JP2001224969A - Method for preparing alloy catalyst and method for manufacturing solid high-polymer type fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an alloy catalyst containing active metals which have a high alloying degree and are more pulverized. SOLUTION: This method includes a state for preparing an alloy colloid solution by adding >=2 kinds of metal salts to an aqueous solution in which a reducing agent consisting of an organic acid is dissolved at the same period in the state of dissolving the metal salts in water and a stage for depositing the alloy colloid particles in the solution on a carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preparing an alloy catalyst, particularly to a method for preparing an electrode catalyst for a polymer electrolyte fuel cell and a method for manufacturing a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Alloy catalysts exhibit a unique catalytic activity that cannot be obtained with a catalyst using a single metal as an active metal, and have been applied to petrochemical and petroleum refining chemical processes or various exhaust gas treatment catalysts. Recently, it has been used as an electrode catalyst for polymer electrolyte fuel cells.

[0003] The alloy catalyst is prepared by melting two or more components of a metal at a high temperature to form an alloy (high-temperature reduction melting method) or by dissolving the metal by a physical method such as sputtering. However, according to these methods, since the metal is melted and alloyed, the particle size of the alloy particles increases, the specific surface area of the alloy particles increases, and there is a problem that high catalytic activity cannot be obtained. Such problems will be specifically described with reference to an alloy electrode catalyst for a fuel cell.

A polymer electrolyte fuel cell has attracted attention as a power source for electric vehicles and spacecraft because it is compact and can extract a high current density. As such an anode electrode catalyst for a fuel cell, a carrier made of carbon is composed of P
What carries the active metal consisting of t is used. However, the catalyst containing Pt as an active metal is poisoned by CO which is likely to be mixed into a fuel gas containing hydrogen, and thus has a problem in that the performance of the battery is lowered.

[0005] From such a fact, the second Pt and Ru etc.
It has been practiced to suppress the poisoning by CO by applying an alloy comprising the components as an active metal of the anode electrode catalyst. In order to suppress poisoning by CO, it is necessary to increase the degree of alloying of platinum with the added second component. Therefore, the active metal made of the Pt-containing alloy is produced by the high-temperature reduction melting method described above or the sputtering method.

However, when a Pt-containing alloy is formed by the high-temperature reduction melting method or the sputtering method, the particle size of the alloy becomes large, so that high catalytic activity cannot be obtained, and the performance of the fuel cell cannot be improved. Was.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preparing an alloy catalyst having a high degree of alloying and containing finely divided active metal.

Another object of the present invention is to provide a method for producing a high-performance polymer electrolyte fuel cell in which an alloy catalyst containing a Pt-containing alloy as an active metal is prevented from being poisoned by CO. I do.

[0009]

The method for preparing an alloy catalyst according to the present invention comprises simultaneously dissolving two or more metal salts in water in an aqueous solution in which a reducing agent comprising an organic acid is dissolved. It is characterized by comprising a step of preparing an alloy colloid solution by adding, and a step of supporting alloy colloid particles in the solution on a carrier.

The method of manufacturing a polymer electrolyte fuel cell according to the present invention is directed to a method of manufacturing a polymer electrolyte fuel cell having an anode and a cathode each comprising a catalyst and a polymer electrolyte. The catalyst for at least one of the electrodes is added at the same time in a state where two or more metal salts (including platinum salts) are dissolved in water in an aqueous solution in which a reducing agent comprising an organic acid is dissolved. And preparing a colloidal Pt-containing alloy solution by the method described above, and a step of supporting the colloidal Pt-containing alloy particles in the solution on a carrier powder.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for preparing an alloy catalyst according to the present invention will be described.

(Alloy colloid preparation step) An alloy colloid solution is prepared by simultaneously adding two or more metal salts dissolved in water to an aqueous solution in which a reducing agent comprising an organic acid is dissolved.

As a method of adding a metal salt, for example,
(A) adding a mixed aqueous solution in which two or more metal salts are dissolved; (b) preparing two or more aqueous solutions in which one metal salt is dissolved, and adding these aqueous solutions at the same time; (C) One or more of the mixed aqueous solution of (a) and one or more of the single aqueous solution of (b) are added at the same time.

The aqueous solution in which the reducing agent comprising the organic acid is dissolved is preferably prepared, for example, by boiling water to remove dissolved oxygen and then dissolving the organic acid. If dissolved oxygen is contained in the aqueous solution, an oxide is likely to be generated, and this oxide tends to cause the alloy colloid particles to easily aggregate, which may increase the particle size of the colloid particles.

The organic acids include alcohols (eg, methanol, ethanol, isopropanol, butanol), citric acids (eg, sodium citrate, potassium citrate, ammonium citrate), ketones (eg, acetone, methyl ethyl ketone), It is preferably composed of at least one organic acid selected from carboxylic acids (eg, acetic acid, formic acid, fumaric acid, malic acid, aspartic acid, succinic acid) and esters (eg, methyl formate).

The composition of the alloy colloid to be prepared is not particularly limited, and may be selected according to the desired composition of the catalyst.
When preparing a catalyst for an electrode for a polymer electrolyte fuel cell,
The composition of the alloy colloid is Pt, Ru, Au, Pd, R
It is preferable to use at least one element selected from h, Ir, Co, Fe, Ni, Cu and Sn.

Examples of the metal salt include a metal chloride, a metal nitrate, and a metal complex.
An example of a metal chloride is chloroplatinic acid, and an example of a metal complex is dinitrodiamine platinum salt.

It is preferable that two or more metal salts are added to an aqueous solution in which a reducing agent composed of an organic acid is dissolved in water at the same time while being dissolved in water, and these are kept at 30 to 110 ° C. With such a configuration, the rate of the alloy formation reaction can be made appropriate, so that the alloy colloid solution can be prepared with high mass productivity. A more preferred range is 40 to 110 ° C.

(Step of Supporting Alloy Colloid on Carrier) An alloy catalyst is obtained by supporting the alloy colloid particles of the obtained alloy colloid solution on a carrier powder.

The carrier is supported on the carrier powder by, for example, a liquid phase adsorption method (adding the carrier powder to the alloy colloid solution at room temperature and stirring to adsorb the alloy colloid particles to the carrier powder, followed by filtration. Washing and drying)
Alternatively, an evaporation to dryness method (a method in which a carrier powder is added to an alloy colloid solution and heated while stirring to disperse the solvent) can be employed.

In some cases, excess ions generated by the reaction with the reducing agent are present in the alloy colloid solution. In such a case, it is preferable that the alloy colloid solution be passed through an ion exchange resin to remove excess ions, ie, cations and anions, before carrying on the carrier powder.

The carrier powder is not particularly limited, and a powder according to a desired catalyst composition is used. Examples of the carrier powder include a porous substance (for example, alumina and silica) and a carbon-based powder. Examples of the carbon-based powder include graphite, carbon black, and activated carbon having electrical conductivity. In particular, the activated carbon is preferably used for an electrode catalyst for a fuel cell.

The amount of active metal carried in the fuel cell electrode catalyst is preferably 10% or more. 10% loading
With the above, the performance of the fuel cell can be further improved.

Next, a method for manufacturing a polymer electrolyte fuel cell according to the present invention will be described.

First, the alloy catalyst prepared by the above-described method (a Pt-containing alloy is used as an active metal) and a solid polymer electrolyte are added to a solvent such as ethanol, and these are stirred to form an anode electrode. Prepare a slurry. On the other hand, the alloy catalyst prepared by the above-described method (a Pt-containing alloy as an active metal) or a catalyst with Pt as an active metal and a solid polymer electrolyte solution are added to a solvent such as ethanol, and these are added. A slurry for a cathode is prepared by stirring.

An electrode cell is prepared by applying the slurry for the anode electrode to one surface of the solid polymer electrolyte membrane and applying the slurry for the cathode electrode to the other surface. A current collector such as carbon paper is attached to both sides of the electrode cell, and a separator is laminated on each current collector, thereby obtaining a single-cell solid polymer fuel cell. The composition of the cathode electrode and the anode electrode can be the same when hydrogen is used as fuel.

As described in detail above, according to the method for preparing an alloy catalyst according to the present invention, two or more metal salts are dissolved in water in an aqueous solution in which a reducing agent comprising an organic acid is dissolved. By preparing the alloy colloid solution by adding the metal ions at appropriate times, each metal ion can be reduced at the same time even when their redox levels are different from each other, so that the degree of alloying of the colloid particles can be increased. In addition, since the reducing agent composed of an organic acid has a lower reducing power than hydrazine and thiosulfate conventionally used, the reduction reaction of metal ions (an example is shown in the following formula (1)) proceeds slowly. In addition, crystal growth due to reduction can be suppressed, and alloy colloid particles can be miniaturized (for example, a particle diameter of 2 to 3 nm). In equation (1), coefficients are omitted.

(Pt ⁴⁺ , Ru ⁴⁺ ) + C ₆ H ₅ O ₇ Na ₃ .11 / 2H ₂ O → (Pt ⁰ , Ru ⁰ ) + (Na ⁺ , CO ² , H ₂ O) (1) By supporting the obtained alloy colloid particles on the carrier powder, the degree of alloying and the specific surface area of the active metal can be improved, so that the activity is improved, in other words, a high activity can be obtained with a small amount of active metal. Alloy catalyst can be provided. Further, by providing the Pt-containing alloy catalyst obtained by the method of the present invention to a polymer electrolyte fuel cell, the activity of the catalyst can be improved and the catalyst can be poisoned by carbon monoxide. Therefore, the performance of the fuel cell can be improved.

Further, in the conventional method using hydrazine or thiosulfate as a reducing agent, the formed alloy colloid tends to aggregate, and it is necessary to add a protective colloid such as a surfactant. The alloy colloid particles obtained according to the present invention can maintain a fine particle state even if no protective colloid is added.

In the method according to the present invention, two or more metal salts dissolved in water are added simultaneously to an aqueous solution in which a reducing agent comprising an organic acid is dissolved.
By preparing the alloy colloid solution while maintaining the temperature at ~ 110 ° C, mass productivity can be increased while suppressing crystal growth by reduction.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail.

Example 1 <Preparation of Alloy Colloid Solution> Sodium citrate (C ₆ H ₅ O ₇ Na ₃ .11 / 2H ₂₎ was added to 1 liter of ion-exchanged water from which dissolved oxygen was sufficiently removed by boiling for 1 hour. O)
10 mmol was added, and a homogeneous solution was prepared under boiling at 100 ° C. To this solution, a mixed aqueous solution of chloroplatinic acid and ruthenium chloride (Pt was 1 mmol, Ru was 1 mmol) was dropped, and these were kept at 100 ° C. and subjected to a reduction treatment for 1 hour. After confirming that the solution changes color from red to black,
Quenched to room temperature. The resulting Pt / Ru alloy colloid solution is passed through an ion exchange resin to remove anions and cations,
Alloy colloid solution 1 was obtained.

<Supporting of Alloy Colloid on Carrier> 2 liters of the above-mentioned alloy colloid solution 1 had a specific surface area of 800 m ² /
g of Ketjen carbon was added and ultrasonically dispersed to obtain a uniform slurry. The obtained aqueous solution is 90
° C and the alloy particles were supported on carbon by evaporating water while stirring.
-The Ru alloy catalyst was used as catalyst 1.

Example 2 The preparation of the alloy colloid solution was as described above, except that ethanol, methanol, isopropanol, butanol, acetic acid, formic acid, acetone, methyl ethyl ketone or methyl formate was used instead of sodium citrate. Pt / Ru alloy colloid solutions 2 to 10 were prepared in the same manner as described in Example 1. Each of the alloy colloid solutions 2 to 10 was supported on Ketjen carbon in the same manner as in Example 1 described above, and the obtained carbon-supported Pt / Ru alloy catalyst was used as catalysts 2 to 10.

In the preparation of the alloy colloid solution, except that ruthenium chloride is replaced by chloroauric acid, palladium chloride, rhodium chloride, iridium chloride, cobalt chloride, iron chloride, nickel chloride, copper chloride or tin chloride, Alloy colloid solutions 11 to 19 composed of Pt and α elements were prepared in the same manner as described in Example 1 (α elements were Au, Pd, Rh, Ir, Co, Fe,
Ni, Cu or Sn). Each alloy colloid solution 1
1 to 19 were supported on Ketjen carbon in the same manner as in Example 1 described above, and the obtained carbon-supported Pt / α alloy catalyst was used as catalysts 11 to 19.

Comparative Example 1 As described below, after Pt and Ru are supported on a carbon-based powder by an impregnation method, Pt and Ru are alloyed by a high-temperature heat treatment to form a carbon-supported Pt.
A Ru alloy catalyst was obtained.

That is, 0.4 g of Ketjen carbon
Sampling was performed, and a mixed aqueous solution of chloroplatinic acid and ruthenium chloride (Pt 2 mmol, Ru 2 mmol) was dropped on carbon, and the mixture was evaporated to dryness while kneading. This was exposed to a nitrogen atmosphere at 900 ° C., and 1% hydrogen was supplied for 1 hour to form a Pt.Ru alloy, and then cooled to room temperature. The obtained carbon-supported Pt.Ru catalyst was used as Comparative Catalyst 1.

Comparative Example 2 A mixed aqueous solution of chloroplatinic acid and ruthenium chloride (Pt: 1 mmol) was added to 1 liter of ion-exchanged water from which dissolved oxygen was sufficiently removed by boiling for 1 hour.
, Where Ru is 1 mmol). Then, 10 mmol of sodium citrate are added and these are brought to 100 ° C.
After performing a reduction treatment for 1 hour while maintaining at
The resulting Pt / Ru alloy colloid solution was passed through an ion exchange resin to remove anions and cations, thereby preparing an alloy colloid solution. This alloy colloid solution was supported on Ketjen carbon in the same manner as in Example 1 described above, and the obtained carbon-supported Pt / Ru alloy catalyst was used as Comparative Catalyst 2.

Comparative Example 3 A platinum colloid solution was prepared in the same manner as described in Example 1 except that ruthenium chloride was not used and only chloroplatinic acid was used. did. This platinum colloid solution was supported on Ketjen carbon in the same manner as in Example 1 described above, and the obtained carbon-supported Pt catalyst was used as Comparative Catalyst 3.

The obtained prototype catalysts 1 to 19 and comparative catalysts 1 to
For No. 3, the average particle size of the alloy particles was measured by a transmission electron microscope as a property evaluation. Further, the degree of alloy was evaluated from the change in the lattice constant of Pt by the X-ray diffraction method. The results and the method of preparing the catalyst are shown in Table 1 below. In addition,
In Table 1, the case where the two-component metal is an alloy is indicated by “○”, and the case of an independent metal mixture is indicated by “×”.

[0041]

[Table 1]

As is clear from Table 1, prototype catalysts 1 to 1 prepared by a method in which aqueous solutions of two kinds of metal salts are added simultaneously to an aqueous solution in which a reducing agent composed of an organic acid is dissolved.
No. 9 shows that the degree of alloying of the active metal is high and the average particle size of the active metal can be reduced.

On the other hand, although the comparative catalyst 1 prepared by the high-temperature reduction method can increase the degree of alloying of the active metal, the average particle diameter of the active metal is larger than those of the prototype catalysts 1 to 19. Understand. Further, Comparative Catalyst 2 prepared by a method of adding an aqueous solution of an organic acid to a mixed aqueous solution of two metal salts can reduce the average particle size of the active metal, but the active metal is not an alloy but a mixture. You can see that.

Example 3 The prototype catalysts 1, 2, 3,
A polymer electrolyte fuel cell is manufactured using the catalysts 4, 5 and the comparative catalysts 1, 2, and 3, and the fuel gas supplied to the anode is CO 2
The power generation performance in the case where was contained was evaluated.

(Preparation of Battery Cell) Water / ethanol mixed water and Nafion solution as a polymer electrolyte solution were added to Catalyst 1, and a slurry was prepared by ultrasonic stirring. The obtained slurry was applied to a Teflon sheet and transferred to both sides of a 50 μm-thick solid polymer film (manufactured by DuPont, trade name: Nafion film) to form an anode electrode. The amount of Pt in the anode was 0.5 mg / cm ² , and the amount of Ru was 0.2 mg / cm ^2.
At 5 mg / cm ² , the Nafion solution was 0.5 mg / cm ² .

On the other hand, a water / ethanol mixed water and a Nafion solution as a polymer electrolyte solution were added to the comparative catalyst 3, and a slurry was prepared by ultrasonic stirring. The resulting slurry was applied to a Teflon sheet and transferred to both surfaces of a 50 μm-thick solid polymer film (manufactured by DuPont, trade name: Nafion film) to form a cathode. Pt in cathode electrode
The amount is 0.5 mg / cm ² and the Nafion solution is 0.5 mg
/ Cm ² . After attaching carbon paper to each of the anode electrode and the cathode electrode, these were sandwiched between a pair of separators to produce a 5 cm square electrode cell 1.

The catalysts contained in the anode electrode were the prototype catalysts 2 to 5 and the comparative catalyst 1 instead of the trial catalyst 1.
Except for using Nos. 1 to 3, the electrode cells 2 to 5 and the comparative electrode cells 1 to 5 were formed in the same manner as described in Example 1 described above.
3 was produced. The cathode electrodes used in each of the electrode cells 2 to 5 and the comparative electrode cells 1 to 3 are the same as those used in the electrode cell 1 described above.

(Evaluation of Power Generation Performance) Obtained Electrode Cells 1 to 5
A power generation test was performed on the comparative electrode cells 1 to 3 under the test conditions described below, and the results are shown in Table 2 below.

Anode side: H ₂ 60%, CO ₂ 20%,
N ₂ 20%, CO 10 ppm, 3ata, temperature 60 ° C.
Hydrogen utilization rate 50% Cathode side: Air (Air), 3ata, temperature 60 ° C,
50% air utilization

[0050]

[Table 2]

As can be seen from Table 2, the prototype catalysts 1 to 5
It can be seen that the electrode cells 1 to 5 using can obtain a higher voltage than the comparative electrode cells 1 to 3.

In the above-described embodiment, an example in which a mixed aqueous solution in which two kinds of metal salts are dissolved, such as a mixed aqueous solution of chloroplatinic acid and ruthenium chloride, has been described.
Instead of a mixed aqueous solution, two kinds of aqueous metal salt solutions are prepared (for example, an aqueous solution of chloroplatinic acid and an aqueous solution of ruthenium chloride),
Except that these aqueous solutions were added at the same time, the prototype catalysts 1 to 19 were the same as described in Examples 1 and 2 above.
Prepared, the same results as described in Table 1 above were obtained.

In the above-described embodiment, Pt ·
Although an example in which the invention is applied to a two-component alloy such as a Ru alloy has been described, when the preparation method according to the present invention is applied to an alloy containing three or more components, an improvement in the degree of alloying and an effect of atomization can be obtained. It was confirmed.

[0054]

As described in detail above, according to the method for preparing an alloy catalyst according to the present invention, the degree of alloying of the active metal can be increased, and the particle size of the active metal can be reduced. A remarkable effect such as high activity can be obtained with an amount of metal. Further, according to the method of manufacturing a polymer electrolyte fuel cell according to the present invention, it is possible to suppress poisoning of an alloy catalyst containing a Pt-based alloy as an active metal by CO and to improve the activity of the catalyst. And a remarkable effect such as an improvement in battery performance can be achieved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanao Yonemura 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Satoru Watanabe Kanagawa-ku, Yokohama-shi Kanazawa-ku, Kanagawa Prefecture 8th Street 1 Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory F-term (reference) 4G069 AA08 BA08A BA08B BA21C BB02A BB02B BC22A BC22B BC31A BC31B BC33A BC33B BC66A BC66B BC67A BC67B BC68A BC68B BC70A BC70B BC71 BC72BBC BCBC BC BC EB19 EC04Y FA02 FB05 FB09 FB45 FC04 5H018 AA06 AS02 AS03 BB17 EE06 EE07 EE08 EE10 EE12 5H026 AA06 CX05 EE05 EE06 EE08 EE12 EE19

Claims (2)

[Claims] A step of preparing an alloy colloid solution by simultaneously adding two or more metal salts dissolved in water to an aqueous solution in which a reducing agent comprising an organic acid is dissolved; Supporting the alloy colloidal particles therein on a carrier. 2. A method for manufacturing a polymer electrolyte fuel cell having an anode and a cathode including a catalyst and a polymer electrolyte, wherein the catalyst of at least one of the anode and the cathode is an organic acid. Preparing a Pt-containing alloy colloid solution by simultaneously adding two or more metal salts (including platinum salts) in a state of being dissolved in water to an aqueous solution in which a reducing agent comprising: Supporting the Pt-containing alloy colloid particles in the solution on a carrier powder.