DIFFERENTIAL PRESSURE ELECTROLYSIS CELL AND DIFFERENTIAL PRESSURE ELECTROLYSIS STACK

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-145183 filed on Aug. 27, 2024, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a differential pressure electrolysis cell and a differential pressure electrolysis stack.

Description of the Related Art

In recent years, research and development have been conducted on differential pressure electrolysis cells and differential pressure electrolysis stacks that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and modern energy.

JP 2019-157213 A discloses a water electrolysis cell which is a differential pressure electrolysis cell. The water electrolysis cell includes an electrolyte membrane/electrode assembly (membrane electrode assembly), an anode current collector, a cathode current collector, an anode separator, and a cathode separator.

The electrolyte membrane/electrode assembly includes an electrolyte membrane, a cathode electrode catalyst layer disposed on one surface of the electrolyte membrane, and an anode electrode catalyst layer disposed on another surface of the electrolyte membrane. In the water electrolysis cell, a voltage is applied between the cathode current collector and the anode current collector, thereby generating an oxygen gas in the anode electrode catalyst layer and generating a hydrogen gas in the cathode catalyst layer. The water electrolysis cell may cause the hydrogen gas generated at the cathode catalyst layer to have a higher pressure than the oxygen gas generated at the anode catalyst layer.

SUMMARY OF THE INVENTION

There is a need for a better differential pressure electrolysis cell and a better differential pressure electrolysis stack.

The present disclosure has the object of solving the aforementioned problem.

A first aspect of the present disclosure is characterized by a differential pressure electrolysis cell including a membrane electrode assembly including an electrolyte membrane, a first electrode catalyst layer stacked on one surface of the electrolyte membrane, and a second electrode catalyst layer stacked on another surface of the electrolyte membrane, a first separator located across the electrolyte membrane from the second electrode catalyst layer, a second separator located across the electrolyte membrane from the first electrode catalyst layer, a first current collector disposed between the first separator and the first electrode catalyst layer, a second current collector disposed between the second separator and the second electrode catalyst layer, and a pressing member sandwiched and held between the second current collector and the second separator and configured to press the second current collector toward the second electrode catalyst layer, wherein the differential pressure electrolysis cell applies a voltage between the first current collector and the second current collector to electrolyze a fluid supplied to the membrane electrode assembly and thereby generate a gas in the second electrode catalyst layer, and is configured to cause the gas to have a higher pressure than a pressure of the fluid, and the pressing member includes a sheet portion that is formed of a polymer material having an electrical insulating property so as to be elastically deformable, and is disposed between the second current collector and the second separator in a state of being compressed and deformed in a stacking direction of the membrane electrode assembly.

A second aspect of the present disclosure is characterized by a differential pressure electrolysis stack including a stack of a plurality of differential pressure electrolysis cells, wherein each of the plurality of differential pressure electrolysis cells is the differential pressure electrolysis cell according to the first aspect.

According to the present disclosure, a better differential pressure electrolysis cell and a better differential pressure electrolysis stack can be provided.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrolysis device including a differential pressure electrolysis stack;

FIG. 2 is a cross-sectional view of a differential pressure electrolysis cell;

FIG. 3 is a cross-sectional view of a differential pressure electrolysis cell according to a first modification;

FIG. 4 is a cross-sectional view of a differential pressure electrolysis cell according to a second modification;

FIG. 5 is a cross-sectional view of a differential pressure electrolysis cell according to a third modification;

FIG. 6A is a cross-sectional explanatory view of the differential pressure electrolysis cell of FIG. 2; and

FIG. 6B is a cross-sectional explanatory view of the differential pressure electrolysis cell of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

In the above-described water electrolysis cell, for example, a metal plate spring (a pressing member) is disposed between the anode separator and the anode current collector. The plate spring presses the anode current collector toward the membrane electrode assembly. In such a configuration, the pressure applied from the plate spring to the electrolyte membrane (the surface pressure of the electrolyte membrane) tends to vary. In addition, since an excessive current flows through the metal plate spring, the loss of power occurs. When the surface pressure of the electrolyte membrane varies and power loss occurs, the electrolysis efficiency of the membrane electrode assembly decreases.

Further, since the anode separator is made of metal, a portion of the surface of the anode separator with which the plate spring comes into contact is coated with a material having an electrical insulating property. The coating prevents metal ions (e.g., iron ions) from eluting from the anode separator. Since the plate spring is in line contact with the coating of the anode separator, a relatively large load acts on the coating. Then, the plate spring repeatedly presses the coating of the anode separator, and the coating of the anode separator may be peeled off.

When the coating of the anode separator is peeled off, metal ions may be eluted. When the eluted metal ions reach the electrolyte membrane, the electrolyte membrane deteriorates.

This reduces the durability of the differential pressure electrolysis cell. In addition, when a voltage is applied between the cathode current collector and the anode current collector, a current locally flows between the plate spring and the anode separator through the portion where the coating is peeled off, and metal corrosion may progress. This reduces the durability of the differential pressure electrolysis cell.

The present disclosure may provide a differential pressure electrolysis cell and a differential pressure electrolysis stack capable of improving electrolysis efficiency and durability.

FIG. 1 is an explanatory perspective view of an electrolysis device 11 including a differential pressure electrolysis stack 10. As shown in FIG. 1, the electrolysis device 11 includes the differential pressure electrolysis stack 10 and a power supply 12. The differential pressure electrolysis stack 10 includes a cell stacked body 14, a pair of terminal plates 16a, 16b, a pair of insulating plates 18a, 18b, and a pair of end plates 20a, 20b.

The cell stacked body 14 is formed by stacking a plurality of differential pressure electrolysis cells 22 in an A direction. The plurality of differential pressure electrolysis cells 22 are stacked in the vertical direction, for example. The plurality of differential pressure electrolysis cells 22 may be stacked in a direction (for example, a horizontal direction) intersecting the vertical direction. The cell stacked body 14 is provided with a fluid inlet portion 24 and a fluid outlet portion 26. The fluid inlet portion 24 introduces a fluid used for electrolysis into the cell stacked body 14. The fluid outlet portion 26 leads out an unreacted fluid or the like that has not reacted in electrolysis to the outside of the cell stacked body 14.

The terminal plate 16a is disposed at one end (an end in an A1 direction) of the cell stacked body 14. The insulating plate 18a is adjacent to the terminal plate 16a in the A1 direction. The end plate 20a is adjacent to the insulating plate 18a in the A1 direction. The terminal plate 16b is disposed at another end (an end in an A2 direction) of the cell stacked body 14. The insulating plate 18b is adjacent to the terminal plate 16b in the A2 direction. The end plate 20b is adjacent to the insulating plate 18b in the A2 direction.

The terminal plate 16a is provided with a terminal portion 28a. The terminal portion 28a is electrically connected via wiring 30a to the power supply 12. The terminal plate 16b is provided with a terminal portion 28b. The terminal portion 28b is electrically connected via wiring 30b to the power supply 12.

The pair of end plates 20a and 20b are connected by a plurality of connecting members 32. The connecting members 32 includes stud bolts 34 and nuts 36. One end portion of each of the stud bolts 34 is fastened to the end plate 20a. Each of the stud bolts 34 is inserted through a hole (not shown) formed in the end plate 20b. The nut 36 is fastened to another end portion of each of the stud bolts 34. Accordingly, the pair of end plates 20a and 20b are fastened in a direction in which the end plates come close to each other by the plurality of connecting members 32, and thus a fastening load is applied to the cell stacked body 14.

FIG. 2 is a cross-sectional view of the differential pressure electrolysis cell 22. As shown in FIG. 2, a fluid supply communication hole 40, a fluid discharge communication hole 42, and a gas lead-out communication hole 44 are formed in the differential pressure electrolysis cell 22 so as to penetrate in the A direction. The fluid supply communication hole 40 is formed in the outer peripheral portion (a radially outward end portion) of the differential pressure electrolysis cell 22. The fluid supply communication holes 40 of the plurality of differential pressure electrolysis cells 22 communicate with each other. The fluid supply communication holes 40 communicate with the fluid inlet portion 24 (see FIG. 1). Each of the fluid supply communication holes 40 is a flow path for supplying the fluid introduced from the fluid inlet portion 24 to a first electrode catalyst layer 76 of the differential pressure electrolysis cell 22.

The fluid discharge communication hole 42 is formed in the outer peripheral portion (a radially outward end portion) of the differential pressure electrolysis cell 22. The fluid discharge communication holes 42 of the plurality of differential pressure electrolysis cells 22 communicate with each other. The fluid discharge communication holes 42 communicates with the fluid outlet portion 26 (see FIG. 1). Each of the fluid discharge communication hole 42 is a flow path for guiding an unreacted fluid or the like that has not reacted in electrolysis in each of the differential pressure electrolysis cells 22 to the fluid outlet portion 26.

The gas lead-out communication hole 44 is formed in the central part of the differential pressure electrolysis cell 22. The fluid supply communication hole 40 and the fluid discharge communication hole 42 are located on opposite sides of the gas lead-out communication hole 44. The gas lead-out communication holes 44 of the plurality of differential pressure electrolysis cells 22 communicate with each other. The gas lead-out communication hole 44 is also formed in the end plate 20b (see FIG. 1). A gas generated in a second electrode catalyst layer 78 of the differential pressure electrolysis cell 22 is discharged to the outside through the gas lead-out communication holes 44 of the differential pressure electrolysis cells 22 and the gas lead-out communication hole 44 in the end plate 20b.

The differential pressure electrolysis cell 22 includes a cell main body 46, a pair of separators 48, and a frame member 50. The cell main body 46 is sandwiched between the pair of separators 48. The frame member 50 is formed in an annular shape so as to surround the cell main body 46. The frame member 50 is formed of, for example, a resin material having an electrical insulating property. A sealing member 52 for preventing the fluid from flowing outside is provided between each of the pair of separators 48 and the frame member 50.

The separator 48 is made of a metal material such as stainless steel. Hereinafter, in the differential pressure electrolysis cell 22 of FIG. 2, the separator 48 of the pair of separators 48 that is positioned in the A1 direction of the cell main body 46 is referred to as a “first separator 48a”, and the separator 48 of the pair of separators 48 that is positioned in the A2 direction of the cell main body 46 is referred to as a “second separator 48b”.

The cell main body 46 includes a membrane electrode assembly 54, a first current collector 56, a protective sheet 58, a flow path member 60, a second current collector 62, a conductive sheet 64, a pressing member 66, a conductive member 68, a sealing member 70, and a pressure resistant member 72.

The membrane electrode assembly 54 is disposed between the first current collector 56 and the second current collector 62. The gas lead-out communication hole 44 is formed in the central part of the membrane electrode assembly 54. The membrane electrode assembly 54 includes an electrolyte membrane 74, the first electrode catalyst layer 76, and the second electrode catalyst layer 78. The electrolyte membrane 74 is a membrane capable of exchanging ions. The electrolyte membrane 74 is, for example, a proton exchange membrane (PEM). The proton exchange membrane is, for example, a fluorine-based polymer membrane. The electrolyte membrane 74 may be an anion exchange membrane (AEM).

The first electrode catalyst layer 76 is stacked on one surface (a surface facing in the A1 direction) of the electrolyte membrane 74. The first electrode catalyst layer 76 is formed in an annular shape (a circular annular shape). A fluid used for electrolysis is supplied to the first electrode catalyst layer 76. The outer diameter of the first electrode catalyst layer 76 is smaller than the outer diameter of the electrolyte membrane 74. The second electrode catalyst layer 78 is stacked on another surface (a surface facing in the A2 direction) of the electrolyte membrane 74. Gas is generated in the second electrode catalyst layer 78 by the electrolysis of the fluid. The second electrode catalyst layer 78 is formed in an annular shape. The outer diameter of the second electrode catalyst layer 78 is smaller than the outer diameter of the electrolyte membrane 74.

The first current collector 56 is formed in an annular shape (a circular annular shape). The first current collector 56 also serves as a diffusion layer for supplying a fluid used for electrolysis to the first electrode catalyst layer 76. The first current collector 56 has a portion formed of a porous member. The protective sheet 58 is disposed between the first electrode catalyst layer 76 and the first current collector 56.

The protective sheet 58 prevents the membrane electrode assembly 54 from being damaged by being pushed by the first current collector 56 due to the gas generated in the second electrode catalyst layer 78. The protective sheet 58 has a plurality of through holes 80 formed therein for allowing a fluid used for electrolysis to pass therethrough.

The flow path member 60 is formed in an annular shape. The flow path member 60 is disposed between the first separator 48a and the first current collector 56. The flow path member 60 supports the first current collector 56. The flow path member 60 is formed with a communication path 82. The communication path 82 guides the fluid introduced from the fluid supply communication hole 40 to the first current collector 56. The communication path 82 guides the unreacted fluid or the like that has not reacted in the electrolysis to the fluid discharge communication hole 42.

The second current collector 62 is formed in an annular shape (circular annular shape). The second current collector 62 also serves as a gas diffusion layer for guiding out the gas generated in the second electrode catalyst layer 78. The second current collector 62 has a portion formed of a porous member.

The outer diameter of the second current collector 62 is smaller than the outer diameter of the membrane electrode assembly 54. In other words, the outer diameter of the second current collector 62 is smaller than the outer diameter of the electrolyte membrane 74. The membrane electrode assembly 54 has an outer peripheral portion 84 protruding outward in the planar direction from the second current collector 62.

The conductive sheet 64 is stacked on a surface of the second current collector 62 facing the A2 direction. The conductive sheet 64 is made of a metal sheet, whose material includes, for example, titanium, or stainless steel. The gas lead-out communication hole 44 is formed in the central part of the conductive sheet 64. The outer diameter of the conductive sheet 64 is substantially the same as the outer diameter of the second current collector 62.

The pressing member 66 is sandwiched between the second separator 48b and the second current collector 62. In other words, the pressing member 66 is sandwiched between the second separator 48b and the conductive sheet 64. The pressing member 66 presses the conductive sheet 64 and the second current collector 62 toward the second electrode catalyst layer 78. In other words, the pressing member 66 presses the conductive sheet 64 toward the second current collector 62. The pressing member 66 is formed in an annular shape (for example, a circular annular shape) and is provided at a position corresponding to the electrolyte membrane 74 and the second current collector 62.

The pressing member 66 includes a sheet portion 86 and a metal plate 88. The sheet portion 86 is formed of a polymer material having an electrical insulating property so as to be elastically deformable. In other words, the sheet portion 86 is formed of a rubber material. The sheet portion 86 is disposed between the second current collector 62 (conductive sheet 64) and the second separator 48b in a state of being compressed and deformed in the stacking direction (the direction A) of the membrane electrode assembly 54. The sheet portion 86 is in surface contact with the second separator 48b and is in surface contact with the conductive sheet 64. The sheet portion 86 is formed in an annular shape (for example, a circular annular shape). The outer diameter of the sheet portion 86 is substantially the same as the outer diameter of the second current collector 62.

The metal plate 88 extends along the sheet portion 86. The metal plate 88 is formed of, for example, stainless steel or the like. The metal plate 88 is formed in an annular shape (for example, a circular annular shape). The metal plate 88 is provided inside the sheet portion 86. In other words, the metal plate 88 is embedded in the sheet portion 86. The metal plate 88 is located at the central part of the sheet portion 86 in the A direction. That is, the sheet portion 86 covers the metal plate 88 from both sides in the stacking direction of the membrane electrode assembly 54. The sheet portion 86 covers the entire surface of the metal plate 88.

The conductive member 68 is disposed in a central hole portion 90 of the pressing member 66. The conductive member 68 is in contact with the inner surface of the sealing member 70.

The conductive member 68 electrically connects the second separator 48b and the conductive sheet 64. The conductive member 68 is made of, for example, a metal material. The conductive member 68 may be made of carbon or the like. The conductive member 68 is sandwiched and held between the second separator 48b and the conductive sheet 64. The gas lead-out communication hole 44 is formed in the central part of the conductive member 68. The conductive member 68 and the conductive sheet 64 are formed with a gas flow path 92 for guiding the gas generated in the second electrode catalyst layer 78 to the gas lead-out communication hole 44.

The sealing member 70 is formed in a circular annular shape. The sealing member 70 has a circular cross section. The sealing member 70 seals between the outer peripheral portion 84 of the membrane electrode assembly 54 and the second separator 48b. That is, the sealing member 70 is in airtight and liquid-tight contact with the outer peripheral portion 84 of the membrane electrode assembly 54, and is in airtight and liquid-tight contact with the second separator 48b. An inner surface of the sealing member 70 facing radially inward is in contact with an outer peripheral end portion of the sheet portion 86.

The sealing member 70 prevents gas generated in the second electrode catalyst layer 78 from leaking to the outside. The second current collector 62, the conductive sheet 64, and the pressing member 66 are disposed inside the sealing member 70. The gas generated in the second electrode catalyst layer 78 is sealed inside the sealing member 70 (a gas storage chamber 94).

In the present embodiment, since the space between the sealing member 70 and the conductive member 68 is blocked by the pressing member 66 (the sheet portion 86), the volume of the gas storage chamber 94 can be reduced as compared with the case where a plate spring is used as the pressing member 66. The sealing member 70 is made of a resin material such as a rubber material.

The pressure resistant member 72 is formed in a circular annular shape. The pressure resistant member 72 is made of, for example, a metal material. The pressure resistant member 72 is disposed so as to surround the sealing member 70 from the radially outward side. The pressure resistant member 72 is sandwiched and held between the outer peripheral portion 84 of the membrane electrode assembly 54 and the second separator 48b. The pressure resistant member 72 is in contact with a radially outward end portion of the sealing member 70. The pressure resistant member 72 prevents the sealing member 70 from expanding radially outward due to the gas (high-pressure gas) present in the gas storage chamber 94. A coating of a material having an electrical insulating property is applied to portions of the second separator 48b facing the pressing member 66, the sealing member 70, and the pressure resistant member 72. The coating prevents elution of metal ions (e.g., iron ions) from the second separator 48b.

Next, a basic operation of the differential pressure electrolysis stack 10 according to the present embodiment will be briefly described. In the present embodiment, as shown in FIGS. 1 and 2, a humidified fluid is supplied to the fluid inlet portion 24 of the differential pressure electrolysis stack 10, and a voltage is applied between the first current collector 56 and the second current collector 62 by the power supply 12. At this time, since the sheet portion 86 has an electrical insulating property, no current flows through the pressing member 66. That is, when a current flows through the second current collector 62, the conductive sheet 64, the conductive member 68, and the second separator 48b, no extra current flows through the pressing member 66.

The fluid supplied to the fluid inlet portion 24 is guided to the first electrode catalyst layer 76 of each of the differential pressure electrolysis cells 22 through the fluid supply communication holes 40. In each of the differential pressure electrolysis cells 22, the fluid is electrolyzed, and gas is thereby generated in the second electrode catalyst layer 78 (the gas storage chamber 94). The gas generated in the second electrode catalyst layer 78 is guided into the gas lead-out communication hole 44 through the gas flow path 92. The gas guided to the gas lead-out communication hole 44 is discharged to an external flow path (not shown). A back pressure valve (not shown) is provided in the external flow path. The gas generated in the second electrode catalyst layer 78 is pressurized by being sealed by the back pressure valve. This makes it possible to make the pressure of the gas generated in the second electrode catalyst layer 78 higher than the pressure of the fluid supplied to the first electrode catalyst layer 76. In the present embodiment, the gas pressure increasing speed can be increased because the volume of the gas storage chamber 94 is small as compared with the case where a plate spring is used as the pressing member 66. In each of the differential pressure electrolysis cells 22, the unreacted fluid and the like that have not reacted in the electrolysis are guided to the fluid outlet portion 26 via the fluid discharge communication hole 42.

In the present embodiment, the differential pressure electrolysis cell 22 may be a differential pressure water electrolysis cell or an electrochemical hydrogen compression cell. Hereinafter, an example in which the differential pressure electrolysis cell 22 is a differential pressure water electrolysis cell and an example in which the differential pressure electrolysis cell 22 is an electrochemical hydrogen compression cell will be described.

In the case where the differential pressure electrolysis cell 22 is a differential pressure water electrolysis cell, for example, the electrolyte membrane 74 may be formed as a proton exchange membrane, the first electrode catalyst layer 76 may be formed as an anode electrode catalyst layer, and the second electrode catalyst layer 78 may be formed as a cathode electrode catalyst layer. In this case, when water is supplied to the first electrode catalyst layer 76, the water is electrolyzed in the first electrode catalyst layer 76, and hydrogen ions and oxygen gas are generated. The hydrogen ions move together with moisture through the electrolyte membrane 74 from the first electrode catalyst layer 76 to the second electrode catalyst layer 78. Thus, hydrogen ions are supplied to the second electrode catalyst layer 78, and the electrolyte membrane 74 is humidified. In the second electrode catalyst layer 78, the hydrogen ions are bonded to generate hydrogen gas. The hydrogen gas generated in the second electrode catalyst layer 78 is guided into the gas lead-out communication hole 44. Unreacted water that was supplied to the first electrode catalyst layer 76 but has not reacted and the oxygen gas generated in the first electrode catalyst layer 76 are guided to the fluid discharge communication hole 42.

In addition, in the case where the differential pressure electrolysis cell 22 is a differential pressure water electrolysis cell, for example, the electrolyte membrane 74 may be formed as an anion exchange membrane, the first electrode catalyst layer 76 may be formed as an anode electrode catalyst layer, and the second electrode catalyst layer 78 may be formed as a cathode electrode catalyst layer. In this case, the water supplied to the first electrode catalyst layer 76 moves from the first electrode catalyst layer 76 to the second electrode catalyst layer 78 in the electrolyte membrane 74. Thus, water is supplied to the second electrode catalyst layer 78, and the electrolyte membrane 74 is humidified. In the second electrode catalyst layer 78, water is electrolyzed to generate hydrogen gas and hydroxide ions. The hydrogen gas generated in the second electrode catalyst layer 78 is guided into the gas lead-out communication hole 44. The hydroxide ions generated in the second electrode catalyst layer 78 move from the second electrode catalyst layer 78 to the first electrode catalyst layer 76 in the electrolyte membrane 74. In the first electrode catalyst layer 76, oxygen gas and water are generated from the hydroxide ions. The water present in the first electrode catalyst layer 76 and the oxygen gas generated in the first electrode catalyst layer 76 are guided to the fluid discharge communication hole 42.

Furthermore, in the case where the differential pressure electrolysis cell 22 is a differential pressure water electrolysis cell, for example, the electrolyte membrane 74 may be formed as a proton exchange membrane, the first electrode catalyst layer 76 may be formed as a cathode electrode catalyst layer, and the second electrode catalyst layer 78 may be formed as an anode electrode catalyst layer. In this case, the water supplied to the first electrode catalyst layer 76 moves from the first electrode catalyst layer 76 to the second electrode catalyst layer 78 in the electrolyte membrane 74. Thus, water is supplied to the second electrode catalyst layer 78, and the electrolyte membrane 74 is humidified. In the second electrode catalyst layer 78, water is electrolyzed to generate hydrogen ions and oxygen gas. The oxygen gas generated in the second electrode catalyst layer 78 is guided into the gas lead-out communication hole 44. The hydrogen ions generated in the second electrode catalyst layer 78 move from the second electrode catalyst layer 78 to the first electrode catalyst layer 76 through the electrolyte membrane 74. In the first electrode catalyst layer 76, the hydrogen ions are bonded to generate hydrogen gas. Unreacted water that was supplied to the first electrode catalyst layer 76 but has not reacted and the hydrogen gas are guided to the fluid discharge communication hole 42.

In addition, in the case where the differential pressure electrolysis cell 22 is a differential pressure water electrolysis cell, for example, the electrolyte membrane 74 may be formed as an anion exchange membrane, the first electrode catalyst layer 76 may be formed as a cathode electrode catalyst layer, and the second electrode catalyst layer 78 may be formed as an anode electrode catalyst layer. In this case, when water is supplied to the first electrode catalyst layer 76, the water is electrolyzed in the first electrode catalyst layer 76, and hydrogen gas and hydroxide ions are generated. The hydroxide ions move together with the moisture from the first electrode catalyst layer 76 to the second electrode catalyst layer 78 through the electrolyte membrane 74. Thus, the hydroxide ions are supplied to the second electrode catalyst layer 78, and the electrolyte membrane 74 is humidified. In the second electrode catalyst layer 78, oxygen gas and water are generated from the hydroxide ions. The oxygen gas generated in the second electrode catalyst layer 78 is guided into the gas lead-out communication hole 44. Unreacted water that was supplied to the first electrode catalyst layer 76 but has not reacted and hydrogen gas generated in the first electrode catalyst layer 76 are guided to the fluid discharge communication hole 42.

In the case where the differential pressure electrolysis cell 22 is an electrochemical hydrogen compression cell, for example, the electrolyte membrane 74 may be formed as a proton exchange membrane, the first electrode catalyst layer 76 may be formed as an anode electrode catalyst layer, and the second electrode catalyst layer 78 may be formed as a cathode electrode catalyst layer. In this case, when the hydrogen gas containing moisture is supplied to the first electrode catalyst layer 76, the hydrogen gas is electrolyzed in the first electrode catalyst layer 76 to generate hydrogen ions. The hydrogen ions move together with the moisture through the electrolyte membrane 74 from the first electrode catalyst layer 76 to the second electrode catalyst layer 78. Thus, hydrogen ions are supplied to the second electrode catalyst layer 78, and the electrolyte membrane 74 is humidified. In the second electrode catalyst layer 78, the hydrogen ions are bonded to generate hydrogen gas. The hydrogen gas generated in the second electrode catalyst layer 78 is introduced into the gas lead-out communication hole 44. Unreacted hydrogen gas that was guided to the first electrode catalyst layer 76 but has not reacted is guided to the fluid discharge communication hole 42.

According to the present embodiment, since the sheet portion 86 is formed of a polymer material having an electrical insulating property so as to be elastically deformable, it is possible to suppress variations in the surface pressure of the electrolyte membrane 74 as compared with the case where a plate spring is used as the pressing member 66. In addition, it is possible to avoid power loss due to extra current flowing through the sheet portion 86. Therefore, the electrolysis efficiency of the differential pressure electrolysis cell 22 can be improved.

The sheet portion 86 is in surface contact with the second separator 48b. That is, the pressure acting on the coating on the second separator 48b can be reduced as compared with the case where a plate spring is used as the pressing member 66. Therefore, the coating can be prevented from being peeled off by the pressing member 66. In accordance with this feature, the generation of metal ions due to the peeling of the coating is suppressed, and thus the deterioration of the electrolyte membrane 74 due to the metal ions can be suppressed. Further, metal corrosion due to local energization can be suppressed.

Therefore, the durability of the differential pressure electrolysis cell 22 can be improved. Therefore, a better differential pressure electrolysis cell 22 and a better differential pressure electrolysis stack 10 can be provided.

In the present embodiment, the pressing member 66 has the metal plate 88 extending along the sheet portion 86. In accordance with such a configuration, the amount of elastic deformation of the sheet portion 86 in the A direction can be reduced as compared with a case where the metal plate 88 is not provided in the sheet portion 86 (a pressing member 66a according to a first modification to be described later). In other words, the amount of compressive deformation of the sheet portion 86 in the direction A when the electrolyte membrane 74 expands due to water absorption can be reduced. Consequently, it is possible to suppress expansion of the electrolyte membrane 74 due to water absorption. That is, the electrolyte membrane 74 can be prevented from spreading outward in the planar direction. That is, blisters of the electrolyte membrane 74 can be suppressed.

First Modification Next, a differential pressure electrolysis cell 22a according to a first modification will be described. FIG. 3 is a cross-sectional view of the differential pressure electrolysis cell 22a according to the first modification. Among the constituent elements of the differential pressure electrolysis cell 22a according to the first modification, those which are the same as the constituent elements of the differential pressure electrolysis cell 22 described above are denoted by the same reference characters, and the detailed description of such elements will be omitted. The same applies to a differential pressure electrolysis cell 22b according to a second modification and a differential pressure electrolysis cell 22c according to a third modification, which will be described later.

As illustrated in FIG. 3, in the differential pressure electrolysis cell 22a according to the first modification, the pressing member 66a is provided instead of the pressing member 66, as compared with the differential pressure electrolysis cell 22 described above. The pressing member 66a is constituted only by the sheet portion 86. That is, the pressing member 66a does not have the above-described metal plate 88.

In accordance with such a configuration, it is possible to provide the differential pressure electrolysis cell 22a capable of improving electrolysis efficiency and durability. Further, since it is not necessary to provide the metal plate 88 inside the sheet portion 86, the configuration of the pressing member 66a can be simplified.

Second Modification Next, the differential pressure electrolysis cell 22b according to the second modification will be described. FIG. 4 is a cross-sectional view of the differential pressure electrolysis cell 22b according to the second modification. As illustrated in FIG. 4, in the differential pressure electrolysis cell 22b according to the second modification, a pressing member 66b is provided instead of the pressing member 66, as compared with the differential pressure electrolysis cell 22 described above.

The pressing member 66b includes a sheet portion 86a and the metal plate 88. The sheet portion 86a includes a first sheet body 100 and a second sheet body 102. The first sheet body 100 is sandwiched and held between the metal plate 88 and the conductive sheet 64. The second sheet body 102 is sandwiched and held between the metal plate 88 and the second separator 48b. An end surface of the metal plate 88 outward in the planar direction is not covered with the sheet portion 86a.

An end surface of the metal plate 88 inward in the planar direction is not covered with the sheet portion 86a.

In accordance with such a configuration, it is possible to provide the differential pressure electrolysis cell 22b capable of improving electrolysis efficiency and durability. Further, since the pressing member 66b has the metal plate 88, the blisters of the electrolyte membrane 74 can be suppressed.

In the differential pressure electrolysis cell 22b according to the second modification, the inner peripheral end portion of the first sheet body 100 and the inner peripheral end portion of the second sheet body 102 may be connected to each other. In this case, the end surface of the metal plate 88 inward in the planar direction is covered with the sheet portion 86a. Therefore, it is possible to prevent the conductive member 68 and the metal plate 88 from being electrically connected to each other.

Third Modification Next, the differential pressure electrolysis cell 22c according to the third modification will be described. FIG. 5 is a cross-sectional view of the differential pressure electrolysis cell 22c according to the third modification. As illustrated in FIG. 5, in the differential pressure electrolysis cell 22c according to the third modification, a pressing member 66c is provided instead of the pressing member 66 and the sealing member 70 is omitted, as compared with the differential pressure electrolysis cell 22 described above.

The pressing member 66c includes the sheet portion 86, the metal plate 88, a sealing portion 104, and a reinforcing portion 106. The sealing portion 104 is made of the same material as the sheet portion 86. That is, the sealing portion 104 is formed of a polymer material having an electrical insulating property so as to be elastically deformable. In other words, the sealing portion 104 is formed of a rubber material.

The sealing portion 104 extends in an annular shape (circular annular shape). The sealing portion 104 seals a space between the outer peripheral portion 84 of the membrane electrode assembly 54, which protrudes outward from the second current collector 62 in the planar direction, and the second separator 48b. The sealing portion 104 is formed integrally with the sheet portion 86. In other words, the sealing portion 104 is connected to the outer peripheral end portion of the sheet portion 86.

The sealing portion 104 is adjacent to the second current collector 62 outward in the planar direction (outward in the radial direction). That is, the sealing portion 104 is in contact with or close to the second current collector 62. The sealing portion 104 presses in the A1 direction a portion (an adjacent portion 110) of the electrolyte membrane 74, which is adjacent to a portion (a pressed portion 108) of the electrolyte membrane 74 pressed by the second current collector 62. The adjacent portion 110 is adjacent to the pressed portion 108 outward in the planar direction (see FIG. 6B). The pressure resistant member 72 is in contact with a radially outward end portion of the sealing portion 104.

The reinforcing portion 106 is provided inside the sealing portion 104. The reinforcing portion 106 is made of metal. The reinforcing portion 106 extends annularly along the sealing portion 104. The reinforcing portion 106 is connected to the outer peripheral portion of the metal plate 88. That is, the reinforcing portion 106 and the metal plate 88 are integrally formed. The reinforcing portion 106 has an L-shaped cross section. The reinforcing portion 106 includes an annular extending portion 106a extending radially outward from the metal plate 88, and an annular protruding portion 106b protruding from the extending portion 106a in the A1 direction.

FIG. 6A is a cross-sectional explanatory view of the differential pressure electrolysis cell 22 of FIG. 2. As shown in FIG. 6A, in the differential pressure electrolysis cell 22, the sealing member 70 has a circular cross section. Therefore, a portion (a seal portion 112) of the membrane electrode assembly 54 pressed by the sealing member 70 is separated from the pressed portion 108 of the membrane electrode assembly 54 outward in the planar direction. In this case, the adjacent portion 110 of the electrolyte membrane 74 is not pressed by the sealing member 70. When the pressed portion 108 is pressed in the A1 direction by the second current collector 62 in such a state, the adjacent portion 110 may be deformed so as to bulge toward a gap portion between the second current collector 62 and the sealing member 70 in the A2 direction.

FIG. 6B is a cross-sectional explanatory view of the differential pressure electrolysis cell 22c of FIG. 5. As shown in FIG. 6B, in the differential pressure electrolysis cell 22c according to the third modification, since the sealing portion 104 is integrally formed with the sheet portion 86, the adjacent portion 110 can be pressed by the sealing portion 104. That is, in the differential pressure electrolysis cell 22c, the seal portion 112 is adjacent to the pressed portion 108. Accordingly, the sealing portion 104 prevents a gap from being formed between the second current collector 62 and the pressure resistant member 72, and thus deformation of the adjacent portion 110 can be suppressed.

In addition, according to the differential pressure electrolysis cell 22c according to the third modification, since the sealing portion 104 is integrally formed with the sheet portion 86, the outer diameter of the sealing portion 104 can be reduced as compared with the case where the sealing member 70 is provided separately from the sheet portion 86 as in the differential pressure electrolysis cell 22 described above. In accordance with this feature, it is possible to reduce the outer diameter of the differential pressure electrolysis cell 22c.

In the differential pressure electrolysis cell 22c, a metal reinforcing portion 106 is provided inside the sealing portion 104. In accordance with such a configuration, the adjacent portion 110 can be favorably pressed by the sealing portion 104.

The reinforcing portion 106 extends annularly along the sealing portion 104. In accordance with such a configuration, the adjacent portion 110 can be favorably pressed by the sealing portion 104.

Further, the reinforcing portion 106 is connected to the metal plate 88. In accordance with such a configuration, the rigidity of the reinforcing portion 106 can be increased.

In the differential pressure electrolysis cell 22c, the sealing portion 104 is in contact with or close to the second current collector 62. In accordance with such a configuration, the volume of the gas storage chamber 94 can be reduced, and thus the pressure increasing speed of the gas generated in the second electrode catalyst layer 78 can be increased.

The differential pressure electrolysis cell 22c according to the third modification is not limited to the above-described configuration. The reinforcing portion 106 may be separated from the metal plate 88.

The following supplementary notes are further disclosed in relation to the above-described embodiments.

Supplementary Note 1

The differential pressure electrolysis cell (22, 22a to 22c) according to the present disclosure includes the membrane electrode assembly (54) including the electrolyte membrane (74), the first electrode catalyst layer (76) stacked on one surface of the electrolyte membrane, and the second electrode catalyst layer (78) stacked on the other surface of the electrolyte membrane, the first separator (48a) located across the electrolyte membrane from the second electrode catalyst layer, the second separator (48b) located across the electrolyte membrane from the first electrode catalyst layer, the first current collector (56) disposed between the first separator and the first electrode catalyst layer, the second current collector (62) disposed between the second separator and the second electrode catalyst layer, and the pressing member (66, 66a to 66c) sandwiched and held between the second current collector and the second separator and configured to press the second current collector toward the second electrode catalyst layer, wherein the differential pressure electrolysis cell applies the voltage between the first current collector and the second current collector to electrolyze the fluid supplied to the membrane electrode assembly and thereby generate the gas in the second electrode catalyst layer, and is configured to cause the gas to have the higher pressure than the pressure of the fluid, and the pressing member includes the sheet portion (86, 86a) that is formed of a polymer material having an electrical insulating property so as to be elastically deformable, and is disposed between the second current collector and the second separator in the state of being compressed and deformed in the stacking direction of the membrane electrode assembly.

In accordance with such a configuration, since the sheet portion is formed of the polymer material having an electrical insulating property so as to be elastically deformable, it is possible to suppress variations in the surface pressure of the electrolyte membrane as compared with the case where a plate spring is used as the pressing member. In addition, it is possible to avoid power loss due to extra current flowing through the sheet portion. Therefore, the electrolysis efficiency of the differential pressure electrolysis cell can be improved.

In addition, such a sheet portion is in surface contact with the second separator. That is, the pressure acting on the coating on the second separator can be reduced as compared with the case where a plate spring is used as the pressing member. Therefore, the coating can be prevented from being peeled off by the pressing member. In accordance with this feature, the generation of metal ions due to the peeling of the coating is suppressed, and thus the deterioration of the electrolyte membrane due to the metal ions can be suppressed. Further, metal corrosion due to local energization can be suppressed.

Therefore, the durability of the differential pressure electrolysis cell can be improved. Therefore, a better differential pressure electrolysis cell and a better differential pressure electrolysis stack can be provided.

Supplementary Note 2

In the differential pressure electrolysis cell according to Supplementary Note 1, the pressing member may include the metal plate (88) provided inside the sheet portion.

In accordance with such a configuration, the amount of elastic deformation of the sheet portion in the stacking direction of the membrane electrode assembly can be reduced as compared with a case where the metal plate is not provided in the sheet portion. In other words, the amount of compressive deformation of the sheet portion in the stacking direction when the electrolyte membrane expands due to water absorption can be reduced. Consequently, it is possible to suppress expansion of the electrolyte membrane due to water absorption. That is, the electrolyte membrane can be prevented from spreading outward in the planar direction. That is, blisters of the electrolyte membrane can be suppressed. In addition, since the outer diameter of the sealing portion can be reduced as compared with a case where the sealing member is provided separately from the pressing member, the outer diameter of the differential pressure electrolysis cell can be reduced.

Supplementary Note 3

In the differential pressure electrolysis cell according to Supplementary Note 1, the pressing member may include the metal plate extending in the planar direction of the membrane electrode assembly, and the sheet portion may cover the metal plate from both sides in the stacking direction.

In accordance with such a configuration, the same effects as those of the differential pressure electrolysis cell according to Supplementary Note 2 are exhibited.

Supplementary Note 4

The differential pressure electrolysis cell according to any one of Supplementary Notes 1 to 3 may further include the sealing portion (104) having the annular shape and being formed of the polymer material having the electrical insulating property so as to be elastically deformable and being configured to seal the gap between the second separator and the outer peripheral portion (84) of the membrane electrode assembly protruding outward in the planar direction from the second current collector, wherein the sealing portion may be formed integrally with the sheet portion.

In accordance with such a configuration, since the sealing portion is integrally formed with the sheet portion, the portion (the adjacent portion) of the membrane electrode assembly, which is adjacent to the portion (the pressed portion) of the membrane electrode assembly pressed by the second current collector, can be pressed by the sealing portion. The adjacent portion is adjacent to the pressed portion outward in the planar direction. Therefore, deformation of the adjacent portion (deformation in which the adjacent portion bulges toward the second separator) can be suppressed.

Supplementary Note 5

In the differential pressure electrolysis cell according to Supplementary Note 4, the reinforcing portion (106) made of metal may be provided inside the sealing portion.

In accordance with such a configuration, the adjacent portion can be more favorably pressed by the sealing portion.

Supplementary Note 6

In the differential pressure electrolysis cell according to Supplementary Note 5, the reinforcing portion may extend annularly along the sealing portion.

In accordance with such a configuration, the adjacent portion can be even more favorably pressed by the sealing portion.

Supplementary Note 7

In the differential pressure electrolysis cell according to Supplementary Note 5, the pressing member may include the metal plate provided inside the sealing portion, and the reinforcing portion may be connected to the metal plate.

In accordance with such a configuration, the rigidity of the reinforcing portion can be increased.

Supplementary Note 8

The differential pressure electrolysis cell according to Supplementary Note 4 may further include the pressure resistant member (72) having the annular shape and covering the sealing portion from outside in the planar direction, wherein the pressure resistant member may be in contact with the sealing portion.

In accordance with such a configuration, the pressure resistant member can inhibit the sealing portion from expanding outward in the planar direction due to the gas generated in the second electrode catalyst layer.

Supplementary Note 9

In the differential pressure electrolysis cell according to Supplementary Note 4, the sealing portion may be in contact with or close to the second current collector.

In accordance with such a configuration, the volume of the gas storage chamber can be reduced, and thus the pressure increasing speed of the gas generated in the second electrode catalyst layer can be increased.

Supplementary Note 10

The differential pressure electrolysis stack (10) according to the present disclosure includes the stack of the plurality of differential pressure electrolysis cells, wherein each of the plurality of differential pressure electrolysis cells is the differential pressure electrolysis cell according to any one of Supplementary Notes 1 to 9.

While the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Within a range that does not depart from the essence and gist of the present disclosure, or within a range that does not depart from the gist and essence of the present disclosure derived from the content described in the claims and equivalents thereof, various additions, substitutions, changes, partial deletions, or the like can be made to such embodiments. These embodiments may also be implemented in combination. For example, in the embodiments described above, the order of the operations and the order of the processes are shown as examples, and the present invention is not limited to such operations and processes. The same applies to the case where numerical values or mathematical expressions are used in the description of the above-described embodiments.