JP2010056051A - Method for producing polyelectrolyte membrane, polyelectrolyte membrane, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polyelectrolyte membrane which achieves both of a methanol barrier property and proton conductivity at high levels inexpensively, provide the polyelectrolyte membrane obtained by the producing method, and provide a membrane-electrode assembly and fuel cell using the polyelectrolyte membrane. <P>SOLUTION: A process includes a membrane forming step of forming a membrane from a polyelectrolyte solution containing a hydrocarbon block-type polyelectrolyte and a solvent to produce a solvent-containing block-type polyelectrolyte membrane, and a heat treatment step of heating the solvent-containing block-type polyelectrolyte membrane. By using this process, the polyelectrolyte membrane with excellent characteristics for a direct methanol fuel cell is obtained, wherein a temperature of the heat treatment is a temperature higher than a heat decomposition start temperature of the block-type polyelectrolyte for structuring the solvent-containing block-type polyelectrolyte membrane, and a residual amount of the solvent in the polyelectrolyte membrane after the heat treatment is not less than 1 wt.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte membrane, a membrane-electrode assembly using the polymer electrolyte membrane, and a fuel cell. More specifically, a method for producing a polymer electrolyte membrane suitable for use in a direct methanol fuel cell, a polymer electrolyte membrane obtained by the production method, a membrane-electrode assembly using the polymer electrolyte membrane, and a fuel cell About.

  In recent years, polymer electrolyte fuel cells have attracted attention as energy devices for houses and automobiles. Among them, a direct methanol fuel cell using methanol as a fuel is attracting attention as a power source for personal computers and portable devices because it can be miniaturized.

  As is well known, a fuel cell is composed of basic minimum units called cells. Each unit cell includes an electrolyte membrane, a catalyst layer provided on both sides of the electrolyte membrane, and a gas diffusion layer provided outside the catalyst layer. Each unit cell is separated and stacked by a separator provided outside the gas diffusion layer to constitute one fuel cell.

  The catalyst layer or the catalyst layer and the gas diffusion layer provided on both sides of the electrolyte membrane constitute an electrode portion of the unit cell, and fuel (hydrogen molecule, aqueous methanol solution, etc.) is supplied to one electrode portion (anode) However, when the catalyst layer is reached through the fine pores (diffusion layer) in the anode, an oxidation reaction occurs in the catalyst layer, and hydrogen ions and electrons are released. Hydrogen ions enter the electrolyte membrane and move in the direction of the other electrode portion (cathode) in the electrolyte membrane. The electrons reach the external circuit through the anode, and reach the catalyst layer on the cathode side through the external circuit.

  At the cathode, the catalyst layer on the cathode side consists of electrons that have reached through the external circuit, hydrogen ions that have moved from the anode into the electrolyte membrane, and oxygen molecules (air) introduced from the outside through the cathode gas diffusion layer. It reacts in it to become water and is discharged out of the system through the gas diffusion layer.

  Further, the electrode in the unit cell of the fuel cell as described above may indicate only the catalyst layer, or may indicate a joined body of the catalyst layer and the gas diffusion layer. An assembly in which the electrolyte membrane is sandwiched between the electrodes is referred to as a membrane-electrode assembly (MEA = Membrane Electrode Assembly). Therefore, the membrane-electrode assembly means an assembly in which an electrolyte membrane is sandwiched between a catalyst layer or a catalyst layer and a gas diffusion layer. That is, the membrane-electrode assembly is an assembly in which at least a catalyst layer is formed on both surfaces of the electrolyte membrane.

  Currently, there are several types of fuel cells, but as described above, they have a common principle that power and heat are extracted directly from fuel (hydrogen or methanol aqueous solution) and oxygen (air) by an electrochemical reaction. They are classified according to the type of electrolyte that serves as a passage for hydrogen ions (protons). The polymer electrolyte fuel cell uses a polymer electrolyte membrane as the electrolyte membrane, and is promising as a power source for automobiles, homes, and portables.

  In the polymer electrolyte fuel cell, a perfluoroalkane polymer electrolyte membrane (fluorine resin ion exchange membrane) represented by “Nafion” (registered trademark of DuPont) is mainly used for the electrolyte membrane. Since it operates at a relatively low temperature from room temperature to almost 100 ° C., it is promising as a power source for automobiles, homes, and portables as described above.

  Among the polymer electrolyte fuel cells, a direct methanol fuel cell (DMFC) using a methanol aqueous solution as a fuel is easy to handle because the fuel is liquid, and auxiliary equipment such as a humidifier. Therefore, it is possible to reduce the size and attract attention as a battery source for portable devices such as personal computers and mobile phones.

  As described above, a direct methanol fuel cell supplies an aqueous methanol solution as a fuel to an anode (fuel electrode). Therefore, if the polymer electrolyte membrane (proton conductive membrane) between the anode (fuel electrode) and the cathode (air electrode) has a low barrier property (methanol barrier property) against methanol, methanol will cause the polymer electrolyte membrane to The phenomenon of permeating and moving to the cathode occurs. This phenomenon is called methanol crossover (MCO), and if such a phenomenon occurs, there is a risk that the power generation performance will deteriorate or methanol will leak from the cathode, causing damage to the battery itself. is there.

  However, since the perfluoroalkane polymer electrolyte membrane used in the conventional solid polymer fuel cell has a low methanol barrier property and easily causes methanol crossover, the configuration of the conventional solid polymer fuel cell When applied directly to a methanol fuel cell, sufficient power generation performance cannot be obtained.

  For these reasons, development of high-performance hydrocarbon-based polymer electrolyte membranes, which replaces perfluoroalkane-based polymer electrolyte membranes conventionally used heavily as solid polymer electrolyte membranes, has been activated (Patent Document 1). . On the other hand, the methanol barrier property of the solid polymer electrolyte membrane and the proton conductivity related to the power generation performance are generally contradictory to each other. At present, the solid polymer electrolyte for high-performance solid polymer fuel cells No solid polymer electrolyte membranes suitable for use in membranes and direct methanol fuel cells are provided.

International Publication No. 2003/033566 Pamphlet

  The present invention has been made in view of the above-described conventional circumstances, and the problem is obtained by a method for producing a polymer electrolyte membrane capable of achieving both methanol barrier properties and proton conductivity at a high level, and the production method. It is an object of the present invention to provide a polymer electrolyte membrane, a membrane-electrode assembly using the polymer electrolyte membrane, and a fuel cell.

  In order to solve the above-described problems, a method for producing a polymer electrolyte membrane according to the present invention comprises forming a polymer electrolyte solution containing a hydrocarbon block polymer electrolyte and a solvent into a membrane, and then forming a solvent-containing block polymer. A method for producing a polymer electrolyte membrane, comprising: a membrane forming step for obtaining an electrolyte membrane; and a heat treatment step for obtaining a polymer electrolyte membrane by heating the solvent-containing block type polymer electrolyte membrane, The temperature is higher than the thermal decomposition start temperature of the hydrocarbon block polymer electrolyte, and the amount of residual solvent in the polymer electrolyte membrane after treatment is 1 wt% or more.

  As described above, the electrolyte membrane used in the present invention is a hydrocarbon block polymer electrolyte membrane obtained from a hydrocarbon block polymer electrolyte. However, in the description of this specification, the electrolyte membrane is not redundant. If necessary, they may be abbreviated as block type polymer electrolyte membranes, polymer electrolyte membranes, and electrolyte membranes. Similarly, the hydrocarbon block polymer electrolyte used to form the electrolyte membrane of the present invention may be abbreviated as a block polymer electrolyte or a polymer electrolyte.

  In the production method having the above-described configuration, the number average molecular weight in terms of polystyrene determined by gel permeation chromatography of the polymer electrolyte constituting the polymer electrolyte membrane after the heat treatment step is a solvent-containing block type polymer electrolyte before the heat treatment. It is desirable that it be higher than the polymer electrolyte constituting the membrane.

  The polymer electrolyte membrane obtained through the heat treatment step is suitable for use in a polymer electrolyte membrane of a direct methanol fuel cell.

  In the manufacturing method of the said structure, it is preferable that 10% or more of the cation exchange group which the said hydrocarbon type block type polymer electrolyte has is a proton type.

  In the manufacturing method having the above configuration, it is preferable that the hydrocarbon block polymer electrolyte is a block copolymer including a block having a cation exchange group and a block having substantially no ion exchange group. .

  As the block having a cation exchange group, the following general formula (1):

［式（１）中、Ａｒ¹¹は、２価の芳香族基を示し、該２価の芳香族基は、置換基を有していてもよい炭素数１〜２０のアルキル基、置換基を有していてもよい炭素数１〜２０のアルコキシ基、置換基を有していてもよい炭素数６〜２０のアリール基、置換基を有していてもよい炭素数６〜２０のアリールオキシ基、及び置換基を有していてもよい炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種を有していてもよく、また、該２価の芳香族基は、少なくとも１つのカチオン交換基が直接芳香環に結合しており、Ｘ¹¹は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を示し、ｄは５以上の整数である。］で表される構造単位を有するものが、好ましい。

[In the formula (1), Ar ¹¹ represents a divalent aromatic group, and the divalent aromatic group represents an optionally substituted alkyl group having 1 to 20 carbon atoms or a substituent. C1-C20 alkoxy group which may have, C6-C20 aryl group which may have a substituent, C6-C20 aryloxy which may have a substituent The divalent aromatic group may have at least one selected from the group consisting of a group and an optionally substituted acyl group having 2 to 20 carbon atoms. A cation exchange group is directly bonded to an aromatic ring, X ¹¹ represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group, and d is an integer of 5 or more. It is. Those having a structural unit represented by the formula:

  Moreover, as a block which has the said cation exchange group, following General formula (2) or (3):

［式（２）および（３）中、Ｒ^１は、それぞれ独立に、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、または炭素数２〜２０のアシル基を表し、Ｘ^１２は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を表し、Ｊ^１はカチオン交換基を表わし、ｐ、ｑは１または２であり、ｄは５以上の整数である。］で表される構造を有するものが、好ましい。

[In the formulas (2) and (3), each R ¹ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or carbon. Represents an aryloxy group having 6 to 20 carbon atoms or an acyl group having 2 to 20 carbon atoms, and X ¹² represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group. It represents, J ¹ represents a cation exchange group, p, q is 1 or 2, d is an integer of 5 or more. It is preferable to have a structure represented by

  Moreover, as a block which does not have the said ion exchange group substantially, following General formula (4):

［式（４）中、Ａｒ²²は、２価の芳香族基を示し、該２価の芳香族基は、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、及び炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種を有していてもよく、Ｘ²²は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を示し、ｅは５以上の整数である。］で表される構造単位を有するものが、好ましい。

[In formula (4), Ar ²² represents a divalent aromatic group, and the divalent aromatic group includes an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and 6 carbon atoms. Or an aryl group having 20 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms, and X ²² may be a direct bond, —O A group represented by-, a group represented by -S-, a carbonyl group or a sulfonyl group, and e is an integer of 5 or more. Those having a structural unit represented by the formula:

  Furthermore, as a block which does not have the said ion exchange group substantially, following General formula (5):

［式（５）中、Ａｒ²、Ａｒ³、Ａｒ⁴、Ａｒ⁵は、互いに独立に、２価の芳香族基を示し、該２価の芳香族基は、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、及び炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種を有していてもよく、Ｘ、Ｘ’は、互いに独立に直接結合または２価の基を表し、Ｙ、Ｙ’は、互いに独立に−Ｏ−で示される基または−Ｓ−で示される基を表し、ａ、ｂ、ｃは互いに独立に０か１を表し、ｎは５以上の整数を表す。］で表される構造単位を有するものが、好ましい。

[In Formula (5), Ar ² , Ar ³ , Ar ⁴ , Ar ⁵ independently represent a divalent aromatic group, and the divalent aromatic group represents an alkyl group having 1 to 20 carbon atoms. , Having at least one selected from the group consisting of an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms. X and X ′ each independently represent a direct bond or a divalent group, Y and Y ′ each independently represent a group represented by —O— or a group represented by —S—, a, b and c each independently represents 0 or 1, and n represents an integer of 5 or more. Those having a structural unit represented by the formula:

  The polymer electrolyte membrane according to the present invention is obtained by the above-described production method according to the present invention.

  The membrane-electrode assembly according to the present invention is characterized by having catalyst layers on both sides of the polymer electrolyte membrane.

  Furthermore, the fuel cell according to the present invention has the above membrane-electrode assembly.

According to the production method of the present invention, a polymer electrolyte membrane having both high methanol barrier properties and proton conductivity can be obtained. The direct methanol fuel cell using the polymer electrolyte membrane of the present invention has high power generation characteristics and low methanol crossover, and the reduction in fuel consumption is reduced based on such characteristics. Can be suitably used.
The polymer electrolyte membrane according to the present invention is particularly suitable for use in a fuel cell. However, the polymer electrolyte membrane is not limited to a polymer electrolyte membrane for a fuel cell, and has barrier properties and ion conductivity against a solvent such as methanol. It can be used for various applications that require characteristics such as.

  In the method for producing a polymer electrolyte membrane of the present invention, first, a polymer electrolyte solution containing a hydrocarbon block type polymer electrolyte and a solvent is formed into a film to obtain a solvent-containing block type polymer electrolyte membrane (film formation). Process). Next, the solvent-containing block type polymer electrolyte membrane is heated (heat treatment step) to obtain a polymer electrolyte membrane.

  In the following, according to the above-described process sequence of the production method of the present invention, a hydrocarbon block type polymer electrolyte, a method for forming a membrane from a polymer electrolyte solution containing the polymer electrolyte and a solvent, and a membrane-containing solvent-containing block The heat treatment method for the polymer electrolyte membrane, the polymer electrolyte membrane obtained by the heat treatment, and the membrane-electrode assembly and fuel cell obtained using this polymer electrolyte membrane will be described.

(Hydrocarbon block polymer electrolyte)
In the production method of the present invention, the hydrocarbon block polymer electrolyte constituting the target hydrocarbon block polymer electrolyte membrane has a cation exchange group, and 50% or more of the total number of atoms is carbon and It is a block type polymer composed of hydrogen. As such a block type polymer, those in which at least 10% of the cation exchange groups are proton type are preferable, and among them, a block in which a cation exchange group is introduced and a block in which an ion exchange group is not substantially introduced. And a block copolymer having at least one of each. By using such a block copolymer, the effect of the present invention remarkably appears.

  As said cation exchange group, a sulfonic acid group, a phosphonic acid group, and a sulfonylimide group are preferable, and you may have these together. Of these, the cation exchange group is particularly preferably a sulfonic acid group.

  The “block type polymer electrolyte” refers to an electrolyte composed of a copolymer in which two or more types of chemically different blocks are bonded directly or via a linking group. The copolymer constituting the block-type polymer electrolyte used in the present invention includes a block having a cation exchange group and a block having substantially no ion exchange group as two or more types of chemically different blocks. It is preferable that it is a block copolymer which has.

  Further, the block type polymer electrolyte used in the present invention is preferably one that forms a microphase separation structure when formed into a membrane, and if a block type polymer electrolyte that forms such a microphase separation structure is used, The effect of the invention appears remarkably. The term “microphase separation structure” as used herein refers to a microscopic structure in the order of the molecular chain size because different polymer segments are bonded by chemical bonds when a block-type polymer electrolyte is formed into a membrane. It refers to the structure formed by phase separation. For example, when viewed with a transmission electron microscope (TEM), a fine phase (microdomain) having a high density of blocks having cation exchange groups and a high density of blocks having substantially no ion exchange groups In other words, the structure is such that the domain width of each microdomain structure, that is, the identity period is several nm to several hundred nm. Those having a microdomain structure of 5 nm to 100 nm are preferable.

  Among the polymer electrolytes, an aromatic block copolymer is preferably included from the viewpoint of heat resistance and ease of recycling. The aromatic block copolymer means a polymer compound having an aromatic ring in the main chain of the polymer chain and having a cation exchange group in the side chain and / or the main chain. As such an aromatic block copolymer, those soluble in a solvent are usually used, and these are preferable because they can be easily formed into a film by a known solution casting method.

  Even if the cation exchange group of these aromatic block copolymers is directly substituted for the aromatic ring constituting the main chain of the polymer, a linking group is added to the aromatic ring constituting the main chain. Or a combination thereof.

  Specific examples of the block copolymer include a block copolymer having a sulfonated aromatic polymer block described in JP-A No. 2001-250567, JP-A No. 2003-3232, and JP-A No. 2004-2004. No. 359925, Japanese Patent Application Laid-Open No. 2005-232439, Japanese Patent Application Laid-Open No. 2003-113136, etc., “a block copolymer having a polyether ketone and a polyether sulfone as a main chain structure and a block having a sulfonic acid group. Polymer ".

  The block copolymer having a cation exchange group is preferably a block including a structure in which a plurality of structural units represented by the following general formula (1) are linked, and a cation per structural unit. Expressed in terms of the number of exchange groups, it has an average of 0.5 or more, and preferably has an average of 1.0 or more.

［式（１）中、Ａｒ¹¹は、２価の芳香族基を示し、該２価の芳香族基は、置換基を有していてもよい炭素数１〜２０のアルキル基、置換基を有していてもよい炭素数１〜２０のアルコキシ基、置換基を有していてもよい炭素数６〜２０のアリール基、置換基を有していてもよい炭素数６〜２０のアリールオキシ基、及び置換基を有していてもよい炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種を有していてもよく、また、該２価の芳香族基は、少なくとも１つのカチオン交換基が直接芳香環に結合しており、Ｘ¹¹は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を示し、ｄは５以上の整数である。］

[In the formula (1), Ar ¹¹ represents a divalent aromatic group, and the divalent aromatic group represents an optionally substituted alkyl group having 1 to 20 carbon atoms or a substituent. C1-C20 alkoxy group which may have, C6-C20 aryl group which may have a substituent, C6-C20 aryloxy which may have a substituent The divalent aromatic group may have at least one selected from the group consisting of a group and an optionally substituted acyl group having 2 to 20 carbon atoms. A cation exchange group is directly bonded to an aromatic ring, X ¹¹ represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group, and d is an integer of 5 or more. It is. ]

  Examples of the alkyl group having 1 to 20 carbon atoms that may have a substituent include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, isobutyl group, n-pentyl group, 2,2-dimethylpropyl group, cyclopentyl group, n-hexyl group, cyclohexyl group, 2-methylpentyl group, 2-ethylhexyl group, nonyl group, decyl group, dodecyl group, hexadecyl group, adamantyl group, Alkyl groups having 1 to 20 carbon atoms such as icosyl group, and fluorine, hydroxyl, nitrile, amino, methoxy, ethoxy, isopropyloxy, phenyl, naphthyl, phenoxy, naphthyl, etc. An oxy group or the like is substituted, and an alkyl group having 1 to 20 carbon atoms in total is exemplified.

  Moreover, as a C1-C20 alkoxy group which may have the said substituent, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butyloxy group, sec-butyloxy group, for example Tert-butyloxy group, isobutyloxy group, n-pentyloxy group, 2,2-dimethylpropyloxy group, cyclopentyloxy group, n-hexyloxy group, cyclohexyloxy group, 2-methylpentyloxy group, 2-ethylhexyloxy group Group, a decyloxy group, an adamantyloxy group, a hexadecyloxy group, an icosyloxy group, etc., and an alkoxy group having 1 to 20 carbon atoms, and these groups include a fluorine atom, a hydroxyl group, a nitrile group, an amino group, a methoxy group, an ethoxy group, Isopropyloxy group, phenyl group, naphthyl group, Phenoxy group, and naphthyloxy group and the like are substituted, the total carbon number and an alkoxy group having 1 to 20.

  Examples of the aryl group having 6 to 20 carbon atoms that may have the substituent include aryl groups such as a phenyl group, a naphthyl group, an anthracenyl group, and a biphenyl group, and a fluorine atom, a hydroxyl group, A nitrile group, an amino group, a methoxy group, an ethoxy group, an isopropyloxy group, a phenyl group, a naphthyl group, a phenoxy group, a naphthyloxy group, and the like are substituted, and an aryl group having 6 to 20 carbon atoms in total is exemplified.

  Examples of the aryloxy group having 6 to 20 carbon atoms that may have a substituent include aryloxy groups such as a phenoxy group, a naphthyloxy group, an anthracenyloxy group, and a biphenyloxy group, and these groups. Substituted with a fluorine atom, hydroxyl group, nitrile group, amino group, methoxy group, ethoxy group, isopropyloxy group, phenyl group, naphthyl group, phenoxy group, naphthyloxy group, etc., and an aryl having a total carbon number of 6 to 20 An oxy group etc. are mentioned.

  Examples of the acyl group having 2 to 20 carbon atoms that may have a substituent include carbon such as acetyl group, propionyl group, butyryl group, isobutyryl group, benzoyl group, 1-naphthoyl group, and 2-naphthoyl group. A number 2 to 20 acyl group, and these groups are substituted with fluorine atom, hydroxyl group, nitrile group, amino group, methoxy group, ethoxy group, isopropyloxy group, phenyl group, naphthyl group, phenoxy group, naphthyloxy group, etc. And an acyl group having a total carbon number of 20 or less.

  Here, d is an integer greater than or equal to 5 which represents the polymerization degree of the said block, The range of 5-1000 is preferable, More preferably, it is 10-1000, Most preferably, it is 20-500. A value of d of 5 or more is preferable because a polymer electrolyte excellent in proton conductivity can be obtained. On the other hand, if the value of d is 1000 or less, it is preferable because the production of the block is easier.

  As a suitable example of the block represented by the general formula (1), a block represented by the following general formula (2) or (3) is preferable.

［式中、Ｒ¹は、それぞれ独立に、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、または炭素数２〜２０のアシル基を表し、Ｘ¹²は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を表し、Ｊ¹はカチオン交換基を表し、ｐ、ｑは１または２であり、ｄは５以上の整数である。］

[In the formula, each R ¹ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aryloxy having 6 to 20 carbon atoms. A group, or an acyl group having 2 to 20 carbon atoms, X ¹² represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group, and J ¹ represents cation exchange. Represents a group, p and q are 1 or 2, and d is an integer of 5 or more. ]

  When the block having an ion exchange group as described above is used, the polymer electrolyte membrane of the present invention can improve the membrane strength in addition to ensuring a high level of proton conductivity and water absorption dimensional stability. Therefore, it is preferable.

R ¹ represents a substituent as described above, and is particularly preferably a hydrogen atom, and a phenylene group or a naphthalenediyl group having substantially no substituent other than a cation exchange group is preferable.

  Specific examples of the block represented by the general formula (2) include structural units represented by the following formulas (2a-1) to (2a-30) when the cation exchange group is represented by a sulfonic acid group. And a block in which d structural units selected from the group are connected. Here, d is the number of definitions equivalent to d in the general formula (2), that is, an integer of 5 or more.

  Moreover, as a specific example of the block represented by the general formula (3), the structure represented by the following (3b-1) to (3b-28) when the cation exchange group is represented by a sulfonic acid group. A block formed by connecting d structural units selected from the group of units can be given. Here, d is the number of definitions equivalent to d in the general formula (2), that is, an integer of 5 or more.

上掲のブロックは、例えば、特開２００４−１９０００２号公報に記載の製造方法などに基づいて製造することができる。

The above-mentioned block can be manufactured based on, for example, a manufacturing method described in JP-A-2004-190002.

  Further, the block having a cation exchange group may be a block having both a structural unit constituting the block represented by the general formula (2) and a structural unit constituting the block represented by the general formula (3). Any block that is formed by connecting d pieces of them may be used.

  Moreover, as a cation exchange group, a carboxylic acid group, a sulfonic acid group, a phosphonic acid group, and a sulfonylimide group are illustrated, and you may have these together. Among them, it is particularly preferable to include a sulfonic acid group that is a strong acid group as a cation exchange group.

Next, the block having substantially no ion exchange group will be described.
Here, “substantially free of ion exchange groups” means that most of the repeating units mainly constituting this block have no ion exchange groups. Specifically, the average number of ion exchange groups per structural unit constituting this block is 0.1 or less, preferably 0.05 or less. It is particularly preferred that no exchange groups are contained.

  Among the blocks having substantially no ion exchange group, a block represented by the following general formula (4) is particularly preferable.

［式（４）中、Ａｒ²²は、２価の芳香族基を示し、該２価の芳香族基は、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、及び炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種を有していてもよく、Ｘ²²は、直接結合、−Ｏ−で示される基、−Ｓ−で示される基、カルボニル基またはスルホニル基を示す。ｅは５以上の整数である。］
ここで、一般式（４）の芳香族基Ａｒ²²の置換基であるアルキル基、アルコキシ基、アリール基、アリールオキシ基およびアシル基の具体的な例示は、上記一般式（１）と同等である。
また、ｅは該ブロックの重合度を表す５以上の整数であり、５〜１０００の範囲が好ましく、さらに好ましくは１０〜１０００であり、特に好ましくは２０〜５００である。ｅの値が５以上であると、膜強度に優れる高分子電解質が得られるため好ましい。一方、ｅの値が１０００以下であれば、該ブロックの製造がより容易であるので好ましい。

[In formula (4), Ar ²² represents a divalent aromatic group, and the divalent aromatic group includes an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and 6 carbon atoms. Or an aryl group having 20 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms, and X ²² may be a direct bond, —O A group represented by-, a group represented by -S-, a carbonyl group or a sulfonyl group; e is an integer of 5 or more. ]
Here, specific examples of the alkyl group, the alkoxy group, the aryl group, the aryloxy group, and the acyl group, which are substituents of the aromatic group Ar ²² in the general formula (4), are equivalent to the above general formula (1). is there.
Moreover, e is an integer greater than or equal to 5 showing the polymerization degree of this block, The range of 5-1000 is preferable, More preferably, it is 10-1000, Most preferably, it is 20-500. A value of e of 5 or more is preferable because a polymer electrolyte having excellent film strength can be obtained. On the other hand, if the value of e is 1000 or less, it is preferable because the production of the block is easier.

  As the block having substantially no ion exchange group, a block represented by the following general formula (5) is particularly preferable.

［式（５）中、ａ、ｂ、ｃは互いに独立に０か１を表し、ｎは５以上の整数を表す。Ａｒ²、Ａｒ³、Ａｒ⁴、Ａｒ⁵は互いに独立に２価の芳香族基を表し、ここで、これらの２価の芳香族基は、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、炭素数６〜２０のアリール基、炭素数６〜２０のアリールオキシ基、及び炭素数２〜２０のアシル基からなる群から選ばれる少なくとも一種で置換されていてもよい。Ｘ、Ｘ’は、互いに独立に直接結合または２価の基を表す。Ｙ、Ｙ’は、互いに独立に−Ｏ−で示される基または−Ｓ−で示される基を表す。］

[In Formula (5), a, b, and c each independently represent 0 or 1, and n represents an integer of 5 or more. Ar ² , Ar ³ , Ar ⁴ , and Ar ⁵ each independently represent a divalent aromatic group, and these divalent aromatic groups are an alkyl group having 1 to 20 carbon atoms, a carbon number 1 to 1 It may be substituted with at least one selected from the group consisting of a 20 alkoxy group, an aryl group having 6 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms. X and X ′ each independently represent a direct bond or a divalent group. Y and Y ′ each independently represent a group represented by —O— or a group represented by —S—. ]

  N in the formula (5) is an integer of 5 or more representing the degree of polymerization related to the block, preferably in the range of 5 to 1000, more preferably 10 to 1000, and particularly preferably 20 to 500. It is preferable that the value of n is 5 or more because a polymer electrolyte having excellent film strength can be obtained. On the other hand, if the value of n is 1000 or less, it is preferable because the production of the block is easier.

  Preferable representative examples of the block represented by the general formula (5) include blocks represented by the following general formulas (5-1) to (5-22).

Specifically, examples of suitable block copolymers to be applied to the present invention include copolymers (6-1) to (6-18) having a combination structure shown in the following (Table 1).
In addition, in the following (Table 1), “the block having a cation exchange group (2a-1), (2a-4), (2a-19), and (2a-25)” respectively represents the general formula. This means the block described using (2a-1), (2a-4), (2a-19), and (2a-25), and similarly, “block having substantially no ion exchange group (5 -1), (5-2), (5-9), (5-10), (5-21), (5-22) "are respectively represented by general formulas (5-1), ( 5-2), the block described using (5-9), (5-10), (5-21), and (5-22).

  Particularly preferred block copolymers include those represented by the following general formulas (7-1) and (7-2).

  In addition, as the block copolymer, the ion exchange capacity of the block copolymer is 0.5 by adjusting the abundance ratio of the block having a cationic group and the block having substantially no ionic group. It is preferable to be in the range of ˜4.0 meq / g, more preferably in the range of 0.8 to 3.5 meq / g. The ion exchange capacity can be determined by a titration method.

  The above-mentioned block type polymer electrolyte can obtain the optimal molecular weight range as appropriate depending on its structure and the like, but generally it is expressed in terms of polystyrene-reduced number average molecular weight by GPC (gel permeation chromatography) method. Preferably, 5000-500000 is more preferable, and 10000-300000 is further more preferable.

  When the average molecular weight is 1000 or more, the film strength tends to be further improved. When the average molecular weight is 1000000 or less, the solubility of the polymer electrolyte in a solvent is improved, and the solution viscosity of the resulting solution is lowered. Therefore, the above molecular weight range is preferable because film formation by the solution casting method is facilitated.

  When at least a part of the cation exchange group of the block type polymer electrolyte is proton type, the thermal decomposition starting temperature of the block type molecular electrolyte is lowered, and accordingly, the heat treatment temperature in the heat treatment described later is also lowered. This is preferable. The ratio of the cation exchange group being proton type is preferably 10% or more. More preferably, it is 50% or more, More preferably, it is 80% or more.

(Solvent-containing block type polymer electrolyte membrane and method for forming the membrane)
The film forming method for obtaining the solvent-containing block type polymer electrolyte membrane from a solution obtained by dissolving the above block type polymer electrolyte in an appropriate solvent is not particularly limited, and spin coating, solution casting Although a known method such as a method can be used, a solvent-containing block type polymer electrolyte membrane is produced on the support material by casting the solution onto a support substrate and reducing the amount of solvent. The solution casting method is particularly preferable because the operation is simple.
As another membrane forming method, a solution obtained by dissolving the block type polymer electrolyte in an appropriate solvent is applied to a porous membrane support, and the block membrane high support is applied to the porous membrane support. A composite membrane composed of a porous membrane-like support and a block-type polymer electrolyte membrane held on the support is obtained by holding the molecular electrolyte and then reducing the amount of solvent in the polymer electrolyte solution. A film-forming method is also possible. This composite membrane may be used as a solvent-containing block type polymer electrolyte membrane to produce the polymer electrolyte membrane of the present invention. As the “porous membrane-like support” used in the membrane forming method, a porous material made of polyimide, polysulfone, polyamide, polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE) or the like is used. A membrane can be used.

The solvent is not particularly limited as long as it can dissolve the block type polyelectrolyte and can be removed thereafter. For example, N, N-dimethylformamide (hereinafter referred to as “DMF”), N, Aprotic polar solvents such as N-dimethylacetamide (hereinafter referred to as “DMAc”), N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”), dimethyl sulfoxide (hereinafter referred to as “DMSO”); or dichloromethane, Chlorinated solvents such as chloroform, 1,2-dichloroethane, chlorobenzene, dichlorobenzene; alcohols such as methanol, ethanol, propanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl Alkylene glycol monoalkyl ethers such as ether is preferably used. Among these suitable solvents, aprotic polar solvents are more preferably used. That is, an aprotic polar solvent such as DMF, DMAc, NMP, DMSO is preferable because of high solubility of the block type polymer electrolyte.
Although the said solvent can also be used independently, you may mix and use 2 or more types as needed.

  The support base material used in the solution casting method is not particularly limited as long as it does not swell or dissolve with the solution and the film obtained after film formation can be peeled off. For example, glass, stainless steel, stainless steel A belt, a polyethylene terephthalate (PET) film, a polytetrafluoroethylene (PTFE) film or the like is preferably used. If necessary, the surface of the substrate may be subjected to release treatment, mirror surface treatment, embossing treatment, or matting treatment.

  The concentration of the block type polymer electrolyte in the solution used for the solution casting method is usually 5 to 40% by weight, preferably 5 to 30% by weight, although it depends on the molecular weight of the used block type polymer electrolyte itself. When this block type polymer electrolyte concentration is 5% by weight or more, a film having a practical film thickness is easy to process, and when it is 40% by weight or less, the solution viscosity of the resulting solution becomes low. Since it becomes easy to obtain the film of the surface, it is preferable.

  Moreover, in this solution casting (film formation process), in order to reduce the amount of solvent and cure the coating film, heating may be performed. In this case, the heating temperature range is the thermal decomposition of the block type polymer electrolyte. It is desirable that the temperature be lower than the starting temperature.

(Heat treatment process of solvent-containing block type polymer electrolyte membrane)
The solvent-containing block type polymer electrolyte membrane is heat-treated to obtain a desired polymer electrolyte membrane. In this heat treatment step, the solvent-containing block-type polymer electrolyte membrane is treated at a temperature higher than the thermal decomposition start temperature of the block-type polymer electrolyte constituting the electrolyte membrane. Preferably, heat is applied at a temperature 10 to 100 ° C, more preferably 20 ° C to 80 ° C higher than the thermal decomposition start temperature. The thermal decomposition starting temperature of the block type polymer electrolyte in this case can be measured by TG / DTA. When heat at a predetermined temperature higher than the thermal decomposition start temperature of the block-type polymer electrolyte is applied to the solvent-containing block-type polymer electrolyte membrane, at that temperature, the block-type polymer electrolyte in a state where the solvent remains The degree of thermal decomposition may be reduced. That is, if the solvent remains even when the block polymer electrolyte is heated at a temperature at which thermal decomposition starts, the molecular weight of the block polymer electrolyte may be increased before the block polymer electrolyte decomposes. Is possible. Preferably, the molecular weight of the block type polymer electrolyte constituting the polymer electrolyte membrane is increased in a range soluble in the solvent as compared with that before the heat treatment. The degree of increase is that the number average molecular weight of the block type polymer electrolyte after the heat treatment step is 1.05 times or more with respect to the number average molecular weight of the block type polymer electrolyte before the heat treatment step. Preferably, it is 1.10 times or more.

  In addition, the heating time in this heat treatment largely depends on the kind of the solvent-containing block type polymer electrolyte membrane and the heat treatment temperature, but the block type high molecular weight constituting the solvent-containing block type polymer electrolyte membrane is In order to suppress the degree of thermal decomposition of the molecular electrolyte and obtain a high treatment effect and productivity, it is preferably 1 minute or longer and 5 hours or shorter, and more preferably 5 minutes or longer and 3 hours or shorter.

  In order to realize the above-mentioned “high molecular weight of the block-type polyelectrolyte within the range soluble in the solvent”, the control of the heating temperature and the heating time within the above range and the remaining in the film during the heat treatment It is important to maintain the amount of solvent so that the amount of residual solvent in the film after heat treatment is 1% by weight or more.

  Here, “the amount of residual solvent in the film of 1% by weight or more” means that the amount of residual solvent is 1% by weight or more with respect to the weight of the entire film. The “residual solvent amount” means the amount of solvent remaining in the film after the heat treatment. Here, “solvent” refers to the solvent used at the time of casting film formation. Further, “after heat treatment” means a time range within 6 hours immediately after the heat treatment step is finished. That is, in the method for producing a polymer electrolyte membrane of the present invention, the residual solvent amount in the polymer electrolyte membrane is 1% by weight in a specific time within a time range of 6 hours or less immediately after completion of the heat treatment step. That's it. This residual solvent amount can be determined by gas chromatography.

That is, in the method for producing a polymer electrolyte membrane of the present invention, a solvent-containing block type polymer electrolyte membrane obtained by forming a polymer electrolyte solution into a membrane is used as a block type constituting the solvent-containing block type polymer electrolyte membrane. Treating at a temperature higher than the thermal decomposition start temperature of the polymer electrolyte, and maintaining the solvent content in the solvent-containing polymer electrolyte membrane so that the residual solvent amount after the heat treatment is 1% by weight or more As a result, the degree of thermal decomposition of the block-type polymer electrolyte is reduced. Preferably, the molecular weight of the block type polymer electrolyte constituting the polymer electrolyte membrane is increased in a range soluble in the solvent as compared with that before the heat treatment. As a result, the obtained polymer electrolyte membrane is made high molecular weight (densified) while maintaining flexibility. Due to such a reaction mechanism, the polymer electrolyte membrane obtained by the production method of the present invention has a solid polymer fuel cell, in particular, which is difficult to permeate methanol while maintaining high proton conductivity, and has excellent handling properties. It will be suitable for direct methanol fuel cells.
When the amount of the residual solvent is less than 1% by weight, the flexibility and handling properties of the film are insufficient. The reason why such an effect is manifest is not necessarily clear, but the present inventor estimates as follows. That is, in the block-type hydrocarbon polymer electrolyte, the block having cation exchange groups has a relatively dense accumulation of cation exchange groups, and the accumulated cation exchange groups react with each other and are good. It is estimated that the methanol barrier property is developed.

  In the above heat treatment step, if the treatment is performed in an atmosphere in which a large amount of oxygen is present during heating, an undesirable side reaction such as oxidation of the polymer electrolyte membrane due to oxygen occurs, so the treatment is performed in a vacuum or under an inert gas. It is desirable.

  Moreover, it is preferable to perform the solution casting (film formation process) demonstrated previously in the temperature range below the thermal decomposition start temperature of a block type polymer electrolyte, and to perform the above-mentioned heat processing continuously after that. By performing solution casting in the temperature range below the thermal decomposition starting temperature in advance, it is possible to prevent the appearance of the film from being deteriorated due to rapid volatilization of the solvent and to maintain the amount of residual solvent in the film during the heat treatment described above. Is also easier. Furthermore, even if the heat treatment for increasing the molecular weight of the subsequent film is performed at a high temperature exceeding the thermal decomposition starting temperature of the block type polymer electrolyte by the solvent component remaining by such control, it can be obtained by the heat treatment. The polymer electrolyte membrane is highly flexible, hardly cracks, and has excellent handling properties.

  The heat-treated polymer electrolyte membrane is preferably converted to a proton type by acid treatment with sulfuric acid or hydrochloric acid. Furthermore, it is preferable to go through a water washing step in order to remove the residual solvent.

  The thickness of the polymer electrolyte membrane of the present invention is not particularly limited, but is preferably 5 to 200 μm. More preferably, it is 8-100 micrometers, Most preferably, it is 15-80 micrometers. A thickness larger than 5 μm is preferable for obtaining a membrane strength that can withstand practical use, and a thickness smaller than 200 μm is preferable for reducing membrane resistance, that is, improving power generation performance.

(Membrane-electrode assembly and fuel cell)
Next, the membrane-electrode assembly (MEA) and fuel cell of the present invention will be described. In the following description, the case where the membrane-electrode assembly of the present invention is applied to a direct methanol fuel cell (DMFC) is described as an example, but the membrane-electrode assembly of the present invention is not limited to DMFC. In addition, it can be used for a fuel cell using hydrogen as a raw material.

  The membrane-electrode assembly of the present invention can be produced by forming at least a catalyst layer on both surfaces of the polymer electrolyte membrane obtained as described above. As a method of forming a catalyst layer on both surfaces of the polymer electrolyte membrane, a catalyst layer is directly formed on the electrolyte membrane, and a catalyst layer is previously formed on a substrate other than the electrolyte membrane. There are two methods for joining the catalyst layer and the electrolyte membrane later.

  The catalyst layer used in the present invention contains a catalyst substance. The catalyst substance is not particularly limited as long as it can activate the oxidation-reduction reaction between methanol and oxygen, and a known substance can be used. For example, noble metals such as platinum and platinum-ruthenium alloys and complex-based electrode catalysts (for example, Fuel Cell Materials Research Group, Polymer Society of Japan, “Fuel cells and polymers”, pages 103 to 112, Kyoritsu Shuppan, 2005 Described in the November 10 issue). Among these, it is preferable to use fine particles of platinum or a platinum ruthenium alloy. Usually, platinum or platinum ruthenium (fine particles) is used as a catalyst for the catalyst layer (first catalyst layer) on the fuel electrode (anode) side, and the catalyst for the catalyst layer (second catalyst layer) on the air electrode side (cathode). Platinum (fine particles) is used. In addition, it is preferable to use a conductive material having the catalyst substance supported on the surface because hydrogen ions and electrons can be easily transported in the catalyst layer. Examples of the conductive material include known materials such as conductive carbon materials such as carbon black and carbon nanotubes, and ceramic materials such as titanium oxide.

  In addition, the catalyst layer applied to the present invention preferably contains a polymer electrolyte. The polymer electrolyte is not particularly limited as long as it has ion conductivity and functions as a binder for binding the catalyst substance, and conventionally known Nafion (trade name) manufactured by DuPont or fat. Group polymer electrolytes and aromatic polymer electrolytes. In addition to the catalyst substance and polymer electrolyte, a water repellent material such as PTFE is further obtained for the purpose of enhancing the water repellency of the catalyst layer, and a pore former such as calcium carbonate is further obtained for the purpose of enhancing the gas diffusibility of the catalyst layer. In some cases, a stabilizer such as a metal oxide is included for the purpose of enhancing the durability of the membrane-electrode assembly.

  In order to diffuse fuel efficiently and uniformly, it is preferable to provide a gas diffusion layer outside the catalyst layer constituting the membrane-electrode assembly of the present invention. The gas diffusion layer is not particularly limited as long as it is conductive, but a porous carbon nonwoven fabric or carbon paper is preferable because it is inexpensive and easy to handle.

  The method for forming the catalyst layer on the electrolyte membrane or on a substrate other than the electrolyte membrane is not particularly limited, and an existing method such as a die coater, screen printing, spray method, ink jet method or the like should be used. Can do.

  The base material other than the electrolyte is not particularly limited as long as it does not swell or dissolve when the catalyst layer is formed. For example, the above-described gas diffusion layer, glass, stainless steel, stainless steel belt, A polyethylene terephthalate (PET) film or the like is preferably used. If necessary, the surface of the base material may be subjected to release treatment, mirror surface treatment, embossing treatment, or matting treatment.

In the case of a method in which a catalyst layer is formed on another substrate in advance and the catalyst layer is bonded to the electrolyte membrane, it is preferable to perform a hot pressing method in which temperature or pressure is applied during bonding. The heating temperature is not particularly limited as long as it is a temperature region or a pressure region in which the membrane is not denatured. Usually, the temperature is preferably 30 ° C. or more and 300 ° C. or less, which improves the bonding property and does not alter the electrolyte membrane. It is more preferably 50 ° C. or higher and 250 ° C. or lower. The pressure membrane is not deformed, preferably 5 kgf / cm ² or more 300 kgf / cm ² or less, 30 kgf / cm ² or more 200 kgf / cm ² or less being more preferred.

  As described above, a membrane-electrode assembly is obtained in which at least the catalyst layer is bonded to both surfaces of the polymer electrolyte membrane obtained by the production method of the present invention. When this membrane-electrode assembly is used in a direct methanol fuel cell (DMFC), it is possible to obtain a fuel cell that is excellent in power generation performance and in which damage to the cell due to methanol crossover is remarkably suppressed.

Examples of the present invention will be described below. However, the examples shown below are suitable examples for explaining the present invention, and do not limit the present invention.
Before moving to the specific description of the examples of the present invention, the polymer electrolytes obtained in each production example, each example and each comparative example, the molecular weight of the polymer electrolyte membrane, the residual solvent amount, proton conductivity, methanol permeation Each measurement method for measuring various values of coefficient and ion exchange capacity (IEC) will be described below.

[Molecular weight measurement]
The number average molecular weight in terms of polystyrene was determined by gel permeation chromatography (GPC) under the following conditions.
GPC measuring device HLC-8220 manufactured by TOSOH
Column TSK-GEL GMHHR-M manufactured by TOSOH
Column temperature 40 ° C
Mobile phase solvent DMAc (LiBr added to 10 mmol / dm ³ )
Solvent flow rate 0.5mL / min

[Residual solvent amount]
The heat-treated polymer electrolyte membrane was placed at room temperature and atmospheric pressure after the heat treatment step, dissolved in a sample solution (dimethylformamide) within 6 hours, and measured by gas chromatography using a GC apparatus. . The obtained measured value was analyzed based on the following analysis method, and the amount of residual solvent remaining in the polymer electrolyte membrane was calculated.
GC device: “6890” (trade name, manufactured by Hewlett-Packard Company)
Analysis method: A calibration curve with the horizontal axis representing the set concentration of the standard solution and the vertical axis representing the peak area value was created, and the amount of residual solvent in the polymer electrolyte membrane was calculated using the following calculation formula.

Residual solvent amount (ppm) = {(PA-Y _ac ) / G _ac } × {SS / PEM}
Where PA: peak area
Y _ac : y-intercept of calibration curve
G _ac : The slope of the calibration curve
SS: Sample solution volume (mL)
PEM: Polymer electrolyte membrane weighing value (g)

[Measurement of proton conductivity (σ)]
New Experimental Chemistry Lecture 19 Polymer resistance (II) 992p (edited by the Chemical Society of Japan, Maruzen) was used to measure the membrane resistance of the polymer electrolyte membrane obtained in each example. However, the cell used was made of carbon, and the platinum electrode with platinum black was not used, and the terminal of the impedance measuring device was directly connected to the cell. First, the polymer electrolyte membrane was set in the cell, and the resistance value was measured. Thereafter, the resistance value was measured again with the polymer electrolyte membrane removed, and the membrane resistance was calculated from the difference between the two. 1 mol / L dilute sulfuric acid was used for the solution brought into contact with both sides of the polymer electrolyte membrane. The proton conductivity was calculated from the film thickness and resistance value when immersed in dilute sulfuric acid.

[Measurement of methanol permeability coefficient (D)]
After each sample of the polymer electrolyte membrane obtained in each example was immersed in a 10 wt% methanol aqueous solution for 2 hours, this sample polymer electrolyte membrane was placed in the center of an H-shaped diaphragm cell consisting of cell A and cell B. The methanol in the cell B after 10 wt% concentration methanol aqueous solution was put in the cell A and pure water was put in the cell B, and left at 23 ° C. for a predetermined time t (sec) from the initial state. The concentration was analyzed, and the methanol permeability coefficient D (cm ² / sec) was determined by the following equation.
D = {(V × L) / (A × t)} × ln {(C 1 -C m) / (C 2 -C n)}
here,
V: Volume of liquid in cell B (cm ³ )
L: Sample polymer electrolyte membrane thickness (cm)
A: Cross-sectional area of sample polymer electrolyte membrane (cm ² )
t: Time (sec)
C ₁ : concentration of methanol in cell B in the initial state (mol / cm ³ )
C ₂ : Methanol concentration (mol / cm ³ ) in the cell B after standing for a predetermined time t
C _m : concentration of methanol in cell A in the initial state (mol / cm ³ )
C _n : Methanol concentration in cell A after leaving for a certain time t (mol / cm ³ )
Since the methanol permeation amount was sufficiently small, V was determined to be a constant value at the initial pure water capacity, and to be determined as an initial concentration (10 wt%) with C _m = C _n .

[Calculation of characteristic parameter (D / σ)]
A polymer electrolyte membrane suitable for a direct methanol fuel cell is a membrane having a high proton conductivity (σ) and a small methanol permeability coefficient (D). As the index, the value of D / σ was calculated as a characteristic parameter from the value obtained above. When this value is small, when the same conductivity (σ) is used, the methanol permeability is low, which indicates that it is excellent as a polymer electrolyte membrane for a direct methanol fuel cell (DMFC).

[Ion exchange capacity of polymer electrolyte membrane (IEC)]
The obtained polymer electrolyte membrane was dried at 110 ° C., and the dry weight was determined with a halogen moisture meter (trade name “HR73” manufactured by METTLER TOLEDO). After immersing in 5 mL of L sodium hydroxide aqueous solution, 50 mL of ion-exchanged water was added and left for 2 hours. Then, it titrated by adding 0.1 mol / L hydrochloric acid gradually to the solution in which this polymer electrolyte membrane was immersed, and the neutralization point was calculated | required. The ion exchange capacity was determined from the amount of 0.1 mol / L hydrochloric acid required for the neutralization point and the absolute dry weight.
Moreover, the salt exchange rate Y (%) was calculated | required based on the following formula (B).
Y = (1-H / T) × 100 (B)
T: Total amount of ion exchange groups per gram of polymer electrolyte membrane before salt substitution treatment H: Amount of ion exchange groups whose counter ion per gram of polymer electrolyte membrane after salt substitution treatment is proton

[Pyrolysis start temperature]
The thermal decomposition start temperature was measured using a TG / DTA simultaneous measurement apparatus (manufactured by Seiko Instruments Inc., trade name “SSC-5200”). The temperature is raised from 30 ° C. to 110 ° C. at 50 ° C./min, held at 110 ° C. for 30 minutes, and then heated from 110 ° C. to 300 ° C. at 5 ° C./min. It was.

(Production Example 1: Production Example of Polymer Electrolyte)
In a flask with a distillation tube under an argon atmosphere, 3,3′-diphenyl-4,4′-dihydroxybiphenyl: 15.32 g (45.28 mmol), 4,4′-difluorodiphenylsulfone: 10.62 g (41 .77 mmol), potassium carbonate: 6.57 g (47.54 mmol), dimethyl sulfoxide (DMSO): 114 ml, and toluene: 18 ml were added and stirred. Next, the bath temperature was raised to 150 ° C., and toluene was distilled off by heating to azeotropically dehydrate water in the system. After the toluene was distilled off, the reaction was carried out at the same temperature for 2 hours. This is called reaction mass [A].

  In a flask equipped with a distillation tube under an argon atmosphere, potassium hydroquinonesulfonate: 4.00 g (17.52 mmol), dipotassium 4,4′-difluorobenzophenone-3,3′-disulfonate: 9.56 g (21.03 mmol) ), Potassium carbonate: 2.54 g (18.40 mmol), DMSO: 60 ml, and toluene: 9 ml were added and stirred. Subsequently, the bath temperature was raised to 130 ° C., and toluene was distilled off by heating to azeotropically dehydrate water in the system. After the toluene was distilled off, the reaction was carried out at the same temperature for 20 hours 30 minutes. This is called reaction mass [B].

  The reaction mass [A] and the reaction mass [B] were mixed while being diluted with DMSO: 68 ml, and the mixture was reacted at 145 ° C. for 33 hours and 30 minutes. After allowing to cool, the reaction mixture was dropped into a large amount of 2 mol / L hydrochloric acid aqueous solution, and the resulting precipitate was collected by filtration, and washed and filtered repeatedly with water until the washing solution became neutral. Next, the filtrate was treated twice with a large excess of hot water for 1 hour, then dried under reduced pressure, and the target polymer electrolyte represented by the following general formula (8) (block copolymer A) 33.33 g was obtained.

このブロック共重合体Ａの数平均分子量は７９０００であり、熱分解開始温度は２１０℃であった。

The number average molecular weight of this block copolymer A was 79000, and the thermal decomposition starting temperature was 210 ° C.

(Production Example 2)
In a flask equipped with a distillation tube under an argon atmosphere, 3,3′-diphenyl-4,4′-dihydroxybiphenyl: 12.68 g (37.48 mmol), 4,4′-difluorobenzophenone: 4.58 g (20. 98 mmol), 4,4′-difluorobenzophenone-3,3′-disulfonate dipotassium: 7.50 g (16.50 mmol), potassium carbonate: 5.44 g (39.36 mmol), N-methylpyrrolidone (NMP): 96 ml And toluene: 44 ml was added and stirred. Subsequently, the bath temperature was raised to 190 ° C., and toluene was distilled off by heating to azeotropically dehydrate water in the system. After the toluene was distilled off, the reaction was carried out at the same temperature for 9 hours 30 minutes. After allowing to cool, the reaction mixture was dropped into a large amount of 2 mol / L hydrochloric acid aqueous solution, and the resulting precipitate was collected by filtration, and washed and filtered repeatedly with water until the washing solution became neutral. Subsequently, the filtrate was treated twice with a large excess of hot water for 1 hour, and then dried under reduced pressure to obtain the desired polymer electrolyte represented by the following general formula (9) (random copolymer A). 18.99 g was obtained.

このランダム共重合体Ａの数平均分子量は４３０００であり、熱分解開始温度は２１５℃であった。

The random copolymer A had a number average molecular weight of 43,000 and a thermal decomposition starting temperature of 215 ° C.

(Production Example 3)
In a flask equipped with an azeotropic distillation apparatus under an argon atmosphere, DMSO: 600 ml, toluene: 200 mL, sodium 2,5-dichlorobenzenesulfonate: 26.5 g (106.3 mmol), the following general formula (terminal chloro type) 10)

で示されるポリエーテルスルホン（住友化学株式会社製、商品名「スミカエクセルＰＥＳ ５２００Ｐ」）：１０．０ｇ、２，２’−ビピリジル：４３．８ｇ(２８０．２ｍｍｏｌ)を入れて攪拌した。その後、バス温を１５０℃まで昇温し、トルエンを加熱留去することで系内の水分を共沸脱水した後、６０℃に冷却した。
次いで、これにビス（１，５−シクロオクタジエン）ニッケル：７３．４ｇ(２６６．９ｍｍｏｌ)を加え、８０℃に昇温し、同温度で５時間攪拌した。放冷後、反応液を大量の６ｍｏｌ／Ｌの塩酸に注ぐことによりポリマーを析出させ濾別した。
その後、６ｍｏｌ／Ｌ塩酸による洗浄・濾過操作を数回繰り返した後、濾液が中性になるまで水洗を行い、減圧乾燥することにより目的とする下記一般式（１１）で示される高分子電解質（ブロック共重合体Ｂ）：１６．３ｇを得た。

(Sumitomo Chemical Co., Ltd., trade name “Sumika Excel PES 5200P”): 10.0 g, 2,2′-bipyridyl: 43.8 g (280.2 mmol) were added and stirred. Thereafter, the bath temperature was raised to 150 ° C., and the water in the system was azeotropically dehydrated by distilling toluene off, followed by cooling to 60 ° C.
Next, bis (1,5-cyclooctadiene) nickel: 73.4 g (266.9 mmol) was added thereto, the temperature was raised to 80 ° C., and the mixture was stirred at the same temperature for 5 hours. After cooling, the reaction solution was poured into a large amount of 6 mol / L hydrochloric acid to precipitate a polymer, which was filtered off.
Thereafter, washing and filtration operations with 6 mol / L hydrochloric acid were repeated several times, followed by washing with water until the filtrate became neutral, and drying under reduced pressure to obtain a target polymer electrolyte represented by the following general formula (11) ( Block copolymer B): 16.3 g was obtained.

このブロック共重合体Ｂの数平均分子量は１１５０００であり、熱分解開始温度は２００℃であった。

This block copolymer B had a number average molecular weight of 115,000 and a thermal decomposition initiation temperature of 200 ° C.

Example 1
The block copolymer A (thermal decomposition starting temperature 210 ° C.) obtained in Production Example 1 was dissolved in NMP so as to be 20% by weight, and then cast on a glass substrate and dried at 80 ° C. under normal pressure ( Film-forming step). Subsequently, it heated in 230 degreeC nitrogen oven for 1 hour (heat-treatment process). The amount of residual solvent in the obtained polymer electrolyte membrane was 4% by weight.

(Example 2)
The same experiment as in Example 1 was performed except that the temperature of the nitrogen oven was 240 ° C. The amount of residual solvent in the obtained polymer electrolyte membrane was 4% by weight.

(Comparative Example 1)
The same experiment as in Example 1 was performed except that the temperature of the nitrogen oven was set to 200 ° C. The amount of residual solvent in the obtained polymer electrolyte membrane was 10% by weight.

(Comparative Example 2)
The block copolymer A obtained in Production Example 1 was dissolved in NMP so as to be 20% by weight, and then cast on a glass substrate and dried at 80 ° C. under normal pressure (filming step). Subsequently, it heated for 30 minutes in 270 degreeC nitrogen oven. The amount of residual solvent in the obtained polymer electrolyte membrane was 0% by weight.

(Comparative Example 3)
The block copolymer A obtained in Production Example 1 was dissolved in NMP so as to be 20% by weight, and then cast on a glass substrate and dried at 80 ° C. under normal pressure (filming step). The obtained polymer electrolyte membrane was washed with running water for 2 hours to remove substantially all of the remaining solvent and dried at room temperature. The membrane was then heated in a nitrogen oven at 240 ° C. for 15 minutes. The obtained membrane was fragile, and it was impossible to measure the methanol permeability coefficient and proton conductivity.

(Comparative Example 4)
The random copolymer A (thermal decomposition start temperature 215 ° C.) obtained in Production Example 2 was dissolved in NMP so as to be 25% by weight, and then cast on a glass substrate and dried at 80 ° C. under normal pressure ( Film-forming step). Subsequently, it heated in 240 degreeC nitrogen oven for 1 hour (heat-treatment process). The amount of residual solvent in the obtained polymer electrolyte membrane was 4% by weight.

(Comparative Example 5)
The random copolymer A obtained in Production Example 2 (pyrolysis temperature initiation degree 215 ° C.) was dissolved in NMP so as to be 25% by weight, and then cast on a glass substrate and dried at 80 ° C. under normal pressure. (Filming process). Subsequently, it heated for 1 hour in 200 degreeC nitrogen oven (heat-treatment process). The amount of residual solvent in the obtained polymer electrolyte membrane was 11% by weight.

(Example 3)
The block copolymer B (thermal decomposition start temperature: 200 ° C.) obtained in Production Example 3 was dissolved in NMP so as to be 20% by weight, and then cast on a glass substrate and dried at room temperature at 80 ° C. ( Film-forming step).
Subsequently, it heated for 30 minutes in 210 degreeC nitrogen oven (heat-treatment process). The amount of residual solvent in the obtained polymer electrolyte membrane was 9% by weight.

(Comparative Example 6)
The same experiment as in Example 3 was performed except that the temperature of the nitrogen oven was set to 200 ° C.
The amount of residual solvent in the obtained polymer electrolyte membrane was 16% by weight.

  In Comparative Example 3, the obtained film was fragile and could not be subjected to post-treatment. For the remaining Examples 1, 2, and 3 and Comparative Examples 1, 2, 4, 5, and 6, The molecular electrolyte membrane was immersed in 1 mol / L hydrochloric acid for 3 hours to substantially convert the cation exchange group into a proton type and washed with running water for 3 hours. The number average molecular weight, proton conductivity (σ), and methanol permeability coefficient (D) of the obtained polymer electrolyte membrane were measured based on each measurement method described above.

  The measurement results of Examples 1 to 3 and Comparative Examples 1 to 6 are shown below (Table 2).

  The above-mentioned examples and comparative examples are examples examined by considering the case where the polymer electrolyte membrane is mainly used for a direct methanol fuel cell. Preferred characteristics as a polymer electrolyte membrane for a direct methanol fuel cell are high proton conductivity (σ) and small methanol permeability coefficient (D), that is, low characteristic coefficient (D / σ). .

As seen in Table 2 above, Examples 1 and 2 and Comparative Example 1 both use block copolymer A as the electrolyte material. And with respect to the thermal decomposition start temperature 210 degreeC, in the comparative example 1, it heat-processes (film-formation) at 200 degrees C or less of the said thermal decomposition start temperature, In Example 1 and 2, from the said thermal decomposition start temperature Heat treatment (film formation) is performed at a high 230 ° C. and 240 ° C. As a result, the characteristic coefficient is 8.5 × 10 ^{−6 in} Comparative Example 1, 7.1 × 10 ⁻⁶ in Example 1, and 6.2 × 10 ^{−6 in} Example 2, and thermal decomposition of the electrolyte material is started. The characteristic coefficient is smaller when the heat treatment is performed at a temperature higher than the temperature.

On the other hand, in Comparative Example 4 and Comparative Example 5, the random copolymer A is used as the electrolyte material. And with respect to the thermal decomposition start temperature 215 degreeC, in the comparative example 4, it heat-processes (film-formation) at 240 degreeC higher than the said thermal decomposition start temperature, and in the comparative example 3, 200 or less below the said thermal decomposition start temperature. Heat treatment (film formation) at ℃. As a result, the characteristic coefficient is 2.6 × 10 ⁻⁵ in Comparative Example 4 and 1.2 × 10 ^{−5 in} Comparative Example 5, and the characteristic coefficient is higher when the heat treatment is performed at a temperature higher than the thermal decomposition start temperature of the electrolyte material. Is getting bigger.

In Comparative Example 2 and Comparative Example 3, the same electrolyte material (block copolymer A) as in Examples 1 and 2 and Comparative Example 1 is used, but in Examples 1 and 2 and Comparative Example 1 above. Unlike the above, the amount of residual solvent after the heat treatment is less than 0.1% by weight. As a result of the residual solvent amount being less than 0.1% by weight, in Comparative Example 2, the characteristic coefficient D / σ is poor (2.5 × 10 ⁻⁵ ), and in Comparative Example 3, the film is fragile and handling properties are reduced. Is getting worse.

Moreover, both Example 3 and Comparative Example 6 use the block copolymer B as the electrolyte material. And with respect to the thermal decomposition start temperature 200 degreeC, in the comparative example 6, it heat-processes (film-formation) at the same 200 degreeC as the said thermal decomposition start temperature, In Example 3, it is 210 higher than the said thermal decomposition start temperature. Heat treatment (film formation) at ℃. As a result, the characteristic coefficient is 1.2 × 10 ^{−5 in} Comparative Example 6 and 9.7 × 10 ^{−6 in} Example 3. The characteristic coefficient is higher when the heat treatment is performed at a temperature higher than the thermal decomposition start temperature of the electrolyte material. Is smaller.

  As described above, according to the present invention, a method for producing a polymer electrolyte membrane that is inexpensive and can achieve both methanol barrier properties and proton conductivity at a high level, and a polymer electrolyte membrane obtained by the production method are provided. And a membrane-electrode assembly and a fuel cell using the polymer electrolyte membrane can be provided. The direct methanol fuel cell using the polymer electrolyte membrane of the present invention has high power generation characteristics and low methanol crossover, and the reduction in fuel consumption is reduced based on such characteristics. Can be suitably used.

Claims (12)

Forming a polymer electrolyte solution containing a hydrocarbon-based block-type polymer electrolyte and a solvent to form a solvent-containing block-type polymer electrolyte membrane, and heating the solvent-containing block-type polymer electrolyte membrane A method for producing a polymer electrolyte membrane comprising a heat treatment step for obtaining a polymer electrolyte membrane by
The temperature of the heat treatment is set to a temperature higher than the thermal decomposition start temperature of the hydrocarbon block polymer electrolyte, and the residual solvent amount of the polymer electrolyte membrane after the heat treatment is set to 1% by weight or more. A method for producing a polymer electrolyte membrane.   The number average molecular weight in terms of polystyrene determined by gel permeation chromatography of the polymer electrolyte constituting the polymer electrolyte membrane after the heat treatment step is a polymer electrolyte constituting the solvent-containing block type polymer electrolyte membrane before the heat treatment The method for producing a polymer electrolyte membrane according to claim 1, wherein the method is higher than that of the polymer electrolyte membrane.   3. The method for producing a polymer electrolyte membrane according to claim 1, wherein the polymer electrolyte membrane after the heat treatment is used as a polymer electrolyte membrane of a direct methanol fuel cell.   The method for producing a polymer electrolyte membrane according to any one of claims 1 to 3, wherein 10% or more of the cation exchange groups of the hydrocarbon-based block polymer electrolyte is a proton type.   The hydrocarbon-based block type polymer electrolyte is a block copolymer composed of a block having a cation exchange group and a block having substantially no ion exchange group. The manufacturing method of the polymer electrolyte membrane of any one of Claims 1. The block having a cation exchange group has the following general formula (1):

[In the formula (1), Ar ¹¹ represents a divalent aromatic group, and the divalent aromatic group represents an optionally substituted alkyl group having 1 to 20 carbon atoms or a substituent. C1-C20 alkoxy group which may have, C6-C20 aryl group which may have a substituent, C6-C20 aryloxy which may have a substituent The divalent aromatic group may have at least one selected from the group consisting of a group and an optionally substituted acyl group having 2 to 20 carbon atoms. A cation exchange group is directly bonded to an aromatic ring, X ¹¹ represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group, and d is an integer of 5 or more. It is. ] The manufacturing method of the polymer electrolyte membrane of Claim 5 characterized by the above-mentioned. The block having a cation exchange group is represented by the following general formula (2) or (3):

[In the formulas (2) and (3), each R ¹ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or carbon. Represents an aryloxy group having 6 to 20 carbon atoms or an acyl group having 2 to 20 carbon atoms, and X ¹² represents a direct bond, a group represented by —O—, a group represented by —S—, a carbonyl group or a sulfonyl group. It represents, J ¹ represents a cation exchange group, p, q is 1 or 2, d is an integer of 5 or more. ] The manufacturing method of the polymer electrolyte membrane of Claim 5 characterized by the above-mentioned. The block having substantially no ion exchange group is represented by the following general formula (4):

[In formula (4), Ar ²² represents a divalent aromatic group, and the divalent aromatic group includes an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and 6 carbon atoms. Or an aryl group having 20 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms, and X ²² may be a direct bond, —O A group represented by-, a group represented by -S-, a carbonyl group or a sulfonyl group, and e is an integer of 5 or more. ] The manufacturing method of the polymer electrolyte membrane of any one of Claims 5-7 characterized by the above-mentioned. The block having substantially no ion exchange group is represented by the following general formula (5):

[In Formula (5), Ar ² , Ar ³ , Ar ⁴ , Ar ⁵ independently represent a divalent aromatic group, and the divalent aromatic group represents an alkyl group having 1 to 20 carbon atoms. , Having at least one selected from the group consisting of an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, and an acyl group having 2 to 20 carbon atoms. X and X ′ each independently represent a direct bond or a divalent group, Y and Y ′ each independently represent a group represented by —O— or a group represented by —S—, a, b and c each independently represents 0 or 1, and n represents an integer of 5 or more. ] The manufacturing method of the polymer electrolyte membrane of any one of Claims 5-7 characterized by the above-mentioned.   A polymer electrolyte membrane obtained by the production method according to claim 1.   11. A membrane-electrode assembly comprising catalyst layers on both sides of the polymer electrolyte membrane according to claim 10.   A fuel cell comprising the membrane-electrode assembly according to claim 11.