Catalyst layer, membrane electrode assembly, and solid polymer-type fuel cell

Abstract

Provided is a catalyst layer with which a solid polymer-type fuel cell having excellent initial power generation performance and power generation performance durability can be formed and in which cracks are less likely to occur.　This catalyst layer comprises a catalyst and a fluorine-containing polymer having an ion exchange group, wherein: the softening temperature of the fluorine-containing polymer is at least 140ºC; the fluorine-containing polymer does not substantially contain a unit having a ring structure; the catalyst contains a porous carrier and a metal supported on the porous carrier; the catalyst has hole parts having a diameter of at least 2 nm and less than 10 nm; and the occupancy rate of the fluorine-containing polymer in the hole parts is 20-60 vol%.

Description

Catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell

[0001] This invention relates to a catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell.

[0002] It is known that the membrane electrode assembly of a polymer electrolyte fuel cell comprises an anode having a catalyst layer, a cathode having a catalyst layer, and a polymer electrolyte membrane disposed between the anode and the cathode. Since oxygen is supplied from the cathode side when the polymer electrolyte fuel cell is in operation, reducing the oxygen transport resistance at the cathode can further improve the performance of the polymer electrolyte fuel cell. For this reason, Patent Document 1 indicates that a fluorine-containing polymer containing units having a ring structure with excellent oxygen permeability is used in the catalyst layer of the cathode.

[0003] International Publication No. 2016-104380

[0004] In recent years, polymer electrolyte fuel cells are sometimes used for long periods of time, so there is a need for further improvement in the durability of each component contained therein. The inventors of this invention have found that when a fluorine-containing polymer containing units having a ring structure as described in Patent Document 1 is used as the catalyst layer of a membrane electrode assembly, cracking of the catalyst layer may occur, indicating room for improvement. Furthermore, polymer electrolyte fuel cells are required to have excellent initial power generation performance and excellent power generation performance durability. Here, excellent power generation performance durability means that the voltage drop is suppressed even when potential fluctuations are repeatedly performed.

[0005] The present invention has been made in view of the above problems, and aims to provide a catalyst layer that can form a polymer electrolyte fuel cell with excellent initial power generation performance and power generation performance durability, and that is less prone to cracking. The present invention also aims to provide a membrane electrode assembly including the catalyst layer, and a polymer electrolyte fuel cell including the membrane electrode assembly.

[0006] The present inventors have diligently studied the above problems and have found that the above problems can be solved by the following configurations: [1] A catalyst layer comprising a fluorine-containing polymer having an ion exchange group and a catalyst, wherein the softening temperature of the fluorine-containing polymer is 140°C or higher, the fluorine-containing polymer substantially does not contain units having a ring structure, the catalyst comprises a porous support and a metal supported on the porous support, the catalyst has pores with a pore diameter of 2 nm or more and less than 10 nm, and the occupancy rate of the fluorine-containing polymer in the pores is 20 to 60 volume%. [2] The catalyst layer according to [1], wherein the fluorine-containing polymer comprises units based on tetrafluoroethylene. [3] The catalyst layer according to [2], wherein the content of the units based on tetrafluoroethylene is 70 mol% or more with respect to the total mass of the fluorine-containing polymer. [4] The catalyst layer according to [2], wherein the content of the units based on tetrafluoroethylene is 78 mol% or more with respect to the total mass of the fluorine-containing polymer. [5] The catalyst layer according to any one of [1] to [4], wherein the fluorine-containing polymer contains a unit represented by formula (A-1) described below. In formula (A-1) described below, R Ｆ１ and R Ｆ２ Each of these independently comprises a perfluoroalkylene group having 1 to 3 carbon atoms, or a perfluoroalkylene group with -CF ２ - is a divalent group substituted with an etheric oxygen atom. [6] The catalyst layer according to any one of [1] to [5], wherein the ion exchange capacity of the fluorine-containing polymer is 0.5 to 1.8 milliequivalents / gram dry resin. [7] The catalyst layer according to any one of [1] to [6], wherein the TQ value of the precursor polymer of the fluorine-containing polymer is 300°C or less. TQ value: When the precursor polymer is melt-extruded using a nozzle with a length of 1 mm and an inner diameter of 1 mm under the conditions of an extrusion pressure of 2.94 MPa, the extrusion amount is 100 mm ３ The temperature at which the temperature is / second. [8] The catalyst layer according to [7], wherein the TQ value is 130°C or higher and 280°C or lower. [9] The specific surface area of ​​the catalyst is 50 to 500 m². ２A catalyst layer according to any one of [1] to [8], wherein the amount is / g.

[10] A catalyst layer according to any one of [1] to [9], wherein the metal is platinum or a platinum alloy.

[11] A catalyst layer according to any one of [1] to

[10] , wherein the ratio of the mass of the fluorine-containing polymer to the mass of the porous support is 0.4 to 1.7.

[12] A catalyst layer according to any one of [1] to

[10] , wherein the ratio of the mass of the fluorine-containing polymer to the mass of the porous support is 0.5 to 1.6.

[13] A catalyst layer according to any one of [1] to

[12] , wherein the occupancy rate is 22 volume% or more.

[14] A catalyst layer according to any one of [1] to

[12] , wherein the occupancy rate is 24 volume% or more.

[15] A catalyst layer according to any one of [1] to

[12] , wherein the occupancy rate is 34 volume% or less.

[16] 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, wherein the catalyst layer of the cathode is the catalyst layer described in any of [1] to

[15] .

[17] A solid polymer fuel cell comprising the membrane electrode assembly described in

[16] .

[0007] According to the present invention, a polymer electrolyte fuel cell with excellent initial power generation performance and power generation performance durability can be formed, and a catalyst layer that is less prone to cracking can be provided. Furthermore, according to the present invention, a membrane electrode assembly including the catalyst layer and a polymer electrolyte fuel cell including the membrane electrode assembly can also be provided.

[0008] This is a cross-sectional view showing an example of a film electrode assembly of the present invention. This image shows the catalyst layer in an unbroken state. This image shows the catalyst layer in a broken state.

[0009] The following definitions of terms apply throughout this specification and the claims unless otherwise specified. “Ion exchange group” means a group capable of exchanging at least some of the ions it contains with other ions, such as the sulfonic acid type functional group and the carboxylic acid type functional group described below. “Sulfonic acid type functional group” refers to an acidic sulfonic acid group (-SO ３ H), and salt-type sulfonic acid groups (-SO ３ M ２ However, M２ is an alkali metal or a quaternary ammonium cation.) is a general term. The "carboxylic acid type functional group" refers to an acid type carboxylic acid group (-COOH) and a salt type carboxylic acid group (-COOM １ . However, M １ is an alkali metal or a quaternary ammonium cation.) is a general term. The "group convertible to an ion exchange group" means a group that can be converted to an ion exchange group by treatments such as hydrolysis treatment, acid formation treatment, etc., and may be referred to as a "precursor group". The "group convertible to a sulfonic acid type functional group" means a group that can be converted to a sulfonic acid type functional group by treatments such as hydrolysis treatment, acid formation treatment, etc. The "group convertible to a carboxylic acid type functional group" means a group that can be converted to a carboxylic acid type functional group by known treatments such as hydrolysis treatment, acid formation treatment, etc.

[0010] The "unit" in a polymer means an atomic group derived from one molecule of the monomer formed by the polymerization of the monomer. The unit may be an atomic group directly formed by the polymerization reaction, or an atomic group in which a part of the atomic group has been converted to another structure by treating the polymer obtained by the polymerization reaction. In addition, the constitutional unit derived from each monomer may be described by a name obtained by attaching "unit" to the monomer name.

[0011] The numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another stepwise described numerical range. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0012] [Catalyst Layer] The catalyst layer of the present invention (hereinafter also referred to as "this catalyst layer") is a catalyst layer comprising a fluorine-containing polymer having ion exchange groups and a catalyst, wherein the softening temperature of the fluorine-containing polymer is 140°C or higher, the fluorine-containing polymer substantially does not contain units having a ring structure, the catalyst comprises a porous support and a metal supported on the porous support, the catalyst has pores with a pore diameter of 2 nm or more and less than 10 nm, and the occupancy rate of the fluorine-containing polymer in the pores is 20 to 60 volume%. Hereinafter, the fluorine-containing polymer contained in this catalyst layer will also be referred to as "polymer H".

[0013] When forming the catalyst layer, if a high-density layer of fluorinated polymer is formed at the interface between the catalyst (especially the metal supported on a porous carrier) and the fluorinated polymer, the oxygen transport resistance increases, which can reduce the initial power generation performance of the polymer electrolyte fuel cell. Therefore, conventionally, fluorinated polymers containing units with a ring structure have been used to form the catalyst layer. This makes it difficult for the polymer chains to be densely arranged, suppressing the formation of the high-density layer and resulting in a polymer electrolyte fuel cell with excellent initial power generation performance. However, due to the ring structure, not only the interface between the catalyst and the fluorinated polymer, but the entire catalyst layer becomes less dense, leading to a problem where the catalyst layer is prone to cracking. To address this problem, the polymer H contained in this catalyst layer substantially does not contain units with a ring structure, which is presumed to reduce the likelihood of cracking in the catalyst layer. Furthermore, despite using polymer H that substantially does not contain units with a ring structure, this catalyst layer can form a polymer electrolyte fuel cell with excellent initial power generation performance. The reason for this is presumed to be that by using polymer H, which has a high softening temperature of 140°C or higher, the polymer chains become less likely to orient when polymer H is adsorbed onto the catalyst (especially the metal supported on the porous support), thereby suppressing the formation of the high-density layer mentioned above.

[0014] Furthermore, the inventors have found that the occupancy rate of the fluorine-containing polymer in the pores of the catalyst contained in the catalyst layer is closely related to the power generation performance and durability of the polymer electrolyte fuel cell, and that when the occupancy rate is 20 to 60 volume%, the power generation performance and durability improve. The details of this reason are not yet clear, but it is presumed to be due to the following: When the fluorine-containing polymer and the metal particles contained in the catalyst come into contact, the metal is ionized and dissolved during the oxidation-reduction reaction process. The dissolved metal ions re-aggregate with other surrounding metal particles, so as the operating time of the polymer electrolyte fuel cell increases, the specific surface area per unit weight of metal in the electrode decreases. In particular, repeated potential fluctuations in the polymer electrolyte fuel cell tend to promote the coarsening of the catalyst. Here, it is thought that the metal contained in the catalyst is abundant in the pores of the porous support (especially the pores corresponding to the specific mesopores described later), and it is presumed that when the occupancy rate is below the upper limit of the above range, the metal contained in the catalyst and the fluorine-containing polymer are not in excessive contact. Therefore, even if potential fluctuations occur repeatedly, the catalytic performance is less likely to deteriorate, which is thought to improve the durability of power generation performance. On the other hand, when the above occupancy rate is above the lower limit of the above range, the metal contained in the catalyst and the fluorine-containing polymer, which plays a role in supplying protons, are located at a moderate distance from each other, and the supply of protons to the catalyst surface is maintained, which is thought to improve the initial power generation performance.

[0015] <Polymer H> Polymer H is not particularly limited as long as it is a fluorine-containing polymer having an ion exchange group, has a softening temperature of 140°C or higher, substantially does not contain units having a ring structure, but it is preferable that it contains perfluoromonomer units, and more preferably that it is a perfluoropolymer having a sulfonic acid type functional group, in order to have excellent initial power generation characteristics. The perfluoromonomer units preferably contain at least one unit A selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units, in order to further improve the initial power generation characteristics of polymer electrolyte fuel cells. Unit A may contain one or both of perfluorovinyl ether units and perfluoroallyl ether units, but it is preferable that it contains perfluoroallyl ether units, and more preferably that it is a perfluoroallyl ether unit, in order to be easy to synthesize.

[0016] The units contained in unit A may or may not have ion exchange groups, but it is preferable that they have ion exchange groups, more preferably that they have sulfonic acid type functional groups, and even more preferably that they have acid type sulfonic acid groups, in order to further improve the initial power generation characteristics of polymer electrolyte fuel cells. When each unit contained in unit A has an ion exchange group, it is preferable that each unit has one or more ion exchange groups, more preferably two or more, in order to easily obtain a high molecular weight polymer while maintaining the content of unit A, and even more preferably two, in order to facilitate the synthesis of perfluoromonomers.

[0017] As the perfluoroallyl ether unit, unit A-1 is preferred because it allows for the easy acquisition of fluorine-containing polymers with a softening temperature within the range described later.

[0018]

[0019] As the perfluorovinyl ether unit, unit A-2 or unit A-3 is preferred.

[0020]

[0021] In formulas A-1 to A-3, R Ｆ１ and R Ｆ２Each of these independently comprises a perfluoroalkylene group having 1 to 3 carbon atoms, or a perfluoroalkylene group with -CF ２ - is a divalent group substituted with an etheric oxygen atom. In the above divalent group, the etheric oxygen atom may be located at the terminal end of the perfluoroalkylene group or between carbon atoms. The number of carbon atoms in the above divalent group is preferably 1 to 3, and more preferably 2 or 3. Ｆ１ and R Ｆ２ A specific example is -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 - These are some of the reasons why R is inexpensive, easy to manufacture, and allows for a higher ion exchange capacity of polymer H. Ｆ１ and R Ｆ２ Each of these is preferably a perfluoroalkylene group having 1 or 2 carbon atoms. In the case of 2 carbon atoms, a straight chain is preferred. Specifically, -CF ２ -, -CF ２ CF ２ - or - CF (CF ３ ) - Preferably, -CF ２ - or -CF ２ CF ２ - is more preferable, -CF ２ - is even more preferable.

[0022] In formula A-2, R Ｆ３ This is a perfluoroalkylene group having 1 to 6 carbon atoms. Ｆ３ A specific example is -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 CF (CF ３ ) OCF ２ CF (CF ３ )-- is one example. R Ｆ３ A perfluoroalkylene group having 1 to 3 carbon atoms is preferred. Specifically, -CF ２ -, -CF ２ CF ２ - or -CF ２ CF (CF ３ ) - Preferably, -CF ２ CF (CF ３ ) - is more preferable. In formula A-2, m is 0 or 1.

[0023] The perfluoromonomer unit may contain units other than unit A. Examples of units other than unit A include perfluoromonomer units that do not have an ion exchange group or its precursor group (hereinafter also referred to as "unit B"). Specific examples of unit B include tetrafluoroethylene (hereinafter also referred to as "TFE") units and hexafluoropropylene units, with TFE units being preferred due to their superior catalyst layer strength.

[0024] The content of unit A is preferably 5 mol% or more, more preferably 6 mol% or more, and even more preferably 8 mol% or more, relative to the total units in polymer H, in order to facilitate the ion exchange capacity and softening temperature to be within the range described later. The content of unit A is preferably 30 mol% or less, more preferably 22 mol% or less, and even more preferably 17 mol% or less, relative to the total units in polymer H, in order to provide excellent strength to the catalyst layer.

[0025] The content of unit B is preferably 70 mol% or more, more preferably 78 mol% or more, and even more preferably 83 mol% or more, relative to the total units in polymer H, from the viewpoint of making the catalyst layer less prone to cracking. The content of unit B is preferably 95 mol% or less, more preferably 94 mol% or less, and even more preferably 92 mol% or less, relative to the total units in polymer H, from the viewpoint of improving the solubility or dispersibility of polymer H in a liquid medium and making it easier to prepare a liquid composition, relative to the total units in polymer H.

[0026] Polymer H substantially does not contain units having a ring structure (hereinafter also referred to as "unit X1"). Examples of ring structures include aliphatic hydrocarbon rings, aliphatic heterocycles, aromatic hydrocarbon rings, aromatic heterocycles, etc. The ring structure may be present in the main chain or in the side chains. Specific examples of unit X1 include the units having a cyclic ether structure described in Japanese Patent No. 4997968 and Japanese Patent No. 5454592. The meaning of polymer H substantially not containing unit X1 is that the content of unit X1 is 1 mol% or less relative to the total units in polymer H, and it is preferable that it contains no unit X1 at all (0 mol%).

[0027] It is preferable that polymer H substantially does not contain units having halogen atoms other than fluorine atoms (hereinafter also referred to as "unit X2"). This makes chain transfer reactions less likely to occur when polymer H is produced by polymerizing monomers, resulting in less oligomer generation during production. Specific examples of unit X2 include chlorotrifluoroethylene units, bromotrifluoroethylene units, iodotrifluoroethylene units, and dichlorodifluoroethylene units. It is preferable that polymer H substantially does not contain unit X2 (0 mol%), similar to unit X1.

[0028] It is preferable that polymer H substantially does not contain units having a crosslinked structure consisting of covalent bonds (hereinafter also referred to as "unit X3"). This makes it easier for polymer H to dissolve or disperse in a liquid medium, so when forming a catalyst layer using a liquid composition containing polymer H, a catalyst, and a liquid medium, the polymer H, catalyst, and liquid medium are uniformly dispersed amongst themselves, making it easier to form a smooth catalyst layer. A crosslinked structure consisting of covalent bonds refers to a structure in which a monomer having a crosslinkable group that can be crosslinked by covalent bonds (for example, a vinyl group, a perfluorovinyl group, etc.) is polymerized, and then the crosslinkable group is crosslinked by covalent bonds. Specific examples of unit X3 include a structure obtained by polymerizing a compound of formulas 8 to 15 (a compound having two crosslinkable groups) described in Japanese Patent Application Publication No. 2001-176524, and then crosslinking the crosslinkable groups not used in polymerization by covalent bonds, or a unit having a structure obtained by crosslinking a monomer having a crosslinkable group that can be crosslinked by covalent bonds simultaneously with the polymerization reaction. The meaning of polymer H substantially containing unit X3 is the same as unit X1, and it is preferable that it contains no unit X3 (0 mol%).

[0029] The softening temperature of polymer H is 140°C or higher, preferably 150°C or higher, and more preferably 160°C or higher, from the viewpoint of superior initial power generation performance of the polymer electrolyte fuel cell. The softening temperature of polymer H is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower, from the viewpoint of preventing cracking of the catalyst layer. The softening temperature of polymer H is determined by the method described in the Examples section below.

[0030] The ion exchange capacity of polymer H is preferably 0.5 to 2.5 milliequivalents / gram dry resin, more preferably 1.0 to 2.2 milliequivalents / gram dry resin, and even more preferably 1.25 to 1.8 milliequivalents / gram dry resin. From the viewpoint of superior initial power generation performance of polymer electrolyte fuel cells, the ion exchange capacity of polymer H is preferably 0.5 milliequivalents / gram dry resin or more, more preferably 1.0 milliequivalents / gram dry resin or more, and even more preferably 1.25 milliequivalents / gram dry resin or more. From the viewpoint of superior strength of the catalyst layer, the ion exchange capacity of polymer H is preferably 3.0 milliequivalents / gram dry resin or less, more preferably 2.5 milliequivalents / gram dry resin or less, even more preferably 2.2 milliequivalents / gram dry resin or less, and particularly preferably 1.8 milliequivalents / gram dry resin or less. The ion exchange capacity of polymer H is determined by the method described in the Examples section below.

[0031] The thickness of the catalyst layer is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and particularly preferably 5 μm or more, from the viewpoint of the strength of the catalyst layer. The thickness of the catalyst layer is preferably 20 μm or less, more preferably 18 μm or less, even more preferably 16 μm or less, and particularly preferably 15 μm or less, from the viewpoint of superior initial power generation performance of the polymer electrolyte fuel cell.

[0032] (Method for producing polymer H) The method for producing polymer H will be explained using the case where polymer H has acidic sulfonic acid groups as an example. One example of a method for producing polymer H is when the acidic sulfonic acid groups in polymer H are precursor groups (specifically, -SO ２ The precursor group of the precursor polymer (hereinafter also referred to as "polymer F"), which is a group represented by F, is an acidic sulfonic acid group (-SO ３ － H ＋ One method is to convert it to the precursor group -SO ２ A specific example of a method for converting the group represented by F to an acidic sulfonic acid group is the -SO group of polymer F. ２ One method involves hydrolyzing the group represented by F to obtain a salt-type sulfonic acid group, and then converting the salt-type sulfonic acid group to an acid-type sulfonic acid group.

[0033] Polymer F contains perfluoromonomer units, -SO ２ A perfluoropolymer having a group represented by F is preferred.

[0034] The perfluoromonomer units in polymer F preferably include at least one unit a selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units. Unit a may include one or both of perfluorovinyl ether units and perfluoroallyl ether units, but it is preferable to include perfluoroallyl ether units, and more preferably perfluoroallyl ether units, from the standpoint of ease of synthesis.

[0035] The unit a may or may not have a precursor group for an ion exchange group, but it is preferable that it has a precursor group for an ion exchange group, specifically a precursor group for a sulfonic acid type functional group (specifically -SO ２ It is more preferable that the group has a group represented by F.

[0036] A specific example of a perfluorovinyl ether unit in unit a is the acidic sulfonic acid group of the perfluorovinyl ether unit in unit A mentioned above, which is -SO ２ One example is a unit that has been changed to a base represented by F.

[0037] In unit a, unit a-1 is preferred as the perfluoroallyl ether unit.

[0038]

[0039] R in equation a-1 Ｆ１ and R Ｆ２ These are R in equation A-1, respectively. Ｆ１ and R Ｆ２ It is synonymous with [the above].

[0040] The perfluoromonomer units in unit a may include units other than unit a. Specific examples of units other than unit a include perfluoromonomer units that do not have ion exchange groups and their precursor groups. Specific examples of perfluoromonomer units that do not have ion exchange groups and their precursor groups are the same as those for polymer H.

[0041] Preferably, the content of each unit in polymer F is the same as the content of each unit in polymer H.

[0042] Polymer F preferably substantially contains at least one unit selected from the group consisting of units having halogen atoms other than fluorine atoms, units having a ring structure, and units having a cross-linked structure consisting of covalent bonds. It is more preferably substantially free of units having a ring structure, and even more preferably substantially free of all of these units. Specific examples of units having halogen atoms other than fluorine atoms, units having a ring structure, and units having a cross-linked structure consisting of covalent bonds are the same as those for polymer H. Note that "substantially free" has the same meaning as in the case of polymer H.

[0043] The TQ value of polymer F is preferably 300°C or less, more preferably 280°C or less, even more preferably 250°C or less, and particularly preferably 230°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 liquid composition. 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, resulting in excellent strength of the catalyst layer. The TQ value is a value related to the molecular weight of the polymer, and the volumetric flow rate is 100 mm. ３ The temperature is expressed as watts per second. The volumetric flow rate is measured by melting and flowing a polymer through a constant-temperature nozzle (inner diameter: 1 mm, length: 1 mm) under a pressure of 2.94 MPa, and measuring the amount of polymer flowing out in mm³. ３ This is expressed in units of per second. The TQ value is an indicator of the molecular weight of the polymer; a higher TQ value indicates a higher molecular weight. The TQ value of polymer F is determined by the method described in the Examples section below.

[0044] <Catalyst> The catalyst includes a porous carrier and a metal supported on the porous carrier. The catalyst has pores with a pore diameter of 2 nm or more and less than 10 nm. The pores are pores derived from the porous carrier constituting the catalyst. The catalyst may have pores with a pore diameter different from the pores with a pore diameter of 2 nm or more and less than 10 nm. In this specification, the pore distribution obtained by the nitrogen adsorption method is also simply referred to as "pore distribution". The above pore diameter is obtained from the pore distribution, and pores with a pore diameter of 50 nm or more and less than 300 nm are referred to as "macropores", pores with a pore diameter of 2 nm or more and less than 50 nm are referred to as "mesopores", and pores with a pore diameter of 2 nm or more and less than 10 nm are also referred to as "specific mesopores". Details of the method for measuring the pore distribution are as described in the Examples section below.

[0045] The total pore volume of the specific mesopores per 1 g of the catalyst is preferably 0.01 cm ３ or more, more preferably 0.02 cm ３ or more. From the point of view of durability performance, it is preferably 0.70 cm ３ or less, more preferably 0.60 cm ３ or less, still more preferably 0.40 cm ３ or less, particularly preferably 0.20 cm ３ or less. The total pore volume of the macropores per 1 g of the catalyst is preferably 0.05 cm ３ or more, more preferably 0.10 cm ３ or more. From the point of view of durability performance, it is preferably 0.70 cm ３ or less, more preferably 0.60 cm ３ or less. The ratio of the total pore volume of the specific mesopores to the total pore volume of the mesopores and macropores is preferably 10% or more, more preferably 20% or more from the point of view of initial performance, and preferably 60% or less, more preferably 50% or less from the point of view of durability performance. Details of the method for measuring the total pore volume of each pore are as described in the Examples section below.

[0046] The specific surface area of the catalyst is preferably 30 - 700 m ２ / g, more preferably 50 - 600 m ２It is more preferable that the value be / g, and 70 to 500m ２ It is even more preferable that the amount is / g. The specific surface area of ​​the catalyst is 30 m², as this provides better initial power generation performance for polymer electrolyte fuel cells. ２ Preferably 50 m ２ More preferably 70 m ２ A value of 1 / g or more is even more preferable. The specific surface area of ​​the catalyst is 700 m² from the viewpoint of oxidation resistance performance of the polymer electrolyte fuel cell. ２ Preferably less than / g, and 600m ２ More preferably less than / g, and 500m ２ A value of less than or equal to / g is even more preferable. The specific surface area of ​​the catalyst is determined by the method described in the Examples section below. Specifically, after degassing the sample to be measured (i.e., the catalyst powder before filling with the fluorine-containing polymer), the specific surface area and pore capacity can be determined by analyzing the results obtained from nitrogen adsorption measurement using the constant-volume method with an automatic specific surface area / pore distribution analyzer (e.g., Shimadzu Corporation's "Tristar II 3020") using the BET method or the BJH method. Unless otherwise specified, the specific surface area of ​​the catalyst refers to the value calculated by the BET method, and the pore capacity of the catalyst refers to the value calculated from pore distribution analysis using the BJH method. The measurement is performed at liquid nitrogen temperature (approximately 77 K), and the measurement conditions (relative pressure range, degassing conditions, etc.) and the type of analysis software are not particularly limited.

[0047] Specific examples of porous carriers include carbon carriers, mesoporous carbon, Ketjenblack, and acetylene black. Specific examples of carbon carriers include carbon black powder, graphitized carbon, carbon fibers, and carbon nanotubes.

[0048] The shape of the porous carrier is not particularly limited, and the average particle diameter of the primary particles of the porous carrier is also not particularly limited as long as it can support the metal. However, the average particle diameter of the primary particles of the porous carrier is preferably 30 nm or more, more preferably 50 nm or more, preferably 300 nm or less, and more preferably 200 nm or less. The average particle diameter of the primary particles of the porous carrier refers to the arithmetic mean of the particle diameters (diameters) of any 100 primary particles of the carrier observed with a TEM (transmission electron microscope). If the observed particle shape is not spherical, it is considered spherical and its diameter is measured.

[0049] The metal is supported on a porous carrier. Specific examples of metals include platinum and platinum alloys. Platinum alloys are preferably alloys 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 alloys of platinum and cobalt.

[0050] The shape of the metal supported on the porous carrier is not particularly limited, but it is preferably particulate. The average particle size (number average particle size D50) of the metal supported on the porous carrier is not particularly limited as long as the performance can be achieved, but it is preferably 1 nm or more, more preferably 2 nm or more, preferably 10 nm or less, and more preferably 5 nm or less. The average particle size of the metal is measured by TEM (transmission electron microscope) or SAXS (small-angle X-ray scattering).

[0051] The amount of metal supported is preferably 20% by mass or more, and more preferably 30% by mass or more, relative to the total mass of the catalyst, in terms of achieving superior power generation efficiency of the polymer electrolyte fuel cell. From the viewpoint of power generation efficiency of the polymer electrolyte fuel cell, the amount of metal supported is preferably 70% by mass or less, and more preferably 60% by mass or less, relative to the total mass of the catalyst.

[0052] The ratio of the mass of polymer H to the mass of the porous carrier (mass of polymer H / mass of porous carrier) is preferably 0.4 to 1.7, more preferably 0.5 to 1.6, and even more preferably 0.6 to 1.4. From the viewpoint of improving the efficiency, power output, and durability of the polymer fuel cell, the ratio of the mass of polymer H to the mass of the porous carrier is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6. From the viewpoint of improving the efficiency, power output, and durability of the polymer fuel cell, the ratio of the mass of polymer H to the mass of the porous carrier is preferably 1.7 or lower, more preferably 1.6 or lower, and even more preferably 1.4 or lower.

[0053] In this specification, the proportion of polymer H in the total volume of a specific mesopore is also referred to as "occupancy rate" (unit: volume %). The occupancy rate is 60 volume % or less, preferably 55 volume % or less, more preferably 50 volume % or less, and even more preferably 34 volume % or less, from the viewpoint of superior power generation performance and durability. The occupancy rate is 20 volume % or more, preferably 22 volume % or more, and more preferably 24 volume % or more, from the viewpoint of superior proton transport performance. The occupancy rate is determined by the method described in the Examples section below. Examples of methods for bringing the occupancy rate within the above range include bringing the ratio of the mass of polymer H to the mass of the porous support within the above range, bringing the specific surface area of ​​the catalyst within the above range, bringing the ion exchange capacity of polymer H within the above range, adjusting the polymerization conditions of polymer H, and adjusting the preparation conditions of the liquid composition of polymer H.

[0054] <Applications> This catalyst layer is suitably used as a catalyst layer for the cathode of a membrane electrode assembly of a polymer electrolyte fuel cell. It may also be used as a catalyst layer for the anode of a membrane electrode assembly of a polymer electrolyte fuel cell, to the extent that it does not impair the effects of the invention. In addition, it may be used as a catalyst layer for electrochemical devices such as methanol fuel cells, alkali chloride electrolysis, polymer electrolyte water electrolysis, redox flow secondary batteries, and electrochemical hydrogen pumps, for the purpose of forming electrochemical devices with excellent initial performance and performance durability.

[0055] [Membrane Electrode Assembly] The membrane electrode assembly of the present invention 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, wherein the catalyst layer of the cathode is the catalyst layer described above. The membrane electrode assembly is suitably used in solid polymer fuel cells. According to the membrane electrode assembly of the present invention, since it has the catalyst layer described above, a solid polymer fuel cell with excellent initial power generation performance and power generation performance durability can be formed.

[0056] Figure 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 11A and a gas diffusion layer 12A, a cathode 14 having a catalyst layer 11C and a gas diffusion layer 12C, and a solid polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14 in contact with the catalyst layer 11A and the catalyst layer 11C.

[0057] In Figure 1, the catalyst layer 11C of the cathode 14 is the catalyst layer described above.

[0058] The method for forming the catalyst layer 11C is not particularly limited, but examples include the following: (i) Applying a catalyst layer forming solution onto a solid polymer electrolyte membrane 15 or a gas diffusion layer 12C and drying it; (ii) Applying a catalyst layer forming solution onto a substrate film, drying it to form a catalyst layer 11C, and transferring this catalyst layer 11 onto the solid polymer electrolyte membrane 15.

[0059] The specific examples of polymer H and catalyst contained in the catalyst layer forming liquid are the same as those of polymer H and catalyst in the catalyst layer described above, so their explanation will be omitted.

[0060] The polymer H content is preferably 1% by mass or more, more preferably 2% by mass or more, and more preferably 5% by mass or less, and more preferably 4% by mass or less, based on the total mass of the catalyst layer forming liquid.

[0061] The catalyst content is preferably 5% by mass or more, more preferably 7% by mass or more, and more preferably 10% by mass or less, and more preferably 9% by mass or less, based on the total mass of the catalyst layer forming liquid.

[0062] Examples of solvents include water and organic solvents, and mixtures thereof may also be used. Examples of organic solvents include alcohols. Specific examples of alcohols include methanol, ethanol, 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. Organic solvents may be used individually or in combination of two or more. In particular, the solvent is preferably a mixed solvent of water and alcohol, and more preferably a mixed solvent of water and ethanol or 1-propanol. The solvent content is preferably 80% by mass or more, more preferably 85% by mass or more, and more preferably 98% by mass or less, and more preferably 95% by mass or less, based on the total mass of the catalyst layer forming liquid. When the solvent is a mixed solvent of water and alcohol, the mass ratio of the alcohol content to the water content (alcohol content / water content) is preferably 0.05 or more, more preferably 0.5 or more, and more preferably 3 or less, and more preferably 2 or less.

[0063] The gas diffusion layer 12C has the function of uniformly diffusing gas into the catalyst layer 11C and also functions as a current collector. Examples of materials for the gas diffusion layer 12C include carbon paper, carbon cloth, and carbon felt. It is preferable that the gas diffusion layer 12C is treated to be water-repellent with polytetrafluoroethylene or the like. In the membrane electrode assembly 10 shown in Figure 1, the gas diffusion layer 12C is included, but the gas diffusion layer is an arbitrary component and does not have to be included in the membrane electrode assembly.

[0064] As the catalyst layer 11A of the anode 13, a known catalyst layer for anodes can be used, and its manufacturing method is the same as that of a known catalyst layer for anodes. A 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, and the gas diffusion layer 12A is an arbitrary component, just like the gas diffusion layer 12C.

[0065] The solid polymer electrolyte membrane 15 is a membrane containing a polymer having ion exchange groups. Examples of polymers having ion exchange groups include the polymer H described above and known polymers having ion exchange groups. A specific example of a known polymer is the polymer -SO, which has units based on the monomer (m31) and units based on tetrafluoroethylene, as described in International Publication No. 2020 / 145287. ２ Polymers in which the group represented by F is converted to a sulfonic acid group, and polymers having units based on the monomer (m32) described in International Publication No. 2020 / 145287 and units based on tetrafluoroethylene -SO ２ Examples include polymers in which the group represented by F has been converted to a sulfonic acid group.

[0066] The solid polymer electrolyte membrane 15 can be formed, for example, by a method (casting method) in which a liquid composition of the polymer is applied to a base film or catalyst layer (catalyst layer 11A and catalyst layer 11C) and dried. The liquid composition is a dispersion in which the polymer is dispersed in a solvent containing at least one of an organic solvent and water.

[0067] It is preferable to perform heat treatment to stabilize the solid polymer electrolyte membrane 15. The heat treatment temperature is preferably 130 to 200°C, although this depends on the type of polymer. The solid polymer electrolyte membrane 15 may also be treated with hydrogen peroxide solution if necessary.

[0068] The solid polymer electrolyte membrane 15 may be reinforced with a reinforcing material. Examples of reinforcing materials include porous materials, fibers, woven fabrics, nonwoven fabrics, etc. Examples of materials for the reinforcing material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, polyphenylene sulfide, etc.

[0069] The solid polymer electrolyte membrane 15 may contain one or more atoms selected from the group consisting of cerium and manganese in order to further improve its durability. Cerium and manganese decompose hydrogen peroxide, which is a substance that causes deterioration of the solid polymer electrolyte membrane 15. It is preferable that cerium and manganese exist as ions in the solid polymer electrolyte membrane 15, but they may exist in any state in the solid polymer electrolyte membrane 15 as long as they exist as ions. The solid polymer electrolyte membrane 15 may also contain silica and heteropoly acids (zirconium phosphate, phosphomolybdic acid, phosphotungstic acid, etc.) as water-retaining agents to prevent drying.

[0070] The membrane electrode assembly 10 is manufactured, for example, by the following methods: (i) forming a catalyst layer (catalyst layer 11A and catalyst layer 11C) on a solid polymer electrolyte membrane 15 to form a membrane catalyst layer assembly, and sandwiching the membrane catalyst layer assembly with gas diffusion layers (gas diffusion layer 12A and gas diffusion layer 12C). (ii) forming a catalyst layer (catalyst layer 11A and catalyst layer 11C) on a gas diffusion layer (gas diffusion layer 12A and gas diffusion layer 12C) to form electrodes (anode 13, cathode 14), and sandwiching the solid polymer electrolyte membrane 15 with these electrodes.

[0071] The membrane electrode assembly 10 may have a carbon layer (not shown) between the catalyst layer and the gas diffusion layer. By arranging the carbon layer, the gas diffusion properties on the surface of the catalyst layer 11 are improved, further enhancing the power generation performance of the fuel cell. The carbon layer may, for example, contain carbon and a nonionic fluorine-containing polymer. A specific example of the carbon is carbon nanofiber with a fiber diameter of 1 to 1000 nm and a fiber length of 1000 μm or less. A specific example of the nonionic fluorine-containing polymer is polytetrafluoroethylene.

[0072] [Solid Polymer Fuel Cell] The solid polymer fuel cell of the present invention includes the membrane electrode assembly described above. Because the solid polymer fuel cell of the present invention includes the membrane electrode assembly described above, it has excellent initial power generation performance and power generation performance durability. The solid polymer fuel cell of the present invention may have separators on both sides of the membrane electrode assembly, with grooves formed therein to serve as gas flow paths. Specific examples of separators include metal separators, carbon separators, separators made of a material mixed with graphite and resin, and separators made of various conductive materials. In solid polymer fuel cells, power generation is performed by supplying an oxygen-containing gas to the cathode and a hydrogen-containing gas to the anode. The membrane electrode assembly described above can also be applied to methanol fuel cells, which generate power by supplying methanol to the anode.

[0073] The present invention will be described in detail below with reference to examples. Examples 1, 5 to 8 are examples, and Examples 2 to 4 and 9 are comparative examples. However, the present invention is not limited to these examples.

[0074] [Ion Exchange Capacity] To determine the ion exchange capacity from the precursor polymer F, the value was obtained by the following procedure. A film of polymer F was vacuum-dried at 120°C for 12 hours. After measuring the mass of the dried polymer film, the film of polymer F was 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 hydrolyze the fluorosulfonyl groups. The ion exchange capacity of polymer F was determined by back titration of the hydrolyzed sodium hydroxide solution with 0.1 mol / L hydrochloric acid. To determine the ion exchange capacity from polymer H, the value was obtained by the following procedure. A film of polymer H was dried in a glove box with nitrogen flow until its weight no longer changed, and its weight was determined. Then, the film of polymer H was 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 was determined by back titrating the amount of remaining sodium hydroxide with 0.1 mol / L hydrochloric acid.

[0075] [１９ F-NMR] １９ F-NMR was performed at a frequency of 282.7 MHz, using CD as the solvent. ３ CN, chemical shift standard: CFCl ３ The measurements were taken under the specified conditions. The compositional analysis of polymer F was performed by adjusting the solution concentration to 0.1% by mass using hexafluorobenzene as the dissolving solvent. The compositional analysis of polymer H was performed using the liquid composition described later, either as is or after adjusting its concentration.

[0076] [Proportion of each unit] Analysis of the proportion of each unit in the polymer derived from monomer units is performed using ion exchange capacity measurements for binary copolymers consisting of two monomer units, and for multipolymers consisting of three or more monomer units. １９ It was calculated from F-NMR measurement values.

[0077] [TQ Value] A flow tester (Shimadzu Corporation, CFT-500A) equipped with a nozzle 1 mm in length and 1 mm in inner diameter was used to melt-extrude polymer F at an extrusion pressure of 2.94 MPa (gauge pressure) while varying the temperature. The extrusion volume of polymer F was 100 mm. ３ The temperature at which the value per second (TQ value) is obtained was determined. If the TQ value exceeds 300°C, the extrusion rate at four points below 300°C was measured, and the TQ value was calculated by extrapolating from these four measurements. Extrapolation was performed using an approximation formula that logarithmically approximates 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.

[0078] [Softening Temperature] Dynamic viscoelasticity measurements were performed on a film made of polymer H using a dynamic viscoelasticity measuring device (DVA-225, manufactured by IT Measurement Control Co., Ltd.) under the following conditions: sample width: 5.0 mm, gripping distance: 15 mm, measurement frequency: 1 Hz, heating rate: 2 °C / min, and tensile mode. The tanδ (loss tangent) was calculated from the ratio of the loss modulus E'' to the storage modulus E' (E'' / E'), and a tanδ-temperature curve was created. The value obtained by reading the peak temperature between -100 and 200 °C from the tanδ-temperature curve was defined as the softening temperature of polymer H. The softening temperature corresponds to the temperature at which the material transitions from a glassy state to a rubbery state. The reference dimensions and film thickness of the film used in the calculation were measured under the conditions of temperature: 23 °C and relative humidity: 50% RH.

[0079] [Pore Distribution Measurement by Nitrogen Adsorption Method] The pore distribution was obtained by analyzing the sample to be measured using an automated specific surface area / pore distribution analyzer (Shimadzu Corporation, model number: Tristar II 3020, measurement method: constant volume nitrogen adsorption method) with the BJH method. The specific surface area and pore capacity of the catalyst, described later, were calculated from the above pore distribution.

[0080] [Occupancy] The coating liquids for forming the cathode catalyst layer described later were applied to a PET film, dried at 80°C for 10 minutes, and the powder obtained by scraping off the coating layer was used as sample 1 of the catalyst to which polymer H was attached. Using the obtained sample 1, pore distribution measurement and analysis were performed by nitrogen adsorption method, and the total volume P of the specific mesopores was determined. １ The following was determined. In addition, a coating solution that did not contain polymer H (i.e., a mixture of catalyst-supported carbon and solvent) was applied to a PET film, dried, and the powder obtained by scraping off the coating layer was used as sample 2 of the catalyst without polymer H attached. The above measurements and analyses were performed using the obtained sample 2 to determine the total volume P of the specific mesopores. ０ We calculated the value of P. １ and P ０ The occupancy rate was calculated using the following formula (1) based on the values. Note that the total volume of the specified mesopores refers to the total pore volume of the specified mesopores. Occupancy rate (volume %) = (P ０ -P １ ) × 100 / P ０

[0081] (Abbreviations) TFE: Tetrafluoroethylene, tBPO: (CH ３ ) ３ COOC (CH ３ ) ３ , 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, HFE-347pc-f:CF ３ CH ２OCF ２ CF ２ H, HCFC-225cb: CClF ２ CF ２ CHClF, V-601: CH ３ OCOC((CH) ３ ) ２ )N=N-C((CH ３ ) ２ COOCH ３ .

[0082] Compound 1

[0083]

[0084] Compound 2

[0085]

[0086] Compound 3

[0087]

[0088] Compound 4

[0089]

[0090] [Synthesis of Polymer F-1] 70.0 g of compound 1 was placed in an autoclave (internal volume 100 mL, stainless steel) and degassed by cooling with liquid nitrogen. The autoclave was heated in an oil bath until the internal temperature reached 125°C, and nitrogen was sealed into the autoclave to a pressure of 0.15 MPa (gauge pressure). 4.52 g of TFE was introduced into the autoclave, and the pressure became 0.86 MPa (gauge pressure). A mixture of 45.5 mg of the polymerization initiator tBPO and 1.52 g of compound 1 was injected into the autoclave through the injection line. Next, 2.00 g of compound 1 was injected through the injection line. Nitrogen gas was then introduced through the injection line to completely inject the residual liquid in the injection line. This operation increased the pressure to 0.95 MPa (gauge pressure). Polymerization was carried out by continuously adding TFE while maintaining the pressure at 0.95 MPa (gauge pressure). After 8 hours, when the amount of TFE added reached 14.79 g, the autoclave was cooled to stop polymerization, and the gas in the system was purged. The reaction solution was diluted with HFC-52-13p, then HFE-347pc-f was added, the polymer was agglomerated, and filtered. Subsequently, the polymer was stirred in HFC-52-13p, and the process of re-aggregating with HFE-347pc-f was repeated twice. Vacuum drying was performed at 180°C for 16 hours to obtain 20.8 g of polymer F-1, a copolymer of TFE and compound 1.

[0091] [Synthesis of Polymer F-2] 70.0 g of compound 1 was placed in an autoclave (internal volume 100 mL, stainless steel) and degassed by cooling with liquid nitrogen. The autoclave was heated in an oil bath until the internal temperature reached 75°C, and nitrogen was sealed into the autoclave to a pressure of 0.29 MPa (gauge pressure). TFE was introduced until the pressure reached 0.60 MPa (gauge pressure). 0.47 g of a mixture of the polymerization initiator V-601 and compound 1 (concentration 15 wt%) was injected into the autoclave through the injection line to start polymerization. TFE was continuously added while maintaining the pressure at 0.60 MPa (gauge pressure), and 0.23 g of the above polymerization initiator and compound 1 mixture (concentration 15 wt%) was added 9.5 hours and 17.5 hours after the start of polymerization to continue polymerization. After 34 hours, when the amount of TFE added reached 5.76 g, the autoclave was cooled to stop polymerization, and the gas in the system was purged. The reaction solution was diluted with HFC-52-13p, then HFE-347pc-f was added, the polymer was agglomerated, and filtered. Subsequently, the polymer was stirred in HFC-52-13p, and the process of re-aggregating with HFE-347pc-f was repeated twice. Vacuum drying was performed at 180°C for 16 hours to obtain 8.83 g of polymer F-2, which is a copolymer of TFE and compound 1.

[0092] [Synthesis of Polymer F-3] 133.16 g of Compound 2, 32.67 g of Compound 3, and 14.1 g of HFC-52-13p were charged into a 230 mL stainless steel autoclave and thoroughly degassed under cooling with liquid nitrogen. 3.94 g of TFE was charged, the temperature was raised to 24°C, and 40.17 mg of PFB dissolved in HFE-347pc-f at a concentration of 2.8 mass% was charged. The charging line was washed with 1.1 g of HCFC-225cb and the reaction was started. After stirring for 8 hours, the autoclave was cooled to stop the reaction. The product was diluted with HFC-52-13p, and then mixed with a mixture of HFC-52-13p:methanol = 8:2 (mass ratio) to agglomerate the polymer and filter it. The polymer was washed in a mixture of HFC-52-13p and methanol in a mass ratio of 7:3, separated by filtration, and the solids were dried under reduced pressure at 80°C overnight to obtain polymer F-3.

[0093] [Synthesis of Polymer F-4] Polymer F-4, a copolymer of TFE and compound 4, was obtained by the method described in Production Example 4 of Japanese Patent Publication No. 2018-55877.

[0094] Table 1 shows the compositions and TQ values ​​of polymers F-1 to F-4.

[0095]

[0096] [Production of Polymers H-1 to H-3] Using polymers F-1 to F-3, films of polymers H-1 to H-3 were obtained by the following method. Polymers F-1 to F-3 were press-molded at a temperature 10°C higher than the TQ value or 260°C, whichever is lower, and at 4 MPa (gauge pressure) to obtain films of polymers F-1 to F-3 (thickness 100 to 250 μm). The films of polymers F-1 to F-3 were immersed in an alkaline aqueous solution shown in Table 2 at 80°C for 16 hours to obtain -SO4 from polymers F-1 to F-3. ２ Hydrolyze F, and -SO ３ The polymer film was converted to K. Furthermore, the polymer film was immersed in a 3 mol / L hydrochloric acid solution at 50°C for 30 minutes, and then immersed in ultrapure water at 80°C for 30 minutes. The cycle of immersion in hydrochloric acid solution and ultrapure water was repeated a total of five times, and the polymer's -SO ３ K to -SO ３ The polymer film was converted to H. The polymer film was repeatedly washed with ultrapure water until the pH of the water in which it was immersed reached 7. The polymer film was sandwiched between filter paper and air-dried to obtain polymer H-1 to polymer H-3 films. The results are shown in Table 2. In Table 2, aqueous solution A has a potassium hydroxide / water ratio of 20 / 80 (mass ratio), aqueous solution B has a potassium hydroxide / dimethyl sulfoxide / water ratio of 15 / 30 / 55 (mass ratio), and aqueous solution C has a potassium hydroxide / methanol / water ratio of 15 / 20 / 65 (mass ratio).

[0097]

[0098] [Preparation of Liquid Composition S-1] 18.0 g of finely cut polymer H-1 film, 252 g of ultrapure water, and 112 g of ethanol were added to a polytetrafluoroethylene (PTFE) container and heated at 180°C for 12 hours. The contents were transferred to a PTFE tray and air-dried under a nitrogen atmosphere at 30°C for 64 hours. The dried polymer H-1 was transferred to a 200 mL glass autoclave and 100.3 g of a mixed solvent of ultrapure water / ethanol (50 / 50 (mass ratio)) was added. After stirring at 250 rpm for 3 hours at 110°C, 13.5 g of ultrapure water was added to dilute it. After stirring at 80°C for 1 hour, the mixture was allowed to cool and filtered using a pressure filter (filter paper: Advantec Toyo Co., Ltd., PF040) to obtain 118.7 g of liquid composition S-1 in which polymer H-1 was dispersed in the mixed solvent at a concentration of 13.9% by mass.

[0099] [Preparation of Liquid Composition S-2] 8.24 g of finely cut polymer H-2 film, 2.5 g of ultrapure water, and 22.4 g of 1-propanol were added to a 200 mL glass autoclave. The mixture was stirred at 300 rpm for 24 hours at 125°C, and then diluted with 3.4 g of ultrapure water and 29.7 g of 1-propanol. After stirring at 125°C for 1.5 hours, the mixture was allowed to cool and filtered using a pressure filter (filter paper: Advantec Toyo Co., Ltd., PF040) to obtain 47.0 g of liquid composition S-2 in which polymer H-2 was dispersed in the mixed solvent at a concentration of 13.7% by mass.

[0100] [Preparation of Liquid Composition S-3] 294.0 g of polymer H-3 film, 335.0 g of ultrapure water, and 622.1 g of 1-propanol were added to a 2.5 L Hastelloy autoclave. The mixture was stirred at 300 rpm for 6 hours at 115°C, and then diluted with 30.0 g of ultrapure water and 475.0 g of 1-propanol. After stirring at 110°C for 1 hour, the solution was allowed to cool and removed from the autoclave. This solution was diluted with 958.0 g of ultrapure water and 225.9 g of 1-propanol, 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 2700 g of liquid composition S-3 in which polymer H-3 was dispersed in the mixed solvent at 11.0% by mass.

[0101] [Preparation of Liquid Composition S-4] Using polymer F-4 as a raw material, a liquid composition S-4 (solid content concentration = 26.0% by mass, ethanol / water = 60 / 40 (mass ratio)) was obtained in which an acid-type sulfonic acid group-containing fluorine polymer (hereinafter also referred to as "polymer H-4") having an ion exchange capacity of 1.10 milliequivalents / gram was dispersed by the method described in Example 4 of Japanese Patent Application Publication No. 2018-55877.

[0102] [Measurement of Physical Properties of Polymers H-1 to H-4] Liquid compositions S-1, S-2, and S-4 were coated onto a 100 μm ethylene-tetrafluoroethylene copolymer (ETFE) sheet using a die coater to form films. These films were dried at 80°C for 15 minutes and then heat-treated at 185°C for 30 minutes to obtain films (50 μm thick) consisting of polymers H-1, H-2, and H-4. For the film consisting of polymer H-3, the film consisting of polymer H-3 obtained in the section "[Production of Polymers H-1 to H-3]" above was used. The physical properties of polymers H-1 to H-4 were measured by performing the aforementioned analysis using the films consisting of polymers H-1 to H-4. The results are shown in Table 3.

[0103]

[0104] [Preparation of coating liquid for catalyst layer formation] <Catalyst (platinum-supported carbon)> The following platinum-supported carbon 1 was prepared as the catalyst. Metal type: platinum particles Platinum particle content relative to the total mass of platinum-supported carbon: 47% by mass Number-average particle diameter of platinum particles: 2.4 nm Type of porous support: Ketjenblack Specific surface area of ​​platinum-supported carbon: 343 m² ２ Total pore volume of specific mesopores (per gram of platinum-supported carbon): 0.16 cm³ / g ３ Ratio of the total pore volume of a specific mesopore to the total pore volume of mesopores and macropores: 36% Total pore volume of macropores (per gram of platinum-supported carbon): 0.28 cm³ ３

[0105] As a catalyst, the following platinum-supported carbon 2 was prepared: Metal type: Platinum particles Platinum particle content relative to the total mass of platinum-supported carbon: 29% by mass Number-average particle size of platinum particles: 2.2 nm Type of porous support: Ketjenblack Specific surface area of ​​platinum-supported carbon: 464 m² ２ Total pore volume of specific mesopores (per gram of platinum-supported carbon): 0.24 cm³ / g ３ Ratio of the total pore volume of a specific mesopore to the total pore volume of mesopores and macropores: 32% Total pore volume of macropores (per gram of platinum-supported carbon): 0.34 cm² ３

[0106] As a catalyst, the following platinum-supported carbon 3 was prepared: Metal type: Platinum particles Platinum particle content relative to the total mass of platinum-supported carbon: 47% by mass Average particle size of platinum particles: 2.3 nm Type of porous support: Acetylene black Specific surface area of ​​platinum-supported carbon: 330 m² ２ Total pore volume of specific mesopores (per gram of platinum-supported carbon): 0.14 cm³ / g ３ Ratio of the total pore volume of a specific mesopore to the total pore volume of mesopores and macropores: 21% Total pore volume of macropores (per gram of platinum-supported carbon): 0.30 cm² ３

[0107] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-1] 4.2 g of platinum-supported carbon 1 was mixed with 25.8 g of water and 16.9 g of ethanol. 12.8 g of liquid composition S-1 was added to this mixture so that the I / C (ratio of the mass of polymer H to the mass of porous support in the platinum-supported carbon) was 0.7. The mixture was dispersed using a planetary ball mill (Ito Seisakusho, model: LP-4) with 5 mm zirconia beads at a rotation speed of 300 rpm for a dispersion time of 180 minutes to obtain the cathode catalyst layer forming coating solution CI-1.

[0108] [Preparation of coating liquid CI-2 for cathode catalyst layer formation] Liquid composition S-2 was used instead of liquid composition S-1, and 3.0 g of platinum-supported carbon 1 was mixed with 21.2 g of water and 8.9 g of ethanol. The same procedure as in Example 5-1 was followed except that 8.1 g of liquid composition S-2 was added to this mixture so that the I / C ratio was 0.7, in order to obtain coating liquid CI-2 for cathode catalyst layer formation.

[0109] [Preparation of coating liquid CI-3 for cathode catalyst layer formation] Liquid composition S-3 was used instead of liquid composition S-1, and 3.0 g of platinum-supported carbon 1 was mixed with 24 g of water and 14 g of ethanol. The same procedure as in Example 5-1 was followed, except that 12 g of liquid composition S-3 was added to this mixture so that the I / C ratio was 0.8.

[0110] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-4] Liquid composition S-4 was used instead of liquid composition S-1, and 3.0 g of platinum-supported carbon 1 was mixed with 21 g of water and 9 g of ethanol. Cathode catalyst layer forming coating solution CI-4 was obtained in the same manner as in Example 5-1, except that 12 g of liquid composition S-4 was added to this mixture so that the I / C ratio was 0.8.

[0111] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-5] Cathode catalyst layer forming coating solution CI-5 is obtained in the same manner as in Example 5-1, except that the water / ethanol ratio in the coating solution is the same as in Example 5-1, and liquid composition S-1, water, and ethanol are added so that the I / C of the cathode catalyst layer forming coating solution CI-1 becomes 0.6.

[0112] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-6] Cathode catalyst layer forming coating solution CI-6 is obtained in the same manner as in Example 5-1, except that the water / ethanol ratio in the coating solution is the same as in Example 5-1, and liquid composition S-1, water, and ethanol are added so that the I / C of the cathode catalyst layer forming coating solution CI-1 becomes 1.0.

[0113] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-7] 3.0 g of platinum-supported carbon 2 is mixed with 19.3 g of water and 12.5 g of ethanol. 12.3 g of liquid composition S-1 is added to this mixture so that the I / C (ratio of the mass of polymer H to the mass of platinum-supported carbon) is 0.8. The mixture is dispersed using a planetary ball mill (manufactured by Ito Seisakusho, model: LP-4) with 5 mm zirconia beads at a rotation speed of 300 rpm for a dispersion time of 180 minutes to obtain the cathode catalyst layer forming coating solution CI-7.

[0114] [Preparation of coating solution CI-8 for cathode catalyst layer formation] The coating solution CI-8 for cathode catalyst layer formation is obtained in the same manner as in Example 5-1, except that platinum-supported carbon 1 in the coating solution CI-1 for cathode catalyst layer formation is replaced with platinum-supported carbon 3.

[0115] [Preparation of Cathode Catalyst Layer Forming Coating Solution CI-9] 3.0 g of platinum-supported carbon 1 was mixed with 21.4 g of water and 13.8 g of ethanol. 20.9 g of liquid composition S-1 was added to this mixture so that the I / C (ratio of the mass of polymer H to the mass of platinum-supported carbon) was 1.8. The mixture was dispersed using a planetary ball mill (Ito Seisakusho, model: LP-4) with 5 mm zirconia beads at a rotation speed of 300 rpm for a dispersion time of 180 minutes to obtain the cathode catalyst layer forming coating solution CI-9.

[0116] [Preparation of coating solution AI-1 for anode catalyst layer formation] Liquid composition S-4 was used instead of liquid composition S-1, and 3.0 g of platinum-supported carbon 1 was mixed with 21 g of water and 9 g of ethanol. A coating solution AI-1 for anode catalyst layer formation was obtained in the same manner as in Example 5-1, except that 12 g of liquid composition S-4 was added to this mixture so that the I / C ratio was 0.8.

[0117] [Example 1] As a solid polymer electrolyte membrane, a copolymer of TFE and compound 4 is used. ２ F group SO ３ A 25 μm thick ion exchange membrane (ion exchange capacity: 1.25 mm equivalent / g dry resin) was prepared from a polymer having acid-type sulfonic acid groups converted to H groups. A coating solution CI-1 for forming a cathode catalyst layer was applied to the above solid polymer electrolyte membrane with a platinum content of 0.2 mg / cm². ２The material was coated with a die coater, dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to obtain a solid polymer electrolyte film with a cathode catalyst layer CC-1 formed on one side. Next, the anode catalyst layer forming solution AI-1 was applied to the ETFE sheet at a platinum content of 0.4 mg / cm². ２ The film was coated with a die coater, dried at 80°C for 10 minutes, and then heat-treated at 150°C for 15 minutes to obtain the anode catalyst layer AC-1. The solid polymer electrolyte membrane surface on which the cathode catalyst layer CC-1 was formed was placed over the anode catalyst layer AC-1, and the film was pressed together at 160°C and 3.0 MPa (absolute pressure) for 2 minutes to bond the anode catalyst layer AC-1 to the solid polymer electrolyte membrane. The ETFE sheet, which is the substrate of the anode catalyst layer AC-1, was then peeled off to form a membrane electrode assembly (electrode area: 25 cm²). ２ ) ME-1 was obtained.

[0118] [Example 2] Except for using the cathode catalyst layer forming coating liquid CI-2 instead of the cathode catalyst layer forming coating liquid CI-1, a membrane electrode assembly ME-2 was obtained in the same manner as in Example 1, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-2 arranged in this order.

[0119] [Example 3] Except for using the cathode catalyst layer forming coating liquid CI-3 instead of the cathode catalyst layer forming coating liquid CI-1, a membrane electrode assembly ME-3 was obtained in the same manner as in Example 1, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-3 arranged in this order.

[0120] [Example 4] Except for using the cathode catalyst layer forming coating liquid CI-4 instead of the cathode catalyst layer forming coating liquid CI-1, a membrane electrode assembly ME-4 was obtained in the same manner as in Example 1, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-4 arranged in this order.

[0121] [Example 5] A membrane electrode assembly ME-5 is obtained in the same manner as in Example 1, except that the coating liquid CI-5 for forming the cathode catalyst layer is used instead of the coating liquid CI-1 for forming the cathode catalyst layer, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-5 arranged in this order.

[0122] [Example 6] A membrane electrode assembly ME-6 is obtained in the same manner as in Example 1, except that the coating liquid CI-6 for forming the cathode catalyst layer is used instead of the coating liquid CI-1 for forming the cathode catalyst layer, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-6 arranged in this order.

[0123] [Example 7] A membrane electrode assembly ME-7 is obtained in the same manner as in Example 1, except that the coating liquid CI-7 for forming the cathode catalyst layer is used instead of the coating liquid CI-1 for forming the cathode catalyst layer, with the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-7 arranged in this order.

[0124] [Example 8] A membrane electrode assembly ME-8 is obtained in the same manner as in Example 1, except that a cathode catalyst layer AC-1, a solid polymer electrolyte membrane, and a cathode catalyst layer CC-8 are arranged in this order.

[0125] [Example 9] Except for using the cathode catalyst layer forming coating liquid CI-9 instead of the cathode catalyst layer forming coating liquid CI-1, a membrane electrode assembly ME-9 is obtained in the same manner as in Example 1, in which the anode catalyst layer AC-1, solid polymer electrolyte membrane, and cathode catalyst layer CC-9 are arranged in this order.

[0126] [Evaluation of initial power generation performance] Membrane electrode assemblies ME-1 to ME-9 are incorporated into a power generation cell along with a gas diffusion layer with a microporous layer, and the power generation performance is 0.7 A / cm². ２ After conditioning for 14 hours with a constant current, the cell temperature was set to 80°C and the back pressure to 50 kPaG, and hydrogen (70% utilization rate) / air (50% utilization rate) was supplied. At a dew point of 45°C on both the anode and cathode sides (relative humidity inside the cell: 20% RH), the current density was 2.0 A / cm². ２The cell voltage (V) was measured. Furthermore, the activity per unit weight of platinum (hereinafter referred to as mass activity) [A / mg] was determined at a cell temperature of 80°C, a back pressure of 50 kPaG, with hydrogen (70% utilization rate) and oxygen (50% utilization rate) supplied, and with a dew point of 45°C on both the anode and cathode sides (relative humidity inside the cell: 20% RH). The mass activity was calculated by measuring the current density at an IR-Free voltage value (voltage obtained by correcting for the internal cell resistance from the obtained voltage characteristics) of 0.9 V in a 1 cm³ platinum chamber. ２ It was determined by dividing by the amount of platinum supported per unit. Also, from the difference in IR-Free voltage between hydrogen / air and hydrogen / oxygen, O ２ Gain was measured. The evaluation criteria were as follows, and the evaluation results are shown in Table 4. A: Cell voltage is greater than 0.400V, O ２ Gain is less than 0.160 and mass activity is greater than 0.100 A / mg B: Cell voltage, O ２ At least one of the gain and mass activity does not satisfy the value described in "A" above.

[0127]

[0128] [Evaluation of Power Generation Performance Durability] At a cell temperature of 80°C and atmospheric pressure, hydrogen (0.05 L / min) / nitrogen (0.2 L / min) were supplied. The anode dew point was 80°C, the cathode dew point was 80°C (relative humidity in the cell: 100% RH), the voltage width was 0.6-1.0 V, the voltage waveform was triangular wave, the scanning speed was 50 mV / sec, and the time required per cycle was 16 sec. 10,000 to 20,000 cycles were performed. Initially, power generation performance evaluations (interim diagnoses) were performed at 100 and 500 cycles, and thereafter every 1,000 cycles. In the power generation performance evaluations (interim diagnoses), the same conditions as in the [Initial Power Generation Performance Evaluation] were used, except for changing the anode dew point to 80°C and the cathode dew point to 80°C (relative humidity in the cell: 100% RH), and the power generation performance was evaluated at 1.4 A / cm². ２ and 2.0 A / cm ２ The voltage value was measured. The voltage value at 10,000 cycles was determined, and the evaluation was made based on the voltage drop from the cell voltage at 500 cycles (the initial stage of durability) according to the following evaluation criteria. The evaluation results are shown in Table 5. A: 1.4 A / cm２ The cell voltage drop (over 10,000 cycles) is less than 0.1V, and the current is 2.0A / cm². ２ The cell voltage drop (over 10,000 cycles) is less than 0.1V. B: 1.4A / cm ２ Cell voltage drop (10,000 cycles), and 2.0 A / cm² ２ The cell voltage drop (over 10,000 cycles) did not meet the value specified in "A" above, or power generation was not possible.

[0129]

[0130] [Calculation of Occupancy Rate] Cathode catalyst layer forming coating liquids CI-1 to CI-9 were applied to a PET film, dried at 80°C for 10 minutes, and the powder obtained by scraping off the coating layer was used as catalyst sample 1 with polymer H attached. In addition, a coating liquid without polymer H (i.e., a mixture of catalyst-supported carbon and solvent) was applied to a PET film, dried, and the powder obtained by scraping off the coating layer was used as catalyst sample 2 without polymer H attached. Using these samples, the pore distribution was determined for each using the method described above, and the occupancy rate (volume %) for each example was calculated. The results are shown in Table 6.

[0131]

[0132] [Evaluation of Crackability of Cathode Catalyst Layers] The surfaces of the cathode catalyst layers CC-1 to CC-9 of the film electrode assemblies ME-1 to ME-9 were observed at a magnification of 200x using a digital microscope (Keyence Corporation, model: VHX-5000) to evaluate the presence or absence of cracks in the catalyst layers. The results are shown in Table 7. As representative examples of surface images of the catalyst layers, Figure 2 shows the surface image of cathode catalyst layer CC-1 (no cracks), and Figure 3 shows the surface image of cathode catalyst layer CC-3 (with cracks).

[0133]

[0134] As shown in Tables 4 to 7, when the catalyst layer of the present invention is used, a polymer electrolyte fuel cell with excellent initial power generation performance and power generation performance durability can be formed, and it was confirmed that cracking of the catalyst layer is less likely to occur (Examples 1, 5 to 8). In contrast, the cathode catalyst layer included in the membrane electrode assembly of Example 2 had too low an occupancy rate, resulting in insufficient initial power generation performance when applied to a polymer electrolyte fuel cell. Furthermore, the cathode catalyst layer included in the membrane electrode assembly of Example 3 was formed using a polymer containing units with a cyclic structure, resulting in cracking. Also, the cathode catalyst layer included in the membrane electrode assembly of Example 4 was formed using a polymer with a low softening temperature, resulting in insufficient initial power generation performance when applied to a polymer electrolyte fuel cell. Finally, the cathode catalyst layer included in the membrane electrode assembly of Example 9 had too high an occupancy rate, resulting in insufficient power generation performance durability when applied to a polymer electrolyte fuel cell. Furthermore, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-212417, filed on December 5, 2024, are incorporated herein by reference as disclosure of the present invention.

[0135] 10 Membrane electrode assembly 11A, 11C Catalyst layer 12A, 12C Gas diffusion layer 13 Anode 14 Cathode 15 Solid polymer electrolyte membrane

Claims

1. A catalyst layer comprising a fluorine-containing polymer having ion exchange groups and a catalyst, wherein the softening temperature of the fluorine-containing polymer is 140°C or higher, the fluorine-containing polymer substantially does not contain units having a ring structure, the catalyst comprises a porous support and a metal supported on the porous support, the catalyst has pores with a pore diameter of 2 nm or more and less than 10 nm, and the occupancy rate of the fluorine-containing polymer in the pores is 20 to 60 volume percent.

2. The catalyst layer according to claim 1, wherein the fluorine-containing polymer comprises units based on tetrafluoroethylene.

3. The catalyst layer according to claim 2, wherein the content of the tetrafluoroethylene-based units is 70 mol% or more with respect to the total mass of the fluorine-containing polymer.

4. The catalyst layer according to claim 2, wherein the content of the tetrafluoroethylene-based units is 78 mol% or more with respect to the total mass of the fluorine-containing polymer.

5. The catalyst layer according to claim 1, wherein the fluorine-containing polymer includes a unit represented by formula (A-1). In formula (A-1), R Ｆ１ and R Ｆ２ Each of these independently comprises a perfluoroalkylene group having 1 to 3 carbon atoms, or a perfluoroalkylene group with -CF ２ The negative sign represents a divalent group substituted with an etheric oxygen atom.

6. The catalyst layer according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer is 0.5 to 1.8 milliequivalents / gram dry resin.

7. The catalyst layer according to claim 1, wherein the TQ value of the precursor polymer of the fluorine-containing polymer is 300°C or less. TQ value: When the precursor polymer is melt-extruded using a nozzle with a length of 1 mm and an inner diameter of 1 mm under the condition of an extrusion pressure of 2.94 MPa, the extrusion amount is 100 mm. ３ This is the temperature at which the temperature is calculated per second.

8. The catalyst layer according to claim 7, wherein the TQ value is 130°C or higher and 280°C or lower.

9. The specific surface area of ​​the catalyst is 50 to 500 m². ２ The catalyst layer according to claim 1, wherein the value is / g.

10. The catalyst layer according to claim 1, wherein the metal is platinum or a platinum alloy.

11. The catalyst layer according to claim 1, wherein the ratio of the mass of the fluorine-containing polymer to the mass of the porous carrier is 0.4 to 1.

7.

12. The catalyst layer according to claim 1, wherein the ratio of the mass of the fluorine-containing polymer to the mass of the porous carrier is 0.5 to 1.

6.

13. The catalyst layer according to claim 1, wherein the occupancy rate is 22% by volume or more.

14. The catalyst layer according to claim 1, wherein the occupancy rate is 24 volume% or more.

15. The catalyst layer according to claim 1, wherein the occupancy rate is 34 volume% or less.

16. 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, wherein the catalyst layer of the cathode is the catalyst layer described in any one of claims 1 to 15.

17. A polymer electrolyte fuel cell comprising the membrane electrode assembly described in claim 16.

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