JP2005332662A - Catalyst for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for reducing a manufacturing cost of a catalyst for a fuel cell having platinum and iridium oxide as catalytic metal. <P>SOLUTION: A conductive catalyst support made of carbon is used as a conductive support for supporting platinum and iridium oxide. This catalyst for a fuel cell can be manufactured by supporting an iridium compound on the conductive catalyst support formed by supporting platinum and by baking the conductive catalyst support formed by supporting platinum and the iridium compound. In baking the iridium compound, it is necessary to note that the conductive catalyst support made of carbon is prevented from burning. The catalyst for a fuel cell may be manufactured by supporting the iridium compound on the conductive catalyst support made of carbon, by baking the conductive catalyst support with the iridium compound supported thereon to produce iridium oxide and by supporting platinum on the conducive catalyst support with the iridium oxide supported thereon. In baking the iridium compound, it can be baked at high temperature because platinum is not supported on the catalyst support. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst used in a fuel cell. The catalyst of this invention is used for the electrode catalyst layer in a polymer electrolyte fuel cell (PEFC), for example.

  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. 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, a polymer electrolyte fuel cell (PEFC) 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.

  In the polymer electrolyte fuel cell, an oxidant such as air is supplied to the oxygen electrode, and hydrogen gas is supplied to the fuel electrode. Electrons are generated by an electrochemical reaction. Platinum is attracting attention as a catalyst for promoting this reaction. And in order to improve the characteristic of a platinum catalyst, the catalyst which uses iridium oxide as a catalyst metal with platinum is proposed (for example, refer patent document 1).

  As a method for preparing the iridium oxide, a method is used in which an iridium compound that is a precursor of the iridium oxide is produced and then fired. Specifically, an iridium hydroxide hydrate is generated by adding an alkali such as potassium hydroxide or sodium hydroxide to an aqueous solution containing an iridium complex. Then, iridium hydroxide hydrate is fired to obtain an iridium oxide.

  Further, by supporting the catalyst metal on the conductive carrier, the catalyst can be effectively used and the handleability is improved. Patent Document 1 discloses metal particles such as gold, ruthenium, and titanium, and ceramic particles such as titanium carbide and zirconium carbide as conductive carriers.

In order to put the fuel cell to practical use, it is required to reduce the raw material cost, and the catalyst is also required to reduce the manufacturing cost.
JP 2000-342965 A

  Accordingly, an object of the present invention is to provide a means for reducing the manufacturing cost of a fuel cell catalyst having platinum and iridium oxide as catalyst metals.

  The present invention is a fuel cell catalyst comprising a carbon conductive support and platinum and iridium oxides supported on the conductive support.

  The fuel cell catalyst of the present invention comprises a step of supporting an iridium compound on a carbon conductive support formed by supporting platinum, and a step of firing the conductive support formed by supporting the platinum and the iridium compound. Can be manufactured by a manufacturing method including:

  The fuel cell catalyst of the present invention comprises a step of supporting an iridium compound on a carbon conductive support, a step of firing a conductive support formed by supporting the iridium compound to generate an iridium oxide, It can be produced by a production method comprising a step of carrying platinum on a conductive carrier carrying the iridium oxide.

  The fuel cell catalyst of the present invention uses a carbon material as a conductive carrier. For this reason, the manufacturing cost of a catalyst is suppressed, and it contributes to the generalization of a fuel cell by extension. Moreover, since it has platinum and iridium oxide as a catalyst metal, it is excellent also in catalyst performance.

  One means for reducing the manufacturing cost is to use a carrier made of an inexpensive material. As the carrier made of an inexpensive material, a carbon material such as carbon black can be considered. However, when platinum and iridium oxides are used as catalyst metals, it has been found difficult to use carbon materials as carriers.

  When the iridium oxide is supported on the carrier, a method is used in which the iridium compound that is the precursor of the iridium oxide is supported on the platinum-supported carrier and then fired. However, it has become clear that the carbon product has a problem of burning with heat during firing if it carries platinum.

  The present inventors have found a means for solving this problem and have completed the present invention. Hereinafter, the present invention will be described in detail.

  The first of the present invention is a fuel cell catalyst comprising a carbon conductive carrier and platinum and iridium oxides supported on the conductive carrier.

  The carbon conductive carrier is a carrier made of carbon and having conductivity. The carbon conductive carrier is not particularly limited, and examples thereof include carbon materials such as carbon black, acetylene black, activated carbon, and graphite. Preferably, carbon black is used. Two or more kinds of conductive carriers may be used in combination. In some cases, a carrier other than these may be used, but a carbon material is preferable from the viewpoint of suppressing the production cost of the catalyst.

The specific surface area of the conductive carrier is not particularly limited, but is preferably 200 to 1600 m ² / g. When a conductive carrier having a specific surface area in this range is used, platinum and iridium oxide can be easily supported with a high degree of dispersion, and aggregation of catalyst particles and improvement in utilization can be achieved.

  Platinum is preferably contained in an amount of 10 to 50% by mass with respect to the total mass of the catalyst. If platinum particles exceeding 50% by mass are present on the surface of the catalyst particles, it is difficult to uniformly disperse, and it may be difficult to carry highly dispersed platinum particles. Moreover, when the abundance of platinum particles is less than 10% by mass, there is a possibility that sufficient catalytic activity for oxygen reduction cannot be obtained.

  Although an iridium oxide is not specifically limited, Preferably it is 1-20 mass% with respect to the mass of the whole catalyst, More preferably, 5-20 mass% is contained. By setting the amount of iridium oxide within this range, it is possible to increase the utilization rate of platinum and greatly promote the reaction between the surface of the platinum particles and the surface of the iridium oxide particles. If iridium oxide exceeding 20% by mass is present on the surface of the catalyst particles, most of the platinum particles are covered with iridium oxide, which may reduce the utilization rate of platinum.

  2nd of this invention is related with one Embodiment of the manufacturing method of the catalyst for fuel cells. The first fuel cell catalyst of the present invention can be produced by the production method described below.

  The production method of the present invention is roughly classified into two types depending on the process. One is a method of preparing a conductive carrier carrying platinum and carrying the iridium oxide on this carrier. The other is a method in which a conductive carrier not carrying platinum is prepared, iridium oxide is carried on this carrier, and then platinum is carried on the carrier carrying iridium oxide.

  Each process has its own advantages. When the step of supporting iridium oxide on a conductive support on which platinum is supported (see FIGS. 1 to 3), a catalyst having a high contact property between platinum and a carbon conductive support is obtained. It is also possible to shift to the iridium supporting step after reliably controlling the size of the platinum particles to be supported. In the iridium loading step, iridium oxide can be deposited on the carrier in the form of fine particles, so the loading is controlled and most of the platinum particles are coated with iridium oxide, resulting in a decrease in catalyst performance. It is also possible to prevent this. Further, when this manufacturing method is adopted, as described above, the carbon conductive carrier may be burned during sintering, and therefore, it is sintered at a relatively low temperature. If the sintering temperature is low, the sintering time tends to be long, but it is easy to control the sintering, and there is a possibility that special equipment for high-temperature sintering can be omitted.

  On the other hand, when adopting a process of supporting iridium oxide on a conductive carrier and then supporting platinum (see FIGS. 4 to 6), platinum is supported when generating iridium oxide by sintering. There is no carbon conductive carrier. For this reason, it is possible to avoid the problem that the carbon conductive support burns due to the heat of the sintering process for supporting the iridium oxide on the support. Since the problem of burning the carbon conductive support by sintering is avoided, sufficient heat treatment can be applied when producing iridium oxide, and iridium oxide with high crystallinity can be produced. It is. In addition, when platinum is supported on a carrier supporting iridium oxide, since a large amount of platinum is present on the surface of the catalyst to be produced, it is possible to improve the utilization efficiency of platinum.

  The two types of production methods are further classified into three types according to the method of depositing the iridium compound on the surface of the support. One is a method in which an iridium compound is precipitated on a conductive support by adding an acid to a solution containing an iridium hydroxide complex (see FIGS. 1 and 4). The other is a method in which an iridium compound is precipitated on a conductive support by stirring a solution containing an iridium hydroxide complex adjusted to a predetermined pH at 85 to 90 ° C. (FIGS. 2 and 5). reference). Still another one is a method in which an iridium compound is precipitated on a conductive support by stirring a liquid containing iridium chloride and a platinum-supported conductive support at 85 to 90 ° C. (see FIGS. 3 and 6). ). Hereinafter, the production method of the present invention will be described in detail for each production process.

  First, the manufacturing method shown in FIG. 1 will be described.

  An alkali metal hydroxide or an alkaline earth metal hydroxide (hereinafter also referred to as “alkali hydroxide”) is added to the aqueous iridium chloride solution.

As iridium chloride, a water-soluble iridium complex is used. Specific examples of iridium chloride include IrCl ₄ , IrCl ₃ , (NH ₄ ) ₂ [IrCl ₆ ], H ₂ [IrCl ₆ ], K ₂ [IrCl ₆ ], Na ₂ [IrCl ₆ ], H ₃ [IrCl ₆ ], K ₃ [IrCl ₆ ], (NH ₄ ) ₃ [IrCl ₆ ] and the like. The concentration of iridium chloride is not particularly limited, but may be about 0.05 to 0.5% by mass.

  The alkali metal hydroxide or alkaline earth metal hydroxide may be appropriately selected from potassium hydroxide, sodium hydroxide, magnesium hydroxide, calcium hydroxide, and the like. When these are added in the form of an aqueous solution, they are convenient for operation. The amount of addition is not particularly limited, but it may be added in an amount 7 to 10 times the iridium atom in terms of hydroxyl group so that an iridium hydroxide complex can be easily formed. The amount of alkali hydroxide added may be controlled based on the pH of the solution. For example, alkali hydroxide is added so that the pH of the solution is 11-12.

Thereafter, the mixed solution is stirred at 40 to 60 ° C. By stirring the mixed solution at 40 to 60 ° C., an iridium hydroxide complex [Ir (OH) ₆ ] ^{3− in} which _six hydroxide ions are coordinated to iridium is formed. By forming a complex solution in which hydroxide ions are coordinated and then precipitating on the support surface, mixing of other components such as chloride ions and sodium ions can be suppressed, and the unit mass of the catalyst can be reduced. The activity can be improved.

  The temperature of the mixed solution does not always have to be kept at 40 to 60 ° C. during the stirring, and it is sufficient that the temperature of the mixed solution is at least 40 to 60 ° C. during the stirring of the mixed solution. However, in order to form an iridium hydroxide complex efficiently, it is good to stir in the state hold | maintained at 40-60 degreeC. The reaction time is not particularly limited, but may be about 4 to 8 hours.

  Next, a carbon conductive carrier (hereinafter also referred to as “platinum carrier”) formed by supporting platinum is dispersed in a solution containing an iridium hydroxide complex. If necessary, the solution containing the iridium hydroxide complex is cooled to room temperature before the platinum-supported carrier is added to the solution. The platinum carrier can be dispersed by ultrasonic waves, stirring, or the like.

  There is no particular limitation on the type of platinum-supported carrier. As for the carrier, as described in the first aspect of the present invention, the carbon conductive carrier is not particularly limited, but carbon black, acetylene black, activated carbon, graphite and the like can be used.

  The amount of platinum supported on the platinum-supported carrier may be determined in consideration of the production cost of the catalyst, the catalyst activity, the type of the carrier, and the like. By supporting a sufficient amount of platinum, it is possible to develop a sufficient catalytic activity. However, since platinum is expensive, it becomes a main factor that increases the manufacturing cost of the catalyst. Preferably, the platinum loading is controlled so that 10 to 50% by mass of platinum is included with respect to the total mass of the catalyst to be produced. As the platinum-supporting carrier, a commercially available carrier may be used, or platinum may be supported on a carbon carrier using an aqueous solution containing a platinum compound.

Subsequently, an acid is added to the liquid containing the iridium hydroxide complex and the platinum-supported carrier to precipitate the iridium compound on the conductive carrier. By adding an acid to neutralize, the iridium compound is deposited on the surface of the carrier. The produced iridium compound is presumed to be [Ir (OH) ₃ (H ₂ O) ₃ ].

  As the acid, for example, hydrochloric acid, perchloric acid aqueous solution, sulfuric acid or the like can be used. The addition amount of the acid may be an amount necessary for precipitation of iridium hydroxide hydrate, and is usually an amount such that the pH of the aqueous solution becomes about 7.5 to 8.5. It is preferable to sufficiently stir after the acid is added. If too much acid is added, the precipitate may be redissolved and an iridium chloride complex may be formed again.

  After the iridium compound is deposited, the platinum-supported carrier on which the iridium compound is deposited is baked to change the iridium compound into an iridium oxide. Prior to calcination, filtration and washing may be performed to prevent impurities from being mixed into the catalyst. The number of times of filtration and washing is not particularly limited. After washing, the conductive carrier carrying platinum and iridium compounds may be dried.

  Firing is preferably performed in an oxidizing atmosphere. More preferably, firing is performed in an air atmosphere. As described above, when a carbon conductive carrier carrying platinum is fired at a high temperature, there is a problem that the carbon conductive carrier burns. For this reason, firing is preferably performed at a low temperature of 200 to 300 ° C., more preferably 200 to 250 ° C., so that carbon does not burn. The firing time depends on the amount of iridium compound supported and the firing atmosphere. If the firing is insufficient, the iridium compound may not be sufficiently changed to iridium oxide. Therefore, it is preferable to set conditions such that the oxidation to iridium oxide proceeds sufficiently. However, in that case, as described above, it is preferable to take care not to burn the carbon conductive carrier.

  As described above, when employing a method in which an iridium compound is precipitated on a conductive support by adding an acid to a liquid containing an iridium hydroxide complex, preparation at a room temperature system is possible. In the process of depositing the iridium compound on the conductive support, if the reaction system is heated to a high temperature, the particles may aggregate. In this regard, when the reaction is allowed to proceed in a room temperature system, it is possible to prevent the particles from agglomerating and improve the dispersibility of the iridium compound.

  The manufacturing method shown in FIG. 2 will be described. In this manufacturing method, addition of an acid, a reducing agent, or the like can be omitted, and by omitting a component to be added, the preparation process can be simplified and contamination of impurities can be prevented.

  An alkali metal hydroxide or an alkaline earth metal hydroxide is added to the aqueous iridium chloride solution. Since the iridium chloride aqueous solution and the alkali hydroxide have already been described, the description thereof is omitted here.

  An iridium hydroxide complex is formed by adding an alkali hydroxide to an iridium chloride aqueous solution. At this time, the pH is controlled to 6-8.

  Next, a platinum carrier is dispersed in a solution containing an iridium hydroxide complex. The platinum carrier can be dispersed by ultrasonic waves, stirring, or the like. Since the platinum carrier has already been described, the description thereof is omitted here.

  The liquid containing the iridium hydroxide complex and the platinum-supported carrier is heated to 85 to 90 ° C. and stirred to precipitate the iridium compound on the platinum-supported carrier. By adopting a technique for precipitating the iridium compound by heating the liquid containing the iridium hydroxide complex, the iridium compound can be more reliably precipitated.

  After the iridium compound is deposited, the platinum-supported carrier on which the iridium compound is deposited is baked to change the iridium compound into an iridium oxide. Since the work after depositing the iridium compound is the same as that in the embodiment of FIG. 1, the description thereof is omitted here.

  The manufacturing method shown in FIG. 3 will be described. In this manufacturing method, addition of an acid can be omitted, and by omitting a component to be added, the preparation process can be simplified and contamination of impurities can be prevented. In addition, there is an advantage that the work is simple.

  A conductive support formed by supporting platinum is dispersed in a solution containing iridium chloride. Since the iridium chloride aqueous solution and the platinum-supported carrier have already been described, the description thereof is omitted here.

  If necessary, a reducing agent may be added to the liquid containing iridium chloride and a platinum support. When a reducing agent is added, iridium metal can be deposited when the iridium compound is deposited on the platinum-supported carrier. Although it does not specifically limit as a reducing agent, Alcohol, such as methanol and ethanol, is mentioned.

  The liquid containing the iridium hydroxide complex and the platinum-supported carrier is heated to 85 to 90 ° C. and stirred to precipitate the iridium compound on the platinum-supported carrier. By adopting a technique for precipitating the iridium compound by heating the liquid containing the iridium hydroxide complex, the iridium compound can be more reliably precipitated.

  After the iridium compound is deposited, the platinum-supported carrier on which the iridium compound is deposited is baked to change the iridium compound into an iridium oxide. Since the work after depositing the iridium compound is the same as that in the embodiment of FIG. 1, the description thereof is omitted here.

  The manufacturing method shown in FIGS. The manufacturing method shown in FIGS. 4 to 6 is a manufacturing method in which iridium oxide is supported on a conductive carrier, and then platinum is supported, unlike the manufacturing method described in FIGS. After supporting the iridium oxide, high temperature firing is possible in the firing step for generating the iridium oxide by using a production method for supporting platinum. The process itself for supporting the iridium compound corresponds to the manufacturing process shown in FIG. 1 except that the conductive support for supporting the iridium compound is a carbon conductive support for not supporting platinum. Similarly, the manufacturing method of FIG. 5 corresponds to the manufacturing method of FIG. 2, and the manufacturing method of FIG. 6 corresponds to the manufacturing method of FIG.

  That is, the manufacturing method of FIGS. 4 to 6 is the same as the manufacturing method described in FIGS. 1 to 3 except that the firing temperature is different and platinum is supported on a conductive carrier supporting iridium oxide. Compliant. The same applies to the process-specific effects. For example, when employing a method of depositing an iridium compound on a conductive support by adding an acid to a liquid containing an iridium hydroxide complex as shown in FIG. 4, preparation in a room temperature system is performed as in FIG. It is possible to improve the dispersibility of the iridium compound. For this reason, below, a baking process and a platinum carrying | support process are demonstrated, and description is abbreviate | omitted about another process.

  Firing is preferably performed in an oxidizing atmosphere. More preferably, firing is performed in an air atmosphere. The firing temperature is preferably 300 to 500 ° C, more preferably 350 to 450 ° C. Even when baked at a high temperature, platinum is not supported on the carbon conductive carrier, so that the carbon carrier is difficult to burn. By baking at a high temperature, it can be present on the carrier as crystalline iridium oxide. Further, by baking, the bond between the carrier and the iridium oxide becomes strong, and the strength as a catalyst is improved.

  The method for supporting platinum on the conductive carrier on which iridium oxide is supported is not particularly limited. For example, a liquid containing a conductive carrier and an aqueous solution containing a platinum compound are mixed, and then the platinum compound is reduced, whereby platinum is supported on the surface of the carrier.

The type of platinum compound is not particularly limited as long as it can be supplied into the reverse micelle as an aqueous solution. Specific examples of the platinum compound include dinitrodiamine platinum (Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ), H ₂ PtCl _{6 and the} like. Since crystals of dinitrodiamine platinum are basically insoluble in water, when dinitrodiamine platinum is used, it may be dissolved in nitric acid to form an aqueous solution and added as a dinitrodiamine platinum nitric acid aqueous solution.

  The density | concentration of platinum in the aqueous solution containing a platinum compound becomes like this. Preferably it is 0.01 mass%-10 mass%, More preferably, it is 0.5 mass%-3 mass%. However, the technical scope of the present invention is not limited to these ranges, and in some cases, the concentration may be outside the above range.

  The method for depositing platinum on the surface of the carrier is not particularly limited, and may be appropriately selected depending on the type of platinum compound. For example, a platinum compound is reduced using a reducing agent to deposit platinum metal. Examples of the reducing agent used at this time include ethanol and methanol.

  The fuel cell catalyst of the present invention is preferably disposed in the electrode catalyst layer of the fuel cell. The electrode catalyst layer may be an air electrode or a fuel electrode. The catalyst of this invention may be arrange | positioned at both. The type of fuel cell is not particularly limited as long as the catalyst of the present invention is applicable. Preferably, the catalyst of the present invention is used for a polymer electrolyte fuel cell.

  By disposing a catalyst having high catalytic performance, a fuel cell having high power generation characteristics can be obtained. The usage application of the fuel cell is not particularly limited. For example, the fuel cell of the present invention is used in a vehicle.

<Example 1>
A catalyst was produced by a production method in which iridium oxide was supported on a conductive carrier supporting platinum (see FIG. 1). As a method for supporting iridium, a method of depositing an iridium compound on a conductive support by adding an acid to a solution containing an iridium hydroxide complex was used. Specifically, a catalyst was prepared by the following means.

  To 50 g of a 1% by mass iridium chloride solution, 26 ml of 1M aqueous sodium hydroxide solution was added dropwise as an alkali metal hydroxide. Pure water is added to a mixed solution of iridium chloride and sodium hydroxide to make a total amount of 100 g, and the mixture is continuously stirred for 6 hours or more while being heated to 40 ° C. Was generated.

The solution containing the iridium hydroxide complex was cooled to room temperature. 10 g of this solution was taken and further pure water was added to prepare a solution containing iridium at a concentration of 0.1% by mass. Here, 1.108 g of carbon black (Ketjen Black ^TM ) carrying platinum at a concentration of 50% by mass was added as a carbon conductive carrier carrying platinum. Then, this solution was ultrasonically dispersed for 10 minutes.

  While continuing stirring at room temperature, 5% by mass of diluted hydrochloric acid was slowly added dropwise until pH = 7, and stirring was further continued for 2 hours. Filtration and washing were repeated 3 times and dried at 80 ° C. for 6 hours or more. Thereafter, firing was carried out at 200 ° C. for 4 hours in an air atmosphere to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Example 2>
A catalyst was produced by a production method in which iridium oxide was supported on a conductive carrier supporting platinum (see FIG. 2). As a method for supporting iridium, a method of precipitating an iridium compound on a conductive carrier by stirring a solution containing an iridium hydroxide complex adjusted to a predetermined pH at 85 to 90 ° C. was used. Specifically, a catalyst was prepared by the following means.

  To 50 g of a 0.1% by mass iridium chloride solution, 1M sodium hydroxide aqueous solution as an alkali metal hydroxide was slowly added dropwise until pH = 7.

To this solution, 1.108 g of carbon black (Ketjen Black ^™ ) carrying platinum at a concentration of 50% by mass was added as a carbon conductive carrier carrying platinum. Thereafter, this solution was ultrasonically dispersed for 10 minutes.

  The slurry in which the platinum-supporting carbon was dispersed was put into a separable flask, heated to 90 ° C. while being refluxed, and then held for 6 hours. After completion of the heat treatment, the mixture was allowed to cool naturally, and filtration and washing were repeated three times, followed by drying at 80 ° C. for 6 hours or more. Thereafter, firing was carried out at 200 ° C. for 4 hours in an air atmosphere to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Example 3>
A catalyst was produced by a production method in which iridium oxide was supported on a conductive carrier supporting platinum (see FIG. 3). As a method for supporting iridium, a method was used in which a liquid containing iridium chloride and a platinum-supporting conductive support was stirred at 85 to 90 ° C. to precipitate an iridium compound on the conductive support. Specifically, a catalyst was prepared by the following means.

1.108 g of carbon black (Ketjen Black ^TM ) carrying platinum at a concentration of 50% by mass was added to 50 g of a 0.1% by mass iridium chloride solution. Thereafter, this solution was ultrasonically dispersed for 10 minutes. Here, 50 ml of ethanol was added as a reducing agent, and further ultrasonically dispersed for 10 minutes.

  The slurry in which the platinum-supporting carbon was dispersed was put into a separable flask, heated to 85 ° C., and then held for 6 hours. After completion of the heat treatment, the mixture was allowed to cool naturally, and filtration and washing were repeated three times, followed by drying at 80 ° C. for 6 hours or more. Thereafter, firing was carried out at 200 ° C. for 4 hours in an air atmosphere to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Example 4>
A catalyst was produced by a production method in which iridium oxide was supported on a conductive carrier not supporting platinum, and further platinum was supported (see FIG. 4). As a method for supporting iridium, a method was used in which an iridium compound was precipitated on a conductive support by adding an acid to a solution containing an iridium hydroxide complex. Specifically, a catalyst was prepared by the following means.

  To 50 g of a 1% by mass iridium chloride solution, 26 ml of 1M aqueous sodium hydroxide solution was added dropwise as an alkali metal hydroxide. Pure water is added to a mixed solution of iridium chloride and sodium hydroxide to make a total amount of 100 g, and the mixture is continuously stirred for 6 hours or more while being heated to 40 ° C., and containing iridium at a concentration of 0.5 mass%. Was generated.

The solution containing the iridium hydroxide complex was cooled to room temperature. 10 g of this solution was taken and further pure water was added to prepare a solution containing iridium at a concentration of 0.1% by mass. Here, 1.05 g of carbon black (Ketjen Black ^™ ) was added as a carbon conductive carrier not supporting platinum. Then, this solution was ultrasonically dispersed for 10 minutes.

  While continuing stirring at room temperature, 5% by mass of diluted hydrochloric acid was slowly added dropwise until pH = 7, and stirring was further continued for 2 hours. Filtration and washing were repeated 3 times and dried at 80 ° C. for 6 hours or more. Next, firing was performed at 400 ° C. for 3 hours in an air atmosphere to produce iridium oxide on the conductive support.

  A conductive carrier formed by supporting iridium oxide and a dinitrodiamine platinum solution containing platinum at a concentration of 0.5% by mass were mixed. The amount of the dinitrodiamine platinum solution used was determined so that the iridium oxide-supporting conductive carrier and the amount of platinum added were the same. Furthermore, 50 ml of ethanol was added as a reducing agent, and ultrasonic dispersion was performed for 10 minutes.

  This slurry was placed in a separable flask and heated to 90 ° C. and then held for 6 hours. After the heat treatment, it was allowed to cool naturally, repeated filtration and washing three times, and dried at 80 ° C. for 6 hours or more to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Example 5>
A catalyst was produced by a production method in which iridium oxide was supported on a conductive carrier not supporting platinum, and further platinum was supported (see FIG. 5). As a method for supporting iridium, a method of precipitating an iridium compound on a conductive carrier by stirring a solution containing an iridium hydroxide complex adjusted to a predetermined pH at 85 to 90 ° C. was used. Specifically, a catalyst was prepared by the following means.

  To 50 g of a 0.1% by mass iridium chloride solution, 1M sodium hydroxide aqueous solution as an alkali metal hydroxide was slowly added dropwise until pH = 7.

To this solution, 1.05 g of carbon black (Ketjen Black ^™ ) was added as a carbon conductive carrier not carrying platinum. Then, this solution was ultrasonically dispersed for 10 minutes.

  The slurry in which the platinum-supporting carbon was dispersed was put into a separable flask, heated to 90 ° C. while being refluxed, and then held for 6 hours. After completion of the heat treatment, the mixture was allowed to cool naturally, and filtration and washing were repeated three times, followed by drying at 80 ° C. for 6 hours or more. Next, firing was performed at 400 ° C. for 3 hours in an air atmosphere to produce iridium oxide on the conductive support.

  A dinitrodiamine platinum solution containing platinum at a concentration of 0.5% by mass and a conductive carrier carrying iridium oxide were mixed. The amount of the dinitrodiamine platinum solution used was determined so that the iridium oxide-supporting conductive carrier and the amount of platinum added were the same. Furthermore, 50 ml of ethanol was added as a reducing agent, and ultrasonic dispersion was performed for 10 minutes.

  This slurry was placed in a separable flask and heated to 90 ° C. and then held for 6 hours. After the heat treatment, it was allowed to cool naturally, repeated filtration and washing three times, and dried at 80 ° C. for 6 hours or more to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Example 6>
A catalyst was prepared by a production method in which iridium oxide was supported on a conductive carrier not supporting platinum, and further platinum was supported (see FIG. 6). As a method for supporting iridium, a method was used in which a liquid containing iridium chloride and a platinum-supporting conductive support was stirred at 85 to 90 ° C. to precipitate an iridium compound on the conductive support. Specifically, a catalyst was prepared by the following means.

As a conductive carrier not carrying platinum, 1.05 g of carbon black (Ketjen Black ^™ ) was added to 50 g of a 0.1% by mass iridium chloride solution. Then, this solution was ultrasonically dispersed for 10 minutes. Here, 50 ml of ethanol was added as a reducing agent, and further ultrasonically dispersed for 10 minutes.

  The slurry in which the platinum-supporting carbon was dispersed was put into a separable flask, heated to 85 ° C., and then held for 6 hours. After completion of the heat treatment, the mixture was allowed to cool naturally, and filtration and washing were repeated three times, followed by drying at 80 ° C. for 6 hours or more. Next, firing was performed at 400 ° C. for 3 hours in an air atmosphere to produce iridium oxide on the conductive support.

  A dinitrodiamine platinum solution containing platinum at a concentration of 0.5% by mass and a conductive carrier carrying iridium oxide were mixed. The amount of the dinitrodiamine platinum solution used was determined so that the iridium oxide-supporting conductive carrier and the amount of platinum added were the same. Furthermore, 50 ml of ethanol was added as a reducing agent, and ultrasonic dispersion was performed for 10 minutes.

  This slurry was placed in a separable flask and heated to 90 ° C. and then held for 6 hours. After the heat treatment, it was allowed to cool naturally, repeated filtration and washing three times, and dried at 80 ° C. for 6 hours or more to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Comparative Example 1>
A dinitrodiamine platinum solution containing platinum at a concentration of 0.5% by mass and carbon black (Ketjen Black ^™ ) as a conductive carrier were mixed. The amount of dinitrodiamine platinum solution used was determined so that the conductive carrier and the amount of platinum added were the same. Furthermore, 50 ml of ethanol was added as a reducing agent, and ultrasonic dispersion was performed for 10 minutes.

  This slurry was placed in a separable flask and heated to 90 ° C. and then held for 6 hours. After the heat treatment, it was allowed to cool naturally, repeated filtration and washing three times, and dried at 80 ° C. for 6 hours or more to obtain a fuel cell catalyst carrying platinum and iridium oxide.

<Evaluation>
0.5 ml of pure water was added to the prepared catalyst and ultrasonically dispersed. This liquid was mixed with a 5 wt% Nafion ^™ solution. The mixing ratio at this time was adjusted so that the mass ratio of catalyst body: Nafion ^™ = 1: 1. Using a micropipette, 10-20 microliters of catalyst ink was uniformly applied to the Au current collector plate. This was dried under reduced pressure at 50 ° C. for 10 minutes to obtain an electrode catalyst for evaluation.

  In order to obtain the exchange current value per platinum mass for each catalyst, that is, the mass activity value (unit: [μA / mg-Pt]) for each catalyst, an electrochemical measurement was performed using the evaluation electrode catalyst thus prepared. The current-voltage characteristics were investigated. The results are shown in Table 1.

  When the production method of the present invention is used, a carbon material can be used as the conductive carrier even when platinum and iridium oxide are used as the catalyst metal. In particular, as shown in Examples 4 to 6, when a method is employed in which an iridium compound is supported on carbon and fired, and then platinum is supported, firing at a high temperature becomes possible.

  The catalyst of the present invention using a carbon material as a conductive support can be manufactured at low cost. Since it has iridium oxide, it is also possible to increase the initial activity for the oxygen reduction reaction. Further, since platinum and iridium oxide can be supported in a highly dispersed manner and the platinum surface can be effectively used, as shown in Table 1, the catalyst has excellent catalytic performance.

  The catalyst of the present invention is used for a fuel cell. For example, it is used as a catalyst for promoting a power generation reaction in an electrode catalyst layer of a polymer electrolyte fuel cell.

It is a flowchart of the manufacturing method using the process which carries | supports an iridium oxide on the electroconductive support | carrier with which platinum is carry | supported. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the conductive carrier by adding an acid to a solution containing the iridium hydroxide complex is used. It is a flowchart of the manufacturing method using the process which carries | supports an iridium oxide on the electroconductive support | carrier with which platinum is carry | supported. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the conductive carrier by stirring a solution containing the iridium hydroxide complex adjusted to a predetermined pH at 85 to 90 ° C. is used. . It is a flowchart of the manufacturing method using the process which carries | supports an iridium oxide on the electroconductive support | carrier with which platinum is carry | supported. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the conductive carrier by stirring a liquid containing iridium chloride and a platinum-supporting conductive carrier at 85 to 90 ° C. is used. If necessary, a reducing agent may be added to the reaction system. It is a flowchart of the manufacturing method using the process which carry | supports an iridium oxide on an electroconductive support | carrier, and carries platinum after that. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the conductive carrier by adding an acid to a solution containing the iridium hydroxide complex is used. It is a flowchart of the manufacturing method using the process which carry | supports an iridium oxide on an electroconductive support | carrier, and carries platinum after that. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the conductive carrier by stirring a solution containing the iridium hydroxide complex adjusted to a predetermined pH at 85 to 90 ° C. is used. . It is a flowchart of the manufacturing method using the process which carry | supports an iridium oxide on an electroconductive support | carrier, and carries platinum after that. As a method for precipitating the iridium compound on the surface of the carrier, a method of precipitating the iridium compound on the electroconductive carrier by stirring a liquid containing iridium chloride and the electroconductive carrier at 85 to 90 ° C. is used. If necessary, a reducing agent may be added to the reaction system.

Claims (16)

  A fuel cell catalyst comprising a carbon conductive support and platinum and iridium oxides supported on the conductive support. ^2. The fuel cell catalyst according to claim 1, wherein the conductive support is carbon black having a specific surface area of 200 to 1600 m ² / g.   The catalyst for a fuel cell according to claim 1 or 2, wherein the platinum is contained in an amount of 10 to 50 mass% with respect to the mass of the entire catalyst.   The catalyst for fuel cells according to any one of claims 1 to 3, wherein the iridium oxide is contained in an amount of 1 to 20% by mass with respect to the mass of the entire catalyst. A step of loading an iridium compound on a carbon conductive carrier carrying platinum;
Firing a conductive carrier carrying the platinum and the iridium compound;
And a method for producing a catalyst for a fuel cell carrying platinum and iridium oxide. The step of supporting the iridium compound on the carbon conductive carrier supporting platinum is as follows.
Adding an alkali metal hydroxide or an alkaline earth metal hydroxide to an aqueous iridium chloride solution and stirring at 40-60 ° C. to form an iridium hydroxide complex;
Dispersing a carbon conductive carrier formed by supporting platinum in a solution containing the iridium hydroxide complex;
6. The method for producing a fuel cell catalyst according to claim 5, wherein an iridium compound is precipitated on the conductive support by adding an acid to the liquid containing the iridium hydroxide complex and the conductive support. . The step of supporting the iridium compound on the carbon conductive carrier supporting platinum is as follows.
Adding an alkali metal hydroxide or an alkaline earth metal hydroxide to an aqueous iridium chloride solution to prepare a solution containing an iridium hydroxide complex having a pH of 6-8;
Dispersing a conductive carrier comprising platinum in a solution containing the iridium hydroxide complex;
The catalyst for a fuel cell according to claim 5, wherein the liquid containing the iridium hydroxide complex and the conductive support is stirred at 85 to 90 ° C to precipitate an iridium compound on the conductive support. Manufacturing method. The step of supporting the iridium compound on the conductive support formed by supporting the platinum,
Dispersing a conductive carrier comprising platinum in a solution containing iridium chloride;
Stirring the liquid containing the iridium chloride and the conductor carrier at 85 to 90 ° C. to precipitate an iridium compound on the conductive carrier;
The manufacturing method of the catalyst for fuel cells of Claim 5 which consists of these.   The step of firing the conductive support is a step of firing the conductive support at 200 to 300 ° C in an air atmosphere, according to any one of claims 5 to 8. Method. Carrying an iridium compound on a carbon conductive carrier;
Firing a conductive carrier carrying the iridium compound to produce an iridium oxide;
A step of supporting platinum on a conductive carrier supporting the iridium oxide;
And a method for producing a catalyst for a fuel cell carrying platinum and iridium oxide. The step of supporting the iridium compound on a carbon conductive support includes
Adding an alkali metal hydroxide or an alkaline earth metal hydroxide to an aqueous iridium chloride solution and stirring at 40-60 ° C. to form an iridium hydroxide complex;
Dispersing a carbon conductive support in a solution containing the iridium hydroxide complex;
11. The method for producing a fuel cell catalyst according to claim 10, wherein an iridium compound is precipitated on the conductive support by adding an acid to a liquid containing the iridium hydroxide complex and the conductive support. . The step of supporting the iridium compound on a carbon conductive support includes
Adding an alkali metal hydroxide or an alkaline earth metal hydroxide to an aqueous iridium chloride solution to prepare a solution containing an iridium hydroxide complex having a pH of 6-8;
Dispersing a carbon conductive support in a solution containing the iridium hydroxide complex;
11. The fuel cell catalyst according to claim 10, wherein the liquid containing the iridium hydroxide complex and the conductive support is stirred at 85 to 90 ° C. to precipitate an iridium compound on the conductive support. Manufacturing method. The step of supporting the iridium compound on a carbon conductive support includes
Dispersing a carbon conductive carrier in a solution containing iridium chloride;
Stirring the liquid containing the iridium chloride and the conductor carrier at 85 to 90 ° C. to precipitate an iridium compound on the conductive carrier;
The manufacturing method of the catalyst for fuel cells of Claim 10 consisting of.   The step of firing the conductive carrier carrying the iridium compound to form an iridium oxide is a step of firing the conductive carrier at 300 to 500 ° C in an air atmosphere. 14. The method for producing a fuel cell catalyst according to any one of 13 above.   The fuel cell by which the catalyst for fuel cells of any one of Claims 1-4 is arrange | positioned at the electrode catalyst layer.   A vehicle equipped with the fuel cell according to claim 15.

Images