Water electrolysis cells and water electrolysis systems

Abstract

In water electrolysis cells and water electrolysis systems, performance is improved by suppressing the rise in electrolysis voltage. [Solution] The device comprises 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 at least one of the spaces between the ion exchange membrane and the anode-side catalyst layer.

Description

Technical Field

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

Background Art

[0002] The practical application of a water electrolysis apparatus for electrolyzing an aqueous solution to produce hydrogen is in progress. The water electrolysis apparatus electrolyzes an aqueous solution to produce hydrogen gas and oxygen gas. The water electrolysis apparatus has a water electrolysis cell. The water electrolysis cell is configured such that a cathode catalyst layer and an anode catalyst layer are disposed on both sides of an ion exchange membrane, current collectors are disposed outside the cathode catalyst layer and the anode catalyst layer, and separators are disposed outside each current collector.

[0003] By the way, in the water electrolysis apparatus, an aqueous potassium hydroxide solution may be used for the purpose of increasing the ionic conductivity of water. In this case, impurities generated during the production of the aqueous potassium hydroxide solution, for example, metal ions and scale components, are included, which may hinder the water electrolysis process. In addition, as a technique for removing ions contained in cathode water with an ion exchange membrane in an ozone water generation apparatus, for example, there is one described in Patent Document 1.

Prior Art Documents

Patent Documents

[0004] [[ID=…]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a water electrolysis apparatus, particularly after the start of water electrolysis, metal ions and scale components accumulate inside the water electrolysis cell. Then, a problem has been confirmed that the resistance of the ion exchange membrane increases, the ion exchange performance deteriorates, and the electrolysis voltage rises. When the electrolysis voltage rises, there is a problem that the water electrolysis performance deteriorates.

[0006] This disclosure aims to solve the aforementioned problems and to provide a water electrolysis cell and water electrolysis system that improve performance by suppressing the rise in electrolysis voltage. [Means for solving the problem]

[0007] To achieve the above objectives, the water electrolysis cell of the present disclosure comprises 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 at least one of the spaces between the ion exchange membrane and the anode-side catalyst layer.

[0008] Furthermore, the water electrolysis system of the present disclosure comprises a water electrolysis cell, an electrolyte channel for supplying an electrolyte to the water electrolysis cell, an electrolyte supply pump provided in the electrolyte channel, a cleaning solution channel for supplying a cleaning solution to the water electrolysis cell to recover metal impurities attached to the metal impurity removal layer, and a cleaning solution supply pump provided in the cleaning solution channel. [Effects of the Invention]

[0009] According to the water electrolysis cell and water electrolysis system disclosed herein, performance can be improved by suppressing the rise in electrolysis voltage. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing the water electrolysis cell of this embodiment. [Figure 2] Figure 2 is an exploded perspective view showing the water electrolysis cell of this embodiment. [Figure 3] Figure 3 is a schematic cross-sectional view of a membrane electrode assembly. [Figure 4] Figure 4 is a schematic cross-sectional view representing the metal impurity removal layer. [Figure 5] Figure 5 is a schematic diagram illustrating a method for manufacturing a membrane electrode assembly. [Figure 6]Figure 6 is a schematic diagram showing a modified example of a method for manufacturing a membrane electrode assembly. [Figure 7] Figure 7 is a graph showing the electrolysis voltage as a function of electrolysis time. [Figure 8] Figure 8 is a schematic diagram showing the water electrolysis system of this embodiment. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure, and where there are multiple embodiments, they may be combinations of these embodiments. Furthermore, the components in the embodiments include those readily conceivable by those skilled in the art, those that are substantially identical, and those that are equivalent.

[0012] [Embodiment] <Water electrolysis device> A water electrolysis device is a device that produces hydrogen (H2) by electrolyzing water (H2O) contained in an electrolyte. A water electrolysis device may, for example, use an anion exchange membrane (AEM). However, a water electrolysis device may also use, for example, a proton exchange membrane (PEM).

[0013] A water electrolysis apparatus comprises, for example, a cell stack, an electrolyte supply unit, and a power supply unit. The cell stack, as will be described later, is an assembly of water electrolysis cells. The electrolyte supply unit supplies electrolyte to the water electrolysis cells. The electrolyte is, for example, pure water or an alkaline aqueous solution. Potassium hydroxide (KOH) is used as the alkaline aqueous solution. 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 voltage to the water electrolysis cells. The power supply unit applies the DC voltage necessary for the electrolysis of the electrolyte between the cathode and anode of the water electrolysis cells.

[0014] <Water electrolysis cell> FIG. 1 is a schematic cross-sectional view showing the water electrolysis cell of the present embodiment.

[0015] As shown in FIG. 1, the water electrolysis cell 10 is a device that causes electrolysis of water contained in an electrolytic solution by externally input electrical energy to generate hydrogen. The water electrolysis cell 10 includes, for example, a cathode-side separator 11, an anode-side separator 12, and a membrane electrode assembly 13.

[0016] <Cathode-side separator> The cathode-side separator 11 is a member that defines one surface of the accommodation space of the water electrolysis cell 10. The cathode-side separator 11 is, for example, in the shape of a rectangular plate. The cathode-side separator 11 is applied with a negative voltage from a power supply unit 14 via, for example, a first power feeder 33 (see FIG. 2) described later. An electrolytic solution supply line L1 is connected to one end of the cathode-side separator 11. An electrolytic solution 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 surface of the accommodation space of the water electrolysis cell 10. The anode-side separator 12 is, for example, in the shape of a rectangular plate. The anode-side separator 12 is applied with a positive voltage from a power supply unit 14 via, for example, a second power feeder 34 (see FIG. 2) described later. An electrolytic solution supply line L3 is connected to one end of the anode-side separator 12. An electrolytic solution discharge line L4 is connected to the other end of the anode-side separator 12.

[0018] <Configuration of the membrane electrode assembly> The membrane electrode assembly (MEA) 13 is a structure assembled from an ion exchange membrane, a catalyst, and a power supply. The membrane electrode assembly 13 is positioned between the cathode-side separator 11 and the anode-side separator 12, and is located in the containment 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 power supply 24, an anode-side power supply 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 is formed by the cathode-side catalyst layer 22 and the cathode-side power supply 24 relative to the ion exchange membrane 21, and the anode is formed by the anode-side catalyst layer 23 and the anode-side power supply 25.

[0019] <Ion exchange membrane> The ion exchange membrane 21 is a membrane that selectively permeates ions. The ion exchange membrane 21 is, for example, a solid polymer electrolyte membrane. The ion exchange membrane 21 is, for example, a hydroxide ion (OH) - ) is a conductive anion exchange membrane (AEM). 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 different type from an anion exchange membrane.

[0020] The ion exchange membrane 21 is, for example, a rectangular sheet and is flexible. The external dimensions of the ion exchange membrane 21 are smaller than the external dimensions of the cathode-side separator 11 or the anode-side separator 12. The ion exchange membrane 21 is positioned between the cathode-side separator 11 and the anode-side separator 12 and is located in the containment space.

[0021] When a voltage is applied to the water electrolysis cell 10 by the power supply unit 14, the ion exchange membrane 21 undergoes the chemical reaction shown below on the cathode side, generating hydrogen from the electrolyte. The generated hydroxide ions move from the cathode side through the membrane electrode assembly 13 to the anode side. 2H2O + 2e - →H2+2OH -

[0022] When a voltage is applied to the water electrolysis cell 10 by the power supply unit 14, the ion exchange membrane 21 undergoes the chemical reaction shown below on the anode side, generating oxygen from the electrolyte. 2OH - → 1 / 2O2 + H2O + 2e -

[0023] As a result, the following chemical reactions occur when considering the entire water electrolysis cell 10. H2O → H2 + 1 / 2O2

[0024] The ion exchange membrane 21 may contain a polystyrene-based or tetraphenyl-based composition in its main chain and an imidazolium group or a quaternary ammonium group in its side chain, as an example of a membrane with relatively high ionic conductivity. Alternatively, the ion exchange membrane 21 may contain 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 have precipitated in the electrolyte. Furthermore, 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 is capable of removing scale components dissolved in the electrolyte at concentrations below saturation. The cathode-side metal impurity removal layer 26 is, for example, in the form of a rectangular sheet. The outer dimensions of the cathode-side metal impurity removal layer 26 are, for example, the same as or larger than the outer dimensions 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 opposite side of 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 have precipitated in the electrolyte. Furthermore, 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 is capable of removing scale components dissolved in the electrolyte at concentrations below saturation. The anode-side metal impurity removal layer 27 is, for example, in the form of a rectangular sheet. The external dimensions of the anode-side metal impurity removal layer 27 are, for example, the same as or larger than the external dimensions 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 to the ion exchange membrane 21.

[0027] The water electrolysis cell 10 of this embodiment has both a cathode-side metal impurity removal layer 26 and an anode-side metal impurity removal layer 27. However, the water electrolysis cell 10 of this embodiment only needs to have at least one of the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 will be 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 is, for example, in the form of a rectangular sheet. The external dimensions of the cathode-side catalyst layer 22 are smaller than, for example, the external dimensions of the ion exchange membrane 21. The cathode-side catalyst layer 22 is provided on the side of the cathode-side metal impurity removal layer 26 opposite to the ion exchange membrane 21. The cathode-side power supply 24 is connected to the cathode-side catalyst layer 22 from the side opposite to the cathode-side metal impurity removal layer 26. A negative voltage is applied to the cathode-side catalyst layer 22 from the power supply unit 14 via the cathode-side separator 11 and the cathode-side power supply 24, and it functions as part of the cathode of the water electrolysis cell 10.

[0029] The cathode catalyst layer can be made of any material that promotes the chemical reaction, and various materials are available. For example, the cathode catalyst layer 22 contains one or more of the following: nickel, nickel alloy, cerium oxide, lanthanum oxide, and platinum (Pt). In addition to the materials mentioned above, the cathode catalyst layer 22 may also contain other materials 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 is, for example, in the form of a rectangular sheet. The external dimensions of the anode-side catalyst layer 23 are smaller than, for example, the external dimensions of the ion exchange membrane 21. The anode-side catalyst layer 23 is provided on the side of the anode-side metal impurity removal layer 27 opposite to the ion exchange membrane 21. The anode-side power supply 25 is connected to the anode-side catalyst layer 23 from the side opposite to the anode-side metal impurity removal layer 27. A positive voltage is applied to the anode-side catalyst layer 23 from the power supply unit 14 via the anode-side separator 12 and the anode-side power supply 25, and it functions as part of the anode of the water electrolysis cell 10.

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

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

[0033] The cathode-side power supply 24 has a structure through which electrolyte and gas can pass. The cathode-side power supply 24 is formed from, for example, a metal mesh structure, a sintered body, fibers, a conductive carbon fiber mesh structure, or a nonwoven fabric. The cathode-side power supply 24 has a predetermined porosity. The external dimensions of the cathode-side power supply 24 are the same as those of the cathode-side catalyst layer 22. The cathode-side catalyst layer 22 and the cathode-side power supply 24 constitute the cathode of the water electrolysis cell 10.

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

[0035] The anode-side power supply 25 has a structure through which electrolyte and gas can pass. The anode-side power supply 25 is formed from, for example, a metal mesh structure, a sintered body, fibers, a conductive carbon fiber mesh structure, or a nonwoven fabric. The anode-side power supply 25 has a predetermined porosity. For example, the anode-side power supply 25 has the same porosity as the cathode-side power supply 24. The external dimensions of the anode-side power supply 25 are the same as those of the anode-side catalyst layer 23. The anode-side catalyst layer 23 and the anode-side power supply 25 constitute the anode of the water electrolysis cell 10.

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

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

[0038] <insulator> The insulators 31 and 32 are components that insulate the outer periphery of the cathode-side separator 11 from the outer periphery of the anode-side separator 12. The insulator 31, located on the cathode side, is a frame-shaped sheet member whose outer shape is slightly larger than the outer shape of the cathode-side separator 11. The insulator 31 contacts the cathode-side header 42 of the cathode-side separator 11 (described later) and covers the cathode-side header 42. The insulator 32, located on the anode side, is a frame-shaped sheet member whose outer shape is slightly larger than the outer shape of the anode-side separator 12. The insulator 32 contacts the anode-side header 44 of the anode-side separator 12 (described later) and covers the anode-side header 44. The materials of the insulators 31 and 32 are not particularly limited as long as they are insulating materials, for example, they are sheet-like resins such as PTFE.

[0039] <Power supply> The power supply unit 33 is an electrical connection unit that transmits a negative voltage applied from the power supply unit 14 to the cathode-side separator 11. The power supply unit 33 is a metal plate member (for example, a copper plate). The power supply unit 33 contacts the cathode-side separator 11 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 power supply unit 33 receives the negative voltage necessary for electrolysis in the water electrolysis cell 10 from the power supply unit 14.

[0040] The power supply unit 34 is an electrical connection part that transmits the positive voltage applied from the power supply unit 14 to the anode-side separator 12. The power supply unit 34 is a metal plate member (for example, a copper plate). The power supply unit 34 contacts the anode-side separator 12 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 unit 33 receives the positive voltage necessary for electrolysis in the water electrolysis cell 10 from the power supply unit 14.

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

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

[0043] The end plate 38 is located on the opposite side of the insulating material 36 from the housing space of the water electrolysis cell 10. The end plate 38 is formed from, for example, a metal plate (for example, a stainless steel plate). The outer dimensions of the end plate 38 are, for example, the same as or larger than the outer dimensions of the insulating material 36.

[0044] The water electrolysis cell 10 is not limited to the configuration described above. For example, the water electrolysis cell 10 may be a multilayer structure in which the cathode separator 11, the anode separator 12, and the membrane electrode assembly 13 are stacked in multiple layers.

[0045] <Configuration of the membrane electrode assembly> Figure 3 is a schematic cross-sectional view representing the film electrode assembly, and Figure 4 is a schematic cross-sectional view representing the metal impurity removal layer.

[0046] As shown in Figure 3, the membrane electrode assembly 13 has the cathode-side metal impurity removal layer 26, cathode-side catalyst layer 22, cathode-side power supply 24, and anode-side power supply 25 stacked in order on one side of the ion exchange membrane 21. On the other side of the ion exchange membrane 21, the membrane electrode assembly 13 has the anode-side metal impurity removal layer 27, anode-side catalyst layer 23, and anode-side power supply 25 stacked in order.

[0047] <Configuration of the metal impurity removal layer> The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 have similar configurations. The cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are layers provided on one side and the other side of the ion exchange membrane 21. The cathode-side metal impurity removal layer 26 is in contact with one side of the ion exchange membrane 21 and also in contact with one side of the cathode-side catalyst layer 22. The anode-side metal impurity removal layer 27 is in contact with the other side of the ion exchange membrane 21 and also in contact with one side of the anode-side catalyst layer 23. Hydroxide ions can pass through the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. In this case, it is preferable that the second surface of the cathode-side catalyst layer 22 and the anode-side catalyst layer 23, which are in contact with the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27, is rougher than the first surface of the ion exchange membrane 21, which is in contact with the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27.

[0048] As shown in Figure 4, the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 remove metal scale and specific metal ions (scale components) contained in the electrolyte. Hydroxide ions can pass through the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. Here, specific metal ions refer to calcium ions, magnesium ions, iron ions, nickel ions, chromium ions, manganese ions, molybdenum ions, etc. These metal ions are impurities contained in trace amounts in the potassium hydroxide reagent when the potassium hydroxide aqueous solution is produced as an electrolyte, and trace metal ions that leach from the stainless steel piping and the metal materials of the components of the water electrolysis cell 10. When they precipitate, they adhere to the ion exchange membrane 21 as scale, 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 chelate resin and a porous layer of 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 consist only of a porous layer of chelate resin, or only of a porous layer of ion exchange resin, or may consist of a porous layer containing both chelate resin and 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 in 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 thickness of the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 is preferably, for example, 3 μm or more and 10 μm or less. Furthermore, the particle size of the chelate resin particles 101 and the ion exchange resin particles 102 is preferably 1 μm or more and 10 μm or less. Since the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are composed of multiple chelate resin particles 101 and multiple ion exchange resin particles 102, there are voids 104 through which the electrolyte can pass.

[0051] The particle binder 103 includes, for example, one or more of the following: a polymer binder, an ionomer, etc. In this embodiment, the particle binder 103 includes both a polymer binder and an ionomer. The polymer binder functions as a binder for the chelate resin particles 101 and the ion exchange resin particles 102. That is, the polymer binder binds the chelate resin particles 101 and the ion exchange resin particles 102 to each other. In this embodiment, for example, a fluorine-based binder can be used as the polymer binder. Examples of fluorine-based binders include polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and tetrafluoroethylene / ethylene copolymer (ETFE). The polymer binder only needs to have the effect of binding the chelate resin particles 101 and the ion exchange resin particles 102, and non-fluorine-based binders can also be used as polymer binders.

[0052] An ionomer is an ion exchange resin component used to reduce the overall electrical resistance of the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. The ionomer can be a cationic polymer in which a quaternary ammonium group is introduced into an aromatic polymer backbone, such as Diaza (bicyclo-octane) polyethersulfone, or 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, ionomers can also be anionic polymers in which anionic functional groups such as sulfonic acid groups or carboxylic acid groups are introduced into a fluorine-based polymer backbone.

[0053] Furthermore, the ionomer includes a second polymer which has a smaller molecular weight than the first polymer contained in the ion exchange membrane 21 and has the same molecular skeleton as the first polymer. The second polymer has a predetermined second molecular weight. The second amount is smaller than the first amount. Note that 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 that of the second polymer, or the molecular weight of the second polymer may be greater than that 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 a membrane electrode assembly> Figure 5 is a schematic diagram illustrating a method for manufacturing a membrane electrode assembly.

[0055] As shown in Figure 5, first, chelate resin particles, ion exchange resin particles, and a binder are added to a solvent and mixed to produce a slurry (mixture). Next, the slurry is applied to one side of the ion exchange membrane 21 and dried to form the cathode-side metal impurity removal layer 26. The slurry is also applied to the other side of the ion exchange membrane 21 and dried to form the anode-side metal impurity removal layer 27.

[0056] Next, a cathode-side catalyst layer 22 is provided on the outer surface of the cathode-side metal impurity removal layer 26 formed on one side of the ion exchange membrane 21, and a cathode-side power supply 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 metal impurity removal layer 27 formed on the other side of the ion exchange membrane 21, and an anode-side power supply 25 is provided on the outer surface of the anode-side catalyst layer 23. This completes the production of the water electrolysis cell 10.

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

[0058] <Modified Method of Manufacturing a Membrane Electrode Assembly> The method for manufacturing the membrane electrode assembly is not limited to the method described above. Figure 6 is a schematic diagram showing a modified example of the method for manufacturing the membrane electrode assembly.

[0059] As shown in Figure 6, first, chelate resin particles, ion exchange resin particles, and a binder are added to a solvent and mixed to produce a slurry (mixture). Next, a cathode-side catalyst layer 22 is formed on one side of the cathode-side power supply 24, and an anode-side catalyst layer 23 is formed on one side of the anode-side power supply 25. Then, the slurry is applied to the surface of the cathode-side catalyst layer 22 and dried to form a cathode-side metal impurity removal layer 26. Additionally, the slurry is 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 metal impurity removal layer 26 is provided on one side of the ion exchange membrane 21. Furthermore, an anode-side metal impurity removal layer 27 is provided on the other side of the ion exchange membrane 21. This completes the production of the water electrolysis cell 10.

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

[0062] <Effects of water electrolysis cell> Figure 7 is a graph showing the electrolysis voltage as a function of electrolysis time.

[0063] As shown in Figure 7, in a conventional water electrolysis cell (dotted line in Figure 7) that does not have a cathode-side metal impurity removal layer 26 and an anode-side metal impurity removal layer 27, the electrolysis voltage gradually increases as the electrolysis time progresses after the start of water electrolysis. This is thought to be due to the accumulation of metal ions and scale components in the electrolyte on the ion exchange membrane, which increases the resistance of the ion exchange membrane. When the resistance of the ion exchange membrane increases, the ion exchange performance decreases, the electrolysis voltage rises, and the water electrolysis performance deteriorates.

[0064] On the other hand, in this embodiment, the water electrolysis cell 10 (solid line in Figure 7) having a cathode-side metal impurity removal layer 26 and an anode-side metal impurity removal layer 27 shows that the electrolysis voltage hardly rises as the electrolysis time progresses after the start of water electrolysis. This is because the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 remove metal ions and scale components from the electrolyte, thereby suppressing the deposition of metal ions and scale components on the ion exchange membrane 21. As a result, the resistance of the ion exchange membrane does not increase, the ion exchange performance does not decrease, and the decrease in water electrolysis performance is suppressed by preventing a gradual rise in the electrolysis voltage.

[0065] In this embodiment, the water electrolysis cell 10 has a cathode-side metal impurity removal layer 26 and an anode-side metal impurity removal layer 27. Therefore, even if the surface pressure of the ion exchange membrane 21 is increased, a short circuit will not occur, good IV characteristics can be obtained, and good current efficiency (100%) can be obtained. Furthermore, the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are positioned between the ion exchange membrane 21 and the cathode-side catalyst layer 22 and the anode-side catalyst layer 23, respectively. As a result, the electrodes do not directly contact the ion exchange membrane 21, and damage to the ion exchange membrane 21 can be prevented.

[0066] <Water electrolysis system> Figure 8 is a schematic diagram showing the water electrolysis system of this embodiment.

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

[0068] Therefore, when the electrolyte supply pumps 55 and 63 are driven, the electrolyte stored in the electrolyte storage section 51 is supplied to the gas-liquid separator 57 via the electrolyte supply channel 53, and then supplied to the cathode side of the water electrolysis cell 10 via the three-way valve 68 through the electrolyte supply channel 61. Also, when the electrolyte supply pumps 56 and 64 are driven, the electrolyte stored in the electrolyte storage section 52 is supplied to the gas-liquid separator 58 via the electrolyte supply channel 54, and then supplied to the anode side of the water electrolysis cell 10 via the three-way valve 69 through the electrolyte supply channel 62. Then, the hydrogen gas generated 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 by the gas discharge channel 59. On the other hand, the oxygen gas generated 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 by the gas discharge channel 60.

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

[0070] The cleaning solution storage sections 71 and 72 store an aqueous hydrochloric acid solution as the cleaning solution. The cleaning solution storage sections 73 and 74 store deionized water as the cleaning solution. The cleaning solution storage sections 75 and 76 store a potassium hydroxide solution as the cleaning solution. The cleaning solution supply channel 77 has one end that branches into three, each connected to a cleaning solution storage section 71, 73, and 75. The other end of the cleaning solution supply channel 77 is connected to the cathode side of the water electrolysis cell 10 via a three-way valve 89. The cleaning solution supply channel 78 has one end that branches into three, each connected to a cleaning solution storage section 72, 74, and 76. The other end of the cleaning solution supply channel 78 is connected to the anode side of the water electrolysis cell 10 via a three-way valve 90. The cleaning solution supply pumps 79 and 80 are provided in the cleaning solution supply channels 77 and 78.

[0071] One end of the cleaning fluid return channel 81 is connected to a three-way valve 68. The other end of the cleaning fluid return channel 81 branches into three, each connected to a cleaning fluid storage section 71, 73, and 75. One end of the cleaning fluid return channel 82 is connected to a three-way valve 69. The other end of the cleaning fluid return channel 82 branches into three, each connected to a cleaning fluid storage section 72, 74, and 76. On-off valves 83, 85, and 87 are provided at each branch at one end of the cleaning fluid supply channel 77. On-off valves 84, 86, and 88 are provided at each branch at one end of the cleaning fluid supply channel 78.

[0072] In the water electrolysis cell 10, the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 (see Figure 1) recover metal impurities from the electrolyte. As a result, metal impurities accumulate on the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27, leading to a decrease in performance. Therefore, by supplying a cleaning solution to the water electrolysis cell 10, the metal impurities accumulated on the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 are removed and recovered.

[0073] The electrolyte supply pumps 55, 56, 63, and 64 are stopped, and the operation of the water electrolysis cell 10 is stopped. In this state, hydrochloric acid aqueous solution, deionized water, and potassium hydroxide solution are supplied to the water electrolysis cell 10 in sequence as cleaning solutions. Specifically, 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. As a result, the hydrochloric acid aqueous solution stored in the cleaning solution storage sections 71 and 72 is supplied to the water electrolysis cell 10 via the cleaning solution supply channels 77 and 78 and the three-way valves 89 and 90, eluting metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. The hydrochloric acid aqueous solution containing the eluted metal impurities is returned to the cleaning solution storage sections 71 and 72 via the cleaning solution return channels 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 storage sections 73 and 74 is supplied to the water electrolysis cell 10 via the three-way valves 89 and 90 through the cleaning solution supply channels 77 and 78, eluting the metal impurities adhering to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27. The ion-exchanged water containing the eluted metal impurities is returned to the cleaning solution storage sections 73 and 74 via the cleaning solution return channels 81 and 82.

[0075] Next, 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 via the cleaning solution supply channels 77 and 78 and the three-way valves 88 and 89, eluting the 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 via the cleaning solution return channels 81 and 82.

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

[0077] [Effects of this embodiment] The water electrolysis cell according to the first embodiment comprises 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 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.

[0078] In the water electrolysis cell according to the first embodiment, metal ions and scale components as metal impurities in the electrolyte are removed by the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27, and their deposition on the ion exchange membrane 21 is suppressed. As a result, the resistance of the ion exchange membrane 21 does not increase, the ion exchange performance does not decrease, the increase in electrolysis voltage is suppressed, and the decrease in water electrolysis performance can be suppressed.

[0079] The water electrolysis cell according to the second embodiment is the same as the water electrolysis cell according to the first embodiment, and furthermore, the metal impurity removal layers 26 and 27 are capable of removing scale contained in the electrolyte. This makes it possible to suppress the deposition of scale on the ion exchange membrane 21.

[0080] The water electrolysis cell according to the third embodiment is a water electrolysis cell according to the first or second embodiment, further comprising metal impurity removal layers 26 and 27 capable of removing scale components dissolved in the electrolyte at concentrations below saturation. This makes it possible to suppress the deposition of scale components on the ion exchange membrane 21.

[0081] The water electrolysis cell according to the fourth embodiment is a water electrolysis cell according to any one of the first to third embodiments, further wherein the metal impurity removal layers 26 and 27 are 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 is applied 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 against the metal impurity removal layers 26 and 27. Therefore, the metal impurity removal layers 26 and 27 absorb the effects of direct pressure from the cathode-side catalyst layer 22 or the anode-side catalyst layer 23, thereby suppressing an increase in the overall electrical resistance of the water electrolysis cell 10.

[0082] The water electrolysis cell according to the fifth embodiment is a water electrolysis cell according to any one of the first to fourth embodiments, further comprising at least one of a porous layer of chelate resin and a porous layer of ion exchange resin in the metal impurity removal layers 26 and 27. As a result, the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 can remove metal ions and scale components as metal impurities while allowing hydroxide ions to pass through.

[0083] The water electrolysis cell according to the sixth embodiment is a water electrolysis cell according to the fifth embodiment, further comprising metal impurity removal layers 26, 27 having at least one of a porous layer made of chelate resin particles and a porous layer made of ion exchange resin particles, and a particle binder that binds the particles together. This allows the chelate resin particles and ion exchange resin particles to be properly bound together by the particle binder, and suppresses the shedding of particles from the porous layer.

[0084] The water electrolysis cell according to the seventh embodiment is a water electrolysis cell according to the fifth or sixth embodiment, further comprising a metal impurity removal layer 26, 27 formed by coating the surface of the ion exchange membrane 21 with a mixture of chelate resin particles 101 and ion exchange resin particles 102 mixed with a particle binder 103, thereby forming a porous layer. This improves the strength of the ion exchange membrane 21 and facilitates the assembly of the water electrolysis cell 10.

[0085] The eighth embodiment of the water electrolysis cell is a water electrolysis cell according to the fifth or sixth embodiment, further comprising a porous layer formed by applying a mixture of chelate resin particles 101 and ion exchange resin particles 102 mixed 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 formation of the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27 directly on the easily damaged ion exchange membrane 21, thereby suppressing damage to the ion exchange membrane 21.

[0086] The water electrolysis cell according to the ninth embodiment is a water electrolysis cell according to any one of the first to eighth embodiments, further comprising a second surface of the cathode-side catalyst layer 22 or anode-side catalyst layer 23 in contact with the metal impurity removal layers 26, 27 that is rougher than the first surface of the ion exchange membrane 21 that is in contact with the metal impurity removal layers 26, 27. As a result, even if the roughness of the second surface of the cathode-side catalyst layer 22 or anode-side catalyst layer 23 is rougher than the roughness of the first surface of the ion exchange membrane 21, the effects of surface pressure can be absorbed by the metal impurity removal layers 26, 27, and the occurrence of defects such as damage to the ion exchange membrane 21 can be suppressed.

[0087] The water electrolysis system according to the tenth embodiment comprises a water electrolysis cell 10, electrolyte supply channels 53, 54, 61, 62 for supplying electrolyte to the water electrolysis cell 10, electrolyte supply pumps 55, 56, 63, 64 provided in the electrolyte supply channels 53, 54, 61, 62, cleaning solution supply channels 77, 78 for supplying cleaning solution to the water electrolysis cell 10 to remove metal impurities attached to the metal impurity removal layers 26, 27, and cleaning solution supply pumps 79, 80 provided in the cleaning solution supply channels 77, 78. As a result, the water electrolysis cell 10 can be regenerated by removing metal impurities attached to the cathode-side metal impurity removal layer 26 and the anode-side metal impurity removal layer 27.

[0088] The water electrolysis system according to the 11th embodiment is a water electrolysis cell according to the 10th embodiment, further comprising supplying hydrochloric acid aqueous solution, ion-exchanged water, and potassium hydroxide solution to the water electrolysis cell 10 in sequence as cleaning solutions. This makes it possible to appropriately 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. [Explanation of symbols]

[0089] 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 feeder 35,36 Insulating material 37, 38 End Plates 50 Water Electrolysis Systems 51, 52 Electrolyte storage section 53, 54, 61, 62 Electrolyte supply channel 55, 56, 63, 64 Electrolyte supply pump 57,58 Gas-liquid separator 59,60 Gas exhaust channel 65,66 Gas exhaust channels 67 Pumps 68, 69 Three-way valve 71, 72, 73, 74, 75, 76 Cleaning fluid reservoir 77,78 Cleaning fluid supply channel 79,80 Cleaning fluid supply pump 81,82 Washing solution return channel 83, 84, 85, 86, 87, 88 Shut-off valves 89,90 Three-way valve 101 Chelate resin particles 102 Particles of ion exchange resin 103 Particle binder 104 void

Claims

1. Ion exchange membrane and, A cathode-side catalyst layer is disposed on one side of the ion exchange membrane, The anode-side catalyst layer is located on the other side of the ion exchange membrane, A metal impurity removal layer is disposed between the ion exchange membrane and the cathode-side catalyst layer, and between the ion exchange membrane and the anode-side catalyst layer, A water electrolysis cell equipped with the following features.

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

3. The aforementioned metal impurity removal layer is capable of removing scale components dissolved in the electrolyte at concentrations below saturation. The water electrolysis cell according to claim 1.

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

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

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

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

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

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

10. A water electrolysis cell according to claim 1, An electrolyte supply channel for supplying electrolyte to the aforementioned water electrolysis cell, An electrolyte supply pump provided in the electrolyte supply channel, A cleaning solution supply channel is provided to the water electrolysis cell to remove metal impurities adhering to the metal impurity removal layer, A cleaning fluid supply pump provided in the cleaning fluid supply channel, A water electrolysis system equipped with the following features.

11. The aqueous hydrochloric acid solution, deionized water, and potassium hydroxide solution are supplied to the aforementioned water electrolysis cell in order. The water electrolysis system according to claim 10.

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