This application claims the benefit of Japanese Application No. 2022-149017, filed on Sep. 20, 2022, the disclosure of which is incorporated by reference herein.
The present invention relates to a water electrolyzer.
A water electrolyzer conventionally known produces hydrogen (H2) through electrolysis of water (H2O). The water electrolyzer has a stack structure with a cell and a separator stacked alternately. Each cell includes an electrolyte membrane and catalyst layers formed on both surfaces of the electrolyte membrane. During implementation of water electrolysis, a voltage is applied between an anode-side catalyst layer and a cathode-side catalyst layer and water is supplied to the anode-side catalyst layer. This causes electrochemical reactions as follows at the anode-side catalyst layer and the cathode-side catalyst layer. As a result, hydrogen is output from the cathode-side catalyst layer.
(anode side)2H2O→4H++O2+4e−
(cathode side) 2H++2e−→H2
Conventional solid polymer water electrolysis is described in Japanese Patent Application Laid-Open No. 2022-023996, for example.
In the water electrolyzer, it is necessary to form flow paths for water, oxygen, and hydrogen supplied or output during the above-described electrochemical reactions and to provide reliable sealing between these flow paths. To meet these conditions, a separator in the conventional water electrolyzer is composed of two metal plates. However, locating two metal plates between one cell and another cell increases cost involved in the separator.
The present invention has been made in view of the foregoing circumstances, and is intended to provide a technique achieving reduction in the number of metal plates to be used as a separator in a water electrolyzer.
To solve the foregoing problem, a first aspect of the present invention is intended for a water electrolyzer comprising a plurality of cells and a plurality of separators, and having a stack structure with the cells and the separators stacked alternately. Each of the cells includes: a base layer including an electrolyte membrane; a catalyst layer layered on a surface of the electrolyte membrane; and a gas diffusion layer layered on a surface of the catalyst layer. Each of the separators includes: a metal plate with a distribution hole; and a ring-like flow path member located between the base layer and the metal plate in a stacking direction and surrounding the distribution hole when viewed in the stacking direction. The flow path member includes a flow path through which the gas diffusion layer and the distribution hole communicate with each other.
According to a second aspect of the present invention, in the water electrolyzer according to the first aspect, each of the cells includes: a cathode catalyst layer that is the catalyst layer layered on the electrolyte membrane on one side; and a cathode gas diffusion layer that is the gas diffusion layer layered on the cathode catalyst layer on the one side, the metal plate includes a hydrogen distribution hole that is the distribution hole for distributing hydrogen output from the cathode gas diffusion layer, each of the separators includes a cathode flow path member that is the flow path member located between a cathode-side surface of the base layer and the metal plate in the stacking direction and surrounding the hydrogen distribution hole when viewed in the stacking direction, and the cathode flow path member includes a hydrogen flow path that is the flow path through which the cathode gas diffusion layer and the hydrogen distribution hole communicate with each other.
According to a third aspect of the present invention, in the water electrolyzer according to the first or second aspect, each of the cells includes: an anode catalyst layer that is the catalyst layer layered on the electrolyte membrane on the other side; and an anode gas diffusion layer that is the gas diffusion layer layered on the anode catalyst layer on the other side, the metal plate includes: a water distribution hole that is the distribution hole for distributing water to be supplied to the anode gas diffusion layer; and an oxygen distribution hole that is the distribution hole for distributing oxygen output from the anode gas diffusion layer, each of the separators includes: a first anode flow path member that is the flow path member located between an anode-side surface of the base layer and the metal plate in the stacking direction and surrounding the water distribution hole when viewed in the stacking direction; and a second anode flow path member that is the flow path member located between the anode-side surface of the base layer and the metal plate in the stacking direction and surrounding the oxygen distribution hole when viewed in the stacking direction, the first anode flow path member includes a water flow path that is the flow path through which the anode gas diffusion layer and the water distribution hole communicate with each other, and the second anode flow path member includes an oxygen flow path that is the flow path through which the anode gas diffusion layer and the oxygen distribution hole communicate with each other.
According to a fourth aspect of the present invention, in the water electrolyzer according to any one of the first to third aspects, the flow path member includes: a first surface contacting the metal plate; and a second surface contacting the base layer, and the flow path is a groove formed at the first surface.
According to a fifth aspect of the present invention, in the water electrolyzer according to the fourth aspect, each of the separators further includes a ring-like seal member arranged on a surface of the metal plate on the opposite side to the flow path member and surrounding the distribution hole when viewed in the stacking direction, when viewed in the stacking direction, the flow path member is arranged at a position overlapping the seal member, and the second surface of the flow path member is a flat surface.
According to a sixth aspect of the present invention, in the water electrolyzer according to the fourth or fifth aspect, the groove penetrates the first surface of the flow path member in a direction in which the gas diffusion layer and the distribution hole are connected to each other.
According to a seventh aspect of the present invention, in the water electrolyzer according to the fourth or fifth aspect, the groove is a recess formed at a part of the first surface except both end portions thereof defined in a direction in which the gas diffusion layer and the distribution hole are connected to each other, and the both end portions of the flow path member are in non-contact with the metal plate.
According to the first to seventh aspects of the present invention, it is possible to cause gas or water to flow between the gas diffusion layer and the distribution hole through the flow path formed at the flow path member. This eliminates a need to form a flow path using a combination of a plurality of metal plates, thereby achieving reduction in the number of the metal plates to be used as the separator.
In particular, according to the second aspect of the present invention, it is possible for hydrogen output from the cathode gas diffusion layer to flow into the hydrogen distribution hole through the hydrogen flow path formed at the cathode flow path member.
In particular, according to the third aspect of the present invention, it is possible for water to be supplied from the water distribution hole to flow into the anode gas diffusion layer through the water flow path formed at the first anode flow path member. It is further possible for oxygen output from the anode gas diffusion layer to flow into the oxygen distribution hole through the oxygen flow path formed at the second anode flow path member.
In particular, according to the fifth aspect of the present invention, it is possible to prevent flow of unintentional gas or water into the distribution hole using the seal member. Furthermore, forming the second surface of the flow path member as a flat surface allows the seal member to contact the base layer more tightly.
A preferred embodiment of the present invention will be described below by referring to the drawings.
A multi-layer structure composed of the electrolyte membrane 51, the anode catalyst layer 61, the anode gas diffusion layer 62, the cathode catalyst layer 71, and the cathode gas diffusion layer 72 is called an membrane-electrode-assembly (MEA). A multi-layer structure composed of the electrolyte membrane 51, the anode catalyst layer 61, and the cathode catalyst layer 71 is called a catalyst-coated membrane (CCM).
The electrolyte membrane 51 is a membrane like a thin plate having ion conductivity (ion-exchange membrane). The electrolyte membrane 51 of the present preferred embodiment is a proton exchange membrane that conducts hydrogen ions (H+). A fluorine-based or hydrocarbon-based polymer electrolyte membrane is used as the electrolyte membrane 51. More specifically, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid is used as the electrolyte membrane 51, for example. The electrolyte membrane 51 has a thickness from 5 to 200 m, for example.
The anode catalyst layer 61 is a catalyst layer that causes electrochemical reaction on an anode side. The anode catalyst layer 61 is layered on an anode-side surface of the electrolyte membrane 51. The anode catalyst layer 61 contains a large number of catalyst particles. The catalyst particles are particles of iridium oxide (IrOx), platinum (Pt), an alloy of iridium (Ir) and ruthenium (Ru), or an alloy of iridium (Ir) and titanium dioxide (TiO2), for example. During use of the water electrolyzer 1, water (H2O) is supplied to the anode catalyst layer 61. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 from the power supply 40. By doing so, by the actions of the applied voltage and the catalyst particles, the water is electrolyzed into hydrogen ions (H+), oxygen (O2), and electrons (e−) in the anode catalyst layer 61.
The anode gas diffusion layer 62 is a layer for supplying water uniformly to the anode catalyst layer 61 and for transmitting oxygen and electrons generated in the anode catalyst layer 61 to the separator 20. The anode gas diffusion layer 62 is layered on an outer surface of the anode catalyst layer 61. Specifically, the anode gas diffusion layer 62 is layered on the surface of the anode catalyst layer 61 on the opposite side to the electrolyte membrane 51. The anode catalyst layer 61 is interposed between the electrolyte membrane 51 and the anode gas diffusion layer 62. The anode gas diffusion layer 62 has electrical conductivity and is made of a porous material. As an example, carbon paper is used as the anode gas diffusion layer 62.
The cathode catalyst layer 71 is a catalyst layer that causes electrochemical reaction on a cathode side. The cathode catalyst layer 71 is formed on a cathode-side surface of the electrolyte membrane 51. Specifically, the cathode catalyst layer 71 is layered on the surface of the electrolyte membrane 51 on the opposite side to the anode catalyst layer 61. The cathode catalyst layer 71 contains a large number of carbon particles on which catalyst particles are supported. The catalyst particles are particles of platinum, for example. Alternatively, the catalyst particles may be prepared by mixing particles of a tiny amount of ruthenium or cobalt into particles of platinum. During use of the water electrolyzer 1, hydrogen ions (H+) and electrons (e−) are supplied to the cathode catalyst layer 71. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 from the power supply 40. By doing so, by the actions of the applied voltage and the catalyst particles, a reduction reaction is caused in the cathode catalyst layer 71 to generate hydrogen gas (H2) from the hydrogen ions and the electrons.
The cathode gas diffusion layer 72 is a layer for transmitting electrons from the separator 20 to the cathode catalyst layer 71 and for transmitting hydrogen generated in the cathode catalyst layer 71 to the separator 20. The cathode gas diffusion layer 72 is layered on an outer surface of the cathode catalyst layer 71. Specifically, the cathode gas diffusion layer 72 is layered on the surface of the cathode catalyst layer 71 on the opposite side to the electrolyte membrane 51. The cathode catalyst layer 71 is interposed between the electrolyte membrane 51 and the cathode gas diffusion layer 72. The cathode gas diffusion layer 72 has electrical conductivity and is made of a porous material. As an example, carbon paper is used as the cathode gas diffusion layer 72.
The separator 20 is a layer that moves electrons between cells 10 next to the separator 20 and forms pathways for water, oxygen, and hydrogen. The separator 20 is interposed between the anode gas diffusion layer 62 and the cathode gas diffusion layer 72 of the cells 10 next to the separator 20. The separator 20 has electrical conductivity and includes a metal plate 21 without permeability to gas and liquid. The metal plate 21 has an anode surface 22 contacting the anode gas diffusion layer 62, and a cathode surface 23 contacting the cathode gas diffusion layer 72.
The metal plate 21 includes a plurality of anode grooves 24 formed at the anode surface 22. Water passes through these anode grooves 24 of the separator 20 and is then supplied to the anode gas diffusion layer 62. Furthermore, oxygen generated in the anode catalyst layer 61 passes through the anode gas diffusion layer 62 and through the anode grooves 24 of the separator 20, and is then output to the outside.
The metal plate 21 includes a plurality of cathode grooves 25 formed at the cathode surface 23. Hydrogen generated in the cathode catalyst layer 71 passes through the cathode gas diffusion layer 72 and through the cathode grooves 25 of the separator 20, and is then output to the outside.
The power supply 40 is a unit that applies a voltage to the stack structure 30 described above. As shown in
During use of the water electrolyzer 1, water is supplied from the anode grooves 24 of the separator 20 to the anode catalyst layer 61 through the anode gas diffusion layer 62. Then, by the actions of a voltage applied from the power supply 40 and the catalyst particles in the anode catalyst layer 61, the water is decomposed into hydrogen ions, oxygen, and electrons. The hydrogen ions propagate through the electrolyte membrane 51 into the cathode catalyst layer 71. The oxygen passes through the anode gas diffusion layer 62 and the anode grooves 24 of the separator 20 and is then output to the outside. The electrons pass through the anode gas diffusion layer 62 and the separator 20 and then flow into an adjacent cell 10. In the adjacent cell 10, these electrons pass through the cathode gas diffusion layer 72 to reach the cathode catalyst layer 71. Then, in the cathode catalyst layer 71, the hydrogen ions and the electrons are combined with each other to generate hydrogen. The generated hydrogen passes through the cathode gas diffusion layer 72 and the cathode grooves 25 of the separator 20 and is then output to the outside. In this way, hydrogen is produced.
The foregoing stack structure 30 of the water electrolyzer 1 will be described next in more detail.
As shown in
The separator 20 includes the metal plate 21. As an example, the metal plate 21 is a titanium thin plate coated with platinum. Alternatively, the metal plate 21 may be made of stainless steel coated with gold, for example. The separator 20 of the present preferred embodiment is formed through presswork on a single metal plate. Employing the presswork makes it possible to form the separator 20 at lower cost than in a case of employing a different forming method such as etching.
The metal plate 21 includes the anode surface 22 shown in
In the present preferred embodiment, as shown in
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The separator 20 includes a plurality of second seal members 84. As shown in
The separator 20 includes a plurality of third seal members 85. As shown in
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The cathode flow path member 91 includes a plurality of hydrogen flow paths 913. In the present preferred embodiment, the hydrogen flow path 913 is a groove formed at the first surface 911 of the cathode flow path member 91. The groove forming the hydrogen flow path 913 penetrates the first surface 911 of the cathode flow path member 91 in a direction in which the cathode gas diffusion layer 72 and the hydrogen distribution hole 28 are connected to each other. In this way, the hydrogen flow path 913 functions as a flow path through which the cathode gas diffusion layer 72 and the hydrogen distribution hole 28 communicate with each other.
Hydrogen in a gaseous form output from the cathode gas diffusion layer 72 passes through the hydrogen flow paths 913 of the cathode flow path member 91 as indicated by arrows with dashes shown in
The above-described first seal member 83 is arranged on a surface of the metal plate 21 on the opposite side to the cathode flow path member 91. When viewed in the stacking direction, the cathode flow path member 91 is arranged at a position overlapping the first seal member 83. Thus, as shown in
As shown in
Like the cathode flow path member 91 described above, the first anode flow path member 92 includes a first surface and a second surface. The first surface is fixed to the anode surface 22 of the metal plate 21 with an adhesive, for example. The second surface contacts the anode-side surface of the base layer 50. Specifically, the first anode flow path member 92 is interposed between the anode surface 22 of the metal plate 21 and the anode-side surface of the base layer 50 in the stacking direction. As shown in
The first anode flow path member 92 includes a plurality of water flow paths 923. In the present preferred embodiment, the water flow path 923 is a groove formed at the first surface of the first anode flow path member 92. The groove forming the water flow path 923 penetrates the first surface of the first anode flow path member 92 in a direction in which the anode gas diffusion layer 62 and the water distribution hole 26 are connected to each other. In this way, the water flow path 923 functions as a flow path through which the anode gas diffusion layer 62 and the water distribution hole 26 communicate with each other.
Water in a liquid form supplied from outside to the water distribution hole 26 passes through the water flow paths 923 of the first anode flow path member 92 and then flows into the anode gas diffusion layer 62. In this way, in the configuration of the present preferred embodiment, the first anode flow path member 92 forms the flow path for water between the water distribution hole 26 and the anode gas diffusion layer 62. By doing so, it becomes unnecessary to form a flow path using a combination of a plurality of metal plates. This achieves reduction in the number of metal plates to be used as the separator 20. As a result, manufacturing cost for the water electrolyzer 1 is reduced.
The above-described second seal member 84 is arranged on a surface of the metal plate 21 on the opposite side to the first anode flow path member 92. When viewed in the stacking direction, the first anode flow path member 92 is arranged at a position overlapping the second seal member 84. Thus, the second surface of the first anode flow path member 92 and the second seal member 84 of the adjacent separator 20 are next to each other across the base layer 50. Furthermore, the second surface of the first anode flow path member 92 is a flat surface. This causes the second seal member 84 to contact the base layer 50 more tightly. As a result, it becomes possible to further improve sealing performance achieved by the second seal member 84.
As shown in
Like the cathode flow path member 91 described above, the second anode flow path member 93 includes a first surface and a second surface. The first surface is fixed to the anode surface 22 of the metal plate 21 with an adhesive, for example. The second surface contacts the anode-side surface of the base layer 50. Specifically, the second anode flow path member 93 is interposed between the anode surface 22 of the metal plate 21 and the anode-side surface of the base layer 50 in the stacking direction. As shown in
The second anode flow path member 93 includes a plurality of oxygen flow paths 933. In the present preferred embodiment, the oxygen flow path 933 is a groove formed at the first surface of the second anode flow path member 93. The groove forming the oxygen flow path 933 penetrates the first surface of the second anode flow path member 93 in a direction in which the anode gas diffusion layer 62 and the oxygen distribution hole 27 are connected to each other. In this way, the oxygen flow path 933 functions as a flow path through which the anode gas diffusion layer 62 and the oxygen distribution hole 27 communicate with each other.
Oxygen in a gaseous form output from the anode gas diffusion layer 62 passes through the oxygen flow paths 933 of the second anode flow path member 93 and then flows into the oxygen distribution hole 27. In this way, in the configuration of the present preferred embodiment, the second anode flow path member 93 forms the flow path for oxygen between the anode gas diffusion layer 62 and the oxygen distribution hole 27. By doing so, it becomes unnecessary to form a flow path using a combination of a plurality of metal plates. This achieves reduction in the number of metal plates to be used as the separator 20. As a result, manufacturing cost for the water electrolyzer 1 is reduced.
The above-described third seal member 85 is arranged on a surface of the metal plate 21 on the opposite side to the second anode flow path member 93. When viewed in the stacking direction, the second anode flow path member 93 is arranged at a position overlapping the third seal member 85. Thus, the second surface of the second anode flow path member 93 and the third seal member 85 of the adjacent separator 20 are next to each other across the base layer 50. Furthermore, the second surface of the second anode flow path member 93 is a flat surface. This causes the third seal member 85 to contact the base layer 50 more tightly. As a result, it becomes possible to further improve sealing performance achieved by the third seal member 85.
The first anode flow path member 92 and the second anode flow path member 93 may have their shapes corresponding to that of the cathode flow path member 91 shown in
The cathode flow path member 91, the first anode flow path member 92, and the second anode flow path member 93 may be made of a porous material such as ceramic. In this case, fine holes of the porous material can be used to form a flow path through which a gas diffusion layer and a distribution hole communicate with each other. Thus, it is not necessary to form a groove as a flow path.
As shown in
The anode outer peripheral regulator 94 is located near the anode outer peripheral seal member 81. As shown in
In particular, in the present preferred embodiment, the anode outer peripheral regulator 94 includes not only the above-described projections 941 but also a plurality of projections 942 projecting toward the opposite side of the stacking direction. As shown in
As shown in
As shown in
The cathode outer peripheral regulator 95 is located near the cathode outer peripheral seal member 82. As shown in
In particular, in the present preferred embodiment, the cathode outer peripheral regulator 95 includes not only the above-described projections 951 but also a plurality of projections 952 projecting toward the opposite side of the stacking direction. As shown in
As shown in
As shown in
The first regulator 96 is located near the first seal member 83. As shown in
In particular, in the present preferred embodiment, the first regulator 96 includes not only the above-described projections 961 but also a plurality of projections 962 projecting toward the opposite side of the stacking direction. When viewed in the stacking direction, the projection 961 and the projection 962 are arranged alternately along the first seal member 83. The projections 962 contact the cathode-side surface of the base layer 50. By doing so, it becomes possible for the first regulator 96 to contact both the base layer 50 of the cell 10 arranged on one side relative to the separator 20 and the base layer 50 of the cell 10 arranged on the other side relative to the separator 20. This allows the first regulator 96 to be positioned stably in the stacking direction. As a result, it becomes possible to further reduce a likelihood that the first seal member 83 will be compressed excessively in the stacking direction.
As shown in
As shown in
The second regulator 97 is located near the second seal member 84. As shown in
In particular, in the present preferred embodiment, the second regulator 97 includes not only the above-described projections 971 but also a plurality of projections 972 projecting toward the opposite side of the stacking direction. When viewed in the stacking direction, the projection 971 and the projection 972 are arranged alternately along the second seal member 84. The projections 972 contact the anode-side surface of the base layer 50. By doing so, it becomes possible for the second regulator 97 to contact both the base layer 50 of the cell 10 arranged on one side relative to the separator 20 and the base layer 50 of the cell 10 arranged on the other side relative to the separator 20. This allows the second regulator 97 to be positioned stably in the stacking direction. As a result, it becomes possible to further reduce a likelihood that the second seal member 84 will be compressed excessively in the stacking direction.
As shown in
The third regulator 98 is located near the third seal member 85. As shown in
In particular, in the present preferred embodiment, the third regulator 98 includes not only the above-described projections 981 but also a plurality of projections 982 projecting toward the opposite side of the stacking direction. When viewed in the stacking direction, the projection 981 and the projection 982 are arranged alternately along the third seal member 85. The projections 982 contact the anode-side surface of the base layer 50. By doing so, it becomes possible for the third regulator 98 to contact both the base layer 50 of the cell 10 arranged on one side relative to the separator 20 and the base layer 50 of the cell 10 arranged on the other side relative to the separator 20. This allows the third regulator 98 to be positioned stably in the stacking direction. As a result, it becomes possible to further reduce a likelihood that the third seal member 85 will be compressed excessively in the stacking direction.
In the above-described preferred embodiment, the metal plate 21 includes the anode outer peripheral regulator 94, the cathode outer peripheral regulator 95, the first regulator 96, the second regulator 97, and the third regulator 98. Alternatively, the metal plate 21 may include only some of these regulators. As an example, the metal plate 21 may include only the anode outer peripheral regulator 94 and the cathode outer peripheral regulator 95 of these regulators. By controlling an interval between the base layers 50 adjacent to each other at the outer peripheral part of the separator 20, it becomes possible to impose restriction to some degree on the amount of compression of each the first seal member 83, the second seal member 84, and the third seal member 85 internal to the outer peripheral part.
Number | Date | Country | Kind |
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2022-149017 | Sep 2022 | JP | national |