Composite electrolyte membrane, membrane electrode assembly using same, and solid polymer fuel cell

Abstract

To achieve high proton conductivity and high dry-wet cycle durability even after a dry-wet cycle in a composite electrolyte membrane composed of a hydrocarbon-based polymer electrolyte and a fluorine-containing polymer porous substrate.SOLUTION: A composite electrolyte membrane includes a composite layer in which a hydrocarbon-based polymer electrolyte and a fluorine-containing polymer porous base material are composited, and the number of pores V generated in the composite layer after the composite electrolyte membrane is repeatedly immersed in water and dried is 100 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a composite electrolyte membrane having a composite layer in which a polymer electrolyte is combined with a porous substrate, and a membrane electrode assembly and a polymer electrolyte fuel cell each using the same. [Background technology]

[0002] Conventionally, membranes made of perfluorosulfonic acid polymer "Nafion" (registered trademark) (manufactured by Chemours Corporation) have been widely used as polymer electrolyte membranes for solid polymer fuel cells and the like. However, while polymer electrolyte membranes made of "Nafion" (registered trademark) exhibit high proton conductivity at low humidification through proton conducting channels resulting from a cluster structure, they are very expensive because they are manufactured through a multi-stage synthesis, and in addition, they have the problem of large fuel crossover due to the aforementioned cluster structure. In addition, problems such as the difficulty of waste disposal after use and recycling of materials have been pointed out.

[0003] In order to overcome these problems, the development of hydrocarbon-based polymer electrolyte membranes that can replace "Nafion" (registered trademark) has been intensified in recent years. However, the hydrocarbon-based polymer electrolyte membranes tend to have large dimensional changes in wet-dry cycles, and there has been a demand for reducing the dimensional changes in order to improve the durability of the wet-dry cycles.

[0004] Therefore, in order to suppress the dimensional change of the electrolyte membrane caused by the dry-wet cycle of the fuel cell, attempts have been made to combine a polytetrafluoroethylene (PTFE) porous substrate with a hydrocarbon-based polymer electrolyte. Generally, hydrocarbon-based polymer electrolytes are soluble only in aprotic polar solvents, but aprotic polar solvents have low affinity with the PTFE porous substrate, and the hydrocarbon-based polymer electrolyte solution dissolved in aprotic polar solvent cannot be impregnated into the PTFE porous substrate, making it difficult to fabricate a composite electrolyte membrane.

[0005] Patent Document 1 proposes a composite electrolyte membrane in which a hydrocarbon-based polymer electrolyte is dissolved in a mixed solvent of N-methylpyrrolidone (NMP) and methanol and then composited with a porous substrate made of PTFE. Patent Document 2 proposes a composite electrolyte membrane in which a porous substrate made of PTFE is impregnated with butanol and then composited with a hydrocarbon-based polymer electrolyte. Patent Document 3 proposes a composite electrolyte membrane in which a porous substrate made of PTFE is subjected to hydrophilization treatment such as plasma treatment and then composited with a hydrocarbon-based polymer electrolyte. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2010-232158 [Patent Document 2] Japanese Patent Publication 2017-114122 [Patent Document 3] International Publication No. 2016 / 148017 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the composite layer of the composite electrolyte membrane made of a hydrocarbon-based polymer electrolyte and a PTFE porous substrate that has been produced in the past, the low affinity between the two materials has not been improved. The interfacial adhesion between the hydrocarbon-based polymer electrolyte and the PTFE porous substrate fiber in the composite layer is low, and when the composite electrolyte membrane is subjected to dry-wet cycle conditions, peeling and void formation easily occur at the interface, resulting in insufficient dry-wet cycle durability and reduced proton conductivity after dry-wet cycles.

[0008] In the composite electrolyte membrane described in Patent Document 1, the affinity between the hydrocarbon-based polymer electrolyte and the PTFE porous substrate is insufficient, and when the composite electrolyte membrane is subjected to dry-wet cycles, interfacial peeling occurs between the hydrocarbon-based polymer electrolyte in the composite layer and the PTFE porous substrate fibers, resulting in the formation of voids and reduced dry-wet cycle durability and proton conductivity.

[0009] Regarding Patent Document 2, as a result of investigating the composite under the conditions described in the document, it was not possible to obtain a composite electrolyte membrane.

[0010] In the composite electrolyte membrane described in Patent Document 3, the affinity with the hydrocarbon-based polymer electrolyte is improved by the hydrophilization treatment of the PTFE porous substrate, and the composite is formed. However, the degree of hydrophilization is uneven between the surface layer and the deep layer of the porous substrate when the hydrophilization treatment is performed with plasma or metallic sodium. In addition, since the reactivity is very high, it is difficult to control the progress of the hydrophilization treatment, and excessive hydrophilization treatment damages the porous substrate and reduces the mechanical strength. Therefore, if a hydrophilization treatment is performed to give sufficient affinity to suppress peeling between the hydrocarbon-based polymer electrolyte and the PTFE porous substrate fiber, the porous substrate is damaged, and the mechanical strength of the composite electrolyte membrane using the treated porous substrate becomes insufficient. On the other hand, if the hydrophilization treatment is performed to a degree that does not damage the porous substrate, the affinity between the hydrocarbon-based polymer electrolyte and the PTFE porous substrate remains low. Therefore, interfacial peeling and void formation between the hydrocarbon-based polymer electrolyte and the PTFE porous substrate fiber in the composite layer occurs with dry-wet cycles, and the dry-wet cycle durability and proton conductivity are reduced.

[0011] An object of the present invention is to achieve high proton conductivity and high mechanical durability even after wet-dry cycles in a composite electrolyte membrane comprising a hydrocarbon-based polymer electrolyte and a fluorine-containing polymer porous substrate. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a composite electrolyte membrane having a composite layer in which a hydrocarbon-based polymer electrolyte and a fluorine-containing polymer porous substrate are composited, wherein the number of pores V generated in the composite layer after the composite electrolyte membrane is repeatedly immersed in water and dried is 100 or less. Effect of the Invention

[0013] According to the present invention, a composite electrolyte membrane having high proton conductivity and high durability against wet-dry cycles even after wet-dry cycles can be provided. In addition, by using the composite electrolyte membrane of the present invention, a polymer electrolyte fuel cell having excellent durability can be provided. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram of a roll-type film production apparatus used in Example 23. [Diagram 2] FIG. 2 is a schematic diagram of a roll-type film production apparatus used in Example 26. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will be described in detail below. In the following description, the symbol "to" indicates a range including both ends of the symbol.

[0016] [Hydrocarbon-based polymer electrolyte] The hydrocarbon-based polymer electrolyte is an electrolyte made of a hydrocarbon-based polymer having an ionic group. As the hydrocarbon-based polymer, an aromatic hydrocarbon-based polymer having an aromatic ring in the main chain is preferable. Here, the aromatic ring may include not only a hydrocarbon-based aromatic ring but also a heterocycle. In addition, a part of the polymer may be composed of an aliphatic unit together with an aromatic ring unit.

[0017] Specific examples of aromatic hydrocarbon polymers include polymers having a structure selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymer, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain together with an aromatic ring. Note that polysulfone, polyethersulfone, polyether ketone, etc. referred to here are general terms for structures having sulfone bonds, ether bonds, and ketone bonds in the molecular chain, and include polyether ketone ketone, polyether ether ketone, polyether ether ketone ketone, polyether ketone ether ketone ketone, and polyether ketone sulfone. The hydrocarbon skeleton may have a plurality of these structures. Among these, the aromatic hydrocarbon polymer is most preferably a polymer having a polyetherketone skeleton, that is, a polyetherketone polymer.

[0018] As the hydrocarbon-based polymer electrolyte, one that forms a bicontinuous or lamellar phase separation structure is suitable. Such a phase separation structure can be expressed in a molded body made of a blend of two or more incompatible polymers, such as a hydrophilic polymer having an ionic group and a hydrophobic polymer having no ionic group, or in a block copolymer made of two or more incompatible segments, such as a segment (A1) containing an ionic group and a segment (A2) not containing an ionic group. In the bicontinuous or lamellar phase separation structure, both the hydrophilic domain and the hydrophobic domain form a continuous phase, so that a continuous proton conductive channel is formed, thereby making it possible to obtain a polymer electrolyte molded body with excellent proton conductivity. Here, the domain means a mass formed by the aggregation of similar substances or segments in one molded body.

[0019] The hydrocarbon polymer having an ionic group is preferably a block copolymer having at least one each of a segment (A1) containing an ionic group and a segment (A2) not containing an ionic group. Here, the segment is a partial structure in a copolymer chain consisting of repeating units exhibiting specific properties, and has a molecular weight of 2000 or more. By using a block copolymer, it is possible to develop a bicontinuous phase separation structure having fine domains compared to a polymer blend, and thus it is possible to achieve better power generation performance and physical durability.

[0020] Hereinafter, an aromatic hydrocarbon segment (A1) or polymer containing an ionic group may be referred to as an "ionic block," and an aromatic hydrocarbon segment (A2) or polymer not containing an ionic group may be referred to as a "non-ionic block." However, the expression "not containing an ionic group" in this specification does not exclude an embodiment in which the segment or polymer contains a small amount of ionic groups within a range that does not inhibit the formation of a phase-separated structure.

[0021] In such a block copolymer, the molar composition ratio (A1 / A2) of the ionic block to the nonionic block is preferably 0.20 or more, more preferably 0.33 or more, and even more preferably 0.50 or more. The molar composition ratio (A1 / A2) is preferably 5.00 or less, more preferably 3.00 or less, and even more preferably 2.50 or less. If the molar composition ratio (A1 / A2) is less than 0.20 or exceeds 5.00, the proton conductivity under low humidification conditions may be insufficient, or the hot water resistance and physical durability may be insufficient. Here, the molar composition ratio A1 / A2 represents the ratio of the molar number of the repeating unit present in the ionic block to the molar number of the repeating unit present in the nonionic block. The "molar number of the repeating unit" is the value obtained by dividing the number average molecular weight of the ionic block and the nonionic block by the molecular weight of the corresponding structural unit.

[0022] The ionic group of the aromatic hydrocarbon polymer may be an ionic group having proton exchange ability. As such functional groups, sulfonic acid groups, sulfonimide groups, sulfate groups, phosphonic acid groups, phosphoric acid groups, and carboxylic acid groups are preferably used. The polymer may contain two or more types of ionic groups. Among them, from the viewpoint of high proton conductivity, it is more preferable that the polymer has at least one selected from sulfonic acid groups, sulfonimide groups, and sulfate groups, and from the viewpoint of raw material cost, it is most preferable that the polymer has a sulfonic acid group.

[0023] In the present invention, it is preferable to use an aromatic hydrocarbon block copolymer as the aromatic hydrocarbon polymer constituting the hydrocarbon polymer electrolyte, and it is more preferable to use a polyetherketone block copolymer. In particular, it is particularly preferable to use a polyetherketone block copolymer containing a segment containing a structural unit (S1) containing an ionic group and a segment containing a structural unit (S2) not containing an ionic group, as shown below.

[0024] [ka]

[0025] (In general formula (S1), Ar 1 ~Ar 4 represents any divalent arylene group, Ar 1 and / or Ar 2 contains an ionic group, and Ar 3 and Ar 4 may or may not contain an ionic group. 1 ~Ar 4 may be optionally substituted, and two or more types of arylene groups may be used independently. * represents a bonding site with general formula (S1) or another structural unit.

[0026] [ka]

[0027] (In general formula (S2), Ar 5 ~Ar 8 represents any divalent arylene group, which may be optionally substituted but does not contain an ionic group. 5 ~Ar 8 may independently use two or more types of arylene groups. * represents a bonding site with general formula (S2) or another structural unit. Here, Ar 1 ~Ar 8 Preferred divalent arylene groups include hydrocarbon arylene groups such as phenylene, naphthylene, biphenylene, and fluorenediyl groups, and heteroarylene groups such as pyridinediyl, quinoxalinediyl, and thiophenediyl, but are not limited thereto. 1 ~Ar 8 is preferably a phenylene group and a phenylene group containing an ionic group, and most preferably a p-phenylene group and a p-phenylene group containing an ionic group. 5 ~Ar 8 may be substituted with a group other than an ionic group, but is preferably unsubstituted in terms of proton conductivity, chemical stability, and physical durability.

[0028] [Fluorine-containing polymer porous base material] A fluorine-containing polymer porous substrate (hereinafter sometimes simply referred to as a "porous substrate") is a porous substrate formed from a polymer having fluorine atoms. Since a polymer having fluorine atoms is generally a hydrophobic compound, by forming a composite with a hydrocarbon-based polymer electrolyte, it is possible to impart water resistance to the composite electrolyte membrane and suppress dimensional changes upon water absorption. Furthermore, since a polymer compound having fluorine atoms generally has low solubility in chemicals and is stable against chemical reactions, it is possible to impart chemical resistance and chemical durability to the composite electrolyte membrane.

[0029] In the present invention, the oxygen atom content of the porous substrate is preferably 10% by mass or less, more preferably 8% or less, and even more preferably 5% or less, as measured by X-ray photoelectron spectroscopy (XPS). If the oxygen atom content exceeds 10%, the water absorption of the porous substrate increases, and the dimensional change when the composite electrolyte membrane absorbs water increases. Specifically, the oxygen atom content of the porous substrate can be measured by the method described in Example (13) below.

[0030] From the viewpoint of water resistance, the porous substrate preferably contains 50% by mass or more of fluorine atoms, more preferably 60% by mass or more of fluorine atoms, and particularly preferably 70% by mass or more of fluorine atoms. The fluorine atom content in the porous substrate is a value measured by ion chromatography of a solution in which the porous substrate is burned and the gas generated is absorbed, and specifically, it can be measured by the method described in Example (8) below.

[0031] In addition, when analyzing the porous substrate present in the composite electrolyte membrane after being composited with the polymer electrolyte, it is possible to extract only the porous substrate by immersing the composite electrolyte membrane in a solvent that dissolves only the polymer electrolyte. The solvent to be used should be selected depending on the chemical species and higher-order structure of the polymer electrolyte material, and for example, aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphontriamide, ester-based solvents such as γ-butyrolactone, ethyl acetate, and butyl acetate, carbonate-based solvents such as ethylene carbonate and propylene carbonate, and alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether are suitable.

[0032] Examples of fluorine-containing polymers constituting the porous substrate include, but are not limited to, polytetrafluoroethylene (PTFE), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene difluoride (PVDF), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy fluororesin (PFA), ethylene chlorotrifluoroethylene copolymer (ECTFE), etc. From the viewpoint of water resistance, PTFE, polyhexapropylene, FEP, and PFA are preferred, and PTFE is particularly preferred because it has high mechanical strength due to molecular orientation.

[0033] Examples of the form of the porous substrate include a stretched microporous membrane in which a porous membrane without pores is stretched in the membrane surface direction to form fine pores, a wet-coagulated microporous membrane in which a fluorine atom-containing polymer compound solution is prepared and formed into a membrane, and then the solution-containing polymer compound is immersed in a poor solvent for the fluorine atom-containing polymer compound while still containing the solvent and coagulated, a nonwoven fabric made of a solution-spun fiber made by spinning a fluorine atom-containing polymer compound solution, and a nonwoven fabric made of a melt-spun fiber made by melting and spinning a fluorine atom-containing polymer compound. Examples of the solution spinning method include a dry spinning method in which a fluorine atom-containing polymer solution discharged in a fibrous form by applying high pressure from a spinneret is dried with hot air, a wet spinning method in which a fluorine atom-containing polymer solution discharged in a fibrous form is immersed in a poor solvent for the fluorine atom-containing polymer compound and coagulated, and electrospinning in which a fluorine atom-containing polymer solution is discharged into a space to which a high voltage is applied and pulled into a fibrous form by static electricity. Examples of the melt spinning method include melt-blow spinning in which a molten fluorine atom-containing polymer is discharged in a fibrous form from a spinneret.

[0034] There is no particular limitation on the thickness of the porous substrate used in the present invention, and this should be determined depending on the application of the composite electrolyte membrane. In practice, however, a membrane thickness of 0.5 to 50 μm is used, and one having a thickness of 2 μm or more and 40 μm or less is preferably used.

[0035] The porosity of the porous substrate before being composited with the hydrocarbon-based polymer electrolyte is not particularly limited, but is preferably 50 to 98%, more preferably 80 to 98%, from the viewpoint of achieving both proton conductivity and mechanical strength of the resulting composite electrolyte membrane. The porosity Y1 (volume %) of the porous substrate is defined as the value calculated by the following formula.

[0036] Y1 = (1-Db / Da) x 100 Da: Specific gravity of the polymer that constitutes the fluorine-containing polymer porous substrate Db: Specific gravity of the entire fluorine-containing polymer porous substrate [Fluorosurfactant] The fluorosurfactant (hereinafter, sometimes simply referred to as "surfactant") used in the present invention is preferably a compound having a fluorine-containing group consisting of a fluorinated alkyl group, a fluorinated alkenyl group or a fluorinated aryl group in which a hydrogen atom in an alkyl group, an alkenyl group or an aryl group is substituted with a fluorine atom, and a solvent-philic group (hydrophilic group or lipophilic group).

[0037] The philic group is preferably a nonionic philic group. When the philic group is ionic, it has high affinity for water, and therefore, when a fluorosurfactant is used as an additive to the electrolyte membrane, the fluorosurfactant is eluted from the electrolyte membrane, causing peeling at the interface between the fluorine-containing polymer porous substrate and the hydrocarbon polymer electrolyte, which may result in a decrease in mechanical durability.

[0038] The fluorine-containing group is preferably a perfluoroalkyl group, a perfluoroalkenyl group or a perfluoroaryl group in which all hydrogen atoms in an alkyl group, an alkenyl group or an aryl group have been substituted with fluorine atoms.

[0039] As the fluorine-containing group, a fluorinated alkenyl group or a fluorinated aryl group is more preferable because of its excellent surface activity, and a fluorinated alkenyl group is even more preferable because it has a flexible structure and exhibits high surface activity.

[0040] The fluorine-containing group preferably has 2 or more carbon atoms, more preferably 4 or more carbon atoms, and particularly preferably 6 or more carbon atoms. The carbon number is preferably 20 or less, more preferably 15 or less, and particularly preferably 10 or less carbon atoms. If the carbon number is less than 2, the volatility and water solubility are high and the fluorine-containing group may not remain in the electrolyte membrane, resulting in reduced physical durability. If the carbon number is more than 20, the affinity with the hydrocarbon-based polymer electrolyte is reduced, and the affinity between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate is insufficient.

[0041] Specifically, examples of the fluorinated alkyl group include ethyl fluoride, propyl fluoride, butyl fluoride, pentyl fluoride, hexyl fluoride, heptyl fluoride, octyl fluoride, nonyl fluoride, and decyl fluoride. Examples of the fluorinated alkenyl group include ethenyl fluoride, propenyl fluoride, butenyl fluoride, pentenyl fluoride, hexenyl fluoride, heptenyl fluoride, octenyl fluoride, nonenyl fluoride, and decenyl fluoride. Among them, hexyl fluoride, heptyl fluoride, octyl fluoride, nonyl fluoride, decyl fluoride, hexenyl fluoride, heptenyl fluoride, octenyl fluoride, nonenyl fluoride, and decenyl fluoride are more preferable because they have low volatility and water solubility and tend to remain in the electrolyte membrane. Here, the "ethyl fluoride group" may be one of five types of functional groups, namely, monofluoroethyl, difluoroethyl, trifluoroethyl, tetrafluoroethyl, and pentafluoroethyl, depending on the number of fluorine atoms contained in one functional group, and in this specification, the "ethyl fluoride group" is used as a general term for these. The same applies to other functional groups such as "propyl fluoride group" and "butyl fluoride group". In addition, the difluoroethyl group is a functional group having two fluorine atoms, and there are three structural isomers, namely, 1,1-difluoroethyl group, 1,2-difluoroethyl group, and 2,2-difluoroethyl group, and in this specification, the term "difluoroethyl group" is used as a general term for these. The same applies to other functional groups such as "trifluoroethyl group" and "tetrafluoroethyl group".

[0042] The structure of the fluorine-containing group can be linear, branched, cyclic, etc., but among them, a branched structure is preferable because the interaction between the fluorine compounds is weakened and the surface tension is easily reduced. In the present invention, a surfactant having a fluorine-containing group having a structure represented by the following formula (F1) is particularly preferable.

[0043] [ka]

[0044] (In formula (F1), * indicates the bonding point to other atomic groups.) As the fluorine-based surfactant, a compound having 10% by mass or more of fluorine atoms in one molecule is preferably used. A compound having 20% ​​by mass or more of fluorine atoms is more preferable, and a compound having 40% by mass or more of fluorine atoms is even more preferable. If the fluorine atom content in one molecule is less than 10% by mass, the effect of improving the affinity between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate becomes insufficient, and interfacial peeling between the hydrocarbon-based polymer electrolyte in the composite layer and the fluorine-containing polymer porous substrate fiber may occur during dry-wet cycles.

[0045] The philic group can be a hydrophilic group or a lipophilic group.

[0046] The hydrophilic group is a functional group having a hydrophilic element selected from the group consisting of oxygen, nitrogen, phosphorus, sulfur and boron, and is preferably a group containing a polyether group, a carboxylate group, a sulfonate group, a phosphite group or a phosphate group, and more preferably a group containing a polyether group, since it forms a hydrogen bond with an ionic group, thereby having excellent affinity with the polymer electrolyte and excellent chemical stability. Among them, a group having a polyalkyl ether structure shown in the following general formula (C1) or a polyacrylate structure shown in general formula (C2) is preferred, and the polyalkyl ether shown in general formula (C1) is more preferred, since it has particularly excellent affinity with the polymer electrolyte.

[0047] [ka]

[0048] (In general formula (C1), q and r are natural numbers satisfying r=2q, and s is an integer of 1 or more and 1000 or less, which means the number of repetitions of the alkyl ether structure. In general formula (C2), R is at least one group selected from a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 1 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms, and t is an integer of 1 or more and 1000 or less, which means the number of repetitions of the acrylate structure. When s or t is 2 or more in (C1) or (C2), the multiple alkyl ether structures or acrylate structures may be the same or different.) The lipophilic group includes fluorine-free alkyl groups, alkenyl groups, alkynyl groups, and phenyl groups.

[0049] As the fluorosurfactant, a compound having a vapor pressure of less than 2 kPa at 150°C is preferred, a compound having a vapor pressure of 1 kPa or less at 150°C is particularly preferred, and a compound having no boiling point, i.e., a compound that starts thermal decomposition without boiling, is most preferred. In the present invention, it is particularly preferred that the fluorosurfactant is a compound having a 5% weight loss temperature of 150°C or higher in thermogravimetric differential thermal analysis. Such a fluorosurfactant does not volatilize or decompose during membrane formation, and can therefore be left in the composite electrolyte membrane, resulting in excellent physical durability.

[0050] The weight-average molecular weight of the fluorosurfactant is preferably at least 1000, more preferably at least 1500, and even more preferably at least 2000. When the weight-average molecular weight of the fluorosurfactant is less than 1000, the affinity between the hydrocarbon-based polymer electrolyte and the fluoropolymer porous substrate decreases due to volatilization during the drying step in membrane formation or dissolution in the electrolyte membrane solution, and interfacial peeling between the hydrocarbon-based polymer electrolyte in the composite layer and the fluoropolymer porous substrate fiber may occur due to dry / wet cycles.

[0051] In the fluorosurfactant, the molecular weight of the fluorine-containing group is preferably at least 200, more preferably at least 400, and even more preferably at least 1000. When the molecular weight of the fluorine-containing group is less than 200, the flexibility and degree of freedom of the molecular chain in the fluorine-containing group is insufficient, resulting in insufficient affinity between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate, and interfacial peeling between the hydrocarbon-based polymer electrolyte in the composite layer and the fluorine-containing polymer porous substrate fiber may occur due to dry-wet cycles.

[0052] Examples of nonionic fluorine-based surfactants that can be preferably used in the present invention include "Megafac" (registered trademark) F-251, F-253, F-281, F-430, F-477, F-551, F-552, F-553, F-554, F-555, F-556, F-557, F-558, F-559, F-560, F-561, and F-56, all of which are manufactured by DIC Corporation. 2, F-563, F-565, F-568, F-570, F-572, F-574, F-575, F-576, R-40, R-40-LM, R-41, R-94, RS-56, RS-72-K, RS-75, RS-76-E, RS-76-NS, DS-21, F444, TF-2066, and AGC's "Surflon" (registered trademark) S-14 1, S-145, S-241, S-242, S-243, S-386, S-420, S-611, S-651, "Ftergent" (registered trademark) 251, 208M, 212M, 215M, 250, 209F, 222F, 245F, 208G, 218GL, 240G, 212P, 220P, 228P, FTX-218, and ...0, 209F, 222F, 245F, 208G, 218GL, 240G, 212P, 22 DFX-18, 710FL, 710FM, 710FS, 730FL, 730FM, 610FM, 683, 601AD, 601ADH2, 602A, 650AC, 681, Mitsubishi Materials Electronic Chemicals Co., Ltd.'s EF-PP31N04, EF-PP31N09, EF-PP31N15, EF-PP31N22, 3M's FC-4430, FC-4432, OMNOVA Examples of such polyurethane foams include PF-151N, PF-636, PF-6320, PF-656, PF-6520, PF-652-NF, and PF-3320 manufactured by Solvay Solutions, TG-9131 and "Zeffle" (registered trademark) GH-701 manufactured by Daikin Industries, Ltd., and "Fluorolink" (registered trademark) A10-P manufactured by Solvay Japan K.K.

[0053] [Polyvinylidene fluoride] Polyvinylidene fluoride includes not only homopolymers of vinylidene fluoride (i.e., pure polyvinylidene fluoride), but also copolymers of vinylidene fluoride with other copolymerizable monomers. As monomers copolymerizable with vinylidene fluoride, for example, one or more of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride, etc. can be used. Such polyvinylidene fluoride-based resins can be obtained by emulsion polymerization or suspension polymerization.

[0054] Furthermore, when the molecular weight of the polyvinylidene fluoride used is large, the adhesion between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate is improved, and therefore the weight-average molecular weight of the polyvinylidene fluoride is preferably 300,000 or more, more preferably 500,000 or more.

[0055] [Affinity improving polymer] A wide range of affinity-improving polymers are used for the purpose of preventing the separation of the interface between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous material.Examples of polymers that have high affinity with the hydrocarbon-based polymer electrolyte include polyurethane, epoxy, polyester, polystyrene, polyamide, polyphthalamide, polyamideimide, polyarylate, polycarbonate, polyetherimide, polyethersulfone, polysulfone, polyphenylene sulfide, liquid crystal polymer, polybenzimidazole, polyetherketone, polyetheretherketone, polysiloxane, and polyvinylidene fluoride.Among these, the above-mentioned polyvinylidene fluoride, which has high affinity with the fluorine-based polymer, is particularly preferred.

[0056] The affinity improving polymer is preferably a polymer having a high molecular weight in order to adhere strongly to the surface of the fluorine-containing polymeric porous fiber, and the weight average molecular weight is preferably 300,000 or more, and more preferably 500,000 or more.

[0057] Here, the above-mentioned fluorosurfactants, polyvinylidene fluoride, and affinity improving polymers are collectively referred to as affinity improvers.

[0058] [Coated porous substrate] The coated porous substrate is a fluorine-containing polymer porous substrate that can be impregnated when droplets of an aprotic polar solvent are placed on the porous substrate, and is a fluorine-containing polymer porous substrate coated with at least a fluorine-based surfactant or polyvinylidene fluoride. The term "impregnable with an aprotic polar solvent" used herein refers to a porous substrate in which, when droplets of N-methyl-2-pyrrolidone (NMP), a representative aprotic polar solvent, are placed on the surface of the fluorine-containing polymer porous substrate, the portion where the droplets are placed becomes transparent within 30 seconds. In order to composite a hydrocarbon-based polymer electrolyte with a fluorine-containing polymer porous substrate, it is preferable to add an affinity improver to the fluorine-containing polymer porous substrate so that the aprotic polar solvent can be impregnated into the fluorine-containing polymer porous substrate. In addition, the term "not impregnated with water" refers to a porous substrate in which, when droplets of water are placed on the surface of the fluorine-containing polymer porous substrate, the portion where the droplets are placed does not become transparent within 120 seconds.

[0059] The affinity improver used for coating the coated porous substrate includes at least a fluorosurfactant or polyvinylidene fluoride, but preferably includes a fluorosurfactant and a coating polymer, and particularly preferably includes a fluorosurfactant and polyvinylidene fluoride. The amount of the fluorosurfactant applied to the fluorine-containing polymer porous substrate is small, and the substrate can be impregnated with aprotic polar solvents, but the application of a polymer coating is superior in terms of suppressing peeling between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate fiber when used as a composite electrolyte membrane. On the other hand, in order to impregnate the fluorine-containing polymer porous substrate with aprotic polar solvents only with the polymer coating, the amount of coating applied is increased compared to the fluorine-containing surfactant. If the amount of coating increases, the proton conductivity decreases when the composite electrolyte membrane is formed.

[0060] The affinity improver to be coated is preferably added at 1% by mass or more, more preferably at 3% by mass or more, based on the mass of the fluorine-containing polymer porous substrate being 100% by mass. Similarly, it is preferably added at 30% by mass or less, more preferably at 20% by mass or less. If it is less than 1% by mass, the affinity between the polymer electrolyte and the porous substrate may decrease, making it impossible to form a composite. If it exceeds 30% by mass, the surfactant becomes excessive, blocking the pores of the fluorine-containing polymer porous substrate, and the proton conductivity of the composite electrolyte membrane may decrease. The weight ratio of the affinity improver can be measured by the weight change before and after coating, or by removing the coating with a solvent capable of dissolving the coating, and then measuring the weight change before and after removing the coating.

[0061] As the affinity improver to be coated, it is preferable to use a compound that is insoluble in the solvent of the hydrocarbon-based polymer electrolyte solution to be impregnated. When such an affinity improver is used, it is possible to prevent the affinity improver from diffusing from the fluorine-containing polymer porous substrate to the polymer electrolyte during impregnation with the hydrocarbon-based polymer electrolyte solution, and to prevent the decrease in proton conductivity due to the presence of the affinity improver while fully exerting its function as an affinity improver.

[0062] [Method of manufacturing coated porous substrate] The method for applying the affinity improver to the fluorine-containing polymer porous substrate includes the following: (1) A method of controlling the amount of affinity improver applied by removing excess solution while pulling up a fluorine-containing polymer porous substrate immersed in the affinity improver solution. (2) A method of casting a solution of an affinity improver onto a fluorine-containing polymer porous substrate (3) A method of laminating a fluorine-containing polymer porous substrate onto a supporting substrate onto which a solution of an affinity improver has been cast and impregnated. Examples include:

[0063] When the affinity improver is liquid or oily, the affinity improver itself may be impregnated instead of the affinity improver solution. However, it is preferable to use a solution of the affinity improver dissolved in a specific solvent in order to adjust the viscosity so that the affinity improver can easily permeate the fluorine-containing polymeric porous substrate, or to dilute the affinity improver so that an excessive amount of the affinity improver is not applied.

[0064] Examples of a method for casting and applying the affinity improver solution include knife coating, direct roll coating, Mayer bar coating, gravure coating, reverse coating, air knife coating, spray coating, brush coating, dip coating, die coating, vacuum die coating, curtain coating, flow coating, spin coating, screen printing, and inkjet coating.

[0065] When the impregnation is performed by the method (3), the solvent can be dried as it is. When the impregnation is performed by the method (1) or (2), the method of drying the solvent of the affinity improver solution while the porous substrate is attached to a separately prepared support substrate is preferable from the viewpoint of reducing wrinkles in the porous substrate and improving the quality.

[0066] [Composite electrolyte membrane] The composite electrolyte membrane of the present invention has a composite layer in which the above-mentioned hydrocarbon-based polymer electrolyte and the above-mentioned fluorine-containing polymer porous substrate or coated fluorine-containing polymer porous substrate are composited, and in a peeling resistance test, the composite electrolyte membrane is repeatedly immersed in water and dried, and then the number of pores V generated in the composite layer is 100 or less. The number of pores V generated in the composite layer is preferably 20 or less, and particularly preferably 10 or less. Specifically, the peeling resistance test is performed by the method described in Example (14).

[0067] The filling rate of the hydrocarbon-based polymer electrolyte in the composite layer is preferably 50% or more, more preferably 60% or more. If the filling rate of the composite layer is reduced, the proton conductive path may be lost, resulting in a reduction in power generation performance. The filling rate of the composite layer in the present invention is a value indicating the ratio of the polymer electrolyte to the total volume of the composite layer, and is specifically measured by the method described in Example (3).

[0068] The composite electrolyte membrane of the present invention may be composed of one such composite layer, or may be composed of two or more composite layers stacked together. In the case of stacking, a plurality of composite layers having different packing rates may be stacked together. In addition, a polymer electrolyte layer that is not composited with a reinforcing material such as a porous substrate made only of a hydrocarbon-based polymer electrolyte may be provided in contact with both sides or one side of the composite layer. By providing such a layer, the adhesion between the composite electrolyte membrane and the electrodes can be improved, and interfacial peeling can be suppressed.

[0069] The composite electrolyte membrane of the present invention has a composite layer, which allows a reduction in the dimensional change rate in the plane direction. The reduction in the dimensional change rate in the plane direction reduces stress caused by swelling and shrinkage that occurs at the edge portion of the electrolyte membrane during wet-dry cycles when used as an electrolyte membrane for a fuel cell, and improves durability. The dimensional change rate λxy in the plane direction of the composite electrolyte membrane is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0070] In addition, the dimensional change rate in the plane direction of the composite electrolyte membrane is preferably small in anisotropy in the MD and TD directions. If the anisotropy is large, it may restrict the cell design of the fuel cell, or stress due to swelling and shrinkage may concentrate on the edge perpendicular to the direction of large dimensional change, causing the electrolyte membrane to break from that part. Specifically, it is preferable that the ratio λMD / λTD of the dimensional change rate λMD in the MD direction to the dimensional change rate λTD in the TD direction in the plane direction of the composite electrolyte membrane satisfies 0.5<λMD / λTD<2.0. Here, the dimensional change rate is an index representing the change in the dimensions of the composite electrolyte membrane in a dry state and the dimensions of the composite electrolyte membrane in a wet state, and is specifically measured by the method described in Example (4).

[0071] In the composite electrolyte membrane of the present invention, the wet tensile modulus per width is preferably 20 N / cm or more, more preferably 30 N / cm or more, and even more preferably 40 N / cm or more. If the wet tensile modulus per width is 20 N / cm or more, softening of the electrolyte membrane in a wet state can be suppressed, and the physical durability as a fuel cell can be further improved. The wet tensile modulus is specifically measured by the method described in Example (16).

[0072] In addition, the wet tensile modulus per width after wet-dry cycles is preferably 20 N / cm or more, more preferably 30 N / cm or more, and even more preferably 40 N / cm or more. If the wet tensile modulus per width is 20 N / cm or more, softening of the electrolyte membrane in a wet state can be suppressed even after wet-dry cycles, and the physical durability of the fuel cell can be further improved. The wet tensile modulus is specifically measured by the method described in Example (17).

[0073] The ratio of the wet tensile modulus per width before and after the wet-dry cycle is preferably 0.8 or more, more preferably 0.9 or more. The wet tensile modulus ratio per width before and after the wet-dry cycle is calculated by dividing the tensile modulus value measured in Example (17) by the tensile modulus value measured in Example (16).

[0074] The thickness of the composite layer in the composite electrolyte membrane of the present invention is not particularly limited, but is preferably 0.5 μm to 50 μm, more preferably 2 μm to 40 μm. If the composite layer is thick, the dry-wet cycle durability of the electrolyte membrane is improved, but the membrane resistance tends to increase. Conversely, if the composite layer is thin, the power generation performance is improved, but problems arise in the dry-wet cycle durability, and problems such as electrical short circuits and fuel permeation tend to occur.

[0075] The content of the affinity improver in the composite electrolyte membrane is preferably 0.005 or more, more preferably 0.01 or more, in terms of mass ratio to the total amount of the hydrocarbon-based polymer electrolyte contained in the composite electrolyte membrane. Also, it is preferably 0.20 or less, more preferably 0.10 or less. If the ratio is less than 0.005, the affinity between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate is insufficient, and the ratio of the hydrocarbon-based polymer electrolyte in the composite layer may decrease, and peeling of the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate fiber may occur due to dry-wet cycles. Also, if the ratio exceeds 0.20, the affinity improver may become excessive, and the proton conductivity of the electrolyte membrane may decrease. The content of the affinity improver here means the amount of the affinity improver remaining in the completed electrolyte membrane, excluding the amount of the affinity improver that falls off during the manufacturing process.

[0076] The affinity improver in the composite electrolyte membrane is preferably unevenly distributed in the electrolyte of the composite layer. Specifically, uneven distribution means that the value of "(affinity improver contained in the composite layer / proportion of electrolyte) / thickness of the composite layer" is 1.2 or more relative to "affinity improver contained in the monolayer / thickness of the monolayer", and more preferably 2.0 or more. A preferred manufacturing form of the composite electrolyte membrane is to coat the affinity improver on the fluorine-containing polymer porous substrate, and then impregnate the substrate with a hydrocarbon-based polymer electrolyte solution to composite the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate. The coated affinity improver may be partially dissolved in the hydrocarbon-based polymer electrolyte solution during the impregnation and drying process, and may move into the monolayer. If the amount of dissolution is large, the affinity between the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate becomes insufficient, which may result in a decrease in the proportion of the hydrocarbon-based polymer electrolyte in the composite layer, and peeling of the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate fibers due to dry-wet cycles. In other words, in a composite electrolyte membrane in which peeling of the hydrocarbon-based polymer electrolyte and the fluorine-containing polymer porous substrate fiber due to dry-wet cycles is suppressed, the affinity improver is unevenly distributed in the composite layer. Even when a fluorosurfactant is added to the electrolyte solution, it is preferable to devise a drying method or the like so that the fluorosurfactant is unevenly distributed in the composite layer.

[0077] [Method for producing composite electrolyte membrane] In the present invention, the composite electrolyte membrane is produced by impregnating a fluorine-containing polymer porous substrate or a coated porous substrate with a hydrocarbon-based polymer electrolyte solution in which the fluorine-based surfactant has been mixed beforehand, or by impregnating a coated porous substrate with the hydrocarbon-based polymer electrolyte solution and then drying to remove the solvent contained in the hydrocarbon-based polymer electrolyte solution. Hereinafter, in this section, the solution containing or not containing a fluorine-based surfactant will be referred to as a hydrocarbon-based polymer electrolyte solution, and the solution containing or not containing a coating will be referred to as a fluorine-containing polymer porous substrate.

[0078] The content of the fluorosurfactant in the hydrocarbon-based polymer electrolyte solution is preferably 0.005 or more, more preferably 0.01 or more, as a mass ratio to the total amount of the hydrocarbon-based polymer electrolyte. Also, it is preferably 0.20 or less, more preferably 0.10 or less. If the ratio is less than 0.005, the affinity between the hydrocarbon-based polymer electrolyte solution and the fluoropolymer porous substrate becomes insufficient, and the ratio of the hydrocarbon-based polymer electrolyte in the composite layer may decrease, and the fibers of the fluoropolymer porous substrate may aggregate. If the ratio is more than 0.20, the surfactant may become excessive, and the proton conductivity of the electrolyte membrane may decrease.

[0079] The concentration of the hydrocarbon-based polymer electrolyte solution is preferably 3 to 40% by mass, more preferably 5 to 25% by mass. If the concentration is within this range, the voids of the porous substrate can be sufficiently filled with the hydrocarbon-based polymer electrolyte, and a composite layer having excellent surface smoothness can be easily obtained. If the concentration of the hydrocarbon-based polymer electrolyte is too low, the efficiency of filling the voids of the porous substrate with the hydrocarbon-based polymer electrolyte decreases, and multiple impregnation treatments may be required. On the other hand, if the concentration of the hydrocarbon-based polymer electrolyte is too high, the solution viscosity may be too high, and the polymer electrolyte may not be sufficiently filled into the voids of the porous substrate.

[0080] The viscosity of the hydrocarbon-based polymer electrolyte solution is preferably 100 to 50,000 mPa·s, more preferably 300 to 10,000 mPa·s. If the viscosity is less than 100 mPa·s, the thickness of the composite electrolyte membrane may be non-uniform. If the viscosity is more than 50,000 mPa·s, the hydrocarbon-based polymer electrolyte may not be sufficiently filled into the voids of the fluorine-containing polymer porous substrate, and the surface smoothness of the composite electrolyte membrane may be deteriorated.

[0081] The solvent used in the hydrocarbon-based polymer electrolyte solution can be appropriately selected depending on the type of polymer. As the solvent, for example, aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphontriamide are preferably used. Examples of the solvent to be mixed with these include carbonate-based solvents such as ethylene carbonate and propylene carbonate, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, alcohol-based solvents such as methanol, ethanol, 1-propanol, and isopropyl alcohol, ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ester-based solvents such as γ-butyrolactone, ethyl acetate, butyl acetate, and ethyl lactate, hydrocarbon-based solvents such as hexane and cyclohexane, aromatic hydrocarbon-based solvents such as benzene, toluene, and xylene, halogenated hydrocarbon-based solvents such as chloroform, dichloromethane, 1,2-dichloroethane, perchloroethylene, chlorobenzene, and dichlorobenzene, ether-based solvents such as diethyl ether, tetrahydrofuran, and 1,4-dioxane, nitrile-based solvents such as acetonitrile, nitrated hydrocarbon-based solvents such as nitromethane and nitroethane, and water. The solvent may be a single solvent or a mixed solvent of two or more kinds.

[0082] The method for impregnating a fluorine-containing polymer porous substrate with a hydrocarbon-based polymer electrolyte solution includes the following: (1) A method of controlling the film thickness by removing excess solution while pulling up a fluorine-containing polymer porous substrate immersed in a hydrocarbon-based polymer electrolyte solution (2) A method of casting a hydrocarbon-based polymer electrolyte solution onto a fluorine-containing polymer porous substrate (3) A method of laminating a fluorine-containing polymer porous substrate onto a supporting substrate onto which a hydrocarbon-based polymer electrolyte solution has been cast and impregnated. Examples include:

[0083] The solvent can be dried in the state where the impregnation is performed by the method (3). When the impregnation is performed by the method (1) or (2), the method of drying the solvent of the polymer electrolyte solution in a state where the porous substrate is attached to a separately prepared support substrate is preferable from the viewpoint of reducing wrinkles and unevenness in thickness of the electrolyte membrane and improving the membrane quality.

[0084] Examples of methods for casting and applying a hydrocarbon-based polymer electrolyte solution include knife coating, direct roll coating, Mayer bar coating, gravure coating, reverse coating, air knife coating, spray coating, brush coating, dip coating, die coating, vacuum die coating, curtain coating, flow coating, spin coating, screen printing, inkjet coating, etc. Here, the device used for casting and applying a hydrocarbon-based polymer electrolyte solution is called a coater.

[0085] After the hydrocarbon-based polymer electrolyte solution is applied onto the substrate, a drying process is performed to form a composite electrolyte membrane. In the drying process, the coating film of the hydrocarbon-based polymer electrolyte solution impregnated into the fluorine-containing polymer porous substrate is heated to evaporate the solvent. The heating means is not particularly limited as long as the solvent can be evaporated, and for example, a heating device such as an oven or heater, or a device that uses infrared rays, hot air, or the like to control the temperature in the vicinity of the composite electrolyte membrane can be used. Heat may also be conducted to the coating film via the substrate. The heating temperature range is preferably close to the boiling point of the solvent and equal to or lower than the glass transition temperature of the electrolyte membrane. It is also possible to remove the solvent without heating by only reducing pressure or introducing an air flow. The drying procedure is as follows: (1) A method in which a hydrocarbon-based polymer electrolyte solution is applied onto a substrate, a fluorine-containing polymer porous substrate is attached and dried, and a hydrocarbon-based electrolyte solution is applied onto the upper surface of the dried membrane and dried to obtain a composite electrolyte membrane. (2) A method in which a hydrocarbon-based polymer electrolyte solution is applied onto a substrate, a fluorine-containing polymer porous substrate is laminated, and the hydrocarbon-based electrolyte solution is applied onto the wet top surface of the membrane and then dried to obtain a composite electrolyte membrane. In particular, in the roll-to-roll process, method (2) is preferable because it can increase the amount of polymer filled in the reinforcing layer and reduce one process.

[0086] The drying time and drying temperature in the drying step can be appropriately determined experimentally, but it is preferable to dry at least to the extent that the film can be a self-supporting film even when peeled off from the substrate. The drying method can be selected from known methods such as heating the substrate, hot air, and infrared heaters. The drying temperature is preferably 200°C or less, more preferably 150°C or less, taking into consideration the decomposition of the polymer electrolyte and surfactant.

[0087] The hydrocarbon-based polymer electrolyte in the solution may be one in which the ionic group forms a salt with an alkali metal or alkaline earth metal cation. In this case, it is also preferable to have a step of exchanging the alkali metal or alkaline earth metal cation with a proton after forming a film on a substrate and drying the film. This step is more preferably a step of contacting the formed film with an acidic aqueous solution. Moreover, the contact is even more preferably a step of immersing the formed film in the acidic aqueous solution. In this step, the protons in the acidic aqueous solution are replaced with cations ionically bonded to the ionic group, and the remaining water-soluble impurities, residual monomers, solvents, residual salts, etc. are simultaneously removed. The acidic aqueous solution is not particularly limited, but it is preferable to use sulfuric acid, hydrochloric acid, nitric acid, acetic acid, trifluoromethanesulfonic acid, methanesulfonic acid, phosphoric acid, citric acid, etc. The temperature and concentration of the acidic aqueous solution should also be appropriately determined, but from the viewpoint of productivity, it is preferable to use an aqueous sulfuric acid solution of 3 mass% or more and 30 mass% or less at a temperature of 0 ° C. to 80 ° C.

[0088] [Method for producing an electrolyte membrane with a catalyst layer] A catalyst coated membrane (CCM) is manufactured by forming a catalyst layer on both sides of the electrolyte membrane obtained in this manner. The method for forming the catalyst layer is not particularly limited, but a method of applying and drying a catalyst layer ink or a method of transferring a catalyst layer using a catalyst layer decal in which a catalyst layer is formed in advance on a decal base material and then drying the same is preferred because the process is simple and the process cost can be reduced.

[0089] In the case of the method of applying the catalyst layer ink, the application method is not particularly limited as long as it is a method that can apply the ink in the desired shape, and the methods described above in the application step of the mixed solution can be used.

[0090] The solvent contained in the catalyst layer ink is not particularly limited as long as it disperses the ionic group-containing polymer electrolyte and the catalyst-supporting carbon particles, but it is preferable to use a solvent that can be easily removed by evaporation by heating. For example, it is preferable to use a solvent with a boiling point of 140° C. or less. Specific examples of the solvent for the catalyst layer ink include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and pentanol; ketones such as acetone, methyl ethyl ketone, pentanone, hexanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, and diisobutyl ketone; ethers such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, and dibutyl ether; esters such as methyl acetate, ethyl acetate, normal propyl acetate, isopropyl acetate, butyl acetate, methyl lactate, ethyl lactate, and butyl lactate; and dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol, which may be used alone or in combination.

[0091] In the case of the method of transferring using a catalyst layer decal, first, a catalyst layer ink is applied onto a substrate, and a drying process is performed as necessary to prepare a catalyst layer decal. Then, the electrolyte membrane is sandwiched between the catalyst layer decal on the cathode electrode side and the catalyst layer decal on the anode electrode side, and the surfaces on which the catalyst layers of both decals are provided are brought into contact with the solid polymer electrolyte membrane, and hot-pressed to obtain an electrolyte membrane with a catalyst layer. The temperature and pressure of the hot press may be appropriately selected depending on the thickness of the electrolyte membrane, the moisture content, the catalyst layer, and the decal substrate, but from the viewpoints of industrial productivity and suppression of thermal decomposition of the polymer material having an ionic group, it is preferable to perform the hot press at a temperature in the range of 0°C to 250°C, and more preferably at a temperature higher than the glass transition temperature of the polymer electrolyte contained in the catalyst layer and 200°C or less. The pressure in the hot press is preferably as low as possible from the viewpoint of protecting the polymer electrolyte membrane and the electrodes, and in the case of flat press, a pressure of 10 MPa or less is preferable.

[0092] As the decal substrate used when applying the catalyst layer ink, a resin film or substrate similar to that used when forming the polymer electrolyte membrane can be used, as well as fluororesins such as polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, ethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer, polyvinylidene fluoride, etc. From the viewpoints of heat resistance, solvent resistance, chemical stability and mold releasability, it is preferable to use a fluororesin film.

[0093] The catalyst layer can be dried by the same method as described above for drying the mixed solution.

[0094] [Application] The composite electrolyte membrane of the present invention can be applied to various applications. For example, it can be applied to medical applications such as artificial skin, filtration applications, ion exchange resin applications such as chlorine-resistant reverse osmosis membranes, various structural material applications, electrochemical applications, humidification membranes, anti-fogging membranes, antistatic membranes, oxygen removal membranes, solar cell membranes, and gas barrier membranes. Among them, it can be preferably used for various electrochemical applications. Examples of electrochemical applications include solid polymer fuel cells, redox flow batteries, water electrolysis devices, chloroalkali electrolysis devices, electrochemical hydrogen pumps, and water electrolysis hydrogen generation devices.

[0095] In a solid polymer electrolyte fuel cell, an electrochemical hydrogen pump, and a water electrolysis hydrogen generation device, a polymer electrolyte membrane is used in a configuration in which a catalyst layer, an electrode substrate, and a separator are laminated in sequence on both sides. Among these, an electrolyte membrane in which a catalyst layer is laminated on both sides (i.e., a layer configuration of catalyst layer / electrolyte membrane / catalyst layer) is called a catalyst-coated electrolyte membrane (CCM), and an electrolyte membrane in which a catalyst layer and a gas diffusion substrate are laminated in sequence on both sides (i.e., a layer configuration of gas diffusion substrate / catalyst layer / electrolyte membrane / catalyst layer / gas diffusion substrate) is called a membrane electrode assembly (MEA). The composite electrolyte membrane of the present invention is suitably used as an electrolyte membrane constituting such a CCM and MEA. EXAMPLES

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. The various measurement conditions are as follows.

[0097] (1) Molecular weight of the polymer The number average molecular weight and weight average molecular weight of the polymer solution were measured by GPC. Using a Tosoh Corporation HLC-8022GPC as an integrated device of an ultraviolet detector and a differential refractometer, and two Tosoh Corporation TSK gel SuperHM-H (inner diameter 6.0 mm, length 15 cm) as GPC columns, the measurements were performed in N-methyl-2-pyrrolidone solvent (N-methyl-2-pyrrolidone solvent containing 10 mmol / L lithium bromide) at a flow rate of 0.2 mL / min, and the number average molecular weight and weight average molecular weight were calculated in terms of standard polystyrene.

[0098] (2) Ion exchange capacity (IEC) The measurement was performed by neutralization titration. The measurement was performed three times and the average value was taken.

[0099] 1. After proton exchange and thorough washing with pure water, the moisture on the surface of the electrolyte membrane was wiped off, and the membrane was vacuum dried at 100°C for 12 hours or more, and the dry weight was calculated.

[0100] 2. 50 mL of a 5 wt% aqueous solution of sodium sulfate was added to the electrolyte membrane and left to stand for 12 hours to perform ion exchange.

[0101] 3. The resulting sulfuric acid was titrated using 0.01 mol / L aqueous sodium hydroxide solution. 0.1 w / v% commercially available phenolphthalein solution for titration was added as an indicator, and the end point was when the color turned light reddish purple.

[0102] 4. IEC was calculated using the following formula.

[0103] IEC (meq / g) = [concentration of sodium hydroxide solution (mmol / ml) × amount dropped (ml)] / dry weight of sample (g).

[0104] (3) Filling rate of the hydrocarbon-based polymer electrolyte in the composite layer (filling rate of the composite layer) The cross section of the composite electrolyte membrane was observed with an optical microscope or scanning electron microscope (SEM), and the thickness of the composite layer consisting of the polymer electrolyte and the fluorinated polymer porous substrate was designated as T1, and if there were other layers outside the composite layer, their thicknesses were designated as T2 and T3. The specific gravity of the polymer electrolyte forming the composite layer was designated as D1, the specific gravities of the polymer electrolytes forming the other layers outside the composite layer were designated as D2 and D3, respectively, and the specific gravity of the composite electrolyte membrane was designated as D. If the IEC of the polymers forming each layer is designated as I1, I2, I3, and the IEC of the composite electrolyte membrane is designated as I, the filling rate Y2 (volume %) of the aromatic hydrocarbon-based polymer electrolyte in the composite layer was calculated by the following formula.

[0105] Y2=[(T1+T2+T3)×D×I-(T2×D2×I2+T3×D3×I3)] / (T1×D1×I1)×100.

[0106] (4) Measurement of dimensional change rate (λxy) by hot water test The composite electrolyte membrane was cut into a square of about 5 cm x about 5 cm, and left to stand for 24 hours in a temperature-controlled and humidity-controlled atmosphere of 23°C ± 5°C and 50% ± 5%, after which the length in the MD direction and the length in the TD direction (MD1 and TD1) were measured with a caliper. The composite electrolyte membrane was immersed in hot water at 80°C for 8 hours, and the length in the MD direction and the length in the TD direction (MD2 and TD2) were measured again with a caliper, and the dimensional change rate in the MD direction and the TD direction in the in-plane direction (λMD and λTD) and the dimensional change rate in the in-plane direction (λxy) (%) were calculated from the following formula.

[0107] λMD = (MD2 - MD1) / MD1 × 100 λTD=(TD2-TD1) / TD1×100 λxy=(λMD+λTD) / 2.

[0108] (5) Proton conductivity The electrolyte membrane was immersed in pure water at 25°C for 24 hours, and then held in a thermohygrostat at 80°C and 25% RH for 30 minutes, and the proton conductivity was measured by a constant potential AC impedance method. As a measuring device, an electrochemical measuring system manufactured by Solartron (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used, and constant potential impedance measurement was performed by a two-terminal method to obtain the proton conductivity. The AC amplitude was 50 mV. A membrane with a width of 10 mm and a length of 50 mm was used as a sample. The measuring tool was made of phenolic resin, and the measuring part was left open. Platinum plates (thickness 100 μm, 2 sheets) were used as electrodes. The electrodes were arranged on the front and back sides of the sample membrane with an interelectrode distance of 10 mm, parallel to each other and perpendicular to the longitudinal direction of the sample membrane.

[0109] (6) Fabrication of membrane electrode assembly (MEA) using composite electrolyte membrane A pair of commercially available electrodes, BASF fuel cell gas diffusion electrodes "ELAT (registered trademark) LT120ENSI" 5g / m2 Pt, cut into 5cm squares, were prepared and stacked facing each other to sandwich the composite electrolyte membrane as the fuel electrode and air electrode, and hot pressed at 150°C and 5 MPa for 3 minutes to obtain an MEA for evaluating dry-wet cycle durability.

[0110] (7) Wet / dry cycle durability The MEA prepared in (6) above was set in a JARI standard cell "Ex-1" (electrode area 25 cm2) manufactured by Eiwa Co., Ltd., and a cycle was repeated in which nitrogen at 160% RH was supplied to both electrodes for 2 minutes at a cell temperature of 80°C, and then nitrogen at 0% RH (dew point -20°C or lower) was supplied to both electrodes for 2 minutes. The amount of hydrogen permeation was measured every 1000 cycles, and the point at which the hydrogen permeation current exceeded 10 times the initial current was regarded as the dry-wet cycle durability.

[0111] The hydrogen permeation amount was measured by supplying hydrogen as fuel gas to one electrode and nitrogen to the other electrode, and the test was performed under humidification conditions: hydrogen gas 90% RH, nitrogen gas: 90% RH. The open circuit voltage was held until it reached 0.2 V or less, and the voltage was swept from 0.2 to 0.7 V at 1 mV / sec, and the current value at 0.7 V was taken as the hydrogen permeation current.

[0112] (8) Measurement of the fluorine atom content in fluoropolymer porous substrates According to the following conditions, a fluorine-containing polymeric porous substrate sample was weighed and burned in a combustion tube of an analyzer. The generated gas was absorbed in a solution, and then a portion of the absorbed solution was analyzed by ion chromatography. <Combustion and absorption conditions> System: AQF-2100H, GA-210 (Mitsubishi Chemical) Electric furnace temperature: Inlet 900℃, Outlet 1000℃ Gas: Ar / O2 200mL / min, O2 400mL / min Absorption solution: H2O2 0.1%, internal standard Br 8μg / mL Absorbed liquid volume: 20mL <Ion chromatography - anion analysis conditions> System: ICS1600 (DIONEX) Mobile phase: 2.7mmol / L Na2CO3 / 0.3mmol / L NaHCO3 Flow rate: 1.50mL / min Detector: Electrical conductivity detector Injection volume: 20μL.

[0113] (9) Chemical structure analysis of surfactants Infrared spectroscopy (IR), 1H nuclear magnetic resonance (NMR), 19F NMR, MALDI-MS and pyrolysis GC / MS analyses were performed to analyze the chemical structures of various surfactants and calculate the content of fluorine atoms and hydrophilic elements (total of oxygen, nitrogen, phosphorus, sulfur and boron).

[0114] (10) Measurement of weight-average molecular weight of surfactants The weight average molecular weight of the surfactant was measured by gel permeation chromatography (GPC) analysis under the following conditions. Apparatus: Gel permeation chromatography (GPC) (instrument no. GPC-27) Detector: UV-visible absorption spectrometer UV (Shimadzu SPD-20AV) Column: TSKgel Super HZM-N x 2 SuperHZ4000, 2500, 1000 each 1 piece Solvent: Tetrahydrofuran (THF) Flow rate: 0.45mL / min Column temperature: 40℃ Injection volume: 0.02mL Standard samples: Tosoh and Agilent monodisperse polyethylene glycol (PEG) Data processing: TRC GPC data processing system.

[0115] (11) Cross-sectional SEM measurement of composite electrolyte membrane Cross-sectional SEM measurement was carried out under the following conditions. From the obtained image, the white area in the center was regarded as the composite layer, and the black areas on both sides were regarded as separate outer layers, and their thicknesses were measured. Equipment: Field emission scanning electron microscope (FE-SEM) S-4800 (Hitachi High-Technologies) Accelerating voltage: 2.0 kV Pretreatment: Cross-sectional samples prepared by the BIB method were coated with Pt and then measured. BIB method: Cross-sectional specimen preparation equipment using an argon ion beam. A shielding plate is placed directly above the specimen, and a broad argon ion beam is irradiated from above to etch the specimen, creating an observation and analysis surface (cross section).

[0116] (12) Amount of surfactant contained in electrolyte membrane According to the following conditions, the electrolyte membrane was weighed and burned in the combustion tube of the analyzer, the generated gas was absorbed in a solution, and a part of the absorbed solution was analyzed by ion chromatography. The contribution of the surfactant was calculated by excluding the contribution of the polymer electrolyte not containing the surfactant, which was measured in advance, and the contribution of the fluorine-containing polymer porous substrate, which was measured in advance by (8), from this analytical value, and the amount of the surfactant contained in the composite electrolyte membrane was calculated from the amount of fluorine atoms contained in the surfactant, and the ratio of the surfactant to the polymer electrolyte contained in the composite membrane (surfactant / polymer electrolyte) was obtained. <Combustion and absorption conditions> System: AQF-2100H, GA-210 (Mitsubishi Chemical Corporation) Electric furnace temperature: Inlet 900℃, Outlet 1000℃ Gas: Ar / O2 200mL / min, O2 400mL / min Absorption solution: H2O2 0.1%, internal standard Br 8μg / mL Absorbed liquid volume: 20mL <Ion chromatography - anion analysis conditions> System: ICS1600 (DIONEX) Mobile phase: 2.7mmol / L Na2CO3 / 0.3mmol / L NaHCO3 Flow rate: 1.50mL / min Detector: Electrical conductivity detector Injection volume: 20μL.

[0117] (13) Measurement of oxygen content in porous substrates using XPS A porous substrate cut into a 5 mm square was rinsed with ultrapure water, dried at room temperature and 67 Pa for 10 hours, cooled with liquid nitrogen for 30 minutes, and processed twice for 5 minutes in a freeze grinder to prepare a sample. The composition of the prepared sample was measured, and the oxygen atom content was calculated. The measurement device and conditions were as follows. Measuring device: Quantera SXM Excitation X-ray: monochromatic Al Kα1,2 line (1486.6 eV) X-ray diameter: 200μm Photoelectron escape angle: 45°.

[0118] (14) Peel resistance test The number V of voids caused by peeling between the hydrocarbon-based polymer electrolyte in the composite layer and the fluorine-containing polymer porous substrate fiber was measured and evaluated by a peeling resistance test under the following conditions.

[0119] 1. Immerse the composite electrolyte membrane in pure water for 10 minutes. 2. Remove the composite electrolyte membrane from the pure water and dry it in a hot air dryer at 100°C for 10 minutes. 3. Repeat steps 1 and 2 10 times. 4. The composite layer was observed by the method described in Example (11). The observation field was 3 cm removed from both ends in the TD direction, and five fields including both ends (3 cm from the ends) were observed at equal intervals in the TD direction. (If the electrolyte membrane is 14 cm in the TD direction, the positions 3, 5, 7, 9, and 11 cm from one end were observed.) 5. If pores were observed in the composite layer region of the obtained image, the length of each pore in the direction of its largest size was measured and taken as the pore size. Observations were made over a 5 μm range in the membrane surface direction for each field of view. The size of the pores within the range was measured, and the number of pores larger than 100 nm was counted. The number of pores V was the total value for the five fields of view. (15) Measurement of the mechanical properties of the electrolyte membrane in a dry state The electrolyte membrane sample was set in the device and a tensile test was performed under the following conditions. The tensile strength and tensile elongation values ​​were taken as the values ​​at the moment when the maximum stress was observed during the test. The elastic modulus was taken as the maximum value calculated using any two points in the measurement data where the difference in strain was 0.3%. The yield stress was taken as the value at the moment when the stress decreased by 0.5%, or if no clear yield point was observed, the value at the 0.2% proof stress point was used. Tensile strength, tensile elongation, tensile elastic modulus, and yield stress were calculated as the average value of five tests.

[0120] Measuring device: Autograph AG-IS (Shimadzu Corporation) Load range: 100N Pulling speed: 100mm / min Test piece: width 10mm x length 100mm Distance between samples: 30 mm Test temperature and humidity: 23±1℃, 50±10RH% Number of trials: n=5.

[0121] (16) Mechanical properties of electrolyte membranes in a wet state The electrolyte membrane specimens were cut to the size of test pieces and immersed in ultrapure water at 23°C for 24 hours, and then removed from the water. Within 10 minutes after removal, a tensile test was performed under the same conditions and method as in (16), and the wet tensile strength, wet tensile elongation, and wet tensile modulus were calculated.

[0122] (17) Mechanical properties of electrolyte membrane after wet-dry cycle in water The electrolyte membrane to be used as a specimen was subjected to steps 1 to 3 in Example (14), and then a tensile test was carried out under the same conditions and method as in Example (16). The wet tensile strength, wet tensile elongation, and wet tensile modulus after the wet-dry cycle were calculated.

[0124] [Synthesis Example 1] (Synthesis of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane (K-DHBP) represented by the following general formula (G1)) In a 500 ml flask equipped with a stirrer, a thermometer and a distillation tube, 49.5 g of 4,4'-dihydroxybenzophenone, 134 g of ethylene glycol, 96.9 g of trimethyl orthoformate and 0.50 g of p-toluenesulfonic acid monohydrate were charged and dissolved. The mixture was then stirred at 78-82 ° C for 2 hours. The internal temperature was then gradually raised to 120 ° C, and the mixture was heated until the distillation of methyl formate, methanol and trimethyl orthoformate completely stopped. After cooling the reaction solution to room temperature, the reaction solution was diluted with ethyl acetate, the organic layer was washed with 100 ml of a 5% aqueous potassium carbonate solution and separated, and the solvent was distilled off. 80 ml of dichloromethane was added to the residue to precipitate crystals, which were then filtered and dried to obtain 52.0 g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane. GC analysis of the crystals revealed that they were 99.9% 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane and 0.1% 4,4'-dihydroxybenzophenone.

[0125] [ka]

[0126] [Synthesis Example 2] (Synthesis of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following general formula (G2)) 109.1 g of 4,4'-difluorobenzophenone (Aldrich reagent) was reacted in 150 mL of fuming sulfuric acid (50% SO3) (Wako Pure Chemical Industries, Ltd. reagent) at 100°C for 10 hours. After that, it was gradually poured into a large amount of water, neutralized with NaOH, and then 200 g of table salt (NaCl) was added to precipitate the synthesized product. The resulting precipitate was filtered and recrystallized with an ethanol aqueous solution to obtain disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the above general formula (G2). The purity was 99.3%.

[0127] [ka]

[0128] [Synthesis Example 3] (Synthesis of oligomer a1 not containing an ionic group represented by the following general formula (G3)) In a 1000mL three-neck flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 16.59g of potassium carbonate (Aldrich reagent, 120mmol), 25.8g (100mmol) of K-DHBP obtained in the above Synthesis Example 1, and 20.3g of 4,4'-difluorobenzophenone (Aldrich reagent, 93mmol) were placed, and after nitrogen replacement, the mixture was dehydrated at 160°C in 300mL of N-methylpyrrolidone (NMP) and 100mL of toluene, heated to remove toluene, and polymerized at 180°C for 1 hour. Reprecipitation purification was performed in a large amount of methanol to obtain an oligomer (terminal: hydroxyl group) that does not contain ionic groups. The number average molecular weight was 10,000.

[0129] In a 500mL three-neck flask equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap, 1.1g of potassium carbonate (Aldrich reagent, 8mmol) and 20.0g (2mmol) of the oligomer a1 (terminal: hydroxyl group) not containing an ionic group were placed, and after nitrogen replacement, the mixture was dehydrated at 100°C in 100mL of N-methylpyrrolidone (NMP) and 30mL of toluene, heated to remove toluene, and 4.0g of decafluorobiphenyl (Aldrich reagent, 12mmol) was placed and reacted at 105°C for 1 hour. Purification was performed by reprecipitation with a large amount of isopropyl alcohol to obtain an oligomer a1 (terminal: fluoro group) not containing an ionic group represented by the following formula (G3). The number average molecular weight was 11,000.

[0130] [ka]

[0131] [Synthesis Example 4] (Synthesis of oligomer a2 containing an ionic group represented by the following general formula (G4)) Into a 1000 mL three-neck flask equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap, 27.6 g of potassium carbonate (Aldrich reagent, 200 mmol), 12.9 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.3 g of 4,4'-biphenol (Aldrich reagent, 50 mmol), 39.3 g (93 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 17.9 g of 18-crown-6 (Wako Pure Chemical Industries, 82 mmol) were placed, and after nitrogen replacement, the mixture was dehydrated at 170°C in 300 mL of N-methylpyrrolidone (NMP) and 100 mL of toluene, and then heated to remove the toluene, followed by polymerization at 180°C for 1 hour. The product was purified by reprecipitation with a large amount of isopropyl alcohol to obtain an oligomer a2 (terminal: hydroxyl group) containing an ionic group represented by the following formula (G4). The number average molecular weight was 16,000.

[0132] [ka]

[0133] (In formula (G4), M represents H, Na or K.) [Synthesis Example 5] (Synthesis of neopentyl 3-(2,5-dichlorobenzoyl)benzenesulfonate represented by the following formula (G5)) 245g (2.1mol) of chlorosulfonic acid was added to a 3L three-neck flask equipped with a stirrer and a condenser, followed by 105g (420mmol) of 2,5-dichlorobenzophenone, and the mixture was allowed to react in a 100℃ oil bath for 8 hours. After the specified time, the reaction solution was slowly poured onto 1000g of crushed ice and extracted with ethyl acetate. The organic layer was washed with saline and dried over magnesium sulfate, after which the ethyl acetate was distilled off to obtain pale yellow crude crystals of 3-(2,5-dichlorobenzoyl)benzenesulfonic acid chloride. The crude crystals were used in the next step without purification.

[0134] 41.1 g (462 mmol) of 2,2-dimethyl-1-propanol (neopentyl alcohol) was added to 300 mL of pyridine and cooled to about 10°C. The crude crystals obtained above were gradually added thereto over about 30 minutes. After the entire amount was added, the mixture was stirred for another 30 minutes to react. After the reaction, the reaction solution was poured into 1000 mL of hydrochloric acid water, and the precipitated solid was collected. The obtained solid was dissolved in ethyl acetate, washed with an aqueous sodium bicarbonate solution and saline, dried over magnesium sulfate, and the ethyl acetate was distilled off to obtain crude crystals. This was recrystallized from methanol to obtain white crystals of neopentyl 3-(2,5-dichlorobenzoyl)benzenesulfonate represented by the above structural formula.

[0135] [ka]

[0136] [Synthesis Example 6] (Synthesis of an oligomer not containing an ionic group represented by the following general formula (G6)) 49.4g (0.29mol) of 2,6-dichlorobenzonitrile, 88.4g (0.26mol) of 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane, and 47.3g (0.34mol) of potassium carbonate were weighed into a 1L three-neck flask equipped with a stirrer, a thermometer, a cooling tube, a Dean-Stark tube, and a three-way cock for nitrogen introduction. After replacing with nitrogen, 346ml of sulfolane and 173ml of toluene were added and stirred. The flask was placed in an oil bath and heated to reflux at 150℃. The water generated by the reaction was azeotroped with toluene and removed from the system using a Dean-Stark tube. After about 3 hours, almost no water was generated. The reaction temperature was gradually increased to remove most of the toluene, and the reaction was continued at 200℃ for 3 hours. Next, 12.3 g (0.072 mol) of 2,6-dichlorobenzonitrile was added, and the mixture was further reacted for 5 hours.

[0137] The resulting reaction solution was allowed to cool, and then diluted with 100 ml of toluene. The precipitate of the by-product inorganic compound was removed by filtration, and the filtrate was poured into 2 liters of methanol. The precipitated product was filtered, collected, dried, and dissolved in 250 ml of tetrahydrofuran. This was reprecipitated in 2 liters of methanol to obtain 107 g of the target compound oligomer represented by the following general formula (G6). The number average molecular weight was 11,000.

[0138] [ka]

[0139] [Synthesis Example 7] (Synthesis of polyethersulfone (PES)-based block copolymer precursor b2' consisting of a segment represented by the following formula (G8) and a segment represented by the following formula (G9)) 1.62 g of anhydrous nickel chloride and 15 mL of dimethyl sulfoxide were mixed and adjusted to 70° C. 2.15 g of 2,2′-bipyridyl was added thereto and stirred at the same temperature for 10 minutes to prepare a nickel-containing solution.

[0140] Here, 1.49 g of 2,5-dichlorobenzenesulfonic acid (2,2-dimethylpropyl) and 0.50 g of Sumika Excel PES5200P (manufactured by Sumitomo Chemical Co., Ltd., Mn = 40,000, Mw = 94,000) represented by the following formula (G7) were dissolved in 5 mL of dimethyl sulfoxide to obtain a solution, to which 1.23 g of zinc powder was added and adjusted to 70 ° C. The nickel-containing solution was poured into this, and a polymerization reaction was carried out at 70 ° C. for 4 hours. The reaction mixture was added to 60 mL of methanol, and then 60 mL of 6 mol / L hydrochloric acid was added and stirred for 1 hour. The precipitated solid was separated by filtration and dried, and 1.62 g of a block copolymer precursor b2' containing segments represented by the following formula (G8) and the following formula (G9) was obtained in a yield of 99%. The weight average molecular weight was 230,000.

[0141] [ka]

[0142] [Polymer electrolyte solution A] A polymer electrolyte solution comprising a block copolymer containing an oligomer represented by (G4) as a segment containing an ionic group and an oligomer represented by (G3) as a segment not containing an ionic group. In a 500mL three-neck flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 0.56g of potassium carbonate (Aldrich reagent, 4mmol) and 16g (1mmol) of oligomer a2 (terminal: hydroxyl group) containing an ionic group obtained in Synthesis Example 4 were placed, and after nitrogen replacement, 100mL of N-methylpyrrolidone (NMP) and 30mL of cyclohexane were dehydrated at 100°C, and the temperature was raised to remove cyclohexane. 11g (1mmol) of oligomer a1 (terminal: fluoro group) not containing an ionic group obtained in Synthesis Example 3 was placed, and the reaction was carried out at 105°C for 24 hours. Block copolymer b1 was obtained by reprecipitation purification in a large amount of isopropyl alcohol. The weight average molecular weight was 340,000.

[0143] The resulting block copolymer was dissolved in 5% by mass N-methylpyrrolidone (NMP) solution, and the polymerization stock solution was directly centrifuged using a Kubota Manufacturing inverter compact high-speed refrigerated centrifuge (model number 6930 equipped with an angle rotor RA-800, 25°C, 30 minutes, centrifugal force 20,000G). The precipitated solids (cake) and the supernatant liquid (coating liquid) were neatly separated, and the supernatant liquid was collected. Next, the mixture was distilled under reduced pressure at 80°C while stirring, and pressure filtered using a 1μm polypropylene filter to obtain polymer electrolyte solution A (polymer electrolyte concentration 13% by mass). The viscosity of polymer electrolyte solution A was 1300mPa·s.

[0144] [Polymer electrolyte solution B] A polymer electrolyte solution comprising a polyarylene-based block copolymer represented by the following general formula (G10): 540 ml of dry N,N-dimethylacetamide (DMAc) was added under nitrogen to a mixture of 135.0 g (0.336 mol) of neopentyl 3-(2,5-dichlorobenzoyl)benzenesulfonate, 40.7 g (5.6 mmol) of the oligomer not containing an ionic group represented by formula (G6) synthesized in Synthesis Example 6, 6.71 g (16.8 mmol) of 2,5-dichloro-4'-(1-imidazolyl)benzophenone, 6.71 g (10.3 mmol) of bis(triphenylphosphine)nickel dichloride, 35.9 g (0.137 mol) of triphenylphosphine, 1.54 g (10.3 mmol) of sodium iodide, and 53.7 g (0.821 mol) of zinc.

[0145] The reaction system was heated with stirring (finally heated to 79°C) and reacted for 3 hours. An increase in viscosity in the system was observed during the reaction. The polymerization reaction solution was diluted with 730 ml of DMAc, stirred for 30 minutes, and filtered using Celite as a filter aid.

[0146] The filtrate was concentrated with an evaporator, 43.8 g (0.505 mol) of lithium bromide was added to the filtrate, and the mixture was reacted at an internal temperature of 110°C for 7 hours under a nitrogen atmosphere. After the reaction, the mixture was cooled to room temperature and poured into 4 L of acetone to coagulate. The coagulated product was collected by filtration, air-dried, pulverized in a mixer, and washed with 1500 ml of 1N hydrochloric acid while stirring. After filtration, the product was washed with ion-exchanged water until the pH of the washing solution became 5 or more, and then dried overnight at 80°C to obtain 23.0 g of the desired polyarylene block copolymer. The weight-average molecular weight of this polyarylene block copolymer after deprotection was 190,000. The obtained polyarylene block copolymer was dissolved in an organic solvent of N-methyl-2-pyrrolidone / methanol = 30 / 70 (mass%) to obtain a polymer electrolyte solution B at 0.1 g / g. The viscosity of polymer electrolyte solution B was 1200 mPa·s.

[0147] [ka]

[0148] [Polymer electrolyte solution C] Polyelectrolyte solution C consisting of random copolymer In a 5L reaction vessel equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 129g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane synthesized in Synthesis Example 1, 93g of 4,4'-biphenol (Aldrich reagent), and 422g (1.0mol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone synthesized in Synthesis Example 2 were placed, and after nitrogen replacement, 3000g of N-methyl-2-pyrrolidone (NMP), 450g of toluene, and 232g of 18-crown-6 (Wako Pure Chemical Reagent) were added. After confirming that all the monomers had dissolved, 304g of potassium carbonate (Aldrich reagent) was added, and the mixture was refluxed at 160°C for dehydration, heated to remove toluene, and desalted and polycondensed at 200°C for 1 hour. The weight average molecular weight was 320,000.

[0149] Next, NMP was added to dilute the polymerization stock solution so that the viscosity became 500 mPa·s, and the polymerization stock solution was directly centrifuged using a Kubota Manufacturing inverter compact high-speed refrigerated centrifuge (model number 6930 with an angle rotor RA-800 set, 25°C, 30 minutes, centrifugal force 20,000G). The precipitated solids (cake) and the supernatant liquid (coating liquid) were neatly separated, so the supernatant liquid was collected. Next, the mixture was distilled under reduced pressure at 80°C while stirring, and NMP was removed until the polymer concentration became 14% by mass. The mixture was then filtered under pressure with a 5 μm polyethylene filter to obtain polymer electrolyte solution C. The viscosity of polymer electrolyte solution C was 1000 mPa·s.

[0150] [Polymer electrolyte solution D] Polyelectrolyte solution D consisting of polyethersulfone-based block copolymer 0.23 g of the block copolymer precursor b2' obtained in Synthesis Example 7 was added to a mixed solution of 0.16 g of lithium bromide monohydrate and 8 mL of NMP, and reacted at 120°C for 24 hours. The reaction mixture was poured into 80 mL of 6 mol / L hydrochloric acid and stirred for 1 hour. The precipitated solid was separated by filtration. The separated solid was dried to obtain a gray-white block copolymer b2 consisting of a segment represented by the above formula (G8) and a segment represented by the following formula (G11). The weight-average molecular weight of the obtained polyethersulfone-based block copolymer was 190,000. The obtained polyethersulfone-based block copolymer was dissolved in an organic solvent of N-methyl-2-pyrrolidone / methanol = 30 / 70 (mass%) so as to have a concentration of 0.1 g / g, to obtain a polymer electrolyte solution D. The viscosity of the polymer electrolyte solution D was 1300 mPa·s.

[0151] [ka]

[0152] [Porous polytetrafluoroethylene (ePTFE) substrate A] Poreflon (registered trademark) HP-045-30 (manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) was simultaneously biaxially stretched three times in the longitudinal and transverse directions to produce an ePTFE porous substrate B with a film thickness of 8 μm and a porosity of 89%. SEM observation revealed that fibrils with an average diameter of 0.3 μm formed an irregular spider web structure.

[0153] [Hydrophilized ePTFE porous base material A'] In a glove box with a dew point of -80°C, ePTFE porous substrate B was immersed in a solution consisting of 30 g of a 1% solution of metallic sodium-naphthalene complex / tetrahydrofuran (THF) and 70 g of THF, and after 3 seconds, it was removed and immediately washed thoroughly with THF to produce a hydrophilic ePTFE porous substrate B' with a film thickness of 8 μm and a porosity of 88%. [Polytetrafluoroethylene (ePTFE) porous substrate B] Poreflon (registered trademark) WP-010-80 (manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) was stretched 10 times in the machine direction, and then heat-treated at 365° C. Then, it was stretched twice in the cross direction to produce an ePTFE porous substrate A with a film thickness of 9 μm and a porosity of 80%. As a result of SEM observation, the structure had nodes with an average diameter of 0.9 μm approximately parallel to the machine direction and fibrils with an average diameter of 0.2 μm approximately parallel to the cross direction.

[0154] [Tetrafluoroethylene-hexafluoropropylene (FEP) copolymer porous substrate C] 75 parts by mass of FEP resin (manufactured by Fluoron Industries Co., Ltd.) and 15 parts by mass of silica fine particles (manufactured by Shin-Etsu Silicones Co., Ltd., QSG-30, average primary particle size 30 nm) as an inorganic filler were thoroughly mixed using a powder mixer.

[0155] This mixture was kneaded at 300° C. using a twin-screw extruder (TEM-35, manufactured by Toshiba Machine Co., Ltd.), and then extruded into strands with a diameter of 2.5 mm, which were then cut into pellets with a length of 2.5 mm.

[0156] The pellets were fed to a single screw extruder (VS40, manufactured by Ikegai Co., Ltd.) with a diameter of 40 mm, and extruded using a flat die with a die width of 700 mm at a die temperature of 333° C. and an extrusion rate of 4.3 kg / hour. The extruded material was taken up at a speed of 4.8 m / minute along a roll adjusted to a surface temperature of 130° C., to obtain an ETFE film.

[0157] The obtained film was stretched 4 times in the longitudinal and transverse directions to produce an FEP copolymer porous substrate B having a thickness of 8 μm and a porosity of 90%.

[0158] [Ethylene-tetrafluoroethylene (ETFE) copolymer porous substrate D] An ETFE copolymer porous substrate D having a thickness of 8 μm and a porosity of 89% was prepared in the same manner as FEP porous substrate B, except that ETFE resin (manufactured by Aldrich) was used instead of FEP resin (manufactured by Fluoron Industries Co., Ltd.). [Porous polytetrafluoroethylene (ePTFE) substrate E] Tetratex (registered trademark) TX1356 (manufactured by Donaldson) is used as the porous substrate E. The film thickness is 8 μm and the porosity is 85%.

[0159] [Example 1] 0.26 g of "Ftergent" (registered trademark) 208G was dissolved in 100 g of polymer electrolyte solution A to prepare an electrolyte-surfactant mixed solution with a mass ratio of polymer electrolyte to surfactant (hereinafter referred to as surfactant / electrolyte) of 0.02. Using a knife coater, this electrolyte-surfactant mixed solution was cast and applied onto a glass substrate, and ePTFE porous substrate A was attached. After holding at room temperature for 1 hour, the ePTFE porous substrate A was sufficiently impregnated with the electrolyte-surfactant mixed solution A, and then dried at 100 ° C. for 4 hours. The electrolyte-surfactant mixed solution A was cast and applied again to the upper surface of the dried membrane, held at room temperature for 1 hour, and then dried at 100 ° C. for 4 hours to obtain a film-like polymer. After immersing in a 10% by mass aqueous sulfuric acid solution at 80 ° C. for 24 hours to cause proton substitution and deprotection reaction, the membrane was immersed in a large excess of pure water for 24 hours to thoroughly wash, and a composite electrolyte membrane (thickness 10 μm) was obtained.

[0160] [Example 2] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 1, except that an electrolyte-surfactant mixed solution with a surfactant / electrolyte ratio of 0.10 was used.

[0161] [Example 3] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 2, except that "Ftergent" (registered trademark) 710FM was used instead of "Ftergent" (registered trademark) 208G.

[0162] [Example 4] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 2, except that "Megafac" (registered trademark) F-555 was used instead of "Ftergent" (registered trademark) 208G.

[0163] [Example 5] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 2, except that the ePTFE porous substrate B was used instead of the ePTFE porous substrate A.

[0164] <Production of composite electrolyte membrane according to second embodiment> [Example 6] 1.5 g of "Ftergent" (registered trademark) 208G was dissolved in 100 g of 2-methoxy-1-methylethyl acetate to prepare a 1.5 mass% solution of "Ftergent" (registered trademark) 208G. Next, the 208G solution was cast and applied onto the ePTFE porous substrate A fixed on a glass substrate using a knife coater, and dried at 100°C for 1 hour to prepare a surfactant-containing ePTFE porous substrate A. The weight of the prepared surfactant-containing ePTFE porous substrate A was increased by 3 wt% compared to the original ePTFE porous substrate A. In addition, when a droplet of NMP was placed on the surface of the surfactant-containing ePTFE porous substrate A, the portion where it was placed became transparent in 3 seconds and was impregnated with NMP. When pure water was placed, it did not become transparent even after 120 seconds had passed, and the pure water did not penetrate.

[0165] Using a knife coater, the polymer electrolyte solution A was cast onto another glass substrate, and the surfactant-containing ePTFE porous substrate A peeled off from the glass substrate was attached. The substrate was held at room temperature for 1 hour to thoroughly impregnate the surfactant-containing ePTFE porous substrate A with the polymer electrolyte solution A, and then dried at 100°C for 4 hours. The polymer electrolyte solution A was cast onto the upper surface of the dried membrane again, held at room temperature for 1 hour, and then dried at 100°C for 4 hours to obtain a film-like polymer. The membrane was immersed in a 10% by mass aqueous sulfuric acid solution at 80°C for 24 hours to carry out proton substitution and deprotection reactions, and then immersed in a large excess of pure water for 24 hours to thoroughly wash the membrane, obtaining a composite electrolyte membrane (thickness 10 μm).

[0166] [Example 7] A composite electrolyte membrane (thickness 10 μm) was obtained in the same manner as in Example 6, except that the surfactant solution was applied so that the weight increase of the prepared surfactant-containing ePTFE porous substrate A was 6 wt % compared to the original ePTFE porous substrate A.

[0167] [Example 8] A composite electrolyte membrane (thickness 10 μm) was obtained in the same manner as in Example 6, except that the surfactant solution was applied so that the weight increase of the prepared surfactant-containing ePTFE porous substrate A was 10 wt % compared to the original ePTFE porous substrate A.

[0168] [Example 9] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 7, except that "Ftergent" (registered trademark) 710FM was used instead of "Ftergent" (registered trademark) 208G.

[0169] [Example 10] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 7, except that "Megafac" (registered trademark) F-555 was used instead of "Ftergent" (registered trademark) 208G.

[0170] [Example 11] 20g of NMP solution (Kureha L#9305) in which polyvinylidene fluoride (PVDF) is dissolved at 5wt%, 80g of 2-methoxy-1-methylethyl acetate, and 1g of "Ftergent" (registered trademark) 710FM solution were mixed to prepare a solution of 1wt% PVDF and 0.5wt% "Ftergent" (registered trademark) 710FM. A composite electrolyte membrane (thickness 10μm) was obtained in the same manner as in Example 8, except that the prepared PVDF + "Ftergent" (registered trademark) 710FM solution was used instead of the "Ftergent" (registered trademark) 208G solution.

[0171] [Example 12] A 0.5 wt% solution of PVDF was prepared by mixing 10 g of NMP solution (Kureha L#9305) in which PVDF was dissolved at 5 wt% and 90 g of 2-methoxy-1-methylethyl acetate. A composite electrolyte membrane (thickness 10 μm) was obtained in the same manner as in Example 7, except that the prepared PVDF solution was used instead of the "Ftergent" (registered trademark) 208G solution.

[0172] [Example 13] 100g of 1wt% NMP solution of polybenzimidazole (PBI) dissolved therein and 1g of "Ftergent" (registered trademark) 208G were mixed to prepare a 1wt% PBI and 1wt% "Ftergent" (registered trademark) 208G solution. A composite electrolyte membrane (thickness 10μm) was obtained in the same manner as in Example 8, except that the prepared PBI + "Ftergent" (registered trademark) 208G solution was used instead of the "Ftergent" (registered trademark) 208G solution.

[0176] [Example 17] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 7, except that the ePTFE porous substrate A was replaced with the porous substrate C.

[0177] [Example 18] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 7, except that the ePTFE porous substrate A was replaced with the porous substrate D.

[0178] [Example 19] An electrolyte-surfactant mixed solution was prepared in the same manner as in Example 1.

[0179] Using a knife coater, this electrolyte-surfactant mixed solution was cast onto a glass substrate, and the ePTFE porous substrate A was attached. After holding at room temperature for 1 hour to thoroughly impregnate the ePTFE porous substrate A with the electrolyte-surfactant mixed solution A, the electrolyte-surfactant mixed solution A was cast again, held at room temperature for 1 hour, and then dried at 100°C for 4 hours to obtain a film-like polymer. After immersing in a 10% by mass aqueous sulfuric acid solution at 80°C for 24 hours to carry out proton substitution and deprotection reactions, the film was immersed in a large excess of pure water for 24 hours to thoroughly wash, to obtain a composite electrolyte membrane (thickness 10 μm).

[0180] [Example 20] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 19, except that an electrolyte-surfactant mixed solution with a surfactant / electrolyte ratio of 0.04 was used.

[0181] [Example 21] A composite electrolyte membrane (thickness 10 μm) was obtained in the same manner as in Example 1, except that an electrolyte-surfactant mixed solution with a surfactant / electrolyte ratio of 0.04 was used and ePTFE porous substrate E was used instead of ePTFE porous substrate A.

[0182] [Example 22] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 20, except that the ePTFE porous substrate E was used instead of the ePTFE porous substrate A.

[0183] [Example 23] An electrolyte-surfactant mixed solution was prepared in the same manner as in Example 20.

[0184] The electrolyte-surfactant mixed solution was applied to a PET substrate, and an ePTFE porous substrate E was attached to the applied solution film. The electrolyte-surfactant mixed solution was then applied to the upper surface of the applied solution film and dried for 10 minutes in a drying oven at 100°C to obtain a film-like polymer. Figure 1 shows a schematic diagram of the roll membrane production device used. In Figure 1, 3 represents the PET substrate, 4 the coating device, 5 the reinforcing material, and 6 the drying oven. The obtained film-like polymer was immersed in a 10% by mass aqueous sulfuric acid solution at 80°C for 24 hours to cause proton substitution and deprotection reactions, and then immersed in a large excess of pure water for 24 hours to thoroughly wash the film, obtaining a composite electrolyte membrane (film thickness 10 μm).

[0185] [Example 24] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 23, except that "Ftergent" (registered trademark) FTX-218 was used instead of "Ftergent" (registered trademark) 208G.

[0186] [Example 25] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Example 9, except that the ePTFE porous substrate E was used instead of the ePTFE porous substrate A.

[0187] [Example 26] 1.5 g of "Ftergent" (registered trademark) 710FM was dissolved in 100 g of 2-methoxy-1-methylethyl acetate to prepare a 1.5 mass% solution of "Ftergent" (registered trademark) 208G. The prepared 710FM solution was then applied onto a PET substrate, and the ePTFE porous substrate E was attached thereto. The substrate was then dried in a drying oven at 100°C for 10 minutes to prepare a surfactant-containing ePTFE porous substrate E. The weight of the prepared surfactant-containing ePTFE porous substrate E was increased by 6 wt% compared to the original ePTFE porous substrate E.

[0188] Next, the polymer electrolyte solution A was applied onto the PET substrate, and the surfactant-containing ePTFE porous substrate E peeled off from the PET substrate was attached onto the coating solution film, dried for 10 minutes in a drying oven at 100 ° C., and then the dried film was rolled up. The polymer electrolyte solution A was applied onto the upper surface of the wound film, and dried for 10 minutes in a drying oven at 100 ° C. to obtain a film-like polymer. Figure 2 shows a schematic diagram of the roll film production device used. In Figure 2, 3 represents the PET substrate, 4 the coating device, 5 the reinforcing material, and 6 the drying oven. The obtained film-like polymer was immersed in a 10% by mass sulfuric acid aqueous solution at 80 ° C. for 24 hours to cause proton substitution and deprotection reactions, and then immersed in a large excess of pure water for 24 hours to thoroughly wash, obtaining a composite electrolyte membrane (film thickness 10 μm).

[0189] [Example 27] In the same manner as in Example 26, a surfactant-containing ePTFE porous substrate E was obtained. Next, the polymer electrolyte solution A was applied onto a PET substrate, the surfactant-containing ePTFE porous substrate E peeled off from the PET substrate was attached onto the applied solution film, the polymer electrolyte solution A was applied onto the upper surface, and the substrate was dried for 10 minutes in a drying oven at 100° C. to obtain a film-like polymer. The obtained film-like polymer was immersed in a 10% by mass aqueous sulfuric acid solution at 80° C. for 24 hours to cause proton substitution and deprotection reactions, and then immersed in a large excess of pure water for 24 hours to thoroughly wash, thereby obtaining a composite electrolyte membrane (film thickness 10 μm).

[0190] [Comparative Example 1] An attempt was made to prepare a composite electrolyte membrane in the same manner as in Example 1, except that polymer electrolyte solution A was used instead of the electrolyte-surfactant mixed solution. However, the polymer electrolyte solution A did not penetrate into the ePTFE porous substrate A, and a composite electrolyte membrane could not be obtained.

[0191] [Comparative Example 2] A composite electrolyte membrane (thickness: 10 μm) was obtained in the same manner as in Comparative Example 1, except that a hydrophilized ePTFE porous substrate A′ was used instead of the ePTFE porous substrate A.

[0192] The composite electrolyte membranes produced in Examples 1-18 and Comparative Examples 1-2 were evaluated for ion exchange capacity (IEC), polymer electrolyte packing rate in the composite layer, peel resistance, dimensional change rate λxy, hygroscopic tensile modulus, tensile modulus after wet-dry cycles, proton conductivity, wet-dry cycle durability, and yield stress. The fluorine atom content and porosity of the fluorine-containing polymer microporous membrane porous substrate were also evaluated. These evaluation results are shown in Table 1. (Regarding wet-dry cycle durability, if the hydrogen permeation current did not exceed 10 times the initial current even after 30,000 cycles, the evaluation was terminated at 30,000 cycles.)

[0193] [Table 1]

[0194] Note 1) A: Block copolymer b1, B: Polyarylene-based block copolymer, C: Random copolymer, D: Polyethersulfone-based block copolymer b2 Note 2) A: Polytetrafluoroethylene (ePTFE) porous substrate, A': Hydrophilized ePTFE porous substrate A', C: Tetrafluoroethylene-hexafluoropropylene (FEP) copolymer porous substrate, D: Ethylene-tetrafluoroethylene (ETFE) copolymer porous substrate, E: Polytetrafluoroethylene (ePTFE) porous substrate E [Explanation of symbols]

[0195] 1:PET base material 2: Coating device 3: Reinforcement 4:Drying oven

Claims

1. A composite electrolyte membrane having a composite layer in which a hydrocarbon-based polymer electrolyte and a fluorine-containing polymer porous substrate are composited, the hydrocarbon-based polymer electrolyte being a polyether ketone-based block copolymer having at least one each of an ionic group-containing segment (A1) and a fluorine-containing polymer porous substrate, the composite electrolyte membrane containing a fluorine-based surfactant or polyvinylidene fluoride, the composite electrolyte membrane being immersed in pure water for 10 minutes and then dried in a hot air dryer at 100°C for 10 minutes 10 times, the number V of voids having a size of 100 nm or more generated in the composite layer being 100 or less in total in five visual fields when observed with a field emission scanning electron microscope with a range of 5 μm in the membrane surface direction as one visual field.

2. 2. The composite electrolyte membrane according to claim 1, wherein the ratio of the wet tensile modulus before and after the wet-dry cycle is 0.8 or more.

3. 3. The composite electrolyte membrane according to claim 1, wherein the oxygen atom content of the fluorine-containing polymer porous substrate is 5% or less.

4. 4. The composite electrolyte membrane according to claim 1, wherein the fluorine-containing polymer porous substrate contains 70% by mass or more of fluorine atoms.

5. 5. The composite electrolyte membrane according to claim 1, wherein the hydrocarbon-based polymer electrolyte is an aromatic hydrocarbon-based polymer having an ionic group.

6. 6. The composite electrolyte membrane according to claim 1, which contains at least a fluorosurfactant or polyvinylidene fluoride as an additive, and which is free of a fluorosurfactant and polyvinylidene fluoride on the electrolyte membrane surface.

7. 7. The composite electrolyte membrane according to claim 1, which contains at least one fluorosurfactant and polymer additive as additives, and which is free of fluorosurfactant and polyvinylidene fluoride on the electrolyte membrane surface.

8. A catalyst-layered electrolyte membrane comprising the composite electrolyte membrane according to any one of claims 1 to 7 and a catalyst layer.

9. A membrane electrode assembly comprising the composite electrolyte membrane according to any one of claims 1 to 7.

10. A solid polymer electrolyte fuel cell comprising the composite electrolyte membrane according to any one of claims 1 to 7.

11. 8. A fluorine-containing polymer porous substrate for use in the composite electrolyte membrane according to claim 1, which is capable of being impregnated with an aprotic polar solvent but is not impregnated with water.

12. The fluorine-containing polymeric porous substrate according to claim 11, which contains at least a fluorine-based surfactant or polyvinylidene fluoride.

13. The fluorine-containing polymer porous substrate according to claim 12, wherein the weight of the fluorine-based surfactant or polyvinylidene fluoride is 20 mass % or less of the fluorine-containing polymer porous substrate.

14. Step 1: impregnating a fluorine-containing polymeric porous substrate with a solution containing at least a fluorine-based surfactant or polyvinylidene fluoride, and removing the solvent; Step 2: impregnating the fluorine-containing polymer porous substrate with the coating obtained in step 1 with a hydrocarbon-based polymer electrolyte solution, and removing the solvent; The method for producing a composite electrolyte membrane according to any one of claims 1 to 7, comprising the steps of:

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