JP2019030846A - Manufacturing method of alloy catalyst - Google Patents

Abstract

To overcome a problem that elements other than Pt of a Pt alloy is eluted and detached when place around a catalyst becomes acid solution environment during fuel cell operation since alloying dose not sufficiently progress in the case that an alloy catalyst for fuel cell is the Pt alloy.SOLUTION: The manufacturing method of an alloy catalyst is a manufacturing method of the alloy catalyst having an alloy particle containing platinum (Pt) and a first element, and has a heat treatment process for heating the alloy catalyst to 650°C or higher and cooling it to 200°C after heating.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an alloy catalyst for a fuel cell, and more particularly to a method for producing an alloy catalyst containing platinum alloy particles.

Improvement of durability and cost is required for widespread use of polymer electrolyte fuel cells (PEFC). In particular, in order to reduce the amount of expensive Pt catalyst used, the development of a cathode catalyst having high oxygen reduction (ORR) activity and durability is indispensable. Up to now, there has been developed an alloy catalyst in which alloy particles (alloy nanoparticles) such as PtM (M = Fe, Co, Ni...) Are supported in a highly dispersed manner. In such a PtM alloy, it has been clarified that a Pt skin layer is spontaneously formed on the alloy surface and exhibits high ORR activity due to the electronic modification effect of the base alloy (for example, Non-Patent Document 1). On the other hand, as described in Non-Patent Document 2, when the Pt skin layer is not uniform, it is reported that it is alloyed in a high temperature region and deactivated to the same level as that of Pt alone. Therefore, as in Patent Document 1 and Non-Patent Documents 3 and 4, in order to maintain the high surface area and activity of the _nanocatalyst , the PtM alloy surface is intentionally coated with a Pt skin layer of two atomic layers (Pt _2AL ). However, methods for preparing Pt _2AL -PtM / C catalysts in which a PtM alloy coated with a Pt skin layer is supported on a carbon (C) support have been found, and these adjustment methods have an inhibitory effect on dealloying. It has been reported.

  Further, as in Patent Document 2, a method for producing a PtRu / C catalyst for the development of an anode catalyst having high resistance to CO (carbon monoxide) has been reported.

WO2014 / 178283 JP2011-072934

T. Toda, H. Igarashi, H. Uchida and M. Watanabe, j. Electrochem. Soc., 146, 3750 (1999). N. Wakabayashi, M. Takeichi, M. Itagaki, H. Uchida and M. Watanabe, J. phys. Chem. B, 109, 5836 (2005). M. Watanabe, H. Yano, D.A.Tryk, and H. Uchida, J. Electrochem. Soc., 163, F455 (2016) M. Chiwata, H. Yano, S. Ogawa, M. Watanabe, A. Iiyama, H. Uchida, Electrochemistry, 84, 133 (2016)

  In the prior art, in the case of a Pt alloy, alloying does not progress sufficiently, so that elements other than Pt of the Pt alloy are eluted and desorbed when the periphery of the catalyst becomes an acidic solution environment such as when the fuel cell is operated. There was a problem.

  The method for producing an alloy catalyst according to the present invention is a method for producing an alloy catalyst having alloy particles containing platinum (Pt) and a first element, wherein the alloy catalyst is heated to 650 ° C. or higher and then heated to 200 ° C. A heat treatment step for cooling;

  ADVANTAGE OF THE INVENTION According to this invention, the acid tolerance of the platinum alloy catalyst containing the element melt | dissolved in an acid can be improved.

It is a figure which shows an example of the flow of the manufacturing method of the alloy catalyst of this invention. It is a figure which shows another example of the flow of the manufacturing method of the alloy catalyst of this invention. It is a figure which shows the imaging result by TEM. It is a figure which shows a particle size distribution. It is a figure which shows Co residual ratio. It is a figure which shows an ORR activity evaluation result. It is a figure which shows the value of area specific activity jk. It is a figure which shows the imaging result by TEM. It is a figure which shows a particle size distribution. It is a figure which shows Ni residual rate.

In the present specification, alloy particles containing a noble metal (Pt) and serving as a core are PtM (M = Fe, Co, Ni, etc.), and a skin layer is formed on the alloy particles by an x atomic layer (AL: Atomic Layer, x: integer of 1 or more) The covered alloy particles with skin layer are _denoted as Pt _xAL -PtM, and the noble alloy particles with skin layer and those supported on the support (y) are _denoted as noble metal alloy supported catalyst Pt _xAL -PtM / y. . When the carrier is carbon, y = C, and when carbon is acetylene black, y = AB. Further, when the skin layer is omitted and a combination of the core alloy (PtM) and the carrier (y) is indicated, it is described as PtM / y. When the temperature and the atmospheric conditions in the heat treatment step are indicated, it is expressed as Pt _xAL- (PtMtt ° C. gght) / y. Here, ttt is the temperature, and gg is the atmospheric gas. In addition, if heat processing (The heat processing process (S-4) mentioned later or heat processing in the conventional low temperature) is performed with respect to the core alloy particle PtM, platinum (Pt) will precipitate on the surface of a core alloy (segregation). Accordingly, the present specification shows information about the title and Pt _1AL PTM as the skin layer 1 atomic layer with at this point.

  The method for producing a noble metal alloy catalyst of the present invention is a method for producing an alloy catalyst having alloy particles containing platinum (Pt) and a first element (for example, cobalt, nickel, iron, etc.), wherein the alloy catalyst is 650. It has a heat treatment step of heating to 200 ° C. or higher and cooling to 200 ° C. after overheating.

  In the alloy catalyst of the present invention, the alloy particles containing platinum (Pt) and the first element (for example, cobalt) itself may form the alloy catalyst, but the alloy particles are supported on the support (for example, carbon). What is a supported catalyst is preferable. It is also effective when the first element is an element that dissolves in an acid.

1. Preparation of alloy particles The alloy catalyst of the present invention, which is a supported catalyst in which alloy particles are supported on a carrier (for example, carbon),
For example, after the alloy particles are supported on the support by the nanocapsule method disclosed in Patent Document 1 or the like, the support can be prepared through the heat treatment step described above. FIG. 1 shows an example of a flow of a method for producing an alloy catalyst of the present invention. FIG. 1 shows an example adapted to a flow for forming alloy particles and supporting them on a carrier by the nanocapsule method. As shown in FIG. 1, a solution preparation step (S-1) for preparing a reverse micelle solution by mixing a solvent having a hydrophilic group, a water-insoluble solvent, and a first precursor, water-insoluble having a reducing action The solution is added to the reverse micelle solution and heated to undergo a reduction step (S-2) for forming alloy particles inside the reverse micelle, and a support step (S-3) for supporting the formed alloy particles on a support. Thus, desired alloy particles supported on the carrier can be produced. After the supporting step, the heat treatment step (S-4) according to the present invention may be performed.

2. Addition of Skin Layer FIG. 2 shows another example of the flow of the method for producing the alloy catalyst of the present invention. FIG. 2 shows an example in which the present invention is applied to a flow for additionally forming a skin layer on the surface of alloy particles. The alloy particles that have undergone the supporting step (S-3) or the heat treatment step (S-4) in FIG. 1 can additionally form a skin layer on the surface of the alloy particles according to the flow shown in FIG. In this case, the alloy particles that have undergone the supporting step (S-3) or the heat treatment step (S-4) are added to an aqueous solution containing the second precursor, and a platinum skin layer is formed on the surface of the alloy particles by hydrogen bubbling. It is preferable to additionally perform a step of depositing (skin layer forming step: S-5).

  In both the examples of FIGS. 1 and 2, the heat treatment step (S-4) described later is incorporated in the alloy catalyst production flow.

  As shown in FIG. 1, the heat treatment step (S-4) may be performed on the alloy catalyst that has undergone the supporting step (S-3). When the skin layer forming step (S-5) is performed without the heat treatment step (S-4) after the supporting step (S-3), the heat treatment is performed after the skin layer forming step (S-5). Step (S-4) may be performed. In the example of FIG. 2, the skin layer forming step (S-5) is performed after the carrying step (S-3). When performing the example of FIG. 2, you may perform the conventional low-temperature heat processing (for example, 400 degreeC) between a support process (S-3) and a skin layer formation process (S-5). If the skin layer forming step (S-5) is performed after the supporting step (S-3) and then the heat treatment step (S-4), the conventional type is performed after the skin layer forming step (S-5) is performed. A low temperature heat treatment (for example, 200 ° C.) may be performed.

(Component metal of alloy particles)
The constituent metal of the alloy particles (noble metal alloy particles) used in the present invention is an alloy of platinum (Pt) and one or more kinds of noble metals / non-noble metals other than platinum. Examples of noble metals other than platinum include palladium, rhodium, iridium, ruthenium and gold, and examples of non-noble metals include iron, cobalt, nickel, manganese, chromium, vanadium, titanium, niobium, molybdenum, lead, tungsten However, as will be described later, the present invention is particularly suitable when a platinum alloy containing an element that dissolves in an acid (for example, the above-described cobalt, iron, nickel, etc.) is used as the noble metal alloy particle. The average particle diameter of the noble metal alloy particles is not particularly limited, but is, for example, 1 to 8 nm. Precious metal alloy particles having an average particle size that is too small are not easy to produce stably, and if the average particle size is too large, the average particle size of the resulting alloy particles also increases accordingly, and mass activity (per unit mass) This is because the (catalytic activity) tends to decrease. Specifically, the average particle diameter of the alloy particles is, for example, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0 nm, and may be within a range between any two of the numerical values exemplified here. In the present specification, the “average particle diameter” means an arithmetic average obtained by measuring the diameter of a circumscribed circle of each fine particle in a TEM image. The number of measurement samples is, for example, 500 or more. The particle diameters of the noble metal alloy particles are preferably as uniform as possible, and 70% or more of the alloy fine particles preferably have a particle diameter within ± 30% of the average particle diameter, and ± 25, 20, or 15%. More preferably, it has a particle size of within.

(Carrier)
The carrier (preferably an electronically conductive carrier) is not particularly limited, and examples thereof include carbon black, acetylene black, amorphous carbon, carbon nanotube, carbon nanohorn, tin oxide, titanium oxide, and other nanoparticles. The amount of catalyst particles supported is not particularly limited, but is, for example, 10 wt% or more and less than 100 wt% with respect to the support. Specifically, this loading amount is, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 wt%, and is within a range between any two of the numerical values exemplified here. (However, 100 wt% is not included).

(Solution preparation process)
The solution preparation step (S-1) is a step of preparing a reverse micelle solution (nanocapsule solution) by mixing a solvent having a hydrophilic group, a water-insoluble solvent, and a noble metal alloy precursor (first precursor). is there.

  As a solvent which has a hydrophilic group, the organic solvent which has a hydroxyl group is mentioned, for example, A higher alcohol etc. are illustrated. Examples of the water-insoluble solvent include organic solvents that form nanocapsules by mixing with the solvent having a hydrophilic group, and examples thereof include higher ethers, aromatic ethers, and higher esters. Preferably, diferniether or the like may be used as the organic solvent.

The noble metal alloy precursor refers to a compound that is reduced to form a raw material for forming noble metal alloy fine particles, and is, for example, one or more metal salts or metal complexes. When producing PtCo alloy particles, for example, acetylacetonate platinum (Pt (acac) ₂ ) and acetylacetonate cobalt (III) (Co (acac) ₃ ) can be used.

(Reduction process)
In the reducing step (S-2), a water-insoluble liquid having a reducing action is added to the reverse micelle solution and heated to form alloy particles inside the reverse micelle.

The noble metal alloy precursor is preferably reduced by supplying and heating a water-insoluble liquid having a reducing action. For this reason, MBR ₃ H, MH (wherein M represents lithium, sodium or potassium, R represents a hydrogen atom or a hydrocarbon group, and the hydrocarbon group is linear or branched as a water-insoluble liquid having a reducing action. However, it may be saturated or unsaturated.) A water-insoluble liquid containing an alcohol and a metal derivative of naphthalene is used.

(Supporting process)
The supporting step (S-3) is a step of supporting the alloy particles formed in the reducing step (S-2) on the carrier. In this specification, the carrier on which the alloy particles are supported is referred to as catalyst-supported particles.

  The mixing of the nanocapsule solution (reverse micelle solution) and the carrier is preferably performed while dispersing the carrier in the same organic solvent (for example, diferniether) as the nanocapsule solution and dropping the nanocapsule solution into the solution. Since the nanocapsule has a hydrophobic group on its outer side, the particles are repelled by the charge of the hydrophobic group and arranged on the surface of the carrier without being too close, so that the alloy particles are supported in a highly dispersed manner. Thus, catalyst-carrying particles in which alloy particles are highly dispersed and supported can be obtained.

(Heat treatment process)
The heat treatment step (S-4) is a heat treatment at rapid heating / cooling and high temperature, and is a core part of the present invention. This heat treatment step (S-4) is preferably a heat treatment in which heating is performed to 650 ° C. or higher, cooling to 200 ° C. after overheating. The maximum temperature reached during heating can be higher than 650 ° C. For example, it is good also as 700, 800, 900 degreeC or more. This maximum temperature can be set as high as possible within a range where aggregation of alloy particles is suppressed. Further, it is more preferable to heat at a heating rate of 50 ° C./min or more. It is more preferable to heat rapidly up to the maximum temperature. Further, it is more preferable that the cooling after overheating is rapidly cooled within 5 minutes from the highest temperature achieved during heating to 200 ° C. This is for preventing aggregation of alloy particles in this heat treatment step.

(Skin layer forming process)
In the skin layer forming step (S-5), the alloy particles that have undergone the supporting step (S-3) or the heat treatment step (S-4) are added to an aqueous solution containing the second precursor (noble metal precursor), and hydrogen is added. This is a step of depositing a platinum skin layer on the surface of the alloy particles by bubbling. By incorporating the skin layer forming step (S-5), the alloy catalyst can be covered with platinum (Pt) by adding an x atomic layer (x is a natural number).

The noble metal precursor refers to a compound that is reduced and forms a noble metal, and examples thereof include noble metal acids, salts, and complexes. As the noble metal precursor, for example, a chlorinated noble metal acid or a salt thereof (eg, potassium salt), a nomine complex of an noble metal, an ethylenediamine complex, an acetylacetonate complex, or the like can be used. When the noble metal is platinum, chloroplatinic acid (eg, hexachloroplatinic acid, tetrachloroplatinic acid), acetylacetonate platinum [Pt (acac) ₂ ], chloroplatinate (eg, potassium chloroplatinate [K ₂ PtCl ₄ ]), platinum ammine complexes, and the like can be used.

  Since hydrogen bubbling is performed in a hydrous solvent, the noble metal precursor needs to be water-soluble. The noble metal precursor preferably has a high solubility such that the entire amount is dissolved at the start of hydrogen bubbling. However, the solubility may be such that a part of the noble metal precursor remains undissolved at the start of hydrogen bubbling.

  The hydrous solvent is a solvent containing water, preferably pure water, but contains components other than water (eg, lower alcohol) as long as it does not completely inhibit the reduction reaction of the noble metal precursor. Also good. The higher the content of water in the hydrous solvent, the better.

  A reaction solution for performing hydrogen bubbling is obtained by dispersing seed metal fine particles in a hydrous solvent and dissolving a noble metal precursor. In one example, a dispersion solution in which seed metal fine particles are dispersed in a water-containing solvent by a method such as ultrasonic dispersion and a solution in which a noble metal precursor is dissolved in a water-containing solvent are prepared, and a reaction solution is prepared by mixing them. can do.

  Hydrogen bubbling can be performed by circulating a reaction gas containing hydrogen gas in the reaction solution. As the reaction gas, pure water hydrogen gas may be used, or diluted hydrogen gas diluted with another gas (eg, an inert gas such as argon or nitrogen) may be used. The temperature of the reaction solution at the time of hydrogen bubbling may be a temperature at which the reaction solution does not solidify or vaporize, for example, 0.1 to 100 ° C. under atmospheric pressure, and 15 to 15 considering the ease of operation. 60 ° C. is preferred. The pH of the reaction solution at the time of hydrogen bubbling is not particularly limited as long as the reduction reaction of the noble metal precursor occurs, but if the pH is too low, the reduction reaction hardly occurs, so the pH at the start of hydrogen bubbling is 0 or more. Is preferred.

  By hydrogen bubbling, the noble metal precursor is reduced on the surface of the alloy particles, a noble metal skin layer is formed so as to cover the alloy particles, and the alloy particles with a skin layer as a product are obtained.

  The average particle diameter of the alloy particles with skin layer is not particularly limited, but is, for example, 2 to 12 nm, specifically, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, and 12 nm. It may be within a range between any two. The alloy particles with a skin layer have a larger specific surface area and a higher mass activity as the average particle size is smaller. However, the alloy particles are more easily eluted and aggregated and are unstable. Therefore, when used under harsh conditions such as an electrode catalyst for a fuel cell for automobiles, the average particle size of the alloy particles with skin layer is relatively increased to give priority to the stability of the alloy particles, For applications that are used under relatively mild conditions, priority can be given to increasing the mass activity by making the average particle size of the alloy particles relatively small. Thus, the preferable average particle size of the alloy particles with skin layer is determined by the application, and the average particle size of the alloy particles and the thickness of the noble metal skin layer are controlled so that metal fine particles having an appropriate average particle size can be obtained. To do. The thickness of the noble metal skin layer can be controlled by changing the amount of the noble metal precursor added. The particle diameters of the alloy particles with skin layer are preferably as uniform as possible, and 70% or more of the alloy particles with skin layer preferably have a particle diameter within ± 30% of the average particle diameter. More preferably, it has a particle size within 20 or 15%.

  If the alloy particles are supported on a carrier, the alloy particles with skin layer, which is the product, are already supported on the carrier, so the alloy particles with skin layer should be used as an electrode catalyst for a fuel cell. Can do.

(Conventional heat treatment)
When the skin layer is formed after the supporting step (S-3) without performing the heat treatment step (S-4), the conventional type is used before entering the skin layer forming step, that is, after adsorbing the alloy particles on the surface of the carrier. It is preferable to perform a low-temperature heat treatment. By this low-temperature heat treatment, the nanocapsule component remaining on the alloy particles can be completely decomposed and removed. The remaining nanocapsule component includes, for example, a hydrophobic group such as an alkyl group. The heat treatment is preferably performed under an inert gas such as argon, nitrogen, or helium. The temperature of the heat treatment varies depending on the type of metal, the metal salt or metal complex as a raw material, and the type of reagent, but is a temperature at which the nanocapsule component is decomposed and the decomposition reaction does not proceed too slowly. A range lower than the temperature at which aggregation occurs is preferable (for example, 400 ° C.). When the noble metal alloy particles are made of an alloy of a noble metal and a non-noble metal, it is preferable to perform heat treatment under a reducing atmosphere (eg, hydrogen gas atmosphere).

  Examples of the method for producing an alloy catalyst of the present invention and comparative examples are shown below. The carrier in any of the examples and comparative examples is acetylene black (AB) which is a kind of carbon black.

(Example _{1: Pt 1AL - (PtCo800 ℃} H 2 ht) / AB)
In this example, using the nanocapsule method, as shown in FIG. 1, the PtCo alloy particles were passed through a solution preparation step (S-1), a reduction step (S-2), and a supporting step (S-3). After preparing the alloy catalyst supported on the carbon support, the heat treatment step (S-4) shown in FIG. 1 was performed to prepare the alloy catalyst. Here, no additional skin layer was formed in the alloy catalyst as shown in FIG. The carrier of this example was a carbon carrier (acetylene black: AB).

First, in the step of adjusting the solution (nanocapsule solution) (step 1: S-1), 0.125 mmol (49 mg) of acetylacetonate platinum (Pt (acac) ₂ ), acetylacetonate cobalt (III) (Co (Acac) ₃ ) 0.125 mmol (44 mg), 1,2-hexadecanediol 1 mmol (260 mg) and diphenyl ether 12.5 ml (13.5 g, 79.3 mmol) were added to a beaker and the mixture was heated to 100 ° C. using a stirrer. Stir and mix for 10 minutes. To this was added 0.25 mmol (85 μl) of oleic acid and 0.25 mmol (80 μl) of oleylamine, and then the temperature was raised to 200 ° C. with stirring, followed by stirring for 20 minutes to obtain a nanocapsule solution.

Next, in the reduction step (Step 2: S-2), 1.0 ml (1 mmol) of 1M LiB (C ₂ H ₅ ) ₃ H · THF solution is gradually added dropwise to the obtained nanocapsule solution over 2 minutes. After stirring for 5 minutes, the temperature was raised to 260 ° C., and the mixture was refluxed at this temperature for 20 minutes to cause a reduction reaction, thereby obtaining a solution A (nanocapsule solution A) containing PtCo particles in the nanocapsules.

  In the supporting step (step 3: S-3), after the solution A is obtained in the reducing step, the temperature of the solution A is lowered to around 100 ° C., and the amount of PtCo supported is 20 wt% with respect to acetylene black. Black (AB) was mixed and stirred, and PtCo alloy particles were supported on a carbon support. And after filtering, it was made to vacuum-dry at 60 degreeC, and the catalyst carrying particle was obtained.

The heat treatment step (S-4) was performed following the support step (S-3), and the catalyst-supported particles obtained in the support step (S-3) were heat-treated. In the heat treatment step (S-4) here, the PtCo / C catalyst is placed in a 5% H ₂ (N ₂ balance) atmosphere in a state in which an organic protective group is present on the surface of the catalyst-carrying particles. Rapid heating was performed to 800 ° C. at a rate of temperature increase of 50 ° C./min, followed by rapid cooling from 800 ° C. Cooling was performed from 800 ° C. to 200 ° C. within 5 minutes. Thus alloy catalyst the PtCo alloy particles are supported on acetylene black _{(AB) (Pt 1AL - (} PtCo800 ℃ H 2 ht) / AB) was obtained. The alloy catalyst thus obtained is designated as catalyst C1.

(Example 2: Pt _2AL- (PtCo 800 ° C H ₂ ht) / AB)
As the alloy catalyst in this example, Pt2AL-PtCo / C having a structure in which the catalyst C1 obtained in Example 1 was further coated with a Pt skin layer and provided with a Pt2 atomic layer skin layer was prepared. That is, the alloy catalyst obtained through S-1 to S-4 in FIG. 1 and the skin layer forming step (S-5) shown in FIG. Since the heat treatment step (S-4) is performed before the Pt skin layer is formed, the heat treatment step (S-4) shown in FIG. 2 is omitted. Also in this example, in the heat treatment step (S-4), rapid heating is performed to 800 ° C. at a rate of temperature increase of 50 ° C./min in 5% H ₂ (N ₂ balance), and then rapidly cooled from 800 ° C. did. Cooling was performed from 800 ° C. to 200 ° C. within 5 minutes. The heat treatment after the coating of the Pt skin layer was performed at a conventional 200 ° C. The carrier of this example was also a carbon carrier (acetylene black: AB).

The Pt skin precursor (noble metal precursor) was tetraammineplatinum platinum (II) ([Pt (NH ₃ ) ₄ ] (OH) ₂ ). Pt1 precursor layer (reaction solution) was prepared by dissolving tetraammineplatinum hydroxide (II) ([Pt (NH ₃ ) ₄ ] (OH) ₂ ) for the Pt1 atomic layer in 20 mL of pure water. The reaction solution was boiled to increase the wettability of PtCo / C. At the beginning of boiling, PtCo / C was partially suspended in the reaction solution or on the surface, but when boiling was continued for about 10 minutes, the entire amount of PtCo / C sank to the bottom of the container, and boiling was terminated at that point did. After that, the reaction solution is kept at 60 ° C. or lower, and hydrogen bubbling is performed under the conditions of 5% hydrogen gas concentration, 60 ° C. temperature, and 1 H for 1 hour. Further coating. The heat treatment after coating the Pt skin layer was performed at a conventional 200 ° C. The alloy catalyst (Pt _2AL- (PtCo 800 ° C. H ₂ ht) / AB) thus obtained is _defined as catalyst C2.

(Example 3: Pt _2AL- (PtCo 800 ° C H ₂ ht) / AB (heat treatment after skin formation))
The difference in the production method of the alloy catalyst of Example 2 is that the heat treatment step (S-4) of FIG. 1 is skipped and the above-described conventional low-temperature heat treatment is performed, and the skin layer formation step (S--) of FIG. 5), the heat treatment step (S-4) is performed. That is, it is an alloy catalyst obtained by performing the heat treatment step (S-4) after the S-1 to S-3 in FIG. 1 and the skin layer forming step (S-5) in FIG. The skin layer forming step was the same as in Example 2, and Pt2AL-PtCo / C having a structure in which a Pt skin layer was covered and a Pt2 atomic layer skin layer was prepared. The alloy catalyst thus obtained (Pt _2AL- (PtCo 800 ° C. H ₂ ht) / AB (heat treatment after skin formation)) is defined as catalyst C3. In the conventional low-temperature heat treatment, the maximum temperature reached 400 ° C. in 5% H ₂ . The carrier of this example was also a carbon carrier (acetylene black: AB).

(Example _{4: Pt 1AL - (PtCo800 ℃} N 2 ht) / AB)
An alloy catalyst was prepared by changing only the atmospheric conditions in the heat treatment step (S-4) of Example 1 from 5% H ₂ (N ₂ balance) to N ₂ . Alloy catalyst thus prepared _{(Pt 1AL - (PtCo800 ℃ N} 2 ht) / AB) of the catalyst C4.

(Example 5: Pt _2AL- (PtCo800 ° C N ₂ ht) / AB)
Only the atmospheric conditions in the heat treatment step (S-4) of Example 2 were changed from 5% H ₂ (N ₂ balance) to N ₂ to prepare an alloy catalyst. The alloy catalyst (Pt _2AL- (PtCo 800 ° C. N ₂ ht) / AB) prepared in this way is designated as catalyst C5.

(Comparative Example _1: Pt 1AL -PtCo / AB)
In addition to the catalyst C1~C5 obtained by Examples 1 to 5 described above, as a comparative example, the heat treatment step (S-4) without traditional method by comparative example alloy catalyst _(Pt 1AL -PtCo / AB) It was created. Comparative example 1 corresponds to a conventional example. Therefore, the alloy particles of this comparative example are only subjected to heat treatment at a low temperature of 5% H ₂ (N ₂ balance) and 400 ° C. This alloy catalyst is referred to as catalyst C6. Specifically, in the production method of Example 3, the alloy catalyst at the stage before the skin layer forming step (S-5) is performed. The carrier of this example was also a carbon carrier (acetylene black: AB).

    In the case where the alloy particles were changed from PtCo to PtNi, Examples 6 to 7 and Comparative Alloys 2 according to Comparative Example 2 were prepared as comparative examples.

(Example _{6: Pt 1AL - (PtNi650 ℃} N 2 ht) / C)
This example is substantially the same as Example 4, but an alloy catalyst was prepared by changing the temperature in the heat treatment step (S-4) to 650 ° C. and changing the alloy particles from PtCo to PtNi. The heat treatment step (S-4) was performed in an N ₂ atmosphere as in Example 4. Alloy catalyst thus prepared _{(Pt 1AL - (PtNi650 ℃ N} 2 ht) / C) of the catalyst C7.

(Example _{7: Pt 1AL - (PtNi800 ℃} N 2 ht) / C)
In this example, compared with Example 6, only the temperature in the heat treatment step (S-4) was set to 800 ° C. An alloy catalyst was prepared using PtNi as the alloy particles in the same manner as in Example 6. Alloy catalyst thus prepared _{(Pt 1AL - (PtNi800 ℃ N} 2 ht) / C) of the catalyst C8.

(Comparative Example _2: Pt 1AL -PtNi / C)
This example is substantially the same as Comparative Example 1, but an alloy catalyst was prepared by replacing the alloy particles from PtCo to PtNi. Similar to Comparative Example 1, the alloy particles of this Comparative Example were only subjected to heat treatment at a low temperature of 5% H ₂ (N ₂ balance) and 400 ° C. Comparative example 2 corresponds to a conventional example. Thus creating an alloy catalyst of _(Pt 1AL -PtNi / C) and the catalyst C9.

(TEM image, particle size distribution)
First, for each of the catalysts of Examples 1 to 5 and Comparative Example 1 (catalysts C1 to C6) obtained for the alloy particles PtCo, the TEM image (TEM image) is shown in FIG. 3, and the particle size distribution (d) is shown. 4 respectively. Here, FIG. 3 (1) is the catalyst C1 (Example 1), (2) is the catalyst C2 (Example 2), (3) is the catalyst C6 (Comparative Example 1), and (4) is the catalyst C3 (Example 3). ) And (5) show TEM images of the catalyst C4 (Example 4), and (6) show the catalyst C5 (Example 5), respectively. Similarly, FIG. 4 (1) shows catalyst C1 (Example 1), (2) shows catalyst C2 (Example 2), (3) shows catalyst C6 (Comparative Example 1), and (4) shows catalyst C3 (Example 3). ), (5) shows the particle size distribution of the catalyst C4 (Example 4), and (6) shows the particle size distribution of the catalyst C5 (Example 5), respectively. As shown in FIG. 4, the particle diameters of the PtCo alloy particles of the catalysts C1 to C6 are 2.9 ± 0.4 nm, 3.2 ± 0.4 nm, 3.0 ± 0.5 nm, 2 0.8 ± 0.3 nm, 3.2 ± 0.5 nm, 2.2 ± 0.3 nm. The particle size distribution was prepared by measuring the particle size of each alloy particle from the TEM shown in FIG. In the figure, d is expressed as “2.9 ± 0.4”, but the value after ± indicates the standard deviation value (nm). About 70% of the measured particle size data falls within the range of the plus and minus values.

  As is apparent from the TEM image of FIG. 3, the alloy particles PtCo are aggregated of the alloy particles PtCo even though they are heated to 800 ° C. in the heat treatment step (S-4). Maintains highly dispersed support on black.

The change in the particle size of the PtCo alloy particles of the catalyst may be compared with the presence or absence of the skin layer forming step. The comparison between the catalyst C1 and the catalyst C2 (Examples 1 and 2) is 2.9 ± 0.4 nm to 3.2 ± 0.4 nm, and the comparison between the catalyst C6 and the catalyst C3 (Comparative Example 1 and Example 3) is 2 .2 ± 0.3 nm to 3.0 ± 0.5 nm, and the comparison between catalyst C4 and catalyst C5 (Examples 4 and 5) increased from 2.8 ± 0.3 nm to 3.2 ± 0.5 nm, respectively. ing. Since the increase in the average particle diameter is 0.3 nm, 0.8 nm, and 0.4 nm, respectively, except for the comparison between the catalyst C6 and the catalyst C3 (Comparative Example 1 and Example 3), the catalyst C2 and C5 have Pt. _1AL -PtCo Pt skin throughout the particle Pt1 atomic layers that is formed has been suggested.

(Acid resistance test)
The acid resistance test of the catalysts C1 to C6 was performed to evaluate the corrosion resistance. In the acid resistance test, each catalyst was placed in a 0.05 M H ₂ SO ₄ solvent at 80 ° C. and stirred (atmosphere was air), and evaluated from the Co elution amount. Actually, the ratio (residual ratio) of Co remaining in the catalyst was determined from the Co elution amount.

(Co residual ratio)
FIG. 5 shows the Co residual ratio of the catalysts C1 to C6. As shown in FIG. 5, the Co residual ratios of the catalysts C1 to C6 were 77.8%, 67.5%, 64.0%, 73.4%, 74.7%, and 23.6%, respectively. Catalyst _{C6 (Pt 1AL -PtCo / AB)} 23.6% and the catalyst _C3 - Comparison with _{(Pt 2AL (PtCo800 ℃ H 2} ht) / AB ( after skin formation heat treatment)) 64.0%, after Pt skinforming Acid resistance is improved by heat treatment at 800 ° C. in an H ₂ atmosphere. That is, it can be seen that heat treatment at 800 ° C. in a Pt skin catalyst (a catalyst in which an alloy particle covers a Pt skin layer) is effective. Catalyst _{C1 (Pt 1AL - (PtCo800 ℃} H 2 ht) / AB) 77.8%, the catalyst _{C4 (Pt 1AL - (PtCo800 ℃} N 2 ht) / AB) 73.4%, the catalyst _C6 (Pt 1AL -PtCo / AB) From the comparison of 23.6%, the acid resistance of the 800 ° C. heat treatment is improved regardless of the H ₂ atmosphere and the N ₂ atmosphere. It can be seen that a heat treatment at 800 ° C. for the PtCo core catalyst (only PtCo alloy particles) is effective. The residual ratio of the catalyst C6 corresponding to the conventional method was 23.6%, but in all of the catalysts C1 to C5 subjected to rapid heating / cooling at 800 ° C. in a part of the preparation stage, Co remained to about 70%, Corrosion resistance has been improved.

(Mass activity: MA _k )
FIG. 6 shows the ORR activity evaluation results of the catalysts C1 to C6. In FIG. 6, the vertical axis represents oxygen reduction reaction (ORR) mass activity (current that can be taken out per gram of Pt (ampere): Mass activity), and its unit is A / gPt. As shown in FIG. 6, the mass activities MA _k (ORR activity per Pt mass) of the catalysts C1 to C6 were 656, 651, 879, 703, 680, and 500 (unit: A / gPt), respectively. Mass active MA _k was highest for catalyst C3 heat treated at 800 ° C. after Pt skin formation.

(Area specific activity j _k )
On the other hand, the area specific activities j _k (specific activities) of the catalysts C1 to C6 are 0.7, 0.8, 0.9, 0.9, 0.9, 0.5 (units), respectively, as shown in FIG. : MA / cm ² ). When heat treatment is performed at 800 ° C. before the skin layer is formed, the heat treatment in the N2 atmosphere is performed with or without the Pt skin layer than the heat treatment in the H2 atmosphere. area specific activity _{j k} was high. This is considered to suggest that the area specific activity j _k influences not only the Co elution rate but also the particle surface and the internal structure.

(PtNi alloy particles)
Also in the case of having PtNi alloy particles, observation by TEM (TEM image), measurement of particle size distribution (d), and acid resistance test were performed. For each of the catalysts of Examples 6 to 7 and Comparative Example 2 (catalysts C7 to C9) obtained for the alloy particles PtNi, the TEM imaging results (TEM images) are shown in FIG. 8, and the particle size distribution (d) is shown in FIG. FIG. 10 shows the Ni residual ratio.

  FIG. 8 (1) is a TEM image of the catalyst C9 (Comparative Example 2), (2) is the catalyst C7 (Example 6), and (3) is the catalyst C8 (Example 7). Similarly, FIG. 9 (1) shows the particle size distribution of the catalyst C9 (Comparative Example 2), (2) shows the catalyst C7 (Example 6), and (3) shows the particle size distribution of the catalyst C8 (Example 7). As shown in FIG. 9, the particle diameters of the PtNi alloy particles of the catalysts C7 to C9 were 2.5 ± 0.4 nm, 2.9 ± 0.8 nm, and 3.0 ± 0.7 nm, respectively. It was.

For the acid resistance test, the same test as in the case of PtCo was performed. As shown in FIG. 10, the remaining rates of Ni in the catalysts C7 to C9 were 63.9%, 84.1%, and 93.1%, respectively. Catalyst _{C9 (Pt 1AL -PtNi / C)} 63.9%, the catalyst _{C7 (Pt 1AL - (PtNi650 ℃} N 2 ht) / C) 84.1%, the catalyst _{C8 (Pt 1AL - (PtNi800 ℃} N 2 ht) / Comparison with C) suggests that the Ni residual ratio is improved by heat treatment at a temperature of 400 ° C. or higher. Obviously, the higher the temperature, the higher the Ni remaining rate is at least 650 ° C. If heat treatment is performed at 800 ° C., the Ni remaining rate is 90% or more.

  The result of each Example in the PtNi alloy particles shows the same characteristics as the PtCo alloy particles, and it shows that the heat treatment at 650 ° C. or higher improves the acid resistance of the Pt alloy particles. Although not described in this specification, similar results are being obtained for PtFe in our experiments. A catalyst used in a fuel cell forms ink when applied to, for example, an electrolyte membrane. At this time, the catalyst material is placed in the environment of a strongly acidic solution. The improvement in acid resistance directly leads to the solution of such a problem that occurs when assembling a fuel cell. In addition, Co and Ni do not elute even under acidic conditions in the actual operating state of the fuel cell (use in the cathode catalyst layer, etc.). High enough. In addition, the method for producing an alloy catalyst of the present invention is an effective solution for these problems.

  Conventionally, high-temperature heat treatment at 650 ° C. or higher has been avoided because of fear of agglomeration of highly dispersed alloy particles. It has become clear to play. In addition, it should be noted that this effect is effective for a material (Co, Ni, Fe, etc.) in which another material element alloyed with Pt is dissolved in an acid. While improving the acid tolerance of the platinum alloy catalyst containing the component which melt | dissolves in an acid, it can prevent the performance deterioration of a fuel cell by the elements other than Pt of an alloy particle being eluted and desorbed in an acidic environment.

The method for producing a noble metal alloy catalyst of the present invention can be used for producing a noble metal alloy catalyst expected to be used in an electric vehicle or the like equipped with PEFC.

Claims (9)

  A method for producing an alloy catalyst having alloy particles containing platinum (Pt) and a first element, comprising a heat treatment step of heating the alloy catalyst to 650 ° C. or higher, and cooling to 200 ° C. after overheating. A method for producing an alloy catalyst. A solution preparation step of preparing a reverse micelle solution by mixing a solvent having a hydrophilic group, a water-insoluble solvent and a first precursor, and adding a water-insoluble liquid having a reducing action to the reverse micelle solution and heating. A reduction step of forming the alloy particles inside the reverse micelle, and a supporting step of supporting the formed alloy particles on a carrier,
The first precursor is a compound that is reduced to form a raw material for forming the alloy particles;
The manufacturing method according to claim 1, wherein after the supporting step, the heat treatment step is performed to manufacture the alloy catalyst in which alloy particles are supported on a carrier. The alloy particles are further added to an aqueous solution containing the second precursor, and further provided with a skin layer forming step of depositing a platinum skin layer on the surface of the alloy particles by hydrogen bubbling,
The second precursor is a compound that is reduced to become a raw material for forming the skin layer,
The manufacturing method according to claim 1, wherein the skin layer forming step is performed before or after the heat treatment step.   The manufacturing method according to any one of claims 1 to 3, wherein a heating rate of the heating is 50 ° C / min or more.   The said cooling is performed in 5 minutes or less from the ultimate temperature reached at the time of overheating to 200 degreeC in 5 minutes or less, The manufacturing method as described in any one of Claim 1 thru | or 4 characterized by the above-mentioned.   The manufacturing method according to claim 1, wherein the ambient temperature is 650 ° C. or higher and 800 ° C. or lower.   The manufacturing method according to claim 1, wherein the heat treatment is performed in a hydrogen gas atmosphere.   The manufacturing method according to claim 1, wherein the first element is an element that dissolves in an acid.   The manufacturing method according to any one of claims 1 to 8, wherein the first element is any one of cobalt (Co), iron (Fe), and nickel (Ni).