JP2007042573A - POLYMER ELECTROLYTE MEMBRANE FOR SOLID POLYMER FUEL CELL, MEMBRANE-ELECTRODE ASSEMBLY AND FUEL CELL - Google Patents

Abstract

Provided are a polymer electrolyte membrane for a polymer electrolyte fuel cell that is economical, environmentally friendly and excellent in moldability and oxidation stability, and a membrane-electrode assembly and a polymer electrolyte fuel cell using the polymer electrolyte membrane. .
A block copolymer comprising a polymer block (A) having an aromatic vinyl compound unit in which α-carbon is a quaternary carbon as a main repeating unit and a flexible polymer block (B) as constituents. A polymer electrolyte membrane for a polymer electrolyte fuel cell, wherein the polymer block (A) has a monovalent anion conductive group or a polyvalent anion conductive group is a polymer block (A). The polymer electrolyte membrane is bonded in a form that crosslinks and / or a polyvalent anion conductive group is bonded in a form that crosslinks the aromatic vinyl compound units in the polymer block (A). And membrane-electrode assemblies and polymer electrolyte fuel cells.

Description

  The present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell, a membrane-electrode assembly using the electrolyte membrane, and a polymer electrolyte fuel cell.

  In recent years, fuel cell technology has been counted as one of the pillars of these new energy technologies as a fundamental solution to energy and environmental problems, and as a central energy conversion system in the future hydrogen energy era. In particular, polymer electrolyte fuel cells (PEFCs) are used for stationary power sources that use both electric power and heat, as well as power sources for electric vehicles and portable devices, from the viewpoint of miniaturization and weight reduction. Application to other power supply devices is under consideration.

  A polymer electrolyte fuel cell is generally configured as follows. First, catalyst layers containing carbon powder carrying a white metal catalyst and a cation conductive binder made of a polymer electrolyte are respectively formed on both sides of a polymer electrolyte membrane having proton conductivity. A gas diffusion layer, which is a porous material through which fuel gas and oxidant gas are passed, is formed outside each catalyst layer. Carbon paper, carbon cloth, or the like is used as the gas diffusion layer. A structure in which the catalyst layer and the gas diffusion layer are integrated is called a gas diffusion electrode, and a structure in which a pair of gas diffusion electrodes is bonded to the electrolyte membrane so that the catalyst layer faces the electrolyte membrane is a membrane-electrode assembly ( MEA (Membrane Electrode Assembly). On both sides of this membrane-electrode assembly, separators having electrical conductivity and airtightness are disposed. A gas flow path for supplying a fuel gas or an oxidant gas (for example, air) to the electrode surface is formed in a contact portion of the membrane-electrode assembly and the separator or in the separator. Electric power is generated by supplying a fuel gas such as hydrogen or methanol to one electrode (fuel electrode) and an oxidant gas containing oxygen such as air to the other electrode (oxygen electrode). That is, at the fuel electrode, the fuel is ionized to produce protons and electrons, the protons pass through the electrolyte membrane, the electrons travel through an external electric circuit formed by connecting both electrodes, and are sent to the oxygen electrode, Water is produced by the reaction. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

  For such a proton exchange type fuel cell, an anion exchange type fuel cell using an anion conductive membrane and an anion conductive binder (anion is usually a hydroxide ion) has been studied. An anion exchange fuel cell is known to reduce overvoltage at the oxygen electrode, and is expected to improve energy efficiency. In addition, when methanol is used as the fuel, it is said that methanol crossover in which methanol permeates the electrolyte membrane between the electrodes is reduced. The structure of the polymer electrolyte fuel cell in this case is basically the same as that of the proton exchange type fuel cell except that an anion conductive membrane and an anion conductive binder are used instead of the proton conductive membrane and the proton conductive binder. Similarly, the mechanism of electric energy generation is that oxygen, water, and electrons react at the oxygen electrode to generate hydroxide ions, and the hydroxide ions react with hydrogen at the fuel electrode through the anion conductive membrane. Thus, water and electrons are generated, and the electrons move through an external electric circuit formed by connecting both electrodes and are sent to the oxygen electrode, and react with oxygen and water again to generate hydroxide ions. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

  As a polymer electrolyte membrane used in a proton exchange type fuel cell, Nafion (registered trademark of Nafion, DuPont), which is a perfluorosulfonic acid polymer, is generally used because it is chemically stable. It has been. However, since Nafion is a fluorine-based polymer, it is very expensive. Further, Nafion has a problem that when methanol is used as a fuel, a phenomenon (methanol crossover) in which methanol permeates the electrolyte membrane from one electrode side to the other electrode side occurs. In addition, the fluorine-containing polymer contains fluorine, and environmental considerations are required during synthesis and disposal.

  From such a background, attempts have been made to develop a cation conductive polymer electrolyte membrane based on a non-fluorine polymer. For example, there is an example in which a polystyrene sulfonic acid polymer electrolyte membrane is used in a solid polymer fuel cell developed by General Electric in the United States in the 1950s. However, since there was not sufficient stability, sufficient battery life could not be obtained.

Moreover, an electrolyte membrane from a sulfonated aromatic polyether ketone sulfonate has been proposed (Patent Document 1).
Further, a structure in which a polystyrene block is made into a cation conductive channel by sulfonated polystyrene block of a block copolymer composed of styrene and a rubber component has been proposed. For example, as a cheap, mechanically and chemically stable polymer electrolyte membrane, a cation conductive membrane made of a sulfonated product of SEBS (polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer) is proposed. (Patent Document 2).
Further, there has been proposed a cation conductive membrane made of a sulfonated product of SiBuS (abbreviation of polystyrene-polyisobutylene-polystyrene triblock copolymer) having an isobutylene skeleton having excellent chemical stability as a rubber component (Patent Document 3). .

On the other hand, an anion conductive polymer electrolyte membrane used in an anion exchange type fuel cell has been proposed in which a monomer having an anion exchange group is subjected to radiation graft polymerization on a base material made of a fluorine-containing polymer (patent) Reference 4).
Moreover, as an anion conductive polymer electrolyte membrane, an electrolyte membrane obtained by forming a resin obtained by aminating a chloromethylated product of an aromatic polysulfone-polythioethersulfone copolymer has been proposed (Patent Document 5).
In addition, an anion exchanger made by introducing a quaternary ammonium group into a copolymer consisting of a polystyrene block and a polyolefin block has been proposed as an anion conductive polymer electrolyte membrane (Patent Document 6), and the polystyrene block and the polyolefin block. There has been proposed an anion exchanger in which copolymers made of these are bonded with a polyvalent amine (Patent Document 7).

JP-A-6-93114 Japanese National Patent Publication No. 10-503788 Japanese Patent Laid-Open No. 2001-210336 JP 2000-331693 A Japanese Patent Laid-Open No. 11-273695 Japanese Patent No. 2735693 Japanese Patent No. 2996752

  However, regarding the conventional cation conductive polymer electrolyte membrane, the sulfonated aromatic polyether ketone described in Patent Document 1 does not have sufficient cation conductivity, so that the performance as a fuel cell is not sufficient. . In addition, if the amount of sulfonation is increased in order to increase the cation conductivity, the membrane becomes brittle and the handling becomes very difficult. In addition, as a result of our actual tests, the sulfonated product of SEBS (polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer) described in Patent Document 2 is clearly insufficient in radical resistance. It became. This indicates that when this membrane is used in a fuel cell, the operable time is limited. In addition, regarding Patent Document 3, it is shown in Patent Document 3 that sulfonated SiBuS has higher chemical stability than sulfonated SEBS proposed in Patent Document 2. The amount of ion exchange after the Fenton reaction, which is an index of mechanical stability, has been reduced to about ½, and the chemical stability is not necessarily sufficient.

On the other hand, regarding a conventional anion conductive polymer electrolyte membrane, the fluorine-containing polymer electrolyte membrane described in Patent Document 4 has the same drawbacks as Nafion. In addition, the electrolyte membrane derived from the aromatic polysulfone-polythioether sulfone copolymer described in Patent Document 5 has a high affinity with water, and due to moisture contained in the reaction gas during power generation and generated water of the oxygen electrode, There is a problem in that the deterioration of the electrolyte membrane itself proceeds and a sufficient operation time cannot be secured. Further, the electrolyte membrane derived from the copolymer composed of the polystyrene block and the polyolefin block described in Patent Document 6 and Patent Document 7 is not sufficient in oxidation stability. Thus, it is economical and highly durable and improved. In fact, no polymer electrolyte membrane for solid polymer fuel cells has been proposed.

  An object of the present invention is to provide a polymer electrolyte membrane for a polymer electrolyte fuel cell that is economical, environmentally friendly, excellent in moldability, excellent in oxidation stability and consequently in durability, and a membrane using the electrolyte membrane- An electrode assembly and a polymer electrolyte fuel cell are provided.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polymer block (A) having a repeating unit of an aromatic vinyl compound whose α-carbon is a quaternary carbon and a flexible polymer It was found that a block copolymer comprising a block (B) as a constituent component and an anion conductive group bonded to the polymer block (A) satisfies the above object as a polymer electrolyte membrane for a solid polymer fuel cell. Completed the invention.

  That is, the present invention relates to a block copolymer composed of a polymer block (A) whose main repeating unit is an aromatic vinyl compound unit whose α-carbon is a quaternary carbon and a flexible polymer block (B). A polymer electrolyte membrane for a polymer electrolyte fuel cell containing a polymer, wherein the polymer block (A) has a monovalent anion conductive group or a polyvalent anion conductive group is a polymer block (A ) Which are bonded in a form that crosslinks each other and / or in which a polyvalent anion conductive group is bonded in a form that crosslinks the aromatic vinyl compound units in the polymer block (A). The present invention relates to an electrolyte membrane.

  In the block copolymer, the polymer block (A) and the polymer block (B) undergo microphase separation, and the polymer block (A) and the polymer block (B) are aggregated. In addition, since the polymer block (A) has an anion conductive group, a continuous phase (ion channel) is formed by the assembly of the polymer blocks (A) and becomes a passage for anions (usually hydroxide ions). Further, the presence of the polymer block (B) makes the block copolymer elastic and flexible as a whole, and formability (assembly property, bonding property) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. Performance, tightenability, etc.). The flexible polymer block (B) is composed of an alkene unit or a conjugated diene unit.

  The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon includes an aromatic vinyl compound unit in which the hydrogen atom bonded to the α-position carbon atom is substituted with an alkyl group, a halogenated alkyl group or a phenyl group. To do.

The anion conductive group is bonded to the polymer block (A), which is necessary for improving the oxidation stability.
Each anion-conducting group forms a salt with an ammonium group which may be substituted with a C1-C8 alkyl group, a methyl group or an ethyl group bonded to a nitrogen atom, or an acid with a counter ion. Pyridyl group, imidazolium group having methyl or ethyl group bonded to nitrogen atom, imidazolyl group forming salt with acid, phosphonium group optionally substituted with methyl group or ethyl group, hydrogen bonded to nitrogen atom A monovalent or divalent group in which a bond is derived from at least one of two nitrogen atoms of ethylenediamine optionally substituted with a methyl group or an ethyl group, and a hydrogen atom bonded to the nitrogen atom is a methyl group or At least two nitrogen atoms of tri-hexamethylenediamine optionally substituted with an ethyl group A bond is drawn from at least one of two nitrogen atoms of a monovalent or divalent group in which a bond is drawn from one or a methylenediamine in which a hydrogen atom bonded to a nitrogen atom is substituted with a methyl group or an ethyl group. Bonded from at least one of the three nitrogen atoms of diethylene (or bis (trimethylene)) triamine in which the hydrogen atom bonded to the nitrogen atom may be substituted with a methyl group or an ethyl group Includes monovalent, divalent or trivalent groups that are available.

  The present invention also relates to a membrane-electrode assembly and a fuel cell using the above electrolyte membrane.

  The polymer electrolyte membrane, membrane-electrode assembly and solid polymer fuel cell of the present invention are economical, environmentally friendly, excellent in oxidation stability and durability, and sufficiently function even under high temperature conditions. . The polymer electrolyte membrane of the present invention is also excellent in moldability.

  Hereinafter, the present invention will be described in detail. The block copolymer constituting the polymer electrolyte membrane of the present invention has an aromatic vinyl compound unit in which α-carbon is a quaternary carbon as a main repeating unit, and at least one anion conductive group is (co). The polymer block (A) having is a constituent component.

  The aromatic vinyl compound in which the α-carbon is a quaternary carbon has an alkyl group (a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-containing hydrogen atom bonded to the α-carbon atom). Aromatic vinyl substituted with a butyl group, isobutyl group or tert-butyl group), a halogenated alkyl group having 1 to 4 carbon atoms (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) or a phenyl group. It is preferable that it is a system compound. Examples of the aromatic vinyl compound serving as a skeleton include styrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, and vinyl pyridine. The hydrogen atom bonded to the aromatic ring of these aromatic vinyl compounds may be substituted with 1 to 3 substituents, and each independently represents an alkyl group having 1 to 4 carbon atoms (methyl group, Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group or tert-butyl group), C1-C4 halogenated alkyl group (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) ) And the like. Specific examples of the aromatic vinyl compound in which the α-carbon is a quaternary carbon include α-methylstyrene. Aromatic vinyl compounds in which the α-carbon is a quaternary carbon may be used alone or in combination of two or more. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization.

  The polymer block (A) may contain one or more other monomer units as long as the effects of the present invention are not impaired. Examples of such other monomers include aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group, isopropyl group, n- Styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, etc.) substituted with a butyl group, an isobutyl group or a tert-butyl group], a conjugated diene having 4 to 8 carbon atoms (specific examples are described in the description of the polymer block (B) described later) The same as in the description of the polymer block (B) described later), (meth) acrylate (methyl (meth) acrylate, ethyl (meth) acrylate) Butyl (meth) acrylate), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl ester Ether (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. The copolymerization form of the aromatic vinyl compound in which the α-carbon is a quaternary carbon and the other monomer needs to be random copolymerization.

  The aromatic vinyl-based compound unit in which the α-carbon in the polymer block (A) is a quaternary carbon is used in order to give sufficient oxidation stability to the finally obtained polymer electrolyte membrane. It is preferable to occupy 50% by mass or more of A), more preferably 70% by mass or more, and even more preferably 90% by mass or more.

  The molecular weight of the polymer block (A) is appropriately selected depending on the properties of the polymer electrolyte membrane, the required performance, other polymer components, and the like. When the molecular weight is large, the mechanical properties such as the tensile strength of the polymer electrolyte membrane tend to be high, and when the molecular weight is small, the electric resistance of the polymer electrolyte membrane tends to be small, and the molecular weight is appropriately adjusted according to the required performance. It is important to choose. The number average molecular weight in terms of polystyrene is usually preferably selected from 100 to 1,000,000, more preferably from 1,000 to 100,000.

  The block copolymer used in the polymer electrolyte membrane of the present invention has a flexible polymer block (B) in addition to the polymer block (A). The polymer block (A) and the polymer block (B) undergo a microphase separation, and the polymer block (A) and the polymer block (B) have a property of gathering together, and the polymer block (A ) Has an anion-conducting group (co), so that an ion channel as a continuous phase is formed by the assembly of the polymer blocks (A) and becomes a passage for anions (usually hydroxide ions). By having such a polymer block (B), the block copolymer becomes elastic and flexible as a whole, and formability (assembly property, bondability) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. , Tightenability, etc.). The flexible polymer block (B) here is a so-called rubber-like polymer block having a glass transition point or softening point of 50 ° C. or lower, preferably 20 ° C. or lower, more preferably 10 ° C. or lower.

  Monomers that can constitute the repeating unit constituting the flexible polymer block (B) include alkenes having 2 to 8 carbon atoms, cycloalkenes having 5 to 8 carbon atoms, and vinylcycloalkenes having 7 to 10 carbon atoms. , A conjugated diene having 4 to 8 carbon atoms and a conjugated cycloalkadiene having 5 to 8 carbon atoms, a vinyl cycloalkene having 7 to 10 carbon atoms in which part or all of the carbon-carbon double bond is hydrogenated, and carbon-carbon. A conjugated diene having 4 to 8 carbon atoms in which some or all of the double bonds are hydrogenated, a conjugated cycloalkadiene having 5 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated, ( (Meth) acrylic acid esters (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate), vinyl esters (vinyl acetate, vinyl propionate, butyrate) Vinyl, vinyl pivalate, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. These may be used alone or in combination. The form in the case of polymerizing (copolymerizing) two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization. Further, when the monomer to be used for (co) polymerization has two carbon-carbon double bonds, any of them may be used for the polymerization, and in the case of a conjugated diene, it is a 1,2-bond. 1,4-bonds may be used, and the ratio of 1,2-bonds to 1,4-bonds is not particularly limited as long as the glass transition point or softening point is 50 ° C. or lower.

When the repeating unit constituting the polymer block (B) has a carbon-carbon double bond as in the case of vinylcycloalkene, conjugated diene or conjugated cycloalkadiene, the polymer of the present invention From the viewpoint of improving the power generation performance of the membrane-electrode assembly using the electrolyte membrane and improving the heat deterioration resistance, the carbon-carbon double bond is preferably hydrogenated at 30 mol% or more, and 50 mol%. The above is more preferably hydrogenated, and more preferably 80 mol% or more is hydrogenated. The hydrogenation rate of the carbon-carbon double bond can be calculated by a commonly used method, for example, iodine value measurement method, ¹ H-NMR measurement or the like.

  The polymer block (B) is an alkene having 2 to 8 carbon atoms from the viewpoint of giving the resulting block copolymer elasticity and, in turn, good moldability in the production of a membrane-electrode assembly and a polymer electrolyte fuel cell. Unit, cycloalkene unit having 5 to 8 carbon atoms, vinylcycloalkene unit having 7 to 10 carbon atoms, conjugated diene unit having 4 to 8 carbon atoms, conjugated cycloalkadiene unit having 5 to 8 carbon atoms, carbon-carbon double 7 to 10 carbon cycloalkene units having some or all of the hydrogenated hydrogen atoms, 4 to 8 carbon conjugated diene units having some or all of the carbon-carbon double bonds hydrogenated, and carbon -A polymer block comprising at least one repeating unit selected from conjugated cycloalkadiene units having 5 to 8 carbon atoms in which some or all of the carbon double bonds are hydrogenated. Preferably, the alkene unit having 2 to 8 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and the conjugated diene unit having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated are selected. More preferably, the polymer block is composed of at least one repeating unit, and the alkene unit having 2 to 6 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and a part or all of the carbon-carbon double bonds are included. It is even more preferable that the polymer block comprises at least one repeating unit selected from hydrogenated conjugated diene units having 4 to 8 carbon atoms. In the above, an isobutene unit is most preferable as an alkene unit having 2 to 6 carbon atoms, and a 1,3-butadiene unit and / or an isoprene unit are most preferable as a carbon number conjugated diene unit.

  As the alkene having 2 to 8 carbon atoms, ethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 1-heptene, 2-heptene, 1 -Octene, 2-octene and the like, and cyclopentene having 5 to 8 carbon atoms include cyclopentene, cyclohexene, cycloheptene and cyclooctene, and vinylcycloalkene having 7 to 10 carbon atoms as vinylcyclopentene, vinylcyclohexene, Examples thereof include vinylcycloheptene and vinylcyclooctene. Examples of the conjugated diene having 4 to 8 carbon atoms include 1,3-butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2 , 3-Dimethyl-1,3-butadiene, 2-ethyl-1,3-butyl Diene, 1,3-heptadiene, 1,4-heptadiene, 3,5-heptadiene and the like, cyclopentadiene, 1,3-cyclohexadiene, and the like as a conjugated cycloalkadiene having 5 to 8 carbon atoms.

  In addition to the above monomers, the polymer block (B) may contain other monomers such as styrene and vinyl as long as the purpose of the polymer block (B) that gives elasticity to the block copolymer is not impaired. Aromatic vinyl compounds such as naphthalene; halogen-containing vinyl compounds such as vinyl chloride may be included. In this case, the copolymerization form of the monomer and other monomer needs to be random copolymerization. The amount of such other monomer used is preferably less than 50% by weight, more preferably less than 30% by weight, based on the total of the above monomers and other monomers. It is still more preferable that it is less than mass%.

Although the structure of the block copolymer which has a polymer block (A) and a polymer block (B) as a structural component is not specifically limited, ABA type | mold triblock copolymer, BAB, as an example Type triblock copolymer, ABA type triblock copolymer or a mixture of BAB type triblock copolymer and AB type diblock copolymer,
A-B-A-B type tetrablock copolymer, A-B-A-B-A type pentablock copolymer, B-A-B-A-B type pentablock copolymer, (A-B ) NX type star copolymer (X represents a coupling agent residue), (BA) nX type star copolymer (X represents a coupling agent residue), and the like. These block copolymers may be used alone or in combination of two or more.

  The mass ratio of the polymer block (A) and the polymer block (B) is preferably 95: 5 to 5:95, more preferably 90:10 to 10:90, and 50:50 to 10 : 90 is even more preferable. When this mass ratio is 95: 5 to 5:95, it is advantageous for the ion channel formed by the polymer block (A) to become a continuous phase by microphase separation, and it is practically sufficient anion conduction. In addition, the ratio of the polymer block (B) that is hydrophobic is appropriate, and excellent water resistance is exhibited.

The block copolymer constituting the polymer electrolyte membrane of the present invention may contain another polymer block (C) different from the polymer block (A) and the polymer block (B).
The polymer block (C) is not particularly limited as long as it is a component that undergoes microphase separation from the polymer block (A) and the polymer block (B). Examples of the monomer constituting the polymer block (C) include aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group). , Styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, etc. substituted with isopropyl group, n-butyl group, isobutyl group or tert-butyl group], conjugated dienes having 4 to 8 carbon atoms (specific examples are polymer blocks described later) (As in the description of (B)), alkenes having 2 to 8 carbon atoms (specific examples are the same as in the description of the polymer block (B) described above), (meth) acrylate (methyl (meth) acrylate) , Ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, pivalic acid) Sulfonyl, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like.

When the polymer block (C) is microphase-separated from the polymer block (A) and the polymer block (B) and does not substantially contain an ionic group and has a function of acting as a constrained phase, this is required. The polymer electrolyte membrane of the present invention having a polymer block (C) tends to have excellent shape stability, durability, and mechanical properties under wet conditions. Preferable examples of the monomer constituting the polymer block (C) in this case include the aromatic vinyl compounds described above. Moreover, the above-mentioned function can be imparted by making the polymer block (C) crystalline.

  When the above-mentioned function depends on the aromatic vinyl compound unit, the aromatic vinyl compound unit in the polymer block (C) preferably occupies 50% by mass or more of the polymer block (C), and 70% by mass. %, More preferably 90% by mass or more. From the same viewpoint as described above, it is desirable that units other than the aromatic vinyl compound unit that can be included in the polymer block (C) are randomly polymerized.

  As a particularly preferable example from the viewpoint of causing the polymer block (C) to microphase-separate from the polymer block (A) and the polymer block (B) and to function as a constrained phase, a polystyrene block; a poly p-methylstyrene block, a poly Polystyrene block such as p- (t-butyl) styrene block; copolymer block composed of two or more kinds of styrene, p-methylstyrene and p- (t-butyl) styrene of any mutual ratio; crystalline water Examples include 1,4-polybutadiene block; crystalline polyethylene block; crystalline polypropylene block and the like.

  As a form in case the block copolymer used by this invention contains a polymer block (C), an ABC type triblock copolymer, an ABCA type tetrablock copolymer, A -B-A-C type tetrablock copolymer, B-A-B-C type tetrablock copolymer, A-B-C-B type tetrablock copolymer, C-A-B-A-C Type pentablock copolymer, CBACBBC type pentablock copolymer, ACCBCA type pentablock copolymer, ACCBAA type pentablock copolymer Block copolymer, A-B-C-A-B type pentablock copolymer, A-B-C-A-C type pentablock copolymer, A-B-C-B-C type pentablock copolymer Polymer, ABACBBC type pentablock copolymer, ABBACB type pentablock copolymer B-A-B-A-C type pentablock copolymer, B-A-B-C-A type pentablock copolymer, B-A-B-C-B type pentablock copolymer, etc. are mentioned. It is done.

  When the block copolymer constituting the polymer electrolyte membrane of the present invention contains a polymer block (C), the proportion of the polymer block (C) in the block copolymer is preferably 40% by mass or less, It is more preferably 35% by mass or less, and further preferably 30% by mass or less.

  Although the number average molecular weight of the block copolymer used in the present invention in a state where the anion conductive group is not introduced is not particularly limited, the number average molecular weight in terms of polystyrene is usually 10,000 to 2,000,000. Preferably, 15,000 to 1,000,000 is more preferable, and 20,000 to 500,000 is even more preferable.

  The block copolymer constituting the polymer electrolyte membrane of the present invention needs to have an anion conductive group in the polymer block (A). Examples of the anion when referring to anion conductivity in the present invention include hydroxide ions. The anion conductive group is not particularly limited as long as the membrane-electrode assembly produced using the polymer electrolyte membrane can express a sufficient anion conductivity. Can be mentioned. The introduction position of the anion conductive group is the polymer block (A) because it is particularly effective for improving the oxidative stability of the entire block copolymer.

In the above formula, R ^{1 to} R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ^{4 to} R ⁹ and R ¹¹ each independently represents a hydrogen atom, a methyl group or an ethyl group, R ¹⁰ represents a methyl group or an ethyl group, X ⁻ represents a hydroxide ion or an acid anion, m represents an integer of 2 to 6, and n represents 2 or 3. In the above, the alkyl group having 1 to 8 carbon atoms is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, 2-ethylhexyl. Groups and the like. There is no particular limitation on the anion, for example, a halogen ion (particularly chloride ^{_{ion), 1 / 2SO 4 2-,}} HSO 4 -, may be mentioned p- toluenesulfonate anion.
Moreover, in the above, when R < ¹ > -R < ⁹ > and R < ¹¹ > are a methyl group or an ethyl group and X < ^- > is a hydroxide ion, since high anion conductivity can be expressed, it is preferable. R ^{1 to} R ¹¹ are more preferably a methyl group.

  There are no particular restrictions on the position at which the anion conductive group is introduced into the polymer block (A), and even if it is introduced into an aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the other units described above It may be introduced into the body unit, but is most preferably introduced into the aromatic ring of the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon from the viewpoint of improving the oxidation stability. At this time, when the introduced anion conductive group is a monovalent group such as (1) to (8) in the above formula, the group is bonded to the polymer block (A). Is a polyvalent group such as (9) to (13) in the above formula, the group is bonded in a form that crosslinks the polymer blocks (A), or the polymer block In (A), the aromatic vinyl compound units are bonded in a form of crosslinking.

  The amount of anion-conducting group introduced is appropriately selected depending on the required performance of the resulting block copolymer, etc., but exhibits sufficient anion conductivity for use as a polymer electrolyte membrane for a polymer electrolyte fuel cell In general, the amount is preferably such that the ion exchange capacity of the block copolymer is 0.30 meq / g or more, and more preferably 0.40 meq / g or more. . The upper limit of the ion exchange capacity of the block copolymer is preferably 3.0 meq / g or less because if the ion exchange capacity is too large, the hydrophilicity tends to increase and the water resistance becomes insufficient.

  The production method of the block copolymer used in the present invention is roughly classified into the following two methods. That is, (1) a method in which a block copolymer having no anion conductive group is first prepared and then anion conductive groups are bonded, and (2) block copolymerization using a monomer having an anion conductive group. This is a method for producing a coalescence.

First, the first manufacturing method will be described.
Depending on the type, molecular weight, etc. of the monomer constituting the polymer block (A) or (B), the production method of the polymer block (A) or (B) can be a radical polymerization method, an anionic polymerization method, a cationic polymerization method, The method is appropriately selected from the coordination polymerization method and the like, but from the viewpoint of industrial ease, the radical polymerization method or the anion polymerization method is preferably selected. In particular, the so-called living polymerization method is preferable from the viewpoint of molecular weight, molecular weight distribution, polymer structure, ease of bonding with the polymer block (B) or the polymer block (A) made of flexible components, and specifically living A radical polymerization method, a living cationic polymerization method or a living anion polymerization method is preferred.

  Specific examples of the production method include a method for producing a block copolymer comprising a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of polyconjugated diene, and poly (α A method for producing a block copolymer comprising a polymer block (A) composed of -methylstyrene) and a polymer block (B) composed of polyisobutene will be described. In this case, it is preferable to produce by a living anionic polymerization method or a living cationic polymerization method from the viewpoint of industrial ease, molecular weight, molecular weight distribution, ease of bonding between the polymer block (A) and the polymer block (B), etc. The following specific synthesis examples are shown.

(1) A method of obtaining an ABA type block copolymer by sequentially polymerizing α-methylstyrene under a temperature condition of −78 ° C. after conjugated diene polymerization using a dianionic initiator in a tetrahydrofuran solvent (Macromolecules , (1969), 2 (5), 453-458),
(2) After bulk polymerization of α-methylstyrene using an anionic initiator, conjugated dienes are sequentially polymerized, and then a coupling reaction is performed with a coupling agent such as tetrachlorosilane. (AB) nX Method for obtaining a mold block copolymer (Kautsch. Gummi,
Kunstst. , (1984), 37 (5), 377-379; Po
lym. Bull. , (1984), 12, 71-77),
(3) An organic lithium compound in a nonpolar solvent is used as an initiator, and a concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass. A polymer obtained by polymerizing α-methylstyrene, a conjugated diene is polymerized to the resulting living polymer, and then a coupling agent is added to obtain an ABA block copolymer.

(4) A concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass using an organolithium compound in a nonpolar solvent as an initiator. Α-methylstyrene is polymerized, the resulting living polymer is polymerized with a conjugated diene, and the resulting α-methylstyrene polymer block and conjugated diene polymer block are formed into a polymer block (C ) To obtain an ABC type block copolymer,
(5) Cationic polymerization of isobutene in the presence of Lewis acid using a bifunctional organic halogen compound at -78 ° C in a mixed solvent of halogenated hydrocarbon and hydrocarbon, followed by addition of diphenylethylene, Further, after adding Lewis acid, α-methylstyrene is polymerized to obtain an ABA type block copolymer (Macromolecules, (1995), 28, 4893-4898), and (6) halogenated carbonization. In a mixed solvent of hydrogen and hydrocarbon at −78 ° C., using a monofunctional organic halogen compound, α-methylstyrene is polymerized in the presence of Lewis acid, and then Lewis acid is further added to polymerize isobutene. After that, a coupling reaction is performed with a coupling agent such as 2,2-bis- [4- (1-phenylethenyl) phenyl] propane, and the ABA block Method for obtaining a polymer (Polym.
Bull. , (2000), 45, 121-128)

When producing a block copolymer comprising as a component a polymer block (A) comprising poly (α-methylstyrene) and a polymer block (B) comprising a conjugated diene compound, a specific method for producing the block copolymer Among these, the methods (3) and (4) are preferable, and the method (3) is particularly preferable.
When producing a block copolymer comprising a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of isobutene as a component, a known method shown in (5) or (6) Is adopted.

  Next, a method for introducing an anion conductive group into the obtained block copolymer will be described. The introduction of the anion conductive group can be performed by a known method. For example, the resulting block copolymer is chloromethylated, then reacted with an amine or phosphine, and further, chlorine ions are replaced with hydroxide ions or other acid anions as necessary.

  The chloromethylation method is not particularly limited, and a known method can be used. For example, a method of adding a chloromethylating agent and a catalyst to a solution or suspension of the block copolymer in an organic solvent and chloromethylating can be used. Examples of the organic solvent include halogenated hydrocarbons such as chloroform and dichloroethane, but are not limited thereto. As the chloromethylating agent, chloromethyl ethyl ether or hydrochloric acid-paraformaldehyde can be used, and as the catalyst, tin chloride, zinc chloride or the like can be used.

The method for reacting the chloromethylated block copolymer with amine or phosphine is not particularly limited, and a known method can be used. For example, a solution or suspension of the obtained chloromethylated block copolymer in an organic solvent, or a film formed by a known method from such a solution or suspension, amine or phosphine is used as it is or as necessary. A method of allowing the reaction to proceed by adding it as a solution in an organic solvent can be used. Examples of the organic solvent for preparing a solution or suspension in the organic solvent include methanol and acetone, but are not limited thereto.
The amine and phosphine are not particularly limited, but those shown below can be preferably used.

In the above ^{formula, R 1 ~R 3, R 6} ~R 11, m and n are defined as above. That is, R ^{1 to} R ³ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ^{6 to} R ^{9 and} R ¹¹ are each independently a hydrogen atom, a methyl group, or an ethyl group, and R ¹⁰ Is a methyl group or an ethyl group, m is an integer of 2 to 6, and n is 2 or 3. R ^{1 to} R ³ , R ^{6 to} R ^{9 and} R ¹¹ are preferably each independently a methyl group or an ethyl group, and R ^{1 to} R ^{3 and} R ^{6 to} R ¹¹ are more preferably a methyl group.

Reaction of the chloromethylated block copolymer with an amine or phosphine introduces an anion-conducting group as already mentioned. Here, when monoamine (1) or phosphine (2) is used, an anion conductive group is introduced into the polymer block (A), but diamine (3) or (4), triamine (5), etc. When the polyvalent amine is used, it may be introduced as a monovalent anion conductive group in the polymer block (A), or may be introduced as a polyvalent anion conductive group. It is considered that the aromatic vinyl compound units may be crosslinked with each other in the polymer block (A).
^Further, and when R 1 to R ³ is an alkyl group having 1 to 8 carbon ^atoms, when R 6 to R ⁹ and ^{R 11} is a methyl group or an ethyl group, anion-conducting group is a quaternary ammonium Group or quaternary phosphonium group.

  Since the anion conductive group introduced above has a chlorine ion as an acid anion, it is converted into a hydroxide ion or another acid anion, preferably a hydroxide ion, if necessary. A method for converting to other ions is not particularly limited, and a known method can be used. For example, when converting to hydroxide ions, a method of immersing a block copolymer into which an anion conductive group is introduced in an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution can be exemplified.

As described above, the amount of the anion conductive group introduced is preferably such that the ion exchange capacity of the block copolymer is 0.30 meq / g or more, such that it is 0.40 meq / g or more. More preferably, it is an amount. Thereby, practical anion conducting performance can be obtained. The ion exchange capacity of the block copolymer into which an anion conductive group is introduced should be measured using an analytical means such as acid value titration method, infrared spectroscopic spectrum measurement, nuclear magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement. Can do.

The second production method of the block copolymer used in the present invention is a method for producing a block copolymer using at least one monomer having an anion conductive group.
As the monomer having an anion conductive group, the following groups can be used.

In formula, R < ¹² >, R <^14> and R < ¹⁶ > represent a hydrogen atom, a C1-C4 alkyl group, a C1-C4 halogenated alkyl group, or a phenyl group, and R < ¹³ > has a hydrogen atom or C1-C1. 8 represents an alkyl group, R ¹⁵ and R ¹⁷ represent a hydrogen atom, a methyl group or an ethyl group, and X ⁻ represents a hydroxide ion or an acid anion. In the above, the alkyl group having 1 to 4 carbon atoms is methyl group, ethyl group, n-propyl group, isopropyl group, isobutyl group, etc., and the halogenated alkyl group having 1 to 4 carbon atoms is chloromethyl group, chloroethyl group, A chloropropyl group etc. are mentioned. Moreover, as a C1-C8 alkyl group, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, 2-ethylhexyl group Etc. The acid anion is not particularly limited, for example, a halogen ion (particularly chloride ^{_{ion), 1 / 2SO 4 2-,}} HSO 4 -, may be mentioned p- toluenesulfonate anion. R ^{12 to} R ¹⁷ are preferably a methyl group or an ethyl group, and more preferably a methyl group. In the above formula (2), the —C (R ¹⁴ ) ═CH ₂ group is preferably bonded to the 4-position or the 2-position.
Among the monomers having an anion conductive group described above, a monomer represented by the formula (1) in which R ¹³ is a methyl group or an ethyl group, particularly a methyl group, is particularly preferable.

  In addition to the block copolymer used in the present invention, the polymer electrolyte membrane of the present invention may contain a softening agent as necessary within a range not impairing the effects of the present invention. Softeners include petroleum-based softeners such as paraffinic, naphthenic or aroma-based process oils, paraffin, vegetable oil-based softeners, plasticizers, etc., and these may be used alone or in combination of two or more. it can.

  The polymer electrolyte membrane of the present invention is further provided with various additives, for example, a phenol-based stabilizer, a sulfur-based stabilizer, a phosphorus-based stabilizer, and a light stabilizer, as long as the effects of the present invention are not impaired. , Antistatic agents, mold release agents, flame retardants, foaming agents, pigments, dyes, whitening agents, carbon fibers and the like may be used alone or in combination of two or more. Specific examples of the stabilizer include 2,6-di-t-butyl-p-cresol, pentaerystyryl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1 , 3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, octadecyl-3- (3,5-di-tert-butyl-4-hydroxy) Phenyl) propionate, triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy- 3,5-di-t-butylanilino) -1,3,5-triazine, 2,2, -thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propi Onate], N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrodinamamide), 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate-diethyl ester, tris -(3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate, 3,9-bis {2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy ] -1,1-dimethylethyl} -2,4,8,10-tetraoxaspiro [5,5] undecane and other phenolic stabilizers; pentaerythrityltetrakis (3-laurylthiopropionate), distearyl Sulfur such as 3,3′-thiodipropionate, dilauryl 3,3′-thiodipropionate, dimyristyl 3,3′-thiodipropionate Stabilizers: trisnonylphenyl phosphite, tris (2,4-di-t-butylphenyl) phosphite, diasteryl pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) ) Phosphorus stabilizers such as pentaerythritol diphosphite. These stabilizers may be used alone or in combination of two or more.

  The polymer electrolyte membrane of the present invention may further contain an inorganic filler, as necessary, as long as the effects of the present invention are not impaired. Specific examples of such inorganic fillers include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina.

  From the viewpoint of ion conductivity, the content of the block copolymer of the present invention in the polymer electrolyte membrane of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, and 90% by mass. % Or more is even more preferable.

  The polymer electrolyte membrane of the present invention preferably has a thickness of about 5 to 500 μm from the viewpoints of performance required as an electrolyte membrane for fuel cells, membrane strength, handling properties, and the like. When the film thickness is less than 5 μm, the mechanical strength of the film and the gas barrier property tend to be insufficient. On the other hand, when the film thickness is thicker than 500 μm, the electric resistance of the film increases and sufficient anion conductivity does not appear, so that the power generation characteristics of the battery tend to be lowered. The film thickness is more preferably 10 to 300 μm.

As the method for preparing the polymer electrolyte membrane of the present invention, any method can be adopted as long as it is a normal method for such preparation. For example, the block copolymer constituting the polymer electrolyte membrane of the present invention or the block can be used. The block copolymer is dissolved or suspended by mixing the copolymer and additives as described above with an appropriate solvent, and cast into a plate-like material such as glass, or coated using a coater or applicator. In addition, a method of obtaining an electrolyte membrane having a desired thickness by removing the solvent under appropriate conditions, a method of forming a film using a known method such as hot press molding, roll molding, extrusion molding, or the like may be used. it can.
Further, the same or different block copolymer solution may be newly applied on the obtained electrolyte membrane layer and dried to be laminated. Further, the same or different electrolyte membranes obtained as described above may be laminated by being pressure-bonded by hot roll molding or the like.

  The solvent used at this time is not particularly limited as long as it can prepare a solution having a viscosity capable of being cast or coated without destroying the structure of the block copolymer. Specifically, halogenated hydrocarbons such as methylene chloride, aromatic hydrocarbons such as toluene, xylene, and benzene, linear aliphatic hydrocarbons such as hexane and heptane, and cyclic aliphatic carbonization such as cyclohexane. Examples thereof include ethers such as hydrogen and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, isopropanol, butanol and isobutyl alcohol, or mixed solvents thereof. Depending on the configuration of the block copolymer, the molecular weight, the ion exchange capacity, etc., one or a combination of two or more can be appropriately selected from the solvents exemplified above and used.

  The solvent removal conditions can be arbitrarily selected as long as the solvent can be completely removed at a temperature below the temperature at which the anion conductive group of the block copolymer of the present invention is removed. In order to express desired physical properties, a plurality of temperatures may be arbitrarily combined, or a combination of ventilation and vacuum may be arbitrarily combined. Specifically, after preliminary drying for several hours under vacuum conditions of room temperature to 60 ° C., the solvent is removed under vacuum conditions of 100 ° C. or higher, preferably 100 to 120 ° C. for about 12 hours. However, the present invention is not limited to these examples.

  The obtained electrolyte membrane can be washed with distilled water or an organic solvent in which the membrane does not dissolve in order to remove low molecular compounds remaining in the membrane. In addition, as a pretreatment before washing, a method of immersing in a basic aqueous solution such as sodium hydroxide in order to convert the anion conductive group into a complete hydroxide type can be employed.

  Next, a membrane-electrode assembly using the polymer electrolyte membrane of the present invention will be described. The production of the membrane-electrode assembly is not particularly limited, and a known method can be applied. For example, a catalyst paste containing an anion conductive binder is applied on the gas diffusion layer by a printing method or a spray method and dried. To form a joined body of the catalyst layer and the gas diffusion layer, and then join the two pairs of joined bodies by hot pressing or the like on both sides of the polymer electrolyte membrane with the catalyst layer inside. There is a method in which a paste is applied to both sides of a polymer electrolyte membrane by a printing method or a spray method, dried to form a catalyst layer, and a gas diffusion layer is pressure-bonded to each catalyst layer by hot pressing or the like. As another production method, a solution or suspension containing an anion conductive binder is applied to both surfaces of the polymer electrolyte membrane and / or the catalyst layer surfaces of the two pairs of gas diffusion electrodes, and the electrolyte membrane and the catalyst layer surface are bonded together. There is a method of joining by thermocompression bonding. In this case, the solution or suspension may be applied to either the electrolyte membrane or the catalyst layer surface, or may be applied to both. As another manufacturing method, first, the catalyst paste is applied to a base film made of polytetrafluoroethylene (PTFE) and dried to form a catalyst layer, and then two pairs of base films on the base film are formed. The catalyst layer is transferred to both sides of the polymer electrolyte membrane by thermocompression bonding, the base film is peeled off to obtain a joined body of the electrolyte membrane and the catalyst layer, and the gas diffusion layer is crimped to each catalyst layer by hot pressing. There is a way. In these methods, these methods may be performed in a state in which the anion conductive group is converted to a salt such as chloride, and a treatment for returning to a hydroxide type by an alkali treatment after bonding may be performed.

  As the anion conductive binder constituting the membrane-electrode assembly, for example, polychloromethylstyrene is reacted with a tertiary amine to form a quaternary ammonium salt, and in the form of a hydroxide if necessary. Can be used. Moreover, you may produce an anion conductive binder from the block copolymer which comprises the polymer electrolyte membrane of this invention. In order to further enhance the adhesion between the electrolyte membrane and the gas diffusion electrode, it is preferable to use an anion conductive binder formed of the same material as the polymer electrolyte membrane.

  The constituent material of the catalyst layer of the membrane-electrode assembly is not particularly limited as the conductive material / catalyst support, and examples thereof include carbon materials. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and the like. These may be used alone or in combination of two or more. The catalyst metal may be any metal that promotes the oxidation reaction of fuel such as hydrogen and methanol and the reduction reaction of oxygen, such as platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, Cobalt, nickel, chromium, tungsten, manganese, palladium, etc., or alloys thereof, for example, platinum-ruthenium alloys are mentioned. Of these, platinum and platinum alloys are often used. The particle size of the metal serving as a catalyst is usually 10 to 300 angstroms. When these catalysts are supported on a conductive material / catalyst carrier such as carbon, the amount of catalyst used is small and advantageous in terms of cost. The catalyst layer may contain a water repellent as necessary. Examples of the water repellent include various thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene copolymer, and polyetheretherketone.

  The gas diffusion layer of the membrane-electrode assembly is made of a material having conductivity and gas permeability, and examples of such a material include porous materials made of carbon fibers such as carbon paper and carbon cloth. Moreover, in order to improve water repellency, this material may be subjected to water repellency treatment.

A polymer electrolyte fuel obtained by inserting the membrane-electrode assembly obtained by the above-described method between a conductive separator material that also serves as a gas supply flow path to the electrode and the electrode chamber separation. A battery is obtained. The membrane-electrode assembly of the present invention uses a pure hydrogen type using hydrogen as a fuel gas, a methanol reforming type using hydrogen obtained by reforming methanol, and hydrogen obtained by reforming natural gas. Natural gas reforming type, gasoline reforming type using hydrogen obtained by reforming gasoline, direct methanol type using methanol directly, etc. can be used as a membrane-electrode assembly for polymer electrolyte fuel cells. is there.
The fuel cell using the polymer electrolyte membrane of the present invention is excellent in oxidation stability, has little deterioration in power generation characteristics over time, and can be used stably for a long time.

EXAMPLES Hereinafter, although an Example, a comparative example, and a reference example are given and this invention is demonstrated further more concretely, this invention is not limited by these Examples.
Reference example 1
Production of block copolymer comprising poly α-methylstyrene (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) In the same manner as the previously reported method (WO 02/40611), A poly α-methylstyrene-b-polybutadiene-polyα-methylstyrene type triblock copolymer (hereinafter abbreviated as mSEBmS) was synthesized. The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained mSEBmS is 76000, the 1,4-bond amount determined from ¹ H-NMR measurement is 55%, and the content of α-methylstyrene unit is 30.0. It was mass%. Further, it was found by composition analysis by ¹ H-NMR spectrum measurement that α-methylstyrene was not substantially copolymerized in the polybutadiene block.
After preparing a cyclohexane solution of synthesized mSEBmS and charging it into a pressure-resistant vessel sufficiently purged with nitrogen, a hydrogenation reaction was performed at 80 ° C. for 5 hours in a hydrogen atmosphere using a Ni / Al Ziegler hydrogenation catalyst. To obtain a poly α-methylstyrene-b-hydrogenated polybutadiene-b-polyα-methylstyrene type triblock copolymer (hereinafter abbreviated as HmSEBmS). The hydrogenation proportion of the resulting HmSEBmS was calculated by ¹ H-NMR spectrum measurement, it was 99.6%.

Example 1
(1) Preparation of quaternary ammonium hydroxide-modified HmSEBmS membrane 100 g of the block copolymer (HmSEBmS) obtained in Reference Example 1 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour, and then nitrogen. After substitution, 650 ml of chloroform was added and dissolved by stirring at 35 ° C. for 2 hours. After dissolution, 135 ml of chloromethyl ethyl ether and 5.7 ml of tin tetrachloride were added and stirred at 35 ° C. for 9 hours. Next, the reaction solution was added to 4 L of methanol, and the precipitate was washed and dried to obtain chloromethylated HmSEBmS. The chloromethylation rate of chloromethylated HmSEBmS was 60.9 mol% of α-methylstyrene units from ¹ H-NMR analysis.
Next, chloromethylated HmSEBmS was dissolved in toluene, cast on a polytetrafluoroethylene sheet and sufficiently dried at room temperature to obtain a cast film having a thickness of 70 μm.
Next, the chloromethyl group was aminated by immersing the obtained cast film in a mixed solution of 30% trimethylamine aqueous solution and acetone in a volume ratio of 1: 1 at room temperature for 24 hours.
Finally, the aminated HmSEBmS membrane was immersed in a 0.5N-NaOH aqueous solution at room temperature for 5 hours for ion exchange to obtain a quaternary ammonium hydroxide-modified HmSEBmS membrane. The film thickness was 100 μm, and the ion exchange capacity was 1.30 meq / g in terms of the value obtained from ¹ H-NMR measurement.

(2) Production of a polymer electrolyte fuel cell unit cell Next, an electrode for a polymer electrolyte fuel cell was produced according to the following procedure. The Pt catalyst-supported carbon was mixed with the chloroform / isobutyl alcohol solution of quaternary ammonium hydroxide group-modified HmSEBmS obtained in (1) (chloroform: isobutyl alcohol = 7: 3.4% by mass) and dispersed uniformly. A paste was prepared. This paste was uniformly applied to one side of a water-repellent treated carbon paper and left for several hours to produce a carbon paper electrode. Both the amount of Pt supported on the produced electrode and the content of the quaternary ammonium hydroxide-modified HmSEBmS were 1.0 mg / cm ² . Next, the membrane (10 cm × 10 cm) produced in (1) is sandwiched between the two carbon paper electrodes (5 cm × 5 cm) produced in the above so that the membrane and the catalyst surface face each other, and the outside is covered with two heat resistant materials The membrane-electrode assembly was fabricated by sandwiching the film and two stainless steel plates in order and hot pressing (60 ° C., 80 kg / cm ² , 2 min).
The membrane-electrode assembly produced above (with the heat-resistant film and stainless steel plate removed) is sandwiched between two conductive separators that also serve as gas supply channels, and the outside of the membrane-electrode assembly is two sheets. An evaluation cell for a polymer electrolyte fuel cell was produced by sandwiching in turn between an electric plate and two clamping plates. In addition, a gasket was disposed between each membrane-electrode assembly and the separator in order to prevent gas leakage from a step corresponding to the thickness of the electrode.

Comparative Example 1
Preparation of Quaternary Ammonium Hydroxide-Modified SEBS Film 100 g of SEBS (styrene- (ethylene-butylene) -styrene) block copolymer [“Septon 8007” manufactured by Kuraray Co., Ltd.] in a glass reaction vessel equipped with a stirrer After vacuum-drying for 1 hour and then purging with nitrogen, 750 ml of chloroform was added and stirred at 35 ° C. for 2 hours to dissolve. After dissolution, 160 ml of chloromethyl ethyl ether and 6.74 ml of tin chloride were added and stirred at 35 ° C. for 8 hours. Next, the reaction solution was added to 4 L of methanol, and the precipitate was washed and dried to obtain chloromethylated SEBS. The chloromethylation rate of chloromethylated SEBS was 60.1 mol% of styrene units from ¹ H-NMR analysis.
Next, a cast film was prepared in the same manner as in Example 1 (1), and amination and ion exchange were performed to obtain a quaternary ammonium hydroxide-modified SEBS film. The film thickness was 100 μm, and the ion exchange capacity was 1.41 meq / g in terms of the value obtained from ¹ H-NMR measurement.

Performance test of the anion exchange type electrolyte membrane produced in Example 1 (1) and Comparative Example 1 as an electrolyte membrane for a polymer electrolyte fuel cell Example 1 (1) in the following tests (1) and (2 ) The ammonium hydroxide group-modified block copolymer film prepared in Comparative Example 1 was used.
(1) Hydroxide ion conductivity measurement A sample of 1 cm × 4 cm was sandwiched between a pair of platinum black-plated platinum electrodes and mounted in an open cell. The measurement cell was installed in a constant temperature and humidity chamber adjusted to a temperature of 60 ° C. and a relative humidity of 90%, and hydroxide ion conductivity was measured by an AC impedance method.
(2) Oxidation stability test A sample was added to a 3 mass% hydrogen peroxide aqueous solution set at 60 ° C, and reacted for 2 hours and 8 hours. Next, the sample was immersed in 0.5N NaOH for 1 hour and then thoroughly washed with distilled water.
(3) Fuel cell single cell output performance evaluation About the polymer electrolyte fuel cell single cell produced in Example 1 (2), the fuel cell output performance was evaluated. Humidified hydrogen was used as the fuel, and humidified oxygen was used as the oxidant. The test was conducted at a cell temperature of 80 ° C. under conditions of hydrogen: 500 ml / min and oxygen: 500 ml / min.

Performance Test Results as Anion Exchange Type Electrolyte Membrane Table 1 shows the results of the ionic conductivity measurement test and the oxidation stability test for the membranes produced in Example 1 (1) and Comparative Example 1.
From the results shown in Table 1, the quaternary ammonium type anion exchange type electrolyte membrane made of the α-methylstyrene block copolymer of the present invention has a quaternary ammonium type whose mass retention rate by SE test is SEBS. It was revealed that the membrane was significantly higher than the anion exchange type electrolyte membrane.

As the power generation characteristics of the polymer electrolyte fuel cell single cell produced in Example 1 (2), the change in voltage with respect to the current density was measured. The results are shown in FIG.
The open voltage of the single cell is about 1.0 V and the maximum output density is 147 mW / cm ^{2. The} quaternary ammonium hydroxide-modified HmSEBmS membrane produced in Example 1 (1) is an electrolyte membrane for a polymer electrolyte fuel cell. It became clear that it could be used as

It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 1 (2)).

Claims (13)

Solid block containing a polymer block (A) having an aromatic vinyl compound unit whose α-carbon is a quaternary carbon as a main repeating unit and a block copolymer having a flexible polymer block (B) as a constituent component A polymer electrolyte membrane for a molecular fuel cell, wherein the polymer block (A) has a monovalent anion conductive group or the polyvalent anion conductive group crosslinks the polymer blocks (A) And / or a polymer electrolyte membrane in which a polyvalent anion conductive group is bonded in a form of crosslinking aromatic vinyl compound units within the polymer block (A). The electrolyte membrane according to claim 1, wherein the proportion of the aromatic vinyl compound unit in which the α-carbon in the polymer block (A) is quaternary carbon is 50% by mass or more. The electrolyte membrane according to claim 1 or 2, wherein the mass ratio of the polymer block (A) to the polymer block (B) is 95: 5 to 5:95. In the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the hydrogen atom bonded to the α-carbon atom is an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, or a phenyl group. The electrolyte membrane according to claim 1, which is a substituted aromatic vinyl compound unit. The flexible polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a cycloalkene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and carbon. A conjugated cycloalkadiene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms in which part or all of the carbon-carbon double bond has been hydrogenated, a conjugated diene unit having 4 to 8 carbon atoms and carbon The electrolyte membrane according to any one of claims 1 to 4, which is a polymer block composed of at least one repeating unit selected from the group consisting of conjugated cycloalkadiene units of formula 5-8. The flexible polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated. The electrolyte membrane according to any one of claims 1 to 4, which is a polymer block comprising at least one repeating unit selected from conjugated diene units. The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon is an α-methylstyrene unit, and the flexible polymer block (B) is a conjugated diene unit having 4 to 8 carbon atoms and one carbon-carbon double bond. 5. The electrolyte membrane according to claim 1, which is at least one repeating unit selected from conjugated diene units having 4 to 8 carbon atoms, all or part of which are hydrogenated. The electrolyte membrane according to any one of claims 1 to 7, wherein the anion conductive group is at least one selected from the following groups (1) to (13).

(In the above formula, R ^{1 to} R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ^{4 to} R ⁹ and R ¹¹ each independently represents a hydrogen atom, a methyl group or an ethyl group. , R ¹⁰ represents a methyl group or an ethyl group, X ⁻ represents a hydroxide ion or an acid anion, m represents an integer of 2 to 6, and n represents 2 or 3. The electrolyte membrane according to claim 8, wherein R ^{1 to} R ⁹ and R ¹¹ are a methyl group or an ethyl group, and X ^- is a hydroxide ion. The electrolyte membrane according to claim 9, wherein R ^{1 to} R ¹¹ are methyl groups. The electrolyte membrane according to any one of claims 1 to 10, wherein the ion exchange capacity of the block copolymer is 0.30 meq / g or more. The membrane-electrode assembly using the electrolyte membrane of any one of Claims 1-11. A polymer electrolyte fuel cell using the electrolyte membrane according to claim 1.

Images