JP2006278194A - Fuel cell and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell and a membrane electrode assembly that improve utilization efficiency of catalyst particles by using a non-porous carbon carrier, and at the same time, that maintain a catalyst particle diameter at less than 5 nm, wherein a highly active PtRu-based catalyst is provided, and that has the catalyst for a fuel cell electrode of which the catalyst particle diameter is less than 5 nm and which is high in catalytic activity. <P>SOLUTION: In the fuel cell having at least a fuel electrode, an oxygen electrode, and a solid polyelectrolyte membrane inserted between these fuel electrode and oxygen electrode, the fuel electrode contains the catalyst in which ternary fine particles composed of a general formula: PtRuN (in the formula, atomic ratio of Pt to Ru is 40:60 to 90:10, and N content is 2 to 50 at.%) are supported on the non-porous carbon carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell having a novel fuel electrode catalyst and a membrane electrode assembly. More particularly, the present invention relates to a fuel cell having a PtRuN fuel electrode catalyst supported on a carbon support and a membrane electrode assembly.

  Conventionally, most of electric energy has been supplied by thermal power generation, hydroelectric power generation or nuclear power generation. However, thermal power generation not only causes large-scale environmental pollution because it burns fossil fuels such as oil and coal, but depletion of resources such as oil has become a problem. In addition, hydropower generation requires large-scale dam construction, and not only is there concern about the destruction of nature, but there are also limited areas for construction. Nuclear power generation is not only fatal in the radioactive contamination at the time of the accident, but also has a problem of decommissioning nuclear reactors that have reached the end of their life, and is moving in a direction that suppresses construction worldwide.

  Wind power generation and solar power generation have been used around the world as power generation methods that do not require large-scale facilities and do not cause environmental pollution. In Japan, wind power generation and solar power generation are actually used in some areas. It has been put into practical use. However, wind power generation has a drawback in that it cannot generate power without wind, and solar power generation cannot generate power without sunlight, and is affected by natural phenomena and cannot provide stable power supply. Further, in wind power generation, the frequency of the generated power fluctuates due to the strength of the wind, causing a failure of electrical equipment.

  Therefore, recently, research and development on a power generation device that can extract electric energy from hydrogen energy, such as a hydrogen fuel cell, has become active. Hydrogen is obtained by electrolyzing water and is not only inexhaustible on the earth, but also contains a large amount of chemical energy per substance, and when used as an energy source, harmful substances and global warming gases Has the advantage of not generating.

  Research on fuel cells using methanol instead of hydrogen gas is also actively conducted. A direct methanol fuel cell that directly uses methanol, which is a liquid fuel, is expected to be a relatively small output power source for household use and industrial use because it is an inexpensive fuel in addition to easy handling of the fuel. The theoretical output voltage of the methanol-oxygen fuel cell is about 1.2 V (25 ° C.), which is almost the same as that of hydrogen fuel, and in principle the same characteristics can be expected.

  In solid polymer fuel cells and direct methanol fuel cells, hydrogen and methanol are oxidized at the anode, and at the same time, oxygen is reduced at the cathode to extract electric energy. Since these oxidation-reduction reactions are difficult to proceed at room temperature, a catalyst is used in the fuel cell. In early fuel cells, platinum (Pt) was deposited and supported on a carbon substrate and used as a catalyst. Pt has catalytic activity for hydrogen oxidation and methanol oxidation, and so far, by controlling the precipitation atmosphere of the Pt catalyst on the carbon substrate, that is, by controlling external factors at the time of precipitation, the particle size of the Pt catalyst particles Attempts have been made to increase the reaction surface area of the Pt catalyst by reducing the diameter as much as possible. For example, in Patent Document 1, when Pt ions are reduced with alcohol and Pt is supported on a carbon substrate, polyvinyl alcohol is added as a protective colloid to the reaction solution to weakly adsorb the protective colloid on the surface of the Pt catalyst particles. , Pt catalyst is being atomized. However, in this method, since the protective colloid is adsorbed on the Pt catalyst surface, it is necessary to remove the protective colloid from the catalyst surface after the synthesis of the Pt fine particles. Patent Document 1 discloses a method of removing protective colloid by performing heat treatment at 400 ° C. in a hydrogen stream after catalyst synthesis. However, in this treatment method, the protective colloid cannot be completely removed from the surface of the Pt catalyst, but the Pt catalyst fine particles are sintered by the heat treatment at 400 ° C., the Pt catalyst particle diameter is increased and the catalytic activity is lowered. There was a problem.

  In the Pt catalyst, carbon monoxide (CO) generated in the methanol oxidation process or a small amount of CO gas contained in the reformed hydrogen gas is chemically adsorbed on the surface of the Pt catalyst, and eventually the catalytic activity is deactivated. There's a problem. This phenomenon is called poisoning of Pt catalyst by CO. In the 1960s, in order to suppress the poisoning of Pt catalysts by CO, the search for elements added to Pt was vigorously conducted. As a result, it was found that addition of Ru to Pt greatly reduces catalyst poisoning by CO (see, for example, Patent Document 2).

Although this Ru itself has no oxidation activity of hydrogen or methanol, it is a co-catalyst that has the effect of rapidly oxidizing CO chemisorbed on Pt to CO ₂ and letting it escape. The function of Ru will be explained using a direct methanol fuel cell as an example. First, as shown in the following reaction formula (1), methanol causes a deprotonation reaction on a Pt catalyst to generate CO. This CO chemisorbs on the Pt catalyst. This is catalyst poisoning by CO. However, in a PtRu catalyst containing Ru, as shown in the following reaction formula (2), Ru reacts with water to produce Ru-OH. Next, as shown in the following reaction formula (3), the CO chemically adsorbed on the surface of the Pt catalyst by the Ru—OH is oxidized and removed as CO ₂ gas. This reaction mechanism is called a bifunctional mechanism.
Pt + CH ₃ OH → Pt-CO + 4H ⁺ + 4e ^- Formula (1)
Ru + H ₂ O → Ru-OH + H ⁺ + e ⁻ Formula (2)
Pt-CO + Ru-OH → Pt + Ru + H ⁺ + e ⁻ + CO ₂ ↑ Equation (3)
When a PtRu catalyst is synthesized by a normal impregnation method, electroless plating method or alcohol reduction method, the particle size becomes 2 to 10 nm, the particle size distribution is large, and there are many catalyst particles having a particle size of 5 nm or more. In general, the activity of the catalyst increases as the surface area per unit weight (specific surface area) increases. When the particle size of the PtRu catalyst is large, the specific surface area is reduced and the catalytic activity is not improved. From this viewpoint, in order to increase the activity of the PtRu catalyst, it is extremely important to reduce the particle size of the PtRu catalyst to less than 5 nm and increase the specific surface area of the catalyst. In this case, the method of reducing the particle size of the PtRu catalyst by adding a protective colloid cannot be used for the above reason.

JP-A-56-155645 In general, it is known that when a Pt catalyst is synthesized using a carbon support having a high specific surface area, the particle size of the Pt catalyst is reduced and a Pt catalyst having a high specific surface area can be obtained. (For example, Reference 3). This tendency is the same for the PtRu catalyst (for example, Reference 4). However, the carbon support having a high specific surface area is porous, and there are very many fine pores in the support. The probability that catalyst particles deposited in the micropores are involved in the oxidation reaction of methanol or hydrogen gas is greatly reduced. For this reason, the use of the porous carbon support goes against the goal of improving the use efficiency of the expensive PtRu catalyst and enhancing the battery characteristics with as little catalyst amount as possible. From the above, it is possible to synthesize a PtRu catalyst having a particle size of less than 5 nm by using a porous carbon support having a high specific surface area, but this has a negative effect from the viewpoint of improving the utilization efficiency of the catalyst. As described above, there is a trade-off relationship between the activity improvement due to the catalyst particle size reduction and the catalyst utilization efficiency improvement. On the other hand, if a non-porous carbon support such as acetylene black or multi-wall carbon nanotube is used, all PtRu catalyst particles can be deposited on the support surface, and the utilization efficiency of the catalyst can be greatly increased. However, since these non-porous carbon supports have no micropores, their specific surface area is as small as 20 to 140 m2 / g (for example, the specific surface area of non-porous multi-wall carbon nanotubes is about 20 to 35 m2 / g). The nonporous acetylene black has a specific surface area of about 60 to 140 m2 / g, and the specific surface area of the nonporous carbon support is, for example, smaller than the specific surface area of 1270 m2 / g of the porous carbon support Ketjen Black 600JD. 2 digits smaller than the digit). It has been shown in the above-mentioned references that the particle size increases when a PtRu catalyst is synthesized using a carbon support having a small specific surface area. As described above, in order to increase the utilization efficiency of the catalyst particles, if a non-porous carbon support having no micropores and having a low specific surface area is used, the particle size of the PtRu catalyst increases and the specific surface area of the PtRu catalyst decreases. As a result, the catalytic activity decreases.

M. Uchida et al., J. Electrochem. Soc. 143, 2245 (1996). M. Uchida et al., J. Electrochem. Soc. 142, 2572 (1995).

  Accordingly, an object of the present invention is to provide a highly active PtRu-based catalyst using a non-porous carbon support to increase the utilization efficiency of catalyst particles, and at the same time to keep the catalyst particle size below 5 nm. Furthermore, it is to provide a fuel cell and a membrane electrode assembly having a novel fuel electrode catalyst having a particle size of less than 5 nm and high catalytic activity.

As means for solving the above-mentioned problems, the invention according to claim 1 is a fuel having at least a fuel electrode, an oxygen electrode, and a solid polymer electrolyte membrane interposed between the fuel electrode and the oxygen electrode. In the battery, the fuel electrode has the following general formula on a carbon support:
PtRuN
The fuel cell is characterized in that a catalyst composed of ternary fine particles shown in FIG.

As means for solving the above-mentioned problem, the invention according to claim 2 is a fuel having at least a fuel electrode, an oxygen electrode, and a solid polymer electrolyte membrane interposed between the fuel electrode and the oxygen electrode. In the battery, the fuel electrode has the following general formula on a carbon support:
PtRuN
(Wherein the atomic ratio of Pt and Ru is 40:60 to 90:10, and the N content is in the range of 2 to 50 at.%). It is a fuel cell characterized by including.

  As means for solving the above-mentioned problem, the invention according to claim 3 is characterized in that the particle size of the PtRuN three-way catalyst for the fuel electrode is in the range of 1 to 3 nm. It is a fuel cell.

As a means for solving the above-mentioned problem, the invention according to claim 4 is that the carbon support is non-porous acetylene black or multi-wall carbon nanotubes, and the specific surface area is 20 to 140 m ² / g. The fuel cell according to any one of claims 1 to 3.
As a means for solving the problem, the invention according to claim 5 is the fuel cell according to claims 1 to 3, wherein the specific surface area of the carbon support is 20 to 300 m ² / g.

  As a means for solving the above-mentioned problems, the invention according to claim 6 is a direct methanol fuel cell, which is a fuel cell according to claims 1 to 5.

  As a means for solving the above-mentioned problems, the invention according to claim 7 is a polymer electrolyte fuel cell, which is a fuel cell according to claims 1 to 5.

As a means for solving the above-mentioned problems, an invention according to claim 8 is directed to a fuel electrode catalyst layer, an oxygen electrode catalyst layer, and a solid height interposed between the fuel electrode catalyst layer and the oxygen electrode catalyst layer. In a membrane electrode assembly comprising a molecular electrolyte membrane, the fuel electrode catalyst layer has the following general formula on a carbon support:
PtRuN
A membrane electrode assembly comprising a catalyst on which ternary fine particles represented by the formula (1) are supported.

As a means for solving the above-mentioned problems, the invention according to claim 9 is directed to a fuel electrode catalyst layer, an oxygen electrode catalyst layer, and a solid height interposed between the fuel electrode catalyst layer and the oxygen electrode catalyst layer. In a membrane / electrode assembly comprising a molecular electrolyte membrane, the fuel electrode catalyst layer is formed on a carbon support with the following general formula:
PtRuN
(Wherein the atomic ratio of Pt and Ru is 40:60 to 90:10, and the N content is in the range of 2 to 50 at.%). It is a membrane electrode assembly characterized by including.

  As a means for solving the above-mentioned problem, the invention according to claim 10 is characterized in that the particle diameter of the fuel electrode PtRuN ternary catalyst fine particles is in the range of 1 to 3 nm. It is a membrane electrode assembly.

As means for solving the above-mentioned problems, the invention according to claim 11 is that the carbon support is non-porous acetylene black or multi-wall carbon nanotubes, and the specific surface area is 20 to 140 m ² / g. 11. The membrane electrode assembly according to claim 8-10.

As a means for solving the above-mentioned problem, the invention according to claim 12 is the membrane electrode assembly according to claims 8 to 10, wherein the specific surface area of the carbon support is 20 to 300 m ² / g. .

  As a means for solving the above problem, the invention according to claim 13 is a membrane electrode assembly according to claims 8 to 12, which is used in a direct methanol fuel cell.

  As a means for solving the problems, the invention according to claim 14 is a membrane electrode assembly according to claims 8 to 12, which is used in a solid polymer fuel cell.

According to the present invention, when a PtRu catalyst is deposited on a carbon support by an electroless plating method, an alcohol reduction method, and an ultrasonic reduction method, a PtRu catalyst is obtained by adding N to PtRu to form a PtRuN ternary catalyst. When particles are deposited on the carbon support, N acts from the inside and outside of the particles to refine the PtRu catalyst particles that are deposited and increase the specific surface area of the catalyst particles. As a result, the catalytic activity may be improved. It's been found. 1 and 2 are schematic cross-sectional views of the PtRuN catalyst fine particles 1 of the present invention obtained by the present invention. From the X-ray photoelectron spectroscopy (XPS), in the PtRuN catalyst particles synthesized by the alcohol reduction method, as shown in FIG. 1, N7 is present as an oxide on the outer surface of the PtRu particles 5 supported on the carbon support 3. In the PtRuN catalyst synthesized by the electroless plating method, as shown in FIG. 2, N7 is present as an oxide on the outer surface of the PtRu particle 5, and N8 is a metal nitride or N simple substance inside the PtRu particle 5. It is suggested that it exists. Therefore, N7 and N8 act from the outside or the inside of the PtRu particle 5 and suppress the particle growth, and as a result, the entire PtRuN catalyst fine particle 1 is considered to be miniaturized.
In general, a Nafion membrane manufactured by DuPont is used as a solid polymer electrolyte membrane between a fuel electrode catalyst layer and an oxygen electrode catalyst layer of a fuel cell. The Nafion membrane is perfluoroalkylsulfonic acid, and because of the high electronegativity of fluorine, the hydrogen atom of the sulfonic acid group easily becomes H ⁺ and dissociates, and exhibits proton conductivity. This indicates that the Nafion membrane has extremely high acidity. Therefore, the interface between the Nafion membrane and the electrode catalyst layer and the catalyst particles pasted with the Nafion resin and the Nafion interface are in a strongly acidic atmosphere. In the past, addition of a third metal element (for example, Mo, Mn, Fe, Co, etc.) has been attempted in order to enhance the CO poisoning resistance of the PtRu catalyst. However, since these transition metals do not have sufficient acid resistance, they are eluted as metal ions when in contact with a strongly acidic Nafion resin. As a result of ion conversion of the eluted metal ions with H ⁺ in the Nafion membrane, the proton conductivity of Nafion is lowered and the battery characteristics are deteriorated. However, unlike conventional third metal elements, N has acid resistance, so that it dissolves very little in an acid, and it has also been discovered that N is suitable as an additive element for fuel cell catalysts.
In the present invention, nonporous acetylene black or multi-wall carbon nanotubes are suitable for the support of the fuel electrode PtRuN catalyst. Since there are no micropores in these non-porous carbon supports, all catalyst particles are deposited on the carbon support surface. For this reason, all the catalysts can contribute to the oxidation reaction of methanol or hydrogen gas fuel. For this reason, it has become possible to increase the catalyst utilization efficiency and to improve the battery characteristics. At the same time, when a catalyst having the same loading rate is used as compared with the case where a conventional porous carbon support is used, the use efficiency of the catalyst is high in the catalyst according to the present invention, so that the battery characteristics can be improved. Accordingly, it is possible to obtain battery characteristics equivalent to or higher than those of conventional batteries with a small amount of catalyst, and to realize Pt saving. In particular, the multi-wall carbon nanotube carrier has a rod-like shape and is bulky as compared with conventionally used carbon black. For this reason, when the catalyst is pasted with Nafion resin and is made into an electrode catalyst film by a press machine, there are more physical voids in the electrode catalyst film than in the conventional carbon black support. For this reason, sufficient diffusion of methanol or hydrogen gas fuel to the PtRuN catalyst is ensured. In the direct methanol fuel cell, the diffusion of CO ₂ gas generated at the anode is also promoted, and as a result, the cell characteristics are improved. Furthermore, when multi-wall carbon nanotubes are used as the catalyst support, the multi-wall carbon nanotubes have a lower specific resistance than conventionally used carbon black. For this reason, it was discovered that IR loss can be suppressed, and as a result, a decrease in battery voltage can be suppressed.

A fuel electrode catalyst for a fuel cell according to the present invention has the following general formula supported on a carbon support:
PtRuN
It consists of ternary fine particles represented by In the formula, the N content is in the range of 2 to 50 at.%. When the N content is less than 2 at.%, The particle size of the PtRu catalyst is not sufficiently reduced, so that the specific surface area of the catalyst does not increase and the catalytic activity cannot be sufficiently increased. On the other hand, when the N content is more than 50 at.%, The PtRu content is lowered, the catalytic activity is deteriorated, and the battery output is lowered.

  The atomic ratio (at.%) Of Pt and Ru in the ternary catalyst is preferably in the range of 40:60 to 90:10. When Pt is less than 40 at.%, The oxidation activity of methanol and hydrogen cannot be sufficiently increased. Moreover, when Pt exceeds 90 at.%, The CO poisoning resistance cannot be sufficiently improved.

By setting the PtRu composition to Pt ₄₀ Ru ₆₀ to Pt ₉₀ Ru ₁₀ , it is considered that the outermost surface composition of the catalyst is optimized and the catalytic activity is enhanced. Further, when N is 2 to 50 at.%, The growth of PtRu catalyst particles can be suppressed, and a catalyst having a large specific surface area and high activity can be obtained. As a result, it is considered that the reactions of the reaction formulas (2) and (3) proceed faster and the methanol oxidation activity is improved. Similarly, in the polymer electrolyte fuel cell, the hydrogen oxidation reaction represented by the formula (4) is considered to proceed faster.

^{_{1 / 2H 2 = → H +}} + e - (4)

The particle size of the PtRuN catalyst is suitably 1 to 3 nm. If the particle size is less than 1 nm, the activity of the synthesized catalyst surface is extremely high, so a compound is formed in the surrounding material and the catalyst surface layer, and the activity of the catalyst itself is lowered. On the other hand, when the particle diameter is larger than 3 nm, the specific surface area of the catalyst cannot be increased sufficiently and the catalytic activity cannot be increased.

The carbon base material used as a catalyst carrier is non-porous, and its specific surface area is suitably ²⁰ to 140 m ² / g. By using a non-porous carbon carrier, all the catalyst particles are deposited on the surface of the carrier, so that the catalyst utilization rate can be increased and the battery characteristics can be improved. When the specific surface area is less than 20 m ² / g, the catalyst cannot be supported sufficiently, and a catalyst having a loading rate of 30 wt.% Or more cannot be synthesized. Further, in the carbon carrier having a specific surface area of more than 140 m ² / g, micropores are present in the carrier. In such a carrier, some of the synthesized catalyst particles are deposited in the micropores, and the probability of contributing to the oxidation reaction of methanol or hydrogen gas is reduced, resulting in a decrease in catalyst utilization efficiency. Therefore, it is not preferable to use a carbon support having a specific surface area of more than 140 m ² / g in order to increase the utilization efficiency of the catalyst and improve the battery characteristics. However, when synthesizing a highly supported catalyst having a catalyst particle diameter of 2 nm and 75 wt.% Or more, it is necessary to use a carbon support having a large specific surface area. Even in this case, the specific surface area of the carbon support is preferably 300 m ² / g or less (for example, Vulcan-P specific surface area 140 m ² / g of Cabot, Vulcan XC-72R specific surface area 254 m ² / g, etc.). When the specific surface area of the carbon support exceeds 300 m ² / g, the fine pores present in the support increase, and as described above, the ratio of the catalyst buried in the fine pores increases and the catalyst utilization efficiency decreases, It causes deterioration of battery characteristics.

As a non-porous carbon support, multi-walled carbon nanotube is a material to be mentioned. The shape of the multi-walled carbon nanotube is completely different from the conventional carbon black particles, and is in the form of a rod. For this reason, when a bulky proton conductive polymer and paste are prepared and press-molded to form an electrocatalyst layer, the presence of many physical voids in the coating film indicates that a scanning electron microscope (SEM) Confirmed by observation. For this reason, the diffusibility of methanol or hydrogen gas fuel to the anode catalyst layer is increased, and the battery characteristics can be improved. In particular, in a direct methanol fuel cell (DMFC), CO ₂ gas is generated by an oxidation reaction at the anode. When multi-wall carbon nanotubes are used as a carrier, the diffusion of CO ₂ gas is promoted by the above-mentioned physical voids, so that the battery characteristics of DMFC can be improved. In addition, the specific resistance of the multiwall carbon nanotube is smaller than that of conventional carbon black. For this reason, IR loss can be suppressed and a decrease in battery voltage can be suppressed.

  The PtRuN catalyst according to the present invention can keep its particle size below 5 nm regardless of the specific surface area of the carbon support. As described above, when a PtRu catalyst is synthesized using a carbon support having a small specific surface area in order to increase the utilization efficiency of the catalyst, its particle size increases and the specific surface area of the catalyst decreases, thereby increasing the catalytic activity. I can't. The PtRuN catalyst of the present invention can suppress the catalyst particle diameter to 1 to 3 nm even when a non-porous carbon support having a small specific surface area is used. Therefore, the PtRuN catalyst according to the present invention is a catalyst material that can simultaneously improve the utilization efficiency of the catalyst and the catalytic activity.

The production method of the PtRuN catalyst fine particles of the present invention by the alcohol reduction method is basically
(1) dispersing a carbon support having a specific surface area of 20 to 300 m ² / g in one or more kinds of alcohols or aqueous alcohol solutions;
(2) dissolving a salt or complex of Pt, a salt or complex of Ru, and an N-containing compound in an alcohol or an alcohol aqueous solution in which a carbon carrier is dispersed;
(3) adjusting the pH value of the alcohol solution containing the carbon support, the salt or complex of Pt, the salt or complex of Ru, and the N-containing compound;
(4) including a step of heating and refluxing with alcohol in an inert atmosphere, on a carbon support, the following general formula:
PtRuN
The fuel electrode catalyst for fuel cells carrying the ternary fine particles shown in FIG.

The method for producing the PtRuN catalyst fine particles of the present invention by electroless plating is basically as follows:
(1) a step of dispersing a carbon support having a specific surface area of 20 to 300 m ² / g in pure water;
(2) dissolving a salt or complex of Pt, a salt or complex of Ru, and an N-containing compound in an aqueous solution in which the carbon support is dispersed;
(3) adjusting the pH value of an aqueous solution in which the carbon support is dispersed and containing a salt or complex of Pt, a salt or complex of Ru, and an N-containing compound;
(4) including a step of performing electroless plating by heating the aqueous solution in the air or in an inert atmosphere, the following general formula on the carbon support:
PtRuN
It produces | generates the fuel electrode catalyst for fuel cells which carry | supported the ternary fine particle shown by these.

The method for producing the PtRuN catalyst fine particles of the present invention by the ultrasonic reduction method is basically as follows:
(1) a step of dispersing a carbon support having a specific surface area of 20 to 300 m ² / g in pure water;
(2) dissolving a salt or complex of Pt, a salt or complex of Ru, and an N-containing compound in an aqueous solution in which the carbon support is dispersed;
(3) adjusting the pH value of an aqueous solution in which the carbon support is dispersed and containing a salt or complex of Pt, a salt or complex of Ru, and an N-containing compound;
(4) irradiating the aqueous solution with ultrasonic waves in the air or in an inert atmosphere, the following general formula on the carbon carrier:
PtRuN
The fuel electrode catalyst for fuel cells carrying the ternary fine particles shown in FIG.

  The particle size of the PtRuN catalyst fine particles produced by the production method of the present invention is reduced by the presence of N compared to the particle size of the conventional PtRu catalyst fine particles. In general, the particle size of the PuRu catalyst produced by the conventional manufacturing method is 2 to 10 nm, but the particle size of the PtRuN catalyst according to the present invention is reduced to 1 to 3 nm. This decrease in particle size increases the specific surface area of the catalyst, which is thought to greatly improve the methanol oxidizing ability and hydrogen oxidizing ability. Another feature of the present invention due to the addition of N is that the particle size distribution is narrower than that of conventional PtRu catalyst fine particles. The particle size distribution of the PtRu catalyst fine particles produced by the conventional method is as wide as 2 to 10 nm, but in the PtRuN catalyst according to the present invention, the particle size distribution is narrowed to 1 to 3 nm.

  The acid used for adjusting the pH value of the synthesis solution to the acidic side is preferably sulfuric acid having a boiling point higher than 200 ° C. In the alcohol reduction method, heating and reflux may be performed at a temperature of about 200 ° C, so in the case of an acid having a boiling point of less than 200 ° C, the acid may be dissipated by heating and refluxing the alcohol. It becomes difficult to maintain the value within a predetermined range. Therefore, hydrochloric acid and nitric acid are not preferred because they have low boiling points and dissipate during heating to reflux. For the same reason, NaOH or KOH is suitable for adjusting the pH value of the synthesis solution to the alkali side.

N-containing compounds that can be used in the method for producing PtRuN catalyst fine particles of the present invention include nitrous acid, nitrite (including both normal and acidic salts), hydrazine, and the like. The salt is preferably an alkali metal salt (sodium nitrite, potassium nitrite, etc.) or an ammonium salt (ammonium nitrite, etc.). The N atom having a valence of +5 is not suitable for the purpose of the present invention because it has the same electronic configuration as He and is chemically stabilized by the octet rule and does not become a source of N. Therefore, nitric acid and nitrates having +5 valent N atoms cannot be used in the present invention. When the PtRuN catalyst is synthesized, the amount of N-containing compound added is preferably in the range of 5% to 100% with respect to the total number of moles of Pt and Ru. If the added amount is less than 5%, the N content is less than 2 at.%, And the effect of atomizing the catalyst is not sufficient.On the other hand, if it exceeds 100%, the N content exceeds 50 at.% And the PtRu content decreases. As a result, the catalytic activity decreases.
Examples of the salt or complex of Pt used in the present invention include dinitrodiamine platinum complex, platinum triphenylphosphine complex, bis (acetylacetonato) platinum (II), hexachloroplatinic acid, and potassium tetrachloroplatinum (II). Etc. These platinum compounds can be used alone or in combination of two or more.

  Examples of the Ru salt or complex used in the present invention include ruthenium chloride hydrate, ruthenium triphenylphosphine complex, and tris (acetylacetonato) ruthenium (III). These ruthenium compounds can be used alone or in combination of two or more.

  In the alcohol reduction method, when a compound for synthesizing a catalyst is dissolved in an alcohol solvent and refluxed at a temperature near the boiling point of the alcohol solvent, the alcohol (R-OH) emits electrons during heating to reflux and Pt and It reduces Ru ions and oxidizes itself to aldehyde (R'-CHO). In the electroless plating method, for example, when nitrite ions, which are reducing agents, are oxidized to nitrate ions, electrons are released, and these electrons are received by Pt and Ru ions and reduced to metal. Hydrazine emits electrons released when hydrazine is oxidized to nitrogen, and Pt and Ru ions are received and reduced to metal. In the ultrasonic reduction method, a high-pressure and high-temperature field is formed by cavitation to generate reducing chemical species, thereby reducing Pt and Ru ions.

  Examples of the alcohol used in the heat reflux treatment of the present invention include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, ethylene glycol, glycerin, tetraethylene glycol, propylene glycol, and isoamyl alcohol. N-amyl alcohol, sec-butyl alcohol, allyl alcohol, 2-ethoxy alcohol and 1,2-hexadecanediol. These alcohols can be used by appropriately selecting one kind or two or more kinds. In refluxing, in order to prevent oxidation of the fine particles, it is preferable to perform reflux while replacing the inside of the reaction system with an inert gas such as nitrogen or argon.

  The heating temperature and reflux time in the alcohol reduction method vary depending on the type of alcohol used. In general, the heating temperature is about 60 to 300 ° C., and the reflux time is in the range of 30 minutes to 6 hours. In the case of the electroless plating method, the general bath temperature is 50 to 90 ° C., and the reduction time is 30 minutes to 2 hours. In the case of the ultrasonic reduction method, the ultrasonic irradiation time is 30 minutes to 4 hours.

  In the present invention, in the case of the alcohol reduction method, the salt or complex of Pt and Ru and the N-containing compound are dissolved in at least one kind of alcohol. This alcohol may contain water in addition to the case of consisting of alcohol alone. In the case of the electroless plating method and the ultrasonic reduction method, the salt or complex of Pt and Ru and the N-containing compound are basically dissolved in pure water. In the electroless plating method and the ultrasonic reduction method, the above-described alcohol may be added as a reduction aid.

The catalyst used in the present invention is suitably 30% by weight or more. When the loading ratio is less than 30 wt.%, The thickness of the catalyst electrode increases when an attempt is made to obtain a constant catalyst coating amount. For this reason, the diffusion resistance of the fuel and the generated CO ₂ gas increases, which is not preferable. The upper limit of the loading rate is not specified. For example, in order to obtain a loading rate of 80 wt.%, When the catalyst particle diameter is 2 nm, the specific surface area of the carrier needs to be 200 m ² / g or more. In order to obtain such a high loading rate catalyst, a porous carbon carrier must be used. Even in such a case, a porous carbon support with as few micropores as possible should be selected and used (for example, Vulcan XC-72R manufactured by Cabot, specific surface area of 254 m ² / g, etc.).

Multi-wall carbon, which is a non-porous carrier, is prepared by dissolving 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of sodium nitrite in 100 ml of ethylene glycol. A 130 m ethylene glycol solution in which 0.5 g of nanotubes (MWCNT, specific surface area 30 m ^{2 /} g) was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of sodium nitrite in 100 ml of ethylene glycol, respectively. AB, specific surface area 68 m ^{2 /} g) 130 ml of ethylene glycol solution in which 0.5 g was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours at 200 ° C. with stirring in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of sodium nitrite in 100 ml of ethylene glycol, respectively. , Specific surface area 140 m ^{2 /} g) 130 g of ethylene glycol solution in which 0.5 g was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. The solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Bis (acetylacetonato) platinum (II) 1.69 mmol, tris (acetylacetonato) ruthenium (III) 1.69 mmol and hydrazine 1.69 mmol were dissolved in 100 ml of ethylene glycol, respectively. 130 ml of ethylene glycol solution in which 0.5 g of MWCNT (specific surface area 30 m ^{2 /} g) was dispersed was added. This solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of hydrazine in 100 ml of ethylene glycol, respectively. Acetylene black (AB, 130 ml of ethylene glycol solution in which 0.5 g of a specific surface area of 68 m ^{2 /} g) was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours at 200 ° C. with stirring in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of hydrazine in 100 ml of ethylene glycol, respectively. Carbon black (CB, ratio) 130 ml of ethylene glycol solution in which 0.5 g of surface area 140 m ^{2 /} g) was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. The solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area of 30 m ^{2 /} g) as a non-porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was carried out at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of acetylene black (AB, specific surface area 68 m ^{2 /} g), which is a non-porous carrier, was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was performed at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of carbon black (CB, specific surface area 140 m ^{2 /} g) as a porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was performed at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area of 30 m ^{2 /} g) as a non-porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was carried out at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of acetylene black (AB, specific surface area 68 m ^{2 /} g), which is a non-porous carrier, was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was performed at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 6.76 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of carbon black (CB, specific surface area 140 m ^{2 /} g) as a porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 12 using a pH meter. The temperature of the solution was raised to 80 ° C. using a hot plate while stirring in the atmosphere, and electroless plating was performed at this temperature for 2 hours to deposit and carry PtRuN catalyst fine particles on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area of 30 m ^{2 /} g) as a non-porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of acetylene black (AB, specific surface area 68 m ^{2 /} g), which is a non-porous carrier, was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of sodium nitrite were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of carbon black (CB, specific surface area 140 m ^{2 /} g) as a porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area of 30 m ^{2 /} g) as a non-porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of acetylene black (AB, specific surface area 68 m ^{2 /} g), which is a non-porous carrier, was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

1.69 mmol of hexachloroplatinic acid hexahydrate, 1.69 mmol of ruthenium trichloride hydrate and 1.69 mmol of hydrazine were dissolved in 400 ml of pure water. In this aqueous solution, 0.5 g of carbon black (CB, specific surface area 140 m ^{2 /} g) as a porous carrier was dispersed. Aqueous sodium hydroxide was added dropwise, and the solution was adjusted to pH 10 using a pH meter. In the atmosphere, this solution was subjected to ultrasonic irradiation treatment for 2 hours using a commercially available ultrasonic cleaner, and PtRuN catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Bis (acetylacetonato) platinum (II) 1.69 mmol, tris (acetylacetonato) ruthenium (III) 1.69 mmol and sodium nitrite 1.69 mmol are each 100 ml of ethylene glycol aqueous solution (ethylene glycol: water = 50 vol.%: 50 vol. %) And a 130 m ethylene glycol aqueous solution (ethylene glycol: water = 50 vol.%: 50 vol.%) In which 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area 30 m ^{2 /} g) as a non-porous carrier is dispersed. ) Was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours with stirring at 130 ° C. in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

Bis (acetylacetonato) platinum (II) 1.69 mmol, tris (acetylacetonato) ruthenium (III) 1.69 mmol, and sodium nitrite 1.69 mmol each in 100 ml ethanol aqueous solution (ethanol: water = 50vol.%: 50vol.%) And a 130 m ethanol aqueous solution (ethanol: water = 50 vol.%: 50 vol.%) In which 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area 30 m ^{2 /} g) as a non-porous carrier was dispersed was added. . An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. The solution was refluxed for 4 hours at 95 ° C. with stirring in a nitrogen gas atmosphere, and PtRuN catalyst fine particles were deposited and supported on the multi-wall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.
(Comparative Example 1)
Bis (acetylacetonato) platinum (II) 1.69 mmol and tris (acetylacetonato) ruthenium (III) 1.69 mmol are dissolved in 100 ml of ethylene glycol, respectively. 30 ml ^{2 /} g) 230 ml ethylene glycol solution in which 0.5 g was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRu catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.
(Comparative Example 2)
Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II) and 1.69 mmol of tris (acetylacetonato) ruthenium (III) in 100 ml of ethylene glycol, respectively, and use acetylene black (AB, specific surface area of 68 m ² ) as a non-porous carrier. / g) 230 ml of ethylene glycol solution in which 0.5 g was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. The solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRu catalyst fine particles were deposited and supported on acetylene black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.
(Comparative Example 3)
Bis dissolved in (acetylacetonato) platinum (II) 1.69 mmol of tris ethylene glycol (acetylacetonato) ruthenium (III) respectively 1.69 mmol 100 ml, as a porous carrier carbon black (CB, specific surface area 140 m ² / g) 230 ml of ethylene glycol solution in which 0.5 g was dispersed was added. An aqueous sulfuric acid solution was added dropwise, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed for 4 hours with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRu catalyst fine particles were deposited and supported on carbon black. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

  The composition of each catalyst obtained in Examples 1 to 20 and Comparative Examples 1 to 3 was examined by X-ray photoelectron spectroscopy (XPS). The particle size was examined with a transmission electron microscope (TEM). The results are shown in Table 1. In Examples 1 to 20, it can be seen that N is added to the PtRu catalyst by adding sodium nitrite or hydrazine in the synthesis system. The concentration of N is around 11 at.%. The atomic ratio of Pt: Ru is around 64:36. The particle size of the PtRuN catalyst obtained in Examples 1 to 20 is reduced to 2 nm or less. Despite the small specific surface area of multi-wall carbon nanotubes (MWCNT), its particle size is reduced to 2 nm. In Example 19, an ethylene glycol aqueous solution was used as the alcohol, and the reflux temperature was lowered from 200 ° C. to 130 ° C. to synthesize the catalyst. The growth of fine particles is suppressed by reducing the synthesis temperature. Therefore, by reducing the synthesis temperature to 130 ° C., a PtRuN catalyst having a particle size of 1.8 nm is obtained. Similarly, in Example 20, an ethanol aqueous solution was used and a PtRuN catalyst was synthesized at a reflux temperature of 95 ° C., and the particle size of the PtRuN catalyst was reduced to 1.5 nm. On the other hand, since Comparative Examples 1 to 3 do not contain N, the particle size of the PtRu catalyst is as large as 7 to 10 nm. From the above results, it can be confirmed that the PtRu catalyst is atomized by adding N.

It was confirmed from an electron micrograph that the multi-wall carbon nanotube-supported PtRuN catalyst obtained in Example 1 had a particle diameter of 2 nm and catalyst fine particles were sufficiently dispersed. On the other hand, in the PtRu catalyst of Comparative Example 1 containing no N, the catalyst particle size was as large as ˜10 nm, the catalyst particles were agglomerated, and it was confirmed by an electron micrograph that the dispersibility was insufficient. From the above results, it is possible to confirm the fine particle action and dispersion action of the PtRu catalyst by adding N.

After adding pure water and an alcohol solution of Nafion (manufactured by DuPont) to the carbon-supported PtRuN catalysts obtained in Examples 1 to 20, the viscosity was adjusted to obtain a catalyst ink. This was coated on a Teflon (registered trademark) sheet so that the coating amount of the PtRuN catalyst was 5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain a methanol electrode catalyst. Further, after adding pure water and an alcohol solution of Nafion (manufactured by DuPont) to a Pt catalyst supported on carbon and stirring it, the viscosity thereof was adjusted to obtain a catalyst ink. This was coated on a Teflon (registered trademark) sheet so that the coating amount of the Pt catalyst was 5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain an oxygen electrode catalyst. Thereafter, a PtRuN methanol electrode catalyst and a Pt oxygen electrode catalyst were hot-pressed on both sides of a solid polymer electrolyte membrane (Nafion membrane 112 manufactured by DuPont) to produce a membrane electrode assembly. A direct methanol fuel cell shown in FIG. 3 was produced using a membrane electrode assembly and a 15 wt.% Methanol aqueous solution as the liquid fuel. In FIG. 3, reference numeral 10 indicates a direct methanol fuel cell. Reference numeral 12 denotes an oxygen electrode side current collector, 14 denotes an oxygen electrode side diffusion layer, 16 denotes a solid polymer electrolyte membrane, 18 denotes a methanol electrode side diffusion layer, 20 denotes a methanol electrode side current collector, and 22 denotes a methanol fuel tank. , 24 is an air introduction hole, 26 is an oxygen electrode Pt catalyst layer, 28 is a methanol electrode PtRuN catalyst layer, and 30 is a methanol fuel introduction hole. The oxygen electrode side current collector 12 has a function as a structure for taking in air (oxygen) through the air introduction hole 24 and also has a current collecting function. The solid polymer electrolyte membrane (DuPont Nafion membrane 112) 16 has a function of transporting protons generated at the methanol electrode to the oxygen electrode side, and a function as a separator for preventing a short circuit between the methanol electrode and the oxygen electrode. It will be. In the direct methanol fuel cell 10 configured as described above, the liquid fuel supplied from the methanol electrode-side current collector 20 is led to the methanol electrode catalyst layer 28 via the methanol electrode-side diffusion layer 18 and is oxidized, and CO. ₂ and converted to electrons and protons. Protons move to the oxygen electrode side through the solid polymer electrolyte membrane 16. At the oxygen electrode, oxygen taken in from the oxygen electrode side current collector 12 is reduced by electrons generated at the methanol electrode, and this reacts with the protons to generate water. In the direct methanol fuel cell 10 shown in FIG. 3, power generation occurs due to such methanol oxidation reaction and oxygen reduction reaction.
(Comparative Example 4)
A direct methanol fuel cell was produced in the same manner as in Example 21 except that the PtRu catalysts in Comparative Examples 1 to 3 were used as the methanol electrode catalyst instead of the PtRuN catalyst in Example 21.

In the direct methanol fuel cells obtained in Example 21 and Comparative Example 4, respectively, the power density was measured. The measurement results are shown in Table 2. In Example 21, since a PtRuN catalyst is used, the catalyst particle size is 2 nm or less. Further, as the catalyst carrier, a carbon carrier which is a non-porous carbon carrier or a porous carrier but has relatively few fine pores is used. For this reason, the catalyst activity is increased, the catalyst utilization efficiency is increased, and the power density is as high as 70 mW / cm ² or more. In the table, it can be seen that the power density increases in the order of CB, AB, and MWCNT in the carbon support. The reason why CB gave the lowest power density is that because CB is a porous carrier, some PtRuN catalysts are buried in the micropores and cannot contribute to the methanol oxidation reaction. Since AB is a non-porous support, it provides a higher power density than CB support. In addition to being non-porous, the MWCNT support has many physical voids in the electrode catalyst layer due to its shape. For this reason, the diffusion of the CO ₂ gas generated at the methanol aqueous solution and the methanol electrode as fuel is promoted. In addition, since the specific resistance of MWCNT is lower than that of CB, IR loss can be reduced, and as a result of suppressing the decrease in battery voltage, it is considered that a high output density was obtained. In Example 19, an ethylene glycol aqueous solution was used as the alcohol, and the reflux temperature was lowered from 200 ° C. to 130 ° C. to synthesize the catalyst. The growth of fine particles is suppressed by reducing the synthesis temperature. Therefore, by reducing the synthesis temperature to 130 ° C., a PtRuN catalyst having a particle size of 1.8 nm is obtained. Similarly, in Example 20, an ethanol aqueous solution was used and a PtRuN catalyst was synthesized at a reflux temperature of 95 ° C., and the particle size of the PtRuN catalyst was reduced to 1.5 nm. As a result of the decrease in the catalyst particle size, the specific surface area of the catalyst is increased and the activity is increased. As a result, the power density shows a high value of 80 mW / cm ² or more. On the other hand, in Comparative Example 4, the particle size of the PtRu catalyst not containing N is as large as ˜10 nm and the output density is as low as 35 mW / cm ² when non-porous MWCNT is used as the support. Even when a carbon support having a specific surface area of 68 m ² / g and 140 m ² / g is used as the support, the particle diameter of the PtRu catalyst is 7 to 8 nm, and the increase in power density is about 5 mW / cm ² .

To the carbon-supported PtRuN catalysts obtained in Examples 1 to 20, pure water and an alcohol solution of Nafion (manufactured by DuPont) were added and stirred, and the viscosity was adjusted to obtain a catalyst ink. This was coated on a Teflon (registered trademark) sheet so that the coating amount of the PtRuN catalyst was 0.5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain a hydrogen electrode catalyst. An alcohol solution of pure water and Nafion (manufactured by DuPont) was added to the carbon-supported Pt catalyst and stirred, and the viscosity was adjusted to obtain a catalyst ink. This was coated on a Teflon (registered trademark) sheet so that the coating amount of the Pt catalyst was 0.5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain an oxygen electrode catalyst. Thereafter, a PtRuN hydrogen electrode catalyst and a Pt oxygen electrode catalyst were hot-pressed on both sides of a solid polymer electrolyte membrane (Nafion membrane 112 manufactured by DuPont) to produce a membrane electrode assembly. Using this membrane electrode assembly and hydrogen gas as a fuel, a polymer electrolyte fuel cell shown in FIG. 4 was produced. In FIG. 4, reference numeral 40 denotes a solid polymer fuel cell. Reference numeral 44 is an oxygen electrode side current collector, 43 is an oxygen electrode side diffusion layer, 41 is a solid polymer electrolyte membrane, 48 is a hydrogen electrode side diffusion layer, 47 is a hydrogen electrode side current collector, and 42 is an air introduction hole. , 45 represents an oxygen electrode Pt catalyst layer, 46 represents a hydrogen electrode PtRuN catalyst layer, and 49 represents a hydrogen fuel introduction hole. The oxygen electrode side current collector 44 has a function as a structure that takes in air (oxygen) through the air introduction hole 42 and also has a current collecting function. The solid polymer electrolyte membrane (DuPont Nafion membrane 112) 41 has a function of transporting protons generated at the hydrogen electrode to the oxygen electrode side and a function as a separator for preventing a short circuit between the hydrogen electrode and the oxygen electrode. It will be. In the polymer electrolyte fuel cell 40 configured as described above, the hydrogen gas supplied from the hydrogen electrode side current collector 47 is led to the hydrogen electrode catalyst layer 46 through the hydrogen electrode side diffusion layer 48, and is oxidized and electrons. These protons move to the oxygen electrode side through the solid polymer electrolyte membrane 41. At the oxygen electrode, oxygen taken in from the oxygen electrode side current collector 44 is reduced by electrons generated at the hydrogen electrode, and this reacts with the protons to generate water. In the polymer electrolyte fuel cell 40 shown in FIG. 4, power generation occurs due to such hydrogen oxidation reaction and oxygen reduction reaction.
(Comparative Example 5)
A polymer electrolyte fuel cell was produced in the same manner as in Example 22 except that the PtRu catalyst obtained in Comparative Examples 1 to 3 was used as a hydrogen electrode catalyst instead of the carbon-supported PtRuN catalyst in Example 22. .

The power density was measured for the polymer electrolyte fuel cells obtained in Example 22 and Comparative Example 5, respectively. Table 3 shows the measurement results. In Example 22, since a PtRuN catalyst is used, the catalyst particle size is 2 nm or less. Further, as the catalyst carrier, a carbon carrier which is a non-porous carbon carrier or a porous carrier but has relatively few fine pores is used. For this reason, the catalyst activity is increased, the catalyst utilization efficiency is increased, and the power density is as high as 200 mW / cm ² or more. In the table, it can be seen that the power density increases in the order of CB, AB, and MWCNT in the carbon support. The reason why CB gave the lowest power density is that because CB is a porous carrier, some PtRuN catalysts are buried in the micropores and cannot contribute to the methanol oxidation reaction. Since AB is a non-porous support, it provides a higher power density than CB support. In addition to being non-porous, the MWCNT support has many physical voids in the electrode catalyst layer due to its shape. For this reason, the diffusion of hydrogen gas as a fuel is promoted. In addition, since the specific resistance of MWCNT is lower than that of CB, IR loss can be reduced and the decrease in battery voltage can be suppressed. In Example 19, an ethylene glycol aqueous solution was used as the alcohol, and the reflux temperature was lowered from 200 ° C. to 130 ° C. to synthesize the catalyst. The growth of fine particles is suppressed by reducing the synthesis temperature. Therefore, by reducing the synthesis temperature to 130 ° C., a PtRuN catalyst having a particle size of 1.8 nm is obtained. Similarly, in Example 20, an ethanol aqueous solution was used and a PtRuN catalyst was synthesized at a reflux temperature of 95 ° C., and the particle size of the PtRuN catalyst was reduced to 1.5 nm. As a result of the decrease in the catalyst particle size, the specific surface area of the catalyst is increased and the activity is increased. As a result, the power density shows a high value of 240 mW / cm ² or more. On the other hand, in Comparative Example 5, the particle size of the PtRu catalyst not containing N is as large as ˜10 nm and the output density is as low as 150 mW / cm ² when non-porous MWCNT is used as the support. Even if a carbon support having a specific surface area of 68 m ² / g and 140 m ² / g is used as the support, the particle diameter of the PtRu catalyst is 7 to 8 nm, and the increase in power density is about 10 mW / cm ² .

Bis (acetylacetonato) platinum (II) 1.69 mmol and tris (acetylacetonato) ruthenium (III) 1.69 mmol were dissolved in 100 ml of erylene glycol and mixed. To this solution, sodium nitrite was weighed in an amount of 0 to 200 mol% based on the total number of moles of Pt and Ru, dissolved in 100 ml of ethylene glycol solution, and added to the solution. A 130 ml ethylene glycol solution in which 0.5 g of multi-wall carbon nanotubes (MWCNT, specific surface area 30 m ^{2 /} g) as a non-porous carrier was dispersed was further added. A sulfuric acid aqueous solution was dropped into this solution, and the pH of the solution was adjusted to 3 using pH test paper. This solution was refluxed for 4 hours with stirring in an oil bath at 200 ° C. in a nitrogen atmosphere, and a PtRuN catalyst was deposited and supported on the multiwall carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

  An X-ray diffraction experiment was performed on the PtRuN catalyst obtained in Example 23, and the particle size of the PtRuN catalyst was estimated by applying Scherrer's equation to the diffraction peak of (220). Also. The composition of the catalyst was investigated by XPS. Furthermore, a direct methanol fuel cell was produced for these PtRuN catalysts in the same manner as in Example 21, and the output density of each cell was measured. The results are shown in Table 4. From the results shown in Table 4, it can be seen that when the N content is 2 at.% Or more, the particle size of the PtRuN catalyst is reduced to less than 3 nm, and a high power density can be obtained. On the other hand, it can be seen that when the N content exceeds 50 at.%, The PtRu content decreases and the output density decreases.

  The catalyst comprising PtRuN fine particles according to the present invention can be used as a fuel electrode catalyst for direct methanol fuel cells (DMFC) and solid polymer fuel cells (PEFC).

1 is a schematic cross-sectional view of a PtRuN catalyst fine particle of the present invention. 1 is a schematic cross-sectional view of a PtRuN catalyst fine particle of the present invention. 1 is a schematic configuration diagram of a direct methanol fuel cell of the present invention. 1 is a schematic configuration diagram of a polymer electrolyte fuel cell of the present invention.

Explanation of symbols

1 PtRuN catalyst particles 3 Carbon support 5 PtRu catalyst particles 7 N
8 N
10 Direct methanol fuel cell 12 Oxygen electrode side current collector 14 Oxygen electrode side diffusion layer 16 Solid polymer electrolyte membrane 18 Methanol electrode side diffusion layer 20 Methanol electrode side current collector 22 Methanol fuel tank 24 Air introduction hole 26 Oxygen electrode Pt Catalyst layer 28 Methanol electrode PtRuN catalyst layer 30 Methanol fuel introduction hole 40 Solid polymer fuel cell 41 Solid polymer electrolyte membrane 42 Air introduction hole 43 Oxygen electrode side diffusion layer 44 Oxygen electrode side current collector 45 Oxygen electrode Pt catalyst layer 46 Hydrogen electrode PtRuN catalyst layer 47 Hydrogen electrode side current collector 48 Hydrogen electrode side diffusion layer 49 Hydrogen fuel introduction hole

Claims (14)

In a fuel cell having at least a fuel electrode, an oxygen electrode, and a solid polymer electrolyte membrane interposed between the fuel electrode and the oxygen electrode, the fuel electrode has the following general formula on a carbon support:
PtRuN
A fuel cell comprising a catalyst composed of ternary fine particles represented by The fuel cell according to claim 1, wherein the fuel electrode has the following general formula on a carbon support:
PtRuN
(Wherein the atomic ratio of Pt and Ru is 40:60 to 90:10, and the N content is in the range of 2 to 50 at.%). A fuel cell characterized by including. 3. The fuel cell according to claim 1, wherein the particle diameter of the PtRuN three-way catalyst for the fuel electrode is in the range of 1 to 3 nm. 4. The fuel cell according to claim 1, wherein the carbon support is non-porous acetylene black or multi-walled carbon nanotube, and a specific surface area thereof is 20 to 140 m ² / g. 4. The fuel cell according to claim 1, wherein the specific surface area of the carbon support is 20 to 300 m ² / g. 6. The fuel cell according to claim 1, wherein the fuel cell is a direct methanol fuel cell. 6. The fuel cell according to claim 1, wherein the fuel cell is a polymer electrolyte fuel cell. In a membrane electrode assembly comprising a fuel electrode catalyst layer, an oxygen electrode catalyst layer, and a solid polymer electrolyte membrane interposed between the fuel electrode catalyst layer and the oxygen electrode catalyst layer, the fuel electrode catalyst layer comprises: The following general formula on the carbon support:
PtRuN
A membrane electrode assembly comprising a catalyst on which ternary fine particles represented by the formula (1) are supported. 9. The membrane electrode assembly according to claim 8, wherein the fuel electrode has the following general formula on a carbon support:
PtRuN
(Wherein the atomic ratio of Pt and Ru is 40:60 to 90:10, and the N content is in the range of 2 to 50 at.%). A membrane electrode assembly characterized by comprising: 10. The membrane electrode assembly according to claim 8, wherein the particle diameter of the fuel electrode PtRuP ternary catalyst fine particles is within a range of 1 to 3 nm. 11. The membrane electrode assembly according to claim 8, wherein the carbon support is non-porous acetylene black or multi-wall carbon nanotube, and the specific surface area is 20 to 140 m ² / g. Joined body. The membrane electrode assembly according to claim 8, wherein the carbon carrier has a specific surface area of 20 to 300 m ² / g. The membrane electrode assembly according to claim 8, wherein the membrane electrode assembly is used in a direct methanol fuel cell. The membrane electrode assembly according to claim 8, wherein the membrane electrode assembly is used in a polymer electrolyte fuel cell.

Images