Water electrolysis stack and water electrolysis system

Abstract

To provide a water electrolysis stack capable of improving durability.SOLUTION: A water electrolysis stack has a cell laminate in which a plurality of water electrolysis cells are laminated. In the cell laminate, inter-cell regions are formed in adjacent water electrolysis cells, and gas flows in the inter-cell regions during water electrolysis.SELECTED DRAWING: Figure 6

Description

Technical Field

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[0001] This application relates to a water electrolysis stack and a water electrolysis system.

Background Art

[0002] In recent years, hydrogen has attracted attention as a CO2-free energy source. As methods for producing hydrogen, there are alkaline water electrolysis, water electrolysis, and the like.

[0003] Water electrolysis may be carried out using a water electrolysis stack. A water electrolysis stack is usually formed by stacking a plurality of water electrolysis cells each having an electrode body and a pair of separators sandwiching the electrode body. Such a water electrolysis stack has a configuration substantially similar to that of a fuel cell stack. Therefore, using a fuel cell as a water electrolysis cell has been considered. For example, Patent Document 1 discloses a water electrolysis / fuel cell device in which a plurality of water electrolysis fuel cell integrated cells are stacked.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a fuel cell stack is used as a water electrolysis stack, the following problems occur. During power generation, a fuel cell stack circulates cooling water through the region existing between fuel cells to cool the fuel cells. That is, an inter-cell region, which is a space for circulating cooling water, is formed between fuel cells. On the other hand, in a water electrolysis stack, reaction water is supplied to the oxygen electrode to carry out water electrolysis. Although the temperature of the water electrolysis stack rises due to water electrolysis, the temperature rise can be controlled by the reaction water. Therefore, in a water electrolysis stack, it is not essential to circulate cooling water for temperature adjustment through the inter-cell region.

[0006] However, when a fuel cell stack is used as a water electrolysis stack to perform water electrolysis, the presence of an inter-cell region presents the following problems. Typically, the inter-cell region is sandwiched between the oxygen electrode of one adjacent water electrolysis cell and the hydrogen electrode of the other water electrolysis cell. During water electrolysis, the oxygen electrode is supplied with reaction water, so the pressure of the reaction water is applied to the inter-cell region. Also, hydrogen is generated at the hydrogen electrode by water electrolysis, so the pressure of the hydrogen is applied to the inter-cell region. In this way, water electrolysis applies pressure to the inter-cell region inward in the stacking direction. This pressure may cause the inter-cell region to deform. If the inter-cell region deforms, the adjacent water electrolysis cells forming it will also deform, potentially disrupting the sealed structure of the water electrolysis cells and compromising watertightness or airtightness. Thus, water electrolysis stacks with an inter-cell region have room for improvement in their durability.

[0007] Therefore, the main purpose of this disclosure is to provide a water electrolysis stack and a water electrolysis system that can improve durability in light of the above circumstances. [Means for solving the problem]

[0008] This disclosure provides the following aspects for solving the above-mentioned problems.

[0009] The first embodiment is a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, wherein an inter-cell region is formed between adjacent water electrolysis cells in the cell stack, and gas flows through the inter-cell region during water electrolysis.

[0010] The second aspect is a water electrolysis cell in which, in the first aspect, the water electrolysis cell comprises an electrode body having an oxygen electrode catalyst layer disposed on one side of an electrolyte membrane and a hydrogen electrode catalyst layer disposed on the other side, an oxygen electrode separator disposed on the oxygen electrode catalyst layer side of the electrode body, and a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side of the electrode body, wherein in the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator, and in adjacent water electrolysis cells, the oxygen electrode separator of one water electrolysis cell and The hydrogen electrode separator of the other water electrolysis cell is adjacent to the water electrolysis stack, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator. The water electrolysis stack comprises a first communication hole connected to the hydrogen electrode and formed to communicate along the stacking direction, a second communication hole connected to the inter-cell region and formed to communicate along the stacking direction, and a first flow path connecting the first and second communication holes. Hydrogen generated at the hydrogen electrode by water electrolysis flows from the first communication hole to the second communication hole via the first flow path and then to the inter-cell region.

[0011] The third embodiment is a water electrolysis stack comprising a first end plate and a second end plate that sandwich a cell stack from the stacking direction, wherein the opening of a first communication hole and the opening of a second communication hole are arranged on the first end plate, and the first flow path connects the opening of the first communication hole and the opening of the second communication hole on the first end plate.

[0012] The fourth embodiment is a water electrolysis stack that, in the third embodiment, comprises a plurality of first connecting holes and a plurality of second connecting holes, wherein the openings of the plurality of first connecting holes and the openings of the plurality of second connecting holes are arranged on a first end plate, and a first flow path connects one of the openings of the first connecting holes and one of the openings of the second connecting holes on the first end plate, and the remaining openings of the first connecting holes that are not connected to the first flow path are sealed.

[0013] The fifth aspect is a water electrolysis stack that, in the fourth aspect, is provided with two first connecting holes and two second connecting holes.

[0014] The sixth embodiment is a water electrolysis stack in which, in the fifth embodiment, a reaction water supply communication hole and a reaction water discharge communication hole are connected to the oxygen electrode and formed to communicate along the stacking direction, and hydrogen flowing in the inter-cell region is discharged from the second communication hole closest to the reaction water supply communication hole.

[0015] The seventh embodiment is a water electrolysis stack in which, in the fifth embodiment, a reaction water supply communication hole and a reaction water discharge communication hole are connected to the oxygen electrode and formed to communicate along the stacking direction, and hydrogen flowing in the inter-cell region is discharged from the second communication hole closest to the reaction water discharge communication hole.

[0016] The eighth embodiment is a water electrolysis system comprising a water electrolysis stack according to any one of the second to seventh embodiments, a second channel, and a hydrogen supply device arranged in the second channel, wherein the water electrolysis stack is provided with two first connecting holes and two second connecting holes, the second channel connects the first connecting holes, and hydrogen flows from one first connecting hole to the other first connecting hole via the second channel by the hydrogen supply device.

[0017] The ninth aspect is a water electrolysis system in which, in the eighth aspect, the water electrolysis stack is connected to an oxygen electrode and is provided with a reaction water supply communication hole and a reaction water discharge communication hole formed in communication along the stacking direction, and hydrogen flowing in the inter-cell region is discharged from the second communication hole closest to the reaction water supply communication hole.

[0018] The tenth embodiment is a water electrolysis system that, in the eighth or ninth embodiment, includes a gas-liquid separator located upstream of the hydrogen supply device in the second flow path.

[0019] The eleventh embodiment is a water electrolysis system comprising one of the second to seventh embodiments of a water electrolysis stack, a gas-liquid separator, a third channel, and an extrusion water supply device located in the third channel, wherein the water electrolysis stack is provided with two first connecting holes and two second connecting holes, the gas-liquid separator is located in the first channel, and the third channel connects the gas-liquid separator to other first connecting holes that are not connected to the first channel, the extrusion water supplied from the extrusion water supply device flows through the other first connecting holes to the hydrogen electrode, is discharged to the first connecting holes along with the hydrogen generated by water electrolysis at the hydrogen electrode, reaches the gas-liquid separator located in the first channel from the first connecting holes, where the hydrogen is separated and flows into the third channel, and the hydrogen separated by the gas-liquid separator flows to the inter-cell region through the second connecting holes.

[0020] The twelfth embodiment is a water electrolysis system comprising the water electrolysis stack of the first embodiment and a gas supply device for supplying gas to the inter-cell region.

[0021] The 13th embodiment is a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, wherein the water electrolysis cell comprises an electrode body having an oxygen electrode catalyst layer disposed on one side and a hydrogen electrode catalyst layer disposed on the other side with an electrolyte membrane in between, an oxygen electrode separator disposed on the oxygen electrode catalyst layer side of the electrode body, and a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side of the electrode body, wherein in the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator, and in adjacent water electrolysis cells, one water electrolysis cell The water electrolysis stack is a water electrolysis stack in which an oxygen electrode separator and a hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator, and the water electrolysis stack comprises a reaction water supply communication hole and a reaction water discharge communication hole connected to the oxygen electrode and communicating along the stacking direction, two second communication holes connected to the inter-cell region and communicating along the stacking direction, and a fourth flow channel connecting the reaction water supply communication hole or reaction water discharge communication hole to the second communication hole, and reaction water flows through the fourth flow channel to the second communication hole and then to the inter-cell region.

[0022] Aspect 14 is a water electrolysis system comprising a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, a fifth flow path, and a pressed water supply device disposed in the fifth flow path. The water electrolysis cell includes an electrode body having an oxygen electrode catalyst layer disposed on one side and a hydrogen electrode catalyst layer disposed on the other side with an electrolyte membrane interposed therebetween, an oxygen electrode separator disposed on the oxygen electrode catalyst layer side of the electrode body, and a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side of the electrode body. In the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator. In adjacent water electrolysis cells, the oxygen electrode separator of one water electrolysis cell and the hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and a cell-intermediate region is formed between the oxygen electrode separator and the hydrogen electrode separator. The water electrolysis stack includes two first communication holes connected to the hydrogen electrode and communicating along the stacking direction, two second communication holes connected to the cell-intermediate region and communicating along the stacking direction, and a first flow path connecting one of the first communication holes and one of the second communication holes. The fifth flow path connects another first communication hole not connected to the first flow path and another second communication hole not connected to the first flow path. The pressed water supplied from the pressed water supply device flows from another second communication hole not connected to the first flow path through the fifth flow path to another first communication hole not connected to the first flow path and then flows into the cell-intermediate region.

Advantages of the Invention

[0023] According to the present disclosure, deformation of the cell-intermediate region can be suppressed, and the durability of the water electrolysis stack can be improved.

Brief Description of the Drawings

[0024] [Figure 1] It is a perspective view of the water electrolysis stack 100. [Figure 2] It is an exploded perspective view of the water electrolysis cell 10. [Figure 3] It is a partial cross-sectional view of the cell stack 20 cut along the stacking direction, focusing on the cell-intermediate region 21. [Figure 4]This is a schematic diagram of the first end plate 31 as viewed from the stacking direction. [Figure 5] This is a schematic diagram illustrating how deformation occurs in the intercellular region 21. [Figure 6] This is a perspective view of the 200 water electrolysis stack. [Figure 7] This is a cross-sectional view focusing on the first channel 211. [Figure 8] This is a cross-sectional view focusing on the first channel 310. [Figure 9] This is an exploded perspective view focusing on the cell stack 20 and the first end plate 31 in the water electrolysis stack 100. [Figure 10] This is an exploded perspective view focusing on the cell stack 20 and the first end plate 31 in the water electrolysis stack 400. [Figure 11] This is a perspective view of the 500 water electrolysis stack. [Figure 12] This is a block diagram of the 1000 water electrolysis system. [Figure 13] This is a block diagram of the 2000 water electrolysis system. [Figure 14] This is a block diagram of the 3000 water electrolysis system. [Figure 15] This is a block diagram of the 4000 water electrolysis system. [Figure 16] This is a block diagram of a 5000 water electrolysis system. [Figure 17] This is a perspective view of the 600 water electrolysis stack. [Figure 18] This is a block diagram of the 6000 water electrolysis system. [Figure 19] This is a block diagram of the 7000 water electrolysis system. [Modes for carrying out the invention]

[0025] (A) Typical water electrolysis stack First, in describing the water electrolysis stack in this disclosure, a typical water electrolysis stack will be explained using a water electrolysis stack 100 as an example.

[0026] [Water electrolysis stack 100] Figure 1 shows a perspective view of the water electrolysis stack 100. Here, the x-direction in Figure 1 is the longitudinal direction, the y-direction is the short-axis direction, and the z-direction is the stacking direction.

[0027] The water electrolysis stack 100 has a cell stack 20 in which a plurality of water electrolysis cells 10 are stacked. The water electrolysis stack 100 also includes a first end plate 31 and a second end plate 32 that sandwich the cell stack 20 from the stacking direction.

[0028] The water electrolysis stack 100 may optionally have a plate having a predetermined function placed between the first end plate 31 and the cell stack 20. Similarly, optionally, a plate having a predetermined function may be placed between the second end plate 32 and the cell stack 20. Examples include terminal plates, insulating plates, and pressure plates. The terminal plates are equipped with terminals that connect to an external power supply, and when a voltage is applied from the power supply to the terminal plates, a voltage is applied to the cell stack 20 placed between the terminal plates. The insulating plates serve to insulate the terminal plates and end plates. The pressure plates have the function of applying a restraining force to the cell stack 20.

[0029] <Water electrolysis cell 10> The water electrolysis cell 10 is a device for performing water electrolysis. Figure 2 shows an exploded perspective view of the water electrolysis cell 10. As shown in Figure 2, the water electrolysis cell 10 comprises an electrode body 11 and a pair of separators (oxygen electrode separator 12, hydrogen electrode separator 13) arranged on both sides of the electrode body 11. A frame-shaped member 14 is also arranged around the electrode body 11.

[0030] In the water electrolysis cell 10, an oxygen electrode 15 is formed between the electrode body 11 and the oxygen electrode separator 12, and a hydrogen electrode 16 is formed between the electrode body 11 and the hydrogen electrode separator 13 (see Figure 3). The oxygen electrode 15 and the hydrogen electrode 16 are spaces through which fluid can flow. Normally, reaction water (water) flows through the oxygen electrode 15. Normally, hydrogen flows through the hydrogen electrode 16.

[0031] (Electrode body 11) The electrode body 11 has a structure in which an oxygen electrode catalyst layer is arranged on one side of an electrolyte membrane, and a hydrogen electrode catalyst layer is arranged on the other side. That is, the electrode body 11 has an electrolyte membrane, an oxygen electrode catalyst layer arranged on one side of the electrolyte membrane, and a hydrogen electrode catalyst layer arranged on the other side of the electrolyte membrane. The electrode body 11 is a sheet-like member having a substantially rectangular shape when viewed in the stacking direction. However, the shape of the electrode body 11 is not limited to this and may be set as appropriate depending on the purpose. For example, it may be a polygonal shape with pentagons or more, or it may be circular or elliptical.

[0032] The electrolyte membrane is a sheet-like component having proton conductivity. The electrolyte membrane contains a proton-conducting ionomer. The type of proton-conducting ionomer is not particularly limited. Examples include polytetrafluoroethylene and fluoroalkyl polymers such as perfluoroalkyl sulfonic acid polymers. Perfluoroalkyl sulfonic acid polymers may be selected from the viewpoint of durability.

[0033] The oxygen electrode catalyst layer is a sheet-like component containing an oxygen electrode catalyst capable of generating oxygen by water electrolysis. The oxygen electrode catalyst is not particularly limited, but examples include metal catalysts. Examples of metal catalysts include those whose composition includes Pt, Ru, Rh, Os, Ir, Pd, and Au. The metal catalyst may also be an oxide of these metals. Typically, it is platinum or a platinum alloy. The oxygen electrode catalyst may also be an electrically conductive carrier (metal-supported catalyst) on which the metal catalyst is supported. The type of carrier is not particularly limited, but examples include carbon carriers. Furthermore, the oxygen electrode catalyst layer may contain a proton-conducting ionomer. The proton-conducting ionomer is not particularly limited. For example, the above-mentioned proton-conducting ionomers can be used.

[0034] The hydrogen electrode catalyst layer is a sheet-like component containing a hydrogen electrode catalyst capable of generating hydrogen by water electrolysis. The hydrogen electrode catalyst is not particularly limited, but examples include metal catalysts. Examples of metal catalysts include those whose composition includes Pt, Ru, Rh, Os, Ir, Pd, and Au. The metal catalyst may also be an oxide of these metals. Typically, it is platinum or a platinum alloy. The hydrogen electrode catalyst may also be an electrically conductive carrier (metal-supported catalyst) on which the metal catalyst is supported. The type of carrier is not particularly limited, but examples include carbon carriers. Furthermore, the hydrogen electrode catalyst layer may contain a proton-conducting ionomer. The proton-conducting ionomer is not particularly limited. For example, the above-mentioned proton-conducting ionomers can be used.

[0035] (Oxygen electrode separator 12, hydrogen electrode separator 13) The oxygen electrode separator 12 and the hydrogen electrode separator 13 are sheet-like members having a substantially rectangular shape when viewed in the stacking direction. However, the shape of the oxygen electrode separator 12 and the hydrogen electrode separator 13 is not limited to this and may be set as appropriate depending on the purpose. For example, they may be polygonal in shape with pentagons or more, or circular or elliptical. The oxygen electrode separator 12 is placed on the oxygen electrode catalyst layer side of the electrode body 11. The hydrogen electrode separator 12 is placed on the hydrogen electrode catalyst layer side of the electrode body 11. The oxygen electrode separator 12 and the hydrogen electrode separator 13 are formed from a conductive material. Examples include resin materials containing carbon material; and metal materials such as iron, copper, stainless steel, and titanium.

[0036] The oxygen electrode separator 12 is provided with first holes 12a and 12b, a reaction water supply hole 12c, a reaction water discharge hole 12d, and second holes 12e and 12f at both ends in the longitudinal direction. The first holes 12a and 12b are for discharging hydrogen generated by water electrolysis from the water electrolysis cell 10 (hydrogen electrode 16). The reaction water supply hole 12c is for supplying reaction water to the water electrolysis cell 10 (oxygen electrode 15). The reaction water discharge hole 12d is for discharging reaction water from the water electrolysis cell 10 (oxygen electrode 15).

[0037] The hydrogen electrode separator 13 has holes that have the same function as the holes in the oxygen electrode separator 12. Specifically, the hydrogen electrode separator 13 has first holes 13a and 13b, a reaction water supply hole 13c, a reaction water discharge hole 13d, and second holes 13e and 13f at both ends in the longitudinal direction.

[0038] A predetermined flow path is formed on the electrode body 11 side surface of the oxygen electrode separator 12 and the hydrogen electrode separator 13. Specifically, on the electrode body 11 side surface of the oxygen electrode separator 12, a reaction water supply hole 12c is formed from the oxygen electrode 1 5 A reaction water channel (not shown) is formed to guide the reaction water supplied to the electrode body 11 and to guide the reaction water guided to the electrode body 11 to the reaction water discharge hole 12d. On the surface of the hydrogen electrode separator 13 on the electrode body 11 side, the hydrogen electrode 1 is formed by water electrolysis. 6 A hydrogen channel (not shown) is formed to guide the hydrogen generated therein to the first holes 13a and 13b.

[0039] On the outer surface of the oxygen electrode separator 12 or the hydrogen electrode separator 13 (the surface opposite to the electrode body 11 side), a sealing member 17 is arranged that encloses both the second holes (second holes 12e, 12f in the case of the oxygen electrode separator; second holes 13e, 13f in the case of the hydrogen electrode separator) and the central part (the region corresponding to the position of the electrode body 11). In Figure 2, the sealing member 17 is arranged on the outer surface of the oxygen electrode separator 12. By arranging the sealing member 17, leakage of the fluid flowing through the inter-cell region 21 to the outside can be suppressed. The inter-cell region 21 will be described later.

[0040] Furthermore, sealing members 18a to 18d are arranged on the outer surface of the oxygen electrode separator 12 or the hydrogen electrode separator 13, independently surrounding the first hole, the reaction water supply hole, and the reaction water discharge hole, respectively. In Figure 2, the sealing members 18a to 18d are arranged on the outer surface of the oxygen electrode separator 12. By arranging the sealing members 18a to 18d, it is possible to suppress leakage of reaction water, hydrogen, or oxygen to the outside between adjacent water electrolysis cells 10.

[0041] (Frame-shaped member 14) The frame-shaped member 14 is a sheet-like member having a substantially rectangular shape when viewed in the stacking direction. However, the shape of the frame-shaped member 14 is not limited to this and may be set as appropriate depending on the purpose. For example, it may be a polygonal shape with pentagons or more, or it may be circular or elliptical. The frame-shaped member 14 is arranged around the electrode body 11. That is, the frame-shaped member 14 has an opening for arranging the electrode body 11. The material of the frame-shaped member 14 is not particularly limited, but insulating resin can be used as an example.

[0042] The frame-shaped member 14, like the oxygen electrode separator 12 and the hydrogen electrode separator 13, is provided with first holes 14a and 14b, a reaction water supply hole 14c, a reaction water discharge hole 14d, and second holes 14e and 14f at both ends in the longitudinal direction.

[0043] On the side of the frame-shaped member 14 facing the oxygen electrode separator 12, a sealing member (dashed line in Figure 2) is provided that encloses the reaction water supply hole 14c, the reaction water discharge hole 14d, and the electrode body 11 (opening of the frame-shaped member 14) together. This prevents the reaction water and oxygen flowing through the oxygen electrode 15 from leaking to the outside. In addition, on the side of the frame-shaped member 14 facing the oxygen electrode separator 12, sealing members (dashed lines in Figure 2) are provided that independently enclose the first holes 14a and 14b, and the second holes 14e and 14f, respectively.

[0044] On the side of the frame-shaped member 14 facing the hydrogen electrode separator 13, a sealing member (not shown) is provided that encloses the first holes 14a and 14b and the electrode body 11 (the opening of the frame-shaped member 14) together. This prevents hydrogen flowing through the hydrogen electrode 16 from leaking to the outside. In addition, on the side of the frame-shaped member 14 facing the hydrogen electrode separator 13, sealing members (not shown) are provided that independently enclose the reaction water supply hole 14c, the reaction water discharge hole 14d, the second holes 14e and 14f.

[0045] (Water electrolysis reaction in water electrolysis cell 10) The water electrolysis reaction in the water electrolysis cell 10 will now be explained. In the water electrolysis cell 10, when reaction water is supplied to the oxygen electrode 15 and a voltage is applied, a water electrolysis reaction occurs in each catalyst layer. First, reaction water is supplied to the oxygen electrode catalyst layer (solid arrow in Figure 2), where oxygen and protons are produced by the water electrolysis reaction. The generated oxygen is guided along with the reaction water to the reaction water channel formed in the oxygen electrode separator 12 and is removed to the outside through the reaction water discharge hole (dotted arrow in Figure 2). The protons generated in the oxygen electrode catalyst layer permeate the electrolyte membrane and reach the hydrogen electrode catalyst layer. Thereupon, the protons combine with electrons, and hydrogen is generated at the hydrogen electrode 16. The generated hydrogen is guided to the hydrogen channel formed in the hydrogen electrode separator 13 and is discharged to the outside through the first hole (dotted arrow in Figure 2).

[0046] <Cell Laminate 20> The cell laminate 20 is formed by stacking multiple water electrolysis cells 10. The number of stacked water electrolysis cells 10 is not particularly limited and may be set appropriately according to the desired performance ratio. For example, the number of water electrolysis cells 10 in the cell laminate 20 may be between 10 and 100.

[0047] Here, in the cell stack 20, an inter-cell region 21 is formed between adjacent water electrolysis cells 10. Specifically, in adjacent water electrolysis cells 10, the oxygen electrode separator 12 of one water electrolysis cell 10 and the hydrogen electrode separator 13 of the other water electrolysis cell 10 are adjacent to each other, and an inter-cell region 21 is formed between the oxygen electrode separator 12 and the hydrogen electrode separator 13. The outer edge of the inter-cell region 21 is surrounded by a sealing member 17, thereby ensuring watertightness or airtightness. The inter-cell region 21 is formed between each water electrolysis cell 10, but it may also be formed between a water electrolysis cell 10 located on the end face of the cell stack 20 and an end plate (first end plate 31 or second end plate 32).

[0048] Figure 3 shows a partial cross-sectional view of the cell stack 20, cut in the stacking direction, focusing on the inter-cell region 21. As shown in Figure 3, the inter-cell region 21 is the space formed between adjacent water electrolysis cells 10. As described above, the oxygen electrode separator 12 has a sealing member 17 on its outer surface (the surface opposite to the electrode body 11 side) that surrounds the central part and the second holes 12e and 12f together. By stacking the hydrogen electrode separator 13 of the adjacent water electrolysis cell 10 on the sealing member 17, the inter-cell region 21 is formed inside the sealing member 17. Thus, since the outer edge of the inter-cell region 21 is sealed by the sealing member 17, the inter-cell region 21 has a structure that prevents the fluid flowing inside from leaking to the outside.

[0049] <Water electrolysis stack 100> The water electrolysis stack 100 is equipped with first communication holes 100a and 100b, a reaction water supply communication hole 100c, a reaction water discharge communication hole 100d, and second communication holes 100e and 100f. The first communication holes 100a and 100b are connected to the hydrogen electrodes 16 of each water electrolysis cell 10 and are formed to communicate along the stacking direction. The reaction water supply communication hole 100c and the reaction water discharge communication hole 100d are connected to the oxygen electrodes 15 of each water electrolysis cell 10 and are formed to communicate along the stacking direction. The second communication holes 100e and 100f are connected to the inter-cell regions 21 and are formed to communicate along the stacking direction. These communication holes function as a manifold. Figure 4 shows a schematic diagram of the first end plate 31 as viewed from the stacking direction.

[0050] The first connecting holes 100a and 100b typically allow hydrogen generated at the hydrogen electrode of each water electrolysis cell 10 to flow through. The first connecting hole 100a communicates with the first holes 12a, 13a, and 14a of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31a of the first connecting hole 100a is located on the first end plate 31. The first connecting hole 100b communicates with the first holes 12b, 13b, and 14b of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31b of the first connecting hole 100b is located on the first end plate 31. In the water electrolysis stack 100, hydrogen is typically extracted from the openings 31a and 31b. Note that the first connecting holes 100a and 100b typically do not penetrate the second end plate 32.

[0051] As described above, the first communication holes 100a and 100b are connected to the hydrogen electrodes 16 of each water electrolysis cell 10. This means that fluid can flow between the first communication holes 100a and 100b and each hydrogen electrode 16. As described above, a sealing member (not shown) is placed on the side of the frame-shaped member 14 facing the hydrogen electrode separator 13, enclosing the first holes 14a and 14b and the electrode body 11 (opening of the frame-shaped member 14) together. By placing the sealing member in this manner, fluid can flow between the first communication holes 100a and 100b and each hydrogen electrode 16.

[0052] The reaction water supply port 100c is typically through which reaction water supplied to each water electrolysis cell 10 flows. The reaction water discharge port 100d is typically through which reaction water discharged from each water electrolysis cell 10 and oxygen generated at the oxygen electrode 15 by water electrolysis flows. The reaction water supply port 100c is in communication with the reaction water supply ports 12c, 13c, and 14c of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31c of the reaction water supply port 100c is located on the first end plate 31. The reaction water discharge port 100d is in communication with the reaction water discharge ports 12d, 13d, and 14d of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31d of the reaction water discharge port 100d is located on the first end plate 31. In the water electrolysis stack 100, reaction water is typically supplied through opening 31c, and reaction water and oxygen are discharged through opening 31d. Typically, the reaction water supply port 100c and the reaction water discharge port 100d do not penetrate the second end plate 32.

[0053] The reaction water supply port 100c and the reaction water discharge port 100d are connected to the oxygen electrode 15 of each water electrolysis cell 10. This means that fluid can flow between the reaction water supply port 100c and the reaction water discharge port 100d and each oxygen electrode 15. As described above, a sealing member (dashed line in Figure 2) is arranged on the oxygen electrode separator 12 side of the frame-shaped member 14, enclosing the reaction water supply port 14c, the reaction water discharge port 14d, and the electrode body 11 (opening of the frame-shaped member 14) together. By arranging the sealing member in this way, fluid can flow between the reaction water supply port 100c and the reaction water discharge port 100d and each oxygen electrode 15.

[0054] The second communication hole 100e communicates with the second holes 12e, 13e, and 14e of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31e of the second communication hole 100e is located on the first end plate 31. The second communication hole 100f communicates with the second holes 12f, 13f, and 14f of each water electrolysis cell 10 and penetrates the first end plate 31. Therefore, the opening 31f of the second communication hole 100f is located on the first end plate 31. Typically, the second communication holes 100e and 100f do not penetrate the second end plate 32. In the water electrolysis stack 100, the second communication holes 100e and 100f and the inter-cell region 21 are not usually used. The reason for this will be explained later.

[0055] The second communication holes 100e and 100f are connected to each inter-cell region 21. This means that fluid can flow between the second communication holes 100e and 100f and each inter-cell region 21. As described above, a sealing member 17 is arranged on the outer surface of the oxygen electrode separator 12, enclosing the second holes 12e and 12f and the central part together. By arranging the sealing member 17 in this way, fluid can flow between the second communication holes 100e and 100f and each inter-cell region 21.

[0056] As shown in Figure 4, openings 31a, 31c, and 31e are typically located at the right end (one end in the longitudinal direction) of the first end plate 31. Openings 31b, 31d, and 31f are typically located at the left end (the other end in the longitudinal direction) of the first end plate 31. Furthermore, openings 31a, 31c, and 31e are arranged from top to bottom (from one side in the short direction) in the order of openings 31c, 31e, and 31a. On the other hand, openings 31b, 31d, and 31f are arranged from top to bottom (from one side in the short direction) in the order of openings 31b, 31f, and 31d. Thus, openings 31a, 31b, 31c, 31d, and 31e, 31f are each located in opposing positions. However, the arrangement of the openings is not limited to this and may be set as appropriate depending on the purpose.

[0057] <Problems with the Water Electrolysis Stack 100> A method for performing water electrolysis using a water electrolysis stack 100 will be described. First, while applying a voltage to the water electrolysis stack 100, reaction water is supplied to the reaction water supply port 100c. The supplied reaction water is then supplied to the oxygen electrode 15 of each water electrolysis cell 10. Water electrolysis then occurs in each water electrolysis cell 10. The oxygen generated at the oxygen electrode 15 by water electrolysis is discharged together with the reaction water from the reaction water discharge port 100d. The hydrogen generated at the hydrogen electrode 16 by water electrolysis is discharged from the first ports 100a and 100b.

[0058] Thus, when water electrolysis is performed using the water electrolysis stack 100, the inter-cell region 21 and the second communication holes 100e and 100f are not used. The reason for this is as follows.

[0059] In a fuel cell stack, power generation produces water and electricity from hydrogen and oxygen. In contrast, in a water electrolysis stack, water electrolysis produces hydrogen and oxygen from water and electricity. Thus, power generation and water electrolysis have an inverse relationship. For this reason, a water electrolysis stack has almost the same configuration as a fuel cell stack. Therefore, the use of fuel cell stacks as water electrolysis stacks is being considered.

[0060] When generating electricity with a fuel cell stack, the temperature of the fuel cell stack rises due to the power generation. Therefore, cooling water is supplied to the inter-cell region to control the temperature of the fuel cell stack. Thus, the inter-cell region is the region in the fuel cell stack through which cooling water is circulated for temperature control. On the other hand, in a water electrolysis stack, as described above, water electrolysis is performed by supplying reaction water to the oxygen electrode. Although the temperature of the water electrolysis stack rises due to water electrolysis, this temperature rise can be controlled by the reaction water. Therefore, there is no need to circulate additional cooling water to the inter-cell region for temperature control. This is why, in the water electrolysis stack 100, the inter-cell region 21 and the second communication holes 100e and 100f are not normally used during water electrolysis.

[0061] However, when water electrolysis is performed using a water electrolysis stack 100 equipped with intercellular regions 21, the presence of these regions causes the following problems. Figure 5 shows a schematic diagram illustrating the deformation that occurs in the intercellular regions 21. Figure 5 corresponds to Figure 3.

[0062] As shown in Figure 5, since reaction water is supplied to the oxygen electrode 15 of one of the water electrolysis cells 10 flanking the intercell region 21, the pressure of the reaction water is applied to the oxygen electrode separator 12 that forms the intercell region 21. Also, since hydrogen is generated at the hydrogen electrode 16 of the other water electrolysis cell 10 flanking the intercell region 21 by water electrolysis, the pressure of the hydrogen is applied to the hydrogen electrode separator 13 that forms the intercell region 21. In this way, water electrolysis applies pressure to the intercell region 21 inward in the stacking direction. In contrast, since no fluid is supplied to the intercell region 21, the pressure is usually lower than these. Therefore, there is a risk that the intercell region 21 may deform due to the differential pressure between the intercell region 21 and the oxygen electrode 15 or hydrogen electrode 16. Specifically, there is a risk that the oxygen electrode separator 12 or hydrogen electrode separator 13 that forms the intercell region 21 may deform. If the inter-cell region 21 deforms, the sealing structure provided by the sealing member inside the water electrolysis cell 10 may collapse, potentially causing reaction water, oxygen, and hydrogen to leak from the water electrolysis cell 10 to the outside. In other words, the watertightness or airtightness of the water electrolysis cell 10 may be compromised.

[0063] (B) Water electrolysis stack of the present disclosure As described above, when water electrolysis is performed using a water electrolysis stack having intercellular regions, the presence of these regions reduces the durability of the water electrolysis stack. The inventors have found that by circulating gas through the intercellular regions during water electrolysis, deformation of the intercellular regions can be suppressed, thereby improving the durability of the water electrolysis stack. The water electrolysis stack of this disclosure will be described below using various embodiments.

[0064] [First Embodiment] of [Water electrolysis stack 200] A water electrolysis stack 200, which is the first embodiment, will be described. The water electrolysis stack 200 has a first flow channel 211 that connects the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f. In other words, the water electrolysis stack 200 is a configuration in which the first flow channel 211 is provided in the water electrolysis stack 100. Below, only the differences from the water electrolysis stack 100 will be described.

[0065] Figure 6 shows a perspective view of the water electrolysis stack 200. As shown in Figure 6, the water electrolysis stack 200 is equipped with a cover member 210 on the first end plate 31. The cover member 210 has a substantially rectangular parallelepiped shape with a cavity inside, and its surface facing the first end plate 31 has an opening. The cover member 210 is positioned to cover the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f, and a fluid passage (first passage 211) is formed inside it that allows fluid to flow between these communication holes. That is, the first passage 211 is formed from the inner surface of the cover member 210 and a part of the surface of the first end plate 31. Therefore, the first passage 211 can be said to be a passage that connects the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f on the first end plate 31. The cover member 210 is fixed to the surface of the first end plate 31. The method for fixing the cover member 210 to the surface of the first end plate 31 is not particularly limited. For example, the cover member 210 can be attached to the first end plate 31 by bolts, adhesive, welding, etc. The shape of the cover member 210 is not limited to the form shown in Figure 6. Any shape that can form the first flow channel 211 inside is acceptable.

[0066] Figure 7 shows a cross-sectional view focusing on the first channel 211. Figure 7 is a partial cross-sectional view taken along the stacking direction with respect to the first connecting hole 100b and the second connecting hole 100f. As shown in Figure 7, hydrogen generated at the hydrogen electrode 16 by water electrolysis flows from the first connecting hole 100b to the second connecting hole 100f via the first channel 211. The hydrogen flowing through the second connecting hole 100f is then supplied to each inter-cell region 21. In this way, hydrogen flows to each inter-cell region 21 during water electrolysis. The hydrogen supplied to the inter-cell region 21 has a pressure equivalent to that of the hydrogen electrode 16. Normally, the pressure of the hydrogen generated at the hydrogen electrode 16 is higher than the pressure of the reaction water supplied to the oxygen electrode 15. Therefore, by circulating hydrogen to the inter-cell region 21, deformation of the inter-cell region 21 can be suppressed. The hydrogen flowing through the inter-cell region 21 is removed to the outside through the second connecting hole 100e.

[0067] As shown in Figures 6 and 7, the cover member 210 may have an opening 212 on its outer surface 210a that can connect to the outside. This allows some of the hydrogen discharged from the first communication hole 100b to be supplied to the second communication hole 100f, while the remaining hydrogen can be taken out to the outside through the opening 212. This increases the number of openings from which hydrogen can be taken out. However, the opening 212 is optional, and the cover member 210 does not have to have an opening 212.

[0068] (Sealing the opening) In the water electrolysis stack 200, a portion of the openings from which hydrogen is extracted may be sealed. Specifically, the opening 31b of the first connecting hole 100b and the opening 31f of the second connecting hole 100f may be connected by the first flow path 211, while the remaining opening 31a of the first connecting hole 100a that is not connected to the first flow path 211 may be sealed. The method of sealing the opening 31a is not particularly limited. For example, the opening 31a may be filled with resin or the like. This prevents hydrogen from being discharged from the opening 31a, thus limiting the number of openings from which hydrogen is discharged and allowing for simplification of the device.

[0069] Furthermore, if the opening 31a is sealed and the cover member 210 does not have an opening 212, the hydrogen generated at the hydrogen electrode 16 by water electrolysis flows through the first channel 211 from the first communication hole 100b to the second communication hole 100f and the inter-cell region 21, and is discharged from the remaining second communication hole 100e that is not connected to the first channel 211. In this case, it becomes possible to extract hydrogen only from the opening 31e of the second communication hole 100e. This makes it possible to simplify the device and suppress the backflow of hydrogen.

[0070] The mechanism for suppressing hydrogen backflow is as follows: During water electrolysis, if the temperature of the water electrolysis stack 200 decreases, the internal pressure in each water electrolysis cell 10 decreases. As a result, hydrogen that has been discharged from the water electrolysis stack 200 returns to the water electrolysis stack 200. This situation is undesirable from the standpoint of poisoning the water electrolysis cell 10. In contrast, if the only opening for hydrogen discharge is the opening 31e of the second communication hole 100e, hydrogen flows from the water electrolysis cell 10 (hydrogen electrode 16) through the first communication hole 100b, the first flow path 211, the second communication hole 100f, the inter-cell region 21, and the second communication hole 100e in this order, and is discharged from the opening 31a. Therefore, even if hydrogen is drawn in through the opening 31a due to a decrease in internal pressure, the hydrogen must pass through these communication holes and the inter-cell region 21, making it difficult for it to reach the water electrolysis cell 10 (hydrogen electrode 16). Thus, these communication holes and intercellular regions 21, especially the large-capacity intercellular regions 21, act as buffers, thereby exhibiting a hydrogen backflow suppression effect.

[0071] Furthermore, while the hydrogen backflow suppression effect is still observed when the cover member 210 has an opening 212, the hydrogen backflow suppression effect is significantly improved when the cover member 210 does not have an opening 212 (i.e., hydrogen is discharged only from the opening 31e).

[0072] The water electrolysis stack 200 is provided with two first connecting holes (100a, 100b) and two second connecting holes (100e, 100f). However, the water electrolysis stack of the present disclosure may be provided with three or more first connecting holes. In this case, the remaining openings of the first connecting holes that are not connected to the first flow path may be sealed. Of the remaining openings of the first connecting holes, at least one opening or all openings may be sealed. The water electrolysis stack of the present disclosure may also be provided with three or more second connecting holes. In this case, the remaining openings of the second connecting holes that are not connected to the first flow path may be sealed, excluding the openings of the second connecting holes connected to the first flow path and the openings of the second connecting holes for hydrogen extraction. Of the remaining openings of the second connecting holes, at least one opening or all openings may be sealed. However, from the standpoint of simplifying the device, the number of first and second communication holes may be set to two each.

[0073] The first embodiment of the water electrolysis stack 200 has been described above. By providing a first flow path 211 in the water electrolysis stack 200, hydrogen can be circulated into the inter-cell region 21 during water electrolysis, thereby increasing the internal pressure of the inter-cell region 21 and suppressing deformation of the inter-cell region 21. Therefore, the durability of the water electrolysis stack 200 can be improved.

[0074] [Second Embodiment] of [Water electrolysis stack 300] A second embodiment, the water electrolysis stack 300, will now be described. The water electrolysis stack 300 differs from the water electrolysis stack 200 in the following respects. Specifically, the water electrolysis stack 200 has a first flow path 211 (cover member 210) on the first end plate 31 that connects the first communication hole 100b and the second communication hole 100f, while the water electrolysis stack 300 has a first flow path 310 that connects the first communication hole 100b and the second communication hole 100f at a position away from the first end plate 31.

[0075] Figure 8 shows a cross-sectional view focusing on the first channel 310. As shown in Figure 8, the first channel 310 is a pipe that connects the first communication hole 100b and the second communication hole 100f at a position away from the first end plate 31. This solves the problem of not being able to connect the first communication hole 100b and the second communication hole 100f on the first end plate 31 by using the first channel 310. The first channel 310 may also have an opening 312 that can be connected to the outside, similar to the cover member 210. In Figure 8, the first channel 310 is shown with a C-shape, but the shape of the first channel 310 is not limited to this. The first channel 310 may consist of a single pipe or multiple pipes.

[0076] [Third Embodiment] of [Water electrolysis stack 400] A third embodiment, the water electrolysis stack 400, will now be described. The water electrolysis stack 400 differs from the water electrolysis stack 200 in the following respects. Specifically, the water electrolysis stack 200 has a first flow path 211 (cover member 210) on the first end plate 31 that connects the first communication hole 100b and the second communication hole 100f, while the water electrolysis stack 400 has a first flow path inside that connects the first communication hole 100b and the second communication hole 100f.

[0077] Figure 9 shows an exploded perspective view of the water electrolysis stack 100, focusing on the cell stack 20 and the first end plate 31. As described above, a sealing member 17 is placed on the outer surface of the water electrolysis cell 10 (oxygen electrode separator 12). Normally, the sealing member 17 encloses the second holes 12e and 12f together with the central part (the region corresponding to the position of the electrode body 11). In contrast, the inventors have found that by changing the shape of these sealing members 17, the first communication hole 100b and the second communication hole 100f can be connected inside the water electrolysis stack 400.

[0078] Figure 10 shows an exploded perspective view of the water electrolysis stack 400, focusing on the cell stack 20 and the first end plate 31. As shown in Figure 10, a sealing member 417 is placed on the outer surface of the water electrolysis cell 10 (oxygen electrode separator 12) located on the outermost surface of the cell stack 20, enclosing the first hole 12b in addition to the second holes 12e and 12f and the central part. This allows the first communication hole 100b and the second communication hole 100f to be connected inside the water electrolysis stack 400. The first communication holes 100b and 100e can also be connected. Therefore, the flow path (communication hole) connecting these communication holes can be said to be the first flow path in the water electrolysis stack 400. In this way, by connecting the first communication hole 100b and the second communication hole 100e or 100f inside the water electrolysis stack 400, the structure of the device can be further simplified.

[0079] In the water electrolysis stack 400, the sealing member 417 is placed on the water electrolysis cell 10 located on the end face of the cell stack 20, but the sealing member 417 may also be placed on the water electrolysis cell 10 inside the cell stack 20. In other words, the sealing member 17 placed between the water electrolysis cells 10 may be changed to the sealing member 417. Even in this case, the first communication hole 100b and the second communication hole 100f can be connected inside the water electrolysis stack 400.

[0080] [Fourth Embodiment] of [Water electrolysis stack 500] A fourth embodiment, the water electrolysis stack 500, will now be described. The water electrolysis stack 500 differs from the water electrolysis stack 200 in the following respects. Specifically, the water electrolysis stack 200 has a first flow path 211 (cover member 210) connecting the first communication hole 100b and the second communication hole 100f, while the water electrolysis stack 500 has a first flow path 511 (cover member 510) connecting the first communication hole 100a and the second communication hole 100e. Thus, the position of the first flow path differs between the water electrolysis stack 500 and the water electrolysis stack 200.

[0081] Figure 11 shows a perspective view of the water electrolysis stack 500. As shown in Figure 11, the water electrolysis stack 500 is equipped with a cover member 510 on the first end plate 31. The shape of the cover member 510 is the same as that of the cover member 210. The cover member 510 is positioned to cover the opening 31a of the first communication hole 100a and the opening 31e of the second communication hole 100e, and a fluid passage (first passage 511) is formed inside the cover member 510 through which fluid can flow between these communication holes. That is, the first passage 511 is formed from the inner surface of the cover member 510 and a part of the surface of the first end plate 31. The shape of the first passage 511 is the same as that of the first passage 211. Therefore, the first passage 511 can be said to be a passage that connects the opening 31a of the first communication hole 100a and the opening 31e of the second communication hole 100e on the first end plate 31.

[0082] By using the cover member 510, hydrogen flows as follows: Hydrogen generated at the hydrogen electrode 16 by water electrolysis flows from the first communication hole 100a to the second communication hole 100e via the first flow path 511. The hydrogen flowing through the second communication hole 100e is then supplied to each inter-cell region 21. Therefore, during water electrolysis, hydrogen flows to each inter-cell region 21. The hydrogen flowing through the inter-cell region 21 is then discharged to the outside through the second communication hole 100f. In this way, the water electrolysis stack 500 achieves the same effect as the water electrolysis stack 200.

[0083] On the other hand, due to the difference in the arrangement of the first flow path, the water electrolysis stack 200 and the water electrolysis stack 500 differ in the following respects.

[0084] In the water electrolysis stack 200, hydrogen generated at each hydrogen electrode 16 by water electrolysis flows through the first channel 211 from the first communication hole 100b to the second communication hole 100f, and then flows to each inter-cell region 21. The hydrogen is then discharged from the second communication hole 100e. As is clear from Figure 4, the second communication hole 100e is the second communication hole closest to the reaction water supply communication hole 100c. Since the water electrolysis reaction is an exothermic reaction, the temperature of the generated hydrogen is higher than the temperature of the reaction water supplied to the water electrolysis stack 200. Therefore, by passing the hydrogen through the second communication hole 100e, which is closest to the reaction water supply communication hole 100c, and discharging it from there, the temperature of the hydrogen can be lowered. Hydrogen generated by water electrolysis may be stored in a hydrogen tank. In this case, the hydrogen may be stored in a compressed state. When comparing hydrogen at the same pressure, the compression efficiency of hydrogen at a lower temperature is higher than that of hydrogen at a higher temperature. Therefore, when storing hydrogen in a compressed state, a lower hydrogen temperature is preferable.

[0085] In contrast, in the water electrolysis stack 500, the hydrogen generated at each hydrogen electrode 16 by water electrolysis flows through the first channel 511 from the first connecting hole 100a to the second connecting hole 100e, and then flows to each inter-cell region 21. The hydrogen is then discharged from the second connecting hole 100f. As is clear from Figure 4, the second connecting hole 100f is the second connecting hole closest to the reaction water discharge connecting hole 100d. As mentioned above, since the water electrolysis reaction is an exothermic reaction, the temperature of the reaction water discharged from the water electrolysis stack 500 is higher than the temperature of the reaction water supplied to the water electrolysis stack 500. Therefore, the temperature of the hydrogen discharged from the second connecting hole 100f is higher than the temperature of the hydrogen discharged from the second connecting hole 100e. When the generated hydrogen is to be immediately burned as a heat source, or when producing ammonia or methane, a higher hydrogen temperature is preferable.

[0086] Here, the water electrolysis stack 500 uses a first channel 511 formed on the first end plate 31, but the form of the first channel applicable to the water electrolysis stack 500 is not limited to this. For example, the first channel of the water electrolysis stack 500 may have the same configuration as the first channel 310 which is a pipe, or it may have the same configuration as the first channel which is a communication hole. In either configuration, the same effect is achieved.

[0087] [Fifth Embodiment] Water electrolysis stack ] A fifth embodiment of the water electrolysis stack of the present disclosure will now be described. The fifth embodiment differs from the water electrolysis stack 200 in the following respects. In the water electrolysis stack 200, hydrogen was circulated into the inter-cell region 21 using the first flow path 211 (cover member 210), but in the fifth embodiment, gas is supplied from the outside to the second communication hole 100e or the second communication hole 100f, and the gas is circulated into the inter-cell region 21. In other words, the water electrolysis stack 100 can be used as is in the fifth embodiment.

[0088] The method for supplying gas to the second communication hole 100e or the second communication hole 100f is not particularly limited, but for example, a gas supply device described later may be used. The type of gas introduced into the inter-cell region 21 is not particularly limited. For example, air, oxygen, hydrogen, or an inert gas (such as nitrogen) may be used.

[0089] The pressure of the gas introduced into the inter-cell region 21 is not particularly limited, but if the gas pressure is too low, the deformation suppression effect of the inter-cell region 21 will be reduced. Comparing the pressure of the oxygen electrode 15 and the pressure of the hydrogen electrode 16, the pressure of the hydrogen electrode 16 is typically higher. Therefore, considering this relationship, the pressure of the gas supplied to the inter-cell region 21 may be set to be equal to or greater than the pressure of the oxygen electrode 15. From the viewpoint of significantly suppressing the deformation of the inter-cell region 21, the pressure of the gas supplied to the inter-cell region 21 may be set to 90% or more of the pressure of the hydrogen electrode 16, and may be equal to or greater than the pressure of the hydrogen electrode 16. There is no particular upper limit to the pressure of the gas supplied to the inter-cell region 21. However, considering the load applied to the water electrolysis stack, the pressure of the gas supplied to the inter-cell region 21 may be set to 110% or less of the pressure of the hydrogen electrode 16.

[0090] If the pressure at the oxygen electrode 15 is greater than the pressure at the hydrogen electrode 16, the pressure of the gas supplied to the intercellular region 21 may be greater than or equal to the pressure at the hydrogen electrode 16, greater than or equal to 90% of the pressure at the oxygen electrode 15, or greater than or equal to the pressure at the oxygen electrode 15. Alternatively, the pressure of the gas supplied to the intercellular region 21 may be less than or equal to 110% of the pressure at the oxygen electrode 16.

[0091] The pressure at the oxygen electrode 15 is equivalent to the pressure of the reaction water supplied to the water electrolysis stack 100. The pressure of the reaction water can be measured using a pressure measuring device. Alternatively, the pressure of the reaction water supply device that supplies the reaction water may be referenced. The pressure at the hydrogen electrode 16 is equivalent to the pressure of the hydrogen discharged from the water electrolysis stack 100. The pressure of the hydrogen discharged from the water electrolysis stack 100 can be measured using a pressure measuring device.

[0092] The water electrolysis stack of the present disclosure has been described above using each embodiment. The water electrolysis stack of the present disclosure can circulate gas in the inter-cell region during water electrolysis. This suppresses deformation of the inter-cell region and improves the durability of the water electrolysis stack.

[0093] (C) Typical water electrolysis system First, in describing the water electrolysis system of this disclosure, a typical water electrolysis system will be described using a water electrolysis system 1000 as an example. The water electrolysis system 1000 uses a water electrolysis stack 100.

[0094] [Water electrolysis system 1000] Figure 12 shows a block diagram of the water electrolysis system 1000. As shown in Figure 12, the water electrolysis system 1000 comprises a water electrolysis stack 100, a power supply 1100, a reaction water supply device 1200, a reaction water supply channel 1210, a reaction water discharge channel 1220, and a hydrogen discharge channel 1300. The water electrolysis system 1000 may also include gas-liquid separators 1410 and 1420. Furthermore, it may include a circulation channel 1230 for circulating the reaction water.

[0095] <Water electrolysis stack 100> As the water electrolysis stack 100 has been described above, its explanation will be omitted here.

[0096] <Power supply 1100> The power supply 1100 is a device for supplying direct current to the water electrolysis stack 100. Such power supplies 1100 are well known. Water electrolysis occurs by supplying reaction water to the water electrolysis stack 100 while passing an electric current through it.

[0097] <Reaction water supply device 1200> The reaction water supply device 1200 is a device that supplies reaction water to each oxygen electrode 15 of the water electrolysis stack 100. The reaction water supply device 1200 may supply reaction water to the water electrolysis stack 100 under pressure. Examples of the reaction water supply device 1200 include known pumps.

[0098] <Reaction water supply channel 1210> The reaction water supply channel 1210 is a pipe connecting the water electrolysis stack 100 and the reaction water supply device 1200. The reaction water supply channel 1210 has the role of carrying reaction water supplied from the reaction water supply device 1200 to the water electrolysis stack 100. The reaction water supply channel 1210 is connected to the opening 31c of the reaction water supply communication hole 100c of the water electrolysis stack 100.

[0099] <Reaction water discharge channel 1220> The reaction water discharge channel 1220 is a pipe connected to the water electrolysis stack 100. If the water electrolysis system 1000 is equipped with a gas-liquid separator 1410, the reaction water discharge channel 1220 connects the water electrolysis stack 100 to the gas-liquid separator 1410. The reaction water discharge channel 1220 has the role of carrying the reaction water discharged from the water electrolysis stack 100. The reaction water discharge channel 1220 is connected to the opening 31d of the reaction water discharge communication hole 100d of the water electrolysis stack 100.

[0100] <Hydrogen discharge channel 1300> The hydrogen discharge channel 1300 is a pipe connected to the water electrolysis stack 100. If the water electrolysis system 1000 is equipped with a gas-liquid separator 1420, the hydrogen discharge channel 1300 connects the water electrolysis stack 100 to the gas-liquid separator 1420. The hydrogen discharge channel 1300 has the role of carrying hydrogen discharged from the water electrolysis stack 100. Reaction water may also flow through the hydrogen discharge channel 1300. This is because reaction water may permeate the electrode body 11 and move from the oxygen electrode 15 to the hydrogen electrode 16. For this reason, the water electrolysis system 1000 may be equipped with a gas-liquid separator 1420 to remove the reaction water flowing through the hydrogen discharge channel 1300.

[0101] Figure 1 2 As shown, the hydrogen discharge channel 1300 has a first pipe 1310 and a second pipe 1320. The first pipe 1310 is connected to the opening 31a of the first communication hole 100a of the water electrolysis stack 100. If the water electrolysis system 1000 includes a gas-liquid separator 1420, the first pipe 1310 connects the opening 31a of the first communication hole 100a of the water electrolysis stack 100 to the gas-liquid separator 1420. The second pipe 1320 connects the opening 31b of the first communication hole 100b of the water electrolysis stack 100 to the first pipe 1310.

[0102] <Gas-liquid separator 1410, 1420> The gas-liquid separators 1410 and 1420 are devices that have the function of separating gaseous and liquid components. Gas-liquid separator 1410 separates oxygen from the reaction water supplied from the reaction water discharge channel 1220. The separated reaction water may be sent to the reaction water supply device 1200 via the circulation channel 1230, or it may be discharged to the outside. The separated oxygen may be sent to the oxygen tank, or it may be discharged to the outside. Gas-liquid separator 1420 separates hydrogen from the reaction water supplied from the hydrogen discharge channel 1300. The separated reaction water may be discharged to the outside. The separated hydrogen may be sent to the hydrogen tank, or it may be discharged to the outside.

[0103] <Circulation channel 1230> The circulation channel 1230 is a pipe connecting the gas-liquid separator 1410 and the reaction water supply device 1200. The circulation channel 1230 serves to carry the reaction water separated by the gas-liquid separator 1410. By providing the circulation channel 1230, the reaction water can be circulated between the water electrolysis stack 100 and the reaction water supply device 1200.

[0104] (D) Water electrolysis system of the present disclosure Next, a water electrolysis system using the water electrolysis stack of this disclosure will be described using various embodiments.

[0105] [First Embodiment] of [Water electrolysis system 2000] The first embodiment, the water electrolysis system 2000, will now be described. The water electrolysis system 2000 differs from the water electrolysis system 1000 mainly in that the water electrolysis stack 100 has been replaced with a water electrolysis stack 200. Below, only the differences from the water electrolysis system 1000 will be described.

[0106] Figure 13 shows a block diagram of the water electrolysis system 2000. As shown in Figure 13, the water electrolysis system 2000 includes a water electrolysis stack 200. The water electrolysis system 2000 also has a hydrogen discharge channel 2300 instead of a hydrogen discharge channel 1300. 。 The hydrogen discharge channel 2300 has a first pipe 2310, a second pipe 2320, and a third pipe 2330.

[0107] In the water electrolysis stack 200, hydrogen generated by water electrolysis flows through the first channel 211 from the first communication hole 100b to the second communication hole 100f, then flows through the inter-cell regions 21, and is subsequently discharged from the second communication hole 100e (opening 31e). Hydrogen is also discharged from the first communication hole 100a (opening 31a). Furthermore, hydrogen is discharged from the opening 212 of the cover member 210. Thus, in the water electrolysis stack 200, there are three openings from which hydrogen is discharged. Therefore, the hydrogen discharge channel 2300 requires three pipes.

[0108] As described above, the first pipe 2310 is connected to the opening 31a of the first communication hole 100a of the water electrolysis stack 100. If the water electrolysis system 2000 is equipped with a gas-liquid separator 1420, the first pipe 2310 connects the opening 31a of the first communication hole 100a of the water electrolysis stack 100 to the gas-liquid separator 1420. The second pipe 2320 connects the opening 212 of the cover member 210 to the first pipe 2310. The third pipe 2330 connects the opening 31e of the second communication hole 100e of the water electrolysis stack 100 to the first pipe 2310. This connects all openings for hydrogen discharge to the hydrogen discharge channel 2300.

[0109] In this case, the opening 31a of the first communication hole 100a of the water electrolysis stack 100 may be sealed. In that case, the hydrogen discharge channel 2300 does not need to have the first pipe 2310. In that case, either the second pipe 2320 or the third pipe 2330 may be connected to the gas-liquid separator 1420, and the other pipe may be merged with the other pipe. Also, if the cover member 210 does not have an opening 212, the hydrogen discharge channel 2300 does not need to have the second pipe 2320.

[0110] The water electrolysis system 2000 has been described above. The water electrolysis stack 200 was used in the water electrolysis system 2000. However, water electrolysis stacks 300, 400, and 500 are also applicable to the water electrolysis system 2000. However, when applying water electrolysis stack 500 to the water electrolysis system 2000, the shape of the hydrogen discharge channel needs to be appropriately modified because the opening from which hydrogen is discharged is different.

[0111] [Second Embodiment] of [Water electrolysis system 3000] A second embodiment of the water electrolysis system 3000 will now be described. The water electrolysis system 3000 differs from the water electrolysis system 2000 in the following respects. Specifically, the water electrolysis system 3000 includes a second flow path 3500 connecting the first communication holes 100a and 100b, and a hydrogen supply device 3510. Furthermore, the water electrolysis system 3000 in the second embodiment may also include a gas-liquid separator 3520.

[0112] Figure 14 shows a block diagram of the water electrolysis system 3000. The second flow path 3500 is a pipe connecting the first communication holes 100a and 100b. In reality, the water electrolysis stack 200 is equipped with a cover member 210 that connects the first communication hole 100b and the second communication hole 100f. Therefore, the second flow path 3500 connects the opening 212 of the first flow path 211 and the opening 31a of the first communication hole 100a. This allows the first communication holes 100a and 100b to be connected in a way that allows gas to flow. As shown in Figure 14, the second flow path 3500 may consist of multiple pipes.

[0113] The hydrogen supply device 3510 is located in the second flow path 3500 and applies pressure to the hydrogen flowing through the second flow path 3500. This causes the hydrogen to circulate between the first communication holes 100a and 100b. The hydrogen supply device 3510 is, for example, a pump.

[0114] The gas-liquid separator 3520 is positioned upstream of the hydrogen supply device 3510 (on the side of the first communication hole 100b) in the second flow path 3500. The gas-liquid separator 3520 separates the hydrogen and reaction water supplied from the first communication hole 100b. This is because, in addition to the hydrogen generated by water electrolysis, reaction water that has permeated from the oxygen electrode 15 to the hydrogen electrode 16 also flows through the first communication hole 100b.

[0115] The movement of hydrogen in the water electrolysis system 3000 is described below. Hydrogen generated at each hydrogen electrode 16 by water electrolysis flows from the first communication hole 100b to the second communication hole 100f via the first flow path 211, flows through the inter-cell region 21, and is discharged from the second communication hole 100e. On the other hand, hydrogen flows from the first communication hole 100b through the opening 212 to the second flow path 3500, and reaches the hydrogen supply device 3510 via the gas-liquid separator 3520. Then, the hydrogen is pushed out by the hydrogen supply device 3510, flows through the first communication hole 100a, flows through each hydrogen electrode 16, and is supplied to the first communication hole 100b. In this way, by using the second flow path 3500, hydrogen circulates through each hydrogen electrode 16 and each inter-cell region 21 via the first communication holes 100a and 100b and the second flow path. Therefore, the opening from which hydrogen is discharged is the opening 31e of the second communication hole 100e.

[0116] Thus, with the water electrolysis system 3000, by applying pressure and circulating hydrogen, hydrogen accumulations remaining in each hydrogen electrode 16, etc., can be flushed out. In other words, hydrogen accumulation can be suppressed. Furthermore, by suppressing hydrogen accumulation, the hydrogen supply efficiency of the water electrolysis stack 200 can be improved. In addition, the water electrolysis system 3000 can reduce the number of hydrogen discharge openings, thus contributing to the simplification of the device.

[0117] As described above, in the fuel cell stack 200, the only opening from which hydrogen is discharged is the opening 31e of the second communication hole 100e. Therefore, the hydrogen discharge channel 3300 may consist only of piping connecting the opening 31e of the second communication hole 100e of the water electrolysis stack 200.

[0118] The water electrolysis system 3000 has been described above. The water electrolysis stack 200 was used in the water electrolysis system 3000. However, water electrolysis stacks 300, 400, and 500 are also applicable to the water electrolysis system 3000. However, when applying the water electrolysis stack 500 to the water electrolysis system 3000, the shape of the hydrogen discharge channel needs to be appropriately modified because the opening from which hydrogen is discharged is different.

[0119] [Third Embodiment] of [Water electrolysis system 4000] A third embodiment, the water electrolysis system 4000, will now be described. The water electrolysis system 4000 differs from the water electrolysis system 2000 in the following respects. Specifically, the water electrolysis system 4000 includes a gas-liquid separator 4610, a third flow path 4620, and an extrusion water supply device 4630. Furthermore, the 4000 water electrolysis system uses a 300 water electrolysis stack.

[0120] Figure 15 shows a block diagram of the water electrolysis system 4000. In Figure 15, the first channel 3 10 is also shown in the diagram. The gas-liquid separator 4610 is located in the first channel 310. The third channel 4620 is connected to the gas-liquid separator 4610 and the first channel 3This is a pipe that connects to the opening 31a of the first communication hole 100a, which is not connected to 10. As shown in Figure 15, the third flow path 4620 may consist of multiple pipes. The extrusion water supply device 4630 is located in the third flow path 4620 and supplies extrusion water (water) to the water electrolysis stack 300. The extrusion water supply device 4630 is, for example, a pump. The hydrogen discharge flow path 4300 is connected to the opening 31e of the second communication hole 100e. In the water electrolysis system 4000, the hydrogen discharge flow path 4300 may consist of a single pipe.

[0121] The movement of the extrusion water will now be explained. The extrusion water supplied from the extrusion water supply device 4630 flows through each hydrogen electrode 16 via the first communication hole 100a. The extrusion water that reaches the hydrogen electrode 16 is discharged to the first communication hole 100b along with the hydrogen generated by water electrolysis. The extrusion water flowing through the first communication hole 100b reaches the gas-liquid separator 4610 located in the first flow path 310, where hydrogen is separated from the extrusion water. The extrusion water then flows through the third flow path 4620 and reaches the extrusion water supply device 4630. In this way, the extrusion water circulates between each hydrogen electrode 16 and the gas-liquid separator 4610 via the first communication holes 100a and 100b, the first flow path 210, and the third flow path 4620.

[0122] The hydrogen separated by the gas-liquid separator 4620 flows through the first channel 310 and through the second communication hole 100f to each inter-cell region 21. The hydrogen discharged from each inter-cell region 21 flows through the second communication hole 100e and is discharged to the hydrogen discharge channel 4300. In this way, hydrogen flows to each inter-cell region 21 during water electrolysis, which improves the durability of the water electrolysis stack.

[0123] According to the water electrolysis system 4000, by circulating the extruded water, hydrogen accumulations remaining in each hydrogen electrode 16 can be flushed out. In other words, hydrogen accumulation can be suppressed. Furthermore, by suppressing hydrogen accumulation, the hydrogen supply efficiency of the water electrolysis stack 300 can be improved. In addition, according to the water electrolysis system 4000, the only opening from which hydrogen is discharged is the opening 31e of the second communication hole 100e. Therefore, the number of openings from which hydrogen is discharged can be reduced, which also contributes to simplifying the device. Furthermore, according to the water electrolysis system 4000, hydrogen is separated from the extruded water using a gas-liquid separator 4610 in the first flow path 310. Then, only hydrogen is circulated to each inter-cell region 21 and discharged from the second communication hole 100e. Here, since the second communication hole 100e is close to the reaction water supply communication hole 100c, the temperature of the hydrogen can be lowered by passing it through the second communication hole 100e before discharging it to the outside. Furthermore, this method significantly lowers the temperature of the hydrogen compared to the case where hydrogen is discharged from the second communication hole 100e along with the extruded water. This is because hydrogen alone has a smaller heat capacity than extruded water accompanied by hydrogen. The effects of obtaining hydrogen at a lower temperature have been described above.

[0124] The above describes the Water Electrolysis System 4000. The Water Electrolysis System 4000 allows for efficient hydrogen extraction while improving the durability of the water electrolysis stack.

[0125] [Fourth Embodiment] of [Water electrolysis system 5000] A fourth embodiment, the water electrolysis system 5000, will now be described. The water electrolysis system 5000 is a configuration in which a gas supply device 5700 is added to the water electrolysis system 1000.

[0126] Figure 16 shows a block diagram of the water electrolysis system 5000. As shown in Figure 16, the water electrolysis system 5 The 000 comprises a gas supply device 5700, a gas supply channel 5710, and a gas discharge channel 5720.

[0127] The gas supply device 5700 is a device that supplies gas to each inter-cell region 21 of the water electrolysis stack 100. The type of gas introduced into the inter-cell region 21 is not particularly limited. Examples include air, oxygen, hydrogen, and inert gases (such as nitrogen). The gas supply device 5700 is, for example, a pump. The gas supply channel 5710 connects the gas supply device 5700 to one of the second communication holes 100e and 100f of the water electrolysis stack 100. The gas discharge channel 5720 connects the gas supply device 5700 to the other of the second communication holes 100e and 100f of the water electrolysis stack 100. In Figure 16, the gas supply channel 5710 connects the gas supply device 5700 to the opening 31e of the second communication hole 100e of the water electrolysis stack 100. The gas discharge channel 5720 connects the gas supply device 5700 to the opening 31f of the second communication hole 100f of the water electrolysis stack 100.

[0128] The pressure of the gas introduced into the inter-cell region 21 is not particularly limited, but if the gas pressure is too low, the deformation suppression effect of the inter-cell region 21 will be reduced. Comparing the pressure of the oxygen electrode 15 and the pressure of the hydrogen electrode 16, the pressure of the hydrogen electrode 16 is typically higher. Therefore, considering this relationship, the pressure of the gas supplied to the inter-cell region 21 may be set to be equal to or greater than the pressure of the oxygen electrode 15. From the viewpoint of significantly suppressing the deformation of the inter-cell region 21, the pressure of the gas supplied to the inter-cell region 21 may be set to 90% or more of the pressure of the hydrogen electrode 16, and may be equal to or greater than the pressure of the hydrogen electrode 16. There is no particular upper limit to the pressure of the gas supplied to the inter-cell region 21. However, considering the load applied to the water electrolysis stack, the pressure of the gas supplied to the inter-cell region 21 may be set to 110% or less of the pressure of the hydrogen electrode 16.

[0129] If the pressure at the oxygen electrode 15 is greater than the pressure at the hydrogen electrode 16, the pressure of the gas supplied to the intercellular region 21 may be greater than or equal to the pressure at the hydrogen electrode 16, greater than or equal to 90% of the pressure at the oxygen electrode 15, or greater than or equal to the pressure at the oxygen electrode 15. Alternatively, the pressure of the gas supplied to the intercellular region 21 may be less than or equal to 110% of the pressure at the oxygen electrode 16.

[0130] The pressure at the oxygen electrode 15 is equivalent to the pressure of the reaction water supplied to the water electrolysis stack. The pressure of the reaction water can be measured using a pressure measuring device. Alternatively, the pressure of the reaction water supply device that supplies the reaction water may be referred to. The pressure at the hydrogen electrode 16 is equivalent to the pressure of the hydrogen discharged from the water electrolysis stack. The pressure of the hydrogen discharged from the water electrolysis stack can be measured using a pressure measuring device.

[0131] The water electrolysis system of the present disclosure has been described above using each embodiment. The water electrolysis system of the present disclosure can circulate gas in the inter-cell region during water electrolysis. This suppresses deformation of the inter-cell region and improves the durability of the water electrolysis stack.

[0132] (E) Modified Water Electrolysis Stacks of the Disclosure The water electrolysis stack described above is a configuration in which gas flows through the intercellular region during water electrolysis. This is to increase the pressure in the intercellular region and suppress deformation of the intercellular region due to the pressure of the adjacent hydrogen or oxygen electrode. In contrast, it is thought that a similar effect can be achieved by flowing a liquid (such as water) instead of gas through the intercellular region, thereby increasing the pressure in the intercellular region. Therefore, the following section will describe a configuration in which liquid flows through the intercellular region.

[0133] [First variation] of [Water electrolysis stack 600] The first modified example, the water electrolysis stack 600, will now be described. The water electrolysis stack 600 is a configuration in which a fourth channel 611 (cover member 610) is provided in the water electrolysis stack 100. The fourth channel 611 connects the reaction water discharge communication hole 100d and the second communication hole 100f.

[0134] Figure 17 shows a perspective view of the water electrolysis stack 600. As shown in Figure 17, the water electrolysis stack 600 is equipped with a cover member 610 on the first end plate 31. The shape of the cover member 610 is the same as that of the cover member 210. The cover member 610 is positioned to cover the opening 31d of the reaction water discharge communication hole 100d and the opening 31f of the second communication hole 100f, and a flow path (fourth flow path 611) is formed inside the cover member 610 through which fluid can flow between these communication holes. That is, the fourth flow path 611 is formed from the inner surface of the cover member 610 and a part of the surface of the first end plate 31. The shape of the fourth flow path 611 is the same as that of the first flow path 211. Therefore, the fourth flow path 611 can be said to be a flow path on the first end plate 31 that connects the opening 31d of the reaction water discharge communication hole 100d and the opening 31f of the second communication hole 100f.

[0135] By using the cover member 610, the reaction water flows as follows: The reaction water flows from the reaction water discharge communication hole 100d to the second communication hole 100f via the fourth flow path 611, and then flows to each inter-cell region 21. The reaction water that has passed through each inter-cell region 21 is discharged from the second communication hole 100e. In this way, in the water electrolysis stack 600, reaction water flows to the inter-cell region 21 during water electrolysis. This increases the internal pressure of the inter-cell region 21, thereby improving the durability of the water electrolysis stack.

[0136] Normally, the pressure of the reaction water is lower than the pressure of the hydrogen electrode 16. Therefore, even if reaction water with normal pressure is circulated through the inter-cell region 21, there is a risk that the deformation suppression effect of the inter-cell region 21 may not be sufficiently obtained. Also, if the pressure of the reaction water is low, there is a concern that the reaction water may flow back. For this reason, the pressure of the reaction water supplied to the water electrolysis stack 600 may be increased above the normal pressure. For example, it may be set to 90% or more of the pressure of the hydrogen electrode 16, or to be higher than the pressure of the hydrogen electrode 16. There is no particular upper limit to the pressure of the gas supplied to the inter-cell region 21. However, considering the load applied to the water electrolysis stack, the pressure of the reaction water may be set to 110% or less of the pressure of the hydrogen electrode 16. The pressure of the reaction water can be changed by adjusting the reaction water supply device.

[0137] The cover member 610 may have an opening 612 that can be connected to the outside. This allows reaction water to be discharged from the opening 612. The opening 612 may have a configuration similar to, for example, the opening 212 of the cover member 210.

[0138] In the water electrolysis stack 600, a fourth channel 611 was formed using a cover member 610. However, the configuration of the fourth channel is not limited to this. For example, the fourth channel may have the same configuration as the first channel 310, which is a pipe, or it may have the same configuration as the first channel, which is a communication hole. In either configuration, the same effect is achieved.

[0139] Furthermore, the water electrolysis stack 600 uses a cover member 610 (fourth channel 611) that connects the opening 31d of the reaction water discharge communication hole 100d and the opening 31f of the second communication hole 100f. However, the position of the cover member (fourth channel) is not limited to this. The cover member 610 (fourth channel 611) may also connect the opening 31c of the reaction water supply communication hole 100c and the opening 31e of the second communication hole 100e. Even in this case, reaction water flows into the inter-cell region 21. However, when the fourth channel connects the reaction water supply communication hole 100c and the second communication hole 100e, the cover member forming the fourth channel must have an opening to take in reaction water from the outside.

[0140] The modifications of the water electrolysis stack of the present disclosure have been described above using the first modification. The modifications of the water electrolysis system of the present disclosure allow water to flow through the inter-cell region during water electrolysis. This suppresses deformation of the inter-cell region and improves the durability of the water electrolysis stack. In addition, since the reaction water can be shared between the hydrogen electrode 16 and the inter-cell region, it also contributes to simplifying the apparatus.

[0141] (F) Modified Water Electrolysis System of the Disclosure The water electrolysis system described above is a configuration in which gas flows through the intercellular region during water electrolysis. On the other hand, the modified water electrolysis system is a configuration in which water flows through the intercellular region during water electrolysis. Since it is possible to increase the pressure in the intercellular region by flowing a liquid (such as water) instead of gas through the intercellular region, it is thought that a similar effect can be achieved. Therefore, the following will describe the configuration in which water flows through the intercellular region.

[0142] [First variation] of [Water electrolysis system 6000] The first modified water electrolysis system, 6000, will now be described. The water electrolysis system 6000 differs from the water electrolysis system 1000 mainly in that the water electrolysis stack 100 has been replaced with a water electrolysis stack 600. Below, only the differences from the water electrolysis system 1000 will be explained.

[0143] Figure 18 shows a block diagram of the water electrolysis system 6000. As shown in Figure 18, the water electrolysis system 6000 has a reaction water discharge channel 6220 instead of the reaction water discharge channel 1220. The reaction water discharge channel 6220 includes a first pipe 6221 and a second pipe 6222.

[0144] The reaction water supplied to the water electrolysis stack 600 flows from the reaction water supply communication hole 100c to each oxygen electrode 15, then flows through the fourth flow path 611 from the reaction water discharge communication hole 100d to the second communication hole 100f, and finally flows to each inter-cell region 21. The reaction water is then discharged from the second communication hole 100e. In addition, the reaction water is also discharged from the opening 612 of the cover member 610. Thus, there are two openings from which the reaction water is discharged in the water electrolysis stack 600. For this reason, the reaction water discharge flow path 6220 has two pipes.

[0145] The first pipe 6221 is connected to the opening 31e of the second communication hole 100e of the water electrolysis stack 600. If the water electrolysis system 6000 includes a gas-liquid separator 1410, the first pipe 6221 connects the opening 31e of the second communication hole 100e of the water electrolysis stack 600 to the gas-liquid separator 1410. The second pipe 6222 connects the opening 612 of the cover member 610 to the first pipe 6221. This connects all openings for discharging reaction water to the reaction water discharge channel 6220. If the cover member 610 does not have an opening 612, the reaction water discharge channel 6220 does not need to include the second pipe 6222.

[0146] The water electrolysis system 6000 uses a water electrolysis stack 600 having a cover member 610 (fourth channel 611) connecting the reaction water discharge port 100d and the second port 100f. However, a water electrolysis stack having a cover member (fourth channel) connecting the reaction water supply port 100c and the second port 100e instead of the cover member 610 is also applicable to the water electrolysis system 6000. In this case, the reaction water is discharged from the reaction water discharge port 100d and the second port 100f. Therefore, when applying such a water electrolysis stack, it is necessary to appropriately change the shape of the reaction water discharge channel because the openings from which the reaction water is discharged are different.

[0147] [2nd variation] of [Water electrolysis system 7000] The second modified water electrolysis system, 7000, will now be described. The water electrolysis system 7000 differs from the water electrolysis system 2000 mainly in that it includes a fifth flow path 7800. Below, only the differences from the water electrolysis system 2000 will be explained.

[0148] Figure 19 shows a block diagram of the water electrolysis system 7000. As shown in Figure 19, the water electrolysis system 7000 comprises a fifth channel 7800, an extrusion water supply device 7810, and a gas-liquid separator 7820.

[0149] The fifth channel 7800 is a pipe that connects the opening 31a of the first communication hole 100a, which is not connected to the cover member 210, and the opening 31e of the second communication hole 100e, which is not connected to the first channel 211. As shown in Figure 19, 5 Flow channel 78 00 may consist of multiple pipes. The extrusion water supply device 7810 is located in the fifth flow path 7800 and circulates the extrusion water within the water electrolysis stack 200. The extrusion water supply device 7810 is, for example, a pump. The gas-liquid separator 7820 is located upstream of the extrusion water supply device 7810 (second communication hole 100e) in the fifth flow path 7800. The hydrogen discharge flow path 7300 is connected to the gas-liquid separator 7820. That is, the hydrogen discharge flow path 7300 consists of a single pipe.

[0150] The movement of the extrusion water is described below. The extrusion water (water) supplied from the extrusion water supply device 7810 flows from the fifth channel 7800 to the first communication hole 100a and reaches each hydrogen electrode 16. The extrusion water that reaches each hydrogen electrode 16 is discharged from each hydrogen electrode 16 along with the hydrogen generated by water electrolysis, flows through the first channel 211 from the first communication hole 100b to the second communication hole 100f, and flows to each inter-cell region 21. Then, from each inter-cell region 21, it passes through the second communication hole 100e and reaches the fifth channel 7800. The extrusion water that reaches the fifth channel 7800 is separated into hydrogen and extrusion water by the gas-liquid separator 7820. The separated hydrogen is discharged to the hydrogen discharge channel 7300. The separated extrusion water flows through the fifth channel 7800 and reaches the extrusion supply device 7810. Thus, in the water electrolysis system 7000, extruded water circulates through each hydrogen electrode 16 and each inter-cell region 21 via the first connecting holes 100a, 100b, the second connecting holes 100e, 100f, and the fifth flow path 7800. The hydrogen separated by the gas-liquid separator 7820 may be sent to a hydrogen tank via the hydrogen discharge flow path 7300.

[0151] According to the water electrolysis system 7000, circulating the extruded water allows for the flushing out of hydrogen deposits accumulated at each hydrogen electrode 16. In other words, hydrogen accumulation can be suppressed. Furthermore, suppressing hydrogen accumulation improves the hydrogen supply efficiency of the water electrolysis stack 200. In addition, according to the water electrolysis system 7000, the only opening through which hydrogen is discharged along with the extruded water is the opening 31e of the second communication hole 100e. Therefore, the number of openings from which hydrogen is discharged can be reduced, contributing to the simplification of the device. Moreover, according to the water electrolysis system 7000, the extruded water is discharged from the second communication hole 100e. Here, since the second communication hole 100e is close to the reaction water supply communication hole 100c, discharging the extruded water to the outside after passing it through the second communication hole 100e can lower the temperature of the hydrogen separated from the extruded water. The effects of obtaining hydrogen at a lower temperature have been described above.

[0152] In this water electrolysis system 7000, a cover member 210 without an opening 212 was used. However, a cover member 210 having an opening 212 may also be used in the water electrolysis system 7000. In this case, extruded water is discharged from the opening 212 along with hydrogen. The extruded water discharged from the opening 212 may be separated into hydrogen and extruded water using a gas-liquid separator. The separated hydrogen may be sent to a hydrogen tank via a hydrogen discharge channel. The separated extruded water may be sent to an extruded water supply device 7810.

[0153] The water electrolysis system 7000 has been described above. The water electrolysis stack 200 was used in the water electrolysis system 7000. However, water electrolysis stacks 300, 400, and 500 are also applicable to the water electrolysis system 7000. However, when the water electrolysis stack 500 is applied to the water electrolysis system 7000, extruded water may be discharged from the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f. For this reason, when applying the water electrolysis stack 500, the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f may be sealed.

[0154] The modifications of the water electrolysis system of the present disclosure have been described above using various modifications. The modifications of the water electrolysis system of the present disclosure allow water to flow through the inter-cell region during water electrolysis. This suppresses deformation of the inter-cell region and improves the durability of the water electrolysis stack. [Explanation of symbols]

[0155] 10 Water electrolysis cell 11 Electrode body 12. Oxygen electrode separator 13 Hydrogen electrode separator 14 Frame-shaped member 15. Oxygen electrode 16 Hydrogen electrode 17, 417 sealing member 18a~18d Sealing material 20-cell stack 21 Inter-cell area 31. First end plate 31a~31f opening 32. Second end plate 100-600 Water Electrolysis Stack 100a, 100b 1st communication hole 100c reaction water supply connection hole 100d Reaction water discharge port 100e, 100f 2nd communication hole 210, 510, 610 Cover components 211, 310, 511 First channel 611 Fourth channel 212, 312, 512, 612 openings 1000-7000 Water Electrolysis Systems 1100 power supply 1200 Reaction water supply device 1210 Reaction water supply channel 1220 Reaction water discharge channel 1230 Circulation channel 1300-4300, 7300 Hydrogen Emission Channel 1310, 2310 First piping 1320, 2320 Second piping 2330 Third Piping 1410, 1420 Gas-liquid separator 3500 Second channel 3510 Extrusion Water Supply Device 3520 Gas-liquid separator 4610 Gas-liquid separator 4620 Third channel 4630 Extrusion Water Supply Device 5700 Gas supply device 5710 Gas supply channel 5720 Gas discharge channel 6220 Reaction water discharge channel 6221 First Piping 6222 Second Piping 7800 Fifth channel 7810 Extrusion Water Supply Device 7820 Gas-liquid separator

Claims

1. It has a cell laminate in which multiple water electrolysis cells are stacked, In the aforementioned cell stack, an inter-cell region is formed between adjacent water electrolysis cells. During water electrolysis, a gas (excluding water vapor) is circulated to increase the internal pressure in the inter-cell region. Water electrolysis stack.

2. The aforementioned water electrolysis cell is An electrode body having an oxygen electrode catalyst layer positioned on one side of an electrolyte membrane and a hydrogen electrode catalyst layer positioned on the other side, An oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode body, The electrode body comprises a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side, In the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator. In adjacent water electrolysis cells, the oxygen electrode separator of one water electrolysis cell and the hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator. The water electrolysis stack according to claim 1.

3. The water electrolysis stack according to claim 1, wherein the gas is hydrogen produced at the hydrogen electrode.

4. If the pressure of the hydrogen electrode is greater than the pressure of the oxygen electrode, the gas pressure in the intercellular region is 90% or more and 110% or less of the pressure of the hydrogen electrode. If the pressure of the oxygen electrode is greater than the pressure of the hydrogen electrode, the gas pressure in the intercellular region is 90% or more and 110% or less of the pressure of the oxygen electrode. The water electrolysis stack according to claim 2.

5. The water electrolysis stack is A first communication hole is formed that is connected to the hydrogen electrode and communicates along the stacking direction, A second communication hole is formed that is connected to the inter-cell region and communicates along the stacking direction, It comprises a first flow path connecting the first communication hole and the second communication hole, The hydrogen generated at the hydrogen electrode by water electrolysis flows through the first channel from the first connecting hole to the second connecting hole, and then flows into the inter-cell region. The water electrolysis stack according to claim 2.

6. The water electrolysis stack according to claim 1, The system includes a pump that supplies the gas to the intercellular region. Water electrolysis system.

7. Having a cell laminate in which a plurality of water electrolysis cells are stacked, In the aforementioned cell stack, an inter-cell region is formed between adjacent water electrolysis cells. During water electrolysis, the liquid flows in such a way that it increases the internal pressure in the inter-cell region. Water electrolysis stack.

8. A water electrolysis stack having a cell stack in which multiple water electrolysis cells are stacked, The aforementioned water electrolysis cell is An electrode body having an oxygen electrode catalyst layer positioned on one side of an electrolyte membrane and a hydrogen electrode catalyst layer positioned on the other side, An oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode body, The electrode body comprises a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side, In the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator. In adjacent water electrolysis cells, the oxygen electrode separator of one water electrolysis cell and the hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator. The pressure of the liquid in the intercellular region is 90% or more and 110% or less of the pressure at the hydrogen electrode. The water electrolysis stack according to claim 7.

9. The water electrolysis stack is A reaction water supply communication hole and a reaction water discharge communication hole are connected to the oxygen electrode and are formed to communicate along the stacking direction, Two second communication holes are formed that are connected to the inter-cell region and communicate along the stacking direction, The system includes a fourth channel connecting the reaction water supply port or the reaction water discharge port with the second port, The aforementioned liquid is reaction water, The reaction water flows through the fourth channel to the second connecting hole and then to the inter-cell region. The water electrolysis stack according to claim 8.

10. A water electrolysis system comprising a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, a fifth channel, and an extrusion water supply device arranged in the fifth channel, The aforementioned water electrolysis cell is An electrode body having an oxygen electrode catalyst layer positioned on one side of an electrolyte membrane and a hydrogen electrode catalyst layer positioned on the other side, An oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode body, The electrode body comprises a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side, In the water electrolysis cell, an oxygen electrode is formed between the electrode body and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode body and the hydrogen electrode separator. In adjacent water electrolysis cells, the oxygen electrode separator of one water electrolysis cell and the hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator. The aforementioned water electrolysis stack is Two first communication holes are formed connected to the hydrogen electrode and communicating along the stacking direction, Two second communication holes are formed that are connected to the inter-cell region and communicate along the stacking direction, A first flow path connecting one of the first communication holes and one of the second communication holes is provided, The fifth channel connects another first communication hole that is not connected to the first channel and another second communication hole that is not connected to the first channel. The extrusion water supplied from the extrusion water supply device flows through the fifth channel from another second communication hole not connected to the first channel to another first communication hole not connected to the first channel, and flows into the inter-cell region. The extruded water in the intercellular region is pressurized. Water electrolysis system.

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