Water electrolysis stack

Abstract

To provide a water electrolysis stack having a connection part connecting a hydrogen electrode manifold and an inter-cell region manifold, and capable of suppressing an increase in a pressure loss of a flow channel due to dew condensation water remaining in the connection part.SOLUTION: A water electrolysis stack includes a cell laminate where a plurality of water electrolytic cells are laminated in a horizontal direction, and a pair of end plates each of which is arranged on both end surfaces in a lamination direction of the cell laminate. An opening of a first inter-cell region manifold is connected to an opening of a hydrogen electrode manifold via a connection part. The hydrogen electrode manifold is arranged closer to the upper side in a vertical direction than the first inter-cell region manifold. An area of a second inter-cell region manifold is greater than an area of the first inter-cell region manifold.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses a differential pressure type high-pressure water electrolysis device in which a load application mechanism is disposed inside a separator, and which can withstand an increase in internal pressure caused by water electrolysis and suppress lifting of the electrode parts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-60944 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the differential pressure type high-pressure water electrolysis apparatus described in Patent Document 1, the electrolyte membrane may be highly compressed by the load application mechanism, which may cause damage. In addition, the separator may be deformed by the load application mechanism, and in order to prevent this, the separator needs to be made thicker, which causes a problem of increased weight. This is because the separator is the only thing that can withstand the force generated by the increase in internal pressure during water electrolysis.

[0005] However, there is a need to increase the pressure in the water electrolysis cell in order to boost the hydrogen generated by water electrolysis. The applicant has been developing a water electrolysis stack that uses a fuel cell stack. Such a water electrolysis stack has an inter-cell region between adjacent water electrolysis cells. In order to meet the above needs in such a water electrolysis stack, the applicant has proposed a water electrolysis stack in which a hydrogen electrode manifold connected to the hydrogen electrode and an inter-cell region manifold connected to the inter-cell region are connected via a connection part such as a pipe, and hydrogen is circulated through the inter-cell region during water electrolysis (Patent Application No. 2023-6431). According to such a water electrolysis stack, the pressure difference between the hydrogen electrode and the inter-cell region can be suppressed, and the deformation of the separator can be suppressed. By suppressing the deformation of the separator, peeling of the seal part of each water electrolysis cell can be suppressed, and leakage can be suppressed. Therefore, since the water electrolysis stack having such a connection part has improved pressure resistance, the pressure in the water electrolysis cell can be increased.

[0006] As a result of further intensive research based on the above-mentioned technology, the inventors came across the problem that the connection part arranged on the outside is cooled by the outside air, and condensation water accumulates inside, increasing the pressure loss and, in some cases, causing the connection part to become clogged.

[0007] In view of the above-described circumstances, a main object of the present disclosure is to provide a water electrolysis stack having a connection portion that connects a hydrogen electrode manifold and an inter-cell region manifold, which can suppress an increase in pressure loss in the flow paths due to condensation water remaining in the connection portion. [Means for solving the problem]

[0008] A first aspect of the present disclosure provides a water electrolysis stack including a cell stack in which a plurality of water electrolysis cells are stacked in a horizontal direction, and a pair of end plates respectively arranged on both end faces in the stacking direction of the cell stack, wherein the water electrolysis cell includes an electrode assembly and a pair of separators, the electrode assembly including a solid electrolyte membrane, an oxygen electrode catalyst layer arranged on one side of the solid electrolyte membrane, and a hydrogen electrode catalyst layer arranged on the other side of the solid electrolyte membrane, the pair of separators including 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, wherein 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 are adjacent to each other, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator, the cell stack includes a pair of oxygen electrode manifolds connected to oxygen electrodes of each water electrolysis cell and formed in communication along the stacking direction, a hydrogen electrode manifold connected to hydrogen electrodes of each water electrolysis cell and formed in communication along the stacking direction, and a pair of inter-cell region manifolds connected to inter-cell regions of each water electrolysis cell and formed in communication along the stacking direction, wherein the pair of inter-cell region manifolds include a first inter-cell region manifold and a second inter-cell region manifold, openings of the pair of oxygen electrode manifolds, hydrogen electrode manifold and the pair of inter-cell region manifolds are formed on one of the end plates, the opening of the first inter-cell region manifold is connected to the opening of the hydrogen electrode manifold via a connection part, the hydrogen electrode manifold is disposed vertically above the first inter-cell region manifold, and the area of ​​the second inter-cell region manifold is larger than the area of ​​the first inter-cell region manifold. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a water electrolysis stack having a connection portion that connects a hydrogen electrode manifold and an inter-cell region manifold, which can suppress an increase in pressure loss in a flow path due to condensed water remaining in the connection portion. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of a water electrolysis stack 100. [Diagram 2] FIG. 2 is a perspective view of the water electrolysis stack 100 with the connection portion 40 removed. [Diagram 3] 2 is a diagram showing a part of a cross section of the cell stack 20 in the stacking direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The water electrolysis stack of the present disclosure will be described using a water electrolysis stack 100 as one embodiment. Fig. 1 shows a perspective view of the water electrolysis stack 100. Fig. 2 shows a perspective view of the water electrolysis stack 100 with the connection portion 40 removed. In Fig. 1, the x direction is the width direction, the y direction is the vertical direction, and the z direction is the stacking direction (horizontal direction).

[0012] As shown in FIG. 1, the water electrolysis stack 100 comprises a cell stack 20 in which a plurality of water electrolysis cells 10 are stacked in a horizontal direction, and a pair of end plates 51, 52 arranged on both end faces of the cell stack 20 in the stacking direction.

[0013] <Water electrolysis cell 10> The water electrolysis cell 10 has an electrode body and a pair of separators (oxygen electrode separator, hydrogen electrode separator) that sandwich the electrode body. The electrode body has a solid electrolyte membrane, an electrode body having an oxygen electrode catalyst layer arranged on one side of the solid electrolyte membrane, and a hydrogen electrode catalyst layer arranged on the other side of the solid electrolyte membrane. The pair of separators consists of an oxygen electrode separator arranged on the oxygen electrode catalyst layer side of the electrode body, and a hydrogen electrode separator arranged on the hydrogen electrode catalyst layer side of the electrode body. In the water electrolysis cell 10, 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. The oxygen electrode and the hydrogen electrode are spaces through which a fluid can flow. Reaction water (water) usually flows through the oxygen electrode. Hydrogen generated by water electrolysis usually flows through the hydrogen electrode.

[0014] The solid electrolyte membrane is a sheet-like member having proton conductivity. For example, proton conductive ionomers such as polyphenylene sulfonic acid polymer, polytetrafluoroethylene, and fluoroalkyl polymer such as perfluoroalkyl sulfonic acid polymer can be used. Perfluoroalkyl sulfonic acid polymer may be selected from the viewpoint of durability.

[0015] The oxygen electrode catalyst layer is a sheet-like member containing an oxygen electrode catalyst capable of generating oxygen by water electrolysis. The oxygen electrode catalyst may be a metal catalyst containing Pt, Ru, Rh, Os, Ir, Pd, and Au in its composition. The metal catalyst may be an oxide of these metals. Typically, it is iridium or iridium oxide. The oxygen electrode catalyst layer may also contain a proton-conductive ionomer. For example, the proton-conductive ionomer described above may be used.

[0016] The hydrogen electrode catalyst layer is a sheet-like member containing a hydrogen electrode catalyst capable of generating hydrogen by water electrolysis. The hydrogen electrode catalyst may be a metal catalyst containing 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 layer may also contain a proton-conductive ionomer. For example, the above-mentioned proton-conductive ionomer may be mentioned.

[0017] The pair of separators are made of conductive materials, such as metal materials such as iron, copper, stainless steel, and titanium.

[0018] The water electrolysis reaction in the water electrolysis cell 10 will be described. In the water electrolysis cell 10, reacted water is supplied to the oxygen electrode and a voltage is applied, causing a water electrolysis reaction. First, reacted water is supplied to the oxygen electrode catalyst layer, where oxygen and protons are generated by the water electrolysis reaction. The generated oxygen is discharged from the water electrolysis cell 10 together with the reacted water. The protons generated in the oxygen electrode catalyst layer permeate the solid electrolyte membrane and reach the hydrogen electrode catalyst layer. The protons that have reached the oxygen electrode then combine with electrons, generating hydrogen at the hydrogen electrode. The generated hydrogen is discharged from the water electrolysis cell 10.

[0019] <Cell stack 20> The cell stack 20 is formed by stacking a plurality of water electrolysis cells 10 in the horizontal direction. 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.

[0020] Fig. 3 shows a part of a cross section in the stacking direction (cross section cut perpendicular to the width direction) of the cell stack 20. As shown in Fig. 3, 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 of one water electrolysis cell 10 is adjacent to the hydrogen electrode separator of the other water electrolysis cell 10, and the inter-cell region 21 is formed between the oxygen electrode separator and the hydrogen electrode separator. The outer edge of the inter-cell region 21 is surrounded by a seal member 22, thereby ensuring watertightness or airtightness. In other words, the inter-cell region is a space formed when adjacent water electrolysis cells 10 are bonded with the seal member 22.

[0021] The cell stack 20 will be further described with reference to FIG. 2. The cell stack 20 includes a pair of oxygen electrode manifolds 31, 32 connected to the oxygen electrodes of the water electrolysis cells 10 and formed in communication with each other along the stacking direction, a pair of hydrogen electrode manifolds 33, 34 connected to the hydrogen electrodes of the water electrolysis cells 10 and formed in communication with each other along the stacking direction, and a pair of inter-cell region manifolds connected to the inter-cell regions 21 of the water electrolysis cells 10 and formed in communication with each other along the stacking direction. Each manifold is a communication hole that passes through the separator of each water electrolysis cell 10 in the stacking direction. An opening of each manifold is formed in the end plate 51. Here, "connection" means that fluids such as reaction water and hydrogen can flow between the manifold and a predetermined space of the water electrolysis cell 10. Typically, a guide path that connects the manifold and a predetermined space of the water electrolysis cell 10 is formed on the surface of the separator.

[0022] The oxygen electrode manifolds 31, 32 pass through the reaction water supplied to each water electrolysis cell 10. For example, when reaction water is supplied to the oxygen electrode manifold 31 of the pair of oxygen electrode manifolds 31, 32, the reaction water passes through the oxygen electrodes of each water electrolysis cell and is discharged from the oxygen electrode manifold 32 together with oxygen produced by the water electrolysis reaction.

[0023] Hydrogen discharged from each water electrolysis cell 10 flows through the hydrogen electrode manifolds 33, 34. Although Fig. 2 shows the water electrolysis stack 100 having a pair of hydrogen electrode manifolds 33, 34, the number of hydrogen electrode manifolds may be one. For example, one of the openings of the pair of hydrogen electrode manifolds 33, 34 (e.g., the opening of the hydrogen electrode manifold 34) may be blocked with a resin or the like. This reduces the number of openings through which hydrogen is discharged, making it possible to simplify the device.

[0024] The pair of inter-cell region manifolds includes a first inter-cell region manifold 35 and a second inter-cell region manifold 36. As shown in Figs. 1 and 2, an opening of the first inter-cell region manifold 35 is connected to an opening of the hydrogen electrode manifold 33 via a connection part 40. Therefore, hydrogen flowing through the hydrogen electrode manifold 33 flows through the first inter-cell region manifold 35 via the connection part 40 and reaches each inter-cell region 21. The hydrogen is then discharged from the second inter-cell region manifold 36. As such, the water electrolysis cell 100 has a structure in which hydrogen generated by water electrolysis flows through each inter-cell region and is discharged to the outside, so that the pressure difference between the hydrogen electrode and the inter-cell region 21 is extremely small, and deformation of the separator can be suppressed.

[0025] The connecting portion 40 is not particularly limited as long as it has a form that connects the respective openings. For example, it may be a pipe that connects the respective openings, or a lid-like member that covers the respective openings.

[0026] <End plates 51, 52> The end plates 51, 52 are members respectively disposed at both ends of the cell stack 20. As shown in Fig. 1, the end plate 51 is formed with openings for a pair of oxygen electrode manifolds 31, 32, a pair of hydrogen electrode manifolds 33, 34, and a pair of inter-cell region manifolds 35, 36. The pair of openings are respectively disposed side by side in the vertical direction at both ends of the end plate 51 in the width direction.

[0027] <Characteristic parts of the water electrolysis cell 100> Next, the characteristic parts of the water electrolysis cell 100 will be described. As shown in FIG. 2, the hydrogen electrode manifold 33 is disposed vertically above the first intercell region manifold 35. As described above, hydrogen generated at the hydrogen electrodes of each water electrolysis cell 10 flows through the hydrogen electrode manifold 33. The hydrogen has high humidity, and the water vapor is cooled and condensed at the connection portion 40 exposed to the outside, which may cause condensation water. In this case, for example, if the hydrogen electrode manifold 33 is disposed vertically below the first intercell region manifold 35, the condensed water will accumulate in the connection portion 40, which is likely to increase the pressure loss of the flow path and may cause the connection portion 40 to be blocked in some cases. In contrast, in the water electrolysis stack 100, the hydrogen electrode manifold 33 is disposed vertically above the first intercell region manifold 35, so the condensed water flows vertically (in the direction of gravity) downward according to gravity. Therefore, the water electrolysis stack 100 prevents water from accumulating at the connection portion 40, prevents an increase in pressure loss in the flow paths, and prevents clogging of the connection portion 40. From the viewpoint of improving this effect, it is preferable that the hydrogen electrode manifold 33 and the first inter-cell region manifold 35 are arranged side by side in the vertical direction, and more preferably adjacent to each other in the vertical direction, as shown in Fig. 2. This allows the reactant water to flow more smoothly.

[0028] The water electrolysis stack 100 is also characterized by the second intercell region manifold 36. That is, the area S36 of the second intercell region manifold 36 is larger than the area S35 of the first intercell region manifold 35. The "area of ​​the manifold" refers to the cross-sectional area of ​​the manifold when cut along a plane perpendicular to the stacking direction. In this manner, the area S36 of the second intercell region manifold 36 is formed larger than the area S35 of the first intercell region manifold 35, thereby reducing the pressure loss of the flow path. The above effect is achieved if the area S36 is even slightly larger than the area S35, but a greater effect is achieved if the area S36 is, for example, 1.2 times or more larger than the area S35. There is no particular upper limit to the area S36, but it may be, for example, 3 times or less than the area S35 due to structural limitations of the water electrolysis stack 100. That is, the area S36 is preferably 1.2 times or more and 3 times or less than the area S35.

[0029] The water electrolysis stack according to the present disclosure has been described above using one embodiment. According to the present disclosure, it is possible to provide a water electrolysis stack having a connection portion that connects a hydrogen electrode manifold and an inter-cell region manifold, which can suppress an increase in pressure loss in a flow path due to condensation water remaining in the connection portion. [Explanation of symbols]

[0030] 10 Water electrolysis cell 20 Cell stack 21 Inter-cell area 22 Sealing material 31, 32 Oxygen electrode manifold 33, 34 Hydrogen electrode manifold 35 First inter-cell area manifold 36 Second inter-cell area manifold 40 Connection 51, 52 End plate 100 Water Electrolysis Stack

Claims

[Claim 1] A water electrolysis stack comprising: a cell stack in which a plurality of water electrolysis cells are horizontally stacked; and a pair of end plates respectively disposed on both end surfaces of the cell stack in a stacking direction, The water electrolysis cell has an electrode assembly and a pair of separators, the electrode assembly includes a solid electrolyte membrane, an oxygen electrode catalyst layer disposed on one side of the solid electrolyte membrane, and a hydrogen electrode catalyst layer disposed on the other side of the solid electrolyte membrane; the pair of separators comprises 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, 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, the oxygen electrode separator of one of the water electrolysis cells is adjacent to the hydrogen electrode separator of the other of the water electrolysis cells, and an inter-cell region is formed between the oxygen electrode separator and the hydrogen electrode separator, The cell stack is a pair of oxygen electrode manifolds connected to the oxygen electrodes of the water electrolysis cells and communicating with each other along the stacking direction; a hydrogen electrode manifold connected to the hydrogen electrodes of each of the water electrolysis cells and communicating with each other along the stacking direction; a pair of inter-cell region manifolds connected to the inter-cell regions of each of the water electrolysis cells and communicating with each other along the stacking direction, the pair of intercell region manifolds comprises a first intercell region manifold and a second intercell region manifold; one end plate has openings for the pair of oxygen electrode manifolds, the hydrogen electrode manifold, and the pair of inter-cell region manifolds; an opening of the first inter-cell region manifold is connected to an opening of the hydrogen electrode manifold via a connection part, the hydrogen electrode manifold is disposed vertically above the first inter-cell region manifold, an area of ​​the second intercell region manifold is greater than an area of ​​the first intercell region manifold; Water electrolysis stack.

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