Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
  • C25B11/032—Gas diffusion electrodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/077—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the compound being a non-noble metal oxide
  • C25B11/079—Manganese dioxide; Lead dioxide
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/70—Assemblies comprising two or more cells
  • C25B9/73—Assemblies comprising two or more cells of the filter-press type
  • C25B9/77—Assemblies comprising two or more cells of the filter-press type having diaphragms
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• This disclosure relates to a catalyst-layered electrolyte membrane, a water electrolysis cell, and a water electrolysis cell stack.
• Water electrolysis (hereinafter sometimes referred to as “water electrolysis”) is a method of producing hydrogen and oxygen from water by electrolysis. For example, among technologies that use hydrogen as an energy source, water electrolysis is a promising technology for sustainable hydrogen production.
• the water electrolysis cell used for water electrolysis comprises an anode separator, anode gas diffusion layer, anode catalyst layer, electrolyte membrane, cathode catalyst layer, cathode gas diffusion layer, and cathode separator.
• Catalysts suitable for water electrolysis are being considered for the anode catalyst layer.
• an oxide containing iridium and manganese in a specific molar ratio has been proposed as an anode catalyst with the reaction activity to produce oxygen and protons from water (see, for example, Non-Patent Documents 1 and 2).
• 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.
• an object of one embodiment of the present disclosure is to provide 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.
• Another object of another embodiment of the present disclosure is to provide a water electrolysis cell and a water electrolysis cell stack including the above-described catalyst layer-equipped electrolyte membrane.
• An anode catalyst layer comprising: an anode catalyst component that is 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; a cathode catalyst layer;
• An electrolyte membrane with a catalyst layer comprising: ⁇ 2> The catalyst layer-equipped 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 ⁇ 0.6
• ⁇ 3> The catalyst layer-equipped 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.
• 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.
• a water electrolysis cell stack comprising a plurality of water electrolysis cells according to ⁇ 4> stacked one on top of the other.
• an electrolyte membrane with a catalyst layer that can reduce the IR-free voltage in a water electrolysis cell that uses an oxide containing iridium and manganese as an anode catalyst.
• a water electrolysis cell and a water electrolysis cell stack including the above-described catalyst layer-equipped electrolyte membrane.
• FIG. 1 is a schematic cross-sectional view of a water electrolysis cell according to an embodiment of the present disclosure. 1 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.
• a numerical range expressed using " ⁇ ” means a range that includes the numerical values written before and after " ⁇ " as the lower and upper limits.
• the upper limit value described in one numerical range may be replaced with the upper limit value of another numerical range described in stages
• the lower limit value described in one numerical range may be replaced with the lower limit value of another numerical range described in stages.
• the upper or lower limit value described in one numerical range may be replaced with the value shown in the examples.
• IR-free voltage means “the cell voltage excluding DC resistance components such as electrolyte membrane resistance and contact resistance.”
• the catalyst-layered electrolyte membrane of the present disclosure comprises: an anode catalyst layer that contains an anode catalyst component that is iridium-containing manganese dioxide (sometimes referred to as "iridium-containing manganese dioxide” in the present disclosure) and has a molar ratio of iridium to manganese of 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 (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.
• an anode catalyst layer that contains an anode catalyst component that is iridium-containing manganese dioxide (sometimes referred to as "iridium-containing manganese dioxide” in the present disclosure) and has a molar ratio of iridium to manganese of
• the “amount of ionomer” in the anode catalyst layer means the content of the ionomer in the anode catalyst layer, and similarly, the “amount of iridium” and the “amount of anode catalyst component” mean the respective contents.
• 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.
• 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
• 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
• the anode catalyst has a reaction activity that generates oxygen and protons from water, and it extracts electrons from water to decompose the water into oxygen and protons.
• the anode catalyst layer in the present disclosure contains iridium-containing manganese dioxide as an anode catalyst.
• the molar ratio of iridium to manganese (hereinafter also referred to as "Ir/Mn ratio") is 0.011 or more and 0.182 or less.
• Ir/Mn ratio the molar ratio of iridium to manganese.
• 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, and there is a concern that the active sites cannot be 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 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 ⁇ -type, ⁇ -type, ⁇ -type, or ⁇ -type crystal structure, and is preferably manganese dioxide having a ⁇ -type crystal structure (hereinafter also referred to as " ⁇ -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 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 PDF (Powder Diffraction File, registered trademark) of the ICDD (International Center for Diffraction Data).
• XRD powder X-ray diffraction
• reference pattern registered in the PDF (Powder Diffraction File, registered trademark) of the ICDD (International Center for Diffraction Data).
• PDF Nos. 14-0644 ( ⁇ -type), 24-0735 ( ⁇ -type), 30-0820 ( ⁇ -type), and 44-0141 ( ⁇ -type) may be used as reference patterns for manganese dioxide having a ⁇ -type, ⁇ -type, ⁇ -type, or ⁇ -type crystal structure, respectively.
• the XRD peak using a Ni filter refers to a peak whose peak top 2 ⁇ is detected in an analysis of an XRD pattern using general analysis software (for example, IGOR Pro 8 manufactured by WaveMetrics or PDXL2 manufactured by Rigaku Corporation).
• 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 perspective of achieving high electrolysis efficiency, it is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, and even more preferably 90% to 100% by mass relative to the total amount of the anode catalyst.
• 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 carrier.
• the catalyst component is preferably supported in a dispersed state on the carrier.
• the support preferably contains 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.
• the anode catalyst may be in the form of particles.
• the D50 diameter of the anode catalyst is preferably 0.5 ⁇ m or more and 20 ⁇ m 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 makes it impossible to apply the anode catalyst uniformly to the proton exchange membrane, resulting in a high IR-free voltage.
• the D50 diameter of the anode catalyst is preferably 1 ⁇ m or more and 10 ⁇ m or less, and more preferably 1.5 ⁇ m or more and 5 ⁇ m or less.
• the "D50 diameter” is the particle diameter [ ⁇ m] at which the cumulative frequency of the particle diameter corresponds to 50% in the cumulative volume particle size distribution obtained by a laser diffraction/scattering method. Note that the D50 diameter is used interchangeably with the "median diameter.”
• the D50 diameter of the anode catalyst may 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 ⁇ m Particle refractive index: 2.2 Particle permeability: Permeable Particle shape: Aspherical Solvent refractive index: 1.333 Ultrasonic pretreatment: 10 minutes
• the average particle diameter of the anode catalyst after application is preferably 0.5 ⁇ m or more and 20 ⁇ m 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 ⁇ m or more and 10 ⁇ m or less, and more preferably 1.5 ⁇ m or more and 5 ⁇ m 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 number of particles.
• SEM scanning electron microscope
• the anode catalyst layer in the present disclosure comprises an ionomer.
• An ionomer is, for example, a resin having an ionically crosslinked ethylene skeleton as its 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, for example, from the viewpoint of obtaining excellent ion conduction.
• m represents an integer from 0 to 10
• n represents an integer from 1 to 10
• x represents an integer from 1 to 20
• y represents an integer of 100 or greater.
• 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.
• the anode catalyst layer may contain components other than the anode catalyst and ionomer described above (so-called other components).
• other components include components with catalytic activity other than the anode catalyst described above, as well as unreacted components and by-reaction components of the raw materials used to produce the anode catalyst described above.
• the thickness of the anode catalyst layer is preferably 0.5 ⁇ m or more and 50 ⁇ m or less. If the thickness of the anode catalyst layer is too thin, contact between the catalyst particles will be poor, increasing cell resistance. If the thickness is too thick, the diffusion length of protons diffusing through the ionomer in the catalyst layer will increase, increasing cell resistance.
• the thickness of the anode catalyst layer is preferably 1 ⁇ m or more and 30 ⁇ m or less, and more preferably 2 ⁇ m or more and 20 ⁇ m or less.
• the amount of iridium per unit area of the anode catalyst layer is preferably in the range of 0.03 mg-Ir/ cm2 to 0.30 mg-Ir/ cm2 , more preferably in the range of 0.05 mg-Ir/ cm2 to 0.20 mg-Ir/ cm2 , and even more preferably in the range of 0.08 mg-Ir/ cm2 to 0.15 mg-Ir/ cm2 .
• “mg-Ir/ cm2" is a unit indicating the amount of iridium per unit area.
• 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 cut out and dissolved in aqua regia to prepare analytical sample solution A.
• Analytical sample solution A is subjected to ICP (inductively coupled plasma) analysis using an ICP emission spectrometer to determine the amount of iridium per unit area of the anode catalyst layer.
• ICP optical emission spectrometer for example, a high-resolution ICP optical emission spectrometer PS3520VDDII (model) manufactured by Hitachi High-Tech Science Corp. can be suitably used.
• the ICP optical emission spectrometer is not limited to this.
• 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 the coating liquid for forming the anode catalyst layer (so-called anode slurry), the amount of anode slurry applied, etc.
• the amount of iridium per unit area of the anode catalyst layer can be determined by the method described in Example 1 below.
• the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component in the anode catalyst layer is -1.40 or more and -0.46 or less.
• the anode reaction occurs at the contact point between iridium and ionomer, but 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.
• 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, and more preferably -1.34 or more and -0.89 or less.
• the proton exchange membrane may be selected from known proton exchange membrane-type solid electrolytes used in water electrolysis.
• Proton exchange membrane-type solid electrolytes have the property of selectively permeating protons (H + ).
• 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.
• a proton exchange membrane is a polymer that has ionic groups and thus has proton conductivity.
• the proton exchange membrane may be, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane.
• 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.
• fluorine-based polymer electrolytes having ionic groups include commercially available products such as "Nafion” (registered trademark) (manufactured by Chemours Inc.), “Aquivion” (registered trademark) (manufactured by Solvay), “Flemion” (registered trademark) (manufactured by AGC Inc.), and "Aciplex” (registered trademark) (manufactured by Asahi Kasei Corporation).
• Nafion (registered trademark) is available in a lineup of NR211, NR212, N115, N117, N1110, etc., and any of these can be used appropriately.
• Aromatic hydrocarbon polymers having aromatic rings in the main chain are preferred as hydrocarbon electrolytes.
• aromatic rings 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.
• the polymer may also contain some aliphatic units in addition to aromatic ring units.
• 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.
• polysulfone polysulfone
• polyethersulfone polyethersulfone
• polyetherketone polyetherketone
• polyetherketone polyetherketone
• polyetherketoneketone polyetherketoneketone
• polyetherketonesulfone polyetherketonesulfone.
• the aromatic hydrocarbon polymer may have a plurality of these structures.
• a polymer having a polyetherketone skeleton, that is, a polyetherketone polymer is particularly preferred.
• the proton exchange membrane may be combined with a reinforcing material.
• a reinforcing material By using a reinforcing material, it becomes less likely that gas leaks or short circuits within the electrode will occur due to membrane damage, for example, when the proton exchange membrane and electrode are joined by hot pressing.
• reinforcing materials include homogeneous porous membranes made from 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 (polyren
• 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.
• the cathode catalyst may include a support.
• the cathode catalyst layer may contain a cathode catalyst in which a catalyst component is supported on a carrier.
• the catalyst component is preferably supported in a dispersed state on the carrier.
• the support may be, for example, carbon. Carbon includes carbon black.
• the cathode catalyst preferably has a carbon support and platinum dispersed and supported on the carbon support.
• the cathode catalyst may also be in the form of particles.
• the cathode catalyst layer can include 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 a description thereof will be omitted here.
• 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.
• the catalyst layer-equipped electrolyte membrane of the present disclosure is as described above, and therefore a detailed description thereof 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 conventionally known water electrolysis cells.
• the anode separator is disposed on the anode gas diffusion layer side.
• 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) to prevent the anode separator from increasing in resistance due to oxidation.
• the coating material include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.
• the anode 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.
• the anode gas diffusion layer may be coated with a corrosion-resistant conductive material (so-called coating material) to prevent the resistance from increasing due to oxidation.
• the coating material include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.
• the cathode gas diffusion layer can be made of materials that allow fluid to flow within the layer, such as porous materials, sintered powder materials, sintered fiber materials, metal mesh, felt, etc.
• 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.
• the water electrolysis cell of the present disclosure may further include other components.
• the other components may be selected from known components of water electrolysis cells.
• Other components include, for example, gaskets and seals.
• each component in the water electrolysis cell of the present disclosure may be determined with reference to known water electrolysis cells.
• the electrolyte membrane is preferably located between the anode catalyst layer and the cathode catalyst layer.
• 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.
• 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.
• FIG. 1 is a schematic cross-sectional view of a water electrolysis cell.
• the water electrolysis cell 100 comprises, from the top of Figure 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.
• a gasket 40 is disposed between the anode separator 60 and the electrolyte membrane 11
• a gasket 50 is disposed between the cathode separator 70 and the electrolyte membrane 11.
• the water electrolysis device 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 a device including the water electrolysis cell stack or the water electrolysis cell according to the present disclosure and other components.
• the other components may be selected from known components of water electrolysis devices.
• Examples of other components include auxiliary equipment such as a power conditioner, a water pump, an ion exchange resin, a heat exchanger, and a dehumidifier.
• Example 1 (Preparation of anode catalyst) A 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 of potassium hexachloroiridate ( K2IrCl6 ) with a concentration of 2.5 g/L at 95 ° C for 96 hours, followed by solid-liquid separation to obtain a mixture. The resulting mixture was dried in the air at 90°C for 2 hours, then allowed to cool to room temperature by natural cooling, and then annealed in the air 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 powder had a ⁇ -type crystal structure from its XRD pattern, a D50 diameter of 3.7 ⁇ m, and an Ir/Mn ratio of 0.043 as analyzed by ICP.
• K2IrCl6 potassium hexachloroiri
• 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.
• 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.
• a cathode slurry was prepared by mixing the cathode catalyst, ionomer, and solvent.
• Pt/C platinum/carbon
• Nafion dispersion Sigma-Aldrich
• appropriate amounts of Pt/C (platinum/carbon) as the cathode catalyst and water and 1-propanol as the solvent were mixed, and then the above-mentioned Nafion dispersion as the ionomer was mixed so that the weight ratio of ionomer to carbon was 1.0 to obtain the cathode slurry.
• 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, thereby producing an electrolyte membrane with a catalyst layer (configuration: anode catalyst layer/proton exchange membrane/cathode catalyst layer).
• the amount of the cathode slurry was adjusted 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 rates of the anode catalyst layer and the cathode catalyst layer were both confirmed to be 100% based on the difference in mass before and after transfer onto the Teflon sheet.
• the catalyst-coated electrolyte membrane thus prepared was cut into a 2 cm square, 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
• the cathode catalyst layer was dissolved in aqua regia to prepare analytical sample solution B.
• Analysis of analytical sample solution A was performed using a high-resolution ICP (inductively coupled plasma) optical emission spectrometer PS3520VDDII (model) manufactured by Hitachi High-Tech Science Corporation.
• the amount of iridium (Ir) per unit area of the anode catalyst layer was measured and found to be 0.20 mg-Ir/ cm2 .
• the Ir/Mn ratio was the same as that of the anode catalyst.
• analytical sample solution A and analytical sample solution B were performed using an Avance NEO400 nuclear magnetic resonance (NMR) spectrometer manufactured by Bruker, and spectra were obtained.
• the NMR analysis was performed using the single pulse method under conditions of a spectral width of 200 kHz, a pulse width of 2.4 ⁇ sec, and a sample rotation speed of 20 kHz.
• analysis of fluorine and sulfur components was performed using ion chromatography, and the ionomer structure was estimated, which matched the composition of the ionomer used.
• the average particle size of 10 randomly selected anode catalysts in the anode catalyst layer was analyzed using SEM and found to be 2.3 ⁇ m.
• a water electrolysis cell was fabricated, which included a catalyst layer-equipped electrolyte membrane, an anode gas diffusion layer, an anode-side separator, a cathode gas diffusion layer, a cathode-side separator, an anode-side end plate, an anode-side current collector, an insulating sheet disposed between the anode-side end plate and the current collector, a cathode-side end plate, a cathode-side current collector, and an insulating sheet disposed between the cathode-side end plate and the current collector.
• the anode-side separator was made of platinum-plated titanium and had an electrode installation area with a length and width of 5 cm each, 26 channels arranged in parallel within a 5 cm side area, with grooves and ridges each 1 mm wide and a depth of 2 mm.
• the cathode side separator was made of carbon and had an electrode installation area with a length and width of 5 cm each, and 26 flow paths arranged in parallel within a 5 cm side area, with grooves and ridges each 1 mm wide and a depth of 2 mm.
• a Pt-plated titanium fiber sintered body was used for the anode gas diffusion layer.
• the cathode gas diffusion layer was made of a carbon material and cut to have a length and width of 5 cm.
• the anode gasket and cathode gasket were made of a polytetrafluoroethylene (Teflon (registered trademark)) sheet with an electrode installation portion cut out.
• the electrode layer was placed in the cut-out portion of the gasket where the electrode mounting portion had been removed, and the anode-side separator, anode gas diffusion layer, catalyst-coated electrolyte membrane, cathode gas diffusion layer, and cathode-side separator were stacked so that the electrode mounting portion overlapped the anode and cathode flow path portions.
• the anode-side and cathode-side separators were then stacked, in this order, with current collector plates (gold-plated copper plates), insulating sheets (Teflon (registered trademark)), and end plates (stainless steel), and the resulting assembly was fastened with bolts to produce a water electrolysis cell.
• current collector plates gold-plated copper plates
• insulating sheets Teflon (registered trademark)
• end plates stainless steel
• the anode separator was equipped with a water inlet and a pipe for discharging the generated oxygen and unreacted water, while the cathode separator was equipped with a pipe for discharging the generated hydrogen.
• the anode and cathode current collectors were each connected to an external power source (Kikusui Electronics Co., Ltd., PWR801L).
• the anode and cathode current collectors were each connected to a low-resistance meter (Tsuruga Electric Co., Ltd., Model 3566), and the resistance value R at 1 kHz was measured.
• Example 2 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 (amount of ionomer/amount of anode catalyst component) was set to ⁇ 1.00.
• 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 4.3 ⁇ m.
• a water electrolysis cell was produced in the same manner as in Example 1 except that the above-mentioned electrolyte membrane with a catalyst layer was used, and the IR-free voltage was measured and found to be 1.525V.
• Example 3 An electrolyte membrane with a catalyst layer was prepared in the same manner as in Example 2, except that the proton exchange membrane was NR115 and the amount of iridium per unit area of the anode catalyst layer was 0.10 mg-Ir/cm2. 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 ⁇ m. A water electrolysis cell was produced in the same manner as in Example 1 except that the above-mentioned catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.553V.
• Example 4 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 2.9 ⁇ m.
• a water electrolysis cell was produced in the same manner as in Example 1 except that the above-mentioned electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.604V.
• Example 5 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 5.0 ⁇ m. A water electrolysis cell was produced in the same manner as in Example 1 except that the above-mentioned electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.644V.
• Example 6 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.3 ⁇ m. A water electrolysis cell was produced in the same manner as in Example 1 except that the above-described catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.637V.
• Example 7 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.7 ⁇ m. A water electrolysis cell was produced in the same manner as in Example 1 except that the above-described electrolyte membrane with a catalyst layer was used, and the IR-free voltage was determined to be 1.654V.
• Example 8 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 2.5 ⁇ m. A water electrolysis cell was produced in the same manner as in Example 1 except that the above-described catalyst layer-equipped electrolyte membrane was used, and the IR-free voltage was determined to be 1.673V.
• Example 2 An electrolyte membrane with a catalyst layer was produced 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 the iridium-containing manganese dioxide was evaluated in the same manner as in Example 1 and was found to be 3.1 ⁇ m.
• a water electrolysis cell was produced in the same manner as in Example 1 except that the above-mentioned electrolyte membrane with a catalyst layer was used, and the IR-free voltage was measured and found to be 1.923 V.
• Table 1 shows the amount of anode catalyst component (mg/cm 2 ), the amount of iridium (Ir) per unit area (mg-Ir/cm 2 ), the type of proton exchange membrane, the amount of ionomer (mg/cm 2 ), the ratio of ionomer amount/anode catalyst component amount, log (ionomer amount/anode catalyst component amount), and the IR-free voltage (V) of the water electrolysis cell at a current density of 0.5 A/cm 2 .
• 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 becomes small.
• the IR-free voltage decreased as the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component increased, whereas in the region where the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component was 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 reasons for this result are thought to be as follows:
• the anode reaction (H 2 O ⁇ 1/2O 2 + 2H + + 2e ⁇ ) occurs at the contact points between iridium and the ionomer.
• the logarithm of the ratio of the amount of ionomer to the amount of anode catalyst component is less than ⁇ 1.30, there is less anode catalyst component than ionomer in the anode catalyst layer, and therefore, as the amount of ionomer is increased, the number of contact points between iridium and the ionomer increases, reducing reaction resistance and decreasing IR-free voltage.
• 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
• Y 0.0873X2 + 0.394X + 1.8609 (X is -1.30 or more)
• Y -1.8841X - 0.9462 (X is less than -1.30)
• the IR-free voltage is desirably 1.70 V or less, more desirably 1.65 V or less, and even more desirably 1.58 V or less. From the results shown in Fig.
• 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
• 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
• 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.
• 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

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