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]

[0001] The present application relates to a water electrolysis stack and a water electrolysis system. [Background technology]

[0002] In recent years, hydrogen has been attracting attention as a CO2-free energy source. Methods for producing hydrogen include alkaline water electrolysis and water electrolysis.

[0003] Water electrolysis is sometimes performed using a water electrolysis stack. A water electrolysis stack is usually formed by stacking a plurality of water electrolysis cells, each of which has 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. For this reason, the use of 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 integrated water electrolysis fuel cell cells are stacked. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-165379 A Summary of the Invention [Problem to be solved by the invention]

[0005] When a fuel cell stack is used as a water electrolysis stack, the following problems arise. When generating electricity, the fuel cell stack cools the fuel cell cells by flowing cooling water through the regions between the fuel cell cells. That is, between the fuel cell cells, there is an inter-cell region, which is a space for circulating the cooling water. Meanwhile, in the water electrolysis stack, water electrolysis is performed by supplying reactant water to the oxygen electrode. Although the temperature of the water electrolysis stack rises due to water electrolysis, the temperature rise can be controlled by the reactant water. Therefore, in the water electrolysis stack, it is not essential to flow cooling water for temperature regulation through the inter-cell region.

[0006] However, when the fuel cell stack is used as a water electrolysis stack to perform water electrolysis, the presence of the inter-cell region causes the following problem. Usually, the inter-cell region is sandwiched between the oxygen electrode of one adjacent water electrolysis cell and the hydrogen electrode of the other adjacent water electrolysis cell. During water electrolysis, reactant water is supplied to the oxygen electrode, and thus the pressure of the reactant water is applied to the inter-cell region. In addition, hydrogen is generated at the hydrogen electrode by water electrolysis, and thus the pressure of the hydrogen is applied to the inter-cell region. In this way, a pressure toward the inside in the stacking direction is applied to the inter-cell region by water electrolysis. Such pressure may cause deformation of the inter-cell region. If the inter-cell region is deformed, the adjacent water electrolysis cells that form the inter-cell region are also deformed, and therefore the sealed structure of the water electrolysis cells may be broken, and the watertightness or airtightness may be impaired. Thus, there is room for improvement in the durability of a water electrolysis stack having an inter-cell region.

[0007] In view of the above-mentioned circumstances, a main object of the present disclosure is to provide a water electrolysis stack and a water electrolysis system capable of improving durability. [Means for solving the problem]

[0008] The present disclosure provides the following aspects for solving the above problems.

[0009] The first aspect is a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, in which 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] In a second aspect, in the first aspect, the water electrolysis cell includes an electrode assembly having an oxygen electrode catalyst layer disposed on one side and a hydrogen electrode catalyst layer disposed on the other side of an electrolyte membrane, an oxygen electrode separator disposed on the oxygen electrode catalyst layer side of the electrode assembly, and a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side of the electrode assembly, and in the water electrolysis cell, an oxygen electrode is formed between the electrode assembly and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode assembly 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 oxygen electrode separator and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator, and the water electrolysis stack includes 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 communication hole and the second communication hole, and 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 flows into the inter-cell region.

[0011] A third aspect is a water electrolysis stack of the second aspect, comprising a first end plate and a second end plate which sandwich the cell stack in the stacking direction, an opening of the first communication hole and an opening of the second communication hole are arranged on the first end plate, and a 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] A fourth aspect is a water electrolysis stack of the third aspect, which includes a plurality of first communication holes and a plurality of second communication holes, wherein openings of the plurality of first communication holes and openings of the plurality of second communication holes are arranged on a first end plate, a first flow path connects one of the openings of the first communication hole and one of the openings of the second communication hole on the first end plate, and the remaining openings of the first communication holes that are not connected to the first flow path are sealed.

[0013] A fifth aspect is the water electrolysis stack of the fourth aspect, further comprising two first communication holes and two second communication holes.

[0014] A sixth aspect is a water electrolysis stack of the fifth aspect, which is connected to an oxygen electrode and includes a reactant water supply passage and a reactant water discharge passage formed to communicate along the stacking direction, and hydrogen circulating through the inter-cell region is discharged from a second passage closest to the reactant water supply passage.

[0015] A seventh aspect is a water electrolysis stack of the fifth aspect, which is provided with a reactant water supply passage and a reactant water discharge passage connected to an oxygen electrode and extending along the stacking direction, and hydrogen circulating through the inter-cell region is discharged from a second passage closest to the reactant water discharge passage.

[0016] An eighth aspect is a water electrolysis system comprising a water electrolysis stack according to any one of the second to seventh aspects, a second flow path, and a hydrogen supply device arranged in the second flow path, wherein the water electrolysis stack is provided with two first communication holes and two second communication holes, the second flow path connects the first communication holes, and the hydrogen supply device causes hydrogen to flow from one first communication hole to the other first communication hole via the second flow path.

[0017] A ninth aspect is a water electrolysis system according to the eighth aspect, wherein the water electrolysis stack is connected to an oxygen electrode and has a reactant water supply passage and a reactant water discharge passage formed to communicate along the stacking direction, and hydrogen circulating through the inter-cell region is discharged from a second passage closest to the reactant water supply passage.

[0018] A tenth aspect is the water electrolysis system according to the eighth or ninth aspect, further comprising a gas-liquid separator disposed upstream of the hydrogen supply device in the second flow path.

[0019] An eleventh aspect provides a water electrolysis system comprising: a water electrolysis stack according to any one of the second to seventh aspects, a gas-liquid separator, a third flow path, and an extrusion water supply device arranged in the third flow path, wherein the water electrolysis stack has two first communication holes and two second communication holes, the gas-liquid separator is arranged in the first flow path, the third flow path connects the gas-liquid separator to another first communication hole that is not connected to the first flow path, the extrusion water supplied from the extrusion water supply device flows through the hydrogen electrode via the other first communication hole and is discharged to the first communication hole together with hydrogen generated by water electrolysis at the hydrogen electrode and reaches the gas-liquid separator arranged in the first flow path from the first communication hole, the hydrogen is separated in the gas-liquid separator and flows into the third flow path, and the hydrogen separated by the gas-liquid separator flows to the inter-cell region via the second communication hole.

[0020] A twelfth aspect is a water electrolysis system comprising the water electrolysis stack of the first aspect and a gas supply device that supplies gas to an inter-cell region.

[0021] A thirteenth aspect is a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, the water electrolysis cells comprising: an electrode assembly having an oxygen electrode catalyst layer arranged on one side and a hydrogen electrode catalyst layer arranged on the other side of an electrolyte membrane; an oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode assembly; and a hydrogen electrode separator arranged on the hydrogen electrode catalyst layer side of the electrode assembly, in which an oxygen electrode is formed between the electrode assembly and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode assembly and the hydrogen electrode separator, and in adjacent water electrolysis cells, The oxygen electrode separator 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 includes a reacted water supply passage and a reacted water discharge passage connected to the oxygen electrode and formed to communicate along the stacking direction, two second communication holes connected to the inter-cell region and formed to communicate along the stacking direction, and a fourth flow path connecting the reacted water supply passage or the reacted water discharge passage to the second communication holes, and the reacted water flows through the fourth flow path to the second communication holes and then to the inter-cell region.

[0022] A fourteenth aspect relates to a water electrolysis system including a water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, a fifth flow path, and an extrusion water supply device arranged in the fifth flow path, in which the water electrolysis cells include an electrode assembly having an oxygen electrode catalyst layer arranged on one side and a hydrogen electrode catalyst layer arranged on the other side of an electrolyte membrane, an oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode assembly, and a hydrogen electrode separator arranged on the hydrogen electrode catalyst layer side of the electrode assembly, in which an oxygen electrode is formed between the electrode assembly and the oxygen electrode separator, and a hydrogen electrode is formed between the electrode assembly and the hydrogen electrode separator, and in which the oxygen electrode separator of one water electrolysis cell and the hydrogen electrode separator of the other water electrolysis cell are mutually connected in adjacent water electrolysis cells. and an inter-cell 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 electrodes and formed to communicate with each other along the stacking direction, two second communication holes connected to the inter-cell region and formed to communicate with each other along the stacking direction, and a first flow path connecting one of the first communication holes and one of the second communication holes, and a fifth flow path connects another first communication hole not connected to the first flow path with another second communication hole not connected to the first flow path, and extrusion water supplied from the extrusion water supply device flows via the fifth flow path from the other second communication hole not connected to the first flow path to the other first communication hole not connected to the first flow path, and then flows into the inter-cell region. Effect of the Invention

[0023] According to the present disclosure, it is possible to suppress deformation of the inter-cell region and improve the durability of the water electrolysis stack. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a perspective view of a water electrolysis stack 100. [Diagram 2] FIG. 2 is an exploded perspective view of the water electrolysis cell 10. [Diagram 3] 2 is a partial cross-sectional view of a cell stack 20 cut in the stacking direction, focusing on an inter-cell region 21. FIG. [Figure 4]3 is a schematic diagram of a first end plate 31 as viewed from the stacking direction. [Diagram 5] 1A to 1C are schematic diagrams illustrating how deformation occurs in an inter-cell region 21. [Figure 6] FIG. 2 is a perspective view of the water electrolysis stack 200. [Figure 7] 2 is a cross-sectional view focusing on a first flow path 211. FIG. [Figure 8] FIG. 2 is a cross-sectional view focusing on a first flow path 310. [Figure 9] FIG. 2 is an exploded perspective view of the water electrolysis stack 100, focusing on the cell stack 20 and the first end plate 31. [Figure 10] 2 is an exploded perspective view of the water electrolysis stack 400, focusing on the cell stack 20 and the first end plate 31. FIG. [Figure 11] FIG. 2 is a perspective view of the water electrolysis stack 500. [Figure 12] FIG. 1 is a block diagram of a water electrolysis system 1000. [Figure 13] FIG. 2 is a block diagram of a water electrolysis system 2000. [Figure 14] FIG. 3 is a block diagram of a water electrolysis system 3000. [Figure 15] FIG. 4 is a block diagram of a water electrolysis system 4000. [Figure 16] FIG. 5 is a block diagram of a water electrolysis system 5000. [Figure 17] FIG. 2 is a perspective view of a water electrolysis stack 600. [Figure 18] FIG. 6 is a block diagram of a water electrolysis system 6000. [Figure 19] FIG. 7 is a block diagram of a water electrolysis system 7000. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] (A) A typical water electrolysis stack First, in describing the water electrolysis stack of the present disclosure, a water electrolysis stack 100 will be described as an example of a typical water electrolysis stack.

[0026] [Water Electrolysis Stack 100] Fig. 1 shows a perspective view of a water electrolysis stack 100. Here, the x direction in Fig. 1 is the longitudinal direction, the y direction is the lateral direction, and the z direction is the stacking direction.

[0027] The water electrolysis stack 100 includes 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 in the stacking direction.

[0028] In the water electrolysis stack 100, a plate having a predetermined function may be arranged between the first end plate 31 and the cell stack 20, if necessary. Similarly, a plate having a predetermined function may be arranged between the second end plate 32 and the cell stack 20, if necessary. Examples of the plate include a terminal plate, an insulating plate, and a pressure plate. The terminal plate has a terminal connected to an external power source, and when a voltage is applied from the power source to the terminal plate, the voltage is applied to the cell stack 20 arranged between the terminal plates. The insulating plate serves to insulate the terminal plate and the end plate. The pressure plate serves to apply a restraining force to the cell stack 20.

[0029] <Water electrolysis cell 10> The water electrolysis cell 10 is a device that performs 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 includes an electrode assembly 11 and a pair of separators (oxygen electrode separator 12 and hydrogen electrode separator 13) disposed on both sides of the electrode assembly 11. In addition, a frame member 14 is disposed around the electrode assembly 11.

[0030] In the water electrolysis cell 10, an oxygen electrode 15 is formed between the electrode assembly 11 and the oxygen electrode separator 12, and a hydrogen electrode 16 is formed between the electrode assembly 11 and the hydrogen electrode separator 13 (see FIG. 3). The oxygen electrode 15 and the hydrogen electrode 16 are spaces through which a fluid can flow. Reaction water (water) normally flows through the oxygen electrode 15. Hydrogen normally 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 disposed on one side of an electrolyte membrane and a hydrogen electrode catalyst layer is disposed on the other side. That is, the electrode body 11 has an electrolyte membrane, an oxygen electrode catalyst layer disposed on one side of the electrolyte membrane, and a hydrogen electrode catalyst layer disposed 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 appropriately set depending on the purpose. For example, it may be a polygonal shape with pentagons or more, a circular shape, or an elliptical shape.

[0032] The electrolyte membrane is a sheet-like member having proton conductivity. The electrolyte membrane includes a proton conductive ionomer. The type of the proton conductive ionomer is not particularly limited. For example, polytetrafluoroethylene and fluoroalkyl polymers such as perfluoroalkylsulfonic acid polymers may be used. Perfluoroalkylsulfonic acid polymers may be selected from the viewpoint of durability.

[0033] The oxygen electrode catalyst layer is a sheet-like member including an oxygen electrode catalyst capable of generating oxygen by water electrolysis. The oxygen electrode catalyst is not particularly limited, but may be, for example, a metal catalyst. The metal catalyst may be, for example, a metal catalyst including Pt, Ru, Rh, Os, Ir, Pd, and Au in its composition. The metal catalyst may be an oxide of these metals. Typically, it is platinum or a platinum alloy. The oxygen electrode catalyst may be an electrically conductive carrier (metal-supported catalyst) that supports a metal catalyst. The type of the carrier is not particularly limited, but may be, for example, a carbon carrier. The oxygen electrode catalyst layer may also include a proton-conductive ionomer. The proton-conductive ionomer is not particularly limited. For example, the above-mentioned proton-conductive ionomer may be included.

[0034] The hydrogen electrode catalyst layer is a sheet-like member including a hydrogen electrode catalyst capable of generating hydrogen by water electrolysis. The hydrogen electrode catalyst is not particularly limited, but may be, for example, a metal catalyst. The metal catalyst may be, for example, a metal catalyst including Pt, Ru, Rh, Os, Ir, Pd, and Au in its composition. The metal catalyst may be an oxide of these metals. Typically, it is platinum or a platinum alloy. The hydrogen electrode catalyst may be an electrically conductive carrier (metal-supported catalyst) that supports a metal catalyst. The type of the carrier is not particularly limited, but may be, for example, a carbon carrier. The hydrogen electrode catalyst layer may also include a proton-conductive ionomer. The proton-conductive ionomer is not particularly limited. For example, the above-mentioned proton-conductive ionomer may be included.

[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 shapes of the oxygen electrode separator 12 and the hydrogen electrode separator 13 are not limited to this and may be appropriately set depending on the purpose. For example, they may be a polygonal shape having pentagons or more sides, a circular shape, or an elliptical shape. The oxygen electrode separator 12 is disposed on the oxygen electrode catalyst layer side of the electrode body 11. The hydrogen electrode separator 12 is disposed 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. For example, a resin material containing a carbon material; a metal material such as iron, copper, stainless steel, or titanium, etc. may be mentioned.

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

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

[0038] Predetermined flow paths are formed on the surfaces of the oxygen electrode separator 12 and the hydrogen electrode separator 13 facing the electrode assembly 11. Specifically, a reactant water flow path (not shown) is formed on the surface of the oxygen electrode separator 12 facing the electrode assembly 11, which guides reactant water supplied to the oxygen electrode 14 from the reactant water supply hole 12c to the electrode assembly 11 and guides the reactant water guided to the electrode assembly 11 to the reactant water discharge hole 12d. A hydrogen flow path (not shown) is formed on the surface of the hydrogen electrode separator 13 facing the electrode assembly 11, which guides hydrogen generated at the hydrogen electrode 15 by water electrolysis to the first holes 13a, 13b.

[0039] A seal member 17 is arranged on the outer surface (the surface opposite to the electrode assembly 11) of the oxygen electrode separator 12 or the hydrogen electrode separator 13, surrounding 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 portion (the region corresponding to the position of the electrode assembly 11). In FIG. 2, the seal member 17 is arranged on the outer surface of the oxygen electrode separator 12. By arranging the seal member 17, it is possible to prevent the fluid flowing through the inter-cell region 21 from leaking to the outside. The inter-cell region 21 will be described later.

[0040] Furthermore, sealing members 18a-18d that independently surround the first hole, the reacted water supply hole, and the reacted water discharge hole, are disposed on the outer surface of the oxygen electrode separator 12 or the hydrogen electrode separator 13. In Fig. 2, the sealing members 18a-18d are disposed on the outer surface of the oxygen electrode separator 12. By disposing the sealing members 18a-18d, it is possible to prevent reacted water, hydrogen, or oxygen from leaking to the outside between adjacent water electrolysis cells 10.

[0041] (Frame-shaped member 14) The frame-shaped member 14 is a sheet-shaped 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 appropriately depending on the purpose. For example, it may be a polygonal shape having pentagons or more, a circular shape, or an elliptical shape. The frame-shaped member 14 is disposed around the electrode body 11. That is, the frame-shaped member 14 has an opening for disposing the electrode body 11. The material of the frame-shaped member 14 is not particularly limited, and may be, for example, an insulating resin.

[0042] Similar to the oxygen electrode separator 12 and the hydrogen electrode separator 13, the frame member 14 has first holes 14a, 14b, a reaction water supply hole 14c, a reaction water discharge hole 14d, and second holes 14e, 14f at both ends in the longitudinal direction.

[0043] A seal member (indicated by a broken line in FIG. 2) is disposed on the surface of the frame member 14 facing the oxygen electrode separator 12, surrounding the reaction water supply hole 14c, the reaction water discharge hole 14d, and the electrode body 11 (the opening of the frame member 14). This makes it possible to prevent the reaction water and oxygen flowing through the oxygen electrode 15 from leaking to the outside. In addition, a seal member (indicated by a broken line in FIG. 2) is disposed on the surface of the frame member 14 facing the oxygen electrode separator 12, surrounding the first holes 14a, 14b and the second holes 14e, 14f, respectively, independently.

[0044] A sealing member (not shown) that surrounds the first holes 14a, 14b and the electrode body 11 (the opening of the frame member 14) is disposed on the surface of the frame member 14 facing the hydrogen electrode separator 13. This makes it possible to prevent hydrogen flowing through the hydrogen electrode 16 from leaking to the outside. In addition, sealing members (not shown) that independently surround the reaction water supply hole 14c, the reaction water discharge hole 14d, and the second holes 14e, 14f are disposed on the surface of the frame member 14 facing the hydrogen electrode separator 13.

[0045] (Water electrolysis reaction in water electrolysis cell 10) The water electrolysis reaction in the water electrolysis cell 10 will be described. In the water electrolysis cell 10, reactive water is supplied to the oxygen electrode 15 and a voltage is applied, causing a water electrolysis reaction in each catalyst layer. First, reactive water is supplied to the oxygen electrode catalyst layer (solid arrow in FIG. 2), and oxygen and protons are generated by the water electrolysis reaction. The generated oxygen is guided together with reactive water to a reactive water flow path formed in the oxygen electrode separator 12, and is taken out through a reactive water discharge hole (dotted arrow in FIG. 2). Protons generated in the oxygen electrode catalyst layer permeate the electrolyte membrane and reach the hydrogen electrode catalyst layer. The protons that have arrived there combine with electrons, and hydrogen is generated at the hydrogen electrode 16. The generated hydrogen is guided to a hydrogen flow path formed in the hydrogen electrode separator 13, and is discharged to the outside through a first hole (dotted arrow in FIG. 2).

[0046] <Cell stack 20> The cell stack 20 is formed by stacking a plurality of water electrolysis cells 10. The number of stacked water electrolysis cells 10 is not particularly limited and may be appropriately set according to the target performance ratio. For example, the number of water electrolysis cells 10 in the cell stack 20 may be 10 or more and 100 or less.

[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 is adjacent to the hydrogen electrode separator 13 of the other water electrolysis cell 10, and the 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 seal member 17, thereby ensuring watertightness or airtightness. The inter-cell region 21 is formed between each water electrolysis cell 10, but may also be formed between a water electrolysis cell 10 arranged on an end face of the cell stack 20 and an end plate (first end plate 31 or second end plate 32).

[0048] Fig. 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 Fig. 3, the inter-cell region 21 is a space formed between adjacent water electrolysis cells 10. As described above, the oxygen electrode separator 12 has the seal member 17 arranged on its outer surface (the surface opposite to the electrode body 11) so as to surround the central portion and the second holes 12e, 12f together, and the hydrogen electrode separator 13 of the adjacent water electrolysis cell 10 is stacked on the seal member 17, thereby forming the inter-cell region 21 inside the seal member 17. As such, the outer edge of the inter-cell region 21 is sealed with the seal member 17, and the inter-cell region 21 has a structure that prevents fluid flowing therethrough from leaking to the outside.

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

[0050] The first communication holes 100a, 100b typically allow hydrogen generated at the hydrogen electrodes of the water electrolysis cells 10 to flow. The first communication holes 100a communicate with the first holes 12a, 13a, 14a of the water electrolysis cells 10 and pass through the first end plate 31. Thus, an opening 31a of the first communication hole 100a is disposed on the first end plate 31. The first communication holes 100b communicate with the first holes 12b, 13b, 14b of the water electrolysis cells 10 and pass through the first end plate 31. Thus, an opening 31b of the first communication hole 100b is disposed on the first end plate 31. In the water electrolysis stack 100, hydrogen is typically extracted from the openings 31a, 31b. The first communication holes 100a, 100b typically do not pass through the second end plate 32.

[0051] As described above, the first communication holes 100a, 100b are connected to the hydrogen electrodes 16 of each water electrolysis cell 10. This means that a fluid can flow between the first communication holes 100a, 100b and each hydrogen electrode 16. As described above, a seal member (not shown) that surrounds the first holes 14a, 14b and the electrode assembly 11 (the opening of the frame member 14) is arranged on the surface of the frame member 14 facing the hydrogen electrode separator 13. By arranging the seal member in this manner, a fluid can flow between the first communication holes 100a, 100b and each hydrogen electrode 16.

[0052] The reacted water supply passage 100c typically carries reacted water supplied to each water electrolysis cell 10. The reacted water discharge passage 100d typically carries reacted water discharged from each water electrolysis cell 10 and oxygen generated at the oxygen electrode 15 by water electrolysis. The reacted water supply passage 100c communicates with the reacted water supply holes 12c, 13c, and 14c of each water electrolysis cell 10 and penetrates the first end plate 31. Thus, an opening 31c of the reacted water supply passage 100c is disposed on the first end plate 31. The reacted water discharge passage 100d communicates with the reacted water discharge holes 12d, 13d, and 14d of each water electrolysis cell 10 and penetrates the first end plate 31. Thus, an opening 31d of the reacted water discharge passage 100d is disposed on the first end plate 31. In the water electrolysis stack 100, reactant water is typically supplied through the opening 31c, and reactant water and oxygen are typically discharged through the opening 31d. The reactant water supply passage 100c and the reactant water discharge passage 100d typically do not penetrate the second end plate 32.

[0053] The reacted water supply passage 100c and the reacted water discharge passage 100d are connected to the oxygen electrodes 15 of each water electrolysis cell 10. This means that a fluid can flow between the reacted water supply passage 100c and the reacted water discharge passage 100d and each oxygen electrode 15. As described above, a seal member (indicated by a broken line in FIG. 2 ) that surrounds the reacted water supply hole 14c, the reacted water discharge hole 14d, and the electrode body 11 (the opening of the frame member 14) is disposed on the surface of the frame member 14 facing the oxygen electrode separator 12. By disposing the seal member in this manner, a fluid can flow between the reacted water supply passage 100c and the reacted water discharge passage 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. Thus, an opening 31e of the second communication hole 100e is disposed 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. Thus, an opening 31f of the second communication hole 100f is disposed 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 described later.

[0055] The second communication holes 100e, 100f are connected to each inter-cell region 21. This means that fluid can flow between the second communication holes 100e, 100f and each inter-cell region 21. As described above, a seal member 17 that surrounds the second holes 12e, 12f and the central portion is disposed on the outer surface of the oxygen electrode separator 12. By disposing the seal member 17 in this manner, fluid can flow between the second communication holes 100e, 100f and each inter-cell region 21.

[0056] As shown in FIG. 4, the openings 31a, 31c, and 31e are typically arranged at the right end (end on one side in the longitudinal direction) of the first end plate 31. The openings 31b, 31d, and 31f are typically arranged at the left end (end on the other side in the longitudinal direction) of the first end plate 31. The openings 31a, 31c, and 31e are arranged in the order of the openings 31c, 31e, and 31a from above (from one side in the lateral direction). On the other hand, the openings 31b, 31d, and 31f are arranged in the order of the openings 31b, 31f, and 31d from above (from one side in the lateral direction). In this way, the openings 31a, 31b, the openings 31c, 31d, and the openings 31e and 31f are arranged at positions facing each other. However, the arrangement positions of the openings are not limited to this and may be set appropriately according to the purpose.

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

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

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

[0060] When the fuel cell stack generates power, 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 a region in the fuel cell stack through which cooling water for temperature adjustment is circulated. On the other hand, in the water electrolysis stack, as described above, reactive water is supplied to the oxygen electrode to perform water electrolysis. Although the temperature of the water electrolysis stack rises due to water electrolysis, the temperature rise can be controlled by the reactive water. Therefore, there is no need to additionally circulate cooling water for temperature adjustment through the inter-cell region. This is the reason why the inter-cell region 21 and the second communication holes 100e, 100f are not usually used during water electrolysis in the water electrolysis stack 100.

[0061] However, when water electrolysis is performed using the water electrolysis stack 100 having the inter-cell region 21, the presence of the inter-cell region causes the following problem. Figure 5 is a schematic diagram illustrating how deformation occurs in the inter-cell region 21. Figure 5 corresponds to Figure 3.

[0062] As shown in FIG. 5 , reacted water is supplied to the oxygen electrode 15 of one of the water electrolysis cells 10 sandwiching the inter-cell region 21, and thus the pressure of the reacted water is applied to the oxygen electrode separator 12 forming the inter-cell region 21. Hydrogen is generated by water electrolysis at the hydrogen electrode 16 of the other water electrolysis cell 10 sandwiching the inter-cell region 21, and thus the pressure of the hydrogen is applied to the hydrogen electrode separator 13 forming the inter-cell region 21. In this manner, a pressure toward the inside in the stacking direction is applied to the inter-cell region 21 by water electrolysis. In contrast, since no fluid is supplied to the inter-cell region 21, the pressure is usually smaller than these pressures. Therefore, the inter-cell region 21 may be deformed due to the pressure difference between the inter-cell region 21 and the oxygen electrode 15 or the hydrogen electrode 16. Specifically, the oxygen electrode separator 12 or the hydrogen electrode separator 13 forming the inter-cell region 21 may be deformed. If the inter-cell region 21 is deformed, the sealed structure formed by the seal members inside the water electrolysis cell 10 may be broken, and reacted water, oxygen, and hydrogen may leak to the outside from the water electrolysis cell 10. In other words, the watertightness or airtightness of the water electrolysis cell 10 may be impaired.

[0063] (B) Water electrolysis stack of the present disclosure Thus, when water electrolysis is performed using a water electrolysis stack having an inter-cell region, there is a problem that the durability of the water electrolysis stack is reduced due to the presence of the inter-cell region. In response to this problem, the present inventors have found that by circulating gas through the inter-cell region during water electrolysis, deformation of the inter-cell region can be suppressed and the durability of the water electrolysis stack can be improved. Hereinafter, the water electrolysis stack of the present disclosure will be described using each embodiment.

[0064] [First embodiment: water electrolysis stack 200] A water electrolysis stack 200 according to a first embodiment will now be described. The water electrolysis stack 200 has a first flow path 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 hydroelectrolysis stack 100 provided with the first flow path 211. Only the differences from the hydroelectrolysis stack 100 will be described below.

[0065] FIG. 6 shows a perspective view of the water electrolysis stack 200. As shown in FIG. 6, the water electrolysis stack 200 includes a cover member 210 on a first end plate 31. The cover member 210 has a generally rectangular parallelepiped shape with a cavity therein, and has an opening on the surface facing the first end plate 31. The cover member 210 is arranged to cover the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f, and a flow path (first flow path 211) through which a fluid can flow between these communication holes is formed inside the cover member 210. That is, the first flow path 211 is formed by the inner surface of the cover member 210 and a part of the surface of the first end plate 31. Therefore, it can be said that the first flow path 211 is a flow path 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. There is no particular limitation on the method for fixing the cover member 210 to the surface of the first end plate 31. For example, the cover member 210 can be attached to the first end plate 31 by bolts, adhesive, welding, or the like. The shape of the cover member 210 is not limited to the form shown in FIG. 6. It may have any shape that allows the first flow path 211 to be formed therein.

[0066] FIG. 7 shows a cross-sectional view focusing on the first flow path 211. FIG. 7 is a partial cross-sectional view cut along the stacking direction of the first communication hole 100b and the second communication hole 100f. As shown in FIG. 7, hydrogen generated in the hydrogen electrode 16 by water electrolysis flows from the first communication hole 100b to the second communication hole 100f through the first flow path 211. Then, hydrogen flowing through the second communication hole 100f is supplied to each inter-cell region 21. In this way, hydrogen flows through each inter-cell region 21 during water electrolysis. The hydrogen supplied to the inter-cell region 21 has a pressure equal to that of the hydrogen electrode 16. Usually, the pressure of 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 through 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 taken out through the second communication hole 100e.

[0067] 6 and 7, the cover member 210 may have an opening 212 on the outer surface 210a that can be connected to the outside. This allows a portion 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 via the opening 212. This allows the number of openings from which hydrogen can be taken out to be increased. However, the opening 212 is optional, and the cover member 210 does not have to have the opening 212.

[0068] (Sealing of openings) In the water electrolysis stack 200, some of the openings through which hydrogen is extracted may be sealed. Specifically, the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f may be connected by the first flow path 211, and the openings 31a of the remaining first communication holes 100a that are not connected to the first flow path 211 may be sealed. There is no particular limitation on the method for sealing the openings 31a. For example, the openings 31a may be filled with a resin or the like. This makes it impossible to discharge hydrogen from the openings 31a, limiting the number of openings through which hydrogen is discharged, and thus simplifying the device.

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

[0070] The mechanism of hydrogen backflow suppression is as follows. When the temperature of the water electrolysis stack 200 drops during water electrolysis, the internal pressure in each water electrolysis cell 10 drops. As a result, hydrogen once discharged from the water electrolysis stack 200 returns to the water electrolysis stack 200. This is undesirable in terms of poisoning of the water electrolysis cell 10. In contrast, if the opening through which hydrogen is discharged is only 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 drop in internal pressure, it is difficult for the hydrogen to reach the water electrolysis cell 10 (hydrogen electrode 16) because it must pass through these communication holes and the inter-cell region 21. In this way, these communication holes and the inter-cell regions 21, especially the inter-cell regions 21 having a large capacity, act as buffers, thereby exerting the effect of suppressing the backflow of hydrogen.

[0071] Although the effect of suppressing hydrogen backflow is achieved even when the cover member 210 has the opening 212, the effect of suppressing hydrogen backflow is significantly improved when the cover member 210 does not have the opening 212 (when hydrogen is discharged only from the opening 31e).

[0072] The water electrolysis stack 200 includes two each of the first communication holes (100a, 100b) and the second communication holes (100e, 100f). However, the water electrolysis stack of the present disclosure may include three or more first communication holes. In this case, the remaining openings of the first communication holes that are not connected to the first flow path may be sealed. Of the remaining openings of the first communication holes, at least one opening or all openings may be sealed. Furthermore, the water electrolysis stack of the present disclosure may include three or more second communication holes. In this case, of the openings of the second communication holes, the remaining openings of the second communication holes that are not connected to the first flow path may be sealed, except for the opening of the second communication hole connected to the first flow path and the opening of the second communication hole for extracting hydrogen. Of the remaining openings of the second communication holes, at least one opening or all openings may be sealed. However, from the perspective of simplifying the device, the number of each of the first communication holes and the second communication holes may be two.

[0073] The water electrolysis stack 200 according to the first embodiment has been described above. The water electrolysis stack 200 is provided with the first flow paths 211, which allows hydrogen to flow through the inter-cell regions 21 during water electrolysis, thereby increasing the internal pressure in the inter-cell regions 21 and suppressing deformation of the inter-cell regions 21. Therefore, the water electrolysis stack 200 can improve durability.

[0074] [Second embodiment: water electrolysis stack 300] A water electrolysis stack 300 according to the second embodiment will now be described. The water electrolysis stack 300 differs from the water electrolysis stack 200 in the following respects: 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 on the first end plate 31, whereas the water electrolysis stack 300 has a first flow path 310 connecting the first communication hole 100b and the second communication hole 100f at a position away from the first end plate 31.

[0075] FIG. 8 shows a cross-sectional view focusing on the first flow path 310. As shown in FIG. 8, the first flow path 310 is a pipe, and connects the first communication hole 100b and the second communication hole 100f at a position away from the first end plate 31. As a result, even if there is a problem that the first communication hole 100b and the second communication hole 100f cannot be connected on the first end plate 31, the problem can be solved by using the first flow path 310. In addition, the first flow path 310 may have an opening 312 that can be connected to the outside, similar to the cover member 210. Note that, although FIG. 8 shows the first flow path 310 having a C-shape, the shape of the first flow path 310 is not limited to this. In addition, the first flow path 310 may be made of a single pipe, or may be made of multiple pipes.

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

[0077] 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, the sealing member 17 is disposed on the outer surface of the water electrolysis cell 10 (oxygen electrode separator 12). Typically, the sealing member 17 surrounds both the second holes 12e, 12f and the central portion (the region corresponding to the position of the electrode body 11). However, the present inventors have found that by changing the shape of the sealing members 17, it is possible to connect the first communication hole 100b and the second communication hole 100f inside the water electrolysis stack 400.

[0078] FIG. 10 shows an exploded perspective view of the cell stack 20 and the first end plate 31 in the water electrolysis stack 400. As shown in FIG. 10, a seal member 417 is disposed on the outer surface of the water electrolysis cell 10 (oxygen electrode separator 12) disposed on the end surface of the cell stack 20, surrounding not only the second holes 12e, 12f and the center portion, but also the first hole 12b. 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 device structure can be further simplified.

[0079] In the water electrolysis stack 400, the sealing members 417 are disposed on the water electrolysis cells 10 arranged on the end faces of the cell stack 20, but the sealing members 417 may be disposed on the water electrolysis cells 10 inside the cell stack 20. In other words, the sealing members 17 disposed between the water electrolysis cells 10 may be changed to the sealing members 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: water electrolysis stack 500] A water electrolysis stack 500 according to a fourth embodiment will now be described. The water electrolysis stack 500 differs from the water electrolysis stack 200 in the following respects. That is, 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, whereas 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 is different between the water electrolysis stack 500 and the water electrolysis stack 200.

[0081] FIG. 11 shows a perspective view of the water electrolysis stack 500. As shown in FIG. 11, the water electrolysis stack 500 includes a cover member 510 on the first end plate 31. The cover member 510 has the same shape as the cover member 210. The cover member 510 is disposed so as to cover the opening 31a of the first communication hole 100a and the opening 31e of the second communication hole 100e, and a flow path (first flow path 511) through which a fluid can flow between these communication holes is formed inside the cover member 510. That is, the first flow path 511 is formed by 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 flow path 511 is the same as the first flow path 211. Therefore, it can be said that the first flow path 511 is a flow path 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] Use of the cover member 510 allows hydrogen to flow 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. Hydrogen flowing through the second communication hole 100e is supplied to each inter-cell region 21. Therefore, during water electrolysis, hydrogen flows through each inter-cell region 21. Hydrogen flowing through the inter-cell region 21 is discharged to the outside through the second communication hole 100f. In this way, the water electrolysis stack 500 provides the same effects as the water electrolysis stack 200.

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

[0084] In the water electrolysis stack 200, hydrogen generated in each hydrogen electrode 16 by water electrolysis flows from the first communication hole 100b to the second communication hole 100f through the first flow path 211, and flows to each inter-cell region 21. Then, hydrogen is discharged from the second communication hole 100e. As is clear from FIG. 4, the second communication hole 100e is the second communication hole closest to the reactant 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 reactant water supplied to the water electrolysis stack 200. Therefore, the temperature of the hydrogen can be lowered by passing the hydrogen through the second communication hole 100e closest to the reactant water supply communication hole 100c and discharging it from there. The hydrogen generated by water electrolysis may be stored in a hydrogen tank. In this case, the hydrogen may be compressed and stored. When hydrogen having the same pressure is compared, the compression efficiency of hydrogen with a lower temperature is higher than that of hydrogen with a higher temperature. Therefore, when storing hydrogen in a compressed state, it is preferable that the hydrogen temperature is low.

[0085] In contrast, in the water electrolysis stack 500, hydrogen generated in each hydrogen electrode 16 by water electrolysis flows from the first communication hole 100a to the second communication hole 100e through the first flow path 511, and then flows to each inter-cell region 21. Then, hydrogen is discharged from the second communication hole 100f. As is clear from FIG. 4, the second communication hole 100f is the second communication hole closest to the reaction water discharge communication hole 100d. As described 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 communication hole 100f is higher than the temperature of the hydrogen discharged from the second communication hole 100e. When the generated hydrogen is immediately combusted as a heat source or when ammonia, methane, or the like is produced, a high hydrogen temperature is preferable.

[0086] Here, the water electrolysis stack 500 uses the first flow path 511 formed on the first end plate 31, but the form of the first flow path applicable to the water electrolysis stack 500 is not limited to this. For example, the first flow path of the water electrolysis stack 500 may have a configuration similar to that of the first flow path 310 which is a pipe, or may have a configuration similar to that of the first flow path which is a communication hole. Either configuration provides the same effect.

[0087] [Fifth embodiment] A fifth embodiment of the water electrolysis stack of the present disclosure will be described. The fifth embodiment differs from the water electrolysis stack 200 in the following respects. That is, in the water electrolysis stack 200, hydrogen is circulated through 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 through the inter-cell region 21. That is, in the fifth embodiment, the water electrolysis stack 100 can be used as is.

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

[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 effect of suppressing deformation of the inter-cell region 21 will be reduced. Comparing the pressure of the oxygen electrode 15 with the pressure of the hydrogen electrode 16, the pressure of the hydrogen electrode 16 is typically higher. Therefore, taking this relationship into consideration, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than the pressure of the oxygen electrode 15. From the viewpoint of significantly suppressing deformation of the inter-cell region 21, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than 90% of the pressure of the hydrogen electrode 16, or may be equal to or 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, taking into consideration the load applied to the water electrolysis stack, the pressure of the gas supplied to the inter-cell region 21 may be equal to or lower than 110% of the pressure of the hydrogen electrode 16.

[0090] When the pressure of the oxygen electrode 15 is higher than the pressure of the hydrogen electrode 16, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than the pressure of the hydrogen electrode 16, may be equal to or higher than 90% of the pressure of the oxygen electrode 15, or may be equal to or higher than the pressure of the oxygen electrode 15. In addition, the pressure of the gas supplied to the inter-cell region 21 may be equal to or lower than 110% of the pressure of the oxygen electrode 16.

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

[0092] The water electrolysis stack according to the present disclosure has been described above using the embodiments. The water electrolysis stack according to the present disclosure can circulate gas through the inter-cell regions during water electrolysis. This can suppress deformation of the inter-cell regions and improve durability of the water electrolysis stack.

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

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

[0095] <Water electrolysis stack 100> The water electrolysis stack 100 has been described above, and therefore a detailed description thereof 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 passing a current through the water electrolysis stack 100 while supplying reactant water thereto.

[0097] <Reaction water supply device 1200> The reaction water supplying device 1200 is a device that supplies reaction water to each oxygen electrode 15 of the water electrolysis stack 100. The reaction water supplying device 1200 may apply pressure to supply reaction water to the water electrolysis stack 100. The reaction water supplying device 1200 may be, for example, a known pump.

[0098] <Reaction water supply flow path 1210> The reacted water supply flow passage 1210 is a pipe that connects the water electrolysis stack 100 and the reacted water supply device 1200. The reacted water supply flow passage 1210 serves to flow the reacted water supplied from the reacted water supply device 1200 to the water electrolysis stack 100. The reacted water supply flow passage 1210 is connected to the opening 31c of the reacted water supply passage 100c of the water electrolysis stack 100.

[0099] <Reaction water discharge flow path 1220> The reacted water discharge flow path 1220 is a pipe connected to the water electrolysis stack 100. When the water electrolysis system 1000 includes the gas-liquid separator 1410, the reacted water discharge flow path 1220 connects the water electrolysis stack 100 and the gas-liquid separator 1410. The reacted water discharge flow path 1220 serves to pass the reacted water discharged from the water electrolysis stack 100. The reacted water discharge flow path 1220 is connected to the opening 31d of the reacted water discharge passage 100d of the water electrolysis stack 100.

[0100] <Hydrogen exhaust flow path 1300> The hydrogen discharge flow path 1300 is a pipe connected to the water electrolysis stack 100. When the water electrolysis system 1000 includes the gas-liquid separator 1420, the hydrogen discharge flow path 1300 connects the water electrolysis stack 100 and the gas-liquid separator 1420. The hydrogen discharge flow path 1300 serves to pass hydrogen discharged from the water electrolysis stack 100. Reaction water may also flow through the hydrogen discharge flow path 1300. This is because the reaction water may permeate the electrode assembly 11 and move from the oxygen electrode 15 to the hydrogen electrode 16. For this reason, the water electrolysis system 1000 may include the gas-liquid separator 1420 to remove the reaction water flowing through the hydrogen discharge flow path 1300.

[0101] 11 , the hydrogen discharge flow path 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 having a function of separating gas components and liquid components. The gas-liquid separator 1410 separates oxygen from the reaction water supplied from the reaction water discharge flow path 1220. The separated reaction water may be sent to the reaction water supply device 1200 via the circulation flow path 1230, or may be discharged to the outside. The separated oxygen may be sent to an oxygen tank, or may be discharged to the outside. The gas-liquid separator 1420 separates hydrogen from the reaction water supplied from the hydrogen discharge flow path 1300. The separated reaction water may be discharged to the outside. The separated hydrogen may be sent to a hydrogen tank, or may be discharged to the outside.

[0103] <Circulation flow path 1230> The circulation flow path 1230 is a pipe that connects the gas-liquid separator 1410 and the reaction water supply device 1200. The circulation flow path 1230 serves to flow the reaction water separated by the gas-liquid separator 1410. By providing the circulation flow path 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 according to the present disclosure will be described using each embodiment.

[0105] [First embodiment: water electrolysis system 2000] A water electrolysis system 2000 according to a first embodiment will be described below. The water electrolysis system 2000 differs from the water electrolysis system 1000 mainly in that the water electrolysis stack 100 is replaced with a water electrolysis stack 200. Only the differences from the water electrolysis system 1000 will be described below.

[0106] Fig. 13 shows a block diagram of a water electrolysis system 2000. As shown in Fig. 13, the water electrolysis system 2000 includes a water electrolysis stack 200. Moreover, instead of the hydrogen discharge flow path 1300, the water electrolysis system 2000 includes a hydrogen discharge flow path 2300 having 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 from the first communication hole 100b to the second communication hole 100f via the first flow path 211, flows into each inter-cell region 21, and is then discharged from the second communication hole 100e (opening 31e). Hydrogen is also discharged from the first communication hole 100a (opening 31a). Hydrogen is further 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 flow path 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. When the water electrolysis system 2000 includes the 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 through which hydrogen is discharged to the hydrogen discharge flow path 2300.

[0109] Here, the opening 31a of the first communication hole 100a of the water electrolysis stack 100 may be sealed. In that case, the hydrogen discharge flow path 2300 does not need to include the first pipe 2310. In that case, it is sufficient to connect either the second pipe 2320 or the third pipe 2330 to the gas-liquid separator 1420 and merge the other pipe into one of the pipes. In addition, if the cover member 210 does not have the opening 212, the hydrogen discharge flow path 2300 does not need to include the second pipe 2320.

[0110] The above describes the water electrolysis system 2000. The water electrolysis system 2000 uses the water electrolysis stack 200. However, the water electrolysis stacks 300, 400, and 500 can also be applied to the water electrolysis system 2000. However, when the water electrolysis stack 500 is applied to the water electrolysis system 2000, the shape of the hydrogen discharge flow path needs to be appropriately changed because the opening through which hydrogen is discharged is different.

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

[0112] FIG. 14 shows a block diagram of a water electrolysis system 3000. The second flow path 3500 is a pipe connecting the first communication holes 100a, 100b to each other. In practice, the water electrolysis stack 200 includes a cover member 210 connecting the first communication hole 100b to the second communication hole 100f. Therefore, the second flow path 3500 connects the opening 212 of the first flow path 211 to the opening 31a of the first communication hole 100a. This allows the first communication holes 100a, 100b to be connected to each other so that gas can flow therebetween. As shown in FIG. 14, the second flow path 3500 may be made up of multiple pipes.

[0113] The hydrogen supply device 3510 is disposed 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, 100b. The hydrogen supply device 3510 is, for example, a pump.

[0114] The gas-liquid separator 3520 is disposed on the upstream side (first communication hole 100b side) of the hydrogen supply device 3510 in the second flow path 3500. The gas-liquid separator 3520 separates the hydrogen and the reaction water supplied from the first communication hole 100b. This is because, in addition to the hydrogen generated by water electrolysis, the 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 will be described. Hydrogen generated in 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 into the inter-cell region 21, and is discharged from the second communication hole 100e. Meanwhile, 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 into 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, 100b, and the second flow path. Therefore, the opening through which hydrogen is discharged is the opening 31e of the second communication hole 100e.

[0116] In this way, the water electrolysis system 3000 applies pressure to circulate hydrogen, thereby flushing out hydrogen pools that accumulate at the hydrogen electrodes 16, etc. In other words, hydrogen pooling can be suppressed. Furthermore, suppressing hydrogen pooling can improve the hydrogen supply efficiency of the water electrolysis stack 200. Furthermore, the water electrolysis system 3000 can reduce the number of openings for discharging hydrogen, which contributes to simplifying the device.

[0117] As described above, the only opening through which hydrogen is discharged in the fuel cell stack 200 is the opening 31e of the second communication hole 100e. Therefore, the hydrogen discharge flow path 3300 may include only a pipe connecting the opening 31e of the second communication hole 100e of the water electrolysis stack 200.

[0118] The above describes the water electrolysis system 3000. The water electrolysis system 3000 uses the water electrolysis stack 200. However, the water electrolysis stacks 300, 400, and 500 can also be applied to the water electrolysis system 3000. However, when the water electrolysis stack 500 is applied to the water electrolysis system 3000, the shape of the hydrogen discharge flow path needs to be appropriately changed because the opening through which hydrogen is discharged is different.

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

[0120] FIG. 15 shows a block diagram of the water electrolysis system 4000. FIG. 15 also shows the first flow path 210. The gas-liquid separator 4610 is disposed in the first flow path 310. The third flow path 4620 is a pipe that connects the gas-liquid separator 4610 and the opening 31a of the first communication hole 100a that is not connected to the first flow path 210. As shown in FIG. 15, the third flow path 4620 may be composed of a plurality of pipes. The extrusion water supply device 4630 is disposed 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 be composed of a single pipe.

[0121] The movement of the extrusion water will be described. 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 together with hydrogen generated by water electrolysis. The extrusion water flowing through the first communication hole 100b reaches the gas-liquid separator 4610 disposed 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 manner, the extrusion water circulates between each hydrogen electrode 16 and the gas-liquid separator 4610 via the first communication holes 100a, 100b, the first flow path 210, and the third flow path 4620.

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

[0123] According to the water electrolysis system 4000, the extrusion water is circulated to flush out hydrogen pools remaining in the hydrogen electrodes 16. That is, hydrogen pools can be suppressed. Furthermore, suppressing hydrogen pools can improve the hydrogen supply efficiency of the water electrolysis stack 300. According to the water electrolysis system 4000, the only opening through which hydrogen is discharged is the opening 31e of the second communication hole 100e. Therefore, the number of openings through which hydrogen is discharged can be reduced, which contributes to simplifying the device. Furthermore, according to the water electrolysis system 4000, the gas-liquid separator 4610 is used in the first flow path 310 to separate hydrogen from the extrusion water. Then, only hydrogen is circulated through each inter-cell region 21 and discharged from the second communication hole 100e. Here, since the second communication hole 100e is close to the reactant water supply communication hole 100c, the temperature of hydrogen can be lowered by passing the hydrogen through the second communication hole 100e before discharging the hydrogen to the outside. This allows the temperature of the hydrogen to be significantly lowered compared to when hydrogen is discharged from the second communication hole 100e together with the extruded water. This is because hydrogen alone has a smaller heat capacity than extruded water containing hydrogen. The effect of obtaining hydrogen at a lower temperature has been described above.

[0124] The above describes the water electrolysis system 4000. The water electrolysis system 4000 can improve the durability of the water electrolysis stack and efficiently extract hydrogen.

[0125] [Fourth embodiment: water electrolysis system 5000] A description will now be given of a water electrolysis system 5000 according to a fourth embodiment. The water electrolysis system 5000 is configured such that a gas supply device 5700 is provided in addition to the water electrolysis system 1000.

[0126] 16 shows a block diagram of a water electrolysis system 5000. As shown in FIG 16, the water electrolysis system 4000 includes a gas supply device 5700, a gas supply flow path 5710, and a gas discharge flow path 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 of the gas include air, oxygen, hydrogen, and inert gas (such as nitrogen). The gas supply device 5700 is, for example, a pump. The gas supply passage 5710 connects the gas supply device 5700 to one of the openings of the second communication holes 100e, 100f of the water electrolysis stack 100. The gas discharge passage 5720 connects the gas supply device 5700 to the other opening of the second communication holes 100e, 100f of the water electrolysis stack 100. In FIG. 16, the gas supply passage 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 passage 5720 connects the gas supply device 5700 and the opening 31 f of the second communication hole 100 f 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 effect of suppressing deformation of the inter-cell region 21 will be reduced. Comparing the pressure of the oxygen electrode 15 with the pressure of the hydrogen electrode 16, the pressure of the hydrogen electrode 16 is typically higher. Therefore, taking this relationship into consideration, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than the pressure of the oxygen electrode 15. From the viewpoint of significantly suppressing deformation of the inter-cell region 21, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than 90% of the pressure of the hydrogen electrode 16, or may be equal to or 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, taking into consideration the load applied to the water electrolysis stack, the pressure of the gas supplied to the inter-cell region 21 may be equal to or lower than 110% of the pressure of the hydrogen electrode 16.

[0129] When the pressure of the oxygen electrode 15 is higher than the pressure of the hydrogen electrode 16, the pressure of the gas supplied to the inter-cell region 21 may be equal to or higher than the pressure of the hydrogen electrode 16, may be equal to or higher than 90% of the pressure of the oxygen electrode 15, or may be equal to or higher than the pressure of the oxygen electrode 15. In addition, the pressure of the gas supplied to the inter-cell region 21 may be equal to or lower than 110% of the pressure of the oxygen electrode 16.

[0130] The pressure of 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 may be referenced to the pressure of a reaction water supply device that supplies the reaction water. The pressure of the hydrogen electrode 16 is equivalent to the pressure of hydrogen discharged from the water electrolysis stack. The pressure of hydrogen discharged from the water electrolysis stack can be measured using a pressure measuring device.

[0131] The water electrolysis system according to the present disclosure has been described above using the embodiments. The water electrolysis system according to the present disclosure can circulate gas through the inter-cell regions during water electrolysis. This can suppress deformation of the inter-cell regions and improve durability of the water electrolysis stack.

[0132] (E) Modifications of the Water Electrolysis Stack of the Present Disclosure The water electrolysis stack described above has a configuration in which gas flows through the inter-cell regions during water electrolysis. This is to increase the pressure in the inter-cell regions and prevent the inter-cell regions from being deformed by the pressure of the adjacent hydrogen electrode or oxygen electrode. In contrast, the pressure in the inter-cell regions can also be increased by flowing a liquid (such as water) through the inter-cell regions instead of a gas, and it is believed that a similar effect can be achieved. Therefore, the configuration in which a liquid flows through the inter-cell regions will be described below.

[0133] [First Modification: Water Electrolysis Stack 600] A description will now be given of a water electrolysis stack 600 according to a first modified example. The water electrolysis stack 600 is configured by providing a fourth flow path 611 (cover member 610) to the water electrolysis stack 100. The fourth flow path 611 connects the reacted water discharge passage 100d and the second passage 100f.

[0134] FIG. 17 is a perspective view of the water electrolysis stack 600. As shown in FIG. 17, the water electrolysis stack 600 includes a cover member 610 on the first end plate 31. The cover member 610 has the same shape as the cover member 210. The cover member 610 is disposed so as to cover the opening 31d of the reactant water discharge passage 100d and the opening 31f of the second communication hole 100f, and a flow path (fourth flow path 611) through which a fluid can flow between these communication holes is formed inside the cover member 610. That is, the fourth flow path 611 is formed by 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 the first flow path 211. Therefore, it can be said that the fourth flow path 611 is a flow path that connects the opening 31d of the reactant water discharge passage 100d and the opening 31f of the second communication hole 100f on the first end plate 31.

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

[0136] Usually, the pressure of the reactive water is lower than the pressure of the hydrogen electrode 16. Therefore, even if reactive water having a normal pressure is circulated through the inter-cell region 21, there is a risk that the effect of suppressing deformation of the inter-cell region 21 cannot be sufficiently obtained. In addition, if the pressure of the reactive water is low, there is a concern that the reactive water may flow back. Therefore, the pressure of the reactive water supplied to the water electrolysis stack 600 may be higher than the normal pressure. For example, the pressure may be 90% or more of the pressure of the hydrogen electrode 16, or may be equal to or higher than the pressure of the hydrogen electrode 16. There is no particular upper limit on the pressure of the gas supplied to the inter-cell region 21. However, taking into consideration the load applied to the water electrolysis stack, the pressure of the reactive water may be 110% or less of the pressure of the hydrogen electrode 16. The pressure of the reactive water can be changed by adjusting the reactive 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 similar configuration to the opening 212 of the cover member 210, for example.

[0138] In the water electrolysis stack 600, the fourth flow path 611 is formed using the cover member 610. However, the form of the fourth flow path is not limited to this. For example, the fourth flow path may have a similar configuration to the first flow path 310 which is a pipe, or may have a similar configuration to the first flow path which is a communication hole. Either configuration provides the same effect.

[0139] In addition, the water electrolysis stack 600 uses a cover member 610 (fourth flow path 611) that connects the opening 31d of the reactant water discharge passage 100d and the opening 31f of the second communication hole 100f. However, the position of the cover member (fourth flow path) is not limited thereto. The cover member 610 (fourth flow path 611) may connect the opening 31c of the reactant water supply passage 100c and the opening 31e of the second communication hole 100e. Even in this case, the reactant water flows through the inter-cell region 21. However, when the fourth flow path connects the reactant water supply passage 100c and the second communication hole 100e, the cover member that forms the fourth flow path needs to have an opening that takes in the reactant water from the outside.

[0140] The above describes the modified water electrolysis stack of the present disclosure using the first modified example. The modified water electrolysis system of the present disclosure allows water to flow through the inter-cell region during water electrolysis. This can suppress deformation of the inter-cell region and improve the durability of the water electrolysis stack. In addition, the reactive water can be shared between the hydrogen electrode 16 and the inter-cell region, which contributes to simplifying the device.

[0141] (F) Modifications of the Water Electrolysis System of the Present Disclosure The water electrolysis system described above is configured so that gas flows through the inter-cell regions during water electrolysis. On the other hand, the water electrolysis system of the modified example is configured so that water flows through the inter-cell regions during water electrolysis. It is considered that the same effect can be achieved even if a liquid (such as water) is circulated through the inter-cell regions instead of a gas, since the pressure in the inter-cell regions can be increased. Therefore, the following describes the configuration in which water flows through the inter-cell regions.

[0142] [First Modification: Water Electrolysis System 6000] A water electrolysis system 6000 according to a first modified example will be described. The water electrolysis system 6000 differs from the water electrolysis system 1000 mainly in that the water electrolysis stack 100 is replaced with a water electrolysis stack 600. Only the differences from the water electrolysis system 1000 will be described below.

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

[0144] The reacted water supplied to the water electrolysis stack 600 flows from the reacted water supply passage 100c to each oxygen electrode 15, then flows from the reacted water discharge passage 100d to the second communication hole 100f via the fourth flow path 611, and flows to each inter-cell region 21. The reacted water is then discharged from the second communication hole 100e. The reacted water is also discharged from the opening 612 of the cover member 610. Thus, the water electrolysis stack 600 has two openings through which the reacted water is discharged. Therefore, the reacted 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. When the water electrolysis system 6000 includes the 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 the reacted water to the reacted water discharge flow path 6220. Note that when the cover member 610 does not include the opening 612, the reacted water discharge flow path 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 flow path 611) connecting the reactant water discharge passage 100d and the second communication hole 100f. However, a water electrolysis stack having a cover member (fourth flow path) connecting the reactant water supply passage 100c and the second communication hole 100e instead of the cover member 610 can also be used in the water electrolysis system 6000. In this case, the reactant water is discharged from the reactant water discharge passage 100d and the second communication hole 100f. Therefore, when using such a water electrolysis stack, the opening through which the reactant water is discharged is different, and therefore the shape of the reactant water discharge flow path needs to be appropriately changed.

[0147] [Second Modification: Water Electrolysis System 7000] A water electrolysis system 7000 according to the second modified example will be described below. The water electrolysis system 7000 differs from the water electrolysis system 2000 mainly in that the water electrolysis system 7000 includes a fifth flow path 7800. Only the differences from the water electrolysis system 2000 will be described below.

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

[0149] The fifth flow path 7800 is a pipe that connects the opening 31a of the first communication hole 100a that is not connected to the cover member 210 and the opening 31e of the second communication hole 100e that is not connected to the first flow path 211. As shown in FIG. 19, the second flow path 3500 may be composed of a plurality of pipes. The extrusion water supply device 7810 is disposed in the fifth flow path 7800, and circulates the extrusion water in the water electrolysis stack 200. The extrusion water supply device 7810 is, for example, a pump. The gas-liquid separator 7820 is disposed in the fifth flow path 7800 upstream of the extrusion water supply device 7810 (at the second communication hole 100e). The hydrogen discharge flow path 7300 is connected to the gas-liquid separator 7820. That is, the hydrogen discharge flow path 7300 is composed of one pipe.

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

[0151] According to the water electrolysis system 7000, the extrusion water is circulated to flush out hydrogen pools remaining in each hydrogen electrode 16. That is, hydrogen pools can be suppressed. Furthermore, suppressing hydrogen pools can improve the hydrogen supply efficiency of the water electrolysis stack 200. According to the water electrolysis system 7000, the only opening through which hydrogen is discharged together with the extrusion water is the opening 31e of the second communication hole 100e. Therefore, the number of openings through which hydrogen is discharged can be reduced, which contributes to simplifying the device. Furthermore, according to the water electrolysis system 7000, the extrusion water is discharged from the second communication hole 100e. Here, since the second communication hole 100e is close to the reactant water supply communication hole 100c, the temperature of the hydrogen separated from the extrusion water can be reduced by discharging the extrusion water to the outside after passing through the second communication hole 100e. The effect of obtaining hydrogen at a low temperature has been described above.

[0152] Here, the water electrolysis system 7000 uses a cover member 210 that does not have the openings 212. However, the water electrolysis system 7000 may use a cover member 210 that has the openings 212. In this case, the extruded water is discharged together with hydrogen from the openings 212. The extruded water discharged from the openings 212 may be separated into hydrogen and the extruded water by a gas-liquid separator. The separated hydrogen may be sent to the hydrogen tank via a hydrogen discharge flow path. The separated extruded water may be sent to the extruded water supply device 7810.

[0153] The water electrolysis system 7000 has been described above. The water electrolysis system 7000 uses the water electrolysis stack 200. However, the water electrolysis stacks 300, 400, and 500 can also be used in the water electrolysis system 7000. However, when the water electrolysis stack 500 is used in the water electrolysis system 7000, extrusion water may also be discharged from the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f. Therefore, when the water electrolysis stack 500 is used, the opening 31b of the first communication hole 100b and the opening 31f of the second communication hole 100f may be sealed.

[0154] The above describes the modified examples of the water electrolysis system according to the present disclosure. The modified examples of the water electrolysis system according to the present disclosure allow water to flow through the inter-cell regions during water electrolysis. This can suppress deformation of the inter-cell regions and improve 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 material 18a to 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 passage 100d Reaction water discharge hole 100e, 100f 2nd communication hole 210, 510, 610 Cover parts 211, 310, 511 First flow path 611 4th Stream 212, 312, 512, 612 openings 1000~7000 Water electrolysis system 1100 power supply 1200 Reaction water supply device 1210 Reaction water supply channel 1220 Reaction water discharge flow path 1230 Circulation flow path 1300~4300, 7300 Hydrogen exhaust flow path 1310, 2310 First pipe 1320, 2320 Second piping 2330 3rd Pipe 1410, 1420 Gas-liquid separator 3500 Second flow path 3510 Extrusion water supply device 3520 Gas-liquid separator 4610 Gas-liquid separator 4620 3rd Stream 4630 Extrusion water supply device 5700 Gas supply equipment 5710 Gas supply channel 5720 Gas exhaust flow path 6220 Reaction water discharge flow path 6221 First pipe 6222 Second piping 7800 5th Stream 7810 Extrusion water supply device 7820 Gas-liquid separator

Claims

1. having a cell stack in which a plurality of water electrolysis cells are stacked, in the cell stack, an inter-cell region is formed between adjacent water electrolysis cells, a gas (excluding water vapor) flows so as to increase the internal pressure of the inter-cell region during water electrolysis, a water electrolysis stack.

2. the water electrolysis cell includes an electrode body having an oxygen electrode catalyst layer disposed on one side with an electrolyte membrane interposed therebetween 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, a hydrogen electrode separator disposed on the hydrogen electrode catalyst layer side of the electrode body, and 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 generated at the hydrogen electrode.

4. When the pressure of the hydrogen electrode is higher than the pressure of the oxygen electrode, the pressure of the gas in the inter-cell region is 90% or more and 110% or less of the pressure of the hydrogen electrode, when the pressure of the oxygen electrode is higher than the pressure of the hydrogen electrode, the pressure of the gas in the inter-cell 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 includes 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 communication hole and the second communication hole, hydrogen generated at the hydrogen electrode by water electrolysis flows from the first communication hole to the second communication hole through the first flow path and into the inter-cell region, the water electrolysis stack according to claim 2.

6. the water electrolysis stack according to claim 1, and a pump for supplying the gas to the inter-cell region, a water electrolysis system.

7. having a cell stack in which a plurality of water electrolysis cells are stacked, in the cell stack, an inter-cell region is formed between adjacent water electrolysis cells, A water electrolysis stack in which a liquid flows so as to increase the internal pressure in the inter-cell region during water electrolysis. Water electrolysis stack. **Claim 8** A water electrolysis stack having a cell stack in which a plurality of water electrolysis cells are stacked, wherein the water electrolysis cell has an electrode body having an oxygen electrode catalyst layer disposed on one side with an electrolyte membrane interposed therebetween 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, 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, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator, wherein the pressure of the liquid in the inter-cell region is 90% or more and 110% or less of the pressure of the hydrogen electrode. The water electrolysis stack according to claim 7. **Claim 9** The water electrolysis stack includes a reaction water supply communication hole and a reaction water discharge communication hole that are connected to the oxygen electrode and formed to communicate along the stacking direction, two second communication holes that are connected to the inter-cell region and formed to communicate along the stacking direction, and a fourth flow path that connects the reaction water supply communication hole or the reaction water discharge communication hole and the second communication hole, wherein the liquid is reaction water, and the reaction water flows through the fourth flow path to the second communication hole and then to the inter-cell region. The water electrolysis stack according to claim 8. **Claim 10** A water electrolysis system including 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, wherein the water electrolysis cell has an electrode body having an oxygen electrode catalyst layer disposed on one side with an electrolyte membrane interposed therebetween 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, 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 the adjacent water electrolysis cells, the oxygen electrode separator of one of the water electrolysis cells and the hydrogen electrode separator of the other water electrolysis cell are adjacent to each other, and a cell-to-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator. The water electrolysis stack comprises two first communication holes that are connected to the hydrogen electrode and formed to communicate along the stacking direction, two second communication holes that are connected to the cell-to-cell region and formed to communicate along the stacking direction, and a first flow path that connects one of the first communication holes and one of the second communication holes. The fifth flow path connects another one of the first communication holes not connected to the first flow path and another one of the second communication holes not connected to the first flow path. The pressed water supplied from the pressed water supply device flows from another one of the second communication holes not connected to the first flow path through the fifth flow path to another one of the first communication holes not connected to the first flow path and then flows into the cell-to-cell region. The pressed water in the cell-to-cell region is pressurized. Water electrolysis system.

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