JP4892811B2 - Electrocatalyst - Google Patents

Description

  The present invention relates to an electrode catalyst that can be used for a fuel cell electrode, preferably a polymer electrolyte fuel cell electrode.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte 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. . The solid polymer fuel cell is characterized by using an electrolyte layer made of a film-like solid polymer membrane.

  In such a polymer electrolyte fuel cell, the polymer electrolyte membrane has an important function of reacting with the catalyst of the anode and transferring protons obtained from the hydrogen gas of the fuel to the cathode. Protons that have moved through the solid polymer membrane react with electrons and oxygen to become water by the cathode catalyst. Thus, the polymer electrolyte fuel cell directly obtains electric energy from the reaction energy obtained by the chemical reaction.

  In the polymer electrolyte fuel cell, the life of the battery is a problem as well as the cost. The battery life is said to be 5000 hours for automobiles and 40,000 hours for home use, and it is required to maintain desired power generation performance over a long period of time. As a solution to this problem, various research and development related to electrode catalysts have been promoted.

  As the conventional electrode catalyst, an electrode catalyst is used in which a catalyst metal such as platinum or a platinum alloy is made fine for both the cathode and the anode and supported on a carrier having a large specific surface area such as carbon black. However, since the electrode reaction at the cathode has a large activation energy, an overvoltage (resistance) is generated at the cathode, which causes the carbon carrier to corrode and disappear when the cathode becomes a noble potential environment (about 0.8 V). Has a problem of freeing and agglomerating to reduce battery life.

In order to solve such problems, Patent Document 1 discloses an electrode catalyst produced using two or more types of carbon powders heat-treated at different heat treatment temperatures as a support. Such an electrode catalyst is produced by adding a catalytic metal to an aqueous solution containing two or more types of carbon powders heat-treated at different heat treatment temperatures and reducing the catalyst metal. In general, carbon powder is known to have a structure similar to a graphite structure by heat treatment at a high temperature of 1000 ° C. or higher, and to improve the corrosion resistance. Therefore, the electrode catalyst described in Patent Document 1 improves the corrosion resistance by heat treating the carbon powder.
JP 2002-273224 A

  However, although the heat-treated carbon powder has improved corrosion resistance, the specific surface area is reduced, so that platinum cannot be supported in a highly dispersed manner. Therefore, the electrode catalyst of patent document 1 uses only the heat-treated carbon powder, and there exists a problem that it is inferior to the activity of an electrode catalyst.

  The object of the present invention is to provide an electrode catalyst with improved corrosion resistance, which exhibits high catalytic activity over a long period of time.

  As a result of intensive studies by the inventor in view of the above problems, it has been found that by using a conductive carbon support having a different graphitization rate in an electrode catalyst, corrosion resistance is improved and high catalytic activity is exhibited. .

That is, the present invention is an electrode catalyst comprising platinum-containing catalyst particles and a conductive carbon carrier having a different graphitization rate that supports the catalyst particles, and the electrode catalyst has a BET specific surface area of 250 to 1600 m. ² / g of an electrocatalyst (1) in which 30 to 90% by mass of the catalyst particles of the total amount of catalyst particles in the electrode catalyst are supported on a non-graphitized conductive carbon support (A), BET Electrocatalyst obtained by supporting 10 to 70% by mass of the catalyst particles of the total amount of catalyst particles in the electrode catalyst on a graphitized conductive carbon support (B) having a specific surface area of 50 to 400 m ² / g (2), wherein the electrode catalyst (1) and the electrode catalyst (2) are mixed in a mass ratio (1) / (2) of 4/1 to 1/2. .

The conductive carbon support (A) that is not graphitized and has a BET specific surface area of 250 to 1600 m ² / g can support catalyst particles such as platinum in a highly dispersed manner on the support. Corrosion resistance can be improved by the graphitized conductive carbon support (B) having a density of 50 to 400 m ² / g. Accordingly, an electrode catalyst including platinum-containing catalyst particles and a conductive carbon support having a different graphitization rate that supports the catalyst particles, wherein the electrode catalyst has a BET specific surface area of 250 to 1600 m ² / g. An electrocatalyst (1) in which 30 to 90 mass% of the total catalyst particles in the electrode catalyst are supported on a non-graphitized conductive carbon support (A), and a BET specific surface area of 50 An electrode catalyst (2) in which 10 to 70% by mass of the catalyst particles of the total amount of catalyst particles in the electrode catalyst are supported on a graphitized conductive carbon support (B) having a particle size of ~ 400 m ² / g; The electrode catalyst of the present invention, wherein the mass ratio (1) / (2) of the electrode catalyst (1) and the electrode catalyst (2) is mixed at 4/1 to 1/2 , High catalytic activity from the stage In addition, by improving the corrosion resistance, such catalytic activity can be stably maintained over a long period of time.

The first of the present invention is an electrode catalyst comprising platinum-containing catalyst particles and a conductive carbon carrier having a different graphitization rate for supporting the catalyst particles, the electrode catalyst having a BET specific surface area of 250 to An electrode catalyst (1) in which 30 to 90% by mass of the catalyst particles of the total amount of catalyst particles in the electrode catalyst are supported on a non-graphitized conductive carbon support (A) of 1600 m ² / g; An electrode in which 10 to 70% by mass of the catalyst particles of the total amount of catalyst particles in the electrode catalyst are supported on a graphitized conductive carbon support (B) having a BET specific surface area of 50 to 400 m ² / g. An electrode catalyst comprising a catalyst (2), wherein the mass ratio (1) / (2) of the electrode catalyst (1) and the electrode catalyst (2) is mixed at 4/1 to 1/2. is there.

  In general, the catalyst carrier used for the electrode catalyst must have a specific surface area sufficient to support the catalyst in a highly dispersed manner and a sufficient electronic conductivity as a current collector. Further, the catalyst carrier is required not to be corroded in a strongly acidic environment such as a perfluorosulfonic acid polymer used as an ion exchange membrane.

  The conductive carbon conventionally used as a catalyst carrier can easily obtain a highly active catalyst with high dispersion loading of a catalyst metal such as platinum, while it is inferior in corrosion resistance and gradually disappears in corrosion over a long period of use. There was a problem.

  In order to solve such problems, attempts have been made to improve the corrosion resistance of the electrode catalyst by heat-treating the conductive carbon and using graphitized carbon as a carrier. Conductive carbon, which is an organic substance, becomes a substance rich in carbon when heated to about 1000 ° C., that is, amorphous carbon, and when further heated, the spread and overlap of the network plane of the carbon six-membered ring is about 1400 ° C. When the temperature is increased to 2300 ° C. or more, a three-dimensional crystal lattice similar to the graphite structure is formed, thereby improving the corrosion resistance.

  Patent Document 1 discloses an electrode catalyst using two or more types of graphitized carbon obtained by heat-treating the conductive carbon at different temperatures as a support. However, while the graphitized carbon is excellent in corrosion resistance, the specific surface area is remarkably lowered by heat treatment, and surface functional groups such as carboxyl groups and carbonyl groups are also burned out, so that it is difficult to carry a highly dispersed catalyst metal. is there. Therefore, there is a possibility that a highly active catalyst cannot be obtained even if only graphitized carbon is used for the carrier.

On the other hand, the electrode catalyst of the present invention can have both the characteristics of the conductive carbon and the graphitized carbon by using conductive carbon carriers having different graphitization rates, and has only high corrosion resistance. Therefore, an electrode catalyst having excellent catalytic activity can be obtained.

  Below, the electrode catalyst of this invention is demonstrated in detail.

In the electrode catalyst of the present invention, specifically, the conductive carbon support having a different graphitization rate is a non-graphitized conductive carbon support (A) having a BET specific surface area of 250 to 1600 m ² / g, A graphitized conductive carbon support (B) having a BET specific surface area of 50 to 400 m ² / g is used.

  The conductive carbon support (A) is not graphitized and preferably has a graphitization rate of less than 50%, more preferably a graphitization rate of 5 to 40%. Thereby, a sufficiently large carrier specific surface area can be obtained, and catalyst particles such as platinum can be supported in a highly dispersed manner.

Specifically, the BET specific surface area of the conductive carbon support (A) is preferably 250 to 1600 m ² / g, particularly preferably 400 to 1200 m ² / g. If the BET specific surface area is in the above range, it is advantageous in that the catalyst particles are highly dispersed on the support.

  The conductive carbon carrier (A) preferably has a conductivity of 0.1 to 100 S / cm, particularly 10 to 100 S / cm. If the electrical conductivity is less than 0.1 S / cm, the electrical resistance may increase, and if it exceeds 100 S / cm, the BET specific surface area may decrease.

  The conductive carbon carrier (A) is not particularly limited, and carbon black such as channel black, furnace black, and thermal black, activated carbon obtained by carbonizing and activating various carbon atom-containing materials can be used. Carbon black is produced by thermal decomposition of a hydrocarbon liquid or gas. Activated carbon uses plant-based wood, sawdust, coconut husk, pulp waste liquor and mineral coal, petroleum coke, petroleum pitch, etc. as raw materials. To be manufactured. More specifically, as the conductive carbon carrier (A), Ketjen Black EC and Ketjen Black EC600JD manufactured by Ketjen Black International Co., Ltd. are used from the viewpoints of obtaining raw materials, easy production and handling of the carrier, and the like; Examples include Vulcan XC-72 and Black Pearl 2000 manufactured by Cabot. The particle size of the conductive carbon carrier (A) is 30 to 1000 nm, preferably 50 to 500 nm.

  The conductive carbon support (B) has been graphitized and preferably has a graphitization rate of 75% or more, more preferably a graphitization rate of 80 to 95%. As a result, the conductive carbon support (B) can improve not only the corrosion resistance but also the conductivity by changing the crystal structure, and further ensure the water repellency by reducing the functional group on the support surface. be able to. Since the carrier has water repellency, water generated by the electrode reaction can be efficiently removed.

The conductive carbon support (B) preferably has a BET specific surface area of 50 to 400 m ² / g, particularly 100 to 350 m ² / g. If the BET specific surface area is in the above range, it is advantageous in that the catalyst particles are highly dispersed on the support.

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

  The conductive carbon carrier (B) has a conductivity of 100 to 1000 S / cm, preferably 200 to 1000 S / cm. If the electrical conductivity is less than 100 S / cm, the electrical resistance may increase.

  The conductive carbon carrier (B) may have a lattice plane spacing Co value of X-ray diffraction of 6.78 to 6.89 mm, preferably 6.82 to 6.88 mm. If the Co value is less than 6.78%, the graphitization rate may be too high and the specific surface area may decrease, and if it exceeds 6.89%, the graphitization rate may be too low to provide sufficient corrosion resistance and conductivity. There is.

  Here, the “lattice plane spacing Co value” is a measure of the graphitization rate, and is the plane spacing of the network plane of the carbon six-membered ring based on the graphite structure of the conductive carbon support (B). This represents the ½ interlayer distance of the lattice constant C in the C-axis direction. Note that the lattice spacing Co value can be calculated from an X-ray diffraction pattern.

  The conductive carbon carrier (B) is not particularly limited, but is heat-treated at 2800 to 3000 ° C. in an inert atmosphere using carbon black specifically listed as the conductive carbon carrier (A) as a raw material. It has been graphitized. The raw material for the conductive carbon carrier (B) may be the same as the conductive carbon carrier (A), or may be different, and heat treatment improves corrosion resistance, conductivity, water repellency, etc. can do.

In the electrode catalyst of the present invention, the amount of catalyst particles supported on the conductive carbon support (A) and the conductive carbon support (B) is a predetermined ratio . That is, the electrode catalyst of the present invention is an electrode catalyst in which 30 to 90% by mass, preferably 50 to 70% by mass of catalyst particles of the total amount of catalyst particles in the electrode catalyst are supported on the conductive carbon support (A). (1) and, 10 to 70% by weight of the total catalyst particle volume definitive to the electrode catalysts on the conductive carbon carrier (B), preferably from 30 to 50% by weight of the electrode catalyst in which the catalyst particles are carried (2 ) and, the including.

  In the electrode catalyst of the present invention, when the amount of catalyst particles supported on the conductive carbon support (A) is less than 30% by mass of the total amount of catalyst particles used in the electrode catalyst, the output characteristics at the beginning of the reaction are deteriorated. If it exceeds 90 mass%, the corrosion resistance of the electrode catalyst may not be improved. In addition, when the amount of catalyst particles supported on the conductive carbon support (B) is less than 10% by mass of the total amount of catalyst particles used in the electrode catalyst, the corrosion resistance of the electrode catalyst may not be improved, If it exceeds 70% by mass, high catalytic activity may not be obtained.

Further, in the electrode catalyst of the present invention, the mass ratio of the electrocatalyst (1) and the electrocatalyst (2) (1) / (2) is 4 / 1-1 / 2, preferably 3 / 1-1 / 1 . If the ratio of the electrode catalyst (1) to the electrode catalyst (2) exceeds 4/1, the corrosion resistance of the electrode catalyst may not be obtained, and the catalytic activity may decrease. There is a risk that high catalytic activity may not be obtained at the beginning of the process.

Examples of the catalyst particles used in the electrode catalyst of the present invention include platinum or a platinum alloy. Since platinum has high catalytic activity, it may be used alone as catalyst particles. However, when the reformed gas is supplied particularly in the anode of the fuel cell, impurities such as sulfur are also supplied in addition to the hydrogen of the fuel, and there is a possibility that the catalytic activity is lowered due to CO poisoning. Accordingly, it may be used as a platinum alloy of platinum with at least one base metal selected from the group consisting of chromium, manganese, iron, cobalt, and nickel, thereby improving toxicity resistance, heat resistance, and the like. it can.

  The platinum alloy has a platinum to base metal ratio of 1: 1 to 5: 1, more preferably 2: 1 to 4: 1. Catalyst particles having

  The smaller the particle size of the catalyst particles used in the present invention, the larger the effective electrode area for the electrode reaction to proceed. Accordingly, the catalytic activity is increased, the amount of catalyst particles used can be reduced, and the cost can be reduced. However, if the particle size of the catalyst particles is too small, it becomes difficult to uniformly disperse and the activity may be reduced. Therefore, the average particle diameter of the catalyst particles is preferably 1 to 10 nm, particularly 1 to 5 nm.

The second invention is a catalyst supporting electrode solid high polymer electrolyte fuel cell that have a catalyst layer containing the electrocatalyst.

  The polymer electrolyte fuel cell generally has a structure in which a membrane / electrode assembly (hereinafter also referred to as “MEA”) is laminated with a separator. The MEA is formed by sandwiching an electrolyte layer between catalyst-carrying electrodes.

  The catalyst-carrying electrode may include a catalyst layer in which an electrode catalyst is highly dispersed and a gas diffusion layer. At least one surface of the catalyst layer is in contact with the electrolyte layer. Since a strongly acidic ion exchange resin such as a perfluorosulfonic acid polymer is used for the electrolyte layer, it is desirable that the catalyst contained in the catalyst layer does not corrode even in a strongly acidic environment. Since the electrode catalyst of the present invention has high corrosion resistance as described above, it can be suitably used for the catalyst layer.

  The catalyst layer contains an ion exchange resin in addition to the electrode catalyst of the present invention. It is preferred that the ion exchange resin coats the electrode catalyst as a binder polymer. Thereby, electronic conductivity can improve and electrode performance can be improved.

  The ion exchange resin is not particularly limited, and the electrolyte layer and the catalyst layer may be the same or different. Specific examples of ion exchange resins include perfluorosulfonic acid polymer-based proton conductors such as Nafion solutions, those obtained by doping a hydrocarbon polymer compound with an inorganic acid such as phosphoric acid, and some proton conductors And organic / inorganic hybrid polymers substituted with the above functional groups, and ion exchange resins made of proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.

  Specific examples of perfluorosulfonic acid polymer proton conductors include not only polymers composed of only carbon atoms and fluorine atoms, but also oxygen atoms if all hydrogen atoms are replaced with fluorine atoms. Polymerized units based on CF2 = CF2 and polymerized units based on CF2 = CF- (OCF2 CFX) m-Op- (CF2) n-SO3 H (wherein X is a fluorine atom or a trifluoromethyl group) And m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1.).

  The gas diffusion layer in the catalyst-carrying electrode of the present invention is not particularly limited, and examples thereof include porous carbon paper that supports the catalyst layer or a porous carbon substrate such as a carbon cloth.

  The catalyst-carrying electrode containing the electrode catalyst of the present invention may be used as an anode or a cathode, but is preferably used as a cathode because it has high corrosion resistance even under strong acid use.

  As the method for producing the catalyst-carrying electrode, in addition to the electrode catalyst and the ion exchange resin, a liquid containing a water repellent, a pore-forming agent, a thickener, a diluting solvent, etc., as required Examples of the known method include formation by spraying, coating, filtration and the like on the gas diffusion layer. Since the catalyst-carrying electrode of the present invention has water repellency due to the conductive carbon carrier (B) contained in the electrode catalyst, it is usually necessary to reduce the amount of water repellent used in the production of the electrode or to use a water repellent. Can also show excellent electrode performance.

The third of the present invention is a polymer electrolyte fuel cell using the catalyst-supporting electrode for a polymer electrolyte fuel cell. The catalyst-carrying electrode using the electrode catalyst of the present invention can exhibit high electrode performance from the beginning of the electrode reaction, and can maintain electrode performance over a long period of time. Therefore, if such a catalyst-carrying electrode is used as a fuel cell electrode, it may be possible to provide a fuel cell that can exhibit high performance over a long period from the beginning of operation. The type of fuel cell is not particularly limited as long as desired cell characteristics can be obtained, but it is used as a polymer electrolyte fuel cell (hereinafter also referred to as “PEFC”) from the viewpoints of practicality and safety. Is preferred.

  The PEFC is as described above, and has a structure in which MEAs are stacked with a separator. Since the electrolyte layer and the catalyst-supporting electrode constituting the MEA are also as described above, the description thereof is omitted here.

  As a separator for sandwiching the MEA, a known one such as carbon paper or carbon cloth may be used. The separator has a function of separating air and fuel gas, and a channel groove may be formed in order to secure the channel. The groove width and pitch of the flow path groove of the separator are not particularly limited, but the gas diffusibility to the electrode is improved as the thickness is reduced, and a groove width of about 0.5 to 1.0 mm is usually used. In addition, in order to prevent water generated at the cathode from staying in the separator flow path, the flow path can be lengthened to increase the flow rate, or the separator can be set up so that the generated water can easily flow from top to bottom. Good.

  MEA production methods include a method of directly forming a catalyst-supporting electrode on an electrolyte layer, a method of forming a catalyst-supporting electrode on a separator and bonding it to an electrolyte layer, and forming a catalyst-supporting electrode on a flat plate. Various methods such as a method of transferring to a layer can be mentioned. When the catalyst-carrying electrode is formed on the separator separately from the electrolyte layer, the catalyst-carrying electrode and the electrolyte layer are joined by a hot press method, an adhesion method (see Japanese Patent Application Laid-Open No. 7-220741) or the like. Is preferred.

  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.

  The fuel cell using the electrode catalyst of the present invention has excellent corrosion resistance as compared with the conventional one and excellent startability, so that it is reliable as a power source for moving bodies such as vehicles and a stationary power source. It is possible to provide a high fuel cell. In addition, regarding the polymer electrolyte fuel cell described above, only one embodiment of the present invention is shown, and the present invention is not limited to this. Accordingly, a fuel cell using the electrode catalyst of the present invention and a fuel cell electrode are included in the scope of the present invention.

As the method for producing the electrode catalyst of the present invention described above, a step of obtaining the electrode catalyst (1) by supporting catalyst particles on the conductive carbon support (A) and calcining the conductive carbon support (A); Carbon is graphitized at 2800 to 3000 ° C. to obtain a conductive carbon support (B), and catalyst particles are supported on the conductive carbon support (B) and calcined, whereby an electrode catalyst (2
) And a step of mixing the electrode catalyst (1) and the electrode catalyst (2).

  In order to support the catalyst particles on the conductive carbon support (A), for example, the conductive carbon support (A) is dispersed in a catalyst particle compound solution, and a reducing agent is added thereto, thereby supporting the catalyst particles in a highly dispersed state. be able to.

  The catalyst particle compound solution is a solution containing a catalyst particle compound such as chloroplatinic acid, chloroplatinum chloride, or dinitrodiammine platinum when Pt is used as the catalyst particles. In order to obtain a platinum alloy, a desired base metal compound such as nitrate, chloride, sulfate, etc. may be dispersed in the solution in addition to platinum. Moreover, water etc. can be used as a solvent which adds a catalyst particle compound.

  In order to disperse the conductive carbon carrier (A) in the catalyst particle compound solution, an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device may be used. What is necessary is just to determine suitably the catalyst particle density | concentration in a catalyst particle compound solution, the mixture ratio of a catalyst particle compound, and a carbon support | carrier (A), etc. so that the obtained electrode catalyst (1) may have a desired characteristic.

  The reducing agent is not particularly limited as long as it can reduce the catalyst particle compound. Sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, hydrazine, formaldehyde, methanol, ethanol, hydrogen , Ethylene, carbon monoxide and the like can be used. By adding the reducing agent, the catalyst particle compound can be supported as catalyst particles on the conductive carbon support (A). By adding an appropriate amount of the reducing agent to the above dispersion of the catalyst particle compound and the conductive carbon carrier (A), heating to 60 to 100 ° C. using a reflux reactor or the like, and then allowing to cool to room temperature. The catalyst particles are reduced and supported.

  Next, the electrode catalyst (1) can be obtained by firing the conductive carbon carrier (A) on which the catalyst particles are supported. You may dry as needed before baking.

  The drying method is not particularly limited as long as a known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blower dryer is used. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  The firing method is performed in an air atmosphere, preferably in an inert atmosphere such as nitrogen, helium, argon, etc., at a firing temperature of 300 to 1000 ° C., preferably 300 to 600 ° C. for about 1 to 6 hours. Good.

  Although the reducing agent is used in the above-described method of supporting the catalyst particles on the conductive carbon support (A), the present invention is not particularly limited to this. For example, various known techniques such as an impregnation method, a coprecipitation method, and a competitive adsorption method can be used. Alternatively, an electrode catalyst may be produced using a microemulsion method described in JP-A-7-246343 and JP-A-10-216517. Also by the microemulsion method, the catalyst particles can be highly dispersed and supported on the conductive carbon support (A).

  In the electrode catalyst of the present invention, the conductive carbon support (B) is obtained by graphitizing by subjecting carbon to heat treatment at 2800 to 3000 ° C.

Specific examples of carbon include carbon black such as channel black, furnace black, and thermal black, and activated carbon obtained by carbonizing and activating various carbon atom-containing materials. The same thing is mentioned. Moreover, the same thing as a conductive carbon support | carrier (A) may be used, and a different thing may be used, and corrosion resistance, electroconductivity, water repellency, etc. can be improved by heat-processing.

  The graphitization of the carbon is performed by heat treatment at 2800 to 3000 ° C. in an inert gas atmosphere such as nitrogen or argon. When the heat treatment temperature is less than 2800 ° C, the carbon graphitization rate is low, so sufficient corrosion resistance cannot be obtained. When the heat treatment temperature exceeds 3000 ° C, the graphitization rate of carbon is too high, and the surface area of the carrier is reduced, so It cannot be supported. Since the heat treatment time varies depending on the type of carbon used, it may be appropriately determined so as to obtain a desired graphitization rate.

  The step of obtaining the electrode catalyst (2) by supporting the catalyst particles on the conductive carbon support (B) and calcining is performed in the same manner as the method of supporting the catalyst particles on the conductive carbon support (A) described above. Just do it.

  In the production method of the present invention, the catalyst particles are supported separately for the conductive carbon support (A) and the conductive carbon support (B). When the catalyst particle compound solution, the conductive carbon support (A) and the conductive carbon support (B) are mixed at the same time, the catalyst particles are preferentially supported on the conductive carbon support (A). There is a possibility that the amount of catalyst supported in (B) decreases, and a desired amount of supported catalyst particles cannot be obtained. Since the amount of the catalyst particles supported is the same as that described in the first electrode catalyst of the present invention, the description thereof is omitted here.

  In the step of mixing the electrode catalyst (1) and the electrode catalyst (2), using a ball mill or the like, the electrode catalyst (1) is adjusted so that the obtained electrode catalyst has the predetermined mixing ratio described above. And the electrode catalyst (2) may be mixed.

  The electrode catalyst of the present invention has a high catalytic activity by using the conductive carbon support (A) and the conductive carbon support (B) as a support, and maintains the catalytic activity for a long time even in this strongly acidic environment. be able to. The conductive carbon carrier (A) can exhibit high catalytic activity from the beginning of the reaction, and the conductive carbon carrier (B) has water repellency. Therefore, such an electrode catalyst is preferably used as a fuel cell electrode catalyst, particularly a cathode catalyst.

  Further, in the method for producing an electrode catalyst according to the present invention, catalyst particles are supported separately on the conductive carbon support (A) and the conductive carbon support (B), so that the desired support of the catalyst particles on each support is provided. It can be carried in an amount.

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

<Example 1>
To 4.0 g of highly conductive carbon black (Ketjen Black EC, manufactured by Ketjen Black International Co., Ltd., conductivity = 1 S / cm, BET specific surface area = 800 m ² / g), dinitrodiammine platinum aqueous solution (Pt concentration 1.0 mass) %) 400 g was added and stirred for 1 hour, and 200 g of ethanol as a reducing agent was mixed and stirred for 1 hour. Then, it heated up to 85 degreeC in 30 minutes, and also, after stirring and mixing at 85 degreeC for 6 hours, it cooled to room temperature in 1 hour.

After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours, and then pulverized in a mortar to obtain catalyst (A1) (average particle diameter of Pt particles 2.5 nm, Pt supported concentration 50%). Got. Next, the catalyst particles were calcined at 300 ° C. for 1 hour in an inert gas flow atmosphere.

Next, highly conductive carbon black (Ketjen Black EC manufactured by Ketjen Black International Co., Ltd., conductivity = 1 S / cm, BET specific surface area = 804 m ² / g) was heat-treated at 2800 ° C. for 10 hours to obtain graphitized carbon. Black (conductivity = 150 S / cm, BET specific surface area = 110 m ² / g, Co value of XRD = 6.88) was obtained.

  To 4.0 g of the graphitized carbon black, 200 g of a dinitrodiammine platinum aqueous solution (Pt concentration 1.0 mass%) was added and stirred for 1 hour, and 200 g of ethanol as a reducing agent was mixed and stirred for 1 hour. Then, it heated up to 85 degreeC in 30 minutes, and also, after stirring and mixing at 85 degreeC for 6 hours, it cooled to room temperature in 1 hour.

  After filtering the precipitate, the obtained solid was dried at 85 ° C. under reduced pressure for 12 hours, and then pulverized in a mortar to obtain catalyst (B1) (average particle diameter of Pt particles 3.5 nm, Pt support concentration 25%). Got. Next, the catalyst particles were calcined at 300 ° C. for 1 hour in an inert gas flow atmosphere.

  The catalyst A1 and the catalyst B1 were mixed at a ratio of 1: 1 to obtain an electrode catalyst.

<Example 2>
In the same manner as in Example 1 except that highly conductive carbon black (Ketjen Black EC600JD manufactured by Ketjen Black International Co., Ltd., conductivity = 1 S / cm, BET specific surface area = 1270 m ² / g) was used, a catalyst ( A2) (average particle diameter of Pt particles 2.5 nm, Pt support concentration 50%) was obtained.

Further, graphitized carbon black (conductivity = 300 S / cm, BET specific surface area) was used in the same manner as in Example 1 except that the highly conductive carbon black (Ketjen Black EC600JD manufactured by Ketjen Black International) was used. = 260 m ² / g, Co value of XRD = 6.87), and using this, catalyst (B2) (average particle diameter of Pt particles 3.5 nm, Pt support concentration 25%) was obtained.

  The catalyst A2 and the catalyst B2 were mixed at a ratio of 3: 1 to obtain an electrode catalyst.

<Comparative Example 1>
To 4.0 g of highly conductive carbon black (Cabot Vulcan XC-72, conductivity = 0.5 S / cm, BET specific surface area = 280 m ² / g), 400 g of dinitrodiammine platinum aqueous solution (Pt concentration 1.0%) In addition, the mixture was stirred for 1 hour, and 200 g of ethanol as a reducing agent was mixed and stirred for 1 hour. Then, it heated up to 85 degreeC in 30 minutes, and also, after stirring and mixing at 85 degreeC for 6 hours, it cooled to room temperature in 1 hour.

  After filtering the precipitate, the obtained solid was dried at 85 ° C. under reduced pressure for 12 hours, and then pulverized in a mortar to obtain catalyst (D1) (average particle diameter of Pt particles 3.5 nm, Pt support concentration 50%). Got. Next, the catalyst particles were calcined at 300 ° C. for 1 hour in an inert gas flow atmosphere.

  Only the catalyst D1 was used as an electrode catalyst.

<Performance evaluation of electrode catalyst>
With respect to the electrode catalysts obtained in Examples 1 and 2 and Comparative Example 1, MEA was produced according to the following procedure, and the performance of the single fuel cell was measured.

  First, MEA was produced in the following procedure.

  First, purified water and isopropyl alcohol are added to the electrode catalysts according to the examples and comparative examples as a cathode, and a Nafion solution containing Nafion (registered trademark) in the same amount as carbon is added and dispersed well with a homogenizer. A foaming operation was added to prepare a catalyst slurry. A predetermined amount was printed on one side of carbon paper (“TGP-H” manufactured by Toray Industries, Inc.), which is a gas diffusion layer (GDL), and dried at 60 ° C. for 24 hours to obtain a catalyst layer. Thereafter, the catalyst layer and the electrolyte layer were joined by hot pressing the surface on which the catalyst layer was applied to the electrolyte layer at 120 ° C. and 0.2 MPa for 3 minutes.

  On the other hand, as the anode, 50% Pt-supported carbon was used as the electrode catalyst, and the anode was prepared in the same manner as the cathode, and the catalyst layer was bonded to the surface opposite to the cathode bonding surface of the electrolyte layer to obtain MEA.

In the MEA, the amount of Pt used for both the anode and cathode was 0.5 mg per apparent electrode area of 1 cm ² , and the electrode area was 300 cm ² . Further, Nafion 112 was used as the electrolyte layer.

  A fuel cell single cell was constructed using the obtained MEA, and performance measurement was performed as follows.

In the measurement, hydrogen was supplied as fuel to the anode side, and air was supplied to the cathode side. Supply pressure for both gases is atmospheric pressure, hydrogen is 80 ° C, air is saturated and humidified at 60 ° C, fuel cell body temperature is set to 80 ° C, hydrogen utilization is 70%, and air utilization is 40%. The operation was continued for 30 minutes at a current density of 0.5 A / cm ² . When power generation was stopped, the current density taken out was set to zero, and then the anode was purged with nitrogen to discharge hydrogen. The cathode was opened at the outlet side at atmospheric pressure. At this time, temperature control of the fuel cell body was not performed, and the stop time was 30 minutes. When restarting operation after stopping, gas was again introduced into the cell under the above conditions to generate power. By repeating this operation-stop cycle, the durability of the single fuel cell was evaluated.

FIG. 1 shows the change of the cell voltage with respect to the number of operation-stop cycles at a current density of 0.5 A / cm ² for each solid polymer electrolyte fuel cell produced using the electrode catalysts of Examples 1 and 2 and Comparative Example 1. It is a graph to represent. As shown in the figure, the fuel cell using the catalyst of the present invention (Examples 1 and 2) has a longer start-stop cycle number than the fuel cell using the conventional catalyst (Comparative Example 1). On the other hand, it was confirmed that the cell voltage decrease rate was small.

It is a graph showing the change with respect to the number of operation-stop cycles of each solid polymer electrolyte fuel cell produced using the electrode catalyst of Examples 1, 2 and Comparative Example 1.

Claims (7)

An electrode catalyst comprising catalyst particles containing platinum, and a conductive carbon support having a different graphitization rate that supports the catalyst particles,
The electrocatalyst has a BET specific surface area of 250 to 1600 m ² / g and the non-graphitized conductive carbon support (A) has 30 to 90% by mass of the catalyst particles in the total amount of catalyst particles in the electrode catalyst. The supported electrocatalyst (1) and the graphitized conductive carbon support (B) having a BET specific surface area of 50 to 400 m ² / g are mixed with 10 to 70 mass of the total catalyst particles in the electrode catalyst. % Of an electrode catalyst (2) on which the catalyst particles are supported,
An electrode catalyst obtained by mixing a mass ratio (1) / (2) of the electrode catalyst (1) and the electrode catalyst (2) at 4/1 to 1/2 .   The electrode catalyst according to claim 1, wherein the conductive carbon support (A) has a conductivity of 0.1 to 100 S / cm, and the conductive carbon support (B) has a conductivity of 100 to 1000 S / cm.   The electrocatalyst according to claim 1 or 2, wherein the conductive carbon support (B) has a lattice plane Co value of X-ray diffraction of 6.78 to 6.89. The catalyst particles, chromium, manganese, iron, cobalt, and at least one base metal and platinum and, the electrode catalyst according to any one of claims 1 to 3 which is an alloy selected from the group consisting of nickel. The electrode catalyst according to claim 4 , wherein the catalyst particles have a mass ratio of platinum to base metal of 1: 1 to 5: 1. A catalyst-supporting electrode for a polymer electrolyte fuel cell having a catalyst layer containing the electrode catalyst according to any one of claims 1 to 5 . A polymer electrolyte fuel cell using the catalyst-supporting electrode for a polymer electrolyte fuel cell according to claim 6 .

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