Water electrolysis method, water electrolysis cell and water electrolysis system

Abstract

The present invention addresses the problem of providing a water electrolysis method which is capable of maintaining a high electrolysis efficiency. The present invention proposes a water electrolysis method wherein: water is supplied to a water electrolysis cell, the inside of which is divided into an anode and a cathode by means of an electrolyte membrane, so as to generate oxygen at the anode and hydrogen at the cathode, respectively; and the electrolyte membrane is provided with a first layer that contains a polymer electrolyte and a second layer that is arranged on the cathode side of the first layer and contains carbon particles.

Description

Water electrolysis method, water electrolysis cell and water electrolysis device

[0001] The present invention relates to a water electrolysis method, a water electrolysis cell, and a water electrolysis device.

[0002] There are known methods for producing oxygen and hydrogen by water electrolysis using a polymer electrolyte membrane. In these water electrolysis methods, water is supplied to an electrolysis cell whose interior is divided into an anode and a cathode by a polymer electrolyte membrane, and oxygen is produced at the anode and hydrogen at the cathode.

[0003] Known methods for supplying water to an electrolysis cell include a method for supplying water only to the anode (see, for example, Patent Document 1), a method for supplying water only to the cathode (see, for example, Patent Document 2), and a method for supplying water to both the anode and the cathode (see, for example, Patent Document 3).

[0004] Japanese Patent Application Laid-Open No. 2021-25116 Japanese Patent Application Laid-Open No. 2020-525653 Japanese Patent Application Laid-Open No. 2021-105194

[0005] In water electrolysis using a polymer electrolyte membrane, maintaining the proton conductivity of the polymer electrolyte membrane is important for maintaining high electrolysis efficiency. However, conventional water electrolysis methods using polymer electrolyte membranes have not been able to maintain sufficiently high electrolysis efficiency.

[0006] In view of the above, an object of the present invention is to provide a water electrolysis method capable of maintaining high electrolysis efficiency.

[0007] The present inventors have discovered that the above-mentioned problems are caused by an environment in which hydrogen peroxide and hydrogen peroxide radicals generated as by-products at the cathode are likely to attack the polymer electrolyte membrane, and have thus achieved the present invention.

[0008] Specifically, the present invention provides a water electrolysis method in which water is supplied to an electrolytic cell the interior of which is partitioned into an anode and a cathode by an electrolyte membrane, and water is electrolyzed to produce oxygen at the anode and hydrogen at the cathode, wherein the electrolyte membrane comprises a first layer containing a polymer electrolyte, and a second layer containing carbon particles on the cathode side of the first layer.

[0009] According to the present invention, it is possible to provide a water electrolysis method capable of maintaining high electrolysis efficiency.

[0010] Fig. 1 is a cross-sectional schematic diagram showing an example of an electrolytic cell that can be used in a water electrolysis method according to an embodiment of the present invention. Fig. 2 is a graph showing the relationship between electrolysis time (evaluation time) and applied voltage in Examples 1 and 2 and Comparative Examples 1 and 2. Fig. 3 is a graph showing the relationship between electrolysis time (evaluation time) and applied voltage in Examples 3 and 4 and Comparative Examples 3 and 4. Fig. 4 is a graph showing the relationship between electrolysis time (evaluation time) and applied voltage in Examples 1 to 4.

[0011] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be implemented with various modifications depending on the purpose and application.

[0012] [Water Electrolysis Method] A water electrolysis method according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a cross-sectional schematic diagram showing an example of an electrolysis cell that can be used in the water electrolysis method according to an embodiment of the present invention.

[0013] The interior of the electrolysis cell 1 is partitioned into an anode 20 and a cathode 30 by an electrolyte membrane 10. The anode 20 and the cathode 30 are each connected to a power source (not shown). These are sandwiched between separators 41 and 42. The electrolyte membrane 10 includes a first layer 11 and a second layer 12, with the second layer 12 disposed on the cathode 30 side. In the present invention, the first layer 11 contains a polymer electrolyte, and the second layer 12 contains carbon particles. The components of the first layer 11 and the second layer 12 will be described in detail later. Preferred electrode embodiments will also be described later.

[0014] Water electrolysis occurs by applying a voltage to the electrodes. When water electrolysis is performed for a long period of time, the first layer 11 deteriorates and the membrane resistance increases, so the applied voltage must be increased to maintain a constant current density. Increasing the applied voltage means that the electrolysis efficiency decreases.

[0015] In water electrolysis using a polymer electrolyte membrane, one of the factors that reduces the electrolysis efficiency is the attack of hydrogen peroxides on the polymer electrolyte. In this specification, the term "hydrogen peroxides" is used as a general term for hydrogen peroxide and the radicals generated by the decomposition of hydrogen peroxide. In water electrolysis, oxygen generated at the anode migrates to the cathode and reacts with hydrogen generated at the cathode to produce hydrogen peroxides as a by-product. These by-products are thought to deteriorate the electrolyte membrane (reducing proton conductivity).

[0016] In the water electrolysis method according to the embodiment of the present invention, a second layer 12 containing carbon particles is disposed on the cathode 30 side of the first layer 11. It is believed that this second layer 12 inhibits hydrogen peroxides by-produced at the cathode 30 from migrating to the first layer 11, thereby inhibiting deterioration of the first layer. Although the mechanism behind this is not clear, it is presumed that the carbon particles contained in the second layer 12 capture or decompose the hydrogen peroxides. Thus, the water electrolysis method according to the embodiment of the present invention exhibits the effects of inhibiting an increase in applied voltage and maintaining high electrolysis efficiency.

[0017] In the water electrolysis method according to the embodiment of the present invention, the method for supplying water to the electrolytic cell is not particularly limited, and known methods can be used. Specific examples of methods for supplying water to the electrolytic cell include a method for supplying water to the anode, a method for supplying water to the cathode, and a method for supplying water to both the anode and the cathode. In the above water supply methods, it is preferable to supply water from outside the electrolytic cell using a means such as a pump. The water electrolysis method according to the embodiment of the present invention can employ any of the above water supply methods. In particular, it is preferable that water is supplied at least to the anode, since promoting the generation of oxygen and protons by the oxidation reaction of water is preferable from the viewpoint of electrolysis efficiency.

[0018] In the water electrolysis method according to the embodiment of the present invention, water (H ２ O) is supplied and electrolyzed to produce oxygen (O ２ ) at the cathode 30 and hydrogen (H ２By supplying water directly to the anode, which requires water for the electrolysis reaction, high electrolysis efficiency can be expected.

[0019] Water may or may not be supplied to the cathode 30. Supplying water to the cathode 30 is expected to promote desorption of hydrogen generated at the cathode 30. On the other hand, if water is supplied to the cathode 30, dissolved oxygen contained in the supply water may react with hydrogen generated at the cathode 30, resulting in the by-production of hydrogen peroxides. Therefore, from the viewpoint of suppressing the by-production of hydrogen peroxides, it is preferable that water not be supplied to the cathode 30 in the water electrolysis method according to the embodiment of the present invention. That is, it is preferable that water be supplied only to the anode 20 in the water electrolysis method according to the embodiment of the present invention.

[0020] In consideration of the above circumstances, it is preferable to use degassed water when supplying water to the cathode 30. For the degassing treatment, known methods such as gas bubbling, decompression treatment, membrane separation, and chemical removal using an oxygen scavenger can be used.

[0021] Furthermore, the water electrolysis method according to the embodiment of the present invention may employ a system in which water is supplied only to the cathode without being supplied to the anode. In this case, the water supplied to the cathode is transported to the anode through the electrolyte membrane. In this case, it is also preferable to use degassed water.

[0022] The water electrolysis method according to the embodiment of the present invention is preferably a proton exchange membrane water electrolysis method using a proton exchange membrane as the electrolyte membrane, but may also be an anion exchange membrane water electrolysis method using an anion exchange membrane.

[0023] [First Layer] The electrolyte membrane used in the water electrolysis method of the present invention has two layers, of which the layer on the anode side in terms of its positional relationship with the second layer described below is referred to as the first layer, and the first layer contains a polymer electrolyte. That is, the first layer functions as a polymer electrolyte layer. Known polymer electrolytes such as fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes can be used as the polymer electrolyte.

[0024] The fluorine-based polymer electrolyte includes a fluorine-based polymer having an ionic group. A fluorine-based polymer is a polymer in which most or all of the hydrogen atoms in the alkyl and / or alkylene groups in the molecule are substituted with fluorine atoms.

[0025] Examples of fluorine-based polymer electrolytes include perfluorocarbon sulfonic acid-based polymers, perfluorocarbon phosphonic acid-based polymers, trifluorostyrene sulfonic acid-based polymers, trifluorostyrene phosphonic acid-based polymers, ethylene tetrafluoroethylene-g-styrene sulfonic acid-based polymers, ethylene-tetrafluoroethylene copolymers, and polyvinylidene fluoride-perfluorocarbon sulfonic acid-based polymers.

[0026] Among these, perfluorocarbon sulfonic acid polymers are preferred from the viewpoint of heat resistance and chemical stability, and examples of such polymers include commercially available products such as "Nafion" (registered trademark) (manufactured by Chemours), "Flemion" (registered trademark) (manufactured by AGC Inc.), and "Aciplex" (registered trademark) (manufactured by Asahi Kasei Corporation).

[0027] Examples of hydrocarbon-based polymer electrolytes include hydrocarbon-based polymers having ionic groups. The term "hydrocarbon-based polymer" refers to a polymer having a main chain whose main structural unit is hydrocarbon.

[0028] The hydrocarbon-based polymer electrolyte is preferably an aromatic hydrocarbon-based polymer having an aromatic ring in the main chain. The aromatic ring may include not only a hydrocarbon-based aromatic ring but also a heterocycle. Furthermore, the aromatic ring unit may also include an aliphatic unit.

[0029] Specific examples of aromatic hydrocarbon-based polymers include polymers having, together with an aromatic ring, a structure selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene-based polymers, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain.

[0030] The polysulfone is a general term for a structure having a sulfone bond in the molecular chain, the polyethersulfone is a general term for a structure having an ether bond and a sulfone bond in the molecular chain, and the polyetherketone is a general term for a structure having an ether bond and a ketone bond in the molecular chain. The aromatic hydrocarbon polymer may have a plurality of these structures.

[0031] As the aromatic hydrocarbon polymer, a polyetherketone polymer is particularly preferred. Examples of the polyetherketone polymer include polyetherketone, polyetherketoneketone, polyetheretherketone, polyetheretherketoneketone, and polyetherketoneetherketoneketone.

[0032] The ionic group may be an ionic group having either cation exchange ability or anion exchange ability, but in the water electrolysis method of the present invention, it is preferable to use a proton-exchangeable ionic group. Examples of such functional groups include a sulfonic acid group, a sulfonimide group, a sulfate group, a phosphonic acid group, a phosphate group, a carboxylate group, an ammonium group, a phosphonium group, and an amino group. Two or more types of ionic groups can be contained in the polymer. Among these, a sulfonic acid group, a sulfonimide group, and a sulfate group are preferred because of their excellent water electrolysis performance, and a sulfonic acid group is more preferred from the viewpoint of raw material costs.

[0033] The ion exchange capacity (IEC) of the polymer electrolyte is preferably 0.1 meq / g or more and 5.0 meq / g or less in terms of the balance between proton conductivity and water resistance. The IEC of the hydrocarbon-based polymer having an ionic group is more preferably 1.0 meq / g or more, and even more preferably 1.4 meq / g or more. The IEC of the hydrocarbon-based polymer having an ionic group is more preferably 3.5 meq / g or less, and even more preferably 3.0 meq / g or less. The IEC of the fluoropolymer having an ionic group is more preferably 0.5 meq / g or more, and even more preferably 0.7 meq / g or more. The IEC of the fluoropolymer having an ionic group is more preferably 1.8 meq / g or less, and even more preferably 1.5 meq / g or less. When the IEC is 0.1 meq / g or more and 5.0 meq / g or less, excellent proton conductivity and water resistance can both be achieved.

[0034] Here, IEC is the molar amount of ionic groups introduced per unit dry weight of the polymer electrolyte, and a larger value indicates a larger amount of ionic groups introduced. In the present invention, IEC is defined as a value determined by neutralization titration.

[0035] The polymer electrolyte used in the first layer is preferably a hydrocarbon-based polymer, more preferably an aromatic hydrocarbon-based block copolymer, and particularly preferably a polyether ketone-based block copolymer, because these have relatively high water electrolysis performance and relatively low oxygen permeability. Here, the block copolymer refers to a block copolymer of a segment containing a structural unit containing an ionic group and a segment containing a structural unit not containing an ionic group.

[0036] The first layer preferably contains a hydrocarbon-based polymer electrolyte as the polymer electrolyte, preferably in an amount of 60 mass % or more, more preferably 75 mass % or more, even more preferably 90 mass %, and particularly preferably 100 mass %, of the hydrocarbon-based polymer electrolyte relative to the total mass of the polymer electrolyte in the first layer.

[0037] The first layer preferably contains a porous substrate to increase its strength. As a form in which the first layer contains a porous substrate, for example, a form having a layered portion (composite portion) containing a porous substrate and a polymer electrolyte, and a layered portion (non-composite portion) containing a polymer electrolyte but not a porous substrate on one or both sides of the composite portion is preferred. In the composite portion, the pores of the porous substrate are preferably filled or impregnated with a hydrocarbon-based polymer electrolyte.

[0038] In the first layer, the thickness ratio of the composite portion when it is laminar is preferably 10 to 90%, more preferably 20 to 80%, and particularly preferably 30 to 70%, with the thickness of the first layer being 100%. Here, the thickness of the composite portion is determined as the thickness of the porous substrate. Specific thicknesses of the composite portion are preferably in the range of 22 to 47 μm, more preferably 25 to 45 μm, and particularly preferably 30 to 43 μm. Furthermore, when the non-composite portion is laminar, the thickness per layer is preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more. Furthermore, the thickness per layer of the non-composite portion is preferably 45 μm or less, more preferably 40 μm or less, and particularly preferably 35 μm or less.

[0039] Examples of the form of the porous substrate include woven fabric, nonwoven fabric, porous film, mesh fabric, etc. Examples of the porous substrate include a hydrocarbon-based porous substrate containing a hydrocarbon-based polymer compound as the main component, and a fluorine-based porous substrate containing a fluorine-based polymer compound as the main component.

[0040] Examples of hydrocarbon polymer compounds include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyacrylate, polymethacrylate, polyvinyl chloride (PVC), polyvinylidene chloride (PVdC), polyester, polycarbonate (PC), polysulfone (PSU), polyethersulfone (PES), polyphenylene oxide (PPO), polyarylene ether polymers, polyphenylene sulfide (PPS), polyphenylene sulfide sulfone, polyparaphenylene (PPP), polyarylene polymers, polyarylene ketone, polyether ketone (PEK), polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole (PBO), polybenzthiazole (PBT), polybenzimidazole (PBI), polyamide (PA), polyimide (PI), polyetherimide (PEI), and polyimide sulfone (PIS).

[0041] Examples of the fluorine-based polymer compound include polytetrafluoroethylene (PTFE), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVdF), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy fluorine resin (PFA), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0042] As the form of the porous substrate, for example, from the viewpoint of reinforcing the relatively thick first layer having a thickness of 40 μm or more, a porous substrate with relatively high strength is preferred, and from that viewpoint, a mesh fabric is preferred. Mesh fabrics have a relatively large fiber diameter and high strength compared to the porous substrates conventionally commonly used in this field. As the material of the fiber constituting the mesh fabric, polyester, liquid crystal polyester, polyphenylene sulfide, polyether ketone, polyether ether ketone, and polyether ketone ketone are preferred. Among these, liquid crystal polyester is particularly preferred from the viewpoint of strength.

[0043] The thickness of the first layer is preferably 40 μm or more and 250 μm or less. From the viewpoint of improving durability, the thickness of the first layer is more preferably 50 μm or more, even more preferably 60 μm or more, and particularly preferably 70 μm or more. On the other hand, if the thickness of the first layer exceeds 250 μm, the water electrolysis performance will be reduced and it will be disadvantageous from the viewpoints of material cost, productivity, and processability. From the above viewpoints, the thickness of the first layer is more preferably 200 μm or less, even more preferably 180 μm or less, and particularly preferably 150 μm or less.

[0044] The first layer may contain various additives, such as antioxidants, surfactants, radical scavengers, hydrogen peroxide decomposers, non-electrolytic polymers, elastomers, and fillers, as long as the effects of the present invention are not impaired.

[0045] When the first layer contains a polymer electrolyte and a porous substrate, the total mass of the polymer electrolyte and the porous substrate is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to the total mass of the first layer. When the first layer does not contain a porous substrate, the mass of the polymer electrolyte is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to the total mass of the first layer.

[0046] When the first layer contains components other than the polymer electrolyte and the porous substrate, the total mass of the other components is preferably less than 20 mass%, more preferably less than 10 mass%, and particularly preferably less than 5 mass%, relative to the total mass of the first layer.

[0047] As described above, the polymer electrolyte used in the first layer is preferably a proton-exchangeable polymer electrolyte, but may also be an anion-exchangeable polymer electrolyte.

[0048] [Second Layer] The electrolyte membrane used in the water electrolysis method of the present invention has two layers, of which the layer on the cathode side relative to the first layer is referred to as the second layer, and the second layer contains at least carbon particles. The carbon particles are not particularly limited, and known particles can be used. Examples include carbon black, activated carbon, carbon nanotubes, carbon nanofibers, and fullerenes. Among these, carbon black is preferred. Examples of carbon black include furnace black, acetylene black, thermal black, channel black, lamp black, gas black, oil black, and ketjen black.

[0049] The carbon particles have a specific surface area of ​​30 to 2,000 m ２ / g. Carbon particles having such a specific surface area are expected to effectively contribute to the capture and decomposition of hydrogen peroxides.

[0050] Furthermore, the carbon particles preferably have, as surface functional groups, acidic groups such as phenolic hydroxyl groups, carboxyl groups, quinone groups, lactone groups, etc. Carbon particles having such surface functional groups are expected to effectively contribute to the capture and decomposition of hydrogen peroxides.

[0051] Furthermore, the carbon particles are preferably carbon particles that do not support a catalytic metal. For example, carbon particles (carbon) that support a catalytic metal such as platinum are generally used in the catalyst layer, but such carbon particles that support a catalytic metal may not fully exhibit the function of capturing or decomposing hydrogen peroxides.

[0052] As described above, the carbon particles are preferably those that do not support a catalytic metal, but a small amount of those that support a catalytic metal can be contained within a range that does not impair the effects of the present invention. In this case, the content is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, when the total amount of the carbon particles is taken as 100% by mass.

[0053] The carbon particles are expected to contribute to the capture and decomposition of hydrogen peroxides, as well as to bond the second layer and the first layer together by an anchor effect.

[0054] The average primary particle size of the carbon particles is preferably 5 nm or more, more preferably 10 nm or more, and particularly preferably 20 nm or more, from the viewpoints of the function of capturing and decomposing hydrogen peroxides, dispersibility, film-forming ability, adhesiveness, etc., and is preferably 500 nm or less, more preferably 200 nm or less, and particularly preferably 100 nm or less.

[0055] The second layer may or may not contain a binder. When the second layer does not contain a binder, the second layer can be formed, for example, by spraying carbon particles onto the first layer. Details will be described later.

[0056] From the viewpoints of film strength and productivity, the second layer preferably contains a binder. Examples of the binder include organic binders and inorganic binders. As the organic binder, various polymers can be used, and as the inorganic binder, known binders that can be prepared by a sol-gel method can be used.

[0057] The second layer preferably contains a polymer as a binder. Examples of such a polymer include nonionic polymers and ionic polymers, which may be used alone or in combination. Examples of nonionic polymers include fluorine-based polymers and hydrocarbon-based polymers.

[0058] Examples of nonionic fluorine-based polymers include polytetrafluoroethylene, poly(vinylidene fluoride), copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and trifluoroethylene, copolymers of vinylidene fluoride and tetrafluoroethylene, and poly(vinylidene fluoride).

[0059] Examples of nonionic hydrocarbon polymers include polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymers, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, polyimide sulfone, and polyvinyl alcohol.

[0060] Examples of the ionic polymer include the above-mentioned fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes.

[0061] The polymer contained in the second layer is preferably a polymer electrolyte from the viewpoint of electrolysis efficiency, and moreover, a fluorine-based polymer electrolyte is particularly preferred from the viewpoints of being relatively resistant to degradation by hydrogen peroxides and improving adhesion between the second layer and a catalyst layer that may be provided in the cathode.

[0062] When the second layer contains a polymer, the ratio (I / C) of the mass (I) of the polymer to the mass (C) of the carbon particles is, from the viewpoints of the durability (suppression of deterioration) of the first layer, electrolysis efficiency, and adhesion between the first layer and the second layer, preferably 0.4 or more, more preferably 0.5 or more, and particularly preferably 0.6 or more, and is preferably 2.0 or less, more preferably 1.6 or less, and particularly preferably 1.4 or less.

[0063] When the second layer contains a binder, the fluorine-based polymer electrolyte content is preferably 60% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass, based on the total mass of the binder.

[0064] The second layer may further contain a known hydrogen peroxide decomposer or radical scavenger. Examples of hydrogen peroxide decomposers include phosphorus-based compounds such as polyphosphoric acid, trimethylphosphine, and alkyl phosphites. Examples of radical scavengers include phenol derivatives such as 2,6-di-tert-butyl-methylphenol, 2,4-dimethyl, and 2,4-di-t-butyl-6-methyl, aromatic amine derivatives such as N,N'-diphenyl-p-phenylenediamine and phenyl-β-naphthylamine, and metal compounds such as Ce, Ru, Mn, Co, and Fe. Among these, Ce compounds are preferred, and Ce oxides are particularly preferred.

[0065] The second layer may contain various additives, such as surfactants, non-electrolytic polymers, elastomers, etc., to the extent that the effects of the present invention are not impaired.

[0066] The content by mass of the carbon particles in the second layer is preferably 25% by mass or more, more preferably 30% by mass or more, and particularly preferably 40% by mass or more, based on the total mass of the second layer, and is preferably 90% by mass or less, more preferably 80% by mass or less, and particularly preferably 70% by mass or less.

[0067] The thickness of the second layer is preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 7 μm or more from the viewpoint of suppressing migration of hydrogen peroxides, while the thickness is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, and particularly preferably 15 μm or less from the viewpoint of ensuring good water electrolysis performance.

[0068] Furthermore, from the viewpoint of ensuring good water electrolysis performance, the ratio (T2 / T1) of the thickness (T2) of the second layer to the thickness (T1) of the first layer is preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less. On the other hand, from the viewpoint of suppressing the migration of hydrogen peroxides and improving durability, the ratio (T2 / T1) is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.06 or more, and particularly preferably 0.07 or more.

[0069] In the electrolyte membrane of the present invention and the membrane electrode assembly (MEA) or catalyst-coated electrolyte membrane (CCM) using the same, it is preferable that the second layer of the electrolyte membrane and a catalyst layer of the cathode described below are disposed in contact with each other, from the viewpoints of electrolysis efficiency and durability.

[0070] [Method for manufacturing electrolyte membrane] Hereinafter, an example of a method for manufacturing an electrolyte membrane will be described. As the polymer electrolyte used in the first layer, a commercially available product such as "Nafion" (registered trademark) (manufactured by Chemours) may be used, or a membrane may be formed by applying a polymer electrolyte solution to a membrane-forming substrate such as a PET film and drying the applied solution.

[0071] The first layer may be in a form in which a layered portion (composite portion) containing a porous substrate and a polymer electrolyte is provided on one or both sides of the layered portion (composite portion) containing a polymer electrolyte and not containing a porous substrate, and a layered portion (composite portion) is provided on one or both sides of the layered portion (composite portion). As a manufacturing method of the above-mentioned form, for example, a method in which a porous substrate is stuck onto the polymer electrolyte solution applied to a membrane-forming substrate and impregnated, and further, a method in which a polymer electrolyte solution is applied to the porous substrate material impregnated with the polymer electrolyte solution by the above-mentioned method and dried.

[0072] The polymer electrolyte may also be one in which the ionic groups form salts with alkali metal or alkaline earth metal cations. In this case, after forming the first layer on the membrane-forming substrate, it is preferable to perform an acid treatment to exchange the alkali metal or alkaline earth metal cations for protons. Here, the acid treatment may be performed by a known method.

[0073] The electrolyte membrane of the present invention can be conveniently produced by laminating the second layer on the first layer. The lamination method can be a spraying method, a coating method, or a transfer method.

[0074] The spraying method involves spraying carbon particles onto a first layer using a nozzle or the like to form and laminate a second layer. After forming the second layer on the first layer, it is preferable to perform heat pressing to improve adhesion. Furthermore, by spraying carbon particles onto the first layer before it is completely dried during the manufacturing process of the first layer, it is possible to improve adhesion between the first layer and the second layer.

[0075] The coating method is a method in which a coating liquid for forming a second layer is applied to a first layer formed on a film-forming substrate, and then dried and laminated. The transfer method is a method in which a transfer sheet in which the second layer is laminated on a transfer substrate and the first layer formed on the film-forming substrate are hot-pressed to transfer the second layer to the first layer. When the coating method or the transfer method is adopted, it is preferable that the second layer contains the above-mentioned binder.

[0076] [Electrodes] The anode and cathode are each made of a material that can be used to form an electrode. The material that can be used to form the electrode is not particularly limited, and materials and structures known in the art can be used. Examples include a stacked structure in which a catalyst layer is stacked on an electrode base material made of a conductive material, and an electrode base material supporting a catalyst. More specific embodiments of the catalyst layer and the electrode base material will be described later. Furthermore, the catalyst supported on the electrode base material can be the catalyst particles used in the catalyst layer described later. Among these, a stacked structure of an electrode base material and a catalyst layer is preferred. When the electrodes have this stacked structure, in a water electrolysis cell, the catalyst layer may be provided on the side opposite the electrolyte membrane side of the electrode base material or on the electrolyte membrane side, but it is preferable that the catalyst layer be located on the electrolyte membrane side.

[0077] The catalyst layer can also be provided on the electrolyte membrane. Hereinafter, an electrode provided with a catalyst layer will be referred to as a "catalyst-coated electrode," and an electrolyte membrane provided with a catalyst layer will be referred to as a "catalyst-coated electrolyte membrane (CCM)." The catalyst layer can be laminated on the electrode substrate or the electrolyte membrane by a known coating method or transfer method.

[0078] [Electrode substrate] The electrode substrate (which may also serve as a gas diffusion layer) is primarily intended for application of voltage and is made of a conductive material, and may be, for example, a porous substrate made of metal, carbon, etc. Examples of metal porous substrates include metal nonwoven fabric, sintered metal fiber, sintered metal powder, and sintered metal foam, while examples of carbon porous substrates include carbon felt, carbon paper, carbon cloth, and sintered graphite particles.

[0079] As the electrode substrate constituting the anode, a metal porous substrate is preferably used, which has excellent corrosion resistance in environments of high potential, the presence of oxygen, strong acidity, etc. From the above-mentioned viewpoints, as the metal constituting the metal porous substrate, titanium, aluminum, nickel, stainless steel, and alloys containing at least one of these metals as the main component are preferred, and titanium and alloys containing titanium as the main component are particularly preferred.

[0080] As the electrode substrate constituting the cathode, from the viewpoints of material cost and electrical conductivity, a porous carbon substrate is preferred, and carbon paper is particularly preferred.

[0081] [Catalyst Layer] The catalyst layer is generally a layer containing catalyst particles and a polymer electrolyte. The catalyst particles generally include metals such as platinum group elements (platinum, ruthenium, rhodium, palladium, osmium, and iridium), iron, lead, gold, silver, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or alloys, oxides, and composite oxides thereof. Carbon particles carrying the catalyst metals (catalyst metal-supported carbon particles) are also commonly used. The carbon particles are not particularly limited as long as they are fine particles, electrically conductive, and do not corrode or deteriorate due to reaction with the catalyst. Carbon black, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerene particles are preferably used.

[0082] Examples of the polymer electrolyte include the fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes described above. As the polymer electrolyte of the catalyst layer, from the viewpoints of gas diffusibility and chemical durability, the fluorine-based polymer electrolyte is preferred, and perfluorocarbon sulfonic acid polymers are more preferred.

[0083] The mass ratio of the catalyst particle content to the polymer electrolyte content in the catalyst layer (catalyst particles / polymer electrolyte) is generally in the range of 1 to 15, and preferably in the range of 1.5 to 13.

[0084] The catalyst layer provided on the cathode (sometimes referred to as the "cathode catalyst layer") and the catalyst layer provided on the anode (sometimes referred to as the "anode catalyst layer") may be made of the same material or different materials.

[0085] The cathode catalyst layer may be any catalyst that generates hydrogen using protons as a raw material as catalyst particles, and preferably contains a platinum catalyst, and it is particularly preferable to use platinum-supported carbon particles.

[0086] The anode catalyst layer may be formed of catalyst particles that generate oxygen using water as a raw material, and preferably uses a noble metal such as iridium, ruthenium, rhodium, or palladium, or an oxide thereof, with iridium oxide being particularly preferred. In this case, the catalyst particles may be single particles or may be supported on titanium oxide or the like.

[0087] [Membrane Electrode Assembly (MEA)] The electrodes constituting the anode and cathode may each be integrated with an electrolyte membrane. An integrated assembly of an electrode and an electrolyte membrane is called a "membrane electrode assembly (MEA)." Examples of the form of the membrane electrode assembly include one in which an electrode base material is laminated on a catalyst-coated electrolyte membrane (CCM) and one in which a catalyst-coated electrode is laminated on an electrolyte membrane.

[0088] The membrane electrode assembly may be one in which the electrolyte membrane and the electrodes are joined together in advance, or one in which the electrolyte membrane and the electrodes are individually arranged in the cell and then joined together in a clamping step.

[0089] The membrane electrode assembly preferably used in the present invention has a configuration of "anode electrode base material / anode catalyst layer / electrolyte membrane / cathode catalyst layer / cathode electrode base material." In the above configuration, it is more preferable to use a catalyst-layered electrolyte membrane in which an anode catalyst layer and a cathode catalyst layer are laminated on an electrolyte membrane. In the above configuration, the cathode catalyst layer is disposed on the second layer side of the electrolyte membrane, and it is preferable that the second layer and the cathode catalyst layer are disposed in contact with each other.

[0090] [Catalyst-Coated Electrolyte Membrane (CCM)] As described above, the catalyst-coated electrolyte membrane has an anode catalyst layer laminated on the first layer side of the electrolyte membrane and a cathode catalyst layer laminated on the second layer side of the electrolyte membrane.

[0091] Examples of methods for laminating a catalyst layer on an electrolyte membrane include a coating method, a transfer method, and a combination of a coating method and a transfer method. These methods are not particularly limited, and any known method can be used.

[0092] As a coating method, a coating liquid for a catalyst layer can be applied to the electrolyte membrane using a known coating method. Specifically, a method can be used in which a coating liquid for a cathode catalyst layer is applied to the second layer side of the electrolyte membrane and dried to form a cathode catalyst layer, and a coating liquid for an anode catalyst layer is applied to the first layer side of the electrolyte membrane and dried to form an anode catalyst layer. The stacking order of the cathode catalyst layer and the anode catalyst layer may be reversed. When a coating method is employed, it is preferable to stack a membrane-forming substrate or a support on the side of the electrolyte membrane opposite to the side to which the coating liquid for a catalyst layer is applied.

[0093] An example of a transfer method is a method in which a cathode catalyst layer transfer sheet in which a cathode catalyst layer is laminated on a transfer substrate and an anode catalyst layer transfer sheet in which an anode catalyst layer is laminated on a transfer substrate are prepared, and the cathode catalyst layer transfer sheet is attached to the second layer side of the electrolyte membrane, and the anode catalyst layer transfer sheet is attached to the first layer side of the electrolyte membrane, and then the resulting sheets are hot-pressed.

[0094] An example of a combined application of the coating method and the transfer method is a method in which a coating liquid for a cathode catalyst layer is first applied to the second layer side of the electrolyte membrane and dried to form a cathode catalyst layer, and then an anode catalyst layer transfer sheet is attached to the opposite side of the electrolyte membrane, followed by hot pressing to transfer the anode catalyst layer. Conversely, a method in which the coating liquid for an anode catalyst layer is applied and then the cathode catalyst layer is transferred may also be used. Furthermore, in the manufacturing process of the catalyst-coated electrolyte membrane, a method in which the second layer of the electrolyte membrane and the cathode catalyst layer are laminated together on the first layer of the electrolyte membrane may be employed. Examples of such a method include a method in which the first layer formed on a membrane-forming substrate and a transfer sheet, on which the cathode catalyst layer and the second layer are sequentially laminated on a transfer substrate, are hot pressed to simultaneously laminate the second layer and the cathode catalyst layer on the first layer.

[0095] [Water Electrolysis Cell and Water Electrolysis Apparatus] The water electrolysis cell of the present invention is a water electrolysis cell whose interior is partitioned into an anode and a cathode by an electrolyte membrane, i.e., the anode electrode and the cathode electrode are separated by the electrolyte membrane, and the electrolyte membrane comprises a first layer containing a polymer electrolyte and a second layer containing carbon particles, with the second layer being disposed on the cathode side. The first layer and the second layer are as described above in detail. The anode and the cathode can also preferably have the same configurations as described above in detail.

[0096] A typical example of the water electrolysis cell of the present invention has a configuration similar to that of the electrolysis cell shown in Fig. 1. The "electrolysis cell" shown in Fig. 1 is synonymous with the "water electrolysis cell," and will therefore be referred to as the "water electrolysis cell" herein.

[0097] That is, the water electrolysis cell of the present invention has an electrolyte membrane 10 disposed between an anode 20 and a cathode 30, thereby dividing the interior thereof. In the example of FIG. 1 , these are sandwiched between separators 41 and 42. The electrolyte membrane 10 includes a first layer 11 and a second layer 12, with the second layer 12 disposed on the cathode 30 side of the first layer 11. In the water electrolysis device of the present invention, a power source (not shown) is connected to the anode 20 and the cathode 30 to apply a voltage. A commonly known water electrolysis device includes, as basic components, a water supply unit that supplies water to the water electrolysis cell, a power supply unit that supplies power to the water electrolysis cell, an oxygen discharge unit that discharges generated oxygen, a hydrogen discharge unit that discharges generated hydrogen, and a water discharge unit that discharges surplus water after electrolysis. The water electrolysis device according to the embodiment of the present invention may also include the above basic components.

[0098] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. The various measurement conditions are as follows.

[0099] [Example 1] [Synthesis of polyether ketone-based block copolymer b1] [Synthesis Example 1] (Synthesis of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane (K-DHBP) represented by the following chemical formula (G1)) In a 500 mL flask equipped with a stirrer, thermometer, and distillation tube, 49.5 g of 4,4'-dihydroxybenzophenone, 134 g of ethylene glycol, 96.9 g of trimethyl orthoformate, and 0.50 g of p-toluenesulfonic acid monohydrate were charged and dissolved. The mixture was then stirred and kept at 78 to 82°C for 2 hours. The internal temperature was then gradually raised to 120°C, and the mixture was heated until the distillation of methyl formate, methanol, and trimethyl orthoformate completely stopped. After cooling this reaction solution to room temperature, the reaction solution was diluted with ethyl acetate, and the organic layer was washed with 100 mL of a 5% aqueous potassium carbonate solution and separated, and the solvent was then evaporated. 80 mL of dichloromethane was added to the residue to precipitate crystals, which were filtered and dried to obtain 52.0 g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane represented by the following chemical formula (G1). GC analysis of the crystals revealed that they were 99.9% 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane and 0.1% 4,4'-dihydroxybenzophenone. The purity was 99.9%.

[0100]

[0101] Synthesis Example 2 (Synthesis of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following chemical formula (G2)) 109.1 g of 4,4'-difluorobenzophenone (Sigma-Aldrich Japan (same) reagent) was reacted in 150 mL of fuming sulfuric acid (50% SO3) (Fujifilm Wako Pure Chemical Industries, Ltd. reagent) at 100°C for 10 hours. Thereafter, the mixture was poured little by little into a large amount of water, neutralized with sodium hydroxide, and then 200 g of table salt (NaCl) was added to precipitate the synthesized product. The obtained precipitate was filtered and recrystallized from an aqueous ethanol solution to obtain disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following chemical formula (G2). The purity was 99.3%.

[0102]

[0103] Synthesis Example 3 (Synthesis of nonionic oligomer a1 represented by the following general formula (G3)) 16.59 g of potassium carbonate (Aldrich reagent, 120 mmol), 25.83 g (100 mmol) of K-DHBP obtained in Synthesis Example 1, and 20.3 g of 4,4'-difluorobenzophenone (Aldrich reagent, 93 mmol) were placed in a 2,000 mL SUS polymerization reactor equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap. After nitrogen substitution, 300 mL of N-methylpyrrolidone (NMP) and 100 mL of toluene were added, and the mixture was dehydrated at 150°C. The temperature was then raised to remove the toluene, and polymerization was carried out at 170°C for 3 hours. Purification by reprecipitation with a large amount of methanol yielded a terminal hydroxyl form of nonionic oligomer a1. The number average molecular weight of the terminal hydroxyl form of this nonionic oligomer a1 was 10,000.

[0104] A 500 mL three-neck flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap was charged with 1.1 g of potassium carbonate (Sigma-Aldrich Japan (same) reagent, 8 mmol) and 20.0 g (2 mmol) of the terminal hydroxy compound of the above nonionic oligomer a1. After replacing the atmosphere inside the flask with nitrogen, 100 mL of NMP and 30 mL of toluene were added, and the mixture was dehydrated at 100°C and then heated to remove the toluene. Furthermore, 2.2 g of hexafluorobenzene (Sigma-Aldrich Japan (same) reagent, 12 mmol) was added, and the reaction was carried out at 105°C for 12 hours. Purification was carried out by reprecipitation with a large amount of isopropyl alcohol, yielding nonionic oligomer a1 (terminal: fluoro group) represented by the following general formula (G3). The number average molecular weight was 11,000.

[0105]

[0106] Synthesis Example 4 (Synthesis of ionic oligomer a2 represented by the following general formula (G4)) 27.6 g of potassium carbonate (Sigma-Aldrich Japan (same manufacturer), reagent, 200 mmol), 12.9 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.3 g of 4,4'-biphenol (Sigma-Aldrich Japan (same manufacturer), reagent, 50 mmol), 39.3 g (93 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 17.9 g of 18-crown-6 (Fujifilm Wako Pure Chemical Industries, Ltd., 82 mmol) were placed in a 2,000 mL SUS polymerization reactor equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap. After nitrogen substitution, 300 mL of NMP and 100 mL of toluene were added, and the mixture was dehydrated at 150°C, heated to remove toluene, and then polymerized at 170°C for 6 hours. The resulting product was purified by reprecipitation with a large amount of isopropyl alcohol to obtain an ionic oligomer a2 (terminal: hydroxy group) represented by the following general formula (G4). The number average molecular weight was 16,000. In general formula (G4), M represents a hydrogen atom, Na, or K.

[0107]

[0108] (Synthesis of Polyetherketone-Based Block Copolymer b1) 16 g of ionic oligomer a2 and 11 g of nonionic oligomer a1 were placed in a 2,000 mL SUS polymerization reactor equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap, and NMP was added so that the total amount of the oligomers charged was 7 wt %, followed by reaction at 105°C for 24 hours.

[0109] The resulting precipitate was recovered by filtration and washed with a large amount of isopropyl alcohol to obtain a block copolymer C1. The polyetherketone-based block copolymer b1 had a weight-average molecular weight of 340,000 and an ion-exchange capacity (IEC) of 2.1 meq / g.

[0110] [Preparation of Electrolyte Membrane] [Preparation of First Layer] A PET film "Lumirror" (registered trademark) 125T60 manufactured by Toray Industries, Inc. was attached to a SUS plate using "Kapton" (registered trademark) tape. The polyetherketone-based block copolymer b1 synthesized above was dissolved in NMP and pressure-filtered using a 1 μm polypropylene filter to prepare a solution (Solution P1, concentration 13% by mass). The solution was cast onto the PET film and dried to obtain a film-like polymer membrane. The resulting solution was then immersed in a 10% by mass aqueous sulfuric acid solution at 80°C for 24 hours to undergo proton substitution and deprotection reactions, followed by thorough immersion in a large excess of pure water for 24 hours to wash, thereby obtaining a first layer. The thickness of this first layer was 90 μm.

[0111] [Lamination of Second Layer] The following second layer coating liquid was cast onto the first layer and dried to laminate the second layer on the first layer. The thickness of this second layer was 10 μm.

[0112] [Preparation of Coating Liquid for Second Layer] Carbon particles: 10 parts by mass of carbon black ("VULCAN" (registered trademark) XC72 manufactured by Cabot Corporation) Binder: 9 parts by mass, converted to solids, of a fluorinated polymer electrolyte ("Nafion" (registered trademark) product number D2020 manufactured by Chemours Corporation) Solvent: A mixed solvent of water and 1-propyl alcohol in a mass ratio of 4:6 The above carbon particles and polymer electrolyte were dispersed in the solvent using a bead mill to prepare a coating liquid with a solids concentration of 10% by mass. The ratio (I / C) of the mass of the polymer electrolyte (I) to the mass of the carbon particles (C) in this coating liquid was 0.9.

[0113] [Preparation of catalyst-coated electrolyte membrane] A catalyst-coated electrolyte membrane was prepared by laminating the following cathode catalyst layer on the second layer side of the electrolyte membrane prepared above, and the following anode catalyst layer on the first layer side. The dry thicknesses of the cathode catalyst layer and the anode catalyst layer were each 11 μm.

[0114] <Cathode catalyst layer> A catalyst layer containing, as a total solid content, 10 parts by mass of catalyst particles (Tanaka Kikinzoku Kogyo K.K. platinum catalyst-supported carbon particles TEC10E50E (platinum support rate 50 mass%), and 5 parts by mass of a fluorine-based polymer electrolyte (Chemours Inc.'s "Nafion" (registered trademark), product number D2020).

[0115] <Anode catalyst layer> The total solid content was catalyst particles (IrO ２ A catalyst layer containing 10 parts by mass of catalyst Elyst Ir75 0480 (Ir content 75%) and 1.3 parts by mass of a fluorine-based polymer electrolyte ("Nafion" (registered trademark) product number D2020 manufactured by Chemours Corporation).

[0116] [Fabrication of Membrane Electrode Assembly] A commercially available gas diffusion electrode 24BCH manufactured by SGL was stacked as a cathode also serving as a gas diffusion layer on the cathode catalyst layer side of the catalyst-layered electrolyte membrane fabricated above, and a commercially available porous titanium sintered body plate was stacked as an anode also serving as a gas diffusion layer, to fabricate a membrane electrode assembly.

[0117] [Water Electrolysis Method] The membrane electrode assembly prepared above was inserted into a JARI standard cell "Ex-1" (electrode area 25 cm) manufactured by Eiwa Corporation. ２ ) and the cell temperature was set to 50°C. Deionized water with an electrical conductivity of 1 μS / cm or less was supplied to both the anode and cathode at a flow rate of 0.2 L / min at atmospheric pressure, and the current density was set to 1.0 A / cm ２ A voltage was applied so that the voltage was equal to or greater than 100 V, and water electrolysis was carried out for 2,000 hours (water electrolysis method 1 in Table 1).

[0118] Comparative Example 1 An electrolyte membrane, a catalyst layer-equipped electrolyte membrane, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that the second layer was not laminated, and water electrolysis was performed in the same manner as in Example 1.

[0119] [Example 2 and Comparative Example 2] Water electrolysis was performed in the same manner as in Example 1 and Comparative Example 1, except that deionized water was supplied only to the anode (water electrolysis method 2 in Table 1). Example 2 corresponds to Example 1, and Comparative Example 2 corresponds to Comparative Example 1, respectively.

[0120] Example 3 An electrolyte membrane, a catalyst-coated electrolyte membrane, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that the first layer in Example 1 was changed to a fluorine-based polymer electrolyte layer (Nafion® Nafion 115, manufactured by Chemours Corporation: thickness 125 μm), and water electrolysis (water electrolysis method 1 in Table 2) was performed in the same manner as in Example 1.

[0121] Comparative Example 3 An electrolyte membrane, a catalyst layer-equipped electrolyte membrane, and a membrane electrode assembly were prepared in the same manner as in Example 3, except that the second layer was not laminated, and water electrolysis was performed in the same manner as in Example 1.

[0122] [Example 4 and Comparative Example 4] Water electrolysis was performed in the same manner as in the water electrolysis methods of Example 3 and Comparative Example 3, except that deionized water was supplied only to the anode (water electrolysis method 2 in Table 2). Example 4 corresponds to Example 3, and Comparative Example 4 corresponds to Comparative Example 3, respectively.

[0123] [Evaluation] For the above Examples and Comparative Examples, the applied voltages and average voltages at electrolysis times of 0, 500, 1,000, and 2,000 hours are shown in Tables 1 and 2. The relationship between electrolysis time and applied voltage is also shown in Figures 2 and 3. In the tables, water electrolysis method 1 is a form in which water is supplied to both the anode and the cathode, and water electrolysis method 2 is a form in which water is supplied only to the anode. The applied voltage at electrolysis time "0 hour" represents the initial applied voltage, the average applied voltage represents the average value of the applied voltage every 25 hours from 0 hour to 2,000 hours, and the voltage increase rate represents the voltage increase rate after 2,000 hours, calculated using the following formula 1: Voltage increase rate (%) = (V １ -V ０ ) / V ０ ×100 ...Formula 1 In the formula, V １ is the applied voltage after 2,000 hours, V ０ represents the initial applied voltage.

[0124] The lower the average applied voltage, the higher the electrolysis efficiency, and the lower the voltage rise rate, the better the durability (the more the electrolysis efficiency can be maintained).

[0125]

[0126]

[0127] It is clear from Tables 1 and 2 and Figs. 2 and 3 that the water electrolysis method of the present invention using an electrolyte membrane in which the second layer is laminated on the first layer has a smaller rate of voltage rise and is superior in durability compared to the water electrolysis method of Comparative Example using an electrolyte membrane in which no second layer is laminated.

[0128] Furthermore, it can be seen that water electrolysis method 2 (water supply only to the anode) has a smaller voltage rise rate and is superior in durability compared to water electrolysis method 1 (water supply to both the anode and cathode).

[0129] Furthermore, Figure 4 shows the relationship between electrolysis time and applied voltage for Examples 1 to 4. It can be seen that Examples 1 and 2 (block copolymer b1) maintained a low applied voltage for 2,000 hours compared to Examples 3 and 4 (Nafion 115), demonstrating that high electrolysis efficiency was maintained. That is, Figure 4 shows that membranes using a hydrocarbon-based polymer electrolyte as the first layer can maintain high electrolysis efficiency for a long period of time compared to membranes using a fluorine-based polymer electrolyte as the first layer.

[0130] REFERENCE SIGNS LIST 1 electrolysis cell 10 electrolyte membrane 11 first layer 12 second layer 20 anode 30 cathode 41, 42 separator

Claims

1. A water electrolysis method in which water is supplied to an electrolytic cell, the interior of which is partitioned into an anode and a cathode by an electrolyte membrane, and the water is electrolyzed to produce oxygen at the anode and hydrogen at the cathode, wherein the electrolyte membrane comprises a first layer containing a polymer electrolyte, and a second layer containing carbon particles on the cathode side of the first layer.

2. The water electrolysis method according to claim 1 , wherein all or part of the carbon particles contained in the second layer are carbon particles that do not support a catalytic metal.

3. The method for water electrolysis according to claim 1 , wherein the second layer comprises a binder.

4. The method for water electrolysis according to claim 3 , wherein all or part of the binder contained in the second layer is a fluorine-based polymer electrolyte.

5. The water electrolysis method according to claim 1 , wherein the first layer has a thickness of 40 μm or more and 250 μm or less.

6. The water electrolysis method according to claim 1, wherein a ratio (T2 / T1) of the thickness (T2) of the second layer to the thickness (T1) of the first layer is 0.03 to 0.

30.

7. The water electrolysis method according to claim 1 , wherein all or part of the polymer electrolyte contained in the first layer is a hydrocarbon-based polymer electrolyte.

8. the anode and the cathode each include a catalyst layer and an electrode base material in this order from the electrolyte membrane side; The water electrolysis method according to claim 1.

9. The water electrolysis method according to claim 8 , wherein the catalyst layer constituting the cathode contains a platinum catalyst.

10. The water electrolysis method according to claim 8 , wherein the second layer of the electrolyte membrane and the catalyst layer of the cathode are arranged in contact with each other.

11. The water electrolysis method according to any one of claims 1 to 10, wherein water is supplied to at least the anode of the electrolytic cell.

12. A water electrolysis cell whose interior is partitioned into an anode and a cathode by an electrolyte membrane, the electrolyte membrane comprising: a first layer containing a polymer electrolyte; and a second layer containing carbon particles on the cathode side of the first layer.

13. A water electrolysis device comprising the water electrolysis cell of claim 12.