Polymer electrolyte composition, polymer electrolyte membrane, electrode catalyst layer, membrane electrode assembly, and solid polymer fuel cell

Abstract

To provide a highly durable polymer electrolyte composition that can give a polymer electrolyte membrane, an electrode catalyst layer, a membrane electrode assembly, and a solid polymer fuel cell.SOLUTION: A polymer electrolyte composition contains a polymer electrolyte (a), and niobium oxide (b) having an average particle size of more than 0.050 μm to 5.0 μm or less as determined by laser diffraction particle size distribution measurement.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polymer electrolyte composition, a polymer electrolyte membrane, an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell.

Background Art

[0002] A fuel cell converts the chemical energy of a fuel directly into electrical energy by electrochemically oxidizing hydrogen, methanol, etc. inside the cell, and is attracting attention as a clean electrical energy source. In particular, a polymer electrolyte fuel cell is expected to be used as an alternative power source for automobiles, a household cogeneration system, a portable generator, etc. because it operates at a low temperature compared to other fuel cells.

[0003] Such a polymer electrolyte fuel cell includes at least a membrane electrode assembly in which electrode catalyst layers constituting an anode and a cathode are joined to both sides of a proton exchange membrane mainly composed of a polymer electrolyte membrane. In some cases, a configuration in which a gas diffusion electrode having a structure in which an electrode catalyst layer and a gas diffusion layer are laminated is joined to both sides of a proton exchange membrane mainly composed of a polymer electrolyte membrane is also referred to as a membrane electrode assembly. The proton exchange membrane is a membrane made of a composition having a strong acidic group such as a sulfonic acid group or a carboxylic acid group in a polymer chain and having the property of selectively permeating protons. Examples of the composition used for such a proton exchange membrane include perfluoro-based proton compositions typified by Nafion (registered trademark, manufactured by DuPont) having high chemical stability.

[0004] During the operation of the fuel cell, fuel (e.g., hydrogen) is supplied to the gas diffusion electrode on the anode side, and an oxidant (e.g., oxygen or air) is supplied to the gas diffusion electrode on the cathode side. When both electrodes are connected by an external circuit, the operation of the fuel cell is realized. Specifically, when hydrogen is used as fuel, hydrogen is oxidized on the anode-side electrode catalyst to generate protons. These protons pass through the proton-conductive polymer in the anode-side electrode catalyst layer, then move through the proton exchange membrane, and reach the cathode-side electrode catalyst through the proton-conductive polymer in the cathode-side electrode catalyst layer. On the other hand, the electrons generated simultaneously with the protons by the oxidation of hydrogen reach the cathode-side gas diffusion electrode through the external circuit. On the cathode-side electrode catalyst, the above-mentioned protons react with oxygen in the oxidant to generate water. At this time, electrical energy is extracted.

[0005] At this time, the proton exchange membrane also needs to serve as a gas barrier partition. If the gas permeability of the proton exchange membrane is high, there is a risk of leakage of hydrogen supplied from the anode side to the cathode side and leakage of oxygen supplied from the cathode side to the anode side, that is, cross leakage. When cross leakage occurs, it becomes a so-called chemical short state and the desired electrical energy cannot be extracted. In addition, hydrogen supplied from the anode side reacts with oxygen supplied from the cathode side to generate hydrogen peroxide. This hydrogen peroxide is decomposed by trace metals (ions such as Fe, Cr, Ni, etc.) contained in the supply piping for the humidifying gas supplied to the fuel cell, and hydroxyl radicals and peroxide radicals are generated. There arises a problem that the deterioration of the proton exchange membrane is accelerated by these radicals.

[0006] In particular, when a fuel cell is mounted on an automobile, it is conceivable that the fuel cell operates under high-temperature conditions exceeding 80°C or under low-humidity conditions with a humidity of 30%RH or less due to reduction of the humidifier. Also, as the bipolar plate sandwiching the membrane electrode assembly of the fuel cell, the use of a metal bipolar plate is expected. When operating under the above-mentioned high-temperature conditions and / or low-humidity conditions, even if a proton exchange membrane made of a perfluorinated proton composition, which is said to have excellent durability, is used as the separator of a fuel cell, there arises a problem that the deterioration of the proton exchange membrane is accelerated. Also, when using a metal bipolar plate, during operation, metals (such as Fe, Cr, Ni, etc.) gradually dissolve out, and as described above, the hydrogen peroxide is decomposed by the ions of the dissolved metals, generating radical species, which may promote the deterioration of the proton exchange membrane.

[0007] As a method for suppressing the deterioration of the proton exchange membrane by radical species as described above, a technique is disclosed in which cerium ions or cerium oxide is contained in the proton exchange membrane, and some of the protons of a part of the sulfonic acid groups of the polymer electrolyte membrane constituting the proton exchange membrane, that is, some of the protons in a plurality of sulfonic acid groups, are replaced with cerium ions, and these cerium ions capture the radical species to suppress the deterioration of the polymer electrolyte membrane (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in the techniques described in Patent Documents 1 and 2, there is a possibility of segregation of cerium ions in the polymer electrolyte membrane, and particularly under acidic conditions, there is a possibility of desorption of cerium caused by segregation, which causes deterioration of the polymer electrolyte membrane by radical species and leads to a decrease in durability.

[0010] Therefore, in the present invention, in view of the problems of the above-described prior art, an object is to provide a polymer electrolyte composition capable of obtaining a polymer electrolyte membrane, an electrode catalyst layer, a membrane-electrode assembly, and a polymer electrolyte fuel cell with high durability.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above-described problems, the present inventors have found that the problems of the above prior art can be solved by specifying a polymer electrolyte composition constituting a polymer electrolyte membrane to contain a polymer electrolyte and fine particles of niobium oxide having a predetermined average particle diameter, and have completed the present invention. That is, the present invention is as follows.

[0012] 〔1〕 A polymer electrolyte (a), niobium oxide (b) having an average particle diameter of more than 0.050 μm and 1.0 not more than 2 μm obtained by laser diffraction particle size distribution measurement, and and the polymer electrolyte (a) is represented by the following general formula (1): -[CF 2 CX 1 X 2 ] a -[CF 2 -CF(-O-(CF 2 -CF(CF 2 X 3 )) b -Oc-(CFR 1 ) d -(CFR 2 ) e -(CF 2 ) f -X 4 )] g - (1) (In general formula (1), X 1 、X 2 and X 3 are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms. a and g satisfy 0 ≦ a < 1, 0 < g ≦ 1, and a + g = 1. b is an integer of 0 or more and 8 or less. c is 0 or 1. d and e are each independently an integer of 0 or more and 6 or less. f is an integer of 0 or more and 10 or less. However, d + e + f is not equal to 0. R 1 and R 2 are each independently a halogen element, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. X 4 is COOZ, SO 3 Z, PO 3 Z 2 , or PO 3 HZ. The Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or amines (NH 4 , NH 3 R 3 , NH 2 R 3 R 4 , NHR 3 R 4 R 5 , NR 3 R 4 R 5 R 6 ). Also, R 3 、R 4 、R 5 and R 6 are an alkyl group or an arene group.) the niobium oxide (b) contains niobium dioxide, Polymer electrolyte composition. 〔2〕 The niobium oxide (b) is Niobium dioxide and niobium pentoxide in The polymer electrolyte composition according to the above 〔1〕. 〔3〕 The polymer electrolyte composition according to the above [1] or [2], wherein the cumulative passing value based on the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the niobium oxide (b) is 30% or more of the whole in the region where the particle diameter is more than 0.050 μm and 5.0 μm or less. 〔4〕 The above [1] to 〔3〕 A polymer electrolyte membrane comprising the polymer electrolyte composition according to any one of the above. 〔5〕 The above [1] to 〔3〕 An electrode catalyst layer comprising the polymer electrolyte composition according to any one of the above. 〔6〕 The above 〔4〕 A membrane electrode assembly having the polymer electrolyte membrane described above, and / or the electrode catalyst layer described above 〔5〕 described in. 〔7〕 The above 〔6〕 A solid polymer fuel cell having the membrane electrode assembly described above.

Advantages of the Invention

[0013] According to the present invention, a polymer electrolyte composition capable of obtaining a highly durable polymer electrolyte membrane, electrode catalyst layer, membrane electrode assembly, and solid polymer fuel cell is obtained.

Modes for Carrying Out the Invention

[0014] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The following present embodiment is an exemplification for explaining the present invention, and is not intended to limit the present invention to the following contents. The present invention can be variously modified and implemented within the scope of its gist.

[0015] 〔Polymer Electrolyte Composition〕 The polymer electrolyte composition of the present embodiment is a polymer electrolyte (a), and Niobium oxide (b) having an average particle diameter obtained by laser diffraction type particle size distribution measurement of more than 0.050 μm and 5.0 μm or less, is contained. Since the polymer electrolyte composition of the present embodiment has the above configuration, a polymer electrolyte membrane, an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell having high durability can be obtained.

[0016] (Polymer electrolyte (a)) The polymer electrolyte (a) used in the present embodiment is preferably a polymer compound having an ion exchange group with an ion exchange equivalent of 0.5 to 3.0 meq / g. By setting the ion exchange equivalent of the polymer electrolyte (a) to 3.0 meq / g or less, when used in a polymer electrolyte membrane, the swelling of the polymer electrolyte membrane is reduced under the high temperature and high humidity conditions during fuel cell operation. By reducing the swelling, a decrease in the strength of the polymer electrolyte membrane can be suppressed, and problems such as the occurrence of wrinkles and peeling of the electrode can be prevented. Furthermore, the problem of a decrease in gas barrier properties can be reduced. On the other hand, by setting the ion exchange equivalent of the polymer electrolyte (a) to 0.5 meq / g or more, the power generation ability of a fuel cell equipped with a polymer electrolyte membrane containing the polymer electrolyte composition of the present embodiment can be maintained well. From the above viewpoints, the ion exchange equivalent of the polymer electrolyte (a) is preferably 0.65 to 2.0 meq / g, more preferably 0.8 to 1.5 meq / g.

[0017] The ion exchange capacity of the polymer electrolyte (a) can be measured as follows. First, immerse a membrane made of a polyelectrolyte (a) in which the counter ion of the ion exchange group is in the proton state in a saturated NaCl aqueous solution at 25°C, and stir the aqueous solution for a sufficient time. Next, neutralize and titrate the protons in the saturated NaCl aqueous solution with a 0.01N sodium hydroxide aqueous solution. After neutralization, filter the resulting membrane made of the polyelectrolyte (a) in which the counter ion of the ion exchange group is in the sodium ion state, rinse it with pure water, further vacuum dry it, and then weigh it. Let the amount of substance of sodium hydroxide required for neutralization be M (mmol), and the mass of the membrane made of the polyelectrolyte in which the counter ion of the ion exchange group is a sodium ion be W (mg), and obtain the equivalent mass EW (g / equivalent) according to the following formula. EW = (W / M) - 22 Furthermore, by taking the reciprocal of the obtained EW value and multiplying it by 1000, the ion exchange equivalent (milli-equivalent / g) can be calculated.

[0018] The materials constituting the polyelectrolyte (a) are not limited to the following, but for example, fluorine-based polyelectrolytes, hydrocarbon-based polymer compounds having an aromatic ring in the molecule and partially fluorinated hydrocarbon-based polymer compounds, and those obtained by introducing an ion exchange group into the hydrocarbon-based polymer compound are preferable. From the viewpoint of chemical stability, fluorine-based polyelectrolytes are preferable, and among them, perfluorocarbon polymer compounds having an ion exchange group are more preferable. Note that the polyelectrolyte composition of this embodiment is not limited to fuel cell applications, and similarly, the polyelectrolyte used in the polyelectrolyte composition can also be applied to applications other than fuel cells. For example, it can also be used in PEM type water electrolysis, RF batteries, alkaline water electrolysis, etc.

[0019] Examples of the hydrocarbon-based polymer compound having an aromatic ring in the molecule and being partially fluorinated, which is the polymer electrolyte (a), include, but are not limited to, for example, polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone, polyether ketone, polyether ether ketone, polythioether ether sulfone, polythioether ketone, polythioether ether ketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, polyimide, polyether imide, polyester imide, polyamide imide, polyarylate, aromatic polyamide, polystyrene, polyester, polycarbonate and other polymer compounds in which a part of the molecule is fluorinated.

[0020] Examples of the hydrocarbon-based polymer compound having an aromatic ring in the molecule and being partially fluorinated, which is the polymer electrolyte (a), include, but are not limited to, for example, polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone, polyether ketone, polyether ether ketone, polythioether ether sulfone, polythioether ketone, polythioether ether ketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, polyimide, polyether imide, polyester imide, polyamide imide, polyarylate, aromatic polyamide, polystyrene, polyester, polycarbonate and other polymer compounds in which a part of the molecule is fluorinated.

[0021] The ion exchange groups to be introduced into the various polymer compounds described above are not limited to the following, but for example, sulfonic acid groups, sulfonimide groups, sulfonamide groups, carboxylic acid groups, phosphoric acid groups, etc. are preferable, and sulfonic acid groups are more preferable.

[0022] In addition, examples of the perfluorocarbon polymer compound having an ion exchange group are not limited to the following, and include, for example, perfluorocarbon sulfonic acid resin, perfluorocarbon carboxylic acid resin, perfluorocarbon sulfonimide resin, perfluorocarbon sulfonamide resin, perfluorocarbon phosphoric acid resin, and amine salts, metal salts, etc. of these resins.

[0023] <Preferred form of the polyelectrolyte (a)> Examples of the perfluorocarbon polymer compound, which is a fluorine-based polyelectrolyte constituting the polyelectrolyte (a), are not limited to the following, and polymers represented by the following general formula (1) are preferably mentioned. -[CF2CX 1 X 2 a -[CF2-CF(-O-(CF2-CF(CF2X 3 )) b -O c -(CFR 1 ) d -(CFR 2 ) e -(CF2) f -X 4 )] g -···(1) (In the general formula (1), X 1 , X 2 and X 3 are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms. a and g satisfy 0≦a<1, 0<g≦1, and a + g = 1. b is an integer of 0 or more and 8 or less. c is 0 or 1. d and e are each independently an integer of 0 or more and 6 or less. f is an integer of 0 or more and 10 or less. However, d + e + f is not equal to 0. R 1 and R 2 are, independently of each other, a halogen element, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. X 4 is COOZ, SO3Z, PO3Z2, or PO3HZ. Here, Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or amines (NH4, NH3R 3 , NH2R 3 R 4 , NHR 3 R 4 R 5 , NR 3 R 4 R 5 R 6 ). Also, R 3 , R 4 , R 5 , and R 6 are an alkyl group or an arene group. )

[0024] As the perfluorocarbon polymer compound which is a fluorine-based polymer electrolyte constituting the polymer electrolyte (a), a perfluorocarbon sulfonic acid resin represented by the following general formula (2) or general formula (3) or a metal salt thereof is particularly preferable. -[CF2CF2] a -[CF2-CF(-O-(CF2-CF(CF3)) b -O-(CF2) c -SO3X)] d -···(2) (In general formula (2), a and d are 0 ≦ a < 1, 0 ≦ d < 1, and a + d = 1. b is an integer of 1 or more and 8 or less. c is an integer of 0 or more and 10 or less. X is a hydrogen atom or an alkali metal atom. ) -[CF2CF2] e -[CF2-CF(-O-(CF2) f -SO3Y)] g -···(3) (In general formula (3), e and g satisfy 0 ≦ e < 1, 0 ≦ g < 1, and e + g = 1. f is an integer from 0 to 10. Y is a hydrogen atom or an alkali metal atom.)

[0025] The perfluorocarbon polymer compound having the ion exchange group that can be used as the polymer electrolyte (a) is not limited to the following, but can be produced, for example, by polymerizing the precursor polymer represented by the following general formula (4) and then performing alkali hydrolysis, acid treatment, etc. -[CF2CX 1 X 2 a -[CF2-CF(-O-(CF2-CF(CF2X 3 )) b -O c -(CFR 1 ) d -(CFR 2 ) e -(CF2) f -X 5 )] g -···(4) (In the general formula (4), X 1 , X 2 and X 3 are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms. a and g satisfy 0 ≦ a < 1, 0 < g ≦ 1, and a + g = 1. b is an integer from 0 to 8. c is 0 or 1. d and e are each independently an integer from 0 to 6. f is an integer from 0 to 10. However, d + e + f is not equal to 0. R 1 and R 2 are each independently a halogen element, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. X 5 is COOR 7 , COR 8 or SO2R 8 . Here, R 7 is a hydrocarbon-based alkyl group having 1 to 3 carbon atoms. R 8 is a halogen element.)

[0026] ​In addition, as the polymer electrolyte (a), for example, a polymer electrolyte having a polymer compound disclosed in International Publication No. 2017 / 033685 can also be used. That is, the polymer electrolyte (a) can be produced, for example, by polymerizing a precursor polymer formed from a polymer compound having a cyclic structure without an ion exchange group in the polymer main chain and a polymer compound having an ion exchange group, or a precursor polymer formed from a polymer compound having two ion exchange groups in the side chain of the perfluorocarbon polymer compound represented by the above general formula (2) or general formula (3), and then performing alkali hydrolysis, acid treatment, etc.

[0027] Each of the above precursor polymers is not limited to the following, but can be produced, for example, by copolymerizing an olefin fluoride compound and a vinyl fluoride compound.

[0028] Here, the olefin fluoride compound is not limited to the following, and examples include compounds of the following general formula (5). CF2=CFZ···(5) (In the general formula (5), Z represents H, Cl, F, a perfluoroalkyl group having 1 to 3 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen.)

[0029] In addition, the vinyl fluoride compound is not limited to the following, and examples include the following compounds. CF2=CFO(CF2) z -SO2F CF2=CFOCF2CF(CF3)O(CF2) z -SO2F CF2=CF(CF2) <N z -SO2F CF2=CF(OCF2CF(CF3)) z -(CF2) z-1 -SO2F CF2=CFO(CF2) z -CO2R CF2=CFOCF2CF(CF3)O(CF2)z -CO2R CF2=CF(CF2) z -CO2R CF2=CF(OCF2CF(CF3)) z -(CF2)2-CO2R (In each formula, Z represents an integer from 1 to 8, and R represents a hydrocarbon-based alkyl group having 1 to 3 carbon atoms.)

[0030] The copolymerization method of the fluorinated olefin compound and the vinyl fluoride compound is not limited to the following, and for example, the methods described later can be mentioned.

[0031] (i) Solution polymerization method The solution polymerization method is a method in which a polymerization solvent such as a fluorinated hydrocarbon is used, and a vinyl fluoride compound and a gas of a fluorinated olefin are reacted in a state of being filled and dissolved in this polymerization solvent to carry out polymerization. Examples of the fluorinated hydrocarbon as the polymerization solvent include, but are not limited to, compounds collectively referred to as "Freons" such as trichlorotrifluoroethane and 1,1,1,2,3,4,4,5,5,5-decafluoropentane.

[0032] (ii) Bulk polymerization method The bulk polymerization method is a method in which a polymerization solvent such as a fluorinated hydrocarbon is not used, and the vinyl fluoride compound itself is used as a polymerization solvent to polymerize a fluorinated olefin compound and a vinyl fluoride compound.

[0033] (iii) Emulsion polymerization method The emulsion polymerization method is a method in which an aqueous solution of a surfactant is used as a polymerization solvent, and a vinyl fluoride compound and a fluorinated olefin gas are reacted in a state of being filled and dissolved in this polymerization solvent to carry out polymerization.

[0034] (iv) Mini-emulsion polymerization or micro-emulsion polymerization method Emulsion polymerization is a method in which an aqueous solution of a surfactant and a co-emulsifier such as alcohol is used, and a vinyl fluoride compound and a gas of a fluorinated olefin are reacted in a state of being filled and emulsified in this aqueous solution to carry out polymerization.

[0035] (v) Suspension polymerization method The suspension polymerization method is a method in which an aqueous solution of a suspension stabilizer is used, and a vinyl fluoride compound and a gas of a fluorinated olefin are reacted in a state of being filled and suspended in this aqueous solution to carry out polymerization.

[0036] As an index of the degree of polymerization of the precursor polymer used for the polyelectrolyte (a) constituting the polyelectrolyte composition of the present embodiment, the melt mass flow rate (hereinafter abbreviated as "MFR") can be used. The MFR of the precursor polymer is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, and even more preferably 0.3 g / 10 min or more. The upper limit of MFR is not limited, but is preferably 100 g / 10 min or less, and more preferably 10 g / 10 min or less. By setting the MFR to 0.01 g / 10 min or more and 100 g / 10 min or less, the moldability such as film formation of the polyelectrolyte membrane tends to be more excellent. Note that the MFR can be measured at 270 °C, a load of 2.16 kgf, and an orifice inner diameter of 2.09 mm based on JIS K-7210.

[0037] The precursor polymer produced as described above is hydrolyzed in a basic reaction liquid, sufficiently washed with warm water or the like, and acid-treated. By this acid treatment, the perfluorocarbon sulfonic acid resin precursor is protonated to become an SO3H form.

[0038] (Niobium oxide (b)) The polyelectrolyte composition of the present embodiment contains niobium oxide (b). By containing niobium oxide (b), in the polyelectrolyte membrane, the electrode catalyst layer, and the membrane electrode assembly using the polyelectrolyte composition of the present embodiment, there is no outflow even under acidic conditions for a long time, and an excellent radical trapping ability is exhibited, enabling stable operation. Niobium oxide (b) has an average particle diameter obtained by laser diffraction particle size distribution measurement of more than 0.05 μm and 5.0 μm or less. When the average particle diameter exceeds 0.05 μm, when combined with polyphenylene sulfide as the above-mentioned polymer electrolyte (a), excellent dispersion stability is achieved, and a uniform polymer electrolyte membrane can be obtained. Moreover, when the average particle diameter is 5 μm or less, a sufficiently large specific surface area can be obtained in niobium oxide (b), excellent radical trapping ability can be exhibited, and a polymer electrolyte membrane having high durability can be obtained. The average particle diameter of niobium oxide (b) is preferably from 0.05 μm to 5.0 μm, more preferably from 0.10 μm to 1.0 μm. The average particle diameter of niobium oxide (b) can be measured by analyzing the scattered light of a laser by the Microtrac method using a laser diffraction / scattering particle size analyzer. Specifically, it can be measured by the method described in the examples below. As a method for controlling the average particle diameter of niobium oxide (b) to exceed 0.05 μm and be 5.0 μm or less, it is not limited to the following, but for example, methods such as jet mills and ball mills that apply high collision / shear energy for pulverization and refinement, and methods such as filtering the solution before preparing the polymer electrolyte composition to remove coarse particles can be mentioned.

[0039] Niobium oxide (b) is preferably at least one niobium oxide selected from the group consisting of niobium dioxide and niobium pentoxide. By using niobium dioxide and / or niobium pentoxide as niobium oxide (b), the types of radicals to be captured increase, and the effect of increasing the overall radical trapping ability can be obtained.

[0040] In the polymer electrolyte composition of this embodiment, the content of niobium oxide (b) is preferably from 0.1 to 5.0% by mass, more preferably from 0.1 to 3.0% by mass, and still more preferably from 0.5 to 3.0% by mass. When the content of niobium oxide (b) is 0.1 to 5.0% by mass, it tends to be possible to obtain a polymer electrolyte membrane, an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell that have high durability while suppressing the decomposition of hydrogen peroxide while maintaining good proton conductivity.

[0041] In the polymer electrolyte composition of the present embodiment, the cumulative passing value based on the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the niobium oxide (b) is preferably 30% or more of the whole in the region where the particle diameter is more than 0.05 μm and 5.0 μm or less from the viewpoint of the balance between dispersion stability and radical scavenging ability. The cumulative passing value based on the volume-based particle size distribution is more preferably 30% or more of the whole in the region where the particle diameter is more than 0.05 μm and 5.0 μm or less, and even more preferably 40% or more. The cumulative passing value based on the volume-based particle size distribution can be determined by the method described in the examples described later. The cumulative passing value based on the volume-based particle size distribution can be controlled to be 30% or more of the whole in the region where the particle diameter is more than 0.05 μm and 5.0 μm or less by controlling the processing time in the particle pulverization step.

[0042] In the polymer electrolyte composition of the present embodiment, the niobium oxide (b) is preferably dispersed in the above-described polymer electrolyte (a). Here, dispersion means that when TEM observation is performed without performing a staining treatment, a phase containing niobium oxide (b) is dispersed in a particulate state in the polymer electrolyte (a component) phase, and means a state of "dispersed in an island shape". That is, it means that the (a) component constitutes the continuous phase and the (b) component constitutes the dispersed phase, taking a sea-island structure. Dispersion in such a state indicates that the portion mainly composed of niobium oxide (b) is uniformly finely dispersed in the portion mainly composed of the polymer electrolyte (a), and is preferable from the viewpoint of durability.

[0043] (Radical scavenger (c)) The polymer electrolyte composition of the present embodiment can further contain a radical scavenger (c). The polymer electrolyte composition of this embodiment can efficiently suppress the generation of radical species and exhibit high durability. In addition, by including a radical scavenger (c), even if radical species are generated by any chance, they can be scavenged by the radical scavenger (c). As a result, in a fuel cell vehicle using a polymer electrolyte membrane made of the polymer electrolyte composition of this embodiment, there is a tendency to remarkably improve the durability of the fuel cell even under high-temperature and low-humidity conditions.

[0044] Examples of the radical scavenger (c) include, but are not limited to, compounds having a functional group that enables the mechanism proposed by known antioxidants. Examples of such functional groups include, but are not limited to, a functional group having a radical chain inhibition function, a functional group having a function of decomposing radicals, and a functional group having a function of inhibiting chain initiation. Examples of the functional group having a radical chain inhibition function include, but are not limited to, a phenolic hydroxyl group, a primary amine, a secondary amine, etc. Examples of the functional group having a function of decomposing radicals include, but are not limited to, a mercapto group, a thioether group, a disulfide group, a phosphite group, etc. containing sulfur, phosphorus, etc. Furthermore, examples of the functional group having a function of inhibiting chain initiation include, but are not limited to, hydrazine, amide, etc. ("Antioxidant Handbook" (published by Taiseisha in 1978)).

[0045] Examples of the radical scavenger (c) also include compounds in which an atom is easily abstracted by a radical, for example, compounds having a hydrogen bonded to a tertiary carbon or a carbon-halogen bond in the structure.

[0046] In addition, the radical scavenger (c) may have a functional group that forms an ionic bond with the polyelectrolyte (a). Examples of such radical scavengers (c) include, but are not limited to, for example, a compound (c-1) having at least one of a primary amine and a secondary amine in the same molecule and / or a compound having a tertiary amine in the same molecule and having at least one selected from the group consisting of sulfur, phosphorus, hydrazine, amide, a phenolic hydroxyl group, a hydrogen bonded to a primary amine, a secondary amine, or a tertiary amine, and a halogen bonded to carbon (c-2).

[0047] Here, examples of the functional group that forms an ionic bond with the polyelectrolyte (a) in the compound (c-1) and the compound (c-2) include, but are not limited to, for example, when the ion exchange group in the polyelectrolyte (a) is a sulfonic acid group, it is a basic functional group, and specifically, nitrogen-containing functional groups such as a primary amine, a secondary amine, and a tertiary amine can be mentioned. Therefore, if it has a primary amine or a secondary amine, it will interact with the ion exchange group of the polyelectrolyte (a) and also have a radical scavenging function (corresponding to the compound (c-1)). On the other hand, when the part that interacts with the ion exchange group of the polyelectrolyte (a) is a tertiary amine, the functional group that forms an ionic bond with the polyelectrolyte (a) is preferably contained in the same molecule separately from the part having a radical scavenging function. Examples of such functional groups are not particularly limited, and include, for example, a phenolic hydroxyl group, a primary and secondary amine, etc. (corresponding to the compound (c-2)).

[0048] More specific examples of the compound (c-1) and the compound (c-2) which are the radical scavenger (c) are as follows.

[0049] Examples of the compound (c-1) include, but are not limited to, for example, aromatic compounds partially substituted with the above functional groups such as polyaniline, unsaturated heterocyclic compounds such as polybenzimidazole, polybenzoxazole, polybenzothiazole, polybenzoxadiazole, phenylated polyquinoxaline, and phenylated polyquinoline.

[0050] Examples of the compound (c-2) include, but are not limited to, compounds having a tertiary nitrogen heterocycle with a sulfonic acid and an acid-base bond in the side chain and having a hydrogen at the benzylic position in the main chain that is easily abstracted by a radical. Specifically, polyvinylpyridine, polyvinylcarbazole, polystyrene into which groups containing a secondary amine and a tertiary amine are introduced into the aromatic ring, and the like can be mentioned.

[0051] Note that the compound (c-1) and the compound (c-2) may be a copolymer or the like of a unit that interacts with the polyelectrolyte (a) having an ion-exchange group and a unit that has a radical scavenging function. By having a portion that interacts with the polyelectrolyte (a) having an ion-exchange group, the compatibility with the polyelectrolyte (a) tends to be further improved. Also, by having a portion that has a radical scavenging function, the chemical durability tends to be further improved.

[0052] In the polyelectrolyte composition of the present embodiment, the content of the compound (c-1) and the compound (c-2) is preferably 0.001 to 50.000% by mass, more preferably 0.005 to 20.000% by mass, still more preferably 0.010 to 10.000% by mass, even more preferably 0.100 to 5.000% by mass, and even more preferably 0.100 to 2.000% by mass in the polyelectrolyte composition. In the polyelectrolyte composition of the present embodiment, by setting the total content of the compound (c-1) and the compound (c-2) within the above range (0.001 to 50.000% by mass), a polyelectrolyte membrane, an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell having high durability while maintaining good proton conductivity tend to be obtained.

[0053] (Thioether compound (d)) The polyelectrolyte composition of the present embodiment may contain a thioether compound (d) in addition to the above-described polyelectrolyte (a), niobium oxide (b) having an average particle diameter of more than 0.050 μm and 5.0 μm or less, and a radical scavenger (c).

[0054] As the thioether compound (d), although not particularly limited, for example, -(R-S) n - (where S is a sulfur atom, R is a hydrocarbon group, and n is an integer of 1 or more) compounds containing such a chemical structure can be mentioned. Specifically, dialkyl thioethers such as dimethyl thioether, diethyl thioether, dipropyl thioether, methyl ethyl thioether, and methyl butyl thioether; cyclic thioethers such as tetrahydrothiophene and tetrahydrothiopyran; aromatic thioethers such as methyl phenyl sulfide, ethyl phenyl sulfide, diphenyl sulfide, and dibenzyl sulfide, etc. can be mentioned. These may be used as monomers, or may be used as polymers such as polyphenylene sulfide (PPS), for example.

[0055] From the viewpoint of durability, the thioether compound (d) is preferably a polymer (oligomer, polymer) with n≧10 in a compound containing the chemical structure of -(R-S) n - (where S is a sulfur atom, R is a hydrocarbon group, and n is an integer of 1 or more), and more preferably a polymer with n≧1,000. A more preferable thioether compound (d) is polyphenylene sulfide (PPS).

[0056] Hereinafter, the polyphenylene sulfide that can be used as the thioether compound (d) will be described. The polyphenylene sulfide that can be used as the component (d) is a polyphenylene sulfide preferably having a para-phenylene sulfide skeleton of 70 mol% or more, more preferably 90 mol% or more.

[0057] The method for producing the polyphenylene sulfide is not limited to the following, but for example, a method of polymerizing a halogen-substituted aromatic compound (such as p-dichlorobenzene) in the presence of sulfur and sodium carbonate; a method of polymerizing a halogen-substituted aromatic compound in a polar solvent in the presence of sodium sulfide or sodium hydrogen sulfide and sodium hydroxide; a method of polymerizing a halogen-substituted aromatic compound in a polar solvent in the presence of hydrogen sulfide and sodium hydroxide or sodium aminoalkanoate; a method of performing self-condensation of p-chlorothiophenol, etc. can be mentioned. In particular, specifically, a method of reacting sodium sulfide and p-dichlorobenzene in an amide-based solvent such as N-methylpyrrolidone or dimethylacetamide or a sulfone-based solvent such as sulfolane is preferably used.

[0058] In addition, the content of the -SX group (S is a sulfur atom, X is an alkali metal or a hydrogen atom) contained in the polyphenylene sulfide as the component (d) is usually 10 μmol / g or more and 10,000 μmol / g or less, preferably 15 μmol / g or more and 10,000 μmol / g or less, more preferably 20 μmol / g or more and 10,000 μmol / g or less with respect to the total amount of the polymer electrolyte (a) and the polyphenylene sulfide (d). When the -SX group concentration is within the above range, the number of reaction active points tends to increase. By using a polyphenylene sulfide whose -SX group concentration satisfies the above range, the miscibility with the polymer electrolyte (a) is improved, so the dispersibility is improved, and higher durability can be obtained under high-temperature and low-humidity conditions.

[0059] Also, as the thioether compound (d), those having an acidic functional group introduced at the terminal can also be preferably used. The acidic functional group to be introduced is not limited to the following, but for example, a sulfonic acid group, a phosphoric acid group, a carboxylic acid group, a maleic acid group, a maleic anhydride group, a fumaric acid group, an itaconic acid group, an acrylic acid group, a methacrylic acid group are preferred. Among these, the sulfonic acid group is more preferred.

[0060] Note that the method for introducing the acidic functional group in the thioether compound (d) is not particularly limited and can be carried out using general methods. For example, for the introduction of a sulfonic acid group, it can be carried out under known conditions using a sulfonating agent such as sulfuric anhydride or fuming sulfuric acid. Such an introduction method is not limited to the following, but for example, it can be carried out under the conditions described in K. Hu, T. Xu, W. Yang, Y. Fu, Journal of Applied Polymer Science, Vol. 91, and E. Montoneri, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 27, 3043 - 3051 (1989).

[0061] Also, as the thioether compound (d), those in which the introduced acidic functional group is replaced with a metal salt or an amine salt are also preferably used. The metal salts include, but are not limited to, for example, alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts are preferably mentioned.

[0062] Furthermore, when the thioether compound (d) is used in powder form in producing the polymer electrolyte composition of this embodiment, the median diameter of the thioether compound (d) is preferably 0.01 - 2.0 μm, more preferably 0.01 - 1.0 μm, still more preferably 0.01 - 0.5 μm, and even more preferably 0.01 - 0.1 μm in a state of being dispersed in water. When the median diameter is within the above range, the dispersibility in the polymer electrolyte (a) is further improved, and it tends to be more excellent in effects such as durability and long life. Note that the median diameter of the thioether compound (d) is not limited to the following, but for example, it can be determined by observation using a particle size distribution meter or a scanning electron microscope (SEM).

[0063] As a method for finely dispersing the thioether compound (d) in the polymer electrolyte (a), although it is not limited to the following, for example, a method of applying high shear during melt kneading with the polymer electrolyte (a) or the like to pulverize and finely disperse, a method of obtaining a mixed solution of the polymer electrolyte (a) and the thioether compound (d), filtering the mixed solution to remove coarse thioether compound (d) particles, and using the filtered solution, etc. may be mentioned.

[0064] When dispersing the thioether compound (d) into the polymer electrolyte (a) by melt kneading, when using polyphenylene sulfide which is suitable as the component (d), the melt viscosity of the polyphenylene sulfide (the value maintained for 6 minutes at 300 °C, a load of 196 N, L / D (L: orifice length, D: orifice inner diameter) = 10 / 1 using a flow tester) is preferably 1 to 10,000 poise from the viewpoint of moldability, and more preferably 100 to 10,000 poise.

[0065] In the polymer electrolyte composition of the present embodiment, the mass ratio (a / d) of the polymer electrolyte (a) to the thioether compound (d) is preferably (a / d) = 60 / 40 to 99.99 / 0.01, more preferably (a / d) = 70 / 30 to 99.95 / 0.05, further preferably (a / d) = 80 / 20 to 99.9 / 0.1, and even more preferably (a / d) = 90 / 10 to 99.5 / 0.5. By setting the mass ratio of the polymer electrolyte (a) to 60 or more, good ion conductivity can be realized, and good battery characteristics tend to be realized. On the other hand, by setting the mass ratio of the thioether compound (d) to 40 or less, the durability in battery operation under high temperature and low humidity conditions tends to be further improved.

[0066] Also, by blending the thioether compound (d) together with the above-mentioned radical scavenger (c), the polymer electrolyte membrane, electrode catalyst layer, and membrane electrode assembly using the polymer electrolyte composition of the present embodiment tend to exhibit extremely high durability even under high temperature and low humidity conditions.

[0067] The mass ratio (c / d) of the radical scavenger (c) to the thioether compound (d) is preferably (c / d) = 1 / 99 to 99 / 1, more preferably (c / d) = 5 / 95 to 95 / 5, even more preferably (c / d) = 10 / 90 to 90 / 10, and even more preferably (c / d) = 20 / 80 to 80 / 20. When the mass ratio (c / d) is within the above range, it tends to be excellent in the balance between chemical stability and durability (dispersibility).

[0068] Furthermore, the content of the total mass of the radical scavenger (c) and the thioether compound (d) in the polyelectrolyte composition is preferably 0.01 to 50% by mass, more preferably 0.05 to 45% by mass, even more preferably 0.1 to 40% by mass, even more preferably 0.2 to 35% by mass, and even more preferably 0.3 to 30% by mass. When the total content of the component (c) and the component (d) is within the above range, it tends to be excellent in the balance between ionic conductivity and durability (dispersibility).

[0069] Also, a preferred form of the polyelectrolyte composition of the present embodiment is a polyelectrolyte solution containing predetermined components having the above-mentioned polyelectrolyte (a) and niobium oxide (b) as essential components. The polyelectrolyte composition in such a form can be processed into the form of the polyelectrolyte membrane and the electrode catalyst layer of the present embodiment.

[0070] (Polyelectrolyte solution) The polyelectrolyte membrane of the present embodiment is formed by the polyelectrolyte composition of the present embodiment containing the polyelectrolyte (a) and niobium oxide (b) as essential components. The polyelectrolyte composition may be used as a polyelectrolyte solution by dissolving or dispersing each of its components in a predetermined solvent simultaneously or separately and then mixing them.

[0071] The polyelectrolyte solution can be used as a material for a polyelectrolyte membrane, an electrode catalyst layer, etc. as it is, or after passing through steps such as filtration and concentration, alone or in mixture with other electrolyte solutions.

[0072] A method for producing a polymer electrolyte solution will be described. As a method for producing a polymer electrolyte solution, although not limited to the following, for example, first, a molded article made of a polymer electrolyte precursor is immersed in a basic reaction liquid and hydrolyzed. By this hydrolysis treatment, the polymer electrolyte precursor is converted into a polymer electrolyte (a). Next, the hydrolyzed molded article is thoroughly washed with warm water or the like, and then acid treatment is performed.

[0073] The acid used for the acid treatment is not particularly limited. For example, mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid are preferable. By this acid treatment, the polymer electrolyte precursor is protonated to become an SO3H form. The molded article (the molded article containing the protonated polymer electrolyte (a)) acid-treated as described above is dissolved and / or suspended in a solvent (a solvent having good affinity with the resin) capable of dissolving and / or suspending the polymer electrolyte (a). Examples of such a solvent include, but are not limited to, water; protic organic solvents such as ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin; aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. These can be used alone or in combination of two or more. In particular, when using a single solvent, water alone is preferable. Also, when using a combination of two or more, a mixed solvent of water and a protic organic solvent is preferable.

[0074] The method of dissolution and / or suspension is not limited to the following, but for example, it is preferably directly dissolved and / or dispersed in the various solvents described above, and more preferably dissolved and / or dispersed in the temperature range of 0 to 250 °C under atmospheric pressure or under the condition of sealed pressurization in an autoclave or the like. In particular, when a protic organic solvent is used as the solvent, the mixing ratio of water and the protic organic solvent can be appropriately selected according to the dissolution method, dissolution conditions, type of the polyelectrolyte (a), total solid content concentration, dissolution temperature, stirring speed, etc. The mass ratio of the protic organic solvent to water is preferably 0.1 to 10 of the protic organic solvent with respect to 1 of water, and more preferably 0.1 to 5 of the protic organic solvent with respect to 1 of water.

[0075] The solution and / or suspension of the polyelectrolyte (a) is not particularly limited, and for example, includes one or more of an emulsion (a liquid in which liquid particles are dispersed as colloidal particles or coarser particles to form an emulsion state), a suspension (a liquid in which solid particles are dispersed as colloidal particles or particles visible under a microscope), a colloidal liquid (a state in which macromolecules are dispersed), a micellar liquid (a lyophilic colloid dispersion system formed by the association of a large number of small molecules by intermolecular forces), etc.

[0076] As described above, the polyelectrolyte solution can be used for producing the polyelectrolyte membrane of the present embodiment and contains niobium oxide (b). Niobium oxide (b) can be contained in the polyelectrolyte solution through a step of adding niobium oxide (b) to the solution of the polyelectrolyte (a), for example.

[0077] In addition, the polyelectrolyte solution may further contain a solvent according to the forming method and application. Such a solvent is not particularly limited, and examples thereof include at least one or more of water, an organic solvent, a liquid resin monomer, and a liquid resin oligomer.

[0078] Examples of the organic solvent include, but are not limited to, alcohols such as methanol, ethanol, 2-propanol, butanol, and octanol; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and amides such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. The organic solvent may be used alone or in combination of two or more kinds.

[0079] In addition, the polymer electrolyte solution can be concentrated or filtered according to the molding method and application. Examples of the concentration method include, but are not limited to, heating to evaporate the solvent and concentration under reduced pressure. When the polymer electrolyte solution is used as a coating solution, the solid content ratio of the polymer electrolyte solution is preferably 0.5 to 50% by mass. When the solid content ratio is 0.5% by mass or more, an increase in viscosity is suppressed, and the handleability tends to be excellent. In addition, when the solid content ratio is 50% by mass or less, the productivity tends to be improved.

[0080] Examples of the filtration method include, but are not limited to, a method of pressure filtration using a filter. Regarding the filter, it is preferable to use a filter medium with a 90% capture particle size that is 10 to 100 times the average particle size of the particles. Examples of such filter media include paper and metal. Particularly when the filter medium is paper, it is preferable that the 90% capture particle size is 10 to 50 times the average particle size of the particles. When using a metal filter, it is preferable that the 90% capture particle size is 50 to 100 times the average particle size of the particles. By setting the 90% capture particle size to be 10 times or more the average particle size, it is possible to suppress the pressure required for liquid feeding from becoming too high and to suppress the filter from clogging in a short period. On the other hand, by setting it to be 100 times or less the average particle size, it is possible to preferably remove aggregates of particles that cause foreign matters in the film and undissolved resin.

[0081] [Polymer electrolyte membrane] The polymer electrolyte membrane of this embodiment contains the polymer electrolyte composition of this embodiment described above. The membrane thickness of the polymer electrolyte membrane of this embodiment is preferably 1 μm or more and 500 μm or less, more preferably 2 μm or more and 100 μm or less, and even more preferably 5 μm or more and 50 μm or less. When the membrane thickness is 1 μm or more, it is possible not only to reduce the inconvenience of direct reaction between hydrogen and oxygen, but also to reduce the likelihood of damage to the polymer electrolyte membrane even when differential pressure, strain, etc. occur during handling during fuel cell manufacturing or during fuel cell operation. On the other hand, when the membrane thickness is 500 μm or less, the ion permeability tends to improve, and the performance as a solid polymer electrolyte membrane tends to improve.

[0082] (Method for manufacturing polymer electrolyte membrane) The method for manufacturing the polymer electrolyte membrane of this embodiment is not particularly limited, and it may be cast and formed using the above-described polymer electrolyte solution, or it may be formed by passing through processes such as melt extrusion and stretching. When performing molding by melt extrusion, from the viewpoint of moldability, after melt-kneading a mixture of a polymer electrolyte precursor, niobium oxide (b), a radical scavenger (c) as needed, and a thioether compound (d), it is preferably extrusion-molded to form a film, and then immersed in a basic reaction liquid and hydrolyzed. By this hydrolysis treatment, the above polymer electrolyte precursor is converted into a polymer electrolyte (a).

[0083] Furthermore, as described above, after the hydrolysis treatment in the basic reaction liquid, the film is sufficiently washed with warm water or the like, and then acid treatment is performed. The acid used for the acid treatment is not limited to the following, but for example, mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid are preferable. By this acid treatment, the polymer electrolyte precursor is protonated and becomes an SO3H form.

[0084] In addition, the polymer electrolyte membrane of this embodiment may be reinforced with porous bodies such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro(alkoxy vinyl ether) copolymer (PFA), polyethylene, and polypropylene, fibers, woven fabrics, non-woven fabrics, etc.; inorganic whiskers such as silica and alumina, and organic fillers made of polytetrafluoroethylene (PTFE), polyethylene, and polypropylene.

[0085] Furthermore, the polymer electrolyte membrane of this embodiment may be subjected to a crosslinking treatment using a crosslinking agent, ultraviolet rays, electron beams, radiation, or the like.

[0086] The polymer electrolyte membrane of this embodiment is preferably heat-treated after molding. By the heat treatment, crystallization of the polymer electrolyte is promoted, and the mechanical strength of the polymer electrolyte membrane can be stabilized. In addition, by the heat treatment, the crystalline part of additives such as the radical scavenger (c) and the thioether compound (d) and the polymer electrolyte part are firmly adhered, and as a result, the mechanical strength tends to be more stabilized.

[0087] The heat treatment temperature is preferably 120°C or higher and 300°C or lower, more preferably 140°C or higher and 250°C or lower, and still more preferably 160°C or higher and 230°C or lower. When the heat treatment temperature is 120°C or higher, the adhesion between the crystalline part and the polymer electrolyte part tends to be further improved. On the other hand, when the heat treatment temperature is 300°C or lower, the characteristics of the polymer electrolyte membrane tend to be further improved. The heat treatment time depends on the heat treatment temperature, but is preferably 5 minutes or longer and 3 hours or shorter, more preferably 10 minutes or longer and 2 hours or shorter.

[0088] [Membrane Electrode Assembly] The membrane electrode assembly of this embodiment has the above-described polymer electrolyte membrane and an electrode catalyst layer. That is, the membrane electrode assembly of this embodiment has the polymer electrolyte membrane of this embodiment and an electrode catalyst layer disposed on the polymer electrolyte membrane. The polymer electrolyte membrane of this embodiment can be used as a component of a membrane electrode assembly and a polymer electrolyte fuel cell. A unit in which two types of electrode catalyst layers, an anode and a cathode, are joined to both sides of the polymer electrolyte membrane is called a membrane electrode assembly (hereinafter sometimes abbreviated as "MEA"). A structure in which a pair of gas diffusion layers are joined to face each other further outside the electrode catalyst layer may also be called an MEA.

[0089] (Electrode Catalyst Layer) The electrode catalyst layer of this embodiment constitutes the membrane electrode assembly. As the electrode catalyst layer, a known electrode catalyst layer used in an MEA can be applied. The electrode catalyst layer preferably contains the above-described polymer electrolyte composition of this embodiment. That is, in the membrane electrode assembly of this embodiment, the electrode catalyst layer preferably contains a polymer electrolyte (a) and niobium oxide (b) having an average particle diameter of more than 0.050 μm and 5.0 μm or less. The electrode catalyst layer of this embodiment can include a polymer electrolyte composition, and, if necessary, fine particles of a catalyst metal and a conductive agent supporting the same. Further, a water repellent may be included if necessary. The catalyst metal used for the electrode catalyst layer is not particularly limited as long as it is a metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen. Although not limited to the following, for example, platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof can be mentioned. Among these, platinum is mainly preferably used.

[0090] The manufacturing method of the membrane electrode assembly (MEA) of this embodiment is not particularly limited, but for example, the following method is performed. First, platinum-supported carbon, which is a catalyst metal, is dispersed in a solution obtained by dissolving a binder ion-exchange resin for the electrode catalyst layer in a mixed solution of alcohol and water to form a paste. A certain amount of this is applied to a PTFE sheet and dried. Next, the coated surfaces of the PTFE sheets are faced to each other, and the above-mentioned polymer electrolyte membrane is sandwiched therebetween, and a membrane electrode assembly (MEA) can be obtained by transfer bonding by hot pressing at 100°C to 200°C. As the binder ion-exchange resin for the electrode catalyst layer, a solution obtained by dissolving an ion-exchange resin in a solvent (such as alcohol or water) is generally used. However, when manufacturing the membrane electrode assembly of this embodiment, from the viewpoint of durability during fuel cell operation, a polymer electrolyte composition containing the above-mentioned polymer electrolyte (a) and niobium oxide (b), which can be used for manufacturing the polymer electrolyte membrane of this embodiment, is used.

[0091] 〔Polymer electrolyte fuel cell〕 The polymer electrolyte fuel cell of this embodiment includes the membrane electrode assembly (MEA) of the above-mentioned this embodiment. The above-described MEA, and an MEA having a structure in which a pair of gas diffusion electrodes are further arranged to face each other, can also be combined with components commonly used in a polymer electrolyte fuel cell such as a bipolar plate and a backing plate to form a polymer electrolyte fuel cell.

[0092] The bipolar plate means a composite material of graphite and resin or a metal plate or the like having grooves formed on its surface for flowing gases such as fuel and oxidant. The bipolar plate has a function of transmitting electrons to an external load circuit, and also has a function as a flow path for supplying fuel and oxidant to the vicinity of the electrode catalyst. By inserting and stacking a plurality of MEAs of the present embodiment between such bipolar plates, the polymer electrolyte fuel cell of the present embodiment can be manufactured.

Examples

[0093] Hereinafter, the present invention will be specifically described with specific examples and comparative examples, but the present embodiment is not limited to the examples described later. The measurement methods of various physical properties and the evaluation methods of characteristics in the examples and comparative examples are as follows.

[0094] 〔Measurement method of physical properties〕 (Measurement of average particle diameter and cumulative passing integral value) The volume average particle diameter of the fine particles of the metal compound in the polymer electrolyte composition was measured using a laser diffraction / scattering particle size analyzer LA-950 manufactured by Horiba, Ltd. As a pretreatment, the particle dispersion liquid was subjected to ultrasonic treatment at 600 W for 1 minute and then measured. The volume average particle diameter obtained by analyzing the scattered light of the laser by the Microtrac method was defined as the average particle diameter of the fine particles of the metal compound. Similarly, the cumulative passing integral value obtained by analyzing the scattered light of the laser by the Microtrac method was defined as the cumulative passing integral value of the fine particles of the metal compound. Thereby, the ratio (%) of the passing integral value in the region where the particle diameter is more than 0.05 μm and 5.0 μm or less with respect to the whole was calculated.

[0095] (Durability Test: Power Generation and OCV Cycle Test) To accelerate the evaluation of the durability of the polymer electrolyte membrane under high-temperature and low-humidity conditions, an accelerated test by power generation and OCV cycle was conducted according to the following procedure. Note that "OCV" means Open Circuit Voltage. The fuel cell single cell fabricated as described below was set in an evaluation apparatus (Fuel Cell Evaluation System 890CL manufactured by Toyo Technica), and a durability test with a cycle of 3 hours of power generation and 3 hours of OCV was conducted.

[0096] The test conditions for power generation were a cell temperature of 90 °C, a humidification bottle temperature of 61 °C (relative humidity 30%RH), hydrogen gas on the anode side, and air gas on the cathode side, each supplied at a gas utilization rate of 75% and 55% at 0.3 A / cm 2 The conditions were such that the gas utilization rates on the anode side and the cathode side were 75% and 55%, respectively. Also, both the anode side and the cathode side were unpressurized (atmospheric pressure).

[0097] Regarding the test conditions for OCV, the cell temperature, the humidification bottle temperature, the supplied gas, and the pressure were the same as those for the power generation test conditions.

[0098] <Deterioration Judgment> The hydrogen leakage current was measured every 100 hours from the test time of 0 hours (L0). Deterioration judgment was made by calculating the difference (L500 - L0) between the hydrogen leakage current at 500 hours after the start of the test (L500) and L0. It was judged that the smaller the value of L500 - L0, the better the durability. Note that when the hydrogen leakage current reached 10 mA / cm 2 or more, it was judged that the membrane was broken even if the test time was less than 500 hours, and the test was terminated.

[0099] The hydrogen leakage current was measured by introducing hydrogen gas to the anode and nitrogen gas to the cathode at 200 cc / min each under unpressurized conditions with the cell temperature and the humidification bottle temperature the same as those for the power generation test conditions. For the measurement, a potentiostat (product name: Solartron 1280B, manufactured by Toyo Technica Co., Ltd.) was used. A voltage of 0.4 V was maintained for 5 minutes, and the current value after 5 minutes was divided by the electrode area to calculate the result.

[0100] <Elution of catalyst> The elution of the catalyst was determined by measuring the metal ion concentration in the waste liquid generated during power generation using ICP-AES under the following conditions and comparing the ion concentrations immediately after the start of operation and at the end. The presence or absence of outflow was judged based on this comparison.

[0101] [Elution test of niobium oxide and niobium fluoride] The presence or absence of elution of niobium oxide or niobium fluoride from the polymer electrolyte membranes of the examples and comparative examples containing niobium oxide or niobium fluoride was evaluated by using an inductively coupled plasma atomic emission spectrometer (ICP-AES device) (SPS3520UV-DD manufactured by SII (SII)) to quantify the amount of Nb contained in the waste liquid immediately after the start of power generation operation and after the end. Hydrofluoric acid-containing 1% nitric acid aqueous solution was added to a niobium standard solution for ICP emission spectrometry (1000 mg / L) to prepare calibration samples of 0 mg / L, 1 mg / L, 10 mg / L, and 50 mg / L. The amount of Nb was measured under the following conditions using ICP-AES to create a calibration curve. The measurement sample was prepared by adding 45 mL of 1% nitric acid aqueous solution to 5 mL of the waste liquid. The measurement sample was also measured using ICP-AES under the same conditions, and the amount of Nb in the waste liquid was calculated from the calibration curve. When the amount of Nb was not detected or was 1 mass ppm or less, it was determined that there was no elution of the catalyst. When it exceeded 1 mass ppm, it was determined that the catalyst had flowed out. (Conditions) High-frequency power: 1.2 kW Plasma gas (Ar) flow rate: 16 L / min Auxiliary gas (Ar) flow rate: 0.5 L / mn Carrier gas (Ar) pressure 0.24 Mpa Carrier gas (Ar) flow rate: 0.3 / min Optical height: 12 mm Nb measurement wavelength: 316.431 nm, R spectrometer

[0102] [Elution test of cerium oxide and cerium nitrate] Similar to the elution tests of niobium oxide and niobium fluoride described above, the presence or absence of elution of cerium oxide or cerium nitrate from the polymer electrolyte membranes of the comparative examples containing cerium oxide or cerium nitrate was evaluated. To a cerium standard solution for ICP emission spectrometry (1000 mg / L), an aqueous solution of 1% nitric acid was added, and calibration curve preparation samples of 0 mg / L, 1 mg / L, 10 mg / L, and 50 mg / L were prepared. The amount of Ce was measured under the following conditions by ICP-AES to prepare a calibration curve. The measurement sample was prepared by adding 45 mL of an aqueous solution of 1% nitric acid to 5 mL of the waste liquid immediately after the start of power generation operation and after the end. The measurement sample was also measured by ICP-AES under the same conditions, and the amount of Ce in the waste liquid was calculated from the calibration curve. When the amount of Ce was not detected or was 1 mass ppm or less, it was determined that there was no elution of the catalyst. When it exceeded 1 mass ppm, it was determined that the catalyst had flowed out. (Conditions) High-frequency power: 1.2 kW Plasma gas (Ar) flow rate: 16 L / min Auxiliary gas (Ar) flow rate 0.5 L / mn Carrier gas (Ar) pressure 0.24 MPa Carrier gas (Ar) flow rate: 0.3 L / min Optical measurement height: 12 mm Ce measurement wavelength: 413.765 nm, L spectrometer

[0103] <Added catalyst aggregation> Added catalyst aggregation was determined to be occurring when the cumulative passage of particles with a particle diameter of 5.0 μm or more increased in the particle size distribution in each particle dispersion and polymer electrolyte solution.

[0104] [Example 1] (Preparation of polymer electrolyte composition) To 100 g of a PFSA (perfluorosulfonic acid resin) dispersion solution (Aquivion dispersion solution, manufactured by Sigma-Aldrich; PFSA content: 25% by mass, water content: 75% by mass) A1 in a poly container, 40 g of 1-propanol was added while stirring with a magnetic stirrer, and after stirring until uniform, it was stirred at 23 °C for 24 hours to obtain a transparent and homogeneous polymer electrolyte solution B1.

[0105] To 100 g of niobium dioxide (manufactured by High Purity Chemical Research Institute) in a predetermined poly container, 900 g of ion-exchanged water was added to prepare a niobium dioxide coarse particle liquid G1. The volume average particle diameter of the niobium dioxide coarse particles was 17.23 μm.

[0106] The niobium dioxide coarse particle liquid G1 was treated with 0.5 mm partially stabilized zirconia beads in a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Laboster LMZ06) for 60 minutes to obtain a niobium dioxide particle dispersion liquid H1. The volume average particle diameter of the niobium dioxide fine particles in the obtained niobium dioxide particle dispersion liquid H1 was 3.13 μm.

[0107] The niobium dioxide coarse particle liquid H1 was treated with 0.1 mm partially stabilized zirconia beads in a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Laboster LMZ06) for 60 minutes to obtain a niobium dioxide particle dispersion liquid I1. The volume average particle diameter of the niobium dioxide fine particles in the obtained niobium dioxide particle dispersion liquid H1 was 0.13 μm.

[0108] To 100 g of the polymer electrolyte solution B1 in a 500 mL poly container, the niobium dioxide particle dispersion liquid I1 obtained above was added while stirring with a magnetic stirrer so that PFSA / niobium dioxide fine particles = 99 / 1 (mass ratio), and then stirred until uniform to obtain a solution J1 of a polymer electrolyte composition containing niobium dioxide particles.

[0109] (Fabrication of Polymer Electrolyte Membrane) The solution J1 of the polymer electrolyte composition was applied onto a Kapton (registered trademark) film (manufactured by Toray DuPont Co., Ltd., 250 mm × 600 mm) as a base film using a bar coater (manufactured by Matsuo Sangyo Co., Ltd., bar No. 200, WET film thickness 300 μm). After that (coating area: width approximately 200 mm × length approximately 500 mm), it was dried in an oven at 120 °C for 30 minutes. The film thus obtained was further heat-treated in an oven at 200 °C for 30 minutes to obtain a polymer electrolyte membrane C1 with a film thickness of approximately 25 μm.

[0110] (Preparation of the electrode catalyst ink) A 25 mass% PFSA dispersion solution (Aquivion dispersion solution, manufactured by Sigma - Aldrich, equivalent weight (EW) 720; PFSA content: 25 mass%, water content: 75 mass%) and an electrode catalyst (TEC10E40E, manufactured by Tanaka Precious Metals Sales Co., Ltd., platinum loading 36.7 mass%) were blended so that the ratio of platinum / perfluorosulfonic acid polymer was 1 / 1.15 (by mass). Next, ethanol was added so that the solid content (the sum of the electrode catalyst and the perfluorosulfonic acid polymer) was 11 mass%, and the mixture was stirred at 3,000 rpm for 10 minutes using a homogenizer (manufactured by AS ONE Corporation) to obtain electrode catalyst ink D.

[0111] (Fabrication of the membrane - electrode assembly (MEA)) Using an automatic screen printing machine (product name: LS - 150, manufactured by Newron Precision Industry Co., Ltd.), the electrode catalyst ink D was applied onto both sides of the polymer electrolyte membrane C1 manufactured as described above such that the platinum amount was 0.2 mg / cm 2 on the anode side and 0.3 mg / cm 2 on the cathode side, and then dried and solidified under the conditions of 140 °C for 5 minutes to obtain a membrane - electrode assembly (MEA) E1.

[0112] (Fabrication of the fuel cell single cell) Gas diffusion layers (product name: GDL35BC, manufactured by MFC Technologies) were stacked on both electrodes of the MEA, and then a gasket, a bipolar plate, and a backing plate were stacked to obtain a fuel cell single cell F1.

[0113] Regarding the polymer electrolyte membrane: C1, MEA: E1, and fuel cell: F1, the results of various evaluations are shown in Table 1.

[0114] [Example 2] A solution J2 of the polymer electrolyte composition was prepared from the polymer electrolyte solution B1 and the niobium dioxide fine particle dispersion liquid I1 so that PFSA / niobium dioxide fine particles = 98 / 2 (mass ratio). Other conditions were carried out in the same manner as in Example 1 to obtain a polymer electrolyte membrane: C2, MEA: E2, and fuel cell: F2. The results of various evaluations are shown in Table 1.

[0115] Reference Example 3 To 100 g of niobium pentoxide (manufactured by High Purity Chemical Laboratory) in a plastic container, 900 g of ion-exchanged water was added to prepare a niobium pentoxide coarse particle liquid G2. The volume average particle diameter of the niobium pentoxide coarse particles was 5.17 μm. The niobium pentoxide coarse particle liquid G2 was treated for 60 minutes using 0.5 mm partially stabilized zirconia beads in a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Laboster LMZ06) to obtain a niobium pentoxide particle dispersion liquid H2. The volume average particle diameter of the niobium dioxide fine particles in the obtained niobium pentoxide particle dispersion liquid H2 was 3.22 μm. The niobium dioxide dispersion liquid H2 was similarly treated for 60 minutes using 0.1 mm partially stabilized zirconia beads in a bead mill to obtain a niobium pentoxide particle dispersion liquid I2. The volume average particle diameter of the niobium pentoxide particles in the obtained niobium pentoxide particle dispersion liquid I2 was 0.15 μm. To 100 g of the PFSA dispersion solution B1 in a 500 mL plastic container, the niobium dioxide fine particle dispersion liquid I2 obtained above was added while stirring with a magnetic stirrer so that PFSA / niobium dioxide fine particles = 99 / 1 (mass ratio), and then stirred until it became uniform to prepare a solution J3 of the polymer electrolyte composition containing niobium dioxide fine particles. Furthermore, according to the above method, a polymer electrolyte membrane: C3, MEA: E3, and fuel cell: F3 were obtained. The results of various evaluations are shown in Table 1.

[0116] ​ Reference Example 4 A polymer electrolyte composition solution J4 was prepared from the polymer electrolyte solution B1 and the niobium pentoxide particle dispersion liquid I2 so that PFSA / niobium pentoxide fine particles = 98 / 2 (mass ratio). Other conditions were carried out in the same manner as Reference Example 3, and a polymer electrolyte membrane: C4, MEA: E4, and a fuel cell: F4 were obtained. The results of various evaluations are shown in Table 1.

[0117] [Example 5] A polymer electrolyte composition solution J5 was prepared from the polymer electrolyte solution B1, the niobium dioxide fine particles I1, and the niobium pentoxide particle dispersion liquid I2 so that PFSA / niobium dioxide fine particles / niobium pentoxide fine particles = 99 / 0.5 / 0.5 (mass ratio). Other conditions were carried out in the same manner as in Example 1, and a polymer electrolyte membrane: C5, MEA: E5, and a fuel cell: F5 were obtained. The results of various evaluations are shown in Table 1.

[0118] [Example 6] A polymer electrolyte composition solution J6 was prepared from the polymer electrolyte solution B1, the niobium dioxide particle dispersion liquid I1, and the niobium pentoxide particle dispersion liquid I2 so that PFSA / niobium dioxide fine particles / niobium pentoxide fine particles = 98 / 1 / 1 (mass ratio). Other conditions were Reference Example carried out in the same manner as 3, and a polymer electrolyte membrane: C6, MEA: E6, and a fuel cell: F6 were obtained. The results of various evaluations are shown in Table 1.

[0119] Reference Example 7 A polymer electrolyte composition solution J7 was prepared from the polymer electrolyte solution B1 and the niobium dioxide particle dispersion liquid H1 so that PFSA / niobium dioxide fine particles = 99 / 1 (mass ratio). Other conditions were carried out in the same manner as in Example 1, and a polymer electrolyte membrane: C7, MEA: E7, and a fuel cell: F7 were obtained. The results of various evaluations are shown in Table 2.

[0120] ​​ Reference Example 8 A polymer electrolyte solution J8 was prepared from the polymer electrolyte solution B1 and the niobium pentoxide particle dispersion H2 so that PFSA / niobium pentoxide particles = 99 / 1 (mass ratio). Other conditions were Reference Example performed in the same manner as in 3 to obtain a polymer electrolyte membrane: C8, MEA: E8, and fuel cell: F8. The results of various evaluations are shown in Table 2.

[0121] [Example 9] As the polymer electrolyte solution, Nafion dispersion (manufactured by Sigma-Aldrich, equivalent weight (EW) 950; PFSA content: 20% by mass, water content: 36% by mass, 1-propanol content: 44% by mass) B2 was used. Other conditions were performed in the same manner as in Example 1 to obtain a polymer electrolyte membrane: C9, MEA: E9, and fuel cell: F9. The results of various evaluations are shown in Table 2.

[0122] [Example 10] B2 was used as the polymer electrolyte solution. Other conditions were performed in the same manner as in Example 2 to obtain a polymer electrolyte membrane: C10, MEA: E10, and fuel cell: F10. The results of various evaluations are shown in Table 2.

[0123] Reference Example 11 B2 was used as the polymer electrolyte solution. Other conditions were Reference Example performed in the same manner as in 3 to obtain a polymer electrolyte membrane: C11, MEA: E11, and fuel cell: F11. The results of various evaluations are shown in Table 2.

[0124] Reference Example 12 B2 was used as the polymer electrolyte solution. Other conditions were Reference Example performed in the same manner as in 4 to obtain a polymer electrolyte membrane: C12, MEA: E12, and fuel cell: F12. The results of various evaluations are shown in Table 2. ​​​

[0125] 〔Example 13〕 B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Example 5, and a polymer electrolyte membrane: C13, MEA: E13, and fuel cell: F13 were obtained. The results of various evaluations are shown in Table 3.

[0126] 〔Example 14〕 B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Example 6, and a polymer electrolyte membrane: C14, MEA: E14, and fuel cell: F14 were obtained. The results of various evaluations are shown in Table 3.

[0127] 〔 Reference Example 15〕 B2 was used as the polymer electrolyte solution. Other conditions were Reference Example carried out in the same manner as in 7, and a polymer electrolyte membrane: C15, MEA: E15, and fuel cell: F15 were obtained. The results of various evaluations are shown in Table 3.

[0128] 〔 Reference Example 16〕 B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Example 6, and a polymer electrolyte membrane: C16, MEA: E16, and fuel cell: F16 were obtained. The results of various evaluations are shown in Table 3.

[0129] 〔Comparative Example 1〕 Using B1 as the polymer electrolyte solution, the polymer electrolyte membrane C17 was prepared according to the above, and MEA: E17 and fuel cell: F17 were obtained. The results of various evaluations are shown in Table 4.

[0130] 〔Comparative Example 2〕 When the niobium dioxide coarse particle liquid G1 was treated with 0.5 mm partially stabilized zirconia beads in a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Laboster LMZ06) for 30 minutes, a niobium dioxide particle dispersion liquid H18 was obtained. The volume average particle diameter of the niobium dioxide fine particles in the obtained H18 was 5.12 μm. To 100 g of the PFSA dispersion solution B1 in a 500 mL poly container, the niobium dioxide fine particle dispersion liquid H18 obtained above was added while stirring with a magnetic stirrer so that PFSA / niobium dioxide fine particles = 99 / 1 (mass ratio), and then stirred until it became uniform to obtain a solution J18 of a polyelectrolyte composition containing niobium dioxide fine particles. According to the above method, a polyelectrolyte membrane: C18, MEA: E18, and fuel cell F18 were obtained. The results of various evaluations are shown in Table 4.

[0131] 〔Comparative Example 3〕 As the particle dispersion liquid, G2 was used instead of I1. Other conditions were carried out in the same manner as in Example 1 to obtain a polyelectrolyte membrane: C19, MEA: E19, and fuel cell F19. The results of various evaluations are shown in Table 4.

[0132] 〔Comparative Example 4〕 The niobium dioxide dispersion liquid H1 was similarly treated with 0.1 mm partially stabilized zirconia beads in a bead mill for 120 minutes to obtain a niobium dioxide particle dispersion liquid I20. The volume average particle diameter of the niobium dioxide particles in the obtained niobium dioxide particle dispersion liquid I20 was 0.038 μm. To 100 g of the PFSA dispersion solution B1 in a 500 mL poly container, when the niobium dioxide particle dispersion liquid I20 obtained above was added while stirring with a magnetic stirrer so that PFSA / niobium dioxide fine particles = 99 / 1 (mass ratio), aggregation occurred in the mixture, and a uniform polyelectrolyte composition could not be obtained.

[0133] 〔Comparative Example 5〕 The niobium pentoxide particle dispersion liquid H2 was similarly treated in a bead mill for 60 minutes using 0.1 mm partially stabilized zirconia beads to obtain a niobium pentoxide particle dispersion liquid I21. The volume average particle diameter of the niobium pentoxide particles in the obtained niobium pentoxide particle dispersion liquid I21 was 0.041 μm. To 100 g of the PFSA dispersion solution B1 in a 500 mL poly container, the niobium pentoxide particle dispersion liquid I21 obtained above was added while stirring with a magnetic stirrer so that PFSA / niobium pentoxide fine particles = 99 / 1 (mass ratio). As a result, aggregation occurred in the mixture, and a uniform polyelectrolyte composition could not be obtained.

[0134] [Comparative Example 6] To 100 g of cerium dioxide (manufactured by High Purity Chemical Research Institute) in a poly container, 900 g of ion-exchanged water was added to prepare a cerium dioxide particle liquid G22. The volume average particle diameter of these cerium dioxide particles was 13.49 μm. The cerium dioxide particle liquid G22 was treated in a bead mill for 60 minutes using 0.5 mm partially stabilized zirconia beads to obtain a cerium dioxide particle dispersion liquid H22. The volume average particle diameter of the cerium dioxide fine particles in the obtained cerium dioxide particle liquid H22 was 2.29 μm. The cerium dioxide dispersion liquid H22 was similarly treated in a bead mill for 60 minutes using 0.1 mm partially stabilized zirconia beads to obtain a cerium dioxide particle dispersion liquid I22. The volume average particle diameter of the cerium dioxide particles in the obtained cerium dioxide dispersion liquid I22 was 0.12 μm. To 100 g of the PFSA dispersion solution B1 in a 500 mL poly container, the cerium dioxide dispersion liquid I22 obtained above was added while stirring with a magnetic stirrer so that PFSA / cerium dioxide fine particles = 99 / 1 (mass ratio). As a result, some aggregation and precipitation occurred. This precipitate was removed using a PTFE pore diameter 1.0 μm membrane filter (manufactured by Advantec Toyo Co., Ltd.) to obtain a solution J22 of a polyelectrolyte composition containing cerium dioxide fine particles as a uniform solution. Further, according to the above method, a polyelectrolyte membrane: C22, MEA: E22, and fuel cell: F22 were obtained. The results of various evaluations are shown in Table 4.

[0135] 〔Comparative Example 7〕 To 100 g of PFSA dispersion solution B1 in a 500 mL poly container, cerium nitrate hexahydrate (manufactured by High Purity Chemical Research Institute) was added while stirring with a magnetic stirrer so that PFSA / cerium nitrate = 99 / 1 (mass ratio), and then stirred until homogeneous to obtain a solution J23 of a polyelectrolyte composition containing cerium nitrate. Further, according to the above method, a polyelectrolyte membrane: C23, MEA: E23, and fuel cell: F23 were obtained. The results of various evaluations are shown in Table 5.

[0136] 〔Comparative Example 8〕 To 100 g of PFSA dispersion solution B1 in a 500 mL poly container, niobium pentafluoride (manufactured by High Purity Chemical Research Institute) was added while stirring with a magnetic stirrer so that PFSA / niobium pentafluoride = 99 / 1 (mass ratio), and then stirred until homogeneous to obtain a solution J24 of a polyelectrolyte composition containing niobium pentafluoride. Further, according to the above method, a polyelectrolyte membrane: C24, MEA: E24, and fuel cell: F24 were obtained. The results of various evaluations are shown in Table 5.

[0137] 〔Comparative Example 9〕 Using B2 as the polyelectrolyte solution, a polyelectrolyte membrane C25 was prepared according to the above, and MEA: E25 and fuel cell: F25 were obtained. The results of various evaluations are shown in Table 5.

[0138] 〔Comparative Example 10〕 B2 was used as the polyelectrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 2 to obtain a polyelectrolyte membrane: C26, MEA: E26, and fuel cell: F26. The results of various evaluations are shown in Table 5.

[0139] 〔Comparative Example 11〕 B2 was used as the polyelectrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 3 to obtain a polyelectrolyte membrane: C27, MEA: E27, and fuel cell: F27. The results of various evaluations are shown in Table 5.

[0140] [Comparative Example 12] B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 4 to obtain a polymer electrolyte membrane: C28, MEA: E28, and fuel cell: F28. The results of various evaluations are shown in Table 5.

[0141] [Comparative Example 13] B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 5 to obtain a polymer electrolyte membrane: C29, MEA: E29, and fuel cell: F29. The results of various evaluations are shown in Table 6.

[0142] [Comparative Example 14] To 100 g of PFSA dispersion solution B2 in a 500 mL poly container, the cerium dioxide particle dispersion liquid I18 obtained in Comparative Example 2 above was added while stirring with a magnetic stirrer so that PFSA / ceria fine particles = 99 / 1 (mass ratio). As a result, some aggregation precipitation occurred. This precipitate was removed using a PTFE membrane filter with a pore diameter of 1.0 μm (manufactured by Advantec Toyo Co., Ltd.) to obtain a solution J30 of a polymer electrolyte composition containing cerium dioxide fine particles as a uniform solution. Further, according to the above method, a polymer electrolyte membrane: C30, MEA: E30, and fuel cell: F30 were obtained. The results of various evaluations are shown in Table 6.

[0143] [Comparative Example 15] B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 7 to obtain a polymer electrolyte membrane: C31, MEA: E31, and fuel cell: F31. The results of various evaluations are shown in Table 6.

[0144] [Comparative Example 16] B2 was used as the polymer electrolyte solution. Other conditions were carried out in the same manner as in Comparative Example 8 to obtain a polymer electrolyte membrane: C32, MEA: E32, and fuel cell: F32. The results of various evaluations are shown in Table 6.

[0145] [Table 1]

[0146]

Table 2

[0147]

Table 3

[0148]

Table 4

[0149]

Table 5

[0150]

Table 6

[0151] As shown in Tables 1 to 6, when the polymer electrolyte membranes added with the niobium oxide fine particles of the above Examples 1 to 16 were used, practically good results were obtained in the above-described durability test.

Industrial Applicability

[0152] The polymer electrolyte composition of the present invention has industrial applicability in the fields of polymer electrolyte membranes, electrode catalyst layers, membrane electrode assemblies, and solid polymer fuel cells.

Claims

1. A polyelectrolyte (a), niobium oxide (b) having an average particle diameter of more than 0.050 μm and 1.0 μm or less obtained by laser diffraction particle size distribution measurement, containing, wherein the polyelectrolyte (a) is represented by the following general formula (1), -[CF₂CX₁X₂]ₐ-[CF₂-CF(-O-(CF₂-CF(CF₂X₃))b-Oc-(CFR₁)d-(CFR₂)e-(CF₂)f-X₄)]g- (1) (In the general formula (1), X₁, X₂ and X₃ are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms.) a and g are 0 ≦ a < 1, 0 < g ≦ 1, and a + g = 1. b is an integer of 0 or more and 8 or less. c is 0 or 1. d and e are each independently an integer of 0 or more and 6 or less. f is an integer of 0 or more and 10 or less. However, d + e + f is not equal to 0. R₁ and R₂ are each independently a halogen element, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group.) X₄ is COOZ, SO₃Z, PO₃Z₂, or PO₃HZ. The Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or amines (NH₄, NH₃R₃, NH₂R₃R₄, NHR₃R₄R₅, NR₃R₄R₅R₆). Also, R₃, R₄, R₅, and R₆ are an alkyl group or an arene group.) wherein the niobium oxide (b) contains niobium dioxide, a polyelectrolyte composition.

2. wherein the niobium oxide (b) is niobium dioxide and niobium pentoxide, the polyelectrolyte composition according to Claim 1.

3. The cumulative passing value based on the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the niobium oxide (b) is 30% or more of the whole in the region where the particle diameter is more than 0.050 μm and 5.0 μm or less, the polyelectrolyte composition according to Claim 1 or 2.

4. A polyelectrolyte membrane containing the polyelectrolyte composition according to any one of Claims 1 to 3.

5. An electrode catalyst layer containing the polyelectrolyte composition according to any one of Claims 1 to 3.

6. A membrane electrode assembly having the polyelectrolyte membrane according to Claim 4 and / or the electrode catalyst layer according to Claim 5.

7. A polymer electrolyte fuel cell having the membrane electrode assembly according to claim 6.

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