Method for manufacturing membrane electrode structure

Abstract

To provide a method for manufacturing a membrane electrode structure capable of suppressing the occurrence of wrinkles in the membrane electrode structure (particularly in an electrolyte membrane) caused by differences in the swelling rates between the electrode and the electrolyte in water.SOLUTION: A first laminate providing step S1a provides a first laminate 70 in which a first ionomer material 71 where an ion exchange capacity is less than a predetermined value and a first electrode 44 are stacked. A second laminate providing step S1b provides a second laminate 72 in which a second ionomer material 73 where the ion exchange capacity is greater than or equal to the predetermined value and a second electrode 46 are stacked. A substrate providing step S1c provides an electrolyte substrate 74. A swelling step S2 swells the first laminate 70, the second laminate 72, and the electrolyte substrate 74. A bonding step S3 bonds the electrolyte substrate 74 and the first ionomer material 71 of the first laminate 70, and also bonds the electrolyte substrate 74 and the second ionomer material 73 of the second laminate 72.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a membrane electrode assembly. [Background technology]

[0002] In recent years, technological developments have been made on electrolysis stacks that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Conventionally, electrolysis devices equipped with electrolysis stacks consisting of multiple stacked electrolysis cells have been known. Electrolysis cells have a membrane electrode assembly. The membrane electrode assembly has a structure in which an electrolyte membrane is sandwiched between a pair of electrodes. Electrolysis cells include water electrolysis cells that electrolyze water and hydrogen electrolysis cells that electrolyze hydrogen (hydrogen gas). An electrolysis stack equipped with a stack of multiple stacked water electrolysis cells is sometimes referred to as a water electrolysis device. An electrolysis stack equipped with a stack of multiple stacked hydrogen electrolysis cells is sometimes referred to as an EHC (Electrochemical Hydrogen Compressor). For example, Patent Document 1 discloses a water electrolysis device equipped with water electrolysis cells. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-157212 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in a water electrolysis device, the membrane electrode assembly absorbs water and swells during electrolysis, causing dimensional changes in the membrane electrode assembly. As a result, the state of the membrane electrode assembly differs between when the water electrolysis device is fully assembled and when it is in use (during electrolysis). In order to make the state of the membrane electrode assembly when the water electrolysis device is fully assembled the same as when it is in use (during electrolysis), it is conceivable to immerse the membrane electrode assembly in water to cause it to swell before assembling it into an electrolysis stack.

[0005] However, with the above-mentioned method, there is a concern that wrinkles may occur in the membrane electrode assembly (particularly the electrolyte membrane) due to differences in swelling ratios when the electrodes and the electrolyte membrane swell with water.

[0006] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0007] An aspect of the present disclosure is a method for producing a membrane electrode assembly used in a differential pressure electrolysis device that includes an electrolyte membrane and a first electrode and a second electrode stacked on either side of the electrolyte membrane, the method comprising supplying an electrolysis fluid to the first electrode, applying a voltage between the first electrode and the second electrode, and producing a second gas at the second electrode that has a higher pressure than a first gas produced at the first electrode, the method comprising the steps of: providing a first laminate in which a first ionomer raw material having an ion exchange capacity per unit area at a predetermined temperature and in an atmosphere with a predetermined humidity that is less than a predetermined value is stacked with the first electrode; a substrate providing step of providing an electrolyte base material having a first surface and a second surface opposite to each other; a swelling step of swelling the first laminate, the second laminate, and the electrolyte base material; and a bonding step of bonding, after the swelling step, the first surface of the electrolyte base material to the first ionomer raw material of the first laminate and bonding the second surface of the electrolyte base material to the second ionomer raw material of the second laminate. [Effects of the Invention]

[0008] According to the present invention, the first stack and the second stack are swollen, and then the first stack and the electrolyte base material are bonded together, and the second stack and the electrolyte base material are bonded together, thereby preventing wrinkles from forming in the electrolyte membrane. Furthermore, in the membrane electrode assembly obtained by this manufacturing method, the ion exchange capacity of the portion of the electrolyte membrane adjacent to the second electrode (the second adjacent portion) is greater than the ion exchange capacity of the portion of the electrolyte membrane adjacent to the first electrode (the first adjacent portion). Therefore, when the differential pressure electrolysis device is a water electrolysis device, preventing the second adjacent portion of the electrolyte membrane, which is on the high-pressure side, from drying out can prevent deterioration of the electrolyte membrane due to a decrease in electrolysis efficiency and an increase in electrical resistance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a differential pressure electrolysis device. [Figure 2] FIG. 2 is a cross-sectional view of the electrolysis cell. [Figure 3] FIG. 3 is a schematic diagram illustrating a method for manufacturing a membrane electrode assembly according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] As shown in FIG. 1 , the differential pressure electrolysis device 10 is configured as an electrolysis stack 10A including a cell stack 12. The electrolysis stack 10A has a generally cylindrical shape overall, but can be configured into various shapes such as a cube. The cell stack 12 has multiple electrolysis cells 14 stacked vertically or horizontally. The electrolysis cells 14 are water electrolysis cells. The electrolysis cells 14 may also be hydrogen electrolysis cells. In the following description, the "stacking direction" refers to the stacking direction (direction A) of the multiple electrolysis cells 14.

[0011] A fluid inlet 15a is provided in the electrolytic cell 14 located at one end (lower end) in the stacking direction among the plurality of electrolytic cells 14. A fluid outlet 15b is provided in the electrolytic cell 14 located at the other end (upper end) in the stacking direction among the plurality of electrolytic cells 14.

[0012] The differential pressure electrolysis device 10 further includes a pair of terminal plates 16a, 16b, a pair of insulating plates 18a, 18b, and a pair of end plates 20a, 20b. The terminal plate 16a, the insulating plate 18a, and the end plate 20a are arranged in this order toward one side of the stacking direction (upward in FIG. 1). The terminal plate 16b, the insulating plate 18b, and the end plate 20b are arranged in this order toward the other side of the stacking direction (downward in FIG. 1).

[0013] Terminal portions 24a and 24b are provided on the terminal plates 16a and 16b, respectively. The terminal portions 24a and 24b are electrically connected to an electrolysis power supply 28 via wires 26a and 26b, respectively.

[0014] The electrolysis stack 10A is held in a state in which the end plates 20a, 20b are integrally fastened together by a pressing mechanism such as a plurality of tie rods 22 extending in the stacking direction. A pipe (not shown) communicating with a high-pressure fluid outlet hole 21 (described later) is connected to the end plate 20a. A back pressure mechanism capable of restricting gas discharge through the high-pressure fluid outlet hole 21 is provided in this pipe. The electrolysis stack 10A may include a box-shaped casing (not shown) that includes the end plates 20a, 20b.

[0015] As shown in FIG. 2, the electrolysis cell 14 includes a membrane electrode assembly 30, a first current feeder 32, a second current feeder 34, a first separator 36, a second separator 38, and a resin frame member 40.

[0016] The membrane electrode assembly 30 has a substantially circular ring shape. The membrane electrode assembly 30 has an electrolyte membrane 42, a first electrode 44, and a second electrode 46. The electrolyte membrane 42 is made of a solid polymer. The electrolyte membrane 42 is made of an ionomer. The electrolyte membrane 42 is a membrane capable of exchanging ions. The first electrode 44 is disposed on one side of the electrolyte membrane 42. The first electrode 44 is an electrode catalyst layer. A fluid used in electrolysis is supplied to the first electrode 44. The second electrode 46 is disposed on the other side of the electrolyte membrane 42. The second electrode 46 is an electrode catalyst layer on the opposite side to the first electrode 44. A voltage is applied between the first electrode 44 and the second electrode 46 by the electrolysis power supply 28 (FIG. 1).

[0017] When the electrolysis cell 14 is a water electrolysis cell, the electrolyte membrane 42 may be an anion exchange membrane or a proton exchange membrane.

[0018] When the electrolyte membrane 42 is an anion exchange membrane, the fluid for electrolysis is alkaline water. When the electrolysis cell 14 is a water electrolysis cell, the electrolyte membrane 42 is an anion exchange membrane, the first electrode 44 and the first power feeder 32 are the anode, and the second electrode 46 and the second power feeder 34 are the cathode, oxygen is produced as a first gas at the first electrode 44, and hydrogen is produced as a second gas at the second electrode 46. On the other hand, when the electrolysis cell 14 is a water electrolysis cell, the electrolyte membrane 42 is an anion exchange membrane, the first electrode 44 and the first power feeder 32 are the cathode, and the second electrode 46 and the second power feeder 34 are the anode, hydrogen is produced at the first electrode 44, and oxygen is produced at the second electrode 46.

[0019] When the electrolysis cell 14 is a water electrolysis cell and the electrolyte membrane 42 is a proton exchange membrane, the fluid used for electrolysis is water (e.g., pure water) with impurities not exceeding a predetermined amount. When the electrolyte membrane 42 is a proton exchange membrane, the first electrode 44 and the first power feeder 32 are the anode, and the second electrode 46 and the second power feeder 34 are the cathode, oxygen is produced at the first electrode 44 and hydrogen is produced at the second electrode 46. On the other hand, when the electrolysis cell 14 is a water electrolysis cell, the electrolyte membrane 42 is a proton exchange membrane, the first electrode 44 and the first power feeder 32 are the cathode, and the second electrode 46 and the second power feeder 34 are the anode, hydrogen is produced at the first electrode 44 and oxygen is produced at the second electrode 46.

[0020] When the electrolysis cell 14 is a hydrogen electrolysis cell, the electrolyte membrane 42 is a proton exchange membrane. In this case, the fluid used in the electrolysis is hydrogen. The first electrode 44 and the first power supply 32 are the anode, and the second electrode 46 and the second power supply 34 are the cathode. At the second electrode 46, hydrogen is produced at a higher pressure than the hydrogen supplied to the first electrode 44.

[0021] A through-hole 42h is formed in the electrolyte membrane 42 approximately at the center in the radial direction. The first electrode 44 is provided on one surface of the electrolyte membrane 42, in a region between the peripheral edge of the through-hole 42h and the outer periphery of the electrolyte membrane 42. A second electrode 46 is provided on a portion of the other surface of the electrolyte membrane 42. The second electrode 46 is provided on the other surface of the electrolyte membrane 42, in a region between the peripheral edge of the through-hole 42h and the outer periphery of the electrolyte membrane 42. The first electrode 44 and the second electrode 46 are formed, for example, in a circular shape. For example, a Ru (ruthenium)-based catalyst is used for the first electrode 44. For example, a platinum catalyst is used for the second electrode 46.

[0022] The electrolyte membrane 42 has a portion adjacent to the first electrode 44 (hereinafter also referred to as the "first adjacent portion 421") and a portion adjacent to the second electrode 46 (hereinafter also referred to as the "second adjacent portion 422"). The ion exchange capacity (IEC) per unit area of ​​the first adjacent portion 421 at a predetermined temperature and in an atmosphere of a predetermined humidity is less than a predetermined value. The ion exchange capacity (IEC) per unit area of ​​the second adjacent portion 422 at a predetermined temperature and in an atmosphere of a predetermined humidity is equal to or greater than a predetermined value. Therefore, at a predetermined temperature and in an atmosphere of a predetermined humidity, the ion exchange capacity per unit area of ​​the second adjacent portion 422 is greater than the ion exchange capacity per unit area of ​​the first adjacent portion 421. The ion exchange capacity is the reciprocal (meq / g) of the weight of the electrolyte membrane 42 in a dry state required to be able to exchange one mole of ions.

[0023] The membrane electrode assembly 30 is disposed between a first current feeder 32 and a second current feeder 34. The first current feeder 32 and the second current feeder 34 are made of, for example, a sintered body (porous conductor) of spherical atomized titanium powder. The first current feeder 32 and the second current feeder 34 have smooth surfaces that are etched after grinding, and the porosity is set within the range of 10% to 50%, preferably 20% to 40%.

[0024] The first power feeder 32 is a power feeder (fluid supply side power feeder) to which a fluid used in electrolysis is supplied. A flow path member 50 is interposed between the first separator 36 and the first power feeder 32. A plurality of holes 50h are formed in the flow path member 50. A protective sheet member 52 is interposed between the first power feeder 32 and the first electrode 44. A plurality of communication holes 52h are formed in the protective sheet member 52.

[0025] The second power feeder 34 is a power feeder on the opposite side to the first power feeder 32. The second power feeder 34 is pressed toward the second electrode 46 by a load-applying mechanism 54. The load-applying mechanism 54 includes a conductive elastic member such as a leaf spring. The load-applying mechanism 54 applies a load to the second power feeder 34 via a metal holder 56. A circular ring-shaped conductive sheet 58 is disposed between the second power feeder 34 and the holder 56.

[0026] A sealing member 60 is disposed between the electrolyte membrane 42 and the second separator 38, radially outward of the electrolysis region of the membrane electrode assembly 30. A pressure-resistant member 62 is disposed radially outward of the sealing member 60. The pressure-resistant member 62 has a generally ring shape. The outer periphery of the pressure-resistant member 62 fits into the inner periphery of the resin frame member 40.

[0027] The first separator 36 and the second separator 38 sandwich the membrane electrode assembly 30 and other components in the stacking direction. The first separator 36 and the second separator 38 are generally disk-shaped and made of, for example, a carbon member. The first separator 36 and the second separator 38 may be formed by press-forming a steel plate, a stainless steel plate, a titanium plate, an aluminum plate, a plated steel plate, or a metal plate whose metal surface has been treated for corrosion prevention. Alternatively, the first separator 36 and the second separator 38 may be formed by cutting the plate and then treating it for corrosion prevention.

[0028] The resin frame member 40 is disposed between the first separator 36 and the second separator 38 so as to surround the membrane electrode assembly 30 and the like. The resin frame member 40 is generally ring-shaped. Sealing members 64a, 64b are provided on both sides of the resin frame member 40. The resin frame member 40 has a fluid inlet hole 40a and a fluid outlet hole 40b. The fluid inlet hole 40a is a flow path for introducing a fluid used in electrolysis. The fluid inlet hole 40a extends along the stacking direction. The fluid inlet holes 40a of the stacked electrolysis cells 14 communicate with each other. A fluid inlet 15a (see FIG. 1 ) is connected to the resin frame member 40 of the electrolysis cell 14 located at one end (lower end) of the multiple electrolysis cells 14 in the stacking direction.

[0029] The fluid outlet hole 40b is a flow path for discharging a mixed fluid containing unreacted fluid that has not been electrolyzed. The fluid outlet hole 40b extends along the stacking direction. The fluid outlet holes 40b of the stacked electrolytic cells 14 communicate with each other. A fluid outlet port 15b (see FIG. 1 ) is connected to the resin frame member 40 of the electrolytic cell 14 located at the other end (upper end) of the electrolytic cells 14 in the stacking direction.

[0030] Each electrolytic cell 14 is provided with a high-pressure fluid outlet hole 21 that penetrates through the radial center along the stacking direction. The high-pressure fluid outlet hole 21 is formed to increase the pressure of gas generated by electrolysis of the fluid used in electrolysis and discharge the gas. The high-pressure fluid outlet holes 21 of the multiple stacked electrolytic cells 14 communicate with each other. The generated gas is discharged from the high-pressure fluid outlet hole 21 in a state where it has been pressurized to, for example, 1 MPa to 80 MPa.

[0031] Next, a method for manufacturing the membrane electrode assembly 30 according to this embodiment will be described.

[0032] As shown schematically in FIG. 3, the method for manufacturing a membrane electrode assembly 30 includes a member providing step S1, a swelling step S2, and a bonding step S3. The member providing step S1 includes a first laminate providing step S1a, a second laminate providing step S1b, and a substrate providing step S1c. The first laminate providing step S1a is a step of providing a first laminate 70. The second laminate providing step S1b is a step of providing a second laminate 72. The substrate providing step S1c is a step of providing an electrolyte substrate 74. Note that the first laminate 70, the second laminate 72, and the electrolyte substrate 74 are ring-shaped, but these shapes are omitted in FIG. 3.

[0033] The first laminate 70 has a first electrode 44 and a first layer made of a first ionomer raw material 71. The first electrode 44 and the first ionomer raw material 71 are stacked on top of each other. For example, the first laminate 70 can be obtained by applying the first ionomer raw material 71 to the surface of the first electrode 44. Alternatively, the first laminate 70 can be obtained by transferring the first electrode 44 to a sheet made of the first ionomer raw material 71.

[0034] The diameter of the first electrode 44 and the diameter of the first ionomer raw material 71 are approximately the same. The thickness t1 of the first ionomer raw material 71 in the stacking direction of the first electrode 44 and the first ionomer raw material 71 is much smaller than the thickness t3 of the electrolyte base material 74. The thickness t1 of the first ionomer raw material 71 is, for example, 5 μm to 50 μm. The thickness t1 of the first ionomer raw material 71 is, for example, 3% to 50% of the thickness t3 of the electrolyte base material 74.

[0035] The second laminate 72 has a second electrode 46 and a second layer made of a second ionomer raw material 73. The second electrode 46 and the second ionomer raw material 73 are laminated together. For example, the second laminate 72 is obtained by applying the second ionomer raw material 73 to the surface of the second electrode 46. Alternatively, the second laminate 72 may be obtained by transferring the second electrode 46 to a sheet made of the second ionomer raw material 73.

[0036] The diameter of the second electrode 46 and the diameter of the second ionomer raw material 73 are approximately the same. The thickness t2 of the second ionomer raw material 73 in the stacking direction of the second electrode 46 and the second ionomer raw material 73 is much smaller than the thickness t3 of the electrolyte base material 74. The thickness t2 of the second ionomer raw material 73 is, for example, 5 μm to 50 μm. The thickness t2 of the second ionomer raw material 73 is, for example, 3% to 50% of the thickness t3 of the electrolyte base material 74.

[0037] The electrolyte base material 74 is made of an ionomer. The electrolyte base material 74 has a first surface 741 and a second surface 742 that are opposite to each other. The thickness t3 of the electrolyte base material 74 is, for example, 100 μm to 150 μm. The electrolyte base material 74 is, for example, circular. The diameter of the electrolyte base material 74 is larger than the diameter of the first laminate 70 and the diameter of the second laminate 72.

[0038] The ion exchange capacity per unit area of ​​the first ionomer raw material 71 at a predetermined temperature and in an atmosphere of a predetermined humidity is less than a predetermined value. At a predetermined temperature and in an atmosphere of a predetermined humidity, the ion exchange capacity per unit area of ​​the first ionomer raw material 71 is smaller than the ion exchange capacity per unit area of ​​the electrolyte base material 74. The ion exchange capacity per unit area of ​​the second ionomer raw material 73 at a predetermined temperature and in an atmosphere of a predetermined humidity is equal to or greater than a predetermined value. At a predetermined temperature and in an atmosphere of a predetermined humidity, the ion exchange capacity per unit area of ​​the second ionomer raw material 73 is larger than the ion exchange capacity per unit area of ​​the electrolyte base material 74. Therefore, at a predetermined temperature and in an atmosphere of a predetermined humidity, the ion exchange capacity per unit area of ​​the second ionomer raw material 73 is larger than the ion exchange capacity per unit area of ​​the first ionomer raw material 71.

[0039] The swelling step S2 is a step of swelling the first laminate 70, the second laminate 72, and the electrolyte base material 74. Specifically, in the swelling step S2, the first laminate 70, the second laminate 72, and the electrolyte base material 74 are immersed in water W. The immersion causes water to penetrate into the first laminate 70, the second laminate 72, and the electrolyte base material 74, causing the first laminate 70, the second laminate 72, and the electrolyte base material 74 to swell. As a result, the thickness t1 and diameter of the swollen first ionomer raw material 71 are larger than the thickness t1 and diameter of the first ionomer raw material 71 before swelling, respectively. The thickness t2 and diameter of the swollen second ionomer raw material 73 are larger than the thickness t2 and diameter of the second ionomer raw material 73 before swelling, respectively. The thickness t3 and diameter of the swollen electrolyte base material 74 are greater than the thickness t3 and diameter of the electrolyte base material 74 before swelling.

[0040] Although the swelling ratio of the first ionomer raw material 71 is greater than that of the first electrode 44, the thickness t1 of the first ionomer raw material 71 is much smaller than the thickness t3 of the electrolyte base material 74, and therefore, the occurrence of wrinkles in the first ionomer raw material 71 is suppressed. Even if wrinkles occur in the first ionomer raw material 71, the size of the wrinkles is very small. Similarly, although the swelling ratio of the second ionomer raw material 73 is greater than that of the second electrode 46, the thickness t2 of the second ionomer raw material 73 is much smaller than the thickness t3 of the electrolyte base material 74, and therefore, the occurrence of wrinkles in the second ionomer raw material 73 is suppressed. Even if wrinkles occur in the second ionomer raw material 73, the size of the wrinkles is very small.

[0041] After the swelling step S2, a bonding step S3 is carried out. The bonding step S3 is a step of bonding the first surface 741 of the electrolyte base material 74 to the first ionomer raw material 71 of the first laminate 70, and bonding the second surface 742 of the electrolyte base material 74 to the second ionomer raw material 73 of the second laminate 72. The bonding step S3 can be carried out using, for example, a hot press device 80.

[0042] The hot press device 80 includes a first die 82, a second die 84, a first holding member 86, and a second holding member 88. The first die 82 is a lower die. The second die 84 is an upper die that is movable in the vertical direction.

[0043] The first holding member 86 is circular ring-shaped. The second holding member 88 is circular ring-shaped. In a preparation step before bonding, the first holding member 86 and the second holding member 88 sandwich the outer peripheral edge of the electrolyte base material 74. As a result, the first holding member 86 faces the first surface 741 of the electrolyte base material 74 and abuts against the outer peripheral edge of the electrolyte base material 74. The second holding member 88 faces the second surface 742 of the electrolyte base material 74 and abuts against the outer peripheral edge of the electrolyte base material 74.

[0044] With the outer peripheral edge of the electrolyte base material 74 sandwiched between the first holding member 86 and the second holding member 88, the electrolyte base material 74 is stretched. Then, the first stack 70 is inserted inside the first holding member 86, and the second stack 72 is inserted inside the second holding member 88. As a result, the electrolyte base material 74 is disposed between the first stack 70 and the second stack 72. In this case, with the first stack 70 disposed inside the first holding member 86, the first ionomer raw material 71 of the first stack 70 comes into contact with the first surface 741 of the electrolyte base material 74. With the second stack 72 disposed inside the second holding member 88, the second ionomer raw material 73 of the second stack 72 comes into contact with the second surface 742 of the electrolyte base material 74.

[0045] In the bonding step S3, the laminate structure 75 consisting of the first laminate 70, the electrolyte base material 74, and the second laminate 72 is sandwiched between a first mold 82 and a second mold 84, and pressure and heat are applied. As a result, the first surface 741 of the electrolyte base material 74 and the first ionomer raw material 71 of the first laminate 70 are bonded to each other, and the second surface 742 of the electrolyte base material 74 and the second ionomer raw material 73 of the second laminate 72 are bonded to each other.

[0046] Even if wrinkles due to swelling have occurred in the first ionomer raw material 71, when the electrolyte base material 74 and the first ionomer raw material 71 are bonded together, the wrinkles in the first ionomer raw material 71 will be integrated with the electrolyte base material 74 and will substantially disappear due to the pressure and heat from the hot press device 80. Similarly, even if wrinkles due to swelling have occurred in the second ionomer raw material 73, when the electrolyte base material 74 and the second ionomer raw material 73 are bonded together, the wrinkles in the second ionomer raw material 73 will be integrated with the electrolyte base material 74 and will substantially disappear due to the pressure and heat from the hot press device 80.

[0047] The electrolyte base material 74, the first ionomer raw material 71, and the second ionomer raw material 73 are integrated to form the electrolyte membrane 42. Thus, the membrane electrode assembly 30 (see also FIG. 2) is obtained by the bonding step S3. Although some water evaporates from the first laminate 70, the electrolyte base material 74, and the second laminate 72 between the completion of the swelling step S2 and the start of the bonding step S3, the first laminate 70, the electrolyte base material 74, and the second laminate 72 remain swollen. Although some water evaporates from the first laminate 70, the electrolyte base material 74, and the second laminate 72 by the bonding step S3, the first laminate 70, the electrolyte base material 74, and the second laminate 72 each retain a sufficient amount of water, so the first laminate 70, the electrolyte base material 74, and the second laminate 72 remain swollen. Therefore, the swollen state of the membrane electrode assembly 30 is maintained even at the completion of the bonding step S3.

[0048] The above-described manufacturing method produces multiple membrane electrode assemblies 30. The multiple membrane electrode assemblies 30 are used to manufacture an electrolysis stack 10A (see FIG. 1 ). In this case, the electrolysis stack 10A is assembled by bringing the multiple membrane electrode assemblies 30 into a swollen state similar to that during electrolysis. This makes it possible to prevent wrinkles from forming in the membrane electrode assemblies 30 during electrolysis.

[0049] This embodiment has the following advantages.

[0050] According to the manufacturing method of the membrane electrode assembly 30, after the first stack 70, the second stack 72, and the electrolyte base material 74 are swollen, the first stack 70 and the electrolyte base material 74 are bonded together, and the second stack 72 and the electrolyte base material 74 are bonded together, so that the occurrence of wrinkles in the electrolyte membrane 42 can be suppressed.

[0051] 2 , when the differential pressure electrolysis device 10 is a water electrolysis device, the moisture in the electrolyte membrane 42 is pushed toward the first electrode 44 by the high-pressure gas generated at the second electrode 46. Therefore, unlike the membrane electrode assembly 30 manufactured by the manufacturing method according to the present embodiment, if the ion exchange capacity of the portion of the electrolyte membrane 42 adjacent to the second electrode 46 (the second adjacent portion 422) is the same as the ion exchange capacity of the portion of the electrolyte membrane 42 adjacent to the first electrode 44 (the first adjacent portion 421), the moisture in the second adjacent portion 422 supplied to the electrolyte membrane 42 through the first electrode 44 is pushed back toward the first electrode 44 by the pressure of the high-pressure gas, and is therefore more likely to dry than the first adjacent portion 421. When the electrolyte membrane 42 dries, the movement of ions in the electrolyte membrane 42 is hindered, which may reduce the efficiency of electrolysis. Furthermore, when the electrolyte membrane 42 dries, the deterioration of the electrolyte membrane 42 (particularly the deterioration of the second adjacent portion 422) due to an increase in electrical resistance may progress.

[0052] In contrast, in the membrane electrode assembly 30 manufactured by the manufacturing method according to this embodiment, the ion exchange capacity of the second adjacent portion 422, which is on the high-pressure side of the electrolyte membrane 42, is greater than the ion exchange capacity of the first adjacent portion 421, which is on the low-pressure side. Therefore, when the differential pressure electrolysis device 10 is a water electrolysis device, the maximum water content of the second adjacent portion 422 can be greater than the maximum water content of the first adjacent portion 421. Therefore, even if water supplied to the electrolyte membrane 42 through the first electrode 44 is pushed back by the pressure of the high-pressure gas generated at the second electrode 46, drying in the second adjacent portion 422 is suppressed, and the obstruction of ion movement within the electrolyte membrane 42 is suppressed. In other words, the variation in the water content of the electrolyte membrane 42 in the thickness direction of the electrolyte membrane 42 can be suppressed. This suppresses drying in the second adjacent portion 422, which is on the high-pressure side of the electrolyte membrane 42, thereby suppressing a decrease in electrolysis efficiency and the progression of deterioration of the electrolyte membrane 42 (particularly deterioration of the second adjacent portion 422).

[0053] 3, the thickness t1 of the first ionomer raw material 71 may be different from the thickness t2 of the second ionomer raw material 73. By making the thickness t1 of the first ionomer raw material 71 and the thickness t2 of the second ionomer raw material 73 different from each other, the moisture amounts of the first adjacent portion 421 and the second adjacent portion 422 of the electrolyte membrane 42 during electrolysis can be adjusted, and drying of the second adjacent portion 422 can be suppressed.

[0054] The first stack 70, the second stack 72, and the electrolyte base material 74 are each circular. The diameter of each of the first stack 70 and the second stack 72 is smaller than the diameter of the electrolyte base material 74. In the bonding step S3, the first stack 70 and the electrolyte base material 74 are bonded inside the first holding member 86 and the second holding member 88 that hold the outer peripheral edge of the electrolyte base material 74, and the second stack 72 and the electrolyte base material 74 are bonded together. This allows the bonding to be performed inside the first holding member 86 and the second holding member 88 while the outer peripheral edge of the electrolyte base material 74 is held by the first holding member 86 and the second holding member 88, thereby enabling the bonding step S3 to be performed smoothly.

[0055] The following additional notes are further disclosed regarding the above embodiment.

[0056] (Supplementary Note 1) A method for manufacturing a membrane electrode assembly (30) according to the present disclosure is a method for manufacturing a membrane electrode assembly used in a differential pressure electrolysis device (10) including an electrolyte membrane (42) and a first electrode (44) and a second electrode (46) stacked on either side of the electrolyte membrane, the method comprising supplying an electrolysis fluid to the first electrode, applying a voltage between the first electrode and the second electrode, and obtaining at the second electrode a second gas having a higher pressure than a first gas obtained at the first electrode, the method comprising the steps of: providing a first stack (70) by stacking a first ionomer raw material (71) having an ion exchange capacity per unit area under an atmosphere at a predetermined temperature and a predetermined humidity that is less than a predetermined value with the first electrode; The method includes a second laminate providing step (S1b) of providing a second laminate (72) obtained by stacking a second ionomer raw material (73) having an ion exchange capacity per unit area in the predetermined humidity atmosphere equal to or greater than the predetermined value and the second electrode; a substrate providing step (S1c) of providing an electrolyte base material (74) having a first surface (741) and a second surface (742) opposite to each other; a swelling step (S2) of swelling the first laminate, the second laminate, and the electrolyte base material; and a bonding step (S3) of bonding the first surface of the electrolyte base material to the first ionomer raw material of the first laminate and bonding the second surface of the electrolyte base material to the second ionomer raw material of the second laminate after the swelling step.

[0057] (Appendix 2) In the method for manufacturing a membrane electrode assembly described in Appendix 1, the thickness (t1) of the first ionomer raw material in the stacking direction between the first electrode and the first ionomer raw material may be different from the thickness (t2) of the second ionomer raw material in the stacking direction between the second electrode and the second ionomer raw material.

[0058] (Appendix 3) In the method for manufacturing a membrane electrode assembly described in Appendix 1 or 2, each of the first laminate, the second laminate, and the electrolyte base material may be circular, and the diameter of each of the first laminate and the second laminate may be smaller than the diameter of the electrolyte base material, and in the joining step, the first laminate and the electrolyte base material may be joined inside a holding member that holds an outer peripheral edge portion of the electrolyte base material, and the second laminate and the electrolyte base material may be joined.

[0059] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments. [Explanation of symbols]

[0060] 10... Differential pressure electrolysis device 30... Membrane electrode assembly 42...Electrolyte membrane 44...First electrode 46... Second electrode 70... First laminate 71...first ionomer raw material 72...second laminate 73...Second ionomer raw material 74...Electrolyte base material

Claims

1. A method for manufacturing a membrane electrode assembly used in a differential pressure electrolysis device, comprising an electrolyte membrane and a first electrode and a second electrode stacked on either side of the electrolyte membrane, the method comprising supplying an electrolysis fluid to the first electrode, applying a voltage between the first electrode and the second electrode, and obtaining a second gas at the second electrode, the second gas having a higher pressure than a first gas obtained at the first electrode, the method comprising: a first laminate providing step of providing a first laminate obtained by laminating a first ionomer raw material having an ion exchange capacity per unit area under an atmosphere at a predetermined temperature and a predetermined humidity that is less than a predetermined value and the first electrode; a second laminate providing step of providing a second laminate obtained by laminating a second ionomer raw material having an ion exchange capacity per unit area at the predetermined temperature and in the predetermined humidity atmosphere equal to or greater than the predetermined value and the second electrode; providing an electrolyte substrate having a first surface and a second surface opposite each other; a swelling step of swelling the first stack, the second stack, and the electrolyte base material; a bonding step of bonding the first surface of the electrolyte base material to the first ionomer raw material of the first laminate and bonding the second surface of the electrolyte base material to the second ionomer raw material of the second laminate after the swelling step.

2. 2. The method for producing a membrane electrode assembly according to claim 1, A method for manufacturing a membrane electrode assembly, wherein a thickness of the first ionomer raw material in a stacking direction between the first electrode and the first ionomer raw material is different from a thickness of the second ionomer raw material in a stacking direction between the second electrode and the second ionomer raw material.

3. 3. The method for producing a membrane electrode assembly according to claim 1 or 2, each of the first stack, the second stack, and the electrolyte base material has a circular shape; a diameter of each of the first stack and the second stack is smaller than a diameter of the electrolyte substrate; In the joining step, the first stack and the electrolyte base material are joined inside a holding member that holds an outer peripheral edge portion of the electrolyte base material, and the second stack and the electrolyte base material are joined.

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