Composition for forming catalyst layer

Abstract

Provided is a catalyst layer-forming composition capable of forming a catalyst layer in which the occurrence of cracks is suppressed. This composition for forming a catalyst layer contains a fluorine-containing polymer having a unit containing a cyclic ether structure and having an ion exchange group, a catalyst, and a solvent, the solvent containing water and an alcohol, the alcohol containing propanol, the content of water being 50% by mass or more with respect to the total mass of the solvent, and the content of ethanol being 50% by mass or more with respect to the total mass of the solvent. The content of propanol is 50% by mass or more with respect to the total mass of the alcohol.

Description

Technical Field

[0001] This invention relates to compositions for forming catalyst layers. Background Technology

[0002] A known solid polymer fuel cell has a membrane electrode assembly 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.

[0003] Since oxygen is supplied from the cathode side during the operation of a solid polymer fuel cell, the performance of the solid polymer fuel cell can be further improved if the oxygen transport resistance at the cathode is reduced. Therefore, Patent Document 1 discloses a catalyst layer for the cathode using a fluoropolymer containing units with a ring structure that have excellent oxygen permeability.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2016-104380 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Solid polymer fuel cells are intended for long-term use, thus requiring further improvements in the durability of their constituent components. The inventors have discovered that when forming a catalyst layer using a catalyst layer forming liquid (catalyst layer forming composition) as described in Patent Document 1, depending on the composition of the catalyst layer forming composition, it is sometimes impossible to sufficiently suppress cracking in the resulting catalyst layer, and there is room for improvement.

[0009] The present invention was made in view of the above-mentioned problems, and its objective is to provide a composition for forming a catalyst layer that can suppress the formation of cracks in the catalyst layer.

[0010] Solution for solving the problem

[0011] The inventors have conducted in-depth research on the above-mentioned problems and found that the above-mentioned problems can be solved by the following configuration. [1]

[0013] A composition for forming a catalyst layer comprises a fluoropolymer, a catalyst, and a solvent.

[0014] The aforementioned fluoropolymer has units comprising cyclic ether structures and ion-exchange groups.

[0015] The solvents mentioned above include water and alcohol.

[0016] The above alcohols include propanol.

[0017] The water content relative to the total mass of the solvent is 50% or more by mass.

[0018] The content of propanol is 50% by mass or more relative to the total mass of the alcohols. [2]

[0020] According to the composition for forming a catalyst layer as described in [1], the catalyst comprises a support and a metal supported on the support.

[0021] The mass ratio of the fluoropolymer to the carrier is 0.75 or more. [3]

[0023] According to the composition for forming a catalyst layer as described in [1] or [2], wherein the specific surface area of ​​the carbon support is 700 m². 2 / g or more. [4]

[0025] The composition for forming a catalyst layer according to any one of [1] to [3], wherein the content of the water is less than 80% by mass relative to the total mass of the solvent. [5]

[0027] The composition for forming a catalyst layer according to any one of [1] to [4], wherein the concentration of the solid component of the composition for forming a catalyst layer is 10% by mass or less. [6]

[0029] The composition for forming a catalyst layer according to any one of [1] to [5], wherein the ion exchange capacity of the fluoropolymer is 0.8 milliequivalents / gram of dry resin or more. [7]

[0031] The composition for forming a catalyst layer according to any one of [1] to [6], wherein the content of the unit comprising the cyclic ether structure is 50 mol% or more relative to all the units contained in the fluoropolymer. [8]

[0033] The composition for forming a catalyst layer according to any one of [1] to [7], wherein the fluoropolymer comprises the unit shown in formula (A-2) described later,

[0034] In equation (A-2),

[0035] R F1 and R F2 Each is independently a perfluoroalkylene group having 1 to 3 carbon atoms, or a divalent group of a perfluoroalkylene group whose -CF2- is replaced by an ether-bonded oxygen atom.

[0036] R F3 It can be a perfluoroalkylene group with 1 to 6 carbon atoms, optionally containing an ether bond oxygen atom.

[0037] m is 0 or 1. [9]

[0039] The composition for forming a catalyst layer according to any one of [1] to [8], wherein the fluoropolymer comprises a tetrafluoroethylene-based unit.

[10]

[0041] The catalyst layer forming composition according to any one of [1] to [9] is used to form the catalyst layer of the cathode in the membrane electrode assembly, the membrane electrode assembly 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.

[11]

[0043] The composition for forming a catalyst layer according to any one of [1] to

[10] , wherein the membrane electrode assembly of

[10] is a membrane electrode assembly for a solid polymer fuel cell.

[0044] The effects of the invention

[0045] According to the present invention, a catalyst layer forming composition capable of forming a catalyst layer that is not prone to cracking can be provided. Attached Figure Description

[0046] Figure 1 This is a cross-sectional view showing an example of a membrane electrode assembly.

[0047] Figure 2 This is a surface image of the catalyst layer corresponding to Example 1-1 in the Examples section.

[0048] Figure 3 This is a surface image of the catalyst layer corresponding to Examples 1-2 in the Examples section.

[0049] Figure 4 This is a surface image of the catalyst layer corresponding to Examples 1-3 in the Examples section.

[0050] Figure 5 These are surface images of the catalyst layer corresponding to Examples 1-6 in the Examples section.

[0051] Figure 6 These are surface images of the catalyst layer corresponding to Examples 1-7 in the Examples section. Detailed Implementation

[0052] Unless otherwise stated, the following definitions apply to this specification and the claims.

[0053] "Ion exchange group" refers to a group that can exchange at least a portion of the ions contained in the group for other ions, such as sulfonic acid functional groups and carboxylic acid functional groups.

[0054] The "sulfonic acid functional group" is the acidic sulfonic acid group (-SO3H) and the salt-type sulfonic acid group (-SO3M). 2 , of which M 2 It is a general term for alkali metal or quaternary ammonium cations.

[0055] The "carboxylic acid functional group" is the acidic carboxylic acid group (-COOH) and the salt-type carboxylic acid group (-COOM). 1 , of which M 1 It is a general term for alkali metals or quaternary ammonium cations.

[0056] "A group that can be converted into an ion exchange group" refers to a group that can be converted into an ion exchange group through treatments such as hydrolysis and acidification; it is sometimes called a "precursor group".

[0057] "A group that can be converted into a sulfonic acid functional group" refers to a group that can be converted into a sulfonic acid functional group through treatments such as hydrolysis and acidification.

[0058] "A group that can be converted into a carboxylic acid functional group" refers to a group that can be converted into a carboxylic acid functional group through known treatments such as hydrolysis and acidification.

[0059] In polymers, a "unit" refers to an atomic group derived from one molecule of a monomer, formed through monomer polymerization. A unit can be a atomic group formed directly through the polymerization reaction, or it can be a portion of the atomic group transformed into a different structural group by processing the polymer obtained through the polymerization reaction. It should be noted that sometimes structural units derived from individual monomers are referred to by labeling their monomer names with the term "unit."

[0060] Furthermore, the unit shown in equation (u11) is denoted as unit (u11). The units shown in other equations are also denoted in the same way.

[0061] The numerical range indicated by "~" refers to the range of values ​​recorded before and after "~" as lower and upper limits. Within the numerical ranges described in this specification, the upper or lower limit recorded in a particular numerical range can be replaced by the upper or lower limit of other numerical ranges described in different stages. Furthermore, within the numerical ranges described in this specification, the upper or lower limit recorded in a particular numerical range can be replaced by the values ​​shown in the embodiments.

[0062] [Composition for catalyst layer formation]

[0063] The catalyst layer forming composition of the present invention (hereinafter also referred to as "the composition") comprises a fluoropolymer, a catalyst, and a solvent, wherein the fluoropolymer has a unit comprising a cyclic ether structure (hereinafter also referred to as "unit A") and has an ion exchange group, the solvent comprises water and an alcohol, wherein the alcohol comprises propanol, the content of the water is 50% by mass or more relative to the total mass of the solvent, and the content of the propanol is 50% by mass or more relative to the total mass of the alcohol.

[0064] Hereinafter, the fluoropolymer containing unit A and ion exchange groups contained in this composition will also be referred to as "polymer H".

[0065] When forming the catalyst layer, if a high-density layer of fluoropolymer is formed at the interface between the catalyst and the fluoropolymer, the oxygen transport resistance increases, leading to a decrease in the power generation performance of the solid polymer fuel cell. To address this issue, when a fluoropolymer containing units with cyclic ether structures is used to form the catalyst layer, the polymer chains become difficult to configure tightly, thus suppressing the formation of the aforementioned high-density layer and easily resulting in a fuel cell with excellent power generation performance.

[0066] On the other hand, the cyclic ether structure weakens the adsorption force between the catalyst and the fluorinated polymer, resulting in the catalyst layer being prone to cracking.

[0067] To address this problem, the inventors have discovered that even when using a fluoropolymer containing units with cyclic ether structures, by optimizing the composition of the solvent used in the formation of the catalyst layer, the adsorption force between the fluoropolymer and the catalyst is improved, thereby suppressing the generation of cracks in the catalyst layer.

[0068] From the viewpoint of storage, the concentration of solid components in this composition is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. From the viewpoint of coatability, it is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0069] Here, the concentration of solid components is calculated based on the mass of the composition before and after heating using the following method.

[0070] After heating 1g of this composition at 180°C for 180 minutes, the mass of the residue is weighed, and the concentration of the solid component is calculated using the following formula.

[0071] Solid component concentration (mass %) = 100 × (mass of residue) / (mass of the entire composition)

[0072] <Polymer H>

[0073] This composition comprises polymer H. Polymer H is a polymer having unit A and having ion-exchange groups.

[0074] From the perspective of obtaining a catalyst layer with better oxygen permeability, unit A is preferably at least one unit selected from the group consisting of unit (u11), unit (u12), unit (u21), unit (u22) and unit (u24).

[0075] In this specification, units (u11), (u12), (u21), (u22), and (u24) are sometimes collectively referred to as “specific cyclic ether structural units”.

[0076]

[0077] R 11 The alkyl group is a divalent perfluoroalkylene group, optionally containing an ether-bonded oxygen atom. When the perfluoroalkylene group contains an ether-bonded oxygen atom, the number of oxygen atoms can be one or more. Furthermore, the ether-bonded oxygen atom can be located between carbon-carbon bonds or at the end of a carbon bond in the perfluoroalkylene group. The perfluoroalkylene group can be linear or branched, preferably linear.

[0078] R 12 R 13 R 15 and R 16 Each is independently a monovalent perfluoroalkyl group or a fluorine atom, optionally containing an ether-bonded oxygen atom. From the perspective of high polymerization reactivity, R... 15 and R 16 Preferably, at least one of them is a fluorine atom, and more preferably both are fluorine atoms.

[0079] R 14 It can be a monovalent perfluoroalkyl group, a fluorine atom, or a -R group, optionally containing an ether bond oxygen atom. 11 (SO2X(SO2R f ) a ) - M + The group shown. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms can be one or more. Furthermore, the ether-bonded oxygen atom can be located between carbon-carbon bonds of the perfluoroalkyl group or at the end of a carbon bond. The perfluoroalkyl group can be linear or branched, preferably linear. In formula (u11), it contains two R groups. 11 At that time, 2 R 11 They can be the same or different.

[0080] M + For H +A monovalent metal cation (e.g., potassium ion, sodium ion) or an ammonium ion in which one or more hydrogen atoms are optionally replaced by a hydrocarbon group (e.g., methyl, ethyl), preferably H from the viewpoint of high conductivity. + .

[0081] R f It is a perfluoroalkyl group, optionally having an ether-bonded oxygen atom, and either straight-chain or branched. The perfluoroalkyl group preferably has 1 to 8 carbon atoms, particularly preferably 1 to 6. It has 2 or more R atoms. f In the case of 2 or more R f They can be the same or different.

[0082] X can be an oxygen atom, a nitrogen atom, or a carbon atom. 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.

[0083] As -(SO2X(SO2R) f ) a ) - M + Specific examples of functional groups include sulfonic acid groups (-SO3). - M + (group), sulfonylimide group (-SO2N(SO2R) f ) - M + (group), or sulfonyl methyl group (-SO2C(SO2R)) f )2) - M + (group).

[0084] Unit (u11) is preferably unit (u11-1).

[0085]

[0086]

[0087] R 21 It is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms with ether-bonded oxygen atoms between carbon-carbon bonds. When the perfluoroalkylene group has ether-bonded oxygen atoms, the number of oxygen atoms can be one or more. The perfluoroalkylene group can be linear or branched, preferably linear.

[0088] R 22 It is a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms with ether-bonded oxygen atoms between carbon-carbon bonds, or -R. 21 (SO2X(SO2R f ) a ) -M + The group shown. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms can be one or more. The perfluoroalkyl group can be linear or branched, preferably linear. In formula (u12), it contains two R groups. 21 At that time, 2 R 21 They can be the same or different.

[0089] M + R f X and a are respectively related to M in equation (u11) + R f X and a have the same meaning.

[0090] Specific examples of element (u12) include element (u12-1) and element (u12-2). In the formula, M... + M of equation (u11) + They have the same meaning.

[0091]

[0092]

[0093] R 41 R 42 R 43 R 44 R 45 and R 46 Each alkyl group can be a monovalent perfluoroalkyl group or a fluorine atom, optionally containing an ether-bonded oxygen atom. When the perfluoroalkyl group contains an ether-bonded oxygen atom, the number of oxygen atoms can be one or more. Furthermore, the ether-bonded oxygen atom can be located between carbon-carbon bonds or at the end of a carbon bond in the perfluoroalkyl group. The perfluoroalkyl group can be linear or branched, preferably linear.

[0094] From the perspective of high polymerization reactivity, R 45 and R 46 Preferably, at least one of them is a fluorine atom, and particularly preferably both are fluorine atoms.

[0095] Unit (u21) is preferably unit (u21-1).

[0096]

[0097]

[0098] s can be 0 or 1, preferably 0.

[0099] R 51 and R 52Each is independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spirocyclic ring formed by interconnection (where s is 0).

[0100] R 53 and R 54 Each is independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms.

[0101] R 55 It is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. From the viewpoint of high polymerization reactivity, R 55 The preferred atom is fluorine.

[0102] Perfluoroalkyl and perfluoroalkoxy compounds can be linear or branched, with linear being preferred.

[0103] Unit (u22) is preferably unit (u22-1).

[0104]

[0105]

[0106] R 71 ~R 76 Each alkyl group can be a monovalent perfluoroalkyl group or a fluorine atom, optionally containing an ether-bonded oxygen atom. When the perfluoroalkyl group contains an ether-bonded oxygen atom, the number of oxygen atoms can be one or more. Furthermore, the ether-bonded oxygen atom can be inserted between carbon-carbon bonds of the perfluoroalkyl group or at the end of a carbon bond. The perfluoroalkyl group can be linear or branched, preferably linear.

[0107] From the perspective of high polymerization reactivity, R 71 ~R 74 The preferred atom is fluorine.

[0108] In the aforementioned specific cyclic ether structural unit, from the perspective of obtaining a catalyst layer with better oxygen permeability, unit A preferably includes at least one unit selected from the group consisting of unit (u21), unit (u22) and unit (u24), and more preferably unit (u22).

[0109] From the perspective of superior power generation characteristics of fuel cells, the content of unit A is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more, relative to all units contained in polymer H.

[0110] From the perspective of further suppressing the generation of cracks in the catalyst layer and having better power generation characteristics, the content of unit A is preferably 87 mol% or less, more preferably 80 mol% or less, and especially preferably 75 mol% or less, relative to all units contained in polymer H.

[0111] Polymer H may contain only one type of unit A, or it may contain two or more types. When it contains two or more types, the above content refers to their total amount.

[0112] From the perspective of excellent power generation characteristics, polymer H preferably does not contain a cyclic ether structure but contains a unit with an ion exchange group (hereinafter also referred to as "unit B").

[0113] The number of ion exchange groups in each unit contained in unit B is preferably one or more. From the perspective of easily obtaining high molecular weight polymers while maintaining the content of unit A, it is more preferably two or more. From the perspective of facilitating the synthesis of monomers, it is even more preferably two.

[0114] Unit B is preferably a perfluorinated monomer unit having an ion-exchange group, and more preferably a perfluorinated polymer unit having a sulfonic acid functional group.

[0115] The perfluorinated monomer units are preferably units (u31), units (A-1), units (A-2), and units (A-3). From the viewpoint of further improving the power generation characteristics of the fuel cell, units (A-1), units (A-2), and units (A-3) are more preferred. From the viewpoint of more significantly demonstrating the effects of the present invention, unit (A-2) is even more preferred.

[0116]

[0117] In formula (u31), Z is a fluorine atom or a trifluoromethyl group, q is 0 or 1, m is an integer from 0 to 3, p is 0 or 1, n is an integer from 1 to 12, and m + p > 0. When m is 2 or 3, multiple Zs can be the same or different.

[0118] In equation (u31), M + For H + A monovalent metal cation (e.g., potassium ion, sodium ion) or an ammonium ion in which one or more hydrogen atoms are optionally substituted with a hydrocarbon group (e.g., methyl, ethyl), preferably H. + .

[0119]

[0120] In equations (A-1) to (A-3), R F1 and R F2 Each is independently a perfluoroalkylene group having 1 to 3 carbon atoms, or a divalent group of a perfluoroalkylene group whose -CF2- is replaced by an ether-bonded oxygen atom.

[0121] In the above divalent groups, the ether-bonded oxygen atom can be located at the end of the perfluoroalkyl group or between carbon atoms.

[0122] The number of carbon atoms in the above-mentioned divalent groups is preferably 1 to 3, more preferably 2 or 3.

[0123] R F1 and R F2 Specific examples include -CF2-, -CF2CF2-, -CF(CF3)-, -CF2CF2CF2-, -CF(CF2CF3)-, -CF(CF3)CF2-, -CF2CF(CF3)-, -C(CF3)(CF3)-, -CF2OCF2CF2-, and -OCF2CF2-.

[0124] From the perspectives of inexpensive raw materials, ease of manufacturing, and the ability to further improve the ion exchange capacity of polymer H, R F1 and R F2 Each of the components is preferably a perfluoroalkylene group having 1 or 2 carbon atoms, or -CF2OCF2CF2- or -OCF2CF2-. In the case of a perfluoroalkylene group having 2 carbon atoms, a straight chain is preferred. Specifically, -CF2-, -CF2CF2- or -CF(CF3)- are preferred, -CF2- or -CF2CF2- are more preferred, and -CF2- is even more preferred.

[0125] In equation (A-2), R F3 It is a perfluoroalkylene group with 1 to 6 carbon atoms that may have ether bonded oxygen atoms.

[0126] As R F3 Specific examples include -CF2-, -CF2CF2-, -CF(CF3)-, -CF2CF2CF2-, -CF(CF2CF3)-, -CF(CF3)CF2-, -CF2CF(CF3)-, -C(CF3)(CF3)-, and -CF2CF(CF3)OCF2CF(CF3)-.

[0127] From the perspectives of inexpensive raw materials, ease of manufacturing, and the ability to further improve the ion exchange capacity of polymer H, R F3 Preferably, it is a perfluoroalkylene group having 1 to 3 carbon atoms. Specifically, it is preferred to be -CF2-, -CF2CF2- or -CF2CF(CF3)-, and more preferably -CF2CF(CF3)-.

[0128] In equation (A-2), m is 0 or 1.

[0129] From the perspective of improving proton conductivity, the content of unit B is preferably 13 mol% or more relative to all units contained in polymer H.

[0130] From the perspectives of improving water repellency, drainage, and power generation efficiency, the content of unit B is preferably less than 50 mol% relative to all units contained in polymer H.

[0131] Polymer H may contain only one type of unit B, or it may contain two or more types. When it contains two or more types, the above content refers to their total amount.

[0132] Polymer H preferably contains tetrafluoroethylene (TFE) units (hereinafter also referred to as "unit C").

[0133] By incorporating unit C, which imparts water repellency, the water expulsion capacity in the catalyst layer is enhanced, further improving the power generation efficiency of the fuel cell.

[0134] The content of unit C is preferably 5 mol% or more relative to all units contained in polymer H.

[0135] From the viewpoint of improving dispersibility in polymer solutions, the content of unit C is preferably 35 mol% or less relative to all units contained in polymer H.

[0136] From the perspective of better power generation characteristics of fuel cells, the softening temperature of polymer H is preferably above 140°C, more preferably above 150°C, and even more preferably above 160°C.

[0137] From the perspective of further suppressing cracks in the catalyst layer, the softening temperature of polymer H is preferably below 300°C, more preferably below 250°C, and even more preferably below 200°C.

[0138] The softening temperature of polymer H was determined by the method described in the Examples section below.

[0139] From the viewpoint of superior fuel cell durability, the ion exchange capacity of polymer H is preferably 0.8 mEq / g dry resin or more, more preferably 1.0 mEq / g dry resin or more, and even more preferably 1.1 mEq / g dry resin or more.

[0140] From the perspective of excellent power generation characteristics, the ion exchange capacity of polymer H is preferably 1.8 milliequivalents / g dry resin or less, more preferably 1.6 milliequivalents / g dry resin or less, and even more preferably 1.5 milliequivalents / g dry resin or less.

[0141] The ion exchange capacity of polymer H was determined by the method described in the Examples section below.

[0142] (Method for manufacturing polymer H)

[0143] As an example of the manufacturing method of polymer H, we will explain the case where polymer H has an acidic sulfonic acid group.

[0144] As an example of a method for manufacturing polymer H, one can exemplify this method by converting the precursor groups of a precursor polymer (hereinafter also referred to as "polymer F") in which the acidic sulfonic acid group is a precursor group (specifically, a group represented by -SO2F) in polymer H into the acidic sulfonic acid group (-SO3). - H + The method.

[0145] As a specific example of a method for converting a precursor group, i.e., the group represented by -SO2F, into an acidic sulfonic acid group, one can exemplify a method of hydrolyzing the group represented by -SO2F of polymer F to prepare a salt-type sulfonic acid group, and then acidifying the salt-type sulfonic acid group to convert it into an acidic sulfonic acid group.

[0146] The TQ value of polymer F is preferably below 300°C, more preferably below 290°C, and even more preferably below 280°C. If the TQ value is below the upper limit, the solubility or dispersibility of polymer H relative to the liquid medium is improved, thus facilitating the preparation of the composition.

[0147] The TQ value of polymer F is preferably 100°C or higher, more preferably 130°C or higher, and even more preferably 160°C or higher. If the TQ value is above the lower limit, polymer H with sufficient molecular weight can be obtained, thus resulting in excellent strength of the catalyst layer.

[0148] The TQ value is a value related to the molecular weight of the polymer, expressed as a volumetric flow rate of 100 mm³ / h. 3 The velocity is expressed as the temperature corresponding to / second. Volumetric flow rate is the rate at which polymer, under pressure of 3 MPa, melts and flows out from a nozzle (inner diameter: 1 mm, length: 1 mm) at a specific temperature, in mm. 3 The unit / second indicates the amount of polymer flowing out. The TQ value serves as an indicator of the polymer's molecular weight; a higher TQ value indicates a higher molecular weight. The TQ value of polymer F is determined using the method described in the Examples section below.

[0149] Catalyst

[0150] This composition contains a catalyst. The catalyst preferably comprises a support (preferably a porous support) and a metal supported on the support.

[0151] From the perspective of further suppressing the formation of cracks in the catalyst layer, the specific surface area of ​​the carbon support is preferably 500 m². 2 / g or more, preferably 700m 2 / g or more, further preferably 800m 2 / g or more.

[0152] From the perspective of the oxidation durability of solid polymer fuel cells, the preferred specific surface area of ​​the carbon support is 1,400 m². 2 / g or less, more preferably 1,300m 2 / g or less, more preferably 1,200m 2 / g or less.

[0153] The specific surface area of ​​the carbon support was determined by the method described in the Examples section below.

[0154] Specific examples of supports (preferably porous supports) include carbon supports, mesoporous carbon, Ketjen black, and acetylene black.

[0155] Specific examples of carbon carriers include carbon black powder, graphitized carbon, carbon fiber, and carbon nanotubes.

[0156] The shape of the carrier (preferably a porous carrier) is not particularly limited. As for the average particle size of the primary particles of the carrier, there is no particular limitation as long as it can support metal. The average particle size of the primary particles of the carrier is preferably 30 nm or more, more preferably 50 nm or more, and preferably 300 nm or less, more preferably 200 nm or less.

[0157] The average particle size of the primary particles of the carrier refers to the arithmetic mean of the particle sizes (diameters) of any 100 primary particles of the carrier observed using TEM (transmission electron microscopy). It should be noted that if the observed particle shape is not spherical, it is considered spherical when measuring the diameter.

[0158] Metals are preferably loaded onto a carrier.

[0159] Platinum and platinum alloys are examples of metals.

[0160] The platinum alloy is preferably an alloy of platinum with at least one metal selected from the group consisting of platinum group metals other than platinum (ruthenium, rhodium, palladium, osmium, iridium), gold, silver, chromium, iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc and tin, and more preferably an alloy of platinum and cobalt.

[0161] The shape of the metal loaded on the carrier is not particularly limited, but it is preferably granular.

[0162] The average particle size (number average particle size D50) of the metal loaded on the carrier is not particularly limited as long as it can perform its function. It is preferably 1 nm or more, more preferably 2 nm or more, and preferably 10 nm or less, more preferably 5 nm or less.

[0163] The average particle size of the metal was determined by TEM (transmission electron microscopy) and SAXS (small angle X-ray scattering).

[0164] From the perspective of achieving better power generation efficiency in fuel cells, the metal loading relative to the total mass of the catalyst is preferably 20% by mass or more, and more preferably 30% by mass or more.

[0165] From the viewpoint of fuel cell power generation efficiency, the metal loading relative to the total mass of the catalyst is preferably 70% by mass or less, more preferably 60% by mass or less.

[0166] When the catalyst includes a support, from the viewpoint of improving the efficiency, output, and durability of the fuel cell, the mass ratio of polymer H in the catalyst to the mass of the support (mass of polymer H / mass of support) is preferably 0.60 or more, more preferably 0.70 or more, and even more preferably 0.75 or more.

[0167] When the catalyst includes a support, from the viewpoint of increasing fuel cell efficiency, output, and durability, the mass ratio of polymer H in the catalyst to the mass of the support is preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.9 or less.

[0168] Solvent

[0169] This composition contains a solvent. The solvent contains water and alcohol.

[0170] Specific examples of alcohols include methanol, ethanol, propanol (specifically, 1-propanol and 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-tetrafluoro-1-octanol.

[0171] An alcohol only needs to contain at least propanol; it can be used alone or in combination with two or more.

[0172] The water content in the solvent is 50% by mass or more relative to the total mass of the solvent, preferably 55% by mass or more, more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably less than 80% by mass, and even more preferably 70% by mass or less. If the water content in the solvent is within the above range, the formation of cracks in the catalyst layer can be further suppressed.

[0173] From the viewpoint of suppressing catalyst layer cracks, the water content in this composition is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more relative to the total mass of the composition. Furthermore, from the viewpoint of the stability of this composition, it is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0174] The alcohol content in this composition, relative to the total mass of the composition, is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more, from the perspective of suppressing the formation of cracks in the catalyst layer. In addition, from the perspective of the stability of this composition, it is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0175] In this composition, the mass ratio of alcohol content to water content (alcohol content / water content) is preferably 0.60 or more, more preferably 0.65 or more, and preferably 0.80 or less, more preferably 0.70 or less.

[0176] The propanol content in the alcohol is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and preferably 100% by mass or less, more preferably 100% by mass. When the propanol content in the alcohol is within the above range, the generation of cracks in the catalyst layer can be further suppressed.

[0177] From the perspective of suppressing catalyst layer cracks, the content of propanol in the solvent is preferably 15% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more relative to the total mass of the solvent. In addition, from the perspective of the stability of the composition, it is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0178] From the perspective of suppressing catalyst layer cracks, the content of propanol in this composition is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more relative to the total mass of the composition. In addition, from the perspective of the stability of this composition, it is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0179] [Membrane electrode assembly]

[0180] The membrane electrode assembly of the present invention includes: 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. The membrane electrode assembly is suitable for use in solid polymer fuel cells.

[0181] The above-described composition can be used to form any catalyst layer in the catalyst layer of the anode and the catalyst layer of the cathode, and is preferably used to form the catalyst layer of the cathode from the viewpoint of being effective for higher current output.

[0182] Figure 1 This is a cross-sectional view showing an example of the membrane electrode assembly 10 of the present invention. The membrane electrode assembly 10 includes: an anode 13, a cathode 14, and a solid polymer electrolyte membrane 15, wherein the anode 13 has a catalyst layer 11A and a gas diffusion layer 12A; the cathode 14 has a catalyst layer 11C and a gas diffusion layer 12C; and the solid polymer electrolyte membrane 15 is disposed between the anode 13 and the cathode 14 in contact with the catalyst layer 11A and the catalyst layer 11C.

[0183] There are no particular limitations on the method for forming the catalyst layer 11C, and the following methods can be cited as examples.

[0184] (i) A method of coating the composition onto a solid polymer electrolyte membrane 15 or a gas diffusion layer 12C and drying it.

[0185] (ii) A method of coating the composition onto a substrate film, drying it to form a catalyst layer 11C, and transferring the catalyst layer 11C onto a solid polymer electrolyte membrane 15.

[0186] The gas diffusion layer 12C has the function of uniformly diffusing gas into the catalyst layer 11C and also functions as a current collector.

[0187] Examples of materials that can be used as the gas diffusion layer 12C include carbon paper, carbon cloth, and carbon felt. The gas diffusion layer 12C is preferably made of polytetrafluoroethylene or similar materials that have undergone hydrophobic treatment.

[0188] It should be noted that, in Figure 1 Although the membrane electrode assembly 10 includes a gas diffusion layer 12C, the gas diffusion layer is an optional component and may not be included in the membrane electrode assembly.

[0189] The catalyst layer 11A of the anode 13 can be a known anode catalyst layer, and its manufacturing method is the same as that of a known anode catalyst layer.

[0190] The specific example of the gas diffusion layer 12A of the anode 13 is the same as the specific example of the gas diffusion layer 12C described above. Both the gas diffusion layer 12A and the gas diffusion layer 12C are optional components.

[0191] The solid polymer electrolyte membrane 15 is a membrane containing a polymer having ion exchange groups.

[0192] Examples of polymers having ion exchange groups include the aforementioned polymer H and polymers having known ion exchange groups.

[0193] Specific examples of known polymers include polymers disclosed in International Publication No. 2020 / 145287, such as polymers in which the -SO2F group of a polymer having units based on monomers (m31) and units based on tetrafluoroethylene is converted to sulfonic acid groups, and polymers disclosed in International Publication No. 2020 / 145287, such polymers in which the -SO2F group of a polymer having units based on monomers (m32) and units based on tetrafluoroethylene is converted to sulfonic acid groups.

[0194] Solid polymer electrolyte membrane 15 can be formed, for example, by coating a liquid composition of polymer onto a substrate film or catalyst layer (catalyst layer 11A and catalyst layer 11C) and drying it (casting method).

[0195] The liquid composition is a dispersion in which a polymer is dispersed in a solvent containing at least one of an organic solvent and water.

[0196] To stabilize the solid polymer electrolyte membrane 15, heat treatment is preferred. The temperature of the heat treatment depends on the type of polymer and is preferably 130~200°C.

[0197] The solid polymer electrolyte membrane 15 can be treated with hydrogen peroxide water as needed.

[0198] The solid polymer electrolyte membrane 15 can also be reinforced by reinforcing materials. Examples of reinforcing materials include porous materials, fibers, woven fabrics, and nonwoven fabrics. Examples of materials that can be used as reinforcing materials include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, and polyphenylene sulfide.

[0199] To further improve durability, the solid polymer electrolyte membrane 15 optionally contains one or more atoms selected from the group consisting of cerium and manganese. Cerium and manganese decompose hydrogen peroxide, a substance that causes degradation of the solid polymer electrolyte membrane 15. Cerium and manganese preferably exist as ions in the solid polymer electrolyte membrane 15, and cerium and manganese can exist in any state in the solid polymer electrolyte membrane 15 as long as they exist as ions.

[0200] The solid polymer electrolyte membrane 15 may contain silica and heteropoly acids (zirconium phosphate, phosphomolybdic acid, phosphotungstic acid, etc.) as water-retaining agents to prevent drying.

[0201] The membrane electrode assembly 10 is manufactured, for example, by the method described below.

[0202] (i) A method of forming a catalyst layer (catalyst layer 11A and catalyst layer 11C) on a solid polymer electrolyte membrane 15 as a membrane catalyst layer conjugate, and clamping the membrane catalyst layer conjugate with a gas diffusion layer (gas diffusion layer 12A and gas diffusion layer 12C).

[0203] (ii) A method of forming catalyst layers (catalyst layer 11A and catalyst layer 11C) on gas diffusion layers (gas diffusion layer 12A and gas diffusion layer 12C) as electrodes (anode 13, cathode 14) and using the electrodes to hold a solid polymer electrolyte membrane 15.

[0204] The membrane electrode assembly 10 may have a carbon layer (not shown) between the catalyst layer and the gas diffusion layer. If a carbon layer is provided, the gas diffuseability of the surface of the catalyst layer 11 is improved, which can further improve the power generation performance of the fuel cell.

[0205] The carbon layer may comprise, for example, carbon and a nonionic fluoropolymer. A specific example of carbon is preferably carbon nanofibers with a diameter of 1 to 1,000 nm and a length of 1,000 μm or less. A specific example of a nonionic fluoropolymer is polytetrafluoroethylene (PTFE).

[0206] Solid polymer fuel cells

[0207] The solid polymer fuel cell of the present invention includes the above-described membrane electrode assembly.

[0208] The solid polymer fuel cell of the present invention may also have separators on both sides of the membrane electrode assembly, the separators being formed with grooves that serve as gas flow paths.

[0209] Specific examples of separators include metal separators, carbon separators, separators made of materials mixed with graphite and resin, and separators made of various conductive materials.

[0210] In solid polymer fuel cells, oxygen-containing gas is supplied to the cathode and hydrogen-containing gas is supplied to the anode to generate electricity.

[0211] It should be noted that the above-mentioned membrane electrode assembly can also be used in methanol fuel cells that supply methanol to the anode to generate electricity.

[0212] Example

[0213] The present invention will be described in detail below with examples. Examples 1-1 to 1-5 are exemplary embodiments, and Examples 1-6 to 1-7 are comparative examples. However, the present invention is not limited to these examples. It should be noted that the mixing amounts of each component in the tables described below represent mass standards.

[0214] [Ion exchange capacity]

[0215] When determining the ion exchange capacity from polymer F as a precursor, the value is obtained through the following steps. Using polymer F... 19 F-NMR measurements were used to calculate the proportion of each unit, and the ion exchange capacity was calculated based on the proportion of unit B.

[0216] The ion exchange capacity was determined from polymer H using the following procedure. Polymer F-1 (described later) was pressed and molded at a temperature lower than the TQ value (10°C above the TQ value or 210°C) and at 4 MPa (gauge pressure) to obtain a polymer F-1 membrane (100 μm thick). The polymer F-1 membrane was immersed in an alkaline aqueous solution (as shown in Table 2) at 80°C for 16 hours to hydrolyze the -SO2F of polymer F-1, converting it to -SO3K. The polymer membrane was then immersed in a 3 mol / L hydrochloric acid aqueous solution at 50°C for 30 minutes, followed by immersion in ultrapure water at 80°C for 30 minutes. This cycle of immersion in hydrochloric acid and ultrapure water was repeated a total of 5 times to convert the -SO3K of the polymer to -SO3H. Washing with ultrapure water was repeated until the pH of the water containing the polymer membrane reached 7. The polymer membrane was then sandwiched between filter paper and air-dried to obtain a polymer H-1 membrane. After drying the polymer H-1 membrane in a nitrogen-fluidized glove box until its weight remained unchanged and the weight was determined, the membrane was immersed in a 0.85 mol / g sodium hydroxide solution (solvent: water / methanol = 10 / 90 (mass ratio)) at 60°C for at least 72 hours to convert the acidic sulfonic acid groups to sodium salt sulfonic acid groups. The residual sodium hydroxide was back-titrated with 0.1 mol / L hydrochloric acid to determine the ion exchange capacity of polymer H-1.

[0217] [ 19 F-NMR]

[0218] 19 F-NMR was determined at a frequency of 282.7 MHz and a chemical shift standard of CFCl3. Compositional analysis of polymer F was performed using hexafluorobenzene as the solvent, with the solution concentration adjusted to 10% by mass.

[0219] [Proportions of each unit]

[0220] The analysis of the proportions of each unit in polymers derived from monomer units is by 19 Calculation of F-NMR values. It should be noted that the content of each unit in fluoropolymer H is approximately the same as the content of each unit in polymer F.

[0221] [TQ value]

[0222] Using a flow tester (Shimadzu Corporation, CFT-500A) equipped with a nozzle of 1 mm length and 1 mm inner diameter, polymer F was melt-extruded while the temperature was varied under an extrusion pressure of 2.94 MPa (gauge pressure). The extrusion amount of polymer F was determined to be 100 mm. 3 The temperature per second (TQ value). It should be noted that when the TQ value exceeds 300℃, the extrusion rate at four points below 300℃ is calculated, and the TQ value is derived by extrapolating from the measurements at these four points. The extrapolation is performed using an approximation derived by logarithmically approximating the correlation between the extrusion rate and the reciprocal of the absolute temperature. For polymers with the same composition, a higher TQ value indicates a larger molecular weight of the polymer.

[0223] [Softening Temperature]

[0224] For solid polymer electrolyte membranes, dynamic viscoelasticity measurements were performed using a dynamic viscoelasticity measuring device (IT Keisoku Seigyo Co., Ltd., DVA-225) under the following conditions: sample width: 5.0 mm, clamp spacing: 15 mm, measurement frequency: 1 Hz, heating rate: 2 °C / min, and tensile mode. Tanδ (loss tangent) was calculated from the ratio of loss modulus E” to storage modulus E’ (E” / E’), and a tanδ-temperature curve was constructed. The peak temperature between -100 and 200 °C from the tanδ-temperature curve was taken as the softening temperature of polymer H. The softening temperature corresponds to the temperature at which the membrane transitions from a glassy to a rubbery state. The reference dimensions and thickness of the membrane used for calculations were determined at a temperature of 23 °C and a relative humidity of 50% RH.

[0225] (abbreviation)

[0226] TFE: Tetrafluoroethylene

[0227] PFB: CF3CF2CF2C(O)OOC(O)CF2CF2CF3

[0228] HFC-52-13p: CF3(CF2)5H

[0229] Compound 1

[0230]

[0231] Compound 2

[0232]

[0233] Compound 3

[0234]

[0235] [Synthesis of Polymer F-1]

[0236] A 2,575 mL stainless steel autoclave was depressurized under ice bath conditions. 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% by mass, and 172.0 g of HFC-52-13p were aspirated and added to the autoclave, and the pressure was reduced again. Then, 56.90 g of TFE was added, and the temperature was raised to 24 °C to begin the reaction. Stirring was performed using a double-helix ribbon blade. The stirring speed was 60 rpm from the start of the reaction until 2.5 hours, 30 rpm from 2.5 hours to 3.5 hours, and 10 rpm from 3.5 hours to 10 hours. After stirring for 10 hours, the autoclave was depressurized, and unreacted compound 2 and TFE were removed by distillation. The product was then diluted with HFC-52-13p and mixed with a mixture of HFC-52-13p and methanol at a mass ratio of 8:2. The polymer was then aggregated and filtered. The polymer was washed in a mixture of HFC-52-13p and methanol at a mass ratio of 7:3, separated by filtration, and the solid components were dried at 80°C and then vacuum dried at 210°C to obtain polymer F-1.

[0237] The composition, ion exchange capacity and TQ value of polymer F-1 are shown in Table 1.

[0238] [Table 1]

[0239]

[0240] [Synthesis of Polymer H-1]

[0241] Using polymer F-1, the powder of polymer H-1 was obtained by the following method.

[0242] Polymer F-1 was pulverized to a diameter of 2 mm. It was then impregnated in an alkaline aqueous solution (as shown in Table 2) at 80°C for 70 hours to hydrolyze the -SO2F content, converting it to -SO3K. The polymer was then impregnated in a 3 mol / L hydrochloric acid aqueous solution at 80°C for 30 minutes, followed by impregnation in ultrapure water at 80°C for 30 minutes. This cycle of impregnation in hydrochloric acid and ultrapure water was repeated a total of 10 times to convert the -SO3K content of the polymer to -SO3H. Washing with ultrapure water was repeated until the pH of the water containing the polymer reached 7. The polymer was then dried with a nitrogen stream to obtain polymer H-1 powder. The results are shown in Table 2.

[0243] In Table 2, aqueous solution A has a mass ratio of potassium hydroxide / dimethyl sulfoxide / water of 15 / 30 / 55.

[0244] [Table 2]

[0245]

[0246] The ion exchange capacity and softening temperature were determined using polymer H-1. The results are shown in Table 3.

[0247] [Table 3]

[0248]

[0249] [Preparation of liquid composition S-1]

[0250] 18.70 g of polymer H-1 powder (details: 18.22 g polymer, 0.48 g water, 97.4% solids concentration), 22.81 g of ultrapure water, and 54.36 g of 1-propanol were added to a 0.2 L glass autoclave. 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 naturally and the solution was removed from the autoclave. 25.6 g of ultrapure water and 25.6 g of 1-propanol were added to this solution for dilution. After stirring at 110 °C for 1 hour, the mixture was allowed to cool naturally and filtered using a pressure filter (filter paper: ADVANTEC Toyo Co., Ltd., PF040). This yielded a liquid composition S-1 in which polymer H-1 was dispersed in a mixed solvent at 10.2% by mass.

[0251] [Preparation of Composition for Forming Cathode Catalyst Layer]

[0252] <Catalyst (Platinum-supported Carbon)>

[0253] As catalysts, platinum-supported carbon 1 and platinum-supported carbon 2 were prepared.

[0254] (Platinum-supported carbon 1)

[0255] Types of metal: Platinum granules

[0256] Platinum particle content relative to the total mass of carbon supporting platinum: 46.9% by mass

[0257] Average particle size of platinum particles: 2.4 nm

[0258] Types of porous supports: carbon supports

[0259] Specific surface area of ​​carbon support: 800 m² 2 / g

[0260] (Platinum-supported carbon 2)

[0261] Types of metal: Platinum granules

[0262] The content of platinum particles relative to the total mass of carbon supporting platinum is 46.9% by mass.

[0263] Average particle size of platinum particles: 2.4 nm

[0264] Types of porous supports: carbon supports

[0265] Specific surface area of ​​carbon support: 140 m² 2 / g

[0266] <Example 1-1>

[0267] 23.7 g of water and 14.2 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 1. 12.5 g of liquid composition S-1 was then added to achieve an I / C ratio (the mass ratio of polymer H to the carbon support) of 0.8 and a solids concentration of 8.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes. Then, 10.7 g of water and 7.1 g of 1-propanol were added to dilute the dispersed mixture to achieve a solids concentration of 6.0% by mass, yielding composition CI-1 for forming the cathode catalyst layer.

[0268] <Example 1-2>

[0269] 23.7 g of water and 14.2 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 1. 12.5 g of liquid composition S-1 was then added to achieve an I / C ratio of 0.8 and a solids concentration of 8.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes to obtain composition CI-2 for forming the cathode catalyst layer.

[0270] <Example 1-3>

[0271] 23.0 g of water and 14.1 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 1. 9.3 g of liquid composition S-1 was added to achieve an I / C ratio of 0.6 and a solids concentration of 8.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes. Then, 9.9 g of water and 6.6 g of 1-propanol were added to dilute the dispersed mixture to a solids concentration of 6.0% by mass, yielding composition CI-3 for forming the cathode catalyst layer.

[0272] <Example 1-4>

[0273] 33.5 g of water and 4.4 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 1. 12.5 g of liquid composition S-1 was then added to achieve an I / C ratio of 0.8 and a solids concentration of 8.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes. Then, 14.2 g of water and 3.6 g of 1-propanol were added to dilute the mixture, resulting in a solids concentration of 6.0% by mass, thus obtaining composition CI-4 for forming the cathode catalyst layer.

[0274] <Example 1-5>

[0275] 7.3 g of water and 9.1 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 2. 1.9 g of liquid composition S-1 was then added to achieve an I / C ratio (weight ratio of ionomer to catalyst carbon) of 0.12 and a solids concentration of 15.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 90 minutes. Then, 15.7 g of water, 5.0 g of 1-propanol, and 7.5 g of liquid composition S-1 were added, resulting in an I / C ratio of 0.6 and a solids concentration of 8.0% by mass. The mixture was then dispersed using the same planetary ball mill with 5 mm zirconia beads at 300 rpm for 90 minutes to obtain composition CI-5 for forming the cathode catalyst layer.

[0276] <Example 1-6>

[0277] 13.9 g of water and 24.0 g of 1-propanol were added and mixed into 3.0 g of platinum-supported carbon 1. 12.5 g of liquid composition S-1 was added to achieve an I / C ratio of 0.8 and a solids concentration of 8.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes. Then, 7.1 g of water and 10.7 g of 1-propanol were added to dilute the mixture, resulting in a solids concentration of 6.0% by mass, thus obtaining composition CI-6 for forming the cathode catalyst layer.

[0278] <Example 1-7>

[0279] 17.3 g of water and 9.9 g of ethanol were added and mixed into 3.0 g of platinum-supported carbon 1. 12.5 g of liquid composition S-1 was added to achieve an I / C ratio of 0.8 and a solids concentration of 10.0% by mass. The mixture was dispersed using a planetary ball mill (Ito Manufacturing Co., Ltd., model: LP-4) with 5 mm zirconia beads at 300 rpm for 180 minutes. Then, 17.1 g of water, 8.0 g of ethanol, and 3.4 g of 1-propanol were added to dilute the mixture to a solids concentration of 6.0% by mass, yielding composition CI-7 for forming the cathode catalyst layer.

[0280] The compositions of the catalyst layer formation compositions of Examples 1-1 to 1-7 are shown in Table 4 below.

[0281] [Evaluation of the crackability of the catalyst layer]

[0282] <Formation of the catalyst layer>

[0283] As a solid polymer electrolyte membrane, an ion exchange membrane with a thickness of 25 μm (ion exchange capacity: 1.25 milliequivalents / gram of dry resin) is prepared. This ion exchange membrane is formed from a polymer with acidic sulfonic acid groups, which is formed by converting the SO2F groups of the copolymer of TFE and compound 3 into SO3H groups.

[0284] The platinum content is 0.2 mg / cm³. 2 In this manner, the catalyst layer forming composition of each example is applied to the above-mentioned electrolyte membrane using a die-coating machine and dried at 80°C for 10 minutes to obtain a laminate in which a catalyst layer (cathode catalyst layer) is formed on one side of a solid polymer electrolyte membrane.

[0285] <Evaluation Methods>

[0286] Surface images of the catalyst layer (cathode catalyst layer) corresponding to each example were obtained using a digital microscope (KEYENCE Co., Ltd., model: VHX-5000) at a magnification of 200x.

[0287] Based on the obtained surface images, the crackability of the catalyst layer was evaluated according to the following criteria. The evaluation results are shown in Table 4 below.

[0288] It should be noted that, as representative examples of surface images of the catalyst layer, surface images of the catalyst layers corresponding to Examples 1-1 to 1-3 are shown below. Figures 2-4 The surface images of the catalyst layers corresponding to Examples 1-6 to 1-7 are shown in Figures 5-6 .

[0289] A: No cracks were detected on the surface of the catalyst layer.

[0290] B: Cracks were identified on the surface of the catalyst layer, but the cracks were small in size.

[0291] C: Large cracks were identified on the surface of the catalyst layer, or medium-sized cracks were identified across the entire surface.

[0292] [Table 4]

[0293]

[0294] As shown in Table 4, it can be confirmed that when using the catalyst composition of the present invention, the generation of cracks in the catalyst layer can be sufficiently suppressed (Examples 1-1 to 1-5).

[0295] Explanation of reference numerals in the attached figures

[0296] 10. Membrane electrode assembly

[0297] 11A, 11C catalyst layer

[0298] 12A, 12C gas diffusion layer

[0299] 13 Anode

[0300] 14 Cathode

[0301] 15 Solid polymer electrolyte membrane

[0302] It should be noted that the entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-182668, filed on October 24, 2023, are incorporated herein as a disclosure of the present invention.

Claims

1. A composition for forming a catalyst layer, comprising a fluoropolymer, a catalyst, and a solvent. The fluoropolymer has units comprising a cyclic ether structure and has ion-exchange groups. The solvent comprises water and alcohol. The alcohol includes propanol. The water content is 50% by mass or more relative to the total mass of the solvent. The content of propanol is 50% by mass or more relative to the total mass of the alcohol.

2. The composition for forming a catalyst layer according to claim 1, wherein, The catalyst comprises a support and a metal supported on the support. The mass ratio of the fluoropolymer to the carrier is 0.75 or higher.

3. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The specific surface area of ​​the carbon carrier is 700 m². 2 / g or more.

4. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The water content is less than 80% of the total mass of the solvent.

5. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The concentration of the solid components in the composition for forming the catalyst layer is less than 10% by mass.

6. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The fluorinated polymer has an ion exchange capacity of 0.8 milliequivalents / gram of dry resin or higher.

7. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The content of the unit containing the cyclic ether structure is 50 mol% or more relative to all units contained in the fluoropolymer.

8. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The fluoropolymer comprises the unit shown in formula (A-2). In equation (A-2), R F1 and R F2 Each is independently a perfluoroalkylene group having 1 to 3 carbon atoms, or a divalent group of a perfluoroalkylene group whose -CF2- is replaced by an ether-bonded oxygen atom. R F3 It can be a perfluoroalkylene group with 1 to 6 carbon atoms, optionally containing an ether bond oxygen atom. m is 0 or 1.

9. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The fluoropolymer comprises tetrafluoroethylene-based units.

10. The catalyst layer forming composition according to claim 1 or 2, used to form the catalyst layer of the cathode in a membrane electrode assembly. The membrane electrode assembly comprises: 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.

11. The composition for forming a catalyst layer according to claim 1 or 2, wherein, The membrane electrode assembly of claim 10 is a membrane electrode assembly for use in solid polymer fuel cells.

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