Method for manufacturing electrode catalysts, method for manufacturing gas diffusion electrodes, and method for manufacturing membrane / electrode assemblies

Abstract

The present invention provides a method of producing an electrode catalyst that offers excellent catalytic activity and excellent durability in an electrode catalyst layer of an MEA for a PEFC. Namely, the present invention is a method of producing an electrode catalyst (having a hollow carbon support that has nanopores having a pore diameter of 1-20 nm and a BET specific surface area of 700-900 m2 / g, and catalyst particles containing Pt supported on the support), the method comprising: a first step for preparing a powder in which catalyst particles are supported on a support; and a second step for accommodating the powder, that is obtained after the first step, in a flow-type reactor, causing NH3 gas to flow therethrough under conditions of 10-100% concentration and 0.1-0.5 MPa pressure, and keeping the temperature at 500°C or higher but less than the temperature of decomposition of ammonia for 5-10 hours to cause the powder and the NH3 gas to chemically react.

Description

Method for manufacturing electrode catalyst, method for manufacturing gas diffusion electrode, and method for manufacturing membrane-electrode assembly

[0001] The present invention relates to a method for producing an electrode catalyst using a hollow carbon support. More specifically, the present invention relates to a method for producing an electrode catalyst suitable for use in a gas diffusion electrode, and more particularly to a method for producing an electrode catalyst suitable for use in a gas diffusion electrode of a fuel cell. The present invention also relates to a method for producing a gas diffusion electrode and a method for producing a membrane-electrode assembly, each of which includes an electrode catalyst obtained by the method for producing an electrode catalyst.

[0002] Polymer electrolyte fuel cells (hereinafter referred to as "PEFCs" as necessary) are being researched and developed as power sources for fuel cell vehicles and home cogeneration systems. The electrode catalysts used in the gas diffusion electrodes of PEFCs are precious metal catalysts made of precious metal particles of platinum group elements such as platinum (Pt).

[0003] For example, a typical conventional electrode catalyst is a "Pt-supported carbon catalyst" (hereinafter referred to as a "Pt / C catalyst" as needed), which is a powder of catalyst particles in which Pt fine particles are supported on a conductive carbon support powder. Non-Patent Documents 1 and 2 disclose a manufacturing method for improving the performance of electrode catalysts, in which a carbon support is treated with nitric acid, then reacted with ammonia gas, and finally the catalyst particles are supported on the carbon support (see the "Experimental" section on pages F770-F771 of Non-Patent Document 1 and the "N-Functionalization of Carbon" and "Synthesis of 16 wt% Pt / N-KB" in the Supporting Information of Non-Patent Document 2). The nitric acid treatment conditions in Non-Patent Document 1 are a 70% aqueous nitric acid solution at 70°C for 30 minutes. The reaction conditions with ammonia gas in Non-Patent Document 1 are ammonia gas (100%, 1 L / min) at 200°C for 4 hours. Furthermore, the nitric acid treatment conditions in Non-Patent Document 2 are a 70% aqueous nitric acid solution at 70°C for 2 hours. The reaction conditions with ammonia gas in Non-Patent Document 2 are ammonia gas treatment (99.98%, 10 L / min) at 200°C, 400°C, and 600°C for 2.5 hours. The electrode catalysts obtained by Non-Patent Documents 1 and 2 are believed to have nitrogen-containing functional groups formed on the carbon support surface. It has been reported that when this electrode catalyst is used in the catalyst layer of an MEA cathode, the dispersion of the ionomer in the catalyst layer is improved, thereby improving the power generation performance of the MEA.

[0004] Furthermore, Non-Patent Document 3 reports the use of a carbon material doped with nitrogen as a heteroatom (an atom other than carbon and hydrogen) as a support for a Pt catalyst. In this case, it is reported that nitrogen doping promotes Pt nucleation on the support, resulting in the production of Pt nanoparticles with small and uniform particle sizes. This case also proposes a mechanism for improving oxygen reduction activity through metal-support interactions and spillover.

[0005] Supports for electrode catalysts include hollow carbon, which has many pores within its primary particles, and solid carbon, which has fewer pores within its primary particles than hollow carbon. Studies have been conducted to improve performance by utilizing the characteristics of each. For example, Patent Document 1 discloses a study using hollow carbon as a support. Patent Document 2 also discloses a study using solid carbon as a support. For example, Patent Document 1 discloses an electrode catalyst configuration in which a porous support (hollow carbon) with an average particle size of 20 to 100 nm is used, and the pore volume and mode diameter of the pore distribution of pores with a pore diameter of 4 to 20 nm are controlled within a predetermined range, and catalyst particles are supported within the primary pores of the support 220. Patent Document 1 mentions that this prevents adsorption of polymer electrolyte onto the surfaces of catalyst particles present within the primary pores, preventing a decrease in the effective reaction surface area of ​​the catalyst while ensuring sufficient gas transportability. Furthermore, it mentions that as a result, activity per catalyst weight is improved, and a fuel cell catalyst layer exhibiting excellent power generation performance can be provided even when the catalyst amount is reduced.

[0006] Furthermore, for example, Patent Document 2 discloses an electrode catalyst (PtCo / C catalyst) for fuel cells, which comprises a solid carbon support and catalyst particles containing an alloy of platinum and cobalt supported on the support. This electrode catalyst has a platinum to cobalt molar ratio of 4 to 11:1 in the alloy and is acid-treated at 70 to 90°C. Patent Document 2 points out that when a PtCo alloy is supported on a hollow carbon support, some of the PtCo alloy is contained within the hollow carbon support. Even if acid treatment is performed to suppress Co elution, it is difficult to sufficiently treat the PtCo alloy present within the support, resulting in the problem of Co elution from the PtCo alloy present within the support. Therefore, Patent Document 2 mentions that by using a solid carbon support instead of a hollow carbon support, it is possible to avoid the PtCo alloy being contained within the support. Furthermore, it is disclosed that this allows for sufficient acid treatment of the PtCo alloy, thereby suppressing Co elution. As a result, it is stated that it is possible to achieve both good initial performance and durability of the fuel cell.

[0007] Patent Document 2 defines solid carbon as follows: Specifically, Patent Document 2 states that solid carbon is carbon with fewer internal voids than hollow carbon. Specifically, it states that solid carbon is carbon with a ratio (t-Pot surface area / BET surface area) of 40% or more between the BET surface area determined by N adsorption and the external surface area determined by t-Pot (the surface area outside the particle calculated from the particle size). The "t-Pot surface area" described in Patent Document 2 is understood to refer to the "t-plot surface area" described in, for example, the technical report "Analysis of Micropore Surface Area by the t-plot Method" published online by MC Evatec Co., Ltd. on February 1, 2019. Analysis of micropore surface area using the t-plot method is one method of analyzing nitrogen adsorption isotherms (adsorption temperature: 77 K). This method involves comparing and converting adsorption isotherm data with standard isotherms to plot a graph of the relationship between the adsorption layer thickness t and the amount of adsorption. In addition to being able to quantify the specific surface area by separating it into the inside and outside of the pores, the shape of the graph can also reveal the trends of the pores.

[0008] Furthermore, examples of solid carbon include carbon described in Japanese Patent No. 4362116, specifically Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Kabushiki Kaisha. Furthermore, Patent Document 3 discloses an electrode catalyst (core-shell catalyst) in which catalyst particles are supported both inside and outside mesopores of a hollow carbon support (more specifically, nanopores formed in the primary particles of the hollow carbon support). This electrode catalyst has a configuration in which, when the particle size distribution of the catalyst particles is analyzed using three-dimensional reconstructed images obtained by electron beam tomography measurement using a STEM (scanning transmission electron microscope), the proportion of catalyst particles supported inside mesopores (more specifically, nanopores formed in the primary particles of the hollow carbon support) is 50% or more. Here, in this specification, the "nanopores" of the hollow carbon support refer to the "nanopores" formed in the "primary particles" of the hollow carbon support, as defined in Non-Patent Document 4 by Uchida et al. (see, for example, Fig. 1). Furthermore, in this specification, the pore diameter of the "nanopores" is 1 to 20 nm. The present patent applicant presents the following publications as publications in which the above-mentioned publicly known inventions are described:

[0009] JP 2013-109856 A, WO 2016 / 063968 A, WO 2019 / 221168 A

[0010] Journal of The Electrochemical Society, 165(10)F770-F779(2018)Nature Materials, Vol9,January 2020, 77-85Prog. Mater. Sci., 82, 445(2016)Phys. Chem. Chem. Phys., 2013, 15 (27), 11236 – 1124

[0011] Toward the widespread adoption of PEFCs, further improvement in the catalytic activity of electrode catalysts, more specifically, in the catalytic layer of an MEA electrode, is required to reduce the amount of Pt used in the MEA and material costs. The inventors investigated improvements to the nitriding treatment using ammonia gas described in Non-Patent Documents 1 and 2 for an electrode catalyst in which multiple catalyst particles containing Pt are supported on a carbon support. They found that adopting a method different from those disclosed in Non-Patent Documents 1 and 2 can provide an electrode catalyst that can further improve the polarization characteristics of the cathode and thereby contribute to improved MEA performance. The present invention has been made in view of these technical circumstances, and aims to provide a method for producing an electrode catalyst that has excellent catalytic activity and excellent durability in the electrode catalyst layer of an MEA for a PEFC. The present invention also aims to provide a method for producing a gas diffusion electrode and a method for producing a membrane electrode assembly (MEA) using an electrode catalyst obtained by the above-mentioned method for producing an electrode catalyst.

[0012] The present inventors have conducted extensive research into improving the nitriding method using ammonia gas described in the aforementioned Non-Patent Documents 1 and 2 for an electrode catalyst having a plurality of catalyst particles containing Pt supported on a hollow carbon support. As a result, they have found that by employing the following method, which differs from the methods disclosed in Non-Patent Documents 1 and 2, an electrode catalyst having excellent catalytic activity and excellent durability in the electrode catalyst layer of an MEA can be more reliably obtained, leading to the completion of the present invention. More specifically, the present invention comprises the following technical features:

[0013] That is, the present invention provides a porous carbon nanotube having nanopores with a pore diameter of 1 to 20 nm and a BET specific surface area (nitrogen adsorption specific surface area) of 700 to 900 m ２ / g, and a plurality of catalyst particles containing Pt supported on the support, the method comprising: a first step of preparing a powder in which the catalyst particles are supported on the support using the support and raw materials for the catalyst particles; and a second step of placing the powder obtained through the first step in a reactor of a flow system, and flowing ammonia gas through the reactor at a concentration of 100% and a pressure of 0.1 MPa to 0.5 MPa, while adjusting the temperature in the reactor to 500°C and maintaining the temperature at 500°C for 5 to 10 hours, thereby causing a chemical reaction between the powder and the ammonia gas.

[0014] As described above, the manufacturing method of the present invention first prepares a powder in which catalyst particles are supported on a hollow carbon support (Step 1), and then performs a treatment with ammonia gas (Step 2). On the other hand, the manufacturing methods described in Non-Patent Documents 1 and 2 described above employ a procedure in which a carbon support is first treated with ammonia gas, and then catalyst particles are supported on the ammonia-treated carbon support. In this respect, the manufacturing method of the present invention differs from Non-Patent Documents 1, 2, and 3 described above. Treating ammonia gas after supporting catalyst particles on a hollow carbon support would result in the loss of the effect of supporting catalyst particles on a support that has been subjected to ammonia treatment described in Non-Patent Document 3. Furthermore, if catalyst particles are supported on a hollow carbon support and then treated with ammonia gas, the catalyst particles may also promote the decomposition reaction of ammonia. This may result in insufficient generation of nitrogen-containing functional groups, which are expected to be generated on the carbon support surface as described in Non-Patent Documents 1 and 2, or may result in the generation of different types of functional groups. However, the present inventors have discovered that an electrode catalyst having excellent catalytic activity and excellent durability in the electrode catalyst layer of an MEA can be more reliably obtained by adopting a procedure different from that of the conventional technology, namely, by treating the hollow carbon support with catalyst particles after supporting the hollow carbon support in ammonia gas. By treating the powder in which catalyst particles are supported on a hollow carbon support in ammonia gas under the reaction conditions of the second step, the electrode catalyst obtained by the manufacturing method of the present invention can exhibit excellent catalytic activity and excellent durability in the electrode catalyst layer of an MEA.

[0015] The detailed reasons why the electrode catalyst of the present invention has excellent catalytic activity and durability have not been fully elucidated. However, the present inventors believe as follows. Specifically, when the pore structure of the catalyst obtained by the manufacturing method of the present invention (Example 1 described below) was analyzed and compared with the pore structure of a conventional Pt catalyst not subjected to ammonia treatment (Comparative Example 1 described below) (comparison of the catalyst alone and the catalyst layer containing the catalyst and ionomer), it was found that, compared to the conventional Pt catalyst, the catalyst of Example 1 of the present invention exhibited significantly reduced levels of ionomer blockage of (1) nanopores within the primary particles of hollow carbon, (2) primary pores within hollow carbon agglomerates, and (3) secondary pores between carbon agglomerates, and the ionomer was dispersed thinly and well on the carbon surface. Furthermore, when used in the catalyst layer of an MEA, the catalyst of the present invention exhibited superior catalyst utilization compared to conventional catalysts. For example, the catalyst of Example 1 described below was found to have approximately twice the Pt catalyst utilization rate of the catalyst of Comparative Example 1.

[0016] The inventors believe that by carrying catalyst particles on a carrier according to the procedure of the present invention and then performing an ammonia treatment, nitrogen-containing hydrophobic organic groups (e.g., cyclic organic groups such as pyridine and pyrrole) and hydrophilic organic groups (including -COOH, -CHO, =C=O, -OH, etc.) originally present on the carbon surface are appropriately dispersed and distributed, suppressing uneven distribution of the ionomer in the catalyst layer and resulting in improved initial performance and improved catalyst utilization when the above-mentioned MEA is fabricated. The inventors conducted a catalytic activity evaluation test for the oxygen reduction reaction using an RDE (rotating disk electrode) for a conventional Pt catalyst that was not subjected to an ammonia treatment (Comparative Example 1 described below) and a catalyst obtained by the manufacturing method of the present invention (Example 1 described below). However, the excellent initial activity and durability obtained in the MEA evaluation test could not be confirmed for the catalyst according to the present invention. Regarding this, the inventors believe that, because the I / C (ionomer mass / catalyst mass) of the electrode catalyst layer prepared in the RDE evaluation test is extremely small (for example, 1 / 10 to 1 / 5) compared to the I / C (0.7 in the examples described below) of the cathode catalyst layer prepared in the MEA evaluation test, it is highly likely that the effect of suppressing uneven distribution of the ionomer in the catalyst layer by modifying the hollow carbon surface as described above is significantly manifested in MEAs with a large I / C.

[0017] The inventors believe that when the catalyst obtained by the manufacturing method of the present invention is used in the catalyst layer of an MEA, uneven distribution of the ionomer and the resulting blockage of the pores are fully suppressed in all pores formed in the catalyst layer (secondary pores, primary pores, and nanopores of the hollow carbon primary particles) compared to conventional catalysts obtained by conventional manufacturing methods, and therefore, reactant gas is sufficiently supplied not only to catalyst particles outside the nanopores but also to catalyst particles inside the nanopores, thereby demonstrating excellent initial activity. Furthermore, when the catalyst obtained by the manufacturing method of the present invention is used in the catalyst layer of an MEA, blockage of the nanopores of the hollow carbon primary particles by the ionomer is fully suppressed compared to conventional catalysts obtained by conventional manufacturing methods. Therefore, the inventors believe that contact between the ionomer and catalyst particles in the nanopores is reduced, and poisoning of the catalyst particles by the ionomer is reduced. From this perspective, the inventors believe that the catalyst obtained by the manufacturing method of the present invention can also demonstrate excellent catalytic activity in the electrode catalyst layer of an MEA.

[0018] Furthermore, the catalyst obtained by the manufacturing method of the present invention suppresses uneven distribution of ionomer in the electrode catalyst layer of an MEA and the resulting blockage of pores, improving the catalyst utilization rate when used as a catalyst layer of an MEA, which is thought to also contribute to improving the drainage properties of the catalyst layer. Therefore, when the MEA generates electricity (especially when generating electricity at a relatively high current density), there are fewer areas in the catalyst layer with poor drainage properties, and it is thought that this sufficiently reduces the uneven concentration of electrode reactions on some catalyst particles, which can lead to sintering or dissolution. Therefore, the inventors believe that the catalyst obtained by the manufacturing method of the present invention can exhibit excellent durability in the electrode catalyst layer of an MEA.

[0019] Here, in the present invention, "hollow carbon" refers to carbon that has more pores (voids) inside it than the solid carbon described above, and refers to conductive carbon that contains the above-mentioned nanopores as part of the pores. Furthermore, in the present invention, the "nanopores" of the primary particles of the hollow carbon support refer to the "nanopores" formed in the "primary particles" of the hollow carbon support, as defined in Non-Patent Document 3 (see, for example, Fig. 1). Furthermore, in the present invention, the pore diameter of the "nanopores" is 1 to 20 nm.

[0020] Furthermore, from the viewpoint of more reliably achieving the effects of the present invention, it is preferable that the hollow carbon support contains a greater number of nanopores with pore diameters (pore entrance sizes) of 1 to 10 nm. It has been reported that the micelle diameter of the polymer electrolyte used in the catalyst layers of the anode and cathode of an MEA is approximately 10 nm (e.g., Y.S.Kim, et al., DOE Hydrogen Program Merit Review and Peer Meeting FC16, (2009)). Therefore, by using a hollow carbon support containing a greater number of pores with pore diameters (pore entrance sizes) of 1 to 10 nm, it becomes more difficult for the polymer electrolyte to penetrate into the nanopores, thereby more reliably preventing contact between the catalyst particles supported inside the nanopores and the polymer electrolyte.

[0021] In the manufacturing method of the present invention, the ammonia gas concentration in the second ammonia treatment is 10 to 100%. By adjusting the ammonia gas concentration within this range, the modification of the catalyst powder surface can be sufficiently promoted. Furthermore, the ammonia gas pressure in the second ammonia treatment is 0.1 MPa to 0.5 MPa. By adjusting the ammonia gas pressure within this range, the modification of the catalyst powder surface can be sufficiently promoted without degrading the catalyst powder. From the viewpoint of simplifying the configuration of the reaction apparatus, the ammonia gas pressure is preferably 0.1 MPa to 0.2 MPa, and more preferably 0.1 MPa. Furthermore, the temperature in the reaction vessel in the second ammonia treatment is adjusted to 500°C or higher and lower than the decomposition temperature of ammonia. By adjusting the temperature in the reaction vessel in the ammonia treatment within this range, the modification of the catalyst powder surface can be sufficiently promoted. Furthermore, the ammonia treatment in the second ammonia treatment is maintained at the above-mentioned reaction temperature for 5 to 10 hours. By adjusting the reaction time to within this range, the surface modification of the catalyst powder can be sufficiently progressed without deteriorating the catalyst powder.

[0022] The production method of the present invention may further include, between Steps 1 and 2, a nitric acid treatment step in which the powder obtained through Step 1 is dispersed in a 0.01 to 1.5 mol / L aqueous nitric acid solution and the resulting dispersion is stirred while being held at 60 to 95°C for 1 to 3 hours; a washing step in which, after the nitric acid treatment step, the solid component in the dispersion is separated from the liquid component and the solid component is washed one or more times with ion-exchanged water; and a drying step in which the solid component obtained through the washing step is filtered and then dried to obtain a powder. The inventors believe that by treating the powder obtained through Step 1 (powder comprising catalyst particles supported on hollow carbon) with an appropriate amount of nitric acid between Steps 1 and 2, existing organic groups (including -COOH, -CHO, =C=O, -OH, etc.) on the powder surface can be partially modified or new organic groups can be generated (moderately increased) on the powder surface, thereby making the further modification of the powder surface by the subsequent ammonia treatment in Step 2 more effective. In this nitric acid treatment, the concentration of the nitric acid aqueous solution is preferably 0.01 to 1.5 mol / L. By setting the concentration within this range, the modification of the catalyst powder surface by nitric acid can be sufficiently promoted without oxidative degradation of the catalyst powder. Furthermore, the temperature of the nitric acid treatment is preferably 60 to 95°C, and the nitric acid treatment time within this temperature range is preferably 1 to 3 hours. By adjusting the temperature and time of the nitric acid treatment within these ranges, the modification of the catalyst powder surface by nitric acid can be sufficiently promoted without oxidative degradation of the catalyst powder.

[0023] Furthermore, in the present invention, from the viewpoint of availability and raw material cost, it is preferable that the hollow carbon support is Ketjen Black EC300J. In this case, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support (Ketjen Black EC300J) is 700 to 900 m ２ / g, and from the viewpoint of obtaining better initial performance and durability of the electrode, it is preferable that the range is 750 to 850 m ２ / g is more preferable.

[0024] In addition, in the electrode catalyst obtained by the production method of the present invention, it is preferable that the catalyst particles are catalyst particles made of Pt (zero-valent) from the viewpoint of obtaining sufficient electrode reaction activity. Furthermore, in the electrode catalyst obtained by the production method of the present invention, at least a portion of the surface of the catalyst particle may be coated with a Pt oxide film to the extent that the catalyst particle can exhibit excellent catalytic activity. In addition, in the electrode catalyst obtained by the production method of the present invention, it is preferable that the catalyst particles are catalyst particles made of a PtNi alloy from the viewpoint of obtaining electrode reaction activity exceeding that of a Pt catalyst. Furthermore, in the electrode catalyst obtained by the production method of the present invention, it is preferable that the catalyst particles have a core-shell structure having a core particle and a shell containing Pt that covers at least a portion of the surface of the core particle, from the viewpoint of obtaining electrode reaction activity and durability exceeding that of a Pt catalyst and reducing the amount of Pt used. Here, it is preferable that the core particle is a particle made of Pd from the viewpoint of obtaining excellent catalytic activity.

[0025] The present invention also provides a method for manufacturing a gas diffusion electrode having a catalyst layer and a gas diffusion layer for supplying a reactant gas to the catalyst layer, the method comprising the step of preparing an ink for forming a catalyst layer, the ink containing at least the electrode catalyst manufactured by the method for manufacturing an electrode catalyst of the present invention described above, a solid polymer electrolyte (ionomer), and a dispersion medium. The gas diffusion electrode obtained by the method for manufacturing a gas diffusion electrode of the present invention is configured to contain the electrode catalyst of the present invention. Therefore, it is easy to configure the electrode to have excellent polarization characteristics when used in an MEA of a PEFC.

[0026] The present invention further provides a method for manufacturing a membrane electrode assembly (MEA) having an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, in which a gas diffusion electrode manufactured by the above-described method for manufacturing an electrode catalyst of the present invention is used for at least one of the anode and the cathode. The MEA obtained by the method for manufacturing a membrane electrode assembly (MEA) of the present invention includes a gas diffusion electrode (GDE) manufactured by the above-described method for manufacturing a GDE of the present invention, thereby facilitating the formation of an MEA for a PEFC with excellent cell characteristics. The present invention also provides a fuel cell stack including an MEA manufactured by the above-described method for manufacturing an MEA of the present invention. A fuel cell stack manufactured by the method for manufacturing a fuel cell stack of the present invention includes an MEA manufactured by the method for manufacturing an MEA of the present invention, and therefore, when used in an MEA for a PEFC, it is easy to form a configuration with excellent cell characteristics.

[0027] The present invention provides a method for producing an electrode catalyst that has excellent catalytic activity and durability in the electrode catalyst layer of an MEA of a PEFC, as well as a method for producing a gas diffusion electrode and a membrane electrode assembly (MEA) that use the electrode catalyst obtained by the method.

[0028] 1 is a schematic cross-sectional view showing a preferred embodiment of an MEA obtained by the manufacturing method of the present invention. FIG. 2 is a schematic cross-sectional view showing a preferred embodiment of an electrode catalyst obtained by the manufacturing method of an electrode catalyst of the present invention, which is contained in at least one of the cathode catalyst layer and the anode catalyst layer of the MEA shown in FIG. 1. FIG. 3 is an enlarged schematic cross-sectional view showing the general configuration of the electrode catalyst shown in FIG. 2. FIG. 3 is a schematic cross-sectional view showing another preferred embodiment of an MEA obtained by the manufacturing method of the present invention. FIG. 4 is a schematic cross-sectional view showing another preferred embodiment of a CCM obtained by the manufacturing method of the present invention. FIG. 5 is a schematic cross-sectional view showing another preferred embodiment of a CCM obtained by the manufacturing method of the present invention. FIG. 6 is a schematic cross-sectional view showing another preferred embodiment of a GDE obtained by the manufacturing method of the present invention. FIG. 7 is a schematic cross-sectional view showing another preferred embodiment of a GDE obtained by the manufacturing method of the present invention. FIG. 8 is a schematic diagram showing a preferred embodiment of a fuel cell stack obtained by the manufacturing method of the present invention. FIG. 9 is a graph showing current-voltage curves (H2 / Air, initial performance comparison) of MEAs produced using electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. 12 is a graph showing current-voltage curves (H2 / O2, initial performance comparison) of MEAs fabricated using electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 13 is a graph showing current-voltage curves (H2 / Air, durability performance comparison) of MEAs fabricated using electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 14 is a graph showing current-voltage curves (H2 / O2, durability performance comparison) of MEAs fabricated using electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 15 is a graph showing CV wave comparison before (BOL) the MEA durability performance evaluation test shown in FIG. 12. FIG. 16 is a graph showing CV wave comparison after (EOL) the MEA durability performance evaluation test shown in FIG. 12. ２ Gain and O of the MEA cathode of Comparative Example 1 ２ 1 is a graph showing a comparison of gains. 2 is a graph showing changes in MA (H2 / O2, initial performance evaluation test) of the MEA cathodes of Example 1 and Comparative Example 1 when the humidification conditions are changed. ２ 1 is a graph showing the results of pore volume distribution measurement by gas adsorption method. ２19 is a graph showing the results of pore volume distribution measurement by gas adsorption method. FIG. 20 is a graph showing the results of calculating the change (decrease) in pore volume before and after adding an ionomer to the catalysts of Example 1 and Comparative Example 1 for the mesopore region with pore diameters of 10 to 50 nm in the pore volume distribution data shown in FIGS. 18 and 19 . FIG. 21 is a TEM photograph of the MEA cathode catalyst layer according to Example 1 (a mixture of the catalyst of Example 1 and the ionomer). FIG. 22 is a TEM photograph of the MEA cathode catalyst layer according to Comparative Example 1 (a mixture of the catalyst of Comparative Example 1 and the ionomer). FIG. 23 is a graph showing the results of calculating the change (decrease) in pore volume before and after adding an ionomer to the catalysts of Example 1 and Comparative Example 1 for the mesopore region with pore diameters of 10 to 50 nm in the pore volume distribution data shown in FIGS. 20 and 21. ２ 1 is a graph showing the results of differential pore volume distribution measurement by gas adsorption method. ２ 25 is a graph showing the results of differential pore volume distribution measurement by gas adsorption method. 26 is a graph showing the results of calculating the pore volumes before and after adding an ionomer to the catalysts of Example 1 and Comparative Example 1 for the nanopore region with pore diameters of 2 to 5 nm in the differential pore volume distribution data shown in Figures 23 and 24. 27 is a TEM photograph of an MEA cathode catalyst layer according to Example 1 (a mixture of the catalyst of Example 1 and the ionomer). 28 is a TEM photograph of an MEA cathode catalyst layer according to Comparative Example 1 (a mixture of the catalyst of Comparative Example 1 and the ionomer).

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] <Membrane Electrode Assembly (MEA)> Fig. 1 is a schematic cross-sectional view showing a preferred embodiment of an MEA obtained by the manufacturing method of the present invention. The MEA 10 shown in Fig. 1 has a configuration including two flat gas diffusion electrodes (cathode 1 and anode 2) arranged facing each other, and a polymer electrolyte membrane (hereinafter referred to as "PEM" as necessary) 3 arranged between the cathode 1 and the anode 2. In the case of this MEA 10, at least one of the cathode 1 and the anode 2 contains an electrode catalyst 20, which will be described later. The MEA 10 can be manufactured by stacking the cathode 1, anode 2, and PEM 3 as shown in Fig. 1 and then crimping them together.

[0031] <Gas Diffusion Electrode (GDE)> The cathode 1, which is a gas diffusion electrode, is configured to include a gas diffusion layer 1gd and a catalyst layer 1c formed on the surface of the gas diffusion layer 1gd facing the PEM 3. The cathode 1 also includes a water-repellent layer (micro porous layer, hereinafter referred to as "MPL" as necessary) 1m disposed between the gas diffusion layer 1gd and the catalyst layer 1c. Similar to the cathode 1, the anode 2, which is also a gas diffusion electrode, is configured to include a gas diffusion layer 2gd, a catalyst layer 2c formed on the surface of the gas diffusion layer 2gd facing the PEM 3, and an MPL 2m disposed between the gas diffusion layer 2gd and the catalyst layer 2c.

[0032] (Catalyst Layer (CL)) In the cathode 1, the catalyst layer 1c is a layer where a reaction proceeds in which water is produced from air (oxygen gas) sent from the gas diffusion layer 1gd and hydrogen ions moving through the PEM 3 from the anode 2. In the anode 2, the catalyst layer 2c is a layer where a reaction proceeds in which hydrogen ions and electrons are produced from hydrogen gas sent from the gas diffusion layer 2gd. At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 contains the electrode catalyst 20 of the present invention.

[0033] (A Preferred Embodiment of the Electrode Catalyst of the Present Invention) A preferred embodiment of the electrode catalyst obtained by the manufacturing method of the present invention will now be described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view showing a preferred embodiment of the electrode catalyst (Pt / C catalyst) contained in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c of the MEA 10 shown in Fig. 1. Fig. 3 is an enlarged schematic cross-sectional view showing the general configuration of the electrode catalyst 20 shown in Fig. 2. As shown in Figs. 2 and 3, the electrode catalyst 20 includes a support 22 which is a hollow carbon support, and catalyst particles 23 supported on the support 22.

[0034] Furthermore, the electrode catalyst 20 shown in FIGS. 2 and 3 preferably satisfies the following conditions in order to more reliably obtain the effects of the present invention. Here, the catalyst particles 23 are made of Pt (zero valence). However, a Pt oxide layer may be formed on the surface of the catalyst particles 23 as long as the effects of the present invention can be obtained. The electrode catalyst 20 preferably has an average crystallite size measured by powder X-ray diffraction (XRD) of 3 to 16.0 nm. Here, the catalyst particles 23 are made of Pt (zero valence). However, a Pt oxide layer may be formed on the surface of the catalyst particles as long as the effects of the present invention can be obtained. Furthermore, the electrode catalyst 20 preferably has a Pt loading rate of 5.6 to 66.5 wt %.

[0035] The support 22 is not particularly limited as long as it is a hollow carbon support that is electrically conductive, has nanopores with a pore diameter of 1 to 20 nm, is capable of supporting the catalyst particles 23, and has a relatively large surface area. Furthermore, the support 22 may contain pores with a pore diameter of less than 1 nm (relatively small pores classified as micropores) or pores with a pore diameter of more than 20 nm and not more than 50 nm (relatively large pores classified as mesopores), as long as the effects of the present invention can be obtained. Furthermore, the support 22 is preferably a hollow carbon support that has good dispersibility in a gas diffusion electrode-forming composition containing the electrode catalyst 20 and has excellent electrical conductivity.

[0036] Examples of hollow carbon carriers include Ketjenblack EC300J and Ketjenblack EC600JD. Commercially available products include those under the trade names "Carbon EPC" and "Carbon EPC600JD" (manufactured by Lion Chemical Co., Ltd.). Detailed characteristics of Ketjenblack EC300J and Ketjenblack EC600JD are described, for example, in a document published online by the Functional Carbon Filler Research Group entitled "Characteristics and Application Development of the Conductive Carbon Black 'Ketjenblack EC'." Other examples of hollow carbon carriers include those under the trade name "MCND (Mesoporous Carbon Nano-Dendrite)" (manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.) and the trade name "Black Pearls 2000" (manufactured by Cabot Corporation).

[0037] Here, from the viewpoint of more reliably obtaining the effects of the present invention, it is preferable that the hollow carbon support is one of Ketjenblack EC300J and Ketjenblack EC600JD. In the case of Ketjenblack EC300J, from the same viewpoint, the BET specific surface area (nitrogen adsorption specific surface area) of the hollow carbon support measured using nitrogen is 700 to 900 m ２ / g, and from the viewpoint of obtaining better initial performance and durability of the electrode, it is preferable that the range is 750 to 850 m ２ It is more preferable that the SiO2 content is 1 / g.

[0038] As shown in FIG. 2, the catalyst particles 23 are supported both inside the nanopores P22 of the support 22 and outside the nanopores P22.

[0039] The manufacturing method of the electrode catalyst 20 is not particularly limited and can be any known method, except that it uses the carrier 22 and raw materials for the catalyst particles 23, and essentially includes the "first step" and "second step" described below, and preferably further includes the "nitric acid treatment step" described below. In the first step, a powder in which the catalyst particles 23 are supported on the carrier 22 is prepared. Pretreatment of the carrier may also be performed in the first step. For example, the carrier 22 is placed in ultrapure water, and a pH adjuster is added to prepare a dispersion whose pH is adjusted to 9 to 13. The dispersion is then stirred and maintained at a temperature of 80 to 99°C, preferably 90 to 99°C, for a predetermined period of time (but without boiling). The dispersion is then cooled to room temperature. This removes gas from the nanopores P22 of the carrier 22, allowing the ultrapure water to sufficiently penetrate into the nanopores P22. This is preferable because when the Pt raw material is subsequently added, the Pt raw material is sufficiently retained within the nanopores P22 of the support 22, and a large number of precursors of Pt catalyst particles are supported inside the nanopores P22 of the support 22.

[0040] The "ultrapure water" used to prepare the above-mentioned aqueous solution in the first step is water having a resistivity R (the reciprocal of the electrical conductivity measured by the JIS standard test method (JIS K0552)) of 3.0 MΩ cm or more, as expressed by the following formula (1). Furthermore, the "ultrapure water" preferably has a water quality equivalent to or purer than "A3" as specified in JIS K0557 "Water for use in testing water and wastewater." This ultrapure water is not particularly limited as long as it has an electrical conductivity that satisfies the relationship expressed by the following formula (1). For example, the ultrapure water may be produced using an ultrapure water production system such as the "Milli-Q Series" (manufactured by Merck Ltd.) or the "Elix UV Series" (manufactured by Nihon Millipore K.K.). R = 1 / ρ (1) In the above formula (1), R represents the resistivity, and ρ represents the electrical conductivity measured by the JIS standard test method (JIS K0552).

[0041] Next, an aqueous solution of water-soluble Pt salt dissolved in ultrapure water is added at room temperature to the dispersion of the support 22 obtained through the pretreatment of the support 22. Next, the temperature of the solution to which the Pt salt has been added is raised to 50°C or higher, and an aqueous solution of a water-soluble reducing agent (preferably an alkaline water-soluble reducing agent) is added. After the addition of the reducing agent, the solution temperature is maintained at 50°C or higher for a predetermined time to allow the reduction reaction to proceed, and then the solution temperature is lowered to room temperature.

[0042] Next, the solid component and the liquid component in the liquid obtained through the reduction treatment are separated, and the solid component (a mixture of the Pt / C catalyst and other impurities) is washed. For example, the solid component in the liquid obtained through the "reduction step" may be separated from the liquid component using a filtering means such as filter paper or filter cloth. The solid component may be washed using the above-mentioned ultrapure water, pure water (resistivity R represented by the above-mentioned formula (1) is 0.1 MΩ cm or more and less than 3.0 MΩ cm), or pure hot water (pure water at a temperature of 40 to 80°C). For example, when pure hot water is used, washing is repeated until the electrical conductivity of the filtrate after washing is less than 10 μS / cm.

[0043] Next, water is separated from the solid component (a mixture of Pt / C catalyst and water) obtained through the above-mentioned washing process. First, the solid component is air-dried, and then dried in a dryer at a predetermined temperature for a predetermined time (drying process). The process following the "drying process" is the "pulverization process." In this "pulverization process," the solid component (Pt / C catalyst) obtained in the "drying process" is made into catalyst powder using a pulverizing means such as a mixer.

[0044] Next, the second step is carried out. In the second step, the powder obtained through the first step is placed in a reactor of a flow system, and ammonia gas is circulated through the reaction vessel at a concentration of 10 to 100% and a pressure of 0.1 MPa to 0.5 MPa while the temperature in the reaction vessel is adjusted to 500°C or higher but lower than the decomposition temperature of ammonia, and maintained for 5 to 10 hours, thereby causing a chemical reaction between the powder and the ammonia gas. The ammonia gas concentration in the ammonia treatment of the second step is 10 to 100%. By adjusting the ammonia gas concentration within this range, the modification of the catalyst powder surface can be sufficiently promoted.

[0045] Furthermore, the ammonia gas pressure in the second ammonia treatment is 0.1 MPa to 0.5 MPa. By adjusting the ammonia gas pressure within this range, the modification of the catalyst powder surface can be sufficiently promoted without degrading the catalyst powder. From the viewpoint of simplifying the configuration of the reaction apparatus, the ammonia gas pressure is preferably 0.1 MPa to 0.2 MPa, and more preferably 0.1 MPa. Furthermore, the temperature in the reaction vessel in the second ammonia treatment is adjusted to 500°C or higher and lower than the decomposition temperature of ammonia. By adjusting the temperature in the reaction vessel in the ammonia treatment within this range, the modification of the catalyst powder surface can be sufficiently promoted. Furthermore, the ammonia treatment in the second step is maintained at the above-mentioned reaction temperature for 5 to 10 hours. By adjusting the reaction time within this range, the modification of the catalyst powder surface can be sufficiently promoted without degrading the catalyst powder.

[0046] Furthermore, in the present invention, a "nitric acid treatment step" may be further included between the first step and the second step. In the nitric acid treatment step, the powder obtained through the first step is dispersed in a 0.01 to 1.5 mol / L aqueous nitric acid solution, and the resulting dispersion is maintained at 60 to 95°C for 1 to 3 hours while stirring. Furthermore, when this nitric acid treatment step is carried out, the method must further include, after the nitric acid treatment step, a washing step (second washing step) in which the solid component and the liquid component in the dispersion are separated and the solid component is washed one or more times with ion-exchanged water, and a drying step (second drying step) in which the solid component obtained through the washing step is filtered and then dried to obtain a powder. In the nitric acid treatment step, the powder obtained through the first step (powder in which catalyst particles are supported on hollow carbon) is treated with an appropriate amount of nitric acid, which makes it possible to partially modify existing organic groups (including -COOH, -CHO, =C=O, -OH, etc.) on the powder surface or to newly generate (moderately increase) such organic groups on the powder surface, and the inventors believe that this makes it possible to more effectively further modify the powder surface by the ammonia treatment in the subsequent second step.

[0047] In this nitric acid treatment, the concentration of the nitric acid aqueous solution is preferably 0.01 to 1.5 mol / L. By setting the concentration within this range, the modification of the catalyst powder surface by nitric acid can be sufficiently promoted without oxidative degradation of the catalyst powder. Furthermore, the temperature of the nitric acid treatment is preferably 60 to 95°C, and the nitric acid treatment time within this temperature range is preferably 1 to 3 hours. By adjusting the temperature and time of the nitric acid treatment within this range, the modification of the catalyst powder surface by nitric acid can be sufficiently promoted without oxidative degradation of the catalyst powder. The washing step (second washing step) and drying step (second drying step) following the nitric acid treatment step may be carried out in the same manner as the washing step and drying step in the first step described above.

[0048] The polymer electrolyte (ionomer) contained in catalyst layer 1c and catalyst layer 2c is not particularly limited as long as it has hydrogen ion conductivity, and known polymer electrolytes can be used. For example, known perfluorocarbon resins having sulfonic acid groups or carboxylic acid groups can be exemplified as polymer electrolytes. Preferred examples of readily available polymer electrolytes having hydrogen ion conductivity include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

[0049] In at least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 shown in FIG. 1, the mass ratio I / C of the mass C of the carrier 22 to the mass I of the polymer electrolyte (ionomer) is set to 0.5 to 1.2, and more preferably, the mass ratio I / C is set to 0.7 to 1.0.

[0050] (Gas Diffusion Layer (GDL)) The gas diffusion layer 1gd provided in the cathode 1 shown in FIG. 1 is a layer provided to supply an oxidant gas (e.g., oxygen gas or air) to the catalyst layer 1c. The gas diffusion layer 1gd also serves to support the catalyst layer 1c. The gas diffusion layer 2gd provided in the anode 2 is a layer provided to supply a reducing gas (e.g., hydrogen gas) to the catalyst layer 2c. The gas diffusion layer 2gd also serves to support the catalyst layer 2c.

[0051] The gas diffusion layer (1gd) shown in FIG. 1 has a function and structure that allows hydrogen gas or air (oxygen gas) to pass through easily and reach the catalyst layer. Therefore, the gas diffusion layer is preferably water-repellent. For example, the gas diffusion layer contains a water-repellent component such as polyethylene terephthalate (PTFE). The material that can be used for the gas diffusion layer (1gd) is not particularly limited, and known materials can be used. For example, carbon paper, or a material made of carbon paper as the main raw material, with optional components such as carbon powder, ion-exchanged water, and a polyethylene terephthalate dispersion as a binder coated on the carbon paper, is preferred.

[0052] (Water-repellent layer (MPL)) As shown in Fig. 1, the cathode 1 has a water-repellent layer (MPL) 1m disposed between the gas diffusion layer 1gd and the catalyst layer 1c. The water-repellent layer 1m has electronic conductivity, water repellency, and gas diffusivity, and is provided to promote the diffusion of oxidant gas to the catalyst layer 1gd and the discharge of reaction product water generated in the catalyst layer 1gd. The configuration of the water-repellent layer 1m is not particularly limited, and any known configuration can be adopted.

[0053] 1 is not particularly limited as long as it has hydrogen ion conductivity, and a known PEM conventionally used in PEFCs can be used. For example, it may be a membrane containing, as a constituent component, any of the polymer electrolytes exemplified above for the catalyst layers 1c and 2c.

[0054] <Modified MEA> While preferred embodiments of the MEA of the present invention (and the catalyst layer and gas diffusion electrode of the present invention) have been described above, the MEA of the present invention is not limited to the configuration of the MEA 10 shown in FIG. 1 . For example, the MEA of the present invention may have the configuration of the MEA 11 shown in FIG. 4 . FIG. 4 is a schematic cross-sectional view showing another preferred embodiment of the MEA of the present invention. The MEA 11 shown in FIG. 4 has a configuration in which a gas diffusion electrode (GDE) 1A having a configuration similar to the cathode 1 in the MEA 10 shown in FIG. 1 is disposed on only one side of a polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the configuration of the catalyst layer of the present invention. That is, the catalyst layer 1c of the GDE 1A has a mass ratio I / C of the mass C of the support 22 of the electrode catalyst 20 to the mass I of the polymer electrolyte (ionomer) of 0.5 to 1.2, more preferably 0.7 to 1.0.

[0055] <Catalyst-Coated Membrane Assembly (CCM)> Next, a preferred embodiment of the catalyst-coated membrane assembly (CCM) of the present invention will be described. FIG. 5 is a schematic cross-sectional view showing a preferred embodiment of the CCM of the present invention. The CCM 12 shown in FIG. 5 has a configuration in which a polymer electrolyte membrane (PEM) 3 is disposed between a cathode catalyst layer 1c and an anode catalyst layer 2c. At least one of the cathode catalyst layer 1c and the anode catalyst layer 2c has the catalyst layer configuration of the present invention. That is, in at least one of the cathode catalyst layer 1c and the anode catalyst layer 2c, the mass ratio I / C of the electrode catalyst 20 carrier mass C to the polymer electrolyte (ionomer) mass I is 0.5 to 1.2, more preferably 0.7 to 1.0.

[0056] <Modified Catalyst-Layer Membrane Assembly (CCM)> While preferred embodiments of the CCM of the present invention have been described above, the CCM of the present invention is not limited to the configuration of the CCM 12 shown in FIG. 5 . For example, the CCM of the present invention may have the configuration of the CCM 13 shown in FIG. 6 . FIG. 7 is a schematic cross-sectional view showing another preferred embodiment of the CCM of the present invention. The CCM 13 shown in FIG. 6 has a configuration in which a catalyst layer 1c having a configuration similar to that of the cathode 1 in the CCM 12 shown in FIG. 5 is disposed on only one side of the polymer electrolyte membrane (PEM) 3. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1A has the configuration of the catalyst layer of the present invention. That is, the catalyst layer 1c of the CCM 13 has a mass ratio N / C of the mass C of the support of the electrode catalyst 20 to the mass N of the polymer electrolyte, which is 0.5 to 1.2, and more preferably 0.7 to 1.0.

[0057] <Gas Diffusion Electrode (GDE)> Next, a preferred embodiment of the gas diffusion electrode (GDE) of the present invention will be described. FIG. 8 is a schematic cross-sectional view showing a preferred embodiment of the GDE of the present invention. The gas diffusion electrode (GDE) 1B shown in FIG. 7 has a configuration similar to the cathode 1 mounted on the MEA 10 shown in FIG. 1. However, the catalyst layer 1c of the gas diffusion electrode (GDE) 1B has the configuration of the catalyst layer of the present invention. That is, the catalyst layer 1c of the gas diffusion electrode (GDE) 1B has a mass ratio I / C of the mass C of the support 22 of the electrode catalyst 20 to the mass I of the polymer electrolyte (ionomer) of 0.5 to 1.2, more preferably 0.7 to 1.0.

[0058] <Modified Gas Diffusion Electrode (GDE)> Although a preferred embodiment of the GDE of the present invention has been described above, the GDE of the present invention is not limited to the configuration of GDE 1B shown in FIG. 7. For example, the GDE of the present invention may have the configuration of GDE 1C shown in FIG. 8. FIG. 9 is a schematic cross-sectional view showing another preferred embodiment of the GDE of the present invention. Compared to GDE 1B shown in FIG. 8, GDE 1C shown in FIG. 8 has a configuration in which a water-repellent layer (MPL) is not disposed between the catalyst layer 1c and the gas diffusion layer 1gd.

[0059] <Composition for forming catalyst layer> Next, a preferred embodiment of the composition for forming a catalyst layer of the present invention will be described. The composition for forming a catalyst layer of this embodiment contains an electrode catalyst 20, a polymer electrolyte, and a main component, and the mass ratio I / C of the mass C of the support 22 of the electrode catalyst 20 to the mass I of the polymer electrolyte (ionomer) is 0.5 to 1.2, more preferably 0.7 to 1.0. Here, the composition of the liquid containing the polymer electrolyte is not particularly limited. For example, the liquid containing the polymer electrolyte may contain the aforementioned polymer electrolyte having hydrogen ion conductivity, water, and an alcohol.

[0060] The composition ratio of the electrode catalyst 20, polymer electrolyte, and other components (water, alcohol, etc.) contained in the catalyst layer-forming composition is appropriately set so as to ensure a good dispersion state of the electrode catalyst 20 in the resulting catalyst layer and improve the power generation performance of the MEA 10 including the catalyst layer. The catalyst layer-forming composition can be prepared by mixing and stirring a liquid containing the electrode catalyst 20 and the polymer electrolyte. A polyhydric alcohol such as glycerin and / or water may be added to adjust the coatability. When mixing the liquid containing the electrode catalyst 20 and the polymer electrolyte, a grinding mixer such as a ball mill or ultrasonic disperser may be used. At least one of the catalyst layer 1c of the cathode 1 and the catalyst layer 2c of the anode 2 shown in FIG. 1 can be formed using a preferred embodiment of the catalyst layer-forming composition of the present invention.

[0061] (Method for manufacturing gas diffusion electrode) Next, an example of a method for manufacturing the gas diffusion electrode of the present invention will be described. The gas diffusion electrode may be formed so as to include the catalyst layer of the present invention, and a known method can be used for the manufacturing method. The gas diffusion electrode can be manufactured more reliably by using the composition for forming a catalyst layer of the present invention. For example, the gas diffusion electrode may be manufactured by applying the composition for forming a catalyst layer onto the gas diffusion layer (or the water-repellent layer of a laminate having a water-repellent layer formed on the gas diffusion layer) and drying it.

[0062] <Fuel Cell Stack> Figure 9 is a schematic diagram showing a preferred embodiment of a fuel cell stack of the present invention. The fuel cell stack 30 shown in Figure 9 has a configuration in which a plurality of unit cells, each of which is the MEA 10 shown in Figure 1, are stacked one on top of the other. The fuel cell stack 30 also has a configuration in which the MEA 10 is disposed between a separator 4 and a separator 5. Gas flow paths are formed in the separator 4 and the separator 5, respectively.

[0063] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0064] (I) Preparation of electrode catalyst to be used in the cathode catalyst layer of the MEA

[0065] (1) Preparation of Pt / C catalyst used in the cathode of the MEA of Example 1 [Pt catalyst particle-supported carbon catalyst "Pt / C catalyst" powder] A Pt / C catalyst powder (Pt loading rate: 49.0 wt %, hereinafter referred to as "Pt / C catalyst A" as needed) in which Pt catalyst particles were supported on carbon black powder was prepared. This Pt / C catalyst A powder was prepared by the following procedure.

[0066] (First Step - Carrier Pretreatment) A commercially available hollow carbon carrier (manufactured by Lion Corporation, trade name "Carbon ECP" (registered trademark) (Ketjenblack EC300J), specific surface area 750 to 800 m) was used. ２ / g} in an aqueous solution (prepared by adding a pH adjuster to ultrapure water) adjusted to pH 9 to 13, and the resulting dispersion was kept at a temperature of 90 to 99°C for about 0.5 hours while stirring (however, the temperature was kept at a state where the dispersion was not boiled).

[0067] The "ultrapure water" used in this first step (carrier pretreatment step) had a resistivity R (the reciprocal of the electrical conductivity measured by the JIS standard test method (JIS K0552)) of 3.0 MΩ cm or more, as expressed by the following formula (2). This "ultrapure water" had a water quality equivalent to or purer than "A3" as specified in JIS K0557 "Water for use in testing water and wastewater." This ultrapure water was produced using ultrapure water production systems "Milli-Q Series" (manufactured by Merck Ltd.) and "Elix UV Series" (manufactured by Nihon Millipore K.K.). R = 1 / ρ (2) In the above general formula (2), R represents the resistivity, and ρ represents the electrical conductivity measured by the JIS standard test method (JIS K0552).

[0068] (First Step - Pt Addition Treatment) A mixed solution was prepared by adding an aqueous solution of water-soluble Pt salt dissolved in ultrapure water to the dispersion obtained through the carrier pretreatment step, and the pH was adjusted to 7 to 12. The mixture was stirred for a predetermined time while maintaining a predetermined temperature of 50°C or higher.

[0069] (First Step - Pt Reduction Treatment) An aqueous solution containing an alkaline water-soluble reducing agent was added to the liquid obtained through the Pt addition treatment step, and the Pt ions in the mixed liquid were reduced to obtain a Pt catalyst particle-supported carbon "Pt / C" powder.

[0070] (First Step - Washing Treatment) Filter paper was used to separate the solid and liquid components in the liquid obtained through the washing treatment step. Next, the solid content remaining on the filter paper (a mixture of Pt / C catalyst and other impurities) was washed using the pure water and pure warm water described above. First, washing with pure water was performed. This washing was repeated until the electrical conductivity of the filtrate after washing was less than 20 μS / cm. Next, washing with pure warm water was performed. This washing was repeated until the electrical conductivity of the filtrate after washing was less than 10 μS / cm.

[0071] (First step - drying step) The solid component (a mixture of Pt / C catalyst and water) on the filter paper obtained after the washing treatment was air-dried in this state. After this air-drying, the solid component on the filter paper was transferred to a porcelain dish and dried in an electric dryer at a predetermined temperature of 60°C or higher for a predetermined time.

[0072] (First Step - Grinding Step) The solid component (Pt / C catalyst) obtained in the drying step was ground using a mixer to obtain a powder of Pt / C catalyst (precursor of Pt / C catalyst A).

[0073] (Step 2) The powder obtained through Step 1 (the precursor powder of Pt / C catalyst A) was placed in a reactor of a flow system, and ammonia gas was passed through the reactor at a concentration of 100% and a pressure of 0.1 MPa while the temperature in the reactor was adjusted to 500°C and maintained at this temperature for 8 hours. Thus, Pt / C catalyst A was obtained. <Measurement of Loading Ratio (ICP Analysis)> The Pt loading ratio (wt%) of this Pt / C catalyst A was measured by the following method. Pt / C catalyst A was immersed in aqua regia to dissolve the metal. Next, the insoluble carbon component was removed from the aqua regia. Next, the aqua regia from which the carbon had been removed was subjected to ICP analysis. As a result of the ICP analysis, the Pt loading ratio of this Pt / C catalyst A was 49.0 wt%.

[0074] (2) Preparation of Pt / C catalyst powder used in the cathode of the MEA of Comparative Example 1 A Pt / C catalyst with a Pt loading rate of 50 wt % manufactured by N.E. CHEMCAT (product name: "SA50BK", hereinafter referred to as "Pt / C catalyst B" as necessary) was prepared as the Pt / C catalyst. The support for this Pt / C catalyst B was a commercially available hollow carbon support {manufactured by Lion Corporation, product name "Carbon ECP" (registered trademark) (Ketjenblack EC300J), specific surface area 750 to 800 m ２ / g} was used.

[0075] (II) Preparation of P / C catalyst used in the anode of the MEAs of Example 1 and Comparative Example 1 The same Pt / C catalyst as Pt / C catalyst B used in the cathode of the MEA of Comparative Example 1 was used as the P / C catalyst for the anode of the MEAs of Example 1 and Comparative Example 1.

[0076] Example 1 An MEA having the same configuration as the MEA 10 shown in FIG. 1 was produced by the following procedure. (1) Production of an Anode Ink for Forming an Anode Catalyst Layer 1.0 g of Pt / C catalyst and ion-exchanged water in an amount eight times the mass of the carbon mass of this catalyst were added to the container of a zirconia ball mill. Zirconia beads were then added and mixed and stirred using a planetary ball mill. Next, ethanol in an amount twice the mass of the ion-exchanged water added to the ball mill was further added to the ball mill. Next, the materials inside the ball mill were mixed again while stirring. After this, 5 wt % Nafion (manufactured by Sigma-Aldric, product name "D521 Nafion") was added to the container of a zirconia ball mill. TM Dispersion Alcohol based: 5 wt% (registered trademark)) was added to achieve an I / C of 0.7, and the mixture was mixed and stirred again. The mixed paste was dispensed into PFA cups (with lids) and rotated overnight on a roll mill. Coating of the cathode catalyst layer ink on the electrolyte membrane: The ink for forming the cathode catalyst layer was loaded into the syringe of a pulse swirl spray applicator (manufactured by Nordson). The ink discharge pressure was set to 13-15 kPa, and the liquid in the syringe was constantly circulated to prevent paste deposition during operation of the spray applicator. The ink was then applied by pulse spray to a polymer electrolyte membrane (manufactured by DuPont under the trade name "Nafion NR212") with an anode on the backside. The application amount was adjusted to achieve a platinum loading of 0.3 mg / cm2. The ink workbench was also heated to 60°C to suppress the solvent evaporation rate and the occurrence of cracks. Through these operations, an anode CCM was obtained.

[0077] (2) Preparation of cathode Ink for forming cathode catalyst layer 0.5 g of Pt / C catalyst and ion-exchanged water with a mass eight times the carbon mass ratio of this catalyst were added to the container of a zirconia ball mill. Next, zirconia beads were added and mixed and stirred using a planetary ball mill. Next, ethanol with a mass four times the mass of the ion-exchanged water added to the ball mill was further added to the ball mill. Next, the materials inside the ball mill were mixed again while stirring. After this, 5 wt% Nafion (manufactured by Sigma-Aldric, product name "D521 Nafion" TMDispersion Alcohol based: 5 wt% (registered trademark)) was added to achieve an I / C of 0.7, and the mixture was mixed and stirred again. The mixed paste was dispensed into PFA cups (with lids) and rotated overnight on a roll mill. Coating of the cathode catalyst layer ink on the electrolyte membrane: The ink for forming the cathode catalyst layer was loaded into the syringe of a pulse swirl spray applicator (Nordson). The ink discharge pressure was set to 13-15 kPa, and the liquid in the syringe was constantly circulated to prevent paste deposition during operation of the spray applicator. The ink was then applied to the backside of the anode-equipped polymer electrolyte membrane (previously prepared anode CCM) using pulse spray. The application amount was adjusted to achieve a platinum loading of 0.1 mg / cm². The ink workbench was also heated to 60°C to suppress the solvent evaporation rate and cracking. A CCM was obtained through the above procedures. This CCM was then dried overnight at approximately 60°C.

[0078] (3) Preparation of MEA The above CCM was sandwiched between two Teflon sheets to form a laminate. This laminate was then placed on a hot press plate and heated to 140°C. Once the plate reached 140°C, a pressure of 2.86 kN was applied and pressed for 3 minutes. After pressing, the Teflon sheets were carefully peeled off to prevent the catalyst layer from peeling off from the polymer electrolyte membrane. This completed the preparation of a CCM. Next, this CCM was placed between two GDLs to form a laminate (MEA). Carbon paper (manufactured by SGL Carbon, product name "SIGRACET 22BB (registered trademark)") was used for the two GDLs.

[0079] Example 2 An MEA was produced under the same conditions and procedures as in Example 1, except that the ammonia treatment conditions in the second step of producing an electrode catalyst were changed to those shown in Table 1.

[0080] Example 3 An MEA was produced under the same conditions and procedures as in Example 1, except for the following changes in the conditions for producing the electrode catalyst. The following nitric acid treatment step was carried out between the first and second steps. The powder obtained after the first step was dispersed in a nitric acid aqueous solution (0.1 mol / L), and the resulting dispersion was stirred and held at 95°C for 2 hours (nitric acid treatment step). Next, after the nitric acid treatment step, the solid and liquid components in the dispersion were separated, and the solid component was washed with ion-exchanged water (washing step). This washing was carried out until the ionic conductivity of the ion-exchanged water discharged after washing the solid component was 10 μS / cm or less. Finally, the solid component obtained after the washing step was filtered and further dried to obtain a powder (drying step).

[0081] Comparative Example 1 An MEA was produced under the same conditions and procedures as in Example 1, except that the ammonia treatment conditions in the second step were not carried out during the production of the electrode catalyst.

[0082] Comparative Example 2 Each MEA was produced under the same conditions and procedures as in Example 1, except that solid carbon (trade name "Denka Black" manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, Ltd., having the same specific surface area as the hollow carbon used in Example 1) was used instead of the hollow carbon used in Example 1.

[0083] <Comparative Example 3> An MEA was produced under the same conditions and procedures as in Example 1, except for the following changes in the manufacturing of the electrode catalyst: - The ammonia treatment conditions of the second step in Example 1 were not performed. - Prior to the first step, the carbon support was subjected to an ammonia treatment under the same conditions as in the second step in Example 1. Next, an MEA was produced under the same conditions and procedures as in the first step in Example 1, except for using the carbon support after the ammonia treatment.

[0084] <Comparative Example 4> An MEA was produced under the same conditions and procedures as in Example 1, except for the following changes in the conditions when producing an electrode catalyst. - The ammonia treatment conditions of the second step in Example 1 were not performed. - Before the first step, the carbon support was subjected to ammonia treatment under the same conditions as in Comparative Example 3, except for the changes made to the conditions shown in Table 2. Next, the first step was carried out under the same conditions and procedures as in the first step in Example 1, except for using the carbon support after the ammonia treatment. - Between the first and second steps, a nitric acid treatment step was carried out under the same conditions as in Example 3. An MEA was produced.

[0085] Comparative Example 5 An MEA was produced under the same conditions and procedures as in Example 1, except for the following changes in the manufacturing of the electrode catalyst: - The ammonia treatment conditions of the second step in Example 1 were not performed. - Prior to the first step, the carbon support was subjected to an ammonia treatment under the same conditions as in Comparative Example 3. Next, the first step was performed under the same conditions and procedures as the first step in Example 1, except that the carbon support after the ammonia treatment was used. - Between the first and second steps, a nitric acid treatment step was performed under the same conditions as in Example 3.

[0086] <Comparative Example 6> An MEA was produced under the same conditions and procedures as in Example 1, except for the following changes in the conditions when producing an electrode catalyst. - The ammonia treatment conditions of the second step in Example 1 were not performed. - Before the first step, the carbon support was subjected to an ammonia treatment under the same conditions as in Comparative Example 3, except for the changes made to the conditions shown in Table 2. Next, the first step was performed under the same conditions and procedures as in the first step in Example 1, except for using the carbon support after the ammonia treatment. - Between the first and second steps, a nitric acid treatment step was performed under the same conditions as in Example 3.

[0087] <Evaluation of Cell Performance> The cell performance of the MEAs of Examples 1 to 3 and Comparative Examples 1 to 6 was evaluated by the following cell performance evaluation method. The MEAs of Examples 1 to 3 and Comparative Examples 1 to 6 were placed in a single fuel cell evaluation device.

[0088] (1) MEA Initial Performance Evaluation Test Next, the power generation reaction was allowed to proceed within each MEA under the following conditions. The single cell (MEA) temperature was set to 80°C. Pure hydrogen or air humidified with saturated steam at 1.0 atmosphere was supplied to the anode. Furthermore, pure oxygen humidified with saturated steam at 80°C at 1.0 atmosphere was supplied to the cathode. The hydrogen and oxygen were adjusted to a stoichiometric ratio of (hydrogen / oxygen) = (1.5 / 2.5). The hydrogen and air were also adjusted to a stoichiometric ratio of (hydrogen / air) = (1.5 / 12.5). The single cells (MEA) were evaluated by controlling the current using an electronic load device attached to the fuel cell single cell evaluation device, and the current-voltage curve (IV curve) obtained by scanning the current value was obtained as data. A graph (not shown) was created by plotting the data from the current-voltage curve with the X axis (current density) on a logarithmic scale, and the current density value (current value per unit area of ​​the electrode) at a voltage of 850 mV was obtained.

[0089] The current density value thus obtained was divided by the platinum weight per unit area of ​​the cathode to calculate the activity per unit weight (mass activity: Mass. Act.) of the platinum contained in the cathode, which was used as an index of the oxygen reduction ability of the catalyst contained in the cathode. The results are shown in Tables 1 and 2. Tables 1 and 2 also show the results of comparing the Mass. Act. values ​​obtained in other Examples and Comparative Examples as relative values ​​(relative ratios) with the Mass. Act. obtained in Comparative Example 1 as the reference (1.0).

[0090] (2) O ２ Gain Measurement Test For the MEAs of Example 1 and Comparative Example 1, air and O were used as the cathode reaction gas. ２ The difference in single cell voltage (IR-free) at each current density point of the IV curve of the above initial performance evaluation test obtained when each of the ２ The gain was measured. ２ For evaluation purposes, the utilization rate of the air was set to five times the utilization rate of the air. The results are shown in Tables 3 and 4.

[0091] (3) MEA Durability Performance Evaluation Test An MEA durability performance evaluation test was conducted for the MEAs of Example 1 and Comparative Example 1. After the initial performance evaluation test, a potential fluctuation treatment was conducted under the conditions adopted in the U.S. DOE's hydrogen and fuel cell project, and then an MEA performance evaluation test was conducted under the same conditions as the initial performance evaluation test. The potential fluctuation treatment conditions were: anode reactant gas: H2, cathode reactant gas: N2, and cathode potential fluctuation conditions: 30,000 cycles of square waves of 0.6 V (held for 3 seconds) - 0.95 V (held for 3 seconds). The mass activity at 850 mV (MA1) measured after the initial performance evaluation test and the mass activity at 850 mV (MA2) measured after the durability performance evaluation test were used to calculate the MA retention rate = 100 × (MA2) / (MA1). The MA retention rate was determined for both the cases where the cathode reactant gas was O2 and the case where air was used. The results are shown in Tables 3 and 4.

[0092] (4) Measurement of ECSA (Electrochemically Effective Surface Area) of Cathode Catalyst For the MEAs of Example 1 and Comparative Example 1, cyclic voltammetry measurements (cell temperature: 40°C, potential sweep rate: 20 mV / sec) were performed on the cathode before the MEA initial performance evaluation test to measure the initial ECSA (ECSA1). Furthermore, cyclic voltammetry measurements (cell temperature: 80°C, potential sweep rate: 20 mV / sec) were also performed after the MEA durability evaluation test to measure the ECSA after the durability evaluation test (ECSA2). Using the two ECSAs, the ECSA retention rate = 100 × (ECSA2) / (ECSA1) was calculated. The results are shown in Tables 3 and 4.

[0093] (5) Measurement of Pt Utilization Rate of Cathode For the MEAs of Example 1 and Comparative Example 1, the theoretical specific surface area of ​​the catalyst particles was calculated using the crystallite diameter measured by XRD of the catalyst particles in the cathode catalyst layer and the measured MSA(CO). Then, using the previously mentioned ECSA1, the Pt utilization rate (catalyst utilization rate) = 100 × (ECSA1) / (theoretical specific surface area) was calculated. The results are shown in Tables 3 and 4.

[0094] FIG. 10 shows current-voltage curves (H2 / Air, initial performance comparison) of MEAs fabricated using the electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 11 shows current-voltage curves (H2 / O2, initial performance comparison) of MEAs fabricated using the electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 12 shows current-voltage curves (H2 / Air, durability comparison) of MEAs fabricated using the electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode. FIG. 13 shows current-voltage curves (H2 / O2, durability comparison) of MEAs fabricated using the electrode catalysts obtained by the manufacturing methods of Example 1 and Comparative Example 1 in the cathode.

[0095] 14 shows a comparison of CV waves before (BOL) the MEA durability performance evaluation test shown in FIG. 12. Furthermore, FIG. 15 shows a comparison of CV waves after (EOL) the MEA durability performance evaluation test shown in FIG. 12. Furthermore, FIG. 16 shows the O of the MEA cathode of Example 1 obtained from the results of FIGS. 10 and 11. ２ Gain and O of the MEA cathode of Comparative Example 1 ２ 17 shows the change in MA (H2 / O2, initial performance evaluation test) of the MEA cathodes of Example 1 and Comparative Example 1 when the humidification conditions are changed.

[0096] In addition, the N of the catalyst of Example 1 is shown in FIG. ２ The results of pore volume distribution measured by gas adsorption method are shown in Fig. 19. Furthermore, the N ２ The results of pore volume distribution measurement by gas adsorption method are shown in Fig. 20. Calculation results of the change (decrease) in pore volume before and after adding the ionomer to the catalysts of Example 1 and Comparative Example 1 are shown in Fig. 20 for the mesopore region with pore diameters of 10 to 50 nm in the pore volume distribution data shown in Fig. 18 and Fig. 19.

[0097] 21 shows a TEM photograph of the MEA cathode catalyst layer according to Example 1 (a mixture of the catalyst of Example 1 and an ionomer). Furthermore, FIG. 22 shows a TEM photograph of the MEA cathode catalyst layer according to Comparative Example 1 (a mixture of the catalyst of Comparative Example 1 and an ionomer). Furthermore, FIG. 23 shows the N of the catalyst of Example 1. ２The results of differential pore volume distribution measurement by gas adsorption method are shown in Fig. 24. Furthermore, the N ２ The results of differential pore volume distribution measurement by gas adsorption method are shown below.

[0098] 25 shows the results of calculating the pore volumes before and after adding an ionomer to the catalysts of Example 1 and Comparative Example 1 for the nanopore region with pore diameters of 2 to 5 nm in the differential pore volume distribution data shown in Figures 23 and 24. Also, Figure 26 shows a TEM photograph of the MEA cathode catalyst layer of Example 1 (a mixture of the catalyst of Example 1 and the ionomer). Furthermore, Figure 27 shows a TEM photograph of the MEA cathode catalyst layer of Comparative Example 1 (a mixture of the catalyst of Comparative Example 1 and the ionomer).

[0099] The results shown in Tables 1 and 2 reveal that the MEAs of Examples 1 to 3 have superior catalytic activity compared to the MEAs of Comparative Examples 1 to 6. Furthermore, the results of the MEAs of Examples 1 to 3 and Comparative Examples 3 to 6 confirm the effectiveness of the production method of the present invention, in which the ammonia treatment is carried out after catalyst particles are supported on the carrier, compared to the conventional production method described in Non-Patent Documents 1 and 2, in which the ammonia treatment of the carrier is carried out first. Furthermore, the results of the MEAs of Examples 1, 2, and 3 confirm the effectiveness of the nitric acid treatment. The results of the MEAs of Examples 1 and 2 confirm that the ammonia pressure in the ammonia treatment is preferably at normal pressure, which is lower than the pressurized state.

[0100] Furthermore, from the results of Example 1 and Comparative Example 1 shown in Figures 18 to 27, it was found that Example 1, compared to Comparative Example 1, sufficiently prevented clogging by the ionomer in pores with a pore diameter in the range of 2 to 5 nm (nanopores within primary particles) of the hollow carbon (see particularly Figures 23 to 27). Furthermore, it was found that Example 1, compared to Comparative Example 1, sufficiently prevented clogging by the ionomer in pores with a pore diameter in the range of approximately 10 nm to approximately 50 nm (primary pores within agglomerates, etc.) (see particularly Figures 20 to 22). As shown in Figure 20, Example 1 showed a slightly larger decrease in pore volume after the addition of ammonia than Comparative Example 1. However, as can be seen from the results in Figures 18 and 19, the pore volumes after the addition of ionomer were approximately the same for Example 1 and Comparative Example 1. In other words, it was found that within the pore diameter range of approximately 10 nm to approximately 50 nm, the reactive gas path and the ion conduction path were appropriately formed for both Example 1 and Comparative Example 1.

[0101] It was found that in Example 1, the degree of blockage by the ionomer of pores (secondary pores between agglomerates, etc.) in the hollow carbon having a pore diameter in the range of about 80 nm or more (particularly 100 nm or more) was greatly reduced compared to Comparative Example 1 (see FIGS. 18 and 19). It was also found that in Example 1, the ionomer was dispersed thinly and in a good state on the carbon surface compared to Comparative Example 1. And, due to this influence, it was found that Example 1 had a catalyst utilization rate that was about twice as high as Comparative Example 1 when used in the catalyst layer of an MEA.

[0102] 17, it was found that Example 1 was particularly superior to Comparative Example 1 when the MEA was humidified at a relative humidity of 50% to 100%. When the MEA was humidified at a relative humidity of less than 50%, Example 1 and Comparative Example 1 showed substantially the same performance. From the above results, it was clear that the MEA according to Example 1 had superior catalytic activity and durability compared to the MEA according to Comparative Example 1.

[0103] According to the present invention, it is possible to produce an electrode catalyst that exhibits excellent catalytic activity and excellent durability. Furthermore, according to the present invention, it is possible to produce a GDE and a CCM that have excellent polarization characteristics and durability, and an MEA that has excellent power generation performance and durability. Therefore, the present invention can be applied not only to the electrical equipment industry, such as fuel cells, fuel cell vehicles, and portable mobile devices, but also to ENE-FARMs, cogeneration systems, and the like, and contributes to the development of the energy industry and environmental technologies.

[0104] REFERENCE SIGNS LIST 1...cathode, 1A, 1B, 1C...gas diffusion electrode (GDE), 1c...catalyst layer (CL), 1m...water-repellent layer (MPL), 1gd...gas diffusion layer (GDL), 2...anode, 2c...catalyst layer (CL), 2m...water-repellent layer (MPL), 2gd...gas diffusion layer (GDL), 3...polymer electrolyte membrane (PEM), 4, 5...separator 10, 11...membrane-electrode assembly (MEA), 12, 13...membrane-catalyst layer assembly (CCM) 20...Pt / C catalyst, 22...support, 23...catalyst particle, 30...fuel cell stack, P22...nanopores in support.

Claims

1. A method for producing a catalyst for an electrode, comprising: a conductive hollow carbon carrier having nanopores with a pore diameter of 1 to 20 nm and a BET specific surface area (nitrogen adsorption specific surface area) of 700 to 900 m ２ / g, and a plurality of catalyst particles containing Pt supported on the carrier, the method comprising: a first step of using the carrier and a raw material of the catalyst particles to prepare a powder in which the catalyst particles are supported on the carrier; a second step of accommodating the powder obtained through the first step in a reactor of a flow system, and while flowing ammonia gas in the reaction vessel under conditions of a concentration of 10 to 100% and a pressure of 0.1 MPa to 0.5 MPa, adjusting the temperature in the reaction vessel to 500°C or higher and lower than the decomposition temperature of ammonia and holding for 5 to 10 hours to cause a chemical reaction between the powder and the ammonia gas.

2. Between the first step and the second step, a nitric acid treatment step of dispersing the powder obtained through the first step in an aqueous nitric acid solution with a concentration of 0.01 to 1.5 mol / L, and holding the resulting dispersion at 60 to 95°C for 1 to 3 hours while stirring; after the nitric acid treatment step, a washing step of separating the solid component and the liquid component in the dispersion and washing the solid component with ion-exchanged water one or more times; and a drying step of filtering the solid component obtained through the washing step and then drying it to obtain the powder. The method for manufacturing a catalyst for an electrode according to claim 1 further includes these steps.

3. The method for manufacturing a catalyst for an electrode according to claim 1 or 2, wherein the hollow carbon carrier is Ketjen EC300J.

4. The method for manufacturing a catalyst for an electrode according to claim 3, wherein the catalyst particles are catalyst particles composed of Pt (zero valence).

5. The method for manufacturing a catalyst for an electrode according to claim 4, wherein the catalyst particles further contain Pt oxide.

6. The method for manufacturing a catalyst for an electrode according to claim 3, wherein the catalyst particles are catalyst particles composed of a PtNi alloy.

7. The method for manufacturing a catalyst for an electrode according to claim 3, wherein the catalyst particles have a core-shell structure having a core particle and a shell containing Pt covering at least a part of the surface of the core particle.

8. A method for manufacturing a gas diffusion electrode having a catalyst layer and a gas diffusion layer for supplying a reaction gas to the catalyst layer, including a step of preparing an ink for forming a catalyst layer containing at least a catalyst for an electrode manufactured by the method for manufacturing a catalyst for an electrode according to any one of claims 1 to 7, a solid polymer electrolyte, and a dispersion medium.

9. A method for manufacturing a membrane / electrode assembly (MEA) having an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, wherein the gas diffusion electrode manufactured by the method for manufacturing a gas diffusion electrode according to claim 8 is used for at least one of the anode and the cathode.