JP2007087853A - Asymmetrical electrolyte membrane, membrane electrode assembly using it, and polyelectrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane which has a high proton conductivity and low crossover of fuel and has no camber, with good adhesiveness with an electrode, and provide a membrane electrode assembly and a polyelectrolyte fuel cell capable of achieving a high output and a high energy capacity using the same. <P>SOLUTION: The asymmetrical electrolyte membrane has respective layers of (A), (B), (C) in this order at least at a part of the electrolyte membrane, and the thickness of the (A) layer and that of the (C) layer are different. The membrane electrode assembly and a polyelectrolyte fuel cell are constructed using this asymmetrical electrolyte membrane. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrolyte membrane that can achieve high output and high energy capacity when used in a polymer electrolyte fuel cell, and more particularly to an asymmetric electrolyte membrane. The present invention also relates to an asymmetric electrolyte membrane and membrane electrode assembly, and a polymer electrolyte fuel cell.

  A fuel cell is a power generation device with low emissions, high energy efficiency, and low burden on the environment. For this reason, it is in the spotlight again in recent years to the protection of the global environment. Compared to conventional large-scale power generation facilities, this is a power generation device expected in the future as a relatively small-scale distributed power generation facility, and as a power generation device for mobile objects such as automobiles and ships. It is also attracting attention as a power source for small mobile devices and portable devices, and is expected to be installed in mobile phones and personal computers in place of secondary batteries such as nickel metal hydride batteries and lithium ion batteries.

  In polymer electrolyte fuel cells, in addition to conventional polymer electrolyte fuel cells using hydrogen gas as fuel (hereinafter sometimes referred to as PEFC), fuel such as methanol is directly used. Direct fuel cells to be supplied are also attracting attention.

  The direct fuel cell has a lower output than the conventional PEFC, but the fuel is liquid and does not use a reformer, so the energy density is high and the usage time of the portable device per filling is long. There is an advantage. In a polymer electrolyte fuel cell, an anode electrode and a cathode electrode in which a reaction responsible for power generation occurs, and a polymer electrolyte membrane serving as a proton conductor between the anode and the cathode constitute a membrane electrode assembly (MEA). A cell in which this MEA is sandwiched between separators is configured as a unit. Here, the electrode is composed of an electrode substrate (also referred to as a gas diffusion electrode or a current collector) that promotes gas diffusion and collects (supply) electricity, and an electrode catalyst layer that actually becomes an electrochemical reaction field. ing.

  For example, in the anode electrode of PEFC, a fuel such as hydrogen gas reacts in the catalyst layer of the anode electrode to generate protons and electrons, and the electrons are conducted to the electrode substrate, and the protons are conducted to the polymer electrolyte membrane. For this reason, the anode electrode is required to have good gas diffusivity, electron conductivity, and proton conductivity. On the other hand, in the cathode electrode, an oxidizing gas such as oxygen or air is reacted with protons conducted from the polymer electrolyte membrane and electrons conducted from the electrode base material in the catalyst layer of the cathode electrode to produce water. For this reason, in the cathode electrode, it is necessary to efficiently discharge the generated water in addition to gas diffusibility, electron conductivity, and proton conductivity.

  Among PEFCs, a direct fuel cell using methanol or the like as a fuel requires performance different from that of a conventional PEFC using hydrogen gas as a fuel. That is, in a direct type fuel cell, a fuel such as a methanol aqueous solution reacts with the catalyst layer of the anode electrode to produce protons, electrons, and carbon dioxide at the anode electrode, and the electrons are conducted to the electrode substrate, and the protons are polymer electrolyte. The carbon dioxide passes through the electrode substrate and is released out of the system. For this reason, in addition to the required characteristics of the anode electrode of the conventional PEFC, fuel permeability such as aqueous methanol solution and carbon dioxide emission are also required. Further, in the cathode electrode of the direct type fuel cell, in addition to the reaction similar to that of the conventional PEFC, fuel such as methanol that has permeated through the electrolyte membrane and oxidizing gas such as oxygen or air are mixed with carbon dioxide in the cathode electrode catalyst layer. Reactions that produce water also occur. For this reason, since generated water becomes more than conventional PEFC, it is necessary to discharge water more efficiently. Conventionally, a perfluoro proton conductive polymer membrane represented by “Nafion” (registered trademark) (manufactured by DuPont) has been used as a polymer electrolyte membrane.

  However, these perfluoro proton conductive polymer membranes have a problem that the fuel permeation of methanol or the like is large in the direct fuel cell, and the cell output and energy efficiency are not sufficient. Perfluoro proton conductive polymers are also very expensive in terms of using fluorine.

In response to this problem, various electrolyte membranes having a multilayer structure for suppressing fuel crossover have been proposed (Non-Patent Document 1, Patent Documents 1 and 2). For example, (Non-Patent Document 1) discloses Nafion (registered trademark) provided with a layer made of polybenzimidazole. (Patent Document 1) discloses a laminated solid electrolyte membrane in which an anion exchange membrane having a weak base type anion exchange group is provided on one surface of an ion exchange membrane. (Patent Document 2) discloses a laminated film of a polymer electrolyte membrane and an aromatic polymer membrane having a super strong acid group.
Journal of Power Sources, 2002, 104, p.79-84 JP-A-11-144745 JP 2004-25793 A

  However, in the conventional technology, high proton conductivity and fuel crossover suppression are not completely realized, and when high proton conductivity is maintained, fuel crossover suppression is not sufficient, and fuel crossover suppression is not possible. However, there is a problem that proton conductivity is low. Furthermore, since it is a laminated film, the warp is severe and there is a problem in the membrane electrode assembly preparation process and the adhesion between the membrane and the electrode. The present invention provides an asymmetric electrolyte membrane having high proton conductivity comparable to that of Nafion (registered trademark), suppressing fuel crossover, having no warpage, and having good adhesion to electrodes. With the goal. A further object of the present invention is to provide a membrane electrode assembly and a polymer electrolyte fuel cell that can achieve high output and high energy capacity.

  The present invention employs the following means in order to solve such problems. That is, the asymmetric electrolyte membrane of the present invention is an electrolyte membrane having the layers (A), (B), and (C) in this order on at least a part of the electrolyte membrane, and the (A) layer and the (C) layer. The film thickness is different. The membrane electrode assembly and the polymer electrolyte fuel cell of the present invention are characterized by using such an asymmetric electrolyte membrane.

  According to the present invention, it is possible to provide an electrolyte membrane having high proton conductivity comparable to that of Nafion (registered trademark), suppressing fuel crossover, having no warpage, and having good adhesion to the electrode, By using a membrane electrode assembly comprising such an electrolyte membrane, it is possible to provide a polymer electrolyte fuel cell that achieves high output and high energy capacity.

  Hereinafter, preferred embodiments of the present invention will be described.

  The asymmetric electrolyte membrane of the present invention is an electrolyte membrane having the layers (A), (B), and (C) in this order on at least a part of the electrolyte membrane, and the membranes of the layers (A) and (C) The thickness is different. The film thicknesses of the (A) layer and the (C) layer of the present invention are different depending on the ionic group density of the polymer used and the film-forming drying temperature, but when the thickness is usually less than 0.5 (μm), the asymmetric electrolyte membrane No warping prevention effect is observed.

The asymmetric electrolyte membrane according to the present invention preferably contains a polymer material having an ionic group from the viewpoint of processability, and it becomes easy to control proton conductivity and suppression of fuel crossover. As such an ionic group, an atomic group having a negative charge is preferable, and one having proton exchange ability is preferable. As such a functional group, a sulfonic acid group (—SO ₂ (OH)), a sulfuric acid group (—OSO ₂ (OH)), a sulfonimide group (—SO ₂ NHSO ₂ R (R represents an organic group)). ), Phosphonic acid groups (—PO (OH) ₂ ), phosphoric acid groups (—OPO (OH) ₂ ), carboxylic acid groups (—CO (OH)), and salts thereof can be preferably employed.

  Two or more kinds of these ionic groups can be contained in the polymer material, and may be preferable by combining them. The combination is appropriately determined depending on the structure of the polymer. Among them, it is more preferable to have at least one of a sulfonic acid group, a sulfonimide group, and a sulfuric acid group from the viewpoint of high proton conductivity, and most preferable to have at least a sulfonic acid group from the viewpoint of hydrolysis resistance.

  When the polymer material in the present invention has a sulfonic acid group, the sulfonic acid group density is preferably 0.1 to 5.0 mmol / g, more preferably 0.5 from the viewpoint of proton conductivity and suppression of fuel crossover. It is -3.5 mmol / g, More preferably, it is 1.0-3.5 mmol / g. By setting the sulfonic acid group density to 0.1 mmol / g or more, conductivity, that is, output performance can be maintained, and by setting it to 5.0 mmol / g or less, as an electrolyte membrane for polymer electrolyte fuel cell In use, sufficient fuel barrier properties and mechanical strength during water absorption can be obtained.

  Here, the sulfonic acid group density is the molar amount of the sulfonic acid group introduced per unit dry weight of the polymer material, and the larger the value, the higher the degree of sulfonation. The sulfonic acid group density of the polymer material to be used can be measured by elemental analysis, neutralization titration, nuclear magnetic resonance spectroscopy or the like. Elemental analysis is preferable from the viewpoint of ease of measurement of sulfonic acid group density and accuracy, and analysis is usually performed by this method. However, the neutralization titration method is used when it is difficult to accurately calculate the sulfonic acid group density by the elemental analysis method such as when a sulfur source is included in addition to the sulfonic acid group. Furthermore, when it is difficult to determine the sulfonic acid group density by these methods, it is possible to use a nuclear magnetic resonance spectrum method.

  As the total film thickness of the asymmetric electrolyte membrane in the present invention, a film having a thickness of usually 3 to 2000 μm is preferably used. A thickness of more than 3 μm is preferable to obtain a membrane strength that can withstand practical use, and a thickness of less than 2000 μm is preferable to reduce membrane resistance, that is, to improve the power generation performance of the polymer electrolyte fuel cell. A more preferable range of the film thickness is 5 to 1000 μm, and a more preferable range is 10 to 500 μm.

  The film thickness of the (B) layer in the present invention is preferably set to 1 to 100 μm. To obtain a membrane in which fuel crossover is suppressed, it is preferably thicker than 1 μm, and in order to reduce membrane resistance, that is, to improve the power generation performance of the polymer electrolyte fuel cell, it is preferably thinner than 100 μm. Moreover, although the film thickness of each layer of (A) and (C) in this invention is suitably selected by the ionic group density and film thickness of (B) layer, the film thickness of (A) layer and (C) layer is In contrast, there is no particular limitation as long as an electrolyte membrane without warp is obtained, but it is usually preferable to set the difference in film thickness to 2 to 20 μm.

  In the method for producing an asymmetric electrolyte membrane in the present invention, for example, a plurality of membranes having different ionic groups formed in advance may be formed by fusion, adhesion, simple superposition, or a plurality of polymer coatings. Depending on the liquid, the coating may be repeated such that coating and drying are repeated, or the film may be formed using a multi-slit die having two or more discharge ports. These methods are not particularly limited, and can be appropriately selected according to the polymer material to be used and the target film performance.

  The thickness of each layer of the asymmetric electrolyte membrane in the present invention can be controlled by various methods. For example, when forming a film by the solvent casting method, it can be controlled by the solution concentration or the coating thickness on the support. For example, when forming the film by the cast polymerization method, it is prepared by the spacer thickness between the plates. You can also Moreover, when forming into a film with a multi slit die, it can control by the clearance adjustment and discharge pressure adjustment of each nozzle | cap | die.

  The film thickness measurement of each layer in the present invention varies depending on the production method, and examples thereof include an electron microscope and an EPMA (electron beam microanalyzer) described later. The total thickness of the asymmetric electrolyte membrane can be measured using Mitutoyo ID-C112 type set on Mitutoyo granite comparator stand BSG-20.

  In the asymmetric electrolyte membrane of the present invention, it is preferable that the ionic group density of the (A) layer and the (C) layer is different from the ionic group density of the (B) layer. Moreover, it is more preferable that the ionic group density of the (A) layer and the (C) layer is higher than the ionic group density of the (B) layer.

  With regard to the level of ionic group density in electrolyte membranes having different ionic group densities, a predetermined portion of the membrane cross section is collected and the sulfonic acid group density is measured by the method described above. It can be measured by an electron beam microanalyzer (EPMA) JXA-8621MX. For example, when a polymer material having a sulfonic acid group as an ionic group is used, the distribution of sulfur element on the electrolyte membrane cross section or the electrolyte surface can be determined by visually observing an EPMA image under the following conditions. The ionic groups of the (A) layer and (C) layer of the present invention are different from the ionic group density of the (B) layer. When the ionic group density is usually less than 0.1 mmol / g, suppression of fuel crossover, The effect of improving the adhesion and the effect of reducing the film resistance are hardly recognized.

Observation conditions for secondary and reflected electron images Acceleration voltage 15 kV
Element distribution analysis (wavelength dispersion method)
Accelerating voltage 15kV
Irradiation current 50nA
Measurement time 30msec
Number of pixels / pixel length 256 × 256 pixels / 0.336 μm / pixel
Analysis beam diameter 〜1μmφ
Analytical X-ray, Spectroscopic Crystal SKα (5.373 angstrom), PET
Sample preparation After sample preparation by a microtome, carbon deposition.

  When the asymmetric type electrolyte membrane in the present invention is formed on a support such as a glass plate, a film, stainless steel, Cr or Ti coated stainless steel, the thickness of the support surface side layer should be thicker than the air surface side layer. Is particularly effective in preventing warping of the electrolyte membrane.

  The asymmetric electrolyte membrane in the present invention is preferably used for a polymer electrolyte fuel cell.

  The ionic group density of each layer of the asymmetric electrolyte membrane in the present invention is such that, for example, the (C) layer is in contact with the anode catalyst from the viewpoint of high output and high energy capacity of the polymer electrolyte fuel cell. In the case where the asymmetric electrolyte membrane is made into a membrane electrode composite, (C) layer> (B) layer and (A) layer> (B) layer are preferable, and (C) layer = (A) layer> (B) The layer configuration is preferred.

  Next, an example of the raw material and manufacturing method for obtaining the asymmetric electrolyte membrane will be described.

  The present invention provides an asymmetric electrolyte membrane that does not have a warp, facilitates a membrane electrode assembly preparation process, improves adhesion between the membrane and the electrode, has high proton conductivity, and suppresses fuel crossover. The material has characteristics for obtaining a film, and the material used is not particularly limited as long as this configuration can be satisfied. However, in general electrolyte membranes, it is difficult and impossible to obtain the specific substance, but at least the following, the raw material and the film forming method are asymmetrical electrolyte membranes that are free of warp, An electrolyte membrane in which the membrane electrode assembly preparation process is easy, the adhesion between the membrane and the electrode can be improved, high proton conductivity and fuel crossover is suppressed can be manufactured.

  The type of polymer used as the polymer material of the present invention is not particularly limited, but for example, a polymer having an ionic group and excellent in hydrolysis resistance is preferable. Specific examples thereof include ionic group-containing polyphenylene oxide, ionic group-containing polyether ketone, ionic group-containing polyether ether ketone, ionic group-containing polyether sulfone, ionic group-containing polyether ether sulfone, ionic group. Containing polyether phosphine oxide, ionic group containing polyether ether phosphine oxide, ionic group containing polyphenylene sulfide, ionic group containing polyamide, ionic group containing polyimide, ionic group containing polyetherimide, ionic group containing polyimidazole, Examples thereof include aromatic hydrocarbon polymers having an ionic group, such as ionic group-containing polyoxazole and ionic group-containing polyphenylene. Here, the ionic group is as described above.

  As for the method of introducing an ionic group into these polymer materials, an ionic group may be introduced into the polymer, or a monomer having an ionic group may be polymerized. Introduction of a phosphonic acid group into a polymer can be performed by a method described in, for example, “Polymer Preprints”, Japan, 51, 750 (2002). Introduction of a phosphate group into the polymer is possible by, for example, phosphate esterification of a polymer having a hydroxyl group. Introduction of a carboxylic acid group into the polymer is possible by, for example, oxidizing a polymer having an alkyl group or a hydroxyalkyl group. Introduction of a sulfonimide group into the polymer is possible, for example, by treating a polymer having a sulfonic acid group with an alkylsulfonamide. The introduction of sulfate groups into the polymer is possible, for example, by sulfate esterification of a polymer having hydroxyl groups. The introduction of the sulfonic acid group into the polymer can be performed, for example, by a method in which the polymer is reacted with chlorosulfonic acid, concentrated sulfuric acid, or fuming sulfuric acid.

  These ionic group introduction methods can be controlled to a desired ionic group density by appropriately selecting conditions such as treatment time, concentration, and temperature. In addition, as a method for polymerizing a monomer having an ionic group, for example, a method described in “Polymer Preprints”, 41 (1) (2000) 237. When a polymer is obtained by this method, the degree of introduction of ionic groups can be easily controlled by the charge ratio of monomers having ionic acid groups. Moreover, when the polymer material to be used has a non-crosslinked structure, the weight average molecular weight is preferably 10,000 to 5,000,000, more preferably 30,000 to 1,000,000. By setting the weight average molecular weight to 10,000 or more, mechanical strength that can be practically used as an electrolyte membrane can be obtained. On the other hand, by setting it to 5 million or less, sufficient solubility can be obtained and good workability can be maintained. The weight average molecular weight can be measured by GPC method.

As described above, a polymer material having a sulfonic acid group is most preferable as a polymer electrolyte fuel cell. As an example of using a polymer material having a sulfonic acid group, —SO ₃ M group (M is a metal) Examples include a method of forming a film of the contained polymer from a solution state, then heat-treating at a high temperature to remove the solvent, and performing proton substitution to form a membrane. The metal M may be any salt as long as it can form a salt with sulfonic acid, but Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, W, and the like are preferable. Among these, Li, Na, K, Ca, Sr, and Ba are more preferable, and Li, Na, and K are more preferable. By forming a film in the state of these metal salts, heat treatment can be performed at a high temperature, and this method is particularly suitable in terms of suppressing fuel crossover.

  The temperature of the heat treatment is preferably 100 to 500 ° C., more preferably 200 to 450 ° C., and further preferably 250 to 400 ° C. in terms of the high proton conductivity of the obtained membrane and the fuel crossover suppression point. A temperature of 100 ° C. or lower has no effect of suppressing fuel crossover, and a temperature of 500 ° C. or higher is not preferable in view of decomposition of the polymer material. Further, the heat treatment time is preferably 10 seconds to 24 hours, more preferably 30 seconds to 1 hour, and further preferably 45 seconds to 30 minutes in terms of proton conductivity, fuel crossover suppression, and productivity. By setting the heat treatment time to 10 seconds or longer, it is possible to sufficiently remove the solvent and to obtain a sufficient fuel crossover suppression effect. In addition, when the time is 24 hours or less, the polymer is not decomposed, proton conductivity and fuel crossover suppression can be maintained, and productivity is also increased.

As described above, the method for producing an asymmetric electrolyte membrane of the present invention is not particularly limited. For example, two or more types of polymers having different -SO ₃ M group densities are prepared and dissolved in an aprotic polar solvent or the like. First, a polymer solution having a higher —SO ₃ M density is applied onto a glass plate or film by an appropriate coating method, the solvent is removed, and then the other —SO ₃ M density is added. A low polymer solution is applied onto the film by an appropriate coating method to remove the solvent, and a polymer solution having a higher —SO ₃ M density is applied to the film by an appropriate coating method to remove the solvent, The method of acid-treating after processing at high temperature can be illustrated.

  As the coating method, various methods such as spray coating, brush coating, dip coating, die coating, curtain coating, flow coating, spin coating, and screen printing can be applied. In the coating method using a solvent, the film can be formed by drying the solvent with heat, the wet coagulation method with a solvent that does not dissolve the polymer, and without the solvent, the method of curing with light, heat, moisture, etc., the polymer is heated and melted, A method of cooling after film formation can be applied. The solvent used for film formation is not particularly limited as long as it can dissolve the polymer material and then remove it. For example, N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2 -Aprotic polar solvents such as pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphontriamide, ester solvents such as γ-butyrolactone, butyl acetate, ethylene carbonate, propylene carbonate, etc. Carbonate solvents, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, or isopropanol Alcohol solvents such as is preferably used.

  In addition, the asymmetric electrolyte membrane of the present invention can be crosslinked as a whole or part of the polymer structure by means such as irradiation. By crosslinking, an effect of further suppressing fuel crossover and swelling with respect to the fuel can be expected, and mechanical strength is improved, which may be more preferable. Examples of radiation irradiation include electron beam irradiation and γ-ray irradiation. By having a cross-linked structure, it is possible to suppress the spread between polymer chains with respect to moisture and fuel intrusion. Since the amount of water absorption can be kept low and the swelling with respect to the fuel can also be suppressed, the fuel crossover can be reduced as a result. Moreover, since a polymer chain can be restrained, heat resistance and rigidity can be imparted. The crosslinking here may be chemical crosslinking or physical crosslinking.

  This crosslinked structure can be formed by a generally known method, for example, by copolymerization of a polyfunctional monomer or electron beam irradiation. In particular, crosslinking with a polyfunctional monomer is preferable from an economical viewpoint, and a copolymer of a monofunctional vinyl monomer and a polyfunctional monomer or a polymer having a vinyl group or an allyl group is crosslinked with a polyfunctional monomer. Things. The cross-linked structure here means a state where there is substantially no fluidity to heat or a state where it is substantially insoluble in a solvent.

  The determination of the crosslinked structure in the present invention is performed based on whether or not it is substantially insoluble in the solvent, and can be specifically determined by the following method. A polymer electrolyte material (about 0.1 g) serving as a specimen is washed with pure water and then vacuum dried at 40 ° C. for 24 hours to measure the weight. The polymer electrolyte material is immersed in a 100-fold weight solvent and heated in a sealed container at 70 ° C. for 40 hours with stirring. Next, filtration is performed using filter paper (No. 2) manufactured by Advantech. During filtration, the filter paper and the residue are washed with the same solvent of 100 times weight, and the eluate is sufficiently eluted in the solvent. Dry the filtrate and determine the weight of the elution. When the elution weight is less than 10% of the initial weight, it is determined to be substantially insoluble in the solvent. When this test was carried out for five types of solvents such as toluene, hexane, N-methylpyrrolidone, methanol and water, and it was determined that all the solvents were substantially insoluble, it was determined that the polymer electrolyte material had a crosslinked structure. To do. In addition, the cross-linked electrolyte membrane that is difficult to stack in the asymmetric electrolyte membrane of the present invention is obtained by, for example, diluting a monomer having an ionic group in an appropriate solvent, impregnating the surface, and then polymerizing the surface layer. The ionic group density can be increased.

In order to produce a polymer electrolyte fuel cell having a high output and a high energy capacity using the asymmetric electrolyte membrane of the present invention, the ionic conductivity and the fuel permeation amount are preferably within the following ranges. For example, when an asymmetric electrolyte membrane having a thickness in the range of 10 μm to 500 μm is used and the fuel is 30 wt% methanol water, the ionic conductivity in 30 wt% methanol water at 25 ° C. is preferably 1 S / cm ² or more. In the case of 1 S / cm ² or more, high output is obtained. Preferably, it is 2 S / cm ² or more, more preferably 3 S / cm ² or more. Although the upper limit is not particularly set, it is preferably larger as long as the membrane does not dissolve or disintegrate with a fuel such as methanol water. Here, after immersing the sample in pure water at 25 ° C. for 24 hours, the ion conductivity is taken out in an atmosphere at 25 ° C. and a relative humidity of 50 to 80%, and the resistance is measured by the following constant potential AC impedance method. Can be sought. Specifically, using an electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) manufactured by Solartron, the sample was applied with a weight of 1 kg between two circular electrodes (made of stainless steel) of φ2 mm and φ10 mm. Clamp (effective electrode area 0.0314 cm ² ). A 15% aqueous solution of poly (2-acrylamido-2-methylpropanesulfonic acid) is applied to the interface between the sample and the electrode. At 25 ° C., constant potential impedance measurement (AC amplitude is 50 mV) is performed to determine ion conductivity in the film thickness direction.

The methanol permeation amount when using 30% by weight methanol water at 25 ° C. is preferably 100 μmol · min− ¹ · cm ⁻² or less. When it is 100 μmol · min ⁻¹ · cm ⁻² or less, it is preferable from the viewpoint of output and energy capacity when used for DMFC. Preferably 50 [mu] mol · min ^-1 · cm ^-2 or less, more preferably most preferably 0Myumol · min ^-1 · cm ^-2 or less 25 [mu] mol · min ^-1 · cm ^-2. The amount of methanol permeation here can be measured by the following method. That is, a sample membrane is sandwiched between H-type cells, pure water is put into one cell, 30 wt% aqueous methanol solution is put into the other cell, both cells are stirred at 20 ° C., 1 hour, 2 hours In addition, the amount of methanol eluted in pure water at the time when 3 hours have elapsed is measured and quantified by a gas chromatography (GC-2010) manufactured by Shimadzu Corporation, and the methanol permeation amount per unit time and unit volume is obtained from the slope of the graph. .

  Further, in the asymmetric electrolyte membrane of the present invention, the mechanical strength is improved, the thermal stability of the ionic group is improved, and the workability is improved within a range that does not impair the ion conductivity and the effect of suppressing the fuel crossover. For this purpose, a network or fine particles made of a polymer or metal oxide may be formed.

  Next, the membrane electrode assembly of the present invention is constituted by using the asymmetric electrolyte membrane described above. That is, the above-mentioned membrane electrode assembly (MEA) is composed of an electrode comprising an electrolyte membrane, an electrode catalyst layer, and an electrode substrate. The electrode catalyst layer here is a layer containing an electrode catalyst that promotes an electrode reaction, an electron conductor, an ion conductor, and the like. As the electrode catalyst contained in the electrode catalyst layer, for example, a noble metal catalyst such as platinum, palladium, ruthenium, rhodium, iridium, gold is preferably used. One of these may be used alone, or two or more of them, such as alloys and mixtures, may be used in combination. Moreover, as an electronic conductor (conductive material) contained in an electrode catalyst layer, a carbon material and an inorganic conductive material are preferably used from the viewpoint of electronic conductivity and chemical stability. Among these, amorphous and crystalline carbon materials are mentioned. For example, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used because of its electron conductivity and specific surface area.

  Furnace Black includes “Vulcan” (registered trademark) XC-72, “Vulcan” (registered trademark) P, “Black Pearls” (registered trademark) 880, “Black Pearls” (registered trademark) 1100, “Black” manufactured by Cabot Corporation. “Pearls” (registered trademark) 1300, “Black Pearls” (registered trademark) 2000, “Legal” (registered trademark) 400, “Ketjen Black” (registered trademark) EC, EC600JD, Mitsubishi Chemical Examples of the acetylene black include “Denka Black” (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, and furan resin can also be used.

  As the form of these carbon materials, in addition to irregular particles, fibers, scales, tubes, cones, and megaphones can also be used. Moreover, you may use what post-processed these carbon materials. In addition, it is preferable in terms of electrode performance that the electron conductor is uniformly dispersed with the catalyst particles. For this reason, it is preferable that the catalyst particles and the electron conductor are well dispersed in advance as a coating liquid. Furthermore, it is also a preferred embodiment to use a catalyst-supporting carbon in which a catalyst and an electron conductor are integrated as an electrode catalyst layer. By using this catalyst-supporting carbon, the utilization efficiency of the catalyst is improved, which can contribute to the improvement of battery performance and cost reduction. Here, even when catalyst-supported carbon is used for the electrode catalyst layer, a conductive agent can be added to further increase the electron conductivity. As such a conductive agent, the above-described carbon black is preferably used.

  Various organic and inorganic materials are generally known as substances having ion conductivity (ion conductors) used for the electrode catalyst layer. However, when used for fuel cells, the ion conductivity is improved. A polymer having an ionic group such as a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group (ion conductive polymer) is preferably used. Among these, from the viewpoint of the stability of the ionic group, a polymer having ion conductivity composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain, or the polymer electrolyte material of the present invention is preferably used. As the perfluoro-based ion conductive polymer, for example, “Nafion” (registered trademark) manufactured by DuPont, “Aciplex” (registered trademark) manufactured by Asahi Kasei Corporation, “Flemion” (registered trademark) manufactured by Asahi Glass Co., Ltd. and the like are preferably used. . These ion conductive polymers are provided in the electrode catalyst layer in the state of a solution or a dispersion.

  At this time, the solvent for dissolving or dispersing the polymer is not particularly limited, but a polar solvent is preferable from the viewpoint of the solubility of the ion conductive polymer. Since the catalyst and the electronic conductors are usually powders, the ionic conductor usually plays a role of solidifying them. It is preferable from the viewpoint of electrode performance that the ionic conductor is added in advance to a coating liquid mainly composed of electrode catalyst particles and an electron conductor when the electrode catalyst layer is produced, and is applied in a uniformly dispersed state. However, the ion conductor may be applied after the electrode catalyst layer is applied.

  Here, examples of the method for applying the ion conductor to the electrode catalyst layer include spray coating, brush coating, dip coating, die coating, curtain coating, and flow coating, and are not particularly limited. The amount of the ion conductor contained in the electrode catalyst layer should be appropriately determined according to the required electrode characteristics and the conductivity of the ion conductor used, and is not particularly limited. The range of 1 to 80% is preferable, and the range of 5 to 50% is more preferable. When the ion conductor is too small, the ion conductivity is low, and when it is too much, the gas permeability may be hindered. Such an electrode catalyst layer may contain various substances in addition to the catalyst, the electron conductor, and the ion conductor. In particular, in order to enhance the binding property of the substance contained in the electrode catalyst layer, a polymer other than the above-described ion conductive polymer may be included.

  Examples of such polymers include polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP) and copolymers thereof, polytetrafluoroethylene, polyperfluoroalkyl vinyl ether (PFA) and the like. Polymers containing fluorine atoms such as copolymers, copolymers thereof, copolymers of monomer units constituting these polymers with other monomers such as ethylene and styrene, or blend polymers can be used. . The content of these polymers in the electrode catalyst layer is preferably in the range of 5 to 40% by weight. When there is too much polymer content, there exists a tendency for an electronic and ionic resistance to increase and for electrode performance to fall.

  In addition, when the fuel is a liquid or gas, the electrode catalyst layer preferably has a structure through which the liquid or gas easily permeates, and preferably has a structure that promotes the discharge of by-products due to the electrode reaction. Moreover, as an electrode base material, an electrical resistance is low and what can collect or supply electric power can be used. Moreover, when using the said electrode catalyst layer also as a collector, it is not necessary to use an electrode base material in particular. Examples of the constituent material of the electrode base material include carbonaceous and conductive inorganic substances. For example, a fired body from polyacrylonitrile, a fired body from pitch, a carbon material such as graphite and expanded graphite, stainless steel, molybdenum And titanium. These forms are not particularly limited, and for example, they are used in the form of fibers or particles. From the viewpoint of fuel permeability, fibrous conductive materials (conductive fibers) such as carbon fibers are preferable.

  As an electrode base material using conductive fibers, either a woven fabric or a non-woven fabric structure can be used. For example, carbon paper TGP series, SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, etc. are used. Examples of the woven fabric include plain weave, oblique weaving, satin weaving, crest weaving, binding weaving, and the like. Moreover, as a nonwoven fabric, it does not specifically limit, such as a paper making method, a needle punch method, a spun bond method, a water jet punch method, and a melt blow method. It may also be a knitted fabric. In particular, when carbon fibers are used in these fabrics, carbonized plain fabric using flame-resistant spun yarn is carbonized or graphitized, and flame-resistant yarn is carbonized after being processed into a nonwoven fabric by the needle punch method or water jet punch method. Alternatively, a graphitized nonwoven fabric, a flameproof yarn, a carbonized yarn, or a mat nonwoven fabric by a paper making method using a graphitized yarn is preferably used. In particular, it is preferable to use a non-woven fabric because a thin and strong fabric can be obtained.

  Examples of the carbon fiber used for the electrode substrate include polyacrylonitrile (PAN) carbon fiber, phenolic carbon fiber, pitch carbon fiber, and rayon carbon fiber. In addition, the electrode base material has a water repellent treatment for preventing gas diffusion / permeability deterioration due to water retention, a partial water repellent treatment for forming a water discharge path, a hydrophilic treatment, and a resistance reduction. For example, carbon powder can be added.

  In the polymer electrolyte fuel cell of the present invention, it is preferable to provide a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer between the electrode substrate and the electrode catalyst layer. In particular, when the electrode base material is a carbon fiber woven fabric or a nonwoven fabric having a large porosity, by providing the conductive intermediate layer, it is possible to suppress performance degradation due to the electrode catalyst layer permeating into the electrode base material.

  The method of producing a membrane electrode assembly (MEA) using the electrode catalyst layer or the electrode catalyst layer and the electrode substrate using the electrolyte membrane of the present invention is not particularly limited. Known methods (for example, the chemical plating method described in “Electrochemistry” 1985, 53, 269. “J. Electrochem. Soc.”: Electrochemical Science and Technology, 1988, 135 (9), 2209 It is possible to apply the gas diffusion electrode hot press bonding method described above. Although integration by hot pressing is a preferable method, the temperature and pressure may be appropriately selected depending on the thickness of the electrolyte membrane, the moisture content, the electrode catalyst layer, and the electrode substrate. Moreover, you may press in the state which the electrolyte membrane contained water, and you may adhere | attach with the polymer which has ion conductivity.

  In particular, the electrolyte membrane of the present invention is suitable for an MEA obtained by a production method having a pressing step in a water-containing state, and an MEA having excellent adhesion between an electrode catalyst layer and an electrolyte membrane can be produced. By increasing the contact area between the anode catalyst layer that generates protons and the electrolyte membrane, proton conductivity is improved, and high output can be achieved as MEA.

  Examples of the fuel for the polymer electrolyte fuel cell of the present invention include oxygen, hydrogen and carbon such as methane, ethane, propane, butane, methanol, isopropyl alcohol, acetone, glycerin, ethylene glycol, formic acid, acetic acid, dimethyl ether, hydroquinone, and cyclohexane. The organic compound of several 1-6 and the mixture of these and water are mentioned, 1 type, or 2 or more types of mixtures may be sufficient. In particular, a fuel containing an organic compound having 1 to 6 carbon atoms is preferably used from the viewpoint of power generation efficiency and simplification of the entire battery system, and an aqueous methanol solution is particularly preferable in terms of power generation efficiency.

  The content of the organic compound having 1 to 6 carbon atoms in the fuel supplied to the membrane electrode assembly is preferably 20 to 70% by weight. When the content is 20% by weight or more, a practical high energy capacity can be obtained, and when the content is 70% by weight or less, the power generation efficiency is increased and a practical high output can be obtained.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these. In addition, the measurement conditions of each physical property are as follows.
(Measuring method)
1. The polymer after stirring and washing in pure water at a sulfonic acid group density of 25 ° C. for 24 hours or more and then vacuum-dried at 100 ° C. for 24 hours was measured by elemental analysis. Analysis of C, H, and N was performed by a fully automatic elemental analyzer varioEL, analysis of S was performed by a flask combustion method / barium acetate titration, and analysis of P was performed by a flask combustion method / phosphovanadomolybdic acid colorimetric method. . The sulfonic acid group density per unit gram (mmol / g) was calculated from the composition ratio of each polymer.
2. Weight average molecular weight The weight average molecular weight of the polymer was measured by GPC. Tosoh HLC-8022GPC as an integrated unit of UV detector and differential refractometer, and Tosoh TSK as a GPC column
Two gel super HM-Hs (inner diameter 6.0 mm, length 15 cm) were used, and N-methyl-2-pyrrolidone solvent (N-methyl-2-pyrrolidone solvent containing 10 mmol / L of lithium bromide was used with a flow rate of 0). Measured at 2 mL / min, and the weight average molecular weight was determined by standard polystyrene conversion.
3. Film thickness It measured using Mitutoyo ID-C112 type | mold set to Mitutoyo granite comparator stand BSG-20.
4). Sludge of the electrolyte membrane A 5 cm x 5 cm electrolyte membrane was placed on a glass substrate and visually observed. The judgment criteria were as follows.

  ○: No warpage is allowed.

  Δ: Slight warping

  X: There is a warp.

XX: Curls.
5. Proton conductivity After the membrane-shaped sample was immersed in pure water at 25 ° C. for 24 hours, it was taken out in an atmosphere at 25 ° C. and a relative humidity of 50 to 80%, and proton conductivity was measured by the constant potential AC impedance method as quickly as possible. As a measuring apparatus, a Solartron electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used. The sample was sandwiched between two circular electrodes (made of stainless steel) of φ2 mm and φ10 mm with a weight of 1 kg. The effective electrode area is 0.0314 cm ² . A 15% aqueous solution of poly (2-acrylamido-2-methylpropanesulfonic acid) was applied to the interface between the sample and the electrode. At 25 ° C., a constant potential impedance measurement with an AC amplitude of 50 mV was performed to determine proton conductivity in the film thickness direction. The value is described per unit area.
6). Methanol permeation amount A film-like sample was immersed in a 30 wt% aqueous methanol solution for 24 hours, and then measured at 20 ° C using a 30 wt% aqueous methanol solution. A sample membrane was sandwiched between the H-type cells, pure water (60 mL) was placed in one cell, and 30 wt% aqueous methanol solution (60 mL) was placed in the other cell. The cell capacity was 80 mL each. Moreover, the opening part area between cells was 1.77 cm < ² >. Both cells were stirred at 20 ° C. The amount of methanol eluted in pure water at the time of 1 hour, 2 hours and 3 hours was measured and quantified with a gas chromatography (GC-2010) manufactured by Shimadzu Corporation. The methanol permeation amount per unit time was determined from the slope of the graph.
7). Observation of distribution state of sulfonic acid group The distribution of elemental sulfur in the cross-sectional direction of the membrane was measured with an electron beam microanalyzer (EPMA) JXA-8621MX manufactured by JEOL under the following conditions. The magnification was adjusted so that the entire cross-section of the film was within the field of view, and the image was analyzed as an image with the color changed depending on the density of the sulfur element. The sulfonic acid group density was determined by visual observation macroscopically, not by a color difference due to a very small measurement point of the EPMA image.

Observation conditions for secondary and reflected electron images Acceleration voltage 15 kV
Element distribution analysis (wavelength dispersion method)
Accelerating voltage 15kV
Irradiation current 50nA
Measurement time 30msec
Number of pixels / pixel length 256 × 256 pixels / 0.336 μm / pixel
Analysis beam diameter 〜1μmφ
Analytical X-ray, Spectroscopic Crystal SKα (5.373 angstrom), PET
Sample preparation After sample preparation by a microtome, carbon deposition.
(Production of membrane electrode composite)
Two carbon fiber cloth base materials were subjected to a 20% ethylene tetrafluoride water repellent treatment, and then a carbon black dispersion containing 20% ethylene tetrafluoride was applied and baked to prepare an electrode base material. On one electrode base material, an anode electrode catalyst coating solution composed of Pt-Ru-supported carbon and Nafion (registered trademark) solution is applied and dried to form an anode electrode on the other electrode base material, Pt A cathode electrode catalyst coating solution composed of supported carbon and Nafion (registered trademark) solution was applied and dried to prepare a cathode electrode.

By holding the asymmetric electrolyte membrane in a configuration in which the (c) layer is in contact with the previously prepared anode electrode and the (a) layer in contact with the cathode electrode, the film is heated and pressed at 100 ° C. for 8 minutes at 50 kgf / cm ^2. A membrane electrode composite was prepared.
(Evaluation of polymer electrolyte fuel cells)
Membrane electrode assembly (MEA) was set in a cell manufactured by Electrochem to make a polymer electrolyte fuel cell. MEA evaluation was performed by flowing a 30% methanol aqueous solution on the anode side and air on the cathode side. In the evaluation, a constant current was passed through the MEA, and the voltage at that time was measured. The measurement was performed until the current was increased successively until the voltage became 10 mV or less. The product of current and voltage at each measurement point is output, and the maximum value (per unit area of MEA) is defined as output (mW / cm ² ).

In the MCO at the MEA, the exhaust gas from the cathode was sampled by a collecting tube. This was evaluated using a total organic carbon meter TOC-VCSH (manufactured by Shimadzu Corporation) or a MeOH permeation measuring device Micro GC CP-4900 (manufactured by GL Sciences). The MCO was calculated by measuring the total of MeOH and carbon dioxide in the sampling gas.
[Synthesis Example 1]
109.1 g of 4,4′-difluorobenzophenone was reacted at 100 ° C. for 10 hours in 150 mL of fuming sulfuric acid (50% SO ₃ ). Thereafter, the mixture was poured little by little into a large amount of water, neutralized with NaOH, and 200 g of sodium chloride was added to precipitate the composite. The resulting precipitate was filtered off and recrystallized with an aqueous ethanol solution to obtain disodium 3,3′-disulfonate-4,4′-difluorobenzophenone.
[Synthesis Example 2]
Potassium carbonate 6.9 g, 4,4 ′-(9H-fluorene-9-ylidene) bisphenol 14.0 g, 4,4′-difluorobenzophenone 5.2 g, and disodium 3,3′-obtained in Synthesis Example 1 above Polymerization was performed at 190 ° C. in N-methylpyrrolidone (NMP) using 6.8 g of disulfonate-4,4′-difluorobenzophenone. Purification was performed by reprecipitation with a large amount of water to obtain polymer A. The density of the sulfonic acid group of the proton-substituted membrane of the obtained polymer A was 1.4 mmol / g and the weight average molecular weight was 260,000 according to elemental analysis.
[Synthesis Example 3]
4.4 g of 4,4 ′-(9H-fluorene-9-ylidene) bisphenol is changed to 14.1 g of 4,4′-dihydroxytetraphenylmethane, 5.2 g of 4,4′-difluorobenzophenone is changed to 4.4 g, and disodium. Polymer B was obtained in the same manner as in Synthesis Example 2 except that 6.8 g of 3,3′-disulfonate-4,4′-difluorobenzophenone was changed to 8.4 g. The density of the sulfonic acid group in the proton-substituted membrane of the obtained polymer B was 1.7 mmol / g and the weight average molecular weight was 220,000 from elemental analysis.
[Synthesis Example 4]
The same as Synthesis Example 2 except that 5.2 g of 4,4′-difluorobenzophenone was changed to 2.6 g and disodium 3,3′-disulfonate-4,4′-difluorobenzophenone 6.8 g was changed to 11.8 g. And polymer C was obtained. The density of the sulfonic acid group of the proton-substituted membrane of the obtained polymer C was 2.4 mmol / g and the weight average molecular weight was 180,000 according to elemental analysis.
[Synthesis Example 5]
6.9 g of potassium carbonate, 7.0 g of 4,4 ′-(9H-fluorene-9-ylidene) bisphenol, 4.0 g of 4,4′-dihydroxydiphenyl ether, and 3.5 g of 4,4′-difluorobenzophenone, and above Polymerization was carried out at 190 ° C. in N-methylpyrrolidone (NMP) using 10.1 g of disodium 3,3′-disulfonate-4,4′-difluorobenzophenone obtained in Synthesis Example 1. Purification was carried out by reprecipitation with a large amount of water, and polymer D was obtained. The density of the sulfonic acid group of the proton-substituted membrane of the obtained polymer D was 2.2 mmol / g and the weight average molecular weight was 180,000 according to elemental analysis.
[Synthesis Example 6]
The same procedure as in Synthesis Example 5 was performed except that 4.0 g of 4,4′-dihydroxydiphenyl ether was changed to 3.7 g of phenylhydroquinone. Purification was carried out by reprecipitation with a large amount of water, and polymer E was obtained. The density of the sulfonic acid group of the proton-substituted membrane of the obtained polymer E was 2.2 mmol / g and the weight average molecular weight was 190,000 according to elemental analysis.
[Example 1]
Polymer C was dissolved in 11 g and N, N-dimethylacetamide 29 g to prepare a 27.5% coating solution. The coating solution was cast-coated on a glass substrate using an applicator, dried at 100 ° C. for 2 hours to remove the solvent, and a (c) layer having a thickness of 20 (μm) was obtained. Next, 8 g of polymer A was dissolved in 32 g of N-methyl-2-pyrrolidone to prepare a 20% coating solution. The coating liquid was applied and dried in the same manner on the (c) layer to obtain a composite film having a thickness of 55 (μm) composed of the (c) layer and the (b) layer. Furthermore, the polymer C coating solution is applied and dried in the same manner on the (b) layer on the composite film comprising the (c) layer and the (b) layer, and the (c) layer, the (b) layer, and the (a) layer. A composite film having a thickness of 72 (μm) was obtained. After leaving to cool and releasing from the glass substrate in purified water, it was immersed in a 1N-hydrochloric acid aqueous solution for 1 day or longer to perform proton substitution, and then immersed in purified water for 1 day or longer and washed to obtain an asymmetric electrolyte membrane.

The warpage state, proton conductivity, and methanol permeation amount of this asymmetric electrolyte membrane are summarized in Table 1.
[Example 2]
Polymer D was dissolved in 10 g and 30 g of N, N-dimethylacetamide to prepare a 25% coating solution. The coating solution was cast-coated on a glass substrate using an applicator, dried at 100 ° C. for 1 hour to remove the solvent, and a (c) layer having a thickness of 20 (μm) was obtained. Next, 4.8 g of polymer B and 14.4 g of N-methyl-2-pyrrolidone were dissolved, and polyamic acid (“Trenis” (registered trademark) # 3000 manufactured by Toray Industries, Inc.) was added to 25% of the coating solution. The mixture was mixed so that the polyamic acid was 60:40 (weight ratio) to obtain a coating solution having a solid content of 22.7%. It was. The coating solution was applied and dried in the same manner on the (c) layer to obtain a composite film having a thickness of 30 (μm) composed of the (c) layer and the (b) layer. Further, the polymer D coating solution is applied and dried in the same manner on the (b) layer on the composite film composed of the (c) layer and the (b) layer, and the (c) layer, (b) layer, and (a) layer are applied. A composite film having a thickness of 45 (μm) was obtained. Furthermore, it heated up to 100-400 degreeC for 40 minute (s), and after heat-processing on the conditions heated at 400 degreeC for 10 minute (s), it stood to cool and released from the glass substrate in refined water. After that, it was immersed in a 1N-hydrochloric acid aqueous solution for 1 day or longer to perform proton substitution, and immersed in purified water for 1 day or longer for cleaning to obtain an asymmetric electrolyte membrane. The warpage state, proton conductivity, and methanol permeation amount of this asymmetric electrolyte membrane are summarized in Table 1.
[Example 3]
Polymer E was dissolved in 10 g and N, N-dimethylacetamide 30 g to prepare a 25% coating solution. The coating solution was cast on a glass substrate using an applicator, dried at 100 ° C. for 1 hour to remove the solvent, and a layer (c) having a thickness of 22 (μm) was obtained. Next, 4.8 g of polymer B and 14.4 g of N-methyl-2-pyrrolidone were dissolved, and polyamic acid (“Trenis” (registered trademark) # 3000 manufactured by Toray Industries, Inc.) was added to 25% of the coating solution. The mixture was mixed so that the polyamic acid was 60:40 (weight ratio) to obtain a coating solution having a solid content of 22.7%. It was. The coating solution was applied and dried in the same manner on the (c) layer to obtain a composite film having a film thickness of 32 (μm) composed of the (c) layer and the (b) layer. Furthermore, the polymer E coating solution is applied and dried in the same manner on the (b) layer on the composite film comprising the (c) layer and the (b) layer, and the (c) layer, (b) layer, (a) layer A composite film having a thickness of 50 (μm) was obtained. Furthermore, it heated up to 100-325 degreeC for 30 minute (s), heat-processed on the conditions heated at 325 degreeC for 10 minutes, Then, it stood to cool, and it released from the glass substrate in refined water. After that, it was immersed in a 1N-hydrochloric acid aqueous solution for 1 day or longer to perform proton substitution, and immersed in purified water for 1 day or longer for cleaning to obtain an asymmetric electrolyte membrane. The warpage state, proton conductivity, and methanol permeation amount of this asymmetric electrolyte membrane are summarized in Table 1.
[Example 4]
Polymer E was dissolved in 10 g and N, N-dimethylacetamide 30 g to prepare a 25% coating solution. The coating solution was cast-coated on a glass substrate using an applicator, dried at 100 ° C. for 1 hour to remove the solvent, and a (c) layer having a thickness of 20 (μm) was obtained. Next, polymer A was dissolved in 2.7 g and N-methyl-2-pyrrolidone 10.8 g, and a polyamic acid (“Trenice” (registered trademark) # 3000 manufactured by Toray Industries, Inc.) was added to a 20% coating solution as polymer B: The mixture was mixed so that polyamic acid = 75: 25 (weight ratio) to obtain a coating solution having a solid content of 20%. It was. The coating solution was applied and dried in the same manner on the (c) layer to obtain a composite film having a thickness of 30 (μm) composed of the (c) layer and the (b) layer. Furthermore, the polymer E coating solution is applied and dried in the same manner on the (b) layer on the composite film comprising the (c) layer and the (b) layer, and the (c) layer, (b) layer, (a) layer A composite film having a thickness of 45 (μm) was obtained. Furthermore, it heated up to 100-400 degreeC for 40 minute (s), and after heat-processing on the conditions heated at 400 degreeC for 10 minute (s), it stood to cool and released from the glass substrate in refined water. After that, it was immersed in a 1N-hydrochloric acid aqueous solution for 1 day or longer to perform proton substitution, and then immersed in purified water for 1 day or longer for cleaning to obtain an asymmetric electrolyte membrane. The warpage state, proton conductivity, and methanol permeation amount of this asymmetric electrolyte membrane are summarized in Table 1.
[Comparative Example 1]
The film thickness of the (c) layer is 15 (μm), the film thickness of the composite film composed of the (c) layer and the (B) layer is 25 (μm), the (c) layer, the (b) layer, and the (a) layer. This was performed in the same manner as in Example 2 except that the thickness of the resulting composite film was changed to 40 (μm).

The warp state, proton conductivity, and methanol permeation amount of this symmetrical electrolyte membrane are summarized in Table 1.
[Comparative Example 2]
The film thickness of the (c) layer is 15 (μm), the film thickness of the composite film composed of the (c) layer and the (b) layer is 25 (μm), the (c) layer, the (b) layer, and the (a) layer. This was performed in the same manner as in Example 4 except that the film thickness of the resulting composite film was changed to 45 (μm).

The warp state, proton conductivity, and methanol permeation amount of this symmetrical electrolyte membrane are summarized in Table 1.
[Comparative Example 3]
Table 1 summarizes the film thickness, warpage, proton conductivity, and methanol permeation rate of the membrane obtained by treating the polymer electrolyte membrane “Nafion” (registered trademark) 117 (manufactured by DuPont) with hot water at 95 ° C. for 1 hour. It was.

  The electrode adhesion of the membrane electrode composites of Examples 1 to 4 and the evaluation results of the polymer electrolyte fuel cell were measured with respect to output and methanol permeation amount, based on Comparative Example 3 (using “Nafion” (registered trademark) 117 membrane). The ratios expressed in the ratios are summarized in the table. In Comparative Example 1, electrode peeling occurred after the membrane electrode composite was joined. Further, Comparative Example 2 was so curled that a membrane electrode assembly could not be prepared.

  In addition, the membrane electrode composites of Examples 1 to 4 were configured by contacting the layer (c) with the anode catalyst to obtain a polymer electrolyte fuel cell.

As is apparent from Tables 1 and 2, the asymmetric electrolyte membranes of Examples 1 to 4 of the present invention are less warped than the conventional multilayer electrolyte membranes, and are excellent in adhesion of the membrane electrode assembly. (MW / cm ² ) and excellent methanol permeation suppression, and better in cell characteristics than a polymer electrolyte fuel cell using “Nafion” (registered trademark) 117.

  The electrolyte membrane of the present invention can be applied to various electrochemical devices (for example, a fuel cell, a water electrolysis device, a chloroalkali electrolysis device, etc.). Among these devices, it is suitable for a fuel cell, and particularly suitable for a fuel cell using a methanol aqueous solution as a fuel.

The use of the polymer electrolyte fuel cell of the present invention is not particularly limited, but mobile devices such as mobile phones, personal computers, PDAs, video cameras (camcorders) and digital cameras, home appliances such as electric shavers and vacuum cleaners, electric tools, etc. , Toys, electric carts, electric wheelchairs, electric-assisted bicycles, motorcycles, passenger cars, buses, trucks and other vehicles and ships, power supplies for mobiles such as railways, stationary generators, rechargeable batteries It is preferably used as an alternative to conventional primary batteries, secondary batteries, solar cells, etc., or a hybrid power source with these.

Claims (7)

An electrolyte membrane having the layers (A), (B), and (C) in this order on at least a part of the electrolyte membrane, wherein the thicknesses of the (A) layer and the (C) layer are different. Type electrolyte membrane. The asymmetric electrolyte membrane according to claim 1, wherein the ionic group density of the (A) layer and the (C) layer is different from the ionic group density of the (B) layer. The asymmetric electrolyte membrane according to claim 2, wherein the ionic group density of the (A) layer and the (C) layer is higher than the ionic group density of the (B) layer. When the asymmetric electrolyte membrane is formed on the support and the (C) layer is on the support surface side, the (C) layer is thicker than the (A) layer, and the (A) layer is on the support surface side ( The asymmetric electrolyte membrane according to claim 1, wherein the A) layer is thicker than the (C) layer.   The asymmetric electrolyte membrane according to any one of claims 1 to 4, which is used for a polymer electrolyte fuel cell. A membrane electrode assembly comprising the asymmetric electrolyte membrane according to any one of claims 1 to 5. A polymer electrolyte fuel cell comprising the asymmetric electrolyte membrane according to claim 1.