JP5590181B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell. In particular, the present invention relates to a fuel cell including a gas diffusion layer having an improved surface.

  In recent years, fuel cells have attracted attention as power sources for electric vehicles and stationary power sources in response to social demands and trends against the background of energy and environmental problems. Fuel cells are classified into various types according to the type of electrolyte, the type of electrode, and the like, and representative types include alkali type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. Among them, a polymer electrolyte fuel cell that can operate at a low temperature (usually 100 ° C. or less) has attracted attention, and in recent years, development and practical application as a low-pollution power source for automobiles is progressing.

  In general, a polymer electrolyte fuel cell (PEFC) is constructed by arranging an anode side electrode and a cathode side electrode on both sides of a polymer ion exchange membrane (cation exchange membrane), respectively, and further outside of the anode side electrode and cathode side electrode. Each is constituted by being sandwiched between a gas diffusion layer and a separator. Usually, a predetermined number of these unit fuel cells are stacked and used as a fuel cell stack by pressing and holding them at a surface pressure of about 0.5 to 3.0 MPa.

  In order to maximize the power generation efficiency of a fuel cell and to achieve high performance, it is important to reduce the electrical contact resistance between the stacked components, and various attempts have been made to reduce the contact resistance. Has been made. For example, in Patent Document 1, a metal, alloy or compound having a small specific resistance is coated on the surface of the gas diffusion layer for the purpose of reducing the contact resistance between the passive film and the gas diffusion layer present on the surface of the metal separator. A fuel cell is disclosed.

JP 2003-123770 A

  However, since corrosion is very likely to occur in the operating environment of the fuel cell, in the fuel cell described above, depending on the metal used, corrosion and performance degradation may occur due to ion elution due to cell reaction. In consideration of durability and elution resistance, it is suitable to use a precious metal such as Au, Pt, or Ag with low activity for coating the gas diffusion layer, but there is a problem that the cost is very high. there were.

  Accordingly, an object of the present invention is to provide a fuel cell in which the electrical contact resistance between a gas diffusion layer and a member adjacent to the gas diffusion layer is reduced while maintaining the fuel cell performance, and a method for manufacturing the fuel cell.

  As a result of intensive investigations to achieve the above object, the present inventors have found that the above object is achieved by a fuel cell including a gas diffusion layer in which the fiber ends protruding in a fluffy manner existing on the surface of the gas diffusion layer are reduced. We have found that this has been accomplished and completed the present invention.

  In the fuel cell of the present invention, the fiber end portion protruding in a fluffy manner existing on the surface of the gas diffusion layer is reduced, so that the contact area between the gas diffusion layer and a member adjacent thereto is increased. Contact resistance is reduced. Therefore, the fuel cell of the present invention can improve the power generation performance.

The schematic cross section of one Embodiment of PEFC of this invention is shown. It is a SEM observation photograph of the surface of the gas diffusion layer of an Example and a comparative example. It is the schematic of the resistance measuring apparatus used when measuring the resistance of an Example and a comparative example. It is a figure which shows the electrical resistance measurement result of an Example and a comparative example.

The present invention provides a fuel cell in which the number of fiber ends protruding in a fluffy manner from the surface of the gas diffusion layer on the surface of at least one of the cathode gas diffusion layer and the anode gas diffusion layer is 5000 / cm ² or less. About.

  As a base material of the gas diffusion layer constituting the unit fuel cell, a cloth material in which carbon fibers and / or metal fibers are knitted and formed into a sheet shape, a nonwoven material material in which fibers are physically entangled and formed into a sheet shape, and fibers In general, a porous substrate such as a paper material made from a binder (binder) is used.

  However, on the surface of the gas diffusion layer containing these porous substrates, there is a portion protruding in a fluffy shape formed by fluffing the fibers constituting the porous substrate. When the separator, the gas diffusion layer, and the solid polymer electrolyte membrane are stacked and sandwiched by applying a surface pressure, the protruding portions contact the separator first and prevent the gas diffusion layer surface from contacting the separator. For this reason, the contact area between the gas diffusion layer and the members (separator, catalyst layer) adjacent to the gas diffusion layer cannot be ensured, and the electrical contact resistance is increased. As a result, the power generation efficiency of the fuel cell may be impaired. In the gas diffusion layer base material of the present invention, since the portion protruding in a fluffy shape is less than that of the conventional gas diffusion layer, the contact area between the gas diffusion layer and the separator can be maximized. And electrical contact resistance between adjacent members (separator, catalyst layer) can be reduced. The term “fluffing” as used herein refers to raising the surface due to friction or other causes as defined in JISP0001 (1998) 7020, in other words, the fiber protrudes from the horizontal surface of the surface. Means the state.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In addition, this invention is not restrict | limited only to the following embodiment. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) which is an embodiment (also referred to as a first embodiment) of a fuel cell of the present invention. FIG. 1 shows a single cell of the fuel cell. The PEFC 10 shown in FIG. 1 includes an electrolyte membrane 12 and a cathode gas diffusion electrode including a cathode catalyst layer 15 and a cathode gas diffusion layer 16 disposed on one surface of the electrolyte membrane 12. In addition, an anode gas diffusion electrode including an anode catalyst layer 13 and an anode gas diffusion layer 14 is disposed on the other surface of the electrolyte membrane 12. In the present application, the “electrolyte membrane-electrode assembly (MEA)” means an assembly having an electrolyte membrane and a pair of gas diffusion electrodes that sandwich the electrolyte membrane. The electrolyte membrane-electrode assembly may be simply referred to as “membrane electrode assembly”.

  The PEFC 10 of the present invention is sandwiched between a pair of separators including a cathode side separator 17 and an anode side separator 18. Here, the cathode gas diffusion layer 16 side surface of the cathode separator 17 is provided with an oxidant gas passage 19 through which an oxidant gas flows during operation, and a coolant is provided on the opposite surface during operation. A circulating cooling channel (not shown) is provided. On the other hand, the anode gas diffusion layer 14 side surface of the anode side separator 18 is provided with a fuel gas flow path 20 through which fuel gas flows during operation, and on the opposite surface, cooling through which coolant flows during operation. A flow path (not shown) is provided. A gasket 21 may be disposed around the PEFC 10 so as to surround the pair of gas diffusion electrodes. The gasket 21 is a seal member, and may have a configuration that is fixed to the outer surface of the MEA electrolyte membrane 12 via an adhesive layer (not shown). The gasket has a function of ensuring the sealing property between the separator and the MEA. Note that the adhesive layer used as necessary preferably corresponds to the shape of the gasket and is arranged in a frame shape on the entire peripheral edge of the electrolyte membrane in consideration of securing adhesiveness.

  First, a gas diffusion layer that is a characteristic part of the fuel cell of the present invention will be described.

(Gas diffusion layer)
The surface of the gas diffusion layer of the fuel cell according to the present invention has fewer portions protruding in a fluffy manner than the conventional gas diffusion layer. The number of fiber ends protruding in a fluffy manner in the conventional gas diffusion layer is about 7500 fibers / cm ² per unit area. On the other hand, the number of fiber ends protruding in a fluffy manner in the gas diffusion layer on the surface of at least one of the anode gas diffusion layer and the cathode gas diffusion layer of the gas diffusion layer of the fuel cell of the present invention is 5000 / cm ² or less. Preferably, it is 2700 lines / cm ² or less, more preferably 2000 lines / cm ² or less. When the number of the portions protruding in the fluff shape of the gas diffusion layer is within such a range, the contact area with the adjacent member increases, so that the contact resistance with the adjacent member decreases. In addition, the lower limit of the number of the part which protruded in the fluff shape of the gas diffusion layer is so preferable that it is small from the point of contact resistance. In the present invention, the number of fiber ends protruding in a fluffy shape within the above range per unit area only needs to be satisfied by at least one of the anode gas diffusion layer and the cathode gas diffusion layer of the gas diffusion layer. However, since the effects of the present invention are remarkably obtained, it is preferable that the surface of either the anode gas diffusion layer or the cathode gas diffusion layer has the number of fiber ends protruding in a fluffy shape within the above range. .

  The number of fiber ends protruding in a fluffy manner means the number of fibers observed in the observation visual field so that the fibers protrude from the surface in the depth direction and the fibers are cut off halfway. Specifically, the number of fiber ends protruding in a fluffy manner is observed by SEM observation of the gas diffusion layer surface at a magnification of 100 to 500 times from a 45 ° inclination angle from the gas diffusion layer surface. The operation of counting the number of fiber ends per area is repeated three times to obtain the average value of the number of fiber ends measured in each operation.

It is preferable that the surface of the gas diffusion layer in which the number of fiber end portions protruding in a fluffy state is 5000 pieces / cm ² or less is arranged at least on the side in contact with the separator in the fuel cell. As will be described later, a carbon particle layer composed of an aggregate of carbon particles containing a water repellent is often present on the catalyst layer side of the gas diffusion layer. In this case, since the carbon particle layer has no problem of fuzz, the contact resistance between the catalyst layer and the gas diffusion layer is rarely a problem. On the other hand, since the porous substrate on which the fluff is generated is in direct contact with the side in contact with the separator, it is preferable to reduce the fluff on the surface of the gas diffusion layer in order to reduce contact resistance. For this reason, it is preferable that the gas diffusion layer surface with reduced fuzzing is disposed at least on the side in contact with the separator in the fuel cell.

  The gas diffusion layer preferably includes a porous substrate. Examples of the porous substrate include cloth, paper-like paper body, nonwoven fabric, paper material, felt and the like. Among these, cloth, nonwoven fabric, and paper material are preferable. Moreover, it is preferable that the material which comprises a porous base material is carbon fiber and / or a metal fiber, in order to make it have electroconductivity. Examples of the metal fiber include metal fibers such as stainless steel, aluminum, and titanium. These may be used alone or in combination of two or more. Among these, carbon cloth, carbon nonwoven fabric, carbon paper, and carbon knit are preferably used because of their high porosity and excellent gas permeability and drainage. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 10 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  Further, in order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer: MPL) made of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the substrate. May be.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include fluorine such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Polymer materials such as polypropylene, polypropylene, and polyethylene. Among them, a fluorine-based polymer material (for example, polytetrafluoroethylene) can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in terms of mass ratio in consideration of the balance between water repellency and electron conductivity. It is good. The thickness of the carbon particle layer is not particularly limited, and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer, but is usually about 1 to 300 μm.

  The gas diffusion layer of the present invention has low contact resistance with the separator and the catalyst layer. For this reason, the coating of noble metals, such as Au, Pt, and Ag as described in Patent Document 1, is not particularly required. For this reason, the fuel cell having the gas diffusion layer of the present invention can be manufactured at low cost while maintaining its performance.

(Method for producing gas diffusion layer)
Although the manufacturing method of the gas diffusion layer of the present invention is not particularly limited, it is preferable that the surface of the gas diffusion layer as a material is processed by polishing. As described above, the gas diffusion layer preferably includes a porous substrate, but the porous substrate includes fibers, and the fibers are fluffy and exist on the surface of the gas diffusion layer. Due to the presence of the fluffy fibers, the contact area with the adjacent member decreased, and the contact resistance between the adjacent members (catalyst layer, separator) increased. By polishing the surface of the gas diffusion layer, the fluffy fibers are polished and the number of fibers protruding from the surface decreases, so that the contact area between the adjacent member and the gas diffusion layer increases, and the contact resistance is reduced. To reduce. In addition, since an inexpensive machining method called polishing is used, the cost can be reduced, and compared with the case where another layer such as a vapor deposition layer is separately provided on the gas diffusion layer, it is simple and particularly large. It doesn't require a lot of equipment. Furthermore, since the method for reducing fuzz is polishing, the polishing conditions required for reducing fuzz can be set easily and in detail using a simple polishing apparatus or material. Since the fluff existing on the surface of the gas diffusion layer exists in a very small range in the depth direction, a method capable of finely modifying the surface like polishing is appropriate as a method for reducing the fuzz. It is also possible to remove the protrusion by pulling out the fiber, but it is difficult to pull out the fiber completely, and the protruding fiber tends to remain on the surface. The layer surface tends to be smooth.

  The method of polishing is not particularly limited, but mechanical polishing is preferable. Mechanical polishing is different from chemical polishing in which chemical polishing is performed by immersing in solutions of various compositions, and electropolishing in which anodic dissolution is performed in a specific solution and electrochemical polishing is performed on the object to be polished. Refers to polishing performed by Mechanical polishing includes all methods of using a polishing agent, a polishing grindstone, a polishing cloth or the like to physically polish manually or mechanically. The mechanical polishing includes, for example, dry or wet mechanical polishing such as belt polishing, hand polishing, buff polishing, lapping polishing, and blast polishing. The mechanical polishing may be performed by one type of polishing method or a combination of two or more types of polishing methods. Among these, from the viewpoint of ensuring mass productivity and surface smoothness, buffing, lapping and a combination of these polishing methods are preferable. If the amount is small, surface polishing may be performed using water resistant paper of # 1000 to # 2000 particles.

When polishing the gas diffusion layer, it is preferable to select and set the polishing conditions appropriately so as to polish and remove the fluffy projecting portion present on the surface of the gas diffusion layer. Polishing and removing the protruding portion includes not only polishing so as to completely remove the protruding portion but also removing the protruding portion from the original gas diffusion layer. The polishing conditions to be considered include pressing force, the rotational speed of the abrasive, and the particle size (roughness) of the abrasive. Specific conditions are appropriately set depending on the hardness of the base material of the gas diffusion layer or the polishing method used. For example, in the case of buffing, the pressing force at the time of polishing is preferably from 0.1 to 500 g / cm ^2, more preferably 1 to 10 g / cm ^2. In the case of buffing, the buff rotation speed is preferably 5 to 3000 rpm, and more preferably 60 to 200 rpm.

  The polishing amount (polishing depth) of the gas diffusion layer is preferably 5 to 150 μm, more preferably 10 to 50 μm, based on the surface of the gas diffusion layer before polishing. Further, when the number of fiber ends protruding from the gas diffusion layer surface before polishing is 100, the number of fiber ends protruding from the gas diffusion layer surface after polishing is preferably It is preferable to set the polishing conditions so as to be 70 or less, more preferably 50 or less, and still more preferably 40 or less. In addition, since the minimum in this case is so preferable that it is small, it is not restrict | limited especially, but it is preferable that it is 10 or more from the ease of manufacture.

  A conventionally well-known thing can be used as an abrasive grain used in the case of grinding | polishing. For example, as the abrasive grains used for buffing, metal oxides such as colloidal silica, fumed silica, ceria, alumina, zirconia, and magnesia, and non-oxides such as diamond and SiC can be used. At this time, the average particle size of the abrasive grains is not particularly limited, but is preferably # 1000 to 2000, which is equivalent to water-resistant paper, and more preferably water-resistant paper # 1200 to 1500. In addition, the average particle diameter of an abrasive grain can be measured as an average value of the particle diameter of the catalyst component investigated from a transmission electron microscope image. Further, for example, as abrasive grains used for lapping, metal oxides such as colloidal silica, ceria, alumina, and zirconia can be used. At this time, the average particle diameter of the abrasive grains is not particularly limited, but is preferably # 1000 to 2000 for water resistant paper, and more preferably 1200 to 1500 for water resistant paper #.

  The buffing may be either dry or wet.

  After the polishing, it is preferable to carry out a cleaning step for the purpose of removing polishing debris. Examples of types of cleaning include ultrasonic cleaning and air blow.

  When polishing the gas diffusion layer, it is preferable to polish at least the surface of the gas diffusion layer in contact with the separator. As described above, a carbon particle layer composed of an aggregate of carbon particles containing a water repellent is often present on the catalyst layer side of the gas diffusion layer. In this case, the contact resistance between the catalyst layer and the gas diffusion layer is rarely a problem. On the other hand, since the side in contact with the separator is usually a porous substrate that generates fuzz, it is preferable to reduce the fuzz on the surface of the gas diffusion layer in order to reduce contact resistance. For this reason, it is preferable to polish at least the surface of the gas diffusion layer on the side in contact with the separator to remove / reduce the fluffy portion on the surface.

  Since the fuel cell of the present invention is characterized by the gas diffusion layer, the other members constituting the MEA and PEFC can be employed in the fuel cell field as they are or as they are appropriately modified. Hereinafter, although each component of PEFC is explained in detail in order, it is not limited only to the following form.

[Electrolyte membrane]
The electrolyte membrane is made of an ion exchange resin and has a function of selectively permeating protons generated in the anode side catalyst layer during PEFC operation along the film thickness direction to the cathode side catalyst layer. The electrolyte membrane of the present invention is particularly preferably a solid polymer electrolyte membrane. The polymer electrolyte membrane also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The specific configuration of the polymer electrolyte membrane is not particularly limited, and conventionally known polymer electrolyte membranes can be appropriately employed in the field of fuel cells. Polymer electrolyte membranes are roughly classified into fluorine-based polymer electrolyte membranes and hydrocarbon-based polymer electrolyte membranes depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include 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. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolyte membranes composed of perfluorocarbon sulfonic acid polymers are used. It is done.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated. Examples include polyetheretherketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolyte membranes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the material selectivity is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is needless to say that other materials may be used without being limited to the above-described materials.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained MEA and PEFC, and is not particularly limited. However, the thickness of the polymer electrolyte membrane is preferably 5 to 300 μm, more preferably 10 to 200 μm, and still more preferably 15 to 150 μm. When the thickness is within such a range, the balance between strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Catalyst layer]
The catalyst layer is a layer where the reaction actually proceeds. Specifically, a hydrogen oxidation reaction proceeds in the anode side catalyst layer, and an oxygen reduction reaction proceeds in the cathode side catalyst layer. The catalyst layer includes a catalyst component, a conductive carrier that supports the catalyst component, and a proton-conductive polymer electrolyte.

  The catalyst component used in the anode side catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Further, the catalyst component used in the cathode side 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. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. However, it goes without saying that other materials may be used. 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-side catalyst varies depending on the type of metal to be alloyed and the like 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 It is preferable to set it as 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added 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. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the anode catalyst layer and the catalyst component used for the cathode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both, and are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode 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 average particle diameter of the catalyst particles 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. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of catalyst particles” in the present invention is the average of the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction or the average particle diameter of the catalyst component determined from a transmission electron microscope image. It can be measured as a value.

  The conductive carrier functions as a carrier for supporting the above-described catalyst component and an electron conduction path involved in the exchange of electrons with the catalyst component.

  Any conductive carrier may be used as long as it has a specific surface area for supporting the catalyst component in a desired dispersed state and sufficient electron conductivity, and the main component is preferably carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3 mass% or less of impurities can be allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry 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. When the specific surface area of the conductive support is in such a range, the balance between the dispersibility of the catalyst component on the conductive support and the effective utilization rate of the catalyst component can be appropriately controlled.

  The size of the conductive carrier is not particularly limited, but from the viewpoint of easy loading, catalyst utilization, and control of the electrode catalyst layer thickness within an appropriate range, the average particle size is 5 to 200 nm, preferably 10 It is good to be about ~ 100 nm.

  In a composite in which a catalyst component is supported on a conductive carrier (hereinafter also referred to as “electrode catalyst”), the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably based on the total amount of the electrode catalyst. Is 30-70 mass%. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the conductive support and the catalyst performance can be appropriately controlled. The supported amount of the catalyst component can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst component can be supported on the 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, in the present invention, a commercially available electrode catalyst may be used. As such commercially available products, for example, electrode catalysts such as those manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., N.E. Chemcat, E-TEK, and Johnson Matthey can be used. These electrode catalysts are obtained by supporting platinum or a platinum alloy on a carbon carrier (supporting concentration of catalyst species: 20 to 70% by mass). In the above, as the carbon carrier, ketjen black, vulcan, acetylene black, black pearl, graphitized carbon carrier (for example, graphitized ketjen black) previously heat treated at high temperature, carbon nanotube, carbon nanohorn, carbon fiber, There is mesoporous carbon.

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the above-described ion exchange resin constituting the polymer electrolyte membrane can be added to the catalyst layer as the polymer electrolyte. When the catalyst layer is a water retention layer, the polymer electrolyte is used as a binder material.

[gasket]
The gasket is disposed around the PEFC so as to surround the pair of gas diffusion electrodes, and has a function of preventing the gas supplied to the catalyst layer from leaking to the outside.

  The material constituting the gasket is not particularly limited, but rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Examples thereof include fluorine-based polymer materials such as polyhexafluoropropylene and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. Moreover, there is no restriction | limiting in particular also in the thickness of a gasket, Preferably it is 50 micrometers-2 mm, More preferably, what is necessary is just to be about 100 micrometers-1 mm.

[Separator]
The MEA is sandwiched between separators to form a single PEFC cell. The PEFC generally has a stack structure in which a plurality of single cells are connected in series. At this time, in addition to the function of electrically connecting each MEA in series, the separator includes a flow path and a manifold through which different fluids such as a fuel gas, an oxidant gas, and a refrigerant flow, and further maintains the mechanical strength of the stack. It also has the function.

  The material constituting the separator is not particularly limited, and conventionally known knowledge can be referred to as appropriate, and examples thereof include carbon materials such as dense carbon graphite and carbon plate, and metal materials such as stainless steel. The size of the separator, the shape of the flow path, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of PEFC.

  The PEFC production method of the present invention is not particularly limited, and can be produced by appropriately referring to conventionally known knowledge in the field of fuel cells.

  As described above, the polymer electrolyte fuel cell has been described as an example, but other fuel cells include alkaline fuel cells, direct methanol fuel cells, micro fuel cells, etc. May be. 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 of the present invention 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. In particular, a vehicle in which system start / stop and output fluctuation frequently occur, Preferably, it can be used particularly suitably for automobile applications.

  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.

As the gas diffusion layer base material, TORAY TGP-H-060 (manufactured by Toray Industries, Inc., thickness 0.19 mm), which is carbon paper, was used. The surface of this gas diffusion layer substrate was polished using # 1000 water resistant paper. Thereafter, alumina particles having a particle diameter of φ0.5 mm were used as abrasive grains, and the surface was buffed with a pressing force of 1 g / cm ² and a buff rotation speed of 60 rpm. As a result, the polishing depth was about 20 μm. After buffing, ultrasonic cleaning was performed.

FIG. 2 shows a surface SEM observation photograph (observed from a 45 ° inclination from the surface of the gas diffusion layer) of the gas diffusion layer (Example 1) thus obtained and the untreated gas diffusion layer (Comparative Example 1). . As can be seen from the figure, in the photograph of the gas diffusion layer surface of Example 1, as compared with Comparative Example 1, it can be seen that the portion of the surface protruding in a fluffy manner is reduced. From the SEM observation photograph, the number of fiber ends protruding in a fluffy manner from the surface of the gas diffusion layer was measured. As a result, Example 1 was 2700 fibers / cm ² and Comparative Example 1 was 7500 fibers / cm ^2. It was.

  In order to obtain the electrical contact resistance of the gas diffusion layers of Example 1 and Comparative Example 1, three pieces of gold foil (thickness 0.1 mm) having a width of 2 mm are provided on an insulating member (acrylic plate having a thickness of 2 mm) at a pitch of 2 mm. An affixed resistance measuring device was produced. A schematic diagram of the measuring device is shown in FIG. A gas diffusion layer was placed thereon, a surface pressure of 1.0 MPa was applied, the electrical resistance was measured with an electrochemical diagnostic device under two conditions of a distance between terminals of 2 mm and 6 mm, and contact resistance was obtained. The electric resistance measurement results are shown in FIG. As a result of the measurement, it was confirmed that the contact resistance of the gas diffusion layer of Example 1 was lower by about 10% than that of Comparative Example 1.

  As described above, by reducing the portion of the gas diffusion layer that protrudes in a fluffy manner, the contact area between the surface of the gas diffusion layer and the separator can be expanded, and the electrical contact resistance can be reduced.

10 polymer electrolyte fuel cell,
12 electrolyte membrane,
13 Anode catalyst layer,
14 Anode gas diffusion layer,
15 cathode catalyst layer,
16 cathode gas diffusion layer,
17 Cathode side separator,
18 anode separator,
19 Oxidant gas flow path,
20 fuel gas flow path,
21 Gasket.

Claims (2)

An electrolyte membrane, a cathode gas diffusion electrode including a cathode catalyst layer and a cathode gas diffusion layer disposed on one surface of the electrolyte membrane, and an anode catalyst layer and an anode gas disposed on the other surface of the electrolyte membrane An anode gas diffusion electrode including a diffusion layer, and a method of manufacturing a fuel cell including an electrolyte membrane-electrode assembly and a separator disposed outside the electrolyte membrane-electrode assembly,
At least one of the cathode gas diffusion layer and the anode gas diffusion layer includes a porous substrate;
The porous substrate is a cloth, nonwoven fabric or paper material made of carbon fiber or metal fiber;
The manufacturing method of a fuel cell including the process of grind | polishing the site | part which protruded in the shape of fluff which exists on the surface of the surface which contact | connects the separator of the said porous base material. 2. The method of manufacturing a fuel cell according to claim 1 , wherein the gas diffusion layer including the porous base material to be polished has a carbon particle layer formed of an aggregate of carbon particles including a water repellent on the catalyst layer side.