JP3651684B1 - Ion exchange membrane - Google Patents

Abstract

A highly reliable ion exchange membrane that is less deteriorated when using a high-concentration fuel such as methanol, and a high-performance fuel cell using the same are provided.
SOLUTION: It is composed of an aromatic hydrocarbon compound containing a sulfonic acid group, and the difference in methanol permeability coefficient measured before and after being immersed in a 5 mol / l aqueous methanol solution at 80 ° C. for 20 hours is 20% or less. The methanol permeation coefficient was stabilized and achieved by performing a treatment of impregnating in a solvent at 80 ° C. or higher.

Description

  The present invention relates to an ion exchange membrane, and more particularly to an ion exchange membrane used in a fuel cell, in particular, a liquid fuel permeation rate with little change with time.

  Fuel cells are attracting attention as environmentally friendly energy devices. A fuel cell is a system that uses an ion exchange membrane as a solid electrolyte and generates electricity by causing a reverse reaction of water electrolysis on an electrode joined thereto. The ion exchange membrane used for this must have proton conductivity as a cation exchange membrane and be sufficiently stable chemically, thermally, electrochemically and mechanically. For this reason, as a thing that can be used over a long period of time, when using a Nafion (trade name) membrane in a fuel cell fueled with a liquid organic fuel such as methanol, mainly a non-perfluorocarbon sulfonic acid type manufactured by DuPont of the United States, For example, the problem of crossover, in which methanol permeates the ion exchange membrane and flows into the air electrode, is remarkable. If this crossover occurs, the liquid fuel and oxidant react directly at the cathode, causing problems such as power reduction and liquid fuel leaking out from the cathode side. Development of a small ion exchange membrane is desired. In addition, high cost has been pointed out as another problem of perfluorocarbon sulfonic acid membranes, and ion exchange membranes that can solve these problems are necessary for practical use of fuel cells.

  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 the sulfonation reaction of these polymers generally tend to be easily removed by heat. As a method for improving this, a monomer having sulfonic acid groups introduced onto electron-withdrawing aromatic rings A sulfonated polyarylethersulfone-based compound having high thermal stability has been reported by polymerizing using a polymer (see, for example, Patent Document 2).

  As an example in which such an ion exchange membrane is applied to a direct methanol fuel cell, which is a type of fuel cell using liquid fuel, a fuel cell having relatively good ion conductivity and relatively good initial power generation characteristics Has been reported (Non-patent Document 2). However, when the operation is repeated, the morphology of the ion exchange membrane is changed, and the methanol permeability is increased. This causes a voltage drop due to the cross leak of methanol, and thus the battery performance is deteriorated. In addition, a decrease in power generation performance must be avoided because it directly leads to a decrease in performance and instability of devices equipped with fuel cells. A report that the morphology of the ion exchange membrane affects the performance of the direct methanol fuel cell is shown in Non-Patent Document 3, for example.

JP-A-6-93114 (pages 15-17) US Patent Application Publication No. 2002/0091225 (page 1-2) Journal of Membrane Science (Netherlands) 1993, 83, p. 211-220 AIChE Fuel Cell Technology: Opportunities and Challenges, 558 (2002) The Electrochemical Society 203rd Meeting-Paris, Abs No. 1169

  The present invention is an ion exchange membrane that is suitable for use in a fuel cell of a type that uses a liquid fuel such as a direct methanol fuel cell, and the liquid fuel permeability is not easily changed. It can be operated stably for a long time.

  As a result of intensive studies, the present inventors have found that an ion exchange membrane having excellent stability in which the morphology of the ion exchange membrane hardly changes can be provided.

  That is, the present invention relates to an ion-exchange membrane of an aromatic hydrocarbon compound containing a sulfonic acid group for a fuel cell using a liquid fuel, that is, a non-perfluorocarbon sulfonic acid-based aromatic hydrocarbon, Is an ion exchange membrane excellent in stability of methanol permeation suppression performance, characterized in that the difference in methanol permeability coefficient measured before and after being immersed in a 5 mol / l methanol aqueous solution at 80 ° C. for 20 hours is 20% or less.

  In the present invention, the aromatic hydrocarbon-based compound containing a sulfonic acid group and the non-perfluorocarbon sulfonic acid-based aromatic hydrocarbon are all substituted with fluorine in the main chain represented by “Nafion (registered trademark)”. It is an aromatic material excluding the formed material, and may be a partial fluoride.

  Further, the ion exchange membrane is characterized in that it is impregnated with a solvent at 80 ° C. or higher.

  In addition, the ion exchange membrane is characterized by being subjected to a treatment of impregnating a liquid containing water and / or alcohol.

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。 Moreover, it is an ion exchange membrane characterized by including the structural component shown by General formula (2) with 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.

  Further, the present invention is an ion exchange membrane / electrode assembly using the above ion exchange membrane.

  The present invention also relates to a fuel cell using the above ion exchange membrane / electrode assembly.

  The present invention is an ion exchange characterized by little change in morphology in liquid fuel, and the ion exchange membrane according to the present invention improves the performance stability of a fuel cell using liquid fuel.

  When a direct methanol fuel cell, which is a type of fuel cell that uses liquid fuel, is operated continuously, the performance changes over time even if the initial performance is good, especially in the range of several tens of hours from the start of power generation. We observed the phenomenon that the battery performance was easy to change. The occurrence of such a change in performance is undesirable because it makes control in a device incorporating a fuel cell more complicated, and improvement is required. The cause of the change in performance may be the effect of changes in the physical properties of the material present in the electrode, such as catalyst poisoning.However, as a result of investigations focused on ion exchange membranes, The underlying ion exchange membranes have been found to contribute to the change in membrane morphology to equilibrate in its power generation environment.

  Therefore, the present invention solves the above-mentioned problems, and is characterized in that an ion exchange membrane having particularly little change in physical properties is used. As a result of intensive studies as a method for observing the presence or absence of changes in physical properties, it was found that the methanol permeability coefficient may be compared before and after being immersed in a 5 mol / l methanol aqueous solution at 80 ° C. for 20 hours. A fuel cell using an ion exchange membrane with a small change in methanol permeability coefficient has a smaller change in cell performance under continuous power generation. In addition, the ion exchange membrane is characterized by little change in the morphology of the membrane.

  The inventors have invented an ion exchange membrane whose difference is 20% or less when compared with methanol permeability coefficient before and after being immersed in a 5 mol / l methanol aqueous solution at 80 ° C. for 20 hours, and uses the ion exchange membrane. The fuel cell showed excellent performance stability during power generation. In addition, as an ion exchange membrane having better performance stability, an ion exchange membrane having a difference in methanol permeability coefficient of 10% or less was invented to realize further performance stability. An ion exchange membrane having a difference in methanol permeability coefficient greater than 20% results in a large change in cell performance, resulting in a fuel cell that is difficult to control.

  Since the above-mentioned problem occurs because there is a portion where the morphology is particularly easy to change in the ion exchange membrane, a method for improving the stability of the ion exchange membrane was invented by a method for stabilizing only the defect of the membrane. Specifically, the ion exchange membrane is characterized by being subjected to a treatment of impregnating with a solvent at 80 ° C. or higher. It is possible to remove the defects of the membrane by previously immersing the ion exchange membrane in a solvent at 80 ° C. or higher. That is, by removing the location where the shape change occurs in the ion exchange membrane before incorporating it into the fuel cell, the shape of the ion exchange membrane hardly changes inside the fuel cell. The fuel cell is easy to control. More preferably, the treatment is performed in a solvent at 90 ° C. or higher, and the treatment time can be shortened. The solvent is not particularly limited, but the treatment is preferably performed in a polar solvent, for example, water, alcohol, ethylene glycol, glycerin, N-methyl-2-pyrrolidone, N, N-dimethyl. Solvents including formamide, N, N-dimethylacetamide and the like are listed as good examples. Since it is necessary to remove the solvent after the treatment in the solvent, the treatment in a solvent containing a component having a boiling point of 200 ° C. or higher as a main component is not preferable because the subsequent steps become complicated. Further, since the liquid fuel is mainly a solution containing water or alcohol (or formed by a chemical reaction during power generation), a solvent containing water and / or alcohol is used as the solvent to be used. It is preferable.

  The ion exchange membrane subjected to such treatment may be a salt type ion exchange membrane or an acid type ion exchange membrane, and is not particularly limited. However, when an acid-type ion exchange membrane is used, care must be taken because some solvents may be hydrolyzed.

  When an ion exchange membrane for a fuel cell is finally used, an acid type is preferable. When treated as a salt type ion exchange membrane, an acidic solution such as a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, or a phosphoric acid aqueous solution is used. It is preferable that the excess acid component be removed by washing with water after being converted into an acid ion exchange membrane by immersion. The concentration and temperature of the acidic solution used for conversion to the acid type can be determined according to the purpose. The conversion rate and the conversion efficiency tend to be higher as the acid having a higher concentration and the higher 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. Moreover, there is no problem even if it preserve | saves in the form containing a solvent as a preservation | save form, However, It can also preserve | save in the dried state.

  Hereinafter, the ion exchange membrane of the present invention and the polymer for producing the ion exchange membrane will be described.

  Examples of the polymer used for the ion exchange membrane include ionomers containing at least one of polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphonic acid, polyvinyl carboxylic acid, and polyvinyl sulfonic acid components. Furthermore, as aromatic polymers, polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymer, polyphenylquinoxaline, polyaryl ketone, polyether ketone, polybenzoxazole, Examples thereof include polymers in which at least one of sulfonic acid groups, phosphonic acid groups, carboxyl groups, and derivatives thereof is introduced into a polymer containing at least one component such as polybenzthiazole and polyimide. 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. However, perfluorocarbon sulfonic acid polymers represented by Nafion and the like are not preferable because the polymer itself tends to cross-leak liquid fuel.

  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 polymer is also compoundable 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 can be said that the use of a sulfonic acid group-containing dihalide is preferable to the use of a sulfonic acid group-containing diol because the degree of polymerization tends to increase and the thermal stability of the obtained polymer increases.

  In addition, 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, those containing the structural component represented by the general formula (2) together with the following general formula (1) are particularly preferred, and are particularly excellent when used in combination with the treatment of the present invention.

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.

  In addition, the polyarylene ether-based polymer containing a sulfonic acid group 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 to 50 mass% or less, it can be set as the composition which utilized the characteristic of the polymer for forming the ion exchange membrane of this invention.

  The polymer for forming the ion exchange membrane of the present invention preferably has a sulfonic acid group content in the range of 0.3 to 3.5 meq / g. When it is less than 0.3 meq / g, there is a tendency that sufficient ion conductivity is not exhibited when it is used as an ion exchange membrane, and when it is more than 3.5 meq / g, the ion exchange membrane has a high temperature and high humidity. When the conditions are met, membrane swelling tends to be too large to be suitable for use. The sulfonic acid group content can be calculated from the polymer composition. More preferably, it is 1.0-3.0 meq / g.

  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. In addition, 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, Various additives such as antibacterial agents, antifoaming agents, dispersants, polymerization inhibitors, radical inhibitors, precious metals for controlling the properties of ion exchange membranes, inorganic compounds and inorganic-organic hybrid compounds, ionic liquids, Etc. may be included. Further, a plurality of items may be mixed as much as possible.

  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. The solvent is preferably removed by drying from the viewpoint 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 2500 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 2500 μm, a non-uniform 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. 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.

  By subjecting the ion exchange membrane obtained as described above to the treatment in the above-described solvent, it is possible to improve the characteristics of the membrane and provide a more excellent ion exchange membrane.

  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 an acid type by an 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 the present invention, the liquid fuel permeability hardly changes. That is, in the ion exchange membrane of the present invention, when the methanol permeability coefficient is compared before and after being immersed in a 5 mol / l methanol aqueous solution at 80 ° C. for 20 hours, the difference becomes an ion exchange membrane with 20% or less, and 10% or less. It is also possible to make it.

  In order to prevent cross leak of liquid fuel, the methanol permeation rate is preferably in the range of 0.1 to 4.0 mmol / m 2 / s, and more preferably less than 2.0 mmol / m 2 / s. Small is desirable.

  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 viewpoint 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, 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 liquid fuel permeation inhibiting ability and its stability. Taking advantage of this characteristic, it can be used as a polymer solid ion exchange membrane of a direct methanol fuel cell using a liquid fuel, for example, 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). The measurement was performed at 20 points on a 5 × 5 cm sample, and the average value was taken as the film thickness. The measurement was performed in a measurement room in which the room temperature was 20 ° C. and the humidity was controlled to 30 ± 5 RH%. The sample used was left in the measurement chamber for 24 hours or more.

<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. Next, 30 ml of the solution was taken out, neutralized with a 10 mM aqueous sodium hydroxide solution (commercial standard solution), and IEC (acid type) was determined from the titration (T) using the following formula.
IEC (meq / g) = 10 T / (30 Ws) × 0.2
(Unit of T: ml Unit of Ws: g)

<Swelling rate>
The swelling rate is determined by measuring the exact dry weight (Ws) of the sample (5 × 5 cm) and the sample after immersing it in ultra pure water at 70 ° C. for 2 hours, and removing excess water droplets existing on the sample surface by Kimwipe (trade name) Was obtained using the following formula from the weight (Wl) measured immediately.
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. The sample cell was sandwiched between 100 ml of 5 mol / liter methanol aqueous solution on one side of the cell and 100 ml of ultrapure water on the other side of the cell. 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]

<Stability of methanol permeability coefficient>
The sample was immersed in a 5 mol / l methanol aqueous solution at 80 ° C. for 20 hours, the methanol permeability coefficient was measured before and after the immersion, and the methanol permeability coefficient was determined by the following formula. A sample having a thickness of about 150 μm was used (the thickness of the sample is not limited. It can be changed and evaluated as appropriate). As a numerical value, it can be said that the lower one is an excellent ion exchange membrane with less performance change.
Stability of methanol permeability coefficient [%] = (methanol permeability coefficient after immersion−methanol permeability coefficient before immersion) / methanol permeability coefficient before immersion × 100 (%)

<Power generation characteristics>
A commercially available 54% platinum / ruthenium catalyst-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd. fuel cell catalyst), a small amount of ultrapure water and isopropanol are stirred in a DuPont 20% Nafion (trade name) solution until uniform. Then, a catalyst paste was prepared. This catalyst paste is uniformly applied and dried on carbon paper TGPH-060 (hydrophobized product) manufactured by Toray so that the amount of platinum deposited is 1.8 mg / cm2, and gas diffusion with an electrode catalyst layer for the anode is performed. A layer was made. Further, in the same manner, an electrode catalyst layer is formed on hydrophobic carbon paper using a commercially available 40% platinum catalyst-supported carbon instead of the platinum / ruthenium catalyst-supported carbon, so that an electrode catalyst layer for a cathode is formed. An attached gas diffusion layer was prepared (0.9 mg-platinum / cm 2). By sandwiching an ion exchange membrane between the two types of gas diffusion layers with an electrode catalyst layer so that the electrode catalyst layer is in contact with the membrane, and pressurizing and heating at 135 ° C. and 2 MPa for 3 minutes by a hot press method An ion exchange membrane / electrode assembly was prepared. This assembly was incorporated into an evaluation fuel cell FC25-02SP manufactured by Electrochem, and the current density was adjusted to 0.005 at a cell temperature of 60 ° C. while supplying a 5 mol / l aqueous methanol solution and air at 60 ° C. to the anode and cathode, respectively. The voltage when the discharge test was conducted at 1 A / cm 2 was examined. The measurement was performed 3 hours and 50 hours after the start of operation.

Example 1
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile such that the molar ratio is 1.00: 2.01: 3.01: 3.37, A mixture of 4,4′-biphenol and potassium carbonate was prepared, 15 g of the mixture was weighed into a 100 ml four-necked flask together with 3.50 g of molecular sieves, and nitrogen was flushed. NMP was used as the solvent. After stirring at 150 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 190-195 ° C. and sufficiently increasing the viscosity of the system (about 6 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 26% NMP solution of polymer was prepared. The polymer solution was thinly drawn by a casting method and dried at 90 ° C. and then 150 ° C. for 5 hours to produce a film. 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 to obtain a green film. The green film was treated with a 15% aqueous methanol solution (sealed system) at 90 ° C. for 10 hours, and then washed with water and dried to produce the ion exchange membrane of Example 1.

Example 2
An ion exchange membrane of Example 2 was produced by the method of Example 1 except that the green film of Example 1 was treated in water at 80 ° C. for 10 hours.

Comparative Example 1
An ion exchange membrane of Example 2 was produced by the method of Example 1 except that the green film of Example 1 was treated in water at 80 ° C. for 10 hours.

Example 2
An ion exchange membrane of Example 3 was produced by the method of Example 1 except that the green film of Example 1 was treated in 105 ° C. water (pressure system) for 1 hour.

Example 3
The ion exchange membrane of Example 4 was produced by the method of Example 1 except that 4,4′-dichlorodiphenyl sulfone was used instead of 2,6-dichlorobenzonitrile in Example 1.

Comparative Example 2
In Example 1, the molar ratio of 3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile, 4,4′-biphenol and potassium carbonate was 1.00: 1. : An ion exchange membrane of Comparative Example 1 was obtained by the method of Example 1 except that it was charged to 50: 2.50: 3.02 and the green film was not treated with an aqueous methanol solution. .

Comparative Example 3
An ion exchange membrane of Comparative Example 2 was prepared by the method of Example 4 except that the green film was not treated with an aqueous methanol solution.

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

The ion exchange membranes of Examples 1 and 2 and the ion exchange membrane of Comparative Example 1 have almost the same characteristics in terms of important physical properties as an ion exchange membrane such as ion conductivity, swelling rate, and methanol permeation rate. When the built-in power generation performance was evaluated in the fuel cell, the initial performance showed similar performance. However, when the continuous operation was performed, the performance of the battery using the membrane of the example hardly changed, whereas the performance of the battery using the ion exchange membrane of Comparative Example 2 was significantly lowered. Although the fuel cell was disassembled for investigation, no defects derived from the joined body such as electrode peeling were observed. The membrane of Comparative Example 2 is inferior in terms of the stability of the methanol permeation coefficient, which is an indicator of the stability of the ion exchange membrane, so that the performance is increased due to the increase in the amount of methanol crossover over time. It is thought that it decreased. Similarly, in the ion exchange membrane of Comparative Example 3 having a low stability of the methanol permeability coefficient, a significant performance decrease was observed, and in contrast, the ion exchange membrane of the Example having excellent stability in the number of methanol permeation systems had excellent performance stability. It has been found that the ion exchange membrane of the present invention is a fuel cell that is easier to control and better when used as a fuel cell. In addition, although it is estimated that it originates in the relationship with the fundamental physical property of an ion exchange membrane, the direction of the polymer shown in Example 1, 2 showed the favorable characteristic compared with the polymer of Example 3 .

Claims (7)

From an aromatic hydrocarbon compound containing a sulfonic acid group in which at least one polyarylene ether compound such as polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone, and polyether ketone polymer is copolymerized. it is characterized in that subjected to a treatment for impregnating the aqueous alcohol solution, the difference between the methanol permeation coefficients measured before and after immersion for 20 hours in 5 mol / l aqueous methanol solution 80 ° C. is 20% or less ion exchange membrane. 2. The ion exchange membrane according to claim 1, which has been subjected to a treatment of impregnation in a solvent of 80 ° C. or higher. 3. The ion exchange membrane according to claim 2, wherein a treatment for impregnating water and an aqueous alcohol solution is performed. The ion exchange membrane according to any one of claims 1 to 3, comprising a component represented by the following general formula (1) 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. A method for producing an ion exchange membrane according to any one of claims 1 to 4. An ion exchange membrane / electrode assembly using the ion exchange membrane according to any one of claims 1 to 5. A fuel cell using the ion exchange membrane / electrode assembly according to claim 6.