JP2006339125A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell with excellent durability through restraint of degradation of electrode catalyst in a catalyst layer. <P>SOLUTION: In the solid polymer fuel cell, a film electrode assembly made by arranging a pair of catalyst layers on either side of the solid polymer electrolyte film is pinched by a separator with a gas flow channel, and the catalyst layer contains an electrode catalyst with catalyst particles carried by a carbon carrier and a solid polymer electrolyte. At least either of the catalyst layers has an average particle size of its catalyst particles getting larger from an inlet side toward an outlet side of the gas flow channel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte fuel cell, and more particularly to a technique for improving a catalyst layer of a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as one of power sources. A fuel cell refers to a device that generates electricity by oxidizing a fuel such as hydrogen or methanol. The power generation efficiency of fuel cells is very high. Moreover, the discharge from the fuel cell using hydrogen as a fuel is water, which is a very useful power source from the viewpoint of protecting the global environment.

  Various fuel cells such as a polymer electrolyte fuel cell, a solid oxide fuel cell, a molten carbonate fuel cell, and a phosphoric acid fuel cell have been proposed as fuel cells. Among these, the polymer electrolyte fuel cell can be operated at a relatively low temperature, and thus is expected as a power source for moving bodies such as automobiles and is being developed.

  The polymer electrolyte fuel cell is also called a polymer electrolyte fuel cell or PEFC, and is a fuel cell using a proton conductive solid polymer electrolyte. The PEFC has a membrane electrode assembly in which a pair of catalyst layers including an electrode catalyst for promoting a power generation reaction, that is, an oxidant electrode catalyst layer and a fuel electrode catalyst layer, are formed on both sides of a proton conductive solid polymer electrolyte membrane. Have. Further, a gas diffusion layer and a separator are disposed outside the catalyst layer. A gas flow path through which gas flows is formed on the catalyst layer side surface of the separator, and the gas used for the power generation reaction diffuses through the gas flow path and the gas diffusion layer and is supplied to the catalyst layer. Moreover, the water produced | generated with the electric power generation reaction is discharged | emitted outside PEFC through a gas diffusion layer, a gas flow path, etc.

  The catalyst layer contains a proton conductive solid polymer electrolyte in addition to the electrode catalyst in which catalyst particles are supported on a carbon support. The conventional catalyst layer has a porous structure in which a solid polymer electrolyte serves as a binder and pores are formed by an aggregate of electrode catalysts. In Patent Document 1, in order to improve the utilization rate of catalyst particles, an electrode catalyst layer is disclosed in which catalyst particles are supported on a conductive carrier, and further, catalyst particles are included in a solid polymer electrolyte.

In such a PEFC, the following power generation reaction proceeds. First, hydrogen contained in the fuel gas supplied to the fuel electrode side is oxidized by the catalyst particles to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ ). Next, the generated protons pass through the solid polymer electrolyte contained in the fuel electrode catalyst layer and the polymer electrolyte membrane in contact with the fuel electrode catalyst layer, and reach the oxidant electrode catalyst layer. In addition, the electrons generated in the fuel electrode catalyst layer are the carbon carrier constituting the fuel electrode catalyst layer, the gas diffusion layer in contact with the polymer electrolyte membrane of the fuel electrode catalyst layer, the separator, and the external circuit. To reach the oxidant electrode catalyst layer. The protons and electrons that have reached the oxidant electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the oxidant electrode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O). In the fuel cell, electricity can be taken out through the power generation reaction described above.
Japanese Patent Laid-Open No. 2003-3228

  In the polymer electrolyte fuel cell, the life of the battery is a problem along with the cost. The battery life is said to be 5000 hours for automobiles and 40,000 hours for home use, and it is required to maintain high power generation performance over a long period of time. However, the conventional polymer electrolyte fuel cell has a problem that sufficient durability is not obtained due to a decrease in power generation performance due to deterioration of the electrode catalyst in the catalyst layer.

  Deterioration of the electrode catalyst in the electrode catalyst layer is particularly likely to occur at a portion where the electrode catalyst layer has a high water content and is exposed to a high potential state during low load operation. In such a part, the catalyst activity of the electrode catalyst is reduced due to the elution of the catalyst particles, and the catalyst activity of the electrode catalyst is reduced due to free aggregation of the catalyst particles due to the disappearance of the corrosion of the carbon support.

  In the electrode catalyst layer, when the electrode catalyst deteriorates at a specific portion, the power generation performance of the entire battery tends to be lowered even if the electrode catalyst does not deteriorate at other portions.

  Further, in the polymer electrolyte fuel cell described in Patent Document 1, the catalyst particles are dispersed in the solid polymer electrolyte in the catalyst layer. The particle diameter of the catalyst particles is fine in order to improve the catalyst utilization rate. In particular, those having an average particle diameter of 1 to 3 nm are used. However, such fine catalyst particles are particularly easy to elute at the above-mentioned specific portion of the electrode catalyst layer, and the catalyst particle components eluted by moving into the solid polymer electrolyte move into the solid polymer electrolyte membrane. There is a problem that not only the catalytic activity is lowered but also the proton conductivity of the solid polymer electrolyte membrane is lowered, which may further reduce the durability of the solid polymer fuel cell. Therefore, in the polymer electrolyte fuel cell described in Patent Document 1, in addition to the above-described deterioration of the electrode catalyst in the catalyst layer, the protons of the polymer electrolyte membrane are further formed by fine catalyst particles contained in the polymer electrolyte. There is a risk of reducing conductivity.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polymer electrolyte fuel cell having excellent durability by suppressing deterioration of an electrode catalyst in a catalyst layer.

  In order to suppress the deterioration of the electrode catalyst in the electrode catalyst layer, it has been found that the corrosion of the carbon support or the elution of the catalyst particles in a specific part of the electrode catalyst layer should be suppressed. Based on such knowledge, the present invention has been completed. That is, the above object is achieved by the polymer electrolyte fuel cell described in (1) and (2) below.

(1) A membrane electrode assembly in which a pair of catalyst layers is disposed on both sides of a solid polymer electrolyte membrane is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the average particle diameter of the catalyst particles increases from the inlet side to the outlet side of the gas flow path.

(2) A membrane / electrode assembly in which a pair of catalyst layers are disposed on both sides of a solid polymer electrolyte membrane is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the crystallinity of the carbon support increases from the inlet side to the outlet side of the gas flow path.

  According to the present invention, it is possible to provide a polymer electrolyte fuel cell having excellent durability.

The first of the present invention is a membrane electrode assembly in which a pair of catalyst layers are arranged on both sides of a solid polymer electrolyte membrane, and is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the average particle diameter of the catalyst particles increases from the inlet side to the outlet side of the gas flow path.

  First, a polymer electrolyte fuel cell (also simply referred to as “PEFC”) of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of a polymer electrolyte fuel cell 150 of the present invention.

  A polymer electrolyte fuel cell 150 shown in FIG. 1 is a membrane electrode junction in which a pair of electrode catalyst layers, that is, a fuel electrode catalyst layer 120a and an oxidant electrode catalyst layer 120c are arranged on both sides of a solid polymer electrolyte membrane 110. The body 100 has a structure further sandwiched between two separators 140a and 140c. Separator 140a, 140c has gas channel 141 for supplying gas supplied from the outside, such as fuel gas containing hydrogen or oxidant gas containing oxygen, to catalyst layers 120a, 120c.

  In the present application, the “membrane electrode assembly” means a laminate having at least a solid polymer electrolyte membrane and a pair of catalyst layers sandwiching the solid polymer electrolyte membrane.

  In the electrode catalyst layer, the portion where the elution of the catalyst particles, which is one of the causes of deterioration of the electrode catalyst, is likely to be a portion where there is a lot of moisture and is exposed to a high potential state during low load operation. This is considered to be caused by the following mechanism. Here, the low load operation specifically includes a no-load state when fuel gas and oxidant gas are supplied, and an idling state of an automobile.

  The moisture generated by the electrode reaction and the moisture contained in the gas supplied through the gas flow path provided in the separator are likely to stay in the catalyst layer, and in the catalyst layer from the inlet side to the outlet side of the gas flow path. The amount of water to be retained increases. The dissolution of the catalyst particles is likely to occur at a location with a lot of moisture, and hardly occurs at a location where it is dry. Further, such dissolution of the catalyst particles is further promoted at a portion where the high potential state (cell voltage of 0.8 V or more) is obtained. For this reason, the dissolution of the catalyst particles that causes a decrease in the durability of the fuel cell tends to occur remarkably as it goes from the inlet side to the outlet side of the gas flow path. Even if there is little dissolution of the catalyst particles on the inlet side of the gas flow path in the catalyst layer, the power generation performance of the entire battery tends to decrease due to the large dissolution of the catalyst particles on the outlet side.

  In addition, catalyst particles having a small particle size have a large specific surface area and high catalytic activity, whereas catalyst particles having a large particle size are excellent in dissolution resistance. In the catalyst layer, high catalyst activity is maintained by disposing catalyst particles with small particle diameters in areas where catalyst particles are unlikely to dissolve and disposing catalyst particles with large particle diameters in areas where catalyst particles are likely to dissolve. However, catalyst particles having a large particle diameter in the catalyst layer can be efficiently suppressed.

  Thus, in the polymer electrolyte fuel cell of the present invention, by increasing the particle diameter of the catalyst particles in a predetermined direction in the catalyst layer, the catalyst activity in the catalyst layer is ensured and at the same time the catalyst particles are eluted. It becomes possible to suppress. Therefore, according to the present invention, it is possible to provide a polymer electrolyte fuel cell capable of maintaining high power generation performance over a long period of time.

  Then, the structure which the catalyst layer in PEFC of this invention has is demonstrated.

  In the present invention, in the catalyst layer disposed on at least one of the fuel electrode side and the oxidant electrode side, the average particle diameter of the catalyst particles is increased from the gas inlet side to the outlet side of the gas supply path of the separator. To do.

  In the present invention, in the catalyst layer, the average particle diameter of the catalyst particles is increased from the gas inlet side to the outlet side of the gas supply path of the separator. Further, in the catalyst layer, from the separator side to the solid polymer electrolyte membrane side It is preferable to increase the average particle diameter of the catalyst particles toward. As a result, catalyst particles having high dissolution resistance can be disposed in the catalyst layer where the catalyst particles are likely to be dissolved, and the durability of the PEFC can be further improved.

  At this time, the average particle diameter of the catalyst particles gradually increases from the inlet side to the outlet side of the gas flow path of the catalyst layer, more preferably from the separator side to the solid polymer electrolyte membrane side. Or may be gradually increased. Among these, since the production of the catalyst layer and the control of the average particle diameter of the catalyst particles in the catalyst layer are easy, the average particle diameter of the catalyst particles is preferably increased stepwise.

  As a preferred embodiment of the catalyst layer having a configuration in which the average particle diameter of the catalyst particles increases from the inlet side to the outlet side of the gas flow path of the catalyst layer, for example, in the surface direction of the membrane electrode assembly, The structure shown in FIG. 2 in which the catalyst layer is divided into two or more regions is exemplified. FIG. 2 is a schematic diagram of the catalyst layer 120. The catalyst layer is divided into two regions, that is, an inlet-side catalyst layer 120i and an outlet-side catalyst layer 120e, in the surface direction (arrow A) of the membrane electrode assembly. The inlet side catalyst layer 120i and the outlet side catalyst layer 120e may contain catalyst particles each having a predetermined average particle diameter. Then, when assembling the polymer electrolyte fuel cell, the inlet side catalyst layer 120i may be arranged on the inlet side of the gas flow path of the separator, and the outlet side catalyst layer 120e may be arranged on the outlet side of the separator.

  When the catalyst layer is composed of two layers of an inlet side catalyst layer and an outlet side catalyst layer, the difference in the average particle diameter of the catalyst particles from the adjacent layer is preferably 0.1 to 4 nm, more preferably 0.1 to 4 nm. It should be 2 nm.

  As the average particle diameter of the catalyst particles in each layer, specifically, the average particle diameter of the catalyst particles contained in the inlet side catalyst layer is preferably 2 to 5 nm, more preferably 2 to 3.5 nm. .

  Moreover, the average particle diameter of the catalyst particles contained in the outlet side catalyst layer is preferably 3 to 6 nm, more preferably 3 to 5.5 nm.

  The ranges of the inlet side catalyst layer and the outlet side catalyst layer in the catalyst layer may be determined in consideration of the durability of the obtained polymer electrolyte fuel cell. The outlet catalyst layer is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer. Thereby, catalyst particles having high dissolution resistance can be contained in a portion where the electrode catalyst is likely to deteriorate due to dissolution of the catalyst particles.

  In the above, the catalyst layer is divided into two regions in the surface direction of the membrane electrode assembly. However, the present invention is not limited to this, and the catalyst layer is further divided into three or more regions in the surface direction of the membrane electrode assembly. It may be divided.

  As a preferred embodiment of the catalyst layer having a configuration in which the average particle diameter of the catalyst particles is increased from the inlet side to the outlet side of the gas flow path, and further from the separator side to the solid polymer electrolyte membrane side. The catalyst layer is divided into two or more regions in the thickness direction of the membrane electrode assembly, and further divided into two or more regions in the surface direction of the membrane electrode assembly, and each region has a predetermined average particle diameter. The structure which contains the catalyst particle which has is mentioned.

  Specifically, the catalyst layer (1) and the catalyst layer (2) are arranged in the thickness direction of the membrane electrode assembly such that the catalyst layer (1) is disposed on the solid polymer electrolyte membrane side. The catalyst layer (1) is formed by arranging an inlet side catalyst layer (1-1) and an outlet side catalyst layer (1-2) in the surface direction of the membrane electrode assembly, In the layer (2), an inlet side catalyst layer (2-1) and an outlet side catalyst layer (2-2) are arranged in the surface direction of the membrane electrode assembly, and each catalyst layer has a predetermined average particle diameter. The structure which contains the catalyst particle which has this is mentioned. More specifically, the catalyst layer 120 shown in FIG. 3 is mentioned. The catalyst layer 120 includes an inlet side catalyst layer (1-1) 121i, an inlet side catalyst layer (2-1) 122i, and an outlet side catalyst layer ( 1-2) 121e and outlet side catalyst layer (2-2) 122e, and each catalyst layer contains catalyst particles having a predetermined average particle diameter.

  Further, when the polymer layer 120 is used as the solid polymer fuel cell, the catalyst layer (1) is disposed on the separator side, the catalyst layer (2) is disposed on the solid polymer electrolyte membrane side, and the inlet side The catalyst layer (1-1) and the inlet side catalyst layer (2-1) are arranged on the inlet side of the gas flow path of the separator, and the outlet side catalyst layer (1-2) and the outlet side catalyst layer (2-2). Is disposed on the outlet side of the gas flow path having the separator.

  When the catalyst layer (1) is composed of at least two layers of the inlet side catalyst layer (1-1) and the outlet side catalyst layer (1-2), the difference in the average particle diameter of the catalyst particles from the adjacent layer is preferably Is 0.1 to 3.0 nm, more preferably 0.1 to 2.0 nm.

  Further, when the catalyst layer (2) is composed of at least two layers of the inlet side catalyst layer (2-1) and the outlet side catalyst layer (2-2), the difference in the average particle diameter of the catalyst particles from the adjacent layers is The thickness is preferably 0.1 to 3.0 nm, more preferably 0.1 to 2.0 nm.

  As the average particle diameter of the catalyst particles in each layer, specifically, the average particle diameter of the catalyst particles contained in the inlet catalyst layer (2-1) is preferably 2 to 4 nm, more preferably 2 to 3 nm. The average particle diameter of the catalyst particles contained in the outlet side catalyst layer (2-2) is preferably 2.5 to 5 nm, more preferably 2.5 to 4 nm.

  The average particle diameter of the catalyst particles contained in the inlet side catalyst layer (1-1) is preferably 2.5 to 5 nm, more preferably 2.5 to 4 nm, and the outlet side catalyst layer (1- The average particle diameter of the catalyst particles contained in 2) is preferably 4 to 6 nm, more preferably 4 to 5 nm.

  At this time, the average particle diameter of the catalyst particles is larger in the outlet side catalyst layer (1-2) than in the inlet side catalyst layer (1-1). The outlet side catalyst layer (2-2) is larger than the side catalyst layer (2-1), and the inlet side catalyst layer (1-1) is larger than the inlet side catalyst layer (2-1). It is preferable that the outlet side catalyst layer (1-2) is larger than the outlet side catalyst layer (2-2).

  The average particle diameter of the catalyst particles in the catalyst layer can be measured by measurement from a TEM photograph of the catalyst-supporting carbon and XRD measurement.

  The range of the inlet side catalyst layer (1-1) and the outlet side catalyst layer (1-2) in the catalyst layer (1), the inlet side catalyst layer (2-1) and the outlet side catalyst layer ( The range 2-2) may be determined in consideration of the durability of the obtained polymer electrolyte fuel cell.

  The inlet catalyst layer (2-1) is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer (2).

  The inlet catalyst layer (1-1) is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer (1).

  The total film thickness of the catalyst layer is preferably 25 μm or less. If the thickness of the entire catalyst layer is too thin, it may not be possible to secure a sufficient amount of catalyst necessary for the electrode reaction, and battery performance and life characteristics may be deteriorated. On the other hand, if the thickness of the catalyst layer is too thick, the power generation performance may be reduced. Therefore, the thickness of the catalyst layer should be determined in consideration of battery performance and life characteristics.

  When the catalyst layer is formed by laminating the catalyst layer (1) and the catalyst layer (2), the thickness of the catalyst layer (2) is preferably 4 to 15 μm, more preferably 6 to 10 μm. . The thickness of the catalyst layer (1) is preferably 2 to 7 μm, more preferably 2 to 5 μm.

  In the above description, the catalyst layers (1) and (2) are divided into two regions toward the surface direction of the membrane electrode assembly. However, the catalyst layer (1) is further directed toward the surface direction of the membrane electrode assembly. And / or (2) may be divided into three or more regions. In this case, another layer may be disposed between the inlet side catalyst layer (1-1, 2-1) and the outlet side catalyst layer (1-2, 2-2). The average particle diameter of the catalyst particles may be increased from 1, 2) toward the outlet catalyst layer (1-2, 2-2).

  In the present invention, in the catalyst layer described above, platinum particles and platinum alloy particles are used as catalyst particles in the electrode catalyst, and the content rate of the platinum alloy particles is high from the inlet side to the outlet side of the gas flow path of the separator. It is preferable to further include the following structure.

  The platinum alloy particles are expected to have a catalytic activity that is the same as or higher than that of platinum, and are excellent in the solubility resistance of the catalyst particles. According to the catalyst layer having the above-described configuration, the platinum particles are arranged at a site where the catalyst particles are hardly dissolved by adjusting the catalyst particle diameter to a predetermined value and further adjusting the content of the platinum alloy particles in the catalyst particles. In addition, the platinum alloy particles can be disposed at a site where the catalyst particles are likely to be dissolved, and the dissolution of the catalyst particles can be further suppressed while maintaining high catalyst activity. Therefore, it is possible to provide a polymer electrolyte fuel cell that can maintain higher power generation performance over a long period of time.

  In the present invention, it is preferable to increase the content of platinum alloy particles from the gas inlet side to the outlet side of the gas supply path of the separator in the catalyst layer. It is preferable to increase the content of platinum alloy particles in the catalyst particles toward the membrane side. As a result, platinum alloy particles having high dissolution resistance can be disposed in the catalyst layer where the catalyst particles are likely to be dissolved, and the durability of the PEFC can be further improved.

  At this time, the content rate of the platinum alloy particles gradually increases from the inlet side to the outlet side of the gas flow path of the catalyst layer, more preferably from the separator side to the solid polymer electrolyte membrane side. Or may be gradually increased. Among these, since the production of the catalyst layer and the control of the content ratio of the platinum alloy particles in the catalyst layer are easy, the content ratio of the platinum alloy particles should be increased stepwise.

  When the catalyst layer is composed of two layers of the inlet side catalyst layer and the outlet side catalyst layer as in the catalyst layer shown in FIG. 2, the content of platinum alloy particles in each layer, specifically, in the inlet side catalyst layer, The content of platinum alloy particles in the contained catalyst particles is preferably 0 to 50% by mass, more preferably 0 to 40% by mass.

  Moreover, the content rate of the platinum alloy particles in the catalyst particles contained in the outlet side catalyst layer is preferably 10 to 100% by mass, more preferably 20 to 100% by mass.

  Moreover, like the catalyst layer shown in FIG. 3, the catalyst layer is composed of an inlet side catalyst layer (1-1), an outlet side catalyst layer (1-2), an inlet side catalyst layer (2-1), and an outlet side catalyst. When it has a layer (2-2), as the content rate of the platinum alloy particles in the catalyst particles in each layer, specifically, the platinum alloy in the catalyst particles contained in the inlet side catalyst layer (2-1) The content rate of the particles is preferably less than 20% by mass, more preferably 0 to 10% by mass, and the content rate of the platinum alloy particles in the catalyst particles included in the exit side catalyst layer (2-2), Preferably it is 10-50 mass%, More preferably, you may be 20-40 mass%.

  The content of the platinum alloy particles in the catalyst particles contained in the inlet catalyst layer (1-1) is preferably 10 to 50% by mass, more preferably 20 to 40% by mass, and the outlet side The content of the platinum alloy particles in the catalyst particles contained in the catalyst layer (1-2) is preferably 30 to 100% by mass, more preferably 60 to 100% by mass.

  At this time, the content rate of the platinum alloy particles in the catalyst particles is higher in the outlet side catalyst layer (2-2) than in the inlet side catalyst layer (2-1), and the inlet side catalyst layer ( 1-1) higher than the outlet side catalyst layer (1-2), higher than the inlet side catalyst layer (2-1) than the inlet side catalyst layer (2-1), The outlet catalyst layer (1-2) is preferably higher than the side catalyst layer (2-2).

  The content of platinum alloy particles in the catalyst particles in the catalyst layer is determined by weighing the amounts of Pt-supported carbon and Pt alloy-supported carbon added to the catalyst layer ink prepared when each catalyst layer is formed. Calculate to find.

  In the present invention, the catalyst layer has a configuration in which the average particle diameter of the catalyst particles increases toward a predetermined direction, more preferably the content of platinum alloy particles in the catalyst particles increases. The mass ratio of platinum in the platinum alloy particles decreases toward a predetermined direction in the layer.

  Specifically, it is preferable that the catalyst layer further has a configuration in which the mass ratio of platinum in the platinum alloy particles decreases from the inlet side to the outlet side of the gas flow path of the separator. In the layer, it is preferable that the mass ratio of platinum in the platinum alloy particles decreases from the separator side to the solid polymer electrolyte membrane side.

  As described above, the platinum alloy particles are excellent in dissolution resistance, but such dissolution resistance increases as the platinum content in the platinum alloy particles decreases. Therefore, by adjusting the mass ratio of platinum contained in the platinum alloy particles in the catalyst layer as described above, the dissolution of the catalyst particles in the catalyst layer can be further suppressed, and the resulting polymer electrolyte fuel cell The durability can be further improved.

  At this time, the mass ratio of platinum in the platinum alloy particles is stepwise from the inlet side to the outlet side of the gas flow path of the catalyst layer, more preferably from the separator side to the solid polymer electrolyte membrane side. It may be smaller or gradually decreased.

  In the polymer electrolyte fuel cell of the present invention, the average particle diameter of the catalyst particles in the electrode catalyst is increased from the inlet side to the outlet side of the gas flow path of the separator, and more preferably the platinum particles are contained in the catalyst particles. The above-described catalyst layer having a configuration in which the rate increases from the inlet side to the outlet side of the gas flow path may be used for at least one of the fuel electrode catalyst layer and the oxidant electrode catalyst layer. Especially, it is preferable to use for both the fuel electrode catalyst layer and the oxidant electrode catalyst layer, more preferably the oxidant electrode catalyst layer in which moisture retention occurs and the catalyst particles are easily dissolved.

  For the PEFC of the present invention, materials used in the conventional PEFC can be similarly used except that the average particle size of the catalyst particles in the catalyst layer increases in a predetermined direction. Hereinafter, the basic configuration of the solid polymer electrolyte membrane, the catalyst layer, and the like will be briefly described. However, these materials are not limited to the exemplified materials and shapes, and conventionally known materials are appropriately used.

  The solid polymer electrolyte membrane is a polymer membrane having proton conductivity. Various materials have been proposed as the solid polymer electrolyte membrane. For example, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resin membranes, ethylene-tetrafluoroethylene copolymer resin membranes manufactured by Dow Chemical Co., Ltd. Fluoropolymer electrolytes such as resin membranes based on fluorostyrene, and hydrocarbon polymer resin membranes having sulfonic acid groups, such as polymer electrolyte membranes and polymer microporous membranes that are generally commercially available Alternatively, a membrane impregnated with a liquid electrolyte or a membrane in which a porous body is filled with a polymer electrolyte may be used.

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

  The catalyst layer includes at least an electrode catalyst in which catalyst particles are supported on a carbon support and a solid polymer electrolyte.

  As the carbon carrier, any carbon carrier may be used as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state, and has sufficient electronic conductivity as a current collector. The main component is carbon. Is preferred. Specifically, carbon black such as ketjen black, channel black, furnace black, thermal black, vulcan, acetylene black, graphitized carbon black obtained by graphitizing the carbon black, activated carbon, coke, natural graphite, artificial graphite, etc. The carbon particle which consists of is mentioned. Carbon black is preferably used because of its high specific surface area and excellent conductivity.

  The shape of the carbon support is not particularly limited, but it is preferably in the form of particles in order to carry the catalyst particles in a highly dispersed manner. The average particle diameter of the carbon particles is 5 to 200 nm, preferably about 10 to 100 nm, from the viewpoint of controlling the thickness of the electrode catalyst layer produced using the electrode catalyst within an appropriate range.

  The catalyst particles used for the electrode catalyst are required to have a catalytic action in the oxidation reaction of hydrogen and / or the reduction reaction of oxygen, and those containing at least platinum are preferably used. Further, the catalyst particles may be an alloy of platinum and other metals in order to improve catalyst activity, poisoning resistance to carbon monoxide, heat resistance, and the like. Specifically, the alloy is at least selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Examples thereof include alloys with one or more metals.

  Among these, from the viewpoint of dissolution resistance, the platinum alloy particles are preferably an alloy of platinum and at least one metal selected from cobalt, ruthenium, and iridium. 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.

  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 includes a eutectic alloy, which is a mixture of the constituent elements as separate crystals, a solid solution in which the constituent elements are completely mixed, and the constituent element is an intermetallic compound or a compound of a metal and a nonmetal. In the present application, any of them may be used.

  In addition to the electrode catalyst, the catalyst layer contains a solid polymer electrolyte. The solid 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. Specifically, perfluorocarbon polymers having sulfonic acid groups such as Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), phosphoric acid, and the like. Hydrocarbon polymer compound doped with inorganic acid such as organic / inorganic hybrid polymer partially substituted with proton conductive functional group, polymer matrix impregnated with phosphoric acid solution or sulfuric acid solution And proton conductors.

  The PEFC of the present invention has a membrane electrode assembly in which a pair of catalyst layers, that is, a fuel electrode catalyst layer and an oxidant electrode catalyst layer are disposed on both sides of a solid polymer electrolyte membrane. In addition, a gas diffusion layer (GDL) may be disposed outside the oxidant electrode catalyst layer.

  As a material used for GDL, a sheet-like material made of carbon paper, carbon cloth, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. GDL is also required to have functions such as electron conductivity and water repellency. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Moreover, if GDL has excellent water repellency, the generated water is efficiently discharged.

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

  Various improvements may be made to the GDL in order to improve performance. For example, GDL gas diffusibility and compressibility may be improved by forming a layer composed of a fluororesin and carbon black on the surface of a carbon fiber woven sheet-like material (for example, Japanese Patent Laid-Open No. Hei 10). -261421, JP-A-11-273688).

  The separator used in the polymer electrolyte fuel cell of the present invention can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and carbon plate, and those made of metal such as stainless steel. . The separator has a function of separating the oxidant gas and the fuel gas, and preferably has a gas flow path for securing the flow paths thereof. The thickness and size of the separator, the shape of the gas flow path, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell. Examples of the shape of the gas flow path in the separator include a meandering shape and a linear shape from one end of the separator to the other end.

  In addition to the above-described ones, various members can be installed in the PEFC of the present invention as necessary. For example, a gasket that prevents leakage of gas supplied to the PEFC to the outside is disposed.

  In the polymer electrolyte fuel cell of the present invention, a stack in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator is formed so that the desired voltage of the polymer electrolyte fuel cell can be obtained. Also good. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The use of the polymer electrolyte fuel cell of the present invention is not particularly limited. Since the polymer electrolyte fuel cell of the present invention is excellent in durability, it is used as a driving power source in a vehicle such as an automobile in which deterioration of the constituent materials of the fuel cell is likely to occur due to frequent repeated starting and stopping. Good.

  As a method for producing a catalyst layer used in the PEFC of the present invention, a conventionally known method of applying and drying a catalyst layer ink containing an electrode catalyst, a solid polymer electrolyte, and the like to a substrate and appropriately using it may be used. it can. Specifically, a method is used in which a plurality of catalyst layer inks containing catalyst particles having different average particle sizes are prepared, and each catalyst layer ink is applied and dried at a predetermined position on the substrate.

  Examples of the solvent that can be used for the catalyst slurry include water and / or alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, and propylene glycol. Examples of the substrate on which the catalyst slurry is applied include a gas diffusion layer, a solid polymer electrolyte membrane, and a sheet-like substrate such as a PTFE sheet.

  For example, when preparing a catalyst layer divided into two regions in the surface direction of the membrane electrode assembly obtained, after applying the catalyst layer ink to a predetermined region of the substrate surface, For example, a method of applying a catalyst layer ink containing catalyst particles having an average particle diameter to the remaining region of the substrate surface is used.

  In the case of preparing a catalyst layer that is divided into two regions in the thickness direction of the membrane electrode assembly and further divided into two regions in the surface direction of the membrane electrode assembly, After applying the catalyst layer ink to a predetermined region of the catalyst layer, the catalyst layer ink containing catalyst particles having an average particle diameter larger than that of the catalyst layer ink is applied to the remaining region of the substrate surface to thereby form the catalyst layer (2). Get. Subsequently, after applying a catalyst layer ink containing catalyst particles having a larger average particle diameter to a predetermined region on the surface of the catalyst layer (2), a larger average is applied to the remaining region on the surface of the catalyst layer (2). A catalyst layer is obtained by applying a catalyst layer ink containing catalyst particles having a particle diameter to obtain the catalyst layer (1).

  The drying of the catalyst layer ink may be performed every time the catalyst layer ink is applied, or may be performed collectively after all the catalyst layer inks are applied. The drying of the catalyst layer ink is not particularly limited, but may be performed at 20 to 25 ° C. for about 0.5 to 2 hours.

The second of the present invention is a membrane electrode assembly in which a pair of catalyst layers are disposed on both sides of a solid polymer electrolyte membrane, and is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the crystallinity of the carbon support increases from the inlet side to the outlet side of the gas flow path.

  The basic structure of the polymer electrolyte fuel cell of the present invention (also simply referred to as “PEFC”) is the same as that of the polymer electrolyte fuel cell schematically shown in FIG. The structure is mentioned.

  In the electrode catalyst layer, the portion where the carbon support that is one of the causes of deterioration of the electrode catalyst is likely to be corroded is likely to be a portion that has a lot of moisture and is exposed to a high potential state during low load operation. This is considered to be caused by the following mechanism.

The moisture generated by the electrode reaction and the moisture contained in the gas supplied through the gas flow path provided in the separator are likely to stay in the catalyst layer, and in the catalyst layer from the inlet side to the outlet side of the gas flow path. The amount of water to be retained increases. The corrosion of the carbon support is caused by an electrochemical oxidation reaction (C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ ) that generates carbon dioxide using water present in the catalyst layer as an oxidizing agent, and proceeds using water as the oxidizing agent. . Further, such a corrosion reaction of the carbon support is further promoted at a portion where a high potential state (cell voltage of 0.8 V or more) is obtained. For this reason, the corrosion of the carbon carrier that causes the deterioration of the electrode catalyst in the electrode catalyst layer tends to occur remarkably as it goes from the inlet side to the outlet side of the gas flow path. Even if the corrosion of the carbon support on the inlet side of the gas flow path in the catalyst layer is small, the power generation performance of the entire battery tends to be reduced due to the large corrosion of the carbon support on the outlet side.

  In addition, a carbon support having low crystallinity has a large specific surface area and can carry catalyst particles in a highly dispersed manner, whereas a carbon support having high crystallinity is excellent in corrosion resistance. In the catalyst layer, high catalytic activity is maintained by disposing a carbon support with low crystallinity at a site where corrosion of the carbon support is unlikely to occur, and a carbon support with high crystallinity at a site where corrosion of the carbon support is likely to occur. However, corrosion of the carbon support can be efficiently suppressed.

  Thus, in the polymer electrolyte fuel cell of the present invention, by increasing the crystallinity of the carbon support in a predetermined direction in the electrode catalyst layer, the start and stop cycle of the fuel cell is repeated, whereby the electrode catalyst layer It is possible to suppress the deterioration of the electrode catalyst due to the carbon corrosion that is particularly likely to occur at the specific part. Therefore, according to the present invention, it is possible to provide a polymer electrolyte fuel cell capable of maintaining high power generation performance over a long period of time.

  Then, the structure which the catalyst layer in PEFC of this invention has is demonstrated.

  In the present invention, in the catalyst layer disposed on at least one of the fuel electrode side and the oxidant electrode side, the crystallinity of the carbon support is increased from the gas inlet side to the outlet side of the gas supply path of the separator. .

  In the present invention, the crystallinity of the carbon support is increased from the gas inlet side to the outlet side of the gas supply path of the separator in the catalyst layer, and further from the separator side to the solid polymer electrolyte membrane side in the catalyst layer. Thus, it is preferable to increase the crystallinity of the carbon support. Thereby, a carbon support with high corrosion resistance can be arranged at a portion where the carbon support of the catalyst layer is likely to be corroded, and the durability of PEFC can be further improved.

  The crystallinity of the carbon support can be easily adjusted by graphitization of the carbon support.

  The graphitization of the carbon carrier is not particularly limited as long as it is conventionally used, such as heat treatment. The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen, argon, or helium. Moreover, although heat processing temperature and heat processing time change with materials of the carbon support | carrier to be used, what is necessary is just to carry out at 2,000-3,000 degreeC for about 5 to 20 hours.

  As described above, the graphitization and the like improve the crystallinity of the carbon support and reduce the specific surface area of the carbon support, and the specific surface area of the carbon support is an indicator of the crystallinity of the carbon support. That is, as a preferred form of the catalyst layer of the present invention, the specific surface area of the carbon support in the catalyst layer is from the inlet side to the outlet side of the gas flow path, more preferably from the separator side to the solid polymer electrolyte membrane side. It becomes a form which becomes small toward.

  At this time, the specific surface area of the carbon support gradually decreases from the inlet side to the outlet side of the gas flow path of the catalyst layer, more preferably from the separator side to the solid polymer electrolyte membrane side. Or may be gradually reduced. In particular, the specific surface area of the carbon support should be reduced stepwise because the production of the catalyst layer and the control of the crystallinity of the carbon support in the catalyst layer are easy.

  As a catalyst layer having a configuration in which the crystallinity of the carbon support increases from the inlet side to the outlet side of the gas flow path of the catalyst layer, as a preferred embodiment, for example, in the surface direction of the membrane electrode assembly The structure shown in FIG. 2 which divides a catalyst layer into two or more area | regions is mentioned. FIG. 2 is a schematic view of the catalyst layer 120 having the inlet side catalyst layer 120i and the outlet side catalyst layer 120e, as described in the first aspect of the present invention. The inlet side catalyst layer 120i and the outlet side catalyst layer 120e may each contain a carbon support having a predetermined specific surface area. Then, when assembling the polymer electrolyte fuel cell, the inlet side catalyst layer 120i may be arranged on the inlet side of the gas flow path of the separator, and the outlet side catalyst layer 120e may be arranged on the outlet side of the separator.

When the catalyst layer is composed of two layers of an inlet side catalyst layer and an outlet side catalyst layer, the difference in specific surface area of the carbon support from the adjacent layer is preferably 10 to 800 m ² / g, more preferably 150 to 700 m ^2. / G.

As the specific surface area of the carbon support in each layer of the carbon support in each layer, specifically, the specific surface area of the carbon support included in the inlet-side catalyst layer is preferably 400 to 1000 m ² / g, more preferably 600～900M ² / G.

The specific surface area of the carbon support contained in the outlet-side catalytic layer is preferably 70~350m ² / g, more preferably preferably set to 100 to 250 m ² / g.

  The ranges of the inlet side catalyst layer and the outlet side catalyst layer in the catalyst layer may be determined in consideration of the durability of the obtained polymer electrolyte fuel cell. The outlet catalyst layer is preferably 40 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer. Thereby, a carbon support with high corrosion resistance can be contained in a portion where the electrode catalyst is likely to be deteriorated due to carbon corrosion.

  In the above, the catalyst layer is divided into two regions in the surface direction of the membrane electrode assembly. However, the present invention is not limited to this, and the catalyst layer is further divided into three or more regions in the surface direction of the membrane electrode assembly. It may be divided.

  As a preferred embodiment of the catalyst layer having a configuration in which the crystallinity of the carbon support is increased from the inlet side to the outlet side of the gas flow path, and further from the separator side to the solid polymer electrolyte membrane side, The catalyst layer is divided into two or more regions in the thickness direction of the membrane electrode assembly, and further divided into two or more regions in the surface direction of the membrane electrode assembly, and carbon having a predetermined specific surface area in each region. A configuration including a carrier is mentioned.

  Specifically, the catalyst layer (1) and the catalyst layer (2) are arranged in the thickness direction of the membrane electrode assembly such that the catalyst layer (1) is disposed on the solid polymer electrolyte membrane side. The catalyst layer (1) is formed by arranging an inlet side catalyst layer (1-1) and an outlet side catalyst layer (1-2) in the surface direction of the membrane electrode assembly, The layer (2) includes an inlet side catalyst layer (2-1) and an outlet side catalyst layer (2-2) arranged in the surface direction of the membrane electrode assembly, and each catalyst layer has a predetermined specific surface area. The structure which contains the carbon support | carrier which has is mentioned. More specifically, there is a catalyst layer 120 having the same configuration as that shown in FIG. 3 described in the first aspect of the present invention. The catalyst layer 120 includes an inlet side catalyst layer (1-1) 121i and an inlet side. A carbon carrier having a catalyst layer (2-1) 122i, an outlet side catalyst layer (1-2) 121e, and an outlet side catalyst layer (2-2) 122e, each having a specific surface area. Is done. Further, when the polymer layer 120 is used as the solid polymer fuel cell, the catalyst layer (1) is disposed on the separator side, the catalyst layer (2) is disposed on the solid polymer electrolyte membrane side, and the inlet side The catalyst layer (1-1) and the inlet side catalyst layer (2-1) are arranged on the inlet side of the gas flow path of the separator, and the outlet side catalyst layer (1-2) and the outlet side catalyst layer (2-2). Is disposed on the outlet side of the gas flow path of the separator.

When the catalyst layer (1) and the catalyst layer (2) are laminated, and the catalyst layer (1) is composed of at least two layers of an inlet side catalyst layer (1-1) and an outlet side catalyst layer (1-2) The difference in specific surface area of the carbon support from the adjacent layer in the catalyst layer (1) is preferably 130 to 700 m ² / g, more preferably 70 to ²⁰⁰ m ² / g.

Further, when the catalyst layer (2) is composed of at least two layers of an inlet side catalyst layer (2-1) and an outlet side catalyst layer (2-2), the difference in specific surface area of the carbon support with the adjacent layer is as follows: preferably 200~800m ² / g, more preferably from to the 300~500m ² / g.

As the specific surface area of the carbon support in each layer, specifically, the specific surface area of the carbon carrier contained in the inlet-side catalyst layer (2-1), preferably 400~1200m ² / g, more preferably 600~900m ² / The specific surface area of the carbon support contained in the outlet side catalyst layer (2-2) is preferably 200 to 900 m ² / g, more preferably 250 to 350 m ² / g.

The specific surface area of the carbon support contained in the inlet catalyst layer (1-1) is preferably 200 to 900 m ² / g, more preferably 250 to 350 m ² / g, and the outlet catalyst layer (1-2). the specific surface area of the carbon carrier contained in, preferably 70 to 250 ² / g, more preferably from 100 to 200 m ² / g.

  At this time, the specific surface area of the carbon support is smaller in the outlet side catalyst layer (2-2) than in the inlet side catalyst layer (2-1), and more in the outlet side than in the inlet side catalyst layer (1-1). The catalyst layer (1-2) is smaller, the inlet side catalyst layer (1-1) is smaller than the inlet side catalyst layer (2-1), and is smaller than the outlet side catalyst layer (2-2). Also, the outlet side catalyst layer (1-2) is preferably made smaller.

  In the present invention, the specific surface area of the carbon support is a value measured by the BET method measured by nitrogen adsorption.

  The range of the inlet side catalyst layer (1-1) and the outlet side catalyst layer (1-2) in the catalyst layer (1), the inlet side catalyst layer (2-1) and the outlet side catalyst layer ( The range 2-2) may be determined in consideration of the durability of the obtained polymer electrolyte fuel cell.

  The inlet catalyst layer (2-1) is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer (2).

  The inlet catalyst layer (1-1) is preferably 30 to 60% by volume, more preferably 40 to 50% by volume, based on the entire catalyst layer (1).

  In the present invention, it is preferable that the above-described catalyst layer further has a configuration in which the average particle diameter of the catalyst particles supported on the carbon support increases in a predetermined direction. As described in the first aspect of the present invention, catalyst particles having a large average particle diameter are excellent in dissolution resistance, and catalyst particles having a small average particle diameter are excellent in catalytic activity. Therefore, by appropriately disposing these in the catalyst layer, it is possible to further suppress the dissolution of the catalyst particles while maintaining high catalyst activity.

  Specifically, as the catalyst layer, it is preferable to increase the average particle diameter of the catalyst particles from the gas inlet side to the outlet side of the gas supply path of the separator in the catalyst layer. It is more preferable to increase the average particle diameter of the catalyst particles from the side toward the solid polymer electrolyte membrane side. As a result, catalyst particles having high dissolution resistance can be disposed in the catalyst layer where the catalyst particles are likely to be dissolved, and the durability of the PEFC can be further improved.

  At this time, the average particle diameter of the catalyst particles gradually increases from the inlet side to the outlet side of the gas flow path of the catalyst layer, more preferably from the separator side to the solid polymer electrolyte membrane side. Or may be gradually increased. Among these, since the production of the catalyst layer and the control of the average particle diameter of the catalyst particles in the catalyst layer are easy, the average particle diameter of the catalyst particles is preferably increased stepwise.

  When the catalyst layer is composed of two layers of the inlet side catalyst layer and the outlet side catalyst layer as in the catalyst layer shown in FIG. 2, the difference in the average particle diameter of the catalyst particles from the adjacent layer is preferably 0.1 to The thickness should be 4 nm, more preferably 0.1 to 2 nm.

  As the average particle diameter of the catalyst particles in each layer, specifically, the average particle diameter of the catalyst particles contained in the inlet side catalyst layer is preferably 2 to 4 nm, more preferably 2 to 3.5 nm. .

  The average particle size of the catalyst particles contained in the outlet side catalyst layer is preferably 2.5 to 6 nm, more preferably 3 to 5.5 nm.

  Moreover, like the catalyst layer shown in FIG. 3, the catalyst layer is composed of an inlet side catalyst layer (1-1), an outlet side catalyst layer (1-2), an inlet side catalyst layer (2-1), and an outlet side catalyst. In the case of having the layer (2-2), in the catalyst layer (1) composed of at least two layers of the inlet side catalyst layer (1-1) and the outlet side catalyst layer (1-2), catalyst particles with adjacent layers The difference in the average particle diameter is preferably 0.1 to 3.0 nm, more preferably 0.1 to 2.0 nm.

  Further, in the catalyst layer (2) composed of at least two layers of the inlet side catalyst layer (2-1) and the outlet side catalyst layer (2-2), the difference in the average particle diameter of the catalyst particles from the adjacent layers is The thickness is preferably 0.1 to 3.0 nm, more preferably 0.1 to 2.0 nm.

  As the average particle diameter of the catalyst particles in each layer, specifically, the average particle diameter of the catalyst particles contained in the inlet catalyst layer (2-1) is preferably 2 to 4 nm, more preferably 2 to 3 nm. The average particle diameter of the catalyst particles contained in the outlet side catalyst layer (2-2) is preferably 2.5 to 5 nm, more preferably 2.5 to 4 nm.

  The average particle diameter of the catalyst particles contained in the inlet side catalyst layer (1-1) is preferably 2.5 to 5 nm, more preferably 2.5 to 4 nm, and the outlet side catalyst layer (1- The average particle diameter of the catalyst particles contained in 2) is preferably 4 to 6 nm, more preferably 4 to 5 nm.

  At this time, the average particle diameter of the catalyst particles is larger in the outlet catalyst layer (1-2) than in the inlet catalyst layer (1-1), and is larger than that in the inlet catalyst layer (2-1). Also, the inlet side catalyst layer (1-1) is larger, the outlet side catalyst layer (2-2) is larger than the inlet side catalyst layer (2-1), and the outlet side catalyst layer (2) is larger. The outlet side catalyst layer (1-2) is preferably larger than -2).

  The total film thickness of the catalyst layer is preferably 25 μm or less. If the thickness of the entire catalyst layer is too thin, it may not be possible to secure a sufficient amount of catalyst necessary for the electrode reaction, and battery performance and life characteristics may be deteriorated. On the other hand, if the thickness of the catalyst layer is too thick, the power generation performance may be reduced. Therefore, the thickness of the catalyst layer should be determined in consideration of battery performance and life characteristics.

  When the catalyst layer is formed by laminating the catalyst layer (1) and the catalyst layer (2), the thickness of the catalyst layer (2) is preferably 4 to 15 μm, more preferably 6 to 10 μm. . The thickness of the catalyst layer (1) is preferably 2 to 7 μm, more preferably 2 to 5 μm.

  In the present invention, in the catalyst layer described above, platinum particles and platinum alloy particles are used as catalyst particles in the electrode catalyst, and the content rate of the platinum alloy particles is high from the inlet side to the outlet side of the gas flow path of the separator. It is preferable to further have a configuration in which the platinum alloy particle content is preferably increased from the separator side toward the solid polymer electrolyte membrane side in the catalyst layer. As a result, platinum alloy particles having high dissolution resistance can be disposed in the catalyst layer where the catalyst particles are likely to be dissolved, and the durability of the PEFC can be further improved. Since the catalyst layer having such a more preferable configuration is the same as that described in the first aspect of the present invention, a specific description such as the value of the content of platinum alloy particles is omitted here.

  Furthermore, the catalyst layer of the present invention preferably has a configuration in which the mass ratio of platinum in the platinum alloy particles decreases from the inlet side to the outlet side of the gas flow path of the separator. It is preferable that the mass ratio of platinum in the platinum alloy particles decreases from the side toward the solid polymer electrolyte membrane side. Thereby, dissolution of the catalyst particles in the catalyst layer can be further suppressed, and the durability of the obtained polymer electrolyte fuel cell can be further improved. Since the catalyst layer having such a more preferable configuration is the same as that described in the first aspect of the present invention, the specific description such as the value of the mass ratio of platinum in the platinum alloy particles is here. Omitted.

  In the polymer electrolyte fuel cell of the present invention, the catalyst layer described above having a configuration in which the crystallinity of the carbon support used as the support for the catalyst particles is increased from the inlet side to the outlet side of the gas flow path of the separator, It may be used for at least one of the fuel electrode catalyst layer and the oxidant electrode catalyst layer. Among them, it is preferably used for the oxidant electrode catalyst layer in which moisture retention occurs and the carbon carrier is easily corroded, and more preferably used for both the fuel electrode catalyst layer and the oxidant electrode catalyst layer.

  For the PEFC of the present invention, materials used in the conventional PEFC can be similarly used except that the crystallinity of the carbon support in the catalyst layer increases in a predetermined direction. The basic configuration of the solid polymer electrolyte membrane, the catalyst layer and the like is not particularly limited, and conventionally known ones are used as appropriate. Specifically, since the same thing as the explanation given in the first of the present invention is raised, the more detailed explanation about PEFC is omitted here.

  In addition, as a method for producing the catalyst layer used in the PEFC of the present invention, a conventionally known method for applying and drying a catalyst layer ink containing an electrode catalyst, a solid polymer electrolyte, and the like to a substrate is appropriately applied and used. be able to. Specifically, a method is used in which a plurality of catalyst layer inks containing carbon carriers having different crystallinity are prepared, and each catalyst layer ink is applied and dried at a predetermined position on the substrate. Specifically, since the same method as described in the first aspect of the present invention is used except that the crystallinity of the carbon support is adjusted instead of the average particle diameter of the catalyst particles, detailed description is omitted here. To do.

  Hereinafter, although the present invention is explained using an example, the technical scope of the present invention is not limited to the following example.

Example 1
For the electrode catalyst 1 in which platinum particles (average particle diameter of about 2.5 nm, supported amount of about 47% by mass) are supported on a carbon support (Ketjen black, specific surface area of about 800 m ² / g), pure water 2.5 Part by weight, 9 parts by weight of a 5 wt% Nafion ^TM solution and 1 part by weight of 1-propanol were mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink A.

Next, pure water 2 is applied to the electrode catalyst 2 in which platinum particles (average particle diameter: about 3.2 nm, supported amount: about 47% by mass) are supported on a carbon support (Ketjen black, specific surface area: about 800 m ² / g). 5 parts by weight, 9 parts by weight of 5 wt% Nafion ^TM solution and 1 part by weight of 1-propanol were mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink B.

Next, pure water 2 was applied to the electrode catalyst 3 in which platinum particles (average particle diameter of about 4.5 nm, supported amount of about 47% by mass) were supported on a carbon support (Ketjen black, specific surface area of about 800 m ² / g). 5 parts by weight, 9 parts by weight of a 5 wt% Nafion ^TM solution and 1 part by weight of 1-propanol were mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink C.

2. Production of Oxidant Electrode Catalyst Layer Using the catalyst layer ink A, catalyst layer ink B, and catalyst layer ink C prepared as described above, an oxidant electrode catalyst layer was formed. In this example, in order to make the structure of the oxidant electrode catalyst layer into a two-layer structure, an oxidant electrode catalyst layer composed of the catalyst layer (1) and the catalyst layer (2) was prepared below.

  First, the catalyst layer (2) was formed on a Teflon sheet having a thickness of 0.08 mm using a screen printer. The application area of the catalyst layer ink is 50 mm × 50 mm as a whole, and the catalyst layer ink A is applied to a portion of 50 mm × 25 mm, and the remaining 50 mm × 25 mm is applied to the catalyst layer ink B. By drying for 1 hour, a catalyst layer (2) (thickness: about 8 μm) was obtained.

  Next, after applying the catalyst layer ink B on the portion of the catalyst layer (2) where the catalyst layer ink A is applied, the catalyst layer is applied on the portion of the catalyst layer (2) where the catalyst layer ink B is applied. Ink C was applied and dried at about 25 ° C. for about 1 hour to obtain catalyst layer (1) (thickness: about 8 μm).

3. Preparation of fuel electrode catalyst layer Next, the catalyst layer ink A prepared above was applied to a 50 mm × 50 mm portion on a Teflon sheet having a thickness of 0.08 mm using a screen printer, and about 25 C. for about 1 hour. Thereby, the thickness of the fuel electrode catalyst layer (thickness of about 10 μm) in which no crack was formed was obtained.

4). Fabrication of PEFC A solid polymer electrolyte membrane (Nafion ^TM 111, thickness 25 μm, size 72 mm × 72 mm) is sandwiched between a Teflon sheet having an oxidant electrode catalyst layer and a Teflon sheet having a fuel electrode catalyst layer. , 2.0 MPa, hot pressing at 150 ° C. for 10 minutes, and then peeling off the Teflon sheet. The obtained joined body was further coated with carbon paper (thickness about 300 μm, size 52 mm × 63 mm) with a carbon layer (carbon black + PTFE particles). A membrane electrode assembly was obtained by sandwiching two sheets.

  The membrane electrode assembly was sandwiched between a pair of separators to produce a PEFC single cell. The separator is provided with a serpentine type gas supply path, and a portion of the catalyst layer (2) where the catalyst layer ink A is applied is brought close to the inlet side of the gas supply path, so that the catalyst layer (2 The membrane electrode assembly was sandwiched between a pair of separators so that the portion coated with the catalyst layer ink B was close to the outlet side of the gas supply path.

5. Evaluation Evaluation of initial power generation characteristics and durability of the PEFC produced above was performed according to the following procedure.

(1) Initial power generation characteristics Cell temperature: 70 ° C., fuel electrode: hydrogen (60% RH, utilization rate 67%), oxidizer electrode: air (50% RH, utilization rate 40%), supply gas is not pressurized Measured. Performs power generation test under these conditions, a 0.1 A / cm ^2, to measure the initial cell voltage at 1.0A / cm ^2. The results are shown in Table 1.

(2) Durability Cell temperature: 70 ° C., Fuel electrode: Hydrogen (100% RH, 500 cc / min), Oxidant electrode: Nitrogen (100% RH, 500 cc / min), supply gas was measured without pressurization . Under this condition, a potentiostat was used, and a potential of 0.5 V was applied to the oxidizer electrode for 5 seconds and then a potential of 1.0 V was applied to the fuel electrode for 5 seconds, after 10,000 cycles. The cell voltage was measured, and the durability was compared with the difference (Δ) between the cell voltage after 10,000 cycles and the initial cell voltage. The results are shown in Table 1.

(Example 2)
1 part by weight of electrode catalyst 4 supporting platinum particles (average particle diameter of about 3 nm, supported amount of about 47% by mass) on a carbon support (Vulcan XC-72, specific surface area of about 270 m ² / g), pure water 2.5 weight 9 parts by weight of a 5 wt% Nafion ^TM solution and 1 part by weight of 1-propanol were mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink B ′.

Next, platinum particles (average particle diameter of about 4.5 nm, on a carbon support (specific surface area of about 120 m ² / g) on a carbon support (specific surface area of about 120 m ² / g) heat treated in a nitrogen gas atmosphere at 2000 ° C. for about 10 hours. With respect to the electrode catalyst 5 supporting a supported amount of about 47% by mass), 2.5 parts by weight of pure water, 9 parts by weight of 5 wt% Nafion ^TM solution, and 1 part by weight of 1-propanol were mixed and dispersed and mixed with a homogenizer. Catalyst layer ink C ′ was prepared.

  A PEFC was prepared and evaluated in the same manner as in Example 1 except that the catalyst ink B 'was used in place of the catalyst ink B and the catalyst ink C' was used in place of the catalyst ink C. The results are shown in Table 1.

(Example 3)
A catalyst layer ink B ′ was prepared in the same manner as in Example 2.

Next, platinum-cobalt alloy particles (average particle diameter of about 4 nm) are applied on a carbon support (specific surface area of about 120 m ² / g) which has been heat-treated in a nitrogen gas atmosphere at 2000 ° C. for about 10 hours. In addition, 2.5 parts by weight of pure water and 9 parts by weight of a 5 wt% Nafion ^TM solution and 1 part by weight of 1-propanol with respect to the electrode catalyst 6 supporting a supported amount of about 50% by weight and a Pt: Co mass ratio of 3: 1) And dispersed and mixed with a homogenizer to prepare catalyst layer ink C ″.

  A PEFC was prepared and evaluated in the same manner as in Example 1 except that the catalyst ink B ′ was used in place of the catalyst ink B and the catalyst ink C ″ was used in place of the catalyst ink C. The results are shown in Table 1.

Example 4
Catalyst layer ink A was prepared in the same manner as in Example 1.

Next, a platinum-cobalt alloy particle (average particle diameter of about 3) is applied on a carbon support (specific surface area of about 300 m ² / g) obtained by heat treating a carbon support (Ketjen Black) in a nitrogen gas atmosphere at 1300 ° C. for about 8 hours. .2 nm, supported amount of about 47% by mass, Pt: Co mass ratio of 5: 1) supported electrode catalyst 7, 2.5 parts by weight of pure water, 9 parts by weight of 5 wt% Nafion ^TM solution, 1-propanol 1 Part by weight was mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink B ′ ″.

Next, platinum-cobalt alloy particles (average particle diameter of about 4) are applied on a carbon support (specific surface area of about 120 m ² / g) obtained by heat treating a carbon support (Ketjen Black) in a nitrogen gas atmosphere at 2000 ° C. for about 10 hours. 2.5 parts by weight of pure water and 9 parts by weight of 5 wt% Nafion ^TM solution with respect to the electrode catalyst 8 supporting 5 nm, supported amount of about 47% by mass, and Pt: Co mass ratio of 3: 1), 1-propanol 1 Part by weight was mixed and dispersed and mixed with a homogenizer to prepare catalyst layer ink C ′ ″.

2. Preparation of Oxidant Electrode Catalyst Layer Using the catalyst layer ink A, catalyst layer ink B ′ ″, and catalyst layer ink C ′ ″ prepared as described above, an oxidant electrode catalyst layer was formed. In this example, in order to make the structure of the oxidant electrode catalyst layer into a two-layer structure, an oxidant electrode catalyst layer composed of the catalyst layer (1) and the catalyst layer (2) was prepared below.

  First, the catalyst layer (2) was formed on a Teflon sheet having a thickness of 0.08 mm using a screen printer. The application area of the catalyst layer ink is 50 mm × 50 mm as a whole, and the catalyst layer ink A is applied to a portion of 50 mm × 25 mm, and the remaining 50 mm × 25 mm is applied to the catalyst layer ink B ′ ″. The catalyst layer (2) (thickness: about 8 μm) was obtained by drying at about 1 hour for about 1 hour.

  Next, after applying the catalyst layer ink B ′ ″ on the portion of the catalyst layer (2) where the catalyst layer ink A is applied, the catalyst layer ink B ′ ″ of the catalyst layer (2) is applied. The catalyst layer ink C ′ ″ was applied onto the dried portion and dried at about 25 ° C. for about 1 hour to obtain a catalyst layer (1) (thickness: about 8 μm).

  A PEFC was prepared and evaluated in the same manner as in Example 1 except that a Teflon sheet on which an oxidant electrode catalyst layer was formed as described above was used. The results are shown in Table 1.

(Comparative Example 1)
The catalyst layer ink A prepared in the same manner as in Example 1 is applied to a 50 mm × 50 mm portion on a 0.08 mm thick Teflon sheet using a screen printer and dried at about 25 ° C. for about 1 hour. Thus, an oxidant electrode catalyst layer (thickness: 15 μm) was obtained.

  Next, the catalyst layer ink A prepared in the same manner as in Example 1 was applied to a 50 mm × 50 mm portion on a 0.08 mm thick Teflon sheet using a screen printer, and about 25 ° C. for about 1 hour. By drying, a fuel electrode catalyst layer (thickness 10 μm) was obtained.

  A PEFC was prepared and evaluated in the same manner as in Example 1 except that a Teflon sheet on which each catalyst layer was formed as described above was used. The results are shown in Table 1.

The cross-sectional schematic diagram of the polymer electrolyte fuel cell of this invention is shown. The schematic diagram of the catalyst layer used for the polymer electrolyte fuel cell of this invention is shown. The schematic diagram of the catalyst layer used for the polymer electrolyte fuel cell of this invention is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Membrane electrode assembly, 110 ... Polymer electrolyte membrane, 120, 120a and 120c ... Catalyst layer, 120i ... Inlet side catalyst layer, 120e ... Outlet side catalyst layer, 121i ... Inlet side catalyst layer (1-1), 121e ... Exit side catalyst layer (1-2), 122i ... Inlet side catalyst layer (2-1), 122e ... Exit side catalyst layer (2-2), 140a and 140c ... Separator, 141 ... Gas supply path, 150 ... Solid Polymer fuel cell.

Claims (9)

A membrane electrode assembly in which a pair of catalyst layers is disposed on both sides of a solid polymer electrolyte membrane is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the average particle diameter of the catalyst particles increases from the inlet side to the outlet side of the gas flow path.   2. The solid polymer fuel cell according to claim 1, wherein the catalyst layer has an average particle diameter of the catalyst particles that increases from the separator side toward the solid polymer electrolyte membrane side. A membrane electrode assembly in which a pair of catalyst layers is disposed on both sides of a solid polymer electrolyte membrane is sandwiched by a separator having a gas flow path,
The catalyst layer is a solid polymer fuel cell comprising an electrode catalyst having catalyst particles supported on a carbon support, and a solid polymer electrolyte,
At least one of the catalyst layers is a polymer electrolyte fuel cell in which the crystallinity of the carbon support increases from the inlet side to the outlet side of the gas flow path.   The polymer electrolyte fuel cell according to claim 3, wherein the catalyst layer has higher crystallinity of the carbon support from the separator side toward the solid polymer electrolyte membrane side. The catalyst layer includes a catalyst layer (1) and a catalyst layer (2) in the thickness direction of the membrane electrode assembly such that the catalyst layer (1) is disposed on the solid polymer electrolyte membrane side. Laminated,
The catalyst layer (1) includes an inlet-side catalyst layer (1-1) and an outlet-side catalyst layer (1-2) arranged in the surface direction of the membrane electrode assembly,
The catalyst layer (2) has an inlet side catalyst layer (2-1) and an outlet side catalyst layer (2-2) arranged in the surface direction of the membrane electrode assembly,
The catalyst particles contained in the inlet catalyst layer (2-1) have an average particle diameter of 2 to 4 nm,
The catalyst particles contained in the outlet catalyst layer (2-2) have an average particle size of 2.5 to 5 nm,
The average particle diameter of the catalyst particles contained in the inlet side catalyst layer (1-1) is 2.5 to 5 nm,
The average particle diameter of the catalyst particles contained in the outlet side catalyst layer (1-2) is 4 to 6 nm,
The average particle diameter of the catalyst particles is larger in the outlet-side catalyst layer (1-2) than in the inlet-side catalyst layer (1-1), and is larger than that in the inlet-side catalyst layer (2-1). The side catalyst layer (2-2) is larger, the inlet side catalyst layer (1-1) is larger than the inlet side catalyst layer (2-1), and the outlet side catalyst layer (2-2). The polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the outlet side catalyst layer (1-2) is larger than the outlet side catalyst layer (1-2). The catalyst particles include platinum particles and platinum alloy particles,
6. The solid polymer fuel cell according to claim 1, wherein the catalyst layer has a higher content of the platinum alloy particles from the inlet side to the outlet side of the gas flow path.   The polymer electrolyte fuel cell according to claim 6, wherein the catalyst layer has a higher content of the platinum alloy particles from the separator side toward the solid polymer electrolyte membrane side.   8. The polymer electrolyte fuel cell according to claim 6, wherein the catalyst layer has a mass ratio of platinum in the platinum alloy particles that decreases from an inlet side to an outlet side of the gas flow path.   The solid polymer fuel cell according to claim 8, wherein the catalyst layer has a platinum mass ratio in the platinum alloy particles that decreases from the separator side toward the solid polymer electrolyte membrane side.

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