JP2007165188A - Membrane-electrode assembly of polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer fuel cell capable of performing stable cell performance in a wide humidity range and a wide operation (current density) range. <P>SOLUTION: A membrane-electrode assembly of the polymer fuel cell is equipped with a pair of electrode catalyst layers 2, 5 between a pair of gas diffusion layers, and a solid polymer membrane 1 between the electrode catalyst layers. The membrane-electrode junction of the polymer fuel cell is equipped with a hydrophilic layer between the solid polymer membrane 1 and the electrode catalyst layers 2, 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane-electrode assembly of a fuel cell, particularly a polymer electrolyte fuel cell, and more particularly, by providing a hydrophilic layer between a polymer electrolyte membrane and an electrode catalyst layer. The present invention relates to an excellent polymer-type fuel cell membrane-electrode assembly that suppresses and prevents drying of a polymer electrolyte membrane under humidification and prevents flooding phenomenon by absorbing generated water under high humidification.

  The fuel cell, whose principle has been clarified by Globe, has high power generation efficiency and can also use exhaust heat, so that it does not allow other power generation methods to follow its usefulness. Also, the reaction formula is

Therefore, the fuel cell is a clean power generation system that generates not only NOx but also SOx. Achieving the practical application of fuel cells that are friendly to the global environment and have high power generation efficiency can bring about changes in science and technology and modern society, and shift to the future of a new energy society.

  The types of such fuel cells are generally phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), polymer electrolyte fuel cells (PEFC), etc., among them polymer fuel cells (PEFC). Can start at room temperature, has few problems of electrolyte dissipation, and has advantages such as high current density.

  However, the electrolyte membrane in a polymer electrolyte fuel cell (PEFC) must always be humidified in order to maintain high ionic conductivity. On the other hand, if the water content is excessive, the gas passage is clogged with water and the gas does not flow easily. (Flooding phenomenon) occurs and the voltage drops rapidly. Further, when the membrane is dried, the ionic conductivity is deteriorated, and a cross leak occurs in which oxygen and hydrogen directly react with each other, and the membrane is damaged.

  Therefore, in order to be able to put a high-performance polymer fuel cell (PEFC) into practical use, comprehensive water management including water generated at the cathode and water moving in the membrane as well as humidification of the membrane must It can be said that it is a supreme proposition for life.

Therefore, the following are conventional techniques related to comprehensive water management.
Patent Document 1 proposes a structure in which an electrode water-repellent layer is provided in the electrode catalyst layer for the purpose of keeping the humidity environment of the electrode catalyst layer in contact with both sides of the electrolyte membrane constant. According to this configuration, the water generated in the electrode catalyst layer (GDL side) or the water condensed from the humidified gas is blocked by the electrode water repellent layer and does not enter the electrode catalyst layer (membrane side). The humidity environment of the cell is kept constant without depending on the operating conditions and the generated voltage characteristics of the cell are stabilized.

  In Patent Document 2 and Patent Document 3, a pore having a large diameter is formed in the electrode catalyst layer on both sides of the electrolyte membrane by a pore forming agent, and a water retention layer is provided between the electrode catalyst layer and the gas diffusion layer. , Improve drainage and water retention in the electrode catalyst layer. Thereby, the progress of carbon corrosion and the flooding phenomenon can be prevented.

  Patent Document 2 and Patent Document 3 are not intended to prevent the polymer electrolyte from directly drying, but are intended to temporarily keep water in the water retaining layer in order to discharge water.

  In Patent Document 4, production of a membrane-electrode assembly having an electrode catalyst layer on both sides of a solid polymer electrolyte membrane and a hydrophilic layer on the outside thereof as disclosed in Patent Document 2 and Patent Document 3 Although a method is disclosed, an object of the present invention is to reduce resistance overvoltage by improving adhesion between an electrode catalyst layer and a diffusion electrode.

In Patent Document 5 and Patent Document 6, the porosity on the electrolyte membrane side is reduced by decreasing the ratio of the electrolyte in the electrode catalyst layer provided on both sides of the polymer electrolyte membrane from the membrane toward the diffusion electrode. A structure for improving hydrophilicity and a method for producing the structure are disclosed. This improves proton conductivity from the membrane to the three-phase interface and reduces resistance overvoltage. In addition, the gas diffusibility is increased by increasing the porosity on the gas diffusion layer side. Both proton conductivity and gas diffusivity can be achieved.
JP 2000-251901 A JP 2004-158387 A JP 2004-158388 A JP 2004-221056 A JP 2002-299960 A Japanese Patent Laid-Open No. 8-88008

  Patent Document 1 proposes a structure in which an electrode water repellent layer is provided in an electrode catalyst layer in contact with both sides of an electrolyte membrane. However, in high humidification and high current operation, there is a problem that gas accumulation is inhibited by the accumulation of water in the electrode catalyst layer outside the electrode water repellent layer, and a flooding phenomenon occurs.

  In Patent Document 2 and Patent Document 3, since the water retention layer is provided between the electrode catalyst layer and the gas diffusion layer on both sides of the electrolyte membrane, the water retention layer is used in high humidification and high current operation. The stored water clogs the gas diffusion path, obstructs gas diffusion from the water retention layer to the electrode catalyst layer on the membrane side, and causes a flooding phenomenon.

  In addition, since the water retention layer is not in contact with the solid polymer electrolyte membrane, there is a problem that the membrane resistance value increases due to the drying of the membrane and the cell voltage decreases under low humidification operation conditions.

  In Patent Document 4, production of a membrane-electrode assembly having an electrode catalyst layer on both sides of a solid polymer electrolyte membrane and a hydrophilic layer on the outside thereof as disclosed in Patent Document 2 and Patent Document 3 A method is disclosed. However, since the present invention aims to reduce the resistance overvoltage by improving the adhesion between the electrode catalyst layer and the diffusion electrode, the water stored in the hydrophilic layer in the high humidification and high current operation causes the gas diffusion path. There is a problem that gas diffusion to the electrode catalyst layer on the membrane side from the hydrophilic layer is hindered and a flooding phenomenon occurs. Further, since the hydrophilic layer is not in contact with the solid polymer electrolyte membrane, the problem that the membrane resistance value increases due to the drying of the membrane and the cell voltage decreases under low humidification conditions has not been improved.

  In Patent Document 5 and Patent Document 6, the porosity on the electrolyte membrane side is reduced by decreasing the ratio of the electrolyte in the electrode catalyst layer provided on both sides of the polymer electrolyte membrane from the membrane toward the diffusion electrode. A structure for improving hydrophilicity and a method for producing the structure are disclosed. However, since water generated during high humidification and high current operation is stored in the electrode catalyst layer, gas diffusion to the nearby catalyst is hindered, resulting in a problem that the utilization rate of the catalyst is lowered and the performance is lowered. .

  Therefore, the present invention provides a hydrophilic layer between the polymer electrolyte membrane and the electrocatalyst layer in order to solve the above problems, thereby providing stable battery performance in a wide humidity range and a wide operation (current density) range. It is an object of the present invention to provide a polymer fuel cell that can be used, for example, a solid polymer fuel cell.

  Thus, as a result of intensive studies by the present inventors to solve the above problems, the objective of comprehensive water management has been achieved by the following means.

That is, in a membrane-electrode assembly of a polymer electrolyte fuel cell comprising a pair of electrode catalyst layers between a pair of gas diffusion layers and a solid polymer membrane between the electrode catalyst layers,
It is an object of the present invention to provide a membrane-electrode assembly for a polymer fuel cell, wherein a hydrophilic layer is provided between the solid polymer membrane and the electrode catalyst layer.

  The polymer fuel cell having the membrane-electrode assembly improves the drainage of the water produced in the electrode catalyst layer by moving the water produced in the electrode catalyst layer to the hydrophilic layer, and the solid electrolyte membrane. It has become possible to provide a polymer fuel cell that improves moisture retention and can exhibit stable battery performance in a wide humidity range and a wide operation (current density) range.

  The membrane-electrode assembly of a polymer fuel cell according to the present invention is a polymer fuel cell comprising a pair of electrode catalyst layers between a pair of gas diffusion layers and a solid polymer membrane between the electrode catalyst layers. In the membrane-electrode assembly, a hydrophilic layer is provided between the solid polymer membrane and the electrode catalyst layer, and the solid polymer fuel cell of the present invention will be described with reference to FIG. .

  The anode side hydrophilic layer 16 and the cathode side hydrophilic layer 17, the anode side electrode catalyst layer 2 and the cathode side electrode catalyst layer 5, the fuel gas diffusion layer 3 and the oxidation are directed outward from the solid polymer membrane 1 at the center. The agent gas diffusion layer 6, the anode side separator 9, and the cathode side separator 11 are disposed.

  The anode side separator 9 and the cathode side separator 11 are provided with gas flow paths 8 and 10 for supplying a fuel gas containing hydrogen to the anode side and an oxidizing gas containing oxygen to the cathode side.

  By providing a hydrophilic layer between the electrode catalyst layer and the solid electrolyte membrane, the generated water generated in the electrode catalyst layer moves to the hydrophilic layer, and the pores in the electrode catalyst layer are blocked by the generated water. Gas diffusion is not hindered. In addition, even a small amount of generated water is effectively collected in the hydrophilic layer provided on both sides of the membrane, so that the membrane is wet even under low humidification conditions, and the cell voltage can be kept high.

More specifically, the proton H ⁺ generated on the anode side moves to the cathode side through the ion conduction path with clustered water molecules, so that the amount of water on the anode side decreases locally. However, by providing a hydrophilic layer between the electrode catalyst layer and the polymer electrolyte membrane, gaseous water molecules in the fuel gas containing hydrogen supplied to the electrode catalyst layer enter the electrode catalyst layer and the hydrophilic layer. When coming, it liquefies by contact. Then, the liquefied water moves to a portion where it is locally reduced due to the water concentration gradient, so that drying of the membrane can be prevented.

  In addition, even when the amount of liquefied water on the anode side becomes excessive and when the amount of water generated on the cathode side becomes excessive, both electrode catalyst layers are in contact with the hydrophilic layer. Therefore, excess water molecules can be absorbed. As a result, the pores in the electrode catalyst layer are not blocked by the generated water, so that the diffusion of gas is not hindered, so that the flooding phenomenon can be prevented and an appropriate amount of water can be managed.

  That is, by providing a hydrophilic layer between the polymer electrolyte membrane and the electrode catalyst layer, in a low humidified state (relative humidity around 40 RT%), the cell resistance value is decreased, energy efficiency is increased, and reaction is improved. Under a high current density (or a highly humidified state) where a lot of produced water is present, the coexistence of the role of suppressing the flooding phenomenon can be achieved.

  Furthermore, when a large amount of water is present in the electrode catalyst layer, the probability that a metal such as platinum as a catalyst for reducing hydrogen reacts with water molecules is increased. As a result, when the water molecule reacts with a metal such as platinum, the efficiency of the catalyst is lowered, and the power generation efficiency can also be lowered. However, by disposing the hydrophilic layer in contact with the electrode catalyst layer, excess water molecules can be absorbed by the hydrophilic layer, so that the probability of reducing the efficiency of the catalyst is considered to be greatly reduced.

  As the catalyst component used in the electrode catalyst layer according to the present invention, the cathode catalyst layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Further, the catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, etc., and alloys thereof. Is done. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like.

  The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as a cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 It is preferable to set it to -70 atomic%. In general, an alloy is a generic term for an element obtained by adding one or more metal elements or non-metal elements to a metal element and having metallic properties.

  The alloy structure consists of a eutectic alloy, which is a mixture of component elements that form separate crystals, a component element that completely dissolves into a solid solution, and a component element that is an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the cathode catalyst layer and the catalyst component used for the anode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the cathode catalyst layer and the anode catalyst layer have the same definition for both, and are collectively referred to as “catalyst components”. However, the catalyst components for the cathode catalyst layer and the anode catalyst layer do not have to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle size of the catalyst particles used for the electrode catalyst, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but in practice the average particle size is too small On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle diameter of the catalyst particles contained in the electrode catalyst is preferably 1 to 30 nm, more preferably 1.5 to 20 nm, even more preferably 2 to 10 nm, and particularly preferably 2 to 5 nm. It is preferably 1 nm or more from the viewpoint of easy loading, and preferably 30 nm or less from the viewpoint of catalyst utilization. The “average particle diameter of the catalyst particles” in the present invention is the average value of the particle diameter of the catalyst component determined from the crystallite diameter or transmission electron microscope image obtained from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction. Can be measured.

  The electrode catalyst used in the catalyst layer according to the present invention is formed by supporting a catalyst component on a conductive material.

  The conductive material may be any material having a specific surface area for supporting the catalyst particles in a desired dispersed state and sufficient electronic conductivity as a current collector. The main component is carbon. Preferably there is. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

The BET specific surface area of the conductive material may be a specific surface area sufficient to support the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. Is good. If the specific surface area is less than 20 m ² / g, the dispersibility of the catalyst component and the polymer electrolyte in the conductive material may be reduced, and sufficient power generation performance may not be obtained, and the specific surface area exceeds 1600 m ² / g. In addition, the effective utilization rate of the catalyst component and the polymer electrolyte may decrease instead.

  In addition, the size of the conductive material is not particularly limited, but from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average particle size is 5 to 200 nm. The thickness is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive material, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to the total amount of the electrode catalyst. Good. When the loading amount exceeds 80% by mass, the degree of dispersion of the catalyst component on the conductive material is lowered, and although the loading amount is increased, the improvement in power generation performance is small and the economic advantage may be lowered. On the other hand, if the loading amount is less than 10% by mass, the catalytic activity per unit mass is lowered, and a large amount of electrode catalyst is required to obtain the desired power generation performance, which is not preferable. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The ion conductive polymer in the electrode catalyst layer according to the present invention is not particularly limited, and known ones can be used, but the same materials as those used for the solid polymer electrolyte can be used, and at least high ion conductivity can be used. Any material that has The cathode catalyst layer / anode catalyst layer (hereinafter also simply referred to as “catalyst layer”) of the present invention contains a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte that contains fluorine atoms in the whole or part of the polymer skeleton and a hydrocarbon-based electrolyte that does not contain fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene A preferred example is a fluoride-perfluorocarbon sulfonic acid polymer.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A sulfonic acid etc. are mentioned as a suitable example.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  The catalyst component can be supported on the conductive material by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

  The polymer electrolyte membrane used in the polymer electrolyte membrane and the electrode layer may be different, but it is preferable to use the same polymer polymer considering the contact resistance between the membrane and the electrode.

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that serves as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained. Although content of the said solid polymer electrolyte contained in an electrode is not specifically limited, It is good to set it as 20-60 mass% with respect to the whole quantity of a catalyst particle.

  In a preferred embodiment of the present invention, the difference between the components of the electrode catalyst layer and the hydrophilic layer is that the catalyst particles are supported on the conductive material. Therefore, the hydrophilic layer is replaced with the polymer electrolyte and the electrode catalyst. By providing it between the layers, the three-phase interface increases and the platinum utilization rate becomes very high. As a result, it contributes to the mass production of fuel cells.

  The polymer electrolyte membrane used for the membrane-electrode assembly of the present invention is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the electrode catalyst layer. In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Liquids such as polymer electrolyte membranes and polymer microporous membranes that are generally available on the market, such as fluoropolymer electrolytes such as resin membranes based on styrene, and hydrocarbon resin membranes with sulfonic acid groups A membrane impregnated with an electrolyte or a membrane in which a porous body is filled with a polymer electrolyte may be used. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 100 μm. From the viewpoint of strength during film formation and durability during MEA operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during MEA operation, it is preferably 300 μm or less.

  The polymer electrolyte membrane includes polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) in addition to the above-described fluorine-based polymer electrolyte and membranes made of hydrocarbon resins having sulfonic acid groups. For example, a porous thin film formed from a material impregnated with an electrolyte component such as phosphoric acid or ionic liquid may be used.

  The electronic conductive material that does not carry the catalyst component used in the hydrophilic layer according to the present invention is sufficient if it has sufficient electronic conductivity as a current collector, and the main component is preferably carbon. Specifically, carbon particles such as carbon nanofibers, carbon nanotubes, carbon nanohorns, carbon nanocoils, etc .; carbon particles such as ketjen black, channel black, furnace black, thermal black, etc., activated carbon, coke, etc. Can be mentioned. These may be used alone or in combination of two or more. In addition, since the carbon particles are excellent in corrosion resistance and water repellency, graphitized particles are preferably used.

  The ion conductive polymer used for the hydrophilic layer according to the present invention is not particularly limited, and examples thereof include materials similar to those used for the solid polymer electrolyte, and any material having at least high ion conductivity may be used. .

  As a material used for the gas diffusion layer (hereinafter referred to as GDL) according to the present invention, a sheet-like material made of carbon paper, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Further, if the GDL has an excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper, and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL.

  In addition, carbon particles and a binder may be disposed on a sheet-like GDL made of carbon paper, nonwoven fabric, carbon fabric, paper-like paper body, felt, etc., and both may be used as a gas diffusion layer. You may use the film itself which consists of particle | grains and a binder as a gas diffusion layer. As a result, since the water repellent material and the carbon particles are uniformly formed on the film itself, the water repellent efficiency is increased as compared with the above application.

Examples of the water repellent material include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, polyethylene, and the like. Is mentioned. Of these, fluororesins are preferred because they are excellent in water repellency and corrosion resistance during electrode reaction.
Incidentally, the “binder” refers to a substance having a role of adhesion, and in the examples according to the present invention, a fluororesin having both a role of a binder and a role of water repellency is used, but it is not necessarily limited thereto. Alternatively, the binder and the water repellent material may be mixed and used as independent substances.

  From the above, a hydrophilic layer is provided between the polymer electrolyte membrane and the electrode catalyst layer, but when water is excessively present in the hydrophilic layer, the water generated in the electrode catalyst layer is caused by capillary force, Easily drained into GDL.

  The anode-side electrode catalyst layer and the cathode-side electrode catalyst layer according to the present invention include a catalyst component, an electronically conductive material, an ion conductive polymer, and, if necessary, a water-repellent material. The hydrophilic layer according to the present invention includes a catalyst component. Includes unsupported electronically conductive materials and ionically conductive polymers.

  Since the electrode catalyst layer contains a water repellent material, the electrode catalyst layer has water repellency, so that the generated water generated in the electrode catalyst layer is more easily discharged to the hydrophilic layer, and the membrane with low humidification. Is suppressed, and the cell voltage can be kept high.

  For the reasons described above, the hydrophilic layer is composed of an electron conductive material and an ion conductive polymer that do not carry a catalyst component, and does not contain a catalyst. The utilization rate will not decrease.

  The thickness of the hydrophilic layer may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 50 μm, more preferably 10 to 20 μm. If the thickness of the hydrophilic layer is less than 5 μm, the strength is weak and the water absorption is not sufficient. On the other hand, if it exceeds 50 μm, the cell resistance value increases and the energy efficiency decreases.

  Similarly, the porosity in the hydrophilic layer may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 30 to 70%, more preferably 40 to 60%.

  The proportion of the ion conductive polymer in the hydrophilic layer is 30 to 70% by mass, more preferably 40 to 60% by mass, based on the total mass of the material constituting the hydrophilic layer, and the catalyst component in the hydrophilic layer. Similarly, the proportion of the electronic conductive material that does not carry slag may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 20 to 60% with respect to the total mass of the material constituting the hydrophilic layer. More preferably, it is 30 to 50%.

  5-50 mass% is preferable with respect to the total mass of the material which comprises all the electrode catalyst layers, and, as for content of the water repellent material contained in the said electrode catalyst layer, More preferably, it is 10-30 mass%. If the content of the water repellent material is less than 5%, the water repellency of the electrode catalyst layer is not sufficient, and if it exceeds 50%, the strength of the electrode catalyst layer is not sufficient, so a catalyst coated electrolyte membrane (CCM: Catalyst coated membrane) is high. The assembly of the molecular electrolyte membrane and the electrode catalyst layer) cannot be produced.

  The porosity of the electrode catalyst layer is preferably 30 to 70%, more preferably 40 to 60%. If the porosity is less than 30%, gas diffusion is not sufficient, and the cell voltage in the high current region decreases. On the other hand, when the porosity exceeds 70%, the strength of the electrode catalyst layer is not sufficient, and the porosity decreases in the transfer process.

  The porosity of the electrode catalyst layer according to the present invention is preferably larger than the porosity of the hydrophilic layer.

  This is because if the porosity of the electrode catalyst layer is larger than the porosity of the hydrophilic layer, gas diffusion in the catalyst layer is good. Specifically, the porosity of the hydrophilic layer is preferably 30% to 70%, more preferably 40% to 60%.

  The difference between the porosity of the electrode catalyst layer and the porosity of the hydrophilic layer is 0% to 40%, more preferably 0% to 20%.

  The proportion of the ion conductive polymer contained in the hydrophilic layer according to the present invention is preferably larger than the proportion of the ion conductive polymer contained in the electrode catalyst layer.

  If the proportion of the ion conductive polymer contained in the hydrophilic layer is larger than the proportion of the ion conductive polymer contained in the electrode catalyst layer, the proton conduction path to and from the membrane is sufficiently secured. is there. Specifically, the ratio of the ion conductive polymer contained in the hydrophilic layer is 30% by mass (this mass% is a provisional unit) to 70% by mass with respect to the total mass of the material constituting the hydrophilic layer. The ratio of the ion conductive polymer contained in the electrode catalyst layer is preferably 40% by mass to 60% by mass with respect to the total mass of the material constituting the electrode catalyst layer.

  The difference between the ion conductive polymer contained in the hydrophilic layer and the ion conductive polymer contained in the electrode catalyst layer is 0% by mass to 40% by mass, more preferably 0% by mass to 20% by mass. preferable.

  In the present invention, a membrane-electrode assembly (MEA) can be produced by a method similar to a conventionally known method except that a hydrophilic layer is provided between the electrode catalyst layer and the polymer electrolyte membrane. For example, the prepared catalyst ink and the hydrophilic layer ink are applied and dried on a transfer mount with a desired thickness to form the cathode-side and anode-side electrode catalyst layers and the hydrophilic layer, respectively. The polymer electrolyte membrane is sandwiched between the electrode catalyst layer and the hydrophilic layer so that the hydrophilic layer is on the inside and bonded by hot pressing or the like, and then the transfer mount is peeled off to obtain the MEA.

  In the catalyst ink of the present invention, the electrode catalyst may be used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the oxidation reaction of hydrogen (anode side) and the reduction reaction of oxygen (cathode side). , May be used. It is preferable that the electrode catalyst is present in the catalyst ink in an amount of 10 to 70% by mass, more preferably 20 to 60% by mass.

  The catalyst ink of the present invention may contain a water-repellent polymer such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer in addition to the electrode catalyst, the electrolyte, and the solvent. . Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged. The amount of the water-repellent polymer added when the water-repellent polymer is used is not particularly limited as long as it is an amount that does not hinder the above-described effects of the present invention. ˜20 mass%.

  Instead of the water repellent polymer or in addition to the water repellent polymer, the hydrophilic ink and the catalyst ink of the present invention may contain a thickener. The use of a thickener is effective when the catalyst ink or the like cannot be applied well on the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, (EG (ethylene glycol), PVA (polyvinyl alcohol)), and the like. The amount of the thickener added when the thickener is used is not particularly limited as long as it does not interfere with the above effect of the present invention. However, the total amount of the hydrophilic ink or the total amount of the hydrophilic ink is not limited. Preferably it is 5-10 mass% with respect to the mass.

  The preparation method of the catalyst ink of the present invention is not particularly limited as long as the electrode catalyst, the electrolyte and the solvent, and if necessary, the water-repellent polymer and / or the thickener are appropriately mixed. The method for preparing the hydrophilic ink is not particularly limited as long as an electrolyte, a solvent, and, if necessary, a thickener are appropriately mixed. When the electrolyte is in a solid state or contains a polar solvent according to the present invention, a predetermined amount of each of the electrode catalyst, the electrolyte and the solvent is mixed. For example, the electrolyte is added to the polar solvent, and the mixture is heated and heated. The catalyst ink can be prepared by stirring and dissolving the electrolyte in a polar solvent and then adding an electrode catalyst thereto. Similarly, a hydrophilic ink can be prepared by adding an electrolyte to a polar solvent, heating and stirring the mixed solution, dissolving the electrolyte in the polar solvent, and then adding it to a conductive material not carrying a catalyst. .

  Furthermore, the solvent constituting the catalyst ink and the hydrophilic ink used in the present invention is not particularly limited, and ordinary solvents used for forming the hydrophilic layer and the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used.

The amount of the solvent used in the present invention is not particularly limited as long as the electrolyte can be completely dissolved, but the electrolyte is preferably in the solvent at a concentration of 5 to 25% by mass, more preferably 5 to 10% by mass. It is the quantity which becomes. At this time, if the concentration of the electrolyte exceeds 25% by mass, a part of the colloid may be formed without completely dissolving the electrolyte. Conversely, if the concentration of the electrolyte is less than 5% by mass, the contained electric field mass If the amount is too small, the molecular chains of the electrolyte polymer are not well entangled and the mechanical strength of the formed electrocatalyst layer and hydrophilic layer may be inferior. In the catalyst ink, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 5 to 35% by mass, more preferably about 5 to 15% by mass in the catalyst ink.
Similarly, in the hydrophilic ink, the solid content concentration of the electrode catalyst, the solid polymer electrolyte, and the like is 5 to 30% by mass, more preferably about 5 to 15% by mass in the hydrophilic ink. .

  The catalyst ink and the hydrophilic ink of the present invention may be used for only one or both of the cathode side electrode catalyst layer and the anode side electrode catalyst layer. In response to changes in the amount of water, the porous structure of the electrode catalyst layer and the hydrophilic layer in the initial state collapses, the porosity decreases, and the amount of reactant gas supplied to the electrode catalyst layer and the hydrophilic layer decreases. Because of the high risk, it is preferably used at least for the cathode-side electrode catalyst layer, and particularly preferably used for the electrode catalyst layer on both the cathode and anode sides.

  Hereinafter, the preferable aspect of the manufacturing method of MEA of this invention is demonstrated. In addition, the following aspects show the preferable aspect of this invention, and the manufacturing method of MEA of this invention is not limited to the following method.

First, the catalyst ink of the present invention is applied and dried on a transfer mount to form an electrode catalyst layer.
Next, a hydrophilic ink is applied and dried thereon to form a hydrophilic layer.

  In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst ink and hydrophilic ink (especially conductive material such as carbon in the ink) to be used. In the above step, the thickness of the electrode catalyst layer and the hydrophilic ink is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). The same thickness as before can be used. Specifically, the electrode catalyst layer has a thickness of 5 to 50 μm, more preferably 5 to 10 μm, and the hydrophilic layer has a thickness of 5 to 50 μm, more preferably 10 to 20 μm.

  The method for applying the catalyst ink and the hydrophilic ink onto the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. Also, the drying conditions of the applied electrode catalyst layer and hydrophilic layer are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer and hydrophilic layer. Specifically, the catalyst ink coating layer (electrode catalyst layer) and the hydrophilic ink coating layer (hydrophilic layer) are placed in a vacuum dryer at room temperature to 100 ° C., more preferably 50 to 80 ° C., 30 to 30 ° C. Dry for 60 minutes. At this time, if the thickness of the catalyst layer or the hydrophilic layer is not sufficient, the coating / drying process is repeated until a desired thickness is obtained. Next, after sandwiching the solid polymer electrolyte membrane with the hydrophilic layer thus prepared, hot pressing is performed on the laminate. In this case, the hot press conditions are not particularly limited as long as the electrode catalyst layer, the hydrophilic layer, and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 100 to 200 ° C, more preferably 110 to 170 ° C. It is preferable to carry out with the press pressure of 1-5 Mpa with respect to an electrode surface. Thereby, the joining property with the solid polymer electrolyte membrane, the hydrophilic layer and the electrode catalyst layer can be enhanced.

  After performing the hot press, the MEA including the electrode catalyst layer, the hydrophilic layer, and the solid polymer electrolyte membrane can be obtained by peeling off the transfer mount. As will be described in detail below, the MEA according to the present invention generally further includes a gas diffusion layer. At this time, the gas diffusion layer is obtained by peeling off the transfer mount in the above method. It is preferable that the joined body is further sandwiched between gas diffusion layers to further join each electrode catalyst layer after joining the electrode catalyst layer, the hydrophilic layer, and the solid polymer electrolyte membrane. Alternatively, a hydrophilic layer and an electrode catalyst layer are previously formed on the surface of the gas diffusion layer to produce a hydrophilic layer-electrode catalyst layer-gas diffusion layer assembly, and then the hydrophilic layer is formed in the same manner as described above. It is also preferable to sandwich and join the solid polymer electrolyte membrane by hot pressing with the electrode catalyst layer-gas diffusion layer assembly.

  In addition to the above hot pressing method, a method of laminating an electrode catalyst layer-hydrophilic layer-polymer electrolyte membrane-hydrophilic layer-electrode catalyst layer-gas diffusion layer on the gas diffusion layer by sequential application may be used. good.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be used as appropriate. Generally, the fuel cell has a structure in which an MEA is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. The thickness of the gas seal portion may be 2 mm to 50 μm, preferably about 1 mm to 100 μm.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. Further, in the examples, unless otherwise specified, “%” represents a mass percentage.

<Example 1>
1) Production of CCM A hydrophilic layer and a catalyst layer were formed on both sides of the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. Carbon black (Vulcan XC-72R) particles manufactured by Cabot Co. were used for the hydrophilic layer. A hydrophilic layer ink was prepared by mixing 1400 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA, and 50 g of carbon black particles, and stirring and mixing them using a rotary homogenizer. The prepared hydrophilic layer ink was weighed and mixed so that the mass ratio of ion conductive polymer / carbon black particles was 1.4: 1.0.

  As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. In addition, fluorinated pitch (Osaka Gas fine particle type) was used as the water repellent material. A catalyst ink was prepared by mixing 1100 g of a 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 5 g of fluoride pitch, 100 g of IPA and 100 g of a Pt-supported carbon catalyst, and stirring and mixing them using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 1.1: 0.1: 1.0.

First, the catalyst ink was printed on the PTFE sheet by screen printing so that the amount of Pt supported was 0.4 mg / cm ² . Subsequently, the hydrophilic layer ink was printed on the PTFE sheet coated with the catalyst ink by screen printing so that the amount of carbon black supported was 0.3 mg / cm ² .

Two PTFE sheets were used, and both sides of the Nafion film were sandwiched so that the printed layer of the PTFE sheet was in contact with the Nafion film, and then the Nafion film was applied by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). To produce a CCM (Catalyst coated membrane).

2) Water repellent treatment of carbon paper Toray carbon paper TPG-H-090 was immersed in a PTFE-based dispersion (neoflon) manufactured by Daikin Industries diluted with pure water so as to have a predetermined concentration and then dried.

3) Production of GDL (microporous layer) Filter paper with a smooth surface obtained by wet dispersion of Cabot carbon black (Vulcan XC-72R) particles and Daikin Industries PTFE dispersion (neoflon). After coating on the top and dewatering by suction, it was transferred onto a water-repellent carbon paper by hot pressing and dried at room temperature, followed by heat treatment at 340 ° C. for 15 minutes.

4) Measurement of IV characteristics of MEA Using CCM and GDL produced as described above, the cell voltage characteristics measurement jig was assembled, and anode / cathode = hydrogen / air, cell temperature 70 ° C., anode relative humidity 100RH%, cathode relative The current-voltage characteristics were measured under the conditions of humidity 40RH% and 100RH% (FIG. 3). In addition, the cell resistance value at a cathode relative humidity of 40 RH% and a current density of 0.4 A / cm ² was measured.

5) Measurement of porosity and pore diameter The pore diameters of the hydrophilic layer and the catalyst layer were measured using a mercury porosimeter. Moreover, the porosity was calculated from the value of the calculated layer thickness and the density of the material used by observing the cross section of the catalyst layer using CCM.

  FIG. 3 shows the IV characteristic measurement results of the MEA produced in this way.

Table 2 summarizes the cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

<Example 2>
A hydrophilic layer and a catalyst layer were formed on both sides of the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. Carbon black (Vulcan XC-72R) particles manufactured by Cabot Co. were used for the hydrophilic layer. A hydrophilic layer ink was prepared by mixing 1400 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA, and 50 g of carbon black particles, and stirring and mixing them using a rotary homogenizer. The prepared hydrophilic layer ink was weighed and mixed so that the mass ratio of ion conductive polymer / carbon black particles was 1.4: 1.0.

  As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. In addition, fluorinated pitch (Osaka Gas Fine Particle Type) was used as the water repellent material. A catalyst ink was prepared by mixing 1100 g of a 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 20 g of fluoride pitch, 100 g of IPA and 100 g of a Pt-supported carbon catalyst, and stirring and mixing them using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 1.1: 0.4: 1.0.

First, the catalyst ink was printed on the PTFE sheet by screen printing so that the amount of Pt supported was 0.4 mg / cm ² . Subsequently, the hydrophilic layer ink was printed on the PTFE sheet coated with the catalyst ink by screen printing so that the amount of carbon black supported was 0.3 mg / cm ² .

Two PTFE sheets were used, and both sides of the Nafion film were sandwiched so that the printed layer of the PTFE sheet was in contact with the Nafion film, and then the Nafion film was applied by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). To produce a CCM (Catalyst coated membrane).

  Except for the above, an MEA was produced in the same steps as in Example 1.

  FIG. 4 shows the IV characteristic measurement results of the MEA produced in this way.

Table 2 summarizes cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

<Example 3>
A hydrophilic layer and a catalyst layer were formed on both sides of the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. Carbon black (Vulcan XC-72R) particles manufactured by Cabot Co. were used for the hydrophilic layer. A hydrophilic layer ink was prepared by mixing 1100 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA and 50 g of carbon black particles, and stirring and mixing them using a rotary homogenizer. The prepared hydrophilic layer ink was weighed and mixed so that the mass ratio of ion conductive polymer / carbon black particles was 1.1: 1.0.

  As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. As the water repellent material, fluorinated pitch (Osaka Gas fine particle type) was used. 2200 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 5 g of fluoride pitch, 100 g of IPA and 100 g of Pt-supported carbon catalyst were mixed, and a catalyst ink was prepared by stirring and mixing using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 2.2: 0.1: 1.0.

First, the catalyst ink was printed on the PTFE sheet by screen printing so that the amount of Pt supported was 0.4 mg / cm ² . Subsequently, the hydrophilic layer ink was printed on the PTFE sheet coated with the catalyst ink by screen printing so that the amount of carbon black supported was 0.3 mg / cm ² .

Two PTFE sheets were used, and both sides of the Nafion film were sandwiched so that the printed layer of the PTFE sheet was in contact with the Nafion film, and then the Nafion film was applied by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). To produce a CCM (Catalyst coated membrane).

  Except for the above, an MEA was produced in the same steps as in Example 1.

  FIG. 5 shows the IV characteristic measurement results of the MEA produced in this way.

Table 2 summarizes cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

<Example 4>
A hydrophilic layer and a catalyst layer were formed on both sides of the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. Carbon black (Vulcan XC-72R) particles manufactured by Cabot Co. were used for the hydrophilic layer. A hydrophilic layer ink was prepared by mixing 1400 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA, and 50 g of carbon black particles, and stirring and mixing them using a rotary homogenizer. The prepared hydrophilic layer ink was weighed and mixed so that the mass ratio of ion conductive polymer / carbon black particles was 1.4: 1.0.

  As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. A catalyst ink was prepared by mixing 1100 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 0 g of fluorinated pitch, 100 g of IPA and 100 g of Pt-supported carbon catalyst, and stirring and mixing them using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 1.1: 0.0: 1.0.

First, the catalyst ink was printed on the PTFE sheet by screen printing so that the amount of Pt supported was 0.4 mg / cm ² . Subsequently, the hydrophilic layer ink was printed on the PTFE sheet coated with the catalyst ink by screen printing so that the amount of carbon black supported was 0.3 mg / cm ² .

Two PTFE sheets were used, and both sides of the Nafion film were sandwiched so that the printed layer of the PTFE sheet was in contact with the Nafion film, and then the Nafion film was applied by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). To produce a CCM (Catalyst coated membrane).

  Except for the above, an MEA was produced in the same steps as in Example 1.

  FIG. 6 shows the IV characteristic measurement results of the MEA produced in this way.

Table 2 summarizes cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

<Comparative Example 1>
A catalyst layer was formed on both sides of the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. A catalyst ink was prepared by mixing 1100 g of a 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA, and 100 g of a Pt-supported carbon catalyst, and stirring and mixing them using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 1.1: 1.0. Subsequently, this ink was printed on the PTFE sheet by screen printing so that the amount of Pt supported was 0.4 mg / cm ² . Using two PTFE sheets, both sides of the Nafion film were sandwiched so that the electrode printing layer of the PTFE sheet was in contact with the Nafion film, and then Nafion was performed by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). CCM (Catalyst coated membrane) was produced by transferring to a membrane.

  Except for the above, an MEA was produced in the same steps as in Example 1.

  FIG. 7 shows the IV characteristic measurement result of the MEA produced in this way.

Table 2 summarizes the cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

<Comparative example 2>
Electrode catalyst layers were formed on both sides of the polymer electrolyte membrane, and then hydrophilic layers were formed on both sides of the electrode catalyst layer sandwiching the polymer electrolyte membrane. As the polymer electrolyte membrane, a Nafion 111 membrane manufactured by DuPont USA was used. Carbon black (Vulcan XC-72R) particles manufactured by Cabot Co. were used for the hydrophilic layer. A hydrophilic layer ink was prepared by mixing 1400 g of 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 100 g of IPA, and 50 g of carbon black particles, and stirring and mixing them using a rotary homogenizer. The prepared hydrophilic layer ink was weighed and mixed so that the mass ratio of ion conductive polymer / carbon black particles was 1.4: 1.0.

  As the catalyst, a 50% supported Pt-supported carbon catalyst (TEC10E50E) was used. In addition, fluorinated pitch (Osaka Gas fine particle type) was used as the water repellent material. A catalyst ink was prepared by mixing 1100 g of a 5% Nafion solution manufactured by Aldrich, 250 g of ultrapure water, 5 g of fluoride pitch, 100 g of IPA and 100 g of a Pt-supported carbon catalyst, and stirring and mixing them using a rotary homogenizer. The produced catalyst ink was weighed and mixed so that the mass ratio of ion conductive polymer / fluorinated pitch / carbon black particles was 1.1: 0.1: 1.0.

First, the hydrophilic layer ink was printed on the PTFE sheet by screen printing so that the amount of carbon black supported was 0.3 mg / cm ² . Next, the catalyst ink was printed on the PTFE sheet coated with the catalyst ink by screen printing so that the amount of Pt supported was 0.4 mg / cm ² on the PTFE sheet.

Two PTFE sheets were used, and both sides of the Nafion film were sandwiched so that the printed layer of the PTFE sheet was in contact with the Nafion film, and then the Nafion film was applied by hot pressing (150 ° C., 20 kgf / cm ² , 5 minutes). To produce a CCM (Catalyst coated membrane).

  Except for the above, an MEA was produced in the same steps as in Example 1.

  FIG. 8 shows the IV characteristic measurement results of the MEA produced in this way.

Table 2 summarizes cell resistance values measured in a low humidification (RH 40%) and low current density region (0.4 A / cm ² ).

  Table 1 summarizes the porosity and pore diameter of the hydrophilic layer and the catalyst layer.

  Comparing FIGS. 3 to 6 and FIG. 7, the polymer fuel cell according to the present invention provided with the hydrophilic layer is superior in energy efficiency because the cell resistance value is lower in Table 2 than the conventional fuel cell. Yes. 3, 4, 6 and 7 are compared, the conventional fuel cell in which the limiting current density is shown in FIG. 1 at both a relative humidity of 40 RT% and a relative humidity of 100 RT% at a high current density. Greater than.

  Comparing FIG. 5 and FIG. 7, the limiting current density is the same as that of the conventional fuel cell at the relative humidity of 100 RT%, but the cell resistance value is much lower in FIG. Yes.

  Further, comparing FIG. 3 to FIG. 6 with FIG. 8 which is a measurement result of the polymer type fuel cell in which the hydrophilic layer of the prior art is provided between the electrode catalyst layer and the GDL, the cell resistance values in Table 2 are as follows. Except for FIG. 5, the polymer type fuel cell in which the hydrophilic layer of the prior art is provided between the electrocatalyst layer and the GDL is lower, but the flood current phenomenon is prevented at a high current density because the limit current density is low. The effect which is the object of the present invention is not exhibited. On the other hand, in FIG. 5, the cell resistance value is lower than that of the prior art, although it is inferior to that of the prior art in terms of preventing flooding. The reason is as follows.

  As described in Table 1, the porosity of the electrode catalyst layer is half that of the hydrophilic layer. That is, since the porosity of the electrode catalyst layer is too low and the pore diameter is small, water generated in the electrode catalyst layer does not move to the hydrophilic layer by capillary force, and as a result, acts as a hydrophilic layer. It is considered that the flooding phenomenon was easily caused by the generated water. Further, it is considered that gas diffusion was not effectively performed due to the low porosity.

  Therefore, the decrease in the limit current density is considered to be the cause of the porosity and the pore diameter, not the position where the hydrophilic layer is provided.

  From the above, considering the balance between the cell resistance value and the limit current density, Examples 1 and 2 in which the porosity of the electrode catalyst layer in Table 1 is larger than the porosity of the hydrophilic layer are the most preferred embodiments. It can be said that there is.

It is a unit cell block diagram of the 1st example in the present invention. It is a conceptual diagram of a unit cell configuration of a conventional polymer fuel cell. It is a cell voltage characteristic of Example 1 of this invention. It is a cell voltage characteristic of Example 2 of this invention. It is a cell voltage characteristic of Example 3 of this invention. It is a cell voltage characteristic of Example 4 of this invention. It is a cell voltage characteristic of the comparative example 1. It is a cell voltage characteristic of the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2 Anode side electrode catalyst layer 3 Fuel gas diffusion layer 4 Anode side gas diffusion electrode 5 Cathode side electrode catalyst layer 6 Oxidant gas diffusion layer 7 Cathode side gas diffusion electrode 8 Gas flow path 9 Anode side separator 10 Gas Flow path 11 Cathode side separator 12 Unit cell 16 Anode side hydrophilic layer 17 Cathode side hydrophilic layer

Claims (8)

In a membrane-electrode assembly of a polymer fuel cell comprising a pair of electrode catalyst layers between a pair of gas diffusion layers and a solid polymer membrane between the electrode catalyst layers,
A membrane-electrode assembly comprising a hydrophilic layer between the polymer membrane and the electrode catalyst layer.   2. The membrane-electrode assembly of a polymer fuel cell according to claim 1, wherein the electrode catalyst layer includes a water repellent material, an ion conductive polymer, and an electronic conductive material carrying a catalyst component.   The membrane-electrode assembly of the polymer fuel cell according to claim 1 or 2, wherein the hydrophilic layer includes an electron conductive material that does not carry a catalyst component and an ion conductive polymer.   The content of the water-repellent material contained in the electrode catalyst layer is 5 to 50% by mass with respect to the total mass of materials constituting all electrode catalyst layers. A membrane-electrode assembly of a polymer fuel cell.   The membrane-electrode assembly for a polymer fuel cell according to claim 1, wherein the porosity of the electrode catalyst layer is 30 to 70%.   6. The membrane-electrode assembly for a polymer fuel cell according to claim 1, wherein the porosity of the electrode catalyst layer is larger than the porosity of the hydrophilic layer.   7. The polymer fuel cell membrane according to claim 3, wherein the proportion of the ion conductive polymer contained in the hydrophilic layer is larger than the proportion of the ion conductive polymer contained in the electrode catalyst layer. An electrode assembly.   A fuel cell comprising the membrane-electrode assembly according to claim 1.

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