JP2010161034A - Method of manufacturing metal catalyst-supporting carbon powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing metal catalyst-supporting carbon powder to be used for a catalyst layer of a solid polymer fuel cell, capable of improving catalyst activity by preventing oxidation of the surface of a metal catalyst, and promoting alloying when supporting another metal catalyst. <P>SOLUTION: The method of manufacturing metal catalyst-supporting carbon powder to be used for a catalyst layer of a solid polymer fuel cell comprises performing heat treatment under a high-concentration carbon dioxide atmosphere after supporting a metal catalyst on carbon powder. The heat treatment temperature is preferably 500-800°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon powder loaded with a metal catalyst such as Pt, which is contained in a catalyst layer of a polymer electrolyte fuel cell.

  A polymer electrolyte fuel cell is provided with a pair of electrodes on both sides of a hydrogen ion conductive solid polymer electrolyte membrane, supplies hydrogen gas as a fuel gas to one electrode (fuel electrode: anode), oxygen gas or air Is obtained as an oxidizing agent to the other electrode (air electrode: cathode) to obtain an electromotive force. Solid polymer fuel cells are expected to be put to practical use as mobile vehicles such as electric vehicles and power sources for small cogeneration systems because they are easy to reduce in size and weight in addition to obtaining high battery characteristics. Yes.

  Usually, a gas diffusible electrode used in a polymer electrolyte fuel cell supplies a catalyst layer containing a catalyst-supporting carbon powder coated with a hydrogen ion conductive polymer electrolyte, and supplies a reaction gas to the catalyst layer. And a gas diffusion layer for collecting electrons. In the catalyst layer, there are voids composed of minute pores formed between the carbon secondary particles or the tertiary particles, and the voids function as a reaction gas diffusion channel.

  As the cathode and anode catalyst supported on the carbon powder, a noble metal such as platinum or a platinum alloy is used. For example, platinum-supported carbon powder is prepared by suspending carbon powder in water, etc., dropping a catalyst metal compound such as chloroplatinic acid, and dropping a reducing agent to deposit platinum on the carbon powder. Is done. The platinum-supported carbon powder is dispersed in a hydrogen ion conductive polymer electrolyte solution to prepare an ink. The ink is applied to a gas diffusion substrate such as carbon paper and dried to produce an electrode. An electrolyte membrane-electrode assembly (MEA) is assembled by sandwiching a solid polymer electrolyte membrane between these two electrodes and performing hot pressing or the like.

  Conventionally, in order to improve the catalytic activity of the metal catalyst-supporting carbon powder as described above, attempts have been made to atomize the metal catalyst to improve the reaction area, or to heat-treat the carbon powder in a specific gas atmosphere. For example, in (Patent Document 1), after conducting a process of activating a conductive carrier in a temperature range of 500 to 1200 ° C. in any one or more gas atmospheres selected from carbon dioxide, water vapor, and air. An electrode catalyst having a metal such as Pt supported thereon is disclosed. However, this electrode catalyst has a problem in that the catalytic activity is hindered because the surface of Pt is oxidized, and thus the obtained performance is insufficient, resulting in an increase in the amount of metal used such as Pt. .

  A method of alloying by supporting a plurality of metals and performing a heat treatment in an inert gas atmosphere is also known. For example, in Patent Document 2, ruthenium is deposited on a platinum-supported catalyst as a hydroxide, and then heat-treated in a mixed gas atmosphere having a partial pressure ratio of nitrogen and carbon dioxide of 5: 1, for example. A method for producing an anode catalyst for a fuel cell, in which an oxide is reduced to a metal and alloyed at the same time, is disclosed. Similarly, this method has a problem that the catalytic metal surface is oxidized, so that alloying is inhibited and the catalytic activity is not sufficiently exhibited.

Furthermore, ion exchange resins such as perfluorosulfonic acid polymers are generally used for the solid polymer electrolyte membrane. These ion exchange resins exhibit high hydrogen ion conductivity for the first time in a humid environment. This is thought to be due to the interposition and accompanying of water molecules in the movement of hydrogen ions. Therefore, in order to operate the fuel cell efficiently, conventionally, water vapor is supplied to the catalyst layer together with the reaction gas, and the polymer electrolyte membrane is always kept in a wet state. However, in order to obtain a wet state, it is necessary to separately provide a humidifier in the air supply path or the hydrogen supply path, which has the disadvantage that the fuel cell becomes larger and the manufacturing cost increases. Therefore, development of a technology that can be operated even under low humidification conditions is desired. However, since the conventional metal catalyst-supported carbon powder has a hydrophobic carbon surface, it has the ability to retain H ₂ O during low humidification. There is also a problem that high fuel cell performance cannot be obtained because of low conductivity of hydrogen ions.

JP 2005-25947 A JP 63-213260 A

  Therefore, in view of the above-described conventional situation, the present invention prevents oxidation of the surface of the metal catalyst in the carbon powder loaded with the metal catalyst used for the catalyst layer of the polymer electrolyte fuel cell, and also carries other metal catalysts. It is an object of the present invention to provide a method for producing the above metal catalyst-supported carbon powder, which can improve the catalytic activity by promoting alloying.

  Another object of the present invention is to provide a method for producing a metal catalyst-supported carbon powder that can obtain high performance under low humidification conditions by increasing the hydrophilicity of the surface of the carbon powder.

  In response to the above problems, the present inventor can reduce the surface of the metal catalyst by heat-treating the metal catalyst carbon powder in a carbon dioxide atmosphere, thereby reducing the surface of the metal catalyst, thereby improving the catalytic activity I found. Further, the inventors have found that the surface of the carbon powder is activated by the heat treatment in a carbon dioxide atmosphere and the hydrophilicity is increased, and the invention has been completed. That is, the gist of the present invention is as follows.

(1) A method for producing a carbon powder carrying a metal catalyst, which is used for a catalyst layer of a polymer electrolyte fuel cell, wherein the metal catalyst is carried on the carbon powder and then heat-treated in a high-concentration carbon dioxide atmosphere. The said manufacturing method which performs.

(2) A method for producing a carbon powder carrying a metal catalyst, which is used for a catalyst layer of a polymer electrolyte fuel cell, wherein two or more metal catalysts are carried on the carbon powder, and then a high concentration carbon dioxide The said manufacturing method which heat-processes in atmosphere and alloys the said 2 or more types of metal catalyst.

(3) The manufacturing method of the metal catalyst carrying | support carbon powder as described in said (1) or (2) whose temperature of heat processing is 500-800 degreeC.

  By the production method of the present invention, the surface of a metal catalyst such as Pt is reduced, and as a result, a metal catalyst-supporting carbon powder exhibiting high catalytic activity can be obtained. Also, when two or more kinds of metal catalysts are supported, the alloying can be promoted and the catalyst performance can be improved. Therefore, the amount of metal catalyst such as Pt used can be reduced.

  Furthermore, since the surface of the carbon powder is activated and functional groups are imparted to the defective portions, the hydrophilicity of the carbon powder is improved, and a metal catalyst-supported carbon powder that exhibits high performance under low humidification conditions can be obtained. .

Hereinafter, the present invention will be described in detail.
The method for producing a metal catalyst-carrying carbon powder of the present invention is characterized in that after a metal catalyst is supported on the carbon powder, heat treatment is performed in a high-concentration carbon dioxide atmosphere.

Although it does not specifically limit as carbon powder which carries a metal catalyst, It is preferable that a specific surface area is 200 m < ² > / g or more. Carbon black is generally used. In addition, graphite, carbon fiber, activated carbon, carbon nanotube, etc. are applicable. Preferable examples include Ketjen EC (trade name, manufactured by Ketjen Black International) and Vulcan (trade name, manufactured by Cabot).

  Examples of the metal catalyst supported on the carbon powder include metals such as platinum, cobalt, nickel, palladium, ruthenium, gold, rhodium, osmium, and iridium. For the purpose of alloying, two or more of the above metals can be selected and used. Furthermore, a complex of the above metal with an organic compound or an inorganic compound, a metal oxide, or the like may be used.

  The metal catalyst can be supported on the carbon powder by a conventional method. Specifically, for example, carbon powder is suspended in water or the like, a catalyst metal compound such as chloroplatinic acid is added dropwise thereto, and a reducing agent is added dropwise to deposit the metal catalyst on the carbon powder. When two or more metal catalysts are supported, a reducing agent may be added after adding another catalyst metal compound to the suspension.

And after carrying | supporting a metal catalyst on carbon powder as mentioned above, it heat-processes in a high concentration carbon dioxide atmosphere. Here, “high concentration” specifically refers to 95% by weight or more, preferably 98% by weight or more, and most preferably 100% by weight. When carbon dioxide is not 100% by weight, the other gas to be contained can be appropriately selected from inert gases such as argon, helium and nitrogen, hydrogen and the like. By this heat treatment, carbon dioxide and carbon powder react to produce carbon monoxide (reaction formula: CO ₂ + C → 2CO). Since the surface of the metal catalyst such as Pt is reduced by the generated reducing CO, a three-phase interface formed in the catalyst layer, that is, an interface composed of a gas, a metal catalyst, and a hydrogen ion conductive polymer electrolyte is formed. Increase the catalytic activity. When two or more kinds of metal catalysts are supported, the metal surface is reduced by reducing CO, so that alloying is promoted and the catalytic activity is improved. Furthermore, since the surface of the carbon powder is activated by the above reaction and a functional group is imparted to the defective portion, the hydrophilicity of the carbon surface is improved. Therefore, hydrogen ion conductivity can be maintained without lowering the H ₂ O retention capacity even under low humidification conditions, and a fuel cell exhibiting high output can be obtained.

  The temperature for performing the heat treatment is preferably 500 to 800 ° C, more preferably 600 to 800 ° C. Within this temperature range, the catalytic metal is not poisoned by the generated reducing CO, and the surface of the metal catalyst can be reduced well. Various conditions such as the heat treatment time can be appropriately set according to the type and amount of the metal catalyst. For example, the heat treatment time is preferably 30 minutes to 4 hours, but is not limited thereto. In addition, when alloying by supporting two or more kinds of metal catalysts, washing with an acid may be performed after heat treatment to remove unalloyed metal. Conditions such as acid concentration, washing time, and washing temperature are appropriately set according to the type of metal catalyst.

  The metal catalyst-carrying carbon powder is obtained by the heat treatment. A coating liquid (ink) for forming a catalyst layer is prepared by adding the metal catalyst-supporting carbon powder and the hydrogen ion conductive polymer electrolyte to a solvent and performing a dispersion treatment by ultrasonic irradiation, bead milling or the like. be able to. Examples of the solvent used here include alcohols such as ethanol, ethylene glycol, and propylene glycol, fluorine-containing alcohols, and fluorine-containing ethers.

  As the hydrogen ion conductive polymer electrolyte to be added to the solvent, a fluorine-containing ion exchange resin or the like is applicable, and in particular, a sulfonic acid type perfluorocarbon polymer is preferably used. A suitable example is Nafion (trade name, manufactured by DuPont). The ratio of the metal catalyst-supported carbon powder to the hydrogen ion conductive polymer electrolyte can be arbitrarily set to a ratio suitable for a desired fuel cell system. Usually, the ratio of the weight of the hydrogen ion conductive polymer electrolyte / the weight of the carbon powder not supporting the metal catalyst is preferably about 0.1 to 1.5, but is not limited thereto.

  In addition to the metal catalyst-supported carbon powder and the hydrogen ion conductive polymer electrolyte, various additives may be added to the solvent as necessary. As an example, there is a case where PTFE, zeolite, or the like is added for the purpose of reinforcing stronger water retention or water repellency or water supply function. When an additive is added, the amount is preferably 10% by weight or less based on the solvent.

  And a catalyst layer can be formed by apply | coating a coating liquid to the carbon polymer etc. used as the solid polymer electrolyte membrane of a fuel cell, or a gas diffusion layer, and making it dry. Alternatively, the catalyst layer may be formed on the polymer electrolyte by transferring a coating prepared by applying the coating solution onto a separately prepared substrate and drying it onto the solid polymer electrolyte membrane. As a means for applying, brush coating, spraying, roll coater, ink jet, screen printing method and the like can be appropriately employed.

  The layer thickness of the catalyst layer in the fuel cell can be appropriately set on both the anode side and the cathode side. Generally, it is 5-20 micrometers, Preferably it is 10-15 micrometers.

  When the anode catalyst layer and the cathode catalyst layer are formed on the gas diffusion layer, the membrane / electrode assembly (MEA) is formed by bonding each catalyst layer and the solid polymer electrolyte membrane by bonding or hot pressing. Assembled. In addition, when each catalyst layer is formed on the solid polymer electrolyte membrane, the anode electrode and the cathode electrode may be constituted only by the catalyst layer, and a gas diffusion layer is disposed adjacent to each catalyst layer. Alternatively, an anode electrode and a cathode electrode may be used.

  As a material for the solid polymer electrolyte membrane sandwiched between the cathode and anode catalyst layers, any material that exhibits good hydrogen ion conductivity under wet conditions is applicable. Examples thereof include a perfluorocarbon polymer having a sulfonic acid group, a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group. Among these, sulfonic acid type perfluorocarbon polymers are preferably used. The solid polymer electrolyte membrane may be the same resin as the hydrogen ion conductive polymer electrolyte contained in the catalyst layer, or may be composed of a different resin.

  The gas diffusion layer can be composed of various materials as long as it has a function of uniformly diffusing gas from the gas flow path formed in the separator to the catalyst layer and conducting electrons between the catalyst and the separator. it can. Generally, carbon materials such as carbon cloth and carbon paper are used. Metal materials such as metal mesh and metal wool can be used as long as they have corrosion resistance in addition to gas diffusibility and electron conductivity.

  In general, a polymer electrolyte fuel cell is manufactured by disposing a separator in which a gas flow path is formed outside the anode and the cathode. Electric power is generated by supplying a gas containing hydrogen to the anode and a gas containing oxygen or air to the cathode.

Next, although this invention is demonstrated further in detail based on an Example and a comparative example, it is not limited to these.
Example 1
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder was set in a heat treatment furnace, and the temperature was raised while circulating CO ₂ gas at 500 cc / min. When the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature with the CO ₂ gas being circulated, and the Pt-supported carbon powder was taken out.

(Example 2)
Commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International Co., Ltd.) 5.0 g, hexahydroxoplatinum nitrate solution containing 4.50 g of platinum, and cobalt nitrate containing 0.5 g of cobalt are added to 0.5 L of pure water and dispersed. I let you. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and a hydroxide of Pt and Co was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained PtCo-supported carbon powder was set in a heat treatment furnace, the temperature was raised while circulating CO ₂ gas at 500 cc / min, and when the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature with the CO ₂ gas flowing, and the PtCo-supported carbon powder was taken out.

(Comparative Example 1)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder was set in a heat treatment furnace, and the temperature was raised while circulating N ₂ gas at 500 cc / min. When the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Thereafter, the mixture was allowed to cool to room temperature while N ₂ gas was circulated, and the Pt-supported carbon powder was taken out.

(Comparative Example 2)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder was set in a heat treatment furnace, and the temperature was raised while circulating Ar gas at 500 cc / min. When the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature while circulating Ar gas, and the Pt-supported carbon powder was taken out.

(Comparative Example 3)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder was set in a heat treatment furnace, the temperature was raised while circulating H ₂ gas at 500 cc / min, and when the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Thereafter, the Pt-supported carbon powder was taken out by cooling to room temperature with the H ₂ gas flowing.

(Comparative Example 4)
Commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International Co., Ltd.) 5.0 g, hexahydroxoplatinum nitrate solution containing 4.50 g of platinum, and cobalt nitrate containing 0.5 g of cobalt are added to 0.5 L of pure water and dispersed. I let you. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and a hydroxide of Pt and Co was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained PtCo-supported carbon powder was set in a heat treatment furnace, the temperature was raised while circulating N ₂ gas at 500 cc / min, and when the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature while N ₂ gas was circulated, and PtCo-supported carbon powder was taken out.

(Comparative Example 5)
Commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International Co., Ltd.) 5.0 g, hexahydroxoplatinum nitrate solution containing 4.50 g of platinum, and cobalt nitrate containing 0.5 g of cobalt are added to 0.5 L of pure water and dispersed. I let you. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and a hydroxide of Pt and Co was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained PtCo-supported carbon powder was set in a heat treatment furnace, and the temperature was raised while circulating Ar gas at 500 cc / min. When the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature while Ar gas was circulated, and PtCo-supported carbon powder was taken out.

(Comparative Example 6)
Commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International Co., Ltd.) 5.0 g, hexahydroxoplatinum nitrate solution containing 4.50 g of platinum, and cobalt nitrate containing 0.5 g of cobalt are added to 0.5 L of pure water and dispersed. I let you. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and a hydroxide of Pt and Co was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained PtCo-supported carbon powder was set in a heat treatment furnace, and the temperature was raised while circulating H ₂ gas at 500 cc / min. When the temperature reached 800 ° C., the heat treatment was carried out for 2 hours. Then, it was allowed to cool to room temperature with H ₂ gas flowing, and the PtCo-supported carbon powder was taken out.

(Comparative Example 7)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder is set in a heat treatment furnace, heated while flowing a 20% CO ₂ /80% N ₂ mixed gas at 500 cc / min. When the temperature reaches 800 ° C., the heat is maintained for 2 hours. Carried out. Thereafter, the mixed gas was allowed to cool to room temperature while flowing, and the Pt-supported carbon powder was taken out.

(Comparative Example 8)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder was set in a heat treatment furnace, heated while flowing a 50% CO ₂ /50% N ₂ mixed gas at 500 cc / min, and when it reached 800 ° C., it was held for 2 hours and heat treated. Carried out. Thereafter, the mixed gas was allowed to cool to room temperature while flowing, and the Pt-supported carbon powder was taken out.

(Comparative Example 9)
A hexahydroxo platinum nitric acid solution containing 5.0 g of commercially available carbon black (trade name; Ketjen EC, manufactured by Ketjen Black International) and 5.0 g of platinum was added to 0.5 L of pure water and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and Pt hydroxide was formed and deposited on the carbon powder. Furthermore, it reduced at 90 degreeC using ethanol, this dispersion liquid was filtered, and the obtained powder was vacuum-dried at 100 degreeC for 10 hours. The obtained Pt-supported carbon powder is set in a heat treatment furnace, heated while circulating a mixed gas of 80% CO ₂ /20% N ₂ at 500 cc / min. Carried out. Thereafter, the mixed gas was allowed to cool to room temperature while flowing, and the Pt-supported carbon powder was taken out.

(Production of membrane / electrode assembly)
After adding distilled water to each of the metal catalyst-supported carbon powders prepared in Examples 1-2 and Comparative Examples 1-9, ethanol was added to form Nafion (trade name, manufactured by DuPont) as an ion conductive polymer electrolyte. Was further added. This mixture was sufficiently stirred and subjected to ultrasonic irradiation and a dispersion process using a bead mill in order to make the particles fine and uniform.

  The dispersed ink for forming the catalyst layer was applied onto a substrate made of Teflon (trade name, manufactured by DuPont) and dried to obtain a catalyst layer. Thereafter, both sides of the solid polymer electrolyte membrane made of Nafion were sandwiched between the above catalyst layers and pressed by hot pressing, and then the Teflon was peeled off to obtain a membrane / electrode assembly (MEA).

(Fuel cell performance evaluation)
In order to compare the catalyst performance at the initial stage, the current-voltage characteristics were measured using an electronic load. Measurement is performed by setting the cell temperature of the single cell to 80 ° C., and passing the heated bubbler through the heated bubbler to the cathode side electrode and passing the heated bubbler through the heated side bubbler to RH 40%, stoichiometric ratio 7.5. The humidified hydrogen was supplied at an RH of 40% and a stoichiometric ratio of 7.5. The load current was 0.2 A / cm ² . In addition, the Pt amount of each catalyst layer as an electrode was 0.3 mg / cm ² . The measurement results are shown in Tables 1 and 2.

From the results shown in Table 1, it was found that both the Pt-supported carbon powder and the PtCo-supported carbon powder were heat-treated in a CO ₂ atmosphere, so that a higher output was obtained than when other gases were used. Further, from the results of Table 2, it was found that when the heat treatment was performed with 100% concentration of CO ₂ , the output was improved as compared with the lower concentration of CO ₂ .

Claims (3)

  A method for producing a carbon powder carrying a metal catalyst, which is used for a catalyst layer of a polymer electrolyte fuel cell, wherein the metal catalyst is carried on a carbon powder and then heat-treated in a high-concentration carbon dioxide atmosphere. Production method.   A method for producing a carbon powder carrying a metal catalyst, which is used for a catalyst layer of a polymer electrolyte fuel cell, wherein two or more metal catalysts are carried on the carbon powder, and then in a high-concentration carbon dioxide atmosphere. The said manufacturing method which heat-processes and alloyes the said 2 or more types of metal catalyst.   The method for producing a metal catalyst-supported carbon powder according to claim 1 or 2, wherein the temperature of the heat treatment is 500 to 800 ° C.