Water electrolysis cell and water electrolysis system

Abstract

A water electrolysis cell and a water electrolysis system comprising: an ion exchange membrane; a cathode-side catalyst layer disposed on one side of the ion exchange membrane; an anode-side catalyst layer disposed on the other side of the ion exchange membrane; and a metal impurity removal layer disposed between the ion exchange membrane and the cathode-side catalyst layer and / or between the ion exchange membrane and the anode-side catalyst layer.

Description

Water electrolysis cell and water electrolysis system

[0001] The present disclosure relates to a water electrolysis cell and a water electrolysis system.

[0002] Water electrolysis devices that produce hydrogen by electrolyzing an aqueous solution are being put into practical use. Water electrolysis devices produce hydrogen gas and oxygen gas by electrolyzing an aqueous solution. The water electrolysis device includes a water electrolysis cell. The water electrolysis cell includes a cathode catalyst layer and an anode catalyst layer disposed on either side of an ion exchange membrane, power feeders disposed on the outside of the cathode catalyst layer and the anode catalyst layer, and a separator disposed on the outside of each power feeder.

[0003] In water electrolysis devices, a potassium hydroxide aqueous solution is sometimes used to increase the ionic conductivity of water. In this case, impurities generated during the production of the potassium hydroxide aqueous solution include, for example, metal ions and scale components, which may interfere with the water electrolysis process. Patent Document 1, for example, describes a technology for removing ions contained in cathode water using an ion exchange membrane in an ozone water generator.

[0004] JP 2010-155227 A

[0005] In water electrolysis devices, metal ions and scale components accumulate inside the water electrolysis cells, particularly after the start of water electrolysis. This increases the resistance of the ion exchange membrane, degrading ion exchange performance and resulting in an increase in electrolysis voltage. This increase in electrolysis voltage also leads to a problem of a decrease in water electrolysis performance.

[0006] The present disclosure is intended to solve the above-mentioned problems, and has an object to provide a water electrolysis cell and a water electrolysis system that improve performance by suppressing an increase in electrolysis voltage.

[0007] To achieve the above object, the water electrolysis cell of the present disclosure includes an ion exchange membrane, a cathode-side catalyst layer disposed on one side of the ion exchange membrane, an anode-side catalyst layer disposed on the other side of the ion exchange membrane, and a metal impurity removal layer disposed at least either between the ion exchange membrane and the cathode-side catalyst layer or between the ion exchange membrane and the anode-side catalyst layer.

[0008] The water electrolysis system according to the present disclosure includes the water electrolysis cell, an electrolyte solution flow path that supplies an electrolytic solution to the water electrolysis cell, an electrolyte solution supply pump provided in the electrolyte solution flow path, a cleaning solution flow path that supplies a cleaning solution to the water electrolysis cell to recover metal impurities adhered to the metal impurity removal layer, and a cleaning solution supply pump provided in the cleaning solution flow path.

[0009] The water electrolysis cell and water electrolysis system of the present disclosure can improve performance by suppressing an increase in electrolysis voltage.

[0010] FIG. 1 is a schematic cross-sectional view of a water electrolysis cell of this embodiment. FIG. 2 is an exploded perspective view of a water electrolysis cell of this embodiment. FIG. 3 is a schematic cross-sectional view of a membrane electrode assembly. FIG. 4 is a schematic cross-sectional view of a metal impurity removal layer. FIG. 5 is a schematic diagram of a method for manufacturing a membrane electrode assembly. FIG. 6 is a schematic diagram of a modified example of the method for manufacturing a membrane electrode assembly. FIG. 7 is a graph showing electrolysis voltage versus electrolysis time. FIG. 8 is a schematic configuration diagram of a water electrolysis system of this embodiment.

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations that combine the embodiments. Furthermore, the components in the embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially identical, and those that are within the so-called equivalent range.

[0012] [Embodiment] <Water Electrolysis Apparatus> The water electrolysis apparatus uses water (H ２ By electrolyzing hydrogen (H ２ The water electrolysis device is, for example, a device using an anion exchange membrane (AEM). However, the water electrolysis device may also be, for example, a device using a proton exchange membrane (PEM: Polymer Electrolyte Membrane).

[0013] The water electrolysis device includes, for example, a cell stack, an electrolyte supply unit, and a power supply unit. The cell stack, which will be described later, is an assembly of water electrolysis cells. The electrolyte supply unit supplies the electrolyte to the water electrolysis cells. The electrolyte is, for example, pure water or an alkaline aqueous solution. An example of the alkaline aqueous solution is potassium hydroxide (KOH). The electrolyte supply unit has a cathode-side supply unit and an anode-side supply unit. The power supply unit is a DC power supply device that applies a voltage to the water electrolysis cells. The power supply unit applies a DC voltage required for electrolysis of the electrolyte between the cathode and anode of the water electrolysis cell.

[0014] <Water Electrolysis Cell> FIG. 1 is a schematic cross-sectional view showing a water electrolysis cell according to this embodiment.

[0015] 1 , the water electrolysis cell 10 is a device that generates hydrogen by electrolyzing water contained in an electrolyte solution using externally input electrical energy. The water electrolysis cell 10 includes, for example, a cathode separator 11, an anode separator 12, and a membrane electrode assembly 13.

[0016] <Cathode-side separator> The cathode-side separator 11 is a member that defines one side of the accommodation space of the water electrolysis cell 10. The cathode-side separator 11 has, for example, a rectangular plate shape. A negative voltage is applied to the cathode-side separator 11 from the power supply unit 14 via, for example, a first power feeder 33 (see FIG. 2 ) described below. An electrolyte supply line L1 is connected to one end of the cathode-side separator 11. An electrolyte discharge line L2 is connected to the other end of the cathode-side separator 11.

[0017] <Anode-side separator> The anode-side separator 12 is a member that defines the other side of the accommodation space of the water electrolysis cell 10. The anode-side separator 12 has, for example, a rectangular plate shape. A positive voltage is applied to the anode-side separator 12 from the power supply unit 14 via, for example, a second power feeder 34 (see FIG. 2 ) described below. An electrolyte solution supply line L3 is connected to one end of the anode-side separator 12. An electrolyte solution discharge line L4 is connected to the other end of the anode-side separator 12.

[0018] <Configuration of Membrane Electrode Assembly> The membrane electrode assembly (MEA) 13 is a structure in which an ion exchange membrane, a catalyst, and a current feeder are assembled. The membrane electrode assembly 13 is disposed between a cathode side separator 11 and an anode side separator 12, and is located in a storage space. The membrane electrode assembly 13 includes, for example, an ion exchange membrane 21, a cathode side catalyst layer 22, an anode side catalyst layer 23, a cathode side current feeder 24, an anode side current feeder 25, a cathode side metal impurity removal layer 26, and an anode side metal impurity removal layer 27. In the membrane electrode assembly 13, the cathode side catalyst layer 22 and the cathode side current feeder 24 form a cathode relative to the ion exchange membrane 21, and the anode side catalyst layer 23 and the anode side current feeder 25 form an anode.

[0019] <Ion Exchange Membrane> The ion exchange membrane 21 is a membrane that selectively transmits ions. The ion exchange membrane 21 is, for example, a solid polymer electrolyte membrane. The ion exchange membrane 21 selectively transmits hydroxide ions (OH － However, the ion exchange membrane 21 is not limited to an anion exchange membrane, and may be, for example, a proton exchange membrane (PEM) of a type different from an anion exchange membrane.

[0020] The ion exchange membrane 21 is, for example, in the form of a rectangular sheet and is flexible. The outer size of the ion exchange membrane 21 is smaller than the outer size of the cathode side separator 11 or the anode side separator 12. The ion exchange membrane 21 is disposed between the cathode side separator 11 and the anode side separator 12 and is located in the storage space.

[0021] When a voltage is applied to the water electrolysis cell 10 by the power supply 14, the following chemical reaction occurs on the cathode side of the ion exchange membrane 21, and hydrogen is produced from the electrolyte. The produced hydroxide ions pass through the membrane electrode assembly 13 from the cathode side to the anode side. ２ O + 2e － →H ２ +2OH －

[0022] When a voltage is applied to the water electrolysis cell 10 by the power supply 14, the following chemical reaction occurs on the anode side of the ion exchange membrane 21, and oxygen is produced from the electrolyte: － →1 / 2O ２ +H ２ O + 2e －

[0023] As a result, the following chemical reactions occur in the water electrolysis cell 10 as a whole: ２ O → H ２ +1 / 2O ２

[0024] The ion exchange membrane 21 may have a polystyrene-based or tetraphenyl-based composition in the main chain and an imidazolium group or a quaternary ammonium group in the side chain, as an example of a membrane with relatively high ionic conductivity. Alternatively, the ion exchange membrane 21 may have a polysulfone-based or bromobutylstyrene-based composition, as an example of a membrane with relatively high oxidation resistance.

[0025] <Cathode-Side Metal Impurity Removal Layer> The cathode-side metal impurity removal layer 26 removes metal scale contained in the electrolyte. Scale refers to a substance in which scale components are precipitated in the electrolyte. The cathode-side metal impurity removal layer 26 selectively removes specific metal ions (scale components) contained in the electrolyte. That is, the cathode-side metal impurity removal layer 26 can remove scale components dissolved in the electrolyte at a concentration equal to or lower than the saturation concentration. The cathode-side metal impurity removal layer 26 is, for example, in the form of a rectangular sheet. The cathode-side metal impurity removal layer 26 has an outer size that is, for example, the same as or larger than the outer size of the ion exchange membrane 21. The cathode-side metal impurity removal layer 26 is provided on one side of the ion exchange membrane 21. The cathode-side catalyst layer 22 is connected to the cathode-side metal impurity removal layer 26 from the side opposite the ion exchange membrane 21.

[0026] <Anode-side metal impurity removal layer> The anode-side metal impurity removal layer 27 removes metal scale contained in the electrolyte. Scale refers to a substance in which scale components are precipitated in the electrolyte. The anode-side metal impurity removal layer 27 selectively removes specific metal ions (scale components) contained in the electrolyte. That is, the anode-side metal impurity removal layer 27 can remove scale components dissolved in the electrolyte at a concentration equal to or lower than the saturation concentration. The anode-side metal impurity removal layer 27 is, for example, in the form of a rectangular sheet. The outer size of the anode-side metal impurity removal layer 27 is, for example, the same as or larger than the outer size of the ion exchange membrane 21. The anode-side metal impurity removal layer 27 is provided on one side of the ion exchange membrane 21. The anode-side catalyst layer 23 is connected to the anode-side metal impurity removal layer 27 from the side opposite the ion exchange membrane 21.

[0027] The water electrolysis cell 10 of this embodiment has both the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27. However, it is sufficient that the water electrolysis cell 10 of this embodiment has at least one of the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27. The cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 are described in detail below.

[0028] <Cathode-side catalyst layer> The cathode-side catalyst layer 22 is a layer (electrode-side catalyst layer) that promotes the chemical reaction of water electrolysis. The cathode-side catalyst layer 22 has, for example, a rectangular sheet shape. The outer size of the cathode-side catalyst layer 22 is, for example, smaller than the outer size of the ion exchange membrane 21. The cathode-side catalyst layer 22 is provided on the surface of the cathode-side metallic impurity removing layer 26 opposite to the ion exchange membrane 21. A cathode-side power supply 24 is connected to the cathode-side catalyst layer 22 from the side opposite to the cathode-side metallic impurity removing layer 26. A negative voltage is applied to the cathode-side catalyst layer 22 from the power supply 14 via the cathode-side separator 11 and the cathode-side power supply 24, and the cathode-side catalyst layer 22 functions as part of the cathode of the water electrolysis cell 10.

[0029] The cathode-side catalyst layer 22 may be made of any material that promotes chemical reactions. For example, the cathode-side catalyst layer 22 may contain one or more of nickel, a nickel alloy, cerium oxide, lanthanum oxide, and platinum (Pt). In addition to the above-mentioned materials, the cathode-side catalyst layer 22 may also contain another material, such as carbon.

[0030] <Anode-side catalyst layer> The anode-side catalyst layer 23 is a layer (electrode-side catalyst layer) that promotes the chemical reaction of water electrolysis. The anode-side catalyst layer 23 has, for example, a rectangular sheet shape. The outer size of the anode-side catalyst layer 23 is, for example, smaller than the outer size of the ion exchange membrane 21. The anode-side catalyst layer 23 is provided on the surface of the anode-side metallic impurity removing layer 27 opposite to the ion exchange membrane 21. An anode-side power supply 25 is connected to the anode-side catalyst layer 23 from the side opposite to the anode-side metallic impurity removing layer 27. A positive voltage is applied to the anode-side catalyst layer 23 from the power supply 14 via the anode-side separator 12 and the anode-side power supply 25, and the anode-side catalyst layer 23 functions as part of the anode of the water electrolysis cell 10.

[0031] The anode-side catalyst layer 23 may be made of any material that promotes chemical reactions, and various materials may be used. For example, the anode-side catalyst layer 23 may contain one or more of nickel, nickel alloy, nickel oxide, copper oxide, iridium oxide, niobium oxide, lead oxide, and bismuth oxide. In addition to the above-mentioned materials, the anode-side catalyst layer 23 may also contain another material, such as carbon.

[0032] <Cathode power supplier> The cathode side power supplier 24 is an electrical connection part that transmits a voltage applied to the cathode side separator 11 to the cathode side catalyst layer 22. The cathode side power supplier 24 is located between the cathode side separator 11 and the cathode side catalyst layer 22, with one surface in contact with the cathode side separator 11 and the other surface in contact with the cathode side catalyst layer 22.

[0033] The cathode side current collector 24 has a structure that allows the electrolyte and gas to pass through it. The cathode side current collector 24 is formed, for example, from a metal mesh structure, a sintered body, fiber, a conductive carbon fiber mesh structure, or nonwoven fabric. The cathode side current collector 24 has a predetermined porosity. The cathode side current collector 24 has the same external size as the cathode side catalyst layer 22. The cathode side catalyst layer 22 and the cathode side current collector 24 together constitute the cathode of the water electrolysis cell 10.

[0034] <Anode power supplier> The anode-side power supplier 25 is an electrical connection part that transmits a voltage applied to the anode-side separator 12 to the anode-side catalyst layer 23. The anode-side power supplier 25 is located between the anode-side separator 12 and the anode-side catalyst layer 23, with one surface in contact with the anode-side separator 12 and the other surface in contact with the anode-side catalyst layer 23.

[0035] The anode side current collector 25 has a structure that allows the electrolyte and gas to pass through it. The anode side current collector 25 is formed, for example, of a metal mesh structure, a sintered body, fiber, a conductive carbon fiber mesh structure, or nonwoven fabric. The anode side current collector 25 has a predetermined porosity. The anode side current collector 25 has, for example, the same porosity as the cathode side current collector 24. The external size of the anode side current collector 25 is the same as the external size of the anode side catalyst layer 23. The anode side catalyst layer 23 and the anode side current collector 25 together constitute the anode of the water electrolysis cell 10.

[0036] FIG. 2 is an exploded perspective view showing the water electrolysis cell of this embodiment.

[0037] As shown in FIG. 2 , the water electrolysis cell 10 includes, in addition to the cathode separator 11, the anode separator 12, and the membrane electrode assembly 13, insulators 31 and 32, power feeders 33 and 34, insulating materials 35 and 36, and end plates 37 and 38, for example.

[0038] <Insulators> The insulators 31, 32 are members that provide insulation between the outer periphery of the cathode side separator 11 and the outer periphery of the anode side separator 12. The insulator 31 arranged on the cathode side is a frame-shaped sheet member whose outer shape is slightly larger than that of the cathode side separator 11. The insulator 31 contacts and covers a cathode side header 42 (described later) of the cathode side separator 11. The insulator 32 arranged on the anode side is a frame-shaped sheet member whose outer shape is slightly larger than that of the anode side separator 12. The insulator 32 contacts and covers an anode side header 44 (described later) of the anode side separator 12. The material of the insulators 31, 32 is not particularly limited as long as it is an insulating material, and may be, for example, a sheet-shaped resin such as PTFE.

[0039] <Power Supply Element> The power supply element 33 is an electrical connection element that transmits a negative voltage applied from the power supply unit 14 to the cathode side separator 11. The power supply element 33 is a metal plate member (e.g., a copper plate). The power supply element 33 contacts the cathode side separator 11, for example, from the side opposite to the housing space of the water electrolysis cell 10, and is electrically connected to the cathode side separator 11. The negative voltage required for electrolysis in the water electrolysis cell 10 is applied to the power supply element 33 from the power supply unit 14.

[0040] The power supply 34 is an electrical connection part that transmits a positive voltage applied from the power supply unit 14 to the anode side separator 12. The power supply 34 is a metal plate member (e.g., a copper plate). The power supply 34 contacts the anode side separator 12, for example, from the side opposite to the housing space of the water electrolysis cell 10, and is electrically connected to the anode side separator 12. The power supply 14 applies to the power supply 33 a positive voltage required for electrolysis in the water electrolysis cell 10.

[0041] <Insulating Material> The insulating material 35 is located on the outside of the power feeder 33. The outer size of the insulating material 35 is, for example, the same as or larger than the outer size of the power feeder 33. The insulating material 36 is located on the outside of the power feeder 34. The outer size of the insulating material 36 is, for example, the same as or larger than the outer size of the power feeder 34.

[0042] <End Plate> The end plate 37 is located on the opposite side of the insulating material 35 with respect to the accommodation space of the water electrolysis cell 10. The end plate 37 is formed, for example, from a metal plate member (e.g., a stainless steel plate). The outer size of the end plate 37 is, for example, the same as or larger than the outer size of the insulating material 35.

[0043] The end plate 38 is located on the opposite side of the insulating material 36 with respect to the accommodation space of the water electrolysis cell 10. The end plate 38 is formed, for example, from a metal plate member (e.g., a stainless steel plate). The outer size of the end plate 38 is, for example, the same as or larger than the outer size of the insulating material 36.

[0044] The water electrolysis cell 10 is not limited to the above-described configuration. For example, the water electrolysis cell 10 may be configured by stacking multiple cathode-side separators 11, anode-side separators 12, and membrane electrode assemblies 13.

[0045] <Configuration of Membrane Electrode Assembly> FIG. 3 is a schematic cross-sectional view showing a membrane electrode assembly, and FIG. 4 is a schematic cross-sectional view showing a metal impurity removal layer.

[0046] 3 , the membrane electrode assembly 13 includes a cathode-side metallic impurity removing layer 26, a cathode-side catalyst layer 22, a cathode-side current collector 24, and an anode-side current collector 25 stacked in this order on one surface of the ion exchange membrane 21. The membrane electrode assembly 13 also includes an anode-side metallic impurity removing layer 27, an anode-side catalyst layer 23, and an anode-side current collector 25 stacked in this order on the other surface of the ion exchange membrane 21.

[0047] <Configuration of metal impurity removal layer> The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 have the same configuration. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are layers provided on one surface and the other surface of the ion exchange membrane 21. The cathode-side metal impurity removal layer 26 contacts one surface of the ion exchange membrane 21 and contacts one surface of the cathode-side catalyst layer 22. The anode-side metal impurity removal layer 27 contacts the other surface of the ion exchange membrane 21 and contacts one surface of the anode-side catalyst layer 23. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are permeable to hydroxide ions. In this case, the second surfaces of the cathode-side catalyst layer 22 and the anode-side catalyst layer 23 in contact with the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 are preferably rougher than the first surface of the ion exchange membrane 21 in contact with the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27.

[0048] As shown in Fig. 4 , the cathode-side metal impurity removing layer 26 and the anode-side metal impurity removing layer 27 remove metal scale and specific metal ions (scale components) contained in the electrolytic solution. The cathode-side metal impurity removing layer 26 and the anode-side metal impurity removing layer 27 allow hydroxide ions to pass through. Here, specific metal ions refer to calcium ions, magnesium ions, iron ions, nickel ions, chromium ions, manganese ions, molybdenum ions, and the like. These metal ions are impurities contained in trace amounts in potassium hydroxide, which serves as a reagent, when producing an aqueous potassium hydroxide solution as the electrolytic solution, and trace metal ions eluted from the metallic materials of the stainless steel piping and the components of the water electrolysis cell 10. When precipitated, these ions adhere to the ion-exchange membrane 21 as scale, thereby increasing the membrane resistance and ultimately causing an increase in the electrolysis voltage of the water electrolysis cell 10.

[0049] The cathode side metal impurity removal layer 26 and the anode side metal impurity removal layer 27 each have at least one of a porous layer of a chelate resin and a porous layer of an ion exchange resin (anion exchange resin). That is, the cathode side metal impurity removal layer 26 and the anode side metal impurity removal layer 27 may each be composed of a porous layer of a chelate resin alone, a porous layer of an ion exchange resin alone, or a porous layer containing a chelate resin and an ion exchange resin.

[0050] In this embodiment, the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 include a plurality of chelate resin particles 101, a plurality of ion exchange resin particles 102, and a particle binder 103. The plurality of chelate resin particles 101 and the plurality of ion exchange resin particles 102 are present at a predetermined ratio (mass ratio or volume ratio). The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are formed to a predetermined thickness T. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 preferably have a thickness of, for example, 3 μm or more and 10 μm or less. The chelate resin particles 101 and the ion exchange resin particles 102 preferably have a particle size of 1 μm or more and 10 μm or less. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are composed of a plurality of particles 101 of chelate resin and a plurality of particles 102 of ion exchange resin, and therefore have voids 104 through which the electrolyte can pass.

[0051] The particle binder 103 includes, for example, one or more of a polymer binder, an ionomer, and the like. In this embodiment, the particle binder 103 includes both a polymer binder and an ionomer. The polymer binder functions as a binder for the chelating resin particles 101 and the ion exchange resin particles 102. In other words, the polymer binder binds the chelating resin particles 101 and the ion exchange resin particles 102 to each other. For example, a fluorine-based binder can be used as the polymer binder in this embodiment. Examples of the fluorine-based binder include polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and tetrafluoroethylene / ethylene copolymer (ETFE). Note that the polymer binder may be any material that has the ability to bind the chelating resin particles 101 and the ion exchange resin particles 102, and non-fluorine-based binders can also be used as the polymer binder.

[0052] The ionomer is an ion exchange resin component for reducing the overall electrical resistance of the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. For example, the ionomer may be a cationic polymer having a quaternary ammonium group introduced into an aromatic polymer skeleton, such as Diaza(bicyclo-octane) polyethersulfone, poly[(p-terphenyl-4,4'-diyl)(N,N-dimethyl-piperidinium-bicarbonate-4,4-diyl)-co-(p-terphenyl-4,4'-diyl)(2,2,2-trifluoro-1-phenylethylidene-diyl)], or poly[(p-terphenyl-4,4'-diyl)(N,N-dimethyl-piperidinium-bicarbonate-4,4-diyl)]. Furthermore, it is also possible to use an anionic polymer in which an anionic functional group such as a sulfonic acid group or a carboxylic acid group is introduced into a fluorine-based polymer skeleton as the ionomer.

[0053] The ionomer also contains a second polymer that has a smaller molecular weight than the first polymer contained in the ion exchange membrane 21 and the same molecular skeleton as the first polymer. The second polymer has a predetermined second amount of molecular weight. The second amount is smaller than the first amount. The relationship between the molecular weight of the second polymer and the molecular weight of the first polymer is not limited to the above, and the molecular weight of the second polymer may be the same as the molecular weight of the second polymer, or may be larger than the molecular weight of the first polymer. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are insulating.

[0054] <Method for Manufacturing Membrane Electrode Assembly> FIG. 5 is a schematic diagram showing a method for manufacturing a membrane electrode assembly.

[0055] 5 , first, chelate resin particles, ion exchange resin particles, and a binder are mixed in a solvent to generate a slurry (mixture). Next, the slurry is applied to one surface of the ion exchange membrane 21 and dried to form a cathode-side metallic impurity removal layer 26. Furthermore, the slurry is applied to the other surface of the ion exchange membrane 21 and dried to form an anode-side metallic impurity removal layer 27.

[0056] Next, a cathode-side catalyst layer 22 is provided on the outer surface of the cathode-side metallic impurity removing layer 26 formed on one surface of the ion exchange membrane 21, and a cathode-side current collector 24 is provided on the outer surface of the cathode-side catalyst layer 22. Furthermore, an anode-side catalyst layer 23 is provided on the outer surface of the anode-side metallic impurity removing layer 27 formed on the other surface of the ion exchange membrane 21, and an anode-side current collector 25 is provided on the outer surface of the anode-side catalyst layer 23. In this manner, the water electrolysis cell 10 is manufactured.

[0057] A cathode-side metallic impurity removal layer 26 is formed on one surface of the ion exchange membrane 21, and an anode-side metallic impurity removal layer 27 is formed on the other surface of the ion exchange membrane 21. This improves the strength of the ion exchange membrane 21 and facilitates assembly of the water electrolysis cell 10.

[0058] <Modification of the method for manufacturing a membrane electrode assembly> The method for manufacturing a membrane electrode assembly is not limited to the method described above. Fig. 6 is a schematic diagram showing a modification of the method for manufacturing a membrane electrode assembly.

[0059] As shown in Fig. 6 , first, chelate resin particles, ion exchange resin particles, and a binder are introduced into a solvent and mixed to generate a slurry (mixture). Next, a cathode-side catalyst layer 22 is formed on one surface of a cathode-side current collector 24, and an anode-side catalyst layer 23 is formed on one surface of an anode-side current collector 25. The slurry is then applied to the surface of the cathode-side catalyst layer 22 and dried to form a cathode-side metal impurity removal layer 26. The slurry is also applied to the surface of the anode-side catalyst layer 23 and dried to form an anode-side metal impurity removal layer 27.

[0060] Next, a cathode-side metallic impurity removing layer 26 is provided on one surface of the ion exchange membrane 21. Furthermore, an anode-side metallic impurity removing layer 27 is provided on the other surface of the ion exchange membrane 21. In this manner, the water electrolysis cell 10 is manufactured.

[0061] A cathode-side metallic impurity removal layer 26 is formed on the surface of the cathode-side catalyst layer 22, and an anode-side metallic impurity removal layer 27 is formed on the surface of the anode-side catalyst layer 23. Therefore, the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 are not formed directly on the ion exchange membrane 21, which is easily damaged, and therefore damage to the ion exchange membrane 21 can be suppressed.

[0062] <Functions and Effects of Water Electrolysis Cell> FIG. 7 is a graph showing electrolysis voltage versus electrolysis time.

[0063] As shown in Fig. 7 , in a conventional water electrolysis cell (dotted line in Fig. 7 ) that does not have a cathode-side metallic impurity removal layer 26 or an anode-side metallic impurity removal layer 27, the electrolysis voltage gradually increases with the passage of electrolysis time after the start of water electrolysis. This is thought to be because metal ions and scale components in the electrolyte accumulate on the ion exchange membrane, increasing the resistance of the ion exchange membrane. When the resistance of the ion exchange membrane increases, the ion exchange performance decreases, causing the electrolysis voltage to increase, and therefore the water electrolysis performance to decrease.

[0064] On the other hand, in the water electrolysis cell 10 of this embodiment having the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 (solid line in Fig. 7 ), the electrolysis voltage hardly increases with the passage of electrolysis time after the start of water electrolysis. This is because the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 remove metal ions and scale components from the electrolytic solution, thereby suppressing the accumulation of metal ions and scale components on the ion exchange membrane 21. Therefore, the resistance of the ion exchange membrane does not increase, and the ion exchange performance does not deteriorate. As a result, the electrolysis voltage hardly increases, and deterioration of water electrolysis performance can be suppressed.

[0065] The water electrolysis cell 10 of this embodiment includes the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27. Therefore, even if the surface pressure of the ion exchange membrane 21 is increased, a short circuit does not occur, and good IV characteristics and good current efficiency (100%) can be obtained. Furthermore, the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 are disposed between the ion exchange membrane 21 and the cathode-side catalyst layer 22 and between the ion exchange membrane 21 and the anode-side catalyst layer 23, respectively. Therefore, the electrodes do not come into direct contact with the ion exchange membrane 21, and damage to the ion exchange membrane 21 can be prevented.

[0066] <Water Electrolysis System> FIG. 8 is a schematic diagram illustrating the configuration of a water electrolysis system according to this embodiment.

[0067] As shown in FIG. 8 , the water electrolysis system 50 includes a water electrolysis cell 10, electrolyte solution reservoirs 51 and 52, electrolyte solution supply flow paths 53 and 54, electrolyte solution supply pumps 55 and 56, gas-liquid separators 57 and 58, gas exhaust flow paths 59 and 60, electrolyte solution supply flow paths 61 and 62, electrolyte solution supply pumps 63 and 64, gas exhaust flow paths 65 and 66, a pump 67, and three-way valves 68 and 69.

[0068] Therefore, when the electrolyte solution supply pumps 55, 63 are driven, the electrolyte solution stored in the electrolyte solution reservoir 51 is supplied to the gas-liquid separator 57 via the electrolyte solution supply channel 53, and then supplied to the cathode side of the water electrolysis cell 10 via the electrolyte solution supply channel 61 and the three-way valve 68. When the electrolyte solution supply pumps 56, 64 are driven, the electrolyte solution stored in the electrolyte solution reservoir 52 is supplied to the gas-liquid separator 58 via the electrolyte solution supply channel 54, and then supplied to the anode side of the water electrolysis cell 10 via the electrolyte solution supply channel 62 and the three-way valve 69. Hydrogen gas produced in the water electrolysis cell 10 is supplied to the gas-liquid separator 57 via the gas discharge channel 65, where the hydrogen gas is separated and collected in the gas discharge channel 59. Meanwhile, oxygen gas produced in the water electrolysis cell 10 is supplied to the gas-liquid separator 58 via the gas discharge channel 66, where the hydrogen gas is separated and collected in the gas discharge channel 60.

[0069] The water electrolysis system 50 also includes cleaning liquid reservoirs 71, 72, 73, 74, 75, and 76, cleaning liquid supply flow paths 77 and 78, cleaning liquid supply pumps 79 and 80, cleaning liquid return flow paths 81 and 82, on-off valves 83, 84, 85, 86, 87, and 88, and three-way valves 89 and 90.

[0070] The cleaning liquid reservoirs 71 and 72 store a hydrochloric acid solution as a cleaning liquid. The cleaning liquid reservoirs 73 and 74 store ion-exchanged water as a cleaning liquid. The cleaning liquid reservoirs 75 and 76 store a potassium hydroxide solution as a cleaning liquid. One end of a cleaning liquid supply flow path 77 branches into three paths, each connected to the cleaning liquid reservoirs 71, 73, and 75. The other end of the cleaning liquid supply flow path 77 is connected to the cathode side of the water electrolysis cell 10 via a three-way valve 89. One end of a cleaning liquid supply flow path 78 branches into three paths, each connected to the cleaning liquid reservoirs 72, 74, and 76. The other end of the cleaning liquid supply flow path 78 is connected to the anode side of the water electrolysis cell 10 via a three-way valve 90. Cleaning liquid supply pumps 79 and 80 are provided in the cleaning liquid supply flow paths 77 and 78.

[0071] One end of the cleaning liquid return flow path 81 is connected to the three-way valve 68. The other end of the cleaning liquid return flow path 81 branches into three paths, which are respectively connected to the cleaning liquid reservoirs 71, 73, and 75. One end of the cleaning liquid return flow path 82 is connected to the three-way valve 69. The other end of the cleaning liquid return flow path 82 branches into three paths, which are respectively connected to the cleaning liquid reservoirs 72, 74, and 76. On-off valves 83, 85, and 87 are provided at each branched portion at one end of the cleaning liquid supply flow path 77. On-off valves 84, 86, and 88 are provided at each branched portion at one end of the cleaning liquid supply flow path 78.

[0072] In the water electrolysis cell 10, the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 (see FIG. 1 ) recover metallic impurities in the electrolytic solution, and therefore performance deteriorates due to the accumulation of metallic impurities in the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27. Therefore, by supplying a cleaning solution to the water electrolysis cell 10, the metallic impurities accumulated in the cathode-side metallic impurity removal layer 26 and the anode-side metallic impurity removal layer 27 are removed and recovered.

[0073] The electrolytic solution supply pumps 55, 56, 63, and 64 are stopped to stop the operation of the water electrolysis cell 10. In this state, hydrochloric acid solution, ion-exchanged water, and potassium hydroxide solution are sequentially supplied as cleaning solutions to the water electrolysis cell 10. That is, first, the on-off valves 83 and 84 are opened, and the on-off valves 85, 86, 87, and 88 are closed. Then, the cleaning solution supply pumps 79 and 80 are driven. Then, the hydrochloric acid solution stored in the cleaning solution reservoirs 71 and 72 is supplied to the water electrolysis cell 10 through the cleaning solution supply flow paths 77 and 78 and the three-way valves 89 and 90, respectively, and metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are eluted. The hydrochloric acid solution containing the eluted metal impurities is returned to the cleaning solution reservoirs 71 and 72 through the cleaning solution return flow paths 81 and 82.

[0074] Next, the on-off valves 85 and 86 are opened, and the on-off valves 83, 84, 87, and 88 are closed. Then, the cleaning solution supply pumps 79 and 80 are driven. As a result, the ion-exchanged water stored in the cleaning solution reservoirs 73 and 74 is supplied to the water electrolysis cell 10 through the cleaning solution supply flow paths 77 and 78 and the three-way valves 89 and 90, and metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are eluted. The ion-exchanged water containing the eluted metal impurities is returned to the cleaning solution reservoirs 73 and 74 through the cleaning solution return flow paths 81 and 82.

[0075] Subsequently, the on-off valves 87 and 88 are opened, and the on-off valves 83, 84, 85, and 86 are closed. Then, the cleaning solution supply pumps 79 and 80 are driven. As a result, the potassium hydroxide solution stored in the cleaning solution reservoirs 75 and 76 is supplied to the water electrolysis cell 10 through the cleaning solution supply flow paths 77 and 78 and the three-way valves 89 and 90, and elutes metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. The potassium hydroxide solution containing the eluted metal impurities is returned to the cleaning solution reservoirs 75 and 76 through the cleaning solution return flow paths 81 and 82.

[0076] The water electrolysis cell 10 is regenerated by sequentially supplying a hydrochloric acid aqueous solution, ion-exchanged water, and potassium hydroxide solution as cleaning solutions to remove metal scale and metal scale components as metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27.

[0077] [Effects of the present embodiment] The water electrolysis cell according to the first aspect includes an ion exchange membrane 21, a cathode-side catalyst layer 22 disposed on one side of the ion exchange membrane 21, an anode-side catalyst layer 23 disposed on the other side of the ion exchange membrane 21, and metal impurity removal layers 26, 27 disposed at least either between the ion exchange membrane 21 and the cathode-side catalyst layer 22 or between the ion exchange membrane 21 and the anode-side catalyst layer 23.

[0078] In the water electrolysis cell according to the first aspect, metal ions as metal impurities and scale components in the electrolytic solution are removed by the cathode-side metal impurity removing layer 26 and the anode-side metal impurity removing layer 27, and are prevented from depositing on the ion exchange membrane 21. As a result, the resistance of the ion exchange membrane 21 does not increase, the ion exchange performance does not deteriorate, an increase in electrolysis voltage is suppressed, and deterioration in water electrolysis performance can be suppressed.

[0079] The water electrolysis cell according to the second aspect is the water electrolysis cell according to the first aspect, and further includes metal impurity removal layers 26, 27 capable of removing scale contained in the electrolytic solution, thereby suppressing scale buildup on the ion exchange membrane 21.

[0080] The water electrolysis cell according to the third aspect is the water electrolysis cell according to the first or second aspect, and further includes the metal impurity removal layers 26, 27 capable of removing scale components dissolved in the electrolytic solution at a concentration equal to or lower than the saturated concentration, thereby suppressing the accumulation of scale components on the ion exchange membrane 21.

[0081] A water electrolysis cell according to a fourth aspect is the water electrolysis cell according to any one of the first to third aspects, further comprising: the metallic impurity removal layers 26, 27 in contact with the ion exchange membrane 21 and also in contact with the cathode-side catalyst layer 22 or the anode-side catalyst layer 23. As a result, when surface pressure acts between the cathode-side catalyst layer 22 or the anode-side catalyst layer 23 and the ion exchange membrane 21, the cathode-side catalyst layer 22 or the anode-side catalyst layer 23 directly presses the metallic impurity removal layers 26, 27. Therefore, the metallic impurity removal layers 26, 27 absorb the effect of the direct pressure from the cathode-side catalyst layer 22 or the anode-side catalyst layer 23, and an increase in the electrical resistance of the entire water electrolysis cell 10 can be suppressed.

[0082] A water electrolysis cell according to a fifth aspect is the water electrolysis cell according to any one of the first to fourth aspects, further comprising: each of the metal impurity removal layers 26, 27 comprising at least one of a porous layer of a chelate resin and a porous layer of an ion exchange resin, whereby the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 allow hydroxide ions to pass through while removing metal ions and scale components as metal impurities.

[0083] A water electrolysis cell according to a sixth aspect is the water electrolysis cell according to the fifth aspect, further comprising: a metal impurity removal layer (26, 27) including at least one of a porous layer made of chelating resin particles and a porous layer made of ion exchange resin particles, and a particle binder that binds the particles together. This allows the chelating resin particles and the ion exchange resin particles to be appropriately bound by the particle binder, thereby preventing the particles from falling out of the porous layer.

[0084] The water electrolysis cell according to the seventh aspect is the water electrolysis cell according to the fifth or sixth aspect, and further comprises the metal impurity removal layer 26, 27 formed by applying a mixture of at least one of chelating resin particles 101 and ion exchange resin particles 102 with a particle binder 103 to the surface of the ion exchange membrane 21 to form a porous layer. This improves the strength of the ion exchange membrane 21 and facilitates assembly of the water electrolysis cell 10.

[0085] The water electrolysis cell according to an eighth aspect is the water electrolysis cell according to the fifth or sixth aspect, further comprising: a porous metal impurity removal layer (26, 27) formed by applying a mixture of at least one of chelate resin particles (101) and ion exchange resin particles (102) with a particle binder (103) to the surface of the cathode-side catalyst layer (22) or the anode-side catalyst layer (23). This prevents the cathode-side metal impurity removal layer (26) and the anode-side metal impurity removal layer (27) from being formed directly on the ion exchange membrane (21), which is susceptible to damage.

[0086] A water electrolysis cell according to a ninth aspect is the water electrolysis cell according to any one of the first to eighth aspects, further comprising: a second surface of the cathode-side catalyst layer 22 or the anode-side catalyst layer 23 in contact with the metallic impurity removing layer 26, 27 that is rougher than the first surface of the ion exchange membrane 21 in contact with the metallic impurity removing layer 26, 27. This allows the metallic impurity removing layers 26, 27 to absorb the effects of surface pressure, even if the second surface of the cathode-side catalyst layer 22 or the anode-side catalyst layer 23 is rougher than the first surface of the ion exchange membrane 21, thereby preventing defects such as damage to the ion exchange membrane 21.

[0087] A water electrolysis system according to a tenth aspect comprises a water electrolysis cell (10), electrolyte solution supply flow paths (53, 54, 61, 62) that supply an electrolytic solution to the water electrolysis cell (10), electrolyte solution supply pumps (55, 56, 63, 64) provided in the electrolyte solution supply flow paths (53, 54, 61, 62), cleaning solution supply flow paths (77, 78) that supply a cleaning solution to the water electrolysis cell (10) to remove metal impurities adhering to the metal impurity removal layers (26, 27), and cleaning solution supply pumps (79, 80) provided in the cleaning solution supply flow paths (77, 78). The water electrolysis system thus enables the water electrolysis cell (10) to be regenerated by removing metal impurities adhering to the cathode-side metal impurity removal layer (26) and the anode-side metal impurity removal layer (27).

[0088] A water electrolysis system according to an eleventh aspect is the water electrolysis cell according to the tenth aspect, further comprising supplying a hydrochloric acid aqueous solution, ion-exchanged water, and a potassium hydroxide solution as cleaning solutions, in that order, to the water electrolysis cell 10. This allows metal scale and metal scale components, as metal impurities, adhering to the cathode-side metallic impurity-removing layer 26 and the anode-side metallic impurity-removing layer 27 to be appropriately removed.

[0089] REFERENCE SIGNS LIST 10 Water electrolysis cell 11 Cathode side separator 12 Anode side separator 13 Membrane electrode assembly 21 Ion exchange membrane 22 Cathode side catalyst layer 23 Anode side catalyst layer 24 Cathode side power supply 25 Anode side power supply 26 Cathode side metal impurity removal layer 27 Anode side metal impurity removal layer 31, 32 Insulator 33, 34 Power supply 35, 36 Insulator 37, 38 End plate 50 Water electrolysis system 51, 52 Electrolyte storage section 53, 54, 61, 62 Electrolyte supply flow path 55, 56, 63, 64 Electrolyte supply pump 57, 58 Gas-liquid separator 59, 60 Gas exhaust flow path 65, 66 Gas exhaust flow path 67 Pump 68, 69 Three-way valve 71, 72, 73, 74, 75, 76 Cleaning liquid reservoir 77, 78 Cleaning liquid supply flow path 79, 80 Cleaning liquid supply pump 81, 82 Cleaning liquid return flow path 83, 84, 85, 86, 87, 88 Opening / closing valve 89, 90 Three-way valve 101 Chelate resin particle 102 Ion exchange resin particle 103 Particle binder 104 Void

Claims

1. A water electrolysis cell comprising: an ion exchange membrane; a cathode-side catalyst layer disposed on one side of the ion exchange membrane; an anode-side catalyst layer disposed on the other side of the ion exchange membrane; and a metal impurity removal layer disposed at least either between the ion exchange membrane and the cathode-side catalyst layer or between the ion exchange membrane and the anode-side catalyst layer.

2. The water electrolysis cell according to claim 1, wherein the metal impurity removal layer is capable of removing scale contained in the electrolyte.

3. The water electrolysis cell according to claim 1, wherein the metal impurity removal layer is capable of removing scale components dissolved in the electrolyte at a concentration equal to or lower than the saturated concentration.

4. The water electrolysis cell according to claim 1, wherein the metal impurity removal layer is in contact with the ion exchange membrane and is in contact with the cathode-side catalyst layer or the anode-side catalyst layer.

5. The water electrolysis cell according to claim 1, wherein the metal impurity removal layer comprises at least one of a porous layer of a chelating resin and a porous layer of an ion exchange resin.

6. The water electrolysis cell according to claim 5, wherein the metal impurity removal layer comprises at least one of the porous layer made of particles of the chelating resin and the porous layer made of particles of the ion exchange resin, and a particle binder that binds the particles together.

7. The water electrolysis cell according to claim 6, wherein the porous layer of the metal impurity removal layer is formed by applying a mixture of at least one of particles of the chelating resin and particles of the ion exchange resin mixed with the particle binder to the surface of the ion exchange membrane.

8. The water electrolysis cell according to claim 6, wherein the porous layer of the metal impurity removal layer is formed by applying a mixture of at least one of the chelating resin particles and the ion exchange resin particles with the particle binder to the surface of the cathode-side catalyst layer or the anode-side catalyst layer.

9. The water electrolysis cell according to claim 1, wherein a second surface of the cathode-side catalyst layer or the anode-side catalyst layer in contact with the metal impurity removing layer is rougher than a first surface of the ion exchange membrane in contact with the metal impurity removing layer.

10. A water electrolysis system comprising: a water electrolysis cell according to claim 1; an electrolyte solution supply flow path that supplies an electrolyte solution to the water electrolysis cell; an electrolyte solution supply pump provided in the electrolyte solution supply flow path; a cleaning solution supply flow path that supplies a cleaning solution to the water electrolysis cell to remove metal impurities adhering to the metal impurity removal layer; and a cleaning solution supply pump provided in the cleaning solution supply flow path.

11. The water electrolysis system according to claim 10, wherein the cleaning solutions, ie, hydrochloric acid aqueous solution, ion-exchanged water, and potassium hydroxide solution, are supplied to the water electrolysis cell in this order.

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