JP5481820B2 - Microporous layer and gas diffusion layer having the same - Google Patents

Description

  The present invention relates to a microporous layer and a gas diffusion layer having the microporous layer. More specifically, the present invention relates to a microporous layer excellent in drainage and a gas diffusion layer having the microporous layer.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. Fuel cells include polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC). )and so on. Among them, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature and obtains a high output density.

  In general, the polymer electrolyte fuel cell has a structure in which an electrolyte membrane-electrode assembly (membrane electrode assembly) is sandwiched between separators. The membrane electrode assembly has a structure in which two electrodes are disposed on both sides of a solid polymer electrolyte membrane, and this is sandwiched between gas diffusion layers. The electrode is a porous material formed of a mixture of an electrode catalyst and a solid polymer electrolyte, and is also called an electrode catalyst layer.

  In the polymer electrolyte fuel cell, electricity can be taken out through the following electrochemical reaction. First, hydrogen contained in the fuel gas supplied to the anode (fuel electrode) side is oxidized by the catalyst particles to become protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the anode-side electrode catalyst layer and the solid polymer electrolyte membrane in contact with the anode-side electrode catalyst layer, and enter the cathode (oxygen electrode) -side electrode catalyst layer. Reach. The electrons generated in the anode-side electrode catalyst layer include a conductive carrier constituting the anode-side electrode catalyst layer, and a gas diffusion layer in contact with a different side of the anode-side electrode catalyst layer from the solid polymer electrolyte membrane The cathode side electrode catalyst layer is reached through the separator and the external circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water. Such an electrochemical reaction mainly proceeds at a three-phase interface where catalyst particles, a solid polymer electrolyte, and a reaction gas such as a fuel gas or an oxidant gas are in contact with each other. Therefore, the gas diffusion layer is required to uniformly supply the supplied reaction gas to the electrode catalyst layer.

  In addition, a solid polymer electrolyte membrane in a fuel cell does not exhibit high proton conductivity unless it is wet. Therefore, it is necessary to make the humidity distribution of the solid polymer electrolyte membrane uniform by humidifying the reaction gas supplied to the solid polymer fuel cell using a gas humidifier or the like.

  Under operating conditions such as high humidification and high current density, the amount of water that moves with protons that move through the polymer electrolyte membrane from the anode to the cathode, and agglomerates in the cathode-side electrode catalyst layer The amount of product water increases. At this time, the generated water stays in the cathode-side electrode catalyst layer and causes flooding that closes the pores that have become the reaction gas supply path. As a result, the diffusion of the reaction gas is inhibited, the electrochemical reaction is hindered, and as a result, the battery performance is lowered.

Therefore, conventionally, a gas diffusion layer in which a carbon layer made of carbon black and a hydrophobic agent is provided as a water-repellent layer on the surface of a carbon fiber fabric is used for a membrane electrode assembly (for example, see Patent Document 1). In the gas diffusion layer, carbon black coated with a hydrophobic agent is aggregated to form a porous structure. Therefore, not only can the reaction gas supplied by humidification be diffused more uniformly, but also excess water can be absorbed by the capillary force and quickly discharged. Therefore, flooding is prevented by such a gas diffusion layer without water accumulating in the catalyst layer and the carbon layer.
JP 2003-89968 A

  However, the fuel cell having the gas diffusion layer described in Patent Document 1 has a problem in that the drainage performance in the high electric density region is insufficient.

  Therefore, the present invention has been made in view of the above circumstances, and provides a gas diffusion layer that can prevent flooding in a high electrical density region (high current density region) and increase a voltage. Objective.

  As a result of intensive studies to solve the above problems, the present inventors have used a microporous layer in which the center of pore distribution is adjusted to a specific range for a gas diffusion layer. It was found that flooding in the density range can be prevented. Based on the above findings, the present invention has been completed.

  According to the present invention, by increasing the pores through which water passes and the pores through which gas passes in the microporous layer, the generated water discharge performance in the current density region is improved and the gas supply amount is increased. be able to. For this reason, the fuel cell using the microporous layer of the present invention can prevent flooding in a high current density region and increase the voltage.

  Embodiments of the present invention will be described below.

  The present invention has at least two types of hole distribution centers, the first hole distribution center exists in a hole diameter range of 5 to 15 μm, and the second hole distribution center is 0.2 to 0.5 μm. The present invention provides a microporous layer that exists in the pore diameter range. Moreover, this invention provides the gas diffusion layer which has a gas diffusion base material layer and the microporous layer of this invention formed on the said gas diffusion base material layer.

Many microporous layers of the prior art have a small hole distribution center diameter as a whole. For example, in a polymer electrolyte fuel cell (PEFC) expected as a power source for an electric vehicle, electricity is taken out through the electrochemical reaction described below at both electrodes (cathode and anode) sandwiching the electrolyte membrane. To get electrical energy. First, hydrogen contained in the fuel gas supplied to the anode (hydrogen electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons pass through the solid polymer electrolyte contained in the electrode catalyst layer and the electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (oxygen electrode) side electrode catalyst layer. Electrons generated in the anode-side electrode catalyst layer pass through the cathode through the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the electrode catalyst layer on the side different from the electrolyte membrane, the separator, and an external circuit. Reach the side electrode catalyst layer. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2). . Here, the water generated by the above reaction particularly stays in the cathode-side electrode catalyst layer and causes a flooding phenomenon that closes the pores that have become the reaction gas supply path. As a result, the diffusion of the reaction gas is inhibited, the electrochemical reaction is hindered, and as a result, the battery performance is lowered. For this reason, generated water needs to be efficiently discharged outside the battery. For example, there are a method of subjecting the gas diffusion layer to water repellency so as to prevent flooding by increasing water repellency, and a method of forming a layer of carbon particle aggregates on the gas diffusion base material layer. In such a gas diffusion layer, the generated water generally does not touch the surface due to the water repellent treatment, and therefore passes through the large-diameter holes. On the other hand, in the small-diameter holes, the generated water does not enter due to the water repellent treatment, and a gas passage is secured. However, for example, since a large amount of generated water is generated in a high current density region of 1 A / cm ² or more, water is clogged even in a small-diameter hole, and a flooding phenomenon occurs due to insufficient gas diffusion capacity in a small diameter, There was a problem that the voltage dropped.

  On the other hand, in the present invention, a gas diffusion layer is obtained by disposing a microporous layer having at least a hole distribution center in the range of pore diameters of 5 to 15 μm and 0.2 to 0.5 μm on the gas diffusion base material layer. It is used as a feature. Here, by forming a hole having a hole distribution center at a hole diameter of 5 to 15 μm (also referred to as a “large-diameter side hole” in this specification), a large amount of generated in a high current density region. Even if it is water, sufficient size for the said generated water to pass through can be ensured. Therefore, since the microporous layer has pores on the large diameter side, generated water can be efficiently discharged even in a high current density region. On the other hand, a hole having a hole distribution center in the hole diameter range of 0.2 to 0.5 μm (also referred to as “hole on the small diameter side” in the present specification) can be used in the presence of a large amount of water. However, it is possible to secure a size that allows a sufficient amount of gas to pass therethrough. Therefore, since the microporous layer has pores on the small diameter side, the amount of gas supplied to each electrode catalyst layer in the high current density region can be increased as compared with the conventional case. Accordingly, the fuel cell using the gas diffusion layer having the microporous layer of the present invention prevents flooding phenomenon in a high current density region, increases the voltage, supplies a sufficient amount of gas, and exhibits high power generation performance. can do.

  The microporous layer of the present invention has at least a first pore distribution center existing in a pore diameter range of 5 to 15 μm and a second pore distribution center present in a pore diameter range of 0.2 to 0.5 μm. Have. Among the above holes, holes on the large diameter side having a hole diameter of 5 to 15 μm mainly discharge water. The small-diameter holes having a hole diameter of 0.2 to 0.5 μm mainly supply gas. That is, in the gas diffusion layer, water penetrates into the pores by capillary action. The force (attraction force) at which water is drawn into the capillary at this time is inversely proportional to the hole diameter. That is, the smaller the hole diameter, the easier the water will enter the hole. In the present invention, since the pores on the large diameter side exist in the gas diffusion layer, the water generated by the cathode electrode is efficiently discharged without remaining in the pores on the large diameter side. Although water accumulates in the small-diameter holes, water is preferentially discharged from the large-diameter holes, and the small-diameter holes are sufficiently large. However, water does not stay so much and a sufficient gas supply can be secured. In particular, a large amount of generated water is generated in a high current density region, but even in such a case, both the large-diameter side and small-diameter side pores are sufficiently large so that the pores are not blocked with water A large amount of water can be efficiently discharged while securing a sufficient gas supply. Therefore, the generated water can be efficiently discharged through the pores on the large diameter side even if the microporous layer is in a high current density region. Further, a sufficient amount of gas can be supplied to each electrode catalyst layer through the small-diameter holes. Further, since the small-diameter side holes exist in addition to the large-diameter side holes, the strength of the gas diffusion layer can be appropriately ensured. Therefore, the fuel cell using the gas diffusion layer having the microporous layer of the present invention can prevent the flooding phenomenon in the high current density region, increase the voltage, and exhibit high power generation performance.

  Here, the hole distribution and the hole distribution center are measured by a mercury intrusion method. Here, the mercury intrusion method is a method in which mercury that does not react with most substances and does not wet is pressed into solid vacancies under pressure, and the pressure applied at that time is pushed (intruded) mercury. This is a technique for measuring the size and volume of vacancies on the sample surface from the relationship of volume. When a cell filled with a sample and mercury is continuously pressurized in a high-pressure vessel, mercury is sequentially injected from a large hole to a small hole. It can theoretically be calculated from the Washburn equation (D = −4σcos θ / P) how much pressure the mercury enters into the pores. Here, P is the applied pressure (mPa), D is the pore diameter (m), σ is the surface tension of mercury (mN / m), and θ is the contact angle (deg.) Between mercury and the pore wall surface. By treating σ and θ as constants, the relationship between the pressure P applied from the Washburn equation and the hole diameter D is obtained, and the hole diameter and its volume distribution are derived by measuring the intrusion volume at that time. In this specification, the hole diameter is calculated assuming that the surface tension σ of mercury is 485 dyn / cm and the contact angle between mercury and the hole wall surface is 130 °. In addition, the average pore diameter of the pores can be measured by a mercury intrusion method using a pore master device manufactured by Quantachrome. The porosity of the microporous layer can also be measured with a similar device.

  As described above, the microporous layer of the present invention is suitably used for a gas diffusion layer, preferably a gas diffusion layer for a fuel cell, particularly a gas diffusion layer for a polymer electrolyte fuel cell (PEFC). Here, the gas diffusion layer may be used for at least one of the cathode side gas diffusion layer and the anode side gas diffusion layer. However, as described above, since water is generated particularly on the cathode side, the gas diffusion layer of the present invention is preferably used at least in the cathode side gas diffusion layer.

  The pores in the microporous layer of the present invention preferably have water repellency as appropriate. By having water repellency, water generated by the electrode can be discharged more favorably, and as a result, deterioration in battery performance can be suppressed / prevented. Here, the water repellency (hydrophobicity) in the surface of the microporous layer or in the pores can be determined by the contact angle between these and water. That is, the larger the contact angle between the microporous layer surface or the surface of the pores and water, the more excellent the water repellency. Specifically, the contact angle between the microporous layer surface or the pore surface and water is preferably 90 ° or more, more preferably 120 ° or more. In such a case, water hardly stays on the surface of the layer or in the pores, so that the water discharging ability can be further improved.

  The thickness of the microporous layer may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but is preferably 10 to 100 μm, more preferably about 25 to 70 μm. When the thickness is in the above range, sufficient mechanical strength and gas and water permeability can be secured.

  The gas diffusion layer of the present invention has a gas diffusion base material layer and the microporous layer of the present invention formed on the gas diffusion base material layer. That is, as shown in FIG. 1, the gas diffusion layer 1 of the present invention has a structure in which the microporous layer 2 of the present invention is formed on the gas diffusion base material layer 3.

  The gas diffusion base material layer in the gas diffusion layer of the present invention is not particularly limited, but is made of a sheet-like material having conductivity and porosity, such as carbon woven fabric, paper-like paper body, felt, and nonwoven fabric. Can be mentioned. By using the porous sheet-like material, the gas supplied from the outside can be uniformly diffused in the gas diffusion base material layer. More specifically, carbon paper, carbon cloth, carbon nonwoven fabric and the like are preferable. A commercial item can also be used for the said sheet-like material, for example, carbon paper TGP series by Toray Industries, Inc., carbon cloth by E-TEK, etc. are mentioned.

  The thickness of the gas diffusion base material layer may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. When the thickness is in the above range, sufficient mechanical strength and gas and water permeability can be secured.

  The gas diffusion base material layer may contain a water repellent in order to further improve drainage and prevent flooding. Here, the water repellent is not particularly limited, but polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and the like. Fluorine polymer materials, polypropylene, polyethylene and the like can be mentioned. The water repellent may be used alone or in the form of a mixture of two or more.

  The gas diffusion base material layer is preferably washed in advance before forming the microporous layer. The cleaning method in this case is not particularly limited, but a method of performing a cleaning treatment by immersing in a solvent and putting it in an ultrasonic cleaning apparatus can be preferably used. Here, the solvent for washing is not particularly limited, and examples thereof include water, lower alcohols such as methanol, ethanol, propanol, and isopropanol. Further, when the gas diffusion base material layer is previously cleaned, it is preferable to dry the gas diffusion base material layer after cleaning. The drying conditions in this case are not particularly limited as long as the solvent in the gas diffusion base material layer can be sufficiently removed, and are appropriately selected depending on the type and amount of the solvent.

  Below, the manufacturing method of the gas diffusion layer (including the formation method of a microporous layer) of this invention is demonstrated.

  That is, first, (i) a nonionic water-soluble solid and / or nonionic porous material, conductive particles, a hydrophobic agent, and a solvent are mixed to prepare an ink, and (ii) in (i) above The gas diffusion layer of the present invention can be formed by forming the microporous layer on the gas diffusion base material layer by applying the produced ink to the gas diffusion base material layer and sintering it.

  In the step (i), a nonionic water-soluble solid and / or a nonionic porous material is used for the ink. When a nonionic substance is used in this way, even when mixed with conductive particles, a hydrophobic agent, and a solvent, an ink is prepared, precipitation with a salt / solution does not occur, and a uniform dispersion can be obtained. Can be obtained. Moreover, the large-diameter side hole and the small-diameter side hole according to the present invention can be formed by enlarging both the large-diameter side hole and the small-diameter side hole. Here, “nonionic” means that the degree of ionization in water is low.

  The nonionic water-soluble solid that can be used in the step (i) is not particularly limited as long as it is soluble in water at room temperature (20 ° C.), but 3 g or more in 100 ml of water at room temperature (20 ° C.), preferably What melt | dissolves 5g or more is preferable. When such a water-soluble material is used, it exists between the conductive particles in the ink in a uniformly dissolved state. On the other hand, when the ink coating film is baked, a nonionic water-soluble solid is deposited in the coating film. Here, the nonionic water-soluble solid is in a state in which it enters directly between the conductive particles. Next, when the nonionic water-soluble solid deposited in the step (ii-1) described in detail below is washed away, the nonionic water-soluble solid present between the conductive particles is removed. Holes can be newly formed. Specifically, examples of the nonionic water-soluble solid include boric acid and urea. Preferably, boric acid is preferred as the nonionic water soluble solid. Since boric acid has a small particle size when deposited, it is possible to easily adjust the pore distribution on the large diameter side and the pore distribution on the small diameter side so as to be the first and second pore distribution centers. These nonionic water-soluble solids are common materials available. For this reason, microporous layers made using these nonionic water-soluble solids provide a desired pore distribution at a low cost, making it possible to produce gas diffusion layers with reduced flooding. It can be used suitably.

  The nonionic porous material that can be used in the step (i) is not particularly limited, but is preferably a nonionic porous material having a porosity of 80% or more, more preferably 90% or more. . Since the nonionic porous body originally has pores, the pores on the large diameter side and the small diameter side can be easily adjusted. In addition, a new large-diameter hole can be produced by a simple method with low work process cost. Since the produced microporous layer has a desired pore distribution, it can be suitably used for producing a gas diffusion layer in which flooding is suppressed. The other chemical properties of the nonionic porous body are not particularly limited, but are preferably hydrophobic. In such a case, flooding can be effectively prevented because the water repellency of the microporous layer is maintained as it is. The material of the nonionic porous body is not particularly limited. Specific examples include metal oxides such as silica, alumina, titania, and zirconia, and composite oxides such as those obtained by treating the surface of titania with alumina. Of these, silica is preferable in consideration of cost and the like. The shape of the nonionic porous body is not particularly limited, but may be any of a sheet shape, a tile shape, a spherical shape, a columnar shape, and a tubular shape. Preferably, it is spherical in the ink, and more preferably fine particles. The nonionic porous body may be in an aggregated form. When the nonionic porous body is agglomerated, or is in the form of a sheet or tile, it is preferable to break it into small pieces in advance. The size of the nonionic porous body is not particularly limited, and will be selected as appropriate depending on the ease of mixing into the ink and the desired pore distribution of the microporous layer, as will be described in detail below. Therefore, hydrophobic silica, particularly hydrophobic silica airgel is preferably used as the nonionic porous body. A commercially available product may be used as the nonionic porous material, for example, hydrophobic silica (manufactured by Matsushita Electric Works Co., Ltd., trade names: hydrophobic silica airgel series, SP-15, SP-30, SP-50). ) Etc. can be used.

  Although the electroconductive particle used by the said process (i) will not be restrict | limited especially if it is excellent in electronic conductivity, An electroconductive carbon particle is preferable. Some moderate pores can also be formed by using the conductive particles and the hydrophobic agent. The carbon particles coated with the hydrophobic agent can be aggregated to form a layer having a porous structure, and the hydrophobic surface can be imparted with hydrophobicity by the hydrophobic agent. Moreover, the pore diameter can be easily controlled to a desired value by adjusting the particle diameter of the carbon particles.

  Here, the conductive carbon particles may be those having excellent electronic conductivity, and examples thereof include carbon black powder, graphite powder, expanded graphite powder, metal powder, and ceramic powder. Carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area. As the carbon particles, commercially available products can be used, such as Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black EC manufactured by Lion, Oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. and the like. In addition to carbon black, there are artificial graphite and carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin and furan resin. In order to improve the corrosion resistance and the like, the carbon particles may be subjected to processing such as heat treatment. The conductive particles may be used alone or in the form of a mixture of two or more. The average particle diameter of the conductive particles is not particularly limited, but is preferably about 100 to 3000 nm. When the conductive particles are not within the above preferred average particle diameter range, the conductive particles once dispersed in a solvent may be subjected to a pulverization treatment. In such a case, the pulverization can be accomplished by a known pulverization method, for example, by pulverization using a jet mill. Moreover, when performing the said grinding | pulverization process, you may add surfactant further to the dispersion liquid of electroconductive particle so that electroconductive particle may disperse | distribute uniformly.

  Examples of the hydrophobic agent include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, and polyethylene. It is done. Of these, fluororesins are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction. In addition, the said hydrophobic agent may be used independently or may be used with the form of 2 or more types of mixtures.

  The mixing ratio of the conductive particles and the hydrophobic agent is such that if there are too many conductive particles, the amount of the hydrophobic agent acting as a binder will decrease and the binding force may decrease, and if there are too many hydrophobic agents, the desired pore size will be obtained. There is a fear that it is not possible. Considering these, the mixing ratio of the conductive particles and the hydrophobic agent is 95: 5 to 60:40, preferably about 90:10 to 80:20 in terms of mass ratio.

  The solvent is not particularly limited, and is appropriately selected depending on the type of nonionic water-soluble solid and / or nonionic porous material, conductive particles, and hydrophobic agent to be used. Specifically, solvents such as water, alcohol solvents such as perfluorobenzene, dichloropentafluoropropane, methanol and ethanol can be used as the solvent. Water, methanol, and ethanol are preferable, and water is more preferable. The said solvent may be used independently or may be used with the form of a 2 or more types of mixture.

  In the next step (ii), the ink produced in the above step (i) is applied to the gas diffusion base material layer and sintered to form a microporous layer on the gas diffusion base material layer.

  Here, the ink produced in the step (i) is applied to the gas diffusion base material layer. Here, the ink application method is not particularly limited, and may be applied using various known techniques such as spraying, knife coater, spin coater and the like. The amount of ink applied is not particularly limited, but is preferably an amount such that the thickness after drying becomes the thickness of the microporous layer.

  Also, the ink coating is preferably dried before sintering. The drying conditions in this case are not particularly limited, but may be 20 to 120 ° C., preferably 60 to 100 ° C., for 5 to 120 minutes, preferably about 5 to 60 minutes. The dried coating film is sintered next, and the sintering conditions are not particularly limited, but are 250 to 450 ° C., preferably 300 to 400 ° C. using a muffle furnace or a firing furnace. It may be performed for about 120 minutes, preferably about 5 to 60 minutes.

  By the step (ii), the microporous layer is formed on the gas diffusion base material layer so as to have the specific hole distribution center according to the present invention. Here, in order to more reliably provide the specific pore distribution center as described above in the microporous layer, (ii-1) When using a nonionic water-soluble solid in step (i) Sintering the ink coating film, washing the sintered coating film with an aqueous solvent, and removing the deposited nonionic water-soluble solid; and / or (ii-2) nonionic in step (i) In the case of using a porous porous material, it is preferable to further perform a step of pulverizing the ink prepared in the step (i) and then applying it to the gas diffusion base material layer. Hereinafter, (ii-1) and (ii-2) will be described.

  In step (ii-1), when a nonionic water-soluble solid is used, after sintering, the nonionic water-soluble solid is washed away with an aqueous solvent to remove the precipitated nonionic water-soluble solid. The microporous layer can be formed. Specifically, it is considered that the specific pore distribution as described above is formed in the microporous layer as follows. That is, after drying and sintering, a coating film is formed in a form in which a nonionic water-soluble solid is deposited between the conductive particles. Here, the nonionic water-soluble solid is present in the coating film with a small particle size. Next, when the coating film of this form is washed with an aqueous solvent, only the nonionic water-soluble solid in the coating film is dissolved, so that the nonionic water-soluble solid is selectively removed from the coating film. In this way, a microporous layer having the first and second hole distribution centers as described above can be formed. The present invention is not limited to the above estimation.

  The aqueous solvent that can be used in the step (ii-1) is not particularly limited as long as it is an aqueous solvent that can wash away a nonionic water-soluble solid. Specifically, water, lower alcohol solvents such as methanol, ethanol and the like can be used. Water is preferably used. In addition, the said aqueous solvent may be used independently or may be used with the form of 2 or more types of mixtures. Moreover, the conditions for washing away the nonionic water-soluble solid precipitated in the coating film with the aqueous solvent may be any conditions that can sufficiently remove the nonionic water-soluble solid and obtain a desired pore distribution. Specifically, the coating film is immersed in an excessive amount of an aqueous solvent, preferably while stirring; the coating film is immersed in an excessive amount of an aqueous solvent and subjected to ultrasonic treatment.

  In step (ii-2), the ink produced in step (i) is pulverized and then applied to the gas diffusion base material layer, whereby the microporous layer of the present invention can be formed. Hereinafter, the method will be described. When a nonionic porous body is pulverized, its structure can be easily broken and easily formed into fine particles. For this reason, the pores can be easily enlarged by pulverizing the ink in advance, whereby the microporous layer having the first and second pore distribution centers can be more reliably formed. In addition, since it is possible to introduce hydrophobic fine particles into the microporous layer by a simple method without using a dispersant or an anti-aggregation agent, a gas diffusion layer free from impurities that affect the catalyst layer and the like can be formed at a low cost. Can be produced.

  In the step (ii-2), when a hydrophobic silica airgel having a high porosity is used as a nonionic porous body, the structure is further fragile by pulverization, so that it can be easily made into fine particles. preferable. In particular, when a relatively large hydrophobic silica airgel is used, it is preferable to divide the hydrophobic silica airgel into small pieces and then throw them into the ink and pulverize them to make fine particles. Thereby, since it atomizes in an ink, it mixes uniformly. When the hydrophobic silica airgel is put in the ink in the form of fine particles, the hydrophobic silica airgel fine particles are light, so that they float on the upper surface of the ink and may not be mixed with the ink uniformly.

  In the step (ii-2), the pulverization method and conditions are not particularly limited as long as they are methods and conditions that can form pores on the large diameter side and the small diameter side in the microporous layer. Specifically, it is preferable to grind the nonionic porous body for 5 to 30 minutes using a homogenizer.

The gas diffusion layer of the present invention obtained by the above method has a first pore distribution center existing in the pore diameter range of 5 to 15 μm, and a second center existing in the pore diameter range of 0.2 to 0.5 μm. A microporous layer having at least a pore distribution center is provided. For this reason, even in a high current density region of 1 A / cm ² or more where a large amount of generated water is generated, a large amount of water is efficiently discharged without blocking the pores with water while ensuring the supply of gas. be able to. Therefore, according to the gas diffusion layer of the present invention, generated water can be efficiently discharged even in a high current density region, and the flooding phenomenon can be effectively suppressed / prevented. Moreover, sufficient strength of the gas diffusion layer can be secured. Therefore, the gas diffusion layer according to the present invention can be suitably applied to an electrolyte membrane-electrode assembly, a fuel cell using the electrolyte membrane-electrode assembly, and a vehicle equipped with the fuel cell. Such an electrolyte membrane-electrode assembly and a fuel cell can prevent flooding in a high current density region, increase the voltage, and exhibit high power generation performance.

  The electrolyte membrane-electrode assembly according to the present invention is sequentially arranged on the other side of the electrolyte membrane, the cathode catalyst layer and the cathode side gas diffusion layer, which are sequentially arranged on one side of the electrolyte membrane, and the electrolyte membrane. An anode catalyst layer and an anode side gas diffusion layer, and at least one of the cathode side gas diffusion layer and the anode side gas diffusion layer is the gas diffusion layer of the present invention. Here, the gas diffusion layer may be used for at least one of the cathode side gas diffusion layer and the anode side gas diffusion layer. However, as described above, since water is generated particularly on the cathode side, the gas diffusion layer of the present invention is preferably used at least in the cathode side gas diffusion layer.

  Here, as the electrolyte membrane-electrode assembly and the fuel cell, known methods and materials can be used except that the gas diffusion layer according to the present invention is used.

  Hereinafter, the electrolyte membrane-electrode assembly and the fuel cell of the present invention will be described for each component.

  FIG. 2 is a schematic cross-sectional view schematically showing the basic configuration (single cell configuration) of the fuel cell of the present invention. The present invention is not limited to this.

  In the fuel cell (single cell) 20 in FIG. 2, the anode side catalyst layer 22 a and the cathode side catalyst layer 22 b are respectively arranged on both sides (front surface and back surface) of the electrolyte membrane 21. Further, on both sides (outside) of the anode side catalyst layer 22a and the cathode side catalyst layer 22b, an anode side gas diffusion layer (GDL) 23a and a cathode side GDL 23b are respectively arranged so as to face each other. (Also referred to as MEA) 24. The present invention is characterized in that the gas diffusion layer according to the present invention is used in at least one of the anode side GDL 23a and the cathode side GDL 23b. The gas diffusion layer of the present invention is preferably used for the cathode side GDL 23b, more preferably for both the anode side GDL 23a and the cathode side GDL 23b. In addition, when not using the gas diffusion layer of this invention for any one GDL, a conventionally well-known gas diffusion layer (GDL) is used similarly. Specifically, the GDLs 23a and 23b are not particularly limited, but are porous substrates based on a sheet-like material having conductivity and porosity, such as carbon woven fabrics, paper-like paper bodies, felts, and nonwoven fabrics. Etc. Similarly to the catalyst layers 22a and 22b, the GDLs 23a and 23b may be subjected to water repellency treatment on the GDLs 23a and 23b using known means in order to increase water repellency and prevent flooding. You may form the layer which consists of carbon particle aggregates.

  In the polymer electrolyte fuel cell having the MEA structure of the present invention, the catalyst layer 22, the GDL 23 and the electrolyte membrane 21 are desirably thin to improve the diffusibility of the fuel gas. Sufficient electrode output cannot be obtained. Accordingly, the MEA 24 having the desired characteristics, and further, the solid polymer fuel cell may be determined as appropriate.

Further, anode and cathode palators 25a and 25b are arranged on both sides (outside) of the GDLs 23a and 23b. Gas flow paths (grooves) 26a and 26b are provided inside the separators 25a and 25b. Through these gas flow paths (grooves) 26a and 26b, a hydrogen-containing gas (for example, H ₂ gas) and an oxygen-containing gas (for example, Air) are passed to the catalyst layers 22a and 22b through the anode-side and cathode-side GDLs 23a and 23b. Supplied respectively. Further, in order to prevent gas from leaking to the outside, gaskets 27 are respectively disposed between the outer peripheral region of the electrolyte membrane 21 and the separators 25a and 25b.

(A) Electrolyte membrane The electrolyte membrane which can be used for the fuel cell of this invention should just have high proton conductivity. Examples of the membrane having high proton conductivity include a polymer or copolymer of a monomer having an ion exchange group such as —SO ₃ H group; or a polymer of a monomer having an ion exchange group and another monomer. A film made of a material can be used. Specific examples of the material of the electrolyte membrane 21 include an electrolyte having a fluorinated resin in which all or part of the polymer skeleton is fluorinated and having an ion exchange group, or an aromatic that does not contain fluorine in the polymer skeleton. An electrolyte having an ion exchange group, which is a group hydrocarbon resin.

Examples of the ion-exchange group is not particularly _{limited, -SO 3 H, -COOH, -PO} (OH) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl group A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ ⁺ , —NH ₃ ^{+ and the} like (R, R ′, R ″ represent an alkyl group, cycloalkyl Anion exchange groups such as a group, an aryl group, and the like.

  Specific examples of the electrolyte having a fluorine resin and having an ion exchange group include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, Asahi Glass). Perfluorocarbon sulfonic acid polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymer, Suitable examples include ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene-g-polystyrene sulfonic acid polymer, and polyvinylidene fluoride-g-polystyrene sulfonic acid polymer.

  Specific examples of the electrolyte that is an aromatic hydrocarbon resin and includes an ion exchange group include a polysulfone sulfonic acid polymer, a polyether ether ketone sulfonic acid polymer, a polybenzimidazole alkyl sulfonic acid polymer, Preferred examples include benzimidazole alkylphosphonic acid polymers, cross-linked polystyrene sulfonic acid polymers, polyethersulfone sulfonic acid polymers, and the like.

  The polymer electrolyte preferably contains a fluorine atom because it is excellent in heat resistance, chemical stability, and the like. Among these, fluorine electrolytes such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like are preferable. In particular, in the present invention, when a polymer electrolyte having a sulfonic acid group such as Nafion (registered trademark, manufactured by DuPont) is used, it is preferable to use one having an EW of about 600 to 1100. In addition, EW (Equivalent Weight) represents the dry film weight per 1 mol of sulfonic acid groups, and means that the specific gravity of sulfonic acid groups is larger as it is smaller.

Further, the amount of the polymer electrolyte is not particularly limited. The ratio (Ionomer / Carbon; I / C) of the polymer electrolyte mass (I) to the conductive carrier mass (C) is 0.5 to 2.0, more preferably 0.7 to 1.6. It is preferable that the amount is small. In such a range, sufficient proton conductivity and gas diffusivity can be achieved. The above I / C ratio is determined by measuring the conductive carrier mass and the electrolyte solid content contained in the catalyst layer to be mixed in advance when preparing the catalyst ink (slurry) described in detail below. It can be calculated and controlled by adjusting the ratio. In addition, the mass (C) of the conductive support when the electrode catalyst layer is analyzed to determine the I / C is obtained by subtracting the mass of the catalyst component from the mass of the electrode catalyst. The mass of the catalyst component can be quantified by inductively coupled plasma emission spectroscopy (ICP). The polymer electrolyte mass (I) in the catalyst layer when the electrode catalyst layer is analyzed to determine the I / C is determined by the structure analysis of the polymer electrolyte by ¹⁹ F NMR and the determination of S atoms by coulometric titration. It is possible to quantify by combining the two.

  The thickness of the electrolyte membrane can be appropriately determined in consideration of the characteristics of the obtained fuel cell, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm. The thickness of the electrolyte membrane is preferably 5 μm or more from the viewpoint of strength during film formation and durability during operation of the fuel cell, and is preferably 300 μm or less from the viewpoint of output characteristics during operation of the fuel cell.

  In the present invention, the constituent member containing the electrolyte component interposed between the anode and cathode electrodes of the fuel cell is referred to as an electrolyte membrane, but is not limited to the name. In view of the intended use used in the fuel cell, for example, even when it is referred to as an electrolyte layer or an electrolyte, it may be included in the electrolyte membrane referred to in the present invention. The same applies to the other component requirements, and the identity is not limited to the name, but the identity may be determined in light of the purpose of use.

(B) Catalyst Layer In the present invention, the catalyst component used in 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, selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof, and the like 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 the cathode catalyst varies depending on the type of metal to be alloyed and can be selected as appropriate. At this time, the catalyst component that can be used for the cathode catalyst layer and the catalyst component that can be used for the anode catalyst layer can be appropriately selected from the 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, the higher the effective electrode area where the electrochemical reaction proceeds, so the oxygen reduction activity becomes higher. A decreasing phenomenon is observed. Therefore, the average particle diameter of the catalyst component 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 size of the catalyst component” in the present invention is the average value of the particle size of the catalyst particles determined from the crystallite size or transmission electron microscope image obtained from the half width of the diffraction peak of the catalyst particles in X-ray diffraction. Can be measured.

  The conductive carrier may have any 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. 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 carrier may be a specific surface area sufficient to support a highly dispersed catalyst component. If the columnar and / or tubular conductive support, BET specific surface area of the conductive support, and it is preferably a ^{1m 2} / ^g~2000m 2 / g approximately. If the specific surface area is about 1 m ² / g or more, the dispersibility of the catalyst component and the polymer electrolyte in the conductive carrier is improved, and sufficient power generation performance is obtained. On the other hand, if it is about 2000 m < ² > / g or less, the high effective utilization factor of a catalyst component and a polymer electrolyte can be hold | maintained effectively.

In the case of a spherical conductive carrier, the BET specific surface area of the conductive carrier is preferably 5 to 2000 m ² / g, more preferably 50 to 1500 m ² / g. Particularly preferred are acetylene black, Vulcan, Ketjen Black, and Black Pearl, in which the conductive carrier has a BET specific surface area of 50 to 2000 m ² / g.

  In addition, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, catalyst utilization, and the thickness of the catalyst layer within an appropriate range, the average particle size is 5 to 1000 nm, Preferably, the thickness is about 50 to 700 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive support, 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. . When the supported amount is 80% by mass or less, it is possible to effectively maintain an excellent degree of dispersion of the catalyst component on the conductive support, and to effectively improve the power generation performance corresponding to the increase in the supported amount. There is an advantage that can be expressed. Further, when the supported amount is 10% by mass or more, the catalyst activity per unit mass is excellent, and desired power generation performance corresponding to the supported amount can be obtained. Therefore, it is excellent in that the carrying amount design for ensuring the desired battery performance can be made relatively easily. The amount of catalyst particles supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  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 is not particularly limited, and a known one can be used, but any member having at least high proton conductivity may be used. 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 a 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-based 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 suitable example is sulfonic acid.

  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 carrier 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.

  In the method of the present invention, the catalyst ink comprising the electrode catalyst, the polymer electrolyte and the solvent as described above is applied to the surface of the polymer electrolyte membrane (or the surface of the polymer electrolyte membrane with the gasket layer partially covered). By applying, a catalyst layer is formed. In this case, the solvent is not particularly limited, and usual solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used. Further, the amount of the solvent used is not particularly limited, and a known amount can be used. In the catalyst ink, the electrocatalyst is 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. It is preferable that the electrode catalyst is present in the catalyst ink in an amount of 5 to 30% by mass, more preferably 9 to 20% by mass.

  The catalyst ink of the present invention may contain a thickener. The use of a thickener is effective when the catalyst ink cannot be successfully applied onto a 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, ethylene glycol (EG), polyvinyl alcohol (PVA), and propylene glycol (PG). 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, but is preferably 5 to 20 with respect to the total mass of the catalyst ink. % By mass.

  The catalyst ink of the present invention is not particularly limited in its preparation method as long as an electrode catalyst, an electrolyte and a solvent, and if necessary, a water-repellent polymer and / or a thickener are appropriately mixed. For example, a catalyst ink can be prepared by adding an electrolyte to a polar solvent, heating and stirring the mixed solution to dissolve the electrolyte in the polar solvent, and then adding an electrode catalyst thereto. Alternatively, after the electrolyte is once dispersed / suspended in a solvent, the dispersion / suspension may be mixed with an electrode catalyst to prepare a catalyst ink. In addition, a commercially available electrolyte solution (for example, DuPont Nafion solution: Nafion dispersed / suspended at a concentration of 5 wt% in 1-propanol) in which the electrolyte is previously prepared in the above other solvent is used as it is. May be used in the method.

  Each catalyst layer is formed by applying the catalyst ink as described above on the polymer electrolyte membrane or on the polymer electrolyte membrane while covering a part of the gasket layer. At this time, the conditions for forming the cathode / anode catalyst layer on the polymer electrolyte membrane are not particularly limited, and can be used in the same manner as known methods or appropriately modified. For example, the catalyst ink is applied onto the polymer electrolyte membrane so that the thickness after drying is 0.1 to 100 μm, more preferably 5 to 20 μm, and 25 to 150 in a vacuum dryer or under reduced pressure. C., more preferably 60 to 120.degree. C., for 5 to 30 minutes, more preferably for 10 to 20 minutes. In addition, in the said process, when the thickness of a catalyst layer is not enough, the said application | coating and drying process is repeated until it becomes desired thickness. In addition, it is preferable at the point from which the desired electric power generation amount is obtained as the thickness of a catalyst layer is 0.1 micrometer or more, and a high output can be maintained as it is 100 micrometers or less.

  The gas diffusion layer of the present invention is placed on the catalyst layer obtained as described above.

(C) Separator The anode and cathode separators are not particularly limited, such as carbon paper, carbon cloth, dense carbon graphite, carbon plates, etc., and metals such as stainless steel, and are conventionally known. Can be used. The separators 25a and 25b have a function of separating air and fuel gas, and gas flow paths (grooves) 26a and 26b processed into a desired shape in order to secure the flow paths are provided. It is desirable that it is formed, and conventionally known techniques can be used as appropriate. The thicknesses and sizes of the separators 25a and 25b, the shapes of the gas flow channel grooves 26a and 26b, and the like are not particularly limited, and may be appropriately determined in consideration of output characteristics of the obtained fuel cell.

(D) Gasket The gasket 27 may be impermeable to gas, particularly oxygen or hydrogen gas, but generally includes a single impermeable portion such as an O-ring made of a gas impermeable material. It only has to be done. Further, if necessary, a composite such as a gas seal tape with an adhesive, which is provided with an adhesive portion for adhesion to the electrolyte membrane 21 and the edges of the oxygen electrode and the fuel electrode catalyst layers 22a and 22b. It is good also as a simple structure. There are no particular limitations on the material that forms the impervious portion of the O-ring or gas seal tape as long as it is impervious to oxygen and hydrogen gas in a state where a predetermined pressure is applied after installation.

  Among the materials constituting the impervious portion, examples of the material constituting the O-ring include rubber materials such as fluorine rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, and polytetrafluoroethylene (PTFE). , Fluorine polymer materials such as polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester.

  On the other hand, examples of the material constituting the impermeable portion such as a gas seal tape include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). . In addition, the material constituting the bonding portion such as a gas seal tape is not particularly limited as long as the electrolyte membrane 21, the oxygen electrode and the fuel electrode catalyst layers 22a and 22b, and the gasket 27 can be closely bonded. For example, hot melt adhesives such as polyolefin, polypropylene, and thermoplastic elastomer, acrylic adhesives, olefin adhesives such as polyester and polyolefin, and the like can be used.

  The method for forming the gasket 27 is not particularly limited, and a known method can be used. For example, the adhesive is applied on the electrolyte membrane 21 or on the electrolyte membrane 21 while covering the edges of the catalyst layer 22 so as to have a thickness of 5 to 30 μm. Thereafter, a method of applying the gas-impermeable material as described above to a thickness of 10 to 200 μm and curing it by heating at 25 to 150 ° C. for 10 seconds to 10 minutes can be used. Alternatively, after a gas-impermeable material is formed into a sheet shape in advance, an adhesive is applied to the impermeable film to form a gasket 27, which is then placed on the electrolyte membrane 21 or a part of the gasket 27. You may affix on the electrolyte membrane 21, covering. At this time, the thickness of the impermeable portion is not particularly limited, but is preferably 15 to 40 μm. The thickness of the adhesive part is not particularly limited, but is preferably 10 to 25 μm.

  About the said gasket 27, you may purchase and use a commercially available thing. The commercial items mentioned here include ordered items or custom-made items manufactured by the manufacturer according to the specifications (size, shape, material, characteristics, etc.) on the purchaser side.

  In the fuel cell having the configuration of the MEA 24 of the present invention, the catalyst layer 22, the GDL 23, and the electrolyte membrane 21 are desirably thin to improve the diffusibility of the fuel gas. No output is obtained. Therefore, it may be determined as appropriate so as to obtain an MEA (fuel cell) having desired characteristics.

  Further, the fuel cell of the present invention has the above-described electrode catalyst layer 22 on the inside, GDL 23 on the outside, uses the electrolyte membrane 21, sandwiches the electrolyte membrane 21 between the catalyst layers 22 from both sides, and performs appropriate hot pressing. The MEA 24 can be manufactured.

  As such hot press conditions, it is desirable to set appropriate temperature and pressure. Specifically, it is desirable to heat to 130 to 200 ° C., preferably 140 to 160 ° C., and hot press at 1 MPa to 5 MPa, preferably 2 MPa to 4 MPa for 1 to 10 minutes, preferably 3 to 7 minutes. If the hot press temperature is 130 ° C. or higher (the film is softened and bonding is easy. If the hot press temperature is 200 ° C. or lower, the film can be prevented from being decomposed. Also, the hot press pressure is 1 MPa or higher. If the hot press pressure is 5 MPa or less, problems such as film perforation can be prevented, and if the hot press time is 1 minute or longer, joining is easy. In addition, if the hot press time is 10 minutes or less, it is possible to prevent defects such as film perforations, etc. The atmosphere during hot pressing is preferably an atmosphere that does not affect the MEA, such as in nitrogen. It is desirable to carry out in an atmosphere.

  In addition, the method for producing the fuel cell of the present invention is not particularly limited, and can be assembled using a conventionally known production technique. For example, a catalyst ink is applied and dried on an electrolyte membrane, followed by hot pressing, the electrode catalyst layer is joined to the electrolyte membrane, and the resulting joined body is sandwiched between gas diffusion layers to form MEA; Ink may be applied to the gas diffusion layer and dried to form an electrode catalyst layer, which may be joined to the electrolyte membrane by hot pressing, or any other known technique may be used as appropriate.

  The type of the fuel cell of the present invention is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but other than that, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small 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 application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

  In particular, the polymer electrolyte fuel cell is useful as a power source for a mobile body such as an automobile in which a mounting space is limited in addition to a stationary power source. In particular, it is particularly preferable to be used as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

Example 1
1. Gas diffusion base material layer Carbon paper (manufactured by Toray Industries, Inc., carbon paper TGP-H-060) was cut into 10 cm square, immersed in ethanol, put into an ultrasonic cleaning device, and washed. After washing, it was put into a drying furnace at 80 ° C. and dried for about 10 minutes.

2. Preparation of Ink 2 g of a surfactant (manufactured by Dow Chemical Co., Triton X-100) and 200 g of pure water were mixed and stirred with a propeller stirrer at 150 rpm for 30 minutes. Next, 5 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to and mixed with this surfactant-dispersed aqueous solution, and stirred at 150 rpm for 30 minutes with a propeller stirring device. The slurry was pulverized using a jet mill so that the average carbon particle diameter was 1 μm. 0.1 g of a small piece of a nonionic porous material (manufactured by Matsushita Electric Works, hydrophobic silica airgel SP-30) was added to the slurry. Thereafter, the slurry was pulverized again with a homogenizer, and 1 g of polytetrafluoroethylene (manufactured by Daikin Industries, Polyflon D-1E) was added and mixed. Further, this mixed slurry was stirred at 150 rpm for 30 minutes with a propeller stirrer, and then an appropriate amount of a thickener was added and stirred to prepare an ink slurry for coating.

3. Production of gas diffusion layer On the carbon paper obtained in the above 2. The ink slurry prepared in step 1 was applied using a knife coater so that the film thickness after drying was 50 μm, then dried at 80 ° C. for 15 minutes, and then further heated at 350 ° C. for 30 minutes. Was done.

Example 2
1. Gas Diffusion Substrate Layer Example 1 In the same manner as described above, a gas diffusion base material layer was obtained.

2. Preparation of Ink 2 g of a surfactant (manufactured by Dow Chemical Co., Triton X-100) and 200 g of pure water were mixed and stirred with a propeller stirrer at 150 rpm for 30 minutes. Next, 5 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to and mixed with this surfactant-dispersed aqueous solution, and stirred at 150 rpm for 30 minutes with a propeller stirring device. The slurry was pulverized using a jet mill so that the average carbon particle diameter was 1 μm. 5 g of boric acid powder (manufactured by Wako Pure Chemical Industries, Ltd.) was added to and mixed with the slurry. Thereafter, the slurry was pulverized again with a homogenizer, and 1 g of polytetrafluoroethylene (manufactured by Daikin Industries, Polyflon D-1E) was added and mixed. Further, this mixed slurry was stirred at 150 rpm for 30 minutes with a propeller stirrer, and then an appropriate amount of a thickener was added and stirred to prepare an ink slurry for coating.

3. Production of gas diffusion layer On the carbon paper obtained in the above 2. The ink slurry prepared in step 1 was applied using a knife coater so that the film thickness after drying was 50 μm, then dried at 80 ° C. for 15 minutes, and then further heated at 350 ° C. for 30 minutes. Was done.

  Next, the gas diffusion layer thus obtained was sufficiently immersed while being stirred in an excessive amount of water.

Comparative Example 1
1. Gas Diffusion Substrate Layer Example 1 In the same manner as described above, a gas diffusion base material layer was obtained.

2. Preparation of Ink 2 g of a surfactant (manufactured by Dow Chemical Co., Triton X-100) and 200 g of pure water were mixed and stirred with a propeller stirrer at 150 rpm for 30 minutes. Next, 5 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to and mixed with this surfactant-dispersed aqueous solution, and stirred at 150 rpm for 30 minutes with a propeller stirring device. The slurry was pulverized using a jet mill so that the average carbon particle diameter was 1 μm. Furthermore, 1 g of polytetrafluoroethylene (manufactured by Daikin Industries, Polyflon D-1E) was added to and mixed with the slurry. Further, this mixed slurry was stirred at 150 rpm for 30 minutes with a propeller stirrer, and then an appropriate amount of a thickener was added and stirred to prepare an ink slurry for coating.

3. Production of gas diffusion layer On the carbon paper obtained in the above 2. The ink slurry prepared in step 1 was applied using a knife coater so that the film thickness after drying was 50 μm, then dried at 80 ° C. for 15 minutes, and then further heated at 350 ° C. for 30 minutes. Was done.

<Void distribution analysis>
With respect to the microporous layers obtained in Examples 1 and 2 and Comparative Example 1, the pore distribution spectrum was analyzed by mercury porosimetry. The result is shown in FIG.

From FIG. 3, in the microporous layers of the present invention obtained in Examples 1 and 2, the first pore distribution center existing in the pore diameter range of 5 to 15 μm and the pore diameter range of 0.2 to 0.5 μm that the second hole distribution centers present to exist Ru divided.

<Evaluation of power generation performance>
For the gas diffusion layers obtained in Examples 1 and 2 and Comparative Example 1, the power generation performance was evaluated according to the following method.

  In a commercially available Nafion solution (Aldrich 5% by mass solution), fine particles of Pt-supported carbon (platinum supported amount: 50% by mass) are set so that the mass ratio of carbon to Nafion is carbon: Nafion = 1: 0.8. Then, a cathode catalyst ink was prepared in a homogenizer (pulverizer) for about 3 hours. An anode catalyst ink was prepared in the same procedure as the cathode catalyst ink.

The ink prepared as described above was applied onto a Teflon sheet used as a mount using a screen printer to prepare a catalyst layer transfer sheet for cathode and anode. As the mount, a PET (polyethylene terephthalate) sheet or the like is excellent in addition to the Teflon sheet. Coating and drying were repeated until the Pt carrying amount reached 0.4 mg / cm ² to prepare a catalyst layer transfer sheet having a predetermined platinum amount.

  Ethanol was sprayed and infiltrated on the catalyst layer surfaces of the cathode and anode catalyst layer transfer sheets prepared as described above, and when the catalyst layer surface was dried, the electrolyte membranes prepared with these transfer sheets were sandwiched. Thereafter, hot pressing was performed at 130 ° C., 6.5 MPa, and a holding time of 10 minutes. The reason for infiltrating with ethanol is to make the catalyst layer and membrane electrolyte flexible and to facilitate the transfer of the catalyst layer. After cooling, the mount of the transfer sheet was peeled off to produce an electrolyte membrane-electrode assembly.

  As the gas diffusion layer, the gas diffusion layers of Examples 1 and 2 and Comparative Example 1 and the gas separator with gas flow path were respectively formed on both sides of the electrolyte membrane-electrode assembly thus manufactured. Arranged. Further, it was sandwiched between gold-plated stainless steel current collector plates to form unit cells for evaluation. In the evaluation unit cell, hydrogen was supplied as fuel to the anode side, and air was supplied as the oxidant to the cathode side. The evaluation conditions are S.I. R. = 1.5 / 2.5, cell temperature 70 ° C, R.I. H. = 20% / 20%.

The results are shown in FIG. From FIG. 4, the electrolyte membrane-electrode assembly using the gas diffusion layer of the present invention of Examples 1 and 2 is 1 A / cm ² or more as compared with the conventional gas diffusion layer of Comparative Example 1 used. It can be seen that the voltage drop is significantly suppressed even in the high current density region.

It is the cross-sectional schematic which represented the gas diffusion layer of this invention typically. 1 is a schematic cross-sectional view schematically showing a basic configuration (single cell configuration) of a fuel cell according to the present invention. 2 is a pore distribution spectrum of a microporous layer produced in Examples 1 and 2 and Comparative Example 1. FIG. It is a graph which shows the electric power generation performance evaluation result of the electrolyte membrane-electrode assembly which has the gas diffusion layer produced in Examples 1, 2 and Comparative Example 1.

Explanation of symbols

1 ... Gas diffusion layer,
2 ... Microporous layer,
3 ... gas diffusion base material layer,
20 ... Fuel cell,
21 ... electrolyte membrane,
22 ... Fuel cell electrode catalyst layer,
22a ... anode catalyst layer,
22b ... cathode catalyst layer,
23 ... Gas diffusion layer,
23a ... anode gas diffusion layer,
23b ... cathode gas diffusion layer,
24 ... electrolyte membrane-electrode assembly (MEA),
25a ... anode separator,
25b ... cathode separator,
26a ... anode side gas flow path (groove),
26b ... cathode side gas flow path (groove),
27 ... gasket.

Claims (9)

It has at least two types of hole distribution centers, the first hole distribution center is present in the hole diameter range of 5 to 15 μm, and the second hole distribution center is in the hole diameter range of 0.2 to 0.5 μm. An existing microporous layer for an electrolyte membrane-electrode assembly . Gas diffusion substrate layer, and the electrolyte membrane according to claim 1 which is formed on the gas diffusion substrate layer - having the electrode junction-body microporous layer, an electrolyte membrane - electrode assembly-body gas diffusion layer. (I) A nonionic water-soluble solid and / or a nonionic porous body, conductive particles, a hydrophobic agent, and a solvent are mixed to produce an ink;
(Ii) A microporous layer is formed on the gas diffusion base material layer by applying the ink prepared in the above (i) to the gas diffusion base material layer and sintering it.
Have
In the case of the nonionic water-soluble solid, in the above (ii), after sintering, it is washed away with an aqueous solvent to remove the precipitated nonionic water-soluble solid; or the nonionic porous body In the case (ii), the gas diffusion layer for an electrolyte membrane-electrode assembly according to claim 2, wherein the ink prepared in (i) is pulverized and then applied to the gas diffusion base material layer. Manufacturing method.   The method of claim 3, wherein the nonionic water-soluble solid is boric acid and / or the nonionic porous body is hydrophobic silica. In the case of the nonionic water-soluble solid, in (ii), the ink coating film is dried at 20 to 120 ° C. for 5 to 120 minutes and then sintered at 250 to 450 ° C. for 5 to 120 minutes; Alternatively, in the case of the nonionic porous material, the method according to claim 3 or 4, wherein in (ii), the ink prepared in (i) is pulverized for 5 to 30 minutes using a homogenizer. An electrolyte membrane, a cathode catalyst layer and a cathode side gas diffusion layer sequentially disposed on one side of the electrolyte membrane, and an anode catalyst layer and an anode side gas diffusion layer sequentially disposed on the other side of the electrolyte membrane An electrolyte membrane-electrode assembly comprising:
At least one of the cathode side gas diffusion layer and the anode side gas diffusion layer is a gas diffusion layer manufactured by the gas diffusion layer according to claim 2 or the method according to any one of claims 3 to 5. An electrolyte membrane-electrode assembly.   The electrolyte membrane according to claim 6, wherein at least the cathode-side gas diffusion layer is the gas diffusion layer according to claim 2 or the gas diffusion layer produced by the method according to any one of claims 3 to 5. An electrode assembly.   A fuel cell using the electrolyte membrane-electrode assembly according to claim 6 or 7.   A vehicle equipped with the fuel cell according to claim 8.