JP2006114469A - Fuel-cell and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new Pt catalyst having a grain size that is less than 5nm. <P>SOLUTION: A heterogeneous catalyst comprises particles containing at least Pt and P and a maximum average grain size of smaller than 5 nm. The grain size of the particles is 1-3 nm and the particles contain 2-50 atom% of P. The particles also contain Ru and the ratio of Pt and Ru in particles is Pt<SB>40</SB>Ru<SB>60</SB>-Pt<SB>90</SB>Ru<SB>10</SB>. The particles further contain a carbon base material, and a carbon base material is carbon black or carbon nanotubes (preferably multilayer carbon nanotubes). The heterogeneous catalyst can be used for a fuel electrode or for an oxygen electrode of the fuel cell or the membrane electrode assembly. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell and a membrane electrode assembly having a novel catalyst at a fuel electrode or an oxygen electrode. More specifically, the present invention relates to a fuel cell and a membrane electrode assembly having a catalyst containing at least Pt and P at a fuel electrode or an oxygen electrode.

  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 decomposing water and not only exists infinitely on the earth, but also contains a large amount of chemical energy per amount of substance. Moreover, when it is used as an energy source, harmful substances and global warming gases are used. It has the advantage that it does not occur.

  Research on fuel cells using methanol instead of hydrogen gas is also actively conducted. A methanol fuel cell that directly uses methanol, which is a liquid fuel, is expected to be a relatively small output power source for household 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 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) has been deposited 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 the external factors at the time of precipitation, the particle size of the Pt catalyst particles Attempts have been made to reduce the diameter as much as possible and increase the reaction surface area of the Pt catalyst. 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, and the protective colloid is weakly adsorbed on the surface of the Pt catalyst particles. , Pt catalyst is made fine. The protective colloid is adsorbed on the surface of the Pt catalyst synthesized by this method. Therefore, it is necessary to remove the protective colloid from the catalyst surface after the synthesis of the catalyst in order to fully exhibit the catalytic activity. For this reason, a method of performing heat treatment at 400 ° C. in a hydrogen stream after synthesis of Pt fine particles has been proposed. However, this treatment method cannot completely remove the protective colloid from the surface of the Pt catalyst, but the Pt catalyst fine particles are sintered with each other by the heat treatment at 400 ° C. to increase the Pt catalyst particle diameter and lower the catalytic activity. There was a problem.

  In addition, the Pt catalyst has a problem that carbon monoxide (CO) generated in the methanol oxidation process or CO contained in hydrogen gas is chemically adsorbed on the Pt catalyst, and eventually the catalytic activity is deactivated. It was. This phenomenon is called catalyst poisoning by CO. In order to suppress the poisoning of the Pt catalyst by CO, an element added to Pt was searched. As a result, it has been discovered that catalyst poisoning by CO is greatly reduced by adding Ru to Pt (see, for example, Patent Document 2).

Although this Ru itself has no oxidation activity of hydrogen or methanol, it is a co-catalyst having a function of quickly oxidizing CO deposited on Pt to CO ₂ and letting it escape. Taking a direct methanol fuel cell as an example, as shown in the following reaction formula (1), a deprotonation reaction occurs on the Pt catalyst particles, and CO is chemically adsorbed on the Pt catalyst particles. This is catalyst poisoning by CO. However, in the PtRu catalyst containing Ru, as shown in the following reaction formula (2), Ru reacts with water to produce Ru-OH, and then, as shown in the following reaction formula (3), CO chemisorbed on the surface of the Pt catalyst particles is oxidized to CO ₂ and removed.
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 an impregnation method, an electroless plating method, or an alcohol reduction method, the particle size is concentrated within a range of 5 to 10 nm. If the PtRu particle size remains large, the effective surface area of the catalyst will not increase and the catalytic activity will not be improved. Therefore, in order to increase the catalytic activity of PtRu, it is effective to increase the effective surface area of the catalyst by setting the PtRu particle size to less than 5 nm. 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. There is a strong demand for the development of an effective method for producing PtRu catalysts of less than 5 nm, but has not been successful.

JP-A-56-155645 JP-A-57-5266

  Accordingly, an object of the present invention is to provide a fuel cell and a membrane electrode assembly having a novel Pt-based catalyst having a particle size of less than 5 nm at the fuel electrode or oxygen electrode.

  As a means for solving the above-mentioned problems, the invention according to claim 1 is a heterogeneous catalyst characterized by comprising particles containing at least Pt and P and having a maximum average particle diameter of less than 5 nm.

  As a means for solving the above-mentioned problems, the invention according to claim 2 is the heterogeneous catalyst according to claim 1, wherein the particle diameter of the particles is 1 nm to 3 nm.

  As a means for solving the above-mentioned problems, the invention according to claim 3 is the heterogeneous catalyst according to claim 1, wherein the particles contain at least 2 atomic% of P.

  As a means for solving the above-mentioned problems, the invention according to claim 4 is the heterogeneous catalyst according to claim 1, wherein the content of P is 2 atom% to 50 atom%.

  As a means for solving the above-mentioned problems, the invention according to claim 5 is the heterogeneous catalyst according to claim 1, further comprising a carbon substrate.

  The invention according to claim 6 as means for solving the above-mentioned problems is that the carbon substrate is at least one selected from the group consisting of carbon black and carbon nanotubes. It is a homogeneous catalyst.

  The invention according to claim 7 as means for solving the problem is the heterogeneous catalyst according to claim 6, wherein the carbon substrate is a multi-walled carbon nanotube.

  As a means for solving the above-mentioned problems, the invention according to claim 8 is the heterogeneous catalyst according to claim 1, wherein the particles further contain Ru.

The invention according to claim 9 as means for solving the above-mentioned problem is that the ratio of Pt and Ru in the particles is Pt ₄₀ Ru _{60 to} Pt ₉₀ Ru _10. System catalyst.

Invention of claim 8, wherein said carbon substrate is characterized by having a specific surface area within the range of from 20m 2 ^/ g~300m 2 ^{/ g} non according to claim 10 as a means for solving the problem It is a homogeneous catalyst.

  The invention according to claim 11 as means for solving the above-mentioned problem includes the step of reducing Pt ions in the presence of a phosphorus-containing reducing agent. is there.

  According to a twelfth aspect of the present invention, the phosphorus-containing reducing agent is a compound derived from any one of phosphorous acid, phosphite, hypophosphorous acid or hypophosphite. The manufacturing method according to claim 11, wherein the manufacturing method is characterized.

  The invention according to claim 13 as means for solving the problem is the manufacturing method according to claim 11, wherein the reduction step is an alcohol reduction or an electroless plating step.

  As a means for solving the above-mentioned problem, the invention according to claim 14 comprises a cathode, an anode, and a polymer electrolyte membrane disposed between the cathode and the anode, and the cathode and / or the anode is claimed. A fuel cell comprising one catalyst.

  The invention according to claim 15 as means for solving the above-mentioned problems is characterized in that metanote and water or hydrogen are supplied to the anode, and oxygen is supplied to the cathode. It is.

  The invention according to claim 16 as means for solving the problem comprises an anode catalyst layer, a cathode catalyst layer, and a polymer electrolyte disposed between the anode catalyst layer and the cathode catalyst layer, An anode catalyst layer and / or a cathode catalyst layer is a membrane electrode assembly comprising the catalyst according to claim 1.

  According to the present invention, when P is added when depositing a Pt-based catalyst on a carbon substrate by an electroless plating method or an alcohol reduction method, when Pt-based catalyst particles are deposited on the carbon substrate, P is converted to Pt. It has been discovered that the Pt-based catalyst particles acting from inside and outside the catalyst particles are refined to increase the surface area of the catalyst particles, and as a result, the catalytic activity is improved. In particular, when the PtRu catalyst fine particles are deposited on the carbon substrate by the alcohol reduction method and the electroless plating method, if the P is added to the PtRu binary catalyst to form a ternary catalyst, the above-mentioned effect of adding Ru It was discovered that P acts from the outside and inside of the particles while maintaining the particle size, and the precipitated PtRu catalyst particles are refined to increase the surface area of the catalyst, resulting in improved catalytic activity.

The fuel cell catalyst according to the present invention has the following general formula supported on a carbon substrate:
PtRuP
It consists of ternary fine particles represented by In said formula, it is preferable that the content rate of P exists in the range of 2 atomic%-50 atomic% with respect to the total mole number of PtRu. If the P content is less than 2 atomic%, the particle size of the catalyst cannot be reduced sufficiently. On the other hand, when the P content is more than 50 atomic%, the PtRu content is too low, and the battery output decreases.

  The atomic ratio (at%) of Pt and Ru in the ternary catalyst is preferably in the range of 40:60 to 90:10. When Ru is less than 10 at%, it is not preferable because the resistance to CO poisoning cannot be sufficiently increased. Moreover, when Pt is less than 40 at%, the catalytic activity for methanol oxidation becomes insufficient, which is not preferable.

By setting the atomic composition of PtRu 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 increased. Further, when the P composition is 2 atomic% to 50 atomic% with respect to the total number of moles of PtRu, it is possible to suppress the particle growth of the PtRu catalyst and obtain a catalyst having a large specific surface area. 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.

  The particle size of the PtRuP catalyst is suitably 1 to 3 nm. When the particle size is less than 1 nm, the activity of the synthesized catalyst surface is extremely high, so that 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, if the particle size is larger than 3 nm, the surface area of the catalyst per unit weight cannot be increased sufficiently, and the catalytic activity cannot be increased.

1 and 2 are schematic cross-sectional views of PtRuP catalyst fine particles 1 obtained from the present invention. From the X-ray photoelectron spectroscopy (XPS analysis), in the PtRuP catalyst particles synthesized by the alcohol reduction method, as shown in FIG. 1, P7 exists as an oxide on the outer surface of the PtRu particles 5 supported on the carbon substrate 3. In the PtRuP catalyst synthesized by the electroless plating method, as shown in FIG. 2, P7 is present as an oxide on the outer surface of the PtRu particle 5, and P8 is a metal phosphide inside the PtRu particle 5. Or it is shown that it exists as phosphorus simple substance. Therefore, it is considered that P7 and P8 act from the outside or the inside of the Pt particles 5, the particle growth is suppressed, and the entire PtRuP catalyst fine particles 1 are miniaturized.
Furthermore, a Nafion membrane manufactured by DuPont is generally used as the solid polymer conductive film between the anode and the cathode of the fuel cell. In the Nafion membrane, the hydrogen atom of the sulfonic acid group becomes H ^+. Proton conductivity is exhibited. Therefore, the interface between the Nafion membrane and the electrode catalyst becomes strongly acidic. The third metal element (for example, Mo, Mn, Fe, Co, etc.) added to the conventional PtRu catalyst has no acid resistance and is eluted and ion-converted with H ^{+ of the} solid polymer conductive film. The proton conductivity of the solid polymer conductive film is lowered, whereas P is different from the conventional third metal element, and is acid-resistant, so it does not elute into acid and is suitable as a catalyst additive element for fuel cells. is there.

The specific surface area of the carbon substrate used as the catalyst carrier is suitably 20 to 300 m ² / g. When the specific surface area is less than 20 m ² / g, the catalyst cannot be supported sufficiently. When the specific surface area exceeds 300 m ² / g, the number of micropores present in the carbon substrate increases, and the catalyst buried in the micropores increases to form a sufficient three-phase interface during the cell reaction. It becomes difficult to function as a catalyst. In general, the bulk decreases as the specific surface area of the carbon substrate increases. When carbon substrates having different bulks are used and a catalyst having the same loading rate (for example, 50 wt%) is produced, when an electrode having the same coating amount (for example, 5 mg / cm ² ) is produced due to the reduction in bulk, the electrode thickness is Decrease. For this reason, the physical space | gap in an electrode coating film reduces, the permeability of a fuel and the diffusibility of the water in an oxygen electrode fall, and a battery characteristic deteriorates. Therefore, it is preferable to use a bulky carrier (a carbon substrate having a small specific surface area) as much as possible for the carbon substrate for a fuel cell. Examples of the carbon substrate that can be used in the present invention include carbon black, acetylene black, and carbon nanotube. These carbon substrates can be used alone or in combination of two or more. When the carbon substrate is a carbon nanotube, the carbon nanotube is preferably a multi-walled carbon nanotube. Since the diameter of the single-walled carbon nanotube is about 1 nm, catalyst particles having a particle diameter of 1 to 3 nm cannot be sufficiently supported.

  The PtRuP catalyst of the present invention is particularly useful as a catalyst for a fuel electrode such as a methanol electrode of a direct methanol fuel cell (DMFC) or a hydrogen electrode of a polymer electrolyte fuel cell (PEFC).

  The PtRuP catalyst fine particles of the present invention can be produced by an electroless plating method or an alcohol reduction method.

The production method of the PtRuP catalyst fine particles of the present invention by the alcohol reduction method is basically:
(1) dispersing a carbon base material in an organic solvent composed of one or more alcohols;
(2) dissolving a Pt salt or complex, a Ru salt or complex, and a P atom-containing compound in an alcohol-based organic solvent in which the carbon substrate is dispersed;
(3) adjusting the pH value of an alcohol solution containing carbon powder and a salt or complex of Pt, a Ru salt or complex, and a P atom-containing compound;
(4) including a step of heating and refluxing with alcohol in an inert atmosphere,
On the carbon substrate, the following general formula:
PtRuP
The catalyst for fuel cells which carry | supported the ternary system fine particle shown by these is produced | generated.

The production method of the PtRuP catalyst fine particles of the present invention by the electroless plating method is basically:
(1) dispersing a carbon substrate in an aqueous solution;
(2) dissolving a Pt salt or complex, a Ru salt or complex, and a P atom-containing compound in an aqueous solution in which the carbon substrate is dispersed;
(3) adjusting the pH value of an aqueous solution containing a carbon powder and a salt or complex of Pt, a Ru salt or complex, and a P atom-containing compound;
(4) including a step of performing electroless plating in the air or in an inert atmosphere,
On the carbon substrate, the following general formula:
PtRuP
The catalyst for fuel cells which carry | supported the ternary system fine particle shown by these is produced | generated.

  The particle size of the PtRuP catalyst fine particles produced by the production method of the present invention is smaller than the particle size of the conventional PtRu catalyst fine particles due to the presence of P. Generally, the particle size of the PtRu catalyst produced by the conventional manufacturing method is about 5 nm to 10 nm, but the particle size of the PtRu catalyst to which P is added according to the present invention is greatly reduced to 1 to 3 nm. This decrease in particle size increases the surface area of the PtRu catalyst, which is considered to greatly improve the hydrogen oxidizing ability or methanol oxidizing ability. Another feature of the PtRuP catalyst fine particles of the present invention is that the particle size distribution range is narrower than the particle size distribution range of conventional PtRu catalyst fine particles. The particle diameter of the PtRu catalyst fine particles produced by the conventional method is distributed in the range of 2 to 10 nm. In the present invention, P is added to the PtRu two-way catalyst to form a PtRuP three-way catalyst. Succeeded to suppress.

  When the PtRuP catalyst is synthesized by the alcohol reduction method and the electroless plating method, the acid used for adjusting the pH of the reaction solution to the acidic side is preferably sulfuric acid. The reason is that when the alcohol is heated and refluxed at a high temperature of about 200 ° C., the boiling point of hydrochloric acid and nitric acid is low, so that it is difficult to evaporate during the heating and reflux to maintain the pH value within a predetermined range. Because. Therefore, in the present invention, the acid used is preferably sulfuric acid having a boiling point of 290 ° C. In addition, sodium hydroxide or potassium hydroxide is suitable as the alkali used for adjusting the pH of the reaction solution to the alkali side for the same reason.

P atom-containing compounds that can be used in the method for producing PtRuP catalyst fine particles of the present invention include phosphorous acid, phosphite, hypophosphorous acid, hypophosphite, and the like. A P atom having a valence of +5 is not suitable for the purpose of the present invention because it has the same electronic configuration as Ne and is chemically stable by the octet rule. Therefore, phosphoric acid (H ₃ PO ₄ ) having +5 valent P atoms cannot be used in the present invention. The salt is preferably an alkali metal salt (for example, sodium phosphite, sodium hydrogen phosphite, sodium hypophosphite, etc.) or an ammonium salt (ammonium phosphite, ammonium hydrogen phosphite, ammonium hypophosphite, etc.). The addition amount of the P atom-containing compound is preferably in the range of 2 atom% to 50 atom% with respect to the total number of moles of Pt and Ru. If the addition amount is less than 2 atomic%, the effect of making the PtRu catalyst fine is not sufficient, while if it exceeds 50%, the characteristics of the catalyst deteriorate. These P atom-containing compounds can be used alone or in combination of two or more.

  Examples of the salt or complex of Pt used in the present invention include platinum acetate, platinum nitrate, dinitrodiamine platinum complex, platinum ethylenediamine complex, platinum triphenylphosphine complex, platinum ammine complex, and bis (acetylacetonato) platinum (II). And hexachloroplatinic acid. 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 acetate, ruthenium nitrate, ruthenium triphenylphosphine complex, ruthenium ammine complex, ruthenium ethylenediamine complex, and tris (acetylacetonato) ruthenium ( III) etc. These ruthenium compounds can be used alone or in combination of two or more.

  In the alcohol reduction method, when refluxing is performed at a temperature near the boiling point of the alcohol solvent, the alcohol (R—OH) reduces the metal ion during the heating and refluxing, and is oxidized to aldehyde (R′—CHO). In the electroless plating method, when the reducing agent is phosphorous acid or phosphite, when phosphorous acid or phosphite is oxidized to phosphoric acid or phosphate, electrons are emitted, and these electrons are received by Pt ions and Ru ions. To metal Pt and metal Ru. Further, when the reducing agent is hypophosphorous acid or hypophosphite, when hypophosphorous acid or hypophosphite is oxidized to phosphorous acid or phosphite, electrons are emitted, and these electrons are converted into Pt ions and Ru ions. Is received and reduced to metal Pt and metal Ru.

  Examples of the alcohol used in the heat reflux treatment of the present invention include methyl alcohol, ethyl alcohol, ethylene glycol, glycerin, propylene glycol, isoamyl alcohol, n-amyl alcohol, sec-butyl alcohol, n-butyl alcohol, isobutyl alcohol, allyl. Examples include alcohol, n-propyl 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 heating reflux treatment vary depending on the type of alcohol used. However, 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 electroless plating, the general bath temperature is 50 to 90 ° C., and the reduction time is 30 minutes to 4 hours.

  In the present invention, the salt or complex of Pt and Ru and the P atom-containing compound are dissolved in an organic solvent composed of at least one kind of alcohol. This alcohol can also contain water other than the case of consisting only of alcohol.

  The loading of the catalyst used in the present invention is preferably in the range of 50 wt% to 70 wt%. When the loading ratio is less than 50 wt%, when a certain amount of catalyst is applied, the thickness of the catalyst coating increases, the diffusibility of the fuel decreases, and the battery characteristics deteriorate. On the other hand, when the loading ratio exceeds 70 wt%, it becomes impossible to deposit on the carbon base material in a state where the entire catalyst is loaded.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of sodium hypophosphite in 100 ml of ethylene glycol, respectively. 100 ml of an ethylene glycol solution in which 0.5 g of a material (Vulcan XC-72R, specific surface area of 254 m ^{2 /} g) was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRuP catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of sodium dihydrogen phosphite in 100 ml of ethylene glycol, respectively. 100 ml of ethylene glycol solution in which 0.5 g of a base material (Vulcan XC-72R, specific surface area 254 m ^{2 /} g) was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRuP catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Comparative Example 1

1.69 mmol of bis (acetylacetonato) platinum (II) and 1.69 mmol of tris (acetylacetonato) ruthenium (III) were dissolved in 100 ml of ethylene glycol, respectively, and a carbon substrate (Vulcan XC-72R, specific surface area). (254 m ^{2 /} g) 100 ml of ethylene glycol solution in which 0.5 g was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRu catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Comparative Example 2

1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of ammonium molybdate were dissolved in 100 ml of ethylene glycol, respectively, (Vulcan XC-72R, specific surface area 254 m ^{2 /} g) 100 ml of ethylene glycol solution in which 0.5 g was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRuMo catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Comparative Example 3

1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of sodium tungstate were dissolved in 100 ml of ethylene glycol, respectively, (Vulcan XC-72R, specific surface area 254 m ^{2 /} g) 100 ml of ethylene glycol solution in which 0.5 g was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRuW catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Comparative Example 4

100 ml of ethylene glycol each with 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of tris (acetylacetonato) iron (III) And 100 ml of an ethylene glycol solution in which 0.5 g of a carbon base material (Vulcan XC-72R, specific surface area of 254 m ^{2 /} g) was dispersed was added. A sulfuric acid aqueous solution was dropped, and the solution was adjusted to pH 3 using pH test paper. This solution was refluxed with stirring at 200 ° C. in a nitrogen gas atmosphere, and PtRuFe catalyst fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

Comparative Example 5

100 ml of ethylene glycol each with 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of bis (acetylacetonato) cobalt (II) And 100 ml of an ethylene glycol solution in which 0.5 g of a carbon base material (Vulcan XC-72R, specific surface area of 254 m ^{2 /} g) was dispersed was added. A sulfuric acid aqueous solution was dropped, 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 PtRuCo catalyst fine particles were supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

  The particle diameters of the catalysts obtained in Examples 1 and 2 and Comparative Examples 1 to 5 were examined with an electron microscope. The results are shown in Table 1 below. The particle diameters of the catalysts obtained in Comparative Examples 1 to 5 were 10 nm, whereas the particle diameters of the PtRuP catalysts obtained in Examples 1 and 2 were within the range of 1 to 3 nm.

  The surfaces of the carbon-supported PtRuP fine particle catalyst obtained in Example 1 and the carbon-supported PtRu fine particle catalyst obtained in Comparative Example 1 were observed with a transmission electron microscope. The results are shown in FIG. (A) is an electron micrograph of the carbon-supported PtRuP fine particle catalyst of Example 1, and (B) is an electron micrograph of the carbon-supported PtRu fine particle catalyst of Comparative Example 1. The black to grayish black portions in the electron micrographs are catalyst particles, and the light gray or grayish white portions are carbon supports. As apparent from the electron micrograph of (A), in the case of the PtRuP catalyst fine particles of the present invention, the particle diameter is almost 1 to 3 nm, the particles are dispersed, and there are almost no aggregates. On the other hand, as is clear from the electron micrograph of (B), in the case of the PtRu catalyst fine particles of Comparative Example 1, those having a particle diameter of 10 nm and aggregates are also present. Thereby, the formation of fine particles of the catalyst due to the addition of P atoms was confirmed.

30 mg of the catalyst obtained in Examples 1 and 2 and Comparative Examples 1 to 5 was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol% and an electrolyte of 1.5 mol / liter, and Au wire was applied to the working electrode and the counter electrode at 25 ° C. Was used to sweep the potential between 0.2 and 0.6 (Vvs.NHE) at a rate of 0.01 V / second, and the methanol oxidation activity was measured. The methanol oxidation current at a potential of 0.6 (V vs. NHE) is shown in Table 2 below. From the results shown in Table 2, the PtRuP catalysts obtained in Examples 1 and 2 had a larger methanol oxidation current than the catalysts obtained in Comparative Examples 1 to 5, and improved methanol oxidation activity. I understand.

The composition of PtRuP obtained in Examples 1 and 2 was examined by fluorescent X-ray. As a result, in Example 1, it was Pt ₅₇ Ru ₃₇ P ₆ , and in Example 2, it was Pt ₅₇ Ru ₃₈ P ₅ .

Pure water and an alcohol solution of Nafion (manufactured by DuPont) were added to the PtRuP catalyst supported on Vulcan XC-72R obtained in Example 1 and stirred, and then the viscosity was adjusted to obtain a catalyst ink. This was applied on a Teflon sheet so that the application amount of the PtRuP catalyst was 5 mg / cm ² . After drying, the Teflon 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 the Pt catalyst supported on the ketjen EC and stirring, the viscosity was adjusted to obtain a catalyst ink. This was applied onto a Teflon sheet so that the amount of Pt catalyst applied was 5 mg / cm ² . After drying, the Teflon sheet was peeled off to obtain an oxygen electrode catalyst. Thereafter, a PtRuP electrode catalyst and a Pt electrode catalyst were hot pressed on both sides of a solid polymer electrolyte membrane (Nafion membrane manufactured by DuPont) to prepare a membrane electrode assembly. Using these methanol electrode, solid polymer electrolyte membrane and oxygen electrode, and a 15 wt% aqueous methanol solution as the liquid fuel, a direct methanol fuel cell shown in FIG. 4 was produced.
In FIG. 4, reference numeral 10 denotes 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 (PtRuP) catalyst layer, and 30 is a methanol fuel introduction hole.
The oxygen electrode side current collector 12 has a function as a structure that takes in air (oxygen) through the air introduction hole 24 and also has a current collecting function. The solid polymer electrolyte membrane (Nafion membrane manufactured by DuPont) 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 oxidized, and CO 2 ₂ is converted into an electron and a proton, and the proton moves 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. 4, power generation occurs due to such methanol oxidation reaction and oxygen reduction reaction.

Comparative Example 6

  A direct methanol fuel cell was produced in the same manner as in Example 3 except that the PtRu catalyst of Comparative Example 1 was used as the methanol electrode catalyst instead of the PtRuP catalyst in Example 3.

Comparative Example 7

  A direct methanol fuel cell was produced in the same manner as in Example 3 except that the PtRuMo catalyst of Comparative Example 2 was used as the methanol electrode catalyst instead of the PtRuP catalyst in Example 3.

Comparative Example 8

  A direct methanol fuel cell was produced in the same manner as in Example 3 except that the PtRuW catalyst of Comparative Example 3 was used as the methanol electrode catalyst instead of the PtRuP catalyst in Example 3.

Comparative Example 9

  A direct methanol fuel cell was produced in the same manner as in Example 3 except that the PtRuFe catalyst of Comparative Example 4 was used as the methanol electrode catalyst instead of the PtRuP catalyst in Example 3.

Comparative Example 10

  A direct methanol fuel cell was produced in the same manner as in Example 3 except that the PtRuCo catalyst of Comparative Example 5 was used as the methanol electrode catalyst instead of the PtRuP catalyst in Example 3.

In each direct methanol fuel cell obtained in Example 3 and Comparative Examples 6 to 10, the power density was measured, and the measurement results are shown in Table 3. As is apparent from the results shown in Table 3, the output density of the direct methanol fuel cell using the PtRuP catalyst of Example 3 as the methanol electrode catalyst is 50 mW / cm ² , whereas Comparative Examples 6 to In a direct methanol fuel cell using a catalyst other than PtRuP catalyst 10 as the methanol electrode catalyst, the output density is 40 mW / cm ² or less, and a PtRuP catalyst having a particle diameter of 1 to 3 nm is used as the methanol electrode catalyst. Thus, it can be understood that the battery characteristics are improved.

1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and sodium hypophosphite (NaPH ₂ O ₂ ) with respect to the total number of moles of Pt and Ru Then, 100 ml of ethylene glycol solution in which 0.5 g of carbon base material (Vulcan XC-72R, specific surface area 254 m ^{2 /} g) was dispersed was added at a ratio of 5 to 100 mol% in 100 ml of ethylene glycol. . A sulfuric acid aqueous solution was dropped into this solution, and the pH of the solution was adjusted to 3 using pH test paper. The solution was refluxed with stirring in an oil bath at 200 ° C. in a nitrogen atmosphere, and PtRuP fine particles were supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

An X-ray diffraction experiment was performed on the PtRuP catalyst obtained in Example 4, and the particle size of the PtRuP catalyst was estimated by applying Scherrer's equation. Also. The composition of the catalyst was examined by X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS). From various analyzes, there is a high possibility that P is present on the surface of the PtRu catalyst. Therefore, XPS that can measure a composition closer to the catalyst surface was used for the P concentration. Furthermore, methanol oxidation characteristics of these PtRuP catalysts were measured. The measurement method is shown below. 30 mg of the catalyst was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol% and an electrolyte of 1.5 mol / liter, and an electric wire of 0.2 to 0.6 (Vvs. NHE) was swept at a rate of 0.01 V / sec, and methanol oxidation activity was measured. The measurement results are shown in Table 4 below. As can be seen from the results shown in Table 4, when 5 to 50 mol% of sodium hypophosphite is added to the total number of moles of PtRu, a high methanol oxidation current can be obtained. In particular, when 50 mol% of hypophosphorous acid is added, the particle size is reduced, and high methanol oxidation activity is obtained. When sodium hypophosphite is added in an amount of 70 mol% or more based on the total number of moles of PtRu, excess sodium hypophosphite inhibits the formation of PtRu fine particles, and the raw material bis (acetylacetonato) platinum (II) Precipitation was observed, and the methanol oxidation activity decreased rapidly.

The charge ratio of bis (acetylacetonato) platinum (II) and tris (acetylacetonato) ruthenium (III) was changed to 1: 2 to 2: 1, and sodium hypophosphite was added to the total number of moles of Pt and Ru. 50 mol% of each was dissolved in 100 ml of ethylene glycol, and 100 ml of ethylene glycol solution in which 0.5 g of a carbon base material (Vulcan XC-72R, specific surface area of 254 m ^{2 /} g) was dispersed was 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. The solution was refluxed with stirring in an oil bath at 200 ° C. in a nitrogen atmosphere, and PtRuP fine particles were supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

An X-ray diffraction experiment was conducted on the PtRuP catalyst obtained in Example 5, and the particle size of the PtRuP catalyst was estimated by applying Scherrer's equation. Also. The composition of the catalyst was examined by fluorescent X-ray. Furthermore, methanol oxidation characteristics of these PtRuP catalysts were measured. The measurement method is shown below. 30 mg of the catalyst was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol% and an electrolyte of 1.5 mol / liter, and an electric wire of 0.2 to 0.6 (Vvs. NHE) was swept at a rate of 0.01 V / sec, and methanol oxidation activity was measured. The measurement results are shown in Table 6 below.

  From the results shown in Table 5, by setting the charging ratio of Pt and Ru to 1: 2 to 2: 1, a PtRuP catalyst having a Pt composition of 40 to 90 at.% And P of 5 at. It can be seen that current is obtained.

Dissolve 1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 0.338 mmol of sodium hypophosphite in 100 ml of ethylene glycol, respectively. 100 ml of ethylene glycol solution in which 0.5 g of material (Vulcan P, specific surface area 140 m ^{2 /} g) was dispersed was 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 gas atmosphere, and PtRuP fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the mixture was filtered, washed and dried to obtain a catalyst.

  The particle size of the catalyst obtained in Example 6 was examined with an electron microscope. The results are shown in Table 6 below. In Example 6, the particle size of the PtRuP catalyst was 1 to 3 nm.

The methanol oxidation activity of the catalyst obtained in Example 6 was examined. The measurement method is described below. 30 mg of the catalyst was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol.% And an electrolyte of 1.5 mol / liter, and an electric potential of 0.2 to 0.6 (V vs. .NHE) was swept at a rate of 0.01 V / sec, and the methanol oxidation activity was measured. The current density at a potential of 0.6 (Vvs.NHE) is shown in Table 7 below. Table 7 also shows the results of Example 1. From the results shown in Table 7, a high methanol oxidation current is obtained in Examples 6 and 1 in which the specific surface areas of the supports are 140 m ² / g and 254 m ² / g. Further, when Vulcan P having a specific surface area of 140 m ² / g is used as the carrier, the methanol oxidation current is increased as compared with Vulcan XC-72R having a specific surface area of 254 m ² / g. This is thought to be because the number of particles of the PtRuP catalyst forming the three-phase interface increased because Vulcan P, which has a small specific surface area, has few pores and a large pore diameter.

1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of sodium hypophosphite are dissolved in 100 ml of ethylene glycol, 100 ml of an ethylene glycol solution in which 0.5 g of a material (Vulcan XC72R, specific surface area of 254 m ^{2 /} g) was dispersed was 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 gas atmosphere, and PtRuP fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the catalyst was obtained by filtration, washing and drying. As a result of observing the particle diameter of the obtained PtRuP catalyst with an electron microscope, it was 1 to 3 nm. As a result of analyzing the composition by fluorescent _X-ray, it was Pt _{65 Ru} 29 _{P 6.}

1.69 mmol of bis (acetylacetonato) platinum (II), 1.69 mmol of tris (acetylacetonato) ruthenium (III) and 1.69 mmol of sodium hypophosphite are dissolved in 100 ml of ethylene glycol, 100 ml of ethylene glycol solution in which 0.5 g of material (Vulcan P, specific surface area 140 m ^{2 /} g) was dispersed was 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 gas atmosphere, and PtRuP fine particles were deposited and supported on the carbon substrate. After completion of the reaction, the catalyst was obtained by filtration, washing and drying. As a result of observing the particle diameter of the obtained PtRuP catalyst with an electron microscope, it was 1 to 3 nm. As a result of analyzing the composition by fluorescent _X-ray, it was Pt _{65 Ru} 29 _{P 6.}

  Example 9 will be described together with Comparative Example 11.

  Example 10 will also be described together with Comparative Example 11.

Comparative Example 11

After adding pure water and an alcohol solution of Nafion (manufactured by DuPont) to each of the PtRuP catalysts obtained in Examples 7 and 8, 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 PtRuP 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 the Pt catalyst supported on the ketjen EC and stirring, the viscosity was adjusted to obtain a catalyst ink. This was applied onto a Teflon (registered trademark) sheet so that the amount of Pt catalyst applied was 5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain an oxygen electrode catalyst. Thereafter, a PtRuP electrode catalyst and a Pt electrode catalyst were hot pressed on both sides of a solid polymer electrolyte membrane (Nafion membrane manufactured by DuPont) to prepare a membrane electrode assembly. Using these methanol electrode, solid polymer electrolyte membrane and oxygen electrode, and a 15 wt% aqueous methanol solution as the liquid fuel, a direct methanol fuel cell shown in FIG. 4 was fabricated and the output density characteristics were examined. The results are shown in Table 8. In Table 8, the output density when the PtRu catalyst of Comparative Example 1 was used as a methanol electrode catalyst is also shown as Comparative Example 11. When Vulcan P having a specific surface area of 140 m ² / g was used as the carrier, an output density of 65 mW / cm ² was obtained. On the other hand, Vulcan XC-72R with a specific surface area of the support of 254 m ² / g had a power density of 59 mW / cm ² . As described above, this is because Vulcan P, which has a small specific surface area, has fewer pores than Vulcan XC-72R and has a larger pore diameter, so the PtRuP catalyst is buried in the fine pores as a catalyst. This is considered to be because the number of particles of the PtRuP catalyst that forms the three-phase interface is increased because the non-operation is further suppressed.

  Example 11 will be described together with Example 12.

After adding pure water and an alcohol solution of Nafion (manufactured by DuPont) to each of the PtRuP catalysts obtained in Examples 7 and 8, 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 PtRuP catalyst was 5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain a hydrogen electrode catalyst. Further, after adding pure water and an alcohol solution of Nafion (manufactured by DuPont) to the Pt catalyst supported on the ketjen EC and stirring, the viscosity was adjusted to obtain a catalyst ink. This was applied onto a Teflon (registered trademark) sheet so that the amount of Pt catalyst applied was 5 mg / cm ² . After drying, the Teflon (registered trademark) sheet was peeled off to obtain an oxygen electrode catalyst. Thereafter, a PtRuP electrode catalyst and a Pt electrode catalyst were hot pressed on both sides of a solid polymer electrolyte membrane (Nafion membrane manufactured by DuPont) to prepare a membrane electrode assembly. Using these hydrogen electrode, solid polymer electrolyte membrane and oxygen electrode, and hydrogen gas as fuel, a solid polymer fuel cell shown in FIG. 5 was produced.
In FIG. 5, the code | symbol 40 shows a polymer electrolyte fuel cell. Reference numeral 44 denotes an oxygen electrode side current collector, 43 denotes an oxygen electrode side diffusion layer, 41 denotes a solid polymer electrolyte membrane, 48 denotes a hydrogen electrode side diffusion layer, 47 denotes a hydrogen electrode side current collector, and 42 denotes an air introduction hole. , 45 represents an oxygen electrode (Pt) catalyst layer, 46 represents a hydrogen electrode (PtRuP) 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 (Nafion membrane manufactured by DuPont) 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. Is. 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. 5, power generation occurs by such an oxidation reaction of hydrogen and a reduction reaction of oxygen.

Comparative Example 12

  A polymer electrolyte fuel cell was produced in the same manner as in Examples 11 and 12, except that the PtRu catalyst synthesized in Comparative Example 1 was used as the hydrogen electrode catalyst.

In the polymer electrolyte fuel cells produced in Examples 11 and 12 and Comparative Example 12, the power density was measured, and the results are shown in Table 9. In Examples 11 and 12, since a PtRuP catalyst having a particle diameter of 1 to 3 nm is used, a high output density is exhibited. Also in the polymer electrolyte fuel cell, the power density is higher in the case of Vulcan P having a smaller surface area of the carrier. As described above, when the support is Vulcan P having a small specific surface area, the PtRuP catalyst fine particles are more likely to form a three-phase interface, and the number of effective catalysts increases, resulting in higher power density. It is thought that it showed. On the other hand, in Comparative Example 15, since the PtRu catalyst having a particle diameter of 10 nm is used, the output density is a low value of 120 mW / cm ² .

The charging ratio of bis (acetylacetonato) platinum (II) and tris (acetylacetonato) ruthenium (III) was 1.5: 1, and sodium hypophosphite was 50 mol% with respect to the total number of moles of Pt and Ru. Each was added and dissolved in 100 ml of ethylene glycol, and 100 ml of ethylene glycol solution in which 0.5 g of carbon base material (Vulcan P, specific surface area 140 m ^{2 /} g) was dispersed was added. At this time, the amounts of bis (acetylacetonato) platinum (II) and tris (acetylacetonato) ruthenium (III) used were adjusted so that the loading ratio of the PtRuP catalyst was 50 wt%. A sulfuric acid aqueous solution was dropped into this solution, and the pH of the solution was adjusted to 3 using pH test paper. The solution was refluxed for 1.5 hours with stirring in an oil bath at 200 ° C. in a nitrogen atmosphere, and PtRuP fine particles were supported on the carbon substrate. After completion of the reaction, filtration, washing and drying were performed to obtain a PtRuP catalyst having a loading rate of 50 wt%.

The charging ratio of bis (acetylacetonato) platinum (II) and tris (acetylacetonato) ruthenium (III) was 1.5: 1, and sodium hypophosphite was 50 mol% with respect to the total number of moles of Pt and Ru. Each was added and dissolved in 100 ml of ethylene glycol, and 100 ml of ethylene glycol solution in which 0.5 g of carbon base material (Vulcan P, specific surface area 140 m ^{2 /} g) was dispersed was added. At this time, the amounts of bis (acetylacetonato) platinum (II) and tris (acetylacetonato) ruthenium (III) used were adjusted so that the loading ratio of the PtRuP catalyst was 60 wt%. A sulfuric acid aqueous solution was dropped into this solution, and the pH of the solution was adjusted to 3 using pH test paper. The solution was refluxed for 1.5 hours with stirring in an oil bath at 200 ° C. in a nitrogen atmosphere, and PtRuP fine particles were supported on the carbon substrate. After completion of the reaction, filtration, washing and drying were performed to obtain a PtRuP catalyst having a loading rate of 60 wt%.

The methanol oxidation activity of the catalysts obtained in Examples 13 and 14 was measured. The measuring method is shown below. 30 mg of the catalyst was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol.% And an electrolyte of 1.5 mol / liter, and an electric potential of 0.2 to 0.6 (V vs. .NHE) was swept at a rate of 0.01 V / sec, and the methanol oxidation activity was measured. The methanol oxidation current at a potential of 0.6 (V vs. NHE) is shown in Table 10 below.

  Example 15 will be described together with Example 16.

A direct methanol fuel cell shown in FIG. 4 was produced using the PtRuP catalyst obtained in Examples 13 and 14. In this case, since the catalyst loading was different between Examples 13 and 14, the amount of catalyst applied on the electrode was the same at 5 mg / cm ² . Table 11 shows the result of measuring the output density. A high power density of 70 mW / cm ² was obtained when the loading ratio of the PtRuP catalyst was 50 wt%, and 80 mW / cm ² when 60 wt%. When the catalyst loading was as high as 60 wt%, a large output density was obtained. This is because the amount of catalyst applied on the electrode is the same at 5 mg / cm ² , but when the catalyst loading is as high as 60 wt%, the thickness of the electrode can be reduced, and the methanol fuel permeability has increased. Conceivable.

  Example 17 will be described together with Example 18.

A polymer electrolyte fuel cell shown in FIG. 5 was produced using the PtRuP catalyst obtained in Examples 13 and 14. In this case, since the catalyst loading was different between Examples 13 and 14, the amount of catalyst applied on the electrode was the same at 5 mg / cm ² . Table 12 shows the result of measuring the output density. High power density of 240 mW / cm ² was obtained at 220mW ^/ cm 2, 60wt% in loading of 50 wt% of PtRuP catalyst. When the catalyst loading was as high as 60 wt%, a large output density was obtained. This is the same when the amount of catalyst applied to the electrode is 5 mg / cm ² , but when the catalyst loading is as high as 60 wt%, the thickness of the electrode can be reduced, so that the permeability of hydrogen gas fuel has increased. it is conceivable that.

0.25 g of carbon base material (Vulcan XC-72R, specific surface area 254 m ^{2 /} g) is dispersed in 60 ml of pure water, 0.844 mmol of hexachloroplatinic acid hexahydrate and ruthenium (III) chloride n hydrate After each 0.844 mmol was dissolved in 60 ml of pure water and added, 5.908 mmol of sodium hypophosphite monohydrate was dissolved in 70 ml of pure water and added. Thereafter, a 3N aqueous sodium hydroxide solution was added dropwise to adjust the solution to pH 11. After stirring for 30 minutes at room temperature, the temperature of the aqueous solution was raised to 80 ° C., and electroless plating was performed for 2 hours with stirring to support the PtRuP catalyst fine particles on the carbon substrate. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

As a result of examining the particle diameter of the catalyst obtained in Example 19 with an electron microscope, it was 1 to 3 nm. Moreover, as a result of analyzing the composition of the catalyst by fluorescent X-ray, it was Pt ₅₉ Ru ₃₄ P ₇ .

The methanol oxidation activity of the PtRuP catalyst obtained in Example 19 was measured. The measuring method is shown below. 30 mg of the catalyst was dispersed in H ₂ SO ₄ having a methanol concentration of 25 vol.% And an electrolyte of 1.5 mol / liter, and an electric potential of 0.2 to 0.6 (V vs. .NHE) was swept at a rate of 0.01 V / sec, and the methanol oxidation activity was measured. The methanol oxidation current at a potential of 0.6 (V vs. NHE) is shown in Table 13 below. Table 13 also shows the methanol oxidation current of PtRu of Comparative Example 1. In the PtRuP catalyst of this example, the particle size was reduced to 1 to 3 nm by addition of P, the active surface area was increased, and a large methanol oxidation current was observed as compared with Comparative Example 1. This example shows that a PtRuP catalyst having a particle size of 1 to 3 nm can be synthesized not only by the alcohol reduction method but also by the electroless plating method. This electroless plating method does not use an organic solvent such as alcohol, and because it can use inexpensive hexachloroplatinic acid and ruthenium chloride as the source of Pt and Ru, it can greatly reduce the cost of the catalyst. Have

Bis (acetylacetonato) platinum (II) 1.69 mmol, tris (acetylacetonato) ruthenium (III) 1.69 mmol and sodium hypophosphite 1.69 mmol were dissolved in 100 ml of ethylene glycol, respectively. 100 ml of ethylene glycol solution in which 0.5 g of nanotubes (diameter 75 nm, specific surface area 30 m ^{2 /} g) was dispersed was added. A sulfuric acid aqueous solution was dropped, and the solution was adjusted to pH 3 using pH test paper. The solution was refluxed for 4 hours at 200 ° C. with stirring in a nitrogen gas atmosphere to deposit and carry PtRuP catalyst fine particles on the multi-walled carbon nanotubes. After completion of the reaction, the catalyst was obtained by filtration, washing and drying.

As a result of examining the particle diameter of the PtRuP catalyst obtained in Example 20 with an electron microscope, it was 1 to 3 nm. The results of examining the composition with a fluorescent _X-ray, was Pt _{65 Ru} 29 _{P 6.}

A direct methanol fuel cell shown in FIG. 4 was produced using the multi-walled carbon nanotube-supported PtRuP catalyst obtained in Example 20 as a methanol electrode. As a result of measuring the power density, a power density of 75 mW / cm ² was obtained. In the case of the PtRuP catalyst supporting multi-walled carbon nanotubes, a higher output density is obtained compared to Examples 9 and 10 using carbon black as a support. This is because multi-walled carbon nanotubes do not have any pores, so that all of the PtRuP catalyst is deposited on the surface of the carrier and the utilization rate of the catalyst is increased. In addition, since the multi-walled carbon nanotube is bulky compared to carbon black, there are many physical voids in the catalyst electrode film, and the diffusibility of the methanol aqueous solution is improved compared to carbon black having a high packing density, and the PtRuP catalyst and methanol. This is because the fuel contact is sufficiently secured. Furthermore, it is considered that the multi-walled carbon nanotube has a lower specific resistance than that of carbon black, so that IR loss can be suppressed.

  The catalyst fine particles comprising at least Pt and P supported on the carbon base material of the present invention are particularly useful as a direct methanol fuel cell (DMFC), but can also be used as a catalyst for a solid polymer fuel cell (PEFC). .

FIG. 3 is a schematic cross-sectional view of PtRuP catalyst fine particles synthesized by the alcohol reduction method of the present invention. It is a typical sectional view of PtRuP catalyst fine particles synthesized by the electroless plating method of the present invention. (A) is an electron micrograph of the surface of PtRuP catalyst fine particles obtained in Example 1, and (B) is an electron micrograph of the surface of PtRu catalyst fine particles obtained in Comparative Example 1. It is a partial schematic block diagram of an example of a direct methanol fuel cell. It is a partial schematic block diagram of an example of a polymer electrolyte fuel cell.

Explanation of symbols

1 PtRuP catalyst fine particles of the present invention 3 Carbon base material 5 PtRu particles 7 P
8P
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 (PtRuP) catalyst layer 30 methanol fuel introduction hole 40 polymer electrolyte fuel cell 41 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 (PtRuP) catalyst layer 47 Hydrogen electrode side current collector 48 Hydrogen electrode side diffusion layer 49 Hydrogen fuel introduction hole

Claims (16)

A heterogeneous catalyst comprising at least Pt and P and having a maximum average particle diameter of less than 5 nm. The heterogeneous catalyst according to claim 1, wherein the particle diameter is 1 nm to 3 nm. 2. The heterogeneous catalyst according to claim 1, wherein the particles contain at least 2 atomic% of P. 2. The heterogeneous catalyst according to claim 1, wherein the P content is 2 to 50 atomic%. The heterogeneous catalyst according to claim 1, further comprising a carbon substrate. 6. The heterogeneous catalyst according to claim 5, wherein the carbon substrate is at least one selected from the group consisting of carbon black and carbon nanotubes. The heterogeneous catalyst according to claim 6, wherein the carbon substrate is a multi-walled carbon nanotube. The heterogeneous catalyst according to claim 1, wherein the particles further contain Ru. The heterogeneous catalyst according to claim 8, wherein the ratio of Pt and Ru in the particles is Pt ₄₀ Ru _{60 to} Pt ₉₀ Ru ₁₀ . Heterogeneous catalyst according to claim 8, wherein said carbon substrate is characterized by having a specific surface area within the range of from ^{20m 2} / ^g~300m 2 / g. The method for producing a heterogeneous catalyst according to claim 1, further comprising the step of reducing Pt ions in the presence of a phosphorus-containing reducing agent. 12. The production method according to claim 11, wherein the phosphorus-containing reducing agent is a compound derived from any of phosphorous acid, phosphite, hypophosphorous acid or hypophosphite. The manufacturing method according to claim 11, wherein the reduction step is an alcohol reduction or an electroless plating step. Consisting of a cathode, an anode, and a polymer electrolyte membrane disposed between the cathode and the anode,
The fuel cell according to claim 1, wherein the cathode and / or the anode comprises the catalyst according to claim 1. 2. The method of generating a voltage by a fuel cell according to claim 1, wherein metanote and water or hydrogen are supplied to the anode and oxygen is supplied to the cathode. An anode catalyst layer, a cathode catalyst layer, and a polymer electrolyte disposed between the anode catalyst layer and the cathode catalyst layer, wherein the anode catalyst layer and / or the cathode catalyst layer is formed from the catalyst according to claim 1. A membrane electrode assembly comprising: