Electrolytic Cell and Electrolysis Device

The present disclosure relates to an electrolytic cell and an electrolysis device. Priority is claimed on Japanese Patent Application No. 2022-90936, filed on Jun. 3, 2022, the content of which is incorporated herein by reference.

Patent Document 1 discloses a membrane electrode assembly used in polymer electrolyte membrane (PEM)-type water electrolysis. In order to improve pressure stability and airtightness at a high differential pressure, in the membrane electrode assembly, a first gas diffusion layer disposed on the front surface side of an ion conductive membrane has a smaller area than the ion conductive membrane, and a second gas diffusion layer disposed on the rear surface side of the ion conductive membrane has the same area as the ion conductive membrane (semi-coherent design).

[Patent Document 1] Published Japanese Translation No. 2009-513820 of the PCT International Publication SUMMARY OF INVENTION

Incidentally, as the deterioration when the electrolytic cell is used, the deterioration of an anode may significantly progress as compared with the deterioration of a cathode, and as a result, the performance of the electrolytic cell may decrease.

The present disclosure has been made in order to solve the above-described problems, and an object thereof is to provide an electrolytic cell and an electrolysis device, which can improve performance.

In order to solve the above-described problems, an electrolytic cell according to the present disclosure includes a first separator, a second separator, an ion exchange membrane configured to be disposed between the first separator and the second separator, and an anion exchange membrane with hydroxide ion conductivity, a cathode configured to be disposed between the first separator and the ion exchange membrane, and an anode configured to be disposed between the second separator and the ion exchange membrane. In a case of being viewed in a first direction in which the ion exchange membrane, the cathode, and the anode overlap each other, an area of the anode is larger than an area of the cathode.

In order to solve the above-described problems, an electrolysis device according to the present disclosure includes an electrolytic cell, an electrolyte supply unit configured to supply an electrolyte to the electrolytic cell; and a power supply unit configured to apply a voltage to the electrolytic cell. The electrolytic cell includes a first separator, a second separator, an ion exchange membrane configured to be disposed between the first separator and the second separator, and an anion exchange membrane with hydroxide ion conductivity, a cathode configured to be disposed between the first separator and the ion exchange membrane, and an anode configured to be disposed between the second separator and the ion exchange membrane. In a case of being viewed in a first direction in which the ion exchange membrane, the cathode, and the anode overlap each other, an area of the anode is larger than an area of the cathode.

According to the electrolytic cell and the electrolysis device of the present disclosure, it is possible to improve the performance.

Hereinafter, an electrolytic cell and an electrolysis device according to the embodiment of the present disclosure will be described with reference to the drawings. In the following description, the same reference signs are assigned to configurations having the same or similar functions. In the present disclosure, “face each other” means that two members overlap each other when viewed in a certain direction and may also include a case where another member (for example, another layer) is present between the two members.

First, a Z direction, an X direction, and a Y direction are defined with reference to. The Z direction is a direction from a first separatorto a second separatordescribed later. The X direction is a direction intersecting (for example, orthogonal to) the Z direction and is a direction from a central portion C of an ion exchange membranedescribed later toward one end portion of the ion exchange membrane. The Y direction is a direction intersecting (for example, orthogonal to) the Z direction and the X direction and is, for example, a depth direction of the paper surface in. In the present disclosure, the term of “area” means an area in a case of being viewed in the Z direction (that is, an area extending in the X direction and the Y direction). In addition, in the present disclosure, the term of “external size” means an external size in the case of being viewed in the Z direction. That is, the terms of “external size” and “area” may mean substantially the same thing and may be appropriately interpreted with each other.

is a schematic configuration diagram showing an overall configuration of an electrolysis deviceaccording to a first embodiment. For example, the electrolysis deviceis a device that generates hydrogen by electrolyzing water contained in an electrolyte. For example, the electrolysis deviceis an anion exchange membrane (AEM)-type electrolytic device. However, the electrolysis deviceis not limited to the above example and may be an electrolysis device having a different type, such as a device for electrolytic reduction of carbon dioxide.

For example, the electrolysis deviceis provided with an electrolytic cell stack, an electrolyte supply unit, and a power supply unit.

The electrolytic cell stackis an assembly of a plurality of electrolytic cells. For example, the electrolytic cell stackis formed by arranging the plurality of electrolytic cellsin one direction. Each electrolytic cellincludes a cathode chamber Sa and an anode chamber Sb. The electrolytic cellwill be described later in detail.

The electrolyte supply unitis a supply unit that supplies an electrolyte to each electrolytic cell. For example, the electrolyte is pure water or an alkaline aqueous solution. The electrolyte supply unitincludes a cathode-side supply unitand an anode-side supply unit

The cathode-side supply unitis a supply unit that supplies an electrolyte to the cathode chamber Sa of each electrolytic cell. For example, the cathode-side supply unitincludes a hydrogen gas-liquid separation device, a first pump, a hydrogen recovery unit, a first electrolyte supply unit, and piping lines Land L.

The hydrogen gas-liquid separation devicestores the electrolyte. A supply port of the hydrogen gas-liquid separation deviceis connected to the cathode chamber Sa of the electrolytic cellvia the piping line L. The first pumpis provided in the middle of the piping line Land sends the electrolyte stored in the hydrogen gas-liquid separation devicetoward the cathode chamber Sa of the electrolytic cell.

The return port of the hydrogen gas-liquid separation deviceis connected to the cathode chamber Sa of the electrolytic cellvia the piping line L. An electrolyte containing hydrogen generated in the electrolytic cellflows into the hydrogen-gas-liquid separation devicefrom the electrolytic cell. The hydrogen gas-liquid separation devicehas a gas-liquid separation unit that separates hydrogen contained in the electrolyte. The hydrogen separated from the electrolyte by the hydrogen gas-liquid separation deviceis recovered by the hydrogen recovery unit. The hydrogen gas-liquid separation deviceis replenished with the electrolyte from the first electrolyte supply unit.

On the other hand, the anode-side supply unitis a supply unit that supplies an electrolyte to the anode chamber Sb of each electrolytic cell. For example, the anode-side supply unitincludes an oxygen gas-liquid separation device, a second pump, an oxygen recovery unit, a second electrolyte supply unit, and piping lines Land LA.

The oxygen gas-liquid separation devicestores the electrolyte. A supply port of the oxygen gas-liquid separation deviceis connected to the anode chamber Sb of the electrolytic cellvia the piping line L. The second pumpis provided in the middle of the piping line Land sends the electrolyte stored in the oxygen gas-liquid separation devicetoward the anode chamber Sb of the electrolytic cell.

The return port of the oxygen gas-liquid separation deviceis connected to the anode chamber Sb of the electrolytic cellvia the piping line LA. An electrolyte containing oxygen generated in the electrolytic cellflows into the oxygen gas-liquid separation devicefrom the electrolytic cell. The oxygen gas-liquid separation devicehas a gas-liquid separation unit that separates oxygen contained in the electrolyte. Oxygen separated from the electrolyte by the oxygen gas-liquid separation deviceis recovered by the oxygen recovery unit. The oxygen gas-liquid separation deviceis replenished with the electrolyte from the second electrolyte supply unit.

The power supply unitis a direct current power supply device that applies a voltage to the electrolytic cell. The power supply unitapplies a direct current voltage desired for the electrolysis of the electrolyte between the anode and the cathode of the electrolytic cell.

Next, the electrolytic cellwill be described in detail.

is a cross-sectional view schematically showing the electrolytic cell. For example, the electrolytic cellincludes a first separator, a second separator, and a membrane electrode assembly.

The first separatoris a member that defines one surface of an internal space S of the electrolytic cell. The internal space S is a space including the cathode chamber Sa and the anode chamber Sb described later. For example, the first separatorhas a rectangular plate shape and includes a metal member. For example, a negative voltage is applied to the first separatorfrom the power supply unitvia a first current collector(refer to) described later.

The first separatorhas a first end portion(for example, a lower end portion) and a second end portion(for example, an upper end portion) located on a side opposite to the first end portion. The above-described piping line Lis connected to the first end portionof the first separator. The above-described piping line Lis connected to the second end portionof the first separator. The first separatorhas a first inner surfacethat faces the cathode chamber Sa described later. A first flow path FPthrough which the electrolyte supplied from the piping line Lflows is formed on the first inner surface. For example, the first flow path FPis a groove provided in the first inner surface. The electrolyte that has flowed through the first flow path FPis discharged to the outside of the electrolytic cellthrough the piping line L. Each structure (for example, a flow path structure) shown inis merely an example and does not limit the content of the present embodiment. For example, various structures can be used as the flow path structure depending on the size, purpose, and use environment of the device. The same applies to each structure shown in other drawings.

The second separatoris a member that is disposed with an internal space S between the second separatorand at least part of the first separatorand that defines the other surface of the internal space S. For example, the second separatorhas a rectangular plate shape and includes a metal member. A positive voltage is applied to the second separatorfrom the power supply unitvia a second current collector(refer to) described later. The first separatorand the second separatorincluded in the same electrolytic cellform an electrolyzerof the electrolytic cellas a pair of separators.

The second separatorhas a first end portion(for example, a lower end portion) and a second end portion(for example, an upper end portion) located on a side opposite to the first end portion. The above-described piping line Lis connected to the first end portionof the second separator. The above-described piping line Lis connected to the second end portionof the second separator. The second separatorhas a second inner surfacethat faces the anode chamber Sb described later. A second flow path FPthrough which the electrolyte supplied from the piping line Lflows is formed on the second inner surface. For example, the second flow path FPis a groove provided in the second inner surface. The electrolyte that has flowed through the second flow path FPis discharged to the outside of the electrolytic cellthrough the piping line LA.

Here, for convenience of description, a configuration in which the first inner surfaceof the first separatorhas a groove for a flow path (first flow path FP) and the second inner surfaceof the second separatorhas a groove for a flow path (second flow path FP) is described. However, for example, the first separatorof the electrolytic cellincluded in the electrolytic cell stack(refer to) may be a bipolar plate having the same groove for a flow path (first flow path FP, shown by a two-dot chain line in) on a surfaceopposite to the first inner surfacein addition to the first inner surface. In addition, the second separatorof the electrolytic cellincluded in the electrolytic cell stackmay be a bipolar plate having the same groove for a flow path (second flow path FP, shown by a two-dot chain line in) on a surfaceopposite to the second inner surfacein addition to the second inner surface. The grooves for flow paths provided on both surfaces of the first separatormay have different shapes and dispositions. In addition, the grooves for flow paths provided on both surfaces of the second separatormay have different shapes and dispositions.

A membrane electrode assembly (MEA)is a structure in which an ion exchange membrane, a catalyst, and a power supply body are assembled. The membrane electrode assemblyis disposed between the first separatorand the second separatorand is located in the internal space S. For example, the membrane electrode assemblyincludes an ion exchange membrane, a cathode catalyst layer, a cathode power supply body, an anode catalyst layer, and an anode power supply body.

The ion exchange membraneis a membrane that selectively allows ions to permeate. For example, the ion exchange membraneis a solid polymer electrolyte membrane. For example, the ion exchange membraneis an anion exchange membrane (AEM) having hydroxide ion conductivity. However, the ion exchange membraneis not limited to the above-described example and may be an ion exchange membrane having a type different from the above-described example. For example, the ion exchange membranehas a rectangular sheet shape. The external size of the ion exchange membraneis smaller than the external size of the first separatoror the second separator. The ion exchange membraneis disposed between the first separatorand the second separatorand is located in the above-described internal space S.

The ion exchange membranehas a first surfacefacing the first inner surfaceof the first separatorand a second surfacelocated on a side opposite to the first surfaceand facing the second inner surfaceof the second separator. In the internal space S, the cathode chamber Sa is defined between the first surfaceof the ion exchange membraneand the first inner surfaceof the first separator. In the internal space S, the anode chamber Sb is defined between the second surfaceof the ion exchange membraneand the second inner surfaceof the second separator.

In the cathode chamber Sa, in a case where a voltage is applied to the electrolytic cell, the following chemical reaction occurs, and hydrogen is generated from the electrolyte. In the present application, the phrase that “XX is generated” may also include a case where another substance is simultaneously generated in association with the generation of XX. The hydroxide ions generated in the cathode chamber Sa pass through the membrane electrode assemblyand move from the cathode chamber Sa to the anode chamber Sb.

In the anode chamber Sb, in a case where a voltage is applied to the electrolytic cell, the following chemical reaction occurs, and oxygen is generated from the electrolyte.

As a result, in a case of being viewed in the electrolytic cellas a whole, the following chemical reaction occurs.

The cathode catalyst layeris a layer that accelerates the chemical reaction in the cathode chamber Sa described above. For example, the cathode catalyst layerhas a rectangular sheet shape. In the present embodiment, the external size of the cathode catalyst layeris smaller than the external size of the ion exchange membrane. The cathode catalyst layeris disposed in the cathode chamber Sa and is adjacent to the ion exchange membrane. In the present application, the term of “adjacent” is not limited to a case where two members are independently adjacent to each other and may also include a case where at least part of one member of the two members enters the other member. For example, part of the cathode catalyst layermay enter a surface portion of the ion exchange membrane. In the present embodiment, the cathode catalyst layeris provided on the first surfaceof the ion exchange membrane. For example, the cathode catalyst layeris formed by applying a material of the cathode catalyst layerto the first surfaceof the ion exchange membrane. A negative voltage is applied to the cathode catalyst layerfrom the power supply unitvia the first separatorand the cathode power supply body, and the cathode catalyst layerfunctions as part of the cathodeof the electrolytic cell.

As a material of the cathode catalyst layer, any material that accelerates the chemical reaction in the cathode chamber Sa described above may be used, and various materials can be used. For example, the cathode catalyst layercontains one or more nickel, a nickel alloy, a cerium oxide, a lanthanum oxide, or platinum. In the present disclosure, the term of “XX oxide” may contain another material other than XX and oxygen. In addition, the cathode catalyst layermay include another material such as carbon in addition to the above-described material. “XX” is any material.

The cathode power supply bodyis an electrical connection portion that transmits a voltage applied to the first separatorto the cathode catalyst layer. The cathode power supply bodyis disposed in the cathode chamber Sa. The cathode power supply bodyis located between the first inner surfaceof the first separatorand the cathode catalyst layerand is in contact with each of the first inner surfaceof the first separatorand the cathode catalyst layer. At least part of the cathode power supply bodymay overlap at least part of at least one of the first separatoror the cathode catalyst layer. The cathode power supply bodyhas a structure in which an electrolyte and gas can pass through the inside. For example, the cathode power supply bodyis made of a metal mesh structure, a sintered body, a fiber, or the like. In the present embodiment, the external size of the cathode power supply bodyis the same as the external size of the cathode catalyst layer. In the present embodiment, the cathodeof the electrolytic cellincludes the cathode catalyst layerand the cathode power supply body.

The anode catalyst layeris a layer that accelerates the chemical reaction in the anode chamber Sb described above. For example, the anode catalyst layerhas a rectangular sheet shape. In the present embodiment, the external size of the anode catalyst layeris smaller than the external size of the ion exchange membrane. The anode catalyst layeris disposed in the anode chamber Sb and is adjacent to the ion exchange membrane. For example, part of the anode catalyst layermay enter the surface portion of the ion exchange membrane. In the present embodiment, the anode catalyst layeris provided on the second surfaceof the ion exchange membrane. For example, the anode catalyst layeris formed by applying a material of the anode catalyst layerto the second surfaceof the ion exchange membrane. A positive voltage is applied to the anode catalyst layerfrom the power supply unitvia the second separatorand the anode power supply body, and the anode catalyst layerfunctions as part of the anodeof the electrolytic cell.

As a material of the anode catalyst layer, any material that accelerates the chemical reaction in the above-described anode chamber Sb may be used, and various materials can be used. For example, the anode catalyst layercontains one or more nickel, a nickel alloy, a nickel oxide, a copper oxide, an iridium oxide, a niobium oxide, a lead oxide, or a bismuth oxide. As described above, the term of “XX oxide” in the present disclosure may contain another material other than XX and oxygen. For example, the term of “nickel oxide” may contain another material such as iron or cobalt in addition to nickel and oxygen. In addition, the term of “copper oxide” may contain another material such as cobalt in addition to copper and oxygen. The term of “iridium oxide” may contain another material such as ruthenium in addition to iridium and oxygen. The term of “lead oxide” may contain another material such as ruthenium in addition to lead and oxygen. The term of “bismuth oxide” may contain another material such as ruthenium, in addition to bismuth and oxygen.

The anode power supply bodyis an electrical connection portion that transmits the voltage applied to the second separatorto the anode catalyst layer.

The anode power supply bodyis disposed in the anode chamber Sb. The anode power supply bodyis located between the second inner surfaceof the second separatorand the anode catalyst layerand is in contact with each of the second inner surfaceof the second separatorand the anode catalyst layer. At least part of the anode power supply bodymay overlap at least part of at least one of the second separatoror the anode catalyst layer. The anode power supply bodyhas a structure in which an electrolyte and gas can pass through the inside. For example, the anode power supply bodyis made of a metal mesh structure, a sintered body, a fiber, or the like. In the present embodiment, the external size of the anode power supply bodyis the same as the external size of the anode catalyst layer. In the present embodiment, the anodeof the electrolytic cellincludes the anode catalyst layerand the anode power supply body.

is an exploded perspective view showing the electrolytic cell. For example, the electrolytic cellincludes the first current collector, the second current collector, a first insulator, a second insulator, a first insulating material, a second insulating material, a first end plate, and a second end plate, in addition to the above-described configuration. In, for convenience of description, a support portionand a sealing portiondescribed later are not shown.

The first current collectoris an electrical connection portion that transmits the negative voltage applied from the power supply unitto the first separator. The first current collectoris a metal plate member (for example, a copper plate). For example, the first current collectoris in contact with the first separatorfrom a side of the electrolytic cellopposite to the internal space S and is electrically connected to the first separator. A negative voltage desired for the electrolysis in the electrolytic cellis applied to the first current collectorfrom the power supply unit. The first current collectormay be shared by two electrolytic cellsadjacent to each other in the electrolytic cell stack.

The second current collectoris an electrical connection portion that transmits the positive voltage applied from the power supply unitto the second separator. The second current collectoris a metal plate member (for example, a copper plate). For example, the second current collectoris in contact with the second separatorfrom a side of the electrolytic cellopposite to the internal space S and is electrically connected to the second separator. A positive voltage desired for the electrolysis in the electrolytic cellis applied to the second current collectorfrom the power supply unit. The second current collectormay be shared by two electrolytic cellsadjacent to each other in the electrolytic cell stack.

The first insulatoris a member that insulates an outer peripheral portion of the first separatorand an outer peripheral portion of the second separator. The first insulatoris a frame-shaped sheet member that is larger than the outer shape of the cathode catalyst layerand the outer shape of the cathode power supply bodyby one size. The first insulatoris attached to the first inner surfaceof the first separatorand covers an end portion of the first inner surface. The material of the first insulatoris not particularly limited as long as the material is an insulating material, and is, for example, a sheet-like resin such as polytetrafluoroethylene (PTFE).

The second insulatoris a member that insulates the outer peripheral portion of the first separatorand the outer peripheral portion of the second separator, similarly to the first insulator. The second insulatoris a frame-shaped sheet member that is larger than the outer shape of the anode catalyst layerand the outer shape of the anode power supply bodyby one size. The second insulatoris attached to the second inner surfaceof the second separatorand covers an end portion of the second inner surface. The material of the second insulatoris not particularly limited as long as the material is an insulating material and is, for example, a sheet-like resin such as PTFE. In addition, the first insulatorand the second insulatorcan also be used as an integrated insulator.

The first insulating materialis located between the first current collectorand the first end plate. For example, the external size of the first insulating materialis the same as the external size of the first current collectoror larger than the external size of the first current collector.