Catalyst for fuel cell and method for producing the same

Abstract

A catalyst for fuel cells, which is a catalyst for fuel cells comprising a carbon powder support and catalyst particles supported on the carbon powder support, the catalyst particles being Pt alloy particles, the catalyst for fuel cells having 0.65 mmol / g or more of hydrophilic groups, and, when 0.5 g of the catalyst for fuel cells is immersed in 30 mL of a 0.5 mol / L aqueous sulfuric acid solution and left for 100 hours at room temperature with stirring, the amount of Pt elution per 1 g of the catalyst for fuel cells is 0.625 mg or less.

Description

Technical Field

[0001] This invention relates to catalysts for fuel cells and methods for manufacturing the same. Background Technology

[0002] Fuel cells are highly anticipated as the next generation of batteries. In particular, solid polymer fuel cells have advantages such as low operating temperature, short start-up time, and small size, and have begun to be used in fields such as power sources for automobiles.

[0003] Solid polymer fuel cells have a structure in which a cathode (air electrode), a solid polymer electrolyte membrane, and an anode (fuel electrode) are stacked in sequence. In this type of solid polymer fuel cell, when oxygen or air is supplied to the cathode and fuel such as hydrogen is supplied to the anode, oxidation and reduction reactions occur at each electrode, generating electricity.

[0004] In fuel cells, the electrodes contain a fuel cell catalyst used to promote the aforementioned oxidation and reduction reactions. Catalysts with a structure in which catalyst particles are supported on a carbon powder support are widely used as fuel cell catalysts. Pt particles and Pt alloy particles are known as catalyst particles for fuel cells.

[0005] For example, Patent Document 1 describes a method for manufacturing a Pt-supported catalyst for reducing Pt precursor compounds in the liquid phase in the presence of support particles. Additionally, Patent Document 2 describes the use of Pt alloy particles as catalyst particles to improve the cathode activity of a solid polymer fuel cell.

[0006] Furthermore, in patent documents 3 and 4, in order to improve the activity (especially the initial activity) of catalysts for fuel cells, it is proposed to introduce hydrophilic groups into the carbon powder support on which Pt is supported. It is believed that the introduction of these hydrophilic groups not only improves the initial activity of the catalyst for fuel cells, but also helps to maintain the catalyst performance when the catalyst for fuel cells is in a low humidification state.

[0007] On the other hand, Patent Document 5 reports a correlation between the durability of Pt-supported catalysts and the solubility of Pt.

[0008] Existing technical documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 08-084930

[0010] Patent Document 2: Japanese Patent Application Publication No. 2003-142112

[0011] Patent Document 3: Japanese Patent Application Publication No. 2011-003492

[0012] Patent Document 4: Japanese Patent Application Publication No. 2012-124001

[0013] Patent Document 5: International Publication No. 2018 / 194007 Summary of the Invention

[0014] The inventors have discovered that in fuel cell catalysts using Pt alloy particles as catalyst particles, if hydrophilic groups are introduced into the fuel cell catalyst according to the teachings of Patent Documents 3 and 4, Pt dissolves in the solvent used during electrode fabrication, causing a decrease in catalyst activity. This phenomenon is considered an obstacle to research on improving the activity of fuel cell catalysts using Pt alloy particles as catalyst particles.

[0015] Therefore, the purpose of this invention is to provide a catalyst for fuel cells and a method for manufacturing the same, which, when using Pt alloy particles as catalyst particles, can achieve both improved catalyst activity and catalyst performance under low humidification conditions, while maintaining high catalyst activity for a long time.

[0016] The present invention is described below.

[0017] Method 1

[0018] A catalyst for a fuel cell comprises a carbon powder support and catalyst particles supported on the carbon powder support.

[0019] The catalyst particles are Pt alloy particles.

[0020] The catalyst for the fuel cell has hydrophilic groups of 0.65 mmol / g or more, and,

[0021] When 0.5g of the fuel cell catalyst is impregnated in 30mL of 0.5mol / L sulfuric acid aqueous solution and kept at room temperature for 100 hours with stirring, the Pt dissolution amount per 1g of the fuel cell catalyst is less than 0.625mg.

[0022] Method 2

[0023] According to the fuel cell catalyst of Method 1, the hydrophilic group is an acidic group.

[0024] Method 3

[0025] According to method 1 or 2, the Pt dissolution amount per 1g of the fuel cell catalyst is less than 0.300mg.

[0026] Method 4

[0027] The catalyst for a fuel cell according to any one of methods 1 to 3, wherein the Pt alloy particles contain:

[0028] Pt, and

[0029] Selected from one or more metals including Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Hf, Ru, Ir, Pd, Os, and Rh.

[0030] Alloy particles.

[0031] Method 5

[0032] The catalyst for a fuel cell according to any one of methods 1 to 4 has an average particle size of 2 nm or more and 10 nm or less.

[0033] Method 6

[0034] An electrode for a fuel cell comprises a fuel cell catalyst according to any one of embodiments 1 to 5.

[0035] Method 7

[0036] The electrode described in Method 6 is a cathode.

[0037] Method 8

[0038] A fuel cell comprising the electrodes described in embodiment 6 or 7.

[0039] Method 9

[0040] A method for manufacturing a catalyst for a fuel cell according to any one of methods 1 to 5, comprising the following steps:

[0041] The catalyst particles are supported on the carbon powder carrier to prepare carbon powder with catalyst particles.

[0042] By contacting the carbon powder supporting the catalyst particles with an oxidant, hydrophilic groups are imparted to the carbon powder supporting the catalyst particles to prepare a catalyst precursor for fuel cells; and

[0043] The catalyst precursor for fuel cells is brought into contact with a reducing agent to prepare a catalyst for fuel cells.

[0044] Method 10

[0045] According to the method of method 9, the oxidant used to contact the carbon powder carrying the catalyst particles is one or more oxidants selected from sulfuric acid, nitric acid, phosphorous acid, potassium permanganate, hydrogen peroxide, chloric acid and chromic acid.

[0046] Method 11

[0047] According to the method of method 9 or 10, the reducing agent used to contact the catalyst precursor for the fuel cell is one or more reducing agents selected from alcohols, carboxylic acids and aldehydes.

[0048] According to the present invention, a catalyst for fuel cells and a method for manufacturing the same are provided. The catalyst for fuel cells has both improved catalyst activity and catalyst performance under low humidification conditions, and maintains high catalyst activity for a long time. Attached Figure Description

[0049] Figure 1 This is a graph showing the relationship between the amount of hydrophilic groups in the catalyst particles obtained in the examples and comparative examples and the catalyst capability under low humidification (performance voltage under low humidification).

[0050] Figure 2 This is a graph showing the relationship between the amount of hydrophilic groups in the catalyst particles obtained in the examples and comparative examples and the amount of Pt dissolved. Detailed Implementation

[0051] Catalysts for Fuel Cells

[0052] The catalyst for fuel cells of the present invention,

[0053] It is a fuel cell catalyst comprising a carbon powder support and catalyst particles supported on the carbon powder support.

[0054] The catalyst particles are Pt alloy particles.

[0055] The catalyst for fuel cells has hydrophilic groups of 0.65 mmol / g or higher, and...

[0056] When 0.5g of the fuel cell catalyst is impregnated in 30mL of 0.5mol / L sulfuric acid aqueous solution and kept at room temperature for 100 hours with stirring, the Pt dissolution amount per 1g of the fuel cell catalyst is less than 0.625mg.

[0057] In the fuel cell catalyst of the present invention, Pt alloy particles are used as catalyst particles. By using Pt alloy particles as catalyst particles, the activity of the fuel cell catalyst can be improved compared with the case where unalloyed Pt particles are used.

[0058] Furthermore, the fuel cell catalyst of the present invention has hydrophilic groups of 0.65 mmol / g or more. By having hydrophilic groups of 0.65 mmol / g or more in the fuel cell catalyst, appropriate hydrophilicity can be imparted to the fuel cell catalyst, thereby improving the catalyst performance under low humidification conditions.

[0059] Furthermore, when 0.5 g of the fuel cell catalyst of the present invention is impregnated in 30 mL of a 0.5 mol / L sulfuric acid aqueous solution and kept at room temperature for 100 hours with stirring, the Pt dissolution amount per 1 g of the fuel cell catalyst is less than 0.625 mg. By achieving a Pt dissolution amount of less than 0.625 mg per 1 g of fuel cell catalyst under the above conditions, the catalytic activity of the obtained electrode can be suppressed by inhibiting the dissolution of Pt into the solvent used in electrode fabrication.

[0060] In the fuel cell catalyst of the present invention, the desired objective of the present invention is achieved through the mechanism of action described above.

[0061] Based on common knowledge in the field, it is believed that increasing the amount of hydrophilic groups in the catalyst for fuel cells can improve the catalyst performance under low humidification conditions, but it also increases the amount of Pt leaching during electrode manufacturing, thus failing to achieve the desired catalyst performance.

[0062] However, the fuel cell catalyst of the present invention achieves a balance between a high amount of hydrophilic groups and a low Pt dissolution rate. This is believed to be due to the fact that the fuel cell catalyst of the present invention is manufactured by a process using a reducing agent after the hydrophilic groups have been incorporated. The reason for the lower Pt dissolution rate through this reducing agent treatment process is not entirely clear, but the inventors speculate as follows.

[0063] That is, it is believed that during electrode manufacturing, the Pt dissolved from the catalyst used in fuel cells is contained in extremely small, microparticle-sized catalyst particles. It is speculated that these microparticle-sized catalyst particles, through a reducing agent treatment process, move on a carbon powder support and are absorbed by other catalyst particles of suitable size, thus becoming non-dissolving. However, this invention is not bound by any specific theory.

[0064] <Carbon Powder Carrier>

[0065] The carbon powder support in the fuel cell catalyst of the present invention can be, for example, carbon black, graphite, carbon fiber, activated carbon, amorphous carbon, nanomaterials, etc. Nanomaterials include carbon nanotubes, graphene, fullerenes, etc.

[0066] Carbon black is particularly suitable as the carbon powder carrier in the fuel cell catalyst of the present invention. There is no particular limitation on the type of carbon black used; any one of Ketjen black, acetylene black, furnace black, or gas black may be used.

[0067] The specific surface area of ​​the carbon powder carrier, as the BET specific surface area determined by nitrogen adsorption, is preferably 50 m². 2 / g or more and 1500m 2 / g or less, preferably 200m 2 / g or more and 1000m2 Below / g, 500m is further preferred. 2 / g or more and 1000m 2 Below / g. Specific surface area is 50m². 2 Carbon powder supports with a density of 1 g or higher have the advantage of being able to support catalyst particles in a highly dispersed manner. On the other hand, a specific surface area of ​​1500 m²... 2 Carbon powder supports with a porosity of less than 1 g have appropriate micropore content, which can improve the oxygen and proton transport efficiency in the reaction of fuel cell electrodes, thus improving catalytic performance.

[0068] The carbon powder carrier in this invention has hydrophilic groups on its surface. This will be discussed later.

[0069] <Catalyst particles>

[0070] The catalyst particles are supported on a carbon powder carrier.

[0071] The catalyst particles in the fuel cell catalyst of the present invention are Pt alloy particles. By using Pt alloy particles as catalyst particles, the activity of the fuel cell catalyst of the present invention is increased.

[0072] Pt alloy particles may contain:

[0073] Pt, and

[0074] Selected from one or more metals including Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Hf, Ru, Ir, Pd, Os, and Rh.

[0075] The alloy particles. This Pt alloy has the advantage of high catalytic activity for oxygen reduction.

[0076] Typically, Pt alloy particles can be Pt-Fe alloys, Pt-Co alloys, or Pt-Ni alloys.

[0077] The percentage of Pt atoms relative to the total number of metal atoms in the Pt alloy particles is used to define the proportion of Pt atoms in the Pt alloy particles. The Pt atom percentage in the Pt alloy particles can be 50 mol% or more, 60 mol% or more, 70 mol% or more, 75 mol% or more, 80 mol% or more, or 85 mol% or more, and can be less than 99 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, or 75 mol% or less. Pt alloy particles with a Pt atom percentage of 50 mol% or more have the advantage of suppressing the performance degradation of fuel cells caused by base metal dissolution. Pt alloy particles with a Pt atom percentage of 99 mol% or less can enjoy the advantages of introducing other metals into Pt, namely, increased catalytic activity for oxygen reduction.

[0078] The average particle size of the catalyst particles is preferably 2 nm or more and 10 nm or less, more preferably 2 nm or more and 7 nm or less, and even more preferably 3 nm or more and 5 nm or less. With an average particle size of 2 nm or more, catalyst particle aggregation can be suppressed during use in fuel cells, maintaining the high catalyst activity desired by this invention for a longer period. On the other hand, with an average particle size of 10 nm or less, the specific surface area of ​​the catalyst particles increases, and the number of catalyst active sites exposed on the surface of the catalyst particles increases, thus improving catalyst activity.

[0079] The average particle size of the catalyst particles mentioned above is obtained from the microcrystalline particle size distribution by XRD.

[0080] As the proportion of the mass of catalyst particles to the total mass of the fuel cell catalyst, the loading of catalyst particles in the fuel cell catalyst of the present invention can be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, and can be 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less. If the loading of catalyst particles is 10% by mass or more, good catalyst activity is exhibited. If the loading of catalyst particles is 60% by mass or less, the carbon powder support with hydrophilic groups is exposed on the catalyst surface with a significant area, ensuring the hydrophilicity of the fuel cell catalyst, thus improving catalyst activity, especially under low humidification conditions.

[0081] <Optional Ingredients>

[0082] As described above, the fuel cell catalyst of the present invention comprises a carbon powder support and catalyst particles supported on the carbon powder support. However, the fuel cell catalyst of the present invention may also contain optional components other than the carbon powder support and catalyst particles.

[0083] <Hydrophilic group>

[0084] The fuel cell catalyst of the present invention has hydrophilic groups of 0.65 mmol / g or more. By having hydrophilic groups of 0.65 mmol / g or more, the fuel cell catalyst can be endowed with appropriate hydrophilicity, thereby improving catalyst performance under low humidification conditions. On the other hand, in order to ensure the chemical stability of the fuel cell catalyst and maintain its activity over a long period of time, the amount of hydrophilic groups in the fuel cell catalyst can be 1.20 mmol / g or less.

[0085] The amount of hydrophilic groups in the catalyst for fuel cells may be 0.67 mmol / g or more, 0.70 mmol / g or more, 0.72 mmol / g or more, 0.75 mmol / g or more, 0.77 mmol / g or more, or 0.80 mmol / g or more, and may be 1.10 mmol / g or less, 1.00 mmol / g or less, 0.95 mmol / g or less, 0.90 mmol / g or less, or 0.85 mmol / g or less.

[0086] The hydrophilic groups of the catalyst for fuel cells of the present invention may be acidic groups. The hydrophilic groups as acidic groups can be quantified by, for example, a titration method.

[0087] In the catalyst for fuel cells of the present invention, hydrophilic groups may exist, for example, on the exposed surface of the carbon powder support (the portion of the surface of the carbon powder support not loaded with catalyst particles), on the surface of catalyst particles, or on both. However, from the viewpoint of improving the hydrophilicity of the catalyst for fuel cells of the present invention while ensuring catalyst activity, it is presumed that the hydrophilic groups may exist on the exposed surface of the carbon powder support, and preferably do not exist on the surface of the catalyst particles.

[0088] <Pt elution amount>

[0089] When 0.5 g of the catalyst for fuel cells of the present invention is impregnated in 30 mL of 0.5 mol / L aqueous sulfuric acid solution and maintained at room temperature for 100 hours under stirring, the Pt elution amount per 1 g of the catalyst for fuel cells is 0.625 mg or less. In the catalyst for fuel cells of the present invention, by setting the Pt elution amount under the above conditions to 0.625 mg or less per 1 g of the catalyst for fuel cells, the elution of Pt into the solvent used when producing the electrode can be suppressed, and the catalytic activity of the obtained electrode can be ensured.

[0090] The Pt elution amount per 1 g of the catalyst for fuel cells under the above conditions may be 0.500 mg or less, 0.400 mg or less, 0.375 mg or less, 0.300 mg or less, 0.250 mg or less, 0.200 mg or less, or 0.125 mg or less, and may also be 0.000 mg.

[0091] Specifically, the Pt elution amount is measured according to the procedure shown in the examples described below.

[0092] 《Method for Manufacturing Catalyst for Fuel Cells》

[0093] The catalyst for fuel cells of the present invention can be manufactured, for example, by a method comprising the following steps:

[0094] Loading catalyst particles on a carbon powder support to prepare catalyst particle-loaded carbon powder (loading step);

[0095] By contacting carbon powder supporting catalyst particles with an oxidant, hydrophilic groups are imparted to the carbon powder supporting catalyst particles to prepare a catalyst precursor for fuel cells (hydrophilic group imparting process); and

[0096] The catalyst precursor for fuel cells is brought into contact with a reducing agent to prepare the catalyst for fuel cells (reduction process).

[0097] The following describes each step of the method for manufacturing the catalyst for fuel cells according to the present invention.

[0098] (Loading process)

[0099] In the loading process, catalyst particles are loaded onto a carbon powder carrier.

[0100] The carbon powder support used can be appropriately selected based on the desired carbon powder support in the fuel cell catalyst. Examples of carbon powder supports include carbon black, graphite, carbon fiber, activated carbon, amorphous carbon, and nanomaterials.

[0101] Catalyst particles, which are Pt alloy particles, can be supported on the surface of a carbon powder support, for example, by any of the following methods.

[0102] (1) A method of sequentially reducing the load of Pt and alloy metal (Method 1):

[0103] In a suitable solvent, in the presence of a carbon powder support, the Pt precursor is reduced to obtain Pt-supported carbon powder with Pt particles supported on the carbon powder support.

[0104] In a suitable solvent, in the presence of Pt-supported carbon powder, the alloy metal precursor is reduced to obtain Pt-alloy metal-supported carbon powder with alloy metal particles supported on the Pt-supported carbon powder; and

[0105] Carbon powder carrying Pt-alloy metal is heated to alloy Pt with the alloy metal, resulting in carbon powder carrying Pt alloy particles and catalyst particles on a carbon powder carrier.

[0106] (2) Other methods for sequentially reducing the loaded Pt and alloy metal (Method 2):

[0107] In a suitable solvent, in the presence of a carbon powder support, the Pt precursor is reduced to obtain Pt-supported carbon powder with Pt particles supported on the carbon powder support.

[0108] In a suitable solvent, in the presence of Pt-supported carbon powder, an alloy metal precursor is contacted with a neutralizing agent to obtain carbon powder with a high-valence alloy metal supported on Pt-supported carbon powder, or carbon powder with a Pt-high-valence alloy metal supported; and

[0109] Heating carbon powder supporting Pt-high valence alloy metal reduces the high valence alloy metal while alloying Pt with the alloy metal, resulting in carbon powder with Pt alloy particles and catalyst particles supported on a carbon powder carrier.

[0110] (3) Method for simultaneously reducing and supporting Pt and alloy metal (Method 3):

[0111] In a suitable solvent, in the presence of a carbon powder support, the Pt precursor and the alloy metal precursor are reduced to obtain a carbon powder supported on a carbon powder support containing Pt particles and alloy metal particles, or a Pt-alloy metal supported powder.

[0112] Carbon powder carrying Pt-alloy metal is heated to alloy Pt with the alloy metal, resulting in carbon powder carrying Pt alloy particles and catalyst particles on a carbon powder carrier.

[0113] (4) Other methods for simultaneously reducing and supporting Pt and alloy metals (Method 4):

[0114] In a suitable solvent, in the presence of a carbon powder carrier, the Pt precursor and the alloy metal precursor are contacted with a neutralizing agent to obtain carbon powder supported on a carbon powder carrier, which contains high-valence Pt and high-valence alloy metal, or high-valence Pt-high-valence alloy metal.

[0115] Carbon powder supporting high-valence Pt and high-valence alloy metal is heated to reduce the high-valence Pt and high-valence alloy metal, while simultaneously alloying Pt with the alloy metal, resulting in carbon powder with Pt alloy particles and catalyst particles supported on a carbon powder carrier.

[0116] In this specification, "alloy metal" refers to metals other than Pt in the Pt alloy that constitutes the catalyst particles. Furthermore, "high valence" for Pt and alloy metals means that the valence of these metal atoms is 1 or higher.

[0117] The following sections will describe methods 1 through 4 for carrying out the loading process.

[0118] (1) A method for sequentially reducing the loading of Pt and alloy metals (Method 1)

[0119] In Method 1, firstly, in a suitable solvent and in the presence of a carbon powder support, the Pt precursor is reduced to obtain Pt-supported carbon powder.

[0120] Pt precursors can be appropriately selected from solvent-soluble Pt compounds. For example, appropriate Pt precursors can be selected from PtCl2, PtCl4, PtBr2, PtS, Pt(CN)2, Pt(NO2)2(NH3)2 (dinitrodiammineplatinum), etc.

[0121] The solvent can be selected from those capable of dissolving the Pt precursor used. For example, hydrochloric acid can be used when the Pt precursor is PtCl2, aqueous hydrobromic acid solution can be used when it is PtBr2, aqueous nitric acid solution can be used when it is dinitrodiamineplatinum, and water can be used when it is PtCl4, PtS, or Pt(CN)2.

[0122] The reduction of the Pt precursor can be carried out using a suitable reducing agent. Examples of reducing agents include alcohols, carboxylic acids, aldehydes, sodium borohydride, and hydrazine. Examples of alcohols include ethanol, examples of carboxylic acids include acetic acid, and examples of aldehydes include acetaldehyde. The reduction can be carried out under an inert atmosphere at a temperature above 60°C and below 100°C for a time of 0.5 hours to 8 hours.

[0123] In this way, Pt-loaded carbon powder with Pt particles loaded on a carbon powder carrier is obtained.

[0124] Next, in a suitable solvent, in the presence of the obtained Pt-supported carbon powder, the alloy metal precursor is reduced to obtain Pt-supported alloy metal carbon powder.

[0125] Alloy metal precursors can be appropriately selected based on the type of alloy metal desired in the fuel cell catalyst.

[0126] The alloy metal precursor can be appropriately selected from solvent-soluble compounds containing the desired alloy metal. For example, it can be hydroxides, chlorides, sulfides, nitrates, sulfates, acetates, etc., of the desired alloy metal.

[0127] The solvent can be selected from those capable of dissolving the alloy metal precursor used. For example, water can be used as a solvent.

[0128] The reduction of alloy metal precursors can be carried out using appropriate reducing agents.

[0129] Reducing agents can be, for example, alcohols, carboxylic acids, aldehydes, sodium borohydride, hydrazine, etc. Examples of alcohols include ethanol and ethylene glycol; examples of carboxylic acids include acetic acid; and examples of aldehydes include acetaldehyde.

[0130] The reduction can be carried out at a temperature above room temperature and below 100°C for a time of more than 0.5 hours and less than 40 hours.

[0131] Thus, carbon powder loaded with Pt alloy metal is obtained, on which Pt-loaded carbon powder is loaded with alloy metal.

[0132] Next, the obtained carbon powder supporting Pt alloy metal is heated to alloy Pt with the alloy metal, thereby obtaining carbon powder supporting Pt alloy particles (carbon powder supporting catalyst particles). Heating can be carried out under an inert atmosphere at a maximum temperature of 600°C or higher and 1200°C or lower. The duration of maintaining the maximum temperature can be 0 hours or higher and 10 hours or lower.

[0133] As described above, carbon powder containing Pt alloy particles and catalyst particles supported on a carbon powder support is obtained.

[0134] (2) Other methods for sequentially reducing the loaded Pt and alloy metal (Method 2):

[0135] In Method 2, the Pt precursor is reduced in a suitable solvent in the presence of a carbon powder support to obtain Pt-supported carbon powder with Pt particles loaded on the carbon powder support. This step can be performed in the same manner as in Method 1.

[0136] Next, in a suitable solvent, in the presence of Pt-loaded carbon powder, the alloy metal precursor is contacted with a neutralizing agent to obtain carbon powder with high-valence alloy metal loaded on Pt-loaded carbon powder, or Pt-high-valence alloy metal loaded carbon powder.

[0137] The alloy metal precursor used herein may be appropriately selected from the substances exemplified as alloy metal precursors in the description of Method 1.

[0138] Neutralizing agents can be, for example, hydroxides, carbonates, phosphates, borates, ammonia, etc. Examples of hydroxides include sodium hydroxide, examples of carbonates include sodium carbonate, examples of phosphates include sodium phosphate, and examples of borates include sodium borate.

[0139] Loading of high-valence alloy metals with neutralizing agents can be carried out at temperatures above room temperature and below 100°C for a period of 0.5 hours to 40 hours.

[0140] In this way, carbon powder with high-valence alloy metal supported on Pt-supported carbon powder can be obtained.

[0141] Next, the obtained carbon powder supported on Pt-high-valence alloy metal is heated to reduce the high-valence alloy metal while alloying Pt with the alloy metal, thereby obtaining carbon powder supported on Pt alloy particles (carbon powder supported on catalyst particles). Heating can be carried out under an inert atmosphere at a maximum temperature of 600°C or higher but below 1200°C. The duration of maintaining the maximum temperature can be 0 hours or more but less than 10 hours.

[0142] Furthermore, in the reduction of high-valence alloy metals by heating, carbon in the carbon powder carrier is considered to play a role as a reducing agent.

[0143] As described above, carbon powder with Pt alloy particles supported on a carbon powder carrier and catalyst particles supported are obtained.

[0144] (3) Method for simultaneously reducing and supporting Pt and alloy metals (Method 3)

[0145] In Method 3, firstly, in a suitable solvent and in the presence of a carbon powder support, the Pt precursor and the alloy metal precursor are reduced to obtain carbon powder supported on Pt-alloy metal.

[0146] The Pt precursor and alloy metal precursor used herein can be appropriately selected from the substances exemplified in the description of Method 1 above, depending on the desired composition of the fuel cell catalyst.

[0147] The reduction of Pt precursors and alloy metal precursors can be carried out using appropriate reducing agents.

[0148] Reducing agents can be, for example, alcohols, carboxylic acids, aldehydes, sodium borohydride, hydrazine, etc. Examples of alcohols include ethanol and ethylene glycol; examples of carboxylic acids include acetic acid; and examples of aldehydes include acetaldehyde.

[0149] The reduction can be carried out at a temperature above room temperature and below 100°C for a time of more than 0.5 hours and less than 40 hours.

[0150] Thus, carbon powder with Pt alloy metal supported on carbon powder is obtained. By heating the obtained carbon powder with Pt alloy metal, Pt is alloyed with the alloy metal to obtain carbon powder with Pt alloy particles (carbon powder with catalyst particles supported). The heating conditions can be directly applied to the heating description in method (1).

[0151] By using the above method (3), carbon powder with Pt alloy particles supported on a carbon powder carrier and catalyst particles can also be obtained.

[0152] (4) Other methods for simultaneously reducing and supporting Pt and alloy metals (Method 4):

[0153] In Method 4, firstly, in a suitable solvent and in the presence of a carbon powder carrier, the Pt precursor and the alloy metal precursor are contacted with a neutralizing agent to obtain carbon powder supported on a carbon powder carrier containing high-valence Pt and high-valence alloy metal, or high-valence Pt-high-valence alloy metal.

[0154] The Pt precursor and alloy metal precursor used herein can be appropriately selected from the substances exemplified in the description of Method 1 above, depending on the desired composition of the fuel cell catalyst.

[0155] Neutralizing agents can be, for example, hydroxides, carbonates, phosphates, borates, ammonia, etc. Examples of hydroxides include sodium hydroxide, examples of carbonates include sodium carbonate, examples of phosphates include sodium phosphate, and examples of borates include sodium borate.

[0156] Loading of high-valence Pt and high-valence alloy metals by neutralizing agents can be carried out at temperatures above room temperature and below 100°C for a period of 0.5 hours to 40 hours.

[0157] Thus, carbon powder with high-valence Pt and high-valence alloy metal supported on carbon powder is obtained, or carbon powder with high-valence Pt-high-valence alloy metal supported on carbon powder. The obtained carbon powder with high-valence Pt-high-valence alloy metal is heated, and while reducing the high-valence Pt and high-valence alloy metal, Pt is alloyed with the alloy metal, thereby obtaining carbon powder with Pt alloy particles (carbon powder with catalyst particles supported). The heating conditions can be directly applied to the heating description in method (1).

[0158] Furthermore, in the reduction of high-valence Pt and high-valence alloy metals by heating, carbon in the carbon powder carrier is considered to act as a reducing agent.

[0159] Through the above method (4), carbon powder with Pt alloy particles supported on a carbon powder carrier and catalyst particles can also be obtained.

[0160] (Hydrophilic group imparting process)

[0161] Next, in the hydrophilic group imparting process, the carbon powder of the obtained catalyst-supported particles is brought into contact with an oxidant to impart hydrophilic groups to the carbon powder of the catalyst-supported particles, thereby preparing a catalyst precursor for fuel cells.

[0162] This process can be carried out in a suitable solvent. For example, the solvent could be water with its pH appropriately adjusted.

[0163] Oxidizing agents used to impart hydrophilic groups can be selected from sulfuric acid, nitric acid, phosphorous acid, potassium permanganate, hydrogen peroxide, chloric acid, chromic acid, etc.

[0164] In the process of imparting hydrophilic groups, heat treatment may be performed during or after contact between the carbon powder carrying the catalyst particles and the oxidant. The heat treatment conditions may be, for example, at a temperature of 60°C or higher and 110°C or lower, for example, for a time of 6 hours or higher and 100 hours or lower.

[0165] This hydrophilic group-imparting process yields a fuel cell catalyst precursor in which hydrophilic groups are imparted to carbon powder supporting catalyst particles. It is believed that hydrophilic groups can also be imparted to the catalyst particles during the hydrophilic group-imparting process. However, it is assumed that the hydrophilic groups imparted to the catalyst particles are removed in the subsequent reduction process.

[0166] (Restoration process)

[0167] In the reduction process, a catalyst precursor for fuel cells is brought into contact with a reducing agent to prepare a catalyst for fuel cells. In this reduction process, it is desirable to adjust the degree of reduction so that hydrophilic groups on the catalyst particles are reduced and removed, but the hydrophilic groups on the carbon powder support are not removed.

[0168] Therefore, the reducing agent used in the reduction process can be a relatively weak reducing agent, such as alcohols like ethanol, carboxylic acids like acetic acid, aldehydes like acetaldehyde, etc.

[0169] This process can be carried out in a suitable solvent. For example, the solvent could be water with its pH appropriately adjusted.

[0170] In the reduction process, at least one of the following can be accompanied by heat treatment: during and after contact between the fuel cell catalyst precursor and the reducing agent. This heat treatment can be carried out at a temperature above room temperature and below 100°C for a duration of 0.5 hours to 48 hours.

[0171] The fuel cell catalyst of the present invention can be prepared by the above method or by a method obtained by those skilled in the art with appropriate modifications to the above method.

[0172] "electrode"

[0173] In another aspect, the present invention relates to the electrode of a fuel cell containing the catalyst of the present invention.

[0174] The electrode contains the fuel cell catalyst of the present invention, and preferably also contains an ionomer.

[0175] As an ionomer, commercially available products such as Nafion (registered trademark) and Aquivion (registered trademark) can be used.

[0176] The catalyst layer contains the fuel cell catalyst of the present invention, and preferably also contains an ionomer. In addition, it may contain optional components such as a binder.

[0177] When the electrode of the fuel cell of the present invention is used as the cathode of the fuel cell, it can achieve the desired purpose of the present invention, and is therefore preferred.

[0178] Fuel Cells

[0179] In another aspect, the present invention relates to a fuel cell comprising the aforementioned fuel cell electrodes.

[0180] The fuel cell of the present invention can be a solid polymer fuel cell.

[0181] Solid fuel cells can, for example, have a structure in which a cathode, a solid polymer electrolyte membrane, and an anode are stacked in sequence, and the cathode can be an electrode containing the fuel cell catalyst of the present invention.

[0182] The solid polymer electrolyte membrane and anode in this solid fuel cell can be well-known solid polymer electrolyte membranes and anodes, respectively.

[0183] The solid fuel cell of the present invention may have an air channel or an oxygen channel on the cathode side and a fuel channel on the anode side.

[0184] The solid fuel cell of the present invention can be manufactured using known methods, except that it uses an electrode containing the fuel cell catalyst of the present invention as the cathode.

[0185] Example

[0186] Example 1

[0187] (1) Loading process (preparation of carbon particles loaded with PtCo alloy)

[0188] 100 parts by weight of commercially available carbon powder (manufactured by Lion Specialty Chemicals Co., Ltd., carbon black, trade name "Ketjen Black") were dispersed in a 0.1 mol / L aqueous nitric acid solution. Then, 42.9 parts by weight (219.9 mmol) of dinitrodiamineplatinum nitric acid solution (based on Pt conversion) were added. Next, 1200 parts by weight of ethanol as a reducing agent were added, and the mixture was stirred for 15 minutes. The mixture was then heated and stirred at 90°C for 2 hours, thereby precipitating Pt particles onto the carbon powder to form Pt-supported carbon particles. The solid components were filtered off and dried to recover the Pt-supported carbon particles. The Pt content in these Pt-supported carbon particles was 30% by weight.

[0189] 142.9 parts by mass of Pt-supported carbon particles were dispersed in pure water, and a cobalt nitrate aqueous solution was added to achieve a final Pt / Co ratio of 7:1 (molar ratio) in the catalyst particles. Then, 4 parts by mass of sodium borohydride as a reducing agent were added, and the mixture was stirred overnight, thereby causing Co particles to precipitate on the Pt-supported carbon particles. The solid component was filtered off and dried in an air-cooled dryer at 80°C for 15 hours to obtain PtCo-supported carbon particles.

[0190] The obtained PtCo-loaded carbon particles were heated at 900°C for 1 hour under an argon atmosphere to obtain PtCo alloy-loaded carbon particles.

[0191] (2) Hydrophilic group imparting process (hydrophilization treatment of carbon particles supporting PtCo alloy)

[0192] The carbon particles supported on PtCo alloy obtained above were added to a 0.5 mol / L nitric acid aqueous solution and stirred at 90°C for 21 hours to perform hydrophilization treatment. Then, the solid components were filtered off and dried in an air dryer at 80°C for 15 hours to obtain carbon particles supported on hydrophilized PtCo alloy (fuel cell catalyst precursor).

[0193] (3) Reduction process (reduction treatment of carbon particles loaded with hydrophilic PtCo alloy)

[0194] The carbon particles supported on the hydrophilic PtCo alloy obtained above were added to an aqueous solution containing 0.1 mol / L nitric acid and 10% ethanol by mass, and heated and stirred at the boiling point (91-92°C) for 2 hours for reduction treatment. The solid components were then filtered off and dried in an air-cooled dryer at 80°C for 15 hours to obtain the catalyst particles of Example 1. These catalyst particles are catalyst particles composed of PtCo alloy particles supported on carbon black. The molar ratio of Pt to Co in these catalyst particles is 7:1.

[0195] Example 2

[0196] In the "(1) loading process", the amount of cobalt nitrate aqueous solution used is adjusted so that the Pt / Co ratio in the final catalyst particles reaches 3:1 (molar ratio). Otherwise, the catalyst particles of Example 2 are obtained in the same way as in Example 1.

[0197] Comparing Examples 1 and 2

[0198] For the carbon particles supported on hydrophilic PtCo alloy obtained in the same manner as in Examples 1 and 2, the "(3) reduction process" was not performed, and each carbon particle supported on hydrophilic PtCo alloy was directly used as the catalyst particles in Comparative Examples 1 and 2.

[0199] Comparative Example 3

[0200] In the "(1) Supporting process", no aqueous solution of cobalt nitrate was added, and no Co reduction treatment using sodium borohydride was performed. Otherwise, the catalyst particles of Comparative Example 3 were obtained in the same manner as Comparative Example 1. The catalyst particles are particles in which Pt particles are supported on carbon black.

[0201] Comparing Examples 4 and 5

[0202] By changing the conditions of "(2) hydrophilic group imparting process" to the conditions shown in Table 1, catalyst particles of Comparative Examples 4 and 5 were obtained in the same manner as Comparative Example 1.

[0203] Evaluation of Catalysts

[0204] (1) Identification of hydrophilic groups and quantification of the amount of hydrophilic groups

[0205] For the catalyst particles obtained in each embodiment and comparative example, the amount of hydrophilic groups in the catalyst particles was quantified by acid-base titration analysis based on the Boehm method.

[0206] (2) Determination of catalyst particle size

[0207] XRD analysis was performed on the catalyst particles obtained in each example and comparative example. The half-width of the peaks appearing in the range of 2θ = 65 to 73° was substituted into the Scherer formula to calculate the particle size.

[0208] (3) Determination of Pt dissolution

[0209] Each of the catalyst particles obtained in the examples and comparative examples was impregnated in 30 mL of 0.5 mol / L sulfuric acid aqueous solution and kept at room temperature for 100 hours. Then, 5 mL of the filtrate obtained by filtering out the catalyst particles was prepared, transferred to a volumetric flask, and made up to 50 mL. The amount of Pt contained in the diluted solution was determined by inductively coupled plasma (ICP) analysis, and the amount of Pt dissolved per 1 g of catalyst particles was calculated.

[0210] (5) Fabrication of a single cell for performance evaluation

[0211] The catalyst particles obtained in the various examples and comparative examples, along with Nafion (manufactured by Sigma-Aldrich) as an ionomer, were dispersed in a mixed solvent consisting of ethanol and water to obtain a dispersion. This dispersion was coated onto one side of a Teflon (registered trademark) sheet and then dried to form a catalyst layer (cathode) on the sheet, thereby obtaining a laminate for cathode transfer.

[0212] Alternatively, instead of the aforementioned catalyst particles, Ketjen black loaded with 30% by mass of Pt is used to form a catalyst layer (anode) on the sheet in the same manner as the cathode, thereby obtaining a laminate for anode transfer.

[0213] The cathode transfer laminate and anode transfer laminate obtained above are stacked with the catalyst layer forming surfaces facing each other, separated by a polymer electrolyte membrane. The cathode and anode are then transferred onto both sides of the polymer electrolyte membrane via hot pressing. After peeling off the sheet, diffusion layers are formed on both sides of the catalyst layer laminate, thereby manufacturing a single cell for performance evaluation.

[0214] (6) Evaluation of catalyst performance

[0215] The performance evaluation single cell obtained in "Preparation of a single cell for performance evaluation" was installed in a fuel cell evaluation system manufactured by Toyo Technica Co., Ltd. Under conditions of a single cell temperature of 80°C and a relative humidity of 50%-RH at both electrodes, the current value was increased from 0.01 A / cm². 2 Change to 2.0 A / cm 2 The voltage of a single cell was measured at various current values.

[0216] The current at this time is 1.0 A / cm. 2 The single-cell voltage at 0.9V was used as the performance voltage under low humidification, serving as an indicator of the catalyst's ability under low humidification. Additionally, using the current and voltage values ​​at this point, a Tafel plot-based analysis was performed. The current value at a single-cell voltage of 0.9V was divided by the catalyst mass to obtain the catalyst mass-activity current, serving as an indicator of catalyst mass activity.

[0217] The results are shown in Table 1. Additionally, Figure 1 This is a graph with the amount of hydrophilic groups in the catalyst particles on the horizontal axis and the performance voltage at low humidification on the vertical axis. Furthermore, Figure 2 This is a graph with the amount of hydrophilic groups in the catalyst particles on the horizontal axis and the amount of Pt dissolved from the catalyst particles on the vertical axis.

[0218]

[0219] Figure 1 It is a coordinate graph with the amount of hydrophilic groups in the catalyst particles as the horizontal axis and the performance voltage at low humidification as the vertical axis.

[0220] Refer to Table 1 and Figure 1The study verified that when the amount of hydrophilic groups in the catalyst particles is above 0.65 mmol / g-cat, the performance voltage is high under low humidification, and the performance is improved under low humidification. However, for catalyst particles showing a high amount of hydrophilic groups above 0.65 mmol / g-cat, there are concerns that the amount of Pt dissolution may increase, leading to a decrease in the mass activity of the catalyst.

[0221] Figure 2 It is a coordinate graph with the amount of hydrophilic groups in the catalyst particles as the horizontal axis and the amount of Pt dissolved from the catalyst particles as the vertical axis.

[0222] Refer to Table 1 and Figure 2 The catalyst particles of Examples 1 and 2, which meet the requirements of this invention, have extremely low Pt dissolution despite having a high amount of hydrophilic groups (over 0.65 mmol / g-cat), and high catalyst mass activity can be expected.

[0223] Furthermore, Table 1 verifies that the catalyst particles of Examples 1 and 2 exhibit improved performance under low humidification and high catalyst activity.

[0224] The above content verifies that when using the catalyst particles of Examples 1 and 2 that meet the requirements of this invention, both performance under low humidification and catalyst mass activity can be achieved.

Claims

1. A catalyst for a fuel cell, comprising a carbon powder support and catalyst particles supported on the carbon powder support. The catalyst particles are Pt alloy particles. The catalyst for the fuel cell is manufactured by a process in which hydrophilic groups are imparted to carbon powder supporting catalyst particles, followed by contact with a reducing agent. The catalyst for the fuel cell has hydrophilic groups of 0.65 mmol / g or more, and, When 0.5g of the fuel cell catalyst is impregnated in 30mL of 0.5mol / L sulfuric acid aqueous solution and kept at room temperature for 100 hours with stirring, the Pt dissolution amount per 1g of the fuel cell catalyst is less than 0.300mg.

2. The catalyst for fuel cells according to claim 1, wherein the hydrophilic group is an acidic group.

3. The catalyst for fuel cells according to claim 1 or 2, wherein the Pt alloy particles contain: Pt, and Selected from one or more metals including Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Hf, Ru, Ir, Pd, Os, and Rh. alloy particles.

4. The catalyst for fuel cells according to any one of claims 1 to 3, wherein the average particle size of the catalyst particles is 2 nm or more and 10 nm or less.

5. An electrode for a fuel cell comprising the fuel cell catalyst according to any one of claims 1 to 4.

6. The electrode according to claim 5, wherein it is a cathode.

7. A fuel cell comprising the electrode as described in claim 5 or 6.

8. A method for manufacturing a catalyst for a fuel cell according to any one of claims 1 to 4, comprising the following steps: The catalyst particles are supported on the carbon powder carrier to prepare carbon powder with catalyst particles. By contacting the carbon powder supporting the catalyst particles with an oxidant, hydrophilic groups are imparted to the carbon powder supporting the catalyst particles to prepare a catalyst precursor for fuel cells; and The catalyst precursor for fuel cells is brought into contact with a reducing agent to prepare a catalyst for fuel cells.

9. The method according to claim 8, wherein the oxidant used to contact the carbon powder supporting the catalyst particles is one or more oxidants selected from sulfuric acid, nitric acid, phosphorous acid, potassium permanganate, hydrogen peroxide, chloric acid and chromic acid.

10. The method according to claim 8 or 9, wherein the reducing agent used to contact the catalyst precursor for the fuel cell is one or more reducing agents selected from alcohols, carboxylic acids and aldehydes.

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