JP2007165025A - Membrane electrode assembly - Google Patents

Abstract

The present invention reduces the temperature difference between a gas diffusion layer and an electrode catalyst layer by using a material having high thermal conductivity for the gas diffusion layer, and suppresses / prevents water from condensing in the gas diffusion layer. A membrane electrode assembly is provided.
In the membrane electrode assembly, comprising: an electrolyte membrane; a pair of electrode catalyst layers that sandwich the electrolyte membrane; and a pair of gas diffusion layers that sandwich the pair of electrode catalyst layers. The layer includes a water repellent layer including a water repellent material and a heat conductive material, and a gas diffusion base, and the water repellent layer is interposed between the electrode catalyst layer and the gas diffusion base. It is a membrane electrode assembly characterized by being arranged.
[Selection figure] None

Description

  The present invention relates to a membrane electrode assembly, particularly a membrane electrode assembly for a fuel cell, and more particularly to a membrane electrode assembly excellent in thermal conductivity, particularly an electrolyte membrane for a fuel cell.

  Currently, we are entering a period of exhaustion of fossil fuels, while the issue of global warming is becoming more serious. Under such circumstances, hydrogen is the most promising new energy source. However, since hydrogen cannot be converted into energy as it is, a new system for mediating hydrogen is required. A typical example is a fuel cell. Fuel cells generally include phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), polymer electrolyte fuel cells (PEFC), etc. Among them, polymer electrolyte fuel cells (PEFC) It can be started at room temperature, has few problems of electrolyte dissipation, and has advantages such as high current density. In PEFC, comprehensive water management, including water generated at the cathode and water moving through the membrane as the membrane is humidified, becomes extremely important for battery performance and lifetime.

  This is because a fuel cell generally uses hydrogen for the fuel electrode (anode electrode) and air or oxygen for the oxidant electrode (cathode electrode), and water is generated at the cathode electrode. In high humidification and high current density operation where liquid water is likely to be generated, the generated water of the cathode accumulates in the electrode layer, and is blocked by the generated water, so that the reactant is not sufficiently supplied to the electrode and the battery output decreases (flooding) Phenomenon). Therefore, in order to increase the output of the fuel cell, it is necessary to discharge water from the electrode catalyst layer.

  In general, in order to improve drainage, Patent Document 1 discloses a method in which a carbon water-repellent layer is provided on a gas diffusion substrate to which a hydrophobic polymer material is added in order to provide a further water-repellent effect. It has been. Further, in Patent Document 2, water repellent treatment and hydrophilic treatment are performed on the gas diffusion base material to control water discharge.

  However, although the drainage performance is improved in Patent Document 1, water generated by condensation of water vapor in the gas diffusion layer cannot be effectively drained, and as a result, it is difficult to suppress and prevent the flooding phenomenon. is there.

Further, in Patent Document 2, generated water is preferentially collected in the hydrophilic portion and drainage from the electrode is improved. However, water always exists in the portion, and once the water is accumulated, The gas passage is blocked, the effective gas passage area is reduced, and the gas is not sufficiently supplied to the electrodes.
JP 2003-89968 A Special table 2002-313200 gazette

  Therefore, in the present invention, there is provided a means for suppressing or preventing water condensation in the gas diffusion layer by eliminating the temperature difference between the gas diffusion layer and the electrode catalyst layer by using a material having high thermal conductivity for the gas diffusion layer. The purpose is to provide.

In order to achieve the above object, as a result of intensive research conducted by the present inventors, an electrolyte membrane, a pair of electrode catalyst layers that sandwich the electrolyte membrane, and a pair of gases that sandwich the pair of electrode catalyst layers In the membrane electrode assembly having a diffusion layer, the gas diffusion layer comprises a water repellent layer containing a water repellent material and a heat conductive material, a gas diffusion base material, and the water repellent layer comprises: It has been found that a membrane / electrode assembly, which is disposed between the electrode catalyst layer and the gas diffusion base material, achieves the above object, and has completed the present invention.

  In a fuel cell that generates heat in the electrode catalyst layer, a temperature gradient always occurs from the electrode catalyst layer to the gas flow path. According to the present invention, regarding the temperature in the gas diffusion layer, since the gas diffusion layer is composed of carbon particles having high thermal conductivity, the temperature drop in the gas diffusion layer is small. As a result, compared with the conventional gas diffusion layer, for the same current density, the gas diffusion layer becomes hot, the relative humidity becomes high, the water vapor is difficult to condense, and the liquid flow prevents the gas flow path. Can be suppressed / prevented.

  A first aspect of the present invention is a membrane electrode assembly comprising an electrolyte membrane, a pair of electrode catalyst layers that sandwich the electrolyte membrane, and a pair of gas diffusion layers that sandwich the pair of electrode catalyst layers. The gas diffusion layer is a membrane electrode assembly that is formed between a water repellent layer containing a water repellent material and a heat conductive material, and a gas diffusion base material and disposed between the electrode catalyst layer. .

  FIG. 2 shows a configuration on the cathode electrode (oxidant electrode) side according to the embodiment of the present invention. An anode electrode (fuel electrode) and a cathode electrode (oxidant electrode) 2 (not shown) are provided on both sides of the solid polymer electrolyte membrane 1, and the gas diffusion base material 4 is water repellent on the cathode electrode (oxidant electrode) 2 side. The gas diffusion layer 5 provided with the layer 3 is provided. In this figure, the cathode (oxidant electrode) side is viewed from the cross-sectional direction.

  The gas diffusion layer has a water repellent layer containing a water repellent material and a heat conductive material, a gas diffusion base material, and a water repellent layer having a high heat conductivity is in contact with the electrode catalyst layer. Since it is disposed, the temperature drop in the water repellent layer can be reduced. Therefore, not only the water repellent layer prevents condensation of water, but also water evaporation can be promoted in the water repellent layer, so that the relative humidity (hereinafter referred to as RH) can be maintained.

  FIG. 1 shows a conceptual diagram of the temperature distribution of the catalyst layer and the gas diffusion layer. The flooding phenomenon is considered to be the inhibition of the transport of reaction gas due to water clogging in the catalyst layer and the gas diffusion layer due to produced water and condensed water vapor. H. Is an important factor.

  That is, when reaction heat generated in the electrode catalyst layer is transferred to the outside of the gas diffusion layer, if the water repellent layer has low thermal conductivity, a rapid temperature drop occurs in the water repellent layer, and the temperature near the electrode catalyst layer Is high, and the temperature in the vicinity of the gas diffusion base material is low. As a result, the water is likely to condense at the low-temperature site, and the amount of water locally condensed at the low-temperature site increases, thereby closing the pores of the porous body and causing a flooding phenomenon. In contrast, in the present invention, since a material having high thermal conductivity is used for the water repellent layer, the water repellent layer is maintained at substantially the same temperature as the electrode catalyst layer. H. This suppresses the rapid increase in water and prevents the phenomenon of local water condensation. Therefore, it is considered that the flooding phenomenon in the water repellent layer can be suppressed. The mechanism according to the present invention is not limited to the above.

  In general, a formula related to heat conduction includes the following Fourier formula.

(In the formula, Q: amount of heat passing through [W], λ: thermal conductivity [W / m · K], A: cross-sectional area of water-repellent layer [m ² ], dT / dr: temperature gradient [K / m] )
For example, the reaction heat in operation at 1 A / cm ² is 37 W, the cross-sectional area is 25 cm ² , the temperature of the electrode catalyst layer is 70 ° C., the thickness of the water-repellent layer is 50 μm, and the thermal conductivity of the conventional water-repellent layer is 0.1. In the case of 1 W / m · K, a temperature difference of about 7 ° C. occurs between the end surface on the gas diffusion substrate side of the water repellent layer and the end surface on the electrode catalyst layer side. This is because the temperature of the electrode catalyst layer is 70 ° C. H. When 70% of the reaction gas is introduced, this corresponds to the condensation of water vapor in the water repellent layer. On the other hand, if a material having a relatively high thermal conductivity, specifically, a material of about 0.2 W / m · K or more is used for the water repellent layer, the temperature drop in the water repellent layer is reduced, Water vapor condensation is suppressed.

  The thermal conductivity of the material having thermal conductivity is preferably 0.2 to 100 (W / m · K), more preferably 0.5 to 10 (W / m · K), and 1 to 5 (W / m · K). More preferred is K). If the thermal conductivity of the material having thermal conductivity is less than 0.2 (W / m · K), the temperature drop in the water-repellent layer becomes large, and the water vapor tends to condense and the flooding phenomenon is likely to occur. is there. On the other hand, if it exceeds 100 (W / m · K), the hydrophobicity of the carbon becomes strong, it becomes difficult to become hydrophilic, it becomes difficult to draw water from the catalyst layer, and the flooding phenomenon may occur easily.

  When the thermal conductivity of the material having thermal conductivity is in the range of 0.2 to 100 (W / m · K), the temperature drop in the water-repellent layer (in contact with the electrode catalyst layer) This is the temperature difference between the end and the end in contact with the gas diffusion base material. The temperature gradually decreases in the water-repellent layer and decreases by 4 ° C. at 0.2 W / mK and by 0.1 ° C. at 100 W / mK. .) Is 0.1 to 4 ° C., and when the thermal conductivity of the material having thermal conductivity is in the range of 0.5 to 10 (W / m · K), the temperature in the water repellent layer Decrease (temperature difference between the end in contact with the electrode catalyst layer and the end in contact with the gas diffusion base material, the temperature gradually decreases in the water-repellent layer, and decreases by 1.5 ° C. at 0.5 W / mK, 10 W / mK, it is 0.1 ° C.) becomes 0.15 to 1.5 ° C., and the material having thermal conductivity has a thermal conductivity in the range of 1 to 5 (W / m · K). Was Temperature drop in the water repellent layer (this is the temperature difference between the end in contact with the electrode catalyst layer and the end in contact with the gas diffusion substrate. The temperature gradually decreases in the water repellent layer, and 1 W / mK Is 1 ° C., 5 W / mK is 0.2 ° C.) is 0.2 to 1 ° C.

  The thickness of the gas diffusion layer in the present invention is preferably 100 to 400 μm, more preferably 150 to 350 μm, and most preferably 200 to 300 μm. 10-100 micrometers is preferable and, as for the thickness of a water repellent layer, 30-80 micrometers is more preferable. 100-300 micrometers is preferable and, as for a gas diffusion base material, 150-200 micrometers is more preferable. When the thickness of the water repellent layer is less than 10 μm, sufficient drainage performance is not obtained, and when it exceeds 100 μm, sufficient gas diffusibility cannot be obtained.

  Further, the porosity of the water repellent layer is preferably 50 to 90%, more preferably 60 to 80%. If the porosity is less than 50%, sufficient diffusibility cannot be obtained. If it exceeds 90%, sufficient strength cannot be obtained.

  As the material having thermal conductivity according to the present invention, known materials can be used, but graphitized carbon is preferable, and examples thereof include carbon black (oil furnace black, acetylene black and the like). Graphitized carbon black, vapor-grown carbon fiber, VGCF, graphitized ketjen black (manufactured by Denki Kagaku Kogyo Co., Ltd.) prepared by heat treating carbon black) in an inert gas at about 3000 ° C. be able to.

  When the material having high thermal conductivity is graphitized carbon, the graphitized carbon has high thermal conductivity (λ = 5 W / m · K), and according to the formula (1), the temperature decrease is about 0. .2 ° C., which can further suppress the flooding phenomenon.

  The “graphitized” structure in this specification refers to a structure in which carbon is connected in a hexagonal shape in a planar shape and laminated. Therefore, the object of the present invention can be achieved as long as the material having thermal conductivity according to the present invention is not only the above-mentioned examples but also carbon having a “graphitized” structure.

  The graphitized carbon according to the present invention is preferably contained in the water-repellent layer at a ratio of 5 to 50% by mass with respect to the mass of the entire water-repellent layer, and more preferably 10 to 40% by mass. Preferably, 20% by mass to 30% by mass is more preferable. If it is less than 5% by mass, sufficient thermal conductivity cannot be obtained, and if it exceeds 50% by mass, the hydrophobicity becomes large and it becomes difficult to induce liquid water from the catalyst layer.

  The present invention also provides a gas diffusion layer in which a water repellent layer containing a water repellent material and a heat conductive material is provided on at least one surface of a gas diffusion substrate.

  On the cathode side, protons generated on the anode side move with water, and further, water is generated by the reaction of oxygen and the transferred protons. Therefore, a large amount of water exists on the cathode side electrode. For this reason, the gas diffusion layer according to the present invention may be disposed on either or both sides of the anode and the cathode, but is preferably disposed at least on the cathode side.

  As the material having water repellency according to the present invention, known materials can be used. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene Examples include fluororesins such as copolymers (FEP), polypropylene, polyethylene, and the like. Among these, PTFE is more preferably used because of its excellent water repellency and corrosion resistance during electrode reaction.

  Examples of the material used for the gas diffusion base material according to the present invention include a sheet-like material made of carbon paper, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like. When the gas diffusion base material has excellent electron conductivity, efficient transport of electrons generated by the power generation reaction is achieved, and the performance of the fuel cell is improved. If the gas diffusion base material has excellent water repellency, the generated water is efficiently discharged.

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

  The polymer electrolyte membrane used in the present invention is not particularly limited and a known one can be used. Examples thereof include the same materials as those used for the electrode catalyst layer, and at least high proton conductivity. Any material that has In this case, the polymer electrolyte is roughly classified into a fluorine-based electrolyte containing a fluorine atom in the whole or a part of the polymer skeleton and a hydrocarbon electrolyte not containing a fluorine atom 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 Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  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 anode-side electrode catalyst layer and the cathode-side electrode catalyst layer according to the present invention include an electrode catalyst and a proton conductive polymer, and if necessary, a water-repellent material. In the present invention, the electrode catalyst is formed by supporting a catalyst component on a conductive material.

  The catalyst component used in the electrode catalyst layer according to the present invention is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction in the cathode catalyst layer, and a known catalyst can be used. 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.

  Although the composition of the alloy depends on the type of metal to be alloyed, platinum is preferably 30 to 90 atomic%, and the metal to be alloyed is preferably 10 to 70 atomic%. The composition of the alloy when the alloy is used as the 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 to 70. It is preferable to use 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 the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. In the present invention, any of them may be used. 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 component used in the catalyst slurry, the higher the effective electrode area where the electrochemical reaction proceeds, and thus the higher the oxygen reduction activity, but in reality 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 component contained in the catalyst slurry is preferably 1 to 30 nm, more preferably 1.5 to 20 nm, still 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 30 nm or less from the viewpoint of catalyst utilization. The “average particle diameter of the catalyst component” 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 width of the diffraction peak of the catalyst component in X-ray diffraction. Can be measured.

  The conductive material may be any material that has a specific surface area for supporting the catalyst component in a desired dispersed state and has 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. Further, as such carbon materials, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl , Carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils as main components. 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 supported amount is less than 10% by mass, the catalytic activity per unit mass decreases, 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 proton 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 polymer electrolyte can be used, and at least high proton 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 containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing 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 Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  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.

  Since the polymer electrolyte is excellent in heat resistance, chemical stability and the like, it preferably contains a fluorine atom. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation) ) And Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

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

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions 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 25-35 mass% with respect to the whole quantity of a catalyst component.

  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.

  It is preferable that the water-repellent layer according to the present invention further includes a hydrophilic material and includes a material having thermal conductivity in the phase of the hydrophilic material.

  3 and 4 are a plan view and a cross-sectional view of a water repellent layer 3 which is a preferred embodiment of the present invention. The water repellent layer 3 has a hydrophobic portion 6 using normal carbon black and a hydrophilic portion 7 using carbon black having high thermal conductivity.

  Since the water repellent layer contains a hydrophilic material, the water generated in the electrode catalyst layer is guided to the hydrophilic material phase by free energy. In addition, since the layer of hydrophilic material (hereinafter also referred to as hydrophilic layer) contains a material having thermal conductivity, the hydrophilic layer is maintained at the same temperature as the high temperature catalyst layer, Water induced in the hydrophilic layer tends to evaporate. As a result, excess water can be vaporized, the amount of water in the electrode catalyst layer can be controlled, and suppression of water in the electrode catalyst layer and reduction of gas passages due to water in the water repellent layer are also suppressed. The phenomenon is thought to be suppressed.

  The content of the hydrophilic material in the water repellent layer is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, and more preferably 20 to 30% by mass with respect to the total mass of the water repellent layer. Further preferred. If it is less than 5% by mass, there are few hydrophilic sites, and it is difficult to induce water from the catalyst layer, and water accumulates in the catalyst layer. On the other hand, if it exceeds 50% by mass, there are many hydrophilic sites and water cannot be evaporated.

As the material having hydrophilicity according to the present invention, known materials can be used. For example, the same Nafion (registered trademark) solution (manufactured by DuPont) as the components of the electrolyte membrane, SiO ₂ dispersion (manufactured by Fuji Silysia, SiO ₂ ). ₂ and water or alcohol dispersions (lower alcohols such as methanol, ethanol, propanol and mixed alcohols thereof are used), TiO ₂ dispersions, Al ₂ O ₃ dispersions, and the like. SiO ₂ dispersion and TiO ₂ dispersion are preferable, and SiO ₂ dispersion is more preferable.

  According to the present invention, in the gas diffusion layer, the amount of the thermal conductive material contained on the inlet side of the gas flow path is less than the amount of the thermal conductive material contained on the outlet side of the gas flow path. preferable. Further, in both the anode-side and cathode-side gas diffusion layers, the amount of the material having thermal conductivity contained in the inlet side of the gas flow path is the same as that of the material having thermal conductivity contained in the outlet side of the gas flow path. The amount is preferably less than the amount, but more preferably in the gas diffusion layer on the cathode side.

  FIG. 6 shows a configuration on the cathode electrode (oxidant electrode) side which is a preferred embodiment of the present invention. The difference from FIG. 2 is that the water repellent layer 3 is divided in the gas flow direction into a hydrophobic portion 6 using normal carbon black and a hydrophilic portion 7 using carbon black having a large thermal conductivity. This is because the hydrophilic part 7 is arranged on the gas outlet side and the hydrophobic part 6 is arranged on the gas inlet side.

  That is, protons generated on the anode side move to the cathode side together with clustered water molecules, and oxygen and protons react on the cathode side to generate water, so that water stays in the cathode side electrode catalyst. This generated water moves to the gas diffusion layer side by using concentration diffusion or vaporized water vapor diffusion as a driving force, and is discharged. However, particularly when a high current is supplied, the water generation reaction further proceeds. The amount of produced water increases from the amount of discharged water, and a large amount of water stays. This is one of the factors of the so-called flooding phenomenon. For this reason, the gas diffusion layer according to the present invention may be disposed on either or both sides of the anode and the cathode, but is preferably disposed on the cathode side.

  However, as in the present invention, by using a thermally conductive material in the vicinity of the gas flow path outlet where the generated water is likely to accumulate in advance, the temperature in the vicinity of the gas flow path outlet is increased, and vaporization of the generated water is promoted. By increasing the discharge speed, the flooding phenomenon can be efficiently suppressed / prevented.

  That is, in the water repellent layer, there is a concentration gradient of the material having thermal conductivity from the exit direction of the gas diffusion substrate to the entrance direction of the gas diffusion substrate, and the concentration decreases toward the entrance direction of the gas diffusion substrate. It is also preferable that a material having thermal conductivity is included only in the vicinity of the outlet of the gas diffusion base material. In the water-repellent layer, the concentration distribution of the material having thermal conductivity from the gas diffusion base material outlet side to the gas diffusion base material inlet side may vary discretely or continuously. It is good, but preferably it varies discretely.

  The range in which the thermally conductive material is used in the vicinity of the gas flow path outlet is such that when the horizontal length from the gas flow path outlet (0%) to the gas flow path inlet (100%) is 100%, the gas flow path outlet is As a reference, a region having a length of 5% from one end as a gas flow channel outlet toward the gas flow channel inlet direction or a region having a length of 50% from one end as a gas flow channel outlet toward the gas flow channel inlet direction Preferably, a region having a length of 10% from one end that is the gas channel outlet toward the gas channel inlet direction or a region having a length of 40% from the one end that is the gas channel outlet toward the gas channel inlet direction More preferably, a region having a length of 20% from one end that is the gas channel outlet toward the gas channel inlet direction or a length of 30% from the one end that is the gas channel outlet toward the gas channel inlet direction A region is more preferred.

  When the heat conductive material is contained in an area of less than 5% from one end of the gas flow path outlet toward the gas flow path entrance direction with reference to the gas flow path outlet, the hydrophilic portion is small, Is difficult to guide from the catalyst layer, and water accumulates in the catalyst layer. In addition, when the thermally conductive material is contained in an area of more than 50% from one end that is the gas channel outlet toward the gas channel inlet direction with reference to the gas channel outlet, there are many hydrophilic parts. This is because water cannot be evaporated.

  In addition, the volume% of the material having thermal conductivity in the vicinity of the outlet of the gas diffusion substrate (ratio of the material having thermal conductivity per unit volume) and the material having thermal conductivity in the vicinity of the inlet of the gas diffusion substrate. The difference between the volume%, that is, the difference between the range in which the thermally conductive material is used near the gas channel outlet and the volume% outside the range is preferably 20 volume% to 100 volume%. This is because the amount of the hydrophilic portion is moderately present in the range of 20% by volume to 100% by volume, and water is effectively induced and the induced water is easily evaporated.

  In the water repellent layer, it is preferable that the amount of the material having thermal conductivity contained on the gas diffusion base side is smaller than the amount of the material having thermal conductivity contained on the electrode catalyst layer side.

  FIG. 5 shows a configuration on the cathode (oxidant electrode) side which is a preferred embodiment of the present invention. The difference from FIG. 2 is that the water repellent layer 3 is divided in a cross-sectional direction into a hydrophobic portion 6 using normal carbon black and a hydrophilic portion 7 using carbon black having a large thermal conductivity. This is that a hydrophilic portion 7 is arranged on the electrode catalyst layer side and a hydrophobic portion 6 is arranged on the gas diffusion base material side.

  That is, in the water repellent layer, there is a concentration gradient of the material having thermal conductivity from the electrode catalyst layer to the gas diffusion base material, and the concentration decreases toward the gas diffusion base material.

  If a material having thermal conductivity is included in the vicinity of the boundary between the electrode catalyst layer and the water-repellent layer along the plane perpendicular to the electrode catalyst layer and the electrode catalyst layer in the water-repellent layer, this boundary is included. The temperature in the nearby region can be increased. Further, since the generated water tends to collect near the boundary between the electrode catalyst layer and the gas diffusion layer, the generated water can be vaporized in this region, and the flooding phenomenon can be efficiently suppressed.

  In the water repellent layer, the concentration distribution of the material having thermal conductivity in the direction perpendicular to the surface of the electrode catalyst layer toward the gas diffusion substrate side may vary discretely or continuously. It is good, but preferably it varies discretely.

  Of course, a layer made of a material having thermal conductivity may be provided between the electrode catalyst layer and the water repellent layer separately from the water repellent layer. In this case, the thickness of the layer made of a material having thermal conductivity is preferably 5 to 25 μm.

  When the concentration gradient is changed discretely, the range in which a material having thermal conductivity is included in the vicinity of the boundary between the water-repellent layer and the electrode catalyst layer in the water-repellent layer is between the water-repellent layer and the electrode catalyst layer. If the thickness of the entire water-repellent layer is 100% by volume based on the boundary, 5% by volume from the one end, which is the boundary between the water-repellent layer and the electrode catalyst layer, toward the gas diffusion base material, which is the perpendicular direction. A region with a thickness of 50% by volume from the one end which is the boundary between the water repellent layer and the electrode catalyst layer to the gas diffusion substrate direction which is a perpendicular direction is preferable, and the water repellent layer and the electrode catalyst layer Diffusion in the direction perpendicular to the region from one end, which is the boundary between the water repellent layer and the electrode catalyst layer, from a region of 10% by volume toward the direction of the gas diffusion base material in the direction perpendicular to the boundary from one end A region with a thickness of 40% by volume in the direction of the base material is more preferable, From one end, which is the boundary with the catalyst layer, to the gas diffusion substrate direction, which is the direction perpendicular to the surface, is 5% by volume or from one end, which is the boundary between the water repellent layer and the electrode catalyst layer, to the direction perpendicular to the surface. A region having a thickness of 50% by volume in the direction of the gas diffusion base material is more preferable. If it is less than 5% by volume, there are few hydrophilic sites, it is difficult to induce water from the catalyst layer, and water tends to accumulate in the catalyst layer. On the other hand, if it is less than 50% by volume, there are many hydrophilic sites and water cannot be evaporated.

  In the water repellent layer, the content of the material having thermal conductivity is preferably 5 to 50% by mass and more preferably 20 to 30% by mass with respect to the total mass of the water repellent layer.

Volume% of the material having thermal conductivity contained in the electrode catalyst layer side (ratio occupied by the material having thermal conductivity per unit volume) and volume% of the material having thermal conductivity contained in the gas diffusion base material side Is preferably 20% by volume to 100% by volume (difference in volume% between the range in which the water repellent layer includes a material having thermal conductivity and the range in which no thermal conductive material is included).
This is because the amount of the hydrophilic portion is moderately present in the range of 20% by volume to 100% by volume, effectively induces water and easily evaporates the induced water.

  Hereinafter, a manufacturing method will be described with respect to an embodiment according to the present invention.

  First, the catalyst slurry of the present invention is applied and dried on a transfer mount to form an electrode catalyst 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 slurry to be used (particularly, a conductive material such as carbon in ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of hydrogen oxidation reaction (anode side) and oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 5 to 20 μm, more preferably 10 to 15 μm.

  The catalyst slurry on 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 are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried at room temperature to 100 ° C., more preferably 50 to 80 ° C. for 30 to 60 minutes in a vacuum dryer. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.

  After sandwiching the solid polymer electrolyte membrane thus produced, hot pressing is performed on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be sufficiently closely joined, but are 100 to 200 ° C., more preferably 110 to 170 ° C. The press pressure is preferably 1 to 5 MPa. Thereby, the joining property of the solid polymer electrolyte membrane and the electrode catalyst layer can be enhanced.

  After hot pressing, the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane can be obtained by removing the transfer mount.

  Next, a gas diffusion layer is prepared. Graphitized carbon and PTFE having high thermal conductivity are used as the water repellent layer, and carbon paper, carbon nonwoven fabric, or carbon cloth is used as the gas diffusion base material.

  A method for producing the water repellent layer will be described below.

  First, carbon black powder is pulverized to a desired particle size, and a dispersion of PTFE (manufactured by Daikin Industries), which is a hydrophobic agent, is mixed at a mass ratio of 60:40 to prepare ink (I). Here, the powder of carbon black is pulverized to a particle size of 1 to 3 μm.

  Further, if necessary, the carbon black powder is further pulverized to a desired particle size (preferably 1 to 3 μm, more preferably 1.5 to 2.5 μm), and the dispersion of the hydrophilic agent is in a mass ratio of 60: Mix at 40 to make ink (I).

  It has been found that when a hydrophilic agent portion of the ink (I) and the ink (II) at a volume% or more is provided, a path is connected in the cross-sectional direction.

  The water repellent layer produced as described above is applied to the gas diffusion base material 4 by a method using a coater device such as a spray coater or bar coater, spray spraying, or the like. It is a method to do. Alternatively, after drying and pulverizing the ink, the powder is spread on the gas diffusion substrate 4. The water-repellent layer has a pore diameter of (50 to 200) nm and a thickness of (25 to 100) μm.

  Next, using the two gas diffusion layers produced as described above, a membrane electrode assembly is produced by sandwiching an electrode including an electrode catalyst layer and a solid polymer electrolyte membrane with the water repellent layer inside.

As the hydrophilic agent, a known material can be used in the same manner as the hydrophilic material according to the present invention. For example, the same Nafion (registered trademark) solution (manufactured by DuPont) as the component of the electrolyte membrane can be used. SiO ₂ dispersion (manufactured by Fuji Silysia, dispersion of SiO ₂ and water or alcohol (lower alcohols such as methanol, ethanol, propanol and mixed alcohol thereof are used)), TiO ₂ dispersion, Al ₂ O ₃ dispersion Etc.

  In the catalyst slurry 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 hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). , May be used. It is preferable that the electrode catalyst is present in the catalyst slurry in an amount such that it is 10 to 50% by mass, more preferably 20 to 30% by mass.

  The catalyst slurry of the present invention has a water repellency such as polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, if necessary, in addition to the electrode catalyst, proton conductive polymer, and solvent. Polymers, thickeners and the like may be included. 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 does not interfere with the above-described effects of the present invention, but is preferably 1 with respect to the total mass of the catalyst slurry. -10 mass%.

  Instead of the water-repellent polymer or in addition to the water-repellent polymer, the catalyst slurry of the present invention may contain a thickener. The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto 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 using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 1 to 5 with respect to the total mass of the catalyst slurry. % By mass. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and a normal solvent used for forming the catalyst layer can be used. Specifically, water or a lower alcohol such as cyclohexanol, ethanol or 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 30 to 70% by mass, more preferably 40 to 60% by mass. It is the quantity which becomes. At this time, if the concentration of the electrolyte exceeds 70% by mass, a part of the colloid may be formed without completely dissolving the electrolyte. Conversely, if the concentration is less than 30% by mass, the contained electrolytic mass is less than 30% by mass. If the amount is too small, the molecular chains of the electrolyte polymer cannot be sufficiently entangled, and the mechanical strength of the formed electrode catalyst layer may be inferior. Moreover, in the catalyst slurry, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 10 to 50% by mass, more preferably about 20 to 30% by mass in the catalyst slurry.

  The catalyst slurry 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, but the anode side is particularly affected by changes in the amount of water produced due to output fluctuations. At least the cathode-side electrode catalyst layer because there is a high risk that the porous structure of the electrode catalyst layer in the initial state collapses due to changes in dryness and moisture, the porosity decreases, and the amount of reactant gas supplied to the electrode catalyst layer decreases. It is preferably used for the electrode catalyst layer on both the cathode and anode sides.

  A second aspect of the present invention is a fuel cell using the electrode according to the first aspect of the present invention.

  The fuel cell using the electrode according to the present invention generally further includes a gas diffusion layer as described in detail below. At this time, the gas diffusion layer is a transfer mount in the above method. It is preferable that the electrode assembly is further bonded to each electrode catalyst layer after the electrode catalyst layer and the solid polymer electrolyte membrane are bonded, by further sandwiching the obtained bonded body with a gas diffusion layer. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, a solid polymer is obtained in the same manner as described above with the electrode catalyst layer-gas diffusion layer assembly. It is also preferable to sandwich and join the electrolyte membrane by hot pressing.

  In addition to the hot pressing method described above, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer by sequentially coating the gas diffusion layer may be used.

  In the present invention, an electrode (membrane electrode assembly) can be produced by a heat treatment similar to a conventionally known method. For example, by applying and drying the prepared catalyst slurry on a transfer mount with a desired thickness, an electrode catalyst layer on the cathode side and the anode side is formed, and the electrode catalyst layer is placed so that the electrode catalyst layer is on the inside. After sandwiching the molecular electrolyte membrane between the electrode catalyst layers and joining them by hot pressing or the like, the catalyst layer was attached to the electrolyte membrane by peeling off the transfer mount.

  The catalyst layer-coated electrolyte membrane thus prepared and the gas diffusion layer (the carbon layer side of the carbon paper coated with the carbon layer) were bonded together to produce an electrode (MEA: membrane electrode assembly).

  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 other than that, typical examples are 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 electrode (membrane electrode assembly) is sandwiched between separators.

  As the material of the separator, any conventionally known material such as a carbon material such as dense carbon graphite or a carbon plate, or a metal material such as stainless steel can be used without limitation. The separator has a function of separating air and fuel gas, and a channel groove for securing these channels 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. In addition, the thickness of the gas seal portion may be about 50 μm to 2 mm, preferably about 100 μm to 1 mm.

  Furthermore, a stack in which a plurality of electrodes (membrane electrode assemblies) 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. In the examples, “%” represents a mass percentage unless otherwise specified.

(First embodiment)
(1) Production of gas diffusion layer Graphitized carbon and PTFE having large thermal conductivity were used as the water repellent layer, and carbon paper was used as the gas diffusion base material.

  A substrate was prepared by punching carbon paper (Carbon Paper TGP-H-060, thickness 200 μm, manufactured by Toray Industries, Inc.) into a 50 mm square. This base material was immersed for 1 minute in a solution prepared by adding an aqueous dispersion of PTFE (polyflon D-1E manufactured by Daikin Industries, Ltd., containing 60% PTFE) to a predetermined concentration with pure water, and then in an oven at 80 ° C. The PTFE was dispersed in the substrate by drying for 20 minutes. At this time, the PTFE content was 10%. As a result, a water-repellent treated gas diffusion base material was obtained.

  On the other hand, a method for producing the water repellent layer is described below.

  The particle diameter (thermal conductivity 1 (W / m · K)) of graphitized ketjen black is pulverized to a desired diameter, and a dispersion of PTFE as a hydrophobic agent (polyflon D-1E manufactured by Daikin Industries, 60% PTFE contained) ) In a mass ratio of 60:40 (graphitized ketjen black: PTFE dispersion) was mixed to prepare a water-repellent layer ink. Here, the carbon black powder was pulverized to a particle size of 3 μm. And it mixed and dispersed for 1 hour with the homogenizer, and also prepared the water-repellent layer ink. This ink was uniformly applied to one surface of the water-repellent treated substrate prepared previously by a spray coater, dried in an oven at 80 ° C. for 1 hour, and further in a muffle furnace at 350 ° C. for 1 hour. Heat treatment was performed. The pore diameter of the water repellent layer was 100 nm and the thickness was 50 μm.

Electrocatalyst layer (2)
Platinum-supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 50 wt%), n-propyl alcohol solution of Nafion (registered trademark) (manufactured by DuPont, containing 5 wt% Nafion), pure water, isopropyl alcohol, The catalyst slurry was prepared by mixing and dispersing for 1 hour using a homogenizer in a glass container in a water bath set to be maintained at 25 ° C. at a mass ratio of 1: 1: 5: 5. Next, the catalyst layer ink was applied on a Teflon sheet using a screen printer and dried in the atmosphere at 25 ° C. for 6 hours, whereby the catalyst layer (platinum mass per 1 cm ² . 4 mg).

Membrane electrode assembly (3)
After two catalyst layers prepared in (2) above are placed on both sides of a solid polymer electrolyte membrane (Nafion 211 (registered trademark)), hot pressing is performed at 130 ° C. and 2 MPa for 10 minutes, and then a Teflon sheet Was peeled off to obtain a joined body. Using the two gas diffusion layers prepared in (1) above, the membrane electrode assembly was manufactured by sandwiching the assembly with the carbon particle layer inside. This was sandwiched between a carbon separator and a current collector plate to obtain an evaluation cell.

(Second embodiment)
A method for producing the water repellent layer will be described below.

Preparation of Gas Diffusion Layer Ketjen Black particle size is pulverized to a desired size, and a dispersion of PTFE, a hydrophobic agent (polyflon D-1E manufactured by Daikin Industries, Ltd., containing 60 wt% PTFE) is mixed at a mass ratio of 60:40 Thus, a water repellent layer ink (1) was prepared.

Further, the graphitized ketjen black (thermal conductivity 1 W / m · K) is pulverized to a desired particle diameter, and the dispersion of the hydrophilic agent SiO ₂ is mass ratio 60:40 (graphitized ketjen black: dispersion of SiO ₂ The ink (2) was prepared by mixing with the liquid. Ink 1 and ink 2 were mixed at a volume ratio of ink (1): ink (2) = 70: 30. The particle sizes of both carbon blacks were the same as in the first example, and carbon paper was used as the gas diffusion substrate in the same manner as in the first example.

  The method of applying the water repellent layer ink (1) and (2) prepared as described above to the gas diffusion base material and other conditions were the same as in the first example, and a membrane electrode assembly and an evaluation cell were prepared. did. The hole diameter and thickness are the same as in the first embodiment.

(Third embodiment)
A method for producing the water repellent layer will be described below.

Production of Gas Diffusion Layer In the gas diffusion layer, the production method of the ink of each layer was the same as in the second example, and carbon paper was used as the gas diffusion substrate as in the first example. First, a hydrophobic ink (3) using ordinary carbon black (Ketjen Black thermal conductivity 0.1 W / m · K) was used as a gas diffusion base material (Carbon Paper TGP-H-060, thickness manufactured by Toray Industries, Inc.) Then, a hydrophilic ink (4) using carbon black having high thermal conductivity (graphitized ketjen black (thermal conductivity 1 W / m · K)) was applied from the upper part thereof.

  The coating method on the gas diffusion substrate was also performed in the same manner as in the first example, and a membrane electrode assembly and an evaluation cell were produced. The pore diameter was the same as in the first example, the thickness of the hydrophilic layer was 10 μm, and the thickness of the hydrophobic layer was 40 μm.

(Fourth embodiment)
In the gas diffusion layer, the method for producing the ink of each layer was the same as in the second example, and the carbon paper was used for the gas diffusion substrate in the same manner as in the first example. Mask the gas diffusion substrate and describe the hydrophobic ink (5) using normal carbon black (Ketjen black thermal conductivity 0.1 W / m · K) as the gas diffusion substrate (the one actually used) After that, the masking is changed to a hydrophobic part and carbon black with high thermal conductivity ((graphitized Ketjen black (thermal conductivity 1 W / m · K) is used as a hydrophilic ink) (6) was applied.

  The coating method on the gas diffusion substrate was also performed in the same manner as in the first example, and a membrane electrode assembly and an evaluation cell were produced. The pore diameter and thickness were the same as in the first example, and the ratio of the lengths of the hydrophilic layer and the hydrophobic layer in the separator channel direction was 1: 4.

(Comparative example)
A gas diffusion layer was prepared in the same manner as in Example 1 except that ketjen black was used for carbon black (thermal conductivity 0.1 W / m · K), and a membrane electrode assembly and an evaluation cell were also prepared in the same manner. .

(Cell evaluation)
The terminal of the cell was attached to the load device, and the voltage for a predetermined current load was measured. The gas humidification method was a bubbling method.

  The power generation evaluation results of the cells produced in the first to fourth examples and the comparative example are shown in FIG. 7 shows. The same electrolyte membrane and catalyst layer were used.

  Evaluation conditions are anode / cathode = hydrogen / air, S.P. R. = 1.5 / 2.5, cell temperature 70 ° C, R.I. H. = 100% / 100%.

  From FIG. 7, under high humidification conditions, the comparative example in which the water-repellent layer was produced using carbon black having a low thermal conductivity showed a voltage drop at a high current density. This is because the temperature is lowered in the water repellent layer, the water vapor is condensed, and the flooding phenomenon is likely to occur. On the other hand, in the first example in which the water repellent layer is produced using carbon black having a high thermal conductivity, the voltage drop at a high current density is small. This is because the temperature drop in the water repellent layer is small, the water vapor hardly condenses, and the flooding phenomenon is suppressed. On the other hand, in the second embodiment in which the water repellent layer is subjected to a hydrophilic treatment and the thermal conductivity of the portion is increased, the flooding phenomenon hardly occurs and the voltage is high as in the first embodiment. This is because the generated water is guided from the catalyst layer to the hydrophilic portion, and the temperature drop is small and the temperature is high, so that the water easily evaporates and the flooding phenomenon is efficiently suppressed.

  In addition, the third and fourth embodiments are water-repellent layers using carbon having positively improved thermal conductivity at the portion where liquid water is accumulated, and more efficiently than the first and second embodiments. Voltage drop due to flooding is suppressed.

It is a conceptual diagram which shows the temperature distribution of the oxidizing agent electrode by the difference in thermal conductivity. It is a block diagram of 1st Example. It is a top view of 2nd Example. It is sectional drawing of 2nd Example. It is a block diagram of 3rd Example. It is a block diagram of 4th Example. It is a figure which shows an electric power generation evaluation result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Cathode catalyst layer 3 ... Water-repellent layer 4 ... Gas diffusion base material 5 ... Gas diffusion layer 6 ... Hydrophobic part in water-repellent layer 7 ... Hydrophilic and high thermal conductivity in water-repellent layer Part

Claims (8)

In a membrane / electrode assembly comprising an electrolyte membrane, a pair of electrode catalyst layers that sandwich the electrolyte membrane, and a pair of gas diffusion layers that sandwich the pair of electrode catalyst layers, the gas diffusion layer is made repellent. A water-repellent layer comprising a water-soluble material and a heat-conductive material; and a gas diffusion base material, and the water-repellent layer is disposed between the electrode catalyst layer and the gas diffusion base material. A membrane electrode assembly characterized by the above.   The membrane electrode assembly according to claim 1, wherein the water repellent layer further includes a hydrophilic material, and the hydrophilic material layer includes a material having thermal conductivity.   The membrane electrode assembly according to claim 1 or 2, wherein the material having thermal conductivity is graphitized carbon.   The membrane electrode assembly according to claim 3, wherein the graphitized carbon is contained in the water-repellent layer at a ratio of 10 to 50 vol% with respect to the volume of the entire water-repellent layer.   In the water-repellent layer, the amount of the material having thermal conductivity contained on the inlet side of the gas channel is smaller than the amount of the material having thermal conductivity contained on the outlet side of the gas channel. The membrane electrode assembly according to any one of the above.   6. The water repellent layer according to claim 1, wherein the amount of the thermal conductive material contained on the gas diffusion base material side is less than the amount of the thermal conductive material contained on the electrode catalyst layer side. 2. The membrane electrode assembly according to item 1.   A gas diffusion layer comprising a water repellent layer comprising a water repellent material and a heat conductive material on at least one surface of a gas diffusion base material.   A fuel cell comprising the membrane electrode assembly according to claim 1 and / or the gas diffusion layer according to claim 7.

Images