JP2013028710A - Ionically-conductive electrolyte membrane, and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ionically-conductive electrolyte membrane that has high ion conductivity even in high-temperature low-humidity condition and has high dimensional stability to moisture variation.SOLUTION: The ionically-conductive electrolyte membrane comprises: a matrix containing a water-repellent polymer; and a hydrophilic polymer that has an ionically-conductive group, wherein the ionically-conductive electrolyte membrane has a domain that is dispersed in the matrix. In the matrix, the domain is extended in a direction of the membrane surface.

Description

  The present invention relates to an ion conductive electrolyte membrane suitably used for a polymer electrolyte fuel cell and the like, and a method for producing the same. The present invention also relates to a fuel cell membrane electrode assembly including the ion conductive electrolyte membrane, and a polymer electrolyte fuel cell including the fuel cell membrane electrode assembly.

  Conventionally, ion conductive electrolyte membranes have been used in polymer electrolyte fuel cells, alkaline electrolytic cells, air humidification modules, and the like. Among these applications, a polymer electrolyte fuel cell has recently attracted attention. In a polymer electrolyte fuel cell, the ion conductive electrolyte membrane functions as an electrolyte for conducting protons, and at the same time, functions as a diaphragm for preventing direct mixing of hydrogen, methanol, and oxygen as fuels.

  Conventional polymer electrolyte fuel cells exhibit their functions by supplying hydrogen or oxygen as a fuel in a sufficiently humidified state and retaining sufficient water in the electrolyte membrane. For this reason, a humidifier or the like is incorporated in the fuel cell system. However, in recent years, it has been required to reduce the number of auxiliary equipment such as a humidifier because of the demand for lower prices for the entire fuel cell system. Therefore, in recent years, there has been an increasing demand for polymer electrolyte fuel cells that can operate under high temperature and low humidity, and electrolyte membranes are also required to have performance in a high temperature and low humidity state.

  As an electrolyte membrane exhibiting high proton conductivity in an environment with low relative humidity, Patent Document 1 discloses a composite polymer electrolyte membrane containing a block copolymer composed of a hydrophilic block and a hydrophobic block and a solid acid. The composite polymer electrolyte membrane has a microphase separation structure composed of a hydrophilic domain formed by the hydrophilic block and a hydrophobic domain formed by the hydrophobic block, and the solid acid is included in the hydrophilic domain. There has been proposed a composite polymer electrolyte membrane characterized in that is localized. In addition, as a microphase separation structure, from the viewpoint of water resistance and film strength, it is described that a structure in which a hydrophilic domain is separated into a cylindrical shape or a spherical shape in which a hydrophilic domain extends in a film thickness direction is preferable in a hydrophobic matrix. .

  However, if the humidifier of the polymer electrolyte fuel cell is removed, the amount of water generated varies with the load variation of the cell, and the humidity changes. According to the study by the present inventors, a structure in which a hydrophilic domain is separated into a cylindrical shape or a spherical shape in which a hydrophilic domain extends in a film thickness direction in a hydrophobic matrix as described in Patent Document 1 is obtained by changing the humidity. It has been found that there is a problem in that the water absorption amount of the membrane changes and the swelling and shrinkage are repeated, and as a result, the electrolyte membrane and the electrode may be peeled off. When the electrolyte membrane and the electrode are peeled off, the battery reaction is difficult to proceed smoothly, resulting in a significant decrease in performance. Further studies by the present inventors have revealed that peeling between the electrolyte membrane and the electrode is likely to occur due to a dimensional change in the film surface direction.

JP 2008-311226 A

  Accordingly, an object of the present invention is to provide an ion conductive electrolyte membrane having high ion conductivity even in a high temperature and low humidity state and having high dimensional stability against humidity change.

The present invention is an ion conductive electrolyte membrane having a matrix containing a water repellent polymer and a domain containing a hydrophilic polymer having an ion conductive group and dispersed in the matrix,
In the matrix, an ion conductive electrolyte membrane in which the domains extend in the film surface direction.

  In the ion conductive electrolyte membrane of the present invention, in the cross section in the film thickness direction, when the maximum length in the film surface direction of the domain is the major axis and the maximum length in the film thickness direction of the domain is the minor axis, It is preferable that the average aspect ratio represented by the minor axis is 2 or more.

  In the ion conductive electrolyte membrane of the present invention, the water-repellent polymer is polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyether ether ketone, It is preferably at least one selected from the group consisting of aromatic polyimide, polyamideimide, and polyetherimide. The hydrophilic polymer is preferably at least one selected from the group consisting of polystyrene sulfonic acid, polyvinyl sulfonic acid, polyisoprene sulfonic acid, and polyacrylamide t-butyl sulfonic acid. It is preferable that the hydrophilic polymer is grafted on the water-repellent polymer.

  The present invention also causes stress to occur in the film surface direction in an ion conductive electrolyte membrane having a matrix containing a water-repellent polymer and a hydrophilic polymer having an ion conductive group and dispersed in the matrix. It is a manufacturing method of said ion conductive electrolyte membrane including a process.

  In the production method of the present invention, the ion conductive electrolyte membrane is immersed in a solvent to swell, the ion conductive electrolyte membrane is fixed to a fixed frame in a swollen state, and stress is generated by removing the solvent. Is preferred.

  The present invention also provides a membrane electrode assembly for a fuel cell comprising the above-described ion conductive electrolyte membrane.

  The present invention is also a polymer electrolyte fuel cell including the fuel cell membrane electrode assembly.

  ADVANTAGE OF THE INVENTION According to this invention, the ion conductive electrolyte membrane which has high ionic conductivity also in a high temperature low humidification state, and has high dimensional stability with respect to a humidity change is provided. The ion conductive electrolyte membrane of the present invention can be suitably used for a fuel cell membrane electrode assembly, and is particularly useful for a polymer electrolyte fuel cell application.

2 is a transmission electron micrograph of the ion conductive electrolyte membrane obtained in Example 1. FIG. (Thickness direction: film thickness direction, Planer direction: film surface direction) 2 is a transmission electron micrograph of an ion conductive electrolyte membrane obtained in Comparative Example 1. (Thickness direction) It is a graph which shows the evaluation result of the repetition area change rate of the ion conductive electrolyte membrane obtained in Example 1 and Comparative Example 1.

  First, the ion conductive electrolyte membrane of the present invention will be described. The ion conductive electrolyte membrane of the present invention has a matrix containing a water-repellent polymer and a domain containing a hydrophilic polymer having an ion conductive group and dispersed in the matrix. And in the said matrix, it has the characteristics that the said domain is extended | stretched in the film surface direction.

  In the present invention, the water-repellent polymer contained in the matrix includes engineering plastic or super engineering plastic aromatic polymers, olefin polymers, and fluorinated olefin polymers in terms of chemical stability and mechanical strength. preferable.

  Specific examples of engineering plastics or super engineering plastics aromatic polymers include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyether ether ketone, polyether ketone, polysulfone, polysulfone. Examples include ether sulfone, polyphenylene sulfide, polyarylate, polyether imide, polyamide imide, aromatic polyimide, and a copolymer containing a repeating unit of these polymers.

  Specific examples of the olefin polymer include polyethylene (eg, high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene), polypropylene, polybutene, polymethylpentene, and a copolymer containing repeating units of these polymers.

  Specific examples of the fluorinated olefin polymer include polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene. , Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, and copolymers containing repeating units of these polymers.

  The water-repellent polymers can be used alone or in combination of two or more. From the viewpoint of solubility necessary for film formation, the water-repellent polymer is polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyether ether ketone, It is preferably at least one selected from the group consisting of aromatic polyimide, polyamideimide, and polyetherimide. From the viewpoint of chemical stability and cost, polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymer More preferably.

  The ion conductive group of the hydrophilic polymer having an ion conductive group is preferably a proton conductive group, and more preferably a sulfonic acid group.

  Examples of the hydrophilic polymer include polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoprene sulfonic acid, polyacrylamide t-butyl sulfonic acid and the like, and these can be used alone or in combination of two or more. . A copolymer obtained by copolymerizing the monomer components of these hydrophilic polymers can also be used. The hydrophilic polymer is preferably at least one selected from the group consisting of polystyrene sulfonic acid, polyvinyl sulfonic acid, polyisoprene sulfonic acid, and polyacrylamide t-butyl sulfonic acid.

  In the ion conductive electrolyte membrane of the present invention, the domain containing the hydrophilic polymer is elongated and dispersed in the film surface direction in the matrix containing the water repellent polymer. In an ion conductive electrolyte membrane having a matrix containing a conventional water repellent polymer and a hydrophilic polymer having an ion conductive group and dispersed in the matrix, the matrix extends in the film thickness direction. Cylindrical domains and spherical domains were dispersed. However, in the present invention, domains having a flat shape extending in the film surface direction are dispersed in the matrix (in the present invention, since the domains are dispersed in the matrix, the layer is It is different from the stacked lamella structure). Thus, the dimensional stability in the film | membrane surface direction with respect to a humidity change improves by taking the flat shape which the domain extended | stretched in the film | membrane surface direction. This is presumably because the film thickness direction is more likely to swell than the film surface direction.

  In the present invention, "the domain containing the hydrophilic polymer extends in the film surface direction in the matrix containing the water-repellent polymer" means that the domain in the film surface direction of the domain when the cross section in the film thickness direction is viewed. When the maximum length is the major axis and the maximum length in the film thickness direction of the domain is the minor axis, the average aspect ratio expressed by the major axis / minor axis is greater than 1, and the average value of the aspect is It is preferably 2 or more, and more preferably 5 or more. In addition, the average value of the aspect ratio can be obtained as an average value obtained by observing a cross section in the film thickness direction with a transmission electron microscope (TEM), obtaining a major axis and a minor axis for 10 or more domains.

  Next, the manufacturing method of the ion conductive electrolyte membrane of this invention is demonstrated. The ion conductive electrolyte membrane of the present invention includes a matrix containing a water-repellent polymer, a hydrophilic polymer having an ion conductive group, and a domain dispersed in the matrix. Can be manufactured by a method including a step of generating stress.

  In the ion conductive electrolyte membrane as a raw material, it is preferable that the domain is spherical because it is easily available and the domain is easily elongated in the film surface direction.

  An ion conductive electrolyte membrane in which spherical domains are dispersed in a matrix can be produced according to a known method, and can also be produced by the following method.

  A preferred example of a method for producing an ion conductive electrolyte membrane in which spherical domains are dispersed in a matrix is a step of irradiating water-repellent polymer fine particles with a radiation monomer, a hydrophilic monomer having a group that can be converted into an ion conductive group, A step of graft polymerization to water-repellent polymer fine particles, a step of preparing a cast solution by dissolving the obtained graft polymer in a solvent, applying the cast solution on a support and drying, a graft weight in the obtained film A step of converting a group that can be converted into an ion-conductive group of the coalescence into an ion-conductive group.

  The average particle size of the water-repellent polymer fine particles is preferably 10 μm to 500 μm, and more preferably 50 μm to 300 μm. If the particle size of the water-repellent polymer fine particles is too large, the speed of the grafting reaction inside the fine particles will be slow, and this process may take a long time and production efficiency may be reduced. If the particle size is too small, it may be difficult to handle the polymer material in each step. The average particle diameter can be measured by a dry sieving method.

  As radiation applied to the water-repellent polymer fine particles, ionizing radiation such as α-rays, β-rays, γ-rays, electron beams and ultraviolet rays is used, and γ-rays and electron beams are particularly suitable. The irradiation dose necessary for graft polymerization is usually preferably 1 to 500 kGy, more preferably 10 to 300 kGy. When the irradiation dose is less than 1 kGy, the amount of radicals generated is reduced, and graft polymerization may be difficult. When the irradiation amount is larger than 500 kGy, there is a possibility that an excessive crosslinking reaction, polymer deterioration or the like occurs.

  In addition, as a method of radical polymerization by radiation irradiation to a polymer, a peroxide method in which irradiation and radical reaction are performed in the presence of oxygen, and a polymer radical method in which irradiation and radical reaction are performed in the absence of oxygen. There is. In the peroxide method, the graft reaction proceeds from an oxygen radical bonded to the polymer, whereas in the polymer radical method, the graft reaction proceeds from a radical generated in the polymer. Here, in order to prevent the graft reaction from being inhibited by the presence of oxygen, it is preferable to perform radical polymerization by a polymer radical method. Therefore, it is preferable to irradiate the water-repellent polymer fine particles with radiation in an inert gas atmosphere or in a vacuum. The temperature during irradiation (irradiation temperature) is preferably -100 to 100 ° C, more preferably -100 to 60 ° C. If the irradiation temperature is too high, the generated radicals are liable to be deactivated. In order to prevent radical deactivation, it is desirable to store the water-repellent polymer fine particles after irradiation at a low temperature not higher than the glass transition temperature of the water-repellent polymer.

  Graft polymerization of a hydrophilic monomer having a group that can be converted into an ion-conducting group onto irradiated water-repellent polymer fine particles is carried out by dispersing the irradiated water-repellent polymer fine particles in a solution of the hydrophilic monomer. It may be performed in a liquid two-phase system. Here again, as described above, in order to prevent reaction inhibition due to the presence of oxygen, it is preferable to carry out in an atmosphere having as low an oxygen concentration as possible.

  The group that can be converted into an ion conductive group of the hydrophilic monomer is preferably a group that can be easily converted into an ion conductive group by hydrolysis or ion exchange in the subsequent step of graft polymerization, such as a sulfonic acid ester group and a sulfonic acid group. A base is more preferred. Specific examples thereof include sulfonic acid fatty acids represented by sulfonic acid alkyl ester groups such as sulfonic acid methyl ester group, sulfonic acid ethyl ester group, sulfonic acid propyl ester group, sulfonic acid butyl ester group, and sulfonic acid cyclohexyl ester group. And sulfonic acid aromatic ester groups such as sulfonic acid phenyl ester groups; metal bases of sulfonic acids represented by alkali metal bases of sulfonic acids such as sodium sulfonate groups and lithium sulfonate groups.

  Specific examples of the hydrophilic monomer include monomers obtained by esterifying or chlorinating sulfonic acid groups such as styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoprene sulfonic acid, and acrylamide t-butyl sulfonic acid. These can be used alone or in combination of two or more.

  As the solvent used for the solution of the hydrophilic monomer, a solvent that dissolves the hydrophilic monomer but does not dissolve the water-repellent polymer fine particles is selected. Specific examples thereof include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene, and aromatic compounds such as phenols such as phenol and cresol, and ethers such as cyclic ethers such as 1,4-dioxane. Etc. Among these, aromatic compounds, particularly aromatic hydrocarbons are preferable. When an aromatic compound is used as a solvent, the monomer can be efficiently dissolved and the shape of the water-repellent polymer fine particles can be maintained. In addition, you may use a solvent individually or in mixture of 2 or more types.

  The monomer concentration of the hydrophilic monomer solution is preferably 0.2 to 3 mol / L, and more preferably 0.5 to 2.5 mol / L. If the monomer concentration is less than 0.2 mol / L, the graft reaction may not proceed sufficiently. When the monomer concentration is higher than 3 mol / L, there is a possibility that reaction outside the water-repellent polymer fine particles, yield reduction, and the like may occur.

  In order to remove dissolved oxygen that inhibits the graft reaction, the hydrophilic monomer solution is preferably loaded into a container such as glass or stainless steel and degassed under reduced pressure or bubbled with an inert gas such as nitrogen. While stirring this hydrophilic monomer solution, the water-repellent polymer fine particles irradiated with radiation are put into the solution to start graft polymerization.

  The reaction time in the graft polymerization is preferably about 10 minutes to 12 hours, and the reaction temperature is preferably 0 to 100 ° C, more preferably 40 to 80 ° C.

  After the grafting reaction, the particulate graft polymer is filtered off from the reaction solution. Further, in order to remove the solvent, unreacted monomer and homopolymer, the graft polymer is washed 3 to 6 times with an appropriate amount of solvent and then dried. As the cleaning solvent, toluene, methanol, isopropyl alcohol, acetone and the like are preferable.

  A cast solution is prepared by dissolving the obtained fine particle graft polymer in a solvent. As the solvent for dissolving the graft polymer, a solvent capable of dissolving the hydrophilic monomer and the water-repellent polymer fine particles in the graft polymerization is preferably selected and used, for example, dimethylacetamide, N-methyl-2-pyrrolidone. And aprotic polar solvents such as dimethylformamide and dimethyl sulfoxide (DMSO).

  The concentration of the graft polymer in the cast solution is preferably 5 to 30% by weight, and more preferably 10 to 25% by weight. If this concentration exceeds 30% by weight, the viscosity of the cast solution is too high, and it becomes difficult to form a cast film having a uniform film thickness. On the other hand, when the concentration is less than 5% by weight, the coating liquid tends to flow, so that it is not easy to obtain a film having a uniform thickness.

  Examples of the support for applying the cast solution include a glass plate, a metal plate, and a resin sheet. The thickness of the film obtained in the casting film drying step is preferably 10 to 70 μm, and the film thickness of the cast film may be determined according to this thickness.

  Application | coating to the support body of cast solution can be performed according to a well-known method.

  Regarding the drying of the applied cast solution, the drying temperature in the case of forming a film having a thickness of 10 to 70 μm is preferably not less than the temperature at which the time required for drying (drying time) is 6 hours, and the drying time is 2 hours. It is more preferable that the temperature be equal to or higher than the temperature. The drying temperature is preferably 20 ° C. or lower than the melting point of the graft polymer, and more preferably 40 ° C. or lower than the melting point of the graft polymer. If the drying temperature is too high and deviates from the above temperature range, the ionic conductivity of the electrolyte membrane may be lowered. If the drying temperature is too low and deviates from the above temperature range, the drying process takes a long time, and the productivity of the electrolyte membrane may be reduced.

  The film thus obtained has groups that can be converted into ion-conducting groups. Therefore, next, the group is converted into an ion conductive group by hydrolysis, ion exchange or the like. This conversion step can be performed according to a known method. For example, when the group is a sulfonic acid alkyl ester group, acid treatment with nitric acid, hydrochloric acid, sulfuric acid, etc., treatment with an aqueous alcohol solution, base in an amine derivative solution What is necessary is just to perform a process etc. When the group is a sulfonic acid metal base, acid treatment with nitric acid, hydrochloric acid, sulfuric acid or the like may be performed. The acid concentration in the acid treatment is preferably about 1N. These treatments may be performed under heating conditions as necessary.

  In addition, you may perform the conversion process to an ion conductive group with respect to the graft polymer before film forming. From the viewpoint of workability, the conversion to an ion conductive group is preferably performed on the film.

  Next, the process of generating stress in the direction of the film surface in the raw material ion conductive electrolyte film, which is a process of the production method of the present invention, will be described.

  This step can be performed by a film swelling method, a film stretching method, a rolling method, or the like.

  In the membrane swelling method, an ion conductive electrolyte membrane as a raw material is immersed in a solvent to swell, and the ion conductive electrolyte membrane is fixed to a fixed frame in a swollen state, and stress is generated by removing the solvent.

  The solvent used in the membrane swelling method is not particularly limited as long as it can swell the raw material ion conductive electrolyte membrane. Examples thereof include toluene, acetone, dimethyl sulfoxide, methyl ethyl ketone, acetylacetone, cyclohexanone, acetic acid. , Acetic anhydride, methyl acetate, ethyl acetate, diethyl carbonate, γ-butyrolactone, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexamethylphosphamide, diethylenetriamine, ethylene oxide, propylene oxide, tetrahydrofuran, dioxane, methanol , Ethanol, isopropyl alcohol, n-butanol, water and the like, and these can be used alone or as a mixed solvent of two or more.

  The fixed frame used for fixing the swollen ion conductive electrolyte membrane is not particularly limited as long as it has rigidity capable of maintaining the size of the swollen ion conductive electrolyte membrane in the film surface direction. Preferably, the four sides of the swollen ion conductive electrolyte membrane are fixed with a fixed frame.

  Desolvation can be performed by heating to the boiling point of the solvent or higher. As the solvent is removed from the swollen domain by this desolvation operation, a shrinkage force is generated in the ion conductive electrolyte membrane. In the film thickness direction, the swollen domain receives the contraction force as it is. However, in the direction of the membrane surface, the ion conductive electrolyte membrane is prohibited from contracting by the fixed frame, and thus a reaction force is generated against the contraction force. By generating stress in the membrane surface direction in this way, the domains in the ion conductive electrolyte membrane extend in the membrane surface direction, and the ion conductive electrolyte membrane of the present invention is obtained.

  In the membrane stretching method, stress is generated by stretching an ion conductive electrolyte membrane as a raw material. At this time, the raw material ion conductive electrolyte membrane may be swollen using a solvent, and the solvent may not be used. The stretching may be either uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. From the viewpoint of reducing uniformity and thickness nonuniformity, stretching using a solvent is preferred. By generating stress in the film surface direction by stretching, the domains in the ion conductive electrolyte film extend in the film surface direction, and the ion conductive electrolyte film of the present invention is obtained.

  In the film swelling rolling method, the raw material ion conductive electrolyte membrane is immersed in a solvent to swell, and both sides of the swollen ion conductive electrolyte membrane are sandwiched by the support from above and below, and the pressure is increased in the film thickness direction at a constant pressure. Applied and desolventized in this state to generate stress in the film surface direction.

  A glass plate, a metal plate, etc. can be used for a support body.

  Desolvation can be performed by heating to the boiling point of the solvent or higher. The domain swollen by desolvation receives pressure from above and below in addition to the contraction force in the film thickness direction. Furthermore, since the solvent escape route is only on the side surface around the membrane, the solvent tends to move in the direction of the membrane surface, and pressure from above and below the membrane also tries to escape in the membrane surface direction. As a result, stress is generated in the film surface direction, and the domains in the ion conductive electrolyte film are elongated in the film surface direction, whereby the ion conductive electrolyte film of the present invention is obtained.

  The ion-conducting electrolyte membrane thus obtained is preferably kept as it is and maintained at a predetermined temperature and time. For example, when the water-repellent polymer is polyvinylidene fluoride and the hydrophilic polymer is polystyrene sulfonic acid, the temperature is preferably 60 to 170 ° C.

  The thickness of the ion conductive electrolyte membrane of the present invention may be appropriately determined according to the use, and is preferably 10 to 70 μm.

  The ion conductive electrolyte membrane of the present invention has high ion conductivity even in a high temperature and low humidity state, and has high dimensional stability against humidity changes. Therefore, it can be suitably used for a membrane electrode assembly for a fuel cell. Therefore, the present invention is also a fuel cell membrane electrode assembly including the ion conductive electrolyte membrane described above. The membrane electrode assembly for a fuel cell can be constituted, for example, by replacing the ion conductive electrolyte membrane of a known fuel cell membrane electrode assembly with the above ion conductive electrolyte membrane.

  The membrane electrode assembly for a fuel cell of the present invention can be suitably used for a polymer electrolyte fuel cell. Therefore, the present invention is also a polymer electrolyte fuel cell including the fuel cell membrane electrode assembly. The polymer electrolyte fuel cell can be constituted, for example, by replacing a membrane electrode assembly for a fuel cell of a known polymer electrolyte fuel cell with the above membrane electrode assembly for a fuel cell. The polymer electrolyte fuel cell can operate stably without a humidifier, and can be constructed at a low price.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these Examples. First, the evaluation method performed about the Example and the comparative example is described.

[Ion exchange capacity (IEC: Ion Exchange Capacity)]
A sufficiently dried and weighed electrolyte membrane (about 12 cm ² , thickness: arbitrary) was immersed in a 3 mol / L sodium chloride aqueous solution and reacted at 60 ° C. for 12 hours or more in a water bath. After cooling to room temperature, the membrane was thoroughly washed with ion-exchanged water, and the reaction solution and the washing solution were mixed with 0.05N sodium hydroxide using a potentiometric automatic titrator (AT-510; manufactured by Kyoto Electronics Industry Co., Ltd.). Titration with an aqueous solution was performed, and the ion exchange capacity was calculated by the following formula.
IEC (meq / g) = (Titration amount (L) × NaOH concentration (N) × 1000) / Dry membrane weight (g)

[Film thickness]
The film thickness was measured using a dial thickness gauge G-6C (1/1000 mm, probe diameter φ5 mm) manufactured by Ozaki Seisakusho. The film thickness was determined as an average value of 10 measurement points.

〔conductivity〕
The measurement was performed in a constant temperature and humidity chamber maintained at 80 ° C. and 60% RH according to the proton conductivity measurement method of the Fuel Cell Practical Use Promotion Council (FCCJ).

[Area change rate]
The electrolyte membrane was cut into a square with a side of 3 cm in a room at 23 ° C. and 40% RH and weighed. Then, it was immersed in ultrapure water all day and night. The electrolyte membrane immersed in water was sandwiched between smooth glass plates, the length of the side was measured using calipers, and the area was calculated. Thereafter, the glass plate was removed, and the weight of the electrolyte membrane holding water was measured.
(Area change rate;%) = 100 × S ₂ / S ₁
However, S ₁ electrolyte membrane specimen area after membrane specimen area before water immersion, S ₂ water immersion.

Example 1 Membrane Swelling Method Polyvinylidene fluoride (PVDF) powder (KF Polymer T # 1100 manufactured by Kureha Chemical Industry Co., Ltd., particle size: about 120 μm) was irradiated with 30 KGy of cobalt 60 γ rays. The obtained PVDF powder was stored at −60 ° C. On the other hand, 11.5 g of styrene sulfonic acid ethyl ester (EtSS) and 13.5 g of toluene as monomer components were put into a test tube, and the EtSS solution was stirred for 30 minutes at room temperature while bubbling with nitrogen, and sufficiently deoxygenated. . Next, 5 g of the PVDF powder was put into this test tube, immersed in an oil bath at 70 ° C., and polymerization was carried out by maintaining the temperature for 2 hours. After completion of the reaction, the reaction solution and powder were taken out and put into 80 ml of acetone at room temperature. The mixture was stirred at room temperature for 30 minutes, and then the supernatant was removed. This operation was repeated 5 times to remove styrene sulfonic acid ethyl ester monomer component and the like. The powder was filtered off and dried overnight in a dryer at 60 ° C. to obtain a styrene sulfonic acid ethyl ester graft copolymer powder.

  25.5 g of N-methyl-2-pyrrolidone was added to 4.5 g of this polymer powder, and this was shaken at 70 ° C. for 1 hour or longer. Then, the defoaming process was performed with the hybrid mixer, and the obtained solution was applied with a gap thickness of 500 μm on the PET film. This was heat-dried at 80 ° C. for 12 hours to obtain a film. The obtained film was immersed in methanol and peeled off from the PET film. Furthermore, it hydrolyzed by processing at 100 degreeC for 1 hour with saturated n-butanol aqueous solution. Then, it was immersed in 1N hydrochloric acid aqueous solution for 1 hour, washed with water, and then immersed in methanol. The thickness of the film immersed in methanol was about 90 μm. The four sides of the membrane swollen with methanol were fixed to a stainless steel fixing frame (9 cm on the outer side and 7 cm on the inner side), and the solvent was removed at 140 ° C. for 12 hours. Then, it naturally cooled to room temperature. The obtained membrane had an ion exchange capacity (IEC) of 1.9 meq / g.

Example 2 Film Swelling Rolling Method In the same manner as in Example 1, a styrene sulfonic acid ethyl ester graft copolymer polymer powder was obtained, formed into a film, and hydrolyzed with a saturated n-butanol aqueous solution at 100 ° C. for 1 hour. Then, it was immersed in 1N hydrochloric acid aqueous solution for 1 hour, washed with water, and then immersed in methanol. Next, the membrane swollen with methanol was sandwiched between the PTFE sheets from both sides, and further sandwiched between the glass plates from above. In this state, the solvent was removed by heat treatment at 80 ° C. for 12 hours. Then, it naturally cooled to room temperature. The obtained membrane had an ion exchange capacity (IEC) of 1.9 meq / g.

Example 3
In the same manner as in Example 1, a styrene sulfonic acid ethyl ester graft copolymer polymer powder was obtained, formed into a film, and hydrolyzed with a saturated aqueous n-butanol solution at 100 ° C. for 1 hour. The obtained film was immersed in isopropyl alcohol. Next, the four circumferences of the film swollen with isopropyl alcohol were fixed to a stainless steel fixing frame (9 cm on the outer side, 7 cm on the inner side), and the solvent was removed at 160 ° C. for 10 minutes. Then, it naturally cooled to room temperature. The obtained membrane had an ion exchange capacity (IEC) of 1.9 meq / g.

Example 4
In the same manner as in Example 1, a styrene sulfonic acid ethyl ester graft copolymer polymer powder was obtained, formed into a film, and hydrolyzed with a saturated aqueous n-butanol solution at 100 ° C. for 1 hour. The obtained film was immersed in pure water. Next, four rounds of the membrane swollen with pure water were fixed to a stainless steel fixing frame (9 cm on the outer side and 7 cm on the inner side), and the solvent was removed at 160 ° C. for 10 minutes. Then, it naturally cooled to room temperature. The obtained membrane had an ion exchange capacity (IEC) of 2.0 meq / g.

Comparative Example 1
In the same manner as in Example 1, a styrene sulfonic acid ethyl ester graft copolymer polymer powder was obtained, formed into a film, and hydrolyzed with a saturated aqueous n-butanol solution at 100 ° C. for 1 hour. Then, it was immersed in 1N hydrochloric acid aqueous solution for 1 hour, washed with water, and then immersed in methanol. Thereafter, the membrane was dried at room temperature without performing a fixing operation. The obtained membrane had an ion exchange capacity (IEC) of 1.9 meq / g.

  Thus, it can be seen that the electrolyte membrane of the present invention has high dimensional stability in the direction of the membrane surface and exhibits good ionic conductivity.

  Next, a cross section in the film thickness direction of the ion conductive electrolyte membrane obtained in Example 1 and Comparative Example 1 was observed with a transmission electron microscope (FE-TEM manufactured by Hitachi, Ltd., model number HF-2000, acceleration voltage 200 kV). did. The sample was prepared by staining a section prepared by the frozen ultrathin section method with an aqueous lead nitrate solution. A TEM photograph of the ion conductive electrolyte membrane obtained in Example 1 is shown in FIG. 1, and a TEM photograph of the ion conductive electrolyte membrane obtained in Comparative Example 1 is shown in FIG. In the TEM photograph, the portion that appears black is the polystyrene sulfonic acid moiety (domain). In the TEM photograph of Comparative Example 1, it can be seen that the spherical black portions are dispersed, whereas in the TEM photograph of Example 1, the black portions are elongated and dispersed in the film surface direction. In the TEM photograph of Example 1, when the maximum length in the film surface direction of the black part is the major axis and the maximum length in the film thickness direction of the black part is the minor axis, the average of the aspect ratio expressed by the major axis / minor axis The value (10 points) was 6.3.

  Furthermore, the following evaluation was performed on the ion conductive electrolyte membranes obtained in Example 1 and Comparative Example 1. The results are shown in FIG.

[Repeated area change rate]
The film | membrane which measured the area change rate was dried at 23 degreeC40% RH for 2 days, and the dimension measurement in a dry state was performed. Subsequently, dimension measurement was performed after being immersed in water for a whole day and night. In addition, the dimensions were measured again after drying at 23 ° C. and 40% RH for 2 days, and the dimensions were measured again after being immersed in water for a whole day and night. The area change rate was determined with the area of the first dry film as 100%.

  FIG. 3 shows that the electrolyte membrane of the present invention has high dimensional stability in the membrane surface direction against humidity changes.

  The ion conductive electrolyte membrane of the present invention is suitable for a proton conductive electrolyte membrane of a polymer electrolyte fuel cell, and is also used for an electrolyte membrane for a lithium ion battery, an electrolysis diaphragm, a water permeable membrane for a humidification module, and the like. be able to.

Claims (9)

An ion conductive electrolyte membrane comprising a matrix containing a water repellent polymer, a hydrophilic polymer having an ion conductive group, and a domain dispersed in the matrix,
An ion conductive electrolyte membrane in which the domains extend in the membrane surface direction in the matrix.   In the cross section in the film thickness direction, when the maximum length in the film surface direction of the domain is the major axis and the maximum length in the film thickness direction of the domain is the minor axis, the average value of the aspect ratio represented by the major axis / minor axis The ion conductive electrolyte membrane according to claim 1, wherein is 2 or more.   The water-repellent polymer is polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyetheretherketone, aromatic polyimide, polyamideimide, and polyetherimide. The ion conductive electrolyte membrane according to claim 1 or 2, which is at least one selected from the group consisting of:   The ion according to any one of claims 1 to 3, wherein the hydrophilic polymer is at least one selected from the group consisting of polystyrene sulfonic acid, polyvinyl sulfonic acid, polyisoprene sulfonic acid, and polyacrylamide t-butyl sulfonic acid. Conductive electrolyte membrane.   The ion conductive electrolyte membrane according to claim 1, wherein the hydrophilic polymer is grafted on the water repellent polymer.   A step of generating stress in a film surface direction in an ion conductive electrolyte membrane having a matrix containing a water-repellent polymer, a hydrophilic polymer having an ion conductive group, and a domain dispersed in the matrix. 2. A method for producing an ion conductive electrolyte membrane according to 1.   The ion-conductive electrolyte according to claim 6, wherein the ion-conductive electrolyte membrane is immersed in a solvent to swell, the ion-conductive electrolyte membrane is fixed to a fixed frame in a swollen state, and stress is generated by removing the solvent. Manufacturing method of electrolyte membrane.   A membrane electrode assembly for a fuel cell, comprising the ion conductive electrolyte membrane according to any one of claims 1 to 5.   A polymer electrolyte fuel cell comprising the fuel cell membrane electrode assembly according to claim 8.

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