JP2004152489A - Catalyst electrode for fuel cell, fuel cell, catalyst carrier particle for fuel cell, and manufacturing method of catalyst electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst electrode for a fuel cell having high usability of a catalyst, and a fuel cell using the electrode. <P>SOLUTION: A carbon nanohorn aggregate 401 is used as a carbon material for use in a catalyst layer of a catalyst carrier carbon particle. A solution of a metallic salt and the aggregate 401 are mixed. By adding a reducing agent into the mixture and stirring and mixing it, a catalyst metal 405 is carried on a surface of the aggregate 401. Then, by performing a reducing-treatment at a low temperature, a particle diameter of the catalyst metal 405 is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst electrode for a fuel cell, a fuel cell, catalyst-carrying particles for a fuel cell, and a method for producing a catalyst electrode for a fuel cell.
[0002]
[Prior art]
A fuel cell is composed of a fuel electrode and an oxidant electrode, and an electrolyte provided therebetween. Fuel is supplied to the fuel electrode and an oxidant is supplied to the oxidant electrode to generate power by an electrochemical reaction. When hydrogen is supplied to the fuel electrode and oxygen is supplied to the oxidant electrode, the electrochemical reaction occurring at each electrode is:
H₂  → 2H⁺  + 2e⁻
And at the oxidant electrode,
1 / 2O₂  + 2H⁺  + 2e⁻  → H₂O
It is. For example, in the case of a battery using a solid electrolyte membrane such as a perfluorosulfonic acid membrane as an electrolyte, 1 A / cm at normal temperature and normal pressure is obtained by the above reaction.²The above high output can be obtained. In order to realize this high output, both electrodes are composed of a mixture of carbon particles carrying a catalytic substance and a solid polymer electrolyte.
[0003]
As described above, the fuel cell using hydrogen as a fuel has been described. In recent years, research and development of a fuel cell using an organic liquid fuel such as methanol have been actively performed. Fuel cells that use organic liquid fuel include those that reform organic liquid fuel into hydrogen gas and use it as fuel, and those that do not reform organic liquid fuel, such as direct methanol fuel cells. A fuel cell directly supplying the fuel electrode is known (Patent Document 1).
[0004]
[Patent Document 1]
JP-A-11-3724
[0005]
In order to improve the characteristics of the fuel cell, it is necessary to increase the surface area of the catalyst substance to increase the catalytic activity at the catalyst electrode. For that purpose, it is necessary to reduce the particle diameter of the catalyst particles and to uniformly disperse them. In conventional catalyst electrodes for fuel cells, as a method of supporting a catalyst substance on carbon particles, a solution prepared by dissolving a catalyst metal salt is made, and after the catalyst substance on a colloid is supported on the carbon particles, reduction is performed. The method of processing was used. This reduction treatment is generally performed in a hydrogen atmosphere at a temperature of 400 ° C. or higher. However, when a reduction treatment is performed at approximately 400 ° C. using a commonly used carbon material such as acetylene black, the average particle size of the catalyst substance is reduced. It was enlarged to about 7 to 10 nm, and aggregation of the catalyst particles occurred. As a result, there has been a problem that the surface area of the catalyst substance becomes small and the catalytic activity at the catalyst electrode is insufficient.
[0006]
[Problems to be solved by the invention]
In view of the above circumstances, an object of the present invention is to provide a catalyst electrode for a fuel cell having a large surface area of a catalyst substance supported on the surface of carbon particles and having high catalytic activity, and a fuel cell using the same. Another object of the present invention is to provide a catalyst electrode for a fuel cell having high catalytic activity, in which a catalyst substance is supported on carbon particles in a favorable dispersed state, and a fuel cell using the same. Still another object of the present invention is to provide a catalyst-carrying particle for a fuel cell having high catalytic activity, in which a catalyst substance having a small particle size is supported in a good dispersion state, and a method for producing a catalyst electrode for a fuel cell using the same. Is to do.
[0007]
[Means for Solving the Problems]
According to the present invention, there is provided a catalyst electrode for a fuel cell including carbon particles supporting a solid polymer electrolyte and a catalyst substance, wherein the carbon particles are carbon nanohorn aggregates in which carbon nanohorns are aggregated in a spherical shape. And a catalyst electrode for a fuel cell, wherein the catalyst material has an average particle size of 5 nm or less.
[0008]
In the catalyst electrode for a fuel cell according to the present invention, since the particle size of the catalyst substance is as extremely small as 5 nm or less, the specific surface area of the catalyst is large and the catalyst efficiency is high. Therefore, high reactivity can be obtained with a small amount of catalyst. Further, since the carbon nanohorn aggregate is used for the carbon particles, the surface area of the carbon particles is extremely large, and the amount of the catalyst substance carried is large. Furthermore, the contact area between the catalyst substance and the solid polymer electrolyte is large due to the three-dimensional structure unique to the carbon nanohorn aggregate. Further, hydrogen ions generated by the catalytic reaction are efficiently transmitted. Therefore, the catalyst electrode for a fuel cell according to the present invention has an extremely large area used for a catalytic reaction, and its output can be improved when used in a fuel cell.
[0009]
In the above-mentioned catalyst electrode for a fuel cell, the average particle diameter of the catalyst substance is set to 5 nm or less, but is more preferably set to 2 nm or less. By doing so, the specific surface area of the catalyst substance can be further reduced. Therefore, the catalyst efficiency when used in a fuel cell is increased, and the output of the fuel cell can be further improved. The lower limit is not particularly limited, but may be, for example, 0.1 nm or more, preferably 0.5 nm or more. By doing so, an electrode having good catalytic efficiency can be obtained with good production stability.
[0010]
In the catalyst electrode for a fuel cell according to the present invention, the catalyst substance may have a substantially spherical shape. Here, “substantially spherical” means that the average value of the ratio of the major axis / minor axis of the catalyst particles is 3 or less. By doing so, the uniformity of the shape of the catalyst substance can be improved, and the specific surface area of the catalyst substance can be further increased. Further, the catalyst substance may be uniformly dispersed on the carbon nanohorn aggregate. Here, “uniformly dispersed” refers to a state in which the formation of agglomerates and secondary particles is suppressed, and the catalyst substance is supported on the surface of the carbon nanohorn aggregate in a favorable dispersed state. By doing so, the surface area used for the catalytic reaction can be further increased. Therefore, when used in a fuel cell, its output can be improved.
[0011]
In the catalyst electrode for a fuel cell according to the present invention, the catalyst substance may be gold or a platinum group metal or an alloy thereof. By doing so, the activity of the catalyst substance can be further improved.
[0012]
In the fuel cell catalyst electrode of the present invention, the carbon nanohorn aggregate may be configured as a single-layer carbon nanohorn aggregate. By doing so, the conductivity of hydrogen ions at the catalyst electrode can be improved. Further, the carbon nanohorn aggregate may be configured as a single-layer graphite nanohorn aggregate composed of a single-layer graphite nanohorn. By doing so, the electric conductivity of the carbon particles is improved, so that the performance of the catalyst electrode can be further improved. Further, the carbon nanohorn aggregate may be supported on carbon fibers, carbon nanofibers, or carbon nanotubes. This makes it possible to suitably adjust the fine structure in the catalyst electrode.
[0013]
According to the present invention, there is provided a fuel cell including a fuel electrode, an oxidizer electrode, and a solid electrolyte membrane sandwiched between the fuel electrode and the oxidizer electrode, wherein the fuel electrode or the oxidizer electrode includes the fuel electrode. A fuel cell is provided, which is a catalyst electrode for a cell. In the fuel cell according to the present invention, since the above-described fuel cell catalyst electrode is used for the fuel electrode or the oxidant electrode, the efficiency of the catalytic reaction at the catalyst electrode is high. Therefore, the output characteristics of the fuel cell can be improved.
[0014]
According to the present invention, a step of mixing a metal salt solution, a carbon nanohorn aggregate, and a reducing agent to support a metal on the surface of the carbon nanohorn aggregate, and after the step of supporting the metal, at least 10 ° C. A step of reducing the metal at a temperature of 100 ° C. or lower. According to the method for producing catalyst-carrying carbon particles for a fuel cell according to the present invention, using a carbon nanohorn aggregate, and by reducing the reduction temperature, the average particle diameter of the catalyst material supported on the carbon nanohorn aggregate surface Can be made as extremely small as 5 nm or less, for example, 1 nm or more and 2 nm or less. Further, the dispersibility of the catalyst substance can be improved.
[0015]
According to the present invention, a step of producing a fuel cell catalyst-carrying particle by the method for producing a fuel cell catalyst-carrying particle, and a coating liquid containing the fuel cell catalyst-carrying particle and a particle containing a solid polymer electrolyte Forming a catalyst layer by applying the catalyst layer on a substrate. According to the method for producing a catalyst electrode for a fuel cell according to the present invention, in the step of forming a catalyst layer, the above-mentioned catalyst-supporting carbon particles for a fuel cell are used, so that a catalyst electrode having high catalytic reaction efficiency can be stably produced. It is.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a specific configuration of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a sectional view schematically showing an example of the structure of the fuel cell according to the present embodiment. The catalyst electrode-solid electrolyte membrane assembly 101 includes a fuel electrode 102, an oxidant electrode 108, and a solid electrolyte membrane 114. The fuel electrode 102 and the oxidant electrode 108 are collectively called a catalyst electrode. The fuel electrode 102 includes a base 104 and a catalyst layer 106. The oxidant electrode 108 includes a base 110 and a catalyst layer 112. One or more catalyst electrode-solid electrolyte membrane assemblies 101 are electrically connected via a fuel electrode side separator 120 and an oxidant electrode side separator 122.
[0018]
In the fuel cell 100 configured as described above, the fuel 124 is supplied to the fuel electrode 102 of each catalyst electrode-solid electrolyte membrane assembly 101 via the fuel electrode separator 120. Further, an oxidizing agent 126 such as air or oxygen is supplied to the oxidizing electrode 108 of each catalyst electrode-solid electrolyte membrane assembly 101 via an oxidizing electrode-side separator 122.
[0019]
The fuel electrode 102 and the oxidant electrode 108 include carbon particles carrying a catalyst and fine particles of a solid polymer electrolyte, and have a structure in which the catalyst layer 106 and the catalyst layer 112 are formed on the bases 104 and 110. The substrate surface may be subjected to a water-repellent treatment.
[0020]
As the bases 104 and 110, a porous base such as carbon paper, a carbon molded body, a carbon sintered body, a sintered metal, or a foamed metal can be used. Further, a water repellent such as polytetrafluoroethylene can be used for the water repellent treatment of the substrate.
[0021]
FIG. 2 is a diagram illustrating a state where the catalyst metal 405 is supported on the surface of the carbon nanohorn aggregate 401. In the fuel cell 100 of FIG. 1, the catalyst-supporting carbon particles and the solid polymer electrolyte 403 having the configuration shown in FIG. 2 are used for the catalyst layer 106 or the catalyst layer 112.
[0022]
As shown in FIG. 2, a carbon nanohorn aggregate 401 in which carbon nanohorns, which are new carbon isotopes consisting only of carbon atoms, are aggregated in a spherical shape is used as the carbon particles carrying the catalyst. Here, the term “spherical” does not necessarily mean a true sphere, but also includes a variety of other shapes such as an elliptical shape and a donut shape.
[0023]
The carbon nanohorn aggregate 401 is a tubular body in which one end of a carbon nanotube has a conical shape, and a plurality of carbon nanohorns are formed around the tube by van der Waals force acting between the conical portions, and the conical portions have a corner (horn). Are assembled in such a way as to protrude from the surface as shown. The diameter of the carbon nanohorn aggregate 401 is 120 nm or less, typically 10 nm or more and 100 nm or less. Each of the carbon nanohorns constituting the carbon nanohorn aggregate 401 has a tube diameter of about 2 nm, a typical length of 30 nm or more and 50 nm or less, and the conical portion has an average inclination angle of about 20 ° in the axial cross section. In order to adopt such a unique structure, the carbon nanohorn aggregate 401 has a packing structure with a very large specific surface area. The carbon nanohorn aggregate 401 is usually at room temperature, 1.01325 × 10⁵It can be manufactured by a laser ablation method using a solid carbon simple substance such as graphite as a target in an inert gas atmosphere of Pa. Further, the size of the pores between the spherical particles of the carbon nanohorn aggregate 401 can be controlled by the production conditions by the laser ablation method, the oxidation treatment after the production, and the like. At the center of the carbon nanohorn aggregate 401, carbon nanohorns may be chemically bonded to each other, or carbon nanotubes may be rounded like a kemari. However, the shape is limited by the structure of the center. is not. In addition, it is conceivable that the center is hollow.
[0024]
Further, the carbon nanohorn constituting the carbon nanohorn assembly 401 may have a closed end at the tip or may not be closed. Further, the apex of the conical shape at one end may end in a rounded shape. When the carbon nanohorns constituting the carbon nanohorn aggregate 401 end at a conical vertex at one end, the vertex of the conical shape is radially aggregated with the rounded vertex outward. Further, the carbon nanohorn may be partially incomplete and have fine pores. Further, the carbon nanohorn aggregate 401 can include carbon nanotubes.
[0025]
The carbon nanohorn aggregate 401 can be a single-layer carbon nanohorn. By doing so, the hydrogen ion conductivity in the carbon nanohorn aggregate 401 can be improved. Further, the carbon nanohorn aggregate 401 can be a single-layer carbon nanohorn aggregate made of a single-layer graphite nanohorn. By doing so, the electrical conductivity of the carbon nanohorn assembly 401 is improved, and when used for a catalyst electrode for a fuel cell, its performance can be improved.
[0026]
As the catalyst metal 405, for example, the following substances can be used. Examples of the catalyst for the fuel electrode 102 include platinum, rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold, silver, nickel, cobalt, lithium, lanthanum, strontium, and yttrium. These may be used alone or in combination of two or more. Can be used. On the other hand, as the catalyst for the oxidant electrode 108, the same catalyst as the catalyst for the fuel electrode 102 can be used, and the above-described exemplary substances can be used. The catalysts of the fuel electrode 102 and the oxidant electrode 108 may be the same or different.
[0027]
The solid polymer electrolyte 403 electrically connects the carbon nanohorn aggregate 401 supporting the catalyst metal 405 and the solid electrolyte membrane 114 on the surface of the catalyst electrode, and allows the fuel 124 to reach the surface of the catalyst metal 405. It has a role and requires hydrogen ion conductivity. Furthermore, when an organic liquid fuel such as methanol is supplied to the fuel electrode 102, fuel permeability is required, and oxygen permeability is required at the oxidant electrode 108. In order to satisfy such requirements, a material excellent in hydrogen ion conductivity and organic liquid fuel permeability such as methanol is preferably used as the solid polymer electrolyte 403. Specifically, an organic polymer having a polar group such as a strong acid group such as a sulfone group or a phosphoric acid group or a weak acid group such as a carboxyl group is preferably used. Examples of such organic polymers include sulfone group-containing perfluorocarbons (such as Nafion (manufactured by DuPont) and Aciplex (manufactured by Asahi Kasei Corporation));
Carboxyl group-containing perfluorocarbon (such as Flemion S membrane (manufactured by Asahi Glass Co., Ltd.));
Copolymers such as a polystyrenesulfonic acid copolymer, a polyvinylsulfonic acid copolymer, a crosslinked alkylsulfonic acid derivative, a fluorine-containing polymer composed of a fluororesin skeleton and sulfonic acid;
A copolymer obtained by copolymerizing acrylamides such as acrylamide-2-methylpropanesulfonic acid and acrylates such as n-butyl methacrylate;
And the like.
[0028]
In addition, as the polymer to be bonded to the polar group, other polybenzimidazole derivatives, polybenzoxazole derivatives, polyethyleneimine cross-linked, polysilamine derivatives, amine-substituted polystyrene such as polydiethylaminoethyl polystyrene, diethylaminoethyl polymethacrylate, etc. Resins having nitrogen or hydroxyl groups, such as nitrogen-substituted polyacrylates;
Hydroxyl-containing polyacrylic resin represented by silanol-containing polysiloxane and hydroxyethyl polymethyl acrylate;
Hydroxyl-containing polystyrene resin represented by parahydroxy polystyrene;
Etc. can also be used.
[0029]
Further, a crosslinkable substituent, for example, a vinyl group, an epoxy group, an acrylic group, a methacryl group, a cinnamoyl group, a methylol group, an azide group, or a naphthoquinonediazide group may be appropriately introduced into the polymer. .
[0030]
The solid polymer electrolyte 403 in the fuel electrode 102 and the oxidant electrode 108 may be the same or different.
[0031]
In FIG. 2, the solid polymer electrolyte 403 is illustrated as being provided only on a part of the carbon nanohorn aggregate 401, but is actually formed on the entire carbon nanohorn aggregate 401.
[0032]
In the fuel cell 100, the solid electrolyte membrane 114 has a role to separate the fuel electrode 102 and the oxidant electrode 108 and to move hydrogen ions and water molecules between the two. For this reason, the solid electrolyte membrane 114 is preferably a membrane having high conductivity of hydrogen ions. Further, it is preferable that the material is chemically stable and has high mechanical strength. As a material constituting the solid electrolyte membrane 114, an organic polymer having a polar group such as a strong acid group such as a sulfone group, a phosphate group, a phosphone group, or a phosphine group, or a weak acid group such as a carboxyl group is preferably used. Such organic polymers include aromatic-containing polymers such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole;
Copolymers such as a polystyrene sulfonic acid copolymer, a polyvinyl sulfonic acid copolymer, a cross-linked alkyl sulfonic acid derivative, a fluorine-containing polymer comprising a fluororesin skeleton and sulfonic acid;
A copolymer obtained by copolymerizing acrylamides such as acrylamide-2-methylpropanesulfonic acid and acrylates such as n-butyl methacrylate;
Sulfone group-containing perfluorocarbon (Nafion (manufactured by DuPont: registered trademark), Aciplex (manufactured by Asahi Kasei Corporation));
Carboxyl group-containing perfluorocarbon (Flemion S membrane (trade name, manufactured by Asahi Glass Co., Ltd.));
And the like. Among these, when aromatic-containing polymers such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole are selected, the permeation of organic liquid fuel can be suppressed, and the battery by crossover can be suppressed. A decrease in efficiency can be suppressed.
[0033]
As the fuel 124 supplied to the fuel cell 100, a gaseous fuel or a liquid fuel can be used. When a gaseous fuel is used, for example, hydrogen can be used. When a liquid fuel is used, the organic compounds contained in the fuel 124 include, for example, alcohols such as methanol, ethanol and propanol, ethers such as dimethyl ether, cycloparaffins such as cyclohexane, hydroxyl group, carboxyl group and amino group. And cycloparaffins having a hydrophilic group such as an amide group, and mono- or di-substituted cycloparaffins. Here, cycloparaffins refer to cycloparaffins and substituted products thereof, and those other than aromatic compounds are used.
[0034]
Next, a method for manufacturing the fuel cell 100 will be described. The method of manufacturing the fuel cell 100 is not particularly limited, but can be manufactured, for example, as follows.
[0035]
First, a method for manufacturing a catalyst electrode will be described. The catalyst metal 405 can be supported on the carbon nanohorn aggregate 401 by a generally used impregnation method. This is a method in which a colloidal catalyst substance obtained by dissolving or dispersing a metal salt of the catalyst metal 405 in a solvent is supported on the carbon nanohorn aggregate 401 and then subjected to a reduction treatment. By performing this reduction treatment at a low temperature of 100 ° C. or less including room temperature, for example, 10 ° C. or more and 100 ° C. or less, the average particle diameter of the catalyst metal 405 supported on the surface of the carbon nanohorn aggregate 401 is 5 nm or less, for example. Very small spherical particles of 1 nm or more and 2 nm or less can be obtained. Further, the catalyst metal 405 can be uniformly dispersed on the carbon nanohorn particles. Next, the catalyst-supported carbon particles and the particles of the solid polymer electrolyte 403 are dispersed in a solvent to form a paste, which is then applied to the substrates 104 and 110 and dried to obtain a catalyst electrode.
[0036]
The particle size of the solid polymer electrolyte 403 in the catalyst paste is, for example, 0.05 μm or more and 1 μm or less. The carbon nanohorn aggregate 401 and the particles of the solid polymer electrolyte 403 are used in a weight ratio of, for example, 2: 1 to 40: 1. The weight ratio between water and solute in the paste is, for example, about 1: 2 to 10: 1. Note that the carbon nanohorn aggregate 401 may be supported on carbon fibers, carbon nanofibers, carbon nanotubes, or the like by heat treatment or the like. By doing so, the fine structure of the catalyst layers 106 and 112 can be adjusted arbitrarily.
[0037]
The method of applying the paste to the bases 104 and 110 is not particularly limited, and for example, a method such as brush coating, spray coating, and screen printing can be used. The paste is applied with a thickness of, for example, about 1 μm or more and 2 mm or less. After applying the paste, the paste is heated at a heating temperature and for a heating time according to the fluororesin to be used, whereby the fuel electrode 102 or the oxidant electrode 108 is produced. The heating temperature and the heating time are appropriately selected depending on the material used. For example, the heating temperature can be 100 ° C. or more and 250 ° C. or less, and the heating time can be 30 seconds or more and 30 minutes or less.
[0038]
The fuel cell 100 is manufactured as follows using the catalyst electrode manufactured by the above method.
[0039]
The solid electrolyte membrane 114 can be manufactured by employing an appropriate method depending on a material to be used. For example, when the solid electrolyte membrane 114 is composed of an organic polymer material, it is obtained by casting and drying a liquid obtained by dissolving or dispersing the organic polymer material in a solvent on a peelable sheet such as polytetrafluoroethylene. be able to.
[0040]
The obtained solid electrolyte membrane 114 is sandwiched between the fuel electrode 102 and the oxidant electrode 108 and hot-pressed to produce the catalyst electrode-solid electrolyte membrane assembly 101. At this time, the surfaces of the fuel electrode 102 and the oxidizer electrode 108 where the catalyst layers 106 and 112 are provided are in contact with the solid electrolyte membrane 114. The conditions for hot pressing are selected according to the material. However, when the solid electrolyte membrane 114 and the solid polymer electrolyte on the surface of the catalyst electrode are composed of an organic polymer having a softening point or a glass transition point, these polymers are used. Above the softening temperature or the glass transition temperature. Specifically, for example, the temperature is 100 ° C. or more and 250 ° C. or less, and the pressure is 1 kg / cm.²More than 100kg / cm²Hereinafter, the time is from 10 seconds to 300 seconds.
[0041]
In the fuel cell 100 obtained as described above, the carbon nanohorn aggregate 401 is used as the catalyst-supporting carbon particles, and the catalyst metal 405 supported on the surface of the carbon nanohorn aggregate 401 has a spherical shape with an average particle diameter of 5 nm or less; Since the catalyst metal 405 is uniformly dispersed, the catalyst utilization efficiency is high and the battery has excellent battery characteristics.
[0042]
The use of the fuel cell according to the present embodiment is not particularly limited. For example, the fuel cell is suitable for a portable small electric device such as a mobile phone, a notebook computer, a PDA (Personal Digital Assistant), various cameras, a navigation system, and a portable music player. Used for
[0043]
【Example】
EXAMPLES Hereinafter, the catalyst electrode for a fuel cell according to the present invention and the fuel cell using the same will be described more specifically with reference to examples, but the present invention is not limited thereto.
[0044]
[Example 1]
The carbon nanohorn aggregate was produced by a laser ablation method. That is, sintered round bar carbon as a solid carbon material is placed in a vacuum vessel, and^-2After depressurizing and evacuating to Pa, Ar gas was discharged to 1.01325 × 10⁵It was introduced so as to have an atmospheric pressure of Pa. Then, the high output CO₂The solid carbon material was irradiated with laser light at room temperature for 30 minutes. Irradiation was performed so that the laser output was 100 W and the pulse width was 20 ms, and the angle between the laser and the surface of the solid carbon material was 120 °. Observation of the soot-like substance thus obtained by a transmission electron microscope (TEM) confirmed that the substance had a carbon nanohorn aggregate structure.
[0045]
The obtained soot-like substance was subjected to ultrasonic treatment (400 kHz, 60 minutes) and decantation four times in ethanol, whereby a carbon nanohorn aggregate consisting of a single particle or several particles could be obtained. The particle diameter of the obtained carbon nanohorn aggregate was in the range of 10 nm or more and 100 nm or less from TEM observation of the particles.
[0046]
Using the carbon nanohorn aggregate obtained above, catalyst-carrying carbon particles were produced. 10 g of carbon nanohorn aggregate was mixed with 500 g of a dinitrodiamineplatinum nitric acid solution containing 3 wt% of platinum serving as a catalyst and stirred, and then 60 ml of a 98 v / v% aqueous ethanol solution was added as a reducing agent. This dispersion was stirred and mixed at a boiling point of about 95 ° C. for 8 hours, and platinum fine particles serving as a catalyst substance were supported on a carbon nanohorn aggregate. The carbon nanohorn aggregate supporting the platinum fine particles was separated by filtration, dried, and reduced in a hydrogen stream at room temperature (20 ° C.) for 5 hours to obtain catalyst-supported carbon particles. The supported amount of platinum was about 50% based on the weight of the carbon nanohorn aggregate.
[0047]
As a result of observing the obtained catalyst-carrying carbon particles by TEM, the platinum supported on the carbon nanohorn aggregate was spherical with an average particle diameter of 1 to 2 nm and a ratio of the major axis / minor axis of the particles of about 1, It was also confirmed that the particles were uniformly dispersed on the carbon nanohorn. Also, when the reduction was performed at each temperature of 60 ° C. and 80 ° C., the shape and size of the platinum particles were almost equal to those when the reduction was performed at room temperature. When the reduction was performed at 400 ° C., the average particle diameter of the platinum particles was a sphere having a diameter of about 5 nm.
[0048]
Therefore, by using a carbon nanohorn aggregate as a carbon material and performing the reduction treatment at a low temperature, the catalyst metal is uniformly dispersed on the surface of the carbon nanohorn aggregate, and the average particle diameter is extremely small as 1 nm to 2 nm. Was completed.
[0049]
[Comparative Example 1]
Using acetylene black (manufactured by Denki Kagaku) as a carbon material, a catalyst metal was supported in the same manner as in Example 1.
[0050]
The obtained catalyst-carrying carbon particles were observed by TEM in the same manner as in Example 1. As a result, the platinum supported on acetylene black had an average particle diameter of about 7 nm. Further, the shape of the platinum particles was not constant, and some particles were aggregated. When the reduction was performed at a normal temperature of 400 ° C., the average particle diameter of the catalyst metal on acetylene black was about 10 nm. Therefore, it was found that by performing the reduction treatment at a low temperature, there was an effect of reducing the size of the catalyst particles even when acetylene black was used.
[0051]
[Example 2]
Using the catalyst-carrying carbon particles (carbon nanohorn aggregates) produced in Example 1, a catalyst electrode for a fuel cell and a fuel cell were produced.
[0052]
As the alcohol solution of the solid polymer electrolyte, a 5% Nafion solution manufactured by Aldrich Chemical Co. was used. When the mass of the solid polymer electrolyte is 0.1 to 0.4 mg / cm²And stirred with n-butyl acetate to obtain a colloidal dispersion of solid polymer electrolyte. The colloid was adsorbed on the surface of the carbon nanohorn aggregate by adding the powder of the carbon nanohorn aggregate supporting platinum in Example 1 to the colloidal dispersion of the polymer electrolyte. The resulting dispersion was made into a paste using an ultrasonic disperser. This paste was applied on carbon paper as a substrate (gas diffusion layer) by a screen printing method, and then dried by heating to produce an electrode for a polymer electrolyte fuel cell. Carbon paper (manufactured by Toray Industries, Inc.) having a thickness of 0.19 mm was used as the base.
[0053]
The obtained fuel cell catalyst electrode was applied to both sides of Nafion 115 manufactured by DuPont at a temperature of 120 to 200 ° C. and a pressure of 50 to 100 kg / cm.²To produce a catalyst electrode-solid electrolyte membrane assembly. This was set in an apparatus for measuring a single cell of a fuel cell.
[0054]
Oxygen and hydrogen (1.01325 × 10⁵(Pa, room temperature). As a result, a high output characteristic of 0.80 W was exhibited. This is presumably because platinum, which is a catalytic substance, became finely spherical on the surface of the carbon nanohorn aggregate, and the specific surface area was increased, thereby improving the catalytic activity and increasing the surface area involved in the catalytic reaction.
[0055]
[Comparative Example 2]
In Comparative Example 1, a catalyst electrode for a fuel cell and a fuel cell were produced and evaluated in the same manner as in Example 2 using acetylene black powder carrying platinum.
[0056]
When the platinum supported on acetylene black was reduced at 400 ° C., the output was 0.60 W, but when the platinum supported on the same acetylene black was reduced at room temperature, The output was 0.65 W. Therefore, although the output characteristics were slightly improved by performing the reduction treatment at a low temperature during the preparation of the catalyst-supporting carbon particles, the output was lower than when the carbon nanohorn aggregate was used as the carbon material.
[0057]
[Example 3]
In the same manner as in Example 1, a solution in which the catalyst metal was dissolved from platinum chloride and ruthenium chloride was prepared so that the catalyst metal became a platinum-ruthenium alloy, and was carried in the form of a carbon nanohorn aggregate. The reduction treatment was performed at room temperature in an argon gas stream containing 4 wt% hydrogen.
[0058]
When the obtained platinum-ruthenium alloy on the catalyst-supporting carbon particles was observed by TEM in the same manner as in Example 1, the catalyst metal had an average particle diameter of 1 to 2 nm and a ratio of the major axis / minor axis of the particles of about 1 to about 1 nm. And it was confirmed that the particles were uniformly dispersed on the carbon nanohorn. Therefore, even when the catalyst metal is a platinum-ruthenium alloy, the carbon nanohorn aggregate is used as the carbon material, and the reduction process is performed at room temperature to reduce the particle size of the catalyst metal, and the surface of the carbon nanohorn aggregate is reduced. It was confirmed that they were uniformly dispersed.
[0059]
[Comparative Example 3]
Using acetylene black (manufactured by Denki Kagaku) as a carbon material, a catalyst metal was carried in the same manner as in Example 3.
[0060]
The obtained catalyst-carrying carbon particles were observed by TEM in the same manner as in Example 1. As a result, the platinum-ruthenium alloy supported on acetylene black had an average particle diameter of about 7 nm. Further, the shape of the catalyst metal was not constant, and some particles were aggregated. When the reduction was performed at a normal temperature of 400 ° C., the average particle diameter of the catalyst metal on acetylene black was about 10 nm. Therefore, it was found that by performing the reduction treatment at a low temperature, there was an effect of reducing the size of the catalyst particles even when acetylene black was used.
[0061]
[Example 4]
Using the catalyst-carrying carbon particles (carbon nanohorn aggregates) obtained in Example 3, a fuel cell was produced in the same manner as in Example 2. 10 v / v% methanol and 1.01325 × 10⁵A direct methanol fuel cell was prepared by supplying oxygen of Pa, and the output characteristics were measured at room temperature.
[0062]
As a result, it was confirmed that the output characteristics were improved up to 0.20 W.
[0063]
[Comparative Example 4]
In Comparative Example 3, a catalyst electrode for a fuel cell and a fuel cell were prepared and evaluated in the same manner as in Example 4 using acetylene black powder supporting platinum.
[0064]
Each of the batteries using the platinum supported on acetylene black reduced at room temperature and 400 ° C. had an output of 0.15 W. Therefore, in each case, the output characteristics were lower than in the case where the carbon nanohorn aggregate was used as the carbon material.
[0065]
From the above Examples and Comparative Examples, the catalyst-carrying carbon particles used for the catalyst electrode are made into carbon nanohorn aggregates, and the reduction treatment when carrying the catalyst metal is performed at a low temperature, thereby reducing the particle diameter of the catalyst metal, and It was possible to disperse uniformly on the surface of the carbon nanohorn aggregate. In addition, it has been clarified that the fuel cell manufactured using the carbon nanohorn aggregate on which the catalyst metal is supported has excellent output characteristics.
[0066]
It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that each embodiment can be appropriately changed within the scope of the technical idea of the present invention. For example, in this embodiment, a battery using hydrogen-oxygen and methanol-oxygen as a fuel is taken, but a battery using reformed hydrogen as a fuel using natural gas, naphtha, or the like, or air using an oxidant as a fuel. It is also possible to apply to a fuel cell or the like.
[0067]
【The invention's effect】
As described above, according to the present invention, the carbon particles are supported on the surface of the carbon particles by setting the average particle diameter of the catalyst material to 5 nm or less by forming the carbon particles into a carbon nanohorn aggregate in which carbon nanohorns are aggregated in a spherical shape. A catalyst electrode for a fuel cell having a large surface area of a catalyst substance and high catalytic activity and a fuel cell using the same are realized. Further, according to the present invention, a catalyst electrode for a fuel cell having high catalytic activity, in which aggregation of a catalyst substance is suppressed and supported in a good dispersion state, and a fuel cell using the same are realized. Further, according to the present invention, a catalyst-supporting particle for a fuel cell having high catalytic activity in which a catalyst substance having a small particle size is supported in a good dispersion state, and a method for producing a catalyst electrode for a fuel cell using the same are realized. You.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing one example of a configuration of a fuel cell according to the present invention.
FIG. 2 is a diagram showing an example of a configuration of a composite electrolyte including a carbon nanohorn aggregate, a catalyst metal, and a solid polymer electrolyte according to the present invention.
[Explanation of symbols]
100 fuel cell
101 Catalyst electrode-solid electrolyte membrane assembly
102 Fuel electrode
104 base
106 catalyst layer
108 Oxidizer electrode
110 base
112 catalyst layer
114 Solid electrolyte membrane
120 Fuel electrode side separator
122 Oxidizer electrode side separator
124 fuel
126 Oxidizing agent
401 Carbon nanohorn aggregate
403 Solid polymer electrolyte
405 catalytic metal

Claims (10)

A fuel cell catalyst electrode comprising carbon particles supporting a solid polymer electrolyte and a catalyst material, wherein the carbon particles are a carbon nanohorn aggregate formed by spherically assembling carbon nanohorns, and the average of the catalyst material A catalyst electrode for a fuel cell, wherein the particle diameter is 5 nm or less. The catalyst electrode for a fuel cell according to claim 1, wherein the catalyst substance is substantially spherical. 3. The fuel cell catalyst electrode according to claim 1, wherein the catalyst material is uniformly dispersed on the carbon nanohorn aggregate. The fuel cell catalyst electrode according to any one of claims 1 to 3, wherein the catalyst substance is gold, a platinum group metal, or an alloy thereof. The fuel cell catalyst electrode according to any one of claims 1 to 4, wherein the carbon nanohorn assembly is a single-layer carbon nanohorn assembly. The fuel cell catalyst electrode according to any one of claims 1 to 5, wherein the carbon nanohorn assembly is a single-layer graphite nanohorn assembly composed of a single-layer graphite nanohorn. The fuel cell catalyst electrode according to any one of claims 1 to 6, wherein the carbon nanohorn aggregate is supported on carbon fibers, carbon nanofibers, or carbon nanotubes. 8. A fuel cell including a fuel electrode, an oxidant electrode, and a solid electrolyte membrane sandwiched between the fuel electrode and the oxidant electrode, wherein the fuel electrode or the oxidant electrode is any one of claims 1 to 7. A fuel cell, which is the catalyst electrode for a fuel cell according to any one of the preceding claims. A solution of a metal salt, a carbon nanohorn aggregate, and mixing a reducing agent, a step of supporting a metal on the surface of the carbon nanohorn aggregate,
After the step of supporting, a step of reducing the metal at a temperature of 10 ° C. or more and 100 ° C. or less,
A method for producing catalyst-carrying particles for a fuel cell, comprising: Producing a catalyst-carrying particle for a fuel cell by the method for producing a catalyst-carrying particle for a fuel cell according to claim 9;
A step of applying a coating solution containing the fuel cell catalyst-carrying particles and particles containing a solid polymer electrolyte to a substrate to form a catalyst layer,
A method for producing a catalyst electrode for a fuel cell, comprising:

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