JP2005209361A - Polyelectrolyte film, its manufacturing method, film-electrode connector for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyelectrolyte film which has little swelling by water, methanol, etc. and a method of manufacturing the same and to provide a film-electrode connector for a fuel cell showing good fuel cell characteristics and the fuel cell. <P>SOLUTION: The polyelectrolyte film is formed by filling up an electrolyte polymer with the state of a polymer in pores of a polyimide porous membrane, and has a proton conductivity with 60°C, a relative humidity of 95% of 4.0×10<SP>-2</SP>S/cm to 1.0 S/cm. The method of manufacturing the polyelectrolyte includes a step of immersing the polyimide porous membrane into the liquid-like article of the electrolyte polymer having a proton conduction function, a step of performing a pressure reducing operation in the immersed state, and a step of filling up the electrolyte polymer into the pores of the polyimide porous membrane. The film-electrode connector, a solid polymer type fuel cell and a direct methanol type fuel cell each uses the polyelectrolyte film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte membrane, a production method thereof, a membrane-electrode assembly for a fuel cell, a solid polymer fuel cell, and a direct methanol fuel cell.

Many perfluorosulfonic acid membranes and hydrocarbon polymer electrolyte membranes have been studied as electrolyte membranes for fuel cells. However, it still has many problems in terms of heat resistance, fuel barrier properties, mechanical strength, price, environment, and the like.
As a method for increasing the heat resistance and strength of the polymer electrolyte membrane and adjusting the fuel permeability, a method of filling a porous substrate with a polymer electrolyte is useful.

  For example, one in which a polymer electrolyte is filled in an olefin porous substrate (Patent Document 1) and one in which a polymer electrolyte is filled in a fluorine-based porous substrate are known (Patent Document 2, Patent Document 3). . However, these porous substrates are insufficient in heat resistance and fuel permeability, and the fluorine-based porous substrate has a problem that the environmental load is large at the time of production or disposal. As a polymer electrolyte membrane using a porous substrate made of a heat-resistant hydrocarbon polymer, for example, an aromatic polyamide porous substrate filled with a perfluorosulfonic acid electrolyte is known (patent document) 4) However, the use of a fluorine-based electrolyte has problems in price and environment as described above.

  In addition, it is known that an aromatic polyimide-based porous substrate is mainly filled with a vinyl polymer electrolyte (Patent Document 5). However, the vinyl polymer electrolyte has low heat resistance and is resistant to radicals. Is also scarce. Also, various porous membranes filled with sulfonated polymers are known (Patent Documents 6 and 7). However, the polymer electrolyte solution to be permeated easily fills the heat-resistant polymer porous substrate with the polymer electrolyte due to the high viscosity of the solution or poor affinity with the heat-resistant polymer porous substrate. And the proton conductivity of the resulting electrolyte membrane is generally low. In addition, it is difficult to uniformly fill the polymer electrolyte, which is a big industrial issue.

  In fuel cells, particularly solid polymer fuel cells and direct methanol fuel cells, electrolyte membranes that pose a problem during long-term use, such as swelling with alcohols such as water and methanol, or hydrogen and methanol. -Permeation of fuel fuel from anode to cathode is problematic because it causes a decrease in electromotive force and a decrease in fuel efficiency.

JP-A-1-22932 JP-A-6-29032 JP-A-9-194609 JP 2002-358879 A JP 2002-083612 A JP-T-2001-514431 US Pat. No. 6,248,469

  An object of the present invention is to provide a polymer electrolyte membrane in which a heat-resistant porous substrate is filled with a heat-resistant polymer electrolyte and has a high proton conductivity and is less swollen by water, a production method thereof, and good fuel cell characteristics. It is an object of the present invention to provide a fuel cell membrane-electrode assembly, a polymer electrolyte fuel cell, and a direct methanol fuel cell.

In the present invention, an electrolyte polymer having a proton conduction function is filled in the pores of a polyimide porous membrane in a polymer state, and the proton conductivity at 60 ° C. and a relative humidity of 95% is 4.0 × 10. ^-2 relates to a polymer electrolyte membrane having a S / cm or more and 1.0 S / cm or less.

Also, the present invention immerses the polyimide porous membrane in a liquid electrolyte polymer having a proton conducting function, and performs the decompression operation in the immersed state to fill the pores of the polyimide porous membrane with the electrolyte polymer. The present invention relates to a method for producing a polymer electrolyte membrane having a proton conductivity of 4.0 × 10 ⁻² S / cm to 1.0 S / cm at 60 ° C. and a relative humidity of 95%.

Furthermore, the present invention relates to a fuel cell membrane-electrode assembly formed by joining a fuel cell electrode to the above polymer electrolyte membrane.
Furthermore, the present invention provides a solid polymer fuel cell having the fuel cell membrane-electrode assembly as a constituent element and a direct methanol fuel cell having the fuel cell membrane-electrode assembly constituent element. About.

According to the present invention, a polymer electrolyte membrane having a high proton conductivity (sometimes referred to as an ionic conductivity) and less swollen by water or the like, a fuel cell membrane-electrode assembly exhibiting good fuel cell characteristics, a solid high Molecular fuel cells and direct methanol fuel cells can be obtained.
Moreover, according to this invention, the polymer electrolyte membrane which has the said characteristics can be obtained easily.

The preferred embodiments of the present invention are listed below.
1) The polymer electrolyte membrane as described above, wherein the electrolyte polymer having a proton conduction function is sulfonated polyethersulfone.
2) Further, the polymer electrolyte membrane having an electrolyte layer on at least one surface thereof.
3) The polymer electrolyte membrane as described above, wherein the polyimide porous membrane has a chemical structure having a 3,3 ′, 4,4′-biphenyltetracarboxylic acid component as a main tetracarboxylic acid component.
4) The polymer electrolyte membrane as described above, wherein the electrolyte polymer liquid having a proton conduction function is a melt or solution of an electrolyte polymer having a proton conduction function and exhibits a Newtonian viscosity in the relationship between stress and shear rate. Manufacturing method.
5) The polymer electrolyte membrane obtained by the above production method.

In this invention, a polyimide porous membrane is used as the porous substrate. By using a polyimide porous membrane as a porous substrate, it becomes possible to effectively suppress dimensional changes due to water and alcohols such as methanol, and prevent or suppress swelling of the electrolyte membrane due to these. be able to.
The said polyimide porous membrane means the porous membrane which uses an aromatic polyimide as a base material.

Examples of the polyimide porous membrane include tetracarboxylic acid components such as aromatic tetracarboxylic dianhydrides such as 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and the like. Diamine component, for example, aromatic diamine such as oxydianiline, diaminodiphenylmethane, paraphenylenediamine, etc. in organic solvent such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide A method of making a polyamic acid solution obtained by polymerization in a porous manner, for example, casting a polyamic acid solution on a flat substrate and bringing it into contact with a solvent displacement rate adjusting material, followed by immersion in a coagulating liquid such as water The polymer solution of the polyimide precursor is cast on a substrate by a method, and a soluble solvent or non-solvent is formed on the cast. Mainly a protective solvent layer, for example methanol, ethanol, propanol, N-methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, diglyme, triglyme or any mixture thereof After a protective layer made of a solvent as a component is laminated, the protective layer is laminated on the casting while maintaining a state in which the polymer solution and the protective solvent layer are not completely mixed and have a concentration gradient. After the polyimide precursor porous film is formed by various methods such as a method of immersing the laminated solution in the coagulating liquid within 5 seconds to 600 seconds, both ends of the polyimide precursor porous film are fixed in the atmosphere at 280 to It can be obtained by heating at 500 ° C. for 5 to 60 minutes. A part (10 mol% or less) of the aromatic tetracarboxylic dianhydride may be replaced with trimellitic anhydride.
As the polyimide precursor, those having an intrinsic viscosity of 2.0 or more, particularly 2.7 or more and 8.0 or less are preferable.

The polyimide porous membrane has a passage through which gas and liquid (for example, alcohol) can pass between both surfaces of the membrane (film), and the porosity is preferably 5 to 95%, preferably It should be 10 to 90%, more preferably 10% to 80%, and most preferably 20 to 80%.
The average pore diameter is preferably 0.001 to 100 μm, preferably 0.01 to 10 μm, more preferably 0.01 μm to 1 μm, and particularly preferably 0.05 to 1 μm. Further, the thickness of the film is preferably 5 to 300 μm, particularly 5 to 100 μm, and more preferably 10 to 80 μm. The porosity, average pore diameter, and film thickness of the porous membrane are preferably designed from the viewpoint of the strength of the obtained membrane and the characteristics when applied, for example, the characteristics when used as an electrolyte membrane.

Examples of the electrolyte polymer having a proton conducting function in the present invention include proton conducting polymers having polar groups such as sulfonic acid groups.
Examples of the electrolyte polymer having proton conductivity include a polymer having a sulfonic acid group and an aromatic ring, preferably a sulfonated ether sulfone.

The sulfonated polyethersulfone can be produced, for example, by the method described in JP-B-42-7799, JP-B-45-21318, JP-A-48-19700, and the like. That is, in an organic polar solvent, a bis (halogenophenyl) sulfone compound and a divalent phenol compound are polycondensed in the presence of an alkali metal compound, or an alkali metal disalt of a divalent phenol synthesized in advance. It can be produced by polycondensation with a bis (halogenophenyl) sulfone compound.

  The organic polar solvent is not particularly limited as long as the produced polymer is dissolved at the polycondensation temperature. For example, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide, pyrrolidones such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone Solvents, piperidone solvents such as N-methyl-2-piperidone, 1,3-dimethyl-2-imidazolinone, 2-imidazolinone solvents such as 1,3-diethyl-2-imidazolinone, hexamethylene sulfoxide, Examples thereof include diphenyl compounds such as γ-butyrolactone, sulfolane, diphenyl ether, and diphenyl sulfone.

  Examples of the alkali metal compound include alkali metals, alkali metal carbonates, alkali metal hydroxides, alkali metal hydrides, and alkali metal alkoxides. In particular, alkali metal carbonates such as potassium carbonate and sodium carbonate are preferred. Prior to polycondensation reaction, the alkali metal compound is pre-heated in an inert gas such as nitrogen gas at 60 to 500 ° C. under normal pressure or reduced pressure for 1 minute or more, N, N-dimethylacetamide and azeotrope What was disperse | distributed in the solvent may be used.

  Examples of the bis (halogenophenyl) sulfone compound include bis (halogenophenyl) sulfone, for example, bis (halogenophenyl) sulfones such as bis (4-chlorophenyl) sulfone and bis (4-fluorophenyl) sulfone, Bis (halogenophenylsulfonyl) benzenes such as 4-bis (4-chlorophenylsulfonyl) benzene and 1,4-bis (4-fluorophenylsulfonyl) benzene, 4,4'-bis (4-chlorophenylsulfonyl) biphenyl Bis (halogenophenylsulfonyl) biphenyls such as 4,4′-bis (4-fluorophenylsulfonyl) biphenyl, and the like. In particular, bis (halogenophenyl) sulfones such as bis (4-chlorophenyl) sulfone and bis (4-fluorophenyl) sulfone are preferred. The above bis (halogenophenyl) compounds can be used in combination of two or more.

  Examples of the divalent phenol compounds include hydroquinone, catechol, resorcin, 4,4′-biphenol, 2,2-bis (4-hydroxyphenyl) propane, and bis (4-hydroxyphenyl). ) Bis (hydroxyphenyl) alkanes such as methane, dihydroxydiphenyl sulfones such as 4,4'-dihydroxydiphenylsulfone, dihydroxydiphenyl ethers, dihydroxydiphenylcycloalkanes, or at least one hydrogen of the benzene ring is methyl Groups, lower alkyl groups such as ethyl group and propyl group, lower alkoxy groups such as methoxy group and ethoxy group, or those substituted with halogen such as chlorine, bromine and fluorine. In particular, hydroquinone, 4,4′-biphenol, 2,2′-bis (4-hydroxyphenyl) propane, and 4,4′-dihydroxydiphenyl sulfone are preferable. Two or more kinds of the above divalent phenol compounds can be mixed and used.

  The amount of each of the above components is not particularly limited, but the amount of the alkali metal compound used is 1 mol equivalent or more, especially 1.1 mol of the alkali metal with respect to 1 mol equivalent of the hydroxy group of the divalent pheno-compound. More than equivalent is preferable. The amount of divalent pheno- used is preferably 1 mol or more, particularly 1.1 mol or more, per 1 mol of the dihalogenodiphenyl compound. The polymerization temperature is usually preferably 140 to 340 ° C. Water produced as a by-product during the reaction is preferably washed out of the system together with an inert gas stream or with an azeotropic dehydrating agent. Examples of the azeotropic dehydrating agent include benzene, toluene, xylene, and aromatic halogen compounds.

  The reduced viscosity of the sulfonated polyether-sulfone obtained by polycondensation of a halogenodiphenyl compound and divalent pheno- is preferably 0.15 or more, particularly preferably 0.2 or more.

  Further, as the sulfonated polyethersulfone, the mass of the hydrophobic segment from the hydrophilic segment containing a sulfonic acid group and the hydrophobic segment not containing a sulfonic acid group described in JP-A-2003-32322 Aromatic polyethersulfone block copolymers in which the ratio of the fraction W1 to the mass fraction W2 of the hydrophilic segment is in the range of 0.6 <W2 / W1 <2.0 are also included. The copolymer is excellent in that it has less influence of humidity and temperature on durability and proton conductivity due to the hydrophobic segment site, and can be suitably used.

In the method of the present invention, an electrolyte polymer having a proton conducting function such as sulfonated polyether sulfone and a polyimide porous membrane are used in combination, and the polyimide porous membrane is immersed in a liquid material of the electrolyte polymer. Then, after performing the pressure-reducing operation in the immersed state, it is necessary to volatilize the solvent as it is and to fill the electrolyte polymer into the pores of the polyimide porous membrane, whereby the proton conductivity is 4.0 × 10 × 10. ^A polymer electrolyte membrane having a density of ⁻² S / cm to 1.0 S / cm can be obtained.

In order to keep the electrolyte polymer having the proton conduction function in a liquid state, it may be either a melt of the electrolyte polymer having the proton conduction function or a solution dissolved in the polar organic solvent. These liquid materials preferably exhibit Newtonian viscosity in the relationship between stress and shear rate. In the region where the polymer melt or solution exhibits non-Newtonian properties, the polymer molecules exhibit various interactions such as entanglement between the molecules. As the viscosity of the solution increases significantly, it is difficult to enter even if the pore is larger than twice the radius of inertia of the polymer molecule. It becomes difficult to uniformly fill the polymer.

Whether the electrolyte polymer solution exhibits Newtonian properties depends on various factors, and cannot be discussed at all. However, the smaller the solution concentration and the smaller the molecular weight, the more the solution becomes newer. Ton characteristics. Accordingly, when the electrolyte polymer to be filled is determined in advance, the critical concentration varies depending on various types. Therefore, it is preferable to determine the solvent type and concentration in consideration of various circumstances.
Further, the smaller the molecular weight of the electrolyte polymer, the higher the critical concentration. Therefore, when filling with a higher concentration solution, an electrolyte polymer having a lower molecular weight may be used.

  The method of filling the electrolyte polymer in the pores of the polyimide porous membrane is not particularly limited. However, when filling with the electrolyte polymer solution, the solvent is removed by volatilization or the like in the final shape. It is necessary to consider the fact that minute volume shrinkage occurs. That is, even if the pores are completely filled with the solution, a space is created if the solvent is removed therefrom. In the electrolyte membrane, since the electrolyte polymer needs to absorb a certain amount of water with swelling in order to exhibit proton conductivity, a space is required in the pores as a margin for swelling of the electrolyte polymer. Is too large, hydrogen molecules and oxygen molecules, which are fuel gases, and methanol in the direct methanol fuel cell will cross over.

  For this reason, for example, it is preferable to employ a method of immersing the porous membrane in an electrolyte polymer solution and performing a decompression operation in the immersed state to fill the electrolyte polymer into the pores of the polyimide porous membrane. According to this method, since the solvent is preferentially vaporized from the electrolyte polymer solution and the uppermost surface, the electrolyte polymer is agglomerated in the pores. A high filling rate can be achieved. Further, by adjusting the amount of charged electrolyte polymer, it is possible to form an electrolyte polymer layer having a desired thickness on both surfaces of the porous membrane.

In addition, a uniform and high filling rate can be achieved by the following method. Hereinafter, it will be specifically described with reference to FIG.
1) An electrolyte polymer liquid 1 having a proton conduction function is cast on a smooth and parallel substrate 2 with a predetermined thickness.
2) The porous film 3 as a base material is covered thereon.
3) Next, the electrolyte polymer liquid is infiltrated into the covered porous membrane by capillary action, and the porous membrane is spontaneously impregnated. At this time, since the upper part of the porous membrane is an opening, the air in the pores of the porous membrane can be removed from the upper part of the membrane without resistance without preventing the electrolyte polymer liquid from infiltrating from the lower part. It is possible to escape. If necessary at this stage, a decompression operation is performed, and the electrolyte polymer liquid is infiltrated into the pores to approximately more than half of the film thickness, preferably 70% or more, more preferably 85% or more. If necessary, heat treatment or the like may be applied to temporarily fix the electrolyte polymer.

4) Next, the electrolyte polymer liquid 4 having a proton conduction function is cast from the upper part of the membrane with a certain thickness to completely cover the porous membrane. When the flow is extended, a spacer, doctor knife or coater is used. In this process step, a decompression operation may be added as necessary.
It is also possible to uniformly fill the porous membrane with the electrolyte polymer by the method comprising the above steps. In the above method, it is preferable to improve the smoothness of the membrane produced by hot pressing after the electrolyte polymer is filled in the pores of the porous membrane.

  In consideration of joining with the electrode, it is preferable that an electrolyte polymer layer is formed on both surfaces of the porous film filled with the electrolyte polymer. If a rigid porous substrate having no proton conductivity appears on the surface, it is disadvantageous in terms of adhesion to electrodes, catalyst utilization efficiency, and durability. According to the method of the present invention, an electrolyte polymer layer can be formed on both surfaces of a porous substrate as an interface-free continuous layer with the electrolyte in the pores without any subsequent operation such as coating. This is advantageous in terms of film characteristics and industrial processes.

In the electrolyte membrane of the present invention, the reciprocal of the methanol permeability coefficient at 25 ° C. is preferably 0.01 m ² h / kg μm or more and 10.0 m ² h / kg μm or less. In particular, the area change rate in a dry state and a wet state at 25 ° C. is 10% or less (0 to 10%).
Since the area change rate of the electrolyte membrane is a factor that damages the interface between the membrane and the electrode when the value is large, the battery performance is greatly improved in terms of performance stability and durability due to on / off of the battery. It is important, and is preferably as small as 0% or more.
When the proton conductivity, the reciprocal of the methanol permeability coefficient, and the area change rate between the dry state and the wet state are out of the above ranges, it is not preferable as an electrolyte membrane for a fuel cell.
The electrolyte membrane is sandwiched between a cathode electrode and an anode electrode to form a solid polymer fuel cell and a direct methanol fuel cell.

The electrolyte membrane-electrode assembly having the electrolyte membrane of the present invention as a constituent element is obtained by forming a catalyst layer containing a noble metal on both surfaces of the electrolyte membrane.
Examples of the noble metal include one selected from the group consisting of palladium, platinum, rhodium, ruthenium, and iridium, and alloys of these substances, combinations of each, or combinations with other transition metals.

A catalyst in which the noble metal particles are supported on carbon fine particles such as carbon black is used.
The carbon fine particles on which the noble metal fine particles are supported preferably include 10% by mass to 60% by mass of the noble metal.
As a method for supporting an electrode catalyst on a conductive material, the conductive material can be used in an aqueous solution containing colloidal particles such as metal oxide or composite oxide of an electrode catalyst component, or an aqueous solution containing a salt such as chloride, nitrate or sulfate. And a method in which these metal components are supported on a conductive material. After the loading, if necessary, reduction treatment may be performed using a reducing agent such as hydrogen, formaldehyde, hydrazine, formate, sodium borohydride or the like. In addition, when the hydrophilic functional group of the conductive material is an acidic group such as a sulfonic acid group, the conductive material is immersed in an aqueous solution of the above metal salt, and the metal component is taken into the conductive material by ion exchange. Thereafter, the reduction treatment may be performed using the above reducing agent.
Further, it is preferable to use a polymer electrolyte and / or an oligomer electrolyte (ionomer) together with the carbon fine particles on which the noble metal fine particles are supported.

The electrolyte membrane-electrode assembly (MEA) is a paste for forming a catalyst layer in which the above-mentioned noble metal fine particles are supported and carbon fine particles and optionally a polymer electrolyte or an oligomer electrolyte (ionomer) are uniformly dispersed in a solvent. Is used to form the catalyst layer on the entire surface of the electrolyte membrane or in a predetermined shape.
The polyelectrolyte or oligomer electrolyte may be any polymer or oligomer having proton conductivity, or any polymer or oligomer that reacts with an acid or base to produce a polymer or oligomer having proton conductivity. There may be mentioned oligomers.

Suitable polyelectrolytes or oligomer electrolytes include fluoropolymers having pendant ion exchange groups such as sulfonic acid groups in the form of protons or salts, such as sulfonic acid fluoropolymers such as Nafion (registered trademark of DuPont), sulfonic acid Examples thereof include fluoro oligomers, sulfonated polyimides, and sulfonated oligomers.
The polymer electrolyte or oligomer electrolyte needs to be substantially insoluble in water at a temperature of 100 ° C. or lower.
The paste for forming the catalyst layer is preferably a mixture obtained by mixing the catalyst particles and the liquid polymer electrolyte, covering the surfaces of the catalyst particles with the polymer electrolyte, and further mixing a fluororesin.

  Suitable solvents for use in the preparation of the catalyst composition ink include alcohols having 1 to 6 carbon atoms, glycerin, ethylene carbonate, propylene carbonate, butyl carbonate, and ethylene. Examples thereof include polar solvents such as carbamate, propylene carbamate, butylene carbamate, acetone, acetonitrile, dimethylformamide, dimethylacetamide, 1-methyl-2-pyrrolidone and sulfolane. The organic solvent may be used alone or as a mixed solution with water.

The paste for forming the catalyst layer obtained as described above is applied to one side of the polymer electrolyte membrane, preferably once or more using screen printing, a roll coater, a comma coater, or the like. The catalyst sheet (film) formed by applying the catalyst layer-forming paste is preferably applied about 1 to 5 times and then applied to the other side in the same manner and dried. An electrode can be produced by thermocompression bonding to form a catalyst layer on both sides of the polymer electrolyte membrane, thereby obtaining an electrolyte membrane-electrode assembly.
In addition, after forming a catalyst layer on the gas diffusion layer base material such as a carbon paper manufactured by Toray Industries, Inc. using screen printing, a roll coater, etc., a hot press or the like is used. And may be joined to the electrolyte membrane.

The electrolyte membrane is filled with electrolyte in the pores of the porous membrane by a simple operation, has high dimensional accuracy, and does not substantially swell with water or methanol. This is suitable as a structure of a fuel cell.
The polymer electrolyte fuel cell or direct methanol fuel cell of the present invention can be obtained by constituting the electrolyte membrane-electrode assembly.
Also, an electrode is produced by forming a catalyst layer on the conductive porous substrate using the catalyst layer forming paste described above, and this electrode is joined to the electrolyte membrane using a hot press. An electrolyte membrane-electrode assembly can be obtained.

  In the present invention, it is possible to fill the pores in the polyimide porous membrane with an electrolyte polymer having a proton conduction function at a high filling degree, and to effectively suppress the methanol crossover. In addition, high proton conductivity can be achieved. In this membrane, the periphery of the electrolyte is constrained by a highly rigid porous membrane, especially a polyimide base material, so that swelling of the electrolyte due to excessive free water is suppressed, and methanol crossover is made Nafion, etc. As compared with the conventional electrolyte membrane, it can be greatly reduced. Moreover, since the volume expansion accompanying freezing of the water or methanol aqueous solution in electrolyte is suppressed, the effect that freezing does not occur easily can be expected.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the scope of the present invention is not limited to these examples.
The air permeability, average pore diameter, and methanol permeability, proton conductivity, and area change rate of the obtained electrolyte membrane were evaluated as follows.

<Air permeability>
It measured according to JIS P8117. A B-type Galley densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The sample membrane is clamped in a circular hole having a diameter of 28.6 mm and an area of 645 mm ² , and air in the cylinder is passed from the test hole to the outside of the cylinder with an inner cylinder weight of 567 g. The time required for 100 cc of air to pass through was measured and used as the air permeability (Gurley value).
<Average pore diameter>
The porous membrane was evaluated based on the bubble point method (ASTM F316, JISK3832). Using a palm porometer from PMI, the penetration path distribution of the porous film was measured by the bubble point method. Further, the average pore diameter was obtained by calculating back from the average flow rate.

<Methanol permeability>
A permeation test (liquid / liquid system) was conducted using a diffusion cell to evaluate the permeability of methanol. First, the cell is set after the membrane to be measured is immersed and swollen in ion-exchanged water. Ion exchange water is added to the methanol permeation side and the supply side, respectively, and stabilized in a thermostatic bath for about 1 hour. Next, the test is started by adding methanol to the supply side to obtain a 10% by weight aqueous methanol solution. The permeation side solution was sampled every predetermined time and the concentration change was traced by obtaining the concentration of methanol by gas chromatographic analysis, and the permeation flow rate, permeation coefficient, and diffusion coefficient of methanol were calculated. The measurement was performed at 25 ° C. to evaluate the methanol permeability.

<Proton conductivity>
The electrodes were brought into contact with the front and back surfaces of the electrolyte membrane at 60 ° C. and 95% relative humidity, and sandwiched between heat resistant resin (polytetrafluoroethylene) plates to fix the membrane and measure proton conductivity.
The membrane used for the measurement was ultrasonically washed in a 1N aqueous hydrochloric acid solution for 5 minutes, then ultrasonically washed three times in ion-exchanged water for 5 minutes each, and then left in ion-exchanged water. The film swollen in water is taken out on a heat-resistant resin (polytetrafluoroethylene) plate, the platinum plate electrode is brought into contact with the front and back of the film, and sandwiched between the heat-resistant resin (polytetrafluoroethylene) plate from the outside 4 Fixed with two screws. The AC impedance was measured by an impedance analyzer (Impedance Analyzer-HP4194A, manufactured by Hewlett-Packard Company), the resistance value was read from the call call plot, and the proton conductivity was calculated.

<Dimension and area change rate>
About the produced electrolyte membrane, the dimensional change rate and the area change rate were measured by the following.
In order to measure the rate of change of the membrane area of the electrolyte membrane accompanying the swelling / shrinkage of the electrolyte polymer, first, the lengths in the x and y directions of the electrolyte membrane sufficiently dried in a dryer at 50 ° C. were determined using a ruler. Measured (condition 1). Next, the length of the electrolyte membrane in the x and y directions was measured while maintaining the electrolyte membrane in a completely swollen state in pure water (Condition 2). The dimensional change rate was calculated | required using the above measurement result, the area was calculated | required by xXy, and the area change rate was computed by the following.
Rate of area change between dry and wet electrolyte membrane: A
A = [Area (Condition 2) −Area (Condition 1)] X100 / Area (Condition 2)

Reference example 1
Preparation of polyimide porous membrane 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, a small amount of 3,3', 4,4'-biphenyltetracarboxylic acid and oxydianiline A polyimide precursor NMP solution in which the molar ratio of the acid component to the diamine component is approximately 1.0 and the total weight of the monomer components is 8.0% by weight is flowed at a constant thickness onto a mirror-polished SUS plate. Then, using a doctor knife having an interval of 100 μm with respect to the liquid surface of the polyimide precursor solution, methanol was uniformly applied as a protective solvent layer and allowed to stand for 1 minute, and then methanol. The entire substrate was put into the bath. In the meantime, the polymer solution and the protective solvent layer were not completely mixed, but the concentration gradient was maintained in the thickness direction, and the polymer was dissolved. After the addition, the mixture was allowed to stand for 5 minutes to precipitate polyamic acid on the substrate. The substrate was taken out and immersed in water for 5 minutes, and then the polyamic acid film deposited on the substrate was peeled off to obtain a polyamic acid film. After this polyamic acid film was dried at room temperature, it was attached to a pin tenter and heat-treated at 340 ° C. to obtain a polyimide porous film.

The obtained polyimide porous membrane has a structure in which polyimide is connected in a network shape on the protective layer lamination surface side, the surface opening ratio is 78%, and the Gurley value is 53 seconds / 100 cc. And had high gas permeability.
The membrane thickness was 27 μm, and the porosity calculated from the weight was 47%. Moreover, the average hole diameter of the through-pass from one surface to the other surface was 0.145 μm, and a coarse through-pass of 0.6 μm or more was not detected in the 8 cm square sample.

Reference example 2
Bis (4-fluorophenyl) sulfone, bis (4-hydroxyphenyl) sulfone, and potassium carbonate were heated and stirred in N, N-dimethylacetamide and toluene to obtain a prepolymer-PES-1 solution.
Further, bis (4-fluorophenyl) sulfone, 4,4′-biphenol and potassium carbonate were heated and stirred in N, N-dimethylacetamide and toluene to obtain a prepolymer-PBP-1 solution.
Separately, prepare a potassium salt solution of PES-1 from PES-1 solution and potassium carbonate, add the potassium salt solution of PES-1 to the PBP-1 solution, and react to obtain copolymer-PES-b-PBP. It was. Further, 98% sulfuric acid treatment was carried out to obtain a sulfonated polymer (BPS).

A sulfonated polyethersulfone polymer (BPS) was dissolved in N, N-dimethylacetamide at a concentration of 15.5% by mass to obtain an electrolyte polymer solution. As a result of measuring the dynamic viscoelasticity and steady flow viscosity of this solution, it was found that it exhibited Newtonian viscosity. A predetermined amount of this solution calculated backward from the desired electrolyte membrane thickness was placed in a glass dish, the polyimide porous membrane of Reference Example 1 was immersed therein, and held under reduced pressure until the impregnating solvent was almost volatilized, Then, after arrange | positioning to a glass plate and apply | coating a fixed quantity of BPS solutions using the coater from the top, it vacuum-dried at 60 degreeC for 2 hours, and also at 150 degreeC for 2 hours. Thereafter, the film was peeled off from the glass dish, and heat treatment was performed at 150 ° C. for 1 hour and then at 200 ° C. for 30 minutes with the four sides of the film being restrained. Thereafter, ion exchange treatment was performed to obtain a polymer electrolyte membrane.
This polymer electrolyte membrane has a proton conductivity of 8.5 × 10 ⁻² S / cm at 60 ° C. and a relative humidity of 95%, a reciprocal of the methanol permeability coefficient of 0.16 m ² h / kg μm, and a dry electrolyte membrane. The rate of change in area between time and wetness was A = 6 (%).
Moreover, the film thickness at the time of drying was 45 micrometers.

The results of observing both surfaces of the polymer electrolyte membrane obtained in Example 1 and the frozen and crushed cross-section with a scanning electron microscope (SEM) are shown in FIG. 3 and FIG.
It was confirmed that both surfaces were covered with the BPS layer. Further, from cross-sectional observation, it was confirmed that BPS, which is an electrolyte polymer having a proton conduction function, was filled in the pores.

Sulfonated polyethersulfone polymer (BPS) was dissolved in N, N-dimethylacetamide at a concentration of 15.5% by mass. Half of a predetermined amount of the solution calculated back from the desired electrolyte membrane thickness is placed in a glass dish, and the polyimide porous membrane obtained in Reference Example 1 is immersed therein and impregnated in a reduced-pressure atmosphere so that most of the solvent is present. It was kept until it volatilized, and then vacuum-dried at 60 ° C. for 2 hours and further at 150 ° C. for 2 hours. Thereafter, the film was peeled off from the glass dish, and after applying a certain amount of the BPS solution using a coater on the glass plate in a state where the four sides of the film were constrained on the glass plate, at 150 ° C. for 1 hour, Subsequently, heat treatment was performed at 200 ° C. for 30 minutes. Thereafter, ion exchange treatment was performed to obtain a polymer electrolyte membrane.
This polymer electrolyte membrane has a proton conductivity of 6.1 × 10 ⁻² S / cm at 60 ° C., a relative humidity of 95%, a reciprocal of the methanol permeability coefficient of 0.13 m ² h / kg μm, and a dry electrolyte membrane. The rate of change in area between time and wetness was A = 4 (%).
Moreover, the film thickness at the time of drying was 37 micrometers.
As a result of cross-sectional observation by SEM, 3-4 μm sulfonated polyethersulfone polymer (BPS) layers were formed on both surfaces of the membrane, and the sulfonated polyethersulfone polymer ( BPS).

Comparative Example 1
When the area change rate during drying and wetting of Nafion 117 (manufactured by DuPont), which is a commercially available perfluoroethylene electrolyte membrane, was measured, it was A = 17 (%). Further, when the film was dried again from the wet state, the film lost smoothness.

Preparation of Membrane-Electrode Assembly (MEA) 1) Preparation of Diffusion Layer A diffusion layer was formed on the carbon paper by the following operation only for the electrode used for the oxygen electrode.
4.0 g of isopropanol (IPA) was added to 0.37 g of XC-72 ground with an agate mortar, and the mixture was sufficiently dispersed by stirring and ultrasonic waves. Thereafter, 0.14 g of a commercially available polytetrafluoroethylene (PTFE) dispersion was added and stirred for about 1 minute to obtain a paste for producing a diffusion layer.
Thereafter, the paste was applied to a carbon paper manufactured by Toray Industries, Inc. by screen printing three times, allowed to dry naturally, and then fired at 350 ° C. for 2 hours.

2) Preparation of catalyst layer for oxygen electrode 46.1% by weight of carbon black (TEC10E50E manufactured by Tanaka Kikinzoku Co., Ltd.) loaded with platinum is mixed with the same amount of ion-exchanged water, and then a commercially available 5% Nafion solution is added. In addition, stirring and ultrasonic waves were repeated for 10 minutes. Thereafter, an appropriate amount of PTFE dispersion was added and stirred to obtain a paste for forming a catalyst layer. By screen printing, the paste was applied three times on the carbon paper with diffusion layer prepared in the previous stage using a screen printer and air-dried three times. A gas diffusion electrode used for the electrode was obtained.

3) Preparation of methanol electrode electrode catalyst layer Carbon black (TEC66E50, Tanaka Kikinzoku Co., Ltd.) carrying 32.7% by mass of platinum and 16.9% by mass of ruthenium was mixed with the same amount of ion-exchanged water. Thereafter, a commercially available 5% Nafion solution was added, and stirring and ultrasonic waves were repeated for 10 minutes. Thereafter, an appropriate amount of PTFE dispersion was added and stirred to obtain a paste for forming a catalyst layer. Using the screen printing method, the paste was applied three times with a screen printing machine onto the carbon paper with a diffusion layer prepared in the previous stage, and the operation was repeated four times until it was naturally dried. -A gas diffusion electrode used for the electrode was obtained.

4) Production of MEA The electrode produced by the above method and the electrolyte membrane produced in Example 1 were joined using a hot press (conditions: 150 ° C., 8 MPa, 3 minutes) to produce an MEA. The amount of catalyst supported on the electrode was 1.6 mg / cm ^{2 for} Anode and 1.00 mg-Pt / cm ² for Cathode.

In order to observe the adhesiveness between the obtained MEA film and the electrode, it was immersed in a 3 mol / L methanol aqueous solution and held for 1 hour, then taken out, dried and observed. The adhesion between the electrode and the electrolyte membrane was maintained visually, and the smoothness of the entire MEA was also maintained.

5) Fabrication of fuel cell and fuel cell power generation test The MEA fabricated in 4) above was incorporated into a fuel cell with an electrode area of 5 cm ² manufactured by Electrochem Inc. to obtain a direct methanol fuel cell, and a cell test was conducted. It was. The power generation conditions were a cell temperature of 50 ° C., 1 and 3 mol / L methanol aqueous solution at Anode at a flow rate of 10 mL / min, and dry oxygen at 100 mL / min at Cathode. The results of the power generation test are shown in FIG.
6) The MEA produced in 4) above was incorporated into a fuel cell having an electrode area of 5 cm ² manufactured by Electrochem Inc., USA, and a fuel cell was obtained. The power generation conditions were a cell temperature of 80 ° C., Anode with hydrogen gas at a flow rate of 3 mL / min, and Cathode with dry oxygen at a flow rate of 100 mL / min. The result of the power generation test is shown in FIG.

Comparative Example 2
An MEA was obtained in the same manner as in Example 3 except that Nafion 112 (manufactured by DuPont) was used as the electrolyte membrane. When the MEA obtained was immersed in a 3 mol / L methanol aqueous solution in order to see the adhesion between the membrane and the electrode, the electrolyte membrane was in a wavy state without maintaining smoothness. When it was kept as it was for 1 hour and then taken out and dried, peeling of the adhesion interface between the electrode and the electrolyte membrane was visually confirmed in several places. Further, the MEA as a whole was greatly distorted, and peeling and destruction of the electrodes occurred when it was incorporated into the fuel cell as it was.

FIG. 1 schematically shows a method of filling a porous membrane with an electrolyte polymer having a proton conduction function, which is an example of a method for producing an electrolyte membrane of the present invention. FIG. 2 shows the results of observation of the surface of the polymer electrolyte membrane obtained in Example 1 with a scanning electron microscope. FIG. 3 is a result of observing a cross section obtained by freezing and crushing the polymer electrolyte membrane obtained in Example 1 with a scanning electron microscope. FIG. 4 is an enlarged view of the central portion (portion of the porous membrane) in FIG. FIG. 5 shows the power generation characteristics of the direct methanol fuel cell in Example 3. FIG. 6 shows the power generation characteristics of the hydrogen-oxygen fuel cell in Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid substance of electrolyte polymer which has proton conduction function 2 Substrate 3 Porous membrane 4 Liquid substance of electrolyte polymer which has proton conduction function

Claims (9)

An electrolyte polymer having a proton conduction function is filled in the pores of the polyimide porous membrane in a polymer state, and the ionic conductivity at 60 ° C. and a relative humidity of 95% is 4.0 × 10 ⁻² S / A polymer electrolyte membrane having a density of cm to 1.0 S / cm. 2. The polymer electrolyte membrane according to claim 1, wherein the electrolyte polymer having a proton conducting function is sulfonated polyethersulfone. The polymer electrolyte membrane according to claim 1 or 2, further comprising an electrolyte layer on at least one surface thereof. The polymer electrolyte membrane according to any one of claims 1 to 3, wherein the polyimide porous membrane has a chemical structure in which a 3,3 ', 4,4'-biphenyltetracarboxylic acid component is a main tetracarboxylic acid component. A polyimide porous membrane is immersed in a liquid electrolyte polymer having a proton conduction function, and the electrolyte polymer is filled in the pores of the polyimide porous membrane by performing a pressure reduction operation in the immersed state. A method for producing a polymer electrolyte membrane having an ionic conductivity at 95% of 4.0 × 10 ⁻² S / cm or more and 1.0 S / cm or less. 5. A fuel cell membrane-electrode assembly obtained by joining a fuel cell electrode to the polymer electrolyte membrane according to claim 1. A fuel cell membrane-electrode assembly obtained by joining a fuel cell electrode to a polymer electrolyte membrane obtained by the production method according to claim 5. A polymer electrolyte fuel cell comprising the membrane-electrode assembly for a fuel cell according to claim 6 or 7 as a constituent element. A direct methanol fuel cell comprising the fuel cell membrane-electrode assembly according to claim 6 or 7 as a constituent element.

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