Membrane electrode assembly and polymer electrolyte fuel cell

Abstract

Provided are a membrane electrode assembly capable of forming a fuel cell which exhibits excellent power generation efficiency, and a solid polymer fuel cell.　A membrane electrode assembly according to the present invention which has an anode having a catalyst layer containing a catalyst and a proton-conductive polymer, also has a cathode having a catalyst layer containing a catalyst and a proton-conductive polymer, and also has a solid polymer electrolyte membrane positioned between the anode and the cathode, wherein: the proton-conductive polymer contained in the anode and / or cathode is a polymer (H) which has a cyclic ether structural unit and has an ion exchange group; the solid polymer electrolyte membrane contains a fluorine-containing polymer (S) having an ion exchange group, and has a thickness of 5-15μm; and the ratio of the content M1 (mol%) of the cyclic ether structural unit to the thickness T1 (μm) of the solid polymer electrolyte membrane is at least 4.5.

Description

[Technical Field]

[0001] The present invention relates to a membrane electrode assembly and a polymer electrolyte fuel cell. [Background technology]

[0002] It is known that a membrane electrode assembly of a polymer electrolyte fuel cell has an anode having a catalyst layer containing a proton-conducting polymer, a cathode having a catalyst layer containing a proton-conducting polymer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. Patent Document 1 discloses the use of a proton-conductive polymer containing a unit having a cyclic ether structure in the catalyst layer of a cathode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5521427 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for further improvement in the power generation efficiency of fuel cells. The present inventors have found that there is room for improvement in the power generation efficiency of fuel cells when a proton-conducting polymer containing a unit having a cyclic ether structure, as described in Patent Document 1, is used in a catalyst layer.

[0005] In view of the above circumstances, an object of the present invention is to provide a membrane electrode assembly and a polymer electrolyte fuel cell that can form a fuel cell with excellent power generation efficiency. [Means for solving the problem]

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that a fuel cell with excellent power generation efficiency can be obtained when, in a membrane electrode assembly having an anode and a cathode each having a catalyst layer, and a solid polymer electrolyte membrane, the catalyst layer of at least one of the anode and cathode contains a polymer (H) having a unit having a cyclic ether structure and having an ion exchange group, the thickness of the solid polymer electrolyte membrane is 5 to 15 μm, and the content of the unit having a cyclic ether structure in the polymer (H) is M1 [mol %] and the thickness of the solid polymer electrolyte membrane is T1 [μm], and the ratio of M1 to T1 (M1 / T1) is 4.5 or more, thereby completing the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configuration. [1] A membrane electrode assembly comprising: an anode having a catalyst layer containing a proton-conducting polymer and a catalyst; a cathode having a catalyst layer containing a proton-conducting polymer and a catalyst; and a solid polymer electrolyte membrane disposed between the anode and the cathode, the proton-conducting polymer contained in the catalyst layer of at least one of the anode and the cathode is a polymer (H) having a unit containing a cyclic ether structure and an ion-exchange group; the solid polymer electrolyte membrane contains a fluorine-containing polymer (S) having an ion-exchange group, The thickness of the solid polymer electrolyte membrane is 5 to 15 μm, A membrane electrode assembly characterized in that, when the content of the unit containing the cyclic ether structure in the polymer (H) is M1 [mol %] and the thickness of the solid polymer electrolyte membrane is T1 [μm], the ratio of M1 to T1 (M1 / T1) is 4.5 or more. [2] The membrane / electrode assembly according to [1], wherein the content of the units containing a cyclic ether structure is 50 to 80 mol % based on the total units contained in the polymer (H). [3] The membrane / electrode assembly according to [1] or [2], wherein the unit containing a cyclic ether structure is at least one unit selected from the group consisting of a unit represented by the formula (u11) described below, a unit represented by the formula (u12) described below, a unit represented by the formula (u21) described below, a unit represented by the formula (u22) described below, and a unit represented by the formula (u24) described below. In formula (u11), R 11 is a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom, and R 12 , R 13 , R 15 and R 16 are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom, and R 14 represents a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom, a fluorine atom, or -R 11 (SO2X(SO2R f ) a ) - M + It is a group represented by M + is H + , a monovalent metal cation or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group, and R f represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, X represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X represents an oxygen atom, a=0; when X represents a nitrogen atom, a=1; and when X represents a carbon atom, a=2. In formula (u12), R 21 is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms and an ether-bonding oxygen atom between the carbon-carbon bonds, and R 22 represents a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms and an ether-bonded oxygen atom between the carbon-carbon bonds, or -R 21 (SO2X(SO2R f ) a ) - M + It is a group represented by M + , Rf , X and a are the same as above. In formula (u21), R 41 , R 42 , R 43 , R 44 , R 45 and R 46 are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. In formula (u22), s is 0 or 1, and R 51 and R 52 are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spiro ring formed by linking together (when s is 0), and R 53 and R 54 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms, and R 55 is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. In formula (u24), R 71 , R 72 , R 73 , R 74 , R 75 and R 76 are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. [4] The membrane / electrode assembly according to [3], wherein the unit containing a cyclic ether structure contains a unit represented by formula (u22). [5] The membrane / electrode assembly according to [4], wherein the content of the formula (u22) in the polymer (H) is M2 [mol %], and the ratio of M2 to T1 (M2 / T1) is 4.5 or more. [6] The polymer (H) further has a unit based on a perfluoromonomer, The membrane / electrode assembly according to any one of [1] to [5], wherein the unit based on the perfluoromonomer does not contain a cyclic ether structure and is a unit having an ion-exchange group. [7] The membrane / electrode assembly according to [6], wherein the unit based on the perfluoromonomer is a unit represented by the formula (u32) described below. In formula (u32), Q 1 is a perfluoroalkylene group which may have an ether-bonded oxygen atom, and Q 2 represents a single bond or a perfluoroalkylene group which may have an ether bond oxygen atom, Y represents a fluorine atom or a monovalent perfluoroalkyl group, q represents 0 or 1, and R f When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2. [8] The membrane / electrode assembly according to any one of [1] to [7], wherein the fluoropolymer (S) has at least one unit represented by the formula (u31) described below and the unit represented by the formula (u32) described below. In formula (u31), Z is a fluorine atom or a trifluoromethyl group, q is 0 or 1, m is an integer of 0 to 3, p is 0 or 1, n is an integer of 1 to 12, m+p>0, and M + is H + , a monovalent metal cation, or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group. In formula (u32), Q 1 is a perfluoroalkylene group which may have an ether-bonded oxygen atom, and Q 2 represents a single bond or a perfluoroalkylene group which may have an ether bond oxygen atom, Y represents a fluorine atom or a monovalent perfluoroalkyl group, q represents 0 or 1, and R f When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2. [9] The membrane / electrode assembly according to any one of [1] to [8], wherein the ion exchange group of the polymer (H) is a group represented by formula (g1). -(SO2X(SO2R f ) a ) - M + (g1) In formula (g1), M + is H + , a monovalent metal cation or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group, and R f When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2.

[10] The membrane / electrode assembly according to any one of [1] to [9], wherein the ion exchange capacity of the polymer (H) is 1.1 to 2.8 meq / g dry resin.

[11] The membrane / electrode assembly according to any one of [1] to

[10] , wherein the polymer (H) has a TQ value of 200 to 330°C.

[12] The membrane electrode assembly according to any one of [1] to [8], which is used in a polymer electrolyte fuel cell.

[13] A polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of [1] to [9]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a membrane electrode assembly and a polymer electrolyte fuel cell that can form a fuel cell with excellent power generation efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The terms used in the present invention have the following meanings. A "unit" in a polymer refers to an atomic group formed by polymerization of a monomer and derived from one molecule of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group formed by treating the polymer obtained by the polymerization reaction to convert part of the atomic group into a different structure. The content (mol %) of each unit relative to all units contained in the polymer can be determined by analyzing the polymer by nuclear magnetic resonance spectroscopy. The term "precursor group of an ion exchange group" refers to a group that can be converted into an ion exchange group by hydrolysis, acidification, or other treatment such as salt exchange with a metal cation. The term "precursor polymer" refers to a polymer in which the ion-exchange groups are in the form of precursor groups and which can be converted into a polymer having ion-exchange groups. The "TQ value" is the volumetric flow rate value of a polymer, and is determined by the method described in the Examples section. The TQ value is an index of molecular weight. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] The unit represented by formula (u11) is written as unit (u11). Units represented by other formulas are written in the same way. Furthermore, the monomer represented by formula (m11) will be referred to as monomer (m11). Monomers represented by other formulas will be similarly referred to. In addition, a group represented by formula (g1) will be referred to as group (g1). Groups represented by other formulas will be similarly referred to. The units (u11), (u12), (u21), (u22) and (u24) may be collectively referred to as "specific cyclic ether structural units". The monomer (m11), the monomer (m12), the monomer (m21), the monomer (m22) and the monomer (m24) may be collectively referred to as "specific cyclic monomers".

[0012] The membrane electrode assembly of the present invention is a membrane electrode assembly comprising: an anode having a catalyst layer containing a proton-conducting polymer and a catalyst; a cathode having a catalyst layer containing a proton-conducting polymer and a catalyst; and a solid polymer electrolyte membrane disposed between the anode and the cathode. Furthermore, the proton-conducting polymer contained in the catalyst layer of at least one of the anode and the cathode has a unit containing a cyclic ether structure (hereinafter also referred to as a "cyclic ether structural unit") and is a polymer (H) having an ion-exchange group. The solid polymer electrolyte membrane contains a fluorine-containing polymer (S) (hereinafter also referred to as "polymer (S)") having an ion-exchange group. The thickness of the solid polymer electrolyte membrane is 5 to 15 μm. Furthermore, when the content of the units containing the cyclic ether structure relative to all units contained in the polymer (H) is M1 [mol %] and the thickness of the solid polymer electrolyte membrane is T1 [μm], the ratio of M1 to T1 (M1 / T1) is 4.5 or more. The membrane electrode assembly of the present invention is suitably used in a polymer electrolyte fuel cell.

[0013] By using the membrane electrode assembly of the present invention, a fuel cell with excellent power generation efficiency can be obtained. Although the details of the reason for this are not clear, it is presumed to be due to the following reasons. It is known that when the polymer (H) has a cyclic ether structural unit, the oxygen permeability of the catalyst layer is excellent, thereby improving the power generation efficiency of the fuel cell. However, the inventors have found through their investigations that there is room for improvement in the power generation efficiency of the fuel cell depending on the thickness of the solid polymer electrolyte membrane and the content of the cyclic ether structural unit in the polymer (H). Based on these problems, the present inventors have focused on the relationship between the thickness of the solid polymer electrolyte membrane and the content of the cyclic ether structural unit in the polymer (H), and have found that if these relationships satisfy a predetermined value (i.e., M1 / T1 is 4.5 or more), a fuel cell with excellent power generation efficiency can be obtained, as will be described later in the Examples section.

[0014] 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly of the present invention. The membrane electrode assembly 10 includes an anode 13 having a catalyst layer 11 and a gas diffusion layer 12, a cathode 14 having the catalyst layer 11 and the gas diffusion layer 12, and a solid polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14 in contact with the catalyst layer 11. In the following description, the anode and the cathode may be collectively referred to as "electrodes."

[0015] [Electrodes (anode and cathode)] The anode 13 and the cathode 14 each have a catalyst layer 11 and a gas diffusion layer 12 .

[0016] <Catalyst layer> The proton-conducting polymer contained in at least one of the catalyst layer 11 of the anode 13 and the catalyst layer 11 of the cathode 14 may be polymer (H), and both may be polymer (H). When the proton-conducting polymer contained in one catalyst layer 11 is polymer (H) and the proton-conducting polymer contained in the other catalyst layer 11 is not polymer (H), the proton-conducting polymer contained in the latter catalyst layer 11 is preferably polymer (S) described below. In the membrane electrode assembly of the present invention, from the viewpoint of gas permeability, it is preferable that the proton-conducting polymer contained in at least the cathode is polymer (H).

[0017] The thickness of the catalyst layer is preferably 1 to 20 μm, particularly preferably 3 to 10 μm, from the viewpoint of facilitating gas diffusion in the catalyst layer and further improving the power generation performance of the polymer electrolyte fuel cell. The thickness of the catalyst layer is a value measured by observing the cross section of the catalyst layer with a scanning electron microscope or the like, and means the arithmetic mean value of 10 arbitrary points.

[0018] (Polymer (H)) The polymer (H) is a polymer having a cyclic ether structural unit and an ion-exchange group. The cyclic ether structural unit is preferably the following specific cyclic ether structural unit, since it allows a catalyst layer with superior oxygen permeability to be obtained.

[0019] [ka]

[0020] In formula (u11), R 11 is a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom. When the perfluoroalkylene group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or more. The oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkylene group or at the carbon atom bond terminal. The perfluoroalkylene group may be linear or branched, but is preferably linear. R 12 , R 13 , R 15 and R 16 R are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. 15 and R 16 In view of high polymerization reactivity, it is preferable that at least one of the groups is a fluorine atom, and it is more preferable that both of the groups are fluorine atoms. In formula (u11), R 14 represents a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom, a fluorine atom, or -R 11 (SO2X(SO2R f ) a ) - M + It is a group represented by the formula (u11). When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or more. The oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group, or at the end of the carbon atom bond. The perfluoroalkyl group may be linear or branched, but is preferably linear. In formula (u11), two R 11If it contains two R 11 may be the same or different from each other. In formula (u11), M + is H + , a monovalent metal cation (e.g., potassium ion, sodium ion) or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group (e.g., methyl group, ethyl group). From the viewpoint of high conductivity, H + is preferred. In formula (u11), R f is a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, and particularly preferably 1 to 6. Two or more R f If there are two or more R f may be the same or different from each other. In formula (u11), X represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2. -(SO2X(SO2R f ) a ) - M + Specific examples of the group include a sulfonic acid group (-SO3 - M + group), sulfonimide group (-SO2N(SO2R f ) - M + group), or sulfonmethide group (-SO2C(SO2R f )2) - M + Examples of such groups include:

[0021] The unit (u11) is preferably the unit (u11-1).

[0022] [ka] In the above formula (u11-1), M + is M in equation (u11) + is synonymous with.

[0023] [ka]

[0024] In formula (u12), R 21 is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms and having an ether-bonding oxygen atom between the carbon-carbon bond. When the perfluoroalkylene group has an ether-bonding oxygen atom, the number of oxygen atoms may be 1 or 2 or more. The perfluoroalkylene group may be linear or branched, but is preferably linear. In formula (u12), R 22 represents a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms and an ether-bonded oxygen atom between the carbon-carbon bonds, or -R 21 (SO2X(SO2R f ) a ) - M + When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or more. The perfluoroalkyl group may be linear or branched, but is preferably linear. In formula (u12), two R 21 If it contains two R 21 may be the same or different from each other. In formula (u12), M + , R f , X and a are the M + , R f , X and a.

[0025] Specific examples of the unit (u12) include the unit (u12-1) and the unit (u12-2). + is M in equation (u11) + is synonymous with.

[0026] [ka]

[0027] [ka]

[0028] In formula (u21), R 41 , R 42 , R 43 , R 44 , R 45 and R 46 are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. The oxygen atom may be located between the carbon-carbon bonds of the perfluoroalkyl group or at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, but is preferably linear. In formula (u21), R 45 and R 46 In view of high polymerization reactivity, it is preferable that at least one of the groups is a fluorine atom, and it is particularly preferable that both of the groups are fluorine atoms.

[0029] The unit (u21) is preferably the unit (u21-1).

[0030] [ka]

[0031] [ka]

[0032] In formula (u22), s is 0 or 1, and 0 is preferred. In formula (u22), R 51 and R 52are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spiro ring formed by linking together (when s is 0). In formula (u22), R 53 and R 54 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms. In formula (u22), R 55 R is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. 55 is preferably a fluorine atom because of its high polymerization reactivity. The perfluoroalkyl group and perfluoroalkoxy group may be linear or branched, but are preferably linear.

[0033] The unit (u22) is preferably the unit (u22-1).

[0034] [ka]

[0035] [ka]

[0036] In formula (u24), R 71 ~R 76 are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. When the perfluoroalkyl group has an ether-bonded oxygen atom, the number of oxygen atoms may be one or two or more. The oxygen atom may be inserted between the carbon-carbon bond of the perfluoroalkyl group or at the carbon atom bond terminal. The perfluoroalkyl group may be linear or branched, but is preferably linear. R 71 ~R 74 is preferably a fluorine atom because of its high polymerization reactivity.

[0037] The content of the cyclic ether structural unit relative to all units contained in the polymer (H) is preferably 30 mol % or more, particularly preferably 50 mol % or more, in view of achieving better power generation efficiency in fuel cells. The upper limit of the content of the cyclic ether structural unit is preferably 100 mol % based on all units contained in the polymer (H), and particularly preferably 80 mol % from the viewpoints of suppressing cracking of the electrode and power generation efficiency. The polymer (H) may contain only one type of cyclic ether structural unit, or may contain two or more types. When two or more types are contained, the above content means the total amount thereof.

[0038] The polymer (H) may further contain a unit based on a perfluoromonomer. However, the unit based on the perfluoromonomer does not contain a cyclic ether structure and contains a unit having an ion exchange group. Hereinafter, such a unit will be simply referred to as a "unit based on a perfluoromonomer." Examples of the unit based on a perfluoromonomer include the unit (u31) and the unit (u32), and the unit (u32) is preferred in terms of better power generation efficiency of the fuel cell.

[0039] [ka]

[0040] In formula (u31), Z is a fluorine atom or a trifluoromethyl group, q is 0 or 1, m is an integer of 0 to 3, p is 0 or 1, n is an integer of 1 to 12, and m+p>0. M + is M in the above equation (u11). + is synonymous with.

[0041] [ka]

[0042] In formula (u32), Q 1is a perfluoroalkylene group which may have an ether-bonding oxygen atom. In formula (u32), Q 2 is a single bond or a perfluoroalkylene group which may have an ether-bonding oxygen atom. Q 1 and Q 2 When the perfluoroalkylene group has an ether-bonding oxygen atom, the number of oxygen atoms may be 1 or 2 or more. The oxygen atom may be located between the carbon atom-carbon atom bonds of the perfluoroalkylene group, or may be located at the end of the carbon atom bond. The perfluoroalkylene group may be linear or branched, but is preferably linear. The number of carbon atoms in the perfluoroalkylene group is preferably 1 to 6, and particularly preferably 1 to 4. When the number of carbon atoms is 6 or less, the boiling point of the raw material fluorine-containing monomer is low, making distillation purification easy. Furthermore, when the number of carbon atoms is 6 or less, the decrease in the ion exchange capacity of the polymer (H) is suppressed, and the proton conductivity is improved.

[0043] Q 2 is preferably a perfluoroalkylene group having 1 to 6 carbon atoms which may have an ether-bonding oxygen atom. 2 is a perfluoroalkylene group having 1 to 6 carbon atoms which may have an ether-bonded oxygen atom, 2 is a single bond, the stability of power generation performance is excellent when the fuel cell is operated for a long period of time. Q 1 and Q 2 At least one of the groups is preferably a perfluoroalkylene group having 1 to 6 carbon atoms and an etheric oxygen atom. A monomer having a perfluoroalkylene group having 1 to 6 carbon atoms and an etheric oxygen atom can be synthesized without going through a fluorination reaction with fluorine gas, and therefore the yield is good and the production is easy.

[0044] In formula (u32), Y is a monovalent perfluoroalkyl group which may have a fluorine atom or an ethereal oxygen atom. Y is preferably a linear perfluoroalkyl group having 1 to 6 carbon atoms which may have a fluorine atom or an ethereal oxygen atom. In formula (u32), q is 0 or 1. In formula (u32), R f , X and a are R in the above formula (u11), respectively. f , X and a.

[0045] As the unit (u32), the units (u32-1) to (u32-3) are preferred, with the unit (u32-1) being particularly preferred, in view of ease of production and ease of industrial implementation.

[0046] [ka]

[0047] The polymer (H) may further contain units based on tetrafluoroethylene (TFE), which imparts water repellency, increases the water discharge ability of the catalyst layer, and improves the power generation efficiency of the fuel cell. The content of units based on tetrafluoroethylene is preferably from 0 to 40 mol %, more preferably from 5 to 35 mol %, and particularly preferably from 5 to 30 mol %, based on all units contained in the polymer (H).

[0048] The total content of units based on perfluoromonomers is preferably from 5 to 40 mol %, more preferably from 10 to 35 mol %, and particularly preferably from 15 to 30 mol %, based on all units contained in the polymer (H). The polymer (H) may contain only one type of unit based on a perfluoromonomer, or may contain two or more types. When two or more types are contained, the above content means the total amount thereof.

[0049] The polymer (H) may further contain units based on tetrafluoroethylene (TFE), which imparts water repellency, increases the water discharge ability of the catalyst layer, and improves the power generation efficiency of the fuel cell. The content of units based on TFE is preferably from 0 to 40 mol %, more preferably from 5 to 35 mol %, and particularly preferably from 5 to 30 mol %, based on all units contained in the polymer (H).

[0050] The polymer (H) may contain units other than those described above (hereinafter also referred to as "other units"). Specific examples of such units include units based on monomers such as perfluoro(3-butenyl vinyl ether), perfluoro(allyl vinyl ether), perfluoroα-olefins (such as hexafluoropropylene), and perfluoro(alkyl vinyl ethers).

[0051] The ion exchange group contained in the polymer (H) is preferably the group (g1).

[0052] -(SO2X(SO2R f ) a ) - M + (g1)

[0053] In group (g1), M + , R f , X and a are the M + , R f , X and a. Specific examples of the group (g1) include a sulfonic acid group (-SO3 - M + group), sulfonimide group (-SO2N(SO2R f ) - M + group), or sulfonmethide group (-SO2C(SO2R f )2) - M + group), and sulfonic acid group (-SO3 - M + group) is preferred. Polymer (H) is a polymer having an ion exchange group. When the cyclic ether structural unit in polymer (H) has an ion exchange group, it does not necessarily have to have other units having an ion exchange group. When the cyclic ether structural unit in polymer (H) does not have an ion exchange group, it must have a unit having an ion exchange group, such as a unit based on a perfluoromonomer.

[0054] A preferred embodiment of the polymer (H) is one containing the unit (u22), as this provides better power generation efficiency in a fuel cell. A more preferred embodiment of the polymer (H) is an embodiment containing the units (u22) and (u32), since this provides particularly excellent power generation efficiency in a fuel cell.

[0055] In the catalyst layer, the content of the polymer (H) is preferably 50 to 200 parts by mass, more preferably 60 to 180 parts by mass, and particularly preferably 70 to 140 parts by mass, per 100 parts by mass of the support (carbon or the like) in the catalyst. When the content of the polymer (H) is within the above range, the power generation efficiency of the fuel cell is further improved.

[0056] When the content of cyclic ether structural units relative to all units contained in the polymer (H) is M1 [mol %] and the thickness of the solid polymer electrolyte membrane is T1 [μm], the ratio of M1 to T1 (M1 / T1) is 4.5 or more. The upper limit of the ratio (M1 / T1) is preferably 16.0, particularly preferably 15.6, from the viewpoint of power generation efficiency.

[0057] When the polymer (H) contains the unit (u22), the content of the unit (u22) relative to all units contained in the polymer (H) is M2 [mol %], and the thickness of the solid polymer electrolyte membrane is T1 [μm], the ratio of M2 to T1 (M2 / T1) is preferably 4.5 or more in order to obtain a more excellent power generation efficiency of the fuel cell. The upper limit of the ratio (M2 / T1) is preferably 16, and particularly preferably 15.6, from the viewpoint of power generation efficiency.

[0058] (Physical Properties) The ion exchange capacity of the polymer (H) is preferably 1.1 to 2.8 meq / g dry resin, more preferably 1.2 to 2.8 meq / g dry resin, and particularly preferably 1.2 to 2.3 meq / g dry resin. If the ion exchange capacity is 1.1 meq / g dry resin or more, the conductivity of the polymer (H) is high, and sufficient cell output can be obtained when used as a polymer for the catalyst layer of a fuel cell. If the ion exchange capacity is 2.8 meq / g dry resin or less, the polymer can be easily synthesized. The TQ value of the polymer (H) is preferably 200 to 330° C. The lower limit of the TQ value is more preferably 210° C. from the viewpoint of preventing cracking of the electrode. The upper limit of the TQ value is more preferably 310° C., particularly preferably 300° C., from the viewpoint of preventing thermal decomposition of the fluororesin. If the TQ value is within this range, the polymer (H) also has excellent hot water resistance.

[0059] (Method for producing polymer (H)) Polymer (H) is produced, for example, by converting the precursor groups of polymer (F) having precursor groups of ion exchange groups obtained by polymerizing a cyclic monomer (preferably a specific cyclic monomer) and at least one of a perfluoromonomer and tetrafluoroethylene, which are used as needed, into ion exchange groups. Each monomer that can be used to produce the polymer (H) will be explained below.

[0060] The unit (u11) is obtained by polymerizing the monomer (m11), and preferred embodiments of the monomer (m11) include the monomers (m11-1) to (m11-4). The monomer (m11) can be synthesized by a known method. In formula (m11), R 11 ~R 16 are the R in equation (u11), respectively. 11 ~R 16 is synonymous with.

[0061] [ka]

[0062] The unit (u12) is obtained by polymerizing the monomer (m12), and preferred embodiments of the monomer (m12) include the monomers (m12-1) and (m12-2). The monomer (m12) can be synthesized by a known method. R in equation (m12) 21 and R 22 are the R in equation (u12), respectively. 21 and R 22 is synonymous with.

[0063] [ka]

[0064] The unit (u21) is obtained by polymerizing the monomer (m21), and preferred embodiments of the monomer (m21) include the monomers (m21-1) and (m21-2). The monomer (m21) can be synthesized by a known method. R in equation (m21) 41 ~R 46 are the R in equation (u21), respectively. 41 ~R 46 is synonymous with.

[0065] [ka]

[0066] The unit (u22) is obtained by polymerizing the monomer (m22), and preferred embodiments of the monomer (m22) include the monomers (m22-1) to (m22-11). The monomer (m22) can be synthesized by a known method. R in equation (m22) 51 ~R 55 and s are the R 51 ~R 55 and s.

[0067] [ka]

[0068] The unit (u24) is obtained by cyclopolymerizing the monomer (m24), and preferred embodiments of the monomer (m24) include the monomers (m24-1) to (m24-3). The monomer (m24) can be synthesized by a known method. R in equation (m24) 71 ~R 76 are the R in equation (u24), respectively. 71 ~R 76 is synonymous with.

[0069] CF(R 71 )=C(R 73 )-O-CF(R 76 )-CF(R 75 )-C(R 74 )=CF(R 72 ) (m24) CF2=CF-O-CF2-CF2-CF=CF2(m24-1) CF2=CF-O-CF2-CF(CF3)-CF=CF2(m24-2) CF2=CF-O-CF(CF3)-CF2-CF=CF2(m24-3)

[0070] For the production of polymer (H), a perfluoromonomer that does not contain a cyclic ether structure but contains a precursor group of an ion exchange group may be used. The perfluoromonomers include the monomer (m31) and the monomer (m32), with the monomer (m32) being preferred in terms of better power generation efficiency of the fuel cell.

[0071] CF2=CF(CF2) q (OCF2CFZ) m O p (CF2) n SO2F (m31)

[0072] The monomer (m31) corresponds to the unit (u31). Z, q, m, p, and n have the same meanings as Z, q, m, p, and n in formula (u31), respectively.

[0073] The monomer (m31) is preferably the monomers (m31-1) to (m31-4). CF2=CFO(CF2) n1 SO2F (m31-1) CF2=CFCF2O(CF2) n4 SO2F (m31-2) CF2=CF(OCF2CF(CF3)) m3 O(CF2) n3 SO2F (m31-3) CF2=CFOCF2CF(CF3)O(CF2) n2 SO2F (m31-4) Here, n1, n2, n3, and n4 are integers of 1 to 8, and m3 is an integer of 1 to 3.

[0074] The monomer (m31) can be synthesized by, for example, the method described in Prog. Polym. Sci., Vol. 12, 1986, pp. 233-237; US Pat. No. 4,330,654; and the like.

[0075] [ka]

[0076] Q 1 , Q 2 , Y and q are the Q 1 , Q 2 , Y and q.

[0077] The monomer (m32) corresponds to the unit (u32). As the monomer (m32), the monomers (m32-1) to (m32-3) are preferred, and the monomer (m32-1) is particularly preferred, since the polymer (H) can be easily produced and industrially implemented.

[0078] [ka]

[0079] The monomer (m32) can be synthesized by the method described in, for example, WO 2007 / 013533 pamphlet, JP 2008-202039 A, and the like.

[0080] Tetrafluoroethylene may be used in the production of polymer (H).

[0081] Monomers other than those mentioned above may be used to produce polymer (H). Specific examples of such monomers include perfluoro(3-butenyl vinyl ether), perfluoro(allyl vinyl ether), perfluoro α-olefins (such as hexafluoropropylene), and perfluoro(alkyl vinyl ethers).

[0082] An example of a method for converting the precursor group (-SO2F) of an ion exchange group into an ion exchange group is shown below. The group represented by -SO2F is a sulfonic acid group (-SO3 - H + ), the following method (i) can be mentioned, in which a group represented by -SO2F is converted into a sulfonimide group (-SO2N(SO2R f ) - H + ) the following method (ii) can be mentioned. (i) A method in which a group represented by -SO2F is hydrolyzed to form a sulfonate, and the sulfonate is converted into an acid form to convert it into a sulfonic acid group. (ii) A method in which a group represented by -SO2F is imidized to form a salt-type sulfonimide group, and then further converted to an acid-type sulfonimide group by converting it to an acid-type sulfonimide group.

[0083] Method (i): Hydrolysis is carried out, for example, by contacting a polymer having a precursor of an ion exchange group with a basic compound in a solvent. Examples of basic compounds include sodium hydroxide and potassium hydroxide. Examples of solvents include water and mixed solvents of water and polar solvents. Examples of polar solvents include alcohols (e.g., methanol, ethanol), dimethyl sulfoxide, etc. The conversion to an acid form is carried out, for example, by contacting the polymer having a sulfonate with an aqueous solution of hydrochloric acid, sulfuric acid, or the like. The hydrolysis and conversion to an acid form are usually carried out at 0 to 120°C.

[0084] Method (ii): The imidization may be carried out by the following method. (ii-1) A group represented by -SO2F and R f How to react with SO2NHM. (ii-2) In the presence of an alkali metal hydroxide, an alkali metal carbonate, MF, ammonia, or a primary to tertiary amine, a group represented by -SO2F and R f How to react with SO2NH2. (ii-3) A group represented by -SO2F and R f A method of reacting with SO2NMSi(CH3)3. Here, M is an alkali metal or primary to quaternary ammonium. The conversion to an acid form is carried out by treating a polymer having a salt form of sulfonimide group with an acid (sulfuric acid, nitric acid, hydrochloric acid, etc.).

[0085] Polymer (H) in which the ion exchange group is a sulfonimide group can also be produced by polymerizing a monomer in which the group represented by —SOF in monomer (m11), (m12), (m31), or (m32) has been converted to a sulfonimide group, with monomer (m21) or monomer (m22). A monomer in which the group represented by -SO2F has been converted into a sulfonimide group can be produced by adding chlorine or bromine to the carbon-carbon double bond of monomer (m11), (m12), (m31) or (m32), converting the group represented by -SO2F into a sulfonimide group by method (ii), and then carrying out a dechlorination or debromination reaction using metallic zinc.

[0086] (catalyst) The catalyst contained in the catalyst layer may be, for example, a supported catalyst in which platinum or a platinum alloy is supported on a carbon support. Specific examples of the carbon support include carbon black powder, graphitized carbon, carbon fiber, and carbon nanotubes. The platinum alloy is preferably an alloy of platinum with at least one metal selected from the group consisting of platinum group metals excluding platinum (ruthenium, rhodium, palladium, osmium, iridium), gold, silver, chromium, iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc, and tin. When a supported catalyst is used, the amount of the catalyst supported is preferably 10 to 80 mass %, particularly preferably 10 to 70 mass %, based on the total mass of the supported catalyst, from the viewpoints of better power generation efficiency of the fuel cell and cost. When a supported catalyst is used, the ratio of the mass of the polymer (H) to the mass of the support (polymer (H) content / support content) is preferably 0.5 to 2.0, particularly preferably 0.6 to 1.8, in terms of excellent power generation efficiency of the fuel cell.

[0087] <Gas diffusion layer> The gas diffusion layer 12 has the function of diffusing gas uniformly in the catalyst layer 11 and also functions as a current collector. Examples of the gas diffusion layer 12 include carbon paper, carbon cloth, and carbon felt. The gas diffusion layer 12 is preferably treated with polytetrafluoroethylene or the like to be water-repellent. Although the membrane electrode assembly 10 in FIG. 1 includes a gas diffusion layer 12, the gas diffusion layer is an optional component and does not necessarily need to be included in the membrane electrode assembly.

[0088] <Other components> The anode 13 and the cathode 14 may have other components in addition to those described above. A specific example of the other member is a carbon layer (not shown) provided between the catalyst layer 11 and the gas diffusion layer 12. The provision of the carbon layer improves the gas diffusion properties on the surface of the catalyst layer 11, thereby further improving the power generation performance of the fuel cell. The carbon layer contains, for example, carbon and a nonionic fluorine-containing polymer. A specific example of the carbon is preferably carbon nanofiber having 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.

[0089] <Method for forming catalyst layer> The catalyst layer 11 can be formed by a known method.

[0090] [Solid polymer electrolyte membrane] The solid polymer electrolyte membrane of the present invention is a membrane containing a polymer (S).

[0091] The thickness of the solid polymer electrolyte membrane of the present invention is 5 to 15 μm. If the thickness of the solid polymer electrolyte membrane is 5 μm or more, the durability of the solid polymer electrolyte membrane during operation with solid polymer fuel is excellent. If the thickness of the solid polymer electrolyte membrane is 15 μm or less, the cell performance of the solid polymer fuel cell is excellent. The thickness of the solid polymer electrolyte membrane is preferably 7 to 15 μm. The thickness of the solid polymer electrolyte membrane is a value measured by observing a cross section of the solid polymer electrolyte membrane with a scanning electron microscope or the like, and means the arithmetic mean value of 10 arbitrary points.

[0092] <Polymer (S)> The polymer (S) is a fluorine-containing polymer having an ion-exchange group contained in the solid polymer electrolyte membrane. The polymer (S) may be any polymer having an ion exchange group and a fluorine atom, but from the viewpoint of high chemical durability, it preferably has units based on the above-mentioned perfluoromonomer that can be contained in the polymer (H). Specific examples of the unit based on a perfluoromonomer in the polymer (S) include the unit (u31) and the unit (u32), and the unit (u32) is particularly preferred in terms of better power generation efficiency of the fuel cell.

[0093] The content of units based on perfluoromonomers is preferably from 5 to 40 mol %, more preferably from 10 to 35 mol %, and particularly preferably from 15 to 30 mol %, based on all units contained in the polymer (S). The polymer (S) may contain only one type of unit based on a perfluoromonomer, or may contain two or more types. When two or more types are contained, the above content means the total amount thereof.

[0094] The polymer (S) may further comprise units based on tetrafluoroethylene (TFE). The content of units based on tetrafluoroethylene is preferably from 50 to 90 mol %, more preferably from 60 to 85 mol %, and particularly preferably from 65 to 80 mol %, based on all units contained in the polymer (S).

[0095] The polymer (S) may contain units other than those mentioned above (hereinafter also referred to as "other units"). Specific examples of such units are the same as the other units in the polymer (H).

[0096] The ion exchange capacity of the polymer (S) is preferably 1.1 to 3.0 meq / g dry resin, more preferably 1.2 to 3.0 meq / g dry resin, and particularly preferably 1.3 to 2.5 meq / g dry resin. If the ion exchange capacity is equal to or greater than the lower limit of the above range, the ionic conductivity of the polymer (S) is increased, and therefore sufficient cell output can be obtained when the membrane electrode assembly is applied to a polymer electrolyte fuel cell. If the ion exchange capacity is equal to or less than the upper limit of the above range, swelling of the polymer (S) when it absorbs water is suppressed, and the mechanical strength of the solid polymer electrolyte membrane is increased. Flooding in the polymer electrolyte fuel cell can be suppressed. The ion exchange capacity of the polymer (S) can be determined by the method described in the Examples section below.

[0097] The TQ value of the precursor polymer (S) of the polymer (S) is preferably from 200 to 350°C, more preferably from 210 to 340°C, and particularly preferably from 220 to 330°C. When the TQ value is equal to or greater than the lower limit of the above range, the polymer (S) has a sufficient molecular weight and is excellent in mechanical strength. When the TQ value is equal to or less than the upper limit of the above range, the solubility or dispersibility of the polymer (S) is improved, making it easy to prepare a liquid composition containing the polymer (S). The TQ value of the precursor polymer (S) is measured by the method described in the Examples section below.

[0098] (Method for producing polymer (S)) The polymer (S) can be produced, for example, by polymerizing a monomer having a precursor group of an ion-exchange group to obtain a polymer, and then converting the precursor group into an ion-exchange group. Specific examples of monomers that can be used in the production of polymer (S) include monomer (m31), monomer (m32), tetrafluoroethylene, perfluoro(3-butenyl vinyl ether), perfluoro(allyl vinyl ether), perfluoro α-olefins (hexafluoropropylene, etc.), and perfluoro(alkyl vinyl ethers) that are exemplified in the production method of polymer (H). The method for converting the precursor group of the ion exchange group into the ion exchange group is the same as in the method for producing polymer (H).

[0099] <Other components> To further improve durability, the solid polymer electrolyte membrane 15 may contain one or more atoms selected from the group consisting of cerium and manganese. Cerium and manganese decompose hydrogen peroxide, a substance that causes deterioration of the solid polymer electrolyte membrane 15. Cerium and manganese are preferably present in the solid polymer electrolyte membrane 15 as ions, but may also be present as sparingly soluble salts, such as cerium oxide. The solid polymer electrolyte membrane 15 may contain silica or heteropolyacid (zirconium phosphate, phosphomolybdic acid, phosphotungstic acid, etc.) as a water-retaining agent to prevent drying.

[0100] The solid polymer electrolyte membrane 15 may be reinforced with a reinforcing material. Examples of the reinforcing material include a porous body, fiber, woven fabric, and nonwoven fabric. Examples of the reinforcing material include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyethylene, polypropylene, and polyphenylene sulfide.

[0101] <Method for forming a solid polymer electrolyte membrane> The solid polymer electrolyte membrane 15 can be formed, for example, by a method (casting method) in which a liquid composition containing the polymer (S) is applied onto the substrate film or catalyst layer 11 and dried. The liquid composition is a dispersion in which the polymer (S) is dispersed in a solvent containing at least one of an organic solvent and water.

[0102] [Method for manufacturing membrane electrode assembly] The membrane electrode assembly 10 is produced, for example, by the following method. (i) A method in which a catalyst layer 11 is formed on a solid polymer electrolyte membrane 15 to form a membrane catalyst layer assembly, and the membrane catalyst layer assembly is sandwiched between gas diffusion layers 12. (ii) A method in which a catalyst layer 11 is formed on a gas diffusion layer 12 to form electrodes (anode 13, cathode 14), and a solid polymer electrolyte membrane 15 is sandwiched between the electrodes.

[0103] [Polymer electrolyte fuel cell] The polymer electrolyte fuel cell of the present invention includes the above-described membrane electrode assembly. The polymer electrolyte fuel cell of the present invention includes the above-mentioned membrane electrode assembly, and therefore has excellent power generation efficiency. The polymer electrolyte fuel cell of the present invention may have separators on both sides of the membrane electrode assembly, each having grooves formed therein to serve as gas flow paths. Specific examples of the separator include a metal separator, a carbon separator, a separator made of a material in which graphite and resin are mixed, and separators made of various conductive materials. In a polymer electrolyte fuel cell, power is generated by supplying a gas containing oxygen to the cathode and a gas containing hydrogen to the anode. The above-described membrane electrode assembly can also be applied to a methanol fuel cell, which generates electricity by supplying methanol to the anode. [Example]

[0104] The present invention will be specifically described below with reference to examples, but is not limited to these examples. Examples 1 to 11 are preparation examples, Examples 12 to 14, Examples 17 to 19, Example 21, Examples 23 to 25, and Examples 27 to 29 are working examples, and Examples 15 to 16, Example 20, Example 22, Example 26, and Example 30 are comparative examples.

[0105] [Ion exchange capacity] The ion exchange capacity of the polymer (H) (polymer after hydrolysis treatment) was determined by the following method. The polymer (H) was placed in a glove box and left to stand in an atmosphere of dry nitrogen for 24 hours or more to dry it. The dry mass of the polymer (H) was measured in the glove box. Polymer (H) was immersed in a 2 mol / L aqueous sodium chloride solution, left to stand at 60°C for 1 hour, and then cooled to room temperature. The aqueous sodium chloride solution in which polymer (H) had been immersed was titrated with a 0.5 mol / L aqueous sodium hydroxide solution to determine the ion exchange capacity of polymer (H).

[0106] [TQ value] Using a flow tester (Shimadzu Corporation, CFT-500D) equipped with a nozzle having a length of 1 mm and an inner diameter of 1 mm, polymer (H) was melt-extruded while changing the temperature under an extrusion pressure of 2.94 MPa (gauge pressure). The extrusion amount of polymer (H) was measured by changing the temperature. 3 The temperature at which the TQ value was reached was calculated as the TQ value.

[0107] [Synthesis of Monomer (m11-1)] Monomer (m11-1) was synthesized according to the method described on pages 37 to 42 of International Publication No. 2003 / 037885.

[0108] [ka]

[0109] [Synthesis of Monomer (m12-1)] A monomer (m12-1) was synthesized according to the method described in Example 1 of JP-A-2006-152249.

[0110] [ka]

[0111] [Synthesis of Monomer (m31-4)] The monomer (m31-4) was synthesized by a known method.

[0112] [ka]

[0113] [Synthesis of Monomer (m31-5)] The monomer (m31-5) was synthesized by a known method. CF2=CFOCF2CF2SO2F (m31-5)

[0114] [Synthesis of Monomer (m32-1)] Compound (m32-1) was synthesized according to the method described in Example 1 of JP-A-2008-202039.

[0115] [ka]

[0116] [Synthesis of Monomer (m21-1)] The monomer (m21-1) was synthesized according to a known method.

[0117] [ka]

[0118] [Synthesis of Monomer (m22-1)] The monomer (m22-1) was synthesized according to a known method.

[0119] [ka]

[0120] [Synthesis of Monomer (m24-1)] The monomer (m24-1) was synthesized according to a known method.

[0121] [ka]

[0122] [Radical polymerization initiator] As radical polymerization initiators, the following compounds (i-1) to (i-3) were prepared.

[0123] <Compound (i-1)>

[0124] [ka]

[0125] <Compound (i-2)> ((CH3)2CHOCOO)2(i-2)

[0126] <Compound (i-3)> (C3F7COO)2(i-3)

[0127] [solvent] As the solvent, the following compounds (s-1) and (s-2) were prepared.

[0128] <Compound (s-1)> CClF2CF2CHClF (s-1)

[0129] <Compound (s-2)> CH3CCl2F (s-2)

[0130] [Example 1: Preparation example] 9.15 g of compound (m22-1), 45.65 g of compound (m32-1), and 6.4 mg of compound (i-2) were placed in a 125 mL stainless steel autoclave and thoroughly degassed under cooling with liquid nitrogen. The mixture was then heated to 40°C and maintained at this temperature for 24.5 hours, after which the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-1). The yield was 4.5 g.

[0131] Polymer (F-1) was immersed in a 50°C aqueous solution containing 20% ​​by mass of methanol and 15% by mass of potassium hydroxide for 40 hours, thereby hydrolyzing the -SO2F groups in polymer (F-1) and converting them to -SO3K groups. The polymer was then immersed in a 3 mol / L aqueous hydrochloric acid solution at room temperature for 2 hours. The aqueous hydrochloric acid solution was replaced, and the same treatment was repeated four more times to obtain polymer (H-1), in which the -SO3K groups in the polymer had been converted to sulfonic acid groups. Polymer (H-1) was thoroughly washed with ultrapure water. The ion exchange capacity and TQ value of polymer (H-1) were measured. The results are shown in Table 1.

[0132] A mixed solvent of ethanol and water (ethanol / water = 60 / 40 mass ratio) was added to the polymer (H-1), the solid content was adjusted to 15 mass%, and the mixture was stirred in an autoclave at 105°C for 8 hours to obtain a liquid composition (D-1) in which the polymer (H-1) was dispersed in the dispersion medium.

[0133] [Example 2: Preparation example] A 230 mL stainless steel autoclave was charged with 32.4 g of compound (m22-1), 166.70 g of compound (m32-1), and 101 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. Then, 3.87 g of tetrafluoroethylene (TFE) was charged, the mixture was heated to 24°C, and stirred for 24 hours. The autoclave was then cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-2). The yield was 45.9 g. Polymer (H-2) was obtained using polymer (F-2) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-2) were measured. The results are shown in Table 1. A liquid composition (D-2) was obtained in the same manner as in Example 1 using the polymer (H-2).

[0134] [Example 3: Preparation example] A 230 mL stainless steel autoclave was charged with 37.45 g of compound (m22-1), 120.20 g of compound (m32-1), and 25.2 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. Then, 4.39 g of TFE was added, and the mixture was heated to 24°C and stirred for 12 hours and 30 minutes. The autoclave was then cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added to coagulate the polymer, and the mixture was filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried overnight at 80°C under reduced pressure to obtain polymer (F-3). The yield was 29.6 g. Polymer (H-3) was obtained using polymer (F-3) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-3) were measured. The results are shown in Table 1. A liquid composition (D-3) was obtained in the same manner as in Example 1 using the polymer (H-3).

[0135] [Example 4: Preparation example] A 125 mL stainless steel autoclave was charged with 8.50 g of compound (m22-1), 59.5 g of compound (m31-4), and 20.4 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. 2.5 g of TFE was then charged, the mixture was heated to 24°C, and stirred for 24 hours. The autoclave was then cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added to coagulate the polymer, and the mixture was filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried overnight at 80°C under reduced pressure to obtain polymer (F-4). The yield was 11.1 g. Polymer (H-4) was obtained using polymer (F-4) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-4) were measured. The results are shown in Table 1. A liquid composition (D-4) was obtained in the same manner as in Example 1 using the polymer (H-4).

[0136] [Example 5: Preparation example] A 125 mL stainless steel autoclave was charged with 9.80 g of compound (m22-1), 37.4 g of compound (m31-5), and 14.1 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. 2.5 g of TFE was then charged, the mixture was heated to 24°C, and stirred for 24 hours. The autoclave was then cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-5). The yield was 10.5 g. Polymer (H-5) was obtained using polymer (F-5) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-5) were measured. The results are shown in Table 1. A liquid composition (D-5) was obtained in the same manner as in Example 1 using the polymer (H-5).

[0137] [Example 6: Preparation example] A 125 mL stainless steel autoclave was charged with 3.5 g of compound (m21-1), 76.33 g of compound (m32-1), and 8.5 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. The mixture was then heated to 40°C and stirred for 24 hours, after which the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-6). The yield was 6.4 g. Using the polymer (F-6), a polymer (H-6) and a liquid composition (D-6) were obtained in the same manner as in Example 1. The ion exchange capacity and TQ value of the polymer (H-6) were measured. The results are shown in Table 1.

[0138] [Example 7: Preparation example] A 125 mL stainless steel autoclave was charged with 5.97 g of compound (m11-1), 13.70 g of compound (m22-1), 13.75 g of compound (s-1), and 17.1 mg of compound (i-1), and the contents were thoroughly degassed under cooling with liquid nitrogen. The contents were then heated to 65°C and maintained for 6 hours, after which the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added to coagulate the polymer, and the mixture was filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-7). The yield was 3.7 g. Polymer (H-7) was obtained using polymer (F-7) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-7) were measured. The results are shown in Table 1. A mixed solvent of ethanol and water (ethanol / water = 60 / 40 mass ratio) was added to the polymer (H-7), the solid content was adjusted to 15 mass%, and the mixture was stirred in an autoclave at 105°C for 8 hours to obtain a liquid composition (D-7) in which the polymer (H-7) was dispersed in the dispersion medium.

[0139] [Example 8: Preparation example] A 125 mL stainless steel autoclave was charged with 15.0 g of compound (m22-1), 15.29 g of compound (m12-1), 10.0 g of compound (s-1), and 23 mg of compound (i-1), and the mixture was thoroughly degassed under cooling with liquid nitrogen. The mixture was then heated to 65°C and stirred for 18 hours, after which the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-8). The yield was 12.0 g. Polymer (H-8) was obtained using polymer (F-8) in the same manner as in Example 1. The ion exchange capacity and TQ value of polymer (H-8) were measured. The results are shown in Table 1. A liquid composition (D-8) was obtained in the same manner as in Example 1 using the polymer (H-8).

[0140] [Example 9: Preparation example] A 230 mL stainless steel autoclave was charged with 21.2 g of compound (m11-1), 170 g of compound (s-1), and 9.5 mg of compound (i-2), and the mixture was thoroughly degassed under cooling with liquid nitrogen. 20 g of TFE was then added, the mixture was heated to 40°C, and stirred for 7 hours. The autoclave was then cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-9). The yield was 11.5 g. Using the polymer (F-9), a polymer (H-9) and a liquid composition (D-9) were obtained in the same manner as in Example 1. The ion exchange capacity and TQ value of the polymer (H-9) were also measured. The results are shown in Table 1.

[0141] [Example 10: Preparation example] A 125 mL stainless steel autoclave was charged with 41.7 g of compound (m24-1), 31.3 g of (m32-1), and 25.0 mg of compound (i-3) dissolved in compound (s-1) at a concentration of 3.2 mass%, and thoroughly degassed under cooling with liquid nitrogen. The mixture was then heated to 20°C and stirred for 20 hours, after which the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), n-hexane was added, and the polymer was coagulated and filtered. The polymer was then stirred in compound (s-1), re-coagulated with n-hexane, and dried under reduced pressure at 80°C overnight to obtain polymer (F-10). The yield was 5.9 g. Using the polymer (F-10), a polymer (H-10) and a liquid composition (D-10) were obtained in the same manner as in Example 1. The ion exchange capacity and TQ value of the polymer (H-10) were measured. The results are shown in Table 1.

[0142] [Example 11: Preparation example] A 125 mL stainless steel autoclave was charged with 49.64 g of compound (m31-4), 28.22 g of compound (s-1), and 38.9 mg of compound (i-3) dissolved in compound (s-1) at a concentration of 3.2 mass%. The mixture was thoroughly degassed under cooling with liquid nitrogen. The temperature was then raised to 30°C, TFE was introduced into the system, and the pressure was maintained at 0.37 MPaG. After stirring for 4.8 hours, the autoclave was cooled to stop the reaction. The product was diluted with compound (s-1), and then compound (s-2) was added to coagulate the polymer, which was then filtered. The polymer was then stirred in compound (s-1), re-coagulated with compound (s-2), and dried under reduced pressure at 80°C overnight to obtain polymer (F-11). The yield was 15.0 g. Using the polymer (F-11), a polymer (H-11) and a liquid composition (D-11) were obtained in the same manner as in Example 1. The ion exchange capacity and TQ value of the polymer (H-11) were also measured. The results are shown in Table 1.

[0143] [Table 1]

[0144] [Example 12] 67 g of liquid composition (D-1) was added to a mixture of 42 g of water and 36 g of ethanol, and 20 g of catalyst was added while stirring with a stirrer to adjust the solids concentration to 22% by mass, yielding a liquid for forming a catalyst layer. If significant heat was generated during stirring, the mixture was stirred while cooling with a chiller or the like. This liquid was applied to a separately prepared sheet made of a copolymer of ethylene and TFE (product name: Aflex 100N, manufactured by Asahi Glass Co., Ltd., thickness 100 μm) (hereinafter referred to as ETFE sheet), dried at 80°C for 30 minutes, and then heat-treated at 160°C for 30 minutes to form a catalyst layer.

[0145] TFE and the above monomer (m32-1) were copolymerized to obtain a polymer (S'-1) (ion exchange capacity: 1.95 meq / g dry resin, TQ value: 236°C). The polymer (S'-1) was molded by melt extrusion to obtain a membrane (thickness: 200 μm) made of the polymer (S'-1). The ion exchange capacity shown in parentheses for polymer (S'-1) represents the ion exchange capacity of the polymer obtained when hydrolyzed by the procedure described below. The membrane was immersed in an aqueous solution containing 20% ​​by mass of potassium hydroxide for 16 hours to hydrolyze the -SO2F groups in the polymer (S'-1) and convert them to -SO3K groups. The membrane was then immersed in a 3 mol / L aqueous hydrochloric acid solution for 2 hours. The aqueous hydrochloric acid solution was replaced, and the same treatment was repeated four more times to convert the -SO3K groups in the polymer to sulfonic acid groups, yielding a membrane-like polymer (S-1). The polymer (S-1) was dispersed in a solvent of water / ethanol=50 / 50 (mass %) to obtain a dispersion having a solid content of 13% (hereinafter also referred to as "dispersion Y1"). This dispersion Y1 was applied to an ETFE sheet using a die coater, dried at 80° C. for 30 minutes, and further subjected to heat treatment at 190° C. for 30 minutes to form a solid polymer electrolyte membrane with a thickness of 15 μm.

[0146] After peeling the ETFE sheet from the solid polymer electrolyte membrane, the solid polymer electrolyte membrane was sandwiched between two catalyst layers with ETFE sheets, and hot-pressed under conditions of a press temperature of 160°C, a press time of 5 minutes, and a pressure of 3 MPa to bond the catalyst layers to both sides of the solid polymer electrolyte membrane. The ETFE sheet was then peeled off from the catalyst layer, and an electrode with an area of ​​25 cm was formed. 2 A membrane catalyst layer assembly of 1000 MPa was obtained.

[0147] A carbon layer made of carbon and polytetrafluoroethylene was formed on a gas diffusion layer made of carbon paper. The membrane / catalyst layer assembly was sandwiched between gas diffusion layers so that the carbon layer and the catalyst layer were in contact with each other, thereby obtaining a membrane / electrode assembly.

[0148] [Examples 13-22] A membrane electrode assembly was produced in the same manner as in Example 12, except that the liquid composition (D-1) used to form the catalyst layer was changed to liquid compositions (D-2) to (D-11), respectively.

[0149] [Evaluation test] <Power generation efficiency> The obtained membrane electrode assemblies of Examples 12 to 22 were incorporated into power generation cells, and the power generation efficiency was evaluated as follows. The temperature of the membrane electrode assembly was maintained at 80°C, and hydrogen (utilization rate 70%) was supplied to the anode, and air (utilization rate 50%) was supplied to the cathode, each pressurized to 150 kPa (absolute pressure). Both hydrogen and air were humidified to a relative humidity of 100% and supplied, and the current density was 0.5 A / cm. 2 The cell voltage when the membrane electrode assembly of Example 22 was used was recorded. The cell voltage value when the membrane electrode assembly of Example 22 was used was set to "1.0" as a standard, and the relative ratio of the cell voltage when the membrane electrode assembly of each example was used was calculated. The results are shown in Table 2.

[0150] [Table 2]

[0151] [Example 23] A membrane / electrode assembly was produced in the same manner as in Example 12, except that the thickness of the solid polymer electrolyte membrane was changed to 10 μm.

[0152] [Examples 24-26] A membrane / electrode assembly was produced in the same manner as in Example 23, except that the liquid composition (D-1) used to form the catalyst layer was changed to a liquid composition shown in Table 3.

[0153] [Evaluation test] <Power generation efficiency> The power generation efficiency was evaluated in the same manner as in Examples 12 to 22, except that the obtained membrane electrode assemblies of Examples 23 to 26 were used. However, the cell voltage value when the membrane electrode assembly of Example 26 was used was standardized as "1.0," and the relative ratio of the cell voltage when the membrane electrode assembly of each example was used was calculated. The results are shown in Table 3.

[0154] [Table 3]

[0155] [Example 27] A membrane electrode assembly was produced in the same manner as in Example 12, except that the thickness of the solid polymer electrolyte membrane was changed to 5 μm.

[0156] [Examples 28-30] A membrane / electrode assembly was produced in the same manner as in Example 27, except that the liquid composition (D-1) used to form the catalyst layer was changed to a liquid composition shown in Table 4.

[0157] [Evaluation test] <Power generation efficiency> The power generation efficiency was evaluated in the same manner as in Examples 12 to 22, except that the obtained membrane electrode assemblies of Examples 27 to 30 were used. However, the cell voltage value when the membrane electrode assembly of Example 30 was used was standardized as "1.0," and the relative ratio of the cell voltage when the membrane electrode assembly of each example was used was calculated. The results are shown in Table 4.

[0158] [Table 4]

[0159] As shown in Tables 2 to 4, it was shown that fuel cells with excellent power generation efficiency can be obtained by using membrane electrode assemblies in which the thickness of the solid polymer electrolyte membrane is 5 to 15 μm and M1 / T1 is 4.5 or more (Examples 12 to 14, Examples 17 to 19, Example 21, Examples 23 to 25, and Examples 27 to 29). [Explanation of symbols]

[0160] 10 Membrane electrode assembly 11 Catalyst layer 12 Gas diffusion layer 13 Anode 14 cathode 15 Solid polymer electrolyte membrane

[0161] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2020-171392, filed on October 9, 2020, are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims

1. A membrane electrode assembly comprising: an anode having a catalyst layer containing a proton-conducting polymer and a catalyst; a cathode having a catalyst layer containing a proton-conducting polymer and a catalyst; and a solid polymer electrolyte membrane disposed between the anode and the cathode, the proton-conducting polymer contained in the catalyst layer of at least one of the anode and the cathode is a polymer (H) having a unit containing a cyclic ether structure and having an ion-exchange group, the solid polymer electrolyte membrane contains a fluorine-containing polymer (S) having an ion-exchange group, The thickness of the solid polymer electrolyte membrane is 5 to 15 μm, a content of the unit having a cyclic ether structure relative to all units contained in the polymer (H) being M1 [mol %], and a thickness of the solid polymer electrolyte membrane being T1 [μm], wherein the ratio of M1 to T1 (M1 / T1) is 4.5 or more.

2. 2. The membrane / electrode assembly according to claim 1, wherein the content of the unit containing a cyclic ether structure is 50 to 80 mol % based on all units contained in the polymer (H).

3. 3. The membrane / electrode assembly according to claim 1, wherein the unit containing a cyclic ether structure is at least one unit selected from the group consisting of a unit represented by formula (u11), a unit represented by formula (u12), a unit represented by formula (u21), a unit represented by formula (u22), and a unit represented by formula (u24). 【Chemical 1】 In formula (u11), R １１ is a divalent perfluoroalkylene group which may have an ether-bonded oxygen atom, and R １２ , R １３ , R １５ and R １６ are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom, and R １４ represents a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom, a fluorine atom, or —R １１ (SO ２ X (SO ２ R ｆ ) ａ ) － M ＋ It is a group represented by the formula: M ＋ Is, H ＋ , a monovalent metal cation or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group, and R ｆ represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, X represents an oxygen atom, a nitrogen atom or a carbon atom, and when X represents an oxygen atom, a=0; when X represents a nitrogen atom, a=1; and when X represents a carbon atom, a=2. In formula (u12), R ２１ is a perfluoroalkylene group having 1 to 6 carbon atoms or a perfluoroalkylene group having 2 to 6 carbon atoms and an ether-bonding oxygen atom between the carbon-carbon bonds, and R ２２ represents a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group having 2 to 6 carbon atoms and an ether-bonded oxygen atom between the carbon-carbon bonds, or -R ２１ (SO ２ X (SO ２ R ｆ ) ａ ) － M ＋ It is a group represented by the formula: M ＋ , R ｆ , X and a are the same as above. In formula (u21), R ４１ , R ４２ , R ４３ , R ４４ , R ４５ and R ４６ are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom. In formula (u22), s is 0 or 1, and R ５１ and R ５２ are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a spiro ring formed by linking together (when s is 0), and R ５３ and R ５４ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 5 carbon atoms, and R ５５ is a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. In formula (u24), R ７１ , R ７２ , R ７３ , R ７４ , R ７５ and R ７６ are each independently a monovalent perfluoroalkyl group which may have an ether-bonded oxygen atom or a fluorine atom.

4. The membrane electrode assembly according to claim 3 , wherein the unit containing a cyclic ether structure includes a unit represented by formula (u22).

5. 5. The membrane electrode assembly according to claim 4, wherein, when the content of the formula (u22) relative to all units contained in the polymer (H) is M2 [mol %], a ratio of the M2 to the T1 (M2 / T1) is 4.5 or more.

6. The polymer (H) further has a unit based on a perfluoromonomer, 6. The membrane / electrode assembly according to claim 1, wherein the unit based on a perfluoromonomer does not contain a cyclic ether structure and is a unit having an ion-exchange group.

7. The membrane electrode assembly according to claim 6, wherein the unit based on a perfluoromonomer is a unit represented by formula (u32): 【Chemistry 2】 In formula (u32), Q １ is a perfluoroalkylene group which may have an ether-bonded oxygen atom, and Q ２ represents a single bond or a perfluoroalkylene group which may have an ether bond oxygen atom, Y represents a fluorine atom or a monovalent perfluoroalkyl group, q represents 0 or 1, and R ｆ When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2.

8. 8. The membrane / electrode assembly according to claim 1, wherein the fluoropolymer (S) has at least one unit represented by formula (u31) or a unit represented by formula (u32): 【Chemistry 3】 In formula (u31), Z is a fluorine atom or a trifluoromethyl group, q is 0 or 1, m is an integer of 0 to 3, p is 0 or 1, n is an integer of 1 to 12, m+p>0, and M ＋ Is, H ＋ , a monovalent metal cation, or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group. In formula (u32), Q １ is a perfluoroalkylene group which may have an ether-bonded oxygen atom, and Q ２ represents a single bond or a perfluoroalkylene group which may have an ethereal oxygen atom, Y represents a monovalent perfluoroalkyl group which may have a fluorine atom or an ethereal oxygen atom, q represents 0 or 1, and R ｆ When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2.

9. 9. The membrane / electrode assembly according to claim 1, wherein the ion exchange group of the polymer (H) is a group represented by formula (g1). -(SO ２ X(SO ２ R ｆ ) ａ ) － M ＋ (g1) In formula (g1), M ＋ Is, H ＋ , a monovalent metal cation or an ammonium ion in which one or more hydrogen atoms may be substituted with a hydrocarbon group, and R ｆ When there are two or more X's, each independently represents a linear or branched perfluoroalkyl group which may have an ether-bonded oxygen atom, and each of the multiple X's independently represents an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a=0; when X is a nitrogen atom, a=1; and when X is a carbon atom, a=2.

10. 10. The membrane / electrode assembly according to claim 1, wherein the ion exchange capacity of the polymer (H) is 1.1 to 2.8 meq / g dry resin.

11. 11. The membrane / electrode assembly according to claim 1, wherein the polymer (H) has a TQ value of 200 to 330°C.

12. The membrane electrode assembly according to any one of claims 1 to 11, which is used in a polymer electrolyte fuel cell.

13. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 12.

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