JPH09161811A - Anode catalyst for polyelectrolyte type fuel cell and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anode catalyst having the composition range different from that of a cathode catalyst for a fuel cell having the conventional platinum- iron alloy phase, excellent in poisoning resistance characteristic against carbon monoxide, rarely having elution, and having a long life. SOLUTION: A platinum-iron alloy phase containing platinum of 84-99 atomic % and iron of 1-16 atomic % is carried on a catalyst carrier. This alloy phase may contain a noble metal selected from palladium, ruthenium, rhodium, and gold. An anode catalyst containing iron of 1-16 atomic % doesn't generate FePt3 generated by the anode catalyst containing iron in the range exceeding 16 atomic %, inferior in poisoning resistance characteristic, and liable to cause deterioration due to elution, thus it has a longer life than before.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anode catalyst for a polymer electrolyte fuel cell containing platinum as a main component and a method for producing the same, more specifically for a polymer electrolyte fuel cell containing at least platinum and iron. The present invention relates to an anode catalyst and a method for manufacturing the same.

[0002]

2. Description of the Related Art Polymer electrolyte fuel cells have a lower operating temperature than oxide electrolyte fuel cells, phosphoric acid fuel cells, etc., and can be operated at high current densities. It is recognized that weight reduction is possible. Therefore, the polymer electrolyte fuel cell is expected as a driving power source for moving bodies such as electric vehicles. As the fuel supplied to this fuel cell, in addition to pure hydrogen, the use of natural gas or methanol reformed gas is being considered because of the ease of environmental maintenance for circulating the fuel. However, natural gas and reformed gas contain carbon dioxide and carbon monoxide in addition to hydrogen, and in particular carbon monoxide poisons the platinum catalyst used in the anode (fuel electrode) of the fuel cell, and It is causing the decline. This problem is particularly remarkable in the polymer electrolyte fuel cell operated at low temperature.

This problem can be avoided by using pure hydrogen, but since pure hydrogen has a smaller energy density than hydrocarbon type fuel, it costs much to store and transport, and
At present, the absolute distribution volume is also small. On the other hand, the natural gas and reformed gas can reduce the concentration of carbon monoxide contained in the gas to several hundred ppm by selective oxidation or the like. At the operating temperature of the polymer electrolyte fuel cell, the platinum catalyst shows deterioration in characteristics even for a few ppm of carbon monoxide. Under these circumstances, it is indispensable to solve an excellent carbon monoxide poisoning-resistant catalyst in order to promote the practical use of the fuel cell, and avoiding poisoning of the anode catalyst by carbon monoxide is the greatest concern in the field. It has become a thing.

On the other hand, it has been proposed to use a noble metal, particularly platinum, and an alloy in which iron is added thereto as a catalyst for fuel cells (for example, JP-A-4-358540 and JP-A-60-7941). The former catalyst described in JP-A-4-358540 is used as a cathode catalyst, and is described only as one kind of many metals that can be alloyed with platinum, and a description regarding a specific manufacturing method and composition. There is no. The latter JP-A-60-79
The platinum-iron catalyst described in Japanese Patent No. 41, intentionally forming a superlattice structure represented by Pt ₃ Fe in order to prevent the life of the cathode catalyst for a fuel cell from being shortened due to the decrease in the surface area. For that purpose, 17 to 42 atom% capable of forming the superlattice structure is specified as the composition range of iron.

However, the present inventor has found that the composition range of iron is
When a platinum-iron alloy containing 17 to 42 atomic% is used as a catalyst for an anode of a fuel cell, it has a specific lattice structure represented by Pt ₃ Fe rather than the effect of preventing reduction of surface area and improving life. It was found that the effect of shortening the service life due to the dissolution in the electrolyte solution is greater, and the life of the fuel cell cannot be extended with a platinum-iron alloy having an iron composition within the above range. The present invention was made based on this finding.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an anode catalyst for a polymer electrolyte fuel cell which is less likely to be poisoned by carbon monoxide even at the operating temperature of the polymer electrolyte fuel cell, and a method for producing the same. The catalyst and the manufacturing method allow the reformed fuel to be used without substantially shortening the life of the fuel cell.

[0007]

An anode catalyst for a polymer electrolyte fuel cell according to the present invention comprises a catalyst carrier, 84% to 99% by atom of platinum and 1 to 16% of atom% supported on the carrier.
% Of iron, the anode catalyst for polymer electrolyte fuel cells being selected from 0.1 to 50 atomic% of palladium, ruthenium, rhodium and gold with respect to the platinum and iron. It may also contain a precious metal. In addition, these catalysts are prepared by precipitating platinum on the carrier by thermal decomposition or reduction with a reducing agent, and optionally supporting the precious metal, and immersing the platinum-supporting catalyst carrier in a solution containing an iron compound. It can be produced by alloying platinum and iron by precipitating iron chloride and / or hydroxide by adjusting pH and heat treating in a reducing atmosphere.

The details of the present invention will be described below. The present invention is intended for an anode catalyst of a polymer electrolyte fuel cell, and particularly to provide an anode catalyst having sufficient resistance to poisoning at a low temperature with respect to carbon monoxide gas contained in a reformed gas. In polymer electrolyte fuel cells, the catalyst may deteriorate due to the elution of the catalyst metal, and the eluted metal ions may exchange ions with the protons of the polymer electrolyte, impairing the conductivity of the electrolyte, which may prolong the life of the fuel cell. Hindering Therefore, in the present invention, the type and addition amount of the additive element, and the metal alloy phase are selected so that the catalyst metal supported on the carrier is not poisoned by carbon monoxide and the cation exchange resin that is the polymer electrolyte is not attacked. It is necessary to make an accurate selection.

In the present invention, platinum is used as the main catalytic metal.
Further, iron is basically selected as the additional element, and a range in which FePt ₃ phase having poor resistance to elution is not formed, that is, a platinum-iron alloy phase containing 1 to 16 atom% of iron with respect to the total amount of platinum and iron is used. Use as a catalyst. Therefore, in the first polymer electrolyte fuel cell anode catalyst of the present invention, 84 to 99 atomic% of platinum and 1
A platinum-iron alloy phase containing ~ 16 atomic% iron is supported on a catalyst carrier to form an anode catalyst for a polymer electrolyte fuel cell. If the iron content is less than 1 atom%, the effect of poisoning resistance to carbon monoxide is reduced, and if it exceeds 16 atom%, Fe-rich FePt ₃ phase, which is easy to elute, is formed.
The elution of the _three phases easily causes deterioration of the catalyst and the electrolyte.

In the second anode catalyst for polymer electrolyte fuel cells of the present invention, 84 to 99 atom% of platinum and 1 to 16 atom% of iron, and 0.1 to 50 atom% of platinum and iron are used. A noble metal selected from palladium, ruthenium, rhodium and gold is supported on a catalyst carrier to form an anode catalyst for polymer electrolyte fuel cells. These noble metals improve the poisoning resistance to carbon monoxide within the above atomic% range without impairing the catalytic activity of hydrogen oxidation in the anode of the fuel cell of the platinum-iron alloy phase. That is, if the amount of the noble metal added is less than 0.1 at%, the noble metal addition effect does not appear, and if it exceeds 50 at%, the activity against hydrogen oxidation is impaired.

It is desirable that the first and second anode catalysts contain 5 to 40% by weight of platinum based on the total weight of the catalyst, which means that if the platinum content is less than 5% by weight. If the amount of platinum required for hydrogen oxidation at the anode of is supported, the weight of the entire catalyst will increase and the electrode sheet will become thicker, and gas diffusion will be the rate-determining factor, leading to deterioration of properties. This is because the particle size of the catalytic metal particles becomes coarse, and the catalyst specific surface area commensurate with the supported amount may not be obtained. Fe in these anode catalysts
An intermetallic compound such as Pt ₃ is not formed, and an alloy phase in which iron is solid-soluted in platinum is often formed. At equilibrium, iron dissolves in platinum at about 17% in atomic% (Kubaschewsk
i, O., "Fe-Pt;Iron-Platinum", pp 91-94, of volume
Iron Binary Phase Diagrams; Springer-Verlag, 1982)
Even if the addition amount is less than 17%, an Fe-rich intermetallic compound phase may appear in the diffusion process during the heat treatment for alloying, and the corrosion resistance may be impaired. In order to avoid such partial segregation and to form a solid solution alloy phase more reliably, heat treatment may be carried out at a temperature higher than a certain level and a holding time within a range where the catalyst metal particles do not coarsen. , For example 400
The heat treatment should be performed at a temperature of ~ 900 ° C for 30 minutes or longer. Regarding the subsequent cooling, if it is within the range of the iron addition amount of the present invention, it may be gradually cooled or rapidly cooled.

The method for producing the above-mentioned anode catalyst for a polymer electrolyte fuel cell according to the present invention is not particularly limited,
In the case of forming an alloy phase containing platinum and iron, a catalyst carrier is preferably a carbon carrier composed of carbon simple substance such as carbon black, acetylene black, furnace black, activated carbon and amorphous carbon, and a platinum compound such as chloroplatinic acid. Dispersed in a solution containing, the platinum compound is deposited on the catalyst carrier by dry thermal decomposition or reduction with a reducing agent, and the platinum-supported catalyst carrier contains iron compounds such as iron chloride, iron nitrate and Mohr's salt By dipping in a solution to evaporate to dryness, or to precipitate iron chloride and / or hydroxide by adjusting pH, and further evaporating to dryness, and subjecting the product to heat treatment in a reducing atmosphere such as a hydrogen stream, It is desirable to manufacture by alloying platinum and iron. The loading of platinum and iron is not limited to platinum-iron, but iron-platinum may be loaded in that order.

In the case of producing the above-mentioned noble metal-containing anode catalyst, a platinum-supported catalyst is produced as described above,
It is desirable that the noble metal compound, for example, the platinum-supported catalyst is immersed in an aqueous solution of a chloride of the noble metal, the noble metal is reduced and precipitated, and iron is carried in the same manner as described above. -Precious metal-It is not limited to iron, and may be performed in any order.

[0014]

EXAMPLES Examples of the anode catalyst for a polymer electrolyte fuel cell and a method for producing the same according to the present invention will be described below, but the present invention is not limited to the examples.

Example 1 Platinum and iron targets were co-sputtered in a vacuum chamber using argon gas to form a 0.5 μm thick platinum-iron alloy thin film on a glass plate with a lead terminal having a diameter of 10 mm. This was fixed to one end surface of a stainless steel rod having a diameter of 8 mm and attached to a rotary electrode device. The alloy composition was confirmed by quantitatively analyzing one of the simultaneously manufactured samples by the ICP method (inductively coupled plasma) method.

Rotating electrode samples prepared with a composition ratio of platinum: iron = 95: 5 (atomic%) and platinum: iron = 85: 15 (atomic%) were separately immersed in a 0.1 M perchloric acid aqueous solution, and Carbon oxide 10
The sample was poisoned by bubbling hydrogen containing 0 ppm for 1 hour. After that, bubbling was continued for 120 minutes, and the infinite diffusion current value, that is, the electrocatalytic reaction current value was plotted against time with the platinum electrode as the counter electrode. The result is shown in FIG. After the measurement, the electrolytic solution was analyzed by the ICP method to confirm the elution of iron. The value was below the detection limit.

[0016]

Comparative Example 1 A rotating electrode sample was prepared under the same conditions as in Example 1 except that pure platinum was used instead of platinum and iron.
The same measurement was performed and the electrode value of the electrocatalytic reaction electrode was plotted. The result is shown in FIG.

[0017]

[Comparative Example 2] Platinum: iron = 80: 20 in the same manner as in Example 1.
A rotating electrode sample having a composition ratio of (atomic%) was manufactured, and the same measurement was performed to plot the electrocatalytic reaction current value. The result is shown in FIG. When elution of iron was confirmed in the same manner as in Example 1, a trace amount of iron was detected. When the alloy phase of this platinum-iron alloy was identified by an X-ray diffractometer using CuKα rays, Pt ₃ Fe and Pt ₃ Fe and a solid solution phase peak were identified.
The peak of the intermetallic compound phase of PtFe was detected. Comparing the electrode of Example 1 and the electrode of Comparative Example 2 from FIG. 1, Comparative Example 2
The electrode of Comparative Example 2 has a higher electric current, but the electrode of Comparative Example 2 has a higher practical value because the electrode of Comparative Example 2 has a large iron elution amount and reaches a life in a relatively short time. .

[0018]

Example 2 Platinum: iron: palladium = 60: 10: 30 (atomic%), platinum: iron: ruthenium = in the same manner as in Example 1.
60:10:30 (atomic%), platinum: iron: rhodium = 70: 10:
20 (atomic%) and platinum: iron: gold = 70:10:20 (atomic%)
A rotating electrode sample having the composition ratio of was prepared, and the same measurement was performed to measure the value of the electrocatalytic reaction current. When elution of iron was confirmed in the same manner as in Example 1, the value was below the detection limit. The initial and 120-minute electrocatalytic reaction current values obtained in this example are summarized in Table 1 together with the same values as in Example 1, Comparative Example 1 and Comparative Example 2.

[0019]

[Table 1]

[0020]

Example 3 10 g of acetylene carbon black powder was impregnated with chloroplatinic acid having a platinum concentration of 150 g / liter, and then subjected to a thermal decomposition treatment so that platinum loadings were 10% and 30% with respect to the catalyst weight. A platinum-supported catalyst was prepared. Each of these catalysts was impregnated with an aqueous solution of iron chloride so as to have a composition ratio of platinum: iron = 85:15 (atomic%), evaporated to dryness, and then hydrogen-
It was alloyed by heat treatment in a mixed gas of nitrogen at 800 ° C for 90 minutes. When the alloy phase of the catalytic metal particles was identified by an X-ray diffractometer using Cuα rays, it was confirmed that the (111), (200),
The peak of Ptα solid solution phase was detected. Further, when the half-width was calculated from the peak of the (220) plane and the particle diameter was calculated, the particle diameters were 6 nm and 7 nm, respectively.

[0021]

Example 4 In the same manner as in Example 3, a platinum-supported catalyst was prepared so that the amount of platinum supported was 50% by weight, and the composition ratio of platinum: iron = 85: 15 (atomic%) was adjusted. After impregnating with an aqueous solution of iron chloride and evaporating to dryness, 80% in a hydrogen-nitrogen mixed gas.
Heat treatment was performed at 0 ° C. for 10 minutes. When the alloy phase of the catalyst metal particles was identified by an X-ray diffractometer, a peak of the α solid solution phase of platinum and a peak of FePt ₃ or FePt intermetallic compound phase were detected. It is presumed that this FePt ₃ or FePt is because the amount of platinum supported deviates from the optimum range of 5 to 40 wt% and the heat treatment time is shorter than the optimum time of 30 minutes or more. This Fe
The peak value of Pt ₃ etc. is extremely small, and it is presumed that the effect on life shortening is slight. Further, when the half-width was calculated from the peak of the Ptα solid solution phase and the particle size was calculated, it was 10 nm. This value is also considered to be because the amount of platinum supported is more than 5 to 40% by weight, and the particle size is increased by this.

[0022]

Industrial Applicability The present invention comprises a catalyst carrier, and a polyelectrolyte which comprises 84% to 99% by atom of platinum and 1% to 16% of iron by atomic% supported on the carrier. A fuel cell anode catalyst (claim 1). The platinum of the present invention
In the iron alloy phase, the iron content is 1 to 16 atomic% and the iron content is 17
It does not form an intermetallic compound represented by FePt ₃ which is present in the atomic% or more. Although FePt ₃ has resistance to surface area reduction, when it is used as an anode catalyst, it easily elutes in the electrolyte of a fuel cell and is poor in poisoning resistance to carbon monoxide, and when used as an anode catalyst for fuel cells,
The anode catalyst having the platinum-iron alloy of the present invention has a sufficiently long life.

The amount of platinum supported on the total catalyst weight is 5 to 40.
The amount of platinum supported is preferably in the range of% by weight. When the amount of platinum supported in this range is used as the anode catalyst, it is possible to provide a fuel cell in which gas diffusion easily occurs and which has fine catalyst particles (claim 2). In the anode catalyst according to claim 1, for example, a catalyst carrier is dispersed in a solution containing a platinum compound, and the platinum compound is deposited on the catalyst carrier by thermal decomposition or reduction with a reducing agent, and the platinum-supported catalyst carrier is made of iron. It can be produced by alloying platinum and iron by immersing in a solution containing a compound, evaporating to dryness or adjusting pH to precipitate iron hydroxide and heat treating in a reducing atmosphere (claim 3). . The heat treatment in this process is performed at a temperature of 400-900 ℃.
When it is carried out for 30 minutes or more, an alloy phase in which iron is solid-solved in platinum is formed, and the production of the FePt ₃ intermetallic compound, which easily elutes, is further reliably suppressed, and a long-life anode catalyst is provided ( Claim 4).

The platinum-iron alloy phase of the above-mentioned anode catalyst is
It may contain 0.1 to 50 atom% of a noble metal selected from palladium, ruthenium, rhodium and gold with respect to platinum and iron (claim 5), and the noble metal is a platinum-iron alloy within the above atomic% range. To improve the poisoning resistance to carbon monoxide without impairing the catalytic activity of hydrogen oxidation at the anode of a two-phase fuel cell. Even in this noble metal-containing anode catalyst, it is desirable that the platinum loading amount is 5 to 40% by weight based on the total weight of the catalyst (Claim 6). When an anode catalyst having a platinum loading amount in this range is used, gas diffusion similarly occurs. A fuel cell having easy and fine catalyst particles can be provided.

The noble metal-containing anode catalyst is prepared by immersing the platinum-supported catalyst carrier in a solution of the compound of the noble metal and reducing the platinum-supported catalyst carrier during the steps of supporting the anode catalyst on platinum and iron. It can also be manufactured by inserting a step of precipitating (Claim 7). In this case as well, when heat treatment is similarly performed at a temperature of 400 to 900 ° C for 30 minutes or more, an alloy phase in which iron is solid-soluted in platinum is formed, and the formation of the FePt ₃ intermetallic compound that easily dissolves as described above is formed. Further, an anode catalyst which is surely suppressed and has a long life is provided (Claim 8).

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between time and electrocatalytic reaction current value in Example 1 and Comparative Examples 1 and 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 391016716 STONHART Associates Incorporated STONEHART ASSOCIATES INCORPORATED United States 06443 Connecticut, Madison, Cottage Road 17, P-O Box 1220 (72) Inventor Masanori Watanabe 82-1 Wadamachi, Kofu City, Japan

Claims (8)

[Claims] 1. A polymer electrolyte fuel cell, comprising a catalyst carrier and at least 84 to 99% by atom of platinum and at least 1 to 16% of iron at the atomic% supported on the carrier. Anode catalyst. 2. The amount of platinum supported on the total catalyst weight is 5 to 40.
The anode catalyst for polymer electrolyte fuel cells according to claim 1, wherein the anode catalyst is contained in a weight percentage. 3. A method for producing an anode catalyst for a polymer electrolyte fuel cell, which comprises a catalyst carrier and 84 to 99% by atom of platinum and 1 to 16% by atom of iron supported on the carrier. In, the catalyst carrier is dispersed in a solution containing a platinum compound, the platinum compound is deposited on the catalyst carrier by thermal decomposition or reduction with a reducing agent, and the platinum-supported catalyst carrier in a solution containing an iron compound. A polymer electrolyte fuel cell, characterized in that the platinum and iron are alloyed by immersing, evaporating to dryness or adjusting pH to precipitate iron chloride and / or hydroxide and heat treating in a reducing atmosphere. Of manufacturing anode catalyst for automobile. 4. The polymer electrolyte fuel cell according to claim 2, wherein the heat treatment is carried out at a temperature of 400 to 900 ° C. for 30 minutes or more to form an alloy phase in which iron is solid-soluted in platinum. Manufacturing method of anode catalyst. 5. A catalyst carrier, and platinum (84 to 99): (1 to 16) platinum and iron supported on the carrier, and palladium (0.1 to 50 atom% based on the platinum and iron). An anode catalyst for a polymer electrolyte fuel cell, comprising a noble metal selected from ruthenium, rhodium and gold. 6. The amount of platinum supported on the total catalyst weight is 5 to 40.
The anode catalyst for polymer electrolyte fuel cells according to claim 5, wherein the anode catalyst is contained in a weight percentage. 7. A catalyst carrier, and platinum and iron (84 to 99): (1 to 16) in atomic% supported on the carrier, and palladium in an amount of 0.1 to 50 atomic% with respect to the platinum and iron. In a method for producing an anode catalyst for a polymer electrolyte fuel cell containing a noble metal selected from ruthenium, rhodium and gold, a catalyst carrier is dispersed in a solution containing a platinum compound,
The platinum compound is deposited on the catalyst carrier by thermal decomposition or reduction with a reducing agent, the platinum-supported catalyst carrier is immersed in a compound solution of a noble metal selected from palladium, ruthenium, rhodium and gold and subjected to reduction treatment. The noble metal is deposited on the catalyst carrier, and the platinum and the noble metal-supported catalyst carrier are immersed in a solution containing an iron compound and evaporated to dryness or pH is adjusted to precipitate iron chloride and / or hydroxide. A method for producing an anode catalyst for a polymer electrolyte fuel cell, comprising alloying the platinum, the noble metal and iron by heat treatment in a reducing atmosphere. 8. The anode catalyst for a polymer electrolyte fuel cell according to claim 7, wherein the heat treatment is carried out at a temperature of 400 to 900 ° C. for 30 minutes or more to form an alloy phase in which iron is solid-soluted in platinum. Production method.