JP5755833B2 - Anode catalyst layer for fuel cells - Google Patents

Description

  The present invention relates to an electrolyte membrane-electrode assembly (hereinafter also referred to as MEA), and particularly to an anode catalyst layer of an MEA for a fuel cell. More specifically, the present invention relates to an anode catalyst layer of a fuel cell MEA having excellent power generation performance and durability.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature. In general, the polymer electrolyte fuel cell has a structure in which MEA is sandwiched between a gas diffusion layer and a separator. The MEA is an electrolyte membrane that is sandwiched between a pair of catalyst layers.

In the polymer electrolyte fuel cell having the MEA as described above, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the anode side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ ). Next, the generated protons pass through the electrolyte contained in the catalyst layer and the electrolyte membrane in contact with the catalyst layer, and reach the cathode catalyst layer. Further, the electrons generated in the anode catalyst layer reach the cathode catalyst layer through the carrier constituting the catalyst layer, the gas diffusion layer in contact with the side of the catalyst layer that is different from the electrolyte membrane, the separator, and the external circuit. The protons and electrons that have reached the cathode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O). In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  However, when the fuel cell falls into a reversal state due to a shortage of hydrogen, the anode side may be at a high potential, and when carbon containing carbon is used as the carrier constituting the anode catalyst layer, the carbon corrodes. There was a problem.

  In order to solve such a problem, it is necessary to keep the potential applied to the anode catalyst layer low. As one measure for reducing the potential, there is a measure of promoting the water electrolysis reaction in the anode catalyst layer. Therefore, conventionally, a technique of adding ruthenium or iridium oxide as a catalyst composition of the anode catalyst layer is known (Patent Document 1).

Special table 2003-508877 gazette

  However, according to the technique of Patent Document 1, corrosion of the conductive carbon material of the anode catalyst layer (hereinafter, also simply referred to as “anode carbon corrosion”) has not been solved as a problem.

  Therefore, an object of the present invention is to provide an anode catalyst layer of a fuel cell MEA that improves durability by suppressing anode carbon corrosion.

  The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by providing an anode catalyst layer containing a catalyst component containing a certain amount or more of iridium, and the present invention has been completed.

  By supporting a certain amount or more of iridium per catalyst coating area constituting the anode catalyst layer, the anode catalyst layer has high water electrolysis activity. At the same time, the hydrogen oxidation activity necessary for the operation of the fuel cell is maintained. By these, anode carbon corrosion at the time of fuel deficiency can be suppressed.

FIG. 1 is a graph showing the amount of water electrolysis reaction at a predetermined potential with respect to the amount of iridium supported per catalyst application area constituting the anode catalyst layer. FIG. 2 is a graph showing the carbon corrosion reaction amount of each conductive carbon material as a carrier constituting the anode catalyst layer with respect to a predetermined potential. FIG. 3 is a graph showing the amount of carbon corrosion reaction when 100 mA / cm ^{2 is} applied to the amount of iridium supported per catalyst application area constituting the anode catalyst layer. FIG. 4 is a graph showing the amount of carbon corrosion reaction when 100 mA / cm ^{2 is} applied to the amount of iridium supported per catalyst application area constituting the anode catalyst layer. FIG. 5 is a graph showing the amount of carbon corrosion reaction when 200 mA / cm ^{2 is} applied to the amount of iridium supported per catalyst application area constituting the anode catalyst layer. FIG. 6 is a graph showing the carbon corrosion inhibition rate when 100 mA / cm ^{2 is} applied with respect to the amount of iridium supported per catalyst application area constituting the anode catalyst layer. FIG. 7 is a graph showing the power generation performance with respect to the amounts of iridium and platinum as catalyst components supported per catalyst application area constituting the anode catalyst layer. FIG. 8 is a graph showing the power generation performance with respect to the thickness of the anode catalyst layer when the amount of the catalyst component carried per catalyst application area is constant. FIG. 9 is a graph showing the amount of carbon corrosion current per amount of carbon used with respect to the amount of iridium as a catalyst component supported per catalyst application area constituting the anode catalyst layer.

<First of the present invention>
A first aspect of the present invention is an anode catalyst layer of an MEA for a fuel cell, comprising a catalyst in which a catalyst component containing 0.005 mg / cm ² or more of iridium is supported on a conductive carbon raw material as a carrier.

[Anode catalyst layer]
First, the anode catalyst layer will be described. In the anode catalyst layer of the present invention, a carbon material having conductivity (also referred to as “conductive carbon material” in this specification) is used as a carrier.

The anode catalyst layer of the present invention is disposed on one side of the MEA electrolyte membrane. And the anode catalyst layer of this invention contains the catalyst by which a catalyst component is carry | supported by the electroconductive carbon material, and contains 0.005 mg / cm < ² > or more of iridium as this catalyst component. It should be noted that during the operation of the fuel cell, it may be in the form of an oxide depending on its potential, so these ranges are converted as iridium simple substance. In this specification, “catalyst layer” includes “catalyst”, and “catalyst” is composed of “support” and “catalyst component”.

In the present invention, 0.005 mg / cm ² or more of iridium is supported on the catalyst application area as a catalyst component constituting the anode catalyst layer. Therefore, when the fuel cell falls into a reversal state in a state of hydrogen shortage, high water electrolysis activity is maintained and anode carbon corrosion is suppressed. On the other hand, if the amount of iridium supported is less than 0.005 mg / cm ² , the effect of suppressing anode carbon corrosion cannot be sufficiently obtained.

In the anode catalyst layer of the present invention, the amount (mg / cm ² ) of iridium as a catalyst component per catalyst coating area is 0.005 mg / cm ² or more, preferably 0.005 to 1.0 mg / cm ^{2. 2} , more preferably 0.01 to 0.3 mg / cm ² . 1.0 mg / cm ² or less is preferable because the effect of suppressing carbon corrosion per amount of iridium added during catalyst preparation is high, that is, the cost can be reduced. Moreover, 0.01 mg / cm < ² > or more is preferable in order to maintain high power generation performance. 0.3 mg / cm ² or less is more preferable because the thickness of the anode catalyst layer can be reduced to a predetermined value or less, the proton transfer resistance can be reduced, and the gas diffusibility can be maintained. This is because the power generation performance can be improved while maintaining carbon corrosion resistance. In addition, in this specification, inductively coupled plasma emission spectroscopy (ICP-AES) is used as a method of measuring (confirming) “mass of catalyst component per catalyst application area (mg / cm ² )”. If the value measured by this method is included in the predetermined amount of the present invention, it is included in the technical scope of the present invention. Further, a method of making “mass of catalyst component per catalyst coating area (mg / cm ² )” can be easily performed by those skilled in the art, and by controlling the slurry composition (catalyst concentration) and the coating amount. The amount can be adjusted.

As described above, in the anode catalyst layer of the present invention, the catalyst component contains at least 0.005 mg / cm ² or more of iridium. In addition, catalyst components other than iridium may be included. Such a catalyst component is not particularly limited, and specifically, platinum, gold, silver, copper, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, Examples thereof include metals such as vanadium, molybdenum, gallium, and aluminum, and alloys thereof. The catalyst component works more effectively when added as a metal rather than an oxide.

The composition of the alloy varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art. The composition of the alloy is preferably 30 to 90 atomic% for platinum and 70 to 10 atomic% for other metals 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 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. However, for reasons of cost, it is preferably about 0.1 mg / cm ² or less even if included.

  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. The size (average particle diameter) of the catalyst component is preferably 1 to 10 nm, more preferably 1 to 5 nm. Here, when the average particle size of the catalyst component is less than 1 nm, although the surface area of the catalyst component is increased, elution is easily caused by a change in potential, and there is a possibility that performance deterioration with time is large. On the other hand, if the average particle size of the catalyst component exceeds 10 nm, the surface area of the catalyst component becomes too small, and it is difficult to ensure a sufficient three-phase interface. In addition, the magnitude | size (average particle diameter) of the catalyst component used for an anode catalyst layer may be the same, or may differ, and is suitably selected so that there may exist a desired effect | action. The “average particle diameter of the catalyst component” in the present invention is measured by the crystallite diameter obtained from the half-value width of the diffraction peak of the substance in X-ray diffraction or the average value of the particle diameter determined from a transmission electron microscope image. be able to.

  In the anode catalyst layer of the present invention, 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.

In the anode catalyst layer of the present invention, the catalyst component loading rate (also referred to as the loading amount) on the carrier is preferably 20 to 60% by mass with respect to the total amount of the catalyst (that is, the carrier and the catalyst component). More preferably, it is good to set it as 30-50 mass%. In the above, the catalyst component is the total of 0.005 mg / cm ² or more of iridium and further the catalyst component when other catalyst components are included. If the supported amount exceeds 60% by mass, the power generation performance may be deteriorated or the structure of the anode catalyst layer may be destroyed. In order to increase the effect of inhibiting carbon corrosion, it is necessary to increase the effective surface area of iridium. Therefore, it is necessary to improve the dispersion, and the catalyst is desired to be as low as possible. However, the catalyst layer thickness increases due to the low loading ratio, resulting in deterioration of gas diffusibility, deterioration of proton conductivity, deterioration of electrical conductivity, or excessive increase in the amount of carbon used, resulting in catalyst due to carbon corrosion. There are adverse effects such as accelerated layer structure destruction. For this reason, it is desired that the catalyst layer thickness of the anode be not more than a predetermined thickness.

The thickness of the anode catalyst layer of the present invention is preferably 0.1 to 6 μm, more preferably 0.1 to 1 μm. By setting it as this range, water electrolysis reaction can fully be exhibited. When the catalyst loading is 0.1 mg / cm ² and the catalyst loading is 30%, the catalyst layer thickness is about 6 μm. If the catalyst loading is 30% or less, the catalyst loading may exceed 6 μm. If it does so, there exists a possibility of causing a performance fall and catalyst layer structure destruction. If too much iridium and other catalyst components are added, the thickness of the catalyst layer is increased, which may reduce the power generation performance. Further, since the amount of noble metal used increases, the cost naturally increases. On the other hand, if the anode catalyst layer thickness is 6 μm or less, the gas diffusibility in the anode catalyst layer can be maintained, so that the power generation performance can be improved. In addition, since the amount of water movement from the electrolyte membrane can be sufficiently secured, the water electrolysis reaction can be continued for a longer time, and it is effective not only for short time hydrogen deficiency but also for long time hydrogen deficiency. it can.

  The thickness of a catalyst layer can be measured by observing the anode catalyst layer of the present invention with a scanning electron microscope (SEM). Since the anode catalyst layer is made flat, it is macroscopically flat, but is not microscopically flat, and a thin portion and a thick portion of the catalyst layer can be generated. The upper limit value of the thickness of the anode catalyst layer in the present invention is 6 μm.

  In the anode catalyst layer of the present invention, a carbon material having conductivity (also referred to as “conductive carbon material” in the present specification) is used as the support.

  Examples of such conductive carbon materials include Ketjen black, Vulcan, acetylene black, black pearl, carbon particles preliminarily heat-treated at high temperature, carbon nanotubes, carbon nanohorns, carbon nanofibers, and the like. In the cathode catalyst layer of the present invention, ketjen black, acetylene black, and ketjen black previously heat-treated at a high temperature are preferable because they can have a specific surface area of a certain level or more. The heat treatment conditions at a high temperature in advance are not particularly limited, but it is preferably performed at 2000 to 2500 ° C. in an inert atmosphere.

As the specific surface area of the conductive carbon material as the support increases, the anodic corrosion is promoted. That is, the smaller the specific surface area, the more the anode corrosion is suppressed. In the anode catalyst layer of the present invention, although not particularly limited, the specific surface area of the conductive carbon material is preferably 250 m ² in view of the object of the present invention, that is, not only the power generation performance but also the suppression of anode carbon corrosion. / G, more preferably less than 150 m ² / g, but from the viewpoint of dispersibility of the catalyst, 100 m ² / g or more is preferable. When the specific surface area is in the above range, the dispersibility of the catalyst component on the carrier is good, sufficient power generation performance can be achieved, and anode carbon corrosion can be significantly suppressed. In the present specification, the specific surface area is a surface area measured by the BET method.

  In the anode catalyst layer of the present invention, the size of the conductive carbon material as a support is not particularly limited, but from the viewpoint of controlling the thickness of the catalyst layer within an appropriate range, the average particle size is 5 to 200 nm, The thickness is preferably about 10 to 100 nm.

  The anode catalyst layer of the present invention contains a proton conductive material.

  The proton conductive material is not particularly limited and a known material can be used, but any member having at least high proton conductivity may be used. Proton conductive materials that can be used at this time are broadly classified into fluorine-based electrolytes containing fluorine atoms in the whole or part of the polymer skeleton and hydrocarbon-based electrolytes not containing fluorine atoms in the polymer skeleton.

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

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

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

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

  In the present invention, it is possible to approximate (calculate) the amount of carbon corrosion allowed to maintain the required power generation performance. Because the endurance time of the fuel cell is finite, by determining the target endurance time, the allowable current of anode carbon corrosion can be determined from the average current density that flows when hydrogen is depleted, the average duration of hydrogen depletion, and the frequency of hydrogen depletion. The current density can be calculated.

  As will be described in detail in the Examples section, in order to obtain sufficient durability, it is preferable that the amount of carbon corrosion current measured in the anode catalyst layer is a predetermined value or less under predetermined conditions. The higher the carbon corrosion current amount per use amount of the conductive carbon material constituting the anode catalyst layer, the higher the carbon corrosion rate, and the lower the durability. On the contrary, the lower the carbon corrosion rate, the lower the carbon corrosion rate. Because it becomes higher.

The predetermined conditions are as follows. That is, as described in detail in the section of the embodiment, the polarization curve on the fuel electrode side in an air atmosphere at a cell temperature of 50 ° C. (anode gas: air RH = 80%, cathode gas: hydrogen RH = 80%, scanning range: 1 V This is when the sum of the current density due to the water electrolysis reaction and the carbon corrosion reaction is 100 mA / cm ^{2 at} the time of acquiring ˜2 V and scanning speed: 5 mV / sec. At that time, the carbon corrosion current amount per amount of the conductive carbon material constituting the anode catalyst layer is preferably a low value from the viewpoint of preventing corrosion, and is preferably 12 A / g or less. By setting it to 12 A / g or less, sufficient durability can be obtained. That is, since the amount of anode carbon corrosion can be reliably reduced, the conductive carbon material constituting the anode catalyst layer can be selected more appropriately. Therefore, the kind of conductive carbon material which comprises an anode catalyst layer, and its addition amount can be made appropriate, and sufficient durability can be obtained. The condition “when the sum of the current densities due to the water electrolysis reaction and the carbon corrosion reaction is 100 mA / cm ² ” assumes this current density as an endurance condition necessary for ensuring practicality. That is, in the case of a fuel cell vehicle, since the average current density with respect to the operation time is about this level, it is considered sufficient to estimate at about “100 mA / cm ² ” unless it is used in a special manner. In Examples described below, "the sum of the current density, 200 mA / cm ^2" were subjected to experiment under the condition that "the sum of the current density, 100 mA / cm ^2" and similar results were obtained. That is, it can be understood that the anode carbon corrosion is significantly suppressed by containing a certain amount (0.005 mg / cm ² ) of iridium as a catalyst component constituting the anode catalyst layer (that is, “0.005 mg / cm ² ). The technical significance of “cm ² ” can also be supported by this result).

  In addition, when the amount of carbon corrosion current is measured under such a predetermined condition, when it is 12 A / g or less, it is estimated that a certain amount or more of iridium is supported as a catalyst component of the anode catalyst layer per catalyst application area. It is presumed that the technical scope of the present invention is at least partially implemented.

In the above, in the anode catalyst layer of the present invention, the amount (mg / cm ² ) of iridium as a catalyst component per catalyst coating area is defined to be 0.005 mg / cm ² or more. Preferably 0.005~1.0mg / cm ^2, more preferably from 0.01~0.3mg / cm ^2. However, it is more preferable to adjust the amount of iridium according to the type of the conductive carbon material as the support constituting the anode catalyst layer. For example, in a conductive carbon material (Carbon type (1) BET specific surface area = 800 m ² / g) having low carbon corrosion resistance, the amount of iridium is preferably 0.096 mg / cm ² or more, and 0.1 mg / cm ² More preferably, it is 0.1 to 1.0 mg / cm ² . In a conductive carbon material (Carbon type (2) BET specific surface area = 250 m ² / g) having a relatively high carbon corrosion resistance, the amount of iridium is preferably about 0.05 mg / cm ² or more, more preferably 0.8. a 05~0.2mg / cm ^2, more preferably from 0.05 to 0.1 / cm ^2. In a conductive carbon material (Carbon type (3) BET specific surface area = 125 m ² / g) having high carbon corrosion resistance, the amount of iridium is preferably about 0.02 mg / cm ² or more, more preferably 0.02 to 0 .15 mg / cm ² , more preferably 0.02 to 0.1 mg / cm ² . The basis for determining these ranges is based on the description of the examples. In this embodiment, only iridium is added as the catalyst component of the anode catalyst layer. However, even if platinum is contained as a catalyst component of the anode catalyst layer, it was found by the examples described later that platinum hardly contributes to the water electrolysis reaction as compared with iridium. It is added that the range of is unchanged.

  Carbon type (1), Carbon type (2) and Carbon type (3) are respectively the least durable, medium durable, and most durable commonly used in the industry. It is classified into a high class. The amount of iridium as a catalyst component of the anode catalyst layer defined in the present invention is effective (lifetime) even when Carbon type (1) of a low durability type is used (confirmed). Is) quantity. That is, when carbon type Carbon type (3) having higher corrosion resistance or a carbon type having higher resistance is used, the life is further extended. Of course, the lifetime may be determined not only by the corrosion resistance of the carbon species but also by the total characteristics of the catalyst layer.

On the other hand, to obtain data on the amount of water electrolysis reaction current (mA / cm ² ), strictly speaking, oxygen measurement and carbon dioxide measurement using a gas analyzer are required.

In order to obtain sufficient durability, as described in detail in the example section, a polarization curve on the fuel electrode side in an air atmosphere at a cell temperature of 50 ° C. (anode gas: air RH = 80%, cathode gas: hydrogen RH = 80%, scanning range: 1 V to 2 V, scanning speed: 5 mV / sec) Current density due to water electrolysis reaction (strictly, the measured current value includes water electrolysis reaction current and carbon corrosion reaction current) This is at 100 mA / cm ² . It is desirable that the potential at that time is 1.635V or less. More preferably, it is 1.5 V or less. In addition, when the potential is measured under such a predetermined condition, if it becomes 1.635 V or less, the amount of carbon corrosion current is estimated to be 12 A / g or less. It is estimated that the target range is implemented at least in part. Such “1.635 V or less” is a condition that allows the “carbon corrosion current amount to be 12 A / g or less” even when the most corrosive carbon species (Carbon type (1)) are used. If it is 1.635 V or less, sufficient water electrolysis activity can be obtained, and anode carbon corrosion at the time of hydrogen deficiency during fuel cell power generation can be sufficiently suppressed. Therefore, the carbon used for the anode can be selected, and the stack durability can be reliably improved while maintaining high performance.

[Method for producing anode catalyst layer of the present invention]
In the first aspect of the present invention, the anode catalyst layer is produced by a method such as a transfer method by using a carrier (catalyst) on which a predetermined amount of the predetermined catalyst component of the present invention is supported, a proton conductive material, and a solvent. it can. The method for producing such an anode catalyst layer is not particularly limited, and a known transfer method can be used in the same manner or with appropriate modification. For example, the following method can be used.

  That is, an anode catalyst ink is prepared. Next, an anode catalyst ink (hereinafter also simply referred to as “catalyst ink”) is applied and dried on a transfer mount to form an anode catalyst layer. At this time, as the transfer mount, a known sheet such as a polyester sheet such as a PTFE (polytetrafluoroethylene) sheet or a PET (polyethylene terephthalate) sheet can be used. The transfer mount is appropriately selected according to the type of catalyst ink (particularly a carrier such as carbon in the ink) to be used. Moreover, it does not restrict | limit especially as a solvent, The normal solvent used for forming a cathode catalyst layer can be used similarly. Specifically, lower alcohols such as water, cyclohexanol, ethanol, n-propyl alcohol, and 2-propyl alcohol can be used. Further, the amount of the solvent used is not particularly limited, and a known amount can be used.

  The catalyst ink may contain a thickener. The use of a thickener is effective when the catalyst ink cannot be successfully applied onto a transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. For example, glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), propylene glycol (PG) and the like can be mentioned. Of these, propylene glycol (PG) is preferably used. The use of propylene glycol (PG) increases the boiling point of the catalyst ink and decreases the solvent evaporation rate. For example, when forming a catalyst layer on an electrolyte membrane by a transfer method, first, a catalyst ink is applied and dried on a transfer mount different from the membrane using a screen printer or the like. At this time, by adding PG to the catalyst ink, the solvent evaporation rate in the applied catalyst ink is suppressed, and it is possible to suppress / prevent the occurrence of cracks in the catalyst layer after the drying process. Further, the amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above-described effects of the present invention, but is preferably 5 with respect to the total mass of the catalyst ink. ˜20 mass%.

  Further, the catalyst ink may contain a water repellent polymer. The use of the water-repellent polymer is effective when the catalyst ink cannot be applied well onto the transfer mount. The water-repellent polymer that can be used in this case is not particularly limited, and a known water-repellent polymer can be used. Examples include fluorine-based polymer materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, and polyethylene. It is done. In addition, the amount of the water-repellent polymer added when the water-repellent polymer is used is not particularly limited as long as it is an amount that does not interfere with the above-described effect of the present invention. Is 0.1 to 20% by mass.

  The preparation method of the catalyst ink is not particularly limited as long as the catalyst, the proton conductive material and the solvent, and if necessary, the water-repellent polymer and / or the thickener are appropriately mixed.

  In addition, the catalyst ink is obtained by dispersing the slurry mixed as described above with an ultrasonic homogenizer, or after thoroughly pulverizing the mixed slurry with an apparatus such as a sand grinder, a circulating ball mill, or a circulating bead mill. It is preferable to prepare by adding a vacuum degassing operation.

  The method for applying the catalyst ink onto the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied.

  In the above method, the drying conditions of the coated anode catalyst layer are not particularly limited as long as the solvent can be completely removed from each catalyst layer. Specifically, the coating layer (catalyst layer) of the catalyst ink is dried in a vacuum dryer at room temperature to 100 ° C., more preferably 50 to 80 ° C., for 1 to 50 hours. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained.

  In this way, an anode catalyst layer can be manufactured.

  The anode catalyst layer of the present invention can be used as a part of a fuel cell MEA. The cathode catalyst layer and the electrolyte membrane of the fuel cell MEA using the anode catalyst layer of the present invention will be described below.

[Cathode catalyst layer]
Since the present invention is characterized by the anode catalyst layer of the MEA for fuel cells, a general form for fuel cells can be applied to the cathode catalyst layer. In addition, in order to avoid duplication of explanation, when the matters explained in the anode catalyst layer are similarly valid, they may not be described in this section.

  The cathode catalyst layer of the present invention is disposed on the other side of the electrolyte membrane. The cathode catalyst layer includes a catalyst in which a catalyst component is supported on a conductive carbon material, and the catalyst component is not particularly limited, but a catalyst component that can be used in the anode catalyst layer described above can be used. 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. The size (average particle diameter) of the catalyst component is preferably 1 to 10 nm, more preferably 1 to 5 nm.

  In the cathode catalyst layer of the present invention, the catalyst component can be supported on the carrier by a known method as described above.

  In the cathode catalyst layer of the present invention, the loading ratio of the catalyst component on the carrier is preferably 20 to 70 mass%, more preferably 30 to 50 mass%, based on the total amount of the catalyst. If the loading is within the above range, it is preferable because a sufficient degree of dispersion of catalyst components on the carrier, improvement in power generation performance, economic advantages, and catalytic activity per unit mass can be achieved.

  In the cathode catalyst layer of the present invention, the thickness of the cathode catalyst layer is preferably 1 to 20 μm, more preferably 2 to 15 μm. By setting it within this range, the catalytic action of the oxygen reduction reaction (cathode side) can be sufficiently exerted.

In the cathode catalyst layer of the present invention, as the support, a conductive carbon material is used as in the anode catalyst layer. However, the specific surface area of the conductive carbon material as a support is not particularly limited, but is preferably less than 250 m ² / g, more preferably less than 150 m ² / g, in order to suppress the carbon corrosion reaction of the cathode. From the viewpoint of dispersibility of the catalyst component, 100 m ² / g or more is preferable. When the specific surface area is in the above range, the dispersibility of the catalyst component on the carrier is good, and the durability of the cathode carbon can be improved.

  The cathode catalyst layer of the present invention contains a proton conductive material. The proton conductive material that can be contained is as described in the anode catalyst layer.

  The method for producing the cathode catalyst layer is also as described for the anode catalyst layer.

[Electrolyte membrane]
In the anode catalyst layer of the present invention, an electrolyte membrane is disposed between the cathode catalyst layer and the anode catalyst layer of the present invention.

  The electrolyte membrane-electrode assembly (MEA) is disposed on one side of the electrolyte membrane, the electrolyte membrane, the cathode catalyst layer, the other side of the electrolyte membrane, the anode catalyst layer of the present invention, Have

  The electrolyte membrane is not particularly limited, and examples thereof include a membrane containing a proton conductive material similar to that used for the anode catalyst layer / cathode catalyst layer. In addition, perfluorosulfonic acid membranes represented by Nafion (registered trademark, manufactured by DuPont) and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), ion exchange resins manufactured by Dow Chemical Company, and ethylene-tetrafluoroethylene copolymer Fluoropolymer electrolytes such as resin membranes and resin membranes based on trifluorostyrene, and hydrocarbon polymer resin membranes having sulfonic acid groups, etc. A membrane, a membrane in which a polymer microporous membrane is impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the electrolyte membrane and the proton conductive material used for each catalyst layer may be the same or different, but the viewpoint of improving the adhesion between each catalyst layer and the electrolyte membrane Therefore, it is preferable to use the same one.

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

  The electrolyte membrane that can be used in the present invention includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) in addition to the above-mentioned fluorine-based polymer electrolyte and membranes made of hydrocarbon resins having sulfonic acid groups. A porous thin film formed from, for example, an electrolyte component such as phosphoric acid or an ionic liquid may be used.

[MEA production method]
The cathode catalyst layer-electrolyte membrane-anode catalyst layer (MEA) can be produced by sandwiching the electrolyte membrane between the cathode catalyst layer and the anode catalyst layer of the present invention and then hot pressing the laminate. Of course, it is not limited to this manufacturing method. At this time, the hot press conditions are not particularly limited as long as each catalyst layer and the electrolyte membrane can be joined sufficiently closely, but are 100 to 200 ° C., more preferably 110 to 170 ° C. It is preferable to carry out at a press pressure of 5 MPa. Thereby, the bondability between the electrolyte membrane and each catalyst layer can be enhanced. After performing the hot press, a laminate (MEA) of cathode catalyst layer-electrolyte membrane-anode catalyst layer can be obtained by peeling off the transfer mount.

  The MEA may further include a gas diffusion layer as will be described in detail below. At this time, the gas diffusion layer can be further bonded to each catalyst layer in the above method by peeling off the transfer mount or further sandwiching the laminate (MEA) prepared above with the gas diffusion layer. preferable. Alternatively, a catalyst layer is previously formed on the surface of the gas diffusion layer to produce a catalyst layer-gas diffusion layer assembly (MEA), and then the catalyst layer-gas diffusion layer assembly is used as an electrolyte in the same manner as described above. It is also preferable to sandwich and bond the films by hot pressing.

  At this time, the gas diffusion layer (GDL) used in the MEA is not particularly limited, and a known one can be used in the same manner. For example, conductive and porous materials such as carbon woven fabric, paper-like paper body, felt, and non-woven fabric can be used. The thing which uses the sheet-like material which has quality as a base material etc. are mentioned. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained. If the thickness exceeds 500 μm, the distance through which gas or water permeates is undesirably increased.

  The method for forming each catalyst layer on the surface of the gas diffusion layer is not particularly limited, and known methods such as a screen printing method, a deposition method, and a spray method can be similarly applied. Moreover, the formation conditions on the gas diffusion layer surface of each catalyst layer are not particularly limited, and the same conditions as in the past can be applied by the specific formation method as described above.

  The gas diffusion layer preferably contains a water repellent in the base material for the purpose of further improving water repellency and preventing a flooding phenomenon. Although it does not specifically limit as said water repellent, It is fluorine-type, such as a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include polymer materials, polypropylene, and polyethylene.

  Moreover, in order to improve water repellency more, the said gas diffusion layer may have a carbon particle layer which consists of an aggregate | assembly of the carbon particle containing a water repellent on the said base material.

  The carbon particles are not particularly limited, and may be conventional ones such as carbon black, graphite, and expanded graphite. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area. The particle size 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 for the carbon particle layer include the same water repellents as those described above used for the substrate. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction.

  In the carbon particle layer, the mixing ratio of the carbon particles to the water repellent may be insufficient to obtain water repellency as expected when there are too many carbon particles. If there are too many water repellents, sufficient electron conductivity may be obtained. May not be obtained. Considering these, the mixing ratio of the carbon particles and the water repellent in the carbon particle layer is preferably about 90:10 to 40:60 in terms of mass ratio.

  The thickness of the carbon particle layer may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

  When a water repellent is contained in the gas diffusion layer, a general water repellent treatment method may be used. For example, after immersing the base material used for a gas diffusion layer in the dispersion liquid of a water repellent agent, the method of heat-drying with oven etc. is mentioned.

  When a carbon particle layer is formed on a substrate in the gas diffusion layer, a slurry is prepared by dispersing carbon particles, a water repellent, and the like in a solvent. Next, the slurry may be applied on a substrate and dried, or the slurry may be dried once and pulverized to form a powder, which may be applied onto the gas diffusion layer. Then, it is preferable to heat-process at about 250-400 degreeC using a muffle furnace or a baking furnace. In the above method, the solvent used for preparing the slurry is not particularly limited. For example, water, perfluorobenzene, dichloropentafluoropropane, alcohol solvents such as methanol and ethanol can be preferably used.

  In addition, the manufacturing method of the joined body including the catalyst layer, the electrolyte membrane, and preferably the gas diffusion layer is not limited to the method described above. That is, a method in which catalyst ink is applied and dried on an electrolyte membrane and then hot-pressed to join the catalyst layer to the electrolyte membrane, and the obtained joined body is sandwiched between gas diffusion layers to form MEA; May be applied and dried on the gas diffusion layer to form a catalyst layer, which may be joined to the electrolyte membrane by hot pressing, or any other known technique may be used as appropriate.

<Second of the present invention>
A second aspect of the present invention is a fuel cell using the first electrolyte membrane-electrode assembly (MEA) of the present invention.

  By using the MEA of the present invention, a highly reliable fuel cell having excellent durability can be provided. Therefore, the present invention also provides a fuel cell using the anode catalyst layer of the present invention.

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

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

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

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

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

  Unlike a normal single cell, in a fuel cell stack configured by combining a plurality of cells, hydrogen deficiency of the anode is likely to occur, so that the effect of improving the durability according to the present invention can be maximized.

<Third invention>
The application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The anode catalyst layer of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

  In particular, the polymer electrolyte fuel cell is useful as a power source for a mobile body such as an automobile in which a mounting space is limited in addition to a stationary power source. In particular, it is particularly preferable to be used as a power source for a mobile body such as an automobile in which corrosion of a carbon support or a catalytic metal (such as Pt) is likely to occur due to a high output voltage required after a relatively long shutdown.

  That is, a third aspect of the present invention is a vehicle equipped with the second fuel cell of the present invention as a motor driving power source. By applying the present invention to a fuel cell stack mounted on a vehicle, unlike a stationary fuel cell stack, a moving fuel cell stack is more prone to hydrogen deficiency in the anode, thereby improving durability. To the fullest.

  In addition, it is preferable that the vehicle further includes a device that detects an abnormality of each individual fuel cell and measures the abnormality.

  An abnormality detection system is a system that detects a cell voltage, for example, and detects a case where the cell voltage greatly deviates from other cells or falls below a predetermined voltage as an abnormality. The fuel cell stack is composed of a plurality of cells, and the number of abnormality detection points may be one cell or one for a plurality of cells. When an abnormality is detected, the current extraction can be stopped, the fuel supply can be increased, or an operation for eliminating the fuel deficiency can be performed. Therefore, in the fuel cell system equipped with the abnormality detection system and the countermeasures thereof, the carbon corrosion deterioration due to the fuel depletion of the fuel electrode can be minimized.

  Anode fuel depletion does not always occur and is a temporary and abnormal condition. Therefore, it is difficult to predict when and in what state. In addition, it is assumed that the frequency of fuel depletion is higher than expected, and in that case, the effect of improving the resistance to carbon corrosion may be lost. From the above, it is most preferable that an abnormality detection system is mounted in order to maximize the effect of improving the carbon corrosion resistance and surely.

  In addition, about such an abnormality detection system, a conventionally well-known thing can be used, for example, what is described in Unexamined-Japanese-Patent No. 2005-100827 is good to use. By applying it to a fuel cell vehicle equipped with an abnormality detection system, hydrogen deficiency can be detected in a short time by detecting hydrogen deficiency. The effect put in can be demonstrated and the effect of durability improvement can be demonstrated to the maximum.

  Hereinafter, the present invention will be described more specifically based on examples. The present invention is not limited to these examples.

<Example 1>
1. Production of Anode Catalyst Layer Iridium and platinum were supported on Ketjen Black (trade name Ketjenblack, BET specific surface area = 800 m ² / g, manufactured by Ketjenblack International) as a conductive carbon material to obtain a catalyst. The average particle diameter of iridium was 5 nm, the supporting rate of iridium was 5.8% by mass, the average particle size of platinum was 5 nm, and the supporting rate of platinum was 47.3% by mass.

15 g of purified water was added to 5 g of this catalyst, and vacuum degassing operation was added for 5 minutes. To this, 10 times the amount of n-propyl alcohol was added, and a solution containing DE2020CS manufactured by DuPont (solution with a solid content of 20%, EW = 1,000) was added. Regarding the content of the polymer electrolyte in the solution, the mass ratio of the solid content to the carbon component mass of the catalyst was Ionomer / Carbon (I / C ratio) = 0.9 / 1.0. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. This was printed on one side of a polytetrafluoroethylene sheet by screen printing in two portions according to the desired thickness and dried at 60 ° C. for 24 hours. The size of the formed anode catalyst layer was 5 cm × 5 cm. The coating layer on the polytetrafluoroethylene sheet was adjusted so that the platinum amount was 0.1 mg / cm ² and the iridium amount was 0.0125 mg / cm ² (anode catalyst layer thickness: 2 to 3 μm). Thus, an anode catalyst layer coated sheet A1 was obtained. Since the catalyst layer is not flat, hereinafter, the thicknesses of all the anode catalyst layers are expressed as ranges. Further, the catalyst layer thickness was measured by observation with a scanning electron microscope (SEM).

2. Production of Cathode Catalyst Layer Platinum was supported on Ketjenblack (trade name Ketjenblack, product name Ketjenblack, BET specific surface area = 800 m ² / g: Carbon Type (1)) as a conductive carbon material. Thereafter, Ketjen Black carrying platinum was treated at 1000 ° C. for 30 minutes in a gas flow atmosphere of 95% volume hydrogen-5% volume nitrogen to obtain a catalyst (average particle diameter of platinum particles 5 nm, platinum loading rate 50.1). Mass%). 15 g of purified water was added to 10 g of the catalyst thus obtained, and a vacuum degassing operation was added for 5 minutes. To this, 10 times the amount of n-propyl alcohol was added, and a solution containing DE2020CS manufactured by DuPont (solution with a solid content of 20%, EW = 1,000) was added. The content of the polymer electrolyte in the solution was such that the mass ratio of the solid content to the carbon mass of the catalyst was Ionomer / Carbon (I / C ratio) = 0.9 / 1.0. The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. This was printed on one side of a polytetrafluoroethylene sheet by screen printing in four portions in an amount corresponding to the desired thickness, and dried at 60 ° C. for 24 hours. The size of the formed cathode catalyst layer was 5 cm × 5 cm. The coating layer on the polytetrafluoroethylene sheet was adjusted so that the platinum amount was 0.40 mg / cm ² (average thickness of the cathode catalyst layer: 11 μm). Thus, a cathode catalyst layer coated sheet B1 was obtained.

3. Production of MEA Nafion NRE211 (film thickness: 25 μm) as a solid polymer electrolyte membrane and catalyst layer formed on the previously produced polytetrafluoroethylene sheet (anode catalyst layer coated sheet A1 on the anode side, cathode catalyst on the cathode side) Layer coated sheets B1) were overlaid. At that time, the anode catalyst layer, the solid polymer electrolyte membrane, and the cathode catalyst layer were laminated in this order. Then, it hot-pressed for 10 minutes at 130 degreeC and 0.8 Mpa, peeled only the polytetrafluoroethylene sheet, and obtained MEA.

4). Performance evaluation of MEA On both sides of the MEA, a commercially available carbon paper with a carbon layer as a gas diffusion layer (24BC manufactured by SGL Carbon Co., Ltd., cut out to a size of 6.0 cm × 5.5 cm, carbon paper thickness of 200 μm), and gas flow An MEA having a gas diffusion layer was prepared by arranging a gas separator with a road and sandwiching it with a metal (copper, iron, etc.) current collector plate plated with gold, and used as an evaluation unit cell.

  The cell temperature is 50 ° C., RH = 80% air is supplied to the anode, and RH = 80% hydrogen is supplied to the cathode. The anode potential is 5 mV / sec from 1 V to 2 V with reference to the cathode potential. Scanned at rising speed. At the anode, oxygen is generated by an electrolysis reaction of water, and at the same time, carbon dioxide is generated by a carbon corrosion reaction. Therefore, since the two oxidation reactions cannot be separated only by measuring the current, by analyzing the gas discharged from the anode during the potential scan, the amount of water electrolysis reaction can be calculated from the amount of increase in oxygen by carbon dioxide. The amount of carbon corrosion reaction was calculated from the amount of increase. By performing the evaluation as described above, it is possible to know how the water electrolysis reaction and the carbon corrosion reaction change depending on the anode catalyst specification.

  In addition, although air is supplied to the anode and hydrogen is supplied to the cathode, the control is reverse to normal, because this is intentionally reversed. In other words, in order to evaluate the water electrolysis activity on the anode side, the evaluation is intentionally performed by reversing (polarizing) the normal fuel cell operation. In the measurement of obtaining a current-potential curve with a conventional cathode, the measurement is performed by reversing the connection of single cells. In this evaluation, in order to accurately measure the potential on the anode side, hydrogen is supplied to the cathode side and the cathode potential is used as a reference. A similar experiment can be performed by supplying nitrogen to the anode. However, since the water electrolysis reaction is performed at about 1.4 V or more, the evaluation time can be shortened by starting measurement from a potential close to that. Therefore, air was used here for the anode so that the open circuit voltage was about 1V.

<Example 2>
In the preparation of the anode catalyst layer, except that the amount of platinum was adjusted to 0.1 mg / cm ² and iridium amount is 0.0333mg / cm ² performs the generation of similarly MEA as in Example 1, water MEA The amount of electrolytic reaction was measured. The iridium loading rate was 14.2% by mass, the platinum loading rate was 43.1% by mass, and the anode catalyst layer thickness was 2-3 μm.

<Example 3>
In the production of the anode catalyst layer, the MEA was produced in the same manner as in Example 1, except that the platinum amount was adjusted to 0 mg / cm ² and (that is, not added) the iridium amount was adjusted to 0.1 mg / cm ² . The amount of water electrolysis reaction of MEA was measured. The iridium loading was 25.9% by mass, and the thickness of the anode catalyst layer was 4 to 5 μm.

<Reference Example 1>
In the production of the anode catalyst layer, the MEA was produced in the same manner as in Example 1 except that the platinum amount was adjusted to 0.1 mg / cm ² and the iridium amount was adjusted to 0 mg / cm ² (that is, not added). The amount of water electrolysis reaction of MEA was measured. The platinum loading was 46.3 mass%, and the anode catalyst layer thickness was 2-3 μm.

  FIG. 1 shows a graph of the amount of water electrolysis reaction with respect to the amount of iridium added to the anode. The horizontal axis is the amount of iridium added, the vertical axis is the amount of water electrolysis reaction current, and the values at anode potentials of 1.5 V and 1.6 V are plotted. From this result, it can be seen that the amount of water electrolysis reaction is almost proportional to the amount of iridium added. From the above results, it is presumed that the amount of iridium added is proportional to the water electrolysis reaction in the potential range governing the water electrolysis reaction activity. Moreover, it is estimated that platinum hardly contributes to water electrolysis reaction.

  Subsequently, the carbon corrosion reaction amount is evaluated.

<Reference Example 2>
MEA was produced in the same manner as in Reference Example 1, and the carbon corrosion reaction amount of MEA was calculated.

<Reference Example 3>
The carbon corrosion reaction of MEA as in Reference Example 2, except that acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., BET specific surface area = 250 m ² / g Carbon Type (2)) was used as the conductive carbon material in the anode catalyst layer. The amount was calculated.

<Reference Example 4>
As the conductive carbon material in the anode catalyst layer, ketjen black (Ketjenblack International product name Ketjenblack, BET specific surface area = 800 m ² / g) was heat-treated (2000-2500 ° C.) under an inert atmosphere. The amount of carbon corrosion reaction of MEA was calculated in the same manner as in Reference Example 2 except that the material (BET specific surface area = 125 m ² / g: Carbon Type (3)) was used.

  FIG. 2 shows the amount of carbon corrosion reaction when the conductive carbon material in the anode catalyst layer is changed. As apparent from FIG. 2, the carbon corrosion amount increases as the anode potential increases. It can be seen that the amount of carbon corrosion reaction current varies greatly depending on the type of conductive carbon material, for example, the surface area exposed to potential varies. The carbon corrosion amount is a value determined if the water content and potential around the carbon are constant regardless of the type and amount of the catalyst component.

Subsequently, FIG. 3 and FIG. 4 (a diagram in which the scale of FIG. 3 is changed) and FIG. 5 will be described. 3-5 can be derived from FIG. 1 and FIG. As described above, it was assumed from FIG. 1 that the water electrolysis activity was proportional to the amount of iridium added. Based on this assumption, from FIG. 1, the anode potential was derived from the water electrolysis reaction amount at 100 mA / cm ² (200 mA / cm ² ), and the carbon corrosion reaction amount was derived from each anode potential. As described above, the carbon corrosion reaction amount relative to the iridium addition amount can be derived (FIGS. 3 to 5).

Specifically, from FIG. 1, the potential (for example, 1.6 V) at a specific water electrolysis reaction amount (for example, 100 mA / cm ² ) and the amount of iridium added at that time (for example, about 0.03 mg / cm 2). ² ) can be derived. On the other hand, each carbon corrosion reaction amount at each anode potential (for example, 1.6 V) can be derived from FIG. Based on these correlations, FIGS. 3 and 4 can be derived (in FIGS. 3 and 4, the carbon corrosion reaction amount was calculated from the water electrolysis reaction amount at 100 mA / cm ² ).

As apparent from FIGS. 3 and 4, it is understood that the carbon corrosion amount (mA / cm ² ) is suppressed as the amount of iridium added (mg / cm ² ) is increased. The amount of carbon corrosion (mA / cm ² ) varies greatly depending on the type of conductive carbon material in the anode catalyst layer, and as a result, the durability varies greatly. However, it can be seen that no matter what kind of conductive carbon material is used, the amount of iridium added is at least 0.005 mg / cm ² . Further, the anode potential was calculated from the amount of water electrolysis reaction at 200 mA / cm ^{2, and} the amount of carbon corrosion reaction current relative to the potential of each conductive carbon material was calculated (FIG. 5). As can be seen from FIG. 5, the amount of carbon corrosion increased as a whole compared to 100 mA / cm ² , but it was insignificant. From this result, even when the anode side becomes a higher potential when the fuel cell falls into a reversal state due to hydrogen shortage, the amount of iridium added must be at least 0.005 mg / cm ^2. I understand.

Next, FIG. 6 shows the relationship of the carbon corrosion inhibition rate (mass%) with respect to the iridium addition amount (mg / cm ² ). Carbon corrosion inhibition rate is reduced in the amount of conductive carbon material in the corrosion test conducted with MEA supporting 0.1 mg / cm ² of platinum containing no iridium and the conductivity reduced in the corrosion test conducted with MEA containing iridium. The value obtained by dividing the difference in the amount of the carbon material by the amount of the conductive carbon material decreased in the corrosion test performed by the MEA supporting 0.1 mg / cm ² of platinum not containing iridium is multiplied by 100. This value is an index showing the effect of suppressing carbon corrosion by adding iridium.

By adding iridium, the potential applied to the anode is suppressed. By suppressing the potential applied to the anode, carbon corrosion is suppressed. As can be seen from FIG. 6, even when the amount of iridium added is small, carbon corrosion is greatly suppressed. On the other hand, it can be seen that the effect of suppressing carbon corrosion hardly increases after exceeding 1.0 mg / cm ² .

  Subsequently, the power generation performance with respect to the amount of iridium added to the anode catalyst layer is measured.

<Example 4>
In the preparation of the anode catalyst layer, the MEA was the same as in Example 1 except that the platinum amount was adjusted to 0 mg / cm ² and the iridium amount was adjusted to 0.005 mg / cm ² (anode catalyst layer thickness: ˜1 μm). Was made into a unit cell for evaluation.

In the evaluation unit cell, hydrogen was supplied as a fuel to the anode side, and oxygen was supplied as an oxidant to the cathode side. The supply pressure of both gases was atmospheric pressure, the hydrogen gas temperature was set to 80 ° C. and relative humidity 80%, the air gas temperature was set to 80 ° C. and relative humidity 80%, and the cell temperature was set to 80 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 10%. Under this condition, the cell voltage when power was generated at a current density of 1 A / cm ² was measured as the initial cell voltage. The cell voltage is a value obtained by correcting the solid polymer electrolyte membrane resistance value at 1 A / cm ² .

<Example 5>
The power generation performance was evaluated in the same manner as in Example 4 except that the amount of iridium was adjusted to 0.01 mg / cm ² (the thickness of the anode catalyst layer: ˜1 μm).

<Example 6>
The power generation performance was evaluated in the same manner as in Example 4 except that the amount of iridium was adjusted to 0.018 mg / cm ² (the thickness of the anode catalyst layer: ˜1 μm).

<Example 7>
The power generation performance was evaluated in the same manner as in Example 4 except that the amount of iridium was adjusted to 0.023 mg / cm ² (the thickness of the anode catalyst layer: ˜1 μm).

<Example 8>
The power generation performance was evaluated in the same manner as in Example 4 except that the amount of iridium was adjusted to 0.054 mg / cm ² (the thickness of the anode catalyst layer: 1 to 2 μm).

<Reference Example 5>
In the production of the anode catalyst layer, the same as Example 4 except that the platinum amount was adjusted to 0.05 mg / cm ² and the iridium amount was 0 mg / cm ² (anode catalyst layer thickness: 1 to 2 μm). An MEA was produced and evaluated as a unit cell for evaluation.

From the results shown in FIG. 7, it is understood that iridium is particularly preferably added in an amount of 0.01 mg / cm ² or more in view of significantly improving the power generation performance. Note that iridium is preferably 0.1 mg / cm ² or less. 0.1 mg / cm ² or less is preferable because the thickness of the anode catalyst layer can be reduced to a predetermined value or less, proton transfer resistance can be reduced, gas diffusibility can be maintained, and high carbon This is because the power generation performance can be improved while maintaining corrosion resistance.

  Next, power generation performance is evaluated with respect to the thickness of the anode catalyst layer.

<Reference Example 6>
As the conductive carbon material in the anode catalyst layer, ketjen black (Ketjenblack International product name Ketjenblack, BET specific surface area = 800 m ² / g) was heat-treated (2000-2500 ° C.) under an inert atmosphere. (BET specific surface area = 125 m ² / g: Carbon Type (3)) was used.

In the preparation of the anode catalyst layer, the platinum amount is 0.1 mg / cm ² and the iridium amount is 0 mg / cm ² (that is, not added), the anode catalyst layer thickness is 1 to 2 μm, and the platinum loading is 50 mass%. Except for the adjustment, the MEA was produced in the same manner as in Example 1 to obtain a unit cell for evaluation.

In the evaluation unit cell, hydrogen was supplied as a fuel to the anode side, and oxygen was supplied as an oxidant to the cathode side. The supply pressure of both gases was atmospheric pressure, the hydrogen gas temperature was set to 80 ° C. and relative humidity 80%, the air gas temperature was set to 80 ° C. and relative humidity 80%, and the cell temperature was set to 80 ° C. The hydrogen utilization rate was 67% and the air utilization rate was 10%. Under this condition, the cell voltage when power was generated at a current density of 1 A / cm ² was measured as the initial cell voltage. The cell voltage is a value obtained by correcting the solid polymer electrolyte membrane resistance value at 1 A / cm ² .

<Reference Example 7>
The power generation performance was evaluated in the same manner as in Reference Example 6 except that the thickness of the anode catalyst layer was adjusted to 4 to 5 μm and the platinum loading rate was 30%.

<Reference Example 8>
The power generation performance was evaluated in the same manner as in Reference Example 6 except that the anode catalyst layer was adjusted to have a thickness of 8 to 9 μm and a platinum loading rate of 20%.

<Reference Example 9>
The power generation performance was evaluated in the same manner as in Reference Example 6 except that the anode catalyst layer was adjusted to have a thickness of 42 to 43 μm and a platinum loading rate of 5%.

  From the result of FIG. 8, it is found that the anode catalyst layer is particularly preferably 6 μm or less in view of maintaining the power generation performance.

Next, FIG. 9 shows the carbon corrosion current (A / g) per use amount of each conductive carbon material constituting the anode catalyst layer with respect to the addition amount of iridium supported per catalyst application area. FIG. 9 can also be necessarily derived from FIGS. The carbon corrosion reaction amount (current density mA / cm ² ) can be derived from FIGS. The mass (g) of the conductive carbon material used to produce the anode catalyst layer can be calculated from the amount of iridium (mg / cm ² ) and the iridium loading (%). From the result, the carbon corrosion current (A / g) per use amount of the conductive carbon material can be derived.

As described above, the durability can be sufficiently obtained by setting it to 12 A / g or less. That is, since the amount of anode carbon corrosion can be reliably reduced, the conductive carbon material constituting the anode catalyst layer can be selected more appropriately. Therefore, the kind of conductive carbon material which comprises an anode catalyst layer, and its addition amount can be made appropriate, and sufficient durability can be obtained. From the viewpoint of “12 A / g or less” from this data, it is preferable to select the amount of iridium added to achieve this, depending on the type of conductive carbon material. That is, in order to obtain a carbon corrosion current of 12 A / g or less per use amount of the conductive carbon material necessary for obtaining sufficient durability, the carbon type (1) having a low carbon corrosion resistance has an iridium content of about 0.8. 1 mg / cm ² or more is preferable. In Carbon type (2), the amount of iridium is preferably about 0.05 mg / cm ² or more. In Carbon type (3) having high carbon corrosion resistance, the amount of iridium is about 0.02 mg / cm ² or more. It turns out that is preferable. This value is shown for the case where only iridium is added as a catalyst to the anode. However, even if platinum is added, the value does not change greatly. Therefore, even when iridium and platinum are added, the amount of iridium remains the above value. It's okay.

  In addition, in order to acquire the data of the said FIG. 9, carbon dioxide measurement by a gas analyzer is needed.

In order to obtain sufficient durability, the polarization curve on the fuel electrode side in an air atmosphere at a cell temperature of 50 ° C. (anode gas: air RH = 80%, cathode gas: hydrogen RH = 80%, scanning range: 1 V to 2 V, scanning (Velocity: 5 mV / sec), the potential when the current density due to the water electrolysis reaction (strictly speaking, the measured current value includes the water electrolysis reaction current and the carbon corrosion reaction current) is 100 mA / cm ² is 1. It is desirable that it is 635V or less. In addition, as shown in FIG. 2, although it changes with carbon types, carbon corrosion can be effectively suppressed by setting it as 1.635V or less. In addition, as described above, 1.635 V is a value calculated backward from the allowable amount of carbon corrosion. In order to make this value lower than this value, at least iridium added to the anode catalyst layer is 0.005 mg / cm ² or more. It is necessary to be.

  As described above, the durability can be sufficiently obtained by setting it to 12 A / g or less. That is, since the amount of anode carbon corrosion can be reliably reduced, the conductive carbon material constituting the anode catalyst layer can be selected more appropriately. Therefore, the kind of conductive carbon material which comprises an anode catalyst layer, and its addition amount can be made appropriate, and sufficient durability can be obtained.

Claims (1)

Includes a catalyst component containing iridium conductive carbon as a carrier has been supported catalyst, the supported amount of the iridium per electrode area 0.005 mg / cm ² or more and 0.0333mg / cm ² or less,
The catalyst component is supported on the conductive carbon by 30 to 60% by mass,
A fuel cell anode catalyst layer having a thickness of 3 μm or less.

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