Membrane electrode assembly, hydrogen production method, and hydrogen production system

Abstract

Provided are a membrane electrode assembly, a hydrogen production method, and a hydrogen production system. The membrane electrode assembly has a structure in which a cathode catalyst layer, a hydroxy ion conducting membrane, and an anode catalyst layer are laminated in this order, wherein the tensile strength (a) and the elongation at break (b) of a water-swellable body of a polymer contained in the cathode catalyst layer and / or the anode catalyst layer and the tensile strength (c) and the elongation at break (d) of a water-swellable body of a hydroxy ion conducting polymer constituting the hydroxy ion conducting membrane satisfy the following relationships (Ri) and (Rii).　(Ri): Tensile strength (a)>tensile strength (c), (Rii): Elongation at break (b)>elongation at break (d)

Description

Membrane electrode assembly, hydrogen production method, and hydrogen production system

[0001] The present invention relates to a membrane electrode assembly, a hydrogen production method, and a hydrogen production system.

[0002] Hydrogen is a clean energy source that does not emit carbon dioxide and is used, for example, as fuel for fuel cell vehicles and household fuel cells. Water electrolysis (electrolysis) is a well-known method for producing hydrogen. Hydrogen can be produced without carbon dioxide emissions by electrolyzing water using a renewable energy power generation system as a power source. Therefore, hydrogen is increasingly attracting attention as a fundamental energy source for a sustainable society.

[0003] Alkaline water electrolysis (AWE), which uses a highly concentrated alkaline aqueous solution as the electrolyte, is a known practical water electrolysis technology. In alkaline water electrolysis, hydrogen bubbles (2H ２ O + 2e － →H ２ +2OH － ) to the anode side, and also prevents the bubble-like oxygen (4OH) generated at the anode (positive electrode). － →O ２ +2H ２ O+4e － In order to prevent OH from migrating to the cathode side, a gas barrier separator (membrane) is disposed between the cathode and the anode. － Anion exchange membrane water electrolysis (AEMWE) has also been proposed, which uses an anion exchange membrane to improve the efficiency of the conduction (transfer) of hydroxy ions. AEMWE can conduct hydroxy ions from the cathode to the anode with high efficiency without using a highly concentrated alkaline aqueous solution as the electrolyte.

[0004] The electrodes (anode catalyst layer and cathode catalyst layer) of an AEMWE are generally formed by mixing a catalyst, in which a precious metal, metal oxide, or the like is optionally supported on a carrier such as carbon, an anionic ionomer that functions as both a binder and an ion conductor, and a liquid medium, applying the mixture to a gas-permeable and electronically conductive conductive substrate (gas diffusion layer), and drying the coating to remove the liquid medium. Next, an anion exchange membrane (hydroxy ion conductive membrane) containing a polymer with hydroxy ion conductivity is sandwiched between the formed anode catalyst layer and cathode catalyst layer, and the anion exchange membrane is bonded to the anode catalyst layer and the cathode catalyst layer by thermocompression bonding under pressure to obtain a membrane electrode assembly (MEA) for the AEMWE. For example, Patent Document 1 describes the following membrane electrode assembly.

[0005] a membrane electrode assembly for use in a water electrolysis apparatus, the membrane electrode assembly comprising: an electrolyte membrane made of an anion exchange membrane; catalyst layers disposed on both sides of the electrolyte membrane; and a conductive substrate laminated on a surface of the catalyst layer opposite to the surface facing the electrolyte membrane, wherein the catalyst layer comprises a catalyst and an anionic ionomer, at least a portion of the anionic ionomer being in contact with the electrolyte membrane while being embedded in the electrolyte membrane, and the membrane electrode assembly has a mixed region in which the anionic ionomer and the electrolyte membrane are mixed together near a boundary between the catalyst layer and the electrolyte membrane.

[0006] The technology described in Patent Document 1 is said to increase the adhesion between the electrolyte membrane and the catalyst layer, thereby reducing the resistance to the movement of hydroxide ions at the interface between the electrolyte membrane and the catalyst layer, and as a result, reducing the resistance of the membrane electrode assembly.

[0007] Japanese Patent Application Laid-Open No. 2023-104047

[0008] The MEA is required to have basic properties as a membrane, such as low gas permeability and low ionic resistance.

[0009] Solar power generation systems, which are widely used as power generation systems that utilize renewable energy, operate during the day and shut down at night when the sun sets. In other words, when water electrolysis is performed using a solar power generation system as a power source, there are times when power is supplied and times when it is not. Furthermore, even during times when power is supplied, the amount of power supplied fluctuates depending on the weather. This tendency for output to fluctuate is common to other power generation systems that utilize renewable energy. Therefore, when producing hydrogen by water electrolysis using a power generation system that utilizes renewable energy as a power source, it is necessary to increase or decrease the amount of water supplied depending on the amount of power supplied, or to stop the water supply during times when power is not supplied. Through extensive research, the inventors have found that, particularly when the water supply is stopped, the amount of water that has permeated the MEA decreases, causing contraction of the hydroxy ion conductive membrane composed of a polymer having highly hydrophilic groups. Contraction of the hydroxy ion conductive membrane is likely to cause peeling (deterioration of adhesion) at the interface between the hydroxy ion conductive membrane and the anode catalyst layer and / or the cathode catalyst layer. This peeling at the interface hinders the migration of hydroxy ions generated in the cathode catalyst layer to the anode catalyst layer, thereby reducing the efficiency of hydrogen production.

[0010] An object of the present invention is to provide a membrane electrode assembly that has low gas permeability and ionic resistance and can sufficiently maintain low resistance even when current or liquid supply is repeatedly turned on and off, and a hydrogen production method and hydrogen production system that use this membrane electrode assembly.

[0011] The above-mentioned problems of the present invention are solved by the following means. [1] A membrane / electrode assembly having a structure in which a cathode catalyst layer, a hydroxy ion conductive membrane, and an anode catalyst layer are laminated in this order, wherein the tensile strength (a) and breaking elongation (b) of a water-swollen body of a polymer contained in the cathode catalyst layer and / or the anode catalyst layer, and the tensile strength (c) and breaking elongation (d) of a water-swollen body of a hydroxy ion conductive polymer constituting the hydroxy ion conductive membrane satisfy the following relationships (Ri) and (Rii): Tensile strength (a) > tensile strength (c) (Ri) Breaking elongation (b) > breaking elongation (d) (Rii) [2] The membrane / electrode assembly according to [1], wherein the absolute value of the difference between the glass transition temperature (e) of the polymer contained in the cathode catalyst layer and / or the anode catalyst layer that satisfy the relationships (Ri) and (Rii) and the glass transition temperature (f) of the hydroxy ion conductive polymer is 1 to 190°C. [3] The membrane / electrode assembly according to [1] or [2], wherein the polymer contained in the cathode catalyst layer and / or the anode catalyst layer, which satisfies the relationship (Ri) and (Rii), is contained in a catalyst layer containing this polymer at a concentration of 5 to 25 mass %. [4] The membrane / electrode assembly according to any one of [1] to [3], wherein the polymer contained in at least the cathode catalyst layer satisfies the relationship (Ri) and (Rii). [5] The membrane / electrode assembly according to any one of [1] to [4], wherein the polymer contained in the anode catalyst layer satisfies the relationship (Ri) and (Rii). [6] The membrane / electrode assembly according to any one of [1] to [5], wherein the molecular weights of the polymers contained in the cathode catalyst layer and the anode catalyst layer are larger than the molecular weight of the hydroxy ion-conductive polymer. [7] A method for producing hydrogen, using the membrane / electrode assembly according to any one of [1] to [6]. [8] A hydrogen production system including the membrane electrode assembly according to any one of [1] to [6].

[0012] The membrane electrode assembly of the present invention has low gas permeability and ionic resistance, and can maintain a sufficiently low resistance even when the current supply or the liquid supply is repeatedly turned on and off. According to the hydrogen production method and hydrogen production system of the present invention, the membrane electrode assembly used has the above-mentioned properties, and hydrogen can be produced while maintaining a sufficiently low resistance even when the current supply or the liquid supply is repeatedly turned on and off.

[0013] FIG. 1 is a longitudinal sectional view showing a schematic diagram of a basic layer structure of one embodiment of a membrane electrode assembly according to the present invention.

[0014] [Membrane electrode assembly]

[0015] The membrane electrode assembly of the present invention can be widely used as a membrane electrode assembly in, for example, water electrolysis, fuel cells, carbon dioxide reduction, toluene protonation, etc. In particular, the membrane electrode assembly of the present invention is suitable as a membrane electrode assembly used for water electrolysis. The membrane electrode assembly of the present invention has excellent hydroxy ion conductivity (low ionic resistance) and sufficiently low gas permeability.

[0016] The membrane / electrode assembly of the present invention has a structure in which a cathode catalyst layer, a hydroxy ion conductive membrane, and an anode catalyst layer are laminated in this order. The tensile strength (a) and breaking elongation (b) of a water-swollen body of the polymer contained in the cathode catalyst layer and / or the anode catalyst layer, and the tensile strength (c) and breaking elongation (d) of a water-swollen body of the hydroxy ion conductive polymer constituting the hydroxy ion conductive membrane, satisfy the following relationships (Ri) and (Rii): Tensile strength (a) > tensile strength (c) (Ri) Breaking elongation (b) > Breaking elongation (d) (Rii). In the following description, the hydroxy ion conductive polymer constituting the hydroxy ion conductive membrane may be referred to as the "polymer constituting the hydroxy ion conductive membrane." Furthermore, the term "catalyst layer" simply refers to both the cathode catalyst layer and the anode catalyst layer.

[0017] In the membrane / electrode assembly of the present invention, the polymer contained in the catalyst layer has properties that make it less likely to break and more likely to stretch when swollen in water than the polymer constituting the hydroxy ion conductive membrane, which is thought to enable the catalyst layer to more easily follow the swelling / shrinkage of the hydroxy ion conductive membrane and improve durability while maintaining low resistance.

[0018] The relationship between (Ri) and (Rii) above needs to be satisfied between the polymer contained in at least one of the cathode catalyst layer and the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane. That is, in one embodiment of the membrane / electrode assembly of the present invention, the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfy the relationship between (Ri) and (Rii) above, while the polymer contained in the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane do not satisfy the relationship between (Ri) and (Rii). In another embodiment of the membrane / electrode assembly of the present invention, the polymer contained in the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfy the relationship between (Ri) and (Rii) above, while the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane do not satisfy the relationship between (Ri) and (Rii). In yet another embodiment of the membrane / electrode assembly of the present invention, the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfy the relationship (Ri) and (Rii) above, and the polymer contained in the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfy the relationship (Ri) and (Rii) above. In the present invention, from the viewpoint of further reducing gas permeability, it is preferable that at least the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfy the relationship (Ri) and (Rii) above. The tensile strength (a), breaking elongation (b), tensile strength (c), and breaking elongation (d) can be measured by the methods described in the Examples. The tensile strength and breaking elongation can be controlled by adjusting the constituent components, molecular weight, crosslink density, etc. of the polymer.

[0019] The polymer contained in the cathode catalyst layer and the polymer contained in the anode catalyst layer may be the same polymer or different polymers. Here, "different polymers" refers to polymers that differ from each other in at least one of tensile strength and elongation at break, regardless of whether the polymers have the same constituent components. That is, even if the constituent components (monomer types used) of the polymer contained in the cathode catalyst layer and the polymer contained in the anode catalyst layer (monomer types used) are the same, if the above properties differ due to differences in molecular weight, constituent ratio, crosslink density, etc., these polymers are considered "different polymers." The polymer contained in the cathode catalyst layer, the polymer contained in the anode catalyst layer, and the polymer constituting the hydroxy ion conductive membrane may be the same polymer type (the constituent components constituting the polymer are the same) or different. From the viewpoint of further enhancing the affinity between the catalyst layer and the hydroxy ion conductive membrane, it is preferable that the polymer types are the same.

[0020] In the relationship of (Ri), the difference between tensile strength (a) and tensile strength (c) ([tensile strength (a)] - [tensile strength (c)]) is preferably 5 MPa or more, more preferably 10 MPa or more, and even more preferably 20 MPa or more. There is no particular upper limit for the difference between tensile strength (a) and tensile strength (c), and it is preferably 100 MPa or less. Therefore, the difference between tensile strength (a) and tensile strength (c) is preferably 5 to 100 MPa, and more preferably 20 to 100 MPa. The difference between tensile strength (a) and tensile strength (c) can be 20 to 80 MPa, 20 to 60 MPa, 20 to 40 MPa, 20 to 28 MPa, or 20 to 26 MPa. In the relationship (Rii), the difference between the breaking elongation (b) and the breaking elongation (d) ([breaking elongation (b)] - [breaking elongation (d)]) is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. The upper limit of the difference between the breaking elongation (b) and the breaking elongation (d) is not particularly limited, and is preferably 400% or less. Therefore, the difference between the breaking elongation (b) and the breaking elongation (d) is preferably 5 to 400%, more preferably 20 to 400%. The difference between the breaking elongation (b) and the breaking elongation (d) can be 20 to 300%, 20 to 200%, 20 to 100%, or 25 to 100%.

[0021] When the polymer contained in the cathode catalyst layer satisfies the above relationships (Ri) and (Rii), the tensile strength (a1) of the water-swollen polymer contained in the cathode catalyst layer is preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, and even more preferably 40 MPa or more. The tensile strength (a1) of the water-swollen polymer contained in the cathode catalyst layer is usually 500 MPa or less, and may be 450 MPa or less. Therefore, the tensile strength (a1) is preferably 10 to 500 MPa, more preferably 10 to 450 MPa, even more preferably 10 to 300 MPa, and most preferably 10 to 200 MPa. Furthermore, the tensile strength (a1) can be 20 to 200 MPa, 20 to 100 MPa, 20 to 80 MPa, or 20 to 70 MPa. When the polymer contained in the cathode catalyst layer satisfies the above relationships (Ri) and (Rii), the breaking elongation (b1) of the water-swollen polymer contained in the cathode catalyst layer is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 50% or more. The breaking elongation (b1) of the water-swollen polymer contained in the cathode catalyst layer is usually 500% or less, and may be 400% or less. Therefore, the breaking elongation (b1) is preferably 10 to 500%, more preferably 20 to 400%, and even more preferably 50 to 400%. The breaking elongation (b1) can be 30 to 300%, 30 to 200%, or 50 to 100%.

[0022] When the polymer contained in the anode catalyst layer satisfies the above relationships (Ri) and (Rii), the tensile strength (a2) of a water-swollen body of the polymer contained in the anode catalyst layer is preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, and even more preferably 40 MPa or more. The tensile strength (a2) of a water-swollen body of the polymer contained in the anode catalyst layer is usually 500 MPa or less, and may be 450 MPa or less. Therefore, the tensile strength (a2) is preferably 10 to 500 MPa, more preferably 10 to 450 MPa, even more preferably 10 to 300 MPa, and most preferably 10 to 200 MPa. The tensile strength (a2) may also be 20 to 200 MPa, 20 to 100 MPa, or 20 to 80 MPa. When the polymer contained in the anode catalyst layer satisfies the above relationships (Ri) and (Rii), the breaking elongation (b2) of the water-swollen polymer contained in the anode catalyst layer is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 50% or more. The breaking elongation (b2) of the water-swollen polymer contained in the anode catalyst layer is usually 500% or less, and may be 400% or less. Therefore, the breaking elongation (b2) is preferably 10 to 500%, more preferably 20 to 400%, and even more preferably 50 to 400%. The breaking elongation (b2) can be 30 to 300%, 30 to 200%, or 50 to 100%.

[0023] The tensile strength (c) of the water-swollen hydroxy ion conductive membrane-constituting polymer is preferably 5 MPa or more, more preferably 10 MPa or more, and even more preferably 12 MPa or more. The tensile strength (c) of the hydroxy ion conductive membrane-constituting polymer is usually 400 MPa or less, and may be 300 MPa or less. Therefore, the tensile strength (c) is preferably 5 to 400 MPa, more preferably 10 to 300 MPa, even more preferably 10 to 100 MPa, and most preferably 10 to 60 MPa. The tensile strength (c) can also be 10 to 40 MPa, or 10 to 30 MPa. The breaking elongation (d) of the water-swollen hydroxy ion conductive membrane-constituting polymer is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. The breaking elongation (d) of the hydroxy ion conductive membrane-constituting polymer is usually 400% or less, and may be 300% or less. Therefore, the breaking elongation (d) is preferably 5 to 400%, more preferably 10 to 300%, and even more preferably 20 to 300%. The breaking elongation (d) can be 10 to 200%, 10 to 100%, or 10 to 80%.

[0024] The absolute value of the difference between the glass transition temperature (e) of the polymer contained in the cathode catalyst layer and / or the anode catalyst layer that satisfies the above relationships (Ri) and (Rii) and the glass transition temperature (f) of the polymer that constitutes the hydroxy ion conductive membrane is preferably 1 to 200°C, more preferably 1 to 190°C, more preferably 1 to 150°C, even more preferably 1 to 140°C, still more preferably 1 to 50°C, and even more preferably 1 to 40°C. The absolute value of the difference may be 10 to 80°C, 15 to 80°C, or 20 to 60°C. In other words, when the catalyst layer that satisfies the above relationships (Ri) and (Rii) is a cathode catalyst layer, it is preferable that the glass transition temperature (e1) of the polymer contained in this cathode catalyst layer and the glass transition temperature (f) of the polymer that constitutes the hydroxy ion conductive membrane satisfy the above relationship. Furthermore, when the catalyst layer satisfying the above relationship between (Ri) and (Rii) is an anode catalyst layer, it is preferable that the glass transition temperature (e2) of the polymer contained in this anode catalyst layer and the glass transition temperature (f) of the polymer constituting the hydroxy ion conductive membrane satisfy the above relationship. Furthermore, when the catalyst layers satisfying the above relationship between (Ri) and (Rii) are both a cathode catalyst layer and an anode catalyst layer, it is preferable that both of the glass transition temperatures (e1) and (e2) satisfy the above relationship with the glass transition temperature (f) of the polymer constituting the hydroxy ion conductive membrane. Note that when each of the above polymers has two or more glass transition temperatures, the smallest glass transition temperature of each polymer is used for comparison.

[0025] The glass transition temperature (e) of the polymer contained in the cathode catalyst layer and / or the anode catalyst layer that satisfies the above relationships (Ri) and (Rii) and the glass transition temperature (f) of the polymer constituting the hydroxy ion conductive membrane more preferably satisfy the relationship glass transition temperature (e) > glass transition temperature (f). The glass transition temperature (e) is preferably −80°C or higher, more preferably −60°C or higher, and even more preferably −50°C or higher. The glass transition temperature (e) is typically 250°C or lower and may be 200°C or lower. Therefore, the glass transition temperature (e) is preferably −80 to 250°C, more preferably −60 to 200°C, and even more preferably −50 to 200°C. The glass transition temperature (f) is preferably −100°C or higher, more preferably −90°C or higher, and even more preferably −80°C or higher. The glass transition temperature (f) is typically 180°C or lower and may be 150°C or lower. Therefore, the glass transition temperature (f) is preferably −100 to 180° C., more preferably −90 to 150° C., and even more preferably −80 to 150° C. In the relationship between (e) and (f), the difference between the glass transition temperature (e) and the glass transition temperature (f) ([glass transition temperature (e)]−[glass transition temperature (f)]) is preferably 5° C. or more, and preferably 10° C. or more. Therefore, the difference between the glass transition temperature (e) and the glass transition temperature (f) is preferably 5 to 150° C.

[0026] The glass transition temperature of each polymer can be measured as follows. - Glass transition temperature - When a commercially available polymer is used, the value listed in the manufacturer's catalog is used as the glass transition temperature of the polymer. When glass transition temperature information from the manufacturer is not available or when synthetic polymer particles are used, the glass transition temperature value in the table in Chapter 36 of Volume 4 of the Polymer Handbook is used. When the glass transition temperature is not listed in the above literature, the glass transition temperature value obtained by measurement under the following measurement conditions is used.

[0027] The glass transition temperature (Tg) is calculated by measuring a dried sample of the polymer using a differential scanning calorimeter: X-DSC7000 (trade name, manufactured by SII Nano Technology Co., Ltd.) under the following measurement conditions. The measurement is performed twice on the same sample, and the result of the second measurement is used. (Measurement conditions) Atmosphere in measurement chamber: Nitrogen gas (50 mL / min) Heating rate: 5°C / min Measurement start temperature: -80°C Measurement end temperature: 250°C Sample pan: Aluminum pan Measurement sample mass: 5 mg Calculation of Tg: Tg is calculated by rounding off the decimal point of the midpoint between the start and end points of the decline in the DSC (differential scanning calorimetry) chart.

[0028] The molecular weight of the polymer contained in the cathode catalyst layer and / or anode catalyst layer that satisfies the above relationship (Ri) and (Rii) is preferably larger than the molecular weight of the polymer that constitutes the hydroxy ion conductive membrane. In the present invention, the molecular weight of the polymer is a weight-average molecular weight. The difference between the molecular weight of the polymer contained in the cathode catalyst layer and / or anode catalyst layer that satisfies the above relationship (Ri) and (Rii) and the molecular weight of the polymer that constitutes the hydroxy ion conductive membrane is preferably 1,000 or more. There is no particular upper limit for the difference between the molecular weight of the polymer contained in the cathode catalyst layer and / or anode catalyst layer that satisfies the above relationship (Ri) and (Rii) and the molecular weight of the polymer that constitutes the hydroxy ion conductive membrane, but it is preferably 10,000. Therefore, the difference between the molecular weight of the polymer contained in the cathode catalyst layer and / or anode catalyst layer that satisfies the above relationship (Ri) and (Rii) and the molecular weight of the polymer that constitutes the hydroxy ion conductive membrane is preferably 1,000 to 10,000, more preferably 1,000 to 7,000. The molecular weight of the polymer contained in the cathode catalyst layer and / or anode catalyst layer that satisfies the above relationship (Ri) and (Rii) is preferably 1,500 or more, more preferably 2,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more. The molecular weight of the polymer is usually 5,000,000 or less, and may be 1,000,000 or less. Therefore, the molecular weight of the polymer is preferably 1,500 to 5,000,000, more preferably 2,000 to 5,000,000, even more preferably 2,000 to 1,000,000, and even more preferably 5,000 to 1,000,000. The molecular weight of the polymer can also be 2,000 to 500,000 or 2,000 to 100,000. The molecular weight of the hydroxy ion conductive membrane-constituting polymer is preferably 500 or more, more preferably 1,000 or more. The molecular weight of the polymer constituting the hydroxy ion conductive membrane is usually 5,000,000 or less, and may be 1,000,000 or less.Therefore, the molecular weight of the polymer constituting the hydroxy ion conductive membrane is preferably 500 to 5,000,000, more preferably 1,000 to 1,000,000, even more preferably 1,000 to 100,000, still more preferably 1,000 to 10,000, and even more preferably 1,000 to 6,000.

[0029] -Measurement of polymer molecular weight- In the present invention, the molecular weight of a polymer is measured by gel permeation chromatography (GPC). The molecular weight refers to the weight average molecular weight in terms of polyethylene oxide. The measurement method is basically a value measured by the method under measurement condition 1 below. However, depending on the type of polymer, an appropriate eluent may be selected and used. (Measurement condition 1) Measuring instrument: HLC-8220GPC (trade name, manufactured by Tosoh Corporation) Column: TOSOH TSKgel 5000PWXL (trade name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (trade name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (trade name, manufactured by Tosoh Corporation) are connected. Carrier: 200 mM sodium nitrate aqueous solution Measurement temperature: 40°C Carrier flow rate: 1.0 ml / min Sample concentration: 0.2 mass% Detector: RI (refractive index) detector If the molecular weight cannot be measured under the above measurement condition 1, such as in the case of a crosslinked structure, measure the molecular weight by static light scattering under the following measurement condition 2. (Measurement condition 2) Measuring instrument: DLS-8000 (trade name, manufactured by Otsuka Electronics Co., Ltd.) Measurement concentration: 0.25, 0.50, 0.75, 1.00 mg / mL Diluent: 0.1 M NaCl aqueous solution Laser wavelength: 633 nm Pinhole: PH1 = Open, PH2 = Slit Measurement angle: 60, 70, 80, 90, 100, 110, 120, 130 degrees Analysis method: Molecular weight is measured from the Zimm square root plot. The dn / dc required for analysis is measured using an Abbe refractometer.

[0030] FIG. 1 shows a preferred embodiment of the membrane electrode assembly of the present invention. In the membrane electrode assembly 4 of FIG. 1, a cathode catalyst layer 2c is formed on one surface of a hydroxy ion conductive membrane 1, an anode catalyst layer 2a is formed on the other surface, and a gas diffusion layer 3 is formed on each of these catalyst layers on the surface opposite the hydroxy ion conductive membrane 1. This membrane electrode assembly 4 has a layered structure in which the gas diffusion layer 3, cathode catalyst layer 2c, hydroxy ion conductive membrane 1, anode catalyst layer 2a, and gas diffusion layer 3 are layered in this order. The anode catalyst layer 2a contains a particulate anode catalyst 21 and a polymer 23 that also functions as a binder, and the anode catalyst 21 is bound by the polymer 23. The cathode catalyst layer 2c contains a particulate cathode catalyst 22 and a polymer 23 that also functions as a binder, and the cathode catalyst 22 is bound by the polymer 23. In FIG. 1, a bipolar plate 5 is further formed on the surface of the two gas diffusion layers 3 of the membrane electrode assembly 4 opposite to the catalyst layer, thereby forming a water electrolysis cell 10 .

[0031] Each member constituting the membrane electrode assembly will be described below.

[0032] <Hydroxy Ion Conductive Membrane> In the present invention, "having hydroxy ion conductivity" means that the ionic conductivity obtained by the following method is 0.1 mS / cm or more. -Ionic Conductivity- A 10 mm x 50 mm rectangular test piece is clamped between a jig (attachment with electrodes) such as Electro Chem BT-115 or the jig described in Electrochemistry, 85, 40, and AC impedance is measured by the four-terminal method. This AC impedance measurement is performed in a 1 M KOH aqueous solution heated to 45°C, at a voltage of 10 mV and a frequency in the range of 1 MHz to 0.1 Hz. The intercept (an extrapolated value is also acceptable) on the real axis of the Nyquist plot is taken as the resistance value R of the test piece, and the ionic conductivity σ is calculated using the following formula. Ion conductivity σ (S / cm) = D (cm) / (W (cm) × T (cm) × resistance value R (Ω)), D: length (cm) of test piece, W: width (cm) of test piece, T: thickness (cm) of test piece. In the present invention, the hydroxy ion conductivity of the hydroxy ion conductive membrane is preferably 0.1 mS / cm to 10 S / cm, more preferably 10 mS / cm to 1 S / cm, and even more preferably 10 mS / cm to 500 mS / cm.

[0033] The hydroxy ion conductive membrane may be in the form of a membrane (single membrane) formed of a hydroxy ion conductive polymer. The hydroxy ion conductive membrane may also be in the form of a porous substrate and the above-mentioned hydroxy ion conductive polymer. For example, the hydroxy ion conductive membrane may be in the form of a laminate of a hydroxy ion conductive polymer membrane and a porous substrate. Alternatively, the hydroxy ion conductive membrane may be in the form of a composite having a porous substrate and a hydroxy ion conductive polymer disposed at least within the pores of the porous substrate. In the form of a composite, the hydroxy ion conductive polymer may be disposed at least within the pores of the porous substrate. The hydroxy ion conductive polymer may be disposed not only within the pores of the porous substrate but also in portions other than the pores. For example, in the form of a composite, the hydroxy ion conductive polymer may cover the surface of the porous substrate. In the present invention, the hydroxy ion conductive membrane is preferably in the form of a membrane (single membrane not including a porous substrate) formed of a hydroxy ion conductive polymer.

[0034] -Hydroxy ion conductive polymer- A wide range of polymers having hydroxy ion conductivity that can be used in membrane electrode assemblies used in water electrolysis, fuel cells, etc. can be used as the hydroxy ion conductive polymer. Examples include ionomers and high water content polymers having polar groups. The hydroxy ion conductive polymer may be an ionic polymer or a nonionic polymer.

[0035] The ionomer is preferably an anionic ionomer. Examples of the ionomer include sulfonated plastic electrolytes such as perfluoroalkanesulfonic acid, sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene, and sulfoalkylated plastic electrolytes such as sulfoalkylated polyether ether ketone, sulfoalkylated polyether sulfone, sulfoalkylated polyether ether sulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene.

[0036] Examples of high water content polymers having polar groups include hydrocarbon polymers (preferably polyolefins, more preferably polyethylene or polypropylene), polyethylene glycol, and polyacrylamide.

[0037] The hydroxy ion conductive polymer preferably does not have a sulfo group.

[0038] In the present invention, the hydroxy ion conductive polymer preferably contains a component (I) derived from a polyfunctional polymerizable monomer (hereinafter simply referred to as "polyfunctional polymerizable monomer IA") having a total of two or more atoms of at least one of oxygen, sulfur, and nitrogen atoms (hereinafter, these three atoms are collectively referred to as "heteroatoms") in a structural portion other than the polymerizable group. In this polymer, the proportion of the component (I) in all structural components is preferably 20% by mass or more, more preferably 30% by mass or more. That is, the hydroxy ion conductive polymer containing the component (I) is preferably a polymer obtained by polymerizing a polymerizable monomer-containing liquid containing 20% ​​by mass or more of the polyfunctional polymerizable monomer IA among all monomers. This polymerization forms a three-dimensional network structure to produce the hydroxy ion conductive polymer. The hydroxy ion conductive polymer containing the component (I) exhibits excellent hydroxy ion conductivity because the structural portion containing the heteroatom effectively increases the polarity of the polymer, allowing it to stably retain more water.

[0039] The polyfunctional polymerizable monomer IA from which the above-mentioned component (I) is derived will now be described.

[0040] In the present invention, the term "polyfunctional polymerizable monomer" refers to a monomer having two or more polymerizable groups in one molecule. In other words, "polyfunctional" refers to having two or more polymerizable groups in one molecule. When the polymerizable group is a chain-polymerizable group, the polyfunctional polymerizable monomer IA is preferably a divalent to hexavalent polyfunctional polymerizable monomer (i.e., a monomer having 2 to 6 chain-polymerizable groups in one molecule), and preferably a divalent to tetravalent polyfunctional polymerizable monomer. When the polymerizable group is a step-polymerizable group, the polyfunctional polymerizable monomer IA is preferably a divalent to hexavalent polyfunctional polymerizable monomer (i.e., a monomer having 2 to 6 step-polymerizable groups in one molecule), and preferably a divalent to pentavalent polyfunctional polymerizable monomer, preferably a divalent to tetravalent polyfunctional polymerizable monomer, and preferably a trivalent to tetravalent polyfunctional polymerizable monomer. By using a polyfunctional polymerizable monomer, more crosslinked structures tend to be formed in the resulting polymer than when a monofunctional polymerizable monomer is used, resulting in a denser film.

[0041] The polymerizable group of the polyfunctional polymerizable monomer IA is not particularly limited as long as it can cause a polymerization reaction, and may be a chain polymerizable group (e.g., a vinyl group (CH ２ ═CH—), vinyl ether group (CH ２ ═CH—O—), vinyl thioether group (CH ２ =CH-S-), acryloyl group (CH ２ ═CH—C(═O)—), methacryloyl group (CH ２ =C(CH ３ )-C(═O)-) and derivatives thereof, and other groups having a carbon-carbon double bond; cyclic ether groups such as an epoxy group (oxiranyl group) or an oxetanyl group); and groups capable of step-growth polymerization include groups that undergo condensation polymerization or polyaddition (hydroxy group, unsubstituted amino group, carboxy group, sulfo group, isocyanate group, acid anhydride group, etc.). The polyfunctional polymerizable monomer IA preferably has two or more chain-polymerizable groups. The polyfunctional polymerizable monomer IA may also have both a chain-polymerizable group and a step-growth polymerizable group. It is also preferable that the polyfunctional polymerizable monomer IA has two or more chain-polymerizable groups and does not have a step-growth polymerizable group. In the present invention, the term "step-growth polymerizable group" refers to a group that reacts with another group to undergo step-growth polymerization under the polymerization reaction conditions of the polyfunctional polymerizable monomer IA to obtain a hydroxy ion-conductive polymer. That is, under these polymerization reaction conditions, if, for example, the above-mentioned "other groups" are not present and step-growth polymerization cannot occur (i.e., if they remain as unreacted groups in the resulting hydroxy ion conductive polymer), even if the polyfunctional polymerizable monomer IA contains groups listed as groups capable of step-growth polymerization, such as the above-mentioned hydroxy group, unsubstituted amino group, carboxy group, sulfo group, isocyanate group, and acid anhydride group, these groups are not "step-growth polymerizable groups." Even if a group is listed as a group capable of step-growth polymerization, if step-growth polymerization cannot occur under the above-mentioned polymerization reaction conditions, the oxygen atom, nitrogen atom, etc. constituting this group will constitute a heteroatom present in a structural part other than the polymerizable group of the polyfunctional polymerizable monomer IA.

[0042] The "polymerizable group" is preferably a group selected from a vinyl group, a vinyl ether group, a vinyl thioether group, an acryloyl group, a methacryloyl group, an epoxy group, and an oxetanyl group, and more preferably a group selected from a vinyl group, an acryloyl group, a methacryloyl group, and an epoxy group. When the polyfunctional polymerizable monomer IA has a styryl group, the "polymerizable group" is a vinyl group. That is, the benzene ring constituting the styryl group constitutes the "structural moiety other than the polymerizable group" defined in the present invention. Similarly, for groups containing a vinyl group other than a vinyl ether group, a vinyl thioether group, an acryloyl group, and a methacryloyl group, the polymerizable group is the vinyl group, and the portion other than the vinyl group constitutes the "structural moiety other than the polymerizable group" defined in the present invention. On the other hand, in the present invention, the chain-polymerizable groups, such as the ether group (-O-) possessed by the vinyl ether group, the thioether group (-S-) possessed by the vinyl thioether group, and the carbonyl group (-C(=O)-) possessed by the acryloyl group and the methacryloyl group, as well as the heteroatoms contained in the sequentially polymerizable groups, such as the hydroxy group, the amino group, the carboxy group, the isocyanate group, the sulfo group, and the acid anhydride, are all considered to be part of the structure of the "polymerizable group" possessed by the polyfunctional polymerizable monomer IA. Therefore, the heteroatoms constituting these polymerizable groups are not atoms constituting the "structural moiety other than the polymerizable group" defined in the present invention.

[0043] As described above, the polyfunctional polymerizable monomer IA has a total of two or more atoms of at least one of oxygen atoms, sulfur atoms, and nitrogen atoms in the structural portion other than the polymerizable group (i.e., the total number of oxygen atoms, sulfur atoms, and nitrogen atoms contained in the structural portion other than the polymerizable group is two or more). The combination of these atoms is not particularly limited, and may be a structure having two or more oxygen atoms in the structural portion other than the polymerizable group and no sulfur atoms and no nitrogen atoms, a structure having two or more sulfur atoms in the structural portion other than the polymerizable group and no oxygen atoms and no nitrogen atoms, or a structure having two or more nitrogen atoms in the structural portion other than the polymerizable group and no oxygen atoms and no sulfur atoms. In addition, two or more different types of heteroatoms may be combined to have two or more (for example, a structure having one sulfur atom and one oxygen atom). In the polyfunctional polymerizable monomer IA, the total number of oxygen atoms, sulfur atoms, and nitrogen atoms contained in the structural moieties other than the polymerizable group is preferably 2 to 160, more preferably 2 to 150, even more preferably 2 to 140, still more preferably 4 to 140, still more preferably 8 to 100, and particularly preferably 10 to 50, although this depends on the size of the structural moieties other than the polymerizable group.

[0044] The structural portion of the polyfunctional polymerizable monomer IA other than the polymerizable group typically contains atoms other than oxygen, sulfur, and nitrogen atoms. The atoms other than oxygen, sulfur, and nitrogen atoms contained in this structural portion are not particularly limited. The atoms other than oxygen, sulfur, and nitrogen atoms contained in this structural portion are typically carbon and hydrogen atoms. Furthermore, when this structural portion has a cationic or anionic structure, it may contain atoms other than oxygen, sulfur, and nitrogen atoms as counter ions. For example, when the structural portion other than the polymerizable group of the polyfunctional polymerizable monomer IA is a cationic structure having a quaternary ammonium group, it may contain halogen ions, hydroxy ions, carbonate ions, etc. as counter ions. It is preferable that the polyfunctional polymerizable monomer IA does not contain fluorine atoms in its structure. The absence of fluorine atoms tends to achieve both high ionic conductivity and high gas barrier properties.

[0045] The structural portion of the polyfunctional polymerizable monomer IA other than the polymerizable group may be linear, may have a branched structure, or may have a cyclic structure.

[0046] In the structural portion other than the polymerizable group of the polyfunctional polymerizable monomer IA, the number of atoms constituting the shortest link structure connecting two adjacent heteroatoms is preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, and even more preferably 3 or less. For example, in structures (i) and (ii) described below, the atom constituting the shortest link structure between two adjacent oxygen atoms is a carbon atom, and the number of atoms (number of carbon atoms) constituting the shortest link structure is 2. In addition, in structure (iii), the atom constituting the shortest link structure between two adjacent oxygen atoms is a carbon atom, and the number of atoms (number of carbon atoms) constituting the shortest link structure is 1. In addition, in structure (iv), when L is phenylene in which the two linking sites are in a para-position relationship with respect to each other, the atom constituting the shortest link structure between the sulfur atom and oxygen atom adjacent to each other via this phenylene is a carbon atom, and the number of atoms (number of carbon atoms) constituting the shortest link structure is 4. In addition, in structure (iv), when (-S(=O) ２ There are no atoms between the two adjacent heteroatoms in the (-S(=O) ２ In the structure (v), the number of atoms constituting the above-mentioned "shortest connected structure" is 0. In structures (v) to (vii), the atom constituting the shortest connected structure between two nitrogen atoms is a carbon atom, and the number of atoms (number of carbon atoms) constituting the shortest connected structure is 2. In structure (viii), the atom constituting the shortest connected structure between two nitrogen atoms is a carbon atom, and the number of atoms (number of carbon atoms) constituting the shortest connected structure is 6.

[0047] The structural portion of the polyfunctional polymerizable monomer IA other than the polymerizable group has two or more groups selected from oxygen atoms, sulfur atoms, and nitrogen atoms, thereby forming a highly polar structure. Specific examples of the structure having a total of two or more atoms of at least one kind of oxygen atoms, sulfur atoms, and nitrogen atoms that the structural portion has include, for example, a polyalkyleneoxy structure, a carbonate structure (—O—C(═O)—O—), a sulfonyl group (—S(═O) ２ a structure having one or more sulfonyl groups (-S(=O) ２ -) and an ether group (-O-) (for example, -O-(CH２ ) ２ -S (=O) ２ - (CH ２ ) ２ -O-), a structure having two or more imino groups (for example, a polyethyleneimine structure), a structure having two or more quaternary ammonium groups, etc. When the polyfunctional polymerizable monomer IA has two or more groups selected from oxygen atoms, sulfur atoms, and nitrogen atoms in a structural portion other than the polymerizable group, a highly polar structure is formed, and a hydroxy ion conductive polymer obtained by polymerizing this or a hydroxy ion conductive membrane containing this polymer can retain more water and have higher hydroxy ion conductivity.

[0048] The chemical formula weight of the structural portion other than the polymerizable groups of the polyfunctional polymerizable monomer IA is preferably 30 to 4,000, more preferably 50 to 3,000, even more preferably 100 to 2,000, and particularly preferably 100 to 1,000. The value obtained by dividing the "chemical formula weight of the structural portion other than the polymerizable groups" by the "total number of oxygen atoms, sulfur atoms, and nitrogen atoms contained in the structural portion other than the polymerizable groups" ("chemical formula weight of the structural portion other than the polymerizable groups" / "total number of oxygen atoms, sulfur atoms, and nitrogen atoms contained in the structural portion other than the polymerizable groups") of the polyfunctional polymerizable monomer IA is preferably 2 to 100, more preferably 2 to 80, even more preferably 4 to 60, and particularly preferably 5 to 50. The molecular weight of the polyfunctional polymerizable monomer IA is preferably 150 to 5,000, more preferably 180 to 4,500, and even more preferably 200 to 3,000.

[0049] The polyfunctional polymerizable monomer IA may have, in a structural portion other than the polymerizable group, at least one of the following structural portions (i) to (viii).

[0050]

[0051] In the above structural portions (i) to (iii) and (vii), n is an integer of 1 or more, preferably 1 to 50, more preferably 2 to 35, even more preferably 3 to 30, still more preferably 4 to 25, still more preferably 5 to 20, still more preferably 5 to 15, and particularly preferably 5 to 10.

[0052] L represents a single bond, an alkylene group, or an arylene group. When L represents an alkylene group, the alkylene group preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 3 carbon atoms, and still more preferably 1 or 2 carbon atoms. When L represents an arylene group, the arylene group preferably has 6 to 18 carbon atoms, more preferably 6 to 14 carbon atoms, and still more preferably 6 to 10 carbon atoms. The arylene group is preferably a phenylene group.

[0053] * indicates the linkage site to other structures.

[0054] The structural portion represented by formula (iv) is preferably a structure represented by the following formula (ix), and is also preferably a structural portion represented by formula (x).

[0055]

[0056] The above-mentioned constituent component (I) (a constituent unit derived from the polyfunctional polymerizable monomer IA) of the hydroxy ion conductive polymer is preferably a nonionic constituent component from the viewpoint of durability against continuous high-temperature operation under alkaline conditions. For example, the constituent component (I) preferably has at least one of the above-mentioned structural units (i) to (iv), and more preferably has structural unit (i) or (ii).

[0057] The hydroxy ion conductive polymer can have one or more types of constituent (I). Here, structural unit (vii) has one nitrogen atom in the structure enclosed in parentheses, but when constituent (I) has only structural unit (vii), n in structural unit (vii) is an integer of 2 or more, and when constituent (I) has structural unit (vii) and any of (i) to (vi) and (viii) in combination, n in structural unit (vii) is an integer of 1 or more.

[0058] Preferred specific examples of the polyfunctional polymerizable monomer IA are shown below, where n is an integer of 1 or more. In the preferred specific examples of the polyfunctional polymerizable monomer IA, the hydroxy ion may be a halogen ion (e.g., a chloride ion) or a carbonate ion.

[0059]

[0060]

[0061] The hydroxy ion conductive polymer may be a polymer composed of component (I), or may contain, in addition to component (I), component (II) derived from a monomer other than the polyfunctional polymerizable monomer IA. Component (II) can be appropriately employed as long as it does not impair the effects of the present invention. Examples include, but are not limited to, components derived from monofunctional or polyfunctional polymerizable monomers having one heteroatom in the structural portion other than the polymerizable group, components derived from monofunctional polymerizable monomers having a total of two or more heteroatoms of at least one type in the structural portion other than the polymerizable group, and components derived from monofunctional or polyfunctional polymerizable monomers having no heteroatoms in the structural portion other than the polymerizable group. The polymerizable group that can be included in the polymerizable monomer from which component (II) is derived is the same as the polymerizable group in the polyfunctional polymerizable monomer IA, and the preferred form of the polymerizable group is also the same. The polymerizable group that can be included in the polymerizable monomer from which component (II) is derived is a polymerizable group that can undergo a polymerization reaction with the polymerizable group in the polyfunctional polymerizable monomer IA.

[0062] The molecular weight of the monomer from which component (II) is derived is preferably 50 to 20,000, more preferably 100 to 10,000.

[0063] As component (II), a structure having an aryl group is preferred, and the aryl group may further have a substituent. Of these, component (II) is preferably a structure having a benzene ring, and more preferably a structure having one benzene ring. As the substituent, a group having an ammonium group, a group having a primary to tertiary amine group, or the like is preferred.

[0064] The proportion of the component (I) in the total components of the hydroxy ion conductive polymer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and may even be 50% by mass or more, or all of the components of the hydroxy ion conductive polymer may be the component (I). By increasing the proportion of the component (I), gas permeability can be further reduced.

[0065] The hydroxy ion conductive polymer can retain a large amount of water due to the highly polar structure of component (I). The water retention capacity of the hydroxy ion conductive polymer is preferably 5% by mass or more, more preferably 5 to 30% by mass, more preferably 5 to 27% by mass, even more preferably 10 to 27% by mass, and particularly preferably 18 to 25% by mass. The water retention capacity of the hydroxy ion conductive polymer can be measured using the "Water Retention Capacity Measurement Method" described below. --Measurement of Water Retention Capacity-- A 0.05 mm thick film of the hydroxy ion conductive polymer is prepared. A test piece measuring 1 cm long x 4 cm wide is cut from the hydroxy ion conductive polymer film and used as the test piece. For the test piece, the mass of the test piece after drying at 60°C under vacuum for 12 hours is defined as WA, and the mass of the test piece after 8 hours of complete immersion in a 0.2 M potassium hydroxide (KOH) aqueous solution is defined as WB. The water retention capacity is calculated using the following formula: Moisture retention capacity (%) = (WB-WA) / WB x 100

[0066] The hydroxy ion conductive polymer can be obtained by preparing a liquid containing a polymerizable monomer and polymerizing the polymerizable monomer.

[0067] When preparing a polymer having component (I), the polymerizable monomers contained in the polymerizable monomer-containing liquid (polyfunctional polymerizable monomer IA and polymerizable monomers other than polyfunctional polymerizable monomer IA that are blended as needed) are as described above. When preparing a polymer having component (I), the proportion of polyfunctional polymerizable monomer IA in all polymerizable monomers in the polymerizable monomer-containing liquid is the same as the "proportion of component (I) in all constituents of the hydroxy ion conductive polymer" described above. That is, the proportion of polyfunctional polymerizable monomer IA in all polymerizable monomers is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and may even be 50% by mass or more, and all polymerizable monomers may be polyfunctional polymerizable monomer IA.

[0068] The polymerizable monomer-containing liquid may contain a solvent or may not contain a solvent. Examples of solvents include water, isopropyl alcohol, methanol, ethanol, acetonitrile, tetrahydrofuran (THF), etc. A mixture of these may also be used. When a solvent is used, the solid content of the polymerizable monomer-containing liquid is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 75% by mass or more. It is also preferable that the polymerizable monomer-containing liquid does not contain a solvent.

[0069] The polymerizable monomer-containing liquid may contain a polymerization initiator in addition to the polymerizable monomer. When the polymerizable group of the monomer is a chain-polymerizable group, the polymerizable monomer-containing liquid usually contains a polymerization initiator. The polymerization initiator can be appropriately selected depending on the polymerizable group possessed by the polymerizable monomer. The polymerization initiator is preferably selected from photopolymerization initiators, thermal polymerization initiators, photocationic polymerization initiators, and thermal cationic polymerization initiators, and combinations of these can also be used. The polymerization initiator can be one that is commonly used for polymerizing polymerizable monomers having chain-polymerizable groups. The content of the polymerization initiator in the polymerizable monomer-containing liquid is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the total polymerizable monomers.

[0070] The method for polymerizing the polymerizable monomer is not particularly limited and can be appropriately selected depending on the type of polymerizable group possessed by the polymerizable monomer and the type of polymerization initiator. This polymerization reaction forms a hydroxy ion conductive polymer having a three-dimensional network structure. In the polymerization reaction, it is preferable to polymerize the polymerizable monomer by either light or heat. The light irradiation conditions and heating conditions can be appropriately set.

[0071] -Porous Substrate- The porous substrate is not particularly limited as long as it has pores that allow water and ions to pass through. It is preferable that the porous substrate has a large number of fine pores that penetrate from the front surface to the back surface. For example, a porous substrate that can be used as a separator for water electrolysis can be used. The constituent material of the porous substrate preferably contains a resin. Examples of constituent materials of the porous substrate include hydrocarbon polymers (preferably polyolefins, more preferably polyethylene or polypropylene), fluoropolymers (polytetrafluoroethylene, etc.), polystyrene, cellulose, polyacrylonitrile, ceramics, etc., and it is preferable to use a hydrocarbon polymer. The porous substrate may be any substrate with a porous structure. For example, it may be a membrane (porous membrane) formed by forming a resin into a film and stretching it to form pores, or it may be a woven fabric or a nonwoven fabric. When the porous substrate is a porous membrane, the porous substrate may be manufactured by a dry method or a wet method, and it is preferable that it is manufactured by a dry method. Here, dry method is the method of forming molten resin into a film, heat treating it, and then stretching it to form pores, and wet method is the method of melting resin and plasticizer (solvent), forming it into a film, stretching it, and then extracting plasticizer to form pores.In the present invention, porous substrate is preferably polyethylene porous membrane, polypropylene porous membrane, polyethylene nonwoven fabric or polytetrafluoroethylene nonwoven fabric, and more preferably polyethylene porous membrane.

[0072] The thickness of the porous substrate is sufficient as long as a hydroxy ion conductive membrane of 5 μm or more and less than 50 μm is obtained. Therefore, it is preferably 5 μm or more and less than 50 μm, more preferably 6 μm or more and 40 μm or less, even more preferably 6 μm or more and 35 μm or less, even more preferably 7 μm or more and 30 μm or less, even more preferably 7 μm or more and 25 μm or less, even more preferably 7 μm or more and 20 μm or less, and particularly preferably 7 μm or more and 15 μm or less. The thickness of the porous substrate is measured after drying the porous substrate.

[0073] The porosity of the porous substrate is preferably 20 to 80%, more preferably 25 to 70%, even more preferably 30 to 60%, even more preferably 35 to 60%, even more preferably 37 to 55%, even more preferably 38 to 50%, and particularly preferably 40 to 50%. The porosity can be determined by calculation from the apparent volume and the theoretical volume, and specifically, can be determined as follows. - Method of calculating porosity - The apparent volume of the porous substrate (the volume of the entire porous substrate including the volume of the pores) is expressed as X (cm ３ ), the weight of the porous substrate is W (g), the true density of the porous substrate is d (g / cm ３ ) and X and the theoretical volume Y (cm ３ ) (Y = W / d) and calculated using the following formula: Porosity (%) = [1 - (Y / X)] x 100

[0074] The tensile strength of the porous substrate is preferably 10 MPa or more, more preferably 20 MPa or more, and even more preferably 30 MPa or more. The tensile strength of the porous substrate is usually 400 MPa or less. Therefore, the tensile strength of the porous substrate is preferably 10 to 400 MPa, more preferably 20 to 400 MPa, and even more preferably 30 to 400 MPa. The breaking elongation of the porous substrate is preferably 10% or more, more preferably 50% or more, and even more preferably 100% or more. The breaking elongation of the porous substrate is usually 500% or less. Therefore, the breaking elongation of the porous substrate is preferably 10 to 500%, more preferably 50 to 500%, and even more preferably 100 to 500%. The tensile strength and breaking elongation of the porous substrate can be measured in the same manner as the method for evaluating mechanical properties described in the examples, except that a porous substrate is used instead of a polymer membrane and is not swollen with water.

[0075] The porous substrate is preferably surface-modified. Surface modification allows a physical or chemical bond to be formed with the hydroxy ion-conductive polymer during synthesis of the hydroxy ion-conductive polymer, thereby further enhancing the adhesion between the hydroxy ion-conductive polymer and the porous substrate. Examples of surface modification methods include corona treatment and plasma treatment. Corona treatment and plasma treatment can be performed by conventional methods.

[0076] As the porous substrate, for example, the “porous substrate film” and “laminated porous substrate film” described in paragraphs

[0018] to

[0023] of JP-A No. 2018-127506, and the “microporous membrane” described in paragraph

[0022] of JP-A No. 2022-181107 are also suitable.

[0077] The thickness of the hydroxy ion conductive membrane is preferably 5 to 50 μm, more preferably 6 to 40 μm, even more preferably 6 to 35 μm, even more preferably 7 to 30 μm, even more preferably 7 to 25 μm, even more preferably 7 to 20 μm, and particularly preferably 7 to 15 μm. The thickness of the hydroxy ion conductive membrane can be 5 to 100 μm, 10 to 100 μm, 20 to 80 μm, or even 30 to 80 μm. The thickness of the hydroxy ion conductive membrane is determined by measuring the thickness at 10 random locations and calculating the arithmetic mean of the 10 measurements. The thickness of the porous substrate described above is determined in a similar manner. When the hydroxy ion conductive membrane is a composite, the thickness of the hydroxy ion conductive membrane may be the same as or thicker than the thickness of the porous substrate. The thickness of the hydroxy ion conductive membrane may be the same as the thickness of the porous substrate during synthesis of the hydroxy ion conductive polymer, or it may be approximately 110 to 120% of the thickness of the porous substrate. When the thickness of the hydroxy ion conductive membrane is greater than that of the porous substrate, the hydroxy ion conductive polymer is introduced into the internal pores in an amount greater than the proportion of the pores (for example, the porous substrate is elongated (expanded) to fill the internal pores with a large amount of polymer, or the hydroxy ion conductive polymer is also provided on the outer surface of the porous substrate). The thickness of the hydroxy ion conductive membrane is measured after drying the hydroxy ion conductive membrane to remove water.

[0078] <Cathode Catalyst Layer> The cathode catalyst layer may be a cathode catalyst layer used in a typical membrane electrode assembly, which contains a cathode catalyst and a polymer.

[0079] The cathode catalyst can be selected depending on the application of the membrane electrode assembly of the present invention. When the membrane electrode assembly of the present invention is a membrane electrode assembly intended for water electrolysis, the cathode catalyst may be any catalyst that electrolyzes water to produce hydrogen (gas). Examples of such cathode catalysts that can be used include platinum-supported carbon particles, platinum-coated titanium, palladium-supported carbon particles, cobalt glyoxime, and nickel glyoxime. When the membrane electrode assembly of the present invention is a membrane electrode assembly intended for fuel cell use, the cathode catalyst may be any catalyst that reacts with oxygen to produce water. Examples of such cathode catalysts that can be used include platinum-supported carbon particles, platinum-coated titanium, palladium-supported carbon particles, cobalt glyoxime, and nickel glyoxime.

[0080] The cathode catalyst is preferably in particulate form. In the cathode catalyst layer, the particulate cathode catalyst is preferably bound by the polymer.

[0081] As the polymer contained in the cathode catalyst layer, for example, the polymers described above as the hydroxy ion conductive polymer can be used.

[0082] The concentration of the polymer contained in the cathode catalyst layer is not particularly limited. When the polymer contained in the cathode catalyst layer satisfies the above relationships (Ri) and (Rii), the concentration of the polymer contained in the cathode catalyst layer is preferably 1 to 30 mass %, more preferably 1 to 25 mass %, even more preferably 3 to 25 mass %, still more preferably 5 to 25 mass %, and particularly preferably 10 to 20 mass %, of the solid content in the catalyst layer.

[0083] The cathode catalyst layer can be formed by preparing an ink for forming a catalyst layer containing a cathode catalyst, a monomer for deriving the polymer, and, if necessary, a solvent, and applying and drying the ink.

[0084] <Anode Catalyst Layer> The anode catalyst layer can be an anode catalyst layer that contains an anode catalyst and a polymer and can be used in a typical membrane electrode assembly.

[0085] The anode catalyst can be selected depending on the application of the membrane electrode assembly of the present invention. When the membrane electrode assembly of the present invention is intended for water electrolysis, the anode catalyst may be one that electrolyzes water to produce oxygen and water. Examples of such anode catalyst include iridium oxide, iridium oxide-coated titanium, iridium ruthenium cobalt oxide, iridium ruthenium tin oxide, iridium ruthenium iron oxide, iridium ruthenium nickel oxide, iridium tin oxide, iridium zirconium oxide, ruthenium titanium oxide, ruthenium zirconium oxide, ruthenium tantalum oxide, and ruthenium titanium cerium oxide. When the membrane electrode assembly of the present invention is intended for fuel cell applications, the anode catalyst may be one that reacts with hydrogen to produce protons. Examples of such anode catalyst include platinum, platinum-supported carbon, and nickel oxide.

[0086] The anode catalyst is preferably in particulate form. In the anode catalyst layer, the particulate cathode catalyst is preferably bound by the polymer.

[0087] As the polymer contained in the anode catalyst layer, for example, the polymers described above as the hydroxy ion conductive polymer can be used.

[0088] The concentration of the polymer contained in the anode catalyst layer is not particularly limited. When the polymer contained in the anode catalyst layer satisfies the above relationships (Ri) and (Rii), the concentration of the polymer contained in the anode catalyst layer is preferably 1 to 30 mass %, more preferably 1 to 25 mass %, still more preferably 3 to 25 mass %, still more preferably 5 to 25 mass %, and still more preferably 10 to 20 mass %, of the solid content in the catalyst layer.

[0089] The anode catalyst layer can be formed by preparing an ink for forming a catalyst layer containing an anode catalyst, a monomer that leads to the above polymer, and, if necessary, a solvent, and applying and drying this ink.

[0090] <Gas Diffusion Layer> The gas diffusion layer can be a layer that can transport gas and moisture and has electronic conductivity. The gas diffusion layer can be a gas diffusion layer used in a typical membrane electrode assembly. Examples of materials that can be used for the gas diffusion layer include carbon fiber nonwoven fabric, carbon paper, carbon plate, stainless steel (SUS) fiber nonwoven fabric, stainless steel sintered body, titanium (Ti) fiber nonwoven fabric, titanium sintered body, nickel (Ni) fiber nonwoven fabric, nickel sintered body, and materials in which each of these substrates is coated with platinum or gold.

[0091] The membrane electrode assembly can be formed by applying a catalyst layer-forming ink to a hydroxy ion conductive membrane, or by bonding a pre-formed catalyst layer to a hydroxy ion conductive membrane. When a gas diffusion layer is provided on the membrane electrode assembly, the catalyst layer-forming ink may be applied to one side of the gas diffusion layer to form a catalyst layer-attached gas diffusion layer, which may then be bonded to the hydroxy ion conductive membrane.

[0092] The lower the ionic resistance of the membrane electrode assembly, the more preferable. ２ Preferably, it is 1 Ωcm or less. ２ More preferably, it is 0.5 Ωcm or less. ２ The ionic resistance is usually 0.01 Ωcm or less. ２ Therefore, the ionic resistance is 0.01 to 2 Ωcm ２ is preferably 0.01 to 1 Ωcm ２ More preferably, 0.01 to 0.5 Ωcm ２ The ionic resistance Rs can be calculated from the ionic conductivity σ of the membrane electrode assembly and the thickness L (cm) of the membrane electrode assembly by the following formula: Ionic resistance Rs (Ωcm ２ ) = thickness L (cm) of membrane / electrode assembly / ionic conductivity σ (S / cm) The ionic conductivity σ of the membrane / electrode assembly can be measured in the same manner as the ionic conductivity of the hydroxy ion conductive membrane. The thickness L of the membrane / electrode assembly is determined in the same manner as the thickness of the hydroxy ion conductive membrane.

[0093] The hydroxy ion conductive membrane preferably has a differential voltage of 0.50 V or less, more preferably 0.30 V or less, and even more preferably 0.25 V or less, as measured by the method described in the Examples ("Resistance Evaluation") below. The differential voltage is usually greater than 0.00 V. Therefore, the differential voltage is preferably greater than 0.00 V and 0.50 V or less, more preferably greater than 0.00 V and 0.30 V or less, and even more preferably greater than 0.00 V and 0.25 V or less. The differential voltage can be measured by the method described in the Examples in a state where the hydroxy ion conductive membrane is incorporated into a water electrolysis cell.

[0094] The hydrogen gas permeability (permeability of hydrogen gas generated on the cathode side to the anode side) of the membrane electrode assembly is preferably less than 1.000 vol% (less than 1 vol%), more preferably less than 0.800 vol%, even more preferably less than 0.500 vol%, and even more preferably less than 0.100 vol%. The hydrogen gas permeability is usually preferably 0.000 vol% (below the detection limit). Therefore, the gas permeability is preferably 0.000 to less than 1.000 vol%, more preferably 0.000 to less than 0.800 vol%, even more preferably 0.000 to less than 0.500 vol%, and even more preferably 0.000 to less than 0.100 vol%. The gas permeability can be measured by the method described in the Examples after incorporating the membrane electrode assembly into a water electrolysis cell.

[0095] [Method for producing hydrogen] The method for producing hydrogen of the present invention is the same as a conventional method for producing hydrogen (water electrolysis) except that the membrane electrode assembly of the present invention is used as the membrane electrode assembly. In the method for producing hydrogen of the present invention, the membrane electrode assembly of the present invention can be configured to have high hydroxy ion conductivity, and in that case, water electrolysis can be performed using not only a high-concentration alkaline aqueous solution but also a lower-concentration alkaline aqueous solution or water.

[0096] [Hydrogen Production System] The hydrogen production system of the present invention is a system (apparatus) suitable for carrying out the hydrogen production method of the present invention. The hydrogen production system of the present invention is similar to a conventional hydrogen production system except that it includes the membrane electrode assembly of the present invention as the membrane electrode assembly. The hydrogen production system of the present invention can be, for example, a water electrolysis system in which the membrane electrode assembly of the present invention is further combined with components used in general water electrolysis, such as bipolar plates.

[0097] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited thereto.

[0098] Example 1 A membrane electrode assembly having the following components and a water electrolysis cell 101 having the membrane electrode assembly were fabricated as follows.

[0099] 1. Preparation of Gas Diffusion Layer 1-a1G with Anode Catalyst Layer 1) Preparation of Ink a1 for Forming Anode Catalyst Layer A 200 mL three-neck flask was charged with 61.5 g of pure water, 18.5 g of isopropyl alcohol, 1.2 g of Monomer m1, and 2.8 g of Monomer m2 to prepare a solution. The mass ratio of Monomer m1 to Monomer m2 was 30:70. Under yellow light, 0.1 g of 2-hydroxy-2-methylpropiophenone (manufactured by TCI) (hereinafter also referred to as "HMP") and 0.1 g of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (manufactured by TCI) (hereinafter also referred to as "EPTBP") were further added to prepare Solution a1. Under yellow light, 0.84 g of liquid a1 and 0.23 g of iridium oxide powder (TEC77100 (trade name), manufactured by Tanaka Kikinzoku Co., Ltd., iridium content 75% by mass) were placed in a 5 mL vial and mixed. During mixing, an ultrasonic homogenizer UH-300 (trade name, manufactured by SMT Corporation) was used to disperse the mixture at a power of 30 W for 2 minutes, cool it at 5°C for 10 minutes, and then disperse it again at a power of 30 W for 2 minutes (a dispersion-cooling-dispersion cycle), which was repeated three times. In this way, ink a1 for forming an anode catalyst layer with a solids content of 25% by mass was prepared. 2) Preparation of gas diffusion layer 1-a1G with anode catalyst layer Under yellow light, ink a1 for forming an anode catalyst layer was applied to the microporous layer side of a carbon fiber nonwoven fabric (GDL-39BB (trade name), manufactured by SGL) having a microporous layer using an applicator until the amount of iridium oxide applied was 0.5 mg / cm. ２ After air drying, the coating was carried out at 100 mJ / cm at 365 nm. ２ A UV irradiator (EXECURE3000 (trade name), manufactured by HOYA Corporation) adjusted to an integrated light dose of 800 mJ / cm 2 was used. ２ The monomer was polymerized by irradiating with UV light so that the anode catalyst layer 1-a1G had an 8 μm-thick anode catalyst layer 1-a1 on the microporous layer.

[0100] 2. Preparation of Gas Diffusion Layer 1-b1G with Cathode Catalyst Layer 1) Preparation of Ink b1 for Forming Cathode Catalyst Layer A 200 mL three-neck flask was charged with 58.1 g of pure water, 17.4 g of isopropyl alcohol, 1.2 g of monomer m1, and 2.8 g of monomer m2 to prepare a solution. The mass ratio of monomer m1 to monomer m2 was 30:70. Under yellow light, 0.1 g of HMP and 0.1 g of EPTBP were further added to prepare solution b1. Under yellow light, 0.8 g of solution b1 and 0.09 g of platinum carbon powder (TEC10E50E (trade name), manufactured by Tanaka Kikinzoku Co., Ltd., platinum content 47% by mass) were mixed in a 5 mL vial. During mixing, an ultrasonic homogenizer UH-300 (trade name, manufactured by SMT Corporation) was used, and the mixture was dispersed at a power of 30 W for 2 minutes, cooled at 5°C for 10 minutes, and then dispersed again at a power of 30 W for 2 minutes (a dispersion-cooling-dispersion cycle) was repeated three times. In this way, an ink b1 for forming a cathode catalyst layer with a solids content of 15% by mass was prepared.

[0101] 2) Preparation of cathode catalyst layer-attached gas diffusion layer 1-b1G Under yellow light, the cathode catalyst layer-forming ink b1 was applied to the microporous layer side of a carbon fiber nonwoven fabric (manufactured by SGL, GDL-39BB (product name)) with a platinum carbon powder coating amount of 0.5 mg / cm using an applicator. ２ After air drying, the coating was carried out at 100 mJ / cm at 365 nm. ２ A UV irradiator (EXECURE3000 (trade name), manufactured by HOYA Corporation) adjusted to an integrated light dose of 800 mJ / cm 2 was used. ２ The monomer was polymerized by irradiating with UV light so that the temperature reached 100° C. Thus, a gas diffusion layer 1-b1G with a cathode catalyst layer was obtained, which had a cathode catalyst layer 1-b1 with a thickness of 20 μm on the microporous layer.

[0102] 3. Preparation of Hydroxy Ion Conductive Membrane 1-c1 1) Preparation of Monomer Composition c1 A 200 mL three-neck flask was charged with 10.0 g of pure water, 3.0 g of isopropyl alcohol, 15.6 g of monomer m1, and 36.4 g of monomer m2 to prepare a solution. The mass ratio of monomer m1 to monomer m2 was 30:70. Under yellow light, 1.0 g of HMP and 1.0 g of EPTBP were further added to prepare a monomer composition c1 with a solids content of 80 mass%. 2) Preparation of Hydroxy Ion Conductive Membrane 1-c1 Under yellow light, an appropriate amount of monomer composition c1 was placed on a 10 μm thick polyethylene terephthalate (PET) film, applied with an applicator, and then air-dried. 100 mJ / cm at 365 nm ２ A UV irradiator (EXECURE3000 (trade name), manufactured by HOYA Corporation) adjusted to an integrated light dose of 300 mJ / cm 2 was used. ２ The monomer was polymerized by irradiating with UV light so that the PET film was removed. In this way, a hydroxy ion conductive membrane 1-c1 with a thickness of 50 μm was produced.

[0103] 4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101. The anode catalyst layer-attached gas diffusion layer 1-a1G and the cathode catalyst layer-attached gas diffusion layer 1-b1G were each 1 cm ２ The plates were punched out to the same shape, and stacked with each catalyst layer side facing inward, sandwiching the hydroxy ion conductive membrane 1-c1, and then pressurized at a surface pressure of 4 MPa. The pressurized stack was sandwiched between two Ni bipolar plates having flow channels and constrained with bolts to maintain a confining pressure of 1 MPa. In this manner, a water electrolysis cell 101 was obtained, which has the same layer structure as the water electrolysis cell 10 shown in FIG. 1 , which has a layer structure of bipolar plate-gas diffusion layer-anode catalyst layer-hydroxy ion conductive membrane-cathode catalyst layer-gas diffusion layer-bipolar plate. This water electrolysis cell 101 has a structure including a membrane electrode assembly D-1 (anode catalyst layer-hydroxy ion conductive membrane-cathode catalyst layer, or gas diffusion layer-anode catalyst layer-hydroxy ion conductive membrane-cathode catalyst layer-gas diffusion layer).

[0104] Example 2 1. Preparation of gas diffusion layer with anode catalyst layer 2-a1G In "1. Preparation of gas diffusion layer with anode catalyst layer 1-a1G" of Example 1, the following modifications were made: instead of using monomer m1 and monomer m2, 4.0 g of monomer m3 (Denacol EX-832 (trade name), manufactured by Nagase ChemteX Corporation) was used; instead of using HMP and EPTBP, 0.4 g of diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate (manufactured by TCI) (hereinafter also referred to as "DPPSH") was used as the polymerization initiator; the ink for forming an anode catalyst layer had a solid content of 45 mass%; and the cumulative light intensity during polymerization was 600 mJ / cm. ２ A gas diffusion layer with an anode catalyst layer 2-a1G having an anode catalyst layer 2-a1 was obtained in the same manner as in "1. Preparation of gas diffusion layer with anode catalyst layer 1-a1G" in Example 1, except that the anode catalyst layer 2-a1 was irradiated with UV light so ...

[0105] 2. Preparation of gas diffusion layer 2-b1G with cathode catalyst layer In "2. Preparation of gas diffusion layer 1-b1G with cathode catalyst layer" of Example 1, 4.0 g of monomer m3 was used without using monomer m1 and monomer m2, 0.4 g of DPPSH was used as the polymerization initiator without using HMP or EPTBP, the ink for forming a cathode catalyst layer had a solid content of 35 mass%, and the cumulative light intensity during polymerization was 600 mJ / cm ２ A gas diffusion layer with a cathode catalyst layer 2-b1G having a cathode catalyst layer 2-b1 was obtained in the same manner as in "2. Preparation of gas diffusion layer with cathode catalyst layer 1-b1G" in Example 1, except that the cathode catalyst layer 2-b1 was irradiated with UV light so that the temperature became 100°C and then heated at 100°C for 15 minutes.

[0106] 3. Preparation of Hydroxy Ion Conductive Membrane 2-c1 72.0 g of monomer m3 was placed in a 200 mL three-neck flask to prepare a solution. Under yellow light, 2.0 g of DPPSH was further added as a polymerization initiator to prepare a monomer composition c2 with a solid content of 100 mass %. Under yellow light, an appropriate amount of monomer composition c2 was placed on a 10 μm thick polyethylene terephthalate (PET) film, applied with an applicator, and then air-dried. 100 mJ / cm at 365 nm ２A UV irradiator (EXECURE3000 (trade name), manufactured by HOYA Corporation) adjusted to an integrated light dose of 300 mJ / cm 2 was used. ２ The film was then irradiated with UV light so that the temperature reached 80°C, and heated at 80°C for 5 minutes to polymerize the monomer. The PET film was then removed. In this way, a hydroxy ion conductive membrane 2-c1 was produced.

[0107] 4. Fabrication of membrane electrode assembly D-2 and water electrolysis cell 102 A membrane electrode assembly D-2 and a water electrolysis cell 102 were fabricated in the same manner as in "4. Fabrication of membrane electrode assembly D-1 and water electrolysis cell 101" in Example 1, except that a gas diffusion layer with an anode catalyst layer 2-a1G, a gas diffusion layer with a cathode catalyst layer 2-b1G, and a hydroxy ion conductive membrane 2-c1 were used.

[0108] Example 3 A membrane electrode assembly D-3 and a water electrolysis cell 103 were produced in the same manner as in "4. Production of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that the hydroxy ion conductive membrane 2-c1 of Example 2 was used instead of the hydroxy ion conductive membrane 1-c1 in "4. Production of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1.

[0109] [Example 4] An anode catalyst layer-equipped gas diffusion layer 4-a1G having an anode catalyst layer 4-a1 was obtained in the same manner as in "1. Preparation of anode catalyst layer-equipped gas diffusion layer 1-a1G" of Example 1, except that in "1. Preparation of anode catalyst layer-equipped gas diffusion layer 1-a1G" of Example 1, the blending amounts of the liquid a1 and iridium oxide were changed so as to satisfy the "monomer amount" and "catalyst amount" respectively shown in Table 1. A membrane electrode assembly D-4 and a water electrolysis cell 104 were prepared in the same manner as in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, the anode catalyst layer-equipped gas diffusion layer 4-a1G was used instead of the anode catalyst layer-equipped gas diffusion layer 1-a1G.

[0110] [Example 5] An anode catalyst layer-equipped gas diffusion layer 5-a1G having an anode catalyst layer 5-a1 was obtained in the same manner as in "1. Preparation of anode catalyst layer-equipped gas diffusion layer 1-a1G" of Example 1, except that in "1. Preparation of anode catalyst layer-equipped gas diffusion layer 1-a1G" of Example 1, the blending amounts of liquid a1 and iridium oxide were changed so as to satisfy the "monomer amount" and "catalyst amount" respectively set forth in Table 1. A cathode catalyst layer-equipped gas diffusion layer 5-b1G having a cathode catalyst layer 5-b1 was obtained in the same manner as in "2. Preparation of cathode catalyst layer-equipped gas diffusion layer 1-b1G" of Example 1, except that in "2. Preparation of cathode catalyst layer-equipped gas diffusion layer 1-b1G" of Example 1, the blending amounts of liquid b1 and platinum carbon powder were changed so as to satisfy the "monomer amount" and "catalyst amount" respectively set forth in Table 1. A membrane electrode assembly D-5 and a water electrolysis cell 105 were produced in the same manner as in "4. Production of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that the anode catalyst layer-equipped gas diffusion layer 1-a1G was replaced with an anode catalyst layer-equipped gas diffusion layer 5-a1G, and the cathode catalyst layer-equipped gas diffusion layer 1-b1G was replaced with a cathode catalyst layer-equipped gas diffusion layer 5-b1G.

[0111] [Example 6] In "2. Preparation of cathode catalyst layer-attached gas diffusion layer 2-b1G" of Example 2, an integrated light amount of 300 mJ / cm ２ A cathode catalyst layer-equipped gas diffusion layer 6-b1G having a cathode catalyst layer 6-b1 was obtained in the same manner as in "2. Preparation of cathode catalyst layer-equipped gas diffusion layer 2-b1G" of Example 2, except that the cathode catalyst layer-equipped gas diffusion layer 1-b1G was replaced with the cathode catalyst layer-equipped gas diffusion layer 6-b1G in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, and a membrane electrode assembly D-6 and a water electrolysis cell 106 were prepared in the same manner as in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that the cathode catalyst layer-equipped gas diffusion layer 6-b1G was used instead of the cathode catalyst layer-equipped gas diffusion layer 1-b1G in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1.

[0112] [Example 7] In "1. Preparation of a gas diffusion layer 2-a1G with an anode catalyst layer" of Example 2, the cumulative light amount during polymerization was 300 mJ / cm ２ A gas diffusion layer with an anode catalyst layer 7-a1G having an anode catalyst layer 7-a1 was obtained in the same manner as in "1. Preparation of gas diffusion layer with an anode catalyst layer 2-a1G" of Example 2, except that the gas diffusion layer with an anode catalyst layer 7-a1G was used instead of the gas diffusion layer with an anode catalyst layer 1-a1G in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1. A membrane electrode assembly D-7 and a water electrolysis cell 107 were prepared in the same manner as in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that the gas diffusion layer with an anode catalyst layer 7-a1G was used instead of the gas diffusion layer with an anode catalyst layer 1-a1G in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1.

[0113] [Comparative Example 1] In "3. Preparation of hydroxy ion conductive film 1-c1" of Example 1, the cumulative light amount was 800 mJ / cm ２ A hydroxy ion conductive membrane x1-c1 was prepared in the same manner as in "3. Preparation of hydroxy ion conductive membrane 1-c1" of Example 1, except that the hydroxy ion conductive membrane x1-c1 was used instead of the hydroxy ion conductive membrane 1-c1 in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1. A membrane electrode assembly D-c1 and a water electrolysis cell c101 were prepared in the same manner as in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1, except that the hydroxy ion conductive membrane x1-c1 was used instead of the hydroxy ion conductive membrane 1-c1 in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" of Example 1.

[0114] Comparative Example 2 In "1. Preparation of gas diffusion layer 1-a1G with anode catalyst layer" of Example 1, the cumulative light amount was 300 mJ / cm ２ An anode catalyst layer-equipped gas diffusion layer x1-a1G having an anode catalyst layer x1-a1 was produced in the same manner as in "1. Production of anode catalyst layer-equipped gas diffusion layer 1-a1G" of Example 1, except that in "2. Production of cathode catalyst layer-equipped gas diffusion layer 1-b1G" of Example 1, the polymer was irradiated with UV light so that the cumulative light intensity was 300 mJ / cm ２A gas diffusion layer with a cathode catalyst layer x1-b1G having a cathode catalyst layer x1-b1 was prepared in the same manner as in "2. Preparation of gas diffusion layer with a cathode catalyst layer 1-b1G" in Example 1, except that in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" in Example 1, the gas diffusion layer with an anode catalyst layer x1-a1G and the gas diffusion layer with a cathode catalyst layer x1-b1G were used instead of the gas diffusion layer with an anode catalyst layer 1-a1G and the gas diffusion layer with a cathode catalyst layer 1-b1G in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" in Example 1.

[0115] Comparative Example 3 A gas diffusion layer x3-a1G with an anode catalyst layer having an anode catalyst layer x3-a1 was obtained in the same manner as in "1. Preparation of gas diffusion layer with an anode catalyst layer 2-a1G" of Example 2, except that 3.6 g of monomer m3 and 0.4 g of monomer m4 (Denacol EX-861 (trade name), manufactured by Nagase ChemteX Corporation) (the mass ratio of monomer m3 to monomer m4 was 90:10) were used in "1. Preparation of gas diffusion layer with an anode catalyst layer 2-a1G" of Example 2. A cathode catalyst layer-attached gas diffusion layer x3-b1G having a cathode catalyst layer x3-b1 was obtained in the same manner as in "2. Preparation of cathode catalyst layer-attached gas diffusion layer 2-b1G" of Example 2, except that 3.6 g of monomer m3 and 0.4 g of monomer m4 (mass ratio of monomer m3 to monomer m4 was 90:10) were used in "2. Preparation of cathode catalyst layer-attached gas diffusion layer 2-b1G" of Example 2. In "3. Preparation of hydroxy ion conductive membrane 2-c1" of Example 2, an integrated light intensity of 600 mJ / cm was used during polymerization. ２A hydroxy ion conductive membrane x3-c1 was prepared in the same manner as in "3. Preparation of hydroxy ion conductive membrane 2-c1" in Example 2, except that the anode catalyst layer-equipped gas diffusion layer x3-a1G, cathode catalyst layer-equipped gas diffusion layer x3-b1G, and hydroxy ion conductive membrane x3-c1 were used instead of the anode catalyst layer-equipped gas diffusion layer 1-a1G, cathode catalyst layer-equipped gas diffusion layer 1-b1G, and hydroxy ion conductive membrane 1-c1 in "4. Preparation of membrane electrode assembly D-1 and water electrolysis cell 101" in Example 1.

[0116] Comparative Example 4 In "3. Preparation of hydroxy ion conductive membrane 2-c1" of Example 2, 64.8 g of monomer m3 and 7.2 g of monomer m4 (mass ratio of monomer m3 to monomer m4 was 90:10) were used, and the cumulative light dose during polymerization was 600 mJ / cm ２ A hydroxy ion conductive membrane x4-c1 was prepared in the same manner as in "3. Preparation of hydroxy ion conductive membrane 2-c1" of Example 2, except that the hydroxy ion conductive membrane x4-c1 was used instead of the hydroxy ion conductive membrane 2-c1 in "4. Preparation of membrane electrode assembly D-2 and water electrolysis cell 102" of Example 2.

[0117] The hydroxy ion conductive membranes obtained above all had an ion conductivity of 0.1 mS / cm to 10 S / cm.

[0118] The materials used in preparing the membrane electrode assembly and water electrolysis cell, the amounts of each component, and the polymerization conditions are summarized in Table 1. The structures of the monomers used are also shown below.

[0119]

[0120]

[0121] [Evaluation of Mechanical Properties] The tensile strength (a) and breaking elongation (b) of the water-swollen bodies of the polymers contained in the cathode catalyst layer and the anode catalyst layer, and the tensile strength (c) and breaking elongation (d) of the water-swollen bodies of the hydroxy ion-conductive polymer constituting the hydroxy ion-conductive membrane were measured as follows. The tensile strength and breaking elongation were measured using an MX-500N motorized measuring stand and a ZTA series force gauge (both trade names, manufactured by Imada Co., Ltd.). Membranes of the polymers contained in the cathode catalyst layer and the anode catalyst layer, and the hydroxy ion-conductive polymer constituting the hydroxy ion-conductive membrane were prepared as follows. The polymers from each layer were dissolved and filtered, and the resulting dissolved polymer was applied to a substrate and dried to obtain a membrane of the polymer. If it is difficult to form a membrane of the polymer, the following method can be used. In the case of the polymers contained in the cathode catalyst layer and the anode catalyst layer, a membrane of the polymer can be obtained by synthesizing the polymer without adding an anode catalyst or a cathode catalyst. Furthermore, in the case of a hydroxy ion conductive polymer constituting a hydroxy ion conductive membrane, a membrane of the polymer alone can be obtained by synthesizing the polymer without using a porous substrate. When the hydroxy ion conductive membrane is in the form of a membrane (single membrane) formed of a hydroxy ion conductive polymer without including a porous substrate, this membrane can be used as is. The membrane of the polymer alone obtained above was cut into 5 mm x 15 mm strips to obtain test specimens. This test specimen was immersed in water at room temperature (25°C) for a day and night so that the entire specimen was immersed, to obtain a water-swollen test specimen. Two parallel benchmark lines were marked at 5 mm intervals in the center of the obtained test specimen, and the specimen was clamped at both ends and pulled at a rate of 0.5 mm / min. The maximum tensile stress at this time was defined as the tensile strength. The breaking elongation was calculated using the following formula. In this way, the tensile strength and breaking elongation were measured. Breaking elongation (%) = 100 x (L - L ０ ) / L ０ L ０ : Gauge distance before test, L: Gauge distance at break

[0122] The tensile strength and elongation at break of each polymer are shown in Table 2 below. As shown in Table 1, in the formation of anode catalyst layer 1-a1, cathode catalyst layer 1-b1, anode catalyst layer 4-a1, anode catalyst layer 5-a1, cathode catalyst layer 5-b1, and hydroxy ion conductive membrane x1-c1, the same monomer species and amounts were used and polymerization was carried out by exposure under the same exposure conditions. Therefore, the polymers contained in anode catalyst layer 1-a1, cathode catalyst layer 1-b1, anode catalyst layer 4-a1, anode catalyst layer 5-a1, cathode catalyst layer 5-b1, and hydroxy ion conductive membrane x1-c1 are substantially the same. Similarly, the polymers contained in the anode catalyst layer 2-a1, cathode catalyst layer 2-b1, and hydroxy ion conductive membrane x3-c1 are substantially the same as each other, the polymers contained in the anode catalyst layer x1-a1, cathode catalyst layer x1-b1, and hydroxy ion conductive membrane 1-c1 are also substantially the same as each other, the anode catalyst layer 7-a1, cathode catalyst layer 6-b1, and hydroxy ion conductive membrane 2-c1 are also substantially the same as each other, and the polymers contained in the anode catalyst layer x3-a1, cathode catalyst layer x3-b1, and hydroxy ion conductive membrane x4-c1 are also substantially the same as each other. For this reason, the obtained polymer numbers P1 to P5 are listed in the "Polymer" section of Table 1, and the tensile strength, breaking elongation, glass transition temperature, and molecular weight of each polymer are summarized in Table 2.

[0123] [Measurement of Glass Transition Temperature] The glass transition temperatures (e) of the polymers contained in the cathode catalyst layer and the anode catalyst layer and the glass transition temperature (f) of the polymer constituting the hydroxy ion conductive membrane were measured according to the method described above.

[0124] [Measurement of Molecular Weight] The molecular weight of the hydroxy ion conductive polymer was measured according to the method described above.

[0125] [Evaluation of Water Electrolysis Cell] A 0.5 M aqueous potassium hydroxide (KOH) solution heated to 60°C was supplied to the cathode catalyst layer and the anode catalyst layer of each of the water electrolysis cells obtained above at a flow rate of 10 mL / min, while being supplied with a current of 0.1 A / cm ２The water electrolysis cells after initial energization were used to carry out the various evaluations described below.

[0126] <Resistance Evaluation> The above initial current (0.1 A / cm ２ The initial voltage (V0) of each water electrolysis cell immediately after the initial energization (energization for 4 hours at 1.0 A / cm) was measured, and a 0.2 M KOH aqueous solution heated to 60°C was supplied to each water electrolysis cell after the initial energization. ２ Current was applied at 100 V for 10 minutes and the voltage (V1) immediately thereafter was measured. From the measured values, V1 - V0 was calculated as the differential voltage. The obtained differential voltage was applied to the following evaluation criteria to evaluate the resistance. The higher the differential voltage, the higher the resistance. -Evaluation criteria for differential voltage- A: More than 0.00 V and 0.25 V or less B: More than 0.25 V and 0.30 V or less C: More than 0.30 V and 0.50 V or less D: More than 0.50 V

[0127] <Evaluation of Hydrogen Gas Permeability> After the initial energization, a 0.2 M KOH aqueous solution heated to 60°C was supplied to each water electrolysis cell, and a current of 0.1 A / cm ２ A current was applied for 10 minutes at 10°C, and the gas recovered from the flow path of the bipolar plate on the anode side was analyzed to evaluate the extent to which hydrogen gas generated on the cathode side permeated to the anode side. Specifically, the gas recovered from the flow path of the bipolar plate on the anode side during the above 10-minute current application was cooled to 10°C, and after removing water vapor, the recovered gas was passed through a gas chromatograph (GC3210G (trade name), manufactured by GL Sciences, column: MS13X (trade name)) to measure the ratio (vol%) of hydrogen gas contained in the recovered gas. The obtained hydrogen gas ratio was evaluated according to the following evaluation criteria. -Evaluation criteria for hydrogen gas permeability (hydrogen gas ratio)- A: Less than 0.100 vol% B: 0.100 vol% or more and less than 0.500 vol% C: 0.500 vol% or more and less than 1.000 vol% D: 1.000 vol% or more

[0128] <Evaluation of repeated current durability> After the initial current application, each water electrolysis cell was subjected to a current application test at 0.1 A / cm while supplying a 0.2 M KOH aqueous solution heated to 60°C. ２After energizing for 1 hour, the solution transfer and energization were stopped and the sample was left for 3 hours. This constitutes one cycle, and energization and de-energization were repeated 500 times. The voltage after 1 cycle and the voltage after 500 cycles were measured to determine the rate of change in voltage. The obtained rate of change in voltage was applied to the following evaluation criteria to evaluate the durability of repeated energization. Rate of change in voltage = [(voltage after 500 cycles - voltage after 1 cycle) / voltage after 1 cycle] x 100 (%) - Evaluation criteria for durability of repeated energization - A: 0.05% or less B: More than 0.05% and 1.00% or less C: More than 1.00% and 2.00% or less D: More than 2.00% and 4.00% or less E: More than 4.00%

[0129]

[0130]

[0131]

[0132] <Notes for Table 1> "-": Indicates that the component was not used. "% by mass" for Monomer 1 and Monomer 2: In the formation of each catalyst layer, this indicates the proportion (% by mass) of each monomer relative to 100% by mass of all polymerizable monomers contained in the ink. In the formation of a hydroxy ion conductive membrane, this indicates the proportion (% by mass) of each monomer relative to 100% by mass of all polymerizable monomers contained in the monomer composition. "Parts by mass" in the monomer amount: Indicates the total amount (parts by mass) of polymerizable monomers when the total amount of all polymerizable monomers and the catalyst amount is 100 parts by mass. Therefore, in the formation of a hydroxy ion conductive membrane, the amount of monomer is 100 parts by mass. "Parts by mass" in the monomer amount is the mass % of the polymer contained in each of the cathode catalyst layer, anode catalyst layer, and conductive layer. "Parts by mass" in the catalyst amount: Indicates the amount (parts by mass) of the catalyst when the total amount of all polymerizable monomers and the catalyst amount is 100 parts by mass. HMP: 2-hydroxy-2-methylpropiophenone EPTBP: ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate DPPSH: diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate IrO ２: Iridium oxide Pt / C: Platinum carbon powder "Solid content": For each catalyst layer, it indicates the solid content contained in the ink. For the hydroxy ion conductive membrane, it indicates the solid content contained in the monomer composition. Polymerization method: When the monomer polymerization was carried out by UV exposure, it is indicated as "UV", and when it was carried out by heating, it is indicated as "thermal". Polymerization conditions: The conditions for UV exposure or heating are indicated. When both UV exposure and heating were carried out, the UV exposure conditions are indicated in the upper row and the heating conditions in the lower row.

[0133] Table 2 shows the properties of each polymer.

[0134]

[0135] Table 3 shows the evaluation results of the membrane electrode assembly and the water electrolysis cell.

[0136]

[0137] <Notes for Table 3> (Ri): * indicates that only the combination of the polymer contained in the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfies the relationship (Ri). (Ri): ** indicates that only the combination of the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane satisfies the relationship (Ri).

[0138] In the membrane electrode assemblies of Comparative Examples 1 and 2, the same hydroxy ion conductive polymer is used as the polymer contained in the cathode catalyst layer, the polymer contained in the anode catalyst layer, and the polymer constituting the hydroxy ion conductive membrane, and therefore the relationship (Ri) and (Rii) are not satisfied. When these membrane electrode assemblies were used as water electrolysis cells, the voltage change rate exceeded 2.00% in a repeated current durability test, resulting in poor repeated durability. Furthermore, in the membrane electrode assembly of Comparative Example 1, the proportion of hydrogen gas contained in the chain gas recovered from the anode side was 1.000 vol% or more, resulting in poor (high) gas permeability. In the membrane electrode assemblies of Comparative Examples 3 and 4, the polymer contained in the cathode catalyst layer and the polymer constituting the hydroxy ion conductive membrane, and the polymer contained in the anode catalyst layer and the polymer constituting the hydroxy ion conductive membrane, satisfy only one of the relationships (Ri) or (Rii). The membrane / electrode assembly of Comparative Example 3, which satisfied the relationship (Rii) but did not satisfy the relationship (Ri), had a hydrogen gas ratio of 1.000 vol% or more in the chain gas recovered from the anode side, resulting in poor (high) gas permeability. Furthermore, when used as a water electrolysis cell, the voltage change rate exceeded 2.00% in a repeated current durability test, resulting in poor repeated durability. On the other hand, the membrane / electrode assembly of Comparative Example 4, which satisfied the relationship (Ri) but did not satisfy the relationship (Rii), when used as a water electrolysis cell, the voltage change rate exceeded 4.00% in a repeated current durability test, resulting in poor repeated durability. In contrast, in the membrane / electrode assemblies of Examples 1 to 7, the polymer contained in the cathode catalyst layer and the hydroxy ion conductive membrane-constituting polymer, and / or the polymer contained in the anode catalyst layer and the hydroxy ion conductive membrane-constituting polymer, satisfied the relationships (Ri) and (Rii). When these membrane electrode assemblies were used in water electrolysis cells, the hydrogen gas ratio was less than 1.000 vol %, the differential voltage was 0.50 V or less, the rate of change in a repeated current test was 2% or less, the gas permeability and resistance were low, and the repeated current durability was excellent. The membrane electrode assembly of Example 2 is an example in which a hydroxy ion conductive polymer having a skeleton different from that of the hydroxy ion conductive polymer used in Example 1 was used.It can be seen that even when the type of hydroxy ion conductive polymer is changed, by satisfying the relationship between (Ri) and (Rii), it is possible to obtain a membrane electrode assembly with low gas permeability and resistance and excellent durability against repeated current application. It is believed that peeling at the interface between the hydroxy ion conductive membrane and the anode catalyst layer and / or the cathode catalyst layer due to swelling / shrinkage of the hydroxy ion conductive membrane was suppressed. In the membrane electrode assemblies of Examples 1 to 3, the absolute values ​​of the differences between the glass transition temperatures of the polymers contained in the anode catalyst layer and the cathode catalyst layer and the glass transition temperature of the polymer constituting the hydroxy ion conductive membrane were 40°C, 20°C, and 190°C, respectively, and the membrane electrode assemblies of Examples 1 and 2 had superior resistance compared to the membrane electrode assembly of Example 3. It can be seen that resistance tends to be lower when the absolute value of this difference is in the range of 1 to 50°C. In the membrane / electrode assembly of Example 1, the polymer contained in the anode catalyst layer was present at a concentration of 15 mass % in the catalyst layer, whereas the polymer contained in the anode catalyst layer was 30 mass % and 1 mass %, respectively, in the membrane / electrode assemblies of Examples 4 and 5. The membrane / electrode assembly of Example 1 did not have any items that met the evaluation standard C in each evaluation, which shows that a good balance of each characteristic tends to be achieved when the amount of polymer contained in each catalyst layer is 5 to 25 mass %.

[0139] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0140] This application claims priority based on Japanese Patent Application No. 2023-161730, filed on September 25, 2023, the contents of which are incorporated herein by reference as part of the present specification.

[0141] REFERENCE SIGNS LIST 1 Hydroxy ion conductive membrane 2a Anode catalyst layer 21 Anode catalyst 23 Ionomer resin 2c Cathode catalyst layer 22 Cathode catalyst 23 Ionomer resin 3 Gas diffusion layer 4 Membrane electrode assembly 5 Bipolar plate 10 Water electrolysis cell

Claims

1. A membrane / electrode assembly having a structure in which a cathode catalyst layer, a hydroxy ion conductive membrane, and an anode catalyst layer are laminated in this order, wherein the tensile strength (a) and breaking elongation (b) of a water-swollen body of a polymer contained in the cathode catalyst layer and / or the anode catalyst layer, and the tensile strength (c) and breaking elongation (d) of a water-swollen body of a hydroxy ion conductive polymer constituting the hydroxy ion conductive membrane satisfy the following relationships (Ri) and (Rii): Tensile strength (a) > tensile strength (c) (Ri); Breaking elongation (b) > Breaking elongation (d) (Rii).

2. The membrane / electrode assembly according to claim 1, wherein the absolute value of the difference between the glass transition temperature (e) of the polymer contained in the cathode catalyst layer and / or the anode catalyst layer satisfying the relationships (Ri) and (Rii) and the glass transition temperature (f) of the hydroxy ion conductive polymer is 1 to 190° C.

3. The membrane / electrode assembly according to claim 2, wherein the polymer contained in the cathode catalyst layer and / or the anode catalyst layer that satisfies the relationship of (Ri) and (Rii) is contained in a catalyst layer containing the polymer at a concentration of 5 to 25 mass %.

4. The membrane / electrode assembly according to claim 3, wherein the polymer contained in at least the cathode catalyst layer satisfies the relationship between (Ri) and (Rii).

5. The membrane electrode assembly according to claim 4, wherein the polymer contained in the anode catalyst layer satisfies the relationship between (Ri) and (Rii).

6. The membrane electrode assembly according to claim 5, wherein the molecular weight of the polymer contained in the cathode catalyst layer and the anode catalyst layer is greater than the molecular weight of the hydroxy ion conductive polymer.

7. A method for producing hydrogen, which uses the membrane electrode assembly according to any one of claims 1 to 6.

8. A hydrogen production system comprising the membrane electrode assembly according to any one of claims 1 to 6.

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