JP2009199983A - Membrane electrode composite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode composite having improved durability by using a simple method of preventing the degradation of durability resulting from reaction between hydrogen cross-leaking from an anode to a cathode and oxygen (air) cross-leaking from the cathode at both the electrodes, while preventing the breakage of a membrane resulting from exothermic reaction (combustion) of cross-leaking gases on a catalyst. <P>SOLUTION: The membrane electrode composite for a polymer electrolyte fuel cell includes the anode and the cathode arranged with at least a polymer electrolyte membrane therebetween. The anode and the cathode each contain a catalyst layer, a conductive layer, and a collector layer in sequence from the polymer electrolyte membrane. At least one of the collector layer and the conductive layer covers the catalyst layer and contacts the polymer electrolyte membrane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly used in 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, 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.

  Solid polymer fuel cells using hydrogen as a fuel (Polymer Electrolyte Fuel Cell, sometimes referred to as PEFC) operate at relatively low temperatures, so they can be used in automobiles, mobile phones, notebook computers, personal digital assistants, etc. Expected to be a mobile power source for portable devices. 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). And this MEA is comprised from the cell pinched | interposed with the electroconductive substance (separator) which can supply a fuel and an oxidizing agent. This cell may be used alone, or may be used as one power generation module by stacking several cells.

  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.

  In many cases, gaseous fuel is used as the fuel for PEFC, and in particular, hydrogen gas is supplied to the anode and oxygen gas (air) is generally supplied to the cathode because of the efficiency of the reaction. Normally, hydrogen gas reacts on the catalyst and passes through the electrolyte membrane as protons, but sometimes passes through the electrolyte membrane as a gas. This mixture of hydrogen leaking from the anode and oxygen at the cathode lowers the potential, which is one of the factors that cause a decrease in output and durability. This phenomenon also occurs from the reverse cathode to the anode, and various methods have been proposed to prevent this cross leak. Patent Document 1 proposes an MEA that uses a sealing material at the edge of an electrode.

Patent Document 2 proposes a method in which an edge seal is applied to an electrode edge portion of a membrane electrode composite via an adhesive.
JP-T-2006-511061 gazette JP 2007-66766 A

  In Patent Document 1, since an edge seal is used, the number of parts is large, and the electrolyte membrane is subjected to mechanical stress due to strain applied when the sealing material is joined, which may reduce the durability of the electrolyte membrane.

  In Patent Document 2, an edge seal is applied to the electrode edge portion of the membrane electrode composite. However, an adhesive is required for the application of the edge seal, and not only the number of parts increases, but also the electrolyte membrane by the adhesive. There was a risk that durability would be reduced. Further, by providing the adhesive layer, the electrolyte membrane and the diffusion layer or the conductive layer are not in direct contact with each other, and the area of the diffusion layer is required to be different between the anode and the cathode.

  In view of the above problems, we can prevent a decrease in durability caused by the reaction of hydrogen leaked from the anode to the cathode and oxygen (air) cross-leaked from the cathode in a simple manner, Furthermore, the present invention is intended to provide a membrane electrode assembly with improved durability by preventing membrane breakage caused by exothermic reaction (combustion) caused by cross leaked gas on the catalyst.

  In order to achieve the above object, the present invention employs the following means. That is, the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises at least an anode and a cathode disposed with a polymer electrolyte membrane interposed therebetween, and the catalyst layer, the conductive layer are arranged in the order that the anode and the cathode are closer to the polymer electrolyte membrane. And a current collector layer.

  According to the present invention, it is possible to prevent a decrease in durability caused by the reaction between hydrogen that has cross-leaked from the anode to the cathode and oxygen (air) that has cross-leaked from the cathode, in a simple manner. It is possible to provide a membrane electrode assembly with improved durability by preventing membrane breakage caused by the exothermic reaction (combustion) of the cross leaked gas on the catalyst.

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

  A membrane for a solid polymer fuel cell, comprising at least an anode and a cathode arranged with a polymer electrolyte membrane interposed therebetween, and the anode and the cathode including a catalyst layer, a conductive layer, and a current collector layer in order from the polymer electrolyte membrane The electrode composite is characterized in that at least one of the current collector and the conductive layer covers the catalyst layer and is in contact with the polymer electrolyte membrane.

  This method is applied to PEFC that uses gaseous fuel such as hydrogen gas. For example, when power is generated by PEFC, hydrogen leaked from the anode to the cathode and oxygen supplied as fuel to the cathode (air) ), And when a reaction occurs on the catalyst, heat may be generated. The exotherm is presumed to be due to the combustion of hydrogen, oxygen, and the catalyst, and is generally higher than the reaction heat that produces water from protons and oxygen during power generation in PEFC.

  Therefore, by taking measures so that hydrogen and oxygen (air) do not come into direct contact with the catalyst layer, the exothermic reaction can be suppressed, and the deterioration and degradation of the membrane electrode assembly can be reduced, thereby improving the durability. Generally, an edge seal or the like is used, but in the present invention, a highly durable membrane electrode assembly can be easily obtained by covering the catalyst layer with a current collector or a conductive layer.

  First, the arrangement relationship of each layer will be described.

  The membrane electrode assembly of the present invention comprises a catalyst layer, a conductive layer, and a current collector layer in the order that at least one of the anode and the cathode is closer to the polymer electrolyte membrane, and each layer is arranged close to the electrolyte membrane. It is arranged so as to cover or have the same area. However, the catalyst layer has the same or smaller area than the conductive layer or the current collecting layer, and it is essential that the conductive layer or the current collecting layer is in contact with the electrolyte membrane. The area here refers to the projected area of the surface with the largest area of the layer, and the large or the same layer is arranged so as to cover the entire projected area of the small or the same layer. Is preferred. Covering here refers to a state where the whole is covered and overlapped.For example, when a conductive layer having a large area is overlaid on a catalyst layer having a small area, the catalyst layer having a small area when viewed from above has an area. A state in which the conductive layer is completely hidden by a large conductive layer.

  In addition, the contact may be that the conductive layer or current collecting layer and the electrolyte membrane are completely in close contact with each other, or the degree of contact may be sufficient, and fuel must enter the gap between the conductive layer or current collecting layer and the electrolyte membrane. There is no particular limitation. However, since it is known that the fuel cross leak often occurs at the electrode edge portion of the membrane electrode assembly, it is more preferable that the fuel is cross-contacted at the edge portion.

  The present invention is preferably applied to both the anode and the cathode in order to improve durability, but the effect can be obtained with either the anode or the cathode. When implemented on either one, it is more preferable to apply to the cathode side. This is because hydrogen molecules having small molecules and high diffusibility are often cross leaked from the anode side to the cathode side.

  It is known that the amount of fuel cross leak and the effect of the invention often depend on the properties of the electrolyte membrane used, and examples of the electrolyte membrane include hydrocarbon electrolyte membranes and fluorine electrolyte membranes. The invention is applicable to all kinds of electrolyte membranes and is not particularly limited. In particular, adaptation with a flammable hydrocarbon-based electrolyte membrane is preferable, and its durability improvement effect is great. For example, when hydrogen leaked from the anode reacts with oxygen on the cathode catalyst, the electrolyte membrane burns due to the exothermic reaction, and the hole becomes larger due to the hydrogen leaking from the generated minute hole, leading to membrane breakage. Assuming that the gas is not directly contacted on the catalyst by covering the catalyst layer according to the present invention, it is assumed that a high temperature exothermic reaction does not occur. On the other hand, even in the case of a fluorine-based electrolyte membrane that is incombustible, there is a concern that the polymer may be decomposed or deteriorated when exposed to a high temperature exothermic reaction.

  In addition, the membrane electrode assembly used in the present invention basically may contain other functional layers as long as the arrangement relationship of the membrane electrode assembly of the present invention is not impaired and the effect is not hindered. 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.

  Next, each layer of the membrane electrode assembly will be described in detail.

  Here, the diffusion layer refers to a current collecting layer (electrode substrate) and a conductive layer. As the electrode base material used for the diffusion layer, one having a low electric resistance can be used, which can collect current or supply power. 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.

  Next, the conductive layer will be described. Usually, it consists of an electron conductor (conductive material) and a binder, and carbon materials and inorganic conductive materials are preferably used for the electron conductor from the viewpoint of chemical stability. Among these, amorphous and crystalline carbon materials are mentioned. A carbon material or an inorganic conductive material may be added.

  For example, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used because of its electronic conductivity and specific surface area. Furnace Black includes Vulcan (registered trademark) XC-72R, Vulcan (registered trademark) P, Black Pearls (registered trademark) 880, Black Pearls (registered trademark) 1100, Black Pearls (registered trademark) 1300, Black Pearls manufactured by Cabot Corporation. (Registered Trademark) 2000, Regal (Registered Trademark) 400, Ketjen Black International (registered trademark) EC, Ketjen Black (registered trademark) EC600JD, Mitsubishi Chemical Corporation # 3150, # 3250, etc. Examples of acetylene black include Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo.

  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, fibers, tubes, cones, megaphones as well as irregular particles can be used. Moreover, you may use what post-processed these carbon materials. Further, metal fine particles such as Au, Pt, Ti, Cu, Al, and stainless steel, particles of tin oxide and indium tin oxide, and electron conductive polymers such as polyaniline and fullerene can be added.

  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.

  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.

  Furthermore, when improving electronic conductivity, you may use an electronic conductor (electrically conductive material), and a carbon material and an inorganic electrically conductive material are used preferably from the point of electronic conductivity or chemical stability. Among these, amorphous and crystalline carbon materials are mentioned. A carbon material or an inorganic conductive material may be added.

  For example, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used because of its electronic conductivity and specific surface area. Furnace Black includes Vulcan (registered trademark) XC-72R, Vulcan (registered trademark) P, Black Pearls (registered trademark) 880, Black Pearls (registered trademark) 1100, Black Pearls (registered trademark) 1300, Black Pearls manufactured by Cabot Corporation. (Registered Trademark) 2000, Regal (Registered Trademark) 400, Ketjen Black International (registered trademark) EC, Ketjen Black (registered trademark) EC600JD, Mitsubishi Chemical Corporation # 3150, # 3250, etc. Examples of acetylene black include Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo.

  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, fibers, tubes, cones, megaphones as well as irregular particles can be used. Moreover, you may use what post-processed these carbon materials. Further, metal fine particles such as Au, Pt, Ti, Cu, Al, and stainless steel, particles of tin oxide and indium tin oxide, and electron conductive polymers such as polyaniline and fullerene can be added.

  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 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 electrolyte membrane used in the membrane electrode assembly 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. In particular, 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 moisture 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 a metal) is contained. Examples include 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 replace with protons 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.

  In addition, the electrolyte membrane and the polymer material having an ionic group used in the present invention can be crosslinked as a whole or a part of the polymer structure by means such as irradiation. 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.

  Further, in the electrolyte membrane used in the present invention, the mechanical strength is improved, the thermal stability of the ionic group is improved, the workability is improved, etc. within a range that does not impair the ionic conductivity and the effect of suppressing the fuel crossover. For this purpose, 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 used in 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.

  The use of the fuel cell of the present invention is not particularly limited, but it is not limited to automobiles such as passenger cars, electric bicycles, buses and trucks, motorcycles, bicycles with electric assist, robots, electric carts, electric wheelchairs, ships, and railways. Power supply, mobile phone, personal computer, PDA, video camera (camcorder), digital camera, handy terminal, RFID reader, portable devices such as various displays, home appliances such as electric shavers and vacuum cleaners, toys, electric tools, homes It can be preferably used as a power supply for a vehicle, and can be suitably used as a substitute for a conventional primary battery such as a stationary generator, a secondary battery, a hybrid power source with these or a solar battery, or for charging.

  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) Endurance power generation performance evaluation of membrane electrode assembly The fabricated membrane electrode assembly is incorporated into an evaluation cell (single cell for electrode area of 5 cm ² ), hydrogen gas is supplied to the anode at 10 mL / min, and air is supplied to the cathode by natural exhalation. did. Leads were attached to the cathode current collector and the anode current collector, and measurement was performed using a Toyo Technica evaluation device, a potentiostat 1470 made by solartron, and a frequency response analyzer made by solartron 1255B. After generating power for 8 hours at a constant current of 200 mA / cm ^{2 at} room temperature, a cycle of stopping for 2 hours was repeated to examine the durability time.

[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.

[Example of catalyst transfer electrode preparation]
15g of Pt-Ru supported carbon catalyst "HiSPEC (registered trademark)" 1000 manufactured by Johnson & Matthey, 2g of Pt supported carbon catalyst TEC10V50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. and 20% "Nafion (registered trademark) manufactured by DuPont ) "The solution 10g was mixed and the catalyst coating liquid A was obtained. The catalyst coating liquid A was applied to a Kapton film “200H” manufactured by Toray DuPont with a knife coater so that the amount of platinum applied was 1 mg / cm ^2, and then dried at 100 ° C. for 15 minutes. Next, a catalyst transfer electrode was obtained by cutting according to a predetermined size.

[Example of conductive layer and current collecting layer]
A carbon cloth “TL-1400W” manufactured by E-TEK (USA) was cut into a predetermined size and used. The carbon layer side was a conductive layer, and the cross side was a current collecting layer.

[Example 1]
The catalyst transfer electrode was cut so that each of the anode and the cathode was a square of 2.3 cm, faced so as to sandwich the electrolyte membrane A on the catalyst layer side, and pressed at 150 ° C. and 5 MPa for 5 minutes. The Kapton film on the surface of the catalyst layer was peeled off to obtain a catalyst layer transfer film A. Further, the carbon cloth was cut so as to be a square with a side 2.5 cm larger than the catalyst layer, and both electrodes were disposed so that the conductive layer and the catalyst layer were in contact and covered the entire catalyst layer (at this time, the electrolyte membrane and the conductive layer were electrically conductive). The layers are in contact). This was pressed at 100 ° C. and 3 MPa for 5 minutes to obtain a membrane electrode assembly A.

  As shown in FIG. 1, the membrane electrode assembly A did not show a rapid voltage drop even after 500 hours as shown in FIG.

[Comparative Example 1]
A carbon cloth cut to a size of 2.3 cm on one side of the catalyst layer transfer film A is arranged in the same manner as in Example 1 and pressed at 100 ° C. and 3 MPa for 5 minutes to obtain a membrane electrode assembly B. It was.

  As shown in FIG. 2, hydrogen leakage occurred in this membrane electrode composite B in 55 hours, and membrane breakage at the electrode edge portion was confirmed. From this, the durability improvement effect by covering the entire catalyst layer with the conductive layer is clear.

[Example 2]
3 g of carbon black “# 3030B” manufactured by Mitsubishi Chemical Corporation, 0.15 g of vinylidene fluoride resin (hereinafter sometimes abbreviated as PVDF) as a binder, “KF polymer # 1300” manufactured by Kureha Chemical Co., Ltd., and N as a solvent -6 g of methyl-2-pyrrolidone was put in a container and stirred until it became uniform to obtain a conductive layer coating solution A. The conductive layer coating liquid A was applied to carbon paper (carbon paper “TGP-H-060” manufactured by Toray Industries, Inc.) in a 2.3 mm square using a spacer, and dried at 100 ° C. for 15 minutes. The conductive layer coating liquid A had a solid content setting amount of 0.5 mg / cm ² , and the carbon paper was further cut to be 1 mm larger and 2.5 cm square around the conductive layer to obtain a diffusion layer A.

  The conductive layer side of the diffusion layer A is disposed so as to be in contact with the catalyst layer transfer film A, and both electrodes are disposed so that the conductive layer and the catalyst layer are in contact with each other and the diffusion layer covers the entire catalyst layer. And the current collecting layer are in contact with each other). This was pressed at 100 ° C. and 3 MPa for 5 minutes to obtain a membrane electrode composite C.

  As shown in FIG. 3, the membrane electrode assembly C did not show a rapid voltage drop even after 500 hours. From this, the durability improvement effect by covering the entire catalyst layer with the conductive layer and the current collecting layer so that the catalyst layer does not come into direct contact with hydrogen and oxygen is clear.

[Example 3]
The conductive layer coating solution A was applied to the anode catalyst layer of the catalyst layer transfer film A in a 2.5 mm square using a spacer so that the conductive layer and the catalyst layer were in contact with each other and the entire catalyst layer was covered. After drying at 100 ° C. for 15 minutes, the cathode side was similarly coated and dried. The solid content setting amount of the conductive layer coating liquid A was 0.5 mg / cm ² . Next, carbon paper (carbon paper “TGP-H-060” manufactured by Toray Industries, Inc.) is cut into 2.3 mm square, placed on the conductive layer of both electrodes, pressed at 100 ° C. and 3 MPa for 5 minutes, and membrane electrode Complex D was obtained.

  As shown in FIG. 4, the membrane electrode assembly D did not show a rapid voltage drop even after 500 hours.

  The membrane electrode assembly of the present invention is suitable for a fuel cell using hydrogen as a fuel. The use of the fuel cell of the present invention is not particularly limited, but is such as electric bicycles, motorcycles, vehicles such as automobiles, buses, trucks, mobiles such as ships, railways, mobile phones, personal computers, PDAs, video cameras, digital cameras. Mobile devices such as cordless vacuum cleaners, toys, robot power supply sources, stationary primary generators such as stationary generators, alternatives to secondary batteries, or hybrid power sources with these or solar cells, or charging It is preferably used for use.

It is a graph of the durable electric power generation evaluation result in 200 mA / cm < ² > constant current of Example 1. FIG. It is a graph of the durable electric power generation evaluation result in the constant current of 200 mA / cm < ² > of the comparative example 1. It is a graph of the endurance power evaluation results in the constant current of 200 mA / cm ² in Example 2. It is a graph of the endurance power generation evaluation result in Example 3 at a constant current of 200 mA / cm ² .

Claims (2)

  A membrane for a solid polymer fuel cell, comprising at least an anode and a cathode arranged with a polymer electrolyte membrane interposed therebetween, and the anode and the cathode including a catalyst layer, a conductive layer, and a current collector layer in order from the polymer electrolyte membrane A membrane electrode assembly for a polymer electrolyte fuel cell, wherein at least one of a current collector and a conductive layer covers the catalyst layer and is in contact with the polymer electrolyte membrane.   The membrane electrode assembly according to claim 1, wherein the polymer electrolyte is a hydrocarbon system.

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