Membrane electrode assembly

Abstract

Provided is a membrane electrode assembly capable of suppressing hydrogen crossover.　The membrane electrode assembly is for solid macromolecule-type water electrolysis and comprises: an anode having a catalyst layer; a cathode having a catalyst layer; and a solid macromolecule electrolyte membrane disposed between the anode and the cathode. At least one of the catalyst layer in the anode and the catalyst layer in the cathode includes a fluorine-containing polymer having an ion exchange group, and having a unit having a cyclic ether structure.

Description

membrane electrode assembly

[0001] The present invention relates to a membrane electrode assembly.

[0002] In order to convert surplus electricity into gas for storage and utilization, polymer electrolyte membrane (PEM) water electrolysis devices are utilized. For example, Patent Literature 1 discloses a PEM water electrolysis device using a catalyst layer containing a fluoropolymer.

[0003] JP 2023-041182 A

[0004] From the viewpoint of safety, PEM water electrolysis devices are required to be able to suppress hydrogen crossover. Hydrogen crossover refers to the permeation of hydrogen gas generated on the cathode side to the anode side when water electrolysis is performed using a PEM water electrolysis device. If the permeated hydrogen gas mixes with oxygen gas generated on the anode side at a concentration above a certain level, there is a risk of explosion or the like.

[0005] The present inventors have found that when a fluorine-containing polymer such as that disclosed in Patent Document 1 is used in the catalyst layer of the anode or cathode, there is room for further improvement in suppressing hydrogen crossover.

[0006] Therefore, an object of the present invention is to provide a membrane electrode assembly that can suppress hydrogen crossover.

[0007] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following configurations. [1] A membrane / electrode assembly for solid polymer water electrolysis, comprising an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode, wherein at least one of the catalyst layer in the anode and the catalyst layer in the cathode contains a fluoropolymer having units having a cyclic ether structure and having ion exchange groups. [2] The membrane / electrode assembly according to [1], wherein the thickness of the solid polymer electrolyte membrane is 25 μm or more. [3] The membrane / electrode assembly according to [1] or [2], wherein the ion exchange capacity of the fluoropolymer is 0.90 to 1.60 meq / g dry resin. [4] The membrane / electrode assembly according to any one of [1] to [3], wherein the content of the units having a cyclic ether structure is 30 mol % or more based on all units contained in the fluoropolymer. [5] The membrane / electrode assembly according to any one of [1] to [4], wherein the softening temperature of the fluoropolymer is 135°C or higher. [6] The membrane / electrode assembly according to any one of [1] to [5], wherein the catalyst layer in the anode comprises the fluoropolymer and a catalyst, and the catalyst comprises an iridium-containing catalyst. [7] The membrane / electrode assembly according to [6], wherein, in the catalyst layer in the anode, the mass ratio of the content of the fluoropolymer to the iridium content of the iridium-containing catalyst is 0.05 to 0.30. [8] The membrane / electrode assembly according to any one of [1] to [7], wherein the catalyst layer in the cathode comprises the fluoropolymer and a catalyst, and the catalyst comprises a carbon support and a platinum-containing catalyst. [9] The membrane / electrode assembly according to [8], wherein, in the catalyst layer in the cathode, the mass ratio of the content of the fluoropolymer to the content of the carbon support is 0.2 to 1.5.

[10] The specific surface area of ​​the carbon support is 60 m ２ / g or more.

[0008] According to the present invention, it is possible to provide a membrane electrode assembly capable of suppressing hydrogen crossover.

[0009] 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly of the present invention.

[0010] The meaning of each term in this specification is as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group for other ions, and examples include sulfonic acid functional groups and carboxylic acid functional groups. A "sulfonic acid functional group" is an acid-type sulfonic acid group (-SO ３ H), and a salt form of sulfonic acid group (—SO ３ M, where M is an alkali metal or a quaternary ammonium cation.) "Carboxylic acid functional group" is a general term for an acid-type carboxylic acid group (-COOH) and a salt-type carboxylic acid group (-COOM, where M is an alkali metal or a quaternary ammonium cation). "Groups that can be converted into ion-exchange groups" refer to groups that can be converted into ion-exchange groups by treatments such as hydrolysis and acid-form conversion, and are sometimes referred to as "precursor groups." "Groups that can be converted into sulfonic acid functional groups" refer to groups that can be converted into sulfonic acid functional groups by treatments such as hydrolysis and acid-form conversion. "Groups that can be converted into carboxylic acid functional groups" refer to groups that can be converted into carboxylic acid functional groups by known treatments such as hydrolysis and acid-form conversion.

[0011] A "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or an atomic group in which a portion of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction. Note that constitutional units derived from individual monomers may be referred to by the name of the monomer followed by "unit." The content (mol %) of each unit relative to the total units contained in the polymer is determined by analyzing the polymer by nuclear magnetic resonance spectroscopy. A unit represented by formula (u11) is referred to as unit (u11). Units represented by other formulas are also referred to in the same manner.

[0012] [Membrane Electrode Assembly] The membrane electrode assembly of the present invention is a membrane electrode assembly for solid polymer water electrolysis, comprising an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode, wherein at least one of the catalyst layer in the anode and the catalyst layer in the cathode contains a fluoropolymer having units having a cyclic ether structure (hereinafter also referred to as "units A") and having ion exchange groups (hereinafter also referred to as "polymer H"). When the membrane electrode assembly of the present invention is used, and polymer H having units A and ion exchange groups is contained in the catalyst layer of the anode or cathode, it is presumed that crossover of hydrogen and oxygen to the respective counter electrodes can be suppressed due to the characteristic units and functional groups of polymer H.

[0013] Fig. 1 is a cross-sectional view showing an example of a membrane electrode assembly of the present invention. The membrane electrode assembly 10 includes an anode 13 having a catalyst layer 11 and a gas diffusion layer 12, a cathode 14 having the catalyst layer 11 and the gas diffusion layer 12, and a solid polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14 in contact with the catalyst layer 11. At least one of the catalyst layer 11 of the anode 13 and the catalyst layer 11 of the cathode 14 contains polymer H. Although the membrane electrode assembly 10 of Fig. 1 includes a gas diffusion layer 12, the gas diffusion layer is an optional component and does not necessarily need to be included in the anode 13 or the cathode 14.

[0014] [Anode and Cathode] <Catalyst Layer> The membrane electrode assembly includes an anode having a catalyst layer and a cathode having a catalyst layer.

[0015] (Catalyst) The catalyst layer may contain a catalyst. The catalyst layer of the anode preferably contains an iridium-containing catalyst (a catalyst containing iridium). Examples of iridium-containing catalysts include iridium oxide catalysts, composite oxide catalysts containing iridium and other metal elements, alloy catalysts containing iridium oxide, and iridium oxide-containing catalysts having a core-shell structure. Examples of the other metals include ruthenium, titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, platinum, and gold. The catalyst may also be supported on an insoluble support. Examples of insoluble supports include known metal oxide supports.

[0016] The iridium-containing catalyst is preferably in particulate form.

[0017] When the catalyst layer contains polymer H and an iridium-containing catalyst, the mass ratio of the polymer H content to the iridium content (polymer H content / iridium content, hereinafter also referred to as "I / Ir") is preferably 0.05 or more, more preferably 0.10 or more, and is preferably 0.40 or less, more preferably 0.30 or less. The mass ratio is also preferably 0.05 to 0.40.

[0018] The catalyst layer of the cathode preferably contains a platinum-containing catalyst (a catalyst containing platinum), more preferably a carbon support and a platinum-containing catalyst, and even more preferably a supported catalyst in which the platinum-containing catalyst is supported on a carbon support. Examples of platinum-containing catalysts include platinum alone, platinum alloys, and platinum alloys having a core-shell structure. Examples of metal elements other than platinum contained in platinum alloys include platinum group metals other than platinum (e.g., ruthenium, rhodium, palladium, osmium, and iridium), gold, silver, chromium, iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc, and tin. Examples of carbon supports include solid carbon supports and hollow carbon supports. In addition, the carbon support may have pores of various sizes (e.g., macropores, mesopores, and micropores). Examples of carbon supports include ketjen black, acetylene black, graphitized carbon, mesoporous carbon, carbon fiber, and carbon nanotubes. The catalyst layer of the cathode may contain a catalyst that does not contain a platinum group metal. Examples of catalysts that do not contain a platinum group metal include metal oxide catalysts, metal oxynitride catalysts, and carbon alloy catalysts.

[0019] The platinum-containing catalyst is preferably particulate. The average particle diameter (number average particle diameter D50) of the platinum-containing catalyst is preferably 1.0 nm or more, more preferably 2.0 nm or more, preferably 10.0 nm or less, more preferably 5.0 nm or less. The average particle diameter of the platinum-containing catalyst is measured, for example, by TEM (transmission electron microscope) and SAXS (small angle X-ray scattering). The amount of the platinum-containing catalyst supported in the supported catalyst is preferably 20.0 mass% or more, more preferably 30.0 mass% or more, preferably 70.0 mass% or less, more preferably 60.0 mass% or less, based on the total mass of the catalyst.

[0020] When the catalyst layer contains polymer H and a platinum-containing catalyst, the mass ratio of the polymer H content to the platinum content (polymer H content / platinum content) is preferably 1.2 or more, more preferably 1.4 or more, and preferably 3.0 or less.

[0021] When the catalyst layer contains a carbon support, the mass ratio of the polymer H content to the carbon support content (polymer H content / carbon support content, hereinafter also referred to as "I / C") is preferably 0.4 or more, more preferably 0.6 or more, from the viewpoint of adhesiveness, and is preferably 1.5 or less, more preferably 1.2 or less. Furthermore, the mass ratio is also preferably 0.2 to 1.5, from the viewpoint of improving material transportability with an increase in the void volume in the cathode.

[0022] When the catalyst layer includes a carbon support, the specific surface area of ​​the carbon support is 60 m ２ / g or more is preferable, and 100m ２ / g or more is more preferable, and 150m ２ / g or more is more preferable. ２ / g or less is preferable, and 1,200m ２ / g or less is more preferable.

[0023] The thickness of the catalyst layer of the anode and the catalyst layer of the cathode is preferably 0.1 to 25 μm, more preferably 3 to 20 μm. The thickness of the anode and the cathode is preferably 5 μm or more, and preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 15 μm or less. The thicknesses of the catalyst layer, anode, and cathode can be measured, for example, using an image obtained by measuring a cross section cut in the thickness direction of the membrane electrode assembly with a laser microscope, and can be the arithmetic average value of the thicknesses at any 20 points.

[0024] (Polymer H) At least one of the catalyst layer in the anode and the catalyst layer in the cathode contains polymer H. Alternatively, both the catalyst layer in the anode and the catalyst layer in the cathode may contain polymer H. Polymer H is a fluorine-containing polymer having units A and having an ion-exchange group.

[0025] The cyclic ether structure in unit A is preferably a cyclic ether structure having a 5-membered ring or a cyclic ether structure having a 6-membered ring. The cyclic ether structure having a 5-membered ring and the cyclic ether structure having a 6-membered ring preferably have one or two etheric oxygen atoms. More specifically, the unit having a cyclic ether structure is preferably at least one unit selected from the group consisting of unit (u11), unit (u12), unit (u21), unit (u22), and unit (u24) shown below.

[0026]

[0027] R １１ is a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom, and the number of carbon atoms in the perfluoroalkylene group is preferably 1 to 10, more preferably 2 to 4. When the perfluoroalkylene group has an ether-bonded oxygen atom, the number of oxygen atoms may be 1 or 2 or more. In addition, the ether-bonded oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkylene group, or may be located at the carbon atom bond terminal. The perfluoroalkylene group may be linear or branched, and linear is preferred. R １２ , R １３ , R １５ and R １６ are each independently a monovalent perfluoroalkyl group which may have an etheric oxygen atom or a fluorine atom, and the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, and more preferably 1 to 3. １５ and R １６ In view of high polymerization reactivity, it is preferable that at least one of R is a fluorine atom, and it is more preferable that both of R are fluorine atoms. １４ represents a monovalent perfluoroalkyl group which may have an etheric oxygen atom, a fluorine atom, or —R １１ (SO ２ X (SO ２ R ｆ ) ａ ) － M ＋In the case where the perfluoroalkyl group has an etheric oxygen atom, the number of oxygen atoms may be one or more. The etheric oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group, or may be located at the end of the carbon atom bond. The perfluoroalkyl group may be linear or branched, preferably linear, and the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 10, more preferably 2 to 4. In formula (u11), two R １１ If it contains two R １１ may be the same or different. ＋ Is, H ＋ , a monovalent metal cation (e.g., potassium ion, sodium ion) or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group (e.g., methyl group, ethyl group). ＋ is preferred. ｆ is a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6. Two or more R ｆ When the ｆ may be the same or different. X is an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0, when X is a nitrogen atom, a=1, and when X is a carbon atom, a=2. -(SO ２ X (SO ２ R ｆ ) ａ ) － M ＋ Specific examples of the group include a sulfonic acid group (—SO ３ － M ＋ group), sulfonimide group (—SO ２ N (SO ２ R ｆ ) － M ＋ group), and sulfonmethide group (—SO ２ C (SO ２ R ｆ ) ２ ) － M＋ Examples include groups.

[0028] The unit (u11) is preferably the unit (u11-1).

[0029] In the above formula, M ＋ is M in formula (u11) ＋ is synonymous with.

[0030]

[0031] R ２１ is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms and having an etheric oxygen atom between the carbon-carbon bond. When the perfluoroalkylene group has an etheric oxygen atom, the number of oxygen atoms may be 1 or 2 or more. The perfluoroalkylene group may be linear or branched, and is preferably linear. R ２２ represents a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms and an etheric oxygen atom between the carbon-carbon bond, or -R ２１ (SO ２ X (SO ２ R ｆ ) ａ ) － M ＋ In the case where the perfluoroalkyl group has an etheric oxygen atom, the number of oxygen atoms may be one or more. The perfluoroalkyl group may be linear or branched, and is preferably linear. In formula (u12), two R ２１ If it contains two R ２１ may be the same or different. ＋ , R ｆ , X and a each independently represent M in formula (u11). ＋ , R ｆ , X and a are synonymous with each other.

[0032] Specific examples of the unit (u12) include the unit (u12-1) and the unit (u12-2). ＋ is M in formula (u11). ＋ is synonymous with.

[0033]

[0034]

[0035] R ４１ , R ４２ , R ４３ , R ４４ , R ４５ and R ４６ are each independently a monovalent perfluoroalkyl group which may have an etheric oxygen atom or a fluorine atom. When the perfluoroalkyl group has an etheric oxygen atom, the number of oxygen atoms may be one or more. The etheric oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group, or at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, with linear being preferred, and the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3. R ４５ and R ４６ In view of high polymerization reactivity, it is preferable that at least one of the groups is a fluorine atom, and it is more preferable that both of the groups are fluorine atoms.

[0036] The unit (u21) is preferably the unit (u21-1).

[0037]

[0038]

[0039] s is 0 or 1, and is preferably 0. ５１ and R ５２ are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spiro ring formed by linking together (when s is 0). ５３ and R ５４ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms. ５５ is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. ５５A fluorine atom is preferred in terms of high polymerization reactivity. The perfluoroalkyl group and perfluoroalkoxy group may be linear or branched, with linear groups being preferred.

[0040] The unit (u22) is preferably the unit (u22-1).

[0041]

[0042]

[0043] R ７１ ~R ７６ are each independently a monovalent perfluoroalkyl group which may have an etheric oxygen atom or a fluorine atom. When the perfluoroalkyl group has an etheric oxygen atom, the number of oxygen atoms may be one or more. The etheric oxygen atom may be inserted between the carbon-carbon bonds of the perfluoroalkyl group, or may be inserted at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, with linear being preferred, and the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3. R ７１ ~R ７４ is preferably a fluorine atom because of its high polymerization reactivity.

[0044] Among the specific cyclic ether structural units described above, the unit A preferably includes at least one unit selected from the group consisting of the unit (u21), the unit (u22), and the unit (u24), and more preferably the unit (u22), in order to obtain a catalyst layer with more excellent oxygen permeability.

[0045] The content of unit A is preferably 30 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, and particularly preferably 60 mol% or more, based on the total units contained in polymer H. From the viewpoint of further suppressing the occurrence of cracks in the catalyst layer, it is preferably 87 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less. Polymer H may contain only one type of unit A, or may contain two or more types. When two or more types are contained, the above content means the total amount thereof.

[0046] Polymer H preferably does not contain a cyclic ether structure and contains units having ion exchange groups (hereinafter also referred to as "units B"). The number of ion exchange groups in each unit contained in unit B is preferably 1 or more, more preferably 2 or more from the viewpoint of facilitating the production of a high molecular weight polymer while maintaining the content of units A, and even more preferably 2 from the viewpoint of facilitating the synthesis of the monomer.

[0047] The unit B is preferably a perfluoromonomer unit having an ion exchange group, more preferably a perfluoropolymer unit having a sulfonic acid functional group. The perfluoromonomer unit is preferably the unit (u31), the unit (A-1), the unit (A-2), or the unit (A-3), more preferably the unit (u31) or the unit (A-2).

[0048]

[0049] In formula (u31), Z is a fluorine atom or a trifluoromethyl group, q is 0 or 1, m is an integer of 0 to 3, p is 0 or 1, n is an integer of 1 to 12, and m+p>0. ＋ Is, H ＋ , a monovalent metal cation (e.g., potassium ion, sodium ion) or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group (e.g., methyl group, ethyl group), ＋ When a plurality of Z's are present, the plurality of Z's may be the same or different.

[0050]

[0051] In formulas (A-1) to (A-3), R Ｆ１ and R Ｆ２ are each independently a perfluoroalkylene group having 1 to 3 carbon atoms, or a perfluoroalkylene group -CF ２- is a divalent group in which an ethereal oxygen atom is substituted. In the divalent group, the ethereal oxygen atom may be located at the terminal of the perfluoroalkylene group or between carbon atoms. The number of carbon atoms in the divalent group is preferably 1 to 3, more preferably 2 or 3. R Ｆ１ and R Ｆ２ Specific examples of the group include -CF ２ -, -CF ２ CF ２ -, -CF(CF ３ ) -, -CF ２ CF ２ CF ２ -, -CF(CF ２ CF ３ ) -, -CF(CF ３ )CF ２ -, -CF ２ CF (CF ３ ) -, -C(CF ３ ) (CF ３ ) -, -CF ２ OCF ２ CF ２ -, and -OCF ２ CF ２ R is preferred because the raw materials are inexpensive, the production is easy, and the ion exchange capacity of polymer H can be increased. Ｆ１ and R Ｆ２ are each independently a perfluoroalkylene group having 1 or 2 carbon atoms, —CF ２ OCF ２ CF ２ - or -OCF ２ CF ２ In the case of a perfluoroalkylene group having two carbon atoms, a linear one is preferred. Specifically, —CF ２ -, -CF ２ CF ２ - or - CF (CF ３ )- is preferred, and -CF ２ -or-CF ２ CF ２ - is more preferred, and -CF ２ - is even more preferred.

[0052] In formula (A-2), R Ｆ３is a perfluoroalkylene group having 1 to 6 carbon atoms. Ｆ３ Specific examples of the group include -CF ２ -, -CF ２ CF ２ -, -CF(CF ３ ) -, -CF ２ CF ２ CF ２ -, -CF(CF ２ CF ３ ) -, -CF(CF ３ )CF ２ -, -CF ２ CF (CF ３ ) -, -C(CF ３ ) (CF ３ )- and -CF ２ CF (CF ３ ) OCF ２ CF (CF ３ )-. In view of the fact that the raw materials are inexpensive, the production is easy, and the ion exchange capacity of polymer H can be made higher, R Ｆ３ is preferably a perfluoroalkylene group having 1 to 3 carbon atoms. Specifically, —CF ２ -, -CF ２ CF ２ -or-CF ２ CF (CF ３ )- is preferred, and -CF ２ -or-CF ２ CF (CF ３ In formula (A-2), m is 0 or 1.

[0053] The content of unit B is preferably 13 mol % or more of all units contained in polymer H from the viewpoint of improving proton conductivity, and is preferably 50 mol % or less from the viewpoint of improving water repellency, drainage, and improving power generation efficiency. Polymer H may contain only one type of unit B, or may contain two or more types. When two or more types are contained, the above content means the total amount thereof.

[0054] Polymer H preferably contains tetrafluoroethylene (TFE) units (hereinafter also referred to as "units C"). By containing units C, water repellency can be imparted. The content of units C is preferably 5 mol% or more and preferably 35 mol% or less, based on all units contained in polymer H. The total content of units A, units B, and units C is preferably 90 mol% or more, more preferably 99 mol% or more, and preferably 100 mol% or less, based on all units contained in polymer H.

[0055] Polymer H may contain a unit (hereinafter also referred to as "unit D") based on a monomer having two or more polymerizable unsaturated bonds. In this specification, a unit based on a monomer that is a monomer containing a cyclic ether structure and has two or more polymerizable unsaturated bonds is treated as unit D. Specific examples of polymerizable unsaturated bonds include a carbon atom-carbon atom double bond (C=C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds in a monomer having two or more polymerizable unsaturated bonds is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, from the viewpoint of more excellent polymerization reactivity. The monomer having two or more polymerizable unsaturated bonds is preferably a monomer having a fluorine atom, more preferably a perfluoromonomer.

[0056] The unit D is preferably a unit represented by formula (u41) from the viewpoint of further suppressing the occurrence of cracks in the catalyst layer. The unit represented by formula (u41) may be in a form that crosslinks two polymer chains, or may be in a form that is incorporated into the same polymer chain.

[0057]

[0058] In formula (u41), Q ４ Q is an oxygen atom or a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom. ４When the perfluoroalkylene group has an etheric oxygen atom, the number of oxygen atoms may be one or two or more. The etheric oxygen atom may be located between the carbon atom-carbon atom bond of the perfluoroalkylene group, or at the end of the carbon atom bond. The perfluoroalkylene group may be linear or branched, and is preferably linear. The number of carbon atoms in the perfluoroalkylene group is preferably 1 to 10, more preferably 2 to 8, and even more preferably 3 or 4.

[0059] Specific examples of the unit D include the unit (u41-1), the unit (u41-2) and the unit (u41-3), and the unit (u41-2) is preferred since it can further suppress the occurrence of cracks in the catalyst layer.

[0060]

[0061] In the above units, m1 and m3 each independently represent an integer of 2 to 8, and preferably 3 or 4. In the above units, m2 and m4 each independently represent an integer of 0 to 5, and m2+m4≧1.

[0062] The content of unit D is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, and even more preferably 0.01 mol% or more, relative to all units contained in polymer H, from the viewpoint of further suppressing cracking of the catalyst layer; and from the viewpoint of more excellent power generation characteristics, it is preferably 10 mol% or less, more preferably 5 mol% or less, even more preferably 1 mol% or less, and particularly preferably 0.2 mol% or less, relative to all units contained in polymer H. Polymer H may contain only one type of unit D, or two or more types. When two or more types are contained, the above content refers to the total amount thereof.

[0063] Polymer H may contain units other than those described above (hereinafter also referred to as "other units"). Specific examples of other units include units based on monomers such as perfluoro(3-butenyl vinyl ether), perfluoro(allyl vinyl ether), perfluoro α-olefins (such as hexafluoropropylene), and perfluoro(alkyl vinyl ethers).

[0064] The softening temperature of Polymer H is preferably 135° C. or higher, more preferably 150° C. or higher, and even more preferably 160° C. or higher, and from the viewpoint of further suppressing cracking of the catalyst layer, is preferably 300° C. or lower, more preferably 250° C. or lower, and even more preferably 200° C. or lower. The softening temperature of Polymer H can be determined by the method described in the Examples section below.

[0065] The ion exchange capacity of the fluoropolymer is, from the viewpoint of ion conductivity, preferably at least 0.80 milliequivalents / g dry resin, more preferably at least 0.90 milliequivalents / g dry resin, and is preferably at most 1.60 milliequivalents / g dry resin, more preferably at most 1.50 milliequivalents / g dry resin, and from the viewpoint that the electrolysis voltage is likely to be lowered, it is still more preferably at most 1.20 milliequivalents / g dry resin, particularly preferably at most 1.10 milliequivalents / g dry resin.

[0066] When the catalyst layer in the anode contains polymer H, the total content of polymer H and the catalyst is preferably 90% by mass or more, more preferably 99% by mass or more, and preferably 100% by mass or less, based on the total mass of the catalyst layer in the anode. When the catalyst layer in the cathode contains polymer H, the total content of polymer H and the catalyst is preferably 90% by mass or more, more preferably 99% by mass or more, and preferably 100% by mass or less, based on the total mass of the catalyst layer in the cathode.

[0067] The method for producing polymer H will be described by taking as an example a case where polymer H has an acid type sulfonic acid group. In one example of the method for producing polymer H, the acid type sulfonic acid group in polymer H is converted into a precursor group (specifically, —SO ２ The precursor group of the precursor polymer (hereinafter also referred to as "polymer F") which is a group represented by an acid type sulfonic acid group (-SO ３ － H ＋ ) is a precursor group. ２ A specific example of a method for converting the group represented by F into an acid type sulfonic acid group is the method of converting the —SO ２ For example, the group represented by F is hydrolyzed to form a salt-type sulfonic acid group, and the salt-type sulfonic acid group is converted into an acid-type sulfonic acid group.

[0068] The TQ value of polymer F is preferably 300°C or less, more preferably 290°C or less. If the TQ value is below the upper limit, the solubility or dispersibility of polymer H in the liquid medium is improved, making it easier to prepare the catalyst ink. The TQ value of polymer F is preferably 100°C or more, more preferably 130°C or more, and even more preferably 160°C or more. If the TQ value is above the lower limit, polymer H having a sufficient molecular weight is obtained, resulting in excellent strength of the catalyst layer. The TQ value is a value related to the molecular weight of the polymer, and is expressed as follows: volume flow rate: 100 mm ３ The volumetric flow rate is expressed in terms of the temperature per second. The polymer is melted and discharged from a nozzle (inner diameter: 1 mm, length: 1 mm) at a constant temperature under a pressure of about 3 MPa, and the amount of the discharged polymer is measured in mm ３ The TQ value is expressed in units of / second. The TQ value is an index of the molecular weight of a polymer, and a higher TQ value indicates a higher molecular weight. The TQ value of Polymer F can be determined by the method described in the Examples section below.

[0069] (Other Components) The catalyst layer may contain other components in addition to the various components described above. Examples of the other components include hydrophobic particles, hydrophilic particles, dispersants, and fibrous carbon. Examples of the hydrophobic particles include polytetrafluoroethylene particles. Examples of the hydrophilic particles include metal oxide particles.

[0070] The catalyst layer can be formed, for example, by applying a catalyst ink containing a catalyst, a liquid medium, and, if necessary, polymer H onto a substrate film to form a coating film, and then drying the coating film to remove the liquid medium from the coating film. The substrate film is preferably a releasable substrate (e.g., an ethylene tetrafluoroethylene sheet). Examples of catalysts include those that can be contained in the catalyst layer described above. The liquid medium preferably contains at least one selected from the group consisting of water and alcohol, and more preferably contains water and alcohol. Specific examples of alcohols include methanol, ethanol, propanol (e.g., 1-propanol, 2-propanol), 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoro-1-propanol, 2,2,3,3-tetrafluoro-1-propanol, 4,4,5,5,5-pentafluoro-1-pentanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 3,3,3-trifluoro-1-propanol, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol, and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol. The alcohol preferably includes propanol. The alcohols may be used alone or in combination of two or more.

[0071] The catalyst layer may be formed by applying a catalyst ink to a solid polymer electrolyte membrane, a gas diffusion layer, or a carbon layer (described later) to form a coating film, and then drying the coating film to remove the liquid medium from the coating film. The formed catalyst layer may be further subjected to a heat treatment. Examples of the heat treatment include a heat press treatment.

[0072] <Gas Diffusion Layer> The anode or cathode in the membrane electrode assembly may be provided with a gas diffusion layer. The gas diffusion layer functions to rapidly diffuse gas generated from the catalyst layer out of the catalyst layer and also functions as a current collector. Specific examples of gas diffusion layers include carbon paper, carbon cloth, carbon felt, sintered titanium oxide fibers, sintered titanium oxide particles, and titanium mesh. Because the anode side has a high potential and carbon materials are prone to oxidation when used, the gas diffusion layer of the anode is preferably sintered titanium oxide fibers, sintered titanium oxide particles, or titanium mesh. The sintered titanium oxide or titanium mesh may be plated with platinum, iridium, or the like, as necessary. The gas diffusion layer of the cathode may be treated with polytetrafluoroethylene to make it water-repellent.

[0073] [Solid Polymer Electrolyte Membrane] The membrane electrode assembly of the present invention includes a solid polymer electrolyte membrane disposed between an anode and a cathode. The solid polymer electrolyte membrane is preferably a membrane containing a polymer with high proton conductivity, more preferably a membrane containing a polymer having an ion exchange group. Examples of the polymer having an ion exchange group include a polymer containing at least one selected from the group consisting of the above-mentioned units B, C, and D.

[0074] The solid polymer electrolyte membrane can be formed, for example, by a method (casting method) in which a liquid composition of a polymer and a liquid medium is applied to a substrate film or a catalyst layer and then dried. Heat treatment is preferably performed to stabilize the solid polymer electrolyte membrane. The heat treatment temperature can be adjusted appropriately depending on the type of polymer, and is preferably 130 to 200°C. The solid polymer electrolyte membrane may be treated with hydrogen peroxide water, if necessary.

[0075] The solid polymer electrolyte membrane may be reinforced with a reinforcing material. Examples of the reinforcing material include porous bodies, fibers, woven fabrics, and nonwoven fabrics. Examples of the reinforcing material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, and polyphenylene sulfide.

[0076] The solid polymer electrolyte membrane may contain at least one element selected from the group consisting of cerium and manganese in order to further improve durability. Cerium and manganese are preferred because they can decompose hydrogen peroxide, a substance that causes deterioration of the solid polymer electrolyte membrane. Cerium and manganese are preferably present in the solid polymer electrolyte membrane in an ionic state, and may be present in any state in the solid polymer electrolyte membrane as long as they are present in an ionic state. The solid polymer electrolyte membrane may contain a water-retaining agent in order to prevent drying. Examples of water-retaining agents include silica and heteropolyacids (e.g., zirconium phosphate, phosphomolybdic acid, and phosphotungstic acid).

[0077] The thickness of the solid polymer electrolyte membrane is preferably 5 μm or more, more preferably 15 μm or more, even more preferably 25 μm or more, particularly preferably 40 μm or more, and is preferably 300 μm or less, more preferably 150 μm or less. The thickness of the solid polymer electrolyte membrane can be measured, for example, using an image obtained by measuring a cross section cut in the thickness direction of the membrane electrode assembly with an optical microscope, and can be the arithmetic average value of thicknesses at any eight points.

[0078] The membrane electrode assembly may be manufactured by the following manufacturing methods: (i) a method in which catalyst layers (catalyst layer in the anode and catalyst layer in the cathode) are formed on a solid polymer electrolyte membrane to form a membrane catalyst layer assembly, and the membrane catalyst layer assembly is sandwiched between gas diffusion layers; or (ii) a method in which catalyst layers (catalyst layer in the anode and catalyst layer in the cathode) are formed on gas diffusion layers to form electrodes (anode 13, cathode 14), and the solid polymer electrolyte membrane is sandwiched between the electrodes.

[0079] The membrane electrode assembly is used in a PEM water electrolysis device. Examples of PEM water electrolysis devices having the membrane electrode assembly include a PEM water electrolysis device having the above-described membrane electrode assembly, a water supply unit that supplies water to the anode catalyst layer side, and a power supply unit electrically connected to the anode catalyst layer side and the cathode catalyst layer side. In the PEM water electrolysis device, when water is supplied to the anode catalyst layer side by the water supply unit and a DC voltage is applied between the anode and cathode by the power supply unit, an electrochemical reaction occurs on the anode catalyst layer side, causing water to decompose and generate oxygen gas and protons, while electrons flow to the power supply unit. On the cathode catalyst layer side, protons are supplied to the cathode catalyst layer side through the solid polymer electrolyte membrane, and electrons supplied from the power supply unit are obtained, generating hydrogen gas. A PEM water electrolysis device having the membrane electrode assembly may have the same configuration as a known water electrolysis device (e.g., an oxygen recovery member that recovers the generated oxygen, a hydrogen recovery member that recovers the generated hydrogen), except for the above-mentioned components.

[0080] The present invention will be described in detail below with reference to examples. Examples 1 and 2 are working examples, and Example 3 is a comparative example. The materials, amounts used, ratios, treatment details, and treatment procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0081] [Measurement Method] [Ion Exchange Capacity] Polymer F-1 and polymer F-2 were press-molded at 210°C and 4 MPa (gauge pressure) at a temperature 10°C higher than the TQ value to obtain films of polymer F-1 and polymer F-2 (thickness: 100 to 250 μm). The films of polymer F-1 and polymer F-2 were immersed in the alkaline aqueous solutions shown in Table 2 at 80°C for 16 hours to measure the -SO ２ F is hydrolyzed to form -SO ３ Furthermore, the membrane of each polymer F was immersed in a 3 mol / L aqueous hydrochloric acid solution at 50°C for 30 minutes, and then in ultrapure water at 80°C for 30 minutes. The cycle of immersion in the aqueous hydrochloric acid solution and immersion in the ultrapure water was repeated five times in total, and the -SO ３ K to -SO３ H. Washing with ultrapure water was repeated until the pH of the water in which each polymer F membrane was immersed reached 7. Each polymer F membrane was sandwiched between filter paper and air-dried to obtain a polymer H-1 membrane and a polymer H-2 membrane. Each obtained polymer H membrane was dried in a nitrogen-flowed glove box until its mass no longer changed, and its mass was determined. The polymer H membrane was then immersed in a 0.85 mol / g sodium hydroxide solution (solvent: water / methanol=10 / 90 (mass ratio)) at 60°C for 72 hours or more to convert the acid-type sulfonic acid groups to sodium salt-type sulfonic acid groups. The ion exchange capacity of polymer H (metabolic equivalents / g dry resin) was determined by back-titrating the amount of remaining sodium hydroxide with 0.1 mol / L hydrochloric acid.

[0082] [Proportion of Each Unit] The proportion of each unit in polymer F derived from a monomer unit was analyzed as follows: １９ The content of each unit contained in Polymer H was calculated from the F-NMR measurement value. The content of each unit contained in Polymer F was almost the same as the content of each unit contained in Polymer F. １９ F-NMR measurement was performed at a frequency of 282.7 MHz, with a chemical shift reference of CFCl ３ The composition analysis of Polymer F was carried out by using hexafluorobenzene as a dissolution solvent and adjusting the solution concentration to 10% by mass.

[0083] [TQ value] Using a flow tester (Shimadzu Corporation, CFT-500A) equipped with a nozzle having a length of 1 mm and an inner diameter of 1 mm, polymer F was melt-extruded while changing the temperature under the condition of an extrusion pressure of 2.94 MPa (gauge pressure). ３ The temperature at which the extrusion rate reached 1 / sec (TQ value) was determined. When the TQ value exceeded 300°C, the extrusion rates at 300°C or lower were determined at four points, and the TQ value was determined by extrapolating from the measured values ​​at the four points. The extrapolation was performed using an approximation formula that logarithmically approximates the correlation between the extrusion rate and the reciprocal of the absolute temperature. For polymer F with the same composition, the higher the TQ value, the higher the molecular weight of polymer F.

[0084] [Softening Temperature] The softening temperature of Polymer H was measured by the following method. Liquid composition S (liquid compositions S-1 and S-2 described below) in which Polymer H was dispersed in a liquid medium was cast into a Petri dish and then annealed to produce a solid polymer electrolyte membrane. Dynamic viscoelasticity measurement was performed on this solid polymer electrolyte membrane using a dynamic viscoelasticity measurement device (manufactured by IT Measurement & Control Co., Ltd., DVA-225) under the following conditions: sample width: 5.0 mm, grip length: 15 mm, measurement frequency: 1 Hz, heating rate: 2°C / min, and tension mode. Tan δ (loss tangent) was calculated from the ratio (E" / E') of the loss modulus E" to the storage modulus E', and a tan δ-temperature curve was created. The peak temperature between -100 and 200°C read from the tan δ-temperature curve was taken as the softening temperature of Polymer H. The softening temperature corresponds to the temperature at which the polymer transitions from a glassy to a rubbery state. The reference dimensions and thickness of the film used in the calculation were measured under the conditions of a temperature of 23° C. and a relative humidity of 50% RH.

[0085] [Synthesis of Polymer F] [Abbreviations] TFE: tetrafluoroethylene PFB: CF ３ CF ２ CF ２ C(O)OOC(O)CF ２ CF ２ CF ３ ・HFC-52-13p:CF ３ (CF ２ ) ５ H ・HCFC-225cb: CClF ２ CF ２ CHClF ・HCFC-141b:CH ３ CCl ２ F

[0086] Compound 1

[0087]

[0088] Compound 2

[0089]

[0090] Compound 3

[0091]

[0092] [Polymer F-1] A stainless steel autoclave with an internal volume of 2575 mL was depressurized in an ice bath, and 1116.02 g of compound 1, 340.92 g of compound 2, 407.78 mg of PFB dissolved in HFC-52-13p at a concentration of 3.2 mass%, and 172.0 g of HFC-52-13p were aspirated and charged into the autoclave, and the pressure was reduced again. Thereafter, 56.90 g of TFE was charged, and the temperature was raised to 24 ° C. to start the reaction. Stirring during the reaction was performed using a double helical ribbon impeller, and the stirring speed was 60 rpm from the start of the reaction until 2.5 hours had elapsed, 30 rpm from 2.5 hours to 3.5 hours had elapsed, and 10 rpm from 3.5 hours to 10 hours had elapsed. After stirring for 10 hours, the autoclave was depressurized, and unreacted compound 2 and TFE were distilled off. The product was then diluted with HFC-52-13p and mixed with a mixed liquid of HFC-52-13p:methanol=8:2 (mass ratio) to coagulate the polymer, which was then filtered. The polymer was washed in a mixed liquid of HFC-52-13p:methanol=7:3 (mass ratio) and separated by filtration. The solid content was dried at 80°C and then vacuum dried at 210°C to obtain Polymer F-1.

[0093] [Polymer F-2] An autoclave (internal volume 230 mL, made of Hastelloy) was charged with 123.8 g of Compound 3, 35.2 g of HCFC-225cb as a liquid medium, and 63.62 mg of 2,2'-azobis(isobutyronitrile) as a polymerization initiator, and cooled with liquid nitrogen to degas. Thereafter, the temperature was raised to 70°C, and TFE was introduced into the system to maintain the pressure at 1.14 MPaG. Polymerization was carried out by continuously adding TFE so that the pressure remained constant at 1.14 MPaG. After 7.9 hours, when the amount of TFE added reached 12.4 g, the autoclave was cooled, and the gas in the system was purged to terminate the polymerization. The obtained polymer solution was diluted with HCFC-225cb, and then HCFC-141b was added to cause coagulation. After washing with HCFC-225cb and HCFC-141b, the product was dried to obtain 25.1 g of polymer F-2 consisting of a copolymer of TFE and compound 3.

[0094]

[0095] [Synthesis of Polymer H] Using each of the polymers F, powders of polymers H-1 and H-2 were obtained by the following method. Each polymer F was cooled with dry ice and then pulverized. The pulverized polymer F was immersed in an alkaline aqueous solution shown in Table 2 at 80°C for 40 hours to remove the -SO ２ F is hydrolyzed to form -SO ３ The resulting polymer was then immersed in a 3 mol / L aqueous hydrochloric acid solution at 80°C for 30 minutes, and then in ultrapure water at 80°C for 30 minutes. This cycle of immersion in the aqueous hydrochloric acid solution and immersion in the ultrapure water was repeated 10 times in total, and the -SO ３ K to -SO ３ The polymers were converted to H. Washing with ultrapure water was repeated until the pH of the water in which the polymers were immersed reached 7. The polymers were dried under a nitrogen flow to obtain powders of each polymer H. The results are shown in Table 2. In Table 2, the ion exchange capacity and softening temperature of polymer H were values ​​measured by the methods described above.

[0096] In Table 2, aqueous solution A is potassium hydroxide / dimethyl sulfoxide / water = 15 / 30 / 55 (mass ratio), and aqueous solution B is potassium hydroxide / methanol / water = 15 / 20 / 65 (mass ratio).

[0097]

[0098] [Preparation of Liquid Composition] [Liquid Composition S-1] In a 0.2 L glass autoclave, 18.70 g of polymer (powder) (breakdown: 18.22 g of polymer H-1, 0.48 g of water, solids concentration 97.4 mass%), 22.81 g of ultrapure water, 54.36 g of 1-propanol were added, and the mixture was stirred at 300 rpm for 13 hours at 115 ° C., and then diluted with 31.0 g of ultrapure water. After stirring at 110 ° C. for 1 hour, the mixture was allowed to cool and the solution was removed from the autoclave. This solution was diluted with 25.6 g of ultrapure water and 25.6 g of 1-propanol, and the mixture was stirred at 110 ° C. for 1 hour, allowed to cool, and filtered using a pressure filter (filter paper: Advantec Toyo Co., Ltd., PF040) to obtain a liquid composition S-1 in which polymer H-1 was dispersed in a liquid medium at 10.2 mass%.

[0099] [Liquid Composition S-2] Using Polymer F-2 as a raw material, a liquid composition S-2 (solid content concentration 26.0% by mass, ethanol / water = 60 / 40 (mass ratio)) in which Polymer H-2 was dispersed was obtained by the method described in Production Example 4 of JP2018-55877A.

[0100] [Preparation of Composition for Forming Catalyst Layer] [Coating Solution CI-1 for Forming Cathode Catalyst Layer] A supported catalyst in which 47.1 mass % of platinum was supported on carbon powder ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., specific surface area of ​​the carbon support: 800 m ２ To 3.0 g of alumina powder (1.0 g / g, average particle size 2.8 nm), 23.6 g of water and 13.9 g of 1-propanol were added and mixed. To this was added 11.1 g of Liquid Composition S-1 so that the I / C was 0.7 and the solids concentration was 8.0 mass%, and the mixture was dispersed in a planetary ball mill (manufactured by Ito Seisakusho, model: LP-4) using 5 mm zirconia beads at a rotation speed of 300 rpm for 90 minutes. Thereafter, 10.5 g of water and 6.9 g of 1-propanol were added, and the mixture was diluted so that the solids concentration after dispersion was 6.0 mass%, to obtain Coating Solution CI-1 for forming a cathode catalyst layer.

[0101] [Coating Solution CI-2 for Forming Cathode Catalyst Layer] A supported catalyst in which 46.2 mass % of platinum is supported on carbon powder ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., specific surface area of ​​the carbon support: 800 m ２ To 85.0 g of a cellulose ester copolymer (coated with 160.2 g of Liquid Composition S-2, 87.4 g of ethanol, and 51.1 g of Zeorolor-H (manufactured by Zeon Corporation) was added 498.4 g of water and 361.1 g of ethanol and mixed. To this was added 247.9 g of a mixed liquid that had been previously mixed and kneaded with 160.2 g of Liquid Composition S-2, 87.4 g of ethanol, and 51.1 g of Zeorolor-H (manufactured by Zeon Corporation) so that the I / C was 0.7 and the solids concentration was 10.1 mass%, and the mixture was dispersed in a planetary ball mill (manufactured by Ito Seisakusho, model: LP-4) using 5 mm zirconia beads at a rotation speed of 300 rpm for 90 minutes to obtain Coating Solution CI-2 for forming a cathode catalyst layer.

[0102] [Coating Solution AI-1 for Forming Anode Catalyst Layer] Ethanol (6.4 g) and water (6.5 g) were added to Liquid Composition S-1 (9.2 g), and a coating solution having a specific surface area of ​​100 m containing 74.8% by mass of iridium was further prepared. ２ / g iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd.) (5.0 g) was added so that the I / Ir was 0.25. The resulting mixture was treated for 90 minutes in a planetary bead mill (rotation speed: 300 rpm) to obtain Coating Solution AI-1 for forming an anode catalyst layer with a solids concentration of 21.9 mass %.

[0103] [Coating Solution AI-2 for Forming Anode Catalyst Layer] Ethanol (9.2 g) and Zeororah-H (manufactured by Zeon Corporation) (5.4 g) were added to Liquid Composition S-2 (17.0 g), and the mixture was mixed for 15 minutes at 2200 rpm using a planetary centrifugal mixer (Thinky, Awatori Rentaro). Ethanol (11.7 g) and water (18.9 g) were added to the mixed composition (13.4 g), and a coating solution containing 74.8% by mass of iridium and having a specific surface area of ​​100 m was prepared. ２ / g iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd., 5.0 g) was added so that I / Ir was 0.25. The resulting mixture was treated for 90 minutes in a planetary bead mill (rotation speed: 300 rpm) to obtain Coating Solution AI-2 for forming an anode catalyst layer with a solids concentration of 22.0 mass %.

[0104] [Example 1] Coating solution CI-1 for forming a cathode catalyst layer was applied onto an ETFE (ethylene tetrafluoroethylene) sheet using a die coater, dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to form a cathode catalyst layer having a thickness of 14 µm and a platinum content of 0.4 mg / cm ２ On another ETFE sheet, anode catalyst layer forming coating solution AI-2 was applied to obtain a cathode catalyst layer CC-1 having an iridium concentration of 1.0 mg / cm. ２ The coating was applied with an applicator so that the thickness was 14 μm, dried at 80° C. for 10 minutes, and then heat-treated at 150° C. for 15 minutes to obtain a 14 μm-thick anode catalyst layer AC-2. ２ F group to SO ３ An ion exchange membrane (ion exchange capacity: 1.25 meq / g dry resin) having a thickness of 50 μm and made of a polymer having acid-type sulfonic acid groups converted to H groups was prepared.

[0105] The surface of the anode catalyst layer AC-2 cut to 4.0 cm x 4.0 cm was placed opposite one surface of the solid polymer electrolyte membrane cut to 7 cm x 7 cm, and the surface of the cathode catalyst layer CC-1 cut to 4.0 cm x 4.0 cm was placed opposite one surface of the solid polymer electrolyte membrane, and the mixture was hot-pressed at a press temperature of 130 ° C. for 10 minutes under a pressure of 2.6 MPa. After the temperature was lowered to 70 ° C., the pressure was released and the membrane was removed. The ETFE sheets of the anode catalyst layer and the cathode catalyst layer were peeled off, and the membrane was heated to an electrode area of ​​16 cm. ２ As a result, a membrane electrode assembly ME-1 was obtained.

[0106] [Examples 2 to 3] In the same manner as in Example 1, a membrane electrode assembly ME-2 and a membrane electrode assembly ME-3 were obtained in which an anode catalyst layer, a solid polymer electrolyte membrane, and a cathode catalyst layer were arranged in this order as shown in the table below.

[0107] [Evaluation of Hydrogen Crossover] The hydrogen concentration in the gas at the anode of each membrane electrode assembly was measured according to the following procedure to evaluate hydrogen crossover. The membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekaert) with a thickness of 0.25 mm and a porosity of 60% by volume, and platinum-plated titanium plates with straight flow channels were used as separators. The electrode area was 16 cm. ２ The membrane electrode assembly was incorporated into a single cell of 1.0 μS / cm and was evaluated. The membrane electrode assembly was clamped so that a pressure of 1.3 MPa was applied to the electrode portions when sandwiching the membrane electrode assembly. Next, in order to sufficiently hydrate the solid polymer electrolyte membrane and the fluoropolymers of both electrodes, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 4 hours. Thereafter, pure water with a conductivity of 1.0 μS / cm or less and a temperature of 80°C was supplied to the anode side at a flow rate of 50 mL / min, and while the back pressure was kept at atmospheric pressure for both the anode and cathode, a current of 32 A (current density 2 A / cm) was applied using a large current potentio / galvanostat HCP-803 (manufactured by Biologic). ２ ) and water electrolysis was carried out for 4 hours as a break-in operation. ２IV (electrolysis voltage) measurements were performed by increasing the current stepwise within the range of 1.0 μS / cm. IV measurements were performed four times. Thereafter, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the cell at 50 mL / min. A current of 3.2 A (current density 0.2 A / cm) was applied using a large current potentiostat / galvanostat HCP-803 (manufactured by Biologic) while maintaining the back pressure at both the anode and cathode at atmospheric pressure. ２ ) for 11 hours at 8 A (current density 0.5 A / cm ２ ) for 7 hours at 16 A (current density 1 A / cm ２ ) for 4 hours and 32 A (current density 2 A / cm ２ ) for 4 hours. After each retention time at each current had elapsed, water was separated from the gas discharged from the anode side, and then the hydrogen concentration in the gas was measured using a micro GC (Agilent 490, manufactured by Agilent). The hydrogen concentration in the gas (volume %, hydrogen content / gas content) at the final measurement point was used to evaluate hydrogen crossover according to the following evaluation criteria: "A": The hydrogen concentration in the gas at the anode was 0.3 volume % or less; "B": The hydrogen concentration in the gas at the anode was greater than 0.3 volume % and less than 0.7 volume %; "C": The hydrogen concentration in the gas at the anode was greater than 0.7 volume %.

[0108]

[0109] It was confirmed that the membrane electrode assembly of the present invention can suppress hydrogen crossover (Examples 1 and 2). It was also confirmed that when the catalyst layer in the cathode contains polymer H, hydrogen crossover can be further suppressed (Example 1).

[0110] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-205868 filed on December 6, 2023 are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0111] 10 membrane electrode assembly 11 catalyst layer 12 gas diffusion layer 13 anode 14 cathode 15 solid polymer electrolyte membrane

Claims

1. A membrane electrode assembly for solid polymer water electrolysis comprising an anode having a catalyst layer, a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode, wherein at least one of the catalyst layer in the anode and the catalyst layer in the cathode contains a fluorine-containing polymer having a unit having a cyclic ether structure and having an ion-exchange group.

2. The membrane electrode assembly according to claim 1, wherein the thickness of the solid polymer electrolyte membrane is 25 μm or more.

3. The membrane / electrode assembly according to claim 1 or 2, wherein the ion exchange capacity of the fluoropolymer is 0.90 to 1.60 meq / g dry resin.

4. The membrane / electrode assembly according to claim 1 or 2, wherein the content of said units having a cyclic ether structure is 30 mol % or more based on the total units contained in said fluoropolymer.

5. The membrane / electrode assembly according to claim 1 or 2, wherein the softening temperature of the fluoropolymer is 135° C. or higher.

6. The membrane electrode assembly according to claim 1 or 2, wherein the catalyst layer in the anode comprises the fluoropolymer and a catalyst, and the catalyst comprises an iridium-containing catalyst.

7. The membrane electrode assembly according to claim 6, wherein in said catalyst layer in said anode, the mass ratio of the content of said fluoropolymer to the iridium content of said iridium-containing catalyst is 0.05 to 0.

40.

8. The membrane electrode assembly according to claim 1 or 2, wherein the catalyst layer in the cathode comprises the fluoropolymer and a catalyst, and the catalyst comprises a carbon support and a platinum-containing catalyst.

9. The membrane electrode assembly according to claim 8, wherein in said catalyst layer in said cathode, the mass ratio of the content of said fluoropolymer to the content of said carbon support is 0.2 to 1.

5.

10. The specific surface area of ​​the carbon support is 60 m ２ The membrane electrode assembly according to claim 8 , wherein the molecular weight of the membrane electrode assembly is 1 / g or more.

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