WO2010150058A1

WO2010150058A1 - Electrode catalyst for fuel cell, method for producing the same, and polymer electrolyte fuel cell using the same

Info

Publication number: WO2010150058A1
Application number: PCT/IB2010/001019
Authority: WO
Inventors: Tetsuo Nagami; Sozaburo Ohashi; Mikihiro Kataoka; Tomoaki Terada; Takahiro Nagata; Yosuke Horiuchi; Akihiro Hori
Original assignee: Toyota Jidosha Kabushiki Kaisha; Cataler Corporation,
Priority date: 2009-06-22
Filing date: 2010-05-04
Publication date: 2010-12-29
Also published as: EP2446495A1; US20170012295A1; CN102804467A; JP5270468B2; US10263260B2; CN102804467B; JP2011003492A; WO2010150058A8; US20120107724A1; EP2446495B1

Abstract

An electrode catalyst for a fuel cell consists principally of a carbon support, and a platinum catalyst or a platinum-alloy catalyst supported on the carbon support. In the electrode catalyst, at least 0.7 mmol of an acid per gram of the electrode catalyst is present on the carbon support.

Description

ELECTRODE CATALYST FOR FUEL CELL, METHOD FOR PRODUCING THE

SAME, AND POLYMER ELECTROLYTE FUEL CELL USING THE SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an electrode catalyst for a fuel cell, a method for producing the electrode catalyst, and a polymer electrolyte fuel cell using the electrode catalyst, which are developed so as to improve the performance of a platinum catalyst or platinum-alloy catalyst.

2. Description of the Related Art

[0002] The cell characteristics of polymer electrolyte fuel cells have remarkably improved for some reasons including the following reasons: 1) polymer electrolyte membranes having a high ion conductivity have been developed, and 2) catalyst-carrying carbon that is coated with a polymer electrolyte of the same type as or a different type from the polymer electrolyte membrane is used as a material that forms an electrode catalyst layer, so that three-dimensional reaction sites are provided in the catalyst layer. The polymer electrolyte fuel cells, which exhibit the improved cell performance, can be easily made compact and lightweight; therefore, it has been expected to put the polymer electrolyte fuel cells to practical use in mobile vehicles, such as electric automobiles, or as a power source of a compact cogeneration system, for example.

[0003] Generally, a gas-diffusible electrode used in a polymer electrolyte fuel cell consists of a catalyst layer containing the catalyst-carrying carbon coated with the polymer electrolyte as described above, and a gas diffusion layer that supplies reaction gas to the catalyst layer and collects electrons. In the catalyst layer, porous portions are present in which micropores are formed among secondary particles or tertiary particles of carbon as a constituent material of the catalyst layer, and the porous portions function as diffusion channels for the reaction gas. A catalyst formed of a noble metal, such as platinum or platinum alloy, which is stable in the polymer electrolyte is generally used as the above-mentioned catalyst.

[0004] For example, a catalyst having a noble metal, such as platinum or platinum alloy, supported on carbon black has been used as cathode and anode catalysts (electrode catalysts) of polymer electrolyte fuel cells. Generally, the platinum-carrying carbon black is prepared by adding sodium hydrogen sulfite to an aqueous acidic platinum-chloride solution, which is then caused to react with hydrogen peroxide to form platinum colloid, supporting the platinum colloid on carbon black, cleaning, and then subjecting the platinum-carrying carbon black to heat treatment as needed.

[0005] Platinum, which is an expensive noble metal, has been desired to exhibit sufficient performance even where a small amount of platinum is carried on a carbon support. Therefore, technologies for enhancing the catalyst activity with a reduced amount of platinum used have been studied. For example, an electrode catalyst for fuel cells as disclosed in Japanese Patent Application Publication 2002-289208 (JP-A-2002-289208) is composed of an electrically conductive carbon material, metal particles that are supported on the conductive carbon material and are less likely be oxidized than platinum under acidic conditions, and platinum that covers outer surfaces of the metal particles. The thus formed electrode catalyst has high durability, and the growth of platinum particles during operation of the fuel cell is suppressed or restricted. More specifically, examples of the metal particles include, for example, alloys comprised of platinum and at least one metal selected from gold, chromium, iron, nickel, cobalt, titanium, vanadium, copper, and manganese.

[0006] In order to improve the utilization factor of noble metal and reduce the amount of noble metal used so as to reduce the cost of manufacture of electrode catalysts, an electrode catalyst as disclosed in Japanese Patent Application Publication No. 2005-25947 (JP-A-2005-25947) is prepared by subjecting highly dispersed carbon having a highly complex structure and a low specific surface area to a process selected from an activation process, oxidation process using nitric acid, a process for making the carbon hydrophilic, and a hydroxyl addition process, so as to activate the surface of the carbon, and then depositing metal on the carbon.

[0007] However, the platinum catalyst or platinum-alloy catalyst of the related art is still insufficient in terms of the oxygen reduction capability, and it has been desired to develop higher-performance catalysts.

SUMMARY OF THE INVENTION

[0008] The invention provides an electrode catalyst for a fuel cell, which offers higher performance than the platinum catalyst or platinum-alloy catalyst of the related art, a method for producing the electrode catalyst, and a polymer electrolyte fuel cell using the electrode catalyst.

[0009] A first aspect of the invention is concerned with an electrode catalyst for a fuel cell, which includes: a carbon support, a platinum catalyst or a platinum-alloy catalyst supported on the carbon support, and at least 0.7 mmol of an acid per gram of the electrode catalyst, which is present on the carbon support.

[0010] To form the electrode catalyst as described above, an acid treatment is conducted on the carbon support carrying platinum or platinum alloy, so that 0.7 mmol/g or more of acid per gram of the catalyst remains on the carbon support. As a result, the catalyst becomes hydrophilic, and the water-hold property around the catalyst is improved, resulting in a reduction in the resistance to proton shift in the catalyst layer, and improved power generation performance at low humidity.

[0011] In the electrode catalyst according to the first aspect of the invention, the platinum-alloy catalyst may consist of an alloy of platinum and at least one metal selected from ruthenium, molybdenum, osmium, cobalt, rhodium, iridium, iron, nickel, titanium, tungsten, palladium, rhenium, chromium, manganese, niobium, and tantalum.

[0012] In the electrode catalyst according to the first aspect of the invention, the carbon support on which the acid is present and the platinum catalyst or the platinum-alloy catalyst is supported may be hydrophilic.

[0013] In the electrode catalyst according to first aspect of the invention, the acid may be present on the carbon support in an amount equal to or greater than 1.0 mmol per gram of the electrode catalyst, or may be present on the carbon support in an amount equal to or greater than 1.31 mmol per gram of the electrode catalyst.

[0014] A second aspect of the invention is concerned with a method for producing an electrode catalyst for a fuel cell, which comprises a carbon support and a platinum catalyst or a platinum-alloy catalyst supported on the carbon support. The method includes the steps of: supporting the platinum catalyst or the platinum-alloy catalyst on the carbon support, and treating the carbon support carrying the platinum catalyst or the platinum-alloy catalyst with an acid, so that at least 0.7 mmol of the acid per gram of the electrode catalyst is present on the carbon support treated with the acid.

[0015] In the method according to the second aspect of the invention, after the carbon support carrying the platinum catalyst or the platinum-alloy catalyst is treated with the acid, the carbon support carrying the platinum catalyst or the platinum-alloy catalyst and treated with the acid may be cleaned. [0016] In the method according to the second aspect of the invention, the platinum-alloy catalyst may consist of an alloy of platinum and at least one metal selected from ruthenium, molybdenum, osmium, cobalt, rhodium, iridium, iron, nickel, titanium, tungsten, palladium, rhenium, chromium, manganese, niobium, and tantalum.

[0017] In the method according to the second aspect of the invention, the carbon support on which the acid is present and the platinum catalyst or the platinum-alloy catalyst is supported may be hydrophilic.

[0018] In the method according to the second aspect of the invention, the acid may be present on the carbon support in an amount equal to or greater than 1.0 mmol per gram of the electrode catalyst, or may be present on the carbon support in an amount equal to or greater than 1.31 mmol per gram of the electrode catalyst.

[0019] A third aspect of the invention is concerned with a polymer electrolyte fuel cell including the electrode catalyst according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [0020] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein:

FIG. 1 is a graph showing the relationship between the catalyst acid amount and the low-humidity efficiency point performance (at 0.2 A/cm²) with regard to Examples 1, 2 and Comparative Examples 1 - 3;

FIG. 2 is a graph showing the relationship between the catalyst acid amount and the low-humidity output point performance (at 1.02 A/cm²) with regard to Examples 1, 2 and Comparative Examples 1 - 3; FIG. 3 is a graph showing the relationship between the catalyst acid amount and the low-humidity efficiency point performance (at 0.2 A/cm²) with regard to Examples 3 - 7 and Comparative Examples 4 - 14; and

FIG. 4 is a graph showing the relationship between the catalyst acid amount and the low-humidity output point performance (at 1.02 A/cm²) with regard to Examples 3 - 7 and Comparative Examples 4 - 14.

DETAILED DESCRIPTION OF EMBODIMENTS

[0021] The inventors reached the present invention by subjecting carbon carrying a platinum catalyst or platinum-alloy catalyst to a particular treatment so as to bring it into a particular carbon state.

[0022] In the following, some examples of this invention and comparative examples will be described in detail. A process for producing a single cell used for evaluation, a method of evaluating the performance of a catalyst of each example, and a method of determining the amount of acid in the catalyst will be described below. [0023] The process for producing a single cell used for evaluation will be described. A single cell for use in a polymer electrolyte fuel cell was formed in the following manner, using a catalyst powder obtained in each example or comparative example. The catalyst powder was dispersed in an organic solvent, and the resulting dispersion liquid was applied by coating to a Teflon sheet to form catalyst layers (i.e., electrodes). The amount of Pt catalyst per lcm² of electrode area was 0.4mg. The electrodes formed from the catalyst powder were attached to each other via a polymer electrolyte membrane by hot press, to provide a membrane-electrode assembly, and diffusion layers were mounted on the opposite sides of the membrane-electrode assembly, to form a single-cell electrode.

[0024] The method of evaluating the catalyst performance will be described. To evaluate the catalyst performance, the initial voltage measurement was conducted in the following manner. The temperature of the single cell was set to 80⁰C, and moisturized air that passed a bubbler heated to 6O⁰C was supplied to the cathode-side electrode at a rate of 2.0 L/min., while moisturized hydrogen that passed a bubbler heated to 6O⁰C was supplied to the anode-side electrode at a rate of 0.5 L/min. In this condition, current voltage characteristics were measured. Comparisons of the performance among the catalysts of the respective examples were made through measurements of voltage values at current densities of 0.2 A/cm and 1.0 A/cm". [0025] The method of determining the acid amount in the catalyst will be described. After 0.5 g of catalyst was added to 20 ml of 0.1N sodium hydroxide, which was then ultrasonically stirred for 20 min., the resulting liquid was subjected to filtration. Then, 0.05 ml of Methyl Orange as an indicator was added to 5 ml of filtrate while it was being stirred, and titration was conducted with 0.05N hydrochloric acid. [0026] Example 1 will be described. Initially, 4.2g of Ketjen EC

(manufactured by Ketjen Black International Company, JAPAN), which is commercially available, and 5.0 g of platinum were added to and dispersed in 0.5L of pure water. About 100 mLof 0.1N ammonia was then added to the resulting liquid to make PH equal to about 10, so that a hydroxide was formed and deposited on carbon. The resulting dispersion liquid was subjected to filtration, and the obtained powder was dried at 100⁰C in a vacuum for 10 hours. Then, the powder was held at 400⁰C for 2 hours in hydrogen gas so as to be reduced, and then held at 1000⁰C for 10 hours in nitrogen gas so as to provide a catalyst powder. The obtained catalyst was thrown into 1 L of 0.5N nitric acid, heated to 80⁰C, and was stirred for 30 min. Then, the catalyst was isolated by filtration, and was dried in a blowing drier at 8O⁰C for 15 hours or longer, to provide a catalyst powder. The acid amount in the catalyst was measured, and the result of the measurement was 1.020 mmol/g-cat.

[0027] Example 2 will be described. A catalyst powder as Example 2 was obtained by preparing a catalyst in the same manner as in Example 1, except that, after the catalyst powder was treated with the acid, it was dried in a vacuum drier at 6O⁰C for 15 hours or longer. The amount of acid in the catalyst was 1.156 mmol/g-cat.

[0028] Comparative Example 1 will be described. A catalyst powder as

Comparative Example 1 was obtained by preparing a catalyst in the same manner as in Example 1, except that the acid treatment (i.e., a process of treating the catalyst powder with an acid) was not conducted. The amount of acid in the catalyst was 0.52 mmol/g-cat.

[0029] Comparative Example 2 will be described. A catalyst powder as Comparative Example 2 was obtained by preparing a catalyst in the same manner as in Example 1, except that, after the acid treatment was conducted, the catalyst was filtered and cleaned with 1 L of pure water, and the filtration and cleaning were repeated until the conductivity of drainage or waste liquid became equal to or lower than 20 μS/cm. The amount of acid in the catalyst was 0.628 mmol/g-cat.

[0030] Comparative Example 3 will be described. A catalyst power as Comparative Example 3 was obtained by preparing a catalyst in the same manner as in

Example 1, except that, after the acid treatment was conducted, the catalyst was filtered and cleaned with IL of pure water only once. The amount of acid in the catalyst was

0.996 mmol/g-cat.

[0031] FIG. 1 shows the relationship between the catalyst acid amount and the low-humidity efficiency point performance (at 0.2 A/cm") with regard to Examples 1, 2 and Comparative Examples 1 - 3 as described above. FIG. 2 shows the relationship between the catalyst acid amount and the low-humidity output point performance (at 1.02

A/cm²) with regard to Examples 1, 2 and Comparative Examples 1 - 3.

[0032] As is understood from FIG. 1 and FIG. 2, Examples of the invention showed high voltage values at both of the current densities, 0.2 A/cm and 1.0 A/cm², since the catalysts of these Examples had an acid that can be hydrophilic. On the other hand, Comparative Examples showed low voltage values at both of the current densities, 0.2 A/cm² and 1.0 A/cm². It is concluded from these results that the catalyst becomes hydrophilic when it contains an acid that can be hydrophilic, and the water-hold property around the catalyst is improved, resulting in a reduction in the resistance to proton shift in the catalyst layer.

[0033] Comparative Example 4 will be described. Initially, 4.71 g of a commercially available carbon powder having a high specific surface area was added to and dispersed in 0.5 L of pure water, to provide a dispersion liquid. A hexahydroxo platinum nitric acid solution containing 4.71 g of platinum and an aqueous solution of cobalt nitrate containing 0.592 g of cobalt were dropped in this order into the dispersion liquid, to be sufficiently brought into contact with carbon. Then, about 5 mL of 0.01N ammonia was added to the resulting liquid to make PH equal to about 9, so that a hydroxide was formed and deposited on the carbon. The resulting dispersion liquid was repeatedly filtered and cleaned until the conductivity of filtration drainage became equal to or lower than 50 μS/cm, and the obtained powder was dried in a vacuum at 100⁰C for 10 hours. Then, after the dried powder was held in hydrogen gas at 500⁰C for 2^' hours so as to be reduced, it was held in nitrogen gas at 700⁰C for 0.5 hour and held in the same gas at 600⁰C for 6 hours, to provide an alloy of platinum and cobalt.

[0034] Furthermore, the catalyst powder was thrown into 0.5 L of 0.5N nitric acid, heated to 8O⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, the catalyst was filtered and cleaned with 1 L of pure water, and the filtration and cleaning were repeated until the conductivity of the cleaning drainage became equal to or lower than 20 μS/cm. Then, the catalyst was isolated by filtration, and was dried in a vacuum drier at 100⁰C for 12 hours or longer, to provide a catalyst powder as Comparative Example 4.

[0035] Comparative Example 5 will be described. A catalyst powder as Comparative Example 5 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.5 hour and held in the same gas at 600⁰C for 12 hours, to provide an alloy of platinum and cobalt.

[0036] Comparative Example 6 will be described. A catalyst powder as Comparative Example 6 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at

700⁰C for 0.5 hour and held in the same gas at 600⁰C for 18 hours, to provide an alloy of platinum and cobalt.

[0037] Comparative Example 7 will be described. A catalyst powder as Comparative Example 7 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 6.5 hours, to provide an alloy of platinum and cobalt.

[0038] Comparative Example 8 will be described. A catalyst powder as Comparative Example 8 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 800⁰C for 6.5 hours, to provide an alloy of platinum and cobalt.

[0039] Comparative Example 9 will be described. A catalyst powder as Comparative Example 9 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.5 hour, to provide an alloy of platinum and cobalt.

[0040] Comparative Example 10 will be described. A catalyst powder as Comparative Example 10 was obtained in the same manner as in Comparative Example 4, except for the following steps. In Comparative Example 10, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.5 hour, to provide an alloy of platinum and cobalt. Furthermore, the catalyst powder was thrown into 0.5 L of 0.5N nitric acid, heated to 8O⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, in Comparative Example 10, the catalyst was isolated by filtration but not cleaned with pure water, and was dried in a vacuum drier at 100⁰C for 12 hours or longer. [0041] Comparative Example 11 will be described. A catalyst powder as Comparative Example 11 was obtained in the same manner as in Comparative Example 4, except for the following steps, hi Comparative Example 11, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.5 hour, to provide an alloy of platinum and cobalt. Furthermore, the catalyst powder was thrown into 0.5 L of 0.5N nitric acid, heated to 80⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, in Comparative Example 11, the catalyst was isolated by filtration but not cleaned with pure water, and was dried in a blowing drier at 8O⁰C for 12 hours or longer. [0042] Example 3 will be described. A catalyst powder as Example 3 was obtained in the same manner as in Comparative Example 4, except that, after the alloying process, the catalyst powder was thrown into 0.5 L of 2N nitric acid, heated to 8O⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, in Example 3, the catalyst was isolated by filtration but not cleaned with pure water, and was dried in a vacuum drier at 100⁰C for 12 hours or longer.

[0043] Example 4 will be described. A catalyst powder as Example 4 was obtained in the same manner as in Comparative Example 4, except for the following steps. In Example 4, after the alloying process, the catalyst powder was thrown into 0.5 L of 2N nitric acid, heated to 80⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, the catalyst was filtered and cleaned with 1 L of pure water, and the filtration and cleaning were repeatedly conducted until the conductivity of the cleaning drainage became equal to or lower than 20 μS/cm. The catalyst was isolated by filtration, and was further thrown into 0.5 L of 0.5N nitric acid and stirred for 30min. at room temperature. Thereafter, the catalyst was isolated by filtration but not cleaned with pure water, and was dried in a vacuum drier at 100⁰C for 12 hours or longer.

[0044] Example 5 will be described. A catalyst powder as Example 5 was obtained in the same manner as in Comparative Example 4, except for the following steps. In Example 5, after the alloying process, the catalyst powder was thrown into 0.5 L of 2N nitric acid, heated to 80⁰C, and was stirred for 30 min., so that cobalt that had not been alloyed was removed by acid cleaning. Then, the catalyst was filtered and cleaned with 1 L of pure water, and the filtration and cleaning were repeatedly conducted until the conductivity of the cleaning drainage became equal to or lower than 20 μS/cm. The catalyst was isolated by filtration, and was further thrown into 0.5 L of 0.5N nitric acid and stirred for 30min. at room temperature. Thereafter, the catalyst was isolated by filtration but not cleaned with pure water, and was dried in a blowing drier at 8O⁰C for 12 hours or longer.

[0045] Example 6 will be described. A catalyst powder as Example 6 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.5 hour, to provide an alloy of platinum and cobalt, and the catalyst powder was thrown into 0.5 L of 0.5N nitric acid, heated to 8O⁰C, and was stirred for 48 hours, so that cobalt that had not been alloyed was removed by acid cleaning. [0046] Comparative Example 12 will be described. A catalyst powder as

Comparative Example 12 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 800⁰C for 0.5 hour, to provide an alloy of platinum and cobalt.

[0047] Comparative Example 13 will be described. A catalyst powder as Comparative Example 13 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 700⁰C for 0.05 hour, to provide an alloy of platinum and cobalt.

[0048] Example 7 will be described, A catalyst powder as Example 7 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 800⁰C for 0.5 hour, to provide an alloy of platinum and cobalt, and that the catalyst powder was thrown into 0.5 L of 0.5N nitric acid, heated to 8O⁰C, and was stirred for 48 hours, so that cobalt that had not been alloyed was removed by acid cleaning.

[0049] Comparative Example 14 will be described. A catalyst powder as Comparative Example 14 was obtained in the same manner as in Comparative Example 4, except that, after the reduction process, the catalyst powder was held in nitrogen gas at 800⁰C for 0.5 hour, to provide an alloy of platinum and cobalt, and the catalyst powder was thrown into 0.5 L of 0.05N nitric acid, heated to 8O⁰C, and was stirred for 48 hours, so that cobalt that had not been alloyed was removed by acid cleaning.

[0050] TABLE 1 below shows, in list form, the remaining acid amount and the power generation performance with regard to Examples 3 - 6 and Comparative Examples 4 - 14. FIG. 3 shows the relationship between the amount of acid in the catalyst and the low-humidity efficiency point performance (at 0.2 A/cm²), with regard to Examples 3 - 6 and Comparative Examples 4 - 14. FIG. 4 shows the relationship between the amount of acid in the catalyst and the low-humidity output point performance (at 1.02 A/cm ), with regard to Examples 3 - 6 and Comparative Examples 4 - 14.

TABLE l

[0051] As is understood from FIG. 3 and FIG. 4, the platinum-alloy catalysts (Examples 3-7) according to the invention showed high voltage values at both of the current densities, 0.2 A/cm² and 1.0 A/cm², since the catalysts of these examples had an acid that can be hydrophilic. On the other hand, Comparative Examples showed low voltage values at both of the current densities, 0.2 A/cm² and 1.0 A/cm². It is concluded from these results that the catalyst becomes hydrophilic when it contains an acid that can be hydrophilic, and the water-hold property around the catalyst is improved, resulting in a reduction in the resistance to proton shift in the catalyst layer.

[0052] In practicing the present invention, carbon carrying a known platinum catalyst or known platinum-alloy catalyst may be used. Also, in practicing the present invention, various types of acids may be used in an acid treatment performed on the platinum or platinum-alloy carrying carbon, and nitric acid may be preferably used. [0053] While some embodiments of the invention have been illustrated above, it is to be understood that the invention is not limited to details of the illustrated embodiments, but may be embodied with various changes, modifications or improvements, which may occur to those skilled in the art, without departing from the scope of the invention. [0054] The electrode catalyst for fuel cells according to the invention has a higher activity than the platinum catalyst or platinum-alloy catalyst of the related art, thus making it possible to reduce the amount of expensive platinum used in the catalyst.

Claims

CLAIMS:

1. An electrode catalyst for a fuel cell, characterized by comprising: a carbon support; a platinum catalyst or a platinum-alloy catalyst supported on the carbon support; and at least 0.7 mmol of an acid per gram of the electrode catalyst, said acid being present on the carbon support.

2. The electrode catalyst according to claim 1, wherein the platinum-alloy catalyst comprises an alloy of platinum and at least one metal selected from ruthenium, molybdenum, osmium, cobalt, rhodium, iridium, iron, nickel, titanium, tungsten, palladium, rhenium, chromium, manganese, niobium, and tantalum.

3. The electrode catalyst according to claim 1 or 2, wherein the carbon support on which the acid is present and the platinum catalyst or the platinum-alloy catalyst is supported is hydrophilic.

4. The electrode catalyst according to any one of claims 1 to 3, wherein the acid is present on the carbon support in an amount equal to or greater than 1.0 mmol per gram of the electrode catalyst.

5. The electrode catalyst according to any one of claims 1 to 3, wherein the acid is present on the carbon support in an amount equal to or greater than 1.31 mmol per gram of the electrode catalyst.

6. A method for producing an electrode catalyst for a fuel cell, which comprises a carbon support and a platinum catalyst or a platinum-alloy catalyst supported on the carbon support, characterized by comprising: supporting the platinum catalyst or the platinum-alloy catalyst on! the carbon support; and treating the carbon support carrying the platinum catalyst or the platinum-alloy catalyst with an acid, so that at least 0.7 mmol of the acid per gram of the electrode catalyst is present on the carbon support treated with the acid.

7. The method according to claim 6, wherein, after the carbon support carrying the platinum catalyst or the platinum-alloy catalyst is treated with the acid, the carbon support carrying the platinum catalyst or the platinum-alloy catalyst and treated with the acid is cleaned.

8. The method according to claim 6 or 7, wherein the platinum-alloy catalyst comprises an alloy of platinum and at least one metal selected from ruthenium, molybdenum, osmium, cobalt, rhodium, iridium, iron, nickel, titanium, tungsten, palladium, rhenium, chromium, manganese_rniobium, and tantalum.

9. The method according to any one of claims 6 to 8, wherein the carbon support on which the acid is present and the platinum catalyst or the platinum-alloy catalyst is supported is hydrophilic.

10. The method according to any one of claims 6 to 9, wherein the acid is present on the carbon support in an amount equal to or greater than 1.0 mmol per gram of the electrode catalyst.

11. The method according to any one of claims 6 to 10, wherein the acid is present on the carbon support in an amount equal to or greater than 1.31 mmol per gram of the electrode catalyst.

12. The method according to any one of claims 6 to 11, wherein the acid with which the carbon support carrying the platinum catalyst or the platinum-alloy catalyst is treated is nitric acid.

13. A polymer electrolyte fuel cell characterized by comprising the electrode catalyst according to any one of claims 1 to 5.