WATER ELECTROLYSIS CELL

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2024-144317 filed on Aug. 26, 2024. The disclosure of the above-identified application, including the specification, drawings, and claims, is incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

A technology to be disclosed in this specification relates to a water electrolysis cell.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2024-62492 (JP 2024-62492 A) discloses a water electrolysis cell. In this water electrolysis cell, a membrane-electrode assembly is disposed in an opening of a frame body made of resin. An anode separator is bonded on one face side of the frame body, and a cathode separator is bonded on the other face side of the frame body. Thus, sealing properties are secured.

SUMMARY

During water electrolysis, oxygen is generated. When this oxygen causes oxidation degradation of the frame body at a peripheral edge portion of the membrane-electrode assembly, the sealing properties cannot be maintained and the durability of the water electrolysis cell decreases.

A water electrolysis cell to be disclosed in this specification includes a membrane-electrode assembly, a frame body made of resin that is provided along a peripheral edge of the membrane-electrode assembly, and a first separator and a second separator that face each other through the membrane-electrode assembly and the frame body and are joined to each other by the frame body. An outer peripheral portion of the membrane-electrode assembly is extended to between a first face of the frame body and the first separator. A surface of the first face includes an antioxidant.

The first face of the frame body is a face which is located close to the membrane-electrode assembly and in which the concentration of generated oxygen becomes high. Containing the antioxidant in this first face can effectively mitigate oxidation degradation of the frame body. The durability of the water electrolysis cell can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is an exploded perspective view of a water electrolysis cell 1; and

FIG. 2 is a partial sectional view along line II-II of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

The antioxidant may include a chelating agent.

Metal ions having flowed out of the membrane-electrode assembly sometimes promote oxidation degradation of the frame body. In the above-described configuration, metal ions having flowed out can be inactivated by the chelating agent. Oxidation degradation of the frame body can more effectively mitigated.

The frame body may include a second face located on the opposite side from the first face. The content concentration of the antioxidant may be higher in the surface of the first face than in a surface of the second face.

The first face is located closer to the membrane-electrode assembly than the second face is. Therefore, the oxygen concentration tends to be higher in the first face than in the second face. In the above-described configuration, since the concentration of the antioxidant is set to be higher in the surface of the first face than in the surface of the second face, oxidation degradation of the frame body can be more effectively mitigated.

The membrane-electrode assembly may include an electrolyte membrane and a first catalyst layer. Outer peripheral portions of the electrolyte membrane and the first catalyst layer may be extended to between the first face of the frame body and the first separator. The first catalyst layer may be in contact with the first face through the electrolyte membrane. The first catalyst layer and the electrolyte membrane may not be in contact with the second face.

The concentration of metal ions having flowed out of the first catalyst layer tends to become higher, and thus oxidation degradation tends to be more promoted, in the first face than in the second face. When the antioxidant flows out, a catalyst in the catalyst layer may become poisoned; therefore, it is desirable to reduce the total amount of antioxidant to be added. In the above-described configuration, since the concentration of the antioxidant is set to be higher in the first face than in the second face, it is possible to achieve both preventing degradation of the first face that is prone to oxidation and mitigating catalyst poisoning.

The frame body may have a structure in which a first resin layer, a core layer, and a second resin layer are stacked in a thickness direction. The first resin layer may constitute the first face. The second resin layer may constitute the second face. The content concentration of the antioxidant may be higher in the first resin layer than in the second resin layer.

Schematic Configuration of Water Electrolysis Cell 1

FIG. 1 shows an exploded perspective view of a water electrolysis cell 1. The water electrolysis cell 1 mainly includes a first separator 10, a second separator 20, a membrane-electrode assembly 40, and a frame body 50. The membrane-electrode assembly 40 electrolyzes water to generate hydrogen and oxygen. The structure of the membrane-electrode assembly 40 will be described later.

The frame body 50 is formed by resin having insulation properties. As shown in FIG. 1, a housing hole 54 penetrating the frame body 50 is provided at the center of the frame body 50. Inside the housing hole 54, the membrane-electrode assembly 40 is disposed. Thus, the frame body 50 surrounds the membrane-electrode assembly 40.

The first separator 10 and the second separator 20 are formed by a gas-impermeable conductive material. Examples of the material of the separators include metal materials, such as stainless steel, and carbon materials. The first separator 10 and the second separator 20 face each other through the membrane-electrode assembly 40 and the frame body 50.

The frame body 50 is provided with a plurality of through-holes 56 around the housing hole 54. The first separator 10 is provided with a plurality of through-holes 16. The second separator 20 is provided with a plurality of through-holes 26. The through-holes 16, 26 are each located so as to coincide with the through-holes 56. As the through-holes 16, 56, 26 connect to one another, each of a first supply passage 61, a first discharge passage 62, a second supply passage 63, a second discharge passage 64, a third supply passage 65, and a drain passage 66 is formed. These flow passages penetrate the water electrolysis cell 1 in a thickness direction. Among the first, second, and third flow passages, two or more flow passages may be used.

Specific Configuration of Water Electrolysis Cell 1

FIG. 2 shows a partial sectional view along line II-II of FIG. 1. The membrane-electrode assembly 40 includes a hydrogen electrode 41, an oxygen electrode 42, and an electrolyte membrane 43. The electrolyte membrane 43 is an ion-exchange membrane that is formed by a solid polymer material and has proton conductivity. The hydrogen electrode 41 includes a first catalyst layer 44 and a first gas diffusion layer 45. The oxygen electrode 42 includes a second catalyst layer 46 and a second gas diffusion layer 47. The first catalyst layer 44 and the second catalyst layer 46 are porous layers in which carbon particles or metal oxides supporting a catalyst are coupled by resin. As the catalyst, for example, iridium (Ir), ruthenium (Ru), platinum (Pt), and alloys composed of Pt and other metals (e.g., Pt alloys with cobalt, nickel, etc. mixed therein) can be used. The first gas diffusion layer 45 and the second gas diffusion layer 47 are conductive members having water permeability and gas permeability.

The electrolyte membrane 43, the hydrogen electrode 41, and the oxygen electrode 42 have a rectangular shape. The hydrogen electrode 41 is similar in size to the electrolyte membrane 43, and the oxygen electrode 42 is smaller than the electrolyte membrane 43. In an upper face 43u of the electrolyte membrane 43, a frame-shaped outer peripheral region PA where the second catalyst layer 46 is not present is formed. In the upper face 43u inside the outer peripheral region PA, an adhesive layer 49 is disposed. The adhesive layer 49 is a layer formed by an adhesive applied. One example of the adhesive is an adhesive including an organic solvent and having ultraviolet-curable properties.

The frame body 50 has a three-layer structure in which a first resin layer 51, a core layer 53, and a second resin layer 52 are stacked in a thickness direction. The core layer 53 is a constituent member having gas sealing properties and insulation properties. The first resin layer 51 is a layer that is bonded to the first separator 10. The second resin layer 52 is a layer that is bonded to the second separator 20. A surface of the first resin layer 51 constitutes a lower face 51b of the frame body 50. A surface of the second resin layer 52 constitutes an upper face 52u of the frame body 50.

The first resin layer 51 and the second resin layer 52 may have properties with lower viscosity and a lower melting point than the core layer 53. Specifically, the first resin layer 51 and the second resin layer 52 may be a thermoplastic resin, such as an acid-modified olefin-based resin or a polyester-based resin. The frame body 50 having a multi-layer structure can be formed by various methods. For example, the frame body 50 may be formed by coextrusion molding.

The first resin layer 51 and the second resin layer 52 include an antioxidant. Various types of antioxidants can be adopted. For example, the antioxidant may be a chelating agent, or may be a phenol-based or aromatic amine-based one, or may be a sulfur-based or phosphorus-based one. Or the antioxidant may be a mixture of these components. In this embodiment, an antioxidant including a chelating agent is used.

The content concentration of the antioxidant is higher in the first resin layer 51 than in the second resin layer 52. That is, the content concentration of the antioxidant is set to be higher in the surface of the lower face 51b than in the surface of the upper face 52u. In this embodiment, the content concentration of the chelating agent is set to be higher in the first resin layer 51 than in the second resin layer 52.

There is an overlap region OA where an outer periphery of the membrane-electrode assembly 40 and an inner periphery of the frame body 50 overlap as seen from a direction perpendicular to the membrane-electrode assembly 40 (z-direction). In the overlap region OA, the frame body 50 is bonded to the upper face 43u of the electrolyte membrane 43 through the adhesive layer 49. Thus, a structure is created in which an outer peripheral portion 40e of the membrane-electrode assembly 40 is extended to between the lower face 51b of the frame body 50 and the first separator 10.

The first catalyst layer 44 is in contact with the lower face 51b of the frame body 50 through the electrolyte membrane 43 and the adhesive layer 49. On the other hand, the first catalyst layer 44 and the electrolyte membrane 43 are not in contact with the upper face 52u of the frame body 50. Thus, a structure is created in which the lower face 51b is located closer to the membrane-electrode assembly 40 than the upper face 52u is.

Operation of Water Electrolysis Cell 1

The first separator 10 is provided with ribs 10r. First flow passages 14 are formed by spaces between the ribs 10r and the membrane-electrode assembly 40. The second separator 20 is provided with ribs 20r. Second flow passages 24 are formed by spaces between the ribs 20r and the membrane-electrode assembly 40.

The hydrogen electrode 41 is supplied with nitrogen through the first supply passage 61 and the first flow passages 14. The oxygen electrode 42 is supplied with pure water through the second supply passage 63 and the second flow passages 24. The supplied pure water is electrolyzed by the membrane-electrode assembly 40. Hydrogen generated from the hydrogen electrode 41 is discharged to an outside through the first flow passages 14 and the first discharge passage 62. Oxygen generated from the oxygen electrode 42 is discharged to the outside through the second flow passages 24 and the second discharge passage 64.

During water electrolysis, oxygen is generated. When this oxygen causes oxidation degradation of the frame body 50, sealing properties cannot be maintained and the durability of the water electrolysis cell 1 decreases. The oxidation degradation is especially conspicuous in the first resin layer 51 inside the overlap region OA (see a region A1).

A first reason will be described. The first resin layer 51 is located closer to the membrane-electrode assembly 40 than the second resin layer 52 is. Therefore, the concentration of the generated oxygen tends to be higher in the lower face 51b of the first resin layer 51 than in the upper face 52u of the second resin layer 52.

A second reason will be described. The first catalyst layer 44 is in contact with the lower face 51b of the first resin layer 51 through the electrolyte membrane 43 and the adhesive layer 49. On the other hand, the first catalyst layer 44 and the electrolyte membrane 43 are not in contact with the upper face 52u of the second resin layer 52. Therefore, the concentration of metal ions having flowed out of the first catalyst layer 44 tends to be higher in the lower face 51b than in the upper face 52u. These metal ions having flowed out promote oxidation degradation of the first resin layer 51.

Effects

In the technology of the embodiment, the first resin layer 51 contains the antioxidant. Thus, oxidation degradation of the first resin layer 51 can be mitigated. The durability of the water electrolysis cell can be enhanced.

In the technology of the embodiment, the antioxidant contains the chelating agent. Thus, metal ions having flowed out can be inactivated by the chelating agent. The oxidation degradation promoting effect of the metal ions can be mitigated.

The oxygen concentration tends to be higher in the lower face 51b of the first resin layer 51 than in the upper face 52u of the second resin layer 52. In the technology of the embodiment, the concentration of the antioxidant is set to be higher in the lower face 51b than in the upper face 52u. Thus, oxidation degradation of the first resin layer 51 can be more effectively mitigated.

The concentration of metal ions having flowed out of the first catalyst layer 44 tends to be higher, and thus oxidation degradation tends to be more promoted, in the lower face 51b than in the upper face 52u. When the chelating agent flows out, catalysts in the first catalyst layer 44 and the second catalyst layer 46 may become poisoned; therefore, it is desirable to reduce the total amount of chelating agent to be added. In the technology of the embodiment, the concentration of the chelating agent is set to be higher in the lower face 51b than in the upper face 52u. Thus, the total amount of chelating agent to be added can be reduced while oxidation degradation of the lower face 51b that is more prone to oxidation is effectively mitigated. It is possible to achieve both preventing oxidation degradation and mitigating catalyst poisoning.

While forms of implementation have been described in detail above, these are merely illustration and do not restrict the claims. The technology described in the claims includes various modifications and changes made to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility independently or in various combinations, and are not restricted to the combinations described in the claims at the time of filing. The technology illustrated in this specification or the drawings achieves a plurality of purposes at the same time, and has technical utility by achieving one of these purposes itself.

Modified Examples

Various forms of containing the antioxidant in the frame body 50 can be adopted. For example, the antioxidant may be contained in the core layer 53. In this case, the antioxidant can be diffused from the core layer 53 to the first resin layer 51 and the second resin layer 52.

The technology of this specification can be applied to various structures. For example, the technology can be applied also to a structure in which the membrane-electrode assembly 40 and the frame body 50 do not overlap and the overlap region OA is not formed.

The frame body 50 is not limited to the three-layer structure. The technology of this specification can be applied also to a frame body having a single-layer structure, a double-layer structure, or a structure with four or more layers.

The content concentration of the antioxidant may be equal in the first resin layer 51 and the second resin layer 52.

The lower face 51b is one example of the first face. The upper face 52u is one example of the second face.