JP2005190712A - Catalyst carrying electrode, mea for fuel cell, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst carrying electrode, an MEA, and a fuel cell, which are superior in catalyst utilization rate and durability. <P>SOLUTION: There is provided the catalyst carrying electrode in which an electrocatalyst is a mixture of at least two or more electrocatalysts having different catalyst utilization rates in the catalyst carrying electrode which contains the electrocatalyst that carries catalyst metal particulates composed of platinum or platinum alloys on a conductive carrier and an electrolyte polymer. By a sacrificial corrosion effect of the electrocatalyst having lower catalyst utilization rate, corrosion of the electrocatalyst having higher catalyst utilization rate is prevented, and the catalyst utilization rate and the durability of the catalyst as a whole are improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst-carrying electrode, an MEA for a fuel cell, and a fuel cell, each of which includes an electrode catalyst in which an electrolyte polymer is filled in the pores of a conductive support constituting the electrode catalyst and an electrode catalyst that is not filled.

  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. . A polymer electrolyte fuel cell uses an electrolyte layer made of a film-like solid polymer membrane, and generally has a built-in structure in which a membrane-electrode assembly (hereinafter also referred to as “MEA”) is laminated with a separator. doing.

  In the MEA, the electrolyte layer is sandwiched between the cathode and the anode, and therefore, the electrode catalyst layer has a structure in which at least one surface is in contact with the electrolyte layer.

  In 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 is supported on a carrier having a large specific surface area such as carbon black in a highly dispersed manner. Since such an electrode catalyst has a large electrode reaction area on the surface of the catalytic metal, the catalytic activity can be increased.

  However, the oxygen reduction reaction at the cathode has a large activation energy, and an overvoltage (resistance) is generated at the cathode, resulting in a noble potential environment of 0.8 V or more, or during repeated start-stop, Pt which is a catalyst component. Elution and corrosion of the carbon support occurs. In particular, at the cathode, protons obtained from hydrogen on the anode side are combined with oxygen supplied to the cathode side to generate water, so that it is considered that a reaction for generating carbon dioxide proceeds through the following chemical formula.

  As a result, the carrier disappears, and the catalytic metal supported on the surface of the carrier is liberated and aggregated. As a result, the catalytic activity is lowered and the battery performance is lowered.

  On the other hand, when fuel shortage occurs in the anode, water electrolysis or carrier oxidation occurs in place of the fuel oxidation reaction in order to maintain a desired current density. Therefore, as in the case of the cathode, the support also corrodes and disappears in the anode, and the catalyst metal is liberated and agglomerated.

  In order to prevent the corrosion of carbon black and improve the life characteristics, the carbon black to be used is preheated at a high temperature to increase the crystallinity and increase the graphitization degree of high corrosion resistance, and the heat treatment temperature is high. As the corrosion resistance is improved, the crystallinity of the heat-treated carbon black is defined (Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). In addition, when the heat treatment is performed, the catalyst-supporting carbon is mixed with a substance that promotes graphitization to perform graphitization of the carbon at a low heat treatment temperature, and an activation treatment with water vapor or the like is performed before or after graphitization, There is also a catalyst having a long life and carrying a catalyst noble metal in a highly dispersed state (Patent Document 5).

On the other hand, it is difficult to control a large amount of carbon black particles at a constant temperature, and as a result of the heat treatment temperature becoming unstable, catalytic activity and corrosion resistance may not be obtained. Therefore, a method of forming an electrode catalyst for a fuel cell by mixing two or more types of carbon heat-treated at different heat treatment temperatures with different electrode catalysts obtained by carrying them on platinum has been proposed (Patent Document 6).
JP 2000-268828 A JP 2001-357857 A JP 2002-15745 A JP 2003-36859 A JP 2000-273351 A Japanese Patent Laid-Open No. 2002-73224

  As described in the above-mentioned documents 1, 2, 3 and 4, in the method of heat treating carbon black in order to prevent the corrosion of carbon black and improve the life characteristics, the corrosion resistance of carbon black improves as the heat treatment temperature increases. In the direction. However, at the same time, the BET specific surface area of carbon black tends to decrease, and the platinum fine particles supported on the carbon black have a larger particle size and lower dispersibility as the heat treatment temperature of the carbon black is higher, resulting in lower catalytic activity. As a result, the power generation cell voltage of the fuel cell is lowered.

  Further, when carbon is graphitized by the method described in Document 5, it is necessary to perform activation treatment with water vapor or the like before or after graphitization, and the operation is complicated.

  Moreover, the method of the above-mentioned document 6 has a problem that the number of steps increases because carbon is processed at different temperatures.

  Accordingly, an object of the present invention is to provide a catalyst-carrying electrode having a high initial cell voltage and excellent durability, and thus exhibiting high catalytic activity over a long period of time.

  As a result of detailed examination of the fuel cell electrode in order to achieve the above object, the following specific relationship was found between the cause of carbon corrosion and the so-called three-phase interface. In the MEA cathode and anode, the electrochemical reaction of hydrogen and oxygen proceeds at the three-phase interface of the gas, the electrolyte polymer, and the electrode catalyst, and the contact rate between the electrolyte polymer and the electrode catalyst becomes an important factor. The electrode catalyst is obtained by supporting platinum fine particles on a conductive carrier such as carbon black. The carrier often takes the form of aggregates of primary particles, and there are many fine pores in the gaps between the primary particle surface and the aggregates of the primary particles. Metal catalyst particles such as platinum are supported in the gaps between the surface pores and the aggregates of the primary particles, but the electrolyte polymer cannot enter these pores. For this reason, there are catalytic metal particles that do not contribute to the formation of the three-phase interface inside the pores. In such an electrode catalyst, carbon corrosion occurs at the interface between carbon and platinum supported on the surface thereof, and in particular, any of the reaction gas, proton, or electron that forms the three-phase interface does not come. It has also been found that it is likely to occur with an electrode catalyst in which a three-phase interface is not formed. A catalyst containing catalytic metal fine particles that do not contribute to the formation of the three-phase interface has a low catalyst utilization rate. Therefore, by using an electrode catalyst with a high catalyst utilization rate and an electrode catalyst with a low catalyst utilization rate, the sacrificial corrosion effect of the electrode catalyst with a low catalyst utilization rate is avoided, and the corrosion of the electrode catalyst with a high catalyst utilization rate is avoided. As a whole, the present inventors have found that the catalyst utilization rate can be improved and the durability can be improved.

  According to the present invention, by using a mixture of catalysts having different catalyst utilization rates, the catalyst utilization rate and the durability of the catalyst can be improved, and power can be supplied stably over a long period of time. Further, the apparatus can be designed compactly with the improvement of the catalyst utilization rate.

  The first of the present invention is a catalyst-carrying electrode comprising an electrocatalyst carrying a catalyst metal fine particle comprising platinum or a platinum alloy on an electroconductive carrier, and an electrolyte polymer, wherein the electrode catalyst has at least two different catalyst utilization rates. A catalyst-supporting electrode, which is a mixture of the above electrode catalysts. Examples of such catalysts having different catalyst utilization rates include a mixture of an electrode catalyst A having a catalyst utilization rate of 70% or more and an electrode catalyst B having a catalyst utilization rate of 30% or less.

  Conventionally, an electrocatalyst has impregnated a platinum aqueous solution with a conductive carrier such as carbon black and added a reducing agent or the like to the platinum to carry platinum fine particles. As shown in FIG. 1, since the aqueous solution can enter the carbon black pores, platinum fine particles are supported on the surface of the primary particles and the pores in the gaps between the aggregates of the primary particles. In the MEA using as the electrode catalyst, the electrolyte polymer coats the surface of the electrode catalyst, but cannot enter into the pores such as the gap between the surface of the primary particles and the aggregates of the primary particles. Fine platinum particles in the pores cannot form a three-phase interface. In the present invention, it was found that when power is generated over a long period using a conventional catalyst as an electrode catalyst, corrosion of platinum-supported carbon proceeds from around the platinum fine particles in the pores where a three-phase interface is not formed. This indicates that a three-phase interface is not formed and the catalyst utilization rate is low, and the sacrificial corrosion effect can be exerted easily. For this reason, when the catalysts having different utilization rates are used in combination, an electrode catalyst having excellent durability is obtained. The catalyst utilization in the present invention is a value calculated by the following method. ECA was measured by the method described in the examples described later, and the geometric area of the catalyst was measured by TEM.

Electrocatalyst A
The electrode catalyst A used in the present invention is an electrode catalyst in which catalytic metal fine particles made of platinum or a platinum alloy are supported on a conductive support, and is an electrode catalyst having a catalyst utilization rate of 70% or more. Such an electrode catalyst can be obtained, for example, by pulverizing the obtained catalyst metal-supported conductive support after supporting the catalyst metal fine particles on the conductive support.

The conductive carrier for supporting the catalyst fine particles is particularly limited as long as it has a specific surface area sufficient to support the catalyst in a highly dispersed manner and sufficient electronic conductivity as a current collector. Although it should not be, it is preferable that the main component is carbon. This is because a sufficiently high electronic conductivity can be obtained and the electric resistance can be lowered. When the electrical resistance of the conductive carrier is high, the internal resistance of the catalyst-carrying electrode is increased, resulting in a decrease in battery performance. Specifically, carbon black such as acetylene black, furnace black, carbon black, activated carbon, meso-face carbon, graphite, channel black, furnace black, thermal black; activated carbon obtained by carbonizing and activating various carbon atom-containing materials; Examples thereof include carbon-based materials such as graphitized carbon, carbon fibers, porous carbon fine particles, carbon nanotubes, and carbon porous bodies. BET specific surface area is preferably 100~2,000m ² / g, more preferably 200~1,600m ² / g. Within this range, the catalyst fine particles can be supported in a highly dispersed manner. Particularly, in the present invention, carbon black such as acetylene black, furnace black, carbon black, activated carbon, mesophase carbon, and graphite is preferable, and the catalyst-supporting metal oxide fine particles can be supported in a highly dispersed state. A catalyst is obtained.

  The catalyst fine particles supported on the conductive carrier are preferably platinum. This is because platinum exhibits high oxygen reduction activity and hydrogen reduction activity. The catalyst fine particles may be used alone, but may be an alloy containing platinum as a main component in order to increase the stability and activity of the catalyst fine particles. Examples of such an alloy include an alloy of a noble metal and a base metal, and the base metal is not particularly limited, and includes at least one base metal selected from the group consisting of chromium, manganese, iron, cobalt, and nickel. In addition, the platinum content rate in an alloy is 45-90 mass%.

  It does not restrict | limit especially as a platinum compound used in order to carry | support platinum or a platinum alloy, These compounds can be used widely. Such compounds include platinum nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halogen salts, nitrites, inorganic salts such as oxalic acid, carboxylates and hydroxides such as formate, Examples include alkoxides and oxides, which can be appropriately selected depending on the type and pH of the solvent in which these are dissolved. Among these, nitrates, carbonates, oxides, and hydroxides are preferable for industrial use, and platinum chloride, dinitrodiamine platinum, and the like are particularly preferable. These platinum concentrations are preferably 0.1 to 5.0% by mass, more preferably 0.1 to 1.0% by mass in terms of metal.

  Platinum ion reducing agents include hydrogen, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, acetic acid and other organic acids or salts thereof, sodium borohydride, formic acid, acetaldehyde. Aldehydes such as formaldehyde, alcohols such as methanol, ethanol and propanol, ethylene, carbon monoxide and the like. In general, the addition amount of the reducing agent is preferably 0.001 to 10 mol, more preferably 0.01 to 1.0 mol, per 1 g of platinum.

  For example, a platinum compound such as chloroplatinic acid is dissolved in water or a mixed solvent of water and alcohol, and a conductive carrier such as carbon is dispersed therein. When a platinum alloy is used as an electrode catalyst, a metal compound to be alloyed with platinum may be further dissolved or dispersed in this solution. When this liquid is heated and stirred, a platinum salt or a reaction product thereof can be deposited on the carbon support. If necessary, the pH in the solution may be adjusted to the alkali side, and platinum and a metal added as necessary may be deposited on the carbon support as, for example, a hydroxide. After supporting the catalyst metal fine particles on the conductive support, after being isolated from the solution, dried, subjected to reduction treatment with hydrogen gas or the like, and then in an inert gas atmosphere such as helium, argon, nitrogen, etc. When calcined at 800 ° C., a catalyst-supporting conductive carrier is obtained.

  Moreover, it is preferable that the average particle diameter of platinum or the catalyst metal fine particle which consists of platinum is 1-10 nm, More preferably, it is 1-6 nm. It is speculated that platinum particles and the like have a higher specific surface area as the average particle size is smaller, so the catalytic activity is also improved. However, even if the catalyst particle size is extremely small, the catalytic activity commensurate with the increase in specific surface area is actually I can't get it. In the present invention, the relationship between the platinum fine particle diameter and the electrode characteristics is found, and if it is less than 1 nm, the surface energy of the platinum fine particle is increased and the stability is lowered, and the catalyst life is shortened. However, since the surface area of the fine particles is small, battery performance may be reduced.

  Moreover, content of the electrode catalyst A used by this invention is 70-90 mass% with respect to all the catalysts (the sum of the electrode catalyst A and the electrode catalyst B), More preferably, it is 70-85 mass%. If it is less than 70% by mass, sufficient activity may not be obtained. Moreover, even if it exceeds 90 mass%, since the quantity of a self-sacrificial catalyst will decrease, durability may fall.

  Next, the catalyst-carrying conductive carrier is pulverized. As a result, the surface area per unit weight is increased, and part of the pores of the conductive support becomes the surface of the conductive support, so that the catalyst metal fine particles can form a three-phase interface, and the catalyst utilization rate is improved. .

  Examples of the pulverization method include a method of pulverizing with a homogenizer for 1 to 5 hours in a solvent, a mechanical pulverization by a pulverizer, a vibration mill, a planetary ball mill, a ball mill, and a jet mill. Solvents that can be used for pulverization by stirring in a solvent include aqueous solvents such as water, organic solvents such as alcohols, ethers, and glycols, as well as electrolyte polymers used in preparing catalyst-supporting electrodes and mixtures thereof. There may be. For example, the electrolyte polymer that can be used at the time of pulverization is a member having at least high proton conductivity, such as various Nafion manufactured by DuPont (registered trademark: Nafion) and perfluorosulfonic acid membranes represented by Flemion, Dow There are ion exchange resins manufactured by Chemical Co., Ltd. and other ionic copolymers (ionomers). Thereby, while being able to maintain the structure of an electrode 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. Among these, as the pulverizing solution, it is preferable to use an electrolyte polymer solution obtained by diluting the electrolyte polymer with water and / or an organic solvent so that the electrolyte polymer concentration becomes 1 to 20% by mass. In this case, the blending amount of the electrode catalyst A is preferably 50 to 90% by mass, and more preferably 65 to 80% by mass. The viscosity of the solvent used for pulverization is preferably 1 to 10,000 cps, and more preferably 100 to 6,500 cps. When pulverized together with the electrolyte polymer, the catalyst catalyst electrode of the present invention can be easily produced by adding and mixing the electrode catalyst B thereto, and the subsequent operation can be simplified.

  In this invention, the standard of a grinding | pulverization is making the average particle diameter of an electrode catalyst into 0.1-1.0 micrometer, More preferably, it is 0.25-0.6 micrometer. When the thickness exceeds 1.0 μm, pulverization is not sufficient, and the ratio of the catalyst metal supported on the pores of the conductive carrier to form a three-phase interface increases. On the other hand, if the thickness is less than 100 μm, the catalyst metal may be peeled off from the conductive support or may be fine, so that the coating of the electrolyte on the catalyst particle surface becomes insufficient, and the ratio at which a three-phase interface cannot be formed may increase.

Electrocatalyst B
The electrode catalyst B is an electrode catalyst in which catalytic metal fine particles made of platinum or a platinum alloy are supported on a conductive carrier, and is an electrode catalyst having a catalyst utilization rate of 30% or less. For example, what supported the catalyst metal fine particle on the electroconductive support | carrier described by the said electrode catalyst A can be used as the electrode catalyst B as it is.

  The electrode catalyst B is 10 to 30% by mass, more preferably 15 to 30% by mass, based on the total electrode catalyst (the sum of the electrode catalyst A and the electrode catalyst B). If the amount is less than 10% by mass, a sufficient self-sacrificing effect cannot be obtained, so that the durability may decrease. If the amount exceeds 30% by mass, the amount of the self-sacrificial catalyst increases, and the durability may decrease.

  Moreover, in the electrode catalyst B, the average particle diameter of the catalyst metal fine particles made of platinum or platinum is preferably 1 to 6 nm, and more preferably 1 to 3 nm. If the thickness is less than 1 nm, the surface energy of the platinum fine particles is increased, the stability is lowered, the catalyst life is shortened, and if it exceeds 6 nm, the activity is lowered, which is disadvantageous.

  The “average particle diameter of the fine particles” in the present invention is based on the average value of the fine particle diameters of the catalyst metal obtained from the crystallite diameter obtained from the half-value width of the diffraction peak of the catalytic metal in X-ray diffraction or a transmission electron microscope image. Can be measured.

  In the present invention, the catalyst-supporting conductive carrier may be pulverized. The catalyst utilization rate can be improved by grinding. As a pulverization method, a method similar to that for the electrode catalyst A can be employed, but the average particle size after pulverization is preferably 0.7 to 2.0 μm. When the thickness is less than 0.7 μm, the sacrificial corrosion effect is reduced. On the other hand, when the thickness is more than 2.0 μm, the surface property of the electrode layer of about 10 μm is usually deteriorated and unevenness is increased, and the film is damaged when MEA is formed. Since it becomes easy, the amount of cross leak of gas is easy and disadvantageous. That is, the catalyst utilization rate of the electrode catalyst A is improved because the catalyst metal fine particles supported inside the pores can form a three-phase interface by pulverization after the metal fine particles are supported, but corrosion with time is prevented. It is not possible. However, since the catalyst metal fine particles are supported inside the pores but a three-phase interface cannot be formed, the use of the electrode catalyst B having a low catalyst utilization rate causes electrons to flow through any of the conductive carriers during power generation. The corrosion of the electrode catalyst B proceeds prior to the electrode catalyst A because the corrosion proceeds more in the catalyst in which the polymer cannot contact and the three-phase interface is not formed. Therefore, when the electrode catalyst B is used together with the electrode catalyst A, the corrosion of the electrode catalyst A can be suppressed by sacrificial corrosion of the electrode catalyst B.

  The catalyst utilization rate is considered to depend on the condition of mixing with the electrolyte generated when the catalyst is pulverized and covering the catalyst surface with the electrolyte. When the pulverization time is short, the particle size also increases, but the electrolyte coating is insufficient, that is, the catalyst surface is not covered with the electrolyte cleanly. A part of the surface is exposed from the coating of the electrolyte, and the platinum utilization rate decreases. In the present invention, durability can be improved by mixing the catalyst surface exposed from a part of such a surface with the one whose surface is cleanly covered with an electrolyte.

  The catalyst-carrying electrode of the present invention comprises the above-mentioned electrode catalyst, electrolyte polymer, and the like by an existing method except that a mixture of the above-mentioned electrode catalysts A and B is used as an electrode catalyst having catalytic metal particles supported on a conductive carrier. It can mix | blend and it can be set as a catalyst carrying electrode. For example, when the electrode catalyst A is pulverized to a mean particle size of 0.25 to 0.6 μm together with the polymer electrolyte polymer, the electrode catalyst B is added thereto, followed by stirring for 10 to 30 minutes to make both catalysts uniform. And then molded according to a conventional method to form a catalyst-carrying electrode. This is shown in FIG. First, the catalyst-supporting conductive carrier for the electrode catalyst A and the above electrolyte polymer solution are mixed and stirred, and the average particle diameter of the electrode catalyst A is pulverized to 0.25 to 0.6 μm. Next, a catalyst-carrying conductive carrier for the electrode catalyst B is added thereto, an electrolyte polymer or a solvent is added as necessary, and both are uniformly mixed to prepare a so-called catalyst ink. What is necessary is just to shape | mold and make a catalyst carrying electrode.

  Further, when both the electrode catalyst A and the electrode catalyst B are pulverized with the electrolyte polymer, both pulverized liquids are mixed and formed according to a conventional method to form a catalyst-supporting electrode. This is shown in FIG. The catalyst-supporting conductive carriers for electrode catalyst A and electrode catalyst B are separately charged and mixed in the electrolyte polymer solution, and pulverized to an average particle size of 0.25 to 0.6 μm and an average particle size of 0.7 to 2.0 μm, respectively. To do. Then, the two solutions are mixed to prepare a so-called catalyst ink, which is molded according to a conventional method to form a catalyst-supporting electrode.

  In addition, the content of the conductive carrier of the electrode catalyst B is preferably 10 to 40% by mass, more preferably 25 to 35% by mass of the conductive carrier of the entire electrode catalyst. If the amount is less than 10% by mass, the sacrificial corrosion effect is reduced, while if it exceeds 40% by mass, the catalyst utilization rate of the entire electrode catalyst may be reduced. The content of the electrolyte polymer contained in the electrode catalyst layer is not particularly limited, but is preferably 10 to 50% by mass with respect to the total amount of the electrode catalyst.

  A second aspect of the present invention is an MEA for a fuel cell comprising an electrolyte membrane, a cathode and an anode, wherein the catalyst-supporting electrode described above is a cathode. In particular, it is suitable for MEA for a polymer electrolyte fuel cell.

  The electrolyte membrane varies depending on the type of fuel cell, but as an electrolyte membrane of a polymer electrolyte fuel cell, perfluorosulfonic acid membranes represented by various Nafion (registered trademark: Nafion) manufactured by DuPont and Flemion Fluorine polymer electrolytes such as ion exchange resins manufactured by Dow Chemical Company, ethylene-tetrafluoroethylene copolymer resin membranes, resin membranes based on trifluorostyrene, and hydrocarbon resins having sulfonic acid groups The present invention is not limited to solid polymer electrolyte membranes such as system membranes, but can also be applied to membranes in which a polymer microporous membrane is impregnated with a liquid electrolyte, and membranes in which a porous body is filled with a polymer electrolyte. In addition, a conventionally well-known thing can be used as an anode.

  In addition, MEA of this invention can manufacture MEA by the conventional conditions except using the catalyst carrying | support electrode which used the mixture of the said electrode catalyst A and B as an electrode catalyst. FIG. 4 shows an aspect in which a catalyst-carrying electrode provided with GDL is laminated on an electrolyte membrane. In the catalyst-carrying electrode of the present invention, the electrode catalyst A and the electrode catalyst B are mixed and used, so that the electrode catalyst A having a high catalyst utilization rate and the electrode catalyst B having an excellent sacrificial corrosion effect coexist. And the effect of improving the durability is exhibited.

  Further, a fuel cell can be formed using the catalyst-carrying electrode or MEA. Since the MEA of the present invention has a high mass activity, if it is used as an electrode for a fuel cell, it is possible to provide a fuel cell with little deterioration in cell characteristics over a long period of time. 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. In addition, as long as the fuel cell of this invention uses the catalyst carrying | support electrode or MEA of this invention, the other requirements may apply what can be used with a fuel cell.

  The fuel cell using the catalyst-carrying electrode or MEA of the present invention is small and can supply an excellent power generation amount as compared with the conventional one. Therefore, it is possible to provide an efficient fuel cell in a small space 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.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.

(Example 1)
(1) Preparation of catalyst-supported conductive support for electrode catalyst A Carbon black (Ketjen Black EC600JD: BET ratio manufactured by Ketjen Black International Co., Ltd.) was added to 1000 g of a chloroplatinic acid aqueous solution containing 0.5% by mass of platinum in terms of metal. 5 g of a surface area of 1,270 m ² / g) was added, and the mixture was sufficiently dispersed using a homogenizer. To this was added 15 g of sodium citrate, and the mixture was heated to 80 ° C. using a reflux reactor, and platinum was supported for reduction. After allowing to cool to room temperature, the carbon on which platinum was supported was filtered off to obtain platinum-supported carbon having a platinum loading of 50% by mass. This is a catalyst-supporting conductive carrier for the electrode catalyst A.

(2) Preparation of catalyst-supported conductive support for electrode catalyst B Carbon black (Ketjen Black EC600JD: BET ratio manufactured by Ketjen Black International Co., Ltd.) was added to 400 g of chloroplatinic acid aqueous solution containing 0.5% by mass of platinum in terms of metal. ² g of a surface area of 1,270 m ² / g) was added, and the mixture was sufficiently dispersed using a homogenizer. To this was added 6 g of sodium citrate, and the mixture was heated to 80 ° C. using a reflux reactor to carry out reduction loading of platinum. After allowing to cool to room temperature, the carbon on which platinum was supported was filtered off to obtain platinum-supported carbon having a platinum loading of 50% by mass. This is a catalyst-supporting conductive carrier for the electrode catalyst B.

(3) Preparation of catalyst ink A catalyst-supported conductive carrier for electrode catalyst A (platinum supported amount: 50% by mass) was weighed in a 3 g beaker, and a polymer electrolyte perfluorosulfonic acid ionomer solution (trade name, manufactured by DuPont). “Nafion”, 5 mass%, IPA: water = 1: 1) was added and mixed for 4 hours using a homogenizer to prepare a catalyst ink. The mass ratio of the polymer electrolyte to the carbon support constituting the catalyst-supporting conductive support for the electrode catalyst A was 1: 1. The average particle diameter of the catalyst-supporting conductive carrier for the electrode catalyst A was 0.4 to 0.6 μm.

  Next, 1 g of a catalyst-carrying conductive carrier (platinum carrying amount: 50% by mass) for the electrode catalyst B is added to this catalyst ink, and the mass ratio of the polymer electrolyte to the carbon carrier constituting the catalyst-carrying conductive carrier is 1. : Add polyelectrolyte perfluorosulfonic acid ionomer solution (made by DuPont, trade name “Nafion”, 5% by mass, IPA: water = 1: 1) so as to be 1, and mix for 30 minutes using a homogenizer. A catalyst ink was prepared.

(4) Fabrication of MEA The catalyst ink was printed on a Teflon (registered trademark) sheet by a screen printing method so that both the anode and the cathode had a platinum content of 0.4 mg / cm ² , dried at 60 ° C. for 24 hours, and then predetermined. Punched to the size of Next, the anode catalyst layer and the cathode catalyst layer are respectively disposed on one side and the other side of a polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont), and the electrode catalyst layer is transferred to the electrolyte membrane by hot pressing. A MEA was created by sandwiching between the two.

(5) Initial characteristics and post-endurance characteristics The MEA is supplied with air heated and humidified to a dew point of 65 ° C at the cathode at a cell temperature of 80 ° C and hydrogen heated and humidified to a dew point of 50 ° C at the anode. The initial characteristics and post-durability characteristics were evaluated at an oxygen utilization rate of 40% and a hydrogen utilization rate of 70%. The post-endurance characteristics were evaluated based on the retention ratio of the power generation cell voltage with respect to the initial value at a current density of 0.5 A / cm ² after 100 hours had passed while the evaluation cell was held at an open circuit voltage.

(6) Corrosion test 0.50 mg / cm ^{2 of} the catalyst ink prepared above was applied to a gold mesh electrode and dried to prepare an electrode. This electrode was used as a working electrode in a 0.5 M sulfuric acid aqueous solution at 60 ° C., and an electrochemical cell was constructed in which a Pt coil was used as a counter electrode and a reversible hydrogen electrode (RHE) was incorporated as a reference electrode. This embodiment is shown in FIG. Cyclic voltammetry is measured while bubbling nitrogen, and is the electrochemically active surface area (ECA: m ² / g, surface area per unit mass) used for the evaluation of the activity of electrode catalysts such as fuel cells. The specific surface area of the catalyst is large and the activity is high). The initial ECA and ECA after applying a voltage of 1 V to the working electrode and flowing the oxidation current for 1 hour were measured, and the value (%) after 1 hour with respect to the initial value was determined to evaluate the corrosivity. The results are shown in Table 1.

(7) Electrocatalyst catalyst utilization ratio Geometrical surface area value obtained from the initial ECA (A) value obtained when performing the corrosion test, and the platinum particle diameter and platinum loading obtained from TEM observation in advance. From the following formula, the platinum utilization rate of the electrode catalyst A was calculated according to the following formula.

(Example 2)
(1) Preparation of catalyst-carrying conductive support for electrode catalyst B In the method for producing electrode catalyst B of Example 1, carbon black (Ketjen Black) added to 400 g of an aqueous chloroplatinic acid solution containing 0.5% by mass of platinum Ketjen Black EC600JD (International Co., Ltd .: BET specific surface area 1,270 m ² / g) The same operation as in Example 1 was carried out except that 2 g was changed to 4.6 g and platinum was supported at 30% by mass. Electrocatalyst B was manufactured.

(2) Preparation of electrode ink and MEA Using the catalyst-carrying conductive carrier for electrode catalyst A prepared in Example 1 and the catalyst-carrying conductive carrier for electrode catalyst B, the ratio of electrode catalyst A is expressed. The catalyst-supporting conductive carriers for the electrode catalyst A and the electrode catalyst B were weighed so as to have the mass shown in Fig. 1, and a catalyst ink was prepared by the same method as in Example 1.

(3) Platinum utilization rate, initial characteristics, post-endurance characteristics and corrosion test Platinum utilization ratios were calculated in the same manner as in Example 1, and initial characteristics, post-endurance characteristics and corrosion tests for power generation cell performance were performed. The results are shown in Table 1.

(Comparative Example 1)
(1) Preparation of electrode ink and MEA The catalyst-carrying conductive carrier for electrode catalyst A and the catalyst-carrying conductive carrier for electrode catalyst B prepared in Example 1 were used. The catalyst-supporting conductive carriers for the electrode catalyst A and the electrode catalyst B were weighed so as to have the mass% shown in FIG. 1, and a catalyst ink was prepared by the same method as in Example 1.

(2) Platinum utilization rate, initial characteristics, post-endurance characteristics and corrosion test Except for using the above catalyst ink, the platinum utilization ratio was calculated in the same manner as in Example 1, and the initial characteristics of power generation cell performance, post-endurance characteristics and A corrosion test was performed. The results are shown in Table 1.

(Comparative Example 2)
(1) Preparation of electrode ink and MEA The catalyst-carrying conductive carrier for electrode catalyst A and the catalyst-carrying conductive carrier for electrode catalyst B prepared in Example 2 were used. The catalyst-supporting conductive carriers for the electrode catalyst A and the electrode catalyst B were weighed so as to have the mass% shown in FIG. 2, and a catalyst ink was prepared by the same method as in Example 2.

(2) Platinum utilization rate, initial characteristics, post-endurance characteristics and corrosion test Except for using the above catalyst ink, the platinum utilization ratio was calculated in the same manner as in Example 2, and the initial characteristics of power generation cell performance, post-endurance characteristics and A corrosion test was performed. The results are shown in Table 1.

Example 3
(1) Preparation of electrode ink and MEA Using the catalyst-carrying conductive carrier for electrode catalyst A prepared in Example 1 and the catalyst-carrying conductive carrier for electrode catalyst B prepared in Example 2, the following method A catalyst ink was prepared.

  A catalyst-supporting conductive support (platinum supported amount: 50% by mass) for electrode catalyst A was weighed in a 2.8 g beaker, and a polymer electrolyte perfluorosulfonic acid ionomer solution (trade name “Nafion”, 5 manufactured by DuPont) Mass%, IPA: water = 1: 1) was added and mixed for 4 hours using a homogenizer to prepare a catalyst ink. The mass ratio of the polymer electrolyte to the carbon support constituting the catalyst-supporting conductive support for the electrode catalyst A was 1: 1.

  A catalyst-supporting conductive support (platinum supported amount: 30% by mass) for the electrode catalyst B was weighed in a 1.2 g beaker, and a polymer electrolyte perfluorosulfonic acid ionomer solution (trade name “Nafion”, manufactured by DuPont, 5 Mass%, IPA: water = 1: 1) was added and mixed for 30 minutes using a homogenizer to prepare a catalyst ink. The mass ratio of the polymer electrolyte and the carbon support constituting the catalyst-supporting conductive support for the electrode catalyst B was 1: 1. Next, the catalyst ink of the electrode catalyst A and the catalyst ink of the electrode catalyst B were mixed and mixed for 10 minutes using a homogenizer to prepare a catalyst ink.

(2) Platinum utilization rate, initial characteristics, post-endurance characteristics and corrosion test Using the catalyst ink, platinum utilization ratio, initial characteristics, post-endurance characteristics and corrosion test were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
The same catalyst-carrying conductive carrier for electrode catalyst A and catalyst-carrying conductive carrier for electrode catalyst B as in Example 3 were used, so that the mass% of electrode catalyst A and electrode catalyst B was in the ratio shown in Table 1. The catalyst ink was prepared by the same method as in Example 3. The platinum utilization was calculated in the same manner as in Example 3, and the initial characteristics, post-endurance characteristics and corrosion test of the power generation cell performance were performed. The results are shown in Table 1.

(Conventional example)
The catalyst-supporting conductive carrier for electrode catalyst A prepared in Example 1 was weighed in a 3 g beaker, and a polymer electrolyte perfluorosulfonic acid ionomer solution (trade name “Nafion”, 5% by mass, IPA: manufactured by DuPont). Water = 1: 1) was added and mixed for 4 hours using a homogenizer to prepare a catalyst ink. The mass ratio of the polymer electrolyte and the carbon support constituting the catalyst-supporting conductive support for the electrode catalyst A was 1: 1. The average particle diameter of the catalyst-supporting conductive carrier for the electrode catalyst A was 0.4 to 0.6 μm. Using this as the catalyst ink, the platinum utilization was calculated in the same manner as in Example 1, and the initial characteristics, post-endurance characteristics, and corrosion test of the power generation cell performance were performed. The results are shown in Table 1 as a conventional example.

  The catalyst-carrying electrode of the present invention is excellent in catalyst utilization and durability, and is useful as a long-life electrode catalyst for fuel cells.

It is a conceptual diagram of the present invention of a conventional electrode catalyst in a catalyst-carrying electrode, and shows a state in which platinum fine particles are carried inside the pores of a conductive carrier but cannot come into contact with an electrolyte polymer. It is process drawing which shows an example of the preparation method of the catalyst carrying | support electrode of this invention. It is process drawing which shows an example of the preparation method of the catalyst carrying | support electrode of this invention. It is a figure which shows typically MEA using the electrode catalyst of this invention. It is a figure which shows the structure of the electrochemical cell used by the corrosion test of the Example.

Claims (8)

In a catalyst-carrying electrode comprising an electrocatalyst carrying a catalyst metal fine particle comprising platinum or a platinum alloy on a conductive support, and an electrolyte polymer,
A catalyst-carrying electrode, wherein the electrode catalyst is a mixture of at least two electrode catalysts having different catalyst utilization rates.   The said electrode catalyst contains the electrode catalyst A and the electrode catalyst B, The catalyst utilization factor of the said electrode catalyst A is 70% or more, The catalyst utilization factor of the said electrode catalyst B is 30% or less. Catalyst-supporting electrode.   The catalyst-carrying electrode according to claim 1 or 2, wherein the content of the electrode catalyst A in the electrode catalyst is 70 to 90 mass% with respect to the total catalyst (the sum of the electrode catalyst A and the electrode catalyst B).   The catalyst-carrying electrode according to any one of claims 1 to 3, wherein the content of the conductive carrier of the electrode catalyst B is 10 to 40% by mass of the conductive carrier of the whole electrode catalyst.   A fuel cell MEA comprising an electrolyte membrane, a cathode, and an anode, wherein the catalyst-supporting electrode according to any one of claims 1 to 4 is a cathode.   A fuel cell using the catalyst-carrying electrode according to claim 1 or the MEA for fuel cell according to claim 5.   3. The method for producing a catalyst-carrying electrode according to claim 2, comprising a step of pulverizing the electrode catalyst A together with a polymer electrolyte polymer, and then stirring after adding the electrode catalyst B. Production method.   3. The method for producing a catalyst-carrying electrode according to claim 2, comprising the step of mixing the electrode catalyst A pulverized with an electrolyte polymer and the electrode catalyst B pulverized with an electrolyte polymer. Method.