JP2008098152A - Manufacturing method of membrane/electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high quality, to suppress the amount of fuel permeation, and to improve durability. <P>SOLUTION: In a manufacturing method of a membrane/electrode assembly for joining an electrolyte membrane containing water to an electrode, by pressing, an air permeable material is arranged at a space to a pressing plate on at least either of electrode and electrolyte membrane in pressing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane electrode assembly used in a polymer electrolyte fuel cell or the like.

  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, as an alternative to secondary batteries such as nickel metal hydride batteries and lithium ion batteries, as a charger for secondary batteries, or in combination with secondary batteries. (Hybrid) is expected to be installed in mobile devices such as mobile phones and personal computers.

  In polymer electrolyte fuel cells (hereinafter sometimes referred to as PEFC), fuel such as methanol is directly supplied in addition to conventional polymer electrolyte fuel cells that use hydrogen gas as fuel. Direct fuel cells 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 the MEA is sandwiched between separators is configured as a unit. Here, the electrode is composed of an electrode base material (also referred to as a gas diffusion electrode or a current collector) that promotes gas diffusion and collects (supply) electricity, and a catalyst layer that actually becomes an electrochemical reaction field. Yes. 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.

  For example, in the case of a fuel cell that uses an aqueous methanol solution as the fuel, increasing the methanol concentration will increase the power generation time and reduce the size of the fuel tank, thereby reducing the size of fuel cell-equipped equipment and carrying less fuel. it can. However, a high concentration of methanol fuel has a problem that the amount of methanol permeating the electrolyte membrane increases and the performance of the fuel cell is greatly deteriorated.

In general, a heating press is used as one method for joining an electrolyte membrane and an electrode. (Patent Document 1). Further, a method has been proposed in which water vapor is released by providing a through-hole in a mold (pressure plate) during hot pressing of a water-containing state (Patent Document 2). In addition, a method of joining an electrode with an expansion pressure of an electrolyte membrane instead of a heating press has been proposed (Patent Document 3).
JP 2005-302665 A JP 2000-54298 A JP 2003-303600 A

  In Patent Document 1, in particular, when an electrolyte membrane or electrode that is in a water-containing state is heated and pressed, there is no escape route for water vapor, and the electrolyte membrane is loaded with water vapor, which deteriorates the appearance of the MEA or decreases durability. was there.

  In Patent Document 2, in a hot press method for a pulp mold molded product in a water-containing state, a through hole is employed in a die of the hot press, and steam is discharged therefrom. However, if this method is applied to the MEA manufacturing method, since the through-holes are formed in the hot press mold, the press pressure cannot be uniformly applied, and the MEA bondability deteriorates. High output and durability cannot be expected.

  Further, in Patent Document 1, it is possible to apply pressure on a bulky electrode in a heating press, but it is not possible to appropriately apply pressure to the electrolyte membrane portion around the electrode, resulting in wrinkles on the electrolyte membrane. It may occur and the appearance may be deteriorated. Furthermore, excessive stress is applied to the electrode edge portion of the electrolyte membrane, resulting in distortion, which has been a major cause of a decrease in durability as an MEA.

  Furthermore, even when the heating temperature is low and water vapor is not generated, the moisture contained in the electrolyte membrane is pressurized and a load is applied to the electrolyte membrane.

  Patent Document 3 proposes a method of joining with an expansion pressure of an electrolyte membrane instead of a heating press. After the superposition of the electrolyte membrane and the electrode is incorporated in the cell, the membrane is joined by the swelling pressure of the electrolyte membrane. However, in this method, since heating is not performed at the time of bonding, the bonding between the electrolyte membrane and the electrode is not performed in detail, and problems such as a decrease in catalyst utilization efficiency and a decrease in output can be considered.

  The present invention has been made in view of the above problems, and can produce a high-quality membrane electrode assembly with less wrinkles, and can suppress the influence of water vapor on the electrolyte membrane, thereby improving the low MCO and durability. A method for producing a membrane electrode assembly is to be provided.

  In order to achieve the above object, the present invention employs the following means. That is, a manufacturing method of a membrane electrode composite in which an electrolyte membrane and an electrode are joined by pressing, wherein a breathable material is disposed between at least one of the electrodes and the electrolyte membrane between the pressure plate at the time of pressing. It is a manufacturing method of a membrane electrode composite.

  According to the present invention, a high-quality membrane electrode assembly with less wrinkles can be produced, and the influence of the water vapor and water during pressing on the electrolyte membrane can be suppressed. A manufacturing method can be provided.

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

  The method for producing a membrane electrode composite of the present invention is a method for producing a membrane electrode composite in which an electrolyte membrane and an electrode in a water-containing state are joined by pressing, and at the time of pressing, on at least one of the electrodes and the electrolyte membrane A breathable material is disposed between the pressure plate and the pressure plate.

  The method for producing a membrane electrode assembly of the present invention is applied when the electrolyte membrane is in a water-containing state. The water content state is a state containing water of 0.1% or more with respect to the weight of the completely dried electrolyte membrane (water content of 0.1% or more). The moisture here may contain an organic solvent or the like in addition to water. It is more effective when applied at 0.5% or more, and more effective in the order of 1% or more, 5% or more, and 10% or more.

  If this manufacturing method is used, high output of MEA can be obtained by joining in a water-containing state, and high-quality MEA with few wrinkles can be obtained. In addition, fuel permeation can be suppressed because there is little influence of swelling or the like caused by water vapor or water generated during pressing. For example, when methanol is used as the liquid fuel, methanol crossover (MCO) can be suppressed. Furthermore, the durability of the MEA is improved because it is difficult for extra stress to be applied to the electrode edge portion.

  As the simplest example of the membrane electrode composite produced in the present invention, the electrode base materials (anode and cathode) 2 and 6, catalyst layers (anode and cathode) 3 and 5 and an electrolyte membrane will be described with reference to FIG. 4 is a membrane electrode assembly arranged adjacently, and a known manufacturing method can be used except that the breathable materials 1 and 7 are arranged on the membrane electrode assembly during pressing.

  Usually, the press is joined by applying pressure to a laminate in which the electrolyte membrane is sandwiched between electrodes of both electrodes. The temperature is appropriately determined experimentally depending on the electrolyte membrane and electrode used, but is preferably 0 ° C. or higher and 300 ° C. or lower. More preferably, it is 20 ° C. or more and 200 ° C. or less. It is preferably heated and pressed, preferably 40 ° C. or higher and 200 ° C. or lower, and more preferably 60 ° C. or higher and 200 ° C. or lower. 80 degreeC or more and 200 degrees C or less are more preferable. Setting the temperature to 0 ° C. or higher is preferable in that the moisture in the electrolyte membrane and the electrode does not freeze. On the other hand, by setting the temperature to 300 ° C. or lower, the polymer material can be prevented from being deteriorated and decomposed.

  The pressure with respect to the electrode area is preferably 0.1 MPa to 500 MPa or less, more preferably 1 MPa to 100 MPa. The pressure of 0.1 MPa or more is preferable in that the bonding property between the membrane and the electrode is improved by pressurization, and the fuel and product permeation failure due to the collapse of the catalyst layer and the diffusion layer is prevented by setting the pressure to 100 MPa or less. Can do.

  Examples of the method of laminating each layer include a method in which an electrode base material is coated with a catalyst layer to form an electrode, and a method in which an electrolyte membrane is directly coated with a catalyst layer to form an electrode. For example, catalyst particles and other additives are mixed in the binder solution and stirred to form a uniform coating solution, such as spray coating, brush coating, dip coating, die coating, curtain coating, flow coating, spin coating, screen printing. A coating technique such as can be applied.

  Furthermore, a method of forming a catalyst layer on a substrate such as a polypropylene film, a polyethylene film, a polyimide film, a polysulfone film, or a polytetrafluoroethylene film and then transferring the catalyst layer to the electrolyte membrane is also preferably used.

  The present invention comprises a breathable material disposed between a pressure plate during pressing of the membrane electrode composite by the above laminating method, and the breathable material is disposed not only on the electrode but also on the electrolyte membrane, that is, the electrode and the electrolyte. By arranging so as to cover the entire surface of the membrane, it is possible to apply such pressure not only on the electrodes but also to the electrolyte membrane appropriately, and it is possible to suppress wrinkles generated in the electrolyte membrane. The entire surface may be substantially the same, and a portion that is not covered to the extent that it does not contradict its purpose may occur.

  Furthermore, it is more preferable to dispose the breathable material in a state where all or a part of the electrolyte membrane other than the power generation region is fixed before pressing. By fixing the electrolyte membrane, wrinkles and distortion generated in the electrolyte membrane can be effectively reduced. The fixing of the electrolyte membrane here means reducing the dimensional change in the film surface direction. For example, a method of attaching the electrolyte membrane to a process paper that can be peeled and fixing it, a frame or a mold around the electrolyte membrane The method of fixing with etc. is mentioned.

  Specifically, a process paper that can be peeled is placed on one side, electrodes and electrolyte membranes are laminated and fixed thereon, and a breathable material is placed on one side for pressing. The process paper here is a film or paper substrate coated with an adhesive, or a sheet that is confidently flexible, as long as the substrate is heat resistant to the temperature of the heating press used. There is no particular limitation. The adhesive strength is preferably such that the electrolyte membrane or electrode can be fixed and the membrane electrode assembly produced after the hot press can be peeled off. Specifically, the adhesive strength measurement is applied to PET according to the JIS method (Z0237). It is preferable that it is 0.01N / 25mm or more and 0.50N / 25mm in the value at the time of performing.

  Further, by using a jig as shown in FIG. 7, the periphery of the electrolyte membrane that is slightly larger than the mold surface as shown in FIG. 8 may be fixed with a frame, and a breathable material may be disposed on the electrolyte membrane and the electrode. The jig used here is not particularly limited as long as the electrolyte membrane is fixed in the film surface direction and the effect of disposing the air-permeable material is not lost.

  Other than the above electrolyte membrane fixing method, the method is not limited as long as the dimensional change in the membrane surface direction of the electrolyte membrane is substantially suppressed.

  Next, the breathable material will be described.

The breathable material must be capable of passing a liquid such as water and a gas such as water vapor. Specifically, since generated steam and exuded water cannot permeate in the thickness direction by the pressure plate, those that can permeate or contain water in the area direction are preferable. Therefore, the breathable material needs to have a certain thickness, and the basis weight per unit area is preferably 5 g / m ² or more per unit area. 10 g / m ² or more ~10000g / m ² or less, more preferably 20 g / m ² or more to 1000 g / m ² or less is more preferred. By setting the basis weight to 5 g / m ² or more, the effect of the breathable material can be obtained.

  As specific examples of the breathable material, woven fabric, non-woven fabric, and paper can be used.

  Examples of the material include polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate, nylons including aramid, celluloses such as rayon and acetate. In addition to synthetic fibers, natural fibers such as cotton and pulp are used. As the woven fabric, plain weaving, oblique weaving, satin weaving, crest weaving, binding weaving and the like are not particularly limited. Moreover, as a nonwoven fabric, it does not specifically limit, such as a papermaking method, a needle punch method, a spun pond method, a water jet punch method, a melt blow method. In particular, a felt-like non-woven fabric that is excellent in air permeability and does not form a mold even when pressure is applied is preferably used.

  Next, the catalyst layer will be described.

  The catalyst layer is usually a layer composed of a known fuel cell or membrane electrode assembly catalyst and a binder, and is not particularly limited. A catalyst here is a catalyst which accelerates | stimulates an electrode reaction, and the catalyst layer may contain an electronic conductor, an ion conductor, etc. other than a catalyst. As the catalyst contained in the catalyst layer, for example, a noble metal catalyst such as platinum, palladium, ruthenium, rhodium, iridium and 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. In the case of using an electron conductor (conductive material), a carbon material or an inorganic conductive material is preferably used from the viewpoint of electron conductivity and chemical stability. Among these, amorphous and crystalline carbon materials are mentioned. Examples of the carbon material are as described above.

  Moreover, when using an electronic conductor, it is preferable from the point of electrode performance that it is disperse | distributing uniformly with a catalyst particle. 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 catalyst-supporting carbon or the like in which the catalyst and the electron conductor are integrated as the 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 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.

  As the substance having ion conductivity (ion conductor) used in the catalyst layer, various organic and inorganic materials are generally known. However, when used in a fuel cell, sulfone which improves ion conductivity. A polymer having an ionic group such as an 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, an ion conductive polymer composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain or a hydrocarbon polymer material 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 catalyst layer in a solution or dispersion state. 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. Moreover, the hydrocarbon-based polymer material preferable as the electrolyte membrane described above can also be suitably used as a substance (ion conductor) having ion conductivity in the catalyst layer. In particular, in the case of a fuel cell using methanol aqueous solution or methanol as a fuel, a hydrocarbon-based polymer material may be effective for durability from the viewpoint of methanol resistance.

  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 containing catalyst particles and an electronic conductor as main constituents when the catalyst layer is prepared, and is applied in a uniformly dispersed state. is there. The amount of the ionic conductor contained in the catalyst layer should be appropriately determined according to the required electrode characteristics and the conductivity of the ionic conductor used, and is not particularly limited, but the weight ratio 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 a catalyst layer may contain various substances in addition to the catalyst, the electron conductor, and the ionic conductor. In particular, in order to improve the binding property of the substance contained in the catalyst layer, a polymer other than the above-described ion conductive polymer may be included. Examples of such a polymer include fluorine atoms such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), polytetrafluoroethylene, and polyperfluoroalkyl vinyl ether (PFA). These copolymers, copolymers of monomer units constituting these polymers and other monomers such as ethylene and styrene, or blend polymers can be used. The content of these polymers in the 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 catalyst layer preferably has a structure in which the liquid or gas easily permeates, and preferably has a structure that promotes the discharge of by-products due to the electrode reaction.

  As the electrode base material, one having a low electric resistance and capable of collecting or feeding power can be used. 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 are used, for example, 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 these fabrics, especially when carbon fibers are used, a plain fabric using flame-resistant spun yarn is carbonized or graphitized woven fabric, and the 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 nonwoven fabric or cloth from the viewpoint of obtaining a thin and strong fabric.

  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. Further, a conductive intermediate layer containing at least an inorganic conductive substance and a hydrophobic polymer can be provided between the electrode substrate and the 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 catalyst layer soaking into the electrode base material.

  As the membrane electrode assembly according to the present invention, if the relationship of the arrangement of each layer is not impaired, another functional layer, for example, a fuel permeation suppression layer, a water repellent layer, a radical trap layer, a fuel reforming layer, An impurity trap layer, a by-product removal layer, an interface adhesion layer, and the like may be disposed.

  The coarse density of the catalyst layer of the present invention can be appropriately determined experimentally depending on the performance of the membrane electrode assembly, etc., and can be made porous by roll press or flat plate press densification, wet coagulation, or the like. .

  As the electrolyte membrane of the membrane electrode composite of the present invention, all electrolyte membranes such as perfluoro-based electrolyte membranes and hydrocarbon-based electrolyte membranes represented by Nafion (registered trademark) (manufactured by DuPont) can be applied. From the viewpoint of reducing fuel permeation and durability, it is preferable to use an electrolyte membrane having high heat resistance, high strength, high tensile elastic modulus and low water content. Specific examples include films having a glass transition temperature of 130 ° C. or more, a tensile modulus of 100 MPa or more, and a moisture content of 40% by weight or less, including ionic group-containing polyphenylene oxide, ionic group-containing polyether ketone, and ionic group-containing poly. Ether 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, ionic group-containing polyoxazole, ionic group-containing polyphenylene, ionic group-containing polyazomethine, ionic group-containing An ionic group-containing polyolefin polymer such as polyimide azomethine, ionic group-containing polystyrene and ionic group-containing styrene-maleimide cross-linked copolymer, and an aromatic hydrocarbon polymer having an ionic group such as a cross-linked product thereof. Can be mentioned. These polymer materials can be used alone or in combination of two or more, and can be used as a polymer blend, a polymer alloy, or a laminated film of two or more layers. Moreover, the introduction method, synthesis method, and molecular weight range of the ionic group and ionic group here are as described above.

In particular, as the ionic group, a polymer material having a sulfonic acid group is most preferable as described above. However, as an example of using a polymer material having a sulfonic acid group, a polymer containing —SO ₃ M group (M is metal) There is a method in which a polymer is formed into a film from a solution state, and then heat-treated at a high temperature to remove the solvent, and proton substitution is performed to form a film. 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. Film formation in the state of these metal salts enables heat treatment at a high temperature, and this method is suitable for a polymer material system that can obtain a high glass transition point and a low water absorption rate.

  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 water absorption of the obtained film. A temperature of 100 ° C. or higher is preferable for obtaining a low water absorption rate. On the other hand, by setting the temperature to 500 ° C. or lower, the polymer material can be prevented from being decomposed.

  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 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 can be maintained, and productivity is increased.

  As the heat treatment method, heat from a hot air dryer or high frequency dielectric heating can be used.

Examples of the method for producing the electrolyte membrane include a method in which a polymer solution is applied by an appropriate coating method, the solvent is removed, and the acid treatment is performed after the treatment at a high temperature.
As the coating method, 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 by heat or high-frequency dielectric heating, the wet coagulation method using a solvent that does not dissolve the polymer, and the method of curing with light, heat, moisture, etc. A method of heating and melting and cooling after film formation can be applied.

  Examples of the solvent used for film formation include N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, hexa Aprotic polar solvents such as methylphosphontriamide, γ-butyrolactone, ester solvents such as butyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, An alkylene glycol monoalkyl ether such as propylene glycol monoethyl ether, or an alcohol solvent such as isopropanol is preferably used.

  As the thickness of the electrolyte membrane to be used, a membrane having a thickness of 3 to 2000 μm is usually 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 in order to reduce membrane resistance, that is, improve power generation performance. 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 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 substrate. 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, the polymer material having an electrolyte membrane and an ionic group according to the present invention can be crosslinked as a whole or a part of the polymer structure by means of irradiation or the like, if necessary. By crosslinking, an effect of further suppressing fuel crossover and swelling with respect to 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.

  In the electrolyte membrane of the present invention, the purpose of improving the mechanical strength, improving the thermal stability of the ionic group, improving the workability, etc. within a range that does not impair the ionic conductivity and the suppression effect of the fuel crossover. Therefore, a filler or inorganic fine particles may be contained, a network or fine particles made of a polymer or metal oxide may be formed, or a film impregnated in a support may be used.

  In the membrane electrode assembly produced by the method of the present invention, an interface resistance reducing material may be used for the purpose of, for example, increasing the contact area between the electrolyte membranes and reducing the interface resistance. The interface resistance reducing material is a material that can follow the surface irregularities of the catalyst layer by softening or coating by heating, and is preferably a material that can mainly reduce the resistance of ion conduction. It may be the same as or different from the electrolyte membrane, and its composition and shape may change between the manufacturing process and the actual use as a fuel cell.

  Further, it is preferable that the fuel does not swell excessively or dissolve, for example, when methanol aqueous solution or methanol is used as the fuel, it satisfies the conditions such as methanol resistance and strength equal to or higher than the electrolyte membrane to be used.

  Fuels for fuel cells using the membrane electrode assembly produced by the method of the present invention include oxygen, hydrogen and methane, ethane, propane, butanemethanol, isopropyl alcohol, acetone, glycerin, ethylene glycol, formic acid, acetic acid, dimethyl ether And organic compounds having 1 to 6 carbon atoms such as hydroquinone and cyclohexane, and mixtures thereof with water, and the like, and may be a single type or a mixture of two or more types. In particular, a fuel containing hydrogen and 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 hydrogen and aqueous methanol are particularly preferable in terms of power generation efficiency. In the case of using an aqueous methanol solution, the concentration of methanol is appropriately selected depending on the fuel cell system to be used, but a concentration as high as possible is preferable from the viewpoint of long-time driving. For example, an active fuel cell having a system that sends a medium necessary for power generation such as a liquid feed pump or a blower fan to a membrane electrode assembly, or an auxiliary machine such as a cooling fan, a fuel dilution system, or a product recovery system has a concentration of methanol. It is preferable to inject 30 to 100% of fuel with a fuel tank or a fuel cassette, dilute it to about 0.5 to 20%, and send it to the membrane electrode assembly. Is preferable in the range of 10 to 100%.

  Further, the fuel cell may be built in the device to be used, or may be used as an external unit. From the viewpoint of maintenance, it is also preferable that the membrane electrode assembly is detachable from the fuel cell.

  The fuel cell performance of the present invention varies depending on the device to be driven, such as the fuel and air supply method, cell shape, flow channel shape, current collection method, electronic circuit design, etc. The number, the number in series and / or parallel, and the like are preferably selected according to the device design as appropriate.

  The performance of the membrane electrode assembly of the present invention is preferably a liquid supply type when used mainly for portable devices. The liquid supply type means that a liquid such as an aqueous methanol solution is supplied to at least one electrode, and the liquid is preferably supplied to the anode side. By supplying liquid, the range of safety and fuel supply selection is expanded, the system can be simplified, the fuel cell can be miniaturized, and it is useful as a power source for portable electronic devices and the like.

  As a use of the fuel cell of the present invention, a power supply source of a moving body is preferable. In particular, mobile phones, personal computers, PDAs, video cameras (camcorders), digital cameras, handy terminals, RFID readers, portable devices such as various displays, home appliances such as electric shavers and vacuum cleaners, electric tools, household power supply equipment, It is preferably used as a power supply source for moving bodies such as passenger cars, automobiles such as buses and trucks, motorcycles, bicycles with electric assistance, robots, electric carts, electric wheelchairs, ships, and railways. Especially in portable devices, it is used not only for power supply sources, but also for charging secondary batteries installed in portable devices, and also suitable for use as a hybrid power supply source used in combination with secondary batteries and solar cells. it can.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, these examples are for understanding this invention better, and this invention is not limited to these.

[Measuring method]
The characteristics in the examples were measured by the methods shown below.

(1) Thickness It was measured using Mitutoyo ID-C112 type set on Mitutoyo granite comparator stand BSG-20.

(2) Performance evaluation of membrane electrode assembly Measurement of fuel (methanol) permeation amount Membrane electrode assembly was incorporated into a single cell “EFC05-01SP” (cell for electrode area 5 cm ² ) manufactured by Electrochem, the cell temperature was set to 50 ° C., and 20% aqueous methanol solution was added to the anode side. Supply at a rate of 5 ml / min, supply synthetic air to the cathode side at a rate of 50 ml / min, and collect the synthetic air discharged from the cathode in a gas collection bag before applying current. Using a gas chromatograph “MicroGC CP4900” with an autosampler manufactured by GL Sciences, the concentrations of both methanol in the sampling gas and carbon dioxide produced by oxidation were measured and calculated. Here, it was assumed that all carbon dioxide was generated from permeated methanol. The cathode air flow rate is L (ml / min), the total concentration of methanol and carbon dioxide by gas chromatography is Z (% by volume), the total volume is V (ml), and the open area (the aqueous methanol fuel in the membrane electrode assembly is The area of direct contact was defined as A (cm ² ), and the following formula was used.

MCO (mol / cm ² / min) = (L + V) × (Z / 100) / (22400 × A)
B. Voltage holding ratio Using Toyo Technica evaluation device, potentiostat 1470 made by solartron and frequency response analyzer made by solartron 1255B, voltage-current characteristics were measured repeatedly and expressed in voltage change at current density of 100 mA / cm ^2. did. When the 10th voltage is Y and the 500th voltage is Z, the voltage holding ratio (%) is represented by Z / Y × 100, which is an index of durability.

(3) Observation of wrinkles and strains of membrane electrode assembly The wrinkles of the electrolyte membrane were visually observed and evaluated in four stages of ◯, Δ, and X, where ◎ was a high-quality one with few wrinkles. In addition, the MEA is sandwiched by polarizing plates stacked so that the deflection is perpendicular, and the image is projected by the Nikon projector “PROFILE PROJECTOR V-10A”. The whitened areas were distorted. The appearance was visually observed, and the case where there were many black parts was evaluated as 4 and evaluated in 4 stages: ○, Δ, and ×.

(4) Measurement of moisture content The weight of the 5 cm square electrolyte membrane (moisture content) was measured, this was dried at 100 ° C. for 4 hours with a vacuum dryer, and then the weight (dry weight) was measured again. The value obtained by dividing the difference by the dry weight was defined as the moisture content.

[Synthesis example of polymer material having ionic group]
6.9 g of potassium carbonate, 14 g of 4,4′-dihydroxytetraphenylmethane, 7 g of 4,4′-difluorobenzophenone, and 5 g of disodium 3,3′-disulfonate-4,4′-difluorobenzophenone Then, polymerization was performed at 190 ° C. in N-methyl-2-pyrrolidone. Purification was carried out by reprecipitation with a large amount of water to obtain polymer A.

[Preparation example of electrolyte membrane]
The above polymer A was dissolved in N-methyl-2-pyrrolidone to obtain a coating solution having a solid content of 25%. The coating solution was cast on a glass plate and dried at 60 ° C. for 10 minutes and further at 100 ° C. for 2 hours to obtain a 51 μm film. Furthermore, after heat-treating under conditions of heating to 200 to 300 ° C. over 1 hour in a nitrogen gas atmosphere and heating at 300 ° C. for 10 minutes, the mixture was allowed to cool and immersed in 1N hydrochloric acid for 12 hours or more to perform proton substitution. The electrolyte membrane A was obtained by immersing it in a large excess of pure water for at least one day and thoroughly washing it.

[Anode electrode production example]
Carbon fiber “TL-1400W” manufactured by E-TEK (USA), Pt-Ru supported carbon catalyst “HiSPEC (registered trademark)” 6000 manufactured by Johnson & Matthey, and 20% “Nafion manufactured by DuPont” (Registered trademark) ”and an anode coating solution consisting of an n-propanol solution were applied and dried at 100 ° C. for 10 minutes. The anode catalyst coating solution was applied to a TL-1400W carbon black coating surface. Next, 10 g of polymer A, 60 g of N-methyl-2-pyrrolidone as a plasticizer, and 40 g of glycerin are placed in a container and stirred until uniform to produce interface resistance-reducing composition A. On electrolyte membrane A, The coating was applied at 3 mg / cm ² and heat-treated at 100 ° C. for 5 minutes. Next, each piece was cut into a square of 2.3 cm to obtain an anode electrode.

[Example of cathode electrode production]
Cathode catalyst coating consisting of carbon fiber "TL-1400W" manufactured by E-TEK (USA) and Pt-supported carbon catalyst TEC10V50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. and 20% "Nafion (registered trademark)" manufactured by DuPont The liquid was applied and dried at 100 ° C. for 15 minutes. The cathode catalyst coating solution was applied to a TL-1400W carbon black coating surface. Next, 10 g of polymer A, 60 g of N-methyl-2-pyrrolidone as a plasticizer, and 40 g of glycerin are placed in a container and stirred until uniform to produce interface resistance-reducing composition A. On electrolyte membrane A, The coating was applied at 3 mg / cm ² and heat-treated at 100 ° C. for 1 minute. Next, each piece was cut into a square of 2.3 cm to obtain a cathode electrode.

[Example 1]
The electrolyte membrane A in a water-containing state (water content 15%) was held between the cathode electrode and the anode electrode and faced so as not to shift. Further, “Industrial Felt GN” manufactured by Amvic Co., Ltd. (weight per unit area 550 g / m ² ) was placed as a breathable material so as to cover the electrode and the electrolyte membrane, and pressed at 100 ° C. and 3 MPa for 5 minutes, and 10% aqueous methanol solution. And membrane electrode assembly A was obtained.

As for the appearance of this membrane electrode composite A, the determination was “ず” because there were not so many wrinkles on the electrolyte membrane. As a result of observation through polarized light, the distortion around the electrode of the electrolyte membrane was small, and the determination was “◯”.
The methanol permeation amount of this membrane electrode assembly A was 3.6 μmol / (cm ² × min). The voltage holding ratio was 86%. A projection photograph in which wrinkles and distortion are observed is shown in FIG.

[Comparative Example 1]
Membrane electrode assembly B was produced in the same manner as in Example 1 except that no breathable material was disposed. The appearance of this membrane electrode composite B was judged as x because of many concentric wrinkles on the electrolyte membrane. As a result of observation through polarized light, the distortion around the electrode of the electrolyte membrane and the concentric wrinkles of the electrolyte membrane were observed. Since a large distortion was observed, the judgment was x.

The methanol permeation amount of this membrane electrode assembly A was 5.3 μmol / (cm ² × min). The voltage holding ratio was 71%.

  From Example 1 and Comparative Example 2, it is better to arrange a breathable material when using a water-containing electrolyte membrane, and the effect of improving durability by reducing MCO and reducing distortion around the electrode. it is obvious. A projection photograph in which wrinkles and distortion are observed is shown in FIG.

[Example 2]
Membrane electrode composite C was produced except that the breathable material of Example 1 was changed to a polypropylene spunbonded nonwoven fabric “Syntex (registered trademark) PSO-4220” (weight per unit area 20 g / cm ² ) manufactured by Mitsui Petrochemical Co., Ltd. did.

  As for the appearance of this membrane electrode composite C, some concentric wrinkles were generated around the electrode. However, since the amount of wrinkles generated in Example 2 was obviously smaller than that in Comparative Example 1, the judgment was ○ . Furthermore, as a result of observation through polarized light, the distortion around the electrode of the electrolyte membrane was seen to be slightly larger than that in Example 1, but the determination was Δ because it was smaller than that in Comparative Example 2.

The methanol permeation amount of this membrane electrode assembly C was 4.4 μmol / (cm ² × min). The voltage holding ratio was 79%. A projection photograph in which wrinkles and distortion are observed is shown in FIG.
[Comparative Example 2]
Membrane electrode assembly D was prepared in the same manner except that the breathable material of Example 1 was disposed only on the electrode and no pressure was applied to the electrolyte membrane portion.

  As for the appearance of this membrane electrode composite D, many concentric wrinkles were found in the electrolyte membrane, so the judgment was x. As a result of observation through polarized light, distortion was seen along the concentric wrinkles of the electrolyte membrane. Judgment is ○ because the surrounding distortion was relatively small.

The methanol permeation amount of this membrane electrode assembly D was 4.2 μmol / (cm ² × min). The voltage holding ratio was 81%.

From Example 1 and Comparative Example 2, the effect of improving the durability by arranging the air-permeable material on the electrode was seen, but the appearance was poor because the film part was not pressed down. A projection photograph in which wrinkles and distortion are observed is shown in FIG.
[Example 3]
The above anode coating solution was applied to a polypropylene spunbonded nonwoven fabric “Syntex (registered trademark) PSO-4220” (weight per unit area 20 g / cm ² ) manufactured by Mitsui Petrochemical Co., Ltd. with a knife coater and dried at 100 ° C. for 10 minutes. did.

Next, 10 g of polymer A, 60 g of N-methyl-2-pyrrolidone as a plasticizer, and 40 g of glycerin are placed in a container and stirred until uniform to produce interface resistance-reducing composition A. On electrolyte membrane A, The coating was applied at 3 mg / cm ² and heat-treated at 100 ° C. for 5 minutes. Next, each piece was cut into a square of 2.3 cm to obtain an anode electrode.

Further, the cathode coating solution was applied to a polypropylene spunbond nonwoven fabric “Syntex (registered trademark) PSO-4220” (weight per unit area 20 g / cm ² ) manufactured by Mitsui Petrochemical Co., Ltd. with a knife coater, and 10 ° C. at 10 ° C. Dried for minutes.

Next, 10 g of polymer A, 60 g of N-methyl-2-pyrrolidone as a plasticizer, and 40 g of glycerin are placed in a container and stirred until uniform to produce interface resistance-reducing composition A. On electrolyte membrane A, The coating was applied at 3 mg / cm ² and heat-treated at 100 ° C. for 5 minutes. Next, each piece was cut into a square of 2.3 cm to obtain a cathode electrode.

  Using this anode electrode and cathode electrode, the electrolyte membrane A in a water-containing state was sandwiched and faced so as not to be displaced and pressed at 100 ° C. and 3 MPa for 5 minutes. After removing from the mold (pressure plate), the non-woven fabric of the anode electrode and cathode electrode was washed with a 10% aqueous methanol solution. A membrane electrode assembly E was obtained by laminating carbon cloth “TL-1400W” manufactured by E-TEK Co., Ltd. as a diffusion layer.

  The appearance of this membrane electrode composite E was evaluated as ◎ with almost no wrinkles on the electrolyte membrane, and the result of observation through polarized light was ◎ because the distortion around the electrode of the electrolyte membrane was considerably small.

This membrane electrode assembly E had a methanol permeation rate of 3.4 μmol / (cm ² × min). The voltage holding ratio was 82%. A projection photograph in which wrinkles and distortion are observed is shown in FIG.
[Example 4]
As the process paper, the electrolyte membrane A in the water-containing state (water content 15%) is sandwiched between the cathode electrode and the anode electrode on the adhesive surface of “SuRemLiner (registered trademark) SRL-1252” manufactured by Lintec Corporation, and fixed on the process paper. did. Furthermore, “industrial felt GN” (weight per unit area 550 g / m ² ) manufactured by Amvic Co., Ltd. was disposed on the upper surface as a breathable material. After pressing at 100 ° C. and 3 MPa for 5 minutes to peel off the process paper, the membrane electrode assembly F was obtained by washing with a 10% methanol aqueous solution.

The appearance of this membrane electrode composite F was judged as ◎ with almost no wrinkles because the electrolyte membrane was fixed, and as a result of observation through polarized light, the distortion around the electrode of the electrolyte membrane was extremely small, and the judgment was ◎. It was.
The amount of methanol permeation of this membrane electrode assembly F was 2.7 μmol / (cm ² × min). The voltage holding ratio was 91%.
[Example 5]
The electrolyte membrane 4 was sandwiched between the electrolyte membrane fixing frames 8 shown in FIG. Next, a polypropylene spunbonded nonwoven fabric “Syntex (registered trademark) PSO-4220” (weight per unit area 20 g / cm ² ) manufactured by Mitsui Petrochemical Co., Ltd. is disposed as a breathable material on the lower surface 11 of the mold shown in FIG. The frame with the electrolyte membrane was further fixed thereon. After placing the other electrode and the air-permeable material, the upper surface 10 of the mold was closed and pressed at 100 ° C. and 3 MPa for 5 minutes. The membrane electrode assembly G was obtained by washing with a 10% aqueous methanol solution.
The appearance of this membrane electrode composite F was judged as ◎ with almost no wrinkles because the electrolyte membrane was fixed, and as a result of observation through polarized light, the judgment was extremely little as the distortion around the electrode of the electrolyte membrane was ◎. .
The amount of methanol permeation of this membrane electrode assembly G was 2.9 μmol / (cm ² × min). The voltage holding ratio was 88%.

  The membrane electrode assembly of the present invention can be applied to membrane electrode assemblies of various electrochemical devices (for example, fuel cells, water electrolysis devices, chloroalkali electrolysis devices, 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.

  Although it does not specifically limit as a use of the fuel cell of this invention, Mobile devices, such as a mobile phone, a personal computer, PDA, a video camera, a digital camera, household appliances, such as a cordless vacuum cleaner, toys, an electric bicycle, a motorcycle, a car, Vehicles such as buses and trucks, ships, moving bodies such as railways, robot power supply sources, stationary generators such as stationary primary batteries, alternatives to secondary batteries, or hybrid power sources with these or solar batteries, or charging It is preferably used for use.

It is a section conceptual diagram of a membrane electrode composite. MEA projection photograph of Example 1 MEA projection photograph of Example 2 MEA projection photograph of Example 3 MEA projection photograph of Comparative Example 1 MEA projection photograph of Comparative Example 2 6 is a conceptual diagram of an electrolyte membrane fixing frame used in Example 5. FIG. It is a conceptual diagram of the metal mold | die used for Example 5. FIG.

Explanation of symbols

1: Breathable material 2: Anode electrode substrate 3: Anode catalyst layer 4: Electrolyte membrane 5: Cathode catalyst layer 6: Cathode electrode substrate 7: Breathable material 8: Electrolyte membrane fixing frame 9: Clamp 10: Mold upper surface 11: Mold lower surface

Claims (4)

  A method of manufacturing a membrane electrode composite in which an electrolyte membrane and an electrode in a water-containing state are joined by pressing, and at the time of pressing, a breathable material is disposed between the pressure plate and at least one of the electrodes and the electrolyte membrane. A method for producing a membrane electrode assembly, characterized by comprising:   The method for producing a membrane electrode assembly according to claim 1, wherein the air-permeable material is disposed so as to cover the entire surface of the electrode and the electrolyte membrane.   The method for producing a membrane electrode assembly according to claim 1 or 2, wherein the press is a heating press.   The method for producing a membrane electrode assembly according to any one of claims 1 to 3, wherein at least a portion other than the power generation region of the electrolyte membrane is fixed in whole or in part before pressing.