JP4720091B2 - Ion exchange membrane - Google Patents

Description

  The present invention relates to an ion exchange membrane, and more particularly to an ion exchange membrane used in a fuel cell and particularly excellent in stability.

  As an example of an electrochemical device using a polymer solid electrolyte as an ionic conductor instead of a liquid electrolyte, a water electrolyzer and a fuel cell can be raised. The ion exchange membrane used for these must have proton conductivity as a cation exchange membrane and must be sufficiently stable chemically, thermally, electrochemically and mechanically. For this reason, perfluorocarbon sulfonic acid membranes, typically “Nafion (registered trademark)” manufactured by DuPont, have been used as long-term usable products. However, if the Nafion membrane is operated under conditions exceeding 100 ° C., the moisture content of the membrane drops rapidly and the membrane softens significantly. Further, in a fuel cell using liquid organic fuel such as a direct methanol fuel cell as a fuel, for example, when methanol is supplied to the fuel electrode side, the methanol permeates the ion exchange membrane to the air electrode side. The problem of crossover that flows in is remarkable. When this crossover occurs, for example, the problem that the liquid fuel and the oxidant directly react with each other and the power decreases, and the problem that the liquid fuel leaks from the air electrode side to the outside occurs. Furthermore, it is pointed out that the cost of the membrane is too high as an obstacle to the establishment of fuel cell technology.

  In order to overcome such drawbacks, various polymer ion exchange membranes in which a sulfonic acid group is introduced into a non-fluorinated aromatic ring-containing polymer have been studied. As a polymer skeleton, considering heat resistance and chemical stability, aromatic polyarylene ether compounds such as aromatic polyarylene ether ketones and aromatic polyarylene ether sulfones can be regarded as promising structures, A sulfonated polyarylethersulfone (for example, see Non-Patent Document 1), a sulfonated polyetheretherketone (for example, see Patent Document 1), sulfonated polystyrene, and the like have been reported. However, sulfonic acid groups introduced onto aromatic rings by sulfonation reaction of these polymers generally tend to be easily removed, and as a method for improving this, monomers having sulfonic acid groups introduced onto electron-withdrawing aromatic rings are used. Thus, a highly stable sulfonated polyarylethersulfone compound has been reported (see, for example, Patent Document 2).

  However, the stability as an ion exchange membrane is still not sufficient, and further improvements are being made. For example, Patent Document 3 and Patent Document 4 describe a method for increasing the stability by crosslinking. Each of these documents is a method of crosslinking two sulfonyl groups via a crosslinking agent, and the stability is improved, but there is a problem that it involves a complicated process and its control.

JP-A-6-93114 (pages 15-17) US Patent Application Publication No. 2002/0091225 (page 1-2) Special table 2001-522401 JP-A-6-93114 Journal of Membrane Science (Netherlands) 1993, 83, p. 211-220

  An object of the present invention is to improve the morphological stability of an ion exchange membrane. For example, the present invention has an effect of improving durability in a fuel cell and reducing methanol cross leak in a direct methanol fuel cell.

  The present invention provides an ion exchange membrane suitable for use as a polymer solid ion exchange membrane having high stability and excellent ion conductivity. The present invention also relates to a manufacturing method and a fuel cell using an ion exchange membrane.

  That is, the present invention is an aromatic hydrocarbon ion-exchange membrane having an acidic functional group, wherein the shape stability is improved by heat treatment at 150 ° C. or higher.

  Moreover, it is said ion exchange membrane, It is the said ion exchange membrane characterized by including a cyano group in a molecule | numerator at least.

  The ion exchange membrane according to any one of the above, wherein the ion exchange membrane has at least a sulfonic acid group as an acidic functional group.

  The ion exchange membrane according to any one of the above, wherein a hydrophilic portion containing a sulfonic acid group is crosslinked by heat treatment.

ただし、Ａｒは２価の芳香族基、Ｙはスルホン基またはケトン基、ＸはＨまたは１価のカチオン種を示す。

ただし、Ａｒ'は２価の芳香族基を示す。 Further, the ion exchange membrane according to any one of the above, wherein the ion exchange membrane includes a component represented by the following general formula (2) together with the following general formula (1).

Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, and X represents H or a monovalent cation species.

However, Ar ′ represents a divalent aromatic group.

  Moreover, it is a manufacturing method of said ion exchange membrane.

  The present invention also relates to a fuel cell using any one of the above ion exchange membranes.

  The present invention is characterized by improving the stability of the ion exchange membrane by crosslinking a part of the acidic functional group by heat treatment of the ion exchange membrane having an acidic functional group. The exchange membrane improves the performance and durability of a fuel cell that operates using liquid fuel or gas fuel as a raw material.

  The present invention relates to an ion exchange membrane characterized by improving the stability of the ion exchange membrane by heat treatment of the ion exchange membrane having an acidic functional group. Specifically, the morphological stability of the ion exchange membrane is improved by activating acidic functional groups such as sulfonic acid groups existing inside the ion exchange membrane by heat treatment and crosslinking with adjacent molecules. . Therefore, in a fuel cell of a type using liquid fuel, it is possible to reduce methanol cross leak, which is the biggest problem in a direct methanol fuel cell, for example, by simple processing. In addition, in a fuel cell using hydrogen gas and an oxidizing gas such as oxygen as a fuel, the deterioration of the ion exchange membrane caused by the swelling and shrinkage of the membrane can be reduced by increasing the morphological stability of the membrane. It becomes possible.

  An ion exchange membrane, particularly one that exhibits good performance as an ion exchange membrane when considering use in a fuel cell, needs to have high ion conductivity, particularly proton conductivity. As a measure for that, it is a preferable method to increase the amount of ionic functional units in the polymer. That is, the idea is to increase the concentration of the ion conductive or proton conductive medium by increasing the amount of acidic functional groups present in the ion exchange membrane. However, when the amount of the acidic functional group is increased, the ion exchange membrane is easily swelled in water, and there is a problem that the membrane is repeatedly swollen and contracted by repeatedly stopping the operation of the fuel cell, leading to deterioration of the membrane. Further, when the operating temperature of the fuel cell is increased, there is a problem that the ion exchange membrane is dissolved.

  Therefore, the method of the present invention improves the morphological stability of the membrane by cross-linking some acidic functional groups with adjacent molecules by heat-treating the ion exchange membrane having acidic functional groups at 150 ° C. or higher. It is. In addition, according to the present invention, even when the amount of acidic functional units in the ion exchange membrane is greatly increased, the swelling when wetted with a solvent such as water is improved because the morphological stability of the membrane is improved. The shrinkage is small, and it also has the effect of suppressing the deterioration of the membrane caused by the swelling shrinkage due to the shutdown of the fuel cell. Note that when heat treatment is performed at a temperature lower than 150 ° C., the crosslinking reaction does not easily proceed, so the influence on the shape stability is small.

  In order to perform a crosslinking treatment via an acidic functional group, it is desirable that the ionic functional group present in the ion exchange membrane is an acid type, and the treatment is performed in an inert gas atmosphere such as nitrogen, helium, or argon. It is preferable. In the case of treating an ion exchange membrane having a functional group in a salt form, it was found that the reaction hardly proceeded when examined at around 150 ° C. However, an acid-type functional group and a salt-type functional group can coexist. In that case, the ratio of the acid-type functional group is preferably 20% or more, more preferably 40% or more and 95% or less. When the proportion of the acidic functional group is lower than 20%, the effect of crosslinking is small. Further, if the treatment is performed in an atmosphere containing a large amount of oxygen, it is not preferable because the film deteriorates due to an undesirable side reaction such as oxidation of the ion exchange membrane by oxygen. The oxygen concentration is preferably at least 10%, more preferably 5% or less. When the oxygen concentration is higher than 10%, the ion exchange membrane is easily oxidized and deteriorated.

  A more excellent material for the ion exchange membrane according to the present invention will be described later, but is not particularly limited. Examples thereof include ionomers containing at least one of polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphonic acid, polyvinyl carboxylic acid, and polyvinyl sulfonic acid component. Furthermore, as aromatic polymers, polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymer, polyphenylquinoxaline, polyaryl ketone, polyether ketone, polybenzoxazole, At least one of sulfonic acid groups, phosphonic acid groups, carboxyl groups, and derivatives thereof, more preferably at least sulfonic acid groups are introduced into a polymer containing at least one component such as polybenzthiazole and polyimide. Polymers. Polysulfone, polyethersulfone, polyetherketone, and the like referred to here are generic names for polymers having a sulfone bond, an ether bond, and a ketone bond in their molecular chains. Polyetherketoneketone, polyetheretherketone, It includes polyether ether ketone ketone, polyether ketone ether ketone ketone, polyether ketone sulfone and the like, and is not limited to a specific polymer structure.

  Among the polymers containing acidic groups, a polymer having a sulfonic acid group on an aromatic ring can be obtained by reacting a polymer having a skeleton as in the above example with a suitable sulfonating agent. Examples of such a sulfonating agent include those using concentrated sulfuric acid or fuming sulfuric acid, which have been reported as an example of introducing a sulfonic acid group into an aromatic ring-containing polymer (for example, Solid State Ionics, 106, P.A. 219 (1998)), those using chlorosulfuric acid (for example, J. Polym. Sci., Polym. Chem., 22, P. 295 (1984)), those using anhydrous sulfuric acid complex (for example, J. Polym Sci., Polym.Chem., 22, P.721 (1984), J. Polym.Sci., Polym.Chem., 23, P.1231 (1985)) and the like are effective. It can carry out by selecting reaction conditions according to each polymer using these reagents. Moreover, it is also possible to use the sulfonating agent described in Japanese Patent No. 2884189.

  Moreover, the said ion exchange functional group containing polymer can also be synthesize | combined using the monomer which contains an ion exchange functional group in at least 1 sort (s) in the monomer used for superposition | polymerization. For example, in a polyimide synthesized from an aromatic diamine and an aromatic tetracarboxylic dianhydride, an acidified polyimide can be obtained by using a sulfonic acid group-containing diamine as at least one aromatic diamine. In the case of polybenzoxazole synthesized from aromatic diamine diol and aromatic dicarboxylic acid, and polybenzthiazole synthesized from aromatic diamine dithiol and aromatic dicarboxylic acid, at least one kind of aromatic dicarboxylic acid contains sulfonic acid group By using dicarboxylic acid or phosphonic acid group-containing dicarboxylic acid, an acidic group-containing polybenzoxazole or polybenzthiazole can be obtained. Polysulfone, polyethersulfone, polyetherketone, etc. synthesized from aromatic dihalide and aromatic diol are synthesized by using sulfonic acid group-containing aromatic dihalide or sulfonic acid group-containing aromatic diol as at least one monomer. I can do it. At this time, it is preferable to use a sulfonic acid group-containing dihalide rather than using a sulfonic acid group-containing diol because the degree of polymerization tends to be high and the thermal stability of the obtained ion-exchangeable functional group-containing polymer is high. It can be said.

  The polymer for forming the ion exchange membrane in the present invention is a polyarylene ether compound such as sulfonic acid group-containing polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, or polyether ketone polymer. Is more preferable.

  Furthermore, among these polyarylene ether compounds, compounds having a cyano group in the molecule are more preferred. Many details are unknown, but when a compound having a cyano group is included in the molecule, the interaction of the cyano group is a polymer that has lower swelling and better shape stability than a compound that does not contain a cyano group. Become.

  Furthermore, among these polyarylene ether compounds, those containing the structural component represented by the general formula (2) together with the following general formula (1) are particularly preferable.

ただし、Ａｒは２価の芳香族基、Ｙはスルホン基またはケトン基、ＸはＨまたは１価のカチオン種を示す。

Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, and X represents H or a monovalent cation species.

ただし、Ａｒ'は２価の芳香族基を示す。

However, Ar ′ represents a divalent aromatic group.

  The component represented by the general formula (2) is preferably a component represented by the following general formula (3).

ただし、Ａｒ'は２価の芳香族基を示す。

However, Ar ′ represents a divalent aromatic group.

  The polymer of the ion exchange membrane of the present invention may contain structural units other than those represented by the general formula (1) and the general formula (2). At this time, it is preferable that structural units other than those represented by the general formula (1) or the general formula (2) are 50% by weight or less. By setting it as 50 mass% or less, it can be set as the composition which utilized the characteristic of this invention.

  Furthermore, as a polymer for forming the ion exchange membrane of the present invention, a polymer containing a constituent represented by the general formula (5) together with the following general formula (4) is particularly preferable. By having a biphenylene structure, it has excellent dimensional stability under high temperature and high humidity conditions, and also has high toughness.

ただし、ＸはＨまたは１価のカチオン種を示す。

X represents H or a monovalent cation species.

  The polyarylene ether-based polymer containing a sulfonic acid group of the present invention can be polymerized by an aromatic nucleophilic substitution reaction containing compounds represented by the following general formulas (6) and (7) as monomers. Specific examples of the compound represented by the general formula (6) include 3,3′-disulfo-4,4′-dichlorodiphenyl sulfone, 3,3′-disulfo-4,4′-difluorodiphenyl sulfone, 3, 3'-disulfo-4,4'-dichlorodiphenyl ketone, 3,3'-disulfo-4,4'-difluorodiphenyl sulfone, and those whose sulfonic acid groups are converted to salts with monovalent cation species Can be mentioned. The monovalent cation species may be sodium, potassium, other metal species, various amines, or the like, but is not limited thereto. Examples of the compound represented by the general formula (7) include 2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4-dichlorobenzonitrile, 2,4-difluorobenzonitrile, and the like. it can.

ただし、Ｙはスルホン基またはケトン基、Ｘは１価のカチオン種、Ｚは塩素またはフッ素を示す。本発明において、上記２，６−ジクロロベンゾニトリルおよび２，４−ジクロロベンゾニトリルは、異性体の関係にあり、いずれを用いたとしても良好なイオン伝導性、耐熱性、加工性および寸法安定性を達成することができる。その理由としては両モノマーとも反応性に優れるとともに、小さな繰り返し単位を構成することで分子全体の構造をより硬いものとしていると考えられている。

Y represents a sulfone group or a ketone group, X represents a monovalent cation species, and Z represents chlorine or fluorine. In the present invention, the above 2,6-dichlorobenzonitrile and 2,4-dichlorobenzonitrile are in an isomer relationship, and any of them is used, good ion conductivity, heat resistance, workability and dimensional stability. Can be achieved. The reason is considered that both monomers are excellent in reactivity and that the structure of the whole molecule is made harder by constituting a small repeating unit.

  In the above-described aromatic nucleophilic substitution reaction, various activated difluoroaromatic compounds and dichloroaromatic compounds can be used in combination with the compounds represented by the general formulas (6) and (7) as monomers. Examples of these compounds include 4,4′-dichlorodiphenyl sulfone, 4,4′-difluorodiphenyl sulfone, 4,4′-difluorobenzophenone, 4,4′-dichlorobenzophenone, decafluorobiphenyl, and the like. However, other aromatic dihalogen compounds, aromatic dinitro compounds, aromatic dicyano compounds and the like that are active in aromatic nucleophilic substitution can also be used.

  In addition, Ar in the structural component represented by the general formula (1) and Ar ′ in the structural component represented by the general formula (2) are generally the same as those described above in the aromatic nucleophilic substitution polymerization. It is a structure introduced from an aromatic diol component monomer used together with the compounds represented by formulas (6) and (7). Examples of such aromatic diol monomers include 4,4′-biphenol, bis (4-hydroxyphenyl) sulfone, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxy). Phenyl) propane, bis (4-hydroxyphenyl) methane, 2,2-bis (4-hydroxyphenyl) butane, 3,3-bis (4-hydroxyphenyl) pentane, 2,2-bis (4-hydroxy-3) , 5-dimethylphenyl) propane, bis (4-hydroxy-3,5-dimethylphenyl) methane, bis (4-hydroxy-2,5-dimethylphenyl) methane, bis (4-hydroxyphenyl) phenylmethane, bis ( 4-hydroxyphenyl) diphenylmethane, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bi (3-methyl-4-hydroxyphenyl) fluorene, 2,2-bis (4-hydroxyphenyl) hexafluoropropane, hydroquinone, resorcin, bis (4-hydroxyphenyl) ketone, etc. Various aromatic diols that can be used for polymerization of polyarylene ether compounds by aromatic nucleophilic substitution reaction can also be used. These aromatic diols can be used alone, but a plurality of aromatic diols can be used in combination.

  When the polyarylene ether-based polymer containing a sulfonic acid group of the present invention is polymerized by an aromatic nucleophilic substitution reaction, an activated difluoroaromatic compound including the compounds represented by the above general formula (6) and general formula (7), and A polymer can be obtained by reacting a dichloro aromatic compound and an aromatic diol in the presence of a basic compound. The polymerization can be carried out in the temperature range of 0 to 350 ° C., but is preferably 50 to 250 ° C. When the temperature is lower than 0 ° C., the reaction does not proceed sufficiently, and when the temperature is higher than 350 ° C., the polymer tends to be decomposed. The reaction can be carried out in the absence of a solvent, but is preferably carried out in a solvent. Examples of the solvent that can be used include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, and the like. And any solvent that can be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents may be used alone or as a mixture of two or more. Examples of the basic compound include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and the like, and those that can convert an aromatic diol into an active phenoxide structure may be used. It can use without being limited to. In the aromatic nucleophilic substitution reaction, water may be generated as a by-product. In this case, regardless of the polymerization solvent, water can be removed from the system as an azeotrope by coexisting toluene or the like in the reaction system. As a method for removing water out of the system, a water absorbing material such as molecular sieve can also be used. When the aromatic nucleophilic substitution reaction is carried out in a solvent, it is preferable to charge the monomer so that the resulting polymer concentration is 5 to 50% by weight. When the amount is less than 5% by weight, the degree of polymerization tends to be difficult to increase. On the other hand, when the amount is more than 50% by weight, the viscosity of the reaction system becomes too high, and the post-treatment of the reaction product tends to be difficult. After completion of the polymerization reaction, the solvent is removed from the reaction solution by evaporation, and the residue is washed as necessary to obtain the desired polymer. Further, the polymer can be obtained by precipitating the polymer as a solid by adding the reaction solution in a solvent having low polymer solubility, and collecting the precipitate by filtration.

  The polyarylene ether-based polymer containing a sulfonic acid group of the present invention preferably has a polymer log viscosity of 0.1 or more. When the logarithmic viscosity is less than 0.1, the membrane tends to become brittle when molded as an ion exchange membrane. The reduced specific viscosity is more preferably 0.3 or more. On the other hand, if the reduced specific viscosity exceeds 5, problems in processability such as difficulty in dissolving the polymer occur, which is not preferable. As a solvent for measuring the logarithmic viscosity, polar organic solvents such as N-methylpyrrolidone and N, N-dimethylacetamide can be generally used. When the solubility in these is low, concentrated sulfuric acid is used. It can also be measured.

  In addition, if necessary, the polymer for forming the ion exchange membrane of the present invention is, for example, an antioxidant, a heat stabilizer, a lubricant, a tackifier, a plasticizer, a cross-linking agent, a viscosity modifier, an antistatic agent, Contains various additives such as antibacterial agents, antifoaming agents, dispersants, polymerization inhibitors, radical inhibitors, inorganic compounds to control the properties of ion exchange membranes, inorganic-organic hybrid compounds, ionic liquids, etc. You can leave.

  The polymer shown above can be made into an ion exchange membrane by any method such as extrusion, rolling or casting. Among these, it is preferable to mold from a solution dissolved in an appropriate solvent. Examples of the solvent include aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and hexamethylphosphonamide, and alcohols such as methanol and ethanol. An appropriate one can be selected, but is not limited thereto. A plurality of these solvents may be used as a mixture within a possible range. The compound concentration in the solution is preferably in the range of 0.1 to 50% by weight. If the concentration of the compound in the solution is less than 0.1% by weight, it tends to be difficult to obtain a good molded product, and if it exceeds 50% by weight, the workability tends to deteriorate. A method of obtaining a molded body from a solution can be performed using a conventionally known method. The most preferable method for forming the ion exchange membrane is a cast from a solution, and the ion exchange membrane can be obtained by removing the solvent from the cast solution as described above. For the removal of the solvent, a method by drying is preferable in view of the uniformity of the ion exchange membrane. Moreover, in order to avoid decomposition | disassembly and alteration of a compound or a solvent, it can also dry at the lowest temperature possible under reduced pressure. Further, when the viscosity of the solution is high, when the substrate or the solution is heated and cast at a high temperature, the viscosity of the solution is lowered and the casting can be easily performed. The thickness of the solution at the time of casting is not particularly limited, but is preferably 10 to 2000 μm. More preferably, it is 50-1500 micrometers. If the thickness of the solution is thinner than 10 μm, the form as an ion exchange membrane tends to be not maintained, and if it is thicker than 2000 μm, a non-uniform polymer ion exchange membrane tends to be easily formed. As a method for controlling the cast thickness of the solution, a known method can be used. For example, the thickness can be controlled with the amount and concentration of the solution with a constant thickness using an applicator, a doctor blade, or the like, and with a cast area constant using a glass petri dish or the like. The cast solution can obtain a more uniform film by adjusting the solvent removal rate. For example, in the case of heating, the evaporation rate can be reduced by lowering the temperature in the first stage. In addition, when immersed in a non-solvent such as water, the coagulation rate of the compound can be adjusted by leaving the solution in air or an inert gas for an appropriate time. The ion exchange membrane of the present invention can have any thickness depending on the purpose, but is preferably as thin as possible from the viewpoint of ion conductivity. Specifically, it is preferably 5 to 300 μm, and more preferably 25 to 250 μm. If the thickness of the ion exchange membrane is less than 5 μm, handling of the ion exchange membrane becomes difficult and a short circuit or the like tends to occur when a fuel cell is produced. If the thickness is greater than 300 μm, the electric resistance value of the ion exchange membrane increases and the fuel cell increases. The power generation performance tends to decrease. In the present invention, it is described as an ion exchange membrane, but it is also preferable to process it into a hollow fiber shape, and a known formulation can be used for processing.

  When the functional group is in the salt form in the ion exchange membrane produced by such a method, it is necessary to convert it to the acid form before heat treatment. The acid conversion method is not particularly defined, but the salt type ion exchange membrane was converted into an acid type ion exchange membrane by immersing it in an acidic solution such as sulfuric acid aqueous solution, hydrochloric acid aqueous solution or phosphoric acid aqueous solution. Thereafter, it is preferable to remove the excess acid component by washing with water. The concentration and temperature of the acidic solution used for conversion to the acid form are not particularly specified and can be adjusted according to the purpose. In addition, there exists a tendency for the conversion rate and conversion efficiency to an acid type to become high, so that a higher concentration acid and a high temperature solution are used. In addition, water that contains cations other than protons must be managed as water used for washing, because it may be returned to salt form again. This is also determined according to the purpose. It is possible. It is also possible to leave a salt-type functional group at an arbitrary ratio.

  By subjecting the ion exchange membrane obtained as described above to the heat treatment described above, the characteristics of the membrane can be improved and a more excellent ion exchange membrane can be provided.

  In the ion exchange membrane of the present invention, the amount of acidic functional groups is preferably in the range of 0.5 to 4.5 meq / g. When the amount is less than 0.5 meq / g, there is a tendency that sufficient ion conductivity is not exhibited when used as an ion exchange membrane, and when the amount is more than 4.5 meq / g, in the ion exchange membrane of the present invention. However, the film swells excessively under high temperature and high humidity conditions and tends to be unsuitable for use. More preferably, it is 1.0-3.5 meq / g. The amount of acidic functional vessel can be experimentally determined from the measurement of ion exchange capacity described later.

  When the ion exchange membrane finally obtained is used, the ionic functional group in the membrane may contain a metal salt, but it is converted into a free acid form by appropriate acid treatment. Is preferred. At this time, the ion conductivity of the ion exchange membrane is preferably 1.0 × 10 −3 S / cm or more. When the ionic conductivity is 1.0 × 10 −3 S / cm or more, a good output tends to be obtained in a fuel cell using the ion exchange membrane, and when the ion conductivity is less than 1.0 × 10 −3 S / cm. Tends to cause a decrease in the output of the fuel cell.

  As an effect of improved stability, swelling and liquid fuel permeability are suppressed. That is, in the ion exchange membrane of the present invention, when comparing membranes having the same amount of acidic groups, the swelling property can be lowered by 10% or more, and the stability is improved. Further, when the rate at which methanol as a typical liquid fuel permeates, that is, the methanol permeation coefficient, is compared with samples having the same film thickness, the permeation coefficient can be reduced by 10% or more compared to the case where heat treatment is not performed. In some cases, it can be reduced by 30% or more. As the methanol permeation rate, the methanol permeation rate is preferably in the range of 0.1 to 5.0 mmol / m 2 / s, and more preferably 4.0 mmol / m in terms of preventing cross leak of the liquid fuel. It is desirable to be smaller than m2 / s. In the ion exchange membrane of the present invention, it is possible to suppress the swelling of the membrane in a better form, so that both high ion conductivity and liquid fuel permeation inhibiting performance can be achieved.

  Moreover, the joined body of the ion exchange membrane of this invention and an electrode can be obtained by installing an electrode in the ion exchange membrane of this invention mentioned above. The type of catalyst, the configuration of the electrode, the type of gas diffusion layer used for the electrode, the joining method, and the like are not particularly limited, and known ones can be used, and a combination of known techniques can also be used. The catalyst used for the electrode can be appropriately selected from the viewpoints of acid resistance and catalytic activity, but platinum group metals and alloys and oxides thereof are particularly preferable. For example, platinum or a platinum-based alloy for the cathode and platinum or a platinum-based alloy or an alloy of platinum and ruthenium for the anode are suitable for high-efficiency power generation. Multiple types of catalysts may be used and may be distributed. There are no particular restrictions on the porosity in the electrode or the type / amount of the ion conductive resin mixed with the catalyst in the electrode. In addition, a method for controlling gas diffusivity represented by impregnation with a hydrophobic compound can be suitably used. In order to join the electrode to the membrane, it is important not to generate a large resistance between the membrane and the electrode. In addition, the membrane is swollen and shrunk, and the mechanical force of gas generation causes peeling and electrode catalyst peeling. It is also important to prevent this from occurring. As a method for producing this joined body, there are conventionally known methods as a known technique for fuel cell or electrode-membrane joining methods in water electrolysis, for example, water-repellent properties such as catalyst-carrying carbon, ion exchange resin and polytetrafluoroethylene. A method in which an electrode is prepared in advance by mixing a material having the above and thermocompression-bonded to a film, or a method in which the mixture is directly deposited on the film by spraying, ink jet, or the like is preferably used. In addition, the membrane is immersed in a solution in which metal ions are cationized, such as platinum group ammine complex ions, by chemical plating, and ion exchange (adsorption) is performed, and then the membrane is brought into contact with the reducing agent solution to form a membrane. A method of reducing the metal ions in the vicinity of the surface and simultaneously diffusing the metal ions inside the film to the surface to form a strong metal deposition layer on the film surface, and the like. Regarding the latter, there is also a method in which a predetermined metal species and amount are plated and grown on an active metal deposition layer using a chemical plating bath.

  In addition, a fuel cell having good performance can be provided by incorporating the ion exchange membrane / electrode assembly into the fuel cell. The type of separator used in the fuel cell, the flow rate of fuel and oxidizing gas, the supply method, the structure of the flow path, etc., the operating method, operating conditions, temperature distribution, fuel cell control method, etc. are not particularly limited. Absent.

  The ion exchange membrane of the present invention is excellent in stability and liquid fuel permeation inhibiting ability while having high ion conductivity. Taking advantage of this characteristic, it can be used as a polymer solid ion exchange membrane of a direct methanol fuel cell or a polymer electrolyte fuel cell, and the fuel cell thus produced exhibits excellent performance.

  Examples of the present invention are shown below, but the present invention is not limited to these Examples.

  Evaluation and measurement methods

<Ion exchange membrane thickness>
The thickness of the ion exchange membrane was determined by measurement using a micrometer (Mitutoyo standard micrometer 0-25 mm 0.01 mm). For the purpose of accurately measuring the thickness, the evaluation was performed in a measurement chamber in which the room temperature was 20 ° C. and the humidity was controlled to 30 ± 5 RH%. In the measurement, the sample used was left in the measurement chamber for 24 hours or more. The measurement was performed at 20 points on a 5 × 5 cm sample, and the average value was taken as the thickness.

<Ion exchange capacity (acid type)>
As the ion exchange capacity (IEC), the amount of acid type functional groups present in the ion exchange membrane was measured. First, as a sample preparation, a sample piece (5 × 5 cm) was dried in an oven at 80 ° C. under a nitrogen stream for 2 hours, further allowed to cool in a desiccator filled with silica gel for 30 minutes, and then the dry weight was measured (Ws). Next, 200 ml of a 1 mol / l sodium chloride-ultra pure aqueous solution and the weighed sample were placed in a 200 ml sealed glass bottle, and stirred in a sealed state at room temperature for 24 hours. Subsequently, 30 ml of the solution was neutralized and titrated with a 10 mM aqueous sodium hydroxide solution (commercial standard solution), and IEC (acid type) was determined from the titration amount (T) using the following formula.
IEC (meq / g) = 10 T / (30 Ws) × 0.2
(Unit of T: ml Unit of Ws: g)
The total ion exchange capacity, which is a measure of the amount of ionic functional groups in the sample, was prepared by immersing the sample in a 2 mol / l sulfuric acid aqueous solution overnight, repeatedly washing with ultrapure water, and drying. It carried out by calculating | requiring the above-mentioned ion exchange capacity about an acid type sample.

<Swelling rate>
The swelling rate is the exact dry weight (Ws) of the sample (5 × 5 cm) and the sample is immersed in ultrapure water at 70 ° C. for 2 hours and then removed, and extra water droplets present on the sample surface are removed by Kimwipe (trade name) Was obtained using the following formula from the weight (Wl) measured immediately. The smaller the swelling rate, the better the shape stability.
Swelling rate (%) = (Wl−Ws) / Ws × 100 (%)

<Ionic conductivity>
The ionic conductivity σ was measured as follows. A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped film sample having a width of 10 mm on a self-made measurement probe (made of polytetrafluoroethylene) in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. The AC impedance at 10 kHz between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. The contact distance between the membrane and the platinum wire is measured by the following formula from the slope Dr [Ω / cm] of the straight line in which the distance between the electrodes is changed from 10 mm to 40 mm at intervals of 10 mm and the distance between the electrodes and the measured resistance value are plotted. Canceled and calculated.
σ [S / cm] = 1 / (film width × film thickness [cm] × Dr)

<Methanol permeation rate and methanol permeation coefficient>
The liquid fuel permeation rate of the ion exchange membrane was measured as a methanol permeation rate and a methanol permeation coefficient by the following method. An ion exchange membrane immersed in a 5 mol / liter aqueous methanol solution adjusted to 25 ° C. (for the preparation of the aqueous methanol solution, use commercially available reagent-grade methanol and ultrapure water (18 MΩ · cm)) for 24 hours. Sandwiched in a cell, 100 ml of 5 mol / liter aqueous methanol solution was poured into one side of the cell, 100 ml of ultrapure water was poured into the other cell, and the cells on both sides were stirred at 25 ° C. It was calculated by measuring the amount of methanol diffusing into ultrapure water using a gas chromatograph (the area of the ion exchange membrane was 2.0 cm 2). Specifically, it was calculated using the following formula from the methanol concentration change rate [Ct] (mmol / L / s) of the cell containing ultrapure water.
Methanol permeation rate [mmol / m2 / s] = (Ct [mmol / L / s] × 0.1 [L]) / 2 × 10 −4 [m2]
Methanol permeability coefficient [mmol / m / s] = Methanol permeation rate [mmol / m2 / s] × film thickness [m]

<Power generation characteristics>
The power generation characteristics were evaluated by the following two methods.
<Power generation evaluation 1>
A commercially available 54% platinum / ruthenium catalyst-supporting carbon (Tanaka Kikinzoku Kogyo Co., Ltd.), a small amount of ultrapure water and isopropanol are mixed in a DuPont 20% Nafion (trade name) solution and stirred until uniform. Thus, a catalyst paste was prepared. The catalyst paste was uniformly applied to Toray carbon paper TGPH-060 so that the amount of platinum deposited was 2 mg / cm 2 and dried to prepare a gas diffusion layer with an electrode catalyst layer for the anode. In addition, by using a commercially available 40% platinum catalyst-supporting carbon (Tanaka Kikinzoku Kogyo Co., Ltd.) instead of platinum / ruthenium catalyst-supporting carbon in the same manner, an electrode catalyst layer is formed on hydrophobic carbon paper. A gas diffusion layer with an electrode catalyst layer for the cathode was prepared (1 mg-platinum / cm 2). An ion exchange membrane is sandwiched between the two types of gas diffusion layers with the electrode catalyst layer so that the electrode catalyst layer is in contact with the ion exchange membrane, and is pressurized and heated at 135 ° C. and 2 MPa for 5 minutes by a hot press method. Thus, an ion exchange membrane / electrode assembly was produced. This joined body was incorporated into an evaluation fuel cell FC25-02SP manufactured by Electrochem, and a 2 mol / l aqueous methanol solution and air of 40 ° C. were supplied to the anode and cathode at a cell temperature of 40 ° C., respectively, and the current density was 0.1 A. A discharge test was conducted at / cm2.
<Power generation evaluation 2>
The gas diffusion layer with the electrode catalyst layer for the cathode shown in the power generation evaluation 1 was also used for the anode, and an ion exchange membrane / electrode assembly was produced by the same method. A discharge test was conducted at a current density of 1 A / cm 2 while supplying hydrogen gas and oxygen gas humidified at 60 ° C. to the anode and the cathode, respectively, at a cell temperature of 80 ° C., and voltage (V) was measured. In addition, the open circuit voltage was observed once every 2 hours while operating for a long time under the same conditions, and the durability was also evaluated with the time when the open circuit voltage was reduced by 50 mV compared to the initial time as the durability time.

Example 1
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile such that the molar ratio is 1.00: 1.02: 2.02: 2.25, 4,4′-biphenol and potassium carbonate were mixed, 15 g of the mixture and 2.71 g of molecular sieve were weighed into a 100 ml four-necked flask together with NMP as a solvent, and nitrogen was allowed to flow. After stirring at 148 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 180-200 ° C. and sufficiently increasing the viscosity of the system (about 6.5 hours). After standing to cool, the precipitated molecular sieve was removed and the mixture was precipitated in water as a strand. The obtained polymer was washed in boiling ultrapure water for 1 hour and then dried. A 28% NMP solution of polymer was prepared. The polymer solution was thinly drawn by a casting method and dried at 100 ° C. and then 145 ° C. for 4 hours. Subsequently, it was immersed in a 2 mol / l sulfuric acid aqueous solution for 2 hours, washed 5 times with water, and then dried at room temperature while being fixed to a frame, thereby producing a green film. The green film was heated in a nitrogen oven at 160 ° C. for 1 hour to produce a heat-treated film. After being left in a nitrogen oven until the temperature reached 80 ° C. or lower, the film was taken out. Subsequently, the water-washing process was implemented 3 times, and the ion exchange membrane of Example 1 was produced by drying at room temperature from the state fixed to the frame.

Example 2
The molar ratio of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile, 4,4′-biphenol, potassium carbonate was 1.00: 0.25: 1. The ion exchange membrane of Example 2 was produced by processing by the method of Example 1 except that it was charged at .25: 1.46.

Example 3
The ion exchange membrane of Example 3 was produced by processing by the method of Example 2 except that the heat treatment temperature of the green film was 200 ° C.

Example 4
The ion exchange membrane of Example 4 was produced by processing by the method of Example 1 except that green films having different thicknesses were used.

Comparative Example 1
An ion exchange membrane of Comparative Example 1 was produced by the method of Example 1 except that the green film was not heat-treated.

Comparative Example 2
An ion exchange membrane of Comparative Example 2 was produced by the method of Example 2 except that the green film was heat-treated at 120 ° C. When the power generation test was performed by the method of power generation evaluation 2, the resistance of the film was low, and it was possible to suppress a decrease in voltage due to an increase in current density. Even at the stage, the gas leaked and showed unstable behavior.

Comparative Example 3
An ion exchange membrane of Comparative Example 3 was prepared by the method of Example 1 except that the acid conversion treatment was not performed and a salt-type green film was used.

  Table 1 shows the physical property evaluation results of Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, and 3.

  The IEC of the ion exchange membrane of an Example has decreased compared with the green film. This is presumably because the crosslinking reaction derived from the sulfonic acid group has progressed. On the other hand, the ion exchange membrane of the comparative example has almost the same IEC as the green film, and it can be seen that the crosslinking reaction does not proceed. When the characteristics of the ion exchange membranes of the example and the comparative example are compared, the example has a lower swelling rate, and the form stability is improved. As a result, it can be seen that even if IEC is high, the methanol permeability coefficient can be kept low, and the performance is better. In the case of the method of power generation evaluation 1, the power generation performance is good because the membranes of the examples have low methanol permeability. On the other hand, when the method of power generation evaluation 2 was used, the initial performance of both the example film and the comparative example film was good (however, when the film of Comparative Example 2 was used, the problem that the open circuit voltage was low) As a result of evaluating the durability, the film of the example was clearly superior. This is thought to be the result of improved swelling and form stability.

  An excellent ion exchange membrane having both ion conductivity and stability can be provided, and a high-performance fuel cell with excellent reliability can be supplied.

Claims (3)

As an ion exchange membrane, it is formed of a polymer containing the structural component represented by the following general formula (1) together with the following general formula (1), and is cross-linked by heat treatment at 150 ° C. or higher, thereby improving morphological stability. Features Aromatic hydrocarbon ion exchange membrane.

Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, and X represents H or a monovalent cation species.

However, Ar ′ represents a divalent aromatic group. Claim 1 A method for producing an ion exchange membrane in the range. Claim 1 A fuel cell using an ion exchange membrane in the range.