JP2008004312A - Ion conductive binder, membrane-electrode assembly and fuel cell - Google Patents

Abstract

Disclosed is an ion conductive binder that has excellent electrode reaction efficiency and is useful for reducing the amount of noble metal catalyst used in a catalyst layer and improving cell efficiency in a membrane-electrode assembly and a polymer electrolyte fuel cell.
A gas constituting a membrane-electrode assembly for a polymer electrolyte fuel cell comprising a polymer electrolyte membrane and two gas diffusion electrodes joined to the polymer electrolyte membrane with the membrane interposed therebetween. An ion-conductive binder used for a diffusion electrode, which is a rubber-like polymer comprising an aromatic vinyl polymer block (A) such as polystyrene and a conjugated diene unit or isobutylene unit such as isoprene and butadiene which may be hydrogenated. A star having a block (B), represented by the formula (A-B-) _n X (wherein X represents a coupling agent residue, n represents a number greater than 2), and has an ion conductive group The ion conductive binder containing a block copolymer.
[Selection figure] None

Description

  The present invention relates to an ion conductive binder used in a membrane-electrode assembly constituting a solid polymer fuel cell, a membrane-electrode assembly using the ion conductive binder, and the membrane-electrode assembly. The present invention relates to a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as a clean power generation system that is friendly to the global environment. Fuel cells are classified into phosphoric acid type, molten carbonate type, solid oxide type, solid polymer type, etc., depending on the type of electrolyte. Among these, polymer electrolyte fuel cells are applicable to electric vehicle power supplies, portable equipment power supplies, and household cogeneration systems that use both electricity and heat from the viewpoints of low-temperature operability, small size, and light weight. It is being considered.

  A polymer electrolyte fuel cell is generally configured as follows. First, on both sides of an electrolyte membrane having proton conductivity, a catalyst layer containing carbon powder carrying a platinum group metal catalyst and an ion conductive binder (ion is usually proton) made of a polymer electrolyte is formed. 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 (Mebrane 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.

  In both the proton exchange type fuel cell and the anion exchange type fuel cell, the electrode reaction is carried out by using a catalyst layer as a reaction site, a catalyst surface, a fuel gas or an oxidant gas, and an ion conductive binder as a polymer electrolyte. Occurs at the interface. The ion conductive binder is used for the purpose of binding the catalyst and increasing the utilization efficiency of the catalyst through the transfer of protons or hydroxide ions from the catalyst layer to the electrolyte membrane. Therefore, a catalyst not coated with an ion conductive binder cannot form a three-phase interface, so it is difficult to contribute to the reaction, and in order to obtain high efficiency, a fuel gas or an oxidant gas is diffused. Therefore, a precise structure design of the catalyst layer such as a pore structure for the catalyst and a dispersed state of the catalyst is important. In addition, in the gas diffusion electrode part, the catalyst surface is covered with water contained in the reaction gas or water generated at the oxygen electrode, and the fuel gas or oxidant gas cannot contact the catalyst surface and power generation stops. In some cases, the electrode reaction may be stopped by preventing the supply or discharge of the fuel gas or the oxidant gas. Therefore, water repellency is required for the gas diffusion electrode part.

  As for joining of the gas diffusion electrode and the electrolyte membrane, a method of joining by hot pressing or the like is known. However, since it is difficult to obtain good bonding strength and electrical bonding state simply by hot pressing, an ion conductive binder is applied as an adhesive resin to the catalyst layer surface of the gas diffusion electrode, and the gas diffusion electrode and It is preferable to improve the adhesion of the electrolyte membrane. For such applications, ion conductive binders are generally used in solution.

  As an ion conductive binder (cation conductive binder) used in a proton exchange type fuel cell, a perfluorocarbon sulfonic acid polymer is used as described in Patent Document 1 and Patent Document 2 because it is chemically stable. Nafion (Nafion, a registered trademark of DuPont, the same shall apply hereinafter) is generally used. However, Nafion has a hydrophobic main chain skeleton that has no sulfonic acid group, and the catalyst coated with the hydrophobic part in the catalyst layer cannot form a three-phase interface. It is thought that it cannot contribute to. Even if the sulfonic acid group content is increased to increase the three-phase interface and increase the catalyst utilization rate, the hydrophilicity of the polymer increases, and the binder itself generates moisture and oxygen electrodes contained in the reaction gas during power generation. It gradually elutes out of the battery system due to water or the like, and the deterioration of the electrode proceeds, so that a sufficient operation time cannot be secured. Further, even if the Nafion content is increased in order to increase the sulfonic acid group content in the electrode catalyst, the diffusion path of the reactant necessary for forming the three-phase interface is blocked, and the electrode reaction efficiency is lowered.

  In addition to fluorine-based electrolytes, for example, aromatic engineering plastic resins into which ion conductive groups such as sulfonic acid groups are introduced have been studied. In addition to aromatic engineering plastic resins, cationic conductive binders made of styrene thermoplastic elastomers have been proposed (Patent Document 3 and Patent Document 4). For example, a sulfonated product of SEBS (polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer) has been proposed, which is hardly soluble in water and has a good bonding strength with an electrolyte membrane. It is disclosed. However, ion conductive binders made of the above-described aromatic engineering plastic resins and styrene thermoplastic elastomers have the same problems as fluorine ion conductive binders.

  In addition, a resin that has been made water-insoluble even with a high ionic group content by introducing a crosslinking group has been studied, but since it is insoluble in organic solvents, it must be suspended in an appropriate solvent and used. Therefore, the dispersibility in the catalyst layer is poor, and it is difficult to form an effective three-phase interface.

  On the other hand, as an anion conductive binder used in an anion exchange type fuel cell, one obtained by converting a sulfonic acid group of a perfluorosulfonic acid polymer into an anion exchange group is known. For example, Patent Document 5 discloses a product obtained by copolymerizing tetrafluoroethylene and CF2 = CFOCF2CF (CF3) O (CF2) 2SO3F and then reacting with N, N, N'-trimethylethylenediamine. Patent Document 6 discloses an anion exchange resin obtained by aminating a chloromethylated product of a copolymer of aromatic polyethersulfone and aromatic polythioethersulfone as an anion conductive binder. Patent Document 7 discloses an anion conductive binder made of a quaternary ammonium group introduced into a polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer or the like as an anion conductive binder. However, the anion conductive binder also has the same disadvantages as the cation conductive binder.

  As described above, an ion conductive binder that is excellent in forming an interface between the catalyst in the catalyst layer and the ion conductive binder and that can achieve a structure that does not block the diffusion path of the reactant has not been developed. In reality, no new ion conductive binder has been proposed to increase the electrode reaction efficiency due to these problems.

Japanese Patent Publication No.2-7398 JP-A-3-208260 JP 2002-164055 A Special Table 2000-513484 JP 2000-331693 A Japanese Patent Laid-Open No. 11-273695 JP 2002-367626 A

  INDUSTRIAL APPLICABILITY The present invention is an environment-friendly, economical, excellent moldability, and excellent electrode reaction efficiency because it does not contain a halogen atom, and a membrane-electrode assembly using the ion-conductive binder And a polymer electrolyte fuel cell using the membrane-electrode assembly.

  As a result of intensive studies to solve the above problems, the present inventors have found that an ion conductive binder composed of a star block copolymer is excellent in moldability and electrode reaction efficiency, and completed the present invention. did.

That is, the present invention
Used for a gas diffusion electrode constituting a membrane-electrode assembly for a polymer electrolyte fuel cell comprising a polymer electrolyte membrane and two gas diffusion electrodes joined to the polymer electrolyte membrane with the membrane interposed therebetween An ion-conductive binder having an aromatic vinyl polymer block (A) and a rubbery polymer block (B) comprising a conjugated diene unit or an isobutylene unit which may be hydrogenated, and a number of more than 2 The ion-conductive binder comprising a star-shaped block copolymer having an ion-conductive group.

  The ion-conductive binder composed of the above star-shaped block copolymer must efficiently form the interface between the catalyst that serves as the electrode reaction field and the ion-conductive binder, and ensure a sufficient diffusion path for the reactants. The electrode reaction efficiency is excellent. Using a block copolymer is advantageous for the formation of a route (ion channel) for transporting ions generated at the electrode to the electrolyte membrane, and also for structural stability in the electrode catalyst layer in a power generation environment. Necessary to provide the necessary hydrophilic-hydrophobic balance function.

  The present invention also relates to a solution or suspension containing the ion conductive binder. The present invention also relates to a membrane-electrode assembly using the ion conductive binder and a fuel cell using the membrane-electrode assembly.

  Since the ion conductive binder of the present invention does not contain a halogen atom, it is environmentally friendly, economical, and excellent in electrode reaction efficiency. Therefore, in the membrane-electrode assembly and the polymer electrolyte fuel cell, the cell efficiency is high. It helps to improve and reduce the amount of noble metal catalyst used in the catalyst layer.

  Hereinafter, the present invention will be described in detail. The ion conductive binder of the present invention is composed of an arm polymer block of more than 2 having an aromatic vinyl polymer block (A) and an optionally hydrogenated conjugated diene polymer block (B). And a star block copolymer having an ion conductive group.

The block structure of the star block copolymer is represented by the following formula, for example, when the polymer block (A) is represented by “A” and the polymer block (B) is represented by “B”, or Can be mentioned.
(A-B-) _n X
(B-A-) _n X
(A-B-A-) _n X
(B-A-B-) _n X
(A-) _nm (B-) _m X
(A-) _m (B-) _nm X
(In the formula, X represents a polyfunctional coupling agent residue, n represents a number exceeding 2, and m represents a number of 1 or more.)
In particular, the block structure of the star block copolymer is a form in which the aromatic vinyl polymer block (A) is bonded to the free terminal side, and the ion conductive group is exposed on the surface of the star block copolymer molecule. Thus, it is preferable because it is easy to introduce at a high density, and (A-B-) _n X is more preferable.

  The total number n of arm polymer blocks constituting the star block copolymer must be greater than 2 and 3 or more in order to increase the electrode reaction efficiency using the block copolymer as a star shape. Is preferable, and 5 or more is more preferable. The upper limit is preferably 50 or less. The number of arm polymer blocks can be determined, for example, by dividing the number average molecular weight of the entire star block copolymer by the number average molecular weight of the arm polymer used for the production. In the present invention, the number average molecular weight is a value calculated in terms of polystyrene by gel permeation chromatography (GPC). The number average molecular weight of the star block copolymer and the number average molecular weight of the arm polymer block constituting the star block copolymer is “number average molecular weight of star block copolymer> 2 × number average molecular weight of arm polymer block” ”. The number average molecular weight of the star block copolymer is appropriately selected depending on the properties and required performance of the ion conductive binder.

  Examples of the aromatic vinyl unit constituting the aromatic vinyl polymer block (A) of the star block copolymer include styrene, α-methylstyrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, vinyl pyridine, etc .; Alkyl group having 1 to 3 hydrogen atoms bonded to the benzene ring of these aromatic vinyl compounds (methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group or tert-butyl group) And a unit composed of an aromatic vinyl compound substituted with p-methylstyrene, 2,4,6-trimethylstyrene, p-tert-butylstyrene and the like. Among them, the aromatic vinyl unit preferably has a structure having no tertiary carbon in order to enhance oxidation stability due to hydrogen peroxide generated by a side reaction of the electrode reaction or hydroxyl radical derived from hydrogen peroxide. α-methylstyrene units are preferred.

  The polymer block (A) may contain one or more other monomer units within a range not impairing the effects of the present invention, preferably 20% by mass or less. Examples of such other monomers include conjugated diene compounds having 4 to 8 carbon atoms such as 1,3-butadiene and isoprene, (meth) acrylic acid esters such as methyl acrylate and methyl methacrylate, and 2 to 2 carbon atoms. 8 alkene, vinyl ester, vinyl ether and the like. The copolymerization form of the aromatic vinyl compound and the other monomer needs to be random copolymerization.

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

  The polymer block (A) is preferably bonded to the free terminal side of the arm polymer constituting the star block copolymer. This is because the ion conductive group can be easily introduced at a high density so as to be exposed on the surface of the star block copolymer molecule, and is effective for forming an interface with the catalyst in the electrode catalyst layer. In addition, since the number of ion groups in the ion conductive binder that functions substantially increases, the content of the ion conductive binder in the electrode catalyst layer may be small, which means that the reactant necessary for forming the three-phase interface is not necessary. This is effective for securing a diffusion path.

  The star block copolymer has a polymer block (B) together with a polymer block (A). Even if ionic groups are introduced in a high content in the polymer block (A), the water resistance is improved by having the polymer block (B), and the ionic conductive binder is prevented from flowing out due to degradation or decomposition during power generation. it can.

  The polymer block (B) possessed by the star block copolymer is a rubber-like polymer block comprising conjugated diene units, hydrogenated conjugated diene units, or isobutylene units. Examples of the conjugated diene unit that can constitute the polymer block (B) include units composed of conjugated diene compounds having 4 to 8 carbon atoms such as 1,3-butadiene and isoprene. The conjugated diene unit and the isobutylene unit can be used alone or in combination of two or more. 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 unit, it is a 1,2-bond. Alternatively, it may be 1,4-bond, and the ratio of 1,2-bond and 1,4-bond is not particularly limited as long as the glass transition point or softening point is 50 ° C. or lower.

  The rubber-like polymer block (B) has a flexible structure, so that the block copolymer is elastic and flexible as a whole, and is molded for production of a membrane-electrode assembly or a polymer electrolyte fuel cell. (Such as assembling, joining and tightening) is improved. The glass transition point or softening point of the polymer block (B) is 50 ° C. or lower, preferably 20 ° C. or lower, more preferably 10 ° C. or lower.

When the repeating unit constituting the polymer block (B) is a conjugated diene and has a carbon-carbon double bond, power generation of the membrane-electrode assembly using the ion conductive binder of the present invention From the viewpoint of improving performance and heat resistance deterioration, it is preferable that 30 mol% or more of such carbon-carbon double bonds are hydrogenated, more preferably 50 mol% or more is hydrogenated, and 80 More preferably, at least mol% 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.

  In addition to the above monomers, the polymer block (B) is a unit of another monomer, such as carbon, within a range that does not impair the purpose of the polymer block (B) that the block copolymer has elasticity. Units such as alkenes of 2 to 8; aromatic vinyl compounds such as styrene and vinyl naphthalene; (meth) acrylic acid esters such as methyl acrylate and methyl methacrylate; vinyl esters; vinyl ethers and the like 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%.

  The structure when the arm polymer constituting the star block copolymer is composed of the polymer block (A) and the polymer block (B) is not particularly limited. Copolymer, A-B-A type triblock copolymer, B-A-B type triblock copolymer, A-B-A-B type tetrablock copolymer, A-B-A-B- Examples include A-type pentablock copolymers and B-A-B-A-B type pentablock copolymers. 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 not particularly limited as long as the ratio is compatible with the ion conductivity and water resistance of the ion conductive binder, and is 95: 5 to 5:95. It is preferably 90:10 to 10:90, more preferably 50:50 to 10:90.

  The star block copolymer constituting the ion conductive binder of the present invention may have 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 does not impair the performance of the present invention. For example, when the polymer block (C) is a crystalline polyolefin block that does not have an ion conductive group, the swelling of the ion conductive binder is suppressed. This is effective in reducing the diffusion inhibition of the reactant due to swelling of the ion conductive binder during power generation.

  When the block copolymer constituting the ion conductivity 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, and 35 The content is more preferably at most mass%, even more preferably at most 30 mass%.

  The number average molecular weight of the block copolymer used in the present invention in a state where the ion conductive group is not introduced is not particularly limited, but 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 star block copolymer constituting the ion conductive binder of the present invention must have an ion conductive group, that is, a cation conductive group or an anion conductive group. In the present invention, when referring to ionic conductivity, protons and the like are mentioned as ions, and hydroxide ions and the like are mentioned as anions. The cation conductive group is not particularly limited as long as the membrane-electrode assembly produced using the ion conductive binder can express sufficient ionic conductivity. ₃ M) or a phosphonic acid group (—PO ₃ HM) (wherein M represents a hydrogen atom, an ammonium ion or an alkali metal ion), a sulfonic acid group, a phosphonic acid group or a salt thereof is preferably used. It is done. As the ion conductive group, a carboxyl group or a salt thereof can also be used. The anion conductive group is not particularly limited as long as the membrane-electrode assembly produced using the ion conductive binder can express sufficient anion conductivity. Can be mentioned.

The ion conductive group may be present at any position in the star block copolymer, but since the ion conductive group can be easily introduced in the production method described later, an aromatic vinyl polymer is used. It is preferably present on the side chain or free end side of the block (A).
The amount of ion-conducting group introduced is appropriately selected depending on the required performance of the resulting block copolymer, etc., but exhibits sufficient ion conductivity to be used as an ion-conducting binder for solid polymer fuel cells 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. . Although there is no restriction | limiting in particular about the upper limit of the ion exchange capacity of a block copolymer, Usually, it is preferable that it is 3 meq / g or less.

  The method for producing the star block copolymer used in the present invention is roughly classified into the following two methods. That is, (1) a method of first producing a star-shaped block copolymer having no ion conductive group and then binding the ion conductive group; (2) using a monomer having an ion conductive group This is a method for producing a shaped block copolymer.

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 a coordination polymerization method and the like, but from the viewpoint of industrial ease, a radical polymerization method, an anionic polymerization method or a cationic polymerization is preferably selected. In particular, a 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 (A), and specifically, a living radical polymerization method or a living anion polymerization method. The living cationic polymerization method is preferred.

In producing the block copolymer constituting the polymer block (A), styrene which is an aromatic vinyl compound in which the α-carbon is a tertiary carbon or a styrene derivative whose aromatic ring is substituted with an alkyl group is used as a polymer block (A). When the main repeating unit is
(1) An anionic polymerization initiator is used in a cyclohexane solvent to polymerize styrene or a styrene derivative under a temperature condition of 20 to 100 ° C., and then polymerize a conjugated diene, and then a polyfunctional monomer such as divinylbenzene. A method of reacting (A-B) _n to obtain an X-type star block copolymer;
(2) Styrene or a styrene derivative is polymerized using an anionic polymerization initiator in a cyclohexane solvent under a temperature condition of 20 to 100 ° C., and then a conjugated diene is polymerized, and then a coupling agent such as tetrachlorosilane is added. A method of adding (A-B) _n X type star (star) block copolymer;
Etc. are known.
When α-methylstyrene, which is a typical example of an aromatic vinyl compound unit in which α-carbon is a quaternary carbon, is used as the main repeating unit of the polymer block (A),
(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, conjugated diene and the like in the resulting living polymer, and then reacting with a polyfunctional monomer such as divinylbenzene (AB) to obtain an _n X-type star 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, and the resulting living polymer is polymerized with a conjugated diene, and then reacted with a coupling agent such as tetrachlorosilane (AB). _N X-type star (star) block copolymer A method of obtaining coalescence;
Etc. are known.

Next, a method for bonding an ion conductive group to the obtained star block copolymer will be described.
First, a method for introducing a cation conductive group into the obtained star-shaped block copolymer will be described. First, a method for introducing a sulfonic acid group into the obtained star block copolymer will be described. Sulfonation can be performed by a known sulfonation method. As such a method, an organic solvent solution or suspension of a block copolymer is prepared, a sulfonating agent is added and mixed, a method of adding a gaseous sulfonating agent directly to the block copolymer, etc. Is exemplified.

  Sulfonating agents used include sulfuric acid, a mixture of sulfuric acid and aliphatic acid anhydride, chlorosulfonic acid, a mixture of chlorosulfonic acid and trimethylsilyl chloride, sulfur trioxide, a mixture of sulfur trioxide and triethyl phosphate. Examples thereof include aromatic organic sulfonic acids represented by 2,4,6-trimethylbenzenesulfonic acid. Examples of the organic solvent to be used include halogenated hydrocarbons such as methylene chloride, linear aliphatic hydrocarbons such as hexane, cyclic aliphatic hydrocarbons such as cyclohexane, and the like. You may use it, selecting suitably from several combinations.

  Next, a method for introducing phosphonic acid groups into the obtained star block copolymer will be described. Phosphonation can be performed by a known phosphonation method. Specifically, for example, an organic solvent solution or suspension of a block copolymer is prepared, and the copolymer is reacted with chloromethyl ether or the like in the presence of anhydrous aluminum chloride to introduce a halomethyl group into the aromatic ring. Thereafter, there may be mentioned a method in which phosphorus trichloride and anhydrous aluminum chloride are added and reacted, followed by a hydrolysis reaction to introduce a phosphonic acid group. Alternatively, a method may be exemplified in which phosphorus trichloride and anhydrous aluminum chloride are added to the copolymer and reacted to introduce a phosphinic acid group into the aromatic ring, and then the phosphinic acid group is oxidized with nitric acid to form a phosphonic acid group.

The degree of sulfonation or phosphonation is as described above until the ion exchange capacity of the block copolymer is 0.30 meq / g or more, particularly 0.40 meq / g or more, but 3.0 meq / g or less. It is desirable to be sulfonated or phosphonated so that Thereby, practical ion conduction performance is obtained. The ion exchange capacity of the sulfonated or phosphonated block copolymer, or the sulfonation rate or phosphonation rate in the polymer block (A) in the block copolymer is determined by acid value titration method, infrared spectroscopic measurement, It can be calculated by using an analytical means such as nuclear magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement.

  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 ^{8 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 introduced with an anion conductive group is determined by a titration method,
It can measure using analytical means, such as an infrared spectroscopy spectrum measurement and a nuclear magnetic resonance spectrum (< ¹ > H-NMR spectrum) measurement.

The second method for producing the star block copolymer used in the present invention is a method for producing a block copolymer using at least one monomer having an ion conductive group.
As the monomer having a cation conductive group, a monomer in which an ion conductive group is bonded to an aromatic vinyl compound is preferable. Specifically, styrene sulfonic acid, α-alkyl-styrene sulfonic acid, vinyl naphthalene sulfonic acid, α-alkyl-vinyl naphthalene sulfonic acid, vinyl anthracene sulfonic acid, α-alkyl-vinyl anthracene sulfonic acid, vinyl pyrene sulfonic acid, α-alkyl-vinylpyrenesulfonic acid, styrenephosphonic acid, α-alkyl-styrenephosphonic acid, vinylnaphthalenephosphonic acid, α-alkyl-vinylnaphthalenephosphonic acid, vinylanthracenephosphonic acid, α-alkyl-vinylanthracenephosphonic acid, vinyl Examples include pyrenephosphonic acid and α-alkyl-vinylpyrenephosphonic acid. Among these, o-, m- or p-styrene sulfonic acid, α-alkyl-o-, m- or p-styrene sulfonic acid is particularly preferable from the viewpoint of industrial versatility and ease of polymerization.

  As the monomer containing a cation conductive group, a monomer in which an ion conductive group is bonded to a conjugated diene compound can also be used. Specifically, 1,3-butadiene-1-sulfonic acid, 1,3-butadiene-2-sulfonic acid, isoprene-1-sulfonic acid, isoprene-2-sulfonic acid, 1,3-butadiene-1-phosphonic acid 1,3-butadiene-2-phosphonic acid, isoprene-1-phosphonic acid, isoprene-2-phosphonic acid and the like.

Examples of the monomer containing a cationic conductive group include vinyl sulfonic acid, α-alkyl-vinyl sulfonic acid, vinyl alkyl sulfonic acid, α-alkyl-vinyl alkyl sulfonic acid, vinyl phosphonic acid, α-alkyl-vinyl phosphone. Acid, vinyl alkyl phosphonic acid, α-alkyl-vinyl alkyl phosphonic acid and the like can also be used. Among these, vinyl sulfonic acid and vinyl phosphonic acid are preferable.
As the monomer containing cationic conductivity, a (meth) acrylic monomer to which an ion conductive group is bonded can also be used. Specific examples include methacrylic acid, acrylic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, and the like.

  The cation conductive group may be introduced in the form of a salt neutralized with a suitable metal ion (for example, alkali metal ion) or counter ion (for example, ammonium ion). For example, a desired ion-conducting group is introduced by producing a polymer using sodium o-, m- or p-styrene sulfonate, or sodium α-methyl-o-, m- or p-styrene sulfonate. it can. Or the block copolymer which made the sulfonic acid group into the salt form can be obtained by ion-exchange by a suitable method.

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.

  The ion conductive binder of the present invention may contain a softening agent as long as the effects of the present invention are not impaired. 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 ion conductive binder of the present invention may further contain various additives as required, for example, phenol stabilizers, sulfur stabilizers, phosphorus stabilizers, light stabilizers, antistatic agents, mold release agents, flame retardants. , Foaming agents, pigments, dyes, brighteners, carbon fibers and the like may be contained singly 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 ion conductive binder of the present invention may further contain an inorganic filler as long as it does not impair the effects of the present invention. 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 ion conductive binder 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 ion conductive binder of the present invention is used in a catalyst layer constituting a gas diffusion electrode of a polymer electrolyte fuel cell, or is used for a joining surface between an electrolyte membrane and a catalyst layer. The ion conductive binder is preferably used for electrodes on both sides of the membrane-electrode assembly, but may be used for only one of them.

  As a method of attaching the ion conductive binder of the present invention to the surface of a catalyst carrier carrying a catalyst, binding the catalyst carriers together, and joining this to a gas diffusion layer or an electrolyte membrane, an ion conductive binder is used. A catalyst paste prepared by mixing a solution or suspension of the above with raw material particles such as a conductive catalyst carrier carrying a catalyst may be applied to a gas diffusion layer or an electrolyte membrane, or a catalyst for a gas diffusion electrode formed in advance. The layer may be impregnated with a solution containing an ion conductive binder.

  The solvent used for the solution or suspension of the ion conductive binder of the present invention is not particularly limited as long as it does not destroy the structure of the block copolymer. Specifically, halogenated hydrocarbons such as methylene chloride, aromatic hydrocarbon solvents such as toluene, xylene, and benzene, linear aliphatic hydrocarbons such as hexane and heptane, and cyclic aliphatic carbonization such as cyclohexane. Hydrogen, ethers such as tetrahydrofuran, alcohols such as methanol, ethanol, propanol, isopropanol, acetonitrile, nitromethane, dimethyl sulfoxide, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, etc. It can be illustrated. These solvents can be used alone or in combination of two or more. Moreover, it is good also as a mixed solution with water to such an extent that the solubility or suspension property of an ion conductive binder is not impaired.

  The density | concentration of the solution or suspension containing an ion conductive binder should just be a density | concentration in which a suitable membrane | film | coat is easy to be formed on the catalyst surface of a catalyst layer, and it is preferable that it is normally 3 mass%-10 mass%. If this concentration is too high, the thickness of the film formed on the catalyst surface will be too large, and diffusion of the reaction gas to the catalyst will be hindered, or a uniform catalyst layer will not be formed, and the utilization efficiency of the catalyst will be reduced. However, the output as a fuel cell may decrease. Also, if this concentration is too low, the viscosity of the solution or suspension is too small, and when applied to the gas diffusion layer, it penetrates deeply into the gas diffusion layer and inhibits gas diffusibility. There is.

  As another method for attaching the catalyst by attaching the ion conductive binder of the present invention to the surface of the catalyst carrier of the catalyst layer, the ion conductive binder powder is used as a raw material for a conductive catalyst carrier or the like carrying the catalyst. The method of mixing with particle | grains and electrostatically applying to a gas diffusion layer or an electrolyte membrane is mentioned.

  As a method of using the ion conductive binder of the present invention on the joint surface between the electrolyte membrane and the catalyst layer, a solution or suspension of the ion conductive binder is applied to the catalyst layer surface formed on the electrolyte membrane or the gas diffusion electrode. Then, an electrolyte membrane and a gas diffusion electrode are bonded together, and a method of thermocompression bonding as necessary, or a fine powder of an ion conductive binder is electrostatically applied to the catalyst layer surface formed on the electrolyte membrane or the gas diffusion electrode, Examples include a method in which an electrolyte membrane and an electrode are bonded together and thermocompression bonded at a temperature equal to or higher than the softening temperature of the ion conductive binder.

  The solution concentration in the case of using a solution containing an ion conductive binder at the joining interface between the electrolyte membrane and the catalyst layer is 3% by mass to 10% by mass for ensuring the adhesion between the polymer electrolyte membrane and the gas diffusion electrode. preferable. If this concentration is too low, the bonding between the electrolyte membrane and the gas diffusion electrode may be incomplete. Moreover, when this density | concentration is too high, the applicability | paintability to the joint surface of a gas diffusion layer will fall, and the permeability to a detail may fall.

  Next, a membrane-electrode assembly using the ion conductive binder 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 ion 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 electrolyte membrane with the catalyst layer inside. There is a method in which a paste is applied to both sides of an 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 yet another production method, a solution or suspension containing an ion conductive binder is applied to both surfaces of the 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 pressure bonding or the like. 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. There is a method in which a catalyst layer is transferred to both sides of an electrolyte membrane by thermocompression bonding, a base film is peeled to obtain a joined body of the electrolyte membrane and the catalyst layer, and a gas diffusion layer is crimped to each catalyst layer by hot pressing. is there. In these methods, these methods may be performed in a state where the ion conductive group is made into a salt with a metal such as Na, and a treatment for returning to a proton type by acid treatment after bonding may be performed.

  In the membrane-electrode assembly of the present invention, the ion conductive binder of the present invention is used for at least one of the electrode catalyst layer and the bonding surface between the gas diffusion electrode and the electrolyte membrane. It is preferably used for both, and in this case, the effect of improving the electrode reaction efficiency of the fuel cell is remarkable.

  Examples of the electrolyte membrane constituting the membrane-electrode assembly include existing perfluorosulfonic acid-based materials such as “Nafion” (registered trademark, manufactured by DuPont) and “Gore-select” (registered trademark, manufactured by Gore). An electrolyte membrane made of a polymer, an electrolyte membrane made of sulfonated polyethersulfone or sulfonated polyetherketone, an electrolyte membrane made of polybenzimidazole impregnated with phosphoric acid or sulfuric acid, and the like can be used. Further, linear, branched (graft), star, etc. having the same polymer block (A) and polymer block (B) as the star block copolymer constituting the ion conductive binder of the present invention. An electrolyte membrane may be prepared from the block copolymer. In order to further enhance the adhesion between the electrolyte membrane and the gas diffusion electrode, it is preferable to use an electrolyte membrane formed from the same material as the polymer in the ion conductive binder used for the gas diffusion electrode.

  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 such as carbon / catalyst support, the amount of catalyst used is small and it is 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 a porous material 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 membrane-electrode assembly obtained by the above method has excellent chemical stability, little deterioration in power generation characteristics over time, and can be used stably for a long time.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited by these Examples.

<Reference Example 1>
Production of Star Block Copolymer (mS-EB) _n X Composed of Poly α-Methylstyrene (Polymer Block (A)) and Hydrogenated Polybutadiene (Polymer Block (B)) Previously reported method (WO 02/40611) In the same manner as in No.), a poly α-methylstyrene-b-polybutadiene diblock copolymer (hereinafter abbreviated as mS-B) was synthesized, and instead of using phenyl benzoate, divinylbenzene was used as the polymer 7 .5 times the molar amount was added, by reacting 17 hours to obtain a star block copolymer of the object (mS-B) n _X. The number average molecular weight of the obtained _{(mS-B) n X (} GPC measurement, polystyrene equivalent) of 393500, its arm polymer number average molecular weight of (mS-B) (GPC measurement, in terms of polystyrene) 37800 ( n = 10.4). ^The amount of 1,4-bond determined from ¹ H-NMR measurement was 52%, the content of α-methylstyrene unit was 33% by mass, the area corresponding to the star polymer obtained from the GPC RI detector, and the total peak The star rate determined from the area ratio was 96%. Further, it was found by composition analysis by ¹ H-NMR spectrum measurement that α-methylstyrene was not substantially copolymerized in the polybutadiene block.
Synthesized _{(mS-B) n} X cyclohexane solution was adjusted sufficiently were charged in a pressure vessel was purged with nitrogen, using a Ni / Al Ziegler hydrogenating catalyst, 60 ° C. under a hydrogen atmosphere Then, a hydrogenation reaction was carried out for 5 hours to obtain (poly α-methylstyrene-b-hydrogenated polybutadiene) _n X-type star block copolymer (hereinafter abbreviated as (mS-EB) _n X). Obtained where the _(mS-EB) hydrogenation ratio of _n X was calculated by ¹ H-NMR spectrum measurement, it was 98.7%.

<Example 1>
(1) Synthesis of Sulfonated (mS-EB) _n X In 68.6 ml of methylene chloride, 34.3 ml of acetic anhydride and 15.3 ml of sulfuric acid were reacted at 0 ° C. to prepare a sulfating reagent. On the other hand, 100 g of the block copolymer (mS-EB) _n X obtained in Reference Example 1 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour, and then purged with nitrogen, and then 1000 ml of methylene chloride was added. The mixture was stirred at 35 ° C. for 2 hours for dissolution. After dissolution, the sulfating reagent was gradually added dropwise over 20 minutes. After stirring for 3 hours at 35 ° C., the polymer solution was poured into 2 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. Repeatedly until the washing and the change in pH of the wash water operations filtration is eliminated, and the final filtration polymer was vacuum dried to obtain a sulfonated (mS-EB) n _X. The resulting sulfonated _(mS-EB) 43.5mol% sulfonation proportion of the benzene rings of _n X of α- methylstyrene units from ¹ H-NMR analysis, and its ion exchange capacity was 1.11meq / g.
(2) Production of a polymer electrolyte fuel cell single cell (MeOH aqueous solution / air system) An electrode for a polymer electrolyte fuel cell was produced by the following procedure. A 3% by mass THF solution of the sulfonated product obtained in (1) was mixed with Pt—Ru alloy catalyst-supporting carbon to prepare a uniformly dispersed paste. This paste was uniformly applied to one side of the carbon paper. After leaving at room temperature for several hours, it was dried under reduced pressure at room temperature for 1 hour.
Further, a Nafion solution was mixed with Pt catalyst-carrying carbon to prepare a uniformly dispersed paste. The water-repellent treated carbon paper was uniformly applied on one side. The prepared electrodes were anode: Pt 1.10 mg / cm ² , Ru 0.82 mg / cm ² , polymer 1.92 mg / cm ² , cathode: Pt 1.01 mg / cm ² , polymer 1.00 mg / cm ^2. It was.

Subsequently, a sulfonated product of the block copolymer HmSEBmS obtained in Comparative Example 1 (2) described later (the sulfonation rate of the benzene ring of the α-methylstyrene unit was 32.1 mol% from ¹ H-NMR analysis, and the ion exchange capacity. Is 0.71 meq / g) formed by a known method, and an electrolyte membrane (9 cm × 9 cm) is sandwiched between carbon paper electrodes (5 cm × 5 cm) on the anode side and cathode side so that the membrane and the catalyst surface face each other, and press (20 kg / cm ² , 8 min) to prepare a membrane-electrode assembly.
The membrane-electrode assembly produced above is sandwiched between two conductive separators that also serve as gas supply channels, and the outside is sandwiched between two current collector plates and two clamping plates in order. An evaluation cell for a polymer electrolyte fuel cell was produced. 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.

<Example 2>
(1) Production of solid polymer fuel cell single cell (MeOH aqueous solution / air system) Using the sulfonated product obtained in Example 1 (1), the same method as in Example 1 (2), A carbon paper electrode on the anode side having the following blending ratio was prepared. The prepared electrodes were anode: Pt 1.10 mg / cm ² , Ru 0.82 mg / cm ² , and polymer 0.96 mg / cm ² .
Next, using the produced anode-side carbon paper and the same cathode-side carbon paper electrode as in Example 1 (2), a polymer electrolyte fuel cell single cell was produced in the same manner as in Example 1 (2). did.

<Comparative Example 1>
(1) Production of block copolymer comprising α-methylstyrene) (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) Previously reported method (Japanese Patent Laid-Open No. 2001-172324) In the same manner, a poly (α-methylstyrene) -b-polybutadiene-poly (α-methylstyrene) type triblock copolymer (hereinafter abbreviated as mSEBmS) was synthesized. The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained mSEBmS is 74000, the 1,4-bond content determined from ¹ H-NMR measurement is 56%, and the content of α-methylstyrene unit is 28.6. 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. The poly (α-methylstyrene) -b-hydrogenated polybutadiene-b-poly (α-methylstyrene) type triblock copolymer (hereinafter abbreviated as HmSEBmS) was obtained. The hydrogenation proportion of the resulting HmSEBmS was calculated by ¹ H-NMR spectrum measurement, it was 99.8%.
(2) Synthesis of sulfonated HmSEBmS In 109.2 ml of methylene chloride, 54.6 ml of acetic anhydride and 24.4 ml of sulfuric acid were reacted at 0 ° C. to prepare a sulfating reagent. On the other hand, 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 purged with nitrogen. And stirred for 2 hours to dissolve. After dissolution, the sulfating reagent was gradually added dropwise over 20 minutes. After stirring for 4 hours at 35 ° C., the polymer solution was poured into 2 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. This washing and filtration operation was repeated until there was no change in the pH of the washing water, and the polymer collected at the end was vacuum dried to obtain sulfonated HmSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the sulfonated HmSEBmS obtained was 50.5 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.09 meq / g.
(3) Production of polymer electrolyte fuel cell single cell (MeOH aqueous solution / air system) Using the obtained sulfonated product, the following blending ratio was obtained in the same manner as in Example 1 (2). A carbon paper electrode on the anode side was prepared. Fabricated electrodes, ^{anode: Pt 1.05mg / cm 2, Ru} 0.84mg / cm 2, was polymer 1.89 mg / cm ^2.
Next, using the produced anode-side carbon paper and the same cathode-side carbon paper electrode as in Example 1 (2), a polymer electrolyte fuel cell single cell was produced in the same manner as in Example 1 (2). did.

<Comparative example 2>
(1) Production of solid polymer type fuel cell single cell (MeOH aqueous solution / air system) Using the sulfonated product obtained in Comparative Example 1 (2), the same method as in Example 1 (2), A carbon paper electrode on the anode side having the following blending ratio was prepared. Fabricated electrodes, ^{anode: Pt 1.05mg / cm 2, Ru} 0.84mg / cm 2, was polymer 0.95 mg / cm ^2.
Next, using the produced anode-side carbon paper and the same cathode-side carbon paper electrode as in Example 1 (2), a polymer electrolyte fuel cell single cell was produced in the same manner as in Example 1 (2). did.

○ Performance test as ion conductive binder of polymer membranes of Examples and Comparative Examples 1) Measurement of ion exchange capacity A sample is weighed (a (g)) in a glass container that can be sealed, and an excessive amount of sodium chloride is contained therein. Saturated aqueous solution was added and stirred overnight. Hydrogen chloride generated in the system was titrated (b (ml)) with a 0.01N NaOH standard aqueous solution (titer f) using a phenolphthalein solution as an indicator. The ion exchange capacity was determined by the following formula.
Ion exchange capacity = (0.01 × b × f) / a

2) Fuel cell single cell output performance evaluation About the polymer electrolyte fuel cell single cell produced in Example 1, Example 2, Comparative example 1, and Comparative example 2, the fuel cell output performance was evaluated. A 1M MeOH aqueous solution was used as the fuel, and air was used as the oxidant. The test was conducted at a cell temperature of 60 ° C. under conditions of an anode flow rate: 1.8 cc / min and a cathode flow rate: 250 cc / min.

Results of performance tests as ion conductive binders Test results of solid polymer fuel cell single cells produced using the ion conductive binders produced in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 Table 1 shows. It was clarified that the ion conductive binder of the present invention has higher battery output and improved battery reaction efficiency compared to an ion conductive binder composed of a linear block copolymer having the same composition. . From Example 1 and Example 2, since the ion-conductive binder of the present invention has a large number of substantially functional ionic groups, the amount of ion-conductive binder forming the catalyst layer is small when compared with the equivalent amount of catalyst supported. Even so, it was revealed that sufficiently high battery performance can be obtained. Further, since the small amount of ion-conductive binder supported favorably secures the diffusion path of the reactant necessary for forming the three-phase interface, the effect of the present invention was clearer. On the other hand, in the case of Comparative Example 2, the diffusion of the reaction product is facilitated by reducing the amount of the ion-conductive binder supported, but the reaction efficiency does not increase because the number of functional ionic groups decreases, and the material diffusion and reaction It is difficult to achieve both field formation.

  As the power generation characteristics of the polymer electrolyte fuel cell single cells produced in Example 1 (3), Example 2 (1), Comparative Example 1 (3), and Comparative Example 2 (1), the change in voltage with respect to the current density is shown. It was measured. The results are shown in FIGS.

It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 1 (3)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 2 (1)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Comparative example 1 (3)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Comparative example 2 (1)).

Claims (9)

  Used for a gas diffusion electrode constituting a membrane-electrode assembly for a polymer electrolyte fuel cell comprising a polymer electrolyte membrane and two gas diffusion electrodes joined to the polymer electrolyte membrane with the membrane interposed therebetween An ion-conductive binder having an aromatic vinyl polymer block (A) and a rubbery polymer block (B) comprising a conjugated diene unit or an isobutylene unit which may be hydrogenated, and a number of more than 2 The ion conductive binder comprising a star-shaped block copolymer having an ion conductive group and comprising an arm polymer block. The polystyrene-reduced number average molecular weight calculated from GPC is the following relational expression:
2. The ion conductive binder according to claim 1, wherein the number average molecular weight of the star block copolymer> 2 × the number average molecular weight of the arm polymer block is satisfied.   The ion conductive binder according to claim 1 or 2, wherein an ion conductive group is present in the polymer block (A). Star block copolymer having the formula _(A-B-) (wherein, X is a coupling agent residue, n represents represents a number greater than 2) n X claims 1 to 3 is represented by The ion conductive binder of any one of these.   The ion conductive binder according to any one of claims 1 to 4, wherein the ion conductive group is a cation conductive group selected from a sulfonic acid group and a phosphonic acid group, and alkali metal salts and ammonium salts thereof. The ion conductive binder according to any one of claims 1 to 4, wherein the ion conductive group is an anion conductive group selected from the following groups (1) to (7).

(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 solution or suspension containing the ion conductive binder of any one of Claims 1-6.   The membrane-electrode assembly using the ion conductive binder of any one of Claims 1-6. A polymer electrolyte fuel cell using the membrane-electrode assembly according to claim 8.

Images