Water electrolysis cell, water electrolysis cell stack, water electrolysis device

Abstract

To provide a water electrolysis cell that suppresses damage to the electrolyte membrane. [Solution] The water electrolysis cell comprises an electrolyte membrane, an anode catalyst layer containing manganese laminated on one side of the electrolyte membrane, a cathode catalyst layer laminated on the other side of the electrolyte membrane, an anode power supply laminated on the anode catalyst layer, a cathode power supply laminated on the cathode catalyst layer, and an oxygen-impermeable portion laminated around the entire circumference between the outer periphery of the anode catalyst layer and the outer periphery of the anode power supply, the inner periphery of which is located on the inner side of the entire circumference, beyond the outer periphery of the overlapping portion which is the outer periphery of the overlapping portion where the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode power supply, and the cathode power supply all overlap in the lamination direction, and which is impermeable to oxygen.

Description

[Technical Field]

[0001] This invention relates to a water electrolysis cell, a water electrolysis cell stack, and a water electrolysis apparatus. [Background technology]

[0002] In recent years, fuel cells and water electrolysis devices that produce hydrogen as fuel for fuel cells have attracted attention as ways to utilize clean energy. Hydrogen can be generated and stored using electricity obtained from renewable energy sources. Various technologies have also been proposed for water electrolysis cells, which include an electrolyte membrane, anode catalyst layer, anode power supply, cathode catalyst layer, and cathode power supply, as components of such water electrolysis devices (see, for example, Patent Document 1). The anode catalyst layer in a water electrolysis cell is generally composed of an anode catalyst and an ionomer. From the standpoint of energy conversion efficiency and durability, iridium oxide catalysts are commonly used as anode catalysts. However, iridium is an expensive precious metal, and cheaper alternative materials are needed to reduce the cost of water electrolysis cells. In recent years, manganese oxide catalysts and iridium-manganese oxide composite materials have been proposed as anode catalysts that are inexpensive and achieve high energy conversion efficiency (for example, Patent Documents 2, 3, and 4). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-73782 [Patent Document 2] Patent Application No. 2024-563542 [Patent Document 3] Japanese Patent Publication No. 2024-84898 [Patent Document 4] Japanese Patent Publication No. 2024-91722 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, as a result of verifying the long-term durability of a water electrolysis cell containing manganese in the anode catalyst, it was found that manganese oxide precipitates around the anode catalyst layer on the electrolyte membrane during operation, damaging the electrolyte membrane. When the electrolyte membrane is damaged, there is a problem that the current efficiency of hydrogen generation defined by Equation 1 decreases, and the energy conversion efficiency of the water electrolysis cell decreases. Equation (1) Current efficiency of hydrogen generation = Hydrogen generation rate (mol / s) ÷ [Applied current value to the electrolysis cell (A) ÷ Faraday constant (C / mol) ÷ 2] × 100% The Faraday constant is approximately 96,485 C / mol.

[0005] The present invention has been made in consideration of the above facts, and an object thereof is to provide a water electrolysis cell, a water electrolysis cell stack, and a water electrolysis apparatus that can suppress damage to the electrolyte membrane.

Means for Solving the Problems

[0006] In view of the above problems, the present invention provides a water electrolysis cell having an electrolyte membrane, an anode catalyst layer containing manganese laminated on one surface of the electrolyte membrane, a cathode catalyst layer laminated on the other surface of the electrolyte membrane, an anode current collector laminated on the anode catalyst layer, and a cathode current collector laminated on the cathode catalyst layer. It has been found that damage to the electrolyte membrane is suppressed by coating the damaged portion of the electrolyte membrane with an oxygen-impermeable material, leading to the solution of the present invention. The gist of the present invention is as follows.

[0007] The water electrolysis cell of the first aspect includes an electrolyte membrane, an anode catalyst layer containing manganese laminated on one surface of the electrolyte membrane, a cathode catalyst layer laminated on the other surface of the electrolyte membrane, an anode current collector laminated on the anode catalyst layer, a cathode current collector laminated on the cathode catalyst layer, a frame shape having an opening, laminated over the entire circumference between the outer peripheral portion of the anode catalyst layer and the anode current collector, and an oxygen non-permeable portion disposed on the inner peripheral side over the entire circumference, where the inner peripheral end of the opening is closer to the inner peripheral side than the outer peripheral end of the overlapping portion where all of the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode current collector, and the cathode current collector overlap in the stacking direction and is non-permeable to oxygen.

[0008] In the water electrolysis cell of the first aspect, the oxygen non-permeable portion disposed on the inner peripheral side of the outer peripheral end of the overlapping portion covers the outer peripheral end of the overlapping portion including the outer peripheral end of the anode catalyst layer over the entire circumference, so that the dissolution of oxygen into the electrolyte membrane is suppressed. As a result, the re-precipitation of manganese in the vicinity of the electrolyte membrane is suppressed, and damage to the electrolyte membrane can be suppressed.

[0009] The water electrolysis cell of the second aspect is the water electrolysis cell of the first aspect, wherein the shortest distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening is 1 mm or more.

[0010] Thus, by setting the shortest distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening to 1 mm or more, the dissolution of oxygen into the electrolyte membrane can be effectively suppressed.

[0011] The water electrolysis cell of the third aspect is the water electrolysis cell of the first and second aspects, wherein the longest distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening is 500 mm or less.

[0012] Thus, by setting the longest distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening to 500 mm or less, the enlargement and high cost of the water electrolysis cell can be suppressed.

[0013] The fourth embodiment of the water electrolysis cell is a water electrolysis cell of any of the first to third embodiments, comprising a gasket disposed on the outside of the outer end surface of the anode power supply, wherein the oxygen-impermeable portion is integrally formed with the gasket.

[0014] According to the water electrolysis cell of the fourth embodiment, the oxygen-impermeable portion can be formed from a part of the gasket.

[0015] The fifth embodiment of the water electrolysis cell stack is a stack of multiple water electrolysis cells from any of the first to fourth embodiments.

[0016] In this way, multiple water electrolysis cells can be stacked to form a cell stack.

[0017] The water electrolysis apparatus of the sixth embodiment comprises a water electrolysis cell of any of the first to fourth embodiments or a water electrolysis cell stack of the fifth embodiment.

[0018] Thus, any of the water electrolysis cells of the first to fourth embodiments or the water electrolysis cell stack of the fifth embodiment can be used in a water electrolysis apparatus. [Effects of the Invention]

[0019] According to this disclosure, damage to the electrolyte membrane can be suppressed. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows a schematic cross-sectional configuration of the water electrolysis apparatus according to this embodiment. [Figure 2] (A) is a plan view of the water electrolysis cell according to this embodiment, as seen from the anode side, and (B) is a plan view as seen from the cathode side. [Figure 3] This figure shows a schematic cross-sectional configuration of a water electrolysis apparatus according to Modification 1 of this embodiment. [Figure 4] This figure shows a schematic cross-sectional configuration of a water electrolysis apparatus according to a modified example 2 of this embodiment. [Modes for carrying out the invention]

[0021] The embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is just one example of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various ways within the scope of its gist. Furthermore, the portion where the electrolyte membrane, anode catalyst layer, cathode catalyst layer, anode power supply, and cathode power supply all overlap in the stacking direction may be referred to as the overlapping portion. In addition, the outer edge of the overlapping portion may be referred to as the outer edge of the overlapping portion.

[0022] As one embodiment of the water electrolysis cell of the present disclosure, a water electrolysis apparatus 10 will be described as an example. Figure 1 shows a schematic cross-sectional view of the water electrolysis apparatus 10, and Figure 2 shows a plan view of the water electrolysis cell 20, with the separators 28 and 38 (described later) omitted, as seen from the anode side.

[0023] The water electrolysis apparatus 10 comprises a water electrolysis cell 20 and a voltage application unit 40. The voltage application unit 40 applies a voltage between separators 28 and 38, which will be described later. The voltage and current between separators 28 and 38 are measured by a voltmeter and an ammeter (not shown), and are controlled by a control unit (not shown) based on the voltage and current values ​​between separators 28 and 38.

[0024] The water electrolysis cell 20 includes an electrolyte membrane 21, and on one side of the electrolyte membrane 21, there is an anode catalyst layer 22, an anode power supply 24, an anode gasket 26, and a separator 28. On the other side of the electrolyte membrane 21, there is a cathode catalyst layer 32, a cathode power supply 34, a cathode gasket 36, and a separator 38.

[0025] [Electrolyte membrane] The electrolyte membrane 21 contains protons (H + There are no particular restrictions on the material as long as it has the property of permeating ), for example, polymer electrolyte membranes (PEMs). Examples of polymer electrolyte membranes include membrane materials formed from fluorine-based polymer electrolytes or hydrocarbon-based polymer electrolytes.

[0026] Fluorinated polymer electrolytes refer to polymers in which most or all of the hydrogen atoms in the alkyl and / or alkylene groups are replaced with fluorine atoms. Representative examples of fluorinated polymer electrolytes include "Nafion" (registered trademark) (manufactured by Chemours K.K.), "Acquivion" (registered trademark) (manufactured by Solvay), "Flemion" (registered trademark) (manufactured by AGC Inc.), and "Aciplex" (registered trademark) (manufactured by Asahi Kasei Corporation).

[0027] As the hydrocarbon-based polymer electrolyte, aromatic hydrocarbon polymers having aromatic rings in the main chain are preferred. Here, the aromatic rings may include not only hydrocarbon aromatic rings consisting only of carbon and hydrogen atoms, such as benzene rings and naphthalene skeletons, but also heterocycles such as pyridine rings, imidazole rings, and thiol rings. Furthermore, some aliphatic units may constitute the polymer together with the aromatic ring units.

[0028] Specific examples of aromatic hydrocarbon polymers include polymers having a structure selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene, polyarylene ketone, polyetherketone, polyarylene phosphine oxide, polyetherphosphine oxide, polybenzoxazole, polybenzthiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain along with an aromatic ring. Note that polysulfone, polyethersulfone, polyetherketone, etc., as used here, are general terms for structures having sulfone bonds, ether bonds, ketone bonds, etc., in their molecular chains, and include polyetherketone ketone, polyetheretherketone, polyetheretherketone ketone, polyetherketone etherketone ketone, polyetherketone etherketone ketone, and polyetherketone sulfone. Aromatic hydrocarbon polymers may have multiple of these structures. Among these, polymers having a polyetherketone skeleton, i.e., polyetherketone polymers, are particularly preferred as aromatic hydrocarbon polymers.

[0029] The electrolyte membrane may be combined with a reinforcing material. Using a reinforcing material can increase the mechanical strength of the water electrolysis cell.

[0030] Specific examples of reinforcing materials include homogeneous porous membranes made of fluorine-based polymers such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PVDF (polyvinylidene fluoride), and FEP (tetrafluoroethylene-hexafluoropropylene copolymer), or thermoplastic resins such as PE (polyethylene) and PP (polypropylene), or engineering plastics such as PI (polyimide), PSF (polysulfone), PES (polyethersulfone), PEEK (polyetheretherketone), PPSS (polyphenylene sulfide sulfone), PPO (polyphenylene oxide), PEK (polyetherketone), PBI (polybenzimidazole), PPS (polyphenylene sulfide), PPP (polyparaphenylene), PPQ (polyphenylquinoxaline), polybenzoxazole (PBO), polybenzothiazole (PBT), and polyparaphenylene terephthalamide (PPTA).

[0031] The thickness of the electrolyte membrane is not particularly limited, but it is preferably 10 μm or more, and more preferably 20 μm or more. Furthermore, it is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. By making the electrolyte membrane thickness above the lower limit above, the mechanical strength of the water electrolysis cell is increased, resulting in a water electrolysis cell that is easy to handle. Conversely, by making it below the upper limit above, it is possible to prevent a decrease in energy conversion efficiency due to the resistance of the electrolyte membrane. Furthermore, there are no restrictions on the shape of the electrolyte membrane; it can be any shape, such as a polygon (triangle, square, pentagon, hexagon, etc.), a circle, or an ellipse.

[0032] [Anode catalyst layer] An anode catalyst layer 22 is laminated on one side of the electrolyte membrane 21. The anode catalyst layer 22 contains a manganese-containing catalyst and an ionomer, and covers the inner surface of the electrolyte membrane 21 from the outer edge to the inner surface. Note that the manganese-containing catalyst is sometimes referred to as a manganese-containing catalyst.

[0033] The amount of manganese-containing catalyst in the anode catalyst layer 22 is not particularly limited, but 1 cm 2 The amount of catalyst per unit is preferably 0.1 mg or more, more preferably 0.5 mg or more. It is also preferably 10.0 mg or less, more preferably 6.0 mg or less, and particularly preferably 3.0 mg or less. Setting the amount of catalyst above the lower limit prevents an increase in activation overpotential and a decrease in energy conversion efficiency, while setting it below the upper limit prevents the anode catalyst layer from becoming excessively thick, increasing the ohmic resistance component and reducing energy conversion efficiency.

[0034] The mixing ratio of catalyst to ionomer in the anode catalyst layer is not particularly limited, but the I / C ratio, calculated by dividing the mass of ionomer in the catalyst layer by the mass of catalyst, is preferably 0.01 or higher, more preferably 0.03 or higher. Furthermore, the I / C ratio is preferably 1.0 or lower, more preferably 0.5 or lower, even more preferably 0.3 or lower, and particularly preferably 0.15 or lower. By setting the ratio of ionomer to catalyst above the lower limit mentioned above, the ion conduction resistance within the catalyst layer can be reduced. Conversely, by setting the ratio of ionomer to catalyst below the upper limit mentioned above, the electron conduction resistance and mass transfer resistance within the catalyst layer can be reduced.

[0035] (Manganese-containing catalyst) A manganese-containing catalyst is a catalyst material containing 1 mass percent or more of manganese. The structure and manufacturing method of the manganese-containing catalyst are not particularly limited, and for example, the manganese oxide material described in Patent Document 2 can be used. The manganese content in the catalyst is analyzed by a known inductively coupled plasma emission spectroscopy method.

[0036] A manganese-containing catalyst may contain one or more secondary metal elements in addition to manganese. Examples of secondary metal elements include one or more elements selected from the group consisting of chromium, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, and gold. Among these, one or more secondary metal elements selected from the group consisting of cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum are preferred, one or more secondary metal elements selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, and platinum are more preferred, one or more secondary metal elements selected from the group consisting of ruthenium and iridium are even more preferred, and iridium is particularly preferred. The inclusion of a secondary metal element in the manganese-containing catalyst enhances its catalytic activity in the oxygen evolution reaction, allowing water electrolysis to proceed with high energy conversion efficiency.

[0037] The content of secondary metal elements in the manganese-containing catalyst is not particularly limited, but if the secondary metal elements are one or more selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, and platinum, the molar ratio of the secondary metal elements to manganese is preferably 1.0 or less, more preferably 0.5 or less, even more preferably 0.3 or less, and particularly preferably 0.18 or less. By keeping the molar ratio of the secondary metal to manganese below the above upper limit, an excessive increase in catalyst costs can be prevented.

[0038] The manganese-containing catalyst may contain, in addition to manganese and a second metal element, one or more third elements selected from the group consisting of carbon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine, and iodine. Among these, the manganese-containing catalyst preferably contains oxygen as the third element component. There are no particular restrictions on the ratio of the third element to manganese and the second metal component. Furthermore, there are no restrictions on the chemical state of manganese and the second metal component.

[0039] The method for producing a manganese-containing catalyst containing a secondary metal element is not particularly limited and can be produced by known methods. For example, iridium-manganese oxide composite materials can be produced by the methods described in Patent Documents 3 and 4.

[0040] (Ionomer) The structure of the ionomer is not particularly limited, but for example, a polymer material with perfluoroethylene as the basic backbone and having perfluoroalkylsulfonic acid side chains can be used.

[0041] [Anode power supply] An anode power supply body 24 is laminated on the anode catalyst layer 22. There are no particular restrictions on the shape or material of the anode power supply body 24, but for example, a porous metal, a sintered metal fiber, a sintered metal powder, a metal mesh, or a metal felt can be used. In addition, to prevent a decrease in electron conductivity due to oxidation of the base metal of the power supply body, a power supply body surface-treated with precious metals such as platinum, gold, or silver, or titanium nitride, titanium carbide, or titanium carbonitride may be used. In this embodiment, as an example, the anode power supply body 24 has the same outer edge as the outer edge of the anode catalyst layer 22.

[0042] An anode gasket 26 is positioned on the outer side of the end face of the anode power supply 24. As shown in Figure 2(A), the anode gasket 26 has an opening 26K. The anode gasket 26 includes an oxygen-impermeable portion 26A that is laminated and sandwiched between the anode catalyst layer 22 and the anode power supply 24. An opening 26E is formed in the oxygen-impermeable portion 26A. There may or may not be a gap between the outer circumference of the anode power supply 24 and the inner circumferential wall formed by the outer circumference of the through-opening 26K of the anode gasket 26.

[0043] The thickness of the oxygen-impermeable portion 26A is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, and particularly preferably 10 μm or more. Also, it is preferably 100 μm or less, and more preferably 50 μm or less. By setting the thickness of the oxygen-impermeable portion 26A to be not less than the above lower limit, the dissolution of oxygen into the electrolyte membrane can be effectively suppressed. By setting the thickness of the oxygen-impermeable portion 26A to be not more than the above upper limit, the anode catalyst layer 22 and the anode current collector 24 can be adhered closely, preventing an increase in contact resistance and a decrease in the energy conversion efficiency of the water electrolysis device.

[0044] The material of the anode gasket 26 is not particularly limited, and for example, it can be formed of silicone rubber, ethylene propylene rubber, polytetrafluoroethylene resin, or vinyl chloride resin. The material of the oxygen-impermeable portion 26A has an oxygen permeability coefficient defined by the amount of oxygen permeation per second when there is a differential pressure of 1 Pa on both sides of a film with a thickness of 1 cm, and the oxygen permeability coefficient is 1×10 -11 cm 3 (STP)·cm / (cm 2 ·s·Pa) or less can be used. The oxygen permeability coefficient is preferably 1×10 -11 cm 3 (STP)·cm / (cm 2 ·s·Pa) or less, more preferably 1×10 -12 cm 3 (STP)·cm / (cm 2 ·s·Pa) or less, even more preferably 1×10 -14 cm 3 (STP)·cm / (cm 2 ·s·Pa) or less, and particularly preferably 1×10 -16 cm 3 (STP)·cm / (cm 2 ·s·Pa) or less can be used. For example, silicone rubber, ethylene propylene rubber, polytetrafluoroethylene, or vinyl chloride resin can be used.

[0045] The oxygen-impermeable portion 26A may be formed integrally with the anode gasket 26, or the oxygen-impermeable portion 26A and the anode gasket 26 may be formed from separate components. As an example, the anode gasket 26 can be formed by laminating a first sheet having an opening 26E for forming the oxygen-impermeable portion 26A, and a second sheet laminated on the first sheet having an opening 26K. As another example, the opening 26E can be formed by arranging adhesive on a single sheet having an opening 26K such that the opening area on one end in the thickness direction is reduced.

[0046] The outer periphery of the overlapping portion 50, where the electrolyte membrane 21, anode catalyst layer 22, cathode catalyst layer 32, anode power supply 24, and cathode power supply 34 all overlap in the stacking direction, is defined as the overlapping portion outer periphery end 50E. The inner periphery of the opening 26E, which is the inner periphery of the oxygen-impermeable portion 26A, is located on the inner periphery side of the entire circumference, beyond the overlapping portion outer periphery end 50E. In the water electrolysis cell 20, the area inside the inner periphery of the opening 26E is referred to as the reaction section 52. The reaction section 52 is the region where the electrolytic reaction occurs, and in this embodiment, it is the part where the reaction in which water is electrolyzed into oxygen and hydrogen occurs. The outer periphery of the reaction section 52 is defined as the reaction outer periphery end 52E.

[0047] The shortest distance S1 between the outer peripheral edge 50E of the overlapping portion and the inner peripheral edge 26E of the opening is preferably 1 mm or more, more preferably 3 mm or more, and particularly preferably 4 mm or more. By setting it to above the lower limit mentioned above, the dissolution of oxygen generated near the inner peripheral edge 26E of the opening of the anode catalyst layer 22 into the electrolyte membrane can be effectively suppressed.

[0048] The maximum distance S2 between the outer peripheral end 50E of the overlapping portion and the inner peripheral end 26E of the opening is preferably 500 mm or less, more preferably 300 mm or less, and particularly preferably 100 mm or less. This is to prevent the electrochemical device from becoming excessively large by making S2 longer than necessary.

[0049] [Cathode catalyst layer] A cathode catalyst layer 32 is laminated on the other side of the electrolyte membrane 21. The cathode catalyst layer 32 contains a cathode catalyst and an ionomer and covers the inner circumferential surface of the other side of the electrolyte membrane 21, which is inside the outer circumferential surface. In this embodiment, as an example, the cathode catalyst layer 32 is sized and shaped so that its outer edge overlaps with that of the anode catalyst layer 22 in a plan view.

[0050] (Cathode catalyst) The cathode catalyst is not particularly limited, and known catalysts can be used. For example, catalysts containing noble metals such as ruthenium, rhodium, palladium, iridium, and platinum can be used. The aforementioned noble metals may also be used as supported catalysts, where the noble metals are supported on a carrier. When the aforementioned noble metals are supported on a carrier, the mass ratio of the noble metals to the carrier is not particularly limited, but the mass ratio of the noble metals to the total mass of the catalyst is preferably 30% by mass or more, and more preferably 45% by mass or more. By using the above mass ratio, it is possible to prevent the cathode catalyst layer from becoming excessively thick, which would increase the electrical conductivity resistance of the cathode catalyst layer and thus reduce the energy conversion efficiency of water electrolysis.

[0051] The amount of cathode catalyst in the cathode catalyst layer 32 is not particularly limited, but 1 cm 2 The amount of catalyst per unit is preferably 0.1 mg or more, more preferably 0.3 mg or more. Furthermore, it is preferably 4.0 mg or less, more preferably 2.0 mg or less, and particularly preferably 1.5 mg or less. Setting the amount of catalyst above the lower limit prevents an increase in activation overpotential and a decrease in energy conversion efficiency, while setting it below the upper limit prevents a decrease in the energy conversion efficiency of water electrolysis due to an excessive thickness of the cathode catalyst layer and an increase in the electrical conductivity resistance of the cathode catalyst layer.

[0052] (Ionomer) The structure of the ionomer is not particularly limited, but for example, a polymer material with perfluoroethylene as the basic backbone and having perfluoroalkylsulfonic acid side chains can be used.

[0053] The mixing ratio of catalyst to ionomer in the cathode catalyst layer is not particularly limited, but the I / C ratio, calculated by dividing the mass of ionomer by the mass of cathode catalyst, is preferably 0.01 or higher, and more preferably 0.1 or higher. Furthermore, the I / C ratio is preferably 2.0 or lower, and more preferably 1.0 or lower. By setting the ratio of ionomer to catalyst above the lower limit mentioned above, the ion conduction resistance within the catalyst layer can be reduced. Conversely, by setting the ratio of ionomer to catalyst below the upper limit mentioned above, the electron conduction resistance and mass transfer resistance within the catalyst layer can be reduced.

[0054] [Cathode power supply] A cathode power supply 34 is laminated on the cathode catalyst layer 32. The shape and material of the cathode power supply 34 are not particularly limited, but for example, a porous metal, a sintered metal fiber, a sintered metal powder, a metal mesh, metal felt, or carbon paper can be used. In this embodiment, as an example, the cathode power supply 34 is sized and shaped so that its outer edge overlaps with that of the cathode catalyst layer 32.

[0055] A separator 28 is stacked on the anode power supply 24, and a separator 38 is stacked on the cathode power supply 34. Separators 28 and 38 can be made of titanium, stainless steel, carbon, or other materials.

[0056] The anode separator 28 may be coated with a corrosion-resistant conductive material to suppress the increase in electron conduction resistance due to oxidation. Examples of coating materials include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0057] A cathode gasket 36 is positioned on the outer side of the end face of the cathode power supply 34. As shown in Figure 2(B), the cathode gasket 36 has a through-opening 36K formed therein, and the cathode power supply 34 is positioned within the through-opening 36K. The material of the cathode gasket 36 is not particularly limited, but it can be made of, for example, silicone rubber, ethylene propylene rubber, polytetrafluoroethylene resin, or vinyl chloride resin. There may or may not be a gap between the outer circumference of the cathode power supply 34 and the inner circumferential wall formed by the outer circumference of the through-opening 36K of the cathode gasket 36.

[0058] Next, the operation and effects of the water electrolysis apparatus 10 of this embodiment will be described.

[0059] Water (H2O) is supplied to the anode power supply 24 and anode catalyst layer 22 of the water electrolysis cell 20 from the outside via an inflow passage (not shown). When a voltage is applied between separator 28 and separator 38, the following reaction (1) occurs on the surface of the anode catalyst layer 22 inside the reaction section 52.

[0060] H2O → 2H + + 0.5O2 + 2e - (1)

[0061] Oxygen (O2) is diffused in the anode power supply 24 and, along with unreacted water (H2O), is sent to the outside through an outflow path (not shown).

[0062] Proton H + The electrons e move to the cathode side through the electrolyte membrane 21 and are supplied by the external wiring. - The reaction (2) yields hydrogen H2, which is then released to the outside via an outlet channel not shown.

[0063] 2H + + 2e - → H2(2)

[0064] The mechanism by which manganese oxide precipitates inside the electrolyte membrane is that manganese contained in the catalyst during electrolysis deposits manganese ions (Mn) inside the electrolyte membrane. 2+It elutes as (3) and reacts with Mn 2+ It reacts with water in the electrolyte membrane to form MnO x H y This generates MnO through reaction (4). x H y It is presumed that manganese oxide (MnO2) is produced when it reacts with oxygen.

[0065] Mn 2+ + xH2O → MnO x H y + (2x-y)H + (3) MnO x H y + (1+y / 4-x / 2)O2→ MnO2+y / 2H2O (4)

[0066] In the water electrolysis cell 20 of this embodiment, the inner circumferential end 26E of the opening is positioned inward from the outer circumferential end 50E of the overlapping portion, thereby reducing the amount of oxygen dissolved into the electrolyte membrane by the oxygen-impermeable portion 26A. As a result, the progress of reaction (4) is suppressed, and the re-deposition of manganese oxide within the electrolyte membrane 21 and damage to the electrolyte membrane 21 due to re-deposition can be suppressed.

[0067] <Example 1> Next, Modification 1 will be described. In Modification 1, parts similar to those in the above embodiment are denoted by the same reference numerals, and their detailed description is omitted. As shown in Figure 3, the size of the cathode power supply 34 is reduced to form the cathode power supply 34A. Note that there may or may not be a gap between the outer circumference of the anode power supply 24A and the inner circumferential wall formed by the outer circumference of the through-opening 26K of the anode gasket 26A. Similarly, there may or may not be a gap between the outer circumference of the cathode power supply 34A and the inner circumferential wall formed by the outer circumference of the through-opening 36K of the cathode gasket 36. In this case, the outer circumference end of the cathode power supply 34A is positioned outside the inner circumferential end 26E of the opening of the anode gasket 26, and the outer circumference end 50E of the overlapping portion coincides with the outer circumference end of the cathode power supply 34A. Even in this case, by positioning the inner circumferential end 26E of the opening inside the overlapping portion outside the outer circumference end 50E, the amount of oxygen dissolving into the electrolyte membrane can be reduced by the oxygen-impermeable portion 26A.

[0068] <Modification 2> Next, a modified example 2 will be described. In modified example 2, parts similar to those in the above embodiment are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0069] As shown in Figure 4, the water electrolysis cell 20-2 of this modified water electrolysis apparatus 10-2 has a cathode catalyst layer 32A instead of the cathode catalyst layer 32 of the above embodiment. There may or may not be a gap between the outer circumference of the anode power supply body 24 and the inner circumferential wall formed by the outer circumference of the through-opening 26K of the anode gasket 26. Similarly, there may or may not be a gap between the outer circumference of the cathode power supply body 34 and the inner circumferential wall formed by the outer circumference of the through-opening 36K of the cathode gasket 36A.

[0070] The cathode catalyst layer 32A is smaller in size than the cathode power supply unit 34, and the outer edge of the cathode catalyst layer 32A is laminated on the inner surface of the cathode power supply unit 34, which is inside the outer edge of the cathode power supply unit 34. In addition, the outer edge of the cathode catalyst layer 32A is positioned outside the inner edge 26E of the opening of the anode gasket layer 26.

[0071] The outer periphery of the overlapping portion 50A, where the electrolyte membrane 21, anode catalyst layer 22, cathode catalyst layer 32A, anode power supply 24, and cathode power supply 34 all overlap in the stacking direction, is defined as the overlapping portion outer periphery end 50E. The inner periphery end 26E, which is the inner periphery of the oxygen-impermeable portion 26A, is positioned further inward than the overlapping portion outer periphery end 50E over its entire circumference, and the overlapping portion outer periphery end 50E coincides with the outer periphery of the cathode catalyst layer 32A.

[0072] Even in this case, oxygen generated near the inner peripheral edge 26E of the opening on the surface of the anode catalyst layer 22, and manganese dissolved on the surface of the anode catalyst layer 22, are suppressed from dissolving into the electrolyte membrane 21 by the oxygen-impermeable portion 26A. [Examples]

[0073] <Examples> (Preparation of anode catalysts) Powdered electrolytic manganese dioxide (product name: FM, manufactured by Tosoh Corporation) was immersed in an iridium salt solution tank filled with an IrCl4 aqueous solution with an iridium chloride (IV) concentration of 1.0 g / L at 95°C for 24 hours, and a mixture was obtained by solid-liquid separation. The obtained mixture was dried in an air atmosphere at 90°C for 2 hours, then cooled to room temperature by natural cooling, and then annealed in an air atmosphere at 450°C for 5 hours to obtain iridium-containing manganese oxide powder, which was used as the anode catalyst in this example. The powder, based on its XRD pattern, has a crystalline structure of β-type manganese dioxide, with a D50 diameter of 4.6 μm, and an Ir / Mn ratio of 0.03 as analyzed by ICP.

[0074] (Fabrication of electrolyte membranes with catalyst layer) An anode slurry was prepared by mixing the above anode catalyst, ionomer, and solvent. A 5% by mass Nafion dispersion (Sigma-Aldrich) was used as the ionomer. Specifically, the above anode catalyst was mixed with appropriate amounts of water and 1-propanol as solvents, and the above Nafion dispersion was mixed with the ionomer so that the mass ratio of the ionomer to the catalyst was 0.05, thereby obtaining an anode slurry.

[0075] Next, a cathode slurry was prepared by mixing the cathode catalyst, ionomer, and solvent. A commercially available Pt / C (platinum / carbon) cathode catalyst was used, and a 5% by mass Nafion dispersion (manufactured by Sigma-Aldrich) was used as the ionomer. Specifically, the Pt / C cathode catalyst was mixed with appropriate amounts of water and 1-propanol as solvents, and the Nafion dispersion was mixed with the ionomer so that the mass of the ionomer relative to the carbon was 1.0, thereby obtaining the cathode slurry.

[0076] The anode slurry and cathode slurry are each 8 cm in length and width. On the corner polytetrafluoroethylene (Teflon®) sheet, spray coating After coating with a tar, the polytetrafluoroethylene sheet was cut with a 1.5 cm width around the edges to obtain a 5 cm square sheet with slurry. The cut-out 5 cm square sheet was then transferred to the central part of an 8 cm square proton exchange membrane (Nafion NR212) using a hot press to fabricate an electrolyte membrane with a catalyst layer (composition: anode catalyst layer / proton exchange membrane / cathode catalyst layer).

[0077] The amount of anode slurry is such that the amount of iridium (Ir) per unit area of ​​the formed anode catalyst layer is 0.2 mg-Ir / cm³. 2 I adjusted it so that it would be as follows. The amount of cathode slurry is such that the amount of platinum (Pt) per unit area of ​​the formed cathode catalyst layer is 0.5 mg-Pt / cm². 2 I adjusted it so that it would be as follows. The transfer rates of both the anode catalyst layer and the cathode catalyst layer were confirmed to be 100% based on the mass difference before and after transfer to the Teflon sheet.

[0078] (Construction of a water electrolysis cell) A water electrolysis cell was fabricated comprising an electrolyte membrane with a catalyst layer, an anode power supply, an anode-side separator, an anode-side gasket, a cathode power supply, a cathode-side separator, a cathode-side gasket, an anode-side end plate, an anode-side current collector, an insulating sheet placed between the anode-side end plate and the current collector, a cathode-side end plate, a cathode-side current collector, and an insulating sheet placed between the cathode-side end plate and the current collector.

[0079] The anode-side separator was made of titanium with Pt plating, with an electrode mounting section that was 5 cm long and 5 cm wide, and 26 channels arranged in parallel within a 5 cm area, each with a groove and ridge width of 1 mm and a depth of 2 mm. The cathode-side separator was made of carbon, with an electrode mounting section that was 5 cm long and 5 cm wide, and 26 channels arranged in parallel within a 5 cm area, each with a groove and ridge width of 1 mm and a depth of 2 mm.

[0080] The anode power supply used a 4.9 cm square Pt-plated titanium fiber sintered body. The cathode power supply used a 5.0 cm square carbon material (manufactured by SGL Carbon Japan Co., Ltd.). The anode gasket was constructed by layering a 38 μm thick polytetrafluoroethylene (Teflon®) sheet with a 4.0 cm square through-hole and a polytetrafluoroethylene (Teflon®) sheet with a 5.0 cm square through-hole. The cathode gasket was constructed using a polytetrafluoroethylene (Teflon®) sheet with a 5.2 cm x 5.4 cm square through-hole. Each power supply component was positioned in the through-opening of the gasket, and the anode separator, anode gasket, anode power supply component, electrolyte membrane with catalyst layer, cathode power supply component, cathode gasket, and cathode separator were stacked so that the flow paths of the anode separator and cathode separator overlapped. A current collector plate, insulating sheet, and end plate were then stacked in order on the outside of each of the anode and cathode separators and fastened with bolts to create a water electrolysis cell.

[0081] In this embodiment, the portion of a 38 μm thick polytetrafluoroethylene (Teflon®) sheet that is located inside a 5.0 cm square through-hole is the oxygen-impermeable portion. The shortest distance S1 between the outer edge of the overlapping portion and the inner edge of the opening is 4.5 mm, and the longest distance S2 between the outer edge of the overlapping portion and the inner edge of the opening is 6.4 mm.

[0082] The anode-side separator was equipped with a water inlet and a pipe for discharging the generated oxygen and unreacted water, while the cathode-side separator was equipped with a pipe for discharging the generated hydrogen and a pipe for circulating nitrogen. A mass flow meter was installed downstream of the hydrogen discharge pipe connected to the cathode-side separator. The hydrogen generation rate measured by the mass flow meter was used to calculate the current efficiency of hydrogen generation according to Equation 1. The current collectors on the anode and cathode sides were connected to an external power supply (PWR1201L, manufactured by Kikusui Electronics Co., Ltd.). After connecting an external power supply to the water electrolysis cell, the temperature of the water electrolysis cell was raised to 80°C, and water was supplied to the water electrolysis cell at a flow rate of 100 ml / min. Potential sweep voltammetry was performed 30 times with a potential range from the open-circuit potential to 2.0 V and a sweep speed of 10 mV / s. After that, the circuit was held open for 30 minutes, and then potential sweep voltammetry was performed again 30 times. Next, the water electrolysis cell has a current density of 3.0 A / cm² per unit area of ​​effective electrode surface area. 2 A constant current of 3.0 A / cm² was applied every week. 2 With the power supply stopped, potential sweep voltammetry was performed five times from the open-circuit potential down to 2.0V at a sweep speed of 10mV / s to evaluate the electrolytic performance characteristics. After evaluating the electrolytic performance characteristics, the current density was 3.0A / cm². 2 The constant current was restored.

[0083] The initial electrolytic performance of the electrolytic cell in this embodiment is 1 A / cm². 2 The voltage was 1.64V. Furthermore, the current efficiency for initial hydrogen production was 100±5%. (3.0A / cm²) 2After a total of 5,000 hours of energization, no decrease in the current efficiency of hydrogen generation was observed, and no damage to the electrolyte membrane was confirmed.

[0084] The structure of the water electrolysis cell in this embodiment is shown in Figure 1. When viewed from the stacking direction, the inner circumferential end 26E, which is the inner circumferential end of the oxygen-impermeable portion 26A, is positioned on the inner circumferential side over the entire circumference, relative to the outer circumferential end 50E, which is the outer circumferential end of the overlapping portion 50 where the electrolyte membrane 21, anode catalyst layer 22, cathode catalyst layer 32, anode power supply 24, and cathode power supply 34 all overlap in the stacking direction. Furthermore, the same effect was confirmed even when the water electrolysis cell structure was as shown in Figures 3 and 4.

[0085] <Comparative Example> The evaluation was carried out in the same manner as in the examples, except that only a sheet of polytetrafluoroethylene (Teflon®) with a 5.2 cm x 5.4 cm through-hole was used as the anode gasket. As a result, the initial electrolytic performance of the electrolytic cell of this comparative example was 1 A / cm². 2 The voltage was 1.66V, and the current efficiency for initial hydrogen production was 100±5%. 3.0A / cm 2 After a total of 335 hours of energization, the current efficiency for hydrogen generation decreased to below 90%, and microscopic observation of the electrolyte membrane revealed damage to the electrolyte membrane.

[0086] From a comparison of the examples and comparative examples, it was confirmed that the water electrolysis cell of the present invention, in which the outer peripheral edge 50E of the overlapping portion is covered by an oxygen-impermeable portion 26A around its entire circumference, solves the problem of damage to the electrolyte membrane due to manganese oxide deposition without impairing electrolysis performance. [Explanation of symbols]

[0087] 10 Water electrolysis equipment 20 Water electrolysis cell 21 Electrolyte membrane 22 Anode catalyst layer 24, 24A Anode power supply 26 Anode gasket layer (gasket) 26A Oxygen-impermeable section 26E Opening inner edge 50, 50A overlapping section 50E Outer edge of overlap area 32, 32A Cathode catalyst layer 34, 34A cathode power supply

Claims

1. Electrolyte membrane, An anode catalyst layer containing manganese is laminated on one side of the electrolyte membrane, A cathode catalyst layer laminated on the other side of the electrolyte membrane, The anode power supply is laminated on the anode catalyst layer, A cathode power supply unit laminated on the cathode catalyst layer, It is frame-shaped with an opening, and is laminated around its entire circumference between the anode catalyst layer and the outer periphery of the anode power supply, with the inner periphery of the opening positioned on the inner side of the entire circumference of the overlapping outer periphery, which is the outer periphery of the overlapping portion where the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode power supply, and the cathode power supply all overlap in the lamination direction, and has an oxygen-impermeable portion that is impermeable to oxygen, Equipped with, water electrolysis cell.

2. The shortest distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening is 1 mm or more. The water electrolysis cell according to claim 1.

3. The maximum distance between the outer peripheral end of the overlapping portion and the inner peripheral end of the opening is 500 mm or less. The water electrolysis cell according to claim 1.

4. The anode power supply unit is equipped with a gasket positioned on the outside of its outer end surface, The oxygen-impermeable portion is formed integrally with the gasket. The water electrolysis cell according to claim 1.

5. A water electrolysis cell stack comprising a plurality of water electrolysis cells according to any one of claims 1 to 4.

6. A water electrolysis apparatus comprising a water electrolysis cell according to any one of claims 1 to 4.

7. A water electrolysis apparatus comprising the water electrolysis cell stack described in Claim 5.

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