JP3826867B2 - Catalyst supporting particle for fuel cell and method for producing catalyst electrode for fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a fuel cell catalyst-carrying particle and a method for producing a fuel cell catalyst electrode.
[0002]
[Prior art]
A fuel cell is composed of a fuel electrode and an oxidant electrode, and an electrolyte provided therebetween. The fuel cell is supplied with fuel, and the oxidant electrode is supplied with an oxidant to generate electricity by an electrochemical reaction. When hydrogen is supplied to the fuel electrode and oxygen is supplied to the oxidizer electrode, the electrochemical reaction that occurs at each electrode is
H₂ → 2H⁺ + 2e⁻
And at the oxidizer 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 the 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 catalyst substance and a solid polymer electrolyte.
[0003]
Although the fuel cell using hydrogen as the fuel has been described above, research and development of a fuel cell using an organic liquid fuel such as methanol has been actively conducted in recent years. Fuel cells that use organic liquid fuels can be used without reforming organic liquid fuels, such as those that reform organic liquid fuels into hydrogen gas and use them as fuel, and direct methanol fuel cells. One that supplies directly to the fuel electrode is known (Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-3724
[0005]
In order to improve the characteristics of the fuel cell, it is necessary to increase the catalytic activity of the catalyst electrode by increasing the surface area of the catalyst material. For that purpose, it is necessary to reduce the particle diameter of the catalyst particles and to disperse them uniformly. In the conventional catalyst electrode for fuel cells, as a method of supporting the catalyst material on the carbon particles, a catalyst metal salt is dissolved to make a solution, and the catalyst material on the colloid is supported on the carbon particles and then reduced. 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 around 400 ° C. using a commonly used carbon material such as acetylene black, the average particle size of the catalyst substance is increased. The size was increased 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 material is reduced and the catalytic activity in the catalyst electrode is insufficient.
[0006]
[Problems to be solved by the invention]
  In view of the above circumstances, the object of the present invention is,grainIt is an object of the present invention to provide a fuel cell catalyst-carrying particle having a high catalytic activity in which a catalyst substance having a small diameter is supported in a good dispersion state, and a method for producing a fuel cell catalyst electrode using the same.
[0007]
[Means for Solving the Problems]
  The present invention relates to a method for producing fuel cell catalyst-carrying particles and a fuel cell catalyst electrode. According to the method for producing the fuel cell catalyst-carrying particles and the fuel cell catalyst electrode of the present invention, the following fuel cell catalyst electrode and fuel cell can be obtained.
  According to the present invention, there is provided a catalyst electrode for a fuel cell comprising carbon particles supporting a solid polymer electrolyte and a catalyst material, wherein the carbon particles are carbon nanohorn aggregates formed by collecting carbon nanohorns in a spherical shape. The catalyst electrode for fuel cells is provided, 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 material is as 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. In addition, since carbon nanohorn aggregates are used for the carbon particles, the surface area of the carbon particles is extremely large and the amount of the catalyst substance supported 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. In addition, 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 can improve its output when used in a fuel cell.
[0009]
In the fuel cell catalyst electrode, the average particle size of the catalyst material is 5 nm or less, but more preferably 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. In addition, although there is no restriction | limiting in particular about a minimum, For example, it is 0.1 nm or more, Preferably it can be 0.5 nm or more. By carrying out like this, the electrode which has favorable catalyst efficiency can be obtained with manufacture 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 major axis / minor axis ratio of the catalyst particles is 3 or less. By doing so, the uniformity of the shape of the catalyst material can be improved, and the specific surface area of the catalyst material can be further increased. Further, the catalyst substance can be uniformly dispersed on the carbon nanohorn aggregate. Here, “uniformly dispersed” refers to a state in which the formation of aggregates and secondary particles is suppressed and the catalyst material is supported on the surface of the carbon nanohorn aggregate in a well 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 of the present invention, the catalyst substance may be gold, a platinum group metal, or an alloy thereof. By doing so, the activity of the catalyst substance can be further improved.
[0012]
In the catalyst electrode for a fuel cell according to the present invention, the carbon nanohorn aggregate may be a single-walled carbon nanohorn aggregate. By doing so, the conductivity of hydrogen ions in the catalyst electrode can be improved. Further, the carbon nanohorn aggregate may be a single-layer graphite nanohorn aggregate composed of single-layer graphite nanohorns. By doing so, the electrical conductivity of the carbon particles is improved, so that the performance of the catalyst electrode can be further improved. Further, the carbon nanohorn aggregate can be supported on carbon fibers, carbon nanofibers, or carbon nanotubes. By doing so, it is possible to suitably adjust the microstructure in the catalyst electrode.
[0013]
According to the present invention, there is provided 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 the fuel electrode. A fuel cell is provided that is a catalyst electrode for a battery. In the fuel cell according to the present invention, since the above-described catalyst electrode for a fuel cell 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, after mixing the metal salt solution, the carbon nanohorn aggregate, and the reducing agent, supporting the metal on the surface of the carbon nanohorn aggregate, and after the supporting process,After the step of drying the support obtained in the previous step and the step of drying, the temperature is 20 ° C. or higher and 80 ° C. or lower.And a step of reducing the metal at a temperature of 1. A method for producing catalyst-carrying particles for a fuel cell is provided. According to the method for producing catalyst-supported carbon particles for a fuel cell according to the present invention, the average particle diameter of the catalyst material supported on the surface of the carbon nanohorn aggregate is obtained by using the carbon nanohorn aggregate and lowering the reduction temperature. Can be made extremely small, for example, 5 nm or less, for example, 1 nm to 2 nm. In addition, the dispersibility of the catalyst substance can be improved.
[0015]
According to the present invention, a coating liquid containing a step of producing fuel cell catalyst-carrying particles by the method for producing fuel cell catalyst-carrying particles, and a fuel cell catalyst-carrying particle and a solid polymer electrolyte-containing particle. And a step of forming a catalyst layer on a substrate. A method for producing a catalyst electrode for a fuel cell is provided. According to the method for producing a catalyst electrode for a fuel cell according to the present invention, since the catalyst-supported carbon particles for a fuel cell are used in the step of forming a catalyst layer, a catalyst electrode having high catalytic reaction efficiency can be produced stably. It is.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a specific configuration of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a cross-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 referred to as a catalyst electrode. The fuel electrode 102 includes a substrate 104 and a catalyst layer 106. The oxidant electrode 108 includes a base 110 and a catalyst layer 112. One or a plurality of 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-side separator 120. Further, an oxidant 126 such as air or oxygen is supplied to the oxidant electrode 108 of each catalyst electrode-solid electrolyte membrane assembly 101 via the oxidant electrode side separator 122.
[0019]
The fuel electrode 102 and the oxidant electrode 108 include carbon particles supporting a catalyst and solid polymer electrolyte fine particles, and the catalyst layer 106 and the catalyst layer 112 are formed on the substrate 104 and the substrate 110. The substrate surface may be subjected to a water repellent treatment.
[0020]
As the substrate 104 and the substrate 110, porous substrates such as carbon paper, a carbon molded body, a carbon sintered body, a sintered metal, and a foam metal can be used. 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 in which the catalytic 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 composed of only carbon atoms, are spherically assembled is used as the carbon particles supporting the catalyst. The term “spherical” as used herein does not necessarily mean a true sphere, but includes a collection of various 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. A plurality of carbon nanohorn aggregates are centered on a tube by van der Waals force acting between the conical parts, and the conical part has a corner (horn). As shown in the figure, they are assembled in a configuration that protrudes from the surface. The diameter of the carbon nanohorn aggregate 401 is 120 nm or less, typically 10 nm or more and 100 nm or less. Each carbon nanohorn 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 cone portion has an average angle of inclination of an axial section of about 20 °. In order to take 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 usually has a room temperature of 1.01325 × 10^FiveIt can be produced by a laser ablation method using a solid carbon simple substance such as graphite as a target in an inert gas atmosphere of Pa. Moreover, 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, or the like. In the central part of the carbon nanohorn aggregate 401, carbon nanohorns are chemically bonded to each other, or a shape in which the carbon nanotubes are rounded like a kicker is conceivable, but is limited by the structure of these central parts. is not. Moreover, what has a hollow center part is also considered.
[0024]
The carbon nanohorn constituting the carbon nanohorn aggregate 401 may be closed at one end or may not be closed. Moreover, you may terminate in the shape where the vertex of the cone shape of the one end was round. When the carbon nanohorns constituting the carbon nanohorn aggregate 401 are terminated with a rounded conical apex at one end, the carbon nanohorns are gathered radially with the rounded apex outward. Further, a part of the structure of the carbon nanohorn may be incomplete and may have fine pores. Furthermore, 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. The carbon nanohorn aggregate 401 can be a single-layer carbon nanohorn aggregate composed of single-layer graphite nanohorns. By doing so, the electrical conductivity of the carbon nanohorn aggregate 401 is improved, so that the performance can be improved when used for the catalyst electrode for a fuel cell.
[0026]
For example, the following materials can be used as the catalyst metal 405. Examples of the catalyst for the fuel electrode 102 include platinum, rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold, silver, nickel, cobalt, lithium, lanthanum, strontium, yttrium, and the like. 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 that for the fuel electrode 102 can be used, and the above-mentioned exemplified substances can be used. The catalyst for 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 carrying 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. Therefore, hydrogen ion conductivity is required. Further, when an organic liquid fuel such as methanol is supplied to the fuel electrode 102, fuel permeability is required, and the oxidant electrode 108 is required to have oxygen permeability. In order to satisfy these requirements, the solid polymer electrolyte 403 is preferably made of a material excellent in hydrogen ion conductivity and organic liquid fuel permeability such as methanol. 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 (Nafion (DuPont), Aciplex (Asahi Kasei), etc.);
Carboxyl group-containing perfluorocarbon (Flemion S membrane (Asahi Glass Co., Ltd.));
Copolymers such as polystyrene sulfonic acid copolymer, polyvinyl sulfonic acid copolymer, cross-linked alkyl sulfonic acid derivative, fluorine resin skeleton and fluorine-containing polymer comprising sulfonic acid;
A copolymer obtained by copolymerizing acrylamides such as acrylamide-2-methylpropanesulfonic acid and acrylates such as n-butyl methacrylate;
Etc. are exemplified.
[0028]
In addition, examples of the polymer to which the polar group is bonded include polybenzimidazole derivatives, polybenzoxazole derivatives, polyethyleneimine cross-linked products, polysilamine derivatives, amine-substituted polystyrenes such as polydiethylaminoethylpolystyrene, diethylaminoethylpolymethacrylate, and the like. Resins having nitrogen or hydroxyl groups, such as nitrogen-substituted polyacrylates;
Hydroxyl group-containing polyacrylic resin represented by silanol-containing polysiloxane and hydroxyethyl polymethyl acrylate;
Hydroxyl group-containing polystyrene resin represented by parahydroxypolystyrene;
Etc. can also be used.
[0029]
In addition, a crosslinkable substituent such as 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 above 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 actually, it is formed on the entire carbon nanohorn aggregate 401.
[0032]
In the fuel cell 100, the solid electrolyte membrane 114 has a role of separating the fuel electrode 102 and the oxidant electrode 108 and moving hydrogen ions and water molecules between the two. For this reason, the solid electrolyte membrane 114 is preferably a membrane having high hydrogen ion conductivity. Further, it is preferably 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. Examples of such organic polymers include aromatic-containing polymers such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole;
Copolymers such as polystyrene sulfonic acid copolymer, polyvinyl sulfonic acid copolymer, cross-linked alkyl sulfonic acid derivative, fluorine resin skeleton and fluorine-containing polymer comprising 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));
Carboxyl group-containing perfluorocarbon (Flemion S membrane (Asahi Glass Co., Ltd .: registered trademark));
Etc. are exemplified. Among these, when an aromatic-containing polymer such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) or alkylsulfonated polybenzimidazole is selected, the permeation of organic liquid fuel can be suppressed, and a battery by crossover A decrease in efficiency can be suppressed.
[0033]
As the fuel 124 supplied to the fuel cell 100, gaseous fuel or liquid fuel can be used. When gaseous fuel is used, for example, hydrogen can be used. When liquid fuel is used, examples of the organic compound contained in the fuel 124 include alcohols such as methanol, ethanol and propanol, ethers such as dimethyl ether, cycloparaffins such as cyclohexane, hydroxyl group, carboxyl group and amino group. , Cycloparaffins having a hydrophilic group such as an amide group, mono- or di-substituted cycloparaffins, and the like can be used. 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. Although there is no restriction | limiting in particular in the manufacturing method of the fuel cell 100, For example, it can produce as follows.
[0035]
  First, the manufacturing method of a catalyst electrode is demonstrated. The catalyst metal 405 can be supported on the carbon nanohorn aggregate 401 by a commonly used impregnation method. This is a method of carrying out a reduction treatment after supporting a colloidal catalyst substance by dissolving or dispersing a metal salt of the catalyst metal 405 in a solvent on the carbon nanohorn aggregate 401. Including room temperature20 ℃ to 80 ℃Low temperatureEvery timeBy performing this reduction treatment, the average particle diameter of the catalyst metal 405 supported on the surface of the carbon nanohorn aggregate 401 can be made into extremely small spherical particles of 5 nm or less, for example, 1 nm to 2 nm. Furthermore, the catalyst metal 405 can be uniformly dispersed on the carbon nanohorn particles. Next, the catalyst-supported carbon particles and the solid polymer electrolyte 403 particles 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, for example, in the range of 2: 1 to 40: 1 by weight ratio. Further, the weight ratio of 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 a carbon fiber, carbon nanofiber, carbon nanotube, or the like by heat treatment or the like. By doing so, the fine structures of the catalyst layer 106 and the catalyst layer 112 can be arbitrarily adjusted.
[0037]
Although there is no restriction | limiting in particular about the coating method of the paste to the base | substrates 104 and 110, For example, methods, such as brush coating, spray coating, and screen printing, can be used. The paste is applied with a thickness of about 1 μm to 2 mm, for example. After the paste is applied, the fuel electrode 102 or the oxidant electrode 108 is manufactured by heating at a heating temperature and a heating time corresponding to the fluororesin to be used. The heating temperature and the heating time are appropriately selected depending on the material to be used. For example, the heating temperature may be 100 ° C. or more and 250 ° C. or less, and the heating time may be 30 seconds or more and 30 minutes or less.
[0038]
The fuel cell 100 is produced as follows using the catalyst electrode produced by the above method.
[0039]
The solid electrolyte membrane 114 can be manufactured by employing an appropriate method depending on the material to be used. For example, when the solid electrolyte membrane 114 is made of an organic polymer material, a liquid obtained by dissolving or dispersing the organic polymer material in a solvent is obtained by casting on a peelable sheet such as polytetrafluoroethylene and drying the resultant. 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 oxidant electrode 108 on which the catalyst layers 106 and 112 are provided are in contact with the solid electrolyte membrane 114. The conditions for hot pressing are selected depending on the material. When the solid polymer electrolyte 114 or the solid polymer electrolyte on the surface of the catalyst electrode is composed of an organic polymer having a softening point or a glass transition point, these polymers are used. The temperature can be higher than the softening temperature or 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.²100 kg / cm or more²Hereinafter, the time is 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 is spherical 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 characteristics are excellent.
[0042]
Although the use of the fuel cell according to the present embodiment is not particularly limited, for example, it is suitable for portable small electric devices 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】
The fuel cell catalyst electrode and the fuel cell using the same according to the present invention will be described more specifically with reference to the following 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 container, and the container is filled with 10^-2After evacuating to Pa, Ar gas was 1.01325 × 10^FiveIt introduced so that it might become the atmospheric pressure of Pa. Next, high output CO₂The solid carbon material was irradiated with laser light for 30 minutes at room temperature. The output of the laser was 100 W, the pulse width was 20 ms, and irradiation was performed so that the angle formed with the solid carbon material surface was 120 °. When the soot-like substance thus obtained was observed with a transmission electron microscope (TEM), it was confirmed to have a carbon nanohorn aggregate structure.
[0045]
The obtained soot-like substance was subjected to ultrasonic treatment (400 kHz, 60 minutes) and decantation in ethanol four times, whereby a carbon nanohorn aggregate composed of single or several particles could be obtained. The particle diameter of the obtained carbon nanohorn aggregate was in the range of 10 nm to 100 nm from TEM observation of the particles.
[0046]
Catalyst-supported carbon particles were produced using the carbon nanohorn aggregates obtained above. 10 g of the carbon nanohorn aggregate was mixed with 500 g of a dinitrodiamine platinum 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 material were supported on the carbon nanohorn aggregate. The carbon nanohorn aggregate on which the platinum fine particles were supported 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 amount of platinum supported was about 50% with respect to the weight of the carbon nanohorn aggregate.
[0047]
As a result of observing the obtained catalyst-carrying carbon particles by TEM, platinum carried on the carbon nanohorn aggregate is spherical with an average particle diameter of 1 to 2 nm and a major axis / minor axis ratio of about 1; Moreover, it was confirmed that it was uniformly dispersed on the carbon nanohorn. Also, when the reduction was performed at 60 ° C. and 80 ° C., the shape and size of the platinum particles were almost the same as 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 spherical shape of about 5 nm.
[0048]
Therefore, by using a carbon nanohorn aggregate as a carbon material and performing a 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, 1 nm to 2 nm. I was able to.
[0049]
[Comparative Example 1]
Acetylene black (manufactured by Denki Kagaku) was used as the carbon material, and a catalyst metal was supported in the same manner as in Example 1.
[0050]
The obtained catalyst-supported carbon particles were observed by TEM in the same manner as in Example 1. As a result, platinum supported on acetylene black had an average particle diameter of about 7 nm. Moreover, 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 the reduction treatment at low temperature has the effect of reducing the catalyst particles even when acetylene black is used.
[0051]
[Example 2]
Using the catalyst-supported carbon particles (carbon nanohorn aggregate) produced in Example 1, a fuel cell catalyst electrode and a fuel cell were produced.
[0052]
As an alcohol solution of the solid polymer electrolyte, a 5% Nafion solution manufactured by Aldrich Chemical Co. was used. The solid polymer electrolytic mass is 0.1 to 0.4 mg / cm.²Then, the mixture was stirred with n-butyl acetate to prepare a colloidal dispersion of solid polymer electrolyte. The powder of the carbon nanohorn aggregate carrying platinum in Example 1 was added to the above-described colloidal dispersion of the polymer electrolyte to adsorb the colloid on the surface of the carbon nanohorn aggregate. The obtained dispersion was made into a paste using an ultrasonic disperser. This paste was applied on a carbon paper serving as a substrate (gas diffusion layer) by screen printing, and then dried by heating to produce a polymer electrolyte fuel cell electrode. Carbon paper (manufactured by Toray Industries, Inc.) having a thickness of 0.19 mm was used as the substrate.
[0053]
The obtained fuel cell catalyst electrode was formed on both surfaces of Nafion 115 manufactured by DuPont at a temperature of 120 to 200 ° C. and a pressure of 50 to 100 kg / cm.²And a catalyst electrode-solid electrolyte membrane assembly was produced by hot pressing. This was set in an apparatus for measuring a single cell of a fuel cell.
[0054]
Oxygen and hydrogen (1.01325 × 10^Five(Pa, room temperature) was used to measure the output characteristics of the cell. As a result, a high output characteristic of 0.80 W was exhibited. This is presumably because platinum, which is a catalyst substance, becomes fine spheres on the surface of the carbon nanohorn aggregate, the catalytic activity is improved by increasing the specific surface area, and the surface area involved in the catalytic reaction is increased.
[0055]
[Comparative Example 2]
Using the acetylene black powder carrying platinum in Comparative Example 1, a fuel cell catalyst electrode and a fuel cell were prepared and evaluated in the same manner as in Example 2.
[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 0.65W. Therefore, although the output characteristics are slightly improved by performing the reduction treatment at a low temperature during the production of the catalyst-supporting carbon particles, the output is lower than when the carbon nanohorn aggregate is 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 was a platinum-ruthenium alloy, and supported in a carbon nanohorn aggregate shape. The reduction treatment was performed at room temperature in an argon gas stream containing 4 wt% hydrogen.
[0058]
When the platinum-ruthenium alloy on the obtained 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 major axis / minor axis ratio of about 1 It was confirmed that it was spherical and was uniformly dispersed on the carbon nanohorn. Therefore, even when the catalyst metal is a platinum-ruthenium alloy, the carbon nanohorn aggregate is used as a carbon material, and the particle size of the catalyst metal is reduced by performing a reduction treatment at room temperature, so that the surface of the carbon nanohorn aggregate is reduced. It was confirmed that it was uniformly dispersed.
[0059]
[Comparative Example 3]
Acetylene black (manufactured by Denki Kagaku) was used as the carbon material, and a catalyst metal was supported in the same manner as in Example 3.
[0060]
The obtained catalyst-supported 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 the reduction treatment at a low temperature has the effect of reducing the catalyst particles even when acetylene black is used.
[0061]
[Example 4]
Using the catalyst-supported carbon particles (carbon nanohorn aggregate) obtained in Example 3, a fuel cell was produced in the same manner as in Example 2. To the fuel electrode and oxidant electrode of the obtained battery, 10 v / v% methanol and 1.01325 × 10^FiveEach of oxygen of Pa was supplied to make a direct methanol fuel cell, and its 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]
A catalyst electrode for a fuel cell and a fuel cell were prepared and evaluated in the same manner as in Example 4 using the acetylene black powder carrying platinum in Comparative Example 3.
[0064]
All 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 all cases, the output characteristics were low as compared with the case where the carbon nanohorn aggregate was used as the carbon material.
[0065]
From the above examples and comparative examples, the catalyst-supporting carbon particles used for the catalyst electrode are made into carbon nanohorn aggregates, and the reduction treatment when supporting the catalyst metal is performed at a low temperature, thereby reducing the particle diameter of the catalyst metal, and It was possible to uniformly disperse the carbon nanohorn aggregate surface. In addition, it has been clarified that the fuel cell produced using the carbon nanohorn aggregate carrying the catalyst metal is excellent in output characteristics.
[0066]
It should be noted that the present invention is not limited to the above-described embodiments, and it is obvious that each embodiment can be appropriately changed within the scope of the technical idea of the present invention. For example, in this example, a battery using hydrogen-oxygen and methanol-oxygen as fuel was taken up, but a battery using reformed hydrogen using fuel such as natural gas or naphtha as fuel, or air as an oxidant was used. It can also be applied to a fuel cell or the like.
[0067]
【The invention's effect】
  As explained above, according to the present invention,,grainA catalyst support particle for a fuel cell having a high catalytic activity in which a catalyst substance having a small diameter is supported in a good dispersion state and a method for producing a catalyst electrode for a fuel cell using the same are realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an example of the configuration of a fuel cell according to the present invention.
FIG. 2 is a diagram showing an example of the configuration of a composite electrolyte including a carbon nanohorn aggregate according to the present invention, a catalytic metal, and a solid polymer electrolyte.
[Explanation of symbols]
100 Fuel cell
101 catalyst electrode-solid electrolyte membrane assembly
102 Fuel electrode
104 Substrate
106 Catalyst layer
108 Oxidant electrode
110 substrate
112 Catalyst layer
114 Solid electrolyte membrane
120 Fuel electrode side separator
122 Oxidant electrode side separator
124 Fuel
126 Oxidizing agent
401 Carbon nanohorn aggregate
403 Solid polymer electrolyte
405 catalytic metal

Claims (2)

Mixing a metal salt solution, a carbon nanohorn aggregate, and a reducing agent, and supporting a metal on the surface of the carbon nanohorn aggregate;
After the step of carrying, the step of drying the carrier obtained in the previous step;
After the step of drying, a step of reducing the metal at a temperature of 20 ° C. or higher and 80 ° C. or lower ;
A method for producing catalyst-supporting particles for a fuel cell, comprising: Producing fuel cell catalyst-carrying particles by the method for producing fuel cell catalyst-carrying particles according to claim 1,
Applying a coating solution containing the fuel cell catalyst-carrying particles and particles containing a solid polymer electrolyte on a substrate to form a catalyst layer;
The manufacturing method of the catalyst electrode for fuel cells characterized by including these.

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