JP2005141920A - Catalyst carrying electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst carrying electrode capable of maintaining superior catalyst activity over a long period by suppressing elution of noble metal components of an electrode catalyst. <P>SOLUTION: The catalyst carrying electrode contains two or more kinds of catalysts carrying conductive materials composed of conductive carrier carrying catalytic particles of different average particle diameter, and a proton conductive member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrode for a fuel cell, preferably an electrode for a polymer electrolyte fuel cell.

  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.

  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 supporting electrodes. Further, the catalyst-carrying electrode can include a catalyst layer in which the electrode catalyst is highly dispersed and a gas diffusion layer. Therefore, at least one surface of the catalyst layer is in contact with the electrolyte layer.

  In such a polymer electrolyte fuel cell, an electrode catalyst oxidizes the hydrogen gas of the fuel at the anode to convert it into protons, and at the cathode it reduces oxygen and combines with the protons that have passed through the electrolyte layer to form water, resulting in chemical reaction. Happens. The polymer electrolyte fuel cell directly obtains electric energy from the reaction energy obtained by the chemical reaction.

  The polymer electrolyte fuel cell has a problem with the cost, but the life of the cell. 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.

  In the conventional electrode catalyst, an electrode catalyst is used in which a catalytic metal such as platinum or a platinum alloy is made fine and supported on a carrier having a large specific surface area such as carbon black for both the cathode and the anode. However, depending on the operating conditions, starting and stopping conditions, the cathode becomes a noble potential environment (about 0.8 V or more). As a result, an electrochemical oxidation reaction of platinum occurs and platinum is eluted, so that there is a problem that the amount of catalyst is reduced and the battery life is shortened.

In response to such a problem, Patent Document 1 describes a fuel cell using an anode in which a metal ion that is alloyed with platinum is added in advance to an electrolyte contained in a catalyst layer of a catalyst-carrying electrode. In the first embodiment of Patent Document 1, the addition of the metal ions is performed by a method of dissolving a metal salt of PdCl ₂ in an electrolyte of 85% phosphoric acid so as to be 10 ⁻⁵ M. Yes.

According to Patent Document 1, by increasing the metal ion concentration in the electrolyte, it is difficult to elute the metal component in the electrode catalyst even when the electrode is at a high potential, and the elution rate of the metal component can be suppressed. It is.
JP-A-11-31529

  However, the method of Patent Document 1 has a problem that the manufacturing cost is high because the noble metal is dissolved in a high concentration in the electrolyte. In addition, chloride ions may deteriorate catalyst performance or promote corrosion of other materials.

  Accordingly, an object of the present invention is to provide a catalyst-carrying electrode that can maintain high catalytic activity for a long period of time by suppressing elution of the noble metal component of the electrode catalyst.

  The present invention is a catalyst-carrying electrode comprising two or more types of catalyst-carrying conductive materials in which catalyst particles having different average particle diameters are carried on a conductive carrier, and a proton conductive member.

  The catalyst-carrying electrode of the present invention includes two or more types of catalyst-carrying conductive materials in which catalyst particles having different average particle diameters are carried on a conductive carrier, so that it can be used in a noble potential environment without increasing the amount of catalyst particles. However, the elution of the catalyst particles can be suppressed. Therefore, the catalyst-carrying electrode of the present invention can be produced at a low cost, and the catalytic activity can be maintained for a long time.

  A first aspect of the present invention is a catalyst-carrying electrode comprising two or more types of catalyst-carrying conductive materials in which catalyst particles having different average particle diameters are carried on a conductive carrier, and a proton conductive member.

  In general, a catalyst-carrying electrode is formed by laminating a catalyst layer containing a catalyst-carrying conductive material, a proton conductive member as an electrolyte, and the like on a gas diffusion layer. Conventionally, a catalyst-carrying conductive material used in a catalyst-carrying electrode is formed by carrying catalyst particles such as platinum on a conductive carrier. An electrode reaction proceeds on the surface of the catalyst particles. Therefore, by miniaturizing the catalyst particles and carrying them in a highly dispersed manner on a conductive carrier, the amount of expensive catalyst particles such as platinum is reduced and the catalytic activity of the catalyst-carrying electrode is improved.

  However, when the catalyst-carrying electrode is used as a cathode, the catalyst-carrying electrode is in a noble potential environment (about 0.8 V or more) depending on operating conditions, starting and stopping conditions. As a result, elution of the catalyst particles occurs and the amount of the catalyst particles decreases, which causes a problem of reducing the performance of the catalyst-carrying electrode.

  With respect to such a problem, the catalyst-carrying conductive material contained in the catalyst-carrying electrode of the present invention has two or more kinds of catalyst particles having different average particle diameters. The catalyst-carrying conductive material can maintain high performance of the catalyst-carrying electrode even when the catalyst-carrying electrode is in a noble potential environment. The reason for this is not necessarily clear, but is considered as follows.

  Catalyst particles with a small average particle diameter have a large specific surface area and thus a high elution rate. In addition, even if catalyst particles having an average particle diameter of a certain value or less are eluted, since the contribution to the electrode reaction is small, the performance deterioration of the catalyst-carrying electrode is not greatly affected. Therefore, when the catalyst-carrying conductive material contains at least two kinds of catalyst particles having different average particle diameters, elution starts preferentially from catalyst particles having a small contribution to the electrode reaction. Thereby, the catalyst concentration around the catalyst particles can be rapidly increased, and it is considered that elution of catalyst particles having a large contribution to the electrode reaction, that is, a large average particle diameter is suppressed.

  In addition, the concentration of catalyst particles around the catalyst particles that contribute to the electrode reaction of the catalyst layer can be increased. Thereby, the usage-amount of the catalyst particle for suppressing the elution of a catalyst particle can be decreased, and manufacturing cost can be lowered.

Furthermore, as shown in the following chemical formula 1, when the platinum ion (Pt ²⁺ ) concentration in the vicinity of the catalyst particles is increased to a certain value or more by elution of the catalyst particles having a small average particle diameter, PtO becomes thermodynamically stable. Therefore, the reaction represented by the following chemical formula 2 occurs due to platinum contained in the catalyst particles having a large average particle diameter that contributes to the activity, and an oxide passive film is formed on the surface of the catalyst particles having a large average particle diameter.

The oxide passivation film improves the corrosion resistance of the catalyst particles and can suppress the elution of the catalyst particles. Moreover, since the said oxide passive film can be easily reduce | restored to platinum if it performs a reduction process, it can maintain catalyst activity suitably.

  Therefore, the catalyst-carrying electrode of the present invention including the catalyst-carrying conductive material on which catalyst particles having different average particle diameters are carried contributes greatly to the electrode reaction of the catalyst particles, that is, the catalyst particles having a large average particle diameter. By effectively suppressing elution, high performance can be maintained over a long period of time.

  Hereinafter, the catalyst-carrying electrode of the present invention will be described in more detail.

  As described above, the catalyst-carrying electrode of the present invention is a catalyst-carrying electrode comprising two or more kinds of catalyst-carrying conductive materials in which catalyst particles having different average particle diameters are carried on a conductive carrier, and a proton conductive member. is there.

  The conductive carrier used for the catalyst-carrying conductive material is required not only to carry catalyst particles but also to have a function as a current collector for taking out electrons to an external circuit or taking them from the external circuit. When the electrical resistance of the conductive carrier is high, the internal resistance of the electrode is increased, and as a result, the performance of the electrode is degraded. Therefore, the electrical resistance of the catalyst carrier included in the electrode must be sufficiently low. Accordingly, it is preferable that the conductive carrier has an electronic conductivity of 0.001 S / cm or more, particularly 0.1 S / cm or more.

  Examples of such a conductive carrier include conductive carbon materials such as carbon black, graphitized carbon, and activated carbon, and metal oxides, metal carbides, metal nitrides, and polymer compounds having electronic conductivity.

  The method of measuring the electronic conductivity of the conductive carrier is based on the relationship between the current and voltage values of the electrodes attached to the indenter while compressing the conductive carrier at a predetermined pressure (uniaxial pressurization, biaxial pressurization, etc.). A publicly known method for obtaining the conductivity can be exemplified.

  The catalyst particles used in the catalyst-carrying conductive material of the present invention preferably contains at least platinum. The catalyst particles may be platinum alone, or may be a noble metal alloy catalyst based on platinum, a noble metal-base metal mixture catalyst, or the like. Since platinum exhibits high oxygen reduction activity, it is preferably used for the catalyst-carrying conductive material. Moreover, stability and activity as catalyst particles can be enhanced by the noble metal alloy catalyst, the noble metal-base metal mixture catalyst, and the like.

  As the noble metal alloy catalyst, specifically, from a group consisting of metals of noble metals other than platinum such as ruthenium, rhodium, palladium, osmium, iridium, gold, silver, chromium, iron, titanium, manganese, cobalt, nickel and copper An alloy of one or more selected metals and platinum is preferred.

Further, the noble metal - as base metal mixture catalyst, specifically, noble metals such as Pt-WO ₃ - metal oxide mixtures.

  The catalyst-carrying conductive material is formed by carrying the catalyst particles on the conductive carrier. The catalyst particles in the catalyst-carrying conductive material have at least two kinds of average particle diameters. In such a catalyst-carrying conductive material, the average particle size of the catalyst-carrying conductive material having the largest average particle size of the catalyst particles is the average particle size of the catalyst-carrying conductive material having the smallest average particle size of the catalyst particles. 1.5 to 20 times, preferably 2 to 10 times, more preferably 2 to 5 times.

When the average particle size of the catalyst in the catalyst-carrying conductive material having the largest average particle size of the catalyst particles exceeds 20 times the average particle size of the catalyst-carrying conductive material in which the average particle size of the catalyst particles is the smallest,
Since the specific surface area of the largest catalyst particles decreases, the catalytic reaction area decreases, and there is a possibility that sufficient catalytic activity cannot be obtained. On the other hand, if the ratio is less than 1.5 times, the difference in specific surface area between the largest catalyst particle and the smallest catalyst particle is small, so that a significant difference in the elution rate of the catalyst particle may not be obtained.

  The catalyst particle average particle diameter of the catalyst-carrying conductive material having the largest average particle diameter of the catalyst particles is 2.0 to 10 nm, preferably 1.0 to 10 nm, more preferably 2.0 to 5.0 nm. . If the average particle size is less than 2.0 nm, there is a risk that a significant difference in the elution rate of the catalyst particles may not be obtained. If the average particle size exceeds 10 nm, the specific surface area of the catalyst particles is reduced, so that sufficient catalytic activity is obtained. Not desirable because there is no fear.

  The catalyst particle average particle diameter of the catalyst-carrying conductive material having the smallest average particle diameter of the catalyst particles is 0.5 to 1.5 nm, preferably 0.75 to 1.5 nm, more preferably 1.0 to 1.5 nm. It is good to do. If the average particle size is less than 0.5 nm, it may be difficult to form catalyst particles. If the average particle size exceeds 1.5 nm, the specific surface area of the catalyst particles will increase and preferential elution of catalyst particles is expected. There is a risk that the intended effect cannot be obtained.

  In the present invention, the average particle diameter of the catalyst metal is the average of the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst metal in X-ray diffraction, or the average particle diameter of the catalyst metal determined from a transmission electron microscope image. Indicates the value.

  In the catalyst-carrying electrode of the present invention, the mixing ratio of the catalyst-carrying conductive material having the largest average particle diameter of the catalyst particles is preferably 50 to 90% by mass, more preferably 55 to 85%, based on the total amount of the catalyst-carrying conductive material. It is 60 mass%, Most preferably, it is 60-80 mass%. If the blending ratio of the catalyst-carrying conductive material having the largest average particle diameter of the catalyst particles is less than 50% by mass, there is a possibility that sufficient electrode performance cannot be obtained because the amount of the catalyst particles contributing to the electrode reaction is small. If the amount exceeds 90% by mass, the amount of catalyst particles eluted preferentially decreases, and the intended effect may not be obtained.

  In the catalyst-carrying electrode of the present invention, the blending ratio of the catalyst-carrying conductive material having the smallest average particle diameter of the catalyst particles is preferably 10 to 50% by mass, more preferably 15%, based on the total amount of the catalyst-carrying conductive material. It is -45 mass%, Most preferably, it is 20-40 mass%. If the blending ratio of the catalyst-carrying conductive material having the smallest average particle diameter of the catalyst particles exceeds 50% by mass, the amount of the catalyst particles preferentially eluted may increase so much that the high catalyst activity of the catalyst-carrying electrode may not be obtained. Furthermore, there is a risk of increasing the manufacturing cost of the obtained electrode. In addition, when the blending ratio is less than 10% by mass, the amount of the catalyst particles eluted preferentially decreases, and the intended effect may not be obtained.

FIG. 1 is a schematic diagram of a catalyst-carrying conductive material in which catalyst particles having two types of average particle diameters are carried. In the catalyst-carrying conductive material shown in FIG. 1, catalyst particles 2 having a large average particle diameter are supported on a conductive carrier 1, and catalyst particles 3 having the next smaller average particle diameter are supported on another conductive carrier 1. Thereafter, these are mixed at a predetermined mixing ratio. When the electrode reaction progresses in the catalyst-carrying conductive material of FIG. 1, the catalyst particles 3 having a small average particle diameter are preferentially eluted to increase the catalyst particle concentration, whereby the catalyst particles 2 having a large average particle diameter are eluted. It can be suppressed. FIG. 1 schematically shows the catalyst-carrying conductive material of the present invention, and the catalyst-carrying conductive material of the present invention is not limited to this.

  As the proton conductive member contained in the catalyst-carrying electrode of the present invention, at least a liquid, solid, gel-like material having high proton conductivity can be used, and phosphoric acid, sulfuric acid, antimonic acid, stannic acid, heteropoly acid, etc. Organic acids / inorganic hybrid polymers, polymers in which a hydrocarbon polymer compound is doped with an inorganic acid such as solid acid, perfluorosulfonic acid ionomer, phosphoric acid, etc., partially substituted with proton conductive functional groups Examples thereof include a gel proton conductive member in which a matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.

  In addition, as the proton conductive member, a mixed conductor having an electronic conductivity such as a hydrogen ion-electron mixed conductor can also be used.

  The proton conductive member is preferably coated with a catalyst-carrying conductive material as a binder polymer. Thereby, while being able to maintain the structure of a catalyst layer stably, the sufficient reaction site (three-phase interface) where an electrode reaction advances can be ensured, and high catalyst activity can be acquired. The content of the proton conductive member contained in the catalyst layer is not particularly limited, but is preferably 20 to 60% by mass with respect to the total amount of the catalyst-carrying conductive material.

  In addition, at the cathode or the like, a large amount of water is generated by an oxygen reduction reaction. Since this generated water may close the pores for the reaction gas to diffuse, it is also important to ensure the water repellency of the catalyst-carrying electrode. Therefore, the catalyst layer may contain a water repellent such as polytetrafluoroethylene (hereinafter referred to as PTFE) as necessary. However, since the water repellent is an insulator, its amount is preferably as small as possible from the viewpoint of the output of the electrode, and its content is preferably 0.01 to 20% by mass with respect to the total amount of the catalyst-carrying conductive material.

  The gas diffusion layer that supports the catalyst layer in the catalyst-carrying electrode of the present invention is not particularly limited, but is a porous body having electron conductivity such as porous carbon paper or a porous carbon substrate such as carbon cloth. Is mentioned.

  The catalyst layer and the gas diffusion layer are desirably thin to improve the reaction gas diffusibility. However, if the thickness is too thin, sufficient electrode output cannot be obtained. Therefore, it may be determined as appropriate so as to obtain an electrode having desired characteristics.

As a method for producing a catalyst-carrying conductive material used for the catalyst-carrying electrode of the present invention, for example,
In this method, catalyst particles are supported on a conductive carrier, and a plurality of catalyst-supporting conductive materials on which catalyst particles having a desired particle diameter are supported are prepared, and then mixed at a predetermined mixing ratio.

  The method for supporting the catalyst particles on the conductive carrier includes known methods, and is not particularly limited. For example, by dispersing a conductive carrier in a catalyst metal compound solution and adding a reducing agent thereto, the catalyst particles can be highly dispersed and supported on the conductive carrier.

  The catalyst metal compound solution is a solution containing a catalyst metal compound such as chloroplatinic acid, chloroplatinum chloride, or dinitrodiammine platinum when Pt is used as the catalyst particles. In order to use the catalyst particles as a noble metal alloy catalyst or the like, it may be dispersed in the solution as a metal compound such as a desired metal nitrate, chloride or sulfate in addition to platinum.

  As a solvent to which the catalytic metal compound is added, water, methanol, ethanol or the like can be used.

  In order to disperse the conductive carrier in the catalyst metal compound solution, an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device may be used. In order to adjust the particle size of the catalyst particles supported on the conductive carrier, it can be prepared according to the catalyst particle concentration in the catalyst metal compound solution, the blending ratio of the catalyst metal compound and the conductive carrier, or the type of reducing agent. . These may be determined as appropriate so that the supported catalyst particles have a desired particle size. For example, the supported catalyst metal particle diameter can be reduced when a reducing agent having a relatively low reducing power is used, when the reaction temperature is lowered, or when the concentration of the catalyst metal compound is lowered.

  In addition, since it is as above-mentioned about a catalyst particle, an electroconductive support | carrier, the description is abbreviate | omitted here.

  The reducing agent is not particularly limited as long as it can reduce the catalytic metal 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 metal compound can be highly dispersed and supported as metal particles on the conductive support.

  An appropriate amount of the reducing agent is added to the above dispersion of the catalytic metal compound and the conductive carrier, and the catalyst is formed on the surface of the conductive carrier by heating to 60 to 100 ° C., preferably 80 to 95 ° C. using a reflux reactor. It is possible to carry out reduction loading of particles. Thereafter, filtration, washing and drying are performed to obtain a catalyst-carrying conductive material containing catalyst particles having a desired particle size.

  In order to alloy the catalyst particles, it is preferable to further perform firing. The calcination method varies depending on the dispersed state of catalyst particles on the conductive support, the particle diameter, and the like, but preferably in an inert atmosphere such as nitrogen, helium, argon, etc., at a calcination temperature of 300 to 1000 ° C., preferably 300 to What is necessary is just to carry out at 600 degreeC for about 1 to 6 hours.

  Although the reducing agent is used in the above-described method of supporting the catalyst particles on the conductive support, 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 support.

  A desired catalyst-carrying conductive material is obtained by mixing the catalyst-carrying conductive material obtained by the above method at the predetermined mixing ratio described above so that two or more kinds of catalyst particles having different average particle sizes are included.

  Next, as a method for producing the catalyst-carrying electrode of the present invention, in addition to the catalyst-carrying conductive material and the proton conductive member, a water repellent, a pore-forming agent, a thickener, a diluting solvent and the like are mixed as necessary. There is a known method for forming a catalyst layer by forming a paste or slurry, and applying this to a desired thickness on a gas diffusion layer or an electrolyte layer described later by a screen printing method, a deposition method, or a spray method. Can be mentioned.

Further, the catalyst particles such as platinum supported on the surface of the conductive carrier may be subjected to a reduction treatment in order to increase the catalytic activity. The reduction treatment may be performed by a known method such as a gas phase method using a reducing gas such as hydrogen or carbon monoxide, or a liquid phase method (wet) using NaBH ₄ , formaldehyde, glucose, hydrazine, or the like. The reduction treatment is not particularly limited after the catalyst-carrying conductive material is produced and the catalyst-carrying electrode is produced. Even when an oxide passivation film is formed on the surface of the catalyst particles during the progress of the electrode reaction, the activity of the catalyst particles can be maintained by performing the reduction treatment.

  The catalyst-carrying electrode of the present invention may be used as an anode or a cathode, but is preferably used as a cathode because elution of catalyst particles can be suppressed even in a noble potential environment.

  The second of the present invention is a fuel cell using the above-described catalyst-carrying electrode of the present invention. The catalyst-carrying electrode using the conductive carrier of the present invention can maintain high electrode performance over a long period of time. Therefore, if such a catalyst-supporting electrode is used as a fuel cell electrode, it may be possible to provide a fuel cell having excellent durability. 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 generally has a structure in which MEAs (membrane-electrode assemblies) are stacked with separators. The MEA is formed by sandwiching an electrolyte layer between catalyst-carrying electrodes. Therefore, at least one side of the catalyst layer in the catalyst-carrying electrode is in contact with the electrolyte layer.

  Since the catalyst-supporting electrode in PEFC is as described above, the description thereof is omitted here. In addition, when the above-described catalyst-supporting electrode is used as a cathode, the anode may be the same as the cathode, or a conventionally known anode electrode described in JP-A No. 2002-151089 may be used. There is no particular limitation.

  The catalyst-carrying conductive material used for the anode may be any material as long as it has a high catalytic activity for the hydrogen oxidation reaction, and the same material as that used for the cathode may be used. The proton conductive member and gas diffusion layer used for the anode may be the same as those for the cathode, and the description thereof is omitted here.

  The electrolyte layer is a film-like solid polymer film made of a proton conductive member. The proton conductive member used for the electrolyte layer is not particularly limited, and examples thereof include the same proton conductive members listed in the catalyst layer described above. Moreover, the proton conductive member used for the catalyst layer and the electrolyte layer may be the same or different.

  A known separator such as carbon paper or carbon cloth may be used as a separator for sandwiching the MEA. 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 is lengthened to increase the flow rate, or the separator is set up so that the generated water can easily flow from top to bottom. Good.

  As a manufacturing method of MEA, a method of directly producing a catalyst-carrying electrode on an electrolyte layer, a method of producing a catalyst-carrying electrode on a separator and bonding it to an electrolyte layer, a catalyst-carrying 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 a desired voltage or the like can be obtained by the PEFC. The shape of the PEFC 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 catalyst-carrying electrode of the present invention can maintain high cell performance over a long period of time as compared with the conventional one. Therefore, it is possible to provide a highly reliable fuel cell as a power source for a moving body such as a vehicle or a stationary power source. 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. Therefore, an electrode fuel cell using the catalyst-carrying electrode of the present invention is included in the scope of the present invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this.

<Example 1>
-Preparation of Pt-supported carbon 1 First, Pt-supported carbon 1 was produced as follows.

  5 g of conductive carbon black (Cabot Vulcan XC-72: electronic conductivity 10 S / cm) was sufficiently dispersed in 500 g of 1.5 wt% Pt-containing chloroplatinic acid aqueous solution using a homogenizer, and then 5 g of sodium citrate was added. In addition, after sufficiently dissolving, the reaction liquid was stirred at 85 ° C. for 4 hours while stirring the reaction solution using a reflux reaction apparatus, and platinum was supported on the surface of carbon black. After the completion of the reaction, the sample solution was allowed to cool to room temperature, and then the platinum-supported carbon black powder was filtered off with a suction filtration device, washed thoroughly with water, and then dried under reduced pressure at 80 ° C. for 6 hours to obtain a Pt-supported carbon powder. 1 was obtained. The obtained Pt-supported carbon powder 1 was quantitatively analyzed by atomic absorption spectrometry. As a result, the Pt-supported amount was 57.9 wt%. From the observation with a transmission electron microscope, the average particle diameter of Pt was estimated to be 3.3 nm.

-Preparation of Pt-supported carbon 2 Next, Pt-supported carbon 2 was produced as follows.

  7 g of conductive carbon black (Cabot Vulcan XC-72: electronic conductivity 10 S / cm) was sufficiently dispersed in 500 g of 0.6 wt% Pt-containing chloroplatinic acid aqueous solution using a homogenizer, and then 50 ml of formaldehyde was added. After mixing well, the reaction solution was stirred using a reflux reactor and refluxed at 50 ° C. for 6 hours to carry reduction of platinum onto the carbon black surface. After completion of the reaction, Pt-supported carbon powder 2 was obtained by the same method as Pt carbon 1. The obtained Pt-supported carbon powder 2 was quantitatively analyzed by atomic absorption spectrometry. As a result, the Pt-supported amount was 28.4 wt%. From the observation with a transmission electron microscope, the average particle diameter of Pt was estimated to be 1.1 nm.

  The obtained Pt-supported carbon 1 and Pt-supported carbon 2 were mixed well at 75:25 (mass ratio) to prepare a cathode catalyst.

<Comparative Example 1>
In the same manner as in Example 1, only Pt-supported carbon 1 was produced as a cathode catalyst.

<Comparative example 2>
In the same manner as in Example 1, only Pt-supported carbon 2 was produced as a cathode catalyst.

<Performance evaluation of electrode catalyst>
With respect to the cathode catalysts obtained in Example 1 and Comparative Examples 1 and 2, 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.

  After adding 2 times the amount of purified water to the weight of the electrocatalyst of each Example and Comparative Example, 0.5 times the amount of isopropyl alcohol is added, and the Nafion solution is added so that the weight of Nafion is 1 time. (Containing 5 wt% Nafion manufactured by Aldrich) was added. The mixed slurry was well dispersed with an ultrasonic homogenizer, followed by addition of a vacuum degassing operation to prepare a catalyst slurry. A predetermined amount of catalyst slurry is printed on one side of carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.), which is a gas diffusion layer (GDL), by a screen printing method and dried at 60 ° C. for 24 hours. Then, the cathode and the electrolyte membrane were joined by hot pressing at 120 ° C. and 0.1 MPa for 10 minutes with the surface on which the catalyst layer was applied aligned with the electrolyte membrane.

  Next, the anode was prepared in the same manner as the cathode except that only Pt-supported carbon 1 was used as the electrode catalyst, and the catalyst layer was joined to the surface opposite to the cathode joining surface of the electrolyte membrane to form MEA. The thickness of the anode and cathode catalyst layers was in the range of 8 to 12 μm for both cells.

In the obtained MEA, the amount of Pt used for both the anode and the cathode was 0.5 mg per 1 cm ^{2 of the} apparent electrode area, and the electrode area was 300 cm ² . As the electrolyte membrane, Nafion 112 (thickness: about 50 μm) was used.

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

In this measurement, when the fuel cell was operated for power generation, 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%. current density 0.5A / cm ² at driving 30 minutes, to go to followed by repeated continuous operation of operating 30 minutes at a current density of 0.05 a / cm ² thereto, the end of the current density 0.5A / cm ² during operation The durability of the single fuel cell was evaluated by observing the change in the average cell voltage for 5 minutes (25 to 30 minutes).

FIG. 2 is a graph showing changes in the cell voltage with respect to the number of load fluctuation cycles at a current density of 0.5 A / cm ² for each solid polymer electrolyte fuel cell configured using Example 1 and Comparative Examples 1 and 2 electrode catalysts. It is. As shown in FIG. 2, the fuel cell using only the conventional Pt-supported carbon 1 of Comparative Example 1 as the electrode catalyst showed a high cell voltage at the start of operation, but the cell voltage with respect to the number of load fluctuation cycles The rate of voltage decrease was large, and the cell voltage decreased to nearly 0.5 V in 400 cycles.

  Furthermore, in the fuel cell using only the Pt-supported carbon 2 having a small Pt average particle diameter of Comparative Example 2 as an electrode catalyst, the cell voltage at the start of operation is considerably lower than the others, and in addition, the cell voltage relative to the number of load fluctuation cycles is The rate of decrease was also great, and the cell voltage decreased to nearly 0.5 V after 150 cycles. From this result, it is suggested that in the comparative example electrode, the catalyst is deteriorated by the load fluctuation cycle of the fuel cell, and thereby the electrode performance is remarkably lowered.

  On the other hand, the fuel cell using the electrode catalyst of Example 1 is significantly different from the case of the electrode catalyst of each comparative example, and the cell voltage at the start of operation was about 0.75 V, but after about 500 cycles, It was found that the cell voltage of 0.7 V was maintained, and the durability was greatly improved as compared with the conventional electrode.

  Although the detailed mechanism by which the deterioration of the battery performance is suppressed is not clear, from this result, the catalyst metal having a significantly different average particle diameter even under conditions where the electrode catalyst according to Example 1 may deteriorate depending on the operating conditions The coexistence of particles in the same catalyst layer suppresses catalyst deterioration, suggesting that cell performance deterioration is effectively suppressed.

The schematic diagram of the catalyst carrying | support conductive material of this invention is shown. Example 1 and Comparative Examples 1 and 2 A graph showing the relationship between the cell voltage at the current density of 0.5 A / cm ² and the number of load fluctuation cycles of each solid polymer electrolyte fuel cell configured using the electrode catalyst is shown.

Explanation of symbols

1 conductive carrier,
2 catalyst particles,
3 Catalyst particles.

Claims (9)

  A catalyst-carrying electrode comprising two or more types of catalyst-carrying conductive materials in which catalyst particles having different average particle diameters are carried on a conductive carrier, and a proton conductive member.   The catalyst-carrying electrode according to claim 1, wherein the conductive carrier has an electronic conductivity of 0.001 S / cm or more.   The catalyst-carrying electrode according to claim 1, wherein the catalyst particles include at least platinum.   The catalyst particle average particle size of the catalyst-carrying conductive material having the largest average particle size of catalyst particles is 1.5 to 20 times the catalyst particle average particle size of the catalyst-carrying conductive material having the smallest average particle size of catalyst particles. The catalyst-carrying electrode according to any one of claims 1 to 3.   The catalyst-carrying electrode according to any one of claims 1 to 4, wherein the catalyst-carrying conductive material having the largest average particle size of the catalyst particles has an average particle size of 2.0 to 10 nm.   The catalyst-carrying electrode according to any one of claims 1 to 5, wherein the catalyst-carrying conductive material having the smallest average particle size of the catalyst particles has an average particle size of 0.5 to 1.5 nm.   The catalyst-carrying electrode according to any one of claims 1 to 6, wherein a mixing ratio of the catalyst-carrying conductive material having the largest average particle diameter of catalyst particles is 50 to 90% by mass with respect to the total amount of the catalyst-carrying conductive material.   The catalyst-carrying electrode according to any one of claims 1 to 7, wherein a mixing ratio of the catalyst-carrying conductive material having the smallest average particle diameter of catalyst particles is 10 to 50% by mass with respect to the total amount of the catalyst-carrying conductive material.   A fuel cell using the catalyst-carrying electrode according to claim 1.

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