JP2005276441A - Ion exchange membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion exchange membrane which is used for a fuel cell and is superior in permeation suppression of liquid fuel. <P>SOLUTION: This is a non-fluorine system ion exchange membrane for fuel cell which is superior in methanol permeation suppression property, and in the formula showing methanol concentration dependency of methanol permeation coefficient of the ion exchange membrane: methanol permeation coefficient [μmol/m/s]=α×(concentration of methanol water solution [mol/l] ), the inclination α is less than 0.08. The ion exchange membrane contains a constituent component as shown in the general formula (2) as well as the general formula (1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 permeation deterrence of liquid fuel.

  As an example of an electrochemical device using an ion exchange membrane as a polymer solid 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 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, when the Nafion (trade name) membrane is used in a fuel cell using liquid organic fuel such as methanol as fuel, the methanol supplied to the fuel electrode side passes through the ion exchange membrane and flows into the air electrode side. The problem is remarkable. When this crossover occurs, there arises a problem that the liquid fuel and the oxidant directly react to reduce power, and that the liquid fuel leaks outside from the air electrode side. A method generally used to suppress the crossover is to limit the concentration of methanol as a fuel, and this is dealt with by using about 3 to 6% diluted methanol. However, when the fuel cell is operated with dilute methanol, the fuel tank becomes large, so the fuel cell size becomes large, which is not practically preferable. From such a viewpoint, an ion exchange membrane that can use a solution containing a high-concentration liquid fuel as a fuel is desired. In addition, as a technique for suppressing the crossover, a technique of increasing the thickness of the ion exchange membrane is also taken. However, as the thickness increases, the methanol permeation coefficient also increases, so the effect of inhibiting methanol permeation was not so great. That is, while the resistance value increases in proportion to the increase in thickness of the ion exchange membrane, the methanol permeation deterrence is not sufficiently improved, so that the effect of increasing the thickness was not expressed well. From such a viewpoint, an ion exchange membrane for a fuel cell having a small thickness dependency of the methanol permeability coefficient is desired. In addition, the reason why such dependence is observed is that the inventors have influenced that the swelling property of the membrane is different between methanol and water while the distribution of methanol concentration occurs inside the ion exchange membrane. I believe that.

  In addition, an ion exchange membrane in which a sulfonic acid group is introduced into a non-fluorinated aromatic ring-containing polymer has been studied, and a polymer obtained by sulfonating a polyarylethersulfone (for example, having excellent chemical and physical stability (for example, Non-patent document 1), sulfonated polyether ether ketone (for example, refer to patent document 1), and the like have been reported. For example, some polymers having liquid fuel permeability somewhat better than Nafion (trade name) have been introduced (see Non-Patent Document 2). However, studies on these membranes have begun in recent years, and the necessity of optimizing the polymer structure in ion exchange membranes using non-fluorine polymers has been shown.

JP-A-6-93114 (pages 15-17) Journal of Membrane Science (Netherlands) 1993, 83, p. 211-220 The Electrochemical Society 203rd Meeting-Paris, Abs No. 1167

  The present invention solves the problem that the liquid fuel permeation inhibiting property of an ion exchange membrane is low, which is regarded as a problem in a fuel cell using a liquid fuel such as a direct methanol fuel cell. The ion exchange membrane of the present invention is an ion exchange membrane that can suppress the amount of crossover of liquid fuel to a low level even when a high concentration liquid fuel is used. Can be used. Furthermore, since the methanol permeability coefficient is less dependent on the film thickness, the ion exchange membrane can effectively exert the effect of increasing the thickness.

  As a result of intensive studies, the present inventors have invented an ion exchange membrane that can suppress the crossover amount of the liquid fuel even when a high concentration liquid fuel is used. In addition, the fuel cell using the ion exchange membrane of the present invention is an excellent fuel cell that can use high-concentration liquid fuel, and in particular, the size of the fuel cell can be reduced.

That is, the present invention is a non-fluorine ion exchange membrane for a fuel cell having proton conductivity, and in the following formula showing the methanol concentration dependence of the methanol permeability coefficient of the ion exchange membrane, the slope α is 0.08 Is an ion exchange membrane excellent in methanol permeation deterrence.
Methanol permeability coefficient [μmol / m / s] = α × (methanol aqueous solution concentration [mol / l])

  In addition, the ion exchange membrane according to the above, wherein the thickness is changed to 50 μm and 200 μm, and when the methanol permeability coefficient of both is compared, the difference in methanol permeability coefficient is within 25%. An ion exchange membrane comprising a polymer.

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。 In addition, the ion exchange membrane includes a constituent represented by the following general formula (1) as well as 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.

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

  Further, the present invention is a fuel cell using the ion exchange membrane / electrode assembly.

  The present invention is an ion exchange characterized in that the permeation of liquid fuel can be suppressed even when the concentration of the liquid fuel contained in the liquid fuel solution is increased. The ion exchange membrane according to the present invention is a liquid It can be used favorably for fuel cells that use fuel, and contributes particularly to miniaturization of fuel cells.

Hereinafter, the present invention will be described in detail. The present invention is a hydrocarbon-based ion exchange membrane having proton conductivity in which an acidic group is introduced onto an aromatic ring with less swelling, and a direct methanol fuel cell, for example, produced using the ion exchange membrane is It is possible to show good power generation performance. As a feature of the ion exchange membrane of the present invention, even if the concentration of liquid fuel such as methanol is high, the permeation of the liquid fuel can be kept low. For example, Nafion (a typical fluorine-based ion exchange membrane) (Trade name), α, which is a coefficient of dependence on the methanol aqueous solution concentration (mol / l) of the methanol permeability coefficient (μmol / m / s) of the ion exchange membrane represented by the following formula, measured by the method described later, is 0.00. In contrast to the result of facilitating permeation at a speed of 14, it can be suppressed to 0.08 or less, and the effect of increasing the permeation amount when using high-concentration methanol can be minimized.
Methanol permeability coefficient [μmol / m / s] = α × (methanol aqueous solution concentration [mol / l])
As a result, even if a high-concentration aqueous methanol solution is used, the cross leak of methanol can be reduced, so that the fuel concentration can be increased and the size of the fuel tank in the fuel cell can be reduced. The value of α is more preferably 0.06 or less, further preferably 0.04 or less, and further preferably 0.02 or less. If the value of α is larger than 0.08, it is not preferable because the fuel becomes an ion exchange membrane that easily cross leaks.

  Further, as a feature of the ion exchange membrane of the present invention, it is possible to effectively suppress the permeation of liquid fuel even when the film thickness is increased. For example, Nafion which is a typical fluorine ion exchange membrane (product) In contrast to the phenomenon that the methanol permeability coefficient of the ion exchange membrane increases as the thickness increases, the ion exchange membrane of the present invention can keep the methanol permeability coefficient constant. As a result, when the membrane thickness of the ion exchange membrane is increased, a function of suppressing methanol permeation can be effectively expressed, and a good ion exchange membrane with little methanol permeation can be provided. That is, in the conventional ion exchange membrane, even if the thickness is doubled, the methanol permeation inhibiting ability is not improved twice, although the effect of effectively increasing the thickness was not exhibited. On the other hand, in the ion exchange membrane of the present invention, the methanol permeation inhibiting ability is doubled, and the effect of increasing the thickness is effective.

  As a method for knowing the thickness dependence of the methanol permeability coefficient, the methanol permeability coefficient tends to increase as the thickness increases. Therefore, an ion exchange membrane having a film thickness of about 50 μm and a film thickness of about 200 μm made of a polymer having the same composition. It is a preferable comparison method to prepare an ion exchange membrane and compare methanol permeability coefficients. It is also possible to produce a plurality of membranes having different thicknesses in the range of about 50 μm to about 200 μm, and obtain the thickness dependence of the methanol permeability coefficient from the relationship between the measured methanol permeability coefficient and thickness. is there. In order to produce ion exchange membranes with different thicknesses, for example, it is desirable to produce ion exchange membranes having various arbitrary thicknesses by stretching the polymer solution from the polymer solution by casting and then removing the solvent. It is a simple method. In producing the polymer solution, it is also possible to take a technique in which an ion exchange membrane already molded to a specific thickness is dissolved in a solvent. Details regarding the method of manufacturing the film will be described later.

  The thickness dependence of the methanol permeability coefficient is preferably as small as possible. When comparing an ion exchange membrane of at least 50 μm and an ion exchange membrane of 200 μm, an ion exchange membrane having a difference in methanol permeability coefficient of less than 25% is preferred, more desirably 15 % Or less, more preferably 10% or less. If the difference in methanol permeability coefficient is greater than 25% in the thickness range above, the effect of inhibiting methanol permeation when the thickness is increased will not be exhibited well, and the negative influence due to increased resistance of the membrane will increase. It is not preferable. It should be noted that when determining the thickness dependence of the methanol permeability coefficient, in order to reduce the experimental error, the methanol permeability coefficient and thickness obtained by investigating a plurality of samples having different film thicknesses between about 50 μm and about 200 μm. A method of obtaining the difference in methanol permeability coefficient from the relational expression seen between

  The ion exchange membrane and the polymer for producing the ion exchange membrane of the present invention include at least one of polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphonic acid, polyvinyl carboxylic acid, and polyvinyl sulfonic acid component. Ionomer containing. 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 the molecular chain thereof. 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 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.

  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.

  Further, 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 and particularly excellent.

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 3.6 meq / g. If it is less than 0.3 meq / g, it tends to not exhibit sufficient ion conductivity when used as an ion exchange membrane, and if it is more than 3.6 meq / g, the ion exchange membrane is not hot and humid. 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 0.5-2.5 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 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 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 finally obtained ion exchange membrane is used, it is preferable that the ionic functional group in the membrane is converted into an acid form by an appropriate acid treatment. 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 is less than 1.0 × 10 ⁻³ S / cm. In some cases, the output of the fuel cell tends to decrease.

  In order to prevent the cross leak of the liquid fuel, it is preferable to use an ion exchange membrane having a small methanol permeability coefficient, specifically, preferably in the range of 0.01 to 0.35 μmol / m / s, More preferably, it is preferably less than 0.3 μmol / m / s, more preferably less than 0.25 μmol / m / s, more preferably less than 0.2 μmol / m / s. Is preferred. When the methanol permeability coefficient is larger than 0.35 μmol / m / s, an ion exchange membrane having a low methanol permeation inhibiting property is obtained. On the other hand, if it is less than 0.01 μmol / m / s, it becomes difficult to achieve both ionic conductivity. From such a viewpoint, those including the constituents represented by the general formula (2) together with the following general formula (1) particularly introduced in the present invention are particularly preferable and excellent.

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.

  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 oxidant gas, the supply method, the structure of the flow path, the structure of the fuel cell, the operation method, operating conditions, temperature distribution, the control method of the fuel cell, etc. It is not limited.

  The ion exchange membrane of the present invention is excellent in liquid fuel permeation deterrence even when a high concentration liquid fuel is used. Moreover, the thickness dependence of liquid fuel permeation suppression is small. Taking advantage of these characteristics, it can be suitably used, for example, as an ion exchange membrane of a direct methanol 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). 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 and titrated with a 10 mM aqueous sodium hydroxide solution (commercially available 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)

<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 an aqueous methanol solution adjusted to 25 ° C. for 24 hours is sandwiched in an H-type cell, and 100 ml of an aqueous methanol solution is added to one side of the cell (a commercially available reagent-grade grade methanol and ultrapure water ( Injecting 100 ml of ultrapure water into the other cell and stirring the cells on both sides at 25 ° C., methanol diffuses into the ultrapure water through the ion exchange membrane. The amount was calculated by measuring 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 / m ² / s] = (Ct [mmol / L / s] × 0.1 [L]) / 2 × 10 ⁻⁴ [m ² ]
Methanol permeability coefficient [μmol / m / s] = Methanol permeation rate [mmol / m ² / s] × film thickness [m] × 1000
In addition, as a method for measuring the methanol concentration dependency of the methanol permeability coefficient, first, as a methanol aqueous solution, a test using a 1.0 mol / l methanol aqueous solution and a 5.0 mol / l methanol aqueous solution was performed. The methanol permeability coefficient was determined. Next, the slope α of the following equation was calculated from the slope of the graph plotting the methanol permeability coefficient and the methanol aqueous solution concentration. The measurement was performed 5 times, and the average value was used for the calculation. In determining the slope α, the intercept is not necessarily 0 (α is calculated assuming that there is an intercept). The reason is that the methanol permeability coefficient does not necessarily change linearly with respect to the concentration of the aqueous methanol solution. However, in determining the methanol aqueous solution concentration dependence of the methanol permeability coefficient in the present invention, as described above, a test using two different concentrations of aqueous methanol solution was performed, and the slope of the straight line obtained from the two points was obtained. Calculated.
Methanol permeability coefficient [μmol / m / s] = α × (methanol aqueous solution concentration [mol / l])

<Power generation characteristics>
Add a commercially available 54% platinum / ruthenium catalyst-supported carbon (Tanaka Kikinzoku Co., Ltd. fuel cell catalyst), a small amount of ultrapure water and isopropanol to a DuPont 20% Nafion (trade name) solution until uniform. Stir to prepare a catalyst paste. This catalyst paste is uniformly applied to Toray carbon paper TGPH-060 (hydrophobized product) so that the amount of platinum deposited is 2 mg / cm ² and dried, and a gas diffusion layer with an electrode catalyst layer for the anode Was made. In addition, in the same manner, an electrode catalyst layer is formed on the hydrophobized carbon paper using a commercially available platinum catalyst-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd. fuel cell catalyst) instead of platinum / ruthenium catalyst-supported carbon. This produced a gas diffusion layer with an electrode catalyst layer for the cathode (1 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 A membrane-electrode assembly was obtained. This assembly was incorporated into an evaluation fuel cell FC25-02SP manufactured by Electrochem, and a current density of 0.1 A / cm ² was supplied while supplying a methanol aqueous solution and air of 40 ° C. to the anode and the cathode at a cell temperature of 40 ° C., respectively. The voltage when the discharge test was conducted was examined. As the methanol aqueous solution, liquids of 1 mol / l and 5 mol / l were used and evaluated individually.

Example 1
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile such that the molar ratio is 1.00: 1.99: 2.99: 3.21; A mixture of 4,4′-biphenol and potassium carbonate was prepared, and 15.1 g of the mixture was weighed into a 100 ml four-necked flask together with 4.20 g of molecular sieves, and then flushed with nitrogen. After adding NMP as a solvent and stirring at 145 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 190-200 ° C. and sufficiently increasing the viscosity of the system (about 5.5 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 25% NMP solution of polymer was prepared. The polymer solution was thinly drawn by a casting method and dried at 100 ° C. and then 150 ° C. overnight 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 in a state of being fixed to a frame to produce an ion exchange membrane of Example 1.

Example 2
3,3′-Disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile, 4,4′-biphenol and potassium carbonate in a molar ratio of 1.00: 2.31: 3. 31: The ion exchange membrane of Example 2 was produced using the method of Example 1 except that it was charged to be 3.46.

Example 3
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 2,6-dichlorobenzonitrile, 4,4′-biphenol and potassium carbonate in a molar ratio of 1.00: 3.25: 4. 25: The ion exchange membrane of Example 3 was produced using the method of Example 1 except that it was charged to be 4.46.

Examples 4, 5, 6, 7
Except for changing the thickness of the polymer solution when the polymer solution is stretched by the casting method, the thickness of the ion exchange membrane of Example 1 is different from that of Example 1, except that the thickness of the polymer solution is changed. 6 and 7 ion exchange membranes were prepared.

Comparative Example 1
A commercially available Nafion (trade name) 117 membrane was used as the ion exchange membrane of Comparative Example 1.

Comparative Example 2
A commercially available Nafion (trade name) 112 membrane was used as the ion exchange membrane of Comparative Example 2.

Comparative Example 3
3,3′-Disulfo-4,4′-dichlorodiphenylsulfone disodium salt, 4,4′-dichlorodiphenylsulfone, 4,4′-biphenol and potassium carbonate in a molar ratio of 1.00: 1.38: 2 .38: The ion exchange membrane of Comparative Example 2 was produced using the method of Example 1 except that the amount was charged to be 3.15. That is, in order to use 4,4′-dichlorodiphenyl sulfone instead of 2,6-dichlorobenzonitrile used in Example 1 and to have a IEC comparable to that of the ion exchange membrane of Example 1, The charging ratio was adjusted.

  The physical property evaluation results of Examples 1, 2, 3, 4, 5, 6, 7 and Comparative Examples 1, 2, 3, are shown in Table 1.

  The results of Examples 1, 2, and 3 and Comparative Examples 1 and 3 conducted as experiments for comparing the effect of methanol concentration on methanol permeability will be compared and discussed. First, from the results of Examples 1, 2, and 3, all of the ion exchange membranes of the present invention have a small increase in methanol permeability coefficient (α is small) when the methanol concentration is increased, and as a result, a high concentration in the power generation test. It can be seen that even when the methanol aqueous solution is used as a fuel, an excellent fuel cell with good power generation performance is obtained. However, the perfluorocarbon sulfonic acid membrane of Comparative Example 1 and the hydrocarbon-based membrane of Comparative Example 3 have a large α value, and when using a high-concentration methanol solution, the amount of methanol crossover increases significantly. When a high-concentration methanol solution was used as a fuel, a dramatic performance degradation occurred. The reason why α was particularly large in the film of Comparative Example 1 is presumed to be due to the strong affinity of fluorine for methanol. On the other hand, the membrane of Comparative Example 3 is a hydrocarbon-based membrane and is a better membrane than Comparative Example 1, but it is considered that the swelling was large and the methanol permeation inhibiting property was not sufficient. The membrane of Comparative Example 3 is an ion exchange membrane that has recently attracted attention as being more useful as an ion exchange membrane for direct methanol fuel cells than a fluorine membrane. However, it has not been sufficiently optimized from the viewpoint of the polymer composition, and the ion exchange membrane shown in the examples did not have a better α value.

  Next, the results of Examples 1, 4, 5, 6, 7 and Comparative Examples 1 and 2, which were conducted as experiments for comparing the thickness dependence of the methanol permeability coefficient, will be compared. When comparing the characteristics of the ion exchange membranes of Comparative Example 1 and Comparative Example 2, the methanol permeation coefficient is highly dependent on the film thickness. Therefore, even if the film thickness is quadrupled, the methanol permeation inhibition is 1.75 times. However, it has been improved, and it can be seen that the increase in resistance is larger than the improvement effect of methanol permeation deterrence. On the other hand, the membrane of the example has a substantially constant methanol permeation coefficient regardless of the thickness. Therefore, when the thickness is increased by 4 times, the methanol permeation inhibiting property is also substantially increased by 4 times, which is an improvement over the ion exchange membrane of the comparative example. It can be said that this is a superior ion exchange membrane having a large effect.

  From the above, the ion exchange membrane of the present invention is a novel ion exchange membrane that works well as an ion exchange membrane for a fuel cell of a type that uses a liquid fuel such as a direct methanol fuel cell. Excellent performance when used in batteries.

  When a fuel cell is used, an ion exchange membrane having excellent liquid fuel permeation deterrence can be provided, and a highly reliable and high performance fuel cell can be supplied.

Claims (5)

A non-fluorine ion exchange membrane for a fuel cell having proton conductivity, characterized in that the slope α is smaller than 0.08 in the following equation showing the methanol concentration dependence of the methanol permeability coefficient. film.
Methanol permeability coefficient [μmol / m / s] = α × (methanol aqueous solution concentration [mol / l]) The ion exchange membrane according to claim 1, wherein the difference in methanol permeation coefficient is within 25% when the methanol permeation coefficients of the two are compared with each other by comparing the methanol permeation coefficients of 50 μm and 200 μm. The ion exchange membrane according to any one of claims 1 to 2, comprising a component represented by the following general formula (1) and the general formula (2).

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. An ion exchange membrane / electrode assembly using the ion exchange membrane according to any one of claims 1 to 3. A fuel cell using the ion exchange membrane / electrode assembly according to claim 4.