JP2001015121A - Catalyst for polymer solid electrolyte type fuel cell and solid electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for a polymer solid electrolyte type fuel cell having excellent electrode performance and carbon monoxide catalyst poisoning resistance, and a low manufacturing cost, and to provide a polymer solid electrolyte type fuel cell. SOLUTION: In a catalyst for a polymer solid electrolyte type fuel cell wherein platinum and two or more kinds of metals are supported on carbon powder carrier, platinum, ruthenium, and molybdenum are supported at the ratio of 1:(0.25-1)(0.2-0.5) (mole ratio). And platinum, ruthenium, and tungsten are supported at the ratio of 1:(0.25-2):(0.25-0.5) (mole ratio). When the particles of each precious metal are supported in such a condition that they are closer to form an alloy, these catalysts improve the carbon monoxide catalyst poisoning resistance of the catalyst more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for a solid polymer electrolyte fuel cell, and more particularly to a solid polymer electrolyte fuel cell catalyst which is reduced in production cost and excellent in poisoning of a carbon monoxide resistant catalyst.

[0002]

2. Description of the Related Art Fuel cells are greatly expected as a next-generation power generation system. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte as an electrolyte is compared with other types of fuel cells. It is promising as a power source for electric vehicles because it can take out power at a low temperature and is compact.

A solid polymer electrolyte fuel cell is formed as a laminated structure including two electrode layers, a hydrogen electrode and an air electrode, and a polymer solid electrolyte layer sandwiched between these electrodes.
Hydrogen is supplied to the hydrogen electrode, and oxygen or air is supplied to the air electrode, and power is taken out by oxidation and reduction reactions generated at the respective electrodes. The two electrodes of a solid polymer electrolyte fuel cell use a noble metal catalyst to promote the electrochemical reaction, particularly a platinum catalyst carrying platinum, and transfer hydrogen ions generated at the hydrogen electrode to the air electrode. In general, a mixture with a solid electrolyte for causing the mixture to be used.

Incidentally, hydrogen supplied as a fuel to the hydrogen electrode of a polymer solid oxide fuel cell is hydrogen obtained by reforming a liquid fuel such as methanol from the viewpoint of handleability and economy. Is being considered for application. However, the hydrogen obtained by this reforming contains carbon monoxide as an impurity in a small amount, which has the problem of deactivating the catalyst. This is because carbon monoxide has a higher adsorption capacity for platinum than hydrogen.
This is due to preferential adsorption on platinum to inhibit hydrogen adsorption / reaction. Such catalyst poisoning due to carbon monoxide in the fuel will affect the spread of fuel cells in the future.

Conventionally, to solve the problem of catalyst poisoning due to carbon monoxide, it has been known that a binary catalyst further supporting ruthenium is effective instead of a catalyst supporting platinum particles alone. Have been. It is believed that this is achieved by utilizing the hydrophilicity of ruthenium to oxidize and remove the carbon monoxide adsorbed on platinum adjacent to the OH ⁻ bonded to the ruthenium. It has been recognized that in order to apply this catalyst to a solid oxide fuel cell, it is practically necessary to support ruthenium at a ratio equal to or higher than that of platinum.

[0006]

However, ruthenium is one of the platinum group metals having a small reserve, and has a disadvantage that it is expensive. Applying a catalyst in which ruthenium is supported at a ratio equal to or higher than that of platinum as in the related art can cause an increase in the cost of the fuel cell.

[0007] In particular, since the polymer solid electrolyte fuel cell is expected to be applied to general consumer materials such as automobiles as described above, the demand for ruthenium will further expand in the future, and the price thereof will further increase. There is a possibility that. Therefore, it can be said that the need for reducing the cost of the catalyst used is extremely high in order to further spread the solid polymer electrolyte fuel cell.

Accordingly, the present invention provides a catalyst for a solid polymer electrolyte fuel cell, which is excellent in the poisoning of a carbon monoxide catalyst without deteriorating the electrode performance, and whose production cost is low, and a solid polymer electrolyte fuel cell. The purpose is to provide.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors first studied a conventional catalyst for a solid polymer electrolyte fuel cell supporting platinum and ruthenium. FIG. 1 is a schematic diagram showing the result of measuring the polarization value in a carbon monoxide mixed hydrogen gas in a hydrogen electrode side half-cell test using a platinum / ruthenium binary catalyst having a changed ruthenium ratio. It is shown in a typical manner. As is clear from FIG. 1, in the platinum / ruthenium binary catalyst, as the supported ratio of ruthenium is increased, the polarization value, that is, the poisoning resistance of the catalyst to the carbon monoxide catalyst is improved. However, this tendency has a limit point when ruthenium is supported about 1.5 times as much as platinum, and no decrease in the polarization value is observed even when ruthenium is further added.

[0010] The present inventors have determined the limit of such a platinum / ruthenium binary catalyst, and while reducing the loading ratio of ruthenium, have found that the binary catalyst has a low carbon monoxide resistant poisoning resistance. We decided to develop a catalyst with characteristics as close as possible to the critical point. As a result of intensive studies, they have found that a catalyst exhibiting sufficient carbon monoxide catalyst poisoning resistance can be obtained by supporting a small amount of a metal element on a platinum / ruthenium binary catalyst. This is claim 1
And a catalyst for a solid polymer electrolyte fuel cell according to claim 2, wherein platinum, ruthenium, and molybdenum are supported at a ratio of 1: 0.25 to 1: 0.2 to 0.5 (molar ratio). And platinum, ruthenium and tungsten:
A catalyst for a solid polymer electrolyte fuel cell supported in a ratio of 0.25 to 2: 0.2 to 0.5 (molar ratio).

According to the present invention, by supporting molybdenum or tungsten at a ratio of 0.25 to 0.5 (platinum is defined as 1), the supported ratio of ruthenium is reduced to a minimum of 0.2.
It can be reduced to 5 (the platinum is 1).
As a result, the cost of the entire catalyst can be reduced. Here, the molybdenum or tungsten loading ratio is set in the range of 0.25 to 0.5 (based on platinum).
This is because when the amount is outside the above range, the poisoning of the catalyst by the carbon monoxide catalyst is rather deteriorated.

Furthermore, the catalyst for a polymer solid oxide fuel cell according to the present invention is more excellent in the carbon monoxide catalyst poisoning resistance when the respective metals are in an alloyed state. The catalyst in which platinum, ruthenium, molybdenum or tungsten is alloyed can be produced by subjecting the catalyst to heat treatment. The alloying by this heat treatment is preferably performed at a temperature in the range of 600 ° C to 900 ° C. At a temperature of 600 ° C. or less, the alloying of the noble metal particles is incomplete, while at a temperature of 900 ° C. or more, the agglomeration of the catalyst particles progresses and the particle size becomes excessive, which affects the activity of the catalyst.

As described above, according to the present invention, the conventional platinum / ruthenium binary catalyst is further supported with molybdenum or tungsten as a third metal at a predetermined ratio, thereby providing an excellent carbon monoxide resistant poisoning catalyst. It shows.
Here, in order to make this catalyst function more effectively, the present inventors further studied a support for supporting these noble metals. As a result, it was concluded that carbon powder having pores having a diameter of 60 angstroms or less at a ratio of 20% or less to all the pores and a specific surface area of 600 to 1200 m ² / g was particularly preferable as a carrier. The following are considered as the reasons.

As described above, the electrode of the hydrogen electrode of the polymer solid oxide fuel cell is a mixture of a catalyst for accelerating the electrode reaction and a solid electrolyte for transmitting hydrogen ions generated by the electrode reaction. The carbon fine powder serving as a carrier of the catalyst has countless fine pores, and the noble metal particles are supported inside the fine pores. However, the solid electrolyte particles have an excessively large particle size as compared with the noble metal particles, and cannot penetrate into extremely small pores having a diameter of 60 Å or less. Therefore, the hydrogen ions generated on the noble metal particles in the micropores are not transmitted to the solid electrolyte. In other words, in the catalyst for a solid polymer electrolyte fuel cell, there is a close relationship between the ratio of the very fine pores in the carrier to all the pores and the utilization efficiency of the catalyst. Therefore, in the present invention, the distribution of the pores of the carrier is limited to 20% or less of the total of the pores, and the utilization efficiency of the catalyst is secured.

Further, the specific surface area of the carrier is preferably from 600 to 1200.
in the range of m 2 ^{/ g,} the specific surface area as 600 meters 2 / ^g or more, while the noble metal particles it is possible to increase the area in which the catalyst is adhered can be dispersed in a state of high specific surface area 1200 m ² This is because if the ratio is too large, i.e., not less than / g, the ratio of ultrafine pores that lowers the utilization efficiency of the catalyst increases. That is, by setting the specific surface area within the above range, the noble metal particles are dispersed in a high state, and the activity per unit mass of the catalyst is improved, while the utilization efficiency of the catalyst can be secured.

As described above, the catalyst for a solid polymer electrolyte fuel cell according to the present invention is excellent in the poisoning resistance of the carbon monoxide catalyst while reducing the loading ratio of ruthenium. Solid electrolyte fuel cell equipped with an electrode containing a catalyst for a solid fuel cell as a hydrogen electrode is a polymer solid electrolyte fuel cell that is less likely to deteriorate electrode performance due to carbon monoxide and has a low manufacturing cost. It can be called a catalyst.

[0017]

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

First Embodiment In this embodiment, a ternary platinum / ruthenium / molybdenum catalyst was manufactured. This ternary catalyst is prepared in advance by preparing a platinum catalyst in which platinum is supported on the above carbon powder, and then supporting ruthenium on the catalyst to first produce a platinum / ruthenium binary catalyst, which is further converted to a molybdenum compound solution. It was manufactured by supporting molybdenum by impregnation. The reason for carrying out the step of supporting each metal separately is to ensure that platinum and ruthenium are supported as close as possible. This will be described in detail below.

[Selection of carrier]
Carbon fine powder used (trade name: Ketjen Black EC)
2 shows the pore distribution. Measurement of pore distribution is gas adsorption method
It is done by. As shown in FIG.
Powder used as a carrier of the catalyst according to the present invention used in the state
Is a fine pore with a small diameter of the order of tens of angstroms.
Low ratio to holes. Also, the specific surface area of this carrier is B
800m when measured by the ET one-point method ²/ G
Was.

[Preparation of Platinum Catalyst] 10 g of the above carbon powder was mixed with 2233 g (platinum content: 6.70 g) of 0.3 wt% platinum solution and stirred, and then 250 ml of 100% ethanol was added as a reducing agent. The boiling point of this solution (about 95 ° C)
For 6 hours, and the platinum was supported on the carbon powder.

[Support of Ruthenium] To 777 g of a 0.3 wt% ruthenium solution (ruthenium content: 2.33 g),
15 g of the platinum catalyst was immersed. Further, 86 ml of 100% ethanol was added, and the mixed solution was brought to the boiling point (about 95%).
C.) for 6 hours with stirring. After completion of the reaction, the mixture was filtered, washed and dried at 60 ° C. to obtain a catalyst.

[Support of molybdenum] The platinum / ruthenium binary catalyst 1 prepared by the above operation was added to 218 g of a 0.4 wt% molybdenum solution (molybdenum: 0.87 g).
5.38 g were immersed. Then, the mixed solution was stirred for 1 hour, filtered, washed, and dried at 60 ° C. to obtain a catalyst.

[Heat Treatment] The heat treatment for alloying platinum, ruthenium, and molybdenum was carried out in a 50% hydrogen gas (nitrogen balance) at 900 ° C. for one hour.

The ratio of each supported metal of the platinum / ruthenium / molybdenum catalyst produced by the above operation is 1: 0.
75: 0.33. This ratio can be easily controlled by changing the ruthenium content and the molybdenum content in the mixed solution.

[0025]

[Experimental Example 1] With respect to the platinum / ruthenium / molybdenum catalyst produced by the above-mentioned production method, the hydrogen electrode side half-cell test was carried out while the ruthenium loading ratio was fixed and the molybdenum loading ratio was changed. Toxicity confirmed. The result of the study is shown in FIG. Measurement is 100p
The test was performed in hydrogen gas mixed with pm carbon monoxide. In FIG. 2, the ordinate represents the polarization value at a current density of 500 mA / cm ² , and the abscissa represents the molybdenum loading ratio when platinum is set to 1, and the polarization value of the electrode catalyst produced at each ratio. Plotted. FIG. 3 shows a platinum / ruthenium binary catalyst (platinum: ruthenium) measured under the same conditions for comparison.
The polarization value (40 mV) of a half cell prepared from ruthenium (4: 6) is shown. Platinum: ruthenium = 4: 6
The reason why the polarization value of the catalyst is described is that the platinum / ruthenium binary catalyst of this composition shows the highest poisoning resistance to the carbon monoxide catalyst as a result of the preliminary test by the present inventors.

FIG. 3 shows that the platinum / ruthenium / molybdenum catalyst to which molybdenum is added in a ratio of 0.2 to 0.5 as in the present invention has almost the same polarization value as the platinum / ruthenium binary catalyst. It was confirmed that the catalyst according to the present invention exhibited sufficient resistance to carbon monoxide catalyst poisoning.

[0027]

Experimental Example 2 Next, the effect of reducing the ruthenium ratio by adding molybdenum was confirmed. FIG. 4 shows half-cell polarization values of a platinum / ruthenium / molybdenum catalyst in which the ratio of ruthenium was changed while the molybdenum loading rate was fixed at 0.3 (with platinum being 1). The measurement is performed in a hydrogen gas mixed with 100 ppm of carbon monoxide, as described above. FIG. 4 shows the polarization value (40 m) of a half cell prepared from a platinum / ruthenium binary catalyst (platinum: ruthenium = 4: 6) measured under the same conditions as described above.
V)

As is apparent from FIG. 4, the polarization value of a catalyst in which molybdenum is further supported on a platinum / ruthenium binary catalyst as in the present invention is smaller than that of a conventional platinum / ruthenium catalyst even if the ruthenium ratio is 1 or less. / Shows almost the same polarization value as the ruthenium binary catalyst. That is, it was confirmed that even when the ruthenium ratio was reduced by the addition of molybdenum, substantially the same poisoning resistance to the carbon monoxide catalyst was exhibited.

Second Embodiment In this embodiment, a ternary platinum / ruthenium / tungsten catalyst was manufactured. However,
A carrier used in the ternary catalyst in the present embodiment, and
The ruthenium loading step and the heat treatment
This is the same as the embodiment. Therefore, avoid duplicate descriptions,
Only the characteristic step of supporting tungsten will be described.

[Tungsten loading] 415 g of a 0.4 wt% tungsten solution (tungsten content: 1.6)
In 6 g), 15.38 g of a platinum / ruthenium binary catalyst was immersed. Then, the mixed solution was stirred for 1 hour, filtered, washed, and dried at 60 ° C. to obtain a catalyst.

The ratio of each supported metal of the platinum / ruthenium / tungsten catalyst produced by the above operation is 1:
0.75: 0.33. This ratio can be easily controlled by changing the metal content in the mixed solution, as in the case of the first embodiment.

[0032]

[Experimental Example 3] The platinum / ruthenium / tungsten catalyst produced by the above-described production method was subjected to a half-cell test on the hydrogen electrode side while changing the tungsten loading ratio in the same manner as in Experimental Example 1, and the carbon monoxide resistant catalyst of each catalyst was obtained. Toxicity was evaluated. FIG. 5 shows the measurement results. The measurement conditions are the same as in Experimental Example 1. In this case, the loading ratio of ruthenium is 0.75 (platinum is 1).

FIG. 5 shows that the platinum / ruthenium / tungsten catalyst to which tungsten is added in a ratio of 0.2 to 0.5 as in the present invention has almost the same polarization value as the platinum / ruthenium binary catalyst. It was confirmed that the catalyst according to the present invention exhibited sufficient resistance to carbon monoxide catalyst poisoning.

[0034]

As described above, according to the present invention, it is possible to obtain a catalyst for a polymer solid oxide fuel cell excellent in the poisoning resistance of a carbon monoxide catalyst while reducing the ruthenium loading ratio as compared with the conventional one. it can. As a result, the cost of the catalyst can be significantly reduced. Further, the catalyst of the present invention can use a suitable fine carbon powder as a carrier, and heat-treat the metal after carrying the metal to alloy the supported metal. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph schematically showing a change in poisoning (polarization value) of a carbon monoxide resistant catalyst when the ruthenium loading rate of a conventional platinum / ruthenium binary catalyst is changed.

FIG. 2 is a graph showing a pore distribution of carbon powder used in the first and second embodiments.

FIG. 3 shows the results obtained by changing the ratio of molybdenum to platinum / molybdenum.
7 is a graph showing a comparison of hydrogen electrode half-cell battery performance of a ruthenium / molybdenum catalyst.

FIG. 4 is a graph showing a comparison of the anode half-cell battery performance of composite catalysts supported at different platinum / ruthenium / molybdenum ratios.

FIG. 5 is a graph showing a comparison of the hydrogen electrode half-cell battery performance of a platinum / ruthenium / tungsten catalyst when the tungsten ratio is changed.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/92 H01M 8/10 8/10 B01J 23/64 103M (72) Inventor Masahiko Inoue Hiratsuka-shi, Kanagawa No. 2-3, Shinmachi Tanaka Kikinzoku Kogyo Co., Ltd. Technology Development Center (72) Inventor Yumi Yamamoto No. 2-3, Shinmachi, Hiratsuka-shi, Kanagawa Prefecture Tanaka Kikinzoku Kogyo Co., Ltd. Technology Development Center F term (reference) 4G069 AA03 AA08 BA08A BA08B BB02A BB02B BC59A BC59B BC60A BC60B BC70A BC70B BC75A BC75B CC32 EC04X EC04Y EC05X EC18X EC18Y EC20 ED07 FA01 FB44 FC08 5H018 AA06 AS02 EE02 EE03 EE05 EE10 HH02 HH04 HH05 5H005 AA06 EE02 H02H02

Claims (5)

[Claims] 1. A catalyst for a solid polymer electrolyte fuel cell in which platinum and two or more metals are supported on a carbon powder carrier, wherein platinum, ruthenium and molybdenum are mixed in a ratio of 1: 0.25 to 1.25.
1: A catalyst for a solid oxide fuel cell, which is supported at a ratio of 0.2 to 0.5 (molar ratio). 2. A catalyst for a solid polymer electrolyte fuel cell in which platinum and two or more metals are supported on a carbon powder carrier, wherein platinum, ruthenium and tungsten are mixed in a ratio of 1: 0.25.
(2) A catalyst for a solid polymer electrolyte fuel cell, which is supported at a ratio of 0.25 to 0.5 (molar ratio). 3. The catalyst for a solid polymer electrolyte fuel cell according to claim 1, wherein the metal particles on the carrier are supported in an alloyed state. 4. The carrier is a carbon powder having pores having a diameter of 60 angstrom or less at a ratio of 20% or less to all the pores and a specific surface area of 600 to 1200 m ² / g. Item 4. The catalyst for a polymer solid oxide fuel cell according to any one of Items 3 to 7. 5. A solid polymer electrolyte fuel cell comprising an electrode comprising the catalyst for a solid polymer electrolyte fuel cell according to claim 1 as a hydrogen electrode.