface (i.e., the microporous membrane). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-204146 Summary of the Invention [Problem to be solved by the invention]

[0006] Diaphragms for alkaline water electrolysis may develop minor defects such as cracks or dents during assembly of the electrolytic cell, or partial wear of the surface due to friction with gas bubbles during electrolysis. Even minor defects can impair gas barrier properties, and therefore diaphragms for alkaline water electrolysis are immediately replaced with new ones when a defect occurs, regardless of the severity. However, replacing diaphragms for alkaline water electrolysis even for minor defects increases the frequency of diaphragm replacement, which is not economical.

[0007] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a technique for repairing a diaphragm having a porous structure for alkaline water electrolysis when a minor defect such as a crack, a dent, or wear occurs in the diaphragm. [Means for solving the problem]

[0008] In order to solve the above problems, a method for repairing a diaphragm for alkaline water electrolysis according to one embodiment of the present disclosure includes: A defective portion that reduces the gas barrier property of a diaphragm for alkaline water electrolysis made of a porous polymer film is welded to change the porous structure of the defective portion into a bulk structure, thereby restoring the gas barrier property of the defective portion. [Effects of the Invention]

[0009] The present disclosure provides a technique for repairing a diaphragm for alkaline water electrolysis having a porous structure when minor defects such as cracks, dents, or wear occur in the diaphragm. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing the overall configuration of an alkaline water electrolytic cell according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view of the alkaline water electrolytic cell for providing a detailed explanation of the support structure for the alkaline water electrolysis diaphragm on the cell body. [Figure 3] FIG. 3 is a development view of a diaphragm for alkaline water electrolysis. [Figure 4]FIG. 4 is a cross-sectional view of a diaphragm for alkaline water electrolysis including a defect. [Figure 5] FIG. 5 is a cross-sectional view of the diaphragm for alkaline water electrolysis including the repaired defective portion of FIG. 4 . [Figure 6] FIG. 6 is a cross-sectional view of a diaphragm for alkaline water electrolysis including a defect. [Figure 7] FIG. 7 is a cross-sectional view of the diaphragm for alkaline water electrolysis including the repaired defective portion of FIG. 6 . [Figure 8] FIG. 8 is a cross-sectional view of a diaphragm for alkaline water electrolysis including a defect. [Figure 9] FIG. 9 is a cross-sectional view of the diaphragm for alkaline water electrolysis including the repaired defective portion of FIG. 8 . DETAILED DESCRIPTION OF THE INVENTION

[0011] Next, embodiments of the present disclosure will be described with reference to the drawings. First, a schematic configuration of a diaphragm 4 for alkaline water electrolysis (hereinafter simply referred to as a "diaphragm 4") to which a repair method for an alkaline water electrolysis membrane according to the present disclosure is applied, and an alkaline water electrolytic cell (hereinafter simply referred to as an "electrolytic cell 1") including the diaphragm 4 will be described.

[0012] [Schematic configuration of electrolytic cell 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an electrolytic cell 1 according to one embodiment of the present disclosure. The electrolytic cell 1 shown in FIG. 1 includes a cell body 2. The interior of the cell body 2 is separated into an anode chamber 48 and a cathode chamber 49 by a diaphragm 4. The anode chamber 48 and the cathode chamber 49 each have an electrolyte supply port and an outlet port for the alkaline solution and gas (hydrogen or oxygen) after electrolysis. An anode assembly 3 is disposed on the anode chamber 48 side of the diaphragm 4 in the electrolytic cell 1. The anode assembly 3 includes a mesh anode 31 facing the diaphragm 4, an anode conductor plate 32 provided integrally with the anode 31 around the anode 31, and a connection terminal 33 disposed on the anode conductor plate 32. A cathode assembly 7 is disposed on the cathode chamber 49 side of the diaphragm 4 in the electrolytic cell 1. The cathode assembly 7 includes a mesh-like cathode 71 facing the diaphragm 4, a cathode conductor plate 72 arranged away from the cathode 71 on the side opposite the diaphragm 4, a connection terminal 73 provided on the cathode conductor plate 72, and a conductive elastic body 74 provided between the cathode 71 and the cathode conductor plate 72. The elastic body 74 presses the cathode 71 against the diaphragm 4, bringing the anode 31 and the diaphragm 4, and the diaphragm 4 and the cathode 71 into close contact with each other.

[0013] The anode 31 is a known electrode that has been used as an anode for alkaline water electrolysis. Known examples of such anodes 31 include those that include a conductive substrate and a catalytic layer coating the surface of the substrate. Examples of the substrate for the anode 31 include nickel, nickel-based alloys, stainless steel, iron, and nickel-coated iron. Examples of the catalytic layer for the anode 31 include nickel-containing materials such as nickel oxide, metallic nickel, nickel hydroxide, and nickel-cobalt oxide. The cathode 71 is a known electrode that has been used as a cathode for alkaline water electrolysis. Known examples of such cathodes 71 include those that include a conductive substrate and a catalytic layer coating the surface of the substrate. Examples of the conductive substrate for the cathode 71 include nickel, nickel-based alloys, stainless steel, iron, and nickel-coated iron. Examples of the catalytic layer for the cathode 71 include precious metal oxides, nickel, cobalt, molybdenum, manganese, and oxides thereof.

[0014] When alkaline water is electrolyzed in the electrolytic cell 1 configured as described above, the anode chamber 48 and the cathode chamber 49 are filled with an electrolyte, and a voltage is applied between the anode 31 and the cathode 71. An alkaline solution such as potassium hydroxide or sodium hydroxide is used as the electrolyte. The concentration of the alkaline solution is not particularly limited, but is preferably about 25-35% by mass. The temperature of the electrolyte is also not particularly limited, but is preferably about 80-100°C. In the cathode chamber 49, electrons are supplied, causing electrolysis of the water in the electrolyte, generating hydrogen gas and hydroxide ions. The hydroxide ions in the cathode chamber 49 permeate the diaphragm 4 and move to the anode chamber 48. In the anode chamber 48, oxygen gas and water are generated from the hydroxide ions.

[0015] [Diaphragm 4] Next, a detailed description will be given of the diaphragm 4 and the support structure for the diaphragm 4. Figure 2 is an enlarged partial cross-sectional view of the electrolytic cell 1, illustrating in detail the support structure for the diaphragm 4 on the cell body 2.

[0016] 1 and 2, the cell body 2 of the electrolytic cell 1 is formed by combining an anode chamber frame 21 that defines the anode chamber 48 and a cathode chamber frame 22 that defines the cathode chamber 49. The anode chamber frame 21 and the cathode chamber frame 22 have frame surfaces 21a and 22a that face each other with a diaphragm 4 or the like disposed therebetween. The frame surface 21a of the anode chamber frame 21 and the frame surface 22a of the cathode chamber frame 22 have substantially the same shape; for example, the frame surfaces 21a and 22a are rectangular or circular strips.

[0017] The anode assembly 3, the diaphragm 4, and the cathode assembly 7 are sandwiched between the frame surface 21a of the anode chamber frame 21 and the frame surface 22a of the cathode chamber frame 22. More specifically, the gasket 24, the anode conductor plate 32 of the anode assembly 3, the diaphragm 4, the spacer 23, the gasket 25, the cathode conductor plate 72 of the cathode assembly 7, and the gasket 26 are arranged in this order between the frame surface 21a of the anode chamber frame 21 and the frame surface 22a of the cathode chamber frame 22.

[0018] The gasket 24 is a sealing material that provides a liquid-tight seal between the anode chamber frame 21 and the anode conductor plate 32. The gasket 25 is a sealing material that provides a liquid-tight seal between the spacer 23 and the cathode conductor plate 72. The gasket 26 is a sealing material that provides a liquid-tight seal between the cathode conductor plate 72 and the cathode chamber frame 22. The gaskets 24, 25, and 26 can be made of materials such as ethylene-propylene-diene rubber (EPDM) and vulcanized or peroxide-crosslinked ethylene-propylene rubber (EPM).

[0019] The spacer 23 separates the diaphragm 4 from the cathode 71. The spacer 23 also sandwiches the diaphragm 4 in the film thickness direction in cooperation with the anode conductor plate 32. The diaphragm 4 is pressed in the film thickness direction from both sides by the anode conductor plate 32 and the spacer 23.

[0020] FIG. 3 is a development view of the diaphragm 4. As shown in FIG. 3, the diaphragm 4 comprises a porous polymer membrane 40 integrally having a sealing region 41 sandwiched between cell components of the electrolytic cell 1 (specifically, the anode conductive plate 32 and the spacer 23), an edge region 44 arranged on the outer periphery of the sealing region 41, and a separator region 43 arranged on the inner periphery of the sealing region 41. The edge region 44 is a strip-shaped region along the outer edge of the diaphragm 4 and is the portion of the diaphragm 4 exposed to the outside of the cell. The inner peripheral edge of the edge region 44 corresponds to the outer peripheral edge of the sealing region 41. The sealing region 41 has substantially the same shape as the frame surface 21a of the anode chamber frame 21 and the frame surface 22a of the cathode chamber frame 22. The inner peripheral edge of the sealing region 41 corresponds to the outer peripheral edge of the separator region 43. The separator region 43 is the portion of the diaphragm 4 exposed to the inside of the cell and functions as a partition wall separating an anode chamber 48 from a cathode chamber 49. 3 is rectangular, the diaphragm 4 is not limited to a rectangular shape and may have any shape that corresponds to the shapes of the anode chamber frame 21 and the cathode chamber frame 22. For example, if the anode chamber frame 21 and the cathode chamber frame 22 are annular, the diaphragm 4 may be circular.

[0021] The membrane 4 includes a porous polymer membrane 40 made of an organic polymer resin and having numerous pores throughout. The organic polymer resin constituting the porous polymer membrane 40 is at least one selected from the group consisting of polysulfone, polyethersulfone, polyphenylsulfone, polyvinylidene fluoride, polycarbonate, polytetrafluoroethylene, polypropylene, polyphenylene sulfide, polyketone, polyetheretherketone, polyimide, and polyetherimide. The porous polymer membrane 40 may contain inorganic particles. The inclusion of inorganic molecules in the membrane 4 makes the membrane 4 hydrophilic, thereby preventing adhesion of oxygen and hydrogen gas bubbles to the membrane surface. Examples of inorganic particles include metal hydroxides or oxides of magnesium, zirconium, titanium, zinc, aluminum, tantalum, and the like; sulfates of calcium, barium, lead, strontium, and the like; nitrides of titanium, zirconium, hafnium, and the like; and carbides of titanium, zirconium, hafnium, and the like.

[0022] [Method for repairing diaphragm 4] Here, a method for repairing the diaphragm 4 will be described. The diaphragm 4 may have minor defects, such as insufficient thickness due to poor coating during membrane production, dents due to wear and abrasion caused by friction with air bubbles during electrolysis, and dents or cracks caused by dropping tools or the like during assembly of the electrolytic cell 1. Such minor defects can be repaired by converting the porous structure of the defective area into a bulk structure by welding. Here, a porous structure is a high-porosity structure having numerous pores, whereas a "bulk structure" is a low-porosity structure with no or almost no voids such as pores. The bulk structure of the present disclosure may include a non-porous structure with no voids such as pores, or a porous structure with pores but an extremely low porosity compared to the porous structure portion of the diaphragm 4. The bulk structure portion of the diaphragm 4 has a lower porosity, a higher density, and a denser structure than the porous structure portion. The porosity of the bulk structure portion of the membrane 4 is 0 or close to 0, and the porosity of the bulk structure portion of the membrane 4 is approximately 1 / 10 or less of the porosity of the other porous structure portions. The porosity is calculated by dividing the total volume by V [m 3], the volume of the gap is v [m 3 ], it can be calculated as v / V.

[0023] For example, the numerous pores present in the defective portion of the diaphragm 4 can be crushed or reduced in size by crushing or melting, thereby processing the defective portion into a bulk structure. Methods that can be used to weld the diaphragm 4 include impulse welding, ultrasonic welding, high-frequency welding, laser welding, hot plate welding, and heat pressing. In this case, the defective portion of the diaphragm 4 is heated by a welding machine, and the resin in the heated area melts and welds, resulting in a bulk structure. In principle, repairs to the diaphragm 4 are performed on the diaphragm 4 in a state where it has been removed from the electrolytic cell 1; however, depending on the location of the diaphragm 4 to be repaired, repairs can also be performed on the diaphragm 4 while it is still installed in the electrolytic cell 1.

[0024] Gas permeation is prevented in the portion of the diaphragm 4 that has become a bulk structure due to repair. Repair restores the gas barrier properties of the diaphragm 4, allowing the repaired diaphragm 4 to continue being used for alkaline water electrolysis. However, because ion exchange does not occur in the portion of the diaphragm 4 that has become a bulk structure due to repair, if the area of ​​the portion that has become a bulk structure is excessive, the electrolysis performance of the electrolytic cell 1 will deteriorate. Therefore, it is desirable to repair the diaphragm 4 when the area of ​​the portion that has become a bulk structure is 10% or less of the area of ​​the separator region 43.

[0025] FIG. 4 is a partial cross-sectional view of a diaphragm 4 including a defective portion D1 where the thickness is locally insufficient. As shown in FIG. 4, defective portion D1, where the thickness of the diaphragm 4 is locally insufficient, has reduced gas barrier properties compared to other portions. FIG. 5 is a cross-sectional view of the diaphragm 4 after the defective portion D1 shown in FIG. 4 has been repaired. As shown in FIG. 5, the diaphragm 4 is repaired by welding the defective portion D1 and its surroundings. In the repaired diaphragm 4, the porous structure of the defective portion D1 has been transformed into a bulk structure by welding, and the gas barrier properties of the defective portion D1 have been restored. Note that in FIG. 5, the light-shaded portion is the bulk structure portion 55 that has been transformed into a bulk structure.

[0026] FIG. 6 is a partial cross-sectional view of a diaphragm 4 including a defective portion D2 having a crack. As shown in FIG. 6, gas permeates through the crack in defective portion D2, resulting in a decrease in gas barrier properties. FIG. 7 is a cross-sectional view of diaphragm 4 after repairing defective portion D2 shown in FIG. 6. As shown in FIG. 7, the diaphragm 4 is repaired by welding defective portion D2 and its surrounding area. In the repaired diaphragm 4, the porous structure of defective portion D2 has been transformed into a bulk structure by welding, and the crack has been sealed by welding, restoring the gas barrier properties of the defective portion. Note that in FIG. 7, the light-shaded portion is bulk structure portion 55 that has been transformed into a bulk structure.

[0027] FIG. 8 is a partial cross-sectional view of a diaphragm 4 including a defect D3 having a through-hole penetrating through the thickness direction. As shown in FIG. 8, the defect D3 having a through-hole reduces gas barrier properties because gas permeates through the through-hole. FIG. 9 is a cross-sectional view of a diaphragm 4 after the defect D3 shown in FIG. 8 has been repaired. As shown in FIG. 9, a backing 47 is placed on the diaphragm 4 to close the through-hole (defect D3), and the backing 47 is welded to the periphery of the through-hole in the diaphragm 4, thereby repairing the diaphragm 4. The backing 47 may be substantially the same as the porous polymer membrane 40 constituting the diaphragm 4. After repair, the through-hole is blocked by the backing 47, and the welded portion, which has become a bulk structure, blocks gas, thereby restoring the gas barrier properties of the defect D3. Note that the light-shaded portion in FIG. 9 is the bulk structure portion 55 that has changed to a bulk structure.

[0028] [Summary] The repair method for the diaphragm 4 for alkaline water electrolysis according to the first aspect of the present disclosure involves welding defective portions D1, D2, D3 that reduce the gas impermeability of the diaphragm 4 for alkaline water electrolysis made of a porous polymer membrane 40 to convert the porous structure of the defective portions D1, D2, D3 into a bulk structure, thereby recovering the gas impermeability of the defective portions D1, D2, D3.

[0029] According to the repair method described above, the gas barrier properties of the defective portions D1, D2, and D3 can be restored by simple processing. Furthermore, repairing the diaphragm 4 allows the diaphragm 4 to be used continuously, which is economical.

[0030] A method for repairing a diaphragm 4 for alkaline water electrolysis according to a second aspect of the present disclosure is the method for repairing a diaphragm 4 for alkaline water electrolysis according to the first aspect, wherein the defective portion D2 has a crack, and the crack is sealed by welding.

[0031] According to the repair method described above, the gas barrier properties of the defective portion D2 can be restored by a simple process. Furthermore, repairing the diaphragm 4 allows the diaphragm 4 to be used continuously, which is economical.

[0032] A method for repairing a diaphragm 4 for alkaline water electrolysis according to a third aspect of the present disclosure is the method for repairing a diaphragm 4 for alkaline water electrolysis according to the first aspect, wherein the defective portion D3 has a through-hole, the through-hole is closed with a backing 47 made of a porous polymer membrane 40, and the peripheral edge of the through-hole and the backing 47 are overlapped and joined by welding.

[0033] According to the repair method described above, the gas barrier properties of the defective portion D3 can be restored by simple processing. Furthermore, repairing the diaphragm 4 allows the diaphragm 4 to be used continuously, which is economical.

[0034] The present disclosure has been presented for purposes of illustration and description and is not intended to be limited to the form disclosed herein. For example, in the foregoing Detailed Description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Also, the features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of symbols]

[0035] 1: Alkaline water electrolysis tank 4: Diaphragm for alkaline water electrolysis 31: Anode 40: Polymer porous membrane 47: Backing 48:Anode chamber 49: Cathode chamber 55: Bulk structure part 71 :Cathode D1-D3: Defective parts

Claims

1. a defective portion that reduces the gas barrier property of the diaphragm for alkaline water electrolysis made of a porous polymer membrane is welded to change the porous structure of the defective portion into a bulk structure, thereby restoring the gas barrier property of the defective portion; A method for repairing diaphragms for alkaline water electrolysis.

2. the defective portion has a crack, and the crack is closed by the welding; The method for repairing a diaphragm for alkaline water electrolysis according to claim 1.

3. The defective portion has a through-hole, and the through-hole is blocked with a backing made of the polymer porous membrane, and the peripheral portion of the through-hole and the backing are overlapped and joined by the welding. The method for repairing a diaphragm for alkaline water electrolysis according to claim 1.

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