Catalyst-layer-equipped electrolyte membrane, water electrolysis cell, and water electrolysis cell stack

Abstract

The present invention provides a catalyst-layer-equipped electrolyte membrane and an application of the same, said catalyst-layer-equipped electrolyte membrane comprising: an anode catalyst layer containing an ionomer and an anode catalyst component that is composed of iridium-containing manganese dioxide, the molar ratio of iridium to manganese in the anode catalyst component being 0.011-0.182, and the logarithm log(amount of ionomer / amount of anode catalyst component) of the ratio of the amount of the ionomer to the amount of the anode catalyst component being −1.40 to −0.46; a proton exchange membrane; and a cathode catalyst layer.

Description

Electrolyte membrane with catalyst layer, water electrolysis cell and water electrolysis cell stack

[0001] The present disclosure relates to a catalyst layer-equipped electrolyte membrane, a water electrolysis cell, and a water electrolysis cell stack.

[0002] Water electrolysis (hereinafter sometimes referred to as "water electrolysis") is a method for producing hydrogen and oxygen from water by electrolysis. For example, among technologies that utilize hydrogen as an energy source, water electrolysis is a promising technology for sustainable hydrogen production.

[0003] A water electrolysis cell used for water electrolysis includes an anode separator, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, a cathode separator, etc. For the anode catalyst layer, catalysts suitable for water electrolysis are being investigated.

[0004] For example, an oxide containing iridium and manganese in a specific molar ratio has been proposed as an anode catalyst having the reaction activity to produce oxygen and protons from water (see, for example, Non-Patent Documents 1 and 2).

[0005] Non-patent document 1: “Amorphous mixed Ir-Mn oxide catalysts for the oxygen evolution reaction in PEM water electrolysis for H2production”, Int. H. Hydrogen Energ. 48 (2023) 10532. Non-patent document 2: “Experimental and theoretical validation of high efficiency and robust electrocatalytic response of one-dimensional (1D) (Mn,Ir)O2:10F nanorods for the oxygen evolution reaction in PEM-based water electrolysis”, ACS Catal. 9 (2019) 2134.

[0006] High electrolysis efficiency is required for water electrolysis cells. For example, it is desirable to reduce the IR-free voltage of water electrolysis cells. Therefore, an object of one embodiment of the present disclosure is to provide a catalyst-coated electrolyte membrane that can reduce the IR-free voltage in a water electrolysis cell that uses an oxide containing iridium and manganese as an anode catalyst. Another object of another embodiment of the present disclosure is to provide a water electrolysis cell and a water electrolysis cell stack that include the catalyst-coated electrolyte membrane.

[0007] Specific means for solving the problems include the following aspects: <1> A catalyst-layered electrolyte membrane comprising: an anode catalyst layer comprising: an ionomer; an anode catalyst layer containing iridium-containing manganese dioxide, wherein the molar ratio of iridium to manganese is 0.011 or more and 0.182 or less; and an ionomer, wherein the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is -1.40 or more and -0.46 or less; a proton exchange membrane; and a cathode catalyst layer. <2> The catalyst-layered electrolyte membrane according to <1>, wherein the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is -1.38 or more and -0.63 or less. <3> The catalyst-coated electrolyte membrane according to <1>, wherein the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is -1.34 or more and -0.89 or less. <4> A water electrolysis cell comprising an anode separator, an anode gas diffusion layer, the catalyst-coated electrolyte membrane according to any one of <1> to <3>, a cathode gas diffusion layer, and a cathode separator. <5> A water electrolysis cell stack comprising a plurality of water electrolysis cells according to <4> stacked one on top of the other.

[0008] According to one embodiment of the present disclosure, there is provided a catalyst layer-equipped electrolyte membrane that can reduce the IR-free voltage in a water electrolysis cell that uses an oxide containing iridium and manganese as an anode catalyst. According to another embodiment of the present disclosure, there are provided a water electrolysis cell and a water electrolysis cell stack that include the catalyst layer-equipped electrolyte membrane.

[0009] 1 is a schematic cross-sectional view of a water electrolysis cell according to an embodiment of the present disclosure; 2 is a graph showing the relationship between the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component and the IR-free voltage;

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be implemented by making appropriate modifications within the scope of the object of the present disclosure. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0011] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] In the numerical ranges described in stages in the present disclosure, the upper limit value described in one numerical range may be replaced with the upper limit value of another numerical range described in stages, and the lower limit value described in one numerical range may be replaced with the lower limit value of another numerical range described in stages. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with a value shown in the examples.

[0013] In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

[0014] In the present disclosure, "IR-free voltage" means "a cell voltage excluding DC resistance components such as electrolyte membrane resistance and contact resistance." By evaluating the IR-free voltage, it is possible to isolate and compare only the reaction resistance, even for catalyst-layered electrolyte membranes with different electrolyte thicknesses.

[0015] [Catalyst-Layered Electrolyte Membrane] The catalyst-layered electrolyte membrane of the present disclosure comprises: an anode catalyst layer containing an anode catalyst component that is iridium-containing manganese dioxide (sometimes referred to as "iridium-containing manganese dioxide" in the present disclosure), where the molar ratio of iridium to manganese is 0.011 or more and 0.182 or less; and an ionomer, wherein the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component (log (amount of ionomer / amount of anode catalyst component)) is −1.40 or more and −0.46 or less; a proton exchange membrane; and a cathode catalyst layer. Note that the "amount of ionomer" in the anode catalyst layer refers to the content of the ionomer in the anode catalyst layer, and similarly, the "amount of iridium" and the "amount of anode catalyst component" refer to the respective contents.

[0016] <Anode catalyst layer> The anode catalyst layer according to the present disclosure comprises an anode catalyst component which is iridium-containing manganese dioxide, in which the molar ratio of iridium to manganese is equal to or greater than 0.011 and equal to or less than 0.182, and an ionomer, wherein the logarithm of the ratio between the amount of the ionomer and the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is equal to or greater than −1.40 and equal to or less than −0.46.

[0017] The anode catalyst has a reaction activity of generating oxygen and protons from water, and decomposes water into oxygen and protons by abstracting electrons from the water. The anode catalyst layer in the present disclosure contains iridium-containing manganese dioxide as the anode catalyst.

[0018] In the iridium-containing manganese dioxide, the molar ratio of iridium to manganese (hereinafter also referred to as the "Ir / Mn ratio") is 0.011 or more and 0.182 or less. In the iridium-containing manganese dioxide, iridium acts as an active site for the reaction, so if the molar ratio of iridium to manganese is too small, the reaction resistance increases. If the molar ratio of iridium to manganese is too large, the amount of iridium becomes excessive, which may prevent the active sites from being used efficiently. The Ir / Mn ratio is more preferably 0.020 or more and 0.150 or less, and more preferably 0.030 or more and 0.120 or less. The Ir / Mn ratio in the iridium-containing manganese dioxide can be quantified by the method described in Example 1 below. The iridium-containing manganese dioxide is manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure, and preferably manganese dioxide having a β-type crystal structure (hereinafter also referred to as "β-type manganese dioxide"). The manganese dioxide contained in the anode catalyst may contain two or more manganese dioxides having different crystal structures. The crystal structure of the iridium-containing manganese dioxide can be identified by comparing the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the manganese dioxide with the XRD pattern (hereinafter also referred to as "reference pattern") registered in the ICDD (International Center for Diffraction Data) Powder Diffraction File (registered trademark) PDF. For example, PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), or 44-0141 (α-type) may be used as the reference pattern for manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure, respectively. In the present disclosure, the XRD pattern may be obtained by XRD measurement using a general powder X-ray diffractometer (for example, an Ultima IV Protectus, manufactured by Rigaku Corporation) under the following conditions:Accelerating current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Continuous scan Scan conditions: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used An XRD peak refers to a peak whose peak top 2θ is detected when an XRD pattern is analyzed using general analysis software (e.g., IGOR Pro 8, manufactured by WaveMetrics, or PDXL2, manufactured by Rigaku).

[0019] The content of the catalytic component (iridium-containing manganese dioxide) in the anode catalyst of the present disclosure is not particularly limited, but from the viewpoint of achieving high electrolysis efficiency, it is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, relative to the total amount of the anode catalyst.

[0020] The anode catalyst may include a support. The anode catalyst layer may include an anode catalyst in which a catalyst component is supported on a support. In this case, the catalyst component is preferably dispersed and supported on the support. The support preferably includes at least one selected from the group consisting of titanium oxide, niobium oxide, and tin oxide, and more preferably at least one selected from the group consisting of titanium oxide, niobium oxide, and tin oxide.

[0021] The anode catalyst may be in the form of particles.

[0022] When the anode catalyst is particulate, the D50 diameter of the anode catalyst is preferably 0.5 μm or more and 20 μm or less. If the D50 diameter is too small, the amount of ionomer required to ensure the contact area between particles in the catalyst layer increases, resulting in a high IR-free voltage. If the D50 diameter is too large, the anode catalyst particles settle in the slurry, impairing the dispersibility of the ionomer and anode catalyst particles. This prevents the catalyst from being uniformly applied to the proton exchange membrane, resulting in a high IR-free voltage. The D50 diameter of the anode catalyst is preferably 1 μm or more and 10 μm or less, and more preferably 1.5 μm or more and 5 μm or less. In the present disclosure, the "D50 diameter" refers to the particle diameter [μm] at which the cumulative frequency of the particle diameter corresponds to 50% in the cumulative volume particle size distribution obtained by laser diffraction / scattering. The D50 diameter is used interchangeably with the "median diameter." The D50 diameter of the anode catalyst can be measured using a general particle size distribution measuring device (for example, device name: MT-3100II, manufactured by Microtrac Bell) under the following conditions: Measurement range: 0.02 to 2000 μm Particle refractive index: 2.2 Particle transparency: transparent Particle shape: non-spherical Solvent refractive index: 1.333 Ultrasonic pretreatment: 10 minutes

[0023] The average particle diameter of the anode catalyst after application is preferably 0.5 μm or more and 20 μm or less. If the average particle diameter is too small, the contact area between particles in the catalyst layer will be small, resulting in high electrical resistance. If the average particle diameter is too large, the reaction area will be small, resulting in high reaction resistance. The average particle diameter of the anode catalyst is preferably 1 μm or more and 10 μm or less, and more preferably 1.5 μm or more and 5 μm or less. The average particle diameter of the anode catalyst can be determined by observing the anode catalyst surface of the catalyst-layered electrolyte membrane with a scanning electron microscope (SEM) and measuring the size of any multiple particles.

[0024] The anode catalyst layer in the present disclosure contains an ionomer. The ionomer is, for example, a resin having an ionically crosslinked ethylene skeleton as a basic structure. The ionomer is not particularly limited, and examples thereof include fluorine-based ionomers, ethylene-based ionomers, urethane-based ionomers, and styrene-based ionomers. The ionomer is preferably a fluorine-based ionomer, and more preferably contains a perfluorosulfonic acid group in the skeleton, from the viewpoint of obtaining excellent ionic conduction, for example.

[0025] An example of the ionomer containing a perfluorosulfonic acid group is an ionomer represented by the following formula (1).

[0026]

[0027] In formula (1), m represents an integer of 0 to 10, n represents an integer of 1 to 10, x represents an integer of 1 to 20, and y represents an integer of 100 or more.

[0028] For example, Nafion (registered trademark) 117, a commercially available ionomer, has a structure in which m≧1, n=2, x=5 to 13.5, and y=1000 in formula (1). The chemical structure of the ionomer can be confirmed by a combination of solid-state NMR (nuclear magnetic resonance) measurement and CHN analysis (atomic analysis of carbon (C), hydrogen (H), and nitrogen (N)). The ratio of the anode catalyst to the ionomer can be confirmed by ICP (inductively coupled plasma) analysis.

[0029] The anode catalyst layer may contain components other than the above-described anode catalyst and ionomer (so-called other components). Examples of the other components include components having catalytic activity other than the above-described anode catalyst, as well as unreacted components and by-reacted components of the raw materials used to produce the above-described anode catalyst.

[0030] The thickness of the anode catalyst layer is preferably 0.5 μm or more and 50 μm or less. If the thickness of the anode catalyst layer is too thin, contact between catalyst particles will be poor, resulting in an increase in cell resistance. If the thickness is too thick, the diffusion length of protons diffusing through the ionomer in the catalyst layer will be long, resulting in an increase in cell resistance. The thickness of the anode catalyst layer is preferably 1 μm or more and 30 μm or less, and more preferably 2 μm or more and 20 μm or less.

[0031] The amount of iridium per unit area of ​​the anode catalyst layer is 0.03 mg-Ir / cm from the viewpoint of efficiently using the reaction active sites in the catalyst layer and reducing the electrical resistance in the catalyst layer. ２ 0.30mg-Ir / cm or more ２ The range is preferably 0.05 mg-Ir / cm ２ 0.20mg-Ir / cm or more ２ The range of 0.08 mg-Ir / cm is more preferable. ２ 0.15mg-Ir / cm or more ２ The following range is more preferable. ２ " is a unit that indicates the amount of iridium per unit area.

[0032] In the present disclosure, the amount of iridium per unit area of ​​the anode catalyst layer is measured by the following method. A 2 cm square piece of the anode catalyst layer is dissolved in aqua regia to prepare an analytical sample solution A. The analytical sample solution A is subjected to ICP (inductively coupled plasma) analysis using an ICP optical emission spectrometer to determine the amount of iridium per unit area of ​​the anode catalyst layer. As the ICP optical emission spectrometer, for example, the PS3520VDDII (model), a high-resolution ICP optical emission spectrometer manufactured by Hitachi High-Tech Science Corporation, can be suitably used. However, the ICP optical emission spectrometer is not limited to this.

[0033] The amount of iridium per unit area of ​​the anode catalyst layer can be controlled by the amount of iridium contained in the catalyst component, the amount of catalyst blended in a coating liquid (so-called anode slurry) for forming the anode catalyst layer, the amount of anode slurry applied, etc. The amount of iridium per unit area of ​​the anode catalyst layer can be quantified by the method described in Example 1 below.

[0034] The logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component in the anode catalyst layer (amount of ionomer / amount of anode catalyst component) is -1.40 or more and -0.46 or less. The anode reaction occurs at the contact point between iridium and the ionomer. If the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is too small, the amount of ionomer in the catalyst layer will be insufficient to increase the contact area with iridium, resulting in a high IR-free voltage. If the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is too large, the amount of anode catalyst component in the catalyst layer will be insufficient to increase the contact area, resulting in a high IR-free voltage. The logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is preferably -1.38 or more and -0.63 or less, more preferably -1.34 or more and -0.89 or less.

[0035] <Proton Exchange Membrane> The proton exchange membrane may be selected from known proton exchange membrane-type solid electrolytes used in water electrolysis. The proton exchange membrane-type solid electrolyte is a membrane-type electrolyte that can exchange protons (H ＋ ) has the property of selectively permeating. Examples of proton exchange membranes include polymer electrolyte membranes (PEMs). Examples of polymer electrolyte membranes include perfluorocarbon membranes having sulfonic acid groups. Examples of perfluorocarbon membranes having sulfonic acid groups include Nafion membranes.

[0036] The proton exchange membrane is a polymer that has proton conductivity due to the presence of ionic groups. The proton exchange membrane may be, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane.

[0037] In the present disclosure, the term "fluoropolymer electrolyte" refers to a polymer in which most or all of the hydrogen atoms in the alkyl and / or alkylene groups have been substituted with fluorine atoms. Representative examples of fluoropolymer electrolytes having ionic groups include commercially available products such as "Nafion" (registered trademark) (manufactured by Chemours), "Aquivion" (registered trademark) (manufactured by Solvay), "Flemion" (registered trademark) (manufactured by AGC), and "Aciplex" (registered trademark) (manufactured by Asahi Kasei Corporation).

[0038] Nafion (registered trademark) is available in a lineup of NR211, NR212, N115, N117, N1110, etc., and any of these can be suitably used.

[0039] The hydrocarbon electrolyte is preferably an aromatic hydrocarbon polymer having an aromatic ring in the main chain. Here, the aromatic ring may include not only hydrocarbon aromatic rings consisting only of carbon atoms and hydrogen atoms, such as benzene rings and naphthalene skeletons, but also heterocycles such as pyridine rings, imidazole rings, and thiol rings. In addition, the polymer may also include some aliphatic units in addition to the aromatic ring units.

[0040] Specific examples of aromatic hydrocarbon polymers include polymers having a structure selected from the group consisting of polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain together with an aromatic ring. Note that the terms "polysulfone," "polyethersulfone," "polyetherketone," and the like are general terms for structures having a sulfone bond, an ether bond, a ketone bond, or the like in the molecular chain, and include polyetherketoneketone, polyetheretherketone, polyetheretherketoneketone, polyetherketoneetherketoneketone, and polyetherketonesulfone. The aromatic hydrocarbon polymer may have a plurality of these structures. As the aromatic hydrocarbon polymer, a polymer having a polyetherketone skeleton, that is, a polyetherketone polymer, is particularly preferred.

[0041] The proton exchange membrane may be combined with a reinforcing material, which makes it less likely that gas leakage or short circuiting within the electrode will occur due to membrane damage when the proton exchange membrane is bonded to the electrode by, for example, hot pressing.

[0042] Specific examples of reinforcing materials include homogeneous porous films made of fluorine-based polymers such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PVDF (polyvinylidene fluoride), and FEP (tetrafluoroethylene-hexafluoropropylene copolymer); thermoplastic resins such as PE (polyethylene) and PP (polypropylene); and 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).

[0043] <Cathode Catalyst Layer> The cathode catalyst layer contains, for example, a cathode catalyst that converts protons generated by the water electrolysis reaction in the anode catalyst layer into hydrogen, and an ionomer. The cathode catalyst converts protons generated by the water electrolysis reaction in the anode catalyst layer described above into hydrogen, and may be selected from known catalysts used in water electrolysis. Examples of catalyst components include platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, molybdenum, tungsten, vanadium, alloys thereof, and oxides thereof.

[0044] The cathode catalyst may include a carrier. The cathode catalyst layer may include a cathode catalyst in which a catalyst component is supported on a carrier. In this case, the catalyst component is preferably dispersed and supported on the carrier. Examples of the carrier include carbon. Examples of the carbon include carbon black.

[0045] The cathode catalyst preferably includes a carbon support and platinum dispersed and supported on the carbon support. The cathode catalyst may be in the form of particles.

[0046] The cathode catalyst layer may contain an ionomer. The ionomer contained in the cathode catalyst layer has the same meaning as the ionomer contained in the anode catalyst layer described above, and preferred embodiments are also the same, so further description will be omitted here.

[0047] [Water Electrolysis Cell] The water electrolysis cell according to the present disclosure includes an anode separator, an anode gas diffusion layer, the above-described electrolyte membrane with a catalyst layer according to the present disclosure, a cathode gas diffusion layer, and a cathode separator.

[0048] The catalyst-coated electrolyte membrane of the present disclosure has been described above, and therefore further description will be omitted here. The anode separator, anode gas diffusion layer, cathode gas diffusion layer, and cathode separator may be made of materials used in conventional water electrolysis cells.

[0049] The anode separator is disposed on the anode gas diffusion layer side. Examples of materials for the anode separator include titanium, stainless steel, and carbon. The anode separator preferably contains titanium from the viewpoint of suppressing oxidation due to oxygen generated on the anode side. The anode separator may be coated with a corrosion-resistant conductive material (so-called coating material) from the viewpoint of suppressing high resistance due to oxidation. Examples of coating materials include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0050] The anode gas diffusion layer can be made of a material that allows fluid to pass through the layer, such as a porous material, a sintered powder material, a sintered fiber material, a metal mesh, or felt. The anode gas diffusion layer may be coated with a corrosion-resistant conductive material (a so-called coating material) to prevent the layer from becoming highly resistive due to oxidation. Examples of coating materials include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0051] The cathode gas diffusion layer may be made of a material that allows fluid to pass through the layer, such as a porous material, a powder sintered material, a fiber sintered material, a metal mesh, or felt.

[0052] The cathode separator is disposed on the cathode gas diffusion layer side. The material of the cathode separator is not particularly limited, and examples thereof include titanium, stainless steel, and carbon.

[0053] The water electrolysis cell of the present disclosure may further include other components, which may be selected from known components of water electrolysis cells, such as gaskets and sealants.

[0054] The arrangement of each component in the water electrolysis cell of the present disclosure may be determined with reference to known water electrolysis cells. In the water electrolysis cell of the present disclosure, the electrolyte membrane is preferably located between the anode catalyst layer and the cathode catalyst layer. In the water electrolysis cell of the present disclosure, the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer are preferably located between the anode gas diffusion layer and the cathode gas diffusion layer. In the water electrolysis cell of the present disclosure, the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode gas diffusion layer, and the cathode gas diffusion layer are preferably located between two separators.

[0055] An example of a water electrolysis cell according to the present disclosure is shown in Fig. 1 . Fig. 1 is a schematic cross-sectional view of the water electrolysis cell. As shown in Fig. 1 , the water electrolysis cell 100 includes, in order from the top of Fig. 1 , an anode separator 60, an anode gas diffusion layer 20, an anode catalyst layer 12, an electrolyte membrane 11, a cathode catalyst layer 13, a cathode gas diffusion layer 30, and a cathode separator 70. Furthermore, in the water electrolysis cell 100, a gasket 40 is disposed between the anode separator 60 and the electrolyte membrane 11, and a gasket 50 is disposed between the cathode separator 70 and the electrolyte membrane 11.

[0056] [Water Electrolysis Apparatus] The water electrolysis apparatus according to the present disclosure may be a water electrolysis cell stack formed by stacking a plurality of the water electrolysis cells according to the present disclosure, or may be an apparatus including the water electrolysis cell stack or the water electrolysis cells according to the present disclosure and other components.

[0057] The other components may be selected from known components of a water electrolysis device, such as auxiliary devices such as a power conditioner, a water pump, an ion exchange resin, a heat exchanger, and a dehumidifier.

[0058] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited to the following examples. The matters shown in the following examples may be appropriately changed without departing from the spirit of the present disclosure.

[0059] Example 1 (Preparation of an anode catalyst) Potassium hexachloroiridate (K ２ IrCl ６ ) K with a concentration of 2.5 g / L ２ IrCl ６ Powder of electrolytic manganese dioxide (product name: FM, manufactured by Tosoh Corporation) was immersed in an iridium salt solution bath filled with an aqueous solution at 95°C for 96 hours, followed by solid-liquid separation to obtain a mixture. The resulting mixture was dried in an air atmosphere at 90°C for 2 hours, then naturally cooled to room temperature, and then annealed in an air atmosphere at 450°C for 5 hours to obtain an iridium-containing manganese oxide powder, which was used as the anode catalyst (catalyst component) of this example. The XRD pattern of this powder indicated that it had a β-type crystal structure, a D50 diameter of 3.7 μm, and an Ir / Mn ratio of 0.043 as analyzed by ICP.

[0060] (Fabrication of Catalyst-Coated Electrolyte Membrane) The anode catalyst, an ionomer, and a solvent were mixed to prepare an anode slurry. A 5 mass % Nafion dispersion (manufactured by Sigma-Aldrich) was used as the ionomer. Specifically, the anode catalyst was mixed with appropriate amounts of water and 1-propanol as a solvent, and the Nafion dispersion as an ionomer was added so that the weight ratio of the ionomer to the catalyst was 0.05, thereby obtaining an anode slurry.

[0061] Next, a cathode catalyst, an ionomer, and a solvent were mixed to prepare a cathode slurry. Commercially available Pt / C (platinum / carbon) was used as the cathode catalyst, and a 5 mass% Nafion dispersion (manufactured by Sigma-Aldrich) was used as the ionomer. Specifically, appropriate amounts of Pt / C (platinum / carbon) as the cathode catalyst and water and 1-propanol as the solvent were mixed, and the Nafion dispersion as the ionomer was added so that the weight ratio of the ionomer to the carbon was 1.0, thereby obtaining a cathode slurry.

[0062] The anode slurry and cathode slurry were each applied using a spray coater onto a polytetrafluoroethylene (Teflon (registered trademark)) sheet measuring 8 cm square, and then a 5 cm square electrode portion was cut out and transferred onto an 8 cm square proton exchange membrane (Nafion NR212) using a hot press to prepare an electrolyte membrane with a catalyst layer (structure: anode catalyst layer / proton exchange membrane / cathode catalyst layer). The amount of cathode slurry was determined so that the amount of platinum (Pt) per unit area of ​​the cathode catalyst layer to be formed was 0.5 mg-Pt / cm. ２ The transfer rate of the anode catalyst layer and the transfer rate of the cathode catalyst layer were both confirmed to be 100% based on the difference in mass before and after transfer onto the Teflon sheet.

[0063] The produced electrolyte membrane with catalyst layer was cut into 2 cm squares, and the anode catalyst layer and cathode catalyst layer were peeled off using a spatula. The anode catalyst layer was dissolved in aqua regia to prepare analytical sample solution A, and the cathode catalyst layer was dissolved in aqua regia to prepare analytical sample solution B. Analytical sample solution A was subjected to ICP analysis using a high-resolution ICP (inductively coupled plasma) optical emission spectrometer PS3520VDDII (model) manufactured by Hitachi High-Tech Science Corporation, and the amount of iridium (Ir) per unit area of ​​the anode catalyst layer was measured, which was 0.20 mg-Ir / cm ２ The Ir / Mn ratio was the same as that of the anode catalyst.

[0064] Furthermore, each of analytical sample solution A and analytical sample solution B was analyzed using an Avance NEO400 nuclear magnetic resonance (NMR) spectrometer manufactured by Bruker, and a spectrum was obtained. The NMR analysis was performed using a single pulse method under conditions of a spectrum width of 200 kHz, a pulse width of 2.4 μsec, and a sample rotation speed of 20 kHz. Furthermore, fluorine and sulfur components were analyzed by ion chromatography, and the structure of the ionomer was estimated, which was consistent with the composition of the ionomer charged. From the estimated ionomer structure and the results of elemental analysis by ion chromatography, the mass of the ionomer contained in the catalyst layer (i.e., the anode catalyst layer) was estimated, and the amount of ionomer per unit area was calculated. Log (amount of ionomer / amount of anode catalyst component) was found to be −1.30.

[0065] The average particle size of 10 randomly selected anode catalysts in the anode catalyst layer was analyzed by SEM and found to be 2.3 μm.

[0066] (Preparation of Water Electrolysis Cell) A water electrolysis cell was prepared comprising a catalyst-coated electrolyte membrane, an anode gas diffusion layer, an anode separator, a cathode gas diffusion layer, a cathode separator, an anode end plate, an anode current collector, an insulating sheet disposed between the anode end plate and the current collector, a cathode end plate, a cathode current collector, and an insulating sheet disposed between the cathode end plate and the current collector. The anode separator was made of platinum-plated titanium and had an electrode mounting area measuring 5 cm in length and width, with 26 parallel flow channels each measuring 1 mm in width and 2 mm deep within a 5 cm side. The cathode separator was made of carbon and had an electrode mounting area measuring 5 cm in length and width, with 26 parallel flow channels each measuring 1 mm in width and 2 mm deep within a 5 cm side. The anode gas diffusion layer was made of Pt-plated titanium fiber sintered compact. The cathode gas diffusion layer was made of carbon material and cut to 5 cm in length and width. The anode and cathode gaskets were made of polytetrafluoroethylene (Teflon®) sheets with electrode placement sections cut out. The electrode layers were placed in the cut-out portions of the gaskets, and the anode separator, anode gas diffusion layer, catalyst-coated electrolyte membrane, cathode gas diffusion layer, and cathode separator were stacked so that the electrode placement sections overlapped the anode and cathode flow path sections. The anode and cathode separators were stacked in this order with current collector plates (gold-plated copper plates), insulating sheets (Teflon®), and end plates (stainless steel), and then fastened with bolts to fabricate a water electrolysis cell.

[0067] 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. The anode-side current collector and the cathode-side current collector were each connected to an external power source (Kikusui Electronics Co., Ltd., PWR801L). The anode-side current collector and the cathode-side current collector were each connected to a low-resistance meter (Tsuruga Electric Co., Ltd., Model 3566), and the resistance value R at 1 kHz was read. After connecting the external power source 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 over a potential range from the open circuit potential to 2.0 V at a sweep rate of 10 mV / s, followed by 30 minutes of open circuit hold and 30 times of potential sweep voltammetry. Next, the current density of the water electrolysis cell was set to 0.5 A / cm ２ The cell voltage E was measured while the battery was held in this state. The IR-free voltage E was calculated based on the following formula from the measured cell voltage E, the resistance value R read from the resistor, and the set current value I. ＩＲ－ｆｒｅｅ was calculated and found to be 1.505 V. ＩＲ－ｆｒｅｅ = E-IR

[0068] Example 2 A catalyst layer-equipped electrolyte membrane was prepared in the same manner as in Example 1, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component (amount of ionomer / amount of anode catalyst component) was set to −1.00. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 4.3 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.525 V.

[0069] Example 3 The proton exchange membrane was NR115, and the amount of iridium per unit area of ​​the anode catalyst layer was 0.10 mg-Ir / cm ２A catalyst layer-equipped electrolyte membrane was prepared in the same manner as in Example 2, except that the average particle size of the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.5 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.553 V.

[0070] Example 4 A catalyst layer-equipped electrolyte membrane was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.82. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 2.9 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.604 V.

[0071] Example 5 An electrolyte membrane with a catalyst layer was prepared in the same manner as in Example 1, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.70. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 5.0 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.644 V.

[0072] Example 6 A catalyst layer-equipped electrolyte membrane was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.70. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.3 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.637 V.

[0073] Example 7 An electrolyte membrane with a catalyst layer was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.60. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.7 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.654 V.

[0074] Example 8 An electrolyte membrane with a catalyst layer was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.52. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 2.5 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.673 V.

[0075] Comparative Example 1 A catalyst layer-equipped electrolyte membrane was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -0.40. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 4.0 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.713 V.

[0076] Comparative Example 2 A catalyst-layered electrolyte membrane was prepared in the same manner as in Example 3, except that the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was set to -1.52. The average particle size of iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.1 μm. A water electrolysis cell was prepared in the same manner as in Example 1, except that the above catalyst-layered electrolyte membrane was used, and the IR-free voltage was determined to be 1.923 V.

[0077] Table 1 shows the amount of the anode catalyst component (mg / cm ２ ), the amount of iridium (Ir) per unit area (mg-Ir / cm ２ ), type of proton exchange membrane, ionomer amount (mg / cm ２), ionomer amount / anode catalyst component amount, log(ionomer amount / anode catalyst component amount), and current density of the water electrolysis cell 0.5 A / cm ２ IR-free voltage (V) at

[0078]

[0079] As shown in Table 1, it was confirmed that the IR-free voltage values ​​of the water electrolysis cells in Examples 1 to 8 were smaller than those in Comparative Examples 1 and 2.

[0080] FIG. 2 is a graph showing the relationship between the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component and the IR-free voltage in Examples and Comparative Examples. As shown in FIG. 2, it was found that when the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is within a specific range, the IR-free voltage value decreases. In a region where the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is smaller than −1.30, the IR-free voltage decreased as the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component increased. On the other hand, in a region where the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is larger than −1.30, the IR-free voltage decreased as the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component decreased. The following is thought to be the reason for these results. The anode reaction (H ２ O → 1 / 2O ２ + 2H ＋ + 2e －) occurs at the contact points between iridium and the ionomer. In a region where the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is smaller than −1.30, there is less anode catalyst component than ionomer in the anode catalyst layer, and therefore, as the amount of ionomer increases, the number of contact points between iridium and ionomer increases, reducing reaction resistance and resulting in a lower IR-free voltage. On the other hand, in a region where the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is larger than −1.30, there is less ionomer than anode catalyst component in the anode catalyst layer, and therefore, as the amount of anode catalyst component increases, there is more contact points between iridium and ionomer, reducing reaction resistance and resulting in a lower IR-free voltage.

[0081] From the examples and comparative examples shown in FIG. 2 , when the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is X and the IR-free voltage is Y, the relationship between X and Y is independent of the composition of the anode catalyst, and is expressed as follows: Y=0.0873X ２ +0.394X + 1.8609 (X is −1.30 or more) Y = −1.8841X − 0.9462 (X is −1.30 or less) To achieve good electrolysis efficiency, the IR-free voltage is preferably 1.70 V or less, more preferably 1.65 V or less, and even more preferably 1.58 V or less. The results shown in FIG. 2 show that at threshold value 1, at which the IR-free voltage is 1.70 V or less, the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is in the range of −1.40 or more and −0.46 or less; at threshold value 2, at which the IR-free voltage is 1.65 V or less, the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is in the range of −1.38 or more and −0.63 or less; and at threshold value 3, at which the IR-free voltage is 1.58 V or less, the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is in the range of −1.34 or more and −0.89 or less.

[0082] The disclosure of Japanese Patent Application No. 2024-029103, filed on February 28, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated herein by reference.

[0083] 10: Electrolyte membrane with catalyst layer 11: Proton exchange membrane (proton exchange membrane type solid electrolyte) 12: Anode catalyst layer 13: Cathode catalyst layer 20: Anode gas diffusion layer 30: Cathode gas diffusion layer 40: Gasket 50: Gasket 60: Anode separator 70: Cathode separator 100: Water electrolysis cell

Claims

1. A catalyst-layered electrolyte membrane comprising: an anode catalyst layer containing an ionomer and an anode catalyst component which is iridium-containing manganese dioxide, wherein the molar ratio of iridium to manganese is 0.011 or more and 0.182 or less; and the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (log (amount of ionomer / amount of anode catalyst component)) is -1.40 or more and -0.46 or less; a proton exchange membrane; and a cathode catalyst layer.

2. The catalyst layer-equipped electrolyte membrane according to claim 1, wherein the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is -1.38 or more and -0.63 or less.

3. The catalyst layer-equipped electrolyte membrane according to claim 1, wherein the logarithm of the ratio of the amount of the ionomer to the amount of the anode catalyst component (amount of ionomer / amount of anode catalyst component) is -1.34 or more and -0.89 or less.

4. A water electrolysis cell comprising an anode separator, an anode gas diffusion layer, the electrolyte membrane with a catalyst layer according to any one of claims 1 to 3, a cathode gas diffusion layer, and a cathode separator.

5. A water electrolysis cell stack comprising a plurality of water electrolysis cells according to claim 4 stacked one on top of the other.

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