Water electrolysis stack

Abstract

To improve water electrolysis efficiency.SOLUTION: The water electrolysis stack includes a plurality of anion exchange membrane type cells that are electrically connected to each other in series and perform water electrolysis, and a manifold structure having a first manifold for supplying an electrolytic solution to the plurality of cells and a second manifold for discharging the electrolytic solution from the plurality of cells, wherein an inner wall surface of one or both of the first manifold and the second manifold has a higher insulating property than the electrolytic solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, there is known a technique for producing gases such as hydrogen by water electrolysis using a water electrolysis stack in which a plurality of cells, each including an electrolyte membrane such as an anion exchange membrane (AEM), are stacked. For example, Patent Document 1 describes a stack including plates that form flow paths for supplying water to each cell. In this stack, the plates are made of a metal such as stainless steel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2023-538279 Summary of the Invention [Problem to be solved by the invention]

[0004] In the stack described in Patent Document 1, the plates that form flow paths for supplying water to each cell are made of metal, and therefore there is a concern that leakage current may occur through the plates between different cells (for example, between anodes), resulting in a decrease in water electrolysis efficiency.

[0005] In consideration of the above circumstances, an object of at least one embodiment of the present disclosure is to improve the efficiency of water electrolysis. [Means for solving the problem]

[0006] In order to solve the above problems, a water electrolysis stack according to one embodiment of the present disclosure includes a plurality of anion exchange membrane cells electrically connected in series to perform water electrolysis, a first manifold for supplying an electrolytic solution to the plurality of cells, and a second manifold for discharging the electrolytic solution from the plurality of cells, wherein an inner wall surface of one or both of the first manifold and the second manifold has higher insulation properties than the electrolytic solution. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a water electrolysis stack according to an embodiment. [Figure 2] FIG. 2 is a top view of a flow path member and a manifold member of the water electrolysis stack shown in FIG. [Figure 3] FIG. 2 is a bottom view of a flow path member and a manifold member of the water electrolysis stack shown in FIG. [Figure 4] FIG. 2 is a partial perspective view of a manifold member. [Figure 5] FIG. 4 is a partial cross-sectional view of a manifold member. DETAILED DESCRIPTION OF THE INVENTION

[0008] The embodiments for carrying out the present disclosure will be described with reference to the drawings. Note that the dimensions and scale of each element in each drawing may differ from those of the actual product. Furthermore, the embodiment described below is an exemplary embodiment that may be envisioned when carrying out the present disclosure. Therefore, the scope of the present disclosure is not limited to the embodiment exemplified below.

[0009] 1. Embodiment 1-1. Overview of water electrolysis stack FIG. 1 is a schematic cross-sectional view of a water electrolysis stack 100 according to an embodiment. The water electrolysis stack 100 is a laminate including anion exchange membrane (AEM) cells 10-1 and 10-2 for performing water electrolysis using an electrolyte. The cells 10-1 and 10-2 are electrically connected in series to each other. Hereinafter, the cells 10-1 and 10-2 may be referred to as cells 10 without distinction. For ease of explanation, FIG. 1 representatively illustrates the cells 10-1 and 10-2, and the water electrolysis stack 100 includes two cells 10. However, in reality, the water electrolysis stack 100 includes several tens to several hundred cells 10, for example.

[0010] The electrolyte is, for example, pure water or an alkaline solution. Preferably, the electrolyte is an aqueous solution of potassium hydroxide (KOH), obtained by dissolving potassium hydroxide at a concentration of 1 M (mol / L) in pure water with a purity of about 20 μS / cm. The electrolyte may contain metal ions such as sodium (Na), magnesium (Mg), or calcium (Ca) as impurities.

[0011] An overview of the water electrolysis stack 100 will be described below with reference to FIG. 1. For convenience, the following description will use the mutually perpendicular X-axis, Y-axis, and Z-axis as appropriate. The Z-axis is an axis parallel to the stacking direction of the cells 10 (described below). Hereinafter, one direction along the X-axis is the X1 direction, and the direction opposite to the X1 direction is the X2 direction. One direction along the Y-axis is the Y1 direction, and the direction opposite to the Y1 direction is the Y2 direction. One direction along the Z-axis is the Z1 direction, and the direction opposite to the Z1 direction is the Z2 direction. The relationship between these directions and the vertical direction is not particularly limited and is arbitrary. Hereinafter, viewing in the direction along the Z-axis may be referred to as a "planar view."

[0012] 1 , the water electrolysis stack 100 includes membrane electrode assemblies (MEA) 20-1 and 20-2, flow path structures 30, 40, and 50, and gaskets 61, 62, 63, and 64. These are stacked in the Z2 direction in the following order: flow path structure 30, gasket 61, membrane electrode assembly 20-1, gasket 62, flow path structure 40, gasket 63, membrane electrode assembly 20-2, gasket 64, and flow path structure 50. Note that hereinafter, the membrane electrode assemblies 20-1 and 20-2 may be referred to as membrane electrode assemblies 20 without distinction.

[0013] Here, the flow path structure 30, the gasket 61, the membrane electrode assembly 20-1, the gasket 62, and a part of the flow path structure 40 constitute a cell 10-1. That is, the cell 10-1 includes the gasket 61, the membrane electrode assembly 20-1, the gasket 62, and a part of the flow path structure 40. The remaining part of the flow path structure 40, the gasket 63, the membrane electrode assembly 20-2, the gasket 64, and the flow path structure 50 constitute a cell 10-2. That is, the cell 10-2 includes the remaining part of the flow path structure 40, the gasket 63, the membrane electrode assembly 20-2, the gasket 64, and the flow path structure 50.

[0014] The membrane electrode assembly 20 is a laminate having a cathode 22, an anode 21, and an anion exchange membrane 23. Here, the cathode 22, the anion exchange membrane 23, and the anode 21 are laminated in this order. That is, the anion exchange membrane 23 is disposed between the cathode 22 and the anode 21. In the example shown in FIG. 1 , the cathode 22 is disposed in a position in the Z1 direction relative to the anion exchange membrane 23, and the anode 21 is disposed in a position in the Z2 direction.

[0015] The anion exchange membrane 23 is also called an AEM (Anion Exchange Membrane) and is an anion exchange membrane that exchanges hydroxide ions (OH -The anion exchange membrane 23 is an electrolyte membrane that selectively transmits anions such as cations, etc. The material constituting the anion exchange membrane 23 is not particularly limited, but examples thereof include polymer materials such as polyacrylonitrile (PAN), polystyrene (PS), polyvinyl alcohol (PVA), and polyethylene oxide (PEO).

[0016] The anion exchange membrane 23 has a first surface F1 and a second surface F2. The first surface F1 and the second surface F2 face in opposite directions. In the example shown in FIG. 1, the first surface F1 faces in the Z2 direction. On the other hand, the second surface F2 faces in the Z1 direction. The thickness of the anion exchange membrane 23 is, for example, about 30 μm.

[0017] The cathode 22 is laminated on the second face F2. In the cathode 22, hydrogen gas is generated by, for example, the following first reaction.

[0018] 4H2O+4e - →2H2+4OH - Although not shown, the cathode 22 has a catalyst layer and a diffusion layer. These are stacked in the order of catalyst layer and diffusion layer in the Z1 direction. Therefore, the catalyst layer is disposed between the second surface F2 and the diffusion layer. The catalyst layer of the cathode 22 is a thin film that promotes the first reaction described above, and is in close contact with the second surface F2. The catalyst layer of the cathode 22 is made of, for example, carbon carrying a metal material such as platinum (Pt). The material constituting the catalyst layer is not particularly limited and may be any material, such as nickel (Ni).

[0019] The diffusion layer of the cathode 22 is an element for efficiently separating and discharging the hydrogen gas generated by the first reaction. The diffusion layer of the cathode 22 is made of, for example, a porous film of nickel (Ni) foam or a carbon-based material. The diffusion layer of the cathode 22 is also electrically conductive and functions as a path for electrons exchanged with the catalyst layer.

[0020] The anode 21 is laminated on the first face F1. In the anode 21, oxygen gas is generated, for example, by the following second reaction.

[0021] 4OH - →O2+2H2O+4e - Although not shown, the anode 21 has a catalyst layer and a diffusion layer. These are stacked in the Z2 direction in the order of catalyst layer and diffusion layer. Therefore, the catalyst layer is disposed between the first surface F1 and the diffusion layer. The catalyst layer of the anode 21 is a thin film that promotes the second reaction described above and is in close contact with the first surface F1. The catalyst layer of the anode 21 is made of a metal material such as iridium (Ir), iron (Fe), or nickel (Ni). The material that makes up the catalyst layer of the anode 21 is not particularly limited and may be made of, for example, an oxide of the metal material described above.

[0022] The diffusion layer of the anode 21 is an element for efficiently separating and discharging oxygen gas generated by the second reaction. The diffusion layer of the anode 21 is made of, for example, a porous membrane of nickel (Ni) foam or a carbon-based material. The diffusion layer of the anode 21 also functions as an element for efficiently supplying the electrolyte to the catalyst layer. In addition, the diffusion layer of the anode 21 is electrically conductive and functions as a path for electrons exchanged with the catalyst layer.

[0023] The above-described membrane electrode assembly 20-1 is disposed between the flow path structure 30 and the flow path structure 40, whereas the membrane electrode assembly 20-2 is disposed between the flow path structure 40 and the flow path structure 50. Here, the flow path structures 30, 40, 50 are fixed to one another with fasteners such as screws or bolts, so that the membrane electrode assembly 20-1 is sandwiched between the flow path structure 30 and the flow path structure 40, and the membrane electrode assembly 20-2 is sandwiched between the flow path structure 40 and the flow path structure 50.

[0024] Anode-side flow paths R1-1 and R1-2, cathode-side flow paths R2-1 and R2-2, and manifolds M1, M2, and M3 are provided in the stack of flow path structures 30, 40, and 50. The manifold M1 is an example of a "first manifold," and the manifolds M2 and M3 are examples of a "second manifold."

[0025] The anode-side flow path R1-1 is a flow path defined by the flow path structure 40 and the anode 21 of the membrane electrode assembly 20-1 in the cell 10-1. The anode-side flow path R1-2 is a flow path defined by the flow path structure 50 and the anode 21 of the membrane electrode assembly 20-2 in the cell 10-2. The cathode-side flow path R2-1 is a flow path defined by the flow path structure 30 and the cathode 22 of the membrane electrode assembly 20-1 in the cell 10-1. The cathode-side flow path R2-2 is a flow path defined by the flow path structure 40 and the cathode 22 of the membrane electrode assembly 20-2 in the cell 10-2.

[0026] The manifold M1 is a distribution channel for supplying the electrolyte to the anode-side flow channel R1-1 of the cell 10-1 and the anode-side flow channel R1-2 of the cell 10-2. The manifold M2 is a collection channel for discharging oxygen and excess electrolyte from the anode-side flow channel R1-1 of the cell 10-1 and the anode-side flow channel R1-2 of the cell 10-2. The manifold M3 is a collection channel for discharging hydrogen and excess electrolyte from the cathode-side flow channel R2-1 of the cell 10-1 and the cathode-side flow channel R2-2 of the cell 10-2. Note that, hereinafter, the anode-side flow channels R1-1 and R1-2 may be referred to as the anode-side flow channel R1 without distinction. The cathode-side flow channels R2-1 and R2-2 may be referred to as the cathode-side flow channel R2 without distinction.

[0027] Preferably, one of the manifolds M1 and M2 is disposed vertically above the cells 10, while the other manifold is disposed vertically below the cells 10. That is, it is preferable to arrange the water electrolysis stack 100 so that one of the X1 and X2 directions is vertically above and the other is vertically below. This can reduce retention of the electrolyte in the cells 10 when operation is stopped.

[0028] As described above, a manifold M1 is provided to distribute the electrolyte to the anode-side flow path R1 of each cell 10. Here, to increase the purity of hydrogen generated at the cathode 22, the electrolyte is not supplied to the cathode-side flow path R2. Furthermore, to prevent mixing of the oxygen generated at the anode 21 and the hydrogen generated at the cathode 22, a manifold M3 is provided to discharge hydrogen and excess electrolyte from the cathode-side flow path R2, in addition to the manifold M2 that discharges oxygen and excess electrolyte from the anode-side flow path R1. Note that a manifold may be provided to distribute the electrolyte to the cathode-side flow path R2 of each cell 10.

[0029] The flow path structure 30 includes a flow path member 31 made of a conductive material and a manifold member 32 made of an insulating material. The flow path structure 40 includes a flow path member 41 made of a conductive material and a manifold member 42 made of an insulating material. The flow path structure 50 includes a flow path member 51 made of a conductive material and a manifold member 52 made of an insulating material. The manifold members 32, 42, and 52 form a manifold structure 70 having manifolds M1, M2, and M3. In this manner, the water electrolysis stack 100 includes the manifold structure 70.

[0030] Each of the flow path members 31, 41, 51 is a plate-like member made of a conductive material such as metal, and is also called a separator.

[0031] The flow path member 31 faces the second surface F2 of the membrane electrode assembly 20-1 across the cathode 22 of the membrane electrode assembly 20-1. Of the pair of plate surfaces of the flow path member 31, the plate surface facing the second surface F2 of the membrane electrode assembly 20-1 is provided with a plurality of cathode-side flow paths R2-1. Each cathode-side flow path R2-1 is defined by the cathode 22 of the membrane electrode assembly 20-1 and the flow path member 31. Hydrogen gas generated at the cathode 22 of the membrane electrode assembly 20-1 by the first reaction flows into each cathode-side flow path R2-1.

[0032] The flow path member 41 faces the first surface F1 of the membrane electrode assembly 20-1 across the anode 21 of the membrane electrode assembly 20-1, and faces the second surface F2 of the membrane electrode assembly 20-2 across the cathode 22 of the membrane electrode assembly 20-2. One of the pair of plate surfaces of the flow path member 41 facing the first surface F1 of the membrane electrode assembly 20-1 is provided with a plurality of anode-side flow paths R1-1. Each anode-side flow path R1-1 is partitioned by the anode 21 of the membrane electrode assembly 20-1 and the flow path member 41. Oxygen gas generated at the anode 21 of the membrane electrode assembly 20-1 by the second reaction flows into each anode-side flow path R1-1. Meanwhile, one of the pair of plate surfaces of the flow path member 41 facing the second surface F2 of the membrane electrode assembly 20-1 is provided with a plurality of cathode-side flow paths R2-2. Each cathode-side flow path R2-2 is defined by the cathode 22 of the membrane electrode assembly 20-2 and the flow path member 41. Hydrogen gas generated at the cathode 22 of the membrane electrode assembly 20-2 by the first reaction flows into each cathode-side flow path R2-2.

[0033] The flow path member 51 faces the first surface F1 of the membrane electrode assembly 20-2 across the anode 21 of the membrane electrode assembly 20-2. Of the pair of plate surfaces of the flow path member 51, the plate surface facing the first surface F1 of the membrane electrode assembly 20-2 is provided with a plurality of anode-side flow paths R1-2. Each anode-side flow path R1-2 is defined by the anode 21 of the membrane electrode assembly 20-2 and the flow path member 51. Oxygen gas generated at the anode 21 of the membrane electrode assembly 20-2 by the second reaction flows into each anode-side flow path R1-2.

[0034] Each of the manifold members 32, 42, and 52 is a frame-shaped member made of an insulating material such as resin or ceramics. Therefore, the manifold member 32 has an opening 32a that penetrates the manifold member 32 in the direction along the Z axis. The flow path member 31 is disposed in the opening 32a. The manifold member 42 has an opening 42a that penetrates the manifold member 42 in the direction along the Z axis. The flow path member 41 is disposed in the opening 42a. The manifold member 52 has an opening 52a that penetrates the manifold member 52 in the direction along the Z axis. The flow path member 51 is disposed in the opening 52a.

[0035] The manifold members 32, 42, and 52 are stacked in this order in the Z2 direction, and the manifold structure 70, which is the stack, is provided with manifolds M1, M2, and M3.

[0036] The gasket 61 is a frame-shaped sealing member that seals the cathode 22 of the membrane electrode assembly 20-1 in the space between the flow path structure 30 and the anion exchange membrane 23 of the membrane electrode assembly 20-1, and is laminated on the anion exchange membrane 23 so as to surround the cathode 22 of the membrane electrode assembly 20-1. The gasket 62 is a frame-shaped sealing member that seals the anode 21 of the membrane electrode assembly 20-1 in the space between the flow path structure 40 and the anion exchange membrane 23 of the membrane electrode assembly 20-1, and is laminated on the anion exchange membrane 23 so as to surround the anode 21 of the membrane electrode assembly 20-1. The gasket 63 is a frame-shaped sealing member that seals the cathode 22 of the membrane electrode assembly 20-2 in the space between the flow path structure 40 and the anion exchange membrane 23 of the membrane electrode assembly 20-2, and is laminated on the anion exchange membrane 23 so as to surround the cathode 22 of the membrane electrode assembly 20-2. The gasket 64 is a frame-shaped sealing member for sealing the anode 21 of the membrane electrode assembly 20-2 in the space between the flow path structure 50 and the anion exchange membrane 23 of the membrane electrode assembly 20-2, and is laminated on the anion exchange membrane 23 so as to surround the anode 21 of the membrane electrode assembly 20-2.

[0037] Each of the gaskets 61, 62, 63, and 64 is made of an elastic material such as vinyl methyl silicone rubber (VMQ), fluororubber (FKM), ethylene propylene diene rubber (EPDM), or polytetrafluoroethylene (PTFE).

[0038] Here, since the manifold M1 penetrates each of the gaskets 61, 62, 63, and 64, each of the gaskets 61, 62, 63, and 64 can constitute a part of the manifold M1. Since the manifold M2 penetrates each of the gaskets 63 and 64, each of the gaskets 63 and 64 can constitute a part of the manifold M2. Since the manifold M3 penetrates each of the gaskets 61 and 62, each of the gaskets 61 and 62 can constitute a part of the manifold M3. Here, each of the gaskets 61, 62, 63, and 64 is made of an insulating material such as the elastic material described above. Note that in FIG. 1, for convenience of explanation, the thicknesses of the membrane electrode assembly 20 and the gaskets 61, 62, 63, and 64 are exaggerated, but these thicknesses are extremely thin, ranging from several tens of μm to approximately 500 μm. Therefore, the gaskets 61, 62, 63, and 64 may be ignored as components of the manifolds M1, M2, and M3, respectively.

[0039] In the water electrolysis stack 100 outlined above, a supply device (not shown) is connected to the manifolds M1 and M2. The supply device is a mechanism that supplies the electrolytic solution to the manifold M1 and recovers oxygen generated by water electrolysis together with excess electrolytic solution from the manifold M2. The supply mechanism includes, for example, a container for storing the electrolytic solution, a liquid delivery mechanism that supplies the electrolytic solution stored in the container to the water electrolysis stack 100, a recovery mechanism that recovers oxygen gas together with excess electrolytic solution, and a gas-liquid separation tank that separates the recovered oxygen gas from the electrolytic solution. The electrolytic solution separated in the gas-liquid separation tank is recovered in the container.

[0040] A recovery mechanism (not shown) is connected to the manifold M3. The recovery mechanism recovers hydrogen generated by water electrolysis together with excess electrolyte from the manifold M3. The recovery mechanism includes, for example, a gas-liquid separation tank that separates hydrogen gas from the electrolyte.

[0041] Furthermore, a DC power supply (not shown) is electrically connected to the flow path member 31 and the flow path member 51 via a current collector plate (not shown). This allows a predetermined amount of current to be supplied from the DC power supply to the water electrolysis stack 100. Here, the cells 10-1 and 10-2 are electrically connected in series. The current density during water electrolysis is, for example, 0.01 A / cm 2 More than 4A / cm 2 The current collector plates are conductive plates that are placed on the outer surfaces of the flow path members 31 and 51, respectively.

[0042] In this state where a plurality of cells 10 are electrically connected in series, if a leakage current occurs between different cells 10 (for example, between the anodes 21), the efficiency of water electrolysis will decrease.

[0043] Therefore, the inner wall surfaces of the manifolds M1, M2, and M3 have higher insulating properties than the electrolyte, which reduces the leakage current that occurs between the multiple cells 10 through the manifold structure 70. This increases the current that contributes to water electrolysis, thereby improving the efficiency of water electrolysis.

[0044] As described above, each of the manifold members 32, 42, and 52 is made of an insulating material, and therefore the manifold structure 70 is made of an insulating material. This makes it possible to make the inner wall surfaces of the manifolds M1 and M2 more insulating than the electrolyte without performing any additional processing other than molding the manifold members 32, 42, and 52 that make up the manifold structure 70. Furthermore, it is possible to more reliably reduce leakage current that occurs between the multiple cells 10 through the manifold structure 70.

[0045] The insulating material constituting the manifold structure 70 is preferably a resin material, which makes it easier to mold the members constituting the manifold structure 70 compared to an embodiment in which a ceramic material is used.

[0046] The insulating material constituting the manifold structure 70 is preferably resistant to corrosion by the electrolyte, thereby increasing the durability of the manifold structure 70.

[0047] 1-2. Flow path structure Fig. 2 is a top view of the flow path member 41 and the manifold member 42 of the water electrolysis stack 100 shown in Fig. 1. Fig. 3 is a bottom view of the flow path member 41 and the manifold member 42 of the water electrolysis stack 100 shown in Fig. 1. Fig. 4 is a partial perspective view of the manifold member 42. Note that Fig. 2 shows the flow path structure 40 as viewed in the Z2 direction. Fig. 3 shows the flow path structure 40 as viewed in the Z1 direction.

[0048] The flow path structure 40 will be described in detail below. Note that for the flow path structures 30 and 50, differences from the flow path structure 40 will be mainly described, and descriptions of matters common to the flow path structure 40 will be omitted.

[0049] As shown in FIG. 2, a plurality of anode-side flow paths R1, distribution flow paths B1, and collecting flow paths B2 are provided on the surface of the flow path member 41 facing the Z1 direction. In the example shown in FIG. 2, each anode-side flow path R1 is formed with a recess extending along the Y axis so that the anode-side flow paths R1 are parallel to one another. The distribution flow path B1 is formed with a recess extending along the X axis and is connected to the ends of the anode-side flow paths R1 in the Y2 direction. The collecting flow path B2 is formed with a recess extending along the X axis and is connected to the ends of the anode-side flow paths R1 in the Y1 direction. The number of anode-side flow paths R1 provided in the flow path member 41 is not limited to the illustrated example and can be any number. Furthermore, the shape and arrangement of each anode-side flow path R1 are also not limited to the illustrated example and can be any number.

[0050] A flow path M1a of a manifold member 42 is connected to an end in the X2 direction of the distribution flow path B1 provided in the flow path member 41. The flow path M1a is a portion of the above-mentioned manifold M1 that is provided in the manifold member 42. The flow path M1a includes flow paths H1 and P1.

[0051] As shown in FIGS. 2 and 4, flow path H1 is formed as a hole penetrating manifold member 42. Flow path P1 is provided on the surface of manifold member 42 facing the Z1 direction and is formed as a recess extending from flow path H1 in the X1 direction. The X1-direction end of flow path P1 is connected to the X2-direction end of distribution flow path B1. Note that the shape and arrangement of flow path M1a are not limited to the example shown in the drawings and are arbitrary.

[0052] On the other hand, a flow path M2a of the manifold member 42 is connected to the end in the X1 direction of the collecting flow path B2 provided in the flow path member 41. The flow path M2a is a portion of the above-mentioned manifold M2 that is provided in the manifold member 42. The flow path M2a includes flow paths H2 and P2.

[0053] Flow path H2 is formed by a hole penetrating manifold member 42. Flow path P2 is provided on the surface of manifold member 42 facing the Z1 direction and is formed by a recess extending from flow path H2 in the X2 direction. The end of flow path P2 in the X2 direction is connected to the end of collecting flow path B2 in the X1 direction. Note that the shape and arrangement of flow path M2a are not limited to the example shown in the figure and are arbitrary.

[0054] As shown in FIG. 3, a surface of the flow path member 41 facing the Z2 direction is provided with a plurality of cathode-side flow paths R2 and a collecting flow path B3. In the example shown in FIG. 3, each cathode-side flow path R2 is formed with a recess extending in the Y-axis direction so that the plurality of cathode-side flow paths R2 are parallel to one another. The collecting flow path B3 is formed with a recess extending in the X-axis direction and is connected to the ends of the plurality of cathode-side flow paths R2 in the Y2 direction. The number of cathode-side flow paths R2 provided in the flow path member 41 is not limited to the illustrated example and may be arbitrary, and may differ from the number of anode-side flow paths R1. The shape and arrangement of each cathode-side flow path R2 are also not limited to the illustrated example and may be arbitrary, and may differ from the shape and arrangement of each anode-side flow path R1.

[0055] A flow path M3a of the manifold member 42 is connected to the end in the X1 direction of the collecting flow path B3 provided in the flow path member 41. The flow path M3a is a portion of the above-mentioned manifold M3 that is provided in the manifold member 42. The flow path M3a includes flow paths H3 and P3.

[0056] Flow path H3 is formed as a hole penetrating the manifold member 42. Flow path P3 is provided on the surface of the manifold member 42 facing the Z2 direction and is formed as a recess extending from flow path H3 in the X2 direction. The X2-direction end of flow path P3 is connected to the X1-direction end of collecting flow path B3. Note that the shape and arrangement of flow paths M3a are not limited to the example shown in the figure and are arbitrary.

[0057] As described above, the manifold member 42 is provided with the flow paths M1a, M2a, and M3a. Although not shown, the manifold member 32 is configured similarly to the manifold member 42 except that the flow paths M1a and M2a are omitted except for the flow path H1. Furthermore, although not shown, the manifold member 52 is configured similarly to the manifold member 42 except that the flow path M3a is omitted. However, the flow path H1 of the manifold member 52 is configured as a recess that does not penetrate the manifold member 52.

[0058] By stacking the above manifold members 32, 42, and 52 in this order, a manifold M1 is formed by the flow path H1 of the manifold member 32, the flow path M1a of the manifold member 42, and the flow path M1a of the manifold member 52. This stacking also forms a manifold M2 by the flow path M2a of the manifold member 42 and the flow path M2a of the manifold member 52. This stacking also forms a manifold M3 by the flow path M3a of the manifold member 32 and the flow path M3a of the manifold member 42.

[0059] As described above, each of the manifold members 32, 42, and 52 is made of an insulating material, and therefore the inner wall surfaces of each of the manifolds M1, M2, and M3 are also made of an insulating material.

[0060] FIG. 5 is a partial cross-sectional view of the manifold member 42. FIG. 5 shows a cross section of the distribution flow path B1 of the flow path M1a. As shown in FIG. 5, a coating film 43 is provided on the inner wall surface of the flow path M1a. That is, the coating film 43 is provided on the bottom and side surfaces of the recess that constitutes the flow path P1 and on the inner wall surface of the hole that constitutes the flow path H1. In this way, the coating film 43 is provided on the inner wall surface of the manifold M1.

[0061] 5, the coating film 43 is provided over the entire surface facing the Z1 direction of the manifold member 42. The coating film 43 is provided not only on the bottom and side surfaces of the recesses that form the flow paths P1 and on the inner wall surfaces of the holes that form the flow paths H1, but also on the surface facing the Z1 direction of the manifold member 42. Note that the coating film 43 may be provided on at least a portion of the inner wall surface of the flow path M1a, but is preferably provided over the entire inner wall surface of the flow path M1a.

[0062] The coating film 43 is made of a material that is insulating and liquid-repellent. The material that makes up the coating film 43 is preferably one that is not only insulating and liquid-repellent but also resistant to corrosion by alkaline solutions, and is preferably a fluorine-based resin such as PFA (perfluoroalkoxyalkane) or PTFE (polytetrafluoroethylene). The thickness of the coating film 43 is not particularly limited and can be any thickness. Note that "liquid-repellent" refers to the ability to repel liquid with respect to an electrolyte solution, and can also be called "water-repellent."

[0063] Although not shown, the coating film 43 is also provided on the inner wall surfaces of the manifolds M2 and M3.

[0064] In this manner, the insulating and liquid-repellent coating film 43 is provided on the inner wall surface of each of the manifolds M1, M2, and M3. This reduces retention of the electrolyte in the manifolds M1, M2, and M3 when the water electrolysis stack 100 is out of operation. As a result, corrosion of the anode 21, the cathode 22, and the like due to reverse current when the water electrolysis stack 100 is out of operation can be reduced.

[0065] When the coating film 43 is made of a fluorine-based resin, the fluorine-based resin not only has insulating properties and liquid repellency but also has corrosion resistance to alkaline solutions, and therefore, corrosion of the anode 21, the cathode 22, and the like due to reverse current when the water electrolysis stack 100 is not operating can be reduced over a long period of time.

[0066] In addition, the coating film 43 may be provided as necessary in at least one of the manifolds M1, M2, and M3, or may be omitted. When the coating film 43 is omitted, each of the manifold members 32, 42, and 52 may be made of a fluorine-based resin such as PFA (perfluoroalkoxyalkane) or PTFE (polytetrafluoroethylene). In this case, even if the coating film 43 is not provided, the same effect as when the coating film 43 is provided can be obtained.

[0067] 2. Variations Specific modified embodiments that can be added to each of the embodiments exemplified above are exemplified below. Two or more embodiments arbitrarily selected from the following examples may be appropriately combined within a range that does not contradict each other.

[0068] 2-1. Variation 1 In the above-described embodiment, an example is given in which each of the manifold members 32, 42, and 52 is made of an insulating material, but this is not limiting. For example, if the above-described leakage current is reduced by the coating film 43, each of the manifold members 32, 42, and 52 may be made of a conductive material such as metal. However, from the viewpoint of suitably reducing the above-described leakage current, it is preferable that each of the manifold members 32, 42, and 52 be made of an insulating material.

[0069] 2-2. Variation 2 In the above-described embodiment, the water electrolysis stack 100 includes two cells 10, but the present invention is not limited to this, and the water electrolysis stack 100 may include three or more cells 10.

[0070] 3. Notes From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0071] (Supplementary Note 1) A first aspect, which is a preferred example of a water electrolysis stack according to the present disclosure, includes a manifold structure having a plurality of anion exchange membrane cells electrically connected in series to perform water electrolysis, a first manifold for supplying an electrolyte to the plurality of cells, and a second manifold for discharging the electrolyte from the plurality of cells, wherein the inner wall surfaces of one or both of the first manifold and the second manifold have higher insulation properties than the electrolyte.

[0072] In the above-described embodiment, the inner wall surface of one or both of the first manifold and the second manifold has higher insulation properties than the electrolyte, thereby reducing leakage current that occurs between the multiple cells through the manifold structure, thereby increasing the current that contributes to water electrolysis and, as a result, improving the efficiency of water electrolysis.

[0073] (Supplementary Note 2) In a second aspect, which is a preferred example of the first aspect, the manifold structure is made of an insulating material. In this aspect, the insulating properties of the inner wall surfaces of the first manifold and the second manifold can be made higher than that of the electrolyte without performing any additional processing other than molding the members that make up the manifold structure. Furthermore, the leakage current that occurs between the multiple cells through the manifold structure can be more reliably reduced.

[0074] (Supplementary Note 3) In a third aspect which is a preferred example of the second aspect, the insulating material is a resin material. In this aspect, molding of the members constituting the manifold structure is easier than in an aspect using a ceramic material.

[0075] (Supplementary Note 4) In a fourth aspect which is a preferred example of the second or third aspect, the insulating material has corrosion resistance against the electrolyte. In the above aspect, the durability of the manifold structure can be improved.

[0076] (Supplementary Note 5) In a fifth aspect which is a preferred example of any of the first to fourth aspects, an insulating and liquid-repellent coating film is provided on an inner wall surface of one or both of the first manifold and the second manifold. In this aspect, retention of the electrolytic solution in the first manifold and the second manifold can be reduced when the water electrolysis stack is out of operation. As a result, corrosion of the anode, cathode, etc. due to reverse current when the water electrolysis stack is out of operation can be reduced.

[0077] (Supplementary Note 6) In a sixth aspect which is a preferred example of the fifth aspect, the coating film is made of a fluororesin. In this aspect, the fluororesin not only has insulating properties and liquid repellency but also corrosion resistance to alkaline solutions, making it possible to reduce corrosion of the anode, cathode, etc. due to reverse current when the water electrolysis stack is not in operation for a long period of time.

[0078] (Supplementary Note 7) In a seventh aspect which is a preferred example of any of the first to sixth aspects, one of the first manifold and the second manifold is disposed vertically above the plurality of cells, and the other manifold is disposed vertically below the plurality of cells. In this aspect, it is possible to reduce retention of the electrolyte in the cells when operation is stopped. [Explanation of symbols]

[0079] 10...cell, 10-1...cell, 10-2...cell, 20...membrane electrode assembly, 20-1...membrane electrode assembly, 20-2...membrane electrode assembly, 21...anode, 22...cathode, 23...anion exchange membrane, 30...flow path structure, 31...flow path member, 32...manifold member, 32a...opening, 40...flow path structure, 41...flow path member, 42...manifold member, 42a...opening, 43...coating film, 50...flow path structure, 51...flow path member, 52...manifold member, 52a...opening, 61...gasket, 62...gasket, 63...gasket, 64...gasket, 70...manifold Electrode structure, 100...water electrolysis stack, B1...distribution flow path, B2...collecting flow path, B3...collecting flow path, F1...first surface, F2...second surface, H1...flow path, H2...flow path, H3...flow path, M1...manifold (first manifold), M1a...flow path, M2...manifold (second manifold), M2a...flow path, M3...manifold (second manifold), M3a...flow path, P1...flow path, P2...flow path, P3...flow path, R1...anode side flow path, R1-1...anode side flow path, R1-2...anode side flow path, R2...cathode side flow path, R2-1...cathode side flow path, R2-2...cathode side flow path.

Claims

1. a plurality of anion exchange membrane type cells electrically connected in series to each other and performing water electrolysis; a manifold structure including a first manifold for supplying an electrolytic solution to the plurality of cells and a second manifold for discharging the electrolytic solution from the plurality of cells; an inner wall surface of one or both of the first manifold and the second manifold has higher insulation properties than the electrolyte; Water electrolysis stack.

2. The manifold structure is made of an insulating material. The water electrolysis stack according to claim 1 .

3. The insulating material is a resin material. The water electrolysis stack according to claim 2 .

4. The insulating material has corrosion resistance to the electrolyte. The water electrolysis stack according to claim 2 .

5. an insulating and liquid-repellent coating film is provided on an inner wall surface of one or both of the first manifold and the second manifold; The water electrolysis stack according to claim 1 or 2.

6. The coating film is made of a fluorine-based resin. The water electrolysis stack according to claim 5 .

7. one of the first manifold and the second manifold is disposed vertically above the plurality of cells, and the other manifold is disposed vertically below the plurality of cells; The water electrolysis stack according to claim 5 .

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