WO2006112368A1

WO2006112368A1 - Electrode catalyst for fuel cell and process for producing the same

Info

Publication number: WO2006112368A1
Application number: PCT/JP2006/307862
Authority: WO
Inventors: Junji Okamura; Kuninori Miyazaki; Koichi Yamamoto
Original assignee: Nippon Shokubai Co., Ltd.
Priority date: 2005-04-15
Filing date: 2006-04-13
Publication date: 2006-10-26
Also published as: TW200642149A; JPWO2006112368A1

Abstract

This invention provides an electrode catalyst having excellent catalytic performance that, even when a large amount of noble metal particles are supported on a carrier, can surely provide a fuel cell having high power generation performance. The electrode catalyst for a fuel cell comprises a noble metal as a catalyst component supported on an electrically conductive carrier and is characterized in that the amount of the noble metal supported based on the total of the electrically conductive carrier and the noble metal is 70 to 90% by mass, the apparent surface area (S1) of the noble metal supported is 25 to 60 m2/g, and the ratio between the apparent surface area (S1) of the noble metal supported and the apparent surface area (S2) of the electrically conductive carrier, i.e., S1/S2, is 0.02/1 to 0.1/1.

Description

Specification

Fuel cell electrode catalyst and method for producing the same

Technical field

[0001] The present invention relates to an electrode catalyst for a fuel cell and a method for producing the same.

Background art

A fuel cell is basically a power generator that generates electric power by electrochemically reacting hydrogen and oxygen. Therefore, although carbon dioxide is produced in the process of producing hydrogen, which is a fuel, most of the others are generated only by electricity, water and heat, and harmful nitrogen oxides and Sulfur oxides are not emitted. In addition, the power generation efficiency is extremely high because the loss of thermal energy and kinetic energy is small as in other power generation systems. Therefore, the fuel cell is expected as an extremely clean and efficient power generation system.

[0003] Fuel cells can be classified according to electrolyte types into phosphoric acid fuel cells, molten carbonate fuel cells, solid polymer fuel cells, solid oxide fuel cells, and the like. Among them, the polymer electrolyte fuel cell can generate power in a lower temperature range than other fuel cells and can be easily downsized. There is a possibility that it can be applied to various applications such as a portable power source.

[0004] A polymer electrolyte fuel cell has an anode and a cathode on both sides of a polymer electrolyte membrane such as perfluorosulfonic acid ion exchange resin that has ion conductivity but does not have electron conductivity. The formed membrane electrode assembly is used as a basic unit. Each electrode includes a catalyst layer containing a polymer electrolyte exhibiting hydrogen ion conductivity and a catalyst on the polymer electrolyte membrane side, and a gas diffusion layer having both air permeability and conductivity on the outside thereof. This gas diffusion layer is made of, for example, carbon paper or carbon cross treated with water repellent treatment with polytetrafluoroethylene (PTFE) or the like. In addition, as an electrode catalyst in each electrode, a catalyst in which a noble metal such as platinum is supported on a conductive carrier such as carbon black has become the mainstream.

[0005] In order to improve the performance of the fuel cell, the content of the noble metal in the electrode catalyst layer may be increased. However, when using an electrode catalyst with a small amount of precious metal, the catalyst layer In order to increase the precious metal content, it is necessary to increase the coating amount of the electrode catalyst, resulting in a thick catalyst layer. When the catalyst layer becomes thicker, the diffusibility of fuel and oxygen in the layer is lowered, which causes a problem that the catalyst performance is lowered. In addition, if an attempt is made to increase the amount of noble metal supported on the conductive support, aggregation of noble metal particles tends to occur, the performance corresponding to the increase in the amount of noble metal supported cannot be improved, and sufficient catalytic activity cannot be obtained. Problems arise.

[0006] Conventionally, various electrode catalysts and methods for producing the same have been developed with the aim of improving the performance of fuel cells. For example, Japanese Patent Application Laid-Open No. 9-167620 discloses a catalyst in which white metal is supported on a conductive support on which Si or the like is deposited. Japanese Patent Application Laid-Open No. 10-334925 describes a catalyst in which platinum and ruthenium are supported and the size of their crystal particles is defined. Japanese Patent Application Laid-Open No. 2000-12043 describes a catalyst in which platinum and ruthenium are supported and their crystal structure is defined. Japanese Patent Laid-Open No. 2004-335252 discloses an electrode catalyst in which the average particle size and the amount of platinum to be supported are defined.

Disclosure of the invention

[0007] As described above, various electrode catalysts for improving the performance of fuel cells have been developed. Some of these take into consideration the loading amount and surface area of the noble metal. However, even if the amount of noble metal supported is specified, further improvement is required, for example, the performance of the obtained electrocatalyst may vary.

[0008] Therefore, an object of the present invention is to provide an electrode catalyst having excellent catalytic performance that can reliably obtain a fuel cell exhibiting power generation performance commensurate with such increase when the content of noble metal in the catalyst layer is increased. is there. Another object of the present invention is to provide a method for producing the electrode catalyst, an electrode composition for a fuel cell using the electrode catalyst, and a fuel cell.

[0009] The present inventors have conducted intensive research on the cause of the case where sufficient power generation performance may not be obtained even if the amount and surface area of the noble metal to be supported are defined. As a result, even if a large amount of noble metal having a small particle size and a large surface area is supported on the support, the surface area of the support on which the noble metal particles are supported and the surface area of the noble metal do not satisfy specific conditions. It was found that the catalyst performance was not fully exhibited. Therefore, the present inventors By examining the relationship between the surface area of the precious metal and the surface area of the carrier, not only by the surface area of the genus, we have clarified experimentally the conditions under which the performance of the catalyst components can be fully demonstrated, and the electrode catalyst that satisfies these conditions has excellent power generation performance As a result, the present invention has been completed.

[0010] The fuel cell electrode catalyst of the present invention is a fuel cell electrode catalyst comprising a conductive carrier carrying a noble metal as a catalyst component,

The amount of noble metal supported is 70 to 90% by mass, the apparent surface area (S1) of the supported noble metal is 25 to 60m ² Zg, and the apparent surface area (S1) of the supported noble metal and the conductive carrier The ratio (S1ZS2) to the apparent surface area (S2) is 0.02Zl to 0.1LZl.

[0011] A fuel cell electrode catalyst composition of the present invention comprises the above fuel cell electrode catalyst and a polymer electrolyte, and the fuel cell of the present invention comprises the fuel cell electrode catalyst composition. It has the electrode formed by.

[0012] Conventionally, as a method for producing an electrode catalyst, a noble metal salt compound is added to a support slurry and then added to a reducing agent to reduce a water-soluble noble metal compound such as a noble metal salt into a noble metal. There are known techniques for loading a carrier onto a carrier. As a reducing agent, formic acid is generally used, but there is an example in which sodium borohydride is used. However, in these conventional production methods, when the amount of noble metal supported is increased, the noble metal is not properly supported on the support, and sufficient catalyst performance may not be exhibited.

[0013] Accordingly, another object of the present invention is to apply a method capable of reliably producing a fuel cell electrode catalyst having high power generation performance.

[0014] In order to solve the above-mentioned problems, the present inventors diligently studied the production conditions of a fuel cell electrode catalyst. As a result, when the water-soluble noble metal compound is reduced and supported on the carrier, the aggregation is achieved by using sodium borohydride as a reducing agent and appropriately adjusting the pH of the reaction mixture when it is added. It was found that the noble metal can be properly supported on the support while suppressing the above.

That is, a method for producing a fuel cell electrode catalyst according to the present invention comprises:

Suspend the conductive carrier particles in water and add a water-soluble noble metal compound to the resulting suspension. A step of applying; and

A step of reducing the water-soluble noble metal compound by adding sodium borohydride to the suspension as a water-soluble reducing agent and supporting the noble metal particles on the conductive carrier particles;

It is characterized by adding sodium borohydride while adjusting so that the pH of the suspension does not exceed 7.

[0016] A fuel cell electrode catalyst that satisfies the requirements of the present invention (hereinafter sometimes simply referred to as "electrode catalyst") can reliably exhibit excellent catalytic performance. This is thought to be because the precious metal component loading is as high as 70% by mass or more and fine noble metal particles do not condense, that is, they are supported on a conductive carrier with high dispersibility. . Therefore, the use of the electrode catalyst of the present invention makes it possible to form a catalyst layer having a high activity with a large amount of noble metal supported and excellent in the diffusibility of the reactant (fuel). High power can be obtained.

[0017] Further, according to the method of the present invention, it is possible to support the noble metal particles on the carrier while effectively preventing aggregation of the noble metal particles. Therefore, a highly active electrode catalyst with a large amount of noble metal can be produced.

[0018] Therefore, the present invention is extremely useful industrially as a fuel cell can be further commercialized.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The fuel cell electrode catalyst of the present invention comprises:

A fuel cell electrode catalyst in which a noble metal is supported on a conductive support as a catalyst component, the amount of noble metal supported is 70 to 90% by mass relative to the total of the conductive support and the noble metal, and the apparent surface area (S1) of the supported noble metal is 25~60m ² Zg, further characterized in that the ratio of the apparent surface area of the supported noble metal and (S1) of the conductive support and an apparent surface area (S2) (S1ZS2) is 0. 02Zl~0. lZl.

[0020] As the "conductive support" of the present invention, any support having sufficient conductivity to function as a support for an electrode catalyst can be used. Specifically, for example, conductivity Examples thereof include conductive carbon materials such as carbon black, activated carbon, graphite, and carbon fiber. Among these, conductive carbon black and activated carbon are preferably used. Further, the specific surface area of the conductive support is preferably 1000 to 4000 m ² / g so that the performance of the noble metal component is sufficiently exhibited even when the noble metal loading is increased to 70 to 90% by mass.

The “noble metal” of the present invention may be any noble metal generally used for an electrode catalyst. Examples thereof include platinum, ruthenium, iridium, rhodium, palladium, gold and silver. These can be used alone or in combination of two or more. Of these, platinum or a combination of platinum and ruthenium is preferably used.

[0022] The electrode catalyst of the present invention may contain a metal element other than a noble metal as a catalyst component. Specifically, for example, manganese, rhenium, tantalum, cerium, lanthanum, indium, conoleto, nickel, tungsten, niobium, gallium, silicon, titanium, etc. are included in the form of metals or oxides. But, okay. These can be used alone or in combination of two or more. Of these, manganese, indium, niobium, lanthanum, cerium, silicon and titanium are preferably used. By adding these, higher catalyst performance can be obtained.

In the present invention, the amount of the noble metal supported relative to the total of the conductive support and the noble metal is 70 to 90% by mass, preferably 70 to 85% by mass. If the amount of noble metal supported is 70% by mass or more, high battery performance can be expected. In addition, if it is 90% by mass or less, the ratio of the noble metal to the conductive support does not become too high, and the apparent surface area of the conductive support in the electrode catalyst is kept moderate. The condition related to a certain ratio (S1ZS2) is easily satisfied, and the battery performance can be improved.

[0024] The amount of the metal component other than the noble metal that may be optionally used is not particularly limited and can be appropriately determined. Usually, it is 0.5 to 4% by mass, preferably 1 to 3% by mass, based on the total mass of the electrocatalyst (support + noble metal + metal component).

The “apparent surface area (S1) of the supported noble metal” in the electrode catalyst of the present invention is the surface area of the supported noble metal per unit mass of the electrode catalyst. The surface area is filled with supported noble metals. It does not include the surface area of noble metals that are not exposed on the surface and cannot function as a catalyst, such as those that are present inside the aggregate when they are gathered. Further, since the surface area is a surface area per electrode catalyst, it can be expressed as m ² Zg-catalyst. Here, it is simply expressed as m ² Zg including the scope of claims. The “surface area (S1) of the supported noble metal” of the present invention is measured by the following method for measuring the amount of carbon monoxide (CO) pulse adsorption. Since carbon monoxide is selectively adsorbed on the supported noble metal and not adsorbed on the conductive support or other metal oxides, the apparent surface area of the supported noble metal in the electrode catalyst is determined according to the CO pulse adsorption measurement method. Can be measured.

[0026] CO pulse adsorption measurement method

Device: Nippon Bell Co., Ltd., catalyst analyzer BEL—CAT

Pretreatment conditions: Treated in a helium stream at 150 ° C for 15 minutes → Reduced in a mixture of hydrogen (5%) and helium at 150 ° C for 15 minutes → Treated in a rim stream at 150 ° C for 15 minutes → Decrease to 50 ° C

Adsorption measurement temperature: 50 ° C

Sample amount: About 10-20mg

In the present invention, the apparent surface area (S1) of the supported noble metal in the electrode catalyst is 25 to 60 m ² Z g, preferably 25 to 45 m ² / g. If the apparent surface area of the supported noble metal is 25 m ² / g or more, sufficient catalytic performance can be obtained. If one method is used to make the noble metal fine particles in a state exceeding 60 m ² Zg, the interaction with the support surface becomes strong and the catalyst performance is adversely affected.

The “apparent surface area (S2) of the conductive support” of the present invention refers to the unit mass of the electrode catalyst in the surface region on the support that can be assumed not to be covered with noble metal particles in the electrode catalyst. The surface area (m ² Zg) of the conductive support. The apparent surface area (S2) is also, but it is capable of representation as well as m ² Zg- catalyst and an apparent surface area of the supported noble metal (S1), simply referred to as m ² Zg. The apparent surface area (S2) of the conductive carrier is defined by the following formula.

[0028] S2 = S3 X (100-M) ÷ 100

S3: BET specific surface area of the carrier itself (m ² Zg)

M: Amount of precious metal supported on the total of the conductive support and precious metal (% by mass) Therefore, the ratio (S1ZS2), which is one of the prescription requirements of the present invention, is calculated by the following equation.

[0029] S1 / S2 = S1 / [S3 X (100-M) ÷ 100]

In the present invention, the apparent surface area (S 1) of the supported noble metal and the apparent surface area (S2) of the support are expressed as it (Sl / S2) i 0.02 / 1-1 to 0.1 / 1, preferably ί or 0.004 1 to 0.1. When this ratio (S1ZS2) is 0.02Z1 or more, the electrode catalyst of the present invention can be prepared without using a support having a high specific surface area with a small volume specific gravity and having significantly developed pores. As a result, since the catalyst layer in the electrode does not become too thick, the diffusibility of fuel, oxygen, etc. in the catalyst layer can be maintained, and the catalyst performance can be enhanced. On the other hand, if it is 0.1Z1 or less, the distance between the noble metal particles on the electrode catalyst can be kept moderate, and the stability of the noble metal fine particles can be maintained to prevent aggregation and improve the catalyst performance. Become.

[0030] The ratio (S1ZS2) of the present invention is an index indicating the dispersibility of the supported noble metal on the support. In the electrocatalyst of the present invention in which this ratio is in the range of 0.02 to 0.1 Zl, it can be said that the noble metal is supported on the support with high dispersibility. In other words, since the amount of noble metal supported is high and the noble metal particles are highly dispersed on the support without causing aggregation, the catalytic performance of the electrode catalyst of the present invention is high and the diffusibility of the reactant is excellent. A catalyst layer can be formed.

[0031] The electrocatalyst of the present invention is suitably used as an electrode catalyst for a polymer electrolyte fuel cell among the powers that can be used as an electrode catalyst for any fuel cell.

[0032] When the electrode catalyst of the present invention is used in a polymer electrolyte fuel cell, in addition to the fuel cell electrode catalyst according to the present invention, a polymer electrolyte is blended to produce a polymer electrolyte fuel cell. The electrode catalyst composition is as follows.

[0033] The polymer electrolyte has a role of delivering protons generated from the fuel by the catalytic reaction to the polymer electrolyte membrane. For example, fluorine resin having sulfonic acid groups such as naphthion (manufactured by DuPont), Flemion (manufactured by Asahi Kasei Co., Ltd.), and Ashbeck (manufactured by Asahi Glass Co., Ltd.), and inorganic substances such as tandastenoic acid and phosphotungstic acid. Can be used.

[0034] The ratio of the polymer electrolyte in the electrode composition of the present invention may be appropriately determined so as to obtain the necessary proton conductivity when used as an electrode. For example, electrocatalyst 10 What is necessary is just to mix | blend a polymer electrolyte suitably in the ratio of 10-200 mass parts with respect to 0 mass parts.

[0035] An electrode layer can be produced from the above-described electrocatalyst composition according to the present invention to provide an electrode for a polymer electrolyte fuel cell. The electrodes (anode and force sword) of the polymer electrolyte fuel cell consist of a catalyst layer on the polymer electrolyte side and a gas diffusion layer on the outside thereof. As this gas diffusion layer, carbon paper or carbon cloth having a thickness of about 100 to 300 m is used as having excellent gas permeability and conductivity. Therefore, when an electrode is formed from the electrode composition of the present invention, a conductive carbon material, a water repellent material, a binder, or the like is added to the electrode catalyst or polymer electrolyte of the present invention as necessary, and water or An electrode can be formed by preparing a paste by uniformly mixing with an organic solvent such as isopropyl alcohol, applying the paste to a gas diffusion layer such as carbon paper, and drying.

[0036] The obtained anode and force sword can be formed into a membrane electrode assembly by hot pressing with a polymer electrolyte membrane interposed therebetween. At this time, in each electrode, it is necessary to dispose the catalyst layer in contact with the polymer electrolyte membrane. Moreover, the pressure and temperature in the hot press may be in accordance with ordinary conditions.

[0037] The obtained membrane / electrode assembly can be made into a polymer electrolyte fuel cell according to a conventional method together with a separator and the like. The solid polymer fuel cell of the present invention thus obtained has extremely high power generation performance because it has a high performance electrode catalyst. Therefore, the polymer electrolyte fuel cell of the present invention is suitable for portable devices, automobile power supplies, household power generation systems, and the like.

[0038] The fuel cell electrode catalyst of the present invention can be produced, for example, by a method including the following steps.

(a) A conductive carrier suspension is obtained by suspending a conductive carrier in water.

(b) A water-soluble noble metal compound is added and dissolved in the suspension.

(c) Sodium borohydride is added as a water-soluble reducing agent to the suspension, and the noble metal compound is reduced in the suspension to precipitate noble metal particles. The deposited noble metal particles are substantially entirely supported on the conductive support.

[0039] The water-soluble noble metal compound used in the above step (b) is not particularly limited, but examples of the water-soluble compound of platinum and ruthenium include dinitrodiammine white. Examples thereof include gold, platinum chloride, ruthenium nitrate, and ruthenium chloride. Regarding the amount of sodium borohydride added, an amount capable of reducing the noble metal compound dissolved in the aqueous solution to a metal and supporting it on the carrier may be used. Usually, 0.1-: LO mass%, preferably 1-5 mass% is added as an aqueous solution.

[0040] It is preferable that the noble metal compound aqueous solution or sodium borohydride is added to the suspension, and the subsequent reduction of the noble metal compound is performed with sufficient stirring of the suspension. These series of operations are preferably performed at a temperature of 0 to 100 ° C, preferably 30 to 70 ° C.

[0041] In the present invention, when reducing the noble metal compound using sodium borohydride, the pH of the suspension is adjusted so as not to exceed 7. That is, sodium borohydride is added while maintaining the pH of the suspension at 7 or lower. When sodium borohydride is added, the pH of the suspension shifts to alkaline with the progress of the reduction reaction, but if the reduction treatment is performed under conditions where the pH exceeds 7, the reason is not clear, but precipitation occurs. Aggregation of the precious metal particles is likely to occur, and it becomes difficult to support the precious metal particles on the conductive support in a highly dispersed state. Therefore, when using sodium borohydride as a water-soluble reducing agent, it is preferable to add an acid as appropriate so that the pH of the suspension does not exceed 7, preferably 4. . As said acid, inorganic acids, such as nitric acid, hydrochloric acid, phosphoric acid, boric acid, can be used, for example. When using other water-soluble reducing agents, make sure that the pH of the suspension does not exceed 7, preferably 4! /.

[0042] According to the method of the present invention, the noble metal compound is directly reduced with the water-soluble reducing agent in the suspension to form noble metal particles in the suspension, and the pH of the suspension does not exceed 7. Therefore, even when the loading amount of the noble metal is 70% by mass or more, the aggregation of the noble metal particles can be prevented, and an electrode catalyst in which the noble metal particles are supported on the conductive support can be obtained. When platinum and ruthenium are used as the noble metals, platinum and ruthenium are alloyed in the suspension. Therefore, according to the method of the present invention, platinum and ruthenium are electrically conductive as an alloy of both. It becomes possible to make it carry | support to a property support | carrier. This alloying is performed at a temperature of 100 ° C or lower, so that aggregation of noble metal particles can be prevented.

[0043] After completion of the reaction, the powder is filtered off and dried to obtain the electrode catalyst of the present invention.

The drying temperature is preferably 120 ° C or less. Example

[0044] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples as well as the present invention. It is also possible to carry out with addition, and they are all included in the technical scope of the present invention.

[0045] Catalyst Preparation Example 1

Carbon black as a carrier (Cabot, BP2000, BET specific surface area: 1500 m ² / g) 2. Og was suspended in lOOmL of pure water to obtain a suspension. In a state where the suspension was stirred, a mixed aqueous solution of di-trodiaminemine platinum and ruthenium nitrate was added so as to be 3.07 g and 1.59 g in terms of platinum and ruthenium, respectively. Next, after adjusting the liquid volume to 300 mL with pure water, 470 mL of a 5% by mass aqueous sodium borohydride solution was dropped while stirring the mixed solution, and platinum and luteyu dissolved in the suspension were dropped. The precursor was reduced. At this time, a 10 mass% nitric acid aqueous solution was added to adjust the suspension so that the pH power of the suspension was not exceeded. The total amount of precipitated platinum and ruthenium fine particles was supported on carbon black. The powder thus obtained was filtered off, washed thoroughly with pure water, and then dried at 110 ° C. in a nitrogen atmosphere to prepare catalyst a.

[0046] When the catalyst a was analyzed, its composition was platinum: ruthenium: carbon black = 46.1: 13.9.30 in terms of mass. Further, the apparent surface area of the supported noble metal in the catalyst a calculated by the CO pulse adsorption amount measuring method was 34 m ² Zg. The apparent surface area (S2) of the conductive support in the electrode catalyst was calculated from the BET specific surface area (1500 mg) of the support itself and the amount of noble metal supported (70% by mass). Table 1 summarizes the precious metal loading, surface area and ratio (S1ZS2) of the precious metal supported. It was confirmed by X-ray diffraction analysis that platinum and ruthenium were alloyed.

[0047] Catalyst Preparation Example 2

Example of catalyst preparation, except that a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was added so that it would be 5.27 g and 2.73 g in terms of platinum and ruthenium, respectively, and the 5% by mass aqueous sodium borohydride solution was 800 mL. Catalyst b was prepared in the same manner as in 1. When the obtained catalyst b was analyzed, the composition was platinum: Um: carbon black = 52. 7: 27. 3:20. The apparent noble metal surface area of the supported noble metal on catalyst b, calculated by the CO pulse adsorption amount measurement method, was 29 m ² / g. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0048] Catalyst Preparation Example 3

Example of catalyst preparation, except that a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was added so that it would be 1.98 g and 1.02 g in terms of platinum and ruthenium, respectively, and the 5 mass% sodium borohydride aqueous solution was changed to 200 mL. Catalyst c was prepared in the same manner as in 1. When the obtained catalyst c was analyzed, the composition was platinum: luteum: carbon black = 40: 20: 40 in terms of mass. The apparent noble metal surface area of the supported noble metal on catalyst c, calculated by the CO pulse adsorption measurement method, was 42 m ² Zg. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0049] Catalyst Preparation Example 4

Example of catalyst preparation except that a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate was added to give platinum and ruthenium equivalents of 1.32 g and 0.68 g, respectively, and the 5 mass% sodium borohydride aqueous solution was changed to 200 mL. Catalyst d was prepared in the same manner as in 1. When the obtained catalyst d was analyzed, its composition was platinum: ruthenium: carbon black = 32.9: 17.1: 50 in terms of mass. The apparent noble metal surface area of the supported noble metal on catalyst d, calculated by the CO pulse adsorption amount measurement method, was 43 m ² Zg. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0050] Catalyst preparation example 5

A catalyst except that a mixed solution of dinitrodiammineplatinum and ruthenium nitrate was added so that it would be 0.57 g and 0.29 g in terms of platinum and ruthenium, respectively, and the 5 mass% sodium hydrogen hydride aqueous solution was changed to 86 mL. Catalyst e was prepared in the same manner as in Preparation Example 1. When the obtained catalyst e was analyzed, the composition was platinum: ruthenium: carbon black = 20: 10: 70 in terms of mass. The apparent noble metal surface area of the supported noble metal in catalyst e, calculated by the CO pulse adsorption amount measurement method, was 30 m ² / g. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0051] Catalyst Preparation Example 6 2. Catalyst f was prepared in the same manner as in Catalyst Preparation Example 1, except that 470 mL of 5% by mass aqueous sodium borohydride solution was used. When the obtained catalyst f was analyzed, the composition was platinum: ruthenium: carbon black = 46.1; 23.9: 30 in terms of mass. The apparent noble metal surface area of the supported noble metal on catalyst f, calculated by the CO pulse adsorption measurement method, was 42 m ² / g. Table 1 summarizes the precious metal loading, surface area and ratio (S1 / S2) of the precious metal supported.

[0052] Catalyst Preparation Example 7

1. Catalyst g was prepared in the same manner as in Catalyst Preparation Example 1 except that 470 mL of a 25% by mass aqueous sodium borohydride solution was used. When the obtained catalyst g was analyzed, the composition thereof was platinum: ruthenium: carbon black = 46.1: 13.9.30 in terms of mass. The apparent noble metal surface area of the supported noble metal in catalyst g, calculated by the CO pulse adsorption amount measurement method, was 55 m ² Zg. Table 1 summarizes the precious metal loading, surface area and ratio (S1ZS2) of the precious metal supported.

[0053] Catalyst Preparation Example 8

Carbon black as a carrier (Cabot Corporation, BP2000, BET specific surface area: 1500 m ² / g) 2. Og was suspended in lOOmL of pure water to obtain a suspension. In a state where the suspension was stirred, a mixed aqueous solution of di-throdianmine platinum and ruthenium nitrate was added so as to be 3.07 g and 1.59 g in terms of platinum and ruthenium, respectively. Subsequently, carbon black black platinum and a ruthenium compound were supported by evaporating to dryness while maintaining at 80 to 90 ° C. in a nitrogen stream using a rotary evaporator. The obtained powder was dried at 110 ° C. and subjected to reduction treatment at 300 ° C. for 2 hours using a hydrogen-containing gas to prepare catalyst h. The obtained catalyst h was analyzed, and its composition was, in terms of mass, platinum: ruthenium: force one bon black = 46.1: 23.9: 30. The apparent noble metal surface area of the supported noble metal at catalyst h, calculated by the CO pulse adsorption measurement method, was 19 m ² Zg. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0054] Catalyst Preparation Example 9

Except for adding a mixed aqueous solution of dinitrodiammineplatinum and ruthenium nitrate to 5.27 g and 2.73 g in terms of platinum and ruthenium, respectively, Similarly, catalyst i was prepared. The obtained catalyst i was analyzed, and its composition was, in terms of mass, platinum: ruthenium: carbon black = 52.7: 27.3: 20. The apparent noble metal surface area of the supported noble metal on catalyst i calculated by the CO pulse adsorption amount measurement method was 13 m ² Zg. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0055] Catalyst Preparation Example 10

Carbon black as a carrier (Cabot Corporation, BP2000, BET specific surface area 1500 m ² / g) l. 87 g was suspended in lOOmL of pure water to obtain a suspension. While stirring this suspension, a mixed water solution of dinitrodiammineplatinum, ruthenium nitrate and indium nitrate was added so that it would be 3.07 g, 1.59 g and 0.13 g in terms of platinum, ruthenium and indium, respectively. . Next, after adjusting the liquid volume to 300 mL with pure water, 470 mL of a 5% by mass aqueous sodium borohydride solution was added dropwise while stirring the mixed liquid, and the total amount of the catalyst components dissolved in the aqueous solution was carbonized. Supported on black. At this time, a 10% by mass aqueous nitric acid solution was added to adjust the pH of the suspension so as not to exceed 7. The powder thus obtained was filtered, washed thoroughly with pure water, and then dried at 110 ° C. in a nitrogen atmosphere to prepare catalyst j. The obtained catalyst j was analyzed, and its composition was, in terms of mass, platinum: ruthenium: indium: carbon black = 46.1: 23.9: 2: 28. The apparent noble metal surface area of the supported noble metal on catalyst j, calculated by the CO pulse adsorption measurement method, was 26 m ² Zg. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S 1 / S2) of the supported noble metal.

[0056] Catalyst Preparation Example 11

The catalyst was prepared in the same manner as in Catalyst Preparation Example 1, except that the aqueous solution of nitric acid was used to force the suspension so that the pH did not exceed 7 (as a result, the pH of the suspension exceeded 7). k was prepared. When the obtained catalyst k was analyzed, the composition was platinum: ruthenium: carbon black = 46.1: 13.9.30 in terms of mass. The apparent surface area of the supported noble metal at catalyst k, calculated by the CO pulse adsorption measurement method, was 30 m ² / g. Table 1 summarizes the amount of noble metal supported, the surface area and ratio (S1ZS2) of the supported noble metal.

[0057] Test example A single cell electrode of a solid polymer fuel cell was prepared using the catalysts a to k (c to e and g to i for comparison) obtained in Catalyst Preparation Examples 1 to 10, and the cell characteristics were measured. The single cell electrode was prepared as follows.

[0058] (1) Creation of single cell electrode

Catalyst sample prepared in catalyst preparation example 0.25 g 5% perfluorosulfonic acid resin solution (Aldrich) 1. Add to 6 g and mix, add pure water to this mixed solution and add the whole To 7.2 mL. Next, the mixture was uniformly dispersed by an ultrasonic disperser to prepare a catalyst-containing paste. This was uniformly coated on carbon paper (made by Torayen earth) so that the supported amount of platinum and ruthenium was 1.5 mg / cm ^2, and then dried for 15 hours to obtain an anode.

[0059] Separately, E—TEK's platinum-supported carbon black (platinum supported amount: 60% by weight, carbon black, Cabot, VulcanXC72) 0.2 g of 5% perfluorosulfonic acid resin solution ( (Aldrich) 1. Add to 6 g and mix, and add pure water to this mixture to make 7.2 mL. Subsequently, it was uniformly dispersed by an ultrasonic disperser to prepare a catalyst-containing paste. This was uniformly applied on carbon paper (made by Torayen earth) so that the amount of platinum supported was 1. OmgZcm ^2, and then dried for 15 hours to form a force sword.

[0060] A Nafion 112 membrane (manufactured by Dupont) is sandwiched between the force sword obtained above and the anode so that the effective electrode area is 5 cm ² so that the surface coated with the catalyst is in contact with the naphthion membrane. A single cell electrode was made by hot pressing for 5 minutes at 130 ° C, lOOkg / cm ² .

[0061] (2) Measurement of battery characteristics

To measure the battery characteristics, the single cell electrode prepared as described above was incorporated in the experimental fuel cell, maintained at a cell temperature of 30 ° C, 5% methanol aqueous solution at the anode, 6 mL, and oxygen gas as the power sword. Was supplied at 0.3LZmin and the current-voltage characteristics were measured. The voltage generated between both electrodes at 40 mAZcm ² was measured. The results are shown in Table 1. In addition, it has shown that it is excellent as a battery characteristic, so that a voltage is high. The underline indicates that it is outside the scope of the present invention.

[0062] [Table 1] Precious metal loading amount

Catalyst S1 / S2 voltage (V)

(Mass%) Apparent surface area (m ² / g)

a 70 34 0.076 / 1 0.380 b 80 29 0.097 / 1 0.380 c (for comparison) 60 42 0.070 / 1 0.376 d (for comparison) 50 43 0.057 / 1 0.372 e (for comparison) 30 30 0.029 / 1 0.365 f 70 42 0.093 / 1 0.380 g (for comparison) 70 55 0.122 / 1 0.375 h (for comparison) 70 19 0.042 / 1 0.370 i (for comparison) 80 13 0.043 / 1 0.368 j 70 26 0.058 / 1 0.382 k 70 30 0.067 / 1 0.378 The above results also show the following.

(1) If the supported amount of noble metal is less than 70% by mass, the apparent surface area of the supported noble metal in each catalyst is 25 to 60m ² Zg and the ratio (S1ZS2) is in the range of 0.02 / 1 to 0.1 lZl. The resulting voltage is reduced (see Catalysts c, d, e). This is because when a catalyst with a small amount of noble metal is applied on a single paper, the amount of coating increases, and as a result, the catalyst layer becomes thicker, and the diffusibility of reactants (such as methanol and water) decreases. Considered for

(2) Even if the supported amount of noble metal is 70-90% by mass and the apparent surface area of the supported noble metal in each catalyst is in the range of 25-60m ² Zg, it can be obtained if the ratio (S1ZS2) exceeds 0.1 lZl. Voltage drops (see Catalyst g).

(3) Increase the load of precious metals! Therefore, when the noble metal is supported on the support according to the conventional method, the apparent surface area of the supported noble metal in each catalyst becomes less than 25 m ² Zg, and the obtained voltage decreases (see catalysts h and i).

(4) The amount of noble metal supported is 70 to 90% by mass, the apparent surface area of the supported noble metal in each catalyst is 25 to 60m ² Zg, and the ratio (S1ZS2) is in the range of 0.02 / 1 to 0.1 lZl. High voltage can be obtained only with an electrocatalyst that satisfies all conditions (see Catalysts a, b, f, j, k)

. This is because even if the amount of noble metal supported is high, the apparent surface area is supported in a state of 25 to 60 m ² Zg, and these noble metal particles are dispersed and supported on the support with a certain interval or more. It is thought to be for this purpose. (5) As a catalyst component, in addition to noble metals, manganese, indium, niobium, lanthanum, cerium, silicon, and titanium power are further increased by containing at least one selected element! A soot voltage is obtained (see Catalyst j).

Claims

The scope of the claims

[1] A fuel cell electrode catalyst in which a noble metal is supported as a catalyst component on a conductive support, the amount of noble metal supported is 70 to 90% by mass relative to the total of the conductive support and the noble metal, and the apparent surface area of the supported noble metal ( S1) is 25 to 60 m ² Zg, and the ratio (S1ZS2) of the apparent surface area (S1) of the supported noble metal to the apparent surface area (S2) of the conductive support is 0.02 Zl to 0.1 lZl. Fuel cell electrode catalyst.

[2] The fuel cell electrode catalyst according to [1], wherein the noble metals are platinum and ruthenium.

[3] A fuel cell electrode catalyst composition comprising the fuel cell electrode catalyst according to claim 1 or 2 and a polymer electrolyte.

[4] A fuel cell having an electrode formed from the electrode catalyst composition for a fuel cell according to claim 3.

[5] A method for producing an electrode catalyst for a fuel cell, comprising:

Suspending conductive carrier particles in water and adding a water-soluble noble metal compound to the resulting suspension; and

A method for producing an electrode catalyst for a fuel cell, comprising adding sodium borohydride while adjusting so that the pH of the suspension does not exceed 7.